An Investigation On Stiffness Of Parallel Mechanism For Maintenance Surface Grinding Civil Aircraft Skin Of Composite Material

The composite material replacing of metal material has been widely used in the new type of civil aviation aircraft.The aircraft skin,as the easily damaged structure,needs to be grinded firstly in the maintenance.Due to the complicated free form surface structure of aircraft skin,it is difficult to ensure the quality of grinding by manual grinding.Meanwhile,the man work has another disadvantage of long time maintenance.To improve the efficiency of grinding,automatic equipment with high stiffness,like asymmetrical parallel mechanism,should be developed into aircraft skin maintenance.In order to meet the requirements of surface grinding for aircraft composite skin repair,a static stiffness rapid modeling strategy for asymmetric parallel mechanisms is systematically studied with the support of the Joint Funds of the National Natural Science Foundation of China & Civil Aviation Administration of China.The problem of inverse position solution is explored,according to the structural characteristics of the asymmetric parallel mechanism.The velocity relationship between the moving platform and the branch chain is obtained.The spatial search method based on kinematics positive solution is used to analyze the composition of the working space of the parallel mechanism by integrating the mechanism scale influence factor and the parameter conditions of the wing.The mapping between the reference points of the branch chain and the moving platform is established,according to the virtual work principle.Based on the idea of substructure comprehensive,the stiffness matrix of the UPS branch chain considering the elasticity of the ball joint and the Hooke hinge is established.The parallelogram branch chain is derived by combining the unit integration method and the matrix displacement method.The stiffness matrix of the branches is constructed by the deformation superposition principle under the interface coordination condition to construct the semi-analytical static stiffness model of the end of the parallel mechanism.The rapid estimation of the static stiffness in the whole domain is realized.The stiffness distribution law in the workspace is obtained.The finite element model of the construction mechanism is analyzed to perform static analysis in the typical pose of the workspace.The anisotropic deformation law of the parallel mechanism is calculated.The difference between the stiffness analytical model and the finite element model is compared to verify the correctness of the static stiffness modeling scheme.The dynamic characteristics of the parallel mechanism are obtained by modal analysis.The resonant parts of parallel mechanisms are found easily.The vibration displacement characteristics of the mechanisms are calculated by the harmonic response analysis.The stiffness performance evaluation index is used by optimize the size of the structure.The project provides theoretical basis and technical support for the localization of maintenance equipment of composite components.