Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-04-28
2001-07-31
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C198S813000, C474S101000
Reexamination Certificate
active
06269231
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to belt tension variation minimizing mechanisms, and more particularly to an electrostatographic reproduction machine having the same for an economical and effective tensioning of closed loop or endless belt components, such as a photoreceptor belt or intermediate transfer belt of the reproduction machine.
BACKGROUND OF THE INVENTION
Electrostatographic marking is a well known and commonly used method of copying or printing documents. Electrostatographic marking is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges so as to create an electrostatic latent image of the desired document on the photoreceptor's surface. Toner particles are then deposited onto that latent image so as to form a toner image. That toner image is then transferred from the photoreceptor onto a substrate such as a sheet of paper. The transferred toner image is then fused to the substrate, usually using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image. The foregoing broadly describes a conventional black and white electrostatographic reproduction machine.
Electrostatographic marking can also produce color images by repeating the above process once for each color of toner that is used to make the composite color image. This can be accomplished using any one of a number of different IOI (image-on-image) processes including, for example, what is referred to as Tandem Xerography, or what is referred to as the REaD (Recharge, Expose, and Develop, Image On Image).
In the Tandem Xerographic process, a plurality of different color toner image forming Xerographic modules each form a color separation toner image of a multicolor original image, and then transfer such color separation images in registration onto an intermediate transfer belt (ITB), for example.
In the REaD process, a charged photoreceptive surface is exposed to a light image which represents a first color, say black. The resulting electrostatic latent image is then developed with black toner particles to produce a black toner image. The charge, expose, and develop process is repeated for a second color, say yellow, then for a third color, say magenta, and finally for a fourth color, say cyan. The various color toner particles are placed on the photoreceptor in superimposed registration so that a desired composite color image results. That composite color image is then transferred and fused onto a substrate.
The REaD process as such can be implemented in a single pass reproduction machine wherein the composite final image is produced in a single pass of the photoreceptor through the machine. It can also be implemented in a multiple pass, for example four passes, of the photoreceptor, wherein only one color toner image is produced during each pass of the photoreceptor through the machine and wherein the composite color image is transferred and fused during the fourth pass.
In an electrostatographic reproduction machine employing any of the processes described above, the endless photoreceptor when a belt, or the endless intermediate transfer belt (ITB), is initially tensioned and set to a tension setting as desired, but ordinarily will experience variations from each such desired tension setting. As can be expected, such variations in the tension are likely to cause registration errors, and may even lead to slack in the belt, and thus adversely affect the life of the belt.
Conventional tensioning mechanisms use a tensioning roller to apply a force in the direction of the bisectrix to the angle of wrap of the belt. The force is conventionally applied by a compressed loading spring. Variations from a desired tension setting are ordinarily caused by movement of the tensioning roller due to two problems, namely: (a) the finite stiffness of the loading spring, and (b) changes in wrap angle of the belt over the tensioning roller. The first problem is counteracted by one current technology method, which generates the force without an associated stiffness; this is accomplished by using either a dead weight or an electromagnetic loading device. These measures do not counteract tension variations due to the second problem.
Another possible technology is to provide the tensioning by means of an active servo whereby the force decreases appropriately as the tensioning roller moves outward. This is an effective technology solution to the problem but it has the disadvantage of raising cost issues.
It should be recognized that the second problem becomes more serious in designs where the angle of wrap on the tensioning roller is relatively small, which is typically the case in small machines such as office reproduction machines.
There is therefore a need for a belt tension variation minimizing mechanism, and for an electrostatographic reproduction machine having the same so as to provide economical and effective tensioning of closed loop or endless belt components, such as a photoreceptor belt or intermediate transfer belt of the reproduction machine.
SUMMARY OF THE INVENTION
In accordance to the present invention, there is provided a tensioning mechanism for minimizing tension variations in a moveable endless belt having a desired tension setting and includes a moveable member for mounting transversely to a direction of movement of the moveable endless belt and into contact with the moveable endless belt; a first assembly including a first rotatable arm having a first end connected to the moveable member, and a second end coupled to a first pivot; and a second assembly including a tensioning force applying roller, and a second rotatable arm having a first end connected to the moveable member and a second end coupled to a second pivot. The second rotatable arm forms a lap angle with the first rotatable arm, and the tensioning force applying roller applies a tensioning force to the moveable member having a force direction that is non-orthogonal relative to the direction of movement of the moveable endless belt, thereby tensioning the moveable endless belt and minimizing variations from the desired tension setting of the moveable endless belt.
REFERENCES:
patent: 5585892 (1996-12-01), Hayano et al.
patent: 5991575 (1999-11-01), Okiyama et al.
patent: 6055398 (2000-04-01), Costanza et al.
patent: 6085053 (2000-07-01), Saeki
patent: 6101353 (2000-08-01), Yu et al.
patent: 6137974 (2000-10-01), Williams et al.
Castelli Vittorio R.
Polatkan Osman T.
Nguti Tallam I.
Royer William J.
Xerox Corporation
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