Patent GB-1129860-A (GB)
Title: Proximity sensing apparatus and sensor therefor
IPC: H03K17/955
Filed: 1966-11-11
Abstract: 1,129,860. Door operation by proximity sensing apparatus. WESTINGHOUSE ELECTRIC CORP. 11 Nov., 1966 [12 Jan., 1966], No. 50636/66. Heading E2M. [Also in Division H2] An elevator installation comprises doors, in the car and at the landings, which are adapted to be moved together, capacitive detectors being each mounted on the panels of the cardoor. The doors are maintained open so long as an object is present outside the car and in the capacitive space field of the detectors. Alternating potential is applied to the detectors in a balanced network, in which the voltage across the detectors is substantially zero when the object is not in the space, and reaches a detectable magnitude to maintain the doors open when the object is present. Each sensor SL, SR, has a capacitance to ground which is varied by the proximity of an object, and comprises a shield 27 connected to a centre-tap on oscillator OSC, the high-potential side of the supply being connected through capacitor C1 or C2 to a concave conductor 25 which extends along the edge of the door-panel. The presence of an object in the space field upsets the balance of this circuit and produces an output signal. In pre-amplifier PR the sensor signal is fed to cathode-follower CF3 associated with phase-shift networks PH1, PH2. The network PH1 and transformer T1 -produces a 180- degrees shift, whilst the transformer and network PH2 are combined to provide a 120- degrees shift. During the first portion of the door-closing operation, the signals from the two sensors are added 120 degrees out-upphase whereby the algebraic sum of equal responses produces a magnitude substantially equal to that of the separate responses. Thus, a person entering the car when the panels are fully opened would not reverse the movements of the panels. The sensitivity of the sensors is reduced as the panels approach the closed position by shunting network PH2, and, finally, the sensors are de-activated entirely as the panels reach the closed position. For this purpose, a number of switches, DS1-DS3 are operated progressively as the panels approach the closed position. Pre-amplifier LH has cathode follower CF1 associated with a summing network which combines the signals from the two sensors, the output cathode follower CF2 feeding a signal to detector DR. Sensitivity-switching relays K1, K3, reduce the signal and then remove it entirely when the panels are near the closed position. In channel SC the signal is filtered and then amplified by stage AMI, a similar circuit being used for bias channel BC which has output cathode follower CF6. The outputs from cathode followers CF5, CF6, are rectifled and filtered, and their difference is applied to pentode PE which causes relay D to drop out when the doors are to be reopened. The output of pentode PE controls the door-operating motor MO which is associated with landing-switch SW, close relay CL, and open relay OP. A probe 29 checks whether the sensing apparatus is operating properly and is actuated, simultaneously with the door-closing relay, when a push-button is operated temporarily to impress a potential between each probe and each concave conductor. The effect of this potential is similar to that of an object in proximity with a sensor. After this effect has produced a proper response, the probe is disconnected and the apparatus operates normally. If the system is not in proper operating condition an indicator is energised.