The invention relates to a method for making a net structure as disclosed in the preamble of independent claim 1, and a net structure as disclosed in the preamble of independent claim 5.

The net structure is especially designed for use as a safety net to prevent falling, flying or swinging objects from inadvertently striking against and damaging a structural member, installation or plant. In addition, small mesh size is often desirable so as to enable the net to stop smaller objects such as hand tools from injuring personnel. Such nets, when installed or mounted, are used instead of protecting walls or a covering structure of solid materials, for example, steel walls or the like, on offshore platforms or other installations. This is, for example, because they give far greater accessibility to the structural member or the plant/installation they are to protect than a conventional protective wall, roof or floor as they can easily be removed, redeployed and installed.

Extreme requirements are placed on the strength of such nets, and consequently in their manufacture rope is used that has the necessary breaking strength and an acceptable expansion coefficient before breaking. Conventionally, the net is provided in that the ropes are knotted together so as to form meshes in a manner which may, for instance, be compared with standard fishing nets or trawl nets. During use, the net is installed as a wall, roof or floor. It is often a requirement that the safety net has minimal deflection when the net is hit by an object in order to prevent damage to the object the safety net is to protect.

As mentioned, conventional nets use knots to provide the net meshes. These knots have greatest strength when the net meshes are in the form of an upright equilateral parallelogram and the strain runs in the direction of the longest extent of the parallelogram. However, the net meshes will easily stretch a great deal in this direction when subjected to an impact load, with substantial and often unacceptable deflection of the net.

It is possible to install the net so that the meshes stand in squares, but then the direction of force is such that the strength of the knots is further substantially reduced, hi addition, the strands of which the net is constructed will not be continuous in the direction of force, i.e., vertically or horizontally, but will run in a stepped pattern where each mesh represents a step, and when subjected to a large load, the net will draw together and will not retain its net structure. This applies in particular in the case of rope made of modern synthetic fibre where strength in relation to weight may be 15 times greater than steel and where conventional net knots do not hold.

The knots also cause the deflection resistance of the net to be adversely affected as they will constitute extension centres for the ropes that are knotted together, with the result that the net wall has greater give than it would have had without the knots. Moreover, the knots will represent a substantial weakening of the breaking strength of the wall structure, and they will result in an unfavourable dimensional increase when the net is folded. Since the nets referred to here are nets of relatively large dimensions, the increase in weight because of the knots will also be noticeable. Moreover, the rope materials used are very expensive and the increase in rope quantity alone due to the knots represents a not insignificant increase in costs.

As a specific example of the closest prior art, reference may be made to US-Al 4 000 344 which describes a net made of standard plaited cord as the basic material and the meshes are made by a threading technique. However, compared with the invention, there is a major difference, namely that the cord passes through and is passed through each mesh corner so that the continuous cord runs in a zig-zag pattern (horizontally or vertically) if the net is stretched out in the pattern of a square. This in turn results in much more slack in the net when it is installed regardless of whether it is installed in diamond-shaped meshes where the side walls themselves, because of the geometric form of the meshes, will give slack, or in a square shape where there will be no continuous strands which prevent stretch, hi column 1, lines 24 to 35 of the document a solution is described in which an intersection is formed between two portions of the length of the netting strand by passing one such length portion through a hole formed in the other of the portions, but it is stated that this solution has the drawback, in certain areas of usage, that the intersection could slip unless special precautions are taken to prevent this slipping. However, a solution as proposed by the present invention is neither taught nor suggested.

As related prior art, reference may also be made to GB-A 303 111 and A 489 200 as well as US-Al 2 402 709, 3 252 676, 5 869 162, 6 408 732, 6 559 077, 3 129 632 and 6 076 448, but the art described in these documents is further from the invention that the previously mentioned US patent and does not solve the problems which on which the invention is based. Thus, there is an obvious potential for improvement of the known methods for making nets of this type, and nets made by the method.

The invention addresses the drawbacks mentioned above and the object thereof is to provide a method for making a net structure and a net structure made by the method, wherein the strength of the net structure is optimised in relation to weight and volume.

This is achieved according to the invention with a method and net structure of the type mentioned in the introduction, which are characterised by that disclosed in the characterising clause of respective patent claims 1 and 5.

Advantageous embodiments of the invention are set forth in the dependent patent claims.

The invention will now be described with reference to the drawings, wherein:

Fig. 1 is a schematic view of a section of a basic embodiment of the net structure according to the invention; and

Fig. 2 is a view of a section of a specific embodiment of the invention.

In Fig. 1 the reference numeral 1 indicates a net structure according to the invention with essentially square net meshes. The reference numerals 2 and 3 indicate cord or rope that is used in the net structure, for the sake of simplicity or clarity designated so-called first rope 2 and second rope 3, whilst the reference numeral 4 indicates a threading-through or feeding-through. The threading-through or feeding-through 4 is shown as a black rectangle. The long side of the rectangle indicates the rope that is threaded through and consequently indicates the shortest portion in the feeding-through direction.

When the net structure 1 is to be made, two essentially parallel first rope groups and two essentially parallel second rope groups are provided, which rope groups are arranged essentially perpendicular to each other, and consist of respective first ropes 2 and second ropes 3. The rope groups are provided as a net structure as can be seen from Fig. 1, with ropes that are vertical and horizontal in the plane of the drawing. The threading-through 4 is provided in that the rope 2, 3 that is to be penetrated is compressed in its longitudinal direction or acted upon in another suitable manner so that a bulge or the like is formed, the strands that form the rope being forced slightly apart, at which point insertion and threading-through can be carried out. This may, for example, be done with a conventional splicing tool that is used to pass the one rope through a second perpendicular rope.

Seen from the left in Fig. 1, the following operations are carried out:

A first vertical first rope 2 is threaded through 4 a first horizontal second rope 3, a second vertical first rope 2 has threaded therethrough 4 the first second rope 3, a third vertical first rope 2 is threaded through 4 the first horizontal second rope 3, a fourth vertical first rope 2 has threaded therethrough 4 the first horizontal second rope 3 etc., and the second horizontal second rope 3 has threaded therethrough 4 the first vertical first rope 2, the second horizontal second rope 3 has threaded therethrough 4 the second vertical first rope 2, the second horizontal second rope 3 has threaded therethrough 4 the third vertical first rope 2, the second horizontal second rope 3 has threaded therethrough 4 the fourth vertical first rope 2 etc. until the whole net has been provided.

The process may of course be carried out in the reverse order, i.e., starting with the respective horizontal second ropes 3 which are threaded through 4, or have threaded therethrough 4, the vertical first ropes 2. The process may also be carried out as a combination of different threading and threading-through sequences.

Summarised briefly, the method according to the invention thus consists in that the ropes 2, 3 that are to form a net structure 1 consisting of net meshes are joined in such manner that the respective corners of each net mesh are provided in that each net mesh is formed by respective perpendicular ropes 2 and 3, of which the one rope 2 or 3 is threaded through the second rope 3 or 2, and the second rope has threaded therethrough the first rope, the sequence between threading-through of rope and threaded-through rope being provided so as to be alternating such that a rope is first threaded through a perpendicular rope, and at a suitable distance from the threading-through, depending on the mesh size, has threaded therethrough a second perpendicular rope that is parallel to the first rope, thereby providing in each mesh corner a fastening together of the ropes when parallel ropes are brought together so that a threaded-through rope rests against a perpendicular, threaded-through rope.

In this way, a net structure is provided in which the respective corners of each net mesh consist of respective perpendicular ropes 2 and 3, of which the one rope 2 or 3 has threaded therethrough the second rope 3 or 2, and the second rope has threaded therethrough the first rope, the sequence between threading-through of rope and threaded-through rope being provided so as to be alternating such that a rope is first threaded through a perpendicular rope, and at a suitable distance from the threading- through, depending on the mesh size, has threaded therethrough a second perpendicular rope which is parallel to the first rope, thereby providing in each mesh corner a fastening together of the ropes when parallel ropes are brought together so that a threaded-through rope rests against a perpendicular, threaded-through rope.

Often, a loop at the end of a piece of cord or rope for direct connection to support structures would be useful in order to ensure minimal stretch in the net. This is done by splicing in a loop at the end of the cords in order to then use the described net-making method, the only difference being that the cords at the location of the splice are thicker than the rest of the cord.

Fig. 2 shows an example of a preferred net structure. In this case, each net mesh is made of two parallel pairs of first rope 2 and two parallel pairs of second rope 3, which are provided perpendicular to one another. The respective two pairs of first rope 2 are provided almost adjacent to each other. The threading and threading-through 4 are provided in the same way as in the net structure in Fig. 1, but since each of the parallel pairs is provided so close to each other, an immediate interlocking of the ropes 2 and 3 will be obtained in the mesh corners and the maximum opening or size of the mesh will be smaller and thus able to stop a small object more effectively. It can be seen clearly from Fig. 2 that because of the directions of threading-through, the ropes in all respective mesh corners will be fastened together. This solution provides a further strengthened net structure in the direction of the adjacent parallel pairs of rope, which will be particularly favourable when the forces caused by the object to be stopped are to be absorbed in one direction, for example, if the net wall is only secured at the top and the bottom.

The net structure according to the invention does not only result in a stronger net with less deflection when subjected to loads than conventional, knotted nets, but the net is also far less voluminous when it is folded up and the weight saving is considerable since there are no knots.

Instead of two parallel pairs of rope or cord, it is also conceivable that the horizontal ropes in Fig. 2 can be replaced by two adjacent horizontal pairs of rope (not shown). Instead of parallel pairs consisting of two ropes, it is also possible that a plurality of ropes may be included in each pair, but because of the costs a solution of this kind will probably only be of interest in certain circumstances.

The rope used consists preferably of a plaited strand structure, but also other suitable structures that will laterally secure a threaded-through rope could of course be used. The rope material is preferably selected from the group comprising "High-Tech" synthetic fibres or the like, such as Aramide, Kevlar, Dyneema, Spectron or similar materials. The diameter of the rope or the cord used is selected according to the load the net has to withstand, the maximum acceptable mesh width and the direction in which the forces are essentially to be absorbed. Of course, a different diameter may be used for the cords in the vertical or horizontal direction so that, e.g., in the horizontal direction the cords have a diameter of 5 mm and in the vertical direction 12 mm. The last would be favourable in cases where, for example, the net is only secured at the top and the bottom.