Patent Publication Number: US-6209299-B1

Title: Double twist twinner with back-twist pay offs and intermediate capstan

Description:
BACKGROUND OF THE INVENTION 
     Electrical cables are commonly used to transmit analog signals and digital data. These cables often include a pre-twisted pair of wires to improve electrical and mechanical properties. These pre-twisted wires are cabled or paired together in a cabling device at typically high speeds which impart significant forces, e.g, tension, to the wires often deforming them. 
     Industry specifications dictating the strain on wires during cabling are stringent, e.g., the wire&#39;s conductor cannot be stretched more than 1/10,000 of an inch measured across the diameter. These specifications can result in a substantial amount of discarded wire. 
     U.S. Pat. No. 3,969,880 to Maillefer et al. describes a cabler that incorporates a capstan or pulling device inside of a rotating doubletwisting bow. The wire is twisted as the wire enters the bow, and then is fed down one side of the bow and twisted again at the other side of the bow after which the wire is taken up. At higher speeds, the capstan must pull the wire with higher tensile forces due to the frictional forces acting on the wire through the bow. This often pulls the wire out of specification. 
     Another prior art system avoids using a capstan and pulls the wire through the bow using the take-up reel. This system suffers from the same deficiency in that the wire is pulled through the bow with increased tension as the rotational speed of the bow increases often resulting in damaged wire. 
     SUMMARY OF THE INVENTION 
     Accordingly, a need exists for a cabler device which pulls wire through a rotating bow with minimal tensile force. 
     A need also exists for a cabler device which can counteract and minimize oscillating forces acting on the wire through the bow. 
     An apparatus to accomplish the foregoing comprises a first twisting device that dispenses a first wire and imparts a pre-twist to the same, a second twisting device that receives the twisted first wire and twists the same about a second wire. A metering device or capstan positioned on the outside of the second twisting device controls the input velocity of the first and second wires. The apparatus can further include a third twisting device that dispenses the second wire and imparts a pre-twist to the same. In a preferred embodiment of the present invention, the second twisting device receives the first and second wires and twins or pairs the same. Preferably, the first and third twisting devices impart a respective back-twist to the first and second wires. 
     A transducer that measures the tension of the first and second wires before the second twisting device twins the same is provided in accordance with the present invention. The tension measurement is forwarded to a controller. 
     According to other aspects of the present invention, a take-up reel and motor are provided on the second twisting device to take-up the twinned first and second wires. The take-up reel motor rotates in response to a control signal from the controller to thereby control the tension of the first and second wires through the second twisting device. 
     According to further aspects of the present invention, the second twisting device includes a traverse assembly to lay the wires onto a take-up reel. The traverse assembly includes a damping mechanism to maintain the tension in the wires substantially constant in a preferred embodiment. 
     The first and third twisting devices each include a pay-off reel that dispenses the first and second wires, each pay-off reel being rotated by a respective pay-off reel motor. The first and third twisting devices each further include a damping mechanism that takes up slack in the dispensing of the first and second wires. 
     Each twisting device includes a bow assembly rotated by a respective motor for twisting the wires. In a preferred embodiment of the present invention, each twisting device is vertically oriented. 
     A dancer assembly, which can also be referred to as a buffer assembly, is associated with the first and third twisting devices for taking up slack in the dispensing of the first and second wires and thereby control tension and velocity of the same. 
     An apparatus is also provided including first twisting means for dispensing a first wire and imparting a twist to the same, second twisting means for receiving the twisted first wire and twisting the same about a second wire. Metering means is positioned on the outside of the second twisting device for controlling the input velocity of the first and second wires. The apparatus can further include third twisting means for dispensing the second wire and imparting a twist to the same. Transducer means is also provided for measuring the tension of the first and second wires before the second twisting twists the same. This measurement is forwarded to a controller which controls the tension or torque of the take-up reel motor such that the tension through the second twisting means is substantially constant. 
     Also in accordance with the present invention, a method of twisting wire is provided comprising measuring the tension of a wire before it enters a twisting device, forwarding the tension measurement to a controller, and controlling the torque of a take-up reel in response to a set of programmed instructions. The take-up reel takes up the twisted wire in response to the tension measurement such that the tension in the twisting device is substantially constant. The method further includes the step of controlling the input speed of the wire with a capstan positioned before the wire enters the twisting device. In a preferred embodiment of the present invention, the wire is back-twisted before entering the twisting device. 
     According to yet a further aspect of the present invention, a back-twist is imparted to a second wire wherein the first and second wires are twinned in the twisting device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1 is a front view of a double twist twinner with integral back twist payoffs and intervening capstan in accordance with the present invention. 
     FIG. 2 is a top view of the inventive twinner of FIG.  1 . 
     FIGS. 3 and 4 are partial cutaway views taken along lines  3 — 3  and  4 — 4 , respectively, of FIG.  2 . 
     FIG. 5 is a front view of the capstan assembly and tension transducer shown in FIG.  1 . 
     FIG. 6 is a partially cutaway side view of the capstan assembly taken along line  6 — 6  of FIG.  5 . 
     FIG. 7 is a side view of the tension transducer taken along line  7 — 7  of FIG.  5 . 
     FIGS. 8-10 are front, side, and top views, respectively, of the traverse mechanism shown in FIG.  1 . 
     FIG. 11 is a graph illustrating the oscillating tension on the wire and inverse control signal to the take-up reel motor as it is pulled through the double twist twinner. 
     FIG. 12 is a flow diagram illustrating the operation of the controller of FIG.  1  and the control algorithm used to control the speed of pay-off motors. 
     FIG. 13 illustrates a control algorithm for the controller with respect to the take-up motor and capstan. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the figures, FIG. 1 depicts a twisting apparatus comprising a double twist twinner with integral back twist payoffs, generally referred to by reference numeral  10 , which has been constructed according to the principles of the present invention. Twisting apparatus  10  includes a first back payoff twister  12 , a second back payoff twister  14 , and a twinning device/cabler  16 . Generally, twisters  12  and  14  dispense respective wires  34 ,  38  and impart a back-twist to the same, the back-twisted wires referred to by respective numerals  34 ′ and  38 ′. These wires are pulled at a substantially constant rate by a capstan assembly  50 , which can also be referred to as a metering device, and twisted and twinned (also referred to as pairing) together and taken-up by twinning device  16 . 
     More particularly, wires  34  and  38  are wrapped about respective pay-off reels  32 ,  33  and held in the cradle assembly  36  of twisters  12 ,  14  by idler pintle assemblies  18 . Idle pintle assemblies  18  of twisters  12 ,  14  are rotated by motors  66  (best seen in FIG. 4) which are controlled by controller  35 . Wires  34 ,  38  pass through fleeting pulley assemblies  76  or damping mechanism to take-up slack in the dispensing of the wires. 
     In a typical implementation, wires  34 ,  38  are insulator-coated conductors. Typically, the conductors are copper. The insulator is typically a thermoplastic or other equivalent resin that has been extruded to continuously coat the conductors. 
     In a preferred embodiment of the present invention, pulley assemblies  76  each include a pulley  77  attached to spring steel, which is biased upwards such that the pulley  77  takes-up any slack in the respective wires  34 ,  38 . Wires  34 ,  38  pass around pulleys  77 ,  79  and over pulleys  81 . Pulleys  77  are positioned on cradle assembly  36  which are held stationary by magnet assemblies  74 . Pulleys  81  are positioned within respective wire guide bows  20 ,  22  which are rotatably supported by a lead-in spindle assembly  59  and a lead-out spindle assembly  60 . The lead-out spindle assemblies  60  include slip ring assemblies  58 . Bows  20 ,  22  are rotated by respective motors  26 ,  28 , which are controlled by controller  35 . 
     Because pulleys  79  are stationary and pulleys  81  rotate with the bows  20  and  22 , the wire is twisted therebetween. Wires  34 ,  38  are threaded along the interior surface of respective bows  20 ,  22  and pass over pulleys  83  which are positioned at the bottom of the bows. Wires  34 ,  38  pass through the lead-out assemblies  60  and pass around exit pulleys  42 . Wires  34 ,  38  are again twisted between pulleys  83  and  42  resulting in back-twisted wires  34 ′,  38 ′. Since the wires are twisted at the top and bottom of bows  20 ,  22 , one twist per complete revolution of bows  20 ,  22 , twisters are commonly referred to as “double twist bows.” 
     Before the back-twisted wires  34 ′,  38 ′ are wrapped around and pulled by capstan  50 , the wires are threaded around a buffer assembly or dancer  40  which takes up any slack between exit pulleys  42  and capstan  52 . Dancer  40  includes a stationary pulley  46  and a pulley  44  moveable in the direction of the double-headed arrows. The position of pulleys  44  are detected by a potentiometer  47  connected to controller  35 . If capstan  50  pulls wires  34 ′,  38 ′ at a faster rate, pulley  44  would move toward pulley  46  precluding the wires from being stretched out of specification. The potentiometer  47  forwards the movement of pulley  44  to controller  35  wherein the controller directs motors  66  to pay-off wire at a faster rate. Similarly, if capstan  50  pulls wires  34 ′,  38 ′ at a slower rate, pulley  44  would move away from pulley  46  to thereby control wire tension and prevent slack in the wires. The controller  35  would then direct motors  66  to pay-off wire at a slower rate. 
     The pre-twisted wires  34 ′,  38 ′ are pulled by capstan  50  which is controlled by controller  35 . FIGS. 5 and 6 illustrate the capstan  50  in more detail. Capstan  50  includes a drive capstan wheel  52  attached to and rotated by drive motor  51 . An idler capstan wheel  54  is provided journaled to a capstan frame  53 . An encoder  80  measures the speed at which motor  51  is rotating and forwards the signal to controller  35 . In a preferred embodiment of the present invention, wires  34 ′,  38 ′ are wrapped around wheels  52  and  54  a total of three times to ensure that the wires do not slip, are pulled at the same velocity, and reduce tension because of the mechanical advantage associated with the pulley system. 
     As particularly illustrated in FIGS. 5 and 7, wires  34 ′,  38 ′ pass around pulley  82  of tension transducer  56  prior to entering the twinning device  16 . Tension transducer  56  measures the tension in the wires and forwards this measurement to controller  35 . In alternative embodiments, the wire tension is measured by a detector in pulleys in the traverse mechanism  68  or by measuring capstan motor current draw. These measurements can be used to supplement or replace information from pulley  82 . 
     Referring again to FIG. 1, twisting device  16  has similar features as found in twisters  12  and  14  wherein the same reference numerals refer to the same or similar elements. Twisting device  16  twins or pairs pre-twisted wires  34 ′,  38 ′ and wraps the resulting twisted, cabled pair  70  onto take-up reel  72 . Twisting device  16  is also a double twister in that it twists and pairs the wires between pulleys  82  and  83  at the lower end and also twists the wires between pulley  81  (best seen in FIG. 3) and pulley  96  (best seen in FIG. 9) at the upper end of the device. Wire guide bow  24  is rotated by motor  30  controlled by controller  35 . 
     As best illustrated in FIGS. 8-10, a traverse assembly  68  is also provided on twinning device  16  to lay cabled pair  70  onto take-up reel  72 . Traverse assembly  68  includes a traverse member  92  slidable along shaft  90 . Member  92  is driven by motor  66  via traverse members  86 ,  88  and traverse pulley  87 . As best seen in FIG. 9, member  92  slidably supports member  102  which rotatably supports pulley  94 . A spring  93 , held in place by collar  100 , resiliently biases member  92  upwards. The cabled pair  70  passes around pulley  96  and over pulley  94  and then it is wound onto take-up reel  72 . Spring  98  interconnects and linearly aligns pulleys  94  and  96 . Spring  94  can move downward to prevent the cabled pair  70  from being overstretched. A mechanical damping system is also provided to reduce oscillations. 
     The twisting apparatus  10  of the present invention provides the capstan  50  on the outside of twinning device  16 . That is to say, the capstan pulls pre-twisted wires  34 ′,  38 ′ from pay-off reels  32 ,  33  before they are cabled together. Unlike prior art systems, this facilitates the reduction in tension on the wires as they pass through twinning device  16 . Reduced tension of the wires through twinning device  16  is desirable because the extreme forces, e.g., centrifugal, in the twinning device increase friction between the wire and bow. Increased tension results in an increase in the force that must be used to pull wires  34 ′,  38 ′ through the bow  24 . This, in turn, affects the electrical characteristics of the twisted pair. Specifically, this tension tends to distort the manner in which the wires are twisted together. For example, the insulation can be compressed to some degree, which reduces the electrical isolation between the wires. In contrast, when the wires are twisted together under reduced tension, the electrical characteristics improve. 
     By placing the capstan  50  outside the twinning device  16 , and specifically upstream of the twinning device, the tension placed on the partially twisted pair passing through bow  24  arises only due to the friction of the wire in the bow, especially when an enclosed bow is used, thereby reducing any tension resulting from atmospheric drag and turbulence. Effectively, the forces required to pull the wires from twisters  12 ,  14  is handled by the capstan  50 . In fact, with proper control of the capstan  50  and the take-up control motor  66 , the partially twisted pair through the bow  24  can be controlled to “float” to some degree. 
     By placing the capstan  50  outside the twinning device  16 , the required bow  24  to line speed ratio can be fixed at its required setting. In a preferred embodiment of the present invention, wire guide bow  24  of the twining device  16  twists cabled pair  70  in the range of about 3,500 to 5,000 twists per minute (tpms), and most preferably about 4,500 tpms. Wire guide bows  20 ,  22  of twisters  12 ,  14  rotate in the range of 0% to 100% of the rotational speed of bow  24 . The lower range (0%) results in no pre-twisting of the wires which is acceptable in applications such as paired telephone wire. The higher range (100%) is used to, for example, to neutralize a wire such that the twinning device untwists the pre-twisted wire. Preferably, bows  20 ,  22  rotate in the range of about 10%-25% of the rotational speed of bow  24 , and most preferably about 20%. Preferably, the cabled pair  70  lay, defined as the distance in which each of the paired wires makes one complete 360 degree revolution about a common axis, is in the range of about ¼″ to 1″. Also in accordance with a preferred embodiment of the present invention, capstan pulls wires  34 ′,  38 ′ with a tension of approximately three pounds. 
     As described above, the tension of wires  34 ′,  38 ′ is measured by the tension transducer  56  which forwards the measurement to the controller  35 . It has been found that the tension of the wires within the twinning device  16  oscillates sinusoidally due to numerous variables including jerking of the wire as it is pulled through the wire guide bow  24 . This oscillation is depicted graphically by reference numeral  104  of FIG.  11 . The controller  35  is programmed to control take-up motor  66  in tension mode such that the sinusoidal fluctuations are minimized or canceled in twinning device  16 . That is to say, the tension can be minimized by anticipating when a sag is going to occur and backing off the tension of take-up motor  66 . This is graphically depicted by reference numeral  106 . In effect, an inverse control signal is introduced to the take-up motor  66  proportional to the oscillation monitored by transducer  56 . 
     The operation of the present invention will now be described. The operator rolls pay-off reels  32 ,  33  and take-up reel  72  onto pneumatically operated lifting assembly  48 . Assembly  48  lifts the reels such that the operator can position them within the idler pintle assemblies  18  without substantial lifting. In alternative embodiments, the lifting assembly is not present and the operator manually lifts pay-off reels  32 , 33  into position. The operator then threads wires  34  and  38  through the fleeting pulley assemblies  76  over pulleys  81 , around respective bows  20 ,  22  and around exit pulleys  42 . Each wire is wound around respective dancer assembly  40 , around capstan  50  and pulley  82  of tension transducer  56 . The wires are threaded over pulley  83  and around bow  24  and through traverse assembly  68  and wound onto take-up reel  72 . The operator initiates operation of the twisting operation  10  at controller  35 . As the tension transducer  56  measures the dynamic tension of the wires, the controller  35  initiates a pre-programmed inverse control signal to take-up motor  66  to minimize tension oscillations within the twinning device  16 . 
     FIG. 12 is a flow diagram illustrating the operation of the controller  35  and the control algorithm used to control the speed of motors  66  in twisters  12 ,  14 . Specifically, the controller  35  polls the potentiometer  47  in each of twisters  12 ,  14 . These potentiometers  47  indicate the amount of wire  34 ,  38  that is held in buffer or dancer assemblies  40 . The speed of motors  66  is controlled to maintain a predetermined amount of buffered wire  34 ,  38 . 
     FIG. 13 illustrates a control algorithm for the controller  35  with respect to the take-up motor  66  and capstan  50 . Specifically, the controller  35  detects wire tension in the bow  24  indirectly by a transducer  56  on pulley  82 . The controller  35  further monitors the speed of capstan  50 . The controller  35  then modulates the torque or tension of take-up motor  66  in twinning device  16  to maintain the proper tension of the wire in twinner  16 , specifically through the bow  24  and onto the take-up reel  72 . Specifically, the torque or tension of motor  66  of twinning device  66  is modulated dynamically to reduce and remove any oscillations in the wire tension. Specifically, there is a resonant frequency associated with wire tension through the bow  24  due to the elasticity of the bow, and spring-like nature of the paired wire. The motor  66  is modulated to modulate the wire tension at this frequency of oscillation, but out of phase with the oscillations, for example,  90  degrees, to reduce these periodic tension fluctuations. 
     Industry specifications regarding the lay of the cabled pair  70  are particularly stringent, e.g., accuracy to within three decimal places. Modulation of the capstan  50  to remove or minimize the paired wire tension oscillations is possible, but not preferred, as such modulation directly affects the input speed of wires  34 ′,  38 ′ into the twinning device  16 . This fluctuation in the input speed of the wires can affect the lay of cabled pair  70 . Thus, the present invention provides a capstan  50  on the outside of the twinning device  16  capable of providing a pair of wires to the twinning device at a constant rate. A take-up reel motor  66  on the inside of the twinning device  16  controls the tension of the wires inside the device to minimize tension therethrough. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.