JPH09325620A - Transfer unit and image forming apparatus including the same - Google Patents

Abstract

(57) Abstract: An image unevenness caused by abrasion of a photosensitive drum due to constant driving of a transfer roller in contact with the photosensitive drum, a shortened life of the photosensitive drum, and a driven rotation of the transfer roller. It is possible to prevent the toner image from shrinking due to the insufficient conveyance power of the transfer material. SOLUTION: The driving force from a driving source 20 is applied to a step gear 16,1.
It is transmitted to the photosensitive drum 15 which is integral therewith via 7. The transfer roller 4 is brought into contact with the photosensitive drum 15 to form a transfer nip portion for nipping and transferring the transfer material, and the gear 21 is attached to the shaft 4a of the transfer roller 4. Shaft 4a and gear 2
An electromagnetic clutch 22 is arranged between the electromagnetic clutch 22 and the first clutch. When the energization of the electromagnetic clutch 22 is turned on, the driving force on the photosensitive drum 15 side is transmitted to the transfer roller 4 via the gear 21, and the transfer roller 4 is actively driven. On the other hand, the electromagnetic clutch 22
When is turned off, the driving force on the photosensitive drum 15 side is not transmitted to the transfer roller, and the transfer roller 4 is driven to rotate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer unit using an electrostatic transfer process, which is mounted on a copying machine, a laser beam printer or the like, and an image forming apparatus having the transfer unit.

[0002]

2. Description of the Related Art A conventional transfer device and its drive mechanism will be described with reference to the perspective view of FIG. 9A and the front view of FIG.

In these figures, reference numeral 15 is a photosensitive drum having a photosensitive layer formed on the outer peripheral surface of a conductive base, and is rotatably supported. The photosensitive drum 15 has stepped gears 16 and 17 fixed to the ends thereof, and the gear 19 fixed to the output shaft of the drive source 20 rotates in the direction of arrow R19, so that the stepped gears 16 and 17 cause the arrow to pass. It is driven to rotate in the R16 direction.

The transfer roller 4 disposed below the photosensitive drum 15 has its shaft 4a rotatably supported at both ends by bearings 61, and the bearing 61 is supported by a compression spring 60 on a guide member 62. By being urged upward along the surface, the surface of the photosensitive drum 15 is brought into contact with the surface of the photosensitive drum 15 with a predetermined contact pressure to form a transfer nip portion. A gear 18 is fixed to the end of the shaft 4a of the transfer roller 4, and meshes with a step gear 17 that is integral with the above-described photosensitive drum 15.
The transfer roller 4 is rotated by a drive source 20 in synchronization with the photosensitive drum 15 via a gear 19, step gears 16 and 17, and a gear 18. That is, the transfer material with the paper contacts the surface of the photosensitive drum 15 when passing through the transfer nip portion.
And the transfer roller 4 that comes into contact with the back surface of the transfer roller 4 applies a conveying force.

The toner image formed on the surface of the photosensitive drum 15 by a developing device (not shown) is transferred by applying a transfer bias having a polarity opposite to that of the toner image to the transfer roller 4 when passing through the transfer nip portion. Transferred to the surface of the material.

[0006]

However, in the transfer roller 4 described above, the rotational drive is such that the stepped gear 17 integrated with the photosensitive drum 15 and the gear 18 integrated with the transfer roller 4 always mesh with each other. As a result, it has the following drawbacks. The transfer roller 4 vibrates at the meshing frequency of the stepped gear 17 and the gear 18, and the impulse of the vibration pitch causes the photosensitive layer of the photosensitive drum 15 to be scraped due to its durability.
Since the photosensitive drum 15 and the step gear 17 are integrated, if the photosensitive drum 15 has uneven rotation, the same place on the surface of the photosensitive drum is always scraped, and this scraping appears on the photosensitive drum with a pitch. Will turn into. As a result, image unevenness occurs at the manifested scraping pitch, and the life of the photosensitive drum 15 is shortened.

As a countermeasure against the above-mentioned drawbacks, a method may be considered in which the transfer roller 4 is driven to rotate with respect to the photosensitive drum 15 so that the photosensitive drum is not scraped and the image unevenness is not generated. However, according to this, a sufficient conveying force of the transfer material at the transfer nip portion cannot be obtained. For this reason, the transfer material is transported by the photosensitive drum 1 only.
5 and the transfer roller 4, that is, for example, when the length of the transfer material in the transport direction is short, the upstream side or the downstream side of the transfer nip portion (the upstream side or the downstream side in the transfer material transport direction). The same applies to the following.) The transfer force is not applied by other transfer means such as a transfer roller (registration roller) and a fixing device, and the transfer material must be temporarily sandwiched and transferred only by the transfer nip portion. If this is not the case, conveyance failure may occur, causing slippage between the surface of the photosensitive drum 15 having the toner image and the surface of the transfer material, and the toner image after transfer onto the transfer material may be partially shrunk. It was

As a method of improving the conveying force at the transfer nip when the transfer roller is driven to rotate, it is conceivable to increase the spring pressure of the compression spring 60, but when the transfer conditions are delicate, This is not a good idea because there is no freedom in setting the spring pressure, which may make it impossible to achieve.

Therefore, according to the present invention, image unevenness due to abrasion of the image carrier (above, the photosensitive drum) due to constant driving of the transfer member (above, the transfer roller) and shortening of the life of the photosensitive drum, and An object of the present invention is to provide a transfer device capable of improving shrinkage of a toner image due to insufficient transfer material conveyance force due to driven transfer member rotation, and an image forming apparatus including the transfer device.

[0010]

According to a first aspect of the present invention (transfer means), a transfer nip portion is formed by contacting an image carrier that is rotationally driven, and a transfer material is nipped by the transfer nip portion. In the transfer means provided with the transfer member to be conveyed,
It is interposed between the image carrier and the transfer member to form a transmission path of a driving force between the image carrier and the transfer member, and the transmission path is cut off to connect the image carrier to the transfer member. It is characterized in that it is provided with a connection / disconnection means capable of selecting the presence / absence of the driving force transmitted to the transfer member.

In the present invention (transfer means) according to claim 2, the connection / disconnection means disconnects the transmission path in accordance with the magnitude of the conveying force with respect to the transfer material nipped and conveyed in the transfer nip portion. It is characterized by

In the present invention (transfer means) according to claim 3, the connection / disconnection means transmits the transfer material when the length of the transfer material sandwiched and transferred in the transfer nip portion in the transfer direction is equal to or shorter than a predetermined length. It is characterized in that the paths are joined and the transmission path is cut off when the paths exceed a predetermined length.

The present invention according to claim 4 (transfer means) is characterized in that the connection / disconnection mechanism is an electromagnetic clutch for connecting / disconnecting the driving force by turning ON / OFF of energization.

According to a fifth aspect of the present invention (transfer means), which has a first gear that rotates integrally with the transfer member and transmits a driving force from the image carrier, the electromagnetic clutch is provided. And being interposed between the transfer member and the first gear. The present invention according to claim 6 (transfer means) has a second gear that rotates integrally with the transfer member, and the electromagnetic clutch and the third gear that meshes with the second gear and the image. It is characterized in that it is interposed between the carrier and the carrier.

According to a seventh aspect of the present invention (transfer means), the connection / disconnection mechanism has a fourth gear which rotates integrally with the transfer member, and a fifth gear which rotates integrally with the image carrier. An engaging / disengaging mechanism for engaging / disengaging the fourth gear with respect to the gear.

The present invention according to claim 8 (image forming apparatus)
Is an image carrier, a toner image forming means for forming a toner image on the image carrier, the above-mentioned transfer means for transferring the toner image onto a transfer material, and the toner image after transfer is fixed on the transfer material. And a fixing unit that allows the fixing unit.

[Operation] The main operation (operation according to claim 1) based on the above configuration is as follows.

The cutting means is interposed between the image carrier and the transfer member to form a transmission path of the driving force and can selectively cut the transmission path. Therefore, when the transmission path is connected. In addition, the driving force is transmitted from the image carrier to the transfer member, and the conveying force can be applied to the transfer material passing through the transfer nip portion by both the image carrier and the transfer member. On the other hand, when the transmission path is cut off, the driving force is not transmitted from the image carrier to the transfer member, so that the transfer force is applied only from the image carrier to the transfer material passing through the transfer nip portion. It

[0019]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1A is a perspective view of a transfer device according to the present invention, an image carrier, and a drive mechanism for driving them. These are used by being incorporated in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer. The image forming apparatus will be described later with reference to FIG.

A drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 15 is used as the image bearing member.
The photosensitive drum 15 is a cylindrical conductive drum base 15b.
(See FIG. 8B) and a photosensitive layer 15a such as OPC (organic optical semiconductor) formed on the surface (outer peripheral surface) of the photosensitive layer 15a. The photosensitive layer 15a is rotatable by an image forming apparatus main body (not shown). It is supported.

At one end of the photosensitive drum 15, stepped gears 16 and 17 composed of a large-diameter gear and a small-diameter gear are integrally fixed. A gear 19 fixed to an output shaft 20a of a motor (driving source) 20 meshes with the large-diameter step gear 16. The photosensitive drum 15 is rotationally driven in the direction of arrow R16 via the step gears 16 and 17 as the gear 19 is rotated in the direction of arrow R19 by the rotation of the motor 20.

Below the photosensitive drum 15, a transfer roller (transfer member) 4 which constitutes a transfer device together with a transfer power source (not shown) is provided. The transfer roller 4 is arranged in parallel with the photosensitive drum 15 and has shafts 4a and 4a (however, only one is shown in the figure) protruding from both ends in the axial direction. Each shaft 4a is rotatably supported by a plate-shaped bearing 4b, and this bearing 4b is supported by a guide member 62 so as to be substantially vertically movable.
The bearing 4b is attached to the upper photosensitive drum 1 by the compression spring 60.
The transfer roller 4 is urged toward
The surface is in contact with the surface of the photosensitive drum 15 with an appropriate pressing force, and a belt-shaped transfer nip portion along the axial direction is formed between them. An electromagnetic clutch (disengagement mechanism) 22 is mounted on a portion of the shaft 4a outside the bearing 4b, and a gear (first gear) 21 is further mounted via the electromagnetic clutch 22. This gear 21
Is meshed with a small-diameter step gear 17 that is integral with the photosensitive drum 15 described above. The electromagnetic clutch 22 is the photosensitive drum 15
It is possible to configure a part of the driving force transmission path from the transfer roller 4 to the transfer roller 4 and connect or disconnect the driving force to select whether or not the driving force is transmitted. The rotation of the step gear 17 causes the electromagnetic clutch 22 to turn O.
When it is N, it is transmitted to the transfer roller 4 via the gear 21 and the electromagnetic clutch 22, while when it is OFF, it is transmitted to the gear 21, but the transfer roller 4 is transmitted. Not transmitted to 4. That is, when the electromagnetic clutch 22 is turned on, the driving force of the drive source 20 is transmitted to the photosensitive drum 15 via the gear 19, the step gears 16 and 17, while the step gear 17, the gear 21, the electromagnetic clutch. It is also transmitted to the transfer roller 4 via 22.
That is, the transfer roller 4 is actively driven and rotated in the direction of arrow R21. On the other hand, when the electromagnetic clutch 22 is turned off, the driving force of the driving source 20 is transmitted to the photosensitive drum 15 in the same manner as described above, but is not transmitted to the transfer roller 4. That is, the transfer roller 4 is driven to rotate by the photosensitive drum 15. If you want to give a large conveying force to the transfer material that passes through the transfer nip,
The electromagnetic clutch 22 is turned on to positively drive the transfer roller 4 to rotate. On the other hand, when a large conveying force is not particularly required, the electromagnetic clutch 22 is turned off and the transfer roller 4 is driven to rotate.

FIGS. 4A, 4B and 4C are vertical sectional views showing a part of an image forming apparatus equipped with the above-mentioned transfer device. The operation of the electromagnetic clutch 22 will be described with reference to FIG. A toner image is formed on the surface of the photosensitive drum 15 of FIG. 8 as described later with reference to FIG. 8A, and the toner image is transferred onto a transfer material P such as paper by the transfer roller 4. Shall be done.

In FIG. 4A, 2 is a paper feed cassette for accommodating the transfer material P, and 3b is the transfer material P in the paper feed cassette 2.
Is a paper feed roller for feeding. Then, the paper feed roller 3b
A registration roller that corrects the skew of the transfer material P and supplies the transfer material P to the photosensitive drum 15 at a predetermined timing in order from the upstream side to the downstream side of the transfer material P that is fed by the transfer roller. 3e, a transfer roller 4 for transferring the toner image on the photosensitive drum 15 to the transfer material P, a fixing device 5 for fixing the toner image on the transfer material P by heating and pressurizing the transfer material P after the toner image transfer, and toner image fixing Discharge rollers 7 and the like for discharging the subsequent transfer material P onto the discharge tray 6 are provided. Further, on the slightly upstream side of the registration roller 3, there is provided a first sensor S1 having a sensor lever 46 that rotates by the passage of the transfer material P and a detection unit 47 that is turned on by the rotation. Further, a second sensor S2 having a sensor lever 48 and a detecting portion 49 having the same structure as the first sensor S1 is arranged slightly downstream of the fixing device 5.

Next, an example of control of the electromagnetic clutch 22 will be described with reference to FIG.

The output signal of the detection section 47 of the first sensor S1 described above is input to the comparison circuit 43 to which the reference signal from the reference signal generation source 51 is applied. When it is determined that the transfer material P has passed through the first sensor S1 based on the signal from the detection unit 47, in response thereto, the electromagnetic clutch drive circuit 4
4 to the electromagnetic clutch 22 to energize the gear 21 (see FIG.
The rotational driving force received by (a)) is transmitted to the transfer roller 4, and the transfer roller 4 is rotationally driven by this force.

Next, the operation of this embodiment will be described with reference to FIGS. 2 (a) to 2 (c).

FIG. 2A shows a state before the start of copying (image formation). At this time, the electromagnetic clutch 22 is turned off.
It remains. 2B, when copying is started, the transfer material P is fed from the paper feed cassette 2 and passes through the registration roller 3e, and the toner image on the photosensitive drum 15 is transferred onto the transfer material P by the transfer roller 4. The state of being transferred is shown. By rotating the sensor lever 46 in the direction of the arrow in the figure, it is detected that the transfer material P is passing through the first sensor S1. At this time, the electromagnetic clutch 22 also remains OFF, and the transfer roller 4 is driven to rotate with respect to the photosensitive drum 15. FIG. 3C illustrates a state immediately after the trailing edge of the transfer material P has finished passing through the first sensor S1.
The sensor lever 46 rotates in the direction of the arrow and returns to the original position, whereby the transfer material P is completely transferred to the first sensor S1.
Passage is detected. At this time, the electromagnetic clutch 22 is turned on, the driving force is transmitted from the gear 21 to the transfer roller 4, and the transfer material P passing through the transfer nip portion is transferred by the photosensitive drum 15 from the front surface side and from the back surface side. Conveyance force is applied to each of the rollers 4.

Further, in the timing when the electromagnetic clutch 22 is turned off and the transfer roller 4 is driven to rotate again, the timing when the transfer material P is conveyed to the fixing device 5 is determined by the second sensor S.
2, the electromagnetic clutch is turned off. Alternatively, the transfer material P is the sensor lever 4 of the first sensor S1.
The time from passing through 6 to passing through the transfer roller 4 is stored as a specific time, and after the specific time has elapsed,
Transfer roller 4 by turning off electromagnetic clutch 22
Return to driven rotation. Of course, a sensor may be separately provided on the downstream side (immediately after) of the transfer roller 4, the passage of the transfer material P is detected, and the electromagnetic clutch 22 is turned off based on the output thereof.

Here, when the length of the transfer material P to be image-formed (transfer material P to be copied) in the transport direction is longer than L _{2 in} FIG. 2A, that is, the first sensor S1 and the first sensor S1 2 is longer than the distance from the sensor S2, the transfer material P
Before the trailing edge of the trailing edge passes through the registration roller 3e, the leading edge reaches the fixing device 5, and the transfer material P always receives the conveying force by the registration roller 3e or the fixing device 5. It may be driven to rotate.

Further, in the present embodiment, the transfer material P
Is required to drive the transfer roller 4 via the gear 21 when the transfer roller 4 needs a transfer force, and is otherwise driven, and the electromagnetic clutch 22 is turned on / off at the timing. Needless to say, it may be appropriately set according to the transfer material transport conditions of the transport system in the image forming apparatus.

In the above description, the example in which the electromagnetic clutch 22 is provided on the transfer roller 4 side as shown in FIG. 1A has been described. However, as shown in FIG. Even if the mechanism) 63 is provided on the photosensitive drum 15 side, substantially the same effect can be obtained. In this case, the step gear 16 and the step gear 17A are separately configured, and one step gear 1
6 is fixed to the photosensitive drum 15, whereas the transfer roller 4
The other step gear 17A meshing with the gear (second gear) 21A integrated with the electromagnetic clutch 63
To be attached via. As a result, the drive source 2
The driving force from 0 is always transmitted to the photosensitive drum 15 via the gear 19, the step gear 16 and the like, whereas
When the electromagnetic clutch 63 is ON, it is transmitted to the transfer roller 4 via the step gear 17A and the gear 21A, while when the electromagnetic clutch 63 is OFF, it is not transmitted.

As described above, when the electromagnetic clutch 63 is provided on the photosensitive drum 15 side, the photosensitive drum 15 is rotatably supported by the image forming apparatus main body (not shown), but is immovable as a whole. Since it is supported, it is advantageous when it is provided on the side of the transfer roller 4 which is movably supported. That is, when it is provided on the transfer roller 4 side, the electromagnetic clutch 22 needs to be biased together with the transfer roller 4 by the compression spring 60, and the biasing force by the compression spring 60 must be increased accordingly. <Second Embodiment> The second embodiment will be described with reference to FIG.
This will be described with reference to the front views of (a) and (b).

In this embodiment, instead of mounting the above-mentioned electromagnetic clutches 22 and 63 as the connecting / disconnecting mechanism, a transfer roller is provided to a step gear (fifth gear) 17B integrated with the photosensitive drum 15. The driving force is transmitted or not to the transfer roller 4 by engaging or disengaging the fourth side gear (fourth gear) 26. Whether or not the driving force is transmitted is realized by moving the gear 26 by an engagement / disengagement mechanism. The engagement / disengagement mechanism includes a lever 27, a solenoid 29, and a compression spring 3 described later.
0, the stopper member 24 and the like.

In FIG. 4, a shaft 25, which is integral with the transfer roller 4, projects from the end of the transfer roller 4.
A key groove 25 a is formed in 5. Gear 26 is shaft 2
5 is fitted in the key groove 25a, and when the gear 26 is rotated, the transfer roller 4 is also rotated. The gear 26 is movable in the thrust direction of the shaft 25, and the movement range is set by the stopper members 23 and 24 and the compression spring 30. Further, the gear 26 is provided with a groove 26a. The tip of the lever 27 is engaged with the groove 26a. A connecting rod 29b connected to a plunger 29a of a solenoid 29 is connected to a base end portion of the lever 27, and an intermediate portion is guided by a guide member 28.

The gear 26 is the ON / OF of the solenoid 29.
By moving the lever 27 in the direction of arrow A corresponding to the shortening and extension of the plunger 29a based on F, the step gear 17B
Is disengaged and meshes again. That is, when the solenoid 29 is turned on, the gear 26 has a lever 27 as shown in FIG.
Is moved in the direction of the arrow A ₁ by the movement of
The meshing with the side gear 17B is released. At this time, if the photosensitive drum 15 is rotating, the transfer roller 4 is driven to rotate accordingly. On the other hand, when the solenoid 29 is off, the gear 26 is moved in the arrow A ₂ direction by the bias of the compression spring 30 and meshes with the step gear 17B as shown in FIG. 5B. At this time, when the photosensitive drum 15 is rotating, the transfer roller 4 is rotationally driven via the gear 26.

In the second embodiment, the solenoid 29 is turned on / off, that is, the transfer roller 4 is driven / driven.
The drive switching timing may be set in the same manner as in the first embodiment.

In this embodiment, unlike the case where the electromagnetic clutches 22 and 63 are used in the first embodiment, the meshing of the gear 26 on the transfer roller 4 side with the step gear 17B on the photosensitive drum 15 side and its engagement. Cancellation is completed. Further, since these operations are performed by the solenoid 29, cost reduction can be achieved. <Third Embodiment> A third embodiment will be described with reference to the perspective view of FIG.
Will be explained.

Reference numeral 31 in the figure is a paper feed cassette, and inside the paper feed cassette 31, side regulating plates 32 and 33 and a rear end regulating plate 37 are movably arranged. The side regulation plate 33 has a transfer material size detection lever 39, and the rear edge regulation plate 37 has a similar transfer material size detection lever 37.
By detecting the levers 39 and 37 with a sensor 40 having a light projecting section 40a and a light receiving section, and a sensor 41 having a light projecting section 41a and a light receiving section 41b.
It is configured to detect the width and length of the transfer material P (length in the transport direction).

Next, the above-mentioned FIGS. 2 (a), 2 (b) and 2 (c).
The operation of the third embodiment will be described with reference to FIG.

The distance L ₁ shown in FIG. 2 (a), i.e. a registration roller 3e and than the distance L ₁ between the fixing device 5, a long length in the conveying direction L _P of the transfer material P to passed (L _P > L
₁ ) is detected by the sensor 41, the electromagnetic clutch 22 or the electromagnetic clutch 63 is turned off in the first embodiment, and the solenoid 29 is turned on in the second embodiment to detect the photosensitive drum 15. The driving force transmitted from the side to the transfer roller 4 side is cut off, and the transfer roller 4 is driven to rotate. On the other hand, when it is detected that L _P <L ₁ , the transfer roller 4 is controlled to be always rotated by gear drive.

That is, for the transfer material P which may not be temporarily provided with the conveying force from the registration roller 3e or the fixing device 5, the transfer roller 4 is provided with a driving force to the transfer material P. Conveyance force is also applied from the transfer roller 4 as appropriate. On the other hand, the transfer roller 4 is always driven to rotate with respect to the transfer material P to which the conveying force is applied from at least one of the registration roller 3e and the fixing device 5.

Here, in the transfer material P with L _P <L ₁ ,
The gear driving of the transfer roller 4 is started from the moment when the transfer material P is conveyed to the registration roller 3e (slightly before the transfer material P rushes into the transfer roller), and immediately after leaving the transfer roller 4, the driven material is returned to the driven state. In other words, only in the transfer state, always
It may be controlled to drive gears.

In this embodiment, the shock of drive switching at the time of transfer is not transmitted to the paper as compared with the above-described first and second embodiments. In addition, a detection error due to a malfunction (rotational defect) of the sensor lever is unlikely to occur. <Fourth Embodiment> A fourth embodiment will be described with reference to FIGS.

In the present embodiment, the sensors 40 and 41 used in the third embodiment, the solenoid 29, and their driver circuits are eliminated, and the photosensitive material 15 side is controlled by the position of the transfer material trailing edge regulating plate 64 of the paper feed cassette 31. The gear 26 on the transfer roller 4 side can be engaged with and disengaged from the stepped gear 17B to reduce the cost.

The structure of the transfer roller 4 and the gear 26 is shown in FIG.
As shown in (a), this is the same as the second embodiment (FIG. 4 (a)). The lever 65 is rotatable around a support shaft 66, and the tip end side is engaged with the groove portion 26 a of the gear 26. As shown in FIG. 7B, the rear end regulation plate 64 has an end portion 64a movable in the direction of arrow C, and when the distance L ₁ and the length L _P are L _P <L ₁ , The end 64a is the lever 6
When it hits the base end of No. 5, the lever 65 is swung, and the gear 26 is thrustly moved to the transfer roller 4 side (the direction in which the mesh with the step gear 17B is released).

Next, the operation will be described with reference to FIGS. 7 (c) and 7 (d).

FIG. 7C shows the case where L _P > L _{1 and} the gear 26 is disengaged from the step gear 17B as described above. On the other hand, FIG. 7D shows that L _P <
In the case of L ₁ , the gear 26 is moved by an arrow A ₃ by the compression spring 30.
A state in which the gear 26 is biased in the direction and the gear 26 is meshed with the step gear 17B is shown.

That is, in accordance with attachment / detachment of the paper feed cassette 31 to / from the image forming apparatus main body, at that time, the paper feed cassette 3
Depending on the size of the transfer material P set in No. 1, the gear 26 can be engaged with and disengaged from the step gear 17B.

In a paper feed tray or the like in which the transfer material regulating plate can be manually operated without attaching or detaching the paper feeding cassette 31, the gear 26 is disengaged by interlocking with the movement of the transfer material regulating plate. It can also be configured to do so. <Fifth Embodiment> FIG. 8A is a vertical cross-sectional view showing a schematic configuration of an example of an image forming apparatus A to which any of the transfer devices of the first to fourth embodiments described above can be mounted. Is. It should be noted that FIG. 1 shows a copying machine in which the process cartridge B is detachably mounted on the image forming apparatus main body 12, and the description of the above description will be omitted below.

The optical system 1 is disposed above the image forming apparatus main body 12. The optical system 1 is an image forming apparatus main body 1
2, a platen glass 1a arranged on the upper surface of the plate 2, a light source 1b for irradiating the image surface of a document placed downward on the platen glass 1a with light, a plurality of mirrors 1c for guiding the reflected light from the image surface to the photosensitive drum 15, The lens 1d and the like are provided.

The process cartridge B develops a toner image by attaching toner to the above-described photosensitive drum 15, the charger 8 for uniformly charging the surface of the photosensitive drum 15, and the electrostatic latent image formed by the exposure of the gloss system 1. And a cleaning device 10 for removing the transfer residual toner remaining on the surface of the photosensitive drum 15 after the toner image is transferred onto the transfer material P. The process cartridge B is attached to the guide 14 of the image forming apparatus main body 12 by sliding it so as to push it from the front side to the back side in FIG. 8A, and conversely pulling it out from the back side to the front side. Slide out and take out.

Below the main body 12 of the image forming apparatus, a feeding / conveying section 3 for the transfer material P is arranged. The transfer material P stored in the paper feed cassette 2 is fed by the paper feed roller 3b and conveyed by the conveyance rollers 3c, 3d, 3d to the registration roller 3e, where skew is corrected and then the photosensitive drum The toner image on the toner image 15 is supplied to the photosensitive drum 15 so that the toner image is transferred by the transfer roller 4. The transfer material P after the toner image transfer is
It is conveyed to the fixing device 5 by the conveyor belt 3f. The fixing device 5 heats and pressurizes the transfer material P carrying an unfixed toner image between the fixing belt 5a and the pressure roller 5b while fixing and fixing the toner image. The transfer material P after fixing the toner image is discharged onto the discharge tray 6 by the discharge roller 3g, and the image formation is completed.

The transfer device according to the present invention is, as described above,
According to the length L _P of the transfer material P as the transfer destination of the toner image in the transport direction, the transfer roller 4 at the time of transfer is positively driven to rotate or passively driven to rotate. .

The transfer apparatus according to the present invention is not limited to the image forming apparatus A having the above-described configuration, but may be applied to any other image forming apparatus such as a laser beam printer or a facsimile including a transfer process. It can be installed.

[0056]

As described above, according to the present invention,
Since it is possible to select the presence or absence of the driving force transmitted from the image carrier to the transfer member, for example, a large conveying force is applied to the transfer material passing through the transfer nip portion between the image carrier and the transfer member. When it is desired to impart the driving force to the transfer member, the driving force is positively driven. On the other hand, when a large conveying force is unnecessary, the driving force is not transmitted to the transfer member and the driven member can be rotated. it can. As a result, image unevenness caused by the abrasion of the image carrier (the “photosensitive drum” in the above) and the shortening of the life of the image carrier due to the continuous driving of the transfer member (the “transfer roller” in the above), and the transfer member It is possible to improve the shrinkage of the toner image due to the insufficient conveyance force of the transfer material due to the driven rotation.

[Brief description of drawings]

FIG. 1A is a perspective view showing a driving portion of a transfer device according to a first embodiment. FIG. 6B is a perspective view showing a driving portion of another transfer device according to the first embodiment.

2A, 2B, and 2C are diagrams showing switching timings of gear driving and driven rotation of the transfer roller according to the first embodiment.

FIG. 3 is a block diagram showing control of an electromagnetic clutch.

FIG. 4 is a perspective view showing a driving portion of the transfer device according to the second embodiment.

5A and 5B are diagrams showing a manner in which a driving force transmitted from a photosensitive drum to a transfer roller is cut off in the second embodiment.

FIG. 6 is a perspective view showing a configuration for detecting the size of a transfer material according to the third embodiment.

FIG. 7A is a perspective view showing a driving portion of the transfer device according to the fourth embodiment. FIG. 6B is a perspective view showing the operation of the trailing edge regulating plate for engaging and disengaging the gear that rotates integrally with the transfer roller with the gear on the photosensitive drum side. FIG. 6C is a diagram illustrating a state where the gear on the transfer roller side is disengaged from the gear on the photosensitive drum side by the trailing edge regulation plate. FIG. 6D is a diagram showing a state in which the gear on the transfer roller side is engaged with the gear on the photosensitive drum side.

FIG. 8A is a vertical cross-sectional view showing a schematic configuration of an image forming apparatus including a transfer device according to the present invention. FIG. 3B is a vertical sectional view showing the configuration of the photosensitive drum.

FIG. 9A is a perspective view showing a driving portion of a conventional transfer device. FIG. 6B is a front view showing a driving portion of a conventional transfer device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical system 2 Paper feed cassette 3 Feeding / conveying section 3e Registration roller 4 Transfer member (transfer roller) 5 Fixing device 8 Charging device 9 Developing device 10 Cleaning device 12 Image forming apparatus main body 15 Image carrier (photosensitive drum) 16 Step gear 17 Step gear 17A Third gear (step gear) 17B Fifth gear (step gear) 20 Drive source 21 First gear (gear) 21A Second gear (gear) 22, 63 Contact / separation means (electromagnetic clutch) 26 Fourth gear (gear) 27 Engagement mechanism (lever) 29 Engagement mechanism (solenoid) 30 Engagement mechanism (compression spring) L ₁ Distance from registration roller to fixing device L ₂ First sensor to second sensor Distance to P Transfer material S1 First sensor S2 Second sensor

Claims (8)

[Claims] 1. A transfer means comprising a transfer member that abuts on a rotationally driven image carrier to constitute a transfer nip portion, and that nips and conveys a transfer material at the transfer nip portion. It is interposed between the image carrier and the transfer member to form a drive force transmission path between the image carrier and the transfer member, and the transmission path is cut off and transmitted from the image carrier to the transfer member. A transfer means comprising a disconnecting means capable of selecting the presence or absence of a driving force. 2. The transfer device according to claim 1, wherein the connecting / disconnecting device connects / disconnects the transmission path according to a magnitude of a conveying force with respect to a transfer material nipped and conveyed in the transfer nip portion. means. 3. The connecting / disconnecting means joins the transmission paths and exceeds a predetermined length when the length of the transfer material nipped and conveyed in the transfer nip portion in the conveyance direction is equal to or less than a predetermined length. In some cases, the transfer path is cut off, The transfer means according to claim 1 or 2. 4. The connection / disconnection mechanism is an electromagnetic clutch that connects / disconnects the driving force by turning ON / OFF of energization.
The transfer means according to the item. 5. A first gear that rotates integrally with the transfer member and that transmits a driving force from the image carrier, wherein the electromagnetic clutch includes a transfer member and a first gear. The transfer means according to claim 4, wherein the transfer means is interposed between the transfer means. 6. A second gear that rotates integrally with the transfer member, wherein the electromagnetic clutch is interposed between a third gear that meshes with the second gear and the image carrier. The transfer means according to claim 4, wherein: 7. The disconnecting mechanism engages the fourth gear with a fourth gear that rotates integrally with the transfer member and a fifth gear that rotates integrally with the image carrier. An engaging / disengaging mechanism for disengagement is provided, and any one of claims 1 to 3 is provided.
The transfer means according to the item. 8. An image carrier, a toner image forming means for forming a toner image on the image carrier, and a transfer means for transferring the toner image onto a transfer material. An image forming apparatus comprising: a fixing unit configured to fix the transferred toner image on the transfer material.