Abstract:
An apparatus for controlling the tension of a traveling yarn includes a rake tensioner having stationary and displaceable yarn tensioning elements in engagement with the traveling yarn, and an electrical coil to which electrical current is supplied by a regulating device. The displaceable yarn tensioning elements and the electrical coil are disposed on a common pivot lever. The electrical coil is pivotable in an air gap through which magnetic field lines pass. The tension of the traveling yarn is controlled as a function of the current supplied to the electrical coil. The present invention, thusly, improves the control of the tension of the traveling yarn in spinning or bobbin winding machines.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of German patent application DE P 10009611.5 filed Feb. 29, 2000, herein incorporated by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to an apparatus for controlling the tension of a traveling yarn in an automatic winding device, particularly such devices having stationary and displaceable yarn tensioning elements in engagement with the traveling yarn for controlling the tension of the traveling yarn in proportion to an electrical coil current generated by an electrical coil via electrical current supplied by a regulating device.  
         BACKGROUND OF THE INVENTION  
         [0003]    German Patent Disclosure DE 37 34 471, discloses a rake tensioner device used to control the tension of yarn traveling between a feed bobbin and a takeup bobbin of an automatic bobbin winder such that the increase in brake force, the tension imposed on the yarn by the rake tensioner, is reduced once the rotational speed of the takeup bobbin has reached a predetermined threshold value. The adjustable yarn tensioning elements of the rake tensioner are adjusted by an electric motor. In this kind of drive mechanism, the forward or reverse motion of the adjustable yarn tensioning elements is generated via gearing which converts the rotary motion of the motor into a linear motion.  
           [0004]    German Patent Disclosure DE 198 58 548, which had not been published by the priority date of the present application, discloses a traversing device for delivering a yarn to a rotationally driven cross-wound bobbin, also known as a cheese, with a traversing yarn guide that is pivotable about a pivot shaft disposed perpendicular to the axis of the cheese. The end of the traversing yarn guide that guides the yarn is moved back and forth by an electrical coil disposed in a magnetic field, the coil generating and controlling the motion of the traversing yarn guide for laying the yarn on a cheese.  
           [0005]    An apparatus of the above identified type for controlling the tension of a traveling yarn is generally know, for example in German Patent Disclosure DE 43 35 089. In that construction, the yarn tension is controlled by an apparatus which can incrementally increase or decrease the yarn tension to a desired value, for instance in order to compensate for an increased unwinding tension. The apparatus for controlling the yarn tension is part of an automatic winding device. To avoid the expense that would be required if such an apparatus were used in every individual winding unit of a bobbin winder, an output signal for controlling the yarn tension is obtained from a specific spindle and other spindles of the bobbin winder are controlled on the basis of this output signal. A tensioning device, for example a rake tensioner, having a pair of cooperating comblike parts and a solenoid acts, via a rod linkage system and an eccentric element, to adjust the degree to which the combs mesh with the traveling yarn, thus adjusting the amount of the contact angle of the yarn relative to the teeth of the combs. This construction results in relatively high inertia within the moving parts and a looseness, or play, in the gears or other transmission elements. Because of the imposed inertia, such yarn tensioners tend to increase the peak values of the yarn tension and to impair the quality of the tension control.  
           [0006]    German Patent Disclosure DE 195 44 202, discloses an apparatus for controlling the tension of yarn to a set-point value. The yarn tension control apparatus is constructed such that a rake tensioner acts as both a tensioner and a yarn tension sensor. The adjustment of the adjustable yarn tensioning elements is accomplished by an electrodynamic drive mechanism made of a plunging coil and cup magnet assembly. A holder with adjustable prong-like yarn tensioning elements is connected to a rod supported vertically by bushing bearings and oriented transverse to direction of travel of the yarn. Linear bearings have the disadvantage of being vulnerable to soiling because of the unavoidable production of dust at the work stations, especially by softeners applied to the traveling yarn. Such a system also has a relatively high mass inertia because the total mass of the plunging coil and the holder must be moved over the entire adjustment distance. This construction hinders the reaction of the yarn tensioning elements to high-frequency fluctuations in the tension of the traveling yarn, thus increasing the incident of peaks of tension in the traveling yarn which impairs the function of the apparatus.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0007]    Thus an object of the present invention is to provide an improved apparatus for controlling the tension of traveling yarn. This object is basically achieved by affixing displaceable yarn tensioning elements of a rake tensioner and an electrical coil to a common pivot lever that has no extraneous transmission components, with a corresponding increase in inertia, nor looseness, or play, in the transmission components. The torque generated by the electrical coil has a direct effect on the tension of the traveling yarn via the displaceable yarn tensioning elements. The control of the yarn tension can be accomplished without delay and without significant friction losses because the moment of inertia of the moving parts is slight, making possible rapid reaction to high-frequency changes in traveling yarn tension. Because of the fast reaction and the low inertia, the present invention is capable of self-monitoring and automatic control to a desired tension, and functions properly even if high-frequency peaks in the tension of the traveling yarn occurs. Hence, relatively high torques available for controlling the pivot lever, and a pivot lever with a short rotating distance, and a correspondingly long adjustment distance for the displaceable yarn tensioning elements, can be attained. Thus, the displaceable yarn tensioning elements can be affixed to the lever arm at a relatively long distance from the pivot axis of the pivot lever, and the applicable lever arm can be correspondingly long and very light in weight. The efficiency of the present invention in applying a requisite torque to the pivot lever is high, whereby the electrical coil can be disposed relatively close to the pivot axis.  
           [0008]    A moment sufficient for effective control of the yarn tension can already be generated with an apparatus that is structurally quite small. The compact, structurally simple design requires little structural outlay which is highly advantageous in machines that have many work stations, such as spinning or bobbin winding machines. The apparatus also requires little space which is extremely desirable, given the limited space available at such work stations.  
           [0009]    The rotatable pivot lever is supported by a rotary bearing, preferably a roller bearing, and is thus supported with little friction. A rotary bearing, compared with a linear bearing, can be better sealed and is markedly less vulnerable to soiling. To further reduce the inertia of the controlling apparatus, a magnet bearing, hydraulic bearing, or air bearing can be used instead of the roller bearing. Additionally, the pivot lever can be made from very lightweight material, thus reducing the mass moment of inertia and the inertia associated with the controlling apparatus.  
           [0010]    The above-described advantages lead individually and in combination to a marked improvement in an apparatus used to control the tension of a traveling yarn, particularly to the quality of the control.  
           [0011]    Further details, features and advantages of the present invention will be disclosed in and understood from the following disclosure of one or more preferred embodiments of the present invention with reference to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a simplified schematic view of a winding station of an automatic bobbin winder in which the present invention may preferably be embodied;  
         [0013]    [0013]FIG. 2 is an elevational view of a preferred embodiment of the present invention;  
         [0014]    [0014]FIG. 3 is a side elevational view of the apparatus of FIG. 2; and  
         [0015]    [0015]FIG. 4 is an elevational view of an alternative preferred embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    In the winding station of a bobbin winder shown in FIG. 1, a traveling yarn  1  is drawn from a feed bobbin  2  and passes through a balloon breaker  3 , a control apparatus  4  for controlling the tension of the traveling yarn  1 , a yarn cleaner  5 , and a stationary yarn guide element  6 , before it is wound onto a rotating cheese  7 . The traversing motion required to wind the cheese  7  is generated by reversing thread roller  8 , which is rotatably driven by a motor M and simultaneously provides the circumferential drive for the cheese  7 . The control apparatus  4  and yarn cleaner  5  are connected to a control unit  9 . FIGS. 2 and 3 show a control apparatus  4 , in which a pivot lever  10  can be seen that is supported by a rotary bearing, preferably a roller bearing  11 , and a shaft  12 . The pivot lever  10  is made from the lightest possible material, for example plastic, so that only a slight moment of inertia in pivoting motions is achieved while maintaining adequate strength in the pivot lever  10 . Displaceable yarn tensioning elements  14 ,  14 ′,  14 ″ are fixedly attached to a lever arm  13  of the pivot lever  10 . Stationary yarn tensioning elements  15 ,  15 ′,  15 ″,  15 ′″ are affixed to the housing, not shown, of the control apparatus  4 . The displaceable yarn tensioning elements  14 ,  14 ′,  14 ″ engage and mesh with the stationary yarn tensioning elements  15 ,  15 ′,  15 ″,  15 ′″ to create a rake tensioner  16 . The traveling yarn  1  follows a zigzag course about the displaceable yarn tensioning elements  14 ,  14 ′,  14 ″ and the stationary yarn tensioning elements  15 ,  15 ′,  15 ″,  15 ′″. Rotation of the pivot lever  10  causes the displaceable yarn tensioning elements  14 ,  14 ′,  14 ″ and the stationary yarn tensioning elements  15 ,  15 ′,  15 ″,  15 ′″ to change their positions relative to one another, thus changing the wrap angle of the traveling yarn  1 , i.e., the angle at which the traveling yarn  1  engages and disengages the individual yarn tensioning elements. Hence the wrap angle of the traveling yarn  1  is dependent on the change in the relative positions of the displaceable yarn tensioning elements  14 ,  14 ′,  14 ″ to the stationary yarn tensioning elements  15 ,  15 ′,  15 ″,  15 ′″. By using the rake tensioner  16 , the tension imposed on the traveling yarn  1  can be controlled as a function of the wrap angle.  
         [0017]    An electrical coil  18  is disposed on a lever arm  17  of the pivot lever  10 . The electrical coil  18  and the lever arm  17  are positioned diametrically opposite the lever arm  13  across the shaft  12 . The electrical coil  18  and the lever arm  17  are rotatable in an air gap  49 , formed between a first yoke  19  and magnets  20 ,  21  affixed to a second yoke  22 . The air gap  49  has a constant gap width. A magnetic field generated by the magnets  20 ,  21  and having magnetic field lines emanating in the direction represented by arrows  23  traverses the air gap  49 . The yokes  19 ,  22  are connected by spokes  24 ,  25 ,  26 . The magnetic field lines passing through the yokes  19 ,  22  and spokes  24 ,  25 ,  26  are not shown for sake of simplicity. Preferably, the magnets  20 ,  21  are permanent magnets and are disposed in opposite polarity upon the second yoke  22 . The pole orientation of the magnets  20 ,  21  is represented by the letters S and N. An electrical current is supplied to the coil  18  via supply lines  27 ,  28 . The supply lines  27 ,  28  extend through bores  29 ,  30  in the shaft  12 , thus subjecting supply lines  27 ,  28  to only slight motions. By supplying a known electrical current to the coil  18 , a torque is brought to bear on the pivot lever  10 , and as a result of the forces exerted by the yarn guide  6  on the displaceable yarn tension elements  14 ,  14 ′,  14 ″, a force equilibrium ensues and a suitable pivoting position of the pivot lever  10  is triggered.  
         [0018]    In another preferred embodiment, shown in FIG. 4, the present invention has a pivot lever  31  comprised of two lever arms  32 ,  33  fixedly attached to each other. Displaceable yarn tensioning elements  34 ,  34 ′,  34 ″ are disposed on the lever arm  32  and are adjustable by rotating the pivot lever  31 . The displaceable yarn tensioning elements  34 ,  34 ′,  34 ″ engage and mesh with stationary yarn tensioning elements  35 ,  35 ′,  35 ″,  35 ′″, affixed to a housing of the control apparatus, to form a rake tensioner  36 .  
         [0019]    The lever arm  33 , acting as a coil holder, is supported, along with the lever arm  32 , by a rotary bearing, preferably a roller bearing  37 , and is pivotable about the axis of the shaft  38 . A magnet bearing, air bearing or other low-friction bearings can replace the roller bearing.  
         [0020]    An electrical coil  39  is wound on the lever arm  33  so that the center axis of the wound electrical coil  39  intersects the axis of the shaft  38 . Electrical current is supplied to the electrical coil  39  by supply lines  40 ,  41 . The supply lines  40 ,  41  are passed through bores in the shaft  38 , thus limiting the motion to which the supply lines  40 ,  41  are subjected.  
         [0021]    An inner yoke  42  is shaped as an annular segment. Opposite the outer circumference of the inner yoke  42  are segmented magnets  44 ,  45  disposed on an outer yoke  43 , also shaped as an annular segment. The inner yoke  42  and the magnets  44 , 45  are separated by an air gap  46  having a constant gap width over its length. The magnets  44 ,  45  are positioned upon the outer yoke  43  so that a magnetic field created by the magnets  44 ,  45  has magnetic field lines  47  emanating from the region of the magnets  44  and toward the shaft  38 , while the magnetic field lines  48  in the region of the magnets  45  are oriented toward the magnets  45 . Field lines are shown only in the region of the air gap  46 . An electrical current is supplied to the electrical coil  39 , imposing a corresponding torque on the pivot lever  31 . An advantageous feature of the disposition of the air gap  46  and the associated electrical coil  39  is that the winding strands  39 ′,  39 ″ of the electrical coil  39  extend into the air gap and are disposed at a relatively long distance from the pivot axis of the pivot lever  31 , so that a relatively high moment can be generated on the basis of the leverage. Because of the orientation of the magnetic field lines  47 , 48  and the current direction in the winding strands  39 ′,  39 ″ of the electrical coil  39 , the current and moment are proportional over the entire relevant pivoting range of the pivot lever  31 . The displaceable yarn tensioning elements  34 ,  34 ′,  34 ″, together with the stationary yarn tensioning elements  35 ,  35 ′,  35 ″,  35 ′″, exert a braking action that controls the yarn tension.  
         [0022]    In any of the above embodiments, electromagnets may replace the permanent magnets. Electromagnets provide a greater magnetic flux density and thus still higher output.  
         [0023]    Other details, not shown or explained in further detail, for instance pertaining to the function of a rake tensioner, the embodiment of coils to which current is supplied, or the disposition of magnets and magnetic fields, can be learned from the references discussed above.  
         [0024]    It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.