A new formulation for indeterminate contact forces in rigid-body statics

Friction forces play an important role in analysis of robotic contact tasks. In most of related studies, only ¿local¿ constraint on friction forces imposed by, for example, Coulomb's law is considered. However, when contact forces are indeterminate, such local constraint is not enough to assess possible friction forces appropriately. Although Omata and Nagata derived additional ¿global¿ constraint on indeterminate friction forces from rigid-body kinematics, it is not accurate in some cases. Thus we propose a modified formulation for indeterminate friction forces in rigid-body statics in this paper. It solves two major problems in Omata and Nagata's formulation. Its validity is successfully demonstrated in numerical examples for evaluation of the robustness of grasping.