Toward robust, whole-hand caging manipulation with underactuated hands

Human in-hand dexterity can be highly fluid and unstructured, but in contrast, prevailing research in robotic manipulation has focused on highly structured, well-controlled motions where contact points are carefully characterized. Maintaining grasp stability through traditional closure conditions during complex within-hand manipulation motions can be difficult, even with highly-articulated end-effectors. However, simple grippers can still achieve an effective range of in-hand manipulation tasks without strict closure conditions, as long as the object can be bounded locally relative to the hand frame. The end-effector can be utilized as a tool to limit the range of possible object poses. We show that the hand-object system's configuration space can be sampled to find a set of manipulation primitives that can reliably constrain the object inside the hand workspace even without feedback, a strategy proposed as whole-hand caging manipulation. Experimental results with a planar (gravity into the page), two-finger underactuated gripper (Yale OpenHand) are presented to validate this manipulation strategy, and it is shown that even though contacts are regularly broken and reformed, the object can be repeatability manipulated within the hand workspace without ejection, enabling challenging behaviors such as sliding and gaiting.