GB2263059A

GB2263059A - Attachment of legs to support platform

Info

Publication number: GB2263059A
Application number: GB9126895A
Authority: GB
Inventors: John Wilfrid Phillips
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1991-12-19
Filing date: 1991-12-19
Publication date: 1993-07-14
Anticipated expiration: 2011-12-19
Also published as: FR2685400B1; GB2290230A; GB2290230B; DE4243082A1; GB2263059B; GB9516595D0; FR2685400A1; GB9126895D0

Abstract

A shock absorbing device suitable for attaching a tripod leg (2) to a support platform (4) incorporates a slipping clutch mechanism (13). The slipping clutch serves to absorb any shock suffered as a result of the tripod being dropped in a "legs deployed" position. Hence the legs (2) are less likely to buckle under impact. … <IMAGE> …

Description

1 2263059 ATTACHMMIT ARRMGEMENT This invention relates to an attachment

arrangement which is particularly suitable for attaching a tripod's legs to its base.

one object of the invention is to provide a quick release mechanism for allowing the legs to be quickly and easily adjusted from one locked position to another, thereby adjusting the tripod height.

Another object of the invention is to provide a tripod which will not fail when dropped onto its legs.

A further object is to provide a light-weight tripod.

One type of energy-absorbing design known to the Applicants comprises a bellows moulded as an integral part of the tripod leg. The purpose of the bellows is to absorb energy, elastically and plastically. However, it was discovered that, particularly when titanium was used as a light-weight material, the bellows would split under a drop test.

Accordingly this invention comprises an arrangement for attaching a supporting leg to a platform in which the arrangement incorporates a slipping clutch mechanism.

The provision of a slipping clutch lessens the damage to a tripod incorporating such an arrangement if the tripod should be dropped when in a "legs deployed" position. The slipping clutch is configured to-Allow rotation of the legs about their points of attachment to the platform. The shock 2 - is thus "absorbed" by the slipping clutch and the legs are less likely to fail. The amount of torque required to initiate slipping may be varied by choice of friction material and/or compressive loading thereof.

According to another aspect of this invention, an arrangement for attaching a supporting leg to a platform comprises inter-operable toothed components and means for releasing said toothed components, one from the other, to enable adjustment of the legs with respect to the platform.

Each toothed component may comprise a cylindrical member having a plurality of circumferential rows of teeth. For example, one member would have an inner toothed surface and the second member would have an outer toothed surface. Such an arrangement thus has the form of a discontinuous spline. The greater the number of rows, the stronger the coupling between the two members. Each row of teeth may be on a different diameter, to facilitate manufacture of the toothed components by an injection moulding process..

An embodiment of the invention will now be described, by way of example only, with reference to the drawings, of which:

Figure 1 is a plan view of a tripod in accordance with the invention; Figure 2 is a cross-sectional view of one of the three attachment arrangements comprising the tripod of Figure 1; z Figures 3 and 4 are perspective views of internal parts of the arrangement of Figure 2; and Figure 5 is a perspective view of the upper part of a leg comprising the tripod of Figure 1.

in Figure 1, a tripod 1 consists of three legs 2 with non-slip, shock absorbing, elastomeric coated feet 3, mounted symmetrically about a centre hub 4. The legs 2 are of fixed length and can be adjusted outwards from the vertical position, to raise or lower the tripod hub 4 with respect to the ground. The height is adjustable in discrete steps.

The height adjustment mechanism consists of two toothed components made from a fibre-reinforced plastics material which are engaged under spring pressure. The inner toothed component 5 of Figure 4 is splined onto a main shaft 6 (see Figure 2) and the outer toothed component 7 of Figure 3 is attached to the top of the leg 2. The outer toothed component 7 has a splined outer surface. Splines 7a interlock with co-operating castellations 2a incorporated at either side of each leg 2 (see Fig. 5). Adhesive Is applied to the relevant surfaces to ensure a rigid joint. The teeth 8 on each of components 5 and 7 are disengaged by operating a lever 9 at the top of each leg 2. The leg 2 can then be rotated about the main shaft 6 to adjust the tripod height. The amount of rotation required to adjust the tripod height from one discrete step to the next is set by the width of the teeth 8 on each toothed component 5 and 7. The teeth 8 are tapered to facilitate engagement.

The legs 2 are made from super-plastically formed titanium, for strength and lightness. The levers 9 are made as plastics injection mouldings in a long fibre glass reinforced "nylon 66". The main shaft 6 is machined from solid titanium.

Referring to Figure 2, each of the three main shafts 6 is attached to the hub 4 by using two disc springs 10 and a nut 11 which screws onto the main shaft 6 so as to clamp radial webs 12 which form part of the hub structure. Friction pads 13 are also incorporated into this clamping arrangement to form a slipping clutch mechanism for protecting the tripod under drop conditions.

The disc springs 10 need to perform a number of functions. They must provide an adequate clamping load on the friction pads 13 and they must transfer torsional drive between the main shaft 6 and the friction pads 13. They also need to transfer bending moments from the main shaft 6 to the hub 4 so that the whole assembly is sufficiently rigid. To achieve the latter two requirements satisfactorily, a hexagon drive between main shaf t 6 and disc springs 10 is recommended, i.e. the disc springs 10 have a hexagonal aperture and the outer surface of the main shaft 6 is correspondingly configured at the appropriate locations along its length.

The compression of the disc springs 10 and thus the frictional effect of the friction pads 13 can be varied by either tightening or slackening the nut 11.

The height adjustment mechanism is facilitated by a coil spring 14 which is held between inner and outer spring housings 15 and 16 respectively. The inner spring housing 15 is secured to a flanged portion of the main shaft 6 by a bolt 17. The outer housing 16 is provided with a flanged end 16a which latches into a detent 7b provided on the outer toothed component 7. The preferred material for the outer spring housing 16 is fibre-reinforced plastics.

The coil spring 14 is compressible under the action of the lever 9, the lever being attached to the outer toothed component by a pivot pin 18.

To unlock a leg 2 f rom the main shaft 6 so that the height of the tripod 1 may be adjusted, the lever 9 is pulled towards the leg 2, manually. In so doing, the outer toothed component 7 is drawn away from and out of engagement with the inner toothed component 5. By virtue of the interlocking detent 7b and flange 16a, the outer spring housing 16 is also pulled along the main shaft 6 with the outer toothed component 7, thereby compressing the spring 14.

While a compressive load is exerted on the lever 9, the inner and outer toothed components (5 and 7) remain disconnected from one another, thus enabling rotation of the leg 2 about the longitudinal axis of the main shaft 6.

Compressive load is transferred from the lever 9 to the height adjustment mechanism via a pressure piece 19 (formed at the lever end of the inner spring housing 15) and an actuating cap 20 (forming part of the lever moulding). These two components (I.e. pressure piece 19 and cap 20) are shaped so that the compressive load is as co-incident with the main shaft's axis as possible. This precaution reduces any tendency for the outer spring housing 16 to jam, or for the inner spring housing 15 to fail under bending.

When the leg 2 (along with the lever 9 and the outer toothed component 7) have been rotated to the desired position, the lever 9 is released. Under the restoring force of the spring 14, the outer spring housing 16 slides back along the main shaft 6 pulling the outer toothed component 7 with it and allowing the lever 9 to pivot back to its initial position. Thus the outer toothed component 7 slides into engagement with the inner toothed component 5 and the leg 2 is locked into its new position.

Under normal operating conditions, the main shaft 6 remains rigidly attached to the hub web 12. This is achieved by virtue of the friction pads 13 which are clamped tightly against the web 12 by the main- shaftmounted disc springs 10. The disc springs 10 are held between a shoulder 6a provided on the main shaft 6 and-the nut 11.

i 7 - Should the tripod 1 be dropped onto its feet 3, the shock suffered may be sufficient to overcome the friction between the friction pads 13 and the web 12. In this case, the disc springs 10 will slip with respect to the web 12, allowing the main shaft 6 and all components attached thereto including the leg 2, to rotate about the hub 4. Thus, instead of failing under the shock, the legs 2 rotate about the hub 4.

The degree of shock sustainable by the tripod before slipping occurs can be varied by either tightening or slackening the nut 11. The point at which slipping occurs is also a function of the type of material comprising the friction pads 13 and this may be varied also to suit requirements.

4

Claims

An arrangement for attaching a supporting leg to a platform, said arrangement incorporating a slipping clutch mechanism.
2. An arrangement as claimed in claim 1 in which the leg is carried on a main shaft, the main shaft is clamped to the platform by means of disc springs, and in which the slipping clutch incorporates friction pads held between the platform and the disc springs.
3. An arrangement as claimed in claim 2 in which each disc spring is provided with a hexagonal aperture which co-operates with a corresponding hexagonally- shaped portion of the main shaft.
4. An arrangement according to any preceding claim further including inter-operable toothed components and means for releasing said toothed components, one from the other, to enable adjustment of the legs with respect to the platform.
5. An arrangement for attaching a supporting leg to a platform, said arrangement comprising inter-operable toothed components and means for releasing said toothed components, one from the other, to enable adjustment of the legs with respect to the platform.

A
6. An arrangement as claimed in claim 4 or claim 5 in which the inter-operable toothed components each comprise a cylindrical m emb er having a plurality of circumferential rows of teeth and in which a f irst toothed component has a toothed inner surface and a second toothed component has a toothed outer surface.
7. An arrangement as claimed in claim 6 in which each of said circumferential rows of teeth on each respective one of said toothed components are located on different diameters.
8. An arrangement as claimed in claim 7 in which each toothed component is made from fibre-reinforced plastics material.
9. An arrangement as claimed in any of claims 4 to 8 in which the means for releasing said toothed components comprises a spring-loaded lever.
10. An arrangement as claimed in any of claims 4 to 9 in which the leg is provided with castellations which interlock with splines incorporated on the outer surface of the first toothed component.
11. A tripod incorporating an arrangement as claimed in any preceding claim.
12. A tripod substantially as hereinbefore described with reference to the drawings.