Electric positioning motor control system, particularly automatic vehicle antenna extension system

Electrical positioning motor control system for automatically de-energizing a commutator-type d-c motor (12) coupled to a positioned element (13) when the positioned element has reached a predetermined position, said system having

• an operator-controlled switch (24, 27) for controlling energization of the motor;
• motor direction-of-operation control switch means (R1, r1, R2, r2) selectively energizing the motor for rotation in either of two directions, or for de-energizing the motor;
• a control circuit (30) having at least one control input (21) coupled to the operator-controlled switch and first and second outputs (31, 32) coupled to control the motor direction switch means (R1, r1, R2, r2), said system comprising, in accordance with the invention,
• a measuring means (18,33) coupled to a connection line (X) of the motor (12), sensing the rotary speed of operation of the motor, when energized, and including analyzing means (33,33') responsive to a time characteristic of the waviness of undulation of motor current in said connection line to produce a motor operation speed signal;
• a motor operation input (34) on said control circuit (30) and receiving the motor speed signal;
• a memory (M) in said control circuit (30) storing a representation of the average value of said time characteristic;
• and
• a speed-signal-responsive circuit (S) in said control circuit (30), connected to and controlling the electrical energy supplied to the motor and disconnecting said energy supply thereto upon sensing drop-off of speed of operation of the motor below a predetermined limit, regardless of the position of the operator-controlled switch means (24).