GB2419632A - Trigger linkage for controlling rock climbing cam device - Google Patents

Abstract

A trigger linkage for controlling cam devices used for safety protection in rock climbing. The linkage, connecting sprung opposed cam pairs A to a control trigger bar D, operating by articulation, thereby obviating the need for flexing of linkage members and avoiding stresses and any linkage failure resulting therefrom, whilst satisfying operational requirements of the device in use. The linkage comprising three interconnected rigid wires, of which paired wires 1 pivotally connect at one end to corresponding paired cams A, and one wire 2 pivotally connects at one end to trigger bar D, all three wires being formed into closed hooks at their other ends, the latter being brought together as an articulated joint in which the overlaid aligned hooked ends of cam wires 1 are joined orthogonally by the hooked end of trigger bar wire 2, the resulting linkage providing precise in-phase manipulation of paired cams A.

Description

TRIGGER LINKAGE FOR CONTROLLING CAM DEVICE

This invention relates to a trigger linkage for controlling cam devices used in the sport of rock climbing.

Cam devices are widely used in rock climbing for protecting the climber from a serious fall, such devices being placed in natural cracks and fissures within the rock face as the climber ascends. One well known type of cam device, to which the invention relates, comprises pairs of similar opposed cam segments pivotally carried on a shaft or twin parallel shafts, the opposed cams being spring-loaded against each other to rotate in a manner such as to open out to fit the crack into which they are placed. The camshaft, or twin camshafts where used, is or are mounted on a stem sufficiently long to protrude from the crack, the end part of the protruding stem being provided with means for making a sliding connection with the climbing rope via a karabiner. Several different commercially produced designs of such cam devices are available to the rock climber, but essentially all provide the same function of causing a pull from the climbing rope to be transmitted through the device stem to the camshaft or camshafts, causing pairs of opposed cams to pivotally open outwards and grip tightly within the crack.

Since the natural tendency of the cam device is to expand and jam inside the rock crack, separate means are required for overcoming this tendency in order to release and withdraw the device from the crack after use. Furthermore, although the device could in some circumstances be placed by simply pushing into the crack, causing the cams to retract against the spring pressure, it is generally advantageous to have means for preretraction, so that the device may be manoeuvred into the optimum placement position before the cams are released. Thus, for both abovedescribed reasons cam devices are provided with means of cam retraction control. In all such devices the means of cam control has been similar (constituting the prior art in the context of the present invention), the prior art basically comprising a two-wire linkage for controlling each opposed cam pair, in which a similar wire connects each cam of the pair to a common manually operated trigger bar mounted and sliding on the aforesaid cam device stem. In climbing use it is important that the control wire linkage between cams and trigger bar has flexibility in order to perform its primary cam retraction function, and accommodate disturbances transmitted from the rope, and not impede alignment of forces within the cam device resulting from a climber's fall. In the prior art two-wire linkage this flexibility is achieved by making each wire in two parts, the part conn3cted to the cam being rigid wire, and the part connected to the trigger bar being flexible cable, the two parts being serially joined together by overlap within a tightly crimped ferrule. The rigid wire part of each prior art control wire is pivotally connected to a point on the cam flank near the profile face, offset from the centre of cam rotation, so as to provide a turning moment. The cable part of each prior art control wire usually comprises one half of a single cable length anchored at mid-length by threading through holes in the trigger bar to simplify connection. The trigger bar is located on the cam device stem at a position accessible to the climber when the device is positioned in the rock crack, cam retraction being brought about by drawing down the trigger bar whilst applying equal and opposite force to the protruding nd face of the stem, in the manner of operating a hypodermic syringe. The above-described prior art two-wire control linkage between cams and trigger bar is used on various cam devices commercially available to the rock climber, and is therefore well known.

The prior art two-wire cam to trigger inkage described above suffers from significant shortcomings in practice. Firstly, the said prior art linkage allows independent rotation of

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each cam within a pair leading to the possibility of paired cams becoming out-of-phase when placed in the rock crack, a condition known as camoffsetting which may cause a serious decrease in the cam device's gripping performance. Secondly, articulation of the said prior art linkage is achieved by flexing of the cable parts of the two wires. Under conditions of use of the cam device such cable flexing is considerable, causing permanent kinking and distortion and associated stress concentrations within the cable, particularly at connection points, leading to progressive cable strand failure and eventual cable fracture, rendering the cam device inoperable. The purpose of the present invention is to provide means of performing the function of cam control whilst overcoming the above-described adverse features inherent in the prior art two-wire cam to trigger control linkage.

According to the present invention there is provided a trigger linkage for controlling cam operation on cam devices used by rock climbers for safety protection, said linkage comprising three interconnected rigid wires linking opposed paired cams to a trigger bar, the three-wire arrangement comprising two similar wires each pivotally connected at one end to one cam of the opposed pair and a wire pivotally connected at one end to a trigger bar, said three wires being each formed into a closed hook at their other ends, the latter being brought together to provide an articulated joint in which the overlaid aligned hooked ends of said two cam connected wires are joined orthogonally by the hooked end of said trigger bar connected wire, the linkage thus formed providing means of precise, in-phase, reliable manipulation of paired cams whilst accommodating normal disturbances encountered by the cam device in use.

A specific embodiment of the invention will now be described by way of example with reference to the following drawings in which: Figure 1 shows a cam to trigger control linkage according to the invention assembled on a known, established, cam device of the rigid stem type Figure 2 shows a cam to trigger control linkage according to the invention assembled on a known, established, cam device of the semi-flexible stem type.

Figure 3 shows the rigid three-wire jointed cam to trigger control linkage according to the invention.

Figure 4 shows in diagrammatic form the rigid three-wire jointed cam to trigger control linkage according to the invention executing the function of device cam retraction.

Figure 5 shows in diagrammatic form the rigid three-wire jointed cam to trigger control linkage according to the invention accommodating disturbances transmitted to the cam device from the climbing rope during normal operation.

With reference to the drawings Fig I shows in front and side elevation a cam to trigger control linkage according to the invention assembled on an established cam device of the rigid stem type, widely used by rock climbers. However, the essential features of the invention thereby illustrated and herewith described are broadly applicable to all various cam devices available to the climber. In order to clearly describe features and functional elements of the cam to trigger control linkage according to the invention, it is expedient to make reference to parts of the established cam device on which the linkage operates.

However, since said parts are well known, the descriptive content of such references is kept to a minimum. Thus, Fig 1 illustrates a cam device placed in a crack of width R in the rock face, the cam device comprising two pairs of opposed spring loaded cams A pivotally carried on a camshaft B, the latter being pivotally mounted on a centrally disposed rigid stem C provided with an aperture in the lower part for connecting to the climbing rope (via additional equipment), and provided with an elongated slot in which slides trigger bar D. With reference to Fig 1, the cam to trigger linkage according to the invention for controlling each pair of opposed cams comprises three interconnected rigid wires, the method of interconnection and connections to cam device members providing the articulations necessary to meet the requirements of use, the three wires comprising two similar cam wires 1, and a trigger wire 2. Each cam wire I is cranked and retained at one end to provide a pivot connection with each cam of an opposed pair as shown, in similar manner to that used for connecting the rigid part of the wire in the prior art two- wire cam to trigger linkage previously described. The other end of each cam wire I is formed into a closed hook, the plane of the hook being substantially perpendicular to the plane of the said crank, the hook being preferably configured as shown. Trigger bar wire 2 is provided with a retained pivot crank connection to the trigger bar at one end, and a closed hook at the other end, the plane of the hook being substantially perpendicular to the plane of the said crank, as shown, and the hook configuration being preferably as shown. The common lengths of cam wires I, and length of trigger wire 2 are selected to suit the particular proportions of the cam device to which they are fitted. On assembly of the three-wire linkage according to the invention, the hooks of the two similar cam wires I are brought into overlaid alignment, and the partly opened hook of the trigger wire 2 is engaged, in the same direction, through both cam wire hooks, before closure to form a three- wire joint as shown. The cam device shown in Fig I comprises two pairs of opposed cams, one pair each side of the central stem, therefore the above- described cam to trigger linkage according to the invention is provided in duplicate as shown.

With reference to the drawings Fig 2 shows in front and side elevation a cam to trigger control linkage according to the invention assembled on an established cam device of the semi-flexible stem type, widely used by rock climbers. The linkage shown in Fig 2 is essentially and functionally that shown in Fig 1, with variations in detail made to accommodate differences between the two cam device types, in particular the different arrangement used for mounting the trigger bar on the stem. Thus, Fig 2 shows a typical semi-flexible stem C comprising a stout cable provided with lugs at each end, on which is slide-mounted captive hollow trigger bar D. Cam wires I are similar to those described with reference to Fig 1, and the three-wire joint connection between cam wire pairs I and trigger wire 2 is also similar to that described with reference to Fig 1. Whilst the lower end of trigger wire 2 could be made similar to trigger wire 2 of Fig I, i.e. employing a cranked pivot connection to trigger bar D, the necessarily hollow nature of the latter lends to an alternative simple pivot connection according to the invention, as shown in sectional views X,Y in Fig 2, in which the end of trigger wire 2 is formed into a closed hook, preferably configured as shown, pivotally captivated on a transverse pin housed and retained in trigger bar D. The three-wire cam to trigger linkage according to the invention achieves motions satisfying the operational requirements of the cam device by relative rotations of the connected rigid members within the articulated joints, providing a taut, precise action.

Importantly, these motions take place in the absence of any of the flexural stresses and distortions that occur in the prior art two-wire linkage previously described. Also of importance in the use of the cam device is the low profile of the linkage, contained within the cam device envelope, as is evident in Figs I and 2.

Fig 3 is an isometric drawing of the rigid three-wire linkage according to the invention showing the various articulations provided. In interest of descriptive clarity, where the linkage connects to the cam device the latter is shown in symbolized form. Also in Fig 3 the pivot joint of trigger wire 2 with trigger bar D is shown as a crank, as depicted in Fig 1. on the understanding that the saiti mint is alsn fInrtinnaIIv niiivaInf tr th nm nivnf accommodated, namely, the general effect is for trigger bar D to tilt from the horizontal as shown, and this is brought about by rotations of trigger wires 2 about their respective hook joints with cam wires 1, and by trigger bar D rotating about pivot joints with trigger wires 2.

Fig 5 is a diagrammatic representation of the rigid three-wire cam to trigger linkage according to the invention with the cam device in typical operation. With reference to Fig 5, the device is placed in a crack of width R in the rock face by the lead climber, whom having placed the device and attached to it the protective climbing rope in usual manner, has continued to ascend above the device. Within the device placement, cam wires I are constrained to occupy a symmetrical position about the axis of camshaft B by the hooked joint with trigger wire 2, as shown. However, cam device stem C, mounted to pivot freely on camshaft B, and attached to the linkage via trigger bar (D), is connected at its lower end to the climbing rope, and therefore normally experiences via the latter erratic pendulous disturbances, as indicated in Fig 5, as the climber ascends.

Moreover, should the climber fall from a position not directly above the device placement, the line of the initial arresting force generated at the device via stem C may be offset from centre, as shown. Since the cam to trigger linkage is slide-connected to stem C, it is important that the linkage accommodates these described motions and forces applied externally to the device stem without hindrance or obstruction to the device function, and without the linkage itself becoming damaged in the process. With reference to Fig 5, the rigid three-wire cam to trigger linkage according to the invention accommodates said device stem motions and forces by trigger wire 2 rotating freely about cam wires I at the three-wire hooked joint as shown (in contrast to the prior art two-wire method which accommodates said stem motions and forces by cable flexing).

The rigid three-wire cam to trigger linkage according to the invention, by virtue of the jointing provided, is capable of separately and simultaneously executing the motions described above with reference to Figs 4 and 5. Moreover, all described motions are achieved irrespective of the inclination of the placed cam device in the crack, or the inclination of the crack in the rock face.

Claims (4)

1. A trigger linkage for controlling the operation of cam devices used by rock climbers for safety protection, said linkage connecting sprung opposed cam pairs to a control trigger bar and comprising three interconnected rigid wires of which paired wires pivotally connect at one end to corresponding paired cams, and one wire pivotally connects at one end to the trigger bar, all three wires being formed into closed hooks at their other ends, the latter being brought together to provide an articulated joint in which the overlaid aligned hooked ends of said paired cam connected wires are joined orthogonally by the hooked end of said trigger bar connected wire.
2. 2. A cam trigger linkage as claimed in Claim 1, the linkage providing means of precise, in-phase manipulation of paired cams whilst accommodating normal disturbances encountered by the cam device in use without impedance to the device's safety function.
3. 3. A cam trigger linkage as claimed in Claim I operating by articulation within the linkage, thereby obviating any need for flexing of linkage member parts and consequently avoiding linkage flexure stresses and any failure of the linkage in use resulting therefrom.
4. 4. A cam trigger linkage substantially as herein described above and illustrated in the accompanying drawings.