Spatial motion constraints in medical robot using virtual fixtures generated by anatomy

In Ear, Nose and Throat (ENT) surgery, the operating volume is very limited. This is especially true in sinus surgery, when the instrument passes through the nasal and sinus cavity to reach the pathological area. The nasal and sinus bones impose geometric constraints on the work volume. During the surgery, the surgeon needs to control the motion of the instrument tip to accomplish some delicate procedure; meanwhile he/she needs to avoid hitting anatomic constraints. In this paper, we present a method to assist the path following task in a constrained area. The system reads the user´s force input and combines it with the planned tip-trajectory to create the tip motion constraints; meanwhile it generates the tool-shaft boundary constraints based on a 3-D geometric model. We map instrument tip motion and boundary information to joint displacements via robot kinematics, and then use a constrained quadratic optimization algorithm to compute the optimal set of corresponding joint displacements. In the preliminary study, we show that robot guidance using cooperative control and virtual fixtures derived from complex geometry can assist users in skilled manipulation tasks, while maintaining desirable properties such as collision avoidance and safety.