Model based control of a linear stage using a contactless optical sensor system

In this paper, we present a model-based tracking control of a positioning stage using laser trackers as contactless position feedback sensor. The laser trackers follow the stage in the complete working range and the position of the stage is determined with the laser triangulation method. Based on this very precise position information a trajectory tracking controller with friction compensation was developed. The dynamical behavior of the stage without friction is modeled as a differential equation second order and the model parameters are identified by experiment. Based on this model a PD controller is designed using pole placement method. In the feedforward path of the trajectory tracking controller a Basic Maxwell-Slip friction model is utilized for friction cancellation. In order to identify the parameters of the friction model the Dynamic NonLinear Regression with direct application of eXcitation (DNLRX) identification algorithm is used. It is shown by experiment that the proposed control approach reduces the tracking error significantly.