Control issues of a fast positioner intended for deflection of a high power laser beam

Abstract

This paper discusses some crucial aspects of control of a fast positioner intended for positioning of a mirror reflecting high power laser beam. Positioner is driven by a two linear movement piezo actuators acting on a common flexible flat spring bending it in two perpendicular directions. The reflector is fixed to this spring. Clearly, the actuator is a dynamic oscillating system. This makes control of positioner demanding. In order to overcome the effects of static nonlinearity, hysteresis and their time evolution, there were proposed two independent closed loop positioning systems each governing each own axis. The simulation investigations allowed for determining the suboptimal structure and parameters of controllers. Two different control loops were investigated and discussed. The simulation experiments shown, that the most efficient controller is able to “mask” the actuator hysteresis while introducing appropriate dynamic damping and stiffness to the controlled system. The concept of the positioner controller was described and some chosen results of laboratory experiments were presented. Finally, the assessment of the control quality is given together with some general conclusions closing the paper.

Keywords

• piezoelectric actuator
• fast positioning unit
• hysteresis
• control error
• positioner
• tracking error
• laser beam reflector