JP2013125108A - Image forming device and color misregistration adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device and a color misregistration adjusting method for adjusting color misregistration without reducing performance of image formation.SOLUTION: The image forming device includes a phase detection sensor for detecting a rotational phase of a photoreceptor drum 3, and a sensor 170 for detecting an image on a transfer belt 61. Periodic functions for approximating deviation from a design value of a line in an adjustment pattern including lines of multiple colors formed on the transfer belt 61 are determined for each color. A small patch 194 including the lines of multiple colors formed on the transfer belt 61 is detected by the sensor 170. A subtraction value between the deviation from the design value of the line in the patch 194 and a value of the periodic function corresponding to the phase of the patch 194 is determined for each color as a correction value. According to the sum of a value of a constant part of the periodic function and the correction value, the timing to form a toner image on a photoreceptor drum 3 is adjusted. Color misregistration can be adjusted between sheets, thereby preventing image formation performance from being reduced.

Description

  The present invention relates to an image forming apparatus and a color misregistration adjustment method capable of adjusting color misregistration in color image formation.

  In recent years, image forming apparatuses capable of forming color images on recording paper have become widespread. Usually, such an image forming apparatus forms a color image on a recording paper using toners of four colors (black, cyan, magenta, and yellow).

  The image forming apparatus includes a photoconductive drum for each color. In image formation, each color toner image is formed on the surface of the photoconductive drum, and these images are sequentially transferred onto an intermediate transfer belt to perform intermediate transfer. A color image is formed on the belt. Thereafter, the color image on the intermediate transfer belt is transferred to the recording paper and fixed on the recording paper by heating and pressurizing processes. As a result, a color image is formed on the recording paper.

  In such image formation, color misregistration occurs in the color image formed on the intermediate transfer belt due to various causes. The color misregistration on the intermediate transfer belt is, for example, that the component dimensions have changed slightly due to replacement of the component parts, or that the component parts (for example, the photosensitive drum, the intermediate transfer belt, etc.) have expanded or contracted due to environmental changes. Is the cause. If color misregistration occurs in the image on the intermediate transfer belt, it is transferred as it is to the recording paper, and a color misaligned image is formed. Therefore, various countermeasures have been studied in order to improve color misregistration.

  For example, Patent Document 1 below discloses a technique for detecting a color shift and correcting the drawing position on the intermediate transfer belt. In Patent Document 1, after forming a color misregistration detection pattern (lines of a plurality of colors) on an intermediate transfer belt, the position of each line of the color misregistration detection pattern is detected by a sensor, and the color is detected based on the detection result. Calculate the amount of deviation.

JP2011-8168A

  However, including Patent Document 1, conventionally, in order to measure a change in the amount of color misregistration (deviation in the paper conveyance direction) due to the eccentricity of the photoconductor drum, the photoconductor drum has one cycle (periphery length) or more. It is necessary to form a long pattern on the intermediate transfer belt, and there is a problem that it takes time for measurement and adjustment.

  In addition, in the case of a job for copying a large amount of originals, the temperature inside the image forming apparatus rises, thereby increasing color misregistration. Therefore, it is desirable to adjust the color misregistration as appropriate during execution of the job. However, in order to perform the adjustment, it is necessary to temporarily interrupt the job, and during that time, there is a problem that image formation cannot be performed and performance is deteriorated. . In addition, when pattern formation, measurement, and adjustment are performed between sheets without interrupting the job, it is necessary to considerably widen the gap between the sheets, and the performance deteriorates.

  Accordingly, an object of the present invention is to provide an image forming apparatus and a color misregistration adjustment method capable of adjusting color misregistration in a short time without degrading image forming performance.

  The above object can be achieved by the following.

  That is, an image forming apparatus according to the present invention includes a predetermined number of photoconductors on which toner images of a predetermined number of colors of two or more are formed, and a transfer unit that transfers the toner image to a recording medium. And a phase detector that detects a reference position of the rotational phase of the photoconductor, and a first design pattern that includes a plurality of lines for each predetermined number of colors and that corresponds to one or more cycles of the rotational phase. A toner image of each color is formed on each photoconductor, and the toner image is transferred onto a transfer unit to form a first transfer image, and positions of lines constituting the first transfer image are defined. Rotation phase that approximates the deviation from the first design pattern of the plurality of lines constituting the first transfer image for each color from the detection result of the image detection unit to be detected and the image detection unit and the phase detection unit Is determined as a variable, and this periodic function is And a transfer image forming unit on the transfer unit based on a second design pattern including a plurality of color lines and corresponding to 1/3 period or less of the rotation phase. A second transfer image is formed, the image detection unit detects the position of each line constituting the second transfer image, and the deviation evaluation unit detects, for each color, the line included in the second transfer image, Calculate the measured deviation, which is the deviation from the second design pattern, calculate the phase of the second transfer image relative to the reference position, and specify the periodic function value corresponding to this phase for each color. The value obtained by subtracting the calculated shift amount from the measured shift amount for each color is determined as a correction value, and a constant of the periodic function is determined for each color. A toner image is formed on the photoconductor according to the value obtained by adding the value of the part and the correction value. To adjust that timing.

  Preferably, the first design pattern is composed of a plurality of second design patterns.

  More preferably, the second design pattern is shorter than the interval between the recording media conveyed adjacently when the transfer of the toner images to the plurality of recording media is continuously performed.

  More preferably, when the transfer of toner images to a plurality of recording media is continuously performed, the transfer image forming unit is not transferred onto the recording medium, and the second transfer image is placed at a predetermined position on the transfer unit. Form.

  Preferably, the periodic function is expressed by α sin θ + β, where θ is the rotational phase, the information specifying the periodic function is α and β, and the value of the constant part of the periodic function is β.

  More preferably, the predetermined number of colors is black, cyan, magenta and yellow, and the second design pattern includes black, cyan, magenta and yellow lines.

  More preferably, the actual measurement is a deviation of the plurality of lines constituting the first transfer image from the first design pattern and a deviation of the lines included in the second transfer image from the second design pattern. The amount of deviation is obtained with reference to the black line.

  In addition, the color misregistration adjustment method according to the present invention includes a predetermined number of photoconductors on which toner images of two or more predetermined colors are formed, and a transfer unit that transfers the toner images to a recording medium. A method for adjusting color misregistration in an apparatus, comprising: a phase detection step for detecting a reference position of a rotational phase of a photoconductor; and a first corresponding to one or more cycles of a rotational phase including a plurality of lines for each predetermined number of colors. Based on the design pattern, a toner image of each color is formed on each of the photoconductors, a step of transferring the toner image onto the transfer hand portion to form a first transfer image, and a first transfer image is formed. From the image detection step for detecting the position of each line and the detection results of the image detection step and the phase detection step, the deviation from the first design pattern of the plurality of lines constituting the first transfer image is approximated for each color. Rotating phase Determining a periodic function as a variable, storing information specifying the periodic function, and a second design pattern including a plurality of color lines and corresponding to 1/3 period or less of the rotational phase; A step of forming a second transfer image on the transfer unit, a step of detecting the position of each line constituting the second transfer image, and a second of the lines included in the second transfer image for each color A step of calculating an actually measured deviation amount that is a deviation from the design pattern, a phase of the second transfer image with respect to the reference position, and a periodic function value corresponding to this phase are specified for each color. A step of calculating using information and determining the amount of calculation deviation, a step of determining, for each color, a value obtained by subtracting the amount of calculation deviation from the actual amount of deviation, and a correction value for each color. Add the constant value and the correction value Depending on the value that is, comprising a step of adjusting the timing of forming a toner image on the photosensitive body.

  According to the present invention, it is possible to adjust color misregistration in a short time. Therefore, the image forming performance is not deteriorated.

  In the present invention, since only one small patch needs to be formed, color misregistration can be adjusted during continuous printing without widening the gap between sheets. Therefore, even when an image is formed continuously for a long time as in the case of copying a large amount of originals, it is possible to appropriately adjust the color misregistration without interrupting the job.

  Further, the amount of toner used for adjustment is small, which is economical.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating a control structure of a program that executes initial adjustment of color misregistration in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a perspective view showing a state in which an adjustment pattern is formed on an intermediate transfer belt. It is a top view which shows the example of the pattern for adjustment. It is a figure which shows one patch in the pattern for adjustment, and its detection signal. It is a perspective view which shows the sensor which detects the rotation state of a photoconductor drum. It is a side view which shows the sensor which detects the rotation state of a photoconductive drum. It is a graph which shows the output signal of the sensor which detects the rotation state of a photoconductor drum. It is a figure which shows the adjustment pattern and the detection signal of the state in which the color shift has not arisen. It is a figure which shows the adjustment pattern and the detection signal of the state which color misalignment has arisen. It is a grab showing a waveform approximating an actual measurement value. It is a figure which shows the relationship between the position of a patch, its detection signal, and the rotation phase of a photoconductor drum. 6 is a flowchart illustrating a control structure of a program for adjusting color misregistration during execution of a print job. FIG. 6 is a perspective view illustrating a state where a patch is formed on an intermediate transfer belt during execution of a print job. FIG. 6 is a diagram illustrating color misregistration that occurs during execution of a print job. FIG. 6 is a diagram illustrating color misregistration adjustment executed during execution of a print job.

  In the following embodiments, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  Referring to FIG. 1, an image forming apparatus 100 according to an embodiment of the present invention forms a multicolor or single color image on a predetermined recording sheet according to image data generated by reading a document. The image forming apparatus 100 includes a main body device 110 and an automatic document feeder (ADF) 120. The main body device 110 includes an optical scanning device 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, a charger 5, an intermediate transfer belt unit 6, a fixing unit 7, a paper feed cassette 81, and a paper discharge tray 91. It is configured. In addition to these, the image forming apparatus 100 also includes components necessary to function as an image forming apparatus.

  An image reading device 90 provided with a document placement table 92 made of transparent glass on which a document is placed is arranged on the upper part of the main body device 110, and an automatic document feeder 120 is attached on the document placement table 92. ing. The automatic document feeder 120 automatically conveys the document on the document table 92. The automatic document feeder 120 is configured to be rotatable in the direction of arrow M, and the document can be placed by hand by opening the document table 92.

  The image data handled in the image forming apparatus 100 is decomposed into color image data using each color of black (K), cyan (C), magenta (M), and yellow (Y), that is, these four color components. Image data. Accordingly, four each of the developing device 2, the photosensitive drum 3, the charger 5, and the cleaner unit 4 are provided so as to form four types of latent images corresponding to the respective colors. Four image stations are configured to process magenta and yellow.

  The charger 5 is a device for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to the charger type as shown in FIG. 1, a contact type roller type or brush type charger is used. Sometimes.

  The optical scanning device 1 is a laser scanning unit (LSU) provided with a laser emitting unit, a reflection mirror, and the like. The optical scanning device 1 includes a polygon mirror that scans a laser beam and optical elements such as a lens and a mirror for guiding the laser light reflected by the polygon mirror to the photosensitive drum 3. As the optical scanning device 1, in addition to such a configuration, for example, an EL or LED writing head in which light emitting elements are arranged in an array can be employed.

  The optical scanning device 1 exposes the charged photosensitive drum 3 according to input image data, thereby forming an electrostatic latent image according to the image data on the surface thereof. The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toner of four colors (YMCK). The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 6 disposed above the photosensitive drum 3 includes an intermediate transfer belt 61, an intermediate transfer belt driving roller 62, an intermediate transfer belt driven roller 63, an intermediate transfer roller 64, and an intermediate transfer belt cleaning unit 65. I have. Four intermediate transfer rollers 64 are provided corresponding to each color of YMCK.

  The intermediate transfer belt driving roller 62, the intermediate transfer belt driven roller 63, and the intermediate transfer roller 64 are driven to rotate while the intermediate transfer belt 61 is stretched. Each intermediate transfer roller 64 supplies a transfer bias described later in order to transfer the toner image on the corresponding photosensitive drum 3 onto the intermediate transfer belt 61.

  The intermediate transfer belt 61 is provided in contact with each photosensitive drum 3. A color toner image (multicolor toner image) is formed on the intermediate transfer belt 61 by sequentially superimposing and transferring the respective color toner images formed on the photosensitive drum 3 onto the intermediate transfer belt 61. The intermediate transfer belt 61 is formed in an endless shape using, for example, a film having a thickness of about 100 μm to 150 μm.

  The toner image is transferred from the photosensitive drum 3 to the intermediate transfer belt 61 by an intermediate transfer roller 64 that is in contact with the back side of the intermediate transfer belt 61. A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 64 in order to transfer the toner image. The intermediate transfer roller 64 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 61. In this embodiment, a roller shape is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the electrostatic images visualized according to the hues on the photosensitive drums 3 are stacked on the intermediate transfer belt 61. The image information (toner density distribution) thus laminated is transferred onto the recording paper by the transfer roller 10 disposed at the contact position between the recording paper and the intermediate transfer belt 61 as the intermediate transfer belt 61 rotates. .

  At this time, the intermediate transfer belt 61 and the transfer roller 10 are pressed against each other at a predetermined nip, and a voltage for transferring the toner onto the recording paper is applied to the transfer roller 10 (what is the toner charging polarity (−))? Reverse polarity (+) high voltage). Further, in order to obtain the nip constantly, either one of the transfer roller 10 and the intermediate transfer belt drive roller 62 is made of a hard material (metal or the like), and the other is made of a soft material such as an elastic roller (elastic rubber roller). , Foaming resin rollers, etc.) are used.

  A first sensor 170 is disposed between the intermediate transfer roller 64 at the final stage and the intermediate transfer belt drive roller 62. The first sensor 170 is disposed on the side where the toner image is formed on the intermediate transfer belt 61. As will be described later, the first sensor 170 is used to detect an adjustment pattern formed on the intermediate transfer belt 61 for detecting and correcting color misregistration.

  Further, as described above, the toner attached to the intermediate transfer belt 61 by contacting the photosensitive drum 3 or the toner remaining on the intermediate transfer belt 61 without being transferred onto the recording paper by the transfer roller 10 is as follows. In order to cause toner color mixing in the process, the toner is removed and collected by the intermediate transfer belt cleaning unit 65. In the intermediate transfer belt cleaning unit 65, for example, a cleaning blade that contacts the intermediate transfer belt 61 is disposed as a cleaning member. The intermediate transfer belt 61 that contacts the cleaning blade is supported by the intermediate transfer belt driven roller 63 from the back side. Has been.

  The paper feed cassette 81 is a tray for storing recording paper used for image formation, and is provided below the optical scanning device 1 of the main body device 110. In addition, recording paper used for image formation can also be placed in the manual paper feed cassette 82. A paper discharge tray 91 provided in the main unit 110 is a tray for collecting printed recording sheets face down, that is, with the printing surface facing down.

  In the main body apparatus 110, the recording paper conveyance path S is set in a substantially vertical direction in order to send the recording paper of the paper feeding cassette 81 and the manual paper feeding cassette 82 to the paper discharge tray 91 via the transfer roller 10 and the fixing unit 7. Is formed. In the vicinity of the recording paper transport path S from the paper feed cassette 81 or the manual paper feed cassette 82 to the paper discharge tray 91, pickup rollers 11a and 11b, a plurality of transport rollers 12a to 12d, a registration roller 13, a transfer roller 10, and A fixing unit 7 and the like are arranged.

  The transport rollers 12 a to 12 d are small rollers for promoting and assisting the transport of the recording paper, and a plurality of transport rollers 12 a to 12 d are provided along the recording paper transport path S. The pickup roller 11 a is arranged near the end of the paper feed cassette 81, picks up recording paper from the paper feed cassette 81 one by one, and supplies it to the recording paper transport path S. Similarly, the pickup roller 11 b is disposed near the end of the manual paper feed cassette 82, picks up recording paper one by one from the manual paper feed cassette 82, and supplies it to the recording paper transport path S.

  The registration roller 13 temporarily holds the recording paper conveyed through the recording paper conveyance path S. Then, the recording paper is conveyed to the transfer roller 10 at the timing when the leading edge of the toner image on the photosensitive drum 3 and the leading edge of the recording paper coincide.

  The fixing unit 7 includes a heat roller 71 and a pressure roller 72. The heat roller 71 and the pressure roller 72 rotate with the recording paper interposed therebetween. Further, the heat roller 71 is set to a predetermined fixing temperature by the control unit based on a signal from a temperature detector (not shown), and by thermocompression bonding the toner to the recording paper together with the pressure roller 72. The multi-color toner image transferred to the recording paper is melted, mixed, and pressed to be thermally fixed to the recording paper. An external heating belt 73 for heating the heat roller 71 from the outside is provided.

  The recording paper conveyance path will be specifically described. As described above, the image forming apparatus 100 is provided with the paper feed cassette 81 that stores recording paper and the manual paper feed cassette 82 in advance. In order to feed the recording paper from these paper feeding cassettes 81 and 82, pickup rollers 11a and 11b are respectively arranged so as to guide the recording paper one by one to the recording paper transport path S.

  The recording paper unloaded from the paper feeding cassettes 81 and 82 is conveyed to the registration roller 13 by the conveying rollers 12a and 12e in the recording paper conveying path S, and the leading edge of the recording paper and the leading edge of the image information on the intermediate transfer belt 61 are connected. The image information is written on the recording paper by being fed into the transfer roller 10 at the matching timing. Thereafter, the recording paper passes through the fixing unit 7, whereby the unfixed toner on the recording paper is melted and fixed by heat, and passes through the conveyance roller 12 b disposed at the end of the recording paper conveyance path S to the discharge tray 91. Discharged.

  The above-mentioned transport path is for a single-sided printing request for recording paper. When double-sided printing is requested, the conveyance roller 12b rotates reversely when the trailing edge of the recording paper that has finished single-sided printing and has passed through the fixing unit 7 as described above is gripped by the final conveyance roller 12b in the conveyance path. By doing so, the recording paper is guided to the transport rollers 12c and 12d. Thereafter, the recording paper is conveyed to the registration roller 13, printed on the back surface of the recording paper in the same manner as described above, and then discharged to the paper discharge tray 91.

  Referring to FIG. 2, the image forming apparatus 100 includes a control unit (hereinafter referred to as a CPU) 130 that controls the entire image forming apparatus 100, a ROM (Read Only Memory) 132 for storing a program and the like, a volatile property, and the like. RAM (Random Access Memory) 134, an HDD (Hard Disk Drive) 136 that is a non-volatile storage device that retains data even when the power supply is interrupted, and a bus 142. The ROM 132 stores programs and data necessary for controlling the operation of the image forming apparatus 100.

  The CPU 130, ROM 132, RAM 134, and HDD 136 are connected to the bus 142. Data (including control information) is exchanged between the units via the bus 142. The CPU 130 reads a program from the ROM 132 onto the RAM 134 via the bus 142, and executes the program using a part of the RAM 134 as a work area. That is, the CPU 130 controls each part of the image forming apparatus 100 according to a program stored in the ROM 132 and realizes each function of the image forming apparatus 100.

  The image forming apparatus 100 includes an image forming unit 150, an image processing unit 152, an image memory 154, and a paper feeding unit 156 in addition to the automatic document feeder 120, the image reading device 90, the operation unit 160, and the first sensor 170 described above. , A second sensor 180, and a timer 190. These are also connected to the bus 142.

  The operation unit 160 receives an input such as an instruction to the image forming apparatus 100 by the user. The operation unit 160 includes an operation panel and an operation key unit (an area other than the operation panel in the operation unit 160). The operation panel 162 includes a display panel configured by a liquid crystal panel and the like, and a touch panel that is disposed on the display panel and detects a touched position. In order to operate the image forming apparatus 100, soft keys are displayed on the display panel, and hard keys are arranged on the operation key unit. The CPU 130 monitors user operations on these keys. The user can press or touch these keys to input an image forming instruction, image forming condition setting, or the like to the image forming apparatus 100. Selection of the key displayed on the display panel is performed by touching a corresponding portion on the touch panel superimposed on the display panel.

  When the user operates the operation unit 160 to instruct image formation, the image data generated by reading the document as described above by the image reading device 90 is temporarily stored in the image memory 154. The image processing unit 152 executes various image processes on the image data stored in the image memory 154. The image data is stored in the HDD 136 as necessary.

  The paper supply unit 156 includes the above-described paper supply cassettes 81 and 82 and holds recording paper for image formation. The image forming unit 150 includes the photosensitive drum 3, the charger 5, the optical scanning device 1, the developing device 2, the transfer roller 10, the fixing unit 7, and the like. The image data read from the image memory 154 or the HDD 136 is As described above, it is formed on the recording paper conveyed from the paper supply unit 156.

  As described above, the first sensor 170 is a sensor for detecting the adjustment pattern formed on the intermediate transfer belt 61 in order to correct the color misregistration. The first sensor 170 is, for example, an optical sensor that includes a light emitting unit and a light receiving unit.

  The second sensor 180 is a sensor for detecting the rotation state of the photosensitive drum 3. For example, the second sensor 180 is an optical sensor including a light emitting unit and a light receiving unit, and is disposed in the vicinity of the circular end surface of the photosensitive drum 3 as described later.

  The CPU 130 receives output signals from the first sensor 170 and the second sensor 180. CPU 130 obtains the current time from timer 190.

  Hereinafter, a program for executing color misregistration correction in the image forming apparatus 100 will be described with reference to FIG. This process is executed at the time of adjustment before shipment of the image forming apparatus 100 or at the time of maintenance (when parts related to image formation are replaced). Therefore, this processing is also referred to as initial adjustment in order to distinguish from the adjustment described later during execution of the print job.

  In step 400, the CPU 130 forms a predetermined adjustment pattern 192 on the intermediate transfer belt 61 as shown in FIG. 4. FIG. 4 shows a portion of the intermediate transfer belt 61 on the photosensitive drum 3 side, and is vertically and horizontally reversed from FIG. In FIG. 4, the intermediate transfer belt 61 on the photosensitive drum 3 side conveys the toner image to the left side.

  As shown in FIG. 5, the adjustment pattern 192 includes four lines of a black line K, a cyan line C, a magenta line M, and a yellow line Y as one group (hereinafter referred to as a patch). A plurality of patches 194 are arranged in a straight line at a predetermined interval. In each patch 194, the black, cyan, magenta, and yellow lines are arranged at equal intervals perpendicular to the transport direction. In FIG. 4, the description of K, C, M, and Y in parentheses indicates that the four photosensitive drums 3 are the photosensitive drums 3 for black, cyan, magenta, and yellow from the right. .

  Here, as shown in FIG. 4, two rows of the adjustment patterns 192 shown in FIG. 5 are formed on the intermediate transfer belt 61 and detected by the two first sensors 170.

  Specifically, as described above, the CPU 130 reads the image data of the adjustment pattern 192 from the HDD 136 onto the image memory 154, rotates the photosensitive drum 3 for black, cyan, magenta, and yellow, and the optical scanning device 1. Is controlled to form an electrostatic latent image of a corresponding color on each photosensitive drum 3, and each electrostatic latent image is visualized by a corresponding color toner by the developing device 2. The exposed toner image is transferred onto the intermediate transfer belt 61 by the rotation of the photosensitive drum 3 as shown in FIG.

  In step 402, the CPU 130 acquires the output signals of the two first sensors 170 and the output signals of the second sensor 180. With respect to the output signals of the two first sensors 170, the same processing is performed independently. Therefore, only the first sensor 170 will be described below.

  The light emitting unit of the first sensor 170 irradiates light on the surface of the intermediate transfer belt 61 that conveys the toner image. The light receiving unit of the first sensor 170 receives light emitted from the light emitting unit of the first sensor 170 and reflected on the intermediate transfer belt 61, and outputs a signal corresponding to the amount of received light. The amount of light received by the light receiving unit of the first sensor 170 depends on the reflectance on the intermediate transfer belt 61. Therefore, when the light from the first sensor 170 is applied to the adjustment pattern 192 to be conveyed, the output signal of the first sensor 170 represents the position information of the adjustment pattern 192 (change in reflectivity depending on the position). . For example, the output signal of the first sensor 170 obtained from one patch 194 of the adjustment pattern 192 as shown in the upper part of FIG. 6 has a waveform as shown in the lower part of FIG. Since the reflectance of the black line K is the smallest, the signal intensity output from the first sensor 170 is the smallest. The valley at the left end of the lower waveform corresponds to the black line K of the patch 194.

  The horizontal axis of the output signal from the first sensor 170 is the time axis. Since the output signal from the first sensor 170 is a reflection signal from the intermediate transfer belt 61 that conveys the toner image at a constant speed (same as the linear speed on the surface of the photosensitive drum 3 rotating at a constant rotation speed), The horizontal axis of the output signal from one sensor 170 corresponds to the position on the intermediate transfer belt 61. That is, the distance on the intermediate transfer belt 61 from the interval on the time axis can be obtained by multiplying the interval on the time axis (for example, seconds) by the speed of the intermediate transfer belt 61 (unit: mm / second, for example). (Unit: mm) can be obtained.

  The rotational phase of the photosensitive drum 3 is obtained from the output signal of the second sensor 180. For example, as shown in FIGS. 7 and 8, a convex portion 32 is provided on the outer edge portion of the circular end surface of one of the four photosensitive drums 3, and the second sensor 180 has a convex portion. 32 is arranged at a position where it can be detected. The convex portion 32 rotates around the rotation shaft 34 of the photosensitive drum 3 by the rotation of the photosensitive drum 3 and passes between the light emitting portion and the light receiving portion of the second sensor 180. In the second sensor 180, when there is no shielding object (convex portion 32) between the light emitting unit and the light receiving unit, the light receiving unit receives light emitted from the light emitting unit. When the convex part 32 passes between the light emitting part and the light receiving part of the second sensor 180, the light from the light emitting part is shielded by the convex part 32, so that the light receiving part receives the light from the light emitting part. I can't. Therefore, the output signal of the second sensor 180 changes at the timing when the convex portion 32 passes through the second sensor 180 every time the photosensitive drum 3 rotates once. The output signal of the second sensor 180 is, for example, as shown in FIG. The valley of the signal indicates that the convex part 32 is detected by the second sensor 180. The adjacent valley is the rotation cycle of the photosensitive drum 3 rotating at a constant speed, and corresponds to the outer peripheral length of the photosensitive drum 3. Since periodic time can be expressed as a phase, it is described below using a phase.

  If acquisition of the output signals of the first sensor 170 and the second sensor 180 is started at the same time, the rotational phase of the photosensitive drum 3 and the first sensor 170 with reference to the position of the valley of the output signal of the second sensor 180. Output signal, that is, the position on the intermediate transfer belt 61 can be made to correspond.

  In step 404, the CPU 130 calculates a color misregistration adjustment value using the output signals of the first sensor 170 and the second sensor 180 acquired in step 402. The lower waveform in FIG. 10 shows a signal output from the first sensor 170 in an ideal case (upper stage in FIG. 10) where the designed patch 194 is formed on the intermediate transfer belt 61. That is, since the interval between the four lines constituting each patch 194 is constant (interval a) and the interval between adjacent patches is also constant (interval b), the deepest valley among the output signals of the first sensor 170. The interval between the four valleys (corresponding to the four lines constituting each patch) starting from (signal strength is minimum) is constant (interval d), and the interval between the deepest valleys is also constant (interval e). .

  However, as described above, the interval between the lines constituting the patch 194 formed on the intermediate transfer belt 61 is actually not as designed for various reasons. This state is shown in FIG. The upper part of FIG. 11 shows one patch 194 of the actual adjustment pattern 192 formed on the intermediate transfer belt 61. In FIG. 11, the state formed in the position as designed is indicated by a broken line.

From the distance P _C between the black line K and the cyan line C, the deviation ΔPC from the design value of the cyan line _C is obtained by ΔP _C = P _C −a. Similarly, from the interval P _M between the black line K and the magenta line M, a deviation ΔP _M from the design value of the magenta line _M is obtained by ΔP _M = P _M −2a. From the interval _{P Y} between the line K and the yellow line Y black, deviation [Delta] P _Y from the design value of the line Y of yellow is obtained in [Delta] P _Y = _P Y -3a. Here, the distance between the lines is the distance between the centers of the lines, but may be any distance between the representative points of the lines. For example, the left end interval of each line or the right end interval of each line may be used.

As described above, when each line constituting the patch 194 formed on the intermediate transfer belt 61 has a deviation from the design value, the output signal from the first sensor 170 is as shown below. A black circle on the time axis represents a representative point of the valley (center of the valley) in the measured output signal of the first sensor 170. An output signal from the first sensor 170 when formed at a designed position is indicated by a broken line, and a representative point of a valley in the output waveform is indicated by a white circle. Deviation [Delta] P _C shown in the upper part of FIG. 11, the [Delta] P _M and [Delta] P _Y, the position of the valley of the signal corresponding to each line of the output signal from the first sensor 170, as shown in the lower Delta] t _C, Delta] t _M and Delta] t _Y shifts. In the output signal of the first sensor 170, Δt _C = t _C −d from the interval t _C between the valley corresponding to the black line K and the valley corresponding to the cyan line C. Similarly, Δt _M = t _M −2d from the interval t _M between the valley corresponding to the black line K and the valley corresponding to the magenta line M. From the interval t _Y between the valley corresponding to the black line K and the valley corresponding to the yellow line Y, Δt _Y = t _Y −3d.

Therefore, for example, the CPU 130 obtains valley intervals (t _C , t _M , t _Y ) from the output signal of the first sensor 170, and as described with reference to FIGS. In consideration of the rotation speed, intervals (P _C , P _M , P _Y ) between the lines constituting the adjustment pattern 192 are obtained, and deviations (ΔP _C , ΔP _M , ΔP _Y ) from the design values are obtained. It is known that the color shift (shift from the design value) thus obtained can be approximated by a sine wave (sine function) when plotted with the rotational phase of the photosensitive drum 3 as the horizontal axis. The graph of FIG. 12 is a sine wave that approximates the deviation of the cyan line C obtained by measurement. The horizontal axis represents the rotational phase θ of the photosensitive drum 3 described later. Reference line L ₀ is corresponds to the design value.

A method of obtaining the phase of each patch 194 will be described with reference to FIG. The relationship between the position of the patch 194, the output signal of the first sensor 170, and the phase is as shown in FIG. The upper part of FIG. 13 shows one patch 194 in the adjustment pattern 192 formed on the intermediate transfer belt 61. The interrupted and lower waveforms are output signals of the first sensor 170 and the second sensor 180, respectively. The phase θ ₁ of each patch 194 includes a valley S ₂ in the output signal of the second sensor 180 and a valley S ₁ corresponding to the black line K of each patch 194 in the output signal of the first sensor 170. Calculate as interval. Valley S ₂ is the plurality detected, may be used one of them. For example, a valley situated before in time than S _1, and may be the closest reference valleys S ₂ in the valley S _1. That is, the position where the convex portion 32 is detected (the valley in FIG. 9) is set as the phase origin.

Sine wave of Figure 12 uses the deviation [Delta] P _C of a plurality of cyan line obtained from the output signal of the first sensor 170 can be determined by a known method such as the least squares method. For example, the CPU 130 calculates parameters α _C and β _C when a sine wave related to cyan is represented by α _C sin θ + β _C. The obtained β _C is the color misregistration adjustment value of cyan. Similarly, the CPU 130 calculates sine wave parameters (α _M , β _M , α _Y , β _Y ) for the magenta line M and the yellow line Y. β _M is a magenta color misregistration adjustment value, and β _Y is a yellow color misregistration adjustment value.

In step 406, the CPU 130 stores the sine wave parameters (α _C , β _C , α _M , β _M , α _Y , β _Y ) obtained in step 404 in the HDD 136. The parameters of the sine wave that approximate the position of each color (C, M, Y) are obtained from each of the two rows of adjustment patterns 192. Therefore, the CPU 130 calculates an average value of the corresponding values and stores it in the HDD 136.

As described above, since the color misregistration adjustment values (β _C , β _M , β _Y ) are obtained for the respective colors (C, M, Y), the electrostatic latent images of the respective colors are thereafter stored on the photosensitive member when the color image is formed. The timing for forming the drum 3 is shifted from the design value by a time corresponding to the color shift adjustment value in consideration of the rotational speed of the photosensitive drum 3. For example, when the adjustment pattern is formed in the transport direction as shown in FIG. 5 and the cyan color misregistration adjustment value β _C is determined as a positive value as shown in FIG. 12, the position of the cyan line C is The cyan transfer line 61 is shifted in the direction opposite to the traveling direction of the intermediate transfer belt 61 from the design value (the cyan line C is formed at a timing later than the design). Therefore, in order to correct the color shift, the color shift is corrected. in time the earliest timing corresponding to the adjustment value beta _C, on the photosensitive drum 3 of cyan to form an electrostatic latent image corresponding to the image data. On the other hand, when the cyan color misregistration adjustment value β _C is determined as a negative value, the position of the cyan line C is shifted in the traveling direction of the intermediate transfer belt 61 from the design value (at an earlier timing than the design). Therefore, in order to correct the color misregistration, the timing corresponding to the color misregistration adjustment value β _C is delayed by a time corresponding to the image data on the cyan photosensitive drum 3. An electrostatic latent image is formed. The same applies to magenta and yellow. As a result, a toner image with improved color misregistration can be formed on the intermediate transfer belt 61, and color misregistration of the image formed on the recording paper can be improved.

Next, a program for correcting color misregistration during execution of a print job will be described with reference to FIG. This process is performed in order to improve color misregistration during job execution when printing is performed continuously for a long time, such as a job for copying a large amount of documents. Here, the initial adjustment of the color misregistration described with reference to FIG. 3 is executed, and the parameters (α _C , β _C , α _M , β _M , α _Y , β _Y ) of the sine wave are stored in the HDD 136. And

  In step 500, the CPU 130 determines whether or not the user has operated the operation unit 160 to input some instruction. If it is determined that it has been operated, control proceeds to step 502. Otherwise, step 500 is repeated.

  In step 502, the CPU 130 determines whether or not the user operation in step 500 is an instruction to execute a print job. If it is a print job execution instruction, control proceeds to step 504. Otherwise, control passes to step 522.

  In step 522, the CPU 130 executes the instructed process. For example, when an operation for setting copy conditions (black / white / color selection, number of copies, copy density, scan resolution, etc.) is received before an instruction to copy a document is issued, the corresponding processing is executed. Thereafter, control proceeds to step 520.

If the instruction in step 502 is execution of a print job, in step 504, the CPU 130 executes the print job. Specifically, a program for executing a print job is started. At this time, the color misregistration adjustment values β _C , β _M , β _Y are read from the HDD 136 and are used to adjust the timing for forming the electrostatic latent image of each color on the photosensitive drum 3.

  In step 506, the CPU 130 determines whether a predetermined number of sheets have been printed. The predetermined number N is preset and stored in the HDD 136. The CPU 130 counts the accumulated number of discharged recording sheets by a program for executing a print job or another program, and stores it in a predetermined area of the RAM 134, for example. The CPU 130 detects the conveyance state of the recording paper using a sensor arranged along the recording paper conveyance path S. For example, the CPU 130 detects the conveyance state of the recording paper on the discharge tray 91 by a sensor installed on the discharge side of the conveyance roller 12d at the final stage. The discharged recording paper is detected and the cumulative number of sheets is counted. The CPU 130 reads the count value K from the RAM 134, determines whether the value is N or more, and determines whether a predetermined number of sheets have been printed. If it is determined that a predetermined number of sheets have been printed (K ≧ N), the count value K is reset to 0, and the process proceeds to step 508. Otherwise (K <N), step 506 is repeated.

  In step 508, the CPU 130 forms a pair of patches 194 on the intermediate transfer belt 61 as shown in FIG. 15. The timing of forming the patch 194 is arbitrary as long as the patch 194 is not formed on the recording paper that is continuously conveyed along the conveyance path S. At this time, a print job for recording paper is executed by another program started in step 504. Accordingly, a toner image to be transferred onto the recording paper and a pair of patches 194 are formed on the intermediate transfer belt 61 at positions that do not overlap with the toner image.

  In step 510, the CPU 130 acquires the current time T 0 from the timer 190 and stores it in the RAM 134, and starts acquiring the output signals of the first sensor 170 and the second sensor 180 as in step 402. Thereby, a waveform as shown in FIG. 6 is acquired. Note that the same processing is performed independently on the output signals of the two first sensors 170. Therefore, only the first sensor 170 will be described below.

  In step 512, the CPU 130 acquires the current time T1 from the timer 190, and determines whether or not a predetermined time has elapsed since the start of signal acquisition in step 510. Specifically, the CPU 130 compares the time information T0 stored in the RAM 134 in step 510 with the acquired current time T1. If it is determined that the predetermined time has elapsed, the control proceeds to step 514. Otherwise, step 512 is repeated. Meanwhile, output signals of the first sensor 170 and the second sensor 180 are acquired.

In step 514, the CPU 130 ends the acquisition of the output signals of the first sensor 170 and the second sensor 180, and the adjustment value for correcting the color shift from the acquired output signals of the first sensor 170 and the second sensor 180. Is calculated. Specifically, the CPU 130 detects four valleys (corresponding to each line) representing the patch 194 from the acquired output signal of the first sensor 170, and the first valley (the valley corresponding to the earliest time) and the other valleys. An interval P _i (i is C, M, Y) of each color i corresponding to the interval (time) with each of the three valleys is obtained. As described above, the spatial interval can be obtained by multiplying the time interval by the constant conveyance speed of the intermediate transfer belt 61. Further, the CPU 130 identifies valleys in the output signal of the second sensor 180, identifies signals (for example, the first valley among the four valleys) representing the patch 194 in the output signal of the first sensor 170, and identifies them. The phase θ ₁ corresponding to the interval (time) is calculated. The phase can be obtained by multiplying the time interval by a constant rotational speed (angular speed) of the photosensitive drum 3. Then, the CPU 130 reads the sine wave parameters α _i and β _i (i = C, M, Y) from the HDD 136, and calculates the displacement γ _{i of the} color i by the following equation.
γ _i = ΔP _i − (α _i sin θ ₁ + β _i )

The meaning of the above processing will be described with reference to FIG. In FIG. 16, the data regarding the cyan line C obtained by the above processing is plotted with the horizontal axis as the phase. The horizontal axis is the rotational phase of the photosensitive drum 3, and the vertical axis is the spatial distance. The actual measurement data relating to the cyan line C is represented by a black circle (θ ₁ , P _C ). A white circle represents a point (θ ₁ , α _C sin θ ₁ + β _C ). The shift γ _i means that the color shift is not sufficiently improved by the initial adjustment of the color shift described with reference to FIG.

In step 516, the CPU 130 adds the deviation γ _i of each color i determined in step 514 to the color deviation adjustment value β _i of each color i stored in the HDD 136 in step 406, thereby obtaining a correction value δ _i (= β _i + Γ _i ) is calculated and stored in the HDD 136. This meaning will be described with reference to FIG. FIG. 17 is a diagram in which a reference line is added to FIG. The current color misregistration correction state (state in which the timing for forming the electrostatic latent image of each color on the photosensitive drum 3 is adjusted according to the color misregistration adjustment values β _C , β _M , β _Y ) is the design reference line L ₀ is in the state of being shifted to the reference line L _1. If the adjustment pattern 192 is formed on the intermediate transfer belt 61 from the actual measurement value (black circle) obtained by forming one patch 194, the measurement value varies in the vicinity of the broken sine wave. That is, in the vicinity of the dashed sine wave mountains, the difference from the reference line L ₁ (color shift) is larger. Therefore, when the reference line L ₁ is shifted by γ _C , the measured values vary above and below the reference line L ₂ , and a large color shift near the broken sine wave peak can be improved. That is, the correction value δ _i is for shifting the reference line L ₀ to the reference line L ₂ .

Since a pair of patches (two patches) 194 is formed, a correction value δ _i is calculated using an average value of two deviations γ _i obtained from the output signal of the first sensor 170 for each patch 194. To do.

  In step 518, the CPU 130 determines whether the print job is completed. If it is determined that the process has been completed, control proceeds to step 520. Otherwise, control returns to step 506.

  In step 520, CPU 130 determines whether an end instruction has been received or not. If it is determined that an end instruction has been received, the program ends. Otherwise control passes to step 500. The end instruction is given, for example, when the image forming apparatus 100 is powered off.

As described above, the correction value δ _i (i is C, M, Y) is obtained for each color (C, M, Y). Thereafter, the correction value δ _i is read from the HDD 136 when the color image is formed, Considering the rotational speed of the body drum 3, the timing for forming the electrostatic latent image of each color i on the photosensitive drum 3 is shifted from the design value by the time corresponding to the correction value δ _i . This makes it possible to correct color misregistration during execution of a print job.

The time from when the patch 194 formed on the intermediate transfer belt 61 is detected by the first sensor 170 to when the CPU 130 calculates the correction value δ _i is short. Therefore, for example, an image formed on the recording sheet immediately after the sheet on which the patch 194 is formed is formed on the subsequent recording sheet even though the color misregistration correction using the correction value δ _i cannot be performed. Color shift correction can be performed on the image using the correction value δ _i .

  In the above description, the measured deviation value ΔP is described as a continuous value. However, since the color deviation actually adjusted is in dot units, the deviation ΔP is obtained as a discrete value in dot units, and the above processing is performed. May be executed.

  In the above description, the case where two rows of adjustment patterns 192 and a pair of patches 194 are formed on the intermediate transfer belt 61 has been described. However, the present invention is not limited to this. For example, one adjustment pattern and one patch may be formed.

  Further, the length of the adjustment pattern only needs to be one or more periods of rotation of the photosensitive drum. The number of patches constituting the adjustment pattern is not limited to 13 shown in FIG. The number may be any number that can determine a sine wave that approximates color misregistration, and there may be three or more patches in one cycle.

  Further, the patch formed in step 508 of FIG. 14 is not limited to a pair. A plurality of pairs of patches may be formed as long as they can be formed between sheets. Further, the patches may not be formed as a pair (that is, at the same timing). Patches may be formed on the left and right (in the direction orthogonal to the transport direction) at different timings. Also in these cases, an average value of correction values obtained for the same color from each patch may be used as the final correction value.

  Further, the patches constituting the adjustment pattern are not limited to those shown in FIG. For example, the color order is arbitrary. The interval a between the lines is arbitrary as long as the color shift can be appropriately plotted as the rotational phase of the photosensitive drum. If the distance a is too large, the size of the patch (the distance between the two lines positioned at both ends in the patch conveyance direction) increases, and the color shift cannot be appropriately plotted as the rotational phase of the photosensitive drum. a is preferably small.

  In the above description, the case where the plurality of lines constituting one patch are designed to be arranged at equal intervals has been described, but the present invention is not limited to this. For example, the distance between the black line K and the cyan line C, the distance between the cyan line C and the magenta line M, and the distance between the magenta line M and the yellow line Y may all be different. Good. Further, the spacing between adjacent patches in the adjustment pattern may not be designed to be the same. In such a case, when the measurement result is plotted in the same manner as in FIG. 12, it is not plotted at equal intervals in the horizontal axis direction (phase direction), but it is possible to obtain a sine wave that approximates the deviation of each color. Therefore, even in such a case, it is possible to form a correction value for color misregistration by forming only one patch as described above.

  Moreover, although the case where the adjustment pattern includes a plurality of one type of patches has been described above, the present invention is not limited to this. The adjustment pattern may include a plurality of types of patches. For example, even if two types of patches are included, the deviation can be calculated based on the design value of the line interval in each patch. When the measurement results are plotted in the same manner as in FIG. An approximate sine wave can be obtained. Even in such a case, similarly to the above, only one patch (any one of two types of patches) can be formed between sheets, and the correction value of color misregistration can be determined.

  Further, the lines constituting the adjustment pattern and the patch may not be orthogonal to the toner image conveyance direction of the intermediate transfer belt. For example, parallel lines inclined at a predetermined angle with respect to the transport direction may be used.

  In the above, as shown in FIG. 13, the phase of the black line K is used as the phase of the patch, but the present invention is not limited to this. The phase of the representative point in the patch may be used, and the phase of the cyan line C, the magenta line M, and the yellow line Y may be used if the size of the patch is small.

  In the above description, as illustrated in FIG. 11, a case has been described in which the deviation of the cyan, magenta, and yellow lines is calculated and adjusted using the black line K as a reference, but is not limited thereto. The deviation of the black, magenta, and yellow lines may be calculated using the cyan line as a reference.

  Further, the method of calculating the shift is not limited to the method of calculating based on any color line constituting the adjustment pattern or patch. It is only necessary to calculate the deviation from the design value (when there is no color deviation), and the predetermined position on the output signal of the first sensor can be used as a reference. Note that, when a line of any color is not used as a reference, an adjustment value can also be calculated by obtaining a deviation for the black line K.

In the above, in step 406 of FIG. 3, the parameters α _C , β _C , α _M , β _M , α _Y , β _Y of the sine wave are stored, but instead, a plurality of points on the sine wave are stored. May be.
That is, a plurality of phases θ and sine wave values α _i sin θ + β _i corresponding to the phases are stored in association with each other. In this case, in step 514 of FIG. 14, the line deviation γ _i of one patch (phase θ ₁ ) formed on the intermediate transfer belt 61 is, for example, stored plural data {θ, α _i sin θ + β _i }. It can be obtained by interpolation. For example, two points sandwiching the phase θ ₁ are specified from a plurality of stored data {θ, α _i sin θ + β _i }, and linear interpolation is performed between the two points to approximate a sine wave corresponding to the phase θ ₁ The value Q is obtained, and the approximate value Q is subtracted from the measured value ΔP _i of the line deviation of one patch (phase θ ₁ ) formed on the intermediate transfer belt to obtain the deviation γ _i (= ΔP _i −Q). be able to.

  Further, the function that approximates the deviation from the design value is not limited to the sine wave. The measured deviation can be approximated and may be a periodic function having the same cycle as the rotation cycle of the photosensitive drum. The constant part of the periodic function can be used as a color shift adjustment value. The constant part of the periodic function is also an average value of one period of the periodic function.

  In the above description, a case has been described in which one patch is formed during execution of one print job, a color shift correction value is calculated, and the color shift is adjusted using the correction value, but the present invention is not limited to this. For example, when a plurality of print jobs are executed in succession, they may be executed after the end of one print job and before the next print job. Moreover, although the case where it performed when the printed recording paper became a predetermined number of sheets was demonstrated, it is not limited to this. For example, it may be executed when a continuous printing time becomes a predetermined time or more. Alternatively, it may be executed when the internal temperature of the image forming apparatus (for example, the temperature of the image forming unit) deviates from a predetermined value range.

  In the above description, the image forming apparatus capable of color printing of four colors has been described. However, the present invention is not limited to this. Any image forming apparatus that forms an image on recording paper by superposing at least two colors of toner may be used. Even in an image forming apparatus using five or more colors of toner, it is possible to adjust the misregistration of each color by executing a process similar to the above using patches including lines of all colors used.

Although the case where one patch includes all four colors has been described above, the present invention is not limited to this. A patch including two colors may be formed. For example, a patch including only the black line K and the cyan line C is formed to obtain a cyan correction value γ _C , and then a patch including only the black line K and the magenta line M is formed to correct the magenta. The value γ _M may be obtained, and finally a patch including only the black line K and the yellow line Y may be formed to obtain the yellow correction value γ _Y. In this case as well, color misregistration can be adjusted between sheets during execution of a print job.

  In the above description, the case where the distance from each color line is calculated based on the black line K has been described. However, the present invention is not limited to this. A color other than black may be used as a reference. Furthermore, a specific color line may not be used as a reference. That is, it is only necessary that the deviation from the design value of each line on the intermediate transfer belt (the deviation from the theoretical position (target position)) can be associated with the rotational phase of the photosensitive drum, and from the design value of each line on the intermediate transfer belt. The reference position for calculating the deviation is arbitrary.

  The image forming apparatus may be connected to a network and have a print function for receiving a print job (print job) from a terminal device connected to the network.

  Further, the mechanism for detecting the rotational phase of the photosensitive drum is not limited to the mechanism as shown in FIGS.

  Further, the position of the first sensor 170 is not limited to the position shown in FIG. 1 (below the intermediate transfer belt 61 and between the final photosensitive drum 3 and the intermediate transfer belt driving roller 62). The first sensor 170 may be disposed above the intermediate transfer belt 61 and between the intermediate transfer belt driving roller 62 and the intermediate transfer belt driven roller 63 (a position close to the intermediate transfer belt driving roller 62 is preferable). Good. Although the transfer roller 10 hits a line constituting the adjustment pattern or patch formed on the intermediate transfer belt 61, the line does not completely disappear, and can be detected by the first sensor.

  The present invention has been described above by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment, and is implemented with various modifications. be able to.

90 image reading apparatus 100 image forming apparatus 110 main body apparatus 120 automatic document feeder 130 control unit (CPU)
132 ROM
134 RAM
136 HDD
142 Bus 150 Image Forming Unit 152 Image Processing Unit 154 Image Memory 156 Paper Feeding Unit 160 Operation Unit 170 First Sensor 180 Second Sensor 190 Timer

Claims (8)

An image forming apparatus comprising: the predetermined number of photoreceptors on which toner images of a predetermined number of colors of two or more are formed; and a transfer unit that transfers the toner image to a recording medium.
Phase detection means for detecting a reference position of the rotational phase of the photoreceptor;
A toner image of each color is formed on each of the photoconductors based on a first design pattern that includes a plurality of lines for each of the predetermined number of colors and that corresponds to one or more cycles of the rotational phase. A transfer image forming means for forming a first transfer image by transferring onto the transfer means;
Image detecting means for detecting the position of each line constituting the first transfer image;
Based on the detection results of the image detection unit and the phase detection unit, the rotational phase is approximated by a deviation from the first design pattern of a plurality of lines constituting the first transfer image for each color. And a deviation evaluation means for storing information for specifying the periodic function,
The transfer image forming unit forms a second transfer image on the transfer unit based on a second design pattern including a plurality of color lines and corresponding to 1/3 period or less of the rotation phase,
The image detecting means detects a position of each line constituting the second transfer image;
The deviation evaluation means is
For each color, calculate a measured deviation amount that is a deviation of the line included in the second transfer image from the second design pattern;
The phase of the second transfer image with respect to the reference position is calculated, and for each color, the value of the periodic function corresponding to the phase is calculated using information specifying the periodic function and is determined as a calculation deviation amount And
For each color, a value obtained by subtracting the calculated shift amount from the measured shift amount is determined as a correction value,
An image forming apparatus that adjusts the timing of forming the toner image on the photoconductor for each color according to a value obtained by adding the value of the constant part of the periodic function and the correction value. .   The image forming apparatus according to claim 1, wherein the first design pattern includes a plurality of the second design patterns.   2. The second design pattern according to claim 1, wherein the second design pattern is shorter than an interval between the recording media conveyed adjacent to each other when the transfer of toner images onto the plurality of recording media is continuously performed. The image forming apparatus according to 2.   When the transfer of the toner images onto the plurality of recording media is continuously performed, the transfer image forming unit is not transferred onto the recording medium, and the second transfer is performed at a predetermined position on the transfer unit. The image forming apparatus according to claim 3, wherein an image is formed. The periodic function is represented by α sin θ + β, where θ is the rotational phase,
Information specifying the periodic function is α and β,
5. The image forming apparatus according to claim 1, wherein the value of the constant portion of the periodic function is β. The predetermined number of colors is black, cyan, magenta and yellow;
6. The image forming apparatus according to claim 1, wherein the second design pattern includes black, cyan, magenta, and yellow lines.   The deviation of the plurality of lines constituting the first transfer image from the first design pattern and the deviation of the lines included in the second transfer image from the second design pattern The image forming apparatus according to claim 6, wherein the measured deviation amount is obtained with reference to a black line. A color misregistration adjustment method in an image forming apparatus, comprising: the predetermined number of photoconductors on which toner images of a predetermined number of colors of 2 or more are respectively formed; and a transfer unit that transfers the toner image to a recording medium.
A phase detection step for detecting a reference position of the rotational phase of the photoconductor;
A toner image of each color is formed on each of the photoconductors based on a first design pattern that includes a plurality of lines for each of the predetermined number of colors and that corresponds to one or more cycles of the rotational phase. Transferring onto the transfer means to form a first transfer image;
An image detection step of detecting the position of each line constituting the first transfer image;
Based on the detection results of the image detection step and the phase detection step, the rotation phase is approximated by a deviation from the first design pattern of a plurality of lines constituting the first transfer image for each color. Determining a periodic function and storing information identifying the periodic function;
Forming a second transfer image on the transfer means based on a second design pattern including a plurality of color lines and corresponding to 1/3 period or less of the rotational phase;
Detecting the position of each line constituting the second transfer image;
Calculating, for each color, a measured deviation amount that is a deviation of the line included in the second transfer image from the second design pattern;
The phase of the second transfer image with respect to the reference position is calculated, and for each color, the value of the periodic function corresponding to the phase is calculated using information specifying the periodic function and is determined as a calculation deviation amount And steps to
Determining, as a correction value, a value obtained by subtracting the calculated shift amount from the measured shift amount for each color;
Adjusting the timing for forming the toner image on the photoconductor according to a value obtained by adding the value of the constant part of the periodic function and the correction value for each color. Color misregistration adjustment method.

Images