Electrophotography – Cleaning of imaging surface – Fibrous brush
Utility Patent
1999-09-28
2001-01-02
Beatty, Robert (Department: 2852)
Electrophotography
Cleaning of imaging surface
Fibrous brush
Utility Patent
active
06169872
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to an electrostatographic printer or copier, and more particularly concerns a flexible belt cleaning apparatus used therein.
In an electrophotographic application such as xerography, a charge retentive surface (ie., photoconductor, photoreceptor or imaging surface) is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. Contacting the latent image with a finely divided electrostatically attractable powder referred to as “toner” develops the image. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. This process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be image-wise discharged in a variety of ways. Ion projection devices where a charge is image-wise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces Additionally,paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed on automatic xerographic devices utilizes a brush with soft conductive fiber bristles or with insulative soft bristles which have suitable triboelectric characteristics. While the bristles are soft for the insulative brush, they provide sufficient mechanical force to dislodge residual toner particles from the charge retentive surface. In the case of the conductive brush, the brush is usually electrically biased to provide an electrostatic force for toner detachment from the charge retentive surface. The fixed radius of commonly used brushes can limit cleaning applications. Toner particles adhere to the fibers (ie. bristles) of the brush after the charge retentive surface has been cleaned. The process of removing toner from these types of cleaner brushes can be accomplished in a variety of ways. Typically, brush cleaners use flicker bars to provide the detoning function which may not sufficiently clean the particles from the brush fibers.
Although electrostatic brush cleaners have proved quite successful, high volume electrostatographic printer or copier applications require higher process speeds and the ability to clean with production color requirements. These requirements include high process speeds, higher toner input masses into the cleaner, better cleaning in a color process than in black and white, and the production printing desire to print to the edge of the page, which leaves untransferred toner densities around the edge of the document which must be cleaned in a single pass through the cleaner.
The cleaning ability of an electrostatic brush cleaner is a function of the number of fibers which are available to clean toner from the photoreceptor and the quantity of toner which can be held by each fiber, as well as the charge on the toner particles and the bias on the fibers. The toner charge and the brush bias can be controlled by preclean corona treatment and brush bias power supplies The number of fibers available to clean toner from the photoreceptor, known as fiber strikes, is a function of brush speed, brush interference to the photoreceptor, brush size, weave density and pile height. The amount of toner which can be held on the tip of a fiber during the cleaning process is a function of the fiber diameter, interference to the photoreceptor, toner charge and fiber bias. As a patch of toner enters the cleaning nip the brush fibers mechanically dislodge the toner from the photoreceptor and electrostatically attract and adhere the toner particles to the fibers. As the fiber proceeds through the cleaning nip, more toner particles are cleaned and electrostatically adhere to the fiber forming what is known as a match head. As the thickness of the match head increases, the electrostatic forces available to hold additional charged toner particles decreases. This is due to the physical spacing of the particles from the biased fiber and the like charge of the toner particles already adhered to the fiber. The match head will cease to increase in size when the electrostatic attractive forces are no longer strong enough to hold dislodged toner particles. At this point the fiber has reached its toner capacity and no further cleaning takes place. Additional toner remaining on the photoreceptor surface will pass through the cleaning nip creating a cleaning failure if all of the available fibers have reached their toner holding capacity.
For an electrostatic brush cleaner which has been optimized for toner charge and brush bias, and which has exceeded the capacity of the fibers to clean toner due to the level of the toner input to the cleaner, the only remaining remedy is to increase the number of fibers available for cleaning. This may be accomplished by adding additional electrostatic brushes biased to the appropriate polarity. Although a multiple brush cleaner would, with enough brushes, be able to clean any desired toner input, such a cleaner would require more space along the photoreceptor belt than would be available and would create additional drag on the photoreceptor belt. To meet high volume printer and copier applications, an electrostatic belt cleaner, which will provide enhanced cleaning capability within available space requirements and without imposing excessive photoreceptor belt drag is needed.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 3,795,025 to Sadamitsu discloses an apparatus for cleaning an electrophotographic photoreceptor. The apparatus includes a pair of brushes rotating in opposite directions. The rotating brushes are enclosed in a brush box and a vacuum system removes toner from the brushes and the inside of the brush box.
U.S. Pat. No. 4,320,774 to Rogers discloses a mechanical toothbrush with a brush drive unit coupled to a rotating device such as an electric motor. The brush drive unit alternately rotates a first belt brush in a first direction while maintaining a second belt brush in a substantially fixed position and rotates the second belt brush in a second direction while maintaining the first belt brush in a substantially fixed position.
U.S. Pat. No. 4,457,615 to Seanor discloses a belt brush constructed of alternate conductive and non-conductive segments, which causes one conductive segment which is being used for charging to be electrically isolated from another conductive segment which is being used for cleaning. Different voltages can be simultaneously applied to each of the segments without adversely affecting the operation of the other. A single detoning roller is provided to remove toner particles from the brush.
U.S. Pat. No. 4,878,093 to Edmunds discloses a dual roll cleaning apparatus. A cleaning housing, which is connected to a vacuum, supports an upstream brush roll cleaner and a downstream foam or poromeric roll cleaner. The brush roll cleaner provides a primary cleaning function, while the foam roll cleaner provides a secondary back up cleaning function.
U.S. Pat. No. 4,999,6
Beatty Robert
Robb Linda M.
Xerox Corporation
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