NailTact: Single-camera based Tactile Fingertip with Nail

Abstract

Vision-based tactile sensing, an economical and widely utilized methodology, has the potential to offer crucial contact geometry information for localizing objectives even in cases of visual occlusion. However, this kind of fingertip sensor is limited. When a person picks up a relatively small object placed on a flat surface with two fingers, they may not only use the pads of their fingers depending on the size of the object but also use their fingernails for small or thin objects. Fingers with nail structures have been shown to be effective in picking up objects like this in robot hands as well. Moreover, in actual work, accidental contact between sensors and surrounding objects such as tables often occurs. Sensors with fingernails can avoid this situation in advance by having the fingernails touch the object before the fingertip touches the object. In this work, we present the NailTact, which can detect the force applied to both the fingertip part and the nail part from the same camera image using a single camera. Using the prototype robot finger, we will verify the sensor response characteristics to the load on the nail and the sensor response when grasping an object with the nail and the situation when the finger makes contact with a table. We also present a simple model that illustrates the relationship between the force applied to the nail and the movement of the marker. In the card-grasping experiment, we not only successfully grasped a very thin object but also measured the grasping force.