Abstract
Ultrasonic waves may be emitted from a transmitter/receiver sonic transducer, or separate transmitter working with a separate receiver, directly or reflected into the opening between doors of an elevator; responses reflected from objects or passengers between the doors which are received within a window of response are utilized to create a door reversal signal. The ultrasonic waves may be shaped into a curtain or sheet by means of a hyperbolic reflector opening downwardly toward the doors. To equalize time of travel for sound waves emanating from a single source on one side to all parts of the door opening, the reflector may also have a parabolic shape. The sound waves may be emitted in a cylindrical pattern to accommodate elevators having circular doors. Multiple reflectors may include a convex reflector to spread the sound waves vertically.
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