Force And Numerical Value Simulation Analysis Of The Passive Over-constraint Parallel Mechanism

Compared to the serial mechanism, the advantages of large stiffness, no accumulatedmotion error, large weight ratio, high degree of modularity, fast response velocity, low cost,high technology added value of parallel mechanism contributed to its application to heavyprecision or fretting occasions though its relatively complex mechanism, relatively smallworking space, and relatively inflexible action. As special parallel mechanism,over-constraint parallel mechanism not only has all advantages of parallel mechanism andbe applied to many important occasions. The force analysis was statically indeterminateproblems and complicated research so that there was few force analysis system research ofover-constrained parallel mechanism. Especially when considering the elastic deformation,the research area was nearly blank. Therefore, the paper would analyze the force ofover-constraint parallel mechanism considering the elastic deformation. And theresearches mainly contained some areas as follows:The kinematic screw system, force screw system, over-constraint force screw system,equivalent force screw system, the relation between equivalent force screw system andsix-dimension external force system were analyzed with screw theory. The stiffness matrixod different branches were obtained based on mechanics and superposition of smalldeformation in condition of elastic deformation. The mechanism stiffness matrix ofover-constraint parallel mechanism was obtained based on deformation compatibilityequation. The constraint force of branches extremity and driving force were calculatedbased on the stiffness matrix of mechanism and branch. Then, the forces of every jointcould be gained according to the branch extremity forces. Finally, the common anduniversal theory system of force analysis of over-constraint parallel mechanism wasestablished. And the force analysis theory basis of over-constraint parallel mechanismwere set up.Simutaneously, some typical over-constraint parallel mechanism were analyzed byapplying the theory, such as3-PRRR dimensional orthogonal moving parallel mechanism,two-DOF spherical parallel mechanism and2UPR+SR rotatic parallel mechanism. A force numeric simulation method was established. The three dimension model ofsome typical over-constraint parallel mechanisms were established, and saved copies asthe fomat Adams and Ansys software could be imported. Besides, the links that needed beflexible were analyzed modal with Ansys finite element software, and modal neutral filewas exported. Finally, the three-dimension rigid-flexible model was established andsimulated by replacing rigid bodies to flexible bodies with Adams.The error and error causes were analyzed between the calculation datas andsimulation datas by comparing and analyzing the results of some typical over-constraintparallel mechanism. Finally, the effective keypoints of over-constraint parallel mechanismforce distribution were obtained by analyzing the similarities and differences of theproposed force analysis theories and applying the theories to calculating the threeover-constraint parallel mechanisms. Finally, two conclusions were gained to analyzepassive over-constraint parallel mechanism.