Single cycle positioning system utilizing a DC motor

A single cycle positioning system utilizing a DC motor having a winding with two ends, comprising:

• a source of DC power;
• a movable member coupled to said motor for controlled cyclical movement thereby;
• means for providing a start signal to initiate movement of said member;
• means associated with said member for providing a stop signal when said member is at a predetermined position within its cycle of movement;
• a motor controller including:
• a first switch coupled between said DC power source and a first end of the motor winding;
• a second switch coupled between the second end of the motor winding and a reference level;
• and
• a third switch coupled between the first end of the motor winding and the reference level;
• and
• control means coupled to receive said start signal and said stop signal for controlling said motor control switches, said control means being operative in response to said start signal for controlling the closure of said first and second switches so as to apply DC power to the winding of said motor, and said control means being operative in response to said stop signal for opening said first switch and closing said second and third switches to effect a dynamic braking of said motor so that said movable member comes to rest at a desired position within a defined range of said predetermined position;
• wherein said source of DC power includes a pair of terminals connectable to a source of AC power and rectification means coupled to said pair of terminals and effective to convert AC power applied to said terminals to DC power, and wherein said control means is operative to determine the AC voltage across said pair of terminals and to pulse width modulate closure of the second switch at a rate inversely related to the determined AC voltage so as to provide a predetermined rms DC voltage across the motor winding after receipt of said start signal and before receipt of said stop signal.