Abstract: A door obstruction detector employs an optical device, such as a segmented Fresnel lens, and a PIR sensor attached to a moving door, so that the optical device causes an image of an object, in a detection zone, to move across a sensing region of the PIR sensor when the door moves. When the object is sensed in the detection zone, a drive signal is generated for controlling movement of the door. Thermistors can be used to compensate for variation in ambient temperature to adjust detection sensitivity.

Abstract: A laser light emitting diode (1, 2) situated at a focal point of a specially shaped lens (3, 4) produces a very thin intense fan-shaped beam. One or two such laser light transmitters are used to radiate a fan-shaped beam which is intercepted by a person or object thereby scattering laser light, by diffuse reflection. A cylindrical lens (5) receives a reflected component and this is detected by sensors (6) which are connected to circuitry including a synchronous detector (12) and comparator network (13, 14). The synchronous detector (12) is driven by a square wave oscillator (8) which modulates the laser light.

Abstract: Proximity sensor apparatus has at least first and second antenna strips arranged along the edge of a structure. The antenna strips receive signals reflected by an object whose proximity is to be detected. Signal processing circuitry is coupled to the antenna strips for receiving and processing the signals picked up by the antenna strips. Proximity detection may occur when the difference in signal strength received by the two antenna strips exceeds a threshold level. In one embodiment, the difference between the maximum and minimum signals is determined and increases the threshold as the difference between signals decreases. In another embodiment, the difference in signal strength is used to determine the position of the object on one side or another of the antenna strips. In yet another embodiment, a bootstrap electrode is positioned behind a single antenna strip and is electrically connected to follow the voltage induced on the antenna strip by the received signal.

Abstract: Proximity detector circuitry of particular value in controlling the operation of elevator car doors. Sensors are set in the edge of the door. The outputs of the sensors are fed to one or more differential amplifiers which produce outputs dependent on the sensors. One such output may be compared in a further differential amplifier with its previous output slightly delayed in time and the results of the comparison used to actuate a door closing/opening control circuit. In addition large outputs arising from major differences in the sensors output may be fed (suitably attenuated) to the closing/opening control circuit.

Abstract: Lift car position control systems are described which use an elongate code bearing member which runs up and down the lift shaft. The member is preferably fixed though it may move with the lift car and cooperates with a moving or fixed detector respectively. The output of the detector is conveniently fed to a microprocessor which in dependence upon its programming and data concerning the lift and the building in which it is installed emits control signals to control the lift motor. The system is particularly valuable as allowing continuous monitoring of rope wear or stretch, lift car over-loading, acceleration, rope slippage and like operating parameters.