Research On Trajectory Tracking Control Strategy Of Upper Limb Rehabilitation Robot Based On Active Disturbance Rejection Control

With the aging of the world’s population,limb defects caused by nervous system diseases are becoming more and more common.It has become an effective means to use rehabilitation robots to assist patients with motor nervous system rehabilitation.Based on the theory of neuroplasticity,rehabilitation robot can help patients with upper limb dysfunction caused by stroke and brain trauma to re-learn the lost upper limb function and promote the reconnection between nerves and brain by providing extensive support and repeated functional training in three-dimensional space.Based on the analysis of the structure of the human upper limb,this paper designs an exoskeleton upper limb rehabilitation robot with Six Degree of Freedom,6-DOF).Its main function is to track the three-dimensional path set by the rehabilitation doctor to pull the affected limb,train the affected limb to complete a series of spatial movements,and realize rehabilitation treatment for patients with upper limb motor dysfunction.Considering that the dynamic system of the upper limb rehabilitation robot has the characteristics of difficult acquisition of motion parameters,severe and irregular external disturbance,this paper takes Active Disturbance Rejection Control(ADRC)as the control theory basis,and designs the trajectory tracking strategy of the6-DOF upper limb rehabilitation robot in the process of rehabilitation training.Active disturbance rejection control does not depend on the accurate data of the model,and the observation compensation mechanism for the disturbance of the system is in good agreement with the upper limb rehabilitation robot system.On the basis of using active disturbance rejection control to track the joint position of upper limb rehabilitation robot,a control strategy combining sliding mode control with active disturbance rejection controller is proposed.The fast Terminal sliding mode-active disturbance rejection control,which combines fast terminal sliding mode control(FTSMC)and active disturbance rejection control,FTSM-ADRC)control strategy not only retains the characteristic of compensating system uncertainties and external disturbances as concentrated disturbances,but also can quickly converge to the bounded area with the participation of sliding mode variable structure.However,this simple fast tracking ability has obvious defects in practical application.The main purpose of rehabilitation equipment is to rebuild the adaptability of muscles and nervous system during the traction of the affected limb.In some cases,forcing the affected limb to move along the track accurately will bring harm to the stiff limb.By adding an impedance control loop based on terminal force feedback outside the position control loop,the running track of the rehabilitation robot can be adjusted according to the human-computer interaction force,which shows the compliance with the patient’s initiative intention and avoids the robot system from causing harm to the patient.The main work is as follows:1)Firstly,the foothold and operation mode of upper limb rehabilitation robot technology are introduced,and the application status at home and abroad is also introduced.Summarized the classic control methods that are easy to be applied to rehabilitation robot system at present and the intelligent control methods that emerged by combining with advanced control concepts.2)By analyzing the structure and movement mechanism of human upper limb,a structural model of 6-DOF upper limb rehabilitation robot which fits the structure of human upper limb and assists limb movement is established by Solid Works software,and its structural logic is tested by means of simulation.Summarize several commonly used spatial posture representation methods at present,and derive the forward/inverse kinematics equation of the system by detailed derivation of D-H method.In addition,in order to effectively control the rehabilitation robot,Lagrange method is used to solve the dynamics equation of the upper limb rehabilitation robot.3)Research on trajectory tracking strategy of upper limb rehabilitation robot based on ADRC.Firstly,the principle of ADRC is introduced.Considering that the upper limb rehabilitation robot will be affected by spasm disturbance in the process of patient rehabilitation training,it is necessary to give consideration to the problem of joint position control and anti-disturbance.A trajectory tracking strategy of upper limb rehabilitation robot based on ADRC is designed,and its convergence is analyzed in detail.In order to verify the effectiveness of the control strategy,a drivable multi-joint model of the upper limb rehabilitation robot is built by Simulink simulation environment to control the trajectory tracking.The MATLAB simulation results show that compared with the traditional PID algorithm,ADRC has excellent control effect in the trajectory tracking process of the upper limb rehabilitation robot,and can track the expected trajectory stably and quickly.4)Research on trajectory tracking of upper limb rehabilitation robot based on sliding mode active disturbance rejection control.Considering that active disturbance rejection control can compensate the spasticity disturbance generated in the rehabilitation training process of patients,it can make patients move according to the original training track without excessive deviation.However,the rapidity of tracking the preset trajectory in an acceptable small range deviation is also an important index for evaluating the rehabilitation effect.After analyzing the theory of sliding mode control,a strategy of fast terminal sliding mode control is designed to improve the control performance of rehabilitation robot.MATLAB simulation results show that the convergence speed of this strategy is obviously better than ADRC,and FTSM-ADRC method has better control performance in the steady-state error range.5)Impedance control of upper limb rehabilitation robot based on terminal force feedback.By analyzing the limb stiffness of patients during rehabilitation training,the outer loop of impedance control based on end force feedback was added to the original position control.Firstly,the relative displacement between the patient and the rehabilitation robot in the limited position is calculated,and the corresponding resistance is calculated by the position-force relationship under the environmental impedance,so as to simulate the end feedback force applied to the robot when the affected limb cannot track the preset trajectory due to stiffness.Combining the structural description of the robot with the knowledge of robot kinematics,the update path that meets the needs of patients is calculated.MATLAB simulation experiments show that the control algorithm can ensure that the tracking accuracy of the upper limb rehabilitation robot can be guaranteed by the method of region division in the training process,and the safety of the patient can be effectively protected by obeying the patient’s stiff limbs.