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Open Access Development of a Series Wrapping Cam and Energy-Storing Spring System for Application in Wearable Robotic Arm Supports

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Gravity-balancing mobile arm support systems have been used to increase the range of motion of individuals with mobility impairment. Ease of use, ergonomics, and assistance profiles have improved significantly, and yet none have successfully transitioned from wheelchair-mounted to fully wearable. We believe that custom design of wrapping cams and lightweight, high-energy-density springs can assist in this goal by reducing weight and profile while offering customization of support torque profiles. A new mechanism called the "series wrapping cam," which utilizes two cams with shared axes that are machined from a single part and operate in series, is introduced. A novel drive cam, spring cam, and spring energy storage mechanism are synthesized and fabricated in order to store and return energy from the custom spring. A functional prototype wearable arm support for the shoulder is developed and evaluated for use as an assistive device for individuals with upper-limb impairment. A compact and lightweight spring was developed from surgical tubing and other components. The spring characteristics were used to model the series cam profiles in order to obtain the desired torque to support the user's arm against gravity about the shoulder with elbow extended. Results of the series wrapping cam cable transmission produced a profile with the desired shape and noticeable offset likely due to unmodeled characteristics of the synthetic rope under load. Hysteresis of movement about the shoulder joint was quantified at between 13% to 17% peak-to-peak, and its effects were only minimally felt throughout the range of motion.
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Document Type: Research Article

Publication date: November 1, 2018

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  • Technology and Innovation, edited and published by the National Academy of Inventors, is a forum for presenting information encompassing the entire field of applied sciences, with a focus on transformative technology and academic innovation. Regular features of T&I include commentaries contributed by the United States Patent and Trademark Office (USPTO) and in-depth profiles of Fellows of the National Academy of Inventors in every issue.

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