An intelligent method for identifying otological drill slippage.

An otological drill is a fundamental apparatus used for bone-milling in ear surgery. A common problem in bone-milling is that the drill bit slips on the bone surface. To improve the operational safety of such a surgery, this article presents a new apparatus combined with an intelligent method for identifying drill slippage. A two-axis force sensor is installed on a modified drill, and it detects the force of the bone's reaction to the drill bit. By integrating the unit reaction forces of the bone and the drill bit on the contact area, the functions of the force signals are deduced, which can reflect changes in the milling parameters. Based upon these functions, the slippage force, which is an important factor in drill slippage, is then extracted. An adaptive filter is specially designed to suppress interference in the slippage force. Drill slippage can be identified by calculating the variations in the filtering results. Five surgeons were invited to carry out an experiment in which they used this method on calvarian bones. Their average recognition rate of drill slippage was 86%, and only 1% of normal millings were identified as milling faults.