Analysis of large range rotational flexure in precision 6-DOF tripod robot

This paper presents an analysis of large range rotational flexure (or compliant) joints which were used in precision 6-DOF (degrees-of-freedom) tripod robot. In traditional parallel robot, the friction in the passive joints is one of major hurdles to achieve the high precision motion and it is necessary that all of the revolute joints should be replaced by the compliant joints to get rid of backlash and clearance effects. Compliant joints have many advantages, such as negligible backlash, stick-slip friction and wear, smooth and continuous displacement, an almost linear displacement relationship between input and output, and an inherently infinite resolution. However, their limited motion range due to the elastic limits of materials restricts their area of application to the fine motion mechanism with small motion range. The leaf-spring mechanism based compliant joints such as cross-strip flexure, cartwheel flexure and axial-strip flexure can provide relatively large rotation range over than 10 degrees. In our tripod robot, the cartwheel flexure and axial-strip flexure were adopted and analytic models of these two complaints are derived and verified by comparing the model´s predictions with FEM (Finite Element Method) simulations. The model prediction accuracy relative to FEM simulations is found to be with errors of less than 14%.