Device and method for processing a workpiece

Abstract

A device for processing a workpiece (W) comprises a main frame (10), which has a tool holder (14) that can be moved relative to the main frame (10), and a counter tool (21). Between the base frame (10) and the tool holder (14) is a lifting device (20), and a counterforce generator (G) is provided, which acts on the tool holder (14) in the direction of the counter tool (21). The tool is preferably an ultrasonic tool with a sonotrode (17), and the counter tool is a rotating anvil (21).

Description

[0001] DEVICE AND METHOD FOR MACHINING A WORKPIECE

[0002] The present invention relates to a device according to the preamble of claim 1 for processing a workpiece, for example, for processing a web of material with ultrasound using a sonotrode. Such a device is known from DE 10 2021 126 774 A1. It is also known from this prior art to arrange the tool on a slide which moves the tool towards the workpiece by means of a force-controlled lifting device and varies the distance to the workpiece.

[0003] When devices of the type described above are used with a rotating anvil as a counter-tool for processing material webs, the problem can arise that—especially at higher web speeds—the tool lifts off the anvil, which is equipped with protrusions. This problem can occur particularly when the counter-tool is provided with a structure for creating transverse seams, since the structure then has ribs extending transversely to the web direction, which can cause the tool to accelerate away from the counter-tool. If, for example, a sonotrode is used as the tool, it can lift off at higher web speeds or...Higher rotational speeds of the counter tool cause the workpiece to be accelerated away from the counter tool, whereby the distance between the sonotrode and the rotary anvil can become so large that the sonotrode lifts off the material web guided between the sonotrode and the counter tool, potentially resulting in incomplete welding. The object of the present invention is to provide a device and a method for machining a workpiece with which flawless machining of a material web is possible even when it exhibits machining patterns extending transversely to the web direction.

[0004] This problem is solved by the characteristics of independent claims.

[0005] According to a first aspect of the present invention, in a device according to the preamble of claim 1, a counterforce generator, which is particularly controllable, is mounted on the tool holder and applies a force impulse to the tool holder oriented in the direction of the counter-tool. With such a counterforce generator, unlike conventional force-controlled gap control systems, a force impulse can be exerted on the tool holder at a specific time, thus counteracting an undesired lifting of the tool from the material web. If the counterforce generator is controllable, the force impulse can be triggered precisely when the tool holder or a tool attached to it is accelerated away from the counter-tool due to inertial forces.

[0006] Although it is already known from DE 100 34 057 A1 to provide an oil- or air-filled damper for damping vibrations of the sonotrode, such a passive damper is not suitable for the present application due to the extremely small strokes occurring in practice, in the range of approximately 0.1 mm, especially since it is not capable of exerting a force impulse over such a short stroke at a specific time.

[0007] The device and method according to the invention are particularly suitable for use with a sonotrode positioned against a rotating anvil, wherein a web of material is guided between the sonotrode and the anvil. It is understood, however, that the invention is also applicable to other processing tools and counter-tools, for example, for welding, sealing, cut-off welding, or cutting processes.

[0008] Advantageous embodiments are described in the description, the drawing and the dependent claims.

[0009] According to a first advantageous embodiment, the counterforce generator can have a friction brake supported on the base frame. Such a friction brake can counteract an unwanted lifting movement of the tool holder or the tool itself in a very short time by pulsating the friction brake. For this purpose, the friction brake can have an actuating cylinder with adjustable piston force.

[0010] According to a further advantageous embodiment, the counterforce generator can have an eddy current brake supported on the base frame, which has the advantage that a braking impulse can be applied without contact and without wear. It can be advantageous if the eddy current brake has an electromagnet with current control and / or a permanent magnet with a variable surface area. In both cases, the braking effect can be actively controlled, namely by appropriately energizing the electromagnet, or by changing the surface area in the case of a permanent magnet interacting with an electrically conductive surface element.

[0011] According to a further specified advantageous embodiment, the eddy current brake for generating a magnetic field comprises a superconductor. In particular, a strong magnetic field can be generated within the eddy current brake by inducing an electric current through a superconductor. The superconductor can be a component made of a superconducting material and configured such that an electric current can be generated, in particular induced, within the superconductor. For example, the superconductor can be configured as a coil-like component in which coil windings are formed with superconducting material.

[0012] Preferably, a high-temperature superconducting material can be used in the superconductor, since this material acquires superconducting properties even when cooled to relatively high temperatures, for example, 77 K or above. In contrast to classical superconducting materials, which usually require cooling to extremely low temperatures of a few Kelvin using liquid helium to achieve superconductivity, high-temperature superconducting materials can achieve superconductivity with a relatively simple cooling method using liquid nitrogen, due to their comparatively high transition temperature.

[0013] It was recognized that strong magnetic fields must be generated in an eddy current brake to achieve sufficiently strong impulses or a sufficiently strong mechanical damping property. This generally requires the generation of strong electric currents when using conventional coils in an electromagnet. Due to power losses, conventional coils must therefore be cooled very efficiently or with high cooling capacity. Furthermore, such coils often require large conductor cross-sections, meaning that the coils and the eddy current brake built with them require a relatively large installation space. However, space is often limited in workpiece machining devices, so integrating a large eddy current brake can be problematic. Since there is essentially no ohmic resistance to the electric current within the superconductor, it can flow with virtually no loss.This allows for low power consumption to generate the current flow. Furthermore, it prevents parts of the eddy current brake from overheating due to power losses during current generation, thus avoiding the need for efficient cooling. Accordingly, using a superconductor enables the generation of very strong magnetic fields within the eddy current brake while keeping power losses low. This allows for smaller dimensions of the superconducting windings and minimizes the required cooling power. Therefore, the use of a superconductor allows for a compact and energy-efficient eddy current brake.

[0014] According to a further advantageous embodiment, the counterforce generator can have an actuator supported on the base frame, with which a force impulse is exerted on the tool holder or on the tool connected thereto at a suitable time, directed in the direction of the counter-tool. Such an actuator can be designed as a linear drive, for example as an electromagnet, linear motor or piezoelectric actuator, and / or have a rotary drive, for example a mechanical system with a crank and connecting rod.

[0015] In a further advantageous embodiment, the counterforce generator can have a magnetic spring supported on the base frame, which can be formed by arranging two magnets with mutually repelling poles side by side, one magnet being attached to the base frame and the other to the tool holder. In this embodiment, firstly, no active control is required, and secondly, it offers the significant advantage that a very large force change can be achieved over a very short distance. By appropriate dimensioning, such a magnetic spring can be mounted so that it exerts a magnetic counterforce on the tool holder only in the event of an unwanted overshoot of the tool holder. The magnets used for a magnetic spring can be either two permanent magnets or at least one electromagnet and another magnet.For example, an electromagnet and a permanent magnet can be arranged opposite each other with the same polarity, whereby the spring force of the magnetic spring can be precisely controlled by appropriately controlling the electromagnet. It is also possible to use two electromagnets to achieve even more precise control.

[0016] According to a further advantageous embodiment, the counterforce generator can have a countermass driven translationally and / or rotationally. In this embodiment, the counterforce generator does not need to be supported on the base frame. Rather, the required force impulse can be generated by moving the countermass towards the anvil if the tool holder moves away from the anvil unintentionally.

[0017] In principle, it can be advantageous if the counterforce generator is slidably attached to the base frame. If the tool holder is moved a greater distance away from the counter tool, for example to insert a web of material into the machining gap, the counterforce generator can follow this movement due to its slidability.

[0018] As mentioned earlier, the unwanted stroke of the tool or tool holder is extremely small, on the order of approximately 0.1 mm. It can therefore be advantageous if the counterforce generator is connected to the tool holder via a lever that translates a stroke of the tool holder into an increased stroke at one end of the lever. In this way, a stroke of 0.1 mm in the tool holder can, for example, be converted into a stroke of 1 mm or more, allowing the required force impulse to be applied along this increased stroke of 1 mm, which is easier to implement from a control perspective.

[0019] According to a further aspect of the present invention, the aforementioned problem is solved by a method for machining a workpiece with a device of the type described above, which has a machining tool on the tool holder. In this method, the counterforce generator is activated at a specific time, thereby counteracting an unwanted impulse of the machining tool away from the counter tool. In contrast to force-controlled gap regulation or a non-actively controllable damper, in this method the counterforce generator is selectively activated at a specific time, so that an impulse-like counterforce is exerted on the machining tool only when it moves away from the counter tool in an undesired manner.

[0020] The point at which the counterforce generator is activated can be selected, for example, based on the acceleration and / or stroke of the tool or tool holder. The tool holder can, for instance, be equipped with an acceleration sensor that detects when it moves away from the counter-tool too quickly. Alternatively or additionally, displacement measurement is also possible.

[0021] Alternatively or additionally, it can also be advantageous if the activation of the counterforce generator is triggered by at least one signal generated by a signal generator controlling an ultrasonic tool. Specifically, when the tool enters the area of ​​a protrusion or crossbar on the anvil, this can be reliably detected from current and / or voltage signals of the signal generator. Thus, this embodiment allows for a very precise determination of the triggering time.

[0022] Alternatively or additionally, the activation of the counterforce generator can also be triggered by signals from a force sensor that measures the force exerted by the tool on the material web. Here, too, signals from such a force sensor allow for a precise determination of when a force impulse is required in the direction of the countertool.

[0023] Furthermore, it can be advantageous to select the activation point of the counterforce generator based on the rotational angle of the counter tool. Since a profile of the counter tool extends along its circumferential surface, the detection of the counter tool's rotational angle can determine when the tool passes over such a profile. Because undesirable movement of the tool away from the counter tool can occur at certain feed rates, the counterforce generator can be activated at these times to prevent this.

[0024] Furthermore, it can be advantageous if activation depends on the rotational speed of the counter tool, since then, for example, activation is only initiated if an unwanted lifting movement of the tool can occur due to the existing path speed.

[0025] The present invention is described below by way of example only, using an advantageous embodiment and with reference to the accompanying drawings.

[0026] Figure 1 shows a highly schematic representation of a device for

[0027] Machining a workpiece with a counterforce generator that has a driven countermass;

[0028] Fig. 2 shows another embodiment with a counterforce generator in the form of a friction brake;

[0029] Fig. 3 shows another embodiment with a counterforce generator in the form of an eddy current brake with electromagnet;

[0030] Fig. 4 shows another embodiment with a counterforce generator in the form of an eddy current brake with permanent magnets;

[0031] Fig. 5 shows another embodiment with a counterforce generator with an actuator;

[0032] Fig. 6 shows another embodiment with a counterforce generator in the form of a magnetic spring; and

[0033] Fig. 7 shows another embodiment with a lever for translating the stroke that occurs.

[0034] Fig. 1 shows a highly schematic representation of a device for processing a workpiece W, for example a web of material, using ultrasound. The device comprises a base frame 10 (not shown in detail) on which a slide 12 is linearly displaceable. The slide 12 is mounted on the base frame 10 via two sliding bearings, for example two recirculating roller bearings 13 and 15, so that it can be displaced vertically (in the illustrated embodiment). A tool holder 14, movable relative to the slide 12, is also provided, on which a tool, for example a sonotrode 17, is arranged. The workpiece W can be processed with the aid of the sonotrode 17; for example, two webs of material can be welded together by positioning the tool or the sonotrode 17 against a counter tool 21, for example a rotatable anvil, and activating it.

[0035] To produce transverse seams, the counter tool 21 in the illustrated embodiment is provided with transverse ribs 23 on its outer surface, with only one transverse rib 23 (enlarged) being shown for simplicity. When the material webs W are guided in the direction of movement M through the gap between the sonotrode 17 and the counter tool 21, the counter tool 21 moves in the direction of the curved arrow, so that the transverse rib 23 comes to lie below that of the sonotrode 17 at a certain point in time. In the position shown in Fig. 1, the counter tool 21 must still travel an angle α before this occurs.

[0036] The slide 12 is connected to the tool holder 14 via two parallel leaf springs 16 and 18, so that the tool holder 14 can be moved parallel to the slide 12.

[0037] A lifting device 20 is provided for moving both the slide 12 and the tool holder 14. This lifting device is arranged between the base frame 10 and the tool holder 14 and causes a lifting movement of the tool holder 14 relative to the slide 12 when the slide 12 is fixed. The lifting device 20 comprises a drive 30, for example a spindle drive, which is pivotally mounted via a joint 29 and is movable in and against the direction of arrow 31. This drive 30 moves a toggle joint 34, which is supported against the base frame 10, such that the tool holder 14 and the slide 12, which is connected to it via leaf springs 16 and 18, can be moved vertically upwards or downwards.

[0038] As further shown in Fig. 1, a fixed stop 22 for the slide 12 is provided on the base frame 10. This stop is adjustable and blocks vertical movement of the slide 12 towards the counter tool 21. The device also includes a fixed stop 24 for the tool holder 14. The fixed stop 24 comprises an upper reference stop and a lower end stop, the latter being located just before the dead center of the toggle joint 34. A force sensor 36 is also provided between the toggle joint 34 and the tool holder 14. This force sensor is connected to a control unit (not shown) that actuates the drive 30 based on the detected force, ensuring that the tool 17 is applied to the counter tool 21 with a desired force, for example, a constant force.

[0039] The device further features a stroke limiter 40 for the two leaf springs 16 and 18, which ensures that the two leaf springs can only be deflected within a limited range. Preload of the two leaf springs 16 and 18 can be achieved by a spring 42, which is provided between the slide 12 and the tool holder 14. The preload can be adjusted and selected such that the tool holder 14 is preloaded against the slide 12 in the direction of the lifting device 20, i.e., away from the workpiece W or the counter tool 21.

[0040] Furthermore, the slide 12 can be connected to the tool holder 14 via an elastic element (not shown), so that the slide and tool holder can be moved together by the lifting device 20, but a certain movement of the tool holder 14 relative to the slide 12 is still possible when the slide 12 hits the fixed stop 22.

[0041] With the device described above, the tool 17 can be moved first by a positioning stroke and then by a working stroke using the lifting device 20. By actuating the drive 30, the toggle joint 34 can be moved such that the tool holder 14, and together with it the slide 12, are moved vertically relative to the base frame 10 in the direction of the counter tool 21. During this movement, at the end of the positioning stroke, the movement of the slide 12 is stopped by the stop 22. However, the tool holder 14 can still be moved further relative to the stationary slide 12, as the leaf springs 16 and 18 make this possible.

[0042] First, the device can be set in its working position, i.e., the ideal operating point is set at which the sonotrode 17 maintains a desired distance relative to the counter tool 21. When moving a material web in the direction of arrow M, material tolerances or temperature fluctuations may necessitate increasing or decreasing the gap width. For this purpose, the force sensor 36 measures the force applied to the tool 17 by the lifting device 20 and controls the movement of the lifting device 20 depending on the measured force. The tool holder 14 can be moved vertically downwards relative to the stationary slide 12 when the toggle joint 20 is further depressed. Likewise, the tool holder 14 can be moved vertically upwards when the toggle joint 20 is opened.

[0043] Therefore, if, starting from the ideal working position shown in Fig. 1, the force sensor 36 detects a decrease in the force flow between the tool 17 and the base frame 10, the drive 30 can be retracted in the direction of arrow 31, causing the tool holder 14 to move vertically downwards. However, the slide 12 does not move due to the preload of the spring 42. This would only occur when the upper stroke limit 40 is reached.

[0044] In the embodiment shown in Fig. 1, a counterforce generator G is mounted on the tool holder 14, which can impart a force impulse to the tool holder 14 oriented in the direction of the counter tool 21. In this embodiment, the counterforce generator G has a countermass m driven translationally in the direction of the counter tool 21. Alternatively or additionally, a rotaryally driven countermass m' can be provided. Actuators, piezoelectric actuators, actuating cylinders, or the like are suitable as translational drives for the countermass m. The rotaryally driven countermass m' can, for example, be driven by an electric motor.

[0045] A schematically depicted control unit 50 is provided for controlling the counterforce generator G. This unit is connected to an angle encoder 52 of the counter tool 21. This provides the control unit 50 with information about the current rotation angle of the counter tool 21. When the counter tool 21 has traveled the distance a shown in Fig. 1, the crossbar 23 is located in the area of ​​the tool 17. Above certain feed rates, the tool 17 or the tool holder 14 may subsequently lift slightly from the material web W. At this point, the control unit 50 can briefly activate the counterforce generator G to trigger a force impulse oriented towards the counter tool 21 by moving the counter mass m and / or m' in the direction of the counter tool 21.

[0046] It is understood that the design of the lifting device 20 and the tool holder 14 can be entirely arbitrary and is not limited to the embodiments shown. For example, the tool holder can simply be a vertically displaceable slide (without leaf springs or the like) which can be moved vertically relative to the base frame 10 by means of any lifting device, for example an actuating cylinder or a linear drive, and positioned against and moved away from the counter tool.

[0047] Fig. 2 shows such a simplified embodiment with a tool holder 14 designed as a vertically movable slide that can be moved vertically on a base frame 10 by means of a lifting device 20. A tool attached to the tool holder 14, for example a sonotrode, is not shown. In this embodiment, a counterforce generator G in the form of a friction brake is provided, which is supported on the base frame 10 and acts on a friction surface 60 fixedly mounted on the tool holder 14. A support frame 62 is fixedly connected to the base frame 10, and an actuator 64, for example a cylinder with adjustable piston force, is mounted on the support frame 62. When the actuator 64 is actuated, it exerts a force on the friction surface 60, which is fixedly connected to the tool holder 14, so that a frictional force acts vertically downwards in the direction of the counter tool 21.The friction brake is controlled by the controller 50, which is connected to the rotary encoder 52 to detect the current rotational position of the counter tool 21. At the appropriate time, the controller 50 then triggers a force impulse in the direction of the counter tool 21 using the friction brake. This impulse can be initiated by analog or digital signals 66. Alternatively or additionally, the controller 50 can also be connected to an acceleration sensor 54, which is attached to the tool holder 14 and / or a machining tool, to determine the triggering time. Fig. 3 shows another embodiment of a counterforce generator G in the form of an eddy current brake, which has an electromagnet 70 that is rigidly connected to the base frame 10 via a holder 72.The electromagnet 70 is controlled by the control unit 50 and energized in such a way that a braking force is exerted on the slide 14 at the appropriate time, since the electromagnet 70 generates eddy currents in an electrically conductive plate 74, which is rigidly connected to the tool holder 14. By appropriately energizing the electromagnet 70, a force impulse oriented towards the counter-tool 21 can be exerted on the tool holder 14 to counteract an unwanted upward movement of the tool holder 14 and thus also of the tool.

[0048] Fig. 4 shows a highly simplified representation of another embodiment with a counterforce generator G in the form of an eddy current brake using permanent magnets 76 that interact with electrically conductive plates 78. The permanent magnets 76 are attached to the base frame 10 but are displaceable in the vertical direction (double arrow 77 in Fig. 4). The electrically conductive plates 78 are fixedly connected to the tool holder 14 and can move vertically between the permanent magnets 77 together with it. By vertically displacing the permanent magnets 77 relative to the base frame 10, the contact area between the permanent magnets 77 and the electrically conductive plates 78 can be changed, thus varying the braking force exerted by the eddy current brake. Adjustment of the permanent magnets 76 can be effected by an actuator controlled by the controller 50.

[0049] Fig. 5 shows another embodiment of a counterforce generator G in the form of an actuator 80, which is fixedly mounted on the base frame 10 and which can exert a force impulse either on the lifting device 20 or on the tool holder 14 when the control unit 50 has received information from the rotary encoder 52 (or from an accelerometer) that this is necessary because the tool is moving away from the counter-tool in an undesired manner. The actuator 80 can have a linear drive, for example a piezoelectric actuator or the like. However, it can also have a rotary drive.

[0050] Fig. 6 shows another embodiment of a counterforce generator G, wherein the device is designed similarly to that of Fig. 1. In this embodiment, the counterforce generator G comprises a magnetic spring supported on the base frame 10, which includes two permanent magnets 90 and 92. Here, the permanent magnet 90 is fixedly mounted on the base frame 10, whereas the other permanent magnet 92 is fixedly mounted on the tool holder 14.

[0051] Both permanent magnets are positioned opposite each other with poles of the same type, so that when the two permanent magnets 90 and 92 approach each other, a braking force oriented towards the counter-tool 21 is generated, which becomes greater the closer the two poles get to each other.

[0052] As already described at the beginning, in most embodiments it can be advantageous if the counterforce generator is slidably attached to the base frame 10 so that the tool holder 14 can be moved away from the counter tool 21 over larger distances, for example to introduce a web of material into the machining gap.

[0053] As mentioned earlier, the (undesired) strokes occurring during operation are extremely small, in the range of approximately 0.1 mm. Since this makes the timely and appropriate application of a force impulse extremely difficult, it can be advantageous to increase the stroke using a lever. Fig. 7 shows such an embodiment, which is similar to that shown in Fig. 1 and Fig. 6. In this embodiment, a lever 90 is connected at its right end to the tool holder 14 and pivotally mounted on the base frame 10 at approximately one-third of its length. This gives the lever 90 a short and a long lever arm, and a stroke movement of the tool holder 14 is translated into an increased stroke movement of the left end of the lever 91.In the area of ​​the left end of the lever 91, a counterforce generator G can then be arranged, whereby an increased stroke is created at this point, which facilitates a suitable application of a force impulse.

[0054] It is understood that the lever can be designed as a single-armed or double-armed lever, and that the pivot joints of the lever can be designed, for example, as solid-body joints.

[0055] According to a further aspect of the present invention, it relates to a method for machining a workpiece with a device of the type described above, wherein a machining tool is attached to the tool holder. In this method, the counterforce generator is activated at a specific time, thereby counteracting an undesired impulse of the machining tool away from the counter tool. In particular, when producing weld seams running transversely to the web direction using a sonotrode and a rotatable anvil, this method, using one of the devices described above, can counteract the lifting of the sonotrode from the material web, so that proper and uninterrupted weld seams can be achieved. The activation time can be determined by a control system that monitors the current rotation angle of the counter tool and / or an acceleration of the tool.detected the tool holder.

Claims

Claims 1. Device for machining a workpiece (W), comprising a base frame (10), a tool holder (14) movable relative to the base frame (10), a counter tool (21) which is in particular rotatable, and a lifting device (20) which is arranged between the base frame (10) and the tool holder (14) and which causes a lifting movement of the tool holder (14) relative to the counter tool (21), characterized in that a counter force generator (G) which is in particular controllable is mounted on the tool holder (14) and which applies a force impulse to the tool holder (14) oriented in the direction of the counter tool (21).

2. Device according to claim 1, characterized in that the counterforce generator (G) has a friction brake (60 - 64) supported on the base frame (10).

3. Device according to claim 2, characterized in that the friction brake has an actuating cylinder (66) with adjustable piston force.

4. Device according to claim 1, 2 or 3, characterized in that the counterforce generator (G) has an eddy current brake supported on the base frame (10).

5. Device according to claim 4, characterized in that the eddy current brake has an electromagnet (70) with a current control (50) and / or permanent magnets (76) with a variable surface coverage.

6. Device according to one of claims 4 and 5, characterized in that the eddy current brake for generating a magnetic field comprises a superconductor.

7. Device according to one of the preceding claims, characterized in that the counterforce generator (G) has an actuator (80) supported on the base frame (10).

8. Device according to claim 7, characterized in that the actuator (80) has a linear drive and / or a rotary drive.

9. Device according to one of the preceding claims, characterized in that, that the counterforce generator (G) has a magnetic spring (90, 92) supported on the base frame.

10. Device according to one of the preceding claims, characterized in that the counterforce generator (G) has a translationally and / or rotationally driven countermass (m, m').

11. Device according to one of the preceding claims, characterized in that the counterforce generator (G) is slidably attached to the base frame.

12. Device according to one of the preceding claims, characterized in that the counterforce generator (G) is connected to the tool holder (14) via a lever (90) which translates a stroke movement of the tool holder (14) into an increased stroke of a lever end (91).

13. Method for machining a workpiece (W) with a device according to one of the preceding claims, which has a machining tool (17), in particular a sonotrode, on the tool holder (14), characterized in that the counterforce generator (G) is activated at a certain time and thereby counteracts an unwanted impulse of the machining tool (17) away from the counter tool (21).

14. Method according to claim 13, characterized in that that the timing is chosen depending on an acceleration and / or stroke of the tool.

15. Method according to claim 13 or 14, characterized in that the timing is selected depending on a rotational angle position of the counter tool.

16. Method according to claim 13, 14 or 15, characterized in that activation takes place depending on a rotational speed of the counter tool (21 ).

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