Background Art A number of levelling devices for ladders are known in the art. Various known devices are relatively complex to-manufacture and attach (especially retrofit) to a ladder. In addition, the construction of some devices renders them more prone to failure. If a levelling mechanism were to fail on a ladder in use, this could be catastrophic, with the risk of injury or death to a user of the ladder.

Australian patent 700860 discloses a self-locking adjustable levelling device for a ladder that includes adjustable support legs for mounting to the stiles of the ladder. However, substantial parts of the locking mechanism are located exterior to the ladder and support legs, and are thus subject to interference, damage and fouling in use, thereby rendering the locking mechanism inactive, ineffective or unsafe. In addition, the ladder is not self-regulating when loaded (ie. when a user is standing thereon). It must be adjusted and locked before user load is applied thereto.

US 4,770, 275 discloses a leveller for ladders which is said to be self-regulating when loaded. A pair of opposing legs telescopically slide within respective opposing stiles, and the upper end of the legs are connected together via a flexible wire rope. The rope passes down through each stile and then across and through

a rung, and in so doing passes up and over the ramp of a convex guide. To cope with uneven ground or a set of steps, the ladder is placed on the ground so that one leg engages the ground and the weight of the ladder pushes that leg up, pulling the wire through from the opposite side and causing the opposite leg to lower until it contacts the ground. The document alleges that if the ground below one leg subsides, tension is removed from the wire rope and readjustment automatically takes place. The document relies on static friction across, in particular, the convex guide, to stop wire rope slipping and thereby lock the legs. There is considerable doubt as to whether this frictional force would be sufficient in all circumstances. For example, it is common in the building industry for tradesmen to step onto or off a roof, from or to the side of a ladder. In so doing, essentially the entire load of the user is removed from the ladder, and this would free up the wire rope of US 4,770, 275 for movement, and render the entire ladder unstable and therefore dangerous.

US 5,044, 468 also discloses a ladder-levelling device, which is said to be self-regulating. However, this device relies on a far more complex (and therefore expensive) hydraulic piston pairing and would be complex to manufacture and purchase. In addition, the mechanism for locking the lower legs in an adjusted position requires a relatively complex valving arrangement. Also, close tolerances would be required in the valve because it is the closing of the valves that prevents hydraulic fluid flow communication between the pistons of opposing legs.

It would be advantageous if a simple self-regulating ladder levelling mechanism could be provided that is both easy to manufacture and easy to retrofit to existing ladders.

Summary of the Present Invention In a first aspect the present invention provides a

levelling mechanism for a ladder having opposing stiles and a plurality of rungs extending between the stiles, the mechanism including: two members, each movable up and down at an in- use lower end of a respective stile; and two connecting elements that each connect to a different point on and extend from one member to connect to a different point on the other such that, as one member moves down with respect to its stile, the other member is caused by the connecting elements to move up with respect to its stile and vice versa.

By providing two connecting elements arranged in this manner, a supporting"cradle"construction can be achieved, which cradle supports the ladder for a full range of member positions and does not require a locking mechanism.

Preferably the two connecting elements extend through one of the rungs of the ladder. The ladder levelling mechanism can thereby be concealed, hiding it away from damage, fouling etc, and thus making it less likely to fail.

Whilst the use of a cradle construction obviates the need for member locking, to provide for fail-safe operation, preferably the mechanism includes a locking means operable on at least one of the members in a manner that prevents movement of both members with respect to their stiles.

Preferably the locking means includes a pivotable lever mounted for pivoting on a rung (eg. the lowest rung) of the ladder to cause one or more pins to extend through an adjacent stile and into engagement with the respective member for that stile. Preferably the lever includes two spring loaded pins which are each biased by a spring to urge towards the member, but which can be disengaged from the member when the lever is pivoted away from the stile.

Preferably in this regard the lever is activateable

by the foot of a user, typically when the user steps up onto the ladder.

As a variation to mounting the pivoting lever on the rung, the lever can be mounted inside one or both of the members for selectively engaging with an adjacent stile to lock movement of the member with respect to that stile.

Preferably, in this regard the lever can be activated remotely. For example, a push bar mounted on the ladder at a height accessible by a user's hands can be provided, and connected to the lever via a connecting member such that, when the push bar is displaced, the connecting member causes the lever to pivot, typically out of engagement with the stile. Preferably, in this regard, the lever is spring-loaded such that it is usually biased towards the stile to lock the member thereagainst.

Preferably the connecting member is a flexible cord or rigid rod.

Preferably the push-bar can be activated at the same time a user lifts the ladder, so that the lever can be disengaged during lifting to allow for free movement/adjustment of the member.

Preferably the push-bar extends through one of the rungs of the ladder, for example, a fifth lowermost rung off the ground (which in many ladders is typically at a height of approximately 1.5 meters from the ground).

Alternatively, instead of pushing the bar, it can be rotated to cause movement of the connecting member and thence pivoting movement of the lever. The push-bar can alternatively be located outside of the rung but adjacent thereto.

Levers can also be provided in each member on either side of the ladder. The push-bar can be connected to those levers via a respective connecting member on either side of the ladder.

Alternatively, instead of using a lever, a locking element can be provided on one (or both) of the connecting elements where it extends through one of the ladder rungs,

which locking element can be selectively engaged by a catch to thereby prevent connecting element (s) movement.

In this regard, the locking element can be defined by a key member located on the or each connecting element and having one or more projecting ribs which are selectively engageable with a catch in the form of a moveable rack of teeth. The ribs can mesh with the teeth to thereby lock the connecting element against movement. Again, in this regard, the rack of teeth may be moved into and out of engagement with the key member by a pivoting lever on the rung or, more preferably, by a push-bar located remote from the rung (e. g. at the fifth lowermost rung), the push-bar being connected to the rack of teeth by a connecting a member. Also, the catch may usually be biased into engagement with the locking element by a spring means.

In another alternative, the locking means can be provided in the form of a floatable pulley supported at each stile, each pulley guiding the connecting elements and being moveable against a respective member by the connecting elements, when weight is placed on the ladder, to lock movement of that member with respect to its stile.

Preferably each connecting element is an elongate inextensible but flexible member that is slidable within a rung. Each connecting element in this regard is typically a cord. When the term"cord"is used herein, it is to be interpreted broadly to include rope, wire, ties, tape, wire rope, etc.

Preferably, one of the connecting elements is connected to an upper part of one member, and extends around a first pulley at that member, and through a rung and then around a second pulley at the other member to a connection at an upper part of the other member; and the other of the connecting elements is connected to a lower part of the one member and extends around either the first pulley or a separate third pulley, through the rung and then around either the second pulley or a separate fourth

pulley, to a connection at a lower part of the other member. Thus, two or four pulleys for guiding the connecting elements through the rung can be provided.

When two pulleys are employed, one in each member, each pulley can be mounted to the ladder (eg. at a rung opening) or incorporated into a floating pulley block that is located adjacent to a respective open end of the rung, and is maintained thereat but biased away therefrom by a spring. In this regard the locking means can be a frictional element on the block that is engagable with the member such that, when weight is placed on the ladder to tend to move the stiles down with respect to the members, the rung acts on the connecting elements, which in turn pull on each block to cause it to be moved against the spring bias until the frictional element engages its respective member, and thereby prevents further movement of the block by the connecting elements, and therefore of the member with respect to its stile.

In another variation the two members can each have a profile that is shaped to enable part of-the member to wrap around a respective stile to better secure the member to its stile. In addition, or alternatively, a cap can be mounted to an in-use upper end of each member, the cap itself optionally being shaped to wrap around the respective stile and guide and facilitate a sliding securement of the member to the stile.

Accordingly, in a second aspect the present invention provides a levelling mechanism for a ladder having opposing stiles and a plurality of rungs extending between the stiles, the mechanism including: two members, each moveable up and down at an in-use lower end of a respective stile; a member connection mechanism arranged such that as one member moves down with respect to its stile, the other member is caused to move up with respect to its stile and vice versa; and

a guide mechanism mountable at an in-use upper end of each member and adapted for capturing at least part of the stile for sliding therewithin to facilitate securement and guided movement of the member with respect to its stile.

Preferably, the guide mechanism is an end-cap fasteningly mounted at the upper end of the member.

Preferably the cap has opposing fingers protruding therefrom, each finger extending around and securing a respective part of the stile to capture the same for sliding within the fingers.

Preferably, the levelling mechanism of the second aspect is otherwise as defined for the first aspect.

In a third aspect the present invention provides a ladder including the mechanism (s) of the first and/or second aspects.

Brief Description of the Drawings Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1 to 4 show, respectively, perspective, front, side and plan, partly sectioned views of a first levelling mechanism for a ladder, in accordance with the present invention; Figure 5 shows a perspective view of a component of the levelling mechanism of Figures 1 to 4; Figures 6 and 7 show, respectively, end and perspective views of an alternative component of the levelling mechanism of Figures 1 to 4; Figures 8 to 10 show detailed sectional views, respectively, in plan, front and side elevation of an alternative locking mechanism for the levelling mechanism of Figures 1 to 4; Figures 11 to 13 show detailed sectional views, respectively in side, front and plan elevation of a remote

activating mechanism for the locking mechanism of Figures 8 to 10; Figures 14 to 16 show detailed sectional views, respectively in plan, front and side elevation of a further alternative locking mechanism for a ladder and levelling mechanism similar to that shown in Figures 1 to 4; Figures 17 to 19 show detailed sectional views, respectively in plan, front and side elevation of a further alternative locking mechanism for a ladder and levelling mechanism similar to that shown in Figures 14 to 16; Figures 20 and 21 show front and side views of a remote activating mechanism for the locking mechanism for Figures 22 and 23; Figures 22 and 23 show detailed sectional front and side views of an alternative locking mechanism to those described in Figures 8 to 19; Figures 24 and 25 show respectively sectional plan and an unsectioned front detail of a guide arrangement for a ladder levelling mechanism in accordance with the invention; Figures 26 and 27 show similar respective views to Figures 24 and 25, but of an alternative guide arrangement; and Figures 28 to 30 show, respectively, front, side and plan, partially sectioned views of a second embodiment of a levelling mechanism for a ladder, in accordance with the present invention.

Modes for Carrying Out the Invention Different levelling mechanism embodiments are shown in the drawings and are described herebelow. Embodiments 1 and 2 can make use of the locking mechanisms of Figures 8 to 24 whilst embodiment 3 makes use of a different locking mechanism.

Embodiment 1 Referring firstly to Figures 1 to 7, a self-levelling mechanism for a ladder 10 is depicted. The ladder has a pair of opposing stiles 12,13, with a plurality of rungs 14 extending between the stiles. At least a lower one of the rungs 14'is hollow for receiving two connecting elements in the form of upper cable 16 and lower cable 17 therethrough (described in greater detail below).

First and second extension legs 18,19 are slidably mounted to respective stiles 12,13, each for effectively extending or shortening the length of the ladder at that side. Each leg has a ground engaging foot 20,21 at a lower end thereof for engaging and stabilising the ladder on ground. Typically polymeric and optionally deformable feet are employed.

Each leg is supported for sliding on its respective stile by being located between opposing stile flanges 22, as best shown in Figures 3 and 4. Alternative arrangements are shown in Figures 24 to 27 (described below). Each leg is also retained for sliding on its respective stile by a mounting bracket 24 (see in particular Figures 5 to 7 which show two different bracket configurations) bolted to its respective stile by bolts or rivets 25 (Figure 1). The use of bolts or the like enables retrofitting of the levelling mechanism to an existing ladder.

Each leg has a pair of lateral flanges 26 defining a channel 28 therebetween (as best shown in Figure 3), and oppositely projecting lips 29 of the bracket 24 retain the leg on the bracket via the lateral flanges. As best shown in Figure 5, a slot 30 is defined on either side of bracket 24 so that the flanges 26 slide and are retained in respective slots 30. Also the bolts 25 can extend through the channel 28. The bracket is thus configured to allow a free but secure sliding of each leg on its respective stile.

The lower rung 14'has opposing open ends 31, which

open into channel 28. Positioned adjacent to each open end 31 are two respective pulleys 36,38. The pulleys are mounted between laterally projecting flanges 40 of bracket 24. Upper pulleys 36 are located on each side of the ladder to support and guide upper cable 16 as shown.

Lower pulleys 38 are located on each side of the ladder to support and guide lower cable 17 as shown.

However, as shown in Figures 6 and 7, the two pulleys can be replaced at either stile with a single double groove pulley 41, which functions in a similar manner to the two pulleys but with a different cord threading arrangement. This threading arrangement is described below in detail for pulley 82 of the second embodiment of Figures 28 to 30 and hence will not be described here. In all other respects the mounting bracket 24 of Figures 6 and 7 is the same as the bracket of Figure 5. The use of two separate pulleys 36,38 also separates and thus better maintains the cables 16 and 17 in a separated orientation within the rung 14'in use.

Also mounted on rung 14'is a locking lever 42. The locking lever pivots about a hinge 44 located in a bracket 46 attached to rung 14'and/or stile 12. The lever is pivotally connected to a pin retaining plate 48, through which a pair of spring-loaded pins 50 extend. Each pin extends through a spring 52, captured in a hollow pin block 54, the spring urging its respective pin to extend through a central wall of stile 12 and into engagement with one of the lateral flanges 26 of leg 18.

A series of holes are formed in the flange 26, so that one or both pins 50 can be located in those holes to lock the leg 18 against movement with respect to its stile. When so locked, the other leg 19 is also locked, because the cables 16,17 cannot now be moved.

When the lever 42 is depressed downwardly (ie. in the directly of arrow D of Figure 2), it urges the plate 48 away from stile 12. The plate engages pins 50, (typically at an enlargement thereof), to move them out of engagement

with the holes in flange 26, thus freeing up leg 18 for sliding.

In use of the ladder 10 on uneven ground, a user locates the ladder in position and, with the locking lever disengaged (depressed), the legs 18,19 are allowed to slide up and down with respect to stiles 12,13. The user manoeuvres the stiles until they are generally vertical, and until the rungs are generally horizontal (ie. until the ladder is"plumb"). On uneven ground, as shown in Figure 1, one leg will be caused (eg. by gravity or by the user) to extend down further than the other to maintain the ladder stiles in a vertical orientation. The cords 16, 17 ensure that as one leg is moved down, the other leg moves up (and vice versa).

A user can now step onto any one of the rungs (eg the lower rung 14'). In so doing the stiles 12,13 and thus each pulley is moved downwardly relative to the legs 18, 19 thus tensioning cords 16 and 17, which then act as a cradle for the ladder.

In a usual mode of usage, a user steps up onto the lower rung 14', and deliberately steps onto lever 42.

This removes the pins 50 from an engagement with flange 26 of leg 18 and thus frees both legs up for sliding with respect to their stiles 12,13. The two cord arrangement 16,17 provides a self adjusting and supporting cradle for the ladder. With the user's weight generally evenly distributed on the ladder, the legs are allowed to automatically adjust until a generally vertical ladder orientation is achieved. The two-cord configuration facilitates this in a smooth and safe manner.

Once the ladder has reached its desired vertical orientation, taking into account any ground subsiding as a result of the user moving their weight on the ladder, the user simply removes their foot from lever 42, and the springs 52 loading the pin 50 draw the lever back up again and urge the pins to move into any aligned hole (s) in flange 26. The employment of two pins maximises the

chance of at least one of those pins being aligned with a hole, or closely near a hole. Thus, the pin (s) rapidly lock the ladder once an optimal vertical orientation has been achieved. The ladder is thus locked in this orientation on uneven ground and the user can now continue to use the ladder for its desired purpose.

Alternative Locking Mechanisms Referring now to Figures 8 to 13, like reference numerals will be used to denote similar or like parts and, where parts differ, different reference numerals will be used.

In this embodiment, the locking mechanism of Figures 1 to 4 is replaced by a mechanism having remote actuation.

This mechanism replaces the lever-locking mechanism 42 of Figures 1 to 4.

This alternative locking mechanism includes a locking plate 56 located within leg 18 and connected for pivoting with respect to flanges 40 of bracket 24, via a U-shaped pivot arm 58. The locking plate pivots about an upper end of pivot arm 58 and is connected thereto via a pair of spaced-apart integral loops 60.

The U-shaped pivot arm 58 also defines a semicircular rearwardly projecting protrusion 62 which defines a passage between the pivot arm and an opposing face of the locking plate, and through which a remote adjustment cable 64 can be threaded. At its lower end, the cable 64 is tied to and extends through the opposing flanges 40 of bracket 24 and at its upper end, cable 64 is connected to a remote actuation mechanism for the locking mechanism (described below with reference to Figures 11 to 13).

A pair of spring arms 66, each having a laterally projecting end 68, extend up from the bracket 24 and engage against the outside of the pivot arm 58 as shown.

The spring urges the pivot arm and thus the locking plate 56 towards flanges 26 of leg 18, unless an oppositely directed force is applied to the spring.

As shown, the locking plate has a number of projecting lugs 70 provided on that face opposing the flanges 26. Typically four such lugs are employed, one adjacent to each corner of the locking plate 56. The lugs are sized and located so as to be alignable with a plurality of holes 72 formed in series along each flange 26 of leg 18. As best shown in Figures 8 and 9, two opposing upper lugs 70 are aligned with respective opposing holes 72 in flange 26 and are urged thereinto by the action of spring arms 66. When so aligned, the holes and lugs are so spaced that the lower two lugs 70 are not aligned with respective holes 72. This makes for easy pivoting removal of the lugs 70 from their holes 72 (as described below). As an alternative, the lower opposing lug 70 can be aligned with respective hole 72, in which case the upper two lugs are not aligned and do not extend into respective holes 72.

Thus, the locking plate 56 prevents sliding movement of leg 18 with respect to its stile 12. This is because the plate 56 is connected via arm 58 to bracket 24, which in turn is connected to the stile 12. However, once the locking plate 56 is pivoted away from flanges 26, the lugs 70 are moved out of respective holes 72, and leg 18 (and hence leg 19) is freed up for sliding movement with respect to the stiles 12,13, in the same manner as described above for Figures 1 to 4.

Pivoting away of the locking plate 56 from flanges 26 is facilitated by a remote actuation mechanism as depicted in Figures 11 to 13. Typically, this remote actuation mechanism is associated with a rung that is at a height readily accessible by a user's hands when standing next to the ladder or on the lowermost rung, for example, a fifth lower most rung 14". In many ladders having standard rung spacings, the fifth rung above the ground is typically about one and a half meters from the ground in use, and this has been found to be an optimal height for locating the actuation mechanism for access by most user's hands.

However, the mechanism can also be located in the sixth or fourth rung above the ground etc.

As will be seen, an upper end of adjustment cable 64 is connected to the stile 12 via a pin-bolt arrangement 74, which is itself bolted to a wall of this stile.

The actuation mechanism includes an adjustment bar 76 which extends right through rung 14", and has an enlarged griphead 78. Typically gripheads are provided at opposite ends of the adjustment bar 76, each for grasping by a respective user's hand.

It will be seen that the cable 64 extends through an eyelet 80 formed through the bar 76, such that movement of the bar causes a movement of the cable 64. For example, as shown in dotted outline in Figure 11, a user can move the bar 76 upwardly in the hollow spacing of rung 14", causing the cable 64 to move therewith. The user can do this, for example, by pressing on opposing gripheads 78 with respective thumbs thereof, whilst gripping around the back of each stile with their fingers of respective hands.

The cable can either be fixed to bar 76 or be slideable therethrough. In either case, by moving the bar in the manner described, the cable is caused to pull upwardly, and this movement is transferred down to the pivot arm 58.

Alternatively, the bar can be moved towards the user or rotated within the rung about its longitudinal axis.

In any case, the cable length is set such that these various movements of the bar translate as a cable pulling or displacement via protrusion 62 to arm 58, sufficient to pivot the locking plate out of engagement with flanges 26 of leg 18 (ie. so that lugs 70 are moved out of their respective holes 72). This then frees the legs 18,19 for sliding movement. As soon as the user releases bar 76 it drops (ie. under the influence of gravity) to its position as shown in Figure 11. This restores the cable to its position of Figures 8 and 9, so that the locking plate pivots back into engagement with the flanges 26, with one of either the upper or lower lug pairs 70 aligning with

and extending into respective holes 72. This again locks the legs against sliding.

As described above for the locking mechanism arrangement of Figures 1 to 4, the mechanism needs only to be employed on one side of the ladder, because the two- cord arrangement translates locking of one leg to a locking of the opposite leg. However, the locking mechanism of Figures 8 to 13 can also be provided on the opposite stile 13.

A further advantage of the hand-activated (remote) locking mechanism is that a user does not need to step onto the lever 42 and disengage it with their foot. For example, a user can pick-up the ladder 10, and grasp it on either side with their hands adjacent to the adjustment bar 76 (ie. adjacent to rung 14"). The user can carry the ladder in this manner with the legs locked but, when positioning the ladder, for example on an uneven surface, can press or rotate the bar 76 forwardly (or rearwardly) with the thumbs, thus unlocking the legs 18,19 for sliding. On uneven ground, the legs then adjust to the appropriate height (as described above) and the user can then release bar 76 to lock the legs in place.

The remote activating mechanism can also be employed for the lever 42 mounted on rung 14'. In other words, this lever can then be operated either by hand or foot.

Because of the unique cradle support arrangement provided by the two chords 16, 17, prior to or even when stepping onto the ladder, the user can check for any ground subsidence and can do this with the legs in an unlocked configuration without the risk of either of the legs sliding upwardly or downwardly. Once satisfied that the ladder is on a sufficiently firm footing, the user can lock the ladder and then climb up it for further use.

Also, because of the unique cradle support arrangement, even if the bar 76 is inadvertently bumped the ladder does not collapse.

Reference will now be made to Figures 14 to 16, and

like reference numerals will be used to denote similar or like parts whereas different components will be indicated by different reference numerals.

Figures 14 to 16 depict an alternative locking mechanism to that shown in Figures 8 to 10, although the locking mechanism can also employ the remote actuation arrangement of Figures 11 to 13. This locking mechanism is housed within a hollow region 90 of a modified stile flange 22'. In addition, the locking plate 56 of Figures 8 to 10 is replaced with a pivot mounted locking plate 92.

In this regard, locking plate 92 is pivotally coupled via a pin 93 to a pivot actuation plate 94. Pin 93 is in turn mounted to a backing plate 95. The actuation plate 94 includes a projecting lug 96 which is received in a cutaway portion 98 of locking plate 92. Furthermore, a rod connection lug 100 projects from the actuation plate 94 to enable a rod or cable 102 to be fastened or tied to the actuation plate.

The locking plate 92 includes two upper and two lower locking lugs 103,104 (similar to projecting lug 70), and in addition a boss 106 projects rearwardly from the locking plate 92. The boss 106 is received within and fastened to a helical spring 107, which urges the plate 92 against movement delimiting shrouds 108. The upper and lower locking lugs 103,104 are aligned with respective holes 109,110 in the stile flange 22. These holes can in turn align with a series of holes 112 formed in a step wall 114 of modified extension leg 18'. As shown in Figures 14 and 15, the upper locking lugs 103 have been urged to extend through their respective holes 109 and aligned holes 112, thus locking the extension leg 18' against movement with respect to the adjacent stile 12.

Thus, in use the locking plate 92 is normally urged out of its locking position by the helical spring, being retained against the shrouds 108, with each of the upper and lower locking lugs sitting in their respective holes 109,110 in the stile flange 22 and the lugs not extending

into any aligned holes 112.

However, when a user actuates rod 102 (e. g. using a rod actuation mechanism as shown in Figures 11 to 13) lug 100 is drawn upwardly, causing the actuation plate to pivot around pin 93. This urges the projecting lug 96 against the locking plate 92 at cutaway portion 98. This in turn causes the plate to pivot around pin 93, twisting spring 107 as shown, and advancing the upper locking lugs 103 into aligned holes 112, thus locking the extension leg 18'against movement with respect to stile flange 22.

Once they are in the locked position, the lugs 103 are held therein by friction, their angled offset, together with the weight of the user on the ladder. When the user steps off the ladder, the rod 102 can be pushed downwardly (i. e. by the remote actuation mechanism) to cause the locking plate 92 to pivot away from extension leg 18'and thereby release the upper locking lugs. It should also be noted that further downward movement of the rod 102 can cause the lower locking lugs 104 to be urged towards extension leg 18'and, for example, into alignment with any adjacent holes 112. Thus, locking may be achieved either by upward or downward extension of rod . 102, depending upon whether the holes 112 are aligned with the upper holes 109 or the lower holes 110.

Reference will now be made to Figures 17 to 19 where like reference numerals are used to denote similar or like parts. Different components are indicated by different reference numerals.

In this locking mechanism embodiment, a locking assembly 120 is mounted within hollow region 90 of stile flange 22'. The locking assembly includes upper and lower pin guide sleeves 122, 123 in which T-shaped pins 124,125 are slidably guided. Each pin has an end shank 126,127 which can be urged out of the end of its respective pin guide sleeve 122, 123 and into an aligned hole 112 in step wall 114. Typically, each pin 124,125 is urged towards the modified extension leg 18"by a respective leaf spring

128,129 which urges against a transversely extending end part 130 of each T-shaped pin. A modified rod 132 extends downwardly in the hollow region 90 from a remote actuation mechanism (such as that shown in Figures 11 to 13). The rod 132 is spring loaded at its lower end by a captured helical spring 134, located between a washer arrangement 136 and a lower end of assembly 120.

The rod 132 extends through an elongate gap 138 in each T-shaped pin, and is formed so as to have angled ramps 139,140 along its length. The ramps are sized and spaced such that as the rod 132 is drawn upwardly, it moves through the elongate gap of each T-shaped pin. When so moved a respective ramp 139,140 eventually and progressively engages against the transverse end part 130 of each T-shaped pin causing the pin to be moved to the right away from leg 18"and against the biasing force of its respective leaf spring 128, 129. This moves each pin and shank 126,127 out of an aligned hole 112, thus freeing extension 18"for sliding with respect to the stile 12. Also, when the rod is moved upwardly, helical spring 34 is compressed, providing a resistive force to rod upper movement. When the rod is released, helical spring is allowed to extend again, drawing the rod downwardly, and allowing the leaf springs 128 and/or 129 to urge their respective T-shaped pins into any hole 112 in alignment with the pin guide sleeves.

In the arrangement shown in Figure 18, the upper pin and shank 126 is in alignment with a respective hole and has been extended thereinto by leaf spring 128. The lower pin shank is not so aligned and as a result pin 125 located away from leg 18", with the end part 130 forcing leaf spring 129 to the right. Thus, extension leg 18"can be locked against movement by either the upper 126 or lower 127 pin end shank.

Reference will now be made to Figures 20 to 23 which depict a different remote actuation mechanism and different locking mechanism to those previously described.

Like reference numerals will be used to denote similar or like parts, and different components will be indicated by different reference numerals.

Referring firstly to Figures 20 and 21, an alternative remote actuation mechanism to that depicted in Figures 11 to 13 is shown. The mechanism is associated with an upper remote rung 14" (e. g. a fifth lowermost rung in the ladder). The actuating mechanism includes a cross bar 150 located outside rung 14"and extending between the opposing stiles 12,13 with a rod or cable 152 extending downwardly from the cross bar.

A short rung connecting rod portion 154 (e. g. which is separate to or an extension of rod 152) extends upwardly from the cross bar 150 and through rung 14". The end of the rod portion is captured within the rung by inserting a pin 156 (e. g. a split pin) therethrough.

Thus, the cross bar can be lifted up (e. g. by the user's thumbs) with reference to the rod 14". When so lifted, the rod 152 is drawn upwardly.

Referring now to Figures 22 and 23, it will be seen that the lower end of rod 152 is attached to a lift arm 158, the lift arm being supported under lowermost rung 14'. The lift arm 158 is connected via projecting fingers 160 to a rack shroud 162. In this regard, the fingers extend through an appropriately sized aperture 164 in rung 14'. Extending within the rack shroud is a rack of teeth 166. The arrangement is such that when the cross bar is lifted upwardly with respect to rung 14", rod 152 acts on lift arm 158 causing it to be raised with respect to rung 14'. This upward movement is in turn is translated to the rack shroud 162 via the fingers 160, causing the rack of teeth 166 to be moved upwardly.

As can also be seen, a double pulley arrangement 168 is mounted within a pulley housing 170 which is inserted into an end of the rung as shown. As previously described, the double pulley guides the cords 16 and 17 which extend through rung 14'. The cords cause the

extension legs 18 and 19 to move upwardly and downwardly during ladder levelling (as previously described).

In this embodiment, the upper cord 16 has a ribbed key 172 fastened thereto. The key has a plurality of ribs 174 extending outwardly therefrom as shown. The ribs are spaced to mesh with the rack of teeth 166 as depicted, to lock the key against movement with respect to the rack of teeth. This in turn locks cord 16 against movement (and hence locks legs 18,19 against movement with respect to their stiles 12,13). When the rack of teeth is lifted out of engagement with the key 172, cord 16 is free for movement around the pulley arrangement, freeing up the extension legs 18,19 for movement with respect to their stiles.

A leaf spring 176 maintains a downward pressure on the rack shroud 162, thus normally locking the key 172 against movement with respect to the rack 166. However, the leaf spring biasing can be overcome when the user pushes upwardly on cross bar 150.

Embodiment 2 Reference will now be made to Figures 24 and 25 where like reference numerals are used to denote similar or like parts, and different reference numerals denote different parts.

In this embodiment, the extension legs 18,19 are replaced with wrap-around extension legs, in this case an extension leg 180. Extension leg 180 includes opposing fingers 182,183 which are each adapted to wrap around a respective flange 22 of the stile 12. In addition, inner fingers 184,185 project from leg 180 and, in conjunction with their respective fingers 182, 183, define in end view a C-shaped profile in which the respective stile flange 22 nests. This arrangement provides for a secure mounting of each leg to its respective stile and facilitates sliding movement of each leg along its respective stile. As best

shown in Figure 24, leg 180 can thus be formed from an extrusion having a constant cross-sectional profile.

Thus, leg 180 can easily be extruded from a light weight and strong metal such as aluminium, or may even be moulded or extruded from plastics.

During such extrusional moulding, excess material is emitted from the legs leaving longitudinal holes 186, 187 in the leg. Each hole can be sealed off using a cap 190.

The cap can optionally be provided with a guide face 192 for sliding engagement with stile flange 22, to further enhance sliding on its respective stile.

Referring now to Figures 26 and 27, where like reference numerals are used to denote similar or like parts, an alternative mechanism for slidingly mounting extension leg 18 to stile flange 22 is depicted. In this embodiment, an end cap 200 is mounted to the in-use upper end of extension leg 18. The end cap has projecting opposing fingers 202,203 which wrap around respective stile flanges 22 as best shown in Figure 26. In addition, the cap has a protruding portion 205 which nests inwardly of and between the stile flanges 22, so that the cap defines essentially C-shaped channels for each stile flange (as best shown in Figure 26). Thus, a standard shape for legs 18,19 can be employed, and then the end cap 200 attached thereto, simplifying the leg construction over that shown in Figures 24 and 25.

A suitable guide bracket can be mounted towards the in-use lower end of stile 12 as necessary. As also shown in Figure 26, a locking mechanism 206 similar to that described in Figures 14 to 16 or 17 to 19 can be located within one of the stile flanges 22 to selectively lock leg 18 against sliding with respect to stile 12.

Embodiment 3 Referring now to Figures 28 to 30, like reference numerals will be used to denote similar or like parts to those of Figures 1 to 5, and different components are

indicated by different reference numerals.

In this embodiment, two cords are used, similar to cords 16 & 17, but for ease of reference will be referred to as cables, namely upper cable 77A and lower cable 77B.

The upper ends of cable 77A are each attached to a respective leg 18,19 via pins 78, and the lower ends of the lower cable are each attached to a respective leg via couplings 79.

Mounted within each leg is a floating pulley block 80. Mounted for rotation within the pulley block is a double groove pulley wheel 82 having a supporting pin 83 located as shown. The upper cable 77A is located in one of those grooves to extend under the pulley wheel (as best shown in Figures 14 and 16) and the lower cable 77B is located in the other of those grooves to extend over the pulley wheel.

Each pulley block is also mounted to a respective stile against general vertical movement with respect thereto by a tubular helical spring 84, with one end of the spring being mounted to the stile central wall 86 (Figure 16) and the other end being mounted to the pulley block at a facing inner wall thereof.

Also mounted at the pulley block inner wall is a pair of frictional buffers 88 which are engageable with lateral flanges 26 of each leg (to prevent the sliding thereof).

In use, the ladder is placed on uneven ground and set in a plumb orientation, with the legs adjusted with respect to their stiles. For example, if the right leg of Figure 7 is moved downwardly, tension is placed on lower cable 77B, and is transmitted around to left coupling 78, thus lifting up the left leg. The length of that cable in the left leg is thus shortened, whereas the length of cable 77A in the right leg is lengthened. The lifting of left leg places tension on upper cable 77A and the length of that cable in the right leg is thus shortened, whereas the length of cable 77A in the left leg is lengthened.

Without weight on the ladder, the biasing force of

spring 84 is sufficient to maintain the pulley block 80 in a floating (ie. spaced) orientation from each leg, thus facilitating the free movement of the lower and upper cables in each pulley block, guided on pulley wheel 82.

Once a user places weight on the ladder (eg. at lower rung 14') the stiles 12, 13 start to move downwardly with respect to each of the leg, thus transferring tension onto each of the cables 77A, 77B. This tension causes each pulley block to be pulled inwardly by the cables, against the outward biasing force of spring 84, so that the buffers 88 engage their respective flanges 26. Once engaged, the pulley block is locked against floating movement within its respective leg, thereby locking the leg with respect to its adjacent stile.

Once the user steps off the ladder, there is no longer tension force imparted to the upper and lower cables, and thus the spring 84 can restore the pulley block into a floating orientation with respect to each leg, thereby unlocking the legs from the stile.

One disadvantage of this second embodiment is that the legs are always locked against sliding movement once a user steps onto the ladder and places weight thereon.

However, the cradling advantage is still provided by the two cables 77A, 77B as described above.

Typically the cord/cable used in each of the embodiments above is relatively non-stretchable but flexible, and is preferably formed from wire rope, braided synthetic rope or cable etc, having integrity of length.

Preferably the majority of components of the levelling mechanism and the ladder itself are formed from appropriate structural materials, typically metals such as aluminium or steel. Some components can also be formed from high strength plastic material.

A number of advantages arise from the preferred embodiments of a levelling mechanism as described.

Firstly, various components of the mechanism are housed or shrouded within the legs, rungs and stiles of the

ladder, thus eliminating user interference therewith (eg by being kicked, bumped, impacted upon, fouled etc).

As a result, integrity of the levelling mechanism and locking mechanism is maintained, leading to long life of the components and overcoming the need for regular servicing etc.

The double cord/cable arrangement provides a safety cradle which does not allow for leg-stile sliding or slippage when loaded, even if the locking mechanism fails or is inadvertently deactivated.

The displacing of one leg causes a corresponding opposite displacement of the other, so that only slight or minimal leg sliding movement to quickly adjust to uneven terrain is required.

The levelling mechanisms described are simple in their configuration, thus enabling for ease of construction.

Many of the components of the levelling mechanism are freely available, and thus fabrication costs can be substantially reduced.

'The mechanism can easily be retrofitted to existing ladders (eg. in a"bolt-on"manner).

'The legs can be shaped or provided with upper end-caps to facilitate easy fitting to existing stile shapes, and also to facilitate smooth and secure guidance in use and over time.

In some embodiments, the locking mechanism is automatically activated upon use of the ladder by a user, making for considerable ease of handling and operation of the ladder on uneven terrain.

Whilst the invention has been described with reference to a number of preferred embodiments, it should be appreciated that the invention can be embodied in many other forms.