US 4,307,456 AGranted

Ultrasonic rangefinder

AssigneeMatsushita Electric Industrial Co., Ltd.

InventorsYukihiko Ise, Shigeru Hayakawa

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Abstract

An ultrasonic rangefinder providing a correct distance measurement and comprising a first transducer for transducing electric signals into ultrasonic waves and transmitting the ultrasonic waves, a second transducer for receiving the ultrasonic waves and transducing the ultrasonic waves into electric signals, a differentiation circuit, and a comparator for comparing a level of a differentiated output signal from the differentiation circuit with an output signal level of the second transducer and detecting a threshold time when the level of the differentiated output signal from the differentiation circuit becomes lower then the output signal level of the second transducer where a threshold signal level of the comparator is automatically varied with respect to a time lapse of the travelling ultrasonic waves coming back to the rangefinder after being reflected by an object, thus overcoming the conventional problems due to the spurious-like direct waves.

Claims10

Dependent claims

An ultrasonic rangefinder comprising:

a first transducer for transducing electric signals into ultrasonic waves and transmitting said ultrasonic waves,
a second transducer for receiving said ultrasonic waves and transducing said ultrasonic waves into electric signals,
a first timer means for determining a starting time for transmitting said ultrasonic waves,
a carrier frequency generator for generating a carrier signal of a frequency of said ultrasonic waves,
a second timer means for generating a pulse having a time width at least as long as a time corresponding to a travelling time of said ultrasonic waves from said first transducer to said second transducer at the time when said first transducer begins to transmit said ultrasonic waves,
a differentiation circuit for differentiating said pulse of said second timer means, and
a comparator for comparing a level of said differentiated output signal from said differentiation circuit with an output signal level of said second transducer and detecting a threshold time when said level of said differentiated output signal from said differentiation circuit means becomes lower than said output signal level of said second transducer.

4 more elements

An ultrasonic rangefinder comprising:

a first transducer for transducing electric signals into ultrasonic waves and transmitting said ultrasonic waves,
a second transducer for receiving said ultrasonic waves and transducing said ultrasonic waves into electric signals,
a first timer means for determining a starting time for transmitting said ultrasonic waves,
a carrier frequency generator for generating a carrier signal of a frequency of said ultrasonic waves,
a second timer means for generating a pulse having a time width at least as long as a time corresponding to a travelling time of said ultrasonic waves from said first transducer to said second transducer at the time when said first transducer begins to transmit said ultrasonic waves,
a differentiation circuit for differentiating said pulse of said second timer means,
a comparator for comparing a level of said differentiated output signal from said differentiation circuit with an output signal level of said second transducer and detecting a threshold time when said level of said differentiated output signal from said differentiation circuit becomes lower than said output signal level of said second transducer,
a logic gate for passing a burst signal made from a pulse signal of said first timer means and said carrier signal of said carrier frequency generator,
a first amplifier for amplifying said burst signal, and
a second amplifier for amplifying said electric signals of said second transducer.

7 more elements

Dependencies are inferred from the claim text.