Abstract:
A textile machine receives yarn from a yarn-feeding device via a yarn-recovering device provided with a motorized reel having a passage for the yarn, which extends between an inlet port open to the middle of the free end of the reel and an outlet port formed on the lateral surface of the reel; the tension of the yarn being maintained constant on a reference value by adjusting elements, on the basis of a measured tension signal generated by a sensor; a consumption indicator being obtained to detect an interruption in the delivery of yarn, the adjusting elements being temporarily disabled and the yarn-recovering device being temporarily enabled to rotate at a speed modulated on the basis of the measured tension signal for maintaining the tension of the yarn constant on the reference value, if an interruption in the delivery of yarn is detected.

Description:
[0001]    The present invention relates to a yarn-feeding/recovering method for textile machines and to an apparatus for carrying out such method. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the textile field, well feeders are known which are provided with a stationary drum on which a motorized swivel arm winds a plurality of yarn loops forming a stock. The yarn, which is unwound from the drum upon request of a textile machine arranged downstream, is subject to a stabilizing brake that maintains the unwinding yarn under a slight tension. The stabilizing brake typically comprises a frustoconical hollow member which is biased with its inner surface against the delivery edge of the drum by manually adjustable elastic means. 
         [0003]    As described in EP 2031106, in order to maintain the feeding tension substantially constant, a controlled brake may be arranged downstream of the feeder, e.g., a foil-based brake of the type described in EP 0622485. This brake is controlled by a feedback loop which receives a measured tension signal from a sensor, then compares it with a reference tension which is indicative of a desired tension, and finally modulates the braking action in such a way as to minimize the difference between the reference tension and the measured tension. 
         [0004]    Feeders are also known in which the yarn is wound on a rotary drum, which draws the yarn from a reel and feeds it to the downstream textile machine In this case, the tension of the yarn unwinding from the feeder is controlled by modulating the speed of rotation of the drum, always on the basis of a signal received from a tension sensor as in the previous case. Accordingly, in other words, the change of tension to be applied is determined by the difference between the yarn-feeding speed and the yarn-drawing speed set in the downstream machine 
         [0005]    As known, certain particular processes, e.g., weaving the heel of socks, require that the yarn fed to the machine is periodically recovered and then returned. This operation is usually carried out by a dedicated recovering device arranged upstream of the machine 
         [0006]    A recovering device of this type is described in EP  1741817  and essentially comprises a motorized reel having an oblique passage defined therein, through which the yarn runs. The passage extends between an inlet port which is axially formed on an end surface of the reel, and an outlet port which is formed on the cylindrical, lateral surface of the reel. When an amount of yarn must be recovered, the downstream machine sends a signal to the recovering device which enables the rotation of the reel, so that the yarn is wound upon the reel. 
         [0007]    As well known to the person skilled in the art, a critical issue of the above systems consists in coordinating the operation of the braking system, which operates on the basis of the measured tension of the yarn, with the operation of the recovering system, which is enabled in response to commands sent from the downstream machine on the basis on a predetermined pattern, with consequent difficulties in accurately controlling the feeding parameters and the state of the yarn during the recovering steps, e.g., in relation to possible, accidental events which may occur, such as a yarn breakage. 
       SUMMARY OF THE INVENTION 
       [0008]    It is a main object of the present invention to provide a method in which the yarn-feeding function and the yarn-recovering function are coordinated with each other in a more reliable and more accured manner with respect to the prior art, particularly in relation to the control of the yarn tension during the recovering step and to the reaction in case of accidental events, such as a yarn breakage; it is also an object to provide an apparatus for carrying out such method. 
         [0009]    The above objects and other advantages, which will better appear from the following description, are achieved by a method having the features recited in claim  1 , as well as by an apparatus having the features recited in claim  7 , while the dependent claims state other advantageous, though secondary features, of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention will be now described in more detail with reference to a few preferred, non-exclusive embodiments, shown by way of non limiting example in the attached drawings, wherein: 
           [0011]      FIG. 1  diagrammatically shows an apparatus for carrying out the method according to the invention; 
           [0012]      FIG. 2  is a side elevation view of a recovering device of a known type used in the apparatus of  FIG. 1 ; 
           [0013]      FIG. 3  is a view similar to  FIG. 2 , which shows the recovering device in a different operative configuration; 
           [0014]      FIG. 4  is a flowchart showing the steps of the method according to the invention; 
           [0015]      FIG. 5  diagrammatically shows an apparatus for carrying out the method according to an alternative embodiment of the invention; 
           [0016]      FIG. 6  is a perspective view of a yarn feeder with rotary drum, which is modified according to the invention to incorporate the apparatus of  FIG. 5 ; 
           [0017]      FIG. 7  is a front elevation view of the yarn feeder of  FIG. 6 ; 
           [0018]      FIG. 8  is a side elevation view of the yarn feeder of  FIG. 6 ; 
           [0019]      FIG. 9  is a broken away view similar to  FIG. 8 , showing the yarn feeder sectioned along axis IX-IX of  FIG. 7 ; 
           [0020]      FIG. 10  is a front elevation, broken away view of the yarn feeder of  FIG. 6  sectioned along axis X-X of  FIG. 8 ; 
           [0021]      FIG. 11  is a Figure similar to  FIG. 7 , showing the yarn feeder to an enlarged scale and in a different operative configuration; 
           [0022]      FIG. 12  is a flowchart showing the steps of the method according to the alternative embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  diagrammatically shows a yarn-feeding/recovering apparatus  10  having a yarn feeder  12  provided with a stationary drum  14  and with a flywheel  16  driven to rotate by a motor  18 . The flywheel draws yarn F from a spool  20  and winds it on drum  14  in the shape of loops forming a stock. 
         [0024]    Yarn F, which is unwound from the drum upon request of a general textile machine  22  arranged downstream, is subject to the braking action of a stabilizing brake adapted to maintain the yarn under a slight tension. The stabilizing brake conventionally comprises a frustoconical hollow member  24  which is biased with its inner surface against the delivery edge of drum  14  by elastic means  26 . 
         [0025]    In a way known per se, yarn F coming out of stabilizing brake is further subject to the braking action of an electronic yarn-braking device (or brake)  28  which is controlled by a tension control block TC of a control unit CU (which is typically incorporated in yarn feeder  12 ). Control unit CU is programmed to modulate the braking action applied to yarn F by electronic brake  28 , on the basis of a signal received from a tension sensor  30 , in such a way as to maintain the tension of the delivered yarn substantially constant on a reference value T_ref. 
         [0026]    The stock on drum  14  is controlled by a triad of sensors. A first sensor  51 , preferably a Hall sensor, detects the passage of magnets M integral with flywheel  16  in order to determine the amount of yarn which is wound on the drum and the winding speed. A second sensor S 2 , preferably a mechanical sensor, provides a binary information about the presence of a minimum amount of yarn at an intermediate area of drum  14 . A third sensor S 3 , preferably an optical sensor, generates one pulse UWP per each loop unwound from the drum. A speed-evaluating block SE processes signals UWP in order to calculate the yarn consumption speed on the basis of the time interval between pulses UWP, and generates an enabling signal LE which enables tension control block TC when this speed is higher than a predetermined threshold value, which is preferably equal to zero in the present embodiment. An apparatus of this type is described in EP 2031106, to which reference should be made for a more detailed description. 
         [0027]    A yarn-recovering device  32  of the type described in EP 1741817 and shown in detail in  FIGS. 2 ,  3 , is arranged between electronic brake  28  and tension sensor  30 . 
         [0028]    Yarn-recovering device  32  comprises a reel  34  keyed to a drive shaft  36  of a motor  38 , preferably a stepping motor or, alternatively, a brushless motor provided with an absolute sensor, in order to measure the real position based on techniques conventional in the field. Reel  34  is arranged with its axis A slanting at a first angle a with respect to the direction of yarn F, indicated by arrow D, so that its end surface  34   a  facing away from motor  38  obliquely faces the incoming yarn. Reel  34  has an axial cylindrical seat  40  at its end surface  34   a . A passage  44  defined within reel  34  extends between an inlet port  44   a  open to axial cylindrical seat  40 , and an outlet port  44   b  open to the lateral, winding surface  34   b  of the reel. Passage  44  is rectilinear and is slanting at a second angle b, which is substantially equal to first angle a, with respect to axis A of the reel. An internally rounded wearproof ring  46  made of ceramic is applied to the edge of cylindrical seat  40 . An inlet yarn-guide eyelet  48  and an outlet yarn-guide eyelet  50  respectively applied upstream and downstream of reel  34  are arranged at the same level of wearproof ring  46 . 
         [0029]    Yarn F passes through upstream yarn-guide eyelet  48 , cylindrical seat  40 , passage  44  and downstream yarn-guide eyelet  50 . By operating motor  38 , as shown in  FIG. 3 , the yarn downstream of the yarn-recovering device is wound on reel  34 . For a more detailed description of yarn-recovering device  32 , reference should be made to EP 1741817. 
         [0030]    With the method according to the invention, as described in the flowchart of  FIG. 4 , electronic brake  28  and yarn-recovering device  32  are alternately enabled as a function of the signals from third sensor S 3 , which are indicative of the yarn comsumption, independently from any other operative signals from downstream machine  22 . 
         [0031]    In detail, as long as signal LE indicates that yarn is being unwound (LE=1), control unit CU continues to modulate the braking action of electronic brake  28  in such a way as to maintain the tension substantially constant at reference value T_ref, while yarn-recovering device remains at a position of minimum interference with the yarn, as shown in  FIG. 2 . When signal LE indicates that yarn is no longer unwound from the drum (LE=0), which circumstance is indicative of the fact that the downstream machine has either stopped to draw yarn or started to return it, control unit CU “freezes” the braking action at the last value and, if measured tension T_meas is lower than a lower threshold tension T_lim_inf, than it enables yarn-recovering device  32  to recover yarn, while its speed V RR  is continuously modulated in such a way as to maintain the tension substantially constant on reference value T_ref. At this stage, the number of revolutions and fractions of revolutions N completed by reel  34  is monitored. 
         [0032]    It should be noted that, with the method according to the invention, reel  34  can rotate at a modulated speed in both directions. In fact, after an initial yarn-recovering step, during which the exceeding yarn is wound on reel  34  in order to maintain the tension at the desired level T_ref, the subsequent request of yarn from the downstream machine will cause reel  34  to rotate in the opposite direction always at a controlled speed, in order to return the yarn; however, before reaching the initial position (N=0) it could have to recover yarn again. When the reel reaches the initial position, control unit CU stops reel  34 , enables electronic brake  28  again, and then the cycle is repeated. 
         [0033]    As shown in the flowchart of  FIG. 4 , two emergency conditions are provided, by which the tension control is bypassed while yarn-recovering device  32  is enabled. A first condition occurs when N reaches a value N_max corresponding to the maximum amount of yarn which can be stored on the reel. In this case, the process is stopped and an alarm signal is generated. The second condition occurs when signal LE indicates that yarn is unwinding from the feeder; this means that the downstream machine is drawing yarn at a speed such that the yarn is sliding on reel  34 . In this case, the tension control is bypassed and the reel is automatically driven to rotate to its resting position N=0. 
         [0034]    Accordingly, with this embodiment, signal LE is used as a comsumption indicator that is indicative of the delivery of yarn from the feeder and, therefore, of the withdrawal of yarn by the downstream machine; on the basis of this indicator, electronic brake  28  and yarn-recovering device  32  are alternately enabled as discussed above. 
         [0035]    Having now reference to  FIG. 5 , a weft feeder  100  is diagrammatically shown, which is provided with a motorized drum  102  on which yarn F′ is wound. Motorized drum  102  draws yarn F′ from a spool  104  and delivers it to a textile machine  106  arranged downstream. The tension of yarn F′ unwinding from the feeder is conventionally controlled in such a way as to remain substantially constant on a reference value T_ref, by a control unit CU′ (which is typically incorporated in yarn feeder  102 ) provided with a tension control block TC′ that modulates the speed of rotation V RP  of drum  102  on the basis of the signals from a tension sensor  108  installed on the feeder. Accordingly, the change of tension to be applied is determined by the difference between the yarn-feeding speed and the yarn-drawing speed set in downstream machine  106 . 
         [0036]    A yarn-recovering device  120  is arranged between motorized drum  102  and the tension sensor; in the present embodiment, it is incorporated in housing  103  of feeder  100 , as shown in more detail in  FIGS. 6-11 . Yarn-recovering device  120  comprises a motorized reel  122  lying with its axis parallel to the axis of motorized drum  102 . Also in this case, the motor (not shown) of reel  122  is preferably a stepping motor or, alternatively, a brushless motor provided with an absolute sensor for measuring its real position. A passage  124  is defined within reel  122 , which extends radially between an inlet port  126 , which is formed at the middle of a free end  122   a  of the reel with its axis inclined with respect to the axis of reel  122 , and an outlet port  128  formed on the lateral winding surface  122   b  of the reel. Inlet port  126  and outlet port  128  are internally rounded for reducing the wear by friction. 
         [0037]    Yarn F′ from spool  104  passes through an inlet yarn-guide eyelet  130  attached to the feeder, is wound between drum  12  and an arm  132  of a conventional tension limiter (which does not fall within the scopes of the present invention and, therefore, will not be further disclosed), runs through passage  124  which, at rest, lies at the resting position of  FIG. 10  such that it substantially does not interfere with the path of the yarn, then engages a sensing element  134  of tension sensor  108 , the latter being also incorporated in housing  103  of the feeder, and finally passes through an outlet yarn-guide eyelet  136  to feed the downstream machine As shown in  FIGS. 6-11 , control unit CU′ is conventially received in a seat  138  of feeder  100 , which also contains tension sensor  108 , and is provided with programming push buttons  140  and with a display  142 . 
         [0038]    With the method according to this alternative embodiment of the invention, which is diagrammatically shown in the flowchart of  FIG. 12 , drum  12  of the feeder and reel  122  of yarn-recovering device  120  are alternately enabled as a function of speed V RP  of drum  102 , independently from any other operative signal from the downstream machine 
         [0039]    In particular, as long as speed V RP  of drum  102  is higher than zero, which circumstance is indicative of the fact that yarn is being delivered by the feeder and, consequently, is being drawn by the downstream machine, drum  102  continues to rotate at a modulated speed, in such a way as to maintain the tension substantially constant on reference value T_ref, while reel  122  remains at its resting position of  FIG. 10 . When speed V RP  of the drum becomes equal to zero, which circumstance is indicative of the fact that the feeder has stopped to feed yarn and, therefore, the downstream machine has either stopped to draw yarn or started to return it, control unit CU′ enables reel  122  to recover yarn at a speed V RR  modulated in such a way as to maintain the tension substantially constant on a reference value T_ref. At this stage, the number of revolutions and fractions of revolutions N completed by reel  122  is monitored. 
         [0040]    Similarly to the previous embodiment, reel  122  can rotate in both directions at a modulated speed. In fact, after an initial yarn-recovering step, in which the exceeding yarn is wound on reel  122  in order to maintain the tension at the desired level T_ref, the next request of yarn from the downstream machine will cause reel  122  to rotate in the opposite direction, always at a controlled speed, in order to return the yarn; however, before reaching the initial position (N=0), it could have to recover yarn again. When the reel reaches the initial position N=0, control unit CU′ stops reel  122 , enables drum  102  again, and then the cycle is repeated. 
         [0041]    With this embodiment, there is also provided an emergency condition, by which the tension control can be bypassed. In particular, when N reaches a value N_max corresponding to the maximum amount of yarn which can be stored on the reel, the process is stopped and an alarm signal is generated. Accordingly, with this embodiment the speed V RP  of the drum is used as a comsumption indicator, which is indicative of the delivery of yarn by the feeder and, consequently, of the withdrawal of yarn by the downstream machine; on the basis of this indicator, drum  102  and reel  122  are alternately enabled according to the above method. 
         [0042]    A few preferred embodiments of the invention have been described herein, but of course many changes may be made by a person skilled in the art within the scope of the claims. In particular, in the first described embodiment a stabilizing brake as described in EP 1059375, which applies a controlled braking action to the unwinding yarn, could be used in lieu of electronic brake  28 . Moreover, in the described embodiments, the yarn-recovering device is always positioned in such a way that, at rest, it can assume positions not interfering with the yarn, as shown in  FIG. 2  for the first embodiment and in  FIG. 10  for the second embodiment. However, depending on the layout of the textile line, the reel could be arranged in such a way as to deviate the yarn even at its resting position in which it applies the minimum braking action upon the yarn. 
         [0043]    The disclosures in Italian Patent Application No. TO2012A000261 from which this application claims priority are incorporated herein by reference.