Continuously monitored supplemental obstruction detector for garage door operator

Claim 1

In an automatic door operator having a motor coupled for moving a door between an open and a closed position covering an opening in response to command signals and for reacting to a door obstruction, the improvement comprising: an obstruction sensor attached to the leading edge of the door, the obstruction sensor comprising a compressible element having first and second ends and at least a pair of conductors extending between the first and second ends, the conductors having a conducive relationship subject to change in response to compression of the compressible element by an obstruction; a controller controlling operation of the motor corresponding to the command signals; an electrical coupling between the controller and at least one of the conductors at the first end of the obstruction sensor for supplying electrical power to the conductors; an oscillator coupled to the conductors at the second end of the obstruction sensor for receiving power from the conductors in the absence of the obstruction and for imparting an oscillating signal to the conductors, whereby the oscillating signal is fed by the electrical coupling to the controller in the absence of the obstruction and the oscillating signal is no fed to the controller when the conducive relationship is changed in response to compression of the compressible element by the obstruction; the controller being responsive to the oscillating signal for responding to the command signals during the presence of the oscillating signal and for at least stopping the motor to stop the door in the absence of the oscillating signal when the motor is closing the door.