Feasibility study- novel optical soft tactile array sensing for minimally invasive surgery

The absence of touch of sense is a widely known drawback of robotic minimally invasive surgery (MIS). This paper proposes a design of optic soft tactile arrays which is promising to be adapted for MIS. The proposed design consists of multiple soft material channels. Each channel is designed using the Bernoulli pipe structure to amplify the sensor´s sensitivity through input and output diameter difference. A multi-core optic fiber cable and a camera are used to capture the change of light intensity caused by the contact forces applied onto the individual soft material channels. The proposed sensor has the following advantages: 1) making use of 3D printing and soft material casting, it is suitable for designing sensors with high density of tactile elements; 2) it also allows the sensor to be designed in an arbitrary shape to fit various MIS applications; 3) compared to other light-intensity based tactile sensor, it is easy to fabricate and miniaturize; it avoids the complexity of attaching reflectors to individual sensing elements; 4) it is immune to electromagnetic interference. In this paper, a prototype which has 3×3 tactile elements in an area of 9.5 × 11 mm² has been developed and test for feasibility study. Also, a noise-filtering algorithm is developed to reduce the imaging noise. Validation experiments were carried out and results show that the average measurable force range for a single tactile element is 0 to 1.622N with an average accuracy of 97%. The sensor has low crosstalk-to-signal ratio, 1.8% on average, and has no signal drift over time.