A Convex Tactile Sensor for Isotropic Tissue Elastic Modulus Estimation Based on the Plane Contact Model

Because of the finite development of tactile feedback in surgical catheter of minimally invasive surgery (MIS), a convex tactile sensor composed of a force sensor, an indenter and some sensitive elements is proposed. To measure the relative hardness and elastic modulus of isotropic tissue contacted with the indenter, the contact model is derived based on the Eshelby-Stroh formula, and is solved based on the boundary conditions of indenter and tissue. The global displacement constraint method, local stress inversion constraint method, and multiple linear superposition are used to overcome the problems of abrupt changes of contact stress at the junctions and non-zero contact stress distributions in non-contact areas. The proposed method has the potential of higher calculation accuracy than Meijers' solution when the termination condition is specified to be smaller. With known width and depth of indentation, it is easy for this sensor to determine the elastic modulus directly according to the measured load compared with the state-of-the-art tactile sensors. Two indenters are processed, and three kinds of silica gel with different elastic moduli are tested. The feasibility and effectiveness of the tactile sensors are verified by comparing the test results with the results of silica gel in the previous study.