Analysis and design of a spherical micromechanism with flexure hinges

The article describes the design of a robotic wrist able to perform spherical motions: its mechanical architecture is based on parallel kinematics and is suitable to be realized at the mini- or micro-scale by means of flexible joints. In view of the preliminary design, a rigid body model has been studied first and the direct and inverse kinematic analyses have been performed, allowing for the determination of theoretical workspace and passive joints displacements. The rigid body dynamic behavior and the operative ranges of the machine have been assessed through the development of an inverse dynamics model. Then, the micro parts have been designed with the help of FEM and multibody software and the study has been focused on the flexures: since the analyses showed that the centre of the spherical motion moves around several millimeters in the workspace, the original kinematic concept has been modified with the introduction of a ball joint constraining the mobile platform to frame so as to prevent unwanted translations.