Development of A Meso-Scale Multi-Axis Magnetic Tactile Sensor For Robotic Surgery

Abstract

Robotic surgical procedures have gained a lot more importance in the previous years. The major limitation of surgical robotic systems is that they lack sense of tactile force feedback during object grasping and tissue manipulation. To increase the awareness of surgical robotic systems a magnetic transduction mechanism based tactile force sensor is proposed. Tactile force sensors developed to date lacked the capability to detect multi-axial forces, flexibility, high dynamic and static force range and frequency response. This thesis aims to address the afore mentioned limitations using design optimization through FEM simulations, decoupling of force using mathematical model and by testing the sensor according to real time applications. The magnetic tactile sensor consists of four SMD Hall sensors with four magnets embedded in the soft elastomer. The movement of magnets due to the applied force causes the change in magnetic flux and thus causing a voltage change in the Hall sensors. FEM simulations are carried out for robust location estimation of the embedded magnets in the elastomer. The sensor is fabricated using two types of elastomers based on their stiffness values. The sensor having elastomer as Ecoflex 00-30 works well for a normal force of 20 N in this direction, 3.5 N in shear direction and 1.5 N in angular direction with sensitivities of 16 mV/N, 30 mV/N and 81 mV/N for normal and shear angular force directions respectively. Similarly, the sensor having elastomer as RTV528 silicone rubber is works well for a force range of 50 N in normal direction, 5.5 N in shear direction and 4 N in angular direction with sensitivities of 2.52 mV/N, 3.4 mV/N and 25 mV/N for normal, shear and angular directions respectively. To assess behaviour of sensor for the dynamic input force the proposed sensor is also tested for the frequency of 4 Hz. The proposed magnetic tactile sensor shows perfectly linear behaviour with a low hysteresis error value of 8.3% and for the repeatability test of the sensor an error of 6.4% is achieved.