Optimal Vibration Control Of A Milling Electrospindle

We present the case study of a five-axis high speed milling electro-spindle on AMBs. A Finite Element Model is developed in order to obtain a state-space model of the flexible shaft. This model is supplemented by a second state-space model, representing the rigid behaviour induced by the closed loop composed of the active magnetic bearings, actuators, sensors and the controller. An active unbalance control algorithm has been developed, based on the considerations of [1]. This method gives an absolute control on the unbalance vibrations. We obtain excellent results, as we expected. But we also aim at milling steel, at a rotational speed close to the rigid modes, and yet this method reduces the stiffness of the bearings at the rotational speed. For stability reasons, we then needed another method that could compensate perfectly the unbalance without adding any closed-loop to the systems. For this open-loop method, a statistical study, considering the variance of the estimator and various extra signals give good insight on the result. We finally present some practical results based on milling experiments.