GelStereo 2.0: An Improved GelStereo Sensor With Multimedium Refractive Stereo Calibration

Visuotactile sensors have significant advantages in high-resolution contact shape sensing, which is crucial for robots to locate and manipulate objects. However, high precision and robust 3-D geometry sensing is still a challenging problem. In this article, we propose an improved GelStereo sensor, named GelStereo 2.0, with a more stable and compact structure. A refractive stereo ray tracing modeling method is proposed to eliminate 3-D geometry reconstruction errors caused by multimedium light refraction. In addition, we introduce a novel calibration method named multiple contact depths to obtain refractive parameters, which only needs a few pressings using calibration boards. Extensive experimental results show that the measurement error of contact surface depth is less than 0.15 mm. Furthermore, two well-calibrated sensors mounted on the gripper are successfully applied to a fingertip bolt screwing task, which demonstrates the effectiveness of the GelStereo 2.0 sensor and the proposed tactile 3-D geometry sensing method.