JP2007025204A - Image forming apparatus and method for controlling the apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent color misregistration due to heating of a secondary transfer roller due to execution of double-sided printing during continuous printing operation in an image forming apparatus that continuously performs printing operation including double-sided printing. .
When double-sided printing is executed during a continuous printing operation, the temperature of the secondary transfer roller is obtained from the number of executed double-sided printing (step S4). Then, a registration control amount establishment process is executed based on the temperature of the secondary transfer roller thus obtained (steps S5 and S6). As a result, when double-sided printing is continuously performed and the temperature of the secondary transfer roller rises, the registration control amount establishment process is performed, so that color misregistration can be effectively prevented. .
[Selection] Figure 4

Description

  The present invention relates to an image forming apparatus that forms a color image by superimposing toner images of different colors on the surface of an intermediate transfer belt, and relates to a technique for correcting a color shift caused by double-sided printing.

  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 moved along an intermediate transfer belt that moves by receiving the rotational force of a driving roller. Provided for each color. A toner image formed at each image forming station is superimposed on the surface of the intermediate transfer belt to form a color image.

  As described above, color misregistration is one of the serious problems in an apparatus that forms a color image by superimposing a plurality of toner images of different colors on the surface of the intermediate transfer belt. This occurs when the transfer positions of a plurality of toner images of different colors to the intermediate transfer belt are shifted from each other, and appears as a change in color tone. In order to solve this problem, a reference pattern image (hereinafter referred to as “registration mark”) for detecting color misregistration is formed on the intermediate transfer belt in advance, and each registration mark is detected by an optical sensor. Find registration mark position information. Based on the positional information, the relative positional relationship between the toner images of the respective colors 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. In this specification, a series of processing from registration mark formation to registration control amount calculation is referred to as “registration control amount establishment processing”.

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 is measured by a temperature sensor as previously proposed, and the registration control amount establishment process is appropriately executed based on the detection result. Then, a new resist control amount may be obtained. However, when double-sided printing is continuously performed, it may not be possible to appropriately cope with the registration control amount establishment process based on 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 is transferred to the first surface of the sheet-like recording material and then thermally fixed by the fixing unit. 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 it is conveyed to the next transfer position, the secondary transfer roller is locally heated by the recording material. The heat of the secondary transfer roller thus heated is transmitted to the intermediate transfer belt and the driving roller, and the temperature of the intermediate transfer belt and the driving roller varies. As a result, the peripheral length of the intermediate transfer belt and the diameter of the driving roller may fluctuate, and the registration control amount may deviate from the optimum value. In other words, the secondary transfer roller is locally heated due to the thermal effect of double-sided printing, and the temperature of the intermediate transfer belt and the driving roller fluctuates, resulting in a problem that the registration control amount deviates from the optimum value. It was.

  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, it is possible to perform a printing operation based on an optimal registration control amount, and color misregistration is achieved. The purpose is to prevent the occurrence.

  The control method of the image forming apparatus according to the present invention includes a drive roller, an intermediate transfer belt that moves by receiving the rotational force of the drive roller, and a secondary transfer that contacts the drive roller at the secondary transfer position via the intermediate transfer belt. An image forming apparatus that includes a roller and forms a color image by superimposing the plurality of toner images on the surface of the intermediate transfer belt while controlling a relative positional relationship of the plurality of toner images of different colors based on a resist control amount. In the apparatus, the first image formed on the surface of the intermediate transfer belt is transferred to the first surface of the sheet-like recording material at the secondary transfer position, and then thermally fixed by a fixing device, and further intermediated on the second surface of the recording material. A control method for causing an image forming apparatus to perform a continuous printing operation for continuously performing a printing operation including a double-sided printing for transferring a second image formed on the surface of a transfer belt at a secondary transfer position, In order to achieve the above purpose, when double-sided printing is executed during a continuous printing operation, a temperature acquisition step for obtaining the temperature of the secondary transfer roller and a temperature of the secondary transfer roller obtained by the temperature acquisition step And a resist establishment step for obtaining a resist control amount by executing a registration control amount establishment process.

  The image forming apparatus according to the present invention includes a drive roller, an intermediate transfer belt that moves by receiving the rotational force of the drive roller, and a secondary transfer that contacts the drive roller at a secondary transfer position via the intermediate transfer belt. A plurality of toner images having different colors, and controlling the relative positional relationship of the plurality of toner images of different colors based on the resist control amount so that a color image can be formed by superimposing the plurality of toner images on the surface of the intermediate transfer belt. The first image formed on the surface of the intermediate transfer belt is transferred to the first surface of the sheet-like recording material at the secondary transfer position, and then thermally fixed by a fixing device and further intermediated on the second surface of the recording material. An image forming apparatus that performs a continuous printing operation for continuously performing a printing operation including a double-sided printing for transferring a second image formed on the surface of a transfer belt at a secondary transfer position, and achieves the above object. Therefore, when double-sided printing is executed during the continuous printing operation, the temperature acquisition means for obtaining the temperature of the secondary transfer roller, and the registration control amount based on the temperature of the secondary transfer roller obtained by the temperature acquisition means And a registration establishment means for obtaining a registration control amount by executing the establishment process.

  In the invention configured as above (image forming apparatus and method for controlling the apparatus), when double-sided printing is executed during continuous printing operation, the recording material heated by the fixing device is conveyed to the secondary transfer position. Therefore, the secondary transfer roller is locally heated by the recording material. Then, the heat of the secondary transfer roller thus heated is transmitted to the intermediate transfer belt and the driving roller, and the temperature of the intermediate transfer belt and the driving roller fluctuates. As a result, the peripheral length of the intermediate transfer belt and the diameter of the driving roller may fluctuate, and the registration control amount may deviate from the optimum value. However, in the present invention, when double-sided printing is performed during the continuous printing operation, the temperature of the secondary transfer roller is obtained, and the registration control amount establishment process is executed based on the temperature. Therefore, when there is a temperature fluctuation of the secondary transfer roller due to the double-sided printing, the registration control amount establishment process is executed based on the temperature fluctuation, so even if double-sided printing is included during the continuous printing operation, A printing operation can be performed based on the optimum registration control amount, and color misregistration can be prevented.

  As described above, when double-sided printing is performed during the continuous printing operation, the secondary transfer roller is heated by the heat-fixed recording material. Therefore, the temperature of the secondary transfer roller is determined from the number of times of double-sided printing performed during the continuous printing operation by utilizing the property of the secondary transfer roller that the temperature increases as the double-sided printing is performed. The temperature may be obtained. When configured in this way, it is not necessary to provide a separate temperature sensor, compared to the case where the temperature of a secondary transfer roller, which will be described later, is obtained by measuring with a temperature sensor, the apparatus configuration can be simplified and the cost can be reduced. Become.

  Further, the image forming apparatus is further configured to have a temperature sensor for measuring the temperature of the secondary transfer roller, and when the double-sided printing is performed during the continuous printing operation, the temperature of the secondary transfer roller is measured. May be obtained by measuring with a temperature sensor.

  Further, the resist establishment process may be configured to execute the establishment process when the temperature of the secondary transfer roller obtained in the temperature acquisition process becomes equal to or higher than a threshold temperature.

  Also, there are cases where a plurality of continuous printing operations are executed at intervals of time, but the temperature of the secondary transfer roller is determined based on the temperature of the secondary transfer roller in the previous continuous printing operation and the current continuous printing operation. It may be affected by the elapsed time until the continuous printing operation. That is, when the elapsed time is short, the current continuous printing operation may be executed while directly dragging the thermal effect of the double-sided printing executed during the previous continuous printing operation. Therefore, in order to accurately obtain the temperature of the secondary transfer roller even when duplex printing is performed during the previous continuous printing operation, the temperature of the secondary transfer roller obtained during the previous continuous printing operation and the previous continuous It is desirable to consider the elapsed time from the printing operation to the current continuous printing operation. Therefore, when duplex printing is performed during the previous continuous printing operation, the temperature of the secondary transfer roller obtained during the previous continuous printing operation and the time elapsed from the previous continuous printing operation to the current continuous printing operation Based on the above, the temperature of the secondary transfer roller obtained during the current continuous printing operation may be corrected. As a result, even when duplex printing is performed during the previous continuous printing operation, the temperature of the secondary transfer roller can be obtained with high accuracy. Therefore, occurrence of color misregistration can be prevented with high accuracy.

  Further, the registration establishment process may be configured to execute the establishment process when the correction value of the secondary transfer roller temperature becomes equal to or higher than the threshold temperature.

A. Regarding the speed fluctuation of the intermediate transfer belt due to double-sided printing In the electrophotographic image forming apparatus, a toner image is formed on the intermediate transfer belt and the recording material stored in a cassette or a manual feed tray is conveyed to the transfer position. Then, the toner image on the intermediate transfer belt 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. Since the toner image is transferred to the recording material that has been fixed and is in a high temperature state, there is a possibility that the temperature of the secondary transfer roller will rise locally. 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.

  FIG. 1 is a graph showing thermal effects in continuous single-sided printing and continuous double-sided printing, and when monochrome printing was continuously performed on A3-sized plain paper using a color laser printer (model number: LP-9000C) manufactured by Seiko Epson. Results are shown. More specifically, the plot in FIG. 9A plots the elapsed time of movement between two points of the intermediate transfer belt when monochrome double-sided printing is continuously performed on 250 sheets (500 sheets in terms of single-sided printing). The plot in FIG. 6B plots the elapsed time of movement between two points of the intermediate transfer belt when 500 sheets of monochrome single-sided printing are continuously performed. 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. Such color misregistration is considered to be caused by a change in the peripheral length of the intermediate transfer belt and a change in the diameter of the drive roller due to double-sided printing. That is, the heat of the secondary transfer roller heated by double-sided printing is transmitted to the intermediate transfer belt and the drive roller to the drive roller, so that the peripheral length of the intermediate transfer belt and the diameter of the drive roller vary. On the other hand, the intermediate transfer belt is wound around a driving roller, and the driving roller is rotated by receiving a driving force from a driving motor, so that the rotational force is applied to the intermediate transfer belt to drive the belt. For this reason, when the peripheral length of the intermediate transfer belt and the diameter of the drive roller change due to heating by double-sided printing, the moving speed of the intermediate transfer belt changes greatly. As a result, color misregistration due to double-sided printing occurs.

  Therefore, in the embodiment according to the present invention, when double-sided printing is executed during the continuous printing operation, the temperature of the secondary transfer roller is obtained, and the registration control amount establishment process is executed based on the result. ing. Hereinafter, specific embodiments will be described in detail.

B. Apparatus Configuration and Operation Hereinafter, two embodiments of an image forming apparatus according to the present invention will be described. Since the apparatus configuration and basic operation of these embodiments are the same and only the operation is partially different, first, 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 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 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 (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, a secondary transfer unit 11, a fixing unit (fixing device) 12, and a sheet conveying mechanism 13 are disposed on the first opening / closing member 3 side. 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, the belt surface 16a is a belt tension surface (surface pulled by the drive roller 14) when the belt is driven, and the peripheral speed is lower than the peripheral speed of the photosensitive drum (image carrier) 20 of each color. have. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Driving.

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

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

  The driving roller 14 and the driven roller 15 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, a primary transfer roller 21 is provided on the back surface of the belt surface 16a facing downward in the transport direction of the intermediate transfer belt 16 so as to face the photosensitive drum 20 of each image forming station Y, M, C, K described later. . These four primary transfer rollers 21 are rotatably supported with respect to the support frame, and are electrically connected to 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. For this reason, when the primary transfer rollers 21 for yellow, magenta, and cyan move close to the photosensitive drum 20, they contact the photosensitive drum 20 with the intermediate transfer belt 16 in between (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, when the primary transfer rollers 21 for yellow, magenta, and cyan move away from the photosensitive drum 20, the photosensitive drum 20 and the intermediate transfer belt 16 of the image forming stations Y, M, and C are separated from each other (FIG. Dashed line in 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 transmission / reception units 53Y, 53M, 53C, and 53K provided in each replacement cartridge and the transmission / reception units 522Y, 522M, 522C, and 522K provided on the main body side are arranged close to each other, and the CPU 521 and the memory of the engine controller 52 are arranged. Wireless communication is performed with 91-94. In this way, information regarding each replacement cartridge is transmitted to the CPU 521, and information in each of the memories 91 to 94 is updated and stored.

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

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

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

  The sheet feeding unit 10 includes a sheet feeding unit including a sheet feeding cassette 35 in which sheets S are stacked and held, and a pickup roller 36 that feeds the sheets S from the sheet feeding cassette 35 one by one. In the first opening / closing member 3, a registration roller pair 37 that defines the sheet feeding timing of the sheet S to the secondary transfer position 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 (fixing device) 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 at the secondary transfer position 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 the RAM 524. 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.

C. First Embodiment FIG. 4 is a flowchart showing an operation from the execution to the end of a continuous printing operation in the first embodiment of the image forming apparatus according to the present invention. FIG. 5 is a diagram showing the timing for executing the registration control amount establishment processing in the first embodiment. 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. Further, the CPU 521 of the engine controller 52 performs color misregistration correction during the continuous printing operation by controlling each part of the apparatus in accordance with a registration control amount adjustment program stored in the ROM 523 in advance.

  First, before starting the printing operation, the double-sided printing count N stored in the RAM 524 is reset to 0 (step S0). Then, a printing operation is executed based on the registration control amount stored in the RAM 524 (step S1).

  Next, it is determined whether the printing mode executed in step S1 is double-sided printing or single-sided printing (step S2). If it is not double-sided printing, the process returns to step S1, and in the case of double-sided printing, steps S3 and S4 are executed. Then, the temperature of the secondary transfer roller 19 is obtained from the number N of double-sided printing already performed. In other words, 1 is added to the count value of the number N of duplex printing (step S3), and the temperature T1 of the secondary transfer roller 19 is obtained from the addition result (step S4) (temperature acquisition step). That is, as described in detail in the section “A. Speed fluctuation of intermediate transfer belt caused by double-sided printing”, when double-sided printing is executed, sheet (recording material) S that is heat-fixed and heated is used. As a result, the image is secondarily transferred, and a local temperature rise of the secondary transfer roller 19 occurs. As described above, the temperature of the secondary transfer roller 19 and the number of times of duplex printing N are related. Therefore, the relationship between the temperature of the secondary transfer roller 19 and the number of times of duplex printing N is obtained in advance, and this relationship is obtained in step S3 by storing this relationship in a non-volatile memory such as the ROM 523 in a function format or a table format. The temperature of the secondary transfer roller 19 can be obtained from the number N of double-sided printings every time double-sided printing is performed. Therefore, in the first embodiment, the CPU 521 determines the temperature T1 of the secondary transfer roller 19 from the number of times of duplex printing N by referring to the above-described table stored in the ROM 523. Thus, in the first embodiment, the CPU 521 and the ROM 523 function as “temperature acquisition means”.

  Next, it is determined whether or not the temperature T1 of the secondary transfer roller obtained as described above is equal to or higher than the threshold temperature Tth (step S5). Then, as indicated by the solid line in FIG. 5, when the number of times of duplex printing is executed, the temperature of the secondary transfer roller 19 rises, and if the determination result in step S5 is YES, the registration control amount is established. Processing is executed (step S6). That is, based on the establishment processing program stored in the ROM 523, a registration mark is formed on the intermediate transfer belt 16, and the position information of the registration mark is detected by the test pattern sensor 18. Then, the CPU 521 obtains a registration control amount based on the position information. Thus, in the first embodiment, steps S5 and S6 function as a “registration establishment process”, and the CPU 521, RAM 523, and test pattern sensor 18 function as “registration establishment means”. If the determination result in step S5 is NO, step S6 is not executed and the process returns to step S1. In step S7, it is determined whether or not to continue printing. If YES is determined, the remaining printing operation is executed in step S8, and then the continuous printing operation is terminated. If NO is determined in step S7, printing is terminated as it is.

  As described above, according to the first embodiment, the temperature of the secondary transfer roller 19 is obtained from the number of times of duplex printing executed during the continuous printing operation. Then, a registration control amount establishment process is executed based on the temperature of the secondary transfer roller 19. Therefore, when the temperature of the secondary transfer roller 19 varies due to double-sided printing, the establishment process is executed based on the temperature variation. Therefore, even if double-sided printing is included during the continuous printing operation, the optimum resist A printing operation can be performed based on the control amount, and color misregistration can be prevented.

D. Second Embodiment FIGS. 6 and 7 are flowcharts showing operations from the execution to the end of a continuous printing operation in the second embodiment of the image forming apparatus according to the present invention. FIG. 8 is a diagram illustrating timing for executing registration control amount establishment processing in the second embodiment. In the image forming apparatus according to the present invention, a plurality of continuous printing operations may be executed at time intervals. In this case, the temperature of the secondary transfer roller 19 may be affected by the temperature of the secondary transfer roller 19 in the previous continuous printing operation and the elapsed time KT from the previous continuous printing operation to the current continuous printing operation. . For example, as shown in FIG. 8, when the elapsed time KT is short, the temperature of the secondary transfer roller 19 that has risen to the temperature Tz due to double-sided printing performed during the previous continuous printing operation is the current continuous printing operation. At the start time, the temperature does not fall to the temperature T0 at the start time of the previous continuous printing operation. Therefore, the current continuous printing operation is executed by directly dragging the thermal effect of double-sided printing in the previous continuous printing operation. Accordingly, in order to accurately obtain the temperature of the secondary transfer roller 19 even when duplex printing is performed during the previous continuous printing operation, the final temperature Tz of the secondary transfer roller 19 obtained during the previous continuous printing operation is obtained. It is desirable to consider the elapsed time KT from the previous continuous printing operation to the current continuous printing operation. Therefore, in the second embodiment, when double-sided printing is performed during the previous continuous printing operation, the current temperature is determined from the final temperature Tz of the secondary transfer roller 19 obtained during the previous continuous printing operation and the previous continuous printing operation. The temperature T1 of the secondary transfer roller 19 obtained in the current continuous printing operation is corrected from the time KT that has elapsed until the printing operation. Below, the characteristic part of 2nd Embodiment is explained in full detail.

  In the second embodiment, when double-sided printing is executed in the previous continuous printing operation, the temperature T1 of the secondary transfer roller 19 obtained from the number N of double-sided printing executed during the current continuous printing operation is stepped. Correction is made in S15. That is, in step S151, it is determined whether double-sided printing has been executed during the previous continuous printing operation. Specifically, the history information of the previous continuous printing operation stored in the RAM 524 is read, and the CPU 521 determines whether double-side printing has been performed. In the second embodiment, as the history information, the RAM 524 stores the final temperature Tz of the secondary transfer roller 19 obtained from the presence / absence of double-sided printing execution and the number of double-sided printing executions during the previous continuous printing operation.

  If YES is determined in step S151, the final temperature Tz of the secondary transfer roller 19 obtained during the previous continuous printing operation stored as history information in the RAM 524 is read (step S152), and the previous continuous printing operation is performed. Is read from the RAM 524 (step S153). Here, the elapsed time KT is the result of the CPU 521 measuring the time from the end of the previous continuous printing operation until the main controller 51 is given an image formation command to execute the current continuous printing operation. Stored in the RAM 524. Then, the secondary transfer roller temperature T1 obtained during the current continuous printing operation is corrected based on the final temperature Tz and the elapsed time KT of the secondary transfer roller 19 during the previous continuous printing operation read out in this way. Is the corrected temperature T2 of the secondary transfer roller 19 (step S154). That is, as described above, the temperature of the secondary transfer roller 19 during the current continuous printing operation is related to the final temperature Tz and the elapsed time KT of the secondary transfer roller 19 during the previous continuous printing operation. Accordingly, these relationships are obtained in advance, and this relationship is stored in the ROM 523 in a function format or a table format. Then, the correction value T2 is obtained by correcting the temperature T1 of the secondary transfer roller 19 during the current continuous printing operation obtained in step S14 based on such a function or table. As a result, even when a plurality of continuous printing operations are executed at time intervals, the temperature of the secondary transfer roller 19 can be accurately obtained. If NO is determined in step S151, the temperature T1 of the secondary transfer roller obtained in step S14 (temperature acquisition process) is directly used as the correction value T2 (step S155). That is, when the double-sided printing is not executed during the previous continuous printing operation, the correction of the temperature T1 of the secondary transfer roller obtained in step S14 is not performed. Next, it is determined whether or not the correction value T2 of the temperature of the secondary transfer roller thus obtained is equal to or higher than the threshold temperature Tth (step S16). Then, as shown by the solid line in FIG. 8, the temperature of the secondary transfer roller 19 is increased by executing the double-sided printing in the current continuous printing operation, and the determination result in step S16 is YES. In the same manner as in the first embodiment, a registration control amount establishment process is executed (step S17). Thus, in the second embodiment, steps S16 and S17 function as a “resist establishment process”. Thereafter, the same flow as steps S7 and S8 of the first embodiment (steps S18 and S19) is executed, and the printing operation is terminated.

  As described above, in the second embodiment, when a plurality of continuous printing operations are performed with a time interval, when duplex printing is performed during the previous continuous printing operation, the secondary obtained during the previous continuous printing operation is obtained. The temperature T1 of the secondary transfer roller 19 obtained in the current continuous printing operation is corrected from the final temperature Tz of the transfer roller and the time KT that has elapsed from the previous continuous printing operation to the current continuous printing operation. Therefore, even when duplex printing is performed during the previous continuous printing operation, the temperature of the secondary transfer roller can be obtained with high accuracy. Therefore, occurrence of color misregistration can be prevented with high accuracy.

<Others>
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 first and second embodiments described above, the temperature of the secondary transfer roller 19 is obtained from the number of times of duplex printing, but a secondary transfer roller temperature sensor 60 is separately provided as shown in FIG. The temperature of the secondary transfer roller 19 may be obtained by a temperature sensor. However, when the temperature of the secondary transfer roller 19 is obtained from the number of times of duplex printing, it is not necessary to provide the temperature sensor 60 separately as compared with the case where the temperature sensor 60 is used for measurement. This is more preferable.

  In the first and second embodiments, only one threshold temperature is provided. However, the threshold temperature is not limited to one, and a plurality of threshold temperatures may be provided. That is, when duplex printing is performed many times, even if the registration control amount establishment process is executed in response to the temperature of the secondary transfer roller 19 being equal to or higher than the threshold temperature Tth, duplex printing is further performed. As a result, the temperature of the secondary transfer roller 19 rises even after the establishment process is executed, and the registration control amount may deviate from the optimum value. On the other hand, for example, as shown in FIG. 10, it may be configured to have Tth1 and Tth2 as threshold temperatures. In such a configuration, even if the temperature of the secondary transfer roller 19 rises again after the temperature of the secondary transfer roller 19 becomes equal to or higher than the threshold temperature Tth1 and the establishment process is executed, the secondary transfer roller 19 rises again. When the temperature of the roller 19 becomes equal to or higher than the threshold temperature Tth2, the registration control amount establishment process is executed again. Therefore, even when double-sided printing is performed many times, it is possible to set the resist control amount to an optimum value and prevent occurrence of color misregistration with high accuracy.

  In the above embodiment, the temperature of the secondary transfer roller 19 is obtained every time double-sided printing is performed, but the timing for obtaining the temperature of the secondary transfer roller 19 is not limited to this. For example, the temperature of the secondary transfer roller 19 may be obtained also when performing single-sided printing. Further, the temperature of the secondary transfer roller 19 may be always obtained.

  In the above-described embodiment, the present invention is applied to a so-called tandem color printer. However, the scope of the present invention is not limited to this, and can be applied to, for example, a so-called four-cycle printer. is there.

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. It is a figure which shows the execution timing of the establishment process 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 second embodiment of the image forming apparatus according to the present invention. It is a figure which shows the execution timing of the establishment process in 2nd Embodiment. FIG. 6 is a diagram showing an electrical configuration of another embodiment of the image forming apparatus according to the present invention. FIG. 6 is a diagram showing still another embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 9 ... Transfer belt unit, 12 ... Fixing unit (fixing device), 14 ... Drive roller, 16 ... Intermediate transfer belt, 19 ... Secondary transfer roller, 52 ... Engine controller, 60 ... Secondary transfer roller 521 ... CPU, 523 ... ROM, 524 ... RAM, D16 ... (intermediate transfer belt) moving direction, S ... sheet (recording material), Y, M, C, K ... image forming station, N ... both sides Number of printing times, T1 ... secondary transfer roller temperature, T2 ... secondary transfer roller temperature correction value, Tth, Tth1, Tth2 ... threshold temperature, KT ... elapsed time

Claims (7)

A drive roller, an intermediate transfer belt that moves by receiving the rotational force of the drive roller, and a secondary transfer roller that contacts the drive roller at the secondary transfer position via the intermediate transfer belt; Formed on the surface of the intermediate transfer belt in an image forming apparatus that forms a color image by superimposing the plurality of toner images on the surface of the intermediate transfer belt while controlling the relative positional relationship of the toner images based on the resist control amount. The transferred first image was transferred to the first surface of the sheet-like recording material at the secondary transfer position, and then thermally fixed by a fixing device, and further formed on the surface of the intermediate transfer belt on the second surface of the recording material. A control method for causing the image forming apparatus to perform a continuous printing operation for continuously performing a printing operation including double-sided printing for transferring a second image at the secondary transfer position,
A temperature acquisition step of obtaining a temperature of the secondary transfer roller when the double-sided printing is executed during the continuous printing operation;
An image forming apparatus comprising: a registration establishing step for obtaining a registration control amount by executing a registration control amount establishment process based on the temperature of the secondary transfer roller obtained in the temperature acquisition step Control method.   The method of controlling an image forming apparatus according to claim 1, wherein the temperature acquisition step is a step of obtaining the temperature of the secondary transfer roller from the number of times of the double-sided printing performed during the continuous printing operation. The image forming apparatus further includes a temperature sensor that measures the temperature of the secondary transfer roller,
The image formation according to claim 1, wherein the temperature acquisition step is a step of obtaining the temperature of the secondary transfer roller by measuring the temperature of the secondary transfer roller when the double-sided printing is executed during the continuous printing operation. Control method of the device. The method for controlling an image forming apparatus according to claim 2, wherein a plurality of continuous printing operations are performed at time intervals.
When the double-sided printing is performed during the previous continuous printing operation, the temperature of the secondary transfer roller obtained during the previous continuous printing operation, the time elapsed from the previous continuous printing operation to the current continuous printing operation, And a method of controlling the image forming apparatus for correcting the temperature of the secondary transfer roller obtained during the current continuous printing operation.   4. The process according to claim 1, wherein the resist establishment process is a process of executing the establishment process when the temperature of the secondary transfer roller obtained in the temperature acquisition process is equal to or higher than a threshold temperature. 5. A method for controlling an image forming apparatus.   The image forming apparatus control method according to claim 4, wherein the registration establishment step is a step of executing the establishment processing when a correction value of the secondary transfer roller temperature becomes equal to or higher than a threshold temperature. A drive roller, an intermediate transfer belt that moves by receiving the rotational force of the drive roller, and a secondary transfer roller that contacts the drive roller at the secondary transfer position via the intermediate transfer belt; A color image can be formed by superimposing the plurality of toner images on the surface of the intermediate transfer belt while controlling the relative positional relationship of the toner images based on the resist control amount, and formed on the surface of the intermediate transfer belt. The transferred first image was transferred to the first surface of the sheet-like recording material at the secondary transfer position, and then thermally fixed by a fixing device, and further formed on the surface of the intermediate transfer belt on the second surface of the recording material. In an image forming apparatus that performs a continuous printing operation for continuously performing a printing operation including double-sided printing for transferring a second image at the secondary transfer position,
Temperature acquisition means for determining the temperature of the secondary transfer roller when the double-sided printing is executed during the continuous printing operation;
An image forming apparatus comprising: a registration establishment unit that executes a registration control amount establishment process based on the temperature of the secondary transfer roller obtained by the temperature acquisition unit to obtain the registration control amount .

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