JPH11174826A - Developing device for electrophotographic image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce vibration when the tracking roll of a developing roll abuts on a photoreceptor and to shorten the covnerging time of the transient vibration. SOLUTION: A housing 30 supporting the tracking roll 28a is energized in the direction of the photoreceptor 1 by a pressure pin 41. Besides, the housing 30 is provided with long holes 32 and 33. Then, pins 35 and 36 provided in a rotary frame are engaged with the holes 32 and 33 so as to support the housing 30. Since the energizing direction of the housing 30 is regulated by the holes 32 and 33 and the like and the roll 28a is energized to the center direction of the photoreceptor 1, the movement is smooth. Besides, since a developing device 10Y is rotated in a forward direction together with the photoreceptor 1 and the roll 28a is controlled so as to abut on the photoreceptor 1 at the same velocity, the vibration at the abutting is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for an electrophotographic image forming apparatus, and more particularly, to an electrophotographic image forming apparatus configured to transfer a plurality of color toner images onto a recording medium by superimposing the toner images. The present invention relates to a developing device of an image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a laser printer, a plurality of color toner images formed on a photoreceptor are transferred onto an intermediate transfer member in a superimposed manner. 2. Description of the Related Art There is known an image forming apparatus that further transfers a toner image onto a recording sheet to obtain a full-color print image. In order to form a color toner image on the photoconductor, a developing device that visualizes an electrostatic latent image formed on the photoconductor with toner according to video data is used.

In order to form a full-color image, development is performed with toner of at least three primary colors, preferably four colors with black added. Therefore, a developing device corresponding to these toner colors is required. Specifically, a developing unit having four developing devices each having a developing roll for charging a developer formed by mixing a toner and a carrier is configured. In the case of a rotary developing unit, a plurality of developing devices arranged on the developing unit at equal angular intervals are set to nine for each color development.
The development is carried out by rotating the developing rolls of each color by a rotation of 0 ° in order to sequentially contact the photoreceptor.

The developing roll must be opposed to the photoreceptor with a certain gap, not in close contact with the photoreceptor. In view of this, a method has been considered in which a tracking roll is provided coaxially with the developing roll, and the tracking roll is pressed against the surface of the photoreceptor to maintain the constant gap. As an example of the tracking roll method, see Japanese Patent Application Laid-Open
There is a color developing device described in US Pat.

By adopting this tracking roll system, there is no need to adjust the gap between the photoconductor and the developing roll at the time of manufacture, and without any adjustment even after the photoconductor is replaced. The gap between the photoconductor and the developing roll can be kept constant.

[0006] On the other hand, in the tracking roll system, the tracking roll separates and comes into contact with the photosensitive member each time the developing device is rotated as described above so that the developing roll appropriately faces the photosensitive member. As a result, an impact is given to the photoreceptor each time the separating / contacting operation is performed.
If the transfer of the toner image is performed, banding (band-like image defect) due to a change in the image position will occur.

However, in order to increase the printing efficiency, it is preferable that image writing and transfer be performed as continuously as possible. Therefore, it is not possible to wait for these operations until the vibration caused by the impact converges. In other words, it is not easy to improve printing efficiency while eliminating image defects.

In view of the above, there has been proposed a developing device for reducing the impact as much as possible (Japanese Patent Laid-Open No. 4-7887).
No. 3). In this developing device, guide rolls are provided on both sides of the developing device, and guide grooves for guiding the guide rolls are provided. By moving the guide roll along the guide groove, the positioning member of the developing device, that is, the tracking roll is gently brought into contact with the photoconductor.

[0009]

According to the developing device described in the latter publication, the impact at the time of contact with the tracking roll can be reduced to some extent, but it has not been sufficient. That is, since the difference between the peripheral speed of the photosensitive member and the moving speed of the tracking roll has not been eliminated, the banding has not yet been eliminated. In particular, in order to improve the printing efficiency, it is desirable that the vibration caused by the impact at the time of contact with the tracking roll be quickly converged, and further improvement has been demanded.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide a developing device of an electrophotographic image forming apparatus capable of obtaining good image quality without banding by further reducing vibration caused by an impact when a tracking roll contacts a photosensitive member.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the object, the present invention is to mount a plurality of developing rolls provided for each color on a rotating device, and to set a photoconductor at a predetermined developing position. In a developing device of an electrophotographic image forming apparatus configured to perform toner development by sequentially facing the drum,
A tracking roll is provided coaxially with the developing roll, for maintaining a constant gap with the photoconductor drum, the tracking roll orbits in the forward direction with the photoconductor drum, and the tracking roll is It is characterized in that the rotation direction and the rotation speed of the rotating device are determined such that the peripheral speed of the tracking roll and the peripheral speed of the photosensitive drum are equal at the time of contact with the photosensitive drum.

In the present invention having the above characteristics, the tracking roll and the photosensitive drum contact while moving in the forward direction. Therefore, the circumferential speed of the tracking roll and the circumferential speed of the photosensitive drum can be made equal at the planned contact position, and the speed difference can be eliminated. As a result, the transient vibration generated at the time of mutual contact can be converged to a steady state in a very short time.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 9 is a main part configuration diagram of a full-color printer as an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, a photosensitive drum 1 (hereinafter simply referred to as a "photosensitive member") as an image carrier is provided so as to be rotatable in the direction of arrow B by a motor (not shown). A charging device, that is, a charging roll (BC) is provided around the photoconductor 1.
R) 8, an exposure device (ROS) 5, a developing unit 10, a primary transfer unit, that is, a primary BTR 2, and a cleaner device 11 are arranged. The developing unit 10 includes four developing devices 10Y, 10M, 10C, and 1 for full-color development.
It consists of 0K. Developing devices 10Y, 10M, 10C, 10
K develops the latent image on the photoreceptor 1 with yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively. When developing the toner of each color, the developing unit 10 is rotated by 90 ° in a direction of arrow A opposite to the direction B by a motor (not shown) so that the developing device of the color comes into contact with the photoconductor 1. Aligned to

The toner images of each color developed on the photoreceptor 1 are sequentially transferred to an intermediate transfer belt (hereinafter, simply referred to as “belt”) 3 by a primary BTR 2, and four color toner images are superimposed. . The belt 3 is composed of rolls 12, 13,
It is stretched between 14 and 15. Of these, roll 1
Reference numeral 2 denotes a drive roll that is coupled to a drive source (not shown) to drive the belt 3. Roll 13 functions as a tension roll that adjusts the tension of the belt 3.
Functions as a secondary transfer device, that is, a backup roll of the secondary BTR 4. A belt cleaner 16 is provided at a position facing the roll 15 with the belt 3 interposed therebetween.
The residual toner on the belt 3 is scraped off by the cleaner blade.

The recording paper pulled out of the recording paper cassettes 17 and 18 into the transport path by the pull-out rolls 19 and 20 is nipped by roll pairs 21, 22 and 23, that is, a secondary B sheet.
The sheet is fed to a contact portion between the TR 4 and the belt 3. The toner image formed on the belt 3 is transferred onto the recording paper at the nip portion, is thermally fixed by the fixing device 24, and is discharged to the tray 25 or the tray 26 (upper surface of the main body).

A reflection type optical sensor 6 is disposed opposite to the belt 3, and detects reflected light from a reflection portion (not shown) such as an aluminum foil provided on the belt 3. The detection signal of the reflected light is used as a reference signal for controlling the image forming timing by the ROS 5 and the transfer timing of the toner image.

Developing devices 10Y, 10M, 10C, 10K
Has a replaceable toner cartridge, a developing roll for applying a developing bias, a toner supply device and a conveying device for supplying toner to the developing roll.

In the image forming apparatus having the above configuration, an image is formed as follows. First, a voltage is applied to the BCR 8 to uniformly negatively charge the surface of the photoreceptor 1 at a predetermined charging portion potential. Subsequently, exposure is performed by the ROS 5 so that the charged image portion on the photoconductor 1 has a predetermined exposure portion potential, and an electrostatic latent image is formed. In other words, a latent image corresponding to an image is formed by turning on / off the ROS 5 based on video data supplied from a control device (not shown).

A developing bias preset for each color is applied to a developing roll of the developing device 10Y or the like, and the latent image is developed with toner when passing through the position of the developing roll, and is visualized as a toner image. . Toner image is primary B
After being transferred to the belt 3 by the TR 2 and further transferred to the recording paper by the secondary BTR 4, it is fed to the fixing device 24. During full-color printing, four color toners are superimposed on a belt and then transferred to recording paper. The toner remaining on the photoreceptor 1 is removed and collected by the cleaner device 11, and finally, the photoreceptor 1 is uniformly discharged to near 0 volts by an unillustrated static eliminator to prepare for the next image forming cycle.

Next, the developing unit 10 will be described in detail. FIG. 2 is a perspective view illustrating the configuration of the developing unit 10. In FIG. 1, a rotary frame constituting the developing unit 10 includes a main frame (not shown) assembled in a cross shape and side frames 27a and 27b provided on both sides of the main frame. It is divided into four regions. The developing unit 10 is rotated by a stepping motor (not shown) for each color toner development. The developing roll 28 and the toner cartridge 29 are housed in the four areas.
Each of the developing devices stored in “0” is provided.

The toner cartridge 29 stores a two-component developer composed of a carrier and a toner, and is supplied to the developing roll 28 little by little. The supply amount is controlled so that the ratio (density) of the toner in the developer is maintained in accordance with the consumption of the toner. The toner supply amount is controlled by the driving speed of a transport unit such as an auger (not shown) provided between the toner cartridge 29 and the developing roll 28.

The arm portions of the side frames 27a and 27b which protrude in four directions and the respective housings 30 are displaceably engaged with each other in the longitudinal direction of the arm portions. The engagement state and displacement direction between the side frames 27a and 27b and the housing will be further described later with reference to FIGS. The developing roll 28 is partially exposed from the housing 30, and the exposed portion contacts the photoreceptor 1 via the tracking roll to perform toner development.

FIG. 1 is an enlarged view of a main part of the developing unit 10. In the drawing, the developing roll 28 is in contact with the photoreceptor 1 via a tracking roll 28a. Slots 32, 33 are provided on the side surface of the housing 30 of the developing device 10Y, and the side frames 2 are provided in the slots 32, 33.
Pins 35 and 36 fixed to the arm portion 34 of 7a are fitted. Similar long holes and pins are provided on the other side surface of the housing 30 and the side frame 27b, respectively. That is, the housing 30 containing the developing roll 28 is supported by the side frames 27a and 27b via the pins 32 and 33.

Behind the housing 30, the housing 3
A pressing device 37 that urges 0 toward the photoconductor 1 is provided. The pressing device 37 includes a cylinder 38 fixed to the main frame, a compression coil spring 39 housed in the cylinder 38, and a pressure pin 40 urged by the compression spring 39.
Consists of The stroke is regulated by a lid 41 over the cylinder 38 so that the pressure pin 40 does not escape from the cylinder 38. The tip of the pressure pin 40 abuts on the rear part of the housing 30 and pushes the housing 30 forward by the elastic force of the compression coil spring 39.

In a state in which the tracking roll 28a is in contact with the photosensitive member 1 at a predetermined position, that is, in the developing position, the tracking roll 28a is slightly pushed back by the photosensitive member 1, and the tracking holes 28 and 33 and the pins 35 and 36 A gap g (see FIG. 3) is formed between them. In other words, the tracking roll 28a and the photoconductor 1 are in contact with each other by a force that pushes back the compression coil spring 39 by a stroke corresponding to the gap g.

Next, the biasing direction of the tracking roll 28a will be described. FIG. 3 shows the tracking roll 28.
It is a schematic diagram which shows the biasing direction of a. In the figure, when the driving roll 28 is urged in the direction of arrow X by the pressure pin 40, the positions of the long holes 32 and 33 are shifted so that the developing roll 28 is displaced toward the rotation center 1C of the photoconductor 1. To determine. In other words, the long hole 32 provided in the housing 30
And a straight line L1 connecting the rotation center 28C of the developing roll 28 and the rotation center 1C of the photoconductor 1 is set to be parallel.

In the developing position where the tracking roll 28a contacts the photosensitive member 1, the side frame 27a
The pins 35, 36 and the long holes 3 are formed so that a gap g is formed between the pins 35, 36 provided in the
2 and 33 are determined.

With the above configuration, the tracking roll 2
8a comes in contact with or separates from the photoreceptor 1, the pin 3
5, 36 and the long holes 32, 33 slide smoothly with each other.
Further, since the gap g is set to be generated, the tracking roll 28a can be brought into contact with the surface of the photoconductor 1 with a stable pressing force by the compression coil spring 39.

The pins 35 and 36 may be shafts having a circular cross section. However, as shown in FIG. 4, a resin member 42 having good slidability is joined around a metal shaft 41. By doing so, the slidability with the long holes 32 and 33 can be further improved, and the fitting accuracy can be easily increased.

Next, the speed control of the stepping motor for rotating the developing unit 10 will be described. FIG. 5 is a velocity diagram of the stepping motor. The vertical axis represents the number of pulses supplied to the stepping motor, and the horizontal axis represents time. In the figure, supply of a pulse is started at time t1. That is, the rotation of the developing unit 10 starts at time t. The number of pulses is increased linearly from the start of rotation, peaks at time t2, and then the number of pulses is reduced to start deceleration.
Then, at time t3, the tracking roll 28a and the photoconductor 1 start contacting. The pulse number p at this time is set so that the peripheral speed of the photoconductor 1 is equal to the peripheral speed of the tracking roll 28a. Further, the developing unit 10 is decelerated, and at time t4, the tracking roll 28a
Reaches the developing position, and the rotation of the developing unit 10 stops.

By controlling the stepping motor according to such a velocity diagram, the tracking roll 28 of the developing unit 10 driven by the stepping motor is controlled.
a can be brought into contact with the photoconductor 1 at a constant speed.

Next, rotation fluctuation of the photosensitive member 1 according to this embodiment will be described. FIG. 6 shows the rotation fluctuation of the photoconductor of the conventional image forming apparatus, FIG. 7 shows the rotation fluctuation of the photoconductor when the parallelism between the straight lines L1 and L2 is slightly deteriorated in the present embodiment, and FIG. FIG. 7 is a waveform diagram illustrating rotation fluctuation of the photoconductor when the parallelism between the straight lines L1 and L2 is increased in the embodiment.

First, FIG. 6 shows a case where the rotation directions of the photosensitive member and the developing unit are the same, that is, a case where the developing unit is rotated in a direction opposite to the rotation direction A of the developing unit 10 shown in FIG. It is. In FIG. 6, the tracking roll contacts the photoconductor at time t10, and the transient vibration at this time converges at time t11. From time t10 to time t1
Up to 1 was 530 ms. In this example, the maximum value of the transient vibration exceeds the measurement range.

FIG. 7 shows a state in which the parallelism between the straight lines L1 and L2 is slightly degraded in this embodiment. The rotation directions of the developing unit and the photoconductor are the same. That is, the tracking roll and the photoconductor come into contact with each other while moving in the forward direction. In the figure, the tracking roll abuts on the photoconductor at time t12, and the transient vibration at this time converges at time t13. From time t12 to time t1
Up to 3, it was 410 ms. In this example, the amount of transient vibration, that is, the speed fluctuation ratio with respect to the photoconductor speed in a steady state, was 11.8%.

FIG. 8 shows a state in which the parallelism between the straight lines L1 and L2 is increased in this embodiment, and the rotation direction of the developing unit and the photosensitive member is the forward direction. In the figure, the tracking roll contacts the photoconductor at time t14, and the transient vibration at this time converges at time t15. It was 300 ms from time t14 to time t15. In this example, the amount of transient vibration was 7.5%.

As can be understood from these examples of fluctuations in the rotation of the photoconductor, the rotation direction of the developing unit and the photoconductor is set to the forward direction, and the speed at the time of contact between the tracking roll and the photoconductor is made equal. In addition, the amount of transient vibration is reduced, and the convergence time of transient vibration can be shortened.

In the case where the rotation direction of the developing unit and the photosensitive member is set to the forward direction, the speed at the time of contact between the tracking roll and the photosensitive member is made constant, and the biasing direction of the tracking roll is considered, In addition, the amount of transient vibration is further reduced, and the convergence time of transient vibration is greatly reduced.

As described above, if the convergence time of the transient vibration is reduced, the image writing can be started in a short time when the tracking roll is set at the developing position. That is, even when the formation interval (inter-image) of each color image is short, the transient vibration can be converged within that time, so that it is possible to improve the efficiency of full-color image printing in which multicolor toners are superimposed.

In this embodiment, a long hole is provided on the housing side of the developing device of each color, and the tracking roll is mounted so as to be able to advance and retreat in cooperation with a pin of a side frame engaged with the long hole. However, contrary to this configuration, the same operation as in the present embodiment can be achieved by providing a long hole in the side frame and providing a pin on the housing side of the developing device of each color.

[0040]

As is apparent from the above description, according to the present invention, the tracking roll and the photosensitive drum can be contacted at a constant speed while moving in the forward direction. As a result, it is possible to reduce the vibration generated at the time of mutual contact, and to converge the transient vibration to a steady state in a very short time. Therefore, it is possible to shorten the time for avoiding the image writing when the tracking roll and the photosensitive drum are in contact with each other, and as a result, it is possible to shorten the inter-image in which the image writing is not performed, thereby improving the printing efficiency.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a main part of a developing device according to an embodiment of the present invention.

FIG. 2 is a perspective view of a developing unit including a developing device according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a biasing direction of a tracking roll.

FIG. 4 is an enlarged view of a main part showing a guide means for a tracking roll.

FIG. 5 is a velocity diagram of a stepping motor for driving a developing unit.

FIG. 6 is a diagram illustrating a speed variation of a photosensitive drum according to a conventional apparatus.

FIG. 7 is a diagram showing a speed variation of the photosensitive drum according to the embodiment of the present invention.

FIG. 8 is a diagram illustrating a speed variation of the photosensitive drum according to the embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration of a color printer including a developing device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Primary BTR, 3 ... Intermediate transfer belt, 4 ... Secondary BTR, 5 ... Exposure device, 8 ... Charging roll, 10 ... Development unit, 11 ... Photoconductor cleaning device, 28 ... Development roll, 28a: tracking roll, 29: toner cartridge, 30: housing, 32, 33: long hole, 34: arm part, 3
5, 36 ... pin, 37 ... pressing device

Claims (4)

[Claims] 1. An electrophotographic image forming apparatus in which a plurality of developing rolls provided for each color are mounted on a rotating device, and toner development is performed by sequentially facing a photosensitive drum at a predetermined developing position. The developing device of the above, further comprising a tracking roll disposed coaxially with the developing roll, for maintaining a constant gap with the photoconductor drum, the tracking roll orbits in the forward direction with the photoconductor drum, and When the tracking roll comes into contact with the photoconductor drum, the rotation direction and the rotation speed of the rotating device are determined so that the rotation speed of the tracking roll and the peripheral speed of the photoconductor drum become equal. Developing device of an electrophotographic image forming apparatus. 2. The apparatus according to claim 1, further comprising: pressing means for pressing said tracking roll against said photosensitive drum; and guide means for restricting a direction of displacement of said tracking roll by said pressing means. Developing device for an electrophotographic image forming apparatus. 3. The guide means according to claim 2, wherein a guide direction of said guide means is determined such that an extension line of a displacement direction of said tracking roll passes through a center of said photosensitive drum. A developing device for an electrophotographic image forming apparatus. 4. A developing device for an electrophotographic image forming apparatus according to claim 2, wherein said pressing means is a spring means for urging a housing supporting said tracking roll.