Research On Dynamic Characteristics Of Parallel Machine Tool Processing Complex Curved Surface Of Marine Propeller

With the advantages of high-speed motion and reconfigurable designing, parallelkinematic mechanism has a broad application prospect in the field of manufacturing. PKMthat based on parallel mechanism owns such advantages while a series of technicalproblems including motion control and error control spots appeared at the same time.Taking6-UPS Parallel kinematic machine with cross cods as the research object, theproblems of forward kinematics analysis, kinematic characteristics analysis, dynamicmodel of revolute joint with clearance, rigid-flexible coupling dynamic analysis and virtualprototype simulation technology are researched deeply.First of all, the background of the study is introduced, the developing history andcurrent situation of kinematics and dynamics of PKM are discussed. The necessity andforward position that rigid-flexible coupling dynamic used in the research of PKM aredemonstrated.Secondly, Lodrigues parameters are used to describe the rotation matrix. In the studyof forward kinematics analysis of the6-UPS PKM with cross rod, position vectorparameters in the basic motion equations is eliminated through the analysis of the couplingrelationships among the position and orientation variables of the moving platform. Then the4th order equations which have three parameters are obtained. With the use of Newtoniterative method, the iterated function that solved the equations is constructed.Through the analysis of the motion Jacobia matrix, the singularity path of the parallelmechanism is calculated. The cond of Jacobia matrix is taken as the index to calculate thechange of dexterity of parallel mechanism under different posture. The characteristic valuesof Jacobia matrix are used to analyze the static stiffness of parallel mechanism. Comparingwith general Stewart mechanism, it can gain that the static stiffness coefficient of them aresimilar, but the symmetry and value of stiffness coefficient of PKM with cross rod are betterthan general Stewart mechanism.In addition, considering rules of change at spherical joint of PKM, clearance analysis isintroduced into the dynamic analysis of parallel mechanism. The relationships of relativekinematics and dynamic constraints in contact model are described by L-N contact modeland improved coulomb friction model. The dynamic characteristics of mechanism are studied quantitatively with cases of different clearance sizes, different accelerations loadedin the moving platform in the dynamics simulation software.Finally, the3-D entity model of PKM is established. Finite element analysis is carriedout on the main motion artifacts and the relevant modal neutral files are exported. In thedynamic analysis software, rigid multi-body dynamics model is set up, the MNFs areimported through flexible processing module, then the rigid-flexible coupling multi-bodydynamics model of PKM is established. The reliability of the model is verified by typicaltrajectory simulation and an comparison analysis of kinematics and dynamics performanceof PKM is also established.