To measure distance accurately and stably by frequencyanalyzing the frequency difference between a frequency sweep signal for generating ultrasonic wave and a reflection ultrasonic signal.
The operation result of a mixer 15 is input in LPF 16. The LPF 16 cuts high frequency component in the calculation results to obtain the frequency difference between a base signal and a reflection signal. The signal extracted by the LPF 16 is input in a frequency analyzer 17 and converted to voltage signal or current signal proportional to the frequency. As this voltage or current signal is in proportion to distance to an object 4, the distance to the object 4 is obtained from the relation between the voltage or current signal and the object 4. In this manner, it becomes unnecessary to set a threshold and capture the edge of pulse for especially obtaining delay. Also it is only a purpose to analyze the frequency even in the case of large unevenraess of the object 4, so that the consideration of uncertain element caused for capturing the level of the pulse is not necessary and stable distance measurement becomes possible.
SHIBAIKE KUNIO
ISHIOKA MASATO
