Tumble stability criterion of integrated locomotion and manipulation

Abstract

We discuss methods to evaluate the stability of robots which execute manipulations and locomotion. The relationship between the center of gravity projection point and the ground contact points is an easy-to-use criterion but it does not take into consideration manipulation counter-force. We propose a concept called "tumble stability", which considers the tumble direction when all ground contact points except 2 are hypothetically lost. If a given, hypothetically lost, ground contact point can produce support force which can suppress that tumble, the walking machine will not tumble; otherwise, it will. Stability during manipulations can be evaluated by incorporating the manipulation counter-force as an external force in this evaluation standard. The stability of the planned manipulation can be determined not only on level ground, but on general topography including rugged terrain, wall surfaces and ceiling surfaces. We introduce the concept of the manipulation counter-force limit as an index to indicate manipulation capabilities. Because this indicates the limit value of the counter-force by which a manipulation can be stably executed, it clarifies the fact that it is effective to make the ground contact points on the side opposite from the manipulation farther and wider in order to heighten manipulation performance.