Equilibrium selection in automated surgery

Certain sub-tasks involved in robot-assisted surgery can be described in terms of steady-state forces or positions that must be maintained during the procedure by the end effector(s). The automatic control system must determine these levels. Methods for mathematically determining these equilibrium forces and positions are developed here. The computation is done in a way that enforces surgeon-provided safety and effectiveness limits, and accounts for the nonlinear properties of soft tissue, as well as actuator and sensor noise and model uncertainties. The problem is formulated as an optimization problem. The case of an exponential-like nonlinear tool-tissue interaction model, based upon prior experimental results, is considered for the example task of endoscopic retraction.