Image forming device and image forming method

Image forming device and image forming method

Technical field

The present invention relates to an image forming apparatus and an image forming method in which an image bearing body forming an electrostatic latent image and a toner carrier bearing toner are arranged facing each other, and a development bias is applied to the toner carrier Press to move the toner from the toner carrier to the image-bearing body, thereby developing the electrostatic latent image.

Background technique

As image forming apparatuses such as copiers, printers, and facsimile devices using electrophotographic technology, there are known a contact development method in which an image carrier and a toner carrier are kept in contact, and a non-contact development method in which the two are kept in a separated state. Device. Among them, in the image forming apparatus of the contact development method, a DC voltage or a developing bias voltage superimposed on the DC voltage with an AC voltage is applied to the toner carrier, and the toner carried on its surface contacts the image carrier. In the case of an electrostatic latent image, according to its surface potential, a part of it moves to the side of the image carrier to form a toner image.

In addition, in an image forming apparatus of the non-contact development method, an alternating voltage as a developing bias is applied to the toner carrier to form an alternating electric field in the gap between the toner carrier and the image carrier, and The alternating electric field causes the toner to fly to form a toner image.

In this type of device, the image density of the toner image may vary due to individual differences in the device, changes in time, or changes in the surrounding environment of the device, such as temperature and humidity. Therefore, various techniques for achieving stable image density have been proposed in the past. As such a technique, for example, there is a technique of forming a small image (patch image) for testing on an image carrier, and optimizing a density control factor that affects the image density based on the density of the patch image. This technology strives to make various changes to the density control factor and form a specified patch image on the image carrier. At the same time, it uses a density sensor set near the image carrier to detect the image density and adjust the density control factor to make the density Consistent with the preset target density, the desired image density is obtained.

For example, in the image density control technology disclosed in Japanese Patent Laid-Open No. 2002-72584, (1) when the main body of the device is powered on, (2) when the process cartridge or developer cartridge is replaced, and (3) when the device is left for a long time. When a new print command is received in an unused state, (4) When the specified number of sheets is printed, the specified toner patch is formed before the following image formation, and the density is changed as a density control factor The developing bias voltage to control the image density.

In this type of image forming apparatus, regardless of whether the power is turned off or on or not, if the state where the operation stopped without image formation continues for a long time, the image formed in the subsequent image forming operation may be formed. It is known to produce periodic density streaks. Although this kind of density streaks can be gradually eliminated by repeating the image forming operation multiple times, the longer the operation is stopped, the time required for the elimination will increase, and sometimes the image quality may be reduced to a level that is difficult to ignore.

In particular, in a conventional image forming apparatus that forms a patch image and adjusts the density control factor, when the patch image is formed after such an operation is stopped, the density of the patch image may fluctuate due to the aforementioned density streaks. Therefore, the adjustment of the density control factor based on the density cannot be performed with high accuracy. As a result, there is a problem that it is difficult to form a stable image.

Summary of the invention

The first object of the present invention is to provide an image forming apparatus and an image forming method, which can form a toner image with good image quality stably by forming a patch image with less density streaks and optimizing the density control factor according to the density. .

The second object of the present invention is to provide an image forming apparatus and an image forming method that can suppress density streaks that appear on the formed image after the operation stop state continues for a long time, and stably form a toner image with good image quality.

The inventors of the present invention have derived the following viewpoints from the results of various experiments on the cause of periodic density streaks in the image forming operation after the operation stop state continues. That is, it can be seen that because the toner adheres to the surface of the toner carrier and is left for a long time, the bond between the toner carrier and the toner is gradually strengthened, and more force is required to peel the toner from the toner carrier. And, the surface state of the toner carrier in the stopped state is different, and the density of the toner in contact with the surface is uneven depending on the position. Therefore, the degree of bonding between the toner and the toner carrier is also uneven, and this density streak is mainly caused by this.

Therefore, in the first aspect of the present invention, in order to achieve the above-mentioned first object, the toner carrier must be rotated more than once before the patch image is formed. As a result, the uneven state of the toner on the toner carrier is eliminated, and density streaks do not appear on the patch image.

In addition, in the second aspect of the present invention, in order to achieve the above-mentioned second object, when image formation is not performed for a predetermined time period, optimization processing of image formation conditions is performed. This prevents the operation stopped state from continuing for a long time.

In addition, in the third aspect of the present invention, in order to achieve the above-mentioned second object, the toner carrier is rotated every predetermined time. As a result, the uneven state of the toner on the toner carrier is eliminated, and density streaks do not appear on the image.

Furthermore, in the fourth aspect of the present invention, in order to achieve the above-mentioned second object, when a predetermined time has elapsed since the previous image formation and the next image formation request is made, the toner carrier must be rotated more than one revolution before image formation is performed. . As a result, the uneven state of the toner on the toner carrier is eliminated, and density streaks do not appear on the image.

In addition, these inventions can be implemented in appropriate combination.

Description of the drawings

Fig. 1 is a diagram showing a first embodiment of the image forming apparatus of the present invention.

FIG. 2 is a block diagram of the electrical structure of the image forming apparatus of FIG. 1. FIG.

Fig. 3 is a cross-sectional view of a developing device of the image forming apparatus.

Fig. 4 is a diagram showing the structure of a density sensor.

Fig. 5 is a schematic flowchart of the optimization process of the concentration control factor in the first embodiment.

Fig. 6 is a flowchart of the initialization operation in the first embodiment.

Fig. 7 is a flowchart of the pre-action in the first embodiment.

8A and 8B are diagrams showing examples of the outline of the substrate of the intermediate transfer belt.

Fig. 9 is a flowchart of spike noise removal processing in the first embodiment.

Fig. 10 is a diagram showing how the spike noise is removed in the first embodiment.

11A, 11B, and 11C are schematic diagrams showing the relationship between the toner particle size and the amount of reflected light.

12A and 12B are graphs showing the correspondence between the toner particle size distribution and the change in the OD value.

Fig. 13 is a flowchart showing the derivation procedure of the control target value in the first embodiment.

14A and 14B are diagrams showing examples of look-up tables for obtaining control target values.

FIG. 15 is a flowchart of the developing bias voltage setting process in the first embodiment.

Fig. 16 is a diagram showing a patch image for high density.

FIGS. 17A and 17B are diagrams showing fluctuations in image density that occur during the rotation period of the photoreceptor.

FIG. 18 is a flowchart of the optimal value calculation process of the average developing bias in the first embodiment.

Fig. 19 is a flowchart of the exposure energy setting process in the first embodiment.

Fig. 20 is a diagram showing a patch image for low density.

Fig. 21 is a flowchart of an optimal value calculation process of exposure energy in the first embodiment.

Fig. 22 is a diagram showing a second embodiment of the image forming apparatus of the present invention.

FIG. 23 is a flowchart showing the image forming operation and the operation stop state in the third embodiment.

24A and 24B are timing charts showing the difference in operation due to the length of the operation stop time.

Fig. 25 is a timing chart showing the operation of each part of the device after the automatic operation is returned to the stop state.

26 is a flowchart of the image forming operation and the operation stop state in the fourth embodiment of the image forming apparatus of the present invention.

27A, 27B, and 27C are timing charts showing differences in device operation caused by the length of the operation stop time.

28 is a flowchart of a modified example of the image forming operation and the operation stop state in the fourth embodiment; FIGS. 29A and 29B are timing charts showing the relationship between the length of the operation stop time and the operation of the device in the processing of FIG. 28.

Fig. 30 is a flowchart showing main processing in the fifth embodiment.

Figure 31 is a flowchart showing the rotating action of the developing roller in the fifth embodiment.

32A, 32B, and 32C are timing charts showing operations in the main processing in the fifth embodiment.

FIG. 33 is a flowchart showing main processing in the sixth embodiment of the image forming apparatus of the present invention.

34A, 34B, and 34C are timing charts showing differences in operation caused by the input timing of the image signal in the main processing of the sixth embodiment.

35A and 35B are diagrams showing operations in a modification example of the main processing.

detailed description

Hereinafter, six embodiments and modifications of the image forming apparatus to which the present invention is applied will be described in sequence. The structure of the apparatus in these embodiments is basically the same, but some of the operations are different from each other. Therefore, first, in the description of the first embodiment, the structure and operation of the device will be described, and for the other embodiments, the differences from the first embodiment will be mainly described. First Embodiment (1) Configuration of Apparatus FIG. 1 is a diagram showing a first embodiment of the image forming apparatus of the present invention. In addition, FIG. 2 is a block diagram showing the electrical structure of the image forming apparatus of FIG. 1. This image forming device superimposes the four color toners of yellow (Y), cyan (C), magenta (M), and black (K) to form a full-color image or only black (K) toner to form a single color Image device. In this image forming apparatus, if an image signal is supplied from an external device such as a host computer to the main controller 11 in response to an imaging request from a user, the engine controller 10 controls the engine unit EG according to instructions from the main controller 11 Each part forms an image corresponding to the image signal on the sheet S. As described later, in this embodiment, the engine controller 10 functions as the "imaging part" of the present invention.

In this engine part EG, the photoreceptor 2 is rotatably arranged in the arrow direction D1 of FIG. 1. Around this photoreceptor 2, a charging unit 3, a rotating developing unit 4, and a cleaning unit 5 are respectively arranged along the rotation direction D1. The charging unit 3 applies a charging bias from the charging control unit 103 to uniformly charge the outer peripheral surface of the photoreceptor 2 to a predetermined surface potential. In this way, in this embodiment, the charging unit 3 functions as the "charged member" of the present invention.

Then, the light beam L is irradiated from the exposure unit 6 to the outer peripheral surface of the photoreceptor 2 charged by the charging unit 3. The exposure unit 6 functions as the "exposure component" of the present invention. The exposure unit 6 exposes the light beam L to the photoreceptor 2 in accordance with the control instruction provided from the exposure control section 102, and forms an image signal corresponding to the photoreceptor 2 on the photoreceptor 2. The electrostatic latent image. For example, after an external device such as a host computer provides an image signal to the CPU 111 of the main controller 11 via the interface 112, the CPU 101 of the engine controller 10 outputs a control signal corresponding to the image signal to the exposure control unit 102 at a predetermined timing. Accordingly, the light beam L is irradiated onto the photoreceptor 2 from the exposure unit 6 to form an electrostatic latent image corresponding to the image signal on the photoreceptor 2. In addition, when a patch image described later is formed as needed, a control signal corresponding to a patch image signal of a predetermined pattern set in advance is supplied from the CPU 101 to the exposure control section 102, and a control signal corresponding to the pattern is formed on the photoreceptor 2. The electrostatic latent image. In this way, in this embodiment, the photoreceptor 2 functions as the "image bearing body" of the present invention.

The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 includes a support frame 40 that can freely rotate about an axis, a rotation drive unit not shown, and a yellow developer that can be freely attached to and detached from the support frame 40 and contains toners of various colors. 4Y, cyan developer 4C, magenta developer 4M, and black developer 4K. As shown in FIG. 2, this developing unit 4 is controlled by the developing device control section 104. Then, the developing unit 4 is rotated and driven according to the control instruction from the developing device control section 104, and at the same time, the developing devices 4Y, 4C, 4M, 4K are selectively positioned to the predetermined developing position facing the photoreceptor 2, The toner of the selected color is applied to the surface of the photoreceptor 2. As a result, the electrostatic latent image on the photoreceptor 2 is developed by the selected toner color. Also, FIG. 1 shows a state where the yellow developer 4Y is positioned at the developing position.

These developers 4Y, 4C, 4M, and 4K all have the same structure. Therefore, the structure of the developing device 4K will be described in detail with reference to FIG. 3, and the structures and functions of the other developing devices 4Y, 4C, and 4M are also the same. Fig. 3 is a cross-sectional view of the developing device of the image forming apparatus. In this developing device 4K, a supply roller 43 and a developing roller 44 are mounted on a housing 41 containing toner T inside through shafts. After the developing device 4K is positioned at the above-mentioned developing position, it serves as the "carrying device of the present invention. The developing roller 44 acting as the image body is in contact with the photoreceptor 2 (contact development method) or is positioned opposite to the photoreceptor 2 with a predetermined gap (non-contact development method), and these rollers 43, 44 are positioned on the side of the main body. The provided rotation drive unit (not shown) cooperates to rotate in a predetermined direction. The developing roller 44 is made of a metal or alloy such as copper, aluminum, stainless steel, etc., to be cylindrical, so as to be applied with a developing bias voltage described later. The two rollers 43 and 44 rotate while contacting to rub the black toner on the surface of the developing roller 44 to form a toner layer with a predetermined thickness on the surface of the developing roller 44.

In addition, in this developing device 4K, a restricting blade 45 is arranged for restricting the thickness of the toner layer formed on the surface of the developing roller 44 to a predetermined thickness. This restricting blade 45 is composed of a plate-shaped member 451 such as stainless steel or phosphor bronze, and an elastic member 452 such as a rubber or resin member attached to the front end of the plate-shaped member 451. The rear end of the plate-shaped member 451 is fixed to the housing 41. In the rotation direction D3 of the developing roller 44, the elastic member 452 mounted on the front end of the plate-shaped member 451 is set to be larger than the rear of the plate-shaped member 451. The end is closer to the upstream side. Then, this elastic member 452 elastically contacts the surface of the developing roller 44, and finally limits the toner layer formed on the surface of the developing roller 44 to a predetermined thickness.

Also, at the end of the housing 41 above the developing roller 44, a sheet material 46 for preventing the toner in the housing 41 from leaking to the outside of the developing device is arranged. The sheet material 46 is formed into a thin plate with an elastic material such as resin or metal. One end of the sheet material 46 is fixed to the housing 41 and the other end elastically contacts the surface of the developing roller 44. Therefore, the toner carried on the developing roller 44 and conveyed to the upper part of the developing roller 44 passes through the contact point with the sheet material 46 and is guided into the housing 41 again. Then, by friction with the supply roller 43 rotating in the direction D4 shown in FIG. 3, the toner that has not been used for development is peeled off the surface of the developing roller 44, and at the same time, the new toner in the developing device is removed. The agent is supplied to the surface of the developing roller 44.

As described above, in this embodiment, the restricting blade 45 functions as the "restricting member" of the present invention, and the supply roller 43 functions as the "peeling member" of the present invention. In addition, in a state where the developing device 4K having such a structure is arranged at the developing position, as shown in FIG. 3, the restricting blade 45 is arranged below the developing roller 44. In addition, the peeling position (peeling position) of the toner from the developing roller 44 passing through the supply roller 43 is located further than the contact position (restricting position) of the developing roller 44 and the restricting blade 45 in the rotation direction D3 of the developing roller 44 It is measured upstream, and it is above this limit position.

In addition, the toner particles constituting the toner layer on the surface of the developing roller 44 are charged by rubbing with the supply roller 43 and the restricting blade 45. The case where the toner is negatively charged will be described below, but by appropriately changing the settings of each part of the device For electric potential, positively charged toner can also be used.

In this way, by the rotation of the developing roller 44, the toner layer formed on the surface of the developing roller 44 is sequentially transported to a position opposed to the photoreceptor 2 on which the electrostatic latent image is formed on the surface. Then, after the developing bias voltage from the developing device control unit 104 is applied to the developing roller 44, the toner carried on the developing roller 44 partially adheres to the various parts of the surface of the photoreceptor 2 according to the surface potential of the photoreceptor 2. In this way, the electrostatic latent image on the photoreceptor 2 is developed into a toner image of the toner color.

As the developing bias applied to the developing roller 44, a DC voltage or a DC voltage superimposed with an AC voltage can be used. Especially when the photoreceptor 2 and the developing roller 44 are separated from the arrangement, the toner can fly between the two. In an image forming apparatus of a non-contact development method that performs toner development, in order to efficiently fly the toner, it is preferable to use a voltage waveform in which an AC voltage such as a sine wave, a triangle wave, or a rectangular wave is superimposed on a DC voltage. Although the magnitude of the DC voltage and the amplitude, frequency, and duty ratio of the AC voltage are arbitrary, in this specification below, regardless of whether the developing bias has an AC component, the DC component (average value) is referred to as Average developing bias voltage Vavg.

Here, as the above-mentioned developing bias in an image forming apparatus of a non-contact developing method, a preferable example will be described. For example, the waveform of the developing bias voltage is a rectangular wave AC voltage superimposed on a DC voltage, the frequency of the rectangular wave is 3kHz, and the peak-to-peak voltage Vpp is 1400V. In addition, as described later, in this embodiment, the developing bias Vavg can be changed as one of the density control factors. However, as its variable range, the influence on the image density or the characteristic deviation of the photoreceptor 2 can be considered. Etc., set to (-110)V to (-330)V, for example. In addition, these numerical values are not limited to the above, and should be appropriately changed in accordance with the device configuration.

In addition, as shown in FIG. 2, each developer 4Y, 4C, 4M, 4K is provided with memories 91 to 94 to store information related to the manufacturer's batch number or use history, and the characteristics of the toner contained in the developer. data. In addition, connectors 49Y, 49C, 49M, and 49K are provided in the respective developers 4Y, 4C, 4M, and 4K. Then, as required, they are selectively connected to the connector 108 provided on the main body side, and data is sent and received between the CPU 101 and the memories 91 to 94 via the interface 105, and the developer-related Management of various information such as consumables management. Furthermore, in this embodiment, the main body connector 108 and the connector 49Y on the developer side are mechanically cooperated to perform data transmission and reception. However, for example, wireless communication and other electromagnetic devices may be used to perform non-contact data transmission and reception. Data sending and receiving. In addition, the memories 91 to 94 storing data unique to each developer 4Y, 4C, 4M, 4K are preferably non-volatile memories, which can be stored even when the power is turned off or the developer is detached from the main body. For the data, as such a non-volatile memory, for example, flash memory, ferroelectric memory, EEPROM, etc. can be used.

Return to Figure 1 and continue the description of the device structure. As described above, the toner image developed by the developing unit 4 is primarily transferred to the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer zone TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched over a plurality of rollers 72 to 75, and a drive section (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotating the roller 73. ). Furthermore, a secondary transfer roller 78 is provided at a position facing the roller 73 with the intermediate transfer belt 71 sandwiched therebetween, and a secondary transfer roller 78 can be moved in contact with and disengaged from the surface of the belt 71 by an electromagnetic clutch (not shown). Thus, when the color image is transferred to the sheet S, the toner images of each color formed on the photoreceptor 2 are superimposed on the intermediate transfer belt 71 to form a color image, and the color image is taken out from the cassette 8 and The color image is secondarily transferred on the sheet S conveyed to the secondary transfer area TR2 between the intermediate transfer belt 71 and the secondary transfer roller 78. In addition, the sheet S on which the color image is formed in this way is conveyed to the discharge tray portion provided on the top surface of the apparatus main body via the fixing unit 9. In addition, the surface potential of the photoreceptor 2 after the primary transfer of the toner image to the intermediate transfer belt 71 is reset by a dissipating member (not shown), and the remaining toner on the surface is removed by the cleaning section 5. , The charging unit 3 performs the next charging. In this way, in this embodiment, the intermediate transfer belt 71 functions as the "intermediate" of the present invention.

Then, when it is necessary to continue to form an image, repeat the above actions to form an image of the required number of pages, end a series of image forming actions, and the device becomes a standby state until a new image signal is received; in this device, for The power consumption in the standby state is suppressed, and the operation is shifted to the stop state. That is, the rotational driving of the photoreceptor 2, the developing roller 44, the intermediate transfer belt 71, and the like is stopped, and at the same time, the application of the developing bias to the developing roller 44 and the charging bias to the charging unit 3 are stopped, and the device is in an operation stop state.

In addition, a cleaner 76, a density sensor 60, and a vertical synchronization sensor 77 are arranged near the roller 75. Among them, the cleaner 76 can be moved closer to/away from the roller 75 by an electromagnetic clutch not shown. Then, while moving to the roller 75 side, the scraper of the cleaner 76 touches the surface of the intermediate transfer belt 71 stretched on the roller 75, and removes the remaining peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Adhering toner. In addition, the vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and serves as a vertical synchronization sensor for obtaining a synchronization signal output in association with the rotation drive of the intermediate transfer belt 71, that is, a vertical synchronization signal Vsync. To play a role. In this way, in this device, in order to coordinate the operation timings of the various parts and at the same time to accurately overlap the toner images formed by the colors, the operations of the various parts of the device are controlled based on the vertical synchronization signal Vsync. Furthermore, the density sensor 60 is arranged to face the surface of the intermediate transfer belt 71 and is configured as described later to measure the toner density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71.

Also, in FIG. 2, reference numeral 113 is an image memory provided in the main controller 11 for storing image signals supplied from an external device such as a host computer via the interface 112; reference numeral 106 is a ROM, used for storing the CPU 101 The executed calculation program or the control data of the control engine part EG, etc.; and the reference number 107 is RAM, which temporarily stores the calculation result or other data in the CPU 101.

Fig. 4 is a structural diagram of a concentration sensor. This density sensor 60 has a light-emitting element 601 such as an LED that functions as the "light-emitting member of the present invention, and is used to irradiate light to the winding area 71 a wound on the roller 75 in the surface area of the intermediate transfer belt 71. In addition, the density sensor 60 is provided with a polarization beam splitter 603, a light receiving unit 604 for monitoring the amount of irradiated light, and an irradiated light amount adjusting unit 605 for adjusting according to the light amount control signal Slc provided from the CPU 101 as described later. The amount of irradiated light.

As shown in FIG. 4, the polarizing beam splitter 603 is arranged between the light-emitting element 601 and the intermediate transfer belt 71, and divides the light emitted from the light-emitting element 601 into an incident light with the irradiation light on the intermediate transfer belt 71. P-polarized light with a polarization direction parallel to the plane and s-polarized light with a polarization direction perpendicular to it. The p-polarized light enters the intermediate transfer belt 71 as it is, while the s-polarized light is taken out from the polarization beam splitter 603 and enters the light receiving unit 604 for monitoring the amount of irradiated light. From then on, the light receiving element 642 of the light receiving unit 604 A signal proportional to the amount of irradiated light is output to the irradiated light amount adjustment unit 605.

The irradiation light quantity adjustment unit 605 performs feedback control on the light emitting element 601 based on the signal from the light receiving unit 604 and the light quantity control signal S1 from the CPU 101 of the engine controller 10, and irradiates the intermediate transfer belt 71 from the light emitting element 601. The irradiation light amount of is adjusted to a value corresponding to the light amount control signal Slc. In this way, in this embodiment, the amount of irradiated light can be changed and adjusted appropriately in a wide range.

In addition, in this embodiment, the input compensation voltage 641 is applied to the output end of the light receiving element 642 provided in the light receiving unit 604 for monitoring the amount of irradiated light. As long as the light amount control signal Slc does not exceed a certain signal level, the light emitting element 601 is maintained in the off state. In this way, erroneous lighting of the light-emitting element 601 caused by noise, temperature drift, or the like is prevented.

In this way, after the light amount control signal Slc of a predetermined level is supplied from the CPU 101 to the irradiation light amount adjustment unit 605, the light emitting element 601 is turned on, and the intermediate transfer belt 71 is irradiated with p-polarized light as the irradiation light. Then, the p-polarized light is reflected by the intermediate transfer belt 71, and the reflected light amount detecting unit 607 detects the light amount of p-polarized light and the light amount of s-polarized light in the light components of the reflected light, and outputs a signal corresponding to each light amount to the CPU 101.

As shown in FIG. 4, the reflected light amount detection unit 607 includes: a polarization beam splitter 671 arranged on the optical path of the reflected light; a light receiving unit 670p that receives p-polarized light passing through the polarization beam splitter 671, and outputs the same p-polarized light And the light receiving unit 670s, which receives the s-polarized light divided by the polarization beam splitter 671, and outputs a signal corresponding to the s-polarized light. In this light-receiving unit 670p, the light-receiving element 672p receives p-polarized light from the polarization beam splitter 671, and the output from the light-receiving element 672p is amplified by the amplifier circuit 673p, and the amplified signal is used as a light quantity signal corresponding to p-polarized light. Vp is output to the CPU 101. In addition, the light receiving unit 670s has the light receiving unit 672s and the amplifier circuit 673s similarly to the light receiving unit 670p, and outputs a light quantity signal Vs corresponding to s-polarized light. Therefore, it is possible to independently obtain the light amounts of two component lights (p-polarized light and s-polarized light) that are different from each other among the light components of the reflected light.

In addition, in this embodiment, the output compensation voltages 674p and 674s are applied to the output ends of the light receiving units 672p and 672s, respectively. Even when the output from each light receiving element is zero, that is, the amount of reflected light is zero, the amplifier circuits 673p and 673s The input potential of is also the specified positive potential. By doing so, it is possible to avoid the dead zone of each amplifier circuit 673p and 673s in the vicinity of the zero input, and to output an appropriate output voltage corresponding to the amount of reflected light.

The signals of these output voltages Vp and Vs are input to the CPU 101 via an A/D conversion circuit not shown. At the same time, the CPU 101 responds to these output voltages Vp at predetermined time intervals (in this embodiment, every 8 msec) as needed. , Vs is sampled. In this way, according to the appropriate timing, such as the timing when the device is turned on, the timing immediately after a certain unit is replaced, etc., the CPU 101 adjusts the density control factors such as the developing bias or exposure energy that affect the image density to stabilize the image. Image density. More specifically, corresponding to a predetermined patch image pattern, the image data pre-stored in the ROM 106 is used as an image signal, and the above-mentioned density control factor is changed for each toner color in multiple stages while performing an image forming operation to form The small test image (patch image) corresponding to the image signal is then detected by the density sensor 60 for its toner density, and based on the result, the density control factor is adjusted as a condition for obtaining a desired image density. The adjustment process of this concentration control factor will be described below.

(2) Adjustment process FIG. 5 is a schematic flowchart of the density control factor adjustment process in this embodiment. The optimization process is composed of the following six sequences according to its processing sequence: initialization action (step S1), pre-action (step S2), deriving control target value (step S3), setting development bias (step S4), setting exposure For energy (step S5) and post-processing (step S6), the details of the operation of each of the above-mentioned sequences will be described below.

A. Initialization operation FIG. 6 is a flowchart of the initialization operation in this embodiment. In this initialization action, first, as a preparatory action (step S101), the developing unit 4 is rotationally driven and positioned to the so-called home position. At the same time, an electromagnetic clutch is used to make the cleaner 71 and the secondary transfer roller 78 transfer from the intermediate The belt 71 moves to the disengaged position. Then, in this state, the driving of the intermediate transfer belt 71 is started (step S102), and then the photoreceptor 2 is started by starting the rotation drive and the discharge operation of the photoreceptor 2 (step S103).

Then, the vertical synchronization signal Vsync indicating the reference position of the intermediate transfer belt 71 is detected, and after the rotation is confirmed (step S104), the application of a predetermined bias voltage to each part of the device is started (step S105). That is, a charging bias is applied from the charging control section 103 to the charging unit 3 to charge the photoreceptor 2 to a predetermined surface potential, and then a predetermined primary transfer bias is applied to the intermediate transfer belt 71 from a bias generating section not shown. Pressure.

From this state, the cleaning operation of the intermediate transfer belt 71 is performed (step S106). That is, the cleaner 76 is brought into contact with the surface of the intermediate transfer belt 71, and in this state, the intermediate transfer belt 71 is rotated approximately one revolution to remove remaining toner or dirt on the surface. Then, the secondary transfer roller 78 to which the cleaning bias is applied is brought into contact with the intermediate transfer belt 71. The polarity of this cleaning bias is opposite to the secondary transfer bias supplied to the secondary transfer roller 78 during normal image forming operations. Therefore, the remaining toner on the secondary transfer roller 78 is transferred to the intermediate transfer. The surface of the printing belt 71 is further removed from the surface of the intermediate transfer belt 71 by a cleaner 76. In this way, after the cleaning operation of the intermediate transfer belt 71 and the secondary transfer roller 78 is completed, the intermediate transfer belt 71 is separated from the secondary transfer roller 71 and the cleaning bias is cut off. Then, it waits for the next vertical synchronization signal Vsync (step S107), and cuts off the charging bias and the primary transfer bias (step S108).

In addition, in this embodiment, it is not limited to the execution of the adjustment process of the density control factor, and the CPU 101 can execute this initialization action independently of other processes as needed. That is, when the next operation is continued (step S109), the initialization operation is ended in a state where the execution of the above-mentioned step S108 is completed, and the next operation is transferred. On the other hand, when the next operation is not scheduled, as a stop process (step S110), the cleaner 76 is detached from the intermediate transfer belt 71, and the discharge operation and the rotational drive of the intermediate transfer belt 71 are stopped. In this case, it is preferable that the intermediate transfer belt 71 be stopped in a state where its reference position is immediately before the position opposed to the vertical synchronization sensor 77. This is because when the intermediate transfer belt 71 is rotationally driven in a subsequent operation, its rotation state is confirmed by the vertical synchronization signal Vsync, and if it is done as described above, it can be determined whether the vertical synchronization is detected immediately after the start of the drive. Signal Vsync to judge whether there is an abnormality in a short time.

B. Pre-action FIG. 7 is a flowchart of pre-action in this embodiment. In this pre-operation, two processes are simultaneously performed as pre-processing before forming a patch image, which will be described later. That is, in order to optimize the density control factor with high accuracy, the operating conditions of each part of the device are adjusted (pre-action 1); in parallel, the developing rollers 44 provided in the respective developing devices 4Y, 4C, 4M, and 4K are performed. Rotation processing (pre-action 2).

B-1. Setting operating conditions (pre-action 1) In the flow on the left side (pre-action 1) shown in FIG. 7, first, the density sensor 60 is calibrated (steps S21a, S21b). In the calibration (1) of step S21a, when the light-emitting element 601 of the detection density sensor 60 is in the off state, the output voltages Vp and Vs of the light receiving units 670p and 670s are stored as dark outputs Vpo and Vso. Next, in the calibration (2) of step S21b, the light quantity control signal Slc supplied to the light emitting element 601 is changed to the two lighting states of low light quantity and high light quantity, and the output voltage of the light receiving unit 670p is detected for each light quantity. Vp. Then, based on the values of these three points, a light-emitting element whose output voltage Vp is at a predetermined reference level (in this embodiment, 3V plus the value of the aforementioned dark output Vpo) when the toner is not attached is obtained 601 standard amount of light. In this way, the level of the light quantity control signal Slc that makes the light quantity of the light emitting element 601 the reference light quantity is calculated, and its value is set as the reference light quantity control signal (step S22). After that, when the light-emitting element 601 needs to be turned on, the CPU 101 outputs this reference light quantity control signal to the irradiation light quantity adjustment unit 605, whereby the light-emitting element 601 is feedback controlled to always emit light at this reference light quantity.

In addition, the output voltages Vpo and Vso when the light-emitting element 601 is in the off state are stored as the "dark output" of the sensor system. When the density of the toner image is detected as described later, the output voltages Vp, Vs By subtracting this value from it, the influence of dark output can be eliminated and the density of the toner image can be detected with high accuracy.

Also, the output signal from the light-receiving unit 672p when the light-emitting element 601 is lit depends on the amount of reflected light from the intermediate transfer belt 71. However, as described later, the surface condition of the intermediate transfer belt 71 is not necessarily optically It is uniform, so when calculating the output in this state, it is better to take the average value of the output within one round of the intermediate transfer belt 71. On the other hand, in the state where the light emitting element 601 is off, it is not necessary to detect the output signal within one circle of the intermediate transfer belt 71 in this way, but in order to reduce the detection error, it is better to average the output signal at several points.

In this embodiment, the surface of the intermediate transfer belt 71 is white, so the reflectance of light is high. If toner of a certain color adheres to the belt 71, the reflectance decreases. Therefore, in this embodiment, as the amount of toner adhesion on the surface of the intermediate transfer belt 71 increases, the output voltages Vp and Vs from the light receiving unit gradually decrease from the reference level. To estimate the amount of toner adhesion, and then estimate the density of the toner image.

In addition, in this embodiment, according to the difference in the reflection characteristics between the color (Y, C, M) toner and the black (K) toner, the density of the patch image of the black toner described later is based on the difference from the patch image. The intensity of the p-polarized light in the reflected light of the image is determined, and the density of the patch image of the color toner is determined based on the light intensity ratio of the p-polarized light and the s-polarized light. Therefore, it can be accurately determined in a wide dynamic range. Find the image density.

Return to Figure 7 for the time being, and continue to explain the pre-action. The surface state of the intermediate transfer belt 71 may not necessarily be said to be optically the same, and the toner may melt and become gradually discolored or dirty as it is used. In order to prevent this change in the surface state of the intermediate transfer belt 71 from causing errors in the detection of the density of the toner image, in this embodiment, a basic overview within 1 week of the intermediate transfer belt 71, that is, no Information on the shading of the surface of the intermediate transfer belt 71 in the state of bearing the toner image. Specifically, the light-emitting element 601 is made to emit light according to the previously calculated reference light quantity, while sampling the output voltages Vp and Vs from the light-receiving units 670p and 670s, the intermediate transfer belt 71 is rotated for one revolution (step S23). Each sample data (the number of samples in this embodiment: 312) is stored in the RAM 107 as a basic profile. In this way, by grasping the density of each part of the surface of the intermediate transfer belt 71 in advance, it is possible to more accurately estimate the density of the toner image formed thereon.

However, the output voltages Vp and Vs from the density sensor 60 are sometimes superimposed with changes in reflectance caused by minute dirt or damage of the roller 75 and the intermediate transfer belt 71, and even electrical noise mixed in the sensor circuit. Spike-like noise caused by other factors. 8A and 8B are diagrams showing examples of the basic outline of the intermediate transfer belt. After the density sensor 60 detects the amount of reflected light from the surface of the intermediate transfer belt 71 and plots it in the range of more than one revolution, as shown in FIG. 8A, the output voltage Vp from the sensor 60 may not only correspond to the intermediate transfer belt 71 The circumference of 71 or its rotation period changes periodically, and spike-like noise with a narrow width is superimposed on its waveform. This noise may contain both components synchronized with the above-mentioned rotation period and irregular components not synchronized with it. Fig. 8B enlarges a part of this sample data string. In this figure, due to the superimposed noise, the two data with the labels Vp(8) and Vp(19) in each sample data are prominently larger than the other data, and the labels Vp(4) and Vp(16) are attached. The 2 data are significantly smaller than the others. Also, the p-polarized light component in the output of the two sensors is described here, but the s-polarized light component can also be considered in the same way.

The detection point diameter of the density sensor 60 is, for example, about 2 to 3 mm, and it is considered that the discoloration or soiling of the intermediate transfer belt 71 generally occurs in a larger area. Therefore, it can be considered that such locally prominent data is affected by the above-mentioned noise. In this way, if the basic profile or the density of the patch image is obtained based on the sample data superimposed with noise, and the density control factor is set based on the result, it may not always be possible to set each density control factor to the optimal state, but the image The quality has deteriorated.

Therefore, in the present embodiment, as shown in FIG. 7, after sampling the sensor output for one circumference of the intermediate transfer belt 71 in step S23, the spike noise removal process is executed (step S24).

Fig. 9 is a flowchart of spike noise removal processing in this embodiment. In this spike noise removal processing, the acquired "original" i.e. unprocessed sample data string is a continuous part of the interval (in this embodiment, the length is equivalent to 21 samples) (step S241), and remove this Among the 21 sample data included in the interval, the level is located after the first 3 and the last 3 data (steps S242 and S243), and the arithmetic average of the remaining 15 data is calculated (step S244). Then, the average value is regarded as the average level in the interval, and the 6 data removed in steps S242 and S243 are replaced with the average value to obtain a "corrected" sample data string with noise removed (step S245 ). Furthermore, the above-mentioned steps S241 to S245 are also repeated for the next section as necessary, and the spike noise is similarly removed (step S246).

Taking the data string shown in FIG. 8B as an example, the spike noise removal by the above-mentioned processing will be described in detail with reference to FIG. 10. Fig. 10 is a schematic diagram of spike noise removal in this embodiment. In the data string of Fig. 8B, it is considered that the two data Vp(8) and Vp(19) which are prominently larger than other data, and the data Vp(4) and Vp(16) which are prominently smaller than the other data appear. The effect of noise. In this spike noise removal processing, since the top 3 of each sample data is removed (step S242 in FIG. 9), 3 data Vp(8) including 2 data considered to contain noise among these data are removed. ), Vp(14) and Vp(19). Similarly, three data Vp(4), Vp(11), and Vp(16) including two data considered to contain noise are also removed (step S243 in FIG. 9). Then, as shown in FIG. 10, by replacing these 6 data with the average value Vpavg of the other 15 data (represented by a circle with a diagonal line), the spike noise contained in the original data string is removed.

Also, when implementing this spike noise removal, the number of samples extracted and the number of data removed are not limited to the above, and can be any number. However, some selection methods may not achieve sufficient noise removal effects, but may instead Increase the error, so it is best to make a cautious decision based on the following viewpoints.

That is, if a data string in a section that is too short for the frequency of occurrence of noise is extracted, the probability that noise is not included in the section where noise removal processing is performed is high, and the number of arithmetic processing increases, so the efficiency is not high. high. On the other hand, if a data string in a too wide interval is extracted, the significant variation in sensor output, that is, the variation reflecting the density variation of the detection object, is averaged, and the original intended density characteristic cannot be accurately obtained.

In addition, since the frequency of noise occurrence is not constant, if only the first few or the last few data of a predetermined number are removed uniformly from the extracted data string, it is possible to connect the data Vp( 11) Data that does not contain noise like Vp(14) is also removed, or on the contrary, the noise cannot be removed sufficiently. Among them, even if a few data that does not contain noise are removed, as shown in Figure 10, the difference between these data Vp(11), Vp(14) and the average value Vpavg is relatively small, so replacing these data with the average value Vpavg causes The error is small. On the other hand, when data containing noise remains without being removed, by replacing other data with the average value obtained by including the data, the error may increase instead. Therefore, the ratio of the number of data removed to the number of samples of the extracted data is preferably determined to be equal to or greater than the frequency of noise generated in the actual device.

In this embodiment, as shown in FIG. 8A, due to the influence of noise, the frequency of the data deviated to the side greater than the original characteristic and the data deviated to the side smaller than the original characteristic are approximately the same, and the frequency of the noise itself The degree is about 25% or less (5 samples or less in 21 samples). Based on this experimental fact, the spike noise removal processing is constituted as described above.

In addition, there are various methods for removing spike noise in addition to the above. For example, by applying a conventionally well-known low-pass filtering process to the "original sample data obtained by sampling, it is also possible to remove spike-like noise. However, in the existing filtering process, although the sharpness of the noise waveform can be alleviated, the result is that not only the data containing noise changes the original value, but also the surrounding data also changes the original value. Therefore, due to the form of noise, there are May cause large errors.

Contrary to this, in this embodiment, the first few/last few data corresponding to the frequency of noise occurrence in each sample data are replaced with average values, while the other data remains intact, so this The possibility of error is very low.

In addition, this spike noise removal processing is not only performed when the above-mentioned basic profile is obtained, but also when obtaining the image density of the toner image as described later, it is also performed on the sample data obtained as the amount of reflected light.

B-2. The rotation operation of the developing device (pre-operation 2) It has been known in the past that when the image formation is performed after the power is turned off or the image formation is not performed even though the power is turned on, the image formation is stopped for a long time. Sometimes periodic density streaks appear on the image. In this specification, this phenomenon is called banding phenomenon. The inventors of the present application have found that this is caused by the following conditions: the toner is carried by the developing roller 44 of each developer and left for a long time. , It is difficult to leave the developing roller 44, and the toner adhesion amount or its adhesion is different on the surface of the developing roller 44, so the toner layer on the developing roller 44 gradually becomes uneven.

Hereinafter, the findings of the inventors of the present application related to the placement of stripes will be explained.

The streak phenomenon most obviously appears on the image that is initially formed after the action is stopped, but the density streaks are not obvious after repeated image formation, and the formation of multiple images is almost disappeared. In addition, in a long-lasting operation stop state or in a high-temperature/high-humidity environment, obvious density streaks will appear especially.

In addition, the placement streak phenomenon also occurs when using a developing roller whose surface is conductive. That is, in a device using a metal developing roller or a developing roller with a conductive layer provided on the surface of a non-conductive material, density streaks caused by the streak phenomenon are noticeable.

In order to reveal the occurrence mechanism of the placement streak phenomenon, the following insights were obtained through experiments and observations using a developer with the structure shown in FIG. 3. First, the occurrence of image density streaks was observed, and as a result, the corresponding relationship between the density of the image and the surface position of the developing roller 44 was as follows. That is, on the surface of the developing roller 44, the image developed by the toner carried on the surface area (hereinafter referred to as the "developing chamber portion") located in the inner position of the developer housing 41 in the stopped state has a high density, and The image developed by the toner carried on the outer surface area of the exposed housing 41 (hereinafter referred to as "exposed portion") has a low density.

In addition, the potential distribution of the toner layer of the developing roller 44 after the operation stop state was continued was measured with a surface potentiometer. As a result, the absolute value of the potential of the toner became lower in the portion corresponding to the developing chamber, but in the portion corresponding to the The exposed part becomes taller. This potential difference gradually becomes smaller as the developing roller 44 is rotated, and soon becomes substantially uniform.

In addition, the toner charge amount (unit: μC/g) and the toner conveyance amount (mg/cm2) on the surface of the developing roller 44 were measured. As a result, the toner conveyance amount was approximately The same, but the toner charge amount is higher on the exposed portion side, and its magnitude is about twice the toner charge amount on the developing chamber portion side. The above-mentioned difference in the potential of the toner layer can be considered to be caused by the difference in the charge amount of the toner.

From the above results, it can be considered that the stand-up streak phenomenon is caused by the position, more specifically, the difference between the developing chamber portion and the exposed portion, based on the charge amount of the toner on the developing roller 44 when the operation is stopped. This difference in charge amount is gradually reduced by the rotation of the developing roller 44. Therefore, it can be considered that the state of the surface of the developing roller 44 that triboelectrically charges the toner is different between the developing chamber portion and the exposed portion after leaving the operation stop state.

When observing the surface of the developing roller 44, a lot of fine powders such as additives falling from the toner with a small particle size or the toner are adhered. The difference in the amount of adhesion of such fine powder and the amount of water contained, etc. affect the frictional charging state between the developing roller 44 and the toner. Therefore, in the inside of the developing device, the toner containing this fine powder component is always in contact with the developing roller 44, and passes through the contact of the supply roller 43 to the developing roller 44, the restricting blade 45, the sheet material 46, etc. , The toner is in a pressed state. Therefore, in the area of the surface of the developing roller 44 that is located inside the developing device (developing chamber portion) in the stopped state of operation, adhesion of fine powder components is likely to occur. In contrast, the toner is only electrostatically attached to the exposed portion exposed to the outside of the developing device, so the adhesion of fine powder components is relatively small.

In this way, when the operation is stopped for a long time, the adhesion state of the fine powder components on the developing roller 44 is not uniform. Therefore, the main cause of the difference in the charge amount of the toner layer is the placement streak phenomenon.

In addition, the occurrence of streaks is also related to the structure of the device. Like the developer 4K of the present embodiment, in the developer provided below the developer roller 44 and used to form a toner layer restriction blade 45 of a predetermined thickness on the developer roller 44, it is particularly prone to cause problems caused by fine powder components. Place the streak phenomenon. This is because such fine powder components tend to stay in the lower part of the developer housing, so there are many fine powder components near the contact position (restriction position) of the restricting blade 45 and the developing roller 44.

In particular, as shown in FIG. 3, the toner peeling of the developing roller 44 is performed on the upstream side of the restricting position in the rotational direction D3 of the developing roller 44, and the peeling position at which the toner is peeled off is lower than the restricting position. In the upper case, the streak phenomenon is even more obvious. That is, around the peeling position, fine powder components newly generated by the friction between the supply roller 43 and the developing roller 44 and peeled off from the developing roller 44 are retained. Then, due to the rotation of the supply roller 43 and the developing roller 44 or the action of gravity, these fine powder components are continuously fed toward the contact position or the restricted position of the supply roller 43 and the developing roller 44, so it is easy to get on the surface of the developing roller 44. The adhesion of the fine powder components occurs, and therefore, the placement streak phenomenon is likely to occur.

In addition, when the surface of the developing roller 44 is formed of a conductive material, the adhesion of the fine powder acting on the mirror image force is relatively large, so even in a device with such a developing roller, the streaking phenomenon is likely to occur.

As the structure of the developing roller, generally the entire roller is formed into a cylindrical shape with the same material, and the core material and sleeve formed of other materials are coaxially combined together. Among them, the structure equivalent to the above can be listed, for example: i) the entire roll or at least the sleeve is formed of metal or alloy; ii) the entire roll or at least the sleeve is formed of conductive rubber or conductive resin; and, iii) The surface of the insulating or conductive roller is covered with a conductive surface layer. The "conductivity" mentioned here means that the volume resistivity is about 1×10-2Ω·m or less. Examples of such materials include metals, oxides or nitrides thereof, or graphite. In addition, as the surface layer of iii) above, in addition to conductive materials such as metals, alloys, and conductive resins, materials in which conductive materials are dispersed in the insulator can be used. As the coating method, plating, evaporation, Cladding, spraying, spraying or dipping etc.

In addition, the occurrence of streaks is also related to the nature of the toner used. That is, in an apparatus that uses a toner containing a wax component as a separation material for preventing fixing offset, the streak phenomenon is likely to occur. This is because the fine powder of wax freed from the toner particles or the toner particles on which the wax component is exposed on the surface are likely to cause toner adhesion to the developing roller 44 due to Van der Waals force.

Returning to Fig. 7, the description of pre-action 2 is continued. After a long time has elapsed under such an uneven surface of the developing roller 44, the device is placed in a stopped state, and the density control factor is re-optimized before the next image is formed, there is a real image caused by the placement of streaks. Concentration streaks may affect this optimization process. In particular, in an image forming apparatus having at least one of the above-mentioned structures, density streaks caused by the placement streak phenomenon are likely to occur, so it is necessary to describe measures for eliminating the placement streak phenomenon.

Therefore, in the image forming apparatus of the present embodiment, in order to eliminate the streaking phenomenon before forming a patch image, the rotation operation of each developing roller 44 is performed. Specifically, as shown in the flow on the right side of FIG. 7 (pre-action 2), first, the yellow developer 4Y is placed at the developing position facing the photoreceptor 2 (step S25), and the average developing bias Vavg is set In order to have the smallest absolute value in the variable range (step S26), the developing roller 44 is rotated at least one revolution by the rotation driving section on the main body side (step S27). Then, while the developing unit 4 is rotated to switch the developing devices (step S28), the other developing devices 4C, 4M, and 4K are sequentially positioned at the developing position, and the developing rollers 44 respectively provided thereon are similarly rotated for more than one revolution. By rotating each developing roller 44 in this way for more than one revolution, the toner layer on the surface of the developing roller 44 is temporarily peeled off by the supply roller 43 and the restricting blade 45 and re-formed. In the patch image that continues to be formed, the toner layer is re-formed in this way. The toner layer in a more uniform state is used for image formation, so density streaks caused by the placement streak phenomenon are unlikely to occur.

In addition, in the pre-action 2 described above, the absolute value of the average developing bias voltage Vavg is minimized in step S26. The reason is as follows.

As described later, the larger the absolute value |Vavg| of the average developing bias voltage Vavg, which is a density control factor that affects the image density, the higher the density of the formed toner image. This is because the greater the absolute value of the average developing bias |Vavg|, the area between the electrostatic latent image on the photoreceptor 2 exposed by the light beam L, that is, the area between the surface area where the toner should be attached and the developing roller 44 The greater the potential difference of, the more the toner movement from the developing roller 44 is promoted, but when the basic profile of the intermediate transfer belt 71 is obtained, such toner movement is undesirable. This is because if the toner moved from the developing roller 44 to the photoconductor 2 is transferred to the intermediate transfer belt 71 in the primary transfer zone TR1, the amount of reflected light from the intermediate transfer belt 71 will be changed. Therefore, the basic overview cannot be obtained correctly.

In this embodiment, as described later, the average developing bias voltage Vavg can be used as one of the density control factors to be changed in multiple stages within a predetermined variable range. Therefore, by setting the average developing bias voltage Vavg to the value with the smallest absolute value within its variable range, the state in which the toner is most difficult to move from the developing roller 44 to the photoreceptor 2 is realized, and the intermediate transfer belt Toner adhesion on 71 is suppressed to a minimum. For the same reason, in a device in which the developing bias has an AC component, it is better to set its amplitude to be smaller than during normal image formation. For example, as described above, in a device in which the peak-to-peak voltage Vpp of the developing bias is set to 1400V, the peak-to-peak voltage Vpp can be set to about 1000V. In a device that uses parameters other than the average developing bias Vavg, such as the duty ratio of the developing bias or the charging bias, as the density control factor, it is also best to appropriately set the density control factor so as to achieve the above-mentioned difficulty. Conditions for toner movement.

In addition, in this embodiment, the processing time is shortened by executing the above-mentioned pre-action 1 and pre-action 2 simultaneously in parallel. That is, in pre-action 1, the intermediate transfer belt 71 is rotated at least one revolution in order to obtain a basic overview, and it is preferable to rotate the intermediate transfer belt 71 for two more revolutions for sensor calibration. A total of three revolutions are required. At the same time, in pre-action 2, the most The developing rollers 44 are rotated as much as possible, and these operations can be performed independently of each other. Therefore, by performing these operations in parallel, it is possible to reduce the time required for the entire adjustment process while ensuring the time required for each process.

C. Deriving the control target value In the image forming apparatus of this embodiment, as described later, two types of toner images are formed as patch images, and each density control factor is adjusted so that the density reaches a predetermined density target value , But this target value is not set to be constant, but is changed according to the working condition of the device. The reason is as follows.

As described above, in the image forming apparatus of this embodiment, the image density is estimated by detecting the amount of reflected light from the toner image developed on the photoreceptor 2 and first transferred to the surface of the intermediate transfer belt 71 . Such a technique for obtaining the image density based on the amount of reflected light of the toner image has been widely used in the past. However, as detailed below, the amount of reflected light from the toner image carried on the intermediate transfer belt 71 (or the corresponding amount of light from the density The corresponding relationship between the sensor output (Vp, Vs) of the sensor 60 and the optical density (OD value) of the toner image formed on the sheet S of the final recording medium is not uniquely determined, but depends on the device or the color palette. The state of the agent changes subtly. Therefore, even if the density control factors are controlled to make the "toner density" based on the sensor output constant as in the prior art, the "image density" of the image finally formed on the sheet S will vary according to the state of the toner. .

One of the reasons for the inconsistency between the sensor output and the OD value on the sheet S is the toner fused on the sheet S through the fixing process, and the toner that is not fixed but only adheres to the surface of the intermediate transfer belt 71. The reflection state of the toner is different. 11A, 11B, and 11C are schematic diagrams of the relationship between the particle size of the toner and the amount of reflected light. As shown in FIG. 11A, in the image Is finally obtained on the sheet S, the toner Tm melted by the heating/pressurization in the fixing process is in a state of being fused on the sheet S. Therefore, its optical density (OD value) reflects the amount of reflected light in a state where the toner is fused, but its size is mainly represented by the toner density on the sheet S (for example, it can be represented by the toner mass per unit area) ) To decide.

In contrast, in the toner image on the intermediate transfer belt 71 that does not undergo a fixing process, each toner particle merely adheres to the surface of the intermediate transfer belt 71 individually. Therefore, even if the toner density is the same (that is, the OD value after fixing is the same), for example, the toner T1 with a small particle size shown in FIG. 11B is adhered with high density, and the toner T1 with a large particle size shown in FIG. In a state where the toner T2 adheres at a lower density and the surface of the intermediate transfer belt 71 is partially exposed, the amount of reflected light may not necessarily be the same. In other words, even if the toner images from before fixing are the same, the image density (OD value) after fixing is not necessarily the same. According to experiments conducted by the inventors of the present application, there is generally a tendency that if the amount of reflected light is equal, if the large particle size toner occupies a high proportion of the toner particles constituting the toner image, then The image density after fixing is high.

In this way, the correspondence between the OD value on the sheet S and the amount of reflected light from the toner image on the intermediate transfer belt 71 changes according to the state of the toner, particularly its particle size distribution. 12A and 12B are corresponding graphs of the particle size distribution of the toner and the change in the OD value. In order to form a toner image, it is desirable that the particle diameters of the toner particles contained in each developer are all concentrated at the design center value. However, as shown in Figure 12A, in fact, its particle size has various forms of distribution, and it goes without saying that the form varies with the type of toner or the manufacturing method. Even toners manufactured according to the same specifications will There are subtle differences according to each manufacturing lot number and each product.

Since the quality or charge amount of these toners of various particle sizes are different, if toners with such particle size distribution are used for image formation, these toners will not be consumed uniformly, but by The device selectively consumes toner of a suitable particle size, while other toners are less consumed and remain in the developer. Therefore, as the toner continues to be consumed, the particle size distribution of the toner remaining in the developing device is also constantly changing.

As mentioned above, the amount of reflected light from the toner image before fixing changes according to the particle size of the toner that constitutes the image. Therefore, even if the density control factors are adjusted to make the amount of reflected light always constant, the amount of reflected light on the sheet S will be fixed after fixing. The image density is not necessarily constant. 12B shows the control of each density control factor so that the amount of reflected light from the toner image is constant, that is, the output voltage from the density sensor 60 is constant, and at the same time, the optical density (OD) of the image on the sheet S when image formation is performed. Value). For example, as shown in the curve a of FIG. 12A, in the case where the particle size of the toner is well concentrated near the center value on the design, as shown in the curve a of FIG. 12B, even if the toner in the developer is With continuous consumption, the OD value is roughly maintained at the target value. Contrary to this, for example, as shown in curve b of FIG. 12A, in the case of using a toner having a wider particle size distribution, as shown in curve b of FIG. 12B, although initially the particle size near the design center value The toner is mainly consumed, and the OD value roughly in line with the target value is obtained. However, as the toner continues to be consumed, the proportion of this toner decreases, and toner with a larger particle size is used instead The image is formed, so the OD value gradually rises. Furthermore, there are the following cases: as shown by the dotted lines in FIG. 12A, the central value of the distribution deviates from the design value from the beginning according to the manufacturing lot number of the toner or the developer. Corresponding to this, the OD on the sheet S The values are also shown by the dashed lines in FIG. 12B, showing various changes as the amount of toner consumption increases.

As the main factor that influences the characteristics of the toner, in addition to the particle size distribution of the toner described above, there are, for example, the state of the pigment dispersion in the toner base particles, or the charging caused by the mixed state of the toner base particles and additives. Sexual changes, etc. In this way, toner characteristics vary slightly from product to product, so the image density on the sheet S is not necessarily constant, and the degree of density change varies depending on the toner used. Therefore, in the conventional image forming apparatus that controls each density control factor so that the output voltage from the density sensor is constant, sometimes the image density fluctuation caused by the deviation of the toner characteristics cannot be avoided, and satisfactory image quality may not be obtained.

Therefore, in this embodiment, according to the operating conditions of the device, the image density evaluation values (described later) that are calculated based on the output from the density sensor 60 and represent the scale of the image density are respectively set for the two types of patch images described later. By adjusting each density control factor so that the evaluation value obtained for each patch image reaches this control target value, the image density on the sheet S is kept constant. FIG. 13 is a flowchart of the control target value derivation process in this embodiment. In this process, for each toner color, the usage status of the toner is obtained, specifically, the initial characteristics such as the particle size distribution of the toner obtained at the time of filling into the developer, and the development The corresponding control target value of the amount of toner remaining in the filter. First, one of the toner colors is selected (step S31). As information for the CPU 101 to estimate the usage status of the toner, it obtains the toner personality information related to the selected toner color and indicates the formation of the exposure unit 6 The dot count value of the dots and the information related to the rotation time of the developing roller (step S32). Here, a case where the control target value corresponding to black is obtained is described as an example, but the same applies to other toner colors.

The "toner personality information is data written in the memory 94 provided in the developer 4K in accordance with the characteristics of the toner filled in the developer 4K. In this device, in view of the fact that the particle size distribution and other characteristics of the above-mentioned toner vary depending on the manufacturing lot number, the characteristics of the toner are classified into 8 types. Then, based on the analysis at the time of manufacturing, it is determined which type of toner the toner belongs to, and the 3-bit data indicating this is given to the developing device 4K as toner personality information. This data is read from the memory 94 when the developing device 4K is installed in the developing unit 4, and stored in the RAM 107 of the engine controller 10.

In addition, the "dot count value" is information for estimating the amount of toner remaining in the developing device 4K. As a method of estimating the remaining amount of toner, it is the easiest to find the cumulative value of the number of pages formed on the image. However, the amount of toner consumed to form an image on one page is not constant, so it is difficult to know the correct amount by this method. margin. On the other hand, the number of dots formed on the photoreceptor 2 by the exposure unit 6 represents the number of dots developed by the toner on the photoreceptor 2, and therefore more accurately reflects the amount of toner consumption. Therefore, in this embodiment, the number of dots when the exposure unit 6 forms the electrostatic latent image on the photoreceptor 2 to be developed by the developer 4K is counted and stored in the RAM 107, and this dot count value is used as the The parameter of the remaining toner of the developer 4K.

In addition, the "developing roller rotation time" is information for estimating the characteristics of the toner remaining in the developing device 4K in more detail. As described above, a toner layer is formed on the surface of the developing roller 44, and a part of the toner is moved to the photoreceptor 2 to perform development. At this time, on the surface of the developing roller 44, the toner that is not used for development is transported to a position in contact with the supply roller 43, and is peeled off by the roller 43 to form a new toner layer, but the development is repeated in this way. The adhesion and peeling of the roller 44 causes the toner to fatigue, and its characteristics gradually change. This change in the characteristics of the toner proceeds with the continuous rotation of the developing roller 44. Therefore, even if the remaining amount of toner in the developer 4K is the same, the characteristics of unused fresh toner and old toner that repeatedly adhere and peel off may be different, and the density of the image formed by them may not be the same. .

Therefore, in this embodiment, the toner contained in the developer 4K is estimated based on the combination of the dot count value indicating the toner remaining amount and the rotation time of the developing roller indicating the degree of change in toner characteristics. The state of the agent, by setting the control target value carefully according to the state, achieves stable image quality.

In addition, this information is also used to manage the wear and tear of each part of the device to improve maintainability. That is, one dot count corresponds to a toner amount of 0.015 mg, and the consumption of 12 million dot counts is approximately 180 g, which is a state where the toner stored in each developer is almost used up. In addition, the cumulative value of the rotation time of the developing roller of 10600 sec is equivalent to A4 continuous printing of 8000 pages, and further image formation is undesirable in terms of image quality. Therefore, in this embodiment, when one of these pieces of information reaches the above-mentioned value, a message notifying that the toner has run out is displayed on a display unit (not shown) to remind the user to replace the developing device.

Based on each piece of information related to the operating status of the device acquired in this way, the control target value is determined according to the status. In this embodiment, the optimal control target value corresponding to the residual toner characteristic estimated from the combination of the toner personality information indicating the type of toner, the dot count value, and the rotation time of the developing roller is experimentally determined in advance. This value is stored in the ROM 106 of the engine controller 10 as a look-up table for each toner type. Based on the acquired toner personality information, the CPU 101 selects a table that should be referred to corresponding to the types of toners in these look-up tables (step S33), and reads the dot count value and the development value corresponding to the time from the table. The value corresponding to the combination of the roller rotation time (step S34).

In addition, in the image forming apparatus of this embodiment, the user can perform a predetermined operation input through an operation unit not shown, and increase or decrease the density of the image to be formed within a predetermined range according to preference or as needed. That is, every time the user increases or decreases the image density by one level, a predetermined compensation value is added or subtracted from the value read from the look-up table, for example, 0.005 is added or subtracted for every level, and the result is The control target value Akt for black at this time is set and stored in the RAM 107 (step S35). In this way, the control target value Akt for black is obtained.

14A and 14B are diagrams showing examples of look-up tables for obtaining control target values. This table is a table to be referred to in the case of using a black toner whose characteristics belong to "Type 0". In this embodiment, corresponding to two types of patch images for high density and low density, which will be described later, respectively, 8 types of tables corresponding to the 8 types of toner characteristics are prepared for each toner color, and stored in the engine. In the ROM 106 provided in the controller 10. Here, FIG. 14A is an example of a table corresponding to a high-density patch image, and FIG. 14B is an example of a table corresponding to a low-density patch image.

Assuming that the toner personality information obtained in the above step S32 indicates "type 0", for example, in the subsequent step S33, the table in FIG. 14 corresponding to the toner personality information "0" is selected from the eight types of tables. Then, the control target value Akt is obtained based on the acquired dot count value and the rotation time of the developing roller. For example, for a high-density patch image, if the dot count value is 1,500,000 counts and the developing roller rotation time is 2,000 sec, referring to FIG. 14A, the value 0.984 corresponding to the combination of these is the control target value Akt in this case. Furthermore, for example, when the user sets the image density to be one level higher than the standard state, the value 0.989 obtained by adding 0.005 to this value becomes the control target value Akt. Similarly, the control target value can be obtained for the patch image for low density.

The control target value Akt obtained in this way is stored in the RAM 107 of the engine controller 10, and the evaluation value obtained from the reflected light amount of the patch image is made to match the control target value in the setting of each density control factor later.

In this way, by performing the above steps S31 to S35, the control target value can be obtained for one toner color, and by repeating the above processing for each toner color (step S36), the control target value can be obtained for all the toner colors. Control target values Ayt, Act, Amt and Akt. Here, the subscripts y, c, m, and k respectively represent the respective toner colors, namely yellow, cyan, magenta, and black, and the subscript t represents the control target value.

D. Setting the development bias In this image forming apparatus, the average development bias Vavg supplied to the developing roller 44 and the energy per unit area of the exposure beam L for exposing the photoreceptor 2 (hereinafter referred to as "exposure") can be changed. Energy") E, by adjusting them to control the image density. Here, it is explained that the variable range of the average developing bias Vavg is changed from the low level side to 6 levels from V0 to V5, and the variable range of the exposure energy E is changed from the low level side to level. There are four levels of 0 to 3 to find the optimum values, but these variable ranges and the number of divisions can be appropriately changed according to the specifications of the device. In addition, in the previously described device in which the variable range of the average developing bias voltage Vavg is set to (-110)V to (-330)V, the lowest level V0 corresponds to the smallest absolute value of the voltage (-110). )V, and the highest level V5 corresponds to (-330)V where the absolute value of the voltage is the largest.

FIG. 15 is a flowchart of the developing bias voltage setting process in this embodiment. In addition, FIG. 16 is a diagram showing a patch image for high density. In this process, first, the exposure energy E is set to level 2 (step S41), and then the average developing bias voltage Vavg is gradually increased by one level from the minimum level V0. At the same time, each bias value is used to form A real image of the patch image for high density (steps S42, S43).

As shown in FIG. 16, corresponding to the average developing bias Vavg changed to 6 levels, 6 patch images Iv0 to Iv5 are sequentially formed on the surface of the intermediate transfer belt 71, but the first 5 patch images Iv0 to Iv0 to Iv5 are sequentially formed on the surface of the intermediate transfer belt 71. Iv4 is formed into length L1. This length L1 is greater than the circumference of the cylindrical photoreceptor 2. The final patch image Iv5 has a length L3 shorter than the 2 circumference of the photoreceptor. The reason for this will be described later. In addition, when the average developing bias Vavg is changed and set, there is a certain time lag until the potential of the developing roller 44 reaches a uniform level, so each patch image interval L2 is formed in consideration of this time lag. On the surface of the intermediate transfer belt 71, the area that can actually carry the toner image is the imaging area 710 shown in the same figure. Due to the shape and arrangement of the patch image as described above, the patch image that can be formed on the imaging area 710 is 3 As shown in FIG. 16, six patch images are formed on the two-round range of the intermediate transfer belt 71.

Here, the reason for setting the patch image length as described above will be described with reference to FIGS. 1, 17A, and 17B. FIGS. 17A and 17B are diagrams showing changes in image density that occur during the rotation period of the photoreceptor. As shown in Fig. 1, the photoreceptor 2 is formed in a cylindrical shape (let its circumference be L0), but due to manufacturing deviations or thermal deformation, etc., its shape may not be a complete cylinder or have an eccentricity. In this case, The image density of the formed toner image may periodically fluctuate in accordance with the circumferential length L0 of the photoreceptor 2. The reason is that the contact pressure between the contact developing device that performs toner development while the photoreceptor 2 and the developing roller 44 are in contact with each other changes, and the two are separately arranged to perform non-contact development of toner development. In the device of the method, the intensity of the electric field that causes the toner to fly between the two changes. Even in any device, the probability of the toner moving from the developing roller 44 to the photoreceptor 2 is periodically performed by the rotation period of the photoreceptor 2. Land changes.

As shown in FIG. 17A, the magnitude of this density variation increases particularly when the absolute value of the average developing bias voltage Vavg |Vavg| is low, and decreases as the value |Vavg| increases. For example, when the absolute value |Vavg| of the average developing bias voltage Vavg is set to a small value to form a patch image, as shown in FIG. 17B, the image density OD has an amplitude of Δ1 due to different positions on the photoreceptor 2. Range changes. Similarly, even when a patch image is formed with another average developing bias voltage, the image density thereof fluctuates within a certain range as shown by the shaded portion of FIG. 17B. In this way, the density OD of the patch image fluctuates not only due to the magnitude of the average developing bias voltage Vavg, but also due to the difference in the formation position on the photoreceptor 2. Therefore, in order to find the optimal value of the average developing bias voltage Vavg from the image density, it is necessary to eliminate the influence of the density fluctuation corresponding to the rotation period of the photoreceptor 2 on the patch image.

Therefore, in this embodiment, a patch image with a length L1 exceeding the circumferential length L0 of the photoreceptor 2 is formed, and as described later, the average density value obtained for the length L0 of the patch image is used as the image density of the patch image. In this way, the influence of density variation corresponding to the rotation period of the photoreceptor 2 on each patch image is effectively suppressed, and as a result, the optimal value of the average developing bias Vavg can be accurately obtained based on the density.

Also, in this embodiment, as shown in FIG. 16, the last patch image Iv5 formed by maximizing the average developing bias voltage Vavg among the patch images Iv0 to Iv5 is made so that the length L3 is smaller than the circumference of the photoreceptor 2. L0. This is because, as shown in FIG. 17B, the patch image formed under the condition that the absolute value of the average developing bias Vavg |Vavg| is large has a small density fluctuation corresponding to the rotation period of the photoreceptor 2, so it is unnecessary as described above. Calculate the average value in the period of the photoreceptor. In this way, the time required for the formation of the patch image and its processing can be shortened, and at the same time, the amount of toner consumption in the formation of the patch image can be reduced.

In this way, in order to eliminate the influence of density fluctuations corresponding to the photoreceptor period on the optimization process of the density control factor, it is preferable to make the length of the patch image longer than the circumference L0 of the photoreceptor 2. However, it is not necessary to adopt this length for all patch images. The length of several patch images should be appropriately determined according to the degree of density fluctuations that occur in each device or the desired image quality level. For example, in the case where the influence of the density variation in the photoreceptor cycle is small, only the patch image Iv0 formed under the condition of the minimum average developing bias voltage Vavg may adopt the length L1, and the other patch images Iv1 to Iv5 may also be used. A length L3 shorter than this is formed.

Conversely, although all patch images may be formed to the length L1, in this case, there is a problem that the processing time and toner consumption increase. In addition, even in the state where the average developing bias voltage Vavg is the largest, from the point of view of image quality, the density fluctuation corresponding to the photoreceptor period is unsatisfactory. Naturally, the variable range of the average developing bias voltage Vavg is determined so as to be at least in the setting When set to its maximum value, this concentration change does not appear. Then, in the case where the variable range of the average developing bias voltage Vavg is set in this way, at least such density fluctuation does not occur in its maximum value. Therefore, the patch image length in this case does not need to be set to L1.

Returning to Fig. 15, the description of the developing bias setting process will be continued. With respect to the patch images Iv0 to Iv5 formed with the average developing bias voltages in this way, the voltages Vp and Vs output from the density sensor 60 are sampled in accordance with the amount of reflected light from the surface thereof (step S44). In this embodiment, 74 points are taken from the patch images Iv0 to Iv4 of length L1 (corresponding to the circumference L0 of the photoreceptor 2), and 21 points are taken for the patch image Iv5 of length L3 (corresponding to the circumference of the developing roller 44). ), the sampling data of the output voltages Vp and Vs from the concentration sensor 60 are obtained in a sampling period of 8 msec. Then, as in the case of deriving the basic profile described above (FIG. 7), after removing the spike noise from the sample data (step S45), based on this data, calculate the "" of each patch image without the influence of the dark output of the sensor system or the basic profile. Evaluation value" (step S46).

As described above, the density sensor 60 in this device exhibits the following characteristics: the output level is the largest when the toner is not attached to the intermediate transfer belt 71, and as the amount of toner increases, its output decreases. Furthermore, since the compensation caused by the dark output is added to this output, it is difficult to directly use the output voltage data from the sensor as information for evaluating the amount of toner adhesion. Therefore, in this embodiment, the obtained data is processed and converted into data that better reflects the size of the toner adhesion amount, that is, an evaluation value, so that subsequent processing can be easily performed.

Taking a patch image of black toner color as an example, the calculation method of the evaluation value will be explained more specifically. The evaluation value Ak(n) of the n-th patch image Ivn (where n=0, 1,..., 5) among the 6 patch images developed with black toner is calculated according to the following formula: Ak(n)= 1-{Vpmeank(n)-Vpo}/{Vpmean_b-vpo} Here, the meaning of each item in the above formula is as follows.

First, Vpmeank(n) is an output voltage Vp corresponding to the p-polarized light component in the reflected light from the n-th patch image Ivn, output from the density sensor 60 and the average value of each sample data sampled after noise removal. That is, for example, the value Vpmeank(0) corresponding to the first patch image Iv0 is detected as the output voltage Vp from the density sensor 60 at the length L0 in the patch image, and then subjected to spike noise removal processing and stored in The arithmetic average of 74 sample data in RAM 107. Among them, the subscript k of each item in the above formula represents a black value.

In addition, Vpo is the dark output voltage from the light-receiving unit 670p acquired in the state where the light-emitting element 601 is turned off in the previous pre-operation 1. In this way, by subtracting the dark output voltage Vpo from the sampled output voltage, the influence of the dark output can be eliminated, and the density of the toner image can be determined with higher accuracy.

Furthermore, Vpmean_b is the basic profile data previously obtained and stored in RAM 107, and is detected on the intermediate transfer belt 71 at the same position as the position where the 74 sample data used to calculate the above Vpmeank(n) are detected. The average value of each sample data.

That is, the evaluation value Ak(n) for the black n-th patch image Ivn is the average value of the sensor output Vp obtained from the surface of the intermediate transfer belt 71 before the toner is attached, and the value obtained from the toner attached The average value of the sensor output Vp obtained by the patch image Ivn is obtained by subtracting the dark output of the sensor and then taking the ratio of the two, and subtracting the value from 1. Therefore, in a state where the toner as a patch image is not attached to the intermediate transfer belt 71 at all, Vpmeank(n)=Vpmean_b, the evaluation value Ak(n) is zero; and the surface of the intermediate transfer belt 71 is In a state where the black toner is completely covered and the reflectance is zero, Vpmeank(n)=Vpo, and the evaluation value Ak(n)=1.

In this way, if the evaluation value Ak(n) is used instead of the value of the sensor output voltage Vp, the influence of the surface condition of the intermediate transfer belt 71 can be eliminated, and the image density of the patch image can be measured with high accuracy. In addition, since the correction is performed in accordance with the density of the patch image on the intermediate transfer belt 71, the accuracy of the measurement of the image density can be further improved. Furthermore, it is possible to normalize the value of the patch image Ivn with a value ranging from the minimum value 0 indicating the state where the toner is not attached to the maximum value 1 indicating the state where the surface of the intermediate transfer belt 71 is covered with high-density toner. Density, so it is particularly suitable for estimating the density of a toner image in subsequent processing.

Also, for toner colors other than black, that is, yellow (Y), cyan (C), and magenta (M), since the reflectance is higher than that of black, even if the toner covers the surface of the intermediate transfer belt 71 In the state, the amount of reflected light is not zero, so sometimes the density cannot be accurately expressed by the evaluation value obtained as described above. Therefore, in this embodiment, as the sample data used in obtaining the evaluation values Ay(n), Ac(n), Am(n) of these toner colors, it is not the output corresponding to the p-polarized light component. The voltage Vp, but the value obtained by subtracting the dark output Vpo from it divided by the value PS obtained by subtracting the dark output Vso from the output voltage Vs corresponding to the s-polarized light component, that is, PS=(Vp -Vpo)/(Vs-Vso) is used as the sample data at each position. In this way, the image density of these toner colors can be estimated with high accuracy. In addition, as in the case of black, by considering the sensor output obtained from the surface of the intermediate transfer belt 71 before the toner is attached, the influence of the surface condition of the intermediate transfer belt 71 is eliminated, and the effect of the surface condition of the intermediate transfer belt 71 is eliminated. The density of the patch image is corrected, so the accuracy of the image density measurement can be improved.

For example, for cyan (C), the evaluation value Ac(n) can be obtained by the following formula Ac(n)=1-{PSmeanc(n)-PSo}/{PSmean_b-PSo}. Here, PSmeanc(n) is the noise-removed average value of the above-mentioned value PS calculated from the sensor outputs Vp and Vs at each position of the n-th patch image Ivn in cyan. In addition, PSo is the above-mentioned value PS corresponding to the sensor outputs Vp and Vs in a state where the surface of the intermediate transfer belt 71 is completely covered with color toner, and is the minimum value PS can take. In addition, PSmean_b is the average value of the above-mentioned value PS calculated from the sensor outputs Vp and Vs sampled as a basic profile at each position of the intermediate transfer belt 71.

By defining the evaluation value corresponding to the color toner as described above, it can be used to indicate the state where the toner is not attached to the intermediate transfer belt 71 at all (at this time, PSmeanc( n)=PSmean_b) from the minimum value 0 to the maximum value 1 representing the state where the belt 71 is completely covered with toner (at this time, PSmeanc(n)=Pso) normalizes the density of the patch image Ivn.

After the toner density of each patch image (more precisely, the evaluation value) is obtained in this way, the optimal value Vop of the average developing bias voltage Vavg is calculated based on the value (step S47). FIG. 18 is a flowchart of the average developing bias optimal value calculation process in this embodiment. In addition, the content of this processing does not depend on the toner color and is the same. Therefore, in Figure 18 and the following, the subscripts (y, c, m, k) of the evaluation value corresponding to the toner color are omitted. ), but it goes without saying that the evaluation value and its target value are different for each toner color.

First, the parameter n is set to 0 (step S471), and the evaluation value A(n), which is A(0), is compared with the previously determined control target value At (for example, Akt in the case of black) (step S472). At this time, if the evaluation value A(0) is above the control target value At, it means that an image density exceeding the target density is obtained at the minimum value V0 of the average developing bias voltage Vavg, so there is no need to discuss the development bias higher than it. The process ends with the average developing bias voltage V0 at this time being the optimal value Vop (step S477).

On the contrary, when the evaluation value A(0) does not reach the target value At, the evaluation value A(1) of the patch image Iv1 formed with the average developing bias V1 of one level higher is read out, and the evaluation value A(1) is calculated with the evaluation value A(0) difference, and it is judged whether this difference value is less than a predetermined value Δa (step S473). Here, when the difference between the two is equal to or less than the predetermined value Δa, the average developing bias voltage V0 is set as the optimum value Vop in the same manner as described above. The reason for this will be detailed later.

On the other hand, when the difference between the two is greater than the predetermined value Δa, step S474 is performed to compare the evaluation value A(1) and the control target value At. At this time, if the evaluation value A(1) is above the target value At, the target value At is greater than the evaluation value A(0) and below A(1), that is, A(0)<AtA(1), so in There is an optimal value Vop of the average developing bias voltage for obtaining the target image density between the average developing bias voltages V0 and V1. That is, V0<VopV1.

Therefore, in this case, step S478 is performed to find the optimal value Vop through calculation. There are various calculation methods. For example, the change in the evaluation value with respect to the average developing bias voltage Vavg can be approximated as an appropriate function in the range of V0 to V1, or the value of this function can be the average development of the target value At. The bias voltage Vavg is taken as its optimal value Vop. Among them, the method of approximating the change in the evaluation value with a straight line is the simplest, but by appropriately selecting the variable range of the average developing bias voltage Vavg, the optimal value Vop can be found with sufficient accuracy. Of course, other methods can also be used, such as introducing a more accurate approximation function to calculate the optimal value Vop, but if the detection error or deviation of the device is considered, it may not be realistic.

On the other hand, when the target value At is greater than the evaluation value A(1) in step S474, n is incremented by 1 (step S475), and the above steps S473 to S475 are repeated to find the optimal value Vop of the average developing bias until When n reaches the maximum value (step S476), but in step S476, even though n reaches the maximum value (n=5), the optimal value Vop is not obtained, that is, when none of the evaluation values corresponding to the 6 patch images reaches the target value, The average developing bias voltage V5 that maximizes the density is set as the optimal value Vop (step S477).

In this way, in this embodiment, the evaluation values A(0) to A(5) corresponding to each patch image Iv0 to Iv5 are compared with the target value At, and the average value used to obtain the target density is calculated based on the magnitude relationship. The optimal value Vop of the developing bias voltage, but as described above, in step S473, when the difference between the evaluation values A(n) and A(n+1) corresponding to two consecutive patch images is less than the predetermined value Δa, The average developing bias voltage Vn is taken as the optimal value Vop. The reason is as follows.

That is, as shown in FIG. 17B, if the average developing bias voltage Vavg increases, the image density OD on the sheet S increases, but the following characteristic is exhibited in the area where the average developing bias voltage Vavg is relatively large: the increase rate decreases , Gradually saturated. This is because after the toner has adhered to a certain degree of high density, even if the amount of toner adhered is increased, the image density does not increase much. In this way, in the area where the increase rate of the image density decreases, if the average developing bias voltage Vavg is increased in order to further increase the image density, although the density will not increase too much, it will only increase the toner consumption excessively. Is unrealistic. On the contrary, in such an area, by setting the density change as low as possible within the allowable range, it is possible to suppress the decrease in image density to the minimum while greatly reducing the toner consumption.

Therefore, in this embodiment, in a region where the increase rate of the image density with respect to the average developing bias voltage Vavg is smaller than a predetermined value, the lowest possible value is set as the optimal value Vop of the average developing bias voltage. Specifically, the evaluation values A(n) and A(n+1) of the density of each patch image Ivn and Iv(n+1) formed with the two average developing bias voltages Vavg of Vn and Vn+1 are respectively shown. When the difference is equal to or less than the predetermined value Δa, the lower average developing bias voltage, that is, the value of Vn is set to its optimum value Vop. Here, it is desirable to choose this value Δa so that when the evaluation values of two images differ only by Δa, the difference in density between the two images cannot be easily distinguished by the naked eye, or the difference in the density of the two images in the device can be The degree of tolerance.

By doing so, although the image density hardly increases, the average developing bias voltage Vavg is prevented from being set to an unnecessarily high value, achieving coordination between image density and toner consumption.

As described above, the optimal value Vop of the average developing bias voltage Vavg that can obtain the predetermined real image density is set to a value in the range from the minimum value V0 to the maximum value V5. In addition, in this image forming apparatus, from the viewpoint of image quality improvement, the surface potential of the electrostatic latent image on the photoreceptor 2 where the toner is not adhered to the image signal (non-lined portion) The potential difference between the average developing bias voltage Vavg and the average developing bias voltage Vavg is always constant (for example, 325V). As described above, if the optimal value Vop of the average developing bias voltage Vavg is obtained, the charging bias supplied from the charging control unit 103 to the charging unit 3 The magnitude of the pressure is also changed accordingly to keep the above-mentioned potential difference constant.

E. Set the exposure energy Next, set the exposure energy E to its optimal value. FIG. 19 is a flowchart of the exposure energy setting process in this embodiment. As shown in FIG. 19, the processing content is basically the same as the previously described development bias setting processing (FIG. 15). That is, first, the average developing bias voltage Vavg is set to the optimum value Vop obtained previously (step S51), and then the exposure energy E is increased by one level from the minimum level 0, and each level is used for each level. A patch image is formed (steps S52, S53). Then, the sensor outputs Vp and Vs corresponding to the amount of reflected light from each patch image are sampled (step S54), spike noise is removed from the sample data (step S55), and at the same time, the density of each patch image is obtained (step S56) Based on the result, the optimal value Eop of the exposure energy is obtained (step S57).

In this processing (Figure 19), the processing content is different from the above-mentioned developing bias setting processing (Figure 15) in that it calculates the exposure energy based on the pattern/number of patch images to be formed and the evaluation value. The optimal value of Eop is calculated, and the other aspects are roughly the same. Therefore, the differences are mainly explained here.

In this image forming apparatus, the surface of the photoreceptor 2 is exposed by the light beam L to form an electrostatic latent image corresponding to the image signal. However, in a high-density image with a relatively large exposed area such as a real image, even if the exposure energy E is changed, The potential distribution characteristics of the electrostatic latent image also do not change much. In contrast, in a low-density image in which exposed areas such as thin-line images or halftone images are scattered on the surface of the photoreceptor 2, the potential distribution characteristics of the exposure energy E greatly vary. This change in the potential distribution characteristics brings about a change in the density of the toner image. That is, the change in exposure energy E does not affect the high-density image much, but greatly affects its density in the low-density image.

Therefore, in this embodiment, a real image with little influence of exposure energy E on image density is first formed as a high-density patch image, and the optimal value of the average developing bias Vavg is calculated based on its density, and at the same time, the exposure energy E is calculated The optimal value is to form a low-density patch image. Therefore, in this exposure energy setting process, a patch image having a different pattern from the patch image (FIG. 16) formed in the average developing bias setting process is used.

Also, although the influence on the high-density image of the exposure energy E is small, if the variable range is made too wide, the density change of the high-density image will also increase. In order to prevent this, as the variable range of the exposure energy E, the surface potential of the electrostatic latent image corresponding to the high-density image (for example, the real image) when the exposure energy is changed from the minimum (level 0) to the maximum (level 3) The change is within 20V, preferably within 10V.

Fig. 20 is a diagram of a patch image for low density. As described above, in this embodiment, the exposure energy E is changed to four levels, and here, each level is used to form one, and a total of four patch images Ie0 to Ie3 are formed. In addition, as shown in FIG. 20, the pattern of the patch image used here is composed of a plurality of thin lines arranged separately from each other. In more detail, it is a dotted line of 1 "ON" and 10 "OFF". pattern. The pattern of the patch image for low density is not limited to this, but if a pattern in which lines or dots are isolated from each other is used in this way, the change in exposure energy E can be reflected on the change in image density, and the optimal value can be found with higher accuracy. .

In addition, the length L4 of each patch image is set to be smaller than the length L1 of the patch image for high density (FIG. 16 ). This is because, in this exposure energy setting process, the average developing bias voltage Vavg has been set to its optimal value Vop. Under this optimal condition, density streaks with a period of 2 cycles of the photoreceptor are not generated (contrary to this). In this state, if density streaks occur, Vop is not the optimal value of the average developing bias voltage Vavg). However, on the other hand, density streaks associated with the deformation of the developing roller 44 may also occur. Therefore, as the density of the patch image, it is better to use a value obtained by averaging over a length equivalent to the circumference of the developing roller 44. Therefore, , The circumferential length L4 of the patch image is set to be larger than the circumferential length of the developing roller 44. In addition, in a non-contact developing device, when the moving speeds (peripheral speeds) of the respective surfaces of the developing roller 44 and the photoreceptor 2 are different, the peripheral speed ratio is taken into consideration, and the length is equal to one revolution of the developing roller 44. The corresponding patch image may be formed on the photoreceptor 2.

In addition, the interval L5 of each patch image can be made smaller than the interval L2 shown in FIG. 16. This is because the energy density of the light beam L from the exposure unit 6 can be changed in a relatively short time. Especially when the light source is composed of a semiconductor laser, the energy density can be changed in an extremely short time. By configuring the shape and arrangement of the patch images in this way, as shown in FIG. 20, all the patch images Ie0 to Ie3 can be formed on one round of the intermediate transfer belt 71, and the processing time is shortened accordingly.

For the low-density patch images Ie0 to Ie3 formed in this way, the evaluation value indicating the image density is obtained in the same manner as in the case of the high-density patch image described earlier. Then, based on this evaluation value and the control target value derived from a separately prepared look-up table for low-density patch images (FIG. 14B) that is different from the previously described look-up table for high-density patch images, the maximum exposure energy is calculated. Good value Eop. FIG. 21 is a flowchart of the calculation process of the optimal value of exposure energy in this embodiment. In this process, similar to the calculation process of the optimal value of the developing bias shown in FIG. 18, the evaluation value and the target value At are sequentially compared starting from the patch image formed with a low energy level, and the evaluation value is calculated to be the target value At. The value of the exposure energy E having the same value determines the optimal value Eop (steps S571 to S577).

However, in the range of exposure energy E that is generally used, the saturation characteristics seen in the relationship between the real image density and the average developing bias do not appear between the thin line image density and the exposure energy E (FIG. 17B), Therefore, the processing corresponding to step S473 in FIG. 18 is omitted. In this way, the optimal value Eop of the exposure energy E that can obtain the desired image density is obtained.

F. Post-processing The optimal values of the average developing bias voltage Vavg and the exposure energy E are respectively determined as described above, and thereafter the image can be formed with a predetermined image quality. Therefore, the density control factor optimization process can be ended at this time, the rotation drive of the intermediate transfer belt 71 etc. can be stopped, the device can be transferred to the standby state, and some adjustment actions can even be performed to control other density control factors. The content of post-processing is arbitrary, so its description is omitted here.

G. Effect As described above, in the optimization process of the density control factor of this embodiment, before the patch image is formed, the rotation of the developing roller 44 provided in the respective developing devices 4Y, 4C, 4M, and 4K is performed. Therefore, the influence of density streaks caused by the unevenness of the toner placed on the surface of the developing roller 44 on the patch image density is effectively suppressed, and the average developing bias Vavg as a density control factor can be obtained with high accuracy based on the image density. And the optimal value of exposure energy E. Then, image formation is performed under such optimized conditions, so that a toner image with good image quality can be stably formed in this image forming apparatus.

In addition, the density sensor 60 is used to detect the amount of reflected light from the patch image area on the intermediate transfer belt 71 before and after the patch image is formed, and the evaluation value corresponding to the patch image density is calculated from these detection results. The density of the patch image is obtained with high accuracy under the influence of the change in the amount of reflected light caused by the discoloration or damage of the patch image area.

Moreover, the developing bias can be set to a minimum, creating a condition that the toner movement from the developing roller 44 to the photoreceptor 2 is difficult to occur, effectively preventing the toner from adhering to the intermediate transfer belt 71 and affecting the detection result, and Since the amount of reflected light from the intermediate transfer belt 71 is detected in parallel with this time, the adjustment process of the density control factor can be performed in a short time. Second Embodiment In the above-mentioned embodiment, the density sensor 60 is arranged opposite to the surface of the intermediate transfer belt 71 to detect the density of the toner image as a patch image that is primarily transferred on the intermediate transfer belt 71. However, this The embodiments of the invention are not limited to this. For example, as shown in FIG. 22, the density sensor may be arranged toward the surface of the photoreceptor 2, and the density of the toner image developed on the photoreceptor 2 may be detected.

Fig. 22 is a diagram showing a second embodiment of the image forming apparatus of the present invention. In the image forming apparatus of this embodiment, by comparing with the image forming apparatus of the first embodiment shown in FIG. 1, it can be seen that instead of the density sensor 60 arranged opposite to the surface of the intermediate transfer belt 71, along the line of the photoreceptor 2 In the rotation direction D1, on the downstream side of the position opposed to the developing roller 44, a density sensor 61 facing the photoreceptor 2 is provided. The other structure and operation are the same as those of the device of the first embodiment, so the same structure is denoted by the same reference numerals and the description is omitted.

The structure of this density sensor 61 is approximately the same as that of the density sensor 60 in the first embodiment shown in FIG. 4, but instead of detecting the surface 71a from the intermediate transfer belt 71, it detects the amount of reflected light from the surface of the photoreceptor 2. This point is different in composition. That is, in this embodiment, the image density of the toner image on the photoreceptor 2 formed as a patch image is obtained, and the density control factor is optimized based on the image density. This process can also be performed basically in the same manner as in the first embodiment, but if the optical properties of the surface are different due to the different materials used, it is necessary to appropriately change the sensitivity and reference light intensity of the sensor according to this situation. Wait.

As described above, the present invention is not only applied to the detection of patch image density on the intermediate transfer belt 71 or the like, but also can be applied to a device for detecting the patch image density on an image carrier such as the photoreceptor 2 or the like. Third Embodiment In the above-mentioned first and second embodiments, the optimization process of the density control factor is performed at the time of turning on the power of the device or after replacing the unit, and at this time, the developing roller is performed before the patch image is formed. The rotation of 44 prevents density streaks from appearing on the patch image. The same effect can also be obtained by the third embodiment of the image forming apparatus of the present invention described below. This third embodiment is an embodiment suitable for an image forming apparatus in which it frequently occurs that the power of the apparatus has been turned on without performing image formation for a long period of time.

For example, a printer installed in an office is always powered on so that image formation can be performed quickly as needed. Even so, it actually supplies image signals to the main controller 11 for imaging frequency according to the user's image formation requirements. The degree is not too high, and sometimes it will continue for several hours without imaging. A power-saving operation mode called "sleep mode" in conventional image forming apparatuses is also provided in view of the usage of such apparatuses to suppress wasteful power consumption in a state where imaging is not performed.

In this way, if the image is left for a long time without imaging, the above-mentioned placement streak phenomenon will occur, and density streaks may occur on the image formed in the next image forming operation. In addition, the image density will gradually change due to changes in the surrounding environment such as temperature. Therefore, in this embodiment, not only when the power is turned on, when a certain unit is replaced, when the power is turned on and the image forming operation is not performed, that is, when the operation stop time continues for a certain period of time, The optimization processing of the concentration control factor is also executed.

FIG. 23 is a flowchart showing the image forming operation and the operation stop state in this embodiment. In addition, FIGS. 24A and 24B are timing charts showing the difference in device operation due to the length of the operation stop time. In this image forming apparatus, it is always judged whether an image signal is input from an external device through the interface 112 (step S701). When the image signal is provided, the series of image forming operations described above are executed to form a corresponding image on the sheet S. The image of the image signal (step S702). Then, this image forming operation is repeated as necessary (step S703) to form a predetermined number of images. In this way, after a series of image forming operations are completed, the rotational driving of the intermediate transfer belt 71 and the like is stopped, and at the same time, the application of the developing bias and the charging bias, etc., is stopped, and the apparatus is turned to the operation stop state (step S704). At this time, in more detail, at the time when the output of the charging bias supplied by the charging control section 103 to the charging unit 3 is stopped, the CPU 101 resets the internal timer and starts the time measurement (step S705), and then returns to step S701. Wait for the input of the image signal. That is, in this embodiment, the CPU 101 uses its internal timer to count the time the device is in the operation stop state, that is, the operation stop time ts.

At this time, if the next image signal is provided quickly, the above steps S702 to S703 are also repeated to form the necessary number of images, and then the internal timer starts timing (step S705). In the case of no image signal provided, Step S706 is entered, and the timing is still continued. Then, when the operation stop time ts reaches the predetermined time t1 described later, the process proceeds to step S707 to perform the optimization process of the above-mentioned concentration control factor, and then proceeds to step S705, after temporarily resetting the internal timer, returns to step S701, in step S706 When the operation stop time ts has not reached the time t1, the process returns directly to step S701.

That is to say, in this device, after the image forming operation is completed, if a new image signal from an external device is not provided in accordance with the user's image forming request, the operation is stopped and the internal timer continues for the operation stop time ts Time, while waiting for the input of the next image signal. Then, as shown in FIG. 24A, when the next image signal is input before the operation stop time ts reaches the predetermined time t1, the device quickly resets from the operation stop state to execute the image forming operation.

On the other hand, as shown in FIG. 24B, in the case where the next image signal is not supplied until the action stop time ts reaches the time t1, the device recovers from the action stop state and starts to perform the above-mentioned optimization process of the density control factor. Then, as soon as its processing ends, it returns to the operation stop state again. At this time, the timer is also temporarily reset, so every time the operation stop time ts thereafter reaches the time t1, the optimization process of the concentration control factor is similarly executed.

The content of the optimization processing here can also adopt the same processing in other known technologies in addition to the optimization processing in the first embodiment described above (steps S3 to S5 in FIG. 5). This is the same in the following embodiments.

As described above, the image forming apparatus of this embodiment is configured such that the image forming operation corresponding to the image signal supplied from the external device, or the operation after the completion of the optimization process of the density control factor of the patch image forming operation is stopped When the time ts reaches the time t1, the optimization processing of the concentration control factor is performed. Therefore, the maximum period during which the operation stopped state continues in this device is about time t1. This time t1 corresponds to the "first predetermined time" in the present invention.

In this way, by periodically performing the optimization process of the density control factor, the operation stop time ts of the device is made to be less than the first predetermined time, thereby, in this image forming apparatus, the toner is suppressed from being carried on the developing roller 44 for a long time. The occurrence of placement streaks caused by placement. Moreover, by suppressing the placement of streaks, the density streaks of the patch image caused by this phenomenon will not occur. Therefore, the density control factor can always be set to an optimal state according to the density of the patch image. As a result, the image is formed here. In the device, a toner image with good image quality can be stably formed.

In addition, since the density control factor always maintains the optimal state even when the operation is stopped, if a new image signal is provided from the outside, the image forming operation can be quickly resumed from the operation stop state, which can quickly respond to user requirements.

As described above, in this embodiment, since the optimization processing of the density control factor is performed at regular intervals, the streaking phenomenon is not prone to occur. Therefore, when performing the optimization process of the density control factor, the rotation of the developing roller 44 is not necessarily required. That is, for the optimization process of the concentration factor in this case, the "pre-action 2" shown in FIG. 7 can be omitted, thereby suppressing the fatigue and deterioration of the developing roller 44 and prolonging the life of the device. However, from the viewpoint of improving the image quality, it is preferable to perform the rotating operation of the developing roller 44 in this case as well.

Here, the question is how to set this first prescribed time. That is, since toner is consumed every time a patch image is formed, in order to keep the running cost of the apparatus to a low level, the frequency of patch image formation should be reduced as much as possible, and it is preferable to make the first predetermined time t1 longer. On the other hand, when the operation stop time ts increases, density streaks due to the placement of streaks will appear. Therefore, from the viewpoint of maintaining image quality, it is preferable to shorten the first predetermined time t1 as much as possible. In this way, it is difficult to arbitrarily determine the first predetermined time t1. Therefore, for example, in a device having a developing device that can accommodate a large amount of toner, or a device that places more emphasis on image quality, the first predetermined time t1 is set to be shorter, for example, set to about 1 hour, and the emphasis is on economy and In a device that allows a certain degree of density streaks in the image, the first predetermined time t1 is lengthened, for example, set to about 3 hours, and the first predetermined time t1 can be appropriately set according to the specifications of the device, toner characteristics, and the like.

Furthermore, various methods can be considered for determining when the image forming operation and the optimization process of the density control factor will start or end. According to the object of the present invention, it is sufficient to determine whether a certain period of time has passed without performing image formation after the completion of the previous image forming operation. Therefore, it is only necessary to start time counting at any point in time when some processing specific to the image forming operation ends or when some processing required to bring the device into an operation stop state is performed. For example, it can be done as follows.

Fig. 25 is a timing chart of the operation of each part of the device when recovering from an operation stop state. With the start or end of the image forming operation or the optimization process of the density control factor, the application of bias voltage or the start and stop of the rotation drive of each part of the device are performed, but the timing of the start and stop operations of any of them can be specified The start and end of the image forming action or optimization process. For example, as shown in FIG. 25, the operation stop time ts can be measured from the time when the application of the charging bias applied to the charging unit 3 is stopped after the image is formed. In addition, for example, when an image signal accompanied by an image formation request is input from the outside, the image signal is received and the timing of the operation stop time ts is ended, or the operation stops when the rotation drive of the intermediate transfer belt 71 starts with the request. Timing of time ts.

In this embodiment, as in the second embodiment described above, the density sensor may be arranged toward the surface of the photoreceptor 2 to detect the density of the toner image as a patch image developed on the photoreceptor 2. This is the same in the following embodiments. Fourth Embodiment The fourth embodiment of the image forming apparatus of the present invention is a further development of the third embodiment described above. In the fourth embodiment, when the operation stop state exceeds the first predetermined time t1, the optimization process of the concentration control factor is performed. This point is the same as that of the third embodiment, but in addition, the following actions are required. That is, when the operation stop time ts has not reached the first predetermined time and is longer than the second predetermined time t2 shorter than the first predetermined time t1, if there is an input of an image signal accompanied by a user's image formation request, the execution is executed first. The density control factor is optimized, and then the image forming action according to the image forming requirement is executed.

26 is a flowchart of the image forming operation and the operation stop state of the fourth embodiment of the image forming apparatus of the present invention. In addition, FIG. 27 is a timing chart of the difference in device operation caused by the length of the operation stop time.

As shown in FIG. 26, in the fourth embodiment, it is always determined whether an image signal according to the user's image formation request is input from the external device through the interface 112 (step S721). Then, when the action stop time ts without input of the image signal reaches the first predetermined time t1, the optimization process of the density control factor is executed (step S729), which is also the same as the third embodiment.

On the other hand, when an image signal is provided, the series of image forming operations described above are performed to form an image corresponding to the image signal on the sheet S (step S724), but in this embodiment, before the image forming operation is performed, The operation stop time ts is compared with the second predetermined time t2 (step S722). When the operation stop time ts is less than t2, step S723 is skipped and the image forming operation is performed directly. At the same time, when the operation stop time ts is longer than t2, execute The above-mentioned density control factor optimization process (step S723), and then image formation corresponding to the provided image signal is performed. (Step S724).

Then, this image forming operation is repeated as necessary (step S725) to form a predetermined number of images. In this way, when a series of image forming operations are completed, the rotational driving of the intermediate transfer belt 71 and the like is stopped, and the application of the developing bias and the charging bias, etc., is stopped, and the apparatus is turned to the operation stop state (step S726). Thus, at the time when the image forming operation is stopped, for example, at the time when the output of the charging bias voltage supplied from the charging control section 103 to the charging unit 3 is stopped, the CPU 101 resets the internal timer and starts its counting (step S727), and returns to step S721 again , Waiting for the input of the image signal.

That is to say, in this device, after the optimization process of the image forming action or density control factor according to the user's image forming request is completed, when there is no new image forming request, the action stops and waits for a new image signal. enter. At this time, the internal timer continues to count the operation stop time ts, and the operation of the device is divided into the following three methods according to when a new image signal is provided.

(1) When ts<t2 (FIG. 27A ), this is a case where a new image signal is input before the operation stop time ts reaches the second predetermined time t2. At this time, step S723 of FIG. 26 is skipped, and therefore, as shown in FIG. 27A, the image forming operation is directly performed based on the input image signal. Then, after it ends, the internal timer is reset, and then the action stop time ts starts counting from zero again.

In this way, in the case of not too long after the previous image is formed, considering that there is no large image density change, the image forming operation is directly executed according to the corresponding input image signal, and the image of the specified image quality can be quickly formed. .

(2) When t2ts<t1 (FIG. 27B) When the operation stop time ts reaches the second predetermined time t2, but before the first predetermined time t1, a new image signal is provided, step S723 shown in FIG. 26 is executed . Therefore, as shown in FIG. 27B, after the image signal is input, the optimization process of the density control factor is first performed, and then the image formation corresponding to the image signal is performed. In the optimization process at this time, since the image forming operation is performed next, the device can be switched to the operation stop state in the subsequent processing (step S6 shown in FIG. 5).

In this way, when the operation stop time ts reaches the second predetermined time t2 or more, by performing the optimization process of the density control factor before the image formation, even after a long time has passed after the previous image formation, the image with the predetermined image can be formed. Quality images.

(3) When ts=t1 (FIG. 27C) This is a case where the operation stop time ts in the absence of a new image signal input reaches the first predetermined time t1. At this time, as in the third embodiment, the optimization process of the density control factor in step S729 of FIG. 26 is executed. Therefore, as shown in FIG. 27C, when the operation stop time ts reaches t1, the optimization process of the density control factor is executed. At this time, since there is no need to continue image formation, it is better to turn the device into an operation stop state in the subsequent processing. Then, at this time, the internal timer is also reset. Therefore, if the state where the image signal is not input continues and the time t1 elapses, the optimization process of the density control factor is also performed.

In this way, in this embodiment, even if an image signal is not provided, the formation of a toner image as a patch image is performed by performing the optimization process of the density control factor every time a certain period of time has elapsed. Therefore, the operation stop time ts does not exceed the first predetermined time t1, so that the occurrence of density streaks caused by the stand-up streak phenomenon is effectively suppressed.

In this way, after the optimization processing of the density control factor, when a new image signal is provided before the time t2 has elapsed, an image corresponding to the image signal can be directly formed.

As described above, in this embodiment, the times t1 and t2 correspond to the "first predetermined time" and the "second predetermined time", respectively. The problem in this embodiment is also how to set the first and second prescribed times t1 and t2. For example, it can be determined as follows. In the correspondence relationship between the action stop time ts and the degree of density streaks caused by the placement streak phenomenon, the maximum value of the action stop time ts of the density streaks of the image that the user is allowed to hold can be taken as the second predetermined time t2, and the patch The maximum value of the action stop time ts where the density streaks generated on the image will not cause obstacles to the optimization process of the density control factor is taken as the first stop time t1.

In this embodiment, it is also possible to suppress the aggravation of the streak phenomenon by forming patch images at regular intervals. Therefore, the rotation of the developing roller 44 is not necessarily a necessary main condition. That is, in the pre-action (FIG. 7) of the above-mentioned embodiment, the rotation action (pre-action 2) of the developing roller 44 may not be performed, and only the pre-action 1 may be performed. As described above, the rotation of the developing roller 44 slightly changes the characteristics of the toner, but this change in characteristics can be minimized by not performing the pre-action 2.

Here, whether or not to perform pre-action 2 can be determined by, for example, the degree of image quality of the device required. That is to say, it can be used separately. For applications that require higher image quality, the density control factor should be optimized with higher accuracy by executing pre-action 2 and for applications that pay more attention to economics such as toner running costs. , Then pre-action 2 may not be performed.

In addition, this processing (FIG. 26) can also be executed with partial changes as shown in FIG. 28. FIG. 28 is a flowchart of a modified example of the image forming operation and the operation stop state of this embodiment. In this modified example, in its step S741, when there is no image signal input, it returns to the same step S741. Therefore, the operation stop state is maintained until the image signal is input. In addition, in step S742, the process is changed by comparing the operation stop time ts with the third predetermined time t3.

That is, if the image signal is input before the operation stop time ts reaches the third predetermined time t3, the image forming operation corresponding to the input image signal is directly performed (step S744). On the other hand, when an image signal is input after the operation stop time ts reaches the time t3 or more, the density control factor adjustment process (step S743) is performed, and then an image forming operation corresponding to the image signal is performed (step S744).

The processing content other than the above is essentially the same as the processing shown in FIG. 26. However, the adjustment processing (step S743) in this case is the same as the adjustment processing (FIG. 5) of the first embodiment, and is accompanied by the rotation operation of the developing roller 44 (preliminary operation 2 shown in FIG. 7).

The basis for this is as follows. That is, before the toner image corresponding to the image signal is formed, the rotation operation of the developing roller 44 (pre-action 2) is performed first, and then the patch image formation operation is performed, thereby suppressing density streaks caused by the streaking phenomenon. These two actions individually also have the effect of reducing the placement of streaks, and performing these actions one after the other will make the effect more significant.

In this way, by performing these two actions continuously, the placement streak phenomenon can be effectively eliminated, so the action of "optimizing the density control factor at regular intervals" in the third and fourth embodiments described above may sometimes be omitted. For example, in an image forming apparatus with an average continuous operation time of about 8 hours per day, if about half of the time, that is, about 4 hours, is the operation stop time, the density streak caused by the stand-up streak phenomenon is tolerable.

Therefore, in such an apparatus, for example, when an image signal is provided when the operation stop time ts is less than 4 hours, the toner image is directly formed based on the image signal, and the image signal is provided when the operation stop time ts has passed 4 hours or more. At this time, the density control factor optimization process is performed along with the rotation of the developing roller 44, and then the toner image is formed. As a result, the occurrence of density streaks caused by the streak phenomenon can be suppressed, and the toner with good image quality can be stably formed. Agent image. This corresponds to a case where the third predetermined time is set to 4 hours in the present invention.

29A and 29B are timing diagrams showing the relationship between the length of the operation stop time and the operation of the device in the processing of FIG. 28. In the case of performing the processing of FIG. 28, when an image signal is input after the operation stop time ts after the end of the image forming operation is less than the predetermined time t3, as shown in FIG. 29A, the image forming operation is directly executed based on the image signal input.

On the other hand, as shown in FIG. 29B, in the case where an image signal is input when the operation stop time ts is greater than or equal to time t3, before the image forming operation is executed, the optimization process is performed in conjunction with the rotation of the developing roller. In this way, when image formation is performed after the operation stop state continues for a long period of time, optimization processing accompanying the rotation operation is performed before that, so that the occurrence of density streaks caused by the stand-up streak phenomenon can be suppressed. In addition, by rotating the developing roller before the patch image is formed, it is possible to prevent the streaking phenomenon from affecting the patch image.

As described above, in this image forming apparatus, a patch image is formed in accordance with the image signal provided by an external device or in the optimization process of the density control factor to form a certain period of time, that is, a time interval within the first stop time t1. Some toner images. Therefore, when the device is powered on, the operation stop state will not continue for more than time t1, effectively suppressing the occurrence of density streaks caused by the placement of streaks. Moreover, even if the image signal is input after a long period of time t2 or more has elapsed before the operation stop time ts reaches the time t1, the density control factor optimization process is performed before the image formation. Therefore, in this case, good formation can be achieved. Quality toner images.

In addition, when performing the optimization process of the density control factor, if the rotation of the developing roller 44 is performed before the patch image is formed, the patch image can be formed with the uniform toner, and the average can be obtained with high accuracy based on the image density. Optimal value of developing bias voltage Vavg and exposure energy E. Then, by performing image formation under such optimized conditions, a toner image with good image quality can be stably formed in the image forming apparatus.

In addition, even if the optimization processing every predetermined time is not performed, if the image signal is input after the operation stop time ts has passed the third predetermined time t3, if the optimization processing accompanying the rotation of the developing roller is performed before the image forming operation, Then, a toner image with good image quality can be formed stably. In addition to the modification examples of the first to fourth embodiments, the present invention is not limited to the above-mentioned embodiments, and various changes can be made in addition to the above-mentioned embodiments as long as they do not depart from the spirit. For example, in each of the above-mentioned embodiments, the following modifications can be implemented.

For example, in each of the above embodiments, the density sensor 60 is composed of a reflective optical sensor that irradiates light toward the surface of the intermediate transfer belt 71 and detects the amount of light reflected from the surface. However, in addition to this, for example, the density sensor may be The light-emitting element and the light-receiving element are arranged facing each other across the intermediate transfer belt to detect the amount of light passing through the intermediate transfer belt.

In addition, for example, in each of the above-mentioned embodiments, a real image is used as a patch image for high density, and an image composed of multiple 1-dot lines with 1 on and 10 off is used as the patch image for low density. However, each patch The pattern of the image is not limited to this, and it may be a halftone image of another pattern or the like.

In addition, for example, the adjustment process of the density control factor of the above-mentioned first embodiment is configured such that after each developer is sequentially placed in the developing position to perform the rotation of each developing roller 44, patch images are sequentially formed while switching each developer again. However, it is also possible to continuously perform the rotation of the developing roller and the formation of the patch image for each developing device. In this case, the number of switching operations of the developing device can be reduced. Therefore, for example, in a device that requires quietness in a standby state, the frequency of operating sounds accompanying the switching of the developing device can be suppressed to a minimum by such a configuration.

In addition, the sequence of the adjustment processing and the optimization processing of the concentration control factor in the above-mentioned embodiments is an example of the above, and other sequences may be used. For example, in the first embodiment, the image forming operation and the adjustment processing of the density control factor are performed in the order of yellow, cyan, magenta, and black, but other orders may be used.

In addition, in each of the above-described embodiments, as a basic overview of the intermediate transfer belt 71, each sampling data obtained by sampling the output of the density sensor 60 for one round of the intermediate transfer belt 71 is stored. However, it is also possible to store the position where the patch image is formed later, that is, to store only the sample data from the patch image area, which can reduce the amount of data that should be stored. In this case, as long as the formation positions of the patch images on the intermediate transfer belt 71 are aligned as much as possible, a common basic profile can be used for calculations for the patch images, which is more effective.

In addition, in each of the above embodiments, the average developing bias and exposure energy, which are the density control factors that control the image density, can be changed, but only one of them can also be changed to control the image density. In addition, other density control factors can also be used. . Furthermore, in each of the above-mentioned embodiments, the configuration is such that the charging bias varies with the average developing bias, but it is not limited to this. The charging bias may be fixed, or it may be independent of the average developing bias. change. Fifth Embodiment In each of the embodiments described so far, even if there is no image forming requirement or before the image forming operation, the toner image is periodically formed as a patch image by optimizing the image forming conditions, thereby preventing the placement of the toner image. The effect of streaks on image quality. On the contrary, in the fifth and sixth embodiments described below, the rotation of the developing roller 44 is performed periodically to eliminate the streaking phenomenon.

Fig. 30 is a flowchart showing the main processing of the fifth embodiment. In the engine controller 10 of the present embodiment, it is determined whether the CPU 101 inputs an image signal from the CPU 111 of the main controller 11 (step S801). When it is determined that the image signal is input, the next flow is entered to execute the image forming operation described previously to form an image of a sheet (step S802). Then, it is judged whether there is a next image to be formed (step S803), and when there is a next image, the process returns to step S802, and the image forming operation for the necessary number of sheets is repeated. In this way, after the image forming operation is completed, as described later, the value n of the electronic counter provided in the CPU 101 is reset to zero (step S804), and at the same time, the apparatus is turned to the operation stop state (step S805).

In addition, in this embodiment, the internal timer of the CPU 101 also counts the time that the engine part EG is in the action stop state, that is, the action stop time ts. As described above, when the engine part EG turns to the action stop state, The internal timer is temporarily reset, and the measurement of the operation stop time ts is restarted (step S806). Although the structure in this example is such that the operation stop time ts of the device is counted from the moment when the self-charging control unit 103 stops applying the charging bias to the charging unit 3, the operation stop time ts may be measured at a timing other than this. ts timing.

In this way, after a series of image forming operations are completed and the apparatus is turned to the operation stop state, it returns to step S801 again, and waits for the input of a new image signal in a standby state.

On the other hand, in step S801, when it is determined that there is no image signal input, the CPU 101 performs processing along the flow on the right. That is, first, it is judged whether the operation stop time ts continuously counted by the internal timer after the operation stop state has reached the predetermined fourth predetermined time t4 (step S807). Here, when the operation stop time ts has not reached the time t4, the process returns to step S801 again and waits for the input of an image signal. Contrary to this, when the operation stop time ts reaches the time t4, the value n of the electronic counter is increased (step S808), and at the same time, the circumferential rotation of the developing roller 44 is executed to eliminate the streaking phenomenon (step S809) .

Figure 31 is a flowchart of the rotation of the developing roller in this embodiment. In this rotation operation, first, the yellow developing device 4Y is arranged at the developing position (step S891), and the developing roller 44 of the developing device 4Y is coupled with the rotation driving portion on the main body side to rotate more than one revolution (step S892). Then, the rotating developing unit 4 is rotated to switch the developing device (step S893), and the other developing devices 4C, 4M, and 4K are similarly made to rotate the developing roller 44 or more. After the rotation operation is completed for all toner colors in this way (step S894), the main processing is returned to.

Returning to Fig. 30, the description of the operation of the main processing is continued. The electronic counter incremented in step S808 counts the number of times the rotation operation is performed. When it is determined in step S810 that the count value n has reached a predetermined value (3 in this example), that is, when the rotation operation has been performed continuously for 3 times, After this rotation operation, the optimization process of the density control factor that affects the image density is then executed (step S811). In the optimization process here, there is no need to re-rotate the developing roller. Furthermore, after performing this optimization process, or after performing the previously described image forming operation, while resetting this count value n to zero (step S804), if the count value n is a value other than 3 in step S810 After the rotation operation ends, the electronic counter does not reset but keeps its count value n directly to make the device return to the operation stop state again (step S805).

In this way, the processing shown in FIG. 30 is performed, the operation stop time ts is counted, and the number of executions n of the rotation operation is counted. Therefore, in this embodiment, since the previous image forming operation ends until the next image signal The action is different if the time elapsed before input is different. 32A, FIG. 32B, and FIG. 32C are timing charts showing the difference in operation according to the input timing of the image signal in the main processing of the present embodiment. After the previous image forming operation is ended, the device is turned to the operation stop state, and the next new image signal is input before the operation stop time ts reaches the predetermined time t4, as shown in FIG. 32A, the image forming operation is directly performed, and the image formation corresponding to this The toner image of the image signal.

In addition, when the operation stop time ts reaches the time t4 in the state where no new image signal is input after the previous image forming operation is completed, as shown in FIG. 32B, the rotation operation is temporarily removed from the operation stop state. Then, as soon as this rotation action ends, the device will again turn to the action stop state, and at the same time, restart the counting of the action stop time ts. Furthermore, when the operation stop time ts reaches the time t4, the rotation operation is executed again, and if a new image signal is input before the operation stop time ts reaches the time t4, the image forming operation is immediately executed.

In this way, in this embodiment, even when a long time has passed without inputting an image signal, the developing roller 44 is rotated every time a certain period of time (t4) has elapsed. However, every time the rotation is repeated, the electronic counter The count value of is incremented. Therefore, as shown in FIG. 32C, when the third rotation operation (that is, n=3) is performed, after the rotation operation, the optimization process of the density control factor is then performed. In other words, if the time t5 has elapsed since the previous image forming operation was completed and there is no image forming request, the optimization process of the density control factor is performed. This time t5 is approximately n times the time t4 in this embodiment.

Here, since the time required for the rotation operation is about several seconds at a time, if the time t4 is set to, for example, 4 hours, the time t5 is about 12 hours. As described above, the image density changes momentarily due to changes in the surrounding environment of the device such as temperature and humidity. Therefore, in order to always obtain images with a certain density stably, it is best to optimize the density control factors as frequently as possible. However, if the optimization process of the density control factor based on the patch image density is too frequent, the amount of toner consumed in the patch image formation will also increase. In particular, in a small image forming apparatus with a small amount of toner that can be accommodated in the developer, the frequency of toner replenishment (or replacement of the developer) will also increase, which reduces the convenience of the apparatus and causes operating costs. The rise.

Therefore, in this embodiment, in the time interval when the surrounding environment change is considered to be small, the occurrence of the streak phenomenon can be prevented by merely performing the rotation of the developing roller without the formation of the patch image. On the other hand, in the time interval when the surrounding environment is considered to have changed significantly after a longer time, the optimization process of the concentration control factor is performed. In this way, image quality and image density can be stabilized, and toner consumption can be minimized. In addition, by performing the rotation of the developing roller before optimizing the density control factor, a patch image without density streaks caused by the placement of streaks can be formed. Therefore, the density control factor can be accurately performed based on the density of the patch image formed in this way. Optimization.

In this way, in this embodiment, the time interval t4 during which the rotation of the developing roller 44 is performed corresponds to the "fourth prescribed time" of the present invention. In addition, after the image forming operation is completed, until the development roller 44 is subjected to the optimization process of the density control factor. The time t5 until the rotation operation corresponds to the "fifth predetermined time" of the present invention.

As described above, in the image forming apparatus of this embodiment, after the previous image forming operation is completed, it becomes a standby state waiting for the input of a new image signal. However, the operation is not always completely stopped during standby. After a certain time t4 has elapsed, the rotation operation of the developing roller 44 is performed temporarily out of the operation stop state. Therefore, it is possible to effectively suppress the occurrence of streaks caused by preventing the device for a long time, and it is possible to stably form a toner image with good image quality without density streaks.

Then, when the time after the end of the image forming operation reaches time t5, which is longer than the above-mentioned time t4, the optimization process of the density control factor is performed, so even when the device is left for a long time, the change in image density can be suppressed to be small. At the same time, since the rotation of the developing roller is performed before the optimization process, the patch image density will not be affected by the placement of streaks, and the density control factor optimization process can be performed with higher accuracy.

Therefore, in this image forming apparatus, the toner consumption is suppressed by reducing the frequency of patch image formation, and the density streak caused by the streak phenomenon and the image density change accompanying changes in the surrounding environment can be effectively suppressed. Stable formation of toner images with good image quality. Sixth Embodiment The sixth embodiment of the image forming apparatus of the present invention will be described below. In the sixth embodiment, the content of the main processing is different from that of the fifth embodiment, and accordingly, the operation in the standby state is different from that of the fifth embodiment. Therefore, the operation in this main processing is mainly explained here.

In the image forming apparatus of the fifth embodiment, even if the image signal is not input, by performing the rotation action of the developing roller 44 at regular intervals, the streak phenomenon is prevented (FIG. 32C). In contrast, in the sixth embodiment, the operation stop state is maintained during the period when no image signal is input, and when a new image signal is input, before the corresponding image forming operation is performed, the operation stop time is determined based on the size of the previous operation stop time. The necessary pre-processing is performed, that is, the rotation action of the developing roller 44 and the optimization processing of the density control factor are performed.

The main processing of the sixth embodiment will be described in more detail with reference to FIG. 33, FIG. 34A, FIG. 34B, and FIG. 34C. FIG. 33 is a flowchart showing the main processing of the sixth embodiment of the image forming apparatus of the present invention. In addition, FIG. 34A, FIG. 34B, and FIG. 34C are timing charts of operation differences caused by the input timing of the image signal in the main processing of this embodiment. In the main processing of this embodiment, similar to the device of the fifth embodiment, the CPU 101 of the engine controller 10 determines whether there is an image signal input (step S901), but in the sixth embodiment, if there is no image signal Input, the device still remains in the stopped state.

Then, when the image signal is input, the operation stop time ts measured by the internal timer is compared with the predetermined time t6 (step S902). At this time, if the operation stop time ts is longer than the time t6, the rotation operation of the developing roller 44 is performed (step S903). The content of this rotating motion is the same as that of the fifth embodiment (FIG. 31). On the other hand, when the operation stop time ts has not reached the time t6, the rotation operation and the following steps S904 and S905 are skipped.

Next, the operation stop time ts is compared with the time t7 which is longer than the predetermined time t6 (step S904). Then, if the operation stop time ts is longer than the time t7, the optimization process of the density control factor is executed (step S905). When the action stop time ts has not reached the time t7, this optimization process is skipped.

In this way, after necessary pre-processing is performed according to the size of the operation stop time ts, the image forming operation is executed, and a required number of images are formed (steps S906 to S907). Then, after the image formation is completed, the device is turned to the operation stop state (step S908), and at the same time, the internal timer that counts the operation stop time ts is reset, a new time measurement is started (step S909), and step S101 is returned.

By performing such main processing, in the apparatus of this embodiment, the operation is distinguished as follows based on the elapse of time from the end of the previous image forming operation to the input of the next image signal. First, when a new image signal is input before the operation stop time ts after the end of the previous image forming operation reaches the predetermined time t6, as shown in FIG. 34A, the image forming operation corresponding to the image signal is immediately executed. In contrast, as shown in FIG. 34B, when a new image signal is input when the operation stop time ts is greater than or equal to time t6 but less than time t7, the image forming operation is executed after the rotation operation of the developing roller 44 is executed. In this way, when the operation stop time ts is long, by rotating the developing roller 44 before image formation, the streak phenomenon can be eliminated, and a toner image with good image quality can be formed. In this way, in this embodiment, the time t6 corresponds to the "sixth prescribed time" of the present invention.

Furthermore, as shown in FIG. 34C, when a new image signal is input after the operation stop time ts exceeds the time t7, the rotation operation of the developing roller 44 and the subsequent optimization processing of the density control factor are executed, and then the image forming operation is executed. In this way, when the operation stop time ts is longer, by executing the optimization process of the density control factor before image formation, it is possible to form a toner image with stable image quality independent of changes in the surrounding environment of the device such as temperature and humidity. In addition, since the rotation of the developing roller 44 is performed before the optimization process thereof, the patch image density is not affected by the streak phenomenon, and the optimization process of the density control factor can be performed with high accuracy. In this way, in this embodiment, the time t7 corresponds to the "seventh prescribed time" of the present invention.

As described above, in the image forming apparatus of this embodiment, when a new image signal is input, the operation is changed according to the size of the operation stop time ts after the previous image forming operation is completed. That is, when the operation stop time ts is less than the time t6, the image forming operation is immediately performed, and when the operation stop time ts is longer than the time t6, the rotation operation of the developing roller 44 is performed. Therefore, the streak phenomenon caused by the developing roller 44 being left carrying the toner can be eliminated before image formation, and a toner image with good image quality without density streaks can be stably formed.

In addition, when the operation stop time ts reaches a longer time t7 or longer, since the density control factor is optimized after the rotation of the developing roller 44, even if the surrounding environment of the device changes due to long-term storage, it can be The fluctuation of the image density caused by the influence is suppressed, and the toner image is formed stably.

In this way, although the actions in the main processing of the above-mentioned fifth and sixth embodiments are somewhat different, the essential technical ideas are the same. That is, by rotating the developing roller 44 according to the size of the operation stop time ts, the streak phenomenon can be eliminated without increasing the toner consumption. At the same time, the image density can be achieved by further optimizing the density control factor as needed. The stability. As a result, in these image forming apparatuses, toner images with good image quality can be stably formed. Therefore, when the present invention is applied to an image forming apparatus, either of the above-mentioned two embodiments can be adopted. In addition, the degree to which the rotation operation of the developing roller 44 and the optimization processing of the density control factor are performed can also be appropriately determined according to the apparatus. There are also modifications of the fifth and sixth embodiments. The present invention is not limited to the above-mentioned embodiment, and various changes can be made in addition to the above-mentioned embodiment as long as it does not deviate from the spirit. For example, in the above embodiments, the operation stop time ts is counted by the internal timer of the CPU 101, but other timing devices can also be used for timing. For example, a timer IC or a counter may be additionally provided in the engine controller 10, This counts the action stop time ts.

In addition, for example, in each of the above-mentioned embodiments, the operation stop time ts is counted from the time when the charging bias applied to the photoreceptor 2 from the charging control unit 103 is stopped, but the timing of starting to calculate the operation stop time ts is not limited to Here, for example, the operation stop time ts may be calculated from the time when the application of the developing bias voltage from the developer control unit 104 to the developing roller 44 is stopped, the rotational driving of the photoreceptor 2 and the rotational driving of the intermediate transfer belt 71 are stopped.

In addition, for example, in the above-mentioned embodiment, when the operation stop time ts exceeds the predetermined time, the rotation of the developing roller 44 is performed, and when the operation stop time ts is longer, the density control factor optimization process is also performed, but Even in the latter case, only the rotation operation of the developing roller 44 may be performed. Even if there is a request from the main controller 11, it is also possible to perform the optimization process of the concentration control factor only when there is a special need.

In addition, for example, the following modifications may also be adopted. 35A and 35B are diagrams showing operations of a modification example of the main processing. In this modified example, every time the operation stop time ts reaches the predetermined time t8, the rotation operation of the developing roller 44 is performed, and the standby time tw after the previous image forming operation is completed is counted in advance. The action stop time ts is stopped and reset due to the execution of the rotation action, and the counting of the standby time tw is not interrupted due to the execution of the rotation action.

Then, when the next image signal is input before the standby time tw reaches the predetermined time t9 (where t9>t8) (FIG. 35A ), the image forming operation corresponding to the image signal is immediately executed. In addition, when the standby time tw reaches the time t9 or more and a new image signal is input (FIG. 35B ), the density control factor optimization process is performed first, and then the image formation corresponding to the image signal is performed.

Even in this modified example, the occurrence of density streaks caused by the streak phenomenon can be suppressed by rotating the developing roller 44 at regular intervals. When the standby time tw is long, the density control factor is executed before the image is formed. The optimized processing can suppress the fluctuation of image density and stably form toner images with good image quality.

In addition, for example, in the above-mentioned fifth embodiment, when the rotation of the developing roller 44 is continuously performed three times, the optimization processing of the density control factor is subsequently performed. Therefore, the time t5 corresponding to the "fifth predetermined time" is equivalent to The "fourth predetermined time" t4 of the present invention is about three times, but the relationship between the two may not necessarily form such an integer ratio. Modifications of the first to sixth embodiments The above-described embodiments are image forming apparatuses having an intermediate transfer belt 71 as an intermediate medium for temporarily carrying the toner image developed on the photoreceptor 2, but the present invention can also be applied to An image forming apparatus having other intermediate media such as a transfer drum or a transfer roller, or an image forming apparatus that does not have an intermediate media and directly transfers the toner image formed on the photoreceptor 2 onto the sheet S as the final transfer material Image forming device.

In addition, each of the above embodiments is an image forming apparatus that can form full-color images with four color toners of yellow, cyan, magenta, and black. However, the toner colors and the number of colors used are not limited to this, and they are arbitrary. For example, the present invention can also be applied to a device that forms a monochrome image using only black toner.

In addition, in each of the above embodiments, the present invention is applied to a printer that performs image forming operations based on image signals from outside the device, but of course the present invention can also be applied: according to the user's imaging requirements, for example, by pressing the copy A copier that generates image signals inside the device and executes image forming actions based on the image signals; or a facsimile device that executes image forming actions based on image signals provided by a communication line.