Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-06-06
2001-11-20
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S303000, C399S308000
Reexamination Certificate
active
06321052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-forming apparatus as represented by a copying machine, a printer, a facsimile, a compounding machine or the like machine. More specifically, the invention relates to an image-forming apparatus equipped with an endless belt which runs being tightly stretched round plural rolls maintaining a high degree of correctness.
2. Prior Art
An image-forming apparatus such as a copying machine or printer is employing a belt running device in which, as shown in
FIG. 18
, an endless belt
200
runs in a direction of an arrow e being tightly stretched round plural rolls
101
,
102
and
103
, an image (toner image) formed on a photosensitive drum or the like by the electrophotographic system is once transferred onto, and carried by, the surface of the endless belt
200
, and is transferred again onto a recording sheet such as recording paper which is conveyed so as to meet the belt
200
, so that the belt running device works as a so-called intermediate transfer belt mechanism.
It has further been known to use the above belt running device as a photosensitive belt mechanism in which an electrostatic latent image corresponding to the image data and the toner image thereof are formed on the surface of an endless belt by the eletrophotographic system, or as a sheet conveyer/transfer belt mechanism in which a recording sheet onto which the image will be finally transferred is held by being adsorbed by the surface of the endless belt and is conveyed to a transfer position of a photosensitive material drum or the like on which the image is formed, and the recording sheet onto which the image is transferred from the photosensitive material drum or the like is discharged.
In the image-forming apparatus which utilizes the above belt running device, however, there occurs a zigzag phenomenon in which an endless belt
200
runs being shifted in the axial direction of the rolls (corresponds to the direction of width of the belt) or the endless belt
200
runs in a tilted manner being deviated from the direction at right angles with the rolls
101
,
102
and
103
, due to error in the production of belt and rolls for supporting the endless belt, error in the parallelism of rolls, and difference in the tension given to the belt at an end and the other end of each of the rolls. Thus, there often occurs a twisting phenomenon in which the endless belt
200
as a whole runs in a state of being twisted like a “figure 8” as shown in FIG.
19
. When the endless belt runs in a state where the zigzag phenomenon or the twisting phenomenon is occurring, the image is not transferred onto a normal position on the endless belt or on the recording sheet in the case of the zigzag phenomenon. Or, in the case of the twisting phenomenon, a distorted image is transferred from the photosensitive drum onto the endless belt which is the intermediate transfer belt, or the image transferred again onto the recording sheet after once transferred onto the endless belt is skewed to a large extent. The above problems induce a new problem in that the image quality becomes defective due to deviation in the colors, color shade and the like in the color image formed by overlapping toner images of plural colors.
In order to solve such problems, the present applicant has proposed an image-forming apparatus (Japanese Patent Laid-Open No. 260590/1998, etc.) which is so constituted that, when the endless belt is running in a zigzag manner or in a twisted manner, an end of the drive roll for supporting and running the endless belt is displaced upward or downward, or an end of a back-up roll supporting the endless belt at a secondary transfer position where the image is transferred onto the recording sheet is displaced upward or downward by using an eccentric cam mechanism or the like, in order to incline the roll as a whole.
However, when one of the rolls supporting the endless belt is so displaced as to be inclined upward or downward, the tension of the endless belt undergoes a change, resulting in the occurrence of a problem that the belt is twisted due to a change in the tension. Here, the change in the tension is as shown in
FIG. 18
b
; i.e., when an end of the roll
101
is inclined upward (white arrow) Yu, the tension applied to the endless belt portion
200
a
on the side inclined upward becomes larger than that of normal condition and, conversely, when the end of the roll
101
is inclined downward (hatched arrow) Yd, the tension applied to the endless belt portion
200
a
on the side inclined downward becomes smaller than that of normal condition. This problem may similarly occur even in the image-forming apparatus proposed by the present applicant in the Japanese Laid-Open Patent Application No. 2000-075680.
SUMMARY OF THE INVENTION
The present invention provides an image-forming apparatus which, when the running state of the belt is to be adjusted by displacing one of the rolls supporting the endless belt, prevents a twist in the belt that stems from a change in the tension of the endless belt accompanying a displacement of the roll.
The image-forming apparatus of the invention is for forming an image depending on the image data, and includes plural rolls supported so as to freely rotate, an endless belt that runs being tightly stretched round the plural rolls, a belt running adjusting mechanism that adjusts the running state of the endless belt by displacing at least an end of one roll, anda tension correction mechanism that corrects a change in the tension of the endless belt that stems from the operation of the belt running adjusting mechanism for displacing the roll, by displacing a contact member that is in contact with the belt along the direction of width thereof.
In this image-forming apparatus, when the roll is displaced by the belt running adjusting mechanism, the contact member of the tension correction mechanism displaces in a desired direction thereby to correct (cancel) a change in the tension of the endless belt that stems from the displacement of the roll. That is, the tension correction mechanism displaces the contact member in a direction in which the tension decreases when the tension is increased by the operation for displacing the roll, and displaces the contact member in a direction in which the tension increases when the tension is decreased by the operation for displacing the roll.
Any contact member can be used without imitation for the tension correction mechanism provided it is capable of correcting a change in the tension of the belt upon coming in contact with the belt in the direction of width thereof and undergoing the displacement. It is allowable to add a new contact member. Desirably, however, the existing part may be utilized. The existing part may be at least a roll among plural rolls supporting the endless belt and other than the roll displaced by the belt running adjusting mechanism, or may be a blade brought into pressed contact with the endless belt. When the contact member is the roll, an end of the roll may be displaced in a predetermined direction to correct a change in the tension of the belt. When the contact member is the blade, the pressure with which the blade comes into contact with the surface of the belt may be so displaced that the tension of the belt changes to assume a desired state. A cleaning blade may be used as the blade.
The tension correction mechanism may be so controlled as to operate after having detected a change (or a twist) in the tension of the endless belt following the operation for displacing the roll by the belt running adjusting mechanism. Desirably, however, the tension correction mechanism should be controlled to operate being interlocked to the displacing operation of the belt running adjusting mechanism. In this case, it is allowed to increase the range of adjusting the belt running state by the belt running adjusting mechanism and to increase the speed of adjustment in addition to quickly coping with a change in the tension of the belt.
The endless belt may be
Hokari Norio
Hoshino Takashi
Kuroda Mitsuaki
Mitamura Yoshihiko
Nishi Naoto
Brase Sandra
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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