Mobile manipulators operating in field environments are susceptible to dangerous and costly rollover or tipover instabilities, particularly when operating on an uneven terrain or when exerting large forces or moments. By monitoring the static and dynamic tipover stability margins of a mobile manipulator it is possible to predict such tipover and take appropriate actions to prevent the tipover from occurring. This paper describes a scheme for automatic tipover prediction, and prevention, which uses the static and dynamic force-angle measures of tipover stability margin. Time-until-tipover prediction is accomplished using estimated gradients of the tipover stability margins, and prevention is accomplished using a combination of the manipulator and platform actuators. Simulation results demonstrate the efficiency and promise of the proposed scheme for automatic tipover prevention.

Mobile manipulators operating in field environments will be required to perform tasks on uneven terrain which may cause the system to approach, or achieve, a dangerous tipover instability. To avoid tipover in an automatic system, or to provide a human operator with an indication of proximity to tipover, it is necessary to define a measure of stability margin. This work presents a new tipover stability measure (the force-angle stability measure) which is easily computed and sensitive to topheaviness. The proposed metric is applicable to systems subject to inertial and external forces, operating over even or uneven terrains. Performance of the measure is demonstrated using a forestry vehicle simulation.