Beyond Humanoid Prosthetic Hands: Modular Terminal Devices That Improve User Performance
Digby Chappell, Barry Mulvey, Shehara Perera, Fernando Bello, Petar Kormushev, Nicolas Rojas
TL;DR
This paper tackles the persistent mismatch between high-functionality humanoid myoelectric prostheses and user needs by proposing task-specific, non-humanoid modular end effectors mounted on the OLYMPIC hand base. Four open-source terminal devices were developed to perform flicking, screwdriving, precision grasping of flat objects, and cutting, with evaluation against a humanoid configuration in a control group and validation through two end-user case studies. Across four tasks, the non-humanoid devices achieved substantially better performance, reduced compensatory motion, and lowered perceived task load, suggesting that modular, task-focused designs can transform daily function and social engagement for users with upper-limb difference. The work emphasizes practical benefits, social aspects of prosthesis use, and a clear path toward broader adoption through open-source hardware and future research on higher DOF, haptics, and personalized device groupings.
Abstract
Despite decades of research and development, myoelectric prosthetic hands lack functionality and are often rejected by users. This lack in functionality can be partially attributed to the widely accepted anthropomorphic design ideology in the field; attempting to replicate human hand form and function despite severe limitations in control and sensing technology. Instead, prosthetic hands can be tailored to perform specific tasks without increasing complexity by shedding the constraints of anthropomorphism. In this paper, we develop and evaluate four open-source modular non-humanoid devices to perform the motion required to replicate human flicking motion and to twist a screwdriver, and the functionality required to pick and place flat objects and to cut paper. Experimental results from these devices demonstrate that, versus a humanoid prosthesis, non-humanoid prosthesis design dramatically improves task performance, reduces user compensatory movement, and reduces task load. Case studies with two end users demonstrate the translational benefits of this research. We found that special attention should be paid to monitoring end-user task load to ensure positive rehabilitation outcomes.