JPH09114238A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device small in size, simple in constitution and capable of eliminating inconvenience caused by the seam of a seamed belt SOLUTION: A developing unit 21 houses toner 28 and is placed on a support, 22 and the whole of the developing unit 21 is energized forward in such a manner that a press spring 23 is interposed at the rear surface. A developing roller 24 is rotatably supported in the opening part, of the lower part of the developing unit 21 and gap rollers 25 are coaxially disposed on both ends. A doctor blade 29 is abutted on the periphery of the developing roller 24, to seal the upper part of the opening of the developing unit 21. A counter roller 26 is arranged to face the developing roller 24, in a state where the seamed belt 27 having a width smaller than that of the counter roller 26 is extended. The gap rollers 25 come into contact with not the seamed belt 27, but the peripheries of the end parts of the counter roller 26 projected outward from both sides of the seamed belt 27, to be exposed. The distance between the periphery of the developing roller 24 and the seamed belt 27 is kept in such a degree that when the seam 27a comes to a developing part, the seam 27a does not come into contact with the periphery of the roller 24. Thus, the relief mechanism, etc., of the support 22 can be dispensed with.

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, and more particularly, to an image forming apparatus for performing development while always maintaining the positioning between an endless image carrier belt having a joint portion and a developing roller constant. .

[0002]

2. Description of the Related Art Conventionally, a photosensitive belt used in an electrophotographic image forming apparatus is roughly classified into a seamless belt having no joint and a seamed belt having a joint. The seamless belt requires substantially the same manufacturing process as the drum-shaped photosensitive member in terms of manufacturing method and is extremely expensive. On the other hand, the seamed belt continuously produces a large sheet, cuts this to a certain length, and then joins the ends to make it easy to mass-produce. Since the length can be freely manufactured, it has many advantages. Therefore, it is common to use a seamed belt for the image forming apparatus, and it is widely used.

4 (a) and 4 (b) are side sectional views showing the structure in the vicinity of a developing device of an electrophotographic image forming apparatus using a seamed belt. To briefly explain this, as shown in FIG. 1A, the seamed belt 1 is stretched by a facing roller 2 and a plurality of rollers (not shown) and driven by a driving roller (not shown) to be indicated by an arrow A in the figure. Moving in a clockwise direction at a constant speed.

A developing roller 3 is arranged in opposition to the opposed roller 2 in parallel with the axial direction thereof. The developing roller 3
The roller is rotatably supported by the opening of the developing device 4, is engaged with a drive mechanism (not shown), and rotates counterclockwise as indicated by arrow B in the drawing. Rotate in the same direction as 2 at the same speed.

In order to maintain the distance between the surface of the seamed belt 1 and the peripheral surface of the developing roller 3 at the facing portion between the facing roller 2 and the developing roller 3 at a constant distance L, which is optimum for developing, the same is coaxial with the developing roller 3. A gap roller 5 having an outer diameter larger than the outer diameter of the developing roller 3 by the distance L is provided. The gap roller 5 is urged to come into pressure contact with the seamed belt 1 by a pressing spring 7 arranged between the back surface of the developing device 4 and the inner wall of the support 6 holding the developing device 4. As a result, the distance between the surface of the seamed belt 1 and the peripheral surface of the developing roller 3 is always maintained at the distance L.

Toner 8 is stored in the developing device 4. The toner 8 is regulated by a doctor blade 9 made of an elastic material such as rubber which is in contact with the developing roller 3 to form a layer having a constant thickness on the surface of the developing roller 3, and the arrow of the developing roller 3 is used. With the rotation in the B direction, the seamed belt 1 and the developing roller 3 are conveyed to the facing portion. On the seamed belt 1, for example, an electrostatic latent image composed of a charging portion having a negative high potential and a negative low potential portion whose potential is attenuated by exposure is formed, and the toner 8 conveyed by the developing roller 3 is the above-mentioned. A toner image is formed (developed) by transferring to a low potential portion.

FIG. 4 (b) shows a seam 1 of a seamed belt 1.
It shows a state where a has moved to the closest contact point (opposing portion) between the opposing roller 2 and the developing roller 3. The seam 1a of the seamed belt 1 is made by stacking belt materials and bonding them by heat welding or the like. For this reason, the belt thickness of the joint surface 1a portion is about twice as large as that of the non-seamed portion. A photoreceptor belt typified by the seamed belt 1 generally has a thickness of about 100 μm in which a base material layer such as PET is about 80 μm and a conductive layer and a photosensitive layer are about 20 μm. Therefore, the thickness of the seam 1a is about 200 μm. As shown in FIG. 2B, load changes occur in the seamed belt 1 at the seam 1a at the moment when the gap roller 5 rides up and at the moment when the gap roller 5 deviates from the riding state. When the seamed belt 1 changes in load, belt running unevenness occurs, and when the belt running unevenness occurs, various inconveniences occur. For example, image blurring occurs and the image quality is inevitable. In order to prevent this, other processes such as exposure (latent image formation) and transfer are temporarily stopped at the timing when uneven running of the belt occurs, and the belt is enlarged for this purpose.
The problems such as the enlargement of the device are derived.

FIG. 5 is a side sectional view showing a structure in the vicinity of a developing device which has been improved so as to eliminate the above-mentioned inconvenience and has been widely used conventionally. As shown in the figure, in the configuration near the improved developing device, a cam 11 that slidably abuts on the back surface of the support 6 of the developing device 4 described above is provided to support the support 6
The developing device side engaging member 12 is provided on the lower side of the
A frame-side engaging member 13 is provided so as to project from the inner wall of the frame of the main body apparatus, and a pulling spring 14 is provided to engage with the developing-unit-side engaging member 12 and the frame-side engaging member 13, respectively. There is. The other structure is the same as the structure before improvement shown in FIG. 4 (a), and is shown with the same numbers as in FIG. 4 (a).

The structure shown in FIG.
The developing device 4, that is, the developing roller 5 is always urged in a direction away from the seamed belt 1 via the support 6, and the position of the support 6 is adjusted by the cam 11. Then, during normal operation, the cam 1 on the back surface of the support 6 is
1 rotates so that its maximum radius circumferential surface abuts on the support 6, and pushes the support 6 toward the opposing roller 2 against the biasing force of the pulling spring 14, whereby the gap roller 5
Is abutted against the seamed belt 1 by being biased by a push spring 7 provided on the back surface of the developing device 4. On the other hand, when the seam 1a of the seamed belt 1 is moved to the facing portion between the developing roller 3 and the facing roller 2, the cam 11 is rotated again in synchronization with the timing of the movement, and the minimum radius circumferential surface is the support member. 6 Face the back. With the rotation of the cam 11, the support 6 is moved in the direction away from the seamed belt 1 by the urging force of the pulling spring 14. That is,
The gap roller 5 is released from the contact with the seamed belt 1. As a result, the problem is solved without the load fluctuation of the seamed belt 1.

[0010]

However, this image forming apparatus has a complicated mechanism. Figure 6 (a) shows
FIG. 2 is a plan view showing a configuration near a developing device of this image forming apparatus. This figure shows a normal plan view in which the front and rear of the device are arranged at the top and bottom of the figure rotated by 90 degrees, with one side face facing upward and the other side face facing downward. Same figure
(b) is a side sectional view thereof. This figure (b) is the same as the side sectional view shown in FIG. However, the state is shown when the seam 1a of the seamed belt 1 described above moves to the facing portion between the developing roller 3 and the facing roller 2. Same figure
The components shown in (a) and (b) are shown with the same numbers as in FIG.

As shown in the figure, in the structure near the developing device of the image forming apparatus, a cam shaft 15 for fixing and rotating the above-mentioned cam 11 and a cam drive motor 16 for rotationally driving the cam shaft 15 are arranged. It is set up. Further, on both sides of the device, the above-mentioned two extension springs 14 for constantly biasing the support body 6 backward and the extension springs 14 are provided.
A developing device side engaging member 12 and a frame side engaging member 13 for respectively locking both ends of the
The contact portion, the locking portion, etc. are configured to include mechanical errors. In addition, as shown in FIGS. 3A and 3B, it is arranged so as to occupy a considerable space in the vicinity of the developing device.

As described above, since the structure is mechanically complicated, mechanical errors of the respective parts are accumulated in the operation, which causes a problem of reliability in accuracy. In addition, there is a problem that the product cost increases because the entire device becomes large.

An object of the present invention is to provide an image forming apparatus having a small size and a simple structure, which eliminates the inconvenience caused by the seam of the seamed belt.

[0014]

SUMMARY OF THE INVENTION According to the present invention, an image is formed by developing a latent image formed on the endless image carrier belt with a toner by a developing roller facing the endless image carrier belt having a joint portion. Applies to equipment.

The image forming apparatus of the present invention comprises a holding means for holding the distance between the surface of the developing roll and the back surface of the endless image carrier belt at a substantially constant value which is equal to or larger than the thickness of the joining portion. The holding means includes, for example, as described in claim 2, a gap roller provided coaxially with the developing roll and a support member for supporting the endless image carrier belt, and the gap roller is provided with the endless shape. It is configured to be in contact with the support member without the intermediary of the image carrier belt.

As a result, the disadvantage caused by the seam of the seamed belt can be eliminated with a small and simple structure.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing a configuration of a main part centering on a developing device of an image forming apparatus according to an embodiment. Further, FIG. 2 (a) shows a partial sectional view of the plane, and FIG. 2 (b) shows a side sectional view thereof.
The plan view of Fig. (A) is a normal plan view in which the front and back of the device are placed at the top and bottom of the figure, rotated by 90 degrees, with one side facing upwards and the other side facing downwards. ing. 2B is the same side sectional view as FIG. 1, except that FIG. 1 is a view showing a state during normal operation.
(b) is a diagram showing a state in which the seam of the seamed belt is moved to a facing portion (developing portion) between the developing roller and the facing roller.

In FIG. 1, the developing device 21 includes a support base 22.
It is mounted on. Rear surface of the developing device 21 (right side in the figure)
A push spring 23 is interposed between the stand and the wall surface of the support base 22 which is erected, and the push spring 23 urges the entire developing device 21 forward (to the left in the drawing). A developing roller 24 is rotatably supported at the lower opening of the developing device 21, and gap rollers 25 are arranged coaxially with the developing roller 24 at both ends of the developing roller 24. Toner 28 is accommodated in the developing device 21, and a doctor blade 29 is provided upright so as to contact the peripheral surface of the developing roller 24 and seal the upper opening of the developing device 21.

On the other hand, a counter roller 26 is arranged facing the developing roller 24. Although not shown, the opposing roller 26 is axially supported by the frame of the main body device,
The seamed belt 27 is stretched and rotated in the counterclockwise direction indicated by arrow D in the figure. As shown in FIG. 2A, the facing roller 26 is wider than the width of the seamed belt 27, and both ends thereof are projected outward from the side edges of the seamed belt 27 and are exposed. The gap roller 25 is urged by the pressing spring 23 through the developing device 21 to come into contact with the exposed peripheral surface of the facing roller 26. As a result, the distance between the peripheral surface of the developing roller 24 and the peripheral surface of the counter roller 27, that is, the back surface of the seamed belt 27 is always maintained constant at the opposing portion between the developing roller 24 and the counter roller 26.

The fixed distance from the back surface of the seamed belt 27 to the peripheral surface of the developing roller 24 is set by appropriately selecting the radius of the gap roller 25.
The thickness is set to an appropriate value equal to or larger than the thickness of the seam 27a. Although the seamed belt 27 has a double seam, it is often a pressure-bonding method using high-frequency welding, and does not necessarily have a double thickness. Therefore, there is almost no need to set the distance from the back surface of the seamed belt 27 to the peripheral surface of the developing roller 24 to be twice or more the thickness of the seamed belt 27, and it is possible to set the distance to or more than the thickness of the seamed belt 27 and within two times.

In this structure, the developing roller 24 has
A high voltage of, for example, 400 V (volt) to 2000 V in which AC is superimposed on DC or AC or DC is applied from a power source (not shown). On the other hand, the toner 28 in the developing device 21
Is charged to a weak negative potential by the doctor blade 29 and adheres to the surface of the developing roller 24 while being regulated to a constant layer thickness, and the developing roller 24 is rotated counterclockwise as indicated by arrow E to develop. Transported to the department.

A negative high voltage is applied to the conductive layer of the seamed belt 27 from a power source (not shown) to charge the photosensitive layer on the surface to a negative high potential, and thereafter, image information from an LED head (not shown) is also applied. The negative low potential portion whose potential is attenuated by the selective exposure according to is formed, and the electrostatic latent image including the low potential portion and the high potential portion is formed on the surface.

The toner 28 charged to the weak negative potential and conveyed on the developing roller 24 is transferred to the low potential portion of the electrostatic latent image formed on the seamed belt 27 in the developing portion and transferred to the toner image. To form. This toner image is transferred to a sheet (not shown) and fixed on the sheet, and image formation is completed.

During such an operation, as shown in FIG. 2B, when the seam 27a of the seamed belt 27 moves to the developing section, which is the facing section between the developing roller 24 and the facing roller 26, the above-mentioned constant value is obtained. Since the distance is set, the peripheral surface of the developing roller 24 does not come into contact with the seam 27a. Further, the gap roller 25 is
Since it is in contact with the facing roller 26 and not in contact with the seamed belt 27, even if the seam 27a of the seamed belt 27 comes to the developing portion as shown in FIG. 6B, the drive of the escape mechanism is driven. Therefore, it is not necessary to avoid the seam 27a, and the seam 27a can be passed through in the normal operating state, so that the seamed belt 27 does not fluctuate in load.

Since the structure for driving the escape mechanism is not used, the accuracy of operation is good, and as shown in FIG. 2 (a),
The structure is simple, and because there is no escape mechanism, the occupied space is reduced and the device can be downsized.

In the above embodiment, the gap roller 25 is brought into contact with the surface of the counter roller 26. However, the present invention is not limited to this, and as shown in FIG. The same effect can be obtained by configuring the support shaft 30 to have an appropriate diameter and contacting the peripheral surface of the support shaft 30. Further, instead of the facing roller 26, for example, FIG.
As shown in (b), the platen plate 31 having a curved surface may be used. In this case as well, the width of the platen plate 31 at both ends is made wider than the width of the seamed belt 27, and the platen plate 31 has a width larger than that of the seamed belt 27. Alternatively, the gap roller 25 may be brought into contact with the outer end portion.

[0027]

As described above, according to the present invention,
The position of the gap roller in the width direction of the main unit is outside the width of the seamed belt and directly contacts the supporting member surface of the seamed belt to maintain a fixed distance so that the seam of the seamed belt does not contact the developing roller and the load fluctuation on the seamed belt Therefore, the cam for coping with the load fluctuation of the seamed belt and its driving device, the biasing mechanism such as the pulling spring and its locking mechanism for assisting the operation of the cam, etc. are unnecessary, and therefore the operation It is possible to reduce the size of the apparatus while improving the accuracy of the above, and thus it is possible to provide an inexpensive and highly reliable image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a configuration of a main part centering around a developing device of an image forming apparatus according to an embodiment.

2A is a partial cross-sectional plan view of FIG. 1, and FIG. 2B is a cross-sectional view of the same side as FIG. 1. The seam of the seamed belt has moved to the facing portion (developing portion) between the developing roller and the facing roller. It is a figure which shows the state at the time.

3 (a) and 3 (b) are views showing another embodiment of the engaging member with the gap roller.

FIGS. 4A and 4B are side sectional views showing a configuration near a developing device of an electrophotographic image forming apparatus using a conventional seamed belt.

FIG. 5 is a side sectional view showing a configuration near a developing device of a conventional improved image forming apparatus.

6A is a plan view of FIG. 5, and FIG. 6B is a sectional view of the same side as FIG. 5, showing a state in which a seam of the seamed belt is moved to a facing portion between a developing roller and a facing roller.

[Explanation of symbols]

 1 Seamed Belt 1a Seam 2 Opposing Roller 3 Developing Roller 4 Developing Device 5 Gap Roller 6 Support 8 Toner 9 Doctor Blade 11 Cam 12 Developing Device Side Engaging Member 13 Frame Side Engaging Member 14 Pull Spring 15 Camshaft 16 Cam Drive Motor 21 Developing device 22 Support base 23 Pushing spring 24 Developing roller 25 Gap roller 26 Opposing roller 27 Seamed belt 27a Seam 28 Toner 29 Doctor blade 30 Support shaft 31 Platen plate

Claims (2)

[Claims] 1. An image forming apparatus for developing a latent image formed on an endless image carrier belt with toner by a developing roller facing a endless image carrier belt having a joint portion, wherein An image forming apparatus comprising: a holding unit that holds a distance from the back surface of the endless image carrier belt to a substantially constant value equal to or larger than the thickness of the joining portion. 2. The holding means comprises a gap roller provided coaxially with the developing roll and a support member for supporting the endless image carrier belt, and the gap roller is supported by the endless image carrier belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be brought into contact with the support member without the interposition of the support member.