Image forming device

Abstract

To provide an image forming apparatus that interposes a coupling having play in a rotation direction in a drive train between a motor and bodies to be driven, and can prevent a deterioration in the accuracy of control of switching the motor from forward rotation to reverse rotation.SOLUTION: An image forming apparatus comprises: one motor 92a that drives to rotate a photoconductor drum 26 and a developing sleeve 71; a coupling that is interposed in at least either one of a drive train between the motor 92a and the developing sleeve 71 or a drive train between the motor 92a and the photoconductor drum 26, and has play in a rotation direction; and a CPU 53 that controls the motor 92a. The CPU 53 forwardly rotates the motor 92a at a speed V1 during image formation, stops the motor 92a after the end of the image formation, subsequently forwardly rotates the motor 92a at a speed V2 slower than the speed V1, and then reversely rotates the motor 92a.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer (for example, a laser beam printer, an LED printer, etc.). [Background technology]

[0002] In an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photosensitive drum, and the electrostatic latent image is developed by a developing unit to form an image. Here, Patent Document 1 describes a configuration in which one motor is used to rotate both the photosensitive drum and the developing sleeve of the developing unit. By driving multiple members with one motor in this way, it is possible to reduce the size and cost of the image forming apparatus compared to a configuration using multiple motors.

[0003] Patent Document 1 also describes a configuration for selectively rotating the photosensitive drum and the developing sleeve. In the configuration of Patent Document 1, a coupling having a predetermined rotation angle is provided in a power transmission mechanism between a drive source and the developing sleeve. With this configuration, both the photosensitive drum and the developing sleeve rotate when the motor is rotated forward. When the motor is rotated backward by the above-mentioned predetermined rotation angle, the developing sleeve does not rotate, and the photosensitive drum rotates in the opposite direction to when the motor is rotating forward. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-234643 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, when the motor is stopped to switch from forward rotation to reverse rotation, the photosensitive drum and developing sleeve, which are the driven bodies, rotate due to inertia after the motor is stopped. Due to the rotation of the driven bodies due to this inertia, the stop position of the coupling, which has play in the rotational direction and is interposed in the drive train between the motor and the driven bodies, deviates from the ideal stop position where the coupling is in a state where the backlash is eliminated in the rotational direction when the motor rotates forward. In this way, when the motor is rotated in reverse in a state where the stop position of the coupling is deviated from the ideal stop position, the timing at which the driven bodies start to rotate in reverse deviates from the ideal timing, and the accuracy of the reverse rotation control deteriorates.

[0006] Therefore, the present invention aims to provide an image forming device that can suppress deterioration in the accuracy of control when switching a motor from forward rotation to reverse rotation in a configuration in which a coupling with rotational play is interposed in the drive train between the motor and the driven body. [Means for solving the problem]

[0007] A representative configuration of an image forming apparatus according to the present invention for achieving the above object includes a photoconductor, a developer carrier that carries a developer and develops an electrostatic latent image formed on the photoconductor, a motor that rotates in a first rotation direction and a second rotation direction opposite to the first rotation direction and drives the photoconductor and the developer carrier to rotate, a coupling provided in at least one of a first drive train that transmits drive from the motor to the developer carrier or a second drive train that transmits drive from the motor to the photoconductor, the coupling having play in the rotation direction of the coupling, and a control unit that controls the motor, the coupling having play in the first rotation direction when an electrostatic latent image formed on the photoconductor is developed, the control unit controlling the motor, At first speed a control unit that controls the motor so as to rotate the photoconductor in the first rotation direction, Third The developer carrier rotates in the rotation direction of FourthIn a state where the motor is rotating in the second rotation direction, the photoconductor rotates in a direction opposite to the third rotation direction, the developer carrier rotates in a direction opposite to the fourth rotation direction, and after the motor rotates in the first rotation direction, when the control unit controls the motor to rotate in the second rotation direction, the control unit controls the motor, which is stopped, to rotate in the first rotation direction. At a second speed lower than the first speed and after controlling the motor to rotate in the second rotational direction, controlling the motor to rotate in the second rotational direction. It is characterized by: Effect of the Invention

[0008] According to the present invention, in an image forming device configured to have a coupling having rotational play in a drive train between a motor and a driven body, it is possible to suppress deterioration in the accuracy of control for switching the motor from forward rotation to reverse rotation. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] 1 is a block diagram showing a system configuration of an image forming apparatus. [Diagram 3] FIG. 2 is a perspective view of the process cartridge. [Figure 4] FIG. 2 is a cross-sectional view of the process cartridge. [Diagram 5] FIG. [Figure 6] FIG. 2 is a cross-sectional view of the drum unit. [Figure 7] FIG. [Figure 8] 3A and 3B are front and rear views of the drive unit. [Figure 9] FIG. 4 is a diagram showing gears of a drive unit. [Figure 10] 2A and 2B are diagrams illustrating configurations of a drive coupling, a drum coupling, and a development coupling. [Figure 11] FIG. 2 is an exploded perspective view of the Oldham coupling. [Figure 12] FIG. 2 is an exploded perspective view of the Oldham coupling. [Figure 13] 4A and 4B are diagrams showing a fitting portion between the developing drive gear, the intermediate member, and the drive coupling of the Oldham coupling; [Figure 14] 5 is a timing chart showing ideal operation timings of each member after the image forming operation is completed. [Figure 15] FIG. 4 is a diagram showing the positional relationship between a development coupling and a drive coupling. [Figure 16] 4 is a flowchart of a reverse rotation sequence. [Figure 17] FIG. 4 is a diagram showing the positional relationship between a development coupling and a drive coupling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Image forming device> The overall configuration of the image forming apparatus according to the present invention will be described below together with the operation during image formation with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, etc. of the components described below are not intended to limit the scope of the present invention unless otherwise specified.

[0011] The image forming apparatus A according to this embodiment is an intermediate tandem type image forming apparatus that transfers four colors of toner, yellow Y, magenta M, cyan C, and black K, as developers onto an intermediate transfer belt, and then transfers the image onto a sheet to form an image. Note that in the following description, although the components that use the above-mentioned toners of each color are given the suffixes Y, M, C, and K, the configurations and operations of the components are essentially the same except for the color of the toner used, and therefore the suffixes will be omitted as appropriate unless a distinction is required.

[0012] Fig. 1 is a schematic cross-sectional view of an image forming apparatus A. As shown in Fig. 1, the image forming apparatus A includes an image forming unit 61 that forms an image on a sheet S. The image forming unit 61 includes process cartridges 65 (65Y, 65M, 65C, 65K), a laser scanner unit 28, a primary transfer roller 31 (31Y, 31M, 31C, 31K), an intermediate transfer belt 30, a secondary transfer roller 51, and a secondary transfer opposing roller 52.

[0013] Each process cartridge 65 (image forming unit) is configured to be detachably attached to the image forming apparatus A. Each process cartridge 65 includes a photosensitive drum 26 (26Y, 26M, 26C, 26K) as a photosensitive member, and a charging roller 27 (27Y, 27M, 27C, 27K). Each process cartridge 65 also includes a developing unit 29 (29Y, 29M, 29C, 29K) having a developing sleeve 71 (71Y, 71M, 71C, 71K) as a developer carrier, and a cleaning blade 45 (45Y, 45M, 45C, 45K). That is, the photosensitive drum 26, the charging roller 27, the developing sleeve 71, and the cleaning blade 45 are integrated as the process cartridge 65.

[0014] Next, the image forming operation will be described. First, when a control unit (not shown) receives an image forming job signal, a sheet S stored in a sheet cassette 22 is conveyed to a registration roller 24 by a feed roller 66. Thereafter, the registration roller 24 conveys the sheet S to a secondary transfer unit formed by a secondary transfer roller 51 and a secondary transfer counter roller 52 at a predetermined timing.

[0015] Meanwhile, in the image forming section 61, the surface of the photosensitive drum 26Y is first charged by the charging roller 27Y. Then, the laser scanner unit 28 irradiates the surface of the photosensitive drum 26Y with laser light in accordance with image data input from an external device (not shown). As a result, an electrostatic latent image in accordance with the image data is formed on the surface of the photosensitive drum 26Y.

[0016] Next, a developing sleeve 71Y of the developing unit 29Y causes yellow toner to adhere to the electrostatic latent image formed on the surface of the photosensitive drum 26Y, forming a yellow toner image (developer image) on the surface of the photosensitive drum 26Y. The toner image formed on the surface of the photosensitive drum 26Y is primarily transferred to the intermediate transfer belt 30 by applying a bias to a primary transfer roller 31Y. Thereafter, the toner remaining on the surface of the photosensitive drum 26Y is scraped off by a cleaning blade 45Y. The cleaning blade 45Y comes into contact with the surface of the photosensitive drum 26Y in a counter direction to the rotation direction of the photosensitive drum 26Y during image formation.

[0017] By a similar process, magenta, cyan and black toner images are also formed on the photosensitive drums 26M, 26C and 26K. Then, by applying a bias to the primary transfer rollers 31M, 31C and 31K, these toner images are transferred and superimposed on the yellow toner image on the intermediate transfer belt 30. As a result, a full-color toner image is formed on the surface of the intermediate transfer belt 30. Thereafter, the toner remaining on the surfaces of the photosensitive drums 26M, 26C and 26K is scraped off by the cleaning blades 45M, 45C and 45K.

[0018] The intermediate transfer belt 30 rotates in accordance with the rotation of the secondary transfer opposing roller 52. As the intermediate transfer belt 30 carrying the full-color toner image moves, the toner image is sent to a secondary transfer section. In the secondary transfer section, a bias is applied to the secondary transfer roller 51, so that the toner image on the intermediate transfer belt 30 is transferred to the sheet S.

[0019] Next, the sheet S onto which the toner image has been transferred is conveyed to a fixing section 36, where it is subjected to a heating and pressure treatment, thereby fixing the toner image on the sheet S to the sheet S. Thereafter, the sheet S onto which the toner image has been fixed is discharged to a discharge section 40 by a discharge roller 38.

[0020] <Control Unit> Next, the system configuration of the image forming apparatus A will be described.

[0021] Fig. 2 is a block diagram showing the system configuration of the image forming apparatus A. As shown in Fig. 2, the image forming apparatus A includes a CPU 53 (control unit), a ROM 54, a RAM 55, a user interface unit 56, a counter 57, a timer 58, and a motor control unit 59.

[0022] ROM 54 stores various control programs and data, such as firmware programs and boot programs for controlling the firmware programs. RAM 55 has a program load area, a work area, and an area for storing various data. CPU 53 controls each device of image forming apparatus A based on the various control programs stored in ROM 54, using RAM 55 as a work area and a temporary storage area for data.

[0023] The user interface unit 56 is connected to an external device such as a touch panel type operation unit (not shown) or a PC via an Internet line, and accepts various jobs from a user via these and transmits the jobs to the CPU 53. The counter 57 counts the number of images formed on the image forming apparatus A and transmits the count value to the CPU 53. The timer 58 performs timekeeping according to instructions from the CPU 53.

[0024] The motor control unit 59 controls a motor 92a which is a drive source for the photosensitive drums 26Y, 26M, and 26C and the developing sleeves 71Y, 71M, and 71C, and a motor 92b which is a drive source for the photosensitive drum 26K and the developing sleeve 71K. The CPU 53 issues instructions to the motor control unit 59 regarding the control of the motors 92a and 92b, and controls the motors 92a and 92b via the motor control unit 59.

[0025] <Process cartridge> Next, the structure of the process cartridge 65 will be described.

[0026] Fig. 3 is a perspective view of the process cartridge 65. Fig. 4 is a cross-sectional view of the process cartridge 65. As shown in Figs. 3 and 4, the process cartridge 65 is made up of a drum unit 42 and a developing unit 29.

[0027] First, the configuration of the drum unit 42 will be described. Fig. 5 is a perspective view of the drum unit 42. Fig. 6 is a cross-sectional view of the periphery of the photosensitive drum 26 in the drum unit 42, and is a diagram showing the state in which the charging roller 27 separates from the photosensitive drum 26 in the order of Fig. 6(a) to Fig. 6(d). As shown in Figs. 5 and 6, the drum unit 42 has the photosensitive drum 26, the charging roller 27, and a cleaning blade 45, and these members are integrally held by the drum container 11.

[0028] The drum container 11 rotatably holds the photosensitive drum 26. A drum coupling 13 that receives a driving force from a drive unit 90, which will be described later, is provided integrally with the photosensitive drum 26 at one end of the drum container 11 in the direction of the rotation axis of the photosensitive drum 26. The drum coupling 13 is disposed on the rear side of the image forming apparatus A in the drum container 11. Furthermore, flange gears 14 are provided integrally with the photosensitive drum 26 at both ends of the photosensitive drum 26 in the direction of the rotation axis.

[0029] The drum container 11 is also provided with a recovery section 16 (FIG. 4) that recovers the toner removed from the surface of the photosensitive drum 26 by the cleaning blade 45. A transport screw 17 is provided inside the recovery section 16 to transport the toner in the recovery section 16 to the outside of the drum unit 42. The transport screw 17 is rotated by a driving force transmitted from the flange gear 14 via an idler gear 67 to transport the toner. The toner transported to the outside of the drum unit 42 by the transport screw 17 is collected in a container (not shown) provided in the image forming apparatus A.

[0030] The drum container 11 is also provided with a bearing 19 that rotatably holds the charging roller 27. The bearing 19 is held in the drum container 11 so as to be slidable in a direction approaching or moving away from the photosensitive drum 26, and is biased toward the photosensitive drum 26 by a spring 12. Due to this biasing force, the charging roller 27 is pressed against the photosensitive drum 26 and rotates in response to the rotation of the photosensitive drum 26.

[0031] One-way clutches 21 are provided on both ends of the charging roller 27. When a torque in the opposite direction to the rotation direction of the charging roller 27 during image formation is applied to the one-way clutch 21, the one-way clutch 21 is locked and rotates integrally with the charging roller 27. When a torque (idling torque) equal to or greater than a predetermined value in the same direction as the rotation direction of the charging roller 27 during image formation is applied to the one-way clutch 21, the locked state is released and the one-way clutch 21 rotates idly without transmitting driving force between the charging roller 27. In this embodiment, the one-way clutch 21 is configured using a latch claw and a rack.

[0032] Further, a spacing member 32 having gear portions 32a that mesh with flange gears 14 provided at both ends of the photosensitive drum 26 is provided on the outer periphery of the one-way clutch 21. The spacing member 32 and the one-way clutch 21 always rotate together regardless of the rotation direction. In other words, when the charging roller 27 rotates in the opposite direction to the rotation direction during image formation in response to the rotation of the photosensitive drum 26, the one-way clutch 21 and the spacing member 32 rotate in conjunction with this. The spacing member 32 separates the charging roller 27 from the photosensitive drum 26 by the operation described below in order to prevent the charging roller 27 from being deformed due to the charging roller 27 being in pressure contact with the photosensitive drum 26 for a long period of time, which would adversely affect image quality.

[0033] That is, as shown in FIG. 6(a), while the image forming apparatus A is performing the image forming operation, the gear portion 32a of the spacing member 32 and the flange gear 14 are separated and do not mesh with each other. When a predetermined time has elapsed after the image forming apparatus A has finished the image forming operation, the photosensitive drum 26 rotates in the opposite direction to the rotation direction during image formation. As a result, the charging roller 27 also rotates in the opposite direction to the rotation direction during image formation, following the rotation of the photosensitive drum 26, and the one-way clutch 21 and the spacing member 32 also rotate. As shown in FIG. 6(b), when the spacing member 32 rotates, the gear portion 32a of the spacing member 32 meshes with the flange gear 14. In this embodiment, when the charging roller 27 rotates 54 degrees, the one-way clutch 21 is locked. As a result, the gear portion 32a of the spacing member 32, which rotates integrally with the one-way clutch 21, meshes with the flange gear 14. Incidentally, until the gear portion 32a of the spacing member 32 meshes with the flange gear 14, the charging roller 27 rotates at a diameter ratio to the photosensitive drum 26. In this embodiment, the diameter of the photosensitive drum 26 is φ30 mm, and the diameter of the charging roller 27 is φ14 mm, so that the amount of rotation of the photosensitive drum 26 is 25.2 degrees.

[0034] 6C, when the photosensitive drum 26 and the charging roller 27 continue to rotate in the direction opposite to the rotation direction during image formation, the one-way clutch 21 and the spacing member 32 also rotate further. When the spacing member 32 rotates further, a force acts on the charging roller 27 in the direction separating it from the photosensitive drum 26 due to the shape of the spacing member 32, and this force separates the charging roller 27 from the photosensitive drum 26 against the biasing force of the spring 12. In this embodiment, when the charging roller 27 rotates further 45 degrees after the gear portion 32a of the spacing member 32 meshes with the flange gear 14, the charging roller 27 separates from the photosensitive drum 26. After the gear portion 32a of the spacing member 32 meshes with the flange gear 14, the charging roller 27 rotates at a gear ratio between the gear portion 32a of the spacing member 32 and the flange gear 14. In this embodiment, the amount of separation between the photosensitive drum 26 and the charging roller 27 is 1 mm, and therefore the amount of rotation of the photosensitive drum 26 is 24 degrees. Note that, when the photosensitive drum 26 rotates in the rotation direction during image formation during the next image formation, the charging roller 27 separated from the photosensitive drum 26 performs an operation opposite to the above-mentioned separating operation, and comes into contact with the photosensitive drum 26 again.

[0035] 6(d), if the photosensitive drum 26 continues to rotate in the direction opposite to the rotation direction during image formation after the charging roller 27 is separated from the photosensitive drum 26, the spacing member 32 may come into contact with the drum container 11, causing a malfunction. In this embodiment, when the charging roller 27 and the photosensitive drum 26 rotate by another 45 degrees (24 degrees in terms of the amount of rotation of the photosensitive drum 26) after being separated from each other, the spacing member 32 comes into contact with the drum container 11. Therefore, in this embodiment, in order to prevent the spacing member 32 from coming into contact with the drum container 11 while separating the charging roller 27 from the photosensitive drum 26, the amount of rotation in the direction opposite to the rotation direction during image formation of the photosensitive drum 26 is set to 49.2 degrees to 73.2 degrees.

[0036] Next, the configuration of the developing unit 29 will be described. Fig. 7 is a perspective view of the developing unit 29. In Fig. 7, a part of the developing container 70 is cut away to explain the internal configuration of the developing unit 29. As shown in Fig. 7, the developing unit 29 includes a developing sleeve 71, a developing blade 72, and conveying screws 73 and 74, and these members are integrally held by the developing container 70.

[0037] The developing container 70 has an opening at a portion facing the photosensitive drum 26, and the developing sleeve 71 is disposed so as to be partially exposed to this opening. The developing sleeve 71 is disposed facing the photosensitive drum 26 with a predetermined gap (240 μm in this embodiment) therebetween. A developing coupling 75 that receives a driving force from a drive unit 90, which will be described later, is provided at one end side of the developing sleeve 71 in the rotational axis direction. The developing sleeve 71 rotates by the driving force transmitted from the drive unit 90 via the developing coupling 75.

[0038] The developing coupling 75 is held by the developing container 70 at one end side in the rotation axis direction of the developing sleeve 71 in the developing container 70, at a position on the rear side of the image forming apparatus A. A D-cut shaped engaging portion (not shown) that engages with the developing coupling 75 is formed on the rotation shaft of the developing sleeve 71, whereby the developing sleeve 71 rotates integrally with the developing coupling 75. A sleeve gear 81 is provided on one end side of the developing sleeve 71 in the developing container 70. The sleeve gear 81 is connected to the rotation shaft of the developing sleeve 71 by a parallel pin (not shown), and rotates integrally with the developing sleeve 71.

[0039] The developing sleeve 71 also includes a magnet roller 76 (FIG. 4) having a plurality of magnetic poles in a non-rotating state. As shown in FIG. 4, the magnet roller 76 has a developing pole S1 in a developing area facing the photosensitive drum 26. The magnet roller 76 also has a transport pole N1, a stripping pole N2, a draw-up pole S2, and a cut pole N3 in this order downstream of the developing pole S1 in the rotation direction of the developing sleeve 71 during image formation. The center positions of these magnetic poles are 60 degrees for the transport pole N1, 180 degrees for the stripping pole N2, 230 degrees for the draw-up pole S2, and 290 degrees for the cut pole N3 along the rotation direction of the developing sleeve 71 during image formation (counterclockwise direction in FIG. 4) when the developing pole S1 is set to 0 degrees. The magnet roller 76 carries the toner by the magnetic force of each magnetic pole and transports the toner to the developing area during image formation.

[0040] That is, the magnet roller 76 first draws up the toner contained in the developing container 70 with the drawing-up pole S2, and causes the developing sleeve 71 to carry the toner. Next, the toner carried on the developing sleeve 71 is made to stand like brush-like spikes with the cutting pole N3. The toner made to stand is then transported to the developing area by the rotation of the developing sleeve 71, and moved onto the photosensitive drum 26 by the developing pole S1. Thereafter, the toner remaining on the developing sleeve 71 gradually rises toward the center position between the transport pole N1 and the stripping pole N2 due to the repulsive magnetic field formed by the transport pole N1 and the stripping pole N2, and is finally stripped off from the developing sleeve 71.

[0041] Further, a developing blade 72 is provided near the developing sleeve 71 with a predetermined gap between it and the developing sleeve 71. The developing blade 72 comes into contact with the toner carried on the developing sleeve 71 to form a toner layer of a predetermined thickness. Specifically, as the developing sleeve 71 rotates, the toner carried on the developing sleeve 71 and made to stand up by the cutting pole N3 passes between the tip of the developing blade 72 and the surface of the developing sleeve 71, thereby regulating the amount of toner and forming a toner layer. Further, a scooping sheet 77 is attached to the developing blade 72 on the side opposite to the side where the developing sleeve 71 is disposed, to prevent the toner from scattering outside the developing container 70.

[0042] The inside of the developing container 70 is partitioned into a developing chamber 79 and an agitating chamber 80 by a partition wall 78 extending in the direction of the rotation axis of the developing sleeve 71. Communication parts (not shown) that connect the developing chamber 79 and the agitating chamber 80 are provided at both ends of the partition wall 78 in the longitudinal direction.

[0043] The developing chamber 79 and the stirring chamber 80 are provided with conveying screws 73 and 74 that rotate to convey toner with their spiral blades. The conveying screws 73 and 74 convey toner in the longitudinal direction of the partition wall 78, and in opposite directions to each other. The conveying screws 73 and 74 are rotated by a driving force transmitted from a sleeve gear 81 that is provided integrally with the developing sleeve 71. When the conveying screws 73 and 74 rotate, the toner circulates between the developing chamber 79 and the stirring chamber 80 via a communication portion (not shown).

[0044] In addition, every time an image forming operation is performed, toner accumulates in the space surrounded by the developing sleeve 71, the developing blade 72, and the scoop sheet 77 in the developing container 70. If the amount of accumulated toner becomes excessive, the accumulated toner may enter the developing area and cause an image defect called a stained image. In order to suppress this, the developing sleeve 71 rotates in the opposite direction to the rotation direction during image formation during non-image formation after a predetermined number of image forming operations, and moves the toner accumulated in the space surrounded by the developing sleeve 71, the scoop sheet 77, and the developing blade 72 to the stirring chamber 80 side. Specifically, the toner raised by the repulsive magnetic field formed by the transport pole N1 and the peeling pole N2 passes through the space surrounded by the developing sleeve 71, the scoop sheet 77, and the developing blade 72 due to the rotation of the developing sleeve 71, and pushes the toner accumulated in this space back to the stirring chamber 80 side. In this embodiment, this operation is performed every time 500 image forming operations are performed on A4 paper.

[0045] Here, if the amount of rotation of the developing sleeve 71 in the direction opposite to the rotation direction during image formation is large and a large amount of toner pumped up by the pumping pole S2 is transported to the development area without passing through the developing blade 72, there is a risk that the toner will scatter outside the developing container 70. In order to prevent this, the amount of rotation of the developing sleeve 71 in the direction opposite to the rotation direction during image formation is set to the angle from the transport pole N1 to the stripping pole N2. That is, in this embodiment, the angle around the rotation axis of the developing sleeve 71 is set to an angle of 60 degrees to 180 degrees.

[0046] <Drive unit> Next, the configuration of the drive unit 90 that drives the process cartridge 65 will be described.

[0047] Fig. 8(a) is a front view of the drive unit 90. Fig. 8(b) is a rear view of the drive unit 90. Fig. 9 is a diagram showing gears included in the drive unit 90. As shown in Figs. 8 and 9, the drive unit 90 includes a box-shaped drive frame 91 formed by a rear frame 91a and a front frame 91b.

[0048] A motor 92a serving as a drive source for the photosensitive drums 26Y, 26M, and 26C and the developing sleeves 71Y, 71M, and 71C, and a motor 92b serving as a drive source for the photosensitive drum 26K and the developing sleeve 71K are fixed to the drive frame 91. In this embodiment, the motors 92a and 92b are DC brushless motors.

[0049] A pinion gear 93a is attached to the shaft of the motor 92a. A drum reduction gear 94a1 meshes with the pinion gear 93a, and drum drive gears 95M and 95C mesh with the drum reduction gear 94a1. A drum reduction gear 94a2 meshes with the drum drive gear 95M and drum drive gear 95Y. Due to the gear ratio of this gear train, the rotation speed of the drum drive gears 95Y, 95M, and 95C is reduced relative to the rotation speed of the motor 92a.

[0050] A pinion gear 93b is attached to the shaft of the motor 92b. The pinion gear 93b meshes with a drum reduction gear 94b, and the drum reduction gear 94b meshes with a drum drive gear 95K. Due to the gear ratio of this gear train, the rotation speed of the drum drive gear 95K is reduced relative to the rotation speed of the motor 92b.

[0051] Further, drive couplings 96Y, 96M, 96C, and 96K that engage with the drum couplings 13 provided in the process cartridges 65Y, 65M, 65C, and 65K are provided coaxially with the drum drive gears 95Y, 95M, 95C, and 95K. Here, as shown in Fig. 10(a), a play α in the rotational direction is provided between the drive coupling 96 of each color and the drum coupling 13. In this embodiment, the play α is set to an angle of 34 degrees around the rotation axis of the photosensitive drum 26.

[0052] With this configuration, the driving force of the motor 92a is transmitted to the drum coupling 13 via the pinion gear 93a, the drum reduction gears 94a1 and 94a2, the drum driving gears 95Y, 95M, and 95C, and the driving couplings 96Y, 96M, and 96C. This causes the photosensitive drums 26Y, 26M, and 26C to rotate. In other words, the pinion gear 93a, the drum reduction gears 94a1 and 94a2, the drum driving gears 95Y, 95M, and 95C, the driving couplings 96Y, 96M, and 96C, and the drum coupling 13 are a driving train that transmits driving force between the motor 92a and the photosensitive drums 26Y, 26M, and 26C. The driving couplings 96Y, 96M, and 96C, and the drum coupling 13 are couplings that are interposed in the driving train between the motor 92a and the photosensitive drums 26Y, 26M, and 26C and have play in the rotational direction.

[0053] The driving force of the motor 92b is transmitted to the drum coupling 13 via the pinion gear 93b, the drum reduction gear 94b, the drum driving gear 95K, and the driving coupling 96K, thereby rotating the photosensitive drum 26K. In other words, the pinion gear 93b, the drum reduction gear 94b, the drum driving gear 95K, and the driving coupling 96K, as well as the drum coupling 13, constitute a driving train that transmits driving force between the motor 92b and the photosensitive drum 26K. The driving coupling 96K and the drum coupling 13 are interposed in the driving train between the motor 92b and the photosensitive drum 26K, and are couplings having play in the rotational direction.

[0054] A development reduction gear 97a meshes with the pinion gear 93a. A plurality of idler gears 98a to 98g are provided to form a gear train with the development reduction gear 97a. The idler gears 98a, 98d, and 98g mesh with development drive gears 99Y, 99M, and 99C, respectively. Due to the gear ratio of this gear train, the rotation speed of the development sleeves 71Y, 71M, and 71C is reduced relative to the rotation speed of the motor 92a so as to be 198% of the rotation speed of the photosensitive drums 26Y, 26M, and 26C.

[0055] The pinion gear 93b meshes with a development drive gear 99K through a gear train formed by a drum deceleration gear 94b, an idler gear 98h, a development deceleration gear 97b, and an idler gear 98i. Due to the gear ratio of this gear train, the rotation speed of the development sleeve 71K is reduced relative to the rotation speed of the motor 92b so as to be 198% of the rotation speed of the photosensitive drum 26K.

[0056] The developing drive gears 99Y, 99M, 99C, and 99K have rotating shafts (not shown) connected to the rotating shafts 100Y, 100M, 100C, and 100K of the developing couplings 75 provided in the process cartridges 65Y, 65M, 65C, and 65K shown in FIG. 8A by the Oldham couplings 1 described later. The developing couplings 75 have rotating shafts 100Y, 100M, 100C, and 100K that form part of the Oldham couplings 1 and engage with the driving couplings 89Y, 89M, 89C, and 89K that engage with the developing couplings 75 provided in the process cartridges 65Y, 65M, 65C, and 65K. As shown in FIG. 10B, a play β in the rotational direction is provided between the driving couplings 89 and the developing couplings 75 of each color. In this embodiment, the play β is set to an angle of 30 degrees around the rotation axis of the developing sleeve 71.

[0057] With this configuration, the driving force of the motor 92a is transmitted to the developing coupling 75 via the pinion gear 93a, the developing reduction gear 97a, the idler gears 98a to 98g, the developing drive gears 99Y, 99M, 99C, and the drive couplings 89Y, 89M, and 89C. This causes the developing sleeves 71Y, 71M, and 71C to rotate. In other words, the pinion gear 93a, the developing reduction gear 97a, the idler gears 98a to 98g, the developing drive gears 99Y, 99M, and 99C, the drive couplings 89Y, 89M, and 89C, and the developing coupling 75 form a drive train that transmits the driving force between the motor 92a and the developing sleeves 71Y, 71M, and 71C. The drive couplings 96Y, 96M, 96C, the drum coupling 13, and the Oldham coupling 1 are interposed in the drive train between the motor 92a and the developing sleeves 71Y, 71M, 71C, and are couplings having play in the rotational direction.

[0058] The driving force of the motor 92b is transmitted to the developing coupling 75 via the pinion gear 93b, the developing reduction gear 97a, the idler gears 98h and 98i, the developing drive gear 99K, and the drive coupling 89K. This rotates the developing sleeve 71K. In other words, the pinion gear 93b, the developing reduction gear 97a, the idler gears 98h and 98i, the developing drive gear 99K, the drive coupling 89K, and the developing coupling 75 form a drive train that transmits the driving force between the motor 92b and the developing sleeve 71K. The drive coupling 96K, the drum coupling 13, and the Oldham coupling 1 are couplings that are interposed in the drive train between the motor 92b and the developing sleeve 71K and have play in the rotational direction.

[0059] As described above, in this embodiment, the rotation speed of the developing sleeve 71 for each color is 198% of the rotation speed of the photosensitive drum 26 for that color. Furthermore, in this embodiment, the diameter of the photosensitive drum 26 is φ30 mm, and the diameter of the developing sleeve 71 is φ18 mm. Therefore, the difference in gear ratio between the photosensitive drum 26 and the developing sleeve 71 is approximately 3.3 times. In other words, when the photosensitive drum 26 makes one rotation, the developing sleeve 71 makes approximately 3.3 rotations.

[0060] <Oldham Coupling> Next, the configuration of the Oldham coupling 1 will be described.

[0061] Fig. 11 is an exploded perspective view of the Oldham coupling 1 as viewed from the front side of the image forming apparatus A. Fig. 12 is an exploded perspective view of the Oldham coupling 1 as viewed from the rear side of the image forming apparatus A. Fig. 13(a) is a diagram showing a fitting portion between the developing drive gear 99 of the Oldham coupling 1 and the intermediate member 3. Fig. 13(b) is a diagram showing a fitting portion between the drive coupling 89 of the Oldham coupling 1 and the intermediate member 3.

[0062] 11 and 12, the Oldham coupling 1 is made up of a developing drive gear 99 (first hub), a drive coupling 89 (second hub), and an intermediate member 3 that transmits driving force between the developing drive gear 99 and the drive coupling 89. The Oldham coupling 1 is rotatably held inside a coupling holder 2 provided on the front frame 91b.

[0063] In the direction of the arrow X, which is the rotation axis direction of the Oldham coupling 1, a recess 3a (first recess) having a rectangular cross section is formed on one end face of the intermediate member 3, which is recessed in the direction of the arrow X and extends in the direction of the arrow Y (first direction) perpendicular to the direction of the arrow X. In addition, in the direction of the arrow X, a recess 3b (second recess) having a rectangular cross section is formed on the other end face of the intermediate member 3, which is recessed in the direction of the arrow X and extends in the direction of the arrow Z (second direction) perpendicular to the directions of the arrow X and the arrow Y. The shapes of the recesses 3a and 3b are the same except that they extend in directions perpendicular to each other. The direction of the rotation axis of the Oldham coupling 1 is the same as the direction of the rotation axis of the development drive gear 99, the direction of the rotation axis of the drive coupling 89, and the direction of the rotation axis of the intermediate member 3.

[0064] In addition, in the rotation axis direction (arrow X direction) of the Oldham coupling 1, a convex portion 99a (first protrusion) that protrudes in the arrow X direction and fits into the recessed portion 3a of the intermediate member 3 is formed at one end of the development drive gear 99. In addition, in the rotation axis direction of the Oldham coupling 1, a convex portion 89a (second protrusion) that protrudes in the arrow X direction and fits into the recessed portion 3b of the intermediate member 3 is formed at one end of the drive coupling 89.

[0065] When the developing drive gear 99 is rotated by the driving force of the motor 92a or the motor 92b, the convex portion 99a of the developing drive gear 99 slides relatively inside the recessed portion 3a while contacting the inner wall of the recessed portion 3a, thereby transmitting the driving force to the intermediate member 3, and the intermediate member 3 rotates. Then, when the intermediate member 3 rotates, the convex portion 89a of the drive coupling 89 slides relatively inside the recessed portion 3b while contacting the inner wall of the recessed portion 3a, thereby transmitting the driving force to the drive coupling 89, and the drive coupling 89 rotates. In this way, even if the rotation axis of the rotation shaft (not shown) of the developing drive gear 99 and the rotation axis of the rotation shaft 100 of the developing coupling 75 are misaligned, the driving force of the motor 92a or the motor 92b is stably transmitted to the rotation shaft 100 of the developing coupling 75 via the Oldham coupling 1.

[0066] As shown in FIG. 13(a), the protruding portion 99a has an edge portion 99a1 (first edge portion) that contacts one inner wall 3a1 (first inner wall) in the width direction of the recessed portion 3a when the Oldham coupling 1 rotates in the direction of the arrow R1. The protruding portion 99a also has an edge portion 99a2 (second edge portion) that contacts the other inner wall 3a2 (second inner wall) in the width direction of the recessed portion 3a when the Oldham coupling 1 rotates in the direction of the arrow R1. The protruding portion 99a also has an edge portion 99a3 (third edge portion) that contacts the inner wall 3a1 of the recessed portion 3a when the Oldham coupling 1 rotates in the direction of the arrow R2, and an edge portion 99a4 (fourth edge portion) that contacts the inner wall 3a2. The edges 99a1 to 99a4 are in surface contact with the inner wall 3a1 or the inner wall 3a2 of the recessed portion 3a by surfaces extending in the directions of the arrow Y and the arrow X. The width direction of the recess 3a is the direction of the arrow Z, which is perpendicular to the direction of the arrow Y in which the recess 3a extends and is the same direction as the direction in which the recess 3b extends. The direction of the arrow R1 is the rotation direction of the Oldham coupling 1 when the motors 92a, 92b rotate in the rotation direction during image formation, and the direction of the arrow R2 is the rotation direction opposite to the direction of the arrow R1.

[0067] Here, when the Oldham coupling 1 rotates in the direction of the arrow R2, the part of the edge 99a1 farthest from the rotation center CT1 (first rotation center) of the development drive gear 99 in the direction of the arrow Y is located closer to the inner wall 3a2 than the rotation center CT1 in the direction of the arrow Z. Also, when the Oldham coupling 1 rotates in the direction of the arrow R2, the part of the edge 99a2 farthest from the rotation center CT1 in the direction of the arrow Y is located closer to the inner wall 3a1 than the rotation center CT1 in the direction of the arrow Z. Also, when the Oldham coupling 1 rotates in the direction of the arrow R1, the part of the edge 99a3 farthest from the rotation center CT1 in the direction of the arrow Y is located closer to the inner wall 3a2 than the rotation center CT1 in the direction of the arrow Z. Also, when the Oldham coupling 1 rotates in the direction of the arrow R1, the part of the edge 99a4 farthest from the rotation center CT1 in the direction of the arrow Y is located closer to the inner wall 3a1 than the rotation center CT1 in the direction of the arrow Z.

[0068] When viewed from the rotation axis direction of the Oldham coupling 1, the convex portion 99a has a shape in which an imaginary line H1 connecting the edge portion 99a1, the edge portion 99a2, the edge portion 99a3, and the edge portion 99a4 forms an approximately rhombus. Specifically, when a corner is formed by an imaginary line extending the edge portion 99a1 and the edge portion 99a4, the angle of the corner is 45 degrees, and when a corner is formed by an imaginary line extending the edge portion 99a2 and the edge portion 99a3, a rhombus is formed in which the angle of the corner is 45 degrees. Note that the approximately rhombus may have a configuration having corners as described above, or may have a shape in which the corners are chamfered as described above.

[0069] With this configuration, when the Oldham coupling 1 rotates in the direction of the arrow R2, a play γ1 is created between the edge 99a1 and the inner wall 3a1 of the recess 3a, and between the edge 99a2 and the inner wall 3a2 of the recess 3a. When the Oldham coupling 1 rotates in the direction of the arrow R1, a similar play γ1 is created between the edge 99a3 and the inner wall 3a1 of the recess 3a, and between the edge 99a4 and the inner wall 3a2 of the recess 3a.

[0070] As shown in Fig. 13(b), the convex portion 89b has the same shape as the convex portion 99a. That is, the convex portion 89a has an edge portion 89a1 (fifth edge portion) that contacts one inner wall 3b1 (third inner wall) in the width direction of the recessed portion 3b when the Oldham coupling 1 rotates in the direction of the arrow R1. The convex portion 89a also has an edge portion 89a2 (sixth edge portion) that contacts the other inner wall 3b2 (fourth inner wall) in the width direction of the recessed portion 3b when the Oldham coupling 1 rotates in the direction of the arrow R1. The convex portion 89a also has an edge portion 89a3 (seventh edge portion) that contacts the inner wall 3b1 of the recessed portion 3b when the Oldham coupling 1 rotates in the direction of the arrow R2, and an edge portion 89a4 (eighth edge portion) that contacts the inner wall 3b2. The edges 89a1 to 89a4 are in surface contact with the inner wall 3b1 or 3b2 of the recess 3b by surfaces extending in the directions of the arrows Z and X. The width direction of the recess 3b is the direction of the arrow Y which is perpendicular to the direction of the arrow Z in which the recess 3b extends and is the same direction as the direction in which the recess 3a extends.

[0071] Here, when the Oldham coupling 1 rotates in the direction of the arrow R2, the part of the edge 89a1 farthest from the rotation center CT2 (second rotation center) of the drive coupling 89 in the direction of the arrow Z is located at a position closer to the inner wall 3b2 than the rotation center CT2 in the direction of the arrow Y. Also, when the Oldham coupling 1 rotates in the direction of the arrow R2, the part of the edge 89a2 farthest from the rotation center CT2 in the direction of the arrow Z is located at a position closer to the inner wall 3b1 than the rotation center CT2 in the direction of the arrow Y. Also, when the Oldham coupling 1 rotates in the direction of the arrow R1, the part of the edge 99a3 farthest from the rotation center CT2 in the direction of the arrow Z is located at a position closer to the inner wall 3b2 than the rotation center CT2 in the direction of the arrow Y. Also, when the Oldham coupling 1 rotates in the direction of the arrow R1, the part of the edge 89a4 farthest from the rotation center CT2 in the direction of the arrow Z is located at a position closer to the inner wall 3b1 than the rotation center CT2 in the direction of the arrow Y.

[0072] When viewed from the rotation axis direction of the Oldham coupling 1, the convex portion 89a has a shape in which an imaginary line H2 connecting the edge portion 89a1, the edge portion 89a2, the edge portion 89a3, and the edge portion 89a4 forms an approximately rhombus. Specifically, when a corner is formed by an imaginary line extending the edge portion 89a1 and the edge portion 89a4, the angle of the corner is 45 degrees, and when a corner is formed by an imaginary line extending the edge portion 89a2 and the edge portion 89a3, a rhombus is formed in which the angle of the corner is 45 degrees. Note that the approximately rhombus may have a configuration having corners as described above, or the corners may be chamfered as in this embodiment.

[0073] With this configuration, when the Oldham coupling 1 rotates in the direction of the arrow R2, a play γ2 is created between the edge 89a1 and the inner wall 3b1 of the recess 3b, and between the edge 89a2 and the inner wall 3b2 of the recess 3b. When the Oldham coupling 1 rotates in the direction of the arrow R1, a similar play γ2 is created between the edge 89a3 and the inner wall 3b1 of the recess 3b, and between the edge 89a4 and the inner wall 3b2 of the recess 3b.

[0074] As described above, according to the configuration of this embodiment, in the Oldham coupling 1, a driving force can be transmitted while providing a rotational play γ1 between the development drive gear 99 and the intermediate member 3 and a rotational play γ2 between the drive coupling 89 and the intermediate member 3. In addition, the edges 99a1-99a4 come into surface contact with the inner wall 3a1 or the inner wall 3a2 of the recess 3a, and the edges 89a1-89a4 come into surface contact with the inner wall 3b1 or the inner wall 3b2 of the recess 3b, so that the strength of the convex parts 99a, 89a when transmitting the driving force can be ensured and deformation can be suppressed.

[0075] <Operation timing of image forming unit after image forming operation> Next, the operation timing when the photosensitive drum 26, the developing sleeve 71, and the charging roller 27 rotate in the direction opposite to the rotation direction during image formation after the image forming operation is completed will be described.

[0076] Fig. 14 is a timing chart showing the ideal operation timing when the photosensitive drum 26, the developing sleeve 71, and the charging roller 27 rotate in the direction opposite to the rotation direction during image formation. As shown in Fig. 14, when the image formation operation is completed, these members stop while the play α between the drive coupling 96 and the drum coupling 13, the play β between the drive coupling 89 and the developing coupling 75, and the play γ1 and γ2 of the Oldham coupling 1 are secured. From this state, the motors 92a and 92b start to rotate in the direction opposite to the rotation direction during image formation. When the motors 92a and 92b start to rotate, the drum drive gear 95 and the developing drive gear 99 start to rotate (timing T1).

[0077] Next, at time T2, the rotation of the development drive gear 99 eliminates the play γ1 of the Oldham coupling 1, and the intermediate member 3 starts to rotate. After that, at time T3, the rotation of the intermediate member 3 eliminates the play γ2 of the Oldham coupling 1, and the drive coupling 89 starts to rotate.

[0078] Next, at time T4, the play α is eliminated by the rotation of the drum drive gear 95, the drum coupling 13 starts to rotate, and the photosensitive drum 26 starts to rotate accordingly. After that, at time T5, the play β is eliminated by the rotation of the drive coupling 89, the developing coupling 75 starts to rotate, and the developing sleeve 71 starts to rotate accordingly.

[0079] Next, at time T6, the gear portion 32a of the spacing member 32 meshes with the flange gear 14 as the photosensitive drum 26 rotates, and the charging roller 27 starts to separate from the photosensitive drum 26. Then, at time T7, the charging roller 27 separates to a predetermined position, completing the separation. Thereafter, at time T8, the developing sleeve 71 rotates to a predetermined rotation angle, and the driving of the motors 92a and 92b is stopped.

[0080] Here, after the driving of the motors 92a and 92b is stopped, the rotating bodies constituting the drive train that transmits the driving force to the photosensitive drum 26 and the rotating bodies constituting the drive train that transmits the driving force to the developing sleeve 71 rotate due to inertia. In particular, while a stopping load is applied to the drive train that transmits the driving force to the photosensitive drum 26 due to the frictional force between the photosensitive drum 26 and the cleaning blade 45, the drive train that transmits the driving force to the developing sleeve 71 does not have such a stopping load, and therefore the amount of rotation tends to be large. Due to this rotation due to inertia, the play α, β, γ1, and γ2 in the rotational direction of each of the above-mentioned couplings after the driving of the motors 92a and 92b is stopped becomes smaller than the ideal size.

[0081] Fig. 15 is a diagram showing the positional relationship between the developing coupling 75 and the drive coupling 89 when the driving of the motors 92a and 92b is stopped after the image forming operation is completed. Fig. 15(a) shows the ideal positional relationship between the developing coupling 75 and the drive coupling 89 without considering the inertia between them. Fig. 15(b) shows the positional relationship between the developing coupling 75 and the drive coupling 89 with the inertia between them taken into consideration.

[0082] As shown in FIG. 15(a), when inertia is not taken into consideration, when the driving of the motors 92a and 92b is stopped, the positional relationship between the developing coupling 75 and the driving coupling 89 is in a state where the play is eliminated in the rotation direction during image formation. At this time, the play β in the direction opposite to the rotation direction during image formation of both is maximum. On the other hand, as shown in FIG. 15(b), when inertia is taken into consideration, the positional relationship between the developing coupling 75 and the driving coupling 89 generates a play in the rotation direction during image formation. At this time, the play β in the direction opposite to the rotation direction during image formation of both is smaller than the ideal value (maximum value). In this way, due to the influence of the rotation of the developing coupling 75 and the driving coupling 89 due to inertia, the play β in the rotation direction of both is smaller than the ideal value (maximum value). In this embodiment, the play β shown in FIG. 15(a) is 30 degrees, and the play β shown in FIG. 15(b) is 2 degrees, which is 28 degrees less than the ideal value (maximum value). Similarly, the play α between the drive coupling 96 and the drum coupling 13 and the play γ1 and γ2 of the Oldham coupling 1 also become smaller than the ideal values.

[0083] In this embodiment, the rotation angle in the direction opposite to the rotation direction of the photosensitive drum 26 during image formation, which is necessary to separate the charging roller 27 from the photosensitive drum 26, is 49.2 degrees to 73.2 degrees. In addition, the play α between the drive coupling 96 and the drum coupling 13 is 34 degrees. Therefore, in order to separate the charging roller 27 from the photosensitive drum 26, it is necessary to rotate the photosensitive drum 26 83.2 degrees by matching the play α of 34 degrees with the rotation amount of the photosensitive drum 26 of 49.2 degrees required to separate the charging roller 27.

[0084] As described above, the reduction ratio between the drive train that drives the photosensitive drum 26 and the drive train that drives the developing sleeve 71 is 3.3, so when the photosensitive drum 26 is rotated 83.2 degrees, the developing sleeve 71 rotates approximately 274.6 degrees. Since the play of each coupling in the drive train for driving the developing sleeve 71 is 120 degrees (β+γ1+γ2), when the photosensitive drum 26 is rotated 83.2 degrees, the ideal value of the amount of rotation of the developing sleeve 71 is approximately 154.6 degrees.

[0085] 15B, when the rotation in the direction opposite to the rotation direction during image formation starts with the play β reduced by 28 degrees from the ideal value, the rotation angle of the developing sleeve 71 will be 182.6 degrees (154.6 degrees + 28 degrees). In this case, since the allowable rotation angle of the developing sleeve 71 is 60 degrees to 180 degrees, the allowable rotation angle of the developing sleeve 71 will be exceeded, and toner may scatter from the developing container 70. That is, the play α, β, γ1, and γ2 deviate from the ideal value due to the rotation caused by inertia, and the operation timing of each component is shifted, so that the accuracy of the control for switching the motors 92a and 92b from the forward rotation, which is the rotation direction during image formation, to the reverse rotation, which is opposite to the forward rotation, is deteriorated.

[0086] <Reverse rotation sequence> In this embodiment, when switching the motors 92a and 92b from forward rotation to reverse rotation in the reverse rotation sequence executed after the image forming operation is completed, the above-mentioned deterioration of the control accuracy during reverse rotation is suppressed. The reverse rotation sequence will be described below with reference to the flowchart shown in FIG.

[0087] 16, when the CPU 53 receives an image formation job signal via the user interface unit 56, it controls the image forming unit 61 to execute an image forming operation (S1, S2). As part of the control of the image forming unit 61, the CPU 53 instructs the motor control unit 59 to rotate the motors 92a and 92b in the rotation direction during image formation (first rotation direction) at a speed V1 (first speed). This causes the motors 92a and 92b to rotate forward, causing the photosensitive drum 26 and the developing sleeve 71 to rotate in the rotation direction during image formation, and an image is formed on the sheet S.

[0088] Next, after the image forming operation is completed, CPU 53 receives information on the count value of the number of sheets on which images have been formed from counter 57, and determines whether the count value of the number of sheets on which images have been formed is 500 or more in the case of A4 paper (S3). If the count value of the number of sheets on which images have been formed is less than 500, CPU 53 instructs motor control unit 59 to stop driving motors 92a and 92b (S9), and proceeds to step S10.

[0089] On the other hand, when the count value of the number of sheets on which images have been formed is 500 or more, the CPU 53 stops driving the motors 92a and 92b via the motor control unit 59 (S4). Then, the CPU 53 instructs the motor control unit 59 to rotate the motors 92a and 92b in the rotation direction during image formation at a speed V2 (second speed) slower than the speed V1 (S5). This causes the motors 92a and 92b to rotate forward at the speed V2. Thereafter, the CPU 53 instructs the motor control unit 59 to stop driving the motors 92a and 92b (S6). The CPU 53 also instructs the counter 57 to reset the count value (S7).

[0090] Here, the speed V2 is a speed at which the rotating bodies constituting the drive trains that transmit driving forces to the photosensitive drum 26 and the developing sleeve 71 do not rotate due to inertia when the motors 92a and 92b driven at the speed V2 are stopped in step S6. In this embodiment, the speed V2 is a speed at which the developing sleeve 71 rotates at 30 rpm.

[0091] The rotation amounts of the motors 92a and 92b in step S5 are the rotation amounts by which the play α, β, γ1, and γ2, which have decreased from the ideal values ​​(maximum values) due to the influence of inertia when the motors 92a and 92b are stopped in step S4, return to the ideal values. In this embodiment, the play β is 30 degrees, and the play γ1 and γ2 are each 45 degrees, so the motors 92a and 92b rotate until the drive coupling 89 rotates at least 120 degrees.

[0092] In this way, by the motors 92a and 92b rotating forward at the speed V2, the positional relationship of each coupling returns to the state in which the backlash is eliminated in the rotation direction during image formation, similar to the state during image formation, and the reduced play α, β, γ1, and γ2 return to the ideal values. That is, the positional relationship between the development coupling 75 and the drive coupling 89 changes from the state shown in Fig. 17(a) to the state shown in Fig. 17(b), and the play β in the direction opposite to the rotation direction during image formation becomes the ideal value.

[0093] Next, the CPU 53 instructs the motor control unit 59 to rotate the motors 92a and 92b in a direction (second rotation direction) opposite to the direction of rotation during image formation (S8). This causes the motors 92a and 92b to rotate in reverse. The rotation amount of the motors 92a and 92b in step S8 is the rotation amount by which the developing sleeve 71 rotates in the direction opposite to the direction of rotation during image formation within the rotation allowance region. This causes the toner accumulated in the space surrounded by the developing sleeve 71, the developing blade 72, and the scooping sheet 77 to return to the stirring chamber 80, thereby suppressing image defects. After that, the CPU 53 instructs the motor control unit 59 to stop driving the motors 92a and 92b (S9).

[0094] Next, the CPU 53 receives information from the timer 58 and determines whether or not a predetermined time (8 hours in this embodiment) has passed since the previous image formation job was completed (S10). If the CPU 53 determines that 8 hours have not passed since the previous image formation job was completed, the process returns to step S1 and waits for reception of an image formation job signal.

[0095] On the other hand, when the CPU 53 determines that 8 hours or more have passed since the end of the previous image formation job, it instructs the motor control unit 59 to rotate the motors 92a and 92b at the speed V2 in the rotation direction during image formation (S11). This causes the motors 92a and 92b to rotate forward at the speed V2. The rotation amount of the motors 92a and 92b here is the same as that in step S5, and is the rotation amount at which the play α, β, γ1, and γ2, which have decreased from the ideal values ​​due to the influence of inertia when the motors 92a and 92b are stopped in step S9, return to the ideal values. Thereafter, the CPU 53 instructs the motor control unit 59 to stop driving the motors 92a and 92b (S12).

[0096] Next, the CPU 53 instructs the motor control unit 59 to rotate the motors 92a and 92b in a direction opposite to the direction of rotation during image formation (S13). This causes the motors 92a and 92b to rotate in reverse. The rotation amount of the motors 92a and 92b in step S13 is an amount by which the charging roller 27 rotates within the rotation allowable range, and an amount by which the developing sleeve 71 rotates does not exceed the rotation allowable range. This causes the charging roller 27 to separate from the photosensitive drum 26, and prevents the charging roller 27 from being in pressure contact with the photosensitive drum 26 for a long period of time, adversely affecting image quality. Thereafter, the CPU 53 instructs the motor control unit 59 to stop driving the motors 92a and 92b (S14), and ends the reverse rotation sequence.

[0097] In this manner, in the reverse rotation sequence, before the motors 92a and 92b are rotated in the reverse direction, the motors 92a and 92b are rotated in the forward direction at a speed V2 slower than the speed V1 during image formation. With this configuration, even if the play α, β, γ1, and γ2 of each coupling is reduced due to rotation caused by inertia, the play α, β, γ1, and γ2 can be made to approach the ideal value before the motors 92a and 92b are rotated in the reverse direction. Therefore, deviation in the operation timing of each member when the motors 92a and 92b are rotated in the reverse direction is suppressed, and deterioration in the accuracy of the control for switching the motors 92a and 92b from forward rotation to reverse rotation is suppressed.

[0098] In this embodiment, the motors 92a, 92b are stopped before rotating forward at the speed V2, but the present invention is not limited to this. That is, the same effect as above can be obtained by reducing the speed from V1 to V2 without stopping the motors 92a, 92b and lengthening the time for which the motors 92a, 92b rotate at the speed V2 compared to the configuration in which the motors 92a, 92b are stopped.

[0099] In addition, in this embodiment, the configuration in which the motors 92a, 92b are stopped after rotating in the forward direction at the speed V2 has been described, but the present invention is not limited to this. That is, the same effect as above can be obtained even if the motors 92a, 92b are rotated in the reverse direction without stopping the driving of the motors 92a, 92b after rotating in the forward direction at the speed V2.

[0100] In addition, in the present embodiment, the configuration in which the Oldham coupling 1 is provided in the drive train that transmits the driving force to the developing sleeve 71 in the drive unit 90 has been described, but the present invention is not limited to this. That is, the same effect as above can be obtained by providing the Oldham coupling 1 in another portion that transmits the driving force, such as in the drive train that transmits the driving force to the photosensitive drum 26.

[0101] In addition, in this embodiment, the configuration in which both the convex portion 99a of the development drive gear 99 and the convex portion 89a of the drive coupling 89 are substantially rhombic in the Oldham coupling 1 have been described, but the present invention is not limited to this. That is, either the convex portion 99a of the development drive gear 99 or the convex portion 89a of the drive coupling 89 may be formed in substantially the same rectangular shape as the concave portion 3a or the concave portion 3b of the intermediate member 3. In addition, the rotation angles of the play α, β, γ1, and γ2 are not limited to the angles described in this embodiment, and can be set to any angle.

[0102] In addition, in this embodiment, a configuration has been described in which the convex portions 99a, 89a are provided on the development drive gear 99 and the drive coupling 89 in the Oldham coupling 1, and the concave portions 3a, 3b are provided on the intermediate member 3, but the present invention is not limited to this. That is, even if convex portions corresponding to the convex portions 99a, 89a are provided on one end and the other end of the intermediate member 3 in the rotation axis direction of the Oldham coupling 1, and concave portions that fit into the convex portions of the intermediate member 3 are provided on the development drive gear 99 and the drive coupling 89, the same effects as those described above can be obtained. [Explanation of symbols]

[0103] 1...Oldham coupling 3...Intermediate member 3a…Recess (first recess) 3b…Recess (second recess) 26...Photosensitive drum (photoconductor) 27...Charging roller 32...Spacer member 53...CPU (control unit) 65...Process cartridge (image forming unit) 71...Developing sleeve (developer carrier) 89...Drive coupling (second hub) 89a...protruding portion (second protruding portion) 92a, 92b...Motor 99...Development drive gear (first hub) 99a...protruding portion (first protruding portion) A: Image forming device

Claims

1. A photoconductor; a developer carrier that carries a developer and develops the electrostatic latent image formed on the photoreceptor; a motor that rotates in a first rotation direction and a second rotation direction opposite to the first rotation direction and drives the photoconductor and the developer carrier to rotate; a coupling provided in at least one of a first drive train that transmits driving force from the motor to the developer carrier or a second drive train that transmits driving force from the motor to the photosensitive member, the coupling having play in a rotational direction of the coupling; a control unit that controls the motor, the control unit controlling the motor so that the motor rotates in the first rotation direction at a first speed when an electrostatic latent image formed on the photoconductor is developed; Equipped with In a state in which the motor rotates in the first rotation direction, the photoconductor rotates in a third rotation direction, and the developer carrier rotates in a fourth rotation direction; In a state in which the motor rotates in the second rotation direction, the photoconductor rotates in a direction opposite to the third rotation direction, and the developer carrier rotates in a direction opposite to the fourth rotation direction, When the control unit controls the motor to rotate in the second rotation direction after the motor rotates in the first rotation direction, the control unit controls the motor, which is stopped, to rotate in the first rotation direction at a second speed lower than the first speed, and then controls the motor to rotate in the second rotation direction.

1. An image forming apparatus comprising:

2. When the control unit controls the motor rotating in the first rotation direction at the first speed to rotate in the second rotation direction, the control unit controls the motor rotating in the first rotation direction at the first speed to rotate in the first rotation direction at a second speed lower than the first speed, and then controls the motor to stop, and then controls the motor to rotate in the second rotation direction.

2. The image forming apparatus according to claim 1,

3. the control unit controls the motor to rotate in the second rotation direction when a number of sheets on which images are formed by the image forming apparatus becomes equal to or greater than a predetermined number.

2. The image forming apparatus according to claim 1,

4. a charging roller that rotates in contact with the photoconductor and charges the photoconductor; a spacing member that separates the charging roller from the photoconductor in response to rotation of the motor in the second rotation direction, the control unit is capable of rotating the motor by a first predetermined amount in the second rotation direction to rotate the developer carrier in the fourth rotation direction without causing the spacing member to perform an operation of spacing the charging roller from the photosensitive member.

4. The image forming apparatus according to claim 3.

5. The charging roller rotates in response to the rotation of the photoconductor, the spacing member moves in conjunction with the rotation of the charging roller while the motor is rotating in the second rotation direction, to space the charging roller from the photoconductor; 5. The image forming apparatus according to claim 4.

6. the control unit controls the motor to rotate in the second rotation direction by a second predetermined amount greater than the first predetermined amount in order to rotate the developer carrier in the fourth rotation direction and to operate the spacing member to space the charging roller from the photosensitive member; the play of the coupling after the motor has rotated the second predetermined amount in the second rotational direction is less than the play of the coupling after the motor has rotated the first predetermined amount in the second rotational direction; 5. The image forming apparatus according to claim 4.

7. a charging roller that rotates in contact with the photoconductor and charges the photoconductor; a spacing member that separates the charging roller from the photoconductor in response to rotation of the motor in the second rotation direction, the control unit controls the motor to rotate in the second rotation direction when a predetermined time or more has elapsed since the image forming apparatus stopped an image forming operation.

2. The image forming apparatus according to claim 1,

8. The charging roller rotates in response to the rotation of the photoconductor, the spacing member moves in conjunction with the rotation of the charging roller while the motor is rotating in the second rotation direction, to space the charging roller from the photoconductor; 8. The image forming apparatus according to claim 7,

9. The coupling is an Oldham coupling.

9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. the Oldham coupling is provided in a drive train that transmits driving force from the motor to the developer carrier; 10. The image forming apparatus according to claim 9,

11. the Oldham coupling includes a first hub, a second hub, and an intermediate member that transmits a driving force between the first hub and the second hub, one of the intermediate member and the first hub has a first recess formed on an end surface of the Oldham coupling in a rotational axis direction, recessed in the rotational axis direction, and extending in a first direction perpendicular to the rotational axis direction, The first recess is a first inner wall on one side in a second direction perpendicular to the rotation axis direction and the first direction; a second inner wall provided on the other side in the second direction and extending parallel to the first inner wall, the other of the intermediate member and the first hub has a first protruding portion that protrudes in the rotation axis direction, is fitted into the first recess, and transmits a driving force between the intermediate member and the first hub, The first protrusion is a first edge portion that comes into contact with the first inner wall when the Oldham coupling rotates in association with the rotation of the motor in the first rotational direction; a second edge portion that comes into contact with the second inner wall when the Oldham coupling rotates in association with the rotation of the motor in the first rotational direction; a third edge portion that comes into contact with the first inner wall when the Oldham coupling rotates in association with the rotation of the motor in the second rotational direction; a fourth edge portion that comes into contact with the second inner wall when the Oldham coupling rotates in association with the rotation of the motor in the second rotational direction, when the first edge contacts the first inner wall and the second edge contacts the second inner wall, the third edge is spaced apart from the first inner wall and the fourth edge is spaced apart from the second inner wall; when the third edge portion contacts the first inner wall and the fourth edge portion contacts the second inner wall, the first edge portion is spaced apart from the first inner wall and the second edge portion is spaced apart from the second inner wall; when the Oldham coupling rotates in conjunction with the rotation of the motor in the second rotation direction, a portion of the first edge portion farthest from a first rotation center that is a rotation center of the first hub in the first direction is located at a position closer to the second inner wall than the first rotation center in the second direction, and a portion of the second edge portion farthest from the first rotation center in the first direction is located at a position closer to the first inner wall than the first rotation center in the second direction, when the Oldham coupling rotates in association with the rotation of the motor in the first rotation direction, a portion of the third edge portion farthest from the first rotation center in the first direction is located at a position closer to the second inner wall than the first rotation center in the second direction, and a portion of the fourth edge portion farthest from the first rotation center in the first direction is located at a position closer to the first inner wall than the first rotation center in the second direction.

11. The image forming apparatus according to claim 9, wherein the image forming apparatus is a multi-layered image forming apparatus.

12. In the Oldham coupling, the first protrusion has a shape in which a substantial rhombus is formed by imaginary lines connecting the first edge portion, the second edge portion, the third edge portion, and the fourth edge portion when viewed from the rotation axis direction.

12. The image forming apparatus according to claim 11.

13. In the Oldham coupling, one of the intermediate member and the second hub has a second recess formed on an end surface in the rotational axis direction, recessed in the rotational axis direction, and extending in the second direction, The second recess is A third inner wall on one side in the first direction; a fourth inner wall provided on the other side in the first direction and extending parallel to the first inner wall, the other of the intermediate member and the second hub has a second protruding portion that protrudes in the rotation axis direction, is fitted into the second recess, and transmits a driving force between the intermediate member and the second hub, The second protrusion is a fifth edge portion that comes into contact with the third inner wall when the Oldham coupling rotates in association with the rotation of the motor in the first rotational direction; a sixth edge portion that comes into contact with the fourth inner wall when the Oldham coupling rotates in association with the rotation of the motor in the first rotational direction; a seventh edge portion that comes into contact with the third inner wall when the Oldham coupling rotates in association with the rotation of the motor in the second rotational direction; an eighth edge portion that comes into contact with the fourth inner wall when the Oldham coupling rotates in association with the rotation of the motor in the second rotational direction, when the fifth edge contacts the third inner wall and the sixth edge contacts the fourth inner wall, the seventh edge is spaced apart from the third inner wall and the eighth edge is spaced apart from the fourth inner wall; when the seventh edge contacts the third inner wall and the eighth edge contacts the fourth inner wall, the fifth edge is spaced apart from the third inner wall and the sixth edge is spaced apart from the fourth inner wall; when the Oldham coupling rotates in conjunction with the rotation of the motor in the second rotation direction, a portion of the fifth edge portion farthest from a second rotation center that is a rotation center of the second hub in the second direction is located at a position closer to the fourth inner wall than the second rotation center in the first direction, and a portion of the sixth edge portion farthest from the second rotation center in the second direction is located at a position closer to the third inner wall than the second rotation center in the first direction, when the Oldham coupling rotates in association with the rotation of the motor in the first rotation direction, a portion of the seventh edge portion farthest from the second center of rotation in the second direction is located at a position closer to the fourth inner wall than the second center of rotation in the first direction, and a portion of the eighth edge portion farthest from the second center of rotation in the second direction is located at a position closer to the third inner wall than the second center of rotation in the first direction.

13. The image forming apparatus according to claim 11 or 12.

14. In the Oldham coupling, when viewed from the rotation axis direction, the second protrusion has a shape in which a substantial rhombus is formed by imaginary lines connecting the fifth edge portion, the sixth edge portion, the seventh edge portion, and the eighth edge portion.

14. The image forming apparatus according to claim 13.

15. the photoconductor and the developer carrier are integrated as an image forming unit, The image forming unit is configured to be detachable from the image forming apparatus.

15. The image forming apparatus according to claim 1,

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