Ultrasonic sensor

Abstract

An ultrasonic sensor, that transmits probe waves which are ultrasonic waves and acquires detection waves including reflected waves which have been reflected from surrounding objects, includes a transmitter/receiver that transmits the probe waves and acquires the detection waves, a detection wave processing section that executes processing for passing a predetermined frequency band which includes the frequency of the probe waves, an amplitude measurement section which measures the amplitude of the detection waves, and a judgement section which judges whether there is adherence of foreign matter on the transmitter/receiver, based on a relationship between a time axis and values of the amplitude of the detection waves during a reverberation interval following the termination of transmitting the probe waves.

1 . An ultrasonic sensor that transmits probe waves which are ultrasonic waves, and acquires detection waves that include reflected waves which have been reflected from surrounding objects, comprising:
 a transmitter/receiver that transmits the probe waves and acquires the detection waves;   a detection wave processing section that executes processing for passing a predetermined frequency band which includes the frequency of the probe waves;   an amplitude measurement section that measures the amplitude of the detection waves; and   a judgement section that judges whether there is adherence of foreign matter on the transmitter/receiver, based on a relationship between a time axis and values of the amplitude of the detection waves during a reverberation interval following the termination of transmitting the probe waves.   
     
     
         2 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section acquires, as the relationship between the time axis and the amplitude, an interval extending from the point at which the amplitude falls below a first threshold value until the amplitude falls below a second threshold value, and executes the judgement based on the acquired interval.   
     
     
         3 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section provides, as the time axis, a prescribed interval that follows the point at which the amplitude falls below a threshold value, and the judgement section acquires a count of a number of local maximums of the amplitude in the prescribed interval, and executes the judgement based on that count.   
     
     
         4 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section provides, as the time axis, a prescribed interval that follows the point at which the amplitude falls below a threshold value, and the judgement section executes the judgement based on the maximum value of the amplitude in the prescribed interval.   
     
     
         5 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section provides, as the time axis, a prescribed interval that follows termination of transmitting the probe waves, and the judgement section acquires a count of a number of local maximums of the amplitude in the prescribed interval, and executes the judgement based on that count.   
     
     
         6 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section provides, as the time axis, a prescribed interval that follows the termination of transmitting the probe waves, and the judgement section executes the judgement based on the maximum value of the amplitude in the prescribed interval.   
     
     
         7 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section acquires, as the relationship between the time axis and the amplitude, an area enclosed by an envelope of values of the amplitude, and executes the judgement based on that area.   
     
     
         8 . The ultrasonic sensor according to  claim 7 , wherein
 the judgement section acquires the area after the amplitude has fallen below a threshold value, and executes the judgement based on that area.   
     
     
         9 . The ultrasonic sensor according to  claim 7 , wherein
 the judgement section acquires respective areas for each of prescribed intervals, following termination of transmitting the probe waves, and executes the judgement based on changes in the areas.   
     
     
         10 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section sets an upper limit value to the values that can be acquired for the amplitude, and when the amplitude of the detection waves is greater than the upper limit value, makes the amplitude of the detection waves the upper limit value.   
     
     
         11 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section executes the judgement by comparing a relationship between the time axis and the amplitude that is based on the acquired detection waves with a predetermined relationship between the time axis and the amplitude.   
     
     
         12 . The ultrasonic sensor according to  claim 1 , wherein
 the detection wave processing section is equipped with a plurality of filters which pass respectively different frequency bands, and   the judgement section compares the relationships between the time axis and the amplitude for the respective outputs passed by the different filters, and executes the judgement by means of the comparison result.   
     
     
         13 . The ultrasonic sensor according to  claim 1 , wherein
 the judgement section acquires the correlation value between a waveform expressing the time-axis variation of the amplitude and a waveform serving as a reference, and executes the judgement by means of the correlation value.   
     
     
         14 . The ultrasonic sensor according to  claim 1 , wherein
 the detection wave processing section is equipped with a plurality of filters which pass respectively different frequency bands, and   the judgement section acquires a correlation value between respective waveforms that express the time-axis variation of the amplitudes passed by the different filters, and executes the judgement by means of the correlation value.   
     
     
         15 . The ultrasonic sensor according to  claim 1 , wherein
 the ultrasonic sensor further acquires the frequency of the probe waves,   the judgement section compares the acquired frequency with a frequency that serves as a reference frequency of the probe waves, and   the ultrasonic sensor executes the judgement by using a first condition that is based on time and amplitude, and a second condition that is based on frequency.