Patent Publication Number: US-2007119142-A1

Title: Thread control device for a textile machine, in particular for a shedding device

Description:
TECHNICAL FIELD  
      The invention relates to a thread control device for a textile machine, in particular for a shedding device, according to the preamble of claim  1 .  
     PRIOR ART  
      Large numbers of thread control devices for textile machines are known. The nearest prior art according to WO 97/08373 discloses a thread control device which is designed with a drive and with a return device for a thread guide member. The thread guide member is in this case moveable in one direction of movement by means of the positively designed drive and in the opposite direction of movement by means of a nonpositive and pneumatically designed return device acting counter to the positive drive.  
      The pneumatic return device has a cylinder/piston assembly, the cylinder chamber of which is designed with an excess pressure valve and with a non-return valve which is connected to a compressed gas source. The gas pressure in the cylinder chamber is in this case set as a function of the operating state of the textile machine. For example, in a creep-speed phase, the gas pressure is kept lower than in a high-speed phase, so that the electric motor can furnish the necessary power for overcoming the load occurring as a result of the compression of the cylinder chamber. In a high-speed phase, the electric motor delivers sufficient power, so that the gas pressure can be increased further in order to prevent a roller on a cam disk of the positive drive from lifting off. Furthermore, the cylinder chamber may be designed with a manually actuable pressure relief valve, in order, when the textile machine is being set up, to minimize the resistance occurring as a result of the compression in the cylinder chamber.  
      The above solution has the disadvantage that the gas pressure in the cylinder chamber has to be adapted to a respective operating state. This necessitates a complicated pressure control device for setting the gas pressure of the cylinder chamber, which requires pressure reducing valves and opening valves for activating each cylinder chamber. Moreover, a complicated electronic control of the valves is necessary in order to adapt the pressure in the cylinder chambers to a respective operating state.  
      To lubricate the cylinder/piston assembly, oil drops onto the piston, for example from above, and, due to hydrodynamic effects, enters the cylinder chamber despite a permanent excess pressure in the latter. The oil which has accumulated in the cylinder chamber may persistently disrupt the operation of the thread control device, since it reduces the air volume in the cylinder chamber to an indeterminate level, thus leading, during operation, to higher incalculable compression pressures in the chamber. In an extreme case where a large part of the cylinder chamber is filled with oil, it is no longer possible for the cylinder to move and further operation of the textile machine would lead to considerable damage.  
      In an improved embodiment of the pneumatic return device described in WO 97/08373, therefore, the valve is designed in such a way that oil separation is also possible in addition to the requirements of stationary operation. The valve is in this case actuated at regular time intervals for a few seconds so as to cause the oil which has accumulated in the compression space to flow out. So that a lifting off of the roller from the eccentric of the positive drive is avoided, the rotational speed of the textile machine has to be reduced during this action (what is known as the care cycle). At creep speed, said valve is likewise opened, so that the pressure in the cylinder chamber does not rise appreciably above the feed pressure. The required power of the motor is thereby reduced, which is necessary so that the main motor can rotate at low rotational speeds and therefore manual rotation on the hand wheel is possible without excessive effort.  
      The disadvantage of the above solution is the high outlay for the electrical/pneumatic activation of the valve. The entire control of the pneumatic drive of the thread control device therefore has a large number of components, such as non-return valves, excess pressure valves, pressure reducing valves, and also electronic control units which make the system more susceptible to faults. Moreover, the efficiency of the textile machine is reduced as a result of the repetitive lowering of the motor rotational speed in order to discharge the lubricating oil, this lowering taking place every  15  minutes. Furthermore, this lowering of the motor rotational speed may have an adverse influence on weaving quality, for example may lead to a slight change in the width of the cloth web produced.  
     PRESENTATION OF THE INVENTION  
      The object of the invention is to improve a thread control device of the type that has been mentioned initially.  
      The set object is achieved by means of the characterizing features of claim  1 . Since the valve has a first valve seat connected to a cylinder chamber, and has a second valve seat, between which a valve member provided with at least one throttle point and prestressed against the first valve seat by means of a spring is moveable, the throttle point being inactive and the valve member shutting off communication with the compressed gas source when the valve member is against the second valve seat, the valve can operate in various operating states without external activation. Furthermore, reliable oil separation is ensured, without additional measures, by the independently operating valve, without a lowering of the rotational speed, a reduction of the maximum compression pressure in the cylinder chamber under part load and a lowering of the compression pressure to the feed pressure at creep speed.  
      Advantageous refinements of the invention are described in claims  2  to  19 .  
      In principle, the most diverse embodiments to the valve designed with two valve seats may be envisaged. A refinement as claimed in claims  2  and  3  is advantageous, according to which the housing has two parts, one part having at one end the first valve seat and the other part being designed as a closing-off part of the housing with a second valve seat and with a passage duct. The valve therefore has as simple a construction as possible, which allows cost-effective production and simple assembly of the valve.  
      The valve housing may, in principle, have various forms, a cylindrical design of the housing according to claim  4  being advantageous. This design allows a good guidance of the piston-like valve member in the housing. Moreover, the piston-like valve member may be provided with a sealing ring in order to seal off the cylinder chamber outwardly. In the version according to claim  4 , it is advantageous to design the throttle points as throttle orifices formed on the valve member. According to claim  5 , it is also conceivable to design the valve member without a sealing ring, in which case a gap between the valve member and the housing wall may serve as a throttle point.  
      The valve may be arranged in a connecting line between the cylinder chamber and the feed pressure chamber. However, a direct arrangement in the cylinder of the cylinder/piston assembly according to claim  6  is advantageous. Furthermore, according to claim  7 , it is advantageous to arrange the valve at a lowermost point of the cylinder. The valve can thus communicate directly with the cylinder chamber, and lubricating oil which has accumulated in the cylinder chamber can thus be led along a short path through the valve into the feed pressure chamber. Correspondingly, the closing-off part of the valve is connected directly to the feed pressure chamber according to claim  8 , in order, again, to minimize the flow resistance and the flow path of the out-flowing oil.  
      The feed pressure chamber may, in principle, be of any desired design. A design as claimed in claims  9  to  12  is advantageous, according to which the feed pressure chamber may be designed with an oil separation outlet arranged at its bottom and according to which a connection for compressed air may be arranged, at a distance from the bottom of the feed pressure chamber, on a lateral wall. This arrangement of a compressed air connection and oil separation outlet prevents oil which has accumulated in the feed pressure chamber from blocking the compressed air connection or from flowing in in a connecting line of the compressed air connection. In principle, any return device may have a separate feed pressure chamber. It is advantageous, however, according to claim  12 , to connect a plurality of return devices to one feed pressure chamber. A simple construction with only one connection for compressed air and with only one oil separation outlet for a plurality of return devices is thereby possible.  
      In principle, the most diverse designs of the pneumatic return device according to the invention may be envisaged. In claims  13  to  16 , a particularly simple design of the valve is described, in which, in conjunction with claims  5  and  6 , the valve may be arranged at a lower point of the cylinder chamber of the cylinder/piston assembly. According to claim  13 , a lower portion of the cylinder may serve as a housing for the valve. The valve space may advantageously be delimited by the cylinder inner face, by a closing-off part closing off the cylinder chamber and by a valve member and be connected directly to a compressed gas source via a connection arranged on the cylinder wall. A first valve seat for the valve member may be formed, according to claim  14 , on an annular stop. According to claim  15 , a second valve seat may be formed on a sleeve part of the closing-off part. When the valve member moves against the second valve seat, the communication of the cylinder chamber with the compressed gas source is shut off and the throttle points on the valve member become inactive. Moreover, it is particularly advantageous, according to claim  16 , to arrange an oil separation outlet directly on the closing-off part.  
      The valve is activated as soon as the pressure in the feed pressure chamber overshoots the switching pressure. The latter depends both on the pressure in the feed pressure chamber and on the prestressing force of the spring. A refinement as claimed in claims  17  and  18  is advantageous, according to which the prestressing force can be set from outside, for example, via a screw.  
      The maximum compression pressure of the valve can be set, according to claim  19 , by means of the flow cross section of the throttle point. If a higher compression pressure is required, the flow cross section of the throttle point is reduced. Owing to the smaller throttle area, communication between the cylinder chamber and the compressed gas source is interrupted earlier, thus achieving a higher maximum compression pressure.  
      By means of the versions according to claims  17  to  19 , the switching pressure and the maximum compression pressure in the cylinder chamber can be set in a simple way. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Exemplary embodiments of the thread control device of the invention are described in more detail below, for a needle-type ribbon weaving machine, by means of the drawings, in which:  
       FIG. 1  shows a needle-type ribbon weaving machine in a side view;  
       FIG. 2  shows a healed frame device with pneumatic return device in a view transverse to the running direction of the warp threads;  
       FIG. 3  shows the pneumatic return device illustrated in  FIG. 2  as a detail and on a larger scale in the basic position;  
       FIG. 4  shows the pneumatic return device illustrated in  FIG. 3  in the compression position;  
       FIG. 5  shows a further exemplary embodiment of a pneumatic return device on a larger scale;  
       FIG. 6  shows the pneumatic return device illustrated in  FIG. 5  in the compression position;  
       FIG. 7   a  shows pressure and piston profiles of the pneumatic return device according to the invention at creep speed;  
       FIG. 7   b  shows pressure and piston profiles of the pneumatic return device under part load; and  
       FIG. 7   c  shows pressure and piston profiles of the pneumatic return device under full load. 
    
    
     WAYS OF IMPLEMENTING THE INVENTION  
       FIG. 1  shows a needle-type ribbon weaving machine with a machine stand  2 , in which is mounted a main drive shaft  4  which drives at least one weft needle  6 , not described in any more detail, a reed  7 , a cloth take-up  8  and a thread control device formed as a healed frame device  10 . The needle-type ribbon weaving machine has a warp beam stand  12  carrying warp beams  14 , from which warp threads  16  are supplied to the healed frame device  10  which opens the warp threads to form a shed  18 . By means of a thread supply device  20 , a weft thread  24  is supplied from a thread bobbin  22  to the weft needle  6  which introduces a weft thread loop into the shed  18 . Successive weft thread loops can be tied off with themselves or by means of a tucking thread  26  which is supplied via a further thread supply device  28  to a knitting needle, not illustrated in any more detail here, in order to tie off and secure an inserted weft thread loop.  
       FIG. 2  shows the healed frame device  10 , in which a plurality of healed frames  30  with thread guide members  31  are connected in each case by means of a link  32 , on the one hand, via a positive drive  35 , to a cam drive  34  and, on the other hand, to a pneumatic return device  36 . The cam drive  34  has pivoting levers  38  which cooperate at a drive point  40  with cams  42  of a camshaft  44 . At the output point  46 , the pivoting levers  38  are articulated on the links  32  via joints  48 . The pivot axes defined by the joints  48  run at right angles with respect to the planes spanned by the healed frames  30 . The distances A of the pivoting levers  38  of the drive points  40  from the respective pivot axes  50  are different between adjacent pivoting levers, the distances B of the output points  46  from the fixed pivot axes  50  also being different, such that, overall, the healed frames are displaceable over extents of different size, in order to form a shed continuously widening and narrowing again, as may be gathered from  FIG. 1 . The pneumatic return device  36  is formed by a cylinder chamber  52 , in which a piston  54  is displaceable, which is connected to the link  32 , in order to compress the piston positively at the working frequency of the cam drive  34 . The cylinder chamber  52  is connected to a valve  56 . The latter is preceded by a feed pressure chamber  58 , via which a compressed gas source  60  is connected, in order to maintain the gas pressure in the cylinder chamber  52 .  
       FIG. 3  and  FIG. 4  show the pneumatic return device on a larger scale during a compression action. In this case,  FIG. 3  illustrates the piston  54  at a top dead center  66 , and  FIG. 4  illustrates the piston  54  at a bottom dead center  68  in a cylinder  64  after compression. The valve housing consists of two parts, a sleeve-like housing  70  with a first valve seat  72 , formed at one end and connected to the cylinder chamber  52 , and a closing-off part  74  which has a second valve seat  76  and a passage duct  78 . The latter is connected to the feed pressure chamber  58 . A valve member  82  provided with throttle points  80  is arranged moveably between the valve seats.  
      In the initial state shown in  FIG. 3 , the valve member  82  is prestressed against the first valve seat  72  by means of the prestressing force of the spring  84 , so that the cylinder chamber  52  and the feed pressure chamber  58  are in communicating connection with one another via the throttle points  80  in the valve member  82  and the passage duct  78  of the closing-off part  74 . In the case of a high pressure in the cylinder chamber  52 , the valve member  82  moves against the second valve seat  76  and interrupts communication between the cylinder chamber  52  and the feed pressure chamber  58 , as illustrated in  FIG. 4 . The throttle points  80  are inactive in this position.  
      The compression/expansion action of the cylinder/piston assembly is described below by means of  FIGS. 3 and 4  and in conjunction with the graphs of  FIGS. 7   a ,  7   b  and  7   c . In the latter, H stands for the stroke of the piston of the cylinder/piston assembly, with UT as bottom dead center and OT as top dead center, and PK stands for the pressure of the gas in the cylinder chamber. PS represents the necessary switching pressure so that the valve member switches from the first valve seat to the second or from the second valve seat to the first. The switching pressure PS can be divided into the feed pressure PD of the compressed gas source and the corresponding pressure PF of the spring force. VZ in this case illustrates the position of the shut-off valve and VO illustrates the position of the valve communicating with the cylinder chamber via the throttle points.  
      First, the piston  54  moves in the cylinder  64  from the top downward and at the same time, in a first phase, displaces air through the throttle points  80  formed on the piston-like valve member  82 , toward the feed pressure chamber  58 . As the piston speed increases, the pressure difference (PK-PD) across the valve member  82  rises, until the switching force generated by the cylinder chamber pressure PK on the valve member  82  overcomes the prestressing force of the spring  84  and the force on the valve member  82  generated by the feed pressure PD, and presses the valve member  82  against the second valve seat  76 . The throttle point  80  of the valve member  82  is then no longer active. By the piston  54  being moved further toward the valve  56 , therefore, the cylinder chamber pressure PK rises sharply during the compression action in the cylinder chamber  52  and reaches its maximum at bottom dead center UT. In the expansion phase, the valve member  80  moves from the second to the first valve seat  76  as soon as the spring force overshoots the force generated on the valve member  80  as a result of the pressure difference (PK-PD). At the end of the expansion phase, corresponding to the top dead center  66  of the piston, the feed pressure PD is established in the cylinder chamber. Moreover, any oil which has accumulated in the cylinder chamber  52  can then flow out through the passage duct  78 . During the next compression action, the out-flowing oil is blown out by the air displaced into the feed pressure chamber  58  and flows out in an oil separation outlet  88  formed on a bottom  86  of the feed pressure chamber. A connection  90  for compressed air is arranged on a lateral wall  92  of the feed pressure chamber and consequently prevents a further backflow of the oil.  
       FIG. 5  and  FIG. 6  show a further design variant of a pneumatic return device on a larger scale during a compression action. In this case,  FIG. 5  again illustrates the piston  54  at a top dead center  66 , and  FIG. 6  illustrates the piston  54  at a bottom dead center  68  in the cylinder  64  after compression of the cylinder chamber  52 . A valve  56   a  is again arranged directly at the lowermost point of the cylinder  64 . The wall of the cylinder in this case serves as a valve housing, and a valve space  94  is delimited by the wall of the cylinder  64 , a closing-off part  74   a  closing off the cylinder  64 , and a piston-like valve member  82   a . A stop  71  designed as a ring is arranged directly inside the cylinder  64  of the cylinder/piston assembly and serves as a first valve seat  72   a  for the piston-like valve member  82   a . The latter is again prestressed against the first valve seat  72   a  by means of a spring  84   a . The spring  84   a  is in this case supported on the closing-off part  74   a  which closes off the cylinder and has an inner sleeve part  96  for guiding the spring  84   a  and the free end of which serves, moreover, as a second valve seat  76   a  for the valve member  82   a . When the latter butts against the second valve seat  76   a , throttle points  80   a  formed in the valve member  82   a  become inactive. Likewise, in this position, a connection  90   a , arranged on the cylinder, for a compressed gas source  60  is shut off by means of the valve member  82   a . Oil which has accumulated in the cylinder chamber  52  can flow out via an oil separation outlet  88   a  formed on the closing-off part  74   a.    
      In the initial state shown in  FIG. 5 , the valve member  82   a  is prestressed against the first valve seat  72   a  by means of the prestressing force of the spring  84   a , so that the cylinder chamber  52  is connected to a compressed gas source via the throttle points  80   a  in the valve member  82   a . In the case of a high pressure in the cylinder chamber  52 , the valve member  82   a  moves against the second valve seat  76   a  and interrupts communication between the cylinder chamber  52  and the compressed gas source  60  by shutting off the connection  90   a  arranged in the cylinder wall, as illustrated in  FIG. 6 . The throttle points  80   a  are inactive in this position.  
      At the end of an expansion phase, feed pressure is established in the cylinder chamber  52 . Any oil which has accumulated in the cylinder chamber  52  can then flow out into the valve space  94  through the throttle points  80   a . During the next compression action, the out-flowing oil is blown out by the air displaced into the valve space  94  and flows out in the oil separation outlet  88   a  formed on a bottom  98  at the closing-off part  74   a . The connection  90   a  for compressed air is arranged, at a distance from the bottom of the closing-off part, on a wall  100  of the cylinder and consequently prevents a further backflow of the oil.  FIGS. 7   a ,  7   b  and  7   c  illustrate the pressure and piston profiles of the return device according to the invention over two load cycles at creep speed for a speed of 800 rev/min ( FIG. 7   a ), for part load at 1000 rev/min ( FIG. 7   b ) and for full load at 4000 rev/min ( FIG. 7   c ).  
      At creep speed to an operating speed of, for example, 800 rev/min ( FIG. 7   a ), continuous pressure compensation takes place via the throttle points of the valve member, so that the cylinder pressure PK does not reach the switching pressure PS necessary for interrupting communication between the cylinder chamber and the compressed gas source. The pressure in the cylinder chamber PK is therefore always of the order of magnitude of the feed pressure PD. The motor load occurring due to the pneumatic drive is consequently low and allows the motor to run quietly and, particularly with the drive switched off, a movement of the thread control device by hand, for example for setting and repair purposes.  
      Under part load at 1000 rev/min ( FIG. 7   b ), the cylinder chamber pressure PK reaches the necessary switching pressure PS during a cycle, whereupon the valve shuts off communication of the compressed gas source with the cylinder chamber and commences compression in the closed-off cylinder chamber. The compression of the cylinder chamber reaches its maximum at a bottom dead center UT. During the subsequent expansion, the cylinder chamber pressure PK falls below the switching pressure PS again. The cylinder chamber is then connected once more to the compressed gas source, and, when a top dead center OT of the piston is reached, the feed pressure PD is established once again in the cylinder chamber. The compression pressure in the cylinder chamber prevents the roller from being lifted off from the eccentric of the positive drive at higher operating speeds.  
      Under full load at 4000 rev/min the necessary switching pressure PS is reached earlier ( FIG. 7   c ) than at lower operating speeds. Compression therefore takes place over a larger stroke, and the maximum compression pressure consequently reaches a higher value than at lower operating speeds. During the subsequent expansion, the necessary switching pressure PS is reached again, whereupon the valve restores the communication of the cylinder chamber with the compressed gas source. The maximum compression pressure is a direct function of the speed of the machine, that is to say, at a higher speed, the maximum compression pressure also increases. This is advantageous both for an efficient operation of the machine and for a satisfactory functioning of the positive drive.  
      By the valve being opened once per work cycle, a continuous outflow of the lubricating oil which has accumulated in the cylinder chamber takes place. A reliable and continuous operation of the plant is consequently possible, without any maintenance cycles for removing the lubricating oil from the cylinder chamber. The tasks and requirements for the valve which are described above take place independently, that is to say without any external activation. The dimensioning of the spring force, of the throttle cross section and of the valve member outside diameter or valve seat diameters affords the independent control functions of the valve.  
      The return device described here for a thread control device consequently fulfills the most diverse requirements independently and at the same time has the least possible outlay in technical terms. The return device can therefore be produced particularly cost-effectively and, owing to its simple construction, is largely maintenance-free and fault-free during operation.  
      The thread control device according to the invention may also be used for individual thread control, for example for a Jacquard machine, furthermore, in a weft thread device for the presentation of individual weft threads.  
     List of Reference Symbols  
     
         
           2  Machine stand  56   a  Valve  
           4  Main drive shaft  58  Feed pressure chamber  
           6  Weft needle  60  Compressed gas source  
           7  Reed  64  Cylinder  
           8  Cloth take-up  66  Top dead center  
           10  Healed frame device  68  Bottom dead center  
           12  Warp beam stand  70  Housing  
           14  Warp beam  71  Stop  
           16  Warp thread  72  First valve seat  
           18  Shed  72   a  First valve seat  
           20  Thread supply device  74  Closing-off part  
           22  Thread bobbin  74   a  Closing-off part  
           24  Weft thread  76  Second valve seat  
           26  Tucking thread  76   a  Second valve seat  
           28  Thread supply device  78  Passage duct  
           30  Healed frame  80  Throttle point  
           31  Thread guide member  80   a  Throttle point  
           32  Link  82  Valve member  
           34  Cam drive  82   a  Valve member  
           35  Positive drive  84  Spring  
           36  Return device  84   a  Spring  
           38  Pivoting lever  86  Bottom  
           40  Drive point  88  Outlet  
           42  Cam  88   a  Outlet  
           44  Cam shaft  90  Connection  
           46  Output point  90   a  Connection  
           48  Joint  92  Wall  
           50  Pivot axis  94  Valve space  
           52  Cylinder chamber  96  Sleeve part  
           54  Piston  98  Bottom  
           56  Valve  100  Wall