JP2014115255A - Ultrasound sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasound sensor that can readily predict the reverberation time even in the presence of an obstacle nearby.SOLUTION: An ultrasound sensor comprises a piezoelectric vibrator 1, a drive unit 2 that drives the piezoelectric vibrator 1, a variable capacity element 4 connected in parallel to the piezoelectric vibrator 1, a signal processor 3 that adjusts the capacity of the variable capacity element 4, and an attenuator 5 that attenuates electric signals outputted from the piezoelectric vibrator 1 and outputs the attenuated signals to the signal processor 3. The signal processor 3 measures the peak voltage of reverberation signals that are generated when ultrasounds are transmitted from the piezoelectric vibrator 1, calculates the Q value of the piezoelectric vibrator 1 on the basis of the measured peak voltage and adjusts the capacity of the variable capacity element 4 on the basis of the calculated Q value of the piezoelectric vibrator 1.

Description

  The present invention relates to an ultrasonic sensor.

  Conventionally, an ultrasonic sensor for transmitting and receiving that is applied to an obstacle detection sensor that detects the presence or absence of an obstacle by receiving a reflected wave from the obstacle after transmitting an ultrasonic wave is known. 1 is disclosed. The ultrasonic sensor described in Patent Document 1 includes a plurality of capacitors connected in parallel to the piezoelectric vibrator, and a plurality of switches that switch a connection state between the piezoelectric vibrator and the capacitor.

  In this ultrasonic sensor, the output signal processing circuit senses the reverberation time of the output of the piezoelectric vibrator based on the received signal from the piezoelectric vibrator, and outputs an on / off control signal corresponding to the reverberation time from the microcomputer. Then, change the ON / OFF combination of multiple switches. Thereby, in this ultrasonic sensor, capacitance compensation of the piezoelectric vibrator is performed, and adjustment is made so as to have a desired reverberation time.

  There is also known an ultrasonic sensor that detects the Q value of an ultrasonic transducer that transmits and receives an ultrasonic pulse, and sets the reception time of the ultrasonic wave according to the detected Q value. Is disclosed. When the detected Q value is small, the ultrasonic sensor described in Patent Document 2 sets the reception time earlier in accordance with the earlier reverberation end time.

JP 2004-343482 A Japanese Unexamined Patent Publication No. 4-083192

  However, when there is an obstacle in the vicinity of the ultrasonic sensor, a reflected wave from the obstacle may be superimposed on the reverberation immediately after the ultrasonic wave is transmitted from the piezoelectric vibrator. The ultrasonic sensor described in Patent Document 1 has a problem that it is difficult to measure the reverberation time because the reverberation and the reflected wave cannot be distinguished when the reflected wave is superimposed on the reverberation. In particular, when an obstacle exists at a distance of about the wavelength of the ultrasonic wave, a plurality of reflected waves from the obstacle are superimposed on the reverberation due to multiple reflection, and therefore, the reverberation time is more difficult to measure.

  Further, even in the ultrasonic sensor described in the cited document 2, since the reflected wave is superimposed on the reverberation and the reverberation cannot be distinguished from the reflected wave, the Q value of the ultrasonic transducer cannot be measured accurately, and the reverberation end time is not obtained. There was a problem that it was difficult to predict.

  The present invention has been made in view of the above points, and an object thereof is to provide an ultrasonic sensor capable of easily predicting reverberation time even when an obstacle is present in the vicinity.

  The ultrasonic sensor of the present invention includes a piezoelectric vibrator that transmits and receives ultrasonic waves, a drive unit that drives the piezoelectric vibrator, a variable capacitance element that is connected in series or in parallel with the piezoelectric vibrator, and the variable capacitance. A signal processing unit that adjusts the capacitance of the element; and an attenuation unit that attenuates an electrical signal output from the piezoelectric vibrator and outputs the attenuated signal to the signal processing unit. The peak voltage of the damped oscillation of the reverberation signal generated when the sound wave is transmitted is measured, the Q value of the piezoelectric vibrator is calculated based on the measured peak voltage, and the calculated Q value of the piezoelectric vibrator is calculated. The capacitance of the variable capacitance element is adjusted based on this.

  In this ultrasonic sensor, it is preferable that the signal processing unit calculates a Q value of the piezoelectric vibrator based on two peak voltages separated from each other by one pulse or more among the damped vibrations of the reverberation signal.

  In this ultrasonic sensor, it is preferable that the signal processing unit measures the peak voltage after skipping the decay vibration pulse of the reverberation signal by a predetermined number of pulses.

  In this ultrasonic sensor, the signal processing unit measures the period of the reverberation signal, determines the number of skips based on the period of the reverberation signal, and attenuates the reverberation signal by the skip number. It is preferable to execute the second process of measuring the peak voltage after skipping the vibration pulse.

  In this ultrasonic sensor, it is preferable that the signal processing unit samples the reverberation signal at a timing delayed by a predetermined time from a zero cross point of the reverberation signal and measures the peak voltage in the adjustment mode.

  In this ultrasonic sensor, the predetermined time is preferably ¼ of the period of the reverberation signal.

  In the present invention, even if there is an obstacle in the vicinity, the reflected wave from the obstacle can be attenuated by the attenuator, so that it is difficult for the reflected wave to be superimposed on the reverberation signal. Therefore, the present invention can easily predict the reverberation time even when there is an obstacle in the vicinity.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows Embodiment 1 of the ultrasonic sensor which concerns on this invention, (a) is a block diagram, (b) is a flowchart figure which shows the outline of operation | movement, (c) is a flowchart figure of the operation | movement in adjustment mode. . (A), (b) is a figure which shows the reverberation waveform of an ultrasonic sensor same as the above, respectively. It is a flowchart figure of the other operation | movement in the adjustment mode of an ultrasonic sensor same as the above. It is a block diagram which shows the other structure in an ultrasonic sensor same as the above. FIG. 8 is a diagram illustrating an ultrasonic sensor according to a second embodiment of the present invention, where (a) is a block diagram and (b) is a flowchart of an operation in an adjustment mode. It is a figure which shows the reverberation waveform of an ultrasonic sensor same as the above. It is a figure which shows Embodiment 3 of the ultrasonic sensor which concerns on this invention, (a) is a block diagram, (b) is a flowchart figure of the calculation process of Q value. It is operation | movement explanatory drawing of an ultrasonic sensor same as the above. It is a flowchart figure which shows the operation | movement of the adjustment mode which abbreviate | omitted calculation of the Q value of the piezoelectric vibrator in the ultrasonic sensor which concerns on this invention.

(Embodiment 1)
Hereinafter, an ultrasonic sensor according to a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, as shown in FIG. 1A, the piezoelectric vibrator 1, the drive unit 2, the signal processing unit 3, the variable capacitance element 4, the attenuation unit 5, the amplification unit 6, and the detection unit. 7. The present embodiment is mounted, for example, on a car body (not shown) of an automobile and used to detect the presence or absence of an obstacle around the vehicle. Moreover, this embodiment calculates the distance to an obstacle, when an obstacle exists in a detection range.

  The piezoelectric vibrator 1 is attached to a container (not shown), and is attached to a bumper of a vehicle body, for example. The piezoelectric vibrator 1 vibrates by receiving an oscillation signal from a driving unit 2 described later, and transmits ultrasonic waves. The piezoelectric vibrator 1 receives the reflected wave reflected by the obstacle and vibrates, thereby converting it into an electric signal based on the reflected wave and outputting it.

  The drive unit 2 includes an oscillator (not shown) that oscillates an oscillation signal having a predetermined frequency, and a switch (not shown) that switches the connection between the oscillator and the piezoelectric vibrator 1. The switch is turned on / off by a drive signal supplied from a control unit 311 described later. Therefore, the drive unit 2 inputs an oscillation signal to the piezoelectric vibrator 1 by a drive signal from the control unit 311 and vibrates the piezoelectric vibrator 1 to transmit ultrasonic waves. An insulating transformer T1 is provided between the piezoelectric vibrator 1 and the drive unit 2. The insulation transformer T1 amplifies the power of the oscillation signal from the drive unit 2.

  The signal processing unit 3 includes an A / D converter 30 and a control block 31. The A / D converter 30 converts the output signal of the piezoelectric vibrator 1 that is an analog signal into a digital signal. The control block 31 is composed of, for example, a microcomputer, and executes various processes upon receiving a digital signal from the A / D converter 30. The control block 31 includes a calculation unit 310 and a control unit 311.

  The calculation unit 310 and the control unit 311 are program modules that function when the control block 31 executes various programs. Of course, the configuration of the control block 31 is not limited to the microcomputer, and the calculation unit 310 and the control unit 311 may be configured by hardware.

  In the normal mode, which will be described later, the calculation unit 310 performs a process of calculating the distance to the obstacle based on the timing of transmission / reception of the ultrasonic wave by the piezoelectric vibrator 1. In addition, in the adjustment mode described later, the calculation unit 310 executes a process of calculating the Q value of the system including the piezoelectric vibrator 1 (hereinafter referred to as “Q value of the piezoelectric vibrator 1”).

  Here, the Q value of the piezoelectric vibrator 1 has a correlation with the reverberation time, which is the time during which reverberation continues when ultrasonic waves are transmitted from the piezoelectric vibrator 1. That is, if the Q value of the piezoelectric vibrator 1 is large, the reverberation time is long, and if the Q value is small, the reverberation time is short. Therefore, the reverberation time can be predicted by calculating the Q value of the piezoelectric vibrator 1.

  The Q value of the piezoelectric vibrator 1 can be obtained from the reverberation attenuation characteristics when the piezoelectric vibrator 1 transmits ultrasonic waves. For example, as shown in FIG. 2A, the peak voltage of the first pulse of the damped oscillation of the electric signal based on reverberation (hereinafter referred to as “reverberation signal”) is V1, and the peak voltage of the second pulse is V2. Then, the Q value of the piezoelectric vibrator 1 can be obtained by the following equation.

Q = -2π / ln (V2 / V1)
The peak voltage of the damped oscillation of the reverberation signal is measured by executing a peak detection process in the calculation unit 310.

  Thus, the Q value of the piezoelectric vibrator 1 can be calculated by measuring the peak voltage of two pulses or several pulses of the damped oscillation of the reverberation signal. For this reason, the reverberation time can be predicted in a short time compared with the case where the reverberation time is directly measured. In order to predict the reverberation time in a shorter time, the number of ultrasonic pulses transmitted from the piezoelectric vibrator 1 may be reduced (for example, only one pulse is transmitted).

  Here, in order to obtain the Q value of the piezoelectric vibrator 1 with higher accuracy, the Q value is sequentially calculated based on the peak voltage of the adjacent pulses of the damped vibration of the reverberation signal, and the average value is calculated by the piezoelectric vibrator 1. The Q value is desirable. For example, the Q value is calculated based on the peak voltage of the first and second pulses of the decaying vibration of the reverberation signal, the Q value is calculated based on the peak voltage of the third and fourth pulses, and the average value of each Q value is calculated. The Q value of the piezoelectric vibrator 1 is assumed. However, in this calculation method, since the Q value needs to be calculated a plurality of times, the load required for processing increases.

  Therefore, it is also possible to measure the peak voltage of two pulses that are separated from each other by one cycle or more out of the damped oscillation of the reverberation signal, and calculate the Q value of the piezoelectric vibrator 1 based on these peak voltages. That is, as shown in FIG. 2B, when the peak voltage of the nth pulse (n is a natural number of 3 or more) of the damped oscillation of the reverberant signal is Vn, the Q value of the piezoelectric vibrator 1 is expressed by the following equation: Can be obtained.

Q = −nπ / ln (Vn / V1)
In this calculation method, since the calculation of the Q value only needs to be performed once, the load required for the processing can be reduced.

  As described above, the control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by giving a drive signal to the drive unit 2. Further, the control unit 311 gives a control signal to a variable capacitor C1 of the variable capacitance element 4 described later based on the Q value calculated by the calculation unit 310. Further, the control unit 311 gives a sampling signal to the A / D converter 30. The A / D converter 30 samples the electrical signal output from the piezoelectric vibrator 1 based on this sampling signal.

  Note that a differentiating circuit (not shown) may be provided separately, and the peak voltage of the damped oscillation of the reverberation signal may be measured using the differentiating circuit. In this configuration, the electrical signal output from the piezoelectric vibrator 1 is differentiated by a differentiation circuit, and the output signal of the differentiation circuit is input to a comparator (not shown). The control unit 311 causes the A / D converter 30 to perform sampling at a timing when the output signal of the comparator becomes zero. Thereby, the peak voltage of the damped oscillation of the reverberation signal can be measured.

  The calculation unit 310 and the control unit 311 operate in one of a normal mode and an adjustment mode based on the operation of the vehicle. The normal mode is a mode for detecting the presence or absence of an obstacle within a detection range (that is, within an ultrasonic wave reachable range). The adjustment mode is a mode in which the Q value of the piezoelectric vibrator 1 is adjusted by adjusting the capacitance of a variable capacitor C1 of the variable capacitance element 4 described later.

  For example, the calculation unit 310 and the control unit 311 operate in the adjustment mode when the driver switches on the power of the accessory of the vehicle using the ignition key or starts the engine, and enters the normal mode after the adjustment mode ends. Switch. Of course, it is not necessary to operate in the adjustment mode every time the accessory is turned on or the engine is started, and the conditions for operating in the adjustment mode may be changed as appropriate. In the present embodiment, the calculation unit 310 and the control unit 311 switch to the adjustment mode on condition that the power supply of the vehicle accessory is switched on.

  The variable capacitance element 4 includes a variable capacitor C1 connected to the piezoelectric vibrator 1 in series or in parallel. In the present embodiment, the variable capacitance element 4 is connected to the piezoelectric vibrator 1 in parallel. The variable capacitor C <b> 1 can adjust the capacitance by a control signal given from the control unit 311. By adjusting the capacitance of the variable capacitor C1, the Q value of the piezoelectric vibrator 1 can be adjusted. Note that the variable capacitance element 4 may be configured by connecting a plurality of series circuits in which capacitors and switches are connected in series as in the conventional example, for example. In this configuration, the capacitance of the variable capacitance element 4 can be adjusted by giving a control signal to each switch from the control unit 311 and appropriately switching on / off of each switch.

  The attenuation unit 5 is provided between the piezoelectric vibrator 1 and the signal processing unit 3 and attenuates an electric signal output from the piezoelectric vibrator 1. In the present embodiment, the attenuation unit 5 is provided in parallel with the series circuit of the amplification unit 6 and the detection unit 7. The amplifying unit 6 amplifies the electrical signal output from the piezoelectric vibrator 1 and outputs it to the detection unit 7. The detector 7 detects the output signal of the amplifier 6 by envelope detection and outputs it to the A / D converter 30 of the signal processor 3. The attenuating unit 5 and the series circuit of the amplifying unit 6 and the detecting unit 7 are connected in parallel.

  The attenuation unit 5 attenuates not only an electric signal based on a reflected wave from an obstacle but also a reverberation signal. However, the level of the reverberation signal is higher than the level of the electric signal based on the reflected wave. For this reason, the attenuating unit 5 only needs to attenuate the electric signal to the extent that the influence of the reflected wave is reduced, and it is preferable to determine that the signal processing unit 3 in the subsequent stage does not saturate.

  In the present embodiment, the connection of the attenuation unit 5 to the signal processing unit 3 and the connection of the amplifying unit 6 and the detection unit 7 to the signal processing unit 3 in the series circuit are switched by the first switch SW1. The first switch SW1 is composed of, for example, a semiconductor switch or a relay. Switching of connection by the first switch SW1 is performed by the control unit 311. That is, the control unit 311 controls the first switch SW1 in the normal mode to connect the series circuit of the amplification unit 6 and the detection unit 7 to the signal processing unit 3. Further, the control unit 311 controls the first switch SW1 in the adjustment mode, and connects the attenuation unit 5 to the signal processing unit 3.

  Hereinafter, the operation of this embodiment will be described. First, the operation in the normal mode will be described. The control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 at a predetermined interval by giving a driving signal to the driving unit 2 at a predetermined interval. Here, when an obstacle exists in the detection range, the ultrasonic wave is reflected by the obstacle. When the piezoelectric vibrator 1 receives this reflected wave, the piezoelectric vibrator 1 converts the reflected wave into an electric signal and outputs it. This electric signal is amplified by the amplifying unit 6 and further envelope-detected by the detecting unit 7 and then input to the A / D converter 30.

  The calculation unit 310 calculates the distance to the obstacle based on the reception timing of the reflected wave obtained based on the output signal of the A / D converter 30 and the ultrasonic wave transmission timing of the piezoelectric vibrator 1. Calculate. Based on the calculation result, the control unit 311 may sound a warning sound from a buzzer (not shown) or display a distance to an obstacle on a display (not shown). The operation in the normal mode is repeated until the vehicle engine is switched off as shown in FIG. Of course, the condition for ending the normal mode need not be limited to switching the engine off, and may be changed as appropriate.

  Next, the operation in the adjustment mode will be described with reference to FIGS. When the power supply of the vehicle accessory is turned on, the calculation unit 310 and the control unit 311 are switched to the adjustment mode. The control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by giving a drive signal to the drive unit 2. A reverberation signal generated by ultrasonic transmission is attenuated by the attenuation unit 5 and then input to the A / D converter 30.

  Then, the calculation unit 310 calculates the Q value of the piezoelectric vibrator 1 based on the damped vibration of the reverberation signal output from the A / D converter 30. Here, the control unit 311 stores a threshold value of the Q value of the piezoelectric vibrator 1 in a memory (not shown) in advance. This threshold is set based on the allowable reverberation time of the piezoelectric vibrator 1. The control unit 311 compares this threshold value with the Q value obtained by the calculation unit 310.

  If the Q value obtained by the calculation unit 310 is larger than the threshold value, the control unit 311 adjusts the capacity of the variable capacitor C1 by giving a control signal, and gives the drive signal to the drive unit 2 to thereby provide the piezoelectric vibrator 1. The ultrasonic wave is transmitted again from. Then, the calculation unit 310 and the control unit 311 again execute the process of calculating the Q value of the piezoelectric vibrator 1 and the process of comparing the obtained Q value with a threshold value. If the Q value obtained by the calculation unit 310 is smaller than the threshold value, the calculation unit 310 and the control unit 311 end the adjustment mode and switch to the normal mode. With the above adjustment mode, the Q value of the piezoelectric vibrator 1 is adjusted to an appropriate value, and the reverberation time is shortened.

  The processing in the adjustment mode by the calculation unit 310 and the control unit 311 may be as follows. First, as illustrated in FIG. 3, the control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by supplying a drive signal to the drive unit 2. Next, the calculation unit 310 calculates the Q value of the piezoelectric vibrator 1 based on the damped vibration of the reverberation signal output from the A / D converter 30. The calculated Q value is stored in the memory. And the control part 311 adjusts the capacity | capacitance of the variable capacitor C1 by giving a control signal.

  The above series of processing is sequentially executed for all selectable capacities of the variable capacitor C1. When the above series of processing is completed, the control unit 311 compares the stored Q values and adjusts the capacitance of the variable capacitor C1 so that the Q value is minimized. In this configuration, since the Q value of the piezoelectric vibrator 1 can be minimized, the reverberation time can be further shortened.

  As described above, in the present embodiment, after the reverberation signal is attenuated by the attenuation unit 5, the reverberation time is predicted by calculating the Q value of the piezoelectric vibrator 1 based on the attenuation vibration of the attenuated reverberation signal. doing. For this reason, in this embodiment, even if there is an obstacle in the vicinity, the reflected wave from the obstacle can be attenuated by the attenuating unit 5, so that the reflected wave is difficult to be superimposed on the reverberation signal. Therefore, in this embodiment, the reverberation time can be easily predicted even when an obstacle exists in the vicinity.

  In the present embodiment, the reverberation time of the piezoelectric vibrator 1 is predicted by calculating the Q value from the difference in the peak voltage of the decaying vibration of the reverberation signal. This has the following advantages. . For example, in the case where the reverberation time of the piezoelectric vibrator 1 is directly measured, the shorter the reverberation time, the shorter the time of damped vibration, which may reduce the measurement accuracy. On the other hand, the difference in the peak voltage of the damped oscillation of the reverberation signal becomes larger when the reverberation time is shorter, and thus the difference is easily measured. In this embodiment, since it aims at shortening reverberation time, the structure which calculates Q value from the difference of the peak voltage of the damping vibration of a reverberation signal is desirable.

  As shown in FIG. 4, a filter unit 8 composed of a low-pass filter may be provided between the attenuation unit 5 and the signal processing unit 3. The filter unit 5 removes noise included in the electrical signal output from the piezoelectric vibrator 1. In this configuration, since the peak voltage of the damped oscillation of the reverberation signal can be measured in a state where noise is removed from the reverberation, the Q value of the piezoelectric vibrator 1 can be calculated stably.

(Embodiment 2)
Hereinafter, an ultrasonic sensor according to a second embodiment of the present invention will be described with reference to the drawings. However, since the basic configuration of the present embodiment is common to that of the first embodiment, common portions are denoted by the same reference numerals and description thereof is omitted. As shown in FIGS. 5A and 5B, the present embodiment includes a comparator 9, a period measurement unit 312, and a counting unit 313.

  The comparator 9 outputs a binary signal by comparing the reverberation signal output from the attenuator 5 with a predetermined threshold value. In the present embodiment, the predetermined threshold is set to zero. Therefore, the output signal of the comparator 9 is a binary signal that switches between a high level and a low level every zero cross of the reverberation signal.

  The period measurement unit 312 measures the period of the reverberation signal for each pulse by counting the period of the binary signal output from the comparator 9 with a timer (not shown). The period measuring unit 312 compares the measured periods for each pulse. The counting unit 313 counts the number of skips for skipping the reverberation signal pulse based on the comparison result in the period measurement unit 312.

  Note that the period measuring unit 312 and the counting unit 313 are program modules that function when the control block 31 executes various programs, like the calculation unit 310 and the control unit 311. Of course, the configuration of the control block 31 is not limited to the microcomputer, and each of the units 310 to 313 may be configured by hardware.

  In the present embodiment, the connection of the attenuation unit 5 to the signal processing unit 3 and the connection of the attenuation unit 5 to the comparator 9 are switched by the second switch SW2. Similar to the first switch SW1, the second switch SW2 is formed of, for example, a semiconductor switch or a relay. Switching of connection by the second switch SW2 is performed by the control unit 311. That is, in the adjustment mode, the control unit 311 controls the second switch SW2 to connect the attenuation unit 5 to the comparator 9 when performing a first process described later. Further, the control unit 311 controls the second switch SW <b> 2 to connect the attenuation unit 5 to the signal processing unit 3 when executing a second process described later.

  Hereinafter, the operation of the adjustment mode in the present embodiment will be described. As shown in FIG. 5B, when the adjustment mode is started, the calculation unit 310 and the control unit 311 first measure the period of the reverberation signal, and perform a first process for determining the number of skips based on the period of the reverberation signal. Run. When the first process is completed, the calculation unit 310 and the control unit 311 execute the second process of measuring the peak voltage after skipping the decay vibration pulses of the reverberation signal by the number of skips.

  The first process will be described. First, the counting unit 313 resets the skip number to an initial value of zero. Next, the control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by giving a drive signal to the drive unit 2. The reverberation signal generated by the ultrasonic wave transmission is attenuated by the attenuation unit 5 and then input to the comparator 9. The period measurement unit 312 measures one period of the reverberation signal from the output signal of the comparator 9 and stores the measured period in the memory. At this time, since only one period is measured, the period measuring unit 312 measures the next one period (that is, measures the period of the second pulse) and stores the measured period in the memory.

  Then, the cycle measuring unit 312 compares the cycle measured this time with the cycle measured last time. As a result of the comparison, when the periods coincide with each other, the first process is terminated and the process proceeds to the second process. If the periods do not match, the counting unit 313 increases the skip number by one. Then, the period measuring unit 312 again measures the next one period and stores the measured period in the memory. Thereafter, the above operation is repeated until the respective periods coincide in the comparison operation.

  Next, the second process will be described. First, the control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by giving a drive signal to the drive unit 2. A reverberation signal generated by ultrasonic transmission is attenuated by the attenuation unit 5 and then input to the A / D converter 30. Then, calculation unit 310 skips the reverberation signal pulse by the number of skips counted by counting unit 313 and then measures the peak voltage of the damped oscillation of the reverberation signal output from A / D converter 30.

  For example, it is assumed that the period of the reverberation signal is stable from the third period of the damped vibration. In this case, as shown in FIG. 6, the calculation unit 310 skips the first and second pulses of the damped oscillation of the reverberation signal and measures the peak voltage of the third and subsequent pulses. Then, the calculation unit 310 calculates the Q value of the piezoelectric vibrator 1 based on the measured peak voltage. Therefore, in the present embodiment, since the Q value of the piezoelectric vibrator 1 is calculated after the period of the damped oscillation of the reverberation signal is stabilized, the accuracy of predicting the reverberation time can be improved.

  In addition, in the second process, the decay vibration pulses of the reverberation signal are skipped by a predetermined number of pulses without executing the first process of measuring the decay vibration period of the reverberation signal in advance. The peak voltage of the damped oscillation of the reverberation signal may be measured. Even in this configuration, since the Q value is calculated after the attenuation signal of the reverberation signal is stabilized to some extent, the accuracy of predicting the reverberation time can be improved. Also, with this configuration, it is possible to reduce the time required for the adjustment mode processing as compared with the case where the period is measured in advance.

(Embodiment 3)
Hereinafter, an ultrasonic sensor according to a third embodiment of the present invention will be described with reference to the drawings. However, since the basic configuration of the present embodiment is common to that of the second embodiment, common portions are denoted by the same reference numerals and description thereof is omitted. The present embodiment is characterized in that, in the adjustment mode, the signal processing unit 3 measures the peak voltage of the decaying vibration of the reverberation signal by sampling the reverberation signal at a timing delayed for a predetermined time from the zero cross point of the reverberation signal. To do.

  As shown in FIG. 7, the output signal of the comparator 9 is input to the control unit 311. Based on the output signal of the comparator 9, the control unit 311 can detect the zero cross point of the reverberation signal. In addition, the control unit 311 acquires reverberation signal cycle data from the cycle measurement unit 312. Hereinafter, the period of the reverberation signal is T1.

  In the adjustment mode, the control unit 311 outputs the sampling signal at a timing delayed by a predetermined time (T1 / 4 in the present embodiment) from the zero cross point of the reverberation signal (see FIG. 8). The A / D converter 30 samples the reverberation signal based on the sampling signal, and outputs a peak voltage of the damped oscillation of the reverberation signal.

  As described above, in the present embodiment, since the signal processing unit 3 performs sampling so as to output only the peak voltage of the damped oscillation of the reverberation signal, the number of samplings can be reduced as compared with the case of always sampling. Therefore, in this embodiment, the load on hardware can be reduced.

  In the present embodiment, since the reverberation signal is sampled at a timing delayed by T1 / 4 from the zero cross point of the reverberation signal, the following advantages are obtained. That is, the vicinity of the peak of the damped oscillation of the reverberation signal is a region where the voltage fluctuation is small, and by sampling in this region, the measurement error of the peak voltage of the damped oscillation of the reverberation signal can be reduced.

  In each of the above embodiments, the capacitance of the variable capacitor C1 is adjusted after calculating the Q value of the piezoelectric vibrator 1, but a method of omitting the calculation of the Q value of the piezoelectric vibrator 1 is also conceivable. Hereinafter, the operation in the adjustment mode in which the calculation of the Q value of the piezoelectric vibrator 1 is omitted will be described with reference to FIG. First, the control unit 311 transmits an ultrasonic wave from the piezoelectric vibrator 1 by giving a drive signal to the drive unit 2. Next, when the calculation unit 310 measures the peak voltage V1 of the first pulse of the damped oscillation of the reverberation signal, the calculation unit 310 compares the peak voltage V1 with preset threshold values VA1 to VZ1 (VA1>...> VZ1). To do.

  For example, if the peak voltage V1 is greater than the threshold value VA1, the arithmetic unit 310 sets the value of the threshold value Vth2 to VA2. If the peak voltage V1 is smaller than the threshold value VA1 and larger than the threshold value VB1, the calculation unit 310 sets the value of the threshold value Vth2 to VB2. Hereinafter, similarly, by comparing the threshold values VA1 to VZ1 with the peak voltage V1, the calculation unit 310 sets the threshold value Vth2 to any value of VA2 to VZ2 (VA2>...> VZ2). That is, the arithmetic part 310 sets the threshold value Vth2 of the peak voltage V2 of the second pulse based on the peak voltage V1 of the first pulse of the damped oscillation of the reverberation signal.

  Then, when the peak voltage V2 of the second pulse of the damped oscillation of the reverberation signal is measured, the control unit 311 compares the peak voltage V2 with the threshold value Vth2. If the peak voltage V2 is larger than the threshold value Vth2, the control unit 311 adjusts the capacity of the variable capacitor C1 by giving a control signal, and gives a drive signal to the drive unit 2 to emit ultrasonic waves from the piezoelectric vibrator 1 again. Send a wave. Then, the control unit 311 executes again the process of setting the threshold value Vth2 and the process of comparing the peak voltage V2 and the threshold value Vth2. If the peak voltage V2 is smaller than the threshold value Vth2, the calculation unit 310 and the control unit 311 end the adjustment mode and switch to the normal mode.

  As described above, even when the calculation of the Q value of the piezoelectric vibrator 1 is omitted, the Q value of the piezoelectric vibrator 1 can be adjusted by adjusting the capacitance of the variable capacitor C1 of the variable capacitance element 4.

DESCRIPTION OF SYMBOLS 1 Piezoelectric vibrator 2 Drive part 3 Signal processing part 4 Variable capacitance element 5 Attenuation part

Claims (6)

Piezoelectric vibrator for transmitting and receiving ultrasonic waves, drive unit for driving the piezoelectric vibrator, variable capacitance element connected in series or in parallel with the piezoelectric vibrator, and signal processing for adjusting the capacitance of the variable capacitance element And an attenuation unit that attenuates an electrical signal output from the piezoelectric vibrator and outputs the attenuated signal to the signal processing unit,
The signal processing unit measures a peak voltage of decay vibration of a reverberation signal generated when ultrasonic waves are transmitted from the piezoelectric vibrator, and calculates a Q value of the piezoelectric vibrator based on the measured peak voltage. And an ultrasonic sensor that adjusts the capacitance of the variable capacitance element based on the calculated Q value of the piezoelectric vibrator.   2. The super value according to claim 1, wherein the signal processing unit calculates a Q value of the piezoelectric vibrator based on two peak voltages separated from each other by one pulse or more among the damped oscillations of the reverberation signal. Sonic sensor.   The ultrasonic sensor according to claim 1, wherein the signal processing unit measures the peak voltage after skipping the damped oscillation pulse of the reverberation signal by a predetermined number of pulses.   The signal processing unit measures the period of the reverberation signal, skips the decay vibration pulse of the reverberation signal by the first process for determining the number of skips based on the period of the reverberation signal, and the skip number. 2. The ultrasonic sensor according to claim 1, wherein the second process of measuring the peak voltage is performed after the first time.   2. The ultrasonic sensor according to claim 1, wherein the signal processing unit samples the reverberation signal at a timing delayed by a predetermined time from a zero cross point of the reverberation signal and measures the peak voltage in the adjustment mode. .   The ultrasonic sensor according to claim 5, wherein the predetermined time is ¼ of a period of the reverberation signal.

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