An active tool holder and robust LPV control design for practical vibration suppression in internal turning

Abstract

This study presents a new system and control design for an active tool holder that can effectively suppress vibration and chatter in internal turning. The controller accounts for the influence of tool deflection during a preceding cut affecting the dynamics of the current cut, a key source of instability in machining processes. To deal with variability in dynamic behavior due to changing of the tool mounting conditions and overhang length, a robust H-infinity controller is synthesized based on a linear-parameter-varying (LPV) description of the machining dynamics. The parametric dependence allows the robustness levels and modal properties of the control system to be easily tuned in a workshop setting to achieve the best possible vibration reduction performance. The controller design accounts for the time-delayed feedback from cutting forces, and also the need to avoid spillover instability of unmodeled high frequency modes. The method is applied using a tool holder that integrates piezoelectric bending actuators and strain sensors in such a way that the overall size and shape of the tool is unaltered, thereby providing the functionality and ease of operation necessary for widespread adoption in manufacturing industries. Experiments conducted on a lathe machine demonstrate that root-mean-square vibration levels can be reduced by over 95% (and peak-to-peak values reduced by approximately 90%) in unstable cutting regimes, allowing high material removal rates with good surface finish. For stable cutting, the system can also reduce vibration by 10% to 50%, depending on cutting conditions.