AU2011253804B2

AU2011253804B2 - An improved locking mechanism

Info

Publication number: AU2011253804B2
Application number: AU2011253804A
Authority: AU
Inventors: Benjamin Hill; John Pitcher
Original assignee: Ames Australasia Pty Ltd
Current assignee: Ames Australasia Pty Ltd
Priority date: 2010-12-02
Filing date: 2011-12-02
Publication date: 2017-02-02
Anticipated expiration: 2031-12-02
Also published as: AU2011253804A1

Abstract

This invention relates to a locking mechanism for telescopic members which locks said members in an extended position, the locking mechanism comprising a first member slidably located within a tubular 5 second member, a follower comprising a neck portion and a shoulder portion inserted within the first member, and a head portion extending from the first member that is resiliently deflectable with respect to said first member by virtue of deflection of said follower neck portion at least, and a track means secured to the second member and defining at least one track, the follower engaging a first track as the first member is extended with respect to the second member, said first track being arranged so as to 0 deflect said follower head portion with respect to said first member as said follower moves along said first track, said track means further comprising a locking recess into which said follower head portion is released, said locking recess holding said follower head portion and preventing collapse of said telescopic members, thereby locking said telescopic members in an extended position. An associated clothesline assembly and supporting strut therefor are also disclosed. co co m4 00) (00

Description

2011253804 02 Dec 2011

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL

Regulation 3.2

Name of Applicant:

Hills Holdings Limited

Actual Inventors:

Benjamin Hill John Pitcher

Address for Service: C/- MADDERNS, GPO Box 2752, Adelaide, South Australia,

Australia

Invention title:

AN IMPROVED LOCKING MECHANISM

The following statement is a full description of this invention, including the best method of performing it known to us. 2 2011253804 02 Dec 2011

TITLE

AN IMPROVED LOCKING MECHANISM FIELD OF THE INVENTION 5 This invention relates to a locking mechanism which will be of use in applications requiring locking between telescoping members.

PRIORITY

This patent application claims priority from Australian Provisional Patent Application No 0 2010905313, titled “AN IMPROVED LOCKING MECHANISM”, and filed on 2 December 2010.

The entire content of this application is hereby incorporated by reference.

BACKGROUND

One example of a locking mechanism is described and illustrated in Australian Patent No 691055. 5 That specification describes how that locking mechanism can be employed in a clothes line assembly of the type described and illustrated in Australian Patent No 553302. Accordingly, the full content of both of these Australian patent specifications should be considered incorporated herein by way of reference. 0 Some users of the locking mechanism of Australian Patent No 691055 found that it was possible to overshoot the locking position during extension, causing the clothes line frame to drop, or be improperly secured in its extended (ie horizontal) position.

It is against this background that the problems and difficulties associated therewith that the present 25 invention has been developed.

Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. 30

SUMMARY OF THE INVENTION

In one aspect, the invention may be said to reside in a locking mechanism for telescopic members which locks said members in an extended position, the locking mechanism comprising a first member slidably located within a tubular second member, a follower comprising a neck portion and a shoulder 35 portion inserted within the first member, and a head portion extending from the first member that is resiliently deflectable with respect to said first member by virtue of deflection of said follower neck 3 2011253804 02 Dec 2011 portion at least, and a track means secured to the second member and defining at least one track, the follower engaging a first track as the first member is extended with respect to the second member, said first track being arranged so as to deflect said follower head portion with respect to said first member as said follower moves along said first track, said track means further comprising a locking recess into 5 which said follower head portion is released, said locking recess holding said follower head portion and preventing collapse of said telescopic members, thereby locking said telescopic members in an extended position.

In one form, the locking means further comprises a mechanism for releasing the locking to allow the 0 first and second members to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower head portion engaging the intermediate track as the first member is further extended with respect to the second member, the intermediate track being arranged to deflect the follower head portion with respect to the first member as said follower head portion moves along said 5 intermediate track, and an exit track spaced from the distal end of the intermediate track such that the follower head portion is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic members can retract when the follower head portion is located in the exit track.

In one form, the intermediate track comprises indication means for indicating to an operator that their 0 extension of the first member with respect to the second member is about to transition the follower head portion from the intermediate track to the exit track.

In one form, the indication means comprise one of more undulations in the intermediate track. 25 In one form, the intermediate track is aligned with the first track but separated from it by the locking recess.

In one form, the first and second members are of rectangular cross-section. 30 In one form, said follower comprises a spigot that engages the track of said track means.

In one form, said track means comprises a moulded polymeric component and wherein a pair of track means are provided, each of the track means located respectively on opposing inside upper and lower walls of said rectangular tube. 35

In one form, said follower comprises a further spigot so that there are a pair of spaced spigots that respectively engage said track means, said pair of spigots having a common central axis. 4 2011253804 02 Dec 2011

In a further aspect, the invention may be said to reside in a locking mechanism for telescopic members which locks said members in an extended position, the locking mechanism comprising a first member slidably located within a tubular second member of rectangular cross-section and upright orientation, a 5 follower attached to said first member that is resiliently deflectable with respect to said first member, and a track means secured to the second member and defining at least one track above and/or below the follower, the follower engaging a first track as the first member is extended with respect to the second member, said first track being arranged so as to deflect said follower with respect to said first member as said follower moves along said first track, said track means further comprising a locking 0 recess into which said follower is released, said locking recess holding said follower and preventing collapse of said telescopic members, thereby locking said telescopic members in an extended position.

In one form, the locking mechanism is in combination with a pivotable cantilever frame for supporting one or more clothes lines, wherein said locking mechanism and said telescopic members are used to 5 hold said frame in a raised position where said telescopic members are extended, and to release said frame to a storage position where said telescopic members are collapsed.

In a further aspect, the invention may be said to reside in a supporting strut for a pivotable cantilever frame for supporting one or more clothes lines, the supporting strut comprising a locking mechanism 0 as described above.

In a further aspect the invention may be said to reside in a clothesline assembly comprising a supporting strut as described above. 25 In a further aspect, the invention may be said to reside in a clothesline assembly comprising a frame which is pivotable between a substantially horizontal, raised position, and a substantially vertical, lowered position, and a supporting strut which swings through a substantially vertical arc of travel as the frame is moved between its raised and lowered positions, the supporting strut comprising a tubular strut body disposed over a strut rod so as to be telescopically shortened and lengthened, and an 30 internal, releasable locking mechanism which permits locking of the supporting strut at a length which sees it supporting the clothesline frame in its raised position, the locking mechanism comprising a follower attached to said strut rod that is resiliently deflectable with respect to said strut rod in a direction substantially orthogonal to the arc of travel of the supporting strut, and a track means secured to the strut body and defining at least one track, the follower engaging a first track as the strut rod is 35 extended with respect to the strut body, said first track being arranged so as to deflect said follower with respect to said strut rod as said follower moves along said first track, said track means further comprising a locking recess into which said follower is released, said locking recess holding said 5 2011253804 02 Dec 2011 follower and preventing collapse of said supporting strut, thereby locking said supporting strut in an extended position.

In one form, the locking mechanism for this further comprises a mechanism for releasing the locking 5 to allow the strut rod and strut body to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower engaging the intermediate track as the first member is further extended with respect to the strut body, the intermediate track being arranged to deflect the follower with respect to the strut rod as said follower moves along said intermediate track, and an exit track spaced 0 from the distal end of the intermediate track such that the follower is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic strut rod and strut body can retract when the follower is located in the exit track.

In one form, the frame and either of the strut rod or strut body are made from the same tubular 5 material.

In one form, the tubular material has a rectangular cross-sectional shape.

In a further aspect, the invention may be said to reside in a supporting strut for a clothesline frame 0 which is pivotable between a substantially horizontal, raised position, and a substantially vertical, lowered position, so that the supporting strut swings through a substantially vertical arc of travel as the frame is moved between its raised and lowered positions, the supporting strut comprising a tubular strut body disposed over a strut rod so as to be telescopically shortened and lengthened, and an internal, releasable locking mechanism which permits locking of the supporting strut at a length which 25 sees it supporting the clothesline frame in its raised position, the locking mechanism comprising a follower attached to said strut rod that is resiliently deflectable with respect to said first member in a direction substantially orthogonal to the arc of travel of the supporting strut, and a track means secured to the strut body and defining at least one track, the follower engaging a first track as the strut rod is extended with respect to the strut body, said first track being arranged so as to deflect said follower 30 with respect to said strut rod as said follower moves along said first track, said track means further comprising a locking recess into which said follower is released, said locking recess holding said follower and preventing collapse of said supporting strut, thereby locking said supporting strut in an extended position. 35 In one form, the follower comprises a neck portion and a shoulder portion inserted within the strut rod, and a head portion extending from the strut rod that is resiliently deflectable with respect to said strut rod by virtue of deflection of said follower neck portion at least. 6 2011253804 02 Dec 2011

In a further aspect, the invention may be said to reside in a clothesline assembly comprising a generally rectilinear frame of tubular material and a supporting strut for the frame comprising a first member slidably located within a tubular second member, wherein one of the first or second members 5 of the support strut is made of the same tubular material as the clothesline frame.

In one form, the tubular material is of rectilinear cross-section.

In one form, the tubular material is of rectangular cross-section. 0

In one form, the like rectangular material of both the frame and the support strut have the same orientation.

In one form, the like rectangular material of both the frame and the upright have an upright 5 orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of this disclosure it will now be described with respect to an exemplary embodiment which shall be described herein with the assistance of drawings wherein: 0

Figures 1 through 4 are exploded perspective views of a strut assembly with a locking mechanism, where Figure 4 provides a detailed view of track means from the strut assembly.

In the following description, like reference characters designate like or corresponding parts throughout 25 the several views of the drawings.

DETAILED DESCRIPTION

The invention has one use in a clothesline assembly comprising a generally rectangular frame supporting lengths of line which extend back and forth across the frame. The frame is supported in an 30 elevated (or extended) position, which is substantially horizontal, by a telescoping supporting strut assembly 1 which comprises a first member (or strut rod) 1A and a second tubular member (or strut body) 2. In use, the frame is lifted from its lowered position where it is substantially vertical to its elevated position, whereupon the first and second members 1A and 2 lock so as to hold the frame horizontal. In order to release the frame into its lowered position the frame is lifted to release the 35 locking mechanism between the first and second members 1A and 2. 7 2011253804 02 Dec 2011

With reference to Figures 1 through 3, it can be seen that the telescoping supporting strut assembly 1 comprises a first member or strut rod 1A of rectangular cross-section, a track means assembly 4, a follower 6 and a second tubular member or strut body 2 of rectangular cross-section.. 5 The track means assembly 4 comprises two halves, a top half 4a and a bottom half 4b in this case, which have slots or channels formed in a wall top wall in the case of the top half 4a, and a bottom wall in the case of the bottom half 4b so that these mirror one another. The halves 4a and 4b are designed to fit together to form a sleeve for insertion into a hollow end of the strut body 2. 0 The track means assembly 4 comprises tabs 5 for securing the track means assembly 4 within the end of the strut body 2 by locating in tab receiving windows 21. Flanges are provided on the end of each half 4a and 4b which abut against the end of the strut body 2 when the tabs 5 locate in their respective windows 21. 5 The follower 6 is moulded from a polymeric material, and comprises a head portion 20, a neck portion 30, a shoulder portion 40 and a tail portion 50. When assembled, all but the head portion 20 of the follower are inserted into the strut rod 1 A, the head portion 20 extending beyond the end of the strut rod 1A. 0 The follower 6 comprises a pair of spigots 22, which are formed by placing a metal rod through the head of the follower 20.

The neck potion 30 is thinned so that there is free space to both sides of this within the strut rod 1 A. 25 The shoulder portion 40 is a rib of such a thickness that this substantially fills the hollow centre of the strut 1 A. In use, this shoulder portion 40 serves as an anchor point for the more flexible, head supporting neck portion 30.

The tail portion 50 includes a portion thinned to the thickness of the neck, and an end portion which 30 forms another rib similar to the shoulder rib.

The follower 6 is attached to the strut rod 1A by means of a rivet 15 through aligned apertures in the strut rod 1A and shoulder rib 40 of the follower 6. 35 As a result of this configuration, any defection of the head portion 20 is as a result of flexure (or bending) of the neck portion 30 only, so this follower 6 is more resistant to flexure that the follower of the arrangement in the prior art document mentioned previously. What is more, the extent of 8 2011253804 02 Dec 2011 deflection of the head portion 20 is now more precisely limited than it was in the follower of the prior art.

In use then, flexure of the neck portion 30 of the follower 6 will permit slight sideways deflection of 5 the head portion 20 from a centre line of the follower 6, with a strong bias of the head portion 20 toward this centre line.

Referring now to Figure 4, where it can be seen how the track means 4 define both a circuit of channels (i.e. the tracks portions) which extend around and define a track island 70, and in inlet 72 to 0 the circuit. The spigots 22 on the head 20 of the follower 6 are designed to engage in and move freely along the channels.

In the first stage of operation of the strut assembly 1, the strut rod 1A is telescopically extending from the strut body 2. Prior to the follower entering the track means assembly 4 at inlet 72, the longitudinal 5 axis of the follower 6 is generally aligned with the longitudinal axis of the strut rod 1 A. There is an opening to the inlet 72 to the circuit that is sufficiently wide to ensure that the spigots 22 pass through the inlet and engages the first track 74.

The first track 74 defines an inclined edge 76 angled so as to cause the head 20 of the follower to be 0 deflected with respect to strut rod 1A as it travels in the direction of extension. The head 20 of the follower 6 is at its maximum deflection when it reaches the end of the inclined edge 76 and the first track continues with a portion that runs parallel to the direction of elongation of the strut rod for a short distance and ends when it meets a locking recess 78. 25 The locking recess 78 includes an angled inlet portion which extends a short distance in the direction of strut retraction and an end portion that extends parallel to the direction of elongation of the strut rod for a short distance in the direction of strut retraction. It is this end portion of the locking recess 78 into which the head 20 of the follower 6 is biased after being released from its deflected state, said end portion of the locking recess holding said follower 6 and preventing collapse of said telescopic 30 members, thereby locking said telescopic members in an extended position.

If the strut rod 1A is further telescopically extended from this locked state, then the head 20 of the follower 6 will be deflected along the inclined edge of the locking recess 78, where said inclined edge feeds the deflected follower into an intermediate track 80 that is aligned with the first track. The 35 intermediate track comprises indication means for indicating to an operator that the strut is about to reach the limit of its extension. 9 2011253804 02 Dec 2011

These indication means take the form of undulations 82 in the edge of the island 70 that defines the intermediate track 80. As the spigots 22 travel over these undulations they give an audible (clicking noises) and tactile (vibration) indication. 5 As the strut is still further extended the spigots of the follower leave the intermediate track 80 and the head 20 of the follower 6 is allowed to return to an undeflected state, simultaneously entering a return track 84 as it does so.

The return track 84 defines an inclined edge 86 angled so as to cause the follower 22 to be deflected 0 with respect to strut rod 1A as it travels in the direction of retraction. The head 22 of the follower 6 is at its maximum deflection when it reaches the end of the inclined edge 86 at which point the return track 84 continues with a portion that runs parallel to the direction of elongation of the strut rod 1A until it meets the inlet 72 to circuit, at which point the head 22 of the follower 6 leaves the return track 84 and the head 22 of the follower 6 is allowed to return to an undeflected state, simultaneously 5 entering the inlet 72 (which doubles as an outlet for the follower) as it does so. With further retraction of the strut rod 1A relative to the strut body 2 the follower 6 leaves the track means 4, and will not return until the strut assembly 1 is extended.

An advantage of the strut assembly 1 is the improved extent of bias of the head 22 of the follower 6 to 0 the centreline of the strut body 1A that is created by the neck 30 of the same, whilst permitting sufficient deflection. This ensures that when the spigots 22 reach the end of a given track, they will enter the next required track, thereby ensuring the correct sequence of operation. This further ensures that the strut assembly gives both a definite audible and tactile indication that it is reaching each of the locking recess 78 and the limit of its extension. 25 A further salient advantage of the above described arrangement is that it is suitable for a strut rod 1A and strut body 2 having a higher height to width ratio. In this way, the strut body 2 can be manufactured from the same steel tubing as that employed for the frame of the clothesline assembly in which the strut assembly 1 is employed. This was not the case with the clothesline assembly of the 30 prior art mentioned above.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any 35 other integer or group of integers. 2011253804 02 Dec 2011 10

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. 5 It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A locking mechanism for telescopic members which locks said members in an extended position, the locking mechanism comprising a first member slidably located within a tubular second member, a follower comprising a head portion, a shoulder portion and a flexible neck portion there between, wherein the head portion extending from the first member is resiliently deflectable with respect to the shoulder portion only by virtue of the flexure of the neck portion, and a track means secured to the second member and defining at least one track, the follower engaging a first track as the first member is extended with respect to the second member, said first track being arranged so as to deflect said follower head portion with respect to said first member as said follower moves along said first track, said track means further comprising a locking recess into which said follower head portion is released, said locking recess holding said follower head portion and preventing collapse of said telescopic members, thereby locking said telescopic members in an extended position.
2. The locking mechanism of claim 1, wherein this further comprises a mechanism for releasing the locking to allow the first and second members to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower head portion engaging the intermediate track as the first member is further extended with respect to the second member, the intermediate track being arranged to deflect the follower head portion with respect to the first member as said follower head portion moves along said intermediate track, and an exit track spaced from the distal end of the intermediate track such that the follower head portion is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic members can retract when the follower head portion is located in the exit track.
3. The locking mechanism of claim 2, wherein the intermediate track comprises indication means for indicating to an operator that their extension of the first member with respect to the second member is about to transition the follower head portion from the intermediate track to the exit track.
4. The locking mechanism of claim 3, wherein the indication means comprise one of more undulations in the intermediate track.
5. The locking mechanism as in any one of claims 2 through 4, wherein the intermediate track is aligned with the first track but separated from it by the locking recess.
6. The locking mechanism as in any one of the preceding claims, wherein the first and second members are of rectangular cross-section.
7. The locking mechanism as in any one of the preceding claims, wherein said follower comprises a spigot that engages the track of said track means.
8. The locking mechanism according to either of claims 6 or 7, wherein said track means comprises a moulded polymeric component and wherein a pair of track means are provided, each of the track means located respectively on opposing inside upper and lower walls of said rectangular tube.
9. The locking mechanism according to claim 8, wherein said follower comprises a further spigot so that there are a pair of spaced spigots that respectively engage said track means, said pair of spigots having a common central axis.
10. The locking mechanism as in any one of the preceding claims, wherein the second member is of an upright orientation and the track means secured to the second member defines at least one track above and below the follower.
11. The locking mechanism of claim 10, wherein this further comprises a mechanism for releasing the locking to allow the first and second members to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower engaging the intermediate track as the first member is further extended with respect to the second member, the intermediate track being arranged to deflect the follower with respect to the first member as said follower moves along said intermediate track, and an exit track spaced from the distal end of the intermediate track such that the follower is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic members can retract when the follower is located in the exit track.
12. The locking mechanism according to any one of the preceding claims, in combination with a pivotable cantilever frame for supporting one or more clothes lines, wherein said locking mechanism and said telescopic members are used to hold said frame in a raised position where said telescopic members are extended, and to release said frame to a storage position where said telescopic members are collapsed.
13. A supporting strut for a pivotable cantilever frame for supporting one or more clothes lines, the supporting strut comprising a locking mechanism as in any one of the preceding claims to a locking mechanism.
14. A clothesline assembly comprising a supporting strut as in claim 13.
15. A clothesline assembly comprising a frame which is pivotable between a substantially horizontal, raised position, and a substantially vertical, lowered position, and a supporting strut which swings through a substantially vertical arc of travel as the frame is moved between its raised and lowered positions, the supporting strut comprising a tubular strut body disposed over a strut rod so as to be telescopically shortened and lengthened, and an internal, releasable locking mechanism which permits locking of the supporting strut at a length which sees it supporting the clothesline frame in its raised position, the locking mechanism comprising a follower attached to said strut rod; the follower comprising a head portion, a shoulder portion and a flexible neck portion there between, wherein the head portion extending from the strut rod is resiliently deflectable with respect to the shoulder portion only by virtue of the flexure of the neck portion; the follower deflectable with respect to said strut rod in a direction substantially orthogonal to the arc of travel of the supporting strut, and a track means secured to the strut body and defining at least one track, the follower engaging a first track as the strut rod is extended with respect to the strut body, said first track being arranged so as to deflect said follower with respect to said strut rod as said follower moves along said first track, said track means further comprising a locking recess into which said follower is released, said locking recess holding said follower and preventing collapse of said supporting strut, thereby locking said supporting strut in an extended position.
16. The clothesline assembly of claim 15, wherein the locking mechanism for this further comprises a mechanism for releasing the locking to allow the strut rod and strut body to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower engaging the intermediate track as the first member is further extended with respect to the strut body, the intermediate track being arranged to deflect the follower with respect to the strut rod as said follower moves along said intermediate track, and an exit track spaced from the distal end of the intermediate track such that the follower is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic strut rod and strut body can retract when the follower is located in the exit track.
17. The clothesline assembly as either of claims 15 or 16, wherein the frame and either of the strut rod or strut body are made from the same tubular material.
18. The clothesline assembly as either claim 17, wherein the tubular material has a rectangular cross-sectional shape.
19. A supporting strut for a clothesline frame which is pivotable between a substantially horizontal, raised position, and a substantially vertical, lowered position, so that the supporting strut swings through a substantially vertical arc of travel as the frame is moved between its raised and lowered positions, the supporting strut comprising a tubular strut body disposed over a strut rod so as to be telescopically shortened and lengthened, and an internal, releasable locking mechanism which permits locking of the supporting strut at a length which sees it supporting the clothesline frame in its raised position, the locking mechanism comprising a follower attached to said strut rod; the follower comprising a head portion, a shoulder portion and a flexible neck portion there between; the head portion extending from the strut rod and resiliently deflectable with respect to the shoulder portion only by virtue of the flexure of the neck portion; the follower deflectable with respect to said strut rod in a direction substantially orthogonal to the arc of travel of the supporting strut, and a track means secured to the strut body and defining at least one track, the follower engaging a first track as the strut rod is extended with respect to the strut body, said first track being arranged so as to deflect said follower with respect to said strut rod as said follower moves along said first track, said track means further comprising a locking recess into which said follower is released, said locking recess holding said follower and preventing collapse of said supporting strut, thereby locking said supporting strut in an extended position.
20. The supporting strut of claim 19, wherein the locking mechanism for this further comprises a mechanism for releasing the locking to allow the strut rod and strut body to telescopically collapse, said releasing mechanism comprising the following further components of said track means, an intermediate track which extends from the locking recess, the follower engaging the intermediate track as the strut rod is further extended with respect to the strut body, the intermediate track being arranged to deflect the follower with respect to the strut rod as said follower moves along said intermediate track, and an exit track spaced from the distal end of the intermediate track such that the follower is released into the exit track as it leaves the end of the intermediate track, and wherein the telescopic strut rod and strut body can retract when the follower is located in the exit track.
21. The supporting strut of either of claims 19 or 20, wherein the intermediate track comprises indication means for indicating to an operator that their extension of the strut rod with respect to the strut body is about to transition the follower head portion from the intermediate track to the exit track.
22. The supporting strut of claim 21, wherein the indication means comprise one of more undulations in the intermediate track.
23. The supporting strut as in any one of claims 19 through 22, wherein the intermediate track is aligned with the first track but separated from it by the locking recess.
24. The supporting strut as in any one of claims 19 through 23, wherein the follower comprises a neck portion and a shoulder portion inserted within the strut rod, and a head portion extending from the strut rod that is resiliently deflectable with respect to said strut rod only by virtue of deflection of said follower neck portion.