A 3-DOF sensor to estimate the force applied to the tip of a surgical instrument

Estimation of the force applied to the tip of a surgical instrument is necessary to render high-fidelity haptic feedback. Accuracy of the force estimation suffers from friction caused by the rubber packing inside the trocar. This paper proposes a 3-DOF force sensor installed to the trocar support. It is possible to estimate the 2-DOF radial force applied to the instrument tip and the 1-DOF axial friction occurring in the trocar by using the 3-DOF force sensor. Accuracy of the estimation, however, deteriorates due to the reaction moment that occurs at the trocar support. An I-shaped force sensor is designed to reduce coupling effect which is caused by the reaction moment. Design parameters of the sensor are optimized to minimize the coupling effect by using ANSYS software. The sensor is manufactured and calibrated using the least-square calibration method. L2 relative error of the estimation of the radial force applied to the instrument tip is less than 6.30 %. The axial reaction force corresponding to the friction is also estimated with relative error less than 8.63 %.