NZ506099A - Lifting systems for concrete components - Google Patents

Abstract

A clutch for use in a lifting of concrete components is disclosed comprising of an annular clutch body (2) engageable over the head of a lifting anchor (8). An accurate locking bolt (10) is moveable within the clutch body (2) between an engaged position, in which the bolt (10) extends through an eye in the head portion of the anchor (8), and a remote release position, such as the ground after erection of the component, to permit removal of the clutch body (2) from the anchor (8). The remote release system comprises of an over-center linkage connected to the bolt (10) and actuated to release the bolt (10) by a downward pull applied by a flexible element such as rope or cable (22). The over center linkage being in an over-center condition when the bolt (10) is in its engaged position such that the linkage locks the bolt (10) in its engaged position, and the release system includes means for preventing the release of the bolt (10) by pulling the flexible element (22) at an angle less than a predetermined angle to the face of the component.

Description

NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION After Provisional PQ2434/99 filed in Australia on 25 August, 1999 Davies Collinson Cave Reference: 2320258 APPLICANT(S) Ramset Fasteners (Aust.) Pty. Limited Maroondah Highway, Croydon North, Victoria 3136, Australia - An Australian company ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent & Trade Mark Attorneys c/- James & Wells Level 9, Ellerslie Tower 6B Cawley Street, Ellerslie, Auckland New Zealand INVENTION TITLE: Lifting systems for concrete components We/I, Ramset Fasteners (Aust.) Pty. Limited, hereby declare the invention for which we pray that a patent be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: INTELLECTUAL PROPERTY OFFICE OF NZ - 2 AUG 2000 RECEIVED P \QPER\RSH\nz506099 spe doc-06/08/01 1 i AUG 2001 Received LIFTING SYSTEMS FOR CONCRETE COMPONENTS The present invention relates to lifting systems for concrete components and more particularly to a lifting clutch for use in lifting of concrete panels and other components.

In US patent 3883170 there is disclosed a lifting system for concrete components comprising a lifting clutch consisting of an annular body carrying an arcuate locking bolt. In use, the bolt engages through an eye in the head portion of a lifting anchor embedded within the concrete component, the head portion of the anchor being exposed within a void formed in the surface of the component, with a part of the body of the clutch also being received within the void. In the lifting clutch disclosed in US patent 3883170 a remote release system for releasing the bolt from the anchor to disengage the lifting clutch from the anchor from the ground after erection of the component involves the use of a Bowden cable. A Bowden cable release system is not a particularly practical form of release system.

The present invention relates to a lifting clutch of the general type disclosed in this US patent but with an improved release system; the lifting clutch of the invention is particularly suitable for use in tilt-up face lifting of concrete panels, but also has general applicability to other lifting situations.

According to a first aspect of the present invention, there is provided a clutch for use in lifting of concrete components, comprising an annular clutch body engageable over the head of a lifting anchor, an arcuate locking bolt movable within the clutch body between an engaged position in which the bolt extends through an eye in the head portion of the anchor and a released position to permit removal of the clutch body from the anchor, and a remote release system for releasing the clutch from the anchor from a remote position such as the ground after erection of the component, said remote release system comprising an over-centre linkage connected to the bolt and actuated to release the bolt by a downwards pull applied by a flexible element such as a rope or cable, said over-centre linkage being in an over-centre condition when the bolt is in its engaged position such that P \OPER\RSH\nz5()G099 spe doc-06/08/01 y 3 the linkage locks the bolt in its engaged position, and the release system including means preventing release of the bolt by pulling the flexible element at an angle less than a predetermined angle to the face of the component.

Advantageously, when the bolt is in its engaged position, the bolt is subject to a resilient bias which acts in a sense to retain the mechanism in its over-centre condition. In one embodiment of the invention, the resilient bias is provided by a resilient stop carried by the body of the clutch and engaged by the bolt in the engaged position of the bolt.

In a preferred embodiment, the over-centre linkage comprises an outer link pivotally mounted within a housing carried by the body of the clutch and an inner link pivoted at one end to the outer link and at another end to the clutch bolt, the flexible element being coupled to a part of the outer link remote from its pivotal mounting either directly or via a further link. Preferably, in the disengaged position of the bolt, a substantial part of the outer link lies externally of the housing to provide visual indication of that state, preferably further facilitated by covering the exposed part of the outer link in a readily visible colour.

Advantageously, in the erected condition of the component the housing extends downwardly from the clutch body adjacent a vertical face of the component and during the release action a lower part of the housing fulcrums against that face to facilitate release.

In one preferred form of the invention the clutch further includes the flexible link interconnecting a shackle plate and the release system. In this way the release P \OPER\RSH\pq6863-00 ramset cap doc-28/07AX> mechanism is prevented from disengaging the clutch from the anchor whilst there is load on the shackle plate during lifting of the concrete component.

According to a another aspect of the present invention, there is provided a clutch 5 for use in lifting of concrete components, comprising an annular clutch body engageable over the head of a lifting anchor, an arcuate locking bolt movable within the clutch body between an engaged position in which the bolt extends through an eye in the head portion of the anchor and a released position to permit removal of the clutch body from the anchor, a shackle plate for connection of the clutch with a lifting cable, said shackle plate 10 being coupled with the clutch to assume a lifting position when under load during lifting of the component and to be moveable from the lifting position when not under said load, a remote release system for releasing the clutch from the anchor from a remote position such as the ground after erection of the component, said remote release system including a linkage connected to operate the bolt and actuated to release the bolt by a downwards 15 pull applied by a flexible element such as a rope or cable, and a flexible link interconnecting said shackle plate and said linkage to prevent releasing actuation of the linkage when said shackle plate is in said lifting position.

Advantageously, the flexible link is a chain. The flexible link need not 20 completely prevent movement of the release linkage. It is sufficient for the movement to be limited sufficiently to prevent disengagement from the anchor.

In a preferred configuration the shackle plate is coupled to the clutch so as to move from the lifting position under the influence of gravity when the load is removed. 25 This allows subsequent operation of the release system.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- P \OPERVRSH\pq6863-QO ramset cap doc-28/07/00 Figure 1 shows a clutch in accordance with a first embodiment of the invention in a condition in which its locking bolt is engaged with a lifting anchor of a panel after the panel has been lifted into its erected condition by a tilt-up lifting operation; Figure 2 is a section corresponding to Figure 1 to show details of the clutch and a release mechanism for the clutch bolt; Figure 3 is a perspective view of the clutch in the condition of Figure 1, the panel and anchor being omitted from this view for clarity of illustration; Figure 4 is a side view similar to Figure 1, but showing the clutch during release with the release mechanism passing through a centre position; Figure 5 is a section corresponding to Figure 4; Figure 6 is a perspective view corresponding to Figure 4, but with the panel and anchor being omitted for clarity of illustration; Figure 7 is a side view similar to Figure 1, but showing the clutch with its bolt released from the anchor and just prior to removal of the clutch body from the anchor; Figure 8 is a section corresponding to Figure 7; Figure 9 is a perspective view corresponding to Figure 7, with the panel and anchor omitted for clarity of illustration; Figure 10 is a sectioned side view similar to Figure 2, but showing a modified embodiment of the invention; Figure 11 is a sectioned side view of the modified embodiment of the invention shown in Figure 10, but showing the clutch with its bolt released from the anchor and just prior to removal of the clutch body from the anchor; Figure 12 is a sectioned side view similar to Figure 2 but showing another embodiment of the invention; and Figure 13 is a sectioned side view of a modified form of the embodiment of Figures 10 and 11.

As shown in Figures 1 to 3 of the accompanying drawings a lifting clutch particularly adapted for use in tilt-up face lifting of concrete panels comprises an annular body 2 carried by a shackle plate 4 to which a crane cable is attached, the lower end of P \0PER\RSH\pq6863-00 ramset cap doc-28/07/00 the shackle plate 4 being mounted within the central aperture of the clutch body 2. The body 2 is apertured at 2a to fit over the head portion of a lifting anchor 8 and the body 2 is releasably lockable to the anchor 8 by an arcuate locking bolt 10 mounted within the body 2 for passage through an eye in the head portion of the lifting anchor. In the drawings, the lifting clutch is illustrated in the configuration it assumes at the end of a tilt-up lifting operation in which the panel 12 extends substantially vertically with the lifting anchor 8 extending substantially horizontally. A remote release mechanism for releasing the clutch from the anchor 8 at the completion of lifting comprises an over-centre or toggle linkage consisting of a first or inner link 14 pivotally attached at an upper end to an adjacent end of the arcuate locking bolt and pivotally attached at a lower end to a second or outer link 16; the upper and lower pivots are designated P, and P2. The second link 16 is pivotally mounted, by pivot P3, within a housing 18 of channel section rigidly attached to the body 2 of the clutch so that the housing 18 projects downwardly from the clutch body in the configuration shown. The base wall 18a of the housing 18 lies closely adjacent to, and faces, the vertical surface of the panel 12 and the base wall 18a of the housing lies opposite the open side of the housing. The pivotal mounting P3 for the second link 16 is formed by a shaft extending between the opposed side walls 18b of the housing 18 and the pivotal connection P2 between the first and second links 14,16 is within the interior of the housing 18. The housing 18 is of robust construction in order to shield the pivotal connections P2 and P3 against damage even under rough handling conditions such as a clutch of this type is likely to undergo during usage on a construction site. Additional robustness is provided by fabricating the second link 16 in the form of two parallel plates 16a which lie on opposite sides of the link 14, with the pivot P2 being formed by a shaft extending between the two plates 16a.

As will be seen in the drawings, the upper portion of the first link 14 is arcuate to conform to the interior shape of the clutch body 2 in the engaged condition of the bolt 10. In the part of the clutch body 2 traversed by the first link 14, the outer wall of the body is slotted (as shown in Figure 3) to permit passage of the first link 14 during engaging and release movement of the locking bolt 10. Figures 1 to 3 show the P \OPER\RSH\pq6863-00 ramset cap doc-28/07/00 configuration of the release mechanism in the engaged or locked condition of the bolt 10. In this condition the outer end of the locking bolt 10 is in firm engagement with a resilient stop 20 within the interior of the clutch body 2 and which applies to the bolt 10 a resilient bias acting in a sense to displace the bolt 10 in a release direction; however 5 this displacement acts to force the release linkage into an over-centre locked condition which locks the bolt 10 against release until the linkage is moved out of its over-centre condition as will subsequently be described. In the over-centre condition the pivot connection P2 between the first link 14 and the second link 16 is to the left of an axis X-X connecting the pivots P, and P3. Release movement of the mechanism requires the 10 second link 16 to be pivoted about its pivot P3 outwardly relative to the housing 18. It will be appreciated from the geometry of the linkage in the condition shown in Figures 1 to 3 that in the over-centre locked condition, the bias acting on the locking bolt 10 due to its engagement with the resilient stop 20 will apply a downwards component of force to the first link 14 and this downwards component of force when the linkage is in its over 15 centre- condition will act to retain the second link 16 in an inner position thus ensuring the integrity of the locking system.

Release of the locking bolt 10 is effected by pivoting the second link 16 outwardly by means of a remote release comprising a cable link 22 coupled to an upper 20 part of the second link 16 above the upper end of the protective housing 18 and a length of rope or cable 22a (see Fig.3) attached to the lower end of link 22 and operable from a remote location such as the ground.. It is to be noted that the initial release movement of the second link 16 will result in upwards displacement of the first link 14 and hence movement of the remote end of the bolt 10 in a sense to cause greater compression of the 25 resilient stop 20 thus further loading the resilient stop 20 until the pivot P2 has moved to the outer side of the axis X-X whereon further outwards movement of the second link 16 will then result in downwards displacement of the upper end of the first link 14 and hence release of the locking bolt 10 from the anchor 8. It will be understood that due to the resilient loading of the stop 20 by the remote end of the locking bolt 10 until the pivot 30 P2 has passed outwardly beyond axis X-X, in other words has passed out of its over- P \CJPER\RSH\pq6863-00 ramset cap doc-28/07/00 centre condition, the stop 20 acts to store strain energy which releases as the linkage passes out of its over-centre condition and thus release of strain energy acts in a sense to assist the release action; the release action is further assisted by the weight of the second link 16 as it pivots outwardly. Figures 4 to 6 illustrate the configuration of the release 5 mechanism during release as the centre condition is reached and Figures 7 to 9 illustrate the configuration of the release mechanism in its fully released state.

To prevent the movement of the first link 14 during release from causing the bolt 10 to jam against the inner surface of the housing 2, the outer end of the first link 14 is 10 formed with a small protuberance 14a which moves along the inner surface of the housing 2 to maintain the outer end of the first link 14 and the adjacent end of the locking bolt 10 in spaced relationship to the inner surface of the housing 2.

During the release action, the lower inner end edge 18c of the housing 18 bears 15 against the vertical surface of the panel 12 to form a fulcrum which facilitates movement of the clutch body 2 off the head of the anchor 8 generally linearly and opposes pivoting movement of the clutch body 2 during release and which might cause jamming of the clutch body on the anchor head.

Engagement of the clutch with a lifting anchor 8 at the commencement of a tilt-up lifting operation in which the panel 12 is lying horizontally with the anchor 8 substantially vertically directed and the housing 18 lying substantially horizontally on the upper surface of the panel involves movement of the second link 16 from its released position substantially externally of the housing 18 to its engaged position substantially 25 internally of the housing. The initial part of the engaging movement can simply be effected by hand to pivot the second link 16 inwardly. However quite a substantial force is required to displace the second link 16 through the centre position into the over-centre locked position, but this can readily be achieved by foot pressure applied to the second link 16; this is in fact quite convenient as prior to the commencement of lifting the 30 housing 18 is resting horizontally on the horizontal panel 12 substantially at ground level P \QPER\RSH\pq6863-00 ramset cap doc-28/07/00 with the outer edge of the second link 16 is projecting above the upper, open, side of the housing 16.

The extension of the second link 16 outside of the housing 18 in the released or 5 disengaged condition of the linkage can to advantage be used to provide indication visible from a remote location that the clutch has not been engaged or is not properly engaged and for this purpose the substantial part of the second link 16 which is within the interior of the housing 18 in the fully engaged condition but is outside of the housing 18 in a fully or partially disengaged condition can be in a prominent colour easily visible from a 10 remote location, particularly by a crane operator so that the crane operator can ascertain absence of complete engagement by seeing an exposed part of the second link 16 of prominent colour.

In addition to the positive locking of the bolt 10 provided by the release 15 mechanism in its over-centre condition, another safety feature is incorporated to prevent accidental release of the clutch. More particularly, the mechanism is designed to ensure that accidental release will not occur, for example by someone tugging on the release rope or cable 22a as may happen for instance if the person trips on the construction site and intuitively grabs hold of the hanging release cable or if the rope or cable 22a 20 becomes snagged during lifting. Instead the release mechanism is designed to permit release only by a deliberate pull on the release rope or cable 22a with the rope or cable 22a (and hence the cable link 22) inclined by more than a predetermined angle to the face of the panel, for example an angle of about 30°. For this purpose the end of the cable link 22 is attached to the upper end of the second link 16 by means of a floating pin 30 25 movable in a vertical slot 32 in the second link 16. The pin 30 is located above an upper edge 18d of the housing 18 (see Figures 1 and 3) and the lower end of the slot 32 when the second link 16 is in its engaged position is located beneath the upper edge 18d so that in the engaged condition the pin 30 rests on that edge. The upper edge 18d is contoured to slope inwardly and downwardly over part of its length to ensure that a downwards pull 30 applied to the cable link 22 either when the cable link is vertical or is inclined at an angle P \OPERVRSH\pq6863-OQ ramset cap doc-2«/07/00 less than the predetermined angle (for example approximately 30° as previously mentioned) will be resisted by the engagement of the pin 30 with the upper edge 18d of the housing and will not result in outwards movement of the link 16 sufficient to cause release unless the cable link 22 is inclined at a sufficient angle to pull the pin 30 clear of 5 the ramped edge 18d of the housing. It is to be noted that engagement of the floating pin 30 with the ramped upper edge 18d while the clutch is being engaged with the anchor prior to lifting is facilitated by movement of the pin along a further ramped edge 18e outwardly of the edge 18d during the closing movement of the second link 16.

As will be well understood by persons involved in tilt-up building construction, the clutch is not released until the erected panel is firmly supported from beneath and has been firmly propped. At that point, the load in the hoisting cable is released, this being signified by lowering of the shackle plate 4. Although when the crane cable is under load there will normally be substantial friction between the bolt 10 and anchor 8 to 15 prevent release of the bolt, there is a possibility that under certain circumstances when the clutch is under load the body 2 of the clutch can pivot slightly about its axis so that the loading is principally taken by engagement of the opposite end edges of the aperture in the clutch body 2 with the opposite side faces of the head portion of the anchor 8 rather than by engagement of the clutch bolt 10 with the anchor thus theoretically 20 enabling the possibility of bolt release prior to release of the lifting load if correct procedures are not observed requiring the lowering of the shackle plate prior to release. To prevent this effect, advantageously the body 2 of the clutch has in a position above the aperture for the anchor head a projection 36 which engages the surface of the void in which the anchor head and clutch body are located during lifting. This engagement 25 prevents the pivoting action just discussed and ensures that the load is principally taken by engagement between the locking bolt 10 and the anchor head thus preventing release when the crane cable is still under load.

It will be appreciated that the over-centre linkage as described, apart from providing a positive locking action on the clutch bolt 10 with release being effected by P \OPER\RSH\pq6863-00 ramset cap doc-2&/07/00 deliberate action of an operator in pulling the release rope or cable at more than a predetermined angle to the face of the panel, the length of the lever arm of the force applied to the second link 16 by the release rope or cable is several times longer than the lever arm of the releasing force applied by the second link 16 to the first link 14 thereby 5 resulting in substantial amplification of the release loading applied by an operator. This force amplification in conjunction with the fulcrum effect between the lower end of the housing 18 and the vertical surface of the erected panel and also the resilient energy released by the resilient stop 20 against the bolt 10 provides an effective release system which permits ease of release of the clutch from the ground. The system is easy to use 10 and is also robust.

Figures 10 and 11 illustrate a modified embodiment of the invention shown in Figures 1 to 9. The same reference numerals have been used to identify corresponding parts. The general operation of the clutch is the same as described with reference to 15 Figures 1 to 9 and only the modifications will be described in detail.

As shown in Figures 10 and 11a third link 16c is connected to link 16. Link 16c includes an eye 16d for connection with one end of a chain 38. The other end of chain 38 is connected with shackle plate 4 by means of a bolt 40. During lifting of the panel 20 12 the shackle plate 4 and crane cable are under load. The shackle plate 4 is free to move in its mounting with clutch body 2 and assumes a lifting position under load dictated by the geometry of the anchor(s) and the panel 12. This lifting position is confined to a predetermined range for selected panels and the length of chain 38 is selected so as to limit the travel of linkages 14, 16 and 16c when the shackle 4 is in the 25 lifting position corresponding to being under load. As seen in Figure 10 the travel of the linkages is limited to less than that required for release of bolt 10 from anchor 8. When the load is removed from the lifting cable and shackle 4 after positioning of the panel 12, shackle 4 moves under the influence of gravity to a position as shown in Figure 11 where the length of chain 38 permits movement of linkages 14, 16 and 16c to release bolt 10 30 from anchor 8 in the manner described above. It will be apparent that the chain 38 thus P \OPER\RSK\pq6863-00 ramset <39 doc-28/07/00 provides an additional level of safety against the unintentional release of the clutch, for example, in the event that the rope or cable 22a is snagged in such a way that movement of the lifting cable causes the rope or cable 22a to be pulled at an angle greater than the predetermined release angle.

Figure 12 shows another embodiment of the invention. The same reference numerals have been used to identify corresponding parts. The general operation of the clutch shown in Figure 12 is similar to that described above in relation to Figures 1 to 11. In particular the configuration of bolt 10 that can be moved between a position in 10 which it engages an anchor 8 and a position in which the clutch can be disengaged and anchor 8 is generally the same.

In this embodiment the release mechanism is however somewhat modified. The release mechanism includes two linkages 14 and 16 pivotally arranged to drive the bolt 15 10 between engaged and disengaged positions through the pivoting movement of linkage 16 about pivot point P3. A cable or rope 22a is used to effect movement of linkage 16. Pivot points P3, P2 and PI are arranged such that in the engaged position the release mechanism is in a centre condition. However unlike the embodiment described in Figures 1 and 11 the clutch of the second embodiment does not include a mechanism that 20 prevents release unless rope or cable 22a is pulled at greater than a predetermined angle. Inadvertent release of the clutch of the second embodiment is prevented solely by means of the modification described in relation to Figures 10 and 11. That is, a chain 38 is connected between linkage 16 and shackle plate 4 to restrict movement of linkage 16 when the shackle plate 4 is under load in a lifting position. This is illustrated in Figure 25 12 where it can be seen that the length of chain 38 prevents the movement of linkage 16 to a position where the bolt 10 is able to disengage anchor 8. As described above in relation to Figures 10 and 11 shackle plate 4 moves under the influence of gravity when load is released. This movement is anti-clockwise as viewed in Figure 12 thus allowing the further movement of linkage 16 and the consequent movement of bolt 10 to a position 30 allowing disengagement from anchor 8.

P \OPER\RSH\pq6863-QO ramset cap doc-28/07/00 Figure 13 illustrates a modified form of the embodiment shown in Figures 10 and 11. In this embodiment the chain 38 connected at one end to the shackle plate 4 is connected at its other end to a lug 50 which forms an extension of the first link 14. The 5 connection of the chain 38 to the first link 14 rather than to the third link 16c as described in connection with the embodiment of Figures 10 and 11 provides substantial advantage in a rigging set-up in which the shackle plate of the illustrated clutch is connected to the shackle plate of a lower clutch via a lifting cable passing around an upper pulley. In a rigging set-up of that type, when the load on the lifting cable is 10 released the shackle plate of the lower clutch might lower for example to a horizontal position to facilitate release of that clutch, but the shackle plate of the upper clutch might itself remain in a more upright position whereby release of the upper clutch is prevented notwithstanding absence of lifting load on the lifting cable. Although in principle it is possible to lower the shackle plate of the upper clutch by pulling on the release rope or 15 cable 22a of that clutch, the force required to lower the shackle plate through the connection effected by the chain 38 acting via link 16c is very substantial as the load applied to the shackle plate of the upper clutch to lower that shackle plate needs also to "lift" the dead weight of the shackle plate of the lower clutch and a substantial part of the lifting cable linking the two shackle plates. In the modification of Figure 13, by coupling 20 the lower end of the chain 38 to the first link 14 rather than the third link 16c, application of force applied by the rope or cable 22a to the link 16c is amplified by the lever action of the second link 16 prior to application of the force to the chain 38 to lower the shackle plate. As a result of this modification, the force needed to be applied to the release rope or cable 22a to effect lowering of the shackle plate in a rigging set-up 25 as described above after removal of the lifting force is substantially reduced.

In this modified version, the upper end of the third link 16c engages the underside of the lug 50 if the link 16c is rotated upwards in a clockwise direction from the position illustrated in Figure 13. This interengagement produces a camming action which has the 30 effect of pivoting the link 16 outwardly through its over-centre locked position thereby P \OPER\RSH\pq6863-00 ramset cap doc-28/07/00 facilitating release of the clutch. This alternative release mode is effected by an operator directly manipulating the link 16c which then acts as a release handle.

The modifications just described with reference to Figure 13 still retain the safety 5 effect achieved by the chain 38 to prevent accidental release of the clutch while there is still lifting load present in the lifting cable.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention.

Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims (12)

P \OPER\RSH\nz506099 spe doc-06/08/01 15- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. A clutch for use in lifting of concrete components, comprising an annular clutch body engageable over the head of a lifting anchor, an arcuate locking bolt movable within 5 the clutch body between an engaged position in which the bolt extends through an eye in the head portion of the anchor and a released position to permit removal of the clutch body from the anchor, and a remote release system for releasing the clutch from the anchor from a remote position such as the ground after erection of the component, said remote release system comprising an over-centre linkage connected to the bolt and actuated to release the 10 bolt by a downwards pull applied by a flexible element such as a rope or cable, said over-centre linkage being in an over-centre condition when the bolt is in its engaged position such that the linkage locks the bolt in its engaged position, and the release system including means preventing release of the bolt by pulling the flexible element at an angle less than a predetermined angle to the face of the component. 15

2. A clutch according to claim 1, wherein when the bolt is in its engaged position, the bolt is subject to a resilient bias which acts in a sense to retain the mechanism in its over-centre condition. 20

3. A clutch according to claim 1 or claim 2, wherein the over-centre linkage comprises an outer link pivotally mounted within a housing carried by the body of the clutch and an inner link pivoted at one end to the outer link and at another end to the clutch bolt, the flexible element acting on a part of the outer link remote from its pivotal mounting. 25

4. A clutch according to claim 3, wherein in the disengaged position of the bolt, a substantial part of the outer link lies externally of the housing to provide visual indication of that state. 30

5. A clutch according to claim 3 or claim 4, wherein in the erected condition of the component the housing extends downwardly from the clutch body adjacent a vertical face P \OPER\RSH\nz5()6()99 spe doc-07/08/01 -16- of the component and during the release action a lower part of the housing fulcrums against that face to facilitate release.

6. A clutch according to claim 1 or claim 2, wherein the over-centre linkage is 5 mounted within a housing carried by the body of the clutch.

7. A clutch according to claim 3 or claim 6, wherein release of the bolt by pulling the flexible element at an angle less than a predetermined angle is prevented by the configuration of the housing. 10 15

8. A clutch according to any one of claims 1 to 7, comprising a flexible link interconnecting a shackle plate of the clutch and the over-centre linkage, whereby the release system is prevented from disengaging the clutch from the anchor whilst there is lifting load on the shackle plate.

9. A clutch according to claim 3 or any claim dependent on claim 3, wherein the over-centre linkage comprises a further link coupled to the outer link, the flexible element being coupled to the outer link via the further link. 20

10. A clutch according to claim 9, wherein release of the locking bolt can also be effected by upwards movement of the said further link acting as a handle for direct application of manual force.

11. A clutch according to claim 3 and claim 8, wherein the flexible link is connected to 25 the said inner link of the linkage.

12. A clutch substantially as hereinbefore described with reference to the accompanying drawings. 30 DATED this 7th day of AUGUST By DAVIES COLLISON CAVE Patent Attorneys for the Applicant