Image forming apparatus and method for controlling rotation of intermediate transfer member

Abstract

To provide a configuration in which a cleaning blade removes residual substances on an intermediate transfer body, the residual substances being prevented more from engaging with the cleaning blade and making cleaning defective.SOLUTION: The number N of executing a forward-backward rotation switching operation of switching the intermediate transfer belt to a forward rotation from a backward rotation is set to be one when the driving torque (the belt driving torque Tr) of the intermediate transfer belt is at least 30 mN / m. The number N of executing the forward-backward rotation switching operation is increased to two when the belt driving torque Tr is in the range of 10-30 mN / m.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus that cleans residues on an intermediate transfer body such as an intermediate transfer belt with a cleaning blade after transferring an image formed on the intermediate transfer body to a sheet. [Background technology]

[0002] Image forming devices such as electrophotographic printers employ an intermediate transfer system in which, for example, images of toner of each color (Yellow, Magenta, Cyan, and K) are formed on separate photosensitive drums, and the Y to K color images formed on each photosensitive drum are superimposed on a rotating intermediate transfer belt for primary transfer, after which the images of each color superimposed on the intermediate transfer belt are secondary transferred onto a recording sheet.

[0003] When transferring an image on an intermediate transfer belt to a recording sheet, ideally, the entire image would be transferred to the sheet. However, in reality, some toner particles may not be transferred and remain on the intermediate transfer belt. Furthermore, paper dust may adhere to the intermediate transfer belt due to contact with the recording sheet. If such toner or paper dust remains on the intermediate transfer belt, it can interfere with subsequent image formation. Therefore, a cleaner is generally provided that scrapes off and removes the residue on the intermediate transfer belt with the tip of a cleaning blade.

[0004] As a configuration with a cleaning blade, Patent Document 1 discloses a configuration in which the intermediate transfer belt is periodically rotated (reversed) in the direction opposite to the forward rotation during normal image formation in order to prevent cleaning defects caused by paper dust or other residues getting caught and remaining trapped at the contact point between the tip of the cleaning blade and the intermediate transfer belt. It is stated that the reverse rotation of the intermediate transfer belt removes the residues caught at the tip of the cleaning blade. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-26380 Summary of the Invention [Problem to be solved by the invention]

[0006] A cleaning blade in contact with the surface of an intermediate transfer belt is prone to gradual deterioration over time, such as wear and creep deformation, even after it is new. As the wear and creep deformation increase, the coefficient of friction between the cleaning blade and the intermediate transfer belt and the contact force of the cleaning blade on the surface of the intermediate transfer belt gradually decrease.

[0007] The lower the friction coefficient and contact force, the less the cleaning blade can scrape off residues from the intermediate transfer belt, making it easier for residues such as paper dust to become trapped between the surface of the intermediate transfer belt and the tip of the cleaning blade.

[0008] In Patent Document 1, the intermediate transfer belt is reversed at regular intervals until the image forming unit reaches the end of its life, but the gradual deterioration of the cleaning blade is not taken into consideration. Therefore, when the cleaning blade is barely deteriorated and the amount of residue trapped at the contact point between the tip of the cleaning blade and the intermediate transfer belt is small, the residue can be removed by reversing the intermediate transfer belt. However, when the cleaning blade subsequently deteriorates and the amount of residue trapped increases, some of the large amount of residue that has been trapped is likely to remain trapped when the same reversal operation of the intermediate transfer belt is performed as when the deterioration is small.

[0009] If residue remains caught in the contact area between the tip of the cleaning blade and the intermediate transfer belt and new residue is caught in the area until the next time the intermediate transfer belt is reversed, the amount of residue may increase too much, resulting in poor cleaning.

[0010] The above-described problem is not limited to the intermediate transfer belt, but can occur in any configuration that includes an intermediate transfer member such as an intermediate transfer drum.

[0011] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus and a method for controlling the rotation of an intermediate transfer body that can more effectively prevent cleaning failures caused by residues getting caught in the contact area between the cleaning blade and the intermediate transfer body than conventional methods when residues on the intermediate transfer body are removed by a cleaning blade. [Means for solving the problem]

[0012] In order to achieve the above object, the image forming apparatus according to the present disclosure is an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in the forward direction to transfer an image formed on the intermediate transfer body to a sheet, and includes: a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a drive unit that performs forward and reverse rotation operations that include at least one switching operation of rotating the intermediate transfer body in the reverse direction and then in the forward direction to remove residue trapped between the intermediate transfer body and the cleaning blade; and a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward and reverse rotation operations to increase in accordance with a decrease in the drive torque of the intermediate transfer body due to deterioration of the cleaning blade. a storage unit that stores a driving torque of the cleaning blade or the intermediate transfer member when the cleaning blade or the intermediate transfer member is new; Equipped with The control unit estimates the current driving torque of the intermediate transfer member, which has decreased since the time when the intermediate transfer member was new, and increases the amount of reverse rotation when the difference between the driving torque when the intermediate transfer member was new and the estimated current driving torque exceeds a threshold value. It is characterized by:

[0013] The control unit may increase the number of times the switching operation is performed, thereby increasing the amount of reverse rotation of the intermediate transfer body.

[0015] The control unit The difference is If a threshold is exceeded, the number of switching operations may be increased.

[0016] Furthermore, if the driving torque of the intermediate transfer body increases after increasing the number of times of the switching operations, the control unit may reduce the number of times of the switching operations to be less than the increased number.

[0017] The control unit also reverses the rotation of the intermediate transfer body in one switching operation. Reversal By increasing the distance, the amount of reverse rotation of the intermediate transfer member may be increased.

[0019] The control unit The difference is If a threshold is exceeded, the reversal distance may be increased.

[0020] Here, if the driving torque of the intermediate transfer member increases after the reverse rotation distance is increased, the control unit may reduce the reverse rotation distance to a value less than the increased distance.

[0021] Also, According to another aspect of the present disclosure, there is provided an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer body to a sheet, the image forming apparatus including: a cleaning blade that contacts the intermediate transfer body to remove residues on the intermediate transfer body after transfer; a drive unit that performs a forward / reverse rotation operation that includes at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction to remove residues trapped between the intermediate transfer body and the cleaning blade; and a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse rotation operation to increase in accordance with a decrease in the drive torque of the intermediate transfer body due to deterioration of the cleaning blade. The control unit When the driving torque of the intermediate transfer body falls below a threshold, the number of times of the switching operation is increased, or the distance by which the intermediate transfer body is reversed in one switching operation is increased, thereby increasing the amount of reverse rotation of the intermediate transfer body; and When the driving torque of the intermediate transfer member falls below a second threshold value that is smaller than the threshold value, it is determined that one or both of the intermediate transfer member and the cleaning blade have reached the end of their lives. Characterized by .

[0022] According to yet another aspect of the present disclosure, there is provided an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer body to a sheet, the image forming apparatus including: a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a drive unit that performs a forward / reverse rotation operation that includes at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction to remove residue trapped between the intermediate transfer body and the cleaning blade; and a control unit that controls the amount of reverse rotation of the intermediate transfer body in the forward / reverse rotation operation to increase in accordance with a decrease in drive torque of the intermediate transfer body due to deterioration of the cleaning blade. The control unit controls the amount of reverse rotation of the intermediate transfer body by taking into account not only the reduction in the driving torque of the intermediate transfer body but also the surrounding environment of the image forming apparatus. Characterized by .

[0023] According to yet another aspect of the present disclosure, there is provided an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer body to a sheet, the image forming apparatus including: a cleaning blade that contacts the intermediate transfer body to remove residues on the intermediate transfer body after transfer; a drive unit that performs a forward / reverse rotation operation that includes at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction to remove residues trapped between the intermediate transfer body and the cleaning blade; and a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse rotation operation to increase in accordance with a decrease in the drive torque of the intermediate transfer body due to deterioration of the cleaning blade. A rotating member that rotates by receiving a driving force from the driving unit, separate from the intermediate transfer body and,the drive unit includes one drive source capable of rotating forward and backward, a first transmission path that transmits the drive force of the drive source to the intermediate transfer body, and a second transmission path that transmits the drive force to the rotating member, wherein a clutch that switches between transmitting and cutting off the drive force is not provided in each of the first transmission path and the second transmission path, a second backlash in the second transmission path is larger than a first backlash in the first transmission path, and the drive unit reverses the intermediate transfer body in the switching operation so that the amount of reverse rotation of the drive source is larger than the first backlash in the first transmission path and is equal to or smaller than the magnitude of the second backlash in the second transmission path. Characterized by .

[0024] Furthermore, a rotating member that rotates by receiving a driving force from the driving unit is provided separately from the intermediate transfer body, and the driving unit includes a driving source that can rotate forward and backward, a first transmission path that transmits the driving force of the driving source to the intermediate transfer body, a second transmission path that branches off from a branch point midway along the first transmission path and transmits the driving force of the driving source to the rotating member, and a torque detection unit interposed between the driving source and the branch point, and the control unit may estimate the driving torque of the intermediate transfer body from the detection result of the torque detection unit.

[0025] According to yet another aspect of the present disclosure, there is provided an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in the forward direction to transfer an image formed on the intermediate transfer body to a sheet, the image forming apparatus including: a cleaning blade that contacts the intermediate transfer body to remove residues on the intermediate transfer body after transfer; a drive unit that performs a forward / reverse operation including at least one switching operation of rotating the intermediate transfer body in the reverse direction and then in the forward direction to remove residues caught between the intermediate transfer body and the cleaning blade; and a drive unit that operates in response to a decrease in drive torque of the intermediate transfer body due to deterioration of the cleaning blade. and a control unit that controls the amount of reverse rotation of the intermediate transfer body to increase during the forward / reverse operation, and a rotating member that receives a driving force from the drive unit and rotates separately from the intermediate transfer body, the drive unit comprising: a drive source that is capable of rotating forward and reverse; a first transmission path that transmits the driving force of the drive source to the intermediate transfer body; a second transmission path that branches off from a branch point on the first transmission path and transmits the driving force of the drive source to the rotating member; and a torque detection unit that is interposed between the drive source and the branch point, and the control unit estimates the driving torque of the intermediate transfer body from a detection result of the torque detection unit; Each of the first transmission path and the second transmission path is not provided with a clutch that switches between transmitting and cutting off the driving force, and the second backlash in the second transmission path is larger than the first backlash in the first transmission path, and when the driving source switches from reverse rotation to forward rotation, the control unit estimates the driving torque of the intermediate transfer body from the result detected by the torque detection unit while the driving force in the forward rotation direction of the driving source is transmitted to the intermediate transfer body through the first transmission path to rotate the intermediate transfer body in the forward direction due to the absence of play in the first transmission path caused by the first backlash, and while the driving force in the forward rotation direction of the driving source is not transmitted to the rotating member through the second transmission path in a state where there is play due to the second backlash in the second transmission path. Characterized by .

[0026] Here, the torque detection unit may be a strain gauge, and the control unit may stop the driving source, which is rotating in the forward direction, before the second transmission path transitions from a state where there is play due to the second backlash to a state where there is no play, and may use the detection value of the strain gauge in the stopped state as the driving torque detected by the torque detection unit.

[0027] The image forming apparatus may also include a photosensitive body and a developing unit that develops an electrostatic latent image on the photosensitive body with a developer, the developing unit including a developer-carrying rotating body that carries the developer, and the rotating member may be one or both of the photosensitive body and the developer-carrying rotating body.

[0028] Furthermore, the drive unit may include a motor that applies a drive force to the intermediate transfer body, and the control unit may estimate a drive torque of the intermediate transfer body based on a current value flowing through the motor.

[0029] The image forming apparatus may also include a photosensitive body on which an image is formed, and a transfer unit that transfers the image formed on the intermediate transfer body to a sheet, wherein the transfer unit further has a primary transfer member that performs primary transfer of the image formed on the photosensitive body onto the intermediate transfer body that rotates forward, the primary transfer member being arranged on the opposite side of the photosensitive body with the intermediate transfer body in between and being capable of being brought into contact with and separated from the intermediate transfer body, and the control unit may bring the primary transfer member into contact with the intermediate transfer body during primary transfer, and separate the primary transfer member from the intermediate transfer body when estimating the driving torque of the intermediate transfer body.

[0030] Furthermore, a photoreceptor on which an image is formed and, and a transfer unit that transfers the image formed on the intermediate transfer body onto a sheet, the transfer unit having a primary transfer member that performs primary transfer of the image formed on the photosensitive body onto the forward rotating intermediate transfer body, and the control unit may apply a transfer bias to the primary transfer member during primary transfer, and cut off application of the transfer bias to the primary transfer member when estimating the driving torque of the intermediate transfer body.

[0031] The present disclosure also provides a method for controlling the rotation of an intermediate transfer body in an image forming apparatus that rotates an intermediate transfer body rotatable in forward and reverse directions in the forward direction, transfers an image formed on the intermediate transfer body to a sheet, and removes residues on the intermediate transfer body after transfer with a cleaning blade. The method includes a driving step of performing a forward / reverse operation in which a switching operation of rotating the intermediate transfer body in the reverse direction and then in the forward direction is performed at least once to remove residues caught between the intermediate transfer body and the cleaning blade, and a control step of controlling the amount of reverse rotation of the intermediate transfer body in the forward / reverse operation to increase in accordance with a decrease in the driving torque of the intermediate transfer body due to deterioration of the cleaning blade. The image forming apparatus includes a storage unit that stores a driving torque of the intermediate transfer body when the cleaning blade or the intermediate transfer body was new, and the control step estimates a current driving torque of the intermediate transfer body that has decreased since the cleaning blade or the intermediate transfer body was new, and when a difference between the driving torque when the cleaning blade or the intermediate transfer body was new and the estimated current driving torque exceeds a threshold value, the amount of reverse rotation is increased. It is characterized by: [Effects of the Invention]

[0032] By doing so, it is possible to prevent cleaning defects caused by residues getting caught in the contact area between the tip of the cleaning blade and the intermediate transfer body. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the outline of the configuration of a belt cleaning unit. [Figure 3] 10(a) to 10(c) are diagrams showing how residues caught in the tip of the cleaning blade are removed by the intermediate transfer belt rotating in the reverse direction and then in the forward direction. [Figure 4] FIG. 2 is a schematic perspective view showing the configuration of a driving force transmission mechanism that transmits the driving force of a driving motor. [Figure 5] FIG. 1(a) is a schematic diagram illustrating which teeth of each gear included in the driving force transmission mechanism are engaged when the drive motor is rotating in the forward direction, and FIG. 1(b) is a schematic diagram illustrating which teeth of each gear included in the driving force transmission mechanism are engaged when the drive motor switches from rotating in the forward direction to rotating in the reverse direction. [Figure 6]5. (a) to (c) are schematic diagrams separately from FIG. 5 for explaining how gears included in the driving force transmission mechanism mesh. [Figure 7] FIG. 2 is a block diagram showing the main configuration of a control unit. [Figure 8] FIG. 10 is a diagram showing an example of the contents of a belt driving torque table. [Figure 9] FIG. 10 is a diagram showing an example of the contents of a forward / reverse rotation switching count table. [Figure 10] FIG. 10 is a diagram showing an example of the contents of a motor forward / reverse rotation amount table. [Figure 11] FIG. 10 is a diagram showing the relationship between the belt driving torque and the likelihood of foreign matter getting caught in the cleaning blade. [Figure 12] FIG. 10 is a schematic diagram comparing two graphs showing how the number of trapped foreign objects changes when a forward / reverse rotation switching operation is performed once for each fixed number of printed sheets. [Figure 13] FIG. 10 is a diagram showing the transition of the number of trapped foreign objects when the number of forward / reverse rotation switches is increased when the belt driving torque is reduced. [Figure 14] 10A is a timing chart showing the forward and reverse rotation of the belt, and FIG. 10B is a diagram showing how the movement distance of the intermediate transfer belt 122 in the reverse and forward directions changes during the forward and reverse rotation of the belt. [Figure 15] FIG. 10 is a diagram illustrating an example of the relationship between the belt driving torque and the number of foreign objects caught per 10 printed sheets. [Figure 16] FIG. 10 is a diagram showing the relationship between the number of printed sheets and the number of trapped foreign matter particles. [Figure 17] FIG. 10 is a diagram showing how the number W of trapped foreign matter changes when the forward / reverse rotation of the belt is switched once every time image formation is performed on 50 sheets of paper. [Figure 18] 10 is a diagram showing the change in the number of trapped foreign objects when the forward / reverse rotation switching operation is repeated twice every time the number of printed sheets reaches 50 when the magnitude of the belt driving torque is 10. FIG. [Figure 19] FIG. 10 is a control flowchart showing a forward / reverse rotation operation of the belt. [Figure 20] FIG. 10 is a diagram illustrating an example of the transition in the number of trapped foreign objects when the magnitude of the belt driving torque is 10 and 5 and the forward / reverse rotation switching operation is repeated four times each time the number of printed sheets reaches 100. [Figure 21] FIG. 10 is a flowchart illustrating a belt driving torque estimation process. [Figure 22] 10A to 10C are schematic diagrams illustrating the meshing of the teeth of the gears included in the drive force transmission mechanism when the intermediate transfer belt switches from reverse rotation to forward rotation and the forward rotation continues. [Figure 23] FIG. 10 is a diagram showing an example of the contents of a forward / reverse rotation switching number table used to correct the forward / reverse rotation switching number. [Figure 24] 10 is a partial flowchart showing only a part of the flowchart of the forward / reverse rotation operation of the belt, taking into consideration the environment around the device. [Figure 25] 10 is a graph illustrating the relationship between the belt driving torque and the number of engagements in two image forming apparatuses having individual differences. FIG. [Figure 26] FIG. 10 is a diagram showing an example of the contents of a forward / reverse rotation switching count table according to a modified example. [Figure 27] 10 is a partial flowchart showing only a part of the flowchart of the forward / reverse rotation operation of the belt when a forward / reverse switching number table according to a modified example is used. [Figure 28] FIG. 10 is a diagram showing an example of the contents of a reverse rotation distance table according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, an embodiment of an image forming apparatus according to the present disclosure will be described with reference to the drawings.

[0035] [1] Overall configuration of image forming device FIG. 1 is a diagram showing the overall configuration of an image forming apparatus 100. As shown in FIG.

[0036] As shown in the figure, image forming device 100 is a so-called tandem color multifunction peripheral (MFP) that is capable of executing image reading jobs, print jobs, copy jobs, etc., and is equipped with an image reading unit 110, an image forming unit 120, a paper feed unit 130 that feeds paper (sheets) to image forming unit 120, an operation panel 140, and a control unit 150.

[0037] The image reading unit 110 executes an image reading job and includes an automatic document feeder (ADF) and a scanner device, both of which are not shown. The automatic document feeder feeds and transports documents one by one from a stack of documents placed on a document tray, while causing the scanner device to read the documents and generate image data.

[0038] The image forming unit 120 is an electrophotographic type and executes a copy job in which an image is formed based on image data generated by the image reading unit 110 and printed on paper, and a print job in which an image is formed based on image data received from an external device and printed on paper.

[0039] In this embodiment, image forming units 121Y, 121M, 121C, and 121K, intermediate transfer unit 121A, etc. are provided, and toner images of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are formed.

[0040] The image forming unit 121K includes a photosensitive drum 1 that rotates in the direction indicated by arrow A, and a charging unit 2, an exposure unit 3, a developing unit 4, a cleaning unit 6, and other components that are arranged around the photosensitive drum 1 along the drum rotation direction A, and forms a K toner image on the photosensitive drum 1. The other image forming units 121Y, 121M, and 121C are basically the same as the image forming unit 121K, and form toner images of the corresponding color (Y, M, or C). The developing unit 4 of each of the image forming units 121Y to 121K has a developing roller 4a that carries developer and is positioned opposite the photosensitive drum 1. The developing roller 4a rotates in the direction indicated by arrow B.

[0041] The intermediate transfer unit 121A is positioned above the image forming units 121Y to 121K, and includes an intermediate transfer belt 122, a drive roller 123, a driven roller 124, four primary transfer rollers 5 arranged opposite the photosensitive drums 1 of each of the image forming units 121Y to 121K via the intermediate transfer belt 122, and a belt cleaning unit 127 that scrapes off residual toner and the like on the intermediate transfer belt 122 with a cleaning blade 312.

[0042] The intermediate transfer belt 122 is stretched between a drive roller 123, a driven roller 124, and four primary transfer rollers 5, and during image formation, it runs in a direction indicated by arrow D (belt running direction) due to the rotational driving force of the drive roller 123.

[0043] Here, the intermediate transfer belt 122 can rotate between the direction indicated by arrow D and the opposite direction (broken arrow Da). When the intermediate transfer belt 122 runs in the direction indicated by arrow D, it is called forward rotation, and when it runs in the opposite direction, indicated by arrow Da, it is called reverse rotation. The reverse rotation of the intermediate transfer belt 122 is performed to remove residue such as paper dust that has become caught between the tip of the cleaning blade 312 and the surface of the intermediate transfer belt 122. Hereinafter, this state of residue being caught is referred to as residue getting caught in the tip of the cleaning blade 312.

[0044] In this embodiment, the amount of reverse rotation of the intermediate transfer belt 122 is variably controlled in accordance with the magnitude of the driving torque of the intermediate transfer belt 122, and residues such as paper dust caught in the tip of the cleaning blade 312 are removed before they become too large and the cleaning performance deteriorates, thereby maintaining the cleaning performance for a long period of time. This control will be described later.

[0045] A secondary transfer roller 125 is disposed at a position facing the drive roller 123 across the intermediate transfer belt 122 .

[0046] The paper feed unit 130 includes paper feed cassettes 131a and 131b, feed rollers 132a and 132b, a pair of paper feed rollers 133a and 133b, a pair of transport rollers 134b, a pair of timing rollers 146, and the like.

[0047] Each of the paper feed cassettes 131a and 131b stores recording sheets, in this case paper S. The feed rollers 132a and 132b feed the paper S stored in the corresponding paper feed cassette 131a or 131b one sheet at a time onto the transport path.

[0048] The paper feed roller pair 133a transports the paper S fed from the paper feed cassette 131a downstream in the transport direction. The paper feed roller pair 133b and the transport roller pair 134b transport the paper S fed from the paper feed cassette 131b downstream in the transport direction. The timing roller pair 146 determines the timing for sending the transported paper S to the secondary transfer position 129, which is the contact position between the secondary transfer roller 125 and the intermediate transfer belt 122.

[0049] The fixing unit 145 presses the fixing belt against a pressure roller to secure a fixing nip, and heats the fixing belt with a heater to maintain a temperature required for fixing.

[0050] The operation panel 140 is located on the front of the device in a position that is easy for the user to operate. The operation panel 140 is provided with keys and a touch panel 141 for receiving input of printing conditions such as the number of copies and density by the user. Various information is displayed on the touch panel 141. This displayed information includes a message display indicating that the intermediate transfer unit 121A, which will be described later, has reached the end of its life. Note that instead of or in addition to the message display, a configuration may be adopted in which a voice message to that effect is output.

[0051] During image formation such as a copy job or a print job, the control unit 150 generates drive signals for driving the laser diodes (not shown) arranged in the exposure units 3 of the imaging units 121Y to 121K from image data for the colors Y to K. The generated drive signals cause the exposure units 3 of the imaging units 121Y to 121K to emit laser beams, which expose and scan the photosensitive drum 1.

[0052] Before being subjected to this exposure scanning, each photosensitive drum 1 is uniformly charged by the charging unit 2, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 1 by exposure to the laser beam.

[0053] In each of the image forming units 121Y to 121K, the electrostatic latent image on the photosensitive drum 1 is developed by the developer carried on the developing roller 4a (developer-carrying rotary member) of the developing unit 4, thereby forming a toner image on the photosensitive drum 1. A transfer bias (transfer current or transfer voltage) is applied to each primary transfer roller 5, and the toner image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 122 by the electrostatic force acting between the photosensitive drum 1 and the corresponding primary transfer roller 5.

[0054] The image forming operation of each photosensitive drum 1 is performed with a staggered timing so that the Y to K color toner images are transferred and superimposed on the same position on the intermediate transfer belt 122. The Y to K color toner images formed on the intermediate transfer belt 122 move to a secondary transfer position 129 as the intermediate transfer belt 122 rotates in the forward direction.

[0055] In accordance with the timing of the image forming operation, paper S is fed from paper feed section 130 via a pair of timing rollers 146, and the paper S is transported while being sandwiched between secondary transfer roller 125 and intermediate transfer belt 122. The toner image on intermediate transfer belt 122 is secondarily transferred onto paper S all at once at secondary transfer position 129 due to the electrostatic force acting between secondary transfer roller 125 and intermediate transfer belt 122.

[0056] The paper S that has passed through the secondary transfer position 129 is transported to the fixing section 145, and as it passes through the fixing nip, the toner image is heated and pressurized to be fixed to the paper S. After that, the paper S is discharged outside the machine via a pair of discharge rollers 147 and stored on a paper discharge tray 148.

[0057] Of the toner image on the photosensitive drum 1, toner that has not been primarily transferred to the intermediate transfer belt 122 and remains on the photosensitive drum 1, and residues including paper dust adhering to the circumferential surface of the photosensitive drum 1 are removed by the drum cleaning unit 6.

[0058] In addition, the toner of the toner image on the intermediate transfer belt 122 that has not been secondarily transferred to the paper S and remains on the intermediate transfer belt 122, as well as residues including paper dust adhering to the surface of the intermediate transfer belt 122, are removed by the belt cleaning unit 127.

[0059] The belt cleaning unit 127 is located around the intermediate transfer belt 122, in the space between the secondary transfer position 129 in the forward direction of the intermediate transfer belt 122 (direction of arrow D) and the primary transfer position of the photosensitive drum 1 of the image creating unit 121Y, which is located at the most upstream side, i.e., the position where the photosensitive drum 1 of the image creating unit 121Y faces the primary transfer roller 5 via the intermediate transfer belt 122.

[0060] [2] Belt cleaning section configuration FIG. 2 is an enlarged cross-sectional view showing the outline of the configuration of the belt cleaning unit 127. As shown in FIG.

[0061] As shown in the figure, the belt cleaning unit 127 includes a housing 311 and a cleaning blade 312. The housing 311 has an opening 310 on the side facing the surface 126 of the intermediate transfer belt 122.

[0062] The cleaning blade 312 is attached to the housing 311. Specifically, a base end 331 of the cleaning blade 312 is attached to a fixed wall 319 extending obliquely upward from a bottom wall 318 of the housing 311 so that a tip end 330 of the cleaning blade 312 protrudes slightly from the opening 310 and abuts against the surface 126 of the intermediate transfer belt 122 in the counter direction, while applying a constant pressing force from the tip end 330 to the driven roller 124, which serves as a backup member, with the intermediate transfer belt 122 sandwiched between them.

[0063] The cleaning blade 312 is made of solid rubber such as urethane rubber and has a flat plate shape with a thickness of about 2 to 5 mm, but is not limited to this and may be made of other materials such as acrylonitrile butadiene rubber (NBR) or have a different shape or thickness. The length of the cleaning blade 312 in the belt width direction (corresponding to the axial direction of the driven roller 124) is approximately the same as or slightly longer than the length of the intermediate transfer belt 122 in the belt width direction.

[0064] When residue T, which includes residual toner, paper dust, lubricant contained in the developer, and the like on the surface 126 of the intermediate transfer belt 122, reaches the portion where the tip 330 of the cleaning blade 312 counter-abuts against the surface 126 of the intermediate transfer belt 122, the residue T is scraped off from the surface 126 of the intermediate transfer belt 122 by the cleaning blade 312. Note that instead of being attached to the fixed wall 319, the cleaning blade 312 may also be configured to press the tip 330 against the surface 126 of the intermediate transfer belt 122 by, for example, a spring (not shown).

[0065] A conveying screw 315 is provided in the inner space of the housing 311 to convey residue T that has been scraped off from the intermediate transfer belt 122 by the cleaning blade 312 and accumulated on the bottom wall 318 of the housing 311 in the belt width direction.

[0066] The residue T transported by the transport screw 315 is collected in a collection container (not shown) disposed outside the housing 311 through a discharge hole (not shown) in the side wall of the housing 311. This prevents the residue T from continuing to accumulate inside the housing 311.

[0067] In this way, most of the residue T on the intermediate transfer belt 122 is removed by the cleaning blade 312, but depending on the shape and size of the residue T, some of the residue T may become caught in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122.

[0068] 3(a) is a schematic diagram showing a state in which a residue (hereinafter referred to as "foreign matter I") is caught in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122. This caught foreign matter I becomes trapped in the tip of the cleaning blade.

[0069] If the number of foreign matter I trapped in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 increases, the contact between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 becomes uneven, and the scraping performance decreases.

[0070] In order to remove this foreign matter I, the intermediate transfer belt 122 is reversed. Specifically, due to the reverse rotation of the intermediate transfer belt 122, the foreign matter I that is caught in the contact portion between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 moves in the reverse direction (the direction indicated by the arrow Da) from this contact portion as shown in FIG. 3(b), and is no longer caught in the tip 330 of the cleaning blade 312.

[0071] 3(c), a forward / reverse rotation switching operation is performed in which the intermediate transfer belt 122 is rotated in the reverse direction and then switched to forward rotation (rotation in the direction indicated by arrow D), whereby foreign matter I coming out from the contact portion between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 is scraped off by the tip 330 of the cleaning blade 312 and stored inside the housing 311 (FIG. 2). This forward / reverse rotation switching operation is performed when no image formation is being performed (when no image formation is being performed).

[0072] Returning to Fig. 1, each of the photosensitive drums 1 of the image forming units 121Y to 121K and the drive roller 123 that rotates the intermediate transfer belt 122 are driven by the driving force of a common drive motor 170. The drive motor 170 is configured such that, for example, the amount of current supplied thereto is variably controlled so that the photosensitive drums 1 and the intermediate transfer belt 122 rotate at a predetermined constant speed.

[0073] Specifically, the current rotation speed of the photosensitive drum 1 and the like is detected by a sensor (not shown) or the like, and if the detected current rotation speed is lower than a constant speed, the amount of current supplied to the drive motor 170 is increased to raise the rotation speed of the drive motor 170, and conversely, if the current rotation speed is higher than the constant speed, the amount of current supplied to the drive motor 170 is reduced to lower the rotation speed of the drive motor 170. By repeating this process alternately, feedback control is performed to maintain the rotation speed at an approximately constant speed. Other control methods may also be used.

[0074] [3] Driving force transmission mechanism of drive motor FIG. 4 is a schematic perspective view showing the configuration of a driving force transmission mechanism 179 that transmits the driving force of the driving motor 170. As shown in FIG.

[0075] As shown in the figure, drive force transmission mechanism 179 includes a two-stage gear 172 that receives the drive force of a rotation shaft 171 of drive motor 170 via an output shaft 171a of a torque detector 176, a gear 173 that meshes with a first gear 181 of two-stage gear 172, a gear 174 that meshes with gear 173, and a gear 175 that meshes with a second gear 182 of two-stage gear 172. Although not shown in the figure, the rotation shaft of gear 174 is connected to the rotation shaft of photosensitive drum 1, and the rotation shaft of gear 175 is connected to the rotation shaft of drive roller 123 of intermediate transfer unit 121A, so that when gear 174 rotates, photosensitive drum 1 rotates, and when gear 175 rotates, drive roller 123 rotates.

[0076] The drive motor 170 can rotate in either forward or reverse direction. Each gear is a spur gear, but other types of gears or couplings may be used as long as they are capable of transmitting drive force and have a backlash of a magnitude described below. The rotation shaft 171 of the drive motor 170 is integral with the input shaft of the torque detector 176.

[0077] The torque detector 176 (torque detection unit) detects the magnitude of the driving torque (load torque) required to rotate the photosensitive drum 1 and intermediate transfer belt 122, which are downstream in the driving force transmission direction from the driving motor 170, i.e., the load side, at a constant speed, and sends the detection result to the control unit 150.

[0078] For example, the stronger the pressing force (hereinafter referred to as "blade contact force") when the tip 330 of the cleaning blade 312 contacts the surface 126 of the intermediate transfer belt 122, the greater the rotational resistance of the intermediate transfer belt 122, and therefore the greater the drive torque than when the rotational resistance is small. Note that even if the drive torque varies, the rotation speed of the drive motor 170 is maintained constant as described above.

[0079] The first gear 181, gear 173, and gear 174 of the two-stage gear 172 each have the same number of teeth and the same pitch circle, and the second gear 181 and gear 175 of the two-stage gear 172 each have the same number of teeth and the same pitch circle. The first gear 181 has fewer teeth than the second gear 182, and the number of teeth, tooth thickness, tooth gap width, etc. of each gear are determined so that the first gear 181 has a larger backlash than the second gear 182. Note that this figure is a schematic diagram for explaining the difference in the number of teeth of each gear, and the number of teeth, tooth thickness, etc. do not match those of the actual gears. The same applies to Figures 5 and 6, which will be described later and which illustrate the difference in backlash.

[0080] 4, when the rotation shaft 171 of the drive motor 170 rotates in the direction indicated by the arrow E, the rotational drive force is transmitted from the first gear 181 of the two-stage gear 172 to the gear 174 via the gear 173 which rotates in the direction indicated by the arrow F, and from the second gear 182 to the gear 175, so that the gear 174 rotates in the direction indicated by the arrow G while the gear 175 rotates in the direction indicated by the arrow H. The rotational drive force of the gear 174 is transmitted to the rotation shaft of each photosensitive drum 1, and the rotational drive force of the gear 175 is transmitted to the rotation shaft of the drive roller 123 which drives the intermediate transfer belt 122 to rotate.

[0081] Therefore, the path from the first gear 181 of the two-stage gear 172 via gears 173 and 174 to the rotation shaft of each photosensitive drum 1 becomes drive transmission path 17A, through which the drive force of the drive motor 170 is transmitted to each photosensitive drum 1. In addition, the path from the second gear 182 of the two-stage gear 172 via gear 175 to the rotation shaft of the drive roller 123 becomes drive transmission path 17B, through which the drive force of the drive motor 170 is transmitted to the intermediate transfer belt 122.

[0082] This drive transmission path 17B is the first transmission path that transmits the drive force of the drive motor 170, which is one drive source, to the intermediate transfer belt 122, and drive transmission path 17A can be said to be the second transmission path that branches off from the second gear 182, which is a branching point midway along drive transmission path 17B (first transmission path), and transmits the drive force of the drive motor 170 to each photosensitive drum 1.

[0083] Since neither drive transmission path 17A nor 17B has a clutch interposed therein that switches between transmitting and cutting off the drive force, each photosensitive drum 1 and intermediate transfer belt 122 rotate simultaneously with the rotation of drive motor 170, provided there is absolutely no backlash in each path.

[0084] When the drive motor 170 rotates in the direction indicated by the arrow E (forward rotation), each photosensitive drum 1 rotates in the direction of the arrow A shown in Figure 1, while the intermediate transfer belt 122 moves in a circular motion in the direction of the arrow D shown in Figure 1, i.e., rotates forward.

[0085] On the other hand, when the drive motor 170 rotates (reversely) in the direction of arrow Ea (dashed line), which is opposite to the direction of arrow E, the gears rotate in the opposite direction to the direction shown in Fig. 4. At this time, the intermediate transfer belt 122 rotates in the direction of arrow Da shown in Fig. 1, that is, rotates in the reverse direction, and each photosensitive drum 1 also rotates (reversely) in the opposite direction to the direction of arrow A shown in Fig. 1.

[0086] In this configuration where no clutch is interposed on the drive transmission paths 17A, 17B, when the intermediate transfer belt 122 is rotated in the reverse direction, each photosensitive drum 1 also rotates in the reverse direction, but it is not preferable to rotate each photosensitive drum 1 in the reverse direction. This is because when the photosensitive drum 1 is rotated in the reverse direction, if any residue such as toner before cleaning remains on the photosensitive drum 1, the residue will move in the direction from the developing roller 4a via the exposure unit 3 toward the charging unit 2, and may scatter around the exposure unit 3 or the charging unit 2, contaminating the exposure unit 3 or the charging unit 2.

[0087] In this embodiment, the magnitude of the backlash is set so that the intermediate transfer belt 122 is reversed to remove foreign matter I caught in the tip 330 of the cleaning blade 312 while preventing each photosensitive drum 1 from rotating in reverse.

[0088] Specifically, the backlash in drive transmission path 17A is set to be larger than the backlash in drive transmission path 17B. As a result, when the drive force generated when drive motor 170 is rotated in the reverse direction is transmitted to intermediate transfer belt 122, the drive force has not yet been transmitted to each photosensitive drum 1, and from the time when intermediate transfer belt 122 actually starts to rotate in the reverse direction until just before the drive force is transmitted to each photosensitive drum 1, that is, in a state where there is play due to the backlash in drive transmission path 17A, it is possible to maintain each photosensitive drum 1 in a stopped state while only intermediate transfer belt 122 is rotated in the reverse direction.

[0089] This will be explained more specifically with reference to the schematic diagrams of FIGS.

[0090] 5(a) and 5(b), the gears included in the driving force transmission mechanism 179 are shown in a star shape to make it easier to see which teeth of the gears mesh with each other.

[0091] 5(a) shows a moment when, due to forward rotation of drive motor 170, two-stage gear 172 rotates in the direction indicated by arrow E, gear 174 rotates in the direction indicated by arrow G, and gear 175 rotates in the direction indicated by arrow H. That is, a tooth surface 482 of tooth 282 of first gear 181 comes into contact with a tooth surface 472 of tooth 272 of gear 173, a tooth surface 473 of tooth 273 of gear 173 comes into contact with a tooth surface 474 of tooth 274 of gear 174, and similarly, a tooth surface 481 of tooth 281 of second gear 182 comes into contact with a tooth surface 475 of tooth 275 of gear 175.

[0092] When the drive motor 170, which is rotating in the forward direction, stops, the inertial force acting on each gear may cause the two abutting tooth surfaces to move slightly apart, but here we will assume that when the drive motor 170 stops, the tooth surfaces of each tooth are in abutting contact as shown in the same figure.

[0093] FIG. 5(b) is a diagram showing the state when the drive motor 170 is switched from forward rotation to a stop, then reverse rotation, and rotated a very small amount.

[0094] When the drive motor 170 starts to rotate reversely, the second gear 182 starts to rotate reversely in the direction of arrow Ea, and the tooth surface 489 of the tooth 289 of the second gear 182 comes into contact with the tooth surface 491 of the tooth 291 of the gear 175, eliminating play due to backlash in the drive transmission path 17B, so that the rotational force of the second gear 182 in the reverse direction is transmitted to the gear 175, and the gear 175 rotates (reverses) in the direction of arrow Ha. As a result, the intermediate transfer belt 122 starts to rotate reversely.

[0095] Meanwhile, after the first gear 181 starts to rotate in the reverse direction in the direction of the arrow Ea at the same time as the second gear 182, the tooth surface 492 of the tooth 292 of the first gear 181 comes into contact with the tooth surface 472 of the tooth 272 of the gear 173, and the rotational force of the first gear 181 in the reverse direction is transmitted to the gear 173, causing the gear 173 to start rotating (reversely) in the direction of the arrow Fa.

[0096] However, at the point when gear 173 starts to rotate in the reverse direction, as indicated by the circle in the figure, tooth surface 471 of tooth 271 of gear 173 does not come into contact with tooth surface 479 of tooth 274 of stopped gear 174, and a gap 478 (a state with play) is opened between tooth surfaces 471 and 479. This gap 478 (play) is caused by the fact that the backlash occurring between the gears in drive transmission path 17A from first gear 181 to photosensitive drum 1 via gears 173 and 174 is larger than the backlash occurring between the gears in drive transmission path 17B from second gear 182 to intermediate transfer belt 122 via gear 175.

[0097] As the first gear 181 continues to rotate in the reverse direction, eventually the tooth surface 471 of the tooth 271 of the gear 173 comes into contact with the tooth surface 479 of the tooth 274 of the gear 174, the play due to the backlash in the drive transmission path 17A disappears, the gear 174 starts to rotate in the reverse direction, and the photosensitive drum 1 is rotated in the reverse direction.

[0098] Therefore, the time from when the drive motor 170 starts to reverse until just before the tooth surface 471 of the tooth 271 of the gear 173 hits the tooth surface 479 of the tooth 274 of the gear 174 (the time during which there is play due to backlash) is the time during which the intermediate transfer belt 122 reverses while the photosensitive drum 1 remains stopped.

[0099] In other words, by making the second backlash occurring in drive transmission path 17A larger than the first backlash occurring in drive transmission path 17B, and setting the amount of rotation (rotation angle) when reversing drive motor 170 to a range greater than the first backlash occurring in drive transmission path 17B and less than the second backlash occurring in drive transmission path 17A, it is possible to reverse the rotation of intermediate transfer belt 122 while keeping photosensitive drum 1 stopped.

[0100] 6(a) to (c) are schematic diagrams for explaining that, assuming that gear 173 shown in FIG. 5 does not exist and first gear 181 directly meshes with gear 174, when drive motor 170 is rotated in the reverse direction from a stopped state, backlash causes gear 174 to rotate while gear 175 remains stopped, and the diagrams show a portion of the tooth row of each of gears 174 and 175 developed in a linear fashion.

[0101] Here, reference numerals 175a, 175b, 175c, 175d, and 175f indicate teeth of the gear 175, and reference numerals 174a, 174b, and 174c indicate teeth of the gear 174. The left-right direction corresponds to the direction of the tooth row in which the teeth are arranged, that is, the actual direction of rotation. Reference numeral 181a indicates one tooth of the first gear 181, and reference numeral 182a indicates one tooth of the second gear 182.

[0102] In Figure 6(a), when the drive motor 170 has stopped after rotating in the forward direction, the tooth surface 175h of the tooth 175a of the gear 175 abuts against the tooth surface 182h of the tooth 182a of the second gear 182, and the tooth surface 174h of the tooth 174a of the gear 174 abuts against the tooth surface 181h of the tooth 181a of the first gear 181.

[0103] 6(b), when the stopped drive motor 170 starts to rotate in the reverse direction, the first gear 181 and the second gear 182 rotate in the reverse direction, i.e., the teeth 181a and 182a move to the right in the figure, and the tooth surface 182j of the tooth 182a comes into contact with the tooth surface 175j of the tooth 175b on the gear 175, which is adjacent to the tooth 175a on the right. At this point, the tooth 181a of the first gear 181 does not come into contact with the tooth surface 174j of the tooth 174b on the gear 174, which is adjacent to the tooth 174a on the right. This is because the pitch of the gear 174 is larger than that of the gear 175.

[0104] As the drive motor 170 continues to rotate in the reverse direction, as shown in Fig. 6(c), the teeth 181a and 182a of the first gear 181 and the second gear 182 move further to the right than the positions shown in Fig. 6(b) (the amount of reverse rotation increases), and the tooth 182a applies a force in the reverse direction (to the right in the example of the figure) to the tooth 175b of the gear 175, causing the gear 175 to rotate in the reverse direction (the row of teeth of the gear 175 moves to the right in the example of the figure). When the gear 175 starts to rotate in the reverse direction, the intermediate transfer belt 122 starts to rotate in the reverse direction.

[0105] 6(c), even when the intermediate transfer belt 122 starts to rotate in the reverse direction, the tooth 181a of the first gear 181 has not yet reached the tooth surface 174j of the tooth 174b of the gear 174. Therefore, the gear 174 remains stopped after the drive motor 170 starts to rotate in the reverse direction.

[0106] As the drive motor 170 continues to rotate in the reverse direction, the tooth surface 181j of the tooth 181a of the first gear 181 eventually comes into contact with the tooth surface 174j of the tooth 174b of the gear 174, and the gear 174 then starts to rotate in the reverse direction, causing the photosensitive drum 1 to rotate in the reverse direction.

[0107] In Figure 6(a), the distance U1 from the tooth surface 181j of the tooth 181a of the first gear 181 to the tooth surface 174j of the tooth 174b of the gear 174 corresponds to the magnitude of the backlash occurring between the first gear 181 and the gear 174 (the second backlash in the drive transmission path 17A).

[0108] Furthermore, a distance U2 from a tooth surface 182j of a tooth 182a of the second gear 182 to a tooth surface 175j of a tooth 175b of the gear 175 corresponds to the magnitude of the backlash (first backlash in the drive transmission path 17B) occurring between the second gear 182 and the gear 175. In the relationship of backlash U1>U2, the difference U3 (=U2-U1) is the maximum reverse rotation amount of the drive motor 170 that can reverse the intermediate transfer belt 122 while keeping the photosensitive drum 1 stopped.

[0109] Therefore, if the amount of reverse rotation of the drive motor 170, i.e., the number of times the drive motor 170 is rotated in the reverse direction, is determined in advance through experiments or the like so that it is greater than the backlash U2 and less than or equal to the backlash U1, it becomes possible to reverse the intermediate transfer belt 122 while keeping the photosensitive drum 1 stopped (without reversing) at any point during the long period from when the intermediate transfer unit 121A is new until the end of its life. This reverse rotation amount is Rb (FIG. 10), which will be described later.

[0110] This control can be said to be control that ends the reverse rotation of drive motor 170 and switches to forward rotation while the reverse rotation of drive motor 170 is being transmitted to intermediate transfer belt 122 through drive transmission path 17B and intermediate transfer belt 122 is rotating in reverse due to the absence of play caused by the second backlash in drive transmission path 17B after drive motor 170 starts rotating in reverse, and while the reverse rotation of drive motor 170 is being transmitted to drive transmission path 17A and the state where there is play caused by the first backlash changes to the state where the play is no longer present.

[0111] In the above description, one drive motor 170 is shared as a drive source for both the photosensitive drum 1 and the intermediate transfer belt 122, but this is not limited to this. For example, the drive motor 170 may also be shared as a drive source for the developing roller 4a. In this case, it is desirable to keep not only the photosensitive drum 1 but also the developing roller 4a stopped when the intermediate transfer belt 122 is rotating in the reverse direction.

[0112] This is because the developer carried by developing roller 4a is configured so that when developing roller 4a rotates forward (in the direction of arrow B in FIG. 1), a regulating member (not shown) regulates the amount of developer transported to the area facing photosensitive drum 1 to a constant amount. In this configuration, when developing roller 4a is rotated in the reverse direction (opposite to the direction of arrow B), this regulation is no longer in place, and much of the developer moves from developing roller 4a to the photosensitive drum 1 side, which could cause it to get stuck in the gap between the photosensitive drum 1 and developing roller 4a or spill out of the housing of developing unit 4.

[0113] In a configuration in which no clutch is interposed on the drive transmission path from the rotating shaft 171 of the drive motor 170 via one or more gears not shown to the developing roller 4a, if the backlash on that drive transmission path is U4, in order to keep both the photosensitive drum 1 and the developing roller 4a stopped when the intermediate transfer belt 122 rotates in the reverse direction, the amount of reverse rotation of the drive motor 170 can be determined to be greater than the backlash U2 and less than the smaller of U1 and U4.

[0114] Furthermore, although photosensitive drum 1 and developing roller 4a have been described as examples of components for which reverse rotation is undesirable, other components, such as paper feed conveying members of paper feed unit 130, such as paper feed roller pair 133a, 133b, conveying roller pair 134b, and timing roller pair 146, can also be applied to a configuration in which drive motor 170 drives them. In this configuration, as in the above, the magnitude of backlash in paper feed unit 130 including each paper feed conveying member can be set larger than backlash U2, and the amount of reverse rotation of drive motor 170 can be determined so that it is equal to or smaller than the magnitude of the backlash in paper feed unit 130 and larger than backlash U2.

[0115] [4] Configuration of the control unit FIG. 7 is a block diagram showing the main components of the control unit 150.

[0116] As shown in the figure, the control unit 150 is composed of a CPU (Central Processing Unit) 151, a ROM (Read Only Memory) 152, a RAM (Random Access Memory) 153, an image memory 154, an image processing circuit 155, a network communication circuit 156, a scanner control circuit 157, an input / output circuit 158, a printer control circuit 159, a drive motor control circuit 160, input / output circuits 161 and 162, a memory circuit 163, and a bus 169.

[0117] The CPU 151, ROM 152, RAM 153, image memory 154, image processing circuit 155, network communication circuit 156, scanner control circuit 157, input / output circuit 158, printer control circuit 159, drive motor control circuit 160, and input / output circuits 161 and 162 are connected to one another via a bus 169. The memory circuit 163 is connected to the input / output circuit 162.

[0118] The CPU 151 , the ROM 152 and the RAM 153 constitute a main control unit 90 .

[0119] The RAM 153 temporarily stores various control variables and data such as the number of copies set on the operation panel 140, and also provides a work area when the CPU 151 executes a program.

[0120] The ROM 152 stores control programs for executing various jobs such as copying and printing. The control programs may also be stored in the storage circuitry 163.

[0121] The CPU 151 operates according to a control program stored in the ROM 152 .

[0122] The image memory 154 temporarily stores image data included in a print job or the like.

[0123] The image processing circuit 155 performs various data processing on the image data of the R, G, and B color components obtained by the image reading unit 110, converting them into image data of the Y, M, C, and K reproduction colors.

[0124] The network communication circuit 156 receives print jobs from external terminal devices via a network.

[0125] The scanner control circuit 157 controls the image reading unit 110 to execute the operation of reading the document.

[0126] The input / output circuit 158 ​​receives an input signal from the operation panel 140 and outputs the received input signal to the main control unit 90. It also receives image data from the main control unit 90 and outputs the received image data to the operation panel 140 to display the image.

[0127] The printer control circuit 159 controls the image forming unit 120 and the paper feeding unit 130 to perform the image forming operation.

[0128] The drive motor control circuit 160 controls the forward and reverse rotation of the drive motor 170 .

[0129] The input / output circuit 161 receives the detection result of the torque detector 176 and sends it to the main control unit 90. The input / output circuit 162 writes data to the memory circuit 163 or reads data from the memory circuit 163.

[0130] The storage circuit 163 will be described later.

[0131] [5] Main control unit The main control unit 90 functions as a general control unit 91, a belt forward / reverse rotation control unit 92, and a belt driving torque estimating unit 93 as a result of the CPU 151 operating in accordance with the control program.

[0132] The overall control unit 91 uniformly controls the image memory 154, image processing circuit 155, network communication circuit 156, scanner control circuit 157, input / output circuit 158, printer control circuit 159, drive motor control circuit 160, input / output circuits 161 and 162, etc., to smoothly execute various jobs such as printing and copying.

[0133] The belt driving torque estimation unit 93 estimates the magnitude of the driving torque of the intermediate transfer belt 122 from the detection result of the torque detector 176. This estimation method will be described later.

[0134] The belt forward / reverse rotation control unit 92 controls the forward and reverse rotation of the intermediate transfer belt 122, specifically, variably controls the number of forward and reverse rotations of the intermediate transfer belt 122 in accordance with the magnitude of the driving torque of the intermediate transfer belt 122 estimated by the belt driving torque estimation unit 93. The details of this variable control will be described later.

[0135] [6] Memory circuit The storage circuit 163 (storage means) is made up of a nonvolatile semiconductor memory. Note that the storage circuit 163 may also be made up of a hard disk.

[0136] The memory circuit 163 has areas for storing a belt driving torque table 164, a forward / reverse rotation switching number table 165, a motor forward / reverse rotation amount table 166, and the like.

[0137] 8, the belt driving torque table 164 is a table for storing the magnitude of the belt driving torque Tr, which is 30 (mN m) in the example shown in the figure, and the magnitude of the belt driving torque Tr is equal to the magnitude of the driving torque estimated by the belt driving torque estimating unit 93. Every time the belt driving torque estimating unit 93 estimates the driving torque, information indicating the magnitude of the estimated driving torque is overwritten (updated) in the belt driving torque table 164.

[0138] The forward / reverse rotation switching count table 165 is a table for storing the range of the belt driving torque Tr and the number of forward / reverse rotation switching counts N of the intermediate transfer belt 122 in association with each other, as shown in FIG. 9, and is generated in advance by experiments or the like and stored.

[0139] As shown in the figure, the belt drive torque Tr and the number of forward / reverse rotation switches N have a relationship in which when the belt drive torque Tr is large, the number of forward / reverse rotation switches N is small, and as the belt drive torque Tr becomes smaller, the number of forward / reverse rotation switches N increases.

[0140] Here, the magnitude of the belt driving torque Tr is divided into three ranges: 30 or more, 10 to 30, and 5 to 10, and a different value of the number of reverse rotations N is associated with each range. The boundaries of these ranges, for example, Tr=30 or 10, become thresholds (first thresholds) for determining the number of forward / reverse rotation switches N according to the magnitude of the belt driving torque Tr.

[0141] When the belt driving torque Tr becomes equal to or less than a predetermined value, 5 (second threshold) in the example shown in the figure, the number of forward / reverse rotation switches N becomes Z, in this case, the life of the intermediate transfer unit 121A is determined.

[0142] 10, the motor forward / reverse rotation amount table 166 is a table for storing the reverse rotation amount R of the drive motor 170, which is predetermined based on the magnitude of backlash in the drive force transmission mechanism 179, and the forward rotation amount R' when the drive motor 170 rotates in the reverse direction and then forward, as shown in FIG. 10. In the example shown in FIG. 10, the reverse rotation amount R is Rb, and the forward rotation amount R' is Ra. When converted into the movement amount of the intermediate transfer belt 122 rotating in the reverse direction (belt reverse distance), the reverse rotation amount Rb of the drive motor 170 is a value that indicates a magnitude of, for example, about 10 mm. When converted into the movement amount of the intermediate transfer belt 122 rotating in the reverse direction and then forward, as shown in FIG. 10, the forward rotation amount Ra of the drive motor 170 is a value that indicates a magnitude of, for example, about 15 mm.

[0143] Next, the reason for variably controlling the number of forward and reverse rotations of the intermediate transfer belt 122 in accordance with the magnitude of the driving torque of the intermediate transfer belt 122 will be specifically described below.

[0144] [7] Regarding foreign matter such as paper dust getting caught in the cleaning blade 11 is a diagram illustrating an example of a graph 501 showing the relationship between the drive torque of the intermediate transfer belt 122 (hereinafter referred to as "belt drive torque") and the likelihood of foreign matter I, such as paper dust, becoming caught in the cleaning blade 312. The likelihood of foreign matter I becoming caught is expressed by the number of trapped foreign matter I or the amount of trapped foreign matter I (volume, etc.). In graph 501, the horizontal axis represents the magnitude of the belt drive torque, and the vertical axis represents the likelihood of foreign matter I becoming caught.

[0145] Graph 501 in the figure shows that the likelihood of foreign matter I getting caught increases as the belt drive torque decreases. This relationship occurs for the following reason: With continued use of the intermediate transfer belt 122 and cleaning blade 312, minute irregularities gradually occur on the surface 126 of the intermediate transfer belt 122, the cleaning blade 312 gradually creeps and deforms, and the tip 330 of the cleaning blade 312 gradually wears down, causing deterioration to proceed.

[0146] The manner and progress of deterioration varies depending on the materials and usage conditions of the intermediate transfer belt 122 and the cleaning blade 312, but deterioration reduces the coefficient of friction between the cleaning blade 312 and the intermediate transfer belt 122, and creep deformation of the cleaning blade 312 reduces the blade contact force.

[0147] This reduction in the coefficient of friction and blade contact force makes it easier for foreign matter I to become caught in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122, and also reduces the rotational resistance of the intermediate transfer belt 122 caused by the cleaning blade 312 in counter-contact with the surface 126 of the intermediate transfer belt 122. As the rotational resistance of the intermediate transfer belt 122 decreases, the drive torque required by the drive motor 170 to rotate the intermediate transfer belt 122 at a constant speed, i.e., the belt drive torque, decreases.

[0148] As described above, as the intermediate transfer belt 122 and cleaning blade 312 deteriorate with the passage of time, the cleaning ability decreases, the belt driving torque decreases, and foreign matter I becomes more likely to get caught in the cleaning blade 312, that is, the number of foreign matter I that gets caught increases. This relationship has been confirmed through experiments by the inventors of the present application.

[0149] The reason why the change in the number of trapped foreign matter I relative to the change in belt drive torque (the slope of graph 501) is greater when the belt drive torque is small than when it is large is thought to be due to the following.

[0150] That is, the weaker the blade contact force, the more easily foreign matter I gets into the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 .

[0151] For example, if one foreign object I enters and gets caught in the contact area, microscopically, the contact pressure between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 becomes weaker in the area immediately to the side of the foreign object I in the belt width direction, making it easier for another foreign object I to enter into the area where the contact pressure is weaker. If another foreign object I enters into the area to the side, the contact pressure in another area immediately to the side of the first foreign object I becomes weaker, making it easier for yet another foreign object I to enter.

[0152] This is thought to be because the weaker the blade contact force, that is, the lower the belt drive torque, the more likely it is that trapped foreign matter I will enter the area immediately to the side in the belt width direction, and the number of trapped foreign matter I will increase at an accelerated rate. Note that the way in which the number of trapped foreign matter I changes depending on the magnitude of the belt drive torque varies to some extent depending on the device configuration, so the change will not necessarily be as shown in graph 501, but the relationship that the lower the belt drive torque, the higher the number of trapped foreign matter will be is common to all devices.

[0153] If the distance of one reverse rotation of the intermediate transfer belt 122 is the same when the number of trapped foreign matter I is small and when the number of trapped foreign matter I is large, most of the trapped foreign matter I can be removed when the number of trapped foreign matter I is small, but when the number of trapped foreign matter I is large, some of the trapped foreign matter I is likely to remain in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122.

[0154] Figure 12 is a schematic diagram comparing graphs 510 and 520 to show how the number W of trapped foreign matter I changes when a forward / reverse switching operation is performed once during non-image formation, specifically during non-transfer, in which the intermediate transfer belt 122 is rotated in the reverse direction and then in the forward direction, after a certain number of printed sheets (here, 50 sheets) are formed by copying or printing.The horizontal axis shows the number of printed sheets, and the vertical axis shows the number W of trapped foreign matter I.

[0155] Graph 510 shows the change in the number W of trapped foreign matter I when the belt drive torque is high, and graph 520 shows the change in the number W of trapped foreign matter I when the belt drive torque is lower than that of graph 510.

[0156] Looking at graph 510, which shows a case where the belt drive torque is high, we see that the number W of trapped foreign matter I increases as the number of printed sheets goes from 0 to 50, and when the number of printed sheets reaches 50, a single forward / reverse rotation switch operation causes the number W of trapped foreign matter I to drop from α1 to approximately zero, and as the number of printed sheets goes from 50 to 100, the number W of trapped foreign matter I increases again, and when the number of printed sheets reaches 100, a single forward / reverse rotation switch operation causes the number W of trapped foreign matter I to drop from α1 to approximately zero; this cycle is repeated every 50 printed sheets. This repetition prevents the number W of trapped foreign matter I from increasing significantly above α1.

[0157] In contrast, graph 520, which shows the case where the belt drive torque is low, shows that the number W of trapped foreign matter I, which increases as the number of printed sheets goes from 0 to 50, is significantly larger than that of graph 510. This is because when the belt drive torque is low, the amount of trapped foreign matter I is greater than when the belt drive torque is high, as shown in FIG.

[0158] In graph 520, when the number of printed sheets reaches 50, the number W of trapped foreign matter I increases to α2 (>α1), and by performing a forward / reverse rotation switching operation once at this point, the number W of trapped foreign matter I drops from α2 to α3 (>0). However, since α3 is greater than zero, some of the trapped foreign matter I remains in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122.

[0159] With only α3 of foreign matter I remaining, as the number of printed sheets increases from 50 to 100, the number W of foreign matter I trapped increases again, and when the number of printed sheets reaches 100, the number W of foreign matter I trapped increases to α4.

[0160] At this point, after one forward / reverse rotation switching operation, the number W of trapped foreign matter I drops from α4 to α5, but α5 is larger than α2, and the number W of trapped foreign matter I increases with each forward / reverse rotation switching operation. If the number of printed sheets continues to increase like this, as shown in graph 520, the number W of trapped foreign matter I will soon reach value β, which corresponds to a cleaning defect, and cleaning defects will occur early.

[0161] Therefore, in this embodiment, when the belt driving torque is small, the number of forward / reverse rotation switches N is increased more than when the torque is large, thereby preventing an increase in the number W of trapped foreign objects I. This will be explained using FIG. 13.

[0162] 13 is a graph 530 showing the change in the number W of trapped foreign objects I when the number of forward / reverse rotation switches N is increased as the belt drive torque decreases, and also shows a graph 510 when the belt drive torque is large. Note that graph 510 is the same as graph 510 shown in FIG.

[0163] 13, the number W of trapped foreign matter I increases to α2 as the number of printed sheets goes from 0 to 50. This is the same as the graph 520 shown in FIG.

[0164] When the number of printed sheets reaches 50, the forward / reverse rotation switching operation is performed twice in succession. Specifically, the intermediate transfer belt 122 is rotated from forward to reverse (first time), forward (first time), reverse (second time), and forward (second time) in this order in succession. The forward / reverse rotation switching operation is performed by controlling the forward / reverse rotation of the drive motor 170. Two consecutive forward / reverse rotation switching operations correspond to a case where the number of forward / reverse rotation switching operations N is 2. In the figure, the first reverse and forward rotation operation is indicated by the symbol P, and the second reverse and forward rotation operation is indicated by the symbol Q. Performing this forward / reverse rotation switching operation two or more times in succession is called a belt forward / reverse rotation operation. This belt forward / reverse rotation operation will be described with reference to FIGS. 14(a) and 14(b).

[0165] FIG. 14(a) is a timing chart 540 showing the forward and reverse rotation of the belt, and FIG. 14(b) is a graph 550 showing how the movement distance of the intermediate transfer belt 122 in the forward and reverse directions changes during the forward and reverse rotation of the belt.

[0166] As shown in Figure 14(a), when the intermediate transfer belt 122 is rotating forward during image formation and the image formation ends at time t1, a non-image formation period begins, during which the intermediate transfer belt 122 is rotated in the reverse direction for a period of time Tb (the drive motor 170 is rotated in the reverse direction). This reversal allows some of the foreign matter I caught in the cleaning blade 312 to be removed. Here, the period of time Tb corresponds to the time required for the drive motor 170 to rotate in the reverse direction by the aforementioned reverse amount Rb, which is predetermined based on the magnitude of the backlash.

[0167] After the time Tb has elapsed (time t2), the intermediate transfer belt 122 is switched from reverse rotation to forward rotation, and the intermediate transfer belt 122 is rotated forward (the drive motor 170 is rotated forward) for the time Ta, that is, until time t3. This is the first forward / reverse rotation switching operation P.

[0168] The time Ta corresponds to the time required for the intermediate transfer belt 122 to move in the forward direction by a distance slightly greater than the reverse rotation amount Rb. For example, if the reverse rotation distance Rd (FIG. 14(b)) of the intermediate transfer belt 122 is 10 mm, this is the time required for the amount of movement in the forward rotation direction (forward rotation distance Rc) to be 15 mm, and this is the forward rotation amount Ra of the drive motor 170.

[0169] 14(b) is a diagram showing an example of a graph 550 showing the magnitude relationship between the reverse rotation distance Rd and the forward rotation distance Rc of the intermediate transfer belt 122, with the horizontal axis representing time and the vertical axis representing the distance traveled by the intermediate transfer belt 122 in the forward rotation direction (upward from the origin 0) and the distance traveled in the reverse rotation direction (downward). Reverse rotation of the intermediate transfer belt 122 causes the intermediate transfer belt 122 to move a distance Rd in the reverse direction, and then forward rotation causes the intermediate transfer belt 122 to move (return) a distance Rc (>Rd) in the forward rotation direction. The reason for this Rc>Rc relationship is to prevent the photosensitive drum 1 from rotating in reverse the second and subsequent times.

[0170] That is, if the rotation is reversed the first time and then switched to forward rotation and the forward rotation is completed, and the state before the reverse rotation, specifically the state of meshing of the gear teeth shown in FIG. 5(a), is restored, then even when the second reverse rotation is started, as in the first reverse rotation, tooth 271 of gear 173 will not come into contact with tooth 274 of gear 174 as shown in FIG. 5(b), and the photosensitive drum 1 will not rotate in reverse.

[0171] On the other hand, if the forward rotation amount Ra of the drive motor 170 is made smaller than the reverse rotation amount Rb, the teeth of each gear will not return to the meshed state shown in Figure 5(a) at the end of the first forward rotation. For example, if tooth 273 of gear 173 is slightly separated from tooth surface 747 of tooth 274 of gear 174, when the second reverse rotation begins, tooth 271 of gear 173 shown in Figure 5(b) will immediately come into contact with tooth 274 of gear 174, causing gear 174 to rotate counterclockwise in the same figure, which could result in reverse rotation of the photosensitive drum 1.

[0172] If there is a certain amount of backlash, it is possible that tooth 271 of gear 173 will not come into contact with tooth 274 of gear 174 during the second reverse rotation, but here the relationship Rc > Rd is used to ensure safety. This relationship is essentially the same as the relationship Ra > Rb.

[0173] Returning to FIG. 14(a), at time t3, a second forward / reverse rotation switching operation Q is initiated to switch the intermediate transfer belt 122 from forward rotation to reverse rotation. The second forward / reverse rotation switching operation Q is the same as the first forward / reverse rotation switching operation. In other words, the intermediate transfer belt 122 is rotated in the reverse direction (the drive motor 170 is rotated in the reverse direction) for a period Tb from time t3 to time t4. This second reverse rotation allows further removal of foreign matter I that was not completely removed during the first reverse rotation and remains caught in the cleaning blade 312. After the reverse rotation is completed, the intermediate transfer belt 122 is rotated in the forward direction (the drive motor 170 is rotated in the forward direction) for a period Ta from time t4 to time t5, and then the intermediate transfer belt 122 is stopped (the drive motor 170 is stopped).

[0174] In addition, the timing chart 540 in Figure 14(a) shows a waveform in which the intermediate transfer belt 122 (effectively, the drive motor 170) switches from forward rotation to reverse rotation and from reverse rotation to forward rotation in an instant, but a certain pause time, for example, of about 0.5 seconds, may be inserted during the switching.

[0175] Returning to Figure 13, when the number of printed sheets reached 50, the forward / reverse rotation switching operations P and Q were performed consecutively, i.e., the forward / reverse rotation switching operation was performed twice, which significantly reduced the number of trapped foreign matter I from α2 to α6. α6 is smaller than the number of trapped foreign matter I, α3, when the forward / reverse rotation switching operation shown in Figure 12 was performed only once, which indicates that even when the belt drive torque was low, most of the foreign matter I that had been caught in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 was able to be removed.

[0176] Next, in graph 530 when the belt drive torque is low, shown in Figure 13, the number W of trapped foreign matter I increases from α6 to α7 as the number of printed sheets increases from 50 to 100. However, once the number reaches 100 sheets, by performing two consecutive forward / reverse rotation switching operations, the number W of trapped foreign matter I drops significantly to α8, and most of the foreign matter I is removed, just as when the number of printed sheets was 50. The number α8 of trapped foreign matter is significantly smaller than the number α5 of trapped foreign matter when the number of printed sheets was 100 in Figure 12.

[0177] By switching between forward and reverse rotation twice at regular intervals, in this case each time the number of printed sheets reaches 50, i.e., at the 50th, 100th, 150th, etc., the number W of trapped foreign matter I changes as shown in graph 530, from α9 to α10, etc.

[0178] Comparing graph 530, which shows the case where the forward / reverse rotation switching operation is performed twice as shown in FIG. 13, with graph 520, which shows the case where the forward / reverse rotation switching operation is performed only once as shown in FIG. 12, it can be seen that the rate of increase in the number W of trapped foreign matter I relative to the number of printed sheets is significantly lower in graph 530 than in graph 520.

[0179] Therefore, performing the forward / reverse rotation switching operation twice in succession delays the time when a cleaning failure occurs compared to a configuration in which the forward / reverse rotation switching operation is performed only once, that is, it is possible to prevent the occurrence of a cleaning failure at an early stage as in the conventional configuration.

[0180] [8] How to determine the number of forward / reverse rotation changes N in relation to the belt drive torque 15 is a graph 560 illustrating the relationship between the belt drive torque Tr and the number Wa of foreign matter I caught per 10 printed sheets, where the horizontal axis represents the belt drive torque Tr and the vertical axis represents the number Wa of foreign matter I caught per 10 printed sheets. Note that graph 560 is similar to graph 501 shown in FIG.

[0181] 15 shows an example in which, in a certain device, when the magnitude of the belt drive torque Tr (mN m) is 30 (for example, when the device is new), and image formation is performed on 10 sheets of paper, the number W of trapped foreign matter I is 1, but when the magnitude of the belt drive torque Tr drops to 10 (for example, when the intermediate transfer belt 122 or cleaning blade 312 has deteriorated to a certain extent), the number W of trapped foreign matter I increases to 5. This example was obtained from experimental results.

[0182] In such a device, when a print or copy job is performed to continuously form images on 50 sheets of paper, the number W of foreign matter I caught at the end of continuous printing of 50 sheets will differ significantly depending on whether the magnitude of the belt drive torque Tr is 30 or 10.

[0183] 16 is a graph showing the relationship between the number of printed sheets and the number W of trapped foreign matter I, and shows that when the number of printed sheets is 50 and the magnitude of the belt drive torque Tr is 30 (graph 561), the number W of trapped foreign matter I is 5 (= 1 × 5), whereas when the magnitude of the belt drive torque Tr is reduced to 10 (graph 562), the number W of trapped foreign matter I increases to 25 (= 5 × 5). This is due to the relationship that the number W of trapped foreign matter I increases dramatically as the belt drive torque Tr decreases, as can be seen from graph 501 shown in FIG.

[0184] Here, the explanation is based on the premise that a single reverse rotation of the intermediate transfer belt 122 removes approximately 30% of the total number of foreign matters I caught in the cleaning blade 312, leaving approximately 70%.

[0185] If the forward / reverse rotation switching operation is performed only once when the number of printed sheets reaches 50, when the magnitude of the belt drive torque Tr is 30, 1 to 2 of the 5 foreign bodies I will be removed, leaving 3 to 4 (graph 561), and when the magnitude of the belt drive torque Tr is 10, 6 to 7 of the 25 foreign bodies I will be removed, leaving 18 to 19 (graph 562).

[0186] Figure 17 shows how the number W of trapped foreign objects I changes when, after continuous printing on the first to 50th sheets of paper is completed, the forward / reverse rotation switching operation is repeated once each time continuous printing on 50 sheets of paper is completed.

[0187] Graph 571 shown in FIG. 17 is a graph showing the change in the number W of trapped foreign matter I when the magnitude of the belt drive torque Tr is 30, and graph 572 is a graph showing the change in the number W of trapped foreign matter I when the magnitude of the belt drive torque Tr is 10.

[0188] It can be seen from graph 571 that when the magnitude of the belt drive torque Tr is 30, the number W of trapped foreign matter I remains within a range of less than 20 even when the number of printed sheets reaches 300.

[0189] On the other hand, when the magnitude of the belt drive torque Tr decreases to 10, graph 572 shows that the number W of trapped foreign matter I increases as the number of printed sheets increases, and after 250 sheets, the threshold value of 70 indicating a cleaning failure is exceeded, leading to the early occurrence of a cleaning failure.

[0190] This means that when the magnitude of the belt drive torque Tr is about 30, one forward / reverse rotation switching operation is sufficient, but when the magnitude of the belt drive torque Tr drops to about 10, one forward / reverse rotation switching operation is not enough, and if it is performed two or more times, early occurrence of cleaning defects can be prevented.

[0191] 18 is a graph 580 showing the change in the number W of trapped foreign matter I when the magnitude of the belt driving torque Tr is 10 and two forward / reverse rotation switching operations are repeated each time the number of printed sheets reaches 50. Graph 580 shows that when the magnitude of the belt driving torque Tr decreases to 10, two forward / reverse rotation switching operations can keep the number W of trapped foreign matter I to around 50, which is significantly smaller than the threshold value of 70 that indicates a cleaning failure, even when the number of printed sheets reaches 300.

[0192] Increasing the number of forward / reverse rotation switches N can reduce or almost eliminate the number W of trapped foreign matter I, but it also increases the time required to remove the foreign matter, reducing print productivity. Also, the distance the intermediate transfer belt 122 can reverse is limited by the magnitude of the backlash described above, so the belt reverse rotation distance Rd cannot be made very long.

[0193] Therefore, by taking into consideration print productivity and the limitations on the distance Rd over which the intermediate transfer belt 122 can be reversed, and determining in advance through experiments or simulations what the number of forward / reverse rotation switches N should be and at what magnitude of the belt drive torque Tr in order to delay as much as possible the increase in the number W of trapped foreign matter I to a level that will result in cleaning failure, it is possible to prevent early occurrence of cleaning failure while suppressing a decrease in print productivity.

[0194] In this embodiment, the number of forward / reverse rotation switches N relative to the belt driving torque Tr is determined as shown in forward / reverse rotation switch count table 165 in FIG. 9, but this is just one example, and it goes without saying that the range of the belt driving torque Tr and the magnitude of the number of forward / reverse rotation switches N shown in forward / reverse rotation switch count table 165 may differ depending on the device configuration.

[0195] [9] Control of belt forward / reverse rotation 19 is a control flowchart of the belt forward / reverse rotation operation. This belt forward / reverse rotation operation is repeatedly executed by the CPU 151 as the belt forward / reverse rotation control unit 92 when a predetermined execution condition is satisfied, in this case, every time image formation is performed on 50 sheets of paper S.

[0196] As shown in the figure, when image formation on the 50th sheet S is completed, the currently stored value of the belt driving torque Tr is read from the belt driving torque table 164 (step S1). In the example of FIG. 8, the belt driving torque Tr=30 is read.

[0197] Next, the forward / reverse rotation switching count table 165 is referenced to obtain the number of forward / reverse belt operations N corresponding to the magnitude of the read belt driving torque Tr (step S2). If the magnitude of the belt driving torque Tr read in step S1 is 30, in the example shown in FIG. 9, it falls within the range of 30≦Tr, so the number of forward / reverse rotation switching count N becomes 1. Also, if the magnitude of the belt driving torque Tr read in step S1 is 10, it falls within the range of 10≦Tr<30, so the number of forward / reverse rotation switching count N becomes 2. Furthermore, if the magnitude of the read belt driving torque Tr is 5 or less, the number of forward / reverse belt operations N becomes Z (life).

[0198] When it is determined that the number of forward and reverse switching operations N is not Z (i.e., "No" in step S3), the process proceeds to step S4. In step S4, the reverse rotation amount Rb (for example, corresponding to a belt reverse rotation distance Rd = 10 mm) and the forward rotation amount Ra (for example, corresponding to a belt forward rotation distance Rc = 15 mm) of the drive motor 170 stored in each column of the reverse rotation amount R and the forward rotation amount R' in the motor forward and reverse rotation amount table 166 are read out, and the read reverse rotation amount Rb and forward rotation amount Ra are set as the target rotation amount when the drive motor 170 rotates. In the next belt forward and reverse rotation operation, the drive motor 170 will rotate forward and reverse by the rotation amount set here.

[0199] Then, in step S5, a belt forward and reverse rotation operation corresponding to the number of forward and reverse switching operations N obtained in step S2 is executed. Specifically, the drive motor 170 is reversed by the reverse rotation amount Rb set in step S4, and then the drive motor 170 is switched to forward rotation by the forward rotation amount Ra, and this forward and reverse switching operation is continuously executed N times to end the process.

[0200] In this way, the number of forward and reverse switching operations N changes according to the magnitude of the belt drive torque Tr, and the forward and reverse switching operations are repeatedly and continuously executed N times.

[0201] After the intermediate transfer unit 121A is newly produced, as time passes, for example, at a certain time point t11, the number of forward and reverse switching operations N corresponding to the belt drive torque Tr1 is N1. If the magnitude of the belt drive torque Tr decreases to Tr2 (<Tr1) at a later time point t12, the number of forward and reverse switching operations N corresponding to the belt drive torque Tr2 may increase to N2 (>N1). Also, if the magnitude of the belt drive torque Tr increases to Tr3 at a time point t13 later than the time point t12 and greater than Tr2 at the time point t12, the number of forward and reverse switching operations N corresponding to the belt drive torque Tr3 may decrease to N3 (<N2).

[0202] In this case, the belt driving torque Tr increases between time t12 and time t13. In the above, an example has been described in which the belt driving torque Tr decreases as the number of printed sheets increases due to deterioration such as wear and deformation of the cleaning blade 312, but this is not necessarily limited to a decrease.

[0203] For example, by repeatedly performing the forward / reverse rotation switching operation multiple times, most of the foreign matter I that was present at the contact point between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 is removed, resulting in an increase in the contact area between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122. This increases the frictional force at the contact point, and the belt drive torque Tr may become higher than before the forward / reverse rotation of the belt.

[0204] Therefore, in each of the forward / reverse rotation operations of the belt performed at regular intervals, the number of forward / reverse rotation switches N may be reduced from the previous time at one time, the number of forward / reverse rotation switches N may be increased from the previous time at the next time, and the number of forward / reverse rotation switches N may be reduced from the previous time at the next time. In any case, by performing the forward / reverse rotation operation of the belt with the number of forward / reverse rotation switches N appropriate for the time, foreign matter I present at the contact portion between the tip 330 of the cleaning blade 312 and the surface 126 of the intermediate transfer belt 122 can be removed, and early occurrence of cleaning defects can be prevented while minimizing deterioration in image formation productivity.

[0205] In step S3, if it is determined that the number of forward and reverse rotation switching times N is Z ("Yes" in step S3), it is determined that the intermediate transfer unit 121A has reached the end of its life (step S6).

[0206] As described above, this lifespan determination is made when the belt drive torque Tr is equal to or less than 5. This is for the following reason: As can be seen from graph 560 in Fig. 15, when the magnitude of the belt drive torque Tr decreases to 5, the number Wa of foreign matter I caught per 10 printed sheets increases to 8, which is significantly more than the 5 that occurs when the belt drive torque Tr is 10.

[0207] Figure 20 is a graph comparing graphs 591 and 592 showing the progress of the number W of trapped foreign objects I when the magnitude of the belt drive torque Tr is 10 and 5, and the forward / reverse rotation switching operation is repeated four times (=N) each time the number of printed sheets reaches 100.

[0208] Looking at graph 591 (dashed line) corresponding to belt drive torque Tr=10, the number W of trapped foreign matter I remains below the threshold value of 70, indicating a cleaning failure, even after 300 printed sheets. Meanwhile, in graph 592 (solid line) corresponding to belt drive torque Tr=5, the number W of trapped foreign matter I decreases with each of the four forward / reverse rotation switching operations performed every 100 sheets. However, because the number of trapped foreign matter I is greater than the number of foreign matter I trapped during image formation, even with four consecutive forward / reverse rotation switching operations, the number W of trapped foreign matter I cannot be removed quickly enough, and it gradually increases. Once the number of printed sheets exceeds about 200, the number W of trapped foreign matter I suddenly increases, as if diverging. When this happens, the forward / reverse rotation of the belt can no longer adequately remove foreign matter I, leading to an early cleaning failure, and the life of intermediate transfer unit 121A is determined.

[0209] The lifespan of the intermediate transfer unit 121A can be considered as the lifespan of one or both of the cleaning blade 312 and the intermediate transfer belt 122. The magnitude of the belt drive torque Tr when the intermediate transfer unit 121A has reached the end of its lifespan can be determined in advance through experiments, etc. In the above example, the lifespan of the intermediate transfer unit 121A is determined when the belt drive torque Tr becomes 5 or less.

[0210] Returning to FIG. 19, in step S7, a warning that intermediate transfer unit 121A has reached the end of its life is displayed on operation panel 140. After this warning is displayed, the process ends. In addition to displaying the warning on operation panel 140, control may be performed, for example, to prohibit all image formation such as copying and printing from the point at which the warning is displayed, or to allow image formation on a minimum of, for example, about 50 sheets of paper and then prohibit image formation thereafter. When a service technician or the like installs a new intermediate transfer unit 121A in the device main body in place of the intermediate transfer unit 121A that has reached the end of its life, the warning and the prohibition on image formation can be canceled, and control may be performed to resume image formation such as copying and printing.

[0211]

[10] Belt drive torque estimation processing 21 is a flowchart showing the belt driving torque estimation process. This process is performed by CPU 151 as belt driving torque estimation unit 93 by acquiring the detection value of torque detector 176 when a predetermined detection condition is met, in this case, when the condition is met that gear 175 is rotating forward and gear 174 is stopped after the belt starts rotating forward after reverse rotation during forward / reverse rotation. The period during which the belt is rotating forward / reverse corresponds to the non-image formation period from time t1 to time t5 shown in FIG. 14(a), for example.

[0212] As shown in the figure, during the forward / reverse rotation of the belt, it is determined whether the intermediate transfer belt 122 has started to rotate forward after rotating in the reverse direction (step S11). This determination is made by detecting the timing when the rotation direction of the drive motor 170 has switched from reverse to forward, that is, when the rotation direction of the drive motor 170 has switched from reverse to forward.

[0213] Here, it is desirable to separate the four primary transfer rollers 5 from the intermediate transfer belt 122 simultaneously with switching the rotation of the intermediate transfer belt 122 from reverse to forward. This is because if the primary transfer rollers 5 remain in contact with the intermediate transfer belt 122, the estimated value of the belt drive torque Tr is more likely to vary due to the influence of the rotational resistance of the primary transfer rollers 5. By separating the primary transfer rollers 5 from the intermediate transfer belt 122, this variation can be avoided. In FIG. 1, the primary transfer rollers 5 in contact with the intermediate transfer belt 122 are indicated by solid lines, and the primary transfer rollers 5 separated from the intermediate transfer belt 122 are indicated by dashed lines. The movement of the primary transfer rollers 5 in contact with and separated from the intermediate transfer belt 122 can be performed using the driving force of the drive motor 170, but it is also possible to adopt a configuration in which they are driven by other actuators such as a solenoid.

[0214] In addition to or instead of separating the primary transfer roller 5 from the intermediate transfer belt 122, it is also possible to adopt a configuration in which the application of the transfer bias to the primary transfer roller 5 is cut off while the primary transfer roller 5 is in contact with the intermediate transfer belt 122.

[0215] If the transfer bias remains applied to the primary transfer roller 5, an electrostatic attraction force acts between the primary transfer roller 5 and the intermediate transfer belt 122, and this electrostatic attraction force is added to the rotational resistance of the intermediate transfer belt 122, which can cause variations in the estimated value of the belt drive torque Tr. Note that it is also possible to adopt a configuration in which the primary transfer roller 5 is not separated or the transfer bias is not cut off, provided that this does not affect the belt drive torque Tr.

[0216] When it is determined that the intermediate transfer belt 122 has started to rotate forward after rotating in the reverse direction ("Yes" in step S11), the detection values ​​of the torque detector 176 are acquired at regular intervals, for example, at intervals of several milliseconds, upon the start of the forward rotation (step S12), and the acquired detection values ​​are temporarily stored (step S13).

[0217] Then, it is determined whether the belt forward rotation distance Rf from the start of the forward rotation of the intermediate transfer belt 122 has reached Rf (step S14). This belt forward rotation distance Rf is a value slightly smaller than the belt forward rotation distance Rc, and is determined in advance through experiments or the like as a value that satisfies the above-mentioned predetermined detection condition. This will be specifically described with reference to Figures 22(a) to 22(c).

[0218] Figure 22(a) is a diagram that schematically shows the meshing state of two-stage gear 172, gear 175, and gear 174 at the end of reverse rotation, and is essentially the same as Figure 6(c). At the end of reverse rotation, each gear is assumed to stop momentarily.

[0219] FIG. 22(b) is a diagram schematically illustrating the meshing state of two-stage gear 172, gear 175, and gear 174 immediately after reverse rotation has ended and forward rotation has begun, showing how tooth 182a of second gear 182 moves leftward in the diagram and comes into contact with tooth 175a of gear 175 as forward rotation begins. At this point, both gears 175 and 174 remain stationary. As forward rotation continues, tooth 182a of second gear 182 moves further leftward in the diagram and pushes tooth 175a of gear 175 leftward, starting forward rotation of gear 175. At this point, gear 174 has not yet moved.

[0220] 22(c) is a schematic diagram showing the state at the point when forward rotation continues and tooth 175a of gear 175 (tooth 182a of second gear 182) has moved (rotated) leftward by Rj. At this point, tooth 181a of first gear 181 is quite close to tooth 174a of gear 174, but is still a distance Rp away and has not yet come into contact with tooth 174a of gear 174. In other words, gear 174 remains stopped.

[0221] 22(c) during forward rotation after reverse rotation, gear 175 rotates forward while gear 174 remains stopped. In other words, the driving force of drive motor 170 during forward rotation is transmitted to intermediate transfer belt 122 by the forward rotation of gear 175, but is not transmitted to photosensitive drum 1. If torque detector 176 detects the driving torque in this state, it is possible to actually measure the driving (load) torque of only intermediate transfer belt 122, excluding photosensitive drum 1, out of photosensitive drum 1 and intermediate transfer belt 122.

[0222] The belt forward rotation distance Rf corresponds to the distance the intermediate transfer belt 122 moves in the forward direction from when the intermediate transfer belt 122 actually starts rotating forward until the amount of movement (amount of rotation) of the gear 175 in the forward direction reaches Rj, that is, from when the state shown in Fig. 22(b) to when the state shown in Fig. 22(c) transitions. A first amount of rotation (rotation angle) in the forward direction of the second gear 182 in a first rotation operation from when the second gear 182 starts rotating forward after the second gear 182 reverses until the tooth 182a of the second gear 182 contacts the tooth 175a of the gear 175 (the state shown in Fig. 22(b)), and a second amount of rotation (rotation angle: equivalent to Rj) in a second rotation operation from when the tooth 182a contacts the tooth 175a to when the state shown in Fig. 22(c) are measured in advance, and measurement by the torque detector 176 is performed only during the second rotation operation after the first rotation operation is completed.

[0223] In FIG. 21, when it is determined that the belt forward rotation distance has reached Rf ("Yes" in step S14), measurement of the belt driving torque by the torque detector 176 is terminated (step S15).

[0224] Then, each detected value of the torque detector 176 stored is read out, and each value is subjected to statistical processing, for example, an average value is calculated. The calculated value is estimated as the current driving torque (belt driving torque Tr) of the intermediate transfer belt 122, and is overwritten and saved in the belt driving torque table 164 (step S16), after which the processing is terminated.

[0225] In the above, in step S12, the detection values ​​of the torque detector 176 are acquired at regular intervals, each acquired detection value is temporarily stored, and the average value of each stored detection value is calculated, but this is not limited to this.

[0226] For example, the torque detector 176 may be configured to use a strain gauge whose distortion changes in accordance with the magnitude of the belt driving torque Tr, and which detects the magnitude of the driving torque from the changed distortion.

[0227] When this configuration is adopted, the strain gauge is configured to detect the belt drive torque Tr at the time when the drive motor 170 stops after rotating in the reverse direction and then forward direction from the magnitude of the strain at that time.

[0228] Then, at the point when the second rotation operation is completed, that is, when the drive transmission path 17B (first transmission path) is rotating forward without play due to the first backlash, and before the drive transmission path 17A (second transmission path) transitions from a state where there is play due to the second backlash to a state where there is no play due to the second backlash, the drive motor 170 rotating forward is stopped, and the magnitude of the drive torque detected by the strain gauge in the stopped state can be used as an estimate of the belt drive torque Tr.

[0229] Furthermore, although the belt drive torque Tr is estimated from the detection result of the torque detector 176, this is not limitative. For example, the belt drive torque Tr may be estimated from the value of the current supplied to the drive motor 170.

[0230] When the driving force of the drive motor 170 rotates the intermediate transfer belt 122 in the forward direction at a constant speed, as the belt driving torque Tr increases, the value of the current flowing through the drive motor 170 increases to maintain the forward rotation at a constant speed. In other words, the value of the current supplied to the drive motor 170 becomes an index value that indicates the magnitude of the belt driving torque Tr.

[0231] Therefore, if the relationship between the supply current value of the drive motor 170 and the belt drive torque Tr is determined in advance by an experiment or the like, and the supply current value of the drive motor 170 during the forward rotation of the intermediate transfer belt 122 from steps S12 to S15 is detected by an ammeter (not shown) or the like, the belt drive torque Tr corresponding to the detected current value can be estimated as the current drive torque of the intermediate transfer belt 122. In this configuration, the torque detector 176 is not necessary.

[0232] By performing this type of belt drive torque estimation process each time the belt rotates forward or backward, the value of the belt drive torque Tr detected at the time the belt rotates forward or backward can be updated each time, and changes in the magnitude of the belt drive torque Tr can be monitored with high accuracy.

[0233] Since the belt driving torque Tr is actually measured during the currently executed forward / reverse belt rotation, the value of the belt driving torque Tr written in the belt driving torque table 164 is read out the next time the belt is rotated forward / reversely (step S1 in FIG. 19) and is used to determine the forward / reverse rotation switching count N. In the above example, it is used the next time the belt is rotated forward / reversely, which is executed when image formation on 50 sheets of paper is completed.

[0234] As described above, in this embodiment, the number of forward / reverse rotation switches N is controlled to increase according to the magnitude of the belt drive torque Tr, which decreases as the cleaning blade 312 and the intermediate transfer belt 122 deteriorate, so that early occurrence of cleaning failures can be prevented while minimizing the decrease in productivity of image formation such as printing.

[0235] The present disclosure is not limited to image forming apparatuses, and may also be a method for controlling the rotation of an intermediate transfer body such as intermediate transfer belt 122. Furthermore, the method may also be a program executed by a computer. Furthermore, the program according to the present disclosure can be recorded on various computer-readable recording media, such as magnetic disks such as magnetic tapes and flexible disks, optical recording media such as DVD-ROMs, DVD-RAMs, CD-ROMs, CD-Rs, MOs, and PDs, and flash memory recording media, and may be produced, transferred, etc. in the form of such recording media, or may be transmitted or supplied in the form of a program via various wired or wireless networks including the Internet, broadcasting, telecommunications lines, satellite communications, etc.

[0236] <Modification> The present disclosure has been described above based on the embodiments, but it goes without saying that the present disclosure is not limited to the above-described embodiments, and the following modified examples can be implemented.

[0237] (1) In the above embodiment, the surrounding environment of the image forming apparatus 100 was not particularly considered. However, the number of forward and reverse rotation switches N can be variably controlled by taking into account the surrounding environment in addition to the magnitude of the belt driving torque Tr.

[0238] For example, the relationship between the belt driving torque Tr and the number of trapped foreign objects W may change depending on the surrounding environment of the image forming apparatus 100.

[0239] For example, whether in a normal temperature and humidity environment (approximately 20°C and 55% RH) or a high temperature and high humidity environment (approximately 30°C and 85% RH), if the coefficient of friction between the cleaning blade 312 and the intermediate transfer belt 122 increases, the belt drive torque Tr increases and the number of trapped foreign matter W decreases. On the other hand, if the way in which the belt drive torque Tr increases and the way in which the number of trapped foreign matter W decreases differs between a normal temperature and humidity environment and a high temperature and high humidity environment, the relationship between the belt drive torque Tr and the number of trapped foreign matter W also differs between a normal temperature and humidity environment and a high temperature and high humidity environment.

[0240] The relationship between the belt drive torque Tr and the number of forward / reverse rotation switches N in the forward / reverse rotation switch count table 165 shown in FIG. 9 is set based on a certain relationship between the belt drive torque Tr and the number of trapped foreign objects W (for example, graph 501 in FIG. 11). Therefore, if this relationship changes depending on the environment, more appropriate foreign object removal control can be performed by correcting the value of the number of forward / reverse rotation switches N relative to the magnitude of the belt drive torque Tr, taking the environment into consideration.

[0241] FIG. 23 is a diagram showing an example of the contents of the forward / reverse switching count table 165a used to correct the forward / reverse switching count N. As shown in FIG.

[0242] In this forward / reverse rotation switching count table 165a, the magnitude of the belt driving torque Tr is divided into the ranges of "25 or more," "10 to 25," and "5 to 10." The ranges of "25 or more" and "10 to 25" differ from the ranges of "30 or more" and "10 to 30" in the forward / reverse rotation switching count table 165 shown in FIG. 9. A high-temperature, high-humidity environment tends to increase the friction coefficient of the cleaning blade 312 and decrease the number of trapped foreign matter W compared to a normal-temperature, normal-humidity environment. Therefore, in a normal-temperature, normal-humidity environment, when the magnitude of the belt driving torque Tr is in the range of 25 to 30, the number of forward / reverse rotation switching count N is set to two (forward / reverse rotation switching count table 165). However, in a high-temperature, high-humidity environment, the number of trapped foreign matter W decreases, so the number of forward / reverse rotation switching count N is set to one, even when the magnitude of the belt driving torque Tr is in the range of 25 to 30, as shown in the forward / reverse rotation switching count table 165a.

[0243] For example, if forward / reverse switching number table 165 is used in a normal temperature and normal humidity environment, and forward / reverse switching number table 165a is used in a high temperature and high humidity environment, the number of forward / reverse operations N of the belt can be determined taking into account the environment as well as the belt drive torque Tr. Switching between the two forward / reverse switching number tables 165 and 165a depending on the environment is equivalent to correcting the threshold value used to determine how many forward / reverse switching numbers N should be.

[0244] Fig. 24 is a partial flowchart showing only the content of the parts that are changed from the flowchart of the forward / reverse rotation of the belt shown in Fig. 19 in the flowchart of the forward / reverse rotation of the belt, which also takes into account the environment around the device. This partial flow corresponds to the correction process that corrects the threshold value for determining the number of forward / reverse switching times N in accordance with the environment. This partial flow is executed between steps S1 and S2 shown in Fig. 19.

[0245] Specifically, it is determined whether the current environment around the image forming apparatus 100 is a normal temperature and humidity environment (step S31). This determination is made based on the results of detection of the temperature and humidity of the space around the image forming apparatus 100 by a temperature and humidity sensor (not shown), but here, an example will be described in which it is determined whether the environment is a normal temperature and humidity environment or a high temperature and high humidity environment.

[0246] If it is determined that the environment is normal temperature and humidity ("Yes" in step S31), the table to be referenced in step S2, which is executed later, is determined to be forward / reverse switching count table 165 (step S32), and the process proceeds to step S2. On the other hand, if it is determined that the environment is not normal temperature and humidity, that is, the environment is high temperature and high humidity ("No" in step S31), the table to be referenced is determined to be forward / reverse switching count table 165a (step S33), and the process proceeds to step S2. In step S2, the forward / reverse switching count N is acquired (set) by referring to table 165 or 165a determined in the previous step S32 or S33.

[0247] In this way, by switching the forward / reverse rotation switching count table according to the environment, i.e., by correcting the threshold value when determining the forward / reverse rotation switching count N, even if a change occurs in the installation environment of the image forming apparatus 100, it becomes possible to set an appropriate value for the forward / reverse rotation switching count N using the threshold value (forward / reverse rotation switching count table) according to the environmental change.

[0248] In the above, an example was described in which table 165 is used in a normal temperature and normal humidity environment and table 165a is used in a high temperature and high humidity environment, but this is not limited to this, and a table suitable for each environment depending on the device configuration is set in advance through experiments, etc.

[0249] In the above example, the coefficient of friction of the cleaning blade 312 is higher in a high-temperature, high-humidity environment than in a normal-temperature, normal-humidity environment, resulting in less trapped foreign matter. Therefore, the number of forward and reverse operations N of the belt is set lower in a high-temperature, high-humidity environment than in a normal-temperature, normal-humidity environment. However, this is not limiting. Depending on the device configuration, the magnitude of the number of forward and reverse operations N of the belt may be reversed due to factors other than the coefficient of friction of the cleaning blade 312. The number of forward and reverse operations N of the belt that is suitable for the device configuration is determined in advance through experiments, etc.

[0250] Furthermore, the table to be used is not limited to the normal temperature and normal humidity environment and the high temperature and high humidity environment, but may also include a table corresponding to a low temperature and low humidity environment (approximately 10° C. and 15% RH), for example.

[0251] Furthermore, although the environmental changes are described as changes in temperature and humidity, the present invention is not limited to these, and for example, only temperature changes or only humidity changes can be used as the environmental changes.Furthermore, the environmental changes are not limited to temperature and humidity, and in cases where the atmospheric pressure differs depending on whether the image forming apparatus 100 is installed at a high altitude or not, and this difference in atmospheric pressure affects the setting of the forward / reverse rotation switching count N, the atmospheric pressure change can also be regarded as the environmental change.

[0252] (2) In the above embodiment, the magnitude of the belt drive torque Tr is estimated from the detection value detected by the torque detector 176 while the intermediate transfer belt 122 rotates in the reverse direction and then forward during the forward / reverse belt operation, and while the photosensitive drum 1 is stopped. However, this is not limited to this.

[0253] For example, if the magnitude of the drive torque (hereinafter referred to as "Trz") required to rotate the photosensitive drum 1 does not change much over a long period of time, the value detected by the torque detector 176 during the forward rotation of the intermediate transfer belt 122 during image formation, minus the drive torque Trz, can be used as an estimated value of the belt drive torque Tr. Alternatively, the torque detector 176 can be disposed midway along the drive transmission path 17B. In this configuration, it is desirable to dispose the torque detector 176 as close as possible to the drive roller 123 that drives the intermediate transfer belt 122 on the drive transmission path 17B.

[0254] (3) In the above embodiment, no particular consideration was given to individual differences in image forming apparatuses 100. However, depending on the individual differences between the apparatuses, the relationship between the belt drive torque and the number of engagements may be as shown in graph 565 (solid line) in FIG. 25 for one apparatus 100 (hereinafter referred to as "apparatus A"), but may be as shown in graph 567 (dashed line) for another apparatus 100 (hereinafter referred to as "apparatus B").

[0255] In such a case, even if a single forward / reverse switching number table 165 can set an appropriate number of forward / reverse belt operations N for device A, it may not be possible to set an appropriate number of forward / reverse switching N for device B.

[0256] This is because individual differences among devices are often caused by variations in the magnitude of rotational resistance of components other than the cleaning blade 312, such as the four primary transfer rollers 5 and the driven roller 124, which vary from device to device.

[0257] For example, if the cleaning blade 312 of devices A and B is actually at the same level of deterioration and has the same number of engagements Wa, but device B is more affected by the rotational resistance of parts other than the cleaning blade 312 than device A, then the estimated value of the belt drive torque Tr of device B will be larger than that of device A. This is shown in graphs 565 and 567.

[0258] That is, when the number of jams Wa is, for example, 5, the magnitude of the belt drive torque Tr in graph 567 showing device B is 15, but the magnitude of the belt drive torque Tr in graph 565 showing device A is 8, and this difference of 7 is the increased torque compared to device A due to the influence of the rotational resistance of parts other than the cleaning blade 312.

[0259] If the degree of deterioration of the cleaning blade 312 is the same in both devices A and B, the number of forward / reverse rotation switches N should be the same; however, when the degree of deterioration of the cleaning blade 312 is the same (when the number of engagements Wa is the same), the belt drive torque Tr in device A is 15 from graph 565, and the belt drive torque Tr in device B is 8 from graph 567, resulting in a difference in the magnitude of the belt drive torque Tr of 7, as mentioned above.

[0260] In this way, even if the degree of deterioration of the cleaning blade 312 is about the same for each device due to individual differences, the magnitude of the belt drive torque Tr is different. In this case, if the forward / reverse rotation switching count table 165 described above is used, the forward / reverse rotation switching count N for device A will be 2, and the forward / reverse rotation switching count N for device B will be 3. This means that even though the degree of deterioration of the cleaning blade 312 is about the same, the forward / reverse rotation switching count N will be different.

[0261] To avoid this, each device can be configured to have a forward / reverse switching count table 165 that takes into account the influence of rotational resistance of parts other than the cleaning blade 312. However, providing a separate forward / reverse switching count table 165 for each device requires setting different values ​​for the range of the belt drive torque Tr (30≦Tr, 10≦Tr<30, etc.) in the forward / reverse switching count table 165 based on experiments or the like for each device at the design stage, which requires a lot of work at the design stage.

[0262] Therefore, instead of this, for example, a configuration can be adopted in which the magnitude Tdn (FIG. 25) of the belt drive torque Tr estimated when the intermediate transfer unit 121A (cleaning blade 312 or intermediate transfer belt 122) was new is stored, a drive torque difference Td between the belt drive torque Tdn when it was new and the current belt drive torque Tr estimated after it was new is calculated, and the forward / reverse rotation switching count N is set from the magnitude of the calculated drive torque difference Td. This drive torque difference Td corresponds to the amount of decrease in the belt drive torque Tr since the intermediate transfer unit 121A was new.

[0263] The belt drive torque Tdn estimated when the belt is new includes the influence of rotational resistance of parts other than the cleaning blade 312. Therefore, by determining the difference in drive torque Td from when the belt is new, it becomes possible to set the number of forward / reverse rotation switches N appropriate for the current degree of deterioration of the cleaning blade 312 for each device, regardless of whether there is an influence of rotational resistance of parts other than the cleaning blade 312 due to individual differences.

[0264] 26 is a diagram showing an example of the contents of a forward / reverse rotation switching count table 165d according to this modification. As shown in the figure, the forward / reverse rotation switching count table 165d has a column for new torque Tdn, a column for drive torque difference Td, and a column for forward / reverse rotation switching count N.

[0265] The value of the belt drive torque Tdn estimated when the intermediate transfer unit 121A was new, Tdn=28 in the example shown in the figure, is written in the column for torque Tdn when new. This estimated value when new can be the value estimated when the belt drive torque estimation process (FIG. 21) was executed when the intermediate transfer unit 121A was new, but instead, for example, an estimated value at the time of production of the image forming apparatus 100 can also be written. Note that, due to differences in the magnitude of rotational resistance of parts other than the cleaning blade 312 caused by individual differences between each apparatus, Tdn may be a different value, such as 30, in other apparatuses.

[0266] In the drive torque difference Td column, each range of the drive torque difference Td for setting the number of forward and reverse switching times N to different numbers is written. This figure shows examples of four different ranges of Td≤10, 10<Td≤20, 20<Td≤30, and 30<Td. Values such as "10" and "20" which are the boundaries of each of these ranges become the thresholds for determining the number of forward and reverse switching times N.

[0267] The smaller the drive torque difference Td, the less the deterioration of the cleaning blade 312 from when it is new, so the number of forward and reverse switching times N is small. The larger the drive torque difference Td, the more the deterioration of the cleaning blade 312 from when it is new has progressed, so the number of forward and reverse switching times N is correspondingly larger. The correspondence relationship between each of these ranges and the number of forward and reverse switching times N is determined in advance by experiments or the like and is stored in the forward and reverse switching times table 165d.

[0268] FIG. 27 is a partial flowchart showing only the content of the part that is changed with respect to the flowchart of the belt forward and reverse operation shown in FIG. 19 in the flowchart of the belt forward and reverse operation when using the forward and reverse switching times table 165d according to this modified example.

[0269] As shown in FIG. 27, the value of the belt drive torque Tr currently stored in the belt drive torque table 164 is read (step S51). This step S51 is the same as step S1 above. Subsequently, referring to the forward and reverse switching times table 165d, the belt drive torque Tdn when new is read (step S52). In the example shown in FIG. 26, Tdn = 28 is read.

[0270] In step S53 shown in FIG. 27, the drive torque difference Td between the read value of the belt drive torque Tr and the belt drive torque Tdn when new is obtained.

[0271] Then, referring to the forward and reverse switching count table 165d, the forward and reverse switching count N corresponding to the magnitude of the obtained drive torque difference Td is acquired (step S54), and the process proceeds to step S3. In the example of FIG. 26, if the drive torque difference Td is 10, since it is in the range of Td ≤ 10, the forward and reverse switching count N = 1 is acquired. If the drive torque difference Td is 20, since it is in the range of 10 < Td ≤ 20, the forward and reverse switching count N = 2 is acquired.

[0272] The fact that the drive torque difference Td increases means that the decrease amount of the belt drive torque Tr from the new product state increases. Each time this decrease amount exceeds the threshold values that are the boundaries of each range in the drive torque difference Td column shown in FIG. 26, in this example, 10, 20, etc., the forward and reverse switching count N increases more than when it does not exceed. Specifically, when the drive torque difference Td (= decrease amount) exceeds 10, the forward and reverse switching count N becomes 2 times, and the forward and reverse switching count N increases compared to 1 time when it is 10 or less.

[0273] By using the drive torque difference Td from the new product state in this way, for each device, the forward and reverse switching count N suitable for the degree of deterioration of the current cleaning blade 312 can be set in a state where the solid difference is eliminated.

[0274] (4) In the above embodiment, the execution count N of the forward and reverse switching operation is variably controlled according to the magnitude of the belt drive torque Tr, but it is not limited to this.

[0275] For example, in the belt forward and reverse operation where the forward and reverse switching operation is performed only once in response to the decrease of the belt drive torque Tr, control can be performed to increase the reverse distance Rd (reverse amount) of the intermediate transfer belt 122. As the belt drive torque Tr becomes smaller, the amount of foreign matter I biting into the cleaning blade 312 increases. Therefore, by increasing the reverse distance Rd of the intermediate transfer belt 122, most of the bitten foreign matter I can be removed.

[0276] FIG. 28 is a diagram showing an example of the contents of a reverse rotation distance table 168 according to this modified example, which replaces the forward / reverse rotation switching count table 165 described above.

[0277] As shown in the figure, the reverse rotation distance table 168 is a table that stores the range of the belt drive torque Tr in association with the reverse rotation distance Rd of the intermediate transfer belt 122, and is generated in advance through experiments, etc. As in the above, the boundaries of each range of the belt drive torque Tr, such as "30" and "10," become threshold values ​​for determining the length of the reverse rotation distance Rd.

[0278] In the forward / reverse belt rotation operation in this modified example, step S2 shown in FIG. 19 is replaced with "referencing the reverse distance table 168 to obtain a reverse distance Rd corresponding to the magnitude of the read belt drive torque Tr," and step S4 is replaced with "determining the reverse rotation amount Rb and forward rotation amount Ra of the drive motor 170 required to move the intermediate transfer belt 122 by the obtained reverse distance Rd and a forward rotation distance Rc that is longer than this, and setting the determined reverse rotation amount Rb and forward rotation amount Ra as the target rotation amount when the drive motor 170 rotates."

[0279] A configuration that variably controls the number of times N the forward / reverse rotation switching operation is performed in accordance with the magnitude of the belt driving torque Tr, and a configuration that variably controls the reverse distance Rd of the intermediate transfer belt 122 in only one forward / reverse rotation operation of the belt in accordance with the magnitude of the belt driving torque Tr are both included in the configuration that controls the amount of reverse rotation of the intermediate transfer body in the forward / reverse rotation operation in accordance with the driving torque of the intermediate transfer body such as the intermediate transfer belt 122 that decreases with deterioration of the cleaning blade 312. Increasing the amount of reverse rotation includes increasing the number of times N the forward / reverse rotation switching operation is performed and increasing the reverse distance Rd in one forward / reverse rotation switching operation.

[0280] This modified example (4) can also be applied to the configuration of modified example (3) above, which uses the difference in driving torque Td from when the belt was new. That is, the reverse rotation distance Rd of the intermediate transfer belt 122 is variably controlled according to the difference in driving torque Td from when the belt was new. Specifically, as the difference in driving torque Td from when the belt was new increases, the reverse rotation distance Rd of the intermediate transfer belt 122 is increased. Note that, if the difference in driving torque Td increases after this increase, control is performed to reduce the reverse rotation distance Rd of the intermediate transfer belt 122, as described above.

[0281] (5) In the above embodiment, an example of a configuration has been described in which the photosensitive drum 1 and the intermediate transfer belt 122 are driven to rotate by the same drive motor 170, but this is not limiting. For example, a configuration in which the photosensitive drum 1 and the intermediate transfer belt 122 are driven to rotate by separate, independent drive sources may also be adopted. In a configuration in which independent drive sources are used, the amount of reverse rotation of the intermediate transfer belt 122 is not limited to the magnitude of the backlash described above. Instead of this, for example, by providing a clutch such as an electromagnetic clutch in the drive transmission path 17A that switches between transmitting and blocking (non-transmitting) the drive force, there is also no need to consider backlash.

[0282] (6) In the above embodiment, the cleaning blade 312 is in counter-contact with the intermediate transfer belt 122. However, the present invention is not limited to this. For example, the tip 330 of the cleaning blade 312 may be in contact with the surface 126 of the intermediate transfer belt 122 in a direction perpendicular to the surface 126, or in the forward rotation direction of the intermediate transfer belt 122 (the direction of arrow D), i.e., in a so-called trailing direction.

[0283] (7) In the above embodiment, an example was described in which the image forming apparatus according to the present disclosure is applied to a tandem color multifunction peripheral, but this is not limited to this. In a configuration in which an image on one or more image carriers is transferred to an intermediate transfer body such as the intermediate transfer belt 122 or an intermediate transfer drum (not shown), and the image transferred to the intermediate transfer body is then transferred to a sheet, and a cleaning blade is used to remove any residue remaining on the intermediate transfer body after transfer, the image forming apparatus according to the present disclosure can be applied to any color image forming apparatus, such as a printer, a copier, or a facsimile machine, or to monochrome image forming apparatus in general.

[0284] Furthermore, although the cleaning blade 312 is made of rubber such as urethane rubber in the above example, the material is not limited to this and may be made of metal such as stainless steel.

[0285] Furthermore, it goes without saying that the materials, sizes, shapes, various values, etc. of the above-mentioned members are not limited to those mentioned above, and appropriate materials, sizes, etc. can be determined depending on the device configuration.

[0286] Furthermore, the contents of the above-described embodiment and the above-described modified examples may be combined with each other. [Industrial Applicability]

[0287] The present disclosure can be applied to an image forming apparatus that removes residues on an intermediate transfer member with a cleaning blade. [Explanation of symbols]

[0288] 1 Photosensitive drum 17A, 17B drive transmission path 92 Belt forward / reverse rotation control section 93 Belt drive torque estimation unit 122 Intermediate transfer belt 127 Belt cleaning section 164 Belt-driven torque table 165, 165a, 165d Forward / reverse switching count table 166 Motor forward / reverse rotation amount table 170 drive motor 176 Torque detector (torque detection unit) 312 Cleaning Blade 478 Backlash play

Claims

1. An image forming apparatus that rotates an intermediate transfer member that is rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer member to a sheet, a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a driving unit that performs a forward / reverse rotation operation including at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction, thereby removing residues trapped between the intermediate transfer body and the cleaning blade; a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse operation so as to increase in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; a storage unit that stores a driving torque of the cleaning blade or the intermediate transfer member when the cleaning blade or the intermediate transfer member is new; Equipped with The control unit estimates the current driving torque of the intermediate transfer member, which has decreased since the time when the intermediate transfer member was new, and increases the amount of reverse rotation when a difference between the driving torque when the intermediate transfer member was new and the estimated current driving torque exceeds a threshold value. An image forming apparatus characterized by:

2. 2. The image forming apparatus according to claim 1, wherein the control unit increases the number of times the switching operation is performed, thereby increasing the amount of reverse rotation of the intermediate transfer member.

3. 3. The image forming apparatus according to claim 2, wherein the control unit increases the number of times the switching operation is performed when the difference exceeds the threshold value.

4. 4. The image forming apparatus according to claim 3, wherein, after increasing the number of times of the switching operation, if the driving torque of the intermediate transfer body increases, the control unit reduces the number of times of the switching operation to a value less than the increased number.

5. The image forming apparatus according to claim 1 , wherein the control unit increases the reverse rotation distance of the intermediate transfer body in one switching operation, thereby increasing the amount of reverse rotation of the intermediate transfer body.

6. The image forming apparatus according to claim 5 , wherein the control unit increases the reverse rotation distance when the difference exceeds the threshold value.

7. 7. The image forming apparatus according to claim 6, wherein, after increasing the reverse rotation distance, if the driving torque of the intermediate transfer body increases, the control unit reduces the reverse rotation distance to a value less than the increased distance.

8. An image forming apparatus that rotates an intermediate transfer member that is rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer member to a sheet, a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a driving unit that performs a forward / reverse rotation operation including at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction, thereby removing residues trapped between the intermediate transfer body and the cleaning blade; a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse operation so as to increase in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; Equipped with when the driving torque of the intermediate transfer body falls below a threshold, the control unit increases the number of times the switching operation is performed or increases the distance by which the intermediate transfer body is reversed in one switching operation, thereby increasing the amount of reverse rotation of the intermediate transfer body; Furthermore, the image forming apparatus is characterized in that, when the driving torque of the intermediate transfer body falls below a second threshold value that is smaller than the threshold value, it is determined that one or both of the intermediate transfer body and the cleaning blade have reached the end of their lives.

9. An image forming apparatus that rotates an intermediate transfer member that is rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer member to a sheet, a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a driving unit that performs a forward / reverse rotation operation including at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction, thereby removing residues trapped between the intermediate transfer body and the cleaning blade; a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse operation so as to increase in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; Equipped with The image forming apparatus is characterized in that the control unit controls the amount of reverse rotation of the intermediate transfer body by taking into account not only the reduction in the drive torque of the intermediate transfer body but also the surrounding environment of the image forming apparatus.

10. An image forming apparatus that rotates an intermediate transfer member that is rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer member to a sheet, a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a driving unit that performs a forward / reverse rotation operation including at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction, thereby removing residues trapped between the intermediate transfer body and the cleaning blade; a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse operation so as to increase in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; a rotating member that rotates by receiving a driving force from the driving unit, separate from the intermediate transfer body; Equipped with The drive unit is a drive source capable of rotating forward and backward; a first transmission path that transmits the driving force of the driving source to the intermediate transfer body and a second transmission path that transmits the driving force to the rotating member, Each of the first transmission path and the second transmission path is not provided with a clutch that switches between transmitting and cutting off the driving force, a second backlash in the second transmission path is larger than a first backlash in the first transmission path; an image forming apparatus characterized in that the drive unit reverses the intermediate transfer body during the switching operation so that the amount of reverse rotation of the drive source is greater than a first backlash in the first transmission path and is equal to or less than a second backlash in the second transmission path.

11. a rotating member that rotates by receiving a driving force from the driving unit, separate from the intermediate transfer body; The drive unit is a drive source capable of rotating forward and backward; a first transmission path that transmits the driving force of the driving source to the intermediate transfer body; and a second transmission path that branches off from a branch point along the first transmission path and transmits the driving force of the driving source to the rotating member. a torque detector interposed between the driving source and the branch point; Equipped with 10. The image forming apparatus according to claim 1, wherein the control unit estimates the driving torque of the intermediate transfer member from the detection result of the torque detection unit.

12. An image forming apparatus that rotates an intermediate transfer member that is rotatable in forward and reverse directions in a forward direction to transfer an image formed on the intermediate transfer member to a sheet, a cleaning blade that contacts the intermediate transfer body to remove residue on the intermediate transfer body after transfer; a driving unit that performs a forward / reverse rotation operation including at least one switching operation of rotating the intermediate transfer body in a reverse direction and then in a forward direction, thereby removing residues trapped between the intermediate transfer body and the cleaning blade; a control unit that controls the amount of reverse rotation of the intermediate transfer body during the forward / reverse operation so as to increase in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; a rotating member that rotates by receiving a driving force from the driving unit, separate from the intermediate transfer body; Equipped with The drive unit is a drive source capable of rotating forward and backward; a first transmission path that transmits the driving force of the driving source to the intermediate transfer body; and a second transmission path that branches off from a branch point along the first transmission path and transmits the driving force of the driving source to the rotating member. a torque detector interposed between the driving source and the branch point; Equipped with the control unit estimates a driving torque of the intermediate transfer member from a detection result of the torque detection unit; moreover, Each of the first transmission path and the second transmission path is not provided with a clutch that switches between transmitting and cutting off the driving force, a second backlash in the second transmission path is larger than a first backlash in the first transmission path; The control unit When the drive source switches from reverse rotation to forward rotation, the play caused by the first backlash in the first transmission path disappears, and the drive force in the forward rotation direction of the drive source is transmitted to the intermediate transfer body through the first transmission path, and the intermediate transfer body rotates forward, and While the driving force of the driving source in the forward rotation direction is not transmitted to the rotating member through the second transmission path in a state where there is play due to the second backlash of the second transmission path, an image forming apparatus including: estimating a driving torque of the intermediate transfer member from a result detected by the torque detection unit;

13. the torque detection unit is a strain gauge, The image forming apparatus according to claim 12, wherein the control unit stops the drive source, which is rotating in the forward direction, before the second transmission path transitions from a state in which there is play due to the second backlash to a state in which there is no play, and in the stopped state, the detection value by the strain gauge is set as the drive torque detected by the torque detection unit.

14. A photoreceptor; a developing unit that develops the electrostatic latent image on the photosensitive member with a developer, the developing unit includes a developer-carrying rotor that carries a developer, 14. The image forming apparatus according to claim 10, wherein the rotating member is one or both of the photosensitive member and the developer carrying rotating member.

15. the drive unit includes a motor that applies a driving force to the intermediate transfer body, 11. The image forming apparatus according to claim 1, wherein the control unit estimates a driving torque of the intermediate transfer member based on a value of a current flowing through the motor.

16. a photoreceptor on which an image is formed; a transfer unit that transfers the image formed on the intermediate transfer body to a sheet, the transfer unit further includes a primary transfer member that primarily transfers the image formed on the photosensitive member onto the intermediate transfer member that rotates in the forward direction; the primary transfer member is disposed on the opposite side of the intermediate transfer body from the photosensitive body, and is capable of being brought into contact with and separated from the intermediate transfer body; The image forming apparatus according to any one of claims 11 to 13 and 15, characterized in that the control unit brings the primary transfer member into contact with the intermediate transfer body during primary transfer, and separates the primary transfer member from the intermediate transfer body when estimating the driving torque of the intermediate transfer body.

17. a photoreceptor on which an image is formed; a transfer unit that transfers the image formed on the intermediate transfer body to a sheet, the transfer unit has a primary transfer member that primarily transfers the image formed on the photosensitive member onto the intermediate transfer member that rotates in the forward direction; The image forming apparatus according to claim 11 or 15, wherein the control unit applies a transfer bias to the primary transfer member during primary transfer, and cuts off application of the transfer bias to the primary transfer member when estimating the driving torque of the intermediate transfer body.

18. 1. A method for controlling rotation of an intermediate transfer body in an image forming apparatus, the method comprising: rotating an intermediate transfer body rotatable in forward and reverse directions in a forward direction, transferring an image formed on the intermediate transfer body to a sheet, and removing any residue on the intermediate transfer body after transfer with a cleaning blade; a driving step of performing a forward / reverse operation of switching the rotation of the intermediate transfer body from reverse rotation to forward rotation at least once to remove residues trapped between the intermediate transfer body and the cleaning blade; a control step of increasing a reverse rotation amount of the intermediate transfer body in the forward / reverse operation in response to a decrease in driving torque of the intermediate transfer body due to deterioration of the cleaning blade; Perform steps including the image forming apparatus includes a storage unit that stores a driving torque of the cleaning blade or the intermediate transfer member when the cleaning blade or the intermediate transfer member is new, The control step estimates a current driving torque of the intermediate transfer member that has decreased since the time of the new product, and increases the reverse rotation amount when a difference between the driving torque of the new product and the estimated current driving torque exceeds a threshold value. A method for controlling the rotation of an intermediate transfer member.

Images