Research On The Control Technologies Of Lower Limb Exoskeleton With Hydraulic Drive

An exoskeleton is a wearable device that provides improved functionality to the human for various tasks,such as rehabilitation therapy,enabling individuals to carry heavy loads,and assisting the disabled and the elderly.As the applications of carrying heavy loads,the exoskeleton can enhance the wearer's body ability and reduce energy consumption.It can be used as a long-range walking assist device for military purposes,too.As function of the auxiliary rehabilitation therapy,the exoskeleton can help the disabled and the elderly for walking and take some loads.Therefore,the exoskeleton can be widely used in military,medical therapy,post-disaster reconstruction and daily life.There are great achievements in the research of the exoskeleton.But,there are still some issues that are not solved in the driving technology,lightweight mechanical structure,the bionic design,the sensor and the control technology.The hydraulic drive and control technology of the lower limb exoskeleton have mainly presented in this paper.The main research work is listed as follows.As a kind of human wearable device,the lower limb power assisted exoskeleton should be combined with the user flexibly and can assist the user effectively.It is necessary to study the human walking gait to understand the human walking characteristics.So,a human walking gait analysis platform was built in our laboratory.It is composed of the image acquisition system,the plantar force measurement system and the data analysis system mainly.The experimental platform can analyze the movement angle data of each joint of the human body in a walking gait cycle,and the dynamic joint torque and power data which can provide reference for the design and the control of the exoskeleton.In this paper,the lower limb power assisted exoskcleton is mainly used for the load assistance.The mechanical structure of the lower limb power assisted exoskeleton was designed and the research of the hydraulic drive system was also carried out.On account of requirement of the lower limb power assisted exoskeleton for the hydraulic drive system,the hydraulic actuator and the hydraulic control system were designed,respectively.The strength check of the hydraulic actuator was completed,too.By the simulation in the AMESim software,the hydraulic drive system was validated.And,the hydraulic actuator was optimized in the finite element analysis software ANSYS.According to the design of the hydraulic drive system,the linear model and the differential equation model with the state space form of the valve controlled hydraulic system were established,respectively.The traditional PID control algorithm becomes worse and unreliable in the uncertain environment.The adaptive sliding mode position control algorithms were proposed for the electrohydraulic servo system in this paper.According to the state space model of valve controlled hydraulic system,the adaptive sliding mode control law is designed in detail,and the global asymptotic stability of the algorithm is proved in the theory of Lyapunov.In order to suppress the chattering of the sliding mode control method,the saturation function was replaced of the switching function in the control law.The feedback velocity and acceleration value of the system are obtained by using the nonlinear integral chain derivative method.The electro-hydraulic servo system experiment platform and the RTW/xPC MATLAB target environment real-time control platform were built in the laboratory.In the experiment,the different frequencies of sinusoidal reference signal were selected in the position tracking.The tracking curves were obtained without the uncertain disturbances and with the uncertain disturbances,respectively.Compared with the traditional PID control,the experiments verified the effectiveness and robustness of the proposed algorithms.The force control of the electro-hydraulic servo system is susceptible to uncertain disturbances and precise control is difficult in force control.To solve this issue,the sliding mode control algorithm with neural network compensation was proposed in the electro-hydraulic servo system.According to the state space model of the valve controlled hydraulic system,the sliding mode control law with the neural network compensation was designed.The algorithm is globally asymptotically stable in the sense of Lyapunov.The observer is designed to obtain the relatively accurate values of the force and the force differential.The experiments were implemented in MATLAB RTW/xPC real-time control environment.Compared with the traditional PID control,the proposed force control algorithms were effective and robust in the force control of electro-hydraulic servo system.The walking states were divided into the two states:single foot support and the double foot support state.In this paper,the dynamic models of the lower limb power assisted exoskeleton were established according to the two states.After analyzing the typical control methods of the exoskeletons,an overall coordination control strategies were designed to meet the lower limb power assisted exoskeleton.The sliding mode control with the fuzzy compensation algorithms were used in the swing leg of the lower limb power assisted exoskeleton.The feasibility,effectiveness and robustness of the proposed algorithm are verified through the experiments.The walking experiments were implemented to validate the control system when the pilot wore the exoskeleton.