Reaction force separation method of surgical tool from unknown dynamics and disturbances by fuzzy logic and perturbation observer of SMCSPO algorithm

In minimally invasive surgery (MIS), surgical tools are sensor-less as it is strictly prohibited to attach any electronic sensor at the instrument tip for the safety constraints. Therefore, the reaction force or any measure of haptics is difficult to estimate. In previous studies, it has shown that, the perturbation observer of sliding mode control with sliding perturbation observer (SMCSPO) can estimate the reaction force acting on the instrument tip. The perturbation is defined as the combination of the uncertainties and nonlinear terms where the major uncertainties arise from the reaction force. However, for dexterity and precise surgery, the surgical system or robot may have more degree of freedoms. In that case, the calculated perturbation by SPO is highly effected by external dynamics, disturbance and nonlinearity. As the perturbation is the summation of various disturbances of the system, it is impossible to separate the external dynamics-effect from it. Moreover, the control input of SMCSPO is also dependent on the estimated perturbation. Therefore in case of gripping an organ, force may increase unnecessarily due to outer disturbances. Fluctuation of control input is also harmful for the sensitive organs. Reaction force does not change rapidly to one control cycle to another, if the instrument´s motion in human body is slow. Taking this as an assumption, this paper proposes a method to avoid a disturbance effect by adding Fuzzy logic in SMCSPO algorithm. The fuzzy rules control over the SPO such a way, so that, the calculated perturbation term becomes more closer to actual reaction force acting on instrument tip even if the external dynamics are present. To evaluate the validity of the proposed method, a three degree of robot carrying the surgical instrument has formed and simulated in RoboticsLab environment. And the simulation results have showed that the estimated perturbation by proposed method followed the actual reaction force.