Abstract:
A device for the formation of a leno selvedge includes a frame for installation on the heddle shafts of a loom. The frame has at least one needle pair for two leno threads. The needle pair is mounted in the frame so that it can pivot around the longitudinal axis of the frame, and the device includes a pivot drive for pivoting the needle pair.

Description:
CROSS-REFERENCE TO RELATE APPLICATIONS 
     This application claims priority of German Patent Application 20 2011 103 312.4 filed Jun. 30, 2011, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention concerns a device for the formation of a leno selvedge including a frame for installation on the heddle shafts of a loom, whereby the frame has at least one needle pair for two leno threads, whereby the needle pair is mounted in the frame in such manner that it can pivot around the longitudinal axis of the frame, whereby for the pivoting of at least one needle pair the device has a pivot drive. 
     BACKGROUND OF THE INVENTION 
     DE-A-1814269 discloses a selvedge apparatus of the type cited above characterized by a frame, whereby at least one needle pair is placed in the frame and whereby the needle pair is oriented in parallel to the longitudinal axis of the frame and can also pivot around the longitudinal axis of the frame. The frame itself is fastened to the last heddle shaft. Such a selvedge apparatus is particularly well suited for the fastening of fiberglass threads or yarns to a leno selvedge with a corresponding fabric. The two needles of the needle pair each have an eye on their end through which the leno thread is passed. In the vicinity of the needle pair, the frame has a slot along the frame through which the core thread is guided. The core thread, in combination with the two leno threads guided through the eyes of the needles and the weft threads, ensures the binding of the selvedge, whereby the weft threads run perpendicular to the core thread. For the alternating pivoting of the at least one needle pair around the longitudinal axis of the frame, the disclosed embodiment describes an electromagnetic drive. 
     The electromagnetic drive comprises an axis mounted in a spool, whereby such a drive has different disadvantages. Such a drive is relatively heavy; this is particularly notable because this drive must be moved using the drive for the heddle shafts. That means that higher weight on the heddle shafts requires a higher drive output for the drive of the loom. Moreover, such a drive is relatively slow, that is, such a drive cannot be used for looms with a high number of picks per minute of 700 or more. Furthermore, an electromagnetic drive is highly inaccurate, so that it cannot be ensured that after each pick the weft thread will be properly tied off. The efficiency is also low. 
     The task of the invention is thus to provide a drive for a device of the type noted above that is very light in weight in order to keep the drive power of the loom low for the movement of the heddle shafts, that moreover works with high precision, is relatively insensitive to contamination, and has a high efficiency. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A drive for a device of the type mentioned above that satisfies these requirements is characterized by the fact that the pivot drive comprises a carrier that, while forming an air gap, has at least two permanent magnets spaced above one another and turned towards one another, whereby a movement member is provided in a pivoting manner on one axis of the frame, whereby the movement member has a head with at least one coil, whereby the head is located in the air gap, whereby the movement member at its end opposite the head is connected to the at least one needle pair. This makes it clear that the described drive is formed according to the principle of a stepper motor, whereby such a stepper motor is characterized by a high degree of efficiency, a high speed, and a high resistance to wear. 
     Advantageous features and embodiments of the invention result from the subclaims. 
     It is particularly provided that the pivot drive is symmetrical in design and also disposed symmetrically on the frame. It follows immediately that during operation of the loom the shafts on which the frames of the devices to form a leno selvedge are disposed largely experience no torque due to the operation of the drives for the needles. 
     According to a further characteristic of the invention, the areal extent of the two magnets is roughly twice the area circumscribed by the coil in the head plus the surface covered by the coil itself. Moreover, the permanent magnets located above one another have polarizations that are opposite one another, that is, each of the two opposing magnets has a different polarization on each end. The polarization on the ends of the two magnets are selected in such a way that the ends of the one magnet are polarized in the inverse manner to the ends of the other opposing magnet. The result is that two magnets are disposed opposite one another but can be physically modeled by a single magnet. 
     The head of the movement member has the coil with two connections. By appropriate repolarization of the voltage source connected to the connections, the head and the coil are now repelled alternately by one side of the opposing magnets, while being attracted by the other side of the opposing magnets. The implementation of this principle leads to an alternating pivoting movement at high frequency. That means that such a drive is particularly suitable for looms with pick counts of 600 to 700 picks per minute or more. Structurally, with respect to the design of the pivot drive, it is provided that the carrier has a circular arc-shaped carrier head with lateral flanges, whereby between the flanges of at least a first permanent magnet and, forming an air gap between it and the first permanent magnet, at least a second permanent magnet is disposed on the carrier head above the first magnet. The second permanent magnet is thereby advantageously arranged on a carrier lid fastened to the flanges. This yields a very simple structural solution that is also cost-effective to manufacture. The drive is also only slightly susceptible to contamination, since the head of the movement member moves in an air gap that is restricted only laterally by the flanges. Since the drive is arranged vertically on the frame of the leno selvedge mechanism, no contamination can collect in the area of the head of the movement member. Any contamination that still collects can easily be blown off. That means that the risk of wear between the head for the coil and the permanent magnets is low. 
     To transmit a pivoting movement of the movement member into the at least one needle pair, the pivot drive has a pivoting mechanism. The pivoting mechanism translates the pivoting movement of the movement member into a rotational movement of the at least one needle pair. To this end, the pivoting mechanism has a coupling arm disposed on the movement member, which is connected to the at least one needle pair through a diversion mechanism. 
     The invention will be explained in more detail based on the embodiment shown in the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the device in a perspective view from the front in an embodiment with two needle pairs; 
         FIG. 1   a  shows a schematic drawing of a cut through line Ia/Ia in  FIG. 1 ; 
         FIG. 2  shows a perspective representation of the pivot drive; 
         FIG. 3  shows the pivot drive from  FIG. 2  in an exploded view; 
         FIG. 4  also shows an exploded view of the connection of the pivot drive to the two needle pairs through the diversion mechanism, whereby only the significant parts are shown. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The leno selvedge device as a whole is denoted with  1 . The leno selvedge device  1  has a frame  2  with two frame rails  3  running parallel to one another, whereby the frame supports the pivot drive denoted with  20 . The pivot drive shows a movement member  25 , whereby the movement member  25  is connected through a coupling arm  30 , through a pivoting mechanism  40 , and through a diversion mechanism  50 , to the two needle pairs  60 . The frame  2  furthermore shows at its end at least one shaft holder  4  for fastening to the first heddle shaft. At the upper end, a thread guide  7  is provided with four eyes, whereby four leno threads  9  are correspondingly guided through this thread guide  7  with four eyes, the thread being guided on the bottom through eyes  62  of the needles  61  of each needle pair. The core thread  10  runs between the needles of a needle pair, whereby the thread is being correspondingly guided from the back through a guide into the frame and out to the front. The guide is provided by a slit  8  in the frame  2  ( FIG. 1   a ). Each needle pair is assigned a slit  8 . Similarly, the leno threads also run from the back through the thread guide downwards through the eyes of the needles to the front and back away from the frame  2 . Both the leno threads and the core threads are shown in  FIG. 1   a  as dotted lines. In  FIG. 1 , neither the leno threads  9  nor the core thread  10  is shown. 
     The following first describes the pivot drive  20 . To do this, we first refer to  FIG. 2  and then to the exploded view in  FIG. 3 .  FIG. 2  shows that the pivot drive denoted with  20  comprises a carrier  21  and a carrier head  21   a , which has one flange  22  on each of its two sides. The carrier head consists of advantageously magnetizable material. The head  26  of coil  26   a  is also formed of electrically nonconductive material; between the flanges  22  there is a first permanent magnet  24  on the carrier head  21   a , as shown in the view in  FIG. 3 . The permanent magnet denoted as  24  in  FIG. 3  has a center line that, however, only has the task of making clear that the actually physically single-piece magnet contains two magnets from an electrical standpoint, due to the fact that on each side of the permanent magnet, as shown in  FIG. 3 , the magnets have different polarization. The permanent magnet  24 , as already mentioned, is on carrier head  21   a  and is surrounded by the flanges  22 . The flanges  22  thus form a stop for the head  26  of movement member  25 . We will revisit this point later. The flanges moreover support the cover  27 , whereby on the cover  27  a second permanent magnet  24   a  is disposed that is formed in the same manner as permanent magnet  24 , with the difference that the polarizations of the two magnets on the sides facing one another are different, as can also be seen in the view in  FIG. 3 . Between the two permanent magnets  24 ,  24   a  there is an air gap  29 , whereby in air gap  29  the head  26  of the movement member  25  is disposed. The movement member  25  is connected by axis  30  to the carrier  21 . 
     For the functioning of the device, it is relevant that the size of the coil (the areal extent) in the head  26  of movement member  25  roughly corresponds to about half the area of one permanent magnet  24 ,  24   a . Coil  26   a  moreover shows connections  26   b , whereby connections  26   b  are connected to a reversible-polarity voltage source (not shown) that is connected to a controller. Upon reversal of the polarity of the voltage source, the head  26 , made of an electrically nonconducting material, of movement member  25  carries out an oscillating movement between the two flanges, whereby the oscillating movement is caused electrically by the fact that the polarity reversal causes the coil to be repelled from one half of the magnet and attracted by the other half of the magnet of the two permanent magnets  24 ,  24   a . Due to the polarity reversal, this is repeated alternately. The functioning is thus similar to that of a stepper motor. The flanges  22  can form a stop for the head, for example if the polarity reversal takes place too late. It can also be imagined that the needle pair is stopped on the frame, so that the frame can also act as a stop. 
     The movement member  25  is connected through a pivoting mechanism  40  and a redirection mechanism  50  to the two needle pairs  60 . The pivoting mechanism  40  comprises the coupling arm  41  and a sliding piece  42 , whereby the sliding piece lies in a movable manner on a guide block  43 . The guide block  43  is formed as an angle, and has two bore holes  44  on its horizontal flank as shown in  FIG. 4 . 
     The two needle pairs  60  are connected through the redirection mechanism  50  to the guide block  43  on one side and to the sliding piece  42  on the other. The redirection mechanism  50  comprises in this context a carrier body  51  that supports the two needles  61  of the needle pair  60  in a vertical orientation and one behind the other. In this case, “one behind the other” means one behind the other running in the direction of the core thread. The carrier body  50  has an axis  52 , whereby axis  52  has a pivot arm  53  that in turn has a pivot pin  54  extending parallel to axis  52 . Pivot pin  54  of each needle pair  60  rests in a bore hole  47  in the sliding piece  42 . 
     A pivoting movement of the coupling arm  25  according to arrow  49  now causes sliding piece  42  to be pivoted as well, along with pivot arm  53 , whereby the axes  52  of each needle pair disposed on the pivot arms  53  are also turned. That means that the needles pivot in the direction of arrow  65 . The pivoting of the needles  61  of needle pair  60  with the leno thread  9  around, the core thread  10  guided between the needles causes the binding of the weft thread, which is not shown. 
     Advantageously in this arrangement, the needles  61  of needle pair  60  have different lengths, whereby the back needle is preferably longer than the front needle. The differing lengths ensure that the leno threads guided through the eyes of the needles can reliably cross the core thread.