JP2008299311A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily correct color misalignment of an image and the absolute position of the image. <P>SOLUTION: This image forming apparatus includes a pattern forming means for forming a predetermined pattern for correcting a position shift of the image, and a detecting means for detecting the pattern for correcting the position shift of the image formed by the pattern forming means. A measuring means measures a time until detecting the pattern for correcting the position shift of the image from a signal for controlling the timing to start image formation (S13, S14). An image forming position is controlled based on the time until detecting the pattern for correcting the position shift of the image from the signal for controlling the timing to start image formation measured by the measuring means (S15-S18). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, such as a copying machine, a printer, a FAX, and a printing machine (including all colors), which are characterized by alignment control of a color image created by superimposing a plurality of color images. .

    In a color image forming apparatus that forms a multi-color image, unlike a black and white image, the images of each color are overlapped. Therefore, if the image position of each color is shifted, the color of the line drawing or character changes, or the color shift or image unevenness occurs. (Color unevenness) occurs. The occurrence of such deviation and unevenness leads to a decrease in image quality. Therefore, it is necessary to match the image positions of the respective colors as much as possible. For this reason, in an image forming apparatus that forms a color image using a plurality of photoconductors, a technology that corrects misregistration between colors caused by various factors such as changes in environmental temperature and changes in internal temperature. Is described in Patent Document 1, for example.

  In the invention described in Patent Document 1, an image position deviation correction pattern of each color is formed on a transfer belt, the correction patterns are detected by a plurality of sensors, and a deviation amount, for example, main scanning, is detected based on signals from the sensors. Directional magnification, main scanning, and sub-scanning resists are detected, and deviations between colors are corrected. Thereby, it is possible to correct not only the environmental change but also the positional shift due to the change with the passage of time, and to obtain a high-quality image without color shift.

JP 2004-295083 A

  In the technique described in Patent Document 1, since the amount of misregistration of other colors with respect to the reference color is detected and the misregistration is corrected, the misregistration between colors due to environmental changes and changes with time can be corrected. However, since the image position of the reference color also changes with the environment and time, the absolute position of the image changes with the environment and time. For example, even if the absolute position of the image is adjusted at the time of shipment from the factory, the image position may subsequently shift, or the image position may change between the first image and the image after outputting a plurality of images. is there. The same can be said for the deviation of the absolute position of the image in the image forming apparatus that forms a monochrome (monochrome) image.

  In addition, for correction of misregistration between colors, it is necessary to form an image misregistration correction pattern for each color. However, during continuous printing, it is necessary to form a pattern in a limited time (distance). May not be formed. If the time (distance) is increased for pattern formation, the printing speed is reduced, which is not preferable.

  The present invention has been made in view of the above, and an object thereof is to provide an image forming apparatus and an image forming method capable of easily correcting an image shift between colors and an absolute position of an image. To do.

In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention includes a pattern forming unit that forms a misregistration correction pattern for image misregistration correction on an image carrier, and a formation A detection unit that detects the misregistration correction pattern, a measurement unit that measures a time until the misregistration correction pattern is detected from a signal that controls timing of image formation start, and an image based on the time And a control unit for controlling the formation position.
The present invention also relates to an image forming method executed by the image forming apparatus.

  According to the present invention, the image forming position is controlled based on the time from the measured signal for controlling the start of image formation to the detection of the misregistration correction pattern. There is an effect that the position can be easily corrected.

Exemplary embodiments of an image forming apparatus and an image forming method according to the present invention are explained in detail below with reference to the accompanying drawings.
(Embodiment 1)

  FIG. 1 is a schematic configuration diagram illustrating a main part of the image forming apparatus according to the first embodiment. In FIG. 1, a light beam scanning device (optical unit) 1 configured as an optical unit includes a laser diode (hereinafter referred to as LD) that is turned on based on image data, and a laser beam (hereinafter referred to as light beam) emitted from the LD. A collimating lens (not shown) that converts the light into a parallel light beam, a cylinder lens (not shown) that focuses in a line parallel to the sub-scanning direction, and a polygon mirror 101 that receives light from the cylinder lens and deflects the light. A polygon motor 102 that rotationally drives the polygon mirror 101 at a high speed, an fθ lens 103 that converts a constant angular velocity scanning of the light beam deflected by the polygon mirror 101 into a uniform velocity scanning, a BTL 104, and a folding mirror 105 are included. With such a configuration, the light beam emitted from the LD is collimated by a collimator lens (not shown), passes through the cylinder lens, is deflected by the polygon mirror 101 rotated by the polygon motor 102, and passes through the fθ lens 103 and the BTL 104. Then, the light is reflected by the folding mirror 105 and scanned on the photosensitive member 106. BTL is an abbreviation for Barrel Toroidal Lens, and has a function of performing focusing in the sub-scanning direction (condensing function and position correction in the sub-scanning direction (surface tilt, etc.)).

  Around the photoconductor 106, a charger 107, a developing unit 108, a transfer unit 109, a cleaning unit 110, and a static eliminator 111 are arranged, and these constitute an image forming means, and charging, which is a normal electrophotographic process, An image is formed on the recording paper P by exposure, development, and transfer. Then, the image is fixed on the recording paper P by a fixing device (not shown).

  In addition, a sensor 12 is provided for detecting a pattern for correcting an image position deviation on the transfer belt 10 (hereinafter referred to as a “position deviation correction pattern”). The sensor 12 is a reflection type optical sensor, is disposed so as to face the transfer belt 10, and detects a misregistration correction pattern formed on the transfer belt 10. A printer control unit 201 described later corrects the image position in the sub-scanning direction based on the detection result.

  FIG. 2 is a diagram illustrating a schematic configuration of an image formation control unit in the image forming apparatus according to the first embodiment. In the figure, a light beam scanning device and an image formation control unit are shown. As a control system, a printer control unit 201, a pixel clock generation unit 202, a synchronization detection lighting control unit 204, an LD control unit 205, a polygon motor drive control unit 206, and a writing start position control unit 209 are provided. Although there is one printer control unit 201 for a plurality of colors, each of the plurality of colors has the same one. The pixel clock generator 202 further includes a reference clock generator 2021, a VCO (Voltage Controlled Oscillator) clock generator 2022, and a phase-synchronized clock generator 2023. Further, a synchronization detection sensor 127 for detecting the light beam is provided on the image writing side at the end of the light beam scanning device 1 in the main scanning direction, and the light beam transmitted through the fθ lens 103 is reflected by the mirror 131 as described above. The light is condensed by the lens 132 and enters the synchronous detection sensor 127. Further, the write start position control unit 209 receives the start side synchronization detection signal XDETP from the synchronization sensor 127 and the pixel clock PCLK from the pixel clock generation unit 202.

  In the light beam scanning device 1 configured as described above, when the light beam passes over the synchronization detection sensor 127, the synchronization detection signal XDETP is output from the synchronization detection sensor 127, and the pixel clock generation unit 202 and the synchronization detection lighting are turned on. The data is sent to the control unit 204 and the writing start position control unit 209, respectively. The pixel clock generation unit 202 generates a pixel clock PCLK that is synchronized with the synchronization detection signal XDETP, and sends it to the LD control unit 205 and the synchronization detection lighting control unit 204.

  The pixel clock generation unit 202 includes a reference clock generation unit 2021, a VCO (Voltage Controlled Oscillator) clock generation unit 2022, and a phase synchronization clock generation unit 2023.

  FIG. 3 is a block diagram illustrating details of the VCO clock generation unit (PLL circuit: Phase Locked Loop) 2022 of the pixel clock generation unit 202. As can be seen from the figure, the VCO clock generator 2022 inputs the reference clock signal FREF from the reference clock generator 2021 and a signal obtained by dividing VCLK by N by the 1 / N divider 20221 to the phase comparator 20222. The phase comparator 20222 compares the falling edges of both signals and outputs an error component at a constant current. Then, an unnecessary high-frequency component and noise are removed by an LPF (low-pass filter) 20223 and sent to the VCO 20224. The VCO 20224 outputs an oscillation frequency depending on the output of the LPF 20223. Accordingly, the frequency of VCLK can be changed by variably controlling the frequency of FREF and the frequency division ratio N from the printer control unit 201. The phase synchronization clock generation unit 2023 generates a pixel clock PCLK synchronized with the synchronization detection signal XDETP from VCLK generated by the VCO clock generation unit 2022.

  The synchronization detection lighting control unit 204 first turns on the LD forced lighting signal BD to forcibly light the LD in order to detect the synchronization detection signal XDETP. However, after detecting the synchronization detection signal XDETP, the synchronization detection signal XDETP is detected. Using the XDETP and the pixel clock PCLK, the LD is turned on at a timing at which the synchronization detection signal XDETP can be reliably detected without causing flare light, and the LD is turned off when the synchronization detection signal XDETP is detected. A signal BD is generated and sent to the LD control unit 205.

  The LD control unit 205 controls the lighting of the LD according to the image data synchronized with the synchronous detection forced lighting signal BD and the pixel clock PCLK. Then, a laser beam is emitted from the LD unit 122, reflected by the mirror surface of the polygon mirror 101, deflected, passes through the fθ lens 103, and scans on the photosensitive member 106.

  The polygon motor control unit 206 controls the rotation of the polygon motor 102 at a specified number of rotations based on a control signal from the printer control unit 201.

  The writing start position control unit 209 includes a main scanning gate signal XLGATE for determining an image writing start timing and an image width, a sub-scanning gate based on a synchronization detection signal XDETP, a pixel clock PCLK, a control signal from the printer control unit 201, and the like. A signal XFGATE is generated. XLGATE is a signal that becomes ‘L’ by the image width in the main scanning direction, and XFGATE is a signal that becomes ‘L’ by the image width in the sub-scanning direction.

  The first sensor 12 that detects the misregistration correction pattern is a light reflection type optical sensor, and image pattern information detected by the sensor 12 is sent to the printer control unit 201. The printer control unit 201 calculates a positional deviation amount based on the image pattern information, generates correction data (setting value) from the positional deviation amount, and stores it in the correction data storage unit 207. The correction data storage unit 207 stores correction data for correcting image position deviation and magnification deviation, that is, data for determining the timing of the XLGATE and XFGATE signals, and data for determining the frequency of the pixel clock PCLK. In accordance with an instruction from the control unit 201, correction data is set in each control unit. The operation panel 208 sends key operation content and input content on the operation panel 208 to the printer control unit 201, and the printer control unit 201 performs control according to the content.

  FIG. 4 is a block diagram showing the configuration of the writing start position control unit. The writing start position control unit 209 includes a main scanning line synchronization signal generation unit 2091, a main scanning gate signal generation unit 2092, and a sub scanning gate signal generation unit 2093. The main scanning line synchronization signal generator 2091 generates a signal XLSYNC for operating the main scanning counter 20921 in the main scanning gate signal generator 2092 and the sub scanning counter 20931 in the sub scanning gate signal generator 2093. The main scanning gate signal generation unit 2092 generates a signal XLGATE that determines the image signal capture timing (image writing timing in the main scanning direction). The sub-scanning gate signal generation unit 2093 generates a signal XFGATE that determines the image signal capture timing (image writing timing in the sub-scanning direction).

  The main scanning gate signal generation unit 2092 compares the counter value of the main scanning counter 20921 operating with XLSYNC and PCLK, the main scanning counter 20921 and the setting value 1 (correction data) from the printer control unit 201, and outputs the result. And a gate signal generation unit 20923 that generates XLGATE from the comparison result of the comparator 20922.

  The sub-scanning gate signal generation unit 2093 includes a control signal from the printer control unit 201, a sub-scanning counter 20931 operated by XLSYNC and PCLK, a counter value of the sub-scanning counter 20931, and a set value 2 (correction data) from the printer control unit 201. ) And outputs a result thereof, and a gate signal generation unit 20933 that generates XFGATE from the comparison result of the comparator 20932.

  The writing start position control unit 209 can correct the writing position in units of one cycle of the clock PCLK for main scanning, that is, in units of one dot, and in sub scanning, in units of one cycle of XLSYNC, that is, in units of one line. Both the main scanning correction data (setting value 1) and the sub scanning correction data (setting value 2) are stored in the correction data storage unit 207.

  FIG. 5 is a timing chart showing the output timing of each signal of the writing start position control unit (main scanning direction) 209. In this figure, the main scanning counter 20921 is reset by XLSYNC, and is counted up by PCLK. When the counter value becomes the set value 1 (in this case, “X”) set by the printer control unit 201, the comparator 20922 The comparison result is output, and XLGATE is set to “L” (valid) by the gate signal generation unit 20923. XLGATE maintains 'L' for the image width in the main scanning direction.

FIG. 6 is a timing chart showing the output timing of each signal of the writing start position control unit (sub-scanning direction) 209. In the figure, the sub-scanning counter 20931 is reset by a control signal (image writing start trigger signal) and is counted up by XLSYNC, which is different from the output timing of the writing start position control unit in the main scanning direction of FIG. Yes. When the counter value reaches the set value 2 (in this case, “Y”) set by the printer control unit 201, the comparison result is output from the comparator 20932, and XFGATE is set to “L” (valid) by the gate signal generation unit 20933. )become. XFGATE maintains 'L' for the image width in the sub-scanning direction.
That is, the writing start position in either the main scanning direction or the sub-scanning direction is determined based on the synchronization signal, not the control signal that is an asynchronous signal.

  FIG. 7 is a diagram illustrating the configuration of the previous stage of the image formation control unit that outputs the image data to the LD control unit 205. In FIG. 7, a line memory 210 is provided in the previous stage. The line memory 210 is configured so that image data captured from a printer controller, a frame memory, a scanner, or the like at the timing of XFGATE is output in synchronization with PCLK only during the period when XLGATE is 'L'. . The output image data is sent to the LD control unit 205, and the LD is turned on at that timing.

  FIG. 8 is a diagram showing a misregistration correction pattern formed on the transfer belt 10. In the present embodiment, the misalignment correction pattern PN forms a horizontal line image on the transfer belt 10 at a preset timing, and the horizontal line image is detected by the sensor 12 as the transfer belt 10 moves in the direction of the arrow. And sent to the printer controller.

  FIG. 9 is a timing chart showing the detection timing of the misregistration correction pattern shown in FIG. The detection timing of the misregistration correction pattern corresponds to the time T until the misregistration correction pattern is detected from the misregistration correction pattern write start signal XFGATE, and this time T is measured and used as the detection timing.

  FIG. 10 is a flowchart showing a processing procedure of image misregistration correction in the present embodiment. In the figure, first, correction data (setting value) stored in the correction data storage unit 207 is set in each control unit (step S11). Here, correction data for the sub-scanning image position, the main-scanning image position, and the main-scanning image magnification determined by the previous correction operation are set. If the correction has never been performed, the initial value (default value set in advance) is obtained. After the setting, a misregistration correction pattern PN shown in FIG. 8 is formed on the transfer belt 10 (step S12), and the misregistration correction pattern PN is detected by the sensor 12 (step S13). From the detected misregistration correction pattern PN, the printer control unit 201 measures the time T from the misregistration correction pattern write start signal XFGATE to the misregistration correction pattern detection (step S14).

  Next, the time T is compared with a prestored reference time T0 (step S15) to determine whether or not to correct (step S16). This determination is performed when the deviation amount is 1/2 or more of the correction resolution. In the case of correction (step S16-Y), correction data is calculated (step S17), and the correction data is stored in the correction data storage unit 207 (step S18). Here, the correction data, that is, the number of lines to be corrected is calculated from the time difference between the time T and the reference time T0, the transfer belt conveyance speed, and the writing density in the sub-scanning direction. This correction data is used in the next image forming operation. The correction data here is a set value of the XFGATE signal that determines the image position in the sub-scanning direction. If correction is not performed, the correction data is not updated.

  This correction processing operation may be performed before the start of the image forming operation, or may be performed between pages during continuous printing. In addition, as shown in FIG. 9, the detection time of the misregistration correction pattern may be calculated by calculating the midpoint of the sensor output and measuring the time by detecting the edge of the misregistration correction pattern. You may do it.

  As for the reference value T0, the time T when the image position is correct may be stored as the reference value T0. For example, the time T is measured when the image position is adjusted at the time of shipment from the factory, and the time is used as a reference. What is necessary is just to memorize | store as value T0.

  The reference value can be changed. Therefore, a mode for measuring the reference value T0 is provided so that the reference value can be easily changed. FIG. 11 is a flowchart showing the procedure for measuring the reference value. In this processing procedure, for example, a reference value is acquired by giving a measurement instruction from the operation panel 208. Also in this processing procedure, the correction data stored in the correction data storage unit 207 is set in each control unit in the same manner as the image misalignment correction process shown in FIG. 10 (step S21). This sets correction data for the sub-scanning image position determined by the previous correction operation, the main-scanning image position, and the main-scanning image magnification. If the correction has never been performed, the initial value (default value set in advance) is obtained. After the setting, the misregistration correction pattern shown in FIG. 8 is formed on the transfer belt (step S22), and the misregistration correction pattern is detected by the sensor 12 (step S23). Based on the detection data from the sensor 12, the printer control unit 201 measures a time T from the write start signal XFGATE for the misalignment correction pattern to the detection of the misalignment correction pattern (step S24), and this time T is used as a reference. Store as time T0 (step S25). The reference value T0 is used in the image misalignment correction operation performed after this operation. Thereby, the reference value T0 can be easily changed.

As described above, according to the present embodiment, the following effects can be obtained. That is, according to the present embodiment, the absolute position of the image can be corrected by an easy means. Further, according to the present embodiment, it is possible to easily cope with a shift in image position due to replacement of a unit. Further, according to the present embodiment, it is possible to correct an image shift between colors that occurs over time.
(Embodiment 2)

  FIG. 12 is a perspective view showing a schematic configuration of an image forming unit of a 4-drum type color image forming apparatus according to the second embodiment, here, a direct transfer type tandem type image forming apparatus. This image forming apparatus includes four sets of image forming units, that is, four image forming units in order to form a color image in which four color images of yellow (Y), magenta (M), cyan (C), and black (BK) are superimposed. A photoconductor 106, a developing unit 108, a charger 107, a transfer unit 109, a cleaning unit 110 (see FIG. 1) and four sets of light beam scanning devices 1 are provided. This method is a so-called tandem type in which four image forming apparatuses shown in FIG. 1 are arranged. The first color image is formed on the recording paper P conveyed in the direction of the arrow by the transfer belt 10, and The second, third, and fourth colors are transferred in this order to form a color image in which the four color images are superimposed on the recording paper, and the image on the recording paper is fixed by a fixing device (not shown). The image forming units for the respective colors are as described with reference to FIG. 1, and the light beam scanning device 1 is provided with the same colors as those shown in the first embodiment.

  In the present embodiment, the first and second sensors 12 and 13 are provided to detect the misalignment correction pattern. The first and second sensors 12 and 13 are both reflective optical sensors, which detect misalignment correction patterns (horizontal line patterns and diagonal line patterns) formed on the transfer belt 10, and based on the detection results. The image position of each color, the main scanning direction between each color, the image position shift in the sub-scanning direction, and the image magnification in the main scanning direction are corrected.

  FIG. 13 is a diagram illustrating a schematic configuration of an image formation control unit in the image forming apparatus according to the second embodiment. The image forming apparatus according to the second embodiment is different from the image forming apparatus according to the first embodiment in that two sensors for detecting a misregistration correction pattern are provided. Others are the same. However, elements other than the printer control unit 201, the correction data storage unit 207, the first sensor 12, the second sensor 13, and the operation panel are individually provided for each color.

  FIG. 14A is a diagram illustrating a relationship between the positional deviation correction pattern formed on the intermediate transfer belt 10 and the sensor. The first and second sensors 12 and 13 detect misregistration correction patterns (horizontal line patterns and diagonal line patterns) PN1, PN2, PN3, and PN4 formed on the transfer belt 10, and based on the detection results, the printer The control unit 201 corrects image position shifts and magnification errors between the colors in the main scanning direction and the sub-scanning direction. The misregistration correction patterns PN1, PN2, PN3, and PN4 are formed at predetermined intervals in the sub-scanning direction as shown in FIG. These misregistration correction patterns PN1, PN2, PN3, and PN4 have a predetermined length in the main scanning direction, and horizontal line patterns BK1, C1, M1, Y1, BK3, and C3 formed at both ends of the transfer belt 10, respectively. , M3, Y3, and oblique line patterns BK2, formed in a sub-scanning direction of the pattern group and downstream of the transfer belt 10 in the rotation direction with an inclination of 45 ° with respect to the longitudinal direction (rotation direction) of the transfer belt. Includes C2, M2, Y2, BK4, C4, M4, Y4. Misalignment correction patterns BK1, C1, M1, Y1, BK2, C2, M2, Y2 formed at one end by the first sensor 12 are detected, and misalignment formed at the other end by the second sensor 13 Correction patterns BK3, C3, M3, Y3, BK4, C4, M4, Y4 are detected.

  That is, when the intermediate transfer belt 10 moves in the direction of the arrow, horizontal line patterns BK1, C1, M1, Y1, BK3, C3, M3, Y3, diagonal line patterns BK2, C2, M2, Y2, BK4, C4 of each color. M4 and Y4 are detected by the first and second sensors 12 and 13, respectively, and the printer control unit 201 calculates the shift amount (time) of each color with respect to the BK pattern. The detection timing of the oblique line pattern changes when the image position and image magnification in the main scanning direction shift, and the detection timing of the horizontal line pattern changes when the image position in the sub scanning direction shifts.

FIG. 14B is a diagram for explaining calculation of the magnification error in the main scanning direction. Specifically, with respect to the main scanning direction, the time from the pattern BK1 to the pattern BK2 is used as a reference, and the time from the positional deviation correction pattern C1 to the pattern C2 is compared to obtain the deviation TBKC12. Is compared with the time of the pattern C3 to the pattern C4, and the deviation TBKC34 is obtained.
TBKC34-TBKC12
Is a magnification error of the cyan image with respect to the black image, and therefore the frequency of the pixel clock is changed by an amount corresponding to the magnification error. Further, the subtraction of the time change (correction) due to the magnification error correction at the position of the first sensor 12 from the TBKC 12 obtained as described above is the main scanning deviation of the cyan image with respect to the black image, and the deviation amount. The timing of the XLGATE signal for determining the writing start timing is changed by an amount corresponding to. The same applies to magenta and yellow.

In the sub-scanning direction, assuming that the ideal time is Tc, the time from the pattern BK1 to the positional deviation correction pattern C1 is TBKC1, and the time from the pattern BK3 to the positional deviation correction pattern C3 is TBKC3.
((TBKC3 + TBKC1) / 2) -Tc
Becomes a sub-scanning deviation of the cyan image with respect to the black image, and the timing of the XFGATE signal for determining the writing start timing is changed by an amount corresponding to the amount. The same applies to magenta and yellow.

  FIG. 15 shows misregistration correction patterns PN5 and PN6 formed on the transfer belt 10. In FIG. These patterns PN5 and PN6 are patterns for measuring the reference time T0 used for correcting the image position of each color in the sub-scanning direction, and are the same as the horizontal line patterns PN1 and PN3 shown in FIG.

  FIG. 16 is a timing chart showing the detection timing of the misregistration correction pattern shown in FIG. The printer control unit 201 measures times Ty, Tm, Tc, and Tbk from the write start signals XFGATE_Y, XFGATE_M, XFGATE_C, and XFGATE_BK of each color misregistration correction pattern to the detection of the corresponding image misregistration correction pattern for each color. To do.

  FIG. 17 is a flowchart showing a processing procedure for measuring the reference time. In this flowchart, first, correction data stored in the correction data storage unit 207 is set in each control unit (step S31). As in the first embodiment, this is the correction data of the main scanning image position, sub-scanning image position, main scanning image magnification determined by the previous correction operation, or the initial value (preliminary if no correction has been performed). Default value). After the setting, misalignment correction patterns PN1, PN2, PN3, and PN4 shown in FIG. 14 are formed on the transfer belt 10 (step S32). The formed misregistration correction patterns PN1, PN2, PN3, and PN4 are detected by the first and second sensors 12 and 13 (step S33), and the misregistration amount of each color with respect to black is calculated by the printer control unit 201 ( Step S34). The printer control unit 201 determines whether or not to correct based on the calculated deviation amount (step S35). Here, correction is performed if the deviation amount is ½ or more of the correction resolution.

  When the correction is made (step S35-Y), the correction data is calculated (step S36), the calculated correction data is stored (step S37), and the correction data is set in each control unit (step S38). The correction data here includes a set value of a pixel clock frequency that determines an image magnification in the main scanning direction, a set value of an XLGATE signal that determines an image position in the main scanning direction, and an XFGATE signal that determines an image position in the sub scanning direction. Is the set value. If correction is not performed, the correction data is not updated.

  Next, misregistration correction patterns PN5 and PN6 shown in FIG. 15 are formed on the transfer belt 10 (step S39), and the patterns PN5 and PN6 are detected by the first and second sensors 12 and 13 (step S40). . The printer control unit 201 measures the time Ty, Tm, Tc, and Tbk from the write start signal XFGATE_Y, XFGATE_M, XFGATE_C, and XFGATE_BK of each color misregistration correction pattern to the detection of the corresponding misregistration correction pattern for each color. (Step S40a). In the present embodiment, since there are two sensors, the first and second sensors 12 and 13, the average value of both outputs is calculated and stored in the correction data storage unit 207 as the reference value T0 (step S40b).

  As for pattern detection, as shown in FIG. 16, the time may be measured by calculating the midpoint of the sensor output, or the time may be measured by detecting the edge of the pattern.

  FIG. 18 is a diagram showing a misalignment correction pattern formed between sheets. In the example of FIG. 18, the process of the flowchart shown in FIG. 17 is completed, and there is no deviation between the colors, and the reference time is stored, and the page is formed between pages (intermediate paper) during continuous printing. The contents of the patterns PN5 and PN6 are the same as the patterns PN5 and PN6 shown in FIG.

  FIG. 19 is a flowchart showing a processing procedure of image misalignment correction processing. The processing shown in this flowchart is executed during image formation. In the figure, first, correction data stored in the correction data storage unit 207 is set in each control unit (step S41). Also in this case, as in steps S101 and S201, the main scanning image position, sub-scanning image position, main scanning image magnification correction data determined by the previous correction operation, or the initial value (if no correction has been performed). Default value set in advance). After the setting, the image forming operation is started (step S42). After the image writing for the first page (first sheet) is completed, the misalignment correction patterns PN5 and PN6 shown in FIG. 18 are formed on the transfer belt 10 (step S43), and the first and second sensors 12, 13 detects a pattern (step S44).

  When the pattern is detected, the printer control unit 201 takes time from detection of the write start signals XFGATE_Y, XFGATE_M, XFGATE_C, and XFGATE_BK of the color misregistration correction patterns PN5 and PN6 to the corresponding color misregistration correction patterns. Ty, Tm, Tc, and Tbk are measured (step S45) and compared with the reference value T0 of each color stored in the correction data storage unit 207 (step S46) to determine whether or not to correct (step S47). . Here, correction is performed if the deviation amount is ½ or more of the correction resolution.

  When correcting (step S47-Y), the correction data is calculated (step S48), the correction data is stored (step S49), and the correction data is set (step S50). The correction data here is a set value of the XFGATE signal that determines the image position of each color in the sub-scanning direction. If correction is not performed, the correction data is not updated. If there is a next page (step S51: Yes), an image forming operation is performed, and the formation, detection, measurement, and correction of the misalignment correction patterns PN5 and PN6 are repeated.

  In the present embodiment, the formation, detection, measurement, and correction of the misalignment correction patterns PN5 and PN6 are performed between pages, but the present invention is not limited to this. For example, it may be performed every 100 sheets. Of course, the number setting may be changed on the operation panel or the like. In the flowchart of FIG. 19, the correction data is reflected on the image of the next page. However, if the correction cannot be made in time for the image formation of the next page, the correction data will be reflected several images later. It becomes from.

  Furthermore, in the misregistration correction patterns PN5 and PN6 shown in FIG. 18, patterns for four colors are formed between pages, but any of one to three colors may be used. When the misregistration correction pattern is formed in this way, the color to be formed is changed for each page, and the time is measured only for the formed color.

As described above, according to the present embodiment, in addition to the same effects as those of the first embodiment, not only the image shift between the colors but also the absolute position of the image can be corrected by an easy means. Play.
(Embodiment 3)

  This embodiment does not use the misalignment correction pattern for measuring the reference time T0 shown in FIG. 15 with respect to the second embodiment, but uses the horizontal line pattern of the misalignment correction pattern in FIG. It is designed to measure. That is, in this example, the reference time T0 is measured using the misregistration correction patterns PN1 and PN3 without using the misregistration correction patterns PN5 and PN6. Except for this point, the image forming apparatus, the light beam scanning apparatus, The image formation control unit, the misregistration correction pattern, and the image misregistration correction procedure are the same as those in the second embodiment.

  FIG. 20 is a flowchart showing a processing procedure of reference time measurement in the third embodiment. In this flowchart, first, correction data stored in the correction data storage unit 207 is set in each control unit (step S61). This setting is the same as steps S11, S31, and S41. After the setting, misalignment correction patterns PN1 to PN4 shown in FIG. 14 are formed on the transfer belt 10 (step S62), and the patterns PN1 to PN4 are detected by the first and second sensors 12 and 13 (step S63). ). Next, as shown in FIG. 16, the printer control unit 201 performs detection from the write start signals XFGATE_Y, XFGATE_M, XFGATE_C, and XFGATE_BK of the color misregistration correction patterns PN1 and PN3 to the corresponding color misregistration correction patterns. The times Ty, Tm, Tc, and Tbk are measured (step S64). Further, the shift amount of each color with respect to black is calculated (step S65), and it is determined whether or not to correct (step S66). The correction is performed when the amount of deviation is ½ or more of the correction resolution, as in step S16 and step S25.

  When the correction is made (step S64-Y), the correction data is calculated (step S67), the correction data is stored in the correction data storage unit 207 (step S68), and the correction data is set in each control unit. The correction data here includes a set value of a pixel clock frequency that determines an image magnification in the main scanning direction, a set value of an XLGATE signal that determines an image position in the main scanning direction, and an XFGATE signal that determines an image position in the sub scanning direction. Is the set value. If correction is not performed, the correction data is not updated. Next, the reference time T0 of each color is calculated by adding or subtracting the correction value of each color to the measured times Ty, Tm, Tc, Tbk (step S69), and stored in the correction data storage unit 207 (step S70). .

  Since there is no correction data for black BK, the measured value is used as the reference time as it is.

  On the other hand, when the measurement value is used as the correction data for the black BK, the reference time T0 for the black BK is measured and stored in advance. In this case, the time T when the image position is correct may be stored as the reference value T0. For example, the time T is measured when the image position is adjusted at the time of factory shipment, and the time is stored as the reference value T0.

  FIG. 21 is a flowchart showing the processing procedure of the image misalignment correction process at this time. In this flowchart, first, correction data stored in the correction data storage unit 207 is set in each control unit (step S81). This case is also the same as step S61. After the setting, misalignment correction patterns PN1 to PN4 shown in FIG. 14 are formed on the transfer belt 10 (step S82), the patterns are detected by the first and second sensors 12 and 13 (step S83), and printer control is performed. The unit 201 measures a time Tbk from the writing start signal XFGATE_BK of the black BK misregistration correction pattern to the detection of the corresponding black BK misregistration correction pattern (step S84). Further, the shift amount of each color with respect to black BK is calculated (step S85).

  Then, the time Tbk is compared with the reference value T0 (step S86), and it is determined whether to correct the image position of the black BK, whether to correct the image position of each color with respect to the black BK, and the image magnification (step S87). In step S87, if the amount of deviation is ½ or more of the correction resolution, correction is performed.

  When correcting (step S87-Y), correction data is calculated (step S88), and the correction data is stored in the correction data storage unit 207 (step S89). The correction data here includes a set value of a pixel clock frequency that determines an image magnification in the main scanning direction, a set value of an XLGATE signal that determines an image position in the main scanning direction, and an XFGATE signal that determines an image position in the sub scanning direction. Is the set value. When correcting the image position of black BK, it is necessary to add or subtract the correction value to the correction value of each color. If correction is not performed, the correction data is not updated.

  When the measurement value is used as the black BK correction data in this way, a mode in which the measurement value is used as the black BK correction data can be set from the operation panel 208. As a result, the reference value can be easily changed. The reference value measurement procedure is the same as the flowchart of FIG. 11 in the second embodiment.

  The correction data stored in the correction data storage unit 207 is set in each control unit during the image forming operation.

  In this embodiment, a direct transfer type tandem image forming apparatus is exemplified as the color image forming apparatus, but each color image formed on the YMCK photoconductor 106 is superimposed on the intermediate transfer belt. Needless to say, the present invention can also be applied to an indirect transfer tandem image forming apparatus that forms a full-color image and transfers the full-color image to a recording sheet at a time to form an image.

  As described above, according to the present embodiment, in addition to the same effects as those of Embodiments 1 and 2, there is an effect that the correction time in the positional deviation correction can be reduced.

  It should be noted that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to Embodiment 1. FIG. 2 is a diagram illustrating a schematic configuration of an image formation control unit in the image forming apparatus according to Embodiment 1. FIG. 3 is a block diagram illustrating details of a VCO clock generation unit of a pixel clock generation unit in Embodiment 1. FIG. It is a block diagram which shows the structure of the writing start position control part in FIG. 5 is a timing chart showing the output timing of each signal in the main scanning direction of the writing start position control unit of FIG. 4. 5 is a timing chart showing the output timing of each signal in the sub-scanning direction of the writing start position control unit of FIG. 4. It is a figure which shows the structure of the front | former stage of the image formation control part which outputs image data to LD control part. FIG. 4 is a diagram illustrating a misregistration correction pattern formed on a transfer belt. FIG. 9 is a timing chart showing detection timing of the misalignment correction pattern shown in FIG. 8. FIG. 4 is a flowchart illustrating a processing procedure for image misregistration correction in the first embodiment. 3 is a flowchart illustrating a reference value measurement processing procedure according to the first embodiment. 6 is a perspective view illustrating a schematic configuration of an image forming unit of a tandem image forming apparatus of a direct transfer system according to Embodiment 2. FIG. 6 is a diagram illustrating a schematic configuration of an image formation control unit in an image forming apparatus in an image forming apparatus according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a relationship between a positional deviation correction pattern formed on an intermediate transfer belt and a sensor in Embodiment 2. It is a figure for demonstrating calculation of the magnification error of the above-mentioned main scanning direction. FIG. 6 is a diagram illustrating a misregistration correction pattern for measuring a reference time formed on an intermediate transfer belt in Embodiment 2. FIG. 16 is a timing chart showing detection timings of the misregistration correction pattern shown in FIG. 15. FIG. 10 is a flowchart illustrating a processing procedure for measuring a reference time in the second embodiment. It is a figure which shows the pattern for position shift correction formed between real paper. 10 is a flowchart illustrating a processing procedure of image misregistration correction processing according to the second embodiment. 10 is a flowchart showing a processing procedure for measuring a reference time in the third embodiment. 10 is a flowchart illustrating a processing procedure of image misalignment correction processing according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light beam scanning device 10 Transfer belt 12,13 Sensor 101 Polygon mirror 103 f (theta) lens 106 Photosensitive drum 107 Charging device 108 Developing unit 109 Transfer device 110 Cleaning unit 111 Electric discharger 122 LD unit 127 Synchronization detection sensor 201 Printer control unit 202 Pixel Clock generation unit 204 Lighting control unit for synchronization detection 205 LD control unit 206 Polygon motor control unit 209 Writing start position control unit PN, PN1, PN2, PN3, PN4, PN5, PN6 Misalignment correction pattern

Claims (13)

A pattern forming unit for forming a misregistration correction pattern for image misregistration correction on the image carrier;
A detection unit for detecting the formed misregistration correction pattern;
A measurement unit for measuring a time from detection of the image formation start timing to detection of the misregistration correction pattern;
A control unit that controls the image forming position based on the time;
An image forming apparatus comprising: A single color image forming unit for forming a single color image for each color, and a color image forming unit for forming a multicolor image by superimposing the single color image;
The image forming apparatus according to claim 1, wherein the pattern forming unit, the detecting unit, and the measuring unit are provided for each color.   The image forming apparatus according to claim 1, wherein the control unit compares a predetermined reference time with the time measured by the measurement unit, and controls the image position based on the comparison result.   The image forming apparatus according to claim 3, wherein the measurement unit measures the reference time when there is an input for instructing measurement of the reference time from the outside. The pattern forming unit forms the misregistration correction pattern for each of a plurality of colors,
The detection unit further includes a correction unit that corrects the positional deviation between the colors based on the detection result of the positional deviation correction pattern for each color,
The control unit controls the measurement unit to measure the reference time immediately after the misalignment correction by the correction unit, and after the misalignment correction, compares the reference time with the time measured by the measurement unit. The image forming apparatus according to claim 3, wherein the image position is controlled from the result. The pattern forming unit forms the misregistration correction pattern for each of a plurality of colors,
The detection unit further includes a correction unit that corrects the positional deviation between the colors based on the detection result of the positional deviation correction pattern for each color,
The control unit calculates the reference time from the time measured by the measurement unit and the correction value calculated by the positional deviation correction when forming the positional deviation correction pattern, and after the positional deviation correction, the reference time and the The image forming apparatus according to claim 3, wherein the image position is controlled based on a comparison result with the measured time.   3. The image formation according to claim 2, wherein the measurement unit measures the time from the signal that controls the timing of starting image formation to the detection of the misregistration correction pattern for only the specific color. apparatus.   The measurement unit determines the time until the correction pattern is detected from a signal for controlling the timing of image formation start during the process of correcting the image positional deviation between the colors by the correction unit, for the specific color. The image forming apparatus according to claim 7, wherein only an image is measured.   The image forming apparatus according to claim 7, wherein the specific color is a reference color for correcting misregistration between colors.   The image forming apparatus according to claim 7, wherein the specific color is black. The color image forming unit includes:
A forming unit that forms a latent image by irradiating image light corresponding to image data onto a rotating or moving image carrier;
A developing unit that is provided for each color and visualizes the latent image;
A transfer unit that forms a multicolor image by transferring the visualized image onto a recording medium to be conveyed;
The image forming apparatus according to claim 2, further comprising: The color image forming unit includes:
A forming unit that forms a latent image by irradiating image light corresponding to image data on the image carrier;
A developing unit that is provided for each color and visualizes the latent image;
A first transfer section that rotates or moves;
A second transfer unit that transfers the visualized image to the first transfer unit, and further transfers the image transferred to the transfer unit onto a recording medium, thereby forming a multicolor image;
The image forming apparatus according to claim 2, further comprising: Forming a misregistration correction pattern for image misregistration correction on the image carrier;
Detecting the formed misregistration correction pattern;
A step of measuring a time from detection of the image formation start timing to detection of the misregistration correction pattern;
Controlling the image forming position based on the time;
An image forming method comprising:

Images