JP2014059336A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that improves accuracy in correction of the color shift amount, while suppressing reduction of productivity.SOLUTION: Test pattern forming means forms a test pattern image 30 transferred onto a second image carrier together with an image, at an end part in a main scanning direction orthogonal to a direction of movement of the second image carrier outside an image formation area where an image is formed by a first image carrier. Control means corrects color shift in the image formation area from a detection result of the test pattern image and pre-stored writing information related to characteristics of a writing position inside and outside of the image formation area in the second image carrier, so as to improve accuracy of color shift correction.

Description

  The present invention relates to an image forming apparatus.

  Image adjustments such as misalignment correction and density correction in multifunction devices (MFP: Multi Function Peripherals) that contain multiple functions such as copiers, copiers, fax machines, and printers in a single housing This is done by forming a test pattern image with toner on an intermediate transfer belt and detecting it with a sensor (see, for example, Patent Document 1).

  Since normal image printing cannot be performed while performing such image adjustment, if image adjustment is frequently performed, the time during which the printing operation cannot be performed for image adjustment, so-called downtime, increases, and the apparatus There was a problem that productivity was lowered. As a method for reducing downtime, a test pattern image is formed outside the image forming area of the intermediate transfer belt at the end in the main scanning direction perpendicular to the conveyance direction of the intermediate transfer belt in parallel with image printing. The method of detecting it is known. Thus, image adjustment (color shift correction) can be performed in real time while printing an image.

  Therefore, Patent Document 2 discloses a configuration in which a test pattern image is formed outside the maximum sheet area allowed by the image forming apparatus.

  However, since the test pattern image is formed outside the maximum paper area allowed by the image forming apparatus in the configuration disclosed in Patent Document 2, it is possible to correct color misregistration in parallel with image printing. However, since the test pattern image is formed only at the end in the main scanning direction outside the image forming area on the intermediate transfer belt, the amount of color misregistration in the image forming area serving as the printing area cannot be detected. . Therefore, there is a problem that the accuracy of correction of the color misregistration amount is not sufficiently high.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus capable of improving the accuracy of color misregistration correction while suppressing a decrease in productivity.

  In order to solve the above-described problems and achieve the object, the present invention provides a second method in which an image formed on a first image carrier is moved to a transfer position facing the first image carrier. A first transfer unit that obtains an image by superimposing and transferring the image on the image bearing member, and a second transfer unit that transfers the image transferred and formed on the second image bearing member to a transfer material; A test pattern image transferred together with the image on the second image carrier is outside the image forming area where the image is formed by the first image carrier and the second image. Based on the test pattern forming means formed at the end in the main scanning direction orthogonal to the moving direction of the carrier, the test pattern detecting means configured to detect the test pattern image, and the detection result of the test pattern image And a control means for correcting the image forming conditions of the image. In the image forming apparatus, the control means includes the detection result of the test pattern image, and the writing information relating to the characteristics of the writing position inside and outside the image forming area in the second image bearing body stored in advance. The color shift in the image forming area is corrected.

  According to the present invention, the test pattern forming means transfers the test pattern image transferred together with the image onto the second image carrier, outside the image forming area where the image is formed by the first image carrier. Therefore, since it is formed at the end portion in the main scanning direction orthogonal to the moving direction of the second image carrier, so-called down time is not generated, and the decrease in productivity can be suppressed. Then, the control means determines the color in the image forming area from the detection result of the test pattern image and the writing information relating to the characteristics of the writing position inside and outside the image forming area in the second image bearing body stored in advance. Since the shift is corrected, the accuracy of the color shift correction can be improved. Therefore, it is possible to improve the accuracy of correcting the color misregistration amount while suppressing the decrease in productivity.

FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration inside the detection sensor shown in FIG. FIG. 3 is a block diagram illustrating an internal configuration of the detection sensor of the image forming apparatus and a functional configuration that controls processing of data detected by the detection sensor in the control unit of the image forming apparatus and subsequent image writing. FIG. 4 is a diagram illustrating a mark in the positional deviation correction pattern image and a waveform example of a mark detection signal from the detection sensor. FIG. 5 is a diagram illustrating a detection sensor and a set of marks scanned by the detection sensor. FIG. 6 is a diagram illustrating an intermediate transfer belt and a detection sensor in the case of forming a misregistration correction pattern image in parallel with the formation of an image to be transferred onto a sheet. FIG. 7 is a diagram for explaining the bending component of the scanning line. FIG. 8 is a diagram for explaining a color misregistration correction method of the image forming apparatus according to the embodiment of the present invention. FIG. 9 is a diagram for explaining another example of color misregistration correction performed by the image forming apparatus according to the embodiment of the present invention. FIG. 10 is a block diagram showing a hardware configuration of the image forming apparatus according to the embodiment of the present invention.

  Exemplary embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. An image forming apparatus 100 exemplified here is an image processing apparatus including, for example, a facsimile apparatus, a printing apparatus (printer), a copying machine, and a multifunction peripheral, and an optical apparatus 101 including optical elements such as a semiconductor laser light source and a polygon mirror; For example, the image forming unit 102 includes a drum-shaped photoreceptor (also referred to as “photoreceptor drum”), a charger, a developing unit, and the like, and a transfer unit 103 including an intermediate transfer belt.

  The optical device 101 deflects light beams BM emitted from a plurality of light sources (not shown), which are semiconductor laser light sources including a laser diode (LD), by a polygon mirror 110 and applies them to scanning lenses 111a and 111b including fθ lenses. Make it incident. The light beams BM are generated in numbers corresponding to yellow (Y), black (K), magenta (M), and cyan (C) images, and are reflected after passing through the scanning lenses 111a and 111b, respectively. Reflected by the mirrors 112y, 112k, 112m, and 112c. For example, the yellow light beam Y passes through the scanning lens 111a, is reflected by the reflecting mirror 112y, and enters the WTL lens 113y. The same applies to the light beams K, M, and C of black, magenta, and cyan, and thus the description thereof is omitted.

  The WTL lenses 113y, 113k, 113m, and 113c reshape each of the incident light beams Y, K, M, and C, and then each of the light beams Y, K, M, and C to the reflecting mirrors 114y, 114k, 114m, and 114c. C is deflected. The light beams Y, K, M, and C are further reflected by reflection mirrors 115y, 115k, 115m, and 115c, and are used as light beams Y, K, M, and C for exposure, respectively. (Also called a body) 120y, 120k, 120m, and 120c are image-wise irradiated.

  Irradiation of the light beams Y, K, M, and C to the photoconductors 120y, 120k, 120m, and 120c is performed using a plurality of optical elements as described above, and thus the photoconductors 120y, 120k, 120m, and 120c are irradiated. Timing synchronization is performed in the main scanning direction and the sub-scanning direction. Hereinafter, the main scanning direction with respect to the photoconductors 120y, 120k, 120m, and 120c is defined as a light beam scanning direction, that is, a direction orthogonal to a conveyance direction of an intermediate transfer belt described later, and the sub-scanning direction is defined with respect to the main scanning direction. Are defined as directions in which the photoconductors 120y, 120k, 120m, and 120c rotate (intermediate transfer belt conveyance direction described later).

  The photoreceptors 120y, 120k, 120m, and 120c include a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum. The photoconductive layers are disposed corresponding to the photoreceptors 120y, 120k, 120m, and 120c, respectively, and surface charges are applied by the chargers 122y, 122k, 122m, and 122c including the corotron, the scorotron, or the charging roller. Is done.

  The electrostatic charges imparted on the photoreceptors 120y, 120k, 120m, and 120c by the respective chargers 122y, 122k, 122m, and 122c are imagewise exposed by the light beams Y, K, M, and C, respectively. As a result, electrostatic latent images are formed on the scanned surfaces of the photoconductors 120y, 120k, 120m, and 120c.

  The electrostatic latent images formed on the scanned surfaces of the photoreceptors 120y, 120k, 120m, and 120c are respectively developed by developing units 121y, 121k, 121m, and 121c including a developing sleeve, a developer supply roller, and a regulating blade. Is done. As a result, developer images are formed on the scanned surfaces of the photoreceptors 120y, 120k, 120m, and 120c.

  The developers carried on the scanned surfaces of the photoconductors 120y, 120k, 120m, and 120c are transported by the primary transfer rollers 132y, 132k, 132m, and 132c to the photoconductors 120y, 120k, 120m, and 120c. The image is transferred onto the intermediate transfer belt 130 moving in the direction of arrow D by 131b and 131c.

  The intermediate transfer belt 130 is conveyed to the secondary transfer section while carrying Y, K, M, and C developers transferred from the scanned surfaces of the photoreceptors 120y, 120k, 120m, and 120c, respectively.

  The secondary transfer unit includes a secondary transfer belt 133 and conveying rollers 134a and 134b. The secondary transfer belt 133 is conveyed in the direction of arrow E by the conveyance rollers 134a and 134b. A sheet P, which is a transfer material such as high-quality paper or a plastic sheet, is supplied to the secondary transfer unit from a sheet storage unit T such as a paper feed cassette by a conveyance roller 135. The secondary transfer unit applies a secondary transfer bias to transfer the multicolor developer image carried on the intermediate transfer belt 130 onto the sheet P held on the secondary transfer belt 133 by suction. The sheet P is supplied to the fixing device 136 along with the conveyance of the secondary transfer belt 133. The fixing device 136 includes a fixing member 137 such as a fixing roller containing silicone rubber, fluorine rubber or the like, pressurizes and heats the paper P and the multicolor developer image, and the paper P is discharged by the paper discharge roller 138. Is discharged to the outside of the image forming apparatus 100 as a printed matter P ′.

  After the multicolor developer image is transferred, the intermediate transfer belt 130 is supplied to the next image forming process after the transfer residual developer is removed by a cleaning unit 139 including a cleaning blade.

  In the vicinity of the transport roller 131a, test pattern images for correcting image forming conditions when forming a color image on the intermediate transfer belt 130 ("test pattern image for correcting misalignment", "test pattern image for correcting density"). Are included, three detection sensors 5a, 5b, 5c are provided.

  The test pattern image is formed on the intermediate transfer belt 130 together with the color image. As the detection sensors 5a, 5b, and 5c, reflection type detection sensors each including a known reflection type photo sensor may be used. Based on the detection results of the detection sensors 5a, 5b, and 5c, various deviation amounts including skew (inclination) of each color with respect to the reference color, main scanning registration deviation amount, sub-scanning registration deviation amount, and main scanning magnification error are calculated. Based on the calculation results, various misalignment amounts relating to image quality adjustment are corrected, and image forming conditions (position misalignment correction, density correction) for forming a color image on the intermediate transfer belt 130 are corrected, and image adjustment is performed. Various processes related to the generation of the test pattern image are executed.

  FIG. 2 is a diagram showing a schematic configuration inside the detection sensor 5a shown in FIG. Although only the detection sensor 5a is shown in FIG. 2, since the internal configuration of each of the detection sensors 5a, 5b, and 5c is common, the description of the detection sensors 5b and 5c is omitted.

  The detection sensor 5a includes one light emitting unit 10a, two light receiving units 11a and 12a, and a condenser lens 13a. The light emitting unit 10a is a light emitting element that generates light, for example, an infrared LED that generates infrared light. The light receiving unit 11a is, for example, a regular reflection type light receiving element, and the light receiving unit 12a is, for example, a diffuse reflection type light receiving element.

  In the detection sensor 5a, the light L1 emitted from the light emitting unit 10a passes through the condenser lens 13a and then reaches a test pattern image (not shown) of the intermediate transfer belt 130. A part of the light is specularly reflected by the test pattern forming region and the toner layer of the test pattern forming region to become specularly reflected light L2, and then retransmits through the condenser lens 13a and is received by the light receiving unit 11a. The The other part of the light is diffusely reflected by the test pattern forming region and the toner layer in the test pattern forming region to become diffusely reflected light L3, and then re-transmitted through the condenser lens 13a and received by the light receiving unit 12a. Is done.

  As the light emitting element, a laser element or the like may be used instead of the infrared LED. In addition, as the light receiving portions 11a and 12a (regular reflection type light receiving element, diffuse reflection type light receiving element), a phototransistor is used, but a phototransistor or an amplifier circuit may be used.

  FIG. 3 shows the internal configuration of the detection sensors 5a, 5b, and 5c of the image forming apparatus 100, and functions for processing data detected by the detection sensors 5a, 5b, and 5c in the control unit of the image forming apparatus 100 and subsequent image writing. It is a block diagram which shows a structure.

  The detection sensors 5a, 5b, and 5c of the image forming apparatus 100 include light emitting units 10a, 10b, and 10c and light receiving units 11a, 11b, 11c, 12a, 12b, and 12c, respectively. In FIG. 3, the condenser lenses 13a, 13b, and 13c shown in FIG. 2 are not shown.

  The control unit of the image forming apparatus 100 includes a CPU 1, a ROM 2, a RAM 3, an I / O (input / output) port 4, and a light emission amount control as functional units related to processing of data detected by the detection sensors 5 a, 5 b, 5 c. Units 14a, 14b, 14c, amplification units (AMP) 15a, 15b, 15c, filter units 16a, 16b, 16c, A / D (analog / digital) conversion units 17a, 17b, 17c, FIFO (First-In First-Out) ) Memory units 18a, 18b, 18c and sampling control units 19a, 19b, 19c are provided. The control unit of the image forming apparatus 100 includes a writing control unit 6, a controller 7, and a light source lighting control unit 8 as functional units related to image writing after the above processing.

  The ROM 2 includes a correction process for correcting image forming conditions when a color image is formed on the intermediate transfer belt 130, and a positional shift amount for calculating a positional shift amount in the main scanning direction when forming a pattern image on the intermediate transfer belt 130. Various programs for controlling the image forming apparatus 100 are stored, including a program composed of procedures executed by the CPU 1 to perform various processes including a calculation process and a pattern image correction process.

  The CPU 1 monitors detection signals from the light receiving portions 11a, 11b, and 11c at an appropriate timing, and emits light so that it can be reliably detected even when the conveyance belt and the light emitting portions 10a, 10b, and 10c are deteriorated. The amount of light emission is controlled by the amount control units 14a, 14b, and 14c so that the level of the light reception signal from the light reception units 11a, 11b, and 11c is always constant. The RAM 3 is an NVRAM, for example, and stores various parameters.

  Next, processing of data detected by the detection sensors 5a, 5b, and 5c will be described with reference to FIG.

  The CPU 1 executes a program stored in the ROM 2 using the RAM 3 as a work area, and controls the light emission amount control units 14a, 14b, and 14c via the I / O port 4 when detecting a test pattern image that will be described in detail later. A light beam having a predetermined light amount is emitted from each of the light emitting units 10a, 10b, and 10c of the detection sensors 5a, 5b, and 5c.

  First, the light beam emitted from the light emitting unit 10a of the detection sensor 5a will be described. The light beam is applied to the test pattern image, and the reflected light is received by the light receiving units 11a and 12a of the detection sensor 5a. The light receiving units 11a and 12a send data signals corresponding to the amounts of received light beams to the amplification unit 15a. The amplifying unit 15a amplifies the data signal and sends it to the filter unit 16a. The filter unit 16a passes only the signal component of line detection in the output signal of the amplification unit 15a and sends it to the A / D conversion unit 17a. The A / D converter 17a converts the output signal of the filter 16a from analog data to digital data. The sampling control unit 19a samples the digital data converted by the A / D conversion unit 17a and stores the sampled data in the FIFO memory unit 18a.

  Similarly, the sampled digital data is stored in the FIFO memory unit 18b for the data signals obtained from the light receiving units 11b and 12b of the detection sensor 5b, and obtained from the light receiving units 11c and 12c of the detection sensor 5c. For the data signal, the sampled digital data is stored in the FIFO memory unit 18c.

  After the detection of the test pattern image is completed in this way, the digital data stored in the FIFO memory units 18a, 18b, and 18c are loaded into the CPU 1 and the RAM 3 by the data bus via the I / O port 4, The CPU 1 executes a program stored in the ROM 2 to perform predetermined calculation processing for each data, and to perform correction processing for correcting image forming conditions when forming a color image on the intermediate transfer belt 130, intermediate transfer Various processes including a positional deviation amount calculation process for calculating a positional deviation amount in the main scanning direction when forming a pattern image on the belt 130 and a pattern image correction process are executed.

  As described above, the CPU 1 and the ROM 2 control the overall operation of the image forming apparatus 100 and function as a control unit that controls processing of data detected by the detection sensors 5a, 5b, and 5c. It fulfills the functions of calculation means and pattern image correction means. It also functions as a means for invalidating the pattern image correction means.

  Thereafter, the CPU 1 performs setting of the writing start timing, setting of changing the pixel clock frequency, and the like for the writing control unit 6 based on the calculated correction amount.

  The writing control unit 6 includes a device that can set the output frequency very finely, for example, a clock generator using a VCO (Voltage Controlled Oscillator), and uses this output as an image clock. The writing control unit 6 drives the light source lighting control unit 8 in accordance with the image data sent from the controller 7 based on the pixel clock, thereby causing the light source to output the light beam BM (see FIG. 1). To write an image.

  Next, a case where a pattern image for correcting misalignment is used as a test pattern image will be described. FIG. 4 is a diagram illustrating a mark in the positional deviation correction pattern image and a waveform example of a mark detection signal from the detection sensor.

  The misregistration correction pattern image is a set of marks of a predetermined pattern for alignment for specular reflection light, and one set of marks 30 includes Y, K, M, and C as shown in FIG. A horizontal line pattern (hereinafter also referred to as a horizontal pattern) and an oblique line pattern (hereinafter also referred to as an oblique pattern) formed in order are included. Eight sets of such marks 30 arranged in the sub-scanning direction are arranged in three rows in the main scanning direction so as to correspond to the detection sensors 5a, 5b, and 5c, thereby obtaining a positional deviation correction pattern image. As will be described later, two sets of marks 30 arranged in the sub-scanning direction may be arranged in two rows in the main scanning direction corresponding to the detection sensors 5a and 5c.

  The horizontal line patterns are four horizontal patterns having a predetermined width and a predetermined length in the horizontal direction with respect to the main scanning direction of the photoconductors 120y, 120k, 120m, and 120c. The diagonal line patterns are four diagonal patterns having a predetermined width and a predetermined length with a predetermined inclination angle (for example, 45 °) with respect to the main scanning direction of the photoconductors 120y, 120k, 120m, and 120c. . This misalignment correction pattern image forms 8 sets × 3 rows of horizontal line patterns and diagonal line patterns corresponding to the colors Y, K, M, and C on the photoconductors 120y, 120k, 120m, and 120c, respectively. By transferring onto the transfer belt 130, it is formed on the intermediate transfer belt 130 in the arrangement as shown in FIG. 4.

  Dotted lines 31a, 31b, and 31c shown in FIG. 4 indicate trajectories that the central portions of the detection sensors 5a, 5b, and 5c scan in the sub-scanning direction on the intermediate transfer belt 130, respectively. FIG. 4 shows an example of an ideal trajectory in which the center portion of each of the detection sensors 5a, 5b, 5c passes through the center portion of the positional deviation correction pattern image.

  FIG. 4 shows an example in which a horizontal line pattern and a diagonal line pattern are formed on the intermediate transfer belt 130 so as to be arranged in the order of Y, K, M, and C from the beginning in the transport direction of the intermediate transfer belt 130. The color lines of the horizontal line pattern and the diagonal line pattern may be arranged in other ways.

  Then, the three mark rows of the misregistration correction pattern image formed on the intermediate transfer belt 130 are detected by the detection sensors 5a, 5b, and 5c arranged in the main scanning direction, respectively.

  A waveform 140 shown in FIG. 4 shows an example of a change in the detection level (detection signal) when the detection sensor 5a detects the mark 30 of the misalignment correction pattern image shown in FIG. In addition, since the same waveform is obtained also about the other detection sensors 5b and 5c, illustration is abbreviate | omitted.

  Since the detection sensors 5a, 5b, and 5c detect the intermediate transfer belt 130 in portions other than the horizontal line pattern and the diagonal line pattern, for example, when the intermediate transfer belt 130 is white, if the detection level is a reference level, a colored horizontal line is detected. The detection level decreases at the pattern and the diagonal line pattern.

  The threshold voltage level (voltage value) indicated by a broken line 141 in FIG. 4 is a horizontal line where a level drop is observed exceeding the threshold voltage value even when the detection level is lowered due to contamination of the intermediate transfer belt 130 or the like. This is a threshold set for detecting a pattern or a diagonal line pattern.

  The detection sensors 5a, 5b, and 5c detect the positions of the horizontal line patterns and the diagonal line patterns for eight sets of the positional deviation correction pattern images, and based on the detection results, the other colors for the reference color (for example, black: K) are detected. Color (yellow: Y, cyan: C, magenta: M) skew, main scanning registration deviation, sub-scanning registration deviation, and main scanning magnification error are measured. Based on this measured value, the amount of deviation between the center position of the detection sensors 5a, 5b, 5c and the center position of the position deviation correction pattern image is obtained, and the position deviation amount referred to when the next position deviation correction pattern image is formed. Remember as. In addition, correction values for various deviation amounts of skew, main scanning registration deviation amount, sub-scanning registration deviation amount, and main scanning magnification error can be obtained.

  Furthermore, if the detection sensor 5a, 5b, 5c detects the mark row for three rows and calculates the average value of the respective detection results, the skew, sub-scanning registration deviation amount, main scanning registration deviation amount and By obtaining the amount of deviation of the main scanning magnification error, the amount of deviation of each color can be obtained with high accuracy, and by correcting the amount of deviation, a high-quality image with extremely little deviation of each color can be formed. Even when two mark rows are detected by the detection sensors 5a and 5c, an average value of the respective detection results may be calculated.

  Various misregistration amounts, correction amount calculation and correction execution commands are performed by a known correction amount calculation unit (not shown). Then, the misalignment correction pattern image that has been detected is removed by the cleaning unit 139 in FIG.

  A specific method for calculating various misregistration amounts when the misregistration correction pattern image shown in FIG. 4 is detected will be described with reference to FIG. FIG. 5 is a diagram showing the detection sensor 5a and a set of marks 30 scanned by the detection sensor 5a. Here, the case where the detection sensor 5a detects the mark 30 of the misalignment correction pattern image will be described, but the same applies to the other detection sensors 5b and 5c.

  The detection sensor 5a detects the horizontal line pattern and the diagonal line pattern of the positional deviation correction pattern image at predetermined sampling intervals and notifies the CPU 1 of FIG. When the CPU 1 receives notifications of detection of the horizontal line pattern and the diagonal line pattern from the detection sensor 5a one after another, the diagonal lines corresponding to the horizontal line patterns and between the horizontal line patterns based on the detection notification interval and the sampling time interval, respectively. Calculate the distance to the pattern. In this way, the lengths between the horizontal line patterns of the same color in the set of marks 30 and the diagonal line patterns corresponding to the horizontal line patterns are obtained, and the obtained lengths are compared. Thus, various misalignment amounts can be calculated.

  For example, in calculating the sub-scanning registration shift amount (color shift amount in the sub-scan direction), a horizontal line pattern is used, and the interval values (y1,1) between the reference color (K) and each pattern of the target color (Y, M, C) are used. m1, c1) is calculated and compared with an ideal interval value (y0, m0, c0) stored in advance, (interval value y1-ideal interval value y0), (interval value m1-ideal interval value) m0) and (interval value c1−ideal interval value c0), the positional deviation amount of the target color (Y, M, C) with respect to the reference color (K) can be calculated.

  In calculating the main scanning registration misregistration amount (color misregistration amount in the main scanning direction), first, the interval values (y2, k2, m2, c2) between the horizontal line pattern and the diagonal line pattern of each color of K, Y, M, and C are used. ) Is calculated. Using the calculated interval value, a difference value between the interval value of the reference color (K) and the interval value of the non-reference color is calculated. The difference value corresponds to the amount of positional deviation in the main scanning direction. This is because the diagonal line pattern is inclined by a predetermined angle with respect to the main scanning direction, and therefore when the deviation occurs in the main scanning direction, the interval between the horizontal line pattern is wider than the interval for other colors. This is to narrow or narrow. That is, the positional deviation amounts in the main scanning direction of black and yellow, black and magenta, and black and cyan are (interval value k2−interval value y2), (interval value k2−interval value m2), and (interval value k2−interval value). calculated in c2). In this way, it is possible to acquire the registration deviation amounts in the sub-scanning direction and the main scanning direction.

  Furthermore, the skew and the main scanning magnification error can be obtained based on the detection results of the different detection sensors 5a, 5b, and 5c. First, in the calculation of the skew component, for example, the skew component can be obtained by calculating the difference between the sub-scanning registration deviation amounts respectively detected by the detection sensor 5a and the detection sensor 5c. Further, the magnification error deviation can be calculated by calculating the difference between the main scanning registration deviation amounts of the detection sensor 5a and the detection sensor 5b and between the detection sensor 5b and the detection sensor 5c. Then, based on the various misregistration amounts acquired as described above, correction processing for correcting image forming conditions when a color image is formed on the intermediate transfer belt 130 is executed.

  For example, the correction processing is performed by adjusting the light emission timings of the light beams Y, K, M, and C with respect to the photoconductors 120y, 120k, 120m, and 120c so that the positional deviation amounts substantially coincide. It can also be performed by adjusting the tilt of a reflection mirror (not shown) that reflects the light beam. The tilt of the reflecting mirror is adjusted by driving a stepping motor (not shown). Note that the amount of misalignment can be corrected by changing the image data. In this way, it is possible to acquire the registration deviation amounts in the sub-scanning direction and the main scanning direction.

  Next, a mode in which a misregistration correction pattern image is formed on the intermediate transfer belt 130 and detected by a detection sensor will be described.

  FIG. 6 is a diagram illustrating the intermediate transfer belt 130 and the detection sensors 5a, 5b, and 5c in the case of forming a positional deviation correction pattern image in parallel with the formation of the image to be transferred onto the paper P.

  Here, an image to be transferred to the paper P is formed in the image forming area P1 on the intermediate transfer belt 130. The image forming area P1 is set according to the paper P to be transferred, and here is A4 horizontal size. Here, the intermediate transfer belt 130 has a width W wider than the width W1 in the main scanning direction of the image forming region P1 having an A4 horizontal size as the width in the main scanning direction. As a result, in the intermediate transfer belt 130, areas where the image to be transferred onto the paper P is not formed, that is, end areas A1 and A2 outside the image forming area, are located outside the image forming area P1 in the main scanning direction. Will exist. The widths of the end regions A1 and A2 in the main scanning direction are equal as long as the image forming region P1 is centered in the main scanning direction of the intermediate transfer belt 130, but may be different.

  The positions of the end regions A1 and A2 in the main scanning direction correspond to the arrangement of the detection sensors 5a and 5c. Therefore, in the end regions A1 and A2, in parallel with the image formation in the image formation region P1, the marks 30 are formed as the misalignment correction pattern image by 8 sets × 2 rows. In this case, detection / correction amount calculation / correction of misregistration is performed using correction pattern images formed on the end portions A1 and A2 over the image forming region P1. Note that four sets of marks are formed in the end region on one side of one image forming region, but the number of sets formed may be changed according to the size of the image forming region. On the other hand, a position deviation correction pattern image is not formed at a position corresponding to the detection sensor 5b overlapping the image forming area P1.

  Also, the formation of the misregistration correction pattern image is started at a predetermined execution timing while the image forming area is continuously formed on the intermediate transfer belt 130. This execution timing is, for example, a timing when continuous printing is performed for 10 pages or more, or when the temperature at a predetermined location in the image forming apparatus 100 is increased by 1 ° C. or more from the reference value.

  In this way, by forming the misalignment correction pattern image in parallel with the formation of the image to be transferred onto the paper P, a so-called downtime is not generated, and a decrease in productivity can be suppressed.

  By the way, as described above, the image formation is performed by scanning the laser diode (LD) beam along the main scanning direction. However, as shown in FIG. 7, the image is curved in the sub scanning direction due to the characteristics of the optical system in the optical device 101. It has a characteristic, so-called scanning line bending. FIG. 7 shows an example of a characteristic A and a characteristic B each having a curve of the scanning line in a different direction. It is known that if the scanning lines of different colors have such curves of the characteristic A and the characteristic B, the image is deteriorated due to a significant color shift.

  In the image forming apparatus 100 according to the embodiment of the present invention, write information is stored in advance in the RAM 3 which is a storage unit. This writing information relates to the characteristics of the writing position inside and outside the image forming area on the intermediate transfer belt 130.

  Hereinafter, an example of color misregistration correction performed by the image forming apparatus 100 will be described. As shown in FIG. 8A, description will be made assuming that the Bk color (A) and the Ma color (B) have the bending components of the characteristics A and B shown in FIG.

  In FIG. 8A, the deviation m1 in the sub-scanning direction of the writing position at the Bk color (A) image center and the deviation in the sub-scanning direction of the writing position at the Ma color (B) image center. The quantity n1 is stored in the RAM 3 as a characteristic value of the writing position. The deviations m1 and n1 are obtained by measuring the beam positions output from the optical device 101 at a plurality of points on the main scanning and calculating the bending amount based on the measurement results. is there. For example, when measuring three points, that is, two image edge portions and one image center portion, (beam sub-scan position at the center of the image)-{(beam position sub-scan position at the right edge of the image) + (image The beam sub-scanning position at the left end)} / 2.

  When the deviations m1 and n1 are not taken into account, as shown in FIG. 8B, only the detection results of the detection sensors 5a and 5c outside the image forming area are used for sub-scanning registration correction, and the correction value is Thus, the value is such that the shift amount calculated from the color shift amount d1 at the detection sensor 5c and the color shift amount d2 at the detection sensor 5a is corrected. For example, the write control unit 6 corrects a correction value: − (d1 + d2) / 2 that corrects the shift amount of (d1 + d2) / 2.

  However, in such a case, the correction at the edge of the image can be performed with high accuracy, but a large color shift remains in the center of the image, and the accuracy of the color shift correction as the entire image is sufficiently high. It's not expensive.

  On the other hand, in the image forming apparatus 100, color misregistration correction is performed using the misregistration amounts m1 and n1 stored in the RAM 3 and the test pattern detection result. For example, as shown in FIG. 8C, using the test pattern detection results d1 and d2 and the shift amounts m1 and n1, the color shift amount is (d1 + d2) / 2− (m1 + n1) / 2. The write control unit 6 corrects the calculated correction value −− ((d1 + d2) / 2− (m1 + n1) / 2} for correcting the deviation amount.

  As a result, even if the entire image is viewed, there is no portion where a large color shift occurs, and an image with a relatively good color shift can be obtained.

  As described above, according to the image forming apparatus 100 according to the embodiment of the present invention, the misalignment correction pattern image is formed in parallel with the formation of the image to be transferred onto the paper P, thereby generating a so-called downtime. No reduction in productivity can be suppressed. In addition, writing information relating to the characteristics of the writing position inside and outside the image forming area on the intermediate transfer belt 130 is stored in the RAM 3 in advance, and color misregistration correction is performed using the writing information and the test pattern detection result. Therefore, the accuracy of color misregistration correction can be improved. Therefore, it is possible to improve the accuracy of correction of the color misregistration amount while suppressing a decrease in productivity.

  FIG. 9 is a diagram for explaining another example of color misregistration correction performed by the image forming apparatus 100 according to the embodiment of the present invention. Also in this example, description will be made assuming that the Bk color (A) and the Ma color (B) have the bending components of the characteristics A and B shown in FIG.

  In FIG. 9A, the writing position sub-scanning amount m1 at the center of the Bk color (A) image and the writing position sub-scanning direction shift amount m2 at predetermined locations on both sides thereof. , M3, the shift amount n1 of the writing position at the center of the Ma color (b) image in the sub-scanning direction, and the shift amounts n2 and n3 of the writing position at the predetermined positions on both sides of the writing position. The characteristic value of the writing position is stored in the RAM 3. For such deviations m1, m2, m3, n1, n2, and n3, the beam position output from the optical device 101 is measured at a plurality of points on the main scan, and the bending amount is calculated based on the measurement result. This is what was sought after.

  As shown in FIG. 9B, when the main scanning width of the transfer paper P2 is A3 (W2: 297 mm), in the image forming apparatus 100, the shift amount m1, stored in the RAM 3, is stored. Color misregistration correction is performed using n1 and the test pattern detection result. For example, using the test pattern detection results d1 and d2 and the shift amounts m1 and n1, the color shift amount is calculated as (d1 + d2) / 2− (m1 + n1) / 2, and the shift amount is corrected. Correction value:-{(d1 + d2) / 2- (m1 + n1) / 2} is corrected by the writing control unit 6.

  On the other hand, as shown in FIG. 9C, when the main scanning width of the transfer paper P3 is A4 (W3: 210 mm), in the image forming apparatus 100, the shift amount m1, stored in the RAM 3, is stored. Color misregistration correction is performed using m2, m2, n1, n2, and n3 and the test pattern detection result. For example, using the test pattern detection results d1 and d2 and the shift amounts m1, m2, m3, n1, n2, and n3, the color shift amount is (d1 + d2) / 2-[{m1- (m2 + n3) / 2. } + {N1− (n2 + n3) / 2}] / 2, and a correction value for correcting this deviation amount: − [(d1 + d2) / 2 − [{m1− (m2 + n3) / 2} + {n1 − (N2 + n3) / 2}] / 2] is corrected by the writing control unit 6.

  By changing the correction amount according to the size of the transfer paper to be output in this way, it is possible to perform color misregistration correction with good accuracy according to the transfer paper.

  In the image forming apparatus 100 according to the embodiment of the present invention described above, the writing information relating to the characteristics of the writing position is obtained by measuring the beam position output from the optical device 101 at a plurality of points on the main scanning. However, in the present invention, an actual image is output, and a characteristic value is detected by a reading device such as a scanner, although it has been described that it is obtained by calculating the amount of bending based on the measurement result. Also good. According to this, even when the optical characteristics of the apparatus change with time, it is possible to output an image and correct the characteristic value, and as a result, it is possible to improve the accuracy of color misregistration correction.

  Even when the image is not actually output, the accuracy of color misregistration correction can be improved by correcting the characteristic value of the stored writing information based on the temperature characteristic of the writing position.

  FIG. 10 is a block diagram illustrating a hardware configuration of the image forming apparatus according to the present embodiment. As shown in the figure, the image forming apparatus 100 has a configuration in which a controller 10 and an engine unit (Engine) 60 are connected by a PCI (Peripheral Component Interface) bus. The controller 10 is a controller that controls the entire image forming apparatus 100 and controls drawing, communication, and input from an operation unit (not shown). The engine unit 60 is a printer engine or the like that can be connected to a PCI bus, and is, for example, a monochrome plotter, a one-drum color plotter, a four-drum color plotter, a scanner, or a fax unit. The engine unit 60 includes an image processing part such as error diffusion and gamma conversion in addition to a so-called engine part such as a plotter.

  The controller 10 includes a CPU 1, a north bridge (NB) 13, a system memory (MEM-P) 12, a south bridge (SB) 14, a local memory (MEM-C) 17, and an ASIC (Application Specific Integrated Circuit). 16 and a hard disk drive (HDD) 18, and the north bridge (NB) 13 and the ASIC 16 are connected by an AGP (Accelerated Graphics Port) bus 15. The MEM-P 12 further includes a ROM 2 and a RAM 3.

  The CPU 1 performs overall control of the image forming apparatus 100, has a chip set including the NB 13, the MEM-P 12, and the SB 14, and is connected to other devices via the chip set.

  The NB 13 is a bridge for connecting the CPU 1 to the MEM-P 12, SB 14, and AGP 15, and includes a memory controller that controls reading and writing to the MEM-P 12, a PCI master, and an AGP target.

  The MEM-P 12 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, a drawing memory for printers, and the like, and includes a ROM 2 and a RAM 3. The ROM 2 is a read-only memory used as a program and data storage memory, and the RAM 3 is a writable and readable memory used as a program and data development memory, a printer drawing memory, and the like.

  The SB 14 is a bridge for connecting the NB 13 to a PCI device and peripheral devices. The SB 14 is connected to the NB 13 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 16 is an image processing application IC (Integrated Circuit) having hardware elements for image processing, and has a role of a bridge for connecting the AGP 15, the PCI bus, the HDD 18, and the MEM-C 17. The ASIC 16 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 16, a memory controller that controls the MEM-C 17, and a plurality of DMACs (Direct Memory) that rotate image data using hardware logic. Access Controller) and a PCI unit that performs data transfer between the engine unit 60 via the PCI bus. An FCU (Facsimile Control Unit) 30, USB (Universal Serial Bus) 40, and IEEE 1394 (the Institute of Electrical and Electronics Engineers 1394) interface 50 are connected to the ASIC 16 via a PCI bus. The operation display unit 20 is directly connected to the ASIC 16.

  The MEM-C 17 is a local memory used as an image buffer for copying and a code buffer, and an HDD (Hard Disk Drive) 18 is a storage for storing image data, programs, font data, and forms. It is.

  The AGP 15 is a bus interface for a graphics accelerator card proposed for speeding up graphics processing. The AGP 15 speeds up the graphics accelerator card by directly accessing the MEM-P 12 with high throughput. .

  In the above embodiment, the image forming apparatus according to the present invention has been described as an example in which the image forming apparatus is applied to a multifunction machine having at least two functions among a copy function, a printer function, a scanner function, and a facsimile function. The present invention can be applied to any image forming apparatus such as a scanner apparatus and a facsimile apparatus.

1 CPU
2 ROM
3 RAM
4 I / O ports 5a, 5b, 5c Detection sensor 6 Write control unit 7 Controller 8 Light source lighting control unit 100 Image forming device 101 Optical device 102 Image forming unit 103 Transfer unit 120y, 120k, 120m, 120c Photoconductor 130 Intermediate transfer belt

Japanese Patent No. 4359199 JP-A-8-6347

Claims (5)

A first image is obtained by superimposing and transferring an image formed on the first image carrier on a second image carrier that moves at a transfer position facing the first image carrier. Transfer means,
Second transfer means for transferring an image transferred and formed on the second image bearing member onto a transfer material;
A test pattern image transferred together with the image on the second image carrier is outside the image forming area where the image is formed by the first image carrier and the second image carrier. Test pattern forming means formed at the end of the main scanning direction orthogonal to the moving direction of the body;
Test pattern detection means configured to detect the test pattern image;
An image forming apparatus comprising: control means for correcting an image forming condition of the image based on a detection result of the test pattern image;
The control means is configured to detect the test pattern image and write information relating to the characteristics of the writing position inside and outside the image forming area in the second image carrier stored in advance. An image forming apparatus that corrects a color misregistration in the apparatus.   The characteristic value of the writing position included in the writing information relates to a difference in writing position along the moving direction of the second image carrier in and out of the image forming area. The image forming apparatus according to claim 1.   The characteristic value of the writing position included in the writing information is a light beam by an optical device that outputs a light beam to the first image carrier when the image is formed on the first image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is obtained by measuring the position of the image forming apparatus.   The characteristic value of the writing position included in the writing information relates to a bending amount of the writing position along the moving direction of the second image bearing body inside and outside the image forming area. The image forming apparatus according to claim 1.   The control unit corrects color misregistration in the image forming area according to a width of the image formed on the second image carrier in the main scanning direction. Item 5. The image forming apparatus according to any one of Items 1 to 4.

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