Design and Simulation of Micro Tactile Sensor for Stiffness Detection of Soft Tissue with Irregular Surface

Tactile sensors become an essential part of many applications in our life. Integrating tactile sensors with surgical tools used in MIS is significant to compensate for the shortage of touch feeling of soft tissues and organs comparing with traditional surgeries. This paper presents a detailed design of a micro tactile sensor for measuring the stiffness of soft tissue with an irregular surface. The sensor consists of five cantilever springs with different stiffness. A spring in the middle has a relatively low stiffness surrounded by 4 springs have relatively equal high stiffness to compensate for the soft tissue contact error in the longitudinal and lateral directions. Sensor parameters are selected to ensure high sensitivity and linearity with taking into consideration the cross-talk effect among the sensor springs tips. A detailed design of the sensor structure in the microscale is conducted based on some constraints related to MEMS fabrication. A finite element analysis (FEA) of the sensor structure is conducted to evaluate sensor structure performance using CoventorWare software. Then, an FEA for the piezo-resistors, as a signal transduction method, is conducted which maps the sensor output to an electrical signal. The results prove that the sensor can differentiate among different soft-tissue stiffness within the selected range independent of the applied distance between the sensor and the tissue with an error below 3% even with inclination angle between the sensor and the tissue ±3°. Furthermore, a linear performance has been achieved between the soft-tissue stiffness and the sensor output.