Motor control system

Abstract

A two-phase motor preferably of the induction or hysteresis type is driven from a variable frequency clock circuit by energizing the motor windings in phase quadrature over the frequency range. Speed control is provided by mechanically modulating a light emitting diode (LED) and photoresistor combination that couples to the clock circuit for determining its frequency of operation. The output of the clock circuit in turn couples to a two-phase generator that drives output bridges associated with the motor in phase quadrature. The photo resistor is characterized by a relatively .[.lone.]. .Iadd.low .Iaddend."off" (return to dark resistance) time constant that provides automatic braking when the speed control is set to zero. The system further includes a feedback circuit responsive to motor load fluctuations sensed by monitoring the DC current drawn by output bridge circuit means associated with the motor for controlling the frequency of operation of the clock circuit. This clock control permits the motor to come up to speed quite quickly with little or no synchronous slippage. If a load which would ordinarily stall the motor at the speed indicated by the mechanical control is .[.the speed.]. .Iadd.placed .Iaddend.on the motor the feedback circuit will slow the clock control so that the motor will run at a speed lower than the mechanically indicated speed rather than stall.

What is claimed is: 
     
       1. In a system for controlling a motor having at least one field winding and a variable frequency oscillator whose output controls motor speed, the improvement comprising speed control means coupled to said oscillator for controlling its output frequency, and including a light source a photo resistor and modulating means disposed intermediate said light source and resistor, said photo resistor characterized by a relatively long off or decay time constant as said photo resistor traverses from its low resistance to high resistance state. 
     
     
       2. The system of claim 1 wherein said decay time constant is on the order of 1.0 seconds or greater. 
     
     
       3. The system of claim 1 wherein said decay time constant is greater than 0.1 seconds. 
     
     
       4. The system of claim 1 wherein said photo resistor is of the lead selenide or lead sulfide type. 
     
     
       5. A system for controlling a multiple phase motor having a plurality of separately energizable field windings, said system comprising; a variable oscillator,   circuit means coupled from said oscillator and responsive to the frequency of operation of said oscillator for driving said field windings,   said drive circuit means including bridge circuit means for providing pulses to the field windings at a repetition rate controlled by the frequency of operation of the oscillator, and a two-phase generator coupled intermediate the oscillator and bridge circuit means,   power supply means providing a DC voltage for said drive circuit means,   feed back means coupled from said power supply means to said drive circuit means for sensing fluctuations in the power drawn by said power supply means and having means for controlling the output frequency of said oscillator inversely with respect to the magnitude of the drawn power,   said two-phase generator having one input coupled from said oscillator and a second input for establishing a bias level for said two-phase generator,   and means coupled from said oscillator to said second input of said two-phase generator for establishing a predetermined bias level for said generator when said oscillator is operating above a predetermined frequency and reducing said biasing level to at least partially inhibit said generator when said oscillator is reduced in frequency below said predetermined frequency.   
     
     
       6. A system for controlling a motor having at least one field winding, said system comprising; a variable oscillator,   circuit means coupled from said oscillator and responsive to the frequency of operation of said oscillator for driving said at least one field winding,   power supply means providing a DC voltage for said drive circuit means,   and feed back means coupled from said power supply means to said drive circuit means for sensing fluctuations in the power drawn by said power supply means and having means for controlling the output frequency of said oscillator inversely with respect to the magnitude of the drawn power,   said feedback means including variable resistance means wherein said resistance increases as said drawn power increases.   
     
     
       7. The system of claim 6 including variable resistance speed control means coupled in series with said variable resistance means, both said variable resistance speed control means and said variable resistance means coupling to said oscillator for controlling the operating frequency thereof. 
     
     
       8. The system of claim 7 wherein said variable resistance speed control means includes a light source and associated photo resistor. 
     
     
       9. The system of claim 7 wherein said variable resistance means includes a light source and associated photo resistor. .Iadd. 10. Apparatus for controlling the speed of an AC motor having at least one field winding comprising, a variable oscillator,   circuit means coupled from said oscillator and responsive to the frequency of operation of said oscillator for driving said at least one field winding with an AC signal of frequency determined by the frequency of operation of said oscillator,   power supply means providing a DC voltage for and delivering a DC current to said circuit means,   and feedback means coupled from said power supply and including means for sensing the DC power drawn from said power supply and having means for controlling the output frequency of said oscillator to be inversely proportional to the magnitude of the DC power drawn by said circuit means from said power supply means,   said means for sensing the DC power drawn from said power supply means comprising resistive means direct coupled to said power supply means and carrying said filtered DC current delivered by said power supply means to said circuit means for providing thereacross a proportional voltage drop as a control signal for controlling the output frequency of said oscillator to be inversely proportional to the magnitude of the DC power drawn by said circuit means from said power supply means. .Iaddend.