Abstract:
The invention relates to a yarn tensioning device (B) comprising a braking body (K) embodied in the form of a truncated conical jacket ( 3 ) which is coaxially positioned on the rounded discharge end ( 2 ) of a storage body ( 1 ) and is pushed to a small diameter end ( 5 ) by the elastic axial force defining a braking effect between the braking body and the discharge end ( 2 ), an axial force generator (P) disposed between a fixed holding element ( 10 ) and the braking body and a centering device (C) provided with a radial working direction and disposed between the holding element ( 10 ) and the braking body, wherein said axial force generator (P) consists of at least one pair of axially superimposed permanent magnets, an intermediate slit is arranged between said permanent magnets and the centering device (C) which is embodied in the form of a axial slide guideway ( 9, 12, 24, 23 ) which is structurally and functionally separated from the permanent magnet pair or contactlessly formed thereby.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a yarn braking device. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a known yarn braking device (EP 0 534 263 A) a mechanical spring constitutes both the axial force generator and the radial centering device. The spring may be an annular radially oriented diaphragm, a radial spiral spring, a conical spiral spring, a cylindrical bellows, or, as shown in FIG. 1 of EP 0 652 312 A, a star-shaped spring arrangement consisting of helical tension springs each of which is hooked into the holder and into the support ring body, respectively. A general problem of mechanical springs is a development of the force which is not uniform in circumferential direction, the susceptibility to aggressive substances, and a tendency to collect lint. A further problem is that the mechanical spring at the same time has to centre in radial direction and has to transmit the axial force on the braking body. This dual function means a compromise between the development of the resilient axial force and of the radial centering force and might be critical in cases of extreme braking effects, i.e. if the same reliable centering of the frustocone coat braking body is necessary in case of an extremely weak braking effect or in case of an extremely strong braking effect. The adjustment range of the braking effect is limited by the nature of the mechanical spring, meaning that the mechanical spring has to be substituted by another as soon as a significant variation of the braking effect is needed. Basically, the braking effect is adjusted by the axial position of the holder in relation to the withdrawal end in order to load the spring more or less. In the case of a very weak braking effect due to the low spring load the centering and automatic return of the dislocated braking body into the centered position may fail, while in the case of an extremely strong adjustment of the braking effect the centering may be too rigid due to the high spring load. An optimal and constant centering effect and the capability of the braking body to automatically return after occurrence of a needed lateral displacement into a perfectly centered position on the withdrawal end of the braking body is, however, a decisive prerequisite for a correct braking function, since the large diameter end region of the frustocone coat braking body only then is able to produce a uniform braking effect along the circumference of the withdrawal end when the small diameter end of the frustocone coat braking body remains perfectly centered. Already small misalignments results in permanent fluctuations of the braking effect and in undesirable variations of the yarn tension. The yarn which rotates during withdrawal from the storage body in the yarn braking device like the hand of a clock in most cases is deflected in the support ring body and then applies a rotating, outwardly directed force on the braking body which force is varying, e.g. in case of a passing knot, and which has to be taken up and compensated permanently by the centering device. For that reason a properly operating centering device has a significant functional importance for this kind of a yarn braking device. 
         [0003]    It is known from DE 195 31 579 A in a small diameter circular disc brake, which the yarn is only passing laterally, to press the braking discs against each other by axially repelling permanent magnet rings. However, due to the only linearly passing yarn the functional requirements for centering are low since the discs are centered mechanically and are inclined in relation to each other during operation. 
         [0004]    Furthermore, it is known for controlled yarn braking devices (DE 198 39 272 A, EP 0 652 312 A, U.S. Pat. No. 5,778,943 A), the braking effect of which either can be modulated or can be switched off completely, to provide a magnetic axial force generator for a basic braking effect or passive position in combination with a mechanical spring arrangement. The axial force generator comprises at least one coil which is supplied with current. In the deenergised condition the axial force generator does not generate any force. 
         [0005]    It is an object of the invention to provide a non-controlled yarn braking device of the kind mentioned in the beginning which is structurally simple and reliable, allows a broad adjustment range of the braking effect and which has good performance even in case of extremely weakly and extremely strongly adjusted braking effects. 
         [0006]    This object is achieved according to one embodiment by providing a yarn braking device for a yarn feeding device, the yarn braking device having an axially stiff, radially deformable braking body with the shape of a frustocone coat, the large diameter end of the braking body being set coaxially over a rounded withdrawal end of a drum-shaped storage body and being pressed resiliently against the withdrawal end from the small diameter end by an axial force defining the braking effect between the braking body and the withdrawal end. An axial force generator acting in the axial direction and a center device acting in the radial direction are also provided, respectively, between a stationary holder and the braking body. The axial force generator is formed by at least one pair of permanent magnets, the permanent magnets of which are aligned axially to each other by the centering device with an intermediate gap, and the centering device includes an axial sliding guiding system which is separated structurally and functionally from the pair of permanent magnets. 
         [0007]    Pursuant to an additional embodiment of the invention, a yarn braking device for a yarn feeding device is provided, the yarn braking device having an axially stiff, radially deformable braking body with the shape of a frustocone coat, the large diameter end of the braking body being set coaxially over a rounded withdrawal end of a drum-shaped storage body and being pressed resiliently against the withdrawal end from the small diameter end by an axial force defining the braking effect between the braking body and the withdrawal end. An axial force generator acting in the axial direction and a centering device acting in a radial direction are also provided, respectively, between a stationary holder and the braking body. The axial force generator and the centering device at the same time are formed by at least one pair of permanent magnets, of which one inner permanent magnet is supported against the holder while the other outer permanent magnet of the pair is supported against the braking body, and the permanent magnets of the pair are aligned to each other via an intermediate gap and such that the direction of the action of the magnet force is inclined obliquely towards the axis of the yarn braking device. Further, the permanent magnets of the pair are generating both axial force components and also radial force components, respectively. 
         [0008]    In accordance with the first embodiment, the pair of the permanent magnets operates without contact and with a function which is not liable to aging, to aggressive substances, to misalignments, does not tend to develop the force irregularly, and which assures a wide adjustment range for the braking effect. The pair of permanent magnets exclusively has to generate the resilient axial force which determines the braking effect while the needed centering of the frustocone coat braking body is carried out at the small diameter end section by the sliding guiding system. The produced centering effect is the same for all adjustments of the braking effect. Both functions, i.e. the generation of the axial resilient force and the axial guidance may by optimised respectively per se since these functions do not interfere with each other during the operation of the yarn braking device. The problem of lint collection and the negative influence of collected lint are eliminated. The structural construction of the yarn braking device is simple and results in high reliability as there are no liable mechanical spring components. 
         [0009]    In the solution according to the second embodiment, the pair of permanent magnets at the same time forms the axial force generator and the centering device, i.e., the small diameter end of the braking body is supported without contact by magnet forces only, and at the same time is axially actuated against the storage body and is radially actuated from all sides in the direction towards the axis of the yarn braking device by radial force components of the magnet effect, and is centered accordingly. Since there is no mechanical contact the yarn braking device is characterised by a prompt and precise response behaviour. The at least one pair of permanent magnets in the yarn braking device forms, so to speak, a virtual or magnetic spring. The respective inner permanent magnet could be provided directly in the braking body or could be integrated even into the material of the braking body, respectively. 
         [0010]    As it is decisive for the desired braking function that the precisely adjustable axial resilient force permanently actuates the always correctly centered frustocone coat braking body against the withdrawal end, the permanent magnets in the pair of permanent magnets could be provided such that they either repel or attract each other, and such that the available mounting space is optimally used. 
         [0011]    In case of single pairs of permanent magnets at least three regularly distributed pairs should be provided. 
         [0012]    Very uniform development of the force can be achieved by ring-shaped permanent magnets which co-act essentially on the same diameters or even on different diameters. 
         [0013]    Alternatively, e.g. for weight reasons, more than three permanent magnet pairs each consisting of single permanent magnets could be distributed in circumferential direction. In this case either a provided axial sliding guiding system will form an anti-rotation mechanism for the permanent magnets within the pairs in order to always align the permanent magnets to each other, or the single permanent magnets could be designed such or/and arranged such that they automatically generate an anti-rotation effect by the magnetic co-action. 
         [0014]    The support ring body of a specific embodiment in which the centering device simultaneously constitutes the anti-rotation mechanism, is held in an outer ring carrying at least three axial guiding pins which are distributed in circumferential direction. The support ring body carries either a ring-shaped permanent magnet or several single permanent magnets, respectively. The holder is formed with a ring section which is equipped with guiding sleeves for the guiding pins and which either is provided with a ring-shaped permanent magnet or with single permanent magnets in a multiple arrangement. Alternatively, the guiding pins also may be anchored in the ring section of the holder, while the guiding sleeves then will be provided in the outer ring. The guiding pins should penetrate the guiding sleeves with a weak slide fit. 
         [0015]    In a further expedient embodiment the outer ring is formed at the inner side with a conical seat for the small diameter end of the braking body. The support ring body is a snap ring which is snapped into the outer ring in order to position the braking body in the seat. This is advantageous in terms of assembly and allows, if needed, a prompt and comfortable replacement of the braking body. 
         [0016]    In a further expedient embodiment the support ring body is secured at a small diameter ring edge of a generally conical cage the large diameter end region of which either is equipped with a ring-shaped permanent magnet or with several single permanent magnets, respectively, and which surrounds the braking body with radial distance. The cage is loosely inserted into a support ring which either includes the other ring-shaped permanent magnet or several single permanent magnets, respectively, and which is provided with axial holder feet which are distributed in circumferential direction. The inner sides of the holder feet define axial sliding guiding surfaces for a counter guiding surface at the outer periphery of the large diameter end region. In the case of ring-shaped permanent magnets an anti-rotation mechanism is not needed. To the contrary, an anti-rotation mechanism may be expedient in case of single permanent magnet pairs, e.g. between the cage and the support ring or between the sliding guiding surfaces and the counter guiding surface. The counter guiding surface may be concavely rounded in an axial section of the cage such that an axially shiftable universal joint or ball joint is formed between the counter guiding surface and the axial guiding surfaces of the holder feet. The universal joint or ball joint, respectively, allows the operation movements of the radially deformable braking body without interference and properly centers the small diameter end of the braking body. 
         [0017]    With a view to a comfortable assembly the holder feet are snap holders having an integrated predetermined bending elasticity for a snap fixation at the ring section of the holder. The cage and the holder feet offer sufficient intermediate spaces such that lint does not collect there, or such that access is provided at any time for cleaning purposes or for an inspection. 
         [0018]    With a view to easy assembly the support ring body should be formed with an outside seat for the small diameter end section of the braking body. The seat is bounded on one side by a shoulder such that the support ring body can be snapped into the ring edge of the cage in order to position the braking body. The seat could be formed partially or in its entirety in the ring edge of the cage. 
         [0019]    In a particularly expedient embodiment which operates without a mechanical axial sliding guiding system each outer single or the ring-shaped permanent magnet is arranged in relation to the axis on a larger diameter than each inner single permanent magnet or the inner ring-shaped permanent magnet. The permanent magnets of the pair or of the pairs, e.g. respectively repelling permanent magnets, co-operate such that forces are generated which are directed obliquely to the axis and such that radial force components of the forces can be used for the centering while the axial force components are used to generate the resilient axial force. The trick of arranging the outer permanent magnet or the outer permanent magnets, respectively, on a larger diameter than the inner permanent magnet or the inner permanent magnets, respectively, results in the effect that the inner permanent magnet in case of a displacement outwardly away from the axis will be exposed to an increasing counter oriented radial force component and then is pressed back with force again in the direction towards the axis. That means that the respective maximum centering radial force component only is generated then when the inner permanent magnet tends to displace outwardly. In this fashions the inner permanent magnet or the inner permanent magnets, respectively, are captured in the magnetic fields of the outer permanent magnets or the outer permanent magnet, respectively, provided that the braking body is contacting the withdrawal rim of the storage body under axial force. The small diameter end of the braking body remains properly centered even in case of forces which act radially outwardly and originate e.g. from the deflection of the yarn at the support ring body or from the passage of a knot. 
         [0020]    In a preferred embodiment the repelling surfaces of the repelling permanent magnets of the pair which repelling surfaces face each other, are inclined obliquely with respect to the axis, even, preferably, are formed conically, and are at least substantially parallel to each other. The radial and the axial force components are generated already by this design of the permanent magnets. 
         [0021]    In an expedient embodiment having two ring-shaped permanent magnets the permanent magnets may be conical rings having a rectangular or trapezoidal cross-section. Already by this form of the permanent magnets the direction of the magnetic action is inclined obliquely towards the axis of the yarn braking device and uniformly along the circumference such that the multiple effect of radial force components and of axial force components is achieved. The radial force components act counter to an outward displacement of the small diameter end and increase the stronger the more the small diameter end is displaced outwardly. 
         [0022]    In an expedient embodiment having single permanent magnets in several pairs distributed along the circumference the outer single permanent magnets are offset in circumferential direction relative to the inner single permanent magnets such that each outer single permanent magnet is directed into the gap between adjacent inner single permanent magnets or vice versa. Since then each inner single permanent magnet at the same time is actuated by the magnetic forces of two outer single permanent magnets from different directions the co-acting permanent magnets automatically constitute a contact free magnetic anti-rotation protection mechanism. Also in this case the inner single permanent magnets ought to be arranged on a smaller diameter than the outer single permanent magnets in order to achieve the necessary centering and return functions. 
         [0023]    In an expedient embodiment the support ring body carries the single inner permanent magnets or the ring-shaped inner permanent magnet, respectively. A conical support cage which grips over the small diameter end of the braking body and which is secured, preferably detachably, at the holder carries the single permanent magnets or the ring-shaped outer permanent magnet, respectively, on a carrying ring. This solution is of advantage with a view to easy manufacturing and easy assembly. 
         [0024]    In a further expedient embodiment a cylindrical extension of the frustocone coat is formed at the small diameter end of the braking body. This measure avoids local overloads at the small diameter end when actuated by the axial force and allows a simple assembly e.g. by only tucking the braking body loosely into the support ring body. 
         [0025]    In a further expedient embodiment an essentially cylindrical extension is provided at the support ring body. The cylindrical extension extends through the carrying ring of the support cage without contacting the carrying ring. This measure stiffens the support ring body and allows to limit the displacement of the braking body in an emergency case under extreme sideward displacement. During normal operation of the yarn braking device, however, there will not be any contact between the extension and the carrying ring. 
         [0026]    It is important for the above-mentioned reasons that an intermediate distance is generated in the direction of the magnet action between the support ring body and the carrying ring of the support cage, the intermediate distance being at least as large as the size of the air gap between the permanent magnets. 
         [0027]    An advantageous handling is achieved when the cylindrical extension of the support ring body at the end protruding beyond the carrying ring of the support cage is equipped with an outwardly directed catching projection, e.g. a ring flange the outer diameter of which is slightly larger than the inner diameter of the carrying ring. During assembly the support ring body first is put against resistance into the carrying ring. During the normal operation of the yarn braking device, i.e., as soon as the braking body abuts at the storage body, the catching projection does not engage at the carrying ring. However, during assembly or during transport, the engagement of the catching projection at the carrying ring assures that the support ring body and the braking body cannot fall out of the carrying ring. 
         [0028]    The magnitude of the axial force of the axial force generator is adjusted by the axial position of the holder in relation to the withdrawal end of the storage body. In order to allow to change the adjusted magnitude of the axial force generated between the permanent magnets precisely and remotely controlled and without manual engagement at the adjustment device of the holder, in an expedient embodiment at least one coil is functionally associated to one of the permanent magnets of the axial force generator in order to allow to generate an auxiliary magnet force which is superimposed on the axial force by selectively supplying current to the coil. The auxiliary magnet force increases or reduces the axial force to a desired extent. So to speak, one of the permanent magnets provided anyway for the suspension of the braking body is used as an armature of a selectively controlled electromagnet. Since the permanent magnets generate a relatively strong axial force a coil and/or a moderate current may be sufficient, which are not particularly strong, to adjust in some cases only a weak increase or decrease of the axial force. The axial effect of the coil or of several coils can be amplified by correspondingly placed iron, preferably soft iron. This embodiment is particularly expedient for a knitting machine, in particular a circular knitting machine at which frequently many yarn feeding devices are installed and where during operation fluctuations in the quality of the knitted fabric may occur which promptly could be compensated for by a change of the braking effect or the knitting yarn tension, respectively. By means of the coils in the yarn braking devices then the axial forces can be changed independently from the value of the respective axial force in one group of or in all yarn feeding devices, respectively, such that by this measure and substantially at the same time the tensions in the knitting yarns are raised or lowered by essentially the same amount. 
         [0029]    In a further embodiment the coil is arranged stationarily outside of the braking body and in association to the permanent magnet of the axial force generator which permanent magnet is supported at the braking body. In this case the permanent magnet provided anyway in the axial force generator is used without additional measures for this additional function. 
         [0030]    In a further embodiment the coil is supported at the braking body and is functionally associated to the permanent magnet which is provided stationarily outside the braking body. The coil is lightweight such that the mass of the braking body remains low. The permanent magnet provided outside the braking body anyway is part of the axial force generator and can be used for this additional function without additional structural measures. 
         [0031]    In a yarn braking device the braking body of which is arranged via a support ring body in a support cage the coil expediently is provided in the support cage or at the support ring body, respectively. Thanks to this placement the coil is located optimally close to the permanent magnet. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0032]    Embodiments of the invention will be explained with the help of the drawings. In the drawings is: 
           [0033]      FIG. 1  is a side view, in partial section, of a yarn braking device, 
           [0034]      FIG. 2  is a sectional view in the section plane II-II in  FIG. 1 , 
           [0035]      FIG. 3  is a sectional view in the section plane III-III in  FIG. 2 , 
           [0036]      FIG. 4  is a perspective view of the yarn braking device of  FIGS. 1 to 3 , 
           [0037]      FIG. 5  is a part of an axial sectional view of another embodiment of the yarn braking device, 
           [0038]      FIG. 6  is a side view of a detail of the yarn braking device of  FIG. 5 , 
           [0039]      FIG. 7  is a side view of a further detail of a yarn braking device of  FIG. 5 , 
           [0040]      FIG. 8  is an axial section of a further embodiment of a yarn braking device, 
           [0041]      FIG. 9  is a detail of  FIG. 8  in enlarged scale and in an axial section, 
           [0042]      FIG. 10  is a detail variant, in a section similar to  FIG. 9 , 
           [0043]      FIG. 11  is an axial section of a detail indicated in  FIG. 8  by a circle, 
           [0044]      FIG. 12  is a perspective explosion illustration of the main components of the yarn braking device of  FIG. 8 , 
           [0045]      FIG. 13  is another perspective view of a component of  FIG. 12 , 
           [0046]      FIG. 14  is a schematic axial section of a further embodiment of a yarn braking device, 
           [0047]      FIG. 15  is an axial section of a further embodiment of a yarn braking device, 
           [0048]      FIG. 16  is a detail variant similar to  FIGS. 9 and 10 , and 
           [0049]      FIG. 17  schematically shows a detail variant of a further embodiment of a yarn braking device. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    A first embodiment of a non-controlled yarn braking device B, shown in  FIG. 4  in a perspective view, is explained with the help of  FIGS. 1 to 4 . The yarn braking device B is mounted in a yarn feeding device F ( FIG. 1 ) comprising a drum-shaped stationary storage body  1  having a rounded withdrawal end  2  and an axis X which is also the axis of the yarn braking device B. A braking body K with the form of a frustocone coat  3  (having a straight line as a generatrice) is provided in the yarn braking device B. The braking body K is put with the large diameter end  4  over the withdrawal end  2  and is pressed against the withdrawal end  2  by an axially resilient force. The axially resilient force defines the braking effect for the yarn in the contact region between the inner side of the frustocone coat  3  and the withdrawal end  2 . During the withdrawal and the run through the yarn braking device the withdrawn yarn is circulating like the hand of a clock. The braking body K e.g. is made from plastic material with or without enforcement, from metal or from a mesh fabric or lattice fabric. In some cases an inner circumferentially continuous braking coating made of wear resistant material may be provided in the braking zone although the inner surface of the braking body K as well may be directly used for braking the yarn. The yarn braking body K is axially relatively stiff but radially easily deformable such that it embraces the withdrawal end  2  and is able to form a wave following the yarn which consequently revolves along the withdrawal rim. The deformability of the braking body K also allows to let knots pass through the braking zone. 
         [0051]    A small diameter end  5  of the braking body K is secured in this embodiment at a support ring body  8 . The support ring body  8  has at the inner side a low friction and wear resistant surface for the contact with the yarn which is deflected in this location. The support ring body  8  is formed as a snap ring and is snapped into the inner side of an outer ring  7 . The outer ring  7  (or the support ring body  8 ) has a conical seat  6  for the small diameter end  5  of the yarn braking body K. The yarn braking body K is replaceably positioned loosely by the snapping effect between the support ring body  8  and the outer ring  7 . 
         [0052]    In the yarn feeding device, which is not shown in detail, a holder  10  is supported stationarily with axial distance from the outer ring  7 . The holder can be adjusted parallel to the axis X. The holder has a ring section  11  forming a passing opening for the withdrawn yarn. A centering device C is provided between the holder  10  and the support ring body  8  which centering device C centers the small diameter end  5  of the yarn braking body on the axis X. In this embodiment, the centering device C, at the same time, constitutes an anti-rotation protection mechanism limiting or suppressing the relative rotation between the outer ring  7  and the holder  10 . Furthermore, an axial force generator P is provided ( FIG. 3 ) between the outer ring  7  and the holder  10 . The axial force generator P resiliently produces the axial force between the holder  10  and the yarn braking body K which axial force is decisive for the braking effect. 
         [0053]    The centering device C in  FIGS. 1 to 4  consists of several axial guiding pins  9  which are distributed in circumferential direction and, in this case, are anchored in the outer ring  7 . The guiding pins  9  are inserted with a weak slide fit into guiding sleeves  12  which are provided in the ring section  11  of the holder  10 . Expediently, a very small radial clearance is provided between the guiding pins  9  and the guiding sleeves  12 . The positions of the guiding pins  9  and the guiding sleeves  12  could be inverted as well. 
         [0054]    The axial force generator P is constituted in this embodiment by repelling permanent magnets  13 ,  14  which are aligned with each other pairwise and in axial direction. Single permanent magnets  13  are contained in pockets  16  of the outer ring, while pockets  15  at the ring section  11  which pockets  15  are axially aligned with the pockets  16  also contain single permanent magnets  14 . 
         [0055]    The adjustment of the axial force between the permanent magnets  13 ,  14  pressing the braking body K against the withdrawal end  2  is carried out by the axial positioning of the holder  10  relative to the withdrawal end  2 . 
         [0056]    In the shown embodiment three guiding pins  9  are provided with equal distances (120°). The guiding pins  9  are structurally and functionally separated from the permanent magnet pairs. Furthermore, twelve regularly distributed (30°) permanent magnet pairs  13 ,  14  are provided. The number of guiding pins  9  and/or of permanent magnet pairs as well may be selected differently. 
         [0057]    Although this is not shown in  FIGS. 1 to 4 , two ring-shaped, one-piece permanent magnets could be provided instead of several single permanent magnet pairs  13 ,  14 . The ring-shaped permanent magnets could be made e.g. from a mass which is bonded by plastic material and which can be magnetised. In a further, not shown, modification of the embodiment of  FIGS. 1 to 4  permanent magnet pairs could be used the permanent magnet of which pairs are attracting each other. This could be realised e.g. by placing a ring like the outer ring  7  on ends of the guiding pins  9  which ends extended beyond the holder  10  and by mounting other attracting permanent magnets at the ring. For example, neodymium permanent magnets or ferrite permanent magnets are particularly suitable. 
         [0058]    A detail variant of the yarn braking device is indicated in dotted lines in  FIG. 1 . A coil  39  which selectively can be supplied with current is magnetically and functionally associated to the permanent magnets  13  which transmit the axial force of the axial force generator P to the braking body K at the outer side such that with current supplied to the coil  39  an auxiliary magnet force  41  can be generated which has essentially the same or the opposite direction of action like the axial force by which auxiliary magnet force  41  the value of the axial force can be increased or decreased. The coil  39  e.g. is placed at a carrier  40  provided at the ring section  11 . 
         [0059]    In the yarn braking device B in  FIGS. 5 to 7  an anti-rotation protection mechanism is dispensed with in comparison to the embodiment of  FIGS. 1 to 4 . The holder  10  is positioned with its ring section  11 ′ very close to the withdrawal end  2  of the storage body  1  at the yarn feeding device (not shown). By this arrangement mounting space is saved at the other side of support ring body  8  which is provided in some cases. 
         [0060]    In this embodiment the braking body K is positioned with the small diameter end  5  in a conical seat  6  which is formed in this case in the support ring  49 . The seat is bounded by a shoulder  8   a . A generally conical cage  18  is supported on the shoulder  8   a  via a ring edge  17 . The ring edge  17  is snapped into the seat  6  in order to secure the small diameter end  5  of the braking body K. The cage  18  is formed with a cone angle which is larger than the cone angle of the braking body K. Furthermore, the cage  18  is provided with several spokes emanating from the ring edge  17  and leading to a ring-shaped large diameter end region  20 . So to speak, the braking body K is sunk into the cage  18  at least with a part of its longitudinal extension. 
         [0061]    The large diameter end region  20  of the cage  18  contains a ring-shaped permanent magnet  13 ′ which is aligned axially by the centering device on a further ring-shaped permanent magnet  14 ′. The ring-shaped permanent magnet  14 ′ is held in a support ring  21 . The support ring  21  has axial and regularly distributed holder feet  22  at the outer side extending in the direction of the large diameter end  4  of the braking body. The holder feet  22  are formed as snap holders with integrated predetermined bending elasticity and are snapped into the ring section  11 ′ of the holder  10 . Axial guiding surfaces  23  for co-action with a counter guiding surface  24  at the outer periphery of the large diameter end region  24 , e.g. formed with a circumferentially continuous extension, are provided at the inner walls of the holder feet  22 . The guiding surfaces  23 ,  24  constitute the centering device C. The counter guiding surface  24  e.g. is convexly rounded as shown in order to create the function of an axially movable universal joint or ball joint, respectively, for centering the braking body K. 
         [0062]    In a not shown modified embodiment of  FIGS. 5 to 7  instead of the two ring-shaped permanent magnets  13 ′,  14 ′ several single permanent magnet pairs could be provided similar to  FIG. 2 . In this case it is expedient to also integrate an anti-rotation protection mechanism into the centering device C, e.g. by means of a circumferential form fit co-action between the guiding surfaces  24 ,  23 . 
         [0063]    In the embodiment in  FIGS. 5 to 7  respective repelling permanent magnets are provided. In a not shown modification instead respectively attracting permanent magnets could be used, e.g. by securing one permanent magnet ring at the upper end of the holder feet  22  which attracts the other ring-shaped permanent magnet which then is provided in the large diameter end region  20 . The cage  18  is loosely inserted with the braking body K into the structure defined by the holder feet  22  and the support ring  21 . A replacement of the braking body K is possible after detaching the holder feet  22  from the ring section  11 ′. In this case either the braking body K is changed together with the cage  18  as one unit, or only the braking body K is replaced after detaching the support ring body  8  from the ring edge  17 , respectively. 
         [0064]    The spokes  19  ( FIG. 6 ) of the cage  18  allow permanent visual inspection or cleaning of the inner components, because the holder feet  22  form large dimensioned intermediate spaces. Except the permanent magnets all components of the yarn braking device could be plastic form parts. This is true also for the embodiment of  FIGS. 1 to 4 . 
         [0065]    A detail variant of the yarn braking device B is indicated by dotted lines in  FIG. 5 . At least one coil  39  is provided in the holder feet  22  such that it co-acts magnetically with the permanent magnet  13 ′ when current is supplied. The coil  39  superimposes an auxiliary magnet force to the axial force generated between the permanent magnets  13 ′,  14 ′. The auxiliary magnet force either has the same or the opposite direction of action as the axial force. The coil  39  in  FIG. 5  is arranged such that it generates an auxiliary magnet force  41  which increases the axial force when the coil  39  is under current. 
         [0066]    In the embodiments of  FIGS. 8 to 17  the axial force generator P and the centering device C at the same time are formed free of contact by the permanent magnet pairs. The permanent magnets (either two rings or several pairs of single permanent magnets distributed in circumferential direction) co-operate with a magnet effect which is directed obliquely to the axis X. Preferably, respectively repelling permanent magnets are used, although (not shown) respectively attracting permanent magnets could be used if arranged accordingly. 
         [0067]    The axial section in  FIG. 8  shows the operative position of the yarn braking device B with the yarn braking body K axially resiliently pressed against the withdrawal rim  2  of the storage body  1 . The support ring body  8  is provided in the small diameter end of the yarn braking body K. The support ring body  8  optimally may be formed with a cylindrical extension. The support ring body  8  carries at the outer side the ring-shaped permanent magnet  13 ′ to which a ring-shaped permanent magnet  14 ′ is aligned essentially axially. The ring-shaped permanent magnet  14 ′ is held in a support cage. As will be explained with the help of  FIGS. 9 ,  10  and  16 , in this case the repelling permanent magnets  13 ′,  14 ′ are arranged such, and/or are constructed such, that the magnet effect is directed obliquely to the axis X of the yarn braking device B and such that by the magnet effect inwardly directed radial force components and axial force components in the direction towards the storage body are generated. The permanent magnet  13 ′ could be directly provided at the braking body K or could be integrated in the material of the braking body K, respectively (e.g. made from magnetplast). 
         [0068]    The support cage  26  shown in  FIG. 9  only partially (with intermediate spaces between the spokes  27 ) has a circumferential continuous carrying ring  37  at the smaller end. The ring-shaped permanent magnet  14 ′ formed as a conical ring of trapezoidal cross-section is positioned inside the carrying ring  37  such that a flat or conical repelling surface (the broader base of the trapezoid) is inclined relative to the axis with an angle which e.g. amounts to about 45°. The ring-shaped permanent magnet  13 ′, also being a conical ring having trapezoidal cross-section and a flat or conical repelling surface at the broader base of the trapezoid is aligned essentially axially to the ring-shaped permanent magnet  14 ′. The permanent magnet  13 ′ is secured in the support ring body  8  the cylindrical extension  29  of which extends without contact through the carrying ring  37 . An air gap is formed between the repelling surfaces of the permanent magnets  13 ′,  14 ′. The radial distance between the extension  29  and the carrying ring  37  is essentially as large as the width of the air gap. A catching projection  38  is formed at the free end of the extension  29 , e.g. a hook-shaped outer flange, the outer diameter of which is slightly larger than the inner diameter of the carrying ring  37 . The support ring body  8  consists of elastic material, e.g. plastic material. The elasticity of the material allows to introduce the catching projection  38  into the carrying ring  37  by overcoming a certain resistance. However, the support ring body  8  only can be pulled out from the carrying ring  37  with significant force and such that it cannot fall out later by itself from the carrying ring  37  or the support cage  26 , respectively. 
         [0069]    The braking body K is equipped at the small diameter end  5  with a cylindrical extension  5 ′ which is connected to the small diameter end  5  via an inwardly rounded shoulder such that a rounded yarn deflection shoulder  5 ″ is formed which is lined with the material of the braking body K. Furthermore, a seat  30  for the yarn braking body K is formed in the support ring body  8 . The yarn braking body K either is only inserted loosely into the support ring body  8  such that in case of a needed replacement of the braking body K the support ring body  8  can be re-used, or in some cases may be bonded, e.g. glued to the support ring body  8 . 
         [0070]    Due to the essentially parallel repelling surfaces of both permanent magnets  13 ,  14  which both are inclined obliquely the repelling force acts obliquely to the right side and downwards to the axis X such that the axial force for pressing the braking body K against the withdrawal rim  2  and at the same time the radial force components for centering the small diameter end  5  of the braking body K are generated by the magnet effect and such that no mechanical contact occurs between the support ring body  8  and the carrying ring  37 . 
         [0071]    Dotted lines in  FIG. 9  indicate that two coils  39 , which may be supplied with current selectively, are situated in the small diameter end of the support cage  26  such that they are functionally associated to the permanent magnet  13 ′ and that they generate an auxiliary magnet force at the permanent magnet  13 ′ when supplied with current. As an alternative, to the contrary, the coil  39 ′ as well could be placed at the braking body K or the support ring body  8 , respectively, and could be functionally associated to the stationary permanent magnet  14 ′, in order to generate the necessary auxiliary magnet force. 
         [0072]    As the yarn braking device B does not need a mechanical centering device or axial guiding device, respectively, when the permanent magnets  13 ′,  14 ′ as well constitute the centering device C, the support ring body  8  in the embodiment of  FIG. 10  is formed without a cylindrical extension  29  as shown in  FIG. 9 . With this measure the moving masses are reduced. The support ring body  8  may form the shoulder region  5 ″ for deflecting the yarn. The braking body K is inserted with the small diameter end  5  directly into the seat  30  of the support ring body  8 , in some cases only loosely, or in other cases bonded thereto. Both permanent magnets  13 ′,  14 ′ are co-operating in this case on the same diameter d on which, so to speak, the magnetic force centers of both permanent magnets  14 ′,  13 ′ are situated. 
         [0073]      FIG. 11  illustrates the detachable fixation of the support cage  26  in a ring body  11  of the not shown holder  10 . The ring body  11  has a flange  32  with insertion openings  33  for latching tongues  35  of the support cage  26 . The latching tongues  35  are hooked in easily detachable fashion behind a shoulder. 
         [0074]    The exploded illustration in  FIG. 12  shows the arrangement of the main components of the yarn braking device e.g. of  FIGS. 8 and 9  with the support cage  26  having the spokes  27 , the latching tongues or latching hooks  25  and the carrying ring  37 , the support ring body  8  having the extension  29  and finally the braking body K having the cylindrical extension  5 ′ shown in  FIG. 9 . The inner ring-shaped permanent magnet  13 ′ is fixed at a shoulder region of the support ring body  8 , e.g. by gluing or by a snap fit. 
         [0075]      FIG. 13  illustrates the positioning of the outer ring-shaped permanent magnet  13 ′ on the inner side of the carrying ring  37  of the support cage  26 . The permanent magnet  14 ′ as well either is glued in or is snapped in. Since the support ring body  8  and the support cage  26  may be injection moulded parts of plastic material the permanent magnets  13 ′,  14 ′ even may be embedded and positioned during by the injection moulding process. The coil  39  (in some cases even several coils) may be placed inside the support cage  26 . 
         [0076]      FIG. 16  shows a modified detail variant of the yarn braking device of  FIGS. 8 ,  9  and  10 . The outer ring-shaped permanent magnet  14 ′ has a larger diameter d 2  and the inner ring-shaped permanent magnet  13 ′ has a smaller diameter d 1 . The further design corresponds with the design as explained with the help of  FIGS. 9 and 10 . The permanent magnets  13 ′,  14 ′ repel each other. Since the outer permanent magnet  14 ′ is acting on the diameter d 2  which is larger than d 1 , the radial component of the repelling force increases when the small diameter end  5  of the braking body K in  FIG. 16  e.g. tends to become displaced upwardly such that an expanded radial range exists within which the inner permanent magnet  13 ′ is forced back and centered by the outer permanent magnet  14 ′. This returning force action is the stronger the more the inner permanent magnet  13 ′ is displaced upwardly. 
         [0077]    In the embodiment of the yarn braking device B shown in  FIG. 14  two ring-shaped permanent magnets  13 ′,  14 ′ (repelling permanent magnets) are provided in the form of conical rings having a rectangular cross-section. The permanent magnets  13 ′,  14 ′ at the same time constitute the axial force generator P and the centering device C. 
         [0078]    The embodiment in  FIG. 15  contains two ring-shaped (conical ring) permanent magnets  13 ′,  14 ′ having rectangular cross-sections (respectively repelling permanent magnets). The outer permanent magnet  14 ′ is provided on a larger diameter d 2  while the inner permanent magnet  13 ′ is provided on a smaller diameter d 1 , in order to achieve, as explained for  FIG. 16 , a larger radial range within which the inner permanent magnet  13 ′ in case of a displacement is returned into the centered position by the increasing force from the outer permanent magnet  14 ′. 
         [0079]    The principle of the magnet effect which acts obliquely to the axis X of the yarn braking device cannot only be realised with ring-shaped permanent magnets, but also can be achieved as shown in  FIG. 17  even with single permanent magnets  13 ,  14  which e.g. may be cylindrical discs or cuboid-shaped blocks, respectively. The permanent magnets  13 ,  14  respectively are distributed pairwise around the circumference of the yarn braking device. The inner single permanent magnets  13  are connected e.g. to the carrying ring  37  or to another holding means. The permanent magnets  13 ,  14  are aligned to each other such that the magnet effect is directed obliquely, e.g. towards a point of intersection  36  to the axis X in order to generate the axial force and at the same time the radial force components. The permanent magnets  14  expediently are arranged at a larger diameter d 2  than the inner permanent magnets  13 . In order to prevent the permanent magnets  13 ,  14  being rotated in relation to each other about the axis X the permanent magnets  13 ,  14  are offset in circumferential direction such that they face the respective gaps between two adjacent other permanent magnets. That is, each permanent magnet  13  at the same time is actuated magnetically and obliquely with forces from two outer permanent magnets  14 . A gap between the outer permanent magnets  14  e.g. is indicated with reference numeral  34 . The inner single permanent magnet  13  is aligned to this gap  34 . The directions of the actions between the outer and the inner permanent magnets  13 ,  14  need not be directed to the same point of intersection  36  on the axis X, but the directions of the actions of the outer repelling permanent magnets  14  as well could intersect the axis X further to the left side than at the point of intersection  36 . Thanks to this arrangement the co-acting permanent magnets  13 ,  14  constitute the axial force generator P and the centering device, in particular, without any mechanical contact, and as soon as the braking body K is pressed against the storage body  1 . The permanent magnets  13  could be provided directly at the braking body K or could even be integrated into the material of the braking body K, respectively. 
         [0080]    The coil or the coils  39 ,  39 ′ expediently are connected to a current control device and a current adjusting device. In order to improve the action of the coil iron material, in particular soft iron could be placed in the vicinity of the coil. In case that a circular knitting machine having many such yarn feeding devices which are equipped with such yarn braking devices B, all coils  39 ,  39 ′ expediently could be controlled by a central current control device and current adjustment device in order to change the axial forces in the yarn braking devices of those yarn feeding devices jointly and independent from the value of the respective pre-adjusted axial force by an e.g. equal amount. In this fashion a trend to a deterioration of the quality of the knitted fabric, caused by a drift or fluctuation of the knitting yarn tension can be compensated for comfortably.