A Controller for Guiding Leg Movement During Overground Walking With a Lower Limb Exoskeleton

This paper describes a lower limb exoskeleton control approach that facilitates a desired movement coordination between the hip and knee joints during the swing phase of gait. An important feature of the proposed controller is that it provides movement guidance while allowing a user to control step time and step length. Specifically, control of step time is enabled by the use of time-invariant movement constraints, while control of step length is enabled by a real-time path-planning feature. As such, the controller provides movement coordination, but still enables a user to retain the step-to-step variability required to maintain balance during walking. The controller was implemented on a lower limb exoskeleton and tested on five healthy subjects. The subjects walked overground in the exoskeleton without a stability aid under two conditions: with the proposed coordination controller (i.e., with sagittal plane movement constraints) and with no control implemented (i.e., without sagittal plane movement constraints). Data from these assessments indicate that the controller provided substantial movement coordination while still allowing subjects substantive control of step time and length across a range of walking speeds.