Small Force Estimation and Velocity Limitation Control for a Tele-Operated 6-DoF Eye Surgery Robot

When performing eye surgery, surgeons traditionally rely on visual feedback through needle insertion to sense tissue. Particularly, in vitreoretinal surgery, the contact force exerted by a surgical robot to avoid damaging healthy tissue is very small and can be below that which a surgeon is able to sense. In this paper, we introduce the small frequency sliding perturbation observer (SFSPO), which is a technique for estimating the very small contact force exerted when the tip of a surgical tool of a 6-Degree of Freedom (DoF) eye surgery robot touches tissue. This contact force is estimated without using any force/torque sensor, and the small feedback force is amplified, meaning the surgeon can feel it as a large reaction force. Furthermore, during lengthy microscopic surgery procedures, surgeons can experience fatigue and tiredness due to the intense focus required. This may result in damage to healthy tissue due to sudden changes in manipulation and the exertion of excessive force. To avoid this problem, force and velocity limitation control is applied. Simulations are conducted, and the experimental results indicate that very small forces below the perception of the surgeon can be sensed using the SFSPO. We have estimated minimum force which is 0.001 N by using SFSPO which is underneath the perception of surgeon. The results also verify successful implementation of the force and velocity limitation control.