Structural Optimization And Experimental Research Of Magnetorheological Damper For Lower Limb Prosthesis

Frequent traffic accidents and natural disasters lead to a gradual increase in the number of amputations every year,which will not only affect the physiological function of patients,but also bring huge psychological burden to patients due to the difficulty of mobility and rehabilitation treatment.Therefore,prosthetics have become an important tool to help them return to normal life.Magnetorheological(MR)damping prosthesis is a semi-active prosthesis.Compared with other similar prostheses,it has simple structure,low energy consumption and high comfort.Especially,the continuous adjustable damping force makes it flexible to adapt to a variety of road conditions.The core part of this kind of prosthesis is the magnetorheological damper.When there is no external magnetic field,the magnetorheological fluid has low viscosity and strong Newtonian fluid properties.Under the action of magnetic field,this liquid will become a Bingham liquid with high viscosity and low fluidity.This change can be adjusted continuously,and its response speed is fast.Therefore,MR damped prosthetic knee joint has become a hotspot.In this paper,a magnetorheological damped lower limb prosthesis was designed,and a threedimensional model of the lower limb prosthesis was established.According to its working principle,it was simplified into a four-link mechanism.The mathematical model of the lower limb prosthesis was established by Lagrange theory.The kinematic and dynamic characteristics of the lower limb prosthesis were studied under different working conditions,and the damping force required by the magnetorheological fluid damper located in the lower limb was obtained.Based on the structural parameters of lower limb prosthesis,a MR damper was designed,and the influence of piston diameter,effective length,shear clearance and other parameters on the output damping force performance of MR fluid damper was analyzed.By analyzing and calculating the reluctance of magnetic circuit,the magnetic circuit of MR damper was designed.A multi-objective particle swarm optimization algorithm was used to optimize the structural parameters of MR fluid damper with damping force and power as optimization objectives.Based on the optimized structural parameters,ANSYS finite element analysis software was used to simulate the magnetic circuit inside the magnetorheological fluid damper.The distribution of magnetic field lines and magnetic flux density inside the magnetorheological fluid damper was analyzed.At the same time,the magnetic flux density and magnetic field distribution in the shear gap of the magnetorheological damper under different excitation currents were compared before and after optimization.It provides theoretical and experimental basis for further development of lower limb prosthesis with MR damping.According to the structural parameters of MR damper for lower limb prosthesis,a prototype of MR damper was developed,a set of performance test experimental platform of MR damper was established,and a specific scheme was designed for each module of the experiment.The response time of MR damper coil,the magnitude of damping force and the response time of damping force under different applied current excitation were studied experimentally.The experimental data were analyzed,and it was verified that the MR damper designed in this paper can meet the needs of human normal walking.