AU700860B2 - Levelling device for a ladder - Google Patents

Description

-2- TITLE LEVELLING DEVICE FOR LADDER This invention relates to a levelling device for apparatus such as ladders and in particular to a self-locking device which prevents adjustment of the legs during use.

When positioning apparatus such as ladders, for safety reasons, the main object is to maintain the feet of the stiles of the apparatus in contact with the ground when the stiles are vertically oriented. To overcome problems associated with positioning such apparatus on uneven terrain, such as sloping ground or steps adjustable support legs have previously been proposed to compensate for differences 10 in the level between the two legs supporting the apparatus.

ooooo While devices with a single adjustable leg have been previously proposed, devices such as those disclosed in US Patent Nos. 2,366,829 and 2,330,825 and Australian Patent No. 583397 disclose systems whereby the ends of each adjustable o S"leg are connected together by a tension means such as a rope or chain such that upward movement of one leg results in a corresponding downward movement of the S.other leg.

It has been recognized that for short ladders a locking means which fixes the position of the adjustable support legs relative to the apparatus may not be required.

However, for ladders longer than about 10 feet in length, it is important that a locking means is provided to prevent this movement. For ease of operation, it is preferred that such a locking device is self-actuating.

It is an object of the invention to provide a levelling device which locks in position while in use.

Accordingly, the invention provides an adjustable levelling device for an apparatus including adjustable support legs for mounting to said apparatus, an elongate connection means attached to at least one of the adjustable support legs, and a locking means for clamping the at least one adjustable support leg to the apparatus, said locking means having at least one pivotable mounting with a guide means for engagement with said elongate connection means and a clamping assembly activated by movement of said at least one mounting member such that tension in said BC:JH:#25368 30 May, 1997 -3connection means pivots the mounting member activating the clamping assembly to clamp the at least one adjustable leg to the apparatus.

In a preferred form of the invention, each adjustable support let is mounted on the outside surface of a stile of a ladder. The clamp assembly preferably includes a clamp member which bears against the respective adjustable support leg and a clamp support adapted to extend through and beyond the respective stile of the ladder, the clamp support connecting the clamp member to the arm member. The adjustable support legs are preferably provided with a slot running longitudinally to allow the adjustable leg support to more without interference from the clamps support when the locking means is disengaged.

The guide means maybe a pivot post, pulley or shaped guide member which ooooo extends from the mounting attached substantially at right angles.

The mounting of the locking means preferably abuts against the respective *.i S"stile of the ladder. The fulcrum includes at least one small protrusion which may locate within a corresponding depression in the stile.

Tension in the connection means is transferred by the guide means to the arm member. The tension causes the arm member to rotate or pivot relative to the stile :about the fulcrum activating the clamp assembly.

Another aspect of the invention provides a ladder incorporating a self-locking device comprising two support stiles, two adjustable support legs mounted on said stiles, an elongate connection means attached to said adjustable support legs and a locking means for clamping at least one of the adjustable legs to the respective stile, said locking means having a pivotable mounting with a guide means extending therefrom for engagement with the elongate connection means and a clamp assembly actuated by movement of the mounting such that tension in said connection means causes the clamping assembly to clamp at least one of the adjustable support leg to the corresponding stile.

In the preferred form of the invention, the clamp assembly includes a clamp member bearing against the respective adjustable support leg and a clamp support which extends through the respective stile of the ladder, the clamp support BC:I:#25368 30 May, 1997 -4connecting the clamp member to the arm member. The clamp support may be slidably received within a chamber in the adjustable leg, the longitudinal position of the clamp support relative to the stile being fixed.

Tension in the connection means is transferred by the guide means to the arm member causing the mounting to pivot relative to the respective stile. The pivotal movement of the mounting cause lateral movement in the clamp support. This lateral movement results in the respective adjustable leg being clamped against the stile of the ladder.

To position the ladder and adjust the support legs, one of the support legs is moved downwardly to release the tension in the tether. The feet of the support legs can then be adjusted so that the feet contact the ground while the ladder is held vertical. When one of the legs is moved downwardly, it is preferable that a corresponding upward movement occurs for levelling purposes.

o Once the ladder is positioned with the feet of the adjustable support legs contacting the ground, the weight of a person on the ladder causes the locking means to engage and clamp the adjustable support legs to the stiles.

When larger heavy ladders are equipped with the levelling device or devices of the present invention, it may be difficult to de activate the clamping action because of the weight of the ladder. To overcome this difficulty, the pivotable mounting of each adjustable leg is provided with an extension towards the opposite mounting. If a sufficient downward force is applied to the extensions, downward pivotal movement of the extension results in the clamp assembly being deactuated.

The respective extensions may be pivotally attached to a plate which can be pushed downwardly under the pressure of an operator's foot to deactivate the clamp assemblies and enable the adjustable legs to move relative to the stiles.

The foregoing and other features, objects and advantages of the present invention will become more apparent from the following description of the preferred embodiment and accompanying drawings of which: Fig. 1 is front view of a preferred embodiment of the invention fitted to a ladder; BC:JtI:#25368 30 May, 1997 Fig. 2 is a bottom plan view of the embodiment shown in Figure 1 along 2-2 Fig. 3 is a sectional view of the locking means along line 3-3 of Figure 1.

Fig. 4 is a side view of the locking means in accordance with the embodiments of Figure 2 and 3, Fig. 5 is a sectional view of a second embodiment of the adjustable support leg and clamp assembly, Fig. 6 is a front view of a second embodiment of the invention fitted to a ladder, and Fig. 7 is a section view through line 7-7 of Figure 6.

Referring to Figures 1 and 2, a ladder 1 is shown consisting of support stiles 2,3 and rungs 4,5 fitted with the levelling device of the present invention.

A levelling device comprises two adjustable support legs 6,7 mounted on to the support stiles 2,3 of the ladder 1. The adjustable legs 6,7 may be provided with *0 feet 12,13 to distribute the weight of the ladder over the ground and further provided with mounting flanges 14, 15 which secures the adjustable legs against the stiles 2,3 while allowing the adjustable legs to slide longitudinally along the stiles a predetermined distance.

The adjustable support legs shown in all of the embodiments are preferably produced from C-shaped or L-shaped channel of extruded steel or aluminium and the ladders for use with the levelling device may be made from aluminium, wood or reinforced fiberglass. The ladders shown in the drawings are C-shaped channel of extruded aluminium.

To secure the longitudinal position of the adjustable support legs relative to the stiles of the ladder, a locking means is provided.

In accordance with an embodiment of the invention, shown in figure 1, the locking means includes a pivotable mounting 19 with a guide means extending therefrom. The mounting 19 is connected to a clamp assembly which is actuated by movement of the mounting 19. The clamp assembly includes a clamp support 17 which extends laterally through an aperture in the respective stile and ends in a clamp member 18 which bears against a preferably longitudinal surface on the BC:JH:n2S368 30 May, 1997 -6corresponding support legs. While the clamp support and clamp member are shown as separate integers it may be convenient to form them as a single item.

One end of a connection means shown as an elongate tether 9 is attached to tabs 10,11 secured to the adjustable support legs 6,7. Since the elongate tether is used to transfer tension from one adjustable leg support to the other, it is preferably made from any inelastic material which has sufficient flexibility for this application.

The elongate tether may be a rope, steel cable wire rope or flat laminated strip with wire rope being preferred.

The adjustable support legs 6,7 have slots, (not shown) extending 10 longitudinally to allow the clamp support to pass through and extend beyond the ooeoo adjustable support legs. This allows the locking means to be attached to the stiles and allow the support legs to be mounted adjacent the clamp support and move freely without interference when the locking means is not engaged.

The elongate tether 9 engages with the guide means 20 on the mounting 19 in such a way that tension in the tether is transferred to the arm member through the S"guide means The guide means 20 is preferably a pivot post, pulley or shaped projection which acts as a fulcrum to guide the tether through a turn of about 90'. In Figures 3 and 4 the guide means is shown as a pulley.

When tension exists in the tether 9, a force is exerted on the mounting 19 causing the mounting to pivot upwardly about the edge 24 of the mounting which abuts against the stiles of the ladder.

This pivotal movement slides the clamp support laterally within the aperture 21 of the stile to pull the clamping member against the adjustable leg. Further tension in the tether forces the adjustable leg against the stile thereby clamping the adjustable leg to the stile.

A return bias (not shown) may be associated with the locking means to provide a small force against the action of the elongate tether 9. As a result, when the tension in the elongate tether is removed, the locking means disengages and the clamp member 17 releases the clamping action on the adjustable support member.

BC:JH:#25368 30 May, 1997 -7- The bias may be a spring mounted on the clamp support 17 and preferably the restitution force in the spring is sufficient to overcome the tension in the elongate tether caused by the weight of the ladder.

To increase the frictional co-efficient between the stile and support legs and enhance the clamping action, a caliper 22 may be provided between the stile and the adjustable support leg. Furthermore, the clamp support 17 may be coated with a low friction coating material such as Teflon (registered trademark) or a lubricant to assist sliding axial movement of the clamp support 17 within aperture 21 and the operation of the locking means.

10 The surface of the mounting 19 abutting the stile of the ladder is provided ooooo with at least one pivotal projection 23. The pivotal projection 23 is preferably provided on the abutting edge 24 of the mounting 19 which acts as a fulcrum when there is tension in the tether and located into a corresponding recess 25 in the stiles.

*i As shown is Figure 3, the mounting 19 is preferably L-shaped and may be provided with two located projections 23.

The projection or projections act as a fulcrum for pivotal movement of the arm member under the force of the tension in the tether.

In the embodiment shown in figures 1-4, the interaction between the adjustable support legs and the clamping assembly is shown in its simplest form.

In these embodiments, the clamping member 18 bears against the outer surface of a. the support leg.

In the embodiment shown in figure 5, the adjustable leg 30 is formed with an additional clamp chamber 31 which enables the clamp element 18A to fit therein.

The chamber 31 has a longitudinal slot 32 which enables relative sliding movement of the clamp support 17A. By providing a clamp chamber 31, the sliding clamp member is protected from interference while the support legs are being adjusted and while the ladder is in use.

When the elongate tether is tensioned, the pivotal movement of mounting 19 causes clamp support 17A to pull the clamping member 18A in the direction of arrow 35 to clamp the adjustable support leg 30 to the ladder stile not shown.

BC:JIt:#25368 30 May, 1997 -8- In use, ladder 1 with a levelling device of the present invention is first aligned vertically against a wall or other structure. The feet 12,13 of the levelling device are adjusted to maintain this orientation by the operator placing his feet on one of the feet of the adjustable support legs while the ladder is substantially unloaded.

As there is little vertical load on the support legs at this stage, the tension in the elongate tether 9 and the subsequent force applied by the locking means is negligible. Therefore only a small force, if any, is required by the worker to adjust the support legs. As discussed above when the ladder is unloaded one leg is positioned by downward movement while the other leg is moved upwardly. Since the tether is a finite length downward movement of one leg requires a corresponding upward movement in the other leg to maintain tension in the tether.

Once positioned the ladder can be loaded by the operator by climbing up the rungs. The weight of the operator is thus applied to the elongate tether causing tension in the tether. The tensile force applied by the tether to the guide means is transferred to the arm member which pivots about its pivot point to clamp the supporting leg to the support stile. This clamping force is proportional to the tension in the elongate tether and is sufficient to prevent movement of the adjustable support leg relative to the stile.

As would be apparent to persons skilled in the art, the locking means on the levelling device is activated whenever the ladder is loaded thus avoiding the dangerous situation where an operator has neglected to activate the locking device.

Figs. 6 and 7 show a second embodiment of the invention which specifically provides a means of deactivating the locking mechanism. In this embodiment, extending mountings 40, 41 are provided each of which extend towards the opposite locking means. The extended mountings 40, 41 are preferably pivotally attached to plate 42 which may extend slightly above the first rung 49 of the ladder 50. The locking means of both adjustable legs can be disengaged by pivotally moving the extended mountings 40, 41 downwardly by depressing plate 42. The downward pivotal movement releases the clamp assemblies 43, 44 allowing the adjustable legs 45, 46 longitudinal movement relative to the stiles 47, 48.

BC:JHI:#25368 30 May, 1997 -9- In order for the locking means 52, 53 to be disengaged, the downward force applied to the extended mountings 40, 41, wall plate 43 must be sufficient to overcome the tension in the tether 51.

It would further be apparent that while the invention is described with reference to ladders, step ladders or other structures with paired legs can use the present invention to compensate for uneven terrain.

o BC:JH:#25368 30 May, 1997 The claims defining the invention are as follows: 1. An adjustable levelling device for an apparatus including adjustable support legs for mounting to said apparatus, an elongate connection means attached to at least one of the adjustable support legs, and a locking means for clamping the at least one adjustable support leg to the apparatus, said locking means having at least one pivotable mounting with a guide means for engagement with said elongate connection means and a clamping assembly activated by movement of said at least one mounting such that when said adjustable support legs are mounted on said apparatus, tension in said connection means pivots the mounting member activating 10 the clamping assembly to clamp at least one adjustable leg to the apparatus.

.oe..i ooo..= 2. The adjustable levelling device in accordance with claim 1 wherein the at least one adjustable support leg is mounted on the outside of a stile of a ladder.

3. The adjustable levelling device in accordance with claim 2 wherein the device includes two adjustable support legs, each adjustable support leg being for mounting to the outside of a stile of a ladder.

4. The adjustable levelling device in accordance with any one of claims 1, 2 or 3 wherein the connection means is a substantially inelastic tether.

The adjustable levelling device in accordance with claim 3 or 4 wherein each adjustable support leg has a corresponding clamp assembly, said clamp assembly including a clamp member for engagement with the respective adjustable support leg and a clamp support leg adapted to extend through the stile of the ladder, the clamp support connecting the clamp member to the mounting.

6. The adjustable levelling device in accordance with any one of the preceding claims wherein each adjustable support leg is provided with a longitudinal slot to enable the adjustable support leg to move relative to the stile when the locking BC:J:#25368 30 May, 1997

Claims (12)

1. 7. The adjustable levelling device in accordance with any one of the preceding claims wherein the guide means is at least one of a pivot post, pulley or shaped guide member extending substantially at right angles to the mounting.
2. 8. The adjustable levelling device in accordance with any one of the preceding claims wherein the pivotable mounting of the locking means is adapted to abut against the respective stile of the ladder.
3. 9. The adjustable levelling device in accordance with claim 8 wherein the mounting has a fulcrum abutting against the respective stile of the ladder for pivotal 10 movement of said mounting relative to said stile, said locking means being engaged and disengaged by pivotal movement of said mounting about said fulcrum.
4. 10. The adjustable levelling device in accordance with any one of claims 6 to 9 wherein the longitudinal slot communicates with a longitudinally extending chamber formed in said adjustable legs, said clamp member being movable longitudinally within said chamber.
5. 11. The adjustable levelling device in accordance with any one of the preceding claims wherein the pivotable mounting is provided with an extension such that sufficient downward pressure on said extension will pivot said mounting to disengage said locking means.
6. 12. A ladder incorporating a self-locking device including two support stilcs, two adjustable support legs mounted on said stiles, an elongate connection means attached to said adjustable support legs and a locking means for clamping at least one of the adjustable legs to the respective stile, said locking means having a pivotable mounting with a guide means extending therefrom for engagement with BC:Jl:#25368M 30May, 1997 12- the elongate connection means and a clamp assembly activated by pivotal movement of the mounting relative to said respective stile such that tension in said connection means causes the clamping assembly to clamp at least one of the adjustable support legs to the corresponding stile.
7. 13. The ladder in accordance with claim 12 wherein the clamp assembly includes a clamp member bearing against the respective adjustable support leg and a clamp support which extends through the respective stile of the ladder, the clamp support connecting the clamp member to the mounting. The ladder in accordance with claim 13 wherein each adjustable support leg 10 is provided with a longitudinal slot, said clamp support extending from said clamp member through said slot and the respective stile to the mounting. The ladder in accordance with claim 14 wherein the longitudinal slot communicates with a longitudinally extending chamber in said adjustable support leg, said clamp member being received within said chamber and adapted to move s:of: 15 longitudinally along said chamber when the locking means is disengaged. 60*16. The ladder in accordance with any one of claims 12 to 15 wherein the 1" pivotable mounting is provided with an extension extending towards the opposite mounting.
8. 17. The ladder in accordance with claim 14 wherein the extended mountings are pivotally attached to a plate, downward pressure on said plate causing pivotable movement of said extended mountings to disengage said locking means.
9. 18. The ladder in accordance with any one of claims 12 to 17 wherein the connection means is a substantially inelastic elongate tether. BC:JII:#25368 10 May, 1997 13
10. 19. The ladder in accordance with any one of claims 12 to 18 wherein the pivotable mounting of the locking means is adapted to abut against the respective stile of the ladder. The ladder according to claim 19 wherein the mounting has a fulcrum abutting against the respective stile of said ladder, said locking means being engaged and disengaged by pivotal movement of said mounting about said fulcrum.
11. 21. The ladder in accordance with any one of claims 12 to 20 wherein the guide means is at least one of a pivot post, pulley, or shaped guide member extending from said mounting. 10 22. An adjustable levelling device substantially as hereinbefore described with reference to the accompanying drawings.
12. 23. A ladder having an adjustable levelling device substantially as hereinbefore described with reference to the accompanying drawings. DATED: 30 May 1997 CARTER SMITH BEADLE Patent Attorneys for the Applicant: PANORAMA QUEST PTY LTD BC:JH:#25368 30 May, 1997 ABSTRACT A self-locking adjustable levelling device for an apparatus and a ladder incorporating a self-locking adjustable levelling device is disclosed. The levelling device includes adjustable support legs 6,7 for mounting to the apparatus 1, an elongate connection means 9 attached to the adjustable support legs 6,7 and a clamping means for clamping the adjustable legs to the apparatus. The locking means for each adjustable support leg includes a mounting 19 with a guide means for engagement with the elongate connection means 9 and a clamping assembly activated by pivotal movement of the mounting. Tension in the connection means 9 pivots the mounting member activating the clamping assembly to clamp the adjustable support leg to the apparatus. o