Electrophotography – Image formation – Development
Reexamination Certificate
1999-11-12
2001-03-27
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Development
C399S291000
Reexamination Certificate
active
06208824
ABSTRACT:
BACKGROUND OF THE INVENTION
Generally, an electrophotographic printing machine includes a photoconductive member which is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to an optical light pattern representing the document being produced. This records an electrostatic image on the photoconductive member corresponding to the informational areas contained within the document. After the electrostatic image is formed on the photoconductive member, the image is developed by bringing a developer material into effective contact therewith. Typically, the developer material comprises toner particles bearing electrostatic charges chosen to cause them to move toward and adhere to the desired portions of the electrostatic image. The resulting physical image is subsequently transferred to a copy sheet. Finally, the copy sheet is heated or otherwise processed to permanently affix the powder image thereto in the desired image-wise configuration.
Development may be interactive or non-interactive depending on whether toner already on the image may or may not be disturbed or removed by subsequent development procedures. Sometimes the terms scavenging and non-scavenging are used interchangeably with the terms interactive and non-interactive. Non-interactive development is most useful in color systems when a given color toner must be deposited on an electrostatic image without disturbing previously applied toner deposits of a different color, or cross-contaminating the color toner supplies. This invention relates to such image-on-image, non-interactive development.
U.S. Pat. No. 4,868,600 to Hays et al. discloses a non-interactive development system wherein toner is first developed from a two-component developer onto a metal-cored donor roll and thereafter disturbed into a powder cloud in the narrow gap between the donor roll and an electrostatic latent image existing on the photoreceptor surface. Development fields created between the donor roll core and the electrostatic latent image harvest some of the toner from the cloud onto the electrostatic image, thus developing it without physically disturbing any previously deposited toner layers. In this method the powder cloud generation is accomplished by thin, AC biased wires strung across the process direction and within the development gap. The wires ride on the toner layer and are biased relative to the donor roll core.
U.S. Pat. No. 4,557,992 to Haneda et al. describes a non-interactive magnetic brush development method wherein a two component developer consisting of magnetically soft carrier materials is carried into close proximity to an electrostatic image and caused to generate a powder cloud by the developer motion due, in part, by the inclusion of an AC voltage applied across the gap between the developer sleeve and the ground plane of the electrostatic image. Cloud generation directly from the surfaces of a two component developer avoids many of the problems created by wires. However, in practice such methods have been speed limited by their low toner cloud generation rate.
U.S. Pat. No. 5,409,791 to Kaukeinen et al. describes a non-interactive magnetic brush development method employing permanently magnetized carrier beads operating with a rotating multipole magnet within a conductive and nonmagnetic sleeve. Magnetic field lines form arches in the space above the sleeve surface creating chains of carrier beads which follow these magnetic field lines. The carrier chains are held in contact with the sleeve and spacing between the developer sleeve and the photoreceptor surface is sufficiently large to maintain the carrier bead chains out of direct contact with the photoreceptor. As the core rotates in one direction relative to the sleeve, the magnetic field lines beyond the sleeve surface rotate in the opposite sense, moving chains in a tumbling action, which transports developer material along the sleeve surface. The strong mechanical agitation very effectively dislodges toner particles generating a rich powder cloud, which can be developed to the adjacent photoreceptor surface under the influence of development fields between the sleeve and the electrostatic image. U.S. Pat. No. 5,409,791 is hereby incorporated by reference.
It has been a problem non-interactive development methods to achieve good solid region development while maintaining good fine line development and vice versa. Many non-interactive development methods function by generating a powder cloud in the gap between the photoreceptor and another member which serves as a development electrode. It is generally observed that this gap should be as small as possible, on the order of 0.010 inches or less. Generally, the larger the gap, the larger become certain image defects in the development of fine lines and edges. As examples of these defects: lines do not develop to the correct width, lines near solid areas are distorted, and the edges of solids are softened, especially at corners. It is understood that these defects are the result of lateral components of the electric field lines occurring due to the charge patterns existing on the imagewise discharged photoreceptor. Electrostatic field lines emanating from the photoreceptor surface reach up from the latent electrostatic image patterns of lines and at the edges of solid areas and arch back toward the adjacent photoreceptor regions. These lateral components of the electric field lines result in displacement from the intended pathway of the charged toner particles and in incomplete development of the latent electrostatic images. Defects due to the electrostatic field arches are less serious in interactive two component development subsystems because toner particles can be delivered through these field arches by carrier particles. Nor are they an issue in interactive single component development because a strong, cross-gap AC field is superposed which impart sufficient toner particle velocity toward the photoreceptor surface to overcome the aforementioned field arch patterns.
SUMMARY OF THE INVENTION
The present invention obviates the problems noted with achieving good solid region development while maintaining good fine line development, by providing An apparatus for non-interactive, dry powder development of electrostatic Images composed of solid areas and fine lines areas on an imageable surface including a housing containing developer material; a magnetic member, spaced a predefined distance from said image, for transporting said developer material from said housing to develop solid areas of said image, said magnetic roll including an magnetic core and a cylindrical sleeve enclosing and rotating about said magnetic core; and a donor member, adjacent to said magnetic roll and spaced from the image receiving member and adapted to transport marking particles to a development zone adjacent the image receiving member; an electrode positioned in the development zone between the image receiving member and the donor member; a voltage supply for electrically biasing said electrode during a developing operation with an alternating current to detach marking particles from said donor member, forming a cloud of marking particles in the development zone, and developing fine line areas of said image from the cloud.
REFERENCES:
patent: 4297972 (1981-11-01), Hwa
patent: 4557992 (1985-12-01), Haneda et al.
patent: 4868600 (1989-09-01), Hays et al.
patent: 5010368 (1991-04-01), O'Brien
patent: 5031570 (1991-07-01), Hays et al.
patent: 5144371 (1992-09-01), Hays
patent: 5276488 (1994-01-01), Schmidlin
patent: 5409791 (1995-04-01), Kaukeinen et al.
patent: 5697035 (1997-12-01), Mashtare et al.
patent: 5907755 (1999-05-01), Takuma et al.
patent: 5911098 (1999-06-01), Gyotoku et al.
patent: 60-061774 (1985-04-01), None
Mashtare Dale R.
Snelling Christopher
Bean, III Lloyd F.
Beatty Robert
Xerox Corporation
LandOfFree
Apparatus for non-interactive electrophotographic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for non-interactive electrophotographic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for non-interactive electrophotographic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2504275