UVtac: Switchable UV Marker-Based Tactile Sensing Finger for Effective Force Estimation and Object Localization

Abstract

Vision-based tactile sensors provide diverse information of external tactile stimuli on the skin of sensors using both marker and reflective membrane images. However, when markers and reflective membranes are used concurrently, conventional opaque markers inevitably disturb the camera's view of the reflective membrane. Thus, simultaneously increasing the quality of tactile information extracted from each visual feature has remained a challenge. In this study, we present a tactile sensing finger, UVtac, that utilizes switchable ultraviolet (UV) markers to decouple the marker and reflective membrane images to offer three-axis force estimation and object localization, whose performances are unaffected by each other. Our UVtac showed improved force estimation performance by using larger-sized UV markers through quantitative evaluation. The UVtac with 1.2 mm diameter markers showed a root mean square error of 0.264 N in estimating normal forces up to 10 N and 0.219 N in estimating the shear forces up to 5 N, when indented with an 8 x 8 mm(2) square tooltip. Based on the object localization experiment, the UVtac was verified to have a 31 % lower root mean square error than the case using opaque black markers. Finally, we demonstrated object alignment and contact force-tracking tasks using the UVtac to emphasize its multifunctionality.