Trajectory following of a Micro Motion Stage Based on Closed- Loop Fem Simulation

Micro motion stages are one of the essential components in field of micro robotics and ultra fine positioning systems. This research presents the optimum design of a 3-DOF micro motion stage and its position control using FEM simulation. This stage to be studied uses a 3 RRR flexure hinge base compliant mechanism driven by three piezoelectric stack actuators to provide micro scale planar motion. First of all parametric modeling of the stage will be fulfilled in ANSYS environment utilizing a commercial piezostack, different types of flexure hinges and different types of flexure hinges. Hence the Jacobian matrix will be achieved for each case. The optimum selection of the hinge form will be achieved upon results of the previous phase. Finally embedded closed-loop FEM approach in ANSYS programming will be used to follow a specified trajectory. Hereby, flexibilities of mechanism and piezoelectric actuator behavior will be modeled with more reliability than any other analytical approach. INTRODUCTION Nowadays, the usage of piezoelectric actuators in the field of precision positioning has been increased significantly as piezoelectric motors, active dampers and etc. The important characteristics of such actuators are unlimited expansion resolution, no need of lubrication, smoothness of movement and zero backlash. Because of the low displacement of piezoelectric actuators, flexural mechanisms are used to magnify the piezostacks displacement amplitude. [1-3] There are some conditions that 2D positioning of components within micrometer or nanometer accuracy, i.e. micro or nano motion stages, is required. For instance, the positioning of samples in scanning tunneling microscopes, the positioning of wafers in micro-lithography [4] and the manipulation of cells in micro-biology [5]. In precision positioning stages configuration of piezostacks and linkages is two-folded: parallel and serial. Ronchi et al. [6] introduced one type of parallel micro stages. Different type of micro positioning instruments including serial micro stages can be found in [7]. Furthermore, micro stages work either with controller (active) or without controller (passive). In some passive stages two linear stages are used separately to produce planar motion. While in the others, combination of two or more microactuators in a monolithic shape leads to planar motion [7]. Eliminating crosstalk is a significant challenge in such a micro stage design. Tien-Fu et al. [8] have proposed a linear control approach for the aforementioned device. The micro-motion stage presented in this paper has two degree-of-freedom. It is a monolithic compliant mechanism with flexure hinges. This stage is designed for the positioning of samples in a scanning-tunneling-microscope (STM). The