Research And Analysis Of Static Stiffness Of New Four-DOF Parallel Mechanism

The innovation and development of science and technology are increasing dramatically,and the parallel mechanism is playing an increasingly important role in the industrial field.The parallel mechanism has the advantages of stable and compact structure,high load-bearing capacity,high precision,low inertia and good dynamic response.However,the parallel mechanism is subjected to the action from external forces during the working process,which will lead to the deformation of the endeffector,thus affecting its dynamic characteristics and its positioning accuracy.In this thesis,the static stiffness performance of the new four-degree-of-freedom parallel mechanism 2UPS+(RPR+RP)U proposed by the project team is studied and analyzed.The static stiffness refers to the ability of the whole machine to maintain the positioning accuracy after the static load is applied to the working end of the mechanism.Therefore,it is particularly important to study the static stiffness of this parallel mechanism.The static stiffness of the proposed new four-degree-of-freedom parallel mechanism is studied in the following main aspects.Firstly,a simple description of the mechanism configuration is made and the mechanism motion space is analyzed.A kinematic mapping model is established for the mechanism,and a static driving/constraining moment model is established to define the evaluation indexes for the parameter factors affecting the performance of the mechanism,so as to lay the foundation for the subsequent optimization of the mechanism.Secondly,the static stiffness model of each part is solved by using the structural matrix splitting method for this mechanism with the help of the principle of virtual work.By using the principle of mechanical superposition,the flexibility model of each part is superimposed to find the static stiffness model of the whole machine.The static stiffness performance evaluation index is defined for the requested model,and the particle swarm optimization algorithm is used to optimize the static platform structure parameter a,the dynamic platform structure parameter c and the rod length parameter q1 to obtain the optimal solution.With the help of the static stiffness analytical model,the variation law of the end stiffness of the mechanism in the task space with the bit shape is analyzed.Thirdly,the finite element analysis software Ansys Workbench module is used to establish the finite element analytical model of the parallel mechanism.Two typical positions of the parallel mechanism are selected to compare the calculation results of the analytical model with the simulation results to verify the correctness of the2UPS+(RPR+RP)U static stiffness model of the parallel mechanism.Finally,using the optimised data,the prototype assembly of the parallel mechanism was completed.