Abstract:
A bottom anchor assembly ( 10 ) for a substantially vertically-oriented elongate safety line ( 70 ) comprises safety line gripping means ( 20 ), safety line tensioning means ( 80 ) and a bracket ( 50 ). The gripping means ( 20 ) includes a manually adjustable clamp ( 20 ) and the tensioning means ( 80 ) includes a hollow shaft ( 40 ) through which the safety line ( 70 ) passes. The hollow shaft ( 40 ) is externally screw-threaded and carries the load-setting means ( 80 ) on its screw-threaded portion ( 41 ). The load-setting means ( 80 ) is adapted to bear against the underside of the bracket ( 50 ) for adjusting the safety line tension to a predetermined value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of application Ser. No. 09/890,771 submitted on Mar. 5, 2002 by Peter Robert Flux with the title SAFETY LINE ANCHOR under 35 U.S.C. 371 from Patent Cooperation Treaty Application PCT/GB00/00371 which was filed on Feb. 8, 2000. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to height safety equipment and, in particular, to an anchoring arrangement suitable for anchoring the lower end of a temporary installation of a flexible elongate safety line disposed in a substantially vertical orientation on a tall structure.  
         [0004]     2. Background Art  
         [0005]     Tall structures such as electricity pylons and radio or satellite communication masts are periodically inspected to determine whether any maintenance work is required. These structures are purposely built to be low maintenance and, because many of them stand in remote locations, they may require inspection only once every ten years, perhaps longer.  
         [0006]     Also, in the interests of public safety, such structures are constructed to discourage easy ascent by non-authorised personnel. Hence, the lower leg portions of metal towers of this type are usually plain metal to a height of at least three meters from ground level, with no foot- or hand-holds. In fact, if such structures were built with access-ways or the like, the access-ways themselves would require periodic inspection for compliance with safety regulations. The interval between routine safety inspections is shorter than the required interval between routine maintenance inspections, so it would significantly increase the frequency of inspection for any kind of permanent access-way to form part of the tall structure.  
         [0007]     Traditionally, personnel who have carried out maintenance inspections on metal towers, pylons, or the like have used rope-access techniques for ascent and making themselves fast at the top. In an effort to minimise some of the hazards associated with such work, the present applicants have devised a fall arrest system that can be installed temporarily on a tall structure for the duration of a routine maintenance inspection, then removed and installed on another tall structure and so on. The advantage of a temporary installation is that it does not require safety inspection in situ. Rather, the system can be removed to a convenient inspection site and inspected whenever necessary.  
         [0008]     The above-mentioned temporary fall arrest system uses known components for the most part, but includes a new bottom anchor assembly for securing a substantially vertically-oriented safety line to the lower portion of a tall structure. The anchor assembly is a quick-release device that is significant in being manually operable to working tension. The new bottom anchor also allows a safety line of indeterminate length to be installed, with the excess line being held on a spool beyond the bottom anchor. The bottom anchor is designed to grip the safety line in a non-destructive fashion so that it can be reused repeatedly for a series of inspections on many tall structures. It can also accommodate differences in height between successive tall structures by allowing a different length of safety line to be passed through it before the gripping action is made.  
         [0009]     In achieving the aforementioned objects, it should be borne in mind that the critical tension in a substantially vertically-disposed safety line is in its upper portion. The lower portion needs to be secured against the effects of buffeting by wind, but the safety line is inherently under tension below the top anchor by virtue of its own weight.  
       SUMMARY OF THE INVENTION  
       [0010]     The invention is a fall arrest bottom anchor assembly for use with a substantially vertically-oriented elongate safety line. The bottom anchor assembly includes a safety line gripper, a safety line tensioner, and a bracket that is adapted to be fixedly mounted. The gripper includes a manually adjustable clamp that can be clamped to the safety line at an adjustable position along its length. The tensioner includes a hollow shaft connected to the gripper. The hollow shaft is adapted to receive the safety line with the safety line extending therethrough and extending both upwardly and downwardly therefrom, and the hollow shaft extends vertically through the fixed bracket downwardly and upwardly from the fixed bracket. The hollow shaft has an externally screw-threaded portion. A load setter of the anchor assembly is threadingly adjustable on the screw-threaded portion of the hollow shaft below the fixed bracket to bear against the underside of said fixed bracket for adjusting the safety line tension to a predetermined value.  
         [0011]     The manually adjustable clamp as disclosed is secured to the safety line below the fixed bracket below the hollow shaft.  
         [0012]     Preferably, the manually adjustable clamp includes of a pair of clamp blocks adapted to be placed in face-to-face opposing relationship around the safety line immediately beneath the hollow shaft. Most preferably, the clamp blocks are provided with mutually-aligned grooves or recesses substantially conforming to the profile of the safety line. The clamp blocks may be loosely clamped to each other using screw-threaded fastening means for initial assembly and may include a further screw-threaded fastener for applying the final clamping torque. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The invention will now be described by way of example only with reference to the drawings, in which:  
         [0014]      FIG. 1  is a perspective view of an embodiment of the present invention in fully-assembled form.  
         [0015]      FIG. 2  is a perspective view of a first manually-adjustable clamping arrangement in accordance with the present invention.  
         [0016]      FIG. 3  is an exploded perspective view of the arrangement depicted in  FIG. 2 .  
         [0017]      FIG. 4  is an exploded perspective view of a tensioning device suitable for use in the present invention.  
         [0018]      FIG. 5  is a close-up perspective view of a tensioning device in the Process of being installed on a bracket in accordance with a preferred embodiment of the invention.  
         [0019]      FIG. 6  is a perspective view of a second manually-adjustable clamping arrangement in accordance with the present invention.  
         [0020]      FIG. 7  is an exploded perspective view of the arrangement of  FIG. 6 .  
         [0021]      FIG. 8  is a perspective view of a third manually-adjustable clamping arrangement in accordance with the present invention.  
         [0022]      FIG. 9  is an exploded perspective view of the arrangement depicted in  FIG. 8 .  
         [0023]      FIG. 10  is a further perspective view of the arrangement depicted in  FIG. 8 .  
         [0024]      FIG. 11  is a further exploded perspective view of the arrangement depicted in  FIG. 8 .  
         [0025]      FIG. 12  is a perspective view of a fourth manually-adjustable clamping arrangement in accordance with the present invention.  
         [0026]      FIG. 13  is a partial exploded perspective view of the arrangement depicted in  FIG. 12 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring firstly to  FIG. 1 , there is shown a perspective view of a bottom anchor assembly  10  attached to a safety line  70  in the form of a multi-stranded metal cable. Typically, the cable diameter for a vertical fall arrest system is 8 mm.  
         [0028]     The bottom anchor assembly consists of a bottom-mounted clamp  20 , an externally screw-threaded hollow shaft  40  projecting upwardly from an upper surface of the clamp  20 , a bracket  50  for attaching the anchor assembly to the lower portion of a tall structure such as an electricity pylon (not shown) and a load-setting device  80  a portion of which is adapted to bear against the underside of the jaws of the bracket  50 . The hollow shaft  40  may include a circlip  49  at its upper end for ensuring that the load-setting device, once installed on the hollow shaft  40 , does not become inadvertently lost.  
         [0029]     Referring now to  FIGS. 2 and 3 , the clamp  20  comprises a pair of clamp blocks  21 ,  31  adapted to be butted together in face-to-face opposing relationship around the safety line  70 . The safety line  70  is omitted from these views for clarity. The clamp blocks  21 ,  31  each have a semi-circular groove  22 ,  32  formed in their respective opposing faces. The grooves  22 ,  32  may be provided with surface formation such as serrations, or a surface finish such as a metal spray for roughening, to enhance the gripping action on the safety line  70 . As shown, one of the clamp blocks  21  is provided with a pair of countersunk bores  23 ,  24  whilst the other clamp block  31  is provided with a pair of threaded bores  33 ,  34  adapted to be in alignment with the countersunk bores  23 ,  24  when the clamp blocks are in opposing relationship. The bores  23 ,  24 ,  33 ,  34  receive respective threaded bolts  25 ,  35  which are used to assemble the clamping unit loosely for initial installation. The clamp block  21  further includes a plain through-hole  26 , whilst the clamp block  31  further includes a third threaded hole  36  adapted to be in alignment with the through-hole  26  when the clamp blocks are in opposing relationship. The holes  26 ,  36  receive a wing nut  27  which is manually tightened to achieve the desired clamping force on the safety line  70 .  
         [0030]     The exploded view of  FIG. 3  does not allow this feature to be shown, but wing nut  27  is preferably captive in one of the clamp blocks, most preferably in the clamp block  31  having the threaded hole  36 .  
         [0031]     Still with reference to  FIGS. 2 and 3 , the clamp blocks  21 ,  31  each have a semi-circular recess  28 ,  38  in their uppermost surfaces, said recesses forming shoulder means  29 ,  39  at the junction of the recesses  28 ,  38  with the grooves  22 ,  32 . The shoulder means  29 ,  39  form a plat form upon which the hollow shaft  40  is positioned during installation of the anchor assembly.  
         [0032]     The hollow shaft  40  is preferably held captive in the recesses  28 ,  38  when the clamp blocks  21 ,  31  are in opposing relationship by virtue of an undercut formation  28   a,    38   a  provided at the base of recesses  28 ,  38 . The undercut formation  28   a,    38   a  is dimensioned to receive a flange  48  at the base of hollow shaft  40 . Preferably, the hollow shaft  40  is still capable of rotation relative to the clamp blocks  21 ,  31 . This enables torsional stresses in the safety line  70  to be relieved whilst maintaining the desired tension.  
         [0033]     Once fully installed, the anchor device behaves like a unitary assembly owing to the capture of the hollow shaft  40  in the clamping means  20 . This also means that the device can be installed the other way up from the orientation shown in the drawings, since the hollow shaft  40  is held captive relative to the safety line  70  by virtue of its engagement in the clamping means  20 .  
         [0034]     The hollow shaft  40  has an external screw thread  41 , the purpose of which is explained in detail below, and a through-bore  42  dimensioned to receive the safety line  70  as a loose sliding fit. The safety line  70  must not be an interference fit in the through-bore  42 , otherwise it becomes difficult to control the tension in the system with precision. Neither is it desirable for the through-bore  42  to be very much wider than the diameter of the safety line  70  since this results in the device being more bulky than necessary and may also increase the likelihood of the safety line chafing at the ends of the hollow shaft  40 .  
         [0035]     Turning now to  FIG. 4 , there is shown an embodiment of a load-setting means  80  in exploded perspective view. The load-setting means  80  comprises, in order from the bottom upwards, a first wing nut  81  having a screw threaded through-hole  81   a  of complementary thread pattern to the external screw thread  41  of the hollow shaft  40 , an annular rubber block  82 , and a second wing nut  83 , also having a screw threaded through-hole  83   a  of complementary thread pattern to the external screw thread  41  of the hollow shaft  40 . In use, the first wing nut  81  acts as a locking nut to secure the second wing nut  83  in position on the hollow shaft  40  when the load-setting means  80  has been adjusted to the desired tension. The rubber block  82  between the first and second wing nuts  81 ,  83  ensures that the assembly does not become locked up.  
         [0036]     Next in order above the second wing nut  83  is a flanged collar  84  having an annular circlip-retaining groove  84   a  at its upper end. Above the collar  84  is a wave spring  85 , then a thrust washer  86  and a spacer  87 . In alternative embodiments, the wave spring may be substituted by a crest spring, a disc spring, or even a compression spring. Also, the thrust washer  86  and the spacer  87  may be an integrally-formed single component. Above the spacer  87  is a tenser disc  88 , typically in the form of a M24, Form D washer. The spacer  87  has a longitudinal dimension such that the jaws of bracket  50  are receivable between the upper surface of thrust washer  86  and the underside of tenser disc  88 . The load-setting means  80  is completed by a retaining circlip  89  at the upper end as viewed in the Figure.  
         [0037]     The components denoted by the reference numerals  85  to  89  form a unitary assembly on the shank of the flanged collar  84 , the circlip  89  being received in the circlip-retaining groove  84   a  of the flanged collar  84 . The flanged collar  84  has a plain bore that enables it to slide freely over the external screw thread  41  of the hollow shaft  40 . The arrangement of the assembled load-setting means  80  is such that the wave spring  85  exerts a compressive force urging the tenser disc  88  into frictional engagement with the upper rim of the spacer  87  and the underside of circlip  89 . This prevents rotation of the tenser disc  88  relative to its immediate neighbours, until the desired tension has been imparted to the system in the manner to be described in more detail below.  
         [0038]     Referring now to  FIG. 5 , this view shows a load-setting means  80  being slotted into the jaws  51 ,  52  of bracket  50 . Here, the load-setting means  80  is shown in an inverted orientation relative to the exploded view of  FIG. 4 . However, inversion of orientation does not affect the working principle of the load-setting means  80 . As previously described, the ends of the bracket jaws  51 ,  52  have down-turned portions in the form of lugs  53 ,  54  (see also  FIG. 1 ) which serve to prevent the accidental removal of the load-setting means from between the jaws  51 ,  52  by inhibiting lateral movement of the load-setting means  80  once the system is adjusted to its predetermined tension. For the sake of clarity, the hollow shaft  40  and the safety line  70  have been omitted from  FIG. 5 , but it will be understood from the explanation below that these features are present when the load-setting means  80  is installed in the bracket  50 .  
         [0039]     Referring once again to  FIG. 1 , bracket  50  is releasably secured to the lower portion of a leg (not shown) of a tall structure such as a metal tower, a pylon, or the like in a known manner. Hollow shaft  40  carrying the load-setting means  80  is fed onto the safety line  70  from the direction of its free end indicated by the reference numeral  71  and positioned roughly adjacent the jaws  51 ,  52  of the bracket  50 . The manually adjustable clamp  20  is then installed on the safety line  70  just beneath the hollow shaft  40  and is fastened to the safety line  70  by manually tightening the wing nut  27 . At this moment during installation of the bottom anchor assembly  10 , the safety line  70  is still free and sufficiently flexible that the load-setting device  80  can be tilted for insertion past the lugs  53 ,  54  of the bracket  50  and thence into the jaws  51 ,  52  thereof. The jaws  51 ,  52  of the bracket  50  are positioned between the thrust washer  86  and the tenser disc  88 . The wing nut  83  is then rotated (by hand) to urge the flanged collar  84  upwards, forcing thrust washer  86  hard against the underside of the jaws  51 ,  52  of the bracket  50 . The flanged collar  84  is moved upwardly relative to the thrust washer  86  by compressing the wave spring  85  until a point is reached when the tenser disc  88  is no longer held captive between the spacer  87  and the circlip  89 , but is rotatable relative thereto. The point at which rotation of the tenser disc  88  is just possible indicates attainment of the desired tension in the system.  
         [0040]     The first wing nut  81  can then be rotated (again by hand) against the resilience of rubber block  82  to lock second wing nut  83  and thereby ensure against relaxation of the tension in the safety line  70 .  
         [0041]     To release the safety line  70  from the bottom anchor assembly  10 , the above procedure is reversed.  
         [0042]     Because the bottom anchor assembly  10  uses a hollow shaft  40  and a non-terminal clamping block  20 , the safety line  70  is permitted to extend beyond the bottom anchor assembly  10 . There is no need to cut the safety line  70  to suit the height of the particular tall structure to which it is being fastened. Rather, the excess (that portion which extends in the direction of arrow  71 ) safety line can be coiled on a spool or drum onto which it can be rewound when the inspection is complete and the safety line installation is dismantled.  
         [0043]     Referring to  FIGS. 6 and 7 , a second alternative clamp  90  which can be used to replace the clamp  20  described above is shown. The clamp  90  operates with an externally screw threaded hollow shaft  91  which functions similar to the hollow shaft  40  described previously to allow the load on the safety line  70  to be set.  
         [0044]     The clamp  90  comprises a partially conical collet grip  92 , a winged nut  93  and circlip  94 . The threaded main body section  93   a  and wing section  93   b  of the winged nut  93  can conveniently be manufactured separately and accordingly are shown exploded apart in  FIG. 7 . However, the main body section  93   a  and wing section  93   b  will be permanently joined, for instance by welding, to form the winged nut  93  and are not intended to be separable in use.  
         [0045]     The collet grip  92  is retained within the end of the hollow shaft  91  by the winged nut  93 , the winged nut  93  having an internal thread arranged to engage the external thread on the hollow shaft  91 .  
         [0046]     The winged nut  93  has a circlip groove  93   c  and a groove  91  a is formed as a gap in the external threads on the hollow shaft  91 . The circlip  94  is held in the circlip groove  93   c  and the circlip groove  91  a to retain the collet grip  92  and winged nut  93  on the hollow shaft  91  and prevent their accidental loss. The width of the circlip groove  91  a must be sufficient to allow the circlip  94  to float within the circlip groove  91  a to allow the full range of movement of the winged nut  93 .  
         [0047]     In operation, the safety line  70 , which is omitted from the figures for clarity, passes through the hollow shaft  91  as before and through the collet grip  92  and winged nut  93 . Manual tightening of the winged nut  93  drives the collet grip  92  into the end of the hollow shaft  91 , urging the collet grip  92  to close and so grip the safety line  70 .  
         [0048]     Preferably, the collet grip  92  is capable of rotation relative to the hollow shaft  91  and winged nut  93  in order to allow torsional stresses in the safety line  70  to be relieved whilst maintaining the desired tension.  
         [0049]     The hollow shaft  91 , like the hollow shaft  40 , may include a circlip  49  at its upper end to ensure that the load setting device, once installed on the hollow shaft  91 , does not become inadvertently lost.  
         [0050]     At the opposite end of the hollow shaft  91  to the clamp  90  a short section at the end of the hollow shaft  91  has no external threads and at least one pair of opposed flat faces  91   b.  The flat faces  91   b  allow the hollow shaft  91  to be gripped by a spanner or similar tool to hold the hollow shaft  91  against rotation so that the winged nut  93  can be tightened or loosened.  
         [0051]     Once fully installed, the anchor device behaves like a unitary assembly owing to the capture of the hollow shaft  91  in the clamping means  90 . This means that, in principle, the device can be installed the other way up from the orientations shown in the drawings. However, it will normally be preferred to only install the device in the orientation shown where the tension applied to the safety line  70  tends to pull the collet grip  92  into tighter engagement with the hollow shaft  91 . The advantage of this orientation is that if a fall arrest event occurs the additional load on the safety line will tend to pull the collet grip  92  into tighter engagement with the hollow shaft  91 . If the orientation were reversed the excess load caused by a full arrest event would have to be carried by the winged nut  93 .  
         [0052]     A third alternative clamping arrangement is shown in FIGS.  8  to  11 .  
         [0053]     In this arrangement an alternative clamp  100  is used, attached to one end of a hollow shaftlol similar to the hollow shaft  40 .  
         [0054]     The clamp  100  comprises a collet grip  104  located within a clamp body  102 . The clamp body  102  has an internal thread (not shown) which engages the external thread on the hollow shaft  101 . Further, the clamp body  102  has a pair of internally threaded radial bores  102   a.  Bolts  103  screw into the bores  102   a  and into corresponding recesses  101  a on the outer surface of the hollow shaft  101  to retain the clamp body  102  on the end of the hollow shaft  101 .  
         [0055]     The collet grip  104  is retained within the clamp body  102  with the narrow end of the collet grip  104  passing through an aperture  102   b  in the clamp body  102 . The collet grip  104  is urged though the aperture  102   b  and held in contact with the clamp body  102  by a spring  105  which is held in compression between the end of the hollow shaft  101  and a washer  106  in contact with the wider end of the collet grip  104 .  
         [0056]     A hollow cover  107  is arranged to have a sliding fit over the outer surface of the clamp body  102  and has two slot shaped apertures  107   a  in its side surface. The bolts  103  and cover  107  are arranged so that the head ends of the bolts  103  which are exposed above the surface of the clamp body  102  pass into the apertures  107   a  to retain the cover  107  over the gripping body  102  while allowing the cover  107  to move axially relative to the clamp body  102  and the hollow shaft  101 .  
         [0057]     The cover  107  has an end aperture  107   b  through which the safety line  70  can pass and is arranged so that the collet grip  104  bears against an inner end surface of the cover  107  around the aperture  107   b.    
         [0058]     In operation, the safety line  70  passes through the clamp  100  and hollow shaft  101  as before. The collet grip  104  is biased by the spring  105  against the clamp body  102  so that the collet grip  104  is biased to grip the safety line  70 . In order to release the collet grip  104  from the safety line  70 , the cover  107  must be urged towards the hollow shaft  101 , that is downwards in the figures, so that the cover  101  urges the collet grip  104  away from the clamp body  102  so that the grip of the collet grip  104  on the safety line  70  is released.  
         [0059]     The collet grip  104  can rotate relative to the hollow shaft  101  in order to enable torsional stresses in a safety line  70  to be relieved while maintaining the desired tension. A circlip  109  may be placed on the end of the hollow shaft  101  opposite the clamp  100  to ensure that the load setting device, once installed on the hollow shaft  101 , does not become inadvertently lost.  
         [0060]     The clamp  100  is further shown in  FIG. 10  which shows the clamp assemble together with the load setting device  80  and safety line  70  and in  FIG. 11  which shows the assemble clamp  100  with the cover  107  removed to show the end of the collet grip  104  protruding from the collet body  102 . For clarity, the safety line  70  is omitted in  FIG. 11 .  
         [0061]     The clamp  100  shown in FIGS.  8  to  12  allows the safety line  70  to be freely pulled through in one direction, downward in the figures, because movement of the cable in this direction will automatically pull the collet grip  104  out of engagement with the clamp body  102  and so release the grip of the collet grip  104  on the safety line  70 , while movement of the safety line  70  in the opposition direction, upwards in the figures, will be prevented because forces applied to the safety line  70  in this direction will urge the collet grip  104  against the gripping body  102  and increase the gripping force exerted on the safety line  70 . This automatic one way action has the advantage of allowing easier adjustment of the assembly to pull though excess safety line. However, the one way gripping action means that the clamp  100  can only be used on one end of the threaded shaft  101 , the top end in the figures.  
         [0062]     A fourth alternative clamp arrangement  110  is shown in  FIGS. 12 and 13 .  
         [0063]     In this clamp  110  a collet grip  112  is urged into one end of a hollow shaft  111  by a winged nut  113  similarly to the arrangement shown in  FIGS. 6 and 7 .  
         [0064]     In the clamp  110  the hollow shaft  111  has at least one flat  111  a extending along most of its length. The flat  111  a stops short of the end of the hollow shaft  111  where the winged nut  113  is located so that the external threads are continuous in this region.  
         [0065]     A second wing nut or hand grip  114  is provided having an engagement mechanism (not shown) arranged to selectively lock the rotational position of the hand grip  114  relative to the hollow shaft  111  and an internal thread able to cooperate with the external thread of the hollow shaft  111 . The gripping mechanism is controlled by two push buttons  114   a  on the hand grip  114 .  
         [0066]     In order to tighten or loosen the clamp  110  the buttons  114   a  are pressed to release the hand grip  114  from the hollow shaft  111  and the hand grip  114  is then rotated along the thread of the hollow shaft  111  to a convenient position. The buttons  114   a  are then released to lock the rotational position of the hand grip  114  relative to the hollow shaft  111 . The hand grip  114  can then be used to hold the hollow shaft  111  in position while the winged nut  113  is rotated to engage or release the collet grip  112  from the safety line  70 .  
         [0067]     The advantage of this arrangement over the arrangement shown in  FIGS. 6 and 7  is that no spanner or other separate tool is required to tighten or release the clamp  110 .  
         [0068]     Although the invention has been particularly described above with reference to specific embodiments, it will be understood that modifications and variations are possible without departing from the scope of the claims which follow.