WH for AR

1-introduction/related-work/2-wearable-haptics.tex

@@ -63,7 +63,7 @@ The rendering of a haptic device is indeed determined by the nature of the actua
 Several actuators are often combined in a haptic device to obtain richer haptic feedback.
 
 \subsubsection{Moving Platforms}
-\label{normal_actuators}
+\label{moving_platforms}
 
 The moving platforms translate perpendicularly on the skin to create sensations of contact, pressure and edges~\cite{pacchierotti2017wearable}.
 Placed under the fingertips, they can come into contact with the skin with different forces, speeds and orientations.
@@ -188,11 +188,6 @@ Virtual data-driven textures were perceived as similar to real textures, except
 The perceived roughness of real surfaces can be then modified when touched by a tool with a vibrotactile actuator attached~\cite{culbertson2014modeling,ujitoko2019modulating} or directly with the finger wearing the vibrotactile actuator~\cite{asano2015vibrotactile}, creating a haptic texture augmentation.
 The objective is not just to render a virtual texture, but to alter the perception of a real, tangible surface, usually with wearable haptic devices, in what is known as haptic augmented reality (HAR)~\cite{bhatia2024augmenting,jeon2009haptic}.
 
-One additional challenge of augmenting the finger touch is to keep the fingertip free to touch the real environment, thus delocalizing the actuator elsewhere on the hand~\cite{ando2007fingernailmounted,friesen2024perceived,normand2024visuohaptic,teng2021touch}.
-Of course, the fingertip skin is not deformed by the virtual texture and only vibrations are felt, but it has been shown that the vibrations produced on the fingertip skin running over a real surface are texture specific and similar between individuals~\cite{manfredi2014natural}.
-A common method vibrotactile rendering of texture is to use a sinusoidal signal whose frequency is modulated by the finger position or velocity~\cite{asano2015vibrotactile,friesen2024perceived,strohmeier2017generating,ujitoko2019modulating}.
-It remains unclear whether such vibrotactile texture augmentation is perceived the same when integrated into visual AR or VR environments or touched with a virtual hand instead of the real hand.
-
 The perceived roughness of real surfaces can be then modified when touched by a tool with a vibrotactile actuator attached~\cite{culbertson2014modeling,ujitoko2019modulating} or directly with the finger wearing the vibrotactile actuator~\cite{asano2015vibrotactile}, creating a haptic texture augmentation.
 The objective is not just to render a virtual texture, but to alter the perception of a real, tangible surface, usually with wearable haptic devices, in what is known as haptic augmented reality (HAR)~\cite{bhatia2024augmenting,jeon2009haptic}.
 One additional challenge of augmenting the finger touch is to keep the fingertip free to touch the real environment, thus delocalizing the actuator elsewhere on the hand~\cite{ando2007fingernailmounted,friesen2024perceived,teng2021touch}.

1-introduction/related-work/4-visuo-haptic-ar.tex

@@ -61,12 +61,48 @@ In a similar setup, but with an optical see-through (OST) AR headset, \textcite{
 While a large literature has investigated these differences in visual perception, as well as for VR, \eg , less is known about visuo-haptic perception in AR and VR.
 
 
-\subsubsection{Wearable Haptics for AR}
+\subsection{Wearable Haptics for AR}
 \label{vhar_haptics}
 
-\subsection{Fingertip-Free Haptic Devices}
+\subsubsection{Fingertip-Free Haptic Devices}
 \label{vhar_devices}
 
+A few wearable haptic devices have been specifically designed to render haptic sensations and improve interaction with virtual and augmented objects in \AR while keeping the fingertip free.
+They all augment the hand perception with virtual haptic sensations, but they differ in the type of rendered object (real or virtual), the rendered haptic property (contact, hardness, texture, etc.), and the position of the actuator on the hand.
+
+\paragraph{Fingernail Actuators}
+
+\textcite{ando2007fingernailmounted} were the first to propose moving the haptic actuator away from the fingertip to allow it to interact freely with the \RE while in \AR.
+As shown in \figref{ando2007fingernailmounted}, they placed a voice-coil on the index nail that generated \qty{20}{\ms} burst impulses at \qty{130}{\Hz}.
+It rendered the sensation of crossing edges of a virtual patterned texture (see \secref{texture_rendering}) on a real sheet of paper, and participants were able to match the virtual patterns to their real counterparts.
+
+This approach was later extended by \textcite{teng2021touch} with Touch\&Fold, a haptic device mounted on the nail but able to unfold its end-effector on demand to make contact with the fingertip when touching virtual objects (see \figref{teng2021touch}).
+This moving platform also contains a \LRA (see \secref{moving_platforms}) and provides contact pressure (\qty{0.34}{\N} force) and texture (\qtyrange{150}{190}{\Hz} frenquencies) sensations.
+%The whole system is very compact (\qtyproduct{24 x 24 x 41}{\mm}), lightweight (\qty{9.5}{\g}), and fully portable by including a battery and Bluetooth wireless communication. \qty{20}{\ms} for the Bluetooth
+When touching virtual objects in \OST-\AR with the index finger, this device was found to be more realistic overall (5/7) than vibrations with a \LRA at \qty{170}{\Hz} on the nail (3/7).
+Still, there is a high (\qty{92}{\ms}) latency for the folding mechanism and this design is not suitable for augmenting real tangible objects.
+
+% teng2021touch: (5.27+3.03+5.23+5.5+5.47)/5 = 4.9
+% ando2007fingernailmounted: (2.4+2.63+3.63+2.57+3.2)/5 = 2.9
+
+To always keep the fingertip, \textcite{maeda2022fingeret} with Fingeret proposed to adapt the belt actuators (see \secref{belt_actuators}) to design a \enquote{finger-side actuator} instead (see \figref{maeda2022fingeret}).
+Mounted on the nail, the device actuates two rollers, one on each side of the fingertip, to deform the skin: When the rollers both rotate inwards (towards the pad) they pull the skin, simulating a contact sensation, and when they both rotate outwards (towards the nail) they push the skin, simulating a release sensation.
+By doing quick rotations, the rollers can also simulate a texture sensation.
+%The device is also very compact (\qty{60 x 25 x 36}{\mm}), lightweight (\qty{18}{\g}), and portable with a battery and Bluetooth wireless communication with \qty{83}{\ms} latency.
+In a user study not in \AR, but involving touching different images on a tablet, Fingeret was found to be more realistic (4/7) than a \LRA at \qty{100}{\Hz} on the nail (3/7) for rendering buttons and a patterned texture (see \secref{texture_rendering}), but not different from vibrations for rendering high-frequency textures (3.5/7 for both).
+However, as for \textcite{teng2021touch}, finger speed was not taken into account for rendering vibrations, which may have been detrimental to texture perception.
+
+\begin{subfigs}{ar_wearable}{Nail-mounted wearable haptic devices designed for \AR. }[
+        \item A voice-coil mounted on the nail to render a virtual haptic texture on a real sheet of paper. Adapted from \textcite{ando2007fingernailmounted}.
+        \item Touch\&Fold is provide contact pressure and vibrations on demand to the fingertip~\cite{teng2021touch}.
+        \item Fingeret is a finger-side wearable haptic device mounted that pulls and pushs the fingertip skin~\cite{maeda2022fingeret}.
+    ]
+    \subfigsheight{34mm}
+    \subfig{ando2007fingernailmounted}
+    \subfig{teng2021touch}
+    \subfig{maeda2022fingeret}
+\end{subfigs}
+
 [@Bau2010Teslatouch] created a touch-based surface rendering textures using electrovibration and friction feedback between the surface and the user's finger.
 They extended this prototype to in [@Bau2012REVEL] to alter the texture of touched real objects using reverse electrovibration. They call this kind of haptic devices that can alter the touch perception of any object without any setup as *intrinsic haptic displays*.
 
@@ -81,8 +117,6 @@ If it is indeed necessary to delocalize the haptic feedback, each of these posit
 
 \cite{tao2021altering}
 
-\cite{maeda2022fingeret}
-
 \subsection{Improving the Interactions with Virtual Objects}
 \label{vhar_interaction}