Multi-objective Optimization And Stiffness Performance Analysis For3-DOF Parallel Manipulators

Due to the fact that the good characteristics that parallel manipulators possess,such as high stiffness, high precision, high loading capacity, fast response, goodvelocity and acceleration, etc, they have been widely used in macro and micro areas,such as driving simulators, parallel kinematic machine tools, telescopic mechanisms,assembly, bio-inspired mine rescue robot, medical devices, nano scale motionmanipulators, sensors, etc.. Recently, focusing on the design synthesis andperformance analysis of two to five degrees of freedom of parallel manipulators hasbecome hot research topic and an important research area. This thesis focuses on themulti-objective optimization and stiffness performance analysis of several threedegrees of freedom of parallel manipulators.The main work of this thesis is generalized as the following:1. Establish the kinematic model and solve the Jacobian matrix for three kinds ofthree degree-of-freedom parallel manipulators;2. Establish the objective function for stiffness, workspace and dexterityoptimization for three kinds of parallel manipulators. The global stiffness andworkspace volume are used as objective functions for the stiffness and workspaceoptimization for the3UPU parallel manipulator, respectively. The sum of the meanvalue and standard deviation of leading diagonal elements of the compliance matrix ofthe3SPS-S manipulator, the global condition index and the condition number ofJacobian matrix are used as objective functions for the stiffness, workspace anddexterity optimization for the3SPS-S parallel manipulator, respectively. The sum ofleading diagonal elements of the stiffness matrix, the global condition index and thecondition number of Jacobian matrix are used as objective functions for the stiffness,workspace and dexterity optimization for the4UPS-PU parallel manipulator,respectively.3. Using stiffness, workspace and dexterity as objective functions as well asapplying different multi-objective optimization methods to establish themulti-objective optimization design model for3UPU,3SPS-S and4UPS-PUmanipulators. Establish the general procedure for the multi-objective optimization problem for the parallel manipulators.4. The4UPS-PU parallel manipulator is used as an example to analyze thestiffness performance based on CCT, and comparing it with the traditional stiffnessmodel. Through comparison, it is shown that the stiffness in each direction under CCTmodel is larger than that of the traditional stiffness model. Furthermore, the3UPS-PUparallel manipulator is used as an example to illustrate the correspondence and thedifferences between several stiffness models. The traditional stiffness model isestablished through the calculation of Jacobian matrix. The kinetostatic compliancematrix model of the3UPS-PU manipulator is established when considering the centralpassive leg as a rigid one by using kinetostatic and the principle of virtual work. Whenparallel manipulators work in or near the singular regions, the leading diagonalelements of the stiffness matrix cannot reflect the stiffness of manipulator, then thedexterous stiffness is used to evaluate the transferring ability of the mechanicalconfiguration. Through comparison among these stiffness models, it is shown that thekinetostatic stiffness model is the closest one to the traditional stiffness model.