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1-background/related-work/2-wearable-haptics.tex
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\section{Augmenting Object Perception with Wearable Haptics}
\label{wearable_haptics}
One of the roles of haptic systems is to render virtual interactions and sensations that are \emph{similar and comparable} to those experienced by the haptic sense with real objects, particularly in a visual \VE \cite{maclean2008it,culbertson2018haptics}.
Due to the high complexity of the haptic sense and the variety of sensations it can feel, haptic actuators and renderings are designed to only address a subset of these sensations.
While it is challenging to create a realistic haptic experience, it is more important to provide the right sensory stimulus \enquote{at the right moment and at the right place} \cite{hayward2007it}.
Haptic systems aim to render virtual interactions and sensations that are \emph{similar and comparable} to those experienced by the haptic sense with real objects \cite{maclean2008it,culbertson2018haptics}.
Due to the high complexity of the haptic sense and the variety of sensations it can feel, haptic actuators and renderings are designed to address only a subset of these sensations.
While it is challenging to create a realistic haptic experience, \ie that reproduce the real object interaction with high fidelity \cite{unger2011roughness,culbertson2015should}, it is more important to provide the right sensory stimulus \enquote{at the right moment and at the right place} \cite{hayward2007it}.
Moreover, a haptic augmentation system should \enquote{modulating the feel of a real object by virtual [haptic] feedback} \cite{jeon2009haptic}, \ie a touch interaction with a real object whose perception is modified by the addition of virtual haptic feedback.
A haptic augmentation system \enquote{modulates the feel of a real object by virtual [haptic] feedback} \cite{jeon2009haptic}, \ie a touch interaction with a real object whose perception is modified by the addition of virtual haptic feedback.
The haptic system should be hand-held or worn, \eg on the hand, and \enquote{not permanently attached to or integrated in the object} \cite{bhatia2024augmenting}.
\subsection{Level of Wearability}
@@ -39,7 +39,7 @@ Such \emph{body-grounded} devices are often heavy and bulky and cannot be consid
\textcite{pacchierotti2017wearable} defined that : \enquote{A wearable haptic interface should also be small, easy to carry, comfortable, and it should not impair the motion of the wearer}.
An approach is then to move the grounding point close to the end-effector (\figref{pacchierotti2017wearable_3}): the interface is limited to cutaneous haptic feedback, but its design is more compact, lightweight, comfortable and portable, \eg in \figref{grounded_to_wearable}.
Moreover, as detailed in \secref{object_properties}, cutaneous sensations are necessary and often sufficient for the perception of the haptic properties of an object explored with the hand, as also argued by \textcite{pacchierotti2017wearable}.
Moreover, as detailed in \secref{object_properties}, cutaneous sensations are necessary and often sufficient for the perception of the haptic properties of an object explored with the hand \cite{pacchierotti2017wearable}.
\begin{subfigs}{grounded_to_wearable}{Haptic devices for the hand with different wearability levels. }[][
\item Teleoperation of a virtual cube grasped with the thumb and index fingers each attached to a grounded haptic device \cite{pacchierotti2015cutaneous}.
@@ -58,8 +58,9 @@ Moreover, as detailed in \secref{object_properties}, cutaneous sensations are ne
\label{wearable_haptic_devices}
We present an overview of wearable haptic devices for the hand, following the categories of \textcite{pacchierotti2017wearable}.
The rendering of a haptic device is indeed determined by the nature of the actuators employed, which form the interface between the haptic system and the user's skin, and therefore the types of mechanical stimuli they can supply.
Several actuators are often combined in a haptic device to obtain richer haptic feedback.
It should be noted that the rendering capabilities of a haptic device is determined by the type of actuators employed.
The actuator forms the interface between the haptic device and the user, and provides the haptic rendering as mechanical stimuli to the user's skin.
Multiple actuators are often combined in a haptic device to provide richer feedback.
\subsubsection{Moving Platforms}
\label{moving_platforms}
@@ -169,9 +170,14 @@ However, they require high voltages to operate, limiting their use in wearable d
\label{tactile_rendering}
Rendering a haptic property consists in modeling and reproducing virtual sensations comparable to those perceived when interacting with real objects \cite{klatzky2013haptic}.
By adding such rendering as feedback timely synchronized with the touch actions of the hand on a real object \cite{bhatia2024augmenting}, the perception of the object's haptic property can be modified.
As we have just seen, the haptic sense being rich and complex (\secref{haptic_hand}), a wide variety of wearable haptic actuators have been developed (\secref{wearable_haptic_devices}) that each provide a subset of the haptic sensations felt by the hand.
We review in this section the rendering methods with wearable haptics to modify perceived roughness and hardness of real objects.
\subsubsection{Haptic Augmentations}
By adding haptic rendering as feedback timely synchronized with the touch actions of the hand on a real object \cite{bhatia2024augmenting}, the perception of the object's haptic property can be modified.
That is both the real and virtual haptic sensations are integrated into a single property perception, \ie the perceived haptic property is modulated by the added virtual feedback.
The integration of the real and virtual sensations into a single property perception is discussed in more details in \secref{sensations_perception}.
%, both the real and virtual haptic sensations are integrated into a single property perception, as presented in \secref{sensations_perception}, \ie the perceived haptic property is modulated by the added virtual feedback.
In particular, the visual rendering of a touched object can also influence the perception of its haptic properties, \eg by modifying its visual texture in \AR or \VR, as discussed in the \secref{visuo_haptic}.
\textcite{bhatia2024augmenting} categorize the haptic augmentations into three types: direct touch, touch-through, and tool-mediated.
@@ -187,7 +193,7 @@ Of course, wearable haptics can also be used in a direct touch context to modify
% \cite{klatzky2003feeling} : rendering roughness, friction, deformation, temperatures
% \cite{girard2016haptip} : renderings with a tangential motion actuator
\subsubsection{Roughness}
\subsubsection{Roughness Augmentation}
\label{texture_rendering}
To modify the perception of the haptic roughness (or texture, see \secref{roughness}) of a real object, vibrations are typically applied to the skin by the haptic device as the user moves over the surface.
@@ -249,7 +255,7 @@ When comparing real textures felt through a stylus with their virtual models ren
\subfig{culbertson2012refined}
\end{subfigs}
\subsubsection{Hardness}
\subsubsection{Hardness Augmentation}
\label{hardness_rendering}
The perceived hardness (\secref{hardness}) of a real surface can be modified by rendering forces or vibrations.
@@ -274,8 +280,8 @@ This stiffness augmentation technique was then extended to allow tapping and pre
\item Diagram of a user tapping the surface \cite{jeon2009haptic}.
\item Displacement-force curves of a real rubber ball (dashed line) and when its perceived stiffness $\tilde{k}$ is modulated \cite{jeon2009haptic}.
]
\subfig[0.38]{jeon2009haptic_1}
\subfig[0.42]{jeon2009haptic_2}
\subfig[0.45]{jeon2009haptic_1}
\subfig[0.45]{jeon2009haptic_2}
\end{subfigs}
\textcite{detinguy2018enhancing} transposed this stiffness augmentation technique with the hRing device (\secref{belt_actuators}): While pressing a real piston with the fingertip by displacement $x_r(t)$, the belt compressed the finger with a virtual force $\tilde{k}\,x_r(t)$ where $\tilde{k}$ is the added stiffness (\eqref{stiffness_augmentation}), increasing the perceived stiffness of the piston (\figref{detinguy2018enhancing}).
@@ -290,8 +296,8 @@ Conversely, the technique allowed to \emph{decrease} the perceived stiffness by
\item Decrease perceived stiffness of hard object by restricting the fingerpad deformation \cite{tao2021altering}.
]
\subfigsheight{35mm}
\subfig{detinguy2018enhancing}
\subfig{tao2021altering}
\subfigbox{detinguy2018enhancing}
\subfigbox{tao2021altering}
\end{subfigs}
\paragraph{Vibrations Augmentations}
@@ -311,7 +317,7 @@ A challenge with this technique is to provide the vibration feedback at the righ
\item Voltage inputs (top) to the voice-coil for soft, medium, and hard vibrations, with the corresponding displacement (middle) and force (bottom) outputs of the actuator.
\item Perceived stiffness intensity of real sponge ("Sp") and wood ("Wd") surfaces without added vibrations ("N") and modified by soft ("S"), medium ("M") and hard ("H") vibrations.
]
\subfigsheight{50mm}
\subfigsheight{49mm}
\subfig{choi2021augmenting_control}
\subfig{choi2021augmenting_results}
\end{subfigs}
@@ -359,7 +365,7 @@ The complexity of the haptic sense has led to the design of numerous haptic devi
While many haptic devices can be worn on the hand, only a few can be considered wearable as they are compact and portable, but they are limited to cutaneous feedback.
If the haptic rendering of the device is timely associated with the user's touch actions on a real object, the perceived haptic properties of the object can be modified.
Several haptic augmentation methods have been developed to modify the perceived roughness and hardness, mostly using vibrotactile feedback and, to a lesser extent, pressure feedback.
However, not all of these haptic augmentations have been already transposed to wearable haptics, and use of wearable haptic augmentations have not been yet studied in the context of \AR.
However, not all of these haptic augmentations have yet been already transposed to wearable haptics, and the use of wearable haptic augmentations has not yet been investigated in the context of \AR.
%, unlike most previous actuators that are designed specifically for fingertips and would require mechanical adaptation to be placed on other parts of the hand.
% thanks to the vibration propagation and the sensory capabilities distributed throughout the skin, they can be placed without adaption and on any part of the hand