DEVICE AND METHOD FOR MACHINING A WORKPIECE

Description

[0001] The present invention relates to a device for ultrasonically processing a workpiece, for example, for processing a material web with a sonotrode. This poses the problem that the workpiece, for example, the material web, is subject to thickness variations, or that temperature fluctuations in the device result in changes in the distance between the tool and counter-tool, so that the distance of the processing tool, for example, the sonotrode, relative to the workpiece or the counter-tool must be adjusted.

[0002] It is known from the prior art to arrange the tool on a carriage, which advances the tool toward the tool using a force-controlled lifting device and varies the distance from the workpiece (see DE 197 53 740 C1). It is also known from the prior art to connect a tool holder for a sonotrode to a base frame via two leaf springs (see DE 103 31 064 A1).

[0003] It is the object of the present invention to provide a device and a method for machining a workpiece, with which machining of workpieces with varying thickness is possible in a structurally simple manner.

[0004] This object is achieved by the features of the independent claims and, in particular, by a device comprising a base frame with a carriage linearly displaceable on the base frame, wherein a tool holder is provided that is movable relative to the carriage and connected to the carriage via two parallel leaf springs. A lifting device is provided for moving the tool holder relative to the carriage, which is arranged between the base frame and the tool holder.

[0005] According to the invention, only a single lifting device is provided, which is supported directly on the base frame and can both move the carriage into a working position and move the tool holder relative to the carriage in order to vary the distance of the tool from the workpiece when the carriage is fixed or blocked. This means that with the help of a single lifting device, the carriage can be moved by a comparatively large adjustment stroke, while with the same lifting device a precise working stroke of the tool holder is possible. The latter can be achieved by using relatively stiff leaf springs, which allow only a small stroke, but with high accuracy and high repeatability. Because the carriage is blocked or fixed during the working stroke, it is subject to only minimal wear.

[0006] Advantageous embodiments are described in the description, the drawing and the subclaims.

[0007] According to a first advantageous embodiment, a fixed stop for the slide, in particular an adjustable one, can be provided on the base frame, so that the slide can be adjusted by the lifting device in the direction of the workpiece until the slide hits the fixed stop.

[0008] According to a further advantageous embodiment, the stroke of the lifting device can comprise an adjustment stroke and a working stroke, wherein the adjustment stroke moves the carriage up to the fixed stop and the working stroke moves the tool holder relative to the carriage when the carriage stops at the fixed stop. In this way, with one and the same lifting device, a movement of the tool holder towards the workpiece and away from the workpiece is still possible after the carriage can no longer move due to hitting the fixed stop. This makes it possible to design the adjustment stroke to be comparatively large so that, for example, when changing materials, the tool can be retracted and then moved back into a working position. The working stroke enables, for example, force-controlled adjustment of the distance between the tool and a counter-tool when the tool is in a working position.

[0009] According to a further advantageous embodiment, a fixed stop for the tool holder can be provided on the base frame. This fixed stop can, for example, comprise an upper and a lower stop, so that the lifting device can be moved to an upper reference position on the one hand and to a lower end position on the other.

[0010] According to a further advantageous embodiment, the lifting device can have a toggle lever mechanism and / or a spindle drive in order to adjust the tool holder in a controlled manner towards a counter-tool.

[0011] According to a further advantageous embodiment, the lifting device can have a force sensor which detects the force applied by the tool to a workpiece in order to thereby control the lifting device in such a way that the tool is adjusted with a constant force in the direction of the counter-tool.

[0012] According to a further advantageous embodiment, a stroke limiter can be provided for the leaf springs so that they can only be deflected within a limited range.

[0013] According to a further advantageous embodiment, the two leaf springs can be preloaded relative to each other in an adjustable manner. This allows the tool holder to be preloaded relative to the carriage in the direction of the lifting device, whereby, with the aid of the lifting device, a lifting movement of the tool holder toward and away from the workpiece is possible even when the carriage hits the fixed stop.

[0014] According to a further advantageous embodiment, the carriage and the tool holder can be connected to each other via an elastic element. This allows the carriage and tool holder to be connected to each other in such a way that they can be moved together by the lifting device. However, when the carriage is abutted against the fixed stop, movement of the tool holder relative to the carriage is still possible if the elasticity of the elastic element is suitably selected.

[0015] According to a further advantageous embodiment, the working stroke can be approximately 5 to 15%, in particular approximately 8 to 12%, in particular approximately 10% of the setting stroke. This allows the tool to be moved relatively far away from a counter-tool, for example, for a material change. At the same time, the gap width between the tool and counter-tool can be finely adjusted in the working position of the tool.

[0016] In the method according to the invention for machining a workpiece with a device of the type described above, the carriage is first moved by the lifting device by an adjustment stroke, in particular up to a fixed stop, whereupon the lifting device subsequently moves the tool holder relative to the carriage within a working stroke, in particular as a function of a force which is applied to the workpiece by the lifting device.

[0017] To set up the fixture, it may be advantageous to adjust the two leaf springs between the two aforementioned steps so that they are located on two parallel, spaced-apart, non-curved planes. This creates an ideal working position, which allows the tool holder to be moved force-controlled toward and away from the counter-tool during operation as part of the working stroke.

[0018] The present invention is described below purely by way of example using an advantageous embodiment and with reference to the accompanying drawings.

[0019] They show: Fig. 1 a highly schematic representation of a device for machining a workpiece in a basic position; Fig. 2 the device of Fig. 1 in a working position; Fig. 3 the device of Fig. 1 and Fig. 2 in a slightly raised working position; and Fig. 4 the device of Fig. 1 in a slightly lowered working position.

[0020] Fig. 1 bis Fig. 4 show a highly schematic representation of a device for processing a workpiece W, for example a material web, using ultrasound. The device comprises a base frame 10 (not shown in detail), on which a carriage 12 can be moved linearly. The carriage 12 is mounted on the base frame 10 via two plain bearings, for example two recirculating roller bearings 13 and 15, such that it can be moved in a vertical direction (in the illustrated embodiment). It is understood that the described device can also be arranged in other orientations, for example such that the carriage is arranged horizontally or at an angle.

[0021] Furthermore, a tool holder 14 is provided, which is movable relative to the carriage 12 and on which a tool, for example, a sonotrode 17, is arranged. With the aid of the sonotrode 17, the workpiece W can be machined; for example, two material webs can be welded together by positioning the tool or sonotrode 17 against a counter-tool 21, for example, a rotatable anvil, and activating it.

[0022] The carriage 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 relative to the carriage 12.

[0023] To move both the carriage 12 and the tool holder 14, a lifting device 20 is provided, one end of which is attached to the base frame 10 and the other end to the tool holder 14. The lifting device 20 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 carriage 12 when the carriage 12 is fixed or locked. The lifting device 20 comprises a drive 30, for example a spindle drive, which is articulated via a joint 29 and is movable in the direction of the double arrow 32. During its movement, it moves a toggle joint 34, which is supported relative to the base frame 10, such that the tool holder 14 and the carriage 12 connected to it via the leaf springs 16 and 18 can be moved vertically upwards or downwards when the carriage 12 is not fixed.

[0024] As the figures further show, a locking device, for example a fixed stop 22 for the slide 12, is provided on the base frame 10. This fixed stop is adjustable and fixes the slide at least in one direction of movement or blocks a vertical movement of the slide 12 in the direction of the counter tool 21. Furthermore, the device comprises a locking device on the base frame 10, for example a fixed stop 24 for the tool holder 14, wherein the fixed stop 24 can comprise an upper reference stop and a lower end stop, the latter being located shortly before the dead center of the toggle joint 34.A force sensor 36 can also be provided between the toggle joint 34 and the tool holder 14, which is connected to a control (not shown) which controls the drive 30 as a function of the detected force so that the tool 17 is positioned against the counter-tool 21 with a desired, for example constant, force.

[0025] The device can further comprise 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. Preloading of the two leaf springs 16 and 18 can be achieved by a spring 42 provided between the carriage 12 and the tool holder 14. The preload can be adjustable and selected such that the tool holder 14 is preloaded against the carriage 12 in the direction of the lifting device 20, i.e., away from the workpiece W or the counter-tool 21.

[0026] Furthermore, the carriage 12 can be connected to the tool holder 14 via an elastic element (not shown) so that the carriage and tool holder can be moved together by the lifting device 20, but a certain movement of the tool holder 14 relative to the carriage 12 is still possible when the carriage 12 strikes the fixed stop 22.

[0027] With the device described above, the tool 17 can be moved with the aid of the lifting device 20, initially by a relatively large adjustment stroke and subsequently by a relatively small working stroke. By actuating the drive 30, the toggle joint 34 can be moved such that first the tool holder 14 and, together with it, the carriage 12 are moved vertically relative to the base frame 10 in the direction of the counter-tool 21. During this movement, the movement of the carriage 12 is stopped at the end of the adjustment stroke, for example, by the fixed stop 22. However, the tool holder 14 can still be moved further relative to the stationary carriage 12, since the leaf springs 16 and 18 make this possible.

[0028] In the Fig. 2 In the position shown, the device is in its working position, ie the ideal working point is set, at which the sonotrode 17 assumes a desired distance from the counter tool 21. When moving a material web in the direction of the arrow M ( Fig. 2 ) Due to material tolerances or temperature fluctuations, it may be necessary to increase or decrease the gap width. For this purpose, the force sensor 36 measures the force applied by the lifting device 20 to the tool 17 and regulates the movement of the lifting device 20 depending on the measured force. In this case, the tool holder 14 can be moved vertically downward relative to the stationary carriage 12 if the toggle joint 20 is further pushed through ( Fig. 3 ). Likewise, the tool holder 14 can be moved vertically upwards when the toggle joint 20 is opened, as shown in Fig. 4 is shown.

[0029] So, if, starting from the ideal working position, which is Fig. 2 If, as shown, the force sensor 36 detects a decrease in the force 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, so that the tool holder 14 moves vertically downward in the direction of arrow 33. However, the carriage 12 does not move due to the pretension of the spring 42. This would only occur when the upper stroke limit 40 is reached.

[0030] Fig. 4 Finally, illustrates a movement of the tool 17 from the ideal working position of Fig. 2 away from the counter-tool 21 if the force sensor 36 detects an undesired increase in the detected force. In this case, the drive 30 can be moved in the direction of arrow 35, so that the tool holder 14 can be moved slightly away from the counter-tool 21 in the direction of arrow 37.

[0031] To set up the device described above, it can first be inserted into the Fig. 1 The tool holder 14 can be moved to the position shown. In this position, the fixed stop 22 is free and the spring 42 is not preloaded. The slide 12 and the tool holder 14 do not yet have a defined position relative to each other.

[0032] In a subsequent first step, an automated measurement of the toggle lever kinematics can be carried out, for which a complete stroke of the drive 30 is moved from the upper reference stop to the lower end stop of the fixed stop 24. In this case, both the stroke of the drive 30 and the stroke of the tool 17 can be recorded so that a working position can be defined based on a characteristic curve (sonotrode stroke over spindle stroke). In a subsequent step, this working position can be approached in order to adjust the relative position between the tool holder 14 and the carriage 12. For this purpose, the adjustable fixed stop 22 can be adjusted so that the two leaf springs are in a non-preloaded horizontal position in which they lie on two parallel, spaced-apart and non-curved planes (cf. Fig. 2 ). It is then possible to increase the preload of the spring 42 to a desired target value.

[0033] Thanks to the setup process described above, the mechanism is in a precise working position during the work process, from which the tool holder 14 only moves within a working stroke. The working stroke can be significantly shorter than the setting stroke, for example, amounting to only 10% of the setting stroke. This makes it possible, for example, to move the tool into the working position by approximately 20 mm (setting stroke). From the working position, the tool can then be moved within the working stroke, for example, by ±2 mm.

Claims

1. Apparatus for processing a workpiece (W) with ultrasound, comprising - a base frame (10); - a slide (12) that is linearly displaceable on the base frame (10); - a tool holder (14) that is movable relative to the slide (12) and that is connected to the slide (12) via two parallel leaf springs (16, 18); and - a lifting device (20) that is arranged between the base frame (10) and the tool holder (14) and that causes a lifting movement of the tool holder (14) relative to the slide (12), wherein - with the lifting device (20), both the slide (12) can be moved relative to the base frame (10) and, when the slide (12) is fixed, the tool holder (14) can be moved relative to the slide (12).

2. Apparatus according to claim 1, characterized in that a stop (22), in particular an adjustable positive abutment, for the slide (12) is provided at the base frame (10).

3. Apparatus according to claim 2, characterized in that the stroke of the lifting device (20) comprises a feeding stroke and a working stroke, with the feeding stroke moving the slide (12) up to the stop (22) and the working stroke moving the tool holder (14) relative to the slide (12) when the slide (12) is stopped.

4. Apparatus according to claim 1, 2 or 3, characterized in that a positive abutment (24) for the tool holder (14) is provided at the base frame (10).

5. Apparatus according to any one of the preceding claims, characterized in that the lifting device (20) has a toggle lever mechanism (34) and / or a spindle drive (30).

6. Apparatus according to any one of the preceding claims, characterized in that the lifting device (20) has a force sensor (36).

7. Apparatus according to any one of the preceding claims, characterized in that a stroke limitation (40) is provided for the leaf springs (16, 18).

8. Apparatus according to any one of the preceding claims, characterized in that the two leaf springs (16, 18) are in particular preloaded against one another in a settable manner.

9. Apparatus according to any one of the preceding claims, characterized in that the slide (12) and the tool holder (14) are connected to one another via an elastic element.

10. Apparatus according to claim 3, characterized in that the working stroke amounts to approximately 5 - 15%, in particular approximately 8 - 12%, of the feeding stroke.

11. Method for processing a workpiece (W) using an apparatus according to any one of the preceding claims, characterized in that a) the slide (12) is first moved by a feeding stroke by the lifting device (20), b) the slide (12) is then stopped, and c) the tool holder (14) is moved relative to the slide (12) by the lifting device (20) when the slide (12) is stopped.

12. Method according to claim 11, characterized in that the tool holder (14) is moved by the lifting device (20) in dependence on a force that is applied to the workpiece (W) by the lifting device (20).

13. Method according to claim 11 or 12, characterized in that, for setting up the apparatus, the two leaf springs (16, 18) are adjusted between steps a) and b) so that they are located on two planes that are spaced apart in parallel and that are not curved.

14. Method according to claim 13, characterized in that, after the adjustment, the tool holder (14) is preloaded against the slide (12) in a direction that faces away from the workpiece (W).