Child prosthetic hand design: no small challenge

Our objective in this project is to develop an improved body-powered hand for toddlers from one to four years of age. The primary design goals are for a hand of acceptable cosmesis to provide useful grasp for children in their play activities while requiring minimal harness force and motion inputs. Guiding constraints for this endeavor are that the hand be safe, simple, rugged, lightweight and low-cost. The hand must be affordable and easy to maintain as well as a functional and attractive device that children will want to use and parents will not be reluctant to show. Observation of toddlers suggests a focus on achieving stable spherical and cylindrical grasp patterns, with some fine-tip prehension. Grasping tests confirm the effectiveness of various combinations of grasp geometries, foams and skins. Modifications of a CAPP II gripper for bidirectional control reduces input cable excursion requirement by 50% while doubling the force output. A cable-free device provides easy object insertion for grasp, while a hand equipped with a nonbinding clutch mechanism provides secure capture.