SERVOMOTOR PULSE WIDTH CONTROL CIRCUIT CAPABLE OF COMPENSATING FOR VARIATIONS IN SUPPLY VOLTAGE

• US 3,743,911 A
• Filed: 06/18/1971
• Issued: 07/03/1973
• Est. Priority Date: 06/18/1971
• Status: Expired due to Term

• Current Assignee: GE Fanuc Automation North America Incorporated, General Electric Company
• Original Assignee: Irvin L. Erler
• Inventors: Erler, Irvin L.
• Primary Examiner(s): Lynch, T. E.
• Application Number:
  US05/154,277
• Time in Patent Office: 746 Days
• Field of Search: 318/599,341,331,629 307/265
• US Class Current: 318/599
• CPC Class Codes: G05D 3/18 delivering a series of pulses
• CPC Class Codes: H02P 29/026 the fault being a power fluctuation
• CPC Class Codes: H02P 7/29 using pulse modulation
• CPC Class Codes: Y10S 388/915 Sawtooth or ramp waveform generator

Abstract

A servomotor control circuit capable of compensating for variations in the output voltage of a poorly regulated or unregulated direct current power supply. A triangular waveform having an amplitude dependent upon the amplitude of the power supply output is compared in first and second comparator amplifiers to normal and inverted forms, respectively, of a motor control signal. The output signals of the comparator amplifiers determine the state of first and second switches connecting opposite terminals of the servomotor to the power supply. The width of a voltage pulse applied to the servomotor is inversely related to the magnitude of the power supply output voltage, making the average applied voltage substantially independent of the magnitude of the power supply output voltage.

Claims

1. For use in a system having a servomotor, a motor control signal source, a direct current power supply and first and second switches for connecting first and second servomotor terminals respectively to the power supply whenever the associated switch is in an on condition, a control circuit for minimizing the effects on servomotor performance of variations in the output voltage of the power supply comprising:

a. a waveform generator connected to the power supply for generating a triangular waveform voltage having an amplitude dependent upon the amplitude of the power supply output voltage;

b. an inverter connected to the motor control signal source for inverting the control signal supplied by the source;

c. a first comparator having a first input connected to the waveform generator, a second input connected to the signal source and an output connected to the first switch; and

d. a second comparator having a first input connected to the waveform generator, a second input connected to the inverter and an output connected to the second switch;

e. each of the comparators operating independently to trigger its associated switch into an on condition whenever the first comparator input exceeds the second comparator input.

2. A control circuit as recited in claim 1 wherein the waveform generator comprises:

a. a square wave generator connected to the DC power supply for generating a square wave having peak positive and negative voltages proportional to the output voltage of the power supply; and

b. an integrator connected to the square wave generator for integrating the generated square wave to derive the triangular waveform voltage.

3. A control circuit as recited in claim 2 wherein said square wave generator comprises:

a. a square wave oscillator having normal and inverted outputs;

b. a first semiconductor device having first and second terminals connecting the device between the power supply and a common terminal, a control terminal connected to one of the oscillator outputs and an output terminal at a point between the semiconductor device and the power supply;

c. a second semiconductor device having first and second terminals connecting the device between the power supply and the common terminal, a control terminal connected to the other of the oscillator outputs and an output terminal at a point between the semiconductor device and the power supply;

d. an inverter connected to the output terminal of one of the semiconductor circuits for inverting an output therefrom; and

e. a current summing junction connected to the output of the inverter and to the output terminal of the other of the semiconductor circuits.

4. A control circuit as recited in claim 2 wherein the integrator comprises:

a. an operational amplifier having an output terminal connected to the first inputs of the first and second comparators and an input terminal;

b. resistance means connected in series between the input terminal and the output of the square wave generator; and

c. a feedback capacitor connected between the input and output terminals of the operational amplifier.

5. A control circuit as recited in claim 3 wherein the integrator comprises:

a. an operational amplifier having an output terminal connected to the first inputs of the first and second comparators and an input terminal connected to the current summing junction; and

b. resistance means connected in series between the input terminal and the output of the square wave generator; and

c. a feedback capacitor connected between the input and output terminals of the operational amplifier.

6. A control circuit as recited in claim 3 wherein each of the semiconductor devices comprises an NPN transistor having its collector terminal connected in circuit with the power supply, its emitter terminal connected to the common terminal and its base terminal connected to one of the outputs of the square wave oscillator.

7. For use in a system having a servomotor, a first signal source for producing a variable unidirectional electrical signal, a direct current power supply, and first and second switching means for connecting first and second servomotor terminals respectively to the power supply whenever the associated switch is in a conducting condition, a control circuit for minimizing the effects on servomotor performance of variations in the output voltage of the power supply including:

a. a second signal source for generating a triangular waveform having an amplitude dependent upon the amplitude of the power supply output voltage;

b. inverting means connected to the output of one of the first and second signal sources for producing an inverted form of the output signal provided by that source;

c. first comparing means connected to the inverting means and to the other of the signal sources, the first comparing means responding when normal output signal is greater than the inverted output signal to drive one of the switching means into conduction; and

d. second comparing means connected to the outputs of the first and second signal sources, the second comparing means responding when the second output signal is greater than the first output signal to drive the other of the switching means into conduction.

8. For use in a system having a servomotor, a direct current power supply and switch means for selectively energizing the servomotor from the power supply, a control circuit for minimizing the effects on servomotor performance of variations in the output voltage of the power supply comprising:

a. a waveform generator responsive to the power supply voltage for generating a triangular waveform signal having a fixed frequency and an amplitude proportional to the amplitude of the power supply voltage; and

b. circuit means responsive to a control signal and to the triangular waveform signal for operating the switching means so that the power supply energizes the servomotor for a time directly proportional to the amplitude of the control signal and inversely proportional to the slope of the triangular waveform signal.

9. A control circuit as recited in claim 8 wherein the circuit means includes comparison circuit means for operating the switching means to selectively energize the servomotor from the power supply when the triangular waveform signal exceeds a first signal level and is less than the control signal level.

10. A control circuit as recited in claim 9 wherein the first signal level is equal in magnitude but of opposite polarity to the control signal.