A Tactile Sensor with Contact Angle Compensation for Robotic Palpation of Tissue Hardness

At present, robot-assisted minimally invasive surgery (RAMIS) has increasingly become the mainstream of operation. In the case of intraoperative tumor palpation with tactile hardness sensors, most existing solutions need to place the sensor normal to the tissue surface. But this requirement cannot always be met due to the limitation of the robot's degree of freedoms and the limited operating space, which causes error in the detected hardness. This paper proposes a piezoelectric tactile sensor that can detect the hardness A even under non-normal contact conditions based on two resonant frequencies (f(RN) and f(RT)) measured in two detection modes - normal and tangential. Since the contact angle theta has opposite effects on the two resonant frequencies, by solving two equations f(N) (A, theta) = f(RN) and f(T) (A, theta) = f(RT), the effect of the contact angle can be eliminated to obtain the compensated hardness. This can improve the accuracy and reliability of tumor palpation in RAMIS.