JP2003202727A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the stabilization of operation and the improvement of an image quality compatible by switching several developing units in a short time. <P>SOLUTION: An image forming apparatus to form an image by developing with toner because several developing units are switched so as to be opposed to a photoreceptive drum and transferring a toner image to a transfer material possesses a developing motor 31, gear trains 32, 51, 52, 34 and 35 to transmit driving force from the developing motor 31 and a gear 42Y provided on the side of the developing unit and connectable/disconnectable to/from a gear 35. The gear trains 51 and 52 are provided with an idle running part which is furnished with a backlash and by which the driving force is not transmitted to the other side until the backlash is clogged when the side of the driving motor 31 or the gear 42Y is driven. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a plurality of developing means and capable of recording color images by sequentially switching the developing means.

[0002]

2. Description of the Related Art In a color image forming apparatus such as a copying machine or a printer, a plurality of color developing devices for supplying toner are sequentially switched and brought into contact with a photoconductor drum to develop a latent image on the photoconductor to develop each color. There is a system in which the final color image is output by superposing.

The color image forming apparatus as described above has a drive source such as a motor on the image forming apparatus main body side for driving the toner supply roller and the like in the color developing device, and transmits the driving force through the gear train. ing. Then, when the color developing device is switched, the drive source is set in a free state or driven in a direction in which the drive source can be connected so that the drive transmitting means such as gears on the main body side and the color developing device side can be connected.

[0004]

However, in the above-mentioned conventional example, when the drive source of the toner supply roller is the pulse motor, the drive source is in the free state or in the direction opposite to the developing state when the color developing device enters the developing position. Since there is a case where step-out occurs when rotated to, it was necessary to hold the stationary state for a certain period of time after the entry was completed and before the development was started.

However, in recent years, there has been a demand for higher image forming speed. In addition, in order not to disturb the color image,
When the color developing device is switched, it is desirable to bring the developing device into contact with the latent image on the photoconductor drum sufficiently before developing it, and to slowly separate it after the development is completed. Therefore, as described above, it is difficult to take a sufficient holding time in a stationary state when switching the color developing device.

Further, for example, a DC brushless motor other than the pulse motor has a problem that it is difficult to reduce the time because the time from the rotation instruction is issued until the speed actually stabilizes varies. .

The present invention is to solve the above problems,
It is an object of the present invention to provide an image forming apparatus capable of switching a plurality of developing means in a short time and achieving both stable operation and improved image quality.

[0008]

A typical constitution according to the present invention for attaining the above object is to develop a toner image by switching a plurality of developing means to an electrophotographic photosensitive member so as to face each other, and transfer the toner image. In an image forming apparatus for forming an image by transferring to a drive source, a drive source, a drive transmitting unit for transmitting a drive force from the drive source, and a developing unit provided on the side of the developing unit and connectable to and detachable from the drive transmitting unit. A drive receiving portion, the transmission transmitting means is provided with backlash, and when the drive source or the drive receiving portion side is driven, an idle running portion that does not transmit the driving force to the other side until the backlash is clogged is provided. Is characterized by.

In the above structure, even if the driving source is in a stationary state (holding state) when the developing unit enters the developing position, the developing unit can enter due to backlash, and the stationary state is maintained during the switching of the developing unit. Therefore, it is possible to abolish or shorten the time in the stationary state after the approach has been completed, which was conventionally required.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is an explanatory longitudinal sectional view showing a schematic structure of a four-color full-color laser beam printer in an electrophotographic image forming apparatus embodying the present invention.

{Outline of image forming operation of color image forming apparatus} The photosensitive drum 1, which is an electrophotographic photosensitive member, is rotated in the direction of the arrow (counterclockwise) in FIG. 1 in synchronization with the rotation of the intermediate transfer belt 5a. The surface of the photosensitive drum 1 is a charging device 2
Is uniformly charged, and the exposure unit 3 irradiates a yellow image with light to form a yellow electrostatic latent image on the photosensitive drum 1. Simultaneously with the formation of the electrostatic latent image, the developing device 4 is driven to dispose the yellow developing device 4Y as a developing unit at the developing position so that the yellow toner adheres to the electrostatic latent image on the photosensitive drum 1. A voltage having substantially the same potential as the charging polarity of the drum 1 is applied to attach yellow toner to the electrostatic latent image for development. Then, a voltage having a polarity opposite to that of the toner is applied to the pressing roller (primary transfer roller) 5j of the intermediate transfer unit 5 to primarily transfer the yellow toner image on the photosensitive drum 1 onto the intermediate transfer belt 5a.

When the primary transfer of the yellow toner image is completed as described above, the next developing device is rotationally moved in the clockwise direction in FIG. 1 and is positioned at the developing position facing the photoconductor drum 1 to transfer the yellow toner image. Similarly to the case, for each of magenta, cyan, and black colors, formation of an electrostatic latent image, development by each color developing device 4M, 4C, 4BK, and primary transfer are sequentially performed, and four color toner images are formed on the intermediate transfer belt 5a. Overlap. When the developing device is switched, a drive mechanism (not shown) moves the photosensitive drum 1 to the developing device 4
Are separated from each other and switched, and contact is performed again after the switching is completed.

During this time, the secondary transfer roller 11 is not in contact with the intermediate transfer belt 5a. At this time, the charging roller 5f as a cleaning unit is also connected to the intermediate transfer belt 5a.
Is in non-contact with.

After the formation of the four color toner images on the intermediate transfer belt 5a, the secondary transfer roller 11 is pressed against the intermediate transfer belt 5a (state of FIG. 1), and the intermediate transfer belt 5 is further pressed.
In synchronism with the rotation of a, the transfer material cassette 19 is fed from the transfer material cassette 19 by a pickup roller 18 or a conveying roller 20 in response to a signal from the control portion 17 and stands by at a predetermined position near the registration roller pair 7. Transfer material S is intermediate transfer belt 5a
And is sent to the nip portion of the secondary transfer roller 11.

Immediately before the registration roller pair 7, there is a pre-registration sensor 14 which detects the leading end of the transfer material S to shut off the rotational driving force of the registration roller pair 7 and makes the transfer material S stand by at a predetermined position. It is provided.

Further, a voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 11, so that the toner image on the intermediate transfer belt 5a is secondarily transferred onto the surface of the transfer material S which has been collectively conveyed. I will do it.

The transfer material S secondarily transferred in this manner
Reaches the fixing device 8 via the conveyor belt unit 12, where the toner images of a plurality of colors are fixed, and then the discharge roller pair
The sheet is conveyed along the discharge guide 15 by the discharge roller pair 13, and is discharged by the discharge roller pair 9 on the discharge tray 10 above the color image forming apparatus A
And the image formation is completed.

On the other hand, after the secondary transfer, the cleaning charging roller 5f is pressed against the intermediate transfer belt 5a to give the residual toner remaining on the intermediate transfer belt 5a an electric charge opposite to that at the time of transfer.

The residual toner to which the opposite electric charge is applied is electrostatically attached to the photosensitive drum 1 and then collected by the cleaning blade 6 for the photosensitive drum.

The collected residual toner is collected and accumulated in the waste toner container 16 by following a conveyance path for conveying the waste toner, which will be described later.

{Developing device} The developing device 4 develops each of the four colors of yellow, magenta, cyan, and black in order to visualize the electrostatic latent image on the photosensitive drum 1. It is composed of vessels 4Y, 4M, 4C and 4Bk.

As shown in FIG. 1, the developing devices 4Y, 4M, 4C and 4Bk are detachably held by a rotary unit 40 which rotates about an axis, and at the time of image formation, the developing devices 4Y, 4M. , 4C, 4Bk are rotationally moved around the shaft while being held by the rotary unit 40, a predetermined developing device stops at a position facing the photoconductor drum 1, and a developing roller 41Y, which is a toner carrier described later,
After the 41M, 41C, and 41Bk are positioned so as to contact the photosensitive drum 1, a visible image is formed corresponding to the electrostatic latent image on the photosensitive drum 1.

During color image formation, the intermediate transfer belt 5
The rotary unit 40 rotates once for each rotation of a, and the yellow developing device 4Y, the magenta developing device 4M, and the cyan developing device 4 are rotated.
The developing process is performed in the order of C and then the black developing device 4Bk.

The color developing devices 4Y, 4M, 4C and 4Bk have the same structure although the colors of the toners stored therein are different. The developing devices 4Y, 4M, 4C, and 4Bk are provided with developing rollers 41Y, 41M, 41C, and 41Bk for the toner in the toner container, which is the main body of the powder container, by a toner stirring member (not shown).
The toner is applied to the outer periphery of the roller in a thin layer and an electric charge is applied to the toner (friction charging).

By applying a developing bias to the developing rollers 41Y, 41M, 41C and 41Bk facing the photoconductor drum 1 on which the latent image is formed, toner development is performed on the photoconductor drum 1 according to the latent image. It is something to do. Toner development is also performed on the magenta developing device 4M, the cyan developing device 4C, and the black developing device 4Bk by the same mechanism as described above.

The developing rollers 41Y, 41M, 41C and 41Bk of the developing devices 4Y, 4M, 4C and 4Bk are high voltage power sources for developing the respective colors provided in the printer main body when the developing devices are rotationally moved to the developing position. And a drive (not shown), and a voltage is sequentially and selectively applied for each color development so that the drive is connected.

{Development Rotary Rotational Drive Configuration} Next, a rotary rotation drive configuration in the case of switching each developing device during development will be described in comparison with a conventional example. It should be noted that here, the case of switching the yellow developing device will be described,
The same applies to other developing devices.

FIG. 2 is an explanatory view showing a conventional example of a developing roller drive system of a color developing device. A developing motor 31 which is a drive source installed on the main body of the image forming apparatus constitutes a gear 32 which constitutes a drive transmitting means. A gear 42Y, which is a drive receiving portion provided in the yellow developing device 4Y, is driven via 33, 34, and 35 to develop the developing roller.
Drive 41Y. The gear 42Y enters from the lower side in the drawing so as to mesh with the gear 35 and comes out upward in the drawing after the development is completed. Therefore, at the time of development, each gear rotating in the direction indicated by the arrow in the drawing is rotated in the opposite direction. Will be made.

FIG. 3 is an explanatory view showing the developing roller drive system of the color developing device of the present embodiment, and the gear 33 constituting a part of the drive transmission means in FIG. 2 is made into a gear 51 and a gear 52. During the development, the protrusion 53 of the gear 51 and the protrusion 54 of the gear 52 are engaged with each other to transmit the drive to the developing roller 41Y as in the conventional example.

FIG. 4 is a perspective explanatory view showing the structure of the gears 51 and 52. A spring 57 as an urging means is hooked between the gears 51 and 52, and the projection 54 separates from the projection 53, It is biased toward 55.

The relationship between the gear 51 and the gear 52 is that the gear 52 rotates and the protrusion 54 comes into contact with the protrusion 55 of the gear 51.
The position where 54 abuts the protrusion 53 of the gear 51 is distant from each other, and there is play in the drive transmission path. That is, as shown in FIG. 3, when the protrusion 54 is in contact with the protrusion 53,
When it rotates in the 55 direction, it has a free running portion to which the driving force is not transmitted until the projection 54 comes into contact with the projection 55 due to clogging.

{Developing Device Switching Operation} Next, the developing device switching operation will be described with reference to FIGS.

FIG. 5 shows a state before the color developing device enters the developing position, at which time the motor 31 is stopped and is in the hold state. Further, the gear 51 and the gear 52 are, as shown in FIG.
Are in contact with each other.

FIG. 6 shows a state in which the color developing device is rotated and the gear 42Y of the yellow developing device is engaged with the gear 35 (connection state).
FIG. In this state, the gear 35 on the image forming apparatus side is rotated by the entry of the gear 42Y.
The rotational force is not transmitted from the gear 52 to the gear 51 until the contact with the protrusion 53, and the motor 31 is not rotated. Therefore, the gear 42Y can enter even when the motor 31 is stationary (holding). A pulse motor is used as the motor 31 in order to improve the rotation accuracy.

After the gear 42Y has finished entering, as shown in FIG. 7, the motor 31 starts to rotate and the gear 51 rotates to bring the projection 53 into contact with the projection 54, resulting in the state shown in FIG. The developing roller 41Y is driven to perform development.

After completion of development, as shown in FIG.
Rotate 31 in the reverse direction to create a gap between protrusion 53 and protrusion 54,
After that, the developing device 4Y is rotated to start escape (separation). The gear 35 is rotated by the gear 42Y also during this escape, but since the gap between the protrusions 53 and 54 is open as described above,
The rotation is not directly transmitted to the motor 31.

When the motor 31 is stopped after the gear 42Y has come out of engagement with the gear 35, as shown in FIG.
The gear 52 is rotated by the urging force of the spring 57 (see FIG. 4), the space between the protrusions 53 and 54 is opened again, and the state returns to the state of FIG. 5 to prepare for the entry of the next color developing device. Thereafter, the developing device is switched by repeating the same process.

On the other hand, in the conventional example, it is necessary to turn off the excitation of the motor 31 or to reverse the state before entering the color developing device and until the completion of the entering so that the gear 42Y can enter. In order to start the normal rotation normally, it is necessary to put it in the hold state for a certain time (several hundreds of msec), and therefore, even if the approach is completed, the normal rotation cannot be performed immediately. However, in this embodiment, since the hold state is set before the completion of the entry of the color developing device, it is possible to start the normal rotation immediately after the completion of the entry.

The above table showing the rotation state of the motor 31 is as follows:
As shown in FIG. 10, the time from the end of development to the start of normal rotation for the next development can be shortened in the present embodiment by the time A in FIG. 10 compared to the case of the conventional example. There is.

If the shortened time is used, for example, to bring the developing roller into contact with the photosensitive drum earlier, the image defect due to the shock of the contact is brought out of the image area to improve the image quality. The motor 31
It is possible to maintain the hold time required for the normal operation of.

[0041]

As described above, according to the present invention, a time margin is produced within a time determined by the overall timing of switching a plurality of developing means, and the image forming apparatus achieves both stable operation and improved image quality. Can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an electrophotographic color image forming apparatus embodying the present invention.

FIG. 2 is a diagram showing a conventional example of a developing roller drive gear train.

FIG. 3 is a diagram showing a state during development of a developing roller drive gear train.

FIG. 4 is a perspective view showing details of a split gear of a developing roller drive gear train.

FIG. 5 is a diagram showing a state of a developing roller drive gear train immediately before entering a color developing device.

FIG. 6 is a diagram showing a state in which the color developing device of the developing roller drive gear train is being entered.

FIG. 7 is a diagram showing a state when the color developing device of the developing roller driving gear train has completed entering.

FIG. 8 is a diagram showing a state in which the color developing device of the developing roller drive gear train is in the process of exiting.

FIG. 9 is a diagram showing a state when the color developing device of the developing roller drive gear train is completely removed.

FIG. 10 is an explanatory diagram showing a time operation timing for switching a developing device as compared with a conventional example.

[Explanation of symbols]

A ... Color image forming apparatus S ... Transfer material 1 ... Photosensitive drum 2 ... Charging device 3 ... Exposure means 4 ... Developer 4Y, 4M, 4C, 4BK ... Developing device 5 ... Intermediate transfer unit 5a ... Intermediate transfer belt 5f ... charging roller for cleaning 5j ... Primary transfer roller 6 ... Cleaning blade 7 ... Registration roller pair 8… Fixer 9 ... Ejection roller pair 10… Ejection tray 11… Secondary transfer roller 12… Conveyor belt unit 13… Ejection roller pair 14… Sensor before cash register 15… Discharge guide 16… Waste toner container 17 ... Control unit 18… Pickup roller 19… Transfer material cassette 20… Conveyor roller 31… Development motor 32, 33, 34, 35… Gear 40… Rotary unit 41Y, 41M, 41C, 41Bk ... Developing roller 42Y ... Gear 51, 52 ... Gear 53, 54, 55… Protrusion 57… Coil spring

Claims (4)

[Claims] 1. An image forming apparatus for forming an image by transferring a toner image to a transfer material by forming a toner image by switching a plurality of developing means to an electrophotographic photosensitive member so as to face each other. Drive transmitting means for transmitting the driving force of the developing means, the drive transmitting means provided on the developing means side, and connected to the drive transmitting means,
A drive receiving portion that can be detached, wherein the drive transmission means is provided with play, and when the drive source or the drive receiving portion side is driven, an idle running portion that does not transmit drive force to the other side until the play is clogged An image forming apparatus characterized by being provided. 2. The image forming apparatus according to claim 1, further comprising an urging means for moving the backlash in a certain direction. 3. The image forming apparatus according to claim 1, wherein the drive source is a pulse motor. 4. The drive transmitted to the drive transmitting means when the drive receiving portion is connected to or disconnected from the drive transmitting means is opposite to the drive direction of the drive source at the time of development. The image forming apparatus described.