Browse Prior Art Database

Limit Cycle Reduction in Fanfold Printers

IP.com Disclosure Number: IPCOM000120362D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Crossland, JF: AUTHOR

Abstract

Fanfold printers normally use tractors at the transfer station to control the paper. The tractors are frequently controlled with a positon servo using an optical encoder coupled to either the tractor shaft or the tractor motor shaft to sense angular displacement. The encoder has the nonlinear effect of quantizing the angular position information. Systems such as this frequently have problems with limit cycling caused by this quantization. One method of dealing with this problem is by introducing position hysteresis.

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Limit Cycle Reduction in Fanfold Printers

      Fanfold printers normally use tractors at the transfer
station to control the paper.  The tractors are frequently controlled
with a positon servo using an optical encoder coupled to either the
tractor shaft or the tractor motor shaft to sense angular
displacement.  The encoder has the nonlinear effect of quantizing the
angular position information.  Systems such as this frequently have
problems with limit cycling caused by this quantization.  One method
of dealing with this problem is by introducing position hysteresis.

      At the center of a position servo of this type is a digital
position error counter.  The output of this counter controls a
Digital-to- Analog Converter (DAC).  The DAC output provides the
input to the compensation filter and the output of this filter
controls the amount of current being delivered to the tractor motor.
The counter is incremented, or decremented, by two signals:  a
reference signal generated by the servo electronics, and the signal
from the encoder.  The reference signal indicates that either forward
or reverse motion is desired, and the encoder indicates either
forward or reverse motion has occurred.  The counter is affected by
the reference and encoder pulses according to the table above.

      A lead compensator, frequently used in position servos,
amplifies higher frequencies of the signals which it receives.
Encoder resolution can be selected such that, while the servo is
running at printing speed, the counter is being incremented and
decremented at a frequency well above the frequencies of mechanical
resonance.  Thus, the compensator's amplification of the position
quan...