Safety arrangement for automatic door operator

Details Safety arrangement for automatic door operator Safety arrangement for automatic door operator

1991-08-26

1992-09-01

Kannan, Philip C.

Movable or removable closures

Safety means responsive to obstruction to closure

Sensing shoe on leading edge

49 28, E05F 1502

Patent

active

051428229

ABSTRACT:
A safety arrangement for an automatic door operator wherein the door edge has mounted thereon a stretched electrically conductive cable which, when deflected upon encountering an obstruction, will change the inductance of a loop of which the cable forms a part. A capacitor is in parallel with this loop so that the capacitor together with the inductance of the loop form a resonant tank circuit. The tank circuit is electrically driven by a voltage controlled oscillator. The phase of the loop current is compared with the phase of the voltage across the capacitor and the phase difference is utilized to control the voltage controlled oscillator to maintain the tank circuit in resonance (i.e, zero phase difference). The detection of a sudden change in phase difference, which occurs when the loop inductance is suddenly changed due to the encountering of an obstruction by the door edge, results in the generation of an obstruction signal for activating the safety feature of the door operator.

REFERENCES:
patent: 3975861 (1976-08-01), Baump et al.
patent: 4115952 (1978-09-01), French
patent: 4335339 (1982-06-01), Brickner
patent: 4369344 (1983-01-01), Diamond
patent: 4943757 (1990-07-01), Richter et al.
patent: 5027552 (1991-07-01), Miller et al.

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