Ultrasonic projection device

Abstract

To further enhance acoustic pressure of ultrasonic waves in an ultrasonic projection device.SOLUTION: An ultrasonic projection device 1 for projecting ultrasonic waves includes: a first block body 2; a second block body 3; and piezoelectric units 4 that are held between the first block body 2 and the second block body 3. A diaphragm 6b is provided at one end on a first block body 2 side in an axial direction of the first block body 2, the second block body 3 and the piezoelectric units 4. A dimension from the one end in the axial direction to the other end on a second block body 3 side is formed so as to substantially coincide with a half wavelength of oscillation generated in the piezoelectric units 4. In between the diaphragm 6b and a base part 6a supporting the diaphragm 6b, a connection part 6c having grooves 6e with smooth inner wall surfaces 6e1 connecting the diaphragm 6b to the base part 6a is provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ultrasonic projection device.

Background Art

[0002] In recent years, small ultrasonic projection devices have been used as ultrasonic sensors for vehicles and parametric speakers that project sound waves with directivity. For example, Patent Document 1 discloses an ultrasonic projection device that transmits vibrations generated in a vibrating portion to a diaphragm to project ultrasonic waves.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the ultrasonic projection device is mounted on a vehicle or the like, it is required to be small and lightweight. Furthermore, it is required that the ultrasonic projection device can project ultrasonic waves with a strong sound pressure while being small and lightweight.

[0005] The present invention has been made in view of the above problems, and an object thereof is to increase the sound pressure of ultrasonic waves in an ultrasonic projection device.

Means for Solving the Problems

[0006] As means for solving the above problems, the present invention adopts the following configuration.

[0007] A first aspect of the present invention is an ultrasonic projection device for projecting ultrasonic waves, comprising a first block body, a second block body, and a vibration generating unit sandwiched between the first block body and the second block body, wherein a diaphragm is provided at one end on the first block body side in the direction of arrangement of the first block body, the dimension from the one end on the first block body side to the other end on the second block body side in the direction of arrangement is formed to substantially coincide with half a wavelength of vibration generated by the vibration generating unit, and a connecting portion is provided between the diaphragm and a base supporting the diaphragm, the connecting portion having a groove with a smooth inner wall surface that connects the diaphragm and the base.

[0008] A second aspect of the present invention adopts a configuration in which, in the first aspect, the tip member having the diaphragm, the connecting portion, and the base portion is provided separately from the first block body, and the tip member is fixed to the first block body.

[0009] A third aspect of the present invention is a configuration in which, in the first aspect described above, the first block body has the diaphragm, the connecting portion, and the base portion.

[0010] A fourth aspect of the present invention is an ultrasonic projection device for projecting ultrasonic waves, comprising a first block body, a second block body, and a vibration generating unit sandwiched between the first block body and the first block body, wherein the first block body has a diaphragm provided on the side opposite to the vibration generating unit in the direction of arrangement of the first block body, the second block body and the vibration generating unit, a base in contact with the vibration generating unit, and a connecting portion provided between the diaphragm and the base, and having a groove with a smooth inner wall surface that connects the diaphragm and the base.

[0011] A fifth aspect of the present invention is a configuration in which, in any of the first to fourth aspects described above, the groove is formed in an annular shape with respect to a central axis along the arrangement direction, and the cross-sectional shape of the plane including the central axis is a semi-elliptical shape that is recessed from the outside to the inside in the radial direction with respect to the central axis.

[0012] A sixth aspect of the present invention is the configuration in the fifth invention described above, wherein the semi-elliptical shape has a minor axis parallel to the central axis and a major axis parallel to the radial direction.

[0013] A seventh aspect of the present invention is a configuration in which, in any of the first to sixth aspects described above, a bolt is provided with the first block body screwed into one end and the second block body screwed into the other end, and in the direction of arrangement, the center of gravity of the bolt is located closer to the second block body than to the first block body.

[0014] An eighth aspect of the present invention adopts a configuration in which, in any of the first to seventh embodiments, the first block body is formed of a material having a lower specific gravity than the second block body.

[0015] A ninth aspect of the present invention adopts a configuration in which, in any of the first to eighth aspects described above, the boundary between the first block body and the vibration generating unit is located at the position of the vibration node generated by the vibration generating unit in the arrangement direction. [Effects of the Invention]

[0016] According to the present invention, a groove is provided in the connection portion that connects the diaphragm to the base that supports the diaphragm. As a result, the edge of the diaphragm can be displaced significantly without being constrained by the connection portion, and the sound pressure of the ultrasonic waves projected from the diaphragm can be increased. Furthermore, since the inner wall surface of the groove is smooth, localized stress concentration on the inner wall surface can be suppressed. As a result, the amplitude of the diaphragm can be increased, and the sound pressure of the ultrasonic waves projected from the diaphragm can be increased. Therefore, according to the present invention, the sound pressure of ultrasonic waves can be increased in an ultrasonic projection device. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 2] It is a cross-sectional view showing a schematic configuration of an ultrasonic projection device according to the first embodiment of the present invention. [Figure 3] It is a result of measuring the admittance characteristics of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 4] It is a result of measuring the vibration displacement on the vibration surface of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 5] It is a measurement result regarding the directivity characteristics of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 6] It is a measurement result regarding the distance characteristics of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 7] It is a measurement result regarding the relationship between the input power and the sound pressure of the ultrasonic projection device according to the first embodiment of the present invention. [Figure 8] It is a schematic configuration diagram of an ultrasonic projection device according to the second embodiment of the present invention. [Figure 9] It is a cross-sectional view showing a schematic configuration of the ultrasonic projection device according to the second embodiment of the present invention. [Figure 10] It is a simulation result showing the sound pressure distribution obtained by changing the minor-axis radius and the major-axis radius of the groove portion in the ultrasonic projection device according to the second embodiment of the present invention. [Figure 11] It is a cross-sectional view showing a schematic configuration of the ultrasonic projection device according to the third embodiment of the present invention. [Figure 12] It is a schematic configuration diagram of an ultrasonic projection device according to the fourth embodiment of the present invention.

Mode for Carrying Out the Invention

[0018] Hereinafter, an embodiment of an ultrasonic projection device according to the present invention will be described with reference to the drawings.

[0019] (First Embodiment) Figure 1 is a schematic diagram of the ultrasonic projection device 1 of this embodiment. Figure 2 is a cross-sectional view showing the schematic configuration of the ultrasonic projection device 1 of this embodiment. As shown in these figures, the ultrasonic projection device 1 of this embodiment is formed in a substantially cylindrical shape with the central axis L as its axis. In the following description, for convenience of explanation, the direction along the central axis L will be referred to as the axial direction. The direction perpendicular to the central axis L will be referred to as the radial direction. Furthermore, in the axial direction, the side of the first block body 2 as seen from the second block body 3 (described later) will be referred to as the front side. Furthermore, the side of the second block body 3 as seen from the first block body 2 will be referred to as the rear side. However, the installation orientation of the ultrasonic projection device 1 of this embodiment is not particularly limited.

[0020] As shown in Figure 1, the ultrasonic projection device 1 of this embodiment comprises a first block body 2, a second block body 3, a piezoelectric unit 4 (vibration generating part), a bolt 5, and a tip member 6. The first block body 2, the second block body 3, and the piezoelectric unit 4 are arranged along the axial direction from rear to front in the order of second block body 3, piezoelectric unit 4, and first block body 2. In other words, the arrangement direction of the first block body 2, the second block body 3, and the piezoelectric unit 4 is axial.

[0021] The first block body 2 is a metal block body formed in a cylindrical shape with a central axis L as its axis. The first block body 2 is made of, for example, aluminum, aluminum alloy, titanium, titanium alloy, stainless steel, iron, etc. As shown in Figure 2, the first block body 2 is provided with a through hole 21 that penetrates in the axial direction. The through hole 21 is formed in the central part of the first block body 2 when viewed from the axial direction. A female thread is formed on the inner wall surface of this through hole 21 for screwing in a bolt 5 and a tip member 6.

[0022] The second block body 3 is a metal block body formed in a cylindrical shape with a central axis L as its axis. In this embodiment, the diameter of the second block body 3 is the same as the diameter of the first block body 2. However, the diameter of the second block body 3 may be different from the diameter of the first block body 2. The second block body 3 is formed from, for example, aluminum, aluminum alloy, titanium, titanium alloy, stainless steel, iron, etc. The second block body 3 may be formed from the same material as the first block body 2, or from a different material than the first block body 2.

[0023] As shown in Figure 2, the second block body 3 is provided with a hole 31 that extends in the axial direction. The hole 31 is formed in the central part of the second block body 3 when viewed from the axial direction. The hole 31 is formed to be recessed from the front surface of the second block body 3 toward the rear. A female thread for screwing a bolt 5 is formed on the inner wall surface of this hole 31. For example, the diameter of the hole 31 is the same as the diameter of the through hole 21 of the first block body 2. However, the diameter of the hole 31 may be different from the diameter of the through hole 21.

[0024] The piezoelectric unit 4 vibrates when power is supplied from a drive unit (not shown). In other words, the piezoelectric unit 4 is a vibration generating unit that generates vibrations. The piezoelectric unit 4 comprises, for example, a plurality of stacked disc-shaped piezoelectric ceramic elements. The piezoelectric unit 4 is formed in an annular shape with a central axis L. In this embodiment, the outer diameter of the piezoelectric unit 4 is slightly smaller than the diameters of the first block body 2 and the second block body 3. However, the outer diameter of the piezoelectric unit 4 may be the same as or larger than the diameters of the first block body 2 and the second block body 3.

[0025] As shown in Figures 1 and 2, in this embodiment, two piezoelectric units 4 are arranged adjacent to each other in the axial direction. However, the number of piezoelectric units 4 can be changed. That is, the ultrasonic projection device 1 may have a single piezoelectric unit 4. Alternatively, the ultrasonic projection device 1 may have three or more piezoelectric units 4.

[0026] These piezoelectric units 4 are positioned axially between the first block body 2 and the second block body 3. The first block body 2 is located in front of the piezoelectric units 4, and the second block body 3 is located behind the piezoelectric units 4. These piezoelectric units 4 are sandwiched between the first block body 2 and the second block body 3.

[0027] The bolt 5 extends along the central axis L and is positioned to overlap with the central axis L. The bolt 5 has male threads formed on its outer surface. As shown in Figure 2, the bolt 5 passes through the annular piezoelectric unit 4, with the first block body 2 fixed to its front end and the second block body 3 fixed to its rear end. The front end (one end) of the bolt 5 is inserted into the through hole 21 of the first block body 2 and is screwed into the female threads formed on the inner wall surface of the through hole 21. The rear end (the other end) of the bolt 5 is screwed into the female threads formed on the inner wall surface of the hole 31 of the second block body 3.

[0028] The first block body 2 and the second block body 3 are screwed onto a bolt 5, and the piezoelectric unit 4 is sandwiched between the first block body 2 and the second block body 3, thereby integrating the first block body 2, the second block body 3, and the piezoelectric unit 4.

[0029] The tip member 6 is a member that is attached to the first block body 2 from the front. The tip member 6 is made of, for example, aluminum, aluminum alloy, titanium, titanium alloy, stainless steel, iron, etc. The tip member 6 may be made of the same material as the first block body 2 and the second block body 3, or it may be made of a different material. As shown in Figure 2, for example, the tip member 6 has a base 6a, a diaphragm 6b, a connecting part 6c, and a shaft part 6d.

[0030] The base 6a directly or indirectly supports the diaphragm 6b, the connecting portion 6c, and the shaft portion 6d. The base 6a is a disc-shaped portion formed in a substantially circular shape when viewed from the axial direction. The connecting portion 6c is connected to the front side of the base 6a. The shaft portion 6d is provided on the rear side of the base 6a. In this embodiment, the diameter of the base 6a is slightly larger than the diameter of the first block body 2. However, the diameter of the base 6a may be the same as or smaller than the diameter of the first block body 2.

[0031] The diaphragm 6b is located in front of the base 6a and is connected to the base 6a via a connecting portion 6c. The diaphragm 6b is a disc-shaped portion formed in a circular shape when viewed from the axial direction. The diaphragm 6b vibrates when vibrations generated by the piezoelectric unit 4 are transmitted to it. Ultrasonic waves are emitted as the diaphragm 6b vibrates. In this embodiment, the diameter of the diaphragm 6b is the same as the diameter of the first block body 2. However, the diameter of the diaphragm 6b may be different from the diameter of the first block body 2. In other words, the diameter of the diaphragm 6b may be larger or smaller than the diameter of the first block body 2.

[0032] The connecting portion 6c is provided between the base portion 6a and the diaphragm 6b and supports the diaphragm 6b. This connecting portion 6c has a groove portion 6e that is provided in an annular shape with respect to the central axis L. The inner wall surface 6e1 of the groove portion 6e connects the diaphragm 6b and the base portion 6a and is a smooth surface. Here, "smooth" means that the entire surface is formed by a curved or flat surface and there are no bent parts.

[0033] As described above, the groove 6e is formed in an annular shape with a central axis L along the axial direction. The cross-sectional shape of the plane containing the central axis L is a semi-elliptical shape that is concave from the radial outside to the inside, as shown in Figure 2. The minor axis of this semi-elliptical shape is parallel to the central axis L. The major axis of this semi-elliptical shape is parallel to the radial direction.

[0034] However, the cross-sectional shape of the groove 6e may be a semi-elliptical shape with its minor axis parallel to the radial direction and its major axis parallel to the central axis L. Furthermore, the cross-sectional shape of the groove 6e may be a semicircular or horseshoe shape. Also, the cross-sectional shape of the groove 6e may be a curved surface overall, or a surface that combines a curved surface and a flat surface without any bent sections.

[0035] The shaft portion 6d is connected to the center of the base portion 6a when viewed from the axial direction and protrudes rearward from the base portion 6a. The shaft portion 6d is formed in a cylindrical shape, and a male thread is formed on its outer circumference, which is screwed into the female thread of the through hole 21 of the first block body 2. The tip member 6 is fixed to the first block body 2 by screwing the shaft portion 6d into the through hole 21 until the rear surface of the base portion 6a abuts against the front surface of the first block body 2.

[0036] In this embodiment of the ultrasonic projection device 1, when power is supplied to the piezoelectric unit 4 from an external drive unit, the piezoelectric unit 4 vibrates. By setting the drive frequency of the piezoelectric unit 4 to the resonant frequency of the ultrasonic projection device 1, the ultrasonic projection device 1 resonates with the vibration of the piezoelectric unit 4. As a result, the diaphragm 6b vibrates strongly, generating ultrasonic waves with high sound pressure. The generated ultrasonic waves are radiated into space. In this embodiment of the ultrasonic projection device 1, the ultrasonic waves generated by the diaphragm 6b are projected into space.

[0037] In this embodiment, the total length of the ultrasonic projection device 1 is set to half the wavelength of the longitudinal vibration when the ultrasonic projection device 1 resonates as described above. In other words, the total length of the ultrasonic projection device 1 is set to half the wavelength of the vibration generated by the piezoelectric unit 4. One end of the ultrasonic projection device 1 in the axial direction is the rear end face of the second block body 3. The other end of the ultrasonic projection device 1 in the axial direction is the front surface of the diaphragm 6b. Therefore, the distance from the rear end face of the second block body 3 to the front surface of the diaphragm 6b is set to half the wavelength of the vibration generated by the piezoelectric unit 4. In this embodiment of the ultrasonic projection device 1, the diaphragm 6b is positioned at the antinode of the longitudinal vibration when the ultrasonic projection device 1 resonates. As a result, the amplitude of the diaphragm 6b can be increased, and ultrasonic waves with higher sound pressure can be output.

[0038] It should be noted that the statement that the total length of the ultrasonic projection device 1 matches half the wavelength of the vibration generated by the piezoelectric unit 4 does not mean that the total length of the ultrasonic projection device 1 matches half the wavelength of the vibration generated by the piezoelectric unit 4 perfectly. Due to errors in the ultrasonic projection device 1, a slight deviation in the total length of the ultrasonic projection device 1 from half the wavelength of the vibration generated by the piezoelectric unit 4 is permissible. If the total length of the ultrasonic projection device 1 approximately matches half the wavelength of the vibration generated by the piezoelectric unit 4, it is possible to output ultrasonic waves with a higher sound pressure.

[0039] For example, the total length of the ultrasonic projection device 1 may be 10% longer than half the wavelength of the vibration generated by the piezoelectric unit 4. Alternatively, the total length of the ultrasonic projection device 1 may be 10% shorter than half the wavelength of the vibration generated by the piezoelectric unit 4. More preferably, the total length of the ultrasonic projection device 1 should be 99% to 101% of half the wavelength of the vibration generated by the piezoelectric unit 4. This is because the sharpness Q of a typical bolt-clamped Langevin transducer (BLT) is 100 or more, and in order to obtain a practical amplitude (i.e., half the peak), the deviation must be within ±1%.

[0040] The ultrasonic projection device 1 of this embodiment, as described above, comprises a first block body 2, a second block body 3, and a piezoelectric unit 4. The piezoelectric unit 4 is sandwiched between the first block body 2 and the second block body 3. The ultrasonic projection device 1 of this embodiment is also provided with a diaphragm 6b. The diaphragm 6b is provided at one end of the first block body 2 on the axial side of the first block body 2, the second block body 3, and the piezoelectric unit 4. Furthermore, in the ultrasonic projection device 1 of this embodiment, the dimension from one end on the first block body 2 side to the other end on the second block body 3 side in the axial direction is half the wavelength of the vibration generated by the piezoelectric unit 4. Alternatively, the dimension from one end on the first block body 2 side to the other end on the second block body 3 side in the axial direction is approximately equal to half the wavelength of the vibration generated by the piezoelectric unit 4. In addition, the ultrasonic projection device 1 of this embodiment is provided with a connecting portion 6c. The connecting portion 6c is provided between the diaphragm 6b and the base portion 6a that supports the diaphragm 6b. Furthermore, the connecting portion 6c has a groove portion 6e having a smooth inner wall surface 6e1 that connects the diaphragm 6b and the base portion 6a.

[0041] In this embodiment of the ultrasonic projection device 1, a groove 6e is provided in the connecting portion 6c that connects the diaphragm 6b and the base portion 6a. As a result, the edge of the diaphragm 6b can be displaced significantly without being constrained by the connecting portion 6c, and the sound pressure of the ultrasonic waves projected from the diaphragm 6b can be increased. Furthermore, since the inner wall surface 6e1 of the groove 6e is smooth, localized stress concentration on the inner wall surface 6e1 can be suppressed. As a result, the amplitude of the diaphragm 6b can be increased, and the sound pressure of the ultrasonic waves projected from the diaphragm 6b can be increased. Therefore, the ultrasonic projection device 1 of this embodiment can increase the sound pressure of the ultrasonic waves.

[0042] Furthermore, in the ultrasonic projection device 1 of this embodiment, the distance from the rear end face of the second block body 3 to the front face of the diaphragm 6b is set to half the wavelength of the vibration generated by the piezoelectric unit 4. In this ultrasonic projection device 1 of this embodiment, the diaphragm 6b is positioned at the antinode of the longitudinal vibration when the ultrasonic projection device 1 resonates. As a result, the amplitude of the diaphragm 6b can be increased, and ultrasonic waves with higher sound pressure can be output.

[0043] Furthermore, the ultrasonic projection device 1 of this embodiment includes a first block body 2 and a separate tip member 6. The tip member 6 has a diaphragm 6b, a connecting portion 6c, and a base portion 6a. The tip member 6 is fixed to the first block body 2. In this ultrasonic projection device 1 of this embodiment, the tip member 6 can be attached to and detached from the first block body 2. Therefore, by replacing the tip member 6, it is possible to easily change, for example, the shape of the diaphragm 6b.

[0044] Furthermore, in the ultrasonic projection device 1 of this embodiment, the groove 6e is formed in an annular shape with a central axis L along the axial direction. In addition, the cross-sectional shape of the groove 6e, with respect to the plane containing the central axis L, is a semi-elliptical shape that is concave from the radial outside to the inside. By providing a groove 6e with such a semi-elliptical cross-sectional shape, it is possible to output ultrasonic waves with high directivity and sound pressure, as will be explained in the embodiments described later.

[0045] Furthermore, in the ultrasonic projection device 1 of this embodiment, the semi-elliptical cross-sectional shape of the groove 6e has a minor axis parallel to the central axis L and a major axis parallel to the radial direction. Therefore, compared to the case where the major axis is parallel to the central axis L, the overall length of the ultrasonic projection device 1 can be shortened, and the ultrasonic projection device 1 can be made more compact.

[0046] [Examples] Next, the results of an experiment using the ultrasonic projection device 1 of the first embodiment described above will be explained as an example. In this example, a bolt-clamped Langevin transducer (BLT) for 60kHz with a length dimension D1 of 41.5mm, as shown in Figure 2, was used as the first block body 2, the second block body 3, and the piezoelectric unit 4. The minor axis radius a of the semi-elliptical cross-sectional shape of the groove 6e was set to 2.2mm. The major axis radius b was set to 4.9mm. The diameter dimension of the base 6a was set to 17mm to facilitate connection between the first block body 2 and the diaphragm 6b. Furthermore, the base 6a was shaped by cutting 1mm off each of two points on the edge so as to sandwich the central axis L. The thickness dimension D2 of the base 6a was set to 1.5mm. The diameter dimension of the diaphragm 6b was set to 15mm. The thickness dimension D3 of the diaphragm 6b was set to 0.5mm. The diameter dimension D4 of the second block body 3 was set to 15mm.

[0047] In this embodiment, the admittance characteristics of the ultrasonic projection device 1 were measured. An impedance analyzer was used for this measurement. The measurement conditions were that the drive voltage was kept constant at 1V. Figure 3 shows the results of the admittedance characteristics measurement. The horizontal axis in Figure 3 represents conductance. The vertical axis in Figure 3 represents susceptance. As shown in Figure 3, the resonant frequency was 48.0 kHz, the conductance value was 1.51 mS, and the sharpness Q was 267.

[0048] Next, the vibration amplitude displacement of the ultrasonic projection device 1 was investigated. In this investigation, the vibration displacement on the vibrating surface (the front surface of the diaphragm 6b) was measured. This measurement was performed using a laser Doppler vibrometer. The measurement range was set to 7.5 mm radially from the center of the diaphragm 6b, and measurements were taken at 0.5 mm intervals in the radial direction. The driving frequency of the piezoelectric unit 4 was set to 48.0 kHz, which is the resonant frequency of the ultrasonic projection device 1. The input current to the piezoelectric unit 4 was kept constant at 50 mA. At this time, the voltage was 34.5 V and the power was 1.7 W.

[0049] Figure 4 shows the results of measuring the vibration displacement on the vibrating surface. The horizontal axis in Figure 4 represents the distance from the center of the diaphragm. The vertical axis in Figure 4 represents the vibration displacement amplitude. As shown in Figure 4, it can be seen that the displacement of the diaphragm 6b increases more rapidly than the displacement at the center as it approaches the edge of the plate. Furthermore, the maximum amplitude was obtained at the edge of the diaphragm, and the ratio of the displacement amplitude at the edge to the center was 22 times.

[0050] Next, the directional characteristics were examined. In this study, the sound pressure of the sound waves projected from the ultrasonic projection device 1 was measured at different angles. A 1 / 8-inch condenser microphone (ACO, TYPE7118) was used for the measurements. In this measurement, the distance between the vibrating surface of the diaphragm 6b and the measurement point was kept constant at 300 mm, the vertical central axis of the vibrating surface was set to 0°, and measurements were taken at 1° intervals within a 90° range on both sides. The driving conditions of the ultrasonic projection device 1 were the same as those used in the examination of vibration displacement amplitude.

[0051] Figure 5 shows the measurement results regarding the directional characteristics. In Figure 5, the horizontal axis represents the angle from the center. In Figure 5, the vertical axis represents sound pressure. As shown in Figure 5, it can be seen that the sound waves radiated from the diaphragm 6b have a high sound pressure in the 0° direction (direction perpendicular to the vibration plane). Furthermore, a maximum sound pressure of 200 Pa was obtained in the 0° direction, and the full width at half maximum was approximately 15°.

[0052] Next, we investigated the distance characteristics. In this investigation, we measured the sound waves projected from the ultrasonic projection device 1 at varying distances from the device. For this measurement, we used the same condenser microphone as in the directivity characteristics investigation. In this measurement, the microphone was placed perpendicular to the central axis of the vibration surface (0° direction), and the distance was varied in 1 mm increments from 1 mm to 300 mm. The driving conditions of the ultrasonic projection device 1 were the same as in the directivity characteristics investigation.

[0053] Figure 6 shows the measurement results regarding the distance characteristics. The horizontal axis in Figure 6 represents the distance from the diaphragm 6b. The vertical axis in Figure 6 represents the sound pressure. As shown in Figure 6, it can be seen that the sound pressure decreases as the distance from the diaphragm 6b increases. Also, the sound pressure at a distance of 300 mm was 190 Pa.

[0054] Next, the relationship between input power and sound pressure was investigated. The sound pressure of the sound waves radiated from the ultrasonic projection device 1 was measured using the same condenser microphone as used in the directivity characteristics study, when the input power to the piezoelectric unit 4 was varied. In this measurement, the microphone was placed at a distance of 300 mm perpendicular to the central axis of the vibration plane (0° direction), and the input power was gradually increased from 0W to 10W. The driving conditions for the ultrasonic projection device 1 were the same as those used in the directivity characteristics study.

[0055] Figure 7 shows the measurement results regarding the relationship between input power and sound pressure. The horizontal axis in Figure 7 represents input power, and the vertical axis represents sound pressure. As shown in Figure 7, the sound pressure increases with increasing input power, and it was found that a large maximum sound pressure of 362 Pa (sound pressure level 145 dB) can be obtained with an input power of 5 W.

[0056] In this embodiment, the admittance characteristics, vibration displacement distribution, directivity characteristics, distance characteristics, and the relationship between input and sound pressure were investigated for the ultrasonic projection device 1. From these investigation results, it was found that it is possible to radiate sound waves with sharp directivity to a relatively long distance, and that a high sound pressure of 362 Pa can be obtained at a distance of 300 mm perpendicular to the vibration surface.

[0057] (Second Embodiment) Next, a second embodiment of the present invention will be described. In the description of this embodiment, parts that are the same as those of the first embodiment described above may be omitted or simplified.

[0058] Figure 8 is a schematic diagram of the ultrasonic projection device 1A of this second embodiment. Figure 9 is a cross-sectional view of the ultrasonic projection device 1A of this second embodiment. As shown in these figures, the ultrasonic projection device 1A of this embodiment does not have the tip member 6 of the first embodiment. On the other hand, in this embodiment, the first block body 2 comprises a base 2a, a diaphragm 2b, and a connecting part 2c. In other words, in this embodiment, the diaphragm 2b is part of the first block body 2.

[0059] The base portion 2a is a cylindrical part formed with a central axis L as its axis. The base portion 2a is provided with a hole portion 2d that extends in the axial direction. The hole portion 2d is formed in the center of the base portion 2a when viewed from the axial direction. The hole portion 2d is formed so as to be recessed from the rear surface of the base portion 2a toward the front. A female thread for screwing a bolt 5 is formed on the inner wall surface of this hole portion 2d. For example, the diameter of the hole portion 2d is the same as the diameter of the hole portion 31 of the second block body 3. However, the diameter of the hole portion 2d may be different from the diameter of the hole portion 31. The base portion 2a directly or indirectly supports the diaphragm 2b and the connecting portion 2c. The connecting portion 2c is connected to the front side of the base portion 2a.

[0060] The diaphragm 2b is located in front of the base 2a and is connected to the base 2a via the connecting portion 2c. The diaphragm 2b is a disc-shaped portion formed in a circular shape when viewed from the axial direction. The diaphragm 2b vibrates when vibrations generated by the piezoelectric unit 4 are transmitted to it. Ultrasonic waves are emitted as the diaphragm 2b vibrates. In this embodiment, the diameter of the diaphragm 2b is the same as the diameter of the base 2a. However, the diameter of the diaphragm 2b may be different from the diameter of the base 2a. In other words, the diameter of the diaphragm 2b may be larger or smaller than the diameter of the base 2a.

[0061] The connecting portion 2c is provided between the base portion 2a and the diaphragm 2b and supports the diaphragm 2b. This connecting portion 2c has a groove portion 2e that is provided in an annular shape with respect to the central axis L. The inner wall surface 2e1 of the groove portion 2e connects the diaphragm 2b and the base portion 2a and is a smooth surface. Here, "smooth" means that the entire surface is formed by a curved or flat surface and there are no bent parts.

[0062] As described above, the groove 2e is formed in an annular shape with a central axis L along the axial direction. The cross-sectional shape of the plane containing the central axis L is a semi-elliptical shape that is concave from the radial outside to the inside, as shown in Figure 9. The minor axis of this semi-elliptical shape is parallel to the central axis L. The major axis of this semi-elliptical shape is parallel to the radial direction.

[0063] However, the cross-sectional shape of the groove 2e may be a semi-elliptical shape with its minor axis parallel to the radial direction and its major axis parallel to the central axis L. Furthermore, the cross-sectional shape of the groove 2e may be a semicircular or horseshoe shape. Also, the cross-sectional shape of the groove 2e may be a curved surface overall, or a surface that combines a curved surface and a flat surface without any bent sections.

[0064] In this embodiment of the ultrasonic projection device 1A, when power is supplied to the piezoelectric unit 4 from an external drive unit, the piezoelectric unit 4 vibrates. By setting the drive frequency of the piezoelectric unit 4 to the resonant frequency of the ultrasonic projection device 1A, the ultrasonic projection device 1A resonates with the vibration of the piezoelectric unit 4. As a result, the diaphragm 2b vibrates strongly, generating ultrasonic waves with high sound pressure. The generated ultrasonic waves are radiated into space. In this embodiment of the ultrasonic projection device 1A, the ultrasonic waves generated by the diaphragm 2b are projected into space.

[0065] In this embodiment, the total length of the ultrasonic projection device 1A is set to half the wavelength of the longitudinal vibration that occurs when the ultrasonic projection device 1A resonates as described above. In other words, the total length of the ultrasonic projection device 1A is set to half the wavelength of the vibration generated by the piezoelectric unit 4. One end of the ultrasonic projection device 1A in the axial direction is the rear end face of the second block body 3. The other end of the ultrasonic projection device 1A in the axial direction is the front surface of the diaphragm 2b. Therefore, the distance from the rear end face of the second block body 3 to the front surface of the diaphragm 2b is set to half the wavelength of the vibration generated by the piezoelectric unit 4. In this embodiment of the ultrasonic projection device 1A, the diaphragm 2b is positioned at the antinode of the longitudinal vibration that occurs when the ultrasonic projection device 1A resonates. As a result, the amplitude of the diaphragm 2b can be increased, and ultrasonic waves with higher sound pressure can be output.

[0066] The ultrasonic projection device 1A of this embodiment, as described above, comprises a first block body 2, a second block body 3, and a piezoelectric unit 4. The piezoelectric unit 4 is sandwiched between the first block body 2 and the second block body 3. The first block body 2 comprises a diaphragm 2b, a base 2a, and a connecting portion 2c. The diaphragm 2b is provided at one end of the first block body 2 opposite to the piezoelectric unit 4 in the axial direction. The base 2a is in contact with the piezoelectric unit 4. The connecting portion 2c is provided between the diaphragm 2b and the base 2a that supports the diaphragm 2b. Furthermore, the connecting portion 2c has a groove 2e with a smooth inner wall surface 2e1 that connects the diaphragm 2b and the base 2a.

[0067] In this embodiment of the ultrasonic projection device 1A, a groove 2e is provided in the connecting portion 2c that connects the diaphragm 2b and the base 2a. As a result, the edge of the diaphragm 2b can be displaced significantly without being constrained by the connecting portion 2c, and the sound pressure of the ultrasonic waves projected from the diaphragm 2b can be increased. Furthermore, since the inner wall surface 2e1 of the groove 2e is smooth, localized stress concentration on the inner wall surface 2e1 can be suppressed. As a result, the amplitude of the diaphragm 2b can be increased, and the sound pressure of the ultrasonic waves projected from the diaphragm 2b can be increased. Therefore, the ultrasonic projection device 1A of this embodiment can increase the sound pressure of the ultrasonic waves.

[0068] Furthermore, in the ultrasonic projection device 1A of this embodiment, the distance from one end of the first block body 2 to the other end of the second block body 3 in the axial direction is half the wavelength of the vibration generated by the piezoelectric unit 4. In other words, according to the ultrasonic projection device 1A of this embodiment, the distance from the rear end face of the second block body 3 to the front face of the diaphragm 2b is set to half the wavelength of the vibration generated by the piezoelectric unit 4. In such an ultrasonic projection device 1A of this embodiment, the diaphragm 2b is positioned at the antinode of the longitudinal vibration when the ultrasonic projection device 1A resonates. As a result, the amplitude of the diaphragm 2b can be increased, and ultrasonic waves with higher sound pressure can be output.

[0069] Furthermore, in the ultrasonic projection device 1A of this embodiment, the diaphragm 2b is part of the first block body 2. Therefore, it is not necessary to provide the tip member 6 separately from the first block body 2, as in the first embodiment. As a result, the overall length of the ultrasonic projection device 1A can be made shorter than that of the first embodiment. In addition, the number of parts in the ultrasonic projection device 1A can be reduced compared to the first embodiment, and the structure can be simplified.

[0070] However, in this embodiment, the dimension from one end of the first block body 2 to the other end of the second block body 3 in the axial direction does not necessarily have to be half a wavelength of the vibration generated by the piezoelectric unit 4. For example, the dimension from one end of the first block body 2 to the other end of the second block body 3 in the axial direction may be one wavelength or 1.5 wavelengths of the vibration. In this way, even if the dimension from one end of the first block body 2 to the other end of the second block body 3 in the axial direction is not half a wavelength of the vibration, the number of parts in the ultrasonic projection device 1A can be reduced compared to the first embodiment because the diaphragm 2b is part of the first block body 2.

[0071] Furthermore, in the ultrasonic projection device 1A of this embodiment, the groove 2e is formed in an annular shape with a central axis L along the axial direction. In addition, the cross-sectional shape of the groove 2e, formed by a plane containing the central axis L, is a semi-elliptical shape that is concave from the radial outside to the inside. By providing a groove 2e with such a semi-elliptical cross-sectional shape, it is possible to output ultrasonic waves with high directivity and sound pressure.

[0072] Furthermore, in the ultrasonic projection device 1A of this embodiment, the semi-elliptical cross-sectional shape of the groove portion 2e has a minor axis parallel to the central axis L and a major axis parallel to the radial direction. Therefore, compared to the case where the major axis is parallel to the central axis L, the overall length of the ultrasonic projection device 1A can be shortened, and the ultrasonic projection device 1A can be made more compact.

[0073] [Examples] Next, the results of a simulation using the ultrasonic projection device 1A of the second embodiment described above will be explained as an example. In this embodiment, the length dimension Da (distance from the rear end of the second block body 3 to the front end of the hole 2d) shown in Figure 9 was set to 35.5 mm. More specifically, the distance from the rear end to the front end of the second block body 3 was 14.8 mm, the distance from the rear end to the front end of the piezoelectric unit 4 was 10.7 mm, and the distance from the rear end of the first block body 2 to the front end of the hole 2d was 10 mm.

[0074] Furthermore, the distance Db from the front end of the hole 2d to the front end of the base 2a was varied from 1 mm to 5 mm in 0.5 mm increments. When the distance Db is 1 mm, the total length of the ultrasonic projection device 1A (distance from the rear end of the second block body 3 to the front surface of the diaphragm 2b) is 41.0 mm. The thickness Dc of the diaphragm 2b was set to 0.5 mm. The minor axis radius a of the semi-elliptical cross-sectional shape of the groove 2e was varied from 2 mm to 2.5 mm in 0.1 mm increments. The major axis radius b of the semi-elliptical cross-sectional shape of the groove 2e was varied from 4 mm to 4.5 mm in 0.1 mm increments. In addition, a specified displacement of 1.5 μm was applied to the rear end of the second block body 3.

[0075] In this embodiment, the sound pressure at a distance of 300 mm in front of the center of the diaphragm 2b was evaluated under the conditions described above. Figure 10 shows the simulation results of the sound pressure distribution obtained by varying the minor axis radius a and the major axis radius b. In plotting the results shown in Figure 10, the highest sound pressure was used among several sound pressures obtained by varying the distance dimension Db while keeping the same minor axis radius a and major axis radius b.

[0076] Figure 10 shows that high sound pressure levels of 100 Pa or more can be obtained regardless of the changes in the minor axis radius a and the major axis radius b. Furthermore, Figure 10 shows a tendency for sound pressure to increase as the minor axis radius a decreases. Also, Figure 10 shows a tendency for sound pressure to increase as the major axis radius b increases.

[0077] In this embodiment, the frequency change was in the range of 54.4 kHz to 60.7 kHz. The change in frequency relative to the change in the minor axis radius a was not large, and the frequency decreased as the major axis radius b increased.

[0078] (Third embodiment) Next, a third embodiment of the present invention will be described. In this description, parts that are the same as those in the second embodiment described above may be omitted or simplified.

[0079] Figure 11 is a cross-sectional view showing the schematic configuration of the ultrasonic projection device 1B of this third embodiment. As shown in this figure, in the ultrasonic projection device 1B of this embodiment, the hole 31 of the second block body 3 is provided penetrating the second block body 3 in the axial direction. In addition, in this embodiment, the bolt 5 is positioned further rearward than in the first embodiment. In this embodiment, as shown in Figure 11, the center of gravity G of the bolt 5 is located closer to the second block body 3 than to the first block body 2.

[0080] In this embodiment of the ultrasonic projection device 1B, since the bolt 5 is positioned at the rear, the distance from the front end of the hole 2d provided in the base 2a to the front end of the base 2a can be made longer. Therefore, the thickness of the base 2a in front of the front end of the hole 2d can be made thicker than in the first embodiment. Consequently, the ultrasonic projection device 1B of this embodiment has improved durability.

[0081] Furthermore, in this embodiment, the first block body 2 may be formed from a material with a lower specific gravity than the second block body 3. In such a case, for example, the first block body 2 may be made of aluminum and the second block body 3 may be made of stainless steel. By forming the first block body 2 from a material with a lower specific gravity than the second block body 3, the first block body 2 is made lighter, making it possible to increase the amplitude of the diaphragm 2b. As a result, the sound pressure can be increased.

[0082] In the first embodiment described above, the first block body 2 and the tip member 6 may be formed from a material with a lower specific gravity than the second block body 3. Also, in the second embodiment described above, the first block body 2 may be formed from a material with a lower specific gravity than the second block body 3. In either case, the amplitude of the diaphragm 6b or diaphragm 2b can be increased, and the sound pressure can be further increased.

[0083] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. In this description, parts that are the same as those in the second embodiment described above may be omitted or simplified.

[0084] Figure 12 is a schematic diagram of the ultrasonic projection device 1C of this fourth embodiment. The dashed line shown in Figure 12 schematically represents the longitudinal vibration wave when the ultrasonic projection device 1C resonates. As shown in Figure 12, in the ultrasonic projection device 1C of this embodiment, the boundary between the first block body 2 and the piezoelectric unit 4 is located at node N. In other words, in the ultrasonic projection device 1C of this embodiment, the boundary between the first block body 2 and the piezoelectric unit 4 is located at the node of the vibration generated by the piezoelectric unit 4 in the axial direction.

[0085] In this way, when the boundary between the first block body 2 and the piezoelectric unit 4 is located at node N, heat generation can be suppressed more effectively than when node N is located inside the piezoelectric unit 4. Furthermore, the end face of the first block body 2 on the piezoelectric unit 4 side is not displaced by vibration. Therefore, the ultrasonic projection device 1C can be easily fixed to an external member via the end face of the first block body 2 on the piezoelectric unit 4 side.

[0086] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to the above embodiments. The shapes and combinations of the various components shown in the above embodiments are examples, and can be modified in various ways based on design requirements, etc., without departing from the spirit of the present invention. [Explanation of Symbols]

[0087] 1... Ultrasonic projection device, 1A... Ultrasonic projection device, 1B... Ultrasonic projection device, 1C... Ultrasonic projection device, 2... First block body, 2a... Base, 2b... Vibrating plate, 2c... Connection part, 2d... Hole, 2e... Groove, 2e1... Inner wall surface, 3... Second block body, 4... Piezoelectric unit (vibration generating part), 5... Bolt, 6... Tip member, 6a... Base, 6b... Vibrating plate, 6c... Connection part, 6d... Shaft, 6e... Groove, 6e1... Inner wall surface, 21... Through hole, 31... Hole, a... Minor axis radius, b... Major axis radius, G... Center of gravity, L... Central axis, N... Node

Claims

1. An ultrasonic projection device that projects ultrasonic waves, The first block body and, The second block body and, A vibration generating unit sandwiched between the first block body and the second block body, A bolt in which the first block body is screwed into one end and the second block body is screwed into the other end, Equipped with, A vibrating plate is provided at one end of the first block body on the side of the first block body in the arrangement direction of the first block body, the second block body, and the vibration generating part. The dimension from one end to the other end on the second block body side in the aforementioned arrangement direction is formed to substantially coincide with half the wavelength of the vibration generated in the vibration generating section. A connecting portion is provided between the diaphragm and the base supporting the diaphragm, the connecting portion having a groove with a smooth inner wall surface that connects the diaphragm and the base. In a cross-sectional shape formed by a plane including a central axis along the aforementioned arrangement direction, when the direction perpendicular to the central axis is defined as the radial direction, the radial dimension of the connecting portion is greater than or equal to the radial dimension of the bolt. Ultrasonic projection device.

2. The tip member having the diaphragm, the connecting portion, and the base is provided separately from the first block body. The tip member is fixed to the first block body. The ultrasonic projection device according to claim 1.

3. The ultrasonic projection device according to claim 1, wherein the first block body comprises the diaphragm, the connecting portion, and the base portion.

4. An ultrasonic projection device that projects ultrasonic waves, The first block body and, The second block body and, A vibration generating unit sandwiched between the first block body and the second block body, A bolt in which the first block body is screwed into one end and the second block body is screwed into the other end, Equipped with, The first block body is A diaphragm provided on the side opposite to the vibration generating part in the arrangement direction of the first block body, the second block body, and the vibration generating part, The base portion that is in contact with the vibration generating portion, A connecting portion is provided between the diaphragm and the base, and has a groove formed therein with a smooth inner wall surface that connects the diaphragm and the base. It has, In a cross-sectional shape formed by a plane including a central axis along the aforementioned arrangement direction, when the direction perpendicular to the central axis is defined as the radial direction, the radial dimension of the connecting portion is greater than or equal to the radial dimension of the bolt. Ultrasonic projection device.

5. The ultrasonic projection device according to any one of claims 1 to 4, wherein the groove is formed in an annular shape with respect to a central axis along the direction of arrangement, and the cross-sectional shape of a plane including the central axis is a semi-elliptical shape that is recessed from the outside to the inside in the radial direction with respect to the central axis.

6. The ultrasonic projection device according to claim 5, wherein the semi-elliptical shape has a minor axis parallel to the central axis and a major axis parallel to the radial direction.

7. In the arrangement direction, the center of gravity of the bolt is located closer to the second block body than to the first block body. An ultrasonic projection device according to any one of claims 1 to 6.

8. The ultrasonic projection device according to any one of claims 1 to 7, wherein the first block body is formed of a material with a lower specific gravity than the second block body.

9. The ultrasonic projection device according to any one of claims 1 to 8, wherein the boundary between the first block body and the vibration generating unit is located at the position of a node of vibration generated by the vibration generating unit in the aforementioned arrangement direction.

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