Detection device having energy transmitters located at vertically spaced apart points along movable doors

A detection system for detecting the presence of an object in the path of a closing sliding door, characterized by:

• a plurality of energy transmitters located at vertically spaced apart points on one vertical edge of the area into which the door slides to a closed position;
• a second vertical edge on said area that is substantially parallel to said one edge, the distance between said one edge and said second edge decreasing as the door closes;
• an energy detector capable of providing an output signal in response to the energy transmitted by each transmitter, and is located on said second vertical edge at a position at which an imaginary straight line between the detector and each transmitter is at an angle greater than 0 but less than 90 degrees to an imaginary line defining the direction in which the door slides;
• means for activating the transmitters sequentially as the door closes;
• means for providing a door control signal when a transmitter is activated and an output signal is not produced by the detector each energy emitter and energy detector having relative motion towards each other as the door closes.