L$^{3}$ F-TOUCH: A Wireless GelSight With Decoupled Tactile and Three-Axis Force Sensing
Wanlin Li, Meng Wang, J. Li, Yao Su, Devesh K. Jha, Xinyuan Qian, Kaspar Althoefer, Hangxin Liu
Abstract
GelSight sensors that estimate contact geometry and force by reconstructing the deformation of their soft elastomer from images would yield poor force measurements when the elastomer deforms uniformly or reaches deformation saturation. Here we present an L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> F-TOUCH sensor that considerably enhances the three-axis force sensing capability of typical GelSight sensors. Specifically, the L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> F-TOUCH sensor comprises: (i) an elastomer structure resembling the classic GelSight sensor design for fine-grained contact geometry sensing; and (ii) a mechanically simple suspension structure to enable three-dimensional elastic displacement of the elastomer structure upon contact. Such displacement is tracked by detecting the displacement of an ARTag and is transformed to three-axis contact force via calibration. We further revamp the sensor's optical system by fixing the ARTag on the base and reflecting it to the same camera viewing the elastomer through a mirror. As a result, the tactile and force sensing modes can operate independently, but the entire L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> F-TOUCH remains <underline xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</u> ight-weight and <underline xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</u> ow-cost while facilitating a wire <underline xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</u> ess deployment. Evaluations and experiment results demonstrate that the proposed L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> F-TOUCH sensor compromises GelSight's limitation in force sensing and is more practical compared with equipping commercial three-axis force sensors. Thus, the L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> F-TOUCH could further empower existing Vision-based Tactile Sensors (VBTSs) in replication and deployment.