JP4622551B2 - Image forming apparatus and color misregistration correction method - Google Patents

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 toner images of different colors, are arranged along the moving direction of a transfer medium. The present invention relates to a technique for correcting color misregistration.

  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.

  One of the serious problems in an image forming apparatus having a plurality of image forming stations is color misregistration. 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. Therefore, in order to solve this problem, a reference pattern image (hereinafter referred to as a “registration mark”) for detecting color misregistration is formed on a transfer medium in advance, and each resist mark is detected by an optical sensor. Find the mark position information. Based on the positional information, the relative positional relationship between the toner images formed by the image forming stations can be grasped. Therefore, the registration control amount for correcting the relative color shift of the toner image is conventionally obtained from the position information, and when the color image is actually formed, the formation position of the toner image of each color is based on the registration control amount. Color misregistration is suppressed by adjusting.

JP 2004-109617 A (page 4)

  By the way, when image formation is performed, the operating environment, particularly the internal temperature of the apparatus (so-called internal temperature) may change. As a result, the registration control amount may deviate from the value obtained as described above, and color misregistration may occur. Here, with respect to fluctuations in the resist control amount caused by fluctuations in the in-machine temperature, the in-machine temperature may be measured by a temperature sensor as conventionally proposed, and the resist control amount may be adjusted based on the measurement result. However, when double-sided printing is continuously performed, it may not be possible to appropriately cope with the adjustment of the resist control amount according to the in-machine temperature. This is because, for example, in the apparatus described in Patent Document 1, the first image formed on the intermediate transfer belt (transfer medium) is transferred to the first surface of the sheet-like recording material and then thermally fixed by the fixing unit. Yes. In parallel with the formation of the second image to be printed on the second surface of the recording material on the intermediate transfer belt, the recording material that has undergone thermal fixing is conveyed again to the secondary transfer position. Then, the second image is transferred to the second surface of the recording material at the secondary transfer position to perform double-sided printing. Therefore, at the time of printing an image on the first surface (single-sided printing), a recording material at room temperature is secondarily transferred at the secondary transfer position. However, in order to perform double-sided printing, two recording materials heated by the fixing unit are used. Since the sheet is conveyed to the next transfer position, parts related to transfer such as the intermediate transfer belt, the driving roller, and the secondary transfer roller are locally heated at the secondary transfer position. As a result, the transfer speed of the intermediate transfer belt fluctuates due to the local thermal effect of the recording material heat-fixed by continuously performing double-sided printing, even though the temperature inside the machine is small. It may deviate from the optimum value.

  The present invention has been made in view of the above problems, and in an image forming apparatus that continuously executes a printing operation including double-sided printing, color misregistration occurs by appropriately adjusting the resist control amount during the continuous printing operation. The purpose is to prevent it effectively.

  According to the present invention, a plurality of image forming stations, each forming a different color toner image, are arranged along a moving direction of a transfer medium moving at a predetermined speed, and the toner images formed by the plurality of image forming stations. The plurality of toner images can be superimposed on the transfer medium while controlling the relative positional relationship based on the resist control amount, and a first image formed on the transfer medium can be formed. Is transferred to the first surface of the sheet-like recording material and thermally fixed, and then a second image formed on the transfer medium is transferred to the second surface of the recording material, and printing operations including double-sided printing are continuously executed. The present invention relates to an image forming apparatus and a color misregistration correction method in the apparatus.

  In the image forming apparatus configured as described above, when double-sided printing is executed during the continuous printing operation, the second image is transferred to the recording material that has been thermally fixed and heated, and the image is transferred onto the transfer medium. A local temperature rise occurs in the area where the image of the above is transferred to the recording material. Then, the moving speed of the transfer medium fluctuates due to this temperature rise, so that the relative positional relationship of the toner images formed by the plurality of image forming stations fluctuates. Such variation is closely related to the number of double-sided printing performed during the continuous printing operation and the transfer time of the second image to the second surface, as will be described in detail later. As the value increases, the fluctuation amount increases.

  Therefore, in the first aspect of the image forming apparatus and the color misregistration correction method according to the present invention, the number of recording materials to be printed on both sides during the continuous printing operation is measured, and the resist control amount is adjusted based on the measurement result. . Therefore, color image formation is executed with a resist control amount adjusted in consideration of a color misregistration factor resulting from double-sided printing. As a result, even if double-sided printing is included in the continuous printing operation, it is possible to effectively prevent color misregistration from occurring during the continuous printing operation.

  In the second aspect of the image forming apparatus and the color misregistration correction method according to the present invention, the transfer time (hereinafter referred to as “second surface transfer time”) during which the second image is transferred to the second surface during the continuous printing operation. Measurement is performed, and the resist control amount is adjusted based on the measurement result. Accordingly, as in the first aspect, color image formation is executed with the resist control amount adjusted in consideration of the cause of color misregistration caused by double-sided printing. As a result, even if double-sided printing is included in the continuous printing operation, it is possible to effectively prevent color misregistration from occurring during the continuous printing operation.

  Here, a direct influence due to variation in the moving speed of the transfer medium due to double-sided printing appears in the relative positional relationship of the toner images between the image stations. Therefore, the toner image shift amount between the image stations is estimated based on the measurement result (the number of printed sheets on both sides and the second surface transfer time), and the registration control amount is adjusted in accordance with the shift amount. During the printing operation, the registration control amount is adjusted to an appropriate value, and color misregistration can be reliably prevented.

  In addition, since the speed fluctuation of the transfer medium due to double-sided printing increases each time double-sided printing is performed, it is desirable to determine the amount of toner image deviation by double-sided printing and adjust the resist control amount each time double-sided printing is performed. . Further, the influence of double-sided printing on the speed fluctuation of the transfer medium differs depending on the size and type of the recording material to be double-sided printed, and the amount of deviation of the toner image due to double-sided printing differs depending on the size and type. Therefore, it is desirable to correct the deviation amount of the toner image according to the size and type of the recording material, and the registration control amount can be adjusted with higher accuracy and more accurately by correcting the deviation amount.

  Further, there are cases where a plurality of continuous printing operations are executed at time intervals, but the degree of influence of the previous continuous printing operation differs depending on the elapsed time from the previous continuous printing operation to the current continuous printing operation. For example, when the elapsed time is relatively long, the transfer medium thermal influence is relieved during the interval returns to the steady state, ignoring or neglect thermal effects of duplex printing which is executed during the previous continuous printing operation It may be possible. On the other hand, when the elapsed time is short, the current continuous printing operation may be executed by directly dragging the thermal effect of the double-sided printing executed during the previous continuous printing operation. Therefore, in order to cope with this, a counting means for counting the time elapsed until the current consecutive printing operation from the previous continuous printing operation, the time measurement result by the timer means, the deviation amount calculated during the previous continuous printing operation Based on the above, the amount of deviation during the current continuous printing operation may be corrected. As a result, even when a plurality of continuous printing operations are executed at time intervals, the registration control amount can be adjusted with higher accuracy and accuracy.

A. Regarding the speed fluctuation of the transfer medium due to double-sided printing In the electrophotographic image forming apparatus, a toner image is formed on the transfer medium and a recording material stored in a cassette or a manual feed tray is conveyed to a transfer position. The toner image on the transfer medium is transferred to the first surface of the recording material. Further, the toner image is thermally fixed on the recording material. In the case of single-sided printing, the paper is discharged as it is toward the paper discharge tray. On the other hand, in the case of duplex printing, the thermally fixed recording material is conveyed again to the transfer position and the toner image is transferred to the second surface. Therefore, when performing single-sided printing (including printing on the first side of double-sided printing), the toner image is transferred to a recording material close to room temperature, whereas when performing the second side of double-sided printing, heat is applied. There is a possibility that the toner image is transferred to the recording material which is fixed and in a high temperature state, and the temperature rises locally at the transfer position. As described above, since the thermal effect is greatly different between single-sided printing and double-sided printing, the thermal effect in single-sided printing and the thermal effect in double-sided printing were measured and compared.

  Figure 1 is a graph showing the thermal effect in the continuous two-sided printing and continuous one-sided printing, manufactured by Seiko Epson color laser printer (model number: LP-9000C) by the time of performing the monochrome printing continuously on plain paper A3 size Results are shown. More specifically, the plot in FIG. 6A shows the movement of the intermediate transfer belt (transfer medium) between two points when monochrome double-sided printing is continuously performed on 250 sheets (500 sheets in terms of single-sided printing). It plots the time, plot in FIG (b) is a plot of the movement elapsed time between two points of the intermediate transfer belt at the time of running the monochromatic single-sided printing 500 sheets continuously (transfer medium) is there. In addition, the straight lines in the figure indicate the relationship between the number of printed sheets and the elapsed movement time in double-sided printing and single-sided printing, respectively. As is apparent from the figure, even if single-sided printing is continuously performed, the elapsed time of movement hardly changes, and the speed fluctuation of the intermediate transfer belt is hardly recognized. On the other hand, in double-sided printing, it can be seen that the elapsed time of movement becomes longer in proportion to the number of double-sided printed sheets, and the speed fluctuation of the intermediate transfer belt is reduced. Incidentally, based on the actual measurement result shown in FIG. 1A, the rate of speed fluctuation per double-sided printing was about -0.001 (%).

  As double-sided printing increases in this way, speed fluctuations occur due to the thermal effect caused by double-sided printing, and the relative positional relationship of the toner images formed by each image forming station may be greatly shifted due to the thermal effect. is there. As a result, although a reference pattern image such as a resist mark is formed in advance to obtain a resist control amount and color misregistration correction is performed based on the resist control amount, color misregistration may occur.

  Therefore, in the embodiment according to the present invention, the number of recording materials to be printed on both sides during the continuous printing operation and the second surface transfer time are measured, and the resist control amount is adjusted based on the measurement result. Hereinafter, specific embodiments will be described in detail.

B. Apparatus Configuration and Operation Hereinafter, four embodiments of the image forming apparatus according to the present invention will be described. However, the apparatus configuration and basic operation of these embodiments are the same, and the operation is only partially different. The configuration and operation of the apparatus common to both will be described, and thereafter, the operation unique to each embodiment will be described.

  FIG. 2 is a diagram showing a basic configuration of the image forming apparatus according to the present invention. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. The device 1 is, black (K), cyan (C), magenta (M), a color printing process to form a four color toner full-color image by superimposing (developer) of yellow (Y), and black (K ) To selectively execute a monochrome printing process 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 plain paper, thick paper, and an OHP transparent sheet.

  2, an image forming apparatus 1 according to the present embodiment includes a housing body 2, a first opening / closing member 3 that is detachably attached to the front surface of the housing body 2 (the right-hand side surface in FIG. 2), 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 includes a driving roller 14 that is rotationally driven by a driving motor (not shown) disposed below the housing body 2, a driven roller 15 that is disposed obliquely above the driving roller 14, An intermediate transfer belt 16 that is stretched between the rollers 14 and 15 and is circulated and driven in the direction of the arrow D16 in the figure, and a belt cleaner 17 that abuts on the surface of the intermediate transfer belt 16 are provided. The driven roller 15 is disposed obliquely above the drive roller 14 (upward on the left hand in FIG. 2). 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 (downward right in FIG. 2) is positioned below. In the present embodiment, belt tensioning surface when the belt surface 16a the belt drive has a (surface to be pulled by the driving roller 14), slower peripheral speed than the peripheral speed of each color photoreceptor drum (image carrier) 20 have. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Is driving.

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

  In the present embodiment, the diameter of the driving roller 14 is smaller than the diameter of the driven roller 15. Thereby, the sheet S after the secondary transfer can be easily peeled by the elastic force of the sheet S itself. The driven roller 15 is also used as a backup roller for the belt cleaner 17. The belt cleaner 17 is provided in the transport direction downward belt surface 16a side, as shown in FIG. 2, comprises a cleaning blade 17a for removing residual toner, and a toner conveying member for conveying the toner removed Yes. The cleaning blade 17a contacts the intermediate transfer belt 16 at a portion where the intermediate transfer belt 16 is wound around the driven roller 15, and cleans and removes toner remaining on the surface of the intermediate transfer belt 16 after the secondary transfer.

  The driving roller 14 and the driven roller 15 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, a primary transfer roller 21 is provided on the back surface of the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 so as to face the photosensitive drum 20 of each image forming station Y, M, C, K described later. . These four primary transfer rollers 21 are rotatably supported with respect to the support frame, and are electrically connected to the primary transfer bias generator 525. From the primary transfer bias generator 525 at an appropriate timing. A primary transfer bias is applied.

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

  A test pattern sensor 18 is installed on the support frame of the transfer belt unit 9 in the vicinity of the drive roller 14. The test pattern sensor 18 is a so-called reflection type optical sensor, a light projecting unit (not shown) that irradiates light toward the intermediate transfer belt 16, and light reflected by the surface of the intermediate transfer belt 16 and a registration mark. Is provided with a light receiving portion (not shown). Then, light is emitted from the light projecting unit to the registration mark on the intermediate transfer belt 16, while the light from the registration mark is received by the light receiving unit and a signal corresponding to the amount of light received by the light receiving unit is a test pattern sensor 18 is output. The registration control amount can be obtained based on the output signal from the test pattern sensor 18. Since many methods for deriving the resist control amount have been conventionally proposed, the description thereof is omitted here.

  The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. Each image forming station Y, M, C, K is provided with a photosensitive drum 20. A charging unit 22, an image writing unit 23, a developing unit 24, and a photoconductor cleaner 25 are disposed around each photoconductor drum 20. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. In FIG. 2, since the image forming stations of the image forming unit 6 have the same configuration, for convenience of illustration, only some of the image forming stations are denoted by reference numerals, and the other image forming stations are omitted. . Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

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

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

  The image writing unit 23 is an array writing 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 photosensitive drum 20 (direction perpendicular to the paper surface of FIG. 2). The head is used and is spaced from the photosensitive drum 20. The array-like writing head has a shorter optical path length and is more compact than the laser scanning optical system. Therefore, it can be disposed close to the photosensitive drum 20 and has the advantage that the entire apparatus can be downsized.

  In this embodiment, the photoconductive drum 20, the charging unit 22, the developing unit 24, and the photoconductive cleaner 25 of each of the image forming stations Y, M, C, and K are replaced with replacement cartridges 6Y, 6M, 6C, and 6K (FIG. 3). ) As a unit. Each replacement cartridge 6Y, 6M, 6C, 6K is provided with non-volatile memories 91-94 for storing information relating to the replacement cartridge. The transmitting and receiving unit 53Y provided in each exchange cartridge, 53M, 53C, and 53K, transceiver 522Y provided on the main body side, 522m, 522C, and 522K are arranged close to each other, CPU 521 and the memory of the engine controller 52 Wireless communication is performed with 91-94. In this way, information regarding each replacement cartridge is transmitted to the CPU 521, and information in each of the memories 91 to 94 is updated and stored.

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

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

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

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

  The secondary transfer roller 19 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, and a pressure roller 46 that presses and biases the heating roller 45. The image secondarily transferred onto the sheet S is heat-fixed on the sheet S at a predetermined temperature (for example, 150 ° C. to 180 ° C.) at a nip formed by the heating roller 45 and the pressure roller 46. In the present embodiment, the fixing unit 12 can be disposed in a space formed obliquely above the intermediate transfer belt 16, in other words, in a space opposite to the image forming unit 6 with respect to the intermediate transfer belt 16. Thus, heat transfer to the electrical component box 5, the image forming unit 6, and the intermediate transfer belt 16 can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced.

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

  In addition, as shown in FIG. 3, 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. 3, 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 this apparatus, a registration control amount establishment process (registration mark formation / detection and registration control amount calculation) is performed at an appropriate timing, for example, immediately after the power is turned on, as part of the initial process, and the relative color shift of the toner image is detected. A registration control amount for correction is obtained and stored in a memory. When a color image is actually formed, the color misregistration is prevented by adjusting the formation position of each color toner image from the memory based on the registration control amount. In the following embodiments, as will be described below, the resist control amount is appropriately adjusted based on the number of double-sided printings during the continuous printing operation and the second surface transfer time, and the color image is adjusted with the adjusted resist control amount. Forming.

C. First Embodiment FIG. 4 is a flowchart showing a first embodiment of an image forming apparatus according to the present invention. FIG. 5 is a flowchart showing the adjustment operation of the registration control amount. 6 and 7 are diagrams schematically showing the adjusting operation. In this apparatus, when an image forming command (printing command) is given to the main controller 51 from an external device such as a host computer, the CPU 511 of the main controller 51 converts the job data into a format suitable for the operation instruction of the engine unit EG, It is sent to the engine controller 52. On the other hand, the engine controller 52 controls each part of the engine unit EG based on job data from the CPU 511 to execute single-sided printing or double-sided printing, and forms an image corresponding to the image signal on the sheet S. Further, not only when a plurality of print commands are included in the image formation command, but also when a plurality of image formation commands are given continuously, the jobs are connected to execute a continuous print operation. The CPU 521 of the engine controller 52 has functions as “measuring means” and “adjustment means” of the present invention as will be described later, and each part of the apparatus according to a registration control amount adjustment program stored in the ROM 523 in advance. Is controlled as follows to correct color misregistration during a continuous printing operation.

  First, when the printing operation is started, the double-sided printing number n stored in the RAM 524 is cleared (step S1). Then, it is determined whether the printing mode is double-sided printing or single-sided printing (step S2). In the case of double-sided printing, steps S3 to S5 are executed to adjust the resist control amount, and then based on the adjusted resist control amount. Execute printing. More specifically, a series of processing is executed as follows.

In step S3, a deviation amount of the toner image between the image forming stations due to the speed fluctuation of the intermediate transfer belt 16 is estimated (step S3). As described in detail in the section “A. Transfer medium speed fluctuation caused by double-sided printing”, when double-sided printing is executed, the moving speed of the intermediate transfer belt 16 increases as the number of double-sided printed sheets increases. fluctuate. The relative positional relationship of the toner images is shifted between the image forming stations due to the speed fluctuation. Therefore, in this embodiment, the following formula R = Ka * PD * n
Where R: deviation amount due to speed fluctuation,
Ka: Speed variation coefficient,
PD: distance between image forming stations,
Based on the above, the deviation amount R of the toner image accompanying the speed fluctuation of the intermediate transfer belt 16 is obtained. Here, a specific description will be given focusing on the amount of deviation between the image forming stations Y and K at both ends, but the same applies to other image forming stations.

In the apparatus according to this embodiment, the distance PD between the image forming stations Y and K is 300 mm. The intermediate transfer belt 16 uses polyimide as a belt base material, and based on the actual measurement result of LP-9000C, the speed fluctuation coefficient Ka, that is, the speed fluctuation rate of the intermediate transfer belt 16 per one-sided printing (−0). .001%). Therefore, the relative position of the toner image formed by the image forming stations Y and K each time one duplex printing is performed is
R = (− 0.001%) * (300 mm) * 1 = 3 μm
It is estimated that it will be shifted gradually.
R = 3 * n (μm)
It is estimated that it will shift. For example, as shown in FIG. 6, as the number of double-sided printed sheets n increases to 5, 10, 20, 30,..., The amount of deviation R (5), R (10), R (20), R (30),... Increase as 15 μm, 30 μm, 60 μm, 90 μm,. Therefore, the registration control amount is adjusted based on the deviation amount R in the next step S4.

  In this registration control amount adjustment process, the relative positional relationship between the toner images is obtained based on the deviation amount R and the dot pitch P obtained in step S3. Specifically, the pitch unit deviation amount PM is obtained from the function equation QUOTIENT (R, P) (step S41), and the minute deviation amount FM is obtained from the function equation MOD (R, P) (step S42). These functional expression QUOTIENT (R, P) and MOD (R, P) value determined by, as shown in FIG. 6, the quotient of the time obtained by dividing the shift amount R at dot pitch P, is To too. That is, it shows how many dots the toner image shift amount obtained by the function equation QUOTIENT (R, P) is shifted, and even if the toner image is shifted by that amount, how much the toner image is within the dot pitch range The value obtained by the functional expression MOD (R, P) indicates whether the deviation occurs. For example, a resolution is 600dpi devices, since the dot pitch P is about 42 .mu.m, the value of QUOTIENT (R, P) and MOD (R, P) for each duplex print number becomes a value shown in FIG.

In the next step S43, it is determined whether or not the minute deviation amount FM exceeds half of the dot pitch P. When the minute deviation amount FM exceeds the value (P / 2), it is determined that the deviation is one dot more than the pitch unit deviation amount PM, and the registration correction amount RR is expressed by the following equation RR = (PM + 1). * P
(Step S44). For example, when the number n of double-sided printed sheets is 10, the minute deviation amount FM is 30 μm, which exceeds 21 (= 42/2) μm, and therefore the resist correction amount RR is P. On the other hand, when the minute deviation amount FM does not exceed the value (P / 2), it is determined that the positional deviation of the toner image is substantially equal to the pitch unit deviation amount PM, and the registration correction amount RR is expressed by the following equation RR = PM *. P
(Step S45). For example, when the number n of double-sided printed sheets is 5, 20, or 30, the minute deviation amounts FM are 15, 18, and 6 μm, respectively, and are 21 (= 42/2) μm or less, so the resist correction amount RR is 0. , P, 2P.

  As described above, in the present embodiment, as shown in FIG. 7, the resist correction amount RR changes stepwise in dot pitch units according to the number n of double-sided printed sheets. When the registration correction amount RR is obtained, the registration control amount is corrected based on the registration correction amount RR (step S46). Then, by controlling the position where the toner image is formed based on the registration control amount, it is possible to suppress color misregistration caused by double-sided printing to less than (P / 2).

  Returning to FIG. 4, the description will be continued. When the adjustment of the registration control amount is completed, the duplex printing number n is incremented by 1 (step S5), and duplex printing is executed. In other words, since the toner image forming position at each image forming station is controlled based on the registration control amount adjusted in step S4, color misregistration can be ensured regardless of the speed fluctuation of the intermediate transfer belt 16 due to double-sided printing. Can be suppressed.

  On the other hand, without adjusting the registration control amount described above when it is determined that simplex printing in step S2, and executes printing based on the registration control amount stored in the current RAM524 proceeds directly to step S6. Further, after the printing is completed, it is determined whether or not the next printing exists, that is, whether or not the printing is continuous (step S7). When there is data to be continuously printed, the process returns to step S2 to perform a series of operations. Execute.

  As described above, according to the first embodiment, measured by the number of sheets S to be printed on both sides during the continuous printing operation (two-sided printing sheets) n the CPU521 internal counter (not shown), the measurement results (both sides Since the registration control amount is adjusted based on the number of printed sheets n), even if the speed fluctuation of the intermediate transfer belt 16 due to double-sided printing occurs, the registration control quantity is adjusted according to the speed fluctuation. Therefore, even if double-sided printing is included in the continuous printing operation, it is possible to effectively prevent color misregistration from occurring during the continuous printing operation.

D. Second Embodiment FIG. 8 is a flowchart showing a second embodiment of the image forming apparatus according to the present invention. In the first embodiment, the registration control amount is adjusted based on the number n of double-sided prints before execution of printing. However, the speed fluctuation of the intermediate transfer belt 16 due to double-sided printing increases every time double-sided printing is performed. As shown in FIG. 8, every time double-sided printing is performed, a deviation amount of the toner image by the single-sided double-sided printing is obtained (steps S14 to S15), and the registration control amount adjusting process (step S4) of the first embodiment is performed. Similarly, the registration control amount may be adjusted (step S16). That is, when the printing operation is started, the deviation amount R stored in the RAM 524 is cleared (step S11), and then printing is executed for each printing operation based on the registration control amount stored in the RAM 524 (step S11). S12). When the printing mode is double-sided printing, the deviation amount Rpr associated with the single-sided double-sided printing is expressed by the following formula: Rpr = Ka * PD
(Step S14). Then, the deviation amount Rpr associated with the duplex printing is added to the original deviation amount R to correct the deviation amount, and the corrected deviation amount R is stored in the RAM 524 (step S15). Further, the registration control amount is adjusted based on the corrected deviation amount R (step S16).

  As described above, the registration control amount is adjusted every time double-sided printing is performed, and the adjusted registration control amount is stored in the RAM 524. Therefore, regardless of whether the next printing mode is double-sided printing or single-sided printing, The printing operation is executed based on the registration control amount adjusted in consideration of the influence of the double-sided printing already executed during the continuous printing operation. Accordingly, color misregistration can be reliably and accurately prevented.

E. Third Embodiment FIG. 9 is a flowchart showing a third embodiment of the image forming apparatus according to the present invention. FIG. 10 is a flowchart showing a speed variation coefficient setting method in the third embodiment. The third embodiment is greatly different from the second embodiment in that the speed variation coefficient Ka is changed according to the type of the sheet S, and other configurations and operations are the same as those in the second embodiment. It is. Therefore, the difference will be mainly described here.

The influence of duplex printing on the speed fluctuation of the intermediate transfer belt 16 differs depending on the type of sheet S to be duplex printed. Therefore, in the third embodiment, the speed variation coefficient setting process (step S18) is performed after the duplex printing is performed and before the deviation amount Rpr associated with the duplex printing is estimated (step S14). That is, every time double-sided printing is performed, the type of the sheet S on which double-sided printing has been performed is determined (step S141). Then, the speed variation coefficient Ka is selected and set from the values Ka1 to Ka3 according to the type of the sheet S (steps S142 to S144). Typical types of sheets S on which double-sided printing is performed by the image forming apparatus are “plain paper”, “thick paper”, and “OHP sheet”, but physical properties, particularly heat capacity, are different from each other. When the inventor of the present application performed the same measurement as described in the section “A. Speed fluctuation of transfer medium caused by double-sided printing” for “thick paper” and “OHP sheet”, the intermediate transfer per double-sided printing was performed. The speed fluctuation rates of the belt 16 were about (−0.002%) and (−0.003%), respectively. Therefore, in this embodiment,
Plain paper: Ka1 = 0.001
Cardboard: Ka2 = 0.002
OHP sheet: Ka3 = 0.003
Is set.

  In the third embodiment, attention is paid to the type of the sheet S. However, the influence of double-sided printing on the speed fluctuation of the intermediate transfer belt 16 differs depending on the size of the sheet S to be double-sided printed. Accordingly, as shown in FIG. 11, to determine the paper size of the duplex printed sheet S (step S145), the determination result three values the speed variation coefficient Ka according to Ka4, KA5, selected from Ka6 ( Steps S146 to S148) may be configured. Further, the speed variation coefficient Ka may be changed and set by combining the type and size of the sheet S.

  As described above, according to the third embodiment, the speed variation coefficient Ka is changed and set according to the type and size of the sheet S printed on both sides. Can be requested. As a result, the registration control amount can be adjusted with higher accuracy and accuracy by correcting the shift amount.

F. Fourth Embodiment FIG. 12 is a flowchart showing a fourth embodiment of the image forming apparatus according to the present invention. FIG. 13 is a flowchart showing a method for estimating the amount of deviation at the start of printing in the fourth embodiment. The fourth embodiment is greatly different from the second embodiment in that the deviation amount due to the previous continuous printing operation is taken into consideration when starting the printing operation, and other configurations and operations are the second embodiment. The form is the same. Therefore, the difference will be mainly described here.

  In the second embodiment, the deviation amount R due to duplex printing is cleared at the start of printing, and the influence of the previous continuous printing operation is not considered at all. However, if the next printing operation is started within a relatively short time from the previous continuous printing operation, the amount of deviation due to double-sided printing performed during the previous continuous printing operation may not be ignored. Therefore, in the fourth embodiment, at the start of printing, the deviation amount R due to double-sided printing is not uniformly cleared, but based on the elapsed time from the previous continuous printing operation to the current printing operation. The influence of the shift amount due to the operation on the current printing operation, that is, the shift amount at the start of printing is estimated (step S19). That is, as shown in FIG. 13, the CPU 521 starts counting the internal timer from the end of the previous printing, and acquires the elapsed time from the previous printing operation to the current printing operation (step S191). Further, the deviation amount due to double-sided printing at the end of the previous continuous printing operation is acquired as the reference deviation amount Rf (step S192).

  And the deviation | shift amount R is set according to the elapsed time acquired by step S191 (step S193-S199). That is, when the elapsed time is short and the printing operation is started in a short time from the previous continuous printing operation, the reference deviation amount Rf is set as the deviation amount R as it is (step S196). Further, as the elapsed time becomes longer, a value smaller than the reference deviation amount Rf is set as the deviation amount R. Further, when a sufficient time has elapsed from the previous continuous printing operation (in this embodiment, when it exceeds 15 minutes), the thermal effect due to double-sided printing is eliminated during printing standby, so the deviation amount R is cleared. (Step S199).

  As described above, according to the fourth embodiment, the deviation amount at the start of printing this time is set according to the elapsed time from the previous continuous printing operation to the current continuous printing operation. Even when the continuous printing operation is executed with a time interval, the registration control amount can be adjusted with higher accuracy and accuracy.

  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-described embodiment, even if the deviation amount due to double-sided printing increases during the continuous printing operation, the registration control amount is adjusted based on the deviation amount, and the color deviation is corrected based on the adjusted registration control amount. When the thermal effect of double-sided printing becomes large, the continuous printing operation is temporarily interrupted, and the registration control amount establishment process (registration mark formation / detection and registration control amount calculation) is performed. May be updated. Further, this update process (registration control amount establishment process) may be performed after the continuous printing operation is completely stopped, or the color image is printed during continuous printing while the movement of the intermediate transfer belt 16 is continued. The registration operation may be updated by temporarily interrupting the forming operation and obtaining a new registration control amount. Among these, in consideration of operation efficiency, operation stability, and the like, it is desirable to temporarily interrupt the color image forming operation and execute the registration control amount update process as described above.

  In the above embodiment, the registration control amount adjustment operation based on the deviation amount R is executed using the functional expressions QUOTIENT (R, P) and MOD (R, P). However, the present invention is not limited to this.

  In the above embodiment, the amount of deviation due to double-sided printing is estimated based on the number of double-sided printed sheets. However, the transfer time during which an image is transferred to the second side of the sheet S during a continuous printing operation, that is, the second side is 2 The transfer time passing through the next transfer region TR2 may be measured by the engine controller 52, and the registration control amount may be adjusted based on the measurement result.

The graph which shows the heat influence in continuous single-sided printing and continuous double-sided printing. 1 is a diagram illustrating a basic configuration 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. 1 is a flowchart illustrating a first embodiment of an image forming apparatus according to the present invention. 5 is a flowchart showing an adjustment operation of a resist control amount. The figure which shows typically the adjustment operation in 1st Embodiment. The figure which shows typically the adjustment operation in 1st Embodiment. 9 is a flowchart illustrating a second embodiment of the image forming apparatus according to the present invention. 9 is a flowchart illustrating a third embodiment of an image forming apparatus according to the present invention. The flowchart which shows the setting method of the speed variation coefficient in 3rd Embodiment. The flowchart which shows the setting method of the speed variation coefficient in 3rd Embodiment. 9 is a flowchart illustrating a fourth embodiment of an image forming apparatus according to the present invention. 6 is a flowchart illustrating a method for estimating a deviation amount at the start of printing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 9 ... Transfer belt unit, 16 ... Intermediate transfer belt, 52 ... Engine controller (measurement means and adjustment means), 521 ... CPU (measurement means and adjustment means), D16 ... (Intermediate transfer belt) movement Direction, R ... Deviation amount of toner image due to double-sided printing, S ... Sheet (recording material), Y, M, C, K ... Image forming station

Claims (9)

A plurality of image forming stations, each of which forms a toner image of a different color, are arranged along the moving direction of the transfer medium moving at a predetermined speed, and relative to the toner images formed by the plurality of image forming stations. The color image can be formed by superimposing the plurality of toner images on the transfer medium while controlling the positional relationship based on the resist control amount, and the first image formed on the transfer medium can be formed. A printing operation including double-sided printing is continuously performed in which the second image formed on the transfer medium is transferred to the second surface of the recording material after being transferred to the first surface of the sheet-like recording material and thermally fixed. In the image forming apparatus to
Measuring means for measuring the number of recording materials to be printed on both sides during a continuous printing operation;
An image forming apparatus comprising: an adjusting unit that adjusts the registration control amount based on a measurement result of the measuring unit. A plurality of image forming stations, each of which forms a toner image of a different color, are arranged along the moving direction of the transfer medium moving at a predetermined speed, and relative to the toner images formed by the plurality of image forming stations. The color image can be formed by superimposing the plurality of toner images on the transfer medium while controlling the positional relationship based on the resist control amount, and the first image formed on the transfer medium can be formed. A printing operation including double-sided printing is continuously performed in which the second image formed on the transfer medium is transferred to the second surface of the recording material after being transferred to the first surface of the sheet-like recording material and thermally fixed. In the image forming apparatus to
Measuring means for measuring a transfer time during which the second image is transferred to the second surface during the continuous printing operation;
An image forming apparatus comprising: an adjusting unit that adjusts the registration control amount based on a measurement result of the measuring unit. The adjusting unit obtains in advance a relationship between a toner image shift amount between each image station generated by a change in speed of the transfer medium by double-sided printing and a value measured by the measuring unit; The toner image shift amount between the image stations at the time when the measurement result is obtained based on the measurement result of the measurement unit and the relation is obtained , and the registration control amount is adjusted according to the shift amount. 3. The image forming apparatus according to 1 or 2. The image forming apparatus according to claim 3, wherein the adjustment unit obtains a deviation amount of the toner image by the double-sided printing every time double-sided printing is performed, and adjusts the registration control amount.   The image forming apparatus according to claim 3, wherein the adjusting unit corrects a deviation amount of the toner image according to a size of a recording material to be printed on both sides.   The image forming apparatus according to claim 3, wherein the adjustment unit corrects a deviation amount of the toner image according to a type of recording material to be printed on both sides. The image forming apparatus according to claim 3, wherein a plurality of continuous printing operations are performed at time intervals.
A time measuring means for measuring the time elapsed from the previous continuous printing operation to the current continuous printing operation;
An image forming apparatus that corrects a deviation amount during a current continuous printing operation based on a timing result by the time measuring unit and a deviation amount obtained during a previous continuous printing operation. A plurality of image forming stations, each of which forms a toner image of a different color, are arranged along the moving direction of the transfer medium moving at a predetermined speed, and relative to the toner images formed by the plurality of image forming stations. The color image can be formed by superimposing the plurality of toner images on the transfer medium while controlling the positional relationship based on the resist control amount, and the first image formed on the transfer medium can be formed. A printing operation including double-sided printing is continuously performed in which the second image formed on the transfer medium is transferred to the second surface of the recording material after being transferred to the first surface of the sheet-like recording material and thermally fixed. In the image forming apparatus, the color misregistration correction method for correcting the color misregistration by controlling the registration control amount,
A measurement process for measuring the number of recording materials to be printed on both sides during a continuous printing operation;
An adjustment step of adjusting the resist control amount based on a measurement result in the measurement step;
A color misregistration correction method comprising: a resist process for correcting a color misregistration by correcting a relative positional relationship of toner images formed by the plurality of image forming stations based on the adjusted resist control amount. . A plurality of image forming stations, each of which forms a toner image of a different color, are arranged along the moving direction of the transfer medium moving at a predetermined speed, and relative to the toner images formed by the plurality of image forming stations. The color image can be formed by superimposing the plurality of toner images on the transfer medium while controlling the positional relationship based on the resist control amount, and the first image formed on the transfer medium is formed into a sheet-like shape. After performing transfer and heat fixing on the first surface of the recording material, continuous printing operation including double-side printing is performed to transfer the second image formed on the transfer medium onto the second surface of the recording material that has undergone the heat fixing. In the image forming apparatus to be executed, a color misregistration correction method for correcting the color misregistration by controlling the registration control amount,
A measuring step of measuring a transfer time during which the second image is transferred to the second surface during the continuous printing operation;
An adjustment step of adjusting the resist control amount based on a measurement result in the measurement step;
A color misregistration correction method comprising: a resist process for correcting a color misregistration by correcting a relative positional relationship of toner images formed by the plurality of image forming stations based on the adjusted resist control amount. .

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