Robotica

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Conf Proc IEEE Eng Med Biol Soc. Author manuscript; available in PMC 2010 March 6.
Published in final edited form as: Conf Proc IEEE Eng Med Biol Soc. 2009 ; 2009: 2119–2124. doi:10.1109/IEMBS.2009.5333984.

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Robotic Lower Limb Exoskeletons Using Proportional Myoelectric ControlDaniel P. Ferris and School of Kinesiology, University of Michigan, Ann Arbor, MI 48109-2013 USA (phone: 734-647-6878; fax: 734-647-2808;) Cara L. Lewis School of Kinesiology, University of Michigan, Ann Arbor, MI 48109-2214 USA
Daniel P. Ferris: ferrisdp@umich.edu; Cara L. Lewis: caralew@umich.edu

Abstract
Robotic lower limb exoskeletons have been built for augmenting human performance,assisting with disabilities, studying human physiology, and re-training motor deficiencies. At the University of Michigan Human Neuromechanics Laboratory, we have built pneumatically-powered lower limb exoskeletons for the last two purposes. Most of our prior research has focused on ankle joint exoskeletons because of the large contribution from plantar flexors to the mechanical work performed duringgait. One way we control the exoskeletons is with proportional myoelectric control, effectively increasing the strength of the wearer with a physiological mode of control. Healthy human subjects quickly adapt to walking with the robotic ankle exoskeletons, reducing their overall energy expenditure. Individuals with incomplete spinal cord injury have demonstrated rapid modification of musclerecruitment patterns with practice walking with the ankle exoskeletons. Evidence suggests that proportional myoelectric control may have distinct advantages over other types of control for robotic exoskeletons in basic science and rehabilitation.

I. Introduction
Engineering teams around the world are currently developing many sophisticated robotic lower limb exoskeletons. Arguably, the most advancedand most internationally visible are Berkeley Bionics’ BLEEX, Cyberdyne’s HAL, and Raytheon Sarcos’ exoskeleton [1]. There are four main purposes for robotic exoskeletons in development: augmenting human performance, assisting with disabilities, studying human physiology, or re-training motor deficiencies. Augmenting human performance refers to exoskeletons that can give neurologically intact,healthy humans capabilities above and beyond what they currently have. This has usually been focused on increasing strength and/or enhancing endurance. Assisting with disabilities refers to exoskeletons that allow individuals with physical disabilities the ability to perform like a non-disabled individual. The goal is for the exoskeleton to provide benefits only when it is being worn. Studying humanphysiology refers to basic science experiments aimed at providing new insight into the biomechanics, neural control, and/or energetic cost of human movement. This is a relatively unexplored purpose but holds considerable potential for improving our understanding of how the human body works. Retraining motor deficiencies refers to the need to rehabilitate individuals with spinal cord injury,stroke, or other neurological disabilities. The goal is to have an individual use the exoskeleton during training so that the individual can then perform better without the exoskeleton later. Most exoskeleton developers have targeted the first two purposes as they hold the greatest potential for creating commercially viable products.

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In the University of Michigan HumanNeuromechanics Laboratory, we have focused on building simple lower limb exoskeletons to provide insight into human locomotion physiology and to be used as possible motor training aids after neurological injury [2–14]. Because these goals rely on having human subjects in a laboratory or clinic setting, it removes many challenging obstacles to creating functional robotic exoskeletons. First, our...