Abstract:
Cores can be engaged and disengaged with a plurality of annular devices fitted over a mandrel. The mandrel has fluid passage communicating with a spaced plurality of radially disposed channels. Pistons in the channels can, in response to fluid pressure, extend outwardly in order to bear on the annular devices. Changes in the volume of fluid inside the fluid passage and the channels are substantially equal to the total displacement of the pistons. Each annular device has an inner ring with at least one camming track rotatably mounted inside an outer ring. The inner ring has an inside portion including a material different from material of said outer ring. The outer ring is fitted inside the core and the inner ring is fitted over the mandrel. A gripping member is fitted in an aperture of the outer ring to move along the camming track. This gripping member is outwardly thrustable through the aperture in accordance with the position of the gripping member in the camming track.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to winding mandrels, and in particular, to winding with a controlled amount of slippage between the mandrel and winding cores.  
           [0003]    2. Description of Related Art  
           [0004]    Sheet material made of paper, plastic or other materials is manufactured in a web that is wound into a relatively large roll. In many instances, this roll is too large for use in other manufacturing processes. For that reason, the web is often unwound and rewound into smaller rolls. In some cases, the web is slit into a plurality of webs that are then simultaneously wound into a number of axially shorter rolls.  
           [0005]    The web is often rewound on an open cylindrical core that is mounted on a driving mandrel. In some cases the cores are locked into a fixed position on the mandrel, but often these cores are allowed to slip. This slippage can be designed to modulate the torque and therefore the tension of the rewinding web. When slippage is contemplated it must be carefully controlled so that the finished product is uniform. Therefore much care has been taken to control the slipping surfaces and the friction between them.  
           [0006]    A known mandrel has slots that carry axially repositionable buttons that can be thrust radially outward to bear on the inside surface of a core. These buttons can be lifted by an underlying bar that is driven by an inflatable bladder contained in the hollow center of a mandrel. A disadvantage with this arrangement is that the friction between the buttons and the inside surface of the cores is variable. This variability is inevitable since the core material will change from job to job.  
           [0007]    Other disadvantages arise from the use of the bladder. In order to prevent premature wear or leaking of the bladder, it must be made of a relatively tough material. On the other hand, significant amount of work must be done to inflate the bladder itself, which reduces the efficiency of the energy transferred to the buttons. Essentially, work is done increasing the volume of fluid inside the bladder, but this fluid increases much greater than would be needed simply to propel the buttons. Moreover, the bladder itself tends to have a somewhat limited service life, thus introducing disadvantageous maintenance requirements.  
           [0008]    Another disadvantage with the bladder design is the difficulty in accurately controlling the friction and therefore the output torque produced by inflating the bladder. Essentially, the bladder has different modes of operation.  
           [0009]    When initially inflated slightly, the bladder bears primarily on the button mechanism without contacting the inner wall of the mandrel. As pressure increases, the bladder engages the inside surface of the mandrel as well as the button mechanism and will deform appropriately to conform to these surfaces.  
           [0010]    Because of the complexity of the interactions in the different modes, the output torque will not be linearly related to bladder pressure. This makes accurately controlling output torque more difficult.  
           [0011]    In U.S. Pat. No. 4,220,291 an inflatable bladder can outwardly thrust balls to engage winding cores. The axial position of these balls is not adjustable.  
           [0012]    Furthermore, if the cores are allowed to slip, their slippage will be determined in part by the friction between the cores and the balls. Also, these balls constitute a relatively small surface area that is subject to rapid wear and therefore high variability. See also U.S. Pat. No. 4,135,677 (air shaft with a pair of expandable sleeves surrounding an internal bladder); and U.S. Pat. No. 4,461,430 (differential winding air shaft). For appurtenant devices see U.S. Pat. No. 4,211,135 (cutting devices); U.S. Pat. No. 5,161,747 (pressing rollers); and U.S. Pat. No. 5,161,899 (bearing assembly allowing exchangeable support of shafts). For non-mandrel winding devices see U.S. Pat. No. 5,156,352.  
           [0013]    In FIG. 11 of U.S. Pat. No. 4,431,142 an inflatable bladder drives steel spheres  52  against the inside of a collar  51 . Rotation of collar  51  in one direction drives locking balls  49  up a ramp to lock against the inside of a core. Reverse rotation releases the core. Frictional slipping is expected between the inside surface of collar  51  and the steel spheres  52 . This represents almost a point contact that will be greatly affected by wear.  
           [0014]    In U.S. Pat. No. 5,279,470 a winding shaft is coupled to a number of winding rings, each ring having a number of spring biased segments. For example in FIG. 6 segments  2  have spring biased balls  10 ′, but these are only centering devices acting to the side of the winding cores  9 .  
           [0015]    In U.S. Pat. No. 4,964,586 an eccentric shaft can radially thrust elements against the inside of a winding core. Relative rotation of the eccentric shaft with respect to the thrust elements is normally prevented by a brake mechanism, but this braking force can be overcome by certain locking devices. The support strength of this arrangement is compromised by reliance on a relatively small, internal eccentric shaft. See also U.S. Pat. No. 4,893,765.  
           [0016]    In U.S. Pat. No. 4,165,050 a plug with camming surfaces can be pressed axially inward to lift cam followers, which may be either cylindrical or spherical. When lifted, cam followers distend resilient ring  22  to clamp onto the inside of reel  34  of a tape cassette. This reference requires manual access at the axis of rotation and would be inappropriate for securing multiple winding cores on a large mandrel. See also U.S. Pat. No. 4,000,866 (disks brought together to expand an elastomeric ring and grip the reels of a videocassette).  
           [0017]    In U.S. Pat. No. 4,763,850 a mechanism employing axially shifting members and rotating links can outwardly thrust gripping members against the inside surface of a yarn bobbin or holder. This arrangement employs a relatively large number of moving components that compromise its reliability.  
           [0018]    In FIG. 3 of U.S. Pat. No. 4,635,871 a rod inside a hollow mandrel can be axially shifted to either extend or retract lugs in order to engage or release a core that may be placed on the mandrel. These lugs are rotated so a corner of the lug bears against the core. This presents a relatively small surface area that would wear rapidly in the presence of core slippage.  
           [0019]    In U.S. Pat. No. 4,21 3,577 separate pressure lines are provided to opposite sides of a hydraulic piston to (a) extend the piston before and while sheet metal is coiled onto the mandrel, and (b) retract the piston when the coil is to be removed. The mandrel is notched to receive one end of the sheet metal strip. Thus, this reference is unconcerned with winding strips onto a separate core and for permitting slippage between the mandrel and core.  
           [0020]    In Figure III of U.S. Pat. No. 4,147,312 hydraulic pressure applied through a hollow mandrel distends diaphragms to press buttons against the inside surface of a core. The buttons are not directly operated by hydraulic pressure, but are operated indirectly through diaphragms.  
           [0021]    In U.S. Pat. No. 4,352,470 four segments  27  can be driven axially up an inclined surface on a mandrel to be thrust outwardly. This mandrel telescopically contracts to alter its length and its utility would therefore be greatly restricted. See also U.S. Pat. No. 5,314,135 (tapered inner tube outwardly thrusts a slotted outer tube against the inner surface of a core); U.S. Pat. No. 5,683,057 (inclined surfaces of retractable collar drives lugs  26  outwardly to clamp to the inside of a core); and U.S. Pat. No. 4,079,896 (shoes driven up a conical surface in a chuck to bear against the inside surface of a core).  
           [0022]    See also U.S. Pat. No. 5,533,691 (hub presses cores axially not radially); U.S. Pat. No. 4,436,249 (mandrel with latch that locks onto a spool); and U.S. Pat. No. 4,325,522 (brake for a cable spool). For other winding machines see U.S. Pat. No. 4,770,360.  
         SUMMARY OF THE INVENTION  
         [0023]    In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided an annular device for intermediating force transfer between a winding mandrel and a core onto which a web is to be wound. The annular device has an inner ring with at least one camming track rotatably mounted inside an outer ring. The inner ring has an inside portion comprising a material different from material of said outer ring. The outer ring is adapted to be fitted inside the core and the inner ring is adapted to be fitted over the mandrel. Also included is a gripping member fitted in an aperture of the outer ring to move along the camming track. This gripping member is outwardly thrustable through the aperture in accordance with the position of the gripping member in the camming track.  
           [0024]    In accordance with another aspect of the invention a web winding assembly is provided that can engage and disengage cores with a plurality of annular devices. The assembly has a mandrel with a spaced plurality of radially disposed channels. The mandrel has a fluid passage communicating with the channels. Also included is a plurality of pistons mounted to reciprocate in different corresponding ones of the channels. The pistons are operable in response to fluid pressure in the channels to extend out of the mandrel in order to bear on the annular devices. Changes in the volume of fluid inside the fluid passage and the channels are substantially equal to the total displacement of the pistons.  
           [0025]    In accordance with yet another aspect of the invention a web winding method is provided which employs annular devices located on a mandrel fitted with core engaging pistons. The method includes the steps of loading the cores over the annular devices. Another step is outwardly driving the pistons with directly applied fluid pressure in order to frictionally engage the annular devices with said pistons. Changes in the volume of fluid inside the mandrel being substantially equal to the total displacement of the pistons. The method also includes the step of locking the cores onto the annular devices. Another step is rotating the mandrel to wind the web, while allowing slippage predominantly between the annular device and the mandrel, in order to avoid slippage predominantly influenced by interface attributes between the cores and the annular devices. The method also includes the step of unlocking and removing the cores from the annular devices.  
           [0026]    In accordance with still yet another aspect of the invention an annular device can intermediate force transfer between a winding mandrel and a core onto which a web is to be wound. The annular device includes an outer ring having at least one aperture and adapted to be fitted inside the core. Also included is a gripping member fitted in the aperture of the outer ring. The annular device also includes an inner ring rotatably mounted inside the outer ring and adapted to be fitted over the mandrel. The inner ring has at least one camming track for receiving and allowing movement of the gripping member therealong. The gripping member is outwardly thrustable through the aperture in accordance with the position of the gripping member in the camming track. The inner ring includes a spacer ring, a cage ring and a rolling member. The spacer ring has the camming track and is adapted to be fitted inside the outer ring. The cage ring is rotatably mounted inside the spacer ring and is adapted to be fitted over the mandrel. The cage ring has at least one ramping track. The rolling member is fitted between the spacer ring and the cage ring to move along the ramping track. The rolling member is outwardly thrustable against the spacer ring in accordance with the position of the rolling member in the ramping track.  
           [0027]    By employing apparatus and methods of the foregoing type, an improved technique is achieved for intermediating the force transfer from a winding mandrel to a core. In the preferred embodiment, an annular ring placed between the mandrel and core can engage both the mandrel and core to permit slipping with respect to the mandrel but not with respect to the core. Therefore one can design the inside surface of the annular device to have a well-established slipping characteristic so that the machine can be operated reliably and repeatably. Because the annular device is locked onto the core, the highly variable slip characteristics of the core do not affect machine operation.  
           [0028]    In the preferred embodiment a pair of concentric, nested rings can rotate relatively, but only to a limited extent. Individual balls ride in a number of camming tracks that are distributed around the periphery of the inner ring. Preferably, the tracks extend in a circumferential direction and are deepest at their centers (although tracks that continually descend until reaching one end are contemplated). The balls are carried in apertures in the outer ring and therefore, when the rings relatively rotate, the balls ride the tracks and are outwardly thrust (or inwardly retract) through the apertures.  
           [0029]    In this preferred embodiment, the mandrel is fitted with a number of pistons that are directly driven by pneumatic pressure. This arrangement avoids the complications associated with using an intermediate diaphragm or bladder. In the preferred mandrel, a predetermined number of pistons (for example three or four) radiate from a number of stations distributed along the length of the mandrel. The pistons at each station are distributed equiangularly, but the piston pattern is shifted from station to station at half the pitch at each station, in order to stagger the pistons. For example, with three or four pistons at each station, the angular spacing at each station is 60° or 45°, respectively, but the pistons pattern can be shifted 30° or 45°, respectively, from station to station.  
           [0030]    With this arrangement, the pistons can be retracted and the annular rings placed in position over the mandrel. Cores can then be loaded over the annular devices. The outer ring can then be rotated relative to the inner ring to lock the annular devices onto the cores. Thereafter, a web can be wound onto the core is in the usual fashion. Once the cores are fully wound, the mandrel (or the cores) can be rotated in a direction to unlock the annular devices so that the cores can be removed. It is not necessary in all cases to produce that relative rotation to induce unlocking. In some instances a separate mechanism, or an axially applied force, may also induce unlocking, and which also enhances removal of the rolls.  
           [0031]    Should the next operation involve cores having different dimensions, the annular devices can be easily replaced. The replacement annular devices can be dimensioned to accommodate various types of cores. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The above brief description as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein:  
         [0033]    [0033]FIG. 1 is an exploded, axonometric view of an annular device in accordance with principles of the present invention;  
         [0034]    [0034]FIG. 2 is an end view, partially in section, of the annular device of FIG. 1 mounted on a mandrel with reciprocating pistons;  
         [0035]    [0035]FIG. 3 is a side view of a pair of the annular devices of FIG. 1 mounted side-by-side with a thrust washer between them;  
         [0036]    [0036]FIG. 4 is a detailed, fragmentary, cross-sectional view of a portion of the annular device of FIG. 1 in a locked condition;  
         [0037]    [0037]FIG. 5 is a detailed, fragmentary, cross-sectional view of the annular device of FIG. 1 in an unlocked condition;  
         [0038]    [0038]FIG. 6 is a detailed, fragmentary, side view of a portion of the inner ring of the annular device of FIG. 1; FIG. 7 is a detailed, fragmentary, side view of a portion of an inner ring that is an alternate to that of FIG. 6;  
         [0039]    [0039]FIG. 8 is an end view, partially in section, of an annular device that is an alternate to that of FIG. 2;  
         [0040]    [0040]FIG. 9 is a side view of the spacer ring of the annular device of FIG. 8;  
         [0041]    [0041]FIG. 10 is a longitudinal-sectional view of the mandrel of FIG. 2; and  
         [0042]    [0042]FIG. 11 is a side view of the mandrel of FIG. 10 fitted with the annular devices of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    Referring to FIGS.  1 - 6 , the illustrated annular device has an inner ring  10  and an outer ring  12 . Outer ring  10  has four equiangularly spaced, conically tapered apertures  14 . Apertures  14  converge in an outward direction at a conical angle of 40°, although other angular dimensions can be used in alternate embodiments. In some embodiments the aperture can be formed with a bushing that establishes the dimensions and materials on the inside faces of the apertures. Also in this embodiment, outer ring  10  is 3.0 inches (7.6 cm) in diameter, ½ inch (1.3 cm) wide, and ⅛ inch (0.32 cm) thick, although other dimensions may be employed depending upon the size of the corresponding core (to be described presently) as well as the desired strength and weight for the outer ring.  
         [0044]    As will be described presently, inner ring  10  will establish a slipping relationship with a driving mandrel. For this reason, the material of inner ring  10  is chosen to provide reliable and repeatable slipping characteristics. In a preferred embodiment, inner ring  10  is formed from a sintered metal such as brass (either all of the ring or just an inside portion). The interstices of the sintered metal are impregnated with a friction moderating substance such as oil and PTFE (polytetrafluoroethylene, known under the commercial brand TEFLON™). In some embodiments, the sintered metal impregnated with a lubricant will be an inner layer fused to the main body of the inner ring.  
         [0045]    The periphery of inner ring  10  has four equiangularly spaced, camming tracks  16 . Tracks  16  are frustro-cylindrical and make a chordal intersection with the periphery of inner ring  10 . Accordingly, the floor of the tracks  16  as shown in the cross-section of FIG. 2 appear as a straight chord, so that the track depth is greatest at the center position of the tracks  16 . Preferably, the camming tracks will be plated with a relatively hard material to avoid wear.  
         [0046]    While four camming tracks are shown, in some embodiments a greater or lesser number may be used. Also, while the illustrated camming tracks are straight, in other embodiments the floor of the camming track can be graded to provide more or less leverage for the gripping actions to be described presently.  
         [0047]    Gripping members  18  are shown herein as four balls  18  dimensioned to ride in camming tracks  16 . The balls  18  are also dimensioned to fit inside the tapered apertures  14  without passing through the apertures. In this embodiment, balls  18  are ¼ inch (0.64 cm) in diameter and are made of stainless steel, although other dimensions and materials may be used in alternate embodiments. In some embodiments, the surface of the balls  18  may be roughened to enhance friction and therefore the gripping capability of the balls.  
         [0048]    When the rings  10  and  12  are relatively rotated to the orientation shown in FIG. 5, ball  18  rests in the central position of camming track  16 , which is the deepest portion of the track. Accordingly, ball  18  is not outwardly thrust and does not extend through aperture  14  to the outside of ring  12 . When the rings  10  and  12  are relatively rotated as shown in FIG. 4, ball  18  rolls to one end of camming track  16 , which is one of the shallowest portions of tracks  16 . Accordingly, ball  18  is outwardly thrust through aperture  14  to partially extend outside ring  12 .  
         [0049]    While spherical gripping members are illustrated, in other embodiments these gripping members may be cylindrical rollers. In the latter case, the aperture through the outer ring may be a trapezoidal prism. In still other embodiments the gripping members may be sliding members having various shapes.  
         [0050]    [0050]FIG. 6 shows camming track  16  with a circumferentially disposed, main groove  1   6 A. Camming track  16  also has an egress groove  16 B, which is an axially disposed, frustro-cylindrical trough transversely intercepting main groove  16 A. When ball  18  is in the central or neutral unlocked position (as shown in FIG. 5) the ball can transfer to transverse groove  16 B, so that the inner and the outer rings  10  and  12  can be detached from each other. Groove  16 B can be made with tight tolerances so that the rings do not detach spontaneously.  
         [0051]    In the alternate embodiment of FIG. 7, alternate ring  1   0 ′ has a circumferentially disposed main groove  1   6 A′ intercepted with an egress groove  1   6 B′, to form a camming groove  16 ′. In this embodiment, the deepest end of groove  16 A′ is at the end adjacent egress groove  16 B′. This arrangement is unidirectional in that a gripping member riding in groove  1   6 A′ will always be thrust (or retracted) for a specified direction of rotation.  
         [0052]    Referring to FIG. 2, mandrel  20  is shown as a shaft with four radially disposed channels  22  which are spaced 90° from each other, although a greater or lesser number of channels may be employed in alternate embodiments. In a constructed embodiment, the channels were spaced 120°. In the illustrated embodiment, mandrel  20  is {fraction (2 1/4)} inches (5.7 cm) in diameter, although other embodiments will employ different mandrel sizes.  
         [0053]    The proximal ends of channels  22  merge into a central fluid passage  24 , so that all channels can be simultaneously pressurized. Channels  22  are cylindrical and contain cylindrical pistons  26 . Pistons  26  have a frustro-conical proximal end and a distal end rounded cylindrically to match the cylindrical outside surface of mandrel  20 . Pistons  26  have an outside diameter of ½ inch (1.3 cm) although other piston sizes are contemplated. Pistons  26  each have an annular groove holding an annular seal  28 . Seal  28  is an annular, channel-shaped member (U-shaped cross-section), also known as a U-cup seal. With this arrangement a pressure applied to fluid passage  24  communicates with each of the channels  22  to drive the pistons  26  outwardly. Also, while pistons directly actuated by pneumatic pressure are shown, in some embodiments a central bladder may press against moving members to provide the same action as it is provided by the pistons.  
         [0054]    Referring to FIGS. 2 and 3, rings  10  and  12  can be rotated to the position shown in FIG. 2 to thrust outwardly gripping members  18 . As shown in FIG. 3 gripping members  18  are thrust against the inside surface of cores  30 . As a result, outer rings  12  can be positively locked onto cores  30 . Therefore, web  32  can be wound onto the cores  30  by rotating rings  12 .  
         [0055]    In most instances, adjacent cores will not be wound side-by-side on a mandrel so as to avoid interference. Instead, cores will be installed on every other device  10 / 12 . Because the cores  30  are locked in place by gripping members  18 , there is no need for spacers to keep the cores  30  centered on annular devices  10 / 12 . In some instances, the cores may be relatively wide and may lock onto more than one of the annular devices  10 / 12 . In some cases, the width of the cores may not be a simple multiple of the annular devices  10 / 12  but may span, for example, {fraction (2 1/2)} devices.  
         [0056]    Regardless, in some cases cores may alternate with spacers to positively establish a gap between webs to avoid interference. Alternatively, the illustrated annular devices composed of rings  10  and  12  may alternate with simple spacers having a greater outside diameter than the outer ring  12  in order to keep cores  30  centered on the annular devices  10 / 12 .  
         [0057]    A thrust washer  34  is located on either side of each annular device  10 / 12 . This washer is preferably a disk made of plastic or TEFLON™. This washer facilitates situations where an adjacent annular device does not have a core and therefore will tend to run at the same speed as the mandrel, that is, without slipping. This requires relative rotation between adjacent annular devices  10 / 1   2  and the thrust washers  34  provides lubrication between adjacent devices. In other embodiments suitable coatings could be applied to the adjacent surfaces to eliminate the need for such washers.  
         [0058]    Referring to FIG. 10, fluid passage  24  is shown running substantially the length of previously mentioned mandrel  20  to communicate with previously mentioned channels  22 . Channels  22  form repetitive bands, each having four channels located at discrete stations, although some embodiments will have fewer or more channels depending on the system requirements. Each of the bands of channels  22  are interleaved with bands of channels  22 ′. Channels  22 ′ are identical to channels  22  but are angularly displaced by 45° (four channel embodiment). For embodiments having three channels per band (120° 0  spacing), the channel pattern will be displaced by 60° from band to band. Therefore the bands composed of channels  22  and  22 ′ form a plurality of axially equidistant bands.  
         [0059]    The driven (left) end of mandrel  20  has a reduced diameter and has bolted to it a collar  36  whose proximal end includes a flange  38  for attaching the mandrel to a complementary driving flange (not shown). Inlet  40  of mandrel  20  connects to a rotary union (not shown) to provide pneumatic pressure to the mandrel.  
         [0060]    Referring to FIG. 11, previously mentioned mandrel  20  is shown fitted with a number of annular devices  10 / 12 , which are held on the left by collar  36 . On the right, annular devices  10 / 12  are held by cap  42 , which is bolted on the distal end  20 A of the mandrel  20 . A pair of bearings  44  and  46  are mounted on the tip of the distal end  20 A of mandrel  20 . Bearing  44  is shown mounted on structure or  48  to support one end of the mandrel under ordinary operating conditions. The second bearing  46  can rest in a pocket formed in lifting device  50 , which can be used to lift mandrel  20 . Such lifting may be useful in order to quickly load or unload cores  30  that have been wound with webs.  
         [0061]    Referring to FIGS. 8 and 9, previously mentioned mandrel  20  is shown fitted with an alternate annular device. Components in this annular device corresponding to those shown in FIG. 2 have the same reference numeral, but increased by  100 . A relatively larger outer ring  112  is fitted with eight gripping members  118 , shown as nylon balls. In this embodiment outer ring  112  is ⅛ inch thick (0.32 cm), 1.0 inch (2.5 cm) wide, and has an outside diameter of 6.0 inches (15.2 cm). Eight balls  118  are fitted in apertures  114 , which are distributed equiangularly around the periphery of outer ring  112 . Balls  118  are in this embodiment ¼ inch ( 0 . 64  cm) in diameter.  
         [0062]    An inner ring is formed herein by an aluminum spacer ring  110 A encircling cage ring  110 B, the latter being formed from the previously mentioned, friction moderating material; namely, sintered brass impregnated with oil and PTFE. Formed in the periphery of spacer ring  110 A are a number of camming tracks  116  and  116 ′. Tracks  116  are contained in one band, while tracks  116 ′ are contained in another axially spaced band. As before, camming tracks  116  each comprise a circumferentially disposed, main groove  116 A and a transverse egress groove  116 B. Camming tracks  116 ′ each also comprise circumferentially disposed, main groove  116 A and transverse egress groove  116 B, but egress groove  116 B′ is substantially longer to accommodate the axial displacement of this band of tracks  116 ′. The camming tracks  116  are separated by a predetermined angle of 90°. The camming tracks  11   6 ′ are also separated by a predetermined angle of 90°. Camming tracks in adjacent bands have a minimum angular separation of half said predetermined angle, or 45 °. For embodiments having an angular separation of 120° in each band, the minimum angular separation between bands of 60°.  
         [0063]    Cage ring  110 B is in this embodiment ¼ inch (0.64 cm) thick and has four ramping tracks  152 . These tracks are identical to tracks  116  and  116 ′, except for being half in number. Accordingly, tracks  152  have egress tracks  158 . A rolling member in the form of a nylon ball  1   54  is shown in track  152 .  
         [0064]    Ball  154  is also showing extending into conical cavity  156 . With this arrangement, relative rotation of rings  110 A and  110 B causes ball  154  to roll from the central position to the shallowest part of track  152 , causing ball  154  to be outwardly thrust and locked into the conical sides of cavity  156 . This locks together rings  110 A and  110 B.  
         [0065]    In some embodiments such a double locking mechanism will not be used and instead, ring  110 B will be press fit into ring  110 A. Also, while the embodiment of FIGS. 8 and 9 are shown achieving a larger working diameter with a smaller mandrel, it is anticipated that in most instances a larger working diameter will be achieved by replacing the smaller mandrel with a larger mandrel. Using a larger mandrel will increase the overall strength of the arrangement.  
         [0066]    To facilitate an understanding of the principles associated with the foregoing apparatus, its operation will be briefly described. Initially, mandrel  20  may be located at a workstation near the winding machine in order to load the mandrel. Alternatively, the distal end  20 A of mandrel  22  may be lifted by carrier  50  after it engages bearing  46 . Once lifted in this fashion, supplies previously loaded onto carrier  50  can then be slid onto mandrel  20 . In still other embodiments the distal end  20 A may be left unsupported or cantilevered as the mandrel  20  is loaded.  
         [0067]    In any event, no pressure will be applied through fluid passage  24  and therefore pistons  26  (FIG. 2) will be in a retracted position. Accordingly, inner ring  10  together with outer ring  12  can be fitted over mandrel  20 . As shown in FIG. 11 the annular devices  10 / 12  can be stacked side-by-side on mandrel  20  with thrust washers  34  in between each device (FIG. 3).  
         [0068]    Outer rings  12  are then rotated to bring ball  18  to the central position in camming tracks  16  as shown in FIG. 5. Balls  18  are then retracted so that cores  30  (FIG. 11) can be fitted over annular devices  10 / 12 . Mandrel  20  can then be installed into its normal operating position in the winding machine.  
         [0069]    Often a relatively wide web will be slit into a number of thinner webs by an upstream sheet slitter. These thinner webs can be separated by grouping alternate slit webs so that adjacent webs are routed onto different paths. For this reason, mandrel  20  in FIG. 11 shows cores  30  on alternate ones of the annular devices  10 / 12 . This resumes that another complementary mandrel will take up the other alternate thin webs.  
         [0070]    Next, the outer rings  12  are rotated (relative to the inner ring  10 ) in the reverse of the winding direction, typically by rotating cores  30  and relying on the friction between the cores and the outer rings. This rotation drives gripping members  18  to the shallow end of camming tracks  16 , so that members  18  are thrust outwardly beyond the perimeter of outer rings  1   2 . Consequently, gripping members  18  lock onto the inside surface of the cores  30 .  
         [0071]    Thereafter, pressure applied through fluid passage  24  to the proximal end of pistons  26  in channels  22  outwardly drives the pistons  26  against the inside surface of inner rings  10  to hold them in place. In contrast to a relatively inefficient, bladder type of design, the increase of the fluid volume inside the mandrel need only increase by the amount needed to displace pistons  26 . Webs  32  (FIG. 3) can now be secured to core  30  by tape or other means. The mandrel  20  is then rotated in the winding direction to wind webs  32  onto core  30 .  
         [0072]    The pressure in passage  24  is regulated to apply a desired frictional force between pistons  26  and inner ring  10 . In particular, a certain amount of slipping is allowed between pistons  26  and inner ring  10 . Because inner ring  10  is impregnated with a lubricant, slipping is facilitated without a high degree of wear and heat. Also, the interface between pistons  26  and inner ring  10  is highly consistent and is under control of the designer; in comparison with an interface with a core that may be made of different materials exhibiting different slipping characteristics.  
         [0073]    This slipping moderates the torque applied by mandrel  20  and therefore the tension on web  32 . Also, by adjusting the pistons this frictional force and slippage can be adjusted during the winding phase to account for the increasing diameter of the wound package and also to adjust the desired tension profile across the package. Also, unlike bladder-type designs that introduce nonlinearities, directly applying pressure to the pistons allows a much more accurate control of the output torque at the produced by the pistons. Regardless, in some situations pistons  26  may be driven against inner ring  10  with such force that no slipping is permitted.  
         [0074]    After the web  32  has been fully wound onto core  30 , the mandrel  20  is decelerated and stopped. The tail of web  32  may be cut, if necessary, and secured by tape or otherwise to the wound package. Thereafter core  30  can be rotated in the winding direction to cause ball  18  to move from the position shown in FIG. 4 to that shown in FIG. 5. Ball  18  can then retract in aperture  14  to the deepest portion of tracks  16  in order to release core  30 . Core  30  and the wound packages can then be removed from mandrel  20  in various ways. For example, mandrel  20  can be removed from the winding machine. Alternatively the mandrel end  20 A can be lifted by carrier  50 , in order to remove the wound package on cores  30 .  
         [0075]    The annular devices  10 / 12  can also be removed at this time and replaced with devices having a different width and diameter. For example, the annular device of FIG. 8 can be placed over mandrel  20  as shown. Thereafter, assuming ring  110 B is fixed, ring  110 A is rotated in the reverse of the winding direction to drive ball  154  to a shallow end of track  152  in order to lock rings  110 A and  110 B together.  
         [0076]    After cores are placed around outer ring  112 , rings  112  (relative to ring  110 A) are rotated in the reverse of the winding direction to drive balls  118  to a shallow end of tracks  116  and  116 ′. This procedure locks the cores to the annular device. Thereafter the process precedes in the same fashion as was described previously in connection with the embodiment of FIG. 2.  
         [0077]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.