Photoreceptor charge control

Details Photoreceptor charge control Photoreceptor charge control

1999-12-01

2001-04-24

Brase, Sandra (Department: 2852)

Electrophotography

Control of electrophotography process

Of plural processes

Reexamination Certificate

active

06223006

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to color imaging processors and, in particular, to photoreceptor charge control that obviates the adverse effects of photoreceptor variation inherent in the photoreceptor as the result of the manufacturing process.
Many xerographic copiers and printers maintain the charge level on the photoreceptor via feedback control by sampling the resultant charge using an electrostatic voltmeter. These InterDocument or InterPage Zone (IDZ or IPZ) readings are taken around the photoreceptor. Many photoreceptors are known to have a once-around variation in the charge level, due primarily to dielectric thickness variations commonly referred to as run-out.
Charge control was first performed in the Xerox 1075™ by examining the density of lightly developed images with a reflective infrared densitometer. These images were sensitive to both development field and toner concentration (the latter being controlled by examining a higher density patch). In subsequent Xerox™ machines (1065™, 5090™, 5100™, 4890™, 5775™) one or more compact Electrostatic Voltmeters (ESV) were used to directly sense the charge levels on the photoreceptor. In each of these machines, images or test patches are placed on the photoreceptor in small regions between customer's prints, such regions being commonly known as IDZs or IPZs. The charge level of such an image is read by the ESV. These readings, sometimes filtered, are compared to a pre-established charge target and adjustments are made to the charging system to bring the readings to target. Because these readings are taken at various points around the photoreceptor, any circumferential variation in the photoreceptor charge level can affect the readings. A typical source of variation is dielectric thickness changes, established during the photoreceptor manufacturing due to run-out in the coating rolls employed to fabricate the photoreceptor. In some photoreceptors this noise can exceed an unacceptable peak-to-peak amplitude of 30 volts.
Some photoreceptors are known to possess a repeatable once-around profile but the amplitude is only about 5-10 volts. This level is at a “just noticeable difference” in color error (delta E
cmc
) and correction of this once-around profile is not necessary. Nor is it practicable due to the broad expanse of the charging zone that is much larger than the structure of the voltage variations.
However, it is still desirable to characterize and correct the charge readings for this variation. This will prevent the charge level from riding this profile as the charge level is maintained, thereby minimizing overall variation in the photoreceptor charge level. Uncorrected voltages will follow the once-around voltage profile of the photoreceptor and cause the average charge level to change. Corrected voltages that cause the average charge level of the photoreceptor to remain constant are quite desirable.
BRIEF SUMMARY OF THE INVENTION
The purposes and intents of the present invention are effected by correcting the voltages that cause the average charge level of the photoreceptor to change so that the charge level remains constant instead of following the once-around voltage profile of the photoreceptor. The forgoing is implemented by reading or measuring the once-around belt signature or voltage profile, Vcharge of the photoreceptor using five ESVs, corresponding to five image separations during a machine setup routine in which the charge output level remains constant. The readings for each of the ESVs are averaged (to find the mean) and the deviations from the mean are smoothed using a 41-term weighting function that properly removes the high frequency reading spikes while retaining the low frequency belt signature. Center weighted averaging of 41 points (n, . . . n±20) where n is a measured point on the photoreceptor that is averaged with the previous twenty readings together with the next twenty readings is initiated a few mm past the photoreceptor seam and ends a few mm before the seam. This insures that no phase shift occurs between the sensor reading position and the filtered correction. The readings are taken approximately every 3 mm around the photoreceptor.
The ESVs, one each for spot color (S), black (K), yellow (Y), magenta (M), and cyan (C) mounted on the respective developer housings and are positioned at five different locations across the width (i.e. direction perpendicular to that of photoreceptor movement) of the photoreceptor to produce a voltage profile characterization that more closely reflects the photoreceptor run-out.
Following is a discussion of prior art, incorporated herein by reference, that may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 5,864,730 granted to Budnik et al on Jan. 26, 1999 relates to a method to provide a highly intelligent automated diagnostic system that identifies the need to replace specific parts to minimize machine downtime rather than require extensive service troubleshooting. In particular, a systematic, logical test analysis scheme to assess machine operation from a simple sensor system and to be able to pinpoint parts and components needing replacement is provided by a series of first level of tests by the control to monitor components for receiving a first level of data and by a series of second level of tests by the control to monitor components for receiving a second level of data. Each of the first level tests and first level data is capable of identifying a first level of part failure independent of any other test. Each of the second level tests and second level data is a combination of first level tests and first level data or a combination of a first level test and first level data and a third level test and third level data. The second level tests and second level data are capable of identifying second and third levels of part failure. Codes are stored and displayed to manifest specific part failures.
U.S. Pat. No. 5,963,761 granted to Budnik et al on Oct. 5, 1999 relates area coverage sensor calibration and algorithm for seam detection noise eliminator on a seamed photoreceptor. The invention disclose an apparatus and method for eliminating random noise and calibrating a seam detection sensor in an electrophotographic printing machine. When the detected centerline remains within the tolerance window the algorithm proceeds as normal. In most cases, however, the center line is shifted outside the tolerance window., either from 2 to −X or +X to N−1. When the centerline falls within either of these two ranges, the algorithm recognizes this fact and assumes that a random noise condition has occurred. It then proceeds to take the previous centerline (C) and add the current photoreceptor belt length to it. This, theoretically, should be exactly where the centerline should have been in the absence of noise. If this condition continues for three successive belt revolutions and the machine completes the job it was running, the algorithm will force the machine to search for the seam at the next cycle up. If the centerline is calculated to be at position 1 or N, the algorithm assumes some drastic change has occurred and an immediate fault is declared. To calibrate the sensor, the calibration algorithm increases the duration of each calibration pulse to 80 ms, and two reads per pulse are instituted. The algorithm then chooses the greater of the two reads on each individual step, thus eliminating any read of the seam that might adversely affect the calibration scheme.
U.S. Pat. No. 5,893,008 granted to Budnik et al on Apr. 6, 1999 discloses a photoreceptor parking deletion including method to provide a highly intelligent, automated diagnostic system that identifies the need to replace specific parts to minimize machine downtime rather than require extensive service troubleshooting

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