JP6326751B2 - Optical writing control apparatus, image forming apparatus, and optical writing apparatus control method - Google Patents

Description

  The present invention relates to an optical writing control device, an image forming apparatus, and an optical writing device control method, and more particularly to a pattern drawn for correcting an image drawing position and a correction process based on a reading result.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, electrophotographic image forming apparatuses are widely used in image forming apparatuses used for outputting digitized documents. In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing a photoreceptor, and the electrostatic latent image is developed using a developer such as toner to form a toner image. Paper output is performed by transferring the toner image onto paper.

  In such an electrophotographic image forming apparatus, the image is formed in the correct range of the paper by aligning the timing of drawing the electrostatic latent image by exposing the photosensitive member and the timing of transporting the paper. Adjustments are made. In addition, in a tandem image forming apparatus that forms a color image using a plurality of photoconductors, the exposure timing of each color photoconductor is adjusted so that the images developed on the photoconductors of each color are accurately superimposed. Is done. Hereinafter, these adjustment processes are collectively referred to as misalignment correction.

  As a specific method for realizing the above-described misregistration correction, a mechanical adjustment method for adjusting the positional relationship between the light source for exposing the photoconductor and the photoconductor, and an image to be output in the misalignment. There is a method by image processing in which an image is finally formed at a suitable position by adjusting accordingly. In the case of this image processing method, a correction pattern is drawn and read so that correction is performed based on the difference between the timing determined by design and the timing at which the pattern is actually read. An image is formed.

  Further, in the above-described image processing method, it is necessary to consider a cyclic error according to the rotation cycle of the intermediate transfer belt to which the toner image is transferred from the photosensitive member that is a rotating member or the photosensitive member corresponding to each color. In the rotation of the photosensitive member or the intermediate transfer belt, if the speed fluctuates during one rotation, the pattern conveyance timing described above also changes periodically, and finally the pattern is transferred onto the intermediate transfer belt. Depending on the position, an error (hereinafter referred to as “periodic error”) occurs in the pattern detection timing.

  As described above, such a cyclic error mainly depends on the eccentricity of the rotation and the distortion of the surface. Therefore, when the fluctuations are summed over one rotation of the intermediate transfer belt, it is theoretically zero. Become. Therefore, in order to reduce such a cyclic error, a correction pattern is drawn over one rotation of the intermediate transfer belt, and the detection result of each pattern is averaged to reduce the error.

  On the other hand, as another method for reducing the cyclic error, a method of forming a pattern for correcting misalignment at a position showing an average speed in the fluctuation of the rotational speed in one rotation of the photosensitive member has been proposed (for example, Patent Document 1). reference).

  When the method disclosed in Patent Document 1 is used, the timing at which a correction pattern can be formed is limited, which increases the time required for misalignment correction and makes it difficult to form an intended pattern. Can be considered. In addition, a configuration for detecting the rotation of the photosensitive member and the intermediate transfer belt is required, leading to a complicated apparatus configuration and high cost. On the other hand, when the correction pattern is drawn over one rotation of the intermediate transfer belt, the above-described problems do not occur.

  However, when a correction pattern is drawn over one rotation of a rotating body such as an intermediate transfer belt, it is necessary to reliably draw the pattern for one rotation of the rotating body, which is required for pattern drawing. The time will be longer.

  The present invention has been made in consideration of the above circumstances, and an error due to the period of a rotating body included in an image forming mechanism when drawing a correction pattern for correcting a position where an image is drawn in an image forming apparatus. The object is to reduce the time required for pattern drawing.

In order to solve the above problems, one aspect of the present invention is an optical writing control device that controls a light source that exposes a photoconductor to form an electrostatic latent image on the photoconductor, and controls the light emission of the light source. A light emission control unit that exposes the photoconductor and a detection signal of a sensor that detects the image in a conveyance path on which an image obtained by developing the electrostatic latent image formed on the photoconductor is transferred and conveyed. The sensor detects a detection signal acquisition unit and a correction pattern for correcting a transfer position to which a developer image obtained by developing the electrostatic latent image formed on the photoconductor in the transport path is transferred. A correction value calculation unit that calculates a correction value for correcting the transfer position based on the detected signal, and the light emission control unit includes a linear horizontal line pattern perpendicular to the conveyance direction of the conveyance path; With respect to the transport direction The light source is controlled to emit light so as to alternately and repeatedly draw a linear oblique line pattern inclined at a constant angle, and the correction value calculation unit draws the horizontal line alternately and repeatedly drawn. In the pattern and the diagonal line pattern, based on the detection period from the detection of the horizontal line pattern to the detection of the diagonal line pattern and the detection period from the detection of the diagonal line pattern to the detection of the horizontal line pattern, The horizontal line is calculated by calculating a correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction , and is alternately and repeatedly drawn in the correction pattern formed on the photoconductor by the light emission control unit. Each of the interval from the pattern to the oblique line pattern and the interval from the oblique line pattern to the horizontal line pattern causes an error in the transfer position. Correction so that the peripheral length of the photosensitive member is divided by using a real number n satisfying m ≦ n / 6 for each order m of the periodic error of the periodic function of the plurality of rotating members that causes the rotation. It is characterized by being drawn at a specified interval .

  Another aspect of the present invention is an image forming apparatus including the optical writing control device.

According to still another aspect of the present invention, there is provided a control method of an optical writing apparatus that controls a light source for exposing a photosensitive member to form an electrostatic latent image on the photosensitive member, wherein the light source is controlled to emit light and the photosensitive member is controlled. By exposing a body, a detection signal of a sensor that detects the image is acquired in a transport path in which an image in which an electrostatic latent image formed on the photoconductor is developed is transferred, and the transport path is acquired. A correction pattern for correcting a transfer position to which a developer image developed from the electrostatic latent image formed on the photosensitive member is transferred based on the detection signal detected by the sensor. A correction value for correcting the image is calculated, and a linear horizontal line pattern perpendicular to the conveyance direction of the conveyance path and a linear oblique line pattern inclined at a predetermined angle with respect to the conveyance direction are alternately and repeatedly drawn. So that the light The correction pattern is drawn by controlling the emission of light, and in calculating the correction value, in the horizontal line pattern and the diagonal line pattern that are alternately and repeatedly drawn, the horizontal line pattern is detected until the diagonal line pattern is detected. A correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction is calculated based on the detection period and the detection period from when the oblique line pattern is detected until the horizontal line pattern is detected. In the correction pattern formed on the photoconductor, an interval from the horizontal line pattern to the diagonal line pattern and an interval from the diagonal line pattern to the horizontal line pattern, which are alternately and repeatedly drawn, are set at the transfer position. For each order m of the periodic error of the periodic function of the plurality of rotating bodies that causes the error, m ≦ n / Drawing with the corrected distance so that the divided value circumferential length of the photosensitive member using the real number n satisfying,
It is characterized by that.

  According to the present invention, when drawing a correction pattern for correcting the position where an image is drawn in the image forming apparatus, an error due to the period of the rotating body included in the image forming mechanism is reduced and the pattern is required to be drawn. Time can be shortened.

1 is a block diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a functional configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a print engine according to an embodiment of the present invention. It is a figure which shows the structure of the optical writing apparatus which concerns on embodiment of this invention. It is a block diagram which shows the structure of the optical writing control part and LEDA which concern on embodiment of this invention. It is a figure which shows the example of the pattern for a correction | amendment based on a prior art. It is a figure which shows the example of the detection timing of the pattern for position shift correction. It is a figure which shows the reference aspect of the detection result of the correction pattern which concerns on embodiment of this invention. FIG. 6 is a diagram illustrating an example of forming a correction pattern for a photosensitive drum and an intermediate transfer belt. It is a figure which shows the relationship between the error amount of a period error, and a rotation phase. It is a figure which shows the reference aspect of the detection result of the correction pattern which concerns on embodiment of this invention. It is a figure which shows the reduction effect of the period error which concerns on embodiment of this invention. It is a figure which shows the example of formation of the pattern for a correction | amendment on the photoconductor drum which concerns on embodiment of this invention, and a comparative example. It is a figure which shows the effect ratio which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an image forming apparatus as an MFP (Multi Function Peripheral) will be described as an example. The image forming apparatus according to the present embodiment is an electrophotographic image forming apparatus, and the correction is based on the configuration of the pattern drawn in the misalignment correction operation for correcting the exposure timing of the photosensitive member, and the pattern reading result. Features in processing.

  FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an engine that executes image formation in addition to the same configuration as an information processing terminal such as a general server or a PC (Personal Computer). That is, the image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 12, an engine 13, an HDD (Hard Disk Drive) 14, and an I / O. F15 is connected via the bus 18. Further, an LCD (Liquid Crystal Display) 16 and an operation unit 17 are connected to the I / F 15.

  The CPU 10 is a calculation unit and controls the operation of the entire image forming apparatus 1. The RAM 11 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The engine 13 is a mechanism that actually executes image formation in the image forming apparatus 1.

  The HDD 14 is a nonvolatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 15 connects and controls the bus 18 and various hardware and networks. The LCD 16 is a visual user interface for the user to check the state of the image forming apparatus 1. The operation unit 17 is a user interface such as a keyboard and a mouse for the user to input information to the image forming apparatus 1.

  In such a hardware configuration, a program stored in a recording medium such as the ROM 12, the HDD 14, or an optical disk (not shown) is read into the RAM 11, and the CPU 10 performs calculations according to those programs, thereby configuring a software control unit. The A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the functional configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes a controller 20, an ADF (Auto Document Feeder) 110, a scanner unit 22, a paper discharge tray 23, a display panel 24, and a paper feed table. 25, a print engine 26, a paper discharge tray 27, and a network I / F 28.

  The controller 20 includes a main control unit 30, an engine control unit 31, an input / output control unit 32, an image processing unit 33, and an operation display control unit 34. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment is configured as a multifunction machine having a scanner unit 22 and a print engine 26. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of paper is indicated by broken arrows.

  The display panel 24 is an output interface that visually displays the state of the image forming apparatus 1 and is an input when the user directly operates the image forming apparatus 1 or inputs information to the image forming apparatus 1 as a touch panel. It is also an interface (operation unit). The network I / F 28 is an interface for the image forming apparatus 1 to communicate with other devices via the network, and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface.

  The controller 20 is configured by a combination of software and hardware. Specifically, a control program such as firmware stored in a ROM 12, nonvolatile memory, and a nonvolatile recording medium such as the HDD 14 or an optical disk is loaded into a volatile memory (hereinafter referred to as memory) such as the RAM 11, and these programs are loaded. The controller 20 is configured by a software control unit configured by calculation of the CPU 10 according to the above and hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire image forming apparatus 1.

  The main control unit 30 plays a role of controlling each unit included in the controller 20 and gives a command to each unit of the controller 20. The engine control unit 31 serves as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like. The input / output control unit 32 inputs a signal or a command input via the network I / F 28 to the main control unit 30. The main control unit 30 controls the input / output control unit 32 and accesses other devices via the network I / F 28.

  The image processing unit 33 generates drawing information based on the print information included in the input print job under the control of the main control unit 30. The drawing information is information for drawing an image to be formed in the image forming operation by the print engine 26 as an image forming unit. The print information included in the print job is image information converted into a format that can be recognized by the image forming apparatus 1 by a printer driver installed in an information processing apparatus such as a PC. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

  When the image forming apparatus 1 operates as a printer, first, the input / output control unit 32 receives a print job via the network I / F 28. The input / output control unit 32 transfers the received print job to the main control unit 30. When receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

  When drawing information is generated by the image processing unit 33, the engine control unit 31 controls the print engine 26 based on the generated drawing information, and executes image formation on the paper conveyed from the paper supply table 25. To do. That is, the print engine 26 functions as an image forming unit. A document on which an image has been formed by the print engine 26 is discharged to a discharge tray 27.

  When the image forming apparatus 1 operates as a scanner, the operation display control unit 34 or the input / output unit is operated in accordance with a user operation on the display panel 24 or a scan execution instruction input from an external PC or the like via the network I / F 28. The control unit 32 transfers a scan execution signal to the main control unit 30. The main control unit 30 controls the engine control unit 31 based on the received scan execution signal.

  The engine control unit 31 drives the ADF 21 and conveys the document to be imaged set on the ADF 21 to the scanner unit 22. Further, the engine control unit 31 drives the scanner unit 22 and images a document conveyed from the ADF 21. If no original is set on the ADF 21 and the original is directly set on the scanner unit 22, the scanner unit 22 takes an image of the set original under the control of the engine control unit 31. That is, the scanner unit 22 operates as an imaging unit.

  In the imaging operation, an imaging element such as a CCD included in the scanner unit 22 optically scans the document, and imaging information generated based on the optical information is generated. The engine control unit 31 transfers the imaging information generated by the scanner unit 22 to the image processing unit 33. The image processing unit 33 generates image information based on the imaging information received from the engine control unit 31 according to the control of the main control unit 30. Image information generated by the image processing unit 33 is stored in a storage medium attached to the image forming apparatus 1 such as the HDD 14. That is, the scanner unit 22, the engine control unit 31, and the image processing unit 33 work together to function as a document reading unit.

  The image information generated by the image processing unit 33 is stored in the HDD 14 or the like as it is according to a user instruction or transmitted to an external device via the input / output control unit 32 and the network I / F 28. That is, the ADF 21 and the engine control unit 31 function as an image input unit.

  Further, when the image forming apparatus 1 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. To do. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

  Next, the configuration of the print engine 26 according to the present embodiment will be described with reference to FIG. As shown in FIG. 3, the print engine 26 according to the present embodiment includes a configuration in which image forming units 106 of respective colors are arranged along an intermediate transfer belt 105 that is an endless moving unit, and is a so-called tandem type. It is said that. In other words, along the intermediate transfer belt 105, which is an intermediate transfer belt on which an intermediate transfer image for transfer onto a sheet (an example of a recording medium) 104 that is separated and fed by a sheet feeding roller 102 from a sheet feeding tray 101 is formed. A plurality of image forming units (electrophotographic process units) 106Y, 106M, 106C, and 106K (hereinafter collectively referred to as the image forming unit 106) are arranged in order from the upstream side in the transport direction of the intermediate transfer belt 105.

  Further, the sheet 104 fed from the sheet feeding tray 101 is stopped once by the registration roller 103 and sent to the image transfer position from the intermediate transfer belt 105 in accordance with the image formation timing in the image forming unit 106.

  The plurality of image forming units 106Y, 106M, 106C, and 106K have the same internal configuration except that the colors of the toner images to be formed, that is, the developer images are different. The image forming unit 106K forms a black image, the image forming unit 106M forms a magenta image, the image forming unit 106C forms a cyan image, and the image forming unit 106Y forms a yellow image. In the following description, the image forming unit 106Y will be described in detail. However, since the other image forming units 106M, 106C, and 106K are the same as the image forming unit 106Y, the image forming units 106M, 106C, and 106K. For each of these components, instead of Y added to each component of the image forming unit 106Y, only the symbols distinguished by M, C, and K are displayed in the figure, and the description is omitted.

  The intermediate transfer belt 105 is an endless belt, that is, an endless belt that is stretched between a driving roller 107 and a driven roller 108 that are rotationally driven. The drive roller 107 is driven to rotate by a drive motor (not shown), and the drive motor, the drive roller 107, and the driven roller 108 function as a drive unit that moves the intermediate transfer belt 105 that is an endless moving unit. To do.

  During image formation, the first image forming unit 106Y transfers a black toner image to the intermediate transfer belt 105 that is driven to rotate. The image forming unit 106Y includes a photoconductor drum 109Y as a photoconductor, a charger 110Y disposed around the photoconductor drum 109Y, an optical writing device 111, a developing device 112Y, a photoconductor cleaner (not shown), and a static eliminator. 113Y and the like. The optical writing device 111 is configured to irradiate light to each of the photosensitive drums 109Y, 109M, 109C, and 109K (hereinafter collectively referred to as “photosensitive drum 109”).

  In the image formation, the outer peripheral surface of the photosensitive drum 109Y is uniformly charged by the charger 110Y in the dark, and then writing is performed by light from the light source corresponding to the black image from the optical writing device 111. An electrostatic latent image is formed. The developing device 112Y visualizes the electrostatic latent image with yellow toner, thereby forming a yellow toner image on the photosensitive drum 109Y.

  This toner image is transferred onto the intermediate transfer belt 105 by the action of the transfer unit 115Y at a position (transfer position) where the photosensitive drum 109Y and the intermediate transfer belt 105 are in contact with or closest to each other. By this transfer, an image of yellow toner is formed on the intermediate transfer belt 105. After the transfer of the toner image is completed, the photosensitive drum 109Y is wiped away with unnecessary toner remaining on the outer peripheral surface by the photosensitive cleaner, and then is neutralized by the static eliminator 113Y and waits for the next image formation.

  As described above, the yellow toner image transferred onto the intermediate transfer belt 105 by the image forming unit 106Y is conveyed to the next image forming unit 106M by driving the roller of the intermediate transfer belt 105. In the image forming unit 106M, a magenta toner image is formed on the photosensitive drum 109M by the same process as the image forming process in the image forming unit 106Y, and the toner image is superimposed and transferred onto the already formed yellow image. Is done.

  The yellow and magenta toner images transferred onto the intermediate transfer belt 105 are further transported to the next image forming units 106C and 106K, and a cyan toner image formed on the photosensitive drum 109C by the same operation, The black toner image formed on the photosensitive drum 109K is superimposed and transferred onto the already transferred image. Thus, a full-color intermediate transfer image is formed on the intermediate transfer belt 105.

  The sheets 104 stored in the sheet feeding tray 101 are sent out in order from the top, and the intermediate transfer formed on the intermediate transfer belt 105 at a position where the conveyance path is in contact with or closest to the intermediate transfer belt 105. The image is transferred onto the paper. As a result, an image is formed on the surface of the sheet 104. The sheet 104 on which the image is formed on the sheet surface is further conveyed, the image is fixed by the fixing device 116, and then discharged to the outside of the image forming apparatus.

  Further, in such an image forming apparatus 1, the error in the interaxial distances of the photosensitive drums 109 Y, 109 M, 109 C, and 109 K, the parallelism error in the photosensitive drums 109 Y, 109 M, 109 C, and 109 K, and the optical writing device 111 Due to the installation error of the LEDA 130 and the writing timing error of the electrostatic latent images on the photosensitive drums 109Y, 109M, 109C and 109K, the toner images of the respective colors do not overlap at positions that should originally overlap, Deviation may occur.

  For the same reason, the image may be transferred to a range that is outside the range where the image is originally transferred on the paper to be transferred. As such misregistration components, skew, registration deviation in the sub-scanning direction, and the like are mainly known. In addition, the expansion and contraction of the intermediate transfer belt due to the temperature change in the apparatus and deterioration with time are known.

  A pattern detection sensor 117 is provided to correct such positional deviation. The pattern detection sensor 117 is an optical sensor for reading the misregistration correction pattern and the density correction pattern transferred onto the intermediate transfer belt 105 by the photosensitive drums 109Y, 109M, 109C, and 109K. A light emitting element for irradiating a pattern drawn on the surface and a light receiving element for receiving reflected light from the correction pattern. As shown in FIG. 3, the pattern detection sensor 117 is supported on the same substrate along the direction orthogonal to the conveyance direction of the intermediate transfer belt 105 on the downstream side of the photosensitive drums 109Y, 109M, 109C, and 109K. Yes.

  In the image forming apparatus 1, the density of the image transferred onto the paper 104 may vary depending on the state change of the image forming units 106 </ b> Y, 106 </ b> M, 106 </ b> C, 106 </ b> K and the state change of the optical writing device 111. . In order to correct such density fluctuations, a density correction pattern formed according to a predetermined rule is detected, and based on the detection result, the drive parameters of the image forming units 106Y, 106M, 106C, and 106K and the optical writing device 111 Density correction for correcting the drive parameter is executed.

  The pattern detection sensor 117 is used to detect a density correction pattern in addition to the above-described position shift correction operation by detecting the position shift correction pattern. Details of the pattern detection sensor 117 and the mode of positional deviation correction and density correction will be described in detail later. The print engine 26 includes a configuration for realizing an information processing function such as the CPU 10 described with reference to FIG. 1 and is controlled and operated by such a configuration.

  A belt cleaner 118 is provided in order to remove the toner of the correction pattern drawn on the intermediate transfer belt 105 in such a drawing parameter correction and prevent the paper conveyed by the intermediate transfer belt 105 from becoming dirty. . As shown in FIG. 3, the belt cleaner 118 is a cleaning blade pressed against the intermediate transfer belt 105 on the downstream side of the driving roller 107 and upstream of the photosensitive drum 109. A developer remover that scrapes off toner adhering to the surface.

  Next, the optical writing device 111 according to the present embodiment will be described. FIG. 4 is a diagram showing an arrangement relationship between the optical writing device 111 and the photosensitive drum 109 according to the present embodiment. As shown in FIG. 4, the irradiation light irradiated to the photosensitive drums 109Y, 109M, 109C, and 109K of the respective colors is LEDA (Light-emitting diode Array) 130Y, 130M, 130C, and 130K (hereinafter, generally referred to as “light source”). LEDA130).

  The LEDA 130 is configured by arranging LEDs, which are light emitting elements, in the main scanning direction of the photosensitive drum 109. The control unit included in the optical writing device 111 controls the lighting / extinguishing states of the LEDs arranged in the main scanning direction for each main scanning line based on the drawing information input from the controller 20. The surface of the photosensitive drum 109 is selectively exposed to form an electrostatic latent image.

  Next, a control block of the optical writing device 111 according to the present embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating a functional configuration of the optical writing device control unit 120 that controls the optical writing device 111 according to the present embodiment, and a connection relationship between the LEDA 130 and the pattern detection sensor 117.

  As shown in FIG. 5, the optical writing device control unit 120 according to the present embodiment includes a light emission control unit 121, a count unit 122, a sensor control unit 123, a correction value calculation unit 124, a reference value storage unit 125, and a correction value storage unit. 126. The optical writing device control unit 120 functions as an optical writing control device that controls the LEDA 130 that is a light source to form an electrostatic latent image on the photosensitive member.

  The optical writing device 111 according to the present embodiment includes information processing mechanisms such as the CPU 10, RAM 11, ROM 12, and HDD 14 as described in FIG. 1, and the optical writing device control unit 120 as shown in FIG. Similar to the controller 20 of the forming apparatus 1, a control program stored in the ROM 12 or the HDD 14 is loaded into the RAM 11 and is operated under the control of the CPU 10.

  The light emission control unit 121 is a light source control unit that controls the LEDA 130 based on image information input from the engine control unit 31 of the controller 20. That is, the light emission control unit 121 also functions as a pixel information acquisition unit. The light emission control unit 121 realizes optical writing on the photosensitive drum 109 by causing the LEDA 130 to emit light at a predetermined line cycle.

  The line cycle in which the light emission control unit 121 controls the light emission of the LEDA 130 is determined by the output resolution of the image forming apparatus 1. However, as described above, the light emission control is performed when scaling is performed in the sub-scanning direction in accordance with the ratio with the paper conveyance speed. The unit 121 performs scaling in the sub-scanning direction by adjusting the line period.

  In addition to driving the LEDA 130 based on the drawing information input from the engine control unit 31, the light emission control unit 121 controls the light emission of the LEDA 130 in order to draw a correction pattern in the drawing parameter correction process described above. .

  As described with reference to FIG. 4, a plurality of LEDAs 130 are provided corresponding to the respective colors. Therefore, as shown in FIG. 5, a plurality of light emission control units 121 are also provided so as to correspond to the plurality of LEDAs 130, respectively. The correction value generated as a result of the positional deviation correction process in the drawing parameter correction process is stored as a positional deviation correction value in the correction value storage unit 126 shown in FIG.

  The light emission control unit 121 corrects the timing for driving the LEDA 130 based on the positional deviation correction value stored in the correction value storage unit 126. In addition, the light emission control unit 121 corrects the position of the image in the main scanning direction, and causes the LEDA 130 to emit light based on the image information for each main scanning line. The correspondence relationship with each LED element included in the LEDA 130 is adjusted based on the misalignment correction value stored in the correction value storage unit 126.

  Specifically, the correction of the drive timing of the LEDA 130 by the light emission control unit 121 is to delay the timing for driving the LEDA 130 to emit light on a line cycle basis based on the drawing information input from the engine control unit 31, that is, to shift the line. It is realized by. On the other hand, since the drawing information is sequentially input from the engine control unit 31 according to a predetermined cycle, in order to delay the light emission timing by shifting the line, the input drawing information is held, It is necessary to delay the read timing.

  Therefore, the light emission control unit 121 has a line memory that is a storage medium for holding drawing information input for each main scanning line, and stores the drawing information input from the engine control unit 31 in the line memory. Hold by. In addition, as a correction | amendment of the drive timing of LEDA130, the fine adjustment of the light emission timing for every line period is also performed other than the adjustment per line period.

  In the positional deviation correction process, the count unit 122 starts counting at the same time as the light emission control unit 121 controls the LEDA 130 to start exposure of the photosensitive drum 109K. The count unit 122 acquires a detection signal output when the sensor control unit 123 detects a misalignment correction pattern based on the output signal of the pattern detection sensor 117. Further, the count unit 122 inputs the count value at the timing when the detection signal is acquired to the correction value calculation unit 124. That is, the count unit 122 functions as a detection timing acquisition unit that acquires pattern detection timing.

  The sensor control unit 123 is a control unit that controls the pattern detection sensor 117. As described above, the misregistration correction pattern formed on the intermediate transfer belt 105 based on the output signal of the pattern detection sensor 117 is a pattern. It is determined that the position of the detection sensor 117 has been reached, and a detection signal is output. That is, the sensor control unit 123 functions as a detection signal acquisition unit that acquires a pattern detection signal from the pattern detection sensor 117.

  In addition, the sensor control unit 123 acquires the signal intensity of the output signal of the pattern detection sensor 117 and inputs it to the correction value calculation unit 124 when performing density correction using the density correction pattern. Further, the sensor control unit 123 adjusts the detection timing of the density correction pattern according to the detection result of the position deviation correction pattern.

  The correction value calculation unit 124 is based on the count value acquired from the count unit 122 and the signal intensity of the detection result of the density correction pattern acquired from the sensor control unit 123. The correction value is calculated based on the reference value for density correction. That is, the correction value calculation unit 124 functions as a reference value acquisition unit and a correction value calculation unit. The reference value storage unit 125 stores a reference value for use in such calculation.

  Next, a misregistration correction operation using the misregistration correction pattern will be described. First, a normal misalignment correction operation will be described as a premise of the misalignment correction operation according to the present embodiment. FIG. 6 is a diagram showing marks (hereinafter referred to as misalignment correction marks) drawn on the intermediate transfer belt 105 by the LEDA 130 controlled by the light emission control unit 121 in a normal misalignment correction operation.

  As shown in FIG. 6, the normal misregistration correction mark 400 includes a plurality of misregistration correction pattern rows 401 in which various patterns are arranged in the sub scanning direction in the main scanning direction (2 in this embodiment). I) It is arranged side by side. In FIG. 6, the solid line represents a pattern drawn by the photosensitive drum 109K, the dotted line represents the photosensitive drum 109Y, the broken line represents the photosensitive drum 109C, and the alternate long and short dash line represents a pattern drawn by the photosensitive drum 109M.

  As shown in FIG. 6, the pattern detection sensor 117 has a plurality (two in the present embodiment) of sensor elements 170 in the main scanning direction, and each misalignment correction pattern row 401 includes each sensor element. It is drawn at a position corresponding to 170. As a result, the optical writing device control unit 120 can detect patterns at a plurality of positions in the main scanning direction, and can correct skew of a drawn image. Further, by averaging the detection results based on the plurality of sensor elements 170, the correction accuracy can be improved.

  As shown in FIG. 6, the misalignment correction pattern row 401 includes an overall position correction pattern 411 and a drum interval correction pattern 412. As shown in FIG. 6, the drum interval correction pattern 412 is repeatedly drawn.

  As shown in FIG. 6, the overall position correction pattern 411 is a line drawn by the photosensitive drum 109Y and parallel to the main scanning direction. The overall position correction pattern 411 is a pattern drawn to obtain a count value for correcting the shift of the entire image in the sub-scanning direction, that is, the transfer position of the image with respect to the paper. The overall position correction pattern 411 is also used by the sensor control unit 123 to correct the detection timing when the drum interval correction pattern 412 and a density correction pattern described later are detected.

  In the overall position correction using the overall position correction pattern 411, the optical writing device control unit 120 performs a write start timing correction operation based on the read signal of the overall position correction pattern 411 by the pattern detection sensor 117.

  The drum interval correction pattern 412 is a pattern drawn to obtain a count value for correcting a shift in drawing timing on the photosensitive drum 109 of each color, that is, an overlapping position where images of each color are overlaid. As shown in FIG. 6, the drum interval correction pattern 412 includes a horizontal line pattern 413 and a diagonal line pattern 414. As shown in FIG. 6, the drum interval correction pattern 412 includes a horizontal line pattern 413 configured as a set of linear patterns perpendicular to the CMYK color transport direction, and a predetermined CMYK color transport direction. An oblique line pattern 414 composed of a set of linear patterns inclined at an angle of is alternately formed.

  The optical writing device control unit 120 corrects misalignment in the sub-scanning direction of each of the photosensitive drums 109K, 109M, 109C, and 109Y based on the reading signal of the horizontal line pattern 413 by the pattern detection sensor 117. On the other hand, in the conventional misregistration correction operation, the optical writing device control unit 120 performs misregistration correction in the main scanning direction of each of the photosensitive drums based on the read signal of the oblique line pattern 414.

  When an error occurs in the main scanning direction with respect to the image transfer position, the detection timing of the oblique line pattern 414 changes according to the inclination of the oblique line. For example, when the inclination of the oblique line is 45 degrees with respect to the sub-scanning direction, the amount of movement of the image transfer position in the main scanning direction and the amount of change in the image detection timing are 1: 1. Therefore, the conventional optical writing device control unit 120 corrects misalignment of the photosensitive drums 109K, 109M, 109C, and 109Y in the main scanning direction according to the change amount of the detection timing of the oblique line pattern 414.

  On the other hand, the optical writing device control unit 120 according to the present embodiment has a period from the detection timing of the horizontal line pattern 413 to the detection timing of the oblique line pattern 414 or from the detection timing of the oblique line pattern 414 to the detection timing of the horizontal line pattern 413. Based on the period, the positional deviation correction in the main scanning direction is performed. This is one of the gist according to the present embodiment.

  Next, a pattern detection method as shown in FIG. 6 will be described. FIG. 7 is a diagram illustrating examples of detection signals of the overall position correction pattern 411, the horizontal line pattern 413, and the oblique line pattern 414 according to the present embodiment. As shown in FIG. 6, the pattern detection sensor 117 exposes the surface of the intermediate transfer belt 105 with a predetermined spot diameter at a predetermined position in the main scanning direction. Each pattern is detected when the reflected light enters the sensor element 170.

  The surface of the intermediate transfer belt 105 according to the present embodiment has a color close to white that substantially reflects the irradiated light. Therefore, as shown in FIG. 7, a steady value with the highest signal intensity of the detection signal is obtained while the light emitted from the pattern detection sensor 117 irradiates the area other than the area where the pattern is formed on the surface of the intermediate transfer belt 105. It is a state.

  In contrast, when the intermediate transfer belt 105 is transported and the light emitted from the pattern detection sensor 117 reaches the area where the pattern is formed, the density of the color on which the pattern is drawn and the pattern among the spot diameters. The signal intensity of the detection signal decreases according to the range covered by. The sensor control unit 123 has a detection threshold setting as shown in FIG. 7, and outputs the detection signal to the counting unit 122 at a timing when the detection signal input from the pattern detection sensor 117 intersects the detection threshold.

  The count unit 122 transmits the count value at the timing when the detection signal is acquired from the sensor control unit 123 to the correction value calculation unit 124. Thus, when one pattern passes exposure light emitted from the pattern detection sensor 117 according to the conveyance of the intermediate transfer belt 105, the pattern reaches the spot diameter and the detection signal decreases. The signal intensity of the detection signal intersects with the detection threshold value twice when the pattern deviates from the spot diameter and returns to the original value, and the count value at each timing is input to the correction value calculation unit 124.

  The correction value calculation unit 124 calculates the detection timing of each pattern based on the count value input from the count unit 122 twice for each pattern. Specifically, the intermediate value of the two count values is obtained assuming that the intermediate value of the two count values corresponds to the peak timing of the detection signal in each pattern.

  In such a configuration, the gist of the present embodiment is the manner of calculating the correction value using the detection result in the positional deviation correction in the main scanning direction. Hereinafter, a correction value calculation operation in the positional deviation correction in the main scanning direction according to the present embodiment will be described.

FIG. 8 is a diagram illustrating a reference mode of the pattern detection result in the positional deviation correction in the main scanning direction according to the present embodiment. As shown in FIG. 8, the detection timing of each horizontal line pattern 413 is indicated by Y _ci , K _ci , M _ci , and C _ci . In addition, the detection timing of the oblique line pattern 414 is indicated by Y _si , K _si , M _si , and C _si . Here, “i” is the order of the number of repetitions of the horizontal line pattern 413 and the oblique line pattern 414 repeatedly drawn.

Then, the optical writing device control unit 120 according to the present embodiment detects the i-th diagonal line from the detection timing of the i-th horizontal line pattern 413 for each color as the detection result for the first main scanning position deviation correction. Reference is made to the periods ΔYi1, ΔKi1, ΔMi1, and ΔCi1 until the detection timing of the pattern 414. Further, as a detection result of the second main scanning position deviation correction, for each respective color, the period from the detection timing of the i-th diagonal pattern 414, to the (i + 1) th horizontal line pattern 41 3 of the detection timing ΔYi2, ΔKi2 , ΔMi2, and ΔCi2.

  Even if the image is shifted in the main scanning direction, the detection timing of the horizontal line pattern 413 does not change. On the other hand, as described above, the detection timing of the oblique line pattern 414 changes according to the inclination of the oblique line according to the main scanning direction of the image. Therefore, the interval between the horizontal line pattern 413 and the oblique line pattern 414 changes depending on the positional deviation of the image in the main scanning direction. The optical writing device control unit 120 according to the present embodiment performs misalignment correction in the main scanning direction based on the change in the interval between the horizontal line pattern 413 and the oblique line pattern 414.

That is, the reference value storage unit 125 stores reference values for Y _ci , K _ci , M _ci , and C _ci shown in FIG. 8 as reference values for correcting misalignment in the sub-scanning direction. Then, the optical writing device control unit 120 corrects the positional deviation of the image in the sub-scanning direction based on the difference between the reading result of the horizontal line pattern 413 and the reference value stored in the reference value storage unit 125.

Further, in the reference value storage unit 125, ΔY _i1 , ΔK _i1 , ΔM _i1 , ΔC _i1, ΔY _i2 , ΔK _i2 , ΔM _i2 , ΔC _i2 shown in FIG. 8 are used as reference values for correcting misalignment in the main scanning direction. Each reference value is stored. Then, the optical writing device control unit 120 corrects misalignment of the image in the main scanning direction based on the difference between the reading result of the horizontal line pattern 413 and the oblique line pattern 414 and the reference value stored in the reference value storage unit 125. Do.

  In such misalignment correction based on the pattern detection timing, the photosensitive drum 109 on which the electrostatic latent image and the toner image are formed, and the intermediate transfer belt 105 that conveys the toner image transferred from the photosensitive drum 109 are used. However, it is performed on the assumption that the toner image always rotates at a constant speed and the toner image is conveyed at a constant speed. However, a periodic error (hereinafter referred to as “periodic error”) based on the eccentricity of the rotating shaft or the like may occur in the conveyance speed of the surface of the rotating body. When such a periodic error occurs, the positional deviation correction is not performed accurately.

  In order to reduce such a cyclic error, in the prior art, the drum interval correction pattern 412 is formed over the entire circumference of the photosensitive drum 109 or the intermediate transfer belt 105, which is a rotating body, and is thus formed. By taking the average of the detection results of the detected patterns, the influence of errors is eliminated.

  FIG. 9 is a diagram illustrating an aspect of a state in which a drum interval correction pattern 412 is formed on the photosensitive drum 109 and the intermediate transfer belt 105. The pattern interval for each set of the horizontal line pattern 413 and the oblique line pattern 414 is adjusted so that an integral number of drum interval correction patterns 412 are formed on the photosensitive drum 109 and the intermediate transfer belt 105 at equal intervals. .

  In FIG. 9, the interval for each set of the horizontal line pattern 413 and the diagonal line pattern 414 is adjusted so that the surface of the photosensitive drum 109 is equally divided into six and the surface of the intermediate transfer belt 105 is equally divided into 48. Yes. In this way, the surface of the photosensitive drum 109 and the intermediate transfer belt 105 is equally divided to form a pattern, the pattern is formed over at least one round, and the detection result of each pattern is averaged, whereby the photosensitive drum The periodic error due to the rotation of the intermediate transfer belt 105 and the intermediate transfer belt 105 can be canceled.

  Specifically, as shown in FIG. 10, the cyclic error due to the rotation of the photosensitive drum 109 and the intermediate transfer belt 105 occurs in a plus direction in a portion having a rotational phase with respect to the average value, and in a minus direction in a certain portion. Occurs and returns to the original in one lap. Therefore, the period error can be canceled by averaging the pattern detection results over one round.

  On the other hand, as described above, in the image forming apparatus according to the present embodiment, the detection timing of the oblique line pattern 414 is not used alone when correcting the misalignment in the main scanning direction, but is adjacent to the horizontal line pattern 413. It is used as an interval. That is, when the image is shifted in the main scanning direction, the interval between the adjacent horizontal line patterns 413 changes due to the detection timing of the oblique line pattern 414 being shifted according to the inclination, so that the main scanning is performed based on the change amount. Judge direction deviation.

  Next, the calculation of the misregistration correction value in the main scanning direction based on the detection result of the misregistration correction pattern according to the present embodiment as described in FIG. 8 will be described. FIG. 8 shows a pattern mode starting from the i-th horizontal line pattern 413.

First, a mode of misalignment correction based on the distance from the horizontal line pattern 413 to the oblique line pattern 414 will be described. In the present embodiment, since the intervals from the horizontal line pattern 413 to the diagonal line pattern 414 for each color of YMCK are designed to be equal, the i-th horizontal line pattern for each color when there is no displacement in the main scanning direction. The distances ΔY _i1 , ΔK _i1 , ΔM _i1 , ΔC _i1 from 413 to the i-th oblique line pattern 414 are the detection timings Y _ci , K _ci , M _ci , C _ci , Y _si , K _si , M _si shown in FIG. , C _si and can be expressed by the following formulas (1) to (4).

Here, assuming that the ideal value of the interval from the horizontal line pattern 413 to the oblique line pattern 414 is D, ΔY _i1 = ΔK _i1 = ΔM _i1 = ΔC _i1 = D when there is no displacement in the main scanning direction. . The ideal value D is stored in the reference value storage unit 125.

  When the main scanning position shift occurs in any color of YMCK, the detection position of the oblique line pattern 414 changes, so the distance from the horizontal line pattern 413 to the oblique line pattern 414 changes. FIG. 11 is a diagram illustrating an aspect in the case where a color shift in the main scanning direction occurs in Y and K in the pattern as illustrated in FIG.

The inclination of the oblique line patterns 414 according to the present embodiment is 45 degrees, for example, as shown in FIG. 11, the color of Y is the main scanning direction [Delta] S _{Yi1, K} colors in the main scanning direction color misregistration of [Delta] S _Ki1 occurs when, [Delta] s _Yi1, [Delta] s _Ki1, respectively [Delta] Y _i1, acts in a direction to spread [Delta] K _i1. Therefore, the Y main scanning color misregistration amount ΔS _{YKi1 with} respect to K can be expressed by the following equations (5) to (7).

The Y main scanning color shift amount ΔS _YKi1 with respect to K can be calculated from the difference between the K and Y pattern intervals as shown in the above equation (7). The correction value calculation unit 124 according to the present embodiment calculates the amount of YMC main scanning position deviation with respect to K by calculating the above calculation in the same way for all colors of YMC.

Next, a description will be given of how misalignment is corrected based on the distance from the oblique line pattern 414 to the horizontal line pattern 413. In the present embodiment, since the intervals from the diagonal line pattern 414 to the horizontal line pattern 413 for each color of YMCK are designed to be equal, if there is no positional deviation in the main scanning direction, the i-th diagonal line pattern for each color The distances ΔY _i2 , ΔK _i2 , ΔM _i2 , ΔC _i2 from 414 to the i + 1th horizontal line pattern 413 are the detection timings Y _{ci + 1} , K _{ci + 1} , M _{ci + 1} , C _{ci + 1} , Y _si , K _si , M _{si shown in FIG.} , C _si and can be expressed by the following formulas (8) to (11).

Here, if the ideal value of the interval from the diagonal line pattern 414 to the horizontal line pattern 413 is D, which is the same as the interval from the horizontal line pattern 413 to the diagonal line pattern 414, ΔY _i2 when no misalignment occurs in the main scanning direction. = ΔK _i2 = ΔM _i2 = ΔC _i2 = D.

When the main scanning position shift occurs in any of the colors YMCK, the detection position of the oblique line pattern 414 changes, so the distance from the oblique line pattern 414 of that color to the horizontal line pattern 413 changes. The inclination of the oblique line patterns 414 according to this embodiment is 45 degrees as described above, as shown in FIG. 11, [Delta] S color Y is the main scanning direction _Yi1, the color shift of [Delta] S _Ki1 color in the main scanning direction of the _K when There occurred, [Delta] s _Yi1, [Delta] s _Ki1, respectively [Delta] Y _i2, acts in the direction of [Delta] K _i2 is narrowed. Therefore, the Y main scanning color misregistration amount ΔS _{YKi2 with} respect to K can be expressed by the following equations (12) to (14).

  As described in the above formulas (5) to (6), the positional deviation amount in the main scanning direction is the direction in which the interval from the horizontal line pattern 413 to the oblique line pattern 414 increases, that is, the downward direction in FIG. It is. On the other hand, in the case of the interval from the oblique line pattern 414 to the horizontal line pattern 413, the interval is narrowed.

Therefore, as shown in the above equations (12) to (14), the Y main scanning color misregistration amount ΔS _YKi2 calculated using the detection result for the second main scanning position deviation correction is an oblique line pattern. It can be calculated by inverting the sign of the interval from 414 to the horizontal line pattern 413. The correction value calculation unit 124 according to the present embodiment calculates the amount of YMC main scanning position deviation with respect to K by calculating the above calculation in the same way for all colors of YMC.

The correction value calculation unit 124 determines the main scanning position deviation amount _ΔSYKi1 based on the interval from the horizontal line pattern 413 to the oblique line pattern 414 and the main scanning position deviation based on the interval from the oblique line pattern 414 to the horizontal line pattern 413. The average value of the amount ΔS _YKi2 is obtained for each color of YMC according to the following formulas (15) to (17), whereby the amount of positional deviation in the main scanning direction with respect to K of each YMC is obtained. Remember.

Here, “k1” in the equations (15) to (17) is the number of detections during the period from the horizontal line pattern 413 to the oblique line pattern 414, that is, the number of detection results for the first main scanning position deviation correction. “K2” is the number of detections in the period from the oblique line pattern 414 to the horizontal line pattern 413, that is, the number of detection results for second main scanning position deviation correction.

Through such processing, the position shift correction amounts ΔS _YK , ΔS _MK , ΔS _{CK in the} main scanning direction with respect to K for each YMC are obtained and stored in the correction value storage unit 126. Then, the light emission control unit 121 adjusts the position of each YMC in the main scanning direction based on the position shift correction amounts ΔS _YK , ΔS _MK , and ΔS _CK stored in this manner, and outputs the image. I do.

Next, the principle that the cyclic error is suppressed in the positional deviation correction in the main scanning direction according to the present embodiment will be described. FIG. 12 is a diagram illustrating the principle that the cyclic error is suppressed in the positional deviation correction operation by the optical writing device 111 according to the present embodiment. When the photosensitive drum 109 and intermediate transfer belt 105 and T the time required for 1 Shukairu, cyclic errors in a certain time t, the following number of frequency of the periodic function as m, periodic function F (t, m) Can be expressed by the following formula (18).

In the above formula (1 8 ), 0 ≦ t <T. Then, considering that the rotation time of one round is T, the following equation (19) is established.

At this time, when the horizontal line pattern and the oblique line pattern are formed at intervals that equally divide the period T, the period error can be expressed by the following equation (20) using Fourier series expansion.
In the above equation (20), ω ₀ is a fundamental angular frequency, and ω ₀ = 2π / T.

When the upper above formula (20) to change by using the synthesis trigonometric function, of formula (21) below is obtained.

That is, according to the above equation (21), all cyclic errors can be expressed by the sum of sine curves and DC components having different orders, amplitudes, and phases, where ω ₀ is m = 1 order angular frequency. Is possible. In the following explanation, explanation will be made based on a periodic error due to Fourier series expansion. For the sake of simplification, a specific description of Y color will be described, but the calculation of MC is the same.

  As an example, consider the case where the integer division number n for dividing one revolution of the photosensitive drum 109 or the intermediate transfer belt 105 is set to a very large value, and the horizontal line pattern 413 and the oblique line pattern 414 are arranged at positions equally divided by n. . The main scanning color misregistration amount of Y with respect to K calculated based on the detection result for the first main scanning misregistration correction and the detection result for the second main scanning misregistration correction is expressed by the above formulas (5) to (7). ) And formulas (12) to (14).

On the other hand, when a periodic error occurs, the periodic function F (t, m) is added to each equation, and the following equations (22) to (25) are obtained.

Here, the interval between the horizontal line pattern 413 and the oblique line pattern 414 is 1 / n times the length of one circle, and n is a very large value, so the interval between the horizontal line pattern 413 and the oblique line pattern 414 is very large. Narrow. As a result, the cyclic errors generated in the first main scanning position deviation correction detection result and the second main scanning position deviation correction detection result adjacent to each other are substantially equal, and the following equation ( 26) and (27) hold.

As described above with respect to the equations (7) and (14), the Y main scanning color misregistration amount ΔS _YKi2 calculated using the detection result for the second main scanning position misalignment correction is an oblique line. Calculation can be performed by inverting the sign of the interval from the pattern 414 to the horizontal line pattern 413. When a cyclic error is added to the above equations (7) and (14), the following equations (26) and (27) are obtained.

Then, the detection result for correcting the first main scanning position deviation and the detection result for correcting the second main scanning position deviation are combined into one set for the adjacent detection results, and the amount of positional deviation for one set is obtained. The following formula (30) is obtained.

  As described in FIG. 8, the pattern for the detection result for the first main scanning position deviation correction, that is, the interval from the horizontal line pattern 413 to the oblique line pattern 414, and the detection for the second main scanning position deviation correction. The pattern for the result, that is, the interval from the oblique line pattern 414 to the horizontal line pattern 413 is alternately arranged in the conveyance direction of the intermediate transfer belt 105.

  In this case, as described above, in the second misalignment correction detection result, since the sign is inverted to obtain the correction value, the influence of the periodic error in the first misalignment correction detection result and the second The sign of the influence of the periodic error in the detection result for correcting the positional deviation is also reversed. Also, as shown in FIG. 12, the direction of the periodic error affecting the detection result of each pattern is opposite between the horizontal line pattern 413 and the oblique line pattern 414.

  Therefore, the cyclic error generated in the first misalignment correction detection result and the cyclic error generated in the second misalignment correction detection result cancel each other as shown in FIG. The effect of canceling the periodic error becomes higher as the distance between the horizontal line pattern 413 and the oblique line pattern 414 becomes smaller. When the division number n approaches infinity, the periodic error in all frequency bands is reduced to correct the positional deviation. be able to.

  Actually, since the oblique line pattern has a width for correcting the main scanning position deviation, the size of the position deviation correction pattern does not become zero, and the division number n becomes a finite value. Therefore, the above equation (30) is established within a range that satisfies the sampling theorem.

  In addition, the period error from the horizontal line pattern 413 to the oblique line pattern 414 is the same as the period from the oblique line pattern 414 to the horizontal line pattern 413 when the positional deviation does not occur. Higher. This is because if the two sections are the same, the amount of the cyclic error that affects each section is also the same.

  Therefore, as described in the above formulas (5) to (7) and the above formulas (12) to (14), the section from the horizontal line pattern 413 to the diagonal line pattern 414, the section from the diagonal line pattern 414 to the horizontal line pattern 413, and Are preferably the same as the ideal value D.

  Further, in order to more effectively exhibit the effect of canceling the periodic error as shown in FIG. 12, the section from the horizontal line pattern 413 to the diagonal line pattern 414 referred to for calculating the correction value, and the diagonal line pattern 414 are used. The number of sections to the horizontal line pattern 413 is preferably the same. That is, the light emission control unit 121 controls the light emission of the LEDA 130 so that each section has the same number when the horizontal line pattern 413 and the oblique line pattern 414 are repeatedly drawn.

  The approximation that the periodic error that affects the detection result for the first misalignment correction and the periodic error that affects the detection result for the second misalignment correction adjacent thereto is the same as the frequency of the periodic error. The lower the frequency, the more accurate the component. Accordingly, the effect of reducing the cyclic error becomes higher as the frequency component of the cyclic error becomes lower.

  Next, the effect of reducing the cyclic error according to this embodiment will be described. FIGS. 13A and 13B are diagrams showing a comparison between the positional deviation correction method according to the present embodiment and the prior art, and FIG. 13A is a diagram for correcting the first and second positional deviations. FIG. 13B is a diagram showing a case where both detection results are used, and FIG. 13B is a diagram showing a case where only the detection result for the first misalignment correction is used.

  As described above, n is an integer division number that divides one circumference of the photosensitive drum 109 or the intermediate transfer belt 105. In other words, when the light emission control unit 121 repeatedly draws the horizontal line pattern 413 and the oblique line pattern 414 alternately, the interval between the two becomes a divisor by an integer corresponding to one round of the photosensitive drum 109 and the intermediate transfer belt 105. The LEDA 130 is controlled to emit light. Horizontal line patterns 413 or diagonal line patterns 414 are alternately formed at each point of one round equally divided by n. k is a section from the horizontal line pattern 413 to the oblique line pattern 414 (hereinafter referred to as “first pattern group”) and a section from the oblique line pattern 414 to the horizontal line pattern 413 (hereinafter referred to as “second pattern group”). This represents the number of pairs formed, and is the maximum integer not exceeding n / 2. When the division number n is an even number, k is n / 2.

  A periodic error that occurs when the main scanning position deviation amount is calculated using only the first pattern group, and a periodic error that occurs when the main scanning position deviation amount is calculated using both the first pattern group and the second pattern group. When the respective amplitude intensity components are compared, the effect ratio can be calculated. The effect ratio is calculated using the Fourier series expansion formula described in the above formulas (20) and (21).

First, the error amount A when only the first pattern set is used can be expressed by the following equation (31).

Further, the error amount B when using both the first pattern group and the second pattern group can be expressed by the following equation (32).

The effect ratio can be expressed by B / A using AB obtained by the above formulas (31) and (32), and is 2 sin (πm / n). Thus, since the effect ratio is independent of the number k of the first pattern group and the second pattern group, it is possible to obtain the same reduction effect regardless of the number of misalignment correction patterns formed. .

  That is, by reducing the number k of the first and second pattern groups, the horizontal line pattern 413 and the oblique line pattern 414 are not formed over the entire circumference of the intermediate transfer belt 105 as described in FIG. It is possible to correct misalignment in the main scanning direction only by forming a pattern in a shorter range such as minutes or 1/3 rounds. As a result, it is possible to reduce the time required for position shift correction and toner consumption.

  Here, the effect ratio of the periodic error of the frequency of the order m changes from the minimum value 0 to the maximum value 2. When the cyclic error can be reduced as compared with the conventional case, that is, when the effect ratio is 1 or less, m ≦ n / 6 is satisfied on the condition that 2 sin (πm / n) ≦ 1.

  FIG. 14 is a graph showing the order m on the horizontal axis and the effect ratio on the vertical axis. As shown in FIG. 14, in the range of m> n / 6, the effect ratio exceeds 1, and the effect of reducing the cyclic error is inferior to that of the conventional case, but in an environment where the cyclic error in the low frequency band is dominant. The periodic error reduction method according to this embodiment is effective.

  Further, when the horizontal line pattern 413 and the oblique line pattern 414 are formed evenly over the 1 / L circumference of the photosensitive drum 109 and the intermediate transfer belt 105, the sum of the periodic errors of the M (L × i: i is a natural number) order frequency is zero. become. By utilizing this characteristic, it is possible to suppress high-order cyclic errors, so that the cyclic error in the low frequency band is reduced by the combination of the first pattern group and the second pattern group described above, and the period in the high frequency band is reduced. By reducing the error by a method of forming a pattern over the 1 / L circumference of the rotator, it is possible to obtain a period error reduction effect in a wide frequency band.

  Further, the effect of reducing the periodic error by using the first pattern group and the second pattern group described above becomes higher as the value of the periodic error affecting the adjacent pattern group is closer. Therefore, the division number n is established even if it is a real number.

  As described above, according to the optical writing control device according to the present embodiment, the horizontal line pattern 413 and the oblique line pattern 414 are alternately formed in the image misalignment correction in the electrophotographic image forming apparatus. Misalignment correction in the main scanning direction is performed using the first pattern group from the oblique line pattern 414 to the oblique line pattern 414 and the second pattern group from the oblique line pattern 414 to the horizontal line pattern 413.

  In such a case, even if a periodic error occurs in the rotating body such as the photosensitive drum 109 or the intermediate transfer belt 105, the influence of the periodic error is caused by the pattern interval of the first pattern group and the pattern interval of the second pattern group. The sign of is reversed. As a result, the cyclic errors in adjacent pattern groups cancel each other, and it is possible to suppress a decrease in misalignment correction accuracy due to the cyclic errors. Therefore, as described with reference to FIG. 9, it is possible to reduce the cyclic error without forming a pattern for correcting misalignment over one rotation of the rotating body.

  As described above, when drawing the correction pattern for correcting the position where the image is drawn in the image forming apparatus, the error due to the period of the rotating body included in the image forming mechanism is reduced, and the pattern is drawn. The time required can be shortened.

  In the above-described embodiment, in the full-color image forming apparatus capable of forming and outputting a plurality of colors of YMCK, as an example, correction of misregistration in the main scanning direction when color misregistration between each color is matched with K as a reference. explained. This is an example, and the same applies to a case where a color other than K is used as a reference.

  Further, the present invention is not limited to color misregistration between colors in an image forming apparatus using a plurality of colors. In that case, it can be similarly realized by obtaining a deviation amount from the reference value D instead of the correction value by comparison with the reference color described in the equations (13) to (15) of the above embodiment.

1 Image forming apparatus 10 CPU
11 RAM
12 ROM
13 Engine 14 HDD
15 I / F
16 LCD
17 Operation unit 18 Bus 20 Controller 21 ADF
22 Scanner unit 23 Paper discharge tray 24 Display panel 25 Paper feed table 26 Print engine 27 Paper discharge tray 28 Network I / F
30 Main control unit 31 Engine control unit 32 Input / output control unit 33 Image processing unit 34 Operation display control unit 101 Paper feed tray 102 Paper feed roller 103 Registration roller 104 Paper 105 Intermediate transfer belts 106K, 106C, 106M, 106Y Image forming unit 107 Drive roller 108 Followed roller 109K, 109C, 109M, 109Y Photoconductor drum 110K Charger 111 Optical writing device 112K, 112C, 112M, 112Y Developer 113K, 113C, 113M, 113Y Static eliminator 115K, 115C, 115M, 115Y Transfer device 116 Fixing device 117 Pattern detection sensor 120 Optical writing device control unit 121 Light emission control unit 122 Count unit 123 Sensor control unit 124 Correction value calculation unit 125 Reference value storage unit 126 Correction value storage units 130, 130K, 130C 130M, 130Y LEDA
170 Sensor element

JP 2011-154291 A

Claims (6)

An optical writing control device for controlling a light source for exposing a photoconductor to form an electrostatic latent image on the photoconductor,
A light emission control unit for controlling the light source to emit light and exposing the photosensitive member;
A detection signal acquisition unit that acquires a detection signal of a sensor that detects the image in a conveyance path in which an image obtained by developing the electrostatic latent image formed on the photosensitive member is transferred and conveyed;
Based on a detection signal detected by the sensor, a correction pattern for correcting a transfer position to which a developer image on which the electrostatic latent image formed on the photoconductor is developed in the transport path is transferred. anda correction value calculation unit for calculating a correction value for correcting the transfer position,
The light emission control unit is configured to repeatedly draw a linear horizontal line pattern perpendicular to the conveyance direction of the conveyance path and a linear oblique line pattern inclined at a predetermined angle with respect to the conveyance direction. Draw the correction pattern by controlling the light emission,
In the horizontal line pattern and the diagonal line pattern that are alternately and repeatedly drawn, the correction value calculating unit detects a detection period from when the horizontal line pattern is detected until the diagonal line pattern is detected and after detecting the diagonal line pattern. Based on a detection period until a horizontal line pattern is detected, a correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction is calculated.
In the correction pattern formed on the photoconductor by the light emission control unit, an interval from the horizontal line pattern to the diagonal line pattern and an interval from the diagonal line pattern to the horizontal line pattern, which are alternately and repeatedly drawn, The circumference of the photoconductor is divided using a real number n satisfying m ≦ n / 6 for each degree m of the cyclic error of the periodic function of a plurality of rotating bodies that causes an error in the transfer position. An optical writing control device, wherein the optical writing control device is drawn with an interval corrected to be a value .   The correction value calculation unit refers to the same number of detection periods from the detection of the horizontal line pattern to the detection of the oblique line pattern and the detection period from the detection of the oblique line pattern to the detection of the horizontal line pattern. The optical writing control apparatus according to claim 1, wherein a correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction is calculated.   The light emission control unit emits the light source such that an interval from the horizontal line pattern to the oblique line pattern and an interval from the oblique line pattern to the horizontal line pattern are the same when no error occurs in the transfer position. The optical writing control device according to claim 1, wherein the optical writing control device controls the optical writing control device. The light emission control unit controls light emission of a plurality of light sources provided for different colors, and exposes a plurality of the photoconductors provided for different colors, thereby causing the horizontal line pattern and the oblique line for each different color. Draw the correction pattern so that the pattern is drawn alternately and repeatedly,
The correction value calculation unit is configured to detect, for each of the different colors, a detection period from when the horizontal line pattern is detected to when the diagonal line pattern is detected and from when the diagonal line pattern is detected to when the horizontal line pattern is detected. 4. The optical writing control device according to claim 1, wherein a correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction is calculated based on a detection period. 5. .   An image forming apparatus comprising the optical writing control device according to claim 1. A method of controlling an optical writing device that controls a light source that exposes a photoconductor to form an electrostatic latent image on the photoconductor,
By controlling the light source to emit light and exposing the photoreceptor,
Obtaining a detection signal of a sensor for detecting the image in a transport path in which an image obtained by developing the electrostatic latent image formed on the photoreceptor is transferred and transported;
Based on a detection signal detected by the sensor, a correction pattern for correcting a transfer position to which a developer image on which the electrostatic latent image formed on the photoconductor is developed in the transport path is transferred. Calculating a correction value for correcting the transfer position;
The light source is controlled to emit light so that a linear horizontal line pattern perpendicular to the conveyance direction of the conveyance path and a linear oblique line pattern inclined at a predetermined angle with respect to the conveyance direction are repeatedly drawn. Draw a correction pattern,
In the calculation of the correction value, in the horizontal line pattern and the diagonal line pattern that are alternately and repeatedly drawn, the detection period from when the horizontal line pattern is detected until the diagonal line pattern is detected and after the diagonal line pattern is detected Based on a detection period until a horizontal line pattern is detected, a correction value for correcting the transfer position in the main scanning direction perpendicular to the transport direction is calculated.
In the correction pattern formed on the photoconductor, an interval from the horizontal line pattern to the oblique line pattern and an interval from the oblique line pattern to the horizontal line pattern, which are alternately and repeatedly drawn, are respectively determined as errors in the transfer position. The peripheral length of the photosensitive member is divided by using a real number n satisfying m ≦ n / 6 for each order m of the periodic error of the periodic function of the plurality of rotating members that causes the occurrence of Draw with corrected intervals,
A method of controlling an optical writing device.