Converter with integrated bolts

Abstract

A converter is disclosed that includes a converter base, a bolt (4) connected to the converter base, a tension element, and at least one piezoelectric element having a through hole through which the bolt (4) passes, the tension element applying tension to the at least one piezoelectric element in the direction of the converter base. The disclosed converter is characterized in that the bolt (4) is material-bonded to the converter base.

Description

[Technical field]

[0001] The present invention relates to a converter for ultrasonic vibrations, the converter being adapted and adapted to convert an AC voltage into acoustic vibrations. [Background technology]

[0002] The converter has a converter base, a bolt, a tension element, and at least one piezoelectric element having a through opening, the bolt of the converter passing through the through opening and the tension element applying tension to the at least one piezoelectric element in the direction of the converter base. The converter base has a threaded hole into which the bolt is screwed. Corresponding converters are known from US 2017 / 274420 and US 2016 / 001498.

[0003] The tension element ensures that the mechanical vibrations of the piezoelectric element are transmitted to the converter base.

[0004] In this case, several piezoelectric elements are often stacked together in the form of disks with bolts and clamped to one surface of the converter base with the aid of a tension element in the form of a screw nut, and by applying an AC voltage to the piezoelectric elements, the piezoelectric elements excite the mechanical vibration of the converter base.

[0005] Many such converters are used in an ultrasonic vibration section consisting of a sonotrode and a converter. The converter or the converter base is screwed onto the sonotrode so that the mechanical vibrations of the converter base are transmitted to the sonotrode. Often such ultrasonic vibration sections also have an amplitude converter arranged between the converter and the sonotrode and intended to convert, i.e. generally increase, the amplitude of the vibrations, thereby amplifying the mechanical vibrations generated by the piezoelectric element.

[0006] In applications, especially in confined spaces, the amplitude converter is often omitted, and so it is necessary to use a converter to generate larger amplitudes. However, in known converters, this results in the formation of overstressed areas in the area where the bolt is screwed into the converter base, which significantly reduces the life of the ultrasonic vibration part. Generally, cracks form in the material near the screw connection over time, which has a negative effect on the vibration behavior.

[0007] This problem has been addressed, for example, by reducing the preload, i.e. the force pressing at least one piezoelectric element against the converter base. However, this reduces the vibration amplitude and quality due to a weaker connection between the piezoelectric element and the converter base, which is not acceptable for all applications. Another possibility is to reduce the amplitude of the applied AC voltage, and thus the amplitude of the ultrasonic vibrations. This measure, too, is not suitable for all applications. In any case, it increases the required processing time.

[0008] Finally, there have been attempts to control stresses by using specially selected corner radii and corresponding undercuts in the bores in the converter base into which the bolts thread, which in fact lead to increased life, but are relatively complicated and therefore expensive.

[0009] In practice, these systems can therefore only be operated at low vibration amplitudes and have a limited operating time.

[0010] Other converters intended to generate small vibration amplitudes are disclosed in WO 2008 / 156116, DE 10023302 and US 2018 / 0304308. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2017 / 274420 [Patent Document 2] US Patent Application Publication No. 2016 / 001498 [Patent Document 3] International Patent Application Publication No. 2008 / 156116 [Patent Document 4] DE 100 23 303 [Patent Document 5] US Patent Application Publication No. 2018 / 304308 Summary of the Invention [Problem to be solved by the invention]

[0012] Based on the above-mentioned prior art, it is therefore an object of the present invention to provide a converter which can be operated at high amplitudes and at the same time ensure long operating times. [Means for solving the problem]

[0013] According to the invention, this problem is solved by: This problem is solved by claim 1.

[0014] A material bond is understood as any connection in which corresponding connection sites, i.e. here the converter bolt and the converter base, are held together by atomic or molecular forces.

[0015] In principle the bolts can be melted or welded to the converter base.

[0016] However, this is time consuming, therefore in a preferred embodiment the bolt and converter base are made from one piece of material, so that the bolt and converter base are integrally formed together.

[0017] According to the present invention, The bolt is provided with a transition radius R at its connection with the converter base that is greater than 0.5 mm, preferably greater than 1 mm, more preferably greater than 2 mm.

[0018] By providing the transition radius, the notch effect coefficient is reduced and the stresses in the material are relieved, which leads to stabilization between the bolt and the converter base. In principle, the larger the transition radius, the greater the stabilization. However, it should be noted that the piezoelectric element is pressed onto the bolt and against the converter base. This requires contact between the piezoelectric element and the converter base over as much of the entire surface as possible in order to transmit the ultrasonic vibrations and not damage the piezoelectric element. The piezoelectric element is usually made of piezoelectric ceramic, which is very brittle and highly sensitive to tensile stresses, which result in deformation. The piezoelectric element must therefore not be located at the transition radius.

[0019] In a further preferred embodiment, it is provided that a spacer disk is provided with a through opening, said spacer disk and said at least one piezoelectric element being arranged such that said bolts pass first through said through openings of said spacer disk and then through said through openings of said at least one piezoelectric element, said spacer disk abutting both said converter base and said piezoelectric element. To ensure optimal force transmission, it is useful for example to use a spacer disk made of titanium or a titanium alloy.

[0020] According to a preferred embodiment, since the converter base and the bolt are made from one piece, from a manufacturing point of view it is not possible to manufacture the surface of the converter base in the connection area with the bolt with high surface quality. A normal lapping process cannot be performed due to the presence of the bolt. However, the inhomogeneity in the surface of the converter base reduces the transmission of vibrations when the piezoelectric element abuts against it. By providing a spacer disc, which can be manufactured with a very high surface quality (roughness Ra less than 0.01 and flatness less than 0.005 mm), a transmission of at least one ultrasonic vibration from the at least one piezoelectric element to the spacer disc is possible with high quality. Even if the spacer disc is pressed against a completely non-flat surface of the converter base, the ultrasonic vibrations are transmitted better than if the piezoelectric element were pressed directly against the surface of the converter base.

[0021] In another preferred embodiment, the through openings of the spacer disk are enlarged on its side facing the converter base. This is obtained, for example, by chamfering the corresponding edges. It is advantageous to design the opposite side of the spacer disk accordingly. This is advantageous in that when assembling the ultrasonic vibration system, it is not necessary to check that the spacer disk is pressed in the correct orientation relative to the converter bolts.

[0022] The widening is particularly advantageous if a transition radius is provided at the connection of the bolt to the converter base, since the spacer disc can rest flat on the converter base even if the transition radius is relatively large. In a preferred embodiment, the widening is designed in such a way that in a cross section parallel to the longitudinal direction along the length I, the through opening of the spacer disc has, on the side facing the converter base, an entrance radius E of more than 0.5 mm, preferably more than 1 mm, particularly preferably more than 2 mm.

[0023] In particular, it is advantageous if the inlet radius E is such that 2R>E>R, preferably 1.2R>E>R, applies.

[0024] In a further preferred embodiment, the bolt has an end facing away from the converter base and provided with an external thread, and in this respect it has been found to be optimal for the external thread to be formed as a buttress thread, which is asymmetrical and has a profile resembling the teeth of a saw.

[0025] As previously mentioned, in a preferred embodiment, the bolt and the converter base are made from a single piece of material.

[0026] By this means, the material consumption is usually high, since the converter bolt has a much smaller extension in the transverse direction, i.e. perpendicular to the longitudinal axis extending along the length I, than the converter base, and therefore, in order to manufacture the bolt, it is necessary to remove a lot of material in the area of ​​the bolt in one piece of manufacture.

[0027] The above-mentioned measures are therefore particularly advantageous when the converter is designed as a sonotrode: the converter base has a welding surface which is intended to come into contact with the material to be processed.

[0028] Such a sonotrode integrated with a converter is also called a compact vibrator, in which the bolt is located inside the sonotrode, i.e. the sonotrode or its converter base has a welding surface intended to come into contact with the material to be processed and a rear side arranged opposite said welding surface, whereby a recess is formed in the rear side where the bolt is located.

[0029] This arrangement of the bolt inside the sonotrode means that practically no additional material is needed to form the bolt, and conversely, this embodiment also saves material, since the converter bolt is kept in place and so the recess in the rear side does not need to be fully drilled.

[0030] In a further preferred embodiment, the converter has a length I from the welding surface to the rear side, the bolt extends in the direction of said length I, preferably said length I corresponding approximately to half the wavelength of ultrasonic vibrations capable of bringing the converter in the form of a sonotrode into a state of resonant vibration.

[0031] In a further preferred embodiment, the position at which the bolts are fastened to the converter base is located around the middle of the length I, i.e. away from the welding surface by a distance d such that 0.4l>d>0.7l applies.

[0032] It is particularly preferred if the at least one piezoelectric element is arranged in the longitudinal direction within the length I, ie between the welding surface and the rear side.

[0033] For example, at least four piezoelectric elements can be provided, each with a through opening, all of which are passed through by a bolt and are arranged longitudinally between the welding surface and the rear side of the converter base, i.e. within the range of length I. This is vibrationally advantageous, since the sonotrode is essentially excited on its inside.

[0034] Further advantages, features and possible applications of the present invention will become apparent from the following description of preferred embodiments and the accompanying drawings. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a perspective view of a converter according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the embodiment of FIG. [Diagram 3] FIG. 3 is a partial cutaway side view of the embodiment of FIG. [Figure 4] FIG. 4 is a cross-sectional view of the embodiment of FIG. 1 without the piezoelectric element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] 1 shows a perspective view of a converter according to the invention. The converter 1 is designed as a sonotrode and has a welding surface 2. The welding surface 2 is in contact with the material to be processed and is intended to transmit ultrasonic vibrations to the material.

[0037] The converter 1 has a converter base 3 with a rear part 10, the rear side of which is arranged opposite the welding surface 2, and a front part 11, as can be clearly seen from the cross section in FIG. 2. Here, a circumferential collar 15 forms the boundary between the front part 11 and the rear part 10. During vibration, standing waves are formed longitudinally along the length I in the converter. The circumferential collar is located in the vicinity of the minimum vibration. The converter can be held on the circumferential collar, for example via an O-ring, without significantly affecting the vibration behavior of the converter.

[0038] The front part 11 with the welded surface 2 is in most parts much thinner than the rear part 10. This results in an amplitude conversion in this front part. In the rear part 10, a recess is formed in the converter base, in which the bolt 4 is integrally connected.

[0039] FIG. 3 shows a partially cut-away side view of the converter 1.

[0040] The converter base 3 has a length I composed of the length of the rear 10 and the length of the front 11 of the converter base 3. This length I therefore defines the distance between the welding surface 2 and the rear side of the converter base. In use, a standing wave with a wavelength corresponding to twice the length I is formed in the converter.

[0041] The front part 11 of the converter base 3 also has a slit 9 which does not extend to the welded surface 2. The slit 9 is arranged on the axis of the bolt 4 in order to improve the vibration behavior of the converter base 3 designed as a sonotrode. A spacer disk 7 with a corresponding central opening is first pressed against the bolt 4. The spacer disk 7 is made of titanium, just like the converter base 3 including the bolt 4, and serves to absorb unevenness on the surface of the converter base in the immediate vicinity of the bolt 4. The spacer disk 7 should rest as flat as possible on the surface of the converter base 3, but small deviations in the surface quality can be accommodated without damaging the spacer disk 7. Furthermore, the spacer disk distributes the force of the bolt uniformly over the piezoelectric element. This prevents the piezoelectric element from being overstressed due to uneven application of the force.

[0042] 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 done, for example, by grinding or lapping.

[0043] Several piezoelectric elements 6, six in the illustrated example, are applied to spacer discs 7, which are intended to transmit an electrical AC voltage signal into mechanical vibrations. On the side of the piezoelectric elements 6 facing away from the converter base 3, a pressure disc 5 is provided, which can be made of steel, for example. The bolt 4 has at its end facing away from the converter base 3 an external thread, which in the illustrated example is designed as a buttress thread, into which a nut 8 engages. By tightening the nut 8, a force is exerted on the pressure disc 5, and via the pressure disc 5 on the piezoelectric elements 6 and thus via the spacer elements 7, vibrations are transmitted to the converter base 3, which is designed as a sonotrode.

[0044] It can be seen that the piezoelectric element 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 and contract in the axial direction, i.e. in the direction of length I, without any influence on the bolt 4. The piezoelectric element can therefore perform acoustic vibrations without being influenced by the bolt 4. Furthermore, care must be taken to ensure that any significant voltage applied to the piezoelectric element is not dispersed through the bolt. For this reason too, a sufficiently large distance is required between the outer diameter of the bolt 4 and the inner diameter of the piezoelectric element 6.

[0045] Figure 4 shows a partially cut-away side view of the converter 1, in which the piezoelectric element 6, as well as the spacer disc 7, pressure element 5 and nut 8 shown in Figures 1 to 3 have been omitted.

[0046] 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. At its end facing away from the converter base, the bolt has a threaded section 14 onto which a nut 8 can be screwed in order to press the piezoelectric elements 6 together with the pressure element 5 and the spacer element 7 against the converter base 3. The described design of the converter bolt 4 and the converter base 3 allows a significant improvement in the operating time of the ultrasonic vibration part 1. The bolt is necessary to hold the nuts 8, so that the necessary force is applied to the piezoelectric elements to press them against the converter base (or against the spacer disc). [Explanation of symbols]

[0047] 1 Converter 2. Welding surface 3 Converter base 4 Volts 5 Pressure Disc 6 Piezoelectric element 7 Spacer disc 8 Nuts 9 Slit 10 Rear 11 Front 12 Transition radius 14 Threaded section 15 Color

Claims

1. A converter comprising a converter base, a bolt (4) connected to the converter base, a tension element, and at least one piezoelectric element (6) having a through-opening, wherein the bolt (4) passes through the through-opening and the tension element applies tension to the at least one piezoelectric element in the direction of the converter base, wherein the bolt (4) is connected to the converter base by material joining, the converter is designed as a sonotrode, the converter base has a welded surface that contacts the material to be processed, the converter base has a rear side located opposite to the welded surface (2), a recess formed on the rear side in which the bolt (4) is positioned, and the bolt (4) is provided such that the connection portion with the converter base has a radius R of a rounded portion under the neck greater than 0.5 mm.

2. The converter according to claim 1, characterized in that the bolt (4) and the converter base are manufactured from a single piece of material.

3. The converter (1) according to claim 1 or 2, characterized in that the bolt (4) is provided such that the radius R of the underhead rounded portion is greater than 1 mm at the connection portion with the converter base.

4. A converter (1) according to claim 1 or 2, characterized in that a spacer disc (7) having a through-opening is provided, and the spacer disc (7) and the at least one piezoelectric element (6) are arranged such that the bolt (4) first passes through the through-opening of the spacer disc (7) and then through the through-opening of the at least one piezoelectric element (6), so that the spacer disc (7) contacts both the converter base and the piezoelectric element (6).

5. The converter (1) according to claim 4, characterized in that the through-opening of the spacer disk (7) is enlarged on the side facing the converter base, and in a cross-sectional view parallel to the longitudinal direction along length I, the through-opening of the spacer disk (7) has a radius E of the entrance curvature larger than 0.5 mm on the side facing the converter base.

6. The converter (1) according to claim 5, which is dependent on claim 3, characterized in that 2R > E > R is applied to the radius E of the rounded portion of the inlet.

7. The converter (1) according to claim 1 or 2, characterized in that the bolt (4) is located on the side away from the converter base and has an end with a male thread.

8. The converter according to claim 1 or 2, characterized in that the converter has a length I from the welded surface to the rear side, the bolt extends in the direction of the length I, and the length I corresponds to half the wavelength of ultrasonic vibrations that can cause the converter, which is designed as a sonotrode, to resonantly vibrate.

9. The converter according to claim 8, characterized in that four piezoelectric elements (6) are provided, each having a through-opening, and they are passed through by the bolt (4), and all of them are arranged in the direction of the length I within the range of the length I.

Images