EP0117120A2

EP0117120A2 - Control mechanism for access equipment

Info

Publication number: EP0117120A2
Application number: EP84300957A
Authority: EP
Inventors: Ridley Stokoe
Original assignee: Aerial Access Equipment Ltd
Current assignee: Aerial Access Equipment Ltd
Priority date: 1983-02-16
Filing date: 1984-02-15
Publication date: 1984-08-29
Also published as: GB8304329D0; EP0117120A3

Abstract

In access equipment of the type in which a working platform or cage is carried at the upper end of a boom assembly comprising a lower boom pivotally mounted on a support structure and an upper boom pivotally connected to the lower boom and in which the pivoting movements are effected by drive means operated by hand levers, stop members are provided associated with the hand levers and the position of the stop members is so controlled in accordance with the angle between the upper boom and the horizontal as to prevent the hand levers being moved into or remaining in operating positions which would increase the angle beyond a predetermined value.

Description

This invention is concerned with control mechanism for access equipment of the kind comprising a working platform or cage carried at a free end portion of a boom assembly which boom assembly comprises a lower boom pivotally mounted at one end portion on a support structure for pivotal movement about a first horizontal axis and an upper boom pivotally connected at one end with the free end portion of the lower boom for pivotal movement about a second horizontal axis, the working platform or cage being pivotally supported at the free end portion of the upper boom. In such equipment separate power operated drive means, usually in the form of hydraulic rams, are provided for moving the two booms about the first and second horizontal axes, and the support structure usually includes a turntable mounted on a mobile platform for rotation about a vertical axis. In known equipment of the kind under consideration the mobile platform may comprise either a self-propelled vehicle or a separately towable trailer.
In known kinds of such access equipment it is usually necessary to provide fairly complex control mechanism incorporating limit switches and valve arrangements whereby the required safety requirements may be met to avoid such sequences of movement of the booms that the cage is moved into positions where the equipment becomes unstable. Furthermore known kinds of access equipment are usually fairly large and heavily constructed and are consequently expensive to manufacture.
In the specification of our co-pending European patent application No. 83 303278.2 (publication No. 0099636) there is disclosed a relatively simple and inexpensive type of access equipment in which the need for elaborate safety control systems is avoided by so constructing the equipment that, in its rest position, the lower boom extends upwardly with respect to the support structure at such an angle that, in operation, the booms cannot move into positions in which the equipment becomes unstable.
It is sometimes desirable to have a greater degree of flexibility in the design of the boom arrangement than is possible with the equipment disclosed in said earlier specification. For example, it may be desired to drop the lower boom to a smaller angle, relative to the support structure, when the equipment is to be moved.
It is one of the objects of the present invention to provide a particularly simple (and inexpensive) control mechanism for hydraulic valve arrangements associated with the rams of access equipment of the kind under consideration which avoids the likelihood of the boom arrangement being brought into unstable positions by inadvertent movement of the valve arrangements.
With this object among others in mind, the access equipment according to the present invention, in which the drive means for effecting pivotal movement of the booms about the respective axes is operated by hand levers, is characterised in that stop members are provided associated with the hand levers and that the stop members are positionally controlled in accordance with the angle between the upper boom and the horizontal so as to prevent the hand levers being moved into or remaining in positions which would increase said angle beyond a predetermined value.
Thus, for example, if the drive means for pivoting the booms are in the form of hydraulic rams, then the hand levers may operate valves controlling the rams.
The stop members may, for example, operate to limit the extent to which the upper boom may be elevated relative to the lower boom and/or the extent to which the lower boom may be lowered relative to the support structure, in any given position of the booms.
It is usual in the case of access equipment of the general type to which the present invention relates, to provide means for maintaining the working platform or cage in a vertical position. In such a case, the positioning of the stop members may be controlled in accordance with the angle between the upper boom and the working platform or cage, since this angle is, of course, a direct indication of the angle between the upper boom and the horizontal. Thus the stop members may be pivotally mounted on the working platform or cage, for example on its supporting frame, and their position may be controlled by means connected to the upper boom or to mechanical link means by which the platform or cage is kept vertical.
The means controlling the position of the stop members may be flexible links each connected at one end to the stop member and at the other end to the upper boom or to the mechanical link means. For example they may be chains or wires. To ensure that the flexible links are kept taut, spring means may be provided to urge the stop members away from the positions in which movement of the hand levers is prevented.
There will now be given, with reference to the accompanying drawings, a more detailed description of access equipment incorporating control mechanism in accordance with the invention. It is, however, to be understood that the equipment is selected for description by way of exemplification, and not by way of limitation of the invention.
In the accompanying drawings:-

Figs. 1 and 2 are side elevational views of a known form of access equipment, the various components being shown somewhat schematically and not necessarily to scale, the equipment being shown in two of several possible working positions;
Fig. 3 is a detail view, in side elevation with parts broken away, showing a cage mounted on an upper boom and parts associated with control mechanism in accordance with the invention;
Fig. 4 is a view corresponding to Fig. 3 but from the opposite side of the cage; and
Fig. 5 is a view, looking in the direction of the arrows A in Figure 4 but to a larger scale than that Figure, of parts of the control mechanism.

The access equipment represented in Figs. 1 and 2 comprises a boom arrangement comprising a lower boom 1 and an upper boom 3, the lower boom 1 being pivoted, at one end portion, to a platform 5 by means of a first pivot 7 and, at its other end portion, to a first end portion of the upper boom 3 by means of a second pivot 9. The other end portion of the upper boom is pivoted, by a third pivot 13, to a cage 11 providing a working platform of the access equipment.
In the use of the illustrative access equipment the cage is movable, in well known manner, into a wide variety of working positions as a consequence of pivotal movement imparted to the upper boom 3 about the pivot 9, and of pivotal movement imparted to the lower boom 1 about the pivot 7, such movements being effected respectively by first and second hydraulic rams 25 and 29, the former being connected between the upper boom 3 and the lower boom 1, and the ram 29 being connected between the lower boom 1 and the turntable platform 5 (by means of a pivot 33). For maintaining the orientation of the cage 11 (in a vertically disposed position) during movements of the booms 1 and 3, there is provided a linkage arrangement of known type, comprising a link 15 pivotally connected at opposite ends to the cage 11 and one arm 17 of a quadrant (itself pivoted about the pivot 9 interconnecting the booms 1 and 3), a second arm 19 of the quadrant being pivotally connected to a link 21, which in turn is pivotally connected at its lower end to the turntable platform 5 by means of a pivot 35. Power for the hydraulic rams is supplied by a power unit (not shown) supported adjacent an end portion of the platform 5 remote from the pivot 7.
The turntable platform 5 is rotatably mounted about a shaft 53 upstanding from a base portion 55 of the equipment, the base. portion 55 being provided with outrigger arms 45 and associated jacks 47 for levelling the equipment on site.
The access equipment is provided with control mechanism ... whereby an operator located in the cage 11 can control the flow of oil under pressure to the hydraulic rams 25 and 29 and can also control slewing mechanism (not shown) for rotating the platform 5 around the shaft 53.
The control mechanism comprises three control valves 61, 63, 65 (see Figure 5) operated respectively by hand levers 67, 69, 71 upstanding from the valves (see also Figures 3 and 4) and positioned to be reached easily by an operator standing in the cage 11. For this purpose the valves are clamped between side plates 73, 75 which are secured to a cage-supporting frame arrangement including a pair of upright members 72 and a cross member 74 (see Figures 3, 4 and 5). The control valve 61 is arranged to control the ram 25 for raising and lowering the upper boom 3; the control valve 65 is arranged to control the ram 29 for raising and lowering the lower boom 1; and the control valve 63 is arranged to control the slewing movements of the platform 5 above referred to. The control valves are so constructed that they are in a neutral position when their hand levers are vertically disposed as shown in the drawings, whereupon the rams and slewing mechanism are held stationary. Movement of the hand levers 67 and 71 away from the cage (clockwise as viewed in Figure 4 or anticlockwise as viewed in Figure 3) causes the rams 25 and 29 to extend; movement of the hand levers in the opposite direction causes the rams to be retracted.
With a view to providing the access equipment with a simple, cheap-to-manufacture, safety control whereby the boom arrangement is not movable into an unstable condition, access equipment in accordance with the invention has, associated with the valves 61, 65, stop members 107, 87 respectively which are arranged to operate as will now be described. As shown in Figure 5, the stop member 87 extends to the left from an upwardly extending arm 85 (Figure 3) of a control lever 81 which is pivotally supported on a pivot pin 79 extending from a boss 77 formed on the side plate 75, the lever 81 being retained on the pin by any convenient means (e.g. a washer and circlip ). The control lever 81 also has a generally horizontally extending arm 83, an outer end portion of which is formed with a lug 89 to which an upper end portion of a chain 93 is adjustably secured by means of an adjusting screw 91. A lower end portion of the chain is secured, by means of a lug 95, to an upper end portion of the link 15 at a locality adjacent to the cage 11. Alternatively, the lug 95 may be provided on a corresponding upper end portion of the upper boom 3. A spring (not shown) may be connected with the control lever 81 in such a manner that it tends to rotate the lever in a clockwise direction as viewed in Figure 3 and maintain the chain 93 taut. As shown in Figures 3 and 5 the stop member 87 extends in front of the hand lever 71 of the control valve 65 (as viewed by the operator when located in the cage). Similarly the stop member 107 is arranged to extend behind the hand lever 67 (as viewed by the operator) from an upstanding arm 105 (see Figure 4) of a control lever 101, having also a generally horizontally extending arm 103, the control lever 101 being pivoted on a pin 99 carried in a boss 97 formed on the side plate 73 as indicated in Figure 5. The arm 103 is formed with a lug 109 connected, by means of an adjusting screw 111, with an upper end portion of a second chain 113, the lower end portion of which is connected to a lug 115 formed on an upper end portion of the link 15 (or the upper boom 3). A spring (not shown) may be connected to the control lever 101 in such manner as to tend to move it in a clockwise direction as viewed in Figure 4 to maintain the chain 113 taut.
In Figure 1 the lower boom 1 is shown in its lowered position, the ram 29 being retracted, the ram 25 has been extended (by movement of the hand lever 67 of the control valve 61 in a clockwise direction as viewed in Figure 4) to raise the upper boom to a desired position. As the upper boom is raised, the angle θ,between the upper boom and the horizontal, increases. If 8 exceeds a certain value,the Centre of Gravity of the equipment becomes sufficiently displaced to cause the equipment to become unstable.
In Figure 2 both the rams 29 and 25 have been extended so that both booms are in a raised position. If, in Figure 2, conditions are such that the angle 8 has reached its maximum value for a stable condition of the equipment, it will be appreciated that, if the valve control lever 71 is operated in a direction to retract the ram 29(without any change in the extension of the ram 25), the angle e would increase beyond the safe limit.
The stop members 87 and 107 and their associated parts are designed to avoid the possibility of the valves 65 and 6l being operated to effect an increase in the angle θ once the safe maximum has been arrived at. It will be appreciated from Figures 3 and 4 that, as the angle 6 is increased, the chains 93 and 113 act to swing the control levers 81 and 101 in such directions (anticlockwise as seen in the respective Figures) that the stop members 87 and 107 approach the hand levers 71 and 67 and eventually ensure that the hand levers are returned to their neutral positions and cannot be displaced therefrom in such directions as to cause the ram 25 to be extended further or the ram 29 (if extended) to be retracted. The adjusting screws 91 and 111 may be adjusted to ensure that the stop members 87 and 107 return the hand levers 71 and 67 to the neutral positions of the associated valves when 8 reaches a given value.

Claims

1. Access equipment comprising a working platform or cage carried at a free end portion of a boom assembly, which boom assembly comprises a lower boom pivotally mounted at one end portion on a support structure for pivotal movement about a first horizontal axis and on upper boom pivotally connected at one end with the free end portion of the lower boom for pivotal movement about a second horizontal axis, said working platform or cage being pivotally supported at the free end portion of the upper boom, pivotal movement of the lower boom relative to the support structure and of the upper boom relative to the lower boom being effected bydrive means operated by hand levers, characterised in that stop members are provided associated with said hand levers and that said stop members are positionally controlled in accordance with the angle between the upper boom and the horizontal so as to prevent said hand levers being moved into or remaining in operating positions which would increase said angle beyond a predetermined value.

2. Access equipment according to claim 1, characterised in that the pivotal movement of the lower boom relative to the support structure and of the upper boom relative to the lower boom are effected by means of hydraulic rams.

3. Access equipment according to claim 2, characterised in that the hydraulic rams are controlled by valves and that said hand levers operate said valves.

4. Access equipment according to any of claims 1 to 3, characterised in that said stop members limit the extent of elevation of the upper boom and/or the extent of lowering of the lower boom respectively.

5. Access equipment according to any of claims 1 to 4, characterised in that means are provided to maintain said working platform or cage in a vertical position.

6. Access equipment according to claim 5, characterised in that said stop members are positionally controlled in accordance with the angle between said upper boom and said working platform or cage.

7. Access equipment according to claim 6, characterised in that said stop members are pivotally mounted relative to said working platform or cage and that their position is controlled by means connected to said upper boom.

8. Access equipment according to claim 6, characterised in that the means to maintain said working platform or cage in a vertical position are mechanical link means connected to said support structure, that said stop members are pivotally mounted relative to said working platform or cage and that their position is controlled by means connected to said mechanical link means.

9. Access equipment according to claim 7 or 8, characterised in that the means controlling the position of said stop members are flexible links each connected at one end to said respective stop member and at the other to said upper boom or to said mechanical link means.

10. Access equipment according to claim 9, characterised in that said flexible links are of chain or wire.

11. Access equipment according to any of claims 1 to 10, characterised in that spring means are provided to urge said stop members away from the positions in which movement of said hand levers is prevented.