In-situ Mechanical Calibration for Vision-based Tactile Sensors.

This paper proposes a novel approach to conduct routine calibration for the changing mechanical parameters over time of a vision-based tactile sensor, without disassembling its overall structure, i.e., in-situ mechanical calibration. Calibration for mechanical parameters, Young's modulus and Poisson's ratio, of a tactile sensor's sensing elastomer, is crucial for its force perception capabilities. However, there are few methods that can retrieve values of these parameters both accurately and conveniently. To address this problem, we propose an in-situ approach to calibrate mechanical parameters other than the verbose traditional evaluation process. This method incorporates the deformation sensing capability of the sensor, the accurate force sensing capability of a force/torque sensor, and most importantly, the deformation-force relationship for an indentation with embedded mechanical parameters of the elastomers. We also present the indentation test setup and the complete pipeline to extract Young's modulus and Poisson's ratio from experimental results. We validate the method by comparing the indentation depths simulated through finite element analysis (FEA) using the calibrated parameters with the indentation depths measured in real experiments. Furthermore, superior contact force distribution can be achieved with the accurate mechanical parameters. The proposed method provides the theoretical basis for accurate, lifelong routine calibration, whether weekly or even daily, which can enhance the applications of tactile sensors in real manipulation scenarios.