DESCRIPTION "MULTIAXIAL WEAVING MACHINE'

Field of the invention

The present invention relates to a weaving machine for producing a multiaxial woven fabric which is obtained by interlacing 4 sets of yarns, the warps, the wefts and other two sets of bias yarns at +45 and -45 degrees.

The use and impact of the multiaxial fabric may be found several different types of products, including:

Technical textiles, such as composites for car and aircraft industry, conveyor belts, inflatable boats, sails, boat hulls, air inflated houses, geotextiles, wall coverings, sport devices, tarpaulins, tents, grinding and lapping disks and many other applications on products that still use traditional technology of gluing together several layers of fabrics, differently oriented. Garments designed to be resistant to tear, with an original texture, easily conformable and dimensionally stable could have a big impact on very different articles such as military and protective clothing.

State of the Art

Multiaxial textile structures are particularly appropriate for technical applications. There is a great difference between those and the conventional woven or knitted fabrics as they are manufactured by the insertion of yarns in, at least, four directions. These reinforcement yarns in the bias directions allow a more precise control of the fabric' s

mechanical properties. This feature is very important and is responsible for the following advantages comparing with the biaxial fabrics:

The anisotropic level of the fabric mechanical properties can be designed and controlled during its manufacture;

- The bias yarns increase the fabric elongation stability when submitted to the shear stresses.

- The present invention represents a low-cost multiaxial weaving machine capable of producing a multiaxial fabric of stable construction with different fill coefficient.

The literature refers to a so-called tetra-axial fabric made of warp, weft and bias yarns, which interlace each other. Such fabric structure is said to have nearly the same resistance to stretching in all directions, i.e., exhibits an isotropic behaviour. By virtue of this property, it finds advantageous applications in the manufacturing of tarpaulins, conveyor belts, inflatable boat, sails, etc.

The first tetraxial fabrics developed in the art consisted of bias yarns crossing in the fabric areas included between the warp and the weft yarns. This fabric geometry does not provide a close bond between yarn layers.

Other efforts to produce a multiaxial fabric have been made, which are reported in patents, namely:

Tetraxial fabrics are known also from the U. S. patent 5,351,722, where a tetraxial fabric is described which contains warp yarns, weft yarns as well as first and second bias yarns crisscrossing each other and both the warp and weft yarns. A first set of warp yarns is overlaid by the weft yarns and, in turn, overlies the bias yarns. A second set of

warp yarns, which alternate with the warp yarns in the first set, overlies the weft yarns and is, in turn, overlaid by the bias yarns. In such tetraxial fabrics a first course of warp yarns is overlaid by the weft yarns and overlies the first and second bias yarns, while a second course of warp yarns, which alternates to the mentioned first yarn course, overlies the weft yarns and is overlaid by the first and second bias yarns.

The European Patent Application 0263392 A2, "Tetraxial woven fabrics and tetraxial weaving machine thereof" describes a machine that manufactures a tetraxial fabric exhibiting an isotropic behaviour which is higher than that of the triaxial fabrics and is composed by weft, warp and bias yarns. This invention uses a set of needle-like components for guiding the bias yarns, circulating them by means of a mechanism whose working principle is not clear and is thought not to be feasible.

The machine currently proposed allows the weaving of a large number of yarns, where the limit is set by the thickness of each needle. In addition, it has a single beater which intervenes twice for each weft drawing-in, thus allowing a clear shed formation after the first said false beating. Other characteristics of the machine of the invention are the presence of a single moving warp, thus a single heddle, in cooperation with two very close stationary bias layers. The single beater simplifies further said synchronisms; in addition the bias yarn pulling system has a simple step-by- step motion.

In the present invention, the bias yarns are stepwise moved directly, without any intermediate parts. In order to achieve

their perfect circulation, a main shaft cam driven latching Transfer Device, which is very effective in the transference of bias yarns from one layer to the other, is used. The present invention also uses two helical grooved cylinders (HCG) with a specific geometry and a deep groove in order to prevent missing bias yarns. In addition, a special stationary but adjustable component called bias yarns squeezing plates are introduced as means of closing the gap between the bias yarns layers to an adjustable optimum minimum.

The present invention requires only one heddle (even though two or more could be used) and only one reed, which through an actuation characterized by two beating operations per cycle (one of them being a false beating, necessary to open the shed and ^" clear the path for the weft insertion) , represents a simple solution to produce multiaxial fabrics. The simplicity and flexibility of this process is such that allows using thinner or thicker yarns to produce multiaxial fabrics with excellent performance characteristics.

Summary of the invention

The present invention concerns a mechanical system for the production of a multiaxial woven fabric. The Multiweave system comprises: warping, bias yarns feeding and criss-cross insertion, shedding, incorporating the heddle, weft feeding and insertion, beating-up mechanism, incorporating the reed, fabric taking-up and winding, producing a multiaxial fabric.

Multweave fabric structures are particularly appropriate for technical applications, since they are manufactured by the insertion of yarns in four directions, which allows a more

precise distribution and control of the fabric's mechanical properties.

The Multiweave system allows the production of a fabric structure where there is criss-crossing between all sets of yarns, which increases the capability for supporting more severe mechanical conditions without failure, namely without delaminating. Simultaneously, the strength-weight ratio is increased, which, for applications such as in the aircraft industry, can be very advantageous. Other important applications are in marine textiles, such as composites for boat and shipbuilding, which are products submitted to severe stressing conditions.

The working principle of the Multiweave is as follows: The bias yarns are feed from two bias beams through a tension compensation device and stepwise moved in two very close and parallel layers in opposite directions by means of an appropriate mechanism. The heddle and the reed are in their lower and retracted positions, out of the plane of the bias yarns, allowing their free criss-crossing. The heddle rises forming the shed and the warps interlace with the bias. The shed is formed between the warp and the two very close parallel layers of the bias yarns. A first (false) beating takes place to clear the shed; The weft yarn is then inserted across the shed to be interlaced with the warps and bias yarns.; A second (real) beating operation takes place which pushes the weft forward and compacts the fabric, at the same time that the heddle moves down to its rest position closing the shed and holding the weft. The taking-up mechanism advances one step and the fabric is wound-up.

Brief description of the drawings

The description that follows makes reference to the attached drawings. In the drawings:

Figure 1 shows a schematic view of the multiaxial fabric; Figure 2 shows a side view of the mechanical system for the production of the multiaxial fabric- Figure 3 shows the bias yarns feeding system;

Figure 4 shows the core of the system (3D detail of figure 2), outstanding the mechanism for the criss-cross insertion of the bias yarns, the shedding system, incorporating the heddle, the beating system, incorporating the reed and the weft insertion system;

Figure 5 shows a 3 D detail of figure 2 but from the rear side, outstanding the mechanism for the criss-cross insertion of the bias yarns, the Stationary Bar and the Transfer Device.

1. warp yarns

2. bias yarn

3. bias yarn

4. weft yarn

5. bearing structure

6. bias beam

7. bias beam

8. circular yarns guiding ring

9. central shaft (to sustain the disc)

10. lower helical grooved cylinder

11. upper helical grooved cylinder

12. stationary bar

13. bias yarns squeezing plate

14. bias yarns squeezing plate

15. swinging bar

16. catching blade

17. heddle

18. main shaft

19. vertical slide

20. vertical slide

21. warp beam

22. the reed

23. heddle shaft

24. temple

25. temple

26. fabric take-up roller

27. fabric take-up roller

28. roller

29. fabric beam

30. bias beam brake

Detailed description

Figure 1 - Schematic view of the multiaxial fabric

This scheme shows the Multiweave structure and how all the yarns, warps, wefts and bias interlace to form the fabric.

Figure 2 - Side view of the Multiweave mechanical system The Multiweave Machine comprises the following elements for guiding the warp yarns, weft yarns and the bias yarns toward a fabric formation area:

- Bias yarns feeding system;

- Mechanism for the criss-cross insertion of the bias yarns ;

- Warping system;

- Shedding system, incorporating the heddle;

- Weft insertion system;

- Beating-up mechanism, incorporating the reed;

- Fabric taking-up system.

Figure 3 - The bias yarns feeding system

This system comprises a bearing structure (5) where the bias beams are mounted (6, 7), similar to that used for feeding the warp yarns .

The bias yarns (2, 3) coming from the bias beams are guided through a circular oriented yarn guiding disc (8) supported by a central rotating shaft (9) in order to reduce the angles between the bias yarns and a plane normal to the axis of the helical grooved cylinders (11) . The discs are provided with radially distributed eyelets to separate and guide bias yarns.

The fact that the bias yarns trajectory varies length with position in a cycle and that the unwinding speed is the same for all them, caused a variation in the bias yarns tension and a considerable amount of free movement. Increasing tension is not suitable as it can cause yarn damage and prevents the correct opening of the shed. Therefore individual tensioners are provided.

Figure 4 shows a 3D detail of figure 2, the core of the system, outstanding the mechanism for the criss-cross insertion of the bias yarns (10), the shedding system, incorporating the heddle (17), and the beating system, incorporating the reed (22) .

Figure 5 shows a 3D detail of figure 2 but from the rear side, outstanding part of the mechanism for the criss-cross insertion of the bias yarns (11), the Stationary Bar (12) and the Transfer Device with swinging bar (15) and catching blade (16) .

The mechanism for the criss-cross insertion of the bias yarns

The mechanism for the criss-cross insertion of the bias yarns comprises two parallel cylindrical elements, here referred to as Helical Grooved Cylinders (10, 11). This solution is based on two screw-like elements for the circulation of the bias yarns, with a lateral stepwise movement during the weaving process .

The two layers of bias yarns are guided, each one by one helical grooved cylinder. These cylinders are provided with helical screw-like grooves, positioned on the central portion of the bias yarns feeding system and in the horizontal direction. They are provided with an helical pitch (pitch of the bias yarns) in the same direction, having a number of helices equal to at least half of the number of bias yarns and are rotated simultaneously, at the same speed and in opposite directions by means of a spur gear mechanism with equal number of teeth.

The bias yarns are therefore moved sideways by the translation effect of the rotational movement of these helical grooved cylinders. That means one rotation of the helical grooved cylinder in one step of the bias yarns. When each of the bias yarns arrives to its last position, it has to be transferred to the other grooved cylinder to start moving in the opposite direction in the other layer.

A Transfer Device is therefore needed in order to transfer the bias yarns. It comprises a swinging bar 15 which is cam operated by main shaft. When appropriate, it goes down on one side (up on the other) and a catching blade (16) catches the bias yarn that has felt off the stationary bar (12) in the

previous cycle. It then swings up (down on the other side) and lifts or lowers the cached yarn. Next the HGC rotate one turn, moving the cached yarns one step by the bias pitch. One more bias yarn falls off the Stationary Bar in each side.

A Stationary Bar (12) is appropriately placed in front of the grooved cylinders (10, 11) and between the two layers of the bias yarns (2, 3) . The role of this bar is to force the bias yarns to stay well in their grooves until the last position is reached and to create a separation between the 2 bias yarns layers.

Summarizing, the bias yarns are guided from the bias yarn feeding system (A), through the discs (8), to the helical grooved cylinders (10, 11) , from above and below the stationary bar (12). The stationary bar has a rectangular shape, allowing bringing it closer to the HGC. It was also designed with ends that can be easily adjusted to provide a fine adjustment in its length which is crucial for tuning its precise insertion in the appropriate groove. The purpose of this bar is also to separate the bias yarns in two distinct layers, upper and lower and force the yarns to stay in good contact and well guided in the grooves of the HGC.

The shedding system

A harness with eyelets performs the shedding motion in a conventional weaving loom, but a multiaxial weaving pattern needs an open heddle to control the shedding. This is due to the fact that, when the bias yarns have their stepwise lateral movement, no heddle or reed can be in the away as in conventional weaving. The heddle is cam operated by the main shaft (18) and appropriately timed with the other mechanisms.

It runs on two vertical slides (19, 20) on each side of the machine .

The beating-up mechanism, incorporating -the reed

The beating-up mechanism is a very important part of a weaving machine. A stable and uniform fabric (multiaxial or biaxial) requires a simple and efficient beating-up system. However, the presence of the bias yarns adds an element of complexity. In fact, unlike a conventional machine, the reed (22) will have to be of an open shape, as it will have to come off the fabric formation area during the bias yarns lateral stepwise movement. The reed needles will be inserted in the spaces between the warp and bias yarns, as much as possible near the heddle (17) . The reed (22) has a simple rotating movement from below the plane of the warp and bias yarns to the fabric fall area, in order to beat the weft yarn and compact the fabric. The reed is also driven by a cam mechanism from the machine main shaft (18).

The weft: insertion system

The weft insertion is performed by means of a rapier mechanism. The rapier moves with a linear motion between a retracted and an extended position and is operated by a cam on the main shaft (18), driving a gear sector and finally a rack and pinion mechanism. The weft needle (4) is positioned on the rack.

The fabric taking-up system

The fabric taking-up system is made up by the taking-up rollers (24, 25, 26, 27 and 28) and the fabric beam (29) . A worm gear drive synchronised with the bias beams winds-up the

fabric at the rate of fabric production. It is provided with a pair of spur gears which can be changed, should it be necessary to modify the taking-up pitch. The fabric winding beam is driven by a chain drive and is fitted with an adjustable slip clutch to adjust fabric tension.

The weaving cycle

The working principle of the multiaxial weaving machine is as follows :

Bias yarns (2, 3) are feed and moved in two layers in opposite directions. Heddle (17) and reed (22) are in their lower and retracted positions, out of the plane of the bias yarns, allowing their free criss-crossing.

Heddle (17) rises forming the shed and warps (1) interlace with bias. Shed is formed between warp and bias yarns in two very close layers.

First (false) beating takes place to clear the shed; this was found necessary as when warp yarns were moved up by the heddle, they were partially held up by the criss-crossing effect of the bias, preventing from obtaining a clear shed which caused difficulties for the insertion of the weft yarn; Weft yarn (4) is inserted across the shed to be interlaced with the warps and bias yarns;

Second beating operation takes place which pushes the weft forward and compact the fabric, at the same time that the heddle moves down to its rest position closing the shed and holding the weft.