JP2018010112A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that, when a photoreceptor or an intermediate transfer body is replaced, stably controls the drive thereof without the occurrence of image defects.SOLUTION: An image forming apparatus 100 comprises: photoreceptor drums 10; drum driving motors that drive to rotate the photoreceptor drums 10; an intermediate transfer body 24; and an intermediate transfer body driving motor that drives to rotate the intermediate transfer body 24. When any one of the photoreceptors 10 and intermediate transfer body 24 is replaced, the image forming apparatus 100 changes a target speed of the photoreceptor drums 10 according to the immediately previous target speed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus.

  An electrophotographic image forming apparatus includes a photoreceptor, a charger, an exposure device, a developing device, an intermediate transfer member, a fixing device, and the like for image formation. The exposure device scans the photoconductor with a laser beam to form an electrostatic latent image on the photoconductor. The direction in which the exposure device scans the photosensitive member with laser light is called the main scanning direction. The developing device develops the electrostatic latent image formed on the photoconductor to form a toner image on the photoconductor. The intermediate transfer member is transferred with a toner image formed on the photosensitive member. The toner image transferred to the intermediate transfer member is transferred to the sheet. The fixing device fixes the toner image transferred to the sheet. In this way, the image forming apparatus forms an image on the sheet.

  The photosensitive member and the intermediate transfer member are rotated at a constant speed in order to maintain the image expansion and contraction and finally the image quality of the image formed on the sheet. The tandem image forming apparatus includes a photoreceptor corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black). In this case, fluctuations in the rotation speed of each photoconductor cause a deviation from the original image forming position and transfer position. Variation in the rotation speed of the intermediate transfer member causes a shift in the transfer position of the image from each photoconductor. In these cases, the images of the respective colors are formed on the sheet by deviating from the original positions. This is a so-called color shift. Color misregistration causes image quality degradation.

  A driving device for rotating the photosensitive member and the intermediate transfer member at a constant speed uses a brushless DC motor, and is often subjected to PLL control. The drive device uses a gear for a drive system between the drive motor, the photoconductor, and the intermediate transfer body in order to drive the photoconductor and the intermediate transfer body at low speed and high torque. Even when the drive motor is controlled at a constant speed due to the influence of the drive system such as the eccentricity of the gear, the rotational speed of the photosensitive member or the intermediate transfer member may not be constant. For this purpose, the driving device detects the rotational speed of the rotating shaft of the driving roller that drives the drum shaft of the photosensitive member and the intermediate transfer member so that the speed of the drum shaft and the rotating shaft becomes constant according to the detection result. Feedback controlled. The drum axis and the rotation axis are called load axes. However, even in the case of constant speed control of the load shaft, it is difficult to make the surface speed of the photosensitive member constant due to, for example, tolerance of the drum diameter of the photosensitive member. In the case of an intermediate transfer member, it is difficult to make the surface speed of the intermediate transfer member constant due to the driving roller diameter and the thickness tolerance of the intermediate transfer member.

  When the surface speeds of the photoconductor and the intermediate transfer body (hereinafter referred to as “surface speed”) coincide, the fine line reproducibility of the image becomes high. However, the central portion of the image is not transferred, and so-called hollowing occurs. The void is reduced by providing a speed difference in the surface speed. The speed difference is set to such an extent that the magnitude relationship does not change due to the eccentricity of the photoconductor and the driving roller and the tolerance of roundness. However, an increase in the surface speed difference between the photosensitive member and the intermediate transfer member affects the image quality. The speed difference is increased, for example, when the frictional force at the contact portion between the photosensitive member and the intermediate transfer member acts as a disturbance. In addition, an increase in the frictional force at the contact portion causes a load that exceeds the rated torque to the drive motor with a higher speed and causes control divergence of the drive motor with a lower speed.

  Therefore, the surface speeds of the photosensitive member and the intermediate transfer member are set to such a speed that the speed difference is as small as possible and the magnitude relationship is not interchanged. The image forming apparatus disclosed in Patent Document 1 detects a load applied to the intermediate transfer member while changing the surface speed of the photosensitive member, and achieves an optimum speed difference based on the relationship between the surface speed of the intermediate transfer member and the load of the photosensitive member. The intermediate transfer member is rotationally driven at a speed. The image forming apparatus disclosed in Patent Document 2 controls the drive motor of one of the photoconductor and the intermediate transfer body so that the load torque of the drive motor that drives the photoconductor and the intermediate transfer body becomes an appropriate value. The difference in surface speed between the toner and the intermediate transfer member is adjusted. As a result, the image forming apparatus avoids control failure.

JP 2012-32515 A JP 2011-118167 A

  The photosensitive member and the intermediate transfer member are consumable parts that need to be replaced periodically. If the target surface speed of the photoconductor and intermediate transfer body is changed while changing from the standard target speed, the difference in surface speed between the photoconductor and the intermediate transfer body will exceed the allowable range due to component tolerances. There is. When the surface speed difference exceeds the allowable range, the relationship between the surface speeds of the photosensitive member and the intermediate transfer member is switched, resulting in image defects and control failure.

  Further, the continuous change in the frictional force between the photosensitive member and the intermediate transfer member largely depends on the change in the surface properties of the photosensitive member and the intermediate transfer member. The frictional force is small at the initial stage of use of the photosensitive member and the intermediate transfer member, but the surface is not rough, but the surface becomes rough and increases with time. For this reason, even when the speed difference between the surface speeds is large at the initial stage of use of the photosensitive member and the intermediate transfer member, image defects and control failures are unlikely to occur, and image defects and control failures are likely to occur due to aging.

  If the target speed of the surface speed of one of the photosensitive member and the intermediate transfer member is changed as in the prior art, color misregistration and magnification change occur when parts are replaced. For this reason, control is required to correct the target speed of the surface speed even immediately after replacement, resulting in downtime. The downtime decreases as the number of changes in the target speed decreases.

  The present invention has been made in view of the above problems, and provides an image forming apparatus that stably controls driving without causing image defects when replacing a rotating image carrier such as a photosensitive member or an intermediate transfer member. The purpose is to do.

  The image forming apparatus of the present invention has a replaceable photoconductor and a developer carrying member that carries a developer and rotates, and an image is formed on the photoconductor using the developer carried on the developer carrying member. The image formed on the photoconductor in the nip portion between the photoconductor and the intermediate transfer body. Transfer means for transferring to the intermediate transfer member, a second motor for rotating the intermediate transfer member, and a first drive for controlling the torque of the first motor so that the rotational speed of the photosensitive member becomes a first target speed. Control means, second drive control means for controlling the torque of the second motor so that the rotational speed of the intermediate transfer member becomes a second target speed slower than the first target speed, and the torque of the first motor. Get hand to get the value to change according to The first drive control means causes the first motor to rotate the photosensitive member, the second drive control means causes the second motor to rotate the intermediate transfer member, and the developer carrier rotates. In one period, the acquisition means acquires a first value that changes according to the torque of the first motor, the first drive control means causes the first motor to rotate the photosensitive member, and the second drive control. Means for causing the second motor to rotate the intermediate transfer member, and obtaining a second value that changes according to the torque of the first motor in the obtaining means in a second period in which the developer carrying member stops rotating. And correcting means for correcting the first target speed based on the first value and the second value, and the first motor after the photoconductor is replaced with another photoconductor. Until the other photoconductor rotates. The standard speed is faster than the corrected first target speed corresponding to the photoconductor before replacement based on the corrected first target speed corresponding to the photoconductor before replacement. It is characterized by being changed.

  According to the present invention, even when the photosensitive member or the intermediate transfer member is replaced, the photosensitive member or the intermediate transfer member can be rotationally driven at an appropriate surface speed without causing a control failure or an image defect.

1 is a configuration diagram of an image forming apparatus. Explanatory drawing of a development process. Explanatory drawing of a development process. The block diagram of a control system. FIG. Explanatory drawing of a drum drive part. FIG. 3 is an explanatory diagram of an intermediate transfer body driving unit. The figure showing the relationship between dynamic friction force and speed difference. The flowchart showing the adjustment process of surface speed. (A), (b) is explanatory drawing of the change of the load torque according to the number of paper passing.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

(Image forming device)
FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus 100 forms an image by electrophotography. The image forming apparatus 100 includes image forming units 1200Y, 1200M, 1200C, and 1200K that form images corresponding to colors of Y (yellow), M (magenta), C (cyan), and K (black). The image forming units 1200Y, 1200M, 1200C, and 1200K are tandem systems arranged on the intermediate transfer member 24. Corresponding to the image forming units 1200Y, 1200M, 1200C, and 1200K, primary transfer rollers 23Y, 23M, 23C, and 23K are provided at positions facing each other with the intermediate transfer member 24 therebetween. An image detection sensor 1004 that detects a toner image formed on the intermediate transfer body 24 is disposed in the vicinity of the intermediate transfer body 24. The image forming apparatus 100 includes a secondary transfer roller 29 and a fixing device 25. In the following description, Y, M, C, and K at the end of the code represent the colors of the images to be formed, and are not added when it is not necessary to distinguish the colors.

  Each color image forming unit 1200 has the same configuration, and includes a photosensitive drum 10, a charger 21, an exposure unit 22, a developing unit 1, and a drum cleaner 26. The photosensitive drum 10K of the image forming unit 1200K that forms a black image is also used when forming a monochrome image in addition to a full-color image. Therefore, in consideration of the product life, the photosensitive drums 10Y, 10M, The drum diameter is formed larger than 10C.

  The photosensitive drum 10 is a drum-shaped replaceable photosensitive member, and is a rotating body that rotates around a drum shaft. The charger 21 uniformly charges the surface of the photosensitive drum 10. The exposure device 22 forms an electrostatic latent image by irradiating the charged surface of the photosensitive drum 10 with laser light modulated based on image data. The developing device 1 develops the electrostatic latent image to form a toner image on the surface of the photosensitive drum 10. The developing device 1Y forms a yellow toner image on the photosensitive drum 10Y with a yellow developer. The developing device 1M forms a magenta toner image on the photosensitive drum 10M with a magenta developer. The developing device 1C forms a cyan toner image on the photosensitive drum 10C with a cyan developer. The developing device 1K forms a black toner image on the photosensitive drum 10K with a black developer.

  The developing device 1 contains a two-component developer containing non-magnetic toner and a low magnetization high resistance carrier. The non-magnetic toner is constituted by using an appropriate amount of a binder resin such as a styrene resin or a polyester resin, a colorant such as carbon black, a dye or a pigment, a release agent such as wax, a charge control agent, or the like. The toner can be produced by a conventional method such as a pulverization method or a polymerization method. The toner is triboelectrically charged negatively with the carrier in the developing device 1. The charged toner adheres to the electrostatic latent image on the photosensitive drum 10 by applying a developing bias potential. As a result, the electrostatic latent image is developed. The developing device 1 is supplied with toner from a toner supply tank 20.

  The toner image formed on the photosensitive drum 10 is transferred to the intermediate transfer member 24 by the primary transfer roller 23. The toner remaining on the photosensitive drum 10 after the transfer is removed by the drum cleaner 26. The intermediate transfer member 24 is a replaceable image carrier formed of an endless belt member, and rotates clockwise in FIG. By rotating the intermediate transfer member 24, the toner images are transferred in the order of the photosensitive drum 10Y, the photosensitive drum 10M, the photosensitive drum 10C, and the photosensitive drum 10K. The intermediate transfer member 24 conveys the transferred toner image to the secondary transfer roller 29 by rotation. The toner image formed on the intermediate transfer member 24 is transferred to the sheet 30 by the secondary transfer roller 29. The toner remaining on the intermediate transfer body 24 after the transfer is removed by the transfer body cleaner 28. The sheet 30 is conveyed to the fixing device 25 by the secondary transfer roller 29 after the toner image is transferred. The fixing device 25 fixes the toner image on the sheet 30. The sheet 30 on which image formation has been completed in this manner is discharged from the fixing device 25 to the outside of the image forming apparatus 100.

(Development processing)
2 and 3 are explanatory diagrams of the developing process by the developing device 1. FIG. The surface of the photosensitive drum 10 is charged to a negative potential Vd by the charger 21. The potential (exposure portion potential) VL of the portion of the photosensitive drum 10 where the electrostatic latent image is formed is neutralized from the potential Vd to 0 [V] side by laser light irradiation. The potential Vd is, for example, −700 [V], and the exposure part potential VL is, for example, −200 [V].

  The developing device 1 conveys the developer containing the negatively charged toner contained therein to the vicinity of the photosensitive drum 10 by the developer carrier 8. The development bias potential Vdc applied to the developer carrier 8 during development is a potential between the potential Vd and the exposure portion potential VL, and is, for example, −550 [V]. The negatively charged toner on the developer carrying member 8 is a portion of the exposure portion potential VL that is relatively closer to the positive potential than the surface potential Vd of the photosensitive drum 10 and the development bias potential Vdc due to the negative development bias potential Vdc. To fly to. As a result, an amount of toner corresponding to the development latent image potential Vcont, which is the difference between the development bias potential Vdc and the exposure portion potential VL, adheres to the photosensitive drum 10. The density of the toner image is determined according to the amount of toner adhering to the photosensitive drum 10. For this purpose, the image density is adjusted by adjusting the development latent image potential Vcont. The negative toner flying on the photosensitive drum 10 is transferred to the intermediate transfer member 24 by the pressure and electric field between the primary transfer roller 23 and the intermediate transfer member 24. At this time, a primary transfer bias potential Vtr 1 having a polarity opposite to that of the toner is applied to the primary transfer roller 23. For example, the primary transfer bias potential Vtr1 is +1500 [V].

(Control system)
FIG. 4 is a configuration diagram of a control system of the image forming apparatus 100 having such a configuration. The control system is built in the image forming apparatus 100. The image forming apparatus 100 performs image forming processing by controlling the operation of each unit by a control system.

  The control system mainly controls the operation of the image forming apparatus 100 by the controller 1001. The controller 1001 includes a CPU (Central Processing unit) 1000 as a main control unit. The CPU 1000 reads out and executes a computer program from a memory (not shown) to control the operation of each unit. The controller 1001 includes a speed setting controller 1002, a color registration controller 1003, an image forming controller 1100Y, 1100M, 1100C, 1100K, and output torque detectors 45Y, 45M, 45C, 45K, 45B. The controller 1001 is connected to the image detection sensor 1004, the image forming units 1200Y to 1200K, and the speed control units 1300Y to 1300K and 1400. The speed controllers 1300Y to 1300K are connected to the drum drive motors 41Y to 41K. The speed controller 1400 is connected to the intermediate transfer member drive motor 42.

  The color registration controller 1003 controls the operation of the image detection sensor 1004 according to the control of the CPU 1000, and performs color registration adjustment processing described later according to the detection result of the image detection sensor 1004. The speed setting controller 1002 adjusts the surface speed, which is the rotational speed of the surfaces of the photosensitive drums 10Y to 10K and the intermediate transfer body 24, under the control of the CPU 1000.

  The image forming controller 1100Y controls the operation of the image forming unit 1200Y in accordance with the control of the CPU 1000. The image forming controller 1100M controls the operation of the image forming unit 1200M in accordance with the control of the CPU 1000. The image forming controller 1100C controls the operation of the image forming unit 1200C in accordance with the control of the CPU 1000. The image forming controller 1100K controls the operation of the image forming unit 1200K in accordance with the control of the CPU 1000.

  The speed control unit 1300Y is a drive control unit that controls the operation of the drum drive motor 41Y in accordance with the control of the speed setting controller 1002. The drum drive motor 41Y rotates the photosensitive drum 10Y. The speed control unit 1300Y inputs a PWM (Pulse Width Modulation) signal representing the load torque of the drum drive motor 41Y to the output torque detection unit 45Y. The output torque detector 45Y transmits a PWM signal to the speed setting controller 1002. The speed controller 1300Y controls the load torque of the drum drive motor 41Y so that the photosensitive drum 10Y rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

  The speed control unit 1300M is a drive control unit that controls the operation of the drum drive motor 41M in accordance with the control of the speed setting controller 1002. The drum drive motor 41M rotates the photosensitive drum 10M. The speed controller 1300M inputs a PWM signal representing the load torque of the drum drive motor 41M to the output torque detector 45M. The output torque detection unit 45M transmits a PWM signal to the speed setting controller 1002. The speed control unit 1300M controls the load torque of the drum drive motor 41M so that the photosensitive drum 10M rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

  The speed control unit 1300C is a drive control unit that controls the operation of the drum drive motor 41C in accordance with the control of the speed setting controller 1002. The drum drive motor 41C rotates the photosensitive drum 10C. The speed controller 1300C inputs a PWM signal representing the load torque of the drum drive motor 41C to the output torque detector 45C. The output torque detector 45C transmits a PWM signal to the speed setting controller 1002. The speed controller 1300C controls the load torque of the drum drive motor 41C so that the photosensitive drum 10C rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

  The speed control unit 1300K is a drive control unit that controls the operation of the drum drive motor 41K in accordance with the control of the speed setting controller 1002. The drum drive motor 41K rotates the photosensitive drum 10K. The speed controller 1300K inputs a PWM signal representing the load torque of the drum drive motor 41K to the output torque detector 45K. The output torque detector 45K transmits the PWM signal to the speed setting controller 1002. The speed control unit 1300K controls the load torque of the drum drive motor 41K so that the photosensitive drum 10K rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

  The speed control unit 1400 is a drive control unit that controls the operation of the intermediate transfer body drive motor 42 according to the control of the speed setting controller 1002. The intermediate transfer body drive motor 42 drives the intermediate transfer body 24 to rotate. The speed controller 1400 inputs a PWM signal representing the load torque of the intermediate transfer body drive motor 42 to the output torque detector 45B. The output torque detection unit 45B transmits the PWM signal to the speed setting controller 1002. The speed controller 1400 controls the load torque of the intermediate transfer body drive motor 42 so that the intermediate transfer body 24 rotates at a predetermined speed (target speed) under the control of the speed setting controller 1002.

(Image formation processing)
When the image forming process is continuously performed on the two sheets 30, the image forming apparatus 100 performs the pre-rotation process, the image forming process, the sheet interval process, and the post-rotation process.

  The pre-rotation process is a process for bringing the drive units such as the drum drive motors 41Y to 41K and the intermediate transfer body drive motor 42 and the high voltage member such as the charger 21 into a stable operation state in order to perform image formation. . In the pre-rotation process, the photosensitive drum 10 and the intermediate transfer member 24 are driven. Since the photosensitive drum 10 and the intermediate transfer member 24 have a large inertia, it takes a predetermined time, for example, 500 milliseconds from the start of driving until reaching the target surface speed (target speed) and stably operating at a constant speed. is there. Details of driving of the photosensitive drum 10 and the intermediate transfer member 24 will be described later. After the photosensitive drum 10 and the intermediate transfer member 24 stably operate at a constant speed, a charging bias is applied to the charger 21. The primary transfer bias potential Vtr1 is applied according to the timing at which the charged portion on the photosensitive drum 10 passes the position of the primary transfer roller 23. The driving portion of the developer carrier 8 and the development bias potential Vdc may be set to a desired rotation speed and a desired potential before the electrostatic latent image formed on the photosensitive drum 10 approaches the developer carrier 8. That's fine. However, in order to prevent the deterioration of the developer, it is desirable that the drive unit of the developer carrier 8 and the development bias potential Vdc reach a desired rotation speed and a desired potential at the slowest possible timing.

  The image forming process is a process of forming a toner image on the photosensitive drum 10 and transferring it to the intermediate transfer member 24. In the image forming process, a laser beam is exposed from the exposure device 22 to the surface of the charged photosensitive drum 10 to form an electrostatic latent image. The developing device 1 visualizes the electrostatic latent image with toner. The primary transfer roller 23 transfers the toner image formed on the photosensitive drum 10 to the intermediate transfer member 24.

  The inter-sheet processing is processing in which each driving unit and high voltage member are operated without performing image forming processing in a minute gap formed between the first sheet and the second sheet.

  The post-rotation process represents a process of stopping each drive unit and the high voltage member. In the post-rotation processing, the photosensitive drum 10 and the intermediate transfer member 24 are stopped after the exposure device 22, the charger 21, the driving unit of the developer carrier 8, the developing bias potential Vdc, the primary transfer bias potential Vtr1, and the charging bias are stopped in this order. Stop rotating.

(Color resist adjustment processing)
The image forming apparatus 100 performs color resist adjustment processing for correcting the position where the toner image is formed on the photosensitive drum 10 by detecting the position of the test image formed on the intermediate transfer member 24 with the image detection sensor 1004. The color registration adjustment process is performed at a predetermined timing set by a user, when the image forming apparatus 100 is installed, after image formation on a predetermined number of sheets, or at a predetermined timing. The color registration adjustment process corrects the change in the toner image formation position over time due to the change in the position of the toner image due to manufacturing variations of the image forming apparatus 100 and the environmental change such as the temperature rise in the apparatus.

  When the start of the color registration adjustment process is instructed, the controller 1001 starts driving the intermediate transfer member 24 and starts the test image forming process. FIG. 5 is an exemplary view of a test image. The test images 702Y, 702M, 702C, and 702K of the respective colors are continuously formed at the detection position of the image detection sensor 1004 on the intermediate transfer body 24 along the rotation direction of the intermediate transfer body 24. The image detection sensor 1004 continuously detects the test images 702Y, 702M, 702C, and 702K according to the rotation of the intermediate transfer member 24.

  The color registration controller 1003 detects the relative positions of the test images 702Y, 702M, 702C, and 702K at the timing when the image detection sensor 1004 detects the test images 702Y, 702M, 702C, and 702K. When the test images 702Y, 702M, 702C, and 702K of the respective colors pass the detection position (two-dot chain line in FIG. 5) of the image detection sensor 1004, the interval between the test images 702Y, 702M, 702C, and 702K is calculated from the passage timing. Is done. For example, Lys and Lms in FIG. 5 represent the positions of the test images 702Y and 702M in the main scanning direction (direction orthogonal to the rotation direction of the intermediate transfer member 24), and the sizes of the test images 702Y and 702M of the respective colors are large and small. A relative positional relationship in the main scanning direction is calculated.

  In addition, Lym in FIG. 5 is a relative difference between the average values of the two passing portions of the test images 702Y and 702M. From Lym, the relative positional relationship of each patch in the sub-scanning direction (the rotation direction of the intermediate transfer member 24) is calculated. In this way, the relative positional relationship between the test images 702Y, 702M, 702C, and 702K of the respective colors is calculated.

  The test images 702Y, 702M, 702C, and 702K for each color as shown in FIG. 5 are taken as a set, and a plurality of test images 702Y, 702M, 702C, and 702K are formed, and the positional relationship is calculated. Various disturbances are applied to each set of test images, resulting in minute variations in image forming positions. By averaging the positional relationships calculated from a plurality of sets of test images, the positional relationships of the test images 702Y, 702M, 702C, and 702K can be accurately detected.

  The color registration controller 1003 repeats such a series of processes until a positional relationship is acquired from a set of a predetermined number of test images. When the acquisition of the predetermined number of positional relationships is completed, the color registration controller 1003 averages the relative positional shifts of the images of the respective colors by the test images 702Y, 702M, 702C, and 702K, and corrects the average positional shift. An adjustment value is calculated. The color registration controller 1003 adjusts the exposure timing of the laser beam by the exposure unit 22 based on the calculated color registration adjustment value.

(Rotational speed control of the photosensitive drum 10 and the intermediate transfer member 24)
FIG. 6 is an explanatory diagram of a drum driving unit that rotationally drives the photosensitive drum 10. The drum drive unit includes a motor gear 31, a first speed detection unit 32, a second speed detection unit 33, an encoder 34, and a drum drive gear 35, and is driven by the drum drive motor 41. The rotation speed of the drum drive motor 41 is controlled by the speed control unit 1300.

  The driving force is transmitted to the drum shaft 101 of the photosensitive drum 10 through the motor gear 31 and the drum driving gear 35 by the driving of the drum driving motor 41. As a result, the photosensitive drum 10 rotates. The encoder 34 is provided on the drum shaft 101. The first speed detection unit 32 and the second speed detection unit 33 monitor the rotation of the encoder 34. The first speed detection unit 32 and the second speed detection unit 33 count the rotation speed of the photosensitive drum 10 (drum shaft 101) as a pulse. The surface speed of the photosensitive drum 10 is represented by the rotational speed of the drum shaft 101 and the drum diameter of the photosensitive drum 10. The first speed detection unit 32 and the second speed detection unit 33 input the rotation speed of the drum shaft 101 to the speed control unit 1300 as first and second speed detection signals. The speed controller 1300 generates a PWM signal as a drive command in accordance with the first and second speed detection signals and inputs the PWM signal to the drum drive motor 41, so that the surface speed of the photosensitive drum 10 becomes constant at the target speed. Feedback control.

  The speed control unit 1300 also inputs the PWM signal to the output torque detection unit 45. The PWM signal represents the electric power necessary to drive the photosensitive drum 10 and is a signal related to the load torque of the drum drive motor 41. The load torque of the drum drive motor 41 represents the load torque of the photosensitive drum 10. Therefore, the PWM signal represents the load torque of the photosensitive drum 10. The target speed is set so that the surface speed of the photosensitive drum 10 is faster than the surface speed of the intermediate transfer member 24, for example, 0.15%.

  FIG. 7 is an explanatory diagram of an intermediate transfer body driving unit that rotationally drives the intermediate transfer body 24. The intermediate transfer body drive unit includes a motor gear 36, a first speed detection unit 37, a second speed detection unit 38, an encoder 39, an intermediate transfer body drive roller 40, and a drive gear 400, and is driven by the intermediate transfer body drive motor 42. The The rotation speed of the intermediate transfer body drive motor 42 is controlled by the speed control unit 1400.

  Driving force of the intermediate transfer body drive motor 42 is transmitted to the intermediate transfer body drive roller 40 via the motor gear 36 and the drive gear 400. The intermediate transfer member 24 is rotated by rotating the intermediate transfer member driving roller 40. The encoder 39 is provided on the intermediate transfer member driving roller 40. The first speed detector 37 and the second speed detector 38 monitor the rotation of the encoder 39. The first speed detector 37 and the second speed detector 38 count the rotation speed of the intermediate transfer body driving roller 40 as a pulse. The first speed detection unit 37 and the second speed detection unit 38 input the rotation speed of the intermediate transfer body driving roller 40 to the speed control unit 1400 as first and second speed detection signals. The speed control unit 1400 generates a PWM signal that is a drive command in accordance with the first and second speed detection signals and inputs the PWM signal to the intermediate transfer body drive motor 42, so that the rotation speed of the intermediate transfer body drive roller 40 becomes the target. Feedback control is performed so that the speed is constant. By controlling the rotation speed of the intermediate transfer member driving roller 40, the surface speed of the intermediate transfer member 24 is controlled.

  The speed controller 1400 also inputs the PWM signal to the output torque detector 45B. The PWM signal represents electric power necessary to drive the intermediate transfer member 24 and is a signal related to the load torque of the intermediate transfer member driving motor 42. The load torque of the intermediate transfer member drive motor 42 represents the load torque of the intermediate transfer member 24.

(Friction at the contact portion between the photosensitive drum 10 and the intermediate transfer member 24)
The developing device 1 supplies toner to the photosensitive drum 10 according to the rotation of the developer carrier 8 during development. Therefore, in order to minimize the toner consumption, it is required that the developer carrier 8 be rotated only for the minimum time necessary for image formation. Specifically, the developer carrier 8 starts rotating at the timing immediately before the image formation after the photosensitive drum 10 and the intermediate transfer body 24 rotate, and stops rotating immediately after the image formation is completed. Therefore, even when the photosensitive drum 10 and the intermediate transfer member 24 are rotating, when the developer carrying member 8 stops rotating, the developer is not supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer member 24. . As a result, the frictional force between the photosensitive drum 10 and the intermediate transfer member 24 increases. In this case, the load on the drum drive motor 41 that rotates the photosensitive drum 10 increases. Further, the load on the intermediate transfer body drive motor 42 that rotates the intermediate transfer body drive roller 40 increases. Even when the developer is not supplied to the nip portion between the photosensitive drum 10 and the intermediate transfer member 24, the drum drive motor 41 and the intermediate transfer member drive motor 42 perform feedback control. Therefore, the current value supplied to the drum drive motor 41 and the intermediate transfer body drive motor 42 increases. The photosensitive drum 10 and the intermediate transfer member 24 are rotated and the developer carrying member 8 is also rotated during the first period. The photosensitive drum 10 and the intermediate transfer member 24 are rotated and the developer carrying member 8 is stopped. Is the second period.

  As the speed difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 increases, the frictional force at the contact portion increases. The friction force between objects includes a static friction force and a dynamic friction force. The frictional force related to the speed difference is the dynamic frictional force. The dynamic friction force is constant without being influenced by the speed difference when the speed difference between the objects is large to some extent. However, the speed difference between the photosensitive drum 10 and the intermediate transfer member 24 is usually about 1% at the maximum. For this reason, the dynamic frictional force between the photosensitive drum 10 and the intermediate transfer member 24 changes under the influence of the speed difference. FIG. 8 is a diagram showing the relationship between the dynamic friction force and the speed difference between the surface speeds. In an apparatus such as the image forming apparatus 100 in which the speed difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 is small, the dynamic friction force increases as the speed difference increases.

(Speed adjustment processing of the photosensitive drum 10 and the intermediate transfer member 24)
FIG. 9 is a flowchart showing a process for adjusting the surface speed of the photosensitive drum 10. FIG. 10 is an explanatory diagram of changes in accordance with the number of sheets (number of sheets on which images have been formed) of PWM signals of the yellow photosensitive drum 10Y and the intermediate transfer member 24.

  When the controller 1001 obtains an instruction to start the image forming process, the controller 1001 starts the image forming process (S11). The controller 1001, which has received the instruction to start the image forming process, performs a pre-rotation process and starts driving each unit of the image forming apparatus 100 (S12). For example, the photosensitive drum 10 and the intermediate transfer member 24 start to rotate. At this time, the developer carrying member 8 has also started to be driven, and a small amount of toner is supplied to the photosensitive drum 10 regardless of the developing bias potential Vdc. As the toner adheres to the photosensitive drum 10 and reaches the intermediate transfer member 24, the frictional force at the contact portion between the photosensitive drum 10 and the intermediate transfer member 24 is reduced. The controller 1001 waits for the time from the start of driving of the developer carrier 8 until the toner reaches the intermediate transfer member 24 (S13). The controller 1001 acquires a PWM signal representing the load torque of the photosensitive drum 10 by the output torque detector 45 after the standby time has elapsed (S14).

  The controller 1001 performs an image forming process after acquiring the PWM signal. After the image forming process, the controller 1001 stops the developing device 1 and stops driving the developer carrier 8 (S15). The controller 1001 waits for a time until the photosensitive drum 10 conveys the toner to the contact portion with the intermediate transfer member 24 after the developer carrying member 8 is stopped (S16). The standby time in S13 and S16 is determined by the drum diameter of the photosensitive drum 10, the position of the developer carrier 8, and the surface speed of the photosensitive drum 10. In this embodiment, the standby time is 110 milliseconds for the color photosensitive drums 10Y, 10M, and 10C, and 290 milliseconds for the black photosensitive drum 10K. The controller 1001 acquires a PWM signal representing the load torque of the photosensitive drum 10 by the output torque detector 45 after the standby time has elapsed, and stores it in a predetermined memory (S17).

  The controller 1001 calculates the difference between the PWM signal acquired in the process of S14 and the PWM signal acquired in the process of S17, and stores it in the memory (S18). The difference between the PWM signals calculated here is the difference between the duty ratios of the PWM signals. The controller 1001 stops driving the photosensitive drum 10 and the intermediate transfer member 24 (S19). The controller 1001 determines whether or not the difference between the PWM signals exceeds a threshold value (S20). This threshold value is a value indicating whether or not the difference of the PW signal corresponds to the speed difference of the surface speed that is harmful to the image to be formed. That is, the controller 1001 determines whether or not the speed difference corresponding to the load torque generated by the speed difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 affects the image.

When the difference between the PWM signals exceeds the threshold (S20: Y), the controller 1001 determines that at least one surface of the photosensitive drum 10 and the intermediate transfer member 24 has changed over time. In this case, the controller 1001 changes the target speed of the surface speed of the photosensitive drum 10 (S21). When changing the target speed, the controller 1001 calculates the target speed of the new surface speed of the photosensitive drum 10 by the following formula using the average value of the differences of the PWM signals stored in the memory.
(Target speed for new surface speed)
= (Current surface speed-Gain * Average difference)

  The controller 1001 that has changed the target speed of the surface speed of the photosensitive drum 10 performs color registration adjustment processing (S22). By performing the color registration adjustment process, the image forming apparatus 100 can suppress the occurrence of color misregistration even when the target speed of the surface speed is individually changed on each photosensitive drum 10.

  After executing the color registration adjustment process or when the difference between the PWM signals does not exceed the threshold value (S20: N), the controller 1001 ends the image forming process (S23). The controller 1001 determines whether or not at least one of the photosensitive drum 10 and the intermediate transfer member 24 needs to be replaced (S24). When the replacement is not necessary (S24: N), the controller 1001 executes the next image forming process (S25). That is, the controller 1001 repeatedly executes the processes of S11 to S23 until at least one of the photosensitive drum 10 and the intermediate transfer member 24 needs to be replaced. Each time the image forming process is executed, the difference value of the PWM signal calculated in S18 is stored in the memory. In the present embodiment, the memory stores a maximum of 30 PWM signal difference values. When the controller 1001 calculates the difference value of the 31st and subsequent PWM signals, the controller 1001 updates the memory with the latest value as needed. The number of PWM signal difference values to be stored is used for calculation of a new target speed of the surface speed, and therefore does not need to be 30 as long as the number is sufficient to eliminate difference value measurement errors and noise.

  Through the above processing, the target speed of the surface speed of the photosensitive drum 10 is changed as needed, and the frictional force between the photosensitive drum 10 and the intermediate transfer member 24 can be reduced. FIG. 10A shows a change in the PWM signal of the photosensitive drum 10Y according to the number of sheets to be passed. The arrow in FIG. 10A represents the timing at which the target speed of the surface speed of the photosensitive drum 10Y is changed. The difference between the PWM signal when the toner is present at the contact portion between the photosensitive drum 10Y and the intermediate transfer member 24 and the PWM signal when the toner is not present is reduced every time the target speed of the surface speed is changed. FIG. 10B shows a change in the PWM signal of the intermediate transfer member 24 according to the number of sheets to be passed. The arrow in FIG. 10B represents the timing at which the target speed of the surface speed of the photosensitive drum 10Y is changed. It can be seen that by changing the target speed of the surface speed of the photosensitive drum 10Y, the frictional force is reduced and the influence on the load of the intermediate transfer member 24 is suppressed. In this way, by changing the target speed of the surface speed of the photosensitive drum 10, fluctuations in the load torque are suppressed, and a stable image forming operation can be realized.

  When replacing at least one of the photosensitive drum 10 and the intermediate transfer member 24 (S24: Y), the controller 1001 sets the target speed of the surface speed of the photosensitive drum 10 after replacement as follows. The photosensitive drum 10 always has variations in drum diameter during the manufacturing process. Control of manufacturing variations is limited. The variation in the drum diameter of the photosensitive drum 10 is a difference in surface speed of ± 0.1%. Similarly, the intermediate transfer member 24 also has a surface speed variation of ± 0.1% due to variations in the outer diameter of the intermediate transfer member driving roller 40, variations in the thickness of the intermediate transfer member 24, and the like. The initial value of the speed difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 is the difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 due to the influence of changes in the ambient temperature and the like. Set in consideration. In this embodiment, the controller 1001 sets the variation in surface speed due to the influence of environmental changes such as changes in the ambient environment temperature as ± 0.01%, and the initial difference in speed between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24. Set the value to 0.21%. By setting the initial value of the speed difference of the surface speed in this way, the relationship between the surface speeds (the surface speed of the photosensitive drum 10 is higher than that of the photosensitive drum 10 and the intermediate transfer member 24). ) Will not reverse. The initial target speed of the surface speed of the photosensitive drum 10 is set 0.21% faster than the surface speed of the intermediate transfer member 24, but is changed by the process of S21.

  When at least one of the photosensitive drum 10 and the intermediate transfer member 24 is replaced, the controller 1001 adds the target speed of the surface speed of the photosensitive drum 10 to the target speed before replacement by the conversion of the speed difference of manufacturing variation. The new target speed is changed (S26, S27). In this embodiment, since the conversion of the speed difference of the variation in manufacturing the photosensitive drum 10 and the conversion of the speed difference of the variation in manufacturing the intermediate transfer member 24 are ± 0.1%, a new target is set. The speed is a value obtained by adding 0.1% to the target speed before replacement. When the new speed difference when the controller 1001 is changed to a new target speed obtained by adding the converted part of the speed difference in manufacturing to the target speed before replacement is equal to or less than the initial value (S28: Y), Different processing is performed when the initial value is exceeded (S28: N).

In the case of less than the initial value The initial value of the speed difference is set so that the surface speed of the photosensitive drum 10 is 0.21% faster than the surface speed of the intermediate transfer member 24 as described above. The surface speed of the replaced photosensitive drum 10 is increased by 0.05% in terms of a speed difference due to manufacturing variations, and the surface speed of the intermediate transfer member 24 is 0. 0 in terms of speed differences due to manufacturing variations. Suppose it is 01% slower. In this case, the set value of the speed difference is 0.21%, but the actual speed difference of the surface speed is 0.27%.

  By the processing up to S24, the target speed of the surface speed of the photosensitive drum 10 is changed so that the speed difference of the actual surface speed is eliminated. As the secular change progresses, the target speed is set to a speed 0.26% slower than the initial value, and the speed difference set value is -0.05% (the surface speed of the photosensitive drum 10 is 0.05% on the set value). Is slow). The target speed is not necessarily 0.27% because the target speed must be set so that the surface speed of the photosensitive drum 10 is always increased for the speed variation (0.01%) due to the influence of changes in the ambient temperature, etc. The speed is 0.26% slower. If the photosensitive drum 10 is replaced in this state, the new target speed becomes a value obtained by adding 0.1% to the target speed before the replacement, and therefore the surface of the photosensitive drum 10 is set so that the set value of the speed difference becomes 0.05%. Just set the speed.

  As described above, the target speed of the surface speed of the photosensitive drum 10 is set as described above instead of taking over the value before the replacement. For this reason, the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 are not reversed. Since the change value of the speed corresponding to the variation of the parts not replaced is used as it is, the speed difference becomes large immediately before acquiring the 30 PWM signals after replacement, and an image defect occurs. It can be suppressed that the downtime is increased beyond the threshold.

When the initial value is exceeded The initial value of the speed difference is set to 0.21%, and the surface speed of the photosensitive drum 10 is 0.07% slower than the converted value of the speed difference due to manufacturing variations. It is assumed that the surface speed of the intermediate transfer member 24 is 0.06% faster in terms of speed difference due to manufacturing variations. In this case, the set value of the speed difference is 0.21%, but the speed difference of the actual surface speed is 0.08%.

  By the processing up to S24, the target speed of the surface speed of the photosensitive drum 10 is changed so that the speed difference of the actual surface speed is eliminated. As the secular change progresses, the target speed is set to a speed 0.07% slower than the initial value, and the set value of the speed difference becomes 0.14%. The target speed must be set so that the speed variation (0.01%) due to the influence of changes in the ambient environment temperature or the like always increases the surface speed of the photosensitive drum 10, so it is not 0.08%. 0.07% slower speed. When the photosensitive drum 10 is replaced in this state, the new target speed becomes a value obtained by adding 0.1% to the target speed before the replacement, and therefore the surface of the photosensitive drum 10 is set so that the set value of the speed difference becomes 0.24%. Just set the speed.

  However, as described above, if the set value of the speed difference is set to 0.21%, the relationship between the surface speeds is not reversed regardless of the photosensitive drum 10 and the intermediate transfer member 24. Therefore, here, the controller 1001 sets the setting value of the speed difference to 0.21%, which is the initial speed difference, instead of 0.24% (S29). By setting the speed difference between the surface speeds as described above, the speed difference becomes large immediately after replacement, resulting in image defects, and exceeding the threshold value, resulting in increased downtime. Can be suppressed.

  In the above description, an example in which the target speed of the surface speed of the photosensitive drum 10 is set has been described, but the target speed of the surface speed is also set in the intermediate transfer member 24 by the same processing. The speed setting controller 1002 of the controller 1001 rotates the photosensitive drum 10 and the intermediate transfer member 24 so that the surface speed becomes the target speed set in this way. The speed setting controller 1002 causes the speed control units 1300 and 1400 to rotate the drum drive motor 41 and the intermediate transfer body drive motor 42 at a rotation speed corresponding to the target speed.

  In order to execute the processing as described above, it is necessary to grasp the replacement status of the photosensitive drum 10 and the intermediate transfer member 24. Therefore, the image forming apparatus 100 includes a sensor for detecting the replacement status of the photosensitive drum 10 and the intermediate transfer member 24.

  In the image forming apparatus of the present embodiment as described above, even when the photosensitive drum 10 and the intermediate transfer member 24 are replaced, the speed difference between the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 is appropriately within a predetermined range. Thus, the target speed of the surface speed can be set. The image forming apparatus 100 can control the surface speeds of the photosensitive drum 10 and the intermediate transfer member 24 at a constant target speed. Therefore, it is possible to minimize downtime while suppressing the occurrence of image defects due to the difference in surface speed between the photosensitive drum 10 and the intermediate transfer member 24.

Claims (10)

An image forming means for forming an image on the photoconductor using the developer carried on the developer carrying body, and having a replaceable photoconductor and a developer carrying body carrying the developer and rotating;
A first motor for rotating the photosensitive member;
An exchangeable intermediate transfer member,
Transfer means for transferring the image formed on the photoconductor to the intermediate transfer body at a nip portion between the photoconductor and the intermediate transfer body;
A second motor for rotating the intermediate transfer member;
First drive control means for controlling the torque of the first motor so that the rotational speed of the photosensitive member becomes a first target speed;
Second drive control means for controlling the torque of the second motor so that the rotational speed of the intermediate transfer member becomes a second target speed that is slower than the first target speed;
Obtaining means for obtaining a value that changes in accordance with the torque of the first motor;
A first period in which the first drive control means causes the first motor to rotate the photosensitive member, the second drive control means causes the second motor to rotate the intermediate transfer member, and the developer carrier rotates. The acquisition means acquires a first value that changes according to the torque of the first motor, the first drive control means causes the first motor to rotate the photoreceptor, and the second drive control means Causing the second motor to rotate the intermediate transfer member, and causing the acquisition unit to acquire a second value that changes according to the torque of the first motor in a second period in which the developer carrier stops rotating; Correction means for correcting the first target speed based on the first value and the second value;
After the photoconductor is replaced with another photoconductor and before the first motor rotates the other photoconductor, the first target speed is corrected corresponding to the photoconductor before the replacement. Based on the first target speed, the speed is changed to a speed faster than the corrected first target speed corresponding to the photoconductor before replacement.
Image forming apparatus. An image forming means for forming an image on the photoconductor using the developer carried on the developer carrying body, and having a replaceable photoconductor and a developer carrying body carrying the developer and rotating;
A first motor for rotating the photosensitive member;
An exchangeable intermediate transfer member,
Transfer means for transferring the image formed on the photoconductor to the intermediate transfer body at a nip portion between the photoconductor and the intermediate transfer body;
A second motor for rotating the intermediate transfer member;
First drive control means for controlling the torque of the first motor so that the rotational speed of the photosensitive member becomes a first target speed;
Second drive control means for controlling the torque of the second motor so that the rotational speed of the intermediate transfer member becomes a second target speed that is slower than the first target speed;
Obtaining means for obtaining a value that changes in accordance with the torque of the first motor;
A first period in which the first drive control means causes the first motor to rotate the photosensitive member, the second drive control means causes the second motor to rotate the intermediate transfer member, and the developer carrier rotates. The acquisition means acquires a first value that changes according to the torque of the first motor, the first drive control means causes the first motor to rotate the photoreceptor, and the second drive control means Causing the second motor to rotate the intermediate transfer member, and causing the acquisition unit to acquire a second value that changes according to the torque of the first motor in a second period in which the developer carrier stops rotating; Correction means for correcting the first target speed based on the first value and the second value;
After the intermediate transfer member is replaced with another intermediate transfer member, the first target speed is corrected before the intermediate transfer member is replaced until the first motor rotates the photosensitive member. Based on the first target speed, the speed is changed to a speed faster than the corrected first target speed corresponding to the photoconductor before the intermediate transfer body is replaced.
Image forming apparatus. An image forming means for forming an image on the photoconductor using the developer carried on the developer carrying body, and having a replaceable photoconductor and a developer carrying body carrying the developer and rotating;
A first motor for rotating the photosensitive member;
An exchangeable intermediate transfer member,
Transfer means for transferring the image formed on the photoconductor to the intermediate transfer body at a nip portion between the photoconductor and the intermediate transfer body;
A second motor for rotating the intermediate transfer member;
First drive control means for controlling the torque of the first motor so that the rotational speed of the photosensitive member becomes a first target speed;
Second drive control means for controlling the torque of the second motor so that the rotational speed of the intermediate transfer member becomes a second target speed that is faster than the first target speed;
Obtaining means for obtaining a value that changes in accordance with the torque of the first motor;
A first period in which the first drive control means causes the first motor to rotate the photosensitive member, the second drive control means causes the second motor to rotate the intermediate transfer member, and the developer carrier rotates. The acquisition means acquires a first value that changes according to the torque of the first motor, the first drive control means causes the first motor to rotate the photoreceptor, and the second drive control means Causing the second motor to rotate the intermediate transfer member, and causing the acquisition unit to acquire a second value that changes according to the torque of the first motor in a second period in which the developer carrier stops rotating; Correction means for correcting the first target speed based on the first value and the second value;
After the photoconductor is replaced with another photoconductor and before the first motor rotates the other photoconductor, the first target speed is corrected corresponding to the photoconductor before the replacement. Based on the first target speed, the speed is changed to a speed slower than the corrected first target speed corresponding to the photoconductor before replacement.
Image forming apparatus. An image forming means for forming an image on the photoconductor using the developer carried on the developer carrying body, and having a replaceable photoconductor and a developer carrying body carrying the developer and rotating;
A first motor for rotating the photosensitive member;
An exchangeable intermediate transfer member,
Transfer means for transferring the image formed on the photoconductor to the intermediate transfer body at a nip portion between the photoconductor and the intermediate transfer body;
A second motor for rotating the intermediate transfer member;
First drive control means for controlling the torque of the first motor so that the rotational speed of the photosensitive member becomes a first target speed;
Second drive control means for controlling the torque of the second motor so that the rotational speed of the intermediate transfer member becomes a second target speed that is faster than the first target speed;
Obtaining means for obtaining a value that changes in accordance with the torque of the first motor;
A first period in which the first drive control means causes the first motor to rotate the photosensitive member, the second drive control means causes the second motor to rotate the intermediate transfer member, and the developer carrier rotates. The acquisition means acquires a first value that changes according to the torque of the first motor, the first drive control means causes the first motor to rotate the photoreceptor, and the second drive control means Causing the second motor to rotate the intermediate transfer member, and causing the acquisition unit to acquire a second value that changes according to the torque of the first motor in a second period in which the developer carrier stops rotating; Correction means for correcting the first target speed based on the first value and the second value;
After the intermediate transfer member is replaced with another intermediate transfer member, the first target speed is corrected before the intermediate transfer member is replaced until the first motor rotates the photosensitive member. Based on the first target speed, the speed is changed to a speed slower than the corrected first target speed corresponding to the photoconductor before the intermediate transfer body is replaced.
Image forming apparatus. The correction unit changes the first target speed in accordance with aging of the photosensitive member and the intermediate transfer member.
The image forming apparatus according to claim 1. The correction means sets the first target speed so that a speed difference between the first target speed and the second target speed is equal to or less than a predetermined value in accordance with aging of the photoconductor and the intermediate transfer body. It is characterized by changing to
The image forming apparatus according to claim 1. The correction means changes the first target speed in accordance with manufacturing variations of the replaced photoconductor or intermediate transfer body.
The image forming apparatus according to claim 1. The correction means adds a converted portion of a difference in speed in manufacturing of the replaced photoconductor or intermediate transfer body to the first target speed set before replacement, thereby obtaining a new first target speed. It is characterized by setting,
The image forming apparatus according to claim 7. The correction means uses the first target speed as it is if the speed difference between the first target speed and the second target speed changed by exchanging the photoconductor or the intermediate transfer body is not more than a predetermined value. The first target speed is newly set when the predetermined value is exceeded,
The image forming apparatus according to claim 1. It comprises a detecting means for detecting the replacement state of the photosensitive member and the intermediate transfer member,
The image forming apparatus according to claim 1.