Methodology Of Multi-objective Optimization For A Five Degree-of-freedom Parallel Manipulator

Aiming at parallel/hybrid robot-based machining center for highly precise and efficient machining of large components in the fields such as aviation,aerospace,and automobile,a 5 degree-of-freedom parallel manipulator(named as T5 PM)is taken as an example to systematically investigate the methodology of kinematic,stiffness analysis and optimization.The following contributions have been made.(1)The approach for multi-objective optimization of parallel manipulator is proposed.Parametric disturbance is firstly analyzed.Pareto-based multi-objective optimization with response surface model and principles of objective matching is then carried out.The general procedure is summarized as formulation of response surface model,establishment of probabilistic constriaint,optimization of multiple objectives and determination of matching principle.(2)Kinematic analysis and optimization of T5 PM is implemented.Inverse position,task workspace and twist/wrench mapping model are investigated.Virtual power transmissibility is defined by the transmissions of twist and wrench.Finally kinematic optimization of T5 PM is accomplished,in which particle swarm algorithm is adopted.(3)Semi-analytical stiffness modeling of T5 PM considering gravitational effects and stiffness experiment are carried out.Taking gravity into account,wrench and deformation mapping models are firstly formulated.Compliance matrices of interlinked revolute joints,substructures are achieved.And the stiffness model of T5 PM is obtained by compliance matrices of substructures.Finally,stiffness experiments are implemented to verify the stiffness model.(4)Stiffness performance indices and parameter sensitivity indices are defined.Firstly,stiffness indices are established based on instantaneous energy and stiffness singularity is discussed.Then,sensitivity indices are proposed via differentiation of the robust state function.Finally,sensitivity analysis of T5 PM is implemented,and main parameters for stiffness optimization are selected.(5)Stiffness performance optimization considering parametric disturbance are carried out.Multi-objective optimization resorting to Pareto-based approach is implemented.Minimum distance selection is employed to search for the matching point.And the optimal parameters can be determined.Above researches plays an important role in the analysis and design of parallel manipulators,furthermore the engineering applications of robot-based mechanism.