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Removal of Cumulative Paper Position Error in Fanfold Printers

IP.com Disclosure Number: IPCOM000120360D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Crossland, JF: AUTHOR

Abstract

Fanfold printers usually use tractors at the transfer station to control the paper. The tractors are frequently controlled with a position servo, using an optical encoder coupled to either the tractor shaft, or the tractor motor shaft, to sense angular displacement. Electrical noise can cause the servo to accumulate position error and cause significant misregistration of the print with respect to the perforation. Because of requirements to register the print to the perforation to within a specified accuracy, this accumulating tractor position error cannot be allowed. The tractor servo must be able to detect and correct these errors as they occur so that they are unable to accumulate.

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Removal of Cumulative Paper Position Error in Fanfold Printers

      Fanfold printers usually use tractors at the transfer
station to control the paper.  The tractors are frequently controlled
with a position servo, using an optical encoder coupled to either the
tractor shaft, or the tractor motor shaft, to sense angular
displacement.  Electrical noise can cause the servo to accumulate
position error and cause significant misregistration of the print
with respect to the perforation.  Because of requirements to register
the print to the perforation to within a specified accuracy, this
accumulating tractor position error cannot be allowed.  The tractor
servo must be able to detect and correct these errors as they occur
so that they are unable to accumulate.

      At the center of the tractor servo is a position error counter.
Under normal circumstances, the value in this counter represents the
difference between the actual location of the tractor shaft and the
desired location. Error in the system can be corrected by loading
this counter with an appropriate value.  Among the servo electronics,
another counter, referred to as the detent counter, monitors tractor
shaft position in such a way that when the tractors stop, the value
in this detent counter is the value that should be in the position
error counter.  If no error has occurred, the value in the detent
counter is equal to the value in the position error counter.  The
detent counter is reset every 1/6 inch so that it cannot accumulate
position error.  This means that accumulating position error can be
defeated by loading the position error counter with the value in the
detent counter every time the tractors stop.

      All fanfold papers have lengths that are integer multiples of
1/6 inch.  The tractors always move paper a distance that is an
integer multiple of the paper length. Therefore, the tractors always
move paper a distance that is an integer multiple of 1/6 inch.

      The tractor encoder has two high resolution quadrature channels
(A and B) that provide...