CONVERTER WITH INTEGRATED BOLT

Description

[0001] The present invention relates to a converter for an ultrasonic vibration unit. The converter is intended and designed to convert an alternating electrical voltage into an acoustic vibration.

[0002] The converter comprises a converter base, a bolt, a clamping element, and at least one piezo element with a through-hole. The converter bolt penetrates the through-hole, and the clamping element clamps the at least one piezo element toward the converter base. The converter base has a threaded bore into which the bolt is screwed. Corresponding converters are known, for example, from US 2017 / 274420 A1 or US 2016 / 001498 A1.

[0003] The clamping element ensures that a mechanical vibration of the piezo element is transferred to the converter base part.

[0004] Often, several piezo elements in disc form are mounted one above the other with a bolt and clamped onto a surface of the converter base part with the help of a clamping element designed as a screw nut, so that by applying an alternating electrical voltage to the piezo elements, the piezo elements stimulate a mechanical vibration of the converter base part.

[0005] Such converters are frequently used in ultrasonic vibration units, which consist of a sonotrode and a converter. The converter or converter base is screwed to the sonotrode, so that a mechanical vibration of the converter base is transmitted to the sonotrode. Such ultrasonic vibration units often also have an amplitude transformer, which is located between the converter and the sonotrode and is designed to transform the amplitude of the vibration, i.e., usually increase it. The mechanical vibration generated by the piezo elements is thereby amplified.

[0006] Especially in applications with limited space, the amplitude transformer is often omitted, so larger amplitudes must be generated with the converter. However, with existing converters, this results in an overstressed area forming near the bolt's screw connection to the converter base, significantly reducing the service life of the ultrasonic vibration unit. Over time, cracks typically form in the material near the threaded connection, negatively impacting the vibration behavior.

[0007] This problem has so far been addressed by, for example, reducing the preload, i.e., the force with which at least one piezo element is pressed against the converter base. However, this reduces the oscillation amplitude and the oscillation quality due to the poorer coupling between the piezo element and the converter base, which is not acceptable for all applications. Another option is to reduce the amplitude of the applied alternating voltage, which consequently also reduces the amplitude of the ultrasonic oscillation. Again, this measure is not suitable for all applications. In any case, it increases the required processing time.

[0008] Finally, attempts were made to control the tension by using special thread forms with specially selected corner radii and a corresponding undercut in the bore of the converter base, into which the bolt is screwed. This does indeed lead to an increase in service life; however, it is comparatively complex and therefore expensive.

[0009] In practice, these systems can therefore only be operated with low vibration amplitudes and also have a limited service life.

[0010] Further converters designed to generate small vibration amplitudes can be found in WO 2008 / 156116, DE 100 23 302 A1 and US 2018 / 0304308 A1.

[0011] Based on the described prior art, it is therefore an object of the present invention to provide a converter that can be operated with high amplitudes and at the same time ensures a long service life. According to the invention, this object is achieved by claim 1

[0012] A material connection is understood to mean all connections in which the connecting partners, ie here the bolt of the converter and the converter base part, are held together by atomic or molecular forces.

[0013] In principle, the bolt can be welded or soldered to the converter base.

[0014] However, this is also complex. Therefore, in a preferred embodiment, the bolt and the converter base are advantageously manufactured from a single piece of material. The bolt and the converter base are therefore formed as a single piece.

[0015] According to the invention, the bolt is provided at its connection point to the converter base part with a transition radius R which is greater than 0.5 mm, preferably >1 mm and particularly preferably >2 mm.

[0016] Providing a transition radius stabilizes the bolt and converter base, as a smaller notch factor reduces the stresses in the material. In principle, the larger the transition radius, the greater the stabilization. However, it is important to note that the piezo element is pushed over the bolt and pressed against the converter base. Contact between the piezo element and converter base is necessary to ensure the fullest possible surface area to transmit the ultrasonic vibration and avoid damaging the piezo element. Piezo elements are usually made of piezoceramics, which are very brittle and therefore sensitive to tensile stresses, e.g., resulting from deformation. The piezo element must therefore not be in contact with the transition radius.

[0017] In a further preferred embodiment, a spacer disk with a through-opening is provided, wherein the spacer disk and the at least one piezo element are arranged such that the bolt first penetrates the through-opening of the spacer disk and then the through-opening of the at least one piezo element, so that the spacer disk rests against both the converter base and the piezo element. The spacer disk, which can be made of titanium or a titanium alloy, for example, is helpful to ensure optimal power transmission.

[0018] Since, according to a preferred embodiment, the converter base and bolt are manufactured from a single piece, it is technically impossible to produce a high-quality surface finish on the surface of the converter base in the area where it connects to the bolt. Conventional lapping processes cannot be performed due to the presence of the bolt. However, any unevenness on the surface of the converter base reduces vibration transmission when the piezo element rests against this surface. By providing a spacer disk, which can be manufactured with a very high surface quality (roughness Ra < 0.01 and flatness < 0.005 mm), at least a high-quality ultrasonic vibration transmission from the at least one piezo element to the spacer disk is possible.If the spacer disc is pressed onto the possibly not entirely flat surface of the converter base, the ultrasonic vibration is still transmitted better than if the piezo element were pressed directly onto the surface of the converter base.

[0019] In a further preferred embodiment, the through-opening of the spacer widens at least on the side facing the converter base. This can be achieved, for example, by providing the corresponding edge with a chamfer. It may be advantageous to also design the other side of the spacer in a similar manner. This has the advantage that, during assembly of the ultrasonic vibration system, it is not necessary to ensure that the spacer is slid onto the converter bolt in the correct orientation.

[0020] The widened portion is particularly advantageous when the bolt is provided with a transition radius at the connection to the converter base, since the spacer disk can then rest flatly on the converter base, even if the transition radius is relatively large. In a preferred embodiment, the widened portion is designed such that the through-opening of the spacer disk, in a sectional view parallel to the longitudinal direction along the length l, has an entry radius E on its side facing the converter base, which is >0.5 mm, preferably >1 mm, and particularly preferably >2 mm.

[0021] In particular, it is advantageous if the entry radius E is: 2 R > E ≥ R , preferably: 1.2 R > E > R

[0022] In a further preferred embodiment, the bolt has an end section facing away from the converter base and provided with an external thread. It has been shown that the external thread is best designed as a buttress thread. The buttress thread is asymmetrical and has a profile resembling a sawtooth.

[0023] As already mentioned above, in a preferred embodiment it is provided that the bolt and the converter base part are made of one piece of material.

[0024] Due to this measure, the material consumption is usually higher, since the bolt of the converter has a significantly smaller extension in the transverse directions, i.e. perpendicular to the longitudinal axis, which runs along the length l, than the converter base part and accordingly in the one-piece production in the area of ​​the bolt a lot of material has to be removed in order to produce the bolt.

[0025] The described measure is therefore particularly advantageous when the converter is designed as a sonotrode. The converter base has a sealing surface designed to come into contact with the material to be processed.

[0026] Such sonotrodes with an integrated converter are also called compact transducers. In a compact transducer, the bolt is located inside the sonotrode. This means that the sonotrode, or rather its converter base, has a sealing surface designed to come into contact with the material being processed, and a rear side opposite the sealing surface. A recess is formed in the rear side in which the bolt is located.

[0027] Due to this arrangement of the bolt within the sonotrode, virtually no additional material is required to form the bolt. In fact, since the converter bolt remains intact, the recess in the rear side does not need to be completely cleared in this design, which actually saves material.

[0028] In a further preferred embodiment, it is provided that the converter has a length l from the sealing surface to the rear side, wherein the bolt extends in the direction of the length l, wherein the length l preferably corresponds approximately to half the wavelength of an ultrasonic oscillation with which the converter designed as a sonotrode can be brought into a resonant oscillation.

[0029] In a further preferred embodiment, it is provided that the position at which the bolt is attached to the converter base part is arranged near the center of the length l, ie from the sealing surface with the distance d, for which the following applies: 0.4 l > d > 0.71, is spaced.

[0030] It is particularly preferred if the at least one piezo element is arranged in the longitudinal direction within the length l, ie between the sealing surface and the back.

[0031] For example, at least four piezo elements can be provided, each with a through-hole through which the bolt passes. These elements are all arranged in the longitudinal direction between the sealing surface and the rear side of the converter base, i.e., within the length l. This has advantages in terms of vibration control, since the sonotrode is now essentially excited internally.

[0032] Further advantages, features, and possible applications of the present invention will become clear from the following description of a preferred embodiment and the accompanying figures. They show: Figure 1 a perspective view of a converter according to the invention, Figure 2 a sectional view through the embodiment of Figure 1 , Figure 3 a partially sectioned side view of the embodiment of Figure 1 and Figure 4 a sectional view through the embodiment of Figure 1 without piezo elements.

[0033] In Figure 1 A perspective view of a converter according to the invention is shown. The converter 1 is designed as a sonotrode and has a sealing surface 2. The sealing surface 2 is intended to come into contact with a material to be processed and to transmit an ultrasonic vibration into the material.

[0034] The converter 1 has a converter base 3, which has a rear portion 10 with a back side arranged opposite to the sealing surface 2, and a front portion 11, as shown in the cross-sectional view of Figure 2 is clearly visible. A circumferential collar 15 represents the boundary between the front section 11 and the rear section 10. During vibration, a standing wave forms in the longitudinal direction along the length l in the converter. The circumferential collar is located near a vibration minimum. The converter can be secured to the circumferential collar, e.g., via O-rings, without significantly influencing the vibration behavior of the converter.

[0035] The front section 11, which has the sealing surface 2, is largely significantly narrower than the rear area 10. This results in an amplitude transformation in this area. In the rear area 10, a recess is formed in the converter base, in which a bolt 4 is integrally connected to the converter base 3.

[0036] In Figure 3 a partially sectioned side view of converter 1 is shown.

[0037] The converter base part 3 has a length l, which is composed of the length of the rear section 10 and the length of the front section 11 of the converter base part 3. The length l thus defines the distance between the sealing surface 2 and the rear side of the converter base part. During use, a standing wave forms in the converter with a wavelength equal to twice the length l.

[0038] In the front section 11 of the converter base part 3, a slot 9 is also provided, which does not extend to the sealing surface 2. The slot 9 is arranged on the axis of the bolt 4 in order to improve the vibration behavior of the converter base part 3, which is designed as a sonotrode. A spacer disk 7 with a corresponding central opening is first pushed over the bolt 4. The spacer disk 7, which, like the converter base part 3 including the bolt 4, can be made of titanium, serves to absorb any unevenness on the surface of the converter base part in the immediate vicinity of the bolt 4. The spacer disk 7, which should rest as flat as possible on the surface of the converter base part 3, can nevertheless tolerate minor deviations in the surface quality without damaging the spacer disk 7. The spacer disk also distributes the force of the bolt evenly across the piezo elements.This prevents the risk of overloading the piezo elements due to uneven force application.

[0039] The upper side of the spacer disc 7, i.e., the side facing away from the surface of the converter base, is preferably provided with a high surface quality. This can be achieved, for example, by grinding or lapping.

[0040] Mounted on the spacer disk 7 are several piezo elements 6, six in the example shown, which are intended to convert an electrical alternating voltage signal into a mechanical oscillation. On the side of the piezo elements 6 facing away from the converter base part 3, there is a thrust washer 5, which can be made of steel, for example. The bolt 4 has an external thread on its end section facing away from the converter base part 3, which in the example shown is designed as a buttress thread, into which a nut 8 engages. By tightening the nut 8, a force is exerted on the thrust washer 5 and, via the thrust washer 5, on the piezo elements 6, which in turn transmit the oscillation via the spacer element 7 to the converter base part 3, which is designed as a sonotrode.

[0041] It can be seen that the piezo elements 6, the spacer disk 7 and the pressure disk 5 have an inner diameter that is slightly larger than the outer diameter of the bolt 4, so that they can expand or contract in the axial direction, i.e. in the direction of length l, without this having any effect on the bolt 4. The piezo elements can therefore perform an acoustic oscillation without this being influenced by the bolt 4. Furthermore, care must be taken to ensure that the considerable electrical voltages applied to the piezo elements are not dissipated via the bolt. For this reason, too, there must be a sufficiently large distance between the outer diameter of the bolt 4 and the inner diameter of the piezo elements 6.

[0042] In Figure 4 is a partially sectioned side view of the converter 1. The Figures 1-3The piezo elements 6 shown as well as the spacer disc 7, the pressure element 5 and the nut 8 have been removed.

[0043] In this figure it can be clearly seen that the bolt has a transition radius 12, which in the example shown is 0.75 mm.

[0044] The bolt has a threaded section 14 at its end facing away from the converter base part, onto which the nut 8 can be screwed in order to press the piezo elements 6 together with the pressure element 5 and the spacer element 7 against the converter base part 3.

[0045] The described one-piece design of the converter bolt 4 and converter base 3 significantly improves the service life of the ultrasonic vibration unit 1. The bolt is required to hold the nut 8, which applies the necessary force to the piezo elements to press them against the converter base (or against the spacer disk). List of reference symbols

[0046] 1 Converter 2 Sealing surface 3 Converter base 4 Bolt 5 Pressure washer 6 Piezo element 7 Spacer 8 Nut 9 Slot 10 Rear section 11 Front section 12 Transition radius 14 Threaded section 15 Collar

Claims

1. Converter having a converter base part, a bolt (4) connected to the converter base part, a tensioning element and at least one piezo element (6) with a through-opening, the bolt (4) penetrating the through-opening and the tensioning element tensioning the at least one piezo element in the direction of the converter base part, wherein the converter is designed as a sonotrode and the converter base part has a welding surface which is intended to come into contact with a material to be processed, and wherein the converter base part has a rear side which is arranged opposite the welding surface (2), wherein a recess is formed in the rear side in which the bolt (4) is arranged, characterized in that the bolt (4) is materially bonded to the converter base part , and the bolt (4) is provided with a transition radius R at its connection point to the converter base part, which is 0.5 mm.

2. Converter according to claim 1, characterized that the bolt (4) and the converter base part are manufactured from one piece of material.

3. Converter (1) according to claim 1 or 2, characterized in that the transition radius R is >1 mm and preferably >2 mm.

4. Converter (1) according to one of the claims 1-3, characterized in that a spacer disc (7) with a through-opening is provided, the spacer disc (7) and the at least one piezo element (6) being arranged in such a way that the bolt (4) first penetrates the through-opening of the spacer disc (7) and then the through-opening of the at least one piezo element (6), so that the spacer disc (7) abuts both the converter base part and the piezo element (6).

5. Converter (1) according to claim 4, characterized in that the through-opening of the spacer disc (7) widens on its side facing the converter base part, the through-opening of the spacer disc (7) preferably having, in a sectional view parallel to the longitudinal direction along the length l, an entry radius E on its side facing the converter base part which is > 0.5 mm, preferably > 1 mm and particularly preferably > 2 mm.

6. Converter (1) according to claim 5, characterized in that the following applies to the entry radius E: 2 R > E ≥ R, wherein the following applies preferably: 1.2 R > E > R.

7. Converter (1) according to any one of claims 1 to 6, characterized in that the bolt (4) has an end portion facing away from the converter base part and provided with an external thread, preferably the external thread being a saw thread.

8. Converter according to one of the claims 1-7, characterized in that the converter has a length I from the welding surface to the rear side, the bolt extending in the direction of the length l, preferably the length I corresponding to half the wavelength of an ultrasonic oscillation with which the converter designed as a sonotrode can be brought into a resonant oscillation.

9. Converter according to claim 8, characterized in that the at least one piezo element (6) is arranged in the longitudinal direction within the length l, preferably at least four piezo elements (6) each with a through-opening being provided, which are penetrated by the bolt (4) and which are all arranged in the longitudinal direction within the length l.