Electricity: measuring and testing – Electrostatic field – Using modulation-type electrometer
Reexamination Certificate
2001-01-29
2002-12-03
Oda, Christine K. (Department: 2858)
Electricity: measuring and testing
Electrostatic field
Using modulation-type electrometer
C324S072500
Reexamination Certificate
active
06489777
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to system for purging a modulator assembly of electrostatic voltmeters. More particularly, the invention is directed to self-enhanced purging of a modulator and probe for electrostatic voltmeters for use in electrophotographic processes.
In an electrostatic imaging process, six stages are utilized to produce an archival quality image on a copy sheet, such as a page of plain paper. These steps are practiced upon and around a photoreceptor element (P/R), such as a photoreceptor belt or drum, hereinafter simply “photoreceptor.” The imaging stages comprise: (1) photoreceptor charging, (2) image formation or exposure, (3) image development, (4) image transfer from the photoreceptor to a copy sheet, (5) fixing of the image on the copy sheet, and (6) restoring the photoreceptor. The process proceeds in a continuous loop and, if a color image is desired, steps (1), (2) and (3) are repeated in sequential stations around the photoreceptor for toner particles of black, magenta, yellow and cyan prior to completing steps (4) through (6) of image transfer, image fixing and restoring the photoreceptor surface to a clean and neutral state.
The second and third process steps of latent image formation on the photoreceptor and image development by applying a desired quantity of toner at a precise location on the photoreceptor latent image require accurate control of an electrostatic charge on the photoreceptor. This can be accomplished by electrostatic charge monitoring and a feedback loop. In particular, in a high speed image development process the toner particles are highly charged and coulomb forces are used to attach charged toner particles to a latent image on the photoreceptor. The magnitude and location of toner deposit is critical to a successful high speed electrophotographic process and thus accurate monitoring and modulation of an electrostatic field around the photoreceptor is essential. In this, electrostatic voltmeters, such as application specific integrated circuit electrostatic voltmeters, measure electrostatic fields or potential without current flow through the electrostatic voltmeter. A typical electrostatic voltmeter includes a modulator assembly having a sensor electrode or probe and a modulator for modulating the electrostatic field that is being measured in relation to the sensor. In this, the modulator assembly is the sensing element of the electrostatic voltmeter. Electrostatic voltmeters of this type are disclosed in U.S. Pat. No. 5,212,451 to Werner, issued May 18, 1993, and U.S. Pat. No. 5,489,850 to Werner et al., issued Feb. 6, 1996, both of which are assigned to the Xerox Corporation and of common assignment with the subject application. The disclosures of these prior art patents are hereby incorporated by reference as though set forth at length.
One problem with current electrostatic voltmeter modulator assemblies in electrophotographic systems is that charged toner particles, which are used for developing electrostatic latent images, tend to be attracted to the modulator and/or probe. Moreover, paper dust, photoreceptor drive surface fines, and other air borne debris within an electrophotographic cabinet tend to be attracted to the modulator and/or electrostatic probe. Air borne contaminants tend to cause errors in the measurement of an electrostatic field.
Such errors are referred to as “drift errors”. One solution to this problem is to provide an air purge in the electrophotographic systems to prevent charge toner particles from getting into the modulator assembly and proximate to the probe by creating a positive air pressure around the modulator and probe. Specifically, an air purge path is provided at the front of the modulator base so that a positive air pressure is created across a sensing aperture in a front plate attached to the modulator base to purge toner particles and other contaminants from the modulator and probe. Such an approach to purging contaminants from the modulator and probe is disclosed in co-pending application Ser. No. 09/770,242 of Werner, title “MODULATOR BASE FOR ELECTROSTATIC VOLTMETER MODULATOR ASSEMBLY”, filed on the same date as the subject application, assigned to the Xerox Corporation and of common assignment with the subject application. The disclosure of the aforementioned co-pending application is hereby incorporated by reference as though set forth at length.
It has, however, been found that contaminants and charged toner particles tend to migrate into the modulator and probe even though an air purge is provided. Accordingly, it would be desirable to provide a system for enhancing the purging of toner and contaminants from the modulator assembly and the probe of electrostatic voltmeters.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that prior art electrostatic voltmeter devices will admit to worthwhile improvement.
It is, therefore, a general object of the invention to provide an improved electrostatic voltmeter system, which will obviate or minimize difficulties of the type previously described.
It is another general object of the invention to provide an improved modulator assembly for an electrostatic voltmeter operable for providing a high level of photoreceptor voltage control for an electrophotographic process.
It is a specific object of the invention to provide an improved modulator assembly of an electrostatic voltmeter having a system for purging the modulator and probe to obtain improved operational reliability of the electrostatic voltmeter.
It is another specific object of the invention to provide an improved modulator assembly having a system for enhanced air purging of the modulator and probe.
It is another specific object of the invention to provide a system for purging a modulator and probe assembly of an electrostatic voltmeter which is easy to fabricate and exhibits enhanced operational efficiency.
It is yet another specific object of the invention to provide an improved system for self-enhanced purging of a modulator and probe of an electrostatic voltmeter, which minimizes the possibility of charged toner particles and other air borne contaminants from settling inside the sensor assembly.
SUMMARY OF THE INVENTION
To achieve at least some of the foregoing objects, the invention provides a modulator assembly of electrostatic voltmeters having a modulator base with a vibratory beam disposed inside the base for oscillating when a vibratory magnetic force is applied to the beam. Advantageously, a vane is located on the beam such that when the beam is oscillated the vane generates air turbulence or currents to purge and displace toner particles and other contaminants from the vicinity of the sensor. The beam has a longitudinal arm member and, preferably, the vane is arranged on the arm member to extend in a lengthwise direction thereof to generate air currents when the arm member oscillates.
Advantageously, the vane is associated with a device that interrupts the electrostatic voltage to modulate the voltage with respect to the sensor, hereinafter simply “chopper”. The chopper and vane are located at one end of the longitudinal arm member of the beam and, more preferably, the van/is integrated with the chopper in a generally L-shape configuration.
REFERENCES:
patent: 3640246 (1972-02-01), Jeromin et al.
patent: 4697920 (1987-10-01), Palm et al.
patent: 5212451 (1993-05-01), Werner
patent: 5311266 (1994-05-01), Madea
patent: 5404210 (1995-04-01), Day
patent: 5489850 (1996-02-01), Werner
patent: 6327447 (2001-12-01), Nakano et al.
patent: 6381438 (2002-04-01), Kubo
patent: 6415121 (2002-07-01), Suzuki et al.
Oda Christine K.
Oliff & Berridg,e PLC
Xerox Corporation
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