Research On A Single Motor Driven 2-DOF VSA For Shoulder-Wrist Joint

Since the 21st century,with the rapid development of science and technology.The improvement in robots application environment and performance requirements,human beings have more and more close contact with robots in their production and life.Improving the safety of human-computer interaction becomes the primary factor of a robot design in the future.The variable stiffness actuator(VSA)can improve the dynamic performance of human-computer interaction and provide safety guarantees for the integration of robots and humans.At present,most of the VS As are one degree of freedom.However,in the application of a bionic robot,it usually needs a multi DOF VSA to realize the flexibility,multi-function,and dexterity of a robot.In this paper,based on the spherical wrist parallel mechanism(SWPM),a two degree of freedom variable stiffness actuator(2-DOF VSA)is designed,which uses a single motor to control its stiffness adjustment.The principle of adjustable stiffness and the mechanical structure of the actuator is analyzed.The mass and volume of the joint is reduced by the parallel arrangement design of the leaf springs group,and the adjustment of the stiffness is realized synchronously.According to the geometrical nonlinearity of small deflection of leaf spring,the analytical formula for actuator rotation stiffness is established.The kinematic model of the SWPM is established to derive its adjustable stiffness model.The accuracy and validity of the results is verified by the stiffness analysis of the 2-DOF VSA model.The main contents of this paper are as follows:(1)A high integration 2-DOF VSA which can be used in a bionic wrist joint or shoulder joint is proposed.Based on the 2-DOF orthogonal motion generated by the spherical wrist parallel mechanism,the stiffness is adjusted by adjusting the effective length of the spring sheets evenly distributed among the spherical wrist,and the 2-DOF stiffness is adjusted synchronously by changing the effective length of multiple spring sheets by a single electric machine.The high integration design of the 2-DOF variable stiffness element driven by a single motor is realized.(2)Theoretical research on VS A based on structural variable stiffness principle of leaf spring.According to the curvature,deflection and rotation angle of the cantilever beam,the stiffness characteristics of the leaf spring under small deformation are analyzed.According to the principle of the cantilever beam,the mathematical model of VS A is established,and its variable stiffness characteristics are analyzed theoretically.(3)Joint simulation analysis of VS As.Through ANSYS and Adams,the effective length of the leaf spring of the mechanism types variable stiffness principle is simulated and analyzed.The statics module of SolidWorks software is used to analyze the key components of the VS A.(4)Build the experiment platform of VS A,compare the static and dynamic stiffness identification experiments of the actuator,and detect its static and dynamic stiffness adjustment performance;compare the position tracking experiment and position step experiment of the VSA,and detect the performance of the actuator in the working process;compare the loading and unloading experiment of the VS A,and detect the lag angle of the VS A;Compare the safety collision experiment,detect the safety in human-computer interaction.By comparing the experimental data with the theoretical analysis and simulation structure,the feasibility and reliability of the proposed VS A is verified.