  The limited workspace in pediatric endoscopic surgery makes surgical suturing
one of the most difficult tasks. During suturing, surgeons have to prevent
collisions between tools and also collisions with the surrounding tissues.
Surgical robots have been shown to be effective in adult laparoscopy, but
assistance for suturing in constrained workspaces has not been yet fully
explored. In this letter, we propose guidance virtual fixtures to enhance the
performance and the safety of suturing while generating the required task
constraints using constrained optimization and Cartesian force feedback. We
propose two guidance methods: looping virtual fixtures and a trajectory
guidance cylinder, that are based on dynamic geometric elements. In simulations
and experiments with a physical robot, we show that the proposed methods
achieve a more precise and safer looping in robot-assisted pediatric endoscopy.
