| Parallel mechanism has been widely used in aerospace,military,medical and health,industrial and other fields in recent years due to its high rigidity,high precision,high load-bearing performance and compact structure.With the continuous improvement of industrial technology,parallel mechanisms are beginning to develop in the direction of high speed and light weight.However,under the condition of high speed and light weight,the motion error of the parallel robot will be caused by the vibration of the system due to the elastic deformation of each branch chain and the existence of the clearance between the motion joint of the connecting members,thus reducing the stability of the system.Based on the above background,the elastodynamics of a 3 translational decoupling parallel mechanism is studied comprehensively in this paper.Firstly,in order to study the effect of flexibility of branched chains on the output kinematic characteristics of parallel mechanisms,the 3-CPaRR spatial decoupled parallel mechanisms is taken as the research object in this study.The kinematics relation of the mechanism is established through the spatial position relation of each branch chain and its mechanism characteristic,and the decoupling characteristic of the mechanism is proved.Based on the spatial rectangular beam element model,finite element theory and Lagrange equation,the elastic dynamic model of 3-CPaRR parallel mechanism under the condition of single-branch flexibility and three-branch flexibility is established respectively through the kinematic coordination relations and dynamic constraints between the branches.and the theoretical model is numerically simulated.The output motion law on the dynamic platform of the system under different conditions is discussed.In order to verify the validity of theoretical modeling,virtual prototype simulation was carried out on 3-CPaRR decoupling parallel mechanism based on UG,Ansys and Adams software.Secondly,based on the spatial position vector model and according to the spatial structure characteristics of the parallel mechanism,the radial and axial kinematic models of the rotating joints with clearances are established respectively,and the kinematic models with clearances at the rotating joints of the branched chains are further established.Based on the Lankarani-Nikravesh contact force model and Coulomb friction model,the normal and tangential mechanical models of the rotating pairs of each branch chain with joint clearance are established,and the force generated by the clearance at each passive joint is transformed to the driving joint.The elastic dynamic model of the 3-CPaRR decoupling parallel mechanism with joint clearance is established.The influence of clearance and joint clearance on the output kinematic characteristics of the parallel mechanism is discussed through an example.Finally,based on the elastodynamic equation of 3-CPaRR decoupling parallel mechanism,the dynamic analysis of the driving component of the system branch chain is studied.Based on the rectangular section model of beam element,the dynamic stress of the driving component of 3-CPaRR decoupling parallel mechanism is discussed by using the fourth strength theory.Based on the elastodynamic model of the system,the natural frequencies and their influencing factors of the parallel mechanism are analyzed through the characteristic equation of the system.The relationship between the physical and geometric parameters of the branched components of the system and the natural frequencies is discussed respectively.Based on the above research on the dynamic characteristics of the parallel mechanism,The parameters of the system's components are optimized by the PSO,which improves the stability of the system and reduces the output error of the mechanism. |
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