US 4,380,723 AGranted

Digital velocity servo

AssigneeDigital Equipment Corporation

InventorsMichael D. Leis, Robert C. Rose

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Abstract

A servo circuit for electronically controlling the operation of an electric motor is disclosed. The rotational frequency of the motor is converted into a varying frequency waveform by a tachometer. The tachometer output is applied to a conversion circuit which includes a peak detector that converts the output waveform of the tachometer into a square-wave signal. The square-wave signal is, in turn, connected to one input of an exclusive-OR gate. The peak detector square-wave signal is also applied to a shift register which, after a time delay, applies the same signal to another input of the exclusive-OR gate. With these connections, the exclusive-OR gate produces a square-wave output whose duty cycle is proportional to the speed of the DC motor. This output can then be either amplified and applied directly to the electric motor to drive it, or integrated and applied to an amplifier to drive the motor in accordance with standard servo techniques.

Claims6

Dependent claims

An electric motor servo control system for controlling the speed of an electric motor comprising:

A. speed signal means for producing a speed signal consisting essentially of pulses whose time period of repitition is proportional to the rotational period of the motor,
B. delay means for receiving the speed signal from said speed signal means and producing a delayed speed signal consisting essentially of pulses delayed from the pulses of the speed signal by a predetermined time interval that is less than the duration of the pulses of the speed signal whenever the speed of the motor is within an intended speed range,
C. logical-combination means for receiving said speed signal and said delayed speed signal and for generating a sequence of constant-width, variable-frequency motor-control pulses wherein the pulse width is substantially equal to said predetermined time interval and the pulse frequency is proportional to the repetition frequency of the speed signal, the duty cycle of the motor-control pulses thereby varying in response to variations of the rotational speed of the motor, and
D. means for receiving the motor-control pulses from said logical-combination means and adapted for coupling to the motor to drive the motor in accordance with the duty cycle of said motor-control pulses.

1 more element

Dependencies are inferred from the claim text.