GB2200402A

GB2200402A - Clamping device for telescopic members

Info

Publication number: GB2200402A
Application number: GB08800924A
Authority: GB
Inventors: Ilan Zadik Samson
Original assignee: Roberts Consolidated Industries; Roberts Consolidated Industries Inc
Current assignee: Roberts Consolidated Industries; Roberts Consolidated Industries Inc
Priority date: 1987-01-16
Filing date: 1988-01-15
Publication date: 1988-08-03
Anticipated expiration: 2008-01-15
Also published as: GB2200402B; GB8701051D0; GB8800924D0

Abstract

A clamping device for attaching a first telescopic member 8 to a second member 12 comprises engaging means 1, 2 having at least two parts for engaging the first member 8 and defining an internal conical space, cones 3, 4 to fit within the conical space for sliding contact with the engaging means, rubber band 5 for urging the engaging means towards the cones radially, the cones being operatively connected to the second member 12 by rods 9, 18 and movable therewith in the direction from the base to the apex of the cone, a compression spring 10 for pressing the cones axially into the conical space to force the engaging means 1, 2 apart against the force of the rubber band 5 and operating means 17, 18 for moving the cones relative to the engaging means. The static coefficient of friction mu , between the inner surface of the engaging means and the surface of the cones, and the dynamic coefficient of friction mu 2 between the outer surface of the engaging means and the inside of the first member are arranged to be in accordance with the equation mu 2 > <2> mu . <IMAGE>

Description

Device This invention relates to a locking. device which may be used to lock in any 'desired position tubes that mate together.

Tubes that mate together by fitting slidably one inside the other have a variety of industrial applications. One such application is in the field of carpet installation in which it is necessary to use a tubular assembly to connect, often over a considerable distance, carpet stretcher having teeth which grip a carpet to its corresponding tail block which bears against a wall. A carpet stretcher that works on this principle is described in U.S. Patent No. 362,278.

The tubular assembly used for the above purpose nor.~~5ly comprises one or more larger, or female, steel tubes and one or more smaller, or male, steel tubes which fit within the larger tubes. The male and female tubes are interlocked with spring biased clips or buttons that fit into diametrically opposed apertures formed in the walls of each tube Locking means of this kind suffers from the disadvantage that it is possible to interlock the tubes only at certain relative positions since locking can only be accomplished where pre-formed apertures exist.

Furthermore, whenever it is necesary to, increase, or reduce, the length of the tubular assembly (as it frequently is when laying carpets), the spring based clips have to be urged inwards and subsequently released to protrude through the appropriate apertures.

Other means for interlocking mating tubes for example tubes used in scaffolding, include pns or bolts which pass through apertures formed in each bube Such locking means suffer from similar disadvantages to those described above.

The present invention overcomes, or at least mitigates, the disadvantages associated with conventional means for interlocking mating tubes. It solves the problem of designing a locking device which does not rely on the existence of preformed apertures in the mating tubes and allows the tubes to be rapidly unlocked, slid to any desired relative position, and locked in that position with minimal annual intervention, Accordingly, the present invention provides a device for attaching a first member to a second member, which device comprises:: (2 t engaging means having at least two parts for engaging the inside of the first member, the engaging means defining internally a conical space, (b) a cone to fit within the conical space for sliding contact with the engaging means, the cone being operatively connected to the second member in use and movable therewith in the direction from the baee to the apex of the cone, (c) a first biasing means for urging radially the engaging means towards the cone axis against the cone, (d') a second biasing means pressing the cone axially .lnto the conical space to'force the engaging means apart against the first, biasing means, and (e) means for mov.ing the cone relative to the engaging means against the action of the second biasing means, with the proviso that, in use, the static coefficient of friction ul between' th'e.inner surface of the engaging means and the surface of the cone and the dynamic coefficient of friction uS between the outer surface of the engaging means and, the inside of the first member are in accordance with the equation ;2 > Su1.

Suitably the engaging means comprises at least two, preferably at, least three, segments of circular cross-section surfaced on the outer surface that engages the second member with a material having a high coefficient of friction, which is asbestos-free.

Advantageously, the inner surface of the engaging means is polished.

Surfacing materials known to be suitable for use in brake linings or friction wheels are excellent for the above purpose, for example friction materials sold by Ferodo (RTM) under the names Ferodo RC, .Ferodo 3908r, Ferodo 3901F and Ferodo FF, provided that u1 is suitably low.

A further valuable surfacing material is that conventionally used in engine or machine mounting pads.

Such materials may be bonded to the outer surface of the engagement means using conventional bonding materials.

Suitably the engagement means comprises a light durable metal, especially aluminium.

The relative coefficient u2 as hereinabove defined is noramlly within the range 0.3 to 0.6, preferably within the range 0.4 to 06 and should not be reduced appreciably at elevated pressures.

Suitably the cone is constructed from, or surfaced with, a material having a relatively low coeffioLent of friction and the value of ;1 as hereinabove defined should normally be within the range 0.05 to O.J, preferably within the range 0105 to 0.2.

Suitably the cone is constructed from a toughened plastics material, or from toughened Teflon (RTM) or nylon.

Preferably the cone is made from a nylon material such as the material available from Du Pont under the Trade Mar.k Delrin.

The first liasing means is conveniently constructed of an elastic material which is stretched around the engaging means in such a way that it does not interfere with the engagement of the inside of the first member. Preferably the first biasing means comprises one or more rubber bands which are positioned in one or more grooves formed around the outer surface of the engaging means.

Alternatively, the first biasing means may be a circular clip of resilient material or an annular coil spring of metal or plastics.

The second biasing means is preferably a compression spring which may be operatively connected to the cone by any convenient method.

Preferably the second biasing means is housed within the second member.

In a preferred embodiment of the invention the second biasing means is operatively connected to the cone by an incompressible rod or cable, which is also the means for moving the cone relative t,o the engaging means.

Preferably the rod passes through the axis of the cone for sliding contact therewith and the bias of the compression spring is transmitted to the cone by an abutment fixed to the rod for abutting the cone or the engagement means. The abutment may suitably comprls,.for example, a rim, lip or pin and/or one or more washers.

In a particularly preferred embodiment of the invention, the rod or cable comprising the means for moving the cone. relative to the engaging means is connected to a lever which is readily accessible to an operator.

In 2 rurtner preferred embodiment the second member to which the device of the, invention is attached in use, or upon which it is permanently mounted, is a male carpet stretcher tube. A lever for moving the means for moving the cone relative to the enaging means may conveniently protrude through an aperture formed in the well of the stretcher tube.

In use, the device of the invention exerts its locking.action by virtue of the frictional force that is produced when the external surface of the engaging means is in contact with the inside of the first member.

Whenever the second member is moved so as to move the cone in the direction from the base to the apex of the cone then the outer surface of the cone slides against the inner surface of the engaging means causing the outer surface of the engaging means to be pushed radially outwards The frictional force resisting movement of the device within the second member is thereby increased.

It may be calculated that, for effective locking, i.e. for the frictional force between the engaging means and the first member to exceed the force with which the cone is being pushed into the engaging means, there are constraints on the relative values of u1, u2 and α wherein α is half the conical angle.The constraints just referred to are related as follows:- tan mC < u2 1 + 1 u2 (1) This can be approximated to: tan or > t C U2 - It may also be calculated that for effective unlocking without ramming i.e. due to the first biassing means, angle L and the relative coefficient of friction 1 must satisfy the equation: tan ot > un 12) In practice, values for w norinally fall within the range 10 -17 .

From formulae (1) and (2), it can be shown that

This can be approximated to LL; u1 It will be apparent from the foregoing description that a device of the invention complsing one cone will lock the first and second members together against a compression force acting axially towards the top of the cone but will not prevent the two membes being separated if an external force acts in the opposite direction.

Accordingly, for certain applications, the device of the invention preferably has two mutually opposed.

cones. Such a device will effectively prevent relative movement of the first and second members in any direction.

In this embodiment the two engaging means are convenientiy integrally formed.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a locking device in accordance with the invention in use, and Figure 2 is a cross-sectional view on the line X-X of Figure 1.

Referring.ta the Figures, a locking device has two aluminium engaging means 1, 2 which are integrally formed with each other, each being constructed from three segments of circular cross-section 1A, 1B, 1C, 2A, 2B, eC.

The segments of the engaging means 1, 2 are pressed against Delrin cones 3, 4 by a rubber band 5 stretched round a groove 6 at the point at which the engaging means 1, 2 are fused, Each segment 1A, lP, 1C, 2A, 2B, 2C is surfaced with a strip of machine mounting pad 7 which in use grips the ,inside wall of a female carpet stretcher tube 8.

The cones 3, 4 are slidably mounted on a rod 9 which is connected to a compression spring 10 mounted within a housing 11 inside a male carpet stretcher tube 12. The rod 9 passes through a journal 13 and through the axis of each cone 3, 4. The bias of the spirng 10 is transmitted to cone 4 via washers 14 held on the rod 9 by a spring clip 15. ' The base of the cone 3 is fixed to the male tube 12 by screws 16. A lever 17 is connected to the rod 9 by a bar 18.

In use, the desired relative position of the female tube 8 and the male tube 12 may be adjusted by manual operation of the lever 17 to move the rod 9 longitudinally against the bias of the spring 10, thereby disenaging the surface 7 of the engaging means 1, 2 from the inside of the female tube 8. The mare tube 12 may then be slid within the female tube 8 to any desired position. Locking may be effected by releasing the lever 17 whereupon the surface 7 of the engagi'ng,means 1, 2 is once again pressed agains tht einside of the female tube 8.

Provision of a spring biased clip 19 allows the male carpet stretcher tube 12 to be connected, in conventional manner, to a,further female carpet stretcher tube (not shown) in.a tubul'ar assembly, the length of which may be rapidly altered using the device of the invention.

The values of α M1 and 2 are in the relationships discussed above.

Claims

Claims

1. A device for attaching a first member to a second member, comprising: (a') enga,ging means having at least two parts for engaging the inside of the first member, the engaging means designing internally a conical space, (b) a cone to flt within the conical space for sliding contact with the engaging means (c) a first biasing means for urging radially the engaging means towards the cone axis against the cone, the cone being operatively connected to the second member in use and movable 'herewith In the direction from the base ,to the apex of the cone, (d) a second biasing means pressing the cone axially into the conical space to force the engaging means apart against the first biasing means, and (e) means for moving the cone relative to the engaging k means against the actionof the second biasing means, with the proviso that the static coefficient of friction 1 between the inner surface of the engaging means and the surface of the.cone and the dynamic coefficient of friction U2 between the outer surface of the engaging means and the inside of the first member are in accordance with the equation

2 > 2 1 2. A device as claimed in claim 1 in which the engaging means is of circular cross-section.

3. A device as claimed in claim 1 or claim 2 in which the engaging means.has at least three parts.

4. A device as claimed in any preceding claim in which the -conical angle of the cone is 2 α where α lies in the range, of from 100 to 17t (both limits included).

5. A device as claimed in any preceding claim in which the first biasing mea.ns comprises an elastic band, a circular clip of a resiiient material, or a cor spring of metai or plastics.

6. A device as claimed in any preceding claim in which the second biasing means comprises a compression spring.

7. A device as claimed in any preceding claim in which the second biasing means is housed within the second member.

8. A device as claimed in any preceding claim in which the means for moving the cone relative to the engaging means comprises en incompressible rod or cable.

9. A device as claimed in claim 8 in which the means for moving the cone relative to the engaging means additionaily comprises an abutment fixed to the rod for abutting th cone or the engaging means.

10. A device as claimed in claim 8 or claim 9 in which the rod passes through the axis of the cone, the cone being- fixed or slidable on the rod or cable.

11, A-device as claimed in any one of claims 8 to 10 in which the rod or cable can be moved by a lever which is accessible to an operator.

12. A device as claimed in any preceding claim in which the engaging means is surfaced with a material suitable for use in brake linings.

'13. A device as claimed in any one of claims 1 to 11 in which the engaging means is surfaced With material conventionally used as engine mounting pads.

14. A device as claimed in any preceding claim in which the engaging means comprises aluminium.

15. A device as claimed in any preceding claim in which the cone comprises toughened nylon.

16. A device as claimed in claim 15 in which the cone comprises Delrin or Tefldn.

17. A device as claimed in any one of the preceding claims in combination with a sad second member to which it is mounted, wherein the second member is a carpet stretcher tube.

18. A device as claimed in any one of the preceding claims in which tan ot 2 Ul where is half the conical angle of the cone.

39. A device as claimed in any one of claims 1-17 in which tan CL u2 - ul

1 + U1 U2 where d is half the con,cai angle of the cone, 20. A device as claimed in any one of claims 1-17 in which

21. A device as claimed in any one of claims 1-17 in which > < 22. A device substantially as herein described with reference to the accompanying drawings;