State identification based on sound analysis during surgical milling process

This paper presents a sound pressure signal acquiring and processing method to perform state identification during surgical milling process. According to the dynamic of surgical milling, it is proved that the magnitude of the sound pressure signal during cortical bone milling is larger than that during cancellous bone milling. The signal recorded by a microphone is decomposed into some frequency sub-bands through the wavelet packet transform (WPT), and the ratio of the WPT energy during bone milling to the WPT energy during free running is calculated to determine that the material being milled is either cortical bone or cancellous bone. The proposed method is experimentally verified through the milling operation in in vitro porcine spines, and the experimental results indicates that the energy ratio during cortical bone milling is larger than that during cancellous bone milling, so the states of the milling operation can be identified correctly.