Triaxial 3-D-Channeled Soft Optical Sensor for Tactile Robots
Matteo Lo Preti, Federico Bernabei, Anderson B. Nardin, Lucia Beccai
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.