Admittance Switching for Stability and Transparency in Human-Robot Collaborative Microsurgery

The Galen Surgical Robot is an admittance controlled collaborative robot that can enhance the performance of surgeons in microsurgery by sharing the load of instruments, preventing hand tremor and improving precision. In mastoidectomy, contacting the temporal bone of the skull and drilling with the robot can be challenging due to potential instability of the coupled surgeon-robot-patient system. In this letter, we investigate how tuning mass and damping gain properties of an admittance controller affect the stability and transparency of this interaction. We generate and make use of stability-transparency maps to aid in the optimal design of the control system. To address the stability/transparency trade-off, we propose gain switching between free motion and contact using an external force sensor or a force sensing tool to detect contact. We simulate critical phases of mastoidectomy surgery on temporal bone phantoms, including first contact with bone and drilling. In agreement with theoretical results, experiments with the proposed controller show significant improvements in transparency and contact stability.