GB2194934A - Aerial work platform - Google Patents

Abstract

An aerial work platform comprises a main boom 21 and a basket support boom 22, in which the main boom is mountable for rotation and elevation or a vehicular support and the basket support boom is articularably connected at one end to the main boom and at the other end to the basket. In the stowed position of the platform the connection point 24 of the main boom to the basket support boom is spaced further from the connection axis 23 of the main boom to the vehicular support than is the connection point 26 of the basket support boom 22 to the basket. Preferably the basket support boom is cranked. 23 <IMAGE>

Description

SPECIFICATION Aerial work platform This invention relates to aerial work platforms, particularly of the type for mounting on a vehicle for gaining access to street lights or other overhead services for maintenance purposes.

Aerial work platforms of the abovementioned type are known and generally comprise a system of hydraulically-operated articulated booms mounted for movement between stowed and elevated positions, the system being connected at one end to a vehicle and carrying a personnel basket at the other end.

The maximum working height or reach is dictated by the size of the vehicle or chassis upon which it is mounted, in that the booms in the stowed position are not able to exceed the statutory overall length allowed for the vehicle, the personnel basket in the stowed position in general being carried closely behind the rear end of the vehicle. With the booms in an elevated position and in the event of an hydraulic power failure, a controlled return to ground level is achieved under the influence of gravity.However, with the booms in the position of maximum elevation, that is, in general, with the booms extending vertically from their mounting point on the vehicle, there is little or no initial turning moment about the articulating connections under the influence of gravity, the main component of which is directed along the booms, and hence it is not always possible easily to initiate the return to ground level, particularly in adverse winds.

Furthermore, in prior art arrangements, it is generally necessary to utilize telescopic booms to achieve particularly high working heights, especially where a component of lateral reach is also required. Such requirements occur for example in work platforms which are intended for operation on motorways or dual carriageway roads equipped with central overhead lighting, particularly of the type which is supported on a boom or other holder which extends across both carriageways from a central support or pylon and it is necessary to reach both ends of the holder from a work platform mounted on a vehicle parked on one of the carriageways.

It is an object of the present invention to provide an aerial work platform which overcomes the disadvantages of known such platforms and in particular which optimises the maximum working height for a given size of vehicle.

According to the present invention, an aerial work platform of the type for attachment to a vehicular support and inciuding a personnel basket articulatably connected to an elevatable boom system for movement between a stowed position and a working position comprises a main boom and a basket support boom, in which the main boom is mountable for rotation and elevation on a vehicular support and the basket support boom is articulatably connected at one end to the main boom and at the other end to the basket, wherein, in the stowed position, the connection point of the main boom to the basket support boom is spaced substantially further from the connection axis of the main boom to the vehicular support than is the connection point of the basket support boom to the basket.Expressed alternatively, the basket support boom/basket pivot point is intermediate the main boom/basket support boom and main boom/vehicular support pivot points when attached to a support and in the stowed position the arrangement is viewed from above.

With the arrangement according to the invention, the length of the main boom, and hence the maximum working height or reach, is extended for a given size of vehicle compared with known arrangements, in that the main boom overhangs the rear end of the vehicle in the stowed position, preferably to an extent approximating to at least 50% of the breadth of the personnel basket. The basket support boom or at least a line joining its points of articulation lies at an acute angle beneath the distal end of the main boom, thereby permitting the personnel basket to be carried closely behind the rear end of the vehicle.

The main boom may be constituted by a single boom or by two or more booms articulatably connected together, thereby providing a three- or multi-boom arrangement, and the length of the boom to which the basket support boom is connected is increased so that the distal end portion thereof overhangs the personnel basket in the stowed position.

Preferably the basket support boom is cranked or otherwise shaped to accommodate the basket and any operatives carried therein when in the stowed or slightly elevated positions without the lower surface of the boom fouling the basket or creating a danger to the operative. With a cranked basket support boom, the boom may include a proximal end portion articulatably connected to the basket and a distal end portion articulatably connected to the main boom, wherein the proximal and distal end portions are at an obtuse angle with respect to each other, whereby in the stowed position the proximal end portion is substantially vertical and the distal end portion overlies the personnel basket with sufficient clearance for safety.

A further advantage of a cranked basket support boom is that the permitted extra length of the main boom allows an acceptable working height to be achieved without elevating the booms to an extent such that the personnel basket is practically vertically about the point of attachment of the main boom to the support. In this way, and in the event of a power failure, the personnel basket is offset with reference to the support attachment point and a sufficiently large moment exists readily to initiate return to ground level under the influence of gravity, the rate of descent being controlled hydraulically in known manner.

However, even where the personnel basket is substantially vertically above the point of attachment of the main boom to the support, the mass of the cranked boom out of the vertical line provides an increased turning moment compared with known arrangements.

Optionally, the attachment of the main boom to the vehicular support is carried on a vertically-extending pedestal or shaft mounted on or in the vehicle, such that the maximum working height may be still further increased.

For example, the attachment may be carried on a telescopic arrangement of concentric tubes. preferably, in any event, the arrangement of the support shaft within the vehicle is such that the rotatable external sleeve terminates downwardly above floor level, thereby allowing equipment to be carried adjacent to or touching the shaft.

The booms in work platforms according to the invention are arranged, in accordance with standard practice, to act via parallelogram-action or box section link rods to maintain the floor or base of the personnel basket substan tially horizontal throughout the range of working positions, from the stowed position to the position of maximum elevation, the link rods preferably being maintained under tensile, rather than compressive, forces.

By way of example and with a van having a length of 4 metres from the attachment point of the main boom to the rear end, it is possible with a two-boom arrangement according to the invention to use a main boom of length 5.5 metres and a basket support (cranked) boom of effective length (directly between its ends) of 3.5 metres, giving a maximum working height to the floor of the personnel basket of 12.5 metres, the-attachment point of the main boom to the vehicle being at a height of 3.5 metres above ground level. This may be extended by carrying the attachment for the main- boom on a vertically-extending pedestal.

In prior-art arrangements, it is generally necessary to utilise a telescopic boom arrangement for such working heights. With vans or other vehicular supports of different dimensions, the maximum working height can of course be increased in a similar way compared with prior art arrangements.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 illustrates diagrammatically a known arrangement of an aerial work platform including two booms, and Figure 2 illustrates diagrammatically an aerial work platform according to the invention and including two booms.

Referring firstly to Figure 1 (prior art), a van is shown generally at 10 and includes a roofmounted system of main and basket support booms 11 and 12 respectively. Boom 11 is pivotally and articulatably attached to the mounting pillar at 13 and is articulatably attached to boom 12 at 14; boom 12 is itself articulatably attached to a personnel basket 15 at 16. As shown in solid outline, the booms are in the stowed position, boom 12 being straight, thereby limiting the length of the boom 11. As shown in dashed outline, with the booms extended to attain maximum height, both booms 11 and 12 are vertical and the turning moment exerted by the personnel basket about pivot points 13 and 14, required to initiate return to ground level in the event of power failure, is minimal.It is to be observed that the distance from point 14 to the axis of the mounting pillar at 13 is substantially the same as the distance of point 16 to the said axis.

Referring to Figure 2, an aerial work platform according to the invention is mounted on a van 20 and includes main and basket support booms 21 and 22 respectively, boom 21 being pivotally and articulatably attached to the mounting pillar at 23 and articulatably attached to boom 22 at 24. Boom 22 is articulatably attached to personnel basket 25 at 26.

According to the invention, the second boom 22 is cranked at 27 so that boom 21 may be extended in length compared with boom 11 (Fig. 1) whereby, in the stowed position, portions of booms 21 and 22 overly the personnel basket 25. The maximum working height or reach is thereby increased by an amount equal to dimension "A" on boom 21 plus the difference between the direct distance between points 24 and 26 (Fig.2) and the length of boom 12 (Fig. 1). It is observed that the point 24 is spaced substantially further from the axis of the mounting pillar at 23 than is the point 26, thereby permitting the increased height and reach afforded by the invention.

Figure 2 also shows various positions of elevation of the work platform, from which it is seen that, even in the position of maximum elevation, the cranked boom 22 provides a greater turning moment about point 24 than does boom 12 about point 14 in the corresponding position (Fig. 1). In addition, the extra length of the booms of the aerial work platform of Fig. 2 enables the maximum working height of the aerial work platform of Fig. 1 to be attained at less than maximum elevation, thus, for that height, still further increasing the turning moment.

Claims (8)

1. An aerial work platform of the type for attachment to a vehicular support and including a personnel basket articulatably connected to an elevatable boom system for movement between a stowed position and a working po sition, the platform comprising a main boom and a basket support boom, in which the main boom is mountable for rotation and elevation on a vehicular support and the basket support boom is articulatably connected at one end to the main boom and at the other end to the basket, wherein, in the stowed position, the connection point of the main boom to the basket support boom is spaced substantially further from the connection axis of the main boom to the vehicular support than is the connection point of the basket support boom to the basket.

2. A work platform according to Claim 1, in which in use attached to a vehicle the main boom overhangs the rear end of the vehicle in the stowed position by at least 50% of the breadth of the personnel basket.

3. A work platform according to Claim 1 or Claim 2, in which the main boom is constituted by two or more booms articulatably connected together.

4. A work platform according to any preceding claim, in which the basket support boom is cranked.

5. A work platform according to Claim 4, in which the basket support boom includes a proximal end portion articulatably connected to the basket and a distal end portion articulatably connected to the main boom, the proximal and distal end portions being at an obtuse angle with respect to each other.

6. A work platform according to any preceding claim, in which the main boom is attachable to the vehicular support via a verticallyextendable pedestal or shaft.

7. A work platform according to any preceding claim and mounted on a vehicular support via a shaft, in which the rotatable external sleeve around the shaft terminates downwardly above the vehicular floor level.

8. A work platform substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.