JP2013003485A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress degradation of a color shift due to switching of a drive control system of an intermediate transfer belt 8 from a belt constant speed control to a motor constant speed control.SOLUTION: A control device 200 is constituted such that when an optical writing position correction processing for correcting an optical writing start timing for photoreceptors 1Y, C, M, and K is performed, a belt constant speed control for adjusting a drive speed of a common drive motor 162 is carried out to allow the intermediate transfer belt 8 to travel at a constant speed based on a detection result by a roller encoder 171, and when a thick paper is used, the motor constant speed control is performed to rotate the common drive motor 162 at a constant speed based on a FG signal in a state in which the optical writing start timing after the correction by the optical writing position correction processing is temporarily corrected based on an algorism or a data table stored in a flush memory.

Description

  The present invention relates to a multicolor image obtained by superimposing and transferring toner images of different colors formed on the surfaces of a plurality of latent image carriers on the surface of an endless belt member or a recording member held on the same surface. The present invention relates to an image forming apparatus that obtains image quality.

  In this type of image forming apparatus, color misregistration may be caused by transferring the toner images of the respective colors out of position in the belt moving direction. One cause of color misregistration is a relative misregistration of the latent image writing position with respect to the latent image carrier of each color. Specifically, when the latent image writing system components such as the reflection mirror and the scanning lens expand and contract with temperature change, the latent image writing position may be relatively shifted between the latent image carriers of the respective colors. When such a shift in the latent image writing position occurs, a relative position shift of the latent image occurs between the latent image carriers of the respective colors, thereby causing a color shift.

  Therefore, in the image forming apparatuses described in Patent Document 1 and Patent Document 2, a writing position correction process for correcting the latent image writing position for each color photoconductor serving as a latent image carrier is periodically performed, so that each color The relative shift of the latent image writing position between the photosensitive members is reduced. In the writing position correction process, first, a predetermined toner image formed on each color photoconductor is transferred to the surface of the belt member to form a color misregistration detection image on the belt surface. Then, based on the timing at which each color toner image in the color misregistration detection image is detected by the reflective photosensor, the amount of misregistration in the belt moving direction in each color toner image is calculated. Next, based on the calculation result, the tilt angle of the reflection mirror of the optical scanning system for writing the latent image is finely adjusted, or the irradiation timing of the scanning light to the photosensitive member is finely adjusted. Thereby, the relative shift of the latent image writing position between the photoconductors of the respective colors can be reduced, and the color shift can be reduced.

  Further, in the image forming apparatus described in Patent Document 2, belt constant speed control for driving the drive motor so as to move the belt member endlessly at a constant speed based on the result of detecting the moving speed of the belt member is performed. Thus, the speed of the belt member is stabilized. Specifically, a rotary encoder is provided on a driven roller that rotates following the endless movement of the belt member among a plurality of stretching rollers that stretch the belt member. The moving speed is detected. Then, when there is a speed fluctuation of the belt member, the detection result of the rotary encoder is fed back to the drive motor so as to generate a speed fluctuation having a phase opposite to the fluctuation. As a result, by suppressing the speed fluctuation of the belt member due to the eccentricity of the drive roller and stabilizing the speed, it is possible to reduce color misregistration due to the belt speed fluctuation.

  However, the present inventors conducted an experiment to further increase the printing speed in a test machine having the same configuration as that of the image forming apparatus described in Patent Document 2, and caused streak-like image disturbance when using thick paper. I found it easier. Specifically, the testing machine transfers a color toner image obtained by primary transfer superimposed on the surface of the belt member from the belt member at the secondary transfer nip formed by contact between the belt member and the secondary transfer roller. It is configured to perform secondary transfer on a recording sheet at once. In such a configuration, when a thick paper is used as the recording paper, when the paper is entered into the secondary transfer nip, the moving speed of the belt member is greatly reduced momentarily due to a sudden load increase. Under the condition that the printing speed is higher than the conventional one, the decrease rate becomes larger than the conventional one. Then, if the speed reduction is fed back to the drive control of the drive motor, the speed of the belt member is excessively increased for a moment. When such an instantaneous speed decrease when entering the thick paper nip and an instantaneous speed increase thereafter occur, the toner image is not normally transferred in the primary transfer from the photoconductor to the belt member, as described above. This caused a streak-like image disturbance. This streak-like image disturbance is far more conspicuous than the color misregistration caused by the eccentricity of the drive roller, and therefore, measures should be taken with priority over the color misregistration.

  Therefore, the present inventors improved the testing machine so that the motor constant speed control based on the FG signal is performed instead of the belt constant speed control described above when using cardboard (hereinafter, this testing machine is referred to as an improved testing machine). ). The FG signal is a signal generated from an FG signal generator (Frequency Generator) that generates a pulse wave every time a predetermined rotational angular displacement is detected for the motor shaft. In the motor constant speed control, the drive motor is driven so as to keep the frequency of the FG signal constant, so that the drive motor is constantly rotated at a predetermined target rotational speed. When the cardboard enters the nip, the speed of the belt member is greatly reduced for a moment, but at this time, the belt is stretched and so on, so that the rotational speed of the drive motor does not decrease so much. For this reason, when the thick paper enters the nip, a rapid decrease in the motor rotational speed is not detected, and the drive motor can be stably rotated at the target rotational speed from the nip entering the thick paper to the nip discharge.

  However, when a trial run was performed with such an improved testing machine, a noticeable color shift occurred. And it turned out that this remarkable color shift is caused by the following causes. That is, in the motor constant speed control, as described above, the drive motor is rotated at a predetermined target rotation speed. If the diameter of the driving roller is a value as designed, the average linear velocity of the belt member at that time is approximately the same value as the predetermined target belt velocity. However, if the diameter of the drive roller deviates from the design value due to expansion and contraction due to processing errors and temperature changes, the average linear velocity of the belt member deviates from the target belt velocity. As a result, the time for moving the toner image transferred onto the belt together with the belt member from the upstream transfer nip to the downstream transfer nip deviates from the design value, thereby causing color misregistration.

  Note that the same problem may occur when a configuration in which the belt constant speed control and the motor constant speed control are switched for some reason is not limited to the configuration in which the motor constant speed control is performed when using cardboard.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, it is an object of the present invention to provide an image forming apparatus capable of suppressing the deterioration of color misregistration caused by switching the belt member drive control method from belt constant speed control to motor constant speed control.

  The inventors correlate the amount of increase in the registration deviation of each color toner image resulting from switching from belt constant speed control to motor constant speed control and the deviation from the design value of the diameter of the drive rotor. The present invention has been completed focusing on the fact that the relationship is established. Specifically, the increase in overlay deviation occurs when the linear speed of the belt member deviates from the target belt speed, and the amount of deviation and the amount of deviation of the linear speed of the belt member from the target belt speed include The correlation is established. A correlation also holds between the amount of deviation of the linear speed of the belt member from the target belt speed and the amount of deviation from the design value of the diameter of the drive rotor. Therefore, a correlation is established between the increase amount of the overlay deviation and the deviation amount from the design value of the diameter of the drive rotor.

  The reason why the diameter of the drive rotator deviates from the design value is that the drive rotator causes a dimensional error due to the limit of processing accuracy, or the drive rotator expands and contracts as the temperature changes. If there is a deviation in the diameter of the drive rotor due to a dimensional error, it is possible to know in advance at the time of shipment from the factory the amount of increase in overlay deviation that occurs when the motor constant speed control is performed due to the deviation in diameter. It is. Further, it is possible to grasp in advance the correction amount of the latent image writing position that can reduce the increase amount. Therefore, if the overlay deviation increases when the motor constant speed control is performed due to the drive rotating body causing a dimensional error from the limit of machining accuracy, the correction amount that has been grasped in advance is used. It is possible to suppress the increase by temporarily correcting the latent image writing position.

  In addition, when the diameter of the drive rotator deviates from the design value due to the expansion and contraction of the drive rotator due to the temperature change, there is a correlation between the deviation amount and the temperature change amount from the predetermined reference temperature. A relationship is established. An algorithm indicating the relationship between the amount of deviation of the diameter and the correction amount of the latent image writing position that can reduce the amount of increase in overlay deviation corresponding to the amount of deviation can be grasped in advance. is there. Therefore, even when the superposition deviation increases when the motor constant speed control is performed due to the deviation of the diameter of the driving rotating body from the design value due to the temperature change, it was grasped in advance. By temporarily correcting the latent image writing position based on the algorithm and the temperature change amount, it is possible to suppress the increase.

  In order to achieve the above object, the present invention provides an image forming means for developing latent images written on a plurality of latent image carriers with toners of different colors, and an endless belt member that is moved endlessly. A transfer means for obtaining a multicolor image by superimposing and transferring the toner images on the plurality of latent image carriers to the surface of the recording medium or a recording sheet held on the surface; A driving rotating body that moves the belt member endlessly while being rotated while being hung around a part of the surface, a driving motor that is a driving source of the driving rotating body, the image forming unit, the transfer unit, and the driving Control means for controlling the driving of the motor, and the control means endlessly moves the belt member at the target belt speed based on the result of detecting the moving speed of the belt member by the belt speed detecting means. The belt constant speed control is performed to control the driving speed of the drive motor so as to move, and the toner image of each color included in the color misregistration detection image formed on the surface of the belt member is detected by the toner image detecting means. In the image forming apparatus, in which the writing position correction processing for individually correcting the latent image writing position for each of the plurality of latent image carriers based on the timing is performed each time a predetermined timing arrives, the drive motor A rotation speed detecting means for detecting the rotation speed of the belt, and when a predetermined condition is satisfied, instead of the belt constant speed control, the drive motor is controlled based on a detection result by the rotation speed detection means. When performing the process of driving the belt member by motor constant speed control for rotating at a target rotation speed and the writing position correction process Regardless of whether or not the predetermined condition is satisfied, the process of driving the belt member with the belt constant speed control and the motor constant speed control are stored in the data storage means. The control means is configured to perform a process of temporarily correcting the latent image writing position after the correction by the writing position correction process based on predetermined data. is there.

  In the present invention, when the motor constant speed control is performed, the drive rotating body is temporarily corrected by temporarily correcting the latent image writing position with respect to the latent image carrier based on the data stored in the data storage means in advance. As a result, the belt member is moved at a linear speed deviating from the target belt speed due to the deviation of the diameter of the toner from the design value, thereby reducing an increase in deviation of toner image superposition. Therefore, it is possible to suppress the deterioration of color misregistration caused by switching the belt member drive control method from belt constant speed control to motor constant speed control.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating an enlarged process unit for Y in the printer. FIG. 3 is a perspective view showing the process unit and a Y photoconductor gear fixed to the printer main body. The perspective view which shows the process drive unit of the printer. FIG. 3 is a perspective view showing a transfer unit of the printer and a common drive motor that drives an intermediate transfer belt and the like. The expansion perspective view which expands and shows the common drive motor and its surrounding structure. FIG. 3 is a schematic diagram showing the transfer unit, each color photoconductor, and each gear supported in the printer main body. FIG. 2 is a schematic diagram illustrating a drive control unit of the printer and various devices electrically connected thereto. FIG. 4 is a schematic diagram for explaining a linear velocity V of the intermediate transfer belt. 6 is a graph showing a speed fluctuation curve synchronized with a driving roller rotation period appearing on a K photoconductor. FIG. 4 is a schematic diagram for explaining a distance from an optical writing position to a transfer nip center position on the surface of a K photoconductor. FIG. 3 is a schematic diagram for explaining a distance between photoconductors. FIG. 3 is an enlarged perspective view showing a part of an intermediate transfer belt of the printer together with an optical sensor unit. FIG. 3 is an enlarged schematic view showing a chevron patch formed on the intermediate transfer belt. The enlarged schematic diagram for demonstrating the overlapping position of each color dot. The enlarged schematic diagram which shows the position of each color dot of the state which has shifted | deviated by 1/4 dot. The enlarged schematic diagram which shows an example of the residual shift which still remains even if it implements a writing position correction process. The enlarged schematic diagram which shows an example of the virtual superposition deviation which generate | occur | produces at the time of implementation of motor constant speed control. 6 is a flowchart illustrating a processing flow in a temporary correction process performed by the control device of the printer. FIG. 4 is an enlarged schematic diagram showing an example in which all the positions of three colors Y, C, and M are shifted to the upstream side in the belt movement direction by a method in which all three positions are uniformly shifted. FIG. 4 is an enlarged schematic diagram illustrating an example in which all three positions of Y, C, and M are shifted uniformly and all the positions are shifted by one dot downstream in the belt movement direction. FIG. 19 is an enlarged schematic diagram illustrating overlay deviation that occurs when motor constant speed control and temporary correction processing are performed from the state of FIG. 18 in the printer.

Hereinafter, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer according to the embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. In this figure, this printer includes four process units 6Y, 6C, 6M, and 6K for forming yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) toner images. Yes. These use Y, C, M, and K toners of different colors as image forming materials, but the other configurations are the same and are replaced when the lifetime is reached. Taking a process unit 6Y for generating a Y toner image as an example, as shown in FIG. 2, a drum-shaped photosensitive member 1Y as a latent image carrier, a drum cleaning device 2Y, a charge eliminating device (not shown), and a charging device 4Y. And a developing unit 5Y. The process unit 6Y can be attached to and detached from the printer body, so that consumable parts can be replaced at a time.

  The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1 </ b> Y is exposed and scanned by the laser beam L to carry a Y electrostatic latent image. The electrostatic latent image of Y is developed into a Y toner image by a developing device 5Y using a Y developer containing Y toner and a magnetic carrier. Then, intermediate transfer is performed on an intermediate transfer belt 8 as a belt member described later. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. The static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. Similarly, in the other color process units (6C, M, K), (C, M, K) toner images are formed on the photoreceptors (1C, M, K), and the intermediate transfer belt 8 is subjected to an intermediate process. Transcribed.

  The developing device 5Y has a developing roll 51Y disposed so as to be partially exposed from the opening of the casing. Further, it also includes two conveying screws 55Y, a doctor blade 52Y, a toner density sensor (hereinafter referred to as T sensor) 56Y, and the like that are arranged in parallel to each other.

  In the casing of the developing device 5Y, a Y developer (not shown) including a magnetic carrier and Y toner is accommodated. The Y developer is frictionally charged while being agitated and conveyed by the two conveying screws 55Y, and is then carried on the surface of the developing roll 51Y. Then, after the layer thickness is regulated by the doctor blade 52Y, the layer is transported to the developing region facing the Y photoreceptor 1Y, where Y toner is attached to the electrostatic latent image on the photoreceptor 1Y. This adhesion forms a Y toner image on the photoreceptor 1Y. In the developing unit 5Y, the Y developer that has consumed Y toner by the development is returned into the casing as the developing roll 51Y rotates.

  A partition wall is provided between the two transport screws 55Y. By this partition wall, the first supply unit 53Y that accommodates the developing roll 51Y, the right conveyance screw 55Y in the drawing, and the like, and the second supply unit 54Y that accommodates the left conveyance screw 55Y in the drawing are separated in the casing. . The right conveying screw 55Y in the drawing is driven to rotate by a driving means (not shown), and supplies the Y developer in the first supply unit 53Y to the developing roll 51Y while being conveyed from the near side to the far side in the drawing. The Y developer conveyed to the vicinity of the end of the first supply unit 53Y by the right conveyance screw 55Y in the drawing enters the second supply unit 54Y through an opening (not shown) provided in the partition wall. In the second supply unit 54Y, the left conveyance screw 55Y in the drawing is driven to rotate by a driving means (not shown), and the Y developer sent from the first supply unit 53Y is the right conveyance screw 55Y in the drawing. Transport in the reverse direction. The Y developer transported to the vicinity of the end of the second supply unit 54Y by the transport screw 55Y on the left side in the drawing passes through the other opening (not shown) provided in the partition wall, and the first supply unit. Return to 53Y.

  The above-described T sensor 56Y composed of a magnetic permeability sensor is provided on the bottom wall of the second supply unit 54Y and outputs a voltage having a value corresponding to the magnetic permeability of the Y developer passing therethrough. Since the magnetic permeability of the two-component developer containing toner and magnetic carrier shows a good correlation with the toner concentration, the T sensor 56Y outputs a voltage corresponding to the Y toner concentration. This output voltage value is sent to a control unit (not shown). This control unit includes a RAM that stores a Vtref for Y that is a target value of an output voltage from the T sensor 56Y. The RAM also stores data for C Vtref, M Vtref, and K Vtref, which are target values of output voltages from a T sensor (not shown) mounted in another developing device. The Y Vtref is used for driving control of a Y toner conveying device to be described later. Specifically, the control unit drives and controls a Y toner conveying device (not shown) so that the value of the output voltage from the T sensor 56Y is close to the Y Vtref, and the Y toner in the second supply unit 54Y. To replenish. By this replenishment, the Y toner concentration in the Y developer in the developing device 5Y is maintained within a predetermined range. The same toner replenishment control using the C, M, and K toner conveying devices is performed for the developing units of other process units.

  In FIG. 1 shown above, an optical writing unit 7 as a latent image writing device is disposed below the process units 6Y, 6C, 6M, and 6K in the drawing. The optical writing unit 7 irradiates the respective photosensitive members in the process units 6Y, 6C, 6M, and 6K with the laser light L emitted based on the image information and exposes it. By this exposure, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 1Y, 1C, 1M, and 1K. The optical writing unit 7 irradiates the photosensitive member through a plurality of optical lenses and mirrors while scanning a laser beam (L) emitted from a light source with a polygon mirror rotated by a motor.

  On the lower side of the optical writing unit 7 in the figure, a paper storage means having a paper storage cassette 26, a paper feed roller 27 incorporated therein, and the like is disposed. The paper storage cassette 26 stores a plurality of transfer papers P, which are sheet-like recording bodies, and a paper feed roller 27 is brought into contact with each uppermost transfer paper P. When the paper feeding roller 27 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is sent out toward the paper feeding path 70.

  A registration roller pair 28 is disposed near the end of the paper feed path 70. The registration roller pair 28 rotates both rollers so as to sandwich the transfer paper P, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above the process units 6Y, 6C, 6M, and 6K, a transfer unit 15 that moves the intermediate transfer belt 8 endlessly while being stretched is disposed. The transfer unit 15 as a transfer means includes a secondary transfer bias roller 19 and a belt cleaning device 10 in addition to the intermediate transfer belt 8 as a belt member. Also provided are four primary transfer bias rollers 9Y, 9C, 9M, 9K, a driving roller 12, a cleaning backup roller 13, a driven roller 14, a tension roller 11, and the like. The intermediate transfer belt 8 is endlessly moved counterclockwise in the figure by the rotational drive of the driving roller 12 while being stretched around these rollers. The primary transfer bias rollers 9Y, 9C, 9M, and 9K hold the intermediate transfer belt 8 that is moved endlessly in this manner between the photoreceptors 1Y, 1C, 1M, and 1K to form primary transfer nips. Yes. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8. All the rollers except the primary transfer bias rollers 9Y, C, M, and K are electrically grounded. The intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof, and the Y, C, and M on the photoreceptors 1Y, 1C, 1M, and 1K are transferred. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8.

  A drive roller 12 as a drive rotator sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The visible four-color toner image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. Then, combined with the white color of the transfer paper P, a full color toner image is obtained. Untransferred toner that has not been transferred onto the transfer paper P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the belt belt cleaning device 10. The transfer paper P on which the four-color toner images are collectively transferred at the secondary transfer nip is sent to the fixing device 20 via the post-transfer conveyance path 71.

  The fixing device 20 forms a fixing nip by a fixing roller 20a having a heat source such as a halogen lamp inside, and a pressure roller 20b that rotates while contacting the roller with a predetermined pressure. The transfer paper P fed into the fixing device 20 is sandwiched between the fixing nips so that the unfixed toner image carrying surface is in close contact with the fixing roller 20a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The transfer sheet P on which the full-color image is fixed in the fixing device 20 exits the fixing device 20 and then reaches a branch point between the paper discharge path 72 and the pre-reversal conveyance path 73. At this branch point, a first switching claw 75 is swingably disposed, and the path of the transfer paper P is switched by the swing. Specifically, by moving the tip of the claw in the direction approaching the pre-reverse feed path 73, the path of the transfer paper P is changed to the direction toward the paper discharge path 72. Further, by moving the tip of the claw in a direction away from the pre-reversal conveyance path 73, the path of the transfer paper P is changed to the direction toward the pre-reversal conveyance path 73.

  When the path to the paper discharge path 72 is selected by the first switching claw 75, the transfer paper P is disposed outside the apparatus after passing through the paper discharge roller pair 100 from the paper discharge path 72. Are stacked on a stack 50a provided on the upper surface of the printer housing. On the other hand, when the path toward the conveyance path 73 before reversal is selected by the first switching claw 75, the transfer paper P enters the nip of the reversing roller pair 21 via the conveyance path 73 before reversal. The reversing roller pair 21 conveys the transfer paper P sandwiched between the rollers toward the stack portion 50a, but reversely rotates the rollers immediately before the rear end of the transfer paper P enters the nip. Due to this reverse rotation, the transfer paper P is transported in the opposite direction, and the rear end side of the transfer paper P enters the reverse transport path 74.

  The reverse conveyance path 74 has a shape extending while curving from the upper side to the lower side in the vertical direction, and the first reverse conveyance roller pair 22, the second reverse conveyance roller pair 23, and the third reverse conveyance in the path. A roller pair 24 is provided. The transfer paper P is transported while sequentially passing through the nips of these roller pairs, so that the upper and lower sides thereof are reversed. After the transfer paper P is turned upside down, it is returned to the paper feed path 70 and then reaches the secondary transfer nip again. Then, this time, the image transfer surface enters the secondary transfer nip while bringing the non-image carrying surface into close contact with the intermediate transfer belt 8, and the second four-color toner image of the intermediate transfer belt is collectively transferred to the non-image carrying surface. The Thereafter, the sheet is stacked on the stack unit 50a outside the apparatus via the post-transfer conveyance path 71, the fixing device 20, the paper discharge path 72, and the paper discharge roller pair 100. A full color image is formed on both sides of the transfer paper P by such reverse conveyance.

  A bottle support portion 31 is disposed between the transfer unit 15 and the stack portion 50a located above the transfer unit 15. The bottle support portion 31 is equipped with toner bottles 32Y, 32C, 32M, and 32K serving as toner storage portions for storing Y, C, M, and K toners. The toner bottles 32Y, 32C, 32M, and 32K are arranged so as to be arranged at an angle slightly inclined from the horizontal, and the arrangement positions are higher in the order of Y, C, M, and K. The Y, C, M, and K toners in the toner bottles 32Y, 32C, 32M, and 32K are appropriately replenished to the developing units of the process units 6Y, 6C, 6M, and 6K, respectively, by a toner conveyance device described later. These toner bottles 32Y, 32C, 32M, and 32K are detachable from the printer main body independently of the process units 6Y, 6C, 6M, and 6K.

  The printer includes four process units 6Y, 6C, 6M, and 6K, and a control device (not shown) as a control unit that controls driving of various devices. The control device includes a main control unit, an optical writing control unit, a drive control unit, and the like. The main control unit includes a CPU (Central Processing Unit) as a calculation means, a RAM (Random Access Memory) as a data storage means, a ROM (Read Only Memory) as a data storage means, etc., and a program stored in the ROM Based on the above, various device control and arithmetic processing are performed. The optical writing control unit controls the optical writing on each color photoconductor by controlling the driving of the optical writing unit 7 based on the image information sent from the external device. The drive control unit includes a CPU, a ROM, a nonvolatile RAM as data storage means, and the like, and drives a shared drive motor and a color photoconductor motor, which will be described later, based on a program stored in the ROM. It is something to control.

  FIG. 3 is a perspective view showing a Y process unit 6Y that can be attached to and detached from the printer main body, and a Y photoconductor gear 151Y fixed to the printer main body. In the figure, the photoconductor gear 151Y is rotatably supported in the printer body. On the other hand, the process unit 6Y is detachable from the printer body. The photosensitive member 1Y of the process unit 6Y includes a cylindrical drum portion and shaft members that protrude from both end surfaces in the rotation axis direction of the process unit 6Y. The shaft members protrude from the unit housing. ing. Of the two shaft members, a well-known coupling is fixed to a shaft member (not shown) existing on the back side in the drawing. A coupling portion 152Y is formed at the rotation center of the photoconductor gear 151Y on the printer main body side. The coupling portion 152Y is coupled in the axial direction to the coupling fixed to the shaft member of the photoreceptor 1Y. By this connection, the rotational driving force of the photoconductor gear 151Y is transmitted to the photoconductor 1Y via the coupling connecting portion. When the process unit 6Y is pulled out from the printer body, the coupling between the coupling (not shown) fixed to the shaft member of the photoreceptor 1Y and the coupling portion 152Y formed on the photoreceptor gear 151Y is released. Regarding the Y process unit 6Y, the mechanism for connecting and releasing the photosensitive member 1Y and the photosensitive member gear 151Y when being attached to and detached from the printer main body has been described. However, the process units for other colors have the same configuration.

  FIG. 4 is a perspective view showing a process driving unit of the printer. This process drive unit has four photoconductor gears 151Y, 151C, 151M, and 151K corresponding to the photoconductors of each color, a process drive motor (not shown), and the like, and is fixed to the printer body. The coupling portions 152Y, C, M, and K of the photoconductor gears 151Y, C, M, and K are projected from a holding plate that holds the photoconductor gear and the like. When the process units for Y, C, M, and K are mounted on the printer main body, the coupling fixed to the shaft member of the Y, C, M, and K photoconductors and the photoconductor gears 151Y and C , M, K couplings 152Y, C, M, K are connected.

  FIG. 5 is a perspective view showing the transfer unit 15 and a common drive motor 162 that drives the intermediate transfer belt and the like. FIG. 6 is an enlarged perspective view showing the common shared drive motor 162 and the surrounding configuration in an enlarged manner. In these drawings, a coupling 160 is fixed to an end portion in the axial direction of the shaft portion 12a of the drive roller 12 that moves the intermediate transfer belt 8 endlessly by its own rotational drive while the intermediate transfer belt 8 is wound around. Has been. On the other hand, a belt drive relay gear 161 is rotatably supported in the printer body, and a coupling portion 161 a is formed at the center of the belt drive relay gear 161. The transfer unit 15 is configured to be detachable from the printer body. 5 and 6 show a state in which the transfer unit 15 is mounted in the printer main body. In this state, the coupling 160 fixed to the driving roller 12 of the transfer unit 15 and the coupling portion 161a of the belt driving relay gear 161 supported in the printer main body are connected in the axial direction. When the transfer unit 15 is removed from the printer body, the coupling 160 fixed to the drive roller 12 of the transfer unit 15 and the coupling portion 161a of the belt drive relay gear 161 supported in the printer body are released. Is done.

  In the printer main body, a shared common drive motor 162 is fixed in the vicinity of the belt relay gear 161, and the motor gear meshes with the belt relay gear 161. When the common drive motor 162 is driven to rotate, the driving force is transmitted to the intermediate transfer belt 8 via the belt relay gear 161, the coupling connecting portion, and the drive roller 12.

  FIG. 7 is a schematic diagram showing the transfer unit 15, the photoreceptors 1Y, 1C, 1M, and 1K for each color, and each gear supported in the printer body. In the figure, in the printer main body, in addition to the photoconductor gears 151Y, C, M, K of each color and the belt drive relay gear 161, the first relay gear 152 for K, the second relay gear 153 for K, and the Y gear. A relay gear 155 and the like are rotatably supported. Further, a color photoconductor motor 154 as an image carrier driving source is fixed.

  In addition to the motor gear of the common shared drive motor 162, the first relay gear 152 for K meshes with the belt drive relay gear 161 described above. In the vicinity of the K first relay gear 152, a K second relay gear 153 in which an input gear portion 153a and an output gear portion 153b are integrally formed on the same axis is disposed. The K first relay gear 152 described above meshes with the input gear portion 153a of the K second relay gear 153. The output gear portion 153b of the K second relay gear 153 meshes with the K photoconductor gear 151K. With the gear arrangement as described above, the rotational driving force of the common shared drive motor 162 is such that the belt relay gear 161, the K first relay gear 152, the K second relay gear 153, and the K photoconductor gear 151. To the K photoconductor 1K. That is, in this printer, the common drive motor 162 functions as a belt drive source that is a drive source of the drive roller 12 and the intermediate transfer belt 8, and is a K photoconductor that is one of the image carrier drive sources. It also functions as a drive source.

  On the other hand, the photoconductors 1Y, 1C, and 1M for Y, C, and M are driven by a drive source that is different from the common drive motor 162. Specifically, the motor gear of the color photoconductor motor 154 as an image carrier driving source fixed in the printer main body is positioned between the C photoconductor gear 151C and the M photoconductor gear 151M. is doing. And it is meshing with these gears simultaneously. Thus, the motor gear of the color photoconductor motor 154 directly transmits the rotational driving force to the C photoconductor gear 151C and also directly to the M photoconductor gear 151M.

  The Y relay gear 155 that is rotatably supported by the printer main body is positioned between the Y photoconductor gear 151Y and the C photoconductor gear 151C, and meshes with the photoconductor gears. Then, the rotational driving force of the C photoconductor gear 151C is transmitted to the Y photoconductor gear through itself.

  FIG. 8 is a schematic diagram showing the control device 200 and various devices electrically connected thereto. One of the stretching members that stretch the belt inside the loop of the intermediate transfer belt 21, and the linear velocity of the driven roller 14 that rotates following the endless movement of the belt is the linear velocity of the intermediate transfer belt 21. Be the same. Therefore, the rotational angular velocity and rotational angular displacement of the driven roller 14 indirectly indicate the endless moving speed of the intermediate transfer belt 21. A roller encoder 171 composed of a rotary encoder is fixed to the shaft member of the driven roller 14. The roller encoder 171 detects the rotational angular velocity and rotational angular displacement of the driven roller 14 and outputs the result to the drive control unit 210. Such a roller encoder 171 functions as a speed fluctuation detecting unit that detects a speed fluctuation of the intermediate transfer belt 8 caused by a change in diameter accompanying a temperature change of the driving roller 12. Also, it functions as a speed detecting means for detecting the endless moving speed of the intermediate transfer belt 8. Based on the output from the roller encoder 171, the drive control unit 210 can grasp the speed fluctuation and the endless moving speed of the intermediate transfer belt 8.

  In this printer, the roller encoder 171 that detects the rotational angular velocity and the rotational angular displacement of the driven roller 14 is used as the speed fluctuation detecting means and the speed detecting means, but those that detect the speed fluctuation and speed by other methods. It may be used. For example, an optical sensor may be used in which a scale in which a plurality of scales are arranged at a predetermined pitch in the circumferential direction of the belt is provided on the intermediate transfer belt, and a belt speed fluctuation or speed is detected based on a time interval for detecting the scales. . Further, an optical image sensor employed in an optical mouse or the like that is an input device of a personal computer may be used as a means for detecting the speed fluctuation or speed of the belt surface. Further, a means for predicting the belt speed based on the result of detecting the temperature inside the apparatus by the temperature sensor and the theoretical value of the thermal expansion of the driving roller 12 may be provided as the detecting means.

  FIG. 9 is a schematic diagram for explaining the linear velocity V of the intermediate transfer belt 8. Since the intermediate transfer belt 8 follows the surface of the drive roller 12, the intermediate transfer belt 8 moves at the same linear velocity as the drive roller 12. A relationship of “V = rω” is established among the linear velocity V of the intermediate transfer belt 8, the radius r of the drive roller 12, and the angular velocity ω of the drive roller 12. When the common drive O 162 is driven at a constant drive speed, the angular speed ω of the drive roller 12 is also constant. Then, if the diameter of the driving roller 12 is deviated from the design value, the linear velocity V of the belt is deviated from the target belt speed along with the deviation, so that the color toner images are misaligned.

  Therefore, the drive control unit 210 performs belt constant speed control that performs acceleration / deceleration control of the common shared drive motor 162 so that the frequency of the pulse signal output from the roller encoder 171 matches the frequency of the reference clock. By this belt constant speed control, the drive speed of the shared common drive motor 162 is controlled so that the driven roller 14 to which the roller encoder 171 is attached is rotated at a constant rotational angular speed. Since the driven roller 14 rotates following the movement of the intermediate transfer belt 8, the rotation of the driven roller 14 at a constant rotational angular speed causes the intermediate transfer belt 8 to move at a constant linear velocity V. It means that That is, the drive control unit 210 moves the intermediate transfer belt 8 at a linear speed V that is substantially the same as the target belt speed by belt constant speed control. By performing such belt constant speed control, the intermediate transfer belt 8 can be moved endlessly at the target belt speed regardless of the diameter change of the drive roller 12.

  In the belt constant speed control, in addition to the deviation of the belt linear velocity V from the target belt speed due to the error in the diameter of the driving roller 12, speed fluctuation in a short period within the belt circumference is also detected. . Examples of the speed fluctuation in a short period within the circumference of the belt include a sudden speed fluctuation when the recording paper enters the secondary transfer nip and a periodic speed fluctuation caused by the eccentricity of the driving roller 12. When the drive roller 12 is eccentric, a subtle speed fluctuation appears in the intermediate transfer belt 8 so as to draw one cycle of a sine curve per rotation of the drive roller 12. In the belt constant speed control described above, such subtle speed fluctuations are detected and the results are reflected in the drive control of the common shared drive motor 162, so that speed fluctuations in a short period can be suppressed.

However, if a subtle speed fluctuation caused by the eccentricity of the drive roller 12 is detected and the result is feedback-controlled to the drive control of the common shared drive motor 162, the speed for the intermediate transfer belt 8 is stabilized instead of being stabilized. The linear velocity of the photoreceptor 1K is slightly changed as shown in FIG. The period of the sine curve speed fluctuation curve in the figure is the same as the rotation period of the drive roller 12. Even if the speed fluctuation of such a period appears on the photoconductor 1K for K, the occurrence of image quality deterioration due to the speed fluctuation can be suppressed as follows. That is, FIG. As shown in 10, the distance between the write-transfer is the distance from the optical writing position P ₁ to the central position P ₂ of the belt moving direction primary transfer nip on the surface of the photosensitive member 1K for K L ₁ is set to an integral multiple of the circumferential length S of the drive roller 12. In this way, it is possible to stabilize the dot shape of the toner image transferred to the belt by making the linear velocity of the photoconductor 1K the same during optical writing and during transfer.

If the setting shown in FIG. 11 is difficult, as shown in FIG. 12, the photoreceptor distance L ₂ is a pitch between the photosensitive member may be set to an integral multiple of the circumferential length S of the drive roller 12. By setting in this way, it is possible to match the linear velocity of the intermediate transfer belt 8 when each position of the toner image in the sub-scanning direction passes through each transfer nip, and to suppress the misregistration of each color.

  By the way, if the drive speed of the common shared drive motor 162 is controlled so that the linear velocity V of the intermediate transfer belt 8 is constant regardless of the diameter of the drive roller 12, the K-use speed increases as the diameter of the drive roller 12 changes. The linear velocity of the photoreceptor 1K is slightly changed. Then, a linear velocity difference is generated between the Y, C, M photoconductors 1Y, C, M driven by the color photoconductor motor 154 and the K photoconductor 1K driven by the common drive motor 162. As a result, an overlay error occurs between the Y, C, and M toner images and the K toner image.

  Therefore, in this printer, as shown in FIG. 8, a drum encoder 172 including a rotary encoder for detecting the rotational angular velocity or the rotational angular displacement is provided on the rotational shaft of the K photoconductor 1K. The data storage means (not shown) of the drive control unit 210 includes lines of the Y, C, and M photoconductors 1Y, M, and C based on the output from the drum encoder 172 (the rotational speed of the K photoconductor). An algorithm or a data table for obtaining a control target of the driving speed of the color photoconductor motor 154 that can make the speed coincide with the linear speed of the K photoconductor 1K is stored. And the drive control part 210 is comprised so that the process which calculates | requires the above-mentioned control target based on the output from the drum encoder 172 may be implemented.

  When the print job starts, first, driving of the common drive motor 162 and the color photoconductor motor 154 is started. The common shared drive motor 162 drives the intermediate transfer belt 8 at the target belt speed by executing belt constant speed control. At this time, the drive speed of the common shared drive motor 162 is a value corresponding to the diameter of the drive roller 12. The linear velocity of the K photoconductor 1 </ b> K is also a value corresponding to the diameter of the drive roller 12. In order to make the linear speeds of the Y, C, and M photoconductors 1Y, C, and M coincide with the linear speed of the photoconductor 1K at this time, the drive control unit 210 acquires an output value from the drum encoder. Then, based on the output value and the above-described algorithm or data table stored in the data storage means, a control target of the driving speed of the color photoconductor motor 154 capable of matching the linear speed is calculated. If the difference between the calculation result and the current set value of the control target exceeds a predetermined threshold value, the control target is corrected to the calculated value because there is a risk of occurrence of overlay deviation due to the linear speed difference. On the other hand, when it is equal to or less than the threshold value, the overlay deviation due to the linear velocity difference is at a level where there is no problem, so the current control target is maintained. Thereafter, when the start flag is OFF, the start flag is turned ON. This start flag is used to determine whether or not to start the flow for image processing. The flow for image processing is a flow for performing optical writing processing or developing processing. The start flag is turned off immediately after the print job starts. In this state, the image processing flow is not started. When the start flag is turned ON, an image processing flow is started and a print job is performed.

  In this way, in this printer, the intermediate transfer belt 8 can be moved endlessly at the target speed regardless of the diameter of the drive roller 12 by controlling the drive speed of the common drive motor 162 by belt constant speed control. In addition, the drive speed of the color photoconductor motor 154 is controlled based on the output from the drum encoder 172 serving as rotation detecting means that reflects the speed of the K photoconductor 1K driven by the shared common drive motor 162. Thus, the linear velocity difference between the photoconductor 1K for K and the photoconductors 1Y, C, and M for Y, C, and M is reduced. As a result, it is possible to suppress the occurrence of misalignment due to the difference in linear velocity between the photoconductors.

  In the printer according to the embodiment, color misregistration also occurs due to sub-scanning registration misalignment of each color toner image. The sub-scanning registration deviation is a phenomenon in which the normal transfer position of the toner image is totally displaced in the sub-scanning direction, which is the moving direction of the intermediate transfer belt 8. The main cause of the sub-scanning registration deviation is that the components of the optical writing unit 7 such as a reflection mirror and a lens expand and contract with temperature changes. During a continuous printing operation in which images are continuously formed on a plurality of recording papers, the temperature of the optical writing unit 7 continues to rise, so that the amount of color misregistration increases as the continuous operation time increases.

  Therefore, the main control unit 220 of the printer performs the following writing position correction process every time a predetermined number of prints are performed. In other words, after the toner images formed on the photoreceptors of the respective colors are transferred side by side on the belt, the amount of misregistration of the toner images of each color is detected based on the timing at which the toner images are detected by an optical sensor as a displacement detection means To do. Then, the sub-scanning registration shift amount is reduced by correcting the latent image writing start timing based on the detection result. As a result, in the continuous print mode, the amount of color misregistration that gradually increases as the number of continuous prints increases can be periodically reduced by periodically performing the writing position correction process.

  FIG. 13 is an enlarged perspective view showing a part of the intermediate transfer belt 8 together with an optical sensor unit 136 as a toner image detecting means. As shown in the figure, the optical sensor unit 136 is opposed to a portion of the intermediate transfer belt 8 that is wound around the drive roller 12 with a predetermined gap therebetween. The main control unit 220 performs a writing position correction process immediately after a power switch (not shown) is turned on or whenever a predetermined number of prints are performed. In this writing position correction process, a color misregistration detection image made up of a plurality of toner images called chevron patches PV is formed on one end, the center, and the other end of the intermediate transfer belt 5 in the width direction. The optical sensor unit 136 includes a first optical sensor 137 that faces one end in the width direction of the intermediate transfer belt 8, a second optical sensor 138 that faces the center, and a third optical sensor 139 that faces the other end. It has. The first optical sensor 137 passes the light emitted from the light emitting means through the condenser lens, reflects the light on the surface of the intermediate transfer belt 8, receives the reflected light by the light receiving means, and determines the voltage according to the amount of light received. Is output. When the toner image in the chevron patch PV formed at one end of the intermediate transfer belt 8 passes immediately below the first optical sensor 137, the amount of light received by the light receiving means of the first optical sensor 137 changes greatly. Accordingly, the main control unit 220 can detect each toner image in the chevron patch PV formed at one end portion in the width direction of the intermediate transfer belt 8. Similarly, each toner image in the chevron patch PV formed at the central portion of the intermediate transfer belt 8 can be detected based on the output from the second optical sensor 138. Further, each toner image in the chevron patch PV formed at the other end of the intermediate transfer belt 8 can be detected based on the output from the third optical sensor 139. Based on the detection timing, it is possible to detect the positional deviation amount of each toner image. As the light emitting means, an LED or the like having an amount of light that can generate reflected light necessary for detecting a toner image is used. As the light receiving means, a CCD in which a large number of light receiving elements are arranged in a straight line is used.

  The main control unit 220 detects each toner image in the chevron patch PV, so that the position in the main scanning direction, the position in the sub-scanning direction (belt moving direction), the magnification error in the main scanning direction, the main scanning in each toner image. Each skew from the direction is detected. The main scanning direction here refers to the direction in which the laser light is phased on the surface of the photosensitive member as it is reflected by the polygon mirror. As shown in FIG. 14, the chevron patch is a posture in which each color toner image of Y, C, M, and K is inclined by about 45 [°] from the main scanning direction at a predetermined pitch in the belt moving direction which is the sub scanning direction. It is a line pattern group arranged. For such Y, C, M toner images in the chevron patch PV, the difference in detection time from the K toner image is read. In this figure, the vertical direction of the paper surface corresponds to the main scanning direction, and after the Y, C, M, and K toner images are arranged in order from the left, the postures are different from those by 90 [°]. , Y toner images are further arranged. Based on the difference between the actual measurement value and the theoretical value for the detection time differences tyk, tck, and tmk with respect to K as the reference color, the shift amount in the sub-scanning direction of each color toner image, that is, the registration shift amount is obtained. Then, based on the registration deviation amount, a correction value of the optical writing start timing for the photosensitive member is calculated, and the result is transmitted to the optical writing control unit 230. The optical writing control unit 230 corrects the optical writing start timing for the Y, C, and M photoconductors based on the correction value sent from the main control unit 220, thereby reducing the registration shift of the toner images of each color. To do. Further, the main control unit 220 obtains the inclination (skew) of each color toner image from the main scanning direction based on the difference in the amount of deviation in the sub-scanning direction between both end portions of the belt. Based on the result, surface tilt correction of the reflecting mirror is performed to reduce skew of each color toner image. As described above, the process of correcting the optical writing start timing based on the detection timing of each toner image in the chevron patch PV, which is a color misregistration detection image, to reduce registration deviation and skew deviation is written position correction. It is processing.

  As in this printer, four laser beams for four photoconductors (1Y, C, M, K) are deflected by a common polygon mirror to perform optical scanning in the main scanning direction for each photoconductor. Then, the optical writing start timing for each photoconductor is corrected in units of time corresponding to writing of one line (one scanning line). In this printer, Y, C, and M registration deviations are corrected based on the position of the K toner image formed on the K photoconductor 1K. Specifically, when the Y, C, M toner image and the K toner image have a registration deviation of one dot (one pixel) or more, the Y, C, M photoconductors 1Y, C, The optical writing start timing for M is shifted back and forth by an integral multiple of the writing time for one line. Thereby, the amount of misalignment in the sub-scanning direction is suppressed to less than 1 dot. However, it is usually not possible to completely eliminate overlay deviation. For example, it is assumed that the Y toner image causes a resist deviation of 5/4 dots from the K toner image. In this case, by shifting the optical writing start timing for the Y photoconductor 1Y back and forth by one line, it is possible to reduce the resist deviation amount to ¼ dot. However, the resist deviation amount for this ¼ dot cannot be made zero.

Next, a characteristic configuration of the printer will be described.
The present inventors conducted an experiment to further increase the printing speed in response to the recent demand for high-speed printing in the printer testing machine having the above basic configuration. Then, when thick paper was used as recording paper, streak-like image disturbance was caused remarkably. It was found that the streak-like image disturbance is caused by an impact when the thick paper enters the secondary transfer nip. Specifically, when the thick paper is made to enter the secondary transfer nip, the moving speed of the intermediate transfer belt 8 is greatly reduced for a moment due to a sudden load increase. Under the condition that the printing speed is higher than the conventional one, the decrease rate becomes larger than the conventional one. Then, if the speed reduction is fed back to the drive control of the common shared drive motor 162, the speed of the intermediate transfer belt 8 is excessively increased for a moment. As described above, when the instantaneous speed decrease at the time of entering the nip of the cardboard and the subsequent instantaneous speed increase occur continuously, the toner image of each color is not normally transferred in the primary transfer nip of each color, and the streak is not detected. The image was disturbed. This streak-like image disturbance is far more conspicuous than the color misregistration caused by the eccentricity of the drive roller 12, and it is necessary to take measures prior to the color misregistration.

  Therefore, the drive control unit 210 of the printer switches the control method of the shared shared drive motor 162 from belt constant speed control to motor constant speed control as necessary. In this motor constant speed control, the common drive motor 162 is driven so as to rotate the motor shaft of the common drive motor 162 at a constant rotational speed based on the FG signal generated from the FG signal generator of the common shared drive motor 162. This is a control method. As is well known, the FG signal generator as the rotation speed detecting means is incorporated in the common drive motor 162 and generates a pulse signal each time the motor shaft of the common drive motor 162 rotates by a predetermined rotation angle. It is. By driving and controlling the common drive motor 162 so that the FG signal has a predetermined frequency, the common drive motor 162 can be rotated at a predetermined rotation speed. When the thick paper enters the nip, the speed of the intermediate transfer belt 8 is greatly reduced for a moment. At this time, the belt is stretched or the minute gap between the gears is narrowed. Does not drop that much. For this reason, in the constant motor speed control, when the cardboard enters the nip, a rapid decrease in the motor rotation speed is not detected, and the common drive motor 162 is stabilized at the target rotation speed from the cardboard nip entry to the nip discharge. Keep rotating. As a result, the speed of the belt member is not excessively increased for a moment immediately after entering the nip of the cardboard. Therefore, by switching the drive method from belt constant speed control to motor constant speed control as necessary, color misregistration due to eccentricity of the drive roller 12 is allowed, but streak-like image disturbance can be suppressed. .

  The drive control unit 210 performs switching from belt constant speed control to motor constant speed control as follows. That is, it is determined based on an instruction command from the user whether or not there is a high possibility of causing streak-like image disturbance. Specifically, the printer includes a thickness information acquisition unit that acquires information on the thickness of the recording paper fed into the secondary transfer nip. An example of such thickness information acquisition means is an operation unit such as a touch panel that receives thickness information input by the user. Further, a thickness detecting unit that detects the thickness of the recording paper based on the amount of movement of the pair of conveying rollers that convey the recording paper while sandwiching the paper may be used. When the recording paper having a relatively small thickness is used, the belt speed fluctuation when the recording paper enters the nip does not become so large. On the other hand, when the recording paper having a relatively small thickness is used, a relatively large belt speed fluctuation occurs when the recording paper enters the nip, so that there is a high possibility of causing streak-like image disturbance. Therefore, the main control unit 220 of the control device 200 controls the drive control unit 210 from the constant belt speed control to the constant motor speed control when the thickness information acquired by the thickness information acquisition unit exceeds a predetermined thickness. A signal instructing switching to is output. Thereby, the drive control part 210 comes to drive the shared drive motor 162 temporarily by motor constant speed control.

  In the monochrome mode, no color misregistration occurs, so it is not always necessary to execute the belt constant speed control. Rather, it is more advantageous to perform motor constant speed control that allows the belt to run stably even when there is a sudden load fluctuation on the belt. Therefore, the main control unit 220 outputs a signal instructing execution of the motor constant speed control to the drive control unit 210 regardless of the thickness of the recording paper in the monochrome mode.

  When there is a high possibility of large belt speed fluctuations when entering the nip as in this printer, or in monochrome mode, switching the control method from belt constant speed control to motor constant speed control will cause streak-like image distortion Can be suppressed.

  However, when the control method is switched from the belt constant speed control to the motor constant speed control, there is a risk of causing a remarkable color shift. This remarkable color shift is caused by the following causes. That is, in the motor constant speed control, the common drive motor 162 is rotated at a predetermined target rotational speed. If the diameter of the driving roller 12 is a value as designed, the average linear velocity V of the driving roller 12 at that time is almost the same value as the target belt speed. However, if a drive roller 12 having a certain dimensional error is used from the viewpoint of cost reduction, the common drive motor 162 is rotated at a predetermined target rotational speed because the roller diameter is deviated from the design value. In this case, the average linear velocity on the roller surface slightly deviates from the target belt speed. Due to this deviation, in the motor constant speed control, the intermediate transfer belt 8 is caused to travel at a linear speed V different from the belt constant speed control. The writing position correction process is performed under the condition of belt constant speed control. However, the color shift can be suppressed only when the common drive motor 162 is driven by belt constant speed control. If the linear speed V of the intermediate transfer belt 8 is shifted from the target belt speed by switching from belt constant speed control to motor constant speed control, color misregistration is caused. If the linear velocity V is changed, the belt moving time required from the upstream primary transfer nip to the downstream primary transfer nip is changed, so that the toner images are overlapped without deviation at each primary transfer nip. It is because it becomes impossible to match.

  FIG. 15 is an enlarged schematic diagram for explaining the overlapping position of each color dot. In the figure, a large circle represents the outline of each color dot. The small circle is a virtual circle indicating the center position of the dot. Moreover, the alphabet shown in this virtual circle has shown the color of the dot. This figure shows a state where the four dots Y, C, M, and K are overlapped with each other without any deviation. For this reason, although there are four dots, only one large circle indicating the dot outline and one small circle indicating the center of the dot are shown. For reference, when the dots of each color are shifted by ¼ dot, the state is shown as in FIG.

  Even if the above-described writing position correction processing is performed, for example, it is assumed that an overlay error (color error) as shown in FIG. 17 remains. In this example, M dots are overlapped with each other without shifting with respect to K dots. On the other hand, Y todd is shifted by 1/4 dot to the downstream side in the belt movement direction with respect to K dot (+1/4 dot). Further, the C dot is shifted by ¼ dot upstream of the K dot in the belt moving direction (−1/4 dot). The amount of misalignment of all four colors is a sum of an absolute value of +1/4 and an absolute value of -1/4, and is ½ dot. As described above, if the writing position correction process is performed, it is possible to reduce the amount of misalignment of the four colors to less than one dot.

  However, if the control method of the common drive motor 162 is switched to the motor constant speed control, the linear deviation V of the intermediate transfer belt 8 is shifted from the target belt speed, thereby increasing the overlay deviation amount. For example, if the linear velocity V of the intermediate transfer belt 8 is originally within a time required for movement between adjacent primary transfer nips (hereinafter referred to as standard movement time between nips), the linear velocity V is 1 more than between primary transfer nips. It is assumed that the belt speed becomes faster than the target belt speed so as to move more by / 4 dots. Then, when the belt is driven for a time that is three times the standard movement time between the nips, the Y dot originally moves from the center of the primary transfer nip for Y to the center of the primary transfer nip for K. As a result, it is located at a position shifted from the center toward the downstream side in the belt movement direction by 1/4 × 3 = 3/4 dots. That is, the Y dot is shifted to the downstream side in the belt movement direction by 3/4 dot with respect to the K dot. In addition, when the belt is driven for a time twice as long as the standard movement time between nips, the C dot moves from the center of the primary transfer nip for C to the center of the primary transfer nip for K. As a result, it is located at a position shifted by 1/4 × 2 = 1/2 dot downstream from the center in the belt moving direction. That is, the C dot is shifted to the downstream side in the belt movement direction by 1/2 dot with respect to the K dot. Further, when the belt is driven for the same time as the standard movement time between the nips, the M dot moves from the center of the primary transfer nip for M to the center of the primary transfer nip for K. , 1/4 × 1 = 1/4 dot is located at a position shifted from the center to the downstream side in the belt movement direction. That is, the M dots are shifted to the downstream side in the belt movement direction by 1/4 dots with respect to the K dots. In this way, the three dots Y, M, and C are shifted to the downstream side in the belt movement direction with respect to the K dots.

  Even if the writing position correction process is performed, it is assumed that the constant motor speed control is performed in a state where a small overlay deviation as shown in FIG. 17 remains. In this motor constant speed control, the linear speed V of the intermediate transfer belt 8 becomes slightly higher than the target belt speed because the diameter of the drive roller 12 is slightly larger than the design value. Assume that the intermediate transfer belt 8 advances by “distance between nips + 1/4 dots” in the standard movement time between nips. Then, the overlay deviation shown in FIG. 17 increases as shown in FIG. In the state shown in FIG. 17, the Y dot is located at a position shifted to the downstream side in the belt movement direction by ¼ dot with respect to the K dot. It shifts to the downstream side in the belt movement direction by 4 dots. As a result, as shown in FIG. 18, one dot is shifted to the downstream side in the belt movement direction with respect to K dots. Further, in the state of FIG. 17, the C dot is located at a position shifted to the upstream side in the belt movement direction by 1/4 dot with respect to the K dot. However, when the motor constant speed control is performed, It is shifted to the downstream side in the belt moving direction by 1/2 dot. As a result, as shown in FIG. 18, one dot is shifted to the upstream side in the belt movement direction with respect to K dots. In addition, in the state of FIG. 17, the M dot overlaps perfectly with the K dot. However, when the motor constant speed control is performed, as shown in FIG. It will shift to the downstream side in the belt movement direction by the amount of dots. The shift amount of the entire four colors is ½ dot in the state of FIG. 17, but increases to 1 dot as shown in FIG.

  Therefore, when the main control unit 220 drives the common drive motor 162 by the motor constant speed control, the main control unit 220 temporarily sets the optical writing start timing for the Y, C, and M photoconductors (1Y, C, and M). Temporary correction processing for correction is performed. In this temporary correction process, Y, C, and M optical writing start timings are temporarily set for Y dots, C dots, and M dots based on the amount of deviation increase stored in the flash memory as data storage means. to correct.

  As a premise for performing such temporary correction processing, the main control unit 220 performs Y, C, and M photoconductors (1Y, C, and M) for Y, C, and M dots, respectively, in the above-described writing position correction processing. The data of the residual shift amount, which is the overlay shift amount with the K dots that remain even after the optical writing start timing is corrected, is stored in the flash memory. In the configuration in which an image is formed with a resolution of 600 [dpi] (1 dot diameter = 42.3 μm) and the residual displacement shown in FIG. 17 remains as an example, for Y dots, “+10.575” Is stored in the flash memory (42.3 × 1/4). For C dots, a residual shift amount of “−10.575” is stored in the flash memory (−42.3 × 1/4). For M dots, a residual shift amount of “0” is stored in the flash memory.

  Further, the main control unit 220 stores, in the flash memory, data on the amount of increase in deviation from K generated when the motor constant speed control is performed for Y, C, and M, respectively. As already described, the data of the increase amount [μm] of the deviation is a large value in the order of Y, C, and M. Each of them is calculated based on a deviation from a design value as a result of measuring the diameter of the drive roller 12 with a precision machine, and is input into the flash memory at the time of factory shipment. If a method of manufacturing the drive roller 12 that has substantially the same diameter for the same lot is adopted, it is efficient because measurement for each lot is sufficient without measuring the diameter of each drive roller 12.

  FIG. 19 is a flowchart illustrating a process flow in the temporary correction process performed by the control device 200. In the control device 200 that has started the temporary correction process, first, the main control unit 200 adds the remaining displacement amount and the displacement increase amount stored in the flash memory for Y, C, and M, respectively. When it is assumed that temporary correction of the optical writing start timing is not performed when the speed control is performed, the overlay displacement amount is calculated as a virtual displacement amount (step 1: hereinafter, step is denoted as S). The residual deviation shown in FIG. 17 remains, and the diameter of the drive roller 12 is slightly larger than the design value, so that the belt is moved by 1/4 dot from the original in the standard movement time between nips. An example in which the belt travels downstream in the belt movement direction by (42.3 μm) is as follows. That is, for Y, a deviation increase amount of “+31.725” is stored in the flash memory (42.3 × 3/4). For C, a deviation increase amount of “+21.15” is stored in the flash memory. For M, a deviation increase amount of “+10.575” is stored in the flash memory. Then, the main control unit 200 obtains a virtual deviation amount of 42.3 [μm] for Y by adding the residual deviation amount = + 10.575 μm and the deviation increase amount = + 31.725 μm. For C, the virtual deviation amount is calculated as +10.575 [μm] by adding the residual deviation amount = −10.575 μm and the deviation increase amount = + 21.15 μm. M is calculated as +10.757 by adding the afterimage shift amount = 0 μm and the shift increase amount + 10.575 μm. As a result, it is grasped that an overlay error as shown in FIG. 18 occurs (hereinafter, the overlay error is referred to as a virtual overlay error).

  Next, the main control unit 220 calculates the amount of misalignment in all four colors as the amount of deviation for each correction mode for the 26 dot position correction modes (S2). Twenty-six dot position correction modes can be established when the dot position is corrected by shifting at least one of the Y, C, and M dots by one dot back and forth from the virtual overlay deviation state. It is. For each of the three colors Y, C, and M, there are three ways of shifting, one dot is shifted upstream in the belt movement direction, and one dot is shifted downstream in the belt movement direction. There are 27 ways in total, but one of them is an uncorrected mode in which all three colors are not shifted. Therefore, there are 26 dot position correction modes. For each of these 26 dot position correction modes, the overlay shift amount for all four colors is calculated as the shift amount for each correction mode. For example, as one of the 26 dot position correction modes, there is a mode in which the Y dot in FIG. 18 is shifted downstream by 1 dot in the belt movement direction (the optical writing start timing is delayed by 1 dot). For this position correction mode, the shift amount for each correction mode is calculated as “+10.575”.

  The reason for obtaining the deviation amount for each correction mode is as follows. That is, as a method of correcting the dot position, the method of shifting all three Y, C, and M positions uniformly and the method of shifting each of the three colors (including the case of not shifting) are changed as necessary. There is a method. When the former method is adopted, if the virtual overlay deviation shown in FIG. 18 is used, either the dot position correction shown in FIG. 20 or the dot position correction shown in FIG. Will be carried out. In the correction shown in FIG. 20, the positions of Y, C, and M dots are all shifted by one dot upstream in the belt movement direction. As a result, the amount of misalignment in all four colors can be reduced from 1 dot in FIG. 18 to 3/4 dots in FIG. On the other hand, in the modification shown in FIG. 21, the positions of Y, C, and M dots are all shifted by one dot downstream in the belt movement direction. As a result, the amount of misalignment for all four colors increases from 1 dot in FIG. 18 to 2 dots in FIG. For this reason, the correction shown in FIG. 20 is employed in the method of uniformly shifting the positions of the three colors Y, C, and M. In the example of the virtual overlay deviation in FIG. 18, when all the three color positions are shifted to the upstream side in the belt movement direction, the deviation amount can be reduced more than the virtual overlay deviation. In some cases, the amount of displacement cannot be reduced more than the virtual overlay displacement, regardless of whether the direction of uniform displacement is upstream or downstream. In such a case, temporary correction of the Y, C, and M optical writing positions is not performed.

  In addition, when adopting the method of changing the shifting method for each of the three colors as necessary as a method for correcting the position of the dots, it is verified whether the shifting amount can be reduced most when the shifting method is adopted. There is a need to. In this printer, for the verification, the above-described 26 kinds of deviation amounts for each correction mode are calculated. In the case of the virtual overlay deviation of FIG. 18, among the 26 correction mode deviation amounts, the deviation amount is reduced most by 1 dot on the upstream side in the belt movement direction as shown in FIG. This is a mode in which the position is not corrected with respect to C dots and M dots. As shown in the figure, the shift amount for the four colors as a whole is ¼ dot, and can be significantly reduced as compared with ¾ dot in FIG. 20.

  Therefore, after calculating the 26 kinds of deviation amounts for each of the correction modes, the main control unit 220 next specifies the one that minimizes the deviation amount for all four colors (S3 in FIG. 18). Then, write temporary correction data, which is temporary correction data of the optical writing start timing, is constructed for each of the three colors Y, C, and M so that the same result as the deviation amount for each correction mode of the specific result can be obtained. S4). For example, in the example shown in FIG. 22, “−1” is constructed as temporary correction data for Y. Further, “0” and “0” are constructed as temporary correction data for C and M. Thereafter, the main control unit 220 transmits Y, C, and M writing temporary correction data to the optical writing control unit 230. Then, after the optical writing control unit 230 individually determines the optical writing start timing for the Y, C, and M photoconductors 1Y, C, and M based on the temporary writing correction data (S5). Each optical writing is performed (S6). By correcting the optical writing start timing and temporarily correcting the optical writing position of Y, C, and M dots in this way, the control method of the common drive motor 162 is changed from the belt constant speed control to the motor constant speed. Deterioration of color misregistration caused by switching to control can be suppressed.

  When the print job is finished, the temporarily corrected optical writing start timing is returned to the original, and then a series of processing flow is finished. Moreover, although the example which implements the process of said S1-S4 in the processing flow of a temporary correction process was demonstrated, the process of said S1-S4 is implemented in the last stage of the above-mentioned write position correction process, and a temporary correction process is carried out. The writing temporary correction data may be constructed in advance before. Further, although an example in which the diameter of the drive roller 12 is larger than the design value has been described, the optical writing position of Y, C, and M dots is temporarily corrected in the same manner even when the diameter is smaller. It is possible. For example, since the diameter of the drive roller 12 is smaller than the design value, it is assumed that the intermediate transfer belt 8 moves only by a distance that is ¼ dot smaller than the distance between nips in the standard movement time between nips. In this case, for Y, a deviation increase amount of “−31.725” is stored in the flash memory (−42.3 × 3/4). For C, a deviation increase amount of “−21.15” is stored in the flash memory. For M, a deviation increase amount of “−10.575” is stored in the flash memory. After obtaining the virtual deviation amount from the deviation increase amount and the above-described residual deviation amount, the deviation amounts for 26 different correction modes may be obtained.

  The printer includes a replacement detection unit that detects that the drive roller 12 has been replaced. The replacement detection means is a unit attachment / detachment detection means for detecting attachment / detachment of the transfer unit 15 to / from the printer main body, and inquires of the user whether or not the drive roller 12 has been replaced after detecting the attachment / detachment of the transfer unit 15. An inquiry program for executing processing. The printer also has data updating means for updating the data of the increase amount of deviation in the flash memory of the main control unit 220 based on the detection result by the replacement detection means. This data updating means is a CD on which the instruction command program stored in the main control unit 220, the printer utility software installed in the personal computer, and the deviation increase amount updating software attached to the drive roller 12 are recorded. -ROM.

  The unit attachment / detachment detection means of the replacement detection means detects attachment / detachment of the transfer unit 15 as long as the power cable is connected to the outlet regardless of the state of the power switch of the printer body. The main control unit 220 activates the inquiry program and inquires the user when the unit attachment / detachment detection unit detects attachment / detachment of the transfer unit. Specifically, a message “Have you replaced the drive roller? Yes, No” is displayed on a touch panel (not shown). When the user touches a “No” portion on the touch panel, the transfer unit 15 is not detected to be replaced. On the other hand, when the “Yes” part is touched, it is considered that the transfer unit 15 has been replaced. In this case, the data update sh plan instruction command program is started and a message “Please set the CD-ROM attached to the drive roller in the optical disk drive of the personal computer” is displayed on the touch panel. When the user sets the CD-ROM in the personal computer in accordance with the instruction, the deviation increasing amount update software recorded in the CD-ROM is automatically started in the personal computer. Then, the deviation increase data stored in the predetermined area of the hard disk of the personal computer is updated to the same value as the deviation increase recorded in the CD-ROM. Further, the printer utility software is automatically started. The automatically started printer utility software is based on the updated deviation increase amount, and the deviation increase amount data recorded in the main control unit 220 of the printer connected to the personal computer via the LAN cable or USB cable. To update the value to the same value as the data in the hard disk. As a result, the deviation increase data is updated to match the diameter of the drive roller 12 after replacement.

  Next, a printer according to an example in which a more characteristic configuration is added to the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to the example is the same as that of the embodiment.

  The drive roller 12 includes a metal cored bar and a rubber layer coated on the surface thereof for the purpose of increasing the gripping force. In such a configuration, when the in-machine temperature changes, the diameter of the driving roller 12 expands and contracts relatively large due to expansion and contraction of rubber. That is, the diameter of the driving roller 12 varies with the variation of the in-machine temperature.

  Therefore, in the printer according to the embodiment, the main control unit 220 stores, in the flash memory, an algorithm indicating the relationship between the in-machine temperature and the deviation increase amount as data of the Y, C, and M deviation increase amount. ing. The relationship is based on the result of measuring the diameter of the drive roller 12 at each temperature with a precision measuring instrument and calculating the amount of increase in deviation at each diameter while intentionally changing the room temperature in a laboratory in a factory. It was built. Specific examples of the algorithm include a data table and a function expression. In any case, it is possible to obtain an increase in deviation corresponding to the temperature inside the machine.

  A temperature sensor for measuring the temperature inside the printer is provided in the printer, and the detection result is transmitted to the main controller 220. In the temporary correction process described above, the main control unit 220 shifts the Y, C, and M at the current diameter of the driving roller 12 based on the detection result by the temperature sensor serving as the temperature detection unit and the algorithm. Find the amount of increase. Then, the result is used to obtain the above-described virtual overlay deviation and 26 kinds of deviation amounts for each correction mode.

  Up to now, the printers configured to transfer the toner images of the respective colors formed on the photoconductors of the respective colors while being superimposed on the intermediate transfer belt 8 have been described. The present invention can also be applied to a configuration in which the image is transferred to a recording sheet. In the printers according to the embodiments and examples, the latent images written on the plurality of latent image carriers by the process units 6Y, M, C, and K, the optical writing unit 7, the control device 200, and the like at various locations are also provided. Image forming means for developing with different color toners is configured.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
In aspect A, the surface of the latent image carrier on the surface of the image forming means and the endless belt member such as the intermediate transfer belt 8 that is moved endlessly or the recording sheet held on the surface. Transfer means such as a transfer unit 15 that obtains a multicolor image by superimposing and transferring the toner images, and the belt member endlessly as the belt member is rotationally driven while being wound around a part of its peripheral surface. A control device 200 that controls driving of a driving rotating body such as a driving roller 12 that is moved, a driving motor such as a common driving motor 162 that is a driving source of the driving rotating body, and the image forming unit, transfer unit, and driving motor. And other control means. Then, based on the result of the control means detecting the moving speed of the belt member by the belt speed detecting means such as the roller encoder 171, the driving speed of the driving motor so as to move the belt member endlessly at the target belt speed. The belt constant speed control is performed, and the toner image of each color included in the color misregistration detection image formed on the surface of the belt member is detected based on the timing detected by the toner image detecting means such as the optical sensor unit 136. A writing position correction process for individually correcting the latent image writing position for each of the plurality of latent image carriers is performed every time a predetermined timing arrives. Furthermore, a rotational speed detecting means such as an FG signal generator for detecting the rotational speed of the drive motor is provided, and when a predetermined condition is satisfied, the rotational speed detecting means is substituted for the belt constant speed control. When the belt member is driven by motor constant speed control for rotating the drive motor at a predetermined target rotational speed based on the detection result by the above-mentioned, the predetermined condition is satisfied. Regardless of whether the belt member is driven by the belt constant speed control and the motor constant speed control is performed, predetermined data stored in a data storage means such as a flash memory is used. The control means such as the control device 200 is configured to temporarily correct the latent image writing position after the correction by the writing position correction process based on . In this configuration, as described above, when the motor constant speed control is performed, the latent image writing position with respect to the latent image carrier is temporarily corrected based on the data stored in advance in the data storage unit. As a result, the increase in deviation in toner image superposition caused by moving the belt member at a linear velocity deviating from the target belt velocity due to the deviation of the diameter of the driving rotator from the design value is reduced. Therefore, it is possible to suppress the deterioration of color misregistration caused by switching the belt member drive control method from belt constant speed control to motor constant speed control.

[Aspect B]
In the aspect B, similarly to the printer according to the embodiment, the control unit uses the data storage unit as the predetermined data to store data on the amount of increase in deviation of the toner images of each color that occurs when the motor constant speed control is performed. In the writing position correction process, the latent image writing position is corrected by correcting the latent image writing start timing for the plurality of latent image carriers, and each color included in the color misregistration detection image is corrected. Based on the timing at which the toner image is detected by the toner image detecting means and the corrected latent image writing start timing, the overlay deviation amount that remains even if the latent image writing start timing is corrected for each color toner image Is stored in the data storage means as a residual deviation amount, and is a temporary correction amount of the latent image writing start timing based on the deviation increase amount and the residual deviation amount. By calculating a timing temporary correction amount (for example, writing temporary correction data) and performing the motor constant speed control, the latent image writing start timing is temporarily corrected based on the timing temporary correction amount. The latent image writing position is temporarily corrected. In such a configuration, even when the residual deviation amount changes with time due to a temperature change or the like in the optical scanning system, the virtual overlay deviation amount corresponding to the changed residual deviation amount can be accurately obtained. The method for correcting the latent image writing position includes a method for individually adjusting the angle of the optical mirror in the optical writing unit 7 for each color, in addition to a method for correcting the latent image writing start timing. When this method is employed, the latent image writing position for each color can be freely adjusted individually, so that the residual deviation amount can be made zero by the writing position correction process. However, the cost increases because a mechanism for individually adjusting the angle of the optical mirror is provided.

[Aspect C]
In the aspect C, as in the printer according to the embodiment, an exchange detection unit that detects the exchange of the drive rotator such as the drive roller 12 is provided, and the data is updated according to the diameter of the drive rotator after the exchange. A data updating means is provided. In such a configuration, even if the drive rotator is replaced, the latent image writing position of each color when performing constant motor speed control can be appropriately and temporarily corrected in accordance with the diameter of the drive rotator after replacement. . As in the printer according to the embodiment, when the color shift increase amount for each color when the motor constant speed control is performed is selected and used according to the in-machine temperature, the temperature and the shift increase amount The data indicating the relationship is updated to the data corresponding to the drive roller 12 after replacement.

[Aspect D]
In the aspect D, similarly to the printer according to the embodiment, the apparatus includes temperature detecting means for detecting the temperature inside the machine such as a temperature sensor, and the control means uses the machine temperature and the deviation increasing amount as the deviation increasing amount data. Is stored in the data storage means, and when the motor constant speed control is performed, the increase amount corresponding to the in-machine temperature based on the detection result by the temperature detection means and the data. The process which asks for is implemented. In such a configuration, even if the diameter of the drive rotator varies due to fluctuations in the in-machine temperature, the latent image writing position can be temporarily corrected appropriately according to the changed diameter.

[Aspect E]
In the aspect E, similarly to the printer according to the embodiment, the control unit sets the latent image writing start timing based on the remaining shift amount and the shift increase amount when the writing position correction process is performed. An amount of misalignment (for example, a virtual overlay error) of each color toner image that occurs when it is assumed that the correction is not temporarily performed is calculated, and the latent image document among a plurality of latent image carriers is calculated based on the calculation result. The latent image writing start timing is temporarily corrected only for the latent image carrier that is determined to require temporary correction of the loading start timing. In such a configuration, as described with the printer according to the embodiment as an example, color misregistration when performing constant motor speed control is compared to a case where the latent image writing start timing is uniformly corrected for all colors. The amount can be reduced.

1Y, C, M, K: photoconductor (latent image carrier)
6Y, C, M, K: Process unit (part of image forming means)
7: Optical writing unit (part of image forming means)
8: Intermediate transfer belt (belt member)
12: Drive roller (drive rotator)
15: Transfer unit (transfer means)
136: Optical sensor unit (toner image detection means)
162: Shared drive motor (drive motor)
171: Roller encoder (belt speed detection means)
200: Control device (control means)

JP2008-139139614 JP 2004-205717 A

Claims (5)

Image forming means for developing latent images written on a plurality of latent image carriers with different color toners, and the surface of an endless belt member that is moved endlessly or a recording sheet held on the surface Transfer means for transferring toner images on the plurality of latent image carriers in a superimposed manner to obtain a multicolor image, and rotating the belt member while rotating the belt member around a part of its peripheral surface. A drive rotator that moves the belt member endlessly, a drive motor that is a drive source of the drive rotator, a control unit that controls the drive of the image forming unit, the transfer unit, and the drive motor. Based on the result of detecting the moving speed of the belt member by the belt speed detecting means, the means controls the driving speed of the driving motor so as to move the belt member endlessly at the target belt speed. The plurality of latent image carriers are controlled based on the timing at which the toner image detecting means detects the toner images of the respective colors included in the color misregistration detection image formed on the surface of the belt member. In the image forming apparatus that performs a writing position correction process for individually correcting the latent image writing position for each time a predetermined timing comes,
While providing a rotational speed detection means for detecting the rotational speed of the drive motor,
When predetermined conditions are satisfied, instead of the belt constant speed control, the belt member is controlled by motor constant speed control for rotating the drive motor at a predetermined target rotational speed based on a detection result by the rotational speed detecting means. And a process of driving the belt member with the belt constant speed control regardless of whether or not the predetermined condition is satisfied. When the motor constant speed control is performed, a process of temporarily correcting the latent image writing position after the correction by the writing position correction process based on predetermined data stored in the data storage means. An image forming apparatus characterized in that the control means is configured to be implemented. The image forming apparatus according to claim 1,
The control means stores, as the predetermined data, data on the amount of increase in overlay error of each color toner image generated when the motor constant speed control is performed in the data storage means, and the writing position correction In the processing, the latent image writing position is corrected by correcting the latent image writing start timing for a plurality of latent image carriers, and the toner image of each color included in the color misregistration detection image is detected by the toner image detecting means. Based on the timing and the latent image writing start timing after correction, the overlay error amount that remains even if the latent image writing start timing is corrected for each color toner image is stored in the data storage means as a residual deviation amount. And storing a temporary timing correction amount, which is a temporary correction amount of the latent image writing start timing, based on the increase amount and the residual deviation amount; When performing constant speed control, the latent image writing position is temporarily corrected by temporarily correcting the latent image writing start timing based on the timing temporary correction amount. An image forming apparatus. The image forming apparatus according to claim 2.
While providing an exchange detection means for detecting the exchange of the drive rotor,
An image forming apparatus, comprising: a data updating unit configured to update the data according to the diameter of the drive rotating body after the exchange. The image forming apparatus according to claim 2 or 3,
Equipped with temperature detection means to detect the temperature inside the machine,
In addition, the control means stores, as the increase amount data, data representing the relationship between the in-machine temperature and the increase amount in the data storage means, and when the motor constant speed control is performed, An image forming apparatus characterized in that a process for obtaining the increase amount corresponding to an in-machine temperature is performed based on a detection result by a detection unit and the data. The image forming apparatus according to claim 2,
Each color toner image generated when it is assumed that the control unit does not temporarily correct the latent image writing start timing based on the residual shift amount and the increase amount when the writing position correction process is performed. Only for the latent image carrier determined to require temporary correction of the latent image writing start timing among the plurality of latent image carriers, based on the calculation result. An image forming apparatus for temporarily correcting the latent image writing start timing.

Images