| 摘要 |
<p>PURPOSE:To detect the presence of an object without fail even when a reflected wave of a level very near to a threshold value is received due to fluctuation of attenuation of an ultrasonic pulse, by providing a plurality of pulse type ultrasonic sensors in parallel and by determining the logical sum of detection outputs by an arithmetic circuit. CONSTITUTION:It is determined by an ultrasonic transmission-reception circuit 1a, for instance, whether a received reflected wave exceeds a prescribed threshold value or not, and an object is determined not to be present when the wave does not exceed the threshold value, while a time delay caused from transmission of an ultrasonic pulse to reception of the reflected wave is measured when the wave exceeds the threshold value. When the time delay is within a prescribed time, the object is determined to be present within a prescribed range of distance and an object detection signal is outputted. Besides, a distance to the object is also measured on the basis of the aforesaid time delay and outputted. Other ultrasonic sensors Sb,... Sn are constructed likewise and the sensors are provided in parallel toward the same object 4 of detection. Detection outputs are inputted to an arithmetic circuit 3, and by determining the logical sum thereof, the object detection signal is outputted.</p> |
