Development of a Three-Axis Inductive Force Sensor For Measuring Tool-Tissue Forces in Robotic Surgery

Abstract

Robotic surgeries are becoming popular because of their benefits over traditional procedures. In robot-assisted surgery, surgeons cannot judge the amount of force the tools exert on a patient's tissues and sensitive internal body parts. This lack of force feedback has been reported to cause damage to healthy tissue and post-surgery complexities. This problem has two parts: one requires building a force sensor to precisely estimate the amount of force applied to the patient during surgery. The other part consists of making an actuator to transfer or define the amount of force to surgeons. This work has proposed a three-axis tactile force sensor that can be integrated with modern robotic surgical tools to estimate the force exerted by the tools, thus solving the first and more critical part of the problem. The working principle opted for this sensor design is a change in the inductance values of the planar coils printed on a printed circuit board (PCB) when a magnetorheological elastomer (MRE) approaches it. The proposed sensor has a simple design, a soft contact surface, low hysteresis and minimum error, making it suitable for tactile force sensing. The proposed sensor is fabricated and tested with two different materials; silicon Ecoflex-30 and silicone RTV-528. Both variants provide different resolution, sensitivity, and force measurement ranges due to the different mechanical properties of the fabrication material. Finite element method (FEM) based analyses are carried out to design and optimize the sensor. A complete experimental characterization is performed to test the sensor's capabilities. The proposed tactile force sensor can measure forces applied in normal, shear, and planar angular directions. The sensor with Ecoflex30 can measure forces up to 25 N and 2.5 N in normal and shear directions, whereas the sensor built with RTV-528 can measure forces up to 30 N and 6 N in similar directions. The proposed sensor can be employed in surgical tools as it has a small footprint and can measure higher forces, making it suitable for various surgical procedures.