Design of a quasi-passive parallel leg exoskeleton to augment load carrying for walking

Design of a Quasi-Passive Parallel Leg Exoskeleton to Augment Load Carrying for Walking
by

Andrew Valiente
B.S., LeTourneau University (2003) Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master’s of Science at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY August 2005 © Massachusetts Institute of Technology 2005. All rightsreserved.

Author . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Department of Mechanical Engineering August 5 2005 Certified by. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hugh Herr Assistant Professor of Media Arts and Sciences, MIT Thesis SupervisorCertified by. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ernesto Blanco Professor of Mechanical Engineering Thesis Supervisor Accepted by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Professor Lallit Anand Chairman, Departmental Committee on Graduate Students

2Design of a Quasi-Passive Parallel Leg Exoskeleton to Augment Load Carrying for Walking
by Andrew Valiente Submitted to the Department of Mechanical Engineering on August 5, 2005, in partial fulfillment of the requirements for the degree of Masters of Science

Abstract
Biomechanical experiments suggest that it may be possible to build a leg exoskeleton to reduce the metabolic cost of walkingwhile carrying a load. A quasi-passive, leg exoskeleton is presented that is designed to assist the human in carrying a 75 lb payload. The exoskeleton structure runs parallel to the legs, transferring payload forces to the ground. In an attempt to make the exoskeleton more efficient, passive hip and ankle springs are employed to store and release energy throughout the gait cycle. To reduce kneemuscular effort, a variable damper is implemented at the knee to support body weight throughout early stance. In this thesis, I hypothesize that a quasi-passive leg exoskeleton of this design will improve metabolic walking economy for carrying a 75lb backpack compared with a leg exoskeleton without any elastic energy storage or variable-damping capability. I further anticipate that thequasi-passive leg exoskeleton will improve walking economy for carrying a 75lb backpack compared with unassisted loaded walking. To test these hypotheses, the rate of oxygen consumption is measured on one human test participant walking on a level surface at a self-selected speed. Pilot experimental data show that the quasi-passive exoskeleton increases the metabolic cost of carrying a 75lb backpack by 39%compared to carrying 75 lbs without an exoskeleton. When the variable-damper knees are replaced by simple pin joints, the metabolic cost relative to unassisted load carrying decreases to 34%, suggesting that the dampening advantages of the damper knees did not compensate for their added mass. When the springs are removed from the aforementioned pin knee exoskeleton, the metabolic cost relative tounassisted load carrying increased to 83%. These results indicate that the implementation of springs is beneficial in exoskeleton design. Thesis Supervisors: Hugh Herr and Ernesto Blanco Title: Assistant Professor of Media Arts and Sciences, MIT Title: Professor of Mechanical Engineering, MIT

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Acknowledgments
I would like to first and foremost thank Jesus Christ my Lord and Saviorfor endowing me with a talent for engineering, and for the myriad of past blessings that he has given me. I would like to thank my advisor Professor Hugh Herr for making the Biomechatronics group at the Media Lab an incredible place to work and for his insight in biomechanics. Thanks to my thesis reader, Ernesto Blanco, for his encouragement and insight in mechanics. Thanks to my coworkers at...