JP2006162652A - Image forming apparatus and color slippage compensation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a color slippage compensation method for preventing the occurrence of a color slippage or deterioration in color tone by carrying out formation of a registration pattern image while taking into consideration a surface state of a transfer medium. <P>SOLUTION: Base information is obtained in the image forming apparatus by detecting the surface of an intermediate transfer belt, especially in a pattern forming region, by a test pattern sensor before formation of the registration pattern image (step S7). Then, the surface state in the pattern forming region is acquired based on the base information, and further, a forming process for the registration pattern image is controlled based on the surface state. Therefore, since the registration pattern image is formed (step S7) while taking into full consideration the surface state of the planned pattern forming region for forming the registration pattern image, detection of position for the registration pattern can be carried out with high accuracy. <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 “resist pattern image”) for detecting color misregistration is formed on a transfer medium in advance, and the resist pattern image is detected by an optical sensor. Thus, position information of the resist pattern image is obtained, and alignment (color misregistration correction) of each toner image is performed based on the position information.

JP 2004-109617 A (page 4)

  By the way, an optical sensor for detecting a resist pattern image formed on a transfer medium has a light projecting part and a light receiving part, and irradiates the resist pattern image on the transfer medium with light from the light projecting part. Light from the resist pattern image is received by the light receiving unit. A signal corresponding to the amount of light received by the light receiving unit is output from the optical sensor, and the resist pattern image is detected based on the output signal. Therefore, it is important to consider the surface of the transfer medium, that is, the ground state. This is because if the surface area on which the resist pattern image is formed on the surface of the transfer medium is dirty, the amount of light received by the light receiving section will fluctuate greatly, and the position detection accuracy of the resist pattern image will be significantly reduced. Because. However, in the conventional apparatus, color misregistration correction is performed without sufficiently considering the surface state (background state) of the transfer medium. Therefore, if the surface of the transfer medium becomes dirty as the accumulated operation time of the apparatus becomes longer, the position detection accuracy of the resist pattern image is lowered. As a result, color misregistration correction cannot be performed satisfactorily, and problems such as printing with a color misregistration state or a desired color tone may not occur.

  The present invention has been made in view of the above problems, and an image forming apparatus and a color misregistration capable of preventing the occurrence of color misregistration and color tone degradation by forming a resist pattern image in consideration of the surface state of a transfer medium. An object is to provide a correction method.

  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. A resist pattern image is formed on the pattern formation region on the surface of the transfer medium so as to be separated in the moving direction, and the resist pattern image is detected by an optical sensor, and colors between a plurality of colors are detected based on an output signal from the optical sensor. An image forming apparatus that corrects misalignment, and in order to achieve the above object, obtains the surface state of the transfer medium based on ground information obtained by detecting the surface of the transfer medium by an optical sensor before forming a resist pattern image. A surface state acquisition unit, and a resist pattern image forming process based on the surface state of the transfer medium acquired by the surface state acquisition unit. It is characterized in that a pattern formation control unit for controlling.

  Also, the color misregistration correction method according to the present invention provides a plurality of image forming stations in which an image forming apparatus in which a plurality of image forming stations each forming a toner image of a different color is arranged along the moving direction of the transfer medium. A color misregistration correction method for correcting a color misregistration of a toner image formed by a toner image formed on a transfer medium pattern forming region by using toner images formed by a plurality of image forming stations as resist pattern images. Between a plurality of colors based on the pattern forming step formed in a moving direction, a pattern detecting step for detecting the resist pattern image to obtain the position information of the resist pattern image, and the position information obtained in the pattern detecting step. The optical sensor detects the transfer medium surface before the pattern forming process A surface state acquisition step for acquiring the surface state of the transfer medium based on the obtained ground information, and a pattern formation control step for controlling the resist pattern formation step based on the surface state of the transfer medium acquired by the surface state acquisition step It is characterized by that.

  In the invention thus configured (image forming apparatus and color misregistration correction method), the optical sensor detects the surface of the transfer medium and obtains the background information before forming the resist pattern image. The surface state of the transfer medium is acquired based on the ground information, and the resist pattern image forming process is controlled based on the surface state. Therefore, the resist pattern image is formed in consideration of the surface state of the transfer medium, and the position detection of the resist pattern image can be performed with high accuracy. As a result, color misregistration correction can be performed appropriately.

  Here, since the resist pattern image is formed in the pattern formation region, only the surface state of the pattern formation region may be acquired as the ground information. Then, the resist pattern image forming process may be stopped when the surface state of the pattern formation region acquired by the surface state acquisition unit (step) is out of the preset appropriate range. . That is, when a resist pattern image is formed in such a surface state pattern formation region, the position detection accuracy of the resist pattern image may be lowered. Accordingly, if the resist pattern image forming process is stopped in such a case, it is possible to prevent the position detection accuracy of the resist pattern image from being lowered, and to prevent inaccurate color misregistration correction from occurring. be able to.

  In addition, in order to determine the surface state of the pattern formation region, a background detection storage unit that stores background detection threshold information corresponding to the appropriate range is further provided, and the above determination is made based on the background detection threshold information and the background information. May be performed. For example, it is possible to determine whether or not the surface state of the pattern formation region is out of the appropriate range by comparing the background information with the background detection threshold information stored in the background detection storage unit.

  Further, when the resist pattern image forming process is stopped as described above, the pattern formation region may be changed, and the resist pattern image may be newly formed in the changed pattern formation region. In this manner, resist pattern image formation / detection and color misregistration correction processing can be executed using different surface regions, and the effectiveness of color misregistration correction can be enhanced.

  Further, the base information is obtained for the entire circumference in the moving direction, and the surface area within the appropriate range is determined as the pattern formation area based on the base information, and the resist pattern image is formed on the pattern formation area. Good. As described above, a pattern formation region suitable for formation of a resist pattern image can be determined before the formation of the resist pattern image. Since the resist pattern image is formed in the pattern formation region, the position detection of the resist pattern image can be performed with high accuracy. As a result, color misregistration correction can be performed appropriately.

  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 drive motor (not shown), a driven roller 15 disposed obliquely above the drive roller 14, and the two rollers. The intermediate transfer belt 16 is stretched between 14 and 15 and is circulated and driven in the direction indicated by the arrow D16. 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 14 a having a thickness of about 3 mm and a volume resistivity of 105 Ω · cm or less is formed on the peripheral surface of the drive roller 14, and is grounded through a metal shaft. The conductive path of the secondary transfer bias supplied from the secondary transfer bias generating unit (not shown) via the secondary transfer roller 19 is used. 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. The test pattern sensor 18 is a so-called reflection type optical sensor, a light projecting unit (not shown) that irradiates light toward the surface of the intermediate transfer belt 16, and the surface of the intermediate transfer belt 16 or a resist pattern image to be described later. A light receiving portion (not shown) that receives the light reflected by the light. The light is emitted from the light projecting unit to the resist pattern image on the transfer medium, while the light from the resist pattern image 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. 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. 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 523Y, 523M, 523C, and 523K to be stored are set in the ROM 523. In the memory spaces 523Y, 523M, 523C, and 523K, the yellow toner threshold TH (Y), the magenta toner threshold TH (M), the cyan toner threshold TH (C), and the black toner threshold TH (K) are respectively patterned. It is stored in advance as threshold information for detection. Further, a memory space 523B for storing background detection threshold information for detecting the surface state of the intermediate transfer belt 16 by the test pattern sensor 18 is set in the ROM 523, and the background detection threshold TH (BT is stored in the memory space 523B. ) Is stored in advance as background detection threshold information. That is, the background detection threshold TH (BT) is a reference for confirming that the surface state of the belt is within an appropriate range without causing the surface of the intermediate transfer belt 16 to become dirty or damaged. Thus, in this embodiment, the ROM 523 functions as the “background detection storage unit” and the “pattern detection storage unit” of the present invention.

  FIG. 4 is a flowchart showing the operation of the image forming apparatus of FIG. 1, and shows the process for acquiring the surface state of the intermediate transfer belt, the formation / detection of the resist pattern image, and the color misregistration correction process. FIG. 5 is a schematic diagram showing an operation for acquiring the surface state of the intermediate transfer belt. FIG. 6 is a schematic diagram showing a pattern detection operation for color misregistration correction. In this apparatus, color misregistration correction processing using a resist pattern image 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 functions as the “surface state acquisition unit” and the “pattern formation control unit” of the present invention in accordance with a program relating to color misregistration correction stored in the ROM 523, so that each part of the apparatus is In this way, the process for acquiring the surface state of the intermediate transfer belt, the formation / detection of the resist pattern image and the color misregistration correction process are executed. Hereinafter, the process for obtaining the surface state of the intermediate transfer belt, the formation / detection of the resist pattern image, and the color misregistration correction process will be described with reference to FIGS.

  First, prior to formation / detection of a resist pattern image and color misregistration correction processing, steps S1 to S6 are executed to acquire the surface state of the intermediate transfer belt. That is, in step S1, the drive roller 14 is driven to rotate by a drive motor (not shown), and the intermediate transfer belt 16 is circulated in the arrow direction D16. Further, the detection of the rotation time is started from the start of the rotation of the intermediate transfer belt 16, and the moving distance of the intermediate transfer belt 16 is calculated. In step S2, the test pattern sensor 16 waits for the movement time of the intermediate transfer belt 16 to reach a predetermined time (Pstart) and the leading position of the pattern formation region Rp moves to the position of the test pattern sensor (light sensor) 18. The light emitting unit 18 (not shown) is turned on, and the detection of the surface state of the intermediate transfer belt 16 by the test pattern sensor 18 is started (step S3).

  Further, as the intermediate transfer belt 16 moves in the transport direction D16, the pattern formation region Rp passes through the test pattern sensor 18, and the light reflected by the pattern formation region Rp is a light receiving portion (not shown) of the test pattern sensor 18. ). The voltage level of the signal output from the test pattern sensor 18 changes according to the amount of received light. For this reason, the surface state of the pattern formation region Rp can be acquired as background information by detecting the voltage level. More specifically, in this embodiment, the background detection threshold TH (BT) is read from the memory space 523B of the ROM 523 and set as background detection threshold information, as shown by the solid line in FIG. It is confirmed that the surface state of the pattern formation region Rp is within an appropriate range by confirming that the applied voltage level is a predetermined level, that is, the background detection threshold TH (BT) or more (step S4).

  Such confirmation is continued until a predetermined time (haba) has elapsed from the start of voltage level detection (step S3) (step S5). This “predetermined time (haba)” is a time corresponding to the length of the pattern formation region Rp in the transport direction (movement direction) D16, and the voltage level is continuously detected and confirmed only for the time (haba). It can be confirmed that the entire surface of the pattern formation region Rp is in a normal surface state. When the confirmation is completed, the light projecting portion of the test pattern sensor 18 is turned off in step S6, and the process for acquiring the surface state of the intermediate transfer belt 16 is completed.

  Next, when it is confirmed that the pattern formation region Rp is in an appropriate surface state over the entire surface as described above, the image forming stations Y, M, C, and K follow the control command from the CPU 521 of the engine controller 52. A resist pattern image is formed, and a resist pattern image is formed in the pattern formation region Rp of the intermediate transfer belt 16 (step S7). 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 K, C, M, and Y at a predetermined interval (for example, 0.5 mm) in the transport 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 part of the resist pattern image is formed in this way, the light projecting portion (not shown) of the test pattern sensor (photosensor) 18 is turned on to enable the test pattern sensor 18 to detect the resist pattern image (step S8). ). That is, the resist pattern images RP (K), RP (C), RP (M), and RP (Y) 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 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 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.

  Further, in this embodiment, focusing on the fact that the change in the voltage level of the output signal is different for each color, the yellow toner threshold TH (Y) and the magenta toner threshold TH (M) suitable for pattern detection for each color. The cyan toner threshold value TH (C) and the black toner threshold value TH (K) are obtained in advance and stored in the ROM 523 as pattern detection threshold information. Then, the position information of the resist pattern image is acquired for each color based on the pattern detection threshold information. For example, when the resist pattern image RP (K) of black toner reaches the test pattern sensor 18, the resist pattern image RP (K) is detected by the sensor 18, and an output signal from the sensor 18 is detected as shown in FIG. The position information of the resist pattern image RP (K) is obtained by comparing the voltage level of the toner and the threshold TH (K) for toner. The same applies to other toner colors. When position information is obtained for all resist pattern images, color misregistration correction is performed based on the position information (step S9).

On the other hand, as shown by the broken line in FIG. 5, for example, the detected light level is lower than the background detection threshold TH (BT), that is, the background of the pattern formation region Rp is dirty, so If it has decreased ("NO" in step S4), it is determined that the surface state of the pattern formation region Rp is defective, the light projecting portion of the test pattern sensor 18 is turned off, and the surface state of the intermediate transfer belt 16 is changed. The acquisition process is completed (step S10). Then, the intermediate transfer belt 16 is stopped at the initial position, and a predetermined time (Pstart) is expressed by the following formula: Pstart = Pstart + haba
(Step S11). As a result, the pattern formation region Rp is changed by a distance corresponding to time (haba) in the transport direction D16, that is, by the length of the pattern formation region. Then, the process returns to step S1 and the surface state acquisition process of the intermediate transfer belt 16 is repeated. As a result, the process of acquiring the surface state of the intermediate transfer belt 16 for the new pattern formation region Rp (steps S1 to S6), the formation (step S7) and detection of the resist pattern image (step S8), and the color misregistration correction process (step S9). ).

  As described above, according to this embodiment, before the formation of the resist pattern image, the test pattern sensor 18 detects the surface of the intermediate transfer belt 16, particularly the pattern formation region Rp, to obtain the base information. Then, the surface state of the pattern formation region Rp is acquired based on the ground information, and the resist pattern image forming process is controlled based on the surface state. As described above, since the resist pattern image is formed after sufficiently considering the surface state of the pattern formation region Rp where the resist pattern image is to be formed, the position detection of the resist pattern image should be performed with high accuracy. Can do. As a result, color misregistration correction can be performed appropriately, and the occurrence of color misregistration and color tone deterioration can be reliably prevented.

  Further, when it is confirmed that the pattern formation region Rp of the intermediate transfer belt 16 is soiled or damaged based on the background information and the belt surface state in the region Rp is not within the proper range, formation of a resist pattern image is performed. Detection and color misregistration correction processing has been stopped. For this reason, useless toner consumption and color misregistration correction time can be suppressed. Further, if necessary, an error message may be displayed on the display unit 54 to notify the user.

  When the resist pattern image forming process is stopped as described above, the pattern formation region Rp is changed and the resist pattern image is newly formed in the changed pattern formation region Rp. Since the resist pattern image formation / detection and the color misregistration correction processing are executed using the different pattern forming regions Rp as described above, the effectiveness of the color misregistration correction can be improved.

  Furthermore, in the above embodiment, the yellow toner threshold TH (Y), the magenta toner threshold TH (M), the cyan toner threshold TH (C), and the black toner threshold TH (K) suitable for pattern detection are set in advance. Since the position information of the resist pattern image is detected and used as the pattern detection threshold information, each toner color is detected even when the voltage level of the output signal from the sensor 18 differs for each toner color as shown in FIG. The position information of the resist pattern image can be detected based on the optimum pattern detection threshold information for both colors.

  By the way, in the above-described embodiment, these pattern detection threshold information is obtained in advance and stored in the ROM 523, but a threshold setting pattern image (hereinafter referred to as “sample pattern”) is formed as follows. The pattern detection threshold information may be obtained. Hereinafter, another embodiment of the present invention will be described with reference to FIGS.

  FIG. 7 is a view showing another embodiment of the image forming apparatus according to the present invention. A feature of this embodiment is that a detection processing circuit 55 that forms a sample pattern image of each color before forming a resist pattern image, and updates and stores pattern detection threshold information of each color based on the detection result of the sample pattern image. This is an added point. Since other basic configurations are the same as those in the embodiment of FIG. 1, they are denoted by the same or corresponding reference numerals and description thereof will be omitted.

  In this detection processing circuit 55, as shown in the figure, a peak hold circuit 551 and a bottom hold circuit 552 are connected to the light receiving portion of the test pattern sensor 18, and the voltage level of the signal output from the light receiving portion is determined. The maximum value and the minimum value are detected by the peak hold circuit 551 and the bottom hold circuit 552, respectively. Further, the maximum value and the minimum value are converted into digital values by the A / D conversion unit 553 and then input to the threshold setting circuit 554. The threshold setting circuit 554 is a circuit for determining the threshold information for pattern detection based on the maximum value and the minimum value of the voltage level. For example, the average value is written in the buffer 555 as the pattern detection threshold information. Further, after such pattern detection threshold information is determined, the threshold setting circuit 554 gives a reset signal to the peak hold circuit 551 and the bottom hold circuit 552 to clear the values held in the respective circuits. Further, when the threshold setting circuit 554 detects the position of the resist pattern image, it reads out pattern detection threshold information corresponding to the toner color of the resist pattern image from the buffer 555 and compares it via the D / A converter 556. Input to the device 557. The comparator 557 compares the voltage level of the output signal from the test pattern sensor 18 with pattern detection threshold information, and outputs the comparison result to the CPU 521 as a pattern detection signal.

  FIG. 8 is a schematic diagram showing the operation of the detection processing circuit of FIG. When the pattern detection threshold information is updated and stored by the detection processing circuit 55 configured as described above, the sample pattern image of each color is placed on the intermediate transfer belt 16 in the same manner as in the case of forming the resist pattern image. Form. That is, a sample pattern image is formed at the image forming stations Y, M, C, and K in accordance with a control command from the CPU 521 of the engine controller 52 and is transferred to the intermediate transfer belt 16 and a part of the surface of the intermediate transfer belt 16. The sample pattern images SP (K), SP (C), SP (M), and SP (Y) of the respective colors are spaced in the (pattern formation region Rp) at a predetermined interval in the transport direction (sub-scanning direction) as shown in FIG. Formed. Regarding the sample pattern images SP (K), SP (C), SP (M), and SP (Y), the shape, size, interval, arrangement, number, and the like are arbitrary.

  When the sample pattern images SP (K), SP (C), SP (M), and SP (Y) are thus formed, the light projecting portion (not shown) of the test pattern sensor 18 is turned on and the sample pattern by the test pattern sensor 18 is turned on. Images SP (K), SP (C), SP (M), and SP (Y) can be detected. Then, the sample pattern images SP (K), SP (C), SP (M), and SP (Y) formed on the intermediate transfer belt 16 move in the transport direction D16 along with the movement of the intermediate transfer belt 16, and the test pattern. After passing through the sensor 18, pattern detection threshold information for each color is obtained and updated / stored in the buffer 555. In any case, the operation is basically the same for the toner color, so only black will be described here.

  While the black sample pattern image SP (K) passes through the test pattern sensor 18, the maximum value PV (K) and the minimum value BV (K) of the voltage level of the signal output from the light receiving unit of the sensor 18 are peak-held. Detection is performed by the circuit 551 and the bottom hold circuit 552, respectively. Then, the threshold setting circuit 554 determines the latest black toner threshold TH (K) based on the maximum value PV (K) and the minimum value BV (K), and writes it in the buffer (K) in the buffer 555. As a result, the existing pattern detection threshold information for black is updated. When the update of the black pattern detection threshold information is thus completed, the peak hold circuit 551 and the bottom hold circuit 552 are reset. For other toner colors, the latest toner thresholds TH (C), TH (M), and TH (Y) are determined in the same manner as black, and the pattern detection threshold information in the buffer 555 is updated.

  As described above, according to this embodiment, the sample pattern images SP (K), SP (C), SP (M), and SP (Y) for each color are formed, and the latest toner is formed based on the sample pattern image. Since the threshold values TH (K), TH (C), TH (M), and TH (Y) are determined as pattern detection threshold information, the position information of the resist pattern image can be accurately detected, and the color Deviation correction can be performed with higher accuracy. Here, the update timing of the pattern detection threshold information using the sample pattern image is arbitrary, but if always performed before forming the resist pattern image, the position information of the resist pattern image is always the latest pattern detection threshold. It can be performed using information and is preferred.

  In this embodiment, the sample pattern image is simply detected by the sensor 18 to determine the toner thresholds TH (K), TH (C), TH (M), and TH (Y). When detecting this, the surface state of the pattern formation region Rp may affect the voltage level of the output signal from the sensor 18. Therefore, as in the previous embodiment, before the sample pattern image is formed, the test pattern sensor 18 acquires the surface state of the intermediate transfer belt 16, particularly the pattern formation region Rp, and further, based on the surface state, the sample pattern image is acquired. The forming process may be controlled. As a result, the sample pattern image is formed after sufficiently considering the surface state of the pattern formation region Rp where the sample pattern image is to be formed, so that the position detection of the sample pattern image can be performed with high accuracy. it can. As a result, the reliability of the pattern detection threshold information can be improved. Further, when it is confirmed that the pattern formation region Rp of the intermediate transfer belt 16 is soiled or damaged based on the background information, and the belt surface state in the region is not within the proper range, formation of the sample pattern image and pattern It is possible to stop useless toner consumption by canceling the detection threshold information. Alternatively, the latest pattern detection threshold information may be determined by forming sample pattern images in different pattern formation regions Rp.

  Furthermore, in the above embodiment, the surface state is acquired only for the pattern formation region Rp before the resist pattern image, the sample pattern image, or the like is formed in the pattern formation region Rp, and the surface state of the pattern formation region Rp is within an appropriate range. It is confirmed that it is within. However, the background information of the entire circumference of the intermediate transfer belt 16 in the transport direction D16 is acquired, the pattern formation area is determined based on the background information, and a resist pattern image, a sample pattern image, and the like are formed on the pattern formation area. You may do it. Hereinafter, this will be described in detail with reference to FIG.

  FIG. 9 is a flowchart showing another embodiment of the image forming apparatus according to the present invention. In this embodiment, prior to the formation / detection of the resist pattern image and the color misregistration correction processing, the drive roller 14 starts to be rotated by a drive motor (not shown) in step S31, and the intermediate transfer belt 16 moves in the arrow direction D16. Circulation driven. Further, the detection of the rotation time is started from the start of the rotation of the intermediate transfer belt 16, and the moving distance of the intermediate transfer belt 16 is calculated.

  At the same time as or after the start of the rotation, the light projecting portion (not shown) of the test pattern sensor 18 is turned on to start detecting the surface state of the intermediate transfer belt 16 by the test pattern sensor 18 (step S32). As a result, the surface of the intermediate transfer belt 16 passes through the test pattern sensor 18 as the intermediate transfer belt 16 moves in the transport direction D16, and the light reflected by the surface of the test pattern sensor 18 (shown in the figure). (Omitted). The voltage level of the signal output from the test pattern sensor 18 changes according to the amount of received light. For this reason, the surface state of the intermediate transfer belt 16 can be acquired as background information by detecting the voltage level.

  Such confirmation is continued until the time corresponding to one rotation of the intermediate transfer belt 16 has elapsed from the start of voltage level detection (step S32), and the background information is acquired (step S33). As a result, the base information can be acquired for the entire circumference of the surface of the intermediate transfer belt. Accordingly, in step S34, the light projecting portion of the test pattern sensor 18 is turned off, and the process for acquiring the surface state of the intermediate transfer belt 16 is completed. Based on the surface state thus obtained, a surface area suitable for forming a resist pattern image is selected as a pattern formation area from the surface of the intermediate transfer belt 16. That is, the surface area of the intermediate transfer belt 16 in the appropriate range is determined as the pattern formation area based on the background information (step S35).

  Subsequently, as in the above embodiment, resist pattern image formation (step S36) / detection (step S37) and color misregistration correction processing (step S38) are executed.

  As described above, according to this embodiment, the background information is acquired for the entire circumference of the intermediate transfer belt 16 in the transport direction (movement direction) D16, and the pattern formation region is selected based on the background information. The pattern formation region can be determined appropriately. Since the resist pattern image is formed in the pattern formation region, the position of the resist pattern image can be detected with high accuracy. As a result, color misregistration correction can be performed appropriately.

  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 present invention is applied to an image forming apparatus that forms a resist pattern image on the intermediate transfer belt 16, but the scope of the present invention is not limited to this, and the intermediate transfer drum The present invention can be applied to all apparatuses that perform color misregistration processing by forming a resist pattern image 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. 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. 4 is a schematic diagram illustrating an operation for acquiring a surface state of an intermediate transfer belt. FIG. 6 is a schematic diagram illustrating a pattern detection operation for color misregistration correction. FIG. 6 is a diagram showing another embodiment of the image forming apparatus according to the present invention. FIG. 8 is a schematic diagram showing the operation of the detection processing circuit of FIG. 7. 6 is a flowchart showing another embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 16 ... Intermediate transfer belt (transfer medium), 16a ... Belt surface (transfer medium surface), 18 ... Test pattern sensor (optical sensor), 52 ... Engine controller (surface state acquisition means, pattern formation control) Means), 55... Detection processing circuit, 521... CPU (surface state acquisition means, pattern formation control means), 523... ROM (pattern detection storage unit, background detection storage unit), 555... Buffer (pattern detection storage unit) ), D16 ... conveying direction (moving direction), Y, M, C, K ... image forming station

Claims (7)

A plurality of image forming stations, each forming a different color toner image, are arranged along the transfer medium moving direction, and the toner image formed by the plurality of image forming stations is used as a resist pattern image on the transfer medium surface An image that is formed on the pattern forming region so as to be separated in the moving direction, and that detects the resist pattern image with an optical sensor and corrects color misregistration between the plurality of colors based on an output signal from the optical sensor. In the forming device,
Surface state acquisition means for acquiring the surface state of the transfer medium based on ground information obtained by the optical sensor detecting the surface of the transfer medium before forming a resist pattern image;
An image forming apparatus comprising: a pattern forming control unit that controls a resist pattern image forming process based on the surface state of the transfer medium acquired by the surface state acquiring unit. 2. The image forming apparatus according to claim 1, wherein a resist pattern image forming process and a color misregistration correction process are performed in a state where a surface state of the pattern forming region is in an appropriate range set in advance.
While the surface state acquisition means acquires the surface state of the pattern formation region as the ground information,
The pattern formation control unit stops the resist pattern image formation process when the surface state of the pattern formation region acquired by the surface state acquisition unit is out of the appropriate range. A background detection storage unit that stores background detection threshold information corresponding to the appropriate range;
The image forming apparatus according to claim 2, wherein the surface state acquisition unit determines whether the surface state of the pattern formation region is out of the appropriate range based on the background detection threshold information and the background information.   4. The pattern forming control unit according to claim 2, wherein when the resist pattern image forming process is stopped, the pattern forming control unit changes a pattern forming region and forms a new resist pattern image in the changed pattern forming region. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein a resist pattern image forming process and a color misregistration correction process are performed in a state where a surface state of the pattern forming region is in an appropriate range set in advance.
While the surface state acquisition means acquires the background information for the entire circumference in the moving direction,
The pattern formation control unit determines a surface region in the appropriate range as the pattern formation region based on the background information acquired by the surface state acquisition unit, and forms an image of a resist pattern image on the pattern formation region Forming equipment. A pattern detection storage unit that stores threshold information for pattern detection, which is a detection reference for a resist pattern image for each toner color;
For each toner color, the position of the resist pattern image on the transfer medium is compared with the output signal obtained by detecting the resist pattern image of the toner color by the optical sensor and the threshold information for pattern detection. Seeking information,
6. The image forming apparatus according to claim 1, wherein color misregistration between the plurality of colors is corrected based on the position information of the plurality of colors. In an image forming apparatus in which a plurality of image forming stations each forming a toner image of a different color are arranged along the moving direction of a transfer medium, color deviation of toner images formed by the plurality of image forming stations is corrected. A color misregistration correction method,
A pattern forming step in which toner images formed by the plurality of image forming stations are formed as resist pattern images on the pattern forming region of the transfer medium separated in the moving direction; and
A pattern detection step of detecting the resist pattern image to obtain position information of the resist pattern image;
A correction step of correcting color misregistration between the plurality of colors based on the position information obtained in the pattern detection step;
A surface state acquisition step of acquiring the surface state of the transfer medium based on ground information obtained by the optical sensor detecting the surface of the transfer medium before the pattern formation step;
And a pattern formation control step for controlling the resist pattern formation step based on the surface state of the transfer medium acquired by the surface state acquisition step.

Images