Design And Study Of A 4-DoF Micro-Motion Platform Based On Compliant Mechanism

The micropoistioning or microoperation devices based on compliant mechanisms are widely used in many emerging fields of high-tech, and play the role of unreplacement especially in MEMS, microrobot and Biomedical Engineering. The thesis aims at designing a micropositioning platform with 4-DoF of DxDyRxRy, and studying the compliance structure based on screw theory.Firstly, the thesis present the methods of constitution of the micropositioning stucture. Using constraint screw principle the conclusion that it’s not possible to construct a centrosymmetric parallel rigid mechanism of the 4-2Rxy2Txy DoF is proved. Using Awtar compliant mechanism as the base strcture of 2-DxDyDoF, the 4-DxDyRxRy DoF compliant mechanism is build by carrying a compliant structure of 2-RxRy DoF which is independently synthesized. Then the entire 3D model is established using SOLIDWORKS.Secondly, the method of analying DoF of compliant mechanism using screw theory is elaborated. By decomposing the whole stucture into series-parallel compliant elements, the matrixes represent the motion and constraint spaces of the compliant translational joint and hook hinge is derived by conversion of coordinates, and then the whole compliant mechanism. The 4-DxDyRxRy is then verified by the motion space matrix of the whole mechanism.Thirdly, by using the force wrench and motion twist concepts, linear flexibility matrix of the compliant translational joint is derived in small deformation condition, and the relative error of axial flexibility between theoretical result and FEM simulation result is 1.3%. For compliant hook hinge the flexibility about its two working rotational axises is simulated. The input flexibility expression of the micro-rotation compliant strcture is derived, it’s the relationship between the two actuation forces or displacement and the two micro-rotation angles of the platform. Then the simplified expression is derived and the relative error between theoretical result and FEM simulation result is 7.3%.Finally, the workspace analysis is presented. Due to the motion decoupling property, the workspace of the 4-DoF compliant mechanism is superposed by that of the Awtar 2-DxDyDoF compliant mechanism and that of the 2-RxRy DoF compliant micro-rotation compliant structure. The platform is deemed to be at its workspace boundary once the material wherever reach its limit of elasticity under the safety factor of 1.3. Through FEM simulation, maximum pitching angle of the platform in even-distributed sixteen directions is obtained, then two ruled surfaces is formed by surface interpolation using MATLAB, and the Inter space between the two ruled surfaces is the micro-rotational workspace. Through FEM simulation, the size of the approximate square workspace area of the Awtar compliant mechanism is also obtained.