Rotary Magnetorheological Flexible Jointwith Variable Stiffness And Damping For Robots

The research of motion bionics shows that the stiffness and damping of animal legs can be adjusted to meet the needs of different external environments under different forms of motion.At present,most of the design of foot robots do not consider the changes of leg stiffness and damping,then can not adapt to the changes of external environment perfectly.If the legs of the robot can display the stiffness and damping adjustment mechanism like the animal legs,the robot can be endowed with strong motion adjustment adaptability.In this paper,based on the adaptability of animals in motion,a flexible joint that can independently adjust the equivalent damping and equivalent stiffness of the system is designed,which has compact structure,high flexibility and low energy consumption.The most innovative design of the rotating flexible joint is to achieve the synergistic effect of variable stiffness and variable damping through the compact structure of two magnetorheological fluid dampers and spring sets.Firstly,a mathematical model of variable stiffness and damping is proposed,and the dynamic equilibrium equation of the model is established.The principle of variable stiffness and damping is analyzed in detail.The effects of structural parameters such as excitation frequency,spring stiffness ratio and damping ratio on the equivalent stiffness and damping of the system are discussed.Secondly,based on the proposed variable stiffness and damping model,the flexible joint structure is synthetically designed.The working principle of joint structure is analyzed from the perspective of mechanics,and the mechanical expressions of equivalent stiffness and equivalent damping are derived.The magnetic circuit of the new dual-barrel magnetorheological fluid damper is designed and analyzed by using the finite element analysis software Ansys.A circumferential elastic assembly based on a short straight spring is designed and its equivalent torsional stiffness is derived.Then,according to the detailed structural design of the joint,a flexible joint prototype was processed.The linear stiffness of the short straight spring obtained by the test is converted into the equivalent torsional stiffness of the elastic component.An experimental platform for joint prototype performance testing was built,and the variable stiffness and damping characteristics of the joint prototype were tested and analyzed.Then the test data and theoretical simulation results are compared and analyzed.The experimental data are fitted to establish the corresponding relationship between the equivalent stiffness and damping and the control currents.Finally,the buffer characteristics experiment of the joint prototype was built to simulate the softness of the robot's contact with the environment during the movement process.The experimental results show that the flexible joint can reduce the peak contact force between the robot and the environment to a certain extent compared with the rigid connection.Adjusting the control current and control speed of the flexible joint can change the peak contact force of the robot at the moment of collision,and improve the motion adaptability of the robot to a certain extent.