Ultrasonic tool and method for machining a workpiece using mechanical ultrasonic vibrations - Patents.com

Abstract

An ultrasonic tool and method for machining a workpiece using mechanical ultrasonic vibrations.

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic tool and a method for machining a workpiece using mechanical ultrasonic vibrations. [Background technology]

[0002] Ultrasonic tools are used, for example, to weld or separate workpieces, in particular webs of material. To this end, the ultrasonic tool has an ultrasonic vibration unit, which has a converter element and a sonotrode. The sonotrode can be connected to the converter element directly or via an amplitude amplifier.

[0003] Various ultrasonic welding devices are known from EP 2 881 184 A1 and from the article "Modelling and Designing of Ultrasonic Welding Systems" by Molewski et al., published in "Archives of Acoustics", vol. 40, No. 1, pp. 93-99 (2015) (Non-Patent Document 1).

[0004] The workpiece, e.g., a plastic film, is usually placed on a counter-tool (anvil), or the workpiece can be continuously transported through the counter-tool. In either case, the workpiece is located between the sonotrode and the counter-tool when it is machined.

[0005] The converter element typically comprises a converter having a number of piezoelectric elements which convert an applied AC voltage into mechanical movement of the same frequency, typically supplied by a generator. Each piezoelectric element is connected to a phase conductor of the generator on the one hand and to a neutral conductor of the generator on the other hand. When an AC voltage is applied to these conductors, the piezoelectric elements alternately lengthen and shorten, thus generating ultrasonic vibrations.

[0006] The piezoelectric element is often arranged in a converter housing, which serves to protect the piezoelectric element as much as possible against environmental influences, and which is often connected to the neutral conductor and is therefore at its potential.

[0007] If a fault occurs in the conductor between the generator and the neutral conductor, for example if it breaks, a fault can occur. The phase conductors supply additional charge, further exciting the piezoelectric elements. This creates a potential at the other end of each piezoelectric element that cannot be dissipated via the neutral conductor due to a fault. This potential is then also applied to the converter housing. This is undesirable for reasons of work safety, since bystanders could come into contact with components that conduct voltage in this way. This problem is usually solved by grounding the converter housing via an additional protective conductor.

[0008] At the same time, contact between the sonotrode and the counter tool must often be detected. 2 ) it is known that a measuring device must be used to detect changes in resistance, current or voltage between the sonotrode and the counter tool, where grounding of the converter housing by a protective conductor has not been possible up to now. Therefore, in such applications extensive safety measures have previously been required, for example complex insulation of the piezoelectric element in the converter housing. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent Application Publication No. 2881184 [Patent Document 2] European Patent No. 0790888 [Non-patent literature]

[0010] [Non-Patent Document 1] Molewski et al., “Modelling and Designing of Ultrasonic Welding Systems”, “Archives of Acoustics”, vol.40, No.1, pp.93-99(2015) Summary of the Invention [Problem to be solved by the invention]

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to improve the operational safety of ultrasonic tools, in which contact between a sonotrode and a counter-tool must be detected. [Means for solving the problem]

[0012] This problem is solved by an ultrasonic tool according to claim 1.

[0013] This problem is solved by an ultrasonic tool for machining a workpiece using mechanical ultrasonic vibrations, the ultrasonic tool including a converter element and a sonotrode, the converter element having a converter with at least one piezoelectric element, and the converter element having a phase conductor and a neutral conductor for a supply conductor of AC voltage. The phase conductor and the neutral conductor form two poles for the converter or the at least one piezoelectric element. The at least one piezoelectric element is arranged to convert AC voltage into mechanical ultrasonic vibrations. The converter element can vibrate resonantly with mechanical ultrasonic vibrations of wavelength λ and is mechanically coupled to the sonotrode. The sonotrode and the converter element are tuned to each other so that the sonotrode can vibrate resonantly with mechanical ultrasonic vibrations of wavelength λ. The sonotrode has a sealing surface, which is arranged to contact the workpiece to be machined. The sealing surface of the sonotrode and the neutral conductor are galvanically insulated. In the event of a fault, a potential may exist on the neutral conductor that cannot be dissipated. Galvanic isolation prevents this potential from being transmitted to the sealing surfaces.

[0014] Preferably, the phase conductors are also galvanically insulated from the sealing surfaces of the sonotrode.

[0015] A plurality of piezoelectric elements are typically arranged one behind the other along the converter axis.

[0016] The piezoelectric washers are polarized and therefore deform when a voltage is applied. They have a positive side and a negative side. The positive sides of all the piezoelectric washers are connected to the same pole, for example, a phase conductor, and the negative sides are all connected to the other pole, in this case, the neutral conductor. This ensures that all the piezoelectric washers deform in the same way, i.e., they all expand (lengthen) or contract at a given voltage. These piezoelectric washers are preferably arranged in succession along the converter axis with alternating polarities opposite to each other, so that two adjacent piezoelectric washers can contact the same electrode (contact washer) located between them.

[0017] To generate an AC voltage, an AC voltage source, also called an ultrasonic generator, is preferably provided, which is connected to the phase and neutral conductors.

[0018] For example, the converter element and the sonotrode can be arranged one behind the other in the direction of propagation of the ultrasonic vibrations. Both the converter element and the sonotrode can have a length of λ / 2 or a multiple of λ / 2 in this direction of propagation. This ensures that when excited with vibrations of wavelength λ, a wave with maximum vibration is formed at the interface between the sonotrode and the converter element due to the reflection of the ultrasonic vibrations at the end of the vibrating stack. The direction of propagation can extend along the converter axis, but it is also possible, for example, for the converter axis and the direction of propagation to be perpendicular to each other. The direction of propagation in particular extends from the converter to the sonotrode and / or in the direction of the sealing surface of the sonotrode.

[0019] Machining of workpieces refers in particular to the separation, joining and (multiple-part) welding of workpieces.

[0020] The sonotrode, the converter element, and the amplitude amplifier, optionally arranged between the sonotrode and the converter element, as a whole may also be referred to as a vibrating stack. If an amplitude amplifier is used, it is also configured so that it can resonate with vibrations having a wavelength λ. Advantageously, the amplitude amplifier also has a length of λ / 2 or a multiple of λ / 2 in the direction of propagation.

[0021] The vibration stack is preferably held (clamped) in a bracket, which preferably engages with the sonotrode, particularly in the region of the vibration nodes. Alternatively, the bracket can also engage with the amplitude amplifier, the converter member, or several of these components. The bracket of the ultrasonic vibration unit can be provided in a known manner, for example as shown in WO 96 / 014202. Since a large number of different brackets are known to those skilled in the art, no specific bracket is shown here for reasons of clarity.

[0022] In a further advantageous development, the bracket is provided with a galvanic insulator to prevent grounding of the sonotrode via the bracket. It is particularly advantageous if the bracket engages the galvanic insulator behind the sealing surface of the sonotrode. In this way, additional insulation of the bracket can be omitted. Therefore, in this case, the bracket does not have any additional insulation.

[0023] Galvanic isolation is understood to mean a device that prevents the flow of current between the neutral conductor and the sealing surface. This can and usually is electrical isolation. Of course, it is also conceivable that the conductor connected to the neutral conductor is connected to the sealing surface of the sonotrode via a non-conductive coupling element, which allows the exchange of signals, for example, by induction. On the other hand, in the case of electrical isolation, the current circuits do not interact with each other. In other words, in the following, electrical isolation is referred to when galvanic isolation is present and signal exchange is excluded.

[0024] In a further advantageous development, the sonotrode has an electrically connected signal terminal, which is electrically connected to the sealing surface and is for a signal voltage, and the neutral conductor and the signal terminal are galvanically insulated, preferably electrically insulated from each other. The signal voltage is applied, in particular, when detecting contact between the sealing surface of the sonotrode and another part, for example, contact with a counter tool (anvil). The galvanic isolation of the neutral conductor and the signal terminal ensures that the signal voltage does not dissipate through the neutral conductor and that, in the event of a fault, the signal voltage and no other voltages are always applied to the sealing surface. This protects the contact detection from destructive effects and also prevents a person from coming into contact with high potentials that do not correspond to the signal voltage via the sonotrode.

[0025] When the bracket engages with the sonotrode, it preferably has galvanic isolation, with one portion of the bracket being conductively connected to the sonotrode, particularly in the region of the vibration nodes, and another portion being galvanically isolated from this portion. In this case, it is possible in the context of the present invention to arrange the signal terminal in contact with the portion of the bracket that is conductively connected to the sonotrode, instead of the sonotrode. In this way, the signal voltage can also be supplied to the sealing surface of the sonotrode. If the signal terminal were arranged on the sonotrode, it would affect the vibration behavior of the vibrating stack. Since this is not the case with the bracket, arranging the signal terminal on the bracket is particularly advantageous.

[0026] The converter member preferably comprises a converter housing in which at least one piezoelectric element is disposed.

[0027] Advantageously, the ultrasonic tool has a protective conductor, preferably disposed in the converter housing. This protective conductor is grounded or can be grounded. Preferably, the ultrasonic tool has a first part, a second part, and a third part. The first part has at least a neutral conductor. The second part has at least the protective conductor and the converter housing. The third part has a sealing surface of the sonotrode and can output or receive a signal voltage via the signal terminal.

[0028] In a preferred embodiment of the present invention, galvanic isolation between the first and second parts can be omitted. The second and third parts are then galvanically isolated. This ensures that the signal voltage is not dissipated through the protective conductor. In this embodiment of the present invention, additional grounding of the converter housing via the protective conductor is possible. In the event of a neutral conductor malfunction, no potential is present on the converter housing because all potential is dissipated through the protective conductor. This additional grounding means that there is no longer any risk of injury to a person coming into contact with the converter housing. There is also no risk of a potential different from the desired potential of the signal voltage being applied to the sonotrode's sealing surface. In this way, contact detection is possible despite the additional grounding of the converter housing.

[0029] The first and second parts can also be galvanically isolated from each other, and most preferably electrically isolated from each other. In that case, the second part is galvanically isolated from the first and third parts. Advantageously, the second part is located between the first and third parts, so that there are two electrical isolations between the neutral conductor (first part) and the sealing surface of the sonotrode (third part). In this way, an additional grounded part is formed between the first part, to which a high voltage may be applied in the event of a fault, and the third part, to which the signal voltage is applied.

[0030] The converter housing may include an insulating housing made of an electrically insulating material defining an insulating space, in which at least one piezoelectric element and a neutral conductor are disposed. In this case, the insulating housing provides galvanic isolation between the first and second parts. The insulating housing is particularly preferably toroidal or hollow cylindrical. The converter element includes a shaft, particularly a converter screw having a shaft surrounded by a toroidal or hollow cylindrical insulating housing. The insulating housing ensures galvanic isolation of the piezoelectric element from the rest of the converter element, particularly from the converter screw that energizes the piezoelectric element. In this case, the insulating housing may include multiple insulating parts, particularly an axially arranged insulating washer and a cylindrical insulating part that provides radial isolation. In this way, the piezoelectric element can remain compressed in the axial direction, thereby ensuring transmission of ultrasonic vibrations. The insulating housing is particularly used for basic insulation of the converter.

[0031] Advantageously, a counter tool having a sealing surface is provided, which is positioned so that the workpiece to be machined can be placed between the sealing surface of the sonotrode and the sealing surface of the counter tool during machining. The sealing surface of the counter tool is preferably grounded. As explained above, contact between the sonotrode and the sealing surface of the counter tool can be detected by applying a signal voltage. In the context of the present invention, it is also possible to apply a signal voltage to the counter tool and instead ground the signal terminal. The counter tool is preferably a roller, in particular a rotating roller, which transports the workpiece during machining. In this way, continuous welding of the workpiece is possible. The counter tool is at least partially electrically conductive.

[0032] The sonotrode, or the entire vibration stack, is preferably movable along an adjustment direction, in particular by means of an adjustment device of the ultrasonic tool. This adjustment device can be part of the bracket. In this way, the sonotrode can be moved towards and away from the counter tool. In this way, the distance between the sonotrode and the counter tool can be adjusted at any time. Also, during machining, in particular if the machining consists of a separation process, the sonotrode or the entire vibration stack can be gradually moved towards the counter tool.

[0033] In a further advantageous development, a voltage source is provided, by which a signal voltage can be supplied to the third part, in particular to the signal terminal, and a sensor is provided for detecting the voltage applied to or dissipated from the third part. When a voltage is applied to or dissipated from the third part, it is detected by the sensor. From this detection, contact between the sealing surfaces can be inferred.

[0034] The alternating voltage applied to the at least one piezoelectric element is advantageously 500 V. rms (root mean square, effective voltage) and 3000V rmsThe signal voltage is preferably between 1000 and 1200 kHz, and preferably has a frequency between 20 kHz and 70 kHz. A low voltage has been found to be advantageous. The gap and contact time between the sealing surfaces during processing are very small due to the high frequency and piezoelectric technology. If the signal voltage is too high, a voltage flashover (arc) occurs before actual contact between the sealing surfaces, allowing the sensor to detect current flow. On the other hand, if the voltage is too low, even slight contact results in little current flow, making early detection of contact difficult. The signal voltage is preferably a DC voltage, more preferably less than 30 V, more preferably less than 25 V, and most preferably between 5 V and 12 V. The inventors have determined that a range of 5 V to 12 V is most suitable for contact detection, with voltages up to 25 V also providing acceptable results. On the other hand, voltages above 30 V result in premature voltage flashover in many applications. The signal voltage may be an AC voltage, but a DC voltage is preferred because it provides a uniform discharge upon contact, allowing for better detection.

[0035] When the sealing surfaces come into contact, a current flows between them. Once the contact is terminated, the potential is re-established by the signal voltage source. This buildup proceeds extremely quickly, since the intervals between individual contacts can be extremely short. It has therefore proven advantageous if the wires establishing the signal voltage are shielded and / or do not exceed a predetermined total capacitance. Therefore, the third part is preferably connected to the voltage source by wires that are shielded and / or have a total capacitance of less than 2500 pF, particularly less than 1500 pF. If the total capacitance is less than 1500 pF, even very short successive contacts can be detected and distinguished. Contacts can still be detected satisfactorily up to 2500 pF, but detection becomes significantly more difficult above 2500 pF.

[0036] In a further advantageous development, the insulation resistance between the second and third parts is at least 5 kΩ, in particular at least 7 kΩ. As a rule, the higher the insulation resistance, the better the galvanic isolation. Of course, in some cases, very high insulation resistances can only be achieved with great effort. The 100 MΩ limit may therefore be considered the upper limit for the insulation resistance, with any higher values ​​being permissible as long as there are no other boundary conditions to the contrary.

[0037] Preferably, an amplitude amplifier is provided between the converter member and the sonotrode. The converter member is mechanically coupled to the amplitude amplifier, and the amplitude amplifier is mechanically coupled to the sonotrode. The sonotrode, amplitude amplifier, and converter member are tuned to one another so that the sonotrode can be vibrated resonantly by mechanical ultrasonic vibrations of wavelength λ. The sonotrode, amplitude amplifier, and converter member form a vibrating stack.

[0038] The sonotrode, the amplitude amplifier and the converter member may also be referred to as components that are connected to one another.

[0039] In a further advantageous development, at least one insulating means is provided, by means of which the sealing surface of the sonotrode and the neutral conductor are galvanically, in particular electrically, isolated. Various possibilities for the configuration of the at least one insulating means are explained below.

[0040] Particularly preferably, at least one insulating means is provided in each case at exactly two locations: on the one hand, at the point where the two corresponding components, i.e., the components to be connected, come into direct contact, i.e., at the point where the ultrasonic vibrations are transmitted from one component to the next in the propagation direction, and on the other hand, at the connection point where the components are held together, which can be achieved in particular by a form fit and / or material lock. Several connection points can also cooperate to hold the components together. Pressing forces are transmitted in particular to the contact points, and pulling forces are transmitted in particular to the connection points.

[0041] The converter element and sonotrode and / or the converter element and amplitude amplifier and / or the amplitude amplifier and sonotrode are preferably connected to one another via at least one connecting element. The connecting element provides a press fit, particularly along the propagation direction. As a result, the respective components are connected to one another so that ultrasonic vibrations can propagate along the ultrasonic tool. Preferably, the connecting element is a screw and / or a threaded bolt and / or a threaded bushing. The at least one connecting element connects the respective components with a clamping force, particularly of at least 20 kN and preferably less than 150 kN, in particular at least 30 kN and / or less than 90 kN. These clamping forces ensure that the components are connected to one another so that ultrasonic vibrations can propagate uniformly. The connecting element is preferably configured as an insulating means and at least partially comprises an insulating coating and / or is at least partially made of an insulating material. In this way, galvanic isolation is provided where the respective components are press-fitted together. The threaded bushing may be a wire thread insert.

[0042] Between the converter element and the sonotrode, in particular between the converter element and the amplitude amplifier and / or between the amplitude amplifier and the sonotrode, preferably at least one insulating element, in particular an insulating washer, is provided, which is configured as an insulating means and consists at least partially of an insulating material and / or has at least partially an insulating coating. The insulating washer particularly preferably has holes, for example, through which the connecting element can pass, i.e. is preferably configured as a ring washer. The insulating washer provides galvanic isolation, in particular at the contact points between the components, through which the ultrasonic vibrations are transmitted to the respective next component in the propagation direction. Therefore, it is particularly preferred to use a connecting element and an insulating element in combination.

[0043] In a further advantageous development, the converter element and / or the amplitude amplifier and / or the sonotrode are configured as insulating means and are at least partially made of insulating material and / or have at least partially an insulating coating. In this way, galvanic isolation by connecting elements and / or insulating elements can be omitted. In this case, the respective components are coated or made of insulating material at the contact points where ultrasonic vibrations are transmitted and / or friction is generated. This reduces the number of components used, which is particularly advantageous for ultrasonic tools, since additional components would change the vibration behavior of the entire vibration stack. The use of a coating has the special advantage that it can be made thin and does not change the vibration behavior of the vibration stack, or only slightly. If a component made of insulating material, such as an insulating washer, is used, this component usually has to be significantly thicker than the coating. In this case, this component has a very strong influence on the vibration behavior of the vibration stack. This is particularly true for the contact points between two components.

[0044] Applying an insulating coating to the thread is possible, but is often difficult due to the delicate nature of the thread profile. In a further advantageous development, a multi-component cascade is provided as the connecting element, preferably with a first cascade section held by a second cascade section in a form-fit manner in the direction of propagation, and the first and / or second cascade sections have an insulating coating at their respective contact points for the form-fit. Alternatively, at least one of the cascade sections can be made of an insulating material. The essential advantage of a cascade is that only one or more contact surfaces need to be coated, not the threaded section. Depending on the design of the cascade, the insulating means at the contact points can be realized by the cascade, or insulating elements, in particular insulating washers, can be used in addition to the cascade.

[0045] In a further advantageous development, the connecting element has a smooth, particularly cylindrical, portion provided with an insulating coating and shrink-fitted into the sonotrode, converter element, or amplitude amplifier. In this case, for example, the sonotrode can be heated, widening the existing bore therein, and the smooth portion can then be introduced into the bore. Upon cooling, the bore contracts again, holding the connecting element in a frictional lock. Smooth particularly means that the portion has a cross-section that does not change along its axial extent and, in particular, does not have a thread. The cross-section can be circular, star-shaped, or otherwise configured. A circle has the advantage that the geometry can be easily formed, for example, by grinding. Shrink-fitting achieves a sufficiently large pressure fit, but at the same time, very narrow tolerances must be observed to avoid overloading the base material with excessive tightening loads. In these embodiments, too, an essential advantage is that the threaded portion does not need to be coated. Alternatively or additionally, the connecting element can have a smooth portion and a threaded attachment that is shrink-fit onto the smooth portion, where the threaded portion has external threads that can be screwed into an internally threaded bore of another component.

[0046] In a further advantageous development, a through hole is provided in the amplitude amplifier, and the amplitude amplifier has a portion with an insulating coating. Alternatively, a part of the converter element, in particular the converter lower portion, can have a through hole and a portion with an insulating coating. In such an embodiment, a screw is further provided, the screw resting with its head on the coated portion and spaced apart from the inner surface of the through hole. If the amplitude amplifier has a through hole, the screw can be screwed into the converter element or the sonotrode by its threaded portion, and if the converter lower portion has a through hole, the screw can be screwed into the amplitude amplifier or the sonotrode by its threaded portion. In such an embodiment, too, no coating is required on the threaded portion. The screw can be a countersunk head screw, which allows the components connected to each other to be automatically centered.

[0047] To ensure sufficient insulation even in the event of unintentional contact, additional insulating means can be provided on the inner wall of the through-hole. These insulating means do not have to be very specific, since they do not need to transmit large forces and only need to ensure electrical resistance. Therefore, these insulating means can be, for example, an insulating sleeve, spray paint, or insulating film.

[0048] In a further advantageous development, a transverse bore extending transversely to the direction of propagation is provided in the converter element, amplitude amplifier, or sonotrode, into which an at least partially coated transverse section with a threaded bore is inserted. This transverse section can be a rectangular parallelepiped slotted piece or a bolt. In this case, the converter element, amplitude amplifier, or sonotrode has, in addition to the transverse bore, a bore concentric with the threaded bore, into which a screw or threaded bolt is arranged, which is connected to the transverse section by the threaded bore. The screw or threaded bolt can be connected to adjacent parts, i.e., to the amplitude amplifier or converter element in the case of a sonotrode, to the converter element or sonotrode in the case of an amplitude amplifier, and back again to the amplitude amplifier or sonotrode in the case of a converter element. In this case, too, coating of the threads is not necessary for a press-fit connection. However, insulating elements, in particular insulating washers or insulating coatings, are additionally required at the contact points between these components.

[0049] In a further advantageous development, the coupling piece, in particular the flange portion, is provided with an insulating means, which is at least partially coated. The coupling piece is fastened to one of the components by means of a screw, in which case the coupling piece has an insulating coating where the screw rests. Again, for a press-fit connection, it is not necessary to coat the thread.

[0050] In ultrasonic tools, large forces and ultrasonic vibrations must be transmitted through an insulating coating or insulating material. The inventors have discovered that not all electrically insulating materials are suitable for galvanic isolation within ultrasonic tools. The insulating coating and / or insulating material preferably comprises at least one of the following materials: ceramic, in particular chromium oxide (Cr2O3) and / or aluminum oxide (Al2O3), glass, and polymer composites, in particular glass-reinforced plastic (GRP) and carbon-reinforced plastic (CRP). These materials have been found to be particularly advantageous both in terms of galvanic isolation and in terms of the transmission of forces and ultrasonic vibrations.

[0051] When selecting the coating thickness, it must be noted that the coating can have an effect on the entire vibration stack depending on its thickness. The coating changes the propagation / transmission of ultrasonic vibrations at the contact points between the corresponding components. If an insulating coating is applied to a threaded portion, it will change the dimensions of the thread, which must be taken into account when initially forming the thread. The insulating material preferably has a thickness of at least 0.02 mm. Even more preferably, the thickness is at most 0.5 mm. It has been shown that coatings below 0.02 mm sometimes provide sufficient insulation. However, particularly in the threaded region, the insulation can be destroyed by threading the corresponding counterpart (e.g., a screw). If the coating is too thin, there is a risk that such damage will result in a voltage flashover, which will reduce or completely eliminate the insulating effect. Thicknesses above 0.5 mm are simply unnecessary from an insulating standpoint. In the region of a normal-sized thread, such a thick coating would crush the thread pitch, thereby hindering the connection process.

[0052] In a further advantageous development, the connection element is a bolt having two axially adjacent externally threaded portions, each having an external thread that are separated from one another, and at least one of the externally threaded portions, particularly exactly one of the externally threaded portions, is coated with an insulating material. A connection element configured in this manner has two threaded portions, each with an external thread, arranged axially one after the other, that do not merge with one another. When the connection element is screwed into one of the components via one threaded portion, the screwing process is possible up to the start of the second threaded portion. There, the internal thread present in the component does not match the thread pitch of the second threaded section, and therefore further screwing is prevented. In these developments, only one of the threaded portions needs to be coated, which significantly reduces the cost of the coating. Nevertheless, with respect to the press fit between the two components, the connection element thus formed provides galvanic isolation between the components. In a further particularly advantageous development, a projection, in particular a surrounding radially extending ridge, is provided between the threaded sections, which prevents further screwing beyond the projection, which projection is preferably likewise coated, since it could come into contact with an uncoated counterpart.

[0053] In a further advantageous development, the connection element is a screw or a threaded bolt additionally equipped with a ring washer, the screw or the threaded bolt and the ring washer being of one piece or several pieces, the screw or the threaded bolt and the ring washer each being configured as an insulating means and at least partially consisting of an insulating material and / or at least partially coated with an insulating material. The screw or threaded bolt provides galvanic isolation with respect to the press fit between the two corresponding components, and the ring washer provides galvanic isolation with respect to the contact surface between the two components. These embodiments are relatively easy to implement, and in particular do not require adaptation of already existing components (sonotrode, amplitude amplifier, converter element). A single-piece design complicates the insulating components but simplifies their assembly. Similarly, a ring washer must have a certain base thickness in the case of a single-piece design, which may negatively affect vibration behavior.

[0054] In a further advantageous development, the connecting element is an element that engages with the outer periphery, in particular a union nut, which has the particular advantage that it is visible from the outside and therefore damage to, for example, the coating or the union nut itself, can be easily detected.

[0055] The various connection elements described above can generally be combined with one another.

[0056] In a further advantageous development, the converter element and sonotrode and / or the converter element and amplitude amplifier and / or the amplitude amplifier and sonotrode are connected to one another via an insulating adhesive, in particular a polyurethane and / or epoxy resin, and in particular the connecting element is connected to the converter element and / or sonotrode and / or amplitude amplifier via an insulating adhesive. The use of adhesive offers the advantage that both galvanic isolation and connection between the components can be achieved in one work step. While it is generally conceivable to use adhesive at the contact points between two components to be connected, a preferred application area for insulating adhesive is to connect a connecting element, for example a screw and / or a threaded bolt, to one of the two components so that the latter can then be screwed into the second component.

[0057] The ultrasonic tool preferably has a control unit, which is particularly configured to perform contact detection. The control unit is preferably connected to an adjusting device and a sensor that detects charges introduced into or dissipated from the third part. The control unit can thereby drive the adjusting device and move the sonotrode closer to or away from the counter tool based on the sensor signal. The control unit can also be connected to a voltage source for a signal voltage, a voltage source for an AC voltage, other sensors, and / or an output device, such as a display or a signal lamp. That is, the control unit can drive the voltage source according to the sensor signal, thereby reducing the amplitude of the AC voltage or completely switching off the AC voltage if too many or too long contacts are detected. The output device allows for the output of a sensor signal that can be perceived by a person, for example, as a warning for too many contacts or as a list of all detected contacts.

[0058] The object of the present invention is also achieved by a method for machining a workpiece by mechanical ultrasonic vibrations using the ultrasonic tool described above. This method is characterized in that the workpiece is placed between a sonotrode and a counter-tool for machining, the workpiece is machined with the ultrasonic tool, and a signal voltage, particularly a signal voltage of less than 100 V, preferably less than 30 V, and most preferably between 5 and 25 V, is applied to a signal terminal of the sonotrode electrically connected to the sealing surface of the sonotrode, preventing current flow between the neutral conductor and the signal terminal, and at least occasionally determining whether a current flows between the sonotrode and the counter-tool and / or whether a voltage drops between the sonotrode and the counter-tool. By applying the signal voltage and determining whether a current flows and / or a voltage drops, it is possible to determine whether contact has been made between the sonotrode and the counter-tool. Galvanic isolation within the ultrasonic tool prevents the signal voltage from dissipating through the neutral conductor, so that contact detection is not impaired. Furthermore, in the event of a fault, there is no risk that the high potential generated by the piezoelectric element will be applied to the sonotrode and / or to the counter tool.

[0059] When machining, a force is preferably applied to the sonotrode and transmitted from the sonotrode to the workpiece, which force ensures uniform transmission of the ultrasonic vibrations to the workpiece.

[0060] The AC voltage (effective voltage) applied to the converter of the ultrasonic tool is preferably 500 V. rms and 3000V rms and preferably has a frequency between 20 kHz and 70 kHz. These voltages and these frequencies effectively enable the generation of ultrasonic vibrations for machining the workpiece.

[0061] The ultrasonic vibrations at the sealing surface of the sonotrode preferably have a frequency of 20 kHz to 70 kHz and / or an amplitude of 5 μm to 50 μm. The frequency of the ultrasonic vibrations corresponds to the frequency of the AC voltage. The amplitude is decisively influenced by the level of the AC voltage, the converter element, the amplitude amplifier, the structural configuration of the sonotrode, and the converter, and thus the at least one piezoelectric element. Contact detection is particularly suitable for amplitudes of 5 μm to 50 μm.

[0062] The workpiece preferably comprises at least a portion of a polymer, in particular a thermoplastic polymer. The workpiece particularly preferably consists entirely of a polymer in the contact area with the sonotrode. The workpiece is preferably at least partially melted by ultrasonic vibrations in the area of ​​the contact surface with the sonotrode during machining. For contact detection, it is particularly advantageous if the workpiece comprises a polymer, in particular in the area of ​​the contact surface with the sonotrode. In a particularly advantageous embodiment, the workpiece comprises multiple parts, in particular multiple webs of material, which are joined together by machining. The webs of material are preferably transported continuously through the area between the sonotrode and the counter tool, in particular by means of rollers. Contact detection according to the present invention is particularly advantageous for such thin components, since their small thickness results in frequent contacts between the sonotrode and the counter tool. Each contact reduces the service life of the sonotrode and the counter tool. Therefore, precise adjustment of the gap between the sonotrode and the counter tool is particularly advantageous. This adjustment can be achieved by the method according to the present invention.

[0063] In a further advantageous development, the duration of at least one current flow and / or voltage drop between the sonotrode and the counter tool is determined, and if this duration exceeds a predetermined time limit, the current flow and / or voltage drop is evaluated as contact between the sonotrode and the sealing surface of the counter tool, the duration of which corresponds to the duration of the current flow or voltage drop. The time limit is preferably greater than 0.01 μs, particularly preferably greater than 1 μs. To eliminate chance, an upper limit of 1000 μs can be set for the time limit. It has been found that current does not only flow when the sonotrode and the counter tool actually come into contact, but can also flow when the sonotrode and the counter tool are very close to each other or only partially in contact. As the sealing surface of the sonotrode vibrates and moves back and forth at the frequency of the ultrasonic vibrations, a voltage flashover occurs between the sonotrode and the counter tool, resulting in a current flow, especially at the extreme positions where the distance between the sealing surfaces is minimal. It has therefore been found to be advantageous not to evaluate each current flow as a contact between the sonotrode and the counter tool, but to evaluate only current flows / voltage drops that last for a predetermined period of time, for example, 1 μs or more. Preferably, therefore, current flows and / or voltage drops whose duration is below a predetermined time limit are ignored and not evaluated as contact. The above-mentioned ranges for the time limit have been found to be particularly advantageous for the above-mentioned frequencies of ultrasonic vibration. Above 1000 μs, it can no longer be considered a single contact.

[0064] In a further advantageous development, the current intensity is determined for at least one current flow and / or voltage drop between the sonotrode and the counter tool, and if the current intensity exceeds a predetermined current limit, the current flow and voltage drop are evaluated as contact between the sealing surfaces. The current limit is greater than 1 mA. To eliminate chance, an upper limit of 300 μs can be set for the current limit. The current intensity also serves as an indicator of how close the sealing surfaces actually are. Therefore, the current intensity can also be used to distinguish between contact and non-contact to be evaluated. Furthermore, sealing surfaces have flat areas and roughness, even if slight. Therefore, it is possible that small areas of the sealing surfaces are already in contact and cause current flow, but these are so small that they should not yet be evaluated as contact. Even in such cases, both limit values ​​are suitable for qualitatively evaluating contact. Determining the current intensity and evaluating contact accordingly can be used instead of or in addition to the duration of the current flow and / or voltage drop. Particularly preferred is to evaluate only current flow and / or voltage drop as a contact when both the time limit and the current limit are exceeded.

[0065] In a further advantageous development, for at least a predetermined (past) period, in particular for the last elapsed milliseconds, - the total number of contacts between the sonotrode and the counter tool, - maximum contact time of contact, - the sum of the contact times of all contacts, At least one of the parameters is determined, which is preferably stored and / or output.

[0066] Determining these parameters is used to evaluate contact detection. For example, if there are only a few contacts within a predetermined period of time, or if there are many but the total contact time is very short, it can be concluded that the sealing faces are not yet close. For each parameter, a limit value can be set, beyond which a predetermined action, for example a warning signal, is generated.

[0067] These parameters can be further machined by a control unit of the ultrasonic tool, which in particular can adjust the position of the ultrasonic tool or the vibrating stack, in particular the sonotrode, reduce or increase the force applied to the sonotrode, output a warning and / or stop the machining process according to one or more of the parameters.

[0068] The invention is illustrated and explained below by way of example in the drawings. [Brief explanation of the drawings]

[0069] [Figure 1] FIG. 1 shows a first embodiment of an ultrasonic tool diagrammatically in cross-section from the side. [Figure 2] FIG. 2 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 3] FIG. 3 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 4] FIG. 4 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 5] FIG. 5 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 6] FIG. 6 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 7] FIG. 7 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 8] FIG. 8 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 9] FIG. 9 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 10] FIG. 10 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 11] FIG. 11 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 12] FIG. 12 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 13] FIG. 13 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 14] FIG. 14 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 15] FIG. 15 shows a schematic representation of another embodiment of an ultrasonic tool. [Figure 16] FIG. 16 shows a schematic representation of another embodiment of an ultrasonic tool. DETAILED DESCRIPTION OF THE INVENTION

[0070] The ultrasonic tool 100 shown in FIG. 1 includes a converter member 10 and a sonotrode 40. The converter member 10 includes a converter 20, a converter lower part 12, a ring-washer-shaped cover plate 16, and a converter screw 18. The converter 20 includes four ring-washer-shaped piezoelectric elements 22, which are arranged one after the other between the converter lower part 12 and the cover plate 16. The converter 20 also includes five electrodes, also referred to as contact washers. Three neutral electrodes 24 and two phase electrodes 26 are also formed in the shape of ring washers. The electrodes 24, 26 are arranged alternately with the piezoelectric elements 22 between the converter lower part 12 and the cover plate 16 along the converter axis K. The electrodes 24 and 26 are arranged alternately with each other. The neutral electrodes 24 are arranged at the bottom and top.

[0071] The converter screw 18 rests on the cover plate 16 with its screw head and extends through all of the holes in the piezoelectric element 22, the electrodes 24, 26, and the cover plate 16. The converter screw 18 is threaded into the converter lower part 12, thereby compactly holding the piezoelectric element 22 and the electrodes 24, 26. Therefore, unlike what is shown in the schematic representation of Figure 1, the piezoelectric element and the electrodes 24, 26 are in direct contact with each other and are held compactly by the converter screw 18. The converter screw 18 is tightened with a sufficient biasing force, for example, 70 kN.

[0072] The converter element 10 further comprises a phase conductor 31 for the supply conductor of the AC voltage and a neutral conductor 33 for the dissipation conductor. The phase conductor 31 and the neutral conductor 33 form two poles for the converter 20. The neutral electrode 24 is connected to the neutral conductor 33, and the phase electrode 26 is connected to the phase conductor 31. The piezoelectric element 22 is polarized and arranged so that it is fully stretched or fully clamped at each point in time, except for the zero position.

[0073] When an AC voltage is applied to the phase conductors 31 and the neutral conductor 33, the piezoelectric element 22 converts the AC voltage into mechanical ultrasonic vibrations, and the converter member 10 is vibrated at resonance by the mechanical ultrasonic vibrations of wavelength λ. In the illustrated embodiment, the ultrasonic vibrations propagate from the converter 20 to the sonotrode 40, i.e., along a propagation direction R that extends downward along the converter axis K. In the illustrated embodiment, the converter member 10 and the sonotrode 40 both have a length of λ / 2 along the propagation direction R. In this way, the sonotrode 40 and the converter member 10 are tuned to each other so that the sonotrode 40 is vibrated at resonance by the mechanical ultrasonic vibrations of wavelength λ.

[0074] The sonotrode 40 has a sealing surface 42 that is provided for contacting a workpiece 200 to be machined. The workpiece 200 is shown here diagrammatically. Often, the workpiece 200 will have multiple parts that are welded together, in particular multiple webs of material that are welded together and together form the workpiece 200.

[0075] The ultrasonic tool 100 further includes a counter tool 110 with a sealing surface 111. The ultrasonic tool 100 is configured to machine a workpiece 200 using mechanical ultrasonic vibrations. The workpiece 200 is placed between the sealing surfaces 42, 111 for machining, or is guided through the gap between the sealing surfaces 42, 111, in either case contacting the sealing surfaces 42, 111. A force in the propagation direction R is also exerted on the workpiece 200, which force may be generated by a bracket adjustment device (not shown). When the ultrasonic vibrations are generated, the workpiece 200 is machined, often resulting in multiple sections, such as webs of material, being connected to one another.

[0076] An insulating means 300 is arranged between the converter member 10 and the sonotrode 40. The insulating means 300 has a connecting element 310 in the form of a screw bolt and an insulating element 350 in the form of an insulating washer. The connecting element 310 and the insulating element 350 are arranged integrally. In the illustrated embodiment, the insulating means 300 is made entirely of ceramic material. The insulating means 300 is screwed into both the converter lower part 12 and the sonotrode 40 by the connecting element 310. The converter lower part 12 and the sonotrode 40 are separated from each other by the insulating means 300 and therefore do not come into contact with each other. In this way, the sealing surface 42 of the sonotrode 40 and the first neutral conductor 33 of the converter 20 are galvanically isolated. Current flow between the converter lower part 12 and the sonotrode 40 is prevented.

[0077] The converter element 10 has a converter housing 11, shown diagrammatically, which shields, inter alia, the piezoelectric element 22 and the electrodes 24, 26 towards the outside. A protective conductor 35 is provided in the converter housing 11 and is connected to earth. The converter housing 11 is connected to the converter lower part 12 in the region of the vibration node.

[0078] The sonotrode 40 has a signal terminal 44 for the signal voltage, electrically connected to the sealing surface 42. The neutral conductor 33 and the signal terminal 44 are galvanically isolated from each other by an insulating means 300.

[0079] The ultrasonic tool 100 has a voltage source 400, which is a DC voltage source. The voltage source 400 is electrically connected, on the one hand, to the signal terminal 44 of the sonotrode 40 via a sensor 410 in the form of a current measuring device, and, on the other hand, to the counter tool 110. In standard use, a DC voltage is applied to the signal terminal 44 and thus to the sealing surface 42 via the voltage source 400. When the sealing surface 42, 111 is contacted during machining of the workpiece 200, a current flows. This current flow can be detected using the sensor 410. For this purpose, the sonotrode 40 and the counter tool 110 are designed to be electrically conductive and are made of, in particular, a metallic material. Therefore, contact between the sealing surfaces 42, 111 can be inferred from the signal of the sensor 410 (contact detection).

[0080] To generate an AC voltage for the converter 20 , an AC voltage source 39 is provided, which is connected to the phase conductors 31 and the neutral conductor 33 .

[0081] If the conductor from the AC voltage source 39 to the neutral conductor 33 breaks, the piezoelectric element 22 may be excited again, which then causes the piezoelectric element to generate a potential on the neutral electrode 24 and the neutral conductor 33. This potential is then also applied to the converter lower part 12. The protective conductor 35 ensures that this potential is dissipated in the event of a fault and that contact with the converter housing 11 does not result in any interference. Furthermore, the insulating means 300 prevents this potential from being applied to the sealing surface 42 of the sonotrode 40 in the event of a fault and thus affecting contact detection. Conversely, to prevent signal voltages from being dissipated via the protective conductor 35, the protective conductor 35 is galvanically isolated by the insulating means 300 from the sealing surface 42 and the signal terminal 44.

[0082] In other embodiments, the insulating means 300 may consist of a material other than ceramic, for example a metal, In these embodiments, the insulating means 300 has an insulating coating on at least one side or over the entire surface.

[0083] In other embodiments, the amplitude amplifier 60 can also be provided between the converter lower part 12 and the sonotrode 40. In that case, the insulating means 300 can be arranged between the converter lower part 12 and the amplitude amplifier 60 or between the amplitude amplifier 60 and the sonotrode 40.

[0084] In FIG. 2, only a portion of the ultrasonic tool 100 is shown, namely the area centered around the contact point 112 between the sonotrode 40 and the amplitude amplifier 60.

[0085] In this embodiment, two insulating means 300 are provided between the sonotrode 40 and the amplitude amplifier 60. A connecting element in the form of a threaded bolt is provided, which is screwed into both the sonotrode 40 and the amplitude amplifier 60. This threaded bolt is coated all around and connects the sonotrode 40 and the amplitude amplifier 60 with a press fit, thus forming a connection point between the components. In this way, the connecting element is configured as the insulating means 300. A further insulating means 300 is provided in the form of an insulating element 350 in the form of an insulating washer. This insulating washer is a ring washer and is arranged at the contact point 112 between the sonotrode 40 and the amplitude amplifier 60. The insulating washer also has an insulating coating, which may be provided all around or only on one of its axial sides, for example, on the upper side 352 or the lower side 354. The connecting element 310 and the insulating element 350 together ensure galvanic isolation between the sonotrode 40 and the amplitude amplifier 60.

[0086] The insulating means 300 shown in FIG. 2 can also be used in other embodiments for the connection between the sonotrode 40 and the converter element 10 or for the connection between the amplitude amplifier 60 and the converter element 10 .

[0087] FIG. 3 shows a portion of the ultrasonic tool 100, centered around the contact point 112 between the sonotrode 40 and the amplitude amplifier 60. In this embodiment, the ultrasonic tool 100 includes an insulating element 350 in the form of a ring-shaped insulating washer and a wire thread insert 320 as the insulating means 300. The wire thread insert 320 may consist entirely of an insulating material or may have an insulating coating. The wire thread insert 320 is threaded into a threaded bore of the sonotrode 40. The same applies to the insulating element 350. Furthermore, a connecting element 310 in the form of a threaded bolt is provided. The threaded bolt is threaded into the amplitude amplifier 60 at one end and into the wire thread insert 320 at the other end. The insulating element 350 and the wire thread insert 320 together form a galvanic isolation between the sonotrode 40 and the amplitude amplifier 60.

[0088] This type of connection can also be used in other embodiments between the sonotrode 40 and the converter element 10 or between the amplitude amplifier 60 and the converter element 10 .

[0089] FIG. 4 shows the ultrasonic tool 100 partially, centered on the contact point 112 between the sonotrode 40 and the amplitude amplifier 60. In this embodiment, neither the sonotrode 40 nor the amplitude amplifier 60 has any holes. An insulating element 350 in the form of an insulating washer without holes is provided between the components 40, 60 as the insulating means 300. However, in other embodiments, the insulating washer may have holes, if this is advantageous, for example, in terms of vibration technology or uniform force transmission. The insulating element 350 represents galvanic isolation at the contact point 112. The sonotrode 40 has an external thread 46, and the amplitude amplifier 60 has a surrounding shoulder 62. Furthermore, a connecting element 310 in the form of a union nut is provided. The union nut has a radially inward projection 316 at its upper end and an internal thread 314 at its lower end. When the union nut is used as specified, the protrusion 316 rests on the shoulder 62 and the inner thread 314 is screwed onto the outer thread 46, thereby connecting the sonotrode 40 and the amplitude amplifier 60 at the connection point with a force fit. The union nut can consist entirely of an insulating material. However, it can also have an insulating coating in individual areas, in particular in the area of ​​the protrusion 316 and preferably all that rests on the shoulder 62. This prevents current from flowing from the amplitude amplifier 60 through the union nut to the sonotrode 40. The union nut and the insulating washer thus form two insulating means 300.

[0090] This type of galvanic isolation can also be used in other embodiments between the sonotrode 40 and the converter element 10 or between the amplitude amplifier 60 and the converter element 10 .

[0091] The ultrasonic tool 100 shown in Fig. 5 similarly comprises a sonotrode 40 and an amplitude amplifier 60. Between the two components 40, 60, at the contact point 112, an insulating means 300 in the form of a flange part is provided, which comprises a ring washer as insulating element 350 and a threaded bolt connected thereto as connecting element 310. The connecting element 310 and the insulating element 350 are constructed integrally. In the illustrated embodiment, an insulating coating is provided on the underside 354 of the insulating washer. In other embodiments, the entire flange part can consist of an insulating material, for example ceramic.

[0092] The insulating washer projects radially relative to the amplitude amplifier 60, forming a flange shoulder 358 there. This flange shoulder 358 extends all the way around. A union nut is provided as a further connecting element 310. The union nut has a radially inward-projecting projection 316 at its upper end and an internal thread 314 at its lower end. The projection 316 rests on the flange shoulder 358, and the thread 314 is screwed onto the external thread 46 of the sonotrode 40. The insulating washer likewise has an insulating coating where the union nut rests, i.e., on its upper side 352. This is not necessary if the flange portion is made entirely of insulating material.

[0093] The flange portion is screwed by a threaded bolt into a threaded hole in the amplitude amplifier 60. An insulating coating galvanically isolates the sonotrode 40 and the amplitude amplifier 60.

[0094] This type of connection can also be used in other embodiments between the sonotrode 40 and the converter element 10 or between the amplitude amplifier 60 and the converter element 10 .

[0095] FIG. 6 shows another embodiment of the ultrasonic tool 100, again centered on the contact point 112 between the two components 40, 60. An insulating means 300 is now arranged between the sonotrode 40 and the amplitude amplifier 60. This configuration includes a flange section that integrally includes an insulating washer as the insulating element 350 and a threaded bolt as the connecting element 310. The flange section is made of an insulating material, for example, ceramic. The insulating means 300 has a number of holes arranged along a track, through which flange screws 356 extend. The insulating means 300 is connected to the sonotrode 40 by the flange bolts 356. For this purpose, the flange bolts 356 are rotated in the threaded holes of the sonotrode. The amplitude amplifier 60 is screwed onto the threaded bolts. The flange bolts 356 are provided with an insulating coating. The flange bolts 356 thus also form the insulating means 300 and the connecting means 310. The insulating coating and insulating material galvanically isolate the sonotrode 40 and the amplitude amplifier 60 from each other. In alternative embodiments, only the flange portion may have an insulating coating and / or the flange bolts 356 may be made of an insulating material.

[0096] This type of connection and insulation can also be used in other embodiments between the sonotrode and the converter element 10 or between the amplitude amplifier 60 and the converter element 10 .

[0097] In the embodiment of the ultrasonic tool 100 shown in Figure 7, a ring-shaped insulating washer is provided as insulating element 350 between the sonotrode 40 and the amplitude amplifier 60. The insulating washer provides galvanic isolation at the contact point 112. A threaded hole is provided in the amplitude amplifier 60. An unthreaded blind hole is provided in the sonotrode 40. The two holes are concentric.

[0098] The ultrasonic tool 100 further comprises a bolt as a connecting element 310, which has a thread at one end and a smooth portion 311 at the other end. The bolt is glued to the sonotrode 40 by an adhesive 360, i.e., a material-locking connection is formed. The bolt extends beyond the upper end of the sonotrode 40. In this way, the amplitude amplifier 60 can be screwed onto the bolt. The adhesive 360 ​​is insulating and provides galvanic isolation at the connection point between the sonotrode 40 and the amplitude amplifier 60.

[0099] In other embodiments, the bolt can have threads around its entire circumference and / or the holes in the sonotrode 40 can have internal threads, in which case the holes do not fit together. When adhesive 360 ​​is introduced into the resulting gap, an undercut and therefore a positive lock is achieved in addition to the material lock.

[0100] The galvanic isolation between the sonotrode 40 and the amplitude amplifier 60 of the type described here can also be used in other embodiments for galvanic isolation between the sonotrode 40 and the converter element 10 or between the amplitude amplifier 60 and the converter element 10.

[0101] FIG. 8 shows a portion of an ultrasonic tool 100 according to another embodiment. In this embodiment, the amplitude amplifier 60 has a through-hole 64, the upper end of which terminates in a step 62. A screw is arranged in the through-hole 64 as a connecting element 310. The screw extends downward from the amplitude amplifier 60 or the through-hole 64 and is threaded into a threaded bore of the sonotrode 40. An additional insulating means (not shown) is provided on the inner wall of the through-hole. This additional insulating means ensures sufficient insulation in the event of unintentional contact between the through-hole 64 and the screw. This additional insulating means does not need to transmit significant forces; it only needs to ensure electrical resistance. This additional insulating means can also be used in other embodiments when no insulating coating is provided between the two components but contact cannot be completely eliminated.

[0102] An insulating washer is further provided as insulating element 350 at contact point 112 between sonotrode 40 and amplitude amplifier 60. This insulating washer has an insulating coating or consists entirely of an insulating material, for example ceramic, thereby forming insulating means 300. An insulating coating is also provided on step surface 66 of step 62, i.e., on the surface on which the screw head of the screw rests. Otherwise, the screw does not come into contact with amplitude amplifier 60. In this way, sonotrode 40 and amplitude amplifier 60 are galvanically isolated. In this way, amplitude amplifier 60 constitutes insulating means 300.

[0103] Above the through hole 64, the amplitude amplifier has an internal thread into which the converter lower part 12 is screwed.

[0104] FIG. 9 shows another embodiment of the ultrasonic tool 100. In this embodiment, the amplitude amplifier 60 has a through-hole 64 with a conical taper at its upper end. A screw serving as a connection element 310 can be inserted into this through-hole 64 from below, and the screw rests on the conical taper on the step surface 66 of the step 62, forming a connection point. At this position, the screw protrudes upward from the through-hole 64 and is threaded into a threaded hole in the converter lower part 12. A ring-shaped insulating washer is arranged as an insulating element 350 between the converter lower part 12 and the amplitude amplifier 60. An insulating coating is arranged on the step surface 66 of the step 62. In this way, the amplitude amplifier 60 constitutes the insulating means 300.

[0105] The insulating washer has an insulating coating or is made entirely of insulating material, thus forming the insulating means 300. In this way, the amplitude amplifier 60 and the converter lower part 12 are galvanically isolated.

[0106] In the embodiment shown in FIG. 10 , the ultrasonic tool 100 includes a sonotrode 40, an amplitude amplifier 60, and a converter lower part 12. The amplitude amplifier 60 has two concentric threaded holes, each with an internal thread. The sonotrode 40 is screwed into the lower hole. The converter lower part 12 has a through-hole 13 that is concentric with the upper threaded hole in the amplitude amplifier. An insulating washer is arranged as an insulating element 350 between the converter lower part 12 and the amplitude amplifier 60. This insulating washer is made of an insulating material or has an insulating coating, thereby forming the insulating means 300. A bolt as a connecting element 310 can be inserted into the through-hole 13 from above. In this case, the screw rests on a step 15 of the converter lower part 12, which has an insulating coating in the area of ​​the step 15. In this way, the converter lower part 12 forms the insulating means 300. A screw is threaded into this threaded hole in the amplitude amplifier to connect the amplitude amplifier 60 with the converter lower part 12 by a press fit. The amplitude amplifier 60 and the converter lower part 12 are galvanically isolated from the insulating coating and also from the insulating washer.

[0107] The upper end of the through hole 13 is provided with an internal thread into which the converter screw 18 can be threaded. In this embodiment, the piezoelectric element 22 can only be added after the connection of the converter lower part 12 and the amplitude amplifier 60, and the converter 20 can be completely constructed.

[0108] The insulating washer and the coating in the area of ​​the step 15 provide galvanic isolation between the amplitude amplifier and the converter lower part 12 .

[0109] 11A, 11B and 11C show another embodiment of the ultrasonic tool 100. Shown is the area centered on the contact point 112 between the sonotrode 40 and the amplitude amplifier 60. The amplitude amplifier 60 has a through-hole 64, which has a step 62 in its lower area. An insulating washer is arranged between the sonotrode 40 and the amplitude amplifier 60 as an insulating element 350, and is formed in a ring shape. The insulating washer is made of an insulating material or has an insulating coating, thereby constituting the insulating means 300.

[0110] The sonotrode 40 has a transverse bore 48 and a central blind bore 49, which communicates with the transverse bore 48. The transverse bore 48 has a rectangular cross section, while the blind bore 49 is circular. A rectangular parallelepiped transverse section 330 in the form of a channel piece can be inserted into the transverse bore 48 from the side. The transverse section 330 has a central threaded bore 332, which is concentric with the blind bore 49. A screw can then be inserted from above through the through-hole 64, which contacts the step 62 and threads into the hole 332 of the channel piece. The channel piece is pulled upward until it abuts against the ceiling of the transverse bore 48. When the screw is further tightened, a clamping force is applied. The transverse section 330 is provided with an insulating coating, while the bore is uncoated. In this way, the transverse section 330 constitutes the insulating means 300. The upper side of the transverse portion 330 abuts the upper side of the transverse hole 48, thereby providing galvanic isolation.

[0111] In other embodiments, the transverse portion 330 may be cylindrical. If the transverse portion 330 is configured as a cylinder, the transverse hole 48 is preferably round or oval in cross section.

[0112] The insulating washer and the transverse portion 330 provide galvanic isolation between the sonotrode 40 and the amplitude amplifier 60 .

[0113] The illustrated embodiment can also be used in the connection between a sonotrode and a converter element 10 or in the connection between an amplitude amplifier and a converter element 10 .

[0114] Alternatively, the transverse portion 330 may be made entirely of insulating material.

[0115] In the embodiment shown in FIG. 12 , the ultrasonic tool 100 includes a converter lower part 12 and an amplitude amplifier 60, which are joined at a contact point 112. The converter lower part 12 includes a through-hole 13. In this embodiment, a cascade of multiple components is provided as the connecting element 310. The cascade includes a threaded bolt with two separate threaded portions. One of the threaded portions is threaded into the internal thread of the converter lower part 12. The other end of the threaded bolt can be threaded into the first cascade part 340. The first cascade part 340 holds the second cascade part 342 in the propagation direction R with a positive lock. The second cascade part 342 has an external thread with which it is connected to the internal thread of the amplitude amplifier 60. The second cascade part 342 has an insulating coating on its upper side 344 and lower side 346. In this way, the second cascade part 342 constitutes the insulating means 300. An upper side 344 of the second cascade part 342 is in contact with the converter lower part 12. A lower side 346 of the second cascade part 342 is in contact with the first cascade part 340. The threaded bolt does not contact the second cascade part 342. Again, additional insulating means, such as an insulating sleeve, can be provided between the threaded bolt and the second cascade part 342. In this way, the converter lower part 12 and the amplitude amplifier 60 are galvanically isolated from each other.

[0116] A cascade of this kind can also be used in the connection between the amplitude amplifier 60 and the sonotrode 40 or in the connection between the sonotrode 40 and the converter element 10 .

[0117] The embodiment shown in Fig. 13 also has a cascade provided as connecting element 310. The essential difference with respect to the embodiment shown in Fig. 12 is that the second cascade 342 has a smaller diameter and is not closed off upwards by the amplitude amplifier 60. For this reason, an insulating washer is provided as insulating element 350 between the amplitude amplifier 60 and the lower converter part 12. This insulating washer consists of an insulating material or has an insulating coating and thereby constitutes the insulating means 300.

[0118] Furthermore, in this embodiment, the second cascade part 342 is not coated. Instead, the first cascade part 340 has an insulating coating on its axial contact surface with the second cascade part 342. Alternatively, in this embodiment, the first cascade part 340 can also consist entirely of an insulating material, for example ceramic. In either case, the first cascade part 340 forms the insulating means 300. In the radial direction, there is no contact between the first cascade part 340 and the second cascade part 342. In this case too, additional insulating means, such as an insulating sleeve, can be provided.

[0119] This type of connection can also be used between the sonotrode 40 and the amplitude amplifier 60 or between the sonotrode 40 and the converter member 10 .

[0120] FIG. 14 shows another embodiment of the ultrasonic tool 100. In this embodiment, a bolt is provided as the connecting element 310, having an externally threaded portion and a smooth portion 311. The smooth portion 311 is provided with an insulating coating, and the bolt is shrink-fitted into a blind hole in the sonotrode 40 via the smooth portion 311. The bolt thus forms the insulating means 300. The threaded portion of the bolt protrudes upward from the sonotrode 40. In this way, the amplitude amplifier 60 can be screwed onto the threaded portion via a threaded hole. Furthermore, a ring-shaped insulating washer is provided at the contact point 112 as the insulating element 350. The insulating washer is made of an insulating material or has an insulating coating, thereby constituting the insulating means 300. In this way, galvanic isolation is established between the sonotrode 40 and the amplitude amplifier 60.

[0121] 15, the ultrasonic tool 100 comprises a sonotrode 40 and an amplitude amplifier 60. At the contact point 112, an insulating washer is provided as an insulating element 350. This insulating washer has a ring shape. The insulating washer consists of an insulating material or has an insulating coating, thereby constituting the insulating means 300.

[0122] The sonotrode 40 has a bolt 47 that is integrally formed with the sonotrode 40. The bolt 47 protrudes upward through a recess in the ring washer. The bolt 47 of the sonotrode 40 is provided with an insulating coating. In this way, the sonotrode 40 forms the insulating means 300. A screw attachment 313 with an external thread is shrink-fitted onto the bolt 47 as the connecting means 310. The amplitude amplifier 60 is screwed onto the external thread of the screw attachment 313 by means of a threaded hole.

[0123] In an alternative embodiment, the insulating panel can be omitted if the upper front end of the sonotrode 40 is provided with an insulating coating.

[0124] This type of connection can also be used in other embodiments between the sonotrode 40 and the converter element 10 or between the amplitude amplifier 60 and the converter element 10 .

[0125] 16 is substantially different from the embodiment shown in FIG. 2 in that the threaded bolt forming the connecting means 310 has two axially adjacent externally threaded portions 317, 318, each provided with an external thread that separates the external threads, and a circumferential ridge between the externally threaded portions 317, 318 that separates the external threads. Only the first externally threaded portion 317 and the ridge are coated with an insulating material. In this way, the threaded bolt forms the insulating means 300.

[0126] Instead of an insulating washer or a coating on the insulating washer, at least one of the two interconnected components, here the sonotrode 40 and the amplitude amplifier 60, can have an insulating coating or can consist at least partially, in particular at the respective contact surfaces, of an insulating material. In that case, the entire insulating washer or its coating can be omitted. This is true for all embodiments with an insulating washer. [Explanation of symbols]

[0127] 10 Converter parts 11 Converter housing 12 Lower part of the converter 13, 64 through holes 15, 62 step part 16 Cover Plate 18 Converter screw 20 Converter 22 Piezoelectric element 24 Neutral electrode 26 phase electrodes 31 Phase conductor 33 Neutral conductor 35 Protective conductor 39 AC voltage source 40 Sonotrode 42 sealing surface 44 signal terminal 46 External thread 47 volts 48 Horizontal hole 49 Blind hole 60 Amplitude Amplifier 66 Stepped surface 100 ultrasonic tools 112 contact points 110 Opposing tool 112 sealing surface 200 workpieces 300 Insulation means 310 Connection elements / thread bolts 311 Smooth part 313 Screw attachment 314 Internal thread 316 Protrusion 317 First externally threaded portion 318 Second externally threaded portion 320 Wire Thread Insert 330 Transverse section 332 screw hole 340 First Cascade Section 342 Second Cascade Section 350 Isolation element 344, 352 upper side 346, 354 lower side 356 flange screw 358 Flange step 360 Adhesive 400 Voltage Source 410 Sensors K Converter axis R Propagation direction

Claims

1. 1. An ultrasonic tool for machining a workpiece using mechanical ultrasonic vibrations, comprising a converter member and a sonotrode, wherein the converter member comprises a converter with at least one piezoelectric element, the converter member having a phase conductor and a neutral conductor for a supply conductor of an AC voltage, the at least one piezoelectric element being configured to convert the AC voltage into mechanical ultrasonic vibrations, the converter member being capable of being vibrated in resonance with mechanical ultrasonic vibrations of wavelength λ, the converter member being mechanically coupled to the sonotrode, and the sonotrode and the converter member being tuned to each other so that the sonotrode can be vibrated in resonance with the mechanical ultrasonic vibrations of wavelength λ, the sonotrode having a sealing surface, the sealing surface being arranged to contact the workpiece to be machined, wherein the sealing surface of the sonotrode and the neutral conductor are galvanically isolated.

2. 2. The ultrasonic tool of claim 1, wherein the sonotrode has an electrically connected signal terminal, the signal terminal being electrically connected to the sealing surface and for a signal voltage, and the neutral conductor and the signal terminal being galvanically isolated.

3. 3. An ultrasonic tool according to claim 1, wherein the converter member has a converter housing in which the at least one piezoelectric element is arranged and a protective conductor is provided, the ultrasonic tool has a first part having at least the neutral conductor, a second part having at least the protective conductor and the converter housing, and a third part having the sealing surface of the sonotrode, and is capable of outputting or receiving a signal voltage via the signal terminal, the second part and the third part being galvanically isolated, and optionally the first part and the second part being further galvanically isolated.

4. 4. The ultrasonic tool of claim 3, further comprising an insulating housing made of an electrically insulating material defining an insulating space inside the converter housing, the at least one piezoelectric element and the neutral conductor being arranged in the insulating space, and the insulating housing preferably having a torus shape or a hollow cylindrical shape.

5. 5. An ultrasonic tool according to claim 1, characterized in that the counter tool, in particular a roller, is provided with a sealing surface, and the counter tool is positioned so that the workpiece to be machined can be placed between the sealing surface of the sonotrode and the sealing surface of the counter tool during machining, preferably the sealing surface of the counter tool being grounded.

6. An ultrasonic tool according to any one of claims 3 to 5, characterized in that a voltage source is provided, by which a signal voltage can be supplied to the third part, and a sensor is provided for detecting an electric charge introduced to or dissipated from the third part.

7. 7. An ultrasonic tool according to claim 6, characterized in that the signal voltage is a DC voltage and is less than 30V, preferably less than 25V, and most preferably between 5V and 12V.

8. 8. An ultrasonic tool according to any one of claims 3 to 7, characterized in that the third part is connected to the voltage source by an electric wire, the electric wire being shielded and / or having a total capacitance of less than 2500 pF, in particular less than 1500 pF.

9. 9. An ultrasonic tool according to any one of claims 3 to 8, characterized in that the insulation resistance between the second part and the third part is at least 5 kΩ, in particular at least 7 kΩ, the insulation resistance being preferably less than 100 MΩ.

10. An ultrasonic tool as described in any one of claims 1 to 9, characterized in that an amplitude amplifier is provided between the converter member and the sonotrode, the converter member is mechanically coupled to the amplitude amplifier and the amplitude amplifier is mechanically coupled to the sonotrode, and the sonotrode, the amplitude amplifier and the converter member are tuned to each other so that the sonotrode can be resonantly vibrated by mechanical ultrasonic vibrations of the wavelength λ.

11. 11. An ultrasonic tool according to any one of claims 1 to 10, further comprising a bracket, said bracket engaging said sonotrode, said converter member and / or said amplitude amplifier.

12. 12. An ultrasonic tool according to any one of claims 1 to 11, characterized in that at least one insulating means is provided, which galvanically isolates the sealing surface of the sonotrode from the neutral conductor.

13. 13. An ultrasonic tool according to claim 12, characterized in that at least one insulating means is provided at exactly two positions, in particular at the contact point between the converter element, the sonotrode and / or the amplitude amplifier, and at the connection point of the converter element, the sonotrode and / or the amplitude amplifier.

14. 14. An ultrasonic tool according to claim 12 or 13, characterized in that the converter element and the sonotrode and / or the converter element and the amplitude amplifier and / or the amplitude amplifier and the sonotrode are connected to each other via at least one connecting element, in particular via a screw and / or a threaded bolt and / or a threaded bushing, in particular with a clamping force of at least 20 kN and preferably less than 150 kN, in particular at least 30 kN and / or less than 90 kN, and the connecting element is configured as an insulating means and at least partially has an insulating coating and / or consists at least partially of an insulating material.

15. 15. An ultrasonic tool according to any one of claims 12 to 14, characterized in that at least one insulating element, in particular an insulating washer, is provided between the converter element and the sonotrode, in particular between the converter element and the amplitude amplifier and / or between the amplitude amplifier and the sonotrode, the insulating element being configured as an insulating means and consisting at least partly of an insulating material and / or having at least partly an insulating coating.

16. An ultrasonic tool according to any one of claims 12 to 15, characterized in that the converter element and / or the amplitude amplifier and / or the sonotrode are configured as insulating means and consist at least partially of an insulating material and / or have at least partially an insulating coating.

17. 17. An ultrasonic tool according to any one of claims 14 to 16, characterized in that a cascade of multiple components is provided as the connecting element, preferably a first cascade part is held in the propagation direction by a second cascade part with a form fit, and the first cascade part and / or the second cascade part have an insulating coating on their respective contact surfaces for the form fit.

18. 18. An ultrasonic tool according to any one of claims 14 to 17, characterized in that the connecting element has a smooth portion, the smooth portion has an insulating coating, and the portion is shrink-fitted into the sonotrode, the converter member or the amplitude amplifier.

19. 19. An ultrasonic tool according to any one of claims 14 to 18, wherein the connecting element has a smooth portion and a threaded attachment, the threaded attachment being shrink fitted onto the smooth portion.

20. 20. An ultrasonic tool as claimed in any one of claims 10 to 19, characterized in that a through hole is provided in the amplitude amplifier, the amplitude amplifier has a portion with an insulating coating, and further a screw is provided, the screw is placed with its head on the coated portion, is spaced from the inner surface of the through hole, and is screwed into the converter member or the sonotrode with its threaded portion.

21. 21. An ultrasonic tool according to any one of claims 1 to 20, characterized in that a transverse hole is provided in the converter element or the amplitude amplifier or the sonotrode, and an at least partially coated transverse section having a threaded hole is inserted into the transverse hole, and the converter element, the amplitude amplifier or the sonotrode has, in addition to the transverse hole, a hole concentric with the threaded hole, and a screw or threaded bolt is arranged in the hole, and the screw or threaded bolt is connected to the transverse section by the threaded hole.

22. 22. An ultrasonic tool according to any one of claims 12 to 21, characterized in that a coupling piece, in particular a flange portion, is provided as an insulating means, the insulating means being fixed to the converter member or the amplitude amplifier or the sonotrode by a screw, the coupling piece having the insulating coating at the location where the screw rests.

23. The insulating coating and / or the insulating material is preferably a ceramic, in particular a chromium oxide (Cr ２ O ３ ), aluminum oxide (Al ２ O ３ 23. An ultrasonic tool according to any one of claims 14 to 22, characterized in that it comprises at least one of the following materials: glass, polymer composites, in particular glass reinforced plastics (GRP) and carbon reinforced plastics (CRP).

24. 24. An ultrasonic tool according to any one of claims 14 to 23, characterized in that the insulating coating has a thickness of at least 0.02 mm and preferably a maximum thickness of 0.5 mm.

25. 25. An ultrasonic tool according to any one of claims 14 to 24, characterized in that the connecting element is a bolt having two axially spaced externally threaded portions, each having an external thread, the external threads being separated from one another, and at least one of the externally threaded portions, in particular exactly one of the externally threaded portions, being coated with an insulating material.

26. 26. An ultrasonic tool according to any one of claims 14 to 25, characterized in that the connecting element is a screw or a threaded bolt with an additional ring washer, the screw or the threaded bolt and the ring washer are configured either as a one-piece unit or a multi-piece unit, and the screw or the threaded bolt and the ring washer are each configured as insulating means and are at least partially made of insulating material and / or at least partially coated with insulating material.

27. 27. An ultrasonic tool according to any one of claims 14 to 26, characterized in that the connecting element is an outer circumferential engaging element, particularly a union nut.

28. 28. An ultrasonic tool according to any one of claims 14 to 27, characterized in that the converter element and the sonotrode and / or the converter element and the amplitude amplifier and / or the amplitude amplifier and the sonotrode are connected to each other via an insulating adhesive, in particular via a polyurethane and / or epoxy resin, in particular the connecting element is connected to the converter element and / or the sonotrode and / or the amplitude amplifier via an insulating adhesive.

29. 29. A method for machining a workpiece by mechanical ultrasonic vibrations using an ultrasonic tool according to any one of claims 1 to 28, comprising: the workpiece is placed between the sonotrode and a counter-tool for machining, and the workpiece is machined by the ultrasonic tool; an electrical signal voltage is generated at a signal terminal of the sonotrode, which is electrically connected to the sealing surface of the sonotrode, in particular a signal voltage of less than 30 V, preferably less than 25 V, and most preferably between 5 V and 12 V, to prevent current flow between the neutral conductor and the signal terminal; determining whether or not, at least temporarily, a current flows between the sonotrode and the counter tool and / or whether or not a voltage between the sonotrode and the counter tool has dropped; A method characterized by:

30. 30. The method according to claim 29, characterized in that the duration of at least one current flow and / or voltage drop between the sonotrode and the counter tool is determined, and if said duration exceeds a predetermined time limit, said current flow and / or said voltage drop is evaluated as a contact between the sealing surfaces with a contact time corresponding to said duration of said current flow or said voltage drop, said time limit being in particular greater than 0.01 μs and particularly preferably greater than or equal to 1 μs.

31. 31. The method according to claim 29 or 30, characterized in that the current intensity is determined for at least one current flow and / or voltage drop between the sonotrode and the counter tool, and if the current intensity exceeds a predetermined current limit value, the current flow and / or voltage drop is evaluated as indicating contact between the sealing surfaces, the current limit value being in particular greater than 1 mA and particularly preferably less than 300 mA.

32. for at least a predetermined period of time, in particular for the most recent milliseconds that have elapsed, - the total number of contacts between the sonotrode and the counter-tool, - the longest contact duration of all contacts, - the sum of the contact times of all contacts, is determined, said parameter being preferably stored and / or outputted; 32. The method of any one of claims 29 to 31.

33. 33. The method according to claim 32, characterized in that, depending on one or more of the parameters, the position of the ultrasonic tool, in particular the position of the sonotrode, is adjusted, the force exerted on the sonotrode is reduced or increased, a warning is output and / or the machining process is stopped, in particular by switching off the AC voltage.

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