Metal working – Method of mechanical manufacture – Roller making
Reexamination Certificate
2001-01-16
2002-07-02
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Roller making
C492S047000
Reexamination Certificate
active
06412175
ABSTRACT:
This invention relates generally to a development apparatus used in ionographic or electrophotographic imaging and printing apparatuses and machines, and more particularly is directed to donor rolls for a development system.
One common element utilized in machinery is a roll. The roll typically includes a body and two journals or stems which extend outwardly from opposed ends of the body. Bearings, either in the form of journals or rolling element bearings, permit the rotatable mounting of the rolls onto a frame of the machinery. The bearings are typically mounted to the outer periphery of the journals of the roll. These rolls, particularly those for use in precision equipment, may be expensive and difficult to manufacture. One particular type of machinery that utilizes rolls to a great extent is that of a printing machine. In a printing machine, a substrate typically in the form of a paper roll or cut paper sheets are fed through various steps in the printing process. The substrate is guided along a paper path by rolls and processing steps are often applied to the substrate through the use of rolls.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam or light flashed upon an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed.
Two component and single component developer materials are commonly used for development. A typical two component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive surface, the toner powder image is subsequently transferred to a copy sheet, and finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
The electrophotographic marking process given above can be modified to produce color images. One color electrophotographic marking process, called image-on-image processing, superimposes toner powder images of different color toners onto the photoreceptor prior to the transfer of the composite toner powder image onto the substrate. While the image on image process is beneficial, it has several problems. For example, when recharging the photoreceptor in preparation for creating another color toner powder image, it is important to level the voltages between the previously toned and the untoned areas of the photoreceptor. Moreover, the viability of printing system concepts such as image-on-image processing usually requires development systems that do not scavenge or interact with a previously developed image. Several known development systems, such as conventional magnetic brush development and jumping single component development, are interactive with the image bearing member, making them unsuitable for use with image-on-image processes.
One particular version of a scavengeless development system uses a plurality of electrode wires closely spaced from a toned donor roll. The donor roll is loaded with toner using conventional two component magnetic brush development. An AC voltage is applied to the wires to generate a toner cloud in the development zone. The electrostatic fields from the latent image attract toner from the toner cloud to develop the latent image.
Since hybrid scavengeless development relies on a continuous, steady toner powder cloud at the nip between the latent image and the donor roller, the speeds at which the rollers operate are significantly higher and the accuracy requirements are much more precise.
The purpose and function of scavengeless development are described more fully in, for example, U.S. Pat. No. 4,868,600 to Hays et al., U.S. Pat. No. 4,984,019 to Folkins, U.S. Pat. No. 5,010,367 to Hays, or U.S. Pat. No. 5,063,875 to Folkins et al, these references are totally incorporated herein by reference.
For proper operation of a donor roll in a hybrid scavengeless development, the diameter tolerance, runout and surface finish requirements of the donor roll are very critical and require very precise dimensions.
Furthermore, donor rolls typically have a long length and a small diameter. For example, donor rolls may have a length of, for example, 18 to 24 inches and a diameter from 1 to 1½ inches.
Precision rolls, whether for use as a donor roll or for another purpose, are typically made by machining a body from a solid cylindrical stock. To provide for journals at opposing ends of the rolls, typically a hole or counterbore is machined in each of the opposed faces of the cylindrical body. Journals are machined from smaller cylindrical stock and are cut to length and fitted into the counterbored apertures in the opposed ends of the cylindrical body.
The processes of counterboring a solid body, of machining cylindrical journals and of inserting the cylindrical journals into the body have several major disadvantages, particularly when used to manufacture a large quantity of high-quality, precision rolls.
Precision rolls, such as those for a donor roll, require a outer periphery that has precision size, roundness and runout requirements with respect to the journals to which bearings are mounted to provide for rotation of the roll. As the roll is rotated about the journals of the roll, the outer periphery of the roll may have an eccentric pattern or runout with respect to the mounting journals. For the proper operation of a donor roll, the runout requirements may be as precise as to be within 0.000,025 meters (25 microns). Obtaining such a low runout is very difficult when utilizing the process steps of counterboring of the body and inserting journals in the counterbores.
Runout measured between the solid body periphery and the counterbore inside diameter must be added to the roundness measured of the solid body as well as to the roundness measured of the journals to accumulate the runout of the assembled roll.
Donor rolls in hybrid scavengeless development systems require certain semiconductive electrical properties for the proper formation of the toner cloud required to develop the latent image. Such semiconductive electrical properties are obtained either through the use of an anodized coating over an aluminum donor roll or by the use of a ceramic coating placed over an aluminum donor roll. A more complete description of the ceramic coating for a donor roll is described more fully for example in U.S. Pat. No. 5,473,418 to Kazakos et al.
The use of a ceramic coating greatly compounds the difficulty in providing an accurate precision donor roll. The application of a ceramic coating to an aluminum donor roll is very expensive in that the ceramic material itself is somewhat expensive and in the fact that the coating process for applying a coating of ceramic to a donor roll is very expensive. A typical process for the application of the ceramic is a thermal spray process. Such thermal spray processes include for example a plasma spray. A thermal spray process causes oxides to form in the ceramic layer.
The oxides form in a somewhat unpredictable manner. Oxides in the ceramic coating result in porosity within the ceramic layer. The oxides produced through the thermal spray process cause porosity in the ceramic layer. This porosity creates problems in obtaining the required surface finish for proper operation of a ceramic roll. Further, the porosity in the surface may lead to arcing between the wires in the donor roll.
The oxides formed in the thermal spray process of the ceramic coating determine or assist in determining the electrical properties, namely the time constant, of the donor roll. Inconsistencies within a donor roll and from donor roll based upon the pr
Echols P. W.
Jimenez Marc
Ryan Andrew D.
Xerox Corporation
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