JPH08146826A - Electrophotographic device - Google Patents

Abstract

PURPOSE: To detect a failure in the rotation of a developing system without providing a monitoring mechanism and to enable quick stopping control by transmitting power to the power transmission mechanism of a recording sheet carrying mechanism with a transmission mechanism for transmitting driving force to a driving roller system. CONSTITUTION: The rotation of a motor 1 is transmitted to a drum output gear 2, a developing output gear 3, a resist output gear 4, a fixing output gear 5 and a paper feeding output gear 6 and for the developing output gear 3 and the resist output gear 4, a developing clutch 7 is provided on the upstream side of the transmission of the output gears 3 and 4 and constituted so that the rotational force of the motor 1 is transmitted to the respective output gears 3 and 4 with the developing clutch 7. Then, a resist clutch 8 is on the downstream side of the transmission of the developing clutch 7, when viewing from a rotational force transmission system and constituted so that even if the developing clutch 7 is in the transmission state of the rotational force, the transmission of the rotational force of the motor 1 to a resist roller can be stopped by the clutch 8. Thus, the failure in the rotation of the developing system can be detected without providing a special monitoring mechanism, to execute the quick stopping control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus having an improved roller drive system.

[0002]

2. Description of the Related Art The electrophotographic system is a recording system in which an image to be recorded is formed as an electrostatic latent image, and the electrostatic latent image is developed with toner to form a visible image. For example, as shown in FIG. By optically forming an image on the charged photosensitive drum 41 by the exposure device 40 or by drawing with an optical beam,
An electrostatic latent image is formed on the photosensitive drum 41, and the electrostatic latent image is visualized (developed) by adhering charged toner using a developing device 42, which is used as a recording medium. A method of obtaining a hard copy by transferring this recording sheet to a recording sheet 43 and then fixing the toner by heating and fusing the toner is widely used in a printer, a copying machine, a print output unit of a facsimile machine, or the like. Has been done.

By the way, in the electrophotographic apparatus having the above-mentioned structure used for a facsimile machine or the like, in order to develop the electrostatic latent image on the photosensitive drum 41, the developing roller 4 is used as a developing machine.
2a is disposed in the vicinity of the downstream of the drawing position of the photosensitive drum 41, is rotated in synchronization with the photosensitive drum 41, and the toner is adhered to the peripheral surface of the developing roller 42a so that the toner acts on the photosensitive drum 41. Apply to the latent image. Further, in synchronization with the rotation of the photosensitive drum 41, a recording sheet 43, which is a sheet-shaped recording medium such as recording paper, is fed by a recording sheet conveying system, and a toner image is transferred to the recording sheet 43.

The recording sheet 43 is composed of a pair of rollers arranged at the entrance of the passage to the photosensitive drum 41, and a registration roller 44 whose rotation and stop timings are controlled, and a registration roller 44 disposed near the registration roller 44. The sheet is guided between the rollers by a guide for guiding the sheet and is conveyed by the rotation of the roller. The registration roller 44 is configured to control the timing of rotation and stop by feeding the recording sheet 43 with the registration roller 44 stopped so that the leading end of the recording sheet 43 is stopped at the position of the registration roller 44. Even if the posture is bent, the posture is corrected to a correct posture (skew correction function), and the rotation start timing of the registration roller 44 is adjusted to the start point position movement of the toner image forming area on the photosensitive drum 41. This is so that the toner image will come to the regular position on the recording sheet.

Therefore, in the above apparatus, it is necessary to rotationally drive the photosensitive drum, rotationally drive the developing roller, and rotationally drive the roller for recording conveyance. Conventionally, a drive motor for the recording paper conveyance system has been used as the driving method. As shown in FIG. 5, even if two developing motor driving motors are provided and driven separately, or one driving motor is used, as shown in FIG.
The gear train A of the developing system that transmits the rotation force to 2a and the gear train B of the recording sheet conveying system that transmits the rotation force from the motor M to the registration rollers 44 are independent of each other. Each of them was controlled via a clutch so that transmission can be performed by intermittent control.

In such a conventional drive system, when foreign matter or the like is mixed into the gear train and the gear train bites it and the gear is locked, if it is a gear of the recording sheet conveying system, the recording sheet is fed. Stop, the recording sheet detector installed at the key point of the recording sheet conveyance path detects the delay of the recording sheet and the non-arrival of the recording sheet. Therefore, it is possible to quickly stop the driving by the control circuit.

That is, in the case of a system for conveying a recording sheet, a good hard copy cannot be obtained due to misalignment unless the position of the image on the photosensitive drum and the position of the recording sheet are properly aligned. Since a detector (sensor) is installed at the required location for monitoring the recording sheet and controlling the feed timing of the photosensitive drum, abnormalities in the recording sheet transport system are detected by a monitoring function such as paper jam detection. The recording sheet conveyance system can be immediately stopped and protected.

However, in the case of the gear of the developing machine system, if the means for detecting it is not provided, the transmission of the rotational driving force is not stopped, so that the recording operation can be performed in the state where the developing machine is not driven. As a result, the apparatus will operate with the recording operation in a defective state. In the worst case, not only the mechanical damage such as gear breakage but also the operation of the apparatus with the recording operation in a defective state may result in overlooking the occurrence of a hard copy defect.

[0009]

As described above, in the conventional method, when the gear for transmitting the rotational driving force of the developing machine system is locked, the state in which the development cannot be performed without the detection means is detected. However, there is a problem in that not only can it not be known, the operation will be continued in the state of poor recording, and in the worst case, gear damage will also occur. However, in order to detect the rotation failure of the transmission driving force transmission gear of the developing system, it is necessary to detect the rotation of the gear. Therefore, it is not easy, and it is necessary to prepare for a significant cost increase. On the other hand, however, there is a strong demand for cost reduction, and there is a trade-off relationship between elimination of rotational defects in the developing system and cost reduction.

Therefore, the object of the present invention is to
An object of the present invention is to provide an electrophotographic apparatus capable of detecting a rotation failure of a developing system without having a special monitoring mechanism and rapidly stopping the control.

[0011]

In order to achieve the above object, the present invention is configured as follows. That is, firstly, the latent image carrier on which the electrostatic latent image is formed has a developing roller for applying toner, and the developing roller imparts toner to develop the electrostatic latent image to develop the toner. An electrophotographic apparatus configured to transfer an image of a latent image bearing member onto a recording sheet by transferring the recording sheet by a recording sheet conveying mechanism, and at least conveying the recording sheet by the recording sheet conveying mechanism. In an electrophotographic apparatus including a means for detecting a defect and a control means for stopping the operation of the apparatus when the conveyance failure is detected by the conveyance failure detection means, a rotary drive source and a rotational force of the rotary drive source are applied to the developing roller. Power is transmitted to the recording sheet conveyance mechanism via a transmission mechanism for transmission.

Secondly, a latent image carrier on which an electrostatic latent image is formed has a developing roller for applying toner,
Toner is applied by the developing roller to develop the electrostatic latent image to obtain a toner image, and the recording sheet conveying mechanism conveys the recording sheet to transfer the toner image on the latent image carrier to the recording sheet. An electrophotographic apparatus, comprising at least a means for detecting a conveyance failure of a recording sheet in a recording sheet conveyance mechanism and a control means for stopping the operation of the apparatus when the conveyance failure is detected by the conveyance failure detection means, and
In a recording sheet conveying mechanism, in an electrophotographic apparatus configured to send a recording sheet to a position for transferring the image and through a registration roller that adjusts skew, a rotary drive source and a rotary force of the rotary drive source are provided. Power is transmitted to the drive system mechanism of the registration roller via a transmission mechanism that transmits to the developing roller. Further, a clutch is used to transmit the rotational force of the rotary drive source, and the resist roller and the developing roller are both driven and stopped by the clutch, and the developing roller clutch is provided upstream of the resist roller clutch. It is configured to be placed. Further, power transmission uses a clutch and a gear, and the maximum transmission torque of the clutch is set to be smaller than the strength of the gear downstream thereof.

[0013]

In the first structure, there is a means for detecting the conveyance failure of the recording sheet in the recording sheet conveying mechanism.
Since the power is transmitted to the recording sheet transport mechanism via the transmission mechanism that transmits the rotational force of the rotary drive source to the developing roller, the transmission mechanism that transmits the rotational force of the rotary drive source to the developing roller is defective in rotation. In this case, the operation failure of the recording sheet conveying mechanism is spread, and therefore the control means stops the operation of the apparatus from the detection output of the detecting means due to the sheet conveying failure of the recording sheet conveying mechanism. As described above, the mechanism for detecting the recording sheet conveyance failure of the recording sheet conveyance mechanism can be used for the emergency stop in the case of the failure of the development roller system drive mechanism. Without using a special detector or monitoring mechanism for operation monitoring, it becomes possible to implement an emergency stop due to a failure of the drive mechanism of the developing roller system, so that it is possible to deal with operation failure without cost. become.

In the case of the second structure, when the gear of the developing system is locked, the gear strength is larger than the maximum transmission torque of the developing clutch, so that the developing clutch is slid to protect the gear, and Since the registration clutch is located downstream of the development clutch, the registration roller is not driven, the lock can be detected as a paper jam, and the recording operation can be stopped promptly.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrophotographic apparatus of the present invention uses one motor as a roller driving source, and the registration roller and the developing roller are driven / stopped by arranging clutches upstream of the rollers, respectively. The two clutches are arranged in series so that the developing clutch is located upstream of the registration clutch, and the maximum transmission torque of the developing clutch is smaller than the strength of the gear downstream thereof. It is what

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

FIG. 1 shows an electrophotographic apparatus which is an embodiment of the present invention. In the figure, 11 is an electrophotographic apparatus main body, and 12 is a photosensitive drum as a latent image carrier. A developing device 13 has a device case 14 for storing toner and a developing roller 15. Reference numeral 16 is a transfer roller, 17 is a cleaning device, 18 is a charge removing device, 19 is a charging device, 20 is an exposure device, 21 is a paper feed cassette in which recording sheets P are stacked and accommodated, 22 is a pickup roller, and 24 is a conveyance guide. Two
Reference numeral 5 is a registration roller, 32 is a fixing device, and 27 is a paper discharge tray.

The photosensitive drum 12 is a cylindrical drum made of a photoconductive material whose resistance changes with light, and the photosensitive drum 12 is rotated in one direction at a constant rotation speed during operation. Around the photosensitive drum 12, the charging device 1
9, the developing roller 15, the transfer roller 16, the cleaning device 17, and the charge removing device 18 are arranged at fixed positions in this order. Reference numeral 20 denotes an exposure device, for example, by scanning the laser beam in the axial direction of the photosensitive drum 12 and controlling the intensity of the laser beam in accordance with a drawing signal such as an image signal, the photosensitive drum 12 is controlled. An exposure optical path of the laser beam is located between the charging device 19 and the developing roller 15 so that the laser beam is exposed to the charged peripheral surface of the photosensitive drum 12 via the charging device 19. It is arranged to.

The charging device 19 is a device for charging the photosensitive drum 12, and the developing roller 15 forms toner on the peripheral surface of the developing roller 15 by adhering toner to the periphery and exposing the developing device to a laser beam. The toner is applied to the formed electrostatic latent image and is developed to form a toner image.

The transfer roller 16 is a roller for transferring the toner image of the photosensitive drum 12 onto the recording sheet sent to the position of the photosensitive drum 12, and the recording sheet is transferred to the photosensitive drum 1.
It has the function of pressing to 2. The cleaning device 17 is a device that removes unnecessary toner remaining on the peripheral surface of the photosensitive drum 12 after the toner image is transferred to the recording sheet, and the charge removing device 18 is a photosensitive drum that has passed the cleaning position of the cleaning device 17. This is a device for removing electric charge that removes the electric charge remaining on the peripheral surface of 12 by shining light on it.

Reference numeral 21 denotes a sheet feeding cassette in which a plurality of recording sheets (cut sheets) which are recording media (recording sheets) are stacked and accommodated, and the recording sheet P accommodated in the sheet feeding cassette 21.
Is conveyed by a pair of conveyance rollers 23 provided at the entrance of the conveyance path of the recording sheet P fed out from the paper feed cassette 21 by the pickup roller 22, and fed to the entrance of the photosensitive drum 12. It is a mechanism in which the inside of 24 is guided and is conveyed to the entrance of the photosensitive drum 12. Reference numeral 25 denotes a pair of registration rollers, which are provided at the entrance of the conveyance guide 24 on the side of the photosensitive drum 12.

The registration roller 25 is a photosensitive drum 12.
Drive control is performed so that the recording sheet P is conveyed at the timing when the head of the latent image forming position (the page head position) is exactly at the position of the transfer roller 16, so that the recording for the previous page is performed for the previous page. After the first recording sheet P is sent out, even if the succeeding recording sheet P arrives, it is in a stopped state, so that when the leading edge of the succeeding recording sheet P reaches the position of the registration roller 25, the registration roller 25 The movement is stopped by 25, and even if the recording sheet P is conveyed in an inclined state, the conveyance guide 24 and the registration roller 25 cooperate to return the recording sheet P to the correct posture and wait. ing. That is, the registration roller 25 has a function of correcting the skew of the recording sheet P and a function of adjusting the supply timing to the photosensitive drum 12.

Reference numeral 26 is a guide for guiding the recording sheet P on which the toner image is transferred through the position facing the transfer roller 16 of the photosensitive drum 12 to the fixing device 32, and the fixing device 32 heats the guided recording sheet P. Then, a device for fixing the toner on the sheet surface is denoted by 27, and a discharge tray 27 is a tray as a tray for receiving the recording sheet P that has passed through the fixing device 32. The fixing device 32 uses, for example, a heat roller, and is configured to receive heat and fix the toner to the sheet when passing between the rollers.

The drive system of this apparatus will be described with reference to FIG. Note that FIG. 3 is a diagram schematically showing the main part of FIG.

The drive system of this device transmits the drive force of one motor to the downstream by a transmission structure centered on a gear transmission mechanism. In FIGS. 2 and 3, 1 is a motor as a drive source. However, for example, a DC (direct current) motor is used. Reference numeral 2 is a drum output gear for driving the photosensitive drum 12, 3 is a development output gear for driving the developing roller 15, 4 is a registration output gear for driving the registration roller 25, 5 is a fixing output gear for driving the fixing device 32, and 6 is It is a paper feed output gear that drives the paper feed unit. 7 is a developing roller 15
A developing clutch that controls the driving / stopping operation of the registration roller 8 and a registration clutch 8 that controls the driving / stopping operation of the registration roller 25.

The rotation of the motor 1 is transmitted to the drum output gear 2, the development output gear 3, the registration output gear 4, the fixing output gear 5 and the paper feed output gear 6, but to the development output gear 3 and the registration output gear 4. On the other hand, a developing clutch 7 is provided on the upstream side of its transmission, and the rotational force of the motor 1 is transmitted to these via the developing clutch 7. That is, the motor 1 for the development output gear 3 and the registration output gear 4 is driven by the development clutch 7.
It is possible to simultaneously control the rotational force transmission of (rotational force contact / separation transmission control).

The registration clutch 8 is on the downstream side of the transmission of the developing clutch 7 as viewed from the rotational force transmission system, and even if the developing clutch 7 is in the rotational force transmitting state, the registration roller 25 is provided.
The transmission of the rotational force of the motor 1 to the motor can be cut off here. The gears on the downstream side of the developing clutch 7 and the registration clutch 8 are configured so that their gear strength is larger than the maximum transmission torque of the clutch.

In such a structure, when the motor 1 is rotationally driven, this rotational force is applied to the drum output gear 2, the fixing output gear 5, and the paper feed output gear 6 by the rotational force transmission mechanism such as a gear or a belt. Is transmitted, the photosensitive drum 12 and the fixing device 32 rotate, and the pickup roller 22 also rotates.

When the developing clutch is engaged, the rotational force is transmitted to the developing output gear 3, the developing roller 13a of the developing device 13 is rotated, and when the registration clutch 8 is engaged, the rotational force is applied to the registration output gear 4. Is transmitted, and the registration roller 25 rotates. Here, the registration clutch 8
Since the feeding timing of the recording sheet P to the photosensitive drum 12 is controlled, it is in a disconnected state until a predetermined timing when the page head position in the toner image forming portion of the photosensitive drum 12 comes to the transfer roller 16 side. Therefore, the registration roller 25 does not rotate until then.

When the photosensitive drum 12 is rotationally driven, the outer peripheral surface of the photosensitive drum 12 is charged by the charging device 19, and the exposure device 20 draws on the charged area of the photosensitive drum 12 to form a latent image. Photosensitive drum 1
When 2 passes the position of the developing device 13, toner is applied to the latent image forming surface from the developing roller 13a of the developing device 13, and a toner image is formed on the outer peripheral surface of the photosensitive drum 12.

On the other hand, the recording paper P stored in the paper feed cassette 21 is fed out by the rotating pickup roller 22, passes through the conveyance guide 24, and the skew is corrected by the registration roller 25. Then, it is fed between the photosensitive drum 12 and the transfer roller 16, but the registration roller 2
Until 5 is rotated, it stops at the position of the registration roller 25 and is in a standby state.

At a predetermined timing when the page head position in the toner image forming portion of the photosensitive drum 12 comes to the transfer roller 16 position side, the registration clutch 8 is controlled to be switched to the connected state, whereby the registration roller 25 is moved. The rotation of the recording sheet P is started and the recording sheet P
Send to the side.

Then, the recording sheet P is sent between the rotating photosensitive drum 12 and the transfer roller 16, and the toner image on the photosensitive drum 12 is transferred to the recording sheet P when it is sandwiched between these and passes. The recording sheet P, which has been transferred, is conveyed to the fixing device 32, where it is fixed, and then discharged to the paper discharge tray 27.

Recording on the recording sheet is performed by such an operation to obtain a hard copy. In this configuration,
The rotation of the motor 1 is performed by the drum output gear 2, the fixing output gear 5,
The rotational force is directly transmitted to the paper feed output gear 6 without passing through the transmission force opening / closing clutch. Therefore, the opening / closing control of the rotational force transmission to the photosensitive drum 12, the fixing device 32, and the pickup roller 22 is performed. Although not possible, the developing roller 15 and the registration roller 25 are configured so that opening / closing control of the rotational force transmission of the motor 1 can be performed by a clutch.

That is, when the developing clutch 7 is engaged, the rotational force is transmitted to the developing output gear 3, and when the registration clutch 8 is further engaged in this state, the rotational force is transmitted to the register output gear 4. Therefore, the registration roller 25
Although the developing roller 15 can be rotated only while the developing roller 15 is being driven, the registration roller 25 is rotationally driven only while the developing roller 15 is being driven. There is no problem even if it is placed in.

That is, the developing clutch 7 and the registration clutch 8 are arranged in series from the motor 1 as viewed from the transmission system, and the development clutch 7 is the registration clutch 8
It is placed upstream of the above, but there is no problem even in such an arrangement state.

When foreign matter or the like is caught in the gear train thus configured and the rotation of the gear is locked, if the locked gear is the gear of the recording sheet conveying mechanism, the pickup roller is used. 22 and registration roller 2
5, the rotational force cannot be transmitted to the other rollers for conveying the recording sheet, and the recording sheet P cannot be fed. At this time, however, the recording sheet P may be stopped in the middle of the conveying path, or the recording sheet P may be stopped. Since the feeding of the sheet is not performed at all times, this state is monitored by the operation of the control circuit (not shown) that monitors the detection output of the recording sheet detection sensor provided at various points of the recording sheet conveyance path and controls the system. Since it can be detected as a paper jam, the driving can be stopped quickly.

When the gear is locked in the transmission system to the developing output gear 3 which transmits the rotational force to the developing roller 15, the registration clutch 8 which is one element of the recording sheet conveying system is a gear of the driving system of the developing roller. If the gear of the drive system of the developing roller does not rotate, the registration clutch 8 will not rotate regardless of how many times the registration clutch 8 is connected.
Since the recording sheet is not rotated, the recording sheet is not sent out to the photosensitive drum 12 at any time. Therefore, a control (not shown) for monitoring the detection output of the recording sheet detection sensor provided at various points of the recording sheet conveyance path is performed. Due to the action of the circuit, this condition is detected as a paper jam, so that also in this case it is possible to stop the drive immediately.

Particularly in the case of this system, the developing clutch 7 is located at the base of transmitting the driving force of the motor 1 which is a power source to the developing system and the registration roller system, and moreover, the gear strength is the same as that of the developing clutch. With the configuration that is larger than the maximum transmission torque, even if the gear of the developing device drive system is locked, the developing clutch will slip and the gear can be protected.

In the prior art, when the gear of the developing roller system is locked, the developing system has nothing to do with the recording sheet conveying system, so the apparatus is stopped unless there is any detecting means for monitoring the driving state of the developing roller system. Can't be made
Since development is not possible, the recording sheets P are discharged one after another in an unrecorded state, which is not only a problem, but also because the rotational force of the motor 1 is applied while the gear is locked, the gear is damaged. However, the transmission system of the developing device drive system is arranged downstream of the drive system of the registration roller 25 so that the drive system of the registration roller 25 can be driven when the development device drive system is moving. By configuring, without providing an extra detector for monitoring the developing device drive system, it becomes possible to detect an abnormality using the detector for paper jam detection and perform an emergency stop of the device, In the unrecorded state, the recording sheets P can be ejected one after another and the occurrence of gear damage can be avoided.

[0041]

As described above in detail, according to the present invention, the power is transmitted to the power transmission mechanism of the recording sheet conveying mechanism via the transmission mechanism for transmitting the driving force to the developing roller system. Since it becomes possible to use a mechanism for detecting a recording sheet conveyance defect of the recording sheet conveyance mechanism for an emergency stop in the case of a defective drive mechanism of the developing roller system,
It is possible to carry out an emergency stop due to a defect in the drive mechanism of the developing roller system without using a special detector or monitoring mechanism for monitoring the operation of the drive mechanism of the developing roller system. It is possible to provide an electrophotographic apparatus capable of dealing with the above.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and is a main part configuration diagram as one embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention, and is a configuration diagram of a driving force transmission mechanism as one embodiment of the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention, and is a schematic configuration diagram of a driving force transmission mechanism having the configuration of FIG. 2.

FIG. 4 is a block diagram of a conventional device.

FIG. 5 is a schematic configuration diagram of a driving force transmission mechanism in a conventional device.

[Explanation of symbols]

 1 ... DC motor 2 ... Drum output gear 3 ... Development output gear 4 ... Registration output gear 5 ... Fixing output gear 6 ... Paper feed output gear 7 ... Development clutch 8 ... Registration clutch 12 ... Photosensitive drum 15 ... Development roller 25 ... Registration roller 32 ... Fixing device P ... Recording sheet

Claims (3)

[Claims] 1. A latent image carrier on which an electrostatic latent image is formed has a developing roller for applying toner, and the developing roller applies toner to develop the electrostatic latent image to form a toner image. In addition to the above, the electrophotographic apparatus is configured to convey the recording sheet by the recording sheet conveying mechanism and transfer the toner image on the latent image carrier to the recording sheet. In an electrophotographic apparatus provided with a detecting means and a control means for stopping the operation of the apparatus when a conveyance defect is detected by the conveyance defect detecting means, a rotary drive source and a rotational force of the rotary drive source are transmitted to the developing roller. An electrophotographic apparatus, characterized in that power is transmitted to the recording sheet conveying mechanism via a transmission mechanism. 2. A latent image carrier on which an electrostatic latent image is formed has a developing roller for applying toner, and the developing roller applies toner to develop the electrostatic latent image to form a toner image. In addition to the above, the electrophotographic apparatus is configured to convey the recording sheet by the recording sheet conveying mechanism and transfer the toner image on the latent image carrier to the recording sheet. The recording sheet conveying mechanism is provided with a detecting unit and a control unit for stopping the operation of the apparatus when the conveyance defect is detected by the conveyance defect detecting unit, and the recording sheet conveying mechanism adjusts the skew and the control for sending out the recording sheet to the transfer position. In an electrophotographic apparatus configured to feed through a registration roller, a rotary drive source and a transmission mechanism that transmits the rotational force of the rotary drive source to the developing roller. The power is transmitted to the drive system mechanism of the registration roller, the registration roller and the developing roller are driven / stopped by respective clutches, and the clutch for the developing roller is arranged upstream of the clutch for the registration roller. An electrophotographic device characterized in that 3. The electrophotographic apparatus according to claim 2, wherein a clutch and a gear are used for power transmission, and the maximum transmission torque of the clutch is smaller than the strength of the gear downstream thereof.