Active constraints for robotic surgery in deforming tissue

• Main Author: Bowyer, Stuart
• Other Authors: Rodriguez y Baena, Ferdinando
• Published: Imperial College London 2014
• Subjects: 617.9
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.724088

Active constraints are collaborative human-robot control algorithms which have a well-established history of use within robot assisted surgery research. This control strategy anisotropically regulates the motion of a human user in such a way that it effectively combines the competencies of surgeons and robots, allowing for improved clinical outcomes and surgeon experience. The significant majority of research previously presented for active constraints focuses on their application to static procedures, where the surgical environment is assumed to be rigid throughout. In this thesis, several research contributions are presented which assist with applying active constraints in surgical procedures within deforming soft tissue. The primary contribution is the formulation of a novel haptic control algorithm, based on friction, which can effectively guide a surgeon in both positioning and orienting a surgical instrument, while guaranteeing that the haptic interaction is energetically dissipative. The proven dissipative formulation of these 'dynamic frictional constraints' ensures that the surgeon always has overall control of a procedure and makes the system resilient to limitations and errors in the robot's comprehension of the surgical environment. To apply active constraints within deforming tissue, it is necessary to compute the geometric relationship between the surgical instruments and the constrained anatomy. A novel bounding volume is proposed which, when used in a hierarchy, exploits the limits of soft tissue deformations to increase the resolution of constraint geometries that can be used at stable control rates. The experimental validation of these research contributions in a clinically realistic nerve dissection simulation and in non-clinical dynamic path-following tasks, shows significant benefits to the user in several metrics characterising surgical accuracy and precision. These results demonstrate that the proposed enhancements of active constraints could lead to increased surgeon performance, fewer complications and improved clinical outcomes in soft tissue surgical procedures.