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.
Highlights
Since many years the piezo elements have been applied successfully for design of actuating and sensing devices
In order to simplify the design of a control system, there were proposed and applied two independent closed loop positioning systems each governing each own axis. This allows for linearization of the angular movement as well as or for isolation of mechanical mirror coupling effect caused by mutual interactions of piezo-actuators acting on the same flat spring
Example: The mirror positioning system presented in introductory section having mass m = 89,9 g, amplitude X = 110 μm, capacitance of piezo actuator C = 4.1 μF, swinging harmonically with frequency f = 1000 Hz and driven by an alternating voltage source with Up = 85 V amplitude, exhibits the demand on maximal mechanical power (12) pm = 47,1 W while the electrical reactive power (5) that can be delivered to actuator equals ppx= 93,1 VAR
Summary
Since many years the piezo elements have been applied successfully for design of actuating and sensing devices. The intrinsically save piezo elements are applied nowadays widely even in areas where atmospheres are prone to explosions and replacing traditional solenoid based valves [1, 4]. In order to simplify the design of a control system, there were proposed and applied two independent closed loop positioning systems each governing each own axis. This allows for linearization of the angular movement as well as or for isolation of mechanical mirror coupling effect caused by mutual interactions of piezo-actuators acting on the same flat spring. The paper contributes to the applied control of the fast piezo-actuating systems It delivers some useful and experimentally proven parametrized structure of the control system.
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