Abstract:
A system for tensioning and locking a safety strand to a plurality of sequentially arranged stanchions is provided. Each stanchion has a stanchion cross section and a passage bore adapted for slidable passage of the safety strand therethrough. The system comprises tensioning means for applying a tensile force to a first end of the safety strand when the safety strand is disposed through the passage bore of each of the sequentially arranged stanchions and a second end of the safety strand is secured to an immovable object. The system further comprises a plurality of locking mechanisms. Each locking mechanism comprises a cable cradle having a receiving channel configured for receiving a portion of the safety strand, a clamping arrangement adapted for engaging and trapping the portion of the safety strand within the receiving channel, and means for securing the cable cradle and clamping arrangement to a selected one of the plurality of stanchions when the safety strand is disposed through the passage bore of the selected stanchion. The cable cradle and means for securing are configured so that when the cable cradle is secured to the selected stanchion, the receiving channel is in registry with the passage bore.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to the field of safety barriers and more particularly to a system for maintaining tension in safety wires. 
         [0002]    It is common practice in the construction industry to build a temporary or movable platform for a construction worker to stand on, and for supporting tools and materials. The platform may be supported by the ground, or may be suspended from above, or may be attached to a nearby large object such as the side of a ship. The platform may also be known as scaffolding, or staging. The platform may be used for constructing ships or constructing buildings. 
         [0003]    It is common practice to place a safety barrier along the outside of the platform, in order to prevent the construction worker from falling from the platform. Falling from the platform may severely injure or kill the construction worker. Similarly, safety barriers may be placed around the perimeter of a dangerous hole or dangerous machinery. The term platform is defined broadly, and includes any approximately horizontal working surface from which a worker may fall. For example, the deck of a ship may be a platform. 
         [0004]    Specifically, one common practice in the industry is to rig a safety strand through posts spaced at regular intervals along one or more edges of the platform. These posts may also be known as safety uprights, poles, or stanchions. The posts may be formed from any rigid member such as steel or iron channel stock having a hollow rectangular cross section, angle iron stock with an “L” shaped cross section, or pipe. The posts may be integrated into a support bracket for the platform, and the support bracket may be bolted or welded to the side of a ship or other structure. Horizontal wood or aluminum decking may link the support brackets to create a horizontal working platform. 
         [0005]    The posts are typically linked with a safety strand in the form of a steel cable, or other line to prevent the construction worker from accidentally falling from the exterior edges of the platform. The steel cable may be positioned at any height, but is typically positioned at about waist high (about four feet high) above the horizontal surface of the platform. Additional cables may be positioned at other heights for additional safety. For example a second cable may be positioned horizontally at about two feet high. At the end of the platform, the cables may be attached directly to the structure. 
         [0006]    The safety strand is attached to the vertical posts by various fastening techniques. One conventional fastening technique involves threading the cable through a hole in the post, looping the cable around the post and then proceeding to the next post. This technique, which may be referred to as “round turn” technique may also include forming a simple overhand knot to secure the strand to the post. 
         [0007]    One problem with the round turn technique is that it requires the strand to be relatively flexible. This may place limitations on the material or diameter of the strand. In some cases, the strand may be sufficiently flexible to form a knot, but the resulting attachment may be relatively loose. This, in turn, may limit the ability to maintain sufficient tension in the strand. 
         [0008]    Another problem with the round turn approach is that, even if a high degree of tension can be established initially, it may be difficult to maintain this tension. Workers have a tendency to lean on safety strands or place materials against them, which places the strand under additional tension. Application and removal of such additional loads can cause the strands to slacken over time. 
         [0009]    The present invention eliminates the “round turn” technique, and creates a stable and secure attachment of the cable to the post. This stable and secure attachment creates and maintains a tight cable with relatively high tension. 
       SUMMARY OF THE INVENTION 
       [0010]    An illustrative aspect of the invention provides a system for tensioning and locking a safety strand to a plurality of sequentially arranged stanchions. Each stanchion has a stanchion cross section and a passage bore adapted for slidable passage of the safety strand therethrough. The system comprises tensioning means for applying a tensile force to a first end of the safety strand when the safety strand is disposed through the passage bore of each of the sequentially arranged stanchions and a second end of the safety strand is secured to an immovable object. The system further comprises a plurality of locking mechanisms. Each locking mechanism comprises a cable cradle having a receiving channel configured for receiving a portion of the safety strand, a clamping arrangement adapted for engaging and trapping the portion of the safety strand within the receiving channel, and means for securing the cable cradle and clamping arrangement to a selected one of the plurality of stanchions when the safety strand is disposed through the passage bore of the selected stanchion. The cable cradle and means for securing are configured so that when the cable cradle is secured to the selected stanchion, the receiving channel is in registry with the passage bore. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention can be more fully understood by reading the following detailed description together with the accompanying drawings, in which like reference indicators are used to designate like elements, 
           [0012]      FIG. 1  is a schematic representation of a safety strand arrangement wherein the safety strand is in a slack condition. 
           [0013]      FIG. 2  is a schematic representation of the safety strand arrangement of  FIG. 1  wherein the safety strand is in a tightened condition. 
           [0014]      FIG. 3  is a schematic representation of the safety strand arrangement of  FIG. 1  wherein the safety strand is in a tightened and locked condition. 
           [0015]      FIG. 4  is a schematic representation of the safety strand arrangement of  FIG. 1  wherein the safety strand is in a tightened and locked condition. 
           [0016]      FIG. 5  is a perspective view a portion of a stanchion having a rectangular cross-section. 
           [0017]      FIG. 6  is a perspective view a portion of a stanchion having an L-shaped cross-section. 
           [0018]      FIG. 7  is a cross-sectional view of a rectangular stanchion to which a locking arrangement according to an embodiment of the invention has been attached. 
           [0019]      FIG. 8  is a side view of the stanchion and locking arrangement of  FIG. 7 . 
           [0020]      FIG. 9  is a top view of an L-shaped stanchion to which a locking arrangement according to an embodiment of the invention has been attached. 
           [0021]      FIG. 10  is a side view of the stanchion and locking arrangement of  FIG. 9 . 
           [0022]      FIG. 11  is a schematic representation of a safety strand arrangement wherein the safety strand is in a tightened and locked condition. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Hereinafter, various embodiments of the invention will be described. As used herein, any term in the singular may be interpreted in the plural, and alternately, any term in the plural may be interpreted to be in the singular. 
         [0024]    The present invention improves the safety of workers by enhancing the reliability of safety strands used to prevent workers and equipment from falling from work platforms or other structures. This is accomplished by reducing the potential for slack in such safety strands, thereby assuring that the safety strands are maintained at their intended position with their designed stability and loading capability. 
         [0025]    Embodiments of the present invention provide a system and method for tensioning and securing a safety strand to the stanchions of a work platform or other structure. The basic methodology of the invention is to apply tension to the strand as it is sequentially routed through and secured to the stanchions. The strand may be secured to some or all of the stanchions using relatively simple hardware without major modification to existing stanchions. Tension nay be applied to the strand using any suitable tensioning mechanism such as a winch. 
         [0026]    As used herein, the term “strand” includes any form of filament or bundle of filaments that can support a tensile load. Strands that may be used in embodiments of the invention include any form of rope, wire or cable and may be formed from any suitable material. 
         [0027]      FIGS. 1-4  illustrate a method of the invention as applied to a typical safety strand arrangement  5 . In this arrangement  5 , a safety strand  30  is set up for protection along a portion of the perimeter of a platform  10 . The safety strand  30  is strung sequentially through a series of stanchions  20 , which serve to support the safety strand at a desired height. Although the stanchions  20  shown in  FIGS. 1-4  are posts having a rectangular cross-section, the method may be applied to L-shaped and other stanchion types as noted above. With reference to  FIGS. 5 and 6 , which illustrate a rectangular stanchion  20  and an L-shaped stanchion  50 , respectively, each stanchion  20  (or  50 ) has a passage  22  (or  52 ) through which the safety strand  30  is passed. 
         [0028]    In the illustrated arrangement, one end of the safety strand  30  is attached to the first stanchion  20   a . This may be done before or after stringing the safety strand  30  through the other stanchions. Alternatively, the safety strand may be strung through the first stanchion  20   a  as well and the first end of the strand  30  attached to another fixed object. Notably, the method of the present invention can also be applied to a safety strand arrangement in which the safety strand is already in place as shown in  FIG. 1 . 
         [0029]    Once the strand  30  has been strung through the stanchions  20 , the safety strand  30  is in a relatively slack condition as is shown schematically in  FIG. 1 . In order to tighten the safety strand  30 , a tensile force is applied to the free end  32  of the safety strand  30 . This tensile force may be applied by manually pulling the free end  32  of the safety strand  30 . In most cases, however, it is desirable to establish a greater tension in the safety strand  30  than can be obtained manually. In such cases, a mechanical tensioning mechanism  120  may be used. The tensioning mechanism  120  may be or include any device or system that can be used to apply tension to the safety strand  30 . The tensioning mechanism  120  may be attached to the final stanchion in a series of stanchions as exemplified by stanchion  20   g  in  FIG. 1 , or may be attached to any fixed structure. As shown in  FIG. 1 , the tensioning mechanism  120  may include a winch  120  and a winch cable  122 . The winch cable  122  may be attached to the free end  32  of the safety strand  30  by a shackle or other attachment mechanism  124 . The winch itself may be a manual crank type mechanism or may be powered such as by an electric motor. 
         [0030]    With the tensioning mechanism  120  attached to the safety strand  30 , a tensile force is applied as shown in  FIG. 2 . The tensile force should not be so great as to snap or substantially bend the posts. A typical tensile force that may be used will be in a range of about 10 foot-pounds to about 100 foot-pounds of force. This tensile force causes the strand  30  to slide through the stanchion passages  22 , which removes the slack from the strand  30 . This causes the strand to be taut along its entire length. It can be seen, however, that releasing the tension will cause the safety strand  30  to return to its slack state. In order to maintain the taut condition, one or more safety strand locking assemblies  110  is attached to the safety strand  30  at selected stanchions  20 . Each locking assembly  110  includes a mechanism for clamping the safety strand  30  to the associated stanchion  20 , thereby preventing the safety strand from sliding through the passage  22 . 
         [0031]    In a preferred method according to the invention, the locking assemblies  110  are applied sequentially beginning with the selected stanchion  20  nearest in line to the fixed end of the safety strand  30 . The sequence continues with the next nearest selected stanchion  20  and so on until the nearest stanchion to the tensioning mechanism  120  ( or the stanchion  20  to which the tensioning mechanism  120  is attached) is reached.  FIG. 3  illustrates the stage of the method where a locking mechanism  110  has been applied to each of the selected stanchions  20   b ,  20   e , and  20   f . It will be understood that a locking mechanism  110  need not be applied to all the stanchions  20 . In this particular case, no locking mechanism  110  was applied to the two stanchions  20   c ,  20   d  at the end of the platform  10 . The actual number of locking mechanisms  10  used depend upon many factors, such as the diameter of the strand  30  and the distance between stanchions  20 . 
         [0032]    With the locking mechanisms  110  in place, the tensile force on the free end  32  of the safety strand  30  may be released. As shown in  FIG. 4 , the safety strand  30  remains taut from the final lock-down stanchion  20   f  to the stanchion  20   a  to which the fixed end of the strand  30  is attached. It can be seen that by locking down the safety strand  30  at multiple points along the strand  30 , the majority of the strand  30  will remain taut even if one of the stanchions  20  were to be bent or broken off or if the strand itself were to break at some point. 
         [0033]    The components of certain embodiments of the invention will now be described in more detail beginning with the locking mechanisms used to secure the strand to typical stanchion configurations. The tensioning system of the invention is designed for flexibility so that it may be easily adapted to existing safety strands and/or stanchions without major modification. Toward that end, the locking mechanisms use a clamping arrangement that can be used on a variety of stanchion configurations, including the square and L-shaped stanchions shown in  FIGS. 5 and 6 . 
         [0034]      FIGS. 7 and 8  and are top and side views of a locking mechanism  210  for that is configured for locking a safety strand  30  to a rectangular stanchion  20 . The rectangular stanchion  20  may be a monolithic block or may be an annular structure as shown in the section view of  FIG. 7 . In either case, the stanchion  20  has a passage  22  sized for slidable passage of the safety strand  30  therethrough. The locking mechanism  210  includes a bracket  212  sized and configured to fit around one side of the rectangular stanchion  20 . The bracket  212  has a U-shaped central portion  211  and a flange  213  extending outward from each leg of the central portion  211 . A pair of mounting holes  217  are formed through each flange  213 . The mounting holes  217  are sized and positioned to receive a U-bolt  216  that is, in turn, sized to fit around the safety strand  30 . The locking mechanism  210  also includes a pair of cradles  214  that has a flat base and a pair of U-shaped cable receiving portions  215  sized to receive the safety strand  30 . The cradles  214  may be attached to the bracket flanges  213  in any suitable fashion such as by bonding or welding. The cradle  214  may also be integrally formed with the bracket  212   
         [0035]    As shown in  FIGS. 7 and 8 , the cradles  214  are configured and positioned so that when the bracket  212  is properly fitted to the stanchion  20  adjacent the passage  22 , the cable receiving portions  215  are in registry with the passage  22 . If a safety strand  30  has been strung through the passage  22 , placement of the bracket  212  in this position causes the safety strand  30  to be received into the cable receiving portions  215  of the cradles  214 . Once in this position, the legs of the U-bolts  216  may be inserted into the mounting holes  217  so that the U-bolt  116  engages and traps the strand  30  against the cradles  214 . Locking nuts  218  are then used to tighten the U-bolts  216  in place, thereby locking the safety strand to the bracket  212  and, thus, the stanchion  20 . 
         [0036]    It will be understood that the bracket  212  need not itself be attached to the stanchion  20 . The action of clamping the strand  30  to the bracket serves to hold the bracket  212  in place. In some embodiments, however, the bracket  212  may be permanently or removably attached to the stanchion  20  in any suitable manner such as by welding or bonding or through the use of threaded fasteners. 
         [0037]    It will also be understood that the bracket  212  and other locking mechanism hardware may be sized to fit any stanchion. By way of example, the locking mechanism  210  may be sized for a typical stanchion having a nominal 2 inch square cross-section with rounded corners and a hollow interior. The mechanism may also be sized to receive and lock a typical steel safety cable having a diameter in a range of 0.25 inch to 0.5 inch. 
         [0038]    In variations of the embodiment illustrated in  FIGS. 7 and 8 , the configuration of the bracket  212  may be adjusted so that it may be fitted to stanchions with other cross sections. For example, the central portion  211  of the bracket  212  may be formed in a semicircle so that the bracket  212  may be fitted to a circular stanchion. The bracket  212  may take on any shape that allows the cable cradles  214  attached to the flanges  213  to be positioned in registration with the cable passage  22  through the stanchion. 
         [0039]      FIGS. 9 and 10  illustrate a locking mechanism  310  that can be used to clamp a safety strand  30  to an L-shaped stanchion  50 . As shown in  FIG. 6 , the L-shaped stanchion  50  has a cable passage hole  52  through one leg  51  of the stanchion. The locking mechanism  310  includes a single cable cradle  314  and a single U-bolt, both similar to the corresponding components of the previous embodiment. Because the stanchion  50  does not have a closed circumference, however, the locking mechanism  310  does not require a mounting bracket. Instead, a pair of mounting holes  54 ,  56  are formed through the second leg  53  of the stanchion. These holes are positioned near the cable passage  52  so that the cable cradle  314  can be positioned to receive a safety strand  30  passed through the cable passage  52  and so that both the safety strand  30  and the cable cradle  314  are trapped against the second leg  53  of the stanchion  50 . By tightening the locking nuts  318 , the U-bolt  316  serves to tightly lock the safety strand  30  to the stanchion  50 , thereby preventing the safety strand  30  from moving through the passage  52 . 
         [0040]    It will be understood that the cable cradle  314  need not be attached directly to the stanchion  50 . In some embodiments, however, the cable cradle  314  may be attached to the stanchion  50  using any suitable bonding or welding process. In some embodiments, the cable cradle  314  may be tacked to the stanchion  50  using a temporary adhesive to assist in installing the locking mechanism  310 . 
         [0041]    While the above embodiments describe a particular form of clamping mechanism, other suitable clamping mechanisms and fasteners may be used to carry out the methods of the invention. 
         [0042]    As previously discussed, the methods of the present invention may be applied to any sequence of stanchions having a hole for passage through and support of a safety strand. The methods may also be applied to stanchions that have more than one passage so that the safety strand is passed through the stanchion more than once.  FIG. 11  illustrates a safety strand arrangement  1005  having a safety strand  1030  and a plurality of stanchions  1020 , each of which has an upper passage  1022  and a lower passage  1024 . In a variation on the previously described locking sequence, a first end of the safety strand  1030  is fixed at a first stanchion  1020   a  at or near the lower passage  1024  of the stanchion  1020   a . The strand  1030  is then passed through the lower passages  1024  of second and third stanchions  1020   b ,  1020   c , upward along the outside of the third stanchion  1020   c , and back through the upper passage  1022  of each of the third, second and first stanchions  1020   c ,  1020   b ,  1020   c . A tensile force may then be applied to the free end  1032  of the safety strand  1030  to draw the safety strand  1030  tight. As shown in  FIG. 11 , this may be accomplished by attaching the free end  1032  of the strand  1030  to a tensioning mechanism  120  such as a winch. Alternatively, the tensile force may be applied manually. Once the tensile force has been applied, the safety strand  1030  may be locked to selected stanchions at one or both of the stanchion passages  1022 ,  1024  using the locking mechanisms  110  previously described. In a preferred approach, this will be done in sequence along the safety strand  1030 , beginning with the location nearest the fixed end of the strand  1030 . Upon completion of the sequence, the safety strand  1030  may be locked to the selected stanchions at two levels to provide additional protection to personnel and equipment. 
         [0043]    It will be understood that stanchions  1020  having upper and lower passages  1022 ,  1024  may also be used to support two separate safety strands  1030 . If such is the case, the earlier methodology may be applied to each separate strand  1030 . 
         [0044]    It will be understood that the methods and systems of the invention are not confined to horizontally disposed platforms and/or vertically positioned stanchions. The stanchions may and safety strand locked to the stanchions may be positioned at any angle. It will also be understood that the stanchions need not be parallel to one another. 
         [0045]    While the foregoing description includes details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the present invention. Modifications to the embodiments described above can be made without departing from the spirit and scope of the invention, which is intended to be encompassed by the following claims and their legal equivalents.