Design of a 3D Printed Hand Prosthesis and Linearly Controlled Rotating Mechanism for Wrist Pronation and Supination Actuated by Nylon 6-6 Polymer Artificial Muscles

Overview

Several arm amputees throughout the world cannot afford prostheses beyond cosmetic hands with basic motor abilities. The project goal was to design an inexpensive hand prosthesis using a 3D printable design and twisted and coiled polymeric (TCP) artificial muscles made of silver-coated nylon 6-6 to reduce the cost of the prototype compared to advanced, myoelectric prostheses. The TCP muscles provide an inexpensive and lightweight alternative to DC motors traditionally used in prosthetic actuation. TCP Muscles were manufactured by inserting twist into the nylon thread and characterized to determine an optimal strategy for actuating the hand using a combination of square wave and pulse wave actuation. Three prototypes were designed based on the author’s measurements to demonstrate a high degree of customization. Grasping tests with objects of varying shapes and masses were used to determine the versatility of each prototype to interact with the wide variety of objects an amputee would come across in daily life. Testing demonstrated that the hand could grasp all the objects tested without the aid of gravity including but not limited to: a Styrofoam cup, a syringe, a candy bar, a computer mouse, a pencil, and a screwdriver. The third prototype integrates a wrist attachment to enable rotational wrist movement for the prosthesis. The wrist mechanism converts the linear motion of the muscle to a rotational movement for wrist pronation and supination. With a low material cost under $200, the prosthesis has the potential to be used as a low-cost system in developing countries.