Abstract:
A conical cam rotates through a greater angle than a conventional planar cam in constricted spaces providing a greater range of movement. A climbing device for obtaining a secure removable fixing in a crevice utilises one or more conical cams to achieve an improved expansion range without loss of strength and without additional weight or complexity.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to cams and camming devices and in particular to camming devices useful for climbing. 
       CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    A right of priority is claimed in relation to UK patent application no. 0600755.3, filing date 14 Jan. 2006. 
       BACKGROUND OF THE INVENTION 
       [0003]    In many circumstances there arises a need to obtain a secure but readily removable fixing in parallel sided or similar fissures in rocks or other materials. 
         [0004]    A common example is that of rock climbers who require anchor points known as ‘belays’ or ‘running belays’ in order to protect themselves as they ascend their chosen route up a cliff. 
         [0005]    Many devices have been devised to achieve this end. Initially these consisted of simple metal wedges, typically incorporating a cable or nylon loop to facilitate the attachment of a rope or other equipment. Many shapes of metal wedge have been developed, including some in the shape of a cam which are able to offer some security even in parallel-sided fissures. In one particular type of device (the ‘Friend’ invented by Jardine) one or more pairs of cams are mounted on an axle and urged apart by springs so that the cam surfaces contact the walls of the fissure. 
         [0006]    It is clearly desirable that a device of this type should be effective in a wide range of sizes of fissure. The cam angle may be defined as the difference in angle between the wall of the fissure at its contact point with the arcuate cam surface and a line joining this contact point to the axle on which the cam pivots (see angle θ in  FIG. 1 ). It has been found that in order for the Friend or other devices of this type reliably to grip the walls of a fissure at varying degrees of expansion it is desirable that the cam angle should remain constant. If the cam angle is increased by modifying the shape of the cams, the expansion range is increased but the security is diminished. Although the optimum cam angle varies with rock type it has been found by practical experiment with fissures in various types of rock that a cam angle θ of between 75 and 78 degrees provides security in most types of rock. 
         [0007]    The maximum size of the Friend device when fully expanded is limited by the size of the cams, more specifically by the distance between the tips of opposing cams (the part of each cam furthest from its axle) when the device is fully extended. The minimum size of the device when fully contracted is reached when the tips of the cams abut on the opposite walls of the fissure (see  FIG. 1 ). The expansion ratio of such a device with an appropriate cam angle is found to be approximately 1:1.6, i.e. the maximum fissure width in which the device may securely be placed is approximately 1.6 times wider than the minimum fissure width in which the device may securely be placed. 
         [0008]    Various means have been developed to increase this expansion ratio. 
         [0009]    One such device employs two axles separated in a direction perpendicular to the support piece. This separation can increase the expansion ratio, albeit to a relatively small degree and with a substantial weight penalty. 
         [0010]    Another invention incorporates a plurality of cams which are engaged sequentially to allow a greater total expansion ratio. Such devices are necessarily wide and heavy due to the large number of cams involved, and they have not achieved commercial exploitation. 
         [0011]    Another invention differentially rotates the cams such that those on one side of the device rotate through a much greater angle than those on the other side, such that in its fully contracted position the tips of the cams on each side project in opposite directions, thereby presenting a narrower profile. 
       REFERENCES &amp; PRIOR ART 
       [0000]    
       
         
           
             U.S. Pat. No. 4,184,657 (‘Friend’), Jardine, 1980 
             U.S. Pat. No. 4,645,149 (‘Fancam’), Lowe, 1987 
             U.S. Pat. No. 5,860,629, Reed, 1999 
             U.S. Pat. No. 6,042,069, Christianson, 2000 
             UK patent no. GB2347360, Arran, 2001 
           
         
       
     
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    According to the present invention there is provided a device for providing an anchor at various sizes of openings in a surface, said device comprising:
       a camming member substantially conical in shape the base edge of which forms an arcuate surface such that the slant height is not constant;   attachment means whereby a load may be attached to said device,
 
whereby the device may be secured between the walls of a opening with a point on the arcuate surface of the camming member in contact with one wall of the opening.
       
 
         [0020]    The point at which conventional planar camming devices may no longer contract to fit within narrower openings is typically reached when the tips of the cams abut on the opposite walls of the opening (see  FIG. 1 ). The conical nature of the present invention&#39;s camming member(s) permits the tip(s) of its cam(s) to extend perpendicularly away from the opening, thereby permitting a greater angle of rotation and an consequently reduced minimum opening size. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0021]      FIG. 1  illustrates the limit of contraction of a conventional planar camming device. 
           [0022]      FIGS. 2   a - 2   d  is a sequence of 3-dimensional representations that illustrate how a conical cam is not constrained by the same contraction limit as is a conventional planar cam. 
           [0023]      FIG. 3  depicts one possible embodiment of the device, comprising only a single conical cam member and an attachment means. 
           [0024]      FIG. 4  depicts a different possible embodiment of the device, additionally comprising spring and cable means to respectively expand and contract the device. 
           [0025]      FIGS. 5   a  and  5   b  are plan-view illustrations of the device embodiment shown in  FIG. 4 . 
           [0026]      FIGS. 6   a  and  6   b  depict a third possible embodiment of the device, in which two conical cam members are employed in conjunction with a conventional planar cam. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    In the following, the term ‘arcuate surface’ is used to describe a continuous section of the base edge of the cone-cam over which the slant height changes uniformly, i.e. at any point on the arcuate surface of the cone-cam the angle of intersection between (i) the tangent of the arcuate surface at said point, and (ii) the line section between said point and the vertex of the cone-cam, is substantially constant. 
         [0028]    It follows that if a cone-cm is placed within a parallel-sided fissure such that the vertex of the cone-cam is in contact with one interior wall of the fissure and a point on the arcuate surface of the cone-cam is in contact with the opposing interior wall of the fissure, then the difference in angle between the opposing interior wall of the fissure and the line section between the two contact points remains constant over a range of fissure widths. This angle is the cam angle θ which is shown in  FIG. 2 . 
         [0029]    Since the cone-cam is conical, any line section between its vertex and a point on its arcuate surface will be contained within the fabric of the cone-cm and as such the cone-cam may withstand compression loads between such contact points in the same way as do conventional planar cams 
         [0030]    The vertex angle is defined as the angle between the axis of a cone and its surface. If a cone-cam has a vertex angle of 45° then opposing sides of the cone-cam extend from the vertex perpendicularly. In particular, when a cone-cam with a vertex angle of 45° is wedged in a fissure in its narrowest functional orientation (i.e. wherein the vertex is in contact with one wall of the fissure and that point on the arcuate surface closest to the vertex is in contact with the opposite wall of the fissure,) part of the cone-cam may extend perpendicularly out of (or alternatively into) the fissure to a distance considerably greater than the width of the fissure itself. 
         [0031]    If the cone-cam is oriented across a vertical parallel fissure such that the vertex contact point is higher than the arcuate surface contact point in a vertical plane perpendicular to that of the fissure&#39;s interior walls, then applying a vertical downwards load to (or near) the vertex will not produce movement of the cone-cam as the force will act to wedge the cone-cam securely between the walls of the fissure. 
         [0032]    Alternatively if the cone-cam is oriented across a vertical parallel fissure such that the vertex contact point is lower than the arcuate surface contact point in a vertical plane perpendicular to that of the fissure&#39;s interior walls, then applying a vertical downwards load to (or near) the arcuate surface contact point will not cause the cone-cam to move as the force will act to wedge the cone-cam securely between the walls of the fissure; One way of achieving this over a range of fissure widths (and associated cone-cam orientations) is to create a channel in the arcuate surface and apply the load via nylon, cable or other flexible material passed along the channel. 
         [0033]    The placement stability of a cone-cam may be improved if created as shown in  FIG. 3 , such that in ordinary operation there are at least three contact points; one (D) on the arcuate surface and more than one (E,F) at points on the cone-cam substantially equidistant from the first. In this arrangement it is noted that the vertex angle of the cone-cam would ideally be reduced from 45° and that this would require an associated change in the curvature of the arcuate surface to achieve the required cam angle. 
         [0034]    A cone-cam may be employed by itself to provide an anchor at various sizes of openings in a surface. Alternatively there are a number of additions which may be employed individually or in combination to improve the range, stability or ease of use of the device. Such additions include, but may not be restricted to, the following:
       Attachment means to connect the device to a load;   A wide, dual or otherwise shaped arcuate surface profile;   A blunted, multi-point or otherwise shaped vertex;   Additional fixed or moveable members attached to or near to the vertex;   Additional fixed or moveable members attached to or near to the arcuate surface;   Actuator means to rotate the cone-cam from a narrower orientation whereby it easily may be inserted into or removed from the surface opening to a wider orientation wherein it may be securely wedged within the surface opening, such means including spring means;   Actuator means to rotate the cone-cam from a wider orientation wherein it may be securely wedged within the surface opening to a narrower orientation whereby it easily may be inserted into or removed from the surface opening, such means including cable means;   Any number of additional similar or dissimilar cone-cams in the same device;   Any number of additional conventional planar cams in the same device.       
 
         [0044]    Such a device may provide an anchor at various sizes of openings in various surfaces. In particular it may be found useful for rock climbers in providing all or part of a belay or running belay. 
         [0045]    There are many possible combinations of features and attributes which could be employed in any single device. Each such device would have relative advantages and disadvantages in terms of expansion range, placement stability, ease of use, weight, manufacturing complexity, cost, etc. 
         [0046]    For illustrative purposes three such devices are detailed below, each describing a different embodiment of the current invention. 
         [0047]    In the first device ( FIG. 3 ) a groove around the vertex of a triangular cross-section cone-cam (A) retains a loop (B) formed by one end of a simple swaged cable. A similar loop (C) in the other end of the cable provides means by which a load may be applied. When the device is inserted into the widest smooth-sided parallel fissure for which it is suitable a point (D) on the arcuate surface will be in contact with one wall of the fissure, and all points along the line section between points E &amp; F will be in contact with the opposite wall of the fissure. In practice it is likely that points E &amp; F of cone-cam A would be moulded so as to protrude in order that exactly 3 points of contact could be achieved in a variety of irregular fissure placements. When the device is inserted into a much narrower smooth-sided parallel fissure the three points of contact may be at Points G, H and J as shown, at which time point D will protrude some distance out of the fissure. Similarly points may be identified for every width of fissure in the operating range of the device. 
         [0048]    In the second device described ( FIG. 4  and plan view  FIG. 5 ), a cone-cam (K) is connected to a head member (L) via an axle (M), about which cone-cam K is able to rotate with respect to head member L. When the device is correctly inserted into a parallel fissure the angle between axle M and each wall of the fissure is approximately 45°. Head member L is shaped such that when the device is correctly inserted there are two points of contact (N) between head member L and the first wall (P) of the fissure. A spring (R) is located on axle M and acts to urge cone-cam K rotationally with respect to head member L toward the device&#39;s fully extended position (as in  FIG. 5   a ), during which rotation a point on the arcuate surface (S) of cone-cam K comes into contact with the second wall (T) of the fissure. A body member (U) is attached to head member L, and a wire (V) connects an attachment point (W) on cone-cam K via a pulley (X) on head member L and a hole (Y) in body member U to a trigger (Z). Pulling trigger Z with respect to body member U acts to urge cone-cam K rotationally with respect to head member L toward its fully contracted position (as in  FIG. 5   b ), as a result of which rotation arcuate surface S is no longer in contact with wall T of the fissure and the device may be removed. 
         [0049]    In the third device described (plan view  FIG. 6 ), two cone-cams (K 1 , K 2 ) and a conventional cam (U) are connected to a head member (L) via axles (M 1 , M 2 ), by means of which both cone-cams are able to rotate in opposite directions with respect to head member L. When the device is correctly inserted into a parallel fissure the angle between each axle M 1 , M 2  and each wall of the fissure is approximately 45°. Springs located on each axle act to urge each cam rotationally toward the device&#39;s fully extended position (as in  FIG. 6   a ), during which rotation points on the arcuate surfaces of each cone-cam K 1 , K 2  and the conventional cam U come into contact with the walls (P, T) of the fissure. A body member is attached to head member L, and wires connect attachment points on each cam via pulleys on head member L to a trigger, as in the second device described above. Pulling the trigger with respect to the body member acts to urge each cam rotationally toward its fully contracted position (as in  FIG. 6   b ), as a result of which rotation each cam&#39;s arcuate surface is no longer in contact with the walls (P, T) of the fissure and the device may be removed.