Investigation of a passive capstan based grasp enhancement feature in a voluntary-closing prosthetic terminal device.

Body-powered prosthetic terminal devices fall into two main categories: voluntary-closing devices, which require the user to exert a force to maintain a grasp, and voluntary opening devices, which generally utilize springs to close and maintain a force. As a result, voluntary-closing devices often have a locking feature that allows the user to relax and transport objects while maintaining a firm grip. In this paper, we examine a new type of capstan-based passive brake mechanism in a voluntary-closing prosthetic terminal device. Three different mechanisms were compared on the benchtop and with human subjects: the passive capstan grasp enhancement, a "pull-to-lock, pull-to-release" mechanism, and a manual cable locking mechanism. Standard tests of prosthetic device dexterity, including the Box and Blocks test and Southampton Hand Assessment Protocol, were performed with an instrumented prosthesis socket simulator with each device. While results are similar across the three mechanisms, the passive capstan mechanism does not require a physical user input to engage or disengage the lock, adding a benefit over the existing mechanisms.

Lightweight custom composite prosthetic components using an additive manufacturing-based molding technique.

Additive manufacturing techniques are becoming more prominent and cost-effective as 3D printing becomes higher quality and more inexpensive. The idea of 3D printed prosthetics components promises affordable, customizable devices, but these systems currently have major shortcomings in durability and function. In this paper, we propose a fabrication method for custom composite prostheses utilizing additive manufacturing, allowing for customizability, as well the durability of professional prosthetics. The manufacturing process is completed using 3D printed molds in a multi-stage molding system, which creates a custom finger or palm with a lightweight epoxy foam core, a durable composite outer shell, and soft urethane gripping surfaces. The composite material was compared to 3D printed and aluminum materials using a three-point bending test to compare stiffness, as well as gravimetric measurements to compare weight. The composite finger demonstrates the largest stiffness with the lowest weight compared to other tested fingers, as well as having customizability and lower cost, proving to potentially be a substantial benefit to the development of upper-limb prostheses.