Enhancement of sensor-less tool fracture detection method applying rotational digital filter

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 in-process 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 invented and applied to drilling tests to improve the detection accuracy. A tool fracture is successfully detected by the proposed method.