Browse Prior Art Database

METHOD OF ELIMINATING MAGNIFICATION ERRORS

IP.com Disclosure Number: IPCOM000026025D
Original Publication Date: 1989-Oct-31
Included in the Prior Art Database: 2004-Apr-05
Document File: 2 page(s) / 96K

Publishing Venue

Xerox Disclosure Journal

Abstract

In an electrophotographic printing machine utilizing a servo motor driven document scanning system to expose the photoconductive drum, the velocity of the electrophotographic system is controlled by a synchronous motor. The speed of the motor is AC line frequency dependent, while the control of the scan carriage speed is dependent on an internal crystal clock frequency. The capabilities of such a system may also include reduction and enlargement performed by varying the scan carriage velocity. Such a system would likely have scan velocities derived around an assumed nominal line frequency, typically 50 or 60 Hz.

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L 'EROX DISCLOSURE JOURNAL

METHOD OF ELIMINATING MAGNIFICATION ERRORS Barry G. Rickett

Proposed Classification

U.S. C1.355/14R Int. C1. G03g 15/00

In an electrophotographic printing machine utilizing a servo motor driven document scanning system to expose the photoconductive drum, the velocity of the electrophotographic system is controlled by a synchronous motor. The speed of the motor is AC line frequency dependent, while the control of the scan carriage speed is dependent on an internal crystal clock frequency. The capabilities of such a system may also include reduction and enlargement performed by varying the scan carriage velocity. Such a system would likely have scan velocities derived around an assumed nominal line frequency, typically 50 or 60 Hz.

A problem arises when the line frequency drifts from the nominal value, causing a variation in the intended velocity of the electrophotographic development system. Because the scanning carriage velocity is decoupled from this line frequency drift, no compensating variation occurs. The problem is manifested in poor copy quality due to magnification or reduction levels that deviate from the nominally selected value.

Resolution of the problem involves accurately measuring the AC line frequency, and adjusting the scan carriage velocity by the ratio of the measured fre uency to the nominal frequency. With the capability to sense

Crossing, a timer and counter can be used to determine the number of zero crossings in a given period. Having determined the actual line frequency in this manner, the problem is resolved by applying the correction to the nominal scan vel...