Low-Cost Disposable Tactile Sensors for Palpation in Minimally Invasive Surgery

Robot-assisted minimally invasive surgery prevents surgeons from manually palpating organs to locate subsurface tumors and other structures. One solution is to use ultrasound; however, it is not always reliable. Tactile sensor arrays have been proposed as an alternative or complementary modality, but current designs have drawbacks including a large number of wires, lack of autoclavability or disposability and high cost. In this paper, four mass-producible, low-cost, sterilizable tactile sensor array designs with minimal wires are presented. Both piezoresistive and capacitive versions have been designed, each with a 2 mm $\times$  2 mm spatial resolution and a scan rate of 30 Hz. Two sizes with 48 or 90 sensing elements are presented for each version. The sensing elements can measure contact pressures with 1 kPa resolution and they have over 84% accuracy in the 25–150 kPa range. The low cost allows the sensors to be made disposable, avoiding the deterioration in performance resulting from repeated autoclaving. The sensors include the analog-to-digital conversion circuit onboard, requiring only two power lines and two digital signal lines to connect them. The small number of output wires allows the sensors to be incorporated into robotic surgical instruments with articulated wrists that do not have the space for a large number of wires. Both sensor versions are shown to be able to detect 6-mm-diameter tumors at a depth of 10 mm in a silicone phantom and in ex vivo tissue samples.