GB2167270A - Ultrasonic vibratory tools - Google Patents

Abstract

An ultrasonic vibratory tool including first and second substantially identical horns 14, 15 driven from a common source of ultrasonic vibration 11, at least one of said first and second horns 14, 15 being coupled to said source 11 through means including a coupling piece 16, 17 which exhibits unitary amplitude gain and which has an acoustic length of half of a wavelength of the vibration conducted thereby or whole multiples thereof, the physical length of the coupling piece determining the difference in height between the operating tips of the first and second horns. Also disclosed is a method of setting such an ultrasonic vibratory tool. <IMAGE>

Description

SPECIFICATION Ultrasonic vibratory tools This invention relates to ultrasonic vibratory tools such as ultrasonic welding or cutting tools.

It is well known to drive two or more substantially identical horns (the operative part of the tool) from a single source of ultrasonic vibration, such that the horns each operate on a workpiece with the same frequency and amplitude of vibration and at the same spacing from the vibratory source. Where the horns are required to operate on different heights of workpiece such that the spacing of the horn tips from the source differs, then if the height difference is equal to half of the wavelength of vibration of the horns, or multiples thereof, then it is a relatively simple matter to use horns the lengths of which differ by the required number of half wavelengths.However, where the height difference is not a multiple of half wavelengths problems arise since only a very small variation in length, from multiples of the half wavelength, can be tolerated if operational efficiency is not to suffer.

U.S. Reissue Patent 28642 shows, in Figure 8, an arrangement for accommodating height differences in other than multiples of half wavelength. In U.S. Reissue Patent 28642 the two horns differ in size and shape and thus transmit different wavelengths of vibration even though they are driven from a common source. Each of the horns is arranged acoustically to be a multiple of half wavelengths in length and thus will exhibit the necessary antinode at its working tip. However, the physical lengths of the horns differ because of the difference in wavelength conducted by the horns.Thus in other words, the size and shape differences between the horns cause the horns to conduct different wavelengths of vibration and thus although each horn has the same acoustic length in terms of multiples of half wavelength of the vibration conducted by each horn, the physical lengths of the horns differ because of the difference in wavelength conducted. Although such an arrangement permits height variations between the working tips of the horns to be accommodated it has several disadvantages. Firstly the horns differ physically and thus by comparison with the use of identical horns there is the added expense of manufacture and storing of different sets of horns.Bearing in mind that the horns may be relatively expensive to manufacture given the accuracy which is needed, and the high material cost where the horns are formed from such materials as titanium, the expensive of manufacture of different ranges of horns is a very significant factor. Secondly the difference in size and shaping of the two horns, while achieving the height difference, also produces an amplitude gain difference between the horns, the result of which is that although both horn tips will vibrate at the same frequency, the amplitude of vibration at the horn tips will differ. Frequently the two horns will be intended to perform simultaneously the same operation on different regions of the same workpiece and in such circumstances a difference in amplitude of the vibration at the horn tips will give rise to different results where in practice the same result is what is required.Thus there are many instances in which the solution to the height difference problem disclosed in U.S. Reissue Patent 28642 will not be satisfactory.

It is an object of the present invention to provide an ultrasonic vibratory tool wherein two or more horns can operate at different heights in relation to the vibratory source and wherein the problems mentioned above are minimised.

In accordance with the present invention there is provided an ultrasonic vibratory tool including first and second substantially identical horns driven from a common source of ultrasonic vibration, at least one of said first and second horns being coupled to said source through means including a coupling piece which exhibits unitary amplitude gain and which has an acoustic length of half of a wavelength of the vibration conducted thereby or whole multiples thereof, the physical length of the coupling piece determining the difference in height between the operating tips of the first and second horns.

Preferably each of said first and second horns is coupled to said source through means including respective first and second coupling pieces, each of said first and second coupling pieces exhibiting unitary amplitude gain and the construction of said first and second coupling pieces differing whereby the physical lengths of the coupling pieces differ while the acoustic lengths of both first and second coupling pieces are half of a wavelength of the vibration conducted thereby or whole multiples thereof, the difference in the physical lengths in the first and second coupling pieces constituting the difference in height of the operating tips of the first and second horns.

Desirably both of said first and second coupling pieces have an acoustic length of one half wavelength of the vibration conducted thereby so that the difference in height of the operating tips of the first and second horns is equal to half of the physical difference in wavelength of the vibration at the output ends of the connecting pieces.

The invention further resides in a method of setting an ultrasonic vibratory tool so that first and second substantially identical horns of the tool have their operating tips at different heights in relation to the common vibratory source comprising introducing between one of the horns and the source a coupling piece exhibiting unitary amplitude gain and having an acoustic length equal to a half wavelength of the vibration conducted thereby or a whole multiple thereof.

Preferably the method includes the step of inserting a respective coupling piece between each of said first and second horns and said source, each of said first and second coupling pieces exhibiting unitary amplitude gain and each of said first and second coupling pieces having an acoustic length which is a half wavelength of the vibration transmitted thereby or a whole multiple thereof while the construction of the first and second coupling pieces differs such that the physical lengths of the horns are different by an amount equal to the difference in height required between the operating tips of the first and second horns.

In the accompanying drawings: Figure 1 is a diagrammatic representation of a known form of ultrasonic vibratory tool and Figure 2 is a view similar to Figure 1 illustrating one embodiment of the present invention, and Figure 3 is a view similar to Figure 2 of the modification.

Referring first to Figure 1 the known ultrasonic tool includes an ultrasonic drive 11 of known form which may be magnetostrictive or piezoelectric and which converts an electrical input into a mechanical, vibratory output at a frequency which is generally referred to as ultrasonic. A preferred frequency range would be from 20KHz. to 40KHz.

The output end of the drive 11 has rigidly secured thereto the input end of a booster or velocity transformer 12, the effect of which is to achieve an amplitude gain so that the amplitude of vibration at the output end of the transformer 12 is greater than that at the input end. The use of such velocity transformers is well known, and while the amplitude of vibration is increased the frequency of vibration is not changed. Thus the input frequency and the output frequency are the same.

The physical length of the transformer 12 from its input end to its output end is equal to a half wavelength or a whole multiple thereof and thus is determined by the frequency of vibration and the constructional parameters of the transformer 12 such as its shape and density, different materials exhibiting different acoustic properties. Thus while physical lengths may be expressed in conventional units of measurement, acoustic lengths are expressed in terms of the wavelength of vibration within the material for a given frequency of vibration. It follows from this therefore that while two items may have an identical acoustic length for a given common frequency of vibration, the two items may differ in physical length as a result of the use of different materials, or different shapings of the two items.

Rigidly secured to the output end of the transformer 12 is a mother-horn or horn carrier 13 which serves as a common support for, and to conduct vibrational energy to, a pair of horns 14, 15. The length of the carrier 13 is a half wavelength or whole multiple thereof and the horns 14, 15 have one end rigidly secured to the output end of the carrier 13 and are substantially identical to each other, having a length equal to a half wavelength or a whole multiple thereof. It will be understood therefore that the free ends, that is to say the working tips, of both the first and second horns 14, 15 will coincide with antinodes and thus will be points of maximum vibration of the tool. Moreover, both working tips will be at the same spacing from the drive 11 and thus can only operate on parts of a workpiece lying in a common plane at right angles to the length of the horns 14, 15.

Referring now to Figure 2, it will be seen that the tool includes a drive 11, a velocity transformer 12, a mother-horn or carrier 13 and first and second horns 14, 15 which are substantially identical to those described in relation to the construction shown in Figure 1.

However, it can be seen that in this embodiment of the invention a first coupling piece 16 is interposed between the carrier 13 and the horn 14 and a second coupling piece 17 is interposed similarly between the carrier 13 and the second horn 15. Moreover it is evident from Figure 2 that the coupling pieces 16, 17 are of different physical lengths, the difference in physical lengths producing a difference in position of the operating tip of the horns 14, 15 in relation to the drive 11. Thus in the embodiment of the invention shown in Figure 2 a height difference "d" exists between the working tips of the horns 14, 15 and thus parts of a workpiece differing in height by "d" can be operated on by the tool shown in Figure 2.

Each of the coupling pieces 16, 17 is symmetrical about the midpoint of its physical length and thus exhibits unitary amplitude gain. Thus by virtue of the unitary amplitude gain of the connecting pieces 16, 17 there is no change in the amplitude of vibration attributable to the connecting piece and thus the working tips of the horns 14 and 15 will vibrate at a common frequency determined by the drive 11 and a common amplitude determined by the velocity transformer 12. Moreover, it will be recognised that it is essential that the physical length of each coupling piece 16,17 is equal to a half wavelength of the vibration transmitted thereby or a whole multiple thereof. It is here that the difference in physical length is achieved since although both coupling pieces are formed from the same material, conveniently steel or aluminium, the difference in shaping gives rise to a difference in the wavelength for a given frequency of vibration. Thus the shaping of the coupling piece 16 produces, for a given frequency of vibration, a wavelength which is greater than that produced by the differently shaped second coupling piece 17 for the same given frequency. Thus the coupling pieces 16, 17 have the same acoustic length but by virtue of the different wavelengths arising from the different shaping, the coupling pieces have different physical lengths.

Assuming that the coupling pieces 16, 17 have an acoustic length of half a wavelength as will normally be the case (as opposed to whole multiples of half wavelengths) then the difference "d" in height of the working tips of the horns 14, 15 will be equal to half the difference of the wavelengths of the coupling pieces 16, 17.

It will be understood therefore that by modifying the shaping of one of the two coupling pieces in relation to the other a fine control over the difference in height of the working tips of the horns 14, 15 can be achieved.

It will be understood that there will be some values of "d" which can be achieved by providing only one of the horns 14, 15 with a coupling piece. The coupling piece which is used will again be of unitary amplitude gain and will have a length of a half wavelength or whole multiples thereof and thus within a predetermined range it is possible by choice of the shaping of the connecting piece to choose the wavelength and thus to determine the physical length of the connecting piece. In such an arrangement, the difference in height "d" of the working tips of the two horns will be equal to the physical length of the coupling piece in use.

It will be recognised however that using frequencies of vibration within the preferred range and normally preferred materials for the manufacture of the connecting piece, there is a minimum connecting piece length. Frequently the difference in height "d" which is required will be less than this minimum, and in order to achieve such values of "d" it will be necessary to use connecting pieces between each horn and the carrier, the value of "d" being achieved by the difference in construction, that is to say shaping and/or material, of the respective coupling pieces.

It will be recognised that while we have described tools having first and second horns the same principle can be applied to tools having more than two horns.

In each instance, a height difference between the working tips of the horns can be achieved which height difference is not required to be a half wavelength or whole multiples thereof and moreover this height difference can be achieved using identical horns with the attendant advantages of economy in cost and storage, and at the same time maintaining the same amplitude and frequency of vibration at the working tips of the horns.

Figure 2 is to some extent diagrammatic and the modification illustrated in Figure 3 is a practical embodiment of Figure 2. The carrier 13 is slotted at 13a to "tune" its charactaristics and its transformer is not shown. The horns 14, 15 are tapered at their working ends, and the curvatures of the coupling pieces 16, 17 are less pronounced.

Claims (8)

1. An ultrasonic vibratory tool including first and second substantially identical horns driven from a common source of ultrasonic vibration, at least one of said first and second horns being coupled to said source through means including a coupling piece which exhibits unitary amplitude gain and which has an acoustic length of half of a wavelength of the vibration conducted thereby or whole multiples thereof, the physical length of the coupling piece determining the difference in height between the operating tips of the first and second horns.

2. A tool as claimed in claim 1 wherein each of said first and second coupling pieces exhibiting unitary amplitude gain and the construction of said first and second coupling pieces differing whereby the physical lengths of the coupling pieces differ while the acoustic lengths of both first and second coupling pieces are half of a wavelength of the vibration conducted thereby or whole multiples thereof, the difference in the physical lengths in the first and second coupling pieces constituting the difference in height of the operating tips of the first and second horns.

3. A tool as claimed in claim 2 wherein both of said first and second coupling pieces have an acoustic length of one half wavelength of the vibration conducted thereby so that the difference in height of the operating tips of the first and second horns is equal to half of the physical difference in wavelength of the vibration at the output ends of the connecting pieces.

4. An ultrasonic tool substantially as hereinbefore with reference to Figure 2 of the accompanying drawings.

5. An ultrasonic tool substantially as hereinbefore with reference to Figure 3 of the accompanying drawings.

6. A method of setting an ultrasonic vibratory tool so that first and second substantially identical horns of the tool have their operating tips at different heights in relation to the common vibratory source comprises introducing between one of the horns and the source a coupling piece exhibiting unitary amplitude gain and having an acoustic length equal to a half wavelength of the vibration conducted thereby or a whole multiple thereof.

7. A method as claimed in claim 6 including the steps of of inserting a respective coupling piece between each of said first and second horns and said source, each of said first and second coupling pieces exhibiting unitary amplitude gain and each of said first and second coupling pieces having an acoustic length which is a half wavelength of the vibration transmitted thereby or a whole multiple thereof while the construction of the first and second coupling pieces differs such that the physical lengths of the horns are different by an amount equal to the difference in height required between the operating tips of the first and second horns.

8. A method of setting an ultrasonic vibratory tool substantially as hereinbefore with reference to Figures 2 and 3 of the accompanying drawings.