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DC Servo Drive Control Algorithm

IP.com Disclosure Number: IPCOM000051997D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Short, P: AUTHOR

Abstract

A control algorithm is known to obtain the duty cycle needed by a pulse-width modulated control signal to drive a DC servo motor for printer carrier operation. The algorithm measures the elapsed time between emitter wheel slots on the motor shaft and subtracts a constant from the elapsed time. This remainder is used to determine the duty cycle required by the pulsewidth modulator to maintain a constant velocity. Variations in load, motor tolerances and changes in temperature will cause the actual velocity of the motor to be altered accordingly until a new equilibrium point of pulse duty cycle and steady-state velocity are reached. This causes wide variations in the actual velocity of operation, both from machine to machine and on a given machine.

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DC Servo Drive Control Algorithm

A control algorithm is known to obtain the duty cycle needed by a pulse- width modulated control signal to drive a DC servo motor for printer carrier operation. The algorithm measures the elapsed time between emitter wheel slots on the motor shaft and subtracts a constant from the elapsed time. This remainder is used to determine the duty cycle required by the pulsewidth modulator to maintain a constant velocity. Variations in load, motor tolerances and changes in temperature will cause the actual velocity of the motor to be altered accordingly until a new equilibrium point of pulse duty cycle and steady- state velocity are reached. This causes wide variations in the actual velocity of operation, both from machine to machine and on a given machine. Described below is an additional control function to the type 0 control system above described to correct for these variations so the actual velocity is kept at the desired value.

The control of a DC servo motor is described by the equation
(1).

Em = K(Vo-V) Eb (1) where Em = motor voltage K = system gain factor

Vo = desired velocity

V = actual velocity

Eb = bias voltage

Maintaining control of the motor at or near constant velocity can be implemented by the approximation to the above equation (1) by implementing the following equation (2). Em/1/ = K/1/ (delta T-delta To) (2) where Em/1/ = the motor voltage K/1/ = a gain factor

delta T = the measured time between motor emitter pulses

delta To = the desired time between motor emitter pulses

In a digital control design, the above equation (2) may be reduced to implementing the function: pdc = (delta T - M) over Kd where pdc = the duty cycle of the pulse/width modulation signal delta T = the measured time between motor emitter pulses

M = a conversion factor chosen to produce the desired

motor voltage for steady/state

operati...