Triaxial 3-D-Channeled Soft Optical Sensor for Tactile Robots

Abstract

Soft optical transducers have the potential to fulfill the need for advanced tactile sensing in robotics. We present a fingertip-shaped soft sensor with optically transparent channels that relies on soft materials and sensor morphology to measure an applied triaxial force. The proposed 3D-channeled sensor has a volume of 2.5cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and experimental results reveal a fifteen-fold increase in voltage compared to its bulk analogous, showcasing a sensitivity of 0.34 N/mV and 0.09 N/mV to tangential and normal forces. A prototype with a diameter of 2mm (0.4x) indicates the feasibility of scaling down the sensor. Force magnitude is estimated with a linear model and then decomposed into its F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</sub> and F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> with an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.93 and 0.98 within a sensing range of 4.05N and 8.50 N, respectively. A coordinate transformation from a covariant to a cartesian reference frame is used to retrieve the direction of the tangential component of the force. The sensor was integrated into a compliant robotic hand as a proof-of-concept to demonstrate real-time operation in typical grasping tasks. The results of this work show new possibilities for scalable optical soft sensors to provide complete local information about the interaction forces in soft/rigid robots.