ULTRASONIC VIBRATION SYSTEM WITH MECHANICAL RESONATOR

Description

[0001] The present invention relates to an ultrasonic oscillation system having a converter which can convert an electrical alternating voltage into a mechanical oscillation, and a sonotrode of mass ms which is intended to be set into oscillation with the mechanical oscillation, wherein the converter is coupled to the sonotrode in such a way that the oscillation generated by the converter generates an oscillation excitation of the sonotrode, wherein the ultrasonic oscillation system is intended to be operated with an oscillation of wavelength λ.

[0002] Such ultrasonic vibration systems are well known. The sonotrode, excited by ultrasonic vibrations at wavelengths λ, is used to process materials. The sonotrode comes into contact with the materials to be processed and excites them at their interfaces with ultrasonic vibrations, allowing local heat to be generated. Typically, the material to be processed is positioned between the sonotrode and a counter-tool, also called an anvil.

[0003] For this purpose, the sonotrode has a so-called sealing surface, which is designed to come into contact with the material to be processed. The shape of the sonotrode is usually adapted so that the sealing surface oscillates across its entire length and width with as constant an amplitude as possible, in order to apply an ultrasonic vibration to the material to be processed as evenly as possible across the entire sealing surface.

[0004] Whenever the sealing surface comes into contact with the material being processed, a force is exerted more or less abruptly on the sonotrode, causing unwanted vibration modes, such as those resulting from the special shape of the sonotrode, to be excited. Irregularities in the material being processed can also cause the material to exert an uneven counterforce on the sonotrode along the sealing surface, for example, inducing a bending vibration or distorting the desired vibration shape. This is particularly pronounced in applications where a relatively hard material, such as metal, is processed with a sealing surface arranged on a peripheral surface.

[0005] This vibration shape distortion can negatively impact the desired longitudinal vibration, resulting in phase shifts and, under certain circumstances, uneven movements along the longitudinal direction. These unwanted vibrational movements are transmitted to the converter and thus to the piezoceramics generally arranged within the converter. However, these are not able to absorb such vibrations in the long term. As a result, the temperature of the piezoceramics increases due to excessive stress, reducing their service life.

[0006] It is therefore already common practice to limit welding times or to take longer breaks between individual welding operations to allow the piezoceramics to cool down. In addition, more or less complex cooling devices are provided to increase the welding time of the piezoceramics. Nevertheless, defects in the ceramic of the piezo elements can occur, reducing their service life. In the worst case, this can lead to breakage of the piezoceramic.

[0007] DE 10 2018 132840 describes an ultrasonic vibration system with a converter and a sonotrode, whereby the vibration generated by the converter generates a vibration excitation of the sonotrode.

[0008] Based on the described prior art, it is therefore an object of the present invention to provide an ultrasonic vibration system in which the problems described are at least reduced.

[0009] According to the invention, this object is achieved in that the ultrasonic oscillation system has a mechanical resonator of mass mr, which can be brought into resonance oscillation with an oscillation having the wavelength λ, wherein the mass mr of the resonator is greater than the mass ms of the sonotrode.

[0010] A mechanical resonator is defined as an oscillating system tuned to a frequency and, if applicable, its multiples, such that the system essentially oscillates only at these frequencies, while excitations at other frequencies are significantly attenuated. The resonator is preferably designed as an oscillating body.

[0011] Because the mass mr of the mechanical resonator is relatively large, distortions of the desired oscillation form are significantly reduced.

[0012] In a preferred embodiment, the mass mr of the resonator is at least 100%, preferably at least 150% and particularly preferably at least 200% greater than the mass ms of the sonotrode.

[0013] It is particularly preferred if the mechanical resonator is located between the converter and the sonotrode. Any unwanted vibrations introduced into the system due to contact between the sonotrode and the material to be processed are therefore initially transferred from the sonotrode to the mechanical resonator, which virtually completely cancels out these unwanted vibrations, so that almost no unwanted vibrations are transmitted to the converter and the piezo elements contained therein. However, the mere coupling of the mechanical resonator to the oscillation system ensures that the oscillation mode of the entire oscillation system remains closer to the desired mode.

[0014] In many cases, an amplitude transformer of mass ma is used between the converter and the sonotrode, which changes the amplitude of the ultrasonic oscillation—but not the frequency. This allows the amplitude of an oscillation generated by the converter to be scaled (usually increased but also decreased) before the oscillation is coupled into the sonotrode.

[0015] If such an amplitude transformer is used, the mechanical resonator can be arranged either between the amplitude transformer and the sonotrode or between the amplitude transformer and the converter, with the latter being particularly preferred. Undesirable vibration modes can also be coupled into the system via the amplitude transformer, so the arrangement of the mechanical resonator between the amplitude transformer and the converter also filters these accordingly.

[0016] The transformation properties of the amplitude transformer also usually ensure that the oscillation amplitude of the unwanted oscillations coupled into the system via the sonotrode is only passed on to the mechanical resonator in a reduced form.

[0017] In a further preferred embodiment, the mass mr of the resonator is greater than the sum of the mass ms of the sonotrode and the mass ma of the amplitude transformer.

[0018] Due to the comparatively large mass of the mechanical resonator, unwanted vibration components are filtered or attenuated more strongly.

[0019] However, it is also possible to design the amplitude transformer as a mechanical resonator in the sense of the present invention. In such a case, no additional component is required. Instead, the mass of the amplitude transformer is increased. However, since a bracket is often provided on the amplitude transformer, the corresponding bracket mount must also be modified due to the larger dimensions of the amplitude transformer. However, this may not be possible in all applications due to space constraints.

[0020] In a preferred embodiment, the mechanical resonator has a length of λ / 2 or a multiple thereof. In these cases, the mechanical resonator can be effectively brought into resonance at the wavelength λ.

[0021] In a further preferred embodiment, the mechanical resonator has a length l and can be brought into resonance with a longitudinal oscillation oriented along the length l with a wavelength λ. In a preferred embodiment, the mechanical resonator has a constant cross-section along at least 80% of its length l, with the mechanical resonator particularly preferably having a constant cross-section along at least 95% of its length. Ideally, the mechanical resonator has a constant cross-section over its entire length.

[0022] Alternatively, the mechanical resonator can also have two sections with different cross-sections, each with a constant cross-section along at least 25% of the length l. In this case, the mechanical resonator not only filters or attenuates distortion components of the desired waveform, but also provides amplitude transformation. This mechanical resonator can be used in addition to an existing amplitude transformer or completely replace it.

[0023] These shapes ensure that other vibration modes are very effectively attenuated or filtered out.

[0024] In a further preferred embodiment, the mechanical resonator has a cross-sectional area that is rotationally symmetrical, with the cross-sectional area preferably being circular. For example, the mechanical resonator can have the shape of a cylinder.

[0025] In a further particularly preferred embodiment, the mechanical resonator has an average cross-sectional area Q and a length l, where Q > 0.5 l 2< , preferably Q > l 2< and best Q > 1.5 l 2< . It has been shown that the large average cross-sectional area (in a sectional view perpendicular to the length I) can filter out unwanted vibration very effectively.

[0026] Significantly larger cross-sectional areas do not bring any additional effect, so that in a further preferred embodiment Q < 5 l 2< , preferably Q < 3 l 2< and best Q < 2 l 2< is.

[0027] In another preferred embodiment, the converter is designed as a mechanical resonator. The large mass mr is thus provided by the converter, so that in this case, too, an additional component can be dispensed with.

[0028] Such an ultrasonic vibration system is particularly preferably used for welding metal.

[0029] 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 side view of an embodiment of the invention, Figure 2 a perspective view of the embodiment of the invention of Figure 1 .

[0030] In Figure 1An embodiment of the invention is shown. The ultrasonic vibration system 1 comprises a sonotrode 2 having a first and a second end face, the end faces being arranged opposite one another, and a circumferential lateral surface connecting the two end faces.

[0031] Furthermore, a converter 6 is provided, which has a plurality, namely 4, piezo crystal stacks 9, which are all oriented perpendicular to the longitudinal direction of the ultrasonic vibration unit 1. These piezo crystal stacks 9 convert an electrical alternating voltage into a mechanical vibration. Due to the star-shaped arrangement of the four piezo crystal stacks 9, in the ultrasonic vibration system 1 in the longitudinal direction, which in Figure 1 marked by an arrow, a longitudinal ultrasonic vibration is excited.

[0032] An amplitude transformer 4 is arranged on the first end face of the sonotrode 2, which transforms the oscillation amplitude of the Figure 1 The vibration coupled into the system from the right is magnified and transferred to the sonotrode 2.

[0033] The sonotrode 2 is designed to weld a material, namely a metal strand in the example shown. For this purpose, the sonotrode 2 has a sealing surface arranged on the outer surface, which can come into contact with the metal strand. The sealing surface is arranged on a section of the outer surface facing the second end face.

[0034] A mechanical resonator 5, which here consists of a cylindrical element, is arranged between the amplitude transformer 4 and the converter 6. The length l of the mechanical resonator 5 corresponds to half the wavelength λ of the excitation oscillation generated by the converter 6. The oscillation of wavelength λ generated by the converter 6 is transmitted from the mechanical resonator 5 to the amplitude transformer 4, which transforms the amplitude, or in this case, increases it, and transmits it to the sonotrode 2. The mechanical resonator 5 has two sections 7, 8, each of which has a constant diameter. However, the diameter of section 7, which is arranged closer to the converter 6, is larger than the diameter of section 8, which is arranged closer to the amplitude transformer 4. Section 8 has a length l 1 and section 7 has a length l 2.A transition section with a length l 3 is arranged between sections 7 and 8. The length of the mechanical resonator 5 is thus composed of the lengths l 1 , l 2 , and l 3 (l = l 1 + l 2 + l 3 ). This embodiment has the advantage that the mechanical resonator 5 additionally performs an amplitude transformation.

[0035] Due to the contact of the sonotrode 2 with the metal strand 3, further vibration modes are excited or distortions of the vibration shape occur, which in turn are transmitted from the sonotrode 2 to the amplitude transformer 4. Because the mechanical resonator 5 of length l is arranged between the amplitude transformer 4 and the converter 6, these vibration modes are almost completely filtered by the mechanical resonator 5, or the distortions are significantly attenuated, so that these vibrations are not transmitted to the converter 6 or the piezo elements in the converter 6.

[0036] By arranging a mechanical resonator 5 in the ultrasonic vibration system 1 according to the invention, disturbing vibrations that impair the piezo crystals are effectively filtered out of the system, thus significantly extending the service life of the piezo elements. List of reference symbols

[0037] 1Ultrasonic oscillation system 2Sonotrode 4Amplitude transformer 5,Resonator 6Converter 7,8Resonator sections 9Piezo crystal stack

Claims

1. Ultrasonic oscillating system (1) having a converter (6) which can convert an electrical alternating voltage into a mechanical oscillation, and a sonotrode (2) of mass ms which is intended to be set into oscillation with the mechanical oscillation, the converter (6) being coupled to the sonotrode (2) in such a way that the oscillation generated by the converter (6) generates an oscillation excitation of the sonotrode (2), wherein the ultrasonic oscillating system (1) is intended to be operated with an oscillation of wavelength λ, wherein the ultrasonic oscillating system has a mechanical resonator (5) of mass mr which can be brought into resonant oscillation with an oscillation of wavelength λ, characterized in that the mass mr of the resonator (5) being larger than the mass ms of the sonotrode (2).

2. Ultrasonic oscillating system (1) according to claim 1, characterized in that the mass mr of the resonator (5) is larger than the mass ms of the sonotrode (2) by at least 100%, preferably by at least 150% and particularly preferably by at least 200%.

3. Ultrasonic oscillating system (1) according to claim 1 or 2, characterized in that the mechanical resonator (5) is arranged between the converter (6) and the sonotrode (2).

4. Ultrasonic oscillating system (1) according to one of claims 1 to 3, characterized in that an amplitude transformer (4) of mass ma is arranged between the converter (6) and the sonotrode (2), the mechanical resonator (5) preferably being arranged between the converter (6) and the amplitude transformer (4).

5. Ultrasonic oscillating system (1) according to claim 4, characterized in that the mass mr of the resonator (5) is larger than the sum of the mass ms of the sonotrode (2) and the mass ma of the amplitude transformer (4).

6. Ultrasonic oscillating system (1) according to one of claims 1 to 3, characterized in that the amplitude transformer is designed as the mechanical resonator.

7. Ultrasonic oscillating system (1) according to one of claims 1 to 6, characterized in that the mechanical resonator (5) has a length l of n λ / 2, where n is a natural number, preferably n=1.

8. Ultrasonic oscillating system (1) according to one of claims 1 to 7, characterized in that the mechanical resonator (5) has a length l and can be brought into resonant oscillation with a longitudinal oscillation oriented along the length l and having the wavelength λ, the mechanical resonator (5) having a constant cross-section along at least 80% of its length, or the mechanical resonator having two sections with different cross-sections, each of which has a constant cross-section along at least 35% of the length I.

9. Ultrasonic oscillating system (1) according to one of claims 1 to 8, characterized in that the mechanical resonator (5) has a cross-sectional area which is rotationally symmetrical, the cross-sectional area preferably being circular.

10. Ultrasonic oscillating system (1) according to claim 9, characterized in that the mechanical resonator (5) has the shape of a cylinder.

11. Ultrasonic oscillating system according to any one of claims 1 to 10, characterized in that the mechanical resonator (5) has an average cross-sectional area Q and a length l, where Q > 0,5l2 preferably Q > l2 and best Q > 1,5l2.

12. Ultrasonic oscillating system according to claim 11, characterized in that Q < 5l2preferably Q < 3l2 and best Q < 2l2.

13. Ultrasonic oscillating system (1) according to one of claims 1, 2 or 7 to 12, characterized in that the converter is designed as the mechanical resonator.

14. Use of an ultrasonic oscillating system (1) according to one of the preceding claims for welding metal.