Electrophotography – Having particular structure – Modular or displaceable
Reissue Patent
1996-02-01
2001-05-01
Braun, Fred L (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C271S184000, C271S902000, C399S116000, C399S119000, C399S405000
Reissue Patent
active
RE037157
ABSTRACT:
BACKGROUND OF THE INVENTION
At the current state of the art, input and output devices associated with a computer operate at an increased rate. Accordingly, a high speed of operation is required of a printer which is to be used as an output device. It should be understood that the printer be capable of providing a high resolution for the images being recorded, but it is also necessary that the printer be compact to reduce the space requirement and facilitates its maintenance. If a high speed of printing operation is realized, this does not assure an actual high speed operation if the apparatus is bulky and it takes a long time for trouble-shooting. Another factor required is a low running cost.
When a record in the form of an endless belt is used, the record extending around the belt rollers must be changed from time to time because of degradation or damage thereof. It will be understood that when the record unit is not mounted on the printer or during its stowage or shipment, an unnecessary application of the tension to the record causes a change in the configuration of the record by producing a curvature in its regions which are pressed against the belt rollers. In addition, if the tension is maintained under adverse environment of high temperature, high humidity and/or low temperature and over a prolonged period of time as experienced during the stowage for shipment, an elongation, surface cracks or degradation of quality of the record may result. Accordingly, a tension release mechanism is provided to avoid these problems in order to release the action of the tensioning mechanism during the replacement, stowage or shipment of the record.
As the record in the form of an endless belt moves along a loop, a static electricity may be produced between the record and a member which supports it. The static electric tends to attract the record to the support member, interfering with a smooth movement of the record.
When a photosensitive member comprises an endless belt which is supported by a drive roller and one or more follower rollers, each of which has a peripheral length that is reduced as compared with the full perimeter of the belt, the space occupied by the photosensitive member within the printer can be reduced, thus resulting in a reduced size of the arrangement. However, with this arrangement, the photosensitive member will have a reduced radius of curvature in its region of contact with the roller or rollers and a slack may be produced in the photosensitive belt between adjacent rollers in a selected region. Therefore, the locations for the exposure station, the charger and the developing unit must be carefully chosen. Specifically, the exposure station must be located in a region of the record where a fluctuation in the running speed of the photosensitive surface is low and having an increased radius of curvature. The developing unit must be located so as to minimize a variation in the developing gap. Finally, the location for the charger must be chosen in a region of the record which is free from a rapid variation in its configuration and where a variation in the position of the photosensitive surface is reduced.
To form a sharp image, it is essential that an electrostatic latent image be formed in accurate conformity to image information. At this end, it is necessary that the surface of the record which has been uniformly charged as a result of a corona discharge from the charger be rendered conductive only in those regions which are exposed and the electric potential of such regions be brought as close to the ground potential or zero volt as possible.
In the above case, it is necessary that the record be connected to a grounding brush in an electrically effective and stable manner.
As the record in the form of the endless belt is driven by the roller, a meandering and an offsetting phenomenon of the belt may occur in which the record shifts in a direction perpendicular to the direction of the drive applied, and which is attributable to a difference in the magnitude of the tension applied to the record by the roller, as measured between the opposite axial ends of the roller, or to an error in the parallelism between the shafts of the rollers. Such phenomenon must be prevented since otherwise an image formed on the record or to be transferred onto a transfer sheet becomes offset.
In one arrangement which is used to prevent this phenomenon, the roller or rollers which support and drive the record in the form of the endless belt is provided with flanges which control the edges of the record to limit the meandering and offsetting of the belt. In another arrangement, at least one of the rollers which support and drive the endless belt is provided with an automatic aligning mechanism including an aligning shaft which utilizes an offsetting force of the belt produced, as the offset occurs to cause the belt to be driven in the oppose direction from the direction of initial off-setting. In the first mentioned arrangement, stresses are produced in the edge of the record as a result of an offsetting action, and produces a deformation in the edge thereof, thus substantially degrading the durability of the record and the reliability of the printer. Hence, when this arrangement is used, the record must have a base of an increased thickness to increase the resistance to deformation. Alternatively, the offsetting action of the belt must be diminished. However, an increased thickness of the base of the record is undesirable since it causes a reduction in the bonding strength of the record layer to the base and an increase in the belt tension as a result of increasing bending stresses. If one elects the choice to diminish the offsetting action of the belt, a delicate adjustment of the tension in the belt is required, resulting in a completed arrangement which requires a high precision. In the second arrangement mentioned above, a roller assembly of a high accuracy is necessary to permit a reliable automatic aligning operation. Again, there results a complex and expansive arrangement which is of an increased size.
If an offset control is performed during the time when a transfer operation is being performed, the movement of the record and the transfer sheet in the respective given directions will be disturbed, disadvantageously producing back stripes or blurring of transferred image. Hence, the offset control should be made when no transfer operation takes place or when the transfer charger is inoperative.
To control an offsetting of the belt, the use of some means which constrains the lateral edge of the belt involves the likelihood that such edge may be deformed or damaged.
The printer according to the invention adopts a magnetic brush developing process in which a magnetic developer is used to convert an electrostatic latent image into a visual image. As is well recognized, in a magnetic brush development process, a developing roller is formed by a non-magnetic cylindrical sleeve and a magnet or magnets disposed inside the sleeve. By producing a relative movement between the sleeve and the magnets, a magnetic brush is formed on the surface of the sleeve for sliding contact with the latent image to convert it into a visual image. The magnetic brush developing process is most popular among the developing processes of dry type in view of its practical feasibility, and is extensively used in copying machines, printers, plotters, and recording systems of facsimile systems.
In the magnetic brush developing process, the toner concentration must be uniform and the height of tuft of the magnetic brush must be substantially constant in order to enable a developing effect free from non-uniformity. Where two-component developer is used, a sufficient agitation must be made to achieve a uniform toner concentration. To form a tuft of the magnetic brush which has a constant height, there must be provided a doctor blade which is mounted at a given spacing from the sleeve surface, thus limiting the developer to a given height as it is formed on the sleeve.
In the prior art practice, the spacing betwe
Ikeda Kunihiko
Kodama Yutaka
Niro Masaichi
Shimura Akira
Suzuki Shigeru
Braun Fred L
Cooper & Dunham LLP
Ricoh & Company, Ltd.
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