Abstract:
The invention relates to a loom comprising a warp thread tensioning device and a shedding device ( 12 ), which comprises pre-tensioned warp threads ( 4 ) in a first shedding position (F 1 ). The loom also comprises a lifting device ( 38 ), which can be driven in an oscillating manner, and followers ( 40 ) for the warp threads ( 4 ), in addition to control means ( 46 ) that can be operated by actuators ( 44 ) in order to selectively engage the warp threads ( 4 ) in the followers ( 40 ) and that displace the warp threads ( 4 ) into a second shedding position (F 3 ). To simplify said loom, a second lifting device ( 48 ), which is common to all warp threads ( 4 ), is provided in order to displace said warp threads ( 4 ) from the first shedding position (F 1 ) into a selection position (F 2 ), in which the first lifting device ( 38 ) is active, and in order to displace non-selected warp threads in unison into the first shedding position (F 1 ) by the pre-tensioning of said warp threads ( 4 ).

Description:
This application claims priority of PCT application PCT/CH2004/000337 having a priority date of Jun. 12, 2003, the disclosure of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a loom. 
     BACKGROUND OF THE INVENTION 
     A loom of the type initially mentioned is known from WO 99/13145. The loom contains a warp thread tensioning device and a shedding device which has warp threads pretensioned into a first shedding position. A lifting device capable of being driven in oscillation is equipped with drivers for the warp threads, there being control means actuable by means of actuators, in order to bring the warp threads selectively into engagement with the drivers which move the warp threads into a second shedding position. There is the disadvantage that, in this loom, the lifting device equipped with the drivers has to move along the entire travel of the warp threads from the first shedding position as far as the second shedding position. The lifting device therefore has to execute a relatively long travel, which, on the one hand, is time-consuming and, on the other hand, requires higher drive forces. In order to avoid this, in WO 99/13145 there is a further exemplary embodiment, in which the warp threads assume a middle shedding position and there are two lifting devices which each have drivers in order to move the warp threads either into the top shedding position or into the bottom shedding position. This requires double the number of drivers, with the result that such a design variant is highly complicated and consequently cost-intensive. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to improve a loom of the type initially mentioned. 
     The set object is achieved by means of the characterizing features of claim  1 . Since the loom has a second lifting device which is common to all the warp threads and which moves the warp threads out of the first shedding position into a switching position effective for the first lifting device, this results, for all the warp threads, in a very simple second lifting device which, moreover, appreciably reduces the switching travel for the first lifting device, so that the first lifting device has to move a warp thread only out of the switching position into the second shedding position. Both lifting devices have to execute only a limited travel for which they require less time. 
     Moreover, since the lifting devices can be active simultaneously, an appreciable increase in the performance of the loom is obtained. In addition, owing to this design, the useful life is also improved owing to the lower susceptibility to wear. The loom also results in lower noise emission. Advantageous refinements of the loom are described below. 
     The second lifting device may be a lifting beam extending over all the warp threads. The lifting travel of the second lifting device may vary greatly, and it is advantageous if, the latter executes at least half the lifting travel of the warp threads in the shed. 
     For the design of the first lifting device, there are various design variants which are already contained in WO 99/13145. An embodiment that is particularly advantageous, includes a first lifting device which has for each warp thread a control drop wire with a driver slot and an assigned driver, preferably of hook-shaped design, for the associated warp thread. The warp thread can be brought selectively into engagement with the driver by means of a control drop wire switchable by means of the actuator. In some embodiments, the driver slot is assigned to the displacement path of the driver and, in the switching region, is guided, via a control slot running obliquely with respect to the direction of displacement of the driver, out of the displacement path of the driver into a widened guide slot of the control drop wire. To facilitate the introduction of the warp thread into the control slot, the guide slot is provided with a run-on side. 
     In principle, the control drop wire may be configured as a sheet steel strip. In one advantageous design, the control drop wire is formed in the shape of a sleeve with two side walls, between which the driver is mounted displaceably. A reliable guidance of the warp thread from and to the driver is thereby achieved. To protect the warp thread, on the one hand, and to facilitate the run of the warp thread through the control drop wire, on the other hand, at least the guide slot and the control slot are offset relative to one another in the two side walls of the control drop wire in the direction of run of the warp thread, in such a way that a deflection of the running warp thread in the control drop wire is lower than 90°, preferably 10°. 
     There are various possibilities for driving the drivers, there being preference, for all the drivers of a row to be movable up and down by means of a common lifting knife. This affords a particularly simple and cost-effective solution. 
     Since the warp threads are moved in each case out of a first shedding position into the second shedding position, their displacement travel is such that the elasticity of the warp thread is not sufficient, as a rule, to ensure satisfactory functioning. It is therefore advantageous if, the warp thread tensioning device has an individual thread tensioner for each warp thread on the run-in side of the warp threads to the shedding device. The tension of the individual warp thread can thereby be adapted more closely to the respective position of the warp thread in the shed. The loom may have the conventional additional catch thread devices. It is more advantageous, however, if, the thread tensioner is at the same time also designed as a catch thread device. 
     In some embodiments, each warp thread is guided via two guide elements which are arranged at a distance from one another and between which is arranged the thread tensioner which engages on the warp thread and exerts a pretension on the warp thread. The pretension may be generated by a tensioning weight. In a more advantageous design, the pretension is generated by a tensioning spring. This also makes it possible, in particular, to arrange the thread tensioner in a position deviating from the vertical. 
     The thread tensioner may be provided with a closed eye. In a more advantageous design however, each thread tensioner has a lateral run-in eye for the warp thread. In some embodiments, each thread tensioner is provided with a guide orifice, by means of which it is mounted on a holder displaceably in the tensioning direction. Expediently, the thread tensioner is provided, in the direction opposite to the pretensioning direction, with a grip part which preferably has a signal part projecting out of the direction of displacement. Such a signal part may be, for example, a projecting head part of the thread tensioner. As a result, a thread tensioner on which a thread fault has occurred can be detected more easily, since it emerges from the plane of the thread tensioners which are operating satisfactorily. 
     It is particularly expedient if, the thread tensioner is arranged on a holder which has a middle contact part which projects on one side and which, insulated, is embedded into lateral contact parts cooperating with the sides of the guide orifice of the thread tensioner. In the event of a faulty warp thread tension, the contact parts come into touch with an end face of the guide orifice, this touch bridging the contacts and thus triggering a fault signal. 
     The thread tensioner can be used in the most diverse possible looms. It is preferably used, however, in a loom in which the warp thread tensioning device has a control device which is connected to the drive of a cloth take-up in such a way as to control the warp beam such that the warp threads as a whole are under a predeterminable tension force. The retaining force may be generated by means of a braking device at the warp let-off. To generate the retaining force in a more advantageous embodiment, the warp beam is provided with specific drive which contains a selflocking gear. The warp thread tensioning device can be further improved by means of the design, according to which it has a back bearer for the warp threads which is pretensioned by means of a tensioning spring device. The tensioning spring device is connected to the control device, so that the drives of the warp beam and of the cloth take-up can be controlled in such a way that the predeterminable tension force is maintained at the back bearer. Various variants may be envisaged for the design of the tensioning spring device. In a particularly advantageous embodiment, the tensioning spring device has a leaf spring with a flexion converter which delivers corresponding control signals to the control device. In addition, the warp thread tensioning device may be designed with a safety device which is operatively connected to the back bearer and which contains an emergency switch which responds when the force of the warp threads which occurs in the back bearer is greater than the set tension force by a determinable safety amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are described in more detail below with reference to the drawings in which: 
         FIG. 1  shows a diagram of a loom in a side view; 
         FIG. 2  shows a detail of the shedding device of the loom of  FIG. 1  on a larger scale; 
         FIG. 3  shows the shedding device of  FIG. 2  in the section III-III; 
         FIGS. 4-8  show various work stages of the shedding device of  FIG. 2 ; 
         FIG. 9  shows the diagram of a further loom with individual thread tensioners in a side view; 
         FIG. 10  shows the thread tensioner of the loom according to  FIG. 9  on a larger scale, and 
         FIG. 11  shows a detail of the device according to  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows diagrammatically a loom which, in general, has a warp let-off  2  which is designed, for example, as a warp beam, from which warp threads  4  arrive at the shedding device  12  via a back bearer  6 , individual thread tensioners  8  and catch thread devices  10 . In the shedding device  12 , the warp threads  4  are opened to form a shed  14  into which can then be introduced a weft thread  16  which is beaten up at the beating-up edge  18 , so that a cloth web  20  is obtained. The cloth web  20 , held by a cloth holder  22 , is taken up via a cloth take-up  24 . A control device  26  serves for controlling the loom. 
     The loom is provided with a thread tensioning device which primarily contains the cloth take-up  24 , the drive  28  of which is controlled by means of the control device  26  such that a predeterminable tension force common to all the warp threads  4  is given as a function of the retaining force of the warp let-off  2 . The retaining force of the warp let-off may be generated by means of a braking device  29  or a specific drive, in which a motor is connected to the warp let-off via a selflocking gear. The warp thread tensioning device additionally contains, for each warp thread  4 , an individual warp thread tensioner  8  which is arranged between two guide elements  30  and, in the example shown, individually pretensions, by means of a pretensioning spring  32 , the warp thread  4  which runs through an eye  34 . 
     In the shedding device  12 , the warp threads  4  are pretensioned into a first shedding position F 1  between a deflecting roller  36  and a cloth holder  22  which may also be designed as an expander. A first lifting device  38  serves for the individual control of the warp threads  4 , said lifting device having drivers  40  which can be moved out of a switching position F 2  into the second shedding position F 3  by means of a lifting beam  42 . With the aid of control means  46  controllable by actuators  44 , the warp threads  4  can be brought selectively into engagement with the drivers  40  when the warp threads have been moved out of the first shedding position F 1  into the switching position F 2  by means of a common second lifting device  48 , as is evident in detail in  FIGS. 1 to 8 . The control means  46  contain control drop wires  50  which are pretensioned by means of a pretensioning spring  52  against a lifting beam  54  on which they stand via a stop  56 . The actuators  44  contain hook parts  58  which cooperate with hook parts  60  on the control drop wires  50  and, in the activated state, hold the control drop wire  50  in the lifted position. A nonactivated actuator  44  enables the displacement travel of the control drop wire  50 . In  FIG. 1 , each control drop wire  50  is symbolized by its switching travel, as illustrated in detail by means of  FIGS. 2 to 8 . Thus, the control drop wires contain a driver slot  62  which lies in the displacement travel of the warp thread  2 . The driver slot has adjoining it upwardly a control slot  64  which guides the warp thread out of the displacement travel of the driver into a widened guide slot  66 , so that it can no longer be grasped by the driver  40 . 
     As may be gathered from  FIGS. 2 and 3 , the control drop wire is designed in the form of a sleeve and has side walls  68 ,  70  which are connected by means of end walls  72 ,  74  and which thus provide a cavity in which the driver  40  is mounted displaceably. In particular, the driver slots  62   a  and  62   b  are arranged in the side walls  68 ,  70  so as to be offset in the direction of run of the thread in such a way that the warp thread, when it passes through the control drop wire, is inclined at an angle α from the vertical with respect to the control drop wire which is smaller than 90°, preferably 40°, in order to keep as low as possible the passage resistance of the warp thread through the control drop wire and consequently the wear of the warp thread, on the one hand, and of the control drop wire, on the other hand. 
     The functioning of the shedding device is illustrated in more detail with reference to  FIG. 1  in conjunction with  FIGS. 2 to 8 . When the control drop wire is in the lifted position, in which it is retained on the actuator, as may be gathered from  FIG. 1  for the actuator on the right and from  FIGS. 2 ,  4  and  5 , the warp thread is guided by means of the second lifting device  40  out of the guide slot  66  via an oblique run-on side  76  into the control slot  64  and by means of the latter into the driver slot  62  in which the warp thread lies in the displacement travel of the driver  40 . During the downward movement of the driver  40 , the warp thread  4  is driven by the hook  40   a  of the driver  40  out of the switching position F 2  into the second shedding position F 3  which is the bottom shedding position. As long as the control drop wire  50  remains in the lifted state, the warp thread  4  is moved to and fro by the amount of the height H 1  only between the switching position F 2  and the bottom shedding position F 3 , as is evident from  FIGS. 2 and 4  to  6 . 
     As soon as the actuator  44  releases the control drop wire  50  and the latter is lowered by the amount of the switching quantity S, during the upward movement of the driver  40  the warp thread passes via the control slot  64  into the widened guide slot  66  and consequently outside the displacement travel of the driver  40 . Then, as may be gathered from  FIGS. 7 and 8 , the warp thread passes again into the displacement travel of the second lifting device  48  and is moved over the height H 2  out of the switching position into the first shedding position F 1  which is the top shedding position. 
       FIG. 9  shows a loom with a special design of the warp thread tensioning device and of the thread tensioners, which loom may have, for example, a shedding device according to the loom of  FIG. 1 . The loom contains a warp beam  2   a , from which warp threads  4  are guided via a back bearer  6   a  to individual thread tensioners  8   a  which are arranged upstream of a shedding device  12   a . The shedding device  12   a  may be designed similarly to the shedding device  12  of the loom of  FIG. 1 , but may also have other designs. The cloth web  20  produced is taken up via a cloth take-up  24   a  and wound up on a cloth beam  80 . The loom contains a control device  26   a  which is designed, in particular, for controlling the warp thread tensioning device. The warp beam  2   a  is actuated by a drive  82  which has a selflocking gear  84 . The drive is controlled by the control device  26   a , specifically as a function of the drive  28   a  of the cloth take-up  24   a  and of a tensioning spring device  86  with which the back bearer  6   a  stands against the warp threads  4 . The control is such that the cloth take-up  24   a  is set as a function of the retaining force of the drive  82  of the warp beam  2   a  such that a predetermined tension force can be maintained at the back bearer  6   a.    
     The warp beam  6   a  is fastened to a rocker  88  which is supported via a supporting device  90  on a leaf spring  92  provided with a flexion converter  94  which transfers its data to the control device  26   a . The supporting device  90  comprises a safety device  96  containing a screw bolt  98 , the head  100  of which is arranged displaceably in a holding bell  102 . The holding bell  102  is connected to the rocker  88 . The head  100  is supported on a stop  104  of the holding bell. A pretensioning spring  106  arranged outside the holding bell  102  is supported, on the one hand, on the screw bolt  98  via a setscrew  108  and on the holding bell  102  via a washer  110  on the other hand so that the head  100  bears with a corresponding pretensioning force against the stop  104  of the holding bell  102 . The screw bolt  98  is connected, further, to the leaf spring  92 . If, then, a tension force higher than the tension force set as permissible on the leaf spring  92  occurs at the back bearer  6   a , the pretensioning spring  106  is compressed and the holding bell  102  is displaced on the screw bolt  98 , with the result that a switch  112  connected to the holding bell  102  is closed and transmits a fault signal to the control device  26   a.    
       FIGS. 10 and 11  show in detail the design of the thread tensioners  8   a  which are at the same time also configured as catch thread devices. The thread tensioners  8   a  are designed as drop wires and each have a guide orifice  114 , by means of which they are mounted on a holder  116  displaceably in the tensioning direction. The holders have a middle contact part  118  which projects on one side and which, insulated, is embedded into lateral contact parts  120 . The latter are connected to the sides of the guide orifice. In the event of a faulty warp tension, the thread tensioners  8   a  are displaced by means of the pretensioning spring  32   a  until the contact parts  118 ,  120  of the holder  116  stand against an end face  124  of the guide orifice  114  and trigger a fault warning. The thread tensioners lie in each case between two guide elements  30   a  for the warp thread  4  which is pieced up to the thread tensioners  8   a  via run-in eyes  34   a . On the side facing away from the pretensioning spring  32   a , the thread tensioners each contain a grip part  126  with a signal part  128  which projects out of the displacement plane of the thread tensioners, so that it is possible to detect those thread tensioners which indicate a broken warp thread and for this reason are no longer in alignment with the remaining signal parts  128 . The signal part  128  is formed by a head part projecting out of the displacement plane. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 List of reference symbols 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 F 1   
                 First shedding position 
               
               
                   
                 F 2   
                 Switching position 
               
               
                   
                 F 3   
                 Second shedding 
               
               
                   
                   
                 position 
               
               
                   
                 H 1   
                 Lift height of the 1st 
               
               
                   
                   
                 lifting device 
               
               
                   
                 H 2   
                 Lift height of the 2nd 
               
               
                   
                   
                 lifting device 
               
               
                   
                 S 
                 Switching quantity 
               
               
                   
                 α 
                 Deflection 
               
               
                   
                 2, 2a 
                 Warp let-off (warp 
               
               
                   
                   
                 beam) 
               
               
                   
                 4 
                 Warp thread 
               
               
                   
                 6, 6a 
                 Back bearer 
               
               
                   
                 8, 8a 
                 Thread tensioner 
               
               
                   
                 10 
                 Catch thread device 
               
               
                   
                 12, 12a 
                 Shedding device 
               
               
                   
                 14 
                 Shed 
               
               
                   
                 16 
                 Weft thread 
               
               
                   
                 18 
                 Beating-up edge 
               
               
                   
                 20 
                 Cloth web 
               
               
                   
                 22 
                 Cloth holder 
               
               
                   
                 24, 24a 
                 Cloth take-up 
               
               
                   
                 26, 26a 
                 Control device 
               
               
                   
                 28, 28a 
                 Drive 
               
               
                   
                 29 
                 Braking device 
               
               
                   
                 30, 30a 
                 Guide element 
               
               
                   
                 32, 32a 
                 Pretensioning spring 
               
               
                   
                 34, 34a 
                 Eye 
               
               
                   
                 36 
                 Deflecting roller 
               
               
                   
                 38 
                 First lifting device 
               
               
                   
                 40 
                 Driver 
               
               
                   
                 40a 
                 Hook 
               
               
                   
                 42 
                 Lifting beam 
               
               
                   
                 44 
                 Actuator 
               
               
                   
                 46 
                 Control means 
               
               
                   
                 48 
                 Second lifting device 
               
               
                   
                 50 
                 Control drop wire 
               
               
                   
                 52 
                 Pretensioning spring 
               
               
                   
                 54 
                 Lifting beam 
               
               
                   
                 56 
                 Stop 
               
               
                   
                 58 
                 Hook part of 44 
               
               
                   
                 60 
                 Hook part of 50 
               
               
                   
                 62 
                 Driver slot 
               
               
                   
                 62a 
                 Driver slot 
               
               
                   
                 62b 
                 Driver slot 
               
               
                   
                 64 
                 Control slot 
               
               
                   
                 66 
                 Guide slot 
               
               
                   
                 68 
                 Side wall 
               
               
                   
                 70 
                 Side wall 
               
               
                   
                 72 
                 End wall 
               
               
                   
                 74 
                 End wall 
               
               
                   
                 76 
                 Run-on side 
               
               
                   
                 80 
                 Cloth beam 
               
               
                   
                 82 
                 Drive 
               
               
                   
                 84 
                 Selflocking gear 
               
               
                   
                 86 
                 Tensioning spring 
               
               
                   
                   
                 device 
               
               
                   
                 88 
                 Rocker 
               
               
                   
                 90 
                 Supporting device 
               
               
                   
                 92 
                 Leaf spring 
               
               
                   
                 94 
                 Flexion converter 
               
               
                   
                 96 
                 Safety device 
               
               
                   
                 98 
                 Screw bolt 
               
               
                   
                 100 
                 Head 
               
               
                   
                 102 
                 Holding bell 
               
               
                   
                 104 
                 Stop 
               
               
                   
                 106 
                 Pretensioning spring 
               
               
                   
                 108 
                 Setscrew 
               
               
                   
                 110 
                 Washer 
               
               
                   
                 112 
                 Switch 
               
               
                   
                 114 
                 Guide orifice 
               
               
                   
                 116 
                 Holder 
               
               
                   
                 118 
                 Contact part 
               
               
                   
                 120 
                 Lateral contact 
               
               
                   
                   
                 parts 
               
               
                   
                 124 
                 End face 
               
               
                   
                 126 
                 Grip part 
               
               
                   
                 128 
                 Signal part