A robust control design is developed to "ize a system's response to unknown disturbances. The method consists of on-line identification of the system's state space equations coupled with an &-optimal controller design. The H , controller is designed such that the maximum of the system's closed-loop transfer function is less than y (y > 0). This robust controller is used to eliminate vibrations in cutting operations of a boring bar with an active dynamic absorber. A boring bar is a metal cutting tool with a large overhang (lenm-todiameter ratio). Due to this large overhang, a typical boring bar is characterized by a low dynamic s m e s s and is therefore susceptible to excessive vibrations during the cutting process. These vibrations o h lead to cutting instability, known as machine tool chatter. In this paper, the control of vibrations of a boring bar with an active dynamic absorber is studied. The robustness of the %-optimal controller is demonstrated by varying the system's dynamic characteristics (i.e., changing the length-todiameter ratio of the boxing bar) without adjusting the calculated control parameters. The results obtained for the H , case are compared to similar results for a linear quadratic regulator control design.
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