JP2012026878A - Ultrasonic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic device in which ultrasonic waves of a plurality of frequencies can be transmitted or received by a single element and the element is easy to design.SOLUTION: An ultrasonic device includes: a piezoelectric element which constitutes a transmitting element and a receiving element and vibrates in a thickness direction and of which the acoustic impedance is Z1; an acoustic member of which the acoustic impedance is Z2 smaller than that of the piezoelectric element; drive signal generating means which generates a drive signal of a predetermined frequency for vibrating the transmitting element; and change means for instructing the drive signal generating means to change the frequency of the drive signal in accordance with a preset switching condition. The drive signal generating means is then provided to generate a plurality of drive signals of which the frequencies are different from each other in such a manner that the single transmitting element transmits and the single receiving element receives a plurality of ultrasonic waves of which the wavelengths are different from each other, meeting λ=4×Ta/(2n-1) ((n) is a positive integer, λn is a wavelength at a time when an ultrasonic wave of a frequency fn is propagated inside the acoustic member), when a thickness of the acoustic member is defined as Ta.

Description

  The present invention relates to an ultrasonic apparatus that transmits an ultrasonic wave and receives a reflected wave thereof to detect the presence / absence and distance of an object to be detected.

  For example, in Patent Document 1, a single ultrasonic transducer (transmitting device or receiving device) having one piezoelectric transducer (piezoelectric device) and one matching plate (acoustic member) has two or more frequency bands. A configuration for use band characteristics is shown.

For example, a disk-shaped piezoelectric vibrator is used as the ultrasonic vibrator, and the wavelength when the ultrasonic wave generated by the vibration in the vibration mode in the thickness direction propagates through the matching plate is λ ₁ , Tm = λ ₁ (n ₁ +1/4) = λ ₂ (n) where λ _{2 is} the wavelength when ultrasonic waves generated by vibration in the vibration mode propagate through the matching plate, and Tm is the thickness of the matching plate. ₂ + 1/4) [n ₁ and n ₂ are different numbers, and are configured to satisfy 0 or a positive integer].

Japanese Patent No. 3455585

  However, in the invention described in Patent Document 1, since a single ultrasonic transducer transmits or receives ultrasonic waves having a plurality of frequencies, the vibration mode in the thickness direction and the vibration mode in the radial direction, that is, a plurality of different vibrations. The ultrasonic transducer must be designed to satisfy the mode resonance condition.

  In view of the above problems, an object of the present invention is to provide an ultrasonic apparatus capable of transmitting or receiving ultrasonic waves having a plurality of frequencies with a single element and easily designing the element.

In order to achieve the above object, the invention described in claim 1
An ultrasonic device that transmits an ultrasonic wave and receives the reflected wave to detect the presence / absence and distance of an object to be detected,
A piezoelectric element that vibrates in the thickness direction and has an acoustic impedance of Z1, which constitutes a transmitting element that transmits ultrasonic waves and a receiving element that receives reflected waves, and one surface is exposed to the space where the object to be detected exists. An acoustic member having a piezoelectric element attached to the opposite surface exposed on the space side and having an acoustic impedance Z2 (<Z1) smaller than that of the piezoelectric element;
Drive signal generating means for generating a drive signal of a predetermined frequency to vibrate the transmitting element;
Changing means for instructing the drive signal generating means to change the frequency of the drive signal in accordance with a preset switching condition,
When the thickness between one surface and the opposite surface of the acoustic member is Ta, the drive signal generating means is
λn = 4 × Ta / (2n−1)
A single transmitting element transmits a plurality of ultrasonic waves having different wavelengths satisfying [n is a positive integer, λn is a wavelength when an ultrasonic wave having a frequency fn propagates through an acoustic member], and a single receiving element Is provided so that a plurality of drive signals having different frequencies fn can be generated.

  In a configuration in which an acoustic member having an acoustic impedance smaller than that of a piezoelectric element is attached to a piezoelectric element that vibrates in the thickness direction, that is, having a vibration mode in the thickness direction, the end on the space side of the acoustic member has no phase change due to reflection. The free end and the end on the piezoelectric element side are fixed ends whose phase changes by π (180 °) due to reflection. Therefore, when the wavelength of the ultrasonic wave propagating in the acoustic member is λ, a standing wave is generated in the acoustic member by entering the thickness Ta of the acoustic member to an odd multiple of λ / 4 and is incident on the acoustic member. It is possible to suppress the ultrasonic waves and the ultrasonic waves reflected at the boundary surface between the acoustic member and the piezoelectric element from interfering with each other, that is, to be in a resonance state.

  As described above, in the present invention, the drive signal generating means mutually transmit the frequency fn so that a single transmitting element transmits and receives a plurality of ultrasonic waves having different wavelengths while satisfying the resonance condition. Are provided so that a plurality of different drive signals can be generated. Therefore, no matter which frequency fn (for example, f1, f2) drive signal is generated, the thickness Ta of the acoustic member is an odd multiple of λn / 4, and the acoustic member is in a resonance state for each drive signal. Thereby, ultrasonic waves of a plurality of frequencies fn can be transmitted by a single transmission element, and ultrasonic waves of a plurality of frequencies fn can be received by a single reception element. Further, when designing the transmitting element and the receiving element, it is only necessary to consider the vibration mode in the thickness direction, so that it is easier to design the transmitting element and the receiving element than in the past.

  Since the acoustic member has an acoustic impedance smaller than that of the piezoelectric element, the acoustic member functions as a so-called acoustic matching member between the piezoelectric element and the space where the detection target exists, thereby reducing reflection loss.

  According to a second aspect of the invention, there is provided filter means for selectively outputting a signal in a frequency band corresponding to the frequency fn of the drive signal among the received signals of the receiving element, and the changing means is for changing the frequency of the drive signal. Accordingly, the filter means may be instructed to change the frequency band to be selectively output.

  According to this, an unnecessary frequency band signal (noise) can be cut by the filter means while receiving ultrasonic waves of a plurality of frequencies fn with a single receiving element.

According to a third aspect of the present invention, the drive signals corresponding to the wavelength λ ₁ = 4 × Ta [n = 1] may be included as the plurality of drive signals.

The amplitude X of the ultrasonic vibration is proportional to the velocity V and inversely proportional to the frequency f, and is represented by X = V / (2πf). When the same sound pressure (amplitude) is applied to the acoustic member, since the ultrasonic vibration is transmitted at the same speed V, the amplitude X becomes the largest at the above-mentioned λ ₁ (f1 having the lowest frequency). Further, the longer the wavelength (the lower the frequency fn), the smaller the attenuation of ultrasonic waves in the air. Therefore, according to the present invention, sensitivity can be improved by these effects.

  According to a fourth aspect of the present invention, the changing means may use the received signal of the receiving element for determining the switching condition. According to this, according to the reception result, the frequency fn of the drive signal and the frequency band selectively output by the filter means can be changed.

  As described in claim 5, the switching condition is based on the distance to the detected object, and the changing means is configured so that the transmitting element is turned on when the distance to the detected object is equal to or less than a preset reference distance. Instructs the drive signal generation means to change the frequency of the drive signal so that the frequency of the ultrasonic wave to be transmitted is lower than the frequency of the ultrasonic wave transmitted by the transmitting element when the distance to the detected object is longer than the reference distance. It is preferable to do.

  When the frequency fn of the ultrasonic wave transmitted from the transmitting element is low (long wavelength), the detection distance is long and the directivity is wide. When the frequency fn of the ultrasonic wave is high (short wavelength), the detection distance is short and the directivity. Becomes narrower. According to the present invention, the drive signal generation means generates a low frequency drive signal when the detected distance is equal to or less than the reference distance, and generates a high frequency drive signal when the detected distance is longer than the reference distance. Therefore, it is possible to transmit an ultrasonic wave suitable for detecting the detected object according to the distance to the detected object.

  According to the sixth aspect of the present invention, the switching condition is based on the presence / absence of the detected object, and the changing means has a frequency higher than the predetermined frequency when the detected object is detected by a drive signal having a predetermined frequency. The drive signal generation means may be instructed to generate the drive signal.

  According to this, for example, when the detected object is relatively close to the ultrasonic apparatus, it is possible to transmit an ultrasonic wave suitable for detecting the detected object.

  In addition, as a switching condition, you may make it change the frequency band of a drive signal, or the selectively output frequency, for example for every predetermined time irrespective of a received signal.

  As described in claim 7, it is preferable that the receiving element includes a reception-only piezoelectric element. According to this, since the influence of reverberation can be reduced as compared with the transmission / reception element, a closer distance can be detected.

  According to an eighth aspect of the present invention, the piezoelectric element may include a transmitting / receiving element that serves as both a transmitting element and a receiving element. According to this, the physique of an ultrasonic device can be reduced in size.

Next, the invention according to claim 9 is:
An ultrasonic device that transmits an ultrasonic wave and receives the reflected wave to detect the presence / absence and distance of an object to be detected,
A piezoelectric element that vibrates in the thickness direction and has an acoustic impedance of Z1, which constitutes a transmitting element that transmits ultrasonic waves and a receiving element that receives reflected waves, and one surface is exposed to the space where the object to be detected exists. An acoustic member having a piezoelectric element attached to the opposite surface exposed on the space side and having an acoustic impedance Z2 (> Z1) greater than that of the piezoelectric element;
Drive signal generating means for generating a drive signal of a predetermined frequency to vibrate the transmitting element;
Changing means for instructing the drive signal generating means to change the frequency of the drive signal in accordance with a preset switching condition,
When the thickness between one surface and the opposite surface of the acoustic member is Ta, the drive signal generating means is
λn = 4 × Ta / 2n
A single transmitting element transmits and receives a plurality of ultrasonic waves having different wavelengths λn satisfying [n is a positive integer, λn is a wavelength when an ultrasonic wave having a frequency fn propagates through an acoustic member]. A plurality of drive signals having different frequencies fn can be generated so as to be received by the element.

  In a configuration in which an acoustic member having a larger acoustic impedance than a piezoelectric element is attached to a piezoelectric element that vibrates in the thickness direction, that is, having a vibration mode in the thickness direction, the end on the space side and the end on the piezoelectric element side of the acoustic member are Both are free ends with no phase change due to reflection. Therefore, when the wavelength of the ultrasonic wave propagating in the acoustic member is λ, a standing wave is generated in the acoustic member by entering the acoustic member thickness Ta to an even multiple of λ / 4, and is incident on the acoustic member. It is possible to suppress the ultrasonic waves and the ultrasonic waves reflected at the boundary surface between the acoustic member and the piezoelectric element from interfering with each other, that is, to be in a resonance state.

  As described above, in the present invention, the drive signal generating means mutually transmit the frequency fn so that a single transmitting element transmits and receives a plurality of ultrasonic waves having different wavelengths while satisfying the resonance condition. Are provided so that a plurality of different drive signals can be generated. Therefore, even if a drive signal having any frequency fn is generated, the thickness Ta of the acoustic member is an even multiple of λn / 4, and the acoustic member is in a resonance state with respect to each drive signal. Thereby, ultrasonic waves of a plurality of frequencies fn can be transmitted by a single transmission element, and ultrasonic waves of a plurality of frequencies fn can be received by a single reception element. Further, when designing the transmitting element and the receiving element, it is only necessary to consider the vibration mode in the thickness direction, so that it is easier to design the transmitting element and the receiving element than in the past.

  Since the acoustic member has an acoustic impedance larger than that of the piezoelectric element, it can protect the piezoelectric element and improve environmental resistance and the like.

As described in the eleventh aspect, the plurality of drive signals may include a drive signal corresponding to the wavelength λ ₁ = 2 × Ta [n = 1]. Since the effect of this invention is the same as the effect of the invention of Claim 3, the description is abbreviate | omitted.

  Since the operational effects of the inventions according to claims 10 and 12 to 16 are the same as the operational effects of the inventions according to claims 2 and 4 to 8, respectively, description thereof is omitted.

1 is a block diagram showing a schematic configuration of an ultrasonic apparatus according to a first embodiment. It is a figure which shows schematic structure of a transmission / reception element among the ultrasonic devices shown in FIG. 1, (a) is the top view seen from the acoustic member side, (b) is sectional drawing which follows the IIB-IIB line | wire of (a). It is. It is a flowchart which shows a drive signal switching process. It is a figure which shows a detection area. It is a figure for demonstrating the resonance state of an acoustic member, (a) has shown the frequency f1 of the drive signal, (b) has shown the frequency f2 of the drive signal. It is a figure which shows the drive waveform of a piezoelectric element, (a) shows the frequency f1, (b) has shown the frequency f2. It is a flowchart which shows the modification of a drive signal switching process. It is a flowchart which shows the modification of a drive signal switching process. In the ultrasonic apparatus which concerns on 2nd Embodiment, it is a figure for demonstrating the resonance state of an acoustic member, (a) has shown the frequency f1 of the drive signal, (b) has shown the frequency f2 of the drive signal. It is a block diagram which shows the other modification of an ultrasonic device. It is a figure which shows the detection area by phase difference adjustment. 11 is a flowchart showing detection area switching processing in the ultrasonic apparatus shown in FIG. 10.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, common or related elements are given the same reference numerals.
(First embodiment)
In the following, the thickness direction (vibration direction) of the piezoelectric element is simply referred to as the thickness direction, and the direction perpendicular to the thickness direction is simply referred to as the vertical direction.

  The ultrasonic device 1 shown in FIG. 1 transmits ultrasonic waves and receives the reflected waves to detect the presence / absence and distance of the detection target, and transmits or receives ultrasonic waves as a main part. The ultrasonic elements 10 and 20 and a drive signal for the ultrasonic element 10 are generated, and the presence / absence of the detection target and the position (distance and direction) of the detection target are calculated based on the reception signals of the ultrasonic elements 10 and 20. The circuit unit 30 is provided. In the present embodiment, the ultrasonic element 10 is a transmitting / receiving element, and the ultrasonic element 20 is a receiving element.

  First, the configuration of the ultrasonic elements 10 and 20 will be described. The ultrasonic elements 10 and 20 have the same structure, and in this embodiment, the transmission / reception element 10 will be described. The configuration of the ultrasonic elements 10 and 20 is basically the same as that of the ultrasonic sensor described in Japanese Patent Application Laid-Open No. 2008-309513 filed by the present applicant, and thus detailed description thereof is omitted.

  As shown in FIGS. 2A and 2B, the ultrasonic element (transmission / reception element) 10 has an acoustic impedance of Z1, and receives a drive signal from the circuit unit 30 and a reflected wave from the detection object, and the like. The piezoelectric element 11 that vibrates in the direction and Z2 (<Z1) whose acoustic impedance is smaller than that of the piezoelectric element 11, and one surface 12a is exposed on the space side where the detection target exists, and is opposite to the one surface 12a exposed on the space side. And an acoustic member 12 having the piezoelectric element 11 attached to the surface 12b. Since the acoustic member 12 has an acoustic impedance smaller than that of the piezoelectric element 11, it functions as a so-called acoustic matching member between the piezoelectric element 11 and the space where the detection target exists.

  In addition, the ultrasonic element 10 covers the surface of the ultrasonic element 10 and the vibration damping member 13 that prevents transmission of vibration from the outside to the acoustic member 12, and is protected from environmental factors such as moisture in the usage environment. A covering material 16, a buffer material 17 that protects the piezoelectric element 11 from an external force load and an impact, and a box-shaped housing 18 that is open at one end for receiving them.

  The ultrasonic element 10 is configured as an operation unit (a so-called paptic switch) of a device for inputting information to a display device as an electronic device, specifically, a display device constituting a vehicle navigation system. The operation unit (ultrasonic element 10) of the input device is arranged on the upper surface of the center console 100 next to the driver's seat, for example, so that the driver who is the operator can operate the vehicle with almost no change in posture. The part can be operated.

  The center console 100 is provided with a mounting portion 100a formed so as to penetrate the casing 18 so as to be inserted therethrough. The ultrasonic element 10 (ultrasonic element 20) is attached to the attachment portion 100a on the side surface in the vicinity of the opening of the housing 18 with one surface 12a of the acoustic member 12 forming the transmission / reception surface exposed to the outside of the center console 100. It has been.

  The piezoelectric element 11 is formed of, for example, a piezoelectric body formed in a square columnar shape made of lead zirconate titanate (PZT) on the opposite surface by sputtering of Pt or Cu, plating, baking of a conductive paste, or the like. It is configured to be sandwiched between a pair of electrodes. The piezoelectric element 11 is attached to an opposite surface 12b of the one surface 12a that transmits and receives the ultrasonic waves of the acoustic member 12 with an adhesive or the like. Reference numeral 14 denotes an electrode formed on the attachment surface 11a for attaching the piezoelectric element 11 to the one surface 12b of the acoustic member 12. Reference numeral 15 denotes an electrode formed on the opposite surface 11b of the attachment surface 11a. Further, as the piezoelectric element 11, a laminated piezoelectric element can be employed according to the required transmission sound pressure. As such a laminated piezoelectric element, for example, a pair of electrodes 14 and 15 are alternately arranged on a piezoelectric body made of PZT and formed in a quadrangular prism shape whose cross section along the vertical direction is equal to the cross section of the acoustic member 12. Those formed in a comb-like shape and those obtained by laminating and integrating a plurality of piezoelectric elements can be employed.

The acoustic member 12 is made of a material having an acoustic impedance larger than that of air and smaller than that of the piezoelectric element 11 and is formed in a square column shape having a substantially square cross section along the vertical direction. In the present embodiment, the acoustic member 12 is formed using a polycarbonate resin (PC). Since the temperature change of the elastic modulus is small in the polycarbonate resin and the polyetherimide resin, the change in the wavelength of the ultrasonic wave accompanying the temperature change can be reduced. The acoustic impedance Z1 of the PZT constituting the piezoelectric element 11 is 24.2 × 10 ⁶ N · s · m ⁻³ , and the acoustic impedance Z2 of the PC constituting the acoustic member 12 is 1.7 × 10 ⁶ N · s · m ^-3, acoustic impedance Z3 of the air is 412N · it s · ^{m -3.} That is, Z1>Z2> Z3.

  The acoustic member 12 has a predetermined thickness Ta that is in a resonance state at the frequency of each drive signal. The thickness Ta is the length between the one surface 12a and the opposite surface 12b. Moreover, the shape of the acoustic member 12 is not limited to a quadrangular prism shape with a substantially square cross section, and may be, for example, a cylinder. Also, a horn shape having a larger cross-sectional area toward the one surface 12a side can be adopted.

  Between the side surface 12 c of the acoustic member 12 and the housing 18, a vibration damping member 13 that fixes the acoustic member 12 to the housing 18 on the side surface 12 c and prevents transmission of vibration from the center console 100 is interposed. Yes. The vibration damping member 13 is bonded and fixed to the side surface 12c of the acoustic member 12 and the inner side surface of the housing 18 with an adhesive or the like.

  The vibration damping member 13 is made of a material having a smaller acoustic impedance than that of the acoustic member 12 and a high damping constant, such as silicon rubber. Preferably, a material having a low elastic modulus and a low density is preferably used. For example, a rubber material, a resin containing pores such as foamed dendrites, a sponge, or the like can be used. The vibration damping member 13 formed of such a material is interposed between the center console 100 and the acoustic member 12, so that ultrasonic waves are applied to the side surface 12 c of the acoustic member 12 via the mounting portion 100 a of the center console 100. It is possible to suppress transmission and noise.

  Moreover, in the material with a low elastic modulus, since the force which restrains the vibration of the acoustic member 12 by an ultrasonic wave is small, attenuation | damping of an ultrasonic vibration can be made small. As a result, ultrasonic noise can be reduced and vibration attenuation can be reduced, so that the ultrasonic detection sensitivity can be improved.

  The covering material 16 is formed so as to cover the exposed portion of the surface of the piezoelectric element 11. The covering material 16 is made of a low elastic modulus material having environmental resistance such as water resistance, oil resistance, chemical resistance and the like, for example, a soft resin such as urethane, a potting material such as rubber and silicone, etc. It is made of a polymer material. The covering material 16 can be formed by forming into a predetermined shape such as a plate using the above-mentioned material and attaching it to the piezoelectric element 11 or by applying a gel-like material to the piezoelectric element 11. . Alternatively, a liquid resin material may be applied to the piezoelectric element 11 and then solidified.

  The covering material 16 is preferably formed as thin as possible so as not to inhibit vibration transmission, as long as the environmental shielding effect can be secured. The covering material 16 is formed so as to cover the end face of the electrode 14 and overlap the acoustic member 12 side. However, in order to reduce vibration attenuation, the overlapping length is preferably as short as possible. Specifically, it is preferably 1 mm or less.

  By providing the covering material 16 on the piezoelectric element 11, environmental factors such as moisture that degrade the piezoelectric element 11 can be blocked, so that ultrasonic detection accuracy can be ensured and reliability can be improved. .

  The buffer material 17 is made of a material having a lower elastic modulus than that of the piezoelectric element 11, for example, a polymer material such as a soft resin such as urethane, a potting material such as rubber or silicone, and the cross section along the vertical direction is the cross section of the piezoelectric element 11. They are formed so as to have the same shape, and are provided between one surface 11 b of the piezoelectric element 11 and the bottom surface 18 a of the housing 18.

  By providing such a buffer material 17, even when an impact is applied to the one surface 12 a of the acoustic member 12 due to a collision of flying objects such as pebbles, the shock absorber 17 transmits the impact transmitted to the piezoelectric element 11. In addition to absorbing and restraining the displacement of the piezoelectric element 11 toward the bottom surface 18 a of the housing 18, the piezoelectric element 11 is cracked or broken such that the piezoelectric element 11 is detached from the one surface 12 b of the acoustic member 12. Can be prevented.

  Further, the buffer material 17 is formed of a material having a lower elastic modulus than the piezoelectric element 11 and is in contact with only the piezoelectric element 11, so that the vibration of the acoustic member 12 and the piezoelectric element 11 due to ultrasonic waves is not hindered. Therefore, the ultrasonic detection sensitivity of the ultrasonic element 10 can be maintained in a good state.

  Furthermore, even when a temperature change occurs in the ultrasonic element 10, there is no possibility that a stress caused by thermal expansion / contraction of the buffer material 17 is applied to the piezoelectric element 11 and a detection error occurs.

  The buffer material 17 can also be formed of the same material as the covering material 16. According to this, the cushioning material 17 and the covering material 16 can be integrally formed, and the cushioning material 17 can exert the action and effect of the covering material 16 and can simplify the manufacturing process. .

  The buffer material 17 is preferably formed such that its resonance frequency is higher than the disturbance vibration band of the device on which the ultrasonic element 10 is mounted. For example, when mounted on a vehicle, a large disturbance vibration is generated in a frequency band of 1 KHz or less, so that the resonance frequency of the buffer material 17 is set to 1 KHz or more. As a result, detection noise can be reduced without resonating due to vibration transmitted from the vehicle, and detection accuracy can be improved.

  In addition, the buffer material 17 is preferably formed so that the resonance frequency thereof substantially matches the resonance frequency of the piezoelectric element 11. Thereby, since the ultrasonic vibration transmitted to the piezoelectric element 11 can be amplified, the detection sensitivity can be improved.

  Next, the circuit unit 30 will be described.

  The circuit unit 30 includes a control circuit 31, a drive signal generation unit 32, a driver 35, amplifiers 36 and 37, bandpass filters 38 and 39, TADs 40 and 41, and a DSP 42.

  The control circuit 31 includes a central processing unit (CPU) (not shown), a read-on memory (ROM) in which various programs executed by the CPU are stored, and operations for various calculations that the CPU executes in accordance with the programs stored in the ROM. A random access memory (RAM) used as an area is provided. A function for instructing the drive signal generation unit 32 to generate a drive signal and a function for instructing a frequency change of the drive signal in accordance with a preset switching condition, and selectively outputting to the bandpass filters 38 and 39. A function for instructing to change the frequency band to be detected, a function for detecting the presence / absence of the detected object and the position (distance and azimuth) of the detected object, and a function for outputting the detection result to an external device. The control circuit 31 corresponds to a changing unit described in the claims.

  The drive signal generation unit 32 corresponds to the drive signal generation means described in the claims, and includes an oscillation unit 33 and a frequency adjustment unit 34. When receiving the instruction signal from the control circuit 31, the oscillating unit 33 generates a pulse signal having the reference frequency f0 for a certain period. The frequency adjustment unit 34 is provided so that the pulse signal of the reference frequency f0 generated by the oscillation unit 33 can be adjusted to a plurality of different frequencies fn.

  The frequency adjustment unit 34 of the present embodiment is configured by connecting a plurality of frequency dividers having different frequency division numbers in parallel, and the control circuit 31 controls the opening and closing of the switches connected in series to each frequency divider. By selecting one frequency divider, the drive signal generation unit 32 outputs a drive signal having a predetermined frequency fn (for example, frequency f1) corresponding to the selected frequency divider.

More specifically, let λn be a wavelength when ultrasonic waves having a frequency fn propagate through the acoustic member 12, and n is a positive integer.
λn = 4 × Ta / (2n−1),
The frequency adjustment unit 34 is set so that the single ultrasonic element 10 transmits and receives a plurality of ultrasonic waves having different wavelengths satisfying the condition and the single ultrasonic element 20 receives the ultrasonic waves.

In the present embodiment, from the frequency adjustment unit 34, a frequency f1 that satisfies λ ₁ = 4Ta (n = 1), a frequency f2 that satisfies λ ₂ = 4Ta / 3 (n = 2), and λ ₃ = 4Ta / 5 (n = The driving signal having the frequency f3 satisfying 3) can be output. More specifically, Ta = 5.9 mm, the frequency f1 is 60 kHz, the frequency f2 is 180 kHz, and the frequency f3 is 300 kHz.

  The driver 35 is a drive circuit that drives the transmission / reception element 10 with a drive signal from the drive signal generation unit 32, and thereby, ultrasonic waves with a predetermined frequency are transmitted from the transmission / reception element 10. In the present embodiment, the driver 35 includes a power amplification circuit such as a transformer.

  The amplifiers 36 and 37 amplify the reception signals of the ultrasonic elements 10 and 20 and output the amplified reception signals to the bandpass filters 38 and 39.

  The band-pass filters 38 and 39 filter the received signals of the ultrasonic elements 10 and 20 amplified by the amplifiers 36 and 37 to remove frequency components that are out of the frequency of the drive signal, in other words. For example, a signal in the same frequency band as the drive signal is extracted from the received signal. The bandpass filters 38 and 39 correspond to the filter means described in the claims.

  In the present embodiment, the frequency of the drive signal output from the frequency adjustment unit 34 in a period in which the transmission / reception element 10 and the reception element 20 can receive the reflected wave of the ultrasonic wave transmitted from the transmission / reception element 10 is detected. Based on the instruction signal from the control circuit 31, the multipliers of the bandpass filters 38 and 39 are set so as to selectively extract signals in the same frequency band. In other words, in the present embodiment, the reception signals having the frequencies f1, f2, and f3 can be selectively output from the bandpass filters 38 and 39, respectively.

  The TADs 40 and 41 are well-known time A / D conversion circuits, and the DSP (digital signal processor) 42 receives signals based on the reception signals of the ultrasonic elements 10 and 20 A / D converted by the TADs 40 and 41. Calculate the amplitude and phase of the signal. These calculation results are output to the control circuit 31. The DSP 42 has a memory.

  Next, an example of the drive signal frequency switching process will be described.

  When the operation unit of the input device can be operated by the operator (for example, the ignition key of the vehicle is turned on and the power of the circuit unit 30 is turned on), the control circuit 31 first causes the frequency adjustment unit 34 to Then, an instruction signal is output so as to set the lowest frequency f1 that can be generated by the drive signal generator 32 (step 10).

  The oscillating unit 33 receives an instruction from the control circuit 31 at a predetermined cycle, and generates a pulse signal having a reference frequency f0 for a certain period. Then, the frequency adjusting unit 34 adjusts the pulse signal having the reference frequency f0 to a predetermined frequency lower than the reference frequency f0, and outputs it as a drive signal (step 11).

  In this way, the drive signal generation is performed periodically with the ignition key turned on. Immediately after the ignition key is turned on, as shown in step 10, a drive signal having a frequency f1 is output.

  The generated drive signal (voltage signal) is transmitted to the piezoelectric element 11 of the transmission / reception element 10 via the driver 35. Thereby, the piezoelectric element 11 vibrates in the thickness direction, the vibration is transmitted to the acoustic member 12, and is transmitted as an ultrasonic wave from the one surface 12a of the acoustic member 12 (step 12). The frequency of this ultrasonic wave matches the frequency of the drive signal.

  After the start of the transmission process, the control circuit 31 is calculated by the DSP 42 when the ultrasonic wave elements 10 and 20 can detect the reflected wave by the detection target (detectable start timing indicated by a broken line arrow in FIG. 6 described later). It is compared whether the amplitude of the received signals of the ultrasonic elements 10 and 20 (step 13) is greater than a predetermined threshold (step 14).

  For example, when the calculated amplitude of one of the ultrasonic elements 10 and 20 is equal to or smaller than the threshold value, the control circuit 31 determines whether or not the corresponding measurement time has elapsed (step 15). If the measurement time has not elapsed, the process returns to step 13 assuming that no reflected wave has been received. On the other hand, if it is determined that the measurement time has been exceeded, it is determined that there is no object to be detected (step 16), the currently set frequency is maintained (step 17), and the process returns to step 11. That is, when it is determined that the detection target does not exist, the process returns to step 11 without instructing the frequency change of the drive signal.

  The above-described measurement time is the time from the timing at which the reflected wave from the detection target can be detected (detectable start timing) to the end at which detection is possible, and varies depending on the frequency of the ultrasonic wave. In the present embodiment, the control circuit 31 uses a measurement time corresponding to the frequency adjusted by the frequency adjustment unit 34 for determination. These measurement times are stored in advance in a nonvolatile memory (not shown).

  When the calculated amplitude of at least one of the ultrasonic elements 10 and 20 is larger than the threshold value in step 14, the control circuit 31 determines that the detected object exists (the detected object exists) (step 18). . Then, the control circuit 31 calculates the distance to the detected object from the timing when the amplitude exceeds the threshold in the reception signals of the ultrasonic elements 10 and 20 determined to have the detected object (step 19). Then, the calculated distance is compared with a corresponding reference distance stored in advance in a nonvolatile memory (not shown) (step 20).

The reference distance is a value that is about the maximum distance (the outermost peripheral portion of the detection area) on the smaller side of the detection area with respect to two frequencies in which the magnitude relationship of the detection area (see FIG. 4 described later) is adjacent. in set, when the three frequencies, as shown in this embodiment has a reference distance alpha ₁ corresponding to the frequency f1, f2, the reference distance alpha ₂ corresponding to the frequency f2, f3. The corresponding reference distance in step 17 is α _{1 for} the frequency f1 and α ₂ for the frequencies f2 and f3.

  When the calculated distance exceeds the reference distance, the control circuit 31 determines whether or not the frequency of the currently set drive signal is f1 having the lowest frequency (step 21). Since the frequency f1 cannot be switched to a frequency lower than the frequency f1, the currently set frequency f1 is maintained (step 17), and the process returns to step 11. That is, the control circuit 31 does not change the frequency.

  On the other hand, if it is not the frequency f1, an instruction signal is output to the frequency adjustment unit 34 so as to switch the currently set frequency to a frequency one step lower (step 22), and the process returns to step 11. For example, when the currently set frequency is f2, the frequency is switched to frequency f1, and when the frequency is frequency f3, the frequency is switched to frequency f2.

  As described above, when the frequency is switched in step 22, a drive signal having the switched frequency is periodically generated until the frequency switching instruction is given again.

  When the calculated distance is equal to or smaller than the reference distance in step 20, the control circuit 31 determines whether the frequency of the drive signal is the highest among the drive signals that can be generated by the drive signal generation unit 32. (Step 23). When the frequency is the highest (f3 in this embodiment), since it is not possible to switch to a higher frequency signal, the currently set frequency is maintained (step 24) and the process returns to step 11. That is, the control circuit 31 does not change the frequency.

  On the other hand, if the currently set frequency is not the highest frequency, the control circuit 31 outputs an instruction signal to the frequency adjustment unit 34 so as to switch the currently set frequency to a frequency one step higher ( Step 25) and return to Step 11. For example, when the currently set frequency is f1, the frequency is switched to frequency f2, and when the frequency is set to frequency f2, the frequency is switched to frequency f3.

  Although omitted in the above flow, when the presence / absence determination of the detected object in step 15 and step 16 and the distance calculation in step 19 are performed, the control circuit 31 outputs these measurement results to the external device.

  Although the description is omitted, the control circuit 31 switches the multipliers of the bandpass filters 38 and 39 to a predetermined multiplier corresponding to the frequency of the drive signal by the same process as the frequency switch process of the drive signal described above. .

Thus, according to the ultrasonic device 1 shown in the present embodiment, a plurality of ultrasonic waves having different frequencies can be transmitted and received at different timings. Specifically, the frequency f1 indicated by a solid line in FIG. 4 (wavelength λ ₁ = 4Ta in the acoustic member 12), the frequency f2 indicated by a one-dot chain line (wavelength λ ₂ = 4Ta / 3 in the acoustic member 12), two Ultrasonic waves having a frequency f3 (wavelength λ ₃ = 4Ta / 5 in the acoustic member 12) indicated by a dashed line can be transmitted and received.

  The detection distance of the ultrasonic elements 10 and 20 is longer as the frequency is lower (longer wavelength) and shorter as the frequency is higher (shorter wavelength). The directivity is wider as the frequency is lower (longer wavelength) and narrower as the frequency is higher (shorter wavelength). Therefore, the detection areas at each frequency of the ultrasonic elements 10 and 20 are different from each other as shown in FIG.

  Next, the effect of the characteristic part of the ultrasonic device 1 according to the present embodiment will be described.

  As shown in FIGS. 5A and 5B, in the configuration in which the acoustic member 12 having an acoustic impedance smaller than that of the piezoelectric element 11 is attached to the piezoelectric element 11 that vibrates in the thickness direction, that is, has a vibration mode in the thickness direction. The space-side end (one surface 12a) of the acoustic member 12 becomes a free end without phase change due to reflection, and the piezoelectric element 11-side end (one surface 12b) changes in phase by π (180 °) due to reflection. It becomes a fixed end.

  Therefore, when the wavelength of the ultrasonic wave propagating through the acoustic member 12 is λ, a standing wave is generated in the acoustic member 12 by setting the thickness Ta of the acoustic member 12 to an odd multiple of λ / 4. It is possible to suppress the ultrasonic waves incident inside and the ultrasonic waves reflected by the boundary surface between the acoustic member 12 and the piezoelectric element 11 from interfering with each other, that is, to be in a resonance state.

5A, in the case of the frequency f1 of the drive signal (wavelength λ ₁ = 4Ta in the acoustic member 12), in FIG. 5B, the frequency f2 of the drive signal (wavelength in the acoustic member 12). λ ₂ = 4Ta / 3) is shown, and in either of FIGS. 5A and 5B, the front surface 12a of the acoustic member 12 is in an abdominal state.

  Thus, according to the present embodiment, a single ultrasonic element 10 transmits a plurality of ultrasonic waves having different wavelengths while satisfying the resonance condition, and a single ultrasonic element 10 or 20 receives each of the ultrasonic waves. The drive signal generator 32 is provided so as to be able to generate a plurality of drive signals having different frequencies fn (specifically, frequencies f1, f2, and f3). Therefore, regardless of which frequency fn drive signal is generated, the thickness Ta of the acoustic member 12 is an odd multiple of λn / 4, and the acoustic member 12 enters a resonance state for each drive signal. Thereby, ultrasonic waves having a plurality of frequencies fn can be transmitted by the single ultrasonic element 10, and ultrasonic waves having a plurality of frequencies fn can be received by the single ultrasonic elements 10 and 20. In other words, it is possible to detect a detection object located at a long distance and a detection object located at a short distance by one ultrasonic element 10, 20. In addition, when designing the ultrasonic elements 10 and 20, only the vibration mode in the thickness direction needs to be considered, so that the ultrasonic elements 10 and 20 can be designed more easily than in the past.

  Since the acoustic member 12 has an acoustic impedance smaller than that of the piezoelectric element 11, it functions as a so-called acoustic matching member between the piezoelectric element 11 and the space where the detection target exists, thereby reducing reflection loss. You can also.

  In the present embodiment, the receiving circuits of the ultrasonic elements 10 and 20 have band-pass filters 38 and 39 as filter means, respectively, and the control circuit 31 as change means responds to the frequency change of the drive signal. The band pass filters 38 and 39 are instructed to change the frequency band to be selectively output (change of the multiplier). Accordingly, unnecessary frequency band signals (noise) can be cut by the band-pass filters 38 and 39 while receiving ultrasonic waves having a plurality of frequencies fn by the single ultrasonic elements 10 and 20.

In the present embodiment, the drive signals corresponding to the wavelength λ ₁ = 4 × Ta [n = 1] are included as the plurality of drive signals generated by the drive signal generation unit 32. The amplitude X of the ultrasonic vibration is proportional to the velocity V and inversely proportional to the frequency f, and is represented by X = V / (2πf). When the same sound pressure (amplitude) is applied to the acoustic member 12, since the ultrasonic vibration is transmitted at the same speed V, the amplitude X is the largest at the above-mentioned λ ₁ (f1 having the lowest frequency). Further, the longer the wavelength (the lower the frequency fn), the smaller the attenuation of ultrasonic waves in the air. Therefore, according to this embodiment, sensitivity can be improved by these effects.

  In the present embodiment, since the control circuit 31 uses the reception signals of the ultrasonic elements 10 and 20 for determining the switching condition, the frequency fn of the drive signal and the multipliers of the bandpass filters 38 and 39 are determined according to the reception result. Can be changed.

  In the present embodiment, the distance to the detected object is set as a switching condition, and the control circuit 31 changes the frequency of the drive signal to the frequency adjustment unit 34 based on the comparison result between the calculated distance and a preset reference distance. It comes to direct. As described above, when the ultrasonic frequency fn is low (long wavelength), the detection distance is long and the directivity is wide. When the ultrasonic frequency fn is high (short wavelength), the detection distance is short and the directivity is low. Narrow. Therefore, it is possible to transmit an ultrasonic wave suitable for detecting the detected object according to the distance to the detected object.

  In particular, in the present embodiment, when the ignition key is turned on, the control circuit 31 first instructs the frequency adjustment unit 34 to generate a drive signal having the frequency f1 in step 10. If the calculated distance is equal to or smaller than the corresponding reference distance in step 20 and is not the highest frequency, in step 25, the frequency is switched to one-step high frequency. Accordingly, the long distance detection mode (frequency f1), the medium distance mode (frequency f2), and the short distance mode (frequency f3) are switched in the order of the directivity and the long detection distance. Even when approaching 20), the detected object can be detected with high accuracy.

  Moreover, in this embodiment, it has the receiving element 20 only for reception as an ultrasonic element. In the case of the transmission / reception element 10, as illustrated in FIGS. 6A and 6B, even if the drive signal application to the piezoelectric element 11 is stopped, reverberation that oscillates for a while occurs. The signal detectable timing is set after reverberation. On the other hand, the receiving element 20 can reduce the influence of reverberation compared to the transmitting / receiving element (ultrasonic element 10), although it has an influence of a sneak wave in which the vibration of the transmitting / receiving element 10 is transmitted. Therefore, the reception signal detectable timing indicated by the broken-line arrow can be set earlier than the transmission / reception element, thereby detecting a short distance.

  In response to an instruction from the control circuit 31, the drive signal generator 32 generates a drive signal having a predetermined frequency fn for a certain period (for example, a predetermined number of pulses). Therefore, the transmission time (and reverberation time) becomes shorter as the drive signal has a higher frequency, and the reception signal detectable timing can be advanced.

  Moreover, in this embodiment, it has the transmission / reception element 10 which serves as a transmission element and a receiving element as an ultrasonic element. Therefore, the physique of the ultrasonic device 1 can be reduced in size as compared with the configuration having only the ultrasonic element dedicated for transmission and the ultrasonic element dedicated for reception.

  In the present embodiment, an example in which the distance to the detection object is a switching condition is shown. However, the switching condition is not limited to the distance. For example, the presence / absence of an object to be detected may be used as the switching condition. Further, for example, the frequency of the drive signal and the multipliers of the band-pass filters 38 and 39 (frequency bands to be selectively output) are changed every predetermined time regardless of the reception signals of the ultrasonic elements 10 and 20. good.

  For example, in the modification shown in FIGS. 7 and 8, the presence / absence of the detected object is used as the switching condition. Steps 30 to 38 shown in FIG. 7 correspond to steps 10 to 18 shown in FIG. 3 described above. If it is determined in step 38 that there is an object to be detected, the control circuit 31 determines whether the frequency of the currently set drive signal is the highest among the drive signals that can be generated by the drive signal generator 32. Is determined (step 39). When the frequency is the highest (f3 in this embodiment), it is not possible to switch to a higher frequency signal, so the currently set frequency is maintained (step 40) and the process returns to step 31. That is, the control circuit 31 does not change the frequency.

  On the other hand, if the currently set frequency is not the highest frequency, the control circuit 31 outputs an instruction signal to the frequency adjustment unit 34 so as to switch the currently set frequency to a frequency one step higher ( Step 41), returning to Step 31. For example, when the currently set frequency is f1, the frequency is switched to frequency f2, and when the frequency is set to frequency f2, the frequency is switched to frequency f3.

  In this way, when a detection target is detected, a configuration may be adopted in which the driving signal is switched to a higher frequency drive signal. According to this, for example, when the detected object is relatively close to the ultrasonic apparatus 1, it is possible to transmit an ultrasonic wave suitable for detecting the detected object.

  In FIG. 8, when it is determined in step 36 that there is no object to be detected, the currently set frequency is not maintained, but the process returns to step 30. Other than that is the same as FIG. According to this, when there is no detected object, since the frequency f1 is the widest in the detection area, the probability of detecting the detected object at the next drive signal generation timing can be increased.

  In this embodiment, the example which the ultrasonic device 1 has the transmission / reception element 10 and the receiving element 20 as an ultrasonic element was shown. However, the ultrasonic device 1 may have at least one transmitting ultrasonic element and at least one receiving ultrasonic element. For example, a configuration having only one transmission / reception element 10 may be employed, or a configuration having one transmission element dedicated for transmission and one reception element dedicated for reception may be employed. However, when the configuration includes a plurality of reception ultrasonic elements, the orientation of the detection target can be detected from the phase difference of the reception signals.

  In the present embodiment, an example is shown in which the drive signal generation unit 32 is provided so as to be able to generate three drive signals having different frequencies (f1, f2, and f3). However, the number of drive signals having different frequencies is not limited to the above example. For example, only two or four or more may be used.

(Second Embodiment)
The configuration of the ultrasonic apparatus 1 according to this embodiment is substantially the same as that of the first embodiment. The difference is that 1) the impedance Z2 of the acoustic member 12 is larger than the impedance Z1 of the piezoelectric element 11, and Z1 <Z2> Z3 (Z3 is the acoustic impedance of air). 2) The ultrasonic wave of frequency fn is acoustic. When the wavelength when propagating through the member 12 is λn and n is a positive integer, the single ultrasonic element 10 transmits and receives a plurality of ultrasonic waves having different wavelengths satisfying λn = 4 × Ta / 2n. However, the frequency adjustment unit 34 is set so that the single ultrasonic element 20 receives.

  As shown in FIGS. 9A and 9B, in the configuration in which the acoustic member 12 having an acoustic impedance larger than that of the piezoelectric element 11 is attached to the piezoelectric element 11 that vibrates in the thickness direction, that is, has a vibration mode in the thickness direction. Both the space-side end portion (one surface 12a) and the piezoelectric element 11-side end portion (one surface 12b) of the acoustic member 12 are free ends that do not change in phase due to reflection.

  Therefore, when the wavelength of the ultrasonic wave propagating through the acoustic member 12 is λ, a standing wave is generated in the acoustic member 12 by setting the thickness Ta of the acoustic member 12 to an even multiple of λ / 4. It is possible to suppress the ultrasonic waves incident inside and the ultrasonic waves reflected by the boundary surface between the acoustic member 12 and the piezoelectric element 11 from interfering with each other, that is, to be in a resonance state.

9A, in the case of the frequency f1 of the drive signal (wavelength λ ₁ = 2Ta in the acoustic member 12), in FIG. 9B, the frequency f2 of the drive signal (wavelength in the acoustic member 12). (λ ₂ = Ta) is shown, and in both FIGS. 9A and 9B, the front surface 12a of the acoustic member 12 is in an abdominal state.

  Thus, according to the present embodiment, a single ultrasonic element 10 transmits a plurality of ultrasonic waves having different wavelengths while satisfying the resonance condition, and a single ultrasonic element 10 or 20 receives each of the ultrasonic waves. The drive signal generator 32 is provided so as to be able to generate a plurality of drive signals having different frequencies fn (for example, the frequencies f1 and f2). Therefore, regardless of the generation of the drive signal of any frequency fn, the thickness Ta of the acoustic member 12 becomes an even multiple of λn / 4, and the acoustic member 12 enters a resonance state for each drive signal. Thereby, ultrasonic waves having a plurality of frequencies fn can be transmitted by the single ultrasonic element 10, and ultrasonic waves having a plurality of frequencies fn can be received by the single ultrasonic elements 10 and 20. In other words, it is possible to detect a detection object located at a long distance and a detection object located at a short distance by one ultrasonic element 10, 20. In addition, when designing the ultrasonic elements 10 and 20, only the vibration mode in the thickness direction needs to be considered, so that the ultrasonic elements 10 and 20 can be designed more easily than in the past.

Further, since the acoustic impedance Z1 of the PZT constituting the piezoelectric element 11 is 24.2 × 10 ⁶ N · s · m ⁻³ , the acoustic member 12 may be formed of a metal material larger than Z1. good. The acoustic member 12 having an acoustic impedance larger than that of the piezoelectric element 11 can protect the piezoelectric element 11 and improve environmental resistance and the like.

In addition to the above effects, the effects described in the first embodiment can be achieved. For example, when a drive signal corresponding to the wavelength λ ₁ = 2 × Ta [n = 1] is included as a plurality of drive signals, the amplitude X is the largest at the above-described λ ₁ (f1 having the lowest frequency). Moreover, since the attenuation of the ultrasonic wave in the air is small, the sensitivity can be improved. Moreover, the modification shown in 1st Embodiment is applicable.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the above-described embodiment, an example in which the frequency of the drive signal generated by the drive signal generation unit 32 and the multipliers of the bandpass filters 38 and 39 are switched according to the switching condition (first switching condition) has been described. However, there are a plurality of transmission elements as ultrasonic elements, and the drive signal generation unit 32 generates a drive signal for each transmission element at the same timing, adjusts at least one phase of the drive signal for each transmission element, A phase difference adjustment unit that adjusts the phase difference of the drive signal is provided, and the change unit adopts a configuration that instructs the phase difference adjustment unit to change the phase difference of each drive signal in accordance with a preset second switching condition. May be.

  For example, the ultrasonic device 1 shown in FIG. 10 has a configuration in which the reception element 20 of the ultrasonic device 1 shown in the first embodiment is replaced with a transmission / reception element 21, and the transmission circuit on the transmission / reception element 21 side is a transmission / reception element. The configuration is the same as the ten transmission circuits. That is, it has a transmission unit 44, a frequency adjustment unit 45, and a driver 46 that constitute the drive signal generation unit 43. Furthermore, in each transmission circuit of the transmission / reception elements 10 and 21, between the drive signal generation unit 32 and the driver 35, for adjusting the phase difference between the drive signal on the transmission / reception element 10 side and the drive signal on the transmission / reception element 21 side, A phase adjustment unit 47 is provided. Such a phase adjustment unit 47 is configured by, for example, connecting a plurality of different phase shifters in parallel, and the control circuit 31 controls the opening and closing of the switches connected in series to each of the phase shifters. A phase shifter is selected.

  The combined directivity of ultrasonic waves transmitted from a plurality of transmission elements (transmission / reception elements 10 and 21 in FIG. 10) varies depending on the phase of the drive signal. For example, the combined directivity when there is no phase difference (same phase) is different from the combined directivity when there is a phase π shift (reverse phase). Therefore, according to the ultrasonic device 1 shown in FIG. 10, the detection area can be changed by switching the phase difference even if the frequency of the drive signal is the same. As a result, the detection range of the detection target can be widened compared to a configuration having only one transmission element.

  In particular, high-frequency ultrasonic waves are effective because the detection distance is short and the directivity is narrowed. FIG. 11 shows that in the configuration capable of generating drive signals of frequencies f1, f2, and f3, there is no phase difference (one-dot chain line in the figure) and phase difference π (two-dot chain line in the figure) for the highest frequency f3. Each detection area is illustrated. In FIG. 11, the detection area of the frequency f2 is omitted for convenience.

  FIG. 12 shows an example of detection area (phase difference) switching processing. The processing shown in FIG. 12b is the same as the modification of the first embodiment (FIG. 7) in the frequency switching processing part.

  As in the above embodiments, when the operation unit of the input device can be operated by an operator (for example, when the ignition key of the vehicle is turned on and the power of the circuit unit 30 is turned on), the control circuit 31 first An instruction signal is output to the frequency adjustment units 34 and 45 to set the lowest frequency f1 that can be generated by the drive signal generation units 32 and 43 (step 50).

  Further, the control circuit 31 outputs an instruction signal to the phase adjustment unit 47 so that there is no phase difference (same phase) (step 51).

  The oscillating units 33 and 44 receive an instruction from the control circuit 31 at a predetermined cycle, and generate a pulse signal having the reference frequency f0 for a certain period at the same timing. The frequency adjustment units 34 and 45 adjust the pulse signal having the reference frequency f0 to a predetermined frequency that is lower than the reference frequency f0 and outputs the same as a drive signal from the frequency adjustment unit 45. On the other hand, on the transmission / reception element 10 side, after adjusting to a predetermined frequency by the frequency adjustment unit 34, the phase is adjusted by the phase adjustment unit 47 so as to be in phase with the drive signal on the transmission / reception element 21 side and output as a drive signal. (Step 52).

  Then, when the ultrasonic waves are transmitted from the transmission / reception elements 10 and 21 (step 53) and the timing at which the reflected waves from the detection target can be detected in the transmission / reception elements 10 and 21, the control circuit 31 calculates the transmission / reception element 10 calculated by the DSP 42. , 21 are compared (step 54) to determine whether the received signal amplitude (step 54) is greater than a predetermined threshold value.

  For example, when the calculated amplitude of one of the transmission / reception elements 10 and 21 is equal to or less than the threshold, the control circuit 31 determines whether or not the corresponding measurement time has elapsed (step 56). If the measurement time has not elapsed, it is determined that no reflected wave has been received, and the process returns to step 54. On the other hand, if it is determined that the measurement time has been exceeded, it is determined that the detected object does not exist (step 57), and the currently set frequency is maintained (step 58).

  Next, it is determined whether or not there is a phase difference (step 59). If there is no phase difference, an instruction signal is output to the phase adjustment unit 47 so that the phase difference becomes π (step 60), and the process returns to step 52. On the other hand, when there is a phase difference (that is, when the phase difference is π), the process returns to step 51. That is, when it is determined that the detection target does not exist, the phase difference between the drive signals of the transmitting and receiving elements 10 and 21 is switched.

  If the calculated amplitude of at least one of the transmission / reception elements 10 and 21 is larger than the threshold value in step 55, the control circuit 31 determines that the detected object is present (the detected object is present) (step 61). The currently set phase difference is maintained (step 62). That is, in this case, the phase difference is not switched.

  Then, the control circuit 31 determines whether or not the currently set frequency of the drive signal has the highest frequency among the drive signals that can be generated by the drive signal generators 32 and 43 (step 63). When the frequency is the highest (for example, frequency f3), it is not possible to switch to a higher frequency signal, so the currently set frequency is maintained (step 64) and the process returns to step 52. That is, the control circuit 31 does not change the frequency.

  On the other hand, when the currently set frequency is not the highest frequency, the control circuit 31 outputs an instruction signal to the frequency adjusting units 34 and 45 so as to switch the currently set frequency to a frequency one step higher. Then (step 65), the process returns to step 52.

  As described above, when the detected object is not detected by the predetermined phase difference based on the presence / absence of the detected object, the control circuit 31 does not change the frequency of the drive signal to determine the predetermined phase difference. A configuration in which the phase adjustment unit 47 (phase difference adjustment unit) is instructed so as to have different phase differences may be employed. According to this, compared with the structure which does not change a phase difference, it can make it easy to find a to-be-detected body.

  In FIG. 10, the drive signal generation units 32 and 43 are provided for each of the transmission / reception elements 10 and 21, but may be combined. Moreover, although the example which provides the phase adjustment part 47 only in the transmission circuit by the side of one transmission / reception element 10 was shown, the phase shift adjustment part was each provided in the transmission circuit of the transmission / reception elements 10 and 21, and this adjusts a phase difference. You may do it. Further, the transmission element and the reception element may be separated. For example, it is good also as a structure provided with two transmitting elements and two receiving elements.

  In the above-described embodiment, an example in which the ultrasonic device 1 is configured as an operation unit (a so-called paptic switch) of a device that inputs information to a display device that forms a navigation system of a vehicle has been described. However, the use of the ultrasonic device 1 is not limited to the above example. For example, it can also be used for a vehicle obstacle detection device. Moreover, it can also be used for applications other than automobiles, for example, obstacle sensors for robots used indoors, operation units for game machines, and the like. For example, when used in an environment where there is a low possibility of moisture or the like entering the ultrasonic elements 10, 20, 21, the covering material 16 need not be provided.

  The configuration of the receiving circuit of the ultrasonic elements 10, 20, and 21 is not limited to the above example. It is sufficient that at least the presence / absence of the detection target can be detected, and it is preferable that the distance to the detection target, preferably the orientation of the detection target, be detected.

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic device 10, 21 ... Ultrasonic element (transmission / reception element)
DESCRIPTION OF SYMBOLS 11 ... Piezoelectric element 12 ... Acoustic member 20 ... Ultrasonic element (receiving element)
31 ... Control circuit 32 ... Drive signal generation unit 34 ... Frequency adjustment unit

Claims (16)

An ultrasonic device that transmits an ultrasonic wave and receives the reflected wave to detect the presence / absence and distance of an object to be detected,
A piezoelectric element that vibrates in the thickness direction and has an acoustic impedance of Z1, which constitutes a transmitting element that transmits ultrasonic waves and a receiving element that receives reflected waves, and one surface is exposed to the space where the object to be detected exists. An acoustic member having the piezoelectric element attached to the opposite surface exposed to the space side and having an acoustic impedance Z2 (<Z1) smaller than that of the piezoelectric element;
Drive signal generating means for generating a drive signal of a predetermined frequency to vibrate the transmitting element;
Change means for instructing the drive signal generation means to change the frequency of the drive signal according to a preset switching condition,
When the thickness between one surface and the opposite surface of the acoustic member is Ta, the drive signal generating means is
λn = 4 × Ta / (2n−1)
A single transmitting element transmits a plurality of ultrasonic waves having different wavelengths satisfying [n is a positive integer, λn is a wavelength when an ultrasonic wave having a frequency fn propagates in an acoustic member]. An ultrasonic device characterized in that a plurality of the drive signals having different frequencies fn can be generated so that the receiving element receives them. Filter means for selectively outputting a signal in a frequency band corresponding to the frequency fn of the drive signal among the reception signals of the reception element;
The ultrasonic device according to claim 1, wherein the changing unit instructs the filter unit to change the frequency band to be selectively output in accordance with a frequency change of the drive signal. The ultrasonic device according to claim 1, wherein the plurality of drive signals include a drive signal corresponding to a wavelength λ ₁ = 4 × Ta [n = 1].   The ultrasonic device according to claim 1, wherein the changing unit uses a reception signal of the receiving element for determining the switching condition. The switching condition is based on the distance to the detected object,
When the distance to the detected object is equal to or less than a reference distance set in advance, the changing means is configured such that the ultrasonic frequency transmitted by the transmitting element is longer than the reference distance. The ultrasonic apparatus according to claim 4, wherein the drive signal generation unit is instructed to change the frequency of the drive signal so that the frequency of the drive signal is lower than the frequency of the ultrasonic wave transmitted by the transmission element. The switching condition is based on the presence or absence of the detected object,
The changing means instructs the drive signal generating means to generate the drive signal having a frequency higher than the predetermined frequency when the detected object is detected by the drive signal having a predetermined frequency. The ultrasonic device according to claim 4 or 5.   The ultrasonic apparatus according to claim 1, wherein the receiving element includes the piezoelectric element dedicated for reception.   The ultrasonic device according to claim 1, wherein the piezoelectric element includes a transmission / reception element serving as the transmission element and the reception element. An ultrasonic device that transmits an ultrasonic wave and receives the reflected wave to detect the presence / absence and distance of an object to be detected,
A piezoelectric element that vibrates in the thickness direction and has an acoustic impedance of Z1, which constitutes a transmitting element that transmits ultrasonic waves and a receiving element that receives reflected waves, and one surface is exposed to the space where the object to be detected exists. An acoustic member having the piezoelectric element attached to the opposite surface exposed to the space side and having an acoustic impedance Z2 (> Z1) larger than that of the piezoelectric element;
Drive signal generating means for generating a drive signal of a predetermined frequency to vibrate the transmitting element;
Change means for instructing the drive signal generation means to change the frequency of the drive signal according to a preset switching condition,
When the thickness between one surface and the opposite surface of the acoustic member is Ta, the drive signal generating means is
λn = 4 × Ta / 2n
A single transmitting element transmits a plurality of ultrasonic waves having different wavelengths satisfying [n is a positive integer, λn is a wavelength when an ultrasonic wave having a frequency fn propagates in an acoustic member]. An ultrasonic device characterized in that a plurality of the drive signals having different frequencies fn can be generated so that the receiving element receives them. Filter means for selectively outputting a signal in a frequency band corresponding to the frequency fn of the drive signal among the reception signals of the reception element;
The ultrasonic device according to claim 9, wherein the changing unit instructs the filter unit to change the frequency band to be selectively output in accordance with a frequency change of the drive signal. 11. The ultrasonic apparatus according to claim 9, wherein the plurality of drive signals include a drive signal corresponding to a wavelength λ ₁ = 2 × Ta [n = 1].   The ultrasonic device according to claim 9, wherein the changing unit uses a reception signal of the receiving element for the determination of the switching condition. The switching condition is based on the distance to the detected object,
When the distance to the detected object is equal to or less than a reference distance set in advance, the changing means is configured such that the ultrasonic frequency transmitted by the transmitting element is longer than the reference distance. The ultrasonic apparatus according to claim 12, wherein the drive signal generation unit is instructed to change the frequency of the drive signal so that the frequency of the drive signal is lower than the frequency of the ultrasonic wave transmitted by the transmission element. The switching condition is based on the presence or absence of the detected object,
The changing means instructs the drive signal generating means to generate the drive signal having a frequency higher than the predetermined frequency when the detected object is detected by the drive signal having a predetermined frequency. The ultrasonic device according to claim 12 or 13.   The ultrasonic device according to claim 9, wherein the receiving element includes the piezoelectric element dedicated to reception.   The ultrasonic device according to any one of claims 9 to 15, wherein the piezoelectric element includes a transmitting / receiving element serving as the transmitting element and the receiving element.

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