Preliminary Design of Musclae-Powered Exoskeleton for Users with Spinal Cord Injury

Abstract

The exercise methods available to individuals with spinal cord injuries are limited, increasing their risk of pressure sores, muscle atrophy, diminished bone strength, and diminished blood flow efficiency. The FES Energy Storing Exoskeleton combines the simplicity of a passive exoskeleton with functional electrical stimulation of the quadriceps muscles, enabling the user to stand and walk using their own muscles. To reduce muscle fatigue, the initial energy supplied by FES is supplemented by gas springs for energy storage and bidirectional clutch mechanisms for joint locking and control. Gas springs have superior energy storage qualities over pneumatic cylinders and elastomer bands due to their high energy-to-weight ratio and constant force properties. A qualitative analysis of joint locking mechanisms has suggested that a bidirectional clutch mechanism has the potential to overcome the sagging exhibited by the wrap springs used in previous versions of the exoskeleton. While the design of the novel clutch mechanism is the subject of a future work, the functionality and benefits of the mechanism are described in the context of the overall performance of the exoskeleton. The revised design is predicted to weigh 10.2 kg, which is 6.8 kg lighter than the previous exoskeleton design, and is significantly lighter than most commercial motorized walking exoskeletons. A detailed CAD model of the improved system has been developed and future work includes creating and validating a physical prototype.