Ultrasonic radiation unit

Abstract

Because it has excellent erosion resistance, it has a long lifespan, and because it has excellent uniformity in vibration displacement distribution, it enables the realization of an ultrasonic radiation unit with minimal cleaning unevenness at a low cost. [Solution] This ultrasonic radiation unit 21 comprises a diaphragm 12, a BLT-type ultrasonic transducer 31, and resonant rods 51 and 59 that resonate at the same frequency and in longitudinal vibration mode as the ultrasonic transducer 31. The multiple ultrasonic transducers 31 are composed of four or more piezoelectric elements 42 made of lead-free piezoelectric ceramics and are arranged at each vertex p2 of a hypothetical regular hexagon H1 in the center of the diaphragm 12. The first resonant rod 51, which has a relatively large cross-sectional area, is positioned at the center p1 of the regular hexagon H1, on the short side 12b of the diaphragm 12 and adjacent to the outside of the regular hexagon H1. The second resonant rod 59, which has a relatively small cross-sectional area, is positioned on the long side 12a of the diaphragm 12 and adjacent to the outside of the regular hexagon H1.

Description

Technical Field

[0001] The present invention relates to an ultrasonic radiation unit that radiates ultrasonic waves from an ultrasonic vibrator.

Background Art

[0002] Conventionally, ultrasonic cleaning apparatuses provided with an ultrasonic radiation unit that performs cleaning of objects to be cleaned (ultrasonic cleaning) by irradiating ultrasonic waves into a cleaning liquid have been put into practical use. Ultrasonic cleaning can act even on the fine details of an object to be cleaned having a complex shape for efficient cleaning, through the combination of the physical action of ultrasonic waves and the chemical action of the cleaning liquid. Therefore, it has become indispensable in the manufacture of precision mechanical components, optical components, liquid crystal displays, semiconductors, and the like.

[0003] The conventional ultrasonic cleaning apparatus 200 shown in FIG. 8 includes a vibration plate 201, which is also called a radiation plate. In many cases, the vibration plate 201 also serves as the bottom of the cleaning tank 202, and is formed of a stainless steel plate with a thickness of several millimeters. A plurality of bolt-clamped Langevin type ultrasonic vibrators 204 are joined to the non-radiation surface 203 of the vibration plate 201 that constitutes the ultrasonic radiation unit. The surface of the vibration plate 201 located on the opposite side of the non-radiation surface 203 serves as the ultrasonic radiation surface 205. For example, when an ultrasonic radiation unit that generates ultrasonic waves of several tens of kHz is used, the ultrasonic cleaning apparatus 200 can be configured such that the object 207 to be cleaned is cleaned by the strong shock wave of cavitation caused by the ultrasonic waves in the cleaning liquid 206.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0005] Incidentally, as the cleaning area of ​​the ultrasonic cleaning device 200 widens, the radiating surface of the diaphragm 201 also increases. Therefore, when constructing an ultrasonic radiation unit, it is ideally desirable to install a large number of ultrasonic transducers 204 on the diaphragm 201, which has a large radiating surface. However, attempting to construct an ultrasonic radiation unit using a large number of ultrasonic transducers 204 increases the manufacturing cost of the device. On the other hand, if the number of ultrasonic transducers 204 is not appropriate for the size of the diaphragm 201, gaps (areas without transducers) will occur between adjacent transducers. As a result, there is a problem in which erosion 208 occurs on the diaphragm 201 due to cavitation. In addition, there is a problem in which uneven cleaning occurs due to the non-uniformity of the vibration displacement distribution on the diaphragm 201 (i.e., variations in sound pressure distribution).

[0006] Therefore, the inventors of the present invention have already proposed an ultrasonic radiation unit in which a resonant rod is placed between multiple ultrasonic transducers (see, for example, Patent Document 1). With this configuration, the area without transducers or resonant rods on the non-radiating surface can be reduced. However, even with such a configuration, it cannot necessarily be said that erosion reduction and uniformity of vibration displacement distribution have been sufficiently achieved.

[0007] This invention has been made in view of the above-mentioned problems, and its purpose is to realize an ultrasonic radiation unit at low cost that has excellent erosion resistance, thus having a long lifespan, and excellent uniformity of vibration displacement distribution, resulting in less uneven cleaning. [Means for solving the problem]

[0008] To solve the above problems, the invention described in claim 1 is an ultrasonic radiation unit comprising: a rectangular diaphragm in plan view having a radiating surface for emitting ultrasonic waves and a non-radiating surface located on the opposite side of the radiating surface, with bolts protruding from the non-radiating surface; a plurality of bolt-fastened Langevin-type ultrasonic transducers, each having a transducer front plate joined to the non-radiating surface; and a plurality of resonant rods that resonate at the same frequency and in a longitudinal vibration mode as the ultrasonic transducers, wherein the plurality of ultrasonic transducers and the plurality of resonant rods are fastened and fixed to the plurality of bolts, and the plurality of ultrasonic transducers are made of lead-free piezoelectric ceramics. The gist of this ultrasonic radiation unit is that it is composed of four or more electrical elements, which are arranged at each vertex of at least one regular hexagon virtually formed in the center of the diaphragm, and the plurality of resonant rods are composed of a first resonant rod having a relatively large cross-sectional area and a second resonant rod having a relatively small cross-sectional area, the first resonant rod being positioned at the center of the regular hexagon and on the short side of the diaphragm and adjacent to the regular hexagon from the outside, and the second resonant rod being positioned on the long side of the diaphragm and adjacent to the regular hexagon from the outside.

[0009] Therefore, according to the invention described in claim 1, since the ultrasonic transducer is constructed using four or more piezoelectric elements made of lead-free piezoelectric ceramics, it is possible to supply a larger driving power to a single transducer compared to one using only two elements. Furthermore, by arranging the ultrasonic transducers with the above configuration at each vertex of at least one regular hexagon virtually formed in the center of a rectangular diaphragm in plan view, the diaphragm can be vibrated efficiently even with a small number of transducers. Moreover, by arranging the first and second resonant rods, which have different cross-sectional areas, in predetermined manner, uniform longitudinal vibration can be obtained over a relatively wide radiating surface of the diaphragm. As a result, the occurrence of erosion in the diaphragm is reduced, and a uniform vibration displacement distribution is more easily obtained.

[0010] Furthermore, since resonant rods have a simpler structure than ultrasonic transducers, which consist of multiple types of components, they can be manufactured relatively inexpensively. Therefore, even in ultrasonic radiation units equipped with diaphragms that require a large cleaning area, for example, by reducing the number of ultrasonic transducers used and employing inexpensive resonant rods, it is possible to realize a device with excellent erosion resistance and uniform vibration displacement distribution at a low cost.

[0011] The invention described in claim 2 is characterized in that, in claim 1, two regular hexagons sharing one side with each other are hypothetically represented in the central part of the diaphragm, and the plurality of ultrasonic transducers are arranged at each vertex of the two regular hexagons.

[0012] The invention described in claim 3 is characterized in that, in claim 1, the number of ultrasonic transducers is less than the total number of the first and second resonant rods, and the number of first resonant rods is greater than the number of second resonant rods.

[0013] The invention described in claim 4 is characterized in that, in claim 1, three or more of the first resonant rods are arranged linearly along the short side of the diaphragm.

[0014] The invention described in claim 5 is characterized in that, in claim 1, the first resonant rod has a diameter (D1) equal to the maximum diameter (D0) of the front plate of the ultrasonic transducer, and the second resonant rod has a diameter (D2) that is 1 / 2 or more and 3 / 4 or less of the maximum diameter of the front plate of the transducer.

[0015] The invention described in claim 6 is characterized in that, in claim 1, the distance between the centers (L1) of the first resonant rod and the ultrasonic transducer adjacent thereto is equal to the distance between the centers (L0) of two adjacent ultrasonic transducers, and the distance between the centers (L2) of the second resonant rod and the ultrasonic transducer adjacent thereto is shorter than the distance between the centers (L0) of two adjacent ultrasonic transducers. [Effects of the Invention]

[0016] As described in detail above, according to the inventions recited in claims 1 to 6, it is possible to realize at low cost an ultrasonic radiation unit that has excellent erosion resistance for a long service life, and also has excellent uniformity of vibration displacement distribution to reduce uneven cleaning. [Brief Description of the Drawings]

[0017] [Figure 1] The schematic configuration diagram showing the ultrasonic cleaning apparatus of the embodiment. [Figure 2] The plan view showing the diaphragm-type ultrasonic radiation unit of the embodiment. [Figure 3] The cross-sectional view taken along line A-A of Figure 2. [Figure 4] The cross-sectional view taken along line B-B of Figure 2. [Figure 5] The table showing the vibration displacement analysis results of Comparative Example 1, Comparative Example 2, and the Example. [Figure 6] The plan view showing a diaphragm-type ultrasonic radiation unit of another embodiment. [Figure 7] The plan view showing a diaphragm-type ultrasonic radiation unit of another embodiment. [Figure 8] The schematic configuration diagram showing a conventional ultrasonic cleaning apparatus. [Mode for Carrying Out the Invention]

[0018] Hereinafter, an embodiment in which the present invention is embodied in an ultrasonic cleaning apparatus will be described in detail based on Figure 1 to Figure 5.

[0019] As shown in Figure 1, the ultrasonic cleaning device 10 includes a metal cleaning tank 11 that stores cleaning liquid W1, and an ultrasonic radiation unit 21. A plurality of bolt holes 11a are provided at the lower end of the cleaning tank 11. The vibration plate 12 in the ultrasonic radiation unit 21 constitutes the bottom of the cleaning tank 11, and is a rectangular metal plate (a stainless steel plate in this embodiment) in plan view with dimensions of 390 mm in length × 240 mm in width × 2.5 mm in thickness. That is, the ultrasonic radiation unit 21 of the present embodiment is a vibration plate type ultrasonic radiation unit in which the vibration plate 12 is disposed at the lower end of the cleaning tank 11 via the packing 1, and the vibration plate 12 is screwed and fixed with bolts 2 and nuts 3. This vibration plate 12 has a radiation surface 13 that radiates ultrasonic waves, and a non-radiation surface 14 located on the opposite side of the radiation surface 13. Stud bolts 15 (see FIG. 3 and FIG. 4) are protrudingly provided at a plurality of positions on the non-radiation surface 14 of the vibration plate 12. A plurality of fixing holes 16 are provided at substantially equal intervals over the entire circumference of the outer peripheral portion of the vibration plate 12.

[0020] As shown in Figure 1, Figure 2, etc., this ultrasonic radiation unit 21 includes the above-described vibration plate 12, a plurality of bolt-tightened Langevin type ultrasonic vibrators 31, and a plurality of resonance rods 51 and 59. The ultrasonic cleaning device 10 of the present embodiment using the above-described ultrasonic radiation unit 21 is configured as a device that cleans the surface of the object 17 to be cleaned (see FIG. 1) accommodated in the cleaning tank 11 by irradiating the cleaning liquid W1 in the cleaning tank 11 with ultrasonic waves from each ultrasonic vibrator 31.

[0021] As shown in Figures 3 and 4, each ultrasonic transducer 31 is a device for irradiating ultrasonic waves and is composed of a transducer front plate 32, a transducer backing plate 33, a drive unit 41, and transducer assembly bolts 34 and nuts 38. In other words, each ultrasonic transducer 31 in this embodiment is a bolt-fastened Langevin type transducer (BLT). The transducer front plate 32 is located on the front end side of the ultrasonic transducer 31. The transducer front plate 32 has a circular and substantially cylindrical shape in plan view. The circular radiating surface of the transducer front plate 32 is joined to the non-radiating surface 14 of the diaphragm 12 via an adhesive such as epoxy resin. The transducer front plate 32 is formed from a metal material such as aluminum, aluminum alloy, stainless steel, or titanium alloy.

[0022] The transducer backing plate 33 is positioned on the rear end side of the ultrasonic transducer 31. The transducer backing plate 33 has a circular and substantially cylindrical shape in plan view, and in this embodiment, its diameter is set to be slightly smaller than that of the transducer front plate 32. The drive unit 41 is made by alternately stacking four piezoelectric elements 42 and four electrode plates 43, and is sandwiched between the transducer front plate 32 and the transducer backing plate 33. The transducer backing plate 33 is made of a metal material such as aluminum, aluminum alloy, stainless steel, or titanium alloy.

[0023] Since the piezoelectric element 42 is annular and the electrode plate 43 is substantially annular with a tab portion in part, the drive unit 41 has a bolt insertion hole 44 that penetrates its own center. Each piezoelectric element 42 is polarized in the thickness direction.

[0024] The piezoelectric element 42 of this embodiment is formed using a lead-free piezoelectric ceramic material. The lead-free piezoelectric ceramic is not particularly limited, but preferred examples include alkali niobate-based piezoelectric ceramic materials and BNT-BT-based piezoelectric ceramic materials mainly composed of bismuth sodium titanate and barium titanate.

[0025] As shown in Figures 3 and 4, a female screw hole 35 is formed in the center of the rear end of the transducer front plate 32, extending along the height direction (up and down direction in Figures 3 and 4) of the transducer front plate 32. This female screw hole 35 does not penetrate the transducer front plate 32. In other words, this female screw hole 35 is open only on the rear surface of the transducer front plate 32. On the other hand, a bolt insertion hole 56 through which a stud bolt 15 is inserted is provided in the center of the front end of the transducer front plate 32, extending along the height direction.

[0026] The female screw hole 35 of the transducer front plate 32 communicates with the bolt insertion hole 44 of the drive unit 41. On the other hand, a through hole 36 is formed in the center of the transducer backing plate 33, extending along the height direction (up and down direction in Figures 3 and 4). The through hole 36 opens on the front side and communicates with the bolt insertion hole 44, and also opens on the rear side. The transducer mounting bolt 34, which has male threads formed on its outer circumference, is inserted from the transducer backing plate 33 side, and its tip reaches the female screw hole 35 on the transducer front plate 32 side via the through hole 36 and the bolt insertion hole 44. In other words, the tip of this transducer mounting bolt 34 stops partway through the transducer front plate 32 and does not reach the diaphragm 12. This transducer mounting bolt 34 is screwed into the female screw hole 35. Then, by screwing a nut 38 onto the protruding portion of the transducer assembly bolt 34 through which the transducer backing plate 33 is inserted, the transducer front plate 32, the drive unit 41, and the transducer backing plate 33 are tightened and fixed together to form a single unit. The metal material used to form the transducer assembly bolt 34 and nut 38 can be any material, but stainless steel is used here.

[0027] Multiple stud bolts 15, which protrude from the non-radiating surface 14 of the diaphragm 12, are screwed into bolt insertion holes 56 of the transducer front plate 32. Through this screwing, multiple ultrasonic transducers 31 are fastened and fixed to the diaphragm 12.

[0028] Each ultrasonic transducer 31 in this embodiment, as shown in Figure 1, is a longitudinal vibration type bolt-clamped Langevin transducer having a longitudinal first-order vibration mode (resonance frequency of 28 kHz for a single unit) in which the axial longitudinal vibration component resonates at λ / 2 (λ: longitudinal vibration wavelength). Each ultrasonic transducer 31 vibrates at the same frequency as the others.

[0029] As shown in Figure 1, an ultrasonic oscillator 19 is electrically connected to each ultrasonic transducer 31. The ultrasonic oscillator 19 supplies high-frequency power to continuously vibrate each ultrasonic transducer 31. This high-frequency power drives each ultrasonic transducer 31, and each ultrasonic transducer 31 irradiates the cleaning liquid W1 in the cleaning tank 11 with ultrasonic waves of 25 kHz (the resonant frequency when the ultrasonic transducer 31 is joined to the diaphragm 12). In this embodiment, the output (driving power) of the ultrasonic waves is set to 600 W, but it is not limited to this and can be set arbitrarily.

[0030] As shown in Figures 1 to 4, the plurality of resonant rods in this embodiment are composed of a first resonant rod 51 having a relatively large cross-sectional area and a second resonant rod 59 having a relatively small cross-sectional area.

[0031] The first resonant rod 51 is a resonator that resonates at the same frequency (a standalone resonant frequency of 28 kHz) and in a longitudinal vibration mode as the ultrasonic transducer 31. The first resonant rod 51 is circular in plan view and is substantially cylindrical. In this embodiment, the first resonant rod 51 has a diameter D1 equal to the maximum diameter D0 of the transducer front plate 32 and is formed to be slightly longer than the ultrasonic transducer 31 (see Figure 4). Specifically, since the maximum diameter D0 of the transducer front plate 32 is 45 mmφ, the diameter D1 of the first resonant rod 51 is also 45 mmφ. A bolt insertion hole 56 through which a stud bolt 15 is inserted is provided in the center of the tip side of the first resonant rod 51, extending along the height direction. The first resonant rod 51 is fastened and fixed to the diaphragm 12 by screwing the stud bolt 15 into the bolt insertion hole 56 of the first resonant rod 51.

[0032] The second resonant rod 59, like the first resonant rod 51, is a resonator that resonates at the same frequency (a single resonant frequency of 28 kHz) and in a longitudinal vibration mode as the ultrasonic transducer 31. The second resonant rod 59 is circular in plan view and is approximately cylindrical. In this embodiment, the second resonant rod 59 has a diameter D2 that is at least half and at least three-quarters of the maximum diameter D0 of the transducer front plate 32 (see Figure 3). If the diameter D2 is too large, it becomes difficult to position the second resonant rod 59 close to the ultrasonic transducer 31, and at the same time, it may become difficult to secure a sufficient distance between the second resonant rod 59 and the long side 12a of the diaphragm 12. Conversely, if the diameter D2 is too small, the effect of installing the second resonant rod 59 may not be fully obtained. Specifically, the maximum diameter D0 of the transducer front plate 32 is 45 mmφ, and the diameter D2 of the second resonant rod 59 is 30 mmφ, which is equivalent to 2 / 3 of that value. Furthermore, the second resonant rod 59 is formed to be slightly longer than the ultrasonic transducer 31. A bolt insertion hole 56 is provided in the center of the tip side of the second resonant rod 59, extending along the height direction, through which a stud bolt 15 is inserted. The second resonant rod 59 is fastened and fixed to the diaphragm 12 by screwing the stud bolt 15 into the bolt insertion hole 56 of the second resonant rod 59.

[0033] The first resonant rod 51 and the second resonant rod 59 are formed using a metal material such as aluminum, aluminum alloy, stainless steel, or titanium alloy. In this embodiment, the first resonant rod 51 and the second resonant rod 59 are formed using the same type of metal material (specifically stainless steel), but they may of course be formed using different types of metal materials.

[0034] Next, the number and layout of the ultrasonic transducers 31, the first resonant rod 51, and the second resonant rod 59 in this ultrasonic radiation unit 21 will be described in detail. In the case of this ultrasonic radiation unit 21, the multiple ultrasonic transducers 31 are arranged at each vertex p2 of at least one regular hexagon H1 that is virtually formed in the center of the diaphragm 12 (see Figure 2). More specifically, in this embodiment, two regular hexagons H1 that share one side with each other are virtually formed in the center of the diaphragm 12. The multiple ultrasonic transducers 31 are then arranged at each vertex p2 of these two regular hexagons H1. In other words, as shown in Figure 2, there are 10 vertices p2 within one diaphragm 12, so this ultrasonic radiation unit 21 is equipped with 10 ultrasonic transducers 31.

[0035] The first resonant rod 51 is positioned at the center p1 of the regular hexagon H1, and in this embodiment, there are two such first resonant rods 51. In addition, the first resonant rods 51 are also positioned on the short side 12b of the diaphragm 12 and adjacent to the regular hexagon H1 from the outside. Specifically, three or more first resonant rods 51 are arranged linearly along the short side 12b of the diaphragm 12. In this embodiment, there are six such first resonant rods 51. Therefore, this ultrasonic radiation unit 21 is equipped with a total of eight first resonant rods 51.

[0036] The second resonant rod 59 is positioned on the long side 12a of the diaphragm 12 and adjacent to the regular hexagon H1 from the outside. In this embodiment, there are six such second resonant rods 59. That is, in this embodiment, the number of ultrasonic transducers 31 is 10, which is less than the total number of first resonant rods 51 and second resonant rods 59 (8 + 6 = 14). Also, the number of first resonant rods 51 is 8, which is more than the number of second resonant rods 59 (6).

[0037] Furthermore, as shown in Figure 2, the center-to-center distance L1 between the first resonant rod 51 and the adjacent ultrasonic transducer 31 is equal to the center-to-center distance L0 between two adjacent ultrasonic transducers 31. Also, the center-to-center distance L2 between the second resonant rod 59 and the adjacent ultrasonic transducer 31 is slightly shorter than the center-to-center distance L0 between two adjacent ultrasonic transducers 31. Note that the above center-to-center distances L0 and L1 are set to be approximately 1.1 to 1.5 times the maximum diameter D0 of the transducer front plate 32. Also, the above center-to-center distance L2 is set to be approximately 0.8 to 0.95 times the above center-to-center distances L0 and L1.

[0038] When operating the ultrasonic cleaning apparatus 10 configured in this way, first, the ultrasonic cleaning apparatus 10 is driven to supply high-frequency power from the ultrasonic oscillator 19 to the multiple ultrasonic transducers 31, causing each ultrasonic transducer 31 to vibrate continuously. As a result, ultrasonic waves are irradiated into the cleaning liquid W1 from the ultrasonic transducers 31. At this time, cavitation is generated in the cleaning liquid W1 as a result of the irradiation of ultrasonic waves, and the object to be cleaned 17 is cleaned by the impact of the rupture of the cavitation.

[0039] Next, we will describe the evaluation test of the ultrasonic radiation unit 21 and its results.

[0040] In this evaluation test, the measurement samples were prepared as follows. An ultrasonic radiation unit 21 identical to that of this embodiment was prepared and designated as the example. The ultrasonic radiation unit 21 of the example is described in the right column of the table in Figure 5 as "10 BLTs + 8 φ45 resonant rods + 6 φ30 resonant rods connected". In addition, an ultrasonic radiation unit was prepared by omitting 6 first resonant rods 51 from the ultrasonic radiation unit 21 of this embodiment and designated as Comparative Example 2. The ultrasonic radiation unit 21 of Comparative Example 2 is described in the middle column of the table in Figure 5 as "10 BLTs + 2 φ45 resonant rods + 6 φ30 resonant rods connected". Furthermore, an ultrasonic radiation unit was prepared by omitting all resonant rods 51 and 59 from the ultrasonic radiation unit 21 of this embodiment and designated as Comparative Example 1. The ultrasonic radiation unit 21 of Comparative Example 1 is described in the left column of the table in Figure 5 as "10 BLTs connected".

[0041] Next, using conventional finite element method analysis, the vibration displacement distribution under water load conditions was analyzed in the diaphragm 12 of the ultrasonic radiation unit of each measurement sample (Example, Comparative Example 1, Comparative Example 2). In this analysis, a diaphragm 12 measuring 390 mm (length) x 240 mm (width) x 2.5 mm (thickness) was used, and the ultrasonic radiation unit was configured by mounting 10 ultrasonic transducers 31 (Honda Electronics Co., Ltd., "HEC-45282Z") with a nominal frequency of 28 kHz on the non-radiating surface 14 of the diaphragm 12. The driving power of each ultrasonic transducer 31 was set to 600 W. The results are shown in Figure 5.

[0042] In Comparative Example 1, in which neither the first resonant rod 51 nor the second resonant rod 59 was used, it was confirmed that the vibration displacement increased in a roughly cross shape in the central part of the diaphragm 12, while the vibration displacement decreased in other areas. In other words, it was found that the unevenness of the vibration displacement distribution was very large in Comparative Example 2. Furthermore, the unevenness of the vibration displacement distribution was particularly large near the center p1 of the regular hexagon H1, making erosion more likely to occur in that area.

[0043] In contrast, in Comparative Example 2, in which multiple second resonant rods 59 were added to Comparative Example 1 and a first resonant rod 51 was added to the center p1 of the regular hexagon H1, it was confirmed that the roughly cross-shaped region with large vibration displacement became slightly wider, and the unevenness of the vibration displacement distribution was somewhat smaller than in Comparative Example 1. This improvement was thought to have been brought about by the addition of multiple second resonant rods 59, etc. However, in Comparative Example 2, it was found that the vibration displacement in the peripheral region of the diaphragm 12 did not become so large.

[0044] Furthermore, in the embodiment in which multiple first resonant rods 51 were added to the regular hexagon H1 at positions adjacent to the outside, it was confirmed that the region with large vibration displacement expanded further to its periphery. Specifically, for example, in Comparative Example 2, although the ultrasonic transducer 31 and the second resonant rod 59 were present in the region indicated by circle R1, the vibration displacement was not very large. On the other hand, in the embodiment, the vibration displacement in the region indicated by circle R1 became sufficiently large, and it was found that the unevenness of the vibration displacement distribution was considerably smaller compared to Comparative Example 2. This improvement was thought to have been brought about by the addition of multiple first resonant rods 51 at the aforementioned adjacent outer positions. In other words, in the embodiment, it was thought that the addition of multiple first resonant rods 51 improved the "diagonal vibration efficiency" of the diaphragm 12, leading to an expansion of the region with large vibration displacement and improved uniformity of the vibration displacement distribution.

[0045] Therefore, according to this embodiment, the following effects can be obtained.

[0046] (1) In the ultrasonic radiation unit 21 of this embodiment, the ultrasonic transducer 31 is constructed using four or more piezoelectric elements 42 made of lead-free piezoelectric ceramics. Therefore, compared to a unit that uses only two piezoelectric elements 42, it is possible to supply a larger driving power to each transducer. Furthermore, in this ultrasonic radiation unit 21, the ultrasonic transducer 31 with the above configuration is arranged at each vertex p2 of two imaginary regular hexagons H1 in the center of the rectangular diaphragm 12 in plan view. Therefore, even with a small number of ultrasonic transducers 31, the diaphragm 12 can be vibrated efficiently. In addition, by arranging the first resonant rod 51 and the second resonant rod 59, which have different cross-sectional areas, in a predetermined manner, uniform longitudinal vibration can be obtained over a relatively wide radiation surface of the diaphragm 12. As a result, the occurrence of erosion in the diaphragm 12 is reduced, and the diaphragm 12 is less likely to wear down, thus extending the lifespan of the device. In addition, a uniform vibration displacement distribution is easier to obtain, and the occurrence of uneven cleaning can be reduced. As a result, we can provide an excellent ultrasonic cleaning device 10 that enables uniform cleaning.

[0047] Furthermore, the first and second resonant rods 51 and 59 of this embodiment, which are made of a single material, have a simpler structure than the ultrasonic transducer 31, which is made of multiple types of parts. Therefore, they can be manufactured at a relatively low cost. Thus, even in an ultrasonic radiation unit 21 equipped with a diaphragm 12 that requires a large cleaning area, for example, it is possible to reduce the number of ultrasonic transducers 31 used and to use inexpensive resonant rods 51 and 59. As a result, a device with excellent erosion resistance and uniformity of vibration displacement distribution can be realized at a low cost.

[0048] (2) In the ultrasonic radiation unit 21 of this embodiment, specifically, two first resonant rods 51 are positioned at the center p1 of the regular hexagon H1, and six first resonant rods 51 are positioned on the short side 12b of the diaphragm 12 and adjacent to the regular hexagon H1 from the outside. Three first resonant rods 51 are linearly arranged along the short side 12b on the right side in Figure 2, and three first resonant rods 51 are linearly arranged along the short side 12b on the left side in Figure 2. In addition, four second resonant rods 59 are positioned on the long side 12a of the diaphragm 12 and adjacent to the regular hexagon H1 from the outside. Furthermore, the number of ultrasonic transducers 31 is less than the total number of first resonant rods 51 and second resonant rods 59, and the number of first resonant rods 51 is greater than the number of second resonant rods 59. With this configuration, the vibration efficiency in the diagonal direction of the diaphragm 12 can be improved in particular. Therefore, it is possible to expand the region of large vibration displacement and improve the uniformity of the vibration displacement distribution.

[0049] The above embodiment may be modified as follows.

[0050] In the above embodiment, two regular hexagons H1 sharing one side each are virtualized in the center of the diaphragm 12, and a plurality of ultrasonic transducers 31 are arranged at each vertex p2 of the two regular hexagons H1 to constitute the ultrasonic radiation unit 21, but the embodiment is not limited to this. For example, as in the ultrasonic radiation unit 21A of another embodiment shown in Figure 6, three regular hexagons H1 sharing at least one side each are virtualized in the center of the diaphragm 12, and a plurality of ultrasonic transducers 31 are arranged at each vertex p2 of the three regular hexagons H1. In the ultrasonic radiation unit 21A, 14 ultrasonic transducers 31, 9 first resonant rods 51, and 8 second resonant rods 59 are used to constitute the unit. Alternatively, as in the ultrasonic radiation unit 21B of another embodiment shown in Figure 7, one regular hexagon H1 is virtualized in the center of the diaphragm 12, and a plurality of ultrasonic transducers 31 are arranged at each vertex p2 of the one regular hexagon H1. The ultrasonic radiation unit 21A is composed of six ultrasonic transducers 31, seven first resonant rods 51, and four second resonant rods 59.

[0051] In the above embodiment, multiple ultrasonic transducers 31 were configured using four piezoelectric elements 42 made of lead-free piezoelectric ceramics, but the invention is not limited to this. For example, multiple ultrasonic transducers 31 may be configured using six or eight piezoelectric elements 42.

[0052] In the above embodiment, the ultrasonic radiation unit 21 was constructed using a first resonant rod 51 and a second resonant rod 59 that are circular in plan view and substantially cylindrical in shape, but it is not limited to this. For example, the ultrasonic radiation unit 21 may be constructed using a first resonant rod 51 and a second resonant rod 59 that are rectangular in plan view and substantially prismatic in shape. In this case, the shapes of the first resonant rod 51 and the second resonant rod 59 may be the same, or they may be different.

[0053] In the above embodiment, the diameter D1 of the first resonant rod 51 was equal to the maximum diameter D0 of the transducer front plate 32, both being 45 mmφ, but this is not limited to this. For example, the diameter D1 of the first resonant rod 51 may be larger or smaller than the maximum diameter D0 of the transducer front plate 32. Incidentally, having the diameter D1 of the first resonant rod 51 equal to the maximum diameter D0 of the transducer front plate 32, as in the above embodiment, is advantageous in achieving uniformity of the vibration displacement distribution.

[0054] In the above embodiment, a stud bolt 15, which is a bolt without a head, was used as the bolt protruding from the non-radiating surface 14 of the diaphragm 12. However, bolts with heads, such as hexagonal bolts, socket head cap screws, or wing bolts, may also be used as the bolt protruding from the non-radiating surface 14.

[0055] In the above embodiment, the diaphragm-type ultrasonic radiation units 21, 21A, and 21B were attached to the bottom of the cleaning tank 11 in the ultrasonic cleaning apparatus 10 via a packing 1, but the invention is not limited to this. For example, the ultrasonic radiation units 21, 21A, and 21B may be of the cleaning tank type, attached to stud bolts protruding from the non-radiating surface of the bottom plate of the cleaning tank 11. Alternatively, the ultrasonic radiation units 21, 21A, and 21B may be of the immersion type, used by being submerged in the cleaning liquid W1 of the cleaning tank 11.

[0056] The ultrasonic radiation units 21, 21A, and 21B of the above embodiment were applied to an ultrasonic cleaning apparatus 10 that performs cleaning using ultrasound, but they may also be applied to apparatuses that perform processing other than cleaning, such as extraction, emulsification, dispersion, mixing, stirring, crushing, and atomization. Specifically, for example, when an ultrasonic radiation unit is applied to an ultrasonic emulsification apparatus, the emulsion can be finely milled to nanoparticles with high efficiency, and effects such as long-term stabilization and reduction of surfactants can be expected. Also, when an ultrasonic radiation unit is applied to an ultrasonic dispersion apparatus, nanoparticles (metal nanoparticles, carbon nanotubes, ceramic nanoparticles, magnetic nanoparticles, etc.) can be dispersed with high efficiency. Furthermore, the ultrasonic radiation unit may be materialized as an ultrasonic processing apparatus that utilizes chemical action. In this case, cavitation can be generated uniformly and efficiently over a wide area, making it possible to increase the amount of radicals generated, such as OH radicals, that are produced by the high temperature and high pressure field during bubble collapse. Therefore, the reaction efficiency of sonochemicals caused by radical species can be increased, and processing such as decomposition and detoxification of harmful substances, sterilization, and polymer polymerization can be performed efficiently. [Explanation of symbols]

[0057] 12: Vibration plate 12a: Long side of the diaphragm 12b: Short side of the diaphragm 13: Radiation surface 14: Non-radiating surface 21, 21A, 21B: Ultrasonic radiation unit 31: Ultrasonic transducer 32: Front panel of the transducer 42: Piezoelectric element 51: 1st resonance bar 59: 2nd resonance bar D0: Maximum diameter of the transducer front plate D1: Diameter of the first resonant rod D2: Diameter of the second resonating rod H1: Regular hexagon L0: Distance between the centers of two adjacent ultrasonic transducers. L1: Distance between the centers of the first resonant rod and the adjacent ultrasonic transducer. L2: Distance between the centers of the second resonant rod and the adjacent ultrasonic transducer. p1: Center of a regular hexagon p2: Vertices of a regular hexagon

Claims

1. A rectangular diaphragm in plan view having a radiating surface that emits ultrasonic waves and a non-radiating surface located on the opposite side of the radiating surface, with bolts protruding from the non-radiating surface, A plurality of bolted Langevin-type ultrasonic transducers, each having a transducer front plate attached to the non-radiating surface, Multiple resonant rods that resonate at the same frequency and in longitudinal vibration mode as the ultrasonic transducer, An ultrasonic radiation unit comprising a plurality of bolts to which a plurality of ultrasonic transducers and a plurality of resonant rods are fastened and fixed, Each of the ultrasonic transducers is composed of four or more piezoelectric elements made of lead-free piezoelectric ceramics, and these elements are arranged at each vertex of a hypothetical regular hexagon in the center of the diaphragm. The plurality of resonant rods are composed of a first resonant rod having a relatively large cross-sectional area and a second resonant rod having a relatively small cross-sectional area. The first resonant rod is positioned at the center of the regular hexagon and on the short side of the diaphragm, and adjacent to the regular hexagon from the outside. The second resonant rod is positioned on the longer side of the diaphragm and adjacent to the regular hexagon from the outside. An ultrasonic radiation unit characterized by the following features.

2. In the central part of the diaphragm, two regular hexagons sharing one side each are virtually formed. Multiple ultrasonic transducers are arranged at each vertex of the two regular hexagons. The ultrasonic radiation unit according to feature 1.

3. The number of ultrasonic transducers is less than the total number of the first and second resonant rods. The number of the first resonant rods is greater than the number of the second resonant rods. The ultrasonic radiation unit according to feature 1.

4. The first resonant rods are arranged in a straight line along the short side of the diaphragm, with three or more rods in total. The ultrasonic radiation unit according to feature 1.

5. The first resonant rod has a diameter equal to the maximum diameter of the front plate of the ultrasonic transducer, The second resonant rod has a diameter that is 1 / 2 or more and 3 / 4 or less of the maximum diameter of the front plate of the transducer. The ultrasonic radiation unit according to feature 1.

6. The distance between the centers of the first resonant rod and the ultrasonic transducer adjacent thereto is equal to the distance between the centers of two adjacent ultrasonic transducers. The distance between the centers of the second resonant rod and the adjacent ultrasonic transducer is shorter than the distance between the centers of two adjacent ultrasonic transducers. The ultrasonic radiation unit according to feature 1.

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