The role of small redundant actuators in precise manipulation

With the goal of developing human-like dextrous manipulation, we investigate how the central nervous system uses the redundant control space of the human hand to perform tasks with force-stiffness requirements. Specifically, while the human hand is actuated by several muscles with varying mechanical advantage (called the moment arm), it is unclear how each muscle is used. Using the Anatomically Correct Testbed (ACT) robotic hand to compute the control solution space and human-subject experiments with surface electromyography to measure biological control strategy, we identified that there is significant redundancy in the control spaces of both muscles with large moment arms and muscles with small moment arms. However, the central nervous system was selective about the solution for muscles with large moment arms, while it chose to span large regions of the available control space for muscles with small moment arms. Furthermore, the biological solution used low-moment-arm muscles at relatively high actuation levels. We summarize by making inferences on why the central nervous system chooses such a strategy and how this can help robotic manipulation.