| 摘要 |
<p>PURPOSE:To enable a vehicle sensor to more accurately detect a vehicle by vertically emitting ultrasonic waves downward from an ultrasonic sensor installed to a prescribed location above a road surface and making the sensor to output when the count value of the number of lacking times of reflected waves from the road surface reaches a prescribed value. CONSTITUTION:Ultrasonic waves transmitted from the transmitter 6 of an ultrasonic sensor 1 are continuously inputted to a receiver 7 directly or after the waves are reflected by a certain object. After amplifying 8 and detecting 10 the ultrasonic waves, only fixed-level signal components of the direct and reflected waves are taken out and inputted to AND gates 12 and 13 in parallel with each other and the received direct and reflected wave signals are separately taken out based on a direct and reflected wave gate signals 14 and 15, and then, a vehicle 2 is detected by using the reflected waves as a detecting element. In addition, when the reflected waves from a road surface 3 when no vehicle 2 exists on the surface 3 are used as a reference wave and other reflected waves from the vehicle 2, etc., are entirely ignored, more accurate detection becomes possible. The timing of taking out the reference wave is decided depending upon the distance between the sensor 1 and road surface 3.</p> |
