Moving an Immovable Limb: Prototyping a Low-Cost, Simplified Robotic Exoskeletal Arm Mobility Aid

Abstract

The purpose of this project was to test the hypothesis that a biomedical robotic exoskeletal mobility aid could be at the same time affordable, unobtrusive, and valuable in its contribution to the quality of life for people with some types of muscular dystrophies or paralysis. Over a million people in the United States alone suffer from paralyzing conditions caused by muscular dystrophies, stroke, and trauma. While there are a number of consumer devices focused on life support, options for maintaining physical and social independence are limited and expensive. Biosignal-controlled exoskeletal robotics are nothing new, but as the industry focuses on advancing the technology, there is a huge overlooked opportunity to use basic robotic technology to help patients in an affordable, accessible manner. Toward this overarching goal, this project focused on prototyping a simple two-degree-of-freedom muscle-controlled exoskeletal arm mobility aid for the purpose of helping someone with an extremely weak or paralyzed arm to perform simple tasks in the plane in front of him, like write on a tablet or reach out to touch the hand of a loved one. The three main elements of mechanical design, electromyography (EMG), and controls comprise the body of this design study and are discussed in detail. The greatest challenges were designing a robust yet unobtrusive mechanism out of low-cost components, balancing and minimizing the effective EMG signals across muscle groups, and working within the limitations of inexpensive prefabricated electronics. The control of the motors is very responsive, although slack in the cables leads to some non-negligible time lag in the response. For the future, other types of control signals could be investigated and compared to EMG performance at this price point. Ultimately, the resulting mechanism achieved its design objectives of an affordable, accessible, unobtrusive EMG-controlled robot that can support the weight and movement of the user’s arm in a plane.