Dynamics of four-wheeled mobile robots on uneven surface applications

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Ayalew, A., 2001. Dynamics of four-wheeled mobile robots on uneven surface applications. PhD, Nottingham Trent University.

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Abstract

Although wheeled locomotion has existed for many decades the application of intelligent techniques to guide mobile platforms, referred to as Wheeled Mobile Robots (WMR) has awaited the advance in information and computation technology. Still the development of wheeled mobile robots lags behind that of stationary manipulators where considerable research effort has been spent. However, the unique advantage of mobile robots, which is their mobility, has attracted significant attention recently in various areas, including industrial material transfer, underground mining, various operations in hazardous environments and unmanned explorations.

So far most of the research work, on WMRs application has been limited to indoor environment with smooth and flat ground surface. There is a distinctive lack of understanding of the behaviour of WMRs when the smooth and flat working surface conditions are not met. The interaction between wheels and ground surface obstacles has so far been ignored. This has made impossible the operational autonomy of wheeled mobile robots in arbitrary ground surface conditions where wheel level obstacles are present.

This work has been undertaken to close the gap between the lack of understanding of WMRs dynamic behaviour and the need to have a complete autonomy of WMRs in any geometrical condition of the ground surface. An analytical modelling approach of the dynamics problem has been followed. For this purpose a rigid-body-dynamics model of a WMR that navigates an uneven ground surface of an arbitrary geometry has been formulated. Undesired dynamic effects such as wheel-ground contact loss, payload instability and harshness of motion of the WMR have been identified as problems of uneven terrain manoeuvre. Analytical expressions that relate the above-mentioned problems to: (a) the geometry of the ground surface (b) the wheel drive forces of the WMR and (c) the velocity of the WMR have been derived. These relationships permit the development of a jerk-minimisation technique.

The rigid body dynamics model of the WMR has been extended to take into account wheel deformations that occur during wheel-obstacle collision. A traction control scheme that enables permanent wheel-ground grip during impact has been proposed. Simulation results of the proposed scheme have shown the effectiveness of the technique to controlling impact between WMRs and wheel obstacles. A mathematical tool has also been devised to enable the estimation of the shock acceleration response at various points on a WMR when its wheels are excited by impact load. Simulation study suggests that this tool may be used in conjunction with the proposed jerk-minimisation technique and the impact-control scheme to improve the safe motion planning and control of WMRs in an environment with wheel level obstacles.

Item Type:

Thesis

Creators:

Ayalew, A.

Date:

2001

ISBN:

9781369316728

Identifiers: