GB2434111A

GB2434111A - Conical cam

Info

Publication number: GB2434111A
Application number: GB0600755A
Authority: GB
Inventors: John Michael Peter Arran
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-01-14
Filing date: 2006-01-14
Publication date: 2007-07-18
Anticipated expiration: 2026-01-14
Also published as: GB2434111B; US20070164180A1; GB0600755D0

Abstract

A device for providing an anchor for various sizes of openings, the device comprising a camming member K substantially conical in shape. The device is particularly useful as a climbing device for obtaining a secure removable fixing in a crevice and may utilise one or more conical cams to achieve an improved expansion range without loss of strength and without additional weight or complexity.

Description

CONICAL CAM

Field of the Invention

This invention relates to cams and camming devices and in particular to camming devices useful for chmbing.

Background of the Invention

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.

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 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.

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 6 in Figure 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 B of between 12 and 15 degrees provides security in most types of rock.

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 Figure 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.

Various means have been developed to increase this expansion ratio.

The Camalot' 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 Another invention, the Fancam', 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.

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 & Prior Art

* US patent no 4,184,657 (Friend'), Jardine, 1980 * US patent no. 4,645,149 (Fancam'), Lowe, 1987 * US patent no 5,860,629, Reed, 1999 * US patent no. 6,042,069, Christianson, 2000 * UK patent no. GB2347360, Arran, 2001

Summary of the Invention

According to the present invention there is provided a conical member we shall refer to as a cone- cam, with the following properties -its base edge forms an arcuate surface; for much of its circumference its slant height changes uniformly as its base edge is traversed.

In the following, the term arcuate surface' is used to describe that continuous section of the base edge of the cone-cam over which the slant height changes uniformly.

As a result of the properties above, 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.

it follows that if a cone-cam 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 e which is shown in Figure 2.

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-cam and as such the cone-cam may withstand compression loads between such contact points in the same way as do conventional planar cams 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.

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'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.

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's interior wails, 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.

The placement stability of a cone-cam may be improved if created as shown in Figure 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 450 and that this would require an associated change in the curvature of the arcuate surface to achieve the required cam angle 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 sta,-1ner.s,;,k;n *L, # _..__.._._._. _____ s_s. _-_. --I--

Claims

Claims I 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 and for a continuous section of its base edge the angle between the tangent to the base edge and a line section between the base edge and the vertex is substantially constant; attachment means whereby a load may be attached to said device
2. The device of claim I wherein said attachment means permits a load to be attached to or about the vertex of the conical member
3. The device of claim 1 wherein said attachment means permits a load to be attached to one or more points on or about the base edge of the conical member
4. The device of claim I wherein the conical member is shaped so as to provide one or more additional points of contact with the same side of said surface opening as contacts a point on or about the vertex.

The device of claim 1 wherein said conical member is shaped so as to provide one or more additional points of contact with the side of said surface opening opposite to that which contacts a point on or about the vertex.

6. The device of claim I additionally comprising actuator means to further secure said device in the surface opening when said device is not subject to a load.

7. The device of claim 6 wherein said actuator means includes spring means.

8 The device of claim 1 additionally comprising actuator means to assist in the removal of said device from the surface opening when said device is not subject to a load.

9 The device of claim 8 wherein said actuator means includes cable means.

10. A device for providing an anchor at various sizes of openings in a surface, said device comprising: One or more similar or dissimilar camming members substantially conical in shape the base edge of each of which forms an arcuate surface such that the slant height is not constant and for a continuous section of its base edge the angle between the tangent to the base edge and a line section between the base edge and the vertex is substantially constant; zero or more non-conical camming members, zero or more non-camming members, support means connecting said conical camming members, non-conical camming members and non-camming members; attachment means whereby a load may be attached to said device.

II. The device of claim 10 additionally comprising actuator means to assist in secunng said device in the surface opening when said device is not subject to a load 12. The device of claim 11 wherein said actuator means acts to rotate one or more of said conical or non-conical camming members 13. The device of claim 11 wherein said actuator means includes spring means 14 The device of claim 10 additionally comprising actuator means to assist in the removal of said device from the surface opening when said device is not subject to a load.

The device of claim 14 wherein said actuator means acts to rotate one or more of said conical or non-conical camming members 16 The device of claim 14 wherein said actuator means includes cable means Amendments to the claims have been filed as follows I 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.

2 The device of claim 1 wherein said attachment means permits a load to be attached to or about the vertex of the conical member.

3. The device of claim 1 wherein said attachment means permits a load to be attached to one or more points on or about the base edge of the conical member.

4 The device of claim 1 wherein the conical member is shaped so as to provide one or more additional points of contact with the same side of said surface opening as contacts a point on or about the vertex.

5. The device of claim I wherein said conical member is shaped so as to provide one or more additional points of contact with the side of said surface opening opposite to that which contacts a point on or about the vertex.

6. The device of claim 1 additionally comprising actuator means to further secure said device in the surface opening when said device is not subject to a load.

7. The device of claim 6 wherein said actuator means includes spring means.

8 The device of claim 1 additionally comprising actuator means to assist in the removal of said device from the surface opening when said device is not subject to a load.

9 The device of claim 8 wherein said actuator means includes cable means 10. The device of claim I additionally comprising one or more similar or dissimilar conical camming members.

11. The device of claim 1 additionally comprising one or more similar or dissimilar non-conical camming members 12. The device of claim I additionally comprising one or more non-camming members to provide additional points of contact with the surface opening.

13. The device of claim I additionally comprising support means connecting said conical camming member and attachment means with any additional conical camming members, non-conical camming members and non-camming members.

14. The device of claim I additionally comprising actuator means to assist in securing said device in the surface opening when said device is not subject to a load 15. The device of claim 14 wherein said actuator means acts to rotate one or more of said conical or non-conical camming members.

16. The device of claim 14 wherein said actuator means includes spring means.

17. The device of claim I additionally comprising actuator means to assist in the removal of said device from the surface opening when said device is not subject to a load.

18. The device of claim 17 wherein said actuator means acts to rotate one or more of said conical or non-conical camming members 19 The device of claim 17 wherein said actuator means includes cable means.