| 摘要 |
PURPOSE:To eliminate the influence of an external noise and secondary reflection and to improve stability and reliability, by varying the period of ultrasonic wave pulse transmission according to the distance to an object, etc., and summing up received signals plural times and extracting signals higher than a prescribed level. CONSTITUTION:A pulse controller 1 which operates corresponding to the value of a counter 11 for counting distance controls a transmission pulse generator 3 to adjust the period of ultrasonic wave pulse transmission so that the longer the distance, the longer the period. The reflected pulse of the transmitted pulse from an obstacle 7 is received plural times and applied through shift registers 9a,9b... to an adder 9; and a sum output having a pulse level greater than the prescribed value is supplied through a pulse level detector 10 to the counter 11 as a counting stop signal. This constitution performs distance measurement free of the influence of an external noise. Further, while the distance is unchanged, the period of the transmitted pulses is varied at random to eliminate the influence of secondary reflection similarly. Thus, the stability and reliability of an ultrasonic wave distance measuring device are improved. |
