Abstract:
A needle webbing machine which comprises two weft needles ( 2   a,    2   b ) which work simultaneously and in opposite directions on both ribbon sides, in addition to knitting needles ( 28   a,    28   b ) which are arranged on both ribbon sides. A yarn lifter ( 18   a,    18   b ) which works individually and which is used to advance a weft thread ( 4   a,    4   b ) to a weft needle ( 2   a,    2   b ), which is open, is provided on each side of the ribbon in order to improve the production thereof.

Description:
This application claims priority of PCT application PCT/CH2006/000489 having a priority date of Oct. 6, 2005, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a method for weaving a ribbon on a needle ribbon weaving machine and to a needle ribbon weaving machine. 
     BACKGROUND OF THE INVENTION 
     A method and a needle ribbon weaving machine for weaving a ribbon of the type initially mentioned are known from DE 40 09 455A. The method described there for producing a ribbon on a needle ribbon weaving machine takes place by means of two closed weft needles operating contradirectionally, the ribbon being woven by both weft needles as a result of insertion into a common shed. The heads of the contradirectionally inserted weft thread loops are secured on each ribbon side by means of wales which are formed in each case from an auxiliary thread and which are located at the two edges of the ribbon. The disadvantage, then, is that always two weft thread loops have to be inserted into a common shed, so that, in the event of a shed change, two weft thread loops, that is to say four weft thread portions, have to be tied in simultaneously. The stability of the ribbon to be produced is impaired as a result. There are also no variations of any kind possible, since closed weft needles having guide loops on which a weft thread is always arranged are used. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to improve the method for weaving a ribbon on a needle ribbon machine having two simultaneously and contradirectionally operating weft needles. 
     Since only that weft which is presented to one of the two weft needles is inserted, any desired weft sequence is possible. Not just two weft threads may be introduced simultaneously into the shed, as is afforded in the prior art, but, in particular, the weft threads may be inserted alternately from ribbon sides to ribbon sides, so that, in the event of each shed change, only one weft thread loop is inserted. Furthermore, it is possible, moreover, to present weft threads even of changing color and quality to the weft needles. This not only affords a mechanically improved quality of the ribbon produced, but the pattern possibility is also increased. 
     On each ribbon side, the weft thread loops may be knitted together with themselves, or, they may be knitted by means of an interlaced auxiliary thread. 
     For the needle ribbon weaving machine serving for carrying out the method, it is essential that an individually operating thread lifter for presenting a weft thread to a weft needle designed to be open is present on each ribbon side. 
     A preferred design of the weft needle which has a fork, arranged on the needle shank, for receiving the weft thread, and also a guide slot for the weft thread, said guide slot running along the needle shank to just short of the fork. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are described in more detail below by means of the drawings showing the weaving region of a needle ribbon weaving machine in various weaving phases, specifically the tie-off of an inserted weft thread loop by means of an auxiliary thread in  FIGS. 1 to 4  and the tie-off of inserted weft thread loops without an auxiliary thread in  FIGS. 5 to 7 . In the drawings: 
         FIG. 1  shows the weaving region during the beating-up of a weft thread loop inserted by the left weft needle in a diagrammatic illustration; 
         FIG. 2  shows the weaving region of  FIG. 1  during the insertion of a weft thread loop by means of the right weft needle; 
         FIG. 3  shows the weaving region of  FIG. 2  with an inserted weft thread loop and before the tie-off of the latter; 
         FIG. 4  shows the weaving region of  FIG. 3  during the beating-up of the weft thread loop inserted by the right weft needle and during the presentation of the weft thread to the left weft needle; 
         FIG. 5  shows the weaving region during the beating-up of a weft thread loop inserted by the right weft needle; 
         FIG. 6  shows the weaving region of  FIG. 5  during the insertion of a weft thread loop inserted by the left weft needle; 
         FIG. 7  shows the weaving region of  FIG. 6  during the interlacing of the inserted weft thread loop. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 4  show the weaving region of a needle ribbon weaving machine with two contradirectionally driven weft needles  2   a ,  2   b  which insert weft threads  4   a ,  4   b  into a shed  6 . In the shed  6  formed from warp threads  8 , the weft threads are beaten up at the beating-up edge  10  by means of a reed  9 , thus giving rise to the ribbon  12 . 
     The weft needles  2   a ,  2   b  are in each case open needles, i.e. they have at the front end of a needle shank  14   a ,  14   b  a fork  16   a ,  16   b , into which the respective weft thread  4   a ,  4   b  is introduced by means of a thread lifter  18   a ,  18   b  movable up and down. The weft needles  2   a ,  2   b  contain in each case guide slots  20   a ,  20   b  which run along the needle shank  14   a ,  14   b  and which reach beyond the forks  16   a ,  16   b . The guide slots  20   a ,  20   b  serve for guiding the weft thread  4   a ,  4   b  when the weft thread is not inserted into the shed  6 , and for making it easier to introduce into the fork  16   a ,  16   b  with the aid of the respective thread lifter  18   a ,  18   b . The web thread loop  22   a ,  22   b  inserted in each case is secured by means of an auxiliary thread  24   a ,  24   b  which is in each case presented to knitting needles  28   a ,  28   b  by means of a thread guide  26   a ,  26   b  such that said auxiliary thread is interlaced with the weft thread loops  22   a ,  22   b.    
     In the position shown in  FIG. 1 , the left weft needle  2   a  has just inserted a weft thread loop  22   a  into the shed  6  and has been beaten up at the beating-up edge  10  by means of the reed  11 . By means of the left thread lifter  18   a , the left weft thread  4   a  is raised on the fork  16   a  of the weft needle  2   a  as a result of the raising of the thread lifter  18   a , to an extent such that said left weft thread cannot be grasped by the fork  16   a  of the weft needle  2   a . On the right side of the shed, the thread lifter  18   b  is lowered and brings the weft thread  4   b  into engagement on the fork  16   b  of the weft needle  2   b , so that, the latter can insert the weft thread loop  22   b  into the open shed  6 , as shown in  FIG. 2 . The left weft needle  2   a  runs, empty, into the shed, the weft thread  4   a  being guided in the guide slot  20   a . When the weft thread loop  22   b  has been inserted completely into the shed, as is evident from  FIG. 3 , the left knitting needle  28   a  grasps the auxiliary thread  24   a  and draws the latter through the inserted weft thread loop  22   b  and further on through the last loop  30   a  of the auxiliary thread  24   a . On the right side, the auxiliary thread  24   b  is interlaced with itself, that is to say with its last loop  30   b , without being drawn through a weft thread loop. After this securing of the inserted weft thread loop  22   b  by means of the auxiliary thread  24   a , the weft needles  2   a ,  2   b  leave the shed, and the reed  11  beats up the weft thread loop thus inserted at the beating-up edge  10 . The thread lifter  18   b  is then raised again and prevents an engagement of the weft thread  4   b  on the fork  16   b  of the weft needle  2   b . Instead, by means of the thread lifter  18   a , the weft thread  4   a  is brought into engagement on the fork  16   a  of the weft needle  2   a , in order, during the next shed opening, to insert a further weft thread loop  22   a  from the left ribbon side in a similar way. 
       FIGS. 5 to 7  show a needle ribbon weaving machine which is constructed similarly to the needle ribbon weaving machine of  FIGS. 1 to 4 , and therefore parts identical to the first exemplary embodiment are given the same reference symbols. Reference is made to the relevant statements with regard to  FIGS. 1 to 4 . In the exemplary embodiment of  FIGS. 5 to 7 , however, no auxiliary threads are used, but, instead, the weft threads  40   a ,  40   b  are interlaced with themselves.  FIG. 6  shows how the weft thread loop  42   a  from the weft thread  40   a  is inserted into the shed by means of the left weft needle  2   a . After complete insertion, the right knitting needle  28   b  grasps the inserted weft thread loop  42   a  and draws the latter through the already knocked-over weft thread loop  42   a . During the insertion of the weft thread loop  42   a  by means of the weft needle  2   a  from the left side of the ribbon, the right weft needle  2   b  moves, empty, through the shed. The weft thread  40   b  is in this case guided in the guide slot  20   b  of the right weft needle  2   b , as may be gathered from  FIG. 7 . As soon as the weft needles  2   a ,  2   b  are drawn back out of the shed, the beating-up of the inserted weft thread loop  42   a  by means of the reed  11  at the beating-up edge  10  takes place, as illustrated in  FIG. 5 . The shed change is followed by the insertion of the weft thread loop on the right side of the ribbon, the operation taking place in a similar way to the insertion of the weft thread on the left ribbon side. 
     LIST OF REFERENCE SYMBOLS 
     
         
           2   a  Weft needle 
           2   b  Weft needle 
           4   a  Weft thread 
           4   b  Weft thread 
           6  Shed 
           8  Warp thread 
           10  Beating-up edge 
           11  Reed 
           12  Ribbon 
           14   a  Needle shank 
           14   b  Needle shank 
           16   a  Fork 
           16   b  Fork 
           18   a  Thread lifter 
           18   b  Thread lifter 
           20   a  Guide slot 
           20   b  Guide slot 
           22   a  Weft thread loop 
           22   b  Weft thread loop 
           24   a  Auxiliary thread 
           24   b  Auxiliary thread 
           26   a  Thread guide 
           26   b  Thread guide 
           28   a  Knitting needle 
           28   b  Knitting needle 
           40   a  Weft thread 
           40   b  Weft thread 
           42   a  Weft thread loop 
           42   b  Weft thread loop