Abstract

Vision-based haptic sensors have become an increasingly common tool for providing both coarse and delicate tactile feedback in robotic fingers. We present a soft, affordable, vision-based tactile sensor named Subblescope, which provides the magnitude and direction of the applied force. The sensor consists of a single layer of Ecoflex incorporating an air bubble inside it, which is injected into the sample while curating to stabilize the bubble. An LED array lights the elastomer, while a camera records the shape change of the bubble during normal and shear force interaction. The sensor is calibrated using a micro-tensile UTM. In the case of normal loading, the sensor has a sensitivity of 248.6 µN over a range of 0.02 N to 2.9 N, with a repeatability of 1.09 % at 0.6 N, and hysteresis of 26.23 µJ between 0.1 N to 0.6 N. In the case of shear loading, the range is 0.02 N to 0.15 N with a sensitivity of 31.31 µN, better than the existing vision-based haptic sensors. The multidirectional loading onto the sensor provides 3D shapes of the bubble simulated in COMSOL. The present concept and design are more compliant for sensing bi-directional force interactions while maneuvering interactive surfaces. Multiple bubbles can be populated in the elastomer for further study towards spatio-temporal sensing.