Author: Rodolfo Antonio Salido Benítez
Completion Date: Sep 1, 2015
Software: Autodesk Fusion 360, Simplify 3D
Place of Creation:California Institute for Biomedical Research. (Calibr)
Techniques: Computer aided design & manufacturing, rapid prototyping, and additive manufacturing.
Materials: Polylactic Acid (PLA), Thermoplastic Elastomer (TPE), nylon fishing lines.
The grasping tool project consists of a personally manufactured 3D printed prosthetic hand designed by Gyrobot Ltd that uses both rigid and elastic 3D printable materials to produce a functional biomimetic grasping tool. The design, published under the name Flexy-Hand 2, effectively uses the capabilities of additive manufacturing technologies to produce an organic looking prosthetic hand that allows the user to grasp a variety of irregular objects. The Flexy-Hand 2 is part of the repertoire of wrist powered devices available for individuals with upper limb mobility needs offered by the e-NABLE community. In contrast with the other popular 3D printed prosthetic hands, the Flexy-Hand 2 design features organic contours and an overall highly biomimetic shape, as opposed to sharp geometric corners and exposed mechanical components used by designs like the Cyborg Beast or the Raptor Reloaded. It is important to highlight that the highly geometric designs have been optimized for additive manufacturing technologies with a wide variety of 3D printing platforms in mind, they minimize overhangs and favor flat surfaces that can be easily 3D printed by resting flat in the print bed.
The design uses thermoplastic elastomer hinges in all joints to allow flexion of fingers and wrist. Flexion is powered by biological wrist movements which are transferred via nylon fishing line tendons to each finger. The flexible hinges favor an extended position when resting and their resistance to flexion can be modulated by adjusting 3D printing parameters, with more plastic density resulting in more resistance. The tension of each finger tendon can be adjusted by tightening screws located in the wrist gauntlet.
image courtesy of 3dprint.com
All printed components were manufactured on a RepRap Kossel 3D printer using PLA and TPE. All models were sliced using Simplify 3D at 200 micron layer resolution. Components were printed without supports nor raft. Flexy-Hand 2 components were downloaded from this repository.
The product is cost effective and easily reproducible with little to no technical skill, but its functions are limited to simple grasping gestures with no adjustable finger positions or finger isolations. I believe it can be easily modified to be a cheap functional cosmesis if extra attention is given to material selection and if detailed cosmetic features are added with air brushing techniques.
This was my first major 3D printing project that was motivated by personal academic goals. It was a catalyst for a deep interest in prosthetics because it demonstrated that I was capable of being an independent yet active participant in their research and development with access to the necessary tools, resources, and platforms to make an impact in the field.