| 摘要 |
PURPOSE:To take a measurement of distance while reducing the evil influence of multiple reflection by exciting an ultrasonic vibrator periodically by an oscillator which has >=2 kinds oscillation frequencies, and selecting the reflected wave of an ultrasonic wave signal from an obstacle as to a frequency and time. CONSTITUTION:A part (A) encircled with a broken line is a circuit which measures the distance from an antenna 1 to the obstacle and consists principally of a reference signal generator 5, pulse counter 6, D-FF 7, and latch 8. A part (B) encircled with a broken line, on the other hand, is a circuit which measures the angle of rotation of the antenna 1 and consists principally of a rotation detector 3, pulse counter 9, and latch 10. Then, a control circuit 11 controls the switching circuit of a transmitted and received signal processor 4 to output only a signal which is reflected directly by the obstacle, so the evil influence of multiple reflection is reduced. Then, a central processor 12 measures the distance from the antenna 1 to the obstacle and the angle of the antenna 1 to recognize the position of the obstacle to begin with excitation control over the ultrasonic vibrator.
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