Apparatus and method for cleaning a donor roll

#This invention relates to an apparatus for maintaining print quality in xerographic development systems by employing an occasional reverse bias donor roll cleaning cycle.

#Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the photoconductive surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam, a light emitting diode (LED) source, or 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. 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 (IOI) processing, superimposes toner powder images of different color toners onto a photoreceptor prior to the transfer of the composite toner powder image onto a substrate. While the IOI process provides certain benefits, such as a compact architecture, there are several challenges to its successful implementation. For instance, the viability of printing system concepts, such as IOI processing, require development systems that do not interact with a previously toned image. Since several known development systems, such as conventional magnetic brush development and jumping single-component development, interact with the image on a receiver, a previously toned image will be scavenged by subsequent development if interacting development systems are used. Thus, for the IOI process, there is a need for scavengeless or noninteractive development systems.

#Other features of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which:

#FIG. 1 is a schematic illustration of a printing apparatus incorporating the inventive features of the present invention.

#FIG. 2 is a schematic illustration of a development station incorporating the present invention.

#While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

#For a general understanding of the features of the system, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements.

#Referring now to the drawings, there is shown a single pass multi-color printing machine in FIG. 1. This printing machine employs the following components: a photoconductive belt 10, supported by a plurality of rollers or bars, 12. Photoconductive belt 10 is arranged in a vertical orientation. Photoconductive belt 10 advances in the direction of arrow 14 to move successive portions of the external surface of photoconductive belt 10 sequentially beneath the various processing stations disposed about the path of movement thereof. The photoconductive belt 12 has a major axis 120 and a minor axis 118. The major and minor axes 120, 118 are perpendicular to one another. Photoconductive belt 10 is elliptically shaped. The major axis 120 is substantially parallel to the gravitational vector and arranged in a substantially vertical orientation. The minor axis 118 is substantially perpendicular to the gravitational vector and arranged in a substantially horizontal direction. The printing machine architecture includes five image recording stations indicated generally by the reference numerals 16, 18, 20, 22, and 24, respectively. Initially, photoconductive belt 10 passes through image recording station 16. Image recording station 16 includes a charging device and an exposure device. The charging device includes a corona generator 26 that charges the exterior surface of photoconductive belt 10 to a relatively high, substantially uniform potential. After the exterior surface of photoconductive belt 10 is charged, the charged portion thereof advances to the exposure device. The exposure device includes a raster output scanner (ROS) 28, which illuminates the charged portion of the exterior surface of photoconductive belt 10 to record a first electrostatic latent image thereon. Alternatively, a LED may be used.