Adaptive Finite Time Control for Wearable Exoskeletons Based on Ultra-local Model and Radial Basis Function Neural Netwo
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
Adaptive Finite Time Control for Wearable Exoskeletons Based on Ultralocal Model and Radial Basis Function Neural Network Jianjun Sun, Jie Wang*, Peng Yang, Yan Zhang, and Lingling Chen Abstract: This paper investigates an adaptive finite time control scheme for wearable exoskeletons to realize trajectory tracking control. The main feature of the proposed scheme is model-free in which no dynamic models are required except for the input and output data. Firstly, a second order ultra-local model is employed to replace the complex dynamic model of wearable exoskeleton as the controlled object, which is a novel designed model. In addition, a nonsingular fast terminal sliding surface is proposed to design the controller to guarantee the finite time convergence of tracking errors, and a radial basis function (RBF) neural network is developed to approximate the lumped disturbance in the ultra-local model. Then the stability of closed-loop system is proved by Lyapunov theory. Finally, to validate the proposed control scheme, virtual prototype is designed in SolidWorks and transferred to MATLAB, then visual simulation program is implemented based on SimMechanics. What’s more, reference trajectories are extracted from the measured data of DELSYS Electromyography (EMG) recording system. The effectiveness of proposed scheme is demonstrated by the simulation results. Keywords: Finite time control, model-free control, radial basis function neural network, ultra-local model, visual simulation, wearable exoskeleton.
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INTRODUCTION
Wearable exoskeletons have been developed for physical assistance and rehabilitation, which can be worn and fit in properly with the operator. Wearable exoskeleton technology has the potential of long-term research due to the increasing aging problem and military/industrial demands. Attempts have been made to apply wearable exoskeletons in different fields. Berkeley Lower Extremity Exoskeleton (BLEEX) [1, 2] is a typical wearable robotic system that can assists carrying heavy loads to reduce the burden of soldiers. Stride Management Assist (SMA) [3] is developed by a versatile control scheme that makes lower limbs responsive to muscle torque by modifying the dynamic response of human limb. Hybird Assistive Limb(HAL) [4] is constructed to support physically disabled person, movement intention also gained by grasping the interaction between person and HAL. Rewalk [5], Active Leg Exoskeleton (ALEX) [6] are successfully applied wearable exoskeletons constructed to assist regain movement ability for patients. Walking assistance exoskeletons [7, 8] are designed for weight support enhancement and help disabled person do desired periodic trajectory tracking training. Moreover, a 5 degree-of-freedom (DOF)
upper-limb exoskeleton is designed in [9], and an adaptive control method with improved safety is proposed as well. In general, wearable exoskeletons have been successfully developed and still possess great research value. Wearable exoskeleton sy
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