Inkjet recording apparatus and method for detecting discharge defect

The present invention relates to an inkjet recording apparatus and a method for detecting ejection defects, and more particularly to a technique for detecting ejection defects of a nozzle that ejects ink droplets.

In recent years, an inkjet recording device (inkjet printer) has become widespread as a recording device for printing and recording an image or the like taken by a digital still camera. The inkjet recording device is equipped with a plurality of recording elements in the head, scans the recording head while ejecting ink droplets from the recording elements onto the recording medium, and records one line of image on the recording paper to record one line of recording medium. An image is formed on the recording paper by transporting and repeating this process.

Inkjet printers use single-length serial heads and record while scanning the head in the width direction of the recording medium, or line heads in which recording elements are arranged over the entire area of one side of the recording medium. There is one that uses. When a line head is used, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements. A printer using a line head eliminates the need for a transport system such as a carriage that scans a short head, and also eliminates the need for complicated scanning control between the movement of the carriage and the recording medium. Moreover, since only the recording medium moves, the recording speed can be increased as compared with a printer using a serial head.

In an inkjet printer, some of the nozzles out of a large number of nozzles may not be ejected for some reason, or the ink ejection amount (dot size dropleted on the recording paper) or flight direction (droplet position) may be inappropriate. Discharge defects such as ink jets may occur. Since the existence of such an inappropriate nozzle causes deterioration of the quality of the recorded image, it is necessary to take measures against it.

Conventionally, as a method of detecting nozzle ejection defects, a method of measuring a test pattern print, a method of measuring a practical print (a printed image of a target for which print output is actually requested), and a method of ejecting inside the head are used. A method for measuring characteristics (physical property values such as resistance value) is known.

In the inkjet recording apparatus and the inkjet recording method disclosed in Patent Document 1, the detection of the non-ejection nozzle detects a change in drive voltage via ink on the recording head substrate by a detection electrode provided in the recording head. It is done.

In the inkjet recording apparatus described in Patent Document 2, a continuous line composed of all nozzles of one head is formed on the test ejection paper at a position where the plurality of heads do not interfere with each other, and the presence or absence of an intermittent portion of the line is determined. It is detected optically or electrically.

In the method and apparatus for manufacturing a color filter described in Patent Document 3, the laser light is performed based on the state when the ink ejected from the inkjet head passes through.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2001-315318</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 6-24008</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 9-101410</text></patcit>

<p> However, in the method of measuring the print of the test pattern, it is necessary to print a dedicated test pattern separately from the target image to be actually printed. Further, the simple pattern is affected by the measurement position error, and there is a problem that it is difficult to detect the ejection defective nozzle. Further, there is a problem that it is affected by the output variation of the line sensor that captures the test pattern.</p><p> In the case of the method of measuring the practical print, since the practical print to be measured is generally a complicated image, it is difficult to judge whether it is an image defect due to a nozzle defect or the original image content, and the influence of the measurement position error is affected. There is a problem that it is difficult to accurately identify the defective ejection nozzle. Further, as in the case of the above test pattern, it is affected by the variation of the line sensor.</p><p> In the inkjet recording apparatus and the inkjet recording method disclosed in Patent Document 1, non-ejection due to air bubbles mixed in the nozzle can be detected, but non-ejection due to other causes such as dust adhesion cannot be detected.</p><p> The inkjet recording apparatus described in Patent Document 2 requires a trial ejection paper, and the paper is wasted.</p><p> In the color filter manufacturing method and manufacturing apparatus described in Patent Document 3, it takes time to detect when the number of nozzles increases. Further, it is necessary to arrange the light emitting element and the light receiving element under the nozzle, and when the head is long, a mechanism for retracting the head is required.</p><p> The present invention has been made in view of such circumstances, and an object of the present invention is to provide an inkjet recording device and a discharge defect detection method capable of detecting ejection failure nozzles without reducing productivity.</p>

<p> In order to achieve the above object, the inkjet recording apparatus according to the present invention includes a print head for ejecting ink droplets and a conveying means for moving the print medium relative to the print head in the feed direction of the print medium. In the inkjet recording apparatus, the transport means includes a hold transport member that holds the print medium and transports the print medium, and a test print control means that controls printing a test image on the hold transport member. The test print control means is provided with a reading means for reading the test image printed on the holding and transporting member.</p><p> According to the present invention, the test image is printed on the holding and transporting member used for transporting the printing medium in the transporting means, and the test image is read by the reading means, so that the printing medium for the test image is unnecessary.</p><p> The print head may be a full-line type print head in which nozzles are arranged over the entire printable area in a direction substantially orthogonal to the print medium transport direction, or a short print head is substantially orthogonal to the print medium transport direction. A shuttle scan type print head that ejects ink droplets while moving in the direction may be used.</p><p> A transport belt may be used or a transport drum may be used as the holding and transporting member.</p><p> The test image includes images, characters, and the like that are preferable for detecting the ejection failure nozzle, and may be composed of a plurality of colors. Further, it may be controlled to print a test image for each color.</p><p> Further, the test image may be an image printed from all nozzles or an image printed from some nozzles. The mode of selecting a part of the nozzles may be a nozzle that is used infrequently or a nozzle that has had a discharge failure in the past.</p><p> Further, the print medium may be held by the holding and conveying member at least in the printing area where the ink droplets are ejected, and is held so as to secure a predetermined flatness in the printing area.</p><p> A line sensor or an area sensor may be used as the reading means. Further, a sensor corresponding to black and white may be used, or a sensor corresponding to a plurality of colors may be used. Further, it may be an embodiment in which a laser beam is irradiated and the reflected light is read.</p><p> In the present specification, the term "printing" refers not only to the formation of characters but also to the concept of forming an image in a broad sense including characters.</p><p> A "printing medium" is a medium (image forming medium) that is printed by a recording head, regardless of the material or shape of continuous paper, cut paper, sticker paper, resin sheet such as OHP sheet, film, cloth, etc. Includes various media.</p><p> The "transport means" is a mode in which the print medium is conveyed to the stopped (fixed) recording head, a mode in which the recording head is moved to the stopped print medium, or a mode in which both the recording head and the print medium are moved. Includes any of the modes of causing.</p><p> According to one aspect of the present invention, the holding and transporting member is provided with a predetermined area for printing the test image, and the test printing control means controls to print the test image in the predetermined area. It is characterized by doing.</p><p> For example, when the holding and transporting member is made to hold the print medium by air suction, a region where the pitch of the air suction holes in the print medium feed direction is wider than that of other regions is provided, and a test image is printed in this region. It may be configured as.</p><p> According to this aspect, since there is an area for printing a test image in a predetermined area, the holding force on the holding and transporting member is high, and the transporting performance is good.</p><p> According to another aspect of the present invention, the holding and transporting member is provided with a plurality of predetermined regions for printing the test image, and the plurality of predetermined regions are used frequently in the transporting direction of the printing medium. It is characterized in that it is arranged at intervals according to a high print medium size.</p><p> According to such an aspect, the interval between the print media is reduced, the productivity is improved, and the transport performance of the large size print medium is improved.</p><p> For example, 10 L size prints having a width (direction substantially orthogonal to the transport direction) of 127 mm and a length (convey direction) of 89 mm are arranged at 5 mm intervals, and a test print area having a length of 20 mm is provided for each 10 sheets. Therefore, since the test print areas are set at intervals of 935 mm, it is possible to frequently check for ejection defects, and since normal L size prints are arranged at narrow intervals of 5 mm in length, they are arranged. Increased productivity of L size prints.</p><p> The spacing between the print media may be adjusted to the size of the most frequently used print medium, or may be adjusted to the least common multiple of the size of the most frequently used print medium and the size of the next most frequently used print medium. Further, the interval of the area for printing the test image may be determined so that a plurality of print media can be fixed.</p><p> According to still another aspect of the present invention, the holding and conveying member is the printing medium and the test so that a predetermined area for performing the test printing comes between the printing media which are continuously conveyed by the conveying means. It is characterized in that it is provided with an alignment means for performing relative alignment with a predetermined area for printing.</p><p> The area for printing the test image may be configured so that the print medium is not placed, or it is detected that the print medium is placed in the area for printing the test image, and the print medium is placed in the print area. When it is, the test image may be controlled not to be printed. This is especially effective when a full-line type line head is provided.</p><p> The alignment means is provided with a detector (sensor) in at least one of the transport means and the drive system for driving the transport means, and is a relative position between the print medium and a predetermined area for test printing by a signal obtained from the sensor. Or may control the relative position between the print medium and a predetermined area for test printing based on the control signal of the drive system (for example, the operation command signal of the motor of the drive system).</p><p> Further, according to another aspect of the present invention, the test print control means is characterized in that the test print is controlled to perform test print in the area between the images.</p><p> According to this aspect, a test image can be printed between this image and the next main image, so that productivity is not reduced. The present image includes a print result on which the target image data is printed.</p><p> Further, according to another aspect of the present invention, the present invention is characterized in that the detection means for detecting the ejection failure nozzle from the test image read by the reading means is provided.</p><p> According to this aspect, since the ejection defective nozzle is detected from the reading result of the test image, when the ejection defective nozzle is detected, the image is corrected by another nozzle and the ejection defective nozzle is recovered. It is possible to improve the image quality.</p><p> The detecting means can detect the presence / absence of landing ink, the landing diameter, and the like, and can determine the ejection failure nozzle from the presence / absence of ejection and the amount of ink ejected, respectively.</p><p> Furthermore, according to another aspect of the present invention, at least the region where the test image is printed in the holding and transporting member has a color that makes it easy to determine the ink color.</p><p> According to such an aspect, it becomes easy to distinguish between the ink droplet and the holding and conveying member, and the reading accuracy is improved.</p><p> Generally, cyan, magenta, yellow, and black are used as ink colors. A color in a wavelength region in which these colors can be easily discriminated may be applied, or a brightness difference from the ink color may be added. That is, it is sufficient that the sensor applied to the reading means can reliably recognize the ink droplets.</p><p> The holding and transporting member may be composed of not only one color but also a plurality of colors corresponding to the printing color, and may be transparent or translucent. If the holding and transporting member is transparent or translucent, it is possible to read an image by transmitted light.</p><p> The colors referred to here include black and white (monochrome).</p><p> Further, according to another aspect of the present invention, at least the region where the test image is printed in the holding and transporting member is made of a material in which the elasticity of the ink droplets is stable.</p><p> According to this aspect, it is possible to stabilize the elasticity of ink droplets when printing a test image, and the reading accuracy is improved. Further, it is preferable that the material is a material that makes it easy to clean the holding and transporting member.</p><p> Considering the prevention of ink droplet aggregation and the ease of cleaning the holding and transporting member, the material of the holding and transporting member is preferably a material having a contact angle of about 40 °. More preferably, the material of the holding and transporting member is a material having a contact angle of about 100 °. The contact angle refers to the contact angle after a certain period of time has passed since the ink droplet was dropped on a predetermined printing medium (that is, the holding and conveying member), and the contact portion (contact) between the ink droplet and the holding and conveying member. The angle between the ink droplet surface and the holding and transporting member in the liquid part).</p><p> Further, according to still another aspect of the present invention, a cleaning means for cleaning the holding and transporting member is provided on the downstream side of the reading means in the printing medium transporting direction.</p><p> According to this aspect, when the test image is read by the reading means, the holding and transporting member can be cleaned, the printing medium can be kept clean, and subsequent test printing can be performed. </p><p> Examples of the cleaning means include a mode of wiping (peeling) with a roller, a blade, and the like, and a mode of immersing the belt in a cleaning liquid (solvent) to remove (dissolve) stains such as ink.</p><p> When it is also used as a surplus ink cleaning member for full-screen printing (borderless image printing), the cleaning means can be simplified.</p><p> Furthermore, according to another aspect of the present invention, the test print control means drops inks of a plurality of colors on the same drip point, and the reading means is used for each color from mixed color dots of the plurality of colors. It is characterized by reading dot information.</p><p> According to this aspect, since the information of a plurality of colors is read from one dot, the test print area can be minimized and the transport performance is improved.</p><p> A color-compatible sensor may be used as the reading means, and the sensor may be provided with a color filter corresponding to each color, or may be provided with an RGB color filter for CMYK ink, for example.</p><p> The present invention also provides a method invention for achieving the above object. That is, the ejection defect nozzle detection method in the inkjet recording apparatus according to the present invention includes a print head for ejecting ink droplets and a conveying means for moving the print medium relative to the print head in the feed direction of the print medium. In the test printing step of printing a test image from the print head to the holding and transporting member for transporting the printing medium provided in the transporting means, and the test printing step. It is characterized by comprising a reading step of reading the test image dropped on the holding and transporting member by a reading means, and a detection step of detecting a discharge defective nozzle from the test image read in the reading step.</p><p> It is preferable to include a nozzle recovery means for performing a recovery operation on the detected ejection failure nozzle and a correction means for correcting the printed image performed by using the ejection failure nozzle.</p>

<p> According to the present invention, since the test image is printed on the holding and transporting member having the transporting means, a printing medium (paper) for printing the test image is unnecessary, and the test image is printed between the images. Since it prints, it does not reduce productivity. When a discharge defective nozzle is detected, a predetermined nozzle recovery operation and a predetermined image correction can be performed.</p><p> Further, the ejection defective nozzle can be detected from the reading result by the reading means, and the test image printed on the holding and transporting member is cleaned after being read by the cleaning means for cleaning the holding and transporting member.</p><p> Since the holding and transporting member is made of a material that stabilizes the elasticity of the ink droplets and has a color that makes it easy to distinguish the color of the ink droplets, the elasticity of the ink droplets is stabilized and the reading accuracy can be improved.</p><p> Furthermore, since multiple colors of ink are printed on the same row and the dots of each color are read from the dots of mixed colors, the area for printing the test image can be minimized and the transport performance is improved. ..</p><p> By providing the alignment means for aligning the test image printing area for printing the test image on the holding and conveying member with the printing medium, the elasticity of ink droplets is ensured in the test printing area and the printing medium is provided in the printing medium conveying area. The holding power of the ink can be increased, and the transport performance is improved. When the test print area is adjusted to the size of the print medium that is frequently used, the interval between the print media can be reduced and the productivity is improved.</p>

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall Configuration of Inkjet Recording Device] FIG. 1 is an overall configuration diagram of an inkjet recording device according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a printing unit 12 having a plurality of printing heads 12K, 12C, 12M, 12Y provided for each color of ink, and each printing head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feed unit 18 for supplying recording paper 16, a decal processing unit 20 for removing curl of the recording paper 16, and a nozzle of the printing unit 12. A suction belt transport unit 22 that is arranged to face the surface (ink ejection surface) and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads the print result by the print unit 12. It is equipped with a paper ejection unit 26 that ejects printed recording paper (printed matter) to the outside.

In FIG. 1, a magazine of roll paper (continuous paper) is shown as an example of the paper feed unit 18, but a plurality of magazines having different paper widths, paper qualities, and the like may be provided side by side. Further, the paper may be supplied by a cassette in which the cut paper is laminated and loaded, instead of or in combination with the roll paper magazine.

When multiple types of recording paper are configured to be usable, an information recorder such as a barcode or wireless tag that records the type information of the paper is attached to the magazine, and the information of the information recorder is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

The recording paper 16 sent out from the paper feed unit 18 is curled due to the remaining winding habit due to being loaded in the magazine. In order to remove this curl, the decal processing unit 20 applies heat to the recording paper 16 with the heating drum 30 in the direction opposite to the winding habit direction of the magazine. At this time, it is more preferable to control the heating temperature so that the printed surface has a slightly weak curl on the outside.

In the case of an apparatus configuration using roll paper, as shown in FIG. 1, a cutter (first cutter) 28 for cutting is provided, and the roll paper is cut to a desired size by the cutter 28. The cutter 28 is composed of a fixed blade 28A having a length equal to or longer than the transport path width of the recording paper 16 and a round blade 28B that moves along the fixed blade 28A, and the fixed blade 28A is provided on the back side of printing. The round blade 28B is arranged on the printing surface side across the transport path. When using cut paper, the cutter 28 is unnecessary.

After the decal processing, the cut recording paper 16 is sent to the suction belt transport unit 22. The suction belt transport unit 22 has a structure in which an endless belt 33 is wound between the rollers 31 and 32, and at least a portion facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 is a horizontal surface (a horizontal surface (). It is configured to form a flat surface).

The belt 33 has a width dimension wider than the width of the recording paper 16, and a large number of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided inside the belt 33 spanned between the rollers 31 and 32 at positions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detecting unit 24. The recording paper 16 on the belt 33 is sucked and held by sucking the suction chamber 34 with the fan 35 to create a negative pressure.

Further, the belt 33 is provided with a test print area (not shown in FIG. 1 and shown as reference numeral 33A in FIG. 9) on which a test image is printed. The test image printed in this test print area is read by the print detection unit 24, and the ejection failure of the print heads 12K, 12C, 12M, 12Y is determined from the reading result. The detailed structure of the belt 33 and the details of the discharge defect detection of the print heads 12K, 12C, 12M, and 12Y will be described later.

The belt 33 is rotated counterclockwise on FIG. 1 by transmitting the power of the motor (not shown in FIG. 1, not shown as reference numeral 88 in FIG. 7) to at least one of the rollers 31 and 32 around which the belt 33 is wound. The recording paper 16 driven in the direction and held on the belt 33 is conveyed from right to left in FIG. The details of the belt 33 will be described later.

When printing a borderless print or the like, ink also adheres to the belt 33. Therefore, the belt cleaning unit 36 is provided at a predetermined position (appropriate position other than the printing area) on the outside of the belt 33. The configuration of the belt cleaning unit 36 is not shown in detail, but there are, for example, a method of niping a brush roll, a water absorption roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case of the method of niping the cleaning roll, the cleaning effect is large when the belt wire speed and the roller wire speed are changed.

It is conceivable to use a roller / nip transfer mechanism instead of the suction belt transfer unit 22, but when the roller / nip transfer is performed in the print area, the roller comes into contact with the printed surface of the paper immediately after printing, so that the image tends to blur. There is a problem. Therefore, as in this example, it is preferable to carry the suction belt so that the image surfaces do not come into contact with each other in the print area.

A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper transport path formed by the suction belt transport unit 22. The heating fan 40 blows heating air onto the recording paper 16 before printing to heat the recording paper 16. By heating the recording paper 16 immediately before printing, the ink can be easily dried after landing.

The printing unit 12 is a so-called full-line type head in which line-type heads having a length corresponding to the maximum paper width are arranged in a direction orthogonal to the paper feed direction (main scanning direction) (see FIG. 2). A detailed structural example will be described later, but as shown in FIG. 2, each print head 12K, 12C, 12M, 12Y has a length exceeding at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. It is composed of a line-type head in which a plurality of ink ejection ports (nozzles) are arranged.

A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the paper transport direction). , 12C, 12M, 12Y are arranged. A color image can be formed on the recording paper 16 by ejecting color inks from the printing heads 12K, 12C, 12M, and 12Y while transporting the recording paper 16.

In this way, according to the printing unit 12 in which the full line head covering the entire width of the paper is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording paper 16 only by doing so (that is, in one sub-scan). As a result, high-speed printing is possible and productivity can be improved as compared with the shuttle type head in which the print head reciprocates in the main scanning direction.

In this example, the configuration of KCMY standard colors (4 colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. You may. For example, it is possible to add a print head that ejects light inks such as light cyan and light magenta.

As shown in FIG. 1, the ink storage / loading unit 14 has a tank for storing ink of a color corresponding to each print head 12K, 12C, 12M, 12Y, and each tank passes through a pipeline (not shown). It communicates with each print head 12K, 12C, 12M, 12Y. Further, the ink storage / loading unit 14 is provided with notification means (display means, warning sound generation means) for notifying when the remaining amount of ink is low, and also has a mechanism for preventing erroneous loading between colors. ing.

The print detection unit 24 includes an image sensor for capturing the drip result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the drip image read by the image sensor.

The print detection unit 24 of this example is composed of a line sensor (reference numeral 24A in FIG. 9) having a light receiving element row wider than the ink ejection width (image recording width) by at least each print head 12K, 12C, 12M, 12Y. Will be done. This line sensor includes an R sensor array in which photoelectric conversion elements (pixels) provided with a red (R) color filter are arranged in a line, and a G sensor array in which a green (G) color filter is provided. It consists of a B sensor array provided with a blue (B) color filter and a color separation line CCD sensor consisting of the sensor. Instead of the line sensor, it is also possible to use an area sensor in which light receiving elements are arranged two-dimensionally.

The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, 12Y of each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, the measurement of the dot size, the measurement of the dot landing position, and the like. Further, the print detection unit 24 is provided with a light source (reference numeral 24B in FIG. 9) for irradiating the dropped dots with light.

A post-drying section 42 is provided after the print detection section 24. The post-drying unit 42 is a means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing dries, a method of blowing hot air is preferable.

When printing on porous paper with dye-based ink, the weather resistance of the image is improved by blocking the pores of the paper with pressure to prevent contact with ozone and other substances that can destroy dye molecules. Has the effect of

A heating / pressurizing section 44 is provided after the post-drying section 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes the image surface with a pressurizing roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

The printed matter thus generated is discharged from the paper ejection unit 26. When the main image (printed with the target image) and the test print are formed in parallel on a large sheet of paper at the same time, the test print portion is separated by the cutter (second cutter) 48. The cutter 48 is provided immediately before the paper ejection section 26, and is for cutting the main image and the test printing section when test printing is performed on the image margin section. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and is composed of a fixed blade 48A and a round blade 48B.

Further, although not shown in FIG. 1, a sorter for accumulating images for each order is provided in the discharge unit 26 of this image.

Next, the structure of the print head 50 will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for each ink color are common, the print heads will be represented by reference numeral 50 below.

FIG. 3 (a) is a plan perspective view showing a structural example of the print head 50, and FIG. 3 (b) is an enlarged view of a part thereof. In addition, FIG. 3 (c) is a plan perspective view showing another structural example of the print head 50, and FIG. 4 is a cross-sectional view showing a three-dimensional configuration of the ink chamber unit (along lines 4-4 in FIG. 3 (a)). (Cross section). In order to increase the density of the dot pitch printed on the recording paper surface, it is necessary to increase the density of the nozzle pitch in the print head 50. As shown in FIGS. 3 (a) to 3 (c) and FIG. 4, the print head 50 of this example has a plurality of inks including a nozzle 51 for ejecting ink droplets and a pressure chamber 52 corresponding to each nozzle 51. It has a structure in which the chamber units 53 are arranged in a staggered matrix, thereby achieving a high density of apparent nozzle pitch.

That is, as shown in FIGS. 3 (a) and 3 (b), the print head 50 in the present embodiment corresponds to the entire width of the print medium in a direction in which a plurality of nozzles 51 for ejecting ink are substantially orthogonal to the print medium feed direction. A full-line head with one or more rows of nozzles arranged over the length of the print.

Further, as shown in FIG. 3C, short two-dimensionally arranged heads 50'may be arranged in a staggered pattern and joined together to have a length corresponding to the entire width of the printing medium.

The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the nozzle 51 and the supply port 54 are provided at both diagonal corners. Each pressure chamber 52 communicates with the common flow path 55 via the supply port 54.

An actuator 58 provided with individual electrodes 57 is joined to the pressure plate 56 forming the top surface of the pressure chamber 52, and the actuator 58 is deformed by applying a driving voltage to the individual electrodes 57 from the nozzle 51. Ink is ejected. When the ink is ejected, new ink is supplied to the pressure chamber 52 from the common flow path 55 through the supply port 54.

As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a constant arrangement along a row direction along the main scanning direction and an oblique column direction having a constant angle θ not orthogonal to the main scanning direction. It has a structure in which patterns are arranged in a grid pattern. Due to the structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a direction of a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles arranged in the main scanning direction is d × cos θ.

That is, the main scanning direction can be treated equivalently as if each nozzle 51 is linearly arranged at a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows (2400 nozzles / inch) are projected so as to be arranged in the main scanning direction. Hereinafter, for convenience of explanation, each nozzle 51 will be described as being linearly arranged at regular intervals (pitch P) along the longitudinal direction (main scanning direction) of the head.

When driving the nozzles with a full-line head having a nozzle row corresponding to the entire width of the paper (recording paper 16), (1) all the nozzles are driven at the same time, and (2) the nozzles are sequentially driven from one side to the other. Driving, (3) Dividing the nozzle into blocks and driving each block sequentially from one side to the other, etc., a row of dots in the width direction of the paper (direction orthogonal to the paper transport direction) Driving a nozzle that prints a line (or a line of dots in multiple rows) is defined as main scanning.

In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scan as described in (3) above is preferable. That is, the nozzles 51-11, 51-12, 51-13, 51-14, 51-15, and 51-16 are combined into one block (the other nozzles 51-21, ..., 51-26 are combined into one block). Nozzles 51-11, 51-12, ..., 51-16 depending on the transport speed of chart paper 16 (as blocks, nozzles 51-31, ..., 51-36 as one block, ...) By driving sequentially, one line is printed in the width direction of the recording paper 16.

On the other hand, by repeatedly moving the above-mentioned full line head and the paper relative to each other, printing of a line (or a line consisting of a plurality of rows of dots) formed by the above-mentioned main scan is called sub-scanning. Define.

In carrying out the present invention, the nozzle arrangement structure is not limited to the illustrated example. Further, in the present embodiment, a method of ejecting ink droplets by deforming an actuator 58 represented by a piezo element (piezoelectric element) is adopted. In carrying out the present invention, an actuator other than the piezo element can be applied to the actuator 58.

FIG. 6 is a schematic view showing the configuration of the ink supply system in the inkjet recording apparatus 10.

The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. The form of the ink supply tank 60 includes a method of replenishing ink from a replenishment port (not shown) and a cartridge method of replacing the entire tank when the remaining amount of ink is low. When changing the ink type according to the intended use, the cartridge method is suitable. In this case, it is preferable to identify the ink type information with a barcode or the like and perform ejection control according to the ink type. The ink supply tank 60 of FIG. 6 is equivalent to the ink storage / loading unit 14 of FIG. 1 described above.

As shown in FIG. 6, a filter 62 is provided between the ink supply tank 60 and the print head 50 in order to remove foreign matter and air bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally, about 20 μm).

Although not shown in FIG. 6, it is also preferable to provide a sub tank in the vicinity of the print head 50 or integrally with the print head 50. The sub tank has a damper effect for preventing fluctuations in the internal pressure of the head and a function for improving refilling.

Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying out or an increase in ink viscosity in the vicinity of the nozzle 51, and a cleaning blade 66 as a means for cleaning the surface of the nozzle 51. There is.

The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. To.

The cap 64 is vertically displaced relative to the print head 50 by an elevating mechanism (not shown). When the power is turned off or when printing is on standby, the cap 64 is raised to a predetermined raised position and brought into close contact with the print head 50 to cover the nozzle 51 surface (ink ejection surface) with the cap 64.

If the specific nozzle 51 is used less frequently during printing or waiting and the ink is not ejected for a certain period of time or longer, the ink solvent in the vicinity of the nozzle evaporates and the ink viscosity increases. In such a state, even if the actuator 58 operates, ink cannot be ejected from the nozzle 51.

Before such a state occurs, the actuator 58 is operated (within the range of viscosity that can be ejected by the operation of the actuator 58), and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged in order to discharge the deteriorated ink (ink near the nozzle whose viscosity has increased). Preliminary ejection (purge, empty ejection, spitting) is performed toward the ink receiver).

Further, when air bubbles are mixed in the ink (inside the pressure chamber 52) in the print head 50, the ink cannot be ejected from the nozzle even if the actuator 58 operates. In such a case, a cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with air bubbles) is removed by suction with the suction pump 67, and the ink removed by suction is sent to the recovery tank 68. ..

In this suction operation, the deteriorated ink whose viscosity has increased (solidified) is sucked out even when the initial ink is loaded into the head or when the use is started after a long stop. Since the suction operation is performed on the entire ink in the pressure chamber 52, the ink consumption becomes large. Therefore, when the increase in viscosity of the ink is small, it is preferable to perform preliminary ejection.

The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink ejection surface (nozzle plate surface) of the print head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign matter adhere to the nozzle plate, the surface of the nozzle plate is wiped off by sliding the cleaning blade 66 onto the nozzle plate to clean the surface of the nozzle plate. When the blade mechanism cleans the dirt on the ink ejection surface, preliminary ejection is performed to prevent foreign matter from being mixed into the nozzle 51 by the blade.

FIG. 7 is a block diagram of a main part showing the system configuration of the inkjet recording apparatus 10. The inkjet recording device 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

The communication interface 70 is an interface unit that receives image data sent from the host computer 86. A serial interface such as USB, IEEE1394, Ethernet, or wireless network or a parallel interface such as Centronics can be applied to the communication interface 70. A buffer memory (not shown) for speeding up communication may be mounted on this portion. The image data transmitted from the host computer 86 is taken into the inkjet recording device 10 via the communication interface 70, and is temporarily stored in the image memory 74. The image memory 74 is a storage means for temporarily storing an image input via the communication interface 70, and data is read / written through the system controller 72. The image memory 74 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

The system controller 72 is a control unit that controls each part such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. The system controller 72 is composed of a central processing unit (CPU) and its peripheral circuits, etc., and performs communication control with the host computer 86, read / write control of the image memory 74, etc., as well as a transport system motor 88 and a heater 89. Generates a control signal to control.

The motor driver 76 is a driver (drive circuit) that drives the motor 88 according to an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 according to the instruction from the system controller 72.

The print control unit 80 has a signal processing function that performs various processing, correction, and the like for generating a signal for print control from the image data in the image memory 74 under the control of the system controller 72, and the generated print. This is a control unit that supplies control signals (print data) to the head driver 84. The print control unit 80 performs necessary signal processing, and controls the ejection amount and ejection timing of ink droplets of the print head 50 via the head driver 84 based on the image data. As a result, a desired dot size and dot arrangement are realized.

The print control unit 80 is provided with an image buffer memory 82, and data such as image data and parameters are temporarily stored in the image buffer memory 82 when the print control unit 80 processes image data. Although the image buffer memory 82 is shown in FIG. 7 in a mode attached to the print control unit 80, it can also be used as the image memory 74. It is also possible to integrate the print control unit 80 and the system controller 72 into a single processor.

The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, 12Y of each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the driving conditions of the head constant.

Further, the print control unit 80 has a test print control unit 90 that controls test printing. The test print control unit 90 generates an image (print data) at the time of test printing (determines the nozzle that ejects ink at the time of test printing, the amount of ink ejected from the nozzle, the ink ejection position, etc.) and at the time of test printing. A discharge signal (drive signal of the actuator 58 shown in FIG. 4) is generated.

The data of the test image read by the print detection unit 24 is temporarily stored in the image buffer memory 82 via the print control unit 80, and is sent to the image processing unit 92.

The image processing unit 92 performs predetermined image processing such as RGB CMY conversion on the image read by the print detection unit 24. The test image data subjected to the image processing is obtained by the determination unit 94 based on the test image data while referring to the set value (nozzle management data) of each nozzle recorded in the set value holding unit 96. It is determined whether the discharge of is normal or abnormal.

This determination result is sent to the system controller 72, and recovery operations such as preliminary ejection and suction are performed on the nozzle determined to be defective in ejection.

[Discharge defect detection] Next, the ejection defect nozzle detection of the inkjet recording device 10 will be described.

The inkjet recording apparatus 10 according to the present invention is configured to drip a test pattern on the belt 33 shown in FIG. 1, read the test pattern by the print detection unit 24, and detect a ejection failure nozzle from the reading result. .. Further, the test pattern is dropleted at different positions on the belt 33 for each ink color, and reading and detection are performed for each color.

FIG. 8 is a schematic view of a portion of the inkjet recording device 10 related to detection of defective ejection nozzles. The parts that are the same as or similar to those in FIG. 1 in FIG. 8 are designated by the same reference numerals, and the description thereof will be omitted.

The print detection unit 24 includes a line sensor 24A and a light source 24B. Light is emitted from the light source 24B to the test pattern dripping from each print head 50 onto the belt 33, and the reflected light is read by the line sensor 24A. In the present embodiment, the color separation line CCD sensor is used as the line sensor, but a line CCD sensor without a color filter may be used. Further, the shape of the dot may be captured by irradiating the laser beam and reading the reflected light.

A belt cleaning unit 36 for cleaning dirt on the belt 33 is provided on the downstream side of the print detection unit 24 in the sub-scanning direction, and the belt cleaning unit 36 cleans the belt 33 on which the test pattern is drip. The belt cleaning unit 36 is also used as a cleaning member for cleaning excess ink during full-screen printing (borderless printing).

In the present embodiment, the cleaning roll 36A is used for the belt cleaning unit 36, but a wiping (peeling) member such as a blade may be used, or the belt 33 is immersed in a solvent (sprayed) to remove the adhered ink. May be used.

The cleaning roll 36A may be in constant contact with the belt 33 or may be in contact only when necessary. When the cleaning roll 36A is in constant contact with the belt 33, the load fluctuation is small and the transport speed is stable, and when the cleaning roll 36A is brought into contact in synchronization with the discharge, the cleaning roll 36A is prevented from being worn.

FIG. 9 shows the details of the belt 33. FIG. 9 is a view of the belt 33 viewed from above (above the print head 50) of FIG.

The belt 33 has a test printing area 33A on which a test pattern is drip, and a recording paper adsorption area 33C in which a large number of air adsorption ports 33B for fixing (air adsorption) the recording paper 16 to the belt 33 are arranged in a matrix. I have. The test printing area 33A and the recording paper adsorption area 33C each have a predetermined length in the sub-scanning direction and are arranged alternately.

Further, the phases of the test printing area 33A and the recording paper adsorption area 33C are controlled so that the recording paper 16 rides on the recording paper adsorption area 33C.

That is, as shown in FIG. 12, the length Lc of the recording paper adsorption region 33C along the sub-scanning direction is set according to the size L2 of the frequently used recording paper 16 (in the embodiment shown in FIG. 12). , N times L2, where n is a positive integer), between the recording paper adsorption area 33C and the next recording paper adsorption area 33C, there is a test print area 33A having a length LA along the sub-scanning direction. It is provided.

In other words, the belt 33 is provided with a test printing area 33A at pitch L1 (length LA of test printing area 33A in the direction along the sub-scanning direction + length LC of recording paper adsorption area in the direction along the sub-scanning direction). This test print area pitch L1 satisfies the relationship of L1 = n × (L2 + L3) + L3.

Here, n is a positive integer, and L3 is the distance between the papers or the test print area and the papers.

If the test printing area 33A has an air suction port 33B, ink will enter the air suction port 33B. Therefore, the air suction port 33B is not arranged in the test printing area 33A.

In this example, the transport control (alignment control) of the belt 33 is performed so that the discharge control of the print head 50 and the position of the belt 33 are aligned. For the motor that drives the belt 33 (roller around which the belt 33 is wound), a motor that can control the rotation amount such as a stepping motor or a servomotor is used, and the position of the belt 33 is controlled by controlling the rotation amount of the motor. Can be controlled.

The amount of rotation of the motor may be calculated from the pulse signal (motor control signal) given to the motor driver 76 shown in FIG. 7, and the amount of movement of the belt may be calculated. A device may be provided, and the amount of rotation of the motor or the amount of movement of the belt 33 may be calculated from the detection pulse (detection signal) obtained from this detector.

By matching the recording paper adsorption area 33C to the size of the frequently used recording paper 16, test printing becomes possible between the images being printed, and productivity is not reduced. Further, if the recording paper adsorption region 33C is set to the least common multiple of the size of the most frequently used recording paper 16 and the size of the next most frequently used recording paper 16, the recording papers 16 of different sizes may be used efficiently.

As the material of the belt 33, a plastic member such as polyimide may be used, or a metal may be used. Moreover, various other members can be used. However, the flatness of the recording paper 16 attracted to the belt 33 must be ensured. Further, for the test printing area 33A, a member having elasticity (fixability) of ink droplets and easy cleaning by the belt cleaning unit 36 is used. Of course, it is preferable that the entire belt 33 including the recording paper adsorption region 33C is made of a material having the above-mentioned performance. FIG. 13 is a flowchart showing the flow of the test print control described above.

When the test print control is started (step S10), the print detection unit 24 detects the rear end (end of the belt 33 on the downstream side in the traveling direction) of the test print area 33A (step S12), and the test print area 33A is detected. Using the rear end as a reference (origin position), counting of pulse signals given to the motor driver (motor driver 76 shown in FIG. 7) of the motor driving the belt 33 is started (step S14), and the process proceeds to step S16.

In step S16, it is determined whether or not the pulse count (number of pulses) is N1, and if the pulse count is not N1 (smaller than N1) (NO determination), the pulse count is continued.

On the other hand, when the pulse count reaches N1, test printing is started (step S18).

Here, the number of pulses N1 is the movement of the belt 33 from the state where the rear end of the test print area 33A is located in the detection area of the print detection unit 24 until the tip of the test print area 33A moves to the print area of the print head 50. The number of pulses corresponding to the amount.

When the test print is executed, the print detection unit 24 reads the test image (step S20), and after the reading result is subjected to the predetermined image processing (step S22), the nozzle is defective in ejection. Whether or not it is determined (step S24).

In step S24, the nozzle determined to be defective in ejection is subjected to recovery processing (cleaning) such as preliminary ejection and suction (step S26), and the normal nozzle not determined to be defective in ejection proceeds to step S28 to print the next test. The trailing edge of region 33A is detected.

When the rear end of the next test print area 33A is detected in step S28, the next pulse count is started (step S30), and it is determined whether or not the pulse count is N2 (step S32).

The number of pulses N2 corresponds to the amount of movement of the belt 33 from the state where the rear end of the test print area 33A is located in the detection area of the print detection unit 24 to the movement of the tip of the recording paper 16 to the print area of the print head 50. There is an embodiment in which the number of pulses is set.

In step 32, if the pulse count is not N2 (if the pulse count is N2 or less) (NO determination), the pulse count is continued, and when the pulse count reaches N2, the feeding of the recording paper 16 is started. Then, the transport control of the belt 33 is performed (step S34), and the process proceeds to step S36.

During the pulse count, the recording paper 16 is temporarily stopped by a resist sensor (not shown) provided in front of the belt, and when the pulse count reaches N2, the recording paper 16 is controlled to start transporting. May be good.

In step S36, it is determined whether or not the pulse count is N3, and if the pulse count is not N3 (if the pulse count is N3 or less) (NO determination), the pulse count is continued and the pulse count is N3. When (YES determination), ink ejection (actual image printing) is started from the print head 50 (step S38).

When the actual image printing is started, it is determined whether or not the number of printed sheets is the set number of sheets (step S40), and if the number of printed sheets is less than or equal to the set number of sheets (NO determination), the process proceeds to step S42 and the number of printed sheets is increased. It is determined whether or not the number of nozzle checks is set.

If the number of prints is less than or equal to the nozzle check set number in step S42 (NO determination), the process proceeds to step S34 and printing is continued.

On the other hand, when the number of prints reaches the number of nozzle checks, printing is stopped, the process proceeds to step S12, and the rear end detection of the test print area 33A is performed.

Further, in step S40, when the number of printed sheets reaches the set number of sheets (YES determination), the print control is terminated (step S44).

The number of pulses N1, N2, and N3 should be determined in consideration of the reading error of the print detection unit 24 and the transport error of the belt 33.

If a highly ink-repellent member having a low ink-friendly property with ink is used, the ink droplets dripping on the belt 33 may not be fixed and may move. Further, if the ink-friendly property with the ink is high, the fixing property to the belt 33 on the belt 33 becomes high, but the landing diameter becomes large and the ink droplets may be aggregated with other ink droplets dropleted nearby. possible. Also, cleaning can be difficult.

In the present embodiment, the contact angle of the ink droplet is applied as a physical property value indicating the relative ink property between the ink droplet and the belt 33. As shown in FIG. 10, the contact angle θ of the ink droplet is represented by the angle formed by the tangent line of the ink droplet and the ink droplet and the droplet surface, and the larger the contact angle, the lower the ink-friendly property (ink droplet). It means that the fixability of the ink is low), and when the contact angle is small, it means that the ink-like property is high (the fixability of the ink droplet is high).

The state in which the ink droplets completely soak into the belt 33 is called a contact angle of 0 °, and the state in which the ink droplets and the drip surface are in contact at one point is called a contact angle of 180 °. Further, since the surface roughness such as the surface roughness of the belt 33 is also related to the fixability of the ink droplets, when the test printing area 33A is made of metal, the surface can be roughened to obtain a desired contact angle. ..

When the contact angle is about 90 °, it is easy to read the ink droplets, and a member preferable for the test printing area 33A is a member having an ink droplet contact angle of 40 ° or more. More preferably, it is a member having a contact angle of 100 ° or more.

Further, the test print area 33A is provided with a brightness difference from the ink color in order to make it easier to recognize the dropped test pattern. Of course, a color different from the ink color may be used. Furthermore, a transparent (semi-transparent) member is used for the test print area 33A, and the line sensor 24A is placed at a position facing the print head 50 across the belt 33 so that the test pattern can be read by transmitted light. Become. Reading using transmitted light can improve the reading accuracy as compared with reading using reflected light.

In the present embodiment, the material and physical property values of the test printing area 33A have been illustrated, but the entire belt 33 may be composed of the same member as the test printing area 33A.

In this embodiment, the mode in which the recording paper 16 is fixed (adsorbed) to the belt 33 by air is illustrated, but the recording paper 16 may be fixed to the belt 33 by electrostatic force or the like. When electrostatic force is used to fix the recording paper 16, the air suction port 33B becomes unnecessary, and it is not necessary to distinguish between the test printing area 33A and the recording paper suction area 33C. In other words, test printing can be performed on all areas of the belt 33, and the recording paper 16 can be adsorbed on all areas.

When the print head 50 becomes longer and longer in the transport direction of the recording paper 16, the misalignment between the nozzles on the upstream side and the nozzles on the downstream side becomes severe. In consideration of skew and the like, suction transport and transport by wrapping around a belt are performed.

If the print head 50 is configured to be retracted so that the test printing paper is flushed, the productivity is affected. However, in the present embodiment, since test printing can be performed without flushing the test printing paper, it is necessary to retract the print head 50. Absent.

If a mechanism is provided to retract the print head 50 in the opposite direction of the belt 33 (above the print head), use this to increase the distance between the print head 50 and the belt 33 to improve reading accuracy. Can be raised. When the print detection unit 24 is integrally formed, the distance between the line sensor 24A and the belt 33 (test print area 33A) is approximately 1 mm or less. In order to secure a predetermined reading accuracy, it is preferable to increase the distance between the line sensor 24A and the belt 33.

When the nozzles are highly integrated, the distance between dots becomes smaller accordingly. As the distance between dots becomes smaller, ink droplets tend to aggregate on the belt 33, so it is preferable to eject the ink droplets at intervals.

FIG. 11 shows an example of dropping a test pattern of the present embodiment. The conditions of this example are the resolution of the print head 50 of 2400 dpi, the contact angle of the ink droplets of 40 °, and the ejection amount of the ink droplets of 10 pl. Under these conditions, the impact diameter of the droplets is φ30 μm to φ40 μm.

The numbers in the dots (reference numerals 100 to 131) shown in FIG. 11 indicate the numbers of the nozzles on which the dots were dropped, and the nozzle rows in the print head 50 are projected so as to line up in the main scanning direction. The order of arrangement is shown. That is, in the projection nozzle row, the first nozzle, the second nozzle, ..., the 15th nozzle, the 16th nozzle, ... Are arranged in this order from the left in FIG.

The dots 116 dropped from the 16th nozzle are arranged at positions adjacent to the dots 101 dropped by the first nozzle in the main scanning direction. After that, dots 132 dripping from the 32nd nozzle, dots 148 dripping from the 48th nozzle (not shown), ... Are dripping in this row. The dot spacing (dot pitch) in each dot sequence along the main scan direction is 15/2400 inches.

On the other hand, in the sub-scanning direction, dots 102 dropped from the second nozzle are arranged at a distance of 15/2400 inches from the dots 101. The distance between the dots 101 and 102 in the main scanning direction is 1/2400 inches. After that, dots 103, ..., which are dropped from the third nozzle, and dots 115, which are dropped from the 15th nozzle, are dropped in the order of 15/2400 inches in the sub-scanning direction and 1/2400 inches in the main scanning direction. Each dot is placed at intervals.

When the test pattern is dropped as described above, the center-to-center distance between each dot and the nearest dot is 15/2400 inches, or about 160 μm. When proper ejection is performed, ink aggregation cannot occur even if variations in nozzles and the like are taken into consideration.

The test pattern data read by the print detection unit 24 is sent to the print control unit 80 shown in FIG. 7 and then temporarily stored in the image buffer memory 82 (storage unit). From this test pattern data, an image processing unit (not shown) performs predetermined image processing for each ink color. In the image processing, the contour of each dot is extracted, and the diameter of each dot and the distance between each dot (distance between centers) are obtained. The information of each dot obtained in this way is compared with the information of the dots that should be originally dropped, and nozzle non-ejection, ejection amount abnormality, ejection direction abnormality (ink droplet flight direction abnormality), etc. are compared. Discharge failure is detected.

When a ejection failure nozzle is detected, droplet correction (image correction) is performed for the next print job. In image correction, substitute dropping is performed from a nozzle close to a nozzle with poor ejection. The substitute droplet may be a mode in which dots larger than a predetermined size are dropleted from a nozzle close to the ejection defective nozzle, or an embodiment in which the ink droplet ejection direction of the proximity nozzle is shifted to cover the ejection defective nozzle. ..

Further, instead of the above-mentioned image correction, it may be controlled to perform a recovery operation on the ejection failure nozzle. The recovery operation includes a suction operation that forcibly sucks the nozzle with poor discharge, and a purge that performs preliminary discharge (flange) on the cap 64 shown in Fig. 6, and the recovery operation is selected according to the nozzle condition. It is good to do it. Of course, a plurality of recovery operations may be used together.

In this embodiment, an embodiment in which a test pattern is printed for each ink color is illustrated, but it is composed of a plurality of colors by ejecting a plurality of inks having different colors other than black to the same drip point and discriminating the color information. It is possible to detect the ejection failure nozzle in the print head 50 corresponding to each color from one dot.

Next, with reference to FIG. 14, an example of a method of reading dot information for each color from dots composed of a plurality of colors other than black will be described. Dots composed of multiple colors are read by a multi-color (RGB) line sensor and processed in the following ink order.

First, test printing is performed with C ink (step S100), and then test printing is performed with M ink at the same point (step S102). Further, a test print is performed at the same point with Y ink (step S104), and the test print is read by the print detection unit 24 (step S106).

The test print read by the print detection unit 24 is decomposed into CMY components (step S110), and each CMY color is detected by the following procedure.

[Processing procedure 1] First, an inappropriate nozzle is detected for the C ink nozzle (step S112). The output of the R sensor is used to evaluate the C ink nozzle.

[Processing procedure 2] The correction amount of the M component is calculated so as to exclude the influence of the C ink (step S114).

[Processing procedure 3] Next, the inappropriate nozzle is detected for the M ink nozzle in consideration of the correction amount of the M component (step S116). The output of the G sensor is used to evaluate the M ink nozzle. However, the inappropriate part of the C ink nozzle is removed, and the detection correction is performed for the other range.

[Processing procedure 4] The correction amount of the Y component is calculated so as to exclude the influence of the C ink and the M ink (step S118).

[Processing procedure 5] Next, the inappropriate nozzle is detected for the Y ink nozzle in consideration of the correction amount of the Y component (step S120). The output of the B sensor is used to evaluate the Y ink nozzle. However, the inappropriate parts of the C ink nozzle and the M ink nozzle are removed, and the detection correction is performed for the other ranges.

The reason why the processing is performed in the order of C M Y according to the above processing procedures 1 to 5 is due to the relationship between the spectral sensitivity of the sensor and the spectral absorption of the coloring material. That is, since the coloring material usually has sub-absorption on the short wavelength side, the C ink has absorption at R and also absorbs at the shorter wavelength side, that is, in the G and B regions. That is, C ink affects the detection of M ink and Y ink. Similarly, M ink affects the detection of Y ink. Therefore, in order to eliminate such an influence, it is preferable to perform the treatment in the order of widening the influence range (that is, in order from the long wavelength side). By doing so, the processing between colors can be performed efficiently.

After that, in step S122, it is determined whether or not each nozzle has a discharge failure, and the nozzle determined to have a discharge failure is subjected to recovery processing (cleaning) such as preliminary discharge and suction (YES judgment). (Step S124) After that, the process proceeds to step S112.

On the other hand, with a normal nozzle (NO determination), ejection failure detection is completed (step S126).

If the dot information for each color can be read from one dot composed of a plurality of colors in this way, the time required for reading and detection can be shortened, and the length of the test print area 33A along the sub-scanning direction can be shortened. can do.

In the inkjet recording apparatus 10 configured as described above, the belt 33 that conveys the recording paper 16 is provided with a test print area 33A, a test pattern is printed in the test print area 33A, and the test pattern is read by the print detection unit 24, and the reading result is read. Since it is configured to detect a nozzle with poor ejection from the nozzle, it is possible to detect an inappropriate nozzle and improve the image quality by recovering the nozzle or replacing it with another nozzle. Further, the recording paper 16 for test printing does not have to be wasted.

Since the print detection unit 24 can be fixed and the landing ink is configured to capture an image, it is not necessary to save the print head 50, and productivity is expected to be improved. Further, the ejection defect can be detected by using the gap between the papers, and it can be detected without reducing the productivity even at the time of printing.

In addition, it is not necessary to save the long head, which makes it possible to simplify the structure and contribute to cost reduction.

In the present embodiment, an inkjet recording device provided with a full-line type print head has been illustrated, but the scope of application of the present invention is not limited to this, and the present invention can also be applied to a shuttle scan type inkjet recording device.

Further, in the present embodiment, the piezo type inkjet recording device is exemplified, but the scope of application of the present invention is not limited to this, and the bubble type inkjet recording device that rapidly heats the ink and ejects the ink by the generated bubbles. Can also be applied to.

<figref num="1">Basic configuration diagram of the inkjet recording device according to the embodiment of the present invention</figref><figref num="2">Top view of the main part around the printing of the inkjet recording device shown in FIG.</figref><figref num="3(a)">Planar perspective view showing a structural example of the print head</figref><figref num="3(b)">Enlarged view of the main part of Fig. 3 (a)</figref><figref num="3(c)">Planar perspective view showing other structural examples of the print head</figref><figref num="4">Sectional view along line 4-4 in Figure 3 (a)</figref><figref num="5">An enlarged view showing the nozzle arrangement of the print head shown in FIG. 3 (a).</figref><figref num="6">Schematic diagram showing the configuration of the ink supply unit in the inkjet recording apparatus according to the present embodiment.</figref><figref num="7">A block diagram of a main part showing a system configuration of an inkjet recording device according to the present embodiment.</figref><figref num="8">Schematic diagram of the part related to ejection failure nozzle detection</figref><figref num="9">Diagram showing the structure of the belt</figref><figref num="10">The figure explaining the contact angle</figref><figref num="11">Diagram illustrating an example of a test pattern</figref><figref num="12">Diagram showing the positional relationship between the belt and the chart paper</figref><figref num="13">Flowchart showing the control flow of discharge failure detection</figref><figref num="14">Flow chart showing the control flow of the application example of discharge failure control shown in FIG.</figref>

Code description

10 ... Inkjet recording device, 12 ... Printing unit, 22 ... Suction belt transport unit, 24 ... Printing detection unit, 33 belt, 33A ... Test printing area, 36 ... Belt cleaning unit , 50, 50'... print head, 72 ... system controller, 80 ... print control unit