Structural Design And Stiffness Division Of Variable Stiffness Soft Joints Analysis And Variable Stiffness Method Improvement

This thesis mainly studies the variable stiffness method of soft robot.In order to solve the problem of insufficient stiffness of soft robot,after comprehensive analysis of soft robot’s driving mode and different variable stiffness modes,it is finally decided to design a soft variable stiffness joint by gas driving mode.The structure of the joint is designed,the constitutive equation of the soft material is established,and the reliability of the constitutive equation is verified by simulation software.The tensile stiffness and bending stiffness of the joint are analyzed.The feasibility of variable stiffness of the joint is verified by simulation software,and the expressions of tensile stiffness and bending stiffness of the joint are summarized.According to the analysis and simulation verification of the influencing factors of joint stiffness,a structure of variable stiffness layer is proposed to improve the joint.The specific contents of this thesis include:(1)Summarize and analyze the different driving forms,structures and variable stiffness modes of soft robot,and finally select the driving mode and variable stiffness principle suitable for your own research.(2)Design the flexible variable stiffness joint and variable stiffness structure proposed in this thesis.(3)According to the strain energy theory,two ideal expansion formulas of strain energy function are preliminarily selected: Mooney-Rivlin model and Yeoh model;The curve fitting of Mooney-Rivlin model and Yeoh model is carried out on the stress-strain data of materials which are subjected to cyclic loading to eliminate the Mullin effect of hyperelastic materials.Finally,Yeoh model is selected to analyze the joint stiffness,and the fitting results are compared by three groups of tensile simulation,which verifies the reliability of the model selection.(4)The tensile stiffness and bending stiffness of the joint are analyzed theoretically,and the simulation comparison of the tensile stiffness and bending stiffness of the joint under different driving pressures verifies the feasibility of variable stiffness joint and the correctness of theoretical analysis.According to the stress and strain of joints under different driving air pressures,the tensile stiffness equation and bending stiffness equation of variable stiffness soft joints are derived.(5)The factors affecting the joint stiffness are analyzed and the reliability of the analysis is verified by simulation.Finally,a variable stiffness layer structure is proposed,which can ensure the joint variable stiffness ability and further improve the flexibility of soft joints.