The force-angle measure of tipover stability margin for mobile manipulators

Mobile manipulators operating in field environments will be required to app ly large forces, or manipulate large loads, and to perform such tasks on un even terrain which may cause the system to approach, or reach, 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 necessa ry to define a measure of available stability margin. This work presents a new tipover stability measure (the Force-Angle. stability measure) which ha s a simple geometric interpretation, is easily computed, and is sensitive t o changes in Center of Mass height. The proposed metric is applicable to sy stems subject to inertial and external forces, operating over even or uneve n terrains. Requirements for computation and implementation of the measure are described, and several different categories of application of the measu re are presented along with useful normalizations. Performance of the Force -Angle measure is demonstrated and compared with that of other stability ma rgin measures using a forestry vehicle simulation. Results show the importa nce of considering both center-of-mass height and system heaviness, and con firm the effectiveness of the Force-Angle measure in monitoring the tipover stability margin.