JP2009012252A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device which can correct an error generated at arranging an optical system and a photosensitive object and the error of the rotating speed of polygon mirror and accuracy of the polygon mirror surface. <P>SOLUTION: In the image formation device, a main scan direction for scanning by a laser beam is divided into two or more areas, and number of pixels N to be printed in each divided area is computed. The number of pixels M printed in each divided area by the laser beam is detected on a recording medium. Based on the computed number of pixels N and the detected number of pixels M, image data is output with the space of a divided clock (n±m) individual (0≤m<n). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms a latent image by scanning a photosensitive member with a laser using a polygon mirror.

  In an image forming apparatus using a laser, a latent image is formed by irradiating a polygon mirror rotating at a constant speed with a laser and scanning the photosensitive member with laser light reflected from the polygon mirror.

Since the pixels of the latent image formed on the photoconductor have a size of several tens of microns, high-precision position control is required. In such an image forming apparatus, it is necessary to improve the accuracy of arranging a laser output unit, an optical system such as a polygon mirror and a lens, and a photosensitive member, the rotation speed of the polygon mirror, and the accuracy of the mirror surface of the polygon mirror.
Japanese Patent Laid-Open No. 10-148773

  However, in the above conventional example, there is a limit in improving the accuracy of arranging the optical system and the photosensitive member, the rotation speed of the polygon mirror, and the accuracy of the polygon mirror mirror surface, and a mechanical error always remains.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of correcting an error that occurs when arranging an optical system and a photoconductor, and an error in the rotational speed of a polygon mirror and the accuracy of a mirror surface of a polygon mirror.

  In order to achieve the above object, an image forming apparatus according to claim 1 forms a latent image by scanning a photosensitive member with laser light, and forms an image by transferring the latent image onto a recording medium. In the image forming apparatus, a main scanning division unit that divides the main scanning direction scanned with the laser beam into a plurality of regions, and a calculation for calculating the number N of pixels to be printed in each region divided by the main scanning division unit Means, detecting means for detecting the number M of pixels printed by the laser beam in each area divided by the main scanning dividing means on the recording medium, image data, a pixel clock, and the pixel clock A divided clock having a frequency n times (n: an integer of 2 or more) is input, and based on the number of pixels N calculated by the calculation means and the number of pixels M detected by the detection means. And an outputting means for outputting the image data at intervals of the divided clock (n ± m) pieces fraction (0 ≦ m <n).

  According to the present invention, it is possible to correct errors that occur when arranging the optical system and the photoconductor, and errors in the rotational speed of the polygon mirror and the accuracy of the mirror surface of the polygon mirror.

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

  FIG. 1 is a schematic longitudinal sectional view showing an internal configuration of an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, an image forming apparatus according to an embodiment of the present invention includes a copying machine 100 capable of color printing. When copying an original image printed on normal paper or the like in the copying machine 100, the original 109 placed on the original table glass 110 is exposed and scanned by the exposure lamp 101. Reflected light from the document 109 is guided to the lens 105 through the reflecting mirrors 102, 103, and 104. Then, the reflected light is condensed on the full color sensor 106 by the lens 105, and a color separation image signal is obtained. The color-separated image signal is sent to the image processing unit 111 through the A / D conversion amplification unit 107, subjected to predetermined processing, and sent to the laser driving unit 112.

  A photosensitive drum (photosensitive member) 119, which is an image carrier, is supported rotatably in the direction of the arrow shown in the drawing. Around the photosensitive drum 119, four developing devices 128, 129, 130, and 131 having different colors are arranged. Then, the color separation image signal input to the laser driving unit 112 is converted into an optical signal and emitted from the laser diode. Laser light emitted from the laser diode is projected onto the surface of the photosensitive drum 119 through an optical system 117 such as a polygon mirror and a lens.

  At the time of image formation, the photosensitive drum 119 is rotated in the direction of the arrow, and a light image is irradiated onto the photosensitive drum 119 for each separated color to form a latent image. Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 119, and a toner image using a resin as a base is formed on the photosensitive drum 119. Further, the toner image on the photosensitive drum 119 is transferred from the cassette 126 (or 127) to the recording medium (for example, recording paper) supplied to the position facing the photosensitive drum 119 via the conveyance system 120 and the transfer drum 122. To do. At this time, as the transfer drum 122 is rotated, the toner image on the photosensitive drum 119 is transferred onto a recording medium carried on the transfer drum 112.

  In this way, a desired number of color images are transferred to the recording medium, and a full color image is formed. In the case of full-color image formation, when the transfer of the four color toner images is completed, the recording medium is separated from the transfer drum 122 and discharged onto the tray 132 via a fixing device 123 having fixing rollers 124 and 125.

  The copying machine 100 receives the image data sent from the external device 145 by the I / F circuit 140 via the host controller 141 and records it in a full color on the recording medium, in addition to reading the original 109 to obtain image data. You can also. The external device 145 is, for example, a host computer such as a personal computer. Further, the image data read by this apparatus can be sent from the I / F circuit 140 to the external device 145 via the host controller 141.

  FIG. 2 is a block diagram showing a configuration of a control system in the copying machine 100 of FIG.

  The copier 100 includes a control unit 300. The control unit 300 includes a CPU, a ROM storing the program, and a RAM for a work area of the CPU. The control unit 300 controls the image processing unit 111, the I / F circuit 140, and the laser driving unit 112, and communicates with the host controller 141 via the I / F circuit 140 through serial communication. The control unit 300 also controls an operation unit 301 for the user to actually operate the copying machine 100.

  FIG. 3 is a block diagram illustrating a configuration of the image processing unit 111 in FIG.

  In FIG. 3, a CCD 201 is a three-line CCD that separates the reflected light from the document 109 and converts it into an electrical signal as an image reading means, and corresponds to the full-color sensor 106 in FIG. An A / D 202 is an A / D conversion unit that converts an analog RGB signal from the CCD 201 into a digital signal, and corresponds to the A / D conversion unit 107 in FIG.

  The shading correction unit 203 corrects the sensitivity of each pixel of the CCD 201 and corrects the inclination of the light amount of the light source. Therefore, the shading correction unit 203 can set a multiplication coefficient for input image data for each pixel. The R (red), G (green), and B (blue) signals are output from the A / D converter 202 as 8-bit digital image signals.

  In the CCD 201, three CCD line sensors for R (red), G (green), and B (blue) are arranged at a constant distance. For this reason, the digital image signal is a signal having a temporal shift generated by the spatial shift. This temporal shift is corrected by the three-line connecting portion 204.

  The input masking unit 205 performs an operation for correcting the RGB spectral characteristics of the CCD 201 to standard RGB spatial characteristics. The LOG conversion unit 206 is a look-up table configured by a RAM, and R (red), G (green), and B (blue) luminance signals are respectively converted into C (cyan), M (magenta), and Y (yellow). Converted to a density signal.

  The output masking / UCR unit 207 performs an operation for removing the color turbidity of toner used for print recording from the input CMY density signal, and generates a Bk (black) signal. The F value correction unit 208 is a correction table for correcting the density value (F value) for each color in accordance with the designation of the density to be printed.

  A scaling unit 209 is a scaling circuit that changes the size of an image. The filter unit 210 is a circuit that performs edge enhancement and smoothing of an image. The sampling unit 212 is a circuit for sampling an image signal and reading data by the CPU.

  The I / O port 213 outputs a TOPC * signal and a CNCTPC * signal. The TOPC * signal is input to the I / F circuit 140, and the CNCTPC * signal is input to the control input of the buffer 215. When the CNCCTPC * signal is “0”, the buffer 215 is enabled and a signal is output, and when it is “1”, the output of the buffer 215 is in a high impedance state and the output is disabled. Further, a signal CNCTPC obtained by inverting the polarity of the CNCTPC * signal by the inverter 216 is input to the control input of the buffer 214. That is, when the control unit 300 exchanges image data with the host controller 141, the I / O port 213 is controlled so that the CNCPPC * signal becomes zero. By changing the value of the CNCTPC * signal, the input to the LOG conversion unit 206 is switched between the output of the buffer 214 and the output of the buffer 215.

  The I / F circuit 140 is an input / output interface for printing data received from the host computer by the copying machine 100 or sending an image read by the copying machine 100 to the host computer. The copying machine 100 can cope with not only the case where the host computer sends an image in the bitmap format but also the case where the image data described in the page description language is sent. That is, when the host computer sends image data in the page description language, the control unit 300 has an interpreter, and the interpreter converts the image data into a bitmap format.

  FIG. 4 is a block diagram illustrating a configuration of the laser driving unit 112 of FIG.

  In FIG. 4, a FIFO 1001 is a buffer that temporarily stores image data input from the LH to the laser driving unit 112. The FIFO 1001 stores the image data LH using the pixel clock CLK, and performs reading using the divided clock n_CLK having a frequency n (n: an integer equal to or greater than 2) times the pixel clock. In the present embodiment, the divided clock is described as being four times the frequency of the pixel clock. The FIFO 1001 receives image data from LH and a write enable signal WE. The FIFO 1001 acquires image data by referring to the write enable signal WE. Further, when the read enable signal RE is input from the control unit 1006, the FIFO 1001 outputs the stored image data.

  The D / A converter 1002 converts the image data output from the FIFO 1001 into an analog image signal. The divided clock generation unit 1004 outputs a triangular wave having a frequency n times the pixel clock to the comparator 1003 and outputs a clock having the same frequency to the FIFO 1001 as a read clock.

  The comparator 1003 compares the analog image data output from the D / A converter 102 with the triangular wave of the divided clock output from the divided clock generation unit 1004. When the analog image data is larger than the triangular wave, 1 is displayed. 0 is output.

  The laser light emitting unit 1005 outputs laser light only to the portion where 1 is input from the comparator 1002.

  The control unit 1006 is a control circuit that controls the timing of reading image data from the FIFO 1001. In this embodiment, the position of the image recorded on the recording medium is corrected by the operation of the control unit 1006. The control unit 1006 operates with the divided clock n_CLK, and controls the timing at which image data is output from the laser emitting unit 1009 by changing the interval at which the read enable signal RE is output to the FIFO 1001.

  FIG. 5A to FIG. 5D are diagrams illustrating an image data output control operation by the control unit 1006 of FIG. Hereinafter, the operation of the image forming apparatus and the control unit 1006 in this embodiment will be described with reference to FIG.

  First, without control by the control unit 1006, image data is read out from the FIFO 1001 every four clocks using a divided clock, and printing is performed on a recording paper (recording medium) at regular pixel intervals in the main scanning direction (FIG. 5A). ). In FIG. 5A, printing is performed for each pixel.

  Next, the printed result as shown in FIG. 5A is placed on the platen glass 110 and read by the image forming apparatus, and the read image is divided into a plurality of regions in the main scanning direction (main scanning dividing means). (In FIG. 5A to FIG. 5D, it is divided into four). Then, the number M of pixels included in each area is detected from the print result (FIG. 5B). In this embodiment, for each of regions 1 to 4 divided into four in the main scanning direction, region 1 has 493 pixels, region 2 has 510 pixels, region 3 has 512 pixels, and region 4 has 488 pixels. Suppose it was included.

  Next, the number N of pixels to be originally printed (the number of corrected pixels) is calculated for each region. Specifically, it is obtained from the width of each area in the main scanning direction and the printing interval. However, in FIG. For example, the width of the area / 25.4 mm × 600 dpi = 500 pixels.

  When the corrected pixel number N is calculated, based on the pixel number M included in each area detected in FIG. 5B and the corrected pixel number N, the correction interval in the control unit 1006 and the FIFO 1001 at the time of correction are calculated. The interval at which image data is read out is determined.

  The operation of the control unit 1006 in each region will be specifically described using the values illustrated in FIGS. 5A to 5D. Here, the correction value and ratio are determined for each region.

  In the area 1, 493 pixels are actually printed with respect to 500 pixels to be originally printed. This indicates that the pixel interval is printed wider than the predetermined interval in the region 1. Therefore, in area 1, every time a predetermined number of pixels is printed by the control unit 1006 at intervals of four divided clocks, image data is output at intervals of three divided blocks to correct the printing position.

  In area 1, correction is performed for 7 pixels by subtracting 493 pixels actually printed from 500 pixels that should be originally printed in area 1 (FIG. 5C). In this embodiment, when the data of the width of three divided blocks is output once, the printing position of 1/4 pixel is corrected. Therefore, by performing 28 corrections in the area 1, printing of 500 pixels is performed. I do. Specifically, data of the width of three divided blocks is output once for every 20 pixels or 21 pixels for correction.

  In the area 2, 510 pixels are actually printed with respect to 500 pixels to be originally printed. This indicates that the pixel interval is printed narrower than the predetermined interval in the area 2. Therefore, in the area 2, every time a predetermined number of pixels is printed with a width corresponding to four divided clocks by the control unit 1006, data having a width corresponding to five divided blocks is output to correct the printing position.

  In area 2, correction is performed for 10 pixels by subtracting 500 pixels to be originally printed from 510 pixels actually printed in area 2 (FIG. 5C). In this embodiment, when the data of the width of 5 divided blocks is output once, the printing position of 1/4 pixel is corrected. Therefore, by performing 40 corrections in the area 2, printing of 500 pixels is performed. Do. Specifically, data of a width corresponding to five divided blocks is output once for every 12 pixels or 13 pixels for correction.

  In the area 3, 512 pixels are actually printed with respect to 500 pixels to be originally printed. This indicates that the pixel interval is printed narrower than the predetermined interval in the area 3. Therefore, in the area 3, every time a predetermined number of pixels is printed with a width corresponding to four divided clocks by the control unit 1006, data having a width corresponding to five divided blocks is output to correct the printing position.

  In area 3, correction is performed for 12 pixels by subtracting 500 pixels to be originally printed from 512 pixels actually printed in area 3 (FIG. 5C). In this embodiment, when the data of the width of 5 divided blocks is output once, the printing position of 1/4 pixel is corrected. Therefore, by correcting 48 times in the area 3, printing of 500 pixels is performed. Do. Specifically, data of a width corresponding to five divided blocks is output once for every 10 pixels or 11 pixels for correction.

  In the area 4, 488 pixels are actually printed with respect to 500 pixels to be originally printed. This indicates that the pixel interval is printed wider than the predetermined interval in the region 4. Therefore, in the area 4, every time a predetermined number of pixels is printed with a width corresponding to four divided clocks by the control unit 1006, data having a width corresponding to three divided blocks is output to correct the printing position.

  In area 4, correction for 12 pixels is performed by subtracting 488 pixels actually printed from 500 pixels to be originally printed in area 4 (FIG. 5C). In this embodiment, when the data of the width of three divided blocks is output once, the printing position of 1/4 pixel is corrected. Therefore, by correcting 48 times in the area 1, 500 pixels can be printed. Do. Specifically, data of the width of three divided blocks is output once for every 10 or 11 pixels for correction.

  FIG. 5D shows the result of printing while performing the correction described above for each area. In FIG. 5D, the correction processing described in FIG. 5C is performed by the control unit 1006 so that 500 pixels are printed in each region, and the maximum error of the printing position in each pixel is the divided clock as the pixel clock. Is equal to or less than ¼ pixel, which is a value obtained by dividing.

  According to the above embodiment, the main scanning direction scanned with the laser beam is divided into a plurality of areas, and the number N of pixels to be printed in each of the divided areas is calculated. Then, the number M of pixels printed by the laser beam in each divided area on the recording medium is detected. The FIFO 1001 receives image data, a pixel clock, and a divided clock having a frequency n times the pixel clock, and divides the image data into divided clocks based on the calculated number N of pixels and the detected number M of pixels. Output at intervals of (n ± m) (0 ≦ m <n). This makes it possible to correct errors that occur when arranging the optical system and the photoconductor, and errors in the rotational speed of the polygon mirror and the accuracy of the mirror surface of the polygon mirror.

  In this embodiment, the number of regions divided in the main scanning direction is four and the frequency of the divided clock is four times that of the pixel clock. However, the correction accuracy can be improved by increasing the number of each region.

  Further, m = 1, a ratio of outputting image data at intervals of (n-1) divided clocks, a rate of outputting image data at intervals of (n + 1) divided clocks, and n divided clocks. The rate at which image data is output at intervals of is determined by the number of pixels N and the number of pixels M.

1 is a schematic longitudinal sectional view showing an internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a control system in the copying machine 100 of FIG. 1. It is a block diagram which shows the structure of the image process part 111 of FIG. FIG. 3 is a block diagram illustrating a configuration of a laser driving unit 112 in FIG. 2. FIG. 5 is a diagram for explaining an image data output control operation by a control unit 1006 in FIG. 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Copier 111 Image processing part 112 Laser drive part 119 Photosensitive drum 140 I / F circuit 300,1006 Control part 1001 FIFO
1002 D / A converter 1004 Divided clock generation unit 1005 Laser emission unit

Claims (3)

In an image forming apparatus that forms a latent image by scanning a photoconductor with a laser beam and forms an image by transferring the latent image onto a recording medium.
Main scanning division means for dividing the main scanning direction scanned with the laser light into a plurality of regions;
Calculating means for calculating the number N of pixels to be printed in each area divided by the main scanning dividing means;
Detecting means for detecting the number M of pixels printed by the laser beam in each region divided by the main scanning dividing means on the recording medium;
Inputs image data, a pixel clock, and a divided clock having a frequency n times (n: an integer greater than or equal to 2) the pixel clock, and the number of pixels N calculated by the calculating means and the pixels detected by the detecting means An image forming apparatus comprising: output means for outputting the image data at an interval of the divided clock (n ± m) (0 ≦ m <n) based on the number M. In each region divided by the main scanning division unit, the output unit outputs a divided clock (n−) if the number N of pixels calculated by the calculation unit and the number M of pixels detected by the detection unit are N> M. m) Output image data at intervals of
In each area divided by the main scanning division means, if the number N of pixels calculated by the calculation means and the number M of pixels detected by the detection means are N <M, the interval is equal to the number of divided clocks (n + m). The image forming apparatus according to claim 1, wherein the image data is output.   M = 1, a ratio of outputting image data at intervals of (n-1) divided clocks, a rate of outputting image data at intervals of (n + 1) divided clocks, and n divided clocks 3. The image forming apparatus according to claim 1, wherein the ratio of outputting image data at intervals is determined by the number of pixels N calculated by the calculation unit and the number of pixels M detected by the detection unit.

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