Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2000-09-25
2001-09-04
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C399S055000, C430S120400
Reexamination Certificate
active
06285840
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a development system as used in xerography, and more particularly concerns a “jumping” development system in which toner is conveyed to an electrostatic latent image by an AC field.
BACKGROUND OF THE INVENTION
In a typical electrostatographic printing process, such as xerography, a photoreceptor is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoreceptor is exposed to a light image of an original document being reproduced. Exposure of the charged photoreceptor selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoreceptor corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoreceptor, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoreceptor. The toner powder image is then transferred from the photoreceptor to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. After each transfer process, the toner remaining on the photoconductor is cleaned by a cleaning device.
One specific type of development apparatus currently used in high-quality xerography is known as a hybrid jumping development (HJD) system. In the HJD system, a layer of toner is laid down evenly on the surface of a “donor roll” which is disposed near the surface of the photoreceptor. Biases placed on the donor roll create two development fields, or potentials, across the gap between the donor roll and the photoreceptor. The action of these fields causes toner particles on the donor roll surface to form a “toner cloud” in the gap, and the toner in this cloud thus becomes available to attach to appropriately-charged image areas on the photoreceptor.
The present invention is a control system for print quality for such a hybrid jumping development system, the control system having as inputs measured reflectivities of test patches of predetermined target halftone densities, such as a 50% halftone screen and an 87.5% halftone screen, and having as outputs changes in the DC bias and AC amplitude of the development field, as well as the initial charging voltage on the photoreceptor and the power associated with an imaging device, such as a laser, which creates the image on the photoreceptor.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 4,610,531 discloses the basic concept of jumping development with an AC field set up between a donor member and a photoreceptor.
U.S. Pat. No. 5,390,004 discloses a control system for a xerographic printing system in which the reflectivity of a set of test patches is measured, and the reflectivities are fed into a fuzzy-logic control system for the xerographic parameters.
U.S. Pat. No. 5,402,214 discloses a control system for a xerographic printing system in which the reflectivity of a test patch is measured, and the DC bias of a field associated with the development unit is adjusted accordingly. When the DC bias is caused to exceed a predetermined maximum, fresh developer is added to the primary developer supply.
U.S. Pat. No. 5,890,042 discloses a hybrid jumping development system, in which a donor roll is loaded with a layer of toner particles by a magnetic roll which conveys toner which adheres to carrier granules.
U.S. Pat. No. 6,035,152 discloses a control system for a xerographic printing system in which the reflectivity of a set of test patches is measured, and the reflectivities are fed into a control system for the xerographic parameters.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided, in an electrostatographic development system wherein toner is conveyed from a donor member over a development gap to a charge receptor by an AC development field in the development gap, a method comprising the following steps. Actual reflectivities are measured of a first test patch having a first target halftone density, and a second test patch having a second target halftone density, thereby determining a first error and a second error respectively. If the first error and the second error have the same sign, there is determined a first change in DC bias which will substantially cure the first error and a second change in DC bias which will substantially cure the second error. The DC bias is then altered according to the smaller of the first change in DC bias and second change in DC bias.
In accordance with another aspect of the present invention, there is provided, in an electrostatographic development system wherein toner is conveyed from a donor member over a development gap to a charge receptor by an AC development field in the development gap, a method comprising the following steps. Actual reflectivities are measured of a first test patch having a first target halftone density, and a second test patch having a second target halftone density, thereby determining a first error and a second error respectively. If the first error and the second error have the same sign, there is determined a first change in DC bias which will substantially cure at least one of the first error and the second error. If the first error and the second error have different signs, there is determined a change in a parameter which will substantially cure at least one of the first error and second error, the parameter being one from a group consisting of DC bias, amplitude of AC component, initial potential on the charge receptor, and power associated with imagewise discharge of the charge receptor.
REFERENCES:
patent: 4610531 (1986-09-01), Hayashi et al.
patent: 5390004 (1995-02-01), Hopkins
patent: 5402214 (1995-03-01), Henderson
patent: 5890042 (1999-03-01), Wong et al.
patent: 5937227 (1999-08-01), Wong et al.
patent: 6035152 (2000-03-01), Craig et al.
patent: 6198886 (2001-03-01), Brewington
Budnik Roger W.
Kauffman Scott L.
Maier Richard M.
Pacer James M.
Chen Sophia S.
Hutter R.
Xerox Corporation
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