We investigate the relevance of surface haptic rendering techniques for tactile devices. We focus on the two major existing techniques and show that they have complementary benefits. The first one, called textsc{S}urface textsc{H}aptic textsc{O}bject (textsc{SHO}), which is based on finger position, is shown to be more suitable to render sparse textures; while the second one, called textsc{S}urface textsc{H}aptic textsc{T}exture (textsc{SHT}), which is based on finger velocity, is shown to be more suitable for dense textures and fast finger movements. We hence propose a new rendering technique, called textsc{L}ocalized textsc{H}aptic textsc{T}exture (textsc{LHT}), which is based on the concept of textit{taxel} considered as an elementary tactile information that is rendered on the screen. By using a grid of taxels to encode a texture, textsc{LHT} is shown to provide a consistent tactile rendering across different velocities for high density textures, and is found to reduce user textit{error rate} by up to 77.68% compared to textsc{SHO}.

We study users' perception of simultaneous tactile textures in ultrasonic devices. We investigate how relevant is providing the user with different complementary and simultaneous textures with respect to the different fingers that can be used to touch the surface. We show through a controlled experiment that users are able to distinguish the number of different textures independently of using fingers from one or two hands. However, our findings indicate that users are not able to differentiate between two different textures, that is to correctly identify each of them, when using fingers from the same hand. Based on our findings, we are then able to outline three relevant guidelines to assist multi-finger tactile feedback ergonomic and devices design.

Previously proposed models of the ultrasonic lubrication of a finger mediated by flat surfaces are not consistent with the experimental results for vibrational amplitudes greater than a few microns. This paper presents experimental data acquired through a dedicated tribometer and proposes an experimental model of ultrasonic lubrication at high vibrational amplitudes.

Ultrasonic vibration of a plate can be used to modulate the friction of a finger pad sliding on a surface. This modulation can modify the user perception of the touched object and induce the perception of textured materials. In the current paper, an elastic model of finger print ridges is developed. A friction reduction phenomenon based on non-Coulombic friction is evaluated based on this model. Then, a comparison with experimental data is carried out to assess the validity of the proposed model and analysis.