ADVANCED METHODS AMD DESIGNS FOR BALANCING A STRANDED ΤΕ ΪΝΑΤΙΟΝ ASSEMBLY

Pate Application of

Richard V, Campbell

CROSS-REFERENCES TO RELATED APPLICATIONS

This non -provisional patent application claims the be efit of an. earlier-ftied provisional application. The first provisional application was assigned serial number 61/984,830. It. listed the sarae inventor.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

DESCRIPTION

Title of the Invention: Advanced Methods and Designs for Balancing a Stranded Termination

Assembly

Technical Field,

S This invention- relates to the field of tensile strength members such as multi-stranded synthetic cables. More specifically, the invention comprises devices and methods for balancing the load carried by a synthetic cable among its constituent strands.

2. Background Art,

A cable must generally be provided with one or more end connections in order to be

S O useful. The end connections allow the cable to carry and transmit a useful load. An end connection may be a simple device ·- such as a large hook - employed to connect the. cable to an anchoring point. Larger synthetic cables typical !y include multiple constituent strands, it is preferable to attach an individual connective device to each strand. Such a connective device is referred to in this disclosure as a "strand termination. ^" Multiple strand terminations are

15 connected together somehow to create a unified cable end connection. The unified cable end connection is referred to in this disclosure as an "overall cable termination."

For small cables simple end-fittings work fairly well. For larger cables, however, more complicated end-fittings are needed in order to produce acceptable break strength. This is particularly true for large, multi-stranded cables made of synthetic filaments (having diameters 0 of 20 mm or more), FIG. 1 shows a cable 10 made iron; advanced high-strength synthetic filaments. Some terminology used in the construction of cables will benefit the reader's understanding, though it is important to know that the terminology varies within the industry. For purposes of this patent application, the smallest individual component of the cable is known as a "filament." A filament is often created by an extrusion process ithough. others are used). 5 Many filaments are grouped together to create a strand 12. The filaments are braided and/or

typically braided and/or twisted together to form cable 10. In other examples the strands may be purely parallel and encased in individual surrounding jackets. In still other examples the strands may be arranged in a "cable lay ^" pattern that is well known in the fabrication of wire ropes.

Many different materials are used for the fi laments in a synthetic cable. These include DYNEBMA, SPECTRA, TECHNORA, TWA RO , EVbAR, VBCTRAR PBO. carbon ftber, nano-tubes, and glass fiber (among many others). In general the individual filaments have a thickness that is less titan that of human hair. The filaments .are very strong in tension, but they are not very rigid. They also tend to have low surface friction. These fects make such synthetic filaments difficult to handle during the process of adding a termination and difficult to organize. ^' The present invention is particularly applicable to terminations made of such high-strength synthetic filaments, for reasons which will be explained in the descriptive text to follow. While the invention could in theory be applied to older cable technologies - such as wire rope - it likely would offer little advantage and the additional time and expense of implementing the invention would not be worthwhile. Thus, the invention is not really applicable to wire rope and other similar cables made of very stiff elements.

The cable shown in FIG. I is a. well-known exemplary construction made by braiding or otherwise interrelating twelve strands together. Polyester ropes using this construction are known to have an external diameter up to about 6 inches (see specification 1L-R-.24750). Even larger polyester ropes are made by constricting parallel sub-ropes in a braided- strand jacket.

When a cable has non-parallel strands the .interrelationship between the strands becomes quite complex. The overall cable has a central axis. Each individual strand is on average .running parallel to the cable's central axis. However, at any given point along the cable's length, no individual strand is parallel to the cable ^' s central axis. When such a cable is loaded, the individual strands move and shift. The cable "clinches" together and strand-to-sfrand .friction becomes a significant component of the cable's performance. When a large amount of tension is

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It is important for (he overall strength of most cables - the ? 2-st?sn<? configuration of FIG. ! being a good exam le - that the overall load be shared equally among the constituent strands. For a 12. - strand construction, the ideal result is that each strand carries exactly 1/12 of the total load, Other cables may have a desired non-equal tension distribution, such as a cable having some relatively large strands and other relatively small strands. However, in all eases, it is preferable to have a t rget" distribution of tension among the constituent strands and to provide a system that meets this target distribution.

High-strength synthetic filaments have very little surface friction and strands made of these filaments also have very little surface friction. Thus, it is possible for one individual, strand to "slip" with respect to neighboring strands. A strand that slips tends to "unload" itself and shift the load it w s carrying to its neighbors. This is obviously an undesirable result.

In order to add an overall cable termination to an end of a mufti-stranded synthetic cable, each individual strand must be cot to length and have a strand termination added (It. is not essential that all strands in the cable undergo this process but -in most embodiments all strands will be involved). The cutting and terminating processes are inherently imperfect. The result will generally be that some terminated strands will wind up being longer than desired while others will wind up being shorter then desired. If a tensile load is placed on the cable with no accommodation tor these manufacturing tolerances,, the relatively "short ^" strands will be loaded first and they will carry moi« load than the relatively long strands.

One approach to reducing this problem is to make the application of a tensile load to each strand individually adjustable. In order to achieve this goal a tension-applying apparatus may be applied io each strand termination individually. Looking again at FIG, I . the reader will note iosv the strands on the free end of cable 10 have been unhraided so that they are individually accessible,

FIG. 2 shows a section view through, a strand termination 30 that has been added to the

4

85 -generally concern potted terminations, but as discussed previously the invention applies to ai; types of termination.

FIG, 2 shows a sectional view through the components used to create the termination. The reader will note that anchor 18 includes an expanding cavity 20 that expands as one proceeds from the portion of the anchor facing the length of cable (the "proximal" end, which is 90 the bottom end in the orientation of the view) toward the portion of the anchor facing in the opposite direction {the "distal" end, which is the top end in the orientation of the view). The expanding cavity in this example is a linear taper between two straight portions - all joined by fillets. Differing wall profiles may be used to create a wide variety of expanding cavities.

The end ^' portion of strand 12 is potted into the expanding cavity in order to lock anchor 95 1 to strand 12. The filaments of the strand are splayed apart and infused with liquid -potting compound (either before or after being placed within expanding cavity 22). The liquid potting compound may be added by a variety of methods, including: (!) "painting ^" or otherwise wetting the filaments with potting compound and then sliding the anchor into position over the painted filaments, (2) positioning the splayed filaments in the cavity and then pouring in pelting 100 compound, (3) pre- etting, the filaments in a separate mold designed to wet the filaments, and (4) injecting pressurized potting compound into the cavity. However the potting compound is introduced, the splayed filaments remain within cavity 20 while the potting compound hardens. Once it has hardened the result is a mechanical interlock between the figment-reinforced "plug" (contained in potted region 22) of solid material and the cavity. Tension applied to the cable will i OS thereby be transmitted to the strand.

The potting compound used is typically a high-strength resin. However, the term "potting compound"" as used in this description means any substance which transitions from a liquid to a solid over time.

Potting is only one approach .kno n in the art, Other common examples include "spike-

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itself - typically referred to as a "spliced eye." The present invention is applicable to any method of ^" creating a termination or, the end of a synthetic filament tensile member. Although S potted examples are shown in these descriptions the invention is not limited to that approach, and the -reader should understand the term "strand termination" to broadly encompass all methods of attaching a device to the end of a strand.

FIG. 2 shows additional components that are added to facilitate the gathering of multiple strands into a single, load-transferring element in the example shown, loading stud 24 has been0 connected to anchor I S via threaded engagement 28. Loading stud 24 includes male thread 26 over a significant length (The threads are shown, schematically but are not actually depicted for purposes of visual clarity). This threaded stud allows the completed assembly to be attached to other things to ultimately create an overall cable termination.

The use of a threaded stud is a "high-end" example. In other instances the anchor will5 simply be a cylinder with a load-hearing flange facing downward in the orientation of FIG. 2.

The connection between the cylinder and another object could then be placing the load-bearing flange against another surface.

FIG. 3 shows the cable after an identical (in this example) strand termination 30 has been added to the end of each strand 12, The reader will observe how a length of each strand is preferably unhraided from the cable structure so that a free length exists proximate the termination. This allows each strand to be manipulated so that it may be attached to another device. A separate device or devices is used to aggregate all the individual strands and strand terminations to a unified load-transferring assembly. This unified assembly will be referred to as an "overall cable termt nation" in order to distinguish it from the individual "strand- terminations"5 applied to each strand. The design of the strand terminations, the overall cable- termination, and the unifying devices employed to create the overall cable termination, can take on many and various forms. The present invention is applicable to all of these forms.

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manufacturing tolerances will generally cause some strands to shift or "slip" relative to others - thereby altering the proportional load sharing that was intended. The present invention bads the cable .in a controlled, and carefully designed manner resulting In a reduction in misalignments and a more evenly distributed load among the cable's constituent strands.

Throughout this disclosure, cables will be used as an example of a tensile strength member. However the invention should not be viewed as being limited to cables. The terra "tensile strength member" or "tensil member" encompasses cables and sub-components of cables such as strands. The invention also encompasses non-cable structures intended to carry loads in tension.

Likewise, the term "anchor ^" should be viewed broadly to encompass virtually anything thai can be attached to a strand or cable. The anchor would ordinarily include some features fec i I statin g attachment - such as a hook or threads,

SUMMARY OF INVENTION

The present invention comprises devices and methods for loading a cable in order to create a desired distribution of the load mon the cable's constituent strands. Strand terminations are applied to many - and possibly all of- the cable's strands. The ultimate goal is to connect the strand terminations to a collector i order to create an overall cable termination. The relationship between each strand termination and the colleetor is allowed to "float" using the inventive process while the cable is tensioned and an appropriate spatial relationship between each strand tensioner and the collector is determined. One the appropriate relationship is found, it is configured to be repeatafale (such as by locking the strand termination in place or by recording its position for later application to the same or similar collector).

In a preferred embodiment, a strand tensioner is provided for each individual strand termination. Tension is applied to the cable through the strand tensioners. Tension may be

BRIEF DESCR IPTION OF DRAWINGS

170 FIG, 1 is an elevati n view, showing the braided structure of an exemplary 12 -strand cable.

FIG, 2 is .a sectional sectional view, showin a termination created on the end of a single cable strand.

FIG. 3 is a perspective view, showing 12 terminations attached to 12 strands in an 175 exemplary cable.

FIG. 4 is a perspective view, Showing a collector used to assemble Ihe 12 terminations of

FIG. 3.

PIG. 5 is a sectional perspective view, showing an exemplary attachment between a termination and a collector.

180 FIG. 6 is a perspective view, showing all ! 2 terminations attached to the collector.

F IG, 7 is a perspective view, showing a particular type of strand tensioner.

FIG, 8 is a side elevation view, showing an assembly used to apply loads to ail the strands in a cable assembly in a controlled fashion.

FIG, 9 is a plot of strand displacement and applied tension over time.

185 FIG. 10 is a plot of strand displacement and applied tension over time.

FIG. 1 1 is. a plot of strand displacement and applied tension over time.

FIG. 12 is a plot of strand displacement over lime for multiple strands.

FIG. 12 is a side elevation view, showing an assembly used to apply loads to all the strands in a cable assembly in a controlled fashion.

190 FIG. 14 is a detailed perspective view, showing a rotation-limiting feature.

FIG, 1 S is a detailed perspective view, showing an alternate embodiment for a strand tensioner.

FIG, 16 is a detailed perspective view, showing an alternate embodiment for a strand

REFERENCE NUMERALS IN T HE DRA WINGS

10 cable

12 strand

IS anchor

20 cavity

22 potted region

24 loading stud

26 male thread

28 threaded engagement

30 termination

34 collector

36 loading flange

38 receiver

40 ut

^• 42 vasher

4 hemi hearing

46 •opening

48 coupler

SO strand tenssoner

52 cylinder

S4 mount

56 rod

58 fixture

66 space frame

68 collector brace

70 primary load fixture

72 hydraulic cylinder

74 attachment

76 boss

78 hole

SO lock wire

82 cross hole

84 castellated nut

86 notch

8 strand te sioner

90 telescoping clevis

92 flat

94 load cell

96 wiring

DESCRIPTION OF EMBODIMENTS

FIG. 4 shows an exemplary device used to gather all the strands into a unified whole and thereby create m overall cable termination. Collector 34 includes twelve receivers 3S, each of which is configured to connect to a single strand termination (In other embodiments a receiver may be configured to connect to m ltiple strand terminations), Coflector 3-4 typically includes some type of load-transferring feature designed to transfer a load from the collector to some external element. Loadin flange 36 is a simple example of a load-transfemng feature, The

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FI 3. 5 ^' shows an exemplary connection between a (semination on a strand arid the collector. Loading stud 24 is passed through opening 46 and through receiver 38 m collector 34. Receiver 38 includes a hemispherical concave portion sized to accept, hemi bearing 44, He-mi bearing 44 and receiver 38 form a ball-and-socket connection thai allows the termination to f late with respect to collector 34. This is a sophisticated, type of connection that won't be included in many embodiments. Many embodirnents will simply use a washer bearing against a flat surface on collector 34. Still other embodiments won ^' t use a threaded stud and will instead simply mate two surfaces together to make the connection.

'Nut 40 can be selectively tightened on loading stud 24 (the threads are not shown in the view) in order to urge washer 42 against hemi bearing 44 and hemi bearing 44 against receiver 38. To appl the inventive method, collector 34 is ordinarily placed in a loading fixture that holds it in position. The far end of the cable to which the strand belongs is likewise held in place (such as by winding it around a capstan or some other means, such as applying an overall cable termination to the far end). A substantial tensile load is then applied to the cable as a whole. Those skilled in the art will then appreciate that by tightening or loosening nut 4 a user can fine tune the tension on the particular strand to which loading stud 24 k attached (as well as its position with respect to collector 34). The ball-and-socket connection .in this embodiment allows the strand termination to align itself with the strand during this process,

FIG, 6 shows n assembly of collector 34 and all twelve strands. The reader will observe that twelve loading studs 24 are i position and a nut 40 is connected to each stud (The loading studs 24 shown in FIG. 6 are longer than depicted in FIG. 5 in order to give art additional x¾nge of adjustment. Also - the threads on the exterior surface of the loading studs are again omitted for purposes of visual clarity). This view illustrates the advantage of including a ball-and-socket connection in some of the embodiments. As each strand emerges from the cable's braided construction it assumes a particular angle with respect to the collector. Some diverge more than

Π

280 The ball-and-socket connection should properly be viewed as one example among many possible ^■ connection types, ^' The reader Is referred to commonly-owned U.S. Patent No. 8,371,01 $ for additional examples regarding the application of an attachment to a sub-component of a larger cable.

The term "collector" in this context should be viewed broadly as anything that is used to

285 collect a tensile load from two or more strand terminations. It may be a unified piece as shown but may also be an assembly of multiple pieces. Further, a "stand-in ^" collector may be used to pre-load the cable and adjust each of the strand terminations (as described subsequently) and the strand terminations may ultimately be connected to an entirely different collector.

It is not common for a user to take an assembly for a large cable such as shown in FIG. 6

290 and place it into service without pre-loading the assembly and testing it it is important to preload the assembl to settle the strands and other components into a stable configuration before the cable is placed into service, in this context it is desirable to know a particular cable's maximum working load in the service environment it is destined to enter. The pre-load process might appl a tension to the cable that is equal to 100% or even as much as 150% of the expected

295 maximum working load.

While most large cables are pre-loaded as a whole, the present invention seeks to preload the cable at the strand level and manipulate the strand termination to collector connections in order to create a desired apportionment of the overall load among the constituent strands. Without careful preloading a large cable assembly will very likely have an uneven distribution of

300 load to each individual strand. The inventive process significantly reduces this phenomenon.

One could use the configuration of FIG. 6 to progressively tighten all twelve nuts and thereby place an initial load on the cable. Such a process would be unlikely to produce an optimal result, however. The present invention -obtains advantages by individually applying tension to the strands so a large, multi-stranded cable.

1 2

be held statically, such as by winding it around a capstan or providing a second collector on the far end.

Collector 34 is held within fixture 58 during the tensioning process. Significantly,, however, it is not generally used to apply any tension to the cable strands during the pre-loading process. During the process, each individual strand iennin&tion is allowed to float with respect to collector 34. ^' Tension to the cable is actually applied directly through the strand -terminations themselves (as will he described subsequently). As tension is applied, the inventive components operate to apportion the overall load among the individual strands in a predetermined arrangement (usually this will be an equal load applied to each strand but there are exceptions). Once the desired pre-load is applied and the strand terminations are adjusted to achieve the desired load apportionment, then the relationship between each strand termination and the collector is established (such as by ^' locking the strand termination, to the collector in the desired position or by recording the desired position .so that it can later be reestablished).

In the embodiment of F G. 13, collector 34, fixture 58, space frames 66, fixture 64, and all the connected components move in unison. ^' This entire assembly may slide within a larger frame or otherwise be stabilized.

is this exemplary apparatus one or more hydraulic cylinders 72 connect primary load fixture 70 to -attachment 74 on the moving assembly. The right, side of the one or more hydraulic cylinders 72 (in the orientation of the view) is fixed to a substantial and stationary anchor point. When the one or more hydraulic cylinders 72 are activated, the moving assembly (along with collector 34) Is urged to the right in the view. This action applies tension to cable 10 (since the far end of the cable is held)..

The frame structures shown are preferably very stout so that a large tensile load may be applied. For some cables it may be desirable to provide a tensile load of I million pounds or more,

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the designed length. Returning to FIG. 3, the reader will recall that each individual strand must be cut to length and have a strand termination added to its free end. The manufacturing tolerances of both the cutting operation and the termination operator ean only go so tar. Some of the strands will wind up being shorter than designed and others will wind up being longer than designed. Of course, when the cable is initially placed under tension, the shorter strands will carry most of the ad and the longer strands may in fact carry very little. For this reason, it is desirable to be able to adjust the -position of each of the strand terminations with respect to the collector.

Looking now at FIG. 6, the reader will recall that the preferred connections between each strand termination and the collector include an adjustment feature. The adjustment feature in the embodiment of FIG, 6 is the nut 40 placed on each loading stud 24. These nuts can- be tightened manually to provide the desired adjustment. There are many other ways to adjust the spatial relationship between a strand termination and the collector. However the adjustment is. made, it is desirable to automate the process of apportioning the load- among the various -strands.

Returning now to FIG.. 13, the reader will observe that each loading stud on each individual strand is attached to a strand tensioner 50, All the strand tensioriers are attached to fixture 64. Thus, when the moving assembly is moved to the right under the force imparted by the one or more hydraulic cylinders 72, it is the strand terssionets (.50) (in this particular embodiment) that actually apply the tension to the cable. The loading stud on each strand passes through the collector but should not transfer any significant forces to the collector, instead, the loading stud is attached to i ts respective strand tensioner 50.

FIG. 7 shows an exemplary strand tensioner 50. This particular strand tensioner includes a hydraulic cylinder 52 with an extending retracting rod 56. Coupler 48 is provided on the free end of the rod. The coupler in this example includes a female threaded hole configured to engage an individual loading s ud 24. The coupler is threaded over the loading stud and a

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include any device able to transmit tension from a strand pensioner to a strand termination, and may include hooks, brackets, and m ny oilier types of devices.

The rotation limiting device prevents rotation between coupler- 48 and loading stud 24 once the coupler is firmly attached- to the loading stud. It is also preferable to limit rotation between rod 56 and cylinder 52. A key way may be used to rotationaliy lock the rod and cylinder together. Mount 54 is provided to attach strand iensioner 50 to an external frame. One or more pivots may be provided on mount 54 so that the angle of strand tensioner SO ma be made adjustable. Appropriate hydraulic connections are provided so that hydraulic pressure may be used to extend and retract rod 56 - if desired.

in a preferred embodiment, strand tens! oners 50 could be viewed as ''passive ^' " devices. In this embodiment, the hydraulic lines leading from each strand tensioner .50 are fed into a common, pressurized reservoir. The reservoir can be contained within pressure comroiler/sensor 60 (see F!G. 13). Returning to FIG. 7, the hydraulic cylinders within each strand tensioner 50 are double-acting cylinders ibr this example. The piston within each of these double-acting cylinders is preferably placed near the mid-poi nt of its range of travel (midway between the two illustrated fluid pons).

One could "plumb"' the cylinders in different wa s. Those skilled in the art will know thai double-acting hydraulic cylinders typically have two hydraulic ports - one on each extreme of the piston's range of travel. The port that is «s«d for the "retract ^** stroke .(causing the rod to retract into the cylinder) is generally located near the rod end of the hydraulic cylinder. All the hydraulic lines leading from the retract ports in this example are connected to a common, pressurised hydraulic reservoir.

Returning to FIG. 13, when the one or more hydraulic cylinders 72 are pressurized to begin moving the fixture 64 and the strand ensioners 50 to the right (in the orientation of FIG. 13), the tension on the cable tends to pull the rods out of the hydraulic cylinders in the strand

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pressurized hydraulic reservoir. As a result, the same pressure winds up being applied to each retract po t.

The result is thai the tension being applied to each individual strand -most be equalized and the motion of the rods within the strand tensioners 50 ensures that this is the ease without the need for any sophisticated active control. A simple operational example will make this point clear. One of the strands in the assembly will draw taut first and this fact will cause the rod in the strand tensioner attached to that particular strand to start moving out of its cylinder.. This will displace hydraulic fluid within that strand tensioner and cause that hydraulic fluid to be expelled out the retract port on the particular strand tensioner. The common reservoir is pressuri ed, so expelling fluid from one cylinder causes the same volume of fluid to be discharged into the other cylinders. As a result, the rods in the other strand tensioners SO actually retract a small distance until thei -attached strands draw taut.

Similar "equalization ^5* displacements take place among all twelve strand tensioners 50, Some rods will extend outward through a small displacement stroke, other rods, will retract through a small displacement stroke, and likely still others will not move much at all. This is why it is a good idea to start the process with the pistons in the hydraulic cylinders within the strand tensioners near the middle of their range of travel, rather than at an extreme. The result is that by moving fixture 64 through a small displacement, all strand tensioners 50 ind up with an equal amount of internal pressure m the hydraulic cylinders and all the connected strands wind up wi th the same amount of tension.

Returning now to FIG. 7, displacement sensor 64 may he provided to monitor the motion of the rod during the tensioning process. The tension actually being applied can he monitored by monitoring the hydraulic pressure applied to the cylinder.

Returning now to FIG. 13, some exemplary operations of the components will he described. This example is applying tension to a 12-strand cable. Thus, fixtur 64 must provide

16

strand tensioner to be adjusted as desired, though some embodiments may include fixed positions. The result in this exam le is a radial pattern of diverging strand tenslcmers. Several space frames 66 are positioned to keep fixtures 58 and 64 in position so that the substantia! tensile forces applied to the strands do not distort the assembly,

in some embodiments the strand tensioners may be remotely located, with the connection to the strand terminations being made with cables passing over pulleys. Other embodiments might use levers or other remote-mounting mechanisms. Thus, the construction shown is properly viewed as exemplary.

Pressure controller/sensor 60 provides hydraulic pressure to each of the twelve strand tensioners. In many instances the same pressure will be fed to all tenssoners, since this will ultimately produce a uniform tension among the strands. If a common pressure is desired, the prior example of simply plumbing all the retract ports on ail the cylinders within strand tensioners 50 to a -common, pressurized reservoir may be used. However,, in other instances it will, be desirable to vary the pressure applied to each tensioner. Thus, pressure controller 60 may he configured to independently apply pressure to each cylinder and to monitor and maintain a selected pressure for each cylinder. This may be desirable tor cable lay constructions, where a higher tension may he applied to the inner strands than the outer strands.

Proces controller 62 preferably receives information regarding the translation of each cable strand (via. an input such as displacement sensor 64} and the tension applied to each strand. Strand tension may be derived from the pressure applied to each strand tensi ^' oner or via some other source - such as a load cell or strain gage placed on the strand termination or on the strand tensioner,

in a representative pre-load operation, pressure would be applied to one or more hydraulic cylinders 72 to pull the slack oat of the cable and apply Increasing tension. Hydraulic pressure will then be created -within the strand tensioners 50 as the load is transferred from

7

loading studs 24 to be pulled further through collector 34 than others (since the longer strands will still have more slack needing to be pulled out, in this example).

Once a uniform tension in all strands has been achieved and the desired total tension has been achieved, t e relative position be ween each strand termination and the collector should be locked in place so that the strands don't shift significantly when the pre-load is removed. Any suitable locking mechanism can be used. For the example of FIG, 6, one would simply appl a uniform amount of torqu to each of the nuts 40 while the strand tensioners 50 maintain tension on the strands.

More generally, the invention seeks to preserve the proper spatial relationship between each strand termination and the collector, so that the proper relatio ship can be recreated when the cable is put into use. One way to preserve this relationship is mechanically locking the strand terminations in the position determined to be correct during the preloading process. There are certainly other ways, however. One could, for example, accurately measure and record the spatial relationship between each strand termination and the collector without mechanically locking the strand terminations in position. Later, the correct spatial relationship would be recreated by adjusting each strand termination until it repeated the previously taken measurements. This could he done with the same collector used in the pre-load process. It could also be done with another substitute collector. For example, the collector used in ^' the pre-load process, might be a modular assembly intended only for the taking of accurate measurements and not for Held use. It might .be equipped with expensive position sensors that one would not wish to install in the field.

As stated previously, cables using synthetic filaments tend to have relatively little surface friction. Thus, if one does not load a stranded termination carefully it is possible for one strand to slip relative to the others in a direction that is roughly parallel to the cable's central axis (a "longitudinal slip"). Once such a slip occurs it is difficult to detect and in many instances

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sli near one of the cable's terminated ends can be a significant problem. The slip produces & localized disturbance in the cable's structure. This will nearly always cause a weakness at the point of the slip and an overall reduction in the cable's breaking- strength. Even If one balances the strand tensions at the ends- of the cable after such a slip, the internal disturbance in the cable's structure will compromise performance. Perhaps mere sjgnifi.c-ant.ly. the compromise in performance may not be detectable without actually testing the cable to the breaking point.

So long as the strands are initially loaded in a controlled manner, holding the tension on the indi idual stran s reasonably even, the region where the strands transition from the free cable structure to the collector should stay reasonably balanced. The goal is primarily the prevention of a slip. The approach is to carefully control and regulate the tension applied to each individual strand so that: no significant imbalance occurs. In the absence of an imbalance a slip is unlikely.

In an open-loop embodiment of the inventive process, one can apply a stepped increase in tension. For example, one may apply a tensile load of 1 % of the anticipated ultimate break strength, check for the tension of the strands, then move up to a 5% load, recheck, then move up to a 10% load, and so on. Automated strand adjustment can allow for continuous tension to be maintained on the cable.

Consistency and repeatability are very important in the cable industry -· particularly where the cables carry large loads. The present -invention seeks to pre-load the cable and adjust each strand termination to the appropriate spatial relationship with the collector without producing a longitudinal slip, in a closed-loop embodiment strand tension and/or position can be monitored and fed to a process controller that automatically adjusts the tension applied to each strand. The loading process is preferably modified in real time in the event that unwanted slippage is detected.

The reader should understand that some minimal sl ippage is inherent In the preloading process, it can likely never he eliminated altogether. But, it is possible by usin the present

1

It is, generally important to control the rotation of the strand during loading. Since the strand itself almost always has some type of twisted construction (such as braided or wound _. ) rotation, is highly related to tension. Thus, it is preferable to apply tension to a strand without5 allowing it to rotate. Further, once the tensioning process is complete, it is preferable to limit rotation between the strand and t e collector, Otherwise the strand may "unwind" itself.

In an exemplary implementation of the closed-loop embodiment, a strand tensioner SO (as described previously) is provided for each strand in a cable. FIG. 13 illustrates one possible fixturing arrangement. The reader w ll recall that collector 34 is simply held in plsce during the 0 tensioning process. The strands pass through the collector but should not transfer any significant forces to the collector as the strand ienstoners go to work. Process controller 62 preferably receives information regarding the translation of each cable strand (via an input such as displacement sensor 64} and the tension applied to each strand. Strand tension ma be derived from the pressure applied to each hydraulic cylinder or via some other source - such as a load S cell or strain gage placed on the strand termination or on the strand teasioner.

in the closed-loop embodiments, process controller 62 ideally includes a processor running a control program. This allows a prescribed "ramp up" of strand tension. However, the process need riot be a fixed one but is more preferably an adaptive process that changes according to the sensor values. FIGs. 9 - 12 illustrate several examples of operation for the0 device of FIG. 8. The reader should bear in mind, however, thai the operational configurations are virtually limitless and so the examples provided should .not be _: viewed as limiting,

PIG. 9 shows an example where tension is steadily raised on all strands at the same time (though only a single strand is plotted). The upper plot shows the linear displacement of the termination affixed to "Strand 1." The lower plot shows the tension applied to the same "Strand5 I . ^"

The first part of the curve is non-linear and represents the initial removal of slack. Once

20

tension applied actually falls (Point A' on the lower plot). The decrease in tension results from the fact that the simod-to-strand friction has transitioned from a static mode to a dynamic mode.

The substantial slip continues until Point B. when Strand ! stops slipping with respect to its neighbors and resumes elastic elo gation. At this point the tension in Strand laJso returns to a linear relationship (Point B" in the lower plot). FIG. 9 represents an "open loop" scenario where tension is ramped up at a fixed rate and no slip detection is included.

However, it may be possible to detect and prevent significant longitudinal slips using the Information available in FIG, 9. The slope of the displacement curve (dy/dx) should remain fairly constant in the absence of a significant slip. By monitoring the rate of change of mis slope (d ² y/dx ² ) the control system can detect a sudden slope increase - which strongly suggests the onset of a slip,

FIG, 10 illustrates this scenario. At Point A in the upper plot process controller 62 detects the onset, of a potentially damaging slip. The controller immediately reduces the applied tension on Strand 1 (see lower plot) so that a smooth displacement is .maintained. Tension continues to be ramped up on the other strands within the cable. The increase in tension on the other strands will tend to ^w re-clench" the previously slipping Strand I (recall the complex braided structure shown in PIG, I ).

Once the controller determines that the slip is under control (such as by monitoring the rate of change of the displacement plot slope, among other methods) tension on Strand 1 is ramped back up (shown as Points B and .8 ^'* ). A normal increase is then continued unless another slip is detected.

In some instances a slip may occur so quickl that the tensioning apparatus cannot respond rapidly enough, in those cases the best approach will be to regulate the tension applied to each strand in such a fashion as to prevent the sli to begin with. If the displacement sensors then detect a slip, this information may still be useful because it informs the operator that the

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Of course, there are many tension.- increasing profiles that are non-linear, in some cable constructions it is advantageous to pulse the application of tension. FIG, 11 shows a plot depicting this type of "ramp up." Agai , the plot shows only one strand in a 12-strand cable, but the plots for the other eleven strands would be similar (in the absence of a slip). Slack is removed and tension is ramped up until Point A. Tension is then stepped, down to a low level and a low-tension interval (from Point A to Point B) is maintained so that the cable structure can stabilize.

At Point B tension is again applied and increased. Another "rest" interval commences at Point C and continues to Point D. This process continues until a desired amount of pre-load has been applied to the cable.

FIG. 12 shows a combined plot f displacement versus time for all twelve s trands in a 1 - strand braided cable. The process controller typically measures and compares the values for all the cable strands as the tensioning process proceeds. Another effective slip detection method is to "scan" for one strand passing too far outside the average for all the strands. In the plot of FIG. 12 one strand (Strand 3) has experienced a substantial longitudinal slip and its displacement has suddenly progressed rapidly beyond that of the other strands. When this condition is detected the controller can reduce the tension on Strand 3 and allow the cable to stabilize as the tension on the other strands is inc reased.

FIG, 8 shows a simplified alternate tensioning fixture. In this embodiment fixture 58 and fixture. 64 are stationary. Tension is applied, to the far end of the cable using another fixture, or some other means such, as by rotating & capstan around which the cable is wound. As described for the embodiment of FIG. 13, the tension on the individual strands is regulated and adjusted using the individual strand tensloners 50. t may be regulated, via connecting them to a common, pressurized .reservoir, or via an active control approach.

Of course, other automated iensk ers could be substituted for the hydraulic cylinder

2,2

585 It k preferable .to secure loading stud .24 so that it does not turn with the nut. A pair of opposing flats 92 are provided on loading stud 24. Telescoping clevis 90 is part of strand tensions- 88. This component includes a clevis notch sized to engage the two flats on the loading stud. FIG. 16 shows telescoping clevis 90 in an activated state, it engages the two .fiats 92 and prevents the rotatio of loading stud 24, In this configuration, the gear drive within

590 strand tens.bn.er 88 rotates nut 44 and thereby increases or decreases the tension on the strand to which loading stud 24 is attached. The control of strand tenskmer 88 ma be manual. On the other hand, strand tension 88 may be substituted tor strand tensioner 50 in the embodiment of FIG . 13. In that ease, strand tensioner 88 could be controlled by process controller 62.

FIG. 17 illustrates a substitute sensing method that could be used tor virtually any

595 embodiment, in this version, the conventional washer between nut 40 and collector 34 has been replaced by toad cell 94. This ad cell is provided with -wiring 96 to connect it to a remote sensor monitor or possibly the process controller itself. Using this load cell the tension or! each strand may be monitored, The wired connection could be replaced by a wireless one having an internal battery with enough energy to last through the preloading process, ft could even be

600 made rechargeable in order to be useful for load monitoring in the field.

Those skilled in the art will appreciate that many other devices and methods could be used in place of the embodiments described. For example:

I . The displacement sensor on the hydraulic cylinders could be replaced by an optical system thai uses light to measure the displacement of each loading stud;

605 2. The pressure sensors in the hydraulic system could be replaced with direct load sensors— such as load cells or strai gages;

3. The threaded connection between the strand tensioner and the loading stud could he replaced with a different type of connection; and

4, Pulsed hydraulic force could be applied to the tensioning process rather than a

23

is not useful while locked into the fixture of FfO. 8. One way to transition to the completed product is to hold the litis! tension within the fixture of FIG. 13 and advance .nuts 40 to a5 tightened position with a specified amount of torque. Once a suitable balance is achieved, the geometric relationship between the strand terminations and the collector is preferably secured so that the "'rel xation" of the cable, won't allow disorganization to resume. There are many, many ways to secure this geometric relationship, PIC. 14 depicts another way this could be done. Castellated nut 84 is used in the place of a conventional nut. The castellated nut is tightened0 against, collector 34 to secure loading stud 24 in place. Two proximate bosses 76 with associated holes 78 are provided on collector 34, Once the castellated nut is in position, lock wire SO is passed around one boss, through a suitable cross hole 82 in loading stud 24 (and through two of the notches 86 on the castellated nut) and around the other boss. Using such a device the rotation of the loading stud is limited and the rotation of the castellated nut is limited.

5 The strand tensioners are then released and the cable can be removed from the fixture and prepared for use. The nuts may be secured in position using other device such a a cottar key, tack welding, or any other suitable method. If desired, the protruding length of loading stud 24 can be removed at that lime.

The tightening of the nuts may be done by automated machinery, since it is .generally0 undesirable for a human operator to come near the collector assembly while the strand tensioners are maintaining tension. The amount of force applied is such thai a component failure could produce a -dangerous condition.

Returning to FIG, 7, those skilled in the art will realize that other components could be used in the place of the threaded engagement between nut 40 and loading stud 24, Once the final S tension is applied, a shim of suitable thickness could be placed between a portion of the ioading stud and the collector. It is also, desirable in some circumstances to clamp the collector from the underside (in the perspective of FIG. 5). A separate, shim or fastener can be used for this nurmvse. CfAftsftm» from hath .'«i¾>.« msn m«?i> th< ^» s«A*»r«> s>f *£ ^■ .» ^■■■ t r»»n«t<< n >A.->s i«»>ci *K*

24

The invention thus described is applicable to my large synthetic cable, it s perhaps most useful for construction where the constituent strands interact in a significant way. T his includes cables having a braided construction, or cable lay construction, it also includes cables made using simple helical twists, as well as other constructions. Such cables are said to have an Interwoven structure. However, the load-balancing aspects of the invention are potentially useful tor all synthetic cables, including those with a purely parallel construction built with parallel strands encased in a wound external jacket.

The invention is also applicable to virtually any defined tensioning plan. The example of FIGs. 10 and J I are only two amon the virtually endless possibilities, Many of the inventive embodiments monitor the amount of tension being applied in the cable through indirect means. An example of this is using the pressure applied to the hydraulic cylinder in the example of FIG. 8. One may easily calculate the applied tension by knowing the pressure. On the other hand, one may simply use pressure as a good proxy for applied tension and base the eontroUing algorithms directly o pressure. Process controller 62 preferably ^' includes a processor running software that can accommodate these and other variations.

Once the desired strand loading plan has been achieved in the fixture, the appropriate spatial relationship between each of the strand terminations and the collector has been established. The term "spatial relationship" will be understood to meari the relative position of strand termination with respect to the collector, in some instances this may be a single linear dimension. Looking at the example of FIG. 6, if one omits a ball-and-socket connection and simply passes the loading studs 24 through holes in the collector 34, then adjusting the nuts 40 will adjust one. linear dimension, in other examples, however, there may be more than one degree of freedom involved.

Many other variations are possible, including:

1 . The "strand tensioner" could assume many forms other than those examples

25

3. The collector could be an assembly of muhiple pieces that are not joined until the cable is put into use; and

tension monitoring for each strand could be via a wireless transmission torn a load cell mounted in each receiver.

Although the preceding description contains significant detail, it should not he construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Those skilled in the art will be able to devise many other embodiments that carry out. the present invention. Thus, the language used in the claims shall define the invention rather than the specific embodiments provided.