A Solution to Control Path Differences in The Feedback Filtered-x LMS Control of Boring Bar Vibration

摘要

The internal turning operation is a common metal working operation that is usually associated with vibration problems. Boring bar vibration affect the result of the machining, in particular the surface finish. Furthermore, the tool life is correlated with the amount of vibration and the acoustic noise introduced. The noise level is sometimes almost unbearable. Generally, the motion of a boring bar is greatest in the cutting speed direction, and related to one of the bars two fundamental bending modes. A self tuning solution that has a high potential to further reduce the vibration problems in internal turning is the adaptive active control of boring bar vibration based on the feedback filtered-x LMS algorithm and boring bars with embedded actuators. The filtered-x LMS requires an estimate of the control path. To obtain a practical estimation of the control path, to avoid internal turning with severe vibration levels, usually requires that the control path is estimated off-line, i.e. the boring bar is not in contact with the workpiece. However, the control path usually differs between continuous cutting operations and when the boring bar is not in contact with the workpiece, and a phase difference of approximately 90 degrees generally occurs at the resonance frequency to be controlled. This phase difference constitutes a severe problem concerning the feedback filtered-x LMS control. By using a short FIR-filter control path estimate sufficient phase accuracy is obtained to enable robust adaptive control of bar vibration, which attenuates the vibration level with up to approximately 40 dB.