Apparatus for detecting the number of objects

Abstract

Apparatus for detecting the number of objects such as persons in which at least one ultrasonic wave signal transmitter-receiver is used to transmit ultrasonic wave signals toward objects the number of which is to be detected, and to process waves reflected therefrom, thus determining the number of such objects existing within a predetermined area. When plural ultrasonic wave transmitter-receivers are used, they are so arranged that their detection regions are partly overlapped, thereby assuring uniform detection sensitivity over the area. A detection time is reduced by simultaneously driving the ultrasonic wave signal transmitter-receivers. The ultrasonic wave transmitter and receiver of each transmitter-receiver may be directed to different points in a target plane within a range permitting the receiver to receive reflected ultrasonic wave signals, thereby equalizing the detection sensitivity in the direction of the difference, thus improving the detection accuracy. Only one ultrasonic wave signal transmitter-receiver may be used for attaining the same effect, which is provided with one transmitter and plural receivers, or with one receiver and plural transmitters, the one transmitter or receiver and the plural receivers or transmitters being directed to respective different points in a target plane within a range permitting the receiver or receivers to receive reflected ultrasonic wave signals.