Fail safe obstruction detector for door operators and door operator system incorporating such detector

摘要

The light beam in an obstruction detector is coded into packets of pulses by a transmitter according to a code generated only by the transmitter. When the light beam is received, the receiver recovers the code signal and supplies it to a code detection circuit. In one preferred embodiment, to detect the code, the code detection circuit supplies the code signal and a delayed version of the code signal to an "exclusive or" gate. In another embodiment, a frequency detection circuit determines whether the code signal detected by the receiver is within a predetermined permissible range. If the code is not present, the door operator system reverses the door if it is closing, and prevents the door from closing if it already is in the up position, or if it is opening. The door operator system will operate in this way not only in response to obstructions, but also, in response to errors and malfunctions in the wiring to the transmitter and receiver, and in the transmitter and receiver themselves.