Optum: A Three-in-One Multimodal Tactile Sensor Based on Optical Fiber Knots for On-Orbit Service

The complex environment of outer space brings great challenges to on-orbit servicing tasks. Here, we report Optum: a frustum-shaped multimodal tactile sensor for a robot to recognize the surface features of a satellite. Based on optical fiber knots (OFNs), the Optum consists of three independent working modules that can measure pressure, hardness, and texture, respectively. Their sensing mechanisms are all based on the force-induced microbending loss of OFNs. A minimum resolution of 0.12 N is achieved for pressure sensing from 0-10 N, and a resolution ranging from 0.03-0.45 is recorded for hardness sensing from 1-30 in Shore A scale. For texture sensing, the sensor can measure wavelengths down to 300 μm. Installed on the end of a robotic arm, the Optum can touch the satellite by adjusting the posture of the arm to achieve a specific tactile sensing function. Free from electromagnetic interference, the Optum would be a valuable tool for on-orbit servicing tasks. As a pilot study, the Optum is implemented in a dual-arm space robot system for a solar panel unfolding task.