JP2007010744A - Image forming apparatus and resist adjustment method for the device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the technology of adjusting a resist with high accuracy without increasing toner consumption and time needed for the resist adjustment. <P>SOLUTION: A glossy belt is used as an intermediate transfer belt. In addition, a test pattern sensor is constructed to detect positive reflecting light. This makes it possible to separately cut and detect a black resist pattern image and color resist pattern images. Accordingly, unlike the invention described in a first patent document in which a pattern for detecting the timing of resist pattern start is not provided other than the resist pattern images, using the detected black resist pattern image as a reference makes it possible to determine whether the resist pattern image has been accurately detected or not. Consequently, the resist can be adjusted with high accuracy without increasing toner consumption and the time needed to detect each resist pattern image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for performing registration adjustment in a so-called tandem type image forming apparatus in which a plurality of image forming stations each forming toner images of different colors are arranged along the moving direction of a transfer belt. is there.

  In this type of 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. It has been. 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, so-called “registration adjustment” is performed as follows. First, a reference pattern image (hereinafter referred to as “resist pattern image”) for detecting color misregistration is formed on a transfer medium in advance. Next, the position information of the resist pattern image is obtained by detecting the resist pattern image with an optical sensor, and each toner image is aligned based on the position information.

  However, when performing resist adjustment, there are cases where the position information of the resist pattern cannot be obtained accurately due to erroneous detection of scratches or dirt on the surface of the transfer medium as a resist pattern image, or because the resist pattern image is not formed. It was. To solve such a problem, in the image forming apparatus described in Patent Document 1, before forming a resist pattern image, a toner image having a predetermined length longer than the resist pattern image in the moving direction of the transfer medium is applied to the resist pattern. The above problem is solved by forming the start timing detection pattern. That is, by making the length of the resist pattern start timing detection pattern longer than that of the resist pattern image, it is determined whether the resist pattern start timing detection pattern or the resist pattern image is based on the pattern length. If a pattern having a predetermined length is detected, it is determined that a resist pattern start timing detection pattern has been detected, the start of the resist pattern image is recognized, and the resist until the next start timing detection pattern is detected is detected. By determining whether or not the number of pattern images is a predetermined number, it is determined whether or not the resist pattern images are accurately detected. For example, when a scratch or the like is erroneously detected as a resist pattern image after the start timing detection pattern is detected until the next start timing detection pattern is detected, a resist pattern image more than a predetermined number of times is detected. When no toner image is formed, a resist pattern image that is less than a predetermined number of times is detected. Therefore, by determining whether or not the detected resist pattern image is a predetermined number of times, it is possible to determine whether or not the resist pattern image has been accurately detected. Then, only when the resist pattern image can be accurately detected, the detected resist pattern image is used for executing the resist adjustment, thereby enabling highly accurate resist adjustment.

JP 2002-214864 A

  However, when a resist pattern start timing detection pattern is formed separately from the resist pattern in order to realize highly accurate resist adjustment, excess toner is used for the resist pattern start timing detection pattern, and the toner consumption is reduced. It will increase. Further, the time required for resist adjustment is increased by the time required to create or detect the resist pattern start timing detection pattern.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique that enables highly accurate registration adjustment without increasing toner consumption and time required for registration adjustment.

  An image forming apparatus according to the present invention is an image forming apparatus in which a black image forming station for forming a black toner image and a color image forming station for forming a color toner image are arranged along the moving direction of the transfer belt. In order to achieve the above object, each of a plurality of toner images formed on a transfer belt by a plurality of image forming stations apart from each other in the moving direction is used as a resist pattern image, and light is emitted to the resist pattern image. A detection means for outputting a signal related to the light reflected by the resist pattern image, and a detection means for detecting the black resist pattern image; Black pattern detection threshold information used as a reference and color pattern detection threshold used as a detection reference for a color resist pattern image The position of the plurality of resist pattern images on the transfer belt by comparing the storage means for storing information, the output signal output from the detection means, the threshold information for black pattern detection and the threshold information for color pattern detection Control means for obtaining information and correcting color misregistration between a plurality of colors based on the position information, and the transfer belt is higher than any resist pattern image formed by a plurality of image forming stations in the regular reflection component It is characterized by comprising a glossy belt having reflectivity.

  Further, in the registration adjusting method in the image forming apparatus according to the present invention, the black image forming station for forming the black toner image and the color image forming station for forming the color toner image are arranged along the moving direction of the transfer belt. In an image forming apparatus, a resist adjustment method for adjusting color misregistration of a toner image formed by a plurality of image forming stations, in order to achieve the above object, a plurality of image forming stations in a regular reflection component as a transfer belt A preparation process for preparing a glossy belt having a higher reflectance than any toner image formed by the above process, and a plurality of image forming stations forming a plurality of toner images separated as a resist pattern image on the transfer belt surface in the moving direction. Resist pattern forming process and multiple resist patterns A light amount detecting step of irradiating the resist pattern image with light and detecting the amount of specularly reflected light from the resist pattern image, a regular reflected light amount from a plurality of resist pattern images, and a black resist pattern image For determining the position information of a plurality of resist pattern images on the transfer belt by comparing the threshold value information for black pattern detection serving as a detection reference for color and the threshold information for color pattern detection serving as a detection reference for a color resist pattern image It is characterized by comprising a detection step and a correction step for correcting color misregistration between a plurality of colors based on position information.

  In the invention thus configured (image forming apparatus and resist adjustment method for the apparatus), the transfer belt has a higher reflectance in the regular reflection component than the resist pattern image formed on the surface of the transfer belt. Is adopted. Further, the resist pattern image formed on the surface of the transfer belt is detected by irradiating the resist pattern image with light and detecting the regular reflection light. In general, a black toner image has a lower reflectance than a color toner image. Therefore, the signal output from the detection means in the present invention has a waveform as shown in FIG. 7, for example. Here, FIG. 7 shows output signals in an image forming apparatus that has three color image forming stations and each color image forming station forms yellow (Y), magenta (M), and cyan (C) color toner images. is there. As shown in FIG. 7, the signal related to the light reflected by the belt surface has the highest voltage level, and the signal related to the light reflected by the black resist pattern image (black pattern detection signal) is a color resist. The waveform has a voltage level lower than a signal (color pattern detection signal) related to light reflected by the pattern image. In the present invention, there are two pieces of pattern detection threshold information, namely, black pattern detection threshold information that serves as a black resist pattern image detection reference and color pattern detection threshold information that serves as a color resist pattern image detection reference. The position information of the resist pattern image is obtained by comparing the output signal as described above and the two pattern detection threshold information. Therefore, the position information of the black resist pattern image and the position information of the color resist pattern image can be separated and detected. Therefore, highly accurate resist adjustment can be performed without increasing the toner consumption and the resist pattern image detection time. The reason for this will be described. In the present invention, since the position information of the black resist pattern image and the position information of the color resist pattern image can be detected separately, the black resist pattern image is detected again after the black resist pattern image is detected. By determining whether or not a predetermined number of color resist pattern images have been detected, it is possible to determine whether or not the resist pattern images have been detected accurately. In other words, the resist pattern image is accurately detected by using the detected black resist pattern image as a reference without providing a resist pattern start timing detection pattern other than the resist pattern image as in the invention described in Patent Document 1. It can be determined whether or not. For example, in the example of FIG. 7, after the black resist pattern image is detected, three color resist pattern images are detected before the black resist pattern image is detected again. Therefore, if there are not actually three color resist pattern images detected, it is determined that the resist pattern image has not been accurately detected, and these detection results are not used for color misregistration correction, thereby achieving high-precision resist adjustment. It becomes possible. Therefore, in the present invention, it is possible to perform highly accurate resist adjustment without increasing the toner consumption and the resist pattern image detection time.

  The color toner image may be cyan, and the light projecting unit may be configured to irradiate the resist pattern image with infrared light. With this configuration, the output signal corresponding to the black resist pattern image and the color output signal corresponding to the color resist pattern image can be more reliably separated and detected. The reason for this will be described. In general, black (K) exhibits a low reflectance over the entire wavelength region. On the other hand, cyan (C) has a region in which the reflectance is reduced and the reflectance is close to that of black (K) in a wavelength region shorter than infrared light. Therefore, when a wavelength with low reflectance of cyan (C) is used as the light irradiated to the resist pattern image, it becomes difficult to detect and separate cyan (C) and black (K). In such a case, a cyan (C) resist pattern image may be erroneously detected as a black (K) resist pattern image, which may hinder high-precision resist control. However, cyan (C) shows a relatively higher reflectance than black (K) in the infrared light region. Therefore, it is possible to provide a sufficient difference in the reflectance between cyan (C) and black (K) by using light having a wavelength in the infrared light region as light applied to the resist pattern image. Therefore, the output signal corresponding to the black resist pattern image and the color output signal corresponding to the color resist pattern image can be separated and detected more reliably, and highly accurate resist control can be performed.

  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.

  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 (the right-hand side surface in FIG. 1), and the housing body 2. 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 drive motor (not shown), a driven roller 15 disposed obliquely above the drive roller 14, and the two rollers. An intermediate transfer belt 16 that is stretched between 14 and 15 and is circulated and driven in the direction of the arrow D16 in the figure, and a cleaning unit 17 that contacts the surface of the intermediate transfer belt 16 are provided. In the present embodiment, a glossy belt having reflection characteristics described later is used as 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 V16 is higher than the peripheral speed V20 of each color latent image carrier 20 described later. (For example, = 1.03 × V20). Thus, the latent image carrier 20 is driven to be pulled by the intermediate transfer belt 16 by setting the peripheral speed V16 of the intermediate transfer belt 16 to be higher than the peripheral speed V20 of each latent image carrier 20. is doing.

  The driving roller 14 and the driven roller 15 are rotatably supported by the support frame 9a. A rotation portion 9b is formed at the lower end of the support frame 9a and is fitted to a rotation shaft (rotation fulcrum) 2b provided on the housing body 2. As a result, the support frame 9 a is rotatable with respect to the housing body 2. On the other hand, a lock lever 9c is rotatably provided at the upper end of the support frame 9a and can be locked to a locking shaft 2c provided in the housing body 2.

The drive roller 14 also serves as a backup roller for the secondary transfer roller 19 constituting the secondary transfer unit 11. As shown in FIG. 1, a rubber layer 14a 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 is grounded through a metal shaft. Thus, a conductive path for the secondary transfer bias supplied from the secondary transfer bias generator (not shown) via the secondary transfer roller 19 is provided. Thus, by providing the driving roller 14 with the rubber layer 14a 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 the image quality is deteriorated. Can be prevented.

  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. Further, the driven roller 15 is also used as a backup roller for the cleaning unit 17. The cleaning unit 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.

  A primary transfer roller 21a is disposed 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 a latent image carrier 20 of each image forming station Y, M, C, K described later. A primary transfer unit 21 is provided. In the primary transfer unit 21, four primary transfer rollers 21a are rotatably supported with respect to the link bar 21b. These primary transfer rollers 21a are electrically connected to a primary transfer bias generator (not shown), and a primary transfer bias is applied from the primary transfer bias generator at an appropriate timing.

  The link bar 21b is rotatably provided in the arrow direction D21 with the primary transfer roller 21a disposed facing the latent image carrier 20 of the black (K) image forming station K as a rotation center. Yes. Then, by actuating an actuator (not shown), the link bar 21b rotates to move to the latent image carrier 20 of the yellow (Y), magenta (M), and cyan (C) image forming stations Y, M, and C. The primary transfer roller 21 a disposed so as to be close to the latent image carrier 20 moves away from the latent image carrier 20. For this reason, when each primary transfer roller 21a moves close to the latent image carrier 20, it comes into contact with the latent image carrier 20 with the intermediate transfer belt 16 in between (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 as will be described later. Conversely, when each primary transfer roller 21a moves away from the latent image carrier 20, the latent image carrier 20 and the intermediate transfer belt 16 of the image forming stations Y, M, and C are separated from each other (broken line in FIG. 1). ). On the other hand, the primary transfer roller 21a disposed facing the latent image carrier 20 of the black (K) image forming station K is in contact with the latent image carrier 20 with the intermediate transfer belt 16 interposed therebetween. It is configured to rotate as it is. Therefore, as shown by the solid line in FIG. 1, the color printing process can be executed by positioning all the primary transfer rollers 21a on the latent image carrier 20 side. On the other hand, as shown by the broken line in the figure, the black primary transfer roller 21a is left and the other primary transfer roller 21a is separated from the latent image carrier 20, thereby performing image formation while performing only monochrome printing processing. Stations Y, M, and C can be set in a non-printing state.

  A test pattern sensor 18 is installed on the support frame 9 a of the transfer belt unit 9 in the vicinity of the drive roller 14. FIG. 3 is a diagram showing the configuration of the test pattern sensor 18. The test pattern sensor 18 receives a specular reflection component of the light projecting unit 181 that irradiates light toward the surface of the intermediate transfer belt 16 and the light reflected by the surface of the intermediate transfer belt 16 and a resist pattern image described later. The light receiving unit 182 is arranged as described above. Then, light is emitted from the light projecting unit 181 to the resist pattern image on the transfer belt 16, while the light from the resist pattern image is received by the light receiving unit 182 and a signal corresponding to the amount of light received by the light receiving unit is generated. Output from the test pattern sensor 18. 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. 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 9 a. It has been. 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. Here, in this embodiment, the image forming station K functions as a “black image forming station” in the present invention, and each of the image forming stations Y, M, and C functions as a “color image forming station” in the present invention. . Each of the image forming stations Y, M, C, and K is provided with a latent image carrier 20 including a photosensitive drum. Further, around each latent image carrier 20, a charging unit 22, an image writing unit 23, and a developing unit 24 are disposed. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. Note that the developing unit 24 attaches a reference numeral only to the image forming station K and omits the reference numerals because the other image forming stations have the same configuration. Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

  The latent image carrier 20 of each of the image forming stations Y, M, C, and K is brought into contact with the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 at the primary transfer position. The image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the driving roller 14. Further, each latent image carrier 20 is driven to rotate at a predetermined peripheral speed V20 in the transport direction of the intermediate transfer belt 16, as indicated by an arrow D20 in the drawing. In this embodiment, in the rotation direction D20 of the latent image carrier 20, the peripheral length of the latent image carrier 20 is shorter than the minimum sheet length, for example, a postcard size.

  The charging unit 22 includes a charging roller 22a having a surface made of elastic rubber. The charging roller 22a is configured to abut on the surface of the latent image carrier 20 at the charging position so as to be driven to rotate, and the driven direction relative to the latent image carrier 20 as the latent image carrier 20 rotates. At the peripheral speed V22a (= V20). The charging roller 22a 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 latent image carrier 20 at the charging position. Further, in this embodiment, a cleaning roller 22 b is further provided as a component of the charging unit 22.

  The image writing unit 23 uses an array-like writing head in which elements such as a liquid crystal shutter including a light emitting diode and a backlight are arranged in a line in the axial direction of the latent image carrier 20. Spaced apart from each other. The array-like writing head has an advantage that the optical path length is shorter than that of the laser scanning optical system, is compact, can be arranged close to the latent image carrier 20, and the entire apparatus can be downsized. In this embodiment, the latent image carrier 20, the charging unit 22, and the image writing unit 23 of each image forming station Y, M, C, K are unitized as replacement cartridges 6Y, 6M, 6C, 6K (FIG. 2). By doing so, the arrangement of the arrayed write head is maintained, and when replacing the replacement cartridge, the arrayed write head is replaced and the new replacement cartridge is adjusted for light quantity and positioned for reuse. It is configured to do. 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. In the present embodiment, the image forming stations Y, M, C, and K are disposed in an oblique direction, and the latent image carrier 20 is in contact with the belt surface 16 a facing downward in the conveyance direction of the intermediate transfer belt 16. Above, the toner storage container 26 is disposed obliquely downward. Therefore, a special configuration is adopted as the developing unit 24. That is, the developing unit 24 is disposed in the toner storage container 26 that stores toner (hatched portion in FIG. 1), the toner storage part 27 formed in the toner storage container 26, and the toner storage part 27. The toner agitating member 29, the partition member 30 formed in the upper part of the toner reservoir 27, the toner supply roller 31 disposed above the partition member 30, and the toner supply roller 31 provided in the partition member 30 The blade 32 is in contact with the toner supply roller 31 and the latent image carrier 20. The developing roller 33 rotates at a peripheral speed V <b> 33, and the regulating blade 34 is in contact with the developing roller 33.

  The latent image carrier 20 is rotated in the transport direction D16 of the intermediate transfer belt 16. Further, the developing roller 33 and the supply roller 31 are rotationally driven in a direction opposite to the rotational direction D20 of the latent image carrier 20 as indicated by an arrow D33 in the drawing. On the other hand, the stirring member 29 is driven to rotate in the direction opposite to the rotation direction of the supply roller 31. Therefore, the toner stirred and carried by the stirring member 29 in the toner reservoir 27 is supplied to the toner supply roller 31 along the upper surface of the partition member 30. In addition, the toner thus supplied is rubbed against the blade 32 and supplied to the surface of the developing roller 33 by the mechanical adhesion force on the surface uneven portion of the supply roller 31 and the adhesion force due to the frictional band power. The toner supplied to the developing roller 33 is regulated to a predetermined thickness by the regulation blade 34. Further, the toner layer thus thinned is conveyed to the latent image carrier 20. Then, at the development position where the development roller 33 and the latent image carrier 20 are in contact with each other by the development bias applied to the development roller 33 from the development bias generator 525 electrically connected to the development roller 33, the normally charged toner is The electrostatic latent image formed by the image writing unit 23 is visualized by moving from the developing roller 33 to the latent image carrier 20.

  In this embodiment, toner development is performed as described above, and so-called simultaneous development cleaning is performed in which residual toner on the latent image carrier 20 is collected by the developing roller 33. In this way, a cleanerless system is configured that collects toner remaining on the surface of the latent image carrier 20 after the primary transfer at the development position.

  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 regulates the sheet feeding timing of the sheet S to the secondary transfer portion, and a secondary transfer unit 2 that is in pressure contact with the drive roller 14 and the intermediate transfer belt 16. A next transfer unit 11, a fixing unit 12, a sheet conveyance mechanism 13, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  In the secondary transfer unit 11, 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 a secondary transfer roller drive mechanism 111 that drives the secondary transfer roller 19 to come into contact with and separate from it. ing. In the secondary transfer roller driving mechanism 111, a rotating lever 42 having a secondary transfer roller 19 rotatably attached to one end thereof is pivotally supported by a fixed shaft 41. Further, a spring 43 is disposed between the other end of the rotation lever 42 and the first opening / closing member 3, and the secondary transfer roller 19 moves in the direction of the arrow in the drawing by the biasing force, and the intermediate transfer belt. 16 and the driving roller 14. Further, the secondary transfer roller driving mechanism 111 has an eccentric cam 44, and this eccentric cam 44 is provided on the spring 43 side of the rotating lever 42. Then, when the eccentric cam 44 is rotated by the driving force of the driving motor via a clutch (not shown), the rotating lever 42 rotates against the spring 43 to separate the secondary transfer roller 19 from the intermediate transfer belt 16. Let

  The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, a pressure roller 46 that presses and biases the heating roller 45, and is swingable on the pressure roller 46. A belt tension member 47, and a heat-resistant belt 49 stretched between the pressure roller 46 and the belt tension member 47. 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 heat-resistant belt 49. 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 color misregistration correction processing 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 apparatus main body 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 image is transferred first on the surface of the sheet S on which the image is transferred in contact with the intermediate transfer belt 16 in the secondary transfer region. It is the opposite surface. 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. In particular, in this embodiment, pattern detection threshold information for detecting the resist pattern image of each color by the test pattern sensor 18 is obtained in order to obtain position information of the resist pattern image for the color misregistration correction processing described below. Memory spaces 523CL and 523K to be stored are set in the ROM 523. Then, as shown in FIG. 4, in the memory spaces 523CL and 523K, the color toner threshold TH (CL) (“color pattern detection threshold information” in the present invention) and the black toner threshold TH (K) (“ Black pattern detection threshold information ") is stored in advance. Thus, in the present embodiment, the ROM 523 functions as the “storage unit” of the present invention.

  FIG. 5 is a flowchart showing the operation of the image forming apparatus shown in FIG. 1, and shows the flow of registration adjustment processing. FIG. 6 is a schematic diagram showing a pattern detection operation for color misregistration correction. In this apparatus, the resist adjustment process using the resist pattern image is executed at an appropriate timing such as when the power is turned on or the cartridge is replaced. More specifically, registration pattern image formation / detection and color misregistration correction processing are executed in accordance with a registration adjustment program stored in the ROM 523. Hereinafter, the resist adjustment process will be described with reference to FIGS.

  First, in accordance with a control command from the CPU 521 of the engine controller 52, a plurality of toner images are formed as resist pattern images by the image forming stations Y, M, C, and K (step S1) (resist pattern forming step). Here, the shape, size, interval, arrangement, number, and the like of the resist pattern image are arbitrary, and many various modes have been conventionally proposed. In this embodiment, for example, as shown in FIG. 6, a belt-like shape (for example, width) that extends in parallel with a part of the surface of the intermediate transfer belt 16 in the direction (main scanning direction) perpendicular to the conveyance direction D16 of the intermediate transfer belt 16. 0.5 mm) resist pattern images are formed in the order of C, M, Y, and K at a predetermined interval (for example, 0.5 mm) in the conveyance direction (sub-scanning direction) D16. The figure shows a black resist pattern image RP (K), a cyan resist pattern image RP (C), a magenta resist pattern image RP (M), a yellow resist pattern image RP (Y), and a black resist pattern image. Only the pattern image RP (K) is shown, but a plurality of patterns are formed for each color.

  When all or a part of the resist pattern image is formed in this way, the light projecting portion 181 of the test pattern sensor (detection means) 18 is turned on so that the test pattern sensor 18 can detect the resist pattern image. Then, the amount of specular reflection from the intermediate transfer belt 16 and the resist pattern image is detected (step S2) (light amount detection step). That is, the resist pattern images RP (C), RP (M), RP (Y), and RP (K) formed on the intermediate transfer belt 16 as described above are moved in the transport direction D16 as the intermediate transfer belt 16 moves. Move and pass the test pattern sensor 18. At this time, the voltage level of the signal output from the test pattern sensor 18 changes according to the change in the amount of regular reflection received by the light receiving unit 182 of the test pattern sensor 18. In the present embodiment, a glossy belt is used as the intermediate transfer belt 16 as described above. This gloss belt has a higher reflectance than any resist pattern image formed on the surface of the gloss belt in the regular reflection component. In general, the black resist pattern image RP (K) exhibits a lower reflectance than the color resist pattern images RP (C), RP (M), and RP (Y). Therefore, the signal output from the test pattern sensor 18 has the highest output level corresponding to the intermediate transfer belt 16 and the lowest output level corresponding to the black resist pattern image RP (K) as shown in FIG. . The output levels corresponding to the color resist pattern images RP (C), RP (M), and RP (Y) correspond to the output level corresponding to the intermediate transfer belt 16 and the black resist pattern image RP (K). Indicates a value between the output levels. Therefore, by measuring the voltage level, the timing at which each resist pattern image passes through the test pattern sensor 18 can be measured, and the position information of the resist pattern image can be acquired. And it becomes possible to obtain | require the mutual space | interval of a resist pattern image based on the positional information.

  In this embodiment, paying attention to the fact that the output signal from the test pattern sensor 18 differs in voltage level between black and color, the color toner threshold TH (CL) and the black toner threshold TH ( K) is obtained in advance and stored in the ROM 523. The black resist pattern image RP (K) and the color resist pattern images RP (C), RP (M), and RP (Y) can be separated and detected. That is, for example, as shown in FIG. 6, the color toner threshold TH (CL) is set between the output level corresponding to the intermediate transfer belt and the output level corresponding to the color resist pattern image, and the black toner threshold TH ( When K) is set between the output level corresponding to the black resist pattern image and the output level corresponding to the color resist pattern image, only the signal corresponding to the black resist pattern image RP (K) The signal corresponding to the color resist pattern images RP (C), RP (M), and RP (Y) below TH (K) is below the color toner threshold TH (CL), but the black toner threshold TH (K). Never fall below. Therefore, if the black toner threshold value TH (K) falls below, it is determined that the black resist pattern image RP (K) has been detected, and if only the color toner threshold value TH (CL) falls below, the color resist pattern By determining that any one of the images RP (C), RP (M), and RP (Y) is detected, the black resist pattern image RP (K) and the color resist pattern images RP (C) and RP (M) , RP (Y) can be separated and detected.

  Next, in the present embodiment, the position detection of the color resist pattern images RP (C), RP (M), and RP (Y) (step S3) is triggered by the position detection (step S3) of the black resist pattern image RP (K). S4) is performed (position detection step). The position detection of the color resist pattern images RP (C), RP (M), and RP (Y) is repeated until the position detection of the black resist pattern image RP (K) is performed again (step S5). When the position detection of the black resist pattern image RP (K) is performed (when YES is determined in step S5), the position detection of the black resist pattern image RP (K) is performed in step S3. In step S5, it is determined whether or not the number of color resist pattern images detected until the position detection of the black resist pattern image RP (K) is performed again matches a predetermined value. And by configuring in this way, it is said that the position information of the resist pattern is not accurately obtained because the scratch or dirt on the surface of the transfer medium is erroneously detected as a resist pattern image or the resist pattern image is not formed. The problem is avoided. That is, for example, when there is a scratch between black resist pattern images and the test pattern sensor 18 erroneously detects this as a color resist pattern image, the number of color resist pattern images detected between step S3 and step S5 is The value is greater than a predetermined value. Further, when the test pattern sensor 18 erroneously detects the above-described scratch as a black resist pattern image, the number of color resist pattern images detected between step S3 and step S5 becomes a value smaller than a predetermined value. As described above, it is possible to determine whether or not there is a false detection of a scratch or the like based on the number of color resist pattern images detected between step S3 and step S5. In this embodiment, since there are three types of color resist pattern images of cyan (C), magenta (M), and yellow (Y), the number of color resist pattern images detected between step S3 and step S5. Only when there are three, it is determined that the resist pattern images RP (C), RP (M), RP (Y), and RP (K) are correctly detected. Then, only when the resist pattern image is correctly detected, these position information is used for the subsequent color misregistration correction. When the resist pattern is not correctly detected, these position information is used for the subsequent color misregistration correction. The position of the color toner image is detected again (step S4). Then, it is determined whether or not the position information of the resist pattern images RP (C), RP (M), RP (Y), RP (K) has reached the number necessary for subsequent color misregistration correction (step S7). The above-described resist pattern images RP (C), RP (M), RP (Y), and RP (K) are detected until the required number is reached. Further, when the required number of position information of the resist pattern images RP (C), RP (M), RP (Y), and RP (K) has been reached, these position information are in accordance with the color misregistration correction command from the CPU 521. The color misregistration correction is performed based on (Step S8) (correction step). Thus, in the present embodiment, the CPU 521 functions as the “control unit” in the present invention.

  As described above, according to this embodiment, a glossy belt is used as the intermediate transfer belt 16, and regular reflection light is detected by the test pattern sensor 18. Therefore, the signal waveform output from the test pattern sensor 18 differs in voltage level change between black and color as shown in FIG. In this embodiment, the position of the resist pattern image is detected with respect to such an output signal by using two threshold values, a color toner threshold TH (CL) and a black toner threshold TH (K). Yes. Therefore, the black resist pattern image and the color resist pattern image can be separated and detected. Therefore, the resist pattern image can be accurately detected by using the detected black resist pattern image as a reference without providing a resist pattern start timing detection pattern other than the resist pattern image as in the invention described in Patent Document 1. It can be determined whether or not. Therefore, it is possible to perform highly accurate resist adjustment without increasing the toner consumption and the resist pattern image detection time.

  In the present embodiment, infrared light is emitted from the light projecting unit 181. As a result, the output signal corresponding to the black resist pattern image and the color output signal corresponding to the color resist pattern image can be more reliably separated and detected. The reason for this will be described. In general, black (K) exhibits low reflectance over the entire wavelength region. On the other hand, cyan (C) has a region in which the reflectance is reduced and the reflectance is close to that of black (K) in a wavelength region shorter than infrared light. Therefore, when a wavelength with low reflectance of cyan (C) is used as the light irradiating the resist pattern image, it becomes difficult to detect cyan (C) and black (K) separately. In such a case, a cyan (C) resist pattern image may be erroneously detected as a black (K) resist pattern image, which may hinder high-precision resist control. However, cyan (C) exhibits a relatively higher reflectivity than black (K) in the infrared region. Therefore, it is possible to provide a sufficient difference in the reflectance between cyan (C) and black (K) by using light having a wavelength in the infrared light region as light applied to the resist pattern image. In addition, the reflectance of yellow (Y) and magenta (M) both decrease from the peak value in the visible light region to the infrared light region, but with the reflectance of black (K). There is a sufficient difference between them. Therefore, by configuring the light projecting unit 181 to emit infrared light, the output signal corresponding to the black resist pattern image and the color output signal corresponding to the color resist pattern image can be more reliably separated and detected. Highly accurate resist control is possible.

  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, the resist pattern image is formed on the intermediate transfer belt 16 in the order of cyan (C), magenta (M), yellow (Y), and black (K). The order is not limited to this, and can be changed as appropriate.

  Next, examples of the present invention will be shown. However, the present invention is not limited by the following examples as a matter of course, and it is needless to say that the present invention can be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. These are all included in the technical scope of the present invention.

  FIG. 7 shows an output result of the test pattern sensor in the embodiment of the present invention. In this example, the glossy belt is based on a TPE alloy made from a vinyl chloride resin composition described in JP-A-2000-319482. Further, light having a wavelength of 940 nm was irradiated from the light projecting portion of the test pattern sensor. As shown in FIG. 7, according to this embodiment, the black resist pattern image Sig (K) is compared with the output signals Sig (C), Sig (M), and Sig (C) corresponding to the color resist pattern image. Indicates a lower output level. Therefore, as shown in the above-described embodiment, by setting the black toner threshold and the color toner threshold, it is possible to separate and detect the black resist pattern image and the color resist pattern image. Therefore, the resist pattern image can be accurately detected by using the detected black resist pattern image as a reference without providing a resist pattern start timing detection pattern other than the resist pattern image as in the invention described in Patent Document 1. It can be determined whether or not. Therefore, it is possible to perform highly accurate resist adjustment without increasing the toner consumption and the resist pattern image detection time.

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. The figure which shows the structure of a test pattern sensor. The figure which shows a part of memory space of ROM with which the apparatus of FIG. 1 was equipped. 2 is a flowchart showing the operation of the image forming apparatus in FIG. 1. FIG. 6 is a schematic diagram illustrating a pattern detection operation for color misregistration correction. The figure which shows the waveform of the output signal of the test pattern sensor in an Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 16 ... Intermediate transfer belt, 18 ... Test pattern sensor, 181 ... Light projecting part, 182 ... Light receiving part, 52 ... Engine controller, 521 ... CPU (control means), 523 ... ROM (storage means), RP (C), RP (M), RP (Y), RP (K) ... resist pattern image, TH (K) ... black toner threshold (black pattern threshold information), TH (CL) ... color toner threshold (Threshold information for color pattern), D16 ... transport direction (moving direction), Y, M, C, K ... image forming station

Claims (3)

In an image forming apparatus in which a black image forming station for forming a black toner image and a color image forming station for forming a color toner image are arranged along the moving direction of the transfer belt,
Each of a plurality of toner images formed on the transfer belt by the plurality of image forming stations apart from each other in the moving direction is used as a resist pattern image, and a light projecting unit for irradiating the resist pattern image with light, and the resist A light receiving unit that receives regular reflection light from the pattern image, and a detection unit that outputs a signal related to light reflected by the resist pattern image;
Storage means for storing black pattern detection threshold information serving as a black resist pattern image detection reference and color pattern detection threshold information serving as a color resist pattern image detection reference;
The positional information of the plurality of resist pattern images on the transfer belt is obtained by comparing the output signal output from the detection means with the black pattern detection threshold information and the color pattern detection threshold information. Control means for correcting color misregistration between the plurality of colors based on the position information,
2. The image forming apparatus according to claim 1, wherein the transfer belt is formed of a glossy belt having a reflectance higher than any resist pattern image formed by the plurality of image forming stations in the regular reflection component.   The image forming apparatus according to claim 1, wherein the color toner image is cyan, and the light projecting unit irradiates the resist pattern image with infrared light. In an image forming apparatus in which a black image forming station for forming a black toner image and a color image forming station for forming a color toner image are arranged along the moving direction of the transfer belt, the image forming apparatus is formed by the plurality of image forming stations. A resist adjustment method for adjusting a color shift of a toner image,
A preparation step of preparing a glossy belt having a higher reflectance than any of the toner images formed by the plurality of image forming stations in the regular reflection component as the transfer belt;
A resist pattern forming step of forming a plurality of toner images spaced apart in the movement direction on the transfer belt surface as resist pattern images by the plurality of image forming stations;
For each of the plurality of resist pattern images, a light amount detection step of irradiating the resist pattern image with light and detecting the amount of specularly reflected light from the resist pattern image;
The amount of specular reflection from the plurality of resist pattern images is compared with black pattern detection threshold information serving as a black resist pattern image detection reference and color pattern detection threshold information serving as a color resist pattern image detection reference. A position detecting step for obtaining position information of the plurality of resist pattern images on the transfer belt,
A correction step of correcting color misregistration between the plurality of colors based on the position information;
A resist adjustment method comprising:

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