JP2013120088A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reverberant vibration in an ultrasonic sensor.SOLUTION: An ultrasonic sensor 1 includes a vibrator 2 for receiving and transmitting an ultrasonic wave, a driving circuit 3 for transmitting the ultrasonic wave from the vibrator 2, and a reverberant vibration suppression circuit 7 for suppressing the reverberant vibration of the vibrator 2. The driving circuit 3 boosts voltage of a transmission signal for transmitting the ultrasonic wave by a transformer 32, and supplies the transmission signal of the boosted voltage to the vibrator 2. The reverberant vibration suppression circuit 7 includes the vibrator 2, a secondary coil (first inductive element) 34 of the transformer 32, a coil (second inductive element) 41, a resistor 42, and a capacitor (capacitive element) 43. The capacitor 43 and the resistor 42 are connected in series to each other, and connected in parallel to the coil 41. An LCR circuit including the resistor 42, the capacitor 43, and the coil 41 is connected between the vibrator 2 and the secondary coil 34. The reverberant vibration suppression circuit 7 absorbs the reverberant vibration of the vibrator 2 by using a resonance phenomenon at a plurality of different resonance frequencies.

Description

  The present invention relates to an ultrasonic sensor that transmits ultrasonic waves and receives ultrasonic waves.

  Conventionally, an ultrasonic sensor transmits an ultrasonic wave and receives an ultrasonic wave reflected by the object, thereby detecting the object and measuring a distance to the object. That is, when the ultrasonic sensor receives an ultrasonic wave after transmitting the ultrasonic wave, the ultrasonic wave reflected by the target object is received and the target object is present. The ultrasonic sensor measures the time of flight of the ultrasonic wave at that time (the time from when the transmission of the ultrasonic wave is started until when the ultrasonic wave reflected by the target object is received) to the target object. Measure the distance.

  As such an ultrasonic sensor, there is one that transmits and receives ultrasonic waves by one same vibrator. That is, in this ultrasonic sensor, an ultrasonic wave is transmitted from the vibrator by driving and vibrating the vibrator, and the ultrasonic wave is received by the vibrator when the vibrator receives the ultrasonic wave and vibrates. The reception signal is output.

  By the way, in such an ultrasonic sensor, since transmission and reception of ultrasonic waves are performed by one and the same transducer, a reception signal as shown in FIG. 8 is output. That is, during transmission of ultrasonic waves, a reception signal R1 based on the ultrasonic transmission voltage of the vibrator is output, and during reception of reverberation vibration of the vibrator, a reception signal R2 due to reverberation vibration of the vibrator is output. And when the ultrasonic wave reflected by the object is received after the reverberation vibration converges, the reception signal by the reception of the ultrasonic wave (reception of the ultrasonic wave reflected by the object) after the output of the reception signal R2 by the reverberation vibration. R3 is output. Further, when the ultrasonic wave reflected by the object is received during the reverberation vibration, the reception signal due to the reception of the ultrasonic wave is output during the output of the reception signal R2 due to the reverberation vibration (overlap with the reception signal R2 due to the reverberation vibration). R3 is output.

  Accordingly, when the ultrasonic wave reflected by the object is received during the reverberation vibration, the reception signal R3 due to the reception of the ultrasonic wave cannot be detected separately from the reception signal R2 due to the reverberation vibration, and the distance to the object is measured. I can't. That is, if the reverberation vibration convergence time E until the reverberation vibration converges is long, the distance to the object at a short distance cannot be measured. In order to be able to measure the distance to an object at a short distance, it is necessary to suppress the reverberation vibration and shorten the reverberation vibration convergence time E.

  Therefore, there is an ultrasonic sensor having a configuration shown in FIG. 9 as an ultrasonic sensor that suppresses reverberation vibration. In the ultrasonic sensor 80, the vibrator 81 is driven by a drive circuit 82, and ultrasonic waves are transmitted from the vibrator 81. The drive circuit 82 includes a drive transistor 83 and a transformer 84. That is, the driving circuit 82 outputs a transmission signal from the driving transistor 83 when the sensor driving signal is input. Then, the drive circuit 82 boosts the voltage of the transmission signal by the transformer 84 and supplies the transmission signal whose voltage has been boosted to the vibrator 81 to drive and vibrate the vibrator 81 by the transmission signal. Ultrasonic waves are transmitted from the vibrator 81.

  Further, the ultrasonic sensor 80 suppresses the reverberation vibration of the vibrator 81 by the reverberation vibration suppression circuit 90. The reverberation vibration suppression circuit 90 includes a vibrator 81, a secondary coil 85 of the transformer 84, and a resistor 91. The reverberation vibration suppression circuit 90 suppresses the reverberation vibration of the vibrator 81 by absorbing the reverberation vibration of the vibrator 81 using a resonance phenomenon. A device that absorbs vibration using the resonance phenomenon is called a dynamic vibration absorber.

  The reverberation vibration suppression circuit 90 is a circuit that generates one resonance point at which the impedance of the reverberation vibration suppression circuit 90 is minimized and two anti-resonance points at which the impedance of the reverberation vibration suppression circuit 90 is maximum. These one resonance point and two anti-resonance points are due to the combined action of the equivalent inductance, equivalent capacitance, equivalent resistance, and secondary coil 85 of the transformer 84 and resistor 91 in the equivalent circuit of the vibrator 81. Arise.

The resonance frequency ω ₁ is the frequency at the resonance point of the reverberation vibration suppression circuit 90 (the frequency at the resonance point at which the impedance of the reverberation vibration suppression circuit 90 is minimum), and the frequency at the anti-resonance point (the impedance of the reverberation vibration suppression circuit 90 is maximum). The frequency of the resonance point is defined as antiresonance frequencies ω _a1 and ω _a2 . The resonance frequency ω ₁ , antiresonance frequencies ω _a1 , and ω _a2 of the reverberation vibration suppression circuit 90 are frequencies represented by the following expressions.

Here, L _P is the equivalent series inductance in the equivalent circuit of the vibrator 81, C _P is the equivalent series capacitance in the equivalent circuit of the vibrator 81, C _S is the equivalent circuit of the vibrator 81 Equivalent parallel capacitance. L ₈₅ is the inductance of the secondary coil 85.

  The reverberation vibration suppression circuit 90 mainly generates vibrations having the same frequency as the resonance frequency of the reverberation vibration suppression circuit 90 (the frequency at the resonance point at which the impedance of the reverberation vibration suppression circuit 90 is minimal) among the reverberation vibrations of the vibrator 81. Absorb using the resonance phenomenon. Then, the reverberation vibration suppression circuit 90 releases the absorbed vibration energy from the resistor 91 as thermal energy. The reverberation vibration of the vibrator 81 is absorbed by the reverberation vibration suppression circuit 90, and the energy of the vibration is released from the resistor 91 of the reverberation vibration suppression circuit 90, so that the vibration is attenuated earlier, and in a short time. Converge.

  The reverberation vibration of the vibrator 81 is generated at the natural frequency (self-resonant frequency) of the vibrator 81. The reverberation vibration suppression circuit 90 is designed so that the resonance frequency of the reverberation vibration suppression circuit 90 is the same as the natural frequency of the vibrator 81. That is, the secondary side of the transformer 84 depends on the natural frequency of the vibrator 81 in the normal temperature environment so that the resonance frequency of the reverberation vibration suppression circuit 90 becomes the same as the natural frequency of the vibrator 81 in the normal temperature environment. The inductance of the coil 85 is selected.

  In addition, an ultrasonic sensor in which a vibrator is driven by a drive circuit having a push-pull configuration is also known in which reverberation vibration is suppressed based on the same concept (for example, see Patent Document 1).

JP 2005-83935 A

  By the way, in the conventional ultrasonic sensor 80, the reverberation vibration suppression circuit 90 uses the resonance phenomenon at one resonance frequency (the frequency of the resonance point at which the impedance of the reverberation vibration suppression circuit 90 is minimized), and thereby the vibrator 81. It is designed to absorb the reverberation vibration. For this reason, in the conventional ultrasonic sensor 80, if one (only) resonance frequency deviates from the natural frequency of the vibrator 81, the reverberation vibration suppressing effect is greatly reduced.

  The natural frequency of the vibrator 81 varies depending on the individual difference of the vibrator 81 (the mass and shape of the vibrator 81, the solid difference of the vibrator or piezoelectric element used in the vibrator 81), and It fluctuates due to a difference in temperature (difference in operating environment temperature of the ultrasonic sensor 80). Therefore, variations due to individual differences in the natural frequency of the vibrator 81 and fluctuations due to temperature differences cause the resonance frequency of the reverberation vibration suppression circuit 90 to deviate from the natural frequency of the vibrator 81.

  Therefore, in the conventional ultrasonic sensor 80, the reverberation vibration suppressing effect may be greatly reduced depending on the individual difference of the transducer 81 and the usage environment of the ultrasonic sensor 80. Further, in the conventional ultrasonic sensor 80, since the reverberation vibration is absorbed using a resonance phenomenon at one resonance frequency, the effect of suppressing the reverberation vibration is small. For these reasons, the conventional ultrasonic sensor 80 cannot sufficiently absorb the reverberation vibration of the vibrator 81 and cannot sufficiently suppress the reverberation vibration of the vibrator 81. As a result, the conventional ultrasonic sensor 80 cannot measure the distance to a near object.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an ultrasonic sensor capable of suppressing reverberation vibration.

  In order to achieve the above object, the ultrasonic sensor according to the present invention suppresses reverberation vibration of an ultrasonic sensor that transmits ultrasonic waves from the vibrator when the vibrator is driven to vibrate. The reverberation vibration suppressing circuit includes a circuit and suppresses the reverberation vibration of the vibrator by absorbing the reverberation vibration of the vibrator by using resonance phenomena at a plurality of different resonance frequencies.

  In the ultrasonic sensor of the present invention, the reverberation vibration suppressing circuit includes a vibrator, a first inductive element, an LCR circuit in which a resistor and a capacitive element connected in series with each other are connected in parallel to the second inductive element, And a circuit comprising an LCR circuit connected between the vibrator and the first inductive element is preferable.

  The ultrasonic sensor according to the present invention further includes a drive circuit that transmits ultrasonic waves from the vibrator, and the drive circuit boosts the voltage of a transmission signal for transmitting ultrasonic waves, and transmits the voltage by boosting the voltage. By supplying a signal to the vibrator, the vibrator is driven and vibrated by this transmission signal, and an ultrasonic wave is transmitted from the vibrator. The first inductive element is a transmission signal provided in the drive circuit. A boosting inductive element that boosts the voltage is preferable.

  In the ultrasonic sensor of the present invention, it is preferable that the drive circuit boosts the transmission signal with a transformer, and the boosting induction element provided in the drive circuit is a secondary coil of the transformer.

  In the ultrasonic sensor of the present invention, the boosting inductive element provided in the drive circuit is preferably an inductive element that boosts the transmission signal by a self-inducing action.

  In the ultrasonic sensor of the present invention, it is preferable that the reverberation vibration suppressing circuit is composed of a circuit having multiple LCR circuits.

  According to the present invention, the reverberation vibration of the vibrator can be suppressed by absorbing the reverberation vibration of the vibrator using resonance phenomena at a plurality of different resonance frequencies.

1 is an electric circuit diagram showing a configuration of an ultrasonic sensor according to a first embodiment of the present invention. The electric circuit diagram which shows the equivalent circuit of the reverberation vibration suppression circuit of the ultrasonic sensor. (A) is a figure which shows the characteristic of the reverberation vibration in the conventional ultrasonic sensor, (b) is a figure which shows the characteristic of the reverberation vibration in the ultrasonic sensor of this invention. The electric circuit diagram which shows the structure of the ultrasonic sensor which concerns on the 2nd Embodiment of this invention. The electric circuit diagram which shows the structure of the ultrasonic sensor which concerns on the 3rd Embodiment of this invention. The electric circuit diagram which shows the structure of the ultrasonic sensor which concerns on the 4th Embodiment of this invention. The electric circuit diagram which shows the structure of the ultrasonic sensor which concerns on the 5th Embodiment of this invention. The figure which shows the relationship between the received signal by the reverberation vibration in the conventional ultrasonic sensor, and the received signal by reception of an ultrasonic wave. The electric circuit diagram which shows the structure of the conventional ultrasonic sensor.

Hereinafter, an ultrasonic sensor according to an embodiment of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 shows a configuration of an ultrasonic sensor according to the first embodiment. The ultrasonic sensor 1 is a device that transmits ultrasonic waves and receives ultrasonic waves. The ultrasonic sensor 1 has a function of detecting an object by measuring transmission and reception of ultrasonic waves and measuring a distance to the object. For example, the ultrasonic sensor 1 is mounted on a moving body such as a vehicle and used to detect an object around the moving body. The ultrasonic sensor 1 includes a vibrator 2, a drive circuit 3, a reception circuit 4, a time measurement unit 5, a control unit 6, and a reverberation vibration suppression circuit 7.

  The vibrator 2 is for transmitting and receiving ultrasonic waves, and has a configuration in which a vibrating body is integrally attached to a piezoelectric element. The vibrator 2 is driven by a time-varying voltage applied to the piezoelectric element, so that the piezoelectric element is driven to vibrate according to the temporal change of the applied voltage, and the vibrating body is connected to the piezoelectric element. Vibrate together. That is, the vibrator 2 is driven by the application of a voltage that changes at the ultrasonic frequency, so that the piezoelectric element vibrates at the ultrasonic frequency, and the vibrating body moves along with the piezoelectric element. Vibrates at a frequency and transmits an ultrasonic wave.

  In addition, the vibrator 2 vibrates together with the vibrating body when the vibrating body vibrates, and the polarization of the piezoelectric element changes according to the vibration, corresponding to the frequency and amplitude of the vibration ( A waveform electric signal (corresponding to the change in polarization) is output as a received signal. That is, the vibrator 2 receives a sound wave (including an ultrasonic wave) and vibrates, thereby receiving the sound wave and outputting a reception signal having a waveform corresponding to the frequency and amplitude of the received sound wave. Further, the transducer 2 outputs a reception signal based on a voltage for transmitting ultrasonic waves during transmission of ultrasonic waves. The vibrator 2 generates reverberation vibration after driving for transmitting ultrasonic waves is stopped, and outputs a reception signal due to the reverberation vibration during the reverberation vibration. The reverberation vibration occurs at the natural frequency (self-resonant frequency) of the vibrator 2. In the present embodiment, the natural frequency of the vibrator 2 is designed to be 72 kHz that is the frequency of the ultrasonic wave in a normal temperature environment.

  The drive circuit 3 is a circuit that transmits ultrasonic waves from the vibrator 2, and includes a drive transistor 31 and a transformer 32. The driving transistor 31 is a junction type PNP transistor. The transformer 32 includes a primary side coil 33 and a secondary side coil 34.

  The driving transistor 31 has an emitter connected to the power supply, a base connected to the control unit 6, and a collector connected to one end of the primary side coil 33 of the transformer 32. The primary coil 33 of the transformer 32 has one end connected to the collector of the driving transistor 31 and the other end connected to the ground. The secondary coil 34 of the transformer 32 has one end connected to the vibrator 2 (piezoelectric element of the vibrator 2) via the coil 41 of the reverberation vibration suppression circuit 7, and the other end connected to the ground.

  A sensor drive signal is supplied from the control unit 6 to the drive circuit 3. The sensor drive signal is a signal that changes between a low level and a high level at a predetermined drive frequency (the frequency of ultrasonic waves, which is 72 kHz in the present embodiment). The sensor drive signal is supplied from the control unit 6 to the drive circuit 3 when the ultrasonic wave is transmitted from the vibrator 2 under the control of the control unit 6, and the sensor drive signal supplied to the drive circuit 3 is driven. Is input to the base of the transistor 31 for use.

  When the sensor driving signal is input to the base, the driving transistor 31 is turned on / off at the driving frequency of the sensor driving signal and outputs a transmission signal. The transmission signal is a signal for transmitting ultrasonic waves from the transducer 2 and is a signal whose voltage changes at the drive frequency of the sensor drive signal.

  The transformer 32 boosts the voltage of the transmission signal output from the driving transistor 31. The boosted voltage is a voltage obtained by multiplying the voltage (power supply voltage) before boosting by the coil turns ratio of the primary side coil 33 and the secondary side coil 34. The transformer 32 outputs a transmission signal obtained by boosting this voltage from the secondary coil 34. The transmission signal output from the secondary coil 34 is supplied to the vibrator 2 (the piezoelectric element of the vibrator 2) through the coil 41 of the reverberation vibration suppression circuit 7.

  When the transmission signal is supplied to the vibrator 2 (the piezoelectric element of the vibrator 2), the vibrator 2 is driven by the transmission signal (a voltage that changes at the drive frequency of the sensor drive signal is applied). As a result, the vibrator 2 vibrates at the drive frequency of the sensor drive signal (the piezoelectric element vibrates at the drive frequency of the sensor drive signal, and the vibrating body vibrates together with the piezoelectric element). The driving frequency ultrasonic wave (72 kHz ultrasonic wave in the present embodiment) is transmitted.

  Thus, the drive circuit 3 outputs a transmission signal from the drive transistor 31 when the sensor drive signal is input from the control unit 6. Then, the drive circuit 3 boosts the voltage of the transmission signal by the transformer 32 and supplies the transmission signal whose voltage has been boosted to the vibrator 2 to drive and vibrate the vibrator 2 by the transmission signal. Ultrasonic waves are transmitted from the vibrator 2.

  The reception circuit 4 processes the reception signal output from the transducer 2 and detects the ultrasonic frequency component signal (the ultrasonic frequency component signal transmitted from the transducer 2) included in the reception signal. . The receiving circuit 4 outputs an ultrasonic component signal indicating the amplitude level (intensity) of the detected ultrasonic component signal. When the signal of the ultrasonic frequency component included in the received signal is due to the reception of the ultrasonic wave by the vibrator 2, the signal level of the ultrasonic component signal is equal to the reception intensity of the ultrasonic wave by the vibrator 2. Correspond.

  Under the control of the control unit 6, the time measuring unit 5 is the time of flight until the ultrasonic wave transmitted from the vibrator 2 is reflected by the object and returns to the vibrator 2 (the vibrator 2 transmits ultrasonic waves). ) Until the time when the vibrator 2 receives the ultrasonic wave reflected by the object.

  That is, when the time measurement unit 5 receives a measurement start signal from the control unit 6, the time measurement unit 5 starts measuring time. The measurement start signal is a signal indicating the start of transmission of ultrasonic waves, and at the same time as the supply of the sensor drive signal from the control unit 6 to the drive circuit 3 is started (that is, when transmission of ultrasonic waves from the transducer 2 is started). At the same time) from the control unit 6 to the time measuring unit 5. Accordingly, the time measuring unit 5 starts measuring time simultaneously with the start of transmission of ultrasonic waves from the transducer 2. Then, the time measurement unit 5 starts from the time measurement start (that is, after the transmission of ultrasonic waves from the transducer 2), and starts from the state where the signal level of the ultrasonic component signal output from the reception circuit 4 is less than the threshold value. Measure the time until the above.

  The reason why the signal level of the ultrasonic component signal output from the receiving circuit 4 becomes higher than the threshold value from the state below the threshold value is after the sensor drive signal supply to the drive circuit 3 is stopped and the reverberation vibration of the vibrator 2 has converged. In FIG. 2, the vibrator 2 receives an ultrasonic wave. This is when the ultrasonic wave transmitted from the vibrator 2 is reflected by the object and the ultrasonic wave reflected by the object is received by the vibrator 2. Therefore, the measurement time by the time measuring unit 5 is the time from when the transducer 2 starts transmitting ultrasonic waves to when the transducer receives ultrasonic waves reflected by the object, and is transmitted from the transducer 2. It is a flight time until the ultrasonic wave reflected by the object returns to the vibrator 2.

  The controller 6 supplies a sensor drive signal to the drive circuit 3 when measuring the distance to the object. At this time, the control unit 6 supplies a sensor drive signal to the drive circuit 3 over a predetermined drive time (for example, 1 ms). In addition, the control unit 6 gives a transmission start signal to the time measurement unit 5 at the same time as the start of supplying the sensor drive signal to the drive circuit 3 (that is, at the same time as the start of transmission of ultrasonic waves from the transducer 2).

  Thereby, the vibrator 2 is driven by the drive circuit 3 over a predetermined drive time, and an ultrasonic wave is transmitted from the vibrator 2 over a predetermined drive time. In addition, a reception signal is output from the transducer 2, an ultrasonic component signal is output from the reception circuit 4, and the ultrasonic wave transmitted from the transducer 2 is reflected by the object by the time measurement unit 5 and returns to the transducer 2. Flight time to come is measured. The control unit 6 detects the object based on the measurement time by the time measurement unit 5 and measures the distance to the object.

  In addition, the control part 6 measures the distance to a target object regularly (for example, every 200 ms). That is, the control unit 6 periodically supplies the sensor drive signal to the drive circuit 3 and supplies a transmission start signal to the time measurement unit 5 to detect the object based on the time measured by the time measurement unit 5. Measure the distance to the object.

  The reverberation vibration suppression circuit 7 is a circuit that suppresses the reverberation vibration of the vibrator 2. The reverberation vibration suppression circuit 7 includes a vibrator 2 and a secondary side coil 34 of the transformer 32 (first inductive element, a boosting inductive element that boosts the voltage of a transmission signal provided in the drive circuit 3. ). The reverberation vibration suppression circuit 7 includes a coil (second induction element) 41, a resistor 42, and a capacitor (capacitance element) 43. The secondary coil 34 of the vibrator 2 and the transformer 32 also serves as a part of the reverberation vibration suppression circuit 7.

  The vibrator 2 (the piezoelectric element used for the vibrator 2) has one end connected to one end of the coil 41 and the other end connected to the ground. The secondary coil 34 has one end connected to the other end of the coil 41 and the other end connected to the ground. The coil 41 is connected between the vibrator 2 and the secondary coil 34, one end side is connected to one end side of the vibrator 2, and the other end side is connected to one end side of the secondary coil 34. .

  The resistor 42 has one end connected to one end of the coil 41 and the other end connected to one end of the capacitor 43. The capacitor 43 has one end connected to the other end of the resistor 42 and the other end connected to the other end of the coil 41. That is, the resistor 42 and the capacitor 43 are connected in series to each other and are connected in parallel to the coil 41.

  That is, the reverberation vibration suppression circuit 7 is a circuit including the vibrator 2, the secondary coil 34, and an LCR circuit in which a resistor 42 and a capacitor 43 connected in series with each other are connected in parallel to the coil 41. ing. The reverberation vibration suppression circuit 7 is a circuit in which an LCR circuit in which a resistor 42 and a capacitor 43 connected in series with each other are connected in parallel to the coil 41 is connected between the vibrator 2 and the secondary coil 34. It has become.

FIG. 2 shows an equivalent circuit of the vibrator 2 of the ultrasonic sensor 1 and an equivalent circuit of the reverberation vibration suppression circuit 7. The equivalent circuit 20 of the vibrator 2 is a circuit having an equivalent series inductance L _P , an equivalent series capacitance C _P , an equivalent resistance R _P , and an equivalent parallel capacitance C _S. The equivalent series inductance L _P corresponds to the inertia (mass of the vibrating body) when the vibrating body of the vibrator 2 vibrates and displaces. Equivalent series capacitance C _P is equivalent to the modulus of elasticity of when the vibration of the vibrator 2 is deformed by the vibration (spring coefficient). Equivalent resistance R _P is one in which the vibrating body of the vibrator 2 corresponds to air resistance or friction resistance when vibrating. The equivalent parallel capacitance C _S corresponds to the capacitance of the piezoelectric element of the vibrator 2 (capacitance generated between the electrodes of the piezoelectric element). Then, the equivalent circuit 20 of the vibrator 2 has a current I _P due to the reverberation vibration of the vibrator 20 (the charge is moved by the polarization of the piezoelectric element of the vibrator 2 being changed by the reverberation vibration of the vibrator 2. Current) flows.

The reverberation vibration suppression circuit 7 is a circuit that generates two resonance points at which the impedance of the reverberation vibration suppression circuit 7 is minimum and three anti-resonance points at which the impedance of the reverberation vibration suppression circuit 7 is maximum. These two resonance points and three anti-resonance points are equivalent inductance L _P , equivalent series capacitance C _P , equivalent resistance R _p , equivalent parallel capacitance C _S , secondary coil 34, coil 41, resistance 42. This is caused by the combined action of the capacitor 43.

The frequency of these two resonance points (the frequency of the resonance point at which the impedance of the reverberation vibration suppression circuit 7 is minimized) is set to the first resonance frequency ω ₁ and the second resonance frequency ω _{2 in} order from the lowest frequency. . Further, the frequencies of these three anti-resonance points (the frequency of the resonance point at which the impedance of the reverberation vibration suppression circuit 7 is maximized) are set in order from the lowest frequency, the first anti-resonance frequency ω _a1 and the second anti-resonance. It is assumed that the frequency is ω _a2 and the third anti-resonance frequency ω _a3 . The first resonance frequency ω ₁ , the second resonance frequency ω ₂ , the first anti-resonance frequency ω _a1 , the second anti-resonance frequency ω _a2 , and the third anti-resonance frequency ω _a3 are respectively different in frequency. is there.

The first resonance frequency ω ₁ , the second resonance frequency ω ₂ , the first anti-resonance frequency ω _a1 , the second anti-resonance frequency ω _a2 , and the third anti-resonance frequency ω _a3 are expressed by the following equations. Frequency.

Here, L _P is the equivalent series inductance in the equivalent circuit 20 of the oscillator 2, C _P is the equivalent series capacitance in the equivalent circuit 20 of the oscillator 2, C _S is the vibrator 2 equivalent This is the equivalent parallel capacitance in the circuit 20. L ₃₄ is the inductance of the secondary coil 34, L ₄₁ is the inductance of the coil 41, and C ₄₃ is the capacitance of the capacitor 43.

The reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 by utilizing the resonance phenomenon at two different resonance frequencies (first resonance frequency ω ₁ and second resonance frequency ω ₂ ), thereby vibrating. The reverberation vibration of the child 2 is suppressed.

That is, the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 using the resonance phenomenon at the _first resonance frequency ω ₁ and uses the resonance phenomenon at the second resonance frequency ω _2. The reverberation vibration of the vibrator 2 is absorbed.

Vibration absorbing characteristics of utilizing the resonance of the first resonant frequency omega ₁ corresponds to the resonance characteristic of the first resonance frequency omega _1, utilizing a resonance phenomenon in the second resonance frequency omega ₂ All the vibration absorption characteristics correspond to the resonance characteristics at the _second resonance frequency ω ₂ . In other words, the vibration absorption characteristic of using the resonance phenomenon at the first resonance frequency ω ₁ is, mainly, as the vibration of a frequency close the vibration of the first resonant frequency ω ₁ and the same frequency to the absorption (frequency ω ₁ strongly And absorbs the vibration having the same frequency as the frequency ω ₁ most strongly). In addition, vibration absorption characteristics of using the resonance phenomenon at the second resonance frequency ω ₂ is, mainly, as the vibration of a frequency close the vibration of the second resonance frequency ω ₂ with the same frequency in absorption (frequency ω ₂ strongly And absorbs vibrations having the same frequency as the frequency ω ₂ most strongly). The reverberation vibration suppression circuit 7 superimposes the vibration absorption characteristics using the resonance phenomenon at the first resonance frequency ω ₁ and the vibration absorption characteristics using the resonance phenomenon at the second resonance frequency ω _2. The reverberation vibration of the vibrator 2 is absorbed by the vibration absorption characteristics.

  The reverberation vibration suppression circuit 7 releases the absorbed vibration energy from the resistor 42 as thermal energy. The reverberation vibration of the vibrator 2 is absorbed by the reverberation vibration suppression circuit 7 and the energy of the vibration is released from the resistor 42 of the reverberation vibration suppression circuit 7, so that the vibration is attenuated faster and in a short time. Converge. Since the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 by using resonance phenomena at two different resonance frequencies, the reverberation vibration suppression circuit 7 has a double motion vibration absorber configuration.

The first resonance frequency ω ₁ and the second resonance frequency ω ₂ are set to be frequencies close to the natural frequency ω ₀ of the vibrator 2 in a room temperature environment. In this case, it is desirable to set ω ₁ lower than ω ₀ and ω ₂ higher than ω ₀ . Further, ω ₁ and ω ₂ may be set so that one of them has the same frequency as ω ₀ and the other has a frequency close to ω ₀ in a room temperature environment. In order for ω ₁ and ω ₂ to be like this, the inductance of the coil 34, the inductance of the coil 41, the resistance value of the resistor 42, the static value of the capacitor 43 according to the natural frequency ω ₀ of the vibrator 2 in a room temperature environment. Electric capacity is selected.

In the present embodiment, the natural frequency ω ₀ of the vibrator 2 is ω ₀ ≈72 kHz in a room temperature environment. In the normal temperature environment, the equivalent series inductance L _P in the equivalent circuit 20 of the vibrator 2 is L _P ≈100 mH, the equivalent series capacitance C _P is C _P ≈50 pF, and the equivalent resistance R _P is , R _P ≈1 kΩ, and the equivalent parallel capacitance C _S is C _S ≈1.5 nF.

On the other hand, in the present embodiment, the inductance L ₃₄ of the secondary coil ₃₄ is L ₃₄ ≈3 mH and the inductance L _{41 of the} coil ₄₁ is L ₄₁ ≈400 μH in a room temperature environment. Further, in a normal temperature environment, the resistance value _{R 42} of the resistor 42 _{is R 42} ≒ 100 [Omega, the capacitance _{C 43} of the capacitor 43 _is a _{C 43} ≒ 15 nF.

The first resonance frequency ω ₁ is ω ₁ ≈58.9 kHz, and the second resonance frequency ω ₂ is ω ₂ ≈81.4 kHz. The first anti-resonance frequency ω _a1 is ω _a1 ≈56.9 kHz, the second anti-resonance frequency ω _a2 is ω _a2 ≈71, 7 kHz, and the third anti-resonance frequency ω _a3 is ω _a3 ≈85.7 kHz.

  FIG. 3A shows the characteristics of reverberation vibration in a conventional ultrasonic sensor, and FIG. 3B shows the characteristics of reverberation vibration in the ultrasonic sensor 1 of the present invention. 3A and 3B, the horizontal axis represents the frequency of the received signal (that is, the frequency of reverberation vibration), and the vertical axis represents the voltage of the received signal (that is, the intensity of reverberation vibration).

  The curve in FIG. 3A shows the voltage of the received signal at a certain time after driving of the vibrator is stopped in the conventional ultrasonic sensor. That is, the curve in FIG. 3A shows a received signal (that is, the intensity of reverberation vibration) due to reverberation vibration at a certain point in the conventional ultrasonic sensor.

  On the other hand, the curve in FIG. 3 (b) shows the voltage of the received signal at a certain point in time after the drive of the vibrator 2 is stopped in the ultrasonic sensor 1 of the present invention. That is, the curve in FIG. 3B shows the received signal (that is, the intensity of the reverberation vibration) due to the reverberation vibration at a certain time in the ultrasonic sensor 1 of the present invention. However, the curve in FIG. 3 (b) shows the conventional curve after driving the vibrator 2 of the ultrasonic sensor 1 of the present invention under the same conditions as in the conventional ultrasonic sensor and stopping the driving of the vibrator 2. When the same predetermined time as in the ultrasonic sensor of FIG.

  As is clear from FIGS. 3A and 3B, the voltage of the received signal due to the reverberation vibration in the ultrasonic sensor 1 of the present invention is lower than the reception signal due to the reverberation vibration in the conventional ultrasonic sensor at all frequencies. It has become. That is, in the ultrasonic sensor 1 of the present invention, reverberation vibration is suppressed as compared with the conventional ultrasonic sensor.

  According to the ultrasonic sensor 1 of the present embodiment, the reverberation vibration of the vibrator 2 is absorbed by using the resonance phenomenon at two different resonance frequencies (frequency at the resonance point where the impedance of the reverberation vibration suppression circuit 7 is minimized). Thus, the reverberation vibration of the vibrator 2 is suppressed. For this reason, even if there are variations in the natural frequency of the vibrator 2 (variations due to individual differences in the mass and shape of the vibrator 2 and the vibrators and piezoelectric elements used in the vibrator 2), the vibrator 2 is not easily affected. Reduction of the reverberation vibration suppression effect can be suppressed. Further, even if there is a fluctuation in the natural frequency of the vibrator 2 (fluctuation due to a difference in temperature of the vibrator 2 (a difference in operating environment temperature of the ultrasonic sensor 1)), it is difficult to be affected by this, and reverberation vibration is suppressed. Reduction in effect is suppressed. In addition, since the reverberation vibration is absorbed by utilizing the resonance phenomenon at two resonance frequencies, the reverberation vibration is also greatly suppressed.

  Therefore, according to the ultrasonic sensor 1 of this embodiment, the reverberation vibration of the vibrator 2 can be more efficiently suppressed. Thereby, it becomes possible to measure the distance to the closer object.

<Second Embodiment>
FIG. 4 shows the configuration of the ultrasonic sensor according to the second embodiment. In the ultrasonic sensor 1 of the present embodiment, the configuration of the drive circuit 3 is different from the configuration of the first embodiment. Other configurations in the present embodiment are the same as those in the first embodiment.

  In the present embodiment, the drive circuit 3 has a push-pull configuration. The drive circuit 3 includes drive transistors 31 a and 31 b and a transformer 32. The driving transistors 31a and 31b are field effect transistors. The transformer 32 includes a primary side coil 33 having a center tap at an intermediate point and a secondary side coil 34.

  The driving transistor 31a has a drain connected to one end of the primary side coil 33 of the transformer 32, a gate connected to the control unit 6, and a source connected to the ground. The driving transistor 31b has a drain connected to the other end of the primary coil 33 of the transformer 32, a gate connected to the control unit 6, and a source connected to the ground. The primary coil 33 of the transformer 32 has a center tap (intermediate point) connected to the power supply, one end connected to the drain of the driving transistor 31a, and the other end connected to the drain of the driving transistor 31b. The secondary coil 34 of the transformer 32 has one end connected to the vibrator 2 (piezoelectric element of the vibrator 2) via the coil 41 of the reverberation vibration suppression circuit 7, and the other end connected to the ground.

  In the present embodiment, the drive circuit 3 is supplied with the first sensor drive signal and the second sensor drive signal from the control unit 6. The first sensor drive signal and the second sensor drive signal are the same as the sensor drive signal in the first embodiment, respectively. However, the first sensor drive signal and the second sensor drive signal are 180 degrees out of phase with each other. That is, when the first sensor drive signal is at a low level, the second sensor drive signal is at a high level, and when the first sensor drive signal is at a high level, the second sensor drive signal is at a low level. The sensor drive signal is supplied from the control unit 6 to the drive circuit 3 when transmitting ultrasonic waves from the vibrator 2 under the control of the control unit 6. The first sensor drive signal supplied to the drive circuit 3 is input to the gate of the drive transistor 31a, and the second sensor drive signal supplied to the drive circuit 3 is input to the gate of the drive transistor 31b. .

  The driving transistor 31a is turned on and off to output a transmission signal when the first sensor driving signal is input to the gate. The driving transistor 31b is turned on and off to output a transmission signal when the second sensor driving signal is input to the gate. The transformer 32 boosts the voltage of the transmission signal output from the driving transistors 31a and 31b. The transformer 32 outputs a transmission signal obtained by boosting this voltage from the secondary coil 34. The transmission signal output from the secondary coil 34 is supplied to the vibrator 2 (the piezoelectric element of the vibrator 2) through the coil 41 of the reverberation vibration suppression circuit 7. When the transmission signal is supplied, the vibrator 2 is driven by the transmission signal and transmits ultrasonic waves, as in the first embodiment.

  According to the ultrasonic sensor 1 of the present embodiment, the reverberation vibration of the vibrator 2 can be more efficiently suppressed as in the first embodiment, and the distance to an object at a shorter distance is measured. It becomes possible.

<Third Embodiment>
FIG. 5 shows a configuration of an ultrasonic sensor according to the third embodiment. The ultrasonic sensor 1 according to the present embodiment is different from the first embodiment in the configuration of the drive circuit 3 and the configuration of the reverberation vibration suppression circuit 7. Other configurations in the present embodiment are the same as those in the first embodiment.

  In the present embodiment, the drive circuit 3 includes a self-induction coil 39 instead of the transformer 32 in the first embodiment.

  The driving transistor 31 has an emitter connected to the power supply, a base connected to the control unit 6, and a collector connected to one end side of the self-induction coil 39. The self-induction coil 39 has one end connected to the collector of the driving transistor 31 and the other end connected to the ground. A connection point between the collector of the driving transistor 31 and one end side of the self-induction coil 39 is connected to the vibrator 2 (piezoelectric element of the vibrator 2) via the coil 41 of the reverberation vibration suppression circuit 7.

  As in the first embodiment, the drive circuit 3 is supplied with a sensor drive signal, and the sensor drive signal supplied to the drive circuit 3 is input to the base of the drive transistor 31.

  As in the first embodiment, the driving transistor 31 outputs a transmission signal when a sensor driving signal is input to the base. The self-induction coil 39 boosts the voltage of the transmission signal output from the driving transistor 31 by a self-induction action. The boosted voltage becomes twice the voltage (power supply voltage) before boosting due to the back electromotive force due to the self-induction action of the self-induction coil 39. Then, the self-induction coil 39 outputs a transmission signal obtained by boosting this voltage from a connection point between the collector of the driving transistor 31 and one end side of the self-induction coil 39. The output transmission signal is supplied to the vibrator 2 (piezoelectric element of the vibrator 2) via the coil 41 of the reverberation vibration suppression circuit 7. When the transmission signal is supplied, the vibrator 2 is driven by the transmission signal and transmits ultrasonic waves, as in the first embodiment.

  As described above, in the present embodiment, the drive circuit 3 boosts the transmission signal by the self-induction coil 39 and supplies the transducer 2 with the transmission signal boosted by this voltage. Drive and vibrate to transmit ultrasonic waves from the vibrator 2.

  Further, in this embodiment, the reverberation vibration suppression circuit 7 is replaced with the self-inductive coil 39 (first inductive element, drive circuit 3) instead of the secondary side coil 34 of the transformer 32 in the first embodiment. Is provided with a boosting inductive element that boosts the voltage of the transmission signal. The self-induction coil 39 also serves as a part of the reverberation vibration suppression circuit 7.

  According to the ultrasonic sensor 1 of the present embodiment, the reverberation vibration of the vibrator 2 can be more efficiently suppressed as in the first embodiment, and the distance to an object at a shorter distance is measured. It becomes possible. In addition, the cost can be reduced by using the self-induction coil 39 instead of the transformer 32 in the first embodiment.

<Fourth Embodiment>
FIG. 6 shows a configuration of an ultrasonic sensor according to the fourth embodiment. The ultrasonic sensor 1 of the present embodiment is different from the first embodiment in the configuration of the reverberation vibration suppression circuit 7. Other configurations in the present embodiment are the same as those in the first embodiment.

  In the present embodiment, the reverberation vibration suppression circuit 7 includes a further coil 51, a resistor 52, and a capacitor 53 in addition to the configuration in the first embodiment.

  The vibrator 2 has one end connected to one end of the coil 51 instead of one end connected to one end of the coil 41 in the first embodiment. The coil 41 has one end connected to the other end of the coil 51 in place of one end connected to the one end of the vibrator 2 in the first embodiment. That is, the coil 51 is connected between the vibrator 2 and the coil 41, one end side is connected to one end side of the vibrator 2, and the other end side is connected to one end side of the coil 41.

  The resistor 42 has one end connected to one end of the coil 51 instead of one end connected to one end of the coil 41 in the first embodiment. That is, the resistor 42 and the capacitor 43 are connected in series to each other and are connected in parallel to the coil 41 and the coil 51.

  The resistor 52 has one end connected to one end of the coil 51 and the other end connected to one end of the capacitor 53. The capacitor 53 has one end connected to the other end of the resistor 52 and the other end connected to the other end of the coil 51. That is, the resistor 52 and the capacitor 53 are connected in series to each other and connected to the coil 51 in parallel.

  That is, in the reverberation vibration suppression circuit 7 of the present embodiment, instead of the coil 41 in the first embodiment, an LCR circuit in which a resistor 52 and a capacitor 53 connected in series with each other are connected in parallel to the coil 51, The circuit has a configuration in which the coil 41 is connected in series.

  From another point of view, the reverberation vibration suppressing circuit 7 of the present embodiment includes a resistor 52 and a capacitor 53 connected in series to each other in parallel to the coil 51 in addition to the configuration in the first embodiment. The circuit includes another LCR circuit. In other words, the reverberation vibration suppression circuit 7 of the present embodiment is a circuit that includes two LCR circuits in which resistors and capacitors connected in series with each other are connected in parallel to the coil. The reverberation vibration suppression circuit 7 of this embodiment is a circuit in which these two (double) LCR circuits are connected between the vibrator 2 and the secondary coil 34.

  One end side of the secondary side coil 34 of the transformer 32 is connected to the vibrator 2 via the coil 41 and the coil 51, and the transmission signal output from the secondary side coil 34 passes through the coil 41 and the coil 51. It is supplied to the vibrator 2.

In the present embodiment, the reverberation suppression circuit 7 generates three resonance points at which the impedance of the reverberation suppression circuit 7 becomes minimum, and generates four anti-resonance points at which the impedance of the reverberation suppression circuit 7 becomes maximum. It has become. These resonance points and antiresonance points are equivalent inductance L _P , equivalent series capacitance C _P , equivalent resistance R _p , equivalent parallel capacitance C _S , secondary coil 34, coil 41, resistor 42, capacitor 43. This is caused by the combined action of the coil 51, the resistor 52, and the capacitor 53.

The frequencies of these three resonance points are set to a first resonance frequency ω ₁ , a second resonance frequency ω ₂ , and a _third resonance frequency ω _{3 in} order from the lowest frequency. Further, the frequencies of these four anti-resonance points are set in order from the lowest frequency, the first anti-resonance frequency ω _a1 , the second anti-resonance frequency ω _a2 , the third anti-resonance frequency ω _a3 , and the fourth anti-resonance frequency ω _a3 . The resonance frequency is _ωa4 . First resonance frequency ω ₁ , second resonance frequency ω ₂ , third resonance frequency ω ₃ , first anti-resonance frequency ω _a1 , second anti-resonance frequency ω _a2 , third anti-resonance frequency ω _a3 The fourth antiresonance frequency ω _a4 is a different frequency.

The reverberation vibration suppression circuit 7 uses the resonance phenomenon at three different resonance frequencies (first resonance frequency ω ₁ , second resonance frequency ω ₂ , and third resonance frequency ω ₃ ) to reverberate the vibrator 2. By absorbing the vibration, the reverberation vibration of the vibrator 2 is suppressed.

That is, the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 by utilizing the resonance phenomenon at the _first resonance frequency ω ₁ . In addition, the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 using a resonance phenomenon at the _second resonance frequency ω ₂ . Further, the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 using a resonance phenomenon at the _third resonance frequency ω ₃ .

The vibration absorption characteristics using the resonance phenomenon at the first, second, and third resonance frequencies ω ₁ , ω ₂ , and ω ₃ are the first, second, and third resonance frequencies ω ₁ , ω, respectively. _2, corresponding to the resonance characteristics in omega _3. That, omega _1, omega _2, the vibration absorption characteristic of utilizing the resonance phenomena in omega ₃ are each primarily, omega _1, omega _2, absorbing the vibrations of the same frequency as _{ω 3 (ω 1, ω 2} , The vibration with the frequency close to ω ₃ is absorbed more strongly, and the vibration with the same frequency as ω ₁ , ω ₂ , and ω ₃ is absorbed most strongly). The reverberation vibration suppressing circuit 7 has a vibration absorption characteristic obtained by superposing vibration absorption characteristics using the resonance phenomenon at the first, second, and third resonance frequencies ω ₁ , ω ₂ , and ω _3. 2 reverberation vibrations are absorbed.

  The reverberation vibration suppressing circuit 7 releases the absorbed vibration energy from the resistors 42 and 52 as thermal energy. Since the reverberation vibration suppressing circuit 7 absorbs the reverberation vibration of the vibrator 2 by using resonance phenomena at three different resonance frequencies, the reverberation vibration suppressing circuit 7 has a triple dynamic vibration absorber configuration.

The first, second, and third resonance frequencies ω ₁ , ω ₂ , and ω ₃ are each set to have a frequency close to the natural frequency ω ₀ of the vibrator 2 in a room temperature environment. In this case, it is desirable that ω ₁ is lower than ω ₀ , ω ₂ is the same frequency as ω _0, and ω ₃ is higher than ω ₀ . In order for ω ₁ , ω ₂ , and ω ₃ to be like this, according to the natural frequency ω ₀ of the vibrator 2 in a room temperature environment, the inductances of the coils 34, 41, 51, the resistance values of the resistors 42, 52, The capacitance of the capacitors 43 and 53 is selected.

In the present embodiment, the natural frequency ω _{0 of} the vibrator 2, the equivalent series inductance L _P in the equivalent circuit 20 of the vibrator 2, the equivalent series capacitance C _P , the equivalent resistance R _P , and the equivalent parallel static in the normal temperature environment. The electric capacity _CS is the same as that in the first embodiment. That is, in a normal temperature environment, ω ₀ ≈72 kHz, L _P ≈100 mH, C _P ≈50 pF, R _P ≈1 kΩ, and C _S ≈1.5 nF.

On the other hand, in this embodiment, in the normal temperature environment, the inductance L _{34 of} the coil ₃₄ , the inductance L _{41 of the} coil 41, the resistance value R ₄₂ of the resistor ₄₂ , and the capacitance C ₄₃ of the capacitor ₄₃ are This is the same as the embodiment. That is, under a normal temperature environment, L ₃₄ ≈3 mH, L ₄₁ ≈400 μH, R ₄₂ ≈100Ω, and C ₄₃ ≈15 nF. Further, in the present embodiment, in a normal temperature environment of the inductance _{L 51} of the coil 51 _{is L 51} ≒ _40μH, the resistance value _{R 52} of the resistor 52 _{is R 52} ≒ 50 [Omega, the electrostatic capacitance C of the capacitor 53 ₅₃ is C ₅₃ ≈150 nF.

  According to the ultrasonic sensor 1 of the present embodiment, the reverberation vibration of the vibrator 2 is absorbed using the resonance phenomenon at three different resonance frequencies (frequency at the resonance point where the impedance of the reverberation vibration suppression circuit 7 is minimized). Thus, the reverberation vibration of the vibrator 2 is suppressed. For this reason, even if the natural frequency of the vibrator 2 varies or even if the natural frequency of the vibrator 2 fluctuates, it is more difficult to be affected, and the effect of suppressing reverberation vibration is reduced. Is further suppressed. In addition, since the absorption of reverberation vibrations utilizes resonance phenomena at three resonance frequencies, the effect of suppressing reverberation vibrations is even greater.

  Therefore, according to the ultrasonic sensor 1 of this embodiment, the reverberation vibration of the vibrator 2 can be more efficiently suppressed. Thereby, it becomes possible to measure the distance to the closer object.

<Fifth Embodiment>
FIG. 7 shows a configuration of an ultrasonic sensor according to the fifth embodiment. The ultrasonic sensor 1 of the present embodiment is different from the fourth embodiment in the configuration of the reverberation vibration suppression circuit 7. Other configurations in the present embodiment are the same as those in the fourth embodiment.

  In the present embodiment, the reverberation vibration suppression circuit 7 has a configuration obtained by further developing the configuration in the fourth embodiment. That is, the reverberation vibration suppression circuit 7 is a circuit provided with M layers (M ≧ 3) of LCR circuits in which resistors and capacitors connected in series with each other are connected in parallel to the coil. The reverberation vibration suppression circuit 7 of this embodiment is a circuit in which these M (M-fold) LCR circuits are connected between the vibrator 2 and the secondary coil 34.

In the present embodiment, the reverberation suppression circuit 7 generates N resonance points (N ≧ 4) at which the impedance of the reverberation suppression circuit 7 is minimal, and anti-resonance at which the impedance of the reverberation suppression circuit 7 is maximum. In this circuit, N + 1 points are generated. The reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 by using resonance phenomena at _N different resonance frequencies (ω ₁ , ω ₂ ,..., Ω _N ). Suppress reverberation vibration. Since the reverberation vibration suppression circuit 7 absorbs the reverberation vibration of the vibrator 2 using resonance phenomena at N different resonance frequencies, the reverberation vibration suppression circuit 7 has a configuration of an N double vibration absorber.

  The reverberation vibration suppression circuit 7 generates N resonance points (N = M + 1) and anti-resonance by multiplying an LCR circuit in which a resistor and a capacitor connected in series with each other are connected in parallel to the coil. The circuit generates N + 1 points.

  Therefore, when the reverberation vibration suppression circuit 7 has four resonance points (N = 4), the LCR circuit in which a resistor and a capacitor connected in series with each other are connected in parallel to the coil is tripled ( M = 3) is sufficient. That is, instead of the coil 51 of the fourth embodiment, an LCR circuit in which a resistor 62 and a capacitor 63 connected in series with each other are connected in parallel to the coil 61 is connected to the coil 51 in series. Just do it.

  Further, when the reverberation vibration suppressing circuit 7 has five resonance points (N = 5), a quadruple LCR circuit in which a resistor and a capacitor connected in series with each other are connected in parallel to the coil ( M = 4) may be set. That is, instead of the coil 61, an LCR circuit in which a resistor 72 and a capacitor 73 connected in series with each other are connected in parallel to the coil 71 may be provided. The same applies to the case where the reverberation vibration suppressing circuit 7 has six or more resonance points (N ≧ 6).

Resonant frequencies ω ₁ , ω ₂ ,..., Ω _N are set to be frequencies close to the natural frequency ω ₀ of the vibrator 2 in a room temperature environment. In this _{case, ω 1, ω 2, ···} , ω higher than ₀ several omega of _N to (or lower), several different lower than omega ₀ (or higher) to desirably. Also, ω ₁ , ω ₂ ,..., Ω _N are set so that one of them has the same frequency as ω ₀ and the rest are set to frequencies close to ω ₀ in a room temperature environment. May be. In this case, it is desirable to have some of the rest above ω _{0 and} some of the rest below ω ₀ .

  According to the ultrasonic sensor 1 of the present embodiment, a vibrator is used by utilizing resonance phenomena at N different resonance frequencies (N ≧ 4) (resonance frequency at which the impedance of the reverberation vibration suppression circuit 7 is minimized). The reverberation vibration of 2 is absorbed, and the reverberation vibration of the vibrator 2 is suppressed. Therefore, the reverberation vibration of the vibrator 2 can be more efficiently suppressed. Thereby, it becomes possible to measure the distance to the closer object.

  In addition, this invention is not restricted to the structure of said each embodiment, A various deformation | transformation is possible. For example, the reverberation vibration suppression circuit may be another circuit as long as the circuit has a plurality of different resonance frequencies.

DESCRIPTION OF SYMBOLS 1 Ultrasonic sensor 2 Vibrator 3 Drive circuit 4 Receiving circuit 5 Time measurement part 6 Control part 7 Reverberation suppression circuit 20 Equivalent circuit of vibrator 31, 31a, 31b Driving transistor 32 Transformer 33 Transformer primary coil 34 Transformer Secondary coil (first inductive element)
39 Self-induction coil (first induction element)
41 Coil (second inductive element)
42 Resistance 43 Capacitor (capacitance element)
51, 61, 71 Coil 52, 62, 72 Resistance 53, 63, 73 Capacitor

Claims (6)

In an ultrasonic sensor that transmits ultrasonic waves from the vibrator by driving and vibrating the vibrator,
A reverberation vibration suppression circuit that suppresses the reverberation vibration of the vibrator,
The reverberation vibration suppressing circuit suppresses reverberation vibration of the vibrator by absorbing reverberation vibration of the vibrator by using resonance phenomena at a plurality of different resonance frequencies. .   The reverberation vibration suppressing circuit includes the vibrator, a first inductive element, and an LCR circuit in which a resistance and a capacitive element connected in series with each other are connected in parallel to a second inductive element, 2. The ultrasonic sensor according to claim 1, comprising a circuit in which the LCR circuit is connected between the first inductive element and the first inductive element. A drive circuit for transmitting ultrasonic waves from the vibrator is further provided, and the drive circuit boosts the voltage of a transmission signal for transmitting ultrasonic waves and supplies the transmitter with the transmission signal obtained by boosting the voltage. The vibrator is driven and vibrated by this transmission signal, and ultrasonic waves are transmitted from the vibrator.
The ultrasonic sensor according to claim 2, wherein the first inductive element is a boosting inductive element that boosts the voltage of the transmission signal provided in the drive circuit. The drive circuit boosts the transmission signal with a transformer,
The ultrasonic sensor according to claim 3, wherein the boosting induction element provided in the drive circuit is a secondary coil of the transformer.   The ultrasonic sensor according to claim 3, wherein the boosting inductive element provided in the drive circuit is an inductive element that boosts the transmission signal by a self-inducing action.   The ultrasonic sensor according to any one of claims 2 to 5, wherein the reverberation vibration suppression circuit includes a circuit including a plurality of the LCR circuits.

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