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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WEARABLE ARM SUPPORT;
Document Type: Research Article
Publication date: November 1, 2018
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