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Compensated Open Loop Stepper Motor Control

IP.com Disclosure Number: IPCOM000080839D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Paska, TM: AUTHOR

Abstract

The performance of a stepper motor, such as stepper motor 10 having output shaft 12, controlled in an open-loop fashion (utilizing no emitter or other control device responsive to rotation of shaft 12) operating at a fixed step rate, will degrade as the motor's applied voltage VSE varies from nominal. The compensated open-loop stepper motor control varies the open-loop step rate (timing) by a voltage-controlled oscillator VCO 14 to compensate for the variations in the applied voltage VSE.

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Compensated Open Loop Stepper Motor Control

The performance of a stepper motor, such as stepper motor 10 having output shaft 12, controlled in an open-loop fashion (utilizing no emitter or other control device responsive to rotation of shaft 12) operating at a fixed step rate, will degrade as the motor's applied voltage VSE varies from nominal. The compensated open-loop stepper motor control varies the open-loop step rate (timing) by a voltage-controlled oscillator VCO 14 to compensate for the variations in the applied voltage VSE.

Resistors R1 and R2 function as a voltage divider and, together with transistor 16 and resistor R4, provide a voltage V1 (VCO INPUT) applied to VCO that is considerably smaller than VSE and is proportional to VSE. The frequency of the output signal of VCO increases from f1 to f2 as V1 applied to VCO increases from 2.1 volts to 2.7 volts, as shown by the graph. V1 nominally is 2.4 volts corresponding to frequency fc. The pulses from VCO 14 are gated by AND circuit 18 when the signal "ACCESS GATE" is raised and are applied to the clock terminals of flip-flops, FF1 and FF2, in logic 20.

Logic 20 also includes exclusive OR circuits 22 and 24 having their plus and minus outputs connected to the J and K inputs of flip-flops FF1 and FF2, as shown, and having one input of each exclusive OR circuit connected to an output of FF1 and FF2, as shown. Another input of each exclusive OR circuit is the +DIRECTION line. AND circuits 26, 27, 28 and 29 are connected to the outputs of flip-flops FF1 and...