Errors obtained by processing the clinical data reach 7.5 mm at the tip in average. Errors obtained with the laboratory apparatus drop from 2.4 mm in average to 0.8 mm when using real-time model update.

No abstract

Surgery may involve precise instrument tip positioning in a minimally invasive way. During these operations, the instrument is inserted in the body through an orifice. The movements of the instrument are constrained by interaction forces arising at the orifice level. The physical constraints may drastically vary depending on the patient's anatomy. This introduces uncertainties that challenge the positioning task for a robot. Indeed, it raises an antagonism: On one side, the required precision appeals for a rigid behavior. On the other side, forces applied at the entry point should be limited, which requires softness. In this paper we choose to minimize forces at the orifice by using a passive ball joint wrist to manipulate the instrument. From a control perspective, this leads to consider the task as a 3 DOF wrist center positioning problem, whose softness can be achieved through conventional low impedance control. However, positioning the wrist center, even with a high static precision, does not allow to achieve a high precision of the instrument tip positioning when the orifice behavior is not known. To cope with this problem, we implement a controller that servos the tip position by commanding the wrist position. In order to deal with uncertainties, we exploit an adaptive control scheme that identifies in real-time the unknown mapping between the wrist velocity and the tip velocity. Both simulations and in vitro experimental results show the efficiency of the control law.

In the context of keyhole surgery, and more particularly of uterine biopsy, the fine automatic movements of a surgical instrument held by a robot with 3 active DOF’s require an exact knowledge of the point of rotation of the instrument. However, this center of rotation is not fixed and moves during an examination. This paper deals with a new method of detecting and updating the interaction matrix linking the movements of the robot with the surgical instrument. This is based on the method of updating the Jacobian matrix which is named the “Broyden method”. It is able to take into account body tissue deformations in real time in order to improve the pointing task for automatic movements of a surgical instrument in an unknown environment.