Hierarchical contact tuning in soft robotic grippers

The compliance of soft robots makes them particularly well suited for grasping applications where target objects are fragile, compliant, or topologically complex, as well as scenarios where target objects have an uncertain size or location. I will explore three modes in which characteristics of the contact interface between soft grippers and their target objects can be strategically tuned and motivate these with challenging scenarios of deep-sea biological sampling and tele-operated physical therapy. First, passive digit structures and materials can be tuned to specific contact pressure and adapt to varying object sizes. For fluidic soft grippers, the target object size, operating pressure, and payload are not independent but can be tuned separately for a given task. Second, active surface structures can be used to increase dexterity of soft grippers by modulating contact friction. Control over friction and grip force or contact pressure can be independently controlled or strategically coupled. Third, the contact point of a grasp can be distributed into a large collection of discrete contacts where each individual contact point is very gentle but collectively sum to a strong grasp. The application of a collective of many spatially distributed contacts can adapt to targets with compliant structures and complex topologies via grasper designs that leverage material and structural compliance. While soft grippers are naturally well suited for gentle grasping, adding each of the three modalities of contact tuning about, passive structural tuning, active interface adaptation, and spatial distribution of discrete contact points, can provide more robust, and adept performance. Furthermore, each modality of contact tuning can be applied independently or implemented simultaneously in a hierarchical soft gripper design.