Augmented Reality (AR) enriches our physical world with digital content and media, such as 3D models and videos, overlaying in real time the camera view of our smartphone, tablet, laptop, or glasses. Despite the recent massive interest for this technology, it is still not possible to receive rich haptic feedback when interacting with augmented environments. This lack is mainly due to the poor diffusion of suitable haptic interfaces, which should be easy to wear, lightweight, compact, and inexpensive. In this paper, we briefly review the state of the art on wearable haptics and its application in AR. Then, we present three AR use cases, considering tasks of manipulation, guidance, and gaming, using both external cameras with standard screens as well as fully-wearable solutions, using the Microsoft HoloLens. We evaluate these tasks enrolling a total of 34 subjects, analyzing performance and user experience when using a 3-DoF wearable device for the fingertip, a 2-DoF wearable device for the proximal finger phalanx, a vibrotactile ring, and a popular sensory substitution technique (interaction force displayed as a colored bar). Results show that providing haptic feedback through the wearable devices significantly improves the performance , intuitiveness, and comfort of the considered AR tasks.
L. Meli, C. Pacchierotti, G. Salvietti, F. Chinello, M. Maisto, A. De Luca, D. Prattichizzo. Combining wearable finger haptics and Augmented Reality: User evaluation using an external camera and the Microsoft HoloLens. IEEE Robotics and Automation Letters, 2018.