JP7828551B2 - Cam drive device, transfer device, and image forming apparatus - Google Patents

Description

This invention relates to a cam drive device, a transfer device, and an image forming device.

Patent Document 1 discloses a cam drive device comprising an eccentric cam (61), a ball bearing (62) that changes its position in accordance with the change in the rotational orientation 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 the stepping motor. The device includes a control unit that controls the output current value from the power supply to generate a stall torque for the stopped stepping motor, varying the current output from the power supply according to the difference in the rotational stopping orientation of the eccentric cam. This control unit suppresses the increase in power consumption caused by adopting a configuration in which the rotation of the eccentric cam is stopped when the non-concentric curved portion of the eccentric cam abuts against the ball bearing.

Japanese Patent Publication No. 2018-097066

In the configuration of Patent Document 1, if the stepping motor becomes unable to be driven due to a motor failure or the like while the secondary transfer roller (17) and the secondary transfer opposing roller (16) have formed a secondary transfer nip, the secondary transfer nip will remain under pressure.

The present invention comprises a support member for supporting a target member, a cam member for moving the support member, an electric motor for rotationally driving the cam member and maintaining the orientation of the cam member, and a backward-direction torque applying means for applying torque to the cam member in a direction that causes the target member to move backward from an opposing member facing the target member, characterized in that the relationship between the magnitudes of the holding torque T1 generated by the electric motor to maintain the orientation of the cam member, the backward-direction torque T2 generated by the backward-direction torque applying means, and the detent torque T3 required to rotate the drive shaft of the electric motor when it is not energized satisfies T1 > T2 > T3 on the rotation axis of the cam member .

According to the present invention, a cam drive device with improved maintainability can be provided.

An overall perspective view of a cam drive device according to an embodiment of the present invention. An overall perspective view showing how the target unit is mounted on a cam drive device according to an embodiment of the present invention. A side view illustrating the movement of the arm member and cam in a cam drive device according to an embodiment of the present invention. A side view illustrating malfunctions when the motor is not energized. An explanatory diagram of the means for applying reverse torque to a cam drive device according to an embodiment of the present invention. A diagram illustrating the set torque of a cam drive device according to an embodiment of the present invention. An explanatory diagram of the second embodiment. A diagram illustrating a comparative example to the second embodiment. An explanatory diagram showing a modified example of a means for applying torque in the backward direction. An explanatory diagram of a first application example of a cam drive device according to an embodiment of the present invention. An overall perspective view of the target unit in the first application example. An explanatory diagram of a second application example of a cam drive device according to an embodiment of the present invention. An explanatory diagram of a third application example of a cam drive device according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 is an overall perspective view of a cam drive device according to an embodiment of the present invention.

The cam drive unit 200 comprises arm members 201a, 201b, cams 202a, 202b, and motors 203a, 203b. Motor 203a is a motor capable of forward and reverse rotation. 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; 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.

Shaft 206a has a pulley 207a at its other end (the end opposite to the side with pulley 205a). A shaft 208, parallel to shaft 206a, has a pulley 209a at its end, and a timing belt 210a is stretched between pulley 209a and pulley 207a on shaft 206a. The shaft 206b has a similar configuration, with a pulley 207b at its other end (the end opposite to the side with pulley 205b). Furthermore, shaft 208 is parallel to shaft 206b. A timing belt 210b is stretched between a pulley at the end of shaft 208 (not shown in Figure 1, but similar to pulley 209a) and pulley 207b on shaft 206b.

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 pulley, causing shaft 208 to rotate. Tensioners 211a and 211b contact the timing belts 210a and 210b from the outside, providing appropriate tension to the timing belts 210a and 210b.

The shaft 208 has a cam 202a at one end (the portion protruding outward from the pulley 209a) and a cam 202b at the other end. The cams 202a and 202b are fitted onto the outer circumference of the shaft 208, and are attached to the shaft 208 by fitting an axial key (for example, one provided on the outer circumference of the shaft 208) into a keyway provided in the cams 202a and 202b that engages with this key. With this configuration, when the shaft 208 rotates, the cams 202a and 202b rotate together with the shaft 208.

On the other hand, the housing frame 212a of the cam drive unit 200 supports the arm member 201a so that it can rotate around axis Xa as a pivot point. Although not shown in Figure 1, a housing frame also exists on the arm member 201b side, similar to the housing frame 212a, and this housing frame supports the arm member 201b so that it can rotate around axis Xb as a pivot point. The arm members 201a and 201b are equipped with cam followers (described later) at positions opposite to the cams 202a and 202b, and the cam followers contact the cam surfaces of the cams 202a and 202b. With this configuration, when the cams 202a and 202b rotate, the cam followers move according to the shape of the cam surfaces, and the arm members 201a and 201b rotate around axes Xa and Xb as pivot points in response.

In this embodiment, motors 203a and 203b are hybrid stepping motors that drive cams 202a and 202b by a predetermined angle using constant pulses. Subsequently, motors 203a and 203b generate holding torque to hold cams 202a and 202b in the predetermined angle position. Furthermore, even when motors 203a and 203b are not energized, detent torque (the torque required to rotate the drive shaft of a motor in an unenergized state) is generated on the motor drive shaft. In this embodiment, motors 203a and 203b are provided separately to drive cams 202a and 202b, but this is not necessarily the only option. For example, shafts 206a and 206b could be combined into a single shaft, allowing a single motor to drive both cams 202a and 202b.

Here, arm members 201a and 201b are examples of "support members," cams 202a and 202b are examples of "cam members," and motors 203a and 203b are examples of "electric motors." Furthermore, shaft 208 is an example of a "rotating shaft," and shafts Xa and Xb are examples of "rotating shafts."

Figure 2 is an overall perspective view showing the cam drive device according to an embodiment of the present invention with the target unit mounted on it.

The cam drive unit 200 is configured to support the target unit 300 between arm members 201a and 201b, as shown by the dashed line. With this configuration, when cams 202a and 202b rotate, the cam followers provided on arm members 201a and 201b move in accordance with the shape of the cam surface, causing arm members 201a and 201b to rotate around axes Xa and Xb as pivot points. As a result, the target unit 300 also rotates together with arm members 201a and 201b around axes Xa and Xb as pivot points.

The shape of the target unit 300 is not limited to a box shape as shown in the figure, and the shape and configuration of the arm members 201a and 201b may be appropriately changed depending on the shape and configuration of the target unit 300. Here, the target unit 300 is just one example of a "target member".

Figure 3 is a side view illustrating the movement of the arm member and cam in a cam drive device according to an embodiment of the present invention.

As described above, the housing frame 212a of the cam drive unit 200 supports the arm member 201a so that the arm member 201a can rotate around axis Xa as a pivot point. The arm member 201a is equipped with a cam follower 213a at a position opposite the cam 202a, and the cam follower 213a is in contact with the cam surface of the cam 202a.

In this embodiment, when the cam 202a is at the position indicated by the solid line in Figure 3, the cam follower 213a is closest to the shaft 208, resulting in the arm member 201a being moved to its furthest backward position. Then, when the cam 202a rotates clockwise around the shaft 208 and moves to the position indicated by the dashed line, the cam 202a moves the cam follower 213a to the position indicated by the dashed line. As a result, the arm member 201a is moved to its furthest forward position via the cam follower 213a.

Furthermore, to return the cam 202a from the dashed line position to the solid line position, the cam 202a is rotated counterclockwise. Note that while Figure 3 explains the movement based on the configuration of the arm member 201a, the arm member 201b has a similar configuration.

Figure 4 is a side view illustrating a malfunction when the motor is not energized. Here, the example given is when the target unit 300 mounted on the cam drive unit 200 is roller R1.

Arm members 201a and 201b rotatably support roller R1. When cams 202a and 202b are in the solid line position, arm members 201a and 201b are in their most retracted position, and therefore roller R1 is also spaced apart from roller R2, as shown by the solid line. Note that roller R2 is a roller fixed in a predetermined position. When cams 202a and 202b are rotated clockwise, and move to the dashed line position, arm members 201a and 201b are in their most forward position, and roller R1 presses against 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 an "opposing member."

As described above, the cam drive unit 200 uses stepping motors 203a and 203b to drive the cams 202a and 202b by a constant pulse, moving them by a predetermined angle, and then generating a holding torque to maintain the position of the cams 202a and 202b. Furthermore, even when the motors 203a and 203b are not energized, detent torque (the torque required to rotate the drive shaft of a motor in an unenergized state) is generated on the drive shafts of the motors 203a and 203b.

Therefore, if motors 203a and 203b fail or the power to the entire device goes out while roller R1 is pressed against roller R2, and motors 203a and 203b can no longer be driven, rollers R1 and R2 will remain pressed against each other. For example, if rollers R1 and R2 are used to transport sheets of paper or other materials, the device should be configured to allow rollers R1 and R2 to be pulled out for maintenance such as sheet jams. However, if rollers R1 and R2 remain pressed against each other, it may be impossible to pull them out, or even if they can be pulled out, problems such as damage to rollers R1 and R2 may occur.

Therefore, in the cam drive device 200 of this embodiment, a means is provided to apply torque to the cams 202a and 202b in a direction that causes roller R1 to retract from roller R2. The configuration of the retraction torque application means will be described below.

Figure 5 is an explanatory diagram of the means for applying reverse torque to a cam drive device according to an embodiment of the present invention.

Figure 5 illustrates a configuration using a spiral spring as a means of applying torque in the backward direction. Cams 202a and 202b are equipped with spiral springs 214a and 214b. In the following description, spiral springs 214a and 214b will be collectively referred to as "spiral spring 214". The spiral spring 214 has its central end P1 fixed to the shaft 208 and its outer end P2 fixed to the side surfaces of cams 202a and 202b. The spiral spring 214 deforms such that its outer diameter decreases when rotated in the winding direction, and increases when rotated in the unwinding direction (opposite to the winding direction). Here, the winding direction of the spiral spring 214 should be such that it applies torque in the backward direction to cams 202a and 202b in the winding direction.

When cams 202a and 202b are in the positions shown in Figure 5, the spiral spring 214 does not apply a backward torque to cams 202a and 202b. As cams 202a and 202b rotate clockwise around shaft 208, the spiral spring 214 rotates in the unwinding direction, deforming while increasing the outer diameter of the spiral. In this state of increased spiral diameter, a restoring force is generated that attempts to wind the spiral spring 214, and this restoring force generates a backward torque.

Furthermore, as shown in the figure, when cams 202a and 202b rotate to their maximum extent in the retraction direction, the arm members 201a and 201b (cam followers 213a and 213b) will come into contact with the cam surfaces of 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 retraction torque.

Figure 6 is an explanatory diagram of the set torque of the cam drive device according to an embodiment of the present invention.

In this embodiment, the allowable value is the maximum torque of motors 203a and 203b used for rotational driving and posture maintenance of cams 202a and 202b in the cam drive device 200, and is hereinafter also referred to as "holding torque." The cam-top detent torque is the torque required to rotate the drive shafts of motors 203a and 203b in the de-energized state, and is hereinafter also referred to as "detent torque." The spiral spring torque is the torque generated by the spiral spring 214 described above, and is hereinafter also referred to as "reverse direction torque."

The holding torque, detent torque, and retraction torque are all expressed as values calculated on the cam's rotation axis, i.e., as torque values applied to cams 202a and 202b on axis 208. The spiral spring torque (retraction torque) changes as shown in Figure 6 depending on the rotation angle of the outer peripheral end P2 of the spiral spring 214. To automatically release the pressure of cams 202a and 202b on cam followers 213a and 213b when motors 203a and 203b are de-energized, the retraction torque is set to be between the holding torque and the detent torque.

Specifically, when the holding torque is T1, the retraction torque is T2, and the detent torque is T3, the relative magnitudes of the three are set to satisfy T1 ≥ T2 > T3, and more preferably T1 > T2 > T3. Note that the component force acting as the retraction torque may change depending on the weight of the target unit 300, the shape configuration of the cams 202a and 202b, etc., and the relative magnitudes of the three may be set appropriately based on the weight of the target unit, the cam shape, etc.

As described above, this embodiment comprises arm members 201a and 201b that support the roller R1, cams 202a and 202b that move the arm members 201a and 201b, motors 203a and 203b that rotationally drive the cams 202a and 202b and maintain their positions, and spiral springs 214a and 214b that apply torque to the cams 202a and 202b in a direction that causes the roller R1 to retract from the roller R2 opposite to the roller R1.

Furthermore, as described above, the arm members 201a and 201b have axes Xa and Xb, respectively. The arm members 201a and 201b rotate around axes Xa and Xb as pivot points in conjunction with the rotation of the cams 202a and 202b, allowing roller R1 to move forward and backward relative to roller R2. The cams 202a and 202b are positioned below axes Xa and Xb.

Furthermore, as described above, the relationship between the holding torque T1 generated by motors 203a and 203b to maintain the posture of cams 202a and 202b, the backward torque T2 generated by spiral springs 214a and 214b, and the detent torque T3 required to rotate the drive shafts of motors 203a and 203b when they are not energized satisfies T1 > T2 > T3 on the rotation axis of cams 202a and 202b.

As a result, when motors 203a and 203b are de-energized, cams 202a and 202b move in a direction that releases the pressure on arm members 201a and 201b (cam followers 213a and 213b). Therefore, even if motors 203a and 203b cannot be driven while rollers R1 and R2 are pressing 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.

Next, a second embodiment will be described using Figures 7 and 8. Figure 7 is an explanatory diagram of the second embodiment, where Figure 7(a) shows the cam in its initial position and Figure 7(b) shows the cam rotated from its initial position. Figure 8 is an explanatory diagram of a comparative example to the second embodiment, where Figure 8(a) shows the cam in its initial position and Figure 8(b) shows the cam rotated from its initial position.

In the comparative example shown in Figure 8, the outer ends P2 of the spiral springs 214 (214a, 214b) are bent into an arc shape. The spiral springs 214 are attached to the cams 202 (202a, 202b) by fixing these outer ends P2 to the side surface of the cams 202 using screws or the like.

In the above configuration, the orientation of the outer end P2 of the spiral spring 214 is not necessarily the same as the rotation direction of the cam 202. For example, while the cam 202 rotates clockwise (indicated by the dashed arrow in Figure 8) around the axis 208 as a pivot point, the outer end P2 of the spiral spring 214 is oriented in the direction indicated by the dashed arrow in Figure 8(b), and their orientations do not coincide.

Thus, when the cam 202 is rotated and spring force is generated while the rotation direction of the cam 202 and the orientation of the spring material of the spiral spring 214 are mismatched (or variable), the force is not applied evenly across the entire spring material. As a result, the spiral spring 214 may buckle, as shown in Figure 8(b). When the spiral spring 214 buckles, the deformation is concentrated in a part of the spiral spring 214, making it impossible to generate the desired spring force. Furthermore, if the spiral spring 214 undergoes plastic deformation due to buckling, the spiral spring 214 becomes unusable.

Therefore, in the second embodiment, the direction in which the outer end P2 of the spiral spring 214 faces is always aligned with the rotational direction of the cam 202.

Specifically, as shown in Figure 7, the outer end P2 of the spiral spring 214 is simply cut while maintaining its spiral shape, and the outer end P2 is supported by being inserted into a support pin 216a (216b) fixed to the side surface of the cam 202. The support pin 216a (216b) has a slit Sa (Sb) into which the outer end P2 of the spiral spring 214 is inserted, and the support pin 216a (216b) is fixed to the side surface of the cam 202 by press-fitting or the like.

Furthermore, the orientation of the slit Sa (Sb) is set so as to be tangential to the rotation center (axis 208) of the cam 202. That is, it is set to be in the same direction as the rotation direction of the cam 202 (the direction indicated by the dashed arrow in Figure 7(b)). This restricts the orientation of the outer end P2 of the spiral spring 214 to always face the rotation direction of the cam 202, thereby reducing the occurrence of buckling deformation of the spiral spring 214 due to the rotation of the cam 202. Here, the support pin 216a (216b) is an example of a "support member".

Note that the support pin 216a (216b) may be a commonly used cotter pin. In the case of a cotter pin, the orientation of the outer end P2 will have some variation due to the play between the plate thickness of the spiral spring 214 and the slit width of the cotter pin. Furthermore, accurately aligning the slit of the cotter pin with the rotational direction of the cam 202 requires high machining precision, making the practical use of cotter pins not easy.

To enable the use of cotter pins as described above, a buckling prevention pin 217a (217b) may be provided on the mounting portion of the spiral spring 214 (the side surface of the cam 202). The buckling prevention pin 217a (217b) is positioned 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 at two points: the support pin 216a (216b) and the buckling prevention pin 217a (217b). By ensuring a sufficient distance between the support pin 216a (216b) and the buckling prevention pin 217a (217b), orientation deviations due to part precision can be suppressed.

Furthermore, the buckling prevention pins 217a (217b) should be positioned on the outer side of the radius of curvature of the spiral spring 214. This is because the spiral spring 214 is pre-formed with a spiral shape at a constant curvature, and the buckling direction always deforms by bulging radially outward. Here, the buckling prevention pins 217a (217b) are an example of a "buckling prevention member."

Figure 9 is an explanatory diagram showing a modified example of the reverse torque application mechanism. Since the configuration is the same as described above, except for the cam member, the same reference numerals are used and their descriptions are omitted.

The cams 215a and 215b (hereinafter collectively referred to as "cam 215") shown in this modified example are provided with a thick-walled portion T1 and a thin-walled portion T2 by providing a recess on the side surface of the cam 215. This shifts the center of gravity of the cam 215 away from the center of rotation, causing torque to be applied in the retraction direction when in contact with the cam followers 213a and 213b.

In this modified example, the backward torque can be applied solely by the shape of the cam 215, and the backward torque is generated only when the cam 215 is in a specific phase. In this modified example, a recess is provided on the side surface of the cam 215 to form a thin-walled portion T2. However, if it is difficult to provide a recess, a weight member may be attached to the side surface of the cam 215 to form a thick-walled portion T1 and obtain an off-center cam.

As described above, in this embodiment, the means for applying torque in the backward direction is an off-center cam 215 whose center of gravity is offset from the center of rotation.

In this modified example, when motors 203a and 203b are de-energized, cams 215a and 215b move in a direction that releases the pressure on arm members 201a and 201b (cam followers 213a and 213b). Therefore, even if motors 203a and 203b cannot be driven while rollers R1 and R2 are pressing 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.

Figures 10 to 13 below illustrate application examples of a cam drive device according to an embodiment of the present invention.

Figure 10 is a schematic diagram showing a first application example, and will be described based on an embodiment applied to an electrophotographic printer as an image forming apparatus.

The printer 500 includes a tandem unit 1 in which image-forming units 100Y, 100M, 100C, and 100K for creating toner images of Y (yellow), M (magenta), C (cyan), and K (black) are arranged in parallel. The image-forming units 100Y to 100K support a photoreceptor module, a charging module, a developing module, and a cleaning module with a common unit frame, and these modules are detachable from the printer body as a single unit. The photoreceptor modules 20Y, 20M, 20C, and 20K each contain drum-shaped photoreceptors 21Y, 21M, 21C, and 21K. The charging modules 30Y, 30M, 30C, and 30K each contain a charging device. The developing modules 40Y, 40M, 40C, and 40K each contain a developing device that develops using a two-component developer containing toner and a magnetic carrier. The cleaning modules 50Y, 50M, 50C, and 50K are equipped with a cleaning device for cleaning the photoreceptors 21Y, 21M, 21C, and 21K.

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

Furthermore, below the tandem section 1 is a transfer unit 2 having an intermediate transfer belt 15. The intermediate transfer belt 15 is an endless belt composed of a single or multiple layers of vinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polyimide, polycarbonate, etc., and moves clockwise in the diagram while stretched across multiple rollers.

Below the transfer unit 2 is a secondary transfer device 4. The secondary transfer device 4 comprises a secondary transfer belt 17a, which is 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 contacts the portion of the intermediate transfer belt 15 that is wrapped around the secondary transfer opposing roller 16 from its front surface, 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 within the secondary transfer nip.

To the left of the secondary transfer device 4 in the diagram is a fixing unit 7 that fixes the toner image transferred onto the recording sheet. The fixing unit 7 has a heating roller with an internal heating element. A transport belt 6 is provided between the secondary transfer device 4 and the fixing unit 7 to transport the recording sheet after the toner image transfer toward the fixing unit 7. Furthermore, a paper feeding unit 3 is provided at the bottom of the printer 500 to feed the recording sheet to the secondary transfer device 4. To the left of the fixing unit 7 in the diagram is a paper discharge unit 8 that transports the recording sheet that has passed through the fixing unit 7 toward the outside of the machine or toward the duplex unit 5.

The intermediate transfer belt 15 has four primary transfer rollers for Y, M, C, and K inside its loop, and the intermediate transfer belt 15 is interposed between these primary transfer rollers and the photoreceptors 21Y to 21K. This causes the front surface of the intermediate transfer belt 15 to come into contact with the photoreceptors 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.

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, the charging devices of the charging modules 30Y-30K uniformly charge the surfaces of the rotating photoreceptors 21Y-21K in the tandem unit 1 to a predetermined charging potential. On the charged surfaces of the photoreceptors 21Y-21K, electrostatic latent images for Y, M, C, and K are formed by optical scanning using laser light emitted by the exposure unit 9 based on the image data. The electrostatic latent images are developed as toner images in the developing modules 40Y-40K, and then sequentially transferred onto the intermediate transfer belt 15, overlapping to form a four-color superimposed toner image. Any remaining toner after the toner image transfer is removed from the surface of the photoreceptors 21Y-21K by the cleaning devices of the cleaning modules 50Y-50K.

In parallel with the toner image formation, the paper feed unit 3 transports the recording sheet until it abuts against the registration roller pair 14. Once the recording sheet hits the registration roller pair 14, transport is temporarily stopped. Then, the registration roller pair 14 resumes rotation in sync with the timing when the toner image on the intermediate transfer belt 15 reaches the secondary transfer nip. As the rotation of the registration roller pair 14 resumes, the toner image is transferred to the recording sheet at the secondary transfer nip in synchronization with the toner image on the intermediate transfer belt 15.

After the toner image transfer, the recording sheet is moved into the fuser unit 7 by the transport belt 6. The fuser unit 7 applies heat and pressure to the toner image on the recording sheet, fixing it to the sheet. The recording sheet then moves to the paper output unit 8. The paper output unit 8's switching claw switches the recording sheet's path to either the output tray outside the machine (left side of the device) or the duplex unit 5 below. The duplex unit 5 inverts the recording sheet and re-feeds it to the secondary transfer nip. The re-feeded recording sheet undergoes a secondary toner image transfer to its reverse side at the secondary transfer nip, after which the paper output unit 8 discharges it onto the output tray.

Furthermore, after passing through the secondary transfer nip, the surface of the intermediate transfer belt 15 is cleaned by the intermediate transfer belt cleaning unit 90 to remove any remaining transfer toner. In a printer 500 with the above configuration, for example, a cam drive device 200 can be applied to the mechanism for contacting and separating the secondary transfer belt 17a from the secondary transfer opposing roller 16.

Figure 11 is an overall perspective view of the target unit in the first application example. The first application example shows an example where the secondary transfer device 4 is applied to the target unit 300 shown in Figure 2.

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

In this case, for example, some office printers are equipped with an interlock mechanism that disconnects the electrical connection to the motor when the printer cover is opened. If a printer has an interlock mechanism, opening the printer cover cuts off the motor's holding current. Therefore, by setting the holding torque T1, retraction torque T2, and detent torque T3 in the relationship T1 > T2 > T3, the secondary transfer nip can be reliably released.

Furthermore, in this application example, the cam drive unit 200 on which the secondary transfer device 4 is mounted is designed to be retractable from the printer 500 in the direction of arrow A. Therefore, if the device becomes unpowered during image formation and a recording sheet remains on the secondary transfer device 4, the recording sheet can be removed by releasing the secondary transfer nip and then pulling out the cam drive unit 200 and the secondary transfer device 4.

Figure 12 is a schematic diagram showing a second application example. This second application example shows the application of the registration roller pair 14 of the printer 500 shown in Figure 10.

The cam drive unit 200 is equipped with one of the rollers 14b that constitute the register roller pair 14. Arm members 201a and 201b rotatably support the roller 14b. When the cams 202a and 202b are in the solid line position, the arm members 201a and 201b are in their most retracted position, and therefore the roller 14b is also spaced apart from the roller 14a, as shown by the solid line. Note that the roller 14a is a roller fixed in a predetermined position on the printer 500 body. When the cams 202a and 202b are rotated clockwise and move to the dashed line position, the arm members 201a and 201b are in their most forward position, and the roller 14b presses against the roller 14a, as shown by the dashed line.

In this example as well, if the cam drive unit 200 is de-energized while the register roller pair 14 has formed a nip, a reversing torque acts on the cams 202a and 202b in the direction of releasing the nip, achieving the same effect as in the first application example. In this example as well, the cam drive unit 200 on which roller 14b is mounted may be made retractable from the printer 500 body to improve accessibility for maintenance work, etc.

Figure 13 is a schematic diagram showing a third application example, which will be explained based on an embodiment applied to an inkjet printer as an image forming apparatus.

The printer 400 is equipped with an inkjet head 401. The head 401 can utilize various methods, including a heating element, piezoelectric element, MEMS element, or electrostatic element. The paper feed cassette 402 stores the recording sheets S, and the paper feed roller 403 picks up the recording sheets S one by one and feeds them out of the paper feed cassette 402. Subsequently, a pair of sheet thickness detection rollers 404a and 404b acquire the thickness of a single recording sheet S.

The recording sheet S moves directly below the head 401 via a transport nip formed by the LF roller 405 and pinch roller 406. An encoder is mounted coaxially with the LF roller 405, allowing detection of the rotation amount of the LF roller 405 in terms of the feed distance of the recording sheet S. The platen 407 supports the recording sheet S from below. The first paper discharge roller 408, together with the first roller 409, grips and transports the recording sheet S as it passes under the head 401. The fuser 410 has a blower fan 411 that heats the recording sheet S, which carries the ink ejected by the head 401, by blowing warm air at a predetermined temperature onto the recording sheet S to dry the ink on the sheet S.

Furthermore, the fuser 410 is equipped with a temperature sensor (thermistor) to detect the hot air temperature. The second paper discharge roller 412, located downstream of the fuser 410, grips and transports the recording sheet S that has passed through the fuser 410, together with the second roller 413. The paper discharge platen 414, located opposite the fuser 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 in the fuser 410.

In the printer 400 with the above configuration, for example, if 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 unit 200 described above. Alternatively, if 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 unit 200. Alternatively, if 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 unit 200.

Furthermore, the cam drive unit 200 can be applied not only to the roller pair but also to the vertical movement of the head 401. When applied to the vertical movement of the head 401, vertical movement becomes possible by fixing the head 401 to the arm members 201a and 201b of the cam drive unit 200. This allows for a wider gap between the head 401 and the platen 407, making it easier to remove the recording sheet S remaining beneath the head 401.

The above is merely an example; the present invention provides specific effects in each of the following embodiments.

The first embodiment is characterized by comprising: a support member (e.g., arm members 201a, 201b) that supports a target member (e.g., the target unit 300 in Figure 2, the roller R1 in Figure 4, etc.); a cam member (e.g., cams 202a, 202b) that moves the support member; an electric motor (e.g., motors 203a, 203b) that rotationally drives the cam member and maintains the position of the cam member; and a retraction torque applying means (e.g., spiral springs 214a, 214b) that applies torque to the cam member in a direction that causes the target member to retract from an opposing member (e.g., the roller R2 in Figure 4, etc.) that faces the target member.

The second embodiment is characterized in that, in the first embodiment, the support member (e.g., arm members 201a, 201b) has a pivot axis (e.g., axes Xa, Xb), and the support member rotates around the pivot axis as a fulcrum in conjunction with the rotation of the cam member (e.g., cams 202a, 202b), allowing the target member (e.g., target unit 300 in Figure 2, roller R1 in Figure 4, etc.) to move forward and backward relative to the opposing member (e.g., roller R2 in Figure 4, etc.), and the cam member is positioned below the pivot axis.

The third embodiment is characterized in that, in the first or second embodiment, the relationship between the holding torque T1 generated by the electric motor (e.g., motors 203a, 203b) to maintain the orientation of the cam member (e.g., cams 202a, 202b), the backward torque T2 generated by the backward torque applying means (e.g., spiral springs 214a, 214b), and the detent torque T3 required to rotate the drive shaft of the electric motor in an unenergized state satisfies T1 > T2 > T3 on the rotation axis of the cam member (e.g., shaft 208).

The fourth embodiment is characterized in that, in any of the first to third embodiments, the retraction torque applying 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).

The fifth aspect is characterized in that, in the fourth aspect, the backward torque is the torque generated by the winding of the spiral spring.

The sixth embodiment is characterized in that, in the fifth embodiment, 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 members (e.g., cams 202a, 202b).

The seventh embodiment is characterized in that, in any of the first to third embodiments, the reversing torque applying means is an off-center cam (for example, cams 215a, 215b) formed by offsetting the center of gravity of the cam member from the center of rotation.

According to the first to seventh embodiments, when the electric motor is de-energized, the cam member moves in a direction that releases the pressure against the support member. Therefore, even if the electric motor cannot be driven while the target member and the opposing member are pressing 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.

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 support members (e.g., support pins 216a, 216b) that support the outer ends (e.g., outer ends P2) of the spiral springs (e.g., spiral springs 214a, 214b) so that these outer ends face the direction of rotation of the cam member (e.g., the direction indicated by the dashed arrow in Figure 7(b)).

The ninth embodiment is characterized in that, in the eighth embodiment, the support member (for example, support pins 216a, 216b) has slits (for example, slits Sa, Sb) into which the outer end (for example, outer end P2) is inserted, and the orientation of the slits is the same as the rotational direction of the cam member (for example, cams 202a, 202b) (for example, the direction indicated by the dashed arrow in Figure 7(b)).

According to the eighth and ninth embodiments, since the outer end of the spiral spring is always supported so that it faces the direction of rotation of the cam member, the deformation of the spring is less likely to concentrate in one area, thus preventing buckling and plastic deformation of the spring.

The tenth embodiment is characterized in that, in the fourth, fifth, sixth, eighth, or ninth embodiment, 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 buckling of the spiral spring.

According to the tenth embodiment, deviations in the orientation of the spiral spring due to part precision can be further suppressed.

200 Cam drive unit 201a, 201b Arm member 202a, 202b Cam 203a, 203b Motor 214a, 214b Spiral spring 300 Target unit

Claims (11)

A support member that supports the target member,
A cam member that moves 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 ,
A cam drive device characterized in that the relationship between the holding torque T1 generated by the electric motor to maintain the posture of the cam member, the backward torque T2 generated by the backward torque applying means, and the detent torque T3 required to rotate the drive shaft of the electric motor when it is not energized satisfies T1 > T2 > T3 on the rotation axis of the cam member . The cam drive device according to claim 1, characterized in that the support member has a pivot axis, and the support member rotates around the pivot axis as a fulcrum in conjunction with the rotation of the cam member, allowing the target member to move forward and backward relative to the opposing member, and the cam member is positioned below the pivot axis. The cam drive device according to claim 1 or 2, characterized in that the means for applying torque in the backward direction is a spiral spring provided between the cam member and the rotating shaft . The cam drive device according to claim 3 , characterized in that the backward torque is a torque generated by winding the spiral spring . The cam drive device according to 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 . The cam drive device according to claim 1 or 2 , characterized in that the means for applying torque in the backward direction is an off-center cam formed by shifting the center of gravity of the cam member away from the center of rotation . The cam drive device according to 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 of the spiral spring faces the rotational direction of the cam member. The cam drive device according to claim 7 , characterized in that the support member has a slit into which the outer end is inserted, and the orientation of the slit is the same as the rotation direction of the cam member. The cam drive device according to claim 3, 4, 5, 7, or 8 , characterized in that the cam member is in contact with a part of the spiral spring and includes a buckling prevention member that prevents buckling of the spiral spring. A transfer apparatus characterized by comprising a cam drive device according to any one of claims 1 to 9 . An image forming apparatus characterized by comprising a cam drive device according to any one of claims 1 to 9, or a transfer device according to claim 10 .