The Research On Joint Dynamic Characteristics Of Assisted Exoskeleton During Load Walking

The assisted exoskeleton related technology comes from the bionics research of human beings on natural organisms.In recent years,governments have paid more and more attention to the research of assisted exoskeleton technology.Key technologies related to the assisted exoskeleton have been continuously developed and improved.At present,the assisted exoskeleton technology has been applied more and more widely in many fields such as military,disaster relief,rehabilitation medical treatment,transportation logistics,scientific research and so on.In the process of the use of assisted exoskeleton,walking movement is the most frequent movement.In this paper,the dynamic characteristics of the assisted exoskeleton during load walking are studied.This paper takes the third-generation exoskeleton experimental prototype developed by Southwest Jiaotong University as the research object.The experimental data of the assisted exoskeleton walking process is collected.Based on the Lagrange equation,the dynamic modeling and analysis of the load-bearing walking process are carried out.Through the virtual prototype,the dynamic simulation analysis of the load-bearing walking process is carried out.Finite element analysis software is used to simulate different gaits and working conditions.Specific research contents are as follows:(1)Considering only the movement of the human body and the assisted exoskeleton in the sagittal plane,the man-machine load-bearing walking is regarded as a five-link structure.The characteristic angles of lower limbs during man-machine load-bearing walking are modeled.The motion parameters are captured by the optical motion capture device under the test subjects wear the assisted exoskeleton and walk with heavy loads at a pace of 3km/h,4.8km/h and 6km/h,respectively,and at a load of 10 kg,30kg and 50 kg,respectively.The collected data of man-machine load-bearing walking movement are processed.The three characteristic angles of ankle,knee and hip are obtained under different loading conditions and asynchronous speed.According to the variation trend of the three characteristic angles,the SINESQR function is used to fit the characteristic Angle variation curve.The motion equations of each characteristic Angle in the process of load-bearing walking under different working conditions are obtained.(2)According to the number of supporting legs in the process of weight-bearing walking,the assisted exoskeleton weight-bearing walking process can be divided into single-leg supporting state and double-leg supporting state.Based on Lagrange equation,the dynamics model of man-machine load-bearing walking under single leg support and double leg support is built.The dynamic models of ankle,knee and hip in the process of load walking under different supporting states are obtained.The dynamics model of ankle,knee and hip is simulated with the equations of motion of each characteristic angle in Simulink simulation module under different working conditions.The curves of torque of the three joints changing with time in the process of load-bearing walking are obtained.The torques of the three joints under different working conditions are compared and analyzed.The results show that the maximum torque of single leg support and double leg support both appear under the condition of walking speed of 6km/h and load of 50 kg.Under the condition of single leg support,the torque of the left knee joint is the largest,and its value is 405.66N·m.The joint torque of the left knee is 134.63N·m,and that of the right knee is 154.64N·m.(3)The 3D model of the assisted exoskeleton is established in the 3D modeling software Solid Works.Based on the virtual prototype analysis software ADAMS,the dynamic simulation analysis of the assisted exoskeleton load walking process under different working conditions was carried out The motion equations of each characteristic angle under different working conditions are applied as excitation to the model for dynamic simulation.The curve of knee torque and angle changing with time under different working conditions is obtained.The torque and angle changes of knee joint under different working conditions are compared and analyzed.The results show that the maximum torque of knee joint increases with the increase of load.The maximum torque is 58.62N·m when the speed is 6km/h and the load is50 kg.The change of step speed has no significant effect on the maximum torque.(4)The finite element analysis software ANSYS Workbench is used to conduct the statics analysis of the assisted exoskeleton structure under the loading condition of 50 kg,which is in the static standing state,the single-leg support state and the double-leg support state.The results of the static analysis are loaded into the simulation model and the modal analysis is performed.Under the conditions of walking speed of 6km/h and loading of 10 kg,30kg and50 kg respectively,the impact load from the ground is obtained by dynamic simulation in the virtual prototype.The obtained excitation is applied to the simulation model and the transient dynamics analysis is carried out.Transient dynamic analysis is carried out.The results show that the stress of the assisted exoskeleton under the single leg support is the largest in the static analysis,and its value is 262.24 MPa.In the modal analysis,in the fourth mode supported by a single leg,the power assisted exoskeleton undergo the largest deformation,with a value of12.51 mm.In the transient dynamic analysis,the stress of the power-assisted exoskeleton is the largest under the loading condition of 50 kg,and its value is 357.76 MPa.