Time-varying Reliability Analysis Of Lower Extremity Exoskeleton Based On Surrogate Model

The lower extremity exoskeleton is a mechatronic device that can be worn on the lower limbs of the human body.It aims to enhance or restore the motor function of the lower limbs of the human body.It has been widely used in the fields of rehabilitation medicine,industrial production and individual combat.However,the lower extremity exoskeleton itself is a kind of mechanical equipment,which has certain institutional operation risks.At the same time,during the service process of the lower extremity exoskeleton,it will be affected by many internal and external uncertain factors.These risks and uncertainties make the lower extremity exoskeleton have dynamic time-varying characteristics,and its kinematics,dynamics,and control characteristics change with time and use conditions,which in turn poses challenges to the reliability and safety of the exoskeleton.In view of the above-mentioned reliability and safety problems in the research and application of lower extremity exoskeletons,this thesis will conduct timevarying reliability analysis on lower extremity exoskeletons to evaluate the performance of the system under different environmental conditions,so as to provide a basis for the design and application of the system.Optimization provides a scientific basis to promote the development and application of lower extremity exoskeleton technology.The main research contents of this thesis include:(1)Movement research and configuration design of lower extremity exoskeletonIn order to gain an in-depth understanding of the kinematic characteristics of the lower limbs,a kinematic model of the lower limbs was established,and the gait analysis of the lower limbs was completed using the experimental data of the human gait,which provided a theoretical basis for the configuration design of the lower limb exoskeleton robot.Then,based on the research on the movement of the lower limbs of the human body,the degree of freedom matching and joint drive design of the hip joint,knee joint and ankle joint are completed.At the same time,the lower extremity exoskeleton was simplified to a certain extent,and the plane simplified kinematics analysis and the establishment of the simplified model were completed,which provides a model basis for the time-varying reliability analysis of the lower extremity exoskeleton.(2)A time-varying reliability analysis method based on the adaptive PC-Kriging methodA time-varying hybrid reliability analysis model is expounded for the case of interval variables in the uncertainty factors of lower extremity exoskeleton.The human-machine coupling consistency is defined according to the coincidence degree of the ideal joint angle trajectory and the actual joint angle trajectory,and the human-machine coupling consistency model under internal uncertainty is established.Aiming at the case that the limit state function in the consistency model is high-dimensional nonlinear,a timevarying reliability analysis method based on the PC-Kriging surrogate model is proposed.This method efficiently evaluates the time-varying reliability of the lower extremity exoskeleton under internal uncertainties,and reveals the consistency rule of the humanmachine coupling of the lower extremity exoskeleton.(3)A time-varying reliability analysis method based on the extreme value moment methodConsidering the influence of external uncertainty(stochastic terrain)on the dynamic time-varying characteristics of the lower extremity exoskeleton,a human-machine coupling consistency model under external uncertainty was established.Aiming at the situation that the PC-Kriging surrogate model method needs to repeatedly evaluate the expensive calculation model,a time-varying reliability analysis method based on the extreme value moment method is proposed.This method efficiently evaluates the timevarying reliability of the lower extremity exoskeleton on stochastic terrain,and enriches the time-varying reliability analysis theory and solution method.