Abstract:
Cable-stranding methods for performing SZ-stranding of strand elements about at least one core member are disclosed. One method includes passing initially spaced apart strand elements through peripheral guide holes and passing at least one core member through a generally central location of at least one guide member. The method also includes actuating a controller that controls the rotation of the at least one guide member and rotating the at least one guide member to form the SZ-stranded assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No. ______, entitled “Cable Stranding Apparatus Employing a Hollow-Shaft Guide Member Driver,” filed on the same day of ______, and which is assigned to the same Assignee as the present application, and which is incorporated by reference herein. 
     
    
     FIELD 
       [0002]    The present disclosure relates to methods for stranding together strand and core members to form stranded cables with an alternating twist direction, and in particular to such methods that employ a hollow-shaft guide member driver. 
       BACKGROUND 
       [0003]    Cable stranding machines are used in cable manufacturing to form cables with multiple strand elements (“strands”) having an alternating twist direction. Such cables are called “SZ” cables because the strands periodically helically twist in opposing “S” and “Z” directions. The SZ stranding configuration eliminates the need for the strand storage containers to be rotated around the cable core member, thereby resulting in less complex, faster-operating stranding machinery. 
         [0004]    The strands, which can be wire, optical fibers, buffer tubes, etc., are stored in storage containers (e.g., spools or “packages”) and pass through a stationary guide or “layplate.” The layplate keeps the strands locally spaced apart as they pass through to a downstream SZ cable-stranding apparatus. Prior art SZ cable-stranding apparatus employ a series of axially arranged and mechanically coupled guides typically in the form of non-stationary (i.e., rotatable) plates called “layplates” similar if not identical to the stationary layplate. The rotatable layplates also serves to keep the strands locally spaced apart during the stranding process to ensure that the strands do not become entangled with each other or the core member as the layplates rotate through their motion profiles. 
         [0005]    In the process of forming an SZ-stranded cable, the layplates are mechanically coupled and driven in alternating rotational directions at progressively slower rates towards the upstream stationary plate as the strands move through the layplates. An SZ-stranded assembly, consisting of the strands wound around the central core member, emerges from the most downstream rotatable layplate. 
         [0006]    In the simplest form of SZ cable-stranding apparatus, tension in the strands provides the mechanical coupling that rotates the layplates. However, this results in poor tension control with a limited range of layplate rotation. More complex and expensive approaches use a series of shafts from a drive member (“prime mover”) and belts and/or gears to synchronize the motion of the rotating layplates to generate the required rotation rate for each layplate. An example of this type of SZ cable-stranding apparatus uses an elastic shaft running parallel to the axis of the oscillator. The torsion of the shaft, in combination with an arrangement of belts, pulleys and/or gears, drives the layplates. 
         [0007]    Generally, mechanically based SZ cable-stranding apparatus are expensive and difficult to maintain. Furthermore, the added rotational inertia of the mechanical components limits the maximum rate at which the rotatable layplates can reverse directions, thereby limiting both line speed and performance. In addition, the mechanical components limit the relative speed differences between successive layplates. This makes it difficult if not impossible to decouple the operation of the individual layplates to optimize the layplate rotational speeds to achieve the smoothest possible SZ stranding operation. 
       SUMMARY 
       [0008]    An aspect of the disclosure is a method of stranding strand elements in an SZ configuration to form an SZ-stranded assembly. The method comprises passing, through at least one guide member, initially spaced apart strand elements through respective guide holes and at least one core member through a generally central location of the guide member. The method also includes actuating a controller that controls the rotation of the guide member and rotating the guide member to form the SZ-stranded assembly. 
         [0009]    Another aspect of the disclosure is a method of forming an apparatus for controlling strand elements and at least one core member in a stranding apparatus. The method includes providing at least one motor having an associated rotating guide member driver. The method also includes providing and operably disposing a guide member at least partially within the rotating guide member driver so that the guide member rotates with the guide member driver, wherein the guide member is configured to receive and individually guide the strand elements and pass the at least one core member. 
         [0010]    Another aspect of the disclosure a method of forming a cable stranding apparatus that strands strand elements about at least one core member in an SZ configuration to form a SZ-stranded assembly. The method includes providing a plurality of motors each having a guide member driver, and aligning the guide member drivers along an apparatus axis. The method also includes providing a plurality of guide members configured to locally spatially separate the individual strand elements and pass the at least one core member. The method further includes disposing and holding stationary one of the guide members upstream of the plurality of motors. The method additionally includes disposing the remaining guide members at least partially within respective guide member drivers so that they rotate with the respective guide member drivers. 
         [0011]    These and other advantages of the disclosure will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more complete understanding of the present disclosure may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a perspective view of an example SZ cable-stranding apparatus according to the present disclosure; 
           [0014]      FIG. 2  is a perspective view of an example hollow-shaft motor showing an exploded view of a guide member attached to the hollow shaft via set screws; 
           [0015]      FIG. 3  is a front-on view and  FIG. 4  is a cross-sectional view of an example guide member of  FIG. 2  in the form of a layplate having a central hole sized to pass the at least one core member, surrounding strand guide holes, and peripheral set-screw holes; 
           [0016]      FIG. 5  is a schematic diagram of an example electronic configuration of the SZ cable-stranding apparatus; and 
           [0017]      FIG. 6  is a schematic overall view of a SZ cable-forming system that includes the SZ cable-stranding apparatus of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Reference is now made to embodiments of the disclosure, exemplary embodiments of which are illustrated in the accompanying drawings. In the description below, like elements and components are assigned like reference numbers or symbols. Also, the terms “upstream” and “downstream” are relative to the direction in which the SZ-stranded cable is formed, starting upstream with the various unstranded strand elements and optional at least one core member, and ending downstream with the formed SZ-stranded assembly and SZ-stranded cable. 
         [0019]      FIG. 1  is a perspective view of an example SZ cable-stranding apparatus (“apparatus”)  10  according to the present disclosure. Apparatus  10  has an upstream input end  11  and a downstream output end  13 . Apparatus  10  includes along an axis A 1  in order from an upstream to a downstream direction as indicated by arrow  12 , a stationary guide member  20 S and at least one hollow-shaft motor  100  that includes a rotatable guide member  20 R operably disposed therein. Here, the term “rotatable” refers to the fact that motor  100  causes the guide member to rotate, as described in greater detail below.  FIG. 1  shows an example configuration of apparatus  10  having a plurality of axially aligned motors  100 . An example type of motor  100  is a high-precision motor such as a servo motor. 
         [0020]    In an example embodiment, adjacent motors  100  are spaced apart by respective distances S, which in many cases is governed by space constraints and the fact that larger guide-member separations result in lower tension variation in the strands. A typical spacing S between motors  100  is between 0.1 m and 2 m, and in an example embodiment the spacing is adjustable, as described below. In some example embodiments, the spacing S is equal between all motors  100 , while in other example embodiments the spacing S is equal between some motors, while in other example embodiments the spacing S is not equal between any of the motors. Providing a variable spacing S between motors  100  may be used to adjust the stranding process. For example, a large spacing downstream helps minimize tension variation while a short spacing upstream shortens the overall length of apparatus  10  with little impact on tension variation. 
         [0021]      FIG. 2  is a perspective view of an example motor  100 . Motor  100  includes a guide member driver in the form of a hollow shaft  102  defined by an axial shaft hole  104  formed therein. An example size of shaft hole  104  is between 1 and 3 inches in diameter, with 2 inches being a commonly available size suitable for use in forming many types of SZ cables. The term “hollow shaft” as used herein in connection with motor  100  is intended to include a motor that contains a through passage concentric with and contained within the rotating structure of the motor. For example, certain types of servo-motors suitable for use herein and discussed in greater detail below include inductively driven rotors that surround and drive a hollow shaft. 
         [0022]    Each motor  100  includes the aforementioned rotatable guide member  20 R operably disposed within shaft hole  104  (see  FIG. 1 ) so that the guide member rotates with the rotation of the hollow shaft. In an example embodiment, rotatable guide member  20 R is disposed in shaft hole  104  and is fixed to hollow shaft  102  by, for example, by set screws (as described below), an adhesive, a flexible or rigid mounting member or fixture, or other known fixing means. 
         [0023]    Each motor  100  includes a position feedback device  106 , such as an optical encoder (see  FIG. 5 , introduced and discussed below). Positional feedback device  106  provides information (in the form of an electrical signal S 3 ) about the rotational position and speed of hollow shaft  102  and thus rotatable guide member  20 R. An example maximum rotational speed of motor  100  is 3,600 rpm and an example maximum theoretical acceleration is 21,582 rad/s 2 . A typical operating rotational speed for motor  100  used in producing SZ cable is about 1,500 rpm with an angular acceleration of about 8,000 rad/s 2 . An exemplary motor  100  for use in apparatus  10  is one of the model nos. CM-4000 hollow-shaft inductively driven servo motors made by Computer Optical Products, Inc., Chatsworth, Calif. Another exemplary motor  100  for use in apparatus  10  is a hollow-shaft gear-based motor, such as those available from Bodine Electric Company, Chicago, Ill. 
         [0024]      FIG. 3  is a face-on view and  FIG. 4  is a cross-sectional view of an example guide member  20  that can be used as stationary guide member  20 S and/or as rotatable guide member  20 R. The example guide member  20  is in the form of a round plate (“layplate”) having a central hole  24  with peripherally arranged smaller guide holes (e.g., eyelets)  28  (six guide holes are shown by way of example). Central hole  24  is sized to pass at least one core member  30  while guide holes  28  are sized to pass individual strand elements (“strands”)  40 . Core member  30  includes, for example, a strength element and/or a cable core member. An example strength element is glass-reinforced plastic (GRP), steel or like strength elements presently used in SZ cables. Example cable core members  30  include buffer tubes, optical fibers, optical fiber cables, conducting wires, insulating wires, and like core members presently used in SZ cables. Example strands  40  include optical fibers, buffer tubes, wires, thread, copper twisted pairs, etc. 
         [0025]    Guide member  20  is arranged in apparatus  10  so that central hole  24  is centered on axis A 1 , and in an example embodiment peripheral guide holes  28  are arranged symmetrically about the central hole. Guide member  20  is configured to maintain the at least one core member  30  and individual strands  40  in a locally spaced apart configuration as the core member and individual strands pass through their respective holes. An example guide member  20  is formed from aluminum. Guide member  20  optionally includes hole liners  44  that line central hole  24  and/or guide holes  28  in a manner that facilitates the passing of core member  30  and/or strands  40  through the guide member. Example materials for hole liners  44  include ceramic, plastic, TEFLON, and like materials. Hole liners  44  preferably have rounded edges that reduce the possibility of core member  30  and/or strands  40  from being snagged, abraded, nicked or cut as they pass through their respective holes. In another example embodiment, central hole  24  and guide holes  28  are provided with rounded edges. 
         [0026]    With reference to  FIG. 2  through  FIG. 4 , in an example embodiment, rotatable guide member  20 R includes peripheral set-screw holes  25 , and hollow shaft  102  includes matching screw holes  25 ′ configured so that the rotatable guide member is attached to the hollow shaft via corresponding set screws  27 . 
         [0027]    In an example embodiment, rotatable guide member  20 R is the same as or is similar to stationary guide member  20 S, and further in an example embodiment are both in the form of layplates such as shown in  FIG. 3  and  FIG. 4 . Motors  100  are axially aligned so that shaft hole  104  and the rotatable guide member  20 R operably disposed therein are centered on axis A 1 . 
         [0028]    With reference again to  FIG. 1 , in an example embodiment, stationary guide member  20 S and each motor  100  are mounted to respective base fixtures  120 , which in turn are mounted to a common platform  130 , such as a base plate or tabletop. In an example embodiment, base fixtures  120  are configured to be fixed in place to platform  130 , while in another example embodiment they are also configured to be positionally adjustable relative to platform  130 . In one example, the positional adjustability is achieved by slidably mounting base fixtures  120  to rails  140 , which allows for axial adjustability of each motor  100 . Movable motors  100  can be axially moved along rails  140  and placed together for “thread up,” i.e., threading the at least one core member  30  and strands  40  through their respective holes  24  and  28  in the various rotatable guide members  20 R, and then axially moved again along the rails to be spaced apart and fixed at select positions during the SZ stranding operation, as discussed below. The positional adjustability of motors  100  allows for the spacings S to be changed so that apparatus  10  can be reconfigured for forming different types of SZ cables or to tune the cable-forming process. In an example embodiment, base fixtures  120  and platform  130  (and optional rails  140 ) are configured so that motors  100  can be added or removed from apparatus  10 . 
         [0029]    With continuing reference to  FIG. 1  and also to the schematic diagram of  FIG. 5 , an example apparatus  10  includes at least one servo driver  150  electrically connected to the corresponding at least one motor  100 . Each servo driver  150  is in turn operably connected to a controller  160 . An example controller  160  is a programmable logic controller (PLC), or a microcontroller. An example controller  160  includes a processor  164  and a memory unit  166 , which constitutes a computer-readable medium for storing instructions, such as a rotation relationship embodied as an electronic gearing profile, to be carried out by the processor in controlling the operation of apparatus  10 . An exemplary controller  160  suitable for use in the present disclosure is Model No. PiC900 PLC made by Giddings and Lewis, LLC, Fond du Lac, Wis. 
         [0030]    Apparatus  10  also includes a linespeed monitoring device  172  operably arranged to measure the speed at which the SZ-stranded assembly  226  or core member  30  travels through the apparatus. Example locations for linespeed monitoring device  172  include downstream of the most downstream motor  100  and adjacent SZ-stranded assembly  226  as shown, or upstream of stationary guide member  20 S and adjacent core member  30 . Intermediate locations can also be used. Linespeed monitoring device  172  is electrically connected to controller  160  and provides a linespeed signal SL thereto. An example linespeed monitoring device  172  is the BETA QUADRATRAK II linespeed monitor, available from Beta LaserMike USA, Inc., Dayton, Ohio. 
         [0031]    In an example embodiment, controller  160  includes instructions (i.e., is programmed with instructions stored in memory unit  166 ) that control the rotational speed and the reversal of rotation of each motor  100  according to a rotation relationship. This rotation relationship between motors  100  is accomplished via motor control signals S 1  provided by controller  160  to the corresponding servo drivers  150 . In an example embodiment, the rotation relationship is embodied as electronic gearing. In response thereto, each servo driver  150  provides its corresponding motor  100  with a power signal S 2  that powers the motor and drives it at a select speed and rotation direction according to the rotation relationship. Position feedback device  106  provides a position signal S 3  that in an example embodiment includes incremental positional information, speed information, and an absolute (reference) position. The reference position is typically a start position of hollow shaft  102 , while the incremental position tracks its rotational position on a regular basis (e.g., 36,000 counts per rotation). The rotational speed of hollow shaft  102  is the change in rotational position with time and is obtained from the position information contained in signal S 3 . Linespeed signal SL provides linespeed information, which is useful for comparing to the rotational speeds of motors  100  to ensure that the rotational speed and linespeed are consistent with the operational parameters of apparatus  10  and the particular SZ-cable being fabricated. 
         [0032]    For apparatus  10  having a plurality of motors  100 , each motor has a different rotational speed, with less rotational speed the farther upstream the motor resides. For an SZ stranded cable, the number n of “turns between reversals&#39;” can vary, with a typical number being n=8. For this example number of turns between reversals, apparatus  10  starts at a neutral point (n=0) where all of the strands  30  and the rotational and stationary guide members  20 R and  20 S are aligned. Controller  160 , through the operation of servo drivers  150 , then causes motors  100  to execute four turns clockwise, and then reverse and execute eight turns counterclockwise. Note that after the first four counterclockwise turns, apparatus  10  returns to and then passes through the neutral point. After the eight counterclockwise turns, apparatus  10  reverses and performes eight clockwise turns. In this way, n=8 turns between reversals is obtained, with rotatable guide members  20 R turning four turns around the neutral point in each direction. 
         [0033]    For apparatus  10  designed to operate with a maximum angular deviation of 120° between two successive rotatable guide members  20 R, the 120° needs to be divided between four turns, or 30° per turn. Thus, as the “first” or most downstream rotatable guide member  20 R undergoes its first revolution, the second (i.e., second most downstream rotatable guide member) must lag the first by 30°, i.e., it only turns 11/12 (i.e., 0.92) of a revolution. This defines the base rotation ratio R, i.e., the range of rotation between the second and first most downstream motors. 
         [0034]    Consider an example for n=+/−4 turns and a maximum angular displacement between two rotatable guide members  20 R of θ MAX =120°. The first rotatable guide member turns a total angle of θ T =1440° (n*360), the second turns 1320°, the third 1200° and so on. The second rotatable guide member  20 R is then driven at a ratio R 2 =1320/1440=0.92. The third guide member  20 R is driven at a ratio R 3 =1200/1320 or 0.91. Generally, for j=the rotatable guide member number, θ MAX =the separation angle, θ T =the total angular rotation (n*360°) for the first guide member, the rotation ratio R j  of guide member j=2, 3, . . . relative to the first guide member is given by R j =1−(j−1)*θ MAX /θ T . 
         [0035]    Example rotation relationships for motors  100  are carried out in a similar manner for different numbers n of turns between reversals, a different total number m of motors, and a different maximum angular deviation θ MAX  between adjacent guide members. The number m of motors  100  needed in apparatus  10  generally depends on the type of SZ cable being formed and related factors, such as the maximum number n of turns between reversals, and θ MAX , which in turn depends on the guide member diameter, the size of the core member  30  and the size of strands  40 . A typical number m of motors  100  ranges from 1 to 20, with between 5 and 12 being a common number for a wide range of SZ cable applications. 
         [0036]    Apparatus  10  can be configured and operated in a number of ways. For example, rather than controller  160  controlling each individual servo driver  150 , in one embodiment the servo drivers are linked together via a communication line  178  and receive information about the rotation of the most downstream motor  100  via an electrical signal S 4 . The upstream servo drivers  150  then calculate the required motor signals S 2  needed to provide the appropriate rotation relationship (e.g., via electronic gearing) to their respective motors  100 . Thus, controller  160  transmits information via signal S 1  about the stranding profile (n turns between reversals, the laylength, etc. . . . ) to the first (i.e., most downstream) servo driver  150 . Each upstream servo driver  150  receives a master/slave profile (e.g. a gear ratio=R) for the motor  100  immediately in front of it via respective signals S 4 . Thus, the upstream servo drivers  150  are slaved to the most downstream servo driver. In this embodiment, controller  160  is mainly for initiating and then monitoring the operation of apparatus  10 . Linespeed information is provided to the most downstream servo driver  150  through controller  160  (i.e., from linespeed monitoring device  178  to controller  160  and then to the most downstream servo driver). 
         [0037]    In a related embodiment, controller  160  transmits the aforementioned stranding profile information via signal S 1  to first servo driver  150 , while each upstream servo driver receives a master/slave profile (e.g. a gear ratio=R) that synchronizes them to the downstream servo driver. Since each upstream servo driver  150  is slaved to the most downstream servo driver, each servo driver requires the position feedback data from the first motor  100 . Linespeed information is provided to the first servo driver  150  through controller  160 . 
         [0038]    In another related embodiment, controller  160  transmits the aforementioned stranding profile information to the first servo driver  150 . Controller  160  also calculates an individualized stranding profile for each upstream motor  100  based on the complete stranding profile that will result in a desired operation for apparatus  10 . In this case, there are no rotational master/slave relationships between motors  100 . Since each motor  100  operates independently of the others, each requires linespeed feedback from linespeed monitoring device  178  and only its own position information. In an example embodiment, the linespeed feedback is provided via controller  160 . 
         [0039]    Thus, in one embodiment, each motor  100  is programmed to rotate with a select speed that is not necessarily slaved of off the “base” rotation ratio R. In an example embodiment, the rotation relationship between the motors has a non-linear form selected to optimize the SZ stranding process. The rotation relationship between two adjacent rotatable guide members  20 R can best be visualized as a function of the angular position θ M  of a “master” guide member  20 R and the angular position θ S  of a corresponding “slave” guide members. Thus, for a prior art mechanical system where the rotation ratio R is fixed, the angular position θ S  of the slave guide member is determined by the function θ S =R*θ M , which is a linear function in θ. In contrast, the rotation relationship programmed into controller  160  can allow for a much more complex functional relationships between the angular positions and rotation speeds of guide members  20 . A non-linear rotation relationship is useful, for example, to minimize tension spikes that can occur during the SZ stranding operation. 
         [0040]      FIG. 6  is a schematic diagram of an example SZ cable-forming system (“system”)  200  that includes apparatus  10  of the present disclosure. System  200  includes strand storage containers  210 , typically in the form of spools or “packages” that respectively hold and pay off individual strands  40  and optionally one or more individual core members  30 . 
         [0041]    System  200  include a strand-guide device  220  arranged immediately downstream of strand storage containers  210 . In an example embodiment, strand-guide device  220  includes a series of pulleys (not shown) that collect and distribute the strands  40  and the at least one core member  30 . SZ cable-stranding apparatus  10  is arranged immediately downstream of strand-guide device  220  and receives at its input end  11  the strands  40  and the at least one core member  30  outputted from the strand-guide device. Apparatus  10  then performs SZ-stranding of the strands about the at least one core member  30 , as described above. Strands  40  and the optional core member  30  exit apparatus  10  at output end  13  as an SZ-stranded assembly  226 , as shown in the close-up view of inset A of  FIG. 6  (see also  FIG. 1 ). SZ-stranded assembly  226  consists of strands  40  wound around the at least one core member  30  in an SZ configuration. 
         [0042]    System  200  includes a coating unit  228  arranged immediately downstream of apparatus  10 . Coating unit includes an extrusion station  230  configured to receive the SZ-stranded assembly  226  and form a protective coating  229  thereon, as shown in the close-up view of inset B in  FIG. 6 , thereby forming the final SZ cable  232 . In an example embodiment, extrusion station  230  includes a cross-head die (not shown) configured to combine the protective coating extrusion material with the SZ-stranded assembly. Example coatings  228  include polyethylene (PE), polyvinyl chloride (PVC), Poly Vinyl Diene Fluorine (PVDF), Nylon, Poly Tetra Flouro Ethylene (PTFE), etc. Coating unit  228  also includes a cooling and drying station  240  is arranged immediately downstream of extrusion station and cools and dries coating  228 . The final SZ cable  232  emerges from coating unit  228  and is received by a take-up unit  250  that tensions the SZ cable and winds it around a take-up spool  260 . 
         [0043]    Apparatus  10  of the present disclosure eliminates the mechanical coupling between rotatable guide members  20 R and in this sense is a gearless and shaftless apparatus. Note that the strands  40  passing through the rotatable guide members  20 R do not establish a mechanical coupling between the guide members because the strands are not used to drive the rotation of the guide members. Without the added rotational inertia and bearing friction associated with mechanical components, faster reversal times and thus higher line speeds are possible for a given lay length. Gear-based SZ cable-stranding apparatus are also subject to extremely high dynamic loads during the reversals. This puts a great deal of stress on the power transmission gears, resulting in frequent maintenance issues. The gearless/shaftless SZ cable-stranding apparatus  10  eliminate these types of maintenance and reliability issues. 
         [0044]    Because the motion of rotatable guide members  20 R is electronically controlled, their rotational velocities in relation to other plates is programmable according to a rotation relationship to carry out rotation profiles (including complex rotation profiles) that result in smoother operation and lower tension variations on strands  40  and the at least on core member  30 . The prior art mechanical approaches limit the rotation profiles of the rotatable guide members, which causes unwanted variations in strand tension. 
         [0045]    It will be apparent to those skilled in the art that various modifications to the present embodiment of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.