Electric motor with locking apparatus

An electric motor comprising a stator and a rotor rotatably supported therein, the motor further comprising commutator means for communicating armature current between the stator and the rotor and locking apparatus comprising, in combination:

• a slotted collar on the rotor comprising circumferentially spaced slots;
• a pin adapted for reciprocal movement between an inserted position in which a free end of the pin is engaged within one of the slots to prevent rotation of the rotor and a retracted position in which the free end of the pin is pulled out of engagement with the one of the slots to allow rotation of the rotor;
• a temperature sensitive actuator comprising first and second springs having ends connected together, said first and second springs exerting opposing forces, one in compression and the other in tension, the second spring being made of a temperature sensitive memory metal and effective at temperatures below a predetermined temperature to allow the first spring to move the pin into its inserted position and at temperatures above the predetermined temperature to move the pin against the first spring to its retracted position,
• the temperature sensitive actuator being electrically conductive and connected in series with the commutator means to carry the motor armature current and be heated thereby so that the pin is automatically placed in its retracted position to allow rotor rotation when armature current is provided to the motor and is automatically placed in its inserted position when armature current is stopped to lock the rotor against rotation.