Content area
Abstract
The kinetostatic analysis and optimization of parallel and hybrid architectures for machine tools are conducted in this thesis.
First, a topological representation of all possible architectures which can provide 5 degrees of freedom between the tool and the workpiece is developed. The most promising kinematic structures are automatically generated based on the Chebychev-Grübler-Kutzbach criterion and some other design criteria.
Then, a generic stiffness model for fully-parallel mechanisms with various types of actuator stiffnesses is established and verified by examples of planar parallel mechanisms in a CAD system. In particular, several new types of spatial parallel kinematic mechanisms with prismatic/revolute actuators whose degree of freedom is dependent on a constraining passive leg connecting the base and the platform are introduced. A general kinetostatic model is established with the consideration of the characteristics of joints and links flexibilities. The model is used to demonstrate that flexible links have significant effects on the stiffness and accuracy of parallel kinematic machines. Examples for 3-dof, 4-dof, 5-dof, 6-dof and the Tricept machine tool families are given in detail to illustrate the results. Stiffness mappings are shown and design guidelines for parallel kinematic machines are concluded.
Finally, the optimization of system parameters in achieving a better system stiffness is performed. This includes the development of a more explicit representation of an objective function in the optimization model. The genetic algorithm is employed to solve this optimization problem. As a result, a significant improvement of the system stiffness is achieved.
