Mechanical Design of a Bioinspired and Customized Prosthetic Hand Finger Based on Six-Bar Linkage

The customization of hand prostheses, by taking into account subject-specific motion and anthropometric characteristics, can potentially reduce the significant abandonment phenomenon and improve usability during activities of daily living. To this aim, additive manufacturing techniques can contribute in mimicking natural hand functions and aesthetics while still reducing complexity and costs. This work presents the design of a 1-DoF finger prosthesis based on a 6-bar linkage with a focus on the kinematic synthesis. We designed a device centered on the specific characteristics of a selected subject to be produced by means of additive manufacturing. The synthesis process is based on anthropometric data obtained with 3D scanning and kinematic joint trajectories collected with an optoelectronic motion capture system, and takes into account fabrication constraints. A set of possible solutions is calculated and multifactor performance is evaluated to maximize the similarity with human motion and minimize the reaction forces loading the mechanism components. An optimal mechanism is selected based on a performance evaluation and on a sensitivity analysis, which aims to guarantee tolerance to geometric parameter variations introduced by the fabrication process. The final solution, which exhibits a bioinspired linear coupling among joint flexion/extension trajectories and high similarity with the human fingertip motion, has been used for the 3D modeling of a finger that was prototyped and preliminary tested to verify the correspondence between the actual and the expected motion.