Research On Motion Accuracy Of 3-PSS Parallel Robot Based On Elastodynamics

The 3-PSS parallel mechanism is composed of a moving platform and a fixed platform,which are connected by three independent motion branches.The mechanism is driven by three drivers.Parallel mechanism are widely used in industry because of their high stiffness,high precision and small inertia.But in the process of movement,because of the elastic deformation of link rod parts with smaller stiffness,the motion accuracy of parallel mechanism is reduced,and its application is limited.Therefore,the research which is concerned with the accuracy of parallel mechanism with flexible robs has important theoretical significance and practical value.In this study,theoretical deduction,simulation and experimental analysis are combined,taking 3-PSS parallel robot with flexible link as the research object,the kinematics model of the mechanism is studied.Taking 3-PSS parallel robot as the research object,the kinematics model of the mechanism is studied.Based on ADAMS,the frequency characteristics of rigid mechanism and rigid-flexible coupling mechanism are simulated.The elastodynamic equation of the mechanism is deduced by using finite element theory and Lagrange equation.And the dynamic characteristics of 3-PSS parallel manipulator with different mechanism parameters are experimentally studied.The main research results of this study are as follows:(1)Aiming at the configuration of 3-PSS parallel mechanism,the forward and inverse kinematics models of 3-PSS parallel manipulator are established according to the motion constraint relationship between the moving platform and the slider,and the kinematics analytical expression of the model is derived in the form of matrix.The cross section of the motion space is reuleaux triangle.The kinematic accuracy and space of the mechanism are affected by the difference between the length of the link rod and the radius of the platform.(2)In ADAMS,rigid models of 3-PSS parallel mechanism and rigid-flexible coupling models of different mechanism parameters are established respectively.The kinematic accuracy of the mechanism is calibrated by using the frequency characteristics of the mechanism.The simulation results show that: When the flexible body is included,the motion accuracy of the mechanism will decrease.The length,cross-section diameter,elastic modulus of the link rod and the load of the moving platform will change the motion accuracy of the rigid-flexible coupling mechanism in varying degrees.(3)By combining the finite element method with the Lagrange equation,the differential equation of motion of the finite element of the link rod is established.Based on the kinematics and dynamics constraints of nodes and parts,the dynamic equation of 3-PSS parallel robot system is deduced.It is concluded that: Specific influence modes of length,cross-section diameter,elastic modulus of link rod and load of moving platform on kinematic accuracy of mechanism;A design criterion for a 3-PSS parallel manipulator is proposed,the relationship between the dynamic characteristics of the system and the kinematic accuracy of the mechanism is established.(4)Vibration signals of 3-PSS parallel manipulator on experimental maneuvering platform with mechanism design parameters are analyzed.The results show that: Different mechanism parameters have different effects on the frequency characteristics of the mechanism.The results are in agreement with the previous conclusions.Namely reasonable mechanism parameters can improve the motion accuracy of 3-PSS parallel robot.The above results show that the research results can guide the design of 3-PSS parallel manipulators with higher motion accuracy and have distinct practical value.