Design And Dynamics Analysis Of Composite Driving Bionic Elbow Joint Based On SMA

Aiming at the problems that traditional rigid joints and nonlinear muscle joints are difficult to meet the needs of new manufacturing mode for adaptive and intelligent production.The SMA-motor composite driving bionic elbow joint with the variable stiffness and high performance is proposed,and the relationship between the coupling elements of the bionic elbow joints and the stiffness and pose is studied.The variable stiffness control model,kinematic and dynamic model of SMA-motor composite driving bionic elbow joint are established and the variable stiffness characteristics,kinematics and dynamics characteristics of bionic elbow joints are analyzed,then the simulation verification is carried out respectively.The main contents of this paper are as follows:(1)Structure design and kinematics research of composite driving bionic elbow jointAiming at the problems of traditional robot joints with low power mass ratio and complex transmission.Inspired by the biological structure of the human elbow joint,the composite driving bionic elbow joint based on SMA and motor is designed and the fourth and fifth joints of the six degree of freedom joint robot is replaced by the composite driving joint.The kinematics model of robot is established based on D-H theory,and the mapping relationship between the composite driving bionic elbow joint and the robot's terminal pose is solved.The theoretical value,the error value and the correction value of neuro fuzzy control of the compound driving joint angle is compared in the direction of robot's terminal pose X,Z and Y,and composite driving bionic elbow joint under fuzzy control with high motion accuracy is further proved and meets design requirements.(2)Study on the variable stiffness of compound driven bionic elbow jointIn view of output stiffness of the traditional rigid joint can not be adjusted and the dual control of force / pose accuracy can not achieve.The variable stiffness control model of compound driving bionic elbow joint is established based on SMA constitutive model,theoretical mechanics and output characteristics of human elbow joint stiffness.By analyzing the output characteristics of composite driving joint stiffness under different heating temperature,different diameter of SMA wire and SMA wire length,thevariable stiffness driving mechanism of compound driven bionic elbow joint explored.The simulation results show that the designed composite driving bionic elbow joint has variable stiffness characteristics and the variable stiffness control of compound driven bionic elbow joint can be realized by changing the diameter of SMA wire,the length of SMA filament and the heating temperature of SMA wire.(3)Study on the dynamics of compound driven bionic elbow jointFor the problems that stress and strain nonlinearity,deformation delay and multi-factor coupling of SMA-motor composite drive joint affect the accuracy of joint motion,the fuzzy control algorithm based on double inputs and four outputs and the spatiotemporal coupling model based on biological gene regulatory network are proposed respectively.By analyzing the effect of feedback information from composite drive joint position and force on joint motion state,then the composite driving joint control model is constructed and the dynamic equations of the combined driving joint pitch motion and rotation motion are derived based on Lagrange dynamics.The results of the study show that the position error and velocity error of composite driving bionic joint pitch and rotation motion are reduced by the regulation model,and the precise position control of bionic elbow joint driven by SMA-motor is realized.