Abstract
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°.
Highlights
A lot of researches on Human-Powered Exoskeleton Systems has been focused on flat terrain walking while stair ascent and vice versa is frequent process on daily life activities
It is evident that this input depends on wearer desired flexion angle and desired admittance parameters. To improve such ordinary admittance control method (OAC) to pretty handle the uncertainties in dynamics model when human intend to change gait we introduce dynamic parameters estimation technique called variable admittance controller (VAC)
We investigate a relation between Variable Admittance Controller (VAC) parameters and interaction force for accurate and perfect human trajectory tracking even when sudden change in current trajectory happens
Summary
A lot of researches on Human-Powered Exoskeleton Systems has been focused on flat terrain walking while stair ascent and vice versa is frequent process on daily life activities. Around thigh wearable force sensor device is designed to act as a sensory feedback tool to monitor the human exoskeleton interaction as well as to use it for gait transition control. The use of this interaction force as a feedback signals for our control system is efficient way for good results. An admittance controller called position based impedance controller, uses the end-effector interaction force feedback to estimate the appropriate joint position. To prove the performance efficiency of proposed we show how to learn admittance controller stiffness parameters on-line using observations stairs ascent trails.
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