Dynamic Optimal Design Of A Novel 5-DON Parallel Mechanism

The dynamic optimal design of a novel 5-degree-of-freedom(DOF)parallel mechanism is investigated,which is designed for 5-axis machining of large structural components in aerospace industry.The thesis explores the issues of topology synthesis,kinematic analysis,elastodynamic modeling and analysis,dynamic optimal design of the proposed parallel mechanism.The main contents are listed as follows:Firstly,the topology synthesis methodology of 2-DOF parallel mechanism with fixed rotational point is proposed based upon Lie Group.The available limbs are classified by the characteristics of displacement subgroup,and the assembly principles of the 2-DOF rotational parallel mechanism are proposed.Then numerous novel topology structures are invented by introducing circular guide,articulated travelling platform and parallelogram structure.Secondly,a novel 5-DOF parallel mechanism T5 is constructed on the basis of PaRot mechanism invented by topology synthesis.Utilizing the closed-loop vector method,the inverse position and forward position of T5 parallel mechanism are analyzed,and the mapping models of velocity and acceleration are carried out with differential operation.Also the workspace of T5 is obtained by means of the boundary search algorithm with considerations of joint angles,strokes of actuated joint and so on.Thirdly,the elastodynamic model of T5 mechanism is established by utilizing the kineto-elastodynamics theory.The elastodynamic equations of limbs and rotational head are formulated,and then the system equations are established based upon the coupling relationship between the node freedoms.To improve the model precise,the flexibilities of components and joints,lumped mass,gravity and the assembling characteristics between different components are taken into consideration.Fourthly,the dynamic characteristics of T5 mechanism are analyzed.The undamped inherent characteristic is solved,and the distributions of the natural frequencies in the workspace are revealed.Then motion errors caused by the elastic deformation and the maximum dynamic stress of T5 are analyzed.It points out that the gravity has a certain effect on the dynamic response,which should be considered in its dynamic optimization.Fifthly,the prototype of T5 mechanism and its control system are developed.Modal experiments with typical pose are carried out,and the results validate the elastodynamic analysis of T5 mechanism.Finally,the effects on dynamic characteristic of sectional and dimensional parameters are analyzed with the aid of Taguchi Method.To minimize the total mass,the sectional parameters and key dimensional parameters are optimized by utilizing the particle swarm algorithm with consideration of rules of stress,maximal elastic displacement and frequency.The aforementioned research lays a theoretical basis for the development of the novel 5-DOF parallel mechanism with excellent dynamic performance.