No abstract

On-line gait control in human-powered exoskeleton systems is still rich research field and represents a step towards fully autonomous, safe and intelligent indoor and outdoor navigation. It is still a big challenge to develop a control strategy which makes the exoskeleton supply an efficient tracking for pilot intended trajectories on-line. Considering the number of degrees of freedom the lower limb exoskeletons are simpler to design, compared to upper limb. The comparison between lower limb and upper limb is useless when consider the control issues, because of the differences in missions and applications. Based on the literature, we aim to give an overview about control strategies of some famous lower limb human power exoskeleton systems. In the state of the art, different control strategies and approaches for different types of lower limb exoskeletons will be compared consider the efficiency and economic issues. Exact estimation of needed joints torques to execute human intended motions on-line with efficient performance, low cost and reliable way is the main goal of studied system's control strategies. We have study different control strategies used for wide known human power augmentation exoskeletons and compare between them in graphs and tables.

Online gait control in human-powered exoskeleton systems is still rich research field and represents a step towards fully autonomous, safe and intelligent navigation. Admittance Controller performs well on flat terrain walking in human-powered exoskeleton systems for acceleration and slowdown. We are the first who proposed Variable Admittance Controller (VAC) for smooth stair climbing control in Human-Powered Exoskeleton Systems. Trajectory correction technique transforms the interaction forces exerted on the exoskeleton from the pilot to appropriate intended joint flexion angles through dynamic viscoelastic models. We demonstrate the proposed control strategy on one degree-of-freedom (1-DOF) platform first, and then extend to the Human power Augmentation Lower Exoskeleton (HUALEX). The experimental results show that the proposed gait transition control strategy can minimize the interaction dynamics with less interaction force between the pilot and the exoskeleton compared to the traditional admittance controller. Compared to Ordinary Admittance Controller, the proposed VAC significantly improve the normalized Mean Squared Error (nMSE) of trajectory tracking from 2.751° to1.105°.