Patent Publication Number: US-9410272-B2

Title: Fabrics simultaneously woven from two distance fabrics

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of Ser. No. 13/319,352 filed Nov. 8, 2011 based on PCT/EP2010/056386 filed May 10, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method for simultaneously weaving two distance fabrics. A distance fabric is a fabric comprising two layers of woven yarns separated by an empty space. In some particular cases, this space can be filled in with different materials, such as a particulate material. Such a distance fabric is sometimes qualified as “three-dimensional structure” and is particularly adapted to be used as artificial turf for sport grounds. 
     2. Brief Description of the Related Art 
     A woven artificial turf is known from WO-A-2007/116290 and includes pile yarns which extend, on two respective heights, from a base layer. This artificial turf can be woven on a face-to-face carpet loom. During weaving, some loops are provided to help the piles to stay upright. These loops provide poor elasticity of the turf. 
     On the other hand, BE-A-1007679 discloses a method for weaving two fabrics having each an inner layer which faces the other fabric during weaving and an outer layer. Connecting warp yarns extend between the inner and outer layers and bind them together. The pattern of those connecting yarns is quite simple since the associated shedding system provides only two positions. Pile warp yarns are interlaced in both inner layers. The required shedding system can provide three positions with respect to both inner weft insertion zones. Since they are interlaced in the inner layers, pile yarns are not held strongly enough for flooring applications. Connecting layer yarn consumption and yarn density are high, in particular on the inner layer of each fabric. This makes it difficult to introduce between the layers of each fabric a particulate material such as sand or rubber granulates. Therefore, such a fabric would not be appropriate to be used as an artificial turf. 
     SUMMARY OF THE INVENTION 
     The invention aims at solving these problems with a new method which makes it possible to simultaneously weave two distance fabrics with high productivity. Their structure can be sophisticated but still easy to produce. Such fabrics can be used as artificial turf or for other purposes. 
     This invention concerns a method for simultaneously weaving two fabrics provided with piles, said method comprising at least the steps of:
         weaving an inner layer and an outer layer for each distance fabric;   binding the inner and outer layers with connecting warp yarns extending between the inner and outer layers;   weaving pile warp yarns between the distance fabrics; and   cutting the pile yarns;       

     wherein
         during weaving, the inner and outer layers of each distance fabric are kept apart by respective lancet means; and   for each pick and for each connecting warp yarn and each pile warp yarn, one selects, on the basis of the information relating to the layer in which said warp yarn has been interlaced in the previous pick, on the basis of the shedding pattern and amongst several predetermined positions, a position to be taken by a shedding element driving said warp yarn during said pick.       

     Thanks to the invention, “three dimensional structures” are no more limited to simple structures since it is possible to manage the shedding elements to take into account on one side geometrical information such as distance from beating points and insertion zones and on the other side patterning information. In particular, two distance fabrics can be manufactured with a high productivity and the connecting warp yarns can efficiently bind the inner and outer layers of each fabric, while they do not lower the elasticity of the fabrics and do not hinder filling of the space between the two layers of each fabric with a particulate material. Moreover, the pile warp yarns can be securely anchored to some layers of the fabrics and participate to the global elasticity of the fabrics. 
     According to advantageous but non compulsory aspects, a method according to the invention can incorporate one or several of the following features:
         The position is selected amongst a number of possible positions equal to M×(N+1), where M is the number of layers where the warp yarn is to be interlaced according to the shedding pattern and N is the number of weft insertion means used to insert weft yarns into the M layers.   The connecting warp yarns are W inwoven successively in each layer of the distance fabric they belong to.   In each distance fabric, connecting warp yarns are divided into two groups of warp yarns which alternate, on the same pick, between the inner and outer layers of the distance fabric.   The pile warp yarns extend between the outer layers of the distance fabrics.   The pile warp yarns are W inwoven in the outer layer of each distance fabric.   Some pile yarns cross from one distance fabric to the other distance fabric over one pick.   The pile warp yarns are divided into two groups of warp yarns which alternate, on the same pick, between the outer layer of the first distance fabric and the outer layer of the second distance fabric.   Groups of connecting warp yarns and groups of pile warp yarns alternate on the same pick respectively between the inner and outer layers of each distance fabric and between the outer layers of the distance fabrics   Three weft yarns are inserted in each pick, in such a way that in a given pick, a weft yarn is inserted in the outer layer of each distance fabric and in the inner layer of a first distance fabric, and in the next pick, a weft yarn is inserted in the outer layer of each distance fabric and in the inner layer of the second distance fabric.       

     The invention also concerns a fabric which can be woven with the method mentioned here-above and, more particularly, a fabric comprising a woven front layer, a woven back layer, connecting yarns extending between the front and back layers and pile yarns protruding from the front layer wherein the pile warp yarns are at least interlaced into the back layer of the fabric and go through its front layer. 
     According to advantageous aspects of the invention, such a fabric can incorporate one or several of the following features:
         Pile yarns are W inwoven in the back layer and/or connecting yarns are W inwoven successively in each layer of the fabric.   The fabric is woven with synthetic yarns and forms an artificial turf.   The piles of the fabric have at least two different lengths.       

     According to another aspect, the invention also concerns a loom which can be used to perform the method mentioned here-above in order to produce the fabric mentioned here-above. Such a loom is for simultaneously weaving two fabrics provided with an inner layer, an outer layer, connecting warp yarns extending between the inner and outer layers and pile yarns extending between the fabrics. This loom comprises, or is connected to, shed forming means and weft insertion means. According to the invention, the loom further comprises two sets of lancet means adapted to keep the inner and outer layers of each fabric apart from each other during weaving and said loom further comprises computation means adapted to select, for each pick and for each connecting warp yarn and each pile warp yarn, on the basis of the information relating to the layer in which said warp yarn has been interlaced in the previous pick, on the basis of the shedding pattern and amongst several predetermined positions, a position to be taken by a shedding element driving said warp yarn during said pick, where said warp yarn does not interfere with said weft insertion means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on the basis of the following description which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures: 
         FIG. 1  is a schematic view of a loom according to the invention used to implement the method of the invention and to produce two fabrics of the invention; 
         FIG. 2  is a schematic view showing the repartition of the warp and weft yarns in the loom of  FIG. 1  during successive picks; 
         FIG. 3  represents the respective positions taken by some pile warp yarns during weaving; 
         FIG. 4  is a view similar to  FIG. 3  showing the respective position taken by the connecting warp yarns during weaving; 
         FIG. 5  is a view similar to  FIG. 3  showing the respective positions taken by the respective binding and filling warp yarns during weaving; 
         FIG. 6  represents a part of an artificial turf made of a fabric according to the invention; and 
         FIG. 7  is a schematic view similar to  FIG. 2  for a second embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A face-to-face three rapier sets loom  2  is represented on  FIG. 1  and used to produce a double carpet  4  particularly adapted to be used as artificial turf. Carpet  4  is made of an upper distance fabric  42  and a lower distance fabric  44  which are separated, after weaving, by a cutting device  6  which cuts piles extending between the two fabrics. Loom  2  also includes a reed  8  which can be moved between the position represented in full lines and the position represented in dashed lines on  FIG. 1 . Loom  2  also includes sixteen heddle frames  10  which are moved by electric servomotors  40 , such as the ones disclosed in EP-A-1 489 208. On  FIG. 1 , only four servomotors  40  are represented, for the sake of clarity. All servomotors are controlled by an electronic control unit  50  which includes computation means, in the form of a microchip  52 , and a memory  54  accessible by microchip  52 . 
     Three sets of rapiers, comprising respectively a bringer and a taker, are used in loom  2 , namely a top rapier set  12 , an intermediate rapier set  14  and a bottom rapier set  16 . 
     Frames  10  are driven by their respective servomotors in order to bring the warp yarns into respective positions where they participate to the shed and do not interfere with the rapier sets  12 - 14 - 16  during insertion. Each frame  10  forms thus a shedding element for loom  2 . 
     A double lancet  20  is introduced in each reed space and comprises a main rod  201 , an upper finger  202  and a lower finger  204 . Parts  201 ,  202  and  204  are integral with each other. Lancets  20  are distributed on the width of loom  2 . 
     As shown on  FIG. 2 , upper fabric  42  comprises a top ground part  422  and a set of piles  424  extending from ground part towards lower fabric  44 . Lower fabric  44  comprises a bottom ground part  442  and a set of piles  444  extending from ground part  442  towards upper fabric  42 . 
     The shape of the lancets  20  is such that the intermediate rapier set  14  can travel between the respective fingers  202  and  204  of each lancet, without interference. 
     Top ground part  422  comprises a back layer BL 2  and front layer FL 2 . Similarly, bottom ground part  442  comprises a back layer BL 4  and a front layer FL 4 . Back and front layers are separated by an empty space in each fabric. Back layers BL 2  and BL 4  are woven externally with respect to fingers  202  and  204 , whereas front layers FL 2  and FL 4  face each other in a center part of loom  2  defined between fingers  202  and  204  of the respective lancets  20 . Therefore, back layers BL 2  and BL 4  form outer layers, whereas front layers FL 2  and FL 4  form inner layers of upper and lower fabrics  42  and  44 . The pile set  424  and  444  extend between inner layers FL 2  and FL 4 . 
     In the present description, the terms “outer” and “inner”, “external” and “internal”, “externally” and “internally” are defined with respect to a central plane Tr of loom  2  which lies between fingers  202  and  204  and includes the cut line of cutting device  6 . An object is “internal” or “inner” with respect to another item when it is closer to plane Tr as this item. Conversely, an object is “external” or “outer” when it is further away from plane Tr with respect to another item. 
     Three insertion zones are provided in loom  2  for rapier sets  12 ,  14  and  16  and they are located symmetrically with respect to a plane Tr, the insertion zone for set  14  being centered on this plane. 
     In the example, fabrics  42  and  44  are used as artificial turf and all yarns constituting these fabrics are synthetic, e.g. made of polyethylene because of its low coefficient of friction. 
     Outer or back layer BL 2  comprises a filling warp yarn  101  and a binding warp yarn  102  which are woven with outer weft yarns  301  introduced within the shed, at every pick, by top rapier set  12 , regularly under and above yarn  101  and above and under yarn  102 . 
     Inner or front layer FL 2  comprises a filling warp yarn  103  and a binding warp yarn  104  woven with inner weft yarns  302  which are introduced within the shed by intermediate rapier set  14 , at every second pick. 
       FIG. 2  shows thirteen picks P1 to P13 of the method of the invention. The pick represented on the left of this figure is not referenced since it does not show all yarns. Inner weft yarns  302  are used to weave front layer FL 2  for even picks (picks P2, P4, . . . ) and they are regularly distributed above and under filling warp yarns  103 . 
     A connecting warp yarn  401  extends between inner and outer layers FL 2  and BL 2  in order to bind these layers. The connecting warp yarn  401  is woven according to 12 pick repeat. 
     At pick P1, connecting warp yarn  401  goes externally with respect to outer weft yarn  301 . At pick P2, connecting warp yarn  401  goes internally with respect to outer weft yarn  301 , that is under this yarn in the representation on  FIG. 2 . At pick P3, yarn  401  goes externally, that is above in the representation on  FIG. 2 , with respect to outer weft yarn  301 . In other words, connecting warp yarn  401  follows a W-shaped path within outer layer BL 2  between picks P1 and P3. Then, connecting warp yarn  401  moves from back layer BL 2  to front layer FL 2  and goes internally with respect to inner weft yarn  302 , at pick P4. Then, connecting yarn  401  alternates between above a weft yarn  302  and under a weft yarn  302  on  FIG. 2 , that is externally and internally, between picks P4 and P8. 
     At pick P9, connecting warp yarn  401  moves back to outer layer BL 2  and goes externally with respect to weft yarn  301 . At pick 10, yarn  401  goes internally with respect to weft yarn  301  and, at pick 11, it goes externally with respect to weft yarn  301 . At pick 12, connecting warp yarn  401  moves back to front layer FL 2 . At pick 13, connecting warp yarn  401  moves back to outer layer BL 2  and recover the position of pick 1. 
     In other words, connecting warp yarn  401  follows a W-shaped path within back layer BL 2 , during picks 1, 2 and 3, 9, 10 and 11. On the other hand, connecting warp yarn follows a W-shaped path within front layer FL 2  during picks 4, 6 and 8. The density of the path of warp yarn  401  in inner layer FL 2  is lower than its density in outer layer BL 2 , since inner weft yarns  302  are woven only on every second pick within front layer FL 2 . 
     Similarly, outer or back layer BL 4  includes a filling warp yarn  105  and a binding warp yarn  106  whereas front layer FL 4  includes a filling warp yarn  107  and a binding warp yarn  108 . 
     Outer weft yarns  303  are introduced within the shed corresponding to back layer BL 4  by bottom rapier set  16  at each pick, whereas inner weft yarns  304  are introduced within front layer FL 4  at every second pick, odd picks in the example in  FIG. 2 . These inner weft yarns  304  are introduced within the shed by intermediate rapier set  14 . Actually, rapier set  14  introduces an inner weft yarn  302  in the inner layer FL 2  of upper fabric  42  at one pick and an inner weft yarn  304  in the inner layer FL 4  of lower fabric  44  on the next pick. In other words, it is possible to use three rapiers sets to constitute four layers, namely outer layers BL 2  and BL 4  with weft yarns  301  and  303  introduced at each pick and inner layers FL 2  and FL 4  with weft yarns  302  and  304  introduced alternatively at every second pick. 
     A second connecting warp yarn  402  is used to bind inner and outer layers FL 4  and BL 4  in a way similar to yarn  401 . More precisely, connecting warp yarns  402  follows a W-shaped path within inner layer FL 4  between picks P1 and P5, by going around, alternatively externally and internally, inner weft yarns  304 . Then, warp yarn  402  goes from inner layer FL 4  to outer layer BL 4  where it follows a W-shaped path, around outer weft yarns  303 , at picks P6, P7 and P8, before going back to front layer FL 4 . At pick 10, connecting warp yarn  402  goes back to outer layer BL 4  where it follows a W-shaped path around outer weft yarns  303 , at picks P10, P11 and P12. 
     Therefore, connecting warp yarns  401  and  402  can be said to be W-inwoven within inner and outer layers FL 2 , FL 4 , BL 2  and BL 4 , which guarantees that these yarns efficiently hold together the layers of each fabric  42  and  44 , these fabrics being qualified as “distance fabrics” insofar as their respective front and back layers can be kept at a distance. 
     In the meaning of the invention, a warp yarn is “W-inwoven” in a layer when it is interlaced with at least three adjacent weft yarns in the same layer. This is the case when a warp yarn follows a W-shaped path with the adjacent weft yarns in the same layer. More precisely, when considering three adjacent weft yarns, the warp yarn goes externally with respect to the two extreme weft yarns and internally with respect to the intermediate weft yarn or internally with respect to the two extreme weft yarns and externally with respect to the intermediate weft yarn. In the meaning of the invention, a warp yarn is also “W-inwoven” in a layer when it is interlaced with five adjacent weft yarns in the same layer. For five adjacent weft yarns, the warp yarn goes externally with respect to the first, third and fifth weft yarns and internally with respect to the second and fourth weft yarns or internally with respect to the first, third and fifth yarns and externally with respect to the second and fourth yarns. 
     Pile warp yarns also belong to fabrics  42  and  44 . A first pile warp yarn  501  goes externally around outer weft yarn  301  at pick P1 and follows the same W-shaped path as yarn  401  within back layer BL 2  at picks P1, P2 and P3. At pick P4, pile warp yarn  501  moves from back layer BL 2  to front layer FL 2  and goes between weft yarns  301  and  302 . At pick P5, pile yarn  501  goes between weft yarns  303  and  304 . At picks P6, P7 and P8, pile yarn  501  follows a W-shaped path within back layer BL 4 . Between picks P8 and P9, pile warp yarn  501  crosses inner layers FL 4  and FL 2  and reaches, at pick 9, the same configuration as at pick P1. In other words, pile warp yarn  501  is W-inwoven in back layers BL 2  and BL 4  whereas it goes through layers FL 2  and FL 4 , when it changes from one fabric to the other. 
     Another pile warp yarn  502  is represented on  FIG. 2  and follows a W-shaped path within back layer BL 4  at picks P2, P3 and P4, before going directly to back layer BL 2  in order to follow a W-shaped path, in this layer, at picks 5, 6 and 7. Then, pile warp yarn  502  moves from back layer BL 2  to back layer BL 4  at picks P8 and P9. More precisely, pile warp yarn  502  goes between weft yarns  301  and  302  at pick P8 and internally with respect to weft yarn  304  at pick P9 before starting a new W-shaped path within back layer BL 4  at picks P10, P11 and P12. Here again, pile warp yarns  501  and  502  are W-inwoven in the outer or back layers BL 2  and BL 4  which ensures firm anchoring of these yarns with respect to these layers, whereas these pile warp yarns regularly go through the volume between the inner and outer layer of each fabric. 
     When a fabric according to the invention is used as an artificial turf as shown on  FIG. 6  for fabric  44 , the volume V between its back layer BL 4  and its front layer FL 4  can be filled with sand S and/or rubber granulates G which provides some elasticity when somebody walks onto the fabric. The front layer FL 4  can move with respect to the back layer BL 4  in an elastic way thanks to the deformation of connecting yarn  402 . Since the pile warp yarns  501  and  502  also go through the volume V, they also participate to the elasticity of the fabric, which is advantageous. 
     The pile warp yarns are moved between their respective positions represented on  FIG. 2  by the first four heddle frames  10  represented on  FIG. 1 , that is the heddle frames which are closer to reed  8 . Each heddle frame  10  is driven by one dedicated servomotor  40  controlled by electronic control unit  50 . As shown on  FIG. 2 , the pile warp yarns are woven according to an eight picks repeat pattern. 
     On  FIG. 3 , the references A 1 -A 8  show the respective positions of pile warp yarn  501  for the eight first picks P1-P8 represented on  FIG. 2 . At pick P1, yarn  501  must go above the three weft yarns  301 ,  304  and  303  respectively inserted in the shed by the rapier sets  12 ,  14  and  16 . Pile warp yarn  501  is then interlaced in the lower back layer BL 4  and must be drawn upwardly so that the eyelet of the corresponding heddle takes a first position A 1  on  FIG. 3 . In the following description, the position of the eyelet of the heddle driving a warp yarn is considered as the position of the warp yarn. This position is actually defined by the position of the corresponding heddle frame  10 . At pick P2, pile warp yarn  501  must go between weft yarns  301  and  302 , that is between rapier sets  12  and  14  so that it takes position A 2 . At pick P3, pile warp yarn  501  is still interlaced in back layer BL 2  and must go above weft yarn  301 , that is above rapier set  12 , so that it takes position A 3 . At pick P4, pile warp yarn  501  is still interlaced in layer BL 2  and must go between weft yarns  301  and  302 , that is between rapier sets  12  and  14 , so that it takes position A 4  which is the same as position A 2 . At pick P5, pile warp yarn  501  is interlaced in back layer BL 2  and must go between weft yarns  303  and  304 , so that it takes position A 5 . At pick P6, pile warp yarn  501  is interlaced in front layer FL 4  and must go under bottom rapier set  16 , so that it takes position A 6 . At pick P7, pile warp yarn  501  is interlaced in back layer BL 4  and must go between weft yarns  303  and  304 , so that it goes between rapier sets  14  and  16  and takes position A 7 . Finally, at pick P8, pile warp yarn  501  is interlaced in layer BL 4  and must go under bottom rapier set  16  in order to go externally with respect to weft yarn  303 , so that it takes position A 8 . At pick P9, pile warp yarn  501  takes position A 1  again and the same pattern as for picks P1 to P8 starts again. 
     Considering that positions A 2  and A 4  are identical, seven positions are required to weave pile warp yarn  501  within the respective layers FL 2 , BL 2 , FL 4  and BL 4  of the upper and lower fabrics  42  and  44 , according to the shedding pattern represented on  FIG. 2 . 
     These seven positions can be programmed thanks to electronic control unit  50  which controls the four servomotors  40  driving the first four heddle frames  10  of loom  2 . Those positions are compatible with the pattern which expresses the theoretical position of the warp yarns with respect to the insertion means. They also geometrically allow insertion means to introduce weft yarns without damaging warp yarns. 
     In order to achieve the above-mentioned positions of pile warp yarn  501 , microchip  52  computes, at each pick, the position A 1 -A 8  to be taken by this yarn, actually the position of a heddle frame  10  supporting a heddle which drives this yarn. Data relating to the shedding pattern to be obtained by the set of servomotors  40  is stored in memory  54 . On the basis of this data, it is possible for microchip  52  to determine, for each pick, in which layer pile warp yarn  501  has been interlaced in the previous pick, this layer being considered as an “origin layer”. This gives the starting point of the line representing the position of yarn  501  on  FIG. 3 . On the basis of this information relating to the origin layer of the pile warp yarn  501 , and on the basis of the shedding pattern to be followed, microchip  52  can determine the position to be taken by pile warp yarn  501 , hence the position of the corresponding heddle frame  10 . Electronic control unit  50  can then control the corresponding servomotor  40  on this basis, as shown with signals S 50  on  FIG. 1 , in order to move each heddle frame towards one of several predetermined positions. This can be done because servomotors can be easily piloted by electronic control unit  50  and reach any position between fixed upper and lower positions. 
     Actually, if one considers pile warp yarn  501  interlaced in one of layers BL 2 , FL 2 , BL 4  and FL 4 , it can take four positions, namely a first position above top rapier set  12 , a second position between top and intermediate rapier sets  12  and  14 , a third position between intermediate and bottom rapier sets  14  and  16  and a fourth position under bottom rapier set  16 . In other words, if N is the number of rapier sets, pile warp yarn  501  originating from one layer can take N+1 positions. Pile warp yarn  501  can be interlaced in either one of layers BL 2 , FL 2 , BL 4  and FL 4  so that it can actually take M×(N+1) positions, where M is the number of layers where pile warp yarn  501  is to be interlaced according to the shedding pattern. In the example represented on the figures, M equals 4. 
     If a pile yarn is to be interlaced in four layers, its position will have to be selected amongst 4×(3+1)=16 predetermined positions. 
     Because of the specific pattern represented on  FIG. 2 , only eight positions A 1 -A 8  are used, and, since positions A 2  and A 4  are identical, the servomotor  40  driving the frame which moves yarn  401  can be programmed with seven reference positions. 
     Thanks to the invention, the respective positions A 1 -A 8  of the pile warp yarns can be achieved without interference between these yarns and the insertion zones of the weft yarns. The four frames  10  represented on  FIG. 3  allow to obtain four different paths for pile warp yarns, namely yarns  501  and  502  and two non-represented yarns. 
     Practically, the seven reference positions of the pile warp yarn  501  depend on the weaving pattern, the location of the beating point of the concerned layer and the distance between the heddle and the beating point of the concerned layer. They can be stored in memory  54  of the electronic control unit  50 . While weaving, electronic control unit  50  determines at each pick the right position of the heddle amongst the stored reference positions and according to the pattern and the layer in which the warp yarn was previously interlaced. This kind of method allows advantageously changing pattern or geometrical parameters that affect reference positions independently. For example, if the distances between layers are modified, the reference position must be changed in a way that still allows the insertion means to function without damaging the warp yarns. 
     The same approach can be followed for pile warp yarn  502  and any other pile warp yarn which is not represented and belongs to fabrics  42  and  44 . Unlike pile warp yarn  501 , pile warp yarn  502  does not goes from top ground part  422  to bottom ground part  442  in a straight vertical way. For example at pick P8, pile warp yarn  502  is placed in position A 4  and remains in this position at pick P9 so that inner weft yarn  304  and outer weft yarn  303  are inserted under pile warp yarn  502 . In other words, pile warp yarn  502  goes from top ground part  422  to bottom ground part  442  over one pick, that is pick P9. The result is that the pile warp yarn  502  is slightly on the skew. 
     Once cut, the pile warp yarn  502  will tend to recover a vertical position but be longer than the cut pile yarn  501 . This is advantageous in case of artificial turf because the appearance of the carpet will be then closer to natural turf since the piles will have two different lengths, like grass blades. It is also possible to obtain more than two different lengths for the piles of the fabric, by having the pile yarns  501 ,  502  or equivalent pile yarns following different paths between back layers BL 2  and BL 4 . 
     As shown on  FIG. 4 , the fifth to eighth heddle frames, with respect to reed  8 , are used to position the connecting warp yarns  401 ,  402  and other non represented connecting warp yarns, in their respective paths represented on  FIG. 2 . The connecting warp yarns are woven according to a twelve pick repeat pattern. With the example of connecting warp yarn  401  on  FIG. 2 , its heddle frame  10  must respectively take the twelve positions B 1 -B 12  represented on  FIG. 4 . The positions B 5 , B 6  and B 7  are the same since connecting warp yarn  401  does not change position between picks P5 and P7. The positions B 3  and B 11  are the same since the connecting warp yarn  401  is interlaced in the outer layer BL 2  and is placed above top rapier set  12  at picks 3 and 11. The positions B 1  and B 9  are the same since the connecting warp yarn  401  is placed above top rapier set  12  at picks 1 and 9 whereas it was interlaced in the inner layer FL 2  at previous picks. The positions B 2  and B 10  are the same since the connecting warp yarn  401  is placed under top rapier set  12  at picks 2 and 10 without changing of layer. The positions B 4  and B 12  are the same since the connecting warp yarn  401  is placed under top rapier set  12  and intermediate rapier set  14  at picks 4 and 12 whereas it was interlaced in the outer layer BL 2  at previous picks 3 and 11. In other words, six different reference positions are used to weave connecting warp yarns according to the pattern shown on  FIG. 2  and loom  2  is designed to provide such positions. 
     If one considers for example an artificial turf application, the pile yarns  501  and  502  extend from one back layer BL 2  to the other BL 4  on a distance of about 70 mm and the distance between the back layer and the front layer in each fabric  42  and  44  is about 15 mm. In these conditions, some positions B 1 -B 8  are so close to each other that they can be merged. For instance, positions B 1  and B 3  can be merged together. The same applies for positions B 2 , B 5  and B 6  and for positions B 4  and B 8 . Therefore, the frame moving connecting yarn  401  can be driven with three reference positions. 
     As for pile warp yarns, the position of the heddle frames driving the connecting warp yarns are determined by electronic control unit  50  on the basis of the layer in which each connecting warp yarn is interlaced in a previous pick and on the basis of the shedding pattern to be followed. However connecting warp yarns are interlaced in two layers which are fed with weft yarns with the help of two rapier sets. Each position is selected amongst 2×(2+1)=6 predetermined positions since any connecting warp yarn can be interlaced in one of layers BL 2  and FL 2  or BL 4  and FL 4  and might have to go externally with respect to outer weft yarns  301 , and  303 , between inner and outer weft yarns or between inner weft yarns  302  and  304 . 
     As shown on  FIG. 5 , the binding and filing warp yarns are driven by the heddles frames  10  which are further away from reed  8  with respect to the frames guiding the pile and connecting warp yarns. This corresponds to the fact that the amplitude of the vertical displacement of the filing and binding warp yarns is smaller than the amplitude of the movements of the pile and connecting warp yarns. Binding warp yarn  102  takes positions C 1  and C 2 , whereas binding warp yarns  106  takes positions D 1  and D 2 , respectively on either side of top rapier set  12  and bottom rapier set  16 . On the other hand, binding warp yarn  104  takes positions E 1  and E 2  whereas binding warp yarn  108  takes positions F 1  and F 2 , respectively on either side of intermediate rapier set  14 . 
     This can also be achieved with electronically driven electrical servo actuators, similar to motors  40 , driven by electronic control unit  50  as explained here-above. 
     In the second embodiment of the invention represented on  FIG. 7 , the same elements as in the first embodiment have the same references. In this embodiment, two connecting warp yarns are used in each fabric, namely a first connecting warp yarn  401  and a second connecting warp yarn  403  in fabric  42 , and a first connecting warp yarn  402  and a second connecting warp yarn  404  in fabric  44 . In this embodiment, one uses a four-rapier sets loom where four weft yarns are inserted within the shed at each pick, one weft yarn  301  in the back or outer layer BL 2  of the upper fabric  42 , a second weft yarn  302  in the front or inner layer FL 2  of the upper fabric, a third weft yarn  303  in the back or outer layer BL 4  of the lower fabric  44  and a fourth weft yarn  304  in the inner or front layer FL 4  of the lower fabric  44 . The connecting warp yarns  401  to  404  are W-inwoven in the respective inner and outer layers FL 2 , FL 4 , BL 2  and BL 4  and are distributed in two sets which cross between inner and outer layers of each fabric between picks P3 and P4 represented on  FIG. 7 . 
     Each layer BL 2 , FL 2 , BL 4  or FL 4  of a fabric comprises one filling warp yarn  101 ,  103 ,  105  or  107  and two binding warp yarns  102  and  102 ′,  104  and  104 ′,  106  and  106 ′,  108  and  108 ′. Layers with double binding warp yarns could also be used in the first embodiment and layers with single binding warp yarns could be used in this embodiment. 
     Moreover, the pile warp yarns  501  and  502  are also W-inwoven in the outer or back layers BL 2  and BL 4  and cross, from one back layer to the other, at the same picks as the connecting warp yarns go from one layer to the other in one fabric. In other words, the change of layer for a connecting warp yarn  401 - 404  or a pile yarn  501 ,  502  takes place simultaneously during the weaving method, so that the connecting warp yarns and the pile yarns extend in the same zone in the volume within each distance fabric  42  and  44 . 
     As in the first embodiment, an electronic control unit drives some servomotors in order to determine, for each pick and for each connecting warp yarn and each pile warp yarn, in which layer this warp yarn has been interlaced in the previous pick. On this basis, and on the basis of the shedding pattern to be followed, the electronic control unit selects, amongst several predetermined positions, a position to be taken by a heddle frame driving the warp yarn. 
     In this embodiment, the number of layers M equals four, whereas the number of weft insertion means equals four, so that the total number of positions which can be taken by each heddle frame is 4×(4+1)=20 if the controlled warp yarn has to be interlaced in the four layers. 
     The invention makes it easy to weave sophisticated “three dimensional structures” by simplifying the management of the shedding means. The user simply has to program reference positions whose number depend on how many layers the warp yarn is interlaced in and how many insertion means are necessary to weave those layers. The electronic control unit analyses for each pick the pattern and the origin layer to determine the right reference position to join. The reference positions can be stored in the form of absolute positions or in the form of offsets. Since they depend on geometrical parameters as the distances between layers, the user can change the shed geometry and the pattern independently. 
     Thanks to electric shedding element which can be programmed to move yarns in every position, unsymmetrical weaving can be achieved. For example, the distances between each inner and outer layers can be different between top and bottom fabrics  42  and  44 . 
     In the examples, the electronic control unit determines for each pick in which layer the warp yarn was previously interlaced. This information could be computed externally by a CAD system from the pattern and stored in memory  54  in the same way as the pattern. 
     In the same way, a CAD system can entirely compute the right position of the shedding means for each pick. The CAD system provides a file of a succession of reference positions which will be stored in the memory  54  of the electronic control unit  50 . In such a case, the CAD system forms a computation means, connected or associated to loom  2  and which selects, for each pick, for each connecting warp yarn and each pile warp yarn and amongst several predetermined positions, a position to be taken by the shedding elements, on the basis of some information relating to the layer in which this warp yarn has been interlaced in the previous pick and on the basis of the shedding pattern. The CAD system fulfills a function similar to microchip  52  mentioned for the first embodiment of the invention. 
     The invention has been described here-above in the case where warp yarns are moved by heddle frames. It is also possible that some or all warp yarns, in particular pile warp yarns and connecting warp yarns, be connected to harness cords driven by respective servomotors such as disclosed in EP-A-0 933 466.