OSCILATION EXCITATION METHOD FOR LANGEVIN ULTRASONIC TRANSDUCER, ULTRASONIC MACHINING METHOD, AND ULTRASONIC TRANSMISSION METHOD

Abstract

A novel mode of ultrasonic oscillation is generated in a Langevin ultrasonic transducer comprising a metal block, a metal block provided with a supporting means protruding in a ring shape on its side surface, and polarized piezoelectric elements fixed between these metal blocks, by connecting the ultrasonic transducer to a base via the supporting means, whereby supporting the ultrasonic transducer on the base in a restrained state, and applying to the piezoelectric elements a voltage having such frequency that the ultrasonic transducer generates an ultrasonic oscillation with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer; this novel ultrasonic oscillation mode is utilized for performing ultrasonic machining methods as well as for ultrasonic transmission method.

Claims

1. A method for generating ultrasonic oscillation in a Langevin ultrasonic transducer comprising a metal block, a metal block provided with a supporting means protruding in a ring shape on side surface thereof, and polarized piezoelectric elements fixed between these metal blocks, which comprises; connecting the ultrasonic transducer to a base via the supporting means, whereby supporting the ultrasonic transducer on the base in a restrained state, and applying to the piezoelectric elements a voltage having such frequency that the ultrasonic transducer generates an ultrasonic oscillation with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer, whereby the ultrasonic oscillation having a mode of back-and-forth motion in a direction perpendicular to planes surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer is generated in the Langevin ultrasonic transducer.

2. The method of claim 1, in which the frequency of the voltage applied to the piezoelectric elements is a resonance frequency in a frequency range lower than a frequency at which a primary axial oscillation is generated.

3. The method of claim 1, in which an oscillation node is present at a site at which the supporting means is connected to the base and the supporting means oscillates in phase with the ultrasonic oscillation.

4. An ultrasonic machining method which comprises: connecting a tool to one end of a Langevin ultrasonic transducer comprising a metal block, a metal block provided with a supporting means protruding in a ring shape on side surface thereof, and polarized piezoelectric elements fixed between these metal blocks; connecting the ultrasonic transducer to a base via the supporting means, whereby supporting the ultrasonic transducer on the base in a restrained state; and applying to the piezoelectric elements a voltage having a such frequency that the ultrasonic transducer generates an ultrasonic oscillation with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer, whereby the tool oscillates with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements of the ultrasonic transducer.

5. The ultrasonic machining method of claim 4, in which the tool rotates on a central axis of the Langevin ultrasonic transducer.

6. The ultrasonic machining method of claim 4, in which the tool is selected from the group consisting of an end mill, a drill, a polishing tool and a grinding tool.

7. The ultrasonic machining method of claim 4, in which the tool moves with back-and-forth motion along a central axis of the Langevin ultrasonic transducer.

8. The ultrasonic machining method of claim 7, in which the tool is selected from the group consisting of a cutting tool, a diaphragm and a welding tool.

9. An ultrasonic transmission method which comprises: connecting a ultrasonic transmission means to one end of a Langevin ultrasonic transducer comprising a metal block, a metal block provided with a supporting means protruding in a ring shape on side surface thereof, and a polarized piezoelectric elements fixed between these metal blocks; connecting the ultrasonic transducer to a base via the supporting means, whereby supporting the ultrasonic transducer on the base in a restrained state; and applying to the piezoelectric elements a voltage having a such frequency that the ultrasonic transducer generates an ultrasonic oscillation with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer, whereby the ultrasonic transmission means oscillates with back-and-forth motion in a direction perpendicular to plane surfaces of the piezoelectric elements of the ultrasonic transducer.

10. The ultrasonic transmission method of claim 9, in which the ultrasonic transmission means is a diaphragm.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0061] FIG. 1 illustrates a constitution of a representative bolted Langevin ultrasonic transducer.

[0062] FIG. 2 illustrates a constitution of a representative ultrasonic machining apparatus.

[0063] FIG. 3 illustrates an example of a constitution of a structure for supporting and fixing an ultrasonic transducer under restraining condition that can be utilized in the method of the invention for generating the ultrasonic oscillation according to the invention.

[0064] FIG. 4 illustrates an example of a constitution of an ultrasonic transducer that can be utilized for the method of the invention for generating the ultrasonic oscillation according to the invention.

[0065] FIG. 5 shows an admittance curve indicating frequency characteristics of the ultrasonic transducer of FIG. 4 under non-restraining condition.

[0066] FIG. 6 shows an admittance curve indicating frequency characteristics of the ultrasonic transducer of FIG. 4 which is restrained by the use of the structure shown in FIG. 3.

[0067] FIG. 7 shows an image of a oscillation mode (Pseudo Zero Order Oscillation) generated in an ultrasonic transducer operated in the method of the inventionbased on the calculation according to FEM.

[0068] FIG. 8 shows an image of a oscillation mode of primary axial oscillationbased on the calculation according to FEM.

[0069] FIG. 9 shows a schematic image of the oscillation mode of Pseudo Zero Order Oscillation utilized in the method of the invention for generation of ultrasonic oscillation.

[0070] FIG. 10 shows a schematic image of the oscillation mode of primary axial oscillation (A) and its enlarged image to make clear the oscillation of the piezoelectric element (B).

[0071] FIG. 11 illustrates another example of an ultrasonic transducer employable in the method of the invention and another example of a constitution of a structure for supporting and fixing an ultrasonic transducer under restraining condition that can be utilized in the method of the invention for generating the ultrasonic oscillation according to the invention.

[0072] FIG. 12 shows an image of an oscillation mode of primary axial oscillation generated in the ultrasonic transducer fixed in the supporting structure shown in FIG. 11based on the calculation according to FEM.

[0073] FIG. 13 illustrates a further example of a constitution of a structure for supporting and fixing an ultrasonic transducer under restraining condition that can be utilized in the method of the invention (A) and shows an oscillation mode utilizing the Zero Order Oscillation and a conventionally employed primary axial oscillation in combination.

[0074] FIG. 14 illustrates a drilling machine for performing the ultrasonic machining method according to the invention.

[0075] FIG. 15 illustrates a polishing (or lapping) machine for performing the ultrasonic machining method according to the invention.

[0076] FIG. 16 illustrates a cutting machine for performing the ultrasonic machining method according to the invention.

[0077] FIG. 17 illustrates a cleaning bath equipped with an ultrasonic transducer for performing the ultrasonic transmission method according to the invention.

[0078] FIG. 18 illustrates an ultrasonic sonar for performing the ultrasonic transmission method according to the invention.

EMBODIMENTS FOR PERFORMING THE INVENTION

[0079] To the best knowledge of the inventor, the presence of a resonance frequency corresponding to an admittance peak appearing on a side lower than the admittance peak corresponding to the resonance frequency for generating the primary axial oscillation, which is employed in the method of generating ultrasonic oscillation of the invention, is not known until now. In the invention, the former resonance frequency is named a resonance frequency for generating Pseudo Zero Order Oscillation. Further, to the best knowledge of the inventor, a method for generating an ultrasonic oscillation according to the Pseudo Zero Order Oscillation is not known.

[0080] For practicing the method of generating the Pseudo Zero Order Oscillation in an ultrasonic transducer according to the invention, it is required in the first step to prepare an ultrasonic transducer provided with a supporting means (or supporting framework, shown in FIG. 4). The supporting means in a shape of a ring is provided for firmly supporting and restraining the ultrasonic transducer onto a base (or a base structure) which is placed outside. Thus prepared ultrasonic transducer is then supported and restrained on the supporting structure of FIG. 3 at the peripheral area by means of the male screw of the housing and the nut. In FIG. 3, the supporting means 6 is attached to the front mass 2b. However, the supporting means can be attached to the rear mass. In addition, while the supporting means is preferably formed on the front mass or rear mass to give a united structure, an independently prepared supporting means can be fixed to the front mass or rear mass, or fixed between the front mass and rear mass.

[0081] In the second step, thus prepared ultrasonic transducer is examined for determining its frequency characteristics using an impedance analyzer, to obtain an admittance curve as shown in FIG. 6. If two admittance peaks are observed in the admittance curve as shown in FIG. 6, it is understood that one admittance peak appearing on a higher frequency side indicates a resonance frequency for generating a primary axial oscillation, and that another admittance peak appearing on a lower frequency side indicates a resonance frequency for generating the Pseudo Zero Order Oscillation.

[0082] The above-mentioned understanding can be confirmed by obtaining an admittance curve of the above-prepared ultrasonic transducer under non-restraining condition and comparing an admittance peak (indicating a resonance frequency for generating a primary axial oscillation) with the above-mentioned admittance peak on the higher frequency side. However, there are cases in which no clear admittance peak indicating a frequency for generating a primary axial oscillation is observed, probably due to the structure of the ultrasonic transducer. In these cases, the frequency for generating a primary axial oscillation can be determined using a known calculation system. Anyway, after determining the resonance frequency for generating a primary axial oscillation, a resonance frequency for generating the Pseudo Zero Order Oscillation can be understood to be a frequency corresponding to an admittance peak appearing on the lower frequency side.

[0083] If three or more admittance peaks are observed in the resulting admittance curve, the resonance frequency for generating a primary axial oscillation is first determined or assumed according to one of the above-mentioned method, and a frequency corresponding to an admittance peak adjacent to the admittance peak corresponding to the resonance frequency for generating a primary axial oscillation.

[0084] The Pseudo Zero Order Oscillation can be generated in the above-mentioned ultrasonic transducer prepared as above. In more detail, the ultrasonic transducer is attached to an ultrasonic machining apparatus, and applying an electric power of a voltage having thus determined resonance frequency for generating the Pseudo Zero Order Oscillation. However, it should be noted that the above-mentioned resonance frequency for generating the Pseudo Zero Order Oscillation is determined using the ultrasonic transducer equipped with neither a collet nor a tool. Accordingly, the resonance frequency for generating Pseudo Zero Order Oscillation may move or vary slightly. Further, a certain movement of the resonance frequency for generating Pseudo Zero Order Oscillation may be observed because of a variation of the condition of restraining the tool-equipped ultrasonic transducer. Therefore, it is desired that movement or variation of the resonance frequency for generating Pseudo Zero Order Oscillation can be continuously traced by means an appropriate ultrasonic generating circuit so as to automatically adjust and determine most appropriate resonance frequency for the purpose.

[0085] There is a case in which an ultrasonic transducer that has the structure of FIG. 4 and is supported and restrained in the supporting structure of FIG. 3 gives no admittance curve in the observation using an impedance detector having two or more impedance peaks. In that case, the desired admittance curve having two or more impedance peaks (as shown in FIG. 6) therein may be obtained by adjusting the restraining condition. If the adjustment of the restraining condition does not result in a favorable result, it may be required to modify the ultrasonic transducer and/or the constitution of structure for supporting and restraining the ultrasonic transducer, with further reference to the constitution of structure for supporting an ultrasonic transducer (shown in FIG. 3) and the shape and sizes of the ultrasonic transducer (shown in FIG. 4).

[0086] For the sake of confirmation, however, it is indicated that the he constitution of structure for supporting an ultrasonic transducer (shown in FIG. 3) and the shape and sizes of the ultrasonic transducer (shown in FIG. 4) are mere representative embodiments, and the ultrasonic transducer and its supporting and restraining system shown in these Figures do not limit an ultrasonic transducer and its supporting and restraining system utilizable for practicing the method of the invention for generating Pseudo Zero Order Oscillation.

[0087] As described above, the inventor has concluded that the ultrasonic oscillation generated by the method of generation of an ultrasonic oscillation according to the invention is an ultrasonic oscillation with back-and-forth motion in a direction perpendicular to planes surfaces of the piezoelectric elements which has no oscillation node within the ultrasonic transducer.

[0088] Details of the data on which the above-mentioned conclusion is derived are again explained hereinbelow.

[0089] As is described hereinbefore, to the best knowledge of the inventor, the presence of an admittance peak observed in an admittance curve on the side of lower frequency is not known. Therefore, in the initial stage, the inventor has not understood what is meant by the presence of the admittance peak on the side of lower frequency in the admittance curve. However, as has been made clear from the explanation on the experimental results presented hereinbefore, a frequency corresponding to the frequency of the admittance peak on the lower frequency side also is a resonance frequency for generating an ultrasonic oscillation in the ultrasonic transducer, and an ultrasonic oscillation can be generated in the ultrasonic transducer by application of a reduced electric power of a voltage having the resonance frequency. Moreover, a lateral vibration is reduced to a lower level.

[0090] In the next stage, the inventor has tried to analyze the newly observed ultrasonic oscillation using an ANSYS which is a commercially available calculation software for the analysis according to Finite Element Method.

[0091] In the analysis, a mode of an ultrasonic oscillation generated in the ultrasonic transducer employed in the experiments has been analyzed by inputting the shape, sizes, material and restraining condition adopted in the experiments into ANSYS. The results of the analysis on the mode of an ultrasonic oscillation are shown in FIG. 7 and FIG. 8.

[0092] As is described hereinbefore, FIG. 7 shows an image indicating an oscillation mode provided by ANSYS under such condition where an electric power of a voltage having a resonance frequency on the lower frequency side is applied to an ultrasonic transducer under restraining. The image shown in FIG. 7 apparently indicates that the oscillation appearing in the ultrasonic transducer is an oscillation in which the ultrasonic transducer oscillates as a whole in one direction and no oscillation node exists within the ultrasonic transducer. On the other hand, an oscillation node exists in the peripheral side of the supporting means in a ring shape of the ultrasonic transducer. The peripheral side of the supporting means corresponds to the site of connection to the base.

[0093] FIG. 8 shows an image indicating an oscillation mode under the restraining condition where an electric power of a voltage having a resonance frequency on the higher frequency side is applied to an ultrasonic transducer under restraining. The image shown in FIG. 8 apparently indicates that the oscillation appearing in the ultrasonic transducer is an oscillation having an oscillation node in the ultrasonic transducer and that the oscillation is a stretching oscillation comprising two axial oscillations each oscillating in an opposite direction from the oscillation node.

[0094] FIG. 9 is a schematic image prepared for explaining the oscillation mode shown in the image of FIG. 7. As is seen in FIG. 9, the ultrasonic oscillation according to the oscillation mode of the invention repeats as a whole movement of a back-and-forth motion. The inner periphery site of the supporting means of the ultrasonic transducer also oscillates with a back-and-forth motion in phase of the ultrasonic transducer. This oscillation mode is the Pseudo Zero Order Oscillation mode referred to in this specification.

[0095] FIG. 10 (A) is a schematic image prepared for explaining the oscillation mode shown in the image of FIG. 8. As is seen in FIG. 10 (A), the ultrasonic oscillation of FIG. 8 has an oscillation node in the vicinity of the central portion (where the piezoelectric elements are placed) and repeats a stretching oscillation (primary axial oscillation). Since the primary axial oscillation is a stretching oscillation, it is assumed that displacement of the lower end of the ultrasonic transducer to which a tool is attached requires an electric power larger than that required in the oscillation according to the Pseudo Zero Order Oscillation shown in FIG. 9.

[0096] FIG. 10 (B) is an enlarged image in which the oscillation of the ultrasonic transducer (shown in FIG. 10 (A)) is schematically shown, and deformation of the piezoelectric elements 3 under assumption is schematically shown. The piezoelectric elements 3 repeat expansion and shrinkage under variation of an applied electric energy. In the expansion, it is considered that the piezoelectric elements deform to expand in the central portion against the pressure applied to the piezoelectric elements. If the expansion of the piezoelectric elements in the central portion does not occur symmetrically, the planes on the upper end and lower end are not completely parallel to the center plane of the stretching oscillation. Therefore, lateral vibration is apt to occur on the upper and lower end planes.

[0097] FIG. 11 shows other examples of the shape and sizes (units: mm) of an ultrasonic transducer and its supporting/restraining structure employable for performing the method for generation of ultrasonic oscillation according to the invention. FIG. 12 is an image indicating an ultrasonic oscillation (Pseudo Zero Order Oscillation) which appears in the ultrasonic transducer of FIG. 11 which is supported and restrained as is seen in FIG. 11. The image of FIG. 12 is obtained by the analysis according to FEM.

[0098] The oscillation seen in the image of FIG. 12 is an oscillation in the same mode as that seen in FIG. 7, that is, an oscillation in which the ultrasonic transducer oscillates back-and-forth as a whole in one direction and no oscillation node exists within the ultrasonic transducer. An oscillation node exists in the peripheral side of the supporting means in a ring shape of the ultrasonic transducer. The peripheral side of the supporting means corresponds to the site of connection to the base.

[0099] The Pseudo Zero Order Oscillation generated in an ultrasonic transducer when practicing the method of the invention can be utilized in combination with the conventionally utilized primary axial oscillation. An embodiment of use of both oscillations in combination is explained by referring to FIG. 13 (A) and FIG. 13 (B).

[0100] The figures seen in FIG. 13 (A) and FIG. 13 (B) respectively show a still further structure for supporting/restraining an ultrasonic transducer according to the invention and an oscillation mode for ultrasonic machining utilizing the Pseudo Zero Order Oscillation and a conventional primary axial oscillation in combination.

[0101] For instance, a cutter is attached to the end of the front mass on the right side in FIG. 13 (A), and thus assembled cutting device is employed in ultrasonic machining. The cutting device can be utilized in a ultrasonic cutting procedure with increase of cutting efficiency and obviation of local fatigue of the cutter, if an ultrasonic oscillation of an oscillation mode performing the Pseudo Zero Order Oscillation and the primary axial oscillation alternately (as seen in 13 (B)) is utilized.

[0102] FIG. 14 illustrates a constitution of a drilling machine for performing an ultrasonic machining method. The drilling is one of the ultrasonic machining performed according to the ultrasonic machining method of the invention. In the drilling machine, the machining tool is a drill which rotates on a central axis of the ultrasonic transducer. In FIG. 14, a circuit for supplying an ultrasonic oscillation-generating energy is not shown. FIG. 14 also shows an apparatus utilizing a Langevin ultrasonic transducer which is employable for generating the Pseudo Zero Order Oscillation of the invention.

[0103] The ultrasonic machining apparatus seen in FIG. 14 comprises a ultrasonic transducer-supporting/rotating apparatus comprising motor 21, axis of motor 22, substrate of motor 23, coupling (connecting means) 24, rotation axis 25, fixed part of rotary transformer 26a, rotary part of rotary transformer 26b, fixed substrate of transformer 27, sleeve 28, rotary substrate of transformer 29, ring for outer spacer 30, case 31, housing 32, outer spacer 33a, outer spacer 33b, and bearing 34 and a Langevin ultrasonic transducer equipped with a tool. The illustrated ultrasonic transducer-supporting/rotating apparatus is as such well known.

[0104] To the bottom of the ultrasonic transducer-supporting/rotating apparatus is fixed (restrained) a Langevin ultrasonic transducer having piezoelectric elements 35a, 35b fixed between a front mass 36 and rear mass 37 by bolt 38, using a nut 39. The apparatus is fixed as such to a base. In the hollow portion of the front mass 36 of the Langevin ultrasonic transducer is placed and fixed a collet 40 by collet nut 41, and a drill 42 (that is a tool) is inserted and fixed in collet 40.

[0105] FIG. 15 illustrates a constitution of a polishing (or lapping) machine for performing an ultrasonic machining method. The polishing (or lapping) is one of the ultrasonic machining performed according to the ultrasonic machining method of the invention. In the polishing machine, the machining tool is a polishing (or lapping or abrasive) tool which rotates on a central axis of the ultrasonic transducer. In FIG. 15, a circuit for supplying an ultrasonic oscillation-generating energy is not shown.

[0106] The ultrasonic machining apparatus seen in FIG. 15 is in the same constitution as that illustrated in FIG. 14.

[0107] Still in the polishing (or lapping) machine of FIG. 15, a Langevin ultrasonic transducer having piezoelectric elements 35a, 35b fixed between a front mass 36 and rear mass 37 by bolt 38, using a nut 39 is fixed to the bottom. To the lower end of the front mass 36 of the Langevin ultrasonic transducer is placed and fixed an abrasive means in the form of ring (tool) 43 is attached via abrasive supporting means 44 (generally made of aluminum alloy).

[0108] FIG. 16 illustrates a constitution of a cutting machine which can be employed for an ultrasonic machining method according to the invention. The tool employed in the machine is a cutter moving in a back-and-forth mode in the axial direction. In the cutting machine, the machine and/or works (to be machined) are moved in the lateral direction so as to vary their relative locations, and the cutter 52 attached to the ultrasonic transducer vibrates in the axial direction (that is a back-and-forth movement). Therefore, the structure of supporting the ultrasonic transducer does not rotate.

[0109] Accordingly, in the polishing machine of FIG. 16, a Langevin ultrasonic transducer having piezoelectric elements 35a, 35b fixed between a front mass 36 and rear mass 37 having a supporting means in a shape of ring 36a by bolt 38, using a nut 39 is placed in the cylindrical housing 51 on its lower side. The machine is fixed as such to a base. In the hollow portion of the front mass 36 of the Langevin ultrasonic transducer is placed and fixed a collet 40 by collet nut 41, and a cutter 52 (that is a tool) is inserted and fixed in collet 40.

[0110] Each of the electrode plates 53a, 53b formed on each of the piezoelectric elements 35a, 35b is electrically connected to a circuit for ultrasonic generation 54 and supplies electric energy to the ultrasonic transducer.

[0111] In the polishing machine of FIG. 16, foamed plastic material 55 is placed within the housing 51 so as to firmly fix the ultrasonic transducer to the housing 51.

[0112] FIG. 17 illustrates an ultrasonic cleaning apparatus equipped with an ultrasonic transducer, for which the ultrasonic transmission method of the invention can be utilized. In the apparatus of FIG. 17, a Langevin ultrasonic transducer having piezoelectric elements 35a, 35b fixed between a front mass 36 and rear mass 37 by bolt 38 using a nut is fixed to the housing 51 using nut 39. On the top of the front mass 36 of the Langevin ultrasonic transducer is placed and fixed a diaphragm (vibrating plate) 56 by means of a bolt 57.

[0113] FIG. 18 illustrates an ultrasonic sonar, for which the ultrasonic transmission method of the invention can be utilized. Still in the ultrasonic sonar of FIG. 18, a Langevin ultrasonic transducer having piezoelectric elements 35a, 35b fixed between a front mass 36 and rear mass 37 by bolt 38 using a nut is fixed to the housing 51 using nut 39. On the top of the front mass 36 of the Langevin ultrasonic transducer is placed and fixed a transmission means 58 for transmitting ultrasonic wave in the air by means of a bolt 57.

[0114] The apparatus and machine employable for practicing the ultrasonic machining method or ultrasonic transmission method are not limited to those shown in the attached Figures.

[0115] The Pseudo Zero Order Oscillation provided by the invention can be employed in a variety of apparatuses and machines using a Langevin ultrasonic transducer as an ultrasonic oscillation-generating means, for example, machines for plastic working utilizing ultrasonic oscillation, such as a bending machine, a deep drawing machine, an ironing machine and a drawing machine utilizing ultrasonic oscillation, a grinding machine utilizing ultrasonic oscillation, a machine using free abrasive, utilizing ultrasonic oscillation, a bonding machine utilizing ultrasonic oscillation, a plastic molding machine utilizing ultrasonic oscillation, a micro-machining machine utilizing ultrasonic oscillation, a dispersing/atomizing apparatus utilizing ultrasonic oscillation, a ultrasonic motor, a machine for operating cataract utilizing ultrasonic oscillation, an ultrasonic crushing machine, an ultrasonic stone crushing machine, an ultrasonic tooth-operating machine, an ultrasonic continuous casting machine, an ultrasonic erosion-evaluating tester, a polyethylene-cross linking apparatus, an ultrasonic dryer, an ultrasonic air sensor, and an ultrasonic flowmeter.