An adaptronic approach to active vibration control of machine tools with parallel kinematics

In recent years, more and more lightweight components are used in machine tools in order to provide advantages in highly dynamic applications because of their reduced mass. One major drawback of these lightweight systems is their sensitivity to structural vibrations which are induced by high jerks during fast positioning and the machining process itself. Moreover, in case of parallel kinematic structures, the dynamic response depends nonlinearly on the actual pose of the mechanism in the workspace. In this paper, a concept for active vibration control for a machine tool with planar parallel kinematics is presented. For this purpose, an adaptronic rod has been developed and integrated into the existing machine tool. The unit consists of a high-power lead-zirconate-titanate piezo stack actuator, which is able to induce forces in longitudinal direction of the rod, and various sensors so that different control concepts from the field of active vibration control can be implemented and tested. Based on a flexible multibody system model of the machine tool, a hierarchical controller consisting of an integrated force feedback as low authority Control combined with a frequency-shaped linear quadratic regulator has been designed. The experimental results presented here demonstrate the ability of the chosen approach to clearly suppress the first dominating resonance without loss of performance in the low frequency range, which is often a serious problem of active damping concepts.