Nonuniform and adaptive coupling stiffness for virtual grasping

Recent virtual grasping approaches involve physical simulation and virtual couplings between tracked and virtual hand configurations. We introduce a nonuniform coupling in which the stiffness of thumb coupling is scaled relative to that of other digits. This shifts the position of grasped objects in the hand, which may impact grasp and release performance. We graphically illustrate the effects on grasped object position, and we experimentally measure impact on object motion during grasp release. In addition to basic nonuniform scaling, we propose adaptive scaling to account for the number and depth of digits involved in multi-finger grasps. We show that one particular choice of adaptive coupling results in a tradeoff of increased object position consistency and decreased release consistency. The knowledge gained from our study will enable researchers to optimize couplings in future work.