Packaging line for a compressible material under plastic film, including a shrink wrapper
The packaging line addresses the challenge of maintaining compressed materials by using movable interlayer modules to synchronize the functional gap and welding, enhancing reliability and throughput.
Patent Information
- Application Number
- FR2023013099
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-11-27
- Publication Date
- 2025-11-14
- Estimated Expiration
- 2043-11-27
AI Technical Summary
Existing packaging lines for compressible materials under plastic film face difficulties in maintaining the compressed state of the material during wrapping due to the complexity of implementing and synchronizing a valve to close the functional gap between the interleaving and shrink wrapper modules, and are not compatible with materials of varying lengths.
A packaging line design that eliminates the need for a valve by using movable interlayer modules to control the functional gap, allowing for synchronized movement with welding means to maintain the compressed state and accommodate materials of varying lengths.
Enables simpler, more reliable, and durable packaging with increased throughput by maintaining the compressed state of materials and facilitating the wrapping process without the need for a separate valve, while accommodating materials of different lengths.
Smart Images
Figure 00000016_0000 
Figure 00000016_0001 
Figure 00000016_0002
Abstract
Description
Title of the invention: Packaging line for a compressible material under plastic film, comprising a shrink wrapper
[0001] The field of the invention is that of the design and manufacture of packaging machines under plastic film, and in particular under polyethylene film.
[0002] More specifically, the invention relates to the design of shrink wrappers and associated equipment.
[0003] It should be noted that the function of a shrink wrapper is to wrap products in plastic film, whether heat-shrinkable or not. The shrink wrapper is generally the first element in a plastic film packaging line, preferably using polyethylene film.
[0004] The operating principle of a shrink wrapper is as follows: an upper plastic film is welded to a lower film to form a substantially vertical film curtain. The product to be wrapped is conveyed by a conveyor towards the pre-formed curtain. The conveying of the product causes it to be pushed against the curtain, which then causes the upper and lower films to unwind from their respective rolls. Photoelectric cells (or any other means) detect the rear end of the product to be wrapped, at which point the conveyor stops. At this stage, a sealing device automatically closes on the upper and lower films behind the product. Generally, a double seal and a cut are performed, thus completing the wrapping of the product.
[0005] At the same time, the film curtain is reconstituted for the next product.
[0006] Of course, each shrink wrapper is designed and manufactured according to the dimensions and characteristics of the products to be packaged.
[0007] According to a classic design of shrink wrappers, the upper plastic film is unwound from a horizontal reel arranged above the conveyor and transversely to it, while the lower plastic film is unwound from a horizontal reel arranged below the conveyor, and also transversely to it.
[0008] Shrink-wrapping, particularly using shrink wrappers, has existed for a number of years now. Initially limited to certain sectors, its use has expanded and continues to grow in all industries.
[0009] In particular, plastic film packaging is now commonly used for compressible insulating materials, such as glass wool or rock wool, or more generally any type of bio-based compressible material such as wood, hemp, cotton, recycled cardboard, PVC fibers...
[0010] Naturally, with such compressible materials, the material is first compressed before packaging, and then the compressed material is maintained during the packaging phase. The aim is obviously to reduce the volume of the packaged compressible products during transport and storage.
[0011] To achieve the compression of the material before packaging, several techniques are known from the prior art.
[0012] According to a first known technique, the compressible material is pushed into a funnel-shaped cavity, which promotes forced compression of the material. Upon exiting the funnel, the material is introduced into a shrink wrapper which wraps the material in plastic film while preserving its compressed state.
[0013] According to another technique described in Figures 1 to 6, a packaging line for a compressible material under plastic film comprises: - a compression module 1 of the material M, comprising a lower compression plate 10 and an upper compression plate 11, movable in height relative to each other from an admission position of the material M in an uncompressed state as illustrated by [Fig.1], to a close position intended to bring the material into a compressed state as illustrated by [Fig.2]; - a shrink wrapper 2, extending from the compression module 1 in a material flow direction D, so as to shrink the material in a compressed state, - an output module 4, comprising a lower output platform 40 and an upper output platform 41 separated from each other in height so as to maintain the material M in a compressed state.
[0014] In a conventional manner, the shrink wrapper also includes: - a lower coil 20; - an upper coil 21; - a lower sealing bar 22 (also referred to as "counter sealing bar") and an upper sealing bar 23, movable relative to each other to, firstly, join the plastic film from the upper reel and the plastic film from the lower reel in order to form a film curtain and, secondly, to weld the lower and upper parts of the film curtain behind the product.
[0015] Conventionally, a double weld is made and a cut is made between the two welds, thus completing the wrapping of the product.
[0016] According to this technique, the line further comprises an interleaving module 3, disposed between the compression module 1 and the shrink wrapper 2, this module comprising a tray lower interlayer 30 and an upper interlayer 31, separated from each other vertically so as to maintain the material in a compressed state.
[0017] This intercalated module is arranged between the compression module and the output module so as to provide a functional gap E, through which the film curtain is intended to extend and through which the upper sealing bar 21 can be moved towards the lower sealing part 20 to make the welds necessary for the proper unfolding of the bundling.
[0018] Furthermore, a valve C is provided to close the functional gap at the level of the upper output tray 41 and the upper intermediate tray 31 during the passage of the material M between the intermediate module and the output module. This valve C is movable, in particular pivotable, between a position in which it closes the functional gap, and a position in which it allows the passage of the welding means through the functional gap once the material M has passed between the intermediate module and the shrink wrapper.
[0019] Thus, according to the prior art, the packaging of a compressible material under plastic film is carried out according to the following steps: - the material M is admitted into the compression module 1, while the lower plate 10 and the lower plate 11 are separated from each other by a height greater than or equal to that of the material M ([Fig.l]); - the upper plate 11 of the compression module 1 is lowered towards the lower plate 10 so as to compress the material M ([Fig.2]); - the material M is transferred from the compression modulus 1 to the intermediate modulus 3.
[0020] It is noted that during these first steps, a film curtain is made beforehand so as to join the film of the lower reel 20 to that of the upper reel 21. In addition, the flap C is kept in the closed position, ensuring closure of the functional space E and ensuring continuity of support between the upper intercalated plate 31 and the upper output plate 41.
[0021] The lower welding bar 20 extends in the plane of the lower intermediate plate 30 and the lower output plate 40.
[0022] Thus, the material M is transferred from the intercalated module 3 to the output module 4, by being pushed against the film curtain extending between the lower reel 20 and the upper reel 21 ([Fig.4]).
[0023] While the conveying of the material M is continued between the lower output tray and the upper output tray, this by unwinding the plastic film from the lower reel 20 and the upper reel 21, the valve C is brought into the opening position of the functional space E ([Fig.5]).
[0024] The lower weld bar 20 and the upper weld bar 21 can then be moved within the functional gap E so as to proceed with the double welding of the plastic film and the cutting between the two welds made ([Fig.6]).
[0025] Such a packaging line ensures the expected result, namely compressing the compressible material and wrapping it in a plastic film while it remains in a compressed state.
[0026] On the other hand, the proper functioning of this prior art conditioning line necessarily implies the implementation of the valve C, otherwise the material M would tend to expand in the functional space, during its passage from the intercalated module 3 to the output module 4.
[0027] However, implementing such a valve is not without difficulties in terms of assembly and adjustment. These difficulties are further compounded by the complexity of controlling the valve, in order to synchronize its opening and closing with the movement of the welding means within the functional gap between the interleaving module and the shrink wrapper.
[0028] Furthermore, the flap necessarily has a certain length in the direction of material flow. However, this flap is not a conveyor. Consequently, materials with a length in the direction of flow shorter than that of the flap are not compatible with such a prior art conditioning line, since they would remain blocked at the flap due to the lack of conveying at that point.
[0029] The invention aims in particular to overcome this drawback of the prior art.
[0030] More specifically, the invention aims to provide a packaging line for a compressible material under plastic film of the type comprising a compression module, a shrink wrapper and an interlayer module disposed between the shrink wrapper and the compression method, which allows the functional gap between the interlayer module and the shrink wrapper to be filled in a simpler, more reliable and more durable way than with the prior art solution.
[0031] The invention also aims to provide such a packaging line which makes it possible to increase packaging rates.
[0032] These objectives, as well as others that will appear subsequently, are achieved thanks to the invention, which relates to a packaging line for a compressible material under plastic film, comprising: - a material compression module, comprising a lower compression plate and an upper compression plate movable in height relative to each other from a material admission position in an uncompressed state to a close position intended to bring the material into a compressed state; - a shrink wrapper, extending from the compression module in one direction of scrolling the material in such a way as to bundle the material in a compressed state, - an output module, in the immediate extension of the shrink wrapper in one direction of material flow, comprising a lower output tray and an upper output tray separated from each other vertically so as to maintain the material in a compressed state, - an interleaving module arranged between the compression module and the shrink wrapper so as to allow a functional gap with the output module, the interleaving module comprising a lower interleaving plate and an upper interleaving plate spaced apart in height so as to maintain the material in a compressed state.
[0033] According to the invention, the packaging line includes means for moving the interlayer module relative to the compression module and / or relative to the output module, the means for moving being controlled so that the interlayer module is adjacent to the compression module and maintains the functional gap with the output module, the functional gap being suitable for allowing the passage of an upper plastic film, a lower plastic film and means for welding the upper plastic film with the lower plastic film to create a film curtain or, alternatively, so that the interlayer module is adjacent to the output module and maintains a space with the compression module.
[0034] Thus, thanks to the invention, it is unnecessary to implement a valve to close the functional gap between the shrink wrapper and the interlayer module to keep the material compressed while it passes through this gap.
[0035] Indeed, the means of moving the intercalated module advantageously replace this valve, by alternatively ensuring the presence of the functional gap when the intercalated module is moved away from the shrink wrapper or, conversely, by ensuring continuity of the respective plates of the intercalated module and the output module, which keeps the material compressed during its transition from the intercalated module to the shrink wrapper.
[0036] It should be noted that the term "in the immediate extension," with regard to the positioning of the output module relative to the shrink wrapper, means that the input of the output module is directly adjacent to the shrink wrapper film, downstream of it in the direction of material flow. Upstream of the film, the interleaving module is likely to occupy a position with no gap with the shrink wrapper, and therefore with no gap, or almost no gap, with the shrink wrapper film. Thus, during the transfer of material from the interleaving module to the output module, the interleaving module and the output module are in close proximity to each other, on either side of the shrink wrapper film.
[0037] According to an advantageous solution, the compression module is fixed and the intercalated module is mobile relative to the compression module.
[0038] More specifically, the intercalated module is mobile in translation relative to the compression module, according to the direction of material flow.
[0039] Independently of this feature or in combination with it, the shrink wrapper can advantageously be fixed and the interleaving module movable relative to the shrink wrapper.
[0040] Again, the intercalated module is mobile in translation in the direction of material flow.
[0041] Of course, in the case where only the intermediate module is mobile, we obtain an embodiment that is both advantageous and simplified from a kinematic point of view.
[0042] Advantageously, the lower intermediate plate and the upper intermediate plate are aligned in height respectively with the lower compression plate and the upper compression plate when they occupy the close position.
[0043] In this case, the lower intermediate tray and the upper intermediate tray are advantageously aligned in height respectively with the lower output tray and the upper output tray.
[0044] It is understood that, in this way, the compressible material is conveyed while remaining in the same plane defined by the set of lower plates of the compression module, the intercalated module and the output module, with the respective upper plates also aligned in height to maintain the compressed state of the material.
[0045] According to an advantageous embodiment, the packaging line further has one and / or the other of the following characteristics: - the lower compression plate carries a first conveyor of the material in a direction of material flow; - the lower intermediate platform carries a second material conveyor in a material flow direction; - the lower output tray carries a third material conveyor in a material flow direction.
[0046] Thus, an advantageous characteristic is retained with regard to integrating the conveying means into the lower platform of each module.
[0047] According to yet another particular feature, the line includes a sensor for detecting the functional gap between the intercalated module and the output module and also includes a control unit capable of receiving a signal of the presence of the functional gap from the sensor for detecting the functional gap, the control unit being parameterized to cause a displacement and a weld by the welding means after receiving the signal of the presence of the functional gap.
[0048] In this way, it is easy to synchronize the movement of the welding means through the functional gap with the movement of the intercalated module towards the compression module, that is to say in a position in which it precisely maintains the functional gap with the output module.
[0049] Other features and advantages of the invention will become more apparent upon reading the following description of a preferred embodiment of the invention, given by way of illustrative and non-limiting example, and the accompanying drawings, among which:
[0050] [Fig-1] illustrates a first phase of conditioning a compressible material with a prior art line;
[0051] [Fig.2] illustrates a second conditioning phase of a compressible material with a prior art line;
[0052] [Fig.3] illustrates a third conditioning phase of a compressible material with a prior art line;
[0053] [Fig.4] illustrates a fourth conditioning phase of a compressible material with a prior art line;
[0054] [Fig.5] illustrates a fifth conditioning phase of a compressible material with a prior art line;
[0055] [Fig.6] illustrates a sixth conditioning phase of a compressible material with a prior art line;
[0056] [Fig.7] illustrates a first conditioning phase of a compressible material with a conditioning line according to the invention;
[0057] [Fig.8] illustrates a second conditioning phase of a compressible material with a conditioning line according to the invention;
[0058] [Fig.9] illustrates a third conditioning phase of a compressible material with a conditioning line according to the invention;
[0059] [Fig. 10] illustrates a fourth conditioning phase of a compressible material with a conditioning line according to the invention;
[0060] [Fig. 11] illustrates a fifth conditioning phase of a compressible material with a conditioning line according to the invention;
[0061] [Fig. 12] illustrates a sixth conditioning phase of a compressible material with a conditioning line according to the invention.
[0062] With reference to figures 7 to 12, a packaging line for a compressible material under plastic film, according to the invention, is described below.
[0063] As schematically illustrated, such a conditioning line according to the invention comprises, in a manner known in the per se, a compression module 1 of a compressible material M, comprising a lower compression plate 10 and an upper compression plate 11, the two plates being movable in height relative to each other. the other to achieve compression of the material M. More precisely, the lower plate 10 is fixed in height and the upper compression plate 11 is mobile in height from an admission position of the material M in an uncompressed state (the gap between the lower compression plate and the upper compression plate being then greater than or equal to the uncompressed height of the material M) to a position close to the lower compression plate, a position in which the material M is brought into a compressed state.
[0064] The packaging line further includes a shrink wrapper 2, arranged downstream of the compression module 1 according to the direction of travel D of the material M in the packaging line. This shrink wrapper is conventionally composed of the following elements: - an upper reel 21 from which an upper film is unwound; - a lower reel 20, from which a lower film is unwound; - a lower welding bar 22 and an upper welding bar 24, intended to be moved towards each other until they meet to make a weld and in particular a double weld of the upper film with the lower film so as to create a film curtain.
[0065] The shrink wrapper (shown in dashed lines in the figures) comprises, in practice, a frame that carries the various elements listed above. According to the present embodiment, the upper and lower reels are respectively above and below the interleaving module. However, it is also possible for the reels to be located to the side of the interleaving module, with angled return rollers to the shrink wrapper, as described, for example, in the text of the patent document published under number FR3108594.
[0066] Downstream of the shrink wrapper, in the direction of material flow, is an output module 4, having a lower output tray 40 and an upper output tray 41. The material M is conveyed between the two trays by pushing the film curtain (and thus unwinding the lower film from the lower reel and the upper film from the upper reel). Furthermore, according to a particular embodiment, this output module incorporates lateral heating means designed to cause shrinkage of the plastic film (provided, of course, that it is heat-shrinkable).
[0067] In the context of the invention, the lower outlet plate 40 and the upper outlet plate 41 are spaced vertically apart from each other so as to maintain the material in a compressed state and, more specifically, in the compressed state as obtained by the compression modulus 1.
[0068] A packaging line according to the invention further comprises an interleaving module 3 disposed between the compression module 1 and the shrink wrapper 2, this module comprising a lower interleaving tray 30 and an upper interleaving tray 31 spaced apart vertically so as to maintain the material in the compressed state obtained by the compression module 1. The arrangement and dimensions of the intercalated module between the compression module 1 and the output module 4 are such that a functional spacing E can be provided between the intercalated module 3 and the output module 4, as will be explained later.
[0069] According to the principle of the invention, the conditioning line further comprises means for moving 5 the intercalated module 3, these means for moving the position of the intercalated module between the compression module 1 and the output module 4. In other words, the intercalated module can be moved relative to the compression module 1 and / or relative to the output module 4, in order to maintain, or not maintain, the functional gap E between the intercalated module 3 and the output module.
[0070] According to the present embodiment, the movement means 5 are controlled so that the intermediate module is moved between two positions, namely: - a first position in which the intermediate module is adjacent to the compression module 1 and maintains the functional gap E with the output module; - a second position in which the intercalated module is adjacent to the output module and leaves a space with the compression module 1.
[0071] The functional gap E is suitable for allowing the passage of the upper plastic film and the lower plastic film, as well as the passage of means for welding the upper plastic film with the lower plastic film in order to create a film curtain extending vertically, or almost, into the input of the output module.
[0072] As previously stated, the welding means comprise a lower welding bar 22 (also referred to as a "counter welding bar") and an upper welding bar 23 designed to cooperate together. In their respective inactive positions, the lower welding bar 22 is located above the level of the lower intermediate tray and the lower bundling tray, while the upper welding bar 23 is located above the upper intermediate tray and the upper bundling tray.
[0073] Means of movement known to those skilled in the art are implemented to make the lower welding bar 22 and the upper welding bar 23 mobile between their inactive position and their welding position. According to the present embodiment, the lower welding bar and the upper welding bar are both vertically mobile towards each other, which reduces the time required for the welding operation (as opposed to the prior art technique where only one of the two bars is mobile, generally the upper bar, and the other is fixed).
[0074] According to a preferred embodiment, the compression module is fixed while that the intercalated module is mobile relative to the compression module, this of course in the direction of material flow.
[0075] In addition, the shrink wrapper and the output module are fixed and the interleaving module is mobile relative to the shrink wrapper and the output module, this of course also in the direction of material flow.
[0076] In other words, the movement means 5 are capable of causing a back-and-forth movement of the intercalated module 3 between the compression module 1 and the output module 4, so as, alternatively, to be adjacent to the compression module 1 and to be separated from the output module 4 or to be adjacent to the output module 4 and to be separated from the compression module 1.
[0077] Moreover, preferably, the lower intermediate plate 30 and the upper intermediate plate 31 are aligned in height with, respectively, the lower compression plate 10 and the upper compression plate 11, when the latter occupy the close position tending to compress the material M.
[0078] In parallel, the lower output tray 40 and the upper output tray 41 are respectively aligned in height with the lower intermediate tray 30 and the upper intermediate tray 31.
[0079] The movement of the material M along the conditioning line, in the direction of material flow D, is ensured by: - the first conveyor 100 carried by the lower compression plate 10; - a second conveyor 300 carried by the lower intermediate platform 30; - a third conveyor 400 carried by the lower exit platform 40.
[0080] Furthermore, the line includes a sensor 6 for detecting the functional gap between the intercalated module 3 and the output module 4. The conditioning line further includes a control unit 7 capable of receiving a signal of the presence of the functional gap from the detection sensor 6, the control unit being parameterized to cause a displacement and a weld by the welding means after receiving the signal of the presence of the functional gap.
[0081] The operation of a packaging line according to the invention is described below.
[0082] The material M is admitted into the compression module while the upper compression plate 11 is separated from the upper compression plate 10 by a height greater than that of the material M ([Fig. 7]). By way of example, in this initial configuration of the conditioning line, the intermediate module is adjacent to the compression module 1 and maintains a functional gap E with the output module 4.
[0083] The upper compression plate 11 is then brought closer to the lower compression plate 10 so as to compress the material, preferably as much as possible. M ([Fig.8]).
[0084] The material M is transferred in the intercalated module 3, between the lower intercalated plate 30 and the upper intercalated plate 31 ([Fig.9]).
[0085] The movement means 5 move the interleaving module 3 towards the shrink wrapper 2 and the output module 4 until it is adjacent to the output module. The material M is drawn between the two platens of the output module by pushing the plastic film curtain according to the known principle of a shrink wrapper ([Fig.10]).
[0086] The means of displacement 5 then cause the displacement of the intercalated module 3 in the direction of the compression module 1, so as to again preserve the functional gap E between the intercalated module 1 and the output module 4 ( [Fig.11]).
[0087] At this stage, the detection sensor 6 sends a signal to the control unit 7, indicating that the functional space E is present. The control unit then commands the movement of the lower welding bar 22 and the upper welding bar 23 so that they come together and perform a weld, in this case a double weld, and a cut of the upper plastic film with the lower plastic film ( [Fig.12]).
[0088] As illustrated in Figures 7 to 12, it should be noted that, according to the present embodiment, the compression module 1 and the interlayer module 3 are sized to receive two batches of material M spaced apart from each other. The mobility of the interlayer module 3 relative to the compression module 1 on the one hand, and relative to the shrink wrapper 2 and the output module on the other, allows for a kind of buffer zone whereby the first batch of material M, in the direction of travel D, is introduced into the shrink wrapper 2 while the other batch of material M remains within the interlayer module 3. During this time, it is then possible to admit two new batches of compression M into the compression module 1 and compress them. This compression phase can be carried out while the batch of material M remaining in the interlayer module is being transferred through the output module.The new batches of material M in their compressed state can then be transferred into the now-released intercalated module 3.
[0089] Such an operation makes it possible to obtain a high rate.
[0090] Furthermore, as previously stated, this output module incorporates lateral heating means designed to induce shrinkage of the (polyethylene) film on the lateral sides of the material. In the embodiment in which two batches of material are admitted simultaneously into the compression module, the modules of the line are synchronized, allowing, in particular, during the phase in which both batches of material are in the output module, for the film to be shrunk on one of the two batches while it is held compressed and remains so after to have exited the output module.
Claims
1. Demands Packaging line for a compressible material (M) under plastic film, comprising: - a material compression module (1), comprising a lower compression plate (10) and an upper compression plate (11) movable in height relative to each other from an admission position of the material in an uncompressed state to a close position intended to bring the material into a compressed state; - a shrink wrapper (2), extending from the compression module (1) in a material flow direction so as to shrink the material in a compressed state, - an output module (4), in the immediate extension of the shrink wrapper (2) in a direction of material flow, comprising a lower output plate (40) and an upper output plate (41) separated from each other vertically so as to maintain the material in a compressed state, - an interlayer module (3) arranged between the compression module (1) and the shrink wrapper (2) so as to allow a functional gap (E) with the output module (4), the interlayer module (3) comprising a lower interlayer plate (30) and an upper interlayer plate (31) separated from each other vertically so as to maintain the material in a compressed state, characterized in that it comprises means for moving (5) the interlayer module (3) relative to the compression module (1) and / or relative to the output module (4), the means for moving (5) being controlled so that the interlayer module (3) adjoins the compression module (1) and maintains the functional gap with the output module (4), the functional gap being suitable for allowing the passage of an upper plastic film, a lower plastic film and means for welding the upper plastic film with the lower plastic film to create a film curtain, or, alternatively, so that the interlayer module (3) adjoins the output module (4) and maintains a space with the compression module (1).
2. Packaging line for a compressible material under plastic film according to claim 1, characterized in that the compression module (1) is fixed and in that the interlayer module (3) is mobile relative to the compression module (1) in a material flow direction.
3. Packaging line for a compressible material under plastic film according to claim 1, characterized in that the shrink wrapper (2) is fixed and in that the interleaving module (3) is mobile relative to the shrink wrapper (2) in a material flow direction.
4. Packaging line for a compressible material under plastic film according to any one of the preceding claims, characterized in that the lower interlayer tray (30) and the upper interlayer tray (31) are aligned in height respectively with the lower compression tray (10) and the upper compression tray (11) when they occupy the close position.
5. Packaging line for a compressible material under plastic film according to claim 4, characterized in that the lower interlayer tray (30) and the upper interlayer tray (31) are aligned in height respectively with the lower exit tray (40) and the upper exit tray (41).
6. Packaging line for a compressible material under plastic film according to any one of the preceding claims, characterized in that the lower compression plate (10) carries a first conveyor (100) of the material in a direction of material flow.
7. Packaging line for a compressible material under plastic film according to any one of the preceding claims, characterized in that the lower intermediate tray (30) carries a second conveyor (300) of the material in a direction of material flow.
8. Packaging line for a compressible material under plastic film according to any one of the preceding claims, characterized in that the lower outlet tray (40) carries a third conveyor (400) of the material in a material scroll direction.
9. Packaging line for a compressible material under plastic film according to claim 1, characterized in that it comprises a sensor for detecting (6) the functional gap between the interlayer module (3) and the output module (4), and in that it also includes a control unit (7) capable of receiving a functional gap presence signal from the functional gap detection sensor (6), the control unit (7) being parameterized to cause movement and welding by welding means after receiving the functional gap presence signal.