Cam drive device, transfer device and image forming device

Abstract

To solve such a problem that a secondary transfer nip is kept pressurized when a stepping motor cannot be driven due to a motor failure or the like in such a state that the secondary transfer nip is formed by a secondary transfer roller and a secondary transfer facing roller.SOLUTION: A cam driver includes: a support member which supports an object member; a cam member which moves the support member; a motor which rotates the cam member and maintains the posture of the cam member; and retracting torque application means which applies torque to the cam member in a direction to move the object member away from a counter member that faces the object member.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a cam drive device, a transfer device, and an image forming apparatus. [Background technology]

[0002] Patent Document 1 discloses a cam drive device having an eccentric cam (61), a ball bearing (62) that changes its position in response to changes in the rotational position of the eccentric cam abutting against it, a stepping motor (63) that is the rotational drive source for the eccentric cam, and a power supply that outputs current to be supplied to the stepping motor.The cam drive device has a control unit that controls the output current value from the power supply so that the current output from the power supply to generate a stall torque in the stopped stepping motor varies depending on the rotational stop position of the eccentric cam, and makes it possible to suppress an increase in power consumption due to the adoption of a mode in which the rotation of the eccentric cam is stopped in a rotational stop position in which the non-concentric curved portion of the eccentric cam abuts against the ball bearing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-097066 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration of Patent Document 1, if the stepping motor cannot be driven due to a motor failure or the like while the secondary transfer roller (17) and the secondary transfer counter roller (16) form a secondary transfer nip, the secondary transfer nip remains pressurized. [Means for solving the problem]

[0005] The present invention provides a device for moving a target member, the device comprising: a support member for supporting a target member; a cam member for moving the support member; an electric motor for driving the cam member to rotate and maintaining the position of the cam member; and a backward torque applying means for applying a torque to the cam member in a direction in which the target member moves backward from an opposing member opposing the target member. a magnitude relationship among a holding torque T1 generated by the electric motor to hold the position of the cam member, a backward torque T2 generated by the backward torque applying means, and a detent torque T3 required to rotate the drive shaft of the electric motor in a non-energized state, satisfies T1>T2>T3 on the rotation shaft of the cam member; It is characterized by: [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a cam drive device with improved maintainability. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an overall perspective view of a cam drive device according to an embodiment of the present invention; [Figure 2] 1 is an overall perspective view showing a state in which a target unit is mounted on a cam drive device according to an embodiment of the present invention; [Figure 3] 5A and 5B are side views illustrating the movement of an arm member and a cam in the cam drive device according to the embodiment of the present invention. [Figure 4] FIG. 10 is a side view illustrating a malfunction when the motor is not energized. [Figure 5] 5A and 5B are explanatory diagrams of a backward torque applying unit of the cam drive device according to the embodiment of the present invention. [Figure 6] 5A and 5B are explanatory diagrams illustrating set torques of the cam drive device according to the embodiment of the present invention. [Figure 7] FIG. 10 is an explanatory diagram of a second embodiment. [Figure 8] FIG. 10 is an explanatory diagram of a comparative example to the second embodiment. [Figure 9] FIG. 10 is an explanatory diagram showing a modified example of the backward torque applying means. [Figure 10] FIG. 2 is an explanatory diagram of a first application example of a cam drive device according to an embodiment of the present invention. [Figure 11] FIG. 10 is an overall perspective view of a target unit in a first application example. [Figure 12] FIG. 10 is an explanatory diagram of a second application example of the cam drive device according to the embodiment of the present invention. [Figure 13]10A and 10B are explanatory diagrams illustrating a third application example of the cam drive device according to the embodiment of the present DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the

[0009] FIG. 1 is an overall perspective view of a cam drive device according to an embodiment of the present invention.

[0010] Cam drive device 200 includes arm members 201a and 201b, cams 202a and 202b, and motors 203a and 203b. Motor 203a is a motor that can rotate forward and backward, and when motor 203a is driven, the rotation of the motor drive shaft is transmitted to shaft 206a via timing belt 204a and pulley 205a, causing shaft 206a to rotate. Motor 203b has a similar configuration to the above, and when motor 203b is driven, the rotation of the motor drive shaft is transmitted to shaft 206b via timing belt 204b and pulley 205b, causing shaft 206b to rotate.

[0011] Shaft 206a is provided with pulley 207a at its other end (the end opposite to the end where pulley 205a is provided). Furthermore, shaft 208, which is provided parallel to shaft 206a, is provided with pulley 209a at its end, and timing belt 210a is wound around pulley 209a and pulley 207a provided on shaft 206a. Shaft 206b has the same configuration as above, and is provided with pulley 207b at its other end (the end opposite to the end where pulley 205b is provided). Furthermore, shaft 208 is also parallel to shaft 206b. Furthermore, timing belt 210b is wound around a pulley (not shown in FIG. 1 but provided similarly to pulley 209a) provided at the end of shaft 208 and pulley 207b provided on shaft 206b.

[0012] With the above configuration, the rotation of shaft 206a is transmitted to shaft 208 via pulley 207a, timing belt 210a, and pulley 209a, and the rotation of shaft 206b is transmitted to shaft 208 via pulley 207b, timing belt 210b, and another pulley, causing shaft 208 to rotate. Tensioners 211a and 211b abut against timing belts 210a and 210b from the outside, applying appropriate tension to timing belts 210a and 210b.

[0013] Shaft 208 is provided with cam 202a at one end (the portion protruding outward from pulley 209a) and cam 202b at the other end. Cams 202a and 202b fit onto the outer periphery of shaft 208 and are attached to shaft 208, for example, by fitting an axial key provided on the outer periphery of shaft 208 into key grooves provided in cams 202a and 202b so as to engage with the key. With the above configuration, when shaft 208 rotates, cams 202a and 202b rotate integrally with shaft 208.

[0014] Meanwhile, housing frame 212a of cam drive device 200 supports arm member 201a so that arm member 201a can rotate about axis Xa. Although not shown in FIG. 1, a housing frame similar to housing frame 212a also exists on the arm member 201b side, and this housing frame supports arm member 201b so that arm member 201b can rotate about axis Xb. Arm members 201a and 201b are provided with cam followers (described below) at positions facing cams 202a and 202b, and the cam followers contact the cam surfaces of cams 202a and 202b. With the above configuration, when cams 202a and 202b rotate, the cam followers move following the shape of the cam surfaces, and arm members 201a and 201b rotate about axes Xa and Xb in response.

[0015] In this embodiment, the motors 203a and 203b are hybrid stepping motors that are driven with a constant pulse to move the cams 202a and 202b by a predetermined angle. The motors 203a and 203b then generate a holding torque to hold the cams 202a and 202b at the positions where they have moved by the predetermined angle. Even when the motors 203a and 203b are not energized, a detent torque (torque required to rotate the drive shaft of a motor in an unenergized state) is generated in the motor drive shaft. While the present embodiment employs separate motors 203a and 203b to drive the cams 202a and 202b, this is not necessarily a limitation. For example, the shafts 206a and 206b may be unified, allowing a single motor to drive the cams 202a and 202b on both sides.

[0016] Here, the arm members 201a and 201b are an example of a "support member," the cams 202a and 202b are an example of a "cam member," and the motors 203a and 203b are an example of an "electric motor." Also, the shaft 208 is an example of a "rotating shaft," and the axes Xa and Xb are an example of a "rotating shaft."

[0017] FIG. 2 is an overall perspective view showing a state in which a target unit is mounted on the cam drive device according to the embodiment of the present invention.

[0018] Cam drive device 200 is configured to support target unit 300 between arm member 201a and arm member 201b, as indicated by the dashed line. With the above configuration, when cams 202a and 202b rotate, the cam followers provided on arm members 201a and 201b move following the shape of the cam surfaces, causing arm members 201a and 201b to rotate about axes Xa and Xb. As a result, target unit 300 also rotates together with arm members 201a and 201b about axes Xa and Xb.

[0019] The shape of the target unit 300 is not limited to the box-like shape shown in the figure, and the shape and configuration of the arm members 201a, 201b may be changed as appropriate depending on the shape and configuration of the target unit 300. Here, the target unit 300 is an example of a "target member."

[0020] FIG. 3 is a side view illustrating the movement of the arm member and the cam in the cam drive device according to the embodiment of the present invention.

[0021] As described above, housing frame 212a of cam drive device 200 supports arm member 201a so that arm member 201a is rotatable about axis Xa. Arm member 201a is provided with cam follower 213a at a position facing cam 202a, and cam follower 213a is in contact with the cam surface of cam 202a.

[0022] In this embodiment, when cam 202a is at the position shown by the solid line in Fig. 3, cam follower 213a is closest to shaft 208, resulting in a state in which arm member 201a has moved furthest in the backward direction. Then, when cam 202a rotates clockwise about shaft 208 and moves to the position shown by the dashed line, cam 202a moves cam follower 213a to the position shown by the dashed line. As a result, arm member 201a is moved furthest in the forward direction via cam follower 213a.

[0023] Furthermore, when returning cam 202a from the broken line position to the solid line position, cam 202a is rotated counterclockwise. Note that while Fig. 3 describes the movement based on the configuration on the arm member 201a side, the same configuration applies to the arm member 201b side.

[0024] 4 is a side view illustrating a malfunction that occurs when the motor is not energized. Here, an example will be described in which the target unit 300 mounted on the cam drive device 200 is the roller R1.

[0025] Arm member 201a and arm member 201b rotatably support roller R1. When cams 202a and 202b are in the solid line positions, arm members 201a and 201b are in their most retracted positions, and roller R1 is also in a position separated from roller R2, as shown by the solid line. Roller R2 is a roller fixed in a predetermined position. When cams 202a and 202b are rotated clockwise and cams 202a and 202b move to the dashed line positions, arm members 201a and 201b are in their most advanced positions, and roller R1 presses roller R2, as shown by the dashed line. Here, roller R1 is an example of a "target member," and roller R2 is an example of a "counter member."

[0026] As described above, the motors 203a and 203b of the cam drive device 200 are stepping motors that are driven with a constant pulse to move the cams 202a and 202b by a predetermined angle, and then generate a holding torque to maintain the position of the cams 202a and 202b. Furthermore, even when the motors 203a and 203b are not energized, a detent torque (torque required to rotate the drive shaft of the motor in the non-energized state) is generated in the drive shaft of the motors 203a and 203b.

[0027] Therefore, if motors 203a and 203b fail or the power to the entire device goes out and motors 203a and 203b cannot be driven while roller R1 is pressed against roller R2, rollers R1 and R2 will remain pressed. For example, if rollers R1 and R2 are devices that transport sheets such as paper, rollers R1 and R2 are configured to be able to be pulled out of the device for maintenance such as to repair a sheet jam. However, if rollers R1 and R2 remain pressed, problems may occur, such as rollers R1 and R2 not being able to be pulled out, or even if they can be pulled out, rollers R1 and R2 may be damaged.

[0028] Therefore, the cam drive device 200 of this embodiment is provided with a means for applying torque to the cams 202a and 202b in a direction in which the roller R1 moves backward from the roller R2. The configuration of the backward torque applying means will be described below.

[0029] FIG. 5 is an explanatory diagram of a backward torque applying means of a cam drive device according to an embodiment of the present invention.

[0030] FIG. 5 illustrates a configuration in which a spiral spring is used as the backward torque applying means. Cams 202a and 202b are equipped with spiral springs 214a and 214b. In the following description, spiral springs 214a and 214b are collectively referred to as "spiral spring 214." Spiral spring 214 has a center end P1 of the spiral fixed to shaft 208 and an outer end P2 of the spiral fixed to the side of cams 202a and 202b. When spiral spring 214 is turned in the winding direction, the outer diameter of the spiral becomes smaller, and when turned in the unwinding direction (the direction opposite to the winding direction), the outer diameter of the spiral becomes larger. Here, the winding direction of spiral spring 214 is preferably oriented in a direction that applies backward torque to cams 202a and 202b in the winding direction.

[0031] 5, spiral spring 214 does not apply a torque in the backward direction to cams 202a and 202b. When cams 202a and 202b rotate clockwise about shaft 208, spiral spring 214 rotates in the unwinding direction, and spiral spring 214 deforms while increasing the outer diameter of the spiral. With the outer diameter of the spiral increased, a restoring force that tries to wind spiral spring 214 is generated, and this restoring force generates a torque in the backward direction.

[0032] As shown in the figure, when the cams 202a and 202b rotate to the maximum in the backward direction, the arm members 201a and 201b (cam followers 213a and 213b) come into contact with the cam surfaces of the cams 202a and 202b with the smallest radius. Therefore, it is preferable to select a spiral spring 214 that can deform within a range that does not interfere with the arm members 201a and 201b and that can obtain the desired backward torque.

[0033] FIG. 6 is an explanatory diagram of the set torque of the cam drive device according to the embodiment of the present invention.

[0034] In this embodiment, the allowable value is the maximum torque of motors 203a, 203b used to rotate and maintain the posture of cams 202a, 202b in cam drive device 200, and is hereinafter also referred to as "maintenance torque." Cam detent torque is the torque required to rotate the drive shafts of motors 203a, 203b in a non-energized state, and is hereinafter also referred to as "detent torque." Spiral spring torque is the torque generated by the above-mentioned spiral spring 214, and is hereinafter also referred to as "reverse torque."

[0035] The holding torque, detent torque, and reverse torque are all converted onto the rotation axis of the cam, that is, shown as torque values ​​applied to cams 202a, 202b on shaft 208. The spiral spring torque (reverse torque) changes as shown in Fig. 6 depending on the rotation angle of outer circumferential end P2 of spiral spring 214. In order to automatically release the pressure of cams 202a, 202b against cam followers 213a, 213b when motors 203a, 203b are de-energized, the reverse torque is set to be between the holding torque and detent torque.

[0036] Specifically, assuming that the holding torque is T1, the reverse torque is T2, and the detent torque is T3, the magnitude relationship among the three is set to satisfy T1 ≥ T2 > T3, and more preferably T1 > T2 > T3. Note that the component force acting as the reverse torque may change depending on the weight of the target unit 300, the shape and configuration of the cams 202a and 202b, etc., and the magnitude relationship among the three may be set appropriately based on the weight of the target unit, the shape of the cam, etc.

[0037] As described above, this embodiment includes arm members 201a and 201b that support roller R1, cams 202a and 202b that move arm members 201a and 201b, motors 203a and 203b that rotate and drive cams 202a and 202b and maintain the posture of cams 202a and 202b, and spiral springs 214a and 214b that apply torque to cams 202a and 202b in a direction that causes roller R1 to move backward from roller R2 that faces roller R1.

[0038] As described above, the arm members 201a and 201b have axes Xa and Xb, and as the cams 202a and 202b rotate, the arm members 201a and 201b rotate about the axes Xa and Xb as fulcrums, allowing the roller R1 to move forward and backward relative to the roller R2, and the cams 202a and 202b are located below the axes Xa and Xb.

[0039] As described above, the magnitude relationship among the holding torque T1 generated by the motors 203a and 203b to hold the position of the cams 202a and 202b, the backward torque T2 generated by the spiral springs 214a and 214b, and the detent torque T3 required to rotate the drive shafts of the motors 203a and 203b in a non-energized state satisfies T1>T2>T3 on the rotation shafts of the cams 202a and 202b.

[0040] As a result, when motors 203a, 203b are de-energized, cams 202a, 202b move in a direction that releases the pressure on arm members 201a, 201b (cam followers 213a, 213b). Therefore, even if motors 203a, 203b cannot be driven while rollers R1 and R2 are pressed against each other, the pressure between rollers R1 and R2 can be released. As a result, a cam drive device with improved maintainability can be provided.

[0041] Next, a second embodiment will be described with reference to Figures 7 and 8. Figure 7 is an explanatory diagram of the second embodiment, with Figure 7(a) showing the cam in its initial position and Figure 7(b) showing the cam after it has rotated from its initial position. Figure 8 is an explanatory diagram of a comparative example to the second embodiment, with Figure 8(a) showing the cam in its initial position and Figure 8(b) showing the cam after it has rotated from its initial position.

[0042] 8, the outer end P2 of the spiral of the spiral spring 214 (214a, 214b) is bent into an arc shape. The spiral spring 214 is attached to the cam 202 by fixing the outer end P2 to the side of the cam 202 (202a, 202b) with a screw or the like.

[0043] In the above configuration, the orientation of outer end P2 of spiral spring 214 is not necessarily the same as the rotation direction of cam 202. For example, cam 202 rotates clockwise (indicated by the dashed arrow in FIG. 8) around shaft 208 as a fulcrum, whereas outer end P2 of spiral spring 214 is oriented in the direction indicated by the dashed arrow in FIG. 8(b), and the orientations of the two do not match.

[0044] In this way, if cam 202 is rotated and a spring force is generated while the rotational direction of cam 202 and the orientation of the spring material of spiral spring 214 do not match (or are variable), the force will not be applied evenly across the entire spring material. As a result, spiral spring 214 may buckle, as shown in FIG. 8(b). If spiral spring 214 buckles, the amount of deformation is concentrated in one part of spiral spring 214, making it impossible to generate the desired spring force. Furthermore, if spiral spring 214 undergoes plastic deformation due to buckling, spiral spring 214 becomes unusable.

[0045] Therefore, the second embodiment is configured so that the direction in which the outer end P2 of the spiral spring 214 faces always faces the rotation direction of the cam 202.

[0046] 7, outer end P2 of spiral spring 214 is simply cut while retaining its spiral shape, and outer end P2 is supported by being inserted into support pin 216a (216b) fixed to the side surface of cam 202. Support pin 216a (216b) has a slit Sa (Sb) into which outer end P2 of spiral spring 214 is inserted, and support pin 216a (216b) is fixed to the side surface of cam 202 by press-fitting or the like.

[0047] Furthermore, the direction of slit Sa (Sb) is provided so as to be tangential to the rotation center (axis 208) of cam 202. In other words, it is provided so as to be oriented in the same direction as the rotation direction of cam 202 (the direction indicated by the dashed arrow in FIG. 7(b)). This restricts the orientation of outer end P2 of spiral spring 214 to always face the rotation direction of cam 202, thereby reducing the occurrence of buckling deformation of spiral spring 214 that accompanies the rotation of cam 202. Here, support pin 216a (216b) is an example of a "support member."

[0048] Note that a commonly used split pin may be used as support pin 216a (216b). In the case of a split pin, the orientation of outer end P2 will have a range of variation due to the effect of play that occurs between the plate thickness of the spring material of spiral spring 214 and the width of the slit in the split pin. Also, high machining precision is required to accurately align the orientation of the slit in the split pin with the rotational direction of cam 202, and it is not easy to actually use a split pin effectively.

[0049] To enable the use of a split pin as described above, a buckling prevention pin 217a (217b) may be further provided on the attachment portion of the spiral spring 214 (the side surface of the cam 202). The buckling prevention pin 217a (217b) is arranged so as to contact a portion of the spiral spring 214. By providing the buckling prevention pin 217a (217b), the orientation of the outer end P2 of the spiral spring 214 can be restricted by two points: the support pin 216a (216b) and the buckling prevention pin 217a (217b). By providing a sufficient distance between the two points, the support pin 216a (216b) and the buckling prevention pin 217a (217b), it is possible to suppress deviation in orientation due to component precision.

[0050] It is preferable to position buckling prevention pin 217a (217b) outside the radius of curvature of spiral spring 214. This is because spiral spring 214 is pre-formed into a spiral shape with a fixed curvature, and the buckling direction is always deformation such that it bulges outward in the radial direction. Here, buckling prevention pin 217a (217b) is an example of a "buckling prevention member."

[0051] 9 is an explanatory diagram showing a modified example of the backward torque applying means. Since the configuration is the same as that described above except for the cam member, the same reference numerals are used and the description thereof will be omitted.

[0052] The cams 215a, 215b (hereinafter collectively referred to as "cam 215") shown in this modified example have thick portions T1 and thin portions T2 by providing recesses on the side surfaces of the cam 215. This shifts the center of gravity of the cam 215 from the center of rotation, so that torque is applied in the backward direction when the cam is in a phase posture in which it is in contact with the cam followers 213a, 213b.

[0053] In this modified example, backward torque can be applied solely by the shape of cam 215, and backward torque is generated only when cam 215 is in a specific phase. Note that in this modified example, a recess is provided on the side surface of cam 215 to form thin portion T2, but if it is difficult to provide a recess, a weight member may be attached to the side surface of cam 215 to form thick portion T1, thereby obtaining an eccentric cam.

[0054] As described above, in this embodiment, the backward torque applying means is the eccentric cam 215, whose center of gravity is shifted from the center of rotation.

[0055] In this modification, when the motors 203a, 203b are de-energized, the cams 215a, 215b move in a direction that releases the pressure on the arm members 201a, 201b (cam followers 213a, 213b). Therefore, even if the motors 203a, 203b cannot be driven while the rollers R1, R2 are pressed against each other, the pressure between the rollers R1, R2 can be released. As a result, a cam drive device with improved maintainability can be provided.

[0056] 10 to 13 show application examples of the cam drive device according to the embodiment of the present invention.

[0057] FIG. 10 is a schematic diagram showing a first application example, and will be described based on an embodiment in which the invention is applied to an electrophotographic printer as an image forming apparatus.

[0058] The printer 500 includes a tandem unit 1 in which imaging units 100Y, 100M, 100C, and 100K are arranged in parallel to form toner images of Y (yellow), M (magenta), C (cyan), and K (black). The imaging units 100Y-100K each support a photosensitive module, a charging module, a developing module, and a cleaning module in a common unit frame, allowing these modules to be detachably mounted to the printer body as a whole. The photosensitive modules 20Y, 20M, 20C, and 20K each include a drum-shaped photosensitive member 21Y, 21M, 21C, and 21K. The charging modules 30Y, 30M, 30C, and 30K each include a charging device. The developing modules 40Y, 40M, 40C, and 40K each include a developing device that performs development using a two-component developer containing toner and a magnetic carrier. The cleaning modules 50Y, 50M, 50C, and 50K include cleaning devices that clean the photoconductors 21Y, 21M, 21C, and 21K.

[0059] An exposure unit 9 is provided above the tandem section 1, and a bottle mounting section 10 that holds toner bottles 150Y, 150M, 150C, and 150K containing developing toner is further provided above the exposure unit 9. The toner bottles 150Y to 150K are detachable from the bottle mounting section 10, and when a bottle becomes empty, it can be removed from the bottle mounting section 10 and replaced with a new toner bottle.

[0060] Also, below the tandem section 1, there is provided a transfer unit 2 having an intermediate transfer belt 15. The intermediate transfer belt 15 is an endless belt made of a single layer or multiple layers of vinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polyimide, polycarbonate, or the like, and moves clockwise in the figure while being stretched over multiple rollers.

[0061] A secondary transfer device 4 is provided below the transfer unit 2. The secondary transfer device 4 includes a secondary transfer belt 17a formed of an endless belt, and a secondary transfer roller 17b that presses the secondary transfer belt 17a toward the secondary transfer opposing roller 16. The secondary transfer belt 17a abuts the front surface of the belt at the location where the intermediate transfer belt 15 is wrapped around the secondary transfer opposing roller 16, forming a secondary transfer nip. A secondary transfer bias is applied to the secondary transfer roller 17b, and the secondary transfer opposing roller 16 is electrically grounded, thereby forming a secondary transfer electric field in the secondary transfer nip.

[0062] On the left side of the secondary transfer device 4 in the drawing, there is a fixing unit 7 that fixes the toner image transferred onto the recording sheet. The fixing unit 7 has a heating roller with a heating element inside. In addition, between the secondary transfer device 4 and the fixing unit 7, there is a conveyor belt 6 that conveys the recording sheet toward the fixing unit 7 after the toner image has been transferred. In addition, at the bottom of the printer 500, there is a paper feed unit 3 that sends the recording sheet to the secondary transfer device 4. Furthermore, on the left side of the fixing unit 7 in the drawing, there is a paper discharge unit 8 that conveys the recording sheet that has passed through the fixing unit 7 outside the machine or toward the duplex unit 5.

[0063] Four primary transfer rollers for Y, M, C, and K are provided inside the loop of the intermediate transfer belt 15, and the intermediate transfer belt 15 is interposed between these primary transfer rollers and the photoconductors 21Y to 21K. This causes the front surface of the intermediate transfer belt 15 to come into contact with the photoconductors 21Y to 21K, forming a primary transfer nip. In the primary transfer nip, a primary transfer bias is applied to the primary transfer rollers to form a primary transfer electric field.

[0064] When the printer 500 receives image data from an external personal computer or the like, it starts a print job and begins driving the intermediate transfer belt 15 and other components. Then, in the tandem unit 1, the charging devices of the charging modules 30Y-30K uniformly charge the surfaces of the rotating photoconductors 21Y-21K to a predetermined charging potential. Electrostatic latent images for Y, M, C, and K are formed on the charged surfaces of the photoconductors 21Y-21K by optical scanning using laser light emitted from the exposure unit 9 based on the image data. The electrostatic latent images are developed into toner images by the developing modules 40Y-40K and then primarily transferred onto the intermediate transfer belt 15 in order so that they overlap, resulting in a four-color superimposed toner image. After the toner image transfer, the cleaning devices of the cleaning modules 50Y-50K remove any residual toner remaining on the surfaces of the photoconductors 21Y-21K from the surfaces of the photoconductors 21Y-21K.

[0065] In parallel with the formation of the toner image, the paper feed unit 3 transports the recording sheet until it hits the pair of registration rollers 14, and once the recording sheet hits the pair of registration rollers 14, the transport is temporarily stopped. The pair of registration rollers 14 then resumes rotation in time with the toner image on the intermediate transfer belt 15 reaching the secondary transfer nip. The toner image is secondarily transferred onto the recording sheet at the secondary transfer nip in synchronization with the toner image on the intermediate transfer belt 15, as the pair of registration rollers 14 resumes rotation.

[0066] After the toner image has been transferred, the recording sheet is moved by a conveyor belt 6 into a fixing unit 7, which applies heat and pressure to the toner image on the recording sheet, fixing the toner image to the recording sheet. The recording sheet then moves to a paper discharge unit 8, whose switching claw operates to switch the path of the recording sheet to either a paper discharge tray outside the machine (on the left side of the device) or the duplex unit 5 below. The duplex unit 5 turns the recording sheet upside down and sends it again to the secondary transfer nip. The toner image is then secondarily transferred to the back side of the resent recording sheet at the secondary transfer nip, after which the paper discharge unit 8 ejects it onto the paper discharge tray.

[0067] After the intermediate transfer belt 15 passes through the secondary transfer nip, an intermediate transfer belt cleaning unit 90 removes any residual toner remaining on the surface of the intermediate transfer belt 15. In the printer 500 configured as described above, the cam drive device 200 can be applied to, for example, a mechanism for moving the secondary transfer belt 17a toward and away from the secondary transfer opposing roller 16.

[0068] 11 is an overall perspective view of the target unit in Application Example 1. Application Example 1 shows an example in which the secondary transfer device 4 is applied as the target unit 300 shown in FIG.

[0069] The cam drive device 200 supports the secondary transfer device 4, an example of a target unit, between the arm members 201a and 201b. A portion of the secondary transfer belt 17a shown in FIG. 10 is exposed on the upper surface of the secondary transfer device 4, and a secondary transfer roller 17b is provided below (on the back side of) the secondary transfer belt 17a, pressing the secondary transfer belt 17a toward the secondary transfer opposing roller 16. With the above configuration, when the cams 202a and 202b (see FIG. 2 for the cam 202b) rotate, the arm members 201a and 201b rotate about the axes Xa and Xb via the cam followers. As a result, the secondary transfer device 4 also rotates about the axes Xa and Xb together with the arm members 201a and 201b. When the cam drive device 200 is de-energized while the secondary transfer nip is formed in the printer 500, a backward torque acts on the cams 202a and 202b in a direction that releases the secondary transfer nip.

[0070] For example, some office printers are equipped with an interlock mechanism that cuts off the electrical connection to the motor when the printer cover is opened. In printers equipped with an interlock mechanism, opening the printer cover cuts off the motor's holding current. Therefore, by setting the holding torque T1, backward torque T2, and detent torque T3 in the following relationship: T1>T2>T3, the secondary transfer nip can be reliably released.

[0071] In addition, in this application example, the cam drive device 200 carrying the secondary transfer device 4 is provided so as to be removable in the direction of arrow A from the printer 500. Therefore, if the printer is de-energized during image formation and a recording sheet remains in the secondary transfer device 4, the recording sheet can be removed by removing the cam drive device 200 and the secondary transfer device 4 after the secondary transfer nip is released.

[0072] 12 is a schematic diagram showing a second application example, in which the registration roller pair 14 of the printer 500 shown in FIG.

[0073] The cam drive device 200 is equipped with roller 14b, one of the pair of registration rollers 14. Arm members 201a and 201b rotatably support roller 14b. When cams 202a and 202b are in the solid line positions, arm members 201a and 201b are in their most retracted positions, and roller 14b is also in a position separated from roller 14a, as shown by the solid line. Note that roller 14a is a roller fixed at a predetermined position on the main body of the printer 500. When cams 202a and 202b are rotated clockwise and cams 202a and 202b move to the dashed line positions, arm members 201a and 201b are in their most advanced positions, and roller 14b presses roller 14a, as shown by the dashed line.

[0074] In this example as well, if the cam drive device 200 is de-energized while the registration roller pair 14 forms a nip, a backward torque acts on the cams 202a and 202b in the direction to release the nip, and the same effect as in Application Example 1 can be obtained. Note that in this example as well, the cam drive device 200 carrying the roller 14b may be made removable from the printer 500 body to improve accessibility for maintenance work, etc.

[0075] FIG. 13 is a schematic diagram showing a third application example, which will be described based on an embodiment in which the invention is applied to an inkjet printer as an image forming apparatus.

[0076] The printer 400 is equipped with an inkjet head 401. The head 401 can be any of a heating element type, a piezoelectric element type, a MEMS element type, an electrostatic element type, etc. A paper feed cassette 402 stores recording sheets S, and a paper feed roller 403 picks up the recording sheets S one by one and feeds them out of the paper feed cassette 402. Next, a pair of sheet thickness detection rollers 404a, 404b obtains the thickness of each recording sheet S.

[0077] The recording sheet S is moved directly below the head 401 by a transport nip formed by the LF roller 405 and pinch roller 406. An encoder is provided coaxially with the LF roller 405, and the amount of rotation of the LF roller 405 can be detected in terms of the feed distance of the recording sheet S. A platen 407 supports the recording sheet S from below. A first discharge roller 408, together with a first roller 409, pinches and transports the recording sheet S that has passed under the head 401. The fixing unit 410 has a blower fan 411 that heats the recording sheet S on which the ink ejected by the head 401 is carried, and blows warm air at a predetermined temperature onto the recording sheet S to dry the ink on the recording sheet S.

[0078] The fixing unit 410 is also equipped with a temperature sensor (thermistor) that detects the temperature of the hot air. A second paper discharge roller 412, provided downstream of the fixing unit 410, sandwiches and transports the recording sheet S that has passed through the fixing unit 410 together with a second roller 413. A paper discharge platen 414, provided opposite the fixing unit 410, supports the recording sheet S from below, similar to the platen 407. In this way, the ink ejected by the head 401 can be dried by the fixing unit 410.

[0079] In the printer 400 configured as described above, for example, when the LF roller 405 and the pinch roller 406 are configured to be able to move toward and away from each other, the LF roller 405 or the pinch roller 406 may be mounted on the cam drive device 200. Alternatively, when the first paper discharge roller 408 and the first roller 409 are configured to be able to move toward and away from each other, the first paper discharge roller 408 or the first roller 409 may be mounted on the cam drive device 200. Alternatively, when the second paper discharge roller 412 and the second roller 413 are configured to be able to move toward and away from each other, the second paper discharge roller 412 or the second roller 413 may be mounted on the cam drive device 200.

[0080] Furthermore, the cam drive device 200 is not limited to the roller pair, but can also be applied to the vertical movement of the head 401. When applied to the vertical movement of the head 401, the head 401 can be moved in the vertical direction by fixing the head 401 to the arm members 201a and 201b of the cam drive device 200. This makes it possible to widen the gap between the head 401 and the platen 407, making it easier to remove the recording sheet S remaining below the head 401.

[0081] The above description is merely an example, and the present invention provides unique effects for each of the following aspects.

[0082] The first aspect is characterized by comprising a support member (e.g., arm members 201a, 201b) that supports a target member (e.g., target unit 300 in FIG. 2, roller R1 in FIG. 4, etc.), a cam member (e.g., cams 202a, 202b) that moves the support member, an electric motor (e.g., motors 203a, 203b) that rotates and drives the cam member and maintains the posture of the cam member, and a backward torque imparting means (e.g., spiral springs 214a, 214b) that imparts torque to the cam member in a direction that causes the target member to retreat from an opposing member (e.g., roller R2 in FIG. 4) that faces the target member.

[0083] The second aspect is characterized in that in the first aspect, the support members (e.g., arm members 201a, 201b) have rotation axes (e.g., axes Xa, Xb), and the support members rotate about the rotation axes as a fulcrum in accordance with the rotation of the cam members (e.g., cams 202a, 202b), allowing the target member (e.g., target unit 300 in FIG. 2, roller R1 in FIG. 4, etc.) to move forward and backward relative to the opposing member (e.g., roller R2 in FIG. 4, etc.), and the cam members are provided at positions below the rotation axes.

[0084] The third aspect is characterized in that in the first or second aspect, the magnitude relationship among the holding torque T1 generated by the electric motor (e.g., motors 203a, 203b) to hold the position of the cam member (e.g., cams 202a, 202b), the backward torque T2 generated by the backward torque imparting means (e.g., spiral springs 214a, 214b), and the detent torque T3 required to rotate the drive shaft of the electric motor in a non-energized state satisfies T1>T2>T3 on the rotation shaft of the cam member (e.g., shaft 208).

[0085] The fourth aspect is characterized in that in any of the first to third aspects, the backward torque imparting means (e.g., spiral springs 214a, 214b) is a spiral spring provided between the cam member (e.g., cams 202a, 202b) and the rotating shaft (e.g., shaft 208).

[0086] A fifth aspect is the fourth aspect, characterized in that the backward torque is a torque generated by winding up the spiral spring.

[0087] The sixth aspect is characterized in that in the fifth aspect, the spring torque of the spiral spring is set between the maximum torque of the electric motor (e.g., motors 203a, 203b) and the detent torque on the cam member (e.g., cams 202a, 202b).

[0088] The seventh aspect is characterized in that, in any of the first to third aspects, the backward torque imparting means is an eccentric cam (e.g., cams 215a, 215b) in which the center of gravity of the cam member is shifted from the center of rotation.

[0089] According to the first to seventh aspects, when the electric motor is de-energized, the cam member moves in a direction that releases the pressure on the support member. Therefore, even if the electric motor cannot be driven while the target member and the opposing member are pressed against each other, the pressure between the target member and the opposing member can be released. As a result, a cam drive device with improved maintainability can be provided.

[0090] The eighth aspect is characterized in that, in any of the fourth to sixth aspects, the cam member (e.g., cams 202a, 202b) is provided with a support member (e.g., support pins 216a, 216b) that supports the outer end (e.g., outer end P2) of the spiral of the spiral spring (e.g., spiral springs 214a, 214b) so that the outer end faces in the rotation direction of the cam member (e.g., the direction indicated by the dashed arrow in Figure 7(b)).

[0091] The ninth aspect is characterized in that, in the eighth aspect, the support member (e.g., support pins 216a, 216b) has a slit (e.g., slit Sa, Sb) into which the outer end (e.g., outer end P2) is inserted, and the direction of the slit is arranged to be the same as the rotation direction of the cam member (e.g., cams 202a, 202b) (e.g., the direction indicated by the dashed arrow in Figure 7(b)).

[0092] According to the eighth and ninth aspects, the outer end of the spiral spring is supported so that it always faces the direction of rotation of the cam member, which makes it difficult for deformation of the spring to be concentrated in one area, thereby preventing buckling and plastic deformation of the spring.

[0093] The tenth aspect is characterized in that in the fourth, fifth, sixth, eighth or ninth aspect, the cam member (e.g., cams 202a, 202b) is provided with a buckling prevention member (e.g., buckling prevention pins 217a, 217b) that contacts a portion of the spiral spring (e.g., spiral springs 214a, 214b) and prevents the spiral spring from buckling.

[0094] According to the tenth aspect, deviation of the direction of the spiral spring due to component precision can be further suppressed. [Explanation of symbols]

[0095] 200 Cam drive unit 201a, 201b Arm members 202a, 202b Cam 203a, 203b Motor 214a, 214b Spiral spring 300 Target Units

Claims

1. a support member for supporting the target member; a cam member for moving the support member; An electric motor that rotates the cam member and maintains the orientation of the cam member, The cam member is provided with a backward torque applying means that applies torque in a direction that causes the target member to retract from the opposing member facing the target member. Equipped with a cam drive device characterized in that the magnitude relationship among a holding torque T1 generated by the electric motor to hold the position of the cam member, a backward torque T2 generated by the backward torque applying means, and a detent torque T3 required to rotate the drive shaft of the electric motor in a non-energized state satisfies T1 > T2 > T3 on the rotation shaft of the cam member.

2. 2. The cam drive device according to claim 1, wherein the support member has a pivot shaft, the support member rotates about the pivot shaft as a fulcrum in accordance with the rotation of the cam member, thereby enabling the target member to move toward and away from the opposing member, and the cam member is located at a position below the pivot shaft.

3. A cam drive device as described in claim 1 or 2, characterized in that the backward torque imparting means is a spiral spring provided between the cam member and the rotating shaft.

4. The cam drive device according to claim 3, characterized in that the backward torque is a torque generated by winding the spiral spring.

5. A cam drive device as described in claim 3 or 4, characterized in that the spring torque of the spiral spring is set between the maximum torque of the electric motor and the detent torque on the cam member.

6. A cam drive device as described in claim 1 or 2, characterized in that the backward torque imparting means is an eccentric cam in which the center of gravity of the cam member is shifted from the center of rotation.

7. A cam drive device described in any one of claims 3 to 5, characterized in that the cam member is provided with a support member that supports the outer end of the spiral of the spiral spring so that the outer end faces in the rotational direction of the cam member.

8. A cam drive device as described in Claim 7, characterized in that the support member has a slit into which the outer end portion is inserted, and the direction of the slit is arranged to be the same as the direction of rotation of the cam member.

9. A cam drive device as described in claim 3, 4, 5, 7 or 8, characterized in that the cam member is provided with a buckling prevention member that contacts a portion of the spiral spring and prevents the spiral spring from buckling.

10. A transfer device characterized by comprising a cam drive device described in any one of claims 1 to 9.

11. An image forming apparatus comprising a cam drive device according to any one of claims 1 to 9, or a transfer device according to claim 10.

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