Self-tuning semi-active tuned-mass damper for machine tool chatter suppression

Tuned mass dampers are simple and efficient devices for suppression of machine tool chatter, which is one of the principal effects limiting productivity in many machining processes. However, their effectiveness depends on a proper tuning of the damper dynamics to the dynamics of the machine. This involves the dynamic characterisation of the machining process, in order to identify the critical resonance frequency, and the possibility of matching the resonance frequency of the damper to frequency. The difficulty of meeting these two requirements has been limiting the use of tuned mass dampers in industrial applications. An improved damper tuning device is presented here trying to overcome these limitations, and its feasibility is demonstrated with simulation and experimental results. On the one hand, the damper incorporates accelerometers and a control strategy that can detect in real time whether chatter is occurring and at which frequency in real time during the machining process. On the other hand, the damper has a variable stiffness spring, actuated by a motor, which allows automatic control of the stiffness, and thus the resonance frequency of the machine. Damping is generated in the damper by eddy currents, altogether providing a quite linear and predictable behaviour.