JP2010281603A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic sensor which can perform high-accuracy azimuth detection, without being affected by variations in the characteristics of a receiving element. <P>SOLUTION: When A/D conversion with respect to a received signal Ra from one of sensing elements is performed, and four pieces of conversion data corresponding to data for one period Tc of an ultrasonic wave are obtained, an in-phase component Ip and a quadrature component Qp are calculated by adding and subtracting the obtained conversion data(S110-S130). When an amplitude Ap calculated from the in-phase component Ip and the quadrature component Qp is larger than a reception detection threshold TH, a reflected wave is considered to have been received, and a phase ϕp(=ϕa) is calculated from the in-phase component Ip and the quadrature component Qp calculated earlier (S140-S160). After that, similarly to the case, obtaining of conversion data, calculation of an in-phase component Ip and a quadrature component Qp, and calculation of a phase ϕp(=ϕb) are performed with respect to a received signal Rb from the other sensing element, and moreover the direction of arrival of the ultrasonic wave is calculated from the difference between the phases ϕa and ϕb(S170-S210). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic sensor that detects the position of an object using ultrasonic waves.

  Conventionally, as shown in FIG. 7, the reflected waves from the object M that transmits ultrasonic waves and reflects the ultrasonic waves are received by a plurality of receiving elements E1, E2 at different positions, and each receiving element E1, E2 is received. From the difference in the reception timing at, that is, the round-trip propagation time difference ΔT (distance difference ΔL = C · ΔT; where C is the speed of sound) required for the ultrasonic wave to reciprocate the distance to the object, each receiving element E1, E2 The phase difference of the received signals is obtained, and the arrival direction of the reflected wave, that is, the azimuth angle θ at which the object M exists is obtained by a known phase monopulse method (see, for example, Patent Document 1).

  In FIG. 7, for ease of viewing the drawing, the round-trip propagation time difference ΔT in the receiving elements E1 and E2 is shown to correspond to a plurality of periods of the ultrasonic frequency. The round-trip propagation time difference ΔT is a length corresponding to one cycle.

Japanese Patent No. 4013864

  By the way, when detecting the reception timing of the reflected wave at the sensor element, it is difficult to detect the rising timing of the reflected wave that is the true reception timing (hereinafter referred to as “actual timing”). As shown in FIG. 8, a comparator is used to detect the timing at which the amplitude of the reflected wave reaches a preset threshold voltage (hereinafter referred to as “detection timing”) as the reception timing. Therefore, in order to improve the detection accuracy of distance and direction, it is necessary to make the relationship between the true timing and the detection timing constant in any receiving element.

  However, the sensitivity of each receiving element varies from element to element. If the amplitude of the received signal varies due to the variation, the relationship between the actual timing and the detection timing changes. In order to cancel this sensitivity variation, it is necessary to provide a receiving circuit for amplifying the received signal and an adjusting circuit for adjusting the sensitivity and offset of the receiving circuit for each receiving element.

In other words, the number of receiving circuits and adjustment circuits required is the same as the number of receiving elements, so that there are problems that the circuit scale becomes large and that adjustment circuits need to be set.
Also, as shown in FIG. 9, the amplitude of the received signal that received the reflected wave becomes smaller as the distance of the object becomes longer as the propagation distance of the ultrasonic wave becomes longer. It is also necessary to change the threshold voltage in accordance with the amplitude of the signal and consequently the timing of receiving the reflected wave.

  However, the amplitude of the received signal varies not only with the timing of receiving the reflected wave (ie, the round-trip propagation time) but also with the material and shape of the object that reflects the ultrasonic wave, the surrounding environmental conditions, etc. There is a problem that it is impossible to reflect the threshold voltage.

  In order to solve the above problems, an object of the present invention is to provide an ultrasonic sensor capable of highly accurate azimuth detection regardless of variations in characteristics of receiving elements.

  In the ultrasonic sensor of the present invention made to achieve the above object, the transmitting / receiving means transmits ultrasonic waves that continue at a constant frequency for a certain period of time, and the reflected waves from the object that reflected the ultrasonic waves have different positions. Received by a plurality of receiving elements, and the detection means detects the in-phase component and the quadrature component of the reception signal by performing quadrature detection on the reception signal supplied from the transmission / reception means.

  Then, the amplitude calculation means obtains the amplitude of the received signal from the detection result of the detection means for one of the receiving elements, and when the calculation result of the amplitude calculation means is equal to or greater than a preset reception detection threshold, The calculating means obtains the phase of the received signal for each receiving element from the detection result of the detecting means for each receiving element.

Then, the azimuth detecting means obtains the phase difference of the received signals between the receiving elements from the calculation result of the phase calculating means, and obtains the arrival direction of the reflected wave from the phase difference.
According to the ultrasonic sensor of the present invention configured as described above, the phase difference of the received signal is not obtained from the propagation time of the ultrasonic wave but is obtained from information obtained by quadrature detection. It can be obtained accurately without being affected by the level or reception detection threshold. As a result, highly accurate azimuth detection can be performed regardless of variations in sensitivity of the receiving elements, distance to the object to be detected, and the like.

  Further, according to the ultrasonic sensor of the present invention, since it is not necessary to adjust the variation in sensitivity of the receiving elements, it is possible to process the received signal from each receiving element with a single circuit, and to reduce the device scale. It can be downsized.

  In this case, for example, the transmission / reception unit includes a selection unit that selectively selects one of the reception elements and supplies a reception signal from the selected reception element to the detection unit, and the phase calculation unit includes the predetermined period of time. What is necessary is just to comprise so that the detection result in the detection means about a some receiving element may be acquired by switching the selection in a selection means within (period in which transmission of an ultrasonic wave is continued).

  In the ultrasonic sensor of the present invention, the detection means may be constituted by, for example, a signal processing means and an addition / subtraction means. That is, the signal processing means generates a signal obtained by sequentially integrating or averaging the received signals at every timing corresponding to a quarter cycle of the ultrasonic wave, and the addition / subtraction means generates the signal D1 generated by the signal processing means. , D2, D3, D4,... Are added and subtracted according to the following equations to calculate the in-phase component Ip and the quadrature component Qp.

Ip = D _4p-3 + D _4p-2 −D _4p−1 −D _4p
Qp = _{D4p-3 -D4p-2 -D4p-1} + _D4p
(However, p = 1, 2, 3, ...)
That is, by integrating or averaging the detection signal every quarter period of the ultrasonic wave, and adding or subtracting four integral values or average values obtained during a time interval equal to one ultrasonic period, The in-phase component Ip and the quadrature component Qp are extracted every time interval equal to one period of the continuous wave.

  Therefore, according to the ultrasonic sensor of the present invention, since quadrature detection can be realized by a simple process (addition / subtraction) executed by a digital circuit using various gate circuits or an arithmetic circuit, the apparatus can be reduced in size and orthogonally crossed. Compared with the case where the detection is performed by an analog circuit, it is possible to improve the environment resistance (resistance to noise and temperature change) and thus the operation reliability.

  By the way, in the ultrasonic sensor of the present invention, the signal processing means may be any circuit that can integrate or average the signal level of the received signal at every timing corresponding to a quarter cycle of the ultrasonic wave. Although a simple circuit may be used, it is desirable to realize it with a digital circuit.

  Specifically, the signal processing means includes, for example, a delay unit that delays and outputs a pulse signal with a delay time corresponding to the signal level of the received signal, and is cascade-connected, and the pulse signal is output from the delay time of each delay unit. The count means uses the pulse delay circuit that transmits the signal while sequentially delaying at the timing corresponding to one quarter of the ultrasonic wave, and determines the number of stages of the delay unit through which the pulse signal has passed in the pulse delay circuit. It is desirable to be configured to count and obtain the count value by the counting means as an integral value or an average value.

  That is, when the pulse delay circuit is operated as described above, the delay time when the pulse signal passes through each delay unit in the pulse delay circuit changes according to the signal level of the received signal. The fluctuation amount is averaged as the pulse signal passes through a plurality of delay units.

  According to the ultrasonic sensor of the present invention configured as described above, since the signal processing means can be configured by only a digital circuit, the other digital circuits can be integrated as one IC chip. The apparatus can be reduced in size.

  In addition, since the ultrasonic wave attenuates according to the propagation distance (and thus the elapsed time from transmission), in the ultrasonic sensor of the present invention, the phase calculation means lowers the reception detection threshold according to the elapsed time from the ultrasonic transmission. You may be comprised so that it may make.

  That is, the longer the elapsed time, the lower the signal level of the received signal, so that the reception detection threshold value is appropriately changed to an optimal value according to the signal level of the received signal. In this case, as shown in FIG. 10, the method of decreasing may be stepwise or continuous.

  According to the ultrasonic sensor of the present invention configured as described above, erroneous detection of a reflected wave due to noise or the like can be suppressed.

The block diagram which shows the whole structure of an ultrasonic sensor. The block diagram including the partial circuit diagram which shows the structure of an A / D converter. The flowchart which shows the content of the direction detection process. Explanatory drawing about a quadrature detection. Explanatory drawing which shows the waveform of a received signal and its amplitude and phase. Explanatory drawing which shows the operation timing of a selector, and the waveform of a received signal. Explanatory drawing which shows the principle of the azimuth | direction detection by an ultrasonic wave. Explanatory drawing regarding the threshold value which detects the presence or absence of a received signal. Explanatory drawing which shows a mode that an ultrasonic wave attenuate | damps according to propagation distance. Explanatory drawing which illustrates the setting method of a reception detection threshold value.

Embodiments of the present invention will be described below with reference to the drawings.
[overall structure]
FIG. 1 is a block diagram showing the overall configuration of the ultrasonic sensor 1.

  As shown in FIG. 1, the ultrasonic sensor 1 includes a transmission / reception unit 2 including a pair of conversion elements 21 and 22 that convert an electric signal into a sound wave and a sound wave into an electric signal, and an activation command C1 is input. Then, a transmission circuit 3 that generates a transmission signal S having a certain frequency belonging to the ultrasonic frequency band for a certain period (for example, about 30 wavelengths) and two reception signals Ra and Rb supplied from the transmission / reception unit 2 A selector 4 that selects and outputs one of them according to the selection command C2 and a supply path for one reception signal Ra supplied from the transmission / reception unit 2 and passes the reception signal Ra to the selector 4 side, and a transmission circuit And a directional coupler 5 that passes the transmission signal S generated by the transmission / reception unit 2 to the transmission / reception unit 2 side.

  That is, of the conversion elements 21 and 22 constituting the transmission / reception unit 2, one conversion element 21 is configured to be used for both transmission and reception, and the other conversion element 22 is configured to be used exclusively for reception. In addition, although it is common to use a piezoelectric element for the conversion elements 21 and 22, it is not restricted to this, What kind of element may be used if the conversion between an electrical signal and a sound wave is possible.

  The ultrasonic sensor 1 also outputs the output of the amplifier 61 that amplifies the output R of the selector 4, the output of the band pass filter (BPF) 62 that extracts the signal in the same frequency band as the transmission signal S from the output of the amplifier 61, and the output of the BPF 62. A receiving circuit 6 comprising an A / D converter 63 for D-converting and outputting, and a known microcomputer mainly composed of a CPU, ROM and RAM, generating a start command C1 and a selection command C2, and transmitting circuit 3. Direction detection for controlling the operation of the selector 4 and obtaining the direction in which the object reflecting the ultrasonic wave exists based on the output (conversion data) Dq (q = 1, 2, 3,...) Of the receiving circuit 6 And a data processing unit 7 that executes at least processing.

  Note that the switch for controlling the passage and blocking of the reception signal in the selector 4 is an analog switch, and the transmission circuit 3, the selector 4, and the reception circuit 6 are configured by a one-chip IC.

  The amplifier 61 is generally a known charge amplifier, but may be a current amplifier, an inverting amplifier, or the like. Further, the BPF 62 may be omitted because the quadrature detection process described later also serves as a filter function.

[Details of A / D converter]
As shown in FIG. 2, the A / D converter 63 connects the delay units 71 in a ring shape, and when the activation signal Pin is input to the first-stage delay unit 71a, the first-stage delay unit 71a to the next-stage delay unit 71. The pulse signal is sequentially transmitted to the pulse signal, and the pulse signal is returned from the last delay unit 71b to the first delay unit 71a, so that the pulse signal circulates (referred to as a ring delay line). RDL)).

  The A / D converter 63 also includes a counter 73 that counts the number of laps of the pulse signal in the pulse delay circuit 72, and a pulse in the pulse delay circuit 72 at the rising (or falling) timing of the sampling signal SCK. A latch & encoder 74 that detects (latches) the arrival position of the signal, converts the detection result into digital data of a predetermined bit representing the number of stages from the head of the delay unit 71 through which the pulse signal has passed, and outputs The latch circuit 75 latches the count value of the counter 73 at the rising (or falling) timing of the sampling signal SCK, the output from the latch circuit 75 is the upper bit data b, and the output from the latch & encoder 74 is the lower bit data a. And the input data DT is input to the rising edge of the sampling signal SCK (or The signal is latched at the timing of (falling), finds the difference from the previous value latched one cycle before the sampling signal SCK, and is activated by the activation command C1 and the subtraction unit 76 that outputs the obtained result as conversion data Dq. And a control unit 78 that generates the signal Pin and the sampling signal SCK. That is, the A / D converter 63 is configured by a known time A / D conversion (TAD) circuit.

  The controller 78 is a period obtained by adding the pulse duration to the time required for the ultrasonic wave to reciprocate the maximum measurement distance of the sensor 1 after activation by the activation command C1 (hereinafter referred to as “reception period”). During this time, the sampling signal SCK is continuously output, and the activation signal Pin is controlled to be at the H level only during the reception period.

  Each delay unit 71 constituting the pulse delay circuit 72 is configured by a gate circuit including an inverter or the like, and each delay unit 71 receives a reception signal R that is an output of the BPF 62 via a buffer 77. Applied as power supply voltage.

  For this reason, the delay time of each delay unit 72 is a time corresponding to the voltage level of the received signal R, and converted data Dq representing the number of delay units 71 that have passed through the pulse delay circuit 72 within the sampling period Ts. Is obtained by averaging (or integrating) the voltage level of the received signal R within the period Ts.

The sampling period Ts is set to a quarter of the period Tc of the ultrasonic wave (transmission signal S) (see FIG. 4).
[Direction detection processing]
Here, the azimuth | direction detection process which CPU of the data processing part 7 performs is demonstrated along the flowchart shown in FIG. This process is started periodically.

  When this process is started, first, in S110, the selector 4 is initialized. Specifically, the selector 4 outputs a selection command C2 for selecting the conversion element 21 (that is, the reception signal Ra). As a result, the reception signal Ra from the conversion element 21 is supplied to the reception circuit 6 via the selector 4.

In S120, the measurement is started by outputting a start command C1 to the transmission circuit 3.
The transmission circuit 3 that has received the start command C1 transmits a transmission signal having a constant frequency for a certain period (about 30 wavelengths). Further, the data processing unit 7 also starts taking in the conversion data Sq supplied from the receiving circuit 6.

In S130, ultrasonic conversion data _D4p-3 , _D4p-2 , _D4p-1 , _D4p (where p = 1, 2, 3,...) For one period Tc of the ultrasonic wave are received. Wait until acquisition from the circuit 6 and when the acquisition is completed, the four converted data D _4p-3 , D _4p-2 , D _4p-1 , D _4p are _{added or} subtracted according to the equations (1) and (2). Thus, quadrature detection processing for calculating the in-phase component Ip and the quadrature component Qp is executed.

Ip = _D4p-3 + _{D4p-2 -D4p-1 -D4p} (1)
Qp = _{D4p-3 -D4p-2 -D4p-1} + _D4p (2)
As shown in FIG. 4, equation (1) corresponds to multiplying the received signal by an approximate sine wave represented by “1” in the first half period and “−1” in the second half period. The first quarter period obtained by dividing one period into “1” is represented by “1”, the second and third quarter periods are represented by “−1”, and the last quarter period is represented by “1”. This corresponds to multiplying the received signal by an approximate cos wave.

  In S140, the amplitude Ap is calculated according to the equation (3) based on the in-phase component Ip and the quadrature component Qp calculated in S130.

  In S150, it is determined whether or not the amplitude Ap calculated in S140 is larger than a preset reception detection threshold TH. Note that the reception detection threshold TH is set so as to decrease as time elapses from the transmission timing in consideration of the attenuation of the ultrasonic wave according to the propagation distance.

  If an affirmative determination is made in S150, it is determined that a reflected wave has been received, and the process proceeds to S160, where the phase φp (= φa) is obtained according to the equation (4) based on the in-phase component Ip and the quadrature component Qp calculated in S130. ) Is calculated.

In S170, the selector 4 is switched by outputting a selection command C2 that causes the selector 4 to select the conversion element 22 (that is, the reception signal Rb).
In S180, as in the previous S130, conversion data _D4p-3 , _D4p-2 , _D4p-1 , and _D4p for one ultrasonic cycle Tc (that is, four) are acquired from the receiving circuit 6. When the acquisition is completed, the four converted data D _4p-3 , D _4p-2 , D _4p-1 , D _4p are _added and subtracted according to the equations (1) and (2) to obtain the in-phase component Ip, An orthogonal component Qp is calculated.

In S190, similarly to the previous S160, the phase φp (= φb) is calculated according to the equation (4) based on the in-phase component Ip and the quadrature component Qp calculated in S180.
In S200, based on the phase difference Δφ (= φa−φb) between the phases φa and φb calculated in the previous S160 and S190, an azimuth angle θ where an object reflecting ultrasonic waves exists using a known phase monopulse technique. Is calculated.

In S210, the measurement result indicating that an obstacle is present is output together with the azimuth angle θ where the obstacle is present, and the present process is terminated.
If a negative determination is made in the previous S150, the process proceeds to S220, where it is determined whether the measurement time has elapsed, and if not, the process returns to S130 assuming that no reflected wave has been received.

On the other hand, if it is determined in S220 that the measurement time has elapsed, the process proceeds to S230, a measurement result indicating that no obstacle is present is output, and the process ends.
[Operation example]
FIG. 5 is an explanatory diagram schematically showing the waveforms of the received signals Ra and Rb.

The envelope of the waveform of the reception signals Ra and Rb (however, the transmitted ultrasonic frequency band) from the conversion elements 21 and 22 has rising and falling portions.
The amplitude Ap calculated from the in-phase component Ip and the quadrature component Qp is a digital value representing the envelope value.

  The phase φp (φa, φb) is an unstable value when there is no signal, and is fixed to a constant value when there is a signal. That is, it can be seen that the phase can be accurately specified as long as the signal exists without detecting the rising timing of the signal.

  In FIG. 5, the amplitude Ap and the phase φp are shown continuously. However, since the quadrature detection output is calculated at every timing corresponding to one period Tc of the ultrasonic wave, in actuality, Takes discrete values.

In FIG. 5, at the timing of time A, the amplitude Ap reaches the reception determination threshold value TH.
The phase φp can be calculated on the basis of the same in-phase component Ip and quadrature component Qp used for calculating the amplitude Ap (and the same conversion data D _4p-3 , D _4p-2 , D _4p-1 , D _4p ). Therefore, the phase φp (= φa) is also obtained at the timing of time A (see the arrow in the figure).

Thereafter, the selector 4 is switched to obtain the phase φp (= φb) at the timing of time B (see the arrow in the figure).
In order to obtain the phase φb at the time B, the selector 4 may be switched at a timing earlier than the time B by at least one ultrasonic cycle Tc. Furthermore, since conversion data Dq after time B is not necessary for this processing, acquisition of conversion data Dq may be stopped at that time.

  If the calculation of the amplitude Ap, the comparison between the amplitude Ap and the reception determination threshold TH, and the calculation of the phase φp can be performed within one ultrasonic cycle Tc, the time difference between the time A and the time B is two cycles. It is enough. However, in order to improve the calculation accuracy of the amplitude Ap and the phase φp (and hence the azimuth angle θ of the object), it may be configured to calculate these using the in-phase component Ip and the quadrature component Qp for a plurality of periods. In that case, the time difference between time A and time B is longer than two periods.

That is, the duration of the transmission signal S may be set to such a length that the necessary conversion data Dq can be reliably obtained in consideration of these conditions.
FIG. 6 is an explanatory diagram showing the waveform of the reception signal R output from the selector 4 together with the waveforms of the reception signals Ra and Rb when the selector 4 is switched at time C.

[effect]
As described above, in the ultrasonic sensor 1, the reflected wave (reception signal R) is detected by comparing the amplitude Ap with the reception determination threshold value TH, and the phase difference between the reception signals Ra and Rb is determined by orthogonal detection. It is calculated from the obtained in-phase component Ip and quadrature component Qp.

  That is, according to the ultrasonic sensor, the phase difference between the reception signals Ra and Rb is not obtained from the propagation time of the ultrasonic wave but from information obtained by quadrature detection. It can be obtained accurately without being affected by the detection threshold TH. As a result, highly accurate azimuth detection can be performed regardless of variations in the sensitivity of the conversion elements 21 and 22 and the distance to the object to be detected.

  In addition, according to the ultrasonic sensor 1, it is not necessary to adjust variations in sensitivity of the conversion elements 21 and 22, so that the reception signals Ra and Rb from the conversion elements 21 and 22 are processed by a single reception circuit 6. be able to. At the same time, according to the ultrasonic sensor 1, since the A / D converter 63 is realized by using a TAD system, it can be configured by a digital circuit, and the apparatus scale can be reduced. Can do.

Furthermore, according to the ultrasonic sensor 1, since the reception determination threshold value TH is changed according to the reception timing, erroneous detection due to noise or the like can be minimized.
[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it can implement in various aspects.

For example, in the above-described embodiment, the two-dimensional conversion detection is performed using two conversion elements. However, two or more conversion elements may be used to perform two-dimensional direction detection.
In the embodiment described above, only the azimuth is detected. However, the distance to the object may be obtained from the timing when the amplitude Ap exceeds the reception determination threshold TH.

In the above embodiment, one of the two conversion elements is configured to be used for both transmission and reception, but a conversion element dedicated for transmission may be provided separately.
In the above embodiment, the data processing unit 7 realizes the quadrature detection executed in S130, the amplitude calculation executed in S140, the phase calculation executed in S160 and S180, and the like as processes executed by the CPU. However, these processes may be realized by a digital circuit including a DSP.

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic sensor 2 ... Transmission / reception part 3 ... Transmission circuit 4 ... Selector 5 ... Directional coupler 6 ... Reception circuit 7 ... Data processing part 21,22 ... Conversion element 61 ... Amplifier 62 ... Band pass filter (BPF) 63 ... A / D converter 71 ... delay unit 72 ... pulse delay circuit 73 ... counter 74 ... encoder 75 ... latch circuit 76 ... subtraction unit 77 ... buffer 78 ... control unit

Claims (5)

Transmitting and receiving means for transmitting ultrasonic waves that continue for a fixed period at a fixed frequency, and receiving reflected waves from an object that has reflected the ultrasonic waves by a plurality of receiving elements having different positions; and
Detecting means for detecting an in-phase component and a quadrature component of the received signal by performing quadrature detection on the received signal supplied from the transmitting / receiving means;
Amplitude calculating means for obtaining the amplitude of the received signal from the detection result of the detecting means for one of the receiving elements;
When the calculation result in the amplitude calculation means is equal to or greater than a preset reception detection threshold, the phase calculation means for obtaining the phase of the reception signal for each reception element from the detection result in the detection means for each reception element When,
Obtaining the phase difference of the received signal between the receiving elements from the calculation result in the phase calculating means, and azimuth detecting means for obtaining the arrival direction of the reflected wave from the phase difference;
An ultrasonic sensor comprising: The transmission / reception means includes selection means for selectively selecting one of the reception elements and supplying a reception signal from the selected reception element to the detection means,
2. The phase calculating unit according to claim 1, wherein the phase calculating unit acquires detection results of the detecting unit for a plurality of the receiving elements by switching selection by the selecting unit within the predetermined period. Ultrasonic sensor. The detection means includes
Signal processing means for generating a signal obtained by sequentially integrating or averaging the received signals for each timing corresponding to a quarter cycle of the ultrasonic wave;
Addition / subtraction means for calculating the in-phase component Ip and the quadrature component Qp by adding / subtracting the signals D1, D2, D3, D4,... Generated by the signal processing means according to the following equation:
_{Ip = D 4p-3 + D} 4p-2 -D 4p-1 -D 4p
Qp = _{D4p-3 -D4p-2 -D4p-1} + _D4p
(However, p = 1, 2, 3, ...)
The ultrasonic sensor according to claim 1, further comprising: The signal processing means includes
A delay unit that delays and outputs a pulse signal with a delay time corresponding to the signal level of the received signal is cascade-connected, and the pulse signal is transmitted while being sequentially delayed by the delay time of each delay unit. When,
Counting means for counting the number of stages of delay units through which the pulse signal has passed in the pulse delay circuit at every timing corresponding to a quarter cycle of the ultrasonic wave,
The ultrasonic sensor according to claim 3, wherein a count value obtained by the counting means is obtained as the integral value or the average value.   5. The ultrasonic sensor according to claim 1, wherein the phase calculation unit decreases the reception detection threshold according to an elapsed time from the transmission of the ultrasonic wave.

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