Dynamic Analysis And Design Of Exoskeleton Of Lower Extremities Under Uncertain Conditions

The lower extremity exoskeleton is a man-machine highly coupled system which combines human brain with machine intelligence,and the strength of the human body with the power of the machine to enhance or restore the strength and endurance of human body,which has a great potential application value in military fight,medical rehabilitation,space exploration,health care and other fields.In the collaborative walking between human and the lower extremity exoskeleton,the mechanical components' threedimensional movement of the exoskeleton is always harmonized with that of the wearer's lower limbs highly,which leads to a tightly coupled relationship between human and the exoskeleton;however,the dynamic properties of the exoskeleton mechanism could be change due to the uncertainty in actual system,which will affect the coordination between human and the lower extremity exoskeleton.Further,the lower extremity exoskeleton is taken as an example to be analyzed in this thesis.Considering the safety and comfort of the wearer,three parts of the research are gradually carried out based on the dynamic characteristics of the exoskeleton mechanism.(1)Based on the mechanism of human lower limbs movement and gait analysis,the exoskeleton dynamic modeling and analysis of lower extremities were carried out.In order to develop the human gait experiment and establish a reasonable exoskeleton mechanical model,the degree of freedom of joint,driving characteristics and movement description of human body's lower limbs are analyzed carefully.Then,the data of the joint angular displacement and the external force of the system under normal human gait are obtained.And the three-dimensional mechanical model of the exoskeleton mechanism is established in this thesis to complete the kinematic and dynamic analysis of the exoskeleton's coordinated walking with the human body.Finally,the rationality of the dynamic model and the correctness of the solution of the dynamic model are verified.(2)The time-dependent reliability analysis of the exoskeleton joint torque is conducted to evaluate the wearing safety of the lower extremities exoskeleton.On the basis of the exoskeleton dynamic model under the ideal condition,the mathematical model of the actual driving moment of the joints of the exoskeleton could be derived.Because of the change of dynamic properties caused by the difference between the actual driving torque and the ideal,the time-variant reliability analysis model of the lower limb exoskeleton is deduced.Finally,the time-varying reliability of the joints is calculated by the Monte Carlo simulation method with considering the characteristics of the limit state function.(3)To make both the safety and comfort of the lower extremities exoskeleton considered adequately,a time-varying reliability based robust optimization model for the exoskeleton of the lower extremities is built and solved.The comfort of wearing exoskeleton is ensured by establishing the objective function that the weighted sum of the difference between the actual driving moment of the exoskeleton and the corresponding ideal driving moment and variance of the actual driving moment.Finally,the optimized model is solved by the improved particle swarm optimization(PSO),and the optimization results show that it has a certain engineering reference value for reducing the deviation and variance of the actual driving torque of the exoskeleton.In this thesis,the structural and unstructured factors of the exoskeleton of the lower extremities are considered,and the safety and comfort indexes of wearing the exoskeleton are combined to carry out the research work on the dynamic analysis and design of the exoskeleton in the lower extremities,which provides a new method for resolving the problem that the safety and comfort of the lower extremity exoskeleton.