GB2120998A

GB2120998A - An access platform

Info

Publication number: GB2120998A
Application number: GB08314771A
Authority: GB
Inventors: David Laurence Johns
Original assignee: Simon Engineering Dudley Ltd
Current assignee: Simon Engineering Dudley Ltd
Priority date: 1982-05-28
Filing date: 1983-05-27
Publication date: 1983-12-14
Also published as: GB8314771D0; GB2120998B

Abstract

An access platform comprises a turntable base (10) mounted on a vehicle (12), a first boom in the form of a parallelogram linkage (15,16,17,18), a second boom (21) pivotally connected to bracket assembly (18,20), and a cage or access platform (23). Bracket assembly (18,20) maintains a constant attitude irrespective of the angle of elevation of the first boom, so that second boom (21) is elevated automatically and simultaneously. Further elevation of second boom (21) is effected by hydraulic cylinder (22). In the travelling position, cage (23) is located at a lower level than the bracket assembly (18,20). <IMAGE>

Description

SPECIFICATION An access platform This invention relates to an access platform of the kind usually, but not essentially, mounted on a vehicle and used to provide access for equipment or personnel to elevated positions above the ground. Apparatus ofthis kind usually comprises a turntable base upon which is mounted an articulated boom system consisting oftwo or more booms pivotallyinterconnected end-to-end, hydraulic actuating cylinders being provided to swing the booms about horizontal axes relative to each other and to the turntable base.

Regulations forthe manufacture and use of equip ment ofthis kind demand that means be provided to preventthe booms from being manoeuvred into positions in which stability ofthe vehicle is reduced to a dangerous extent causing, in extreme cases, the vehicle two overturn. Many systems have been devised to prevent this, such as complex systems of stops which when the booms approach a potentially unstable condition, cause control valves to be operated to preventfurthermovement. Such systems are proneto breakdown, are expensive to maintain, and can sustain damage when the equipment is in use.

In an alternative system, there is provided a compensator mechanism which causes elevation automatically ofthe second boom relative to the first, as the first is raised, which allows the booms to be fully extended vertically but prevents them from being fully extended horizontally. In this way, the centre of gravityofthe boom system remains within the bounds ofthe supporting structure which in the case of a vehicle is conveniently a set of ground-engaging jacks which extend from the vehicle platform into contactwith the ground.

An object ofthe present invention is to provide an access platform including a compensator mechanism to maintain stability naturally, whilstthe design of the booms affords easy access to the platform for the operator and permits the use of lighter and thus less expensive structural parts, and reduces the length of the booms in a retracted or travelling condition.

According to the present invention there is provided an access platform comprising a turntable base upon which is mounted an articulated boom system consisting of two or more booms pivotally interconnected generally end-to-end, and hydraulic actuating cylindersto swing the booms about horizontal axes relative to each other and to the turntable base, characterised in that a first or lowermost boom consists of a parallelogram linkage with one end connected pivotallyto the turntable base, the other end being a bracket assembly which maintains a constant attitude irrespective of the angle of elevation ofthe lowermost boom, and in that a second boom is pivotally connected to said bracket assembly, an hydraulic actuating cylinderfor said second boom being connected between the latter and said bracket assembly.

An embodiment ofthe invention will now be described, by way of example only, with reference to the accompanying drawing which illustrates schematically an access platform incorporating the features of the invention.

The platform is shown in this example as being mounted via a turntable base 10own the deck or chassis 11 of a vehicle generally indicated at 12. The vehicle has a pair of ground-engaging jacks 13 which are lowered when the access platform is to be elevated.

The access platform comprises a first boom generally indicated at 14 and consisting of a pair of elongate parallel members 15 and 16 pivotally connected at spaced positions to an upper part 17 of the tu rntable base 10 and carrying attheirfree ends a bracket 18 to which the members 15 and 16 are also pivotally connected. Thus the part 17, the members 15 and 16 and the bracket 18 form a parallelogram linkage. An hydraulic actuating cylinder 19 extending between the part 17 andthe boom 14isadaptedto be extended thus to elevate the boom 14 relative to the turntable base 10.

A second bracket 20 fixed with respect two the bracket 18 carries one end of a second or upper boom 21 which is pivotally connected to the bracket 20. An hydraulic actuating cylinder 22 extends between the boom 21 and the bracket assembly 18,20 and is extendible to elevate the second boom relative to the said bracket.

At the free end of the boom 21 there is pivotally mounted an access cage or working platform 23.

Means (not shown) is provided to maintain the cage 23 level for all configurations ofthe boom assembly.

The equipment is shown with the lower boom 14 horizontal and the upper boom 21 inclined downwardlyfrom the free end thereof, so that the cage 23 is in a position affording ready access forthe operator, i.e. a travelling position. The system may be elevated from thetravelling position to various elevated positions some of which are illustrated as examples.

From the travelling position, if cylinder 19 is extended the lower boom 14 may be manoeuvered to positionAwith brackets 18 and 20 maintaining a constant attitude in space, owing to the parallelogram configuration of boom 14. Thus upper boom 21 assumes position B. With the lower boom 14fully elevated the upper boom 21 may be further elevated by extension of actuating cylinder 22to move through position Cto its fully elevated position D.

In an alternative manoeuvre, cylinder 19 may remain closed whilst cylinder 22 is extended to elevate boom 21 to position E. Subsequent extension of cylinder 19thus causes boom 14to be elevated into position Awhereupon boom 21 will assume position D.

Should both cylinders 19 and 22 be raised simul taneouslyfrom the travelling position, then cage 23 may be elevated in a substantially straight line vertically.

Furthermore, by arranging for cylinder 22 to be otherthan fully closed in the travelling position,then even when boom 14is raised from its travelling position cage 23 may remain in its lowermost position byfurtherclosing cylinder 22.

Since cylinder 22 is connected between the upper boom 21 and the bracket assembly 18,20, of the parallelogram linkage, the geometry of the system is such that cylinder 22 is maintained in compression and a substantially constant hydraulic pressure is required to elevate the second boom. This feature enables actuating cylinders of lighter construction than are normally required for equipment of this kind, to be employed. Usualiythe actuating cylinderforthe upper boom of a pair is connected betweenthetwo booms, and in such an arrangement betweenthetwo booms, and in such an arrangement it is not possible to achieve substantially constant hydraulic pressure.

Arrangement of the upper boom 21 alongside the lower boom 14 enables the cage 23 to descend into its position for ready access ofthe operator, thus also minimising the overall length of the apparatus in the travelling position.

Itwili be appreciated that a system of this kind wherein elevation of the second boom is effected automatically in compensation for elevation ofthe lower boom, enables the booms to assume an almost vertical disposition at maximum height without the risk of creating an excessive overturning moment in the condition where the booms are at full horizontal reach to one side or the other oftheturntable base.

The straight configuration of full height enables maximum height achievement whilst the length of the booms is minimised, thus minimising the overall length ofthe structure in the travelling position, the bracket assembly 18,20 being located overthe driver's cab ofthe vehicle.

Claims

1. An access platform comprising a turntable base upon which is mounted an articulated boom system consisting of two or more booms pivotally interconnected generally end-to-end, and hydraulic actuating cylindersto swing the booms about horizontal axes relative to each other and to the turntable base, characterised in that a first or lowermost boom consists of a parallelogram linkage with one end connected pivotallyto the turntable base, the other end being a bracket assemblywhich maintains a constant attitude irrespective of the angle of elevation ofthe lowermost boom, and in that a second boom is pivotally connected to said bracket assembly, an hydraulic actuating cylinderforsaidsecond boom being connected between the latter and said bracket assembly.

2. An access platform according to Claim 1, wherein said booms are connectedtogethersuch that with the lowermostboom generallyhorizontal,the second boom maybe inclined downwardly therefrom such thatthe outermost end ofthe boom assembly is at a lower level than said bracket assembly.

3. An access platform according to Claim 1 or Claim 2, including an access cage or working platform pivotally mounted at the outermost end of the boom assembly, and means for maintaining the cage of platform level for all configurations ofthe boom assembly.

4. An access platform according to any preceding claim, wherein the hydraulic actuating cylinder for said second boom is maintained in compression and a substantially constant hydraulic pressure is required to elevate the second boom.

5. An access platform according to any preceding claim, wherein the second boom is mounted alongside the lower boom thus to enable the outermost end ofthe second boom to descend to a level lowerthan that of said bracket assembly.

6. An access platform according to any preceding claim, wherein said bracket assemblycomprises afirst bracketto which the parallelogram linkage of said lowermost boom is connected at spaced positions thereon, and a second bracketfixed to said first bracket and pivotally carrying the second or uppermost boom,the hydraulic actuating cylinderforsaid second boom being connected between the latter and said second bracket.

7. An access platform according to any preceding claim, wherein said turntable base is mounted on the deck, wherein said turntable base is mounted on the deck or chassis of a vehicle towards the rear end thereof such thatthe boom assembly may be folded to a travelling position in which the bracket assembly is located over the driver's cab.

8. An access platform substantialiy as hereinbefore described with reference to and as illustrated in the accompanying drawing.