Method for assembling biaxially oriented polyethylene terephthalate strips

Abstract

A method for assembling a first biaxially oriented polyethylene terephthalate strip and a second biaxially oriented polyethylene terephthalate strip for manufacturing an inflatable structure of a deployable kit for space debris capture, the method comprising the steps of: a) arranging a stack of the first strip and the second strip on a bearing face of an anvil, b) applying a sonotrode to compress said stack between a welding face of the sonotrode and the bearing face of the anvil, c) welding the two strips by the emission of ultrasound by the sonotrode through the stack.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for joining biaxially oriented polyethylene terephthalate strips

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to the field of deorbiting space debris, more precisely to such deorbiting from a deployable kit comprising an inflatable structure and a net, and, more particularly still, to a method of assembling Mylar™ strips for the manufacture of such an inflatable structure.

[0005] STATE OF THE ART

[0006] The INSIDeR (Innovative Net & Space Inflatable structure for active Debris Removal) system aims to safely deorbit space debris of various sizes. This system is a kit comprising a flexible, high-strength net serving as a capture system capable of capturing large objects and adapting to different debris morphologies and tumbling speeds, and a tubular inflatable structure supporting the net serving as a net deployment system and ensuring debris movement control and damping.

[0007] The inflatable structure comprises an assembly of sections, notably tubular, composed of sheets of biaxially oriented polyethylene terephthalate (BOPET) also commonly called Mylar™.

[0008] Inflatable Mylar™ structures intended to be sent into space are known from the prior art and are assembled by gluing. However, gluing does not provide long-term strength and therefore runs the risk of delamination.

[0009] STATEMENT OF THE INVENTION

[0010] An aim of the invention is to enable the assembly of sections of an inflatable structure of a deployable kit for capturing space debris which makes it possible to produce an inflatable structure which is resistant over the long term for use in space, preferably at least ten years, more preferably at least twenty years. An aim of the invention is therefore to enable the production of an inflatable structure which has good mechanical strength at very high inflation pressures, preferably around 2 x 10 6 Pa (20 bar).

[0011] Another object of the invention is to enable the production of an inflatable structure which is watertight and continuous, i.e. made of a single material. According to a first aspect, a method is proposed for assembling a first strip of biaxially oriented polyethylene terephthalate and a second strip of biaxially oriented polyethylene terephthalate for the manufacture of an inflatable structure of a deployable kit for capturing space debris, the method comprising the steps of: a) arranging a stack of the first strip and the second strip on a bearing face of an anvil, b) applying a sonotrode to compress said stack between a welding face of the sonotrode and the bearing face of the anvil, c) welding the first and second strips by emitting ultrasound through the stack by the sonotrode.

[0012] According to advantageous and non-limiting characteristics, taken alone or in combination when technically possible:

[0013] - welding is carried out by performing a relative movement between the sonotrode and the stack;

[0014] - the first strip and the second strip are deformed simultaneously with welding so as to create a mechanical anchoring of the first strip in the second strip;

[0015] - welding is carried out substantially without mechanical deformation of the first strip and the second strip;

[0016] - the method comprises a step a1) prior to step b) of placing a filler material between the first strip and the second strip, said filler material melting at least partially during welding;

[0017] - the filler material is linear polyester, preferably polyethylene terephthalate and even more preferably biaxially oriented polyethylene terephthalate;

[0018] - the first strip and the second strip are parts of different biaxially oriented polyethylene terephthalate sheets;

[0019] - the first strip and the second strip are parts of the same sheet of biaxially oriented polyethylene terephthalate;

[0020] - the ultrasounds are emitted at a frequency between 25 kHz and 40 kHz. According to a second aspect, there is provided a method for manufacturing an inflatable structure of a deployable kit for capturing space debris comprising the steps of: i) assembling a first strip of biaxially oriented polyethylene terephthalate and a second strip of biaxially oriented polyethylene terephthalate by implementing the method as described above so as to form an assembly of biaxially oriented polyethylene terephthalate, ii) winding the assembly produced in step i) so as to cover a first edge of the assembly with a second edge of the assembly so as to form a tube, iii) assembling the first edge and the second edge by implementing the method as described above.

[0021] Advantageously, the weld made in step i) is a shear weld and the weld made in step iii) is a peel or shear weld.

[0022] According to a third aspect, there is provided a system for implementing the method as described above, comprising:

[0023] - an ultrasonic generator,

[0024] - a sonotrode adapted to emit the ultrasound generated by the generator from a welding face,

[0025] - an anvil having a support face arranged opposite the welding face of the sonotrode.

[0026] According to advantageous and non-limiting characteristics, taken alone or in combination when technically possible:

[0027] - the anvil and the sonotrode take the form of rollers;

[0028] - the support face of the anvil and / or the welding face of the sonotrode have hollow areas and protruding areas;

[0029] - the support face of the anvil and the welding face of the sonotrode are smooth.

[0030] According to a fourth aspect, there is provided an inflatable structure of a deployable kit for capturing space debris comprising a first strip of biaxially oriented polyethylene terephthalate and a second strip of biaxially oriented polyethylene terephthalate joined by welding, characterized in that the inflatable structure is capable of being inflated up to 2 x 10 6 Pa (20 bars). Particularly advantageously, said welding is carried out by emitting ultrasound through a stack of said strips.

[0031] DESCRIPTION OF FIGURES

[0032] Other characteristics and advantages of the present invention will appear on reading the following description of a preferred embodiment. This description will be given with reference to the appended figures including:

[0033] Figure 1 represents a deployable kit;

[0034] Figure 2 illustrates a set of assembled sections rolled up on itself and shear welded;

[0035] Figure 3 illustrates a system for assembling biaxially oriented polyethylene terephthalate strips;

[0036] Figure 4 shows strips of shear welded sections;

[0037] Figure 5 represents the steps of a manufacturing process for an inflatable structure;

[0038] Figure 6 illustrates a system for joining biaxially oriented polyethylene terephthalate strips during a welding step;

[0039] Figure 7 shows strips of welded sections in peel;

[0040] Figure 8 illustrates a set of assembled sections rolled up on itself and welded in peel;

[0041] Figure 9 illustrates a system for joining biaxially oriented polyethylene terephthalate strips during an edge welding step of a set of sections.

[0042] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0043] Kit

[0044] Referring to Figure 1, there is provided a deployable kit 100 for capturing space debris. The deployable kit 100 comprises an inflatable structure 1 and advantageously a net 2. The deployable kit 100 is adapted to be deployed in space in order to capture space debris such as decommissioned satellites. Before using the kit 100, it is necessary to inflate the inflatable structure 1. Advantageously, the inflatable structure 1 is able to be inflated up to 2 x 10 6 Pa (20 bars). This pressure ensures that the inflatable structure 1 remains inflated in space. The inflatable structure 1 is composed of a plurality of sections 10. These sections 10 are made of biaxially oriented polyethylene terephthalate (BOPET) also commonly known as Mylar™. This material is suitable for the temperature and pressure constraints to which the inflatable structure is subjected in space.

[0045] The inflatable structure 1 comprises a plurality of assembled sections 10. Figure 2 illustrates a portion of the inflatable structure 1 comprising two assembled sections 10a, 10b. The manufacture of the inflatable structure 1 notably comprises the assembly of the sections 10 together by welding. The assembly of the sections 10 by welding instead of gluing in fact makes it possible to obtain an inflatable structure 1 that is more resistant to temperature and pressure constraints in space, including as the structure ages.

[0046] A method for manufacturing an inflatable structure 1, a method and a system 6 for assembling strips of biaxially oriented polyethylene terephthalate for manufacturing an inflatable structure 1 will thus be described.

[0047] Tape assembly system

[0048] Referring to Figure 3, the system 6 comprises an anvil 3, a sonotrode 4 and an ultrasonic generator.

[0049] The anvil 3 is typically an anvil used during welding operations, in particular ultrasonic welding. The anvil 3 has a bearing face 31. This bearing face 31 is in particular adapted to receive one or more sheets of biaxially oriented polyethylene terephthalate for welding. Advantageously, the anvil 3 takes the form of a wheel.

[0050] The ultrasonic generator 5 is a typical ultrasonic generator. Preferably, the ultrasonic generator 5 is adapted to emit ultrasound at a frequency between 25 kHz and 40 kHz.

[0051] The sonotrode 4 is a metal part adapted to transmit the ultrasound from the ultrasonic generator to a sheet (or a stack of sheets) arranged on the bearing face 31 of the anvil 3 while applying mechanical pressure to said sheet (or a stack of sheets). The sonotrode 4 is connected to the ultrasonic generator 5 and is adapted to emit the ultrasound generated by the ultrasonic generator 5. The sonotrode 4 is a typical sonotrode 4 for ultrasonic welding. The welding face 41 of the sonotrode 4 is arranged opposite the bearing face 31 of the anvil 3. The sonotrode 4 has a welding face 41 adapted to be arranged opposite, and advantageously in contact with, one or more sheets arranged on the bearing face 31 of the anvil 3 to weld them ultrasonically. The sonotrode 4 is adapted to emit ultrasound from its welding face 41. Advantageously, the sonotrode 4 takes the form of a roulette.

[0052] The sonotrode and anvil assembly allows the vibrations emitted by the sonotrode to be concentrated at the level of the material in contact with the sonotrode, in order to locally heat the material. In this respect, the anvil not only serves as a support for the sheet(s) to be welded, but also to absorb the vibrations emitted by the sonotrode in order to ensure their concentration at the welding interface and to limit the transmission of these vibrations to the rest of the system.

[0053] According to a preferred embodiment, the anvil 3 and the sonotrode 4 each take the form of a roller, which allows the sheet(s) to be moved for continuous ultrasonic welding. This provides high productivity, making the assembly process particularly interesting on an industrial scale.

[0054] According to a particular embodiment, the bearing face 31 of the anvil 3 and / or the welding face 41 of the sonotrode 4 have hollow areas and protruding areas distributed according to a predetermined pattern. The bearing face 31 and / or the welding face 41 are therefore not smooth. The pattern of the rollers is defined to optimize the movement of the molten material between the anvil and the sonotrode in order to homogenize the weld. This pattern can also make it possible to ensure the positioning of a sheet of biaxially oriented polyethylene terephthalate, i.e. a section 10, during welding since the sheet is less likely to slip and move. In addition, it allows mechanical anchoring between two strips of biaxially oriented polyethylene terephthalate simultaneously with welding so as to ensure the connection between the two strips.

[0055] According to a preferred embodiment, the bearing face 31 of the anvil 3 and / or the welding face 41 of the sonotrode 4 are smooth. Advantageously, the bearing face 31 of the anvil 3 and the welding face 41 of the sonotrode 4 are smooth. This has the advantage of limiting the mechanical deformations of the biaxially oriented polyethylene terephthalate sheets during welding. These deformations are not desired because they can weaken the sheet and the inflatable structure 1 obtained will be more fragile.

[0056] Processes

[0057] To manufacture an inflatable structure 1, a step i) of assembling sections 10 is implemented. To implement step i), a method of assembling strips 12, 14 of sections 10 will be implemented.

[0058] The sections 10 are initially flat and each take the form of a sheet of biaxially oriented polyethylene terephthalate. Figure 4 illustrates a first section 10a and a second section 10b flat. With reference to Figures 3 to 5, in a step a), a stack of a strip 12 of the first section 10a, hereinafter called first strip 12, and a strip 14 of the second section 10b, hereinafter called second strip 14, is arranged on the bearing face 31 of the anvil 3.

[0059] The first strip 12 and the second strip 14 are in this step a) parts of sections 10, i.e. of different biaxially oriented polyethylene terephthalate sheets. The sections 10a, 10b are stacked only at a part of each.

[0060] Advantageously, in a step a1), a filler material 8 is arranged between the first strip 12 and the second strip 14. The filler material 8 allows the implementation of a weld of the strips 12, 14 together which is more solid.

[0061] Preferably, the filler material 8 is preferably linear polyester, preferably polyethylene terephthalate (PET) and even more preferably biaxially oriented polyethylene terephthalate. Thus, the connection between two strips 12, 14 is continuous, the inflatable structure 1 is made of a single type of material and is thus more resistant.

[0062] Then, in a step b), as illustrated in figure 6, the sonotrode 4 is applied to compress the stack between the welding face 41 of the sonotrode 4 and the bearing face 31 of the anvil 31.

[0063] Furthermore, the ultrasonic generator 5 is activated so as to generate ultrasound which is thus emitted by the sonotrode 4 from the bearing face 41. Advantageously, the ultrasound is emitted at a frequency of between 25 kHz and 40 kHz. In a step c), the first strip 12 and the second strip 14 are welded by emitting ultrasound through the stack.

[0064] In the case where the bearing face 31 of the anvil 3 and / or the welding face 41 of the sonotrode 4 have hollow zones and protruding zones, the material of the stack, i.e. the first strip 12 and the second strip 14, are deformed simultaneously with the welding so as to create a mechanical anchoring of the first strip 12 in the second strip 14. In other words, in addition to being subjected to ultrasound, the first strip 12 in the second strip 14 are subjected to mechanical deformation. This makes it possible in particular to ensure the connection between the first strip 12 and the second strip 14 which are connected by welding and by mechanical deformation.

[0065] In the case where the bearing face 31 of the anvil 3 and the welding face 41 of the sonotrode 4 are smooth, the welding is carried out substantially without mechanical deformation of the first strip 12 and the second strip 14. Thus, the material of the first strip 12 and the second strip 14 is not weakened, which makes it possible to obtain a more resistant inflatable structure 1, less likely to disintegrate in space.

[0066] In the case where a filler material 8 is arranged between the strips 12, 14, the strips 12, 14 are less mechanically deformed, which makes it possible to obtain a more solid and resistant weld. Indeed, in this case, there is only a small deformation at the interface between the internal face of each strip 12, 14 and the filler material 8. In addition, the filler material 8 melts at least partially, making the weld more resistant.

[0067] Advantageously, the weld is formed by performing a relative movement between the sonotrode 4 and the stack. In other words, one and / or the other of the sonotrode 4 and the anvil 3, when they are in the form of rollers, are driven in rotation so as to cause the stack to move. Thus, the weld is performed along the entire length of the first strip 12 and the second strip 14.

[0068] The weld of the first strip 12 and the second strip 14 may be a peel weld (i.e., a weld which is stressed in tension, in a direction perpendicular to the interface between the strips formed by the weld) or a shear weld (i.e., a weld which is stressed in shear, in a direction coplanar to the interface between the strips formed by the weld).

[0069] Figure 6 illustrates a system 6 and a stack of strips of sections 10a and 10b lying flat during a shear welding step. The strips 12, 14 of sections 10a and 10b of Figure 4 are shear welded. Shear welding in practice allows a stronger weld.

[0070] Figure 7 illustrates strips 12, 14 welded in peel. In certain cases which will be explained later, this type of welding is easier to implement.

[0071] At the end of step i), sections 10 are assembled together. Advantageously, at least three sections 10 are assembled, it being understood that the number of sections can vary, this number being chosen to ensure a satisfactory compromise between the mechanical strength and the sealing of the assembly. Advantageously, all the sections 10 of the inflatable structure 1 are connected to each other, each section 10 being flat. The assembled sections 10 form an assembly 7 illustrated in figures 4 and 7. The assembly 7 of figures 4 and 7 comprises two sections 10a, 10b.

[0072] Then, in a step ii), the set 7 of sections 10 is wound so as to cover a first edge 71 of the set 7 with a second edge 72 of the set 7 so as to form a tube as illustrated in figures 2 and 8. In figure 2, the set 7 is wound so as to allow the implementation of a shear weld between the edges 71 and 72. In figure 8, the set 7 is wound so as to allow the implementation of a peel weld between the edges 71 and 72. Finally, in a step iii), the edges 71 and 72 are assembled by ultrasonic welding in the same way as the strips 12 and 14 in step i).

[0073] In other words, steps a) to c) of assembling strips are again implemented for the edges 71, 72, that is to say that the strips 12, 14 correspond to the edges 71, 72. In still other words, step iii) consists of implementing steps a) to c) previously described by substituting the terms “first strip 12” and “second strip 14” by, respectively, “first edge 71” and “second edge 72”. In this case, the edges 71, 72 forming the strips are part of the same sheet of biaxially oriented polyethylene terephthalate, said sheet being the assembly 7.

[0074] More precisely, in a step a), a stack of the first edge 71 and the second edge 72 is arranged on the bearing face 31 of the anvil 3.

[0075] Advantageously, in a step a1), a filler material 8 is arranged between the first edge 71 and the second edge 72.

[0076] Then, in a step b), as illustrated in figure 9, the sonotrode 4 is applied to compress the stack between the welding face 41 of the sonotrode 4 and the bearing face 31 of the anvil 31.

[0077] Furthermore, the ultrasonic generator 5 is activated so as to generate ultrasound which is thus emitted by the sonotrode 4 from the bearing face 41. In a step c), the first edge 71 and the second edge 72 are welded by emitting ultrasound through the stack.

[0078] At the end of step iii), the inflatable structure 1, or at least a part of the inflatable structure 1, is formed.

[0079] Figure 9 illustrates the peel welding step of the edges 71 and 72. Peel welding is in this case easier to implement than shear welding.

[0080] In the case of a shear weld of the edges 71 and 72, it will be necessary to insert the anvil 3 or preferably the sonotrode 4 into the tube formed by the assembly 7, for example using a robotic arm to carry out the welding. The feasibility of this type of welding depends on the diameter of the tube formed by the assembly 7.

Claims

CLAIMS 1. Method for manufacturing an inflatable structure (1) of a deployable kit (100) for capturing space debris comprising the steps of: i) assembling a first strip (12) of biaxially oriented polyethylene terephthalate and a second strip (14) of biaxially oriented polyethylene terephthalate so as to form an assembly (7) of biaxially oriented polyethylene terephthalate by implementing the following steps: - arrangement of a stack of the first strip (12) and the second strip (14) on a bearing face (31) of an anvil (3), - application of a sonotrode (4) to compress said stack between a welding face (41) of the sonotrode (4) and the support face (31) of the anvil (3), - welding the first and second strips (12, 14) by emission of ultrasound through the stack by the sonotrode (14), ii) winding the assembly (7) carried out in step i) so as to cover a first edge (71) of the assembly (7) with a second edge (72) of the assembly (7) so as to form a tube, iii) assembly of the first edge (71) and the second edge (72) by implementing the following steps: - arrangement of a stack of the first edge (71) and the second edge (72) on the bearing face (31) of the anvil (3), - application of the sonotrode (4) to compress said stack between the welding face (41) of the sonotrode (4) and the support face (31) of the anvil (3), - welding of the first and second edges (71, 72) by emission of ultrasound through the stack by the sonotrode (14).

2. Method according to claim 1, in which the weld made in step i) is a shear weld and the weld made in step iii) is a peel or shear weld.

3. Method according to any one of claims 1 and 2, in which the welding steps are carried out by carrying out a relative movement between the sonotrode (4) and the stack.

4. Method according to any one of claims 1 to 3, in which, during the welding step in step i), the first strip (12) and the second strip (14) are deformed simultaneously with the welding so as to create a mechanical anchoring of the first strip (12) in the second strip (14) and / or, during the welding step in step iii ... the first edge (71) and the second edge (72) simultaneously with welding so as to create a mechanical anchoring of the first edge (71) in the second edge (72).

5. Method according to any one of claims 1 to A, wherein the welding in step i) is carried out substantially without mechanical deformation of the first strip (12) and the second strip (14) and / or the welding in step iii) is carried out substantially without mechanical deformation of the first edge (71) and the second edge (72).

6. Method according to claim 5, comprising a step prior to the welding step of step i) of arranging a filler material (8) between the first strip (12) and the second strip (14), said filler material (8) melting at least partially during welding and / or comprising a step prior to the welding step of step iii) of arranging a filler material (8) between the first edge (71) and the second edge (72), said filler material (8) melting at least partially during welding.

7. Method according to claim 6, in which the filler material (8) is linear polyester, preferably polyethylene terephthalate and even more preferably biaxially oriented polyethylene terephthalate.

8. Method according to any one of claims 1 to 7, in which the ultrasound is emitted at a frequency between 25 kHz and 40 kHz.

9. Inflatable structure (1) of a deployable kit (100) for capturing space debris comprising a first strip (12) of biaxially oriented polyethylene terephthalate and a second strip (14) of biaxially oriented polyethylene terephthalate assembled by welding, characterized in that the inflatable structure (1) is capable of being inflated up to 2 x 10 6 Pa (20 bars).

10. Inflatable structure (1) according to claim 9, characterized in that said welding is carried out by emission of ultrasound through a stack of said strips (12, 14).

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