2-DOF Controller Design for Precise Positioning a Spindle Levitated with Active Magnetic Bearings

This article describes the design of a high performance 2-DOF controller for an electromechanical system consisting of a rotary flexible spindle hovered by Active Magnetic Bearings (AMB). The purpose of such a controller is to achieve the better positioning possible of the spindle by means of a good stabilization mechanism and by counteracting the vibrations generated naturally by the rotation. The implementation of this controller is based on three main blocks, a stabilization block, a vibration minimization block and, if needed, a dynamics decoupler block between the previous ones. The stabilization controller is designed utilizing a MIMO decoupling technique. With the aim of proving its effectiveness, two different stabilization controllers (PID and H∞) are presented. On the other hand, an adaptive feedforward algorithm which is in charge of the vibration minimization is implemented. In order to not feedback the vibration and, therefore, to decouple the controller's dynamics, the implementation of a variable Notch filter is discussed. It is demonstrated that this optional block can enhance or impoverish the behavior of the system depending on several factors such as resonances or rotational speed measurement.Experimental results and simulations are provided to show the effectiveness of the complete design process.