Study On Gait Planning And Trajectory Tracking Control Of Rehabilitation Carrier Type Lower Extremity Exoskeleton

Wearable exoskeleton combines strong machine power provided by robot with human intelligence,becoming a new type of mechatronics system,which can provide physical support,motion assistance,strength enhancement and other functions.Under the situation of trend of aging population becoming increasingly serious and individual combat capability needing to be improved urgently,the exoskeleton has become a research hotspot in the field of robotics with a broad application prospect in rehabilitation medicine,military,scientific research and industrial production.In this paper,a lower extremity exoskeleton for rehabilitation and carrying was studied,which had 10 degrees of freedom(DOFs).Based on the structure design and modeling of this man-machine integrated system,stable gait planning and trajectory tracking control were studied according to the emphasis of rehabilitation and carrying.The major contents are as followed:1)Structure design of lower extremity exoskeleton system.After classification and analysis of existing research results,the number of DOFs and their configuration were determined according to the characteristics of human walking.Then the structure design could be completed.2)Establishment of kinematic and dynamic model of supporting leg and swing leg.The hybrid characteristics of lower extremity exoskeleton system were obtained by walking analysis,then kinematic and dynamic analysis of supporting leg and swing leg were carried out.Kinematic analysis used modified D-H method,including direct and inverse kinematics.Based on the kinematics,the Lagrange equation method was used to obtain dynamic model.Combined with the discrete envent dynamics described by switching system,the hybrid model of lower extremity exoskeleton system was established.In order to simulate the real environment and simplify the construction of hybrid system's mathematical model and the design of controller,a virtual prototype of the exoskeleton system was established in ADAMS.3)Planning of stable gait.The characteristic of carrying indicated that the exoskeleton robot dominated and drove the wearer to walk normally,making stable gait planning an important research topic.Based on zero moment point(ZMP)theory,ZMP must always be kept in the support domain during stable walking.The constraint conditions of planned gait were determined by human walking analysis,and three spline interpolation was used to calculate parameterized continuous trajectory.Combined with the calculation of ZMP stability margin,the objective function of genetic algorithm was designed for optimizing gait parameters.The desired joint gait could be obtained through inverse kinematics,and its stability was verified by dynamics simulation in ADAMS.4)Research of trajectory tracking control.The final realization of stable walking required each DOF to track the desired trajectory accurately.Based on system's mathematical,the torque calculation and PD feedback controller was designed.As to the virtual prototype without precise mathematical model,TDE-iPID and TDE-iPIDESMC controller were designed under the model-free control thought.TDE-iPID used time delay estimation to obtain utral-local model of system,and formed the control loop through the intelligent PID feedback.The time delay estimation error model was established based on TDE-iPID,and the equivalent sliding mode control(ESMC)was used to compensate the error.Through the co-simulation between MATLAB/Simulink and ADAMS,the reasonability and validity of TDE-iPID trajectory tracking control strategy and the improvement of tracking results by ESMC are verified.