Linear Instruments

W Paul Wilson, Jr

Ronald E Ross

A servo amplifier for d-c servo motors which converts the error signal into pulses which are amplified in a saturating amplifier to drive the motor. Both the duty cycle and the repetition rate of the pulses vary with the error signal. At large error signals the duty cycle is 100 percent, i.e., 'full on'; at small error signals the duty cycle is low and the pulses spaced far apart. As the system approaches balance the pulses become shorter and less frequent, and the motor slows. The circuit comprises a signal integrator which drives two comparators, one for positive signals and the other for negative. The integrator generates a ramp voltage in a direction opposite to the polarity of its input, and is reset automatically by reset pulses of controlled and variable length when a comparator set point is reached. The reset pulses are the pulses which are amplified to drive the servo motor. In this system, reducing the gain does not produce a widened dead band, but only increases the time required for rebalance. The dead band is considerably more tightly controlled than in prior systems. A novel overload shutdown circuit cuts off the input to the power amplifiers when a large, off-scale input signal occurs for longer than a predetermined time.

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Fountain Valley, CA, United States of America

W Paul Wilson, Jr