Abstract:
A system and method for winding at least one continuous strand of material ( 210 ) on a rotating support ( 212 ) to form a strand package or cake includes a rotatable traversing apparatus ( 216 ) for causing the at least one strand of material to reciprocate along a length of the rotating support ( 212 ) for even distribution in forming the package or cake. A plurality of strands can be wound simultaneously, the traversing apparatus having a form and operating orientation that generally maintains a parallel separation of the several strands while being wound on the support. The strand material may be, for example, glass, and a winding system may further include a source of glass strands, including a source of glass fibers ( 102 ) and a grouping mechanism ( 108, 208 ) for grouping respective pluralities of glass fibers into respective strands of glass fiber.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to winding filaments or strands comprising a plurality of filaments onto a rotating support to form a bobbin, cake, or the like. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is generally known in the art to wind elongate filaments or strands onto a rotating support to form cakes (sometimes also referred to in the art as bobbins or packages or spools or rolls) of the wound material. 
         [0003]    In the field of glass fiber materials, it is generally known to draw a plurality of glass fibers passing molten glass from a molten glass source through a bushing assembly having a plurality of bushings to obtain a corresponding plurality of glass fibers. A predetermined number of the thus obtained glass fibers are grouped to obtain a respective glass fiber strand (sometimes referred to in the art as a split). 
         [0004]    One or more glass fiber strands are then wound on a rotatable spindle having an axis of rotation to form a cake or bobbin. 
         [0005]      FIG. 1  is a schematic illustration of a conventional glass fiber strand winding system  100  in accordance with the foregoing. 
         [0006]    Bushing assembly  102  includes a plurality of bushings through which a molten glass (from a conventional source of molten glass, not shown) is drawn to form a plurality (as many as several thousands) of individual glass filaments  104 . A conventional sizing composition may be optionally deposited on glass filaments  104  by a conventional sizing device  106 . In an example of a conventional sizing device, filaments  104  may be passed through or adjacent to the sizing device  106  to deposit a predetermined sizing composition, for example, by passing the filaments  104  against a surface (such as a roller) wetted with the sizing composition. The sizing composition may be useful, for example, for protecting the glass filaments from breakage or to enhance bonding with a reinforcing matrix, if used later to create a composite material. 
         [0007]    Next, the filaments  104  are separated by a separating device  108  into several groups of filaments to obtain respective glass fiber strands (sometimes referred to as splits)  110 , each glass fiber strand  110  having a plurality of filaments, up to about 200 filaments each. The conventional separating device  108  has, for example, a plurality of spaced apart teeth like a comb. Accordingly, each group of filaments is separated from other groups by the teeth of the separating device  108  to define the corresponding plurality of generally planar glass fiber strands  110 . 
         [0008]    The one or more glass fiber strands  110  are thereafter wound on a spindle or other elongate rotating support  112  to obtain a wound cake  114  of glass fiber strands. 
         [0009]    It is known in the art to use a mechanical traversing apparatus  116  to laterally displace the one or more glass fiber strands along an axial length of the spindle  112  in order to distribute the glass fiber strands during winding, so as to obtain a cake  114  that is wound consistently and, particularly, that can unwound reliably when desired. The conventional traversing apparatus in  FIG. 1  is indicated very schematically at  116 , and generally functions by displacing the glass fiber strands  110  in a reciprocating fashion back and forth along an axial portion of the spindle  112  while the glass fibers strands  110  are being wound onto spindle  112 , in order to create a uniform cake  114 . 
         [0010]    Some conventional examples of traversing apparatus  116  include devices driven to rotate about an axis, having various rectilinear and curvilinear bars, blades, surfaces, and the like that are inclined in predetermined orientations relative to the axis of rotation of the device. The conventional traversing apparatuses are placed so as to be in contact with the one or more glass fiber strands  110 , downstream of the separating device  108  and upstream of the rotating spindle  112 . The arrangement of the bars on the traversing apparatus  116 , which selectively contact the glass fiber strands  110  as a function of the rotation of the traversing apparatus  116 , generally displaces the glass fiber strands in a reciprocating fashion back and forth along an axis of rotation of the traversing apparatus  116  so as to deposit the glass fiber strands  110  along an axial length of the cake  114  being wound. 
         [0011]    Examples of conventional traversing apparatuses are disclosed in, for example, U.S. Pat. No. 5,669,564; U.S. Pat. No. 3,292,872; U.S. Pat. No. 2,989,258; U.S. Pat. No. 3,946,957; U.S. Pat. No. 3,399,841; U.S. Pat. No. 4,239,162; U.S. Pat. No. 3,819,344; U.S. Pat. No. 3,861,608; U.S. Pat. No. 3,784,121; and U.S. Pat. No. 3,356,304. 
         [0012]    As seen in  FIG. 2 , once several cakes  114  are wound, the plurality of respective glass fiber strands  110  wound about each cake  114  as illustrated in  FIG. 1  is thereafter pulled from a plurality of cakes  114 , as represented in  FIG. 2 . The several pluralities of glass fiber strands  110  taken from the plurality of cakes  114  are thereafter wound together to form a “roving assembly” (sometimes referred to as a “multi-end” (in reference to the amassed grouping of glass fiber strands) package)  120 . 
         [0013]    For example, in  FIG. 2 , each of the three cakes  114  may each comprise 12 wound glass fiber strands. To manufacture roving assembly  120 , each group of 12 glass fiber strands from each cake  114  are taken together and wound to form the roving assembly  120 . Thus, the roving assembly  120  should provide 36 glass fiber strands when it is unwound in subsequent use. 
         [0014]    Roving assembly  120  is typically used as a source of continuous glass fiber, for example, for subsequent production of chopped glass fiber for use as a composite material reinforcement. In such use, the roving assembly is unwound at relatively high speed to provide the glass fiber for subsequent manufacturing processes. However, conventionally known defects in the manufacture of the roving assembly cause later problems. 
         [0015]    One major defect is a variation in the number of strands wound in the final roving assembly. This can in turn cause variations in the amount of glass material that is actually in a given roving assembly, compared to an expected amount. In some cases, this problem can be traced back to manufacture of the cakes  114 . In particular, if the respective glass fiber strands  110  are not kept at a desired separation while the cake  114  is wound, this can cause glass fiber strands  110  to stick together, sometimes over a non-trivial length, particularly after a sizing deposited by the sizing device  106  is cured. This problem can occur very quickly while the cakes  114  are wound, given the rate of winding (sometimes as much as 25 meters of strand material per second). In effect, there may be fewer glass fiber strands  110  than expected, because the strands adhere to one another. 
         [0016]    Another conventionally recognized defect is the generation of loops in the strands in the roving assembly after the roving assembly  120  is wound. Most generally, this is caused by strands being unevenly (in a lengthwise sense) wound onto a respective cake  114  during manufacture. For example, in a cake having tapered or conical ends when seen from the side (similar to the truncated ellipsoidal form of cake  114  seen in  FIGS. 1 and 2 ), the length of a given strand that is wound on the cake will be lower as a function of the proximity of that strand to an axial end of the cake. (As the diameter of the cake at its axial end is smaller than at its middle, the length of strands wound at the end of the cake is shorter than the length of strands wound towards the axial center of the cake.) 
         [0017]    For example, in  FIG. 1 , the linear extent of leftmost glass fiber strand  110 ′ that is wound onto spindle  112  will vary depending on how far strand  110 ′ is from the left end A of cake  114 , as the collective group of strands is reciprocally traversed by traversing apparatus  116 . That is, a shorter length of strand  110 ′ will be wound onto spindle  112  when the strand  110 ′ is closest to end A of cake  114  because the diameter of the cake at that point is the smallest. Greater and greater lengths of strand  110 ′ are wound onto spindle  112  as the group of strands is traversed to the right by traversing apparatus  116  because the diameter of the cake  114  (corresponding to the instant position of strand  110 ′) progressively increases. Obviously, this variance is reversed when the group of strands is subsequently traversed towards the left. 
         [0018]    Furthermore, when the group of glass fiber strands is considered collectively in this context, it is evident that at a given moment longer and longer lengths of the respective strands to the right of strand  110 ′, respectively, are wound on the spindle  112 . Thus, each glass fiber strand is wound onto the spindle at different rates and when the cake is unwound, the respective strands pulled from a given cake will have different lengths. Theoretically, this effect cancels itself out in a “roundtrip” of the group of fiber strands (i.e., when the group of fiber strands completes a full trip in one sense and a return trip, thanks to traversing apparatus  116 ). However, that depends on keeping the strands in the same order as the strands  110  are traversed back and forth. As a practical matter, this happens rarely, at least partly due to problems with conventional traversing apparatuses. 
         [0019]    Accordingly, when a collection of glass fiber strands is unwound from the cake  114 , some of the glass fiber strands may be longer than others. This excess length is sometimes referred to as “catenary” and manifests itself as loose or slack portions of strand that tend to twist and loop. 
         [0020]    Another possible cause of loops in conventional winding apparatuses is that the conventional traversing apparatuses may be too slow in causing the one or more glass fiber strands to change in direction in the above-described reciprocal movement. Particularly when more than one glass fiber strand is wound into a cake, problems with the required reciprocal movement can cause the plurality of glass fiber strands to linger or pause at one of the extreme ends of the traversing apparatus instead of smoothly changing direction along the traversing apparatus. Because the winding of the cake  114  onto spindle  112  is continuous, any significant pause in the traversing movement causes several layers of glass fiber strands to be quickly wound at a single axial point along the cake, instead of distributing the glass fiber strands along the cake  114  as it is wound. Combined with the previously noted problem of adhesion between strands, a cake suffering from these defects may be prone to problems during unwinding, such as “bird&#39;s nests” or tangles, when a disorganized, possibly self-adhered, portion of glass fiber strands is pulled en masse from the otherwise smoothly wound cake. 
         [0021]    These tangles of glass fiber strands can cause significant disruption during production (bearing in mind that the entire process depends on the smooth and consistent winding and unwinding of glass fiber strands) and loss of product yields (as the tangled fiber strands cannot be used commercially). 
         [0022]    It is therefore of interest to improve systems for winding glass fiber strands into cakes, taking into account the above-mentioned problems. 
         [0023]    A previous attempt to address these types of issues led to using a traversing apparatus having an oblique cylindrical form, comprising a pair of bar supports and a plurality of straight bars or struts extending in parallel and regularly distributed about a circumference of the apparatus. However, the axis of rotation of this type of traversing apparatus is inclined relative to the direction of extension of the plurality of bars extending between the bar supports. 
         [0024]    Prior art traversing apparatuses with curved bars suffer from problems as glass fiber strands slide along the bars, such as changes in strand separation (including mixing of the order of the strands during sliding), and inconsistent variations in sliding speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The presently described invention will be even more clearly understandable with reference to the drawings appended hereto, in which: 
           [0026]      FIG. 1  is a schematic representation of a conventional system for winding a plurality of strands, particularly glass fiber strands, into a cake or the like; 
           [0027]      FIG. 2  is a schematic representation of a conventional process of winding a roving assembly using multiple fiber strands taken from multiple cakes of the type represented in  FIG. 1 ; 
           [0028]      FIG. 3  is a perspective view of a traversing apparatus for fiber strands according to the present invention, relative to a spindle onto which the fiber strands is wound; 
           [0029]      FIG. 4   a  is an end view of the traversing apparatus of  FIG. 3 , seen along an axis of rotation X of the traversing apparatus; 
           [0030]      FIG. 4   b  is a partial side view of the traversing apparatus of  FIG. 3  illustrating an angular relationship between respective bars of the apparatus; 
           [0031]      FIG. 5   a  is a schematic representation of the orientation of first and second groups of primary bar members of the traversing apparatus of  FIGS. 3 and 4 , relative to respective conical surfaces; 
           [0032]      FIG. 5   b  is schematic end view of the traversing apparatus, taken along its axis of rotation, further illustrating the orientation of the first group of primary bar members on an oblique conical surface; 
           [0033]      FIG. 5   c  is the same schematic end view as in  FIG. 5   b , but illustrating the arrangement of the second group of primary bar members on another oblique conical surface; and 
           [0034]      FIG. 6  is a partial perspective view of a traversing device according to the present invention illustrating effective planar surfaces defined by adjacent primary bar members of the traversing apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    The present invention is directed to a traversing apparatus for use in a system for winding fiber strands, particularly but not necessarily only glass fibers, into a cake or the like. The traversing apparatus of the present invention has a geometry designed to evenly and consistently displace fiber strands, particularly, a plurality of fiber strands, onto a rotating spindle onto which the fiber strands are wound to form the desired cake. 
         [0036]      FIG. 3  is a partial detailed plan view of part of a winding system corresponding to that schematically illustrated in  FIG. 1 . 
         [0037]    Specifically in  FIG. 3 , a traversing apparatus  216  according to the present invention is rotatably mounted on a shaft or the like  250 . The shaft  250  is driven to rotate about an axis of rotation X by conventional mechanical drive means, such as a motor (not shown here). A rotatably mounted spindle  212  is provided downstream of traversing apparatus  216 , and is driven to rotate about an axis of rotation X′ by conventional mechanical driving means, such as a motor (not shown here). Axis X′ may be generally parallel to axis X. As in the conventional system of  FIG. 1 , a plurality of spaced apart and generally parallel fiber strands  210  is wound about spindle  212 . Fiber strands  210  are obtained from a source upstream of traversing apparatus  216 . In one example, the fiber strands  210  are glass fiber strands, each glass fiber strand comprising a respective plurality of individual glass fibers drawn from a conventional bushing assembly  102  and grouped by a conventional separating device  208  such as that described with reference to  FIG. 1 . 
         [0038]    In order to simplify the written description of the invention, a plurality of fiber strands  210  are mentioned herein, but the invention can be applied to a single fiber strand. 
         [0039]      FIG. 4   a  is an end view of traversing apparatus  216  looking along axis of rotation X. Corresponding features in  FIGS. 3 and 4   a  are correspondingly numbered. 
         [0040]    In general, traversing apparatus  216  includes opposing first and second bar supports  222   a ,  222   b . First and second bar supports  222   a ,  222   b  can be generally parallel with one another and are preferably, but not necessarily, skew relative to the shaft  250 , as seen in  FIG. 3 . First and second bar supports  222   a ,  222   b  may optionally include one or more openings  223  formed therethrough, possibly to modify the weight of the apparatus as needed, to alter moments of inertia in the rotating apparatus, etc. Bar supports  222   a ,  222   b  are made of any conventional rigid material suitable for the operating environment, particularly with respect to temperature and with respect to chemical reactivity (the material should not chemically react) relative to fiber strands being wound and relative to any corresponding chemicals used. In one particular example, the bar supports  222   a ,  222   b  may be made out of metal generally, and may in particular be aluminum. 
         [0041]    A plurality of bar members extends between respective peripheries of the first and second bar supports  222   a ,  222   b . More specifically, a first group of primary bars  224   a ,  224   b ,  224   c  are adjacent to one another and extend between a part of the periphery of first bar support  222   a  and part of a periphery of second bar support  222   b . Similarly, a second group of primary bars  226   a ,  226   b ,  226   c  extends between another part of the periphery of first bar support  222   a  and another part of the periphery of second bar support  222   b.    
         [0042]    The provision, as illustrated, of three primary bars in each group of primary bars is by way of example only. The number of primary bars in each group can be varied if the general geometric conditions described herein are respected. In general, the same number of primary bars is to be provided in the first and second pluralities of primary bars. Also, in general, a relatively small number of primary bars in each group is preferred, in part to reduce the overall friction caused by contact between the strands  210  and the primary bars. 
         [0043]    As will be discussed in more detail below, the first group of primary bars  224   a ,  224   b ,  224   c  is arranged relative to one another so as to lie on the surface of a first cone  500   a . (See, for example,  FIGS. 5A and 5B .) The second group of primary bars  226   a ,  226   b ,  226   c  is arranged relative to one another so as to line on the surface of a second, different cone  500   b , oriented in a direction opposite to that of cone  500   a . (See, for example,  FIGS. 5A and 5C .) As will be appreciated more fully taking into account the description below, the primary bars of the first group  224   a ,  224   b ,  224   c  have a generally negative slope relative to the axis of rotation X along a direction from first bar support  222   a  towards second bar support  222   b . Conversely, the primary bars  226   a ,  226   b ,  226   c  of the second group have a positive slope relative to the axis of rotation X along a direction from first bar support  222   a  towards second bar support  222   b.    
         [0044]    With this arrangement, primary bars  224   a  and  224   b  are coplanar, as are primary bars  224   b  and  224   c . Likewise, primary bars  226   a  and  226   b  are coplanar, as are primary bars  226   b  and  226   c . See, particularly,  FIG. 6 , which is a partial end view of the traversing apparatus  216  with bar support  222   a  removed to illustrate the relative planes defined by adjacent bars (indicated by broken lines). The coplanar relationship between the primary bars in each respective plurality of primary bars ensures a smooth sliding motion of the fiber strands  210  as each bar comes into contact with the strands  210  as the traversing apparatus  216  rotates in operation. 
         [0045]    However, opposed primary bars of the first and second pluralities (that is,  224   a  and  226   a , and  224   c  and  226   c ) are skewed (i.e., are not coplanar) relative to each other. See, for example,  FIG. 4   b  and  FIG. 6 . More particularly, opposed primary bars of the first and second pluralities ( 224   a ,  226   a ;  224   c ,  226   c ) have different “signs” (i.e., bars  224   a  and  224   c  have negative slopes, while bars  226   a  and  226   c  have positive slopes, as discussed above). 
         [0046]    If the plurality of fiber strands  210  were to be transitioned directly from bar  226   a  to bar  224   a  (or from bar  224   c  to bar  226   c ), the skewed relationship between the bars would negatively affect the smooth movement of the strands along the traversing apparatus. That is, if a plurality of fiber strands  210  were to transition directly from bar  226   a  to bar  224   a , the fiber strands would in fact transition from all of the fiber strands  210  sliding along bar  226   a  in one direction at a certain velocity to a point at which a leading part of the fiber strands  210  slide onto bar  224   a  while a trailing part of the fiber strands  210  remain in contact with bar  226   a  (the traversing apparatus rotating away from the reader in  FIG. 3  in the sense of the arrow shown about axis X). Keeping in mind that the slope of bar  226   a  tends to cause the fiber strands  210  to slide in a first direction, the opposing slope (i.e., having an opposite sign) of bar  224   a  would impart a “conflicting” impulse to the fiber strands  210  to start sliding in the opposite direction, causing the group of fiber strands  210  to bunch together and disrupt the desired separation of fiber strands. It will be appreciated that this will directly cause the separation and movement of the fiber strands  210  to be upset, and will negatively affect how the fiber strands  210  are wound onto spindle  212 . In particular, this disruption of smooth travel of the fiber strands  210  can even cause stresses sufficient to break the fiber strands  210  and will random placement of the fiber strands  210  on spindle  212 . 
         [0047]    To address this problem, auxiliary bars  228   a ,  228   b  are provided. 
         [0048]    First auxiliary bar  228   a  extends between first and second bar supports  222   a ,  222   b , between primary bar  224   a  of the first group and primary bar  226   a  of the second group. More specifically, first auxiliary bar  228   a  extends from a location on first bar support  222   a  closely adjacent to the end of primary bar  224   a  located on first bar support  222   a . First auxiliary bar  228   a  is mounted at the second bar support  222   b  at a location closely adjacent to the end of primary bar  226   a  located on the second bar support  222   b.    
         [0049]    Second auxiliary bar  228   b  extends between first and second bar supports  222   a ,  222   b , between primary bar  224   c  and primary bar  226   c , in a manner similar to first auxiliary bar  228   a.    
         [0050]    By orienting the first and second auxiliary bars  228   a ,  228   b  in this manner, each auxiliary bar  228   a ,  228   b  in effect changes the sign of its slope when the traversing apparatus  216  rotates, so as to provide a continuous transition from negatively sloped bar  224   a  to positively sloped bar  226   a , and from negatively sloped bar  224   c  to positively sloped bar  226   c  (or vice versa, depending on the direction of rotation of the traversing apparatus  216  about axis X). 
         [0051]    As is clearly illustrated in  FIG. 6 , for example, the presence of first auxiliary bar  228   a  between primary bars  224   a  and  226   a  addresses the skew relationship between primary bars  224   a  and  226   a . Primary bar  224   a  and first auxiliary bar  228   a  are coplanar, and first auxiliary bar  228  and primary bar  226   a  are coplanar. Thus, as the traversing apparatus  216  rotates, fiber strands  210  sliding along the respective bars of the apparatus can smoothly transition between primary bars  224   a  and  226   a , thanks to intermediate first auxiliary bar  228   a . As mentioned above, if first auxiliary bar  228   a  were not present, the traversing motion of the fiber strands  210  would be irregular and discontinuous as the strands moved from contact with bar  224   a  to contact with bar  226   a , because bars  224   a  and  226   a  are skewed relative to each other. 
         [0052]    Likewise, the provision of second auxiliary bar  228   b  between primary bars  224   c  and  226   c  addresses the same problems as the provision of first auxiliary bar  228   a.    
         [0053]    Returning to  FIG. 3 , the rotating spindle  212  imparts a tensile force T in the fiber strands  210  while winding the fiber strands  210  thereon. Traversing apparatus  216  is positioned relative to spindle  212  in operation so as to at least slightly deflect fiber strands  210  along a direction generally perpendicular to tensile force T so as to generate a force component pointing generally radially inward (i.e., generally towards shaft  250 ). This generated force component tends to press the fiber strands  210  against the bars of the traversing apparatus. In particular, the respective bars of the traversing apparatus  216  are arranged (as discussed further below) in order to cause the fiber strands  210  to be pressed against adjacent bars in sequence (such as bars  224   a ,  224   b  in  FIG. 3 ). The bars which contact the fiber strands  210  progressively change as the traversing apparatus  216  rotates about axis X. 
         [0054]    As mentioned, a respective pair of adjacent bars (whether primary or auxiliary) are arranged so as to be coplanar. The fact that the bars are coplanar helps generate a continuous motion of the fiber strands  210  as they slide along respective bars as the traversing apparatus  216  turns. 
         [0055]    In addition, each adjacent pair of bars either converges or diverges relative to one another along a direction from the first bar support  222   a  towards the second bar support  222   b . The “rate” of the convergence or divergence of bars (i.e., how rapidly the bars converge or diverge over the distance between the first and second bar supports  222   a ,  222   b ) varies between respective pairs of bars. In a specific non limitative example, it is relatively greatest between first and second auxiliary bars  228   a ,  228   b , and the primary bars to either side thereof; that is, between first auxiliary bar  228   a  and bars  224   a  and  226   a , respectively, and between second auxiliary bar  228   b  and primary bars  224   c  and  226   c , respectively. As mentioned previously, first auxiliary bar  228   a  extends from a location on the first bar support  222   a  relatively close to an end of primary bar  224   a  (and comparatively distant from an end of primary bar  226   a ), to a location on the second bar support  222   b  relatively close to an end of primary bar  226   a  (and comparatively distant from an end of primary bar  224   a ). Similarly, second auxiliary bar  228   b  extends from a location on the first bar support  222   a  relatively close to an end of primary bar  224   c  (and comparatively distant from an end of primary bar  226   c ), to a location on the second bar support  222   b  relatively close to an end of primary bar  226   c  (and comparatively distant from an end of primary bar  224   c ). See, for example,  FIGS. 3 ,  4   b , and  6 . 
         [0056]    As the traversing apparatus  216  rotates about axis X, different ones of the bars (primary and auxiliary) are sequentially pressed against fiber strands  210 . Each of these bars is at a respective angle relative to axis X, taken in a direction from the first bar support  222   a  towards the second bar support  222   b . These variations are obtained by appropriately mounting respective ends of respective bars to the first and second bar supports  222   a ,  222   b . More particularly, a given bar is mounted so that its first end is mounted to the first bar support  222   a  at a given distance from the axis X (with respect to a plane in which the axis of rotation X lies), whereas its second end may be mounted to second bar support  222   b  so as to be at a greater distance from axis X (resulting in positively angled bar, relative to axis X in the direction from first bar support  222   a  to second bar support  222   b ), or the second end may be mounted at a smaller distance from axis X at the second bar support  222   b  (resulting in a negatively sloped bar). 
         [0057]    In view of the foregoing, the first group of primary bars ( 224   a ,  224   b ,  224   c ) are arranged relative to each so as to extend between a periphery of the first bar support  222   a  and a corresponding periphery of the second bar support  222   b . As can be seen in, for example,  FIGS. 3 and 6 , the bars  224   a ,  224   b ,  224   c  are relatively spaced apart at the first bar support  222   a , and converge towards each other so as to be relatively close to one another at the second bar support  222   b . Conversely, the second group of primary bars ( 226   a ,  226   b ,  226   c ) are relatively close together at the first bar support  222   a  and diverge so as to be relatively spaced apart at the second bar support  222   b.    
         [0058]    The magnitude of the slope of each of the primary bars can be different. For example, the slope of each of the primary bars  224   a ,  224   b ,  224   c  may progressively increase (i.e., become more negative) or decrease (i.e., become less negative), depending on the direction of rotation of the traversing apparatus  216 ). Likewise, each respective primary bar  226   a ,  226   b ,  226   c  may become increasingly or decreasingly positive. By adjusting the magnitude of slope of each pair of sloped bars (positively or negatively), the movement of the fiber strands  210  sliding along the bars can be further controlled (particularly with respect to the speed at which the fiber strands  210  slide along the primary bars). 
         [0059]    In general, the cyclic transition from the negatively sloped first group of primary bars  224   a ,  224   b ,  224   c  to the positively sloped second group of primary bars  226   a ,  226   b ,  226   c  as the traversing apparatus  216  rotates drives the desired reciprocal traversing movement of the plurality of strands  210 . More specifically, the negatively sloped primary bars  224   a ,  224   b    224   c  tend to cause the fiber strands  210  sliding therealong to slide towards the second bar support  222   b . Conversely, the positively sloped primary bars  226   a ,  226   b ,  226   c  tend to cause the fiber strands  210  to slide towards the first bar support  222   a . By inducing this reciprocating movement of the fiber strands  210 , the fiber strands  210  are caused to move back and forth along an axial length of the spindle  212  so as to evenly form a cake. 
         [0060]    The primary and auxiliary bars are made of a material suitable for permitting the fiber strands  210  to slide therealong as described above without excessive friction, which can damage the fiber strands  210 . The material of the primary and auxiliary bars should also be appropriate for the environment in which the winding operation takes place, taking into account, for example and without limitation, temperature and potential chemical reactivity with the material used to make the fiber strands  210 . Depending on the particular application, some appropriate materials for making the primary and auxiliary bars are metal, resin (optionally reinforced with glass fibers), or wood. The bars may be attached to the first and second bar supports  222   a ,  222   b  by conventional means appropriate to the material of the bar supports and the material of the bars. Metal bars could be welded or soldered to metal bar supports, or, as illustrated in  FIGS. 3 and 4  by way of example, ends of the respective bars could be fixed in holes formed in the bar supports. 
         [0061]    Geometrically, the first group of primary bars  224   a ,  224   b ,  224   c  and the second group of primary bars  226   a ,  226   b ,  226   c  can be considered as lying on respective conical surfaces. For example,  FIG. 5   a  schematically illustrates primary bars  224   a ,  224   b ,  224   c  arranged on a frustoconical surface  500   a . Likewise, primary bars  226   a ,  226   b ,  226   c  are arranged on the surface of a second frustoconical surface  500   b . The frustoconical surfaces  500   a  and  500   b  are oriented in generally opposite directions. (It should be noted that “conical” and “frustoconical” as used here should be considered effectively interchangeable, the latter only referring to the fact that a complete conical surface, as such, is not illustrated in  FIGS. 5   a - 5   c .) 
         [0062]    In a particular example, the conical surfaces  500   a ,  500   b  are each oblique conical surfaces. In addition,  FIG. 5   a  illustrates the conical surfaces  500   a ,  500   b  as being co-axial, but the axes of the conical surfaces  500   a ,  500   b  may be more generally parallel, and not necessarily co-axial. 
         [0063]    The slopes of the primary bars relative to the axis of rotation can be globally characterized (and controlled) as a function of how oblique the conical surfaces  500   a ,  500   b  are. More particularly, the force component that tends to move the fiber strands  210  in one direction or the other along the traversing apparatus can be made to progressively increase from primary bar to primary bar as the traversing apparatus rotates by increasing how oblique the conical surfaces are, particularly by progressively increasing the slopes of the bars of the respective pluralities of primary bars. Progressively increasing the traversing force on the plurality of strands (in alternating positive and negative senses) can be helpful in overcoming sliding resistance between the fiber strands  210  and the primary and auxiliary bars over which the fiber strands  210  slide, thereby resulting in an even better deposition of the fiber strands in forming a cake. 
         [0064]      FIGS. 5   b  and  5   c  further schematically illustrate the arrangement of the respective groups of primary bars on respective oblique conical surfaces. Both  FIGS. 5   b  and  5   c  generally correspond to the illustration of traversing device  216  in  FIG. 3 , viewed along the axis X of shaft  250  in the direction indicated by line IV-IV in  FIG. 3 . 
         [0065]    In  FIG. 5   b , frustoconical surface  500   a  (like that seen in  FIG. 5   a ) extends into the page, such that base  502  generally corresponds with the plane of first bar support  222   a , and distal (with respect to the reader) top surface  504  corresponds with the plane of second bar support  222   b.    
         [0066]    In  FIG. 5   c , frustoconical surface  500   b  (like that seen in  FIG. 5   a ) extends relatively out of the page, such that base  506  corresponds with the plane of second bar support  222   b , and proximal (with respect to the reader) top surface  508  corresponds with the plane of first bar support  222   a.    
         [0067]    In  FIGS. 5   a - c  auxiliary bars  228   a ,  228   b  are selectively omitted for clarity. 
         [0068]      FIG. 6  is a partial perspective view of traversing apparatus  216  in which first bar support  222   a  is omitted in order to illustrate the coplanarity of respective pairs of adjacent bars, as discussed above. In particular, as discussed above, it can be seen how the provision of auxiliary bar  228   a  between primary bars  224   a  and  226   a  defines a coplanar pair of bars  224   a ,  228   a  and a coplanar pair of bars  228   a ,  226   a , instead of leaving just the above-described skewed positional relationship between primary bars  224   a  and  226   a . The same effect can be seen in the provision of auxiliary bar  228   b  between primary bars  224   c  and  226   c.    
         [0069]    Although the present invention has been described above with reference to certain particular examples for the purpose of illustrating and explaining the invention, it is to be understood that the invention is not limited solely by reference to the specific details of those examples. More specifically, a person skilled in the art will readily appreciate that modifications and developments can be made in the preferred embodiments without departing from the scope of the invention as defined in the accompanying claims.