Abstract: An improved garage door operator of the motor-driven chain-and-sprocket type comprising a molded plastic gear case assembly supporting an output shaft for rotation relative thereto. A molded plastic worm wheel is loosely disposed on the shaft for limited rotation relative thereto and is driven by a reversible electric motor through a worm. Camming surfaces on the worm wheel and a second element which is fixedly disposed on the shaft form a low-torque coupling such that under normal conditions the motor drives the shaft to move the garage door. If the door encounters an obstacle and is unable to move, continued rotation of the motor drives the cam surface of the second element up the cam surface of the wheel so as to axially shift the second element relative to the gear case to trip a reversing switch. A rachet knob projects outside of the gear case permitting manual adjustment of the low-torque coupling.

Abstract: An improved garage door operator of the motor-driven chain-and-sprocket type comprising a molded plastic gear case assembly supporting an output shaft for rotation relative thereto. A molded plastic worm wheel is loosely disposed on the shaft for limited rotation relative thereto and is driven by a reversible electric motor through a worm. Camming surfaces on the worm wheel and a second element which is fixedly disposed on the shaft form a low-torque coupling such that under normal conditions the motor drives the shaft to move the garage door. If the door encounters an obstacle and is unable to move, continued rotation of the motor drives the cam surface of the second element up the cam surface of the wheel so as to axially shift the second element relative to the gear case to trip a reversing switch. Up and down limits are established by means of a small threaded shaft which is driven off of the worm wheel and which produces linear displacement of a limit switch actuator traveler.