Ultrasonic projection device

Abstract

To provide an ultrasonic projection device that can be miniaturized and has good vibration characteristics. [Solution] An ultrasonic projection device 100 comprising a base portion 20 having a vibration generating unit 4 that generates vibration in the axial direction O, and a vibration unit 13 provided on the axial end side of the base portion that projects ultrasonic waves, wherein the base portion has a housing portion 2s that penetrates or is recessed in the radial direction R perpendicular to the axial direction and can accommodate the vibration generating unit from the outside of the base portion, and the resonance frequency f1 of the longitudinal vibration along the axial direction of the vibration unit and the resonance frequency f2 of the bending vibration along the radial direction of the housing portion satisfy f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.3.

Description

Technical Field

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

Background Art

[0002] As an ultrasonic source that generates strong vibrations, there is a bolt-tightened Langevin oscillator (BLT) etc. (Patent Document 1). Generally, a bolt-tightened Langevin oscillator has a structure in which a plurality of cylindrical piezoelectric elements are laminated and sandwiched by metal members, and a bolt is inserted through the central hole of the piezoelectric element and a metal part is screwed. However, in the case of such a structure, there is a problem that the overall dimensions (diameter) increase by the size of the bolt, making miniaturization difficult. Therefore, in order to reduce the dead space due to the bolt, a technique has been developed in which a piezoelectric element is housed inside a cylindrical side member, an internal thread is formed on the inner surface of the side member, and a front member and a back member arranged at both ends of the side member are screwed to the side member (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the case of a structure in which the housing of the ultrasonic source is arranged on the outer peripheral side of the piezoelectric element, the thin-walled housing on the outer peripheral side flexes with the vibration of the piezoelectric element, generating unnecessary flexural vibrations and affecting the vibration of the entire ultrasonic source. That is, an object of the present invention is to provide an ultrasonic projection device that can be miniaturized and has good vibration characteristics.

Means for Solving the Problems

[0005] To solve the above problems, the present invention provides an ultrasonic projection device comprising: a base portion having a vibration generating unit that generates vibrations in the axial direction; and a vibration unit provided on the axial end side of the base portion that projects ultrasonic waves, wherein the base portion has a housing portion that penetrates or is recessed in the radial direction perpendicular to the axial direction and can accommodate the vibration generating unit from the outside of the base portion, and the resonance frequency f1 of the longitudinal vibration of the vibration unit along the axial direction and the resonance frequency f2 of the bending vibration of the housing portion along the radial direction satisfy f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.3.

[0006] With this ultrasonic projection device, the vibration generating unit can be housed in the housing from the outside of the base (casing), allowing the use of a cylindrical vibration generating unit without through holes. This reduces the overall dimensions (diameter) of the ultrasonic projection device, enabling miniaturization. Furthermore, if f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.3 is satisfied, the flexural vibration of the housing section is suppressed from influencing the longitudinal vibration of the vibrating section (resonance), resulting in an ultrasonic projection device with good vibration characteristics.

[0007] In the ultrasonic projection device of the present invention, when the distance from the tip of the vibrating part to the rear end of the base part along the axial direction is defined as the total length L of the base part, the vibration generating part may be located at the center Ce of the total length L in the axial direction. With this ultrasonic projection device, the vibration plane of the piezoelectric element coincides with the vibration node, so the direction of extension of the piezoelectric element and the direction of longitudinal vibration are aligned, allowing for efficient driving.

[0008] In the ultrasonic projection device of the present invention, the total length L may be a length corresponding to half the wavelength when the resonant frequency f1 is present. While a larger overall length L yields greater vibration displacement from the vibration-generating section, it also leads to the problem of generating many vibration modes in the region where higher-order flexural vibrations occur. Therefore, setting the overall length L to half the wavelength at the resonant frequency f1 suppresses the generation of unwanted vibration modes. Furthermore, since the vibration section and the antinode of the vibration coincide, vibration can be obtained efficiently.

[0009] In the ultrasonic projection device of the present invention, the minimum thickness of the housing portion may be 0.5 mm or more. Since it is difficult to manufacture (process) products with a minimum thickness of less than 0.5 mm in the housing section, setting the minimum thickness to 0.5 mm or more makes manufacturing easier. [Effects of the Invention]

[0010] This invention provides an ultrasonic projection device that can be miniaturized and has good vibration characteristics. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view showing the external appearance of an ultrasonic projection device according to an embodiment of the present invention. [Figure 2] This is a front view from the radial direction of an ultrasonic projection device according to an embodiment of the present invention. [Figure 3] This figure shows the analysis results of the resonance frequency and generated displacement of an ultrasonic projection device according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a perspective view showing the external appearance of an ultrasonic projection device 100 according to an embodiment of the present invention, and Figure 2 is a front view of the ultrasonic projection device 100. The ultrasonic projection device 100 is suitably used as a powerful airborne ultrasonic source for applications such as haptics, ultrasonic levitation, ultrasonic atomization, intraocular pressure testing, non-destructive testing, defoaming, insect repellent, and parametric speakers.

[0013] As shown in FIG. 1, the ultrasonic projection device 100 has a base portion 20 that extends in the direction of axis O and has an elongated columnar shape, and a vibration portion 13 that is provided at the tip of the base portion 20 in the direction of axis O and projects ultrasonic waves. Also, in this example, a connecting portion 15 for connecting these is provided between the vibration portion 13 and the base portion 20, but the connecting portion 15 is not essential. For example, the tip of the base portion 20 may be integrally pointed, and the tip surface thereof may constitute the vibration portion.

[0014] More specifically, the base portion 20 has a cylindrical housing 2, a housing portion 2s that penetrates in the radial direction R perpendicular to the direction of axis O, and two cylindrical piezoelectric units 4. The housing portion 2s is open from the outside of the base portion 20 (housing 2) to a size that can accommodate the two piezoelectric units 4. Specifically, in this example, when viewed from the radial direction R, the opening dimension of the housing portion 2s is larger than the outer dimension of the two piezoelectric units 4 stacked in the direction of axis O.

[0015] Furthermore, in this example, on the rear end side of the housing 2 with respect to the housing portion 2s, a male screw that penetrates in the direction of axis O is provided, and a bolt 7 is screwed onto this male screw. And a disc-shaped pressing plate 5 is attached to the tip of the bolt 7, and the pressing plate 5 can move forward and backward in the housing portion 2s in the direction of axis O as the bolt 7 advances and retreats.

[0016] Then, with the pressing plate 5 retracted to the rear end side, the two piezoelectric units 4 are housed inside the housing portion 2s, and when the bolt 7 is advanced to move the pressing plate 5 to the tip side, the piezoelectric units 4 are sandwiched and held between the tip side wall surface of the housing portion 2s and the pressing plate 5. Thereby, the vibration of the piezoelectric unit 4 is transmitted to the base portion 20.

[0017] On the other hand, a block body 10 is fixed to the tip of the base portion 20. And, slightly on the tip side from the center of the block body 10 in the direction of axis O, one elliptical through hole 10h that penetrates two opposing side surfaces (penetrates in the radial direction R) is provided. Note that the bolt 10d protrudes from the block body 10 toward the rear end side, and by screwing the bolt 10d into the female screw provided at the tip of the base portion 20, the block body 10 can be fixed to the tip of the base portion 20.

[0018] And, among the block body 10, a member 11 is constituted by a portion on the rear end side (the base portion 20 side) from the through hole 10h and becomes a part of the base portion 20, and a portion on the front end side from the through hole 10h constitutes the vibrating portion 13. Also, among the block body 10, a portion overlapping with the through hole 10h in the axial direction O constitutes a connecting portion 15 that connects the vibrating portion 13 and the base portion 20. The connecting portion 15 refers to a portion having a smaller area than the vibrating surface 13a of the vibrating portion 13 when viewed in the direction along the radial direction R.

[0019] Examples of the shape of the vibrating surface 13a of the vibrating portion 13 include a circular shape and a polygonal shape. In this example, the shape of the vibrating surface 13a is rectangular, which has the advantages of being easy to manufacture (process) the vibrating portion 13 and being easy to arrange a large number of ultrasonic projection devices 100 adjacent to each other.

[0020] With such a configuration, the piezoelectric unit 4 vibrates in the axial direction O, and generates vibrations in the axial direction O through the base portion 20 connected to the piezoelectric unit 4. Then, the vibration from the base portion 20 (and the member 11 integrally fixed to the tip thereof) is transmitted to the vibrating portion 13 through the connecting portion 15, and the vibrating portion 1'3 projects ultrasonic waves.

[0021] In the present invention, since the piezoelectric unit 4 may be accommodated in the accommodating portion 2s from the outside of the base portion 20 (housing 2), a (circular) columnar piezoelectric unit 4 without a through hole can be used. As a result, the overall dimensions (diameter) of the ultrasonic projection device 100 can be reduced, and miniaturization can be achieved.

[0022] The piezoelectric unit 4 corresponds to the "vibration generating portion" in the claims. The piezoelectric unit 4 can use, for example, a piezoelectric ceramic element. In this example, two piezoelectric units 4 are arranged adjacent to each other in the direction of axis O. However, the number of piezoelectric units 4 can be changed.

[0023] Furthermore, the piezoelectric unit 4 vibrates when power is supplied from a drive unit (not shown). One example of a method for supplying power to the piezoelectric unit 4 is to sandwich electrode plates (not shown) between the piezoelectric unit 4 and the electrode plates at the + and - positions shown in Figure 1, and then pull them out to the outside through the opening of the housing 2s to supply power. Alternatively, the base 20 (housing 2) may be used as the body earth (ground). Furthermore, an insulating film or insulating coating may be provided between the housing section 2s and the electrode plate to prevent short circuits.

[0024] The housing 2 and the block body 10 can be made of metal, such as aluminum, aluminum alloy, titanium, titanium alloy, stainless steel, or iron.

[0025] Next, the distinctive features of the present invention will be described. As shown in Figure 2, the resonance frequency f1 of the longitudinal vibration LV along the axis O of the vibrating section 13 and the resonance frequency f2 of the flexural vibration DV along the radial R of the housing section 2s satisfy either f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.3. If f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.3 is satisfied, the flexural vibration of the housing section 2s is suppressed from influencing (resonating) the longitudinal vibration of the vibrating section 13, and an ultrasonic projection device with good vibration characteristics can be obtained.

[0026] Here, as shown in Figure 3, when the horizontal axis (f2 / f1) is in the AR region of approximately 0.7 to 1.3, with 1 as the boundary, the value of the vertical axis (resonant frequency of flexural vibration / resonant frequency in the vertical direction) is high. The vertical axis U = (resonance frequency of flexural vibration / resonance frequency in the vertical direction) indicates that a higher value means that the resonance frequency of unwanted vibrations (flexural vibrations) increases relative to the resonance frequency of the desired vibration (vertical vibration), meaning that unwanted vibrations are generated. Therefore, if we set the (f2 / f1) region outside the AR (0.7~1.3) range, that is, f2≦f1×0.7 or f2≧f1×1.3, we can suppress unwanted vibrations and obtain an ultrasonic projection device with good vibration characteristics.

[0027] The analysis in Figure 3 was performed as follows. First, set the resonant frequency f1 to 40kHz and set the total length L as follows. Then, as shown in Figure 2, when the MP section vibrates in the direction O at f1, the natural frequency when the MP section flexes in the radial direction R, and the maximum displacements of the longitudinal and flexural vibrations were determined from structural analysis using the finite element method with COMSOL Multiphysics (analysis software). The length and width (corresponding to the thickness of the housing section 2s) of the model piece MP in the axial direction O were varied in various ways to obtain the data for the numerous plots in Figure 3.

[0028] The actual resonant frequencies f1 and f2 of the ultrasonic projection device 100 can be measured using a laser Doppler vibrometer or similar device. Specifically, the resonant frequency f1 can be measured by irradiating the vibration surface 13a (Figure 2) of the vibrating part 13 with a laser in the direction of axis O. The frequency is swept, and the frequency with the strongest vibration is adopted as f1. Similarly, the resonant frequency f2 can be measured by irradiating the housing section 2s (Figure 2) with a laser in the radial direction R. The frequency is swept across multiple positions in the housing section 2s, and the frequency with the strongest vibration is adopted as f2.

[0029] In this example, as shown in Figure 2, when the total length L of the base portion is defined as the distance from the tip (vibration surface 13a) of the vibrating portion 13 to the rear end of the base portion 20 along the axial direction O, the piezoelectric unit 4 may be positioned at the center Ce of the total length L in the axial direction O. In this way, the vibration nodes coincide with the vibration plane of the piezoelectric element, allowing for efficient vibration application. In particular, it is more preferable that the center Cp of the piezoelectric unit 4 along the axial direction O coincides with the center Ce. Furthermore, when multiple piezoelectric units 4 are stacked in the direction of axis O, the center Cp is defined as the center of the total length between the leading piezoelectric unit 4 and the last piezoelectric unit 4.

[0030] In this example, the total length L may be half the wavelength at the resonant frequency f1. While a larger overall length L results in greater vibrational displacement due to the piezoelectric unit 4, it also leads to the problem of generating many vibration modes in regions where higher-order deflection vibrations occur. Therefore, setting the overall length L to half the wavelength at the resonant frequency f1 can suppress the generation of unwanted vibration modes.

[0031] The minimum thickness of the storage section 2s may be 0.5 mm or more. Manufacturing (processing) is difficult for containers with a minimum thickness of less than 0.5 mm.

[0032] The present invention is not limited to the embodiments described above, and it goes without saying that it extends to various modifications and equivalents that fall within the spirit and scope of the present invention. In the above embodiment, the housing portion 2s was a through hole penetrating in the radial direction R, but it may also be a recess that is concave in the radial direction R.

[0033] The housing section 2s only needs to be large enough to accommodate the piezoelectric unit 4 from the outside of the base section 20 (housing 2), and the opening dimensions should be at least larger than the outer dimensions of one piezoelectric unit 4. For example, the opening dimensions of the housing section 2s are made slightly larger than the outer dimensions of one piezoelectric unit 4, and the retaining plate 5 is set significantly further back than this opening. Then, the piezoelectric units 4 can be placed one by one through the opening of the housing section 2s, and the placed piezoelectric units 4 can be dropped towards the retaining plate 5 side (rear end side) inside the housing section 2s. The next piezoelectric unit 4 can then be placed through the housing section 2s and dropped towards the rear end side in the same manner, thereby stacking multiple piezoelectric units 4 within the housing section 2s. [Explanation of Symbols]

[0034] 2 cabinets 2s storage section 4. Vibration generating section 13. Vibration section 20 Base section 10h through hole 100 Ultrasonic projection device O axis R radial direction

Claims

1. A base portion having a vibration generating section that generates vibrations in the axial direction, A vibrating section is provided on the tip side of the base portion in the axial direction and projects ultrasonic waves, An ultrasonic projection device equipped with, The base portion has a housing portion that penetrates or is recessed in the radial direction perpendicular to the axial direction, and is capable of housing the vibration generating portion from the outside of the base portion. An ultrasonic projection device characterized in that the resonant frequency f1 of the longitudinal vibration of the vibrating part along the axial direction and the resonant frequency f2 of the flexural vibration of the housing part along the radial direction satisfy f2 ≤ f1 × 0.7 or f2 ≥ f1 × 1.

3.

2. The ultrasonic projection device according to claim 1, characterized in that when the distance from the tip of the vibrating part to the rear end of the base part along the axial direction is defined as the total length L of the base part, the vibration generating part is located at the center Ce of the total length L in the axial direction.

3. The ultrasonic projection device according to claim 1 or 2, characterized in that the total length L is a length corresponding to half the wavelength when the resonant frequency f1 is present.

4. The ultrasonic projection device according to claim 1 or 2, characterized in that the minimum thickness of the housing portion is 0.5 mm or more.

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