Patent Publication Number: US-11662534-B2

Title: Online helix adjustment to control connector location on preconnectorized tapered assemblies

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 17/002,883 filed Aug. 26, 2020, which claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/895,219 filed on Sep. 3, 2019, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The disclosure relates generally to optical fiber cables and more particularly to optical fiber cables that have drop cables that run along at least a portion of the length of a main distribution cable. Optical fiber cables are used to transmit data over distance. Generally, large distribution cables that carry a multitude of optical fibers from a hub are sub-divided at network nodes, which are further sub-divided, e.g., to the premises of individual subscribers. Generally, these subdivisions involve splicing a cable tether into a main distribution line. Cable splicing at specific locations along a main distribution line is a delicate and time consuming process that requires precise placement of the cable tether and that involves the risks of cutting the wrong fibers and providing environmental exposure to the cable interior. 
     SUMMARY 
     In one aspect, embodiments of the disclosure relate to a method of preparing a bundled cable. In the method, a plurality of subunits is wound around a central member in one or more layers of subunits to form the bundled cable. For a section of the central member, each layer of subunits has a pitch over which a subunit of the layer of subunits makes one revolution around the section of the central member and a length of the subunit required to make the one revolution. The subunits are configured to have a nominal helical length equal to the ratio of a nominal length to a nominal pitch. Further, in the method, a measurement of the bundled cable is monitored, and a winding rate of the plurality of subunits is adjusted based on the measurement in order to account for deviations from the nominal helical length. 
     In another aspect, embodiments of the disclosure relates to a method of preparing a bundled cable. In the method, a central member is provided having an outer central member surface defining a central member diameter. A plurality of subunits is provided. Each of the plurality of subunits has an outer subunit surface defining a subunit diameter. In the method, the subunit diameter and the central member diameter are monitored. The plurality of subunits is wound around a central member in one or more layers of subunits to form the bundled cable. For a section of the central member, each layer of subunits has a pitch over which a subunit of the layer of subunits makes one revolution around the section of the central member and a length of the subunit required to make the one revolution. The subunits are configured to have a nominal helical length equal to the ratio of a nominal length to a nominal pitch. A winding rate of the plurality of subunits is adjusted based on the monitoring of the subunit diameter and of the central member diameter in order to account for deviations from the nominal helical length. 
     In still another aspect, embodiments of the disclosure relates to a system for preparing a bundled cable. The system includes a payoff reel configured to provide a run of a central member, a strander configured to wind a plurality of subunits around the central member to form the bundled cable, and a monitoring system configured to take at least one measurement of at least one of the central member, the plurality of subunits, or the bundled cable. The strander is configured to adjust a winding rate for the plurality of subunits based on the measurement from the monitoring system. 
     In yet another aspect, embodiments of the disclosure relate to a bundled optical fiber cable. The bundled optical fiber cable includes a central member having a first end and a second end. The first end and the second end define a length of the bundled optical fiber cable. The bundled optical fiber cable also includes plurality of subunits wound around the central member. Each of the plurality of subunits includes a subunit jacket having an inner surface and an outer surface. The inner surface defines a central bore containing at least one optical fiber. The plurality of subunits have a variable pitch along the length of the central member, and the outer surface of the subunit jacket of each of the plurality of subunits is an outermost surface of the bundled optical fiber cable. 
     Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. 
         FIG.  1    depicts partial perspective view of a bundled optical cable, according to an exemplary embodiment. 
         FIG.  2    depicts a cross-sectional view of the bundled optical cable of  FIG.  1   . 
         FIGS.  3 A- 3 B  are schematic depictions of an aerial installation and a duct installation of a bundled optical fiber, according to an exemplary embodiment; 
         FIG.  4    provides a schematic representation of the geometric relationship between a subunit and a central member during winding, according to an exemplary embodiment; 
         FIG.  5    depicts another geometric relation pertaining to the helical length of the stranded unit, according to an exemplary embodiment; 
         FIG.  6    depicts a cross-section of a bundled cable demonstrating the r dimension, according to an exemplary embodiment; 
         FIG.  7    is a schematic depiction of a system for performing a winding rate adjustment, according to an exemplary embodiment; and 
         FIGS.  8 A- 8 B  depict an embodiment of subunit indexing to provide a desired helical length, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring generally to the figures, various embodiments of a method for producing a bundled optical fiber cable are provided. A bundled optical fiber cable includes a plurality of subunits wound around a central member, and each of the plurality of subunits is configured to branch from the cable at a particular branching point along the length of the cable. These cables provide the advantage of being assembled and connectorized in the factory such that the bundled optical fiber cable can be easily deployed without labor-intensive splicing in the field. However, the subunit length must be precise in order that the connectorized end accurately corresponds to drop points in the field. In this regard, the components of the cable have nominal dimensions, but often, the components deviate in dimension by fractions of a millimeter. Over the length of a cable (e.g., a 1 kilometer (km) cable), these small deviations in component size add up to a large deviation in the subunit length and, ultimately, the position of the connectorized end. In certain instances, the deviations in length can be tens of inches. 
     To account for the deviation in component dimensions, according to the present disclosure, the dimensions of the components prior to winding or the dimensions of the bundled cable after winding are determined. These dimensions are used to adjust the winding rate of the subunits around the central member to ensure that the connectorized ends are accurately terminated at a desired position relative to the branch point. For example, if the connector is running long, the winding rate is increased to decrease the laylength, using more of the subunit, and conversely, if the connector is running short, the winding rate is decreased to increase the laylength, using less of the subunit. Advantageously, the winding rate can be changed without changing the lines speed at which the central member and subunits are being pulled through the winding system. Other aspects and advantages will be described in relation to these and other embodiments provided herein and in the figures. These embodiments are presented by way of illustration and not by way of limitation. 
       FIG.  1    depicts an embodiment of a bundled optical fiber cable  10  in a partial sectional view taken over a portion of the length of the bundled optical fiber cable  10 . As can be seen, the bundled optical fiber cable  10  includes a central member  12  (e.g., an optical fiber cable or an overcoated strength element) and a plurality of subunits  14  that are wound around the outside of the central member  12 . In embodiments, the subunits  14  are helically wound around the central member  12 . For example, in embodiments, the subunits  14  may have an S-winding or a Z-winding around the central member  12 . Additionally, in embodiments, the subunits  14  may have an SZ winding around the central member  12 . That is, the subunits  14  may have an S-winding followed by a reversal to a Z-winding, then a reversal to S-winding, etc. 
       FIG.  2    provides a detailed cross-sectional view of an embodiment of the bundled cable  10 . As can be seen, the subunits  14  are substantially evenly spaced around a circumference of the central member  12 . In embodiments, the central member  12  may be an optical fiber cable (as shown in  FIG.  2   ), a power transmission cable, or a central strength member (e.g., a glass-reinforced plastic (GRP) rod optionally jacketed with a polymeric material). 
     In the embodiment depicted, the bundled cable  10  includes thirteen subunits  14 . In embodiments, as few as a single subunit  14  can be provided around the central member  12 . In general, the maximum number of subunits  14  that can be provided around the central member  12  is limited by the installation parameters (e.g., duct size) or manufacturing capabilities (e.g., winding equipment) for the bundled cable  10 . For instance, given an installation parameter of a two inch duct size, the maximum number of subunits  14  that can be provided around the central member  12  may be thirty-nine subunits in embodiments. In still other embodiments, the subunits  14  are arranged in multiple layers around the central member  12 . Taking the two inch duct again as an example, the bundled cable  10  may include an innermost layer of the seven subunits  14  around a jacketed GRP rod central member  12  with an intermediate layer of thirteen subunits  14  and an outer layer of another nineteen subunits  14  (7+13+19=39 subunits). In embodiments, the subunits  14  contain optical fibers and/or power transmission elements. Additionally, in embodiments, the subunits  14  may be “dummy cables” that do not contain any optical fibers or power transmission element but which provide structural support around the cable. 
       FIG.  2    depicts the structure of an embodiment of a bundled cable  10  in which the central member  12  is an optical fiber cable and the subunits  14  are drop cables. In the embodiment depicted, the central member  12  includes an outer jacket  16  having an inner surface  17  and an outer surface  18 . In the embodiment depicted, the inner surface  17  defines a cable bore  19  within which a plurality of optical fibers  20  are disposed. The optical fibers  20  can be arranged in a variety of suitable ways within the central member  12 . In the embodiment depicted, the optical fibers  20  are arranged in a stack  21  of ribbons  22 . In particular, the optical fibers  20  are arranged into a stack  21  of sixteen ribbons  22 , defining a plus-shaped cross-section. In the embodiment depicted, the total number of optical fibers  20  in the stack  21  of ribbons  22  is 288. In embodiments, a single stack can contain up to 864 optical fibers  20 . As shown in  FIG.  2   , the stack  21  is surrounded by a stack wrap  24 , which, in embodiments, may provide color coding for multiple-stack configurations and/or water-blocking properties. In embodiments, the central member  12  includes multiple stacks  21 , e.g., from one stack to twelve stacks. Central members  12  of the type described are available from Corning Incorporated, Corning, N.Y., such as those marketed under the trademark RocketRibbon™. Alternatively, the optical fibers  20  may be arranged in a central tube (or a plurality of buffer tubes) in a loose tube configuration. Central members  12  of this type are available from Corning Incorporated, Corning, N.Y., such as those marketed under the trademarks ALTOS®, SST-Ribbon™, and SST-UltraRibbon™. 
     As can also be seen in the embodiment depicted in  FIG.  2   , the subunits  14  each include a plurality of optical fibers  20  disposed within a central tube  26 . In embodiments, the subunits  14  contain from one optical fiber  20  up to thirty-six optical fibers  20  depending on the particular needs of the installation. In embodiments, the central tube  26  is surrounded by a plurality of tensile elements  28  (e.g., yarns of aramid, glass, and/or basalt fibers). The tensile elements  28  are surrounded by a subunit jacket  30 . In embodiments, the subunit jacket  30  has an outer surface  32 , and for the subunits  14  immediately surrounding the central member  12 , the outer surface  32  of the subunits  14  contacts the outer surface  18  of the outer jacket  16  of the central member  12 . In embodiments, the subunits  14  may be bonded (e.g., welded or adhered) to the central member  12  at one or more locations along the length of the central member  12 . Further, in embodiments, the outer surface  32  of the subunit jacket  30  may define an outermost surface of the bundled cable  10 . That is, no further jacketing material is applied around the subunits (not including any periodically spaced bindings, wraps, or ties which may be used to keep the subunits  14  bound to the central member  12 ). 
       FIGS.  3 A and  3 B  depict a schematic representation of a bundled cable  10  with a subunit  14  branching from the central member  12  at a branch point  34 . To provide enough slack to make a connection at the branch point (TBP)  34  and to properly position the subunit  14 , the subunit  14  is terminated at a particular location along the length of the bundled cable  10 . As shown in  FIGS.  3 A and  3 B , the bundled cable  10  may be marked with a pole alignment marker (PAM)  36 . During installation, the bundled cable  10  is positioned such that the pole alignment marker  36  is substantially centered on an installation pole or other alignment structure. As can be seen, the subunits  14  in the bundled cables  10  shown in FIGS.  3 A and  3 B are preconnectorized with a connector  38 . In the embodiment shown, the connectors  38  are attached to the bundled cable  10  with a tie wrap  40 . 
     Depending on the type of installation, the subunit  14  may be terminated at different lengths.  FIG.  3 A  depicts the layout for an aerial installation, and  FIG.  3 B  depicts the layout for a duct installation. As can be seen, for both layouts, the branch point  34  may be positioned within about 5 ft (+/−6 in) from the pole alignment marker  36 . In the aerial layout of  FIG.  3 A , the subunit  14  nominally terminates about 1 ft (+/−6 in) prior to the pole alignment marker  36 . In the duct layout of  FIG.  3 B , the subunit  14  terminates nominally about 5 ft (+/−6 in) past the pole alignment marker  36 . As will be discussed below, a variety of factors dictate whether the subunits  14  are able to be accurately positioned at the nominal termination points along the length of the bundled cable  10  such that during installation the subunits  14  will be located at the desired position relative to the pole alignment marker  36 . 
     Because the subunits  14  are wound around a central member  12 , the actual, fully-extended length of the subunits  14  is longer than the length along the central member  12 .  FIG.  4    illustrates this point with a depiction of a single subunit  14  wound around a central member  12 . To accurately position the connector  38  along the bundled cable  10 , the total length of each subunit  14  prior to winding needs to be known. Otherwise, the winding machine has to be stopped when the desired termination point is reached so that the subunit  14  can be connectorized on-line. As shown in  FIG.  4   , the winding of the subunit  14  around the central member  12  defines a pitch circle having radius r. Further, the length over which the subunit  14  completes one revolution around the central member  12  is referred to as the pitch P (which is also known as “laylength”). The extended length of subunit  14  necessary to complete one revolution is referred to as the length L, and the length L can be determined through a relationship between the radius r of the pitch circle and the pitch P as shown in  FIG.  5   . In particular, the length L is the hypotenuse of a right triangle having a first side length of P and a second side length of 2πr. Accordingly, from  FIGS.  4  and  5   , it can be seen that at least two factors that directly affect length L are pitch P and radius r. Other factors that affect length L will be discussed below but include forces that elongate the subunit  14  or central member  12  or introduce additional twist (affecting pitch P)). 
     Specifically, from the geometric relationship shown in  FIG.  5   , a ratio between the length L and pitch P, referred to as the helical length HL (L/P=HL), can be determined from the pitch P and radius r based on the following equation: 
     
       
         
           
             
               H 
               ⁢ 
               
                   
               
               ⁢ 
               L 
             
             = 
             
               
                 1 
                 + 
                 
                   
                     ( 
                     
                       
                         2 
                         ⁢ 
                         π 
                         ⁢ 
                         r 
                       
                       P 
                     
                     ) 
                   
                   2 
                 
               
             
           
         
       
     
     In general, pitch P is nominal based on the cable design, and thus, the main variable affecting helical length HL is the radius r of the pitch circle. That is, during cable stranding, the machinery will be set up to produce a specified pitch P, but as will be discussed below, small deviations in radius r ultimately affect the actual pitch P of the subunit as stranded around the central member  12 . As can be seen in  FIG.  6   , the radius r of the pitch circle is essentially equal to the sum of the radius r su  of the subunit  14  and the radius r cm  of the central member  12 . While each of the subunit  14  and the central member  12  has a nominal diameter, the diameter is variable over the length of each subunit  14  and central member  12  in practice, e.g., resulting from variability in the extrusion process. 
     To demonstrate the effect that even a small variation in the diameter of the central member  12  has on the helical length HL of the subunit  14 , a simulation was performed with a bundled cable  10  having six subunits  14  stranded around a jacketed GRP central member  12 . In the simulation, each subunit  14  has a nominal outer diameter of 4.0 mm, and the central member  12  has a nominal outer diameter of 4.4 mm. A variability of +/−0.1 mm in the diameter of the central member  12  was considered. The simulation was a Monte Carlo simulation involving 5000 iterations of winding subunits having a 4.0 mm diameter helically around central members  12  having a normal distribution of diameters between 4.3 mm and 4.5 mm (i.e., nominal 4.4 mm with +/−0.1 mm deviation). According to the simulations, a connector movement of +/−2 inches developed over 100 meters (m). Thus, over the length of a 300 m cable, the deviation would already be at the level of tolerance discussed above with respect to aerial and duct installations described in relation to  FIGS.  3 A and  3 B . As the length of the bundled cable grows, the connector movement increases. For example, a cable that is 1 km long would have a connector displacement of as much as 20 inches. 
     Moreover, this simulation only considered one source of deviation (the diameter of the central member  12 ). The diameters of the subunits  14  could also vary along their length. Besides the dimensions of the components of the bundled cable  10 , other factors affect the actual pitch and helical length of the subunits  14 . The tension at which the central member  12  and subunits  14  are pulled through the processing line affects their lengths during the stranding operation. For example, a higher tension will create more elongation in the central member  12  and/or subunits  14  than a lower tension during stranding. After stranding, there may be a relaxation that causes the central member or subunits  14  to shrink back, affecting pitch. Further, the stranding and pulling of the cable creates torsional error that affects pitch. When multiple factors are considered, the deviation in connector placement increases to about 3.5 inches per 100 m. Additionally, in embodiments in which multiple layers of subunits are provided, the deviation in connector placement can increase further still. As shown in  FIG.  6   , the subunits  14  have a small gap between them around the circumference of the central member  12 . In outer layers, this gap can become compressed, leading to an additional source of deviation. In addition, deviation in connector placement in a second layer can be as much as about 5.7 inches per 100 m and in a third layer can be as much as about 6.2 inches per 100 m. 
     To accommodate the potentially large deviations in the position of the subunits as the result of small deviations in the dimensions of the subunits, monitoring the dimensions of the subunits and/or central member as the subunits are wrapped around the central member and adjusting the rate at which the subunits are wound around the central member is employed.  FIG.  7    depicts a system  100  for adjusting the winding rate. In the system  100 , the central member  12  is carried on a payoff reel  110 . The central member  12  runs through a strander  120 , such as a rigid or planetary strander, which winds or wraps the subunits  14  around the central member  12 . The central member  12  and subunits  14  pass through a closing point  130  to create the bundled cable  10 . The bundled cable  10  is pulled by a caterpuller  140 , and the bundled cable  10  is taken up on a take-up reel  150 . In other embodiments, the strander  120  could be a drum twist strander that rotates the payoff and takeup reels  110 ,  120  in lieu of rotating the outer subunits  14  around the central member  12 . 
     To adjust the winding rate, the diameter of the central member  12 , the diameter of the subunits  14 , the diameter of the bundled cable  10 , and/or the pitch P of the subunits  14  are monitored. For example, as shown in  FIG.  7   , the system  100  includes monitoring stations  160   a ,  160   b , and  160   c . Monitoring station  160   a  is positioned upstream of the strander  120  to capture the diameter of the central member  12 . Monitoring station  160   b  is positioned proximate to the strander  120  (e.g., near the subunit feed for the strander  120 ) in order to capture the dimensions of the subunits  14 . Further, monitoring station  160   c  is positioned after the closing point  130  to capture the dimensions of the bundled cable  10  or to capture the pitch P of the subunits  14 . In embodiments, only monitoring station  160   c  is used, and the dimensions of the bundled cable  10  are used to adjust the winding rate for the upstream cable. In other embodiments, only monitoring stations  160   a  and  160   b  are used to measure the dimensions of the individual components to adjust the winding ratio downstream of the monitoring stations  160   a ,  160   b.    
     In embodiments, the monitoring stations  160   a ,  160   b ,  160   c  directly measure the dimensions of the central member  12 , subunits  14 , and/or bundled cable  10  using a probe, such as a non-contact laser. In embodiments used in conjunction with the measuring probes, a vision system may be located at monitoring station  160   c  that measures the pitch (or laylength) by capturing images of the bundled cable  10 . The vision system compensates for errors in the laylength based on torsional effects leading into the caterpuller  140 . Another way to measure the correct location for landing the connector is by measuring length of the individual subunits as well as the length of the central member and adjusting the laylength based on maintaining a desired ratio between the lengths. 
     By monitoring the dimensions of the bundled cable  10  or cable component, the winding rate of the strander  120  can be adjusted to increase or decrease the pitch P so that the connector is accurately positioned in relation to pole access markers along the length of the bundled cable  10 . Advantageously, the feed rates of the central member  12  and subunits  14  do not have to be adjusted, which allows for the desired production rate to be maintained despite deviations in component size. Thus, using a system  100  as depicted in  FIG.  7   , the minor deviation in component dimensions can be accommodated through adjusting of the winding rate as shown in Table 1, below. 
     In Table 1, a bundled cable having a subunit diameter of 4.0 mm was used with a central member having a nominal diameter of 4.4 millimeters (mm). The laylength (pitch P) for such a cable was 125 mm. As can be seen in a comparison of Example 1 (no deviation) and Examples 2 and 3 (negative deviation and positive deviation, respectively), each bundled cable had no deviation in length (L). However, the winding rate was increased by 1.9 rpm for Example 2 and decreased by 1.9 rpm for Example 3. The winding rates caused Example 2 to have a shorter pitch than Example 1 and caused Example 3 to have a longer pitch than Example 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Properties of Subunits and Central Member 
               
               
                 used in Bundled Cable Simulations 
               
            
           
           
               
               
               
               
            
               
                   
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Unit Diameter (mm) 
                 4.0 
                 4.0 
                 4.0 
               
               
                 Layer 1 Units 
                 6 
                 6 
                 6 
               
               
                 Central Member Diameter (mm) 
                 4.4 
                 4.3 
                 4.5 
               
               
                 Layer 1 Pitch (mm) 
                 125.00 
                 123.51 
                 126.49 
               
               
                 Layer 1 Helical Length (HL or L/P) 
                 1.022 
                 1.022 
                 1.022 
               
               
                 Helix length variation (in/100 m) 
                 0.000 
                 0.000 
                 0.000 
               
               
                 Rotational speed (rpm) 
                 160.0 
                 161.9 
                 158.1 
               
               
                   
               
            
           
         
       
     
     Besides winding rate, the final properties of the bundled cable can be influenced by providing accurately cut subunits for winding around the central member  12 .  FIGS.  8 A and  8 B  depict an embodiment of an indexed subunit  14 . As can be seen in  FIG.  8 A , the subunit  14  includes a number of coordinated index marks  170   a ,  170   b ,  170   c . Each set of index marks  170   a ,  170   b ,  170   c  is separated by the desired total length TL of the subunit  14 . In preparing the subunit  14  for winding, the subunit  14  is connectorized at an end. As shown in  FIG.  8 A , the subunit  14  has a preselected connectorization index point and a corresponding index point for trimming the subunit to length. Accordingly, if a successful connectorization is made at index mark  170   a , the subunit  14  is trimmed at the corresponding index mark  170   a  at the opposite end of the subunit to provide the desired total length TL of the subunit  14  as shown in  FIG.  8 B . If the connectorization at index mark  170   a  is not successful, then connectorizaion is attempted at index mark  170   b , and so on, and the corresponding index mark is used to trim the subunit  14  to the desired length thereafter. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein the article “a” is intended include one or more than one component or element, and is not intended to be construed as meaning only one. 
     It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.