Model-Free Control of a Class of High-Precision Scanning Motion Systems with Piezoceramic Actuators

Abstract

To enhance the precision of coarse long-stroke motion axes, complementary short-stroke fine positioning stages are usually introduced. Being mechanically attached, the motion of the combined positioning stages needs to be controlled and synchronized. Therefore, typically suitable model-based controllers of fine stages are designed according to the sophisticated models and identification techniques used. Due to their appealing features, Piezocermamic-based fine positioning stages were successfully utilized in many applications, which recently sparked their use in high-acceleration motion found in wafer scanners, for example, where high-precision motion is required despite the resulting high inertial forces involved. Unfortunately, hard nonlinear behavior is associated with piezoelectric actuators, which adds to the complexity of modeling, control, and synchronization processes. To overcome such a burden, in this study, the design procedure of a model-free control and synchronization technique of piezocermamic-based fine positioning stages is introduced and verified experimentally using a representative precision motion system comprising a planner stage and a uni-axial fine stage under step-and-scan trajectories commonly used in wafer scanners. Despite its simplicity, the herein proposed design procedure can be seamlessly extended to other robotics and automation applications.