GB2300681A

GB2300681A - Telescopic joint

Info

Publication number: GB2300681A
Application number: GB9509409A
Authority: GB
Inventors: William Charles Kingham Heller
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-05-10
Filing date: 1995-05-10
Publication date: 1996-11-13
Also published as: GB9509409D0

Abstract

A telescopic joint (10) has inner and outer cylindrical members (20,30). The inner member (30) has a series of recesses (60,60') formed in it, located in one of which is an O-ring or garter spring (40). The end (50) of the outer member (20) is flared to provide a sloped interior surface. In use, the inner member is slid into the outer member until the ring (40) abuts this inner surface of the end portion (50). An axial force F applied to the joint causes the flared end portion (50) to compress the ring (40) in a direction F' both radial and axial, preventing the ring from shearing out of the recess (60) whilst providing a strong joint. The relative positions at which the inner and outer tubes (20,30) engage may be altered by removing the ring (40) from the recess (60) and rolling it into one of the other recesses (60'). The joint finds application in such articles as camera monopods and wading staffs.

Description

Telescopic Joint This invention relates to a telescopic joint.

A number of different techniques are known which allow two or more telescoping members, such as camera tripod legs, to be releasably locked together at different positions along the members' lengths.

One such joint consists of two generally tubular members, the outer diameter of one being smaller than the inner diameter of the other to provide a sliding fit. One end of the outer member is formed of a resilient material which is tapered to form a frustoconical portion. This part cone has a series of radially spaced slots extending from the smaller end of it along a portion of its length, and an axial hole of a diameter slightly larger than the external diameter of the inner member. A thread is cut into the outer wall of the outer member to the rear of the frustoconical end portion. In use, a collar having an internally threaded cam is placed onto the inner member, the latter then being slid into hole in the frustoconical portion of the outer member.To lock the inner member in a desired location relative to the outer member, the collar is slid along the inner member and over the part conical section of the outer member. Rotating the collar then causes its internal thread to engage with the external thread on the outer member, the internally formed cam thereby compressing the slots in the frustoconical portion and locking the outer member against the inner member.

The problem with this and other known telescoping joints is the maximum load they can bear. Even if a substantial torque is applied to the collar in the above joint, so that the slotted frustoconical portion grips the inner member firmly, it will be apparent that the compressive force which grips this member acts in a radial direction only. The load placed on this joint in use, however, is substantially axial. Thus, the joint can only bear relatively small loads, and is suitable solely for applications such as camera tripods and the handle of fishing nets.

It is an object of the present invention to provide a telescoping joint which alleviates the problems of the prior art.

According to the present invention there is provided a telescopic joint comprising first and second cylindrical members arranged to be slidably moveable relative to one another, the first member having a recessed portion containing engagement means, the engagement means abutting a portion of the second member to prevent movement of the second member past the engagement means.

In use, an axial force is applied to this joint thus compressing the second member against the engagement means. Because the engagement means is located in the recess, the former cannot dislodge from the latter and merely compresses further into the wall of the recess.

The axial force which may be applied to such a joint is significantly higher than that which may be applied to prior art joints, and thus permits a range of applications, e.g. in chair and table legs, to be realised.

Preferably, the first member is an inner member which is a slidable fit within the second, outer member. This inner member may have a plurality of recessed portions, and the engagement means may be moveable between these.

The plurality of recesses permits the two members to be engaged at different relative positions, and thus, for example, the outer member may be raised or lowered relative to the inner. Preferably, the plurality of recessed portions are spaced substantially equidistantly along the inner member.

Preferably, the second member has a tapered inner portion against which the engagement means may abut. This minimises any risk of the engagement means shearing out of the recess.

The angle of taper of this tapered inner portion may be between 10 and 30 , and preferably 20 . In one embodiment, this taper has a seat at its narrower end. This seat permits even heavier loads to be borne.

The diameter of the engagement means in use may be substantially identical with that of the seat.

The engagement means may be a ring in the form of an O- ring or garter spring, depending on the load to be applied to the joint. In such arrangements, the ring should have a degree of resilience to allow it to be moved when it is not in engagement between the first and second members.

The depth of the recess is preferably such that the outer radius of the ring when in said recess is larger than the outer radius of the first member.

The invention also extends particularly, but not exclusively, to a wading staff or camera monopod having the joint of the present invention.

The present invention can be put into practice in various ways which will now be described by way of example with reference to the accompanying drawings in which : Figure 1 is a sectional view of a first embodiment of a telescopic joint according to the present invention; Figure 2 is a perspective view of a wading staff incorporating the joint of figure 1; and, Figure 3 is a sectional view of a second embodiment of a telescopic joint according to the present invention.

The joint 10 of figure 1 consists of two coaxial cylindrical tubes, circular in section, the inner tube 30 being a slidable fit within the outer tube 20. A series of axially equidistant recesses 60, 60' are formed in the circumference of the inner tube 30, for example by turning or pressing a series of grooves in its surface.

In one exemplary joint, the inner and outer tubes are formed of aluminium, although nylon or other plastics materials may be employed depending on the load to be borne. The inner tube 30 has an external diameter of 18 mm and a 1 mm wall thickness; the outer tube 20 has an internal diameter of 19 mm and a 1.5 mm wall thickness.

The recesses are formed by pressing as may be seen from the Figure, to produce a generally U-shaped groove the minimum external diameter of which is 15 mm.

The end of the outer tube 20 is flared to a maximum external diameter of 23 mm, suitably by using pipe expanders, to produce a tapered profile end portion 50.

Again depending on the maximum envisaged load on the joint, either a rubber O-ring or a metal garter spring 40 of internal diameter 15 mm and approximately 2.5 mm thick when unstressed may be used. This is rolled onto the inner tube 30 until it drops into the desired recess 60.

The inner tube is then slid into the outer tube 20 (i.e., the inner is pushed from left to right in the Figure relative to the outer), until the ring 40 slides inside the tapered end portion 50. As will be appreciated from the above exemplary dimensions, the outer diameter of the ring 40 is slightly greater than the internal diameter of the outer tube 20 but less than the maximum diameter of the flared end of the pipe 50. Thus the ring comes to rest against the tapered interior surface of the flared end portion 50.

Owing to the tapered shape of this portion 50, application of an axial load F to the joint causes the ring 20 to be forced in a direction F' having both a radial and axial component. The reaction against the axial component thus provides the strength to the joint, whilst the reaction against the radial component locks the ring 20 in the recess 60. It is thus necessary that the angle of taper of the flared portion's inner surface 50 be neither too steep nor too shallow: if too steep, an insufficient radial component is generated, and if too shallow, the O-ring (especially if made of rubber) may become wedged in the region 70 indicated in Figure 1.

Suitably, the angle of taper is about 20 .

It will be apparent to the skilled person that the joint described above will still operate and provide the strength advantages of the invention even if the flared portion 50 is omitted. In this case, however, the outer tube 20 will then press against the ring 20 along a line substantially parallel to the direction of force F. There is then an increased risk that the ring 20 will be caused to spring out of the recess 60 because there is no radial component of force holding it in place.

The adjustable nature of the joint will now be described with reference to Figure 2, which shows one exemplary application of the joint described above.

It is sometimes necessary for an angler.to enter a river, for example, in order to avoid entanglement of the fishing line and hook with trees and bushes on the banks of the river. When fishing for salmon or trout, the river tends to be fast flowIng and it is common practice to use a stick or staff to assist balance. This may, for example, be the handle of a landing net.

The problem with known wading staffs is that they tend to be of fixed length. This is inconvenient since the depth of a river can vary significantly.

A wading staff 100 incorporating the joint of the present invention has a handle 120 with a strap 110, together with a shaft 20 which corresponds to the outer tube 20 of Figure 1. A leg portion 30, again corresponding to the inner tube 30 of Figure 1, telescopes inside the shaft 20. A foot 130, having a removable felt pad on its base, is provided at the end of the leg distal from the shaft.

To set the desired length of the wading staff, a rubber O-ring (not shown) is rolled along the leg until it drops into the desired recess 60'. The leg 30 is then pushed into the shaft 20 until the O-ring abuts the flared end portion 50, as already described. Air damping is conveniently provided inside the shaft 20 so that the 0 ring does not immediately drop away from the flared portion 50 under gravity once the staff is held upright.

In order to readjust the length of the staff, the leg 30 is pulled away from the shaft 20 until the O-ring is exposed. The ring can then be rolled into one of the other recesses 60' to shorten or lengthen the staff.

It has been found that a staff using this joint can bear a substantial load - certainly well in excess of the full weight of the human body leaning upon it. Furthermore, the O-ring joint prevents ingression of water into the shaft 20 of the staff.

Figure 3 shows a second embodiment of the present invention, similar features to those in Figure 1 being labelled accordingly. Here, the profile of the end section 50' differs from that shown in Figure 1, and has been found to permit substantially heavier loads to applied to the joint. Once again the inner radius of the end portion 50 is tapered at an angle of around 20 , but the narrower end of the taper ends in a seat 55 which is machined to have a diameter identical with that of the compressed ring. In order to ensure maximum load bearing capability in this embodiment, the ring 40 is a garter spring.It will be appreciated that the modified profile of the end section 50' causes substantially all of the end seat 55 to push against the ring 40 in the recess 60 in the inner member, because of the relative diameters of the seat 55' and ring 40; the garter spring is thereby prevented from collapsing which is why the joint is able to bear heavier loads.

In the first embodiment of Figure 1, using a garter spring against the tapered inner surface of the outer member causes the outer member to rupture if too heavy a load is applied. This problem is alleviated by using the arrangement shown in Figure 3, because of the manner in which the outer member pushes against the ring 40.

There are a multitude of other applications envisaged for the joint described above. For example, a camera monopod using this joint would easily support a stills camera even if it had a heavy telephoto lens attached to it, with substantially no risk of the gradual shortening in length due to slipping of the joint which will be familiar to photographers. Such a monopod may have a handle to which a screw-in adapter for holding the camera may be attached.

Other applications include tables and swivel chairs, lamp and microphone stands and television monitors, as well as horse jumps and crowd control barriers. Inner and outer cylindrical members of other sectional shapes than circular are also envisaged - for example oval or square.

Claims

1. A telescopic joint comprising first and second cylindrical members arranged to be slidably moveable relative to one another, the first member having a recessed portion containing engagement means, the engagement means abutting a portion of the second member to prevent movement of the second member past the engagement means.

2. A telescopic joint as claimed in claim 1, in which the first member is an inner member which is a slidable fit within the second, outer member.

3. A telescopic joint as claimed in claim 1 or claim 2, in which the first member has a plurality of recessed portions.

4. A telescopic joint as claimed in claim 3, in which the engagement means is movable between the plurality of recessed portions.

5. A telescopic joint as claimed in 3 or claim 4, in which the plurality of recessed portions are spaced substantially equidistantly along the inner member.

6. A telescopic joint as claimed in any one of the preceding claims, in which the second member has a tapered inner portion against which the engagement means may abut.

7. A telescopic joint as claimed in claim 6, in which the angle of taper is between 15 and 25".

8. A telescopic joint as claimed in claim 7, in which the angle of taper is substantially 200.

9. A telescopic joint as claimed in any one of claims 6, 7 or 8, further comprising a seat at the narrower end of the tapered inner portion.

10. A telescopic joint as claimed in claim 9, in which, in use, the diameter of the engagement means is substantially identical to the diameter of the seat.

11. A telescopic joint as claimed in any one of the preceding claims, in which the engagement means is a ring in the form of an O-ring or garter spring.

12. A telescopic joint as claimed in claim 11, in which the depth of the recess is such that the outer radius of the ring when in said recess is larger than the outer radius of the member having the recess.

13. A telescopic joint as claimed in any one of the preceding claims in combination with a wading staff.

14. A telescopic joint as claimed in any one of the preceding claims in combination with a camera monopod.

15. A telescopic joint constructed and arranged substantially as specifically described with reference to and as shown in Figure 1, or as shown in Figure 2, or as shown in Figure 3 of the accompanying drawings.