Abstract
While most optical tactile sensors rely on measuring surface displacement, insights from continuum mechanics suggest that measuring shear strain provides key information for tactile sensing. In this work, we introduce an optical tactile sensing principle based on shear strain detection. A silicone rubber layer, dyed with color inks, is used to quantify the shear magnitude of the sensing layer. This principle was validated using the NUSense camera-based tactile sensor. The wide-angle camera captures the elongation of the soft pad under mechanical load, a phenomenon attributed to the Poisson effect. We tested the robustness of the sensor by subjecting the outermost layer to multiple load (8 N) cycles using a 5 mm in radius ball head indenter. The physical and optical properties of the inked pad proved essential and remained stable over time, exhibiting only low variance.