Leveraging the Fulcrum Point in Robotic Minimally Invasive Surgery

In robotic Minimally Invasive Surgery (MIS) the incision point acts as a fulcrum around which the surgical instrument pivots. The fulcrum point has been the topic of much research. Mechanisms have been invented to enforce instrument motion about such a fulcrum. Other systems establish a fulcrum through coordinated control of their joints. For laparoscopists, the fulcrum point is an obstacle to overcome through a lot of training. For robots, it is a hurdle requiring careful consideration. In this paper, new estimation methods are proposed to exploit the properties of a fulcrum and turn its presence into an advantage. The paper starts by presenting a novel fulcrum estimation method that is robust against measurement noise and quantization effects. A general fulcrum refinement method is proposed next. This method can be used as add-on to ameliorate alternative estimation approaches. It is shown how the fulcrum can also be leveraged to get accurate, high-bandwidth estimates of the instrument tip. The quality with which the instrument tip is estimated has a large impact on the performance of advanced guidance schemes, such as haptic virtual walls. User tests are included, demonstrating substantially improved guidance thanks to the algorithms presented in this work.status: publishe