JP2008051943A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of widening a distortion correctable range, without causing the amount of a memory to be used to increase, when performing distortion correction for alignment between respective colors. <P>SOLUTION: The distortion amount, from a reference color when each color is set as the reference color, is calculated for each color, and distortion line amount when each color is set as the reference color is calculated, based on the calculated distortion amount and the resolution of image data in a subscanning direction; and then the maximum value of the distortion line amount, when each color is set as the reference color is calculated for each color, based on the calculated distortion line amount. If the maximum value of the distortion line amount, when black is set as the reference color is equal to or under the predetermined number of lines, black is set as the reference color. If the maximum value of the distortion line amount, when black is set as the reference color is not equal to or under the predetermined number of lines, the color whose maximum value of the distortion line amount becomes a minimum is set as the reference color. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus, and in particular, forms a toner image of a plurality of colors on an intermediate transfer medium based on a color input image stored in a line memory, and transfers the formed toner image to a transfer medium. The present invention relates to a color image forming apparatus for forming an image.

  In the tandem color image forming apparatus, the alignment technique between the colors Y, M, C, and K is an important problem because of its configuration. Therefore, in a tandem color image forming apparatus, a predetermined pattern (correction pattern) is formed on the transfer belt with each color toner, and each color correction pattern formed on the transfer belt is subjected to an optical sensor. As a result, the amount of misregistration between each color is calculated for each factor such as registration deviation in the main scanning direction, registration deviation in the sub-scanning direction, main scanning magnification deviation, and skew deviation so that they match each other. Many have a function of reducing color misregistration by performing feedback correction (for example, Patent Document 1).

  This correction process is performed when the environment such as temperature changes when the image forming apparatus is turned on, or when a certain number of sheets have been printed. By performing this correction process periodically, the correction process is performed. The amount of color misregistration between the colors is always kept within a certain range.

  When correcting color misregistration by image processing, it is possible to use a method of correcting a color misregistration between colors by accumulating a part of an image in a line memory and reading while switching the reading position. As a related technology, before forming an image according to image data on a print sheet, the image memory (RAM) is divided into a plurality of storage areas (line memories) along the main scanning direction, and The storage capacity is defined so as to monotonously increase or decrease monotonously along the sub-scanning direction, image data is recorded in the image memory (RAM) along the sub-scanning direction, and in accordance with the tilt amount and tilt direction with respect to the sub-scanning direction. An image forming apparatus including an image correction apparatus that reads image data from an image memory is disclosed (Patent Document 2).

  However, in the conventional technology, a part of an image is accumulated in each of a plurality of storage areas (line memories), and read while switching the reading position, thereby shifting the image divided in the main scanning direction to each color by shifting in the sub scanning direction. Therefore, there is a problem that the range in which distortion correction can be performed is limited to the range of a storage area (line memory) in which image data is stored.

  For example, when the resolution of the image data in the sub-scanning direction is 600 dpi and the number of line memories is n, the maximum range that can be corrected is (n−1) × 25400 ÷ 600 (μm). There is a limit to the range that can be used.

JP 2006-47934 A JP 2003-285473 A

  The present invention has been made in view of the above, and in the case of performing distortion correction for aligning positions between colors, the range in which distortion correction can be performed can be expanded without increasing the amount of memory used. An object is to provide a color image forming apparatus.

  In order to solve the above-described problems and achieve the object, the present invention is based on an image storage unit that holds a color input image for each color in units of lines, and a color input image stored in the image storage unit. And a color image forming apparatus for transferring a plurality of color toner images formed by the image processing unit onto an intermediate transfer member, on the intermediate transfer medium. A correction pattern forming unit that forms a correction pattern for correcting misregistration of each color; a correction pattern detection unit that detects the correction pattern formed on the intermediate transfer body by the correction pattern forming unit; and the correction pattern detection Based on the correction pattern detected by the means, a distortion amount calculation for calculating a distortion amount for each color when each of the plurality of colors is a reference color And a distortion line amount when each color of the plurality of colors is a reference color based on the distortion amount for each color calculated by the distortion amount calculation unit and the resolution in the sub-scanning direction of the input image of the color. The distortion line amount calculation means for each color, the reference color determination means for determining the reference color based on the distortion line amount calculated by the distortion line amount calculation means, and the reference color determination means A line number determining means for determining the number of lines to be accumulated in the image accumulating means on the basis of the distorted line amount of each color with respect to the reference color, and the image based on the number of lines determined by the line number determining means. Write control means for writing each color in the storage means; and distortion correction means for correcting distortion of each color written in the image storage means by the write control means. It is characterized in.

  In the invention, it is preferable that the reference color determination unit sets, as a reference color, a color having a minimum maximum value among the distortion line amounts of the colors calculated by the distortion line amount calculation unit. .

  In the invention, it is preferable that the reference color determination unit sets, as a reference color, a color having a minimum total value among the distortion line amounts of the colors calculated by the distortion line amount calculation unit. Features.

  Further, in the present invention, the distortion amount calculation unit further calculates a distortion amount of each of the plurality of colors with respect to a horizontal reference, and the reference color determination unit calculates the horizontal reference calculated by the distortion amount calculation unit. In other words, the color with the least amount of distortion is used as the reference color.

  In the present invention, when the amount of distortion lines for the reference color determined by the reference color determining means exceeds the number of lines determined by the line number determining means, the fact is notified.

  Further, in the present invention, the distortion amount calculation unit further calculates a distortion amount of each color of the plurality of colors with respect to a horizontal reference, and the distortion line amount calculation unit calculates a distortion amount of each color of the plurality of colors with respect to the horizontal reference and Based on the resolution of the input image of the color in the sub-scanning direction, a distortion line amount of each color of the plurality of colors with respect to the horizontal reference is calculated, and the distortion correction unit is configured to calculate the horizontal reference calculated by the distortion line amount calculation unit. The distortion of all the plurality of colors with respect to the horizontal reference is corrected when the sum of the maximum values of the distortion line amounts of the respective colors of the plurality of colors is less than the number of lines that can be stored in the image storage means. .

  According to the present invention, the number of lines to be stored in the image storage unit is determined based on the distortion line amount of each color with respect to the reference color, and each color is written to the image storage unit based on the determined number of lines. Since the distortion of each color written in is corrected, the range in which distortion can be corrected can be expanded without increasing the amount of memory used.

  Exemplary embodiments of a color image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiment described below.

(First embodiment)
First, an image forming principle of the color image forming apparatus 100 according to the first embodiment will be described with reference to FIG. FIG. 1 is a front view of the image processing unit 1, the exposure device 9, and the transfer belt 3 for explaining the image forming principle of the color image forming apparatus 100.

  In the color image forming apparatus 100 according to the first embodiment, four operations inside the image processing unit 1 that form images of different colors (yellow: Y, magenta: M, cyan: C, black: K), respectively. The image units 1Y, 1M, 1C, and 1K are of a dandem type that are arranged in a line along a transfer belt 3 that conveys a printing sheet 2 as a transfer medium. The transfer belt 3 is provided between a driving roller 4 that rotates and a driven roller 5 that rotates and is driven to rotate in the direction of the arrow in FIG. A paper feed tray 6 in which the transfer paper 2 is stored is provided below the transfer belt 3. The transfer sheet 2 at the uppermost position among the transfer sheets 2 stored in the sheet feed tray 6 is fed toward the transfer belt 3 during image formation, and is attracted onto the transfer belt 3 by electrostatic adsorption. The sucked transfer paper 2 is conveyed to the image forming unit 1Y, where yellow image formation is performed.

  As shown in the figure, the image forming units 1Y, 1M, 1C, and 1K include photosensitive drums 7Y, 7M, 7C, and 7K, and chargers disposed around the photosensitive drums 7Y, 7M, 7C, and 7K, respectively. 8Y, 8M, 8C, 8K, developing devices 10Y, 10M, 10C, 10K, and photoreceptor cleaners 11Y, 11M, 11C, 11K.

  The surface of the photosensitive drum 7Y of the image forming unit 1Y is uniformly charged by the charger 8Y, and then exposed by the exposure unit 9 with the laser beam LY corresponding to the yellow image, thereby forming an electrostatic latent image. . The formed electrostatic latent image is developed by the developing device 10Y, and a toner image is formed on the photosensitive drum 7Y. This toner image is transferred to the transfer paper 2 by the transfer device 12Y at a position (transfer position) where the photosensitive drum 7Y and the transfer paper 2 on the transfer belt 3 are in contact with each other. ) Is formed. In the photoreceptor drum 7Y after the transfer, unnecessary toner remaining on the drum surface is cleaned by the photoreceptor cleaner 11Y to prepare for the next image formation.

  In this way, the transfer paper 2 on which the single color (yellow) is transferred by the image forming unit 1Y is conveyed to the image forming unit 1M by the transfer belt 3. Similarly, the toner image (magenta) formed on the photosensitive drum 7M is transferred onto the transfer paper 2 in a similar manner. The transfer paper 2 is further conveyed sequentially to the image forming unit 1C and the image forming unit 1K, and similarly, the formed toner image is transferred to the transfer paper 2, thereby forming a color image on the transfer paper 2. Go.

  Then, the transfer paper 2 on which the color image is formed through the image forming unit 1K is peeled off from the transfer belt 3, fixed by the fixing device 13, and then discharged.

  Next, the correction pattern 14 will be described. In the tandem color image forming apparatus 100 according to the first embodiment, an alignment technique between each color is an important issue because of its configuration. Color misregistration between colors includes registration misalignment in the main scanning direction, registration misalignment in the sub-scanning direction, main scanning magnification misalignment, skew misalignment, and the like. Therefore, in the color image forming apparatus 100 according to the first embodiment, before the actual color image forming operation is performed on the transfer paper 2, the misregistration correction between the respective colors using the correction pattern 14 is performed. Yes.

  FIG. 2 is a perspective view of the transfer belt 3 showing a state in which the correction pattern 14 is formed on the transfer belt 3. In the color image forming apparatus 100 according to the first embodiment, a correction pattern 14 for correcting color misregistration of each color is formed on the transfer belt 3 by the exposure unit 9 for correcting misregistration. Detection is performed by detection sensors 15, 16, and 17 for detection. In the first embodiment, as shown in the figure, a plurality of detection sensors 15, 16, and 17 are arranged at both ends and the center of the transfer belt 3 in the main scanning direction. The correction pattern 14 is formed corresponding to the arrangement positions of 15, 16, and 17. Such a correction pattern 14 is detected when the transfer belt 3 rolls in the conveyance direction shown in the figure and sequentially passes through the detection sensors 15, 16, and 17. When this correction pattern 14 is detected, various deviation amounts (main scanning magnification deviation amount, main scanning registration deviation amount, sub-scanning registration deviation amount, skew correction amount, distortion amount) are calculated from the detection result. An arithmetic process is performed, and a correction amount of each shift component is calculated from the color shift amount.

  Next, the overall configuration of the color image forming apparatus 100 according to the first embodiment will be described. FIG. 3 is a diagram illustrating an example of a configuration of a mechanism that performs distortion correction of the color image forming apparatus 100 according to the first embodiment. In the color image forming apparatus 100 according to the first embodiment, as shown in the figure, three detection sensors 15, 16, 17, an engine control unit 110, a printer controller 180, a scanner 182 and an LD control unit. The configuration includes 190K, 190M, 190C, and 190Y.

  The detection sensors 15, 16, and 17 are for detecting the correction pattern 14 transferred to the transfer belt 3 in order to calculate the positional deviation of each color image. The detection sensors 15, 16, and 17 detect the position of the correction pattern 14 and output an analog detection signal.

  As shown in the figure, the engine control unit 110 roughly includes a pattern detection unit 120, a CPU 130, a RAM 140, an image processing unit 150, and a writing processing unit 160.

  The pattern detection unit 120 amplifies the detection signals output from the detection sensors 15, 16, and 17, converts the amplified analog detection signals into digital data, and stores the converted digital data in the RAM 140.

  The CPU 130 calculates a color misregistration amount from digital data that is a detection signal of the position of the correction pattern 14 stored in the RAM 140, and calculates a color misregistration amount for correcting the color misregistration correction amount from the calculated color misregistration amount. Here, as the color misregistration amount, the distortion amount of each color, the magnification error amount in the main scanning direction, the registration misregistration amount in the main scanning direction and the registration misregistration amount in the sub scanning direction (hereinafter referred to as main sub resist misregistration amount), the skew deviation amount. and so on. Also, as the color misregistration correction amount, from these various misregistration amounts, each color distortion correction amount, main scanning magnification correction amount, main scanning direction registration correction amount, and sub scanning direction registration correction amount (hereinafter referred to as main sub registration correction amount). Amount) and skew correction amount.

  Further, the CPU 130 calculates a distortion line amount for each color when each color is used as a reference color based on the resolution of the image data and the calculated distortion amount for each color (Y, M, C, K). A reference color is determined from Y, M, C, and K based on the determined distortion line amount, and the number of lines in the line memory 170 is determined based on the distortion line amount of each color with respect to the determined reference color. Note that the reference color refers to a color that serves as a reference position when calculating the distortion amount of each color.

  The RAM 140 is for temporarily recording digital data of the correction pattern 14 obtained from the pattern detection unit 120 via the CPU 130. The RAM 140 may be replaced with a non-volatile memory (for example, NV-RAM), and the digital data of the correction pattern 14 may be recorded in the non-volatile memory.

  The image processing unit 150 performs various image processing according to each image data received by the printer controller 180 or each image data acquired from the scanner 182, and transfers the image data subjected to the image processing to the writing control unit 160. .

  The writing control unit 160 receives the image data transferred from the image processing unit 150, performs various writing processes on the received image data, changes to LD data, and performs the LD control units 190K, 190M, 190C, and 190M. Transfer LD data.

  The LD control units 190K, 190M, 190C, and 190Y are provided in the exposure unit 9, and control the irradiation of the laser beams LY, LM, LC, and LK to the photosensitive drums 7Y, 7M, 7C, and 7K by the exposure unit 9. Is for. By irradiating the laser beams LY, LM, LC, and LK, toner images are formed on the photosensitive drums 7Y, 7M, 7C, and 7K. The formed toner image is transferred to the printing paper 2 and output.

  The printer controller 180 is for receiving image data transmitted from an external device (for example, a PC) via a network. The printer controller 180 transfers the received image data to the image processing unit 150.

  The scanner 182 is for acquiring image data by reading a document image. The scanner 182 transfers the acquired image data to the image processing unit 150.

  Here, the write control unit 160 included in the engine control unit 110 will be further described with reference to FIG. FIG. 4 is a diagram illustrating an example of the configuration of the write control unit 160 according to the first embodiment. As shown in the figure, the write control unit 160 of the first embodiment broadly includes a write control unit 161K, 161M, 161C, 161Y, an input image control unit 169, and a line memory 170. Yes.

  As shown in the figure, each color write control unit 161K, 161M, 161C, 161Y includes a distortion correction processing unit 162, a write image processing unit 164, an LD data output unit 166, and a correction pattern generation unit for each color. 168.

  The distortion correction processing unit 162 performs distortion correction of image data.

  The writing image processing unit 164 performs various types of image processing using the image data stored in the line memory 170.

  The LD data output unit 166 sends a correction write command (LDDATA) to the LD control unit 190 in accordance with the main / sub resist correction amount calculated by the CPU 130, and performs control to correct a write timing shift due to laser light irradiation. It is. Also, the LD data output unit 166 sends an image frequency change command (LDDATA) corresponding to the main scanning magnification correction amount calculated by the CPU 130 to the LD control unit, and performs correction control of magnification error in the main scanning direction. It is. The LD data output unit 166 sends a command (LDDATA) for forming the correction pattern 14 on the transfer belt 3 to the LD control unit 190. In addition, the LD data output unit 166 includes a device that can set the output frequency very finely, for example, a clock generator (not shown) using a voltage controlled oscillator (VCO) for each color.

  The correction pattern generation unit 168 is for generating image data of the correction pattern 14 to be transferred to the transfer belt 3 in order to calculate correction values for correcting the color misregistration of each color on the transfer belt 3. .

  The input image control unit 169 receives the image data transferred from the image processing unit 150, stores the received image data in the line memory 170, and stores the stored image data for each color write control unit 161K, 161M, 161C, 161Y. The input image control unit 169 stores each color in the line memory 170 based on the distortion line amount calculated by the CPU 130.

  The line memory 170 is a memory for sequentially storing the image data transferred from the image processing unit 150.

  Next, characteristic portions of the color image forming apparatus 100 according to the first embodiment will be described with reference to FIG.

  First, the distortion amount will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of a method for calculating the distortion amount of each color when black is used as a reference color. The method for calculating the distortion amount of each color shown in the figure is to obtain the distortion amount of each color (C, M, Y) with respect to black as the reference color. As shown in the lower part of the figure, when the cyan image is distorted, the distortion amount (C_Dis_LM) between the cyan detection sensors 15 and 17 is obtained as C_Dis_LM = KC_M-KC_L. The distortion amount (C_Dis_MR) between the cyan detection sensors 17 and 16 is obtained as C_Dis_MR = KC_R-KC_M.

  Next, the distortion line amount will be described. When the sub-scanning resolution is 600 dpi, the distance moved by shifting one line is obtained as 25400 [μm] / 600. Therefore, shifting by one line moves 42.3 [μm]. Divide each shift amount by the movement amount per line (42.3 [μm]) and round off the decimal point to an integer unit. The amount of line deviation (distortion line amount) is calculated.

  Assume that C_Dis_LM = 50 [μm] and C_Dis_MR = 200 [μm] can be obtained from the detection result of the correction pattern 14 due to the distortion of the scanning beam of the exposure unit 9. In this case, if the distortion line amount (C_Dis_LM_Shift) between cyan L and M is obtained, C_Dis_LM_Shift = 50 / 42.3 = 1 [Line], and if the distortion line amount (C_Dis_MR_Shift) between cyan M and R is obtained, C_Dis_MR_Shift = 200 / 42.3 = 5 [Line].

  Accordingly, when the above input image is output as LD data as it is, as shown in FIG. 6 (2), on the printing paper 2, from the left end to the center as compared with the case where there is no distortion as shown in FIG. 6 (1). Will be shifted downward by one line. Further, the image from the center to the right end is further shifted downward by 5 lines.

  In this case, as shown in FIG. 6 (3), the main scanning is divided into two, ie, the number of lines (distortion line amount) +1 from the left end to the center. Further, from the center to the right end, the main scanning is divided into 6 divisions of the number of lines of deviation amount (distortion line amount) +1. Then, as shown in FIG. 6 (4), if an image shifted up by one line in the right direction is output, the left and right image positions are parallel on the printing paper 2 as shown in FIG. 6 (5). Will be output.

  In practice, input image data is sequentially stored in the distortion correction line memory 170, and the distortion correction processing units 162K, 162M, 162C, and 162Y determine which line memory data is read in each divided area. It is the structure which outputs the image of FIG. 6 (4) by switching. Therefore, it is only necessary to obtain the address of the division position with respect to the main scanning direction and the information about whether to shift in the + direction or one direction of the sub-scanning at each division position.

  In the example shown in FIG. 6, since the main scanning direction is divided into eight, the address of the division position and the information on whether to shift to the + side or the − side of the sub-scan at each division position are calculated. . Here, the values are obtained when the main scanning interval is divided based on the distortion correction amounts detected for the right half and the left half, respectively, but the scanning line distortion is distorted by a quadratic function. Since there are many cases, the amount of deviation at the positions of the detection sensors 15, 16, and 17 may be approximated by a quadratic function to obtain the division position for main scanning.

  If the number of pixels in the main scanning direction is 4800 pixels as shown in FIG. 6 (3), the line is shifted downward by one line from the left end to the center. Therefore, the 1200th pixel is shifted upward by one line. Also, since the shift from the center to the right end is 6 lines downward, the shift is made upward every 400 pixels. Then, as shown in FIG. 6 (6), the first line outputs white pixels up to 4399 pixels, the image data of the first line memory from the 4400th pixel, and the second line extends to the 3999th pixel. Sequentially reads out the white pixels, the image data in the first line memory from 4000 pixels to 4399 pixels, and the image data in the second line memory from 4400 pixels, and outputs them. ), The left and right image positions can be corrected to be parallel.

  FIG. 7A is a diagram illustrating an example of the configuration of the line memory 170. The line memory 170 shown in FIG. 5A has a line memory of 2 lines for black as a reference color and 7 lines for color colors (M, C, Y), and the number of lines is fixed for each color. . According to the configuration of the line memory 170 shown in FIG. 6A, the number of lines necessary to correct the inclination of n lines is n + 1, and one line is used for image input (for writing). The amount of distortion that can be corrected is a maximum of ± 5 lines.

  As shown in FIG. 7A, the reason why the number of lines of the color (M, C, Y) is larger than the number of lines of black is that when black is used as the reference color, the color (M, C, Y) This is because, in Y), more line memory is required than black, which is the reference color, in order to perform distortion correction. As shown in FIG. 7A, when the number of lines is fixed for each color as shown in FIG. 7A, the writing control unit 160 uses the speed of the input image and the writing image as shown in FIG. In order to perform the conversion, line memories 170K, 170M, 170C, and 170Y for each color are required. Note that since black, which is the reference color, does not require distortion correction, the writing control unit 160 does not include a black (K) distortion correction processing unit 162K, as shown in FIG.

  Table 1-1 shows an example of the distortion amount of each color (M, C, Y) when the reference color is black. As shown in Table 1-1, the distortion amount of each color with respect to the reference color black (K) is K: 0 [μm], M: −70 [μm], C: −180 [μm], Y: It is assumed that it is 30 [μm]. In this case, when the resolution in the sub-scanning direction is 600 dpi, the amount of movement of one line is 42.3 [μm] as described above, so the distortion line amount of each color is as shown in Table 1-2. K: 0 line, M: +2 line, C: +4 line, Y: -1 line. In this case, the maximum value of the distortion line amount is 4, and when the line memory 170 shown in FIG. 7A, which is ± 5 of the correction range amount, is used, distortion correction can be performed.

  However, as shown in Table 2-1, the distortion amount of each color with respect to the reference color black (K) is K: 0 [μm], M: +70 [μm], C: +240 [μm], Y: As shown in Table 2-2, the distortion line amount of each color when −30 [μm] and the resolution in the sub-scanning direction is 600 dpi is K: 0 line, M: −2 line, and C: −. 6 lines, Y: +1 line. Therefore, the maximum value of the distortion line amount is 6, and when the line memory 170 shown in FIG. 7A, which is ± 5 lines or less of the correction range amount, is used, one line cannot be corrected for cyan.

  Therefore, the color image forming apparatus 100 according to the first embodiment uses the line memory 170 in common for each color (K, M, C, Y), and allows each color to be set as a reference color. The limited memory is effectively used, and the possible range of distortion correction is expanded. That is, according to Tables 2-1 and 2-2, when magenta is used as the reference color, the maximum value of the distortion line amount becomes ± 5 lines or less of the correction range amount. Therefore, in the first embodiment, in such a case, as shown in FIG. 7B, magenta is used as a reference color, and line memory is assigned to each color (K, C, Y) excluding magenta, thereby causing distortion. The maximum line amount is ± 5 lines or less so that distortion correction can be performed.

  With the above configuration, an image forming process performed by the color image forming apparatus 100 according to the first embodiment will be described with reference to FIG. FIG. 9 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the first embodiment.

  First, the correction pattern generation units 168K, 168M, 168C, and 168Y generate the correction pattern 14 (step SA-1). The image data of the correction pattern 14 is formed by being transferred to the transfer belt 3 via the LD data output units 166K, 166M, 166C, 166Y and the LD control units 190K, 190M, 190C, 190Y. Here, the correction pattern 14 formed on the transfer belt 3 is detected by detection sensors 15, 16, and 17.

  Subsequently, when the position information of the correction pattern 14 transferred to the transfer belt 3 is detected by the detection sensors 15, 16, and 17, the pattern detection unit 120 detects the position of the correction pattern detected by the detection sensors 15, 16, and 17. By acquiring the information, the correction pattern 14 is detected (step SA-2).

  Next, the CPU 130 calculates the main scanning magnification deviation amount, the main / sub-registration deviation amount, and the skew deviation amount from the position information of the correction pattern 14 detected by the detection execution in step SA-2. Then, a main scanning magnification correction amount, a main / sub resist correction amount, and a skew correction amount are calculated from the respective color misregistration amounts (step SA-3).

  Further, the CPU 130 calculates a distortion amount [μm] for each color when each color of Y, M, C, and K is set as a reference color (step SA-4). Here, the distortion amount calculation processing performed in step SA-4 will be described with reference to FIG. The position (line) at which the first correction pattern 14 is detected is used as a reference position, and the position (line) at which the upper left black correction pattern 14 shown in FIG.

  First, the black distortion amount is calculated with reference to the reference position. Specifically, the distortion amount (K_Dis_LM) between the black detection sensors 15 and 17 and the distortion amount (K_Dis_MR) between the detection sensors 17 and 16 are calculated. Following this, the amount of distortion of each color (C, M, Y) is calculated. In the example shown in the figure, first, the interval between the reference position and cyan detected by the detection sensor 15 (KC_L), the interval between the reference position and cyan detected by the detection sensor 17 (KC_M), the reference position and the detection sensor. The interval between cyan detected at 16 (KC_R) is obtained. Then, the distortion amount (C_Dis_LM) between the cyan detection sensors 15 and 17 is obtained from the equation C_Dis_LM = KC_L-KC_M, and the distortion amount (C_Dis_MR) between the cyan detection sensors 17 and 16 is calculated as C_Dis_MR = KC_M−. Obtained from the equation of KC_R. Then, the magenta distortion amount and the yellow distortion amount are obtained by the same method. Further, the CPU 130 calculates a distortion amount when the reference color is each color (M, C, Y) based on a difference from the distortion amount of each color obtained in step SA-4.

  Returning to FIG. 9, the CPU 130 calculates the distortion line amount for each color calculated in step SA-4 (step SA-5). For example, as shown in Table 2-1, when black is used as a reference color, the distortion amount of each color is K: 0 [μm], M: +70 [μm], C: +240 [μm], Y: −. When the resolution is 30 [μm] and the resolution in the sub-scanning direction is 600 dpi, the distortion line amount of each color can be obtained by the distortion amount [μm] /42.3 [μm], as shown in Table 2-2. As shown, K: 0 line, M: -2 line, C: -6 line, Y: +1 line.

  Next, the CPU 130 calculates the maximum value (absolute value) of the distortion line amount when each color is the reference color based on the distortion line amount calculated in step SA-5 (step SA-6). For example, as shown in Table 2-2, the distortion line amounts of each color when black is the reference color are K: 0 line, M: -2 line, C: -6 line, and Y: +1 line, respectively. In this case, the maximum value (absolute value) is 6 lines.

  Next, when the maximum value (absolute value) of the distortion line amount of each color when black is used as the reference color is equal to or less than the predetermined number of lines (step SA-7: Yes), black is determined as the reference color ( Step SA-8). The reason why black is used as the reference color in preference to other colors is that black is used most frequently in images such as text and ruled lines, so black prevents the occurrence of steps at the seam, which is a side effect of distortion correction. It is to do. In the case of the line memory 170 shown in FIG. 7B, the predetermined number of lines is ± 5 lines as described above.

  On the other hand, when the maximum value (absolute value) of the distortion line amount of each color when black is used as the reference color exceeds the predetermined number of lines (step SA-7: No), the maximum distortion line amount is further increased. When there is a reference color whose value (absolute value) is equal to or less than the predetermined number of lines (step SA-9: Yes), the color having the minimum maximum value (absolute value) is determined as the reference color (step SA-10). .

  Further, when the maximum value (absolute value) of the distortion line amount of each color when black is used as the reference color exceeds a predetermined number of lines (step SA-7: No), the maximum value of the distortion line amount ( If there is no reference color whose absolute value is equal to or less than the predetermined number of lines (step SA-9: No), an error message is returned to notify the user (step SA-11). Transition to SA-10.

  When the reference color is determined, a distortion correction amount (number of moving lines) for each color is calculated (step SA-12), and printing processing is performed based on the color misregistration correction amounts calculated in step SA-3 and step SA-12. (Step SA-13) The image forming process is finished.

  Here, the printing process performed in step SA-13 will be described with reference to FIG. FIG. 11 is a flowchart showing the procedure of the printing process.

  First, in order to correct the main scanning magnification deviation, the pixel clock frequency of each color is set based on the main scanning magnification correction amount calculated in step SA-3 (step SA-131). Specifically, the writing control unit 160 changes the image frequency based on the calculated magnification error amount of each color.

  Next, in order to correct the registration in the main scanning direction, the main scanning delay amount of each color is set based on the main scanning direction registration correction amount calculated in step SA-3 (step SA-132). The main scanning write timing is adjusted depending on from which position of the main scanning counter which operates with the synchronization detection signal of each color as a trigger.

  Next, in order to correct the registration in the sub-scanning direction, the main scanning delay amount of each color is set based on the sub-scanning direction registration correction amount calculated in step SA-3 (step SA-133). Specifically, it is performed by adjusting the writing timing of sub-scanning. Here, sub-scanning color misregistration correction will be briefly described with reference to FIG.

  FIG. 12 is a timing chart showing the sub-scanning write timing when correcting sub-scanning color misregistration. The writing control unit 160 counts the number of lines based on the start signal (STTRIG_N) from the CPU 130 and outputs a sub-scan timing signal (* _FSYNC_N) to the image processing unit 150. The image processing unit 150 outputs a sub-scanning gate signal (* _IPFGATE_N) to the write control unit 160 using * _FSYNC_N as a trigger, and transfers image data (* _IPDATA [7: 0] _N). When correcting the sub-scanning registration, the sub-scan delay amount (* _mfcntld) from the start signal is changed according to the detected misregistration amount. Normally, the misregistration amount with reference to black is set to color (M, C , Y) is reflected in the sub-scan delay amount, and the timing of * _FSYNC_N is changed to perform sub-scan alignment.

  Returning to FIG. 11, when the sub-scan delay amount is set in step SA-133, a reference color for correcting distortion is set (step SA-134). Specifically, the reference color determined in step SA-8 or step SA-11 is set.

  Next, in order to perform distortion correction, a distortion correction amount for each color other than the reference color is set (step SA-135). Specifically, the setting is performed based on the distortion correction amount of each color calculated in step SA-12.

  When various settings are completed by the processing up to step SA-135, printing of the image data on the printing paper 2 is started (step SA-136). Specifically, the LD data output unit 166 sends an image frequency change command (LDDATA) corresponding to the main scanning magnification correction amount, a correction write command (LDDATA) corresponding to the main / sub resist correction amount, to the LD control unit 190. Send to Accordingly, the laser light LY, LM, LC, LK is irradiated on the photosensitive drums 7Y, 7M, 7C, 7K by the exposure unit 9 under the control of the LD control unit 190, and the photosensitive drums 7Y, 7M, 7C, 7K are irradiated. A toner image is formed on the top, and the formed toner image is transferred to the printing paper 2 and output.

  As described above, the color image forming apparatus 100 according to the first embodiment calculates the amount of distortion (μm) from the reference color when each of Y, M, C, and K is used as the reference color. Based on the calculated distortion amount and the resolution of the image data in the sub-scanning direction, the distortion line amount when each color of Y, M, C, and K is used as a reference color is calculated, and based on the calculated distortion line amount of each color. Thus, the maximum value (absolute value) of the distortion line amount when each color of Y, M, C, and K is set as the reference color is calculated. If the maximum value of the distortion line amount when black is the reference color is equal to or less than the predetermined number of lines, black is set as the reference color. Also, if the maximum distortion line amount when black is the reference color is not less than the predetermined number of lines and there is a reference color with the maximum distortion line amount less than the predetermined number of lines, the maximum The color with the smallest value is set as the reference color. If the maximum distortion line amount when black is the reference color is not less than the predetermined number of lines and there is no reference color with the maximum distortion line amount less than the predetermined number of lines, use An error message is notified to the user, and the color having the minimum maximum value is set as the reference color.

  Therefore, according to the color image forming apparatus 100 of the first embodiment, the amount of distortion (μm) with respect to the reference color when each color of Y, M, C, and K is set as the reference color is calculated and calculated. Based on the distortion amount and the resolution of the image data in the sub-scanning direction, the distortion line amount when each color of Y, M, C, K is used as a reference color is calculated, and based on the calculated distortion line amount of each color, The maximum value (absolute value) of the distortion line amount when each color of Y, M, C, and K is used as a reference color is calculated. If the maximum value of the distortion line amount when black is the reference color is equal to or less than the predetermined number of memory lines, the black is used as the reference color. Black that is easy to prevent can be preferentially used as a reference color.

  In addition, even when the maximum value of the distortion line amount when black is the reference color is not less than the predetermined number of lines, when there is a reference color having the maximum value of the distortion line amount not more than the predetermined number of lines, Since the color having the smallest maximum value is used as the reference color, the possible range of distortion correction can be expanded without increasing the number of lines.

  In addition, if there is no reference color with the maximum distortion line amount equal to or less than the predetermined number of memory lines, an error message is notified to the user, so that the user cannot obtain a high-accuracy image in advance. Can know.

(Second Embodiment)
Next, a color image forming apparatus 100 according to a second embodiment of the present invention will be described. In the description of the second embodiment, the description overlapping the description of the color image forming apparatus 100 of the first embodiment described above may be omitted.

  First, characteristic parts of the color image forming apparatus 100 of the second embodiment will be described.

  According to the line memory 170 of the first embodiment, the correction range amount is ± 5. The distortion line amount when each color of Y, M, C, and K is set as the reference color is calculated for each color (see Table 3-1), and the maximum value (absolute value) of the calculated distortion line amount is As shown in Table 3-2, when the reference color K is 6, the reference color M is 6, the reference color C is 7, and the reference color Y is 7, the correction range amount is ± 5. In the line memory 170 (see FIG. 7B), the number of lines required for distortion correction is exceeded regardless of which color is used as a reference color, and a range that cannot be corrected is generated.

  Therefore, the line memory 170 of the second embodiment can be shared by each color as shown in FIG. 13A, and any number of line memories can be used for each color. Since 8 lines are required for writing each color (Y, M, C, K), as shown in FIG. 13A, when the number of lines in the line memory 170 is 23 lines, It can be used arbitrarily for each color within 15 lines.

  Specifically, as shown in Table 3-2, the total value of the maximum values (absolute values) of the distortion line amounts when the colors Y, M, C, and K are used as the reference colors is the reference color K: 14, when the reference color M is 11, the reference color C is 19, and the reference color Y is 16, the number of lines that can be arbitrarily used for each color is 15. Therefore, black or magenta can be used as the reference color. For example, when magenta is used as the reference color, if the line memory 170 as shown in FIG. 13B is assigned, the distortion correction range can be further expanded without increasing the number of lines in the line memory 170. .

  With the above configuration, an image forming process performed by the color image forming apparatus 100 according to the second embodiment will be described with reference to FIG. FIG. 14 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the second embodiment. It is assumed that the total number of lines in the line memory 170 is 23 lines as shown in FIG. Therefore, the predetermined number of lines described below is 15 lines. Here, a description will be given of parts different from the flow of the image forming process described in FIG. 9 of the first embodiment.

  In the first embodiment, when the distortion line amounts are calculated in step SA-5 when the Y, M, C, and K colors are used as the reference colors, respectively, Y is calculated based on the calculated distortion line amounts. The maximum value (absolute value) of the distortion line amount when each color of M, C, K was used as the reference color was calculated (step SA-6).

  On the other hand, in the second embodiment, when the distortion line amounts are calculated in the case where the respective colors Y, M, C, and K are used as the reference colors in step SA-5, the calculated distortion line amounts are obtained. Based on this, the total value of the absolute values of the distortion line amounts when the respective colors Y, M, C, and K are used as reference colors is calculated (step SA-14).

  For example, as shown in Table 3-2, when black is used as a reference color, the distortion line amounts are K: 0 line, M: +2 line, C: +6 line, and Y: -6 line, respectively. The total value is 14.

  Next, when the total value of the distortion line amounts of the respective colors when black is used as the reference color is equal to or less than the predetermined number of lines (step SA-15: Yes), black is determined as the reference color (step S15). SA-16).

  On the other hand, the total absolute value of the distortion line amounts of each color when black is used as the reference color exceeds the predetermined number of lines (step SA-15: No), and further, the absolute value of the distortion line amount. If there is a reference color whose total value is equal to or less than the predetermined number of lines (step SA-17: Yes), the color having the minimum absolute value of the distortion line amount is determined as the reference color (step SA-18). ).

  Further, the total value of the absolute values of the distortion line amounts of the respective colors when black is used as the reference color exceeds the predetermined number of lines (step SA-15: No), and further, the absolute value of the distortion line amount. If there is no reference color that makes the total value less than or equal to the predetermined number of lines (step SA-17: No), an error message is returned to the user (step SA-19), and the processing procedure is as follows. Move to SA-18.

  As described above, the color image forming apparatus 100 according to the second embodiment calculates the distortion amount (μm) of each color when the colors Y, M, C, and K are used as reference colors, and calculates the calculated distortion. Based on the amount and the resolution in the sub-scanning direction, the distortion line amount of each color when each color of Y, M, C, K is used as a reference color is calculated, and based on the calculated distortion line amount, Y, M, C , K, when the reference colors are used as the reference colors, the sum of absolute values of the distortion line amounts of the respective colors is calculated. When the total value of the absolute values of the distortion line amounts when black is used as the reference color is equal to or less than a predetermined number of lines, black is used as the reference color. Further, a reference color in which the absolute value of the distortion line amount when black is the reference color is not less than the predetermined number of lines, and the total absolute value of the distortion line amount is less than or equal to the predetermined number of lines. If there is a color, the color having the minimum absolute value is the reference color. Further, a reference color in which the absolute value of the distortion line amount when black is the reference color is not less than the predetermined number of lines, and the total absolute value of the distortion line amount is less than or equal to the predetermined number of lines. When there is no error, an error message is notified to the user, and the color having the minimum maximum value is set as the reference color.

  Therefore, according to the color image forming apparatus 100 of the second embodiment, the total value of the absolute values of the distortion line amounts of the respective colors when the colors Y, M, C, and K are used as the reference colors is calculated. If the total absolute value of the distortion line amount is less than or equal to the predetermined number of lines when the reference color is used as the reference color, the total absolute value of the distortion line amount when black is the reference color and black is the reference color Is not less than the predetermined number of lines, and there is a reference color with the total absolute value of the distortion line amount equal to or less than the predetermined number of lines, the color with the minimum absolute value is the reference color. Therefore, the possible range of distortion correction can be further expanded without increasing the number of memory lines 170.

(Third embodiment)
Next, a color image forming apparatus 100 according to a third embodiment of the present invention will be described. In the description of the third embodiment, the description overlapping the description of the color image forming apparatus 100 of the first to second embodiments described above may be omitted.

  First, characteristic portions of the color image forming apparatus 100 according to the third embodiment will be described.

  When the inclination of the reference color is large, the adjustment is performed with the image inclined with respect to the paper. On the other hand, when the color closest to the horizontal is used as the reference color, an effect that the image can be corrected so as to be almost horizontal with respect to the paper can be obtained. Therefore, in the third embodiment, the distortion amount of each color of Y, M, C, and K with the detection sensors 15, 16, and 17 as the horizontal reference is calculated, and the horizontal reference is calculated based on the calculated distortion amount. The color with the least amount of distortion is used as the reference color.

  A method of calculating the distortion amount of each color of Y, M, C, and K using the positions of the detection sensors 15, 16, and 17 as a horizontal reference will be described with reference to FIG. FIG. 15 is a diagram illustrating an example of a method for calculating the distortion amount of each color with reference to the detection sensors 15, 16, and 17. Note that, since the calculation method of the distortion amount using the detection sensors 15, 16, and 17 as the horizontal reference is the same for each color, black and cyan will be described as a representative here.

  First, the detection interval between the detection sensor 15 serving as the horizontal reference and the black detected by the detection sensor 15 (ZK_L) is obtained. Similarly, the black interval (ZK_M) detected by the detection sensor 17 and the detection sensor 17 and the black interval (ZK_R) detected by the detection sensor 16 and the detection sensor 16 are obtained. Similarly, ZC_L, ZC_M, and ZC_R shown in the figure are obtained using the detection sensors 15, 16, and 17 as a horizontal reference. Subsequently, a distortion amount (K_Dis_LM) between the black detection sensors 15 and 17 is obtained from an expression of K_Dis_LM = ZK_L-ZK_M, and a distortion amount (K_Dis_MR) between the black detection sensors 17 and 16 is calculated as K_DIS_MR = ZK_M-ZK_R. Obtained from the equation Further, the distortion amount (C_Dis_LM) between the cyan detection sensors 15 and 17 is obtained from the equation C_Dis_LM = ZC_L-ZC_M, and the distortion amount (C_Dis_MR) between the cyan detection sensors 17 and 16 is calculated as C_DIS_MR = ZC_M-ZC_R. Calculate from the formula.

  In the third embodiment, when any color is used as a reference color and the total value of absolute values is equal to or smaller than a predetermined number of lines, the horizontal reference is calculated based on the distortion amount of each color calculated by the above-described method. Therefore, the color with the least amount of distortion is used as the reference color.

  With the above configuration, an image forming process performed by the color image forming apparatus 100 according to the third embodiment will be described with reference to FIG. FIG. 16 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the third embodiment. Here, a different part from the flow of the image forming process described in FIG. 14 of the second embodiment will be described.

  In the image forming process of the second embodiment, when the main scanning magnification correction amount, main / sub resist correction amount, and skew correction amount are calculated in step SA-3, Y, M, C, K are calculated in step SA-4. The amount of distortion when each color was used as a reference color was calculated. In contrast, in the image forming process of the third embodiment, when the main scanning magnification correction amount, main / sub resist correction amount, and skew correction amount are calculated in step SA-3, the processing of step SA-4 is executed. Before, the distortion amounts of the respective colors Y, M, C, and K with respect to the detection sensors 15, 16, and 17 are calculated (step SA-20). Referring to FIG. 18, the detection sensor 15 that is the horizontal reference and the black detected by the detection sensor 15 (ZK_L), and the black detection that is detected by the detection sensor 17 that is the horizontal reference and the detection sensor 17 (ZK_M). Then, the horizontal reference detection sensor 16 and the black interval (ZK_R) detected by the detection sensor 16 are obtained, and the distortion amount (K_Dis_LM) between the black detection sensors 15 and 17 is obtained from the equation K_Dis_LM = ZK_L-ZK_M. Further, the amount of distortion (K_Dis_MR) between the black detection sensors 17 and 16 is obtained from the equation K_DIS_MR = ZK_M-ZK_R.

  In the image forming process according to the second embodiment, when the total value of the absolute values of the distortion line amounts of each color (C, M, Y) when black is used as a reference color is equal to or less than a predetermined number of lines. In (Step SA-15: Yes), black is determined as the reference color (Step SA-16). On the other hand, in the image forming process of the third embodiment, when the absolute value of the distortion line amount of each color is equal to or less than the predetermined number of lines, regardless of which color is the reference color (step SA-21). : Yes), based on the distortion amount of each color using the detection sensors 15, 16, and 17 calculated in step SA-20 as the horizontal reference, the color having the smallest distortion amount with respect to the horizontal reference is set as the reference color (step SA). -22).

  On the other hand, the absolute value of the distortion line amount is the case where the total value of the absolute value of the distortion line amount of each color is not less than the predetermined number of lines (step SA-21: No) regardless of which color is the reference color. When there is a reference color whose total value is equal to or less than the predetermined number of lines (step SA-23: Yes), the color having the minimum absolute value of the distortion line amount is determined as the reference color (step SA- 24).

  Further, the absolute value of the distortion line amount is a case where the total value of the absolute values of the distortion line amounts of the respective colors is not less than the predetermined number of lines regardless of which color is the reference color (step SA-21: No). When there is no reference color that makes the total value of the number of lines equal to or less than the predetermined number of lines (step SA-23: No), an error message is returned to the user (step SA-25), and the processing procedure is step SA. To -24.

  In the third embodiment, the sum of the absolute values of the distortion line amounts of the respective colors is not less than or equal to the predetermined number of lines regardless of which color is the reference color (step SA-21: No). Further, when there is a reference color having the total absolute value of the distortion line amount equal to or less than the predetermined number of lines (step SA-23: Yes), in step SA-24, the total absolute value of the distortion line amount is Although the minimum color is used as the reference color, the color with the least amount of distortion relative to the horizontal reference is used as the reference color. If a color with a small amount is used as a reference color and the number of lines is equal to or less than a predetermined number of lines, a configuration in which the second color with the least amount of distortion is used as a reference color may be used.

  As described above, the color image forming apparatus 100 according to the third embodiment calculates the distortion amount of each color using the detection sensors 15, 16, and 17 as a horizontal reference, and any color is used as a reference color. When the total absolute value of the distortion amount of each color is equal to or less than the predetermined number of lines, the color having the smallest distortion amount with respect to the horizontal reference is set as the reference color.

  Therefore, according to the color image forming apparatus 100 of the third embodiment, the distortion amount of each color with the detection sensors 15, 16 and 17 as the horizontal reference is calculated, and any color is used as the reference color. When the total absolute value of the distortion amount is equal to or smaller than the predetermined number of lines, the color having the least distortion amount with respect to the horizontal reference is set as the reference color, so that the image is nearly horizontal with respect to the printing paper 2. Thus, distortion correction can be performed.

(Fourth embodiment)
Next, a color image forming apparatus 100 according to a fourth embodiment of the present invention will be described. In the description of the fourth embodiment, the description overlapping the description of the color image forming apparatus 100 of the first to third embodiments described above may be omitted.

  First, characteristic parts of the color image forming apparatus 100 according to the fourth embodiment will be described.

  When the inclination of the reference color is large, the adjustment is performed with the image inclined with respect to the paper. Therefore, in the above-described third embodiment, the image having the least distortion amount with respect to the horizontal reference is used as the reference color, so that the image is corrected to be close to the horizontal with respect to the paper. On the other hand, when all the colors Y, M, C, and K are corrected for distortion with respect to the horizontal reference, an effect that the image can be made more horizontal with respect to the paper can be obtained. Therefore, in the fourth embodiment, the distortion amounts of the respective colors Y, M, C, and K with respect to the horizontal reference are calculated, and distortion correction is performed for all the colors Y, M, C, and K with respect to the horizontal reference.

  That is, in the fourth embodiment, when the total absolute value of the distortion line amount with respect to the horizontal reference is equal to or less than a predetermined number of lines, the detection sensors 15, 16, and 17 that are the horizontal reference are used as the reference. Distortion correction for all colors of M, C, and K is performed.

  With the above configuration, an image forming process performed by the color image forming apparatus 100 according to the fourth embodiment will be described with reference to FIG. FIG. 17 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the fourth embodiment. Here, a part different from the flow of the image forming process described in FIG. 16 of the third embodiment will be described.

  In the image forming process of the third embodiment, if the total value of the absolute values of the distortion line amounts of each color is equal to or less than the predetermined number of lines regardless of which color is the reference color (step SA-21: Yes), Based on the distortion amount of each color with respect to the detection sensors 15, 16, and 17, which is the horizontal reference calculated in step SA-20, the color having the smallest distortion amount with respect to the horizontal reference is determined as the reference color (step SA-22). .

  In contrast, in the image forming process of the fourth embodiment, the distortion of each color with respect to the horizontal reference is based on the distortion amount of each color with the detection sensors 15, 16, and 17 calculated in step SA-20 as the horizontal reference. When the line amount is calculated (step SA-26), and the total value of the absolute values of the distortion line amounts of the respective colors with respect to the horizontal reference calculated in step SA-26 is equal to or less than the predetermined number of lines (step SA-27). : Yes), the distortion correction amount is calculated based on the horizontal reference (step SA-28).

  On the other hand, when the sum of the absolute values of the distortion line amounts of the respective colors with respect to the horizontal reference calculated in step SA-26 is not less than the predetermined number of lines (step SA-27: No), the processing procedure proceeds to step SA-21. Is done.

  As described above, the color image forming apparatus 100 according to the fourth embodiment calculates the distortion amount of each color using the detection sensors 15, 16, and 17 as a horizontal reference, and based on the calculated distortion amount of each color. If the distortion line amount of each color for the detection sensors 15, 16, and 17 that are the horizontal reference is calculated, and the total absolute value of the calculated distortion line amounts of each color is equal to or less than a predetermined number of lines, Y, Distortion correction is performed with respect to the horizontal reference for all colors M, C, and K.

  Therefore, the color image forming apparatus 100 according to the fourth embodiment has all the colors Y, M, C, and K when the total absolute value of the distortion line amounts with respect to the horizontal reference is equal to or less than a predetermined number of lines. Since the distortion correction is performed with respect to the horizontal reference, the image can be corrected closer to the horizontal with respect to the paper.

2 is a front view of the image processing unit 1, the exposure device 9, and the transfer belt 3 for explaining the image forming principle of the color image forming apparatus 100. FIG. 2 is a perspective view of the transfer belt 3 showing a state in which a correction pattern 14 is formed on the transfer belt 3. FIG. 2 is a diagram illustrating an example of a configuration of a mechanism that performs distortion correction of the color image forming apparatus 100. FIG. 3 is a diagram illustrating an example of a configuration of a writing control unit 160. FIG. It is a figure which shows an example of the method of calculating the distortion amount of each color at the time of setting black as a reference color. It is a figure for demonstrating the amount of distortion lines. 2 is a diagram illustrating an example of a configuration of a line memory 170. FIG. 3 is a diagram illustrating an example of a configuration of a writing control unit 160. FIG. 3 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the first embodiment. It is a figure for demonstrating the calculation method of the distortion amount of each color which uses black as a reference color. It is a flowchart which shows the procedure of a printing process. It is a timing chart which shows the timing of writing of sub-scanning. 2 is a diagram illustrating an example of a configuration of a line memory 170. FIG. 6 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the second embodiment. It is a figure which shows an example of the method of calculating the distortion amount of each color on the basis of the detection sensors 15, 16, and 17. 10 is a flowchart illustrating a procedure of image forming processing performed by the color image forming apparatus 100 according to the third embodiment. 14 is a flowchart illustrating a procedure of image forming processing performed in the color image forming apparatus 100 according to the fourth embodiment.

Explanation of symbols

14 correction pattern 15, 16, 17 detection sensor 100 color image forming apparatus 110 engine control unit 120 pattern detection unit 130 CPU
140 RAM
150 Image processing unit 160 Write control unit 170 Line memory

Claims (6)

An image accumulating unit that holds a color input image for each color in units of lines; and an image processing unit that forms a plurality of color toner images based on the color input image accumulated in the image accumulating unit, In a color image forming apparatus for transferring a plurality of color toner images formed in an image process unit onto an intermediate transfer member,
A correction pattern forming means for forming a correction pattern for correcting the misregistration of each color on the intermediate transfer medium;
A correction pattern detecting means for detecting the correction pattern formed on the intermediate transfer member by the correction pattern forming means;
Based on the correction pattern detected by the correction pattern detection unit, a distortion amount calculation unit that calculates a distortion amount for each color when each color of the plurality of colors is a reference color;
Based on the distortion amount for each color calculated by the distortion amount calculation unit and the resolution in the sub-scanning direction of the input image of the color, the distortion line amount when each color of the plurality of colors is used as a reference color is determined for each color. Distortion line amount calculating means for calculating
Reference color determination means for determining the reference color based on the distortion line amount calculated by the distortion line amount calculation means;
Line number determining means for determining the number of lines to be accumulated in the image accumulating means based on the distortion line amount of each color with respect to the reference color determined by the reference color determining means;
Based on the number of lines determined by the number-of-lines determination means, a writing control means for writing each color into the image storage means,
Distortion correcting means for correcting distortion of each color written in the image storage means by the writing control means;
A color image forming apparatus comprising:   2. The reference color determination unit according to claim 1, wherein the reference color determination unit sets, as a reference color, a color having a minimum maximum value among the distortion line amounts of the colors calculated by the distortion line amount calculation unit. Color image forming apparatus.   2. The reference color determining means uses, as a reference color, a color having a minimum sum of maximum values among the distortion line quantities of the respective colors calculated by the distortion line quantity calculating means. The color image forming apparatus described in 1. The distortion amount calculating means further calculates a distortion amount of each color of the plurality of colors with respect to a horizontal reference,
2. The color image forming apparatus according to claim 1, wherein the reference color determination unit sets a color having the least distortion amount relative to the horizontal reference calculated by the distortion amount calculation unit as a reference color.   5. The system according to claim 1, wherein when the amount of distortion lines for the reference color determined by the reference color determination unit exceeds the number of lines determined by the line number determination unit, the fact is notified. The color image forming apparatus according to one. The distortion amount calculating means further calculates a distortion amount of each color of the plurality of colors with respect to a horizontal reference,
The distortion line amount calculation means calculates the distortion line amount of each color of the plurality of colors with respect to the horizontal reference based on the distortion amount of each color of the plurality of colors with respect to the horizontal reference and the resolution in the sub-scanning direction of the input image of the color. Calculate
The distortion correction unit, when the total value of the maximum distortion line amount of each color of the plurality of colors with respect to the horizontal reference calculated by the distortion line amount calculation unit is less than the number of lines that can be stored in the image storage unit, The color image forming apparatus according to claim 1, wherein distortions of all of the plurality of colors with respect to the horizontal reference are corrected.

Images