Patent ID: 7253890
Filing Date: 2007-08-07
Classification: G01V

Abstract:
1. An arrangement for detecting an object in a door entranceway bounded by upright walls, comprising: a) a transmitter supported by one of the walls for transmitting a light beam across the entranceway toward the other of the walls; b) a reflector supported by the other of the walls for reflecting the light beam across the entranceway toward the one of the walls; c) a receiver supported by the one of the walls for receiving the light beam reflected by the reflector when the object is absent from the entranceway, and for receiving light reflected by the object when the object is present in the entranceway; and d) a controller having a memory which stores a reference arrival time of the light beam at the receiver when the object is absent from the entranceway, and for measuring an obstacle arrival time of the light at the receiver when the object is present in the entranceway, and for generating a control signal indicative of object presence in the entranceway when the measured obstacle arrival time is less than the reference arrival time by a given margin, wherein the reference arrival time corresponds to the time for the light beam to be transmitted by the transmitter across the entranceway and received by the receiver when the object is absent from the entranceway, and wherein the obstacle arrival time corresponds to the time for the light beam to be transmitted by the transmitter and received by the receiver when the object is present in the entranceway.