Patent Publication Number: US-2016230317-A1

Title: Method and Device for Applying Forces and Motions to Warp Threads of Weaving Machine

Description:
TECHNICAL FIELD 
     The present invention relates to a method and an apparatus or device for applying forces and motions to warp threads of a weaving machine. 
     PRIOR ART 
     Regarding weaving machines, apparatuses or devices are known in the prior art, with which forces and motions can be applied to the warp threads of a weaving machine. 
     For example, such an apparatus is shown by DE 2 731 046 A1, which is regarded as the closest prior art. This relates to an apparatus for compensating the warp thread tension forces on a weaving machine with a moveably supported, itself stiff, continuous backrest or whip roll, characterized in that the backrest or whip roll is supported or braced from at least one pressure cushion extending essentially in the longitudinal direction of the backrest or whip roll. 
     WO 1997/030201 A1 shows a tensioning apparatus for a warp thread sheet, in which a tensioning roll is provided, which is supported at several points along its length in a spring-elastic yielding or resilient manner by means of support rollers. 
     From WO 2008/077383 A1, a backrest or whip roll for a weaving machine is known, in which warp thread motions in the warp direction are compensated by a thread deflecting element arranged pivotably on a leaf spring. 
     DE 199 15 952 A1 describes a method in which the oscillating motions of a backrest or whip roll about its longitudinal central axis occur selectively either in a positively constrained controlled manner or in an unconstrained controlled manner, or respectively in which a positively constrained controlled motion is superimposed on an unconstrained motion. 
     Backrest or whip rolls, or respectively tensioning rolls serve as thread deflecting elements for warp threads of the weaving machine between the warp beam and the weaving plane. Furthermore, in the above mentioned apparatuses, spring elements are provided, which apply spring forces to the thread deflecting element at several points over the width of the warp thread sheet, whereby a uniform distribution of these spring forces is achieved. Through the spring-yielding or resilient suspension of the thread deflecting elements, when there are tension force variations in the warp threads, a motion of the thread deflecting element that counteracts the tension force variation will arise. 
     In that regard, the arrangements of the spring elements and of the thread deflecting elements on the weaving machine in the prior art are generally embodied so that despite the compensating motion of the spring-yielding or resilient suspended thread deflecting elements, during the weaving cycle the warp thread tension force will be greater in the open shed position of the warp threads than in the closed shed position, which is also called the shed closure. 
     When weaving very dense or tight woven fabrics it has now been found that in the weaving cycle of the weaving machine, a higher warp thread tension force is required in the region or range of the reed beat-up, in order to actually achieve a required high weft set or pick density. In the weaving cycle, the reed beat-up of the weaving machine generally occurs a short time after the shed closure. However, as explained above, this is the region or range in which the warp thread tension forces are low. Moreover, due to the low moving masses of the thread deflecting elements of the above described apparatuses, rapid compensating movements of the thread deflecting elements arise when there are rapid tension force variations in the warp threads, so that the sudden beat-like increase of the warp thread tension force caused by the reed beat-up is at least partially again compensated out. 
     It is an object of the present invention to provide a method and an apparatus or device for applying forces and motions to warp threads of a weaving machine, in which a compensation of tension force fluctuations is made possible in certain regions or ranges of the weaving cycle, while in other regions or ranges no compensation or even a targeted increase of the warp thread tensions can be achieved. 
     DESCRIPTION OF THE INVENTION 
     The object is achieved by a method as well as an apparatus or device according to the independent claims. 
     The method according to the invention comprises the following method steps: 
     1) The warp threads are deflected by a thread deflecting element, whereby the thread deflecting element is supported pivotably about a pivot axis. With regard to the pivot axis, this can also involve a kinematically effective virtual axis. 
     2) Spring forces are applied to the thread deflecting element, and particularly over several force application points. In that regard, the force application points are distributed along a first line that extends parallel to the pivot axis. These force application points are arranged distributed over the width of the thread deflecting element. For a uniform distribution of the load introduction it is thereby provided that more than three force application points are present. In that regard, these points can be arranged at the outer ends but also in the center region or area of the thread deflecting element. In that regard, the force application points shall encompass not only geometrically exactly defined points, but rather very generally geometric areas or locations are intended, at which a force transmission between components takes place. These force application locations or force application points are distributed along a line, but do not need to lie exactly on this first line, and can also have a surficial extension or expanse. Thus, it involves geometric locations of which the spacing distances from one another essentially extend in the direction of a common line. The spring forces are applied by at least one spring element. 
     3) Application of a prescribed, positively constrained oscillating motion onto the thread deflecting element, wherein the motion is applied by a drive means via a drive element. 
     Through the application of a prescribed positively constrained oscillating motion, it is achieved that the thread deflection element takes up a defined position at all times in the weaving cycle. During a weaving cycle, the motion also comprises standstills. These standstills, can, for example, be dead center points in which the motion only comes to a standstill at a particular point, in order to then be immediately continued in the opposite direction. Standstill of the motion however may also exist as a rest region, in which the moved element does not change its position for a certain time within a weaving cycle. 
     The application of the spring forces according to method step 2) does not change the motion of the thread deflecting element. There is also no superposition of motions. The method is set up so that the magnitude of the warp thread tension forces and the motion or the position of the thread deflecting element is not determined by the thread forces, but rather is determined only by the application of the prescribed positively constrained oscillation motion by the drive means. 
     An increase of the warp thread tension force due to the motion of the warp threads from the closed shed into the open shed brings about an increase of the forces that are exerted by the warp threads onto the thread deflecting element. In contrast, upon moving the warp threads from the open shed to the closed shed, the forces that are exerted on the thread deflecting element decrease. According to the present invention, these forces support themselves partially via the thread deflecting element on the spring element and partially via the drive element on the drive means. Through the application of the spring forces in addition to the application of the positively constrained oscillating motion onto the thread deflecting element, a support or unloading of the positively constrained drive is achieved. Without this support, the warp thread tension forces that act on the thread deflecting element would be supported via the drive element on the drive means, for example an eccentric drive or an electric motor. Without the spring support, drive elements and drive means would have to be dimensioned considerably larger, which would lead to increased costs. 
     Especially preferably, the spring element comprises an adjustable spring characteristic curve. Due to the adjustability of the spring characteristic curve, an adaptation to various different levels of the warp tensions or warp thread tension forces in various different woven fabrics can be achieved, without having to exchange spring elements for such adaptation. Through the possibility of adapting the spring characteristic curve to various different warp tension levels and/or warp threads with various different elastic behaviors, this also gives rise to a simplification in the layout of the drive means, and particularly if these are controlled electrically or electro-pneumatically. 
     Preferably the thread deflecting element is arranged lying on or adjacent to the at least one spring element, so that the above mentioned partial support of the forces acting on the thread deflecting element can be realized in a simple manner. In other words, the thread deflecting element is advantageously embodied and arranged in such a manner so that it is supported on the at least one spring element. In this regard, the thread deflecting element can lie in contact on the at least one spring element. The supporting arrangement is achieved advantageously via at least one contact surface between the thread deflecting element and the at least one spring element. 
     Especially advantageous is the application of the positively constrained oscillation motion onto the thread deflecting element via several connection points via which the thread deflecting element is connected with the drive element. Most preferably, these connection points are distributed over the width of the thread deflecting element, and thus extend along a second line that extends parallel to the pivot axis. For a uniform distribution of the load introduction it is advantageous in that regard if more than three connection points are present. In that regard, these points can be arranged on the outer ends but also in the central area or region of the thread deflecting element. 
     Regarding the arrangement and distribution of the connection points along the second line, once again very general geometric locations or areas are intended, at which a connection between components occurs. These connection locations or points are distributed along the second line, but do not need to lie exactly on this line, and can also have a surficial extension or expanse. Thus, this involves geometric locations of which the spacing distances from one another extend essentially in the direction of a common, namely the second, line. 
     By means of the drive, a targeted influence of the warp thread tension forces is achieved in a manner that takes into account the weaving technological requirements. 
     For example, as drive means, consideration is given to mechanical transmissions with a non-uniform transmission ratio with eccentric elements or cam discs. 
     However, for an optimal adaptation of the positively constrained oscillating motion of the thread deflecting elements to the required tension force progression it is advantageous if the drive means for the thread deflecting element, for example an electric motor, is electronically controlled, and if the positively constrained oscillating motion of the thread deflecting element is prescribed in an electronically controlled manner by a control unit of the weaving machine via the electric motor or another suitable drive means. 
     Generally that would use the control unit in which also the weave pattern for the motion of the shedding means with the warp threads in the weaving machine is stored. The electronic data set that contains the weave pattern, in addition to the information regarding the sequence of open shed position or closed shed position of the warp threads, can also contain an information regarding the motion sequence of the warp threads on the way from the open shed to the closed shed. This motion pattern of the warp threads is achieved through vertically moved shedding means, for example by heald shafts or heddles, which are driven by a mechanically or electronically controlled dobby or head motion machine, or an eccentric machine. Thus, in the case of an electronically controlled drive means, the motion sequence of the thread deflecting element can be adapted in a targeted manner to the motion sequence of the warp threads, whereby it is possible to achieve an optimal compensation of those oscillations of the warp thread tension forces, which are caused by the change from the open shed to the closed shed. 
     In order to optimally configure this compensation, it can be necessary to apply the positively constrained oscillating motion of the thread deflecting element through the drive means in such a manner so that a dead center point of this motion lies within the weaving cycle at the point at which the majority of the warp threads is located in the closed shed, namely at the shed closure point; or at least closer to the shed closure point than at the point of the reed beat-up. Preferably, this dead center point involves the point or at least the region in the positively constrained oscillating, essentially horizontally extending, motion progression of the thread deflecting element, in which the thread deflecting element has the largest horizontal spacing distance from the weaving reed within a weaving cycle. Here, this dead center point is referred to as the rear dead center point of the motion of the thread deflecting element. 
     The arrangement of the spring element is generally selected so that, within a weaving cycle, this spring element exerts the smallest spring force onto the spring deflecting element at the described rear dead center point of the motion of the thread deflecting element. In that regard, the arrangement of the thread deflecting element and the spring element is selected so that the spring element is tensioned the least in the rear dead center point and the most in the front dead center point. The front dead center point of the oscillating motion of the thread deflecting element is that point or region of the motion at which the thread deflecting element horizontally has the smallest spacing distance from the weaving reed. 
     The motion sequences or progressions coming into consideration here can also comprise, at their dead center points or in the end positions, so-called rest regions in which during the weaving cycle the motion of the thread deflecting elements temporarily comes to a standstill. With the presence of such a rest region, in connection with the present invention, the term dead center point of a motion shall be understood as that point within the motion progression or the motion curve, that lies in the middle or center of such a rest region. In these considerations, rotational speed fluctuations of the drives are not considered, so that the here-intended middle or center of a rest region can thus be geometrically or computationally determined. For example, from a motion curve or table in which the position values of a component (e.g. of the thread deflecting element) are entered over an angular axis with constant step width or interval. In that regard, defining the angular axis uses those angle steps that are carried out by a main drive shaft of the weaving machine over one rotation, namely over 360° rotational angle. 
     Generally the method according to the invention is carried out in such a manner so that a dead center point of the positively constrained oscillating motion lies on the motion curve between the shed closure point and the immediately subsequent reed beat-up point or at one of these points. 
     The dead center point of this motion within a weaving cycle can lie closer to the reed beat-up than the immediately preceding shed closure, or vice versa. 
     Generally the point of the reed beat-up in the weaving cycle lies not long after the point of the closed shed. In the time span between closed shed and reed beat-up, while the warp threads already move in the direction of the open shed, but during that the warp thread tension force does not yet increase significantly. In order to nonetheless achieve a tension force in the warp threads at the reed beat-up, which tension force is necessary for weaving with a high pick density or weft set, in a specific derivation or modification of the above described variant of the method, the rear dead center point of the motion of the thread deflecting element is laid into the region of the reed beat-up; or at least closer to the reed beat-up than the shed closure on the motion curve of the thread deflecting element. 
     In the reed beat-up, the previously inserted weft thread is pushed forward against the interlacing point or fabric edge by the weaving reed of the weaving machine, and there, it is pressed more or less tightly against the already existing fabric. 
     For producing very tight or dense woven fabrics, a high pressure applied by the weaving reed is necessary. In this process, tension force peaks are caused in the warp threads between thread deflecting element and weaving reed. In the described method variant, after the shed closure point, the thread deflecting element is not moved horizontally in the direction toward the weaving reed, that is to say in the direction toward the front dead center point, but rather remains stationary or is even moved in the opposite direction until it has reached its rear dead center point. 
     Through this process it is achieved that the increased warp thread tension force that is necessary for tight dense woven fabrics is present at the reed beat-up. 
     With an exclusively spring-yielding or resilient suspended arrangement of the thread deflecting element, without positively constrained prescribed motion, and with only low masses of the thread deflecting element that is supported at several points over the width of the weaving machine, in this phase of the weaving cycle the warp thread tension force would decrease because the spring element would yield. 
     However, for other types of woven fabrics it can be advantageous if the warp thread tension force is reduced in a defined manner in the region of the reed beat-up. For example, this applies for terry fabrics in which a portion of the warp threads shall be pushed up to form terry loops during the reed beat-up. For this process it is advantageous if during it the tension force in the participating warp threads is reduced in a positively constrained manner. In order to achieve this, in a further modified method variant, during the pushing-up of the terry loops, the thread deflecting element for the participating warp threads can be moved in the direction toward its front dead center point, thus to the position at which the horizontal spacing distance to the weaving reed is the smallest. 
     In a further variant, the method according to the invention additionally offers the possibility, through the control unit of the weaving machine via the electronically controllable drive means, to differently prescribe the positively constrained oscillating motion of the thread deflecting element according to the weave pattern for various different weaving cycles. Through the weave pattern it is determined which shedding means with the warp threads guided therein will go into the upper shed in the next weaving cycle, and which will go into the lower shed. Only for a pure plain weave (1:1) are all warp threads always in motion during a weaving cycle, that is to say all warp threads go either into the upper shed or into the slower shed. In other weave patterns, a portion of the warp threads remains without motion in the upper shed or the lower shed during the complete weaving cycle. Here, the term weaving cycle is understood as the functional sequence of the weaving machine from one beat-up of the weaving reed until the next beat-up of the weaving reed against the fabric edge. 
     In most cases, all warp threads participating in the weaving process are drawn off from only one single warp beam and are deflected into the weaving plane over a single thread deflecting element. In the normal weaving process, a portion of the warp threads is located in the lower shed in one weaving cycle, then changes through the closed shed into the upper shed and is located in the upper shed in the following weaving cycle. Another portion of the warp threads is analogously moved in the opposite direction, that is to say this portion of the warp threads is located in the upper shed in one weaving cycle, then changes through the closed shed into the lower shed, and is located in the lower shed during the following weaving cycle. 
     Here the term upper shed refers to the course of the warp thread sheet that upwardly bounds the loom shed, while the warp threads in the lower shed downwardly bound the loom shed. The term closed shed position or shed closure refers to the point of the motion curve at which the warp threads coming from the top or respectively from the bottom encounter one another. At this encountering, for a short time in the weaving cycle, the vertical interspace, i.e. the loom shed, between the participating warp thread sheets is closed. The interspace between the warp threads that are not moved in the current weaving cycle, but rather remain stationary in the upper shed or lower shed, is not closed. For these warp threads, no shed change takes place, that is to say no closed shed position is run through. Depending on whether only some or all warp threads of the weaving machine run through the closed shed position within a weaving cycle, this gives rise to different requirements for the compensation of the tension force variations in the total sheet of the warp threads that are deflected over the thread deflecting element. 
     With a positively constrained, oscillatingly-driven thread deflecting element it is therefore advantageous, if the prescribed motion can be adapted to the alternating tension force relationships for various different binding or weave patterns; that is to say if the positively constrained oscillating motion of the thread deflecting element can be differently prescribed according to the weave pattern for various different weaving cycles. 
     Furthermore, for the realization of the invention it is suitable or sensible to embody the amplitudes and the positions of the dead center points of the prescribed oscillating motion of the thread deflecting element in an electronically and/or mechanically adjustable manner. 
     An apparatus or device for carrying out the method according to the invention comprises a thread deflecting element that is supported pivotably about a pivot axis. Moreover, at least one spring element is present, whereby spring forces can be applied onto the thread deflecting element through the spring element at more than three force application points. In that regard, the force application points lie along a first line, which extends parallel to the pivot axis of the thread deflecting element. 
     Furthermore a drive means is provided, and a drive element. For example, a gear transmission and/or an electric motor can be utilized as the drive means. However, hydraulically or pneumatically acting drive means are also utilizable. A drive shaft with a lever arm or other drive elements with which oscillating pivoting motions can be transmitted or produced, for example, serve as drive elements. In any event, drive means and drive element are embodied in such a manner so that a prescribed positively constrained oscillating motion can be applied onto the thread deflecting element by the drive means via the drive element. That means, that in the transmission path of the motion between the drive means and the thread deflecting element, no transmission or connecting elements are present, which falsify the prescribed motion sequence of the thread deflecting element or change it in an unforeseen manner. A transmission of this prescribed positively constrained oscillating motion via elastic elements, for example via leaf springs on which the thread deflecting element is secured, would lead to such a falsification or to a superposition of the targeted prescribed motion with a different motion that is determined by the adjustedly set spring characteristic curve and the current actual warp thread tension force, which is undesired in the scope of the invention. 
     By means of the invention, the forces on the thread deflecting element can be braced or supported partially via the thread deflecting element on the at least one spring element and partially via the drive element on the drive means. 
     Preferably a contact surface, which is in contact with the at least one spring element, is present on the thread deflecting element. Hereby, the thread deflecting element lies in contact on the spring element via the mentioned contact surface. Then the spring forces are applied to the thread deflecting element via the contact surface. Hereby the inventive partial support of the forces acting on the thread deflecting element can be realized in a simple manner. 
     For realizing the mentioned advantageous contact of the thread deflecting element on the at least one spring element, these elements preferably are embodied as independent components. 
     In an advantageous variant, the drive element is connected with the thread deflecting element at more than three connection points along a second line, whereby the second line extends parallel to the pivot axis. Regarding the arrangement and distribution of the force application points and the connection points along the first or second line, that which has been explained above once again pertains. Very generally, geometrical locations are intended, at which a force transmission or connection between components is achieved. These locations or points are distributed along the first or the second line, but do not need to lie exactly on the respective line and can also have a surficial extension or expanse. Thus, this relates to geometric locations of which the spacing distances from one another extend essentially in the direction of the applicable virtual line. 
     The described type of the connection between thread deflecting element and drive element leads to the result that the prescribed positively constrained oscillating motion is transmitted onto the thread deflecting element, not only to the right and to the left of the thread deflecting element, thus outside of the warp thread sheet, but rather extending over the width of the warp thread sheet or of the thread deflecting element also at positions within or below the warp thread sheet. The introduction of the motions and spring forces distributed along the first and second line reduces the deformation of the thread deflecting element, because the forces are distributed better. The reduced deformation contributes to the result that the positively constrained oscillating motion of the thread deflecting element deviates only slightly from the prescribed motion. 
     Especially preferably, the spring characteristic curve of the spring element is adjustable. In order to apply the spring forces onto the thread deflecting element uniformly over the width of the warp thread sheet in the described manner, it is advantageous in this regard, if the spring element is embodied as a gas-filled hollow body, of which the volume is elastically variable or changeable, wherein the spring characteristic curve is adjustable in that the pressure in the gas is varied or changed. For example, the hollow body can be embodied as an air-filled rubber hose or elongated pressure cushion, of which the longitudinal axis extends over the width of the warp thread sheet or of the thread deflecting element. 
     However, it is also possible to use leaf springs distributed over the width of the thread deflecting element, in order to apply the spring forces onto the thread deflecting element. Through arrangements or devices with which the respective effective length of such a leaf spring can be changed, thereby an adjustability of the spring characteristic curve is achieved also in this embodiment variant. 
     The spring deflecting element itself can, for example, be embodied as a profile member with a longitudinal axis, whereby the longitudinal axis extends parallel to the pivot axis. 
     For the deflecting of the warp threads it is further advantageous if the thread deflecting element comprises a curved deflecting surface that extends parallel to the pivot axis at a first spacing distance from the pivot axis. 
     Furthermore, the thread deflecting element can comprise one or more contact surfaces, via which, for example through a gas-filled hollow body or by means of leaf springs, the spring forces can be applied onto the thread deflecting element. In that regard, the contact surfaces extend parallel to the pivot axis at a second spacing distance from the pivot axis, whereby the second spacing distance is smaller than the first spacing distance. Through this arrangement it is achieved that the spring forces between pivot axis and contact surface are applied on the thread deflecting element. 
     A further embodiment of the apparatus is characterized in that the drive element is embodied as a drive axle of which the longitudinal axis coincides with the virtual pivot axis, whereby the thread deflecting element is secured on the drive axle, as mentioned above, via several connection points. 
     A weaving machine with an apparatus according to the invention is equipped with adjusting means with which the dead center points of the positively constrained oscillating motion of the thread deflecting element are adjustable. These adjusting means can be of a mechanical or electronic type. 
     With a mechanical adjustment, for example a cam disc or an eccentric disc is released from the associated drive shaft, and is then connected again with the drive shaft in the running direction or contrary to the running direction. If the drive means for the thread deflecting element is electronically controllable, it is suitable if the weaving machine includes a control unit in which data for the prescribing of the positively constrained oscillating motion of the thread deflecting element can be calculated or computed with the aid of processor means and/or can be stored in memory means. Thereby, various different dead center points of the positively constrained oscillating motion can also be prescribed. 
     Many weaving machines comprise shedding means and a control unit, so that the warp threads are movable by the shedding means according to a weave pattern stored in the control unit. 
     For equipping such a weaving machine with an apparatus according to the invention, a control unit is provided, which comprises processor means through which the positively constrained oscillating motion progressions of the thread deflecting element can be calculated or computed dependent on the respective weave pattern. In this manner, a program-controlled adaptation of this motion to the various different weave types and binding patterns can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematic illustration of a side view of a weaving machine with an embodiment of the apparatus or device according to the invention; 
         FIG. 2  section, detail view from  FIG. 1 ; 
         FIG. 3  view of the weaving machine according to  FIG. 1  from the rear; 
         FIG. 4  motion progressions and progressions of the warp thread tension force on a weaving machine when carrying out an embodiment of the method according to the invention; and 
         FIG. 5  motion progressions and progressions of the warp thread tension force on a weaving machine when carrying out a further embodiment of the method according to the invention. 
     
    
    
     ADVANTAGEOUS EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows the side view of a weaving machine with an embodiment of the apparatus according to the invention;  FIG. 2  shows a cut-out portion thereof. 
     On its rear side, the weaving machine comprises a warp beam  22  from which the warp threads  1  are drawn off. In the present example, the warp threads  1  are guided over a deflecting pipe  28  to the thread deflecting element  2 . The warp threads  1  are deflected out of the drawing-off direction into the weaving plane by the thread deflecting element  2 . In the present example, for monitoring the warp threads  1 , there is provided a warp stop motion device  24 , which limits the vertical motion of the warp threads in the rear shed, namely between shedding means  11  and warp beam  22 , yet does not hinder the horizontal motion of the warp threads. 
     In the weaving plane, the warp threads  1 ,  1 ′ are guided through shedding means  11 ,  11 ′ and a weaving reed  27  into the front region of the weaving machine. The warp threads  1 ,  1 ′ are moved vertically by the shedding means  11 ,  11 ′, whereby a loom shed  23  is formed of the warp threads of the upper shed  1  and of the lower shed  1 ′. 
     The motion of the shedding means  11 ,  11 ′ is derived from a weave pattern that is stored in the control unit  16  of the weaving machine. On the front side of the weaving machine, the woven fabric is again deflected and rolled up. The weft thread  25  is inserted into the loom shed  23  between the weaving reed  27  and the fabric edge  26 , and is beat-up or pressed against the fabric edge  26  by the weaving reed  27  upon the reed beat-up. The thread deflecting element  2  is arranged pivotably about a pivot axis  3 . The pivot axis  3  is embodied as a drive axle  8 , which is driven by a drive unit  7  of an electric motor and a coaxially arranged transmission. The electric motor is electronically controlled by the control unit  16 . The control unit  16  contains a control program and memory means for the calculation or computation and/or the storing of the data for the positively constrained oscillating motion  38  of the thread deflecting element  2 . 
       FIG. 2  shows that the thread deflecting element  2  comprises a carrier  19 , via which it is secured on a machined surface of the drive axle  8  with the aid of screws  20 . Moreover, the thread deflecting element  2  has a curved deflecting surface  14  over which the warp threads  1  are deflected from the warp beam  22  or from the deflecting pipe  28  into the weaving plane. Moreover, a contact surface  15  is present on the thread deflecting element  2 , which surface is in contact with a spring element  4 . In this regard, the thread deflecting element  2  lies on the spring element  4  via the mentioned contact surface  15 . The spring forces are applied onto the thread deflecting element  2  via the contact surface  15 . The spring element  4  is embodied as a gas-filled hollow body, which is arranged between the contact surface  15  and a transverse carrier or cross beam  18  of the weaving machine frame  17 , wherein the cross beam  18  extends parallel to the pivot axis  3 . The spring forces are thus applied onto the thread deflecting element  2  via a plurality of force application points  5 , wherein the force application points  5  extend along a virtual line  6  on the contact surface  15 , which line  6  extends parallel to the pivot axis  3 . In the present example, the hollow body  4  is an elastic hose, of which the volume is changeable by changing the gas pressure. Presently, a further carrier profile, which partially surrounds the elastic hose  4 , is arranged between the elastic hose  4  and the cross beam  18 . On one side the carrier profile for the hose  4  is secured on the cross beam  18  of the weaving machine frame  17 , and on the other side it is secured on the bearing housings  21  of the drive axle  8 . The bearing housings  21  of the drive axle  8  are braced or supported on a stationary component of the machine frame  17  of the weaving machine. In the present case, also the deflecting pipe  28  is secured on this component. 
     Through the varying or changing of the gas pressure in the elastic hose, i.e. the spring element  4 , the spring constant thereof is changed, so that the spring characteristic curve of the spring element  4  is adjustable. That means that the relationship between the spring force and the spring travel or displacement is adjusted by changing the gas pressure. A pneumatic valve with a pressure measuring device or pressure gage is provided for changing the gas pressure. Presently, the valve is connected to a central compressed air supply, which is not shown. The pneumatic valve and the pressure gage have the function of a pressure source for compressed air as the gas filling  12  for the elastic hollow body. The pressure source is schematically illustrated in  FIG. 1  as a compact structural unit  13 . 
       FIG. 3  shows the view of a weaving machine according to  FIGS. 1 and 2  from the warp beam side. In this illustration, the warp threads  1  are omitted in order to keep the view onto the details of the thread deflecting element  2  clear. Furthermore in this illustration, the area of the weaving machine below the warp beam axis is cut off. The carrier  19  of the thread deflecting element  2  is connected with the drive axle  8  at several connection points  9  via the screws  20 . The drive axle  8  is supported, at several places over the width, in bearings on the machine frame  17 . In order to provide space for the housings  21  of these bearings, the carrier  19  of the thread deflecting element  2  comprises a cut-out opening at each bearing housing  21  of the drive axle  8 . Over the width of the weaving machine, the connection points  9  are arranged along a virtual line  10 , which extends parallel to the drive axle  8 . It is clear that small deviations of the position of the screws  20  in the vertical direction have no influence on the described function. Rather, it is significant that the screws  20 , that is to say the connection points  9 , are distributed over the width of the thread deflecting element  2  or of the weaving machine along the line  10  in such a manner so that the drive forces are applied onto the thread deflecting element  2  distributed over the width of the weaving machine. The spacing distances of the connection points  9  or of the screws  20  relative to one another in a direction parallel to the pivot axis  3  are larger than the spacing distances in a direction perpendicular to the pivot axis  3 . That avoids deformations that could occur with a one-sided application of the drive forces. This is supported by a distribution of the bearing housings  21  over the width of the weaving machine. 
       FIG. 3  further shows that the drive unit  7  is mounted on the end face of the drive axle  8 . Motor and transmission of the drive unit and the drive axle  8  are arranged coaxially. In this manner, the oscillatingly applied motor torque is transmitted in a substantially loss-free manner onto the drive axle  8 . The structural unit  7  of electric motor and transmission is secured via a motor carrier on the side wall of the machine frame  17 . 
       FIGS. 4 and 5  show examples for prescribed motion progressions  38  and the progressions of tension forces in the warp threads  1 ,  1 ′ resulting therefrom, on a weaving machine during the performance of the method according of the present invention. 
       FIGS. 4 and 5  differ from one another in that the rear dead center points  39 ,  39 ′ of the positively constrained oscillating motion of the thread deflecting element  2  are differently prescribed in both Figures. 
     In order to obtain a persuasive illustration, in the diagrams of  FIGS. 4 and 5 , the motion progression  30 ,  32 ,  33 ,  38  are illustrated in a normalized form. That is to say, the amplitude of the respective motion progression  30 ,  32 ,  33 ,  38  between maximum value and minimum value has respectively been normalized to 1. The axis interval or division of the ordinate axis of the illustrated diagrams is oriented to this normalization. 
     On the abscissa, angle values from 0 to 720 angular degrees are illustrated. These angle values refer to the rotational angle of a main drive shaft of the weaving machine, which is rotated further by 360 angular degrees, i.e. by one rotation, during one weaving cycle. Thus, the diagrams show a cut-out portion over two weaving cycles of the weaving machine=720 angular degrees. 
     Both  FIGS. 4, 5  show the same motion progression  30  of the weaving reed  27 , which is characterized by reed beat-up points  31  respectively at 0 degrees, at 360 angular degrees and at 720 angular degrees. 
     In the rest areas or regions lying therebetween, the weaving reed  27  is located in the rest position, thus in the proximity of the shedding means  11  on the weaving machine (see  FIG. 1 ). At this time the shedding means  11 ,  11 ′, for example heald shafts  11 ,  11 ′, are located in the upper shed or in the lower shed. One refers to that as open shed. At this time, a weft insertion is carried out. 
     The diagrams further show the motion progression  32 ,  33  of two heald shafts  11 ,  11 ′ that are moved opposite one another into the upper shed (+ 0 . 5 ) or into the lower shed (− 0 . 5 ). Such a shed change is characterized in that the participating heald shafts  11 ,  11 ′ and the warp threads  1 ,  1 ′ moved by these heald shafts change the position, namely from the top to the bottom or from the bottom to the top, not within one weaving cycle, but rather between two successive weaving cycles. The point at which both heald shafts  11 ,  11 ′ encounter one another on their way or path, is referred to as the shed closure point, shed closure, or closed shed  34 . In the diagrams of the  FIGS. 4 and 5 , the shed closure  34  lies approximately at 320 angular degrees, thus shortly before the reed beat-up point  31 . At this location, the motion progressions  32  and  33  of the two heald shafts  11 ,  11 ′ run through the value 0.0 on the ordinate axis. 
     A progression of the warp thread tension forces  35  that arises solely from such an oppositely running motion  32 ,  33  of the two heald shafts  11 ,  11 ′ is illustrated with a dash-dotted line in the  FIGS. 4 and 5 . The maximum of the warp thread tension forces  35  arises in the open shed, while the minimum arises in the closed shed  34 . This progression of the warp thread tension forces  35  represents the progression that would result if the thread deflecting element  22  were connected immovably or stationarily with the machine frame  17 , i.e. so-called rigid backrest or whip roll. Thus, the warp thread tension force progression  35  results solely from the geometric variations or changes of the running course of the warp threads  1 ,  1 ′ on their way or path from the upper shed into the lower shed (compare  FIG. 1 ) and from the stiffness of the warp threads  1 , thus the capability of the warp threads  1  to compensate tension force variations through the elasticity of the warp threads themselves. 
     This elastic compensation is supported by the provision of a spring  4  on the thread deflecting element  2 ; the warp threads  1  are less strongly loaded. In the  FIGS. 4 and 5 , the warp thread tension force progression  36  is illustrated with a dotted line, which would result with a spring-yielding support of the thread deflecting element  2 . In comparison with the tension force progression for a “rigid backrest or whip roll”  35 , one can recognize that the warp thread tension force  36  increases less strongly during the motion  32 ,  33  of the heald shafts  11 ,  11 ′ from the closed shed to the open shed. That is caused by the fact that, with increasing warp thread tension force  36 , the spring-yielding supported thread deflecting element  2  is increasingly loaded by the warp threads  1  running over it. The spring  4  is compressed and the thread deflecting element  2  moves in the direction toward the weaving reed  27 . Thereby the warp thread tension force  36  is reduced. This reduction is desired in principle, in order to limit the maximum arising warp thread tension force. That this is achieved, becomes clear by comparing the progressions  35 ,  36 . However, by use of a spring-yielding supported backrest or whip roll, or thread deflecting element  2 , the warp thread tension force  36  is reduced already in the region or range of the reed beat-up  31 . This can be undesirable in terms of weaving technology, if especially tight or dense woven fabrics, i.e. woven fabrics with a high weft set, are to be woven. 
     That can be counteracted through the use of a prescribed oscillating motion  38  of the thread deflecting element. 
     The prescribed oscillating motion progression  38  of the thread deflecting element  2  is illustrated as a sinusoidal function in both Figures. This is a function that is very easy to realize. Through corresponding programming of the control unit  16  for the control of the drive unit  7 , of course also more-complex motion progressions  38  can be realized, for example such with unsymmetrical progression or with rest phases. In the present example, a symmetrical progression of the oscillating motion  38  without rest phases is prescribed. The motion  38  has two dead center points, the dead center point  39  at the value 0.0 on the ordinate axis, the dead center point  40  at the value −1.0. The dead center point  39  (or  39 ′ in  FIG. 5 ) at 0.0 presently represents the rearmost position of the motion  38  of the thread deflecting element  2 . In this position, the thread deflecting element  2  has the largest spacing distance from the weaving reed  27 , while in the other front dead center point  40  it has the smallest spacing distance from the weaving read  27 . 
     Through a reduction of the spacing distance of the thread deflecting element  2  relative to the weaving reed  27 , the warp thread tension forces  35 ,  36 ,  37  are reduced, while they are increased by an enlargement of the spacing distance. 
     As set forth above, it can be necessary to produce a higher warp thread tension force in the region or range of the reed beat-up  31 , than is achieved with a spring-yielding supported thread deflecting element  2 . On the other hand, one wishes to avoid that the warp thread tension forces become so high in the open shed as occurs with use of a rigid unsprung backrest or whip roll. This goal is achieved through the application, onto the thread deflecting element  2 , of a sinusoidal oscillating motion  38  with a dead center point  39  in the vicinity of the shed closure  34  and the other dead center point  40  in the open shed. This becomes clear in the progression of the warp thread tension force  37  that results due to the above described positively constrained oscillating motion  38  of the thread deflecting element  2 . The comparison of the progressions  36  and  37  in  FIG. 4  makes this clear. Already here, one sees that the progression of the warp thread tension force  37 , which arises from the prescribed oscillating motion  38  of the thread deflecting element  2 , is higher at the reed beat-up  31  than the tension force progression  36  for only a spring-yielding support of the thread deflecting element  2 . This effect can be further strengthened if the rear dead center point  39  of the prescribed oscillating motion  38  of the thread deflecting element  2  is positioned at a time point that is located between the shed closure time point  34  and the reed beat-up  31 , or is even closer to the reed beat-up  31  than the shed closure time point  34 . 
     In  FIG. 5  it is illustrated, how the relationships change relative to  FIG. 4 , if the rear dead center point  39 ′ of the prescribed oscillating motion  38  of the thread deflecting element  2  lies at 350 angular degrees, i.e. after the shed closure  34  in the vicinity of the reed beat-up  31 . One can see that at the reed beat-up point  31 , the warp thread tension forces  37 ′ have been further increased in comparison to the progression  37  in  FIG. 4 . One also sees, however, that in the warp thread tension force progression  37 ′, the maximum warp thread tension forces in the open shed nonetheless do not become higher than with the exclusive use of a spring-yielding supported thread deflecting element (progression  36 ) and significantly lower than with a stationary thread deflecting element (progression  35 ). 
     Because, according to the invention, the thread deflecting element  2  is additionally spring-yieldingly or resiliently supported, a reduction of the loading of the drive means  7  results from the difference between the two curves  37  and  36  in  FIG. 4  or  FIG. 5 . 
     As already mentioned above, here only normalized motion progressions  30 ,  32 ,  33 ,  38  are illustrated. Of course, the actual motion amplitudes and the actual geometric positions of the dead center points  39 ,  40  of the motion  38  of the thread deflecting element  2  must be adapted to the actual amplitudes of the motions  32 ,  33  of the shedding means  11  as well as to the geometric relationships in the loom shed  23 . For that it is suitable to embody the amplitudes and the positions of the dead center points  39 ,  40  to be electronically and/or mechanically adjustable. 
     In the above considerations, it was not taken into account that during the reed beat-up  31  when pressing the inserted weft thread  25  against the fabric edge  26 , a sudden pulse-like increase of the warp tension can arise. The magnitude and duration of this pulse is dependent on the textile-technical behavior of warp and weft threads. These connections and dependencies are, however, understood by the skilled artisan, so that the consideration thereof in the realization of the invention does not cause any problems. 
     Through the utilization of the method according to the invention and the apparatus according to the invention, it is made possible to carry out weaving with high weft set without impermissible increase of the warp thread tension force  37  with a relatively low loading of the drive means  7  for the thread deflecting element  2 . 
     REFERENCE NUMBERS 
       1 ,  1 ′ Warp threads in the upper shed or lower shed 
       2  Thread deflecting element 
       3  Pivot axis 
       4  Spring element 
       5  Force application points 
       6  First line 
       7  Drive unit 
       8  Drive axle 
       9  Connection points 
       10  Second line 
       11 ,  11 ′ Shedding means 
       12  Gas filling 
       13  Pressure source 
       14  Curved deflecting surface 
       15  Contact surface 
       16  Control unit 
       17  Machine frame 
       18  Cross-beam or transverse carrier 
       19  Carrier of the thread deflecting element 
       20  Screws 
       21  Bearing housing 
       22  Warp beam 
       23  Loom shed 
       24  Warp stop motion device 
       25  Weft thread 
       26  Fabric edge 
       27  Weaving reed 
       28  Deflecting pipe 
       30  Motion progression of weaving reed 
       31  Reed beat-up point 
       32  Motion progression of heald frame  1   
       33  Motion progression of heald frame  2   
       34  Shed closure point 
       35 , 36 , Progression of warp thread tension forces 
       37 , 37 ′ 
       38  Motion progression of thread deflection element 
       39 ,  39 ′ Rear dead center point of motion of thread deflecting element 
       40  Front dead center point of motion of thread deflecting element