Detection of tool fracture is important to avoid tool breakage and ensure cutting accuracy. Though additional sensors are generally used for monitoring a tool condition, installing them causes high cost and increase of failure rate. In this study, a novel inprocess method to detect a tool fracture is proposed on the basis of a disturbance observer theory. It uses only servo information in a ballscrew driven stage and never requires external sensors. Furthermore, a rotational digital filter is

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... vented and applied to drilling tests to improve the detection accuracy. A tool fracture is successfully detected by the proposed method.