JP2019135809A - Ultrasonic transducer - Google Patents

Abstract

To provide an ultrasonic transducer in which a piezoelectric element is difficult to break and the sensitivity of reception is maintained.SOLUTION: The present invention includes: a cylindrical case body 1 with one open end 2 and the other end 3 having one bottomed end 5; and a piezoelectric element 10 in the case body 1. The bottomed surface 5 is a vibration surface 5 having a longer axis direction and a shorter axis direction in an orthogonal two-axial coordinate system. The vibration surface 5 includes a first region 11, to which the piezoelectric element 10 is fixed, and a pair of second regions 12, which are adjacent to the first region 11 at both sides in the shorter axis direction and extend along the longer axis direction, the second region 12 having a lower rigidity than that of the first region 11.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ultrasonic transducer.

  There is an ultrasonic transducer that is used in a vehicle or the like and detects an obstacle using an ultrasonic wave or measures a distance to the obstacle (for example, Patent Documents 1 and 2). In the ultrasonic transducer shown in Patent Document 1, a vibration surface to which a piezoelectric element (a piezoelectric vibrator in the document) is fixed is provided on one end surface of a cylindrical case body (a support body in the document), and the vibration surface has a long axis. Direction and a minor axis direction. In the ultrasonic transducer mounted on the vehicle, the major axis direction of the vibration surface is matched with the height direction of the vehicle, and the minor axis direction is matched with the lateral width direction of the vehicle. Accordingly, the ultrasonic transducer can have a directivity that is narrow in the vehicle height direction and wide in the vehicle width direction, and it is possible to detect and measure a wide range of obstacles while suppressing unnecessary detection of the road surface and the like.

  Patent Document 2 shows an ultrasonic transducer in which a piezoelectric vibrator is housed in a cylindrical case body (sensor housing in the literature) having a circular cross section and a bottom surface at one end. The case body has an oval opening and bottom surface, and a piezoelectric element (a piezoelectric vibrator in the literature) is arranged on the bottom surface, and the bottom surface vibrates as a vibration surface by the piezoelectric element. A major axis direction and a minor axis direction exist on the vibration surface. As a result, the directivity in the major axis direction of the vibration surface can be narrowed, and the ultrasonic transducer is installed so that the major axis direction of the vibration surface is the height direction of the vehicle. False detection of detecting an object (for example, a curb for parking) as an obstacle can be suppressed.

JP-A 61-234698 JP 2002-58091 A

  As described above, the ultrasonic transducer of Patent Document 1 has a vertically long shape having a short axis direction and a long axis direction on the vibration surface. Therefore, when mounted on a vehicle, the ultrasonic transducer is narrow in the vehicle height direction and wide in the vehicle width direction. Directivity can be obtained. Here, since the transducer is mounted at a position visible from the outside of the vehicle in the vehicle, it is required to be downsized. However, the downsizing of the transducer causes the size of the vibration surface to be narrowed, the diaphragm is difficult to deform, and the resonance frequency is increased. Therefore, in order to set the resonance frequency of the vibration surface to a practical resonance frequency, it is necessary to reduce the thickness of the diaphragm having the vibration surface. When the thickness of the diaphragm is reduced, when an external force is applied to a surface (outer surface) opposite to the vibration surface of the diaphragm, the external force is easily transmitted from the diaphragm to the piezoelectric element. For this reason, the ultrasonic transducer mounted on the vehicle is likely to break the piezoelectric element when subjected to vibrations and impacts caused by stepping stones from the outside.

  On the other hand, in the ultrasonic transducer of Patent Document 2, a piezoelectric element is arranged at the center of the vibration surface in the major axis direction (contributing direction in the vertical direction), and the diaphragm having the vibration surface has a center of thickness at both ends in the major axis direction. It is configured to be thinner than the thickness of the part. Therefore, compared with the case where the vibration surface having the same resonance frequency and the same shape has a uniform thickness, the thickness of the portion where the piezoelectric element is arranged becomes thicker, and the piezoelectric element is arranged in the major axis direction of the vibration surface. The central part is less likely to deform than when the thickness of the vibration surface is uniform. Further, the vibration surface has a constant thickness of the diaphragm in the minor axis direction, and the thickness of the portion where the piezoelectric element is disposed is the same thickness as the central portion in the major axis direction. For this reason, in the minor axis direction of the vibration surface, the central portion where the piezoelectric element is disposed is less likely to be deformed than when the thickness of the vibration surface is uniform. Further, as described above, the piezoelectric element is fixed to the center of the vibration surface. As a result, the vibration surface that receives the force generated by the driving of the piezoelectric element is less likely to be deformed, so that high sound pressure cannot be output outward from the piezoelectric element. Also, when receiving the piezoelectric element, the deformation of the vibration surface is reduced, so that the deformation of the piezoelectric element is reduced and the reception sensitivity is lowered.

  In view of the above circumstances, there is a need for an ultrasonic transducer that maintains the reception sensitivity and is less likely to damage the piezoelectric element.

  A characteristic configuration of an ultrasonic transducer according to the present invention includes a cylindrical case body having one end opened and a bottom surface at the other end, and a piezoelectric element accommodated in the case body. A vibration surface having a major axis direction and a minor axis direction in a coordinate system, wherein the vibration surface is adjacent to the first region to which the piezoelectric element is fixed, and to the first region at both ends in the minor axis direction. And a pair of second regions extending along the major axis direction, wherein the second region is configured to have lower rigidity than the first region.

  As in this configuration, the vibration surface of the ultrasonic transducer has a pair of second regions having rigidity lower than that of the first region to which the piezoelectric element is fixed on both sides of the piezoelectric element in the minor axis direction. The second region can be easily deformed on the surface. As a result, the vibration surface is easily deformed even in the minor axis direction, so that the thickness of the first region to which the piezoelectric element is fixed can be increased in the vibration plate having the vibration surface. As a result, even if an external force acts on the outer surface of the diaphragm opposite to the vibration surface, the external force is difficult to be transmitted from the diaphragm to the piezoelectric element. Reliability is improved. In addition, since the vibration surface has the second region extending along the major axis direction, the piezoelectric element and the vibration surface when ultrasonic waves are transmitted and received are mainly subjected to bending deformation in the major axis direction, and the minor axis direction. Bending deformation is suppressed. As a result, since the bending deformation in the short axis of the first region of the vibration surface is reduced, the bending stress applied to the piezoelectric element can be reduced, and the piezoelectric element caused by the bending stress can be transmitted even when high sound pressure ultrasonic waves are transmitted and received. Can be prevented from being damaged.

  Another characteristic configuration is that the second region is formed by a groove formed in the vibration surface.

  According to this configuration, the vibration surface can have the second region with low rigidity only by forming the groove on the vibration surface. Thereby, a 2nd area | region can be easily provided in a vibration surface.

  Another feature is that the second region is longer than the piezoelectric element in the major axis direction.

  According to this configuration, since the second region is longer than the piezoelectric element in the long axis direction of the vibration surface, the strain distribution during vibration of the vibration surface is more strained in the long axis direction than in the short axis direction. growing. Thereby, the ultrasonic transducer can more reliably suppress the bending deformation of the piezoelectric element in the minor axis direction of the vibration surface.

It is a top view of a 1st embodiment. It is II-II arrow sectional drawing of FIG. It is a figure which shows the distortion distribution in a short axis direction. FIG. 4 is a cross-sectional view taken along arrow IV-IV in FIG. 1. It is a figure which shows the distortion distribution in a major axis direction. It is a top view of a comparative example. It is VII-VII arrow sectional drawing of FIG. It is a figure which shows the distortion distribution in the short-axis direction of a comparative example. It is a figure which shows the distortion distribution in the major axis direction of a comparative example. It is sectional drawing which shows another form. It is a top view which shows another form. It is XII-XII arrow sectional drawing of FIG.

  Embodiments of an ultrasonic transducer according to the present invention will be described below with reference to the drawings.

  1 to 3 show an ultrasonic transducer 100 according to the present invention. FIG. 1 is a plan view of the ultrasonic transducer 100 viewed from behind. The ultrasonic transducer 100 includes a cylindrical case body 1 having one end 2 opened and a bottom surface 5 at the other end 3, and a piezoelectric element 10 accommodated in the case body 1. The case body 1 has a circular outer cross section, and a hollow portion 4 having an elliptical cross section is formed inside the case body 1. The axial center Z of the outer shape of the case body 1 coincides with the axial center of the hollow portion 4.

  The bottom surface 5 has the same shape as the cross section of the hollow portion 4 and is a vibration surface having a major axis direction Y and a minor axis direction X in an orthogonal biaxial coordinate system. A piezoelectric element 10 is fixed to the vibration surface (bottom surface) 5. In the case body 1, the diaphragm 6 including the vibration surface 5 has an outer surface 7. The outer surface 7 is a surface of the diaphragm 6 opposite to the vibration surface 5. The piezoelectric element 10 has a rectangular flat plate shape and is configured to be able to transmit and receive ultrasonic waves. The case body 1 including the vibration surface 5 is formed of a light alloy such as highly elastic aluminum or a synthetic resin.

  The vibration surface 5 includes a first region 11 to which the piezoelectric element 10 is fixed, a pair of second regions 12 that are adjacent to the first region 11 and extend along the major axis direction Y on both ends in the minor axis direction X. Have The piezoelectric element 10 has the same width as the minor axis direction X of the first region 11. The second region 12 is configured to have lower rigidity than the first region 11. Specifically, in the second region 12, a groove portion 13 is formed in the diaphragm 6 from the vibration surface 5 side. As a result, the thickness T2 in the second region 12 is thinner than the thickness T1 along the axis Z direction of the diaphragm 6 in the first region 11.

  The shape of the vibration surface 5 is an elliptical shape having a major axis direction Y and a minor axis direction X. Thereby, the ultrasonic transducer 100 emits ultrasonic waves that are narrow in the long axis direction Y and wide in the short axis direction X. Similarly, since the vibration surface 5 has an elliptical shape, the ultrasonic transducer 100 has a reception sensitivity that is narrow in the long axis direction Y and wide in the short axis direction X.

  In the ultrasonic transducer 100 configured as described above, when an electrical signal having a predetermined frequency is transmitted to the piezoelectric element 10 via a lead wire (not shown), the piezoelectric element 10 is parallel to the vibrating surface 5. In response to the electrical signal, the vibration surface 5 vibrates and ultrasonic waves are radiated into the outside air. The ultrasonic waves are transmitted for a short time, and after the reverberation time has elapsed, switching from transmission to reception is performed using transmission / reception switching means (not shown). The ultrasonic wave radiated into the outside air hits an object (obstacle) and the reflected wave reaches the ultrasonic transducer 100. The reflected wave is received by extracting the piezoelectric element 10 as a voltage after vibrating and deforming the piezoelectric element 10 together with the vibration surface 5. By measuring the time from when the ultrasonic wave is transmitted from the piezoelectric element 10 until it hits the object (obstacle) and the reflected wave is received by the piezoelectric element 10, the vibration surface 5 and the object (obstacle) The distance can be calculated.

  The piezoelectric element 10 is formed in a rectangular shape. The piezoelectric element 10 has the same width as the first region 11 in the minor axis direction X, and a pair of groove portions 13 (second regions 12) are adjacent to both sides of the first region 11. The piezoelectric element 10 is arranged such that when the vibration surface 5 is deformed to be a concave surface, the strain in the cross section (FIG. 5) along the major axis direction Y falls within a region where the strain is a compressive strain. In the diaphragm 6 including the vibration surface 5, the thickness T2 of the second region 12 may be less than or equal to half the thickness T1 of the first region 11. When the thickness T2 of the second region 12 is less than or equal to half the thickness T1 of the first region 11, the difference in rigidity between the first region 11 and the second region 12 increases, so that the vibration surface 5 is high in the first region 11. The deformation of the second region 12 can be facilitated while maintaining the rigidity.

  6 and 7 are diagrams showing a conventional ultrasonic transducer A as a comparative example of the ultrasonic transducer 100 of the present embodiment. In the ultrasonic transducer A, the diaphragm 6 including the vibration surface 5 is configured with a constant plate thickness. The rest is the same as the structure of the ultrasonic transducer 100 shown in FIGS.

  FIG. 8 shows a strain distribution in the minor axis direction X of the vibration surface 5 of the ultrasonic transducer A. FIG. 9 shows a strain distribution in the major axis direction Y of the vibration surface 5 of the ultrasonic transducer A. As shown in FIGS. 8 and 9, the strain in the minor axis direction X is larger than the strain in the major axis direction Y at the central portion of the vibration surface 5. For this reason, the piezoelectric element 10 is easily subjected to stress due to deformation under the distortion of the vibration surface 5.

  On the other hand, in the ultrasonic transducer 100 of the present embodiment, the vibration surface 5 has a pair of grooves 13 as the second region 12, and therefore the second region 12 in the vibration surface 5 is shear-deformed with respect to the displacement in the axial center Z direction. Therefore, the thickness T1 of the first region 11 in which the piezoelectric element 10 is disposed can be increased without changing the resonance frequency of the diaphragm 6 (see FIG. 3). As a result, even if an external force acts on the outer surface 7 on the side opposite to the vibration surface 5 in the diaphragm 6, the external force is difficult to be transmitted from the diaphragm 6 to the piezoelectric element 10, so that the piezoelectric element 10 is not easily damaged. Thus, the reliability of the ultrasonic transducer 100 is improved.

  In addition, since the vibration surface 5 has a pair of groove portions 13 (second regions 12) extending along the major axis direction Y, the piezoelectric element 10 and the vibration surface 5 when ultrasonic waves are transmitted and received have a long axis. The bending deformation in the direction Y is mainly performed, and the bending deformation of the first region 11 in the minor axis direction X is suppressed. As a result, since both the vibration amplitude of the first region 11 of the vibration surface 5 in the minor axis direction X and the bending deformation of the piezoelectric element 10 are reduced, the bending stress applied to the piezoelectric element 10 can be reduced, and the high sound pressure can be reduced. Even when ultrasonic waves are transmitted and received, damage to the piezoelectric element 10 due to bending stress can be suppressed.

  Furthermore, in the present embodiment, the pair of grooves 13 as the second region 12 is formed longer than the piezoelectric element 10 in the major axis direction Y of the vibration surface 5. With this configuration, the strain distribution during vibration of the vibration surface 5 has a larger strain in the major axis direction Y than that in the minor axis direction X. As a result, the ultrasonic transducer 100 can more reliably suppress the bending deformation of the piezoelectric element 10 in the minor axis direction X of the vibration surface 5.

  In FIG. 4, the broken line indicates one state when the vibration surface 5 vibrates in the long axis direction Y. FIG. 5 shows the surface strain in the major axis direction Y on the bonding surface of the piezoelectric element 10 on the vibration surface 5. Compressive strain is generated at the central portion in the major axis direction Y, and tensile strain is generated at both ends in the major axis direction Y. When the vibration surface 5 is thus deformed, the boundary line between the compressive strain and the tensile strain in the major axis direction Y is along the minor axis direction X. For this reason, when the vibration surface 5 is deformed by vibration as shown in FIG. 4, the region to which the compressive strain is applied is substantially rectangular on the surface (first region 11) to which the piezoelectric element 10 is bonded. become. As a result, by forming the piezoelectric element 10 in a rectangular shape, the piezoelectric element 10 is efficiently driven in the first region 11, so that reception sensitivity can be improved. In addition, when the piezoelectric element 10 is rectangular, the yield in manufacturing the piezoelectric element 10 is improved, and the manufacturing cost of the ultrasonic transducer 100 can be reduced.

[Another embodiment]
(1) In the above embodiment, the configuration in which the pair of grooves 13 are formed on the vibration surface 5 to form the second region 12 is shown. However, as shown in FIG. A pair of grooves 14 may be formed on the outer surface 7 on the opposite side. Further, as shown in FIGS. 11 and 12, the second region 12 may be configured by providing a plurality of concave portions 15 on the vibration surface 5 along the long axis direction Y. Thus, the second region 12 is configured by a thickness portion (thickness T2) having the recess 15 and a thickness portion 16 (thickness T1) that is the same as the first region 11. In addition, you may change the shape and arrangement | positioning of several recessed part 15 suitably.

(2) In the diaphragm 6 of the ultrasonic transducer 100, the second region 12 may be made of a material different from the case body 1, such as an elastic member.

  The present invention can be widely used for ultrasonic transducers.

1: Case body 2: One end 3: The other end 4: Hollow part 5: Vibration surface (bottom surface)
6: Diaphragm 7: Outer surface 10: Piezoelectric element 11: 1st area | region 12: 2nd area | region 13: Groove part 14: Groove part 15: Hole part 100: Ultrasonic transducer T1: Thickness of 1st area | region T2: Thickness of 2nd area | region X: minor axis direction Y: major axis direction Z: shaft center

Claims (3)

A cylindrical case body having one end opened and a bottom surface on the other end;
A piezoelectric element housed in the case body,
The bottom surface is a vibrating surface having a major axis direction and a minor axis direction in an orthogonal biaxial coordinate system,
The vibration surface has a first region to which the piezoelectric element is fixed, and a pair of second regions extending along the major axis direction adjacent to the first region on both ends in the minor axis direction. And
The ultrasonic transducer configured such that the second region has lower rigidity than the first region.   The ultrasonic transducer according to claim 1, wherein the second region is configured by a groove formed in the vibration surface.   The ultrasonic transducer according to claim 1, wherein the second region is longer than the piezoelectric element in the major axis direction.

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