Ultrasonic vibration system with overvoltage protection and ultrasonic welding installation having such a system

Abstract

The present invention relates to an ultrasonic vibration system with overvoltage protection and to an ultrasonic welding installation having such an ultrasonic vibration system, characterized in that a voltage-limiting protective component having a first and a second terminal is provided.

Description

[0001] Herrmann Ultraschalltechnik GmbH & Co. KG

[0002] Our reference number: 240886WO

[0003] Ultrasonic vibration system with surge protection and ultrasonic welding system with such a

[0004] The present invention relates to an ultrasonic vibration system with overvoltage protection and an ultrasonic welding system with such an ultrasonic vibration system.

[0005] A typical ultrasonic vibration system consists of a converter, which transforms an alternating electrical voltage into a mechanical vibration, and a sonotrode connected to the converter. The converter contains at least one piezoelectric element, and in practice often several. An alternating electrical voltage is applied to these piezoelectric elements, causing them to deform due to the piezoelectric effect and generate a mechanical vibration. The voltage is supplied via a phase conductor and discharged via a neutral conductor.

[0006] The sonotrode is rigidly coupled to the converter and is also excited by its mechanical vibration. Both the converter and the sonotrode are tuned to a common resonant frequency, resulting in a high vibration intensity.

[0007] Often, an amplitude transformer is located between the converter and the sonotrode, changing the amplitude of the oscillation while keeping the frequency constant. The sonotrode is designed to come into contact with a material in order to shape, weld, or cut it. For this purpose, the material to be processed is usually positioned between the sonotrode and a counter-tool, also called an anvil.

[0008] The piezoelectric elements are usually housed in a converter casing that protects them from environmental influences. This casing is typically connected to the neutral conductor and assumes its potential.

[0009] However, if the line between the generator and the neutral conductor is interrupted, for example by a break, a fault occurs: The phase conductor continues to supply the piezoelectric elements, and the excitation continues. A potential builds up at the other end of the piezoelectric elements, which, due to the missing connection to the neutral conductor, is not dissipated. This potential can then be present on the metallic converter housing or arc to the converter housing and is transmitted to the sonotrode via the metallic mounting of the ultrasonic transducer. Since this poses a potential safety hazard, a person could unintentionally touch live parts. To prevent this, the converter housing is usually additionally grounded via a protective conductor.

[0010] In certain applications, however, contact between the sonotrode and the counter-tool must also be detected. EP 0 790 888 B1 describes how a measuring device can determine changes in resistance, current flow, or voltage between the sonotrode and the counter-tool. In this configuration, grounding the converter housing via a protective conductor has not been feasible until now, which is why complex safety precautions such as insulating the piezoelectric elements within the converter housing have been necessary.

[0011] WO 2024 / 051918 A1 therefore proposes galvanically isolating the sealing surface of the sonotrode from the neutral conductor. In the event of a fault, a potential can now be present on the neutral conductor without being transferred to the sealing surface. This galvanic isolation is achieved, for example, by an insulating element between the sonotrode and the converter.

[0012] However, this solution is complex to manufacture, as it is necessary to ensure the most loss-free transmission of the mechanical vibration generated by the piezoelectric elements to the sonotrode, despite the insulation between the sonotrode and the converter.

[0013] The object of the present invention is therefore to provide an ultrasonic vibration system or an ultrasonic welding system that allows safe operation and at the same time dampens the mechanical vibration generated by the converter as little as possible.

[0014] With regard to the ultrasonic vibration system, this problem is solved by providing a voltage-limiting protective component with a first and a second terminal, wherein the first terminal is electrically connected to the sonotrode and the second terminal is electrically connected to a neutral conductor or ground. The voltage-limiting protective component is designed such that, when a voltage U greater than Umax is applied between the first and second terminals, it provides an electrical connection between the first and second terminals, and when a voltage U less than Umin is applied between the first and second terminals, it does not provide an electrical connection between the first and second terminals, where Umax is greater than or equal to Ummin.

[0015] Typically, the voltage-limiting protective component will have its second terminal electrically connected to ground, as this is the preferred embodiment. Therefore, it will always be assumed in the following that the second terminal is connected to ground. However, the present invention also functions in principle if the second terminal is connected to the neutral conductor, since the neutral conductor, although it carries away the charge supplied via the phase conductor, is also typically connected to ground with low resistance.

[0016] Typically, U max and U min be roughly the same. U mThe voltage ax could, for example, be 9V. As soon as the voltage between the sonotrode and ground exceeds 9V, an electrical connection to ground is established due to the voltage-limiting protective component, thus grounding the sonotrode. However, if the voltage is lower than Umin (e.g., also 9V), no connection is established, and the sonotrode can be used with such a low voltage for electrical contact detection between the sonotrode and the counter-tool.

[0017] In a preferred embodiment, the voltage-limiting protective component is a protection diode, a varistor, a thyristor, or a gas discharge tube. A Zener diode or a TVS diode is particularly preferred as the voltage-limiting protective component.

[0018] A varistor consists of a sintered mixture of metallic oxides, usually zinc oxide, which acts as a semiconducting material. The central component of the varistor is often zinc oxide granules mixed with small amounts of other metal oxides, such as bismuth, cobalt, and antimony oxide. This mixture gives the material its special voltage-dependent resistance properties. Metallic contacts are located on both sides of the metal oxide layer, i.e., the first and second terminals. The function of the varistor is based on the non-linear relationship between voltage and resistance. Crucially, at low voltages, the varistor exhibits high resistance and therefore allows very little current to flow, effectively remaining inactive. However, if a voltage spike occurs and the voltage exceeds a certain threshold, i.e.,When the voltage rises above the maximum permissible voltage (Umax), the structure of the metal oxide grains at the interfaces changes, and the varistor suddenly becomes low-resistance. This causes the current flow to increase drastically, creating a ground connection. A thyristor is a semiconductor device, typically consisting of four layers with alternating positive and negative doping. The thyristor can be switched between a non-conducting and a conducting state. The thyristor is then configured so that, in the event of an overvoltage, it conducts the current to ground, quickly reducing the voltage to a safe level. As long as the voltage remains within the normal range, the thyristor remains non-conducting, and the current flow in the main circuit is unaffected. However, if an overvoltage occurs, an additional circuit is activated, sending a trigger signal to the gate terminal of the thyristor.This trigger voltage brings the thyristor into the conducting state, so that the thyristor is virtually short-circuited and the entire charge accumulated on the sonotrode is discharged directly to ground.

[0019] A gas discharge tube consists of a housing filled with a special noble gas that defines a specific ignition point. Under normal operating conditions, the noble gas remains insulating when the voltage between the sonotrode and ground is less than Umax. However, if an overvoltage occurs, the gas inside the gas discharge tube ionizes, leading to an abrupt discharge of the charge from the sonotrode through the tube.

[0020] A standard semiconductor diode consisting of a simple pn-layer structure is used as the protection diode. It has an anode and a cathode terminal. The protection diode is connected in reverse bias in parallel with the sonotrode, so that under normal conditions the diode blocks current and does not conduct. However, if a voltage spike occurs that exceeds the diode's reverse voltage, the diode becomes conductive and conducts the current.

[0021] The Zener diode has a similar structure, but the breakdown voltage can be calibrated very precisely by suitable doping of the layers.

[0022] The TVS diode has a similar structure to a Zener diode, but is designed to absorb high energy pulses for short periods. It therefore typically has a thicker semiconductor layer to absorb higher energies and exhibits a shorter response time. Like the Zener diode, the TVS diode is operated in reverse bias and remains high-impedance during normal operation. Only when a certain voltage, namely U, is applied does it change direction. maxIf the voltage exceeds a certain threshold, the TVS diode suddenly becomes low-resistance and dissipates any charge from the sonotrode to ground via the connection. Both unipolar and bipolar TVS diodes can be used here. As previously mentioned, the ultrasonic vibration system often has a converter housing in which at least one piezoelectric element is located. This housing is also electrically connected to the sonotrode. The first connection can therefore be attached to any component that is electrically connected to the sonotrode. Ideally, the connection of the first terminal is made in such a way that the vibration of the ultrasonic vibration system is not affected as much as possible. The ultrasonic vibration system often has a mounting bracket designed to connect it to a machine stand.This mounting bracket can also be electrically connected to the sonotrode, so that the first terminal of the voltage-limiting protective component is connected to the bracket. To minimize the impact of the mounting bracket on the vibration behavior, it is positioned at a point within the ultrasonic vibration system where there is a minimum in the standing wave forming within the system.

[0023] The task mentioned at the beginning is also solved by an ultrasonic welding system with the described ultrasonic vibration system.

[0024] In a preferred embodiment, the ultrasonic welding system has a voltage and / or current source which is capable of supplying a voltage U to the sonotrode. k to be applied to the mass which is smaller than Umax and preferably smaller than Umin.

[0025] This measure enables contact detection between the sonotrode and metallic material or between the sonotrode and the counter-tool. If contact occurs between the sonotrode and an electrically conductive, grounded element, the voltage supplied by the voltage and / or current source will collapse.

[0026] Advantageously, an ammeter is provided, which is arranged and configured to measure the current flow from the voltage and / or current source to the sonotrode. Upon contact between the sonotrode and an electrically conductive, grounded element, the charge applied to the sonotrode by the voltage and / or current source will dissipate and can then be detected by the ammeter.

[0027] The protective function of the voltage-limiting protective component according to the invention depends on its functionality. However, unlike wired ground connections, voltage-limiting protective components have a shorter service life, requiring regular inspection and / or replacement. Manual inspection is very time-consuming and interrupts ultrasonic processing with the ultrasonic welding system.

[0028] In a further preferred embodiment, a control device is therefore provided which is arranged and set up to check the function of the voltage-limiting protective component.

[0029] In a preferred embodiment, the control device ensures that a control voltage Uc is applied between the sonotrode and ground, wherein Uc is greater than UMAX, and if the current measuring device does not measure a current I greater than zero, the function of the voltage-limiting protection component is evaluated as faulty.

[0030] The control voltage Uc can be generated, for example, with the voltage and / or current source used to generate the voltage U. K is planned.

[0031] Advantageously, the control device is designed in such a way that, if the function of the voltage-limiting protective component is deemed faulty, it prevents a voltage from being applied to the piezo element.

[0032] In a further preferred embodiment, the ultrasonic welding system is arranged and configured such that whenever an alternating electrical voltage is to be applied to the at least one piezoelectric element, the ultrasonic welding system first checks the function of the voltage-limiting protective component using the control device, and only applies the alternating electrical voltage to the at least one piezoelectric element if the test is passed. This ensures that there is no danger whatsoever to the operating personnel of the ultrasonic welding system.

[0033] Further features and possible applications of the present invention will become clear with reference to the following description of a preferred embodiment and the accompanying figure. It shows:

[0034] Figure 1 is a schematic representation of an embodiment according to the invention.

[0035] Figure 1 shows a schematic representation of an embodiment of an ultrasonic welding system 1 according to the invention. This system comprises a converter 2, which has a stack of piezoelectric elements connected via a cable to a high-voltage supply 6. The high-voltage supply 6 can be used to set the piezoelectric elements into mechanical motion. The converter 2 is connected to a sonotrode 3. An amplitude transformer could be arranged between the converter 2 and the sonotrode 3. The converter 2 and the sonotrode 3 are mounted in a cast holder 5. The cast holder 5 is designed and arranged such that it securely holds the ultrasonic vibration unit, which consists of the converter 2 and the sonotrode 3, while attenuating the ultrasonic vibration generated in the ultrasonic vibration unit as little as possible and is also electrically insulated from the roller 4.

[0036] Opposite the sonotrode 3 is a counter-tool 4, for example a cylindrical one, which is also referred to as an anvil. A metal contact detector 9 provides a connection between the holder 5 and the counter-tool 4. The metal contact detector 9 generates a voltage U. k of e.g. 7 V between the sonotrode 3 and the counter tool 4, and on the other hand measures any current flow that may be taking place between sonotrode 3 and counter tool 4.

[0037] This allows detection of whether the sonotrode 3 is touching the counter-tool 4 or not. If the ultrasonic welding system 1 is used to cut a material, which is usually positioned between the sonotrode 3 and the counter-tool 4, the metal contact detection 9 indicates the end of the cutting process. Even if no cutting is desired, the metal contact detection can be useful for detecting an accidental cut. Even if no material is positioned between the sonotrode 3 and the counter-tool 4, contact between the two components is generally undesirable, so the metal contact detection can also be used here. Furthermore, a current flow can occur immediately before the material is cut, for example, if there is no surface contact yet, which can also be detected by the metal contact detection.

[0038] Since a high supply voltage 6 is present at converter 2 during operation of the ultrasonic vibration unit, protective measures, such as grounding the bracket 5, are usually necessary. However, if the bracket 5 were connected to ground, the metal contact detection 9 would no longer function as intended.

[0039] Therefore, in the illustrated embodiment, the bracket 5 is connected to a ground wire 8 via a diode 7. The diode 7 is reverse-biased, so that it decouples the ground wire 8 from the bracket 5 up to a voltage Umax. However, if the voltage rises above Umax, the diode 7, designed as a TVS diode, switches and connects the bracket 5 to ground. This ensures that if, due to a fault condition, the high voltage 6 applied to the converter 2 is present at the bracket 5, the diode 7 switches and dissipates the high voltage via the ground wire 8.

[0040] The functionality of diode 7 can be easily tested by applying a voltage greater than U to the metal contact detection 9 before commissioning the ultrasonic vibration unit. ma x is. In this state, it is then detected whether the diode 7 is switching, i.e., whether the charge located on the sonotrode 3 is dissipating or not. Only if it dissipates properly is the functionality of the diode ensured and the ultrasonic welding system 1 can be put into operation.

[0041] Regarding the sign list

[0042] 1 ultrasonic welding system

[0043] 2 converters 3 sonotrodes

[0044] 4 anvil

[0045] 5 bracket

[0046] 6 High-voltage supply

[0047] 7 TVS diode 8 Ground connection

[0048] 9 Unit for metal contact detection

Claims

P a t e n t a n s p r ü c h e 1. Ultrasonic vibration system with a converter for converting an alternating electrical voltage into a mechanical vibration and a sonotrode connected to the converter, wherein the converter is preferably connected to the sonotrode via an amplitude transformer, wherein the converter has at least one piezoelectric element, characterized in that a voltage-limiting protective component with a first and a second connection is provided, wherein the first connection is electrically connected to the sonotrode and the second connection is electrically connected to a neutral conductor or ground, wherein the voltage-limiting protective component is configured such that, when a voltage U greater than Umax is applied between the first and second connections, it provides an electrical connection between the first and second connections, and when a voltage U less than U is applied between the first and second connections, it does not provide an electrical connection. minis, does not provide an electrical connection between the first and second terminals, where Umax is greater than or equal to Um.

2. Ultrasonic vibration system according to claim 1, characterized in that the voltage-limiting protective component is a protective diode, a varistor, a thyristor or a gas discharge tube, wherein preferably the voltage-limiting protective component is a Zener diode or a TVS diode.

3. Ultrasonic vibration system according to one of the preceding claims characterized in that the converter has a housing in which the at least one piezoelectric element is arranged, wherein the housing is electrically connected to the sonotrode.

4. Ultrasonic vibration system according to one of the preceding claims characterized in that the ultrasonic vibration system has a holder which is provided for connecting the ultrasonic vibration system to a machine stand, wherein the holder is electrically connected to the sonotrode and the first connection of the voltage-limiting protective component is connected to the holder.

5. Ultrasonic welding system with an ultrasonic vibration system according to one of the preceding claims, characterized in that a voltage and / or current source is provided which is capable of applying a voltage Uk relative to ground to the sonotrode which is smaller than Umax and preferably smaller than Umin.

6. Ultrasonic welding system according to claim 5, characterized in that a current measuring device is provided which is arranged and configured in such a way as to measure a current flow from the voltage and / or current source to the sonotrode.

7. Ultrasonic welding system according to claim 5 or 6, characterized in that a control device is provided which is arranged and configured to check the function of the voltage-limiting protective component.

8. Ultrasonic welding system according to claim 7, characterized in that the control device ensures that a control voltage Uc is applied between the sonotrode and ground, wherein U c is greater than U MAX, and if the current meter does not measure a current I greater than zero, the function of the voltage-limiting protective component is considered faulty.

9. Ultrasonic welding system according to claim 8, characterized in that if the function of the voltage-limiting protective component is deemed to be faulty, the control device is configured in such a way as to prevent a voltage from being applied to the piezoelectric element.

10. Ultrasonic welding system according to claim 8 or 9, characterized in that the ultrasonic welding system is arranged and configured such that whenever an alternating electrical voltage is to be applied to the at least one piezoelectric element, the ultrasonic welding system first checks the function of the voltage-limiting protective component by means of the control device, and only applies the alternating electrical voltage to the at least one piezoelectric element if the test is passed.

Images