Controlling the penetration of flexible bone tissue using the stapedotomy microdrill

In this paper a surgical robotic system is described for microdrilling a stapedotomy. The stapedotomy procedure is a delicate operation that is challenging to achieve successfully owing to the fact that, under manual control, the surgeon is working at the thresholds of human perception and dexterity. The automated drilling system described in this paper is sensory guided along a single tool axis. Information on the state of the drilling process is derived from feed force and torque sensory data with respect to time and displacement. The information on the state of the process is used to select the strategy to move the drill bit along its trajectory in order to achieve a minimum level of protrusion of the drill bit beyond the far surface of the stapes footplate. The drilling system is able automatically to determine the unknowns of tissue thickness, hardness and flexibility. Detection of the onset of breakthrough, key to establishing the thickness, is by identification of features in the multiple sensory data that signify this condition. The system demonstrates acceptable performance in the laboratory with positional errors with respect to flexible target positions of approximately 20 μm.