Image forming apparatus and main scanning scale factor correcting method therefor

【0001】

[Technical field to which the invention belongs]

According to the present invention, the input image signal is pixel-divided-modulated, the laser light source is modulated and driven based on the pixel-divided-modulated image signal, and the laser light emitted from the laser light source scans the latent image carrier. The present invention relates to an image forming apparatus for forming a latent image on a latent image carrier and a method for correcting the main scanning magnification thereof.

【0002】

[Conventional technology]

Generally, in an image forming apparatus such as a laser beam printer or a digital copier, a semiconductor laser is driven by a laser beam drive circuit, a laser beam emitted from the semiconductor laser is modulated by an image signal, and the modulated laser beam is generated. Is configured to form a latent image by performing a raster scan on a photosensitive drum with a rotating multi-sided mirror (polygon mirror) .

【0003】

Here, in an apparatus having a plurality of semiconductor lasers, the magnification of the latent image image differs depending on each position on the photosensitive drum irradiated by the laser beam from each semiconductor laser. Further, since the surface accuracy of the polygon mirror is different, the writing position of the latent image is different for each surface. Further, in the image forming apparatus capable of double-sided printing, the image size after printing is different even if the ratio of the latent image images on both sides is the same due to the shrinkage of the paper size after fixing.

【0004】

On the other hand, a method has been proposed in which the length between image data is controlled by adding an image clock for transferring image data at an arbitrary point to correct the size of the printed image (see Patent Document 1). ..

【0005】

[Patent Document 1]

Japanese Unexamined Patent Publication No. 2000-238342 [0006]

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional example, since the image clock is corrected, the image data to be interpolated is fixed, and a space is generated in a place where the image clock is slightly lengthened, which may impair the print quality.

【0007】

An object of the present invention is to provide an image forming apparatus capable of appropriately correcting a main scanning magnification without deteriorating print quality, and a method for correcting the main scanning magnification thereof. Another object of the present invention is to provide an image forming apparatus capable of appropriately correcting the main scanning magnification by delaying the writing start position for each preset line for a preset time, and a method for correcting the main scanning magnification.

【0008】

[Means for solving problems]

The present invention comprises a pixel division modulation means for pixel-dividing and modulating an input image signal on a pixel-by-pixel basis and outputting the pixel-division-modulated image signal on a pixel-by-pixel basis in synchronization with a fixed-frequency image clock. A driving means that modulates and drives a laser light source based on an image signal output from the modulation means, and a laser beam emitted from the laser light source so as to form a latent image on the latent image carrier. An image forming apparatus including a scanning means for scanning the data, wherein the pixel division modulation means is used for each one or more correction points on one line scanned by the laser beam on the latent image carrier. The last bit of the pixel-divided-modulated pixel data of the pixel located before the correction point is added as the first bit of the pixel-divided-modulated pixel data of the pixel located at the correction point, and each located after the correction point. It has a correction means for generating pixel data of a new pixel added on the one line by sequentially shifting the pixel data of the pixel divided and modulated by the pixel to the next pixel in bit units. It is characterized in that the pixel data of the generated new pixels is output in synchronization with the fixed frequency image clock.

【0009】

Further, the present invention comprises a pixel division modulation means for pixel-dividing and modulating an input image signal on a pixel-by-pixel basis and outputting the pixel-division-modulated image signal on a pixel-by-pixel basis in synchronization with a fixed-frequency image clock. The driving means that modulates and drives the laser light source based on the image signal output from the pixel division modulation means, and the latent image support by the laser light emitted from the laser light source so as to form a latent image on the latent image carrier. An image forming apparatus including scanning means for scanning on a body, wherein the pixel division modulation means is one on one line scanned by the laser beam on the latent image carrier. For each of the two or more correction points, the first bit of the pixel data divided and modulated by the pixel located at the correction point is added as the first bit of the pixel data divided and modulated by the pixel located at the correction point. Pixel data of new pixels added on the one line is generated by sequentially shifting the pixel data of the pixels sequentially divided and modulated for each pixel located after the correction point to the next pixel in bit units. It has a correction means, and is characterized in that the pixel data of the generated new pixel is output in synchronization with the fixed frequency image clock.

【0010】

Further, the one or more correction points are predetermined.

【0011】

Further, the number of the one or more correction points is determined to be an integral multiple of the resolution of the pixel division modulation of each pixel in the pixel division modulation means.

【0012】

Further, the image forming apparatus has an image writing reference signal output means for outputting an image writing reference signal, and the timing at which the pixel data output is started in synchronization with the fixed frequency image clock is set as the image writing reference. It is characterized in that the signal is delayed for a predetermined time for each preset line.

【0013】

Further, the present invention comprises a pixel division modulation means for pixel-dividing and modulating an input image signal on a pixel-by-pixel basis and outputting the pixel-division-modulated image signal on a pixel-by-pixel basis in synchronization with a fixed-frequency image clock. A driving means that modulates and drives a laser light source based on an image signal output from the pixel division modulation means, and a latent image carrier with laser light emitted from the laser light source so as to form a latent image on the latent image carrier. A method for correcting the main scanning length of an image forming apparatus including a scanning means for scanning the top, wherein each correction point on one line scanned by the laser beam on the latent image carrier is said to be the same. The last bit of the pixel-divided-modulated pixel data of the pixel located before the correction point is added as the first bit of the pixel-divided-modulated pixel data of the pixel located at the correction point, and each located after the correction point. A step of generating pixel data of a new pixel added on the one line by shifting the pixel data sequentially divided and modulated by the pixel to the next pixel in bit units, and the generated pixel data. It is characterized by having a step of outputting pixel data of new pixels in synchronization with the fixed frequency image clock.

【0014】

Further, the present invention comprises a pixel division modulation means for pixel-dividing and modulating an input image signal on a pixel-by-pixel basis and outputting the pixel-division-modulated image signal on a pixel-by-pixel basis in synchronization with a fixed-frequency image clock. The driving means that modulates and drives the laser light source based on the image signal output from the pixel division modulation means, and the latent image support by the laser light emitted from the laser light source so as to form a latent image on the latent image carrier. It is a main scanning magnification correction method of an image forming apparatus including a scanning means for scanning on a body, and for each one or more correction points on one line scanned by the laser beam on the latent image carrier. The first bit of the pixel-divided-modulated pixel data of the pixel located at the correction point is added as the first bit of the pixel-divided-modulated pixel data of the pixel located at the correction point, and each pixel located after the correction point is added. A step of generating pixel data of a new pixel added on the one line by sequentially shifting the pixel data of the pixel division-modulated pixel of the pixel to the next pixel in bit units, and the generated new pixel data. It is characterized by having a step of outputting pixel data of various pixels in synchronization with the fixed frequency image clock.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

【0016】

First, the principle of the main scanning magnification correction process in the present invention will be described with reference to FIG. FIG. 1 is a conceptual diagram showing a configuration example of an image signal processed by the main scanning magnification correction process according to the present invention.

【0017】

In the main scanning magnification correction process according to the present invention, for each one or more correction points on one line scanned by the laser beam on the photosensitive drum, the pixels located in front of the correction points are divided and modulated. The last bit of the data is added as the first bit of the pixel data divided and modulated by the pixel located at the correction point, and the pixel data obtained by sequentially dividing and modulating each pixel after the correction point is added. By shifting to the next pixel in bit units, pixel data of a new pixel added on one line is generated. Then, the pixel data of the generated new pixels is output in synchronization with the image clock of a fixed frequency. Here, the main scanning magnification means the width when scanning in the main scanning direction by the laser beam on the photosensitive drum.

【0018】

As shown in FIG. 1, for example, the pixel data constituting the image signal is composed of a χ-bit pixel-divided-modulated data string, and all the image data in FIG. 1 are on the same line. Exists. Then, here, as the correction points in the main scanning magnification correction process, the l-th surface pixel, the m-th pixel, and the n-th pixel on the same line are assumed.

【0019】

First, for the l-th pixel, as shown in FIG. 1 (a), the final bit data of the (l-1) -th pixel, that is, the χ-th bit data is added as the first bit of the l-th pixel. .. In the l-th pixel, the final bit data of the (l-1) th pixel is added to the first bit, so the final bit data originally present in the l-th pixel is the next pixel (l + 1). It is moved to the first bit of the second pixel. Then, in each of the subsequent pixels, bit data is sequentially transferred to the next pixel one bit at a time.

【0020】

Due to this transfer of bit data to the next pixel, for example, in the (m-1) th pixel, the first bit data is the previous pixel (m-2) th final bit data, as shown in FIG. 1 (b). It is assumed that the final bit data becomes the original (χ-1) th bit data. In the mth pixel, the first bit data is the last bit data (χth bit) of the (m-1) th pixel, and the last bit data is the original (χ-2) th bit data. Suppose it becomes.

【0021】

Here, assuming that the pixel on the m-th plane is the next correction point, the final bit data of the (m-1) th pixel is the (χ-1) th bit data, so this (χ-1) th pixel. Bit data is added as the first bit of the mth pixel. As a result, data is transferred from the m-th pixel to the (m + 1) pixel by 2 bits at a time. That is, the (χ-1) th bit data and the χth bit data originally present in the mth pixel are transferred as the first bit data and the next bit data of the (m + 1) th pixel. Along with this, in each pixel after the (m + 1) th, the data is sequentially transferred to the next pixel by 2 bits in the same manner as described above.

【0022】

Then, due to the transfer of bit data to the next pixel, for example, as shown in FIG. 1 (c), the (χ-2) bit data from the beginning of the (n-1) th pixel is the previous pixel (n-). 2) It is said that the data is shifted from the last (χ-2) bits to the (χ-2) bits, and the last bit data of the (n-1) th pixel is originally the data corresponding to the first bit of the (n-1) th pixel. To do.

【0023】

Here, assuming that the nth pixel is the pixel corresponding to the correction point, in this nth pixel, the last bit of the (n-1) th pixel is added to the first bit, so that it is the nth pixel. The data of the pixel of is the same as the data of the (n-1) th pixel. Along with this, the (n + 1) th pixel is similarly composed of the same data as the nth pixel.

【0024】

Thus, in this example, the number of pixels n on one line is increased to (n + 1). That is, the main scanning magnification correction process makes it possible to increase the number of pixels in one line and correct the main scanning magnification.

【0025】

Next, a specific configuration of the image forming apparatus capable of executing the scanning magnification correction process will be described with reference to FIGS. 2 to 4. FIG. 2 is a vertical cross-sectional view schematically showing the configuration of the image forming apparatus according to the embodiment of the present invention, FIG. 3 is a block diagram schematically showing the configuration of the exposure control unit 10 of FIG. 2, and FIG. 4 is FIG. It is a block diagram which shows the structure of the image processing circuit of.

【0026】

As shown in FIG. 2, the image forming apparatus includes a document feeding device 1 capable of loading a plurality of documents and a scanner unit 4 configured to be movable in the sub-scanning direction. The document feeding device 1 conveys a plurality of loaded originals one by one from the beginning onto the platen glass 2. The scanner unit 4 includes a lamp 3 for illuminating the document conveyed on the platen glass 2, and a reflection mirror 5 for guiding the reflected light from the document on the platen glass 2 to the reflection mirror 6. .. The reflection mirror 6 guides the reflected light from the reflection mirror 5 to the lens 8 in cooperation with the reflection mirror 7, and the lens 8 forms an image of the reflected light on the image sensor unit 9. The image sensor unit 9 converts the formed light image into an electric signal, and the electric signal is input to the exposure control unit 10 as an image signal after being subjected to a predetermined process.

【0027】

The exposure control unit 10 emits a laser beam based on the input image signal, and exposes and scans the photosensitive drum 11 with the laser beam. By the exposure scanning of the laser beam, a latent image corresponding to the laser beam is formed on the photosensitive drum 11. The latent image formed on the photosensitive drum 11 is visualized as a toner image by the toner supplied from the developer 13.

【0028】

Further, at the timing synchronized with the start of irradiation of the laser beam, a sheet is fed from the cassette 14 or the cassette 15, and the sheet is conveyed to the transfer unit 325 via the transfer path 331. The toner image on the photosensitive drum 11 is transferred by the transfer unit 16 onto the conveyed sheet. The sheet on which the toner image is transferred is conveyed to the fixing portion 17.

【0029】

In the fixing portion 17, the toner image on the sheet is thermally pressed and fixed on the sheet. The sheet that has passed through the fixing portion 17 is discharged to the outside via the paper ejection roller pair 18.

【0030】

The surface of the photosensitive drum 11 after the transfer of the toner image is cleaned by the cleaner 25 and then statically eliminated by the auxiliary charger 26. Then, after the residual charge on the surface of the photosensitive drum 11 is erased by the pre-exposure lamp 27 to obtain a good charge in the primary charger 28, the surface of the photosensitive drum 11 is charged by the primary charger 28. ..

【0031】

By repeating the above series of steps, it is possible to form a plurality of images.

【0032】

Further, in this image forming apparatus, a double-sided pass 29 is provided to enable double-sided printing. At the time of double-sided printing, the sheet after single-sided printing is inverted and guided to the double-sided pass 29, and this sheet is conveyed again to the photosensitive drum 11 via the double-sided pass 29. Then, a corresponding image is formed on the other surface of the sheet in the same manner as described above.

【0033】

As shown in FIG. 3, the exposure control unit 10 pixel-divide-modulates an image signal input from the outside and outputs the pixel-divided-modulated image signal in synchronization with the image clock, and an image processing circuit 36 and an image. It has a laser driving device 31 that drives a semiconductor laser 43 based on a pixel-divided modulated image signal output from the processing circuit 36. A photodiode sensor (PD sensor; not shown) that detects a part of the laser beam is provided inside the semiconductor laser 43, and the laser drive device 31 uses the detection signal of the PD sensor to APC of the semiconductor laser 43. (Auto Power Control) Control. The laser light emitted from the semiconductor laser 43 becomes substantially parallel light via an optical system having a collimator lens, an aperture, and the like, and is incident on the polygon mirror (rotating multifaceted mirror) 33 with a predetermined beam diameter. The polygon mirror 33 rotates at a constant angular velocity in a predetermined direction, and along with this rotation, the laser beam incident on the polygon mirror 33 is reflected as a deflection beam that continuously changes the angle. The laser beam reflected as a deflecting beam is focused by the f-θ lens 34. At the same time, since the f-θ lens 34 corrects the distortion aberration so as to guarantee the temporal linearity of the scan, the laser light passing through the f-θ lens 34 is equal to the photosensitive drum 11 in a predetermined direction. Combined scanning is performed at high speed. A beam detect sensor (not shown) that detects the laser light reflected from the polygon mirror 33 is provided near one end of the photosensitive drum 11, and the detection signal of this sensor is the rotation of the polygon mirror 33. It is used as a synchronization signal for synchronizing data writing.

【0034】

In such a laser drive device 31, in order to keep the amount of laser light during one scan constant, the output of the laser beam is detected in the light detection section during one scan to reduce the drive current of the semiconductor laser 43 to 1. It employs a drive system that holds it during scanning.

【0035】

As shown in FIG. 4, the image processing circuit 36 has a control signal generation circuit 101, and the control signal generation circuit 101 has a FIFO control signal 102 for a FIFO (First In-First Out Memory) clock generation circuit 105. A PS conversion control signal 103 for the parallel-serial (hereinafter abbreviated as PS) clock generation circuit 107 and an SP conversion control signal 104 for the serial-parallel (hereinafter abbreviated as SP) clock generation circuit 109 are generated. The FIFO clock generation circuit 105 generates a read clock 106 for the FIFO 112 based on the reference clock 111 and the FIFO control signal 102. The PS clock generation circuit 107 generates a conversion clock 108 for the PS conversion circuit 118 based on the reference clock 111 and the PS conversion control signal 103. The SP clock generation circuit 109 generates the SP conversion clock 110 for the SP conversion circuit 120 based on the reference clock 111 and the SP conversion control signal 110. Further, the SP conversion clock 110 is output as an image clock.

【0036】

The FIFO write address reset signal 113 and the write clock 114 are supplied to the FIFO (First In-First Out Memory) 112 from the main body control unit (not shown), and the image signal is supplied from the external image generation unit (not shown). Is input in pixel units. That is, 16-bit write pixel data 115 is input to the FIFO 12. From the FIFO 112, 16-bit read pixel data 117 is output by the read clock 106 from the FIFO clock generation circuit 105 and the read address reset signal 116 input from the main body control unit (not shown).

【0037】

The read pixel data 117 output from the FIFO 112 is input to the PS conversion circuit 118. The PS conversion circuit 118 converts the input 16-bit read pixel data 117 into a serial pixel signal 119 by the PS conversion clock 108 and outputs the data. The output serial pixel signal 119 is input to the SP conversion circuit 120. The SP conversion circuit 120 converts the input serial pixel signal 119 into a 16-bit parallel pixel signal 121 by the SP conversion clock 110 and outputs the signal. The BD signal 151 output from a BD sensor (not shown) is counted by the line counter 150, and for example, the line select signal 152 that circulates in units of 4 lines is output. The delay time generation circuit 153 generates four types of delay times 154 that correspond to the line select signal 152 and are synchronized with the SP conversion control signal 110. The timing adjustment circuit 155 delays the parallel signal 121 for each line according to the delay time 154 and outputs it as image data 156.

【0038】

Further, the image processing circuit 36 can also be configured as shown in FIG.

【0039】

In the figure, the description of what is indicated by the same number as in FIG. 4 is omitted. Reference numeral 122 denotes a beam detector, which receives the beam light L emitted from the semiconductor laser (not shown) and generates a beam detection signal 123 which is an electric signal by the photoelectric effect. The beam period measurement circuit 124 measures the period of the beam detection signal 123, and inputs the result as a beam period signal 125 to the difference value measurement circuit 128. The reference cycle generation circuit 126 generates a reference cycle signal 127 set by the resolution, scanning speed, and optical characteristics, and the cycle comparison circuit 28 compares the cycles of the beam cycle signal 125 and the reference cycle signal 127, and the result is the result. Based on this, the parallel-serial (hereinafter abbreviated as PS) conversion control signal generation circuit 130 sets the correction amount, and the PS conversion position signal 131 input from the control signal generation circuit 101 determines the position of the pixel to be corrected. The control signal 103 is used and output to the PS clock generation circuit 107.

【0040】

Further, the image processing circuit 36 can be configured as shown in FIG.

【0041】

In the figure, the description of what is indicated by the same number as in FIG. 4 is omitted.

【0042】

Reference numeral 142 denotes a Hall element, which is used as a Hall element output signal 143 by generating a potential difference due to a change in the magnetic field generated by the rotation of the scanner motor 141. The Hall element output signal 143 is converted into a rotation detection signal 145 having a predetermined voltage level by the rotation detection signal generation circuit 144.

【0043】

The rotation unevenness due to the low frequency fluctuation of the scanner motor 141 can be detected by the rotation cycle measurement circuit 146 by measuring the cycle of the rotation detection signal 145. The rotation cycle measurement circuit 146 output signal is input to the difference value measurement circuit 128 as the rotation cycle signal 149.

【0044】

The reference rotation cycle generation circuit 147 generates a reference rotation cycle signal 148 set by the resolution, scanning speed, number of polygon mirror surfaces, etc., and the cycle comparison circuit 128 determines the period between the rotation cycle signal 149 and the reference rotation cycle signal 148. Based on the result of comparison, the correction amount is set by the parallel-serial (hereinafter abbreviated as PS) conversion control signal generation circuit 130, and the correction amount is set by the PS conversion position signal 131 input from the control signal generation circuit 101. The PS conversion control signal 103 that determines the position is used and output to the PS clock generation circuit 107.

【0045】

Next, the operation of the image processing circuit 36 will be described with reference to FIG. FIG. 5 is a timing chart of the main blocks in the image processing circuit of FIG.

【0046】

The reference clock (REFCLK) 111 (shown in FIG. 5 (a)) is the read clock (FIFOCLK) 106 (shown in FIG. 5 (b)), the PS conversion clock (PSCLK) 108 (shown in FIG. 5 (e)) and It is a reference signal of the SP conversion clock (SPCLK) 110 (shown in FIG. 5 (g)), and is a frequency proportional to the resolution of the pixel division modulation with respect to the frequency of the SP conversion clock 110 which is the image clock. In the present embodiment, when the resolution of the pixel division modulation is 16 bits, the frequency of the reference clock (REFCLK) 111 is set to 16 times the SP conversion clock 110.

【0047】

The read clock (FIFOCLK) 106 (shown in Fig. 5 (b)) is a clock for instructing the read timing from the FIFO 112 in 1-pixel units, and when reading the next pixel to which data has been added, the first bit The timing is delayed by one data so that the last bit of the previous pixel arrives at. After that, the same period is set until the bit is added again in the pixel.

【0048】

The PS conversion control signal 103 (shown in FIG. 5D) is a control signal for thinning out the clock so that the output data of the FIFO 112 is not updated at the first bit of the pixel to which the bit is added. Due to this PS conversion control signal 103, in the PS output data (serial pixel signal) 119 (shown in FIG. 5 (f)), the first bit of the FIFO address (n; shown in FIG. 5 (c)) is not updated and the front pixel is not updated. The last bit of is added.

【0049】

The SP conversion clock (SPCLK) 110 (shown in FIG. 5 (g)) has a frequency of 1/16 of the read clock (FIFOCLK) 106 and is output as an image clock that defines one pixel section.

【0050】

The PS output data 119 (corresponding to the FIFO address (n)) in which the last bit of the previous pixel is added to the first bit by this SP conversion clock (SPCLK) 110 is a 16-bit parallel pixel signal (SPDATA) 121 (Fig.). It is converted to (shown in 5 (h)) and output.

【0051】

The delay time 154 (shown in FIG. 5 (j)) on an arbitrary line is synchronized with the BD signal 151 (shown in FIG. 5 (i)), and the delay time is set by the conversion clock 108. The parallel pixel signal (SPDATA) 121 is output as image data 156 (shown in FIG. 5 (k)) that starts in synchronization with the delay time 154.

【0052】

A specific example of the main scanning magnification correction process in the present embodiment will be described with reference to FIG. FIG. 6 is a diagram showing a configuration example of pixel data processed by the main scanning magnification correction process of the image processing circuit 36 of FIG.

【0053】

In the present embodiment, one pixel is 16-bit data, the total number of pixels in one line is 7000, and the total number of pixels after the main scanning magnification correction processing is 7001 with respect to the total number of pixels of 7000. Described in.

【0054】

When 1 pixel / 16 bit data is added to all 7000 pixels on one line on average, the address (that is, correction point) of the pixel to which 1 pixel / 16 bit data is added is the 412th and 824th. , 1236th, 1648th, 2060th, 2472th, 2834th, 3296th, 3708th, 4210th, 4532th, 4944th, 5356th, 5768th, 6180th, 6592th. (412 7000 pixels ÷ 17) [0055]

Here, for example, if the 412th pixel data is [A] hex and the 411st pixel data is [5] hex, in the 412th pixel, the final bit data "0" of the 411th pixel is set to the first bit. Is added. As a result, the 412th pixel data becomes as follows.<img file="JP2004351908A_D0001.tif" /> 【0056】

Along with this, the final bit data "0" of the 412th pixel is transferred to the first bit of the 413th pixel, and the 413th pixel data [4] hex is configured as follows.<img file="JP2004351908A_D0002.tif" /> 【0057】

Similarly, for each pixel data after the 414th pixel, the last bit data of each pixel is transferred to the first bit of the next pixel. In this way, in each pixel data from the 412th to the 823rd, the data is transferred bit by bit.

【0058】

Next, consider the case of the 824th pixel. Here, the 823rd pixel data is [7] hex, and the 824th pixel data is [F] hex. In the 823rd pixel data, the previous bit data has already been transferred to the last bit, and in the 824th pixel data, the 823rd final bit data "0" has already been transferred to the first bit. ing. Here, since the 824th pixel is the pixel of the correction point, the final bit "0" of the 823rd pixel data is added to the 824th first bit. As a result, the 824th pixel data becomes as follows.<img file="JP2004351908A_D0003.tif" /> 【0059】

Along with this, the final bit data "1" of the 824th pixel data is transferred to the first bit of the 825th pixel data. Here, before the transfer of the final bit data, the final bit data of the 824th pixel data before correction has already been transferred to the first bit of the 825th pixel data. Therefore, the 825th pixel data [3] hex is as follows.<img file="JP2004351908A_D0004.tif" /> 【0060】

Therefore, in each pixel data after the 825th, the data is transferred by 2 bits. Then, in the pixel corresponding to the next correction point, the final bit data of the previous pixel data is similarly added.

【0061】

Here, the last correction point is the 6592th pixel data, the 6591th pixel data before correction is [1] hex, and the 6592th pixel data before correction is [6] hex. Then, due to the transfer of the above bit data, the data from 2 to 16 bits of the 6590th pixel data before correction is transferred to the 6591th image data, and the final bit is originally the first bit. The existing data has been migrated. Further, the data from 2 to 16 bits of the 6591th pixel data before correction is transferred to the 6592th image data, and the data originally in the first bit is transferred to the final bit. .. Since the 6592th pixel is the correction point, the 6591th final bit data "1" is added to the first bit of the 6592th pixel data. As a result, the 6592th pixel data becomes as follows.<img file="JP2004351908A_D0005.tif" /> 【0062】

As described above, the 6592th pixel data after the correction is the 6591th pixel data before the correction. Then, in each pixel after this pixel, data is transferred to the next pixel by 16 bits, and finally, new pixel data for the 7001st pixel is formed. That is, the number of pixels in one line is increased, and by increasing the number of pixels, the main scanning magnification can be corrected without impairing the print quality.

【0063】

For example, in an image forming apparatus capable of double-sided printing as in the present embodiment, the main scanning magnification for each side of the sheet during double-sided printing can be appropriately corrected, and each after printing due to shrinkage of the paper during fixing. It is possible to solve the problem that the image size is different on the surface.

【0064】

A specific example of delaying the writing start position by a predetermined time for each preset line during the main scanning magnification correction processing in the present embodiment will be described with reference to FIG. 7. Here, the case where the delay time is set in each of the four line cycles will be described. FIG. 7 is the timing chart. The beam detect (hereinafter abbreviated as BD) signal is a signal detected by the BD sensor and determines the image writing position. Set the delay time until the output of the image data for the BD signal as follows. The delay times τ1 to τ4 may be all different values or only partially different values.

【0065】

(4n + 1) Line: Delay time τ1 (4n + 2) Line: Delay time τ2 (4n + 3) Line: Delay time τ3 (4n + 4) Line: Delay time τ4 (n 0) [ 0066]

As a result, the 1st line, the 5th line, the 9th line, ..., The (4n + 1) line, ... Start the data output from the time delayed by τ1 from the BD signal. Similarly, the 2nd line, the 6th line, the 10th line, ..., The (4n + 2) line, ... Start the data output from the time delayed by τ2 from the BD signal. The same applies to the following lines, so they will be omitted.

【0067】

Yet another method will be described with reference to FIG. The BD signal is a signal detected by the BD sensor and determines the image writing position. Set the delay time until the output of the image data for the BD signal as follows. The delay times τ1 to τ4 are different from each other, and are set within an arbitrary time of the same delay range Δτ.

【0068】

(4n + 1) Line: Delay variable width a τ1 τ1a ~ τ1b (4n + 2) Line: Delay time τ2 τ2a ~ τ2b (4n + 3) Line: Delay time τ3 τ3a ~ τ3b (4n + 4) ) Line: Delay time τ4 τ4a ~ τ4b (n 0) τ = τ1b-τ1a = τ2b-τ2a = τ3b-τ3a = τ4b-τ4a [0069]

As a result, the 1st line, 5th line, 9th line, ..., (4n + 1) line, ... Starts data output from the time delayed by any time in τ1 from the BD signal. .. Similarly, the 2nd line, 6th line, 10th line, ..., (4n + 2) line, ... Starts data output from the time delayed by any time in τ2 from the BD signal. To do. The same applies to the following lines, so they will be omitted.

【0070】

In the present embodiment, the image forming apparatus capable of double-sided printing has been described, but even in an image forming apparatus capable of simultaneously scanning on different lines by using a plurality of laser beams, for example, two laser beams, the main scanning magnification is also described. By the correction process, the main scanning magnification of each laser beam can be corrected to be the same. In this case, the main scanning magnification of one of the laser beams may be corrected so that the main scanning magnification of one of the laser beams matches the main scanning magnification of the other laser beam. Alternatively, the main scanning magnification of each laser beam may be corrected. Further, the above-mentioned main scanning magnification correction processing can be applied to the correction of the main scanning magnification between each color in an image forming apparatus having an exposure means (photosensitive drum) for each of the yellow, magenta, cyan, and black colors. Needless to say, there is.

【0071】

Further, in the present embodiment, for each one or more correction points on one line scanned by the laser beam on the photosensitive drum, the final bit of the pixel data divided and modulated by the pixels located in front of the correction points. Is added as the first bit of the pixel data divided and modulated by the pixels located at the correction point, and the pixel data obtained by sequentially dividing and modulating the pixels for each pixel located after the correction point is next in bit units. By shifting to pixels, pixel data of new pixels added on one line is generated, but instead of this, pixel division modulation of the pixels located at the correction points is performed for each correction point. The first bit of the pixel data is added as the first bit of the pixel data divided and modulated by the pixel located at the correction point, and the pixels are sequentially divided and modulated for each pixel located after the correction point. By shifting the pixel data to the next pixel in bit units, the pixel data of a new pixel added on one line may be generated.

【0072】

[Effect of the invention]

As described above, according to the present invention, for each one or more correction points on one line scanned by the laser beam on the latent image carrier, pixel division modulation of the pixels located in front of the correction points The final bit of the pixel data is added as the first bit of the pixel data divided and modulated by the pixel located at the correction point, and the pixels are sequentially divided and modulated for each pixel located after the correction point. By shifting the pixel data to the next pixel in bit units, the pixel data of a new pixel added on one line is generated, and the pixel data of the generated new pixel is synchronized with the image clock of a fixed frequency. Since the data is output, the main scanning magnification can be appropriately corrected without degrading the print quality.

【0073】

Further, according to the present invention, for each one or more correction points on one line scanned by the laser beam on the latent image carrier, the head of the pixel data divided and modulated by the pixels located at the correction points. A bit is added as the first bit of the pixel data of the pixel located at the correction point and the pixel data is divided and modulated, and the pixel data of the pixel sequentially divided and modulated for each pixel located after the correction point is added bit by bit. By shifting to the next pixel, the pixel data of a new pixel added on one line is generated, and the pixel data of the generated new pixel is output in synchronization with the fixed frequency image clock, so that the print quality The main scanning magnification can be corrected appropriately without dropping.

【0074】

Further, by delaying the line start position for each preset line by a preset time with respect to the image writing position signal and adjusting the magnification so as to be the same in each line, the print quality is not deteriorated. It has the effect of being able to correct the print ratio.

[Simple explanation of drawings]

FIG. 1 is a conceptual diagram showing a configuration example of an image signal processed by the main scanning magnification correction process according to the present invention.

FIG. 2 is a vertical cross-sectional view schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention.

3 is a block diagram schematically showing the configuration of the exposure control unit 10 of FIG. 2. FIG.

4 is a block diagram showing a configuration of the image processing circuit of FIG. 3. FIG.

5 is a timing chart of a main block in the image processing circuit of FIG. 4. FIG.

6 is a diagram showing a configuration example of pixel data processed by the correction processing of the image processing circuit of FIG. 4. FIG.

FIG. 7 is a timing chart for delaying the writing start position by a predetermined time.

FIG. 8 is another timing chart for delaying the writing start position by a predetermined time.

9 is a block diagram showing another configuration of the image processing circuit of FIG. 3. FIG.

10 is a block diagram showing another configuration of the image processing circuit of FIG. 3. FIG.

[Explanation of symbols]

Ten Exposure control unit 11 Photosensitive drum 31 Laser drive device 33 Polygon mirror 34 f-θ lens 36 Image processing circuit 43 Semiconductor laser 101 Control signal generation circuit 105 FIFO clock generation circuit 107 PS clock generation circuit 109 SP clock generation circuit 112 FIFO 118 PS conversion circuit 120 SP conversion circuit