Speed and torque control for fractional horsepower motors

• US 4,233,549 A
• Filed: 12/08/1978
• Issued: 11/11/1980
• Est. Priority Date: 12/08/1978
• Status: Expired due to Term

• Current Assignee: Baxter Travenol Laboratories Incorporated
• Original Assignee: Baxter Travenol Laboratories Incorporated
• Inventors: Dighe, Kamalakar D.
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US05/967,862
• Time in Patent Office: 704 Days
• Field of Search: 318/317, 318/341, 318/345 B, 318/345 F, 318/246, 318/345 E
• US Class Current: 388/819
• CPC Class Codes: H02P 7/29 using pulse modulation
• CPC Class Codes: Y10S 388/916 Threshold circuit

Abstract

Power control circuitry for supplying pulses of power from a power source to a fractional horsepower motor with a plurality of power pulses applied to the motor during each half cycle of the power source waveform for more uniform speed and torque characteristics of the motor at low speeds. A timing capacitor in a motor speed control portion of the circuitry has a constant sum of resistances in the charge and discharge paths for fixed frequency of power pulses applied to the motor. The timing capacitor is electrically connected to a wiper arm of a variable resistor located in both the charge and discharge paths such that resistance may be shifted between the paths to vary the duty cycle of the pulses over a wide range. A pulse generating portion of the circuitry includes a threshold comparator and a trigger comparator to respectively monitor the voltage on the timing capacitor for high or low conditions and cause a bi-stable circuit to change output states upon the occurrence of either condition to generate a train of pulses. The bi-stable circuit is adapted to control the conductive states of transistors in series connection between the motor and the power source to apply repetitive constant-frequency, variable duty cycle pulses of power from the power source to the motor in accordance with the train of pulses. Related methods are also disclosed.

Claims

1. A motor speed control system for supplying power from an electrical power source to an electric motor, comprising, in combination:

a capacitor having one terminal connected to a plane of reference potential;

a source of unidirectional current of relatively constant voltage;

means including a capacitor charge circuit serially comprising a first resistor, a first diode, and a second resistor connected between said current source and the remaining terminal of said capacitor, for periodically charging said capacitor;

means including a capacitor discharge circuit serially comprising a third resistor, a fourth resistor, and a second diode connected between the remaining terminal of said capacitor and said plane of reference potential for periodically discharging said capacitor;

timing circuit means serially included in said capacitor discharge circuit between said second diode and said plane of reference potential, and including a voltage capacitor responsive to the voltage level across said capacitor for periodically rendering said discharge circuit operative to discharge said capacitor;

electronic switch means serially connected between the electrical power source and the electric motor and responsive to said timing circuit for applying pulses to said motor having a repetition rate and duty cycle dependent on the charging and discharging of said capacitor;

means including a diode connected between the juncture of said first resistor and said first diode, and the juncture of said second diode and said timing circuit for disabling said capacitor charge circuit upon operation of said capacitor discharge circuit; and

said second and third resistors comprising respective sections of a potentiometer having a user-adjustable tap connected to said capacitor whereby the duty cycle of the pulses applied to said electric motor are varied without varying the frequency thereof for smooth speed control of the motor over a wide range of speeds.

2. A motor speed control system as defined in claim 1 wherein the electrical power source is an alternating current source, and the repetition rate of said pulses applied to the electric motor is greater than the frequency of the alternating current source.

3. A motor speed control system as defined in claim 2 wherein said source of unidirectional current comprises a rectifier for converting the alternating current source to a direct current.

4. A motor speed control system as defined in claim 1 wherein said timing circuit means include a first voltage comparitor circuit responsive to the voltage across said capacitor for initiating operation of said charge circuit, and a second voltage comparitor responsive to the voltage across said capacitor for initiating operation of said discharge circuit.

5. A motor speed control system as defined in claim 4 wherein said timing circuit means comprise a monolithic linear integrated timing circuit.