Patent Publication Number: US-7721574-B2

Title: Yarn-recovering device for textile machines

Description:
The present invention relates to a yarn-recovering device for textile machines, particularly sock-knitting machines and knitting machines in general. 
   BACKGROUND OF THE INVENTION 
   As is known, knitting machines draw the yarn either directly from a spool or through a yarn-feeding device which draws the yarn from the spool and feeds it to the machine under a regulated tension. 
   For certain particular machinings, such as the knitting of the heel in the sock-manufacturing processes, the yarn fed to the machine must be periodically recovered, and then returned more or less progressively. Since neither the traditional feeders nor the spools are capable of recovering the yarn previously fed, this function is performed by a dedicated yarn-recovering device located upstream of the machine. 
   To this purpose, devices are known which are provided with a pneumatically operated rocking arm having an eyelet mounted to its free end, through which the yarn passes. At rest, the arm is arranged with its eyelet aligned to the running direction of the yarn, between two stationary eyelets which are also passed through by the yarn. By rotating the arm, the yarn is deviated from its rectilinear path and a length of yarn is consequently recovered. 
   The above known devices provided with a rocking arm have the main drawback that their yarn-recovering capacity, i.e., the maximum length of yarn recoverable at each operation, is rather limited since strictly correlated to the length of the arm, which of course, for size reasons, cannot exceed predetermined values, typically in the range 300 to 400 mm. 
   Moreover, the operation of the arm can subject the yarn upstream of the device to considerable peaks of tension, which circumstance, as well known to the person skilled in the art, is undesirable because it may cause the yarn to brake and may affect the accuracy and the exactness of the feeding process. 
   SUMMARY OF THE INVENTION 
   Therefore, it is a main object of the present invention to provide a yarn-recovering device for textile machines which has a recovering capacity much higher than the known devices and which, in operation, does not subject the upstream yarn to harmful peaks of tension. 
   The above object and other advantages, which will better appear below, are achieved by a yarn-recovering device having the features recited in claim  1 , while the dependent claims state other advantageous, though secondary, features of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  diagrammatically shows the positioning of a general yarn-recovering device with respect to a knitting machine; 
       FIG. 2  is a side elevation view of a yarn-recovering device according to the invention, at rest; 
       FIG. 3  is a view similar to  FIG. 2  showing the device in operation; 
       FIG. 4  is a side elevation view of a yarn-recovering device of  FIG. 1  in an alternative configuration, at rest; 
       FIG. 5  is a view similar to  FIG. 4 , showing the device in operation; 
       FIG. 6  is a block diagram of a control system for governing the yarn-recovering device according to the invention; 
       FIG. 7  is a diagrammatical perspective view showing a separate element of the control system of  FIG. 6 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With initial reference to  FIG. 1 , a general yarn-recovering device is intended to be arranged upstream of a general knitting machine  12  in order to intercept the yarn drawn by the machine either directly from a spool  14 , or through a yarn feeder  16  which draws the yarn from spool  14  and feeds it to machine  12  under a regulated tension. 
   Yarn-recovering device  10  according to the invention comprises a reel  18  keyed to a driving shaft  20 . of a motor  22  and arranged with its axis A sloping at a first angle a with respect to the direction of the incoming yarn indicated by arrow D, with its free end  18   a  facing the incoming yarn at an angle. A cylindrical, axial cavity  26  is formed at free end  18   a  of the reel. A passage  28  is formed between an inlet port  28   a  that is open to axial cavity  26  and an outlet port  28   b  that is open to lateral surface  18   b  of the reel. Passage  28  is rectilinear and is inclined at a second angle β substantially equal to first angle α with respect to axis A of the reel. A ceramic, yarn-guide eyelet  30  provided with a beveled inner surface is applied to the rim of axial cavity  26 . A pair of yarn-guide eyelets  32 ,  24  are respectively arranged upstream and downstream of reel  18  and are aligned to the outermost section of axial cavity  26 . 
   In operation, yarn F fed to the downstream machine passes through upstream yarn-guide eyelet  32 , axial cavity  26 , passage  28  and downstream yarn-guide eyelet  34 . At rest, reel  18  is motionless at the resting position of  FIG. 2 , with passage  28  aligned to eyelets  32 ,  34  without interfering with the yarn. When it is required to recover yarn from the downstream machine, motor  22  is operated in a first direction and, consequently, the yarn downstream of the reel is wound on reel  18  ( FIG. 3 ), while the yarn upstream of the reel is not subjected to floatations because cavity  26  rotates about its axis. Yarn-guide eyelet  30  protects yarn F from wear due to friction against the edge of axial cavity  26 . For returning the. yarn, reel  18  is rotated to the initial position in the opposite direction, with the skew opening aligned to the path of the yarn. 
   In  FIGS. 4 ,  5  an alternative configuration of yarn-recovering device  10  is shown, in which the axis of reel  18  is parallel to, and substantially coincides with, the incoming direction D′ of the yarn, i.e., angle α is equal to zero. 
     FIGS. 6 ,  7  show a position control system for governing the above described yarn-recovering device. 
   In  FIG. 6 , motor  22  is provided with a position sensor SP for measuring the position of driving shaft  20  and sending an absolute, measured position signal meas_pos to a position control loop PL. Control loop PL comprises a subtracter block  40  in which a position error Pos_err is calculated by subtracting measured position signal meas_pos from a reference position signal ref_pos. Position error pos_err is sent to a compensator block  41 , such as a proportional integral compensator (PI) or a proportional integral derivative compensator (PID), which is programmed to generate a reference torque signal torq_ref such as to minimize the position error. Reference torque signal torq_ref is then sent to a current feedback loop  42  connected to control the current through motor  22  by feedback. A controller CU is programmed to vary reference position signal pos_ref on the basis of the operative state of the downstream machine. In particular, when the device is at rest in its resting position, i.e., while the yarn is processed by the downstream machine, controller CU generates a reference position signal corresponding to the resting position of  FIG. 2 . On the contrary, when it is required to recover yarn from the downstream machine, controller CU generates a reference position signal pos_ref such as to rotate reel  18  at the angle needed to recover the desired length of yarn. When the yarn must be returned to the downstream machine, controller CU generates the reference position signal again corresponding to the resting position. Reference position signal corresponding to the resting position may be either programmed in the factory or, preferably, a manual calibration procedure may be provided, in which the operator manually positions reel  18  at its non-interference position, in which inlet port  28   a  and outlet port  28   b  are aligned to direction D of incoming yarn F. Thereafter, by pushing a button associated to controller CU, such position is stored as resting position that will be called up at each start for aligning the yarn-recovering device. 
     FIG. 7  shows an absolute position sensor particularly suitable to the present application, because of its low costs and reduced sizes. A diametrically polarized, cylindrical permanent magnet M, preferably a rare earth magnet, such as samarium-cobalt or iron-boron, is coaxially anchored to one end of driving shaft  20  of motor  22 . An integrated circuit IC is arranged near the magnet at right angles to the axis of shaft  20 , and bears four Hall sensors, H 1 , H 2 , H 3 , H 4  arranged to form a square, whereby the two pairs of opposite sensors H 1 , H 3  and H 2 , H 4  are alternately excited during the rotation of the magnet, with the sensors of each pair which are simultaneously excited in opposing directions, as shown by arrows −B, +B. Integrated circuit IC contains the circuitry (not shown) required for calculating the position of magnet M on the basis of the signals from the Hall sensors. 
   A few preferred embodiments of the invention have been described herein, but of course many changes may be made by the person skilled in the art within the scope of the inventive concept. In particular, although in the above-described example inlet port  28   a  of passage  28  is very close to the axis of rotation of reel  18 , whereby the incoming yarn is not subjected to floatations and tension peaks during the rotation, however, with certain applications in which slight flotations can be tolerated the inlet port  28   a  can be located at a position farther from axis A. Moreover, passage  28 , which connects the inlet port to the outlet port, could have different shapes and sizes. For example, in case of a hollow reel, the passage could simply consist of the cavity within the reel. Further, passage  28  could directly lead to the front surface of the reel, without need for any axial cavity  26 . 
   The disclosures in Italian Patent Application No. TO2005A000469 from which this application claims priority are incorporated herein by reference.