Land vehicles – Wheeled – Running gear
Reexamination Certificate
1999-02-01
2001-07-24
English, Peter C. (Department: 3619)
Land vehicles
Wheeled
Running gear
C280S124111, C280S124134, C280S124179, C267S255000
Reexamination Certificate
active
06264221
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a base structure for a mobile access platform.
Access platforms generally have a cage for an operator that is mounted on the end of a hydraulically-operated boom. The boom is mounted on a base structure and can be moved up and down or from side-to-side under the control of an operator in the cage.
There are two main types of access platform. The first of these is mounted on a trailer and has stabiliser legs that may be brought into engagement with the ground to stabilise the platform. This type of platform cannot be moved during use.
The second type of access platform is provided with wheels and is fully mobile. It does not have stabiliser legs and is stabilised solely by the weight of the base unit and the counter-weight attached to the boom. This type of platform is normally self-propelled and may be driven from the cage even whilst the boom is raised. The present invention relates to mobile access platforms of this general type, in which the base unit does not have stabiliser legs.
In mobile access platforms, the wheels are normally mounted on rigid axles without any form of suspension and the tyres are very hard. This is essential to ensure that the base unit does not tilt when the boom is extended to one side of the base and to provide the necessary stability. The base unit must also be very heavy, and the wheels and tyres normally provide a significant part of the weight of the base.
One disadvantage of providing a completely rigid chassis with no suspension is that when the mobile access platform is standing on a slightly uneven surface, one of the wheels may be raised slightly off the ground. Whilst this does not seriously affect the stability of the platform, since the weight of the lifted wheel still contributes to the overall weight of the base, it can be disconcerting for the operator. Also, if the lifted wheel is a drive wheel, drive from that wheel will be lost.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a base structure for a mobile access platform that mitigates at least one of the afore-mentioned disadvantages.
According to the present invention there is provided a base structure for a mobile access platform, the base structure including a chassis having at least two pairs of wheels, at least a first one of said pairs of wheels including a suspension mechanism including, for each wheel, a swing arm member on which the wheel is mounted, said swing arm member being arranged to pivot about a substantially horizontal pivot axis, a stop member arranged to engage the swing arm member so as to limit upwards movement thereof, and biassing means arranged exert a biassing force on the swing arm member to urge the swing arm member upwards towards the stop member, the biassing force being less than the force needed to maintain the swing arm member in engagement with the stop member when the wheel is unsupported, the arrangement being such that the swing arm members normally engage the stop members when the mobile access platform is standing on flat, level ground.
Because the swing arms cannot move upwards from their normal position, the platform cannot tilt significantly, this being essential for its stability. The swing arms can however drop down below their normal positions in engagement with the stop members, and all four wheels thus maintain contact with the ground even when the platform is standing on ground that is not completely flat. This improves the confidence of the operator and maintains drive from both of the drive wheels. However, as the swing arm is biassed upwards towards the stop member, the weight of that arm and wheel still contributes to the overall weight of the base structure and therefore to the stability of the platform. The stability is not therefore compromised.
Advantageously, said biassing means is arranged to exert a biassing force on the swing arm member that is greater than 80%, and preferably 90%, of the force needed to maintain the swing arm member in engagement with the stop member when the wheel is unsupported. For example, the swing arm and wheel may typically weigh approximately 200 kg and the biassing member (for example a spring or hydraulic actuator) may be arranged to exert a force on the swing arm that is sufficient to support a weight of approximately 180 kg. Therefore, when the platform is standing on uneven ground and one of the wheels drops down out of engagement with the stop member to rest against the ground, the force exerted by that wheel on the ground is only approximately 20 kg and the remaining 180 kg still contributes to the overall weight of the base.
Said first pair of wheels advantageously comprises the driven wheels of the mobile access platform, which may be the rear wheels of the mobile access platform. The front, steerable wheels may be mounted on a rigid axle.
The base structure may include means for controlling the biassing force exerted on the swing arms, and said means for controlling the biassing force may include an actuator means that is arranged to reduce, when actuated, the biassing force exerted on the swing arms. Thus, when the platform tips and one of the wheels drops down out of engagement with the stop member to rest against the ground, the force exerted by that wheel on the ground may be increased, so improving the drive from that wheel. The actuator may be controlled automatically to prevent actuation when the boom is raised, thereby ensuring the stability of the platform.
REFERENCES:
patent: 1064613 (1913-06-01), Coggin
patent: 1402890 (1922-01-01), Reed
patent: 1507009 (1924-09-01), Strietmann
patent: 2531933 (1950-11-01), Clark
patent: 2744761 (1956-05-01), Steele
patent: 2840386 (1958-06-01), McFarland et al.
patent: 3767223 (1973-10-01), Bottenberg
patent: 3770290 (1973-11-01), Bottalico
patent: 0 662 446 A1 (1995-07-01), None
patent: 2 292 929 (1996-03-01), None
patent: WO 97/07009 (1997-02-01), None
English Peter C.
Merchant & Gould P.C.
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