Advanced Robotics, Vol. 20, No. 9, pp. 967–988 (2006)
VSP and Robotics Society of Japan 2006.
Also available online - www.vsppub.com
Full paper
Design of an electrically actuated lower extremity
exoskeleton
ADAM ZOSS and H. KAZEROONI
∗
Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA
Received 13 September 2005; accepted 27 March 2006
Abstract—Human exoskeletons add the strength and endurance of robotics to a human’s innate
intellect and adaptability to help people transport heavy loads over rough, unpredictable terrain. The
Berkeley lower extremity exoskeleton (BLEEX) is the first human exoskeleton that was successfully
demonstrated to walk energetically autonomous while supporting its own weight plus an external
payload. This paper details the design of the electric motor actuation for BLEEX and compares
it to the previously designed hydraulic actuation scheme. Clinical gait analysis data was used to
approximate the torques, angles and powers required at the exoskeleton’s leg joints. Appropriately
sized motors and gearing are selected, and put through a thorough power analysis. The compact
electric joint design is described and the final electric joint performance is compared with BLEEX’s
previous hydraulic actuation. Overall, the electric actuation scheme is about twice as efficient and
twice as heavy as the hydraulic actuation.
Keywords: Exoskeleton; robotics; biomechanics; electric motor; actuation.
1. INTRODUCTION
Although wheels are useful for moving heavy loads over flat surfaces, legged
locomotion has many advantages on rough and unpredictable terrain. Legs can
adapt to a wide variety of environments, such as rocky slopes and staircases,
which are impassable by wheeled vehicles. However, legged robots have difficulty
balancing and navigating while maneuvering through the inherently rough terrains
that favor legs over wheels. Lower extremity exoskeletons seek to bypass these
problems by closely integrating a human’s intelligence and adaptability with the
strength and endurance of robotic legs.
Berkeley’s lower extremity exoskeleton (BLEEX) is comprised of two actuated
anthropomorphic robotic legs that a person ‘wears’ (Fig. 1). As the person moves
∗
To whom correspondence should be addressed. E-mail: kazerooni@berkeley.edu
