ROLLER ELECTRODE ARRANGEMENT, APPARATUS COMPRISING A ROLLER ELECTRODE ARRANGEMENT, AND METHOD FOR APPLYING A HIGH-FREQUENCY ALTERNATING ELECTRIC FIELD TO TWO PLASTIC MATERIAL PORTIONS

Abstract

A roller electrode assembly (1) for applying a high-frequency alternating electric field to a workpiece (5a, 5b) has a core (2) which is at least partially made of electrically conductive material and surrounded by a tire (3) which can be filled with a protective gas and is made of a dielectric material.

Claims

1. Roller electrode assembly (1) for applying a high-frequency electric alternating field to two plastic sections of at least one workpiece (5a, 5b) for joining the sections by plastic high-frequency welding, comprising a core (2) which consists at least partially of electrically conductive material and is surrounded by a tire (3) which can be filled with a protective gas and consists of a dielectric material.

2. Roller electrode assembly (1) according to claim 1, wherein the frequency of the alternating field lies within an ISM band.

3. Roller electrode assembly (1) according to claim 1, wherein it is spherical or at least substantially spherical or cylindrical or at least substantially cylindrical.

4. Apparatus for applying a high-frequency alternating electric field to a workpiece (5a, 5b), comprising a high-frequency generator (4) and at least one roller electrode assembly (1) according to claim 1.

5. Apparatus according to claim 4, further comprising a counter-electrode assembly (1) which is designed according to claim 1.

6. Apparatus according to claim 4, wherein the roller electrode assembly (1) or at least one of the roller electrode assemblies (1) is arranged to be actuated to transport the workpiece (5a, 5b) to be processed.

7. Apparatus according to claim 4, further comprising an apparatus (11) for contactless energy transfer to the at least one roller electrode assembly (1).

8. Apparatus according to claim 4, further comprising a table as a counter-pressure element.

9. Apparatus according to claim 8, wherein the roller electrode assembly (1) is guided by an axis system or on a articulated robot.

10. Apparatus according to claim 4, wherein the protective gas is selected from the following group: sulphur hexafluoride or a gas mixture containing sulphur hexafluoride, a fluoronitrile or a gas mixture containing a fluoronitrile; a fluoroketone or a gas mixture containing fluoroketone, carbon dioxide or a gas mixture containing carbon dioxide.

11. Apparatus according to claim 4, wherein the tire (3) has a valve for introducing and/or removing the protective gas.

12. Method for applying a high-frequency electric alternating field to two plastic sections of at least one workpiece (5a, 5b) for joining the sections by plastic high-frequency welding, by means of an apparatus according to claim 4, wherein a force is applied to the at least one workpiece (5a, 5b) to be processed is acted upon with a force by a roller electrode assembly (1) according to claim 1, the frequency of the alternating field lying within an ISM band.

13. Method according to claim 12, wherein the transmission of the electrical high frequency to the roller electrode assembly (1) or at least to one of the roller electrode assemblies (1) is performed in a contactless manner.

14. Method according to claim 12, wherein the apparatus applies the force to the at least one workpiece (5a, 5b) in such a way that the protective gas inside the tire (3) is displaced so that the core (2) rests directly on the tire (3) in the center of a pressure zone (13).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Further advantages, features and details of the invention can be found in the following description of preferred embodiments as well as in the drawings; these are shown in:

[0052] FIG. 1 an assembly comprising two roller electrodes 7 according to the prior art,

[0053] FIG. 2 an assembly comprising a roller electrode 7 and a flat counter electrode 8 according to the prior art,

[0054] FIG. 3 a roller electrode assembly 1 according to an embodiment of the present invention,

[0055] FIG. 4 a sidewards cutaway drawing according to FIG. 3 with further details,

[0056] FIG. 5 an assembly comprising the roller electrode assembly 1 according to FIG. 3,

[0057] FIG. 6 a sidewards cutaway drawing according to FIG. 5 with further details,

[0058] FIG. 7 an assembly comprising two roller electrode assemblies 1 according to a further embodiment of the present invention,

[0059] FIG. 8 a sidewards cutaway drawing according to FIG. 7 with further details in a first version,

[0060] FIG. 9 a sidewards cutaway drawing according to FIG. 7 in a second version and

[0061] FIG. 10 a sidewards cutaway drawing according to FIG. 7 in a third version.

DETAILED DESCRIPTION

[0062] FIG. 1 shows an assembly comprising two roller electrodes 7 according to the prior art.

[0063] FIG. 2 shows an assembly according to the prior art which, in comparison to the assembly according to FIG. 1, comprises a flat counter electrode 8 instead of the lower roller electrode 7, for example in the form of a table.

[0064] FIG. 3 shows a roller electrode assembly 1 according to an embodiment of the present invention. The roller electrode assembly 1 comprises a core 2 and a tire 3, which can be filled with a protective gas and consists of a dielectric material, hereinafter referred to as tire 3. Furthermore, an axis of rotation 20 is shown.

[0065] FIG. 4 shows a cutaway side view according to FIG. 3, where further details are visible, in particular demi-axes 15 of the roller electrode assembly 1 and an interior 16 of tire 3. From the view shown in FIG. 4 it can be clearly seen that mainly a tread of core 2 is surrounded by tire 3. Dielectric cover plates 17 are arranged laterally.

[0066] FIG. 5 shows an assembly similar to FIG. 2 but with a roller electrode assembly 1 as shown in FIG. 3.

[0067] FIG. 6 shows a sidewards cutaway drawing according to FIG. 5, with further details visible, in particular a generator 4, a collector 10 and supply lines 9. The dotted arrows between FIGS. 5 and 6 illustrate the position of an outer circumference of tire 3, an outer circumference of core 2 and an inner circumference of tire 3.

[0068] The outer circumference of core 2 is also indicated by a circular dotted line in FIGS. 3, 5 and 7.

[0069] FIG. 7 shows an assembly similar to FIG. 1 but with two roller electrode assemblies 1 according to a further embodiment of the present invention.

[0070] FIGS. 8 to 10 show sidewards cutaway drawings according to FIG. 7 in three versions, with further details visible, for example the dielectric cover plates 17, the demi-axes 15, the generator 4 with the supply line 9, the devices 11 for contactless transmission and in each case the interiors 16 of the tires 3. The embodiments of FIGS. 8, 9 and 10 differ in each case with respect to their interconnection, in particular with respect to their contact with the generator 4. In the embodiments according to FIGS. 8 to 10, at least one of the roller electrode assemblies 1 is in contactless connection with the generator 4 via a device for transmission 11.

[0071] From FIGS. 3 to 10 it can be seen that tire 3 does not exclusively rest on one tread of core 2, but also partially surrounds both sides of core 2. That section of both sides of the core 2 which is not surrounded by the tire 3 is covered by a dielectric cover disk 17.

[0072] The devices for contactless transmission 11 are U-shaped electrodes that partially surround the roller electrode assembly 1.

[0073] In FIG. 8, the roller electrode assembly 1 shown below, which acts as a counter electrode, is grounded via the contactless transmission device 11. An output of the generator 4 is also grounded.

[0074] In FIG. 9, both roller electrode assemblies 1 are connected to generator 4, but with opposite polarity.

[0075] In FIG. 10, a grounded support table 12 is provided in addition to the assembly according to FIG. 7.

[0076] For the sake of clarity, not all the features shown in all the figures are designated by reference numbers.

[0077] With reference to FIGS. 1 to 10, the operation of the apparatus of the invention is explained as follows:

[0078] Apparatuses comprising at least one roller electrode 7 are known from the state of the art. They weld two workpieces 5a, 5b or two sections of one workpiece together.

[0079] In an apparatus according to FIG. 1, both roller electrodes 7 rotate in opposite directions around the rotation axes 20, as indicated by the arrows inside the roller electrodes 7. The roller electrodes 7 move relative to the workpieces 5a, 5b in the direction of an arrow 19.

[0080] In an apparatus according to FIG. 2, the roller electrode 7 rotates and thus moves in the direction of arrow 19 along the workpieces to be welded 5a, 5b, which are mounted on a flat counter electrode 8, which usually functions as a table or as part of a table. In both versions of known apparatuses, for example, undesired plasma formation and plasma discharge occurs in an essentially wedge-shaped area indicated by arrows 6, since in this area the field strength of the electric field emitted or generated by the roller electrodes 7 is very strong. The risk of such a plasma discharge with spark formation and the associated undesired effects and dangers increases proportionally to the field strength and is therefore highest in the assemblies shown in FIGS. 1 and 2 in the immediate vicinity of a pressure zone within which the workpieces 5a, 5b are pressed together by the electrodes 7, 8.

[0081] A length 13 of the respective pressure zone, i.e. the section within which the workpieces 5a, 5b are subjected to pressure, is indicated below the apparatuses for the sake of clarity.

[0082] In the assembly according to FIG. 3, the core 2 is the actual electrode, which is surrounded by the tire 3. The roller electrode assembly 1 is shown separately in FIGS. 3 and 4. FIGS. 5 and 6 show the roller electrode assembly 1 in operating position together with a flat counter electrode 8.

[0083] The deformation of the tire 3 of the roller electrode assembly 1 is clearly visible in FIG. 5, which leads to a significantly increased length 13 of the pressure zone compared to the assembly according to FIG. 2. Furthermore, FIG. 5 shows that the immediate vicinity of the point where the electrode or core 2 and the flat counter electrode 8 come closest to each other is provided or filled by tire 3. Those regions of the essentially wedge-shaped areas indicated by arrows 6, where air is present and plasma can be formed, have a significantly greater distance between the electrodes, i.e. in FIG. 5 the core 2, and the flat counter electrode 8, compared to the assembly according to FIG. 2. Thus, the field strength and consequently the danger of plasma discharges is also significantly reduced.

[0084] FIG. 5 also clearly shows that the core 2, i.e. the actual electrode, approximately in a center of the pressure zone, comes so close to the workpiece 5a or the upper section to be welded that a field strength sufficient for welding is guaranteed.

[0085] Here the use of the inflatable tire 3 offers a further advantage. Both the contact pressure applied to at least one workpiece 5a, 5b and the length of the contact pressure zone can be determined by the degree of inflation of tire 3. For example, several test runs can be conducted with different filling levels of tire 3 to determine which filling level produces the best welding result. This can depend, among other things, on the length of the pressure zone 13 and/or the pressure applied.

[0086] FIG. 6 shows that the generator 4, which produces the high-frequency alternating electrical voltage, is connected to the core 2 via a supply line 9 and a collector 10, which is designed in the form of a sliding contact. Furthermore, the flat counter electrode 8 is grounded and there is a coupling between the reference potential and the generator 4 via the principle of capacitive coupling between the flat counter electrode 8 and the generator 4.

[0087] The mode of operation of the apparatuses shown in FIGS. 7 to 10 and the advantages of using the roller electrode assemblies 1 are analogous to those described above in FIGS. 3 to 6. The mode of operation and advantages of course apply both to the roller electrode assemblies 1 shown above in FIGS. 7 to 10 and to the roller electrode assemblies 1 shown below, which represent the counter-electrode. Only for illustration purposes, one of the essentially wedge-shaped areas 14 is shown in FIG. 7 in a disproportionately enlarged form and not only indicated by an arrow 6. Due to the curvature of tire 3, area 14 is actually only approximately wedge-shaped, and of course, it is not actually present as a delimited area.

[0088] As shown in FIG. 8, only the upper roller electrode assembly 1 is connected to a first output of generator 4. Accordingly, the roller electrode assembly 1 shown below and a second output of generator 4 are grounded.

[0089] By “+HV” and “−HV” in many figures a polarity of the voltage produced by generator 4 is shown as a snapshot. The polarity of the outputs of generator 4 of course changes with the frequency of the alternating voltage generated.

[0090] Compared to the assembly shown in FIG. 8, according to which the roller electrode assembly 1 shown in the bottom of the figure and the generator 4 are grounded, the assemblies according to FIGS. 9 and 10 have the advantage that the roller electrode assemblies 1 shown in the bottom of the figures are connected to the generator 4. The lower and the upper roller electrode assemblies 1 are applied with opposite polarity of the electrical alternating voltage according to the assemblies shown in FIGS. 9 and 10. This can further reduce the risk of plasma discharges, since the difference of potential between the electrodes or cores 2 does not result from a difference to the grounded zero potential.

[0091] The grounded support table 12 further increases safety.

[0092] Although only some preferred examples of the invention have been shown and described, it is obvious that the skilled person can add numerous modifications without departing from the spirit and scope of the invention.

[0093] For example, instead of a table, a frame or the like may be considered.

[0094] Furthermore, all of the above-mentioned embodiments may include such a table, frame or the like for storing the workpieces to be joined 5a, 5b or for holding them during welding. Such a table, such a frame or the like can thus be used solely for holding or storing the workpieces 5a, 5b or sections to be joined, or additionally as a counter pressure element and, if necessary, counter-electrode.

[0095] In all embodiments, tire 3 can either be provided only on the tread of core 2 or partially surround core 2, as shown in FIGS. 3 to 10. It is also conceivable that tire 3 completely surrounds core 2, thus making the dielectric cover plates 17 dispensable. In this case, tire 3 should preferably be arranged in such a way that it can effectively prevent sparking by plasma formation. The assembly as shown in FIGS. 3 to 10 is particularly preferred, where the tread of core 2 and directly adjacent sections of the side surfaces of core 2, but not the entire side surfaces, are covered by tire 3.

[0096] The dielectric cover plates 17 can also be dispensed with.

[0097] If welding of two workpieces 5a, 5b is mentioned, the welding of two sections of one or more workpieces shall always be encompassed.

[0098] The device 11 for contactless transmission does not necessarily have to be designed as a U-shaped electrode; other such devices can also be used. These can work according to the principle of capacitive coupling, but other possibilities of contactless energy transmission can also be considered. Of course, with regard to all roller electrode assemblies 1, both a contacting transmission as shown in FIG. 6 and a contactless transmission as shown in FIGS. 8 to 10 can be considered.

[0099] The direction of movement 19 in the figures always refers to the movement of the roller electrode assemblies 1 relative to the workpieces 5a, 5b, so it is a relative indication. Although the roller electrode assembly 1 is preferably moved relative to the workpieces 5a, 5b, the opposite case is also possible. If the workpieces 5a, 5b to be welded are moved relative to one or two fixed roller electrode assemblies 1, the movement of these workpieces 5a, 5b is carried out in the opposite direction of arrow 19 with respect to FIGS. 5 and 7.

[0100] Furthermore, in all embodiments comprising two roller electrode assemblies 1, it may be considered to connect only one of the roller electrode assemblies 1 to the generator 4 and to ground the second roller electrode assembly 1. Especially with regard to FIGS. 7 to 10, this applies to both the roller electrode assembly 1 shown at the top and to the roller electrode assembly 1 shown at the bottom.

[0101] The demi-axes 15 can of course be beared in suitable bearings (not shown). The demi-axes 15 can be electrically insulated to prevent, for example, a user from coming into direct contact with the demi-axes 15.

TABLE-US-00001 Reference number list 1 Roller electrode assembly 34 2 Core 35 3 Tires 36 4 Generator 37 5 Workpiece 38 6 Arrow 39 7 roller electrode 40 8 Planar counter electrode 41 9 Supply line 42 10 collector 43 11 Device for contactless transmission 44 12 Grounded support table 45 13 Length of the pressure zone 46 14 Wedge-shaped area 47 15 demi-axes 48 16 Interior 49 17 Dielectric cover plate 50 18 51 19 Direction of movement 52 20 axis of rotation 53 21 54 22 55 23 56 24 57 25 58 26 59 27 60 28 61 29 62 30 63 31 64 32 65 33 66