GB2481449A

GB2481449A - A levelling device

Info

Publication number: GB2481449A
Application number: GB201010729A
Authority: GB
Inventors: Martin Paul Warren
Original assignee: WARRENTECH Ltd
Current assignee: WARRENTECH Ltd
Priority date: 2010-06-25
Filing date: 2010-06-25
Publication date: 2011-12-28
Also published as: GB201010729D0; WO2011161458A1

Abstract

A levelling device 2 for a ladder comprises a rigid body 4, and pair of movable stiles 6, 8. A transmission mechanism 10 connects the stiles such that displacement of one of the stiles in a first direction is compensated by displacement of the other stile in the opposite direction. A locking mechanism 12 is included for locking the transmission mechanism when a force is applied to both stiles in the same direction, that is when the device is settled on the ground and weight is applied to it. The stiles are thus prevented from any relative movement providing a stable footing. The locking mechanism can be a toothed wheel 44 or a valve in a hydraulic system (fig 9). The body of the levelling device can be secured to the bottom of a ladder and the stiles moved to accommodate uneven support surfaces.

Description

A LEVELLING DEVICE

This invention relates to a levelling device for a ladder.

Known ladders have a pair of upwardly extending stiles, interconnected by a plurality of horizontally extending rungs. In use, the lower ends, or "feet" of the stiles rest on the ground, and, with the stiles inclined at approximately 75 degrees from the vertical, the upper ends of the stiles rest against an upright surface, such as a wall, relative to which a user of the ladder wishes to be elevated.

When used on ground which is not level, or which is uneven, or on steps, it is often difficult to position the ladder so that it may be ascended safely since it is essential that the weight of both the ladder and the user are borne equally by the feet of both stiles and that the ladder is vertical. Usually when ladders are used in such circumstances, the user has to support one of the feet with chocks. This is inconvenient, time consuming, and inherently less safe than when the ladder is used on level, even ground.

Devices for accommodating uneven surfaces have previously been proposed.

W00220933 discloses an arrangement in which two extension legs are slidably carried by respective rods attached to legs of a ladder. The extension legs are suspended by a flexible tether which extends through a hollow rung of the ladder so that as one of the extension legs is pulled downwards with respect to the ladder, the other extension leg is drawn upwards. Locking controls are provided to lock the extension legs directly to the rods in the legs of the ladder. The locking controls comprise steel rings located about the rods which are connected by a second flexible tether via a lower rung of the ladder. An upward force is exerted on both extension legs to tension the second tether thus inclining the steel rings thereby locking the extension legs with respect to the rods.

US6336521 discloses a device in which a tubular support arch (arcuate bar) is slidably received by brackets secured to the feet of a ladder. The ends of the support arch are provided with feet. The support arch may be adjusted to accommodate sloped surfaces and locked to the brackets to hold it in position during use. Release mechanisms are provided to allow adjustment.

These devices lock the support arch/extension legs directly to the connecting brackets/ladder to prevent movement of the arch/legs with respect to the ladder when in use.

According to a first aspect of the invention, there is provided a levelling device for a ladder comprising a rigid body; a pair of stiles movable with respect to the body; a transmission mechanism connecting the stiles such that displacement of one of the stiles in a first direction causes displacement of the other stile in a substantially opposite second direction; and a locking mechanism for locking the transmission mechanism when a force is applied to both stiles in substantially the same direction thereby preventing displacement of the stiles with respect to the body.

The locking mechanism may comprise a rotatable wheel which is locked against rotation to lock the transmission mechanism.

The transmission mechanism may comprise a flexible or articulated element connected to each stile, whereby the flexible or articulated element is arranged to rotate the wheel when the stiles are displaced in opposite directions.

The levelling device may further comprise a first guide disposed between the wheel and a stile and a second guide disposed between the wheel and the other stile, the flexible or articulated member being arranged with respect to the first guide, second guide and wheel such that when a force is applied to both stiles in substantially the same direction, the flexible or articulated member exerts a force on the wheel in a substantially opposite direction.

The locking mechanism may comprise a locking element which engages with the wheel to lock the wheel against rotation.

The wheel may have a toothed periphery, wherein the locking element engages the toothed periphery to lock the transmission mechanism.

The wheel may be movably coupled to the rigid body for displacement into and out of engagement with the locking element. The locking mechanism may comprise a bias for biasing the wheel out of engagement with the locking element. The wheel may be mounted on a locking arm which is pivotally connected to the rigid body. The biasing means may comprise a resilient element acting between the rigid body and the locking arm.

The locking element may be coupled to the body so as to be displaceable laterally, from a nominal position, with respect to the direction of displacement of the wheel. The locking element may be biased towards the nominal position, for example by a resilient element such as a spring.

The locking mechanism may comprise a braking means for braking lateral displacement of the locking element. The braking means may comprise a receiving element which is pivotally connected to the body such that displacement of the engaging element by the wheel in the direction in which the wheel is moved causes the receiving element to pivot into braking engagement with the locking element.

The receiving element may be resiliently biased to an unlocked position in which the braking engagement with the locking element is released.

The receiving element may be one of two receiving elements which are resiliently biased towards an unlocked position by respective resilient elements which have different spring constants.

The levelling device may further comprise a retaining device for limiting displacement of the stiles with respect to the body, the retaining device comprising a cable which interconnects the stiles and a cable guide for guiding the cable between the stiles.

A resilient means may be disposed between the cable guide and the wheel for tensioning the cable.

The body may be provided with securing means for securing the device to a ladder, for example, for securing the device to the stiles at the foot of the ladder.

The securing means may comprise at least two removable brackets, each bracket comprising a plate having a first portion for contacting the body and a second portion for contacting the ladder spaced away from the first portion, and an intermediate portion defined between the first portion and the second portion, wherein the intermediate portion is arranged with respect to the first and second portions such that when a force is applied perpendicularly to the intermediate portion a moment is generated about the first portion which presses the second portion against the ladder.

The intermediate portion of each bracket may be provided with a slot for receiving a ladder rung.

The intermediate portion of each bracket may be provided with a series of slots for receiving a fastener for fastening the bracket to the body portion and for applying the force to the intermediate portion when fastened.

The second portion may comprise a lip which is arranged such that when a force is applied perpendicularly to the intermediate portion the lip is pressed against the ladder to clamp the ladder against the body.

It will be appreciated that the securing means described above may be used to secure other devices or objects to ladders and is therefore an invention which may be used independently of the levelling device.

The transmission mechanism may be a hydraulic transmission wherein the locking mechanism comprises a locking valve which is closed to lock the transmission when a force is applied to both stiles in substantially the same direction.

According to a second aspect of the invention, there is provided a ladder comprising a levelling device according to the first aspect of the invention.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a perspective view of a levelling device for a ladder; Figure 2 is a cut-away perspective view of the levelling device shown in Figure 1 in an unlocked configuration; Figure 3 is a sectional view of the levelling device as shown in Figure 2; Figure 4 is a sectional view of the levelling device shown in Figures 1 to 3 in a locked configuration; Figure 5 is a partial sectional view of the locking mechanism of the levelling device as shown in Figure 3; Figure 6 is a partial sectional view of the locking mechanism of the levelling device as shown in Figure 4; Figure 7 is a perspective view of the levelling device shown in Figure 1 attached to a ladder; Figure 8 is a side view of the levelling device shown in Figure 1 attached to a ladder; Figure 9 is a front perspective view of the levelling device shown in Figure 1 attached to a ladder; and Figure 10 is a sectional view of a variant of a levelling device.

Figures 1 and 2 show a levelling device 2 comprising a body 4, first and second stiles 6,8 disposed at opposite sides of the body 4, a transmission 10 interconnecting the stiles 6, 8 and a locking mechanism 12 for locking the transmission 10.

The body 4 is oblong and each stile 6, 8 is slidably received at either end of the body 4.

In the embodiment shown, the body 4 comprises a rigid box section formed by a back plate 14, a front plate 16, a top plate 18 and a bottom plate 20. The back plate 14 is folded over at each end to form guide sections 22, 24 for receiving the stiles 6, 8. The folded ends of the back plate 14 are secured to the middle portion of the back plate 14 by connecting rods 5, 86, 88. The front plate 16 is fastened to the back plate 14 and extends from the first guide section 22 to the second guide section 24. The top and bottom plates 18, 20 extend respectively over the top and bottom of the back plate 14 and the front plate 16 to form an enclosed box section. The stiles 6, 8 are supported by the guide sections 22, 24, and can move with respect to the body 4 along their length. The stiles 6, 8 are substantially parallel and project both upwardly and downwardly from the body 4. The stiles 6, 8 are of equal length.

Each stile 6, 8 comprises two elongate flanges 26, 28 joined by a connecting web 30 which extends perpendicularly to the flanges 26, 28. Each stile 6, 8 thus has an I-shaped cross-section. The stiles 6, 8 are arranged so that the web 30 is perpendicular to the length of the body 4. The stiles 6, 8 are provided with feet 32 at their lower ends and bungs/feet 34 at their upper ends. The feet 32 and bungs/feet 34 are secured to the ends of the stiles 6, 8 by fasteners such as screws.

Referring to Figures 2 and 3. the transmission 10 comprises a chain 36 which is fastened at one end to an upper portion of the first stile 6 and at the other end to an upper portion of the second stile 8. Each end of the chain 36 is fastened by flanged plates 38 which extend through a T-shaped aperture 40 in the web 30 of each respective stile 6, 8 to secure the chain 36. The flanges of the plate 38 prevent the plate 38 from being pulled through the T-shaped aperture 40 when the chain 36 is tensioned.

The chain 36 extends downwardly along the first stile 6 and under a first guide wheel 42 which is rotatably mounted to the back plate 14. The chain 36 passes from the first guide wheel 42 over a locking wheel 44, which constitutes part of the locking mechanism 12, and under a second guide wheel 46 which is rotatably mounted to the back plate 14. The chain 36 extends from the second guide wheel 46 upwardly along the second stile 8 to where it attaches to the upper portion of the second stile 8. The attaching mechanism at the second stile is the same as described at the first stile. The chain 36 is thus arranged in a substantially W-shape about the guide wheels 42, 46 and locking wheel 44.

The guide wheels 42, 46 are pulleys having a peripheral groove for guiding the chain 36.

The locking wheel 44 has teeth 48 for engaging the linkages of the chain 36. The locking wheel 44 may be a sprocket, for example a sprocket having thirty-two teeth 48.

The locking mechanism 12 further comprises a locking lever 50 which is pivotally connected at one end to a region of the back plate 14 which is adjacent the second stile 8. The locking lever 50 comprises two parallel beams joined at the ends away from the pivot by an end plate. The locking lever 50 extends away from the pivot in a direction which is away from and substantially perpendicular to the second stile 8. The locking wheel 44 is rotatably mounted between the beams of the locking lever 50. The locking wheel 44 is arranged such that it is mid-way between the guide wheels 42, 46 and above the guide wheels 42, 46 with respect to the upward direction. A torsion spring 52 is provided about the pivot of the locking lever 50 and acts between a pin 54, secured to the back plate 14, and the locking lever 50, to bias the locking lever 50 upwardly. The pin 54 is positioned above the locking lever 50 to act as a stop which limits displacement of the locking lever 50 in an upward direction.

The locking mechanism 12 further comprises first and second locking arms 56, 58 which are pivotally connected to the back plate 14. The pivotal axes of the locking arms 56, 58 are coaxial with the respective axes of rotation of the first and second guide wheels 42, 46. The locking arms 56, 58 extend from their pivots towards each other. The locking arms 56, 58 pivot independently of rotation of the guide wheels 42, 46.

Each locking arm 56, 58 is similar in construction to the locking lever 50 and so each comprises two parallel beams connected at their distal ends by an end plate.

First and second torsion springs 60, 62 are disposed about the respective pivot axes of the locking arms 56, 58. Each torsion spring 60,62 acts between a respective pin 61, 63 connected to the back plate 14 and the corresponding locking arm 56, 58 to bias each locking arm 56, 58 upwardly. The first torsion spring 60 is less stiff than the second torsion spring 62. The pins 61, 63 are positioned above the respective locking arms 56, 58 to act as stops which limit displacement of the locking arms 56, 58 in an upward direction.

As shown in Figure 5, a circular bore 64, 66 extends through the end plate of each of the locking arms 56, 58. The bores 64, 66 have identical diameters. A bar 68 having a cylindrical cross section extends through the bores 64, 66. The diameter of the bar 68 is less than the diameter of the bores 64, 66 such that, when the axis of the bar 68 is aligned with the axis of the bores 64, 66, the bar 68 is held loosely within the bores 64, 66. An engaging element 70, in the form of a disc, is formed integrally with the bar 68.

The engaging element 70 is positioned mid way along the bar 68 and extends radially outwardly from the bar 68. The outer circumferential surface of the engaging element 70 has a profiled cross-section which, in the embodiment shown, converges in a radially outward direction. For instance, the outer circumferential surface of the engaging element 70 may have a V-shaped cross-section. The engaging element 70 is held in a nominal, for example central, position between the locking arms 56, 58 by compression springs 72, 74 disposed on either side of the engaging element 70, between the engaging element 70 and the respective end plates of the locking arms 56, 58. The compression springs 72, 74 have the same stiffness. The nominal position is the position of the engaging element 70 when substantially aligned with the rotational axis of the locking wheel 44. The engaging element 70 is able to travel laterally (i.e. in the axial direction of the bar 68) by a distance which is at least equal to one whole pitch width of a tooth 48; for example, between 0.5 pitch widths and 1.5 pitch widths from the nominal position in either direction.

Referring to Figure 4, the levelling device 2 further comprises a retaining device 76 for limiting downward displacement of the stiles 6, 8 with respect to the body 4. The retaining device 76 comprises a cable 78 and a cable guide 80. The cable guide 80 has tubes 82 connected by respective pylons 84 to the pivot point of the locking wheel 44. The cable guide 80 is rotatably connected to the locking lever 50. The cable 78 is secured at one end to a lower portion of the first stile 6 and at the other end to a lower portion of the second stile 8. The cable 78 extends from the first stile 6 over a first connecting rod 86, through the tubes 82 and over a second connecting rod 88 to the second stile 8. The cable 78 is secured to the stiles 6, 8 by fasteners such as bolts.

Clamping brackets 86 are used to secure the levelling device 2 to a ladder, as shown in Figure 7. Each bracket 86 comprises a plate 88 having a first end portion 90 for contacting the body 4, a second end portion 92 for contacting the side of the stiles of a ladder and a middle portion 94 which extends between the first and second end portions 90, 92. The first and second end portions 90, 92 project perpendicularly from the middle portion 94 in substantially opposite directions. The second end portion 92 has a lip 96 along the distal edge for engagement with ladder stiles. Elongate slots 98 are provided in the middle portion 94 for receiving fasteners, such as screws. A recess 100 is provided in the second end portion 92 and the lip 96 for receiving a ladder rung.

The clamping brackets 86 are arranged such that the distal edge of the first end portion abuts the body 4 and the middle portion 94 lies substantially parallel to, and spaced away from the surface of the body 4 to which it is adjacent. The clamping brackets 86 are secured to the body 4 by fasteners which pass through the slots 98. Tightening the fasteners generates a moment about the first portion 90 which presses the second end portion 92 and the lip 96 against the ladder stiles thereby clamping the levelling device 2 to the ladder.

Prior to use, the levelling device 2 is assembled with a ladder by placing the body 4 on the ladder stiles below or adjacent to the lower rung of a ladder, as shown in Figure 7, and secured to the ladder as described above. The brackets 86 can be arranged such that the lower rung is supported by the top edge of the brackets 86 or, as shown in Figure 7, the lower edge of the recess 100. Alternatively, the brackets 86 can be inverted so that the lower rung can be supported by the opposite edge of the bracket 86 or the opposite edge of the recess 100. The clamping brackets 86 can therefore be arranged in four different configurations. Furthermore, the slots 98 provide different mounting positions for the brackets 86 with respect to the body 4. The slots 98 and the different mounting configurations thus enable the levelling device 2 to be spaced at different distances from the ends of the ladder stiles thereby enabling variation in the distance from the lower rung to the ends of the stiles between ladders to be accommodated. The preferred position of the levelling device 2 with respect the ladder is with feet of the ladder just above the bottom of the body 4.

In use, the levelling device 2 and ladder to which it is secured are lowered towards the ground. Where the ground is uneven, the first stile 6, for example, may be brought into contact with the ground before the second stile 8. As the levelling device 2 is lowered further, the first stile 6 is displaced upwardly with respect to the body 4. The displacement of the first stile 6 draws the chain 36 over the guide wheels 42, 46 and the locking wheel 44 causing them to rotate. The guide wheels 42, 46 and the locking wheel 44 act as a pulley system so that, as the first stile 6 is displaced upward, the second stile 8 is pulled downward with respect to the body 4. The displacement of the second stile 8 in a downward direction is equal to the displacement of the first stile 6 in the upward direction. Displacement of both stiles 6, 8 continues until both stiles 6, 8 are in contact with the ground. It will be appreciated that the lowering process may also involve a rotation of the levelling device 2 so that the device 2 and the ladder to which it is secured can be lowered into an upright position. Once both stiles 6, 8 are in contact with the ground, further lowering of the body 4 causes the body 4 to move downwards relatively to the stationary stiles 6, 8. The chain 36 is thus tensioned between the two stiles 6, 8 and pulls downwards on the locking wheel 44 to draw the locking wheel 44 into engagement with the engaging element 70. The downward motion of the locking wheel 44 rotates the locking lever 50 against the torsion spring 52.

As the teeth 48 of the locking wheel 4 contact the locking element 70 they force the locking element 70 downwards. At the same time, contact of the outer surface of the engaging element 70 with the surface of a tooth 48 causes the engaging element 70 and the bar 68 to be displaced laterally. The engaging element 70 is pressed against one or other of the compression springs 72, 74. Lateral displacement of the engaging element 70 accommodates imperfect alignment of the engaging element 70 with the mid point between adjacent teeth 48 and so avoids angular adjustment of the locking wheel 44 during the locking process. The engaging element 70 can be displaced by a distance which is at least equal to the width of a tooth in either direction.

Consequently, the locking mechanism 12 can be locked at the desired arrangement of the stiles 6, 8. The levelling device 2 thus provides an infinite resolution of adjustment.

Further downward motion of the locking wheel 44 forces the engaging element 70 downwards. This rotates the locking arms 56, 58 with respect to the body 4 against the respective torsion springs 60, 62. As the locking arms 56, 58 rotate the axes of the bores 64, 66 are inclined with respect to the axis of the bar 68. The edges at opposite ends of the respective bores 64, 66 are brought into biting contact with the bar 68. The edges of each bore 64, 66 thus brake lateral movement of the bar 68, and inhibit lateral displacement of the engaging element 70. The braking force increases as the downward force on the levelling device 2 increases. A sufficient downward force will therefore lock the bar 68 against the edges of the bores 64, 66 and so prevent further lateral displacement of the bar 68 and engaging element 70. Rotation of the locking wheel 44, and hence displacement of the stiles 6, 8 is prevented. Locking is achieved by a high force low contact point friction.

Figures 4 and 6 show the levelling device 2 in a locked configuration and in which the stiles 6, 8 have been displaced in opposite directions. It will be appreciated that the levelling device 2 can be locked when the stiles 6, 8 are level. The maximum displacement of the stiles 6, 8 may be limited by stops provided on the body 4 or the stiles 6, 8.

The diameters and arrangement of the guide wheels 42, 46 are such that the angle of feed of the chain 36 from the guide wheels 42, 46 to the locking wheel 44 when in a locked configuration is sufficient to transfer a substantial proportion of the upwards reaction force applied to the stile 6, 8 as a downward force on the locking wheel 44.

This ensures that the locking mechanism 12 does not disengage as a consequence of changes in the load distribution on the stiles 6, 8 when supporting a ladder.

In some circumstances, the apex of a tooth 48 aligns precisely with the apex of the engaging element 70 in which case the tooth 48 does not displace the engaging element 70 laterally. However, the lower stiffness of the first torsion spring 60, with respect to the second torsion spring 62, means that the first locking arm 56 is rotated into a locked position before the second locking arm 58. The initial locking of the bar 68 with the first locking arm 56 causes the bar 68 to pivot with the first locking arm 56.

The pivoting of the bar 68 with the first locking arm 56 tilts the engaging element 70 and so rotates the apex of the engaging element 70 out of alignment with the apex of the tooth 48. Subsequent deflection of the second locking arm 58 releases the bar 68 with respect to the first locking arm 56 so that the engaging element 48 and the bar 68 are displaced laterally by the tooth 48 in the manner described above until the bar 68 is again locked by the two locking arms 56, 58. The undesirable situation in which the locking element 48 rests against the apex of a tooth 48 is thus avoided.

When one or both stiles 6, 8 are lifted from the ground, the torsion spring 52 acts on the locking lever 50 to disengage the locking wheel 44 from the engaging element 70 and return the locking wheel 44 to an unlocked position. The transmission 10 is thus unlocked and the stiles 6, 8 are free to slide in opposite directions within the guide sections 22, 24. The springs 72, 74 return the engaging element 70 to the nominal position.

The levelling device 2 provides simple operation in which locking and unlocking of the stiles 6, 8 is automatic in response to setting or lifting the levelling device 2.

During adjustment of the stiles 6, 8, the cable 78 of the retaining device 76 slides through the tubes 82 to accommodate displacement of the stiles 6, 8. If the levelling device 2 is lifted from the floor, the cable of the retaining device prevents the stiles 6, 8 sliding out of the body 4. When the levelling device 2 is locked, the small upward motion of both stiles 6, 8, which occurs as the locking wheel 44 is pulled downwards introduces a small amount of slack in the cable 78. Simultaneously, the downward motion of the locking lever 50 draws the cable guide 80 downwards thus drawing in the slack. The arrangement of the cable guide 80 is such that the downward motion of the lever 50 is sufficient to draw in the slack without restricting or preventing engagement of the locking mechanism 12.

A spirit level, for determining horizontal and vertical orientation, may be disposed on the top panel 18 of the body 4 for assistance in orienting a ladder to which the device is fitted. The top panel 18 may be inclined to the length of the stiles 6,8 at an angle which is determined by a desired, for example a correct, inclination angle of a ladder.

The top panel 18 may, for example, be inclined at 70 degrees to the stiles 6, 8. The spirit level thus provides a "level" reading when the ladder, to which the levelling device is attached, is placed at the correct angle against a support, such as a wall, as shown in Figures 8 and 9.

In a variant of the invention, a spring may be disposed between the cable guide and the locking wheel or locking lever to resist displacement of the locking wheel away from the cable guide. The stiffness of the spring is selected so that the cable is drawn downwards with the locking wheel to accommodate slack, but does not restrict or prevent engagement of the locking mechanism.

A variant of the invention comprises lower feet 32 which stand proud of the guide sections 22, 24, and forward of the body 4. Consequently, if the levelling device 2 is mounted upside down, clamping of the device 2 to a ladder locks the lower feet 32 against the ladder stiles thereby preventing operation of the levelling device 2.

An alternative embodiment of the levelling device comprises a compressive transmission link, for example an hydraulic system, illustrated in Figure 9. Stiles (not shown) and lower rung (not shown) of a ladder are securely mounted to a body 114, relative to which a pair of auxiliary stiles 120A, 120B may move linearly. The body 114 contains a pair of hydraulic cylinders 140A, 140B and a connecting pipe 150 connecting the upper ends of the cylinders 140A, 140B. Each auxiliary stile has a piston 160A, 160B rigidly mounted thereto, which moves within the cylinders 140A, 140B. The upward movement of one auxiliary stile 120A (for example) will move its piston 160A upward within the respective cylinder 140A, resulting in transmission of hydraulic fluid from cylinder l4OAto cylinder 140B, via the connecting pipe 150, and a corresponding downwards movement of the piston 1 60B of the other auxiliary stile 120B. The relative positions of the auxiliary stiles 120A, 120B are locked by a pair of locking pistons 190A, 190B moveable within bores 200A, 200B. The locking pistons 190A, 190B each include a cross bore 210, which allows transmission of fluid along the connecting pipe 150, and are biased upwardly within their bores 200A, 200B by springs 220. When weight is applied to the body 114, the pressure in the hydraulic system increases. The hydraulic feedback loops 240A, 240B allow the application of hydraulic pressure to the upper faces 250A, 250B of the pistons 1 90A, 1 90B, causing a force on the pistons in a downward direction. Hydraulic pressure is also applied to the pistons within the cross bores 210, but this produces no net force since it is applied equally to both upper and lower cross bore surfaces. The downward force on the pistons 190 causes them to move bodily downwards against bias springs 220, to block the connecting pipe 150, thus hydraulically locking the relative positions of the auxiliary stiles 120A, 120B.

If weight is applied unequally to the stiles 120A, 120B when the device is locked, the hydraulic pressure in the cylinder on the side to which the weight is applied is greater than the pressure in the other cylinder. An hydraulic lock is maintained under these conditions as one or other of the pistons 1 90A, 190B is urged downwards under the greater hydraulic pressure, thus preventing flow from one cylinder to the other via the connecting pipe 150, and hence maintaining the locked positions of the auxiliary stiles 120A, 120B.

Claims

CLAIMS1. A levelling device for a ladder comprising: a rigid body; a pair of stiles movable with respect to the body; a transmission mechanism connecting the stiles such that displacement of one of the stiles in a first direction causes displacement of the other stile in a substantially opposite second direction; and a locking mechanism for locking the transmission mechanism when a force is applied to both stiles in substantially the same direction thereby preventing displacement of the stiles with respect to the body.
2. A levelling device according to claim 1, in which the locking mechanism comprises a rotatable wheel which is locked against rotation to lock the transmission mechanism.
3. A levelling device according to claim 2, wherein the transmission mechanism comprises a flexible or articulated element connected to each stile, whereby the flexible or articulated element is arranged to rotate the wheel when the stiles are displaced in opposite directions.
4. A levelling device according to claim 3, wherein a first guide is disposed between the wheel and a stile and a second guide is disposed between the wheel and the other stile, the flexible or articulated member being arranged with respect to the first guide, second guide and wheel such that when a force is applied to both stiles in substantially the same direction, the flexible or articulated member exerts a force on the wheel in a substantially opposite direction.
5. A levelling device according to anyone of claims 2 to 4, wherein the locking mechanism comprises a locking element which engages with the wheel to lock the wheel against rotation.
6. A levelling device according to claim 5, wherein the wheel has a toothed periphery and the locking element engages the toothed periphery to lock the transmission mechanism.
7. A levelling device according to claim 5 or 6, wherein the wheel is movably coupled to the rigid body for displacement into and out of engagement with the locking element.
8. A levelling device according to claim 7, wherein the locking mechanism comprises a bias for biasing the wheel out of engagement with the locking element.
9. A levelling device according to claim 7 or 8, wherein the wheel is mounted on a locking arm which is pivotally connected to the rigid body.
10. A levelling device according to claim 9 when appendantto claim 8, wherein the biasing means comprises a resilient element acting between the rigid body and the locking arm.
11. A levelling device according to any one of claims 7 to 10, wherein the locking element is coupled to the body so as to be displaceable laterally, from a nominal position, with respect to the direction of displacement of the wheel.
12. A levelling device according to claim 11, wherein the locking element is biased towards the nominal position.
13. A levelling device according to claim 11 or 12, wherein the locking mechanism comprises a braking means for braking lateral displacement of the locking element.
14. A levelling device according to claim 13, in which the braking means comprises a receiving element which is pivotally connected to the body such that displacement of the engaging element by the wheel in the direction in which the wheel is moved causes the receiving element to pivot into braking engagement with the locking element.
15. A levelling device according to claim 14, wherein the receiving element is resiliently biased to an unlocked position in which the braking engagement with the locking element is released.
16. A levelling device according to claim 15, wherein the receiving element is one of two receiving elements which are resiliently biased towards an unlocked position by respective resilient elements which have different spring constants.
17. A levelling device according to any one of claims 7 to 16, comprising a retaining device for limiting displacement of the stiles with respect to the body, the retaining device comprising a cable which interconnects the stiles and a cable guide for guiding the cable between the stiles.
18. A levelling device according to claim 17, in which a resilient means is disposed between the cable guide and the wheel for tensioning the cable.
19. A levelling device according to any one of the preceding claims, wherein the body is provided with securing means for securing the device to a ladder.
20. A levelling device according to claim 19, wherein the securing means comprises at least two removable brackets, each bracket comprising a plate having a first portion for contacting the body and a second portion for contacting the ladder spaced away from the first portion, and an intermediate portion defined between the first portion and the second portion, wherein the intermediate portion is arranged with respect to the first and second portions such that when a force is applied perpendicularly to the intermediate portion a moment is generated about the first portion which presses the second portion against the ladder.
21. A levelling device according to claim 20, wherein the intermediate portion of each bracket is provided with a slot for receiving a ladder rung.
22. A levelling device according to claim 20 or 21, wherein the intermediate portion of each bracket is provided with a series of slots for receiving a fastener for fastening the bracket to the body portion and for applying the force to the intermediate portion when fastened.
23. A levelling device according to any one of claims 20 to 22, wherein the second portion comprises a lip which is arranged such that when a force is applied perpendicularly to the intermediate portion the lip is pressed against the ladder to clamp the ladder against the body.
24. A levelling device according to claim 1, wherein the transmission mechanism is a hydraulic transmission and the locking mechanism comprises a locking valve which is closed to lock the transmission when a force is applied to both stiles in substantially the same direction.
25. A levelling device substantially as described herein with reference to Figures 1 to 9, or Figure 10.
26. A ladder comprising a levelling device according to any one of the preceding claims.*::r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB 1010729.0 Examiner: Alan Jones Claims searched: 1-26 Date of search: 28 October 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X 1-3, 5, 6 GB2383601 A & 19 at (LEES) See e.g. fig 1, body 4, 5, stiles 6, 7, articulated transmission least mechanism 8, locking wheel 21, 22 operated by weight on device [00361 X 1-3,5,6 US1516988A & 19 at (REDMAN) See e.g. fig 1, body 9, stiles 8, articulated transmission least mechanism 18, 20, locking wheel 14, 17 X 1, 19 & U52008/190696 Al 24 at least (PIKE ET AL) See e.g. fig 1A: body 16, stiles 20, hydraulic transmission 24, locking valve 25 discussed in paragraphs [00671, [00681, paragraph [0111] states use with ladder.X l&l9at US5007503A least (STURM) See e.g. fig 4, abstract, body 40, stiles 70, flexible transmission element 60, locking mechanism 42 & col. 4 lines 26-44 X 1 & 19 at U54770275 A least (WILLIAMS) See e.g. fig 1: body 1, 2, stiles 3, flexible transmission element 4 brake/guide block 5, 6 & col. 3 lines 31-49 X 1 & 19 at U52969 126 A least (GARDNER) See e.g. fig 2, body 22, stiles 16, 17, compressible transmission element 18 locks against surface 28 & col. 3 lines 17-23 Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent documents classified in the following areas of the UKCX: Worldwide search of patent documents classified in the following areas of the IPC 1E06C The following online and other databases have been used in the preparation of this search report Online: WPI, EPODOC Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk *.:r: INTELLECTUAL . ... PROPERTY OFFICE 19 International Classification: Subclass Subgroup Valid From EO6C 0007/44 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk