Phase locked servo loop circuit

Claim 1

A phase locked servo control system loop for changing the speed of a direct current motor operating under varying load conditions to maintain a constant predetermined motor speed comprising: reference pulse means for providing a first control signal of a series of successive pulses having a substantially fixed repetition rate in accordance with a predetermined desired operation of said motor; speed responsive means operatively connected to sense the speed of said motor for providing a second control signal output of successive electrical pulses having a repetition rate proportional to actual rotation of said motor; pulse responsive means electrically coupled to receive successive pulses from said reference pulse means and said speed responsive means for providing a train of output pulses of varying pulse width having a pulse width time duration dependent on the phase difference between individual successive pulses of first control signals generated by said reference pulse means and individual successive pulses of second control signals generated by said speed responsive source; detector means operatively coupled to said pulse responsive means and to gating control means for supplying a pulsed output control signal whenever the time interval between each second control signal pulse is less than the time interval between each first control signal pulse; coincidence means having inputs electrically coupled to receive output signals from said pulse responsive means and said detector means for producing an output in response to identical output signals; overspeed responsive means coupled to receive signals from said coincidence means and said speed responsive means for supplying output pulse signals in response to said motor overspeed; control logic circuit means coupled to accept output pulse signals from said overspeed responsive means for preventing said reference pulse means first control signals from being received by said pulse responsive means; and switching means operatively connected to receive an electrical output from said pulse responsive means for supplying current to said motor in response to the time duration of the pulses for maintaining the rotation of the motor at its predetermined desired operation. thereby causing the switching means from supplying current to the motor until such time as the motor speed decreases to cause said second control signal pulse to occur at the same time as said first control signal pulse at which time the predetermined desired operation of said motor is reached.