Access tower

An access tower has two mutually spaced side parts extending from a base part to the top part; and inclined cross parts each extending from one side part to the other. The cross parts are arranged one above another and inclined in opposite senses. The cross parts are rigid and are connected to the side parts. The lower one of two successive oppositely inclined cross parts has its upper end connected to an articulation node to which the lower end of the upper one of said two successive oppositely inclined cross parts is connected. A section of the side part opposite said articulation node, which section extends between the upper end of said upper cross part and the lower end of said lower cross part, is collapsible so that said upper cross part together with the portion of the tower above it can be lowered into a position in which said upper cross part extends substantially parallel to said lower cross part. A releasable locking device is provided to prevent collapse of said collapsible section.

BACKGROUND TO THE INVENTION

Mobile access towers are used to provide a platform for safe working at heights. They conventionally consist of a variety of loose individual components slotted together by hand to form square or rectangular staging. Further components are used to brace the staging in the horizontal and vertical plane. Additional height is gained by repeating the process whereby a second set of staging is mounted upon the first set. As more height is required the task of lifting individual components up to the elevated height becomes more laborious and time consuming.

SUMMARY OF THE INVENTION

The present invention provides an access tower comprising: a base part; a top part; two mutually spaced side parts extending from the base part to the top part; and inclined cross parts each extending from one side part to the other and having an upper end and a lower end, the inclined cross parts being arranged one above another and inclined in opposite senses, the inclined cross parts being rigid and being connected to the side parts; wherein the lower one of two successive oppositely inclined cross parts has its upper end connected to an articulation node to which the lower end of the upper one of said two successive oppositely inclined cross parts is connected, a section of the side part opposite said articulation node, which section extends between the upper end of said upper inclined cross part and the lower end of said lower inclined cross part, being collapsible so that said upper inclined cross part together with the portion of the tower above it can be lowered into a position in which said upper inclined cross part extends substantially parallel to said lower inclined cross part, a releasable locking device being provided to prevent collapse of said collapsible section.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The access tower illustrated inFIGS. 1 to 9comprises two mutually spaced side parts1,2extending from a base part3to a top part4. The base part3comprises a generally rectangular frame6provided with four lockable castors7and four stabilizers or outriggers8which are movable from a working position (FIGS. 1,2,4,5), in which they lie outside the frame6, and a non-working position (FIG. 3), in which they lie inside the frame6and out of contact with the ground.

The top part4comprises a generally rectangular working platform9with an access hatch. Four uprights11support a handrail12extending around the working space above the platform9. Each upright11is collapsible to bring the handrail12closer to the platform9for transport and storage. Each upright11folds about a hinge13and is releasably lockable in the extended position, e.g. by the type of locking device described below. Pairs of uprights11on opposite sides of the access tower are connected by horizontal safety rails14. Flexible elements16, such as wires or cables, are connected between the opposite pairs of uprights11. Toe boards17(preferably made of resilient plastics material) are mounted on the periphery of the working platform9, outside the uprights11.

The right-hand side part1(as viewed inFIG. 1) is in the form of two mutually parallel columns18connected by rigid horizontal members19so as to constitute a ladder. The left-hand side part2also presents two mutually parallel columns21. In the presently described embodiment there is a free space between the columns21, allowing access to the ladder (18/19) from inside the access tower.

At the front and back of the access tower there are inclined rigid cross parts22-24, each extending from one of the side parts1,2to the other. A first or lower inclined cross part22has its lower end pivotally connected to the base part6at an articulation node26, and a lower end of the side part2is also pivotally connected to the base part6at the same articulation node26; the pivot axes do not necessarily coincide. The upper end of the first or lower cross part22is rigidly connected to an upright part27to which lower ends of a pair of second or upper inclined cross parts23are pivotally connected, at an articulation node28. A lowermost section1aof the right-hand side part1has its lower end pivotally connected to the base part6at an articulation node29and has its upper end pivotally connected to the upper end of the first inclined cross part22at the articulation node28.

The upper ends of the second or upper inclined cross parts23are pivotally connected to an upright part31, at an articulation node32. A lowermost section2aof the side part2(opposite the articulation node28) has its upper end pivotally connected to the lower end of the upright part31, at the articulation node32. An uppermost section2bof the side part2has its lower end pivotally connected to the upper end of the upright part31, at the articulation node32, and has its upper end pivotally connected to the top part4at an articulation node33.

A further or third inclined cross part24has its lower end rigidly connected to the upper end of the upright part31and has its upper end pivotally connected to the top part4at an articulation node34. An uppermost section1bof the side part1(opposite the articulation node32) has its lower end pivotally connected to the upper end of the upright part27, at the articulation node28, and has its upper end pivotally connected to top part4at the articulation node34.

As best seen inFIG. 2, the inclined cross parts22-24lie outside the columns of the side parts1,2. In the present embodiment there are inclined cross parts at both the front and the back. However, it may be possible for one set of cross parts to be omitted and for the inclined cross parts to be positioned between the columns of the side parts.

The sections1a,1b,2a,2bare each collapsible. In the present embodiment they are each foldable. In particular, taking section2aas an example, as shown inFIGS. 1 and 6to9, they each comprise a first or upper portion36and a second or lower portion37pivotally connected together by a hinge38(FIG. 1) which allows folding in one direction only (inwards, towards the opposite side part, in the present embodiment). The hinge (FIGS. 6 to 9) comprises a disc39on the first portion36mounted between a pair of lugs41on the second portion37by means of a pivot pin (not shown). A locking lever42is pivotally mounted on the second portion37so as to be movable between a locking position (shown in solid line inFIG. 9), in which it is selectively engageable with a first notch43in the disc39to prevent collapse of the foldable section and with a second notch44to prevent unfolding of the collapsed section during transit, and a release position (shown in broken line).

To assist in erection of the tower, the second section37contains a spring-loaded tension element46which is received in a peripheral groove47in the disc39and is connected to the first section36so that the tension element46is wound on to the disc39as the section is collapsed (folded). Thus the tension element46resists collapse and, conversely, assists erection of each section1a,1b,2a,2b.

FIG. 3shows the fully collapsed condition of the access tower. The top part4has been collapsed by folding the uprights11inwards about their hinges13. The sections1a,1b.2a,2bof the side parts1,2have been collapsed by folding them inwards about their hinges38. The inclined cross parts22-24extend substantially parallel to one another.

To erect the access tower, referring first toFIG. 4, the castors7are first locked and the outriggers8are deployed, so that the base part3is stable. Then the hand rail12is raised while the uprights11are unfolded and then locked.

Referring now toFIG. 5, the lowermost section1aof the side part1and the uppermost section2bof the side part2are unfolded and locked. In this condition the access tower is in an intermediate erected state, providing an intermediate working height which is smaller than the full working height. The top part4is accessible by climbing up the outside of the partly-erected side part1.

To fully erect the access tower, the remaining sections2a,1bare unfolded and locked, so that the condition shown inFIGS. 1 and 2is achieved. It will be noted that the two second cross parts23and the upright parts27,31together constitute a parallelogram mechanism which links the third cross part24to the first cross part22so that, as the third cross part24is raised (or lowered), it remains substantially parallel to the first cross part22. Consequently, the working platform9remains level as it is moved between the intermediate height (FIG. 5) and the full height (FIG. 1).

The parallelogram mechanism (23,27,31) includes a tension spring48which assist in raising the third cross part24. In the fully erected state (FIG. 1) the tension spring48extends along the smaller diagonal of the parallelogram; as the cross parts23,24are lowered this diagonal becomes the larger one (seeFIGS. 3 to 5), so that tension is built up in the tension spring48. It is to be noted that one or more springs could be provided at different locations in the parallelogram mechanism to achieve the same effect.

To further assist erection of the access tower, torsion springs could be provided in one or more of the pivotal connections at one or more of the articulated nodes26,28,29,32,33,34, the torsion spring being mounted externally or in a hub of the pivotal connection.

A second embodiment of the access tower, shown inFIG. 10, differs from the first embodiment only in the construction of the parallelogram mechanism. In the second embodiment the uprights27,31are connected by a single inclined cross part23and by a pair of mutually parallel flexible parts49, such as wires or cables. The resulting parallelogram mechanism may be provided with a tension spring (48) as described above.

A third embodiment of the access tower, shown inFIGS. 11 and 12, differs from the first embodiment in that there is no parallelogram mechanism. A single second inclined cross part23replaces the pair of cross parts23of the first embodiment. The overall height is less than that of the first embodiment.

A fourth embodiment of the access tower is shown inFIGS. 13 and 14to illustrate an alternative locking device51and a piston and cylinder device52(for releasing stored potential energy to assist in erection of the access tower) in an access tower which is similar to the third embodiment but has only a single set of inclined cross parts22-24, arranged between the columns of the side parts1,2.

The embodiments described above have been provided by way of example only. Various modifications may be made within the scope of the invention.

For example, although the collapsible sections have been described as foldable, one or more of them could be collapsed in another convenient way, e.g. telescopically. Instead of being foldable inwardly, one or more of the foldable sections may be foldable outwardly, if desired. One or more of the foldable sections may be made up of more than two portions hinged together.

The hinge arrangement shown inFIGS. 6 to 9could be replaced by a simple hinge connecting the first and second portions of the collapsible section, and a releasable locking device and an associated tension spring could be positioned between the columns of the side parts.

To increase the maximum working height of the access tower, yet more collapsible sections and inclined cross parts may be added to the structure.