Electric door operator with slip clutch and dynamic braking

Abstract

An automatic door closer providing for use as a light duty door opener and having a slip clutch for protecting the electric gear drive power unit from damage due to overspeeding on excess loads applied by overriding manual door operation. Zener diodes across the power supply to the electric drive motor effectively throw a heavy electrical load on the motor and cause the clutch to slip if the motor is sufficiently oversped and caused to act as a higher voltage bucking generator, as by manually forcing the door substantially faster in the direction in which it is being driven. A direct current motor is used at considerably lower than its rated voltage so that electrical power may be safely applied continuously for holding the door closed with the motor stalled, and without the clutch slipping, with the clutch set to slip only when the force applied thereto is significantly higher than the force required to stall the motor yet safe for the drive unit. When the internal friction of the gear drive is added to the stalling force upon manually pushing open the closed door, the clutch is caused to slip and the door may thus be forcefully opened without damage to the drive unit. A switch actuated by the drive unit operating linkage on the output side of the clutch simultaneously removes power from the motor and connects a heavy electrical load thereto when the drive unit has driven the opening door to a predetermined stopping position. The motor then acts as a generator under the heavy load to resist farther motor rotation sufficiently so that the inertia force of the opening door causes the clutch to slip until the inertia force of the door is dissipated. A bypass diode permits automatic time-delayed application of closing power to the motor by bypassing the open switch which has removed opening power from the motor.

Dependencies are inferred from the claim text.