Abstract:
A cable anchor utilizes a spring assembly to reduce tensile stresses on a cable over a wide range of tensile forces. Some examples utilize a plurality of springs, with each spring sequentially acting to reduce tensile stresses on the cable as the tensile force increases. Other examples utilize a reel that permits movement of the cable through rotation of the reel to further reduce stress on the cable.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application Ser. No. 61/089,241, filed on Aug. 15, 2008, and having the title, “Cable Anchor.” 
    
    
     TECHNICAL FIELD 
     The present invention relates to cable anchors. More specifically, the invention provides a cable anchor that cushions a tensile force applied to a cable. 
     BACKGROUND INFORMATION 
     Some electrical equipment, for example, underground mining equipment, is electrically powered using long, heavy electrical cables. As one example, a mining shuttle car used for transporting the mined substance out of the mine stores the electrical cable on a reel. The cable extends from the reel to a cable anchor mounted on the mine wall, and then to a power supply. As the shuttle car or other equipment approaches the cable anchor, the cable is wound onto the reel. As the equipment passes the cable anchor, and begins to travel away from the cable anchor, the movement of the equipment away from the cable anchor applies a tensile force to the cable, actuating a change in the direction of rotation of the reel, unwinding the cable. 
     Electrical cables are designed to withstand only limited amounts of tensile stress. For example, a typical electrical mining cable is rated to withstand about 200 lb. to about 600 lb. of force. As a shuttle car or other electrical vehicle passes the cable anchor, the tensile stress exerted on the cable may exceed the rating of the cable, causing premature cable wear. 
     Some presently available cable anchors include elastomeric bands that are intended to stretch in response to a tensile force, thereby reducing the tensile stress on the electrical cable. Other cable anchors utilize a single spring for the same purpose. These devices do not provide for stress reduction over the entire range of force to which the cable anchor may be exposed, and are themselves subject to premature wear. Additionally, many presently available cable anchors channel the cable around a reel that is too small in diameter, thereby bending the cable to a greater degree than the cable is designed to withstand. 
     Dual spring arrangements are known in the field of semiautomatic firearms, as explained in U.S. Pat. No. 4,204,113 to Seecamp. The spring arrangement disclosed by this patent is directed towards providing sufficient forward bias to the slide of a compact semiautomatic handgun having insufficient space for a single spring relative to the slide&#39;s distance of travel. Although the possibility of different spring rates is suggested by this patent, the patent is entirely directed towards maximizing the ability of the spring assembly to fit within the minimized available space when the spring assembly is compressed while also providing sufficient force when the spring assembly is expanded into a greater available space. Nothing within this patent discloses a means of providing tensile stress relief over a very wide range of applied tensile forces. 
     U.S. Pat. No. 4,040,332 to Border et al. discloses a variable spring rate equilibrator for an artillery piece. The equilibrator utilizes a pair of springs separated by a piston. A stop member prevents movement of the piston beyond a predetermined point as the artillery piece is elevated, so that only one spring is acting on the artillery piece. As the artillery piece is lowered, the piston moves away from the stop member, so that both springs can act on the artillery piece. This patent is therefore directed towards applying or removing the force of one of the two springs based on the position of the center of mass of the artillery piece, and not towards reducing a tensile stress over a wide range of applied tensile forces. 
     Accordingly, there is a need for a cable anchor that provides for tensile stress reduction over a greater range of tensile forces, that reduces the wear to which the cable is subjected, and which is itself durable. 
     SUMMARY 
     The above needs are met by a cable anchor having a connection for securing the cable anchor to a fixed location, a cable securing device, and a spring assembly disposed therebetween. One example of the cable anchor includes a spring assembly having a first spring having a first spring strength, and a second spring having a second spring strength. The second spring strength is higher than the first spring strength. The first spring and second springs are structured to act in a substantially parallel direction, and are also structured to bias the cable securing device towards the connection. 
     Another example of the cable anchor includes a connection for securing the cable anchor to a fixed location, a cable securing device, and a spring assembly disposed therebetween. The cable securing device includes a reel structured to hold the cable around its circumference. A reel housing is structured to receive the reel therein. The reel housing defines an open top that is structured to permit passage of the reel with the cable disposed thereon. The open bottom is structured to permit passage of the cable therethrough and to resist passage of the reel therethrough. 
     These and other aspects of the cable anchor will become more apparent through the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially cutaway isometric front view of a cable anchor. 
         FIG. 2  is a partially cutaway front elevational view of the cable anchor of  FIG. 1 . 
         FIG. 3  is a cutaway side elevational view of the cable anchor of  FIG. 1 , showing the upper spring compressed and the lower spring relaxed. 
         FIG. 4  is a cutaway side elevational view of the cable anchor of  FIG. 1 , showing both the upper spring and lower spring compressed. 
         FIG. 5  is a cutaway side elevational view of an alternative cable anchor, showing the inner and outer springs relaxed. 
         FIG. 6  is a cutaway side elevational view of an alternative cable anchor, showing the inner spring compressed and outer spring relaxed. 
         FIG. 7  is a cutaway side elevational view of an alternative cable anchor, showing the inner and outer springs compressed. 
     
    
    
     Like reference characters denote like elements throughout the drawings. 
     DETAILED DESCRIPTION 
     Referring to the drawings, a cable anchor  10  is illustrated. The cable anchor  10  includes a connector  12  a cable securing device  14  and a spring assembly  16  connecting the connector  12  and cable securing device  14 . 
     Some examples of the connector  12  provide a simple aperture  18  for mounting the cable anchor  10  in a desired location, for example, an upper portion of the wall of a mine. Other examples may provide a swivel  20  to provide a greater range of motion for the cable anchor  10 , so that the cable anchor  10  may pivot towards the direction of a tensile force, keeping the direction of the force substantially parallel with the cable. 
     Referring to  FIGS. 3-4 , the rod  22  extends downward from the connector  12 , passing through an opening  24  defined within a top plate  26  of a generally tubular housing  28 . A reciprocating plate  30  is secured to the lower end of the rod  22 . In the illustrated example, a lower portion  32  of the rod  22  is threaded, so that one or more nuts  34 ,  36  may be used to secure the reciprocating plate  30  to the lower portion  32  of the rod  22 . In the illustrated example, the nut  36  serves as a locknut to resist rotation of the nut  34 , as well as to provide additional bearing surface against the threads to resist the forces applied to the reciprocating plate  30 . The lower and  38  of the housing  28  may be open, facilitating access to the nuts  34 ,  36  and reciprocating plate  30 . 
     A plurality of springs are contained within the housing  28 . In the illustrated example of  FIGS. 1-4 , a pair of springs  40 ,  42  are illustrated. The rod  22  passes through each of the springs  40 ,  42 . A spring dividing plate  44  separates the spring  40  from the spring  42 , with the rod  22  passing through a suitable opening with the spring dividing plate  44 . The spring dividing plate  44  is free to slide along the rod  22 . The springs  40 ,  42  are selected to compress over different ranges of compression forces. In the illustrated example, the spring  40  is structured to compress over a lower range of forces, for example, about 100 lb. to about 500 lb. of force, and the spring  42  is structured to compress over a higher range of forces, for example, about 450 lb. to about 1,300 lb. of force. Other spring arrangements are possible. As one alternative, the location of the springs  40 ,  42  may be reversed. Alternatively, more than two springs may be used, and the springs may be positioned within the housing  28  in any order. In other alternative examples, two or more of the springs may be nested, with the weaker spring being longer than the stronger spring to ensure that the weaker spring undergoes substantial compression before the stronger spring begins to compress. 
     An example of a cable anchor  11  having a spring assembly  72  utilizing nested springs is illustrated in  FIGS. 5-7 . The spring assembly  72  includes a generally tubular housing  74  having a top wall  76  and an open bottom  78 . A coupling sleeve  80  is slidably mounted within the housing  74 . The coupling sleeve  80  is generally tubular, having a closed top end  82  and an open bottom end  84 . The bottom end  84  includes an outwardly extending circumferential flange  86  having an outer edge  88  that is adjacent to or abuts the inner surface of the tubular housing  74 . An opening  90  defined within the top wall  76  is structured to receive the coupling sleeve  80 . As before, a rod  22  extends downward from the connector  12 , passing through an opening  92  defined in the top end  82  of the coupling sleeve  80 . A reciprocating plate  30  is secured to the lower end of the rod  22 . In the illustrated example, a lower portion  32  of the rod  22  is threaded, so that one or more nuts  34 ,  36  may be used to secure the reciprocating plate  30  to the lower portion  32  of the rod  22 . In the illustrated example, the nut  36  serves as a locknut to resist rotation of the nut  34 , as well as to provide additional bearing surface against the threads to resist the forces applied to the reciprocating plate  30 . The open end  78  of the housing  74  facilitates access to the nuts  34 ,  36  and reciprocating plate  30 . 
     A pair of springs  94 ,  96  are contained within the illustrated example of the spring assembly  72 . The inner spring  94  surrounds the rod  22 , extending from the reciprocating plate  30 , into the coupling sleeve  80 , and ends adjacent to the top end  82  of the coupling sleeve  80 . The outer spring  96  surrounds the coupling sleeve  80 , extending from the top wall  76  of the housing  74  to the circumferential flange  88  of the coupling sleeve  80 . The inner spring  94  and outer spring  96  are selected to compress over different ranges of compression forces. In the illustrated example, the inner spring  94  is structured to compress over a lower range of forces, for example, about 100 lb. to about 500 lb. of force, and the outer spring  96  is structured to compress over a higher range of forces, for example, about 450 lb. to about 1,300 lb. of force. In other examples, the spring compression forces may be reversed, so that the outer spring is structured to compress prior to compression of the inner spring. 
     Referring to  FIGS. 1-2  as well as  FIGS. 3-4 , a reel housing  46  is secured to the tubular housing  28 . In the illustrated example, the reel housing  46  is secured to the lower portion of the tubular housing  28 . The reel housing  46  includes a rear wall  48  directly abutting the tubular housing  28 . A pair of convex side walls  50 ,  52  extending outward from either end of the rear wall  48 . A front wall  54  connects the side walls  50 ,  52  opposite the rear wall  48 . The reel housing  46  is generally tapered, narrowing from top to bottom. The bottom edges of the side walls  50 ,  52  include radiused portions  68 ,  70 , having a sufficiently large radius to resist damage to a cable resulting from severe bending. The top of the reel housing  46  defines a top opening  56 . Likewise, the bottom of the reel housing  46  defines a bottom opening  58 . The rear wall  48  of the reel housing  46  may be secured to the tubular housing  28  by welding, or by appropriate mechanical fasteners. Additionally, the straps  60  may extend around the tubular housing  28  and reel housing  46  to further secure the tubular housing  28  to the reel housing  46 . 
     A reel  62  is disposed within the reel housing  46 . The reel  62  has a diameter sufficiently large that the reel will not get through the bottom opening  58 , and sufficiently small so that the reel  62  will fit through the top opening  56 . The reel  62  also has a sufficiently large diameter so that, when a cable is channeled around the reel  62 , the cable is not bent beyond the design specifications of the cable. Some examples of the reel  62  are at least about 9 inches in diameter. The reel  62  defines a circumferential channel  64 , structured to receive an electrical cable  66  therein. In the illustrated example, referring specifically to  FIG. 2 , the electrical cable  66  extends upward through the opening  58 , around a circumferential channel  64  of the reel  62 , and down through the opening  58 . With the cable  66  in place, the reel  62  is held within the reel housing  46  by gravity and by any tensile forces applied to the cable  66 . In some examples, a hole  65  may be provided in the reel  62 . A bolt  67  may pass through the hole  65  in the reel, and the hole  69  in the reel housing  46 . Although the hole  69  matches the diameter of the bolt  67 , the hole  65  is significantly larger in diameter than the bolt  67 , permitting some movement of the reel  62  with respect to the housing  46 . 
     In the illustrated example, the tubular housing  28 , reel housing  46 , reciprocating plate  30 , spring dividing plate  44 , rod  22 , and strap  60  are made from steel. Other metals may be used provided that they have sufficient strength. The reel  62  may be made from any suitable metal, or from suitable polymers, for example, polyurethane. 
     In use, the cable anchor  10  or  11  is secured to an appropriate location, for example an upper portion of a mine wall, using the connector  12 . With the reel  62  outside of the reel housing  46 , the cable  66  is extended from the mine shuttle car (or other equipment) upward through the opening  58 , around the reel  62 , and then down through the opening  58 . The cable  66  is then extended towards and connected to an appropriate power supply. The cable  66  and reel  62  are then lowered into the housing  46 . At this point, friction between the cable  66  and the bottom edges of side walls  50 ,  52  respectively resists rotation of the reel  62 , without totally preventing all rotation of the reel  62 . 
     At rest, the cable anchor  10  will be in the configuration illustrated in  FIGS. 1 and 2 . In this condition, both the spring  40  and spring  42  are relaxed. As a shuttle car or other equipment passes the cable anchor  10 , a downward force is applied to the cable  66 . As this force increases beyond the minimum strength needed to compress the spring  40 , spring  40  begins to compress, until it reaches the configuration illustrated in  FIG. 3 . Before the spring  40  reaches full compression, the increasing force applied to the cable  66  causes the spring  42  to begin to compress. The spring  42  continues to compress until the maximum force is reached, or until the spring  42  is fully compressed, as illustrated in  FIG. 4 . As the shuttle car passes the cable anchor  10 , the reel within the shuttle car reverses direction, reducing the tension on the cable  66  and returning the cable anchor  10  to the configuration of  FIG. 3  and then to the configuration of  FIGS. 1-2 . 
     Likewise, the cable anchor  11  of  FIGS. 5-7  will begin in the configuration of  FIG. 5 , with both the inner spring  94  and outer spring  96  relaxed. As a shuttle car or other equipment passes the cable anchor  11 , a downward force is applied to the cable  66 . As this force increases beyond the minimum strength needed to compress the inner spring  94 , the inner spring  94  begins to compress, until it reaches the configuration illustrated in  FIG. 6 . Before the inner spring  94  reaches full compression, the increasing force applied to the cable  66  causes the outer spring  96  to begin to compress, causing the coupling sleeve  82  slide upward within a housing  74 . The outer spring  96  continues to compress until the maximum force is reached, or until the outer spring  96  is fully compressed, as illustrated in  FIG. 7 . As the shuttle car passes the cable anchor  11 , the reel within the shuttle car reverses direction, reducing the tension on the cable  66  and returning the cable anchor  11  to the configuration of  FIG. 6  and then to the configuration of  FIG. 7 . 
     Regardless of whether the cable anchor  10  or the cable anchor  11  is used, the reel  62  may rotate to a small degree against the friction between the cable  66  and bottom edges  68 ,  70  of the walls  50 ,  52 , thereby permitting the cable to move a small distance towards the direction of the tensile force, further reducing the tensile stress on the cable  66 . 
     A variety of modifications to the above-described embodiments will be apparent to those skilled in the art from this disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention. The appended claims, rather than to the foregoing specification, should be referenced to indicate the scope of the invention.