JP2006189625A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing color slurring or the lowering of a color tone or the like from occurring by forming a registration mark while restraining an edge effect. <P>SOLUTION: The registration mark RM (Y) is a toner image including a first line pattern LP1, a second line pattern LP2 and a two-dimensional pattern TP, which are extended in a main scanning direction X, and the first line pattern LP1, the two-dimensional pattern TP and the second line pattern LP2 are arranged separately from each other in this order in a conveying direction D16. Namely, the line patterns LP1 and LP2 extended in the main scanning direction X are respectively formed separately on the upstream side and the downstream side of the two-dimensional pattern TP in the conveying direction D16. Therefore, the edge effect in the conveying direction D16 is restrained, so that the position of each registration mark RM is accurately detected by a test pattern sensor 18. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a so-called tandem color image forming apparatus in which a plurality of image forming stations, each of which forms a toner image of a different color, are arranged along the moving direction of a transfer medium, and corrects color misregistration. It is related to the technology.

  As this type of image forming apparatus, for example, an apparatus described in Patent Document 1 is known. In this image forming apparatus, an image forming station in which a charging unit, an image writing unit, and a developing unit are arranged around a latent image carrier such as a photosensitive drum is provided for each color along a transfer medium such as a transfer belt. Yes. A toner image formed at each image forming station is superimposed on a transfer medium to form a color image.

  Incidentally, color misregistration is one of the serious problems in an image forming apparatus having a plurality of image forming stations. This occurs when the transfer positions of the toner images formed at different image forming stations onto the transfer medium are shifted from each other, and appear as a change in color tone. In order to solve this problem, a reference pattern image (hereinafter referred to as “registration mark”) for detecting color misregistration is formed on a transfer medium in advance, and each registration mark is detected by an optical sensor. Registration mark position information is obtained, and alignment (color misregistration correction) of each toner image is performed based on the position information.

JP 2004-109617 A (page 4)

  In order to perform color misregistration correction based on registration mark position information with high accuracy in a tandem image forming apparatus, registration mark detection accuracy is important. However, in the prior art, sufficient consideration has not been made in this regard, and a strip-shaped solid image is simply adopted as a registration mark, resulting in a decrease in detection accuracy due to a so-called edge effect. More specifically, when a two-dimensional solid image is formed as described above, the toner particles are particularly concentrated on the edge of the registration mark due to the edge effect. For this reason, the toner density locally increases at the end of the registration mark, and the output signal from the optical sensor varies greatly. As a result, the registration mark detection accuracy based on the output signal of the optical sensor is lowered, color misregistration correction cannot be performed satisfactorily, and problems such as printing with a color misregistration state and a desired color tone cannot be obtained. Problems sometimes occurred.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of preventing occurrence of color misregistration or color tone deterioration by forming a resist mark while suppressing the edge effect. To do.

  In the image forming apparatus according to the present invention, a plurality of image forming stations, each forming a toner image of a different color, are arranged along the moving direction of the transfer medium, and the toner images formed by the plurality of image forming stations are arranged. Image formation that forms resist marks on the transfer medium surface apart in the moving direction, detects each resist mark with an optical sensor, and corrects color misregistration between multiple colors based on an output signal from the optical sensor In order to achieve the above object, each of the plurality of image forming stations uses a toner image including a linear pattern extending in the main scanning direction substantially orthogonal to the moving direction and a two-dimensional pattern as a registration mark. The linear pattern and the two-dimensional pattern are formed and spaced apart from each other in the moving direction.

  When the registration mark is composed of only a two-dimensional pattern as in the prior art, toner concentration occurs at the edge of the registration mark due to the edge effect as described above, and the density of the edge compared to the center of the registration mark is increased. Becomes higher. In particular, density fluctuations at the end substantially perpendicular to the moving direction are one of the main factors that cause the output of the optical sensor to fluctuate greatly, and are a major obstacle to accurately detecting registration mark position information. Therefore, in the present invention, a linear pattern extending in the main scanning direction substantially orthogonal to the moving direction of the transfer medium is formed apart from the two-dimensional pattern in the moving direction. A registration mark is configured. By providing the linear pattern in this way, the edge effect in the moving direction is suppressed, and the registration mark position detection by the optical sensor can be performed with high accuracy. As a result, color misregistration correction can be performed appropriately.

  Here, as a specific method for obtaining the registration mark position information by the optical sensor, for example, (1) the output signal obtained when the upstream portion of the registration mark in the moving direction of the transfer medium passes through the optical sensor. The position information can be detected based on the change, or (2) the position information can be detected based on the change in the output signal obtained when the downstream portion of the registration mark in the moving direction of the transfer medium passes through the optical sensor. In particular, when the position information of the registration mark is acquired by the former (1), it is desirable that each image forming station is formed so that the linear pattern is formed away from the two-dimensional pattern on the upstream side in the moving direction. Thereby, the edge effect on the upstream side in the moving direction is suppressed, and the position detection accuracy can be increased. On the other hand, when the position information of the registration mark is acquired by the latter (2), it is desirable that each image forming station is formed so that the linear pattern is spaced apart from the two-dimensional pattern on the downstream side in the moving direction. As a result, the edge effect on the downstream side in the moving direction is suppressed, and the position detection accuracy can be increased.

  In addition, a registration mark in which a linear pattern is formed on the upstream side and the downstream side in the moving direction with respect to the two-dimensional pattern may be used. That is, each of the plurality of image forming stations forms a toner image including first and second linear patterns extending in the main scanning direction substantially orthogonal to the moving direction and a two-dimensional pattern as registration marks. You may comprise so that a linear pattern, a two-dimensional pattern, and a 2nd linear pattern may be spaced apart from each other in this order in the moving direction.

  As for the two-dimensional pattern, in addition to the solid image pattern that has been widely used in the past, a lattice pattern in which linear patterns are arranged in a lattice, a screen pattern that has been screen-processed, a slit pattern in which linear patterns are arranged in a predetermined direction, etc. Can be used. In particular, it is preferable to use a halftone pattern such as a lattice pattern, a screen pattern, or a slit pattern as a two-dimensional pattern because the amount of toner consumed for forming each resist mark can be suppressed.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. The apparatus 1 includes a color printing process for forming a full color image by superposing four color toners (developers) of black (K), cyan (C), magenta (M), and yellow (Y), and black (K ) To selectively execute monochromatic printing processing for forming a monochrome image using only toner. In this image forming apparatus 1, when an image forming command (printing command) is given to the main controller 51 from an external device such as a host computer, the engine controller 52 controls each part of the engine unit EG in accordance with the command from the main controller 51. Then, a predetermined image forming operation is executed, and an image corresponding to the image forming command is formed on a sheet (recording material) S such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  In FIG. 1, an image forming apparatus 1 according to the present embodiment includes a housing body 2, a first opening / closing member 3 that is detachably mounted on the front surface of the housing body 2 (right-hand side surface in FIG. 1), And a second opening / closing member 4 (also serving as a paper discharge tray) mounted on the upper surface so as to be freely opened and closed. The first opening / closing member 3 is provided with an opening / closing lid 3 a that can be opened and closed on the front surface of the housing body 2. The opening / closing lid 3a can be opened / closed in conjunction with or independently of the first opening / closing member 3.

  In the housing main body 2, an electrical component box 5 containing a power circuit board, a main controller 51, and an engine controller 52 is provided. An image forming unit 6, a blower fan 7, a transfer belt unit 9 and a paper feed unit 10 are also disposed in the housing body 2. On the other hand, on the first opening / closing member 3 side, a secondary transfer unit 11, a fixing unit 12 and a sheet conveying mechanism 13 are disposed. In this embodiment, the consumables in the image forming unit 6 and the paper feeding unit 10 are configured to be detachable from the apparatus main body. The consumables and the transfer belt unit 9 can be removed and repaired or exchanged.

  The transfer belt unit 9 is disposed below the housing body 2 and is driven to rotate by a black drive motor described later, and a driven roller 15 disposed obliquely above the drive roller 14. An intermediate transfer belt 16 that is stretched between the rollers 14 and 15 and driven to circulate in the direction of the arrow D16 in the figure, and a belt cleaner 17 that abuts against the surface of the intermediate transfer belt 16. The driven roller 15 is disposed obliquely above the drive roller 14 (upward on the left hand in FIG. 1). For this reason, the intermediate transfer belt 16 rotates and moves in the direction D16 while being inclined. Further, the belt surface 16a in which the belt conveyance direction D16 when the intermediate transfer belt 16 is driven is downward (right downward in FIG. 1) is positioned below. In the present embodiment, the belt surface 16a is a belt tension surface (surface pulled by the drive roller 14) when the belt is driven, and the peripheral speed is lower than the peripheral speed of the photosensitive drum (image carrier) 20 of each color. have. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Driving.

The drive roller 14 also serves as a backup roller for the secondary transfer roller 19. A rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 14, and the illustration is omitted by grounding through a metal shaft 2. A conductive path of the secondary transfer bias supplied from the secondary transfer bias generator through the secondary transfer roller 19 is used. Thus, by providing the driving roller 14 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet S enters the secondary transfer portion to be transmitted to the intermediate transfer belt 16, and deterioration of image quality is prevented. can do.

  In the present embodiment, the diameter of the driving roller 14 is smaller than the diameter of the driven roller 15. Thereby, the sheet S after the secondary transfer can be easily peeled by the elastic force of the sheet S itself. The driven roller 15 is also used as a backup roller for the belt cleaner 17. The belt cleaner 17 is provided on the side of the belt surface 16a facing downward in the transport direction, and includes a cleaning blade 17a that removes residual toner and a toner transport member that transports the removed toner, as shown in FIG. Yes. The cleaning blade 17a contacts the intermediate transfer belt 16 at a portion where the intermediate transfer belt 16 is wound around the driven roller 15, and cleans and removes toner remaining on the surface of the intermediate transfer belt 16 after the secondary transfer.

  The driving roller 14 and the driven roller 15 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, a primary transfer roller 21 is provided on the back surface of the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 so as to face the photosensitive drum 20 of each image forming station Y, M, C, K described later. . These four primary transfer rollers 21 are rotatably supported with respect to the support frame, and are electrically connected to a primary transfer bias generator (not shown), and generate the primary transfer bias at an appropriate timing. A primary transfer bias is applied from the portion.

  The support frame is rotatable with respect to the housing main body 2 in the arrow direction D21 with the drive roller 14 as a rotation center. Then, by actuating an actuator (not shown), the support frame is rotated to face the photosensitive drums 20 of the yellow (Y), magenta (M), and cyan (C) image forming stations Y, M, and C. The primary transfer roller 21 arranged in this manner approaches the photosensitive drum 20 and moves away from the photosensitive drum 20. For this reason, when the primary transfer rollers 21 for yellow, magenta, and cyan are moved closer to the photosensitive drum 20, they are brought into contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween (solid line in FIG. 1). This contact position is the primary transfer position, and the toner image is transferred to the intermediate transfer belt 16 at the primary transfer position. Conversely, when the primary transfer rollers 21 for yellow, magenta, and cyan move away from the photosensitive drum 20, the photosensitive drum 20 and the intermediate transfer belt 16 of the image forming stations Y, M, and C are separated from each other (FIG. Dashed line in 1). On the other hand, the primary transfer roller 21 disposed facing the photosensitive drum 20 of the black (K) image forming station K rotates while being in contact with the photosensitive drum 20 with the intermediate transfer belt 16 interposed therebetween. Is configured to do. Therefore, as shown by the solid line in FIG. 1, the color printing process can be executed by positioning all the primary transfer rollers 21 on the photosensitive drum 20 side. On the other hand, as shown by a broken line in FIG. 5, the intermediate transfer belt is executed while only the monochrome printing process is performed by leaving the primary transfer roller 21 for black and separating the other primary transfer roller 21 from the photosensitive drum 20. 16 is separated from the image forming stations Y, M, and C, and yellow, magenta, and cyan colors can be set to a non-printing state. Note that the primary transfer roller 21 for black may also be configured to move away from the photosensitive drum 20 as necessary.

  Further, a test pattern sensor 18 is installed on the support frame of the transfer belt unit 9 in the vicinity of the drive roller 14 as an “optical sensor” of the present invention. The test pattern sensor 18 is a so-called reflection type optical sensor, and includes a light projecting portion (not shown) that irradiates light toward the surface of the intermediate transfer belt 16, a surface of the intermediate transfer belt 16, and a registration mark described later. A light receiving unit (not shown) for receiving the reflected light is provided. Then, light is emitted from the light projecting unit to the registration mark on the intermediate transfer belt 16, while the light from the registration mark is received by the light receiving unit and a signal corresponding to the amount of light received by the light receiving unit is a test pattern sensor 18 is output. Then, each color toner image on the intermediate transfer belt 16 is positioned based on the output signal from the test pattern sensor 18, and the density of each color toner image is detected to correct the color shift and image density of each color image. The configuration of the registration mark used in this embodiment will be described in detail later.

  In this embodiment, in addition to the sensor 18, a vertical synchronization sensor 60 (FIG. 2) that detects a characteristic part of the intermediate transfer belt 16 (for example, a protrusion protruding in the width direction) is attached to the support frame. ing. For this reason, a vertical synchronization signal (reference signal) is output every time the characteristic portion of the intermediate transfer belt 16 passes the sensor 60.

  The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. Each image forming station Y, M, C, K is provided with a photosensitive drum 20. A charging unit 22, an image writing unit 23, a developing unit 24, and a photoconductor cleaner 25 are disposed around each photoconductor drum 20. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. In FIG. 1, since the image forming stations of the image forming unit 6 have the same configuration, for convenience of illustration, only some of the image forming stations are denoted by reference numerals, and the other image forming stations are omitted. . Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

  The photosensitive drums 20 of the image forming stations Y, M, C, and K are disposed so as to be in contact with the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 at the primary transfer position TR1. Each of these photosensitive drums 20 is connected to a dedicated drive motor and is driven to rotate at a predetermined peripheral speed in the conveyance direction of the intermediate transfer belt 16 as indicated by an arrow D20 in the figure.

  The charging unit 22 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to be driven to rotate in contact with the surface of the photosensitive drum 20 at a charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 20 as the photosensitive drum 20 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown), and receives the charging bias from the charging bias generator to charge the surface of the photosensitive drum 20 at the charging position.

  As shown in FIG. 3, the image writing unit 23 uses an array-like writing head 232 in which light emitting diodes 231 are arranged in a line in the axial direction of the photosensitive drum 20, and is spaced apart from the photosensitive drum 20. ing. That is, the plurality of light emitting diodes 231 are arranged in a line in the main scanning direction X substantially orthogonal to the conveyance direction (corresponding to the “movement direction” of the present invention) D16 of the intermediate transfer belt 16, and the drive driver of FIG. When all the light emitting diodes 231 are turned on simultaneously by 526, a one-dot line-like latent image pattern is formed on the photosensitive drum 20 as shown in FIG. Further, when the intermediate transfer belt 16 is moved by n (n = 2, 3,...) Dots while all the light emitting diodes 231 are turned on, a latent image pattern of n dot lines is formed as shown in FIG. It is formed. Then, it is possible to form the “linear pattern” of the present invention by developing the line latent image with toner. Of course, various two-dimensional patterns can be formed by controlling lighting / extinction of each light emitting diode 231 in accordance with a drive command from the drive driver 526.

  The array-like writing head 232 configured as described above has a shorter optical path length than the laser scanning optical system, is compact, can be disposed close to the photosensitive drum 20, and can reduce the size of the entire apparatus. Have advantages. In this embodiment, the photoconductive drum 20, the charging unit 22, the developing unit 24, and the photoconductive cleaner 25 of each of the image forming stations Y, M, C, and K are replaced with replacement cartridges 6Y, 6M, 6C, and 6K (FIG. 2). ) As a unit. Each replacement cartridge 6Y, 6M, 6C, 6K is provided with non-volatile memories 91-94 for storing information relating to the replacement cartridge. The transmission / reception units 53Y, 53M, 53C, and 53K provided in each replacement cartridge and the transmission / reception units 522Y, 522M, 522C, and 522K provided on the main body side are arranged close to each other, and the CPU 521 and the memory of the engine controller 52 are arranged. Wireless communication is performed with 91-94. In this way, information regarding each replacement cartridge is transmitted to the CPU 521, and information in each of the memories 91 to 94 is updated and stored.

  Next, details of the developing unit 24 will be described on behalf of the image forming station K. The developing unit 24 includes a toner storage container 26 for storing toner, two toner agitation supply members 28 and 29 disposed in the toner storage container 26, and a partition member disposed in proximity to the toner agitation supply member 29. 30, a toner supply roller 31 disposed above the partition member 30, a developing roller 33 that contacts the toner supply roller 31 and the photosensitive drum 20 and rotates in a direction indicated by an arrow at a predetermined peripheral speed, and a developing roller And a regulating blade 34 abutting on the bearing 33.

  In each developing unit 24, the toner stirred and carried by the toner stirring supply member 29 is supplied to the toner supply roller 31 along the upper surface of the partition member 30. The toner thus supplied is supplied to the surface of the developing roller 33 via the supply roller 31. The toner supplied to the developing roller 33 is regulated to a predetermined layer thickness by the regulating blade 34 and is conveyed to the photosensitive drum 20. The charged toner is developed at a developing position where the developing roller 33 and the photosensitive drum 20 come into contact with each other by a developing bias applied to the developing roller 33 from a developing bias generator (not shown) electrically connected to the developing roller 33. Moves from the developing roller 33 to the photosensitive drum 20, and the electrostatic latent image formed by the image writing unit 23 is visualized.

  In this embodiment, a photoreceptor cleaner 25 is provided in contact with the surface of the photoreceptor drum 20 on the downstream side of the primary transfer position TR1 in the rotation direction D20 of the photoreceptor drum 20. The photoconductor cleaner 25 is in contact with the surface of the photoconductor drum 20 to remove the toner remaining on the surface of the photoconductor drum 20 after the primary transfer.

  The sheet feeding unit 10 includes a sheet feeding unit including a sheet feeding cassette 35 in which sheets S are stacked and held, and a pickup roller 36 that feeds the sheets S from the sheet feeding cassette 35 one by one. In the first opening / closing member 3, a registration roller pair 37 that defines the timing of feeding the sheet S to the secondary transfer region TR 2, and a secondary transfer unit that is pressed against the drive roller 14 and the intermediate transfer belt 16. A secondary transfer roller 19, a fixing unit 12, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  The secondary transfer roller 19 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, and a pressure roller 46 that presses and biases the heating roller 45. The image secondarily transferred to the sheet S is fixed to the sheet S at a predetermined temperature at a nip formed by the heating roller 45 and the pressure roller 46. In the present embodiment, the fixing unit 12 can be disposed in a space formed obliquely above the intermediate transfer belt 16, in other words, in a space opposite to the image forming unit 6 with respect to the intermediate transfer belt 16. Thus, heat transfer to the electrical component box 5, the image forming unit 6, and the intermediate transfer belt 16 can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced.

  Further, the sheet S thus subjected to the fixing process is conveyed to a second opening / closing member (discharge tray) 4 provided on the upper surface portion of the housing body 2 via the discharge roller pair 39. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position behind the pair of discharge rollers 39. The rotation direction of the discharge roller pair 39 is reversed, whereby the sheet S is conveyed along the duplex printing conveyance path 40. Then, it is put on the conveyance path again before the registration roller pair 37. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 16 in the secondary transfer region TR2 is transferred first. It is the opposite side of the surface that was made. In this way, images can be formed on both sides of the sheet S.

  In addition, as shown in FIG. 2, the apparatus 1 includes a display unit 54 that is controlled by the CPU 511 of the main controller 51. The display unit 54 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 511, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, and the like. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 513 denotes an image memory provided in the main controller 51 for storing an image given from an external device such as a host computer via the interface 512. Reference numeral 523 denotes a ROM for storing a calculation program executed by the CPU 521, control data for controlling the engine unit EG, and the like. Reference numeral 524 denotes a RAM for temporarily storing calculation results in the CPU 521 and other data. is there.

  FIG. 5 is a diagram showing the operation of the image forming apparatus of FIG. In this apparatus, color misregistration correction processing using registration marks is executed at an appropriate timing such as when the power is turned on or cartridge replacement. More specifically, the CPU 521 of the engine controller 52 controls each part of the apparatus as follows in accordance with a program relating to color misregistration correction stored in the ROM 523 to execute registration mark formation / detection and color misregistration correction processing.

  First, in accordance with a control command from the CPU 521 of the engine controller 52, a registration mark RM that combines a linear pattern and a two-dimensional pattern is formed at the image forming stations Y, M, C, and K. The overall dimensions of each registration mark RM The mutual interval, arrangement, and number of the plurality of registration marks RM formed on the intermediate transfer belt 16 are arbitrary, and many various modes have been proposed. In this embodiment, for example, as shown in FIG. 6, a belt-like shape (for example, width 0...) Extending parallel to the main scanning direction X perpendicular to the conveyance direction D16 of the intermediate transfer belt 16 is partially formed on the surface of the intermediate transfer belt 16. 5 mm) registration marks RM are formed in the order of K, C, M, and Y at a predetermined interval (for example, 0.5 mm) in the conveyance direction (sub-scanning direction) D16. FIG. 4A shows a yellow registration mark RM (Y), a black registration mark RM (K), a cyan registration mark RM (C), a magenta registration mark RM (M), and a yellow registration mark. Although only RM (Y) is shown, a plurality of RM (Y) are formed for each color.

  Here, the yellow registration mark RM (Y) is enlarged and the configuration thereof will be described with reference to FIG. In this embodiment, the registration mark RM (Y) is a toner image including a first linear pattern LP1, a second linear pattern LP2, and a two-dimensional pattern TP extending in the main scanning direction X, as shown in FIG. The first linear pattern LP1, the two-dimensional pattern TP, and the second linear pattern LP2 are spaced apart from each other in this order in the transport direction D16. In this embodiment, a solid image pattern is adopted as the two-dimensional pattern TP. Although the yellow registration mark RM (Y) has been described, the registration marks RM (K), RM (C), and RM (M) for other toner colors are similarly configured.

  When all or part of the registration mark RM having such a configuration is formed, the test pattern sensor 18 can detect the registration mark RM by turning on the light projecting portion (not shown) of the test pattern sensor (optical sensor) 18. And That is, the registration marks RM (K), RM (C), RM (M), and RM (Y) formed on the intermediate transfer belt 16 as described above move in the transport direction D16 as the intermediate transfer belt 16 moves. Then, it passes through the detection area 181 of the test pattern sensor 18. At this time, the voltage level of the signal received by the light receiving unit (not shown) of the test pattern sensor 18 and output from the test pattern sensor 18 changes according to the amount of light received. Therefore, by measuring the voltage level, the timing at which each registration mark RM passes through the test pattern sensor 18 can be measured, and the position information of the registration mark RM can be acquired. And it becomes possible to obtain | require the mutual space | interval of the registration mark RM based on the positional information. When position information is obtained for all registration marks RM, color misregistration correction is performed based on the position information.

  As described above, according to this embodiment, since each registration mark RM is configured as described above, position information of the registration mark RM can be detected with high accuracy. As a result, color misregistration correction can be performed appropriately. The reason is as follows. That is, when the registration mark is composed of only the two-dimensional pattern TP as in the prior art, toner concentration occurs at the end of the registration mark RM due to the edge effect as described above, and compared with the central portion of the registration mark RM. As a result, the density of the edge becomes high. In particular, the density variation at the end portion (left and right end portions in FIG. 5B) substantially orthogonal to the transport direction D16 is large, and therefore the output of the test pattern sensor 18 varies greatly. On the other hand, in this embodiment, linear patterns LP1 and LP2 extending in the main scanning direction X are formed apart from each other on the upstream side and the downstream side of the two-dimensional pattern TP in the transport direction D16. Therefore, the edge effect in the transport direction D16 is suppressed, and the position of each registration mark RM can be accurately detected by the test pattern sensor 18. Note that the line widths of the linear patterns LP1 and LP2 in the transport direction D16 and the separation distance from the two-dimensional pattern TP are closely related to the suppression effect of the edge effect, and can be appropriately determined experimentally or by simulation. it can.

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, a solid image pattern is adopted as the two-dimensional pattern TP, but the two-dimensional pattern TP is not limited to this, and any one can be adopted. For example, as shown in FIG.
(a) a lattice pattern composed of vertical lines extending in the main scanning direction X and horizontal lines extending in the transport direction D16;
(b) a grid pattern composed of lines extending in the main scanning direction X and diagonal lines;
(c) screened screen pattern,
(d) A stripe pattern composed of straight lines may be used as the two-dimensional pattern TP.

  Further, the position information is detected based on the change in the output signal obtained when the upstream portion of the registration mark RM formed on the intermediate transfer belt 16 moves in the transport direction D16 and passes through the detection area 181 of the test pattern sensor 18. In this case, it is important to suppress the edge effect on the upstream side. Therefore, when such a detection method is adopted, as shown in FIG. 7, the registration mark RM may be formed by the upstream linear pattern LP1 and the two-dimensional pattern TP. On the contrary, when the position information is detected based on the change of the output signal obtained when the downstream portion of the registration mark RM moves in the transport direction D16 and passes through the detection area 181 of the test pattern sensor 18, on the downstream side It is important to suppress the edge effect. Therefore, when such a detection method is adopted, as shown in FIG. 8, the registration mark RM may be formed by the downstream linear pattern LP2 and the two-dimensional pattern TP.

  In the above embodiment, the image writing unit is configured by the array-like write head 232 in which the light-emitting diodes 231 are arranged in a row as light-emitting elements. For example, organic EL elements are used as the light-emitting elements. May be. FIG. 9 is a schematic perspective view of an image writing unit using an organic EL element. In the figure, details of the line head provided in the image writing unit 23 are shown. In the writing head 232 of each image writing unit 23, the light emitting element array composed of the organic EL elements 233 is held in a long housing. The image writing section 23 is driven by a TFT 235 formed on the same glass substrate 234, on which a light emitting section of a light emitting element array composed of organic EL elements 233 is placed on a glass substrate 234. The gradient index rod lens array 236 constitutes an imaging optical system, and a gradient index rod lens 237 arranged in front of the light emitting unit is stacked. The housing covers the periphery of the glass substrate 234 and the side facing the photosensitive drum 20 is open. In this way, light is emitted from the gradient index rod lens 237 to the photosensitive drum 20. A light-absorbing member (paint) is provided on the surface of the housing that faces the end surface of the glass substrate 234.

  FIG. 10 is a cross-sectional view of the image writing unit in the sub-scanning direction. The image writing unit 23 includes a light emitting element array composed of organic EL elements 233 attached facing the rear surface of the gradient index rod lens array 236 in the housing, and an organic EL element 233 in the light emitting element array 233 from the rear surface of the housing. And an opaque cover 238 for shielding the light emitting element array. Further, the cover 238 is pressed against the rear surface of the housing by the fixed plate spring 239, so that the inside of the housing is sealed light-tight. That is, the glass substrate 234 is optically sealed with the housing by the fixed plate spring 239. For this reason, total reflection at the end face of the glass substrate 234 can be prevented and light can be efficiently absorbed. A plurality of fixed leaf springs 239 are provided in the longitudinal direction of the housing.

  A writing head in which elements such as a liquid crystal shutter provided with a backlight are arranged in a line in the axial direction of the photosensitive drum 20 may be used. Of course, you may employ | adopt the image writing part comprised by a laser scanning optical system.

  Furthermore, in the above embodiment, the present invention is applied to an image forming apparatus that forms a registration mark on the intermediate transfer belt 16, but the scope of application of the present invention is not limited to this, and an intermediate transfer drum, The present invention can be applied to all apparatuses that perform color misregistration processing by forming a registration mark on a transfer medium such as a transfer sheet.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a schematic diagram showing a schematic configuration of a write head. FIG. 4 is a diagram showing a line latent image formed by the writing head of FIG. 3. The figure which shows the relationship between a registration mark and a test pattern sensor. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 5 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 6 is a view showing still another embodiment of the image forming apparatus according to the present invention. The schematic perspective view of the image writing part using an organic EL element. FIG. 3 is a cross-sectional view of the image writing unit in the sub-scanning direction.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 16 ... Intermediate transfer belt (transfer medium), 18 ... Test pattern sensor (optical sensor), D16 ... Transport direction (moving direction), LP1, LP2 ... Linear pattern, RM, RM (K), RM (C), RM (M), RM (Y) ... Registration mark, TP ... Two-dimensional pattern, X ... Main scanning direction, Y, M, C, K ... Image forming station

Claims (4)

A plurality of image forming stations, each forming a different color toner image, are arranged along the transfer medium moving direction, and the toner images formed by the plurality of image forming stations are used as registration marks on the surface of the transfer medium. In the image forming apparatus, the registration marks are formed apart from each other in the moving direction, and each registration mark is detected by an optical sensor, and color misregistration between the plurality of colors is corrected based on an output signal from the optical sensor.
Each of the plurality of image forming stations forms a toner image including a linear pattern extending in a main scanning direction substantially orthogonal to the moving direction and a two-dimensional pattern as the registration mark,
The image forming apparatus, wherein the linear pattern and the two-dimensional pattern are spaced apart from each other in the moving direction. The position information of each of the plurality of registration marks is detected based on a change in an output signal obtained when an upstream portion of the registration mark in the moving direction passes through the optical sensor, and the position information is The image forming apparatus according to claim 1, wherein color misregistration is corrected based on the image forming apparatus.
Each of the plurality of image forming stations is an image forming apparatus that forms the straight line pattern on the upstream side in the moving direction with respect to the two-dimensional pattern. Position information of each of the plurality of registration marks is detected based on a change in an output signal obtained when a downstream portion of the registration mark in the moving direction passes through the optical sensor, and the position information is included in the plurality of position information. The image forming apparatus according to claim 1, wherein color misregistration is corrected based on the image forming apparatus.
Each of the plurality of image forming stations is an image forming apparatus that forms the straight line pattern on the downstream side in the moving direction with respect to the two-dimensional pattern. A plurality of image forming stations, each forming a different color toner image, are arranged along the transfer medium moving direction, and the toner images formed by the plurality of image forming stations are used as registration marks on the surface of the transfer medium. In the image forming apparatus, the registration marks are formed apart from each other in the moving direction, and each registration mark is detected by an optical sensor, and color misregistration between the plurality of colors is corrected based on an output signal from the optical sensor.
Each of the plurality of image forming stations forms a toner image including first and second linear patterns extending in a main scanning direction substantially orthogonal to the moving direction and a two-dimensional pattern as the registration mark,
The image forming apparatus, wherein the first linear pattern, the two-dimensional pattern, and the second linear pattern are spaced from each other in the order in the movement direction.

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