Research On Integrated Design And Control Strategy Of Four-link Magnetorheological Prosthesis

As an important limb joint of the human body,the lower limbs can not only provide standing support for the human body,but also help the human body to achieve complex movements and maintain body balance.In recent years,amputation accidents caused by factors such as diseases,traffic accidents,natural disasters,industrial injuries,and population aging have increased year by year.Amputees can only help themselves to move by wearing artificial limbs.At present,the quality of prostheses in the domestic market is uneven.Among them,the passive prosthesis with a hydraulic/pneumatic damper as the main damping element has a large structure size and long response time,which cannot achieve good coordination between the prosthesis and the amputee.Due to the addition of active motors to provide active power,active prostheses have complex structures,cumbersome controls,high power consumption,and high costs,making them difficult to apply to most amputees’ families.Compared with the two,the semi-active magnetorheological prosthesis based on magnetorheological damper(MRD)has the advantages of fast response time,low energy consumption,and continuous controllable damping,and has become one of the important research directions of intelligent prosthetics.one.However,most of the existing magnetorheological prostheses directly use commercial MRD,which leads to a large space occupation of the MRD,which cannot meet the design requirements of the prosthesis,and the connection between the damper and the large and small leg parts swings back and forth during the movement.Affects the locomotor gait of the prosthetic.In addition,the magnetorheological prosthetic system is a nonlinear coupling system,and its control algorithm often has problems such as periodic disturbances,low control accuracy,and cumbersome and complicated control.Based on this,this paper mainly carries out research work from the following aspects.1.To accurately simulate the motion of the human knee joint,a four-link magnetorheological prosthesis based on MRD is proposed and designed,including a four-link mechanism,MRD,and other components,and its kinematics and dynamics models are established.According to the gait information of the human body and the ideal instantaneous rotation center trajectory of the knee joint,the structural parameters of the four-bar linkage mechanism are obtained by optimizing the particle swarm optimization algorithm,and the MRD layout,structural size,and required damping force requirements are determined at the same time.2.Aiming at the requirements of magnetorheological prosthetics,a prosthetic-oriented MRD is designed,which mainly includes the structural size design and material selection of each component,and the magnetic circuit calculation is performed on it.At the same time,its mechanical model is established based on the Bingham model.Multi-physics field coupling simulation and dynamic performance simulation are carried out on the designed MRD to obtain the static magnetic field characteristics at the effective damping gap under different currents,the dynamic flow field characteristics of the MRF under the action of the magnetic current field,and the dynamic performance under different vibration excitations.And then verify the feasibility of the MRD design.3.Process the MRD prototype and test its dynamic performance.In order to enable MRD to accurately output the damping force required by the prosthesis,based on the experimental data of MRD and the improved hyperbolic tangent model,the forward mechanical model of MRD was established by parameter identification,and its inverse mechanical model was established based on BP neural network.4.Aiming at the problems of periodic disturbance and low control precision in the magnetorheological prosthetic system,a control algorithm of PD+ iterative learning is proposed,and the convergence of the PD+ iterative learning algorithm is proved based on the convergence analysis.The motion simulation system of the magneto-rheological prosthesis is built by Matlab/Simulink and Adams to realize the tracking control of the motion trajectory of the magneto-rheological prosthesis.5.To test the performance of the designed four-link magnetorheological prosthesis,the prototype of the four-link magnetorheological prosthesis was processed and its experimental test system was built.The motion angle based on iterative learning + PD control algorithm was tested and compared with the ideal step.The results show that the four-link magnetorheological prosthesis based on iterative learning + PD control can effectively track the ideal gait trajectory as the pace increases,which further verifies the effectiveness of the algorithm.