Planning and control during reach to grasp using the three predominant UB hand IV postural synergies

In this paper, a method to derive the three predominant synergies and their temporal weights for planning grasps of the UB Hand IV (University of Bologna Hand, version IV) is proposed. The method adopted to define the postural synergies from experiments is based on the kinematic structure of the robotic hand and on the taxonomy of the grasps of common objects. The control strategy, exploiting postural synergies, that drives the hand during reach to grasp is further described. During prehension the hand moves continuously in a configuration space of highly reduced dimensionality with respect to its degrees of freedom. The experiments confirm that the UB Hand IV works efficiently in a synergy based framework for grasp planning and prehension control. It is shown that the introduction of the third predominant synergy significantly improves the grasping synthesis and performance, especially for the adduction/abduction motion of the thumb.