AU760586B2 - Castor wheel assembly for a ladder - Google Patents

Description

This invention relates to an improved castor assembly for a ladder, especially a step-ladder to enable the ladder to be conveniently moved from one location to another.

It is well known for ladders to be provided with castors to facilitate their movement from one location to another. One known arrangement utilises spring operated castors which are biased downwardly and which retract against the force of the springs when a user of the ladder exerts a downward force against the ladder, such as by stepping on the first rung thereof. While this system is generally satisfactory, there is the disadvantage that springs with different spring tensions are required for different ladder sizes due to the widely varying weights of different ladders.

Another castor wheel system which is currently available in the market place 15 is described and illustrated in Australian Patent Application No. 72672/96 in the name of Custom Ladder Company Pty Ltd. This system makes use of two sets of "o• castors which are independently raised and lowered by separate actuators, whereby a user of the ladder, depending on which side of the step ladder he is located, can S. retract one of the castor sets and then subsequently lift the end of the ladder which is S 20 closest to him off the ground and hold it off the ground while the ladder is moved to a different location thereby using the other set of castors to aid in the movement of the ladder. When a heavy ladder is being used, the need for one end of the ladder to be lifted and maintained clear of the ground while the ladder is being moved, is ergonomically undesirable particularly for people with back problems. Furthermore, moving a ladder in a tilted position is unstable and may result in the user losing control of the ladder.

It is the main object of the present invention to provide an improved castor assembly for a ladder wherein the castors may be moved from a ladder immobile retracted position into an extended transporting position positively, easily and conjointly, and which allows the ladder to be moved from place to place in a stable manner without the need to lift either end of the ladder.

1 It is further object of the present invention to provide an improved castor assembly for a ladder wherein the castors of the assembly, are securely locked in place when the ladder is being moved around, and which can be easily moved to their retracted position with the legs of the ladder stably supported on the ground, upon a downward force being applied eg by means of the user's foot, to a bottom rung or tread of the ladder.

It is still further object of the present invention to provide a ladder castor assembly which is of extremely simple and inexpensive construction and can be readily fitted to the base of a step ladder between the ends thereof.

According to this invention therefore, there is provided an improved castor assembly for a step ladder or platform ladder of the A-frame type having a ladder section extending upwardly from the ground at an angle thereto and a stabilising support frame which is spaced from the ladder section and fixed rigidly with respect thereto, and a pair of lower side braces which extend between and interconnect the ladder section and the stabilising support frame near the bottom ends thereof, said castor assembly including at least three castor wheels which are mounted to a pivotal sub-frame moveable between a first retracted position in which the ladder is stably supported on a horizontal surface by the legs of the ladder section and the stabilising support frame and a second transporting extended position in which the castors project below the base of the ladder and stably support the ladder on the ground S• with the feet of the ladder section and the stabilising support frame elevated thereabove, linkage means connected between the sub-frame and the lower side braces of the ladder for swingably supporting the sub-frame for movement between said first and second positions, locking means for locking the castor sub-frame in its said second transporting position, and actuating means attached to said sub-frame for operating said linkage means in order to move said sub-frame from its said first to its locked said second position, °0 wherein the locking means comprises a resilient locking clip and the resilient locking FRAp can be released by applying downward pressure to the ladder section.

Preferably the locking means comprises co-operable catch and catch engaging members. The catch can be a resilient locking clip fixed to a leg of the stabilising support frame near its bottom end, and the catch engaging member is a short length locking pin which is fixedly secured to an end of the sub-frame, the locking pin being held captive by the locking clip when the sub-frame is in its extended transporting position. Desirably there are two sets of locking clips and locking pins, one on each side of the sub-frame at its end remote from the actuating means.

Preferably the actuating means comprises a foot pedal or rail which is attached centrally to a crossbar which in turn connects to part of said linkage means, the cross-bar extending between a pair of opposite longitudinal side rails of the subframe, the foot pedal being located approximately midway between the pair of stiles o of the ladder section. In lieu of a foot pedal, a hand operated lever attached to the 15 sub-frame adjacent one side thereof, could be employed in order to move the subframe assembly between its retracted and extended positions.

Desirably the castor sub-frame is provided with four castor wheels, a first pair being mounted adjacent the leading ends of the pair of longitudinal side rails, with a 20 second pair of wheels being mounted adjacent the trailing ends of said longitudinal side rails.

Preferably, the linkage means comprises sets of pivotal link arms which form an approximate parallelogram linkage.

With this invention, in order to operate the castor wheel system, the operator simply applies downward pressure to the actuating foot rail or pedal so as to cause the parallelogram linkage to rotate, until the castor wheels come into contact with the ground, whereupon the bottom ends of the ladder and the stabilising support frame lift off the ground and the distal ends of the sub-frame side rails are engaged by their associated locking clips. The bottom ends of the ladder are retained in an elevated position above the ground until a downward pressure is applied to the bottom rung of the ladder, eg by a person standing on the bottom rung, this causing the sub-frame to disengage from the locking clips and in turn swing upwardly to its retracted position to thereby allow the bottom ends of the ladder assembly to rest stably on the ground. In the retracted position, the castor wheels may still make contact with the ground but all of the weight of the ladder is transmitted to the feet or bottom ends of the ladder section and the stabilising support frame.

In order to more fully describe the present invention, a preferred embodiment thereof is described hereunder in some further detail with reference to and illustrated in the accompanying drawings wherein: Fig 1 is a front perspective view of a ladder assembly which incorporates the castor wheel system upon which the ladder is adapted to be rollingly transported *o°9.

from one location to another, according to this embodiment of the invention; oooo Fig 2 is a fragmentary perspective view of the castor sub-frame assembly fitted 9.

15 to the base of the ladder assembly when in its extended transporting position; Fig 3 is a fragmentary side elevational view of the ladder assembly with the castor sub-frame in its extended transporting position, with the bottom ends of the o°°9* ladder legs being lifted clear of the ground; while Fig 4 is a view similar to Fig 3 showing the castor sub-frame in its retracted 20 non-transporting position, with the ladder being stably supported on the ground by its four legs.

Referring to Figs 1 to 4 of the drawings, there is shown a step ladder assembly of the non-folding A-frame type which comprises an inclined ladder section 11, an approximate vertical stabilising support frame 12, a horizontal platform 13 extending between and secured to the ladder section 11 and support frame 12 at the upper ends thereof, and a pair of opposed lower side braces 14 which extend between and are secured to the legs 15, 16 respectively of the ladder section 11 and support frame 12 near the bottom ends thereof.

In accordance with the main feature of the present invention, the base of the ladder assembly 10 is provided with a castor sub-frame assembly 18 upon which the ladder is adapted to be rollingly transported from one location to another, the castor sub-frame assembly 18 comprising a pair of opposite longitudinally extending side rails 19, 19' which are pivotally coupled to the lower side braces 14 by means of an approximate parallelogram linkage comprising sets of transversely aligned linkage arms 20, 21, the linkage arms being arranged so that the sub-frame 18 can move between a retracted non-transporting position wherein the legs 15, 16 of the ladder engage the ground in order to stably support the ladder thereon, and an extended transporting position wherein the castor wheels 23 project below the bottom ends of the legs 15, 16 and stably support the ladder assembly 10 on the ground with the bottom ends of the legs 15, 16 elevated thereabove.

S°The movement of the sub-frame 18 is actuated by means of a foot pedal or rail which is secured centrally of the sub-frame 18 to a cross-frame member 26 which o extends between the opposite sides of the sub-frame with its opposite ends being 15 fixed to respective front inner link arms 20. With the sub-frame in its retracted position, downward pressure applied to the foot pedal or rail 25 by the user of the ladder, will cause the link arms 20, 21 to simultaneously rotate anticlockwise and lower the sub-frame 18 to its extended transporting position.

20 With the castor sub-frame 18 in its extended transporting position, the trailing ends of the side rails 19, 19' are locked in position by means of locking clips 27 secured to the inner faces of the legs 16 of the support frame 12 adjacent the bottom ends thereof, the resilient clips 27 clippingly engaging a short-length vertical locking pin, tube or rod 28 which is fixedly secured to the trailing end of each sub-frame side rail 19, 19'. It will be appreciated that as the sub-frame 18 swings downwardly to its extended transporting position, the sub-frame is displaced longitudinally relative to the braces 14, and pins 28 will automatically engage the clips 27, with pressure being applied by the castor wheels against the ground causing the bottom ends of the legs 16 to be lifted off the ground and retained in an elevated locked position by virtue of the locking engagement between the clips 27 and their associated locking pins 28.

With the sub-frame in its extended transporting position, the ladder assembly 10 can be conveniently rolled along the ground and transported from one location to another without having to lift a portion of the ladder.

To return the castor wheels 23 to their retracted positions, it is necessary to cause the link arms 20, 21 to rotate in a clockwise direction so as to displace the subframe 18 in a direction away from the locking clips 27 and disengage the locking pins or tubes 28 from the clips 27. In this embodiment this can be achieved by the user of the ladder applying a downward pressure to the ladder section 11, eg by the user standing on the bottom rung 29 of the ladder section 11. The sub-frame 18 is thereby displaced upwardly and the bottom ends of the legs 15, 16 of the ladder assembly once again make firm contact with the ground. In the retracted position, the castor wheels 23 may make non-pressure contact with the ground; however no weight is borne by the castor sub-frame 18.

o*oo o* o• 15 Of course, the castor sub-frame 18 can also be moved to its retracted position by placing one's foot underneath the foot pedal 25 and lifting it upwardly so as to effect clockwise rotation of the link arms 20, 21.

It will be appreciated that the locking clips 27, instead of being fixed to the 20 bottom ends of the legs 16 of the support frame 12 maybe located on the sub-frame 18 itself, with the locking pins 28 in turn being attached to the legs 16. Various other 0.0.

types of catch mechanisms may be utilised in order to lockingly retain the sub-frame 18 in its transporting position. In addition, for large heavy duty ladders, it may be necessary for two vertically aligned clips 27 to be used at each side of the support frame 12 to ensure that the castor sub-frame is securely held in its ladder transporting position.

Although a preferred embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that other modifications may be made without departing from the true spirit and scope of the invention.

A brief consideration of the above described embodiment will indicate that the invention provides for a very simple and inexpensive castor assembly which can be readily fitted to A-frame step ladders so as to allow the ladder to be conveniently and readily transported from one location to another without having to lift a portion of the ladder during its transport.

S S

Claims (11)

1. In a step ladder or platform ladder of the A-frame type having a ladder section extending upwardly from the ground at an angle thereto and a stabilising support frame which is spaced from the ladder section and fixed rigidly with respect thereto, and a pair of lower side braces which extend between and interconnect the ladder section and the stabilising support frame near the bottom ends thereof, a castor assembly which includes: at least three castor wheels which are mounted to a pivotal sub-frame movable between a first retracted position in which the ladder is stably supported on a horizontal surface by the legs of the ladder section and the stabilising support frame and a second transporting extended position in which the castors project below the base of the ladder and stably support the ladder on the ground with the feet of the ladder section and the stabilising support frame elevated thereabove, linkage means connected between the sub-frame and the lower side braces of the ladder for swingably supporting the sub-frame for movement between said first and second positions, locking means for locking the castor sub-frame in its said second transporting position, and actuating means attached to said sub-frame for operating said linkage means in order to move said sub-frame from its said first to said second position, wherein the locking means comprises a resilient locking clip and the resilient locking clip can be released by applying downward pressure to the ladder section.

2. The ladder assembly according to claim 1 wherein said resilient locking clip is on said support frame and a clip engaging member is on said sub-frame, said clip S: being arranged to automatically engage said clip engaging member when the sub- frame is moved from its said first position to its said second position. ooo• ooo• .i

3. The ladder assembly according to claim 2 wherein the resilient locking clip is 0 fixed to a leg of the stabilising support frame near its bottom end and said catch qi gaging member is a short length rod or pin fixedly secured to an end of the sub- fe, said rod or pin being held captive by its associated said locking clip when the sub-frame is in its extended transporting position.

4. The ladder assembly according to claim 3 wherein there are sets of said locking clips and said locking pins on opposite sides respectively of said sub-frame at its end remote from the actuating means.

The ladder assembly according to any one of the preceding claims wherein said actuating means comprises a foot pedal or rail which extends between a pair of opposite longitudinal side rails of said sub-frame, said foot pedal being located approximately mid-way between the stiles of said ladder section.

6. The ladder assembly according to claim 5 wherein said linkage means Scomprises pivotal link arms pivotally attached to said lower side braces so as to S depend therefrom, said pivotal link arms forming an approximate parallelogram 15 linkage.

7. The ladder assembly according to claim 6 wherein there are four sets of pivotal link arms, each set comprising a pair of transversely aligned parallel arms pivotally attached adjacent their upper ends to opposite sides of a respective said 20 lower side brace, with their lower ends being pivotally attached to opposite sides of a respective said side rail.

8. The ladder assembly according to claim 5 wherein said castor sub-frame is provided with four castor wheels, a first pair of said wheels being mounted adjacent the leading ends of the pair of longitudinal side rails of the sub-frame, with a second pair of said castor wheels being mounted adjacent the trailing ends of said longitudinal side rails.

9. The ladder assembly according to any one of the preceding claims wherein said castor wheels, when the castor sub-frame is in its retracted position, make non- pressure contact with the horizontal surface on which the ladder is supported.

The ladder assembly according to any one of the preceding claims wherein said castor wheels are of the steerable type.

11. A castor wheel assembly for a step ladder or platform ladder of the A-frame type, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings. Dated this 4 th day of August, 1999. HILLS INDUSTRIES LIMITED By its Patent Attorneys MADDERNS 0 *000 o o o 0 oooo