The TU hand: Using compliant connections to modulate grasping behavior

Guided by the notion that the five-fingered anthropomorphic hand is a good general purpose manipulator, Team Tulsa approached the hand-in-hand portion of the grasping and manipulation competition using a simplified anthropomorphic hand. The hand had a simplified thumb, fixed in the opposed position, and only two actuators. Motions of the fingers and thumb were coupled together using a “ties and skips” architecture where thumb and finger tendons were tied to specific coils of a “mainspring” in a manner that produced the best behavior across the wide range of challenges. The actuators could move or deform the spring in common mode, which resulted in an enveloping grasp) or differential mode (which resulted in a pinch grasp) and superimpose the two modes. The compliant nature of the hand allowed the fingers to conform to the object as the grasp was acquired. This strategy allowed the retrieval of all objects from the basket (all on the first or second attempt by the volunteer), and scooping peas from the dish, but could not operate the hammer (due to its weight) the syringe, or the scissors (as they required increased dexterity).