JP2002341672A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate defective transfer caused by incomplete contact between a belt type image carrier and a transfer paper by preventing a gap at the entrance part of a transfer position from changing even in the case the belt type image carrier expands and contracts due to an environmental change. SOLUTION: As for the image forming device provided with the belt type image carrier 61, a transfer means 9 facing the image carrying surface of the belt type image carrier at the transfer position, and a tension roller 66 for imparting a tension to the belt type image carrier in press contact with the rear side of the belt type image carrier on the upstream side of the transfer means, the device is provided with a supporting member 102 for pivotally supporting the tension roller by one end and supporting a backup member 101 which comes into contact with the rear side of the image carrying surface of the belt type image carrier by the other end, and the supporting member is freely rocked with a fulcrum 103 positioned at the middle part as a center, and the supporting member is constituted so that the tension roller and the backup member can alternately and freely go in and out toward the rear side of the belt type image carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a photoreceptor belt or an intermediate transfer belt as a belt-shaped image carrier.
In particular, the present invention relates to an image forming apparatus that can effectively prevent transfer failure on transfer paper caused by expansion and contraction of a belt-shaped image carrier due to environmental changes such as temperature and humidity.

[0002]

2. Description of the Related Art An endless belt made of an elastic material is used as a photosensitive member or an intermediate transfer member as an image carrier provided in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine. Many. As shown in FIG. 3, this type of belt-shaped image carrier 150 is endlessly stretched by a plurality of rollers including a driving roller (not shown) and driven rollers 151 and 152, and is driven by a driving force from the driving roller. It is driven to rotate in a predetermined direction.
The belt-shaped image carrier 150 travels while carrying the toner image, and transfers the toner image onto the transfer paper P at the transfer position T.
At the transfer position T, a transfer unit (transfer roller) 155 for applying a transfer bias to the toner image is driven by a driven roller 151.
The transfer paper P conveyed toward the transfer position is pressed against the belt-shaped image carrier 150 by the roller 151 and the transfer means 155. The roller 152 is a tension roller, and the spring 1
The tension is applied to the belt-shaped image carrier by being elastically urged in the arrow direction by 53. At the transfer position T, it is necessary to bring the transfer paper P into close contact with the image holding member 150 immediately before the entrance of the transfer position in order to obtain good transfer performance. By the way, a photoreceptor belt as the image holding member 150,
Alternatively, since the circumference of the intermediate transfer belt expands and contracts due to changes in the surrounding environment such as temperature and humidity, a roller (tension roller) 152 that applies tension to the belt immediately upstream of the transfer position is used.
If there is, the gap at the transfer entrance changes. In particular, when the belt-shaped image carrier shrinks in a low-temperature and low-humidity environment, the gap at the transfer entrance portion widens (the position indicated by the broken line in FIG. 3), which may cause transfer failure.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has a belt-shaped image carrier suspended endlessly around a plurality of rollers and driven to rotate, and a belt-shaped image carrier at a transfer position. Image forming apparatus comprising: a transfer unit facing an image bearing surface of the image forming apparatus; and a tension roller that presses against a back surface of the belt-shaped image carrier on the upstream side of the transfer unit and applies tension to the belt-shaped image carrier. In the apparatus, even when the belt-shaped image carrier expands and contracts due to environmental fluctuations,
An object of the present invention is to solve a transfer failure caused by a poor adhesion between a belt-shaped image carrier and a transfer sheet without changing a gap at an entrance portion of a transfer position.

[0004]

According to a first aspect of the present invention, there is provided a belt-shaped image carrier which is endlessly suspended between a plurality of rollers and is driven to rotate, and a belt-shaped image carrier at a transfer position. An image comprising: a transfer unit facing the image bearing surface of the body; and a tension roller that presses against the back surface of the belt-shaped image carrier and applies tension to the belt-shaped image carrier upstream of the transfer unit. In the forming apparatus, a support member that supports the tension roller at one end while supporting a backup member that abuts on the back surface of the image carrier surface of the belt-shaped image carrier at the other end is provided, and the support member is provided at an intermediate portion. The present invention is characterized in that it is swingable about a fulcrum at which it is located, and that a tension roller and a backup member can be alternately protruded toward the rear surface of the belt-shaped image carrier. The invention according to claim 2 is characterized in that the backup member does not contact the back surface of the belt-shaped image carrier in a normal environment in which the belt-shaped image carrier has little expansion and contraction. The invention according to claim 3 is characterized in that the belt-shaped image carrier is an intermediate transfer belt made of an elastic material.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIG. 1 is a front view showing a schematic configuration of a printer as an image forming apparatus according to an embodiment of the present invention. This printer includes a photosensitive belt 1 as a latent image carrier wound around a plurality of support rollers 11, 12, and 13. The photoreceptor belt 1 is driven to rotate clockwise as indicated by an arrow A in the figure.
Charger 3, optical writing unit 7, four developing devices 5
K, 5C, 5M, 5Y, an intermediate transfer belt (belt-shaped image carrier) 61 as an intermediate transfer body, a photoconductor cleaning device 4, and the like are arranged. An organic photosensitive layer is formed on the surface of the photosensitive belt 1. Reference numeral 64 denotes primary transfer means for transferring the toner image on the photosensitive belt 1 onto the intermediate transfer belt 61. The intermediate transfer belt 61 is stretched endlessly by support rollers 62, 63, 65, and 66, and is driven in the direction of arrow B by a drive roller (for example, 62). Reference numeral 66 denotes a tension roller.
One support roller 65 forms a transfer position T between itself and a transfer roller (transfer means) 9, at which transfer paper P fed from the paper feed unit 8 passes through a transport path 80. Supplied. Reference numeral 81 denotes a pickup roller, 82 denotes a transport roller, and 83 denotes a registration roller. Reference numeral 110 denotes a cleaning device. The transfer paper on which the toner image has been transferred from the intermediate transfer belt 61 by the transfer bias from the transfer roller 9 is fixed by the fixing device 100,
Emitted outside the machine.

When an image forming operation (printing operation) is performed by the printer, a high voltage is applied to the charger 3 so that the photosensitive belt 1 is uniformly charged. Then, in an image signal processing unit (not shown), color image information, for example, a color image signal sent from an external computer is converted into an optical writing signal and sent to the optical writing unit 7. In the optical writing unit 7, a laser as a light source is controlled based on the optical writing signal, and Black (K), Cyan (C), and Magen are transmitted via a polygon mirror, an f / θ lens, and a reflection mirror.
Optical writing corresponding to the image signals of ta (M) and Yellow (Y) is performed, and an electrostatic latent image is formed on the photosensitive belt 1. The electrostatic latent image on the photoreceptor belt 1 is developed for each color by each of the developing devices 5K, 5C, 5M, and 5Y having each color toner. Thus, a toner image is formed on the photosensitive belt 1 for each color. By applying a charge having a polarity opposite to that of the toner from the primary transfer roller 64 to the intermediate transfer belt 61 at a contact portion between the photosensitive belt 1 and the intermediate transfer belt 61, the toner image on the photosensitive belt 1 is transferred to the intermediate transfer belt 61. Transcribed above. By repeating this toner image formation and transfer operation four times,
A four-color superimposed color toner image is formed on the intermediate transfer belt 61. The color toner image on the intermediate transfer belt 61 is transferred by a paper transfer roller 9 as a secondary transfer member onto transfer paper as a recording material sent from a paper feed cassette 8 by a pair of conveyance rollers 82 and 83. . The transfer paper to which the color toner image has been transferred is conveyed to the fixing device 100, and the toner image is fused and fixed. Intermediate transfer belt 61
Is a urethane-based elastic belt, and the driving roller 6
2. Cleaning opposing roller 63, bias roller 6
4. It is suspended in the transfer opposing roller 65 and the tension roller 66 and rotates in the direction B in the figure. The rollers other than the tension roller 66 are fixed in position with respect to the frame of the intermediate transfer unit, and the tension on the belt is applied by the tension roller 66. It is efficient that the tension suspension direction of the tension roller 66 is perpendicular to the line connecting the drive roller 62 and the transfer opposing roller 65.

As described above, the circumference of the intermediate transfer belt 61 changes depending on the environment. As a result, the angle of the belt on the transfer roller entrance side changes, and the belt shrinks particularly in a low-temperature and low-humidity environment, and the gap on the transfer roller entrance side becomes wide. For this reason, poor transfer may occur due to poor adhesion between the transfer paper and the belt. Tension roller 66
Is rotatably supported by one end of a support member 102 separate from the frame of the unit, and the support member 102 is pivotally supported (rotated) in a direction indicated by an arrow about a fulcrum 103 provided at an intermediate portion thereof. Have been. At the end opposite to the tension roller 66 with the fulcrum 103 interposed therebetween, a backup member 101 is provided which is in contact with the back surface of the intermediate transfer belt 61. Since the support member 102 is urged in the counterclockwise direction by a spring (elastic member) 104, the tension roller 66 is pressed against the back surface of the belt, and tension is applied to the intermediate transfer belt 61. When the belt 61 contracts in a low-temperature and low-humidity environment, the tension roller 66 is pushed up inside the belt loop as shown by a broken line in FIG. 2. For this reason, the backup member 101 located on the opposite side with respect to the fulcrum 103 abuts on the back surface of the belt 61 against the tension of the spring 104 around the fulcrum 103 to prevent the gap on the transfer entrance side from expanding. For this reason, the transfer paper P entering the transfer position T from the conveyance path 80 regardless of changes in temperature and humidity is always pressed against the image bearing surface of the belt under ideal pressure and in close contact with the transfer paper P and carried. The toner image can be transferred. If the circumferential length of the belt 61 becomes longer when an environmental change such as a rise in the ambient temperature occurs, the belt expands further outward than the solid line position, but in this case, the gap at the transfer position increases. Since this is not the case, transferability to transfer paper does not decrease. As described above, the tension roller 66 and the backup member 101 abutting on the back surface of the toner image carrier surface of the belt-shaped image carrier 61 are supported by the same member 102 with the fulcrum 103 interposed therebetween. Even if the roller 66 is pushed up inside the loop of the belt, on the contrary, the backup member 101
Protruding outward, it is possible to prevent the gap at the transfer entrance portion from widening, and it is possible to suppress the occurrence of transfer failure.

As shown by the solid line in FIG. 3, the backup member 101 is set so as not to come into contact with the belt in a normal temperature environment, which is advantageous in extending the life of the belt. That is, when the backup member comes into contact with the back surface of the belt-shaped image carrier, the sliding resistance naturally increases, and the probability that the back surface of the belt is damaged increases. When the sliding resistance is increased, the accuracy of the color superposition position of each color toner is reduced. When a flaw is generated on the back surface of the belt, it causes a stripe-like image unevenness corresponding to the flaw. But,
In the present invention, the contact between the backup member 101 and the back of the belt is minimized in order to minimize such an increase in the sliding resistance, so that the above-described disadvantage can be solved. If a material having low sliding resistance is used as the material of the backup member, the resistance during sliding can be further reduced. In addition,
In the case of an intermediate transfer belt having elasticity, transfer failure is likely to occur due to particularly large expansion and contraction due to environmental fluctuation. However, according to the present invention, such a problem can be solved. In the above embodiment, the intermediate transfer belt 6 is used as the belt-shaped image carrier.
However, the present invention is also applicable to a belt-shaped photoconductor used in an image forming apparatus configured to transfer a toner image on a belt-shaped photoconductor to a transfer material at a transfer position. be able to.

[0009]

As described above, according to the present invention, a belt-shaped image carrier which is suspended endlessly by a plurality of rollers and driven to rotate, faces the image-bearing surface of the belt-shaped image carrier at the transfer position. An image forming apparatus comprising: a transfer unit; and a tension roller that presses the back surface of the belt-shaped image carrier on the upstream side of the transfer unit to apply tension to the belt-shaped image carrier. Even when the body expands and contracts due to environmental fluctuations, it is possible to solve the transfer failure caused by the poor adhesion between the belt-shaped image carrier and the transfer paper without changing the gap at the entrance of the transfer position. . That is, in the invention of claim 1, a tension roller,
Since the backup member contacting the back side of the image carrier surface of the belt-shaped image carrier is supported by the same member across the fulcrum, even if the belt is contracted and the tension roller is pushed up, the backup member protrudes, so the transfer entrance It is possible to prevent the gap between the portions from widening, and it is possible to suppress the occurrence of transfer failure. According to the second aspect of the present invention, the backup member is separated from the rear surface of the belt-shaped image carrier under a normal environment. It is possible to prevent the occurrence of streak-like image unevenness corresponding to the back surface damage and scratches, and to prevent the color overlay position accuracy of each color toner from decreasing. According to the third aspect of the present invention, the above configuration is applied to a belt-shaped image carrier made of an elastic material, so that a further excellent effect is exhibited.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a main configuration of the present invention.

FIG. 3 is an explanatory view of a conventional example.

[Explanation of symbols]

Reference Signs List 1 photoreceptor belt, 3 charger, 4 cleaning device, 5 developing device, 7 optical writing unit, 11, 1
2, 13 support roller, 61 intermediate transfer belt (belt-shaped image carrier), 62, 63, 64, 65 support roller,
66 tension roller, 101 backup member,
102 support member, 103 fulcrum, 104 elastic member.

Claims (3)

[Claims] A belt-shaped image carrier suspended endlessly around a plurality of rollers and driven to rotate; a transfer unit facing an image bearing surface of the belt-shaped image carrier at a transfer position; and an upstream side of the transfer unit. A tension roller that presses against the back surface of the belt-shaped image bearing member to apply tension to the belt-shaped image bearing member, wherein the tension roller is pivotally supported at one end while being attached to the other end. A support member that supports a backup member that is in contact with the back side of the image carrier surface of the belt-shaped image carrier, wherein the support member is swingable about a fulcrum located at an intermediate portion, and An image forming apparatus, wherein a tension roller and a backup member are alternately protruded toward a rear surface. 2. The image forming apparatus according to claim 1, wherein the backup member is not in contact with the back surface of the belt-shaped image carrier in a normal environment in which the belt-shaped image carrier has little expansion and contraction. . 3. The image forming apparatus according to claim 1, wherein the belt-shaped image carrier is an intermediate transfer belt made of an elastic material.