Patent Application
20180304308
The present invention relates to an oscillation generation method for Langevin ultrasonic transducer, and particularly relates to a method of generating an ultrasonic oscillation of a novel mode. Further, the invention relates to an ultrasonic machining method and an ultrasonic transmission method, either of which utilizes the ultrasonic oscillation of a novel mode.
A variety of ultrasonic transducers utilizing piezoelectric elements as the ultrasonic generating means are known. One of representative ultrasonic transducers is a Langevin ultrasonic transducer which comprises a pair of metal blocks and polarized piezoelectric elements fixed between the metal blocks. In particular, a bolted Langevin ultrasonic transducer which comprises a pair of metal blocks and polarized piezoelectric elements fixed firmly between the metal blocks by means of a bolt is known as Langevin ultrasonic transducer for generating an ultrasonic oscillation with increased energy. Therefore, the bolted Langevin ultrasonic transducers have been studied in the use of ultrasonic machining procedures such as cutting, plastic working, and abrasive grain machining. Further, a variety of ultrasonic transducers find their uses in combination with a diaphragm or an oscillation transmitting means to transmit the generated ultrasonic oscillation to the outside. For instance, ultrasonic workings such as ultrasonic cleaning, metal welding, plastic working, ultrasonic atomizing, ultrasonic emulsifying, and ultrasonic dispersing; and utilization for a variety of ultrasonic transmitting means such as sonar (e.g., fish detector), ultrasonic crack detector, medical echo detection system, and flow meter, are studied and utilized.
A variety of ultrasonic transducers including the bolted Langevin ultrasonic transducer are known with their constitutions. For the sake of reference, a constitution of a representative bolted Langevin ultrasonic transducer and its working embodiment are briefly explained hereinafter, by referring to the attached
It is expected that the use of ultrasonic machining apparatus is to reduce electric energy required for the machining and to improve accuracy and precision of the machining. Nevertheless, it appears that the conventional ultrasonic machining apparatuses cannot give satisfactory results, and hence, ultrasonic machining is still not widely employed.
Therefore, it is desired that electric energy required to generate an ultrasonic oscillation in an ultrasonic transducer is reduced and the accuracy/precision of machining is increased.
The inventor of the present inventor has until now continued studies for developing a number of ultrasonic transducers which work with reduced electric energy for generating an ultrasonic oscillation and for improving accuracy and precision of machining. Some of these studies results in inventing new system for generating ultrasonic oscillation. One of the recent inventions is disclosed in Patent Publication 1 (WO 2014/017460 A1).
Patent Publication 1 discloses a support structure which supports an oscillating complex comprising a tool and an ultrasonic oscillator with increased stability and reducing leakage of ultrasonic oscillation generated in the oscillating complex to a base supporting the complex, whereby enabling application of oscillation energy to the tool at an increased efficiency. The support structure comprises engagement of a flange formed on the oscillating complex and a flange formed on a separately provided supporting base, in which the engagement is made by bringing one surface of the flange of the oscillating complex into contact with the flange of the supporting base under stress, provided that the flange of the oscillating complex is not bonded to the flange of the supporting base, and that the flange of the oscillating complex engaged with the flange of the supporting base oscillates in the thickness direction of the same flange when the oscillating complex oscillats.
The ultrasonic machining apparatus utilizing the support structure described in Patent Publication 1 is able to solve a portion of the problems observed in the conventional ultrasonic machining apparatuses employing the known ultrasonic transducer. However, as a result of the inventor's further studies, it has been confirmed that the ultrasonic machining apparatus described in Patent Publication 1 cannot reduce the required electric energy at well satisfactory level and further cannot improve machining accuracy and precision at well satisfactory level.
Accordingly, it is an object of the invention to provide a new system employing a new structure of ultrasonic transducer and a new mode of ultrasonic oscillation which enables reduction of electric energy and improvement of machining accuracy and precision at well satisfactory levels.
In the first stage, the inventor of the present invention has studied the mechanism of generation of ultrasonic oscillation for the purpose of modifying the supporting structure of an ultrasonic transducer.
In the beginning of the study, the inventor has designed a model of a new supporting structure for firmly supporting an ultrasonic transducer, which is shown in
The electric energy of a voltage having a prescribed frequency is supplied to the piezoelectric elements 3a, 3b of the bolted Langevin ultrasonic transducer 1 through a hole formed on the housing 11 from an ultrasonic oscillating circuit 8 arranged outside of the housing 11.
In the second stage, oscillation characteristics of an ultrasonic transducer supported and fixed onto the supporting structure shown in
The bolted Langevin ultrasonic transducer 1 having a structure and sizes shown in
The admittance curve of
In contrast, the admittance curve of
The presence of the two admittance peaks observed in the admittance curve of
Based on the above-mentioned understanding, the inventor has conducted additional experiments comprising measurements of axial displacement of the lower end of the front mass 2b under oscillation in the axial direction by applying an electric energy of a voltage having a frequency near to either of the above-identified two resonance frequency to a bolted Langevin ultrasonic transducer 1 of
As a result of the above-mentioned measurement of the axial displacement of the lower end of the front mass 2b using a laser Doppler vibration indicator, the following data have been obtained.
The axial displacement of the lower end of the front mass 2b measured when an electric power of a voltage having a frequency of 43.86 kHz (which is near to the frequency of the larger admittance peak seen in
In contrast, the axial displacement of the lower end of the front mass 2b measured when an electric power of a voltage having a frequency of 23.64 kHz (which is near to the frequency of the smaller admittance peak seen in
Accordingly, it was concluded that the axial displacement caused by ultrasonic oscillation (primary axial oscillation) observed in the ultrasonic transducer when an electric power of a voltage having a frequency corresponding to the frequency of the relatively large admittance peak observed in the admittance curve of
In contrast, the electric power required for generating ultrasonic oscillation to cause essentially same displacement in the generation was approx. 1/7 (0.5 W/3.5 W) in the latter case, as compared from the former case.
Accordingly, it was concluded that an electric power required for generating an ultrasonic oscillation in a bolted Langevin ultrasonic transducer of
In the next stage, a collet equipped with a tool was placed in the tapered hollow of the front mass 2b of the bolted Langevin ultrasonic transducer having the constitution of
In advance of the measurement of the displacements, an admittance curve for the bolted Langevin ultrasonic transducer of
In consideration of the frequency of the admittance peak, an electric power of a voltage having a frequency of 30.20 kHz (for the higher resonance frequency) or a voltage having a frequency of 21.09 kHz (for the lower resonance frequency) was applied to the bolted Langevin ultrasonic transducer.
The above-mentioned measurements indicate the following:
in the case that an ultrasonic oscillation is generated in the ultrasonic transducer having a tool by applying an electric power of a voltage having the higher resonance frequency, the axial displacement of the front end of the tool was 8.33 μm p-p, the lateral displacement of the front end of the tool was 0.787 μm p-p, and the electric power required for the generation of ultrasonic oscillation was 1.17 W; and
in the case that an ultrasonic oscillation is generated in the ultrasonic transducer having a tool by applying an electric power of a voltage having the lower resonance frequency, the axial displacement of the front end of the tool was 7.70 μm p-p, the lateral displacement of the front end of the tool was 0.248 μm p-p, and the electric power required for the generation of ultrasonic oscillation was 0.31 W.
Accordingly, it was concluded that the axial displacement of the front end of the tool caused by the ultrasonic oscillation generated in either case was essentially the same, while the lateral displacement of the front end of the tool caused by the ultrasonic oscillation generated by the application of electric power of a voltage having a lower resonance frequency was approx. ⅓ (0.248/0.787), as compared with the lateral displacement of the front end of the tool caused by the ultrasonic oscillation (primary axial oscillation) generated by the application of electric power of a voltage having a high resonance frequency. In addition, the electric power required for the generation of ultrasonic oscillation was approx. ¼ (0.31/1.17) in the case that the ultrasonic oscillation was generated by applying an electric power of a voltage having the lower resonance frequency, as compared with the case that the ultrasonic oscillation was generated by applying an electric power of a voltage having the higher resonance frequency, that is, a primary axial oscillation. Thus, the electric power required for generation of an ultrasonic oscillation was prominently reduced.
From the experimental results described above, it was concluded that the electric power required for generation of an ultrasonic oscillation is prominently reduced if an electric power of a voltage having a resonance frequency seen in a frequency area lower than a resonance frequency for generating the primary axial oscillation. In addition, the lateral oscillation (rolling vibration) accompanying the axial oscillation is also prominently reduced.
In the additional stage, the inventor studied the characteristics of the ultrasonic oscillation generated in the ultrasonic transducer when an electric power of a voltage having a resonance frequency corresponding to an admittance peak appearing on a side lower than an admittance peak corresponding to the resonance frequency for generating a primary axial oscillation, using “ANSYS” (available ANSYS Japan), a commercially available software for analysis according to FEM (Finite Element Method).
In the study, an ultrasonic oscillation generated in the Langevin ultrasonic transducer of
The analytical image of ultrasonic oscillation produced in the ultrasonic transducer when an electric power of a voltage having a resonance frequency corresponding to the admittance peak appearing on the side lower than the admittance peak corresponding to the frequency for the primary axial oscillation, which was given by the analysis according to FEM by means of ANSYS is shown in
As is clear from the analytical image of
Accordingly, it is concluded that the Pseudo Zero Order Oscillation is clearly different from the primary axial oscillation that has one node in the ultrasonic transducer and two divided portions oscillating in opposite axial directions from the site of node. Therefore, it is assumed that the oscillation according to the Pseudo Zero Order Oscillation mode shows such advantages as reduction of loss of electric power applied to the ultrasonic transducer and reduction of lateral oscillation.
In contrast, the oscillation caused by the application of an electric power of a voltage having a resonance frequency generating the primary axial frequency has one node in the ultrasonic transducer, and the oscillation is divided from the site of node to give oscillations in the opposite directions. This is seen in
Thus, the present invention was obtained based on the new discovery on the ultrasonic oscillation of the Langevin ultrasonic transducer.
Accordingly, there is provided by the invention 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.
Further, there is provided a method of the invention 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.
Furthermore, there is provided a method of the invention 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.
Furthermore, there is provided 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.
Furthermore, there is provided an ultrasonic machining method of the invention, in which the tool rotates on a central axis of the Langevin ultrasonic transducer.
Furthermore, there is provided an ultrasonic machining method of the invention, in which the tool is selected from the group consisting of an end mill, a drill, a polishing tool and a grinding tool.
Furthermore, there is provided an ultrasonic machining method of the invention, in which the tool moves with back-and-forth motion along a central axis of the Langevin ultrasonic transducer.
Furthermore, there is provided an ultrasonic machining method of the invention, in which the tool is selected from the group consisting of a cutting tool, a diaphragm and a welding tool.
Furthermore, there is provided 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.
The method according to the invention enables to generate in an ultrasonic transducer an ultrasonic oscillation of a novel mode, which is named Pseudo Zero Order Oscillation. The ultrasonic machining method of the invention utilizing the Pseudo Zero Order Oscillation enables not only to save an electric power for performing ultrasonic machining but also to improve machining accuracy or precision. In addition, the ultrasonic transmitting method of the invention utilizing the Pseudo Zero Order Oscillation enables to save an electric power for the transmission. Further, the ultrasonic transmission with high efficiency is expected, because the Pseudo Zero Order Oscillation is transmitted with increased directivity.
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.
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
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
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.
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.
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.
There is a case in which an ultrasonic transducer that has the structure of
For the sake of confirmation, however, it is indicated that the he constitution of structure for supporting an ultrasonic transducer (shown in
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.
Details of the data on which the above-mentioned conclusion is derived are again explained hereinbelow.
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.
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.
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
As is described hereinbefore,
The oscillation seen in the image of
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
The figures seen in
For instance, a cutter is attached to the end of the front mass on the right side in
The ultrasonic machining apparatus seen in
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.
The ultrasonic machining apparatus seen in
Still in the polishing (or lapping) machine of
Accordingly, in the polishing machine of
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.
In the polishing machine of
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-216119 | Oct 2015 | JP | national |
| 2015-232362 | Nov 2015 | JP | national |
| 2016-040472 | Feb 2016 | JP | national |
| 2016-097209 | May 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/080514 | 10/14/2016 | WO | 00 |
