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This study describes a systematic approach to generate control signals of a tactile simulator to render the touch of textile fabrics. As a friction modulation tactile surface is used, control signals were generated from tribological measurements on real surfaces. Forces were acquired from an artificial finger, with a texture mimicking fingerprints. Then the signals are processed in frequency domain and send as control signal to the tactile stimulator. This paper focusses on the potential benefits of including the fingerprint information in the simulation of fabrics for achieving realistic tactile perception. A sensory analysis with 36 participants was carried out using the generated control signals, and results show a better discrimination without fingerprint information.

Skin integrity assessment is a very important matter in the nursing care, especially for patients with low mobility. However, the methodology of skin analysis is limited by a lack of reliable yet portable tools. In this paper, a new sensor is proposed for skin mechanical impedance characterisation, aiming to provide an objective assessment of skin health. The device consists in a microcontroller connected to a Langevin transducer. Using the vector control method, the reference vibration of the transducer is assured, and the mechanical impedance is observed. To ensure the repeatability of the measurements, tests in the morning and in the afternoon were taken. To verify if the device can distinguish sites with different mechanical properties on the same body, tests were made on 2 different body sites: the palm of the hand and the volar forearm. Measurements of skin hydration were also taken, to find a potential correlation of these parameters and skin acoustical mechanical impedance. Results have shown that the measurements provided by the device are mostly reliable, and reveal a fair correlation between mechanical impedance and hydration, in the level of stratum corneum, the outermost layer of skin. Also, the device is able to show the difference on the mechanics of the skin in the different body sites tested, independently of the hydration.

Synchronization of audio-tactile stimuli represents a key feature of multisensory interactions. However, information on stimuli synchronization remains scarce, especially with virtual buttons. This work used a click sensation produced with traveling waves and auditory stimulus (a bip-like sound) related to a virtual click for a psychological experiment. Participants accomplish a click gesture and judge if the two stimuli were synchronous or asynchronous. Delay injection was performed on the audio (haptic first) or the click (audio first). In both sessions, one stimulus follows the other with a delay ranging from 0−700ms . We use weighted and transformed 3-up/1-down staircase procedures to estimate people's sensitivity. We found a threshold of 179ms and 451ms for the auditory first and haptic first conditions, respectively. Statistical analysis revealed a significant effect between the two stimuli' order for threshold. Participants' acceptable asynchrony decreased when the delay was on the haptic rather than on the audio. This effect could be due to the natural experience in which the stimuli tend to be first tactile and then sonorous rather than the other way around. Our findings will help designers to create multimodal virtual buttons by managing audio-tactile temporal synchronization.

This work presents the control of a piezoelectric interface that combines two vibration modes of a plate to render the haptic feeling of a button click. By principle, the two vibration modes create an elliptical motion of particles of a beam that can induce a lateral force to the fingerpulp. In this device, the synchronization of the modes’ vibrations is essential, and can be obtained with a closed loop control. In the paper, we present the control in the (d,q) frame, because it can ensure the dynamic performances to achieve a compelling haptic feedback, yet being robust besides the external disturbances produced by the user’s finger. The proposed method could achieve a 2 ms response time, and the haptic feedback was perceived by 100% of users in a psychophysical study.

In this article, several modes are controlled simultaneously both in phase and amplitude on an haptic display. To achieve this, modulation/demodulation control combined with mixed spatial/frequency filters is developed. It is then applied to produce a predefined velocity field both in space and time on a plate. The experimental results show good agreement with theory.

When a finger touches an ultrasonic vibrating plate, a non-sinusoidal contact force is produced. This force is called acoustic finger force. In a setup where closed-loop control is performed on the vibration amplitude, a component of the acoustic finger force can be measured at the fundamental vibration frequency of the plate. This calculation is obtained from the measurement of the variation of the controller voltage between the no-load case and when a finger is present. This calculation is made for a group of twelve participants. From these results a PCA (Principal Component Analysis) model is created. This model permits estimation of the acoustic finger force response of a participant at any vibration amplitude, based on a one or two point measurement. Finally, a linear relation between the PCA coefficients and the friction reduction is proposed. The objective of this relation would be to ultimately provide the means to create an amplitude reference calibration based on the desired friction reduction level, and thus be able to produce a standardized tactile feedback for each user, despite the biomechanical differences in finger pad properties between subjects.

Modulated-Demodulated control (or vector control) allows to simultaneously impose amplitude and phase of a resonator. Moreover, the working frequency in the case of discrete-controller is substantially lower than the resonance frequency. However, the design of a such controller can be complex. In this paper, we outline a design directly in the baseband. To do so, the oscillator is modelled as a non-dimensional Multi-Input-Multi-Output system. An optimal control (Linear Quadratic Regulator) framework can then be used to design the controller. Thanks to ad hoc performances criteria, the weighting matrices are systematically specified according to the desired closed-lop time response. The methodology is validated by an experimental results on a plate actuated using piezoelectric patches.

Ultrasonic travelling waves possess the capability to induce net shear forces on the finger pulp, which finds utility in various applications. This study specifically investigates their potential in generating vibrotactile cues through force modulation. Two experiments are outlined herein. In the first, we assess the detection threshold, estimated at 1.5 μm peak-peak for a modulation frequency of 75 Hz. Remarkably, this threshold closely aligns with that observed in conventional vibrotactile indentation and remains consistent regardless of the force modulation method employed. In the second experiment, we correlate the amplitude of a travelling wave tactile display with the vibration amplitude of a shaker to achieve equivalent vibration intensity. Our findings reveal a substantial amplitude ratio range experienced on the travelling wave device, spanning from 24 to 155, which is pivotal in optimizing vibrotactile stimulator design. Additionally, we demonstrate that vibrations below 1 μm yield negligible net lateral forces on the finger pulp. These results underscore the potential of ultrasonic travelling waves in enhancing tactile feedback systems.

The Vector Control Method applied to piezoelectric transducers is a promising way to track the resonance fre-quency as well as to control the vibration speed. Similar to the modulation-demodulation techniques, the (d,q) transformation applied here takes advantage of the recent advances in microcontrollers. Moreover, engineers can make a bridge between the control of brushless DC motors and piezoelectric actuators and two simple PI controllers, one for each axis are tuned in order to precisely control the vibration amplitude components in axis d and axis q. This paper presents the procedure to tune the PI controllers. First, the model in the rotating reference frame is given. A procedure, based on the LQR approach, is used to calculate the parameters of the PI controllers based on the desired closed loop response time. In the (d,q) reference frame, the second order type response of the system becomes two first order systems, coupled if the system is operated outside its resonance. By taking into account these couplings, the closed loop system can be accelerated, yet ensuring stable operation. In addi-tion to the control, environment’s acoustic impedance can be derived, on line. Finally, we present experimental results, obtained on a haptic display. The model and the measures are consistent, and confirms the approach: the vibration amplitude can be tuned with a response time less than 10ms.

This paper aims to investigate the semantic perceptual space of synthetic tactile textures rendered via an ultrasonic based haptic tablet and the parameters influencing this space. Through a closed card sorting task, 30 participants had to explore 32 tactile-only textures and describe each texture using adjectives. A factorial analysis of mixed data was conducted. Results suggest a 2 dimensional space with tactile textures belonging to a continuum of rough to smooth adjectives. Influence of waveform and amplitude is shown to play an important role in perceiving a texture as smooth or rough, and spatial period is a possible modulator of different degrees of roughness or smoothness. Finally, we discuss how these findings can be used by designers on tactile feedback devices.

In this paper, a psychophysical experiment is designed and setup to perform the comparison between lateral and normal ultrasonic vibration for friction modulation on haptic devices at the same vibration amplitudes. Thanks to a simple analytical modelling relying on mechanical contact, the results obtained are explained. A parametric analysis of this comparison is then performed.

In this paper, we present a method to observe the fundamental of the acoustical finger force for the case of a friction reduction based haptic interface. The capability of the method to be achieved on-line, in a small micro-controller is established. We show a correlation between this measurement and the friction when sliding the finger. A model that predicts the friction coefficient and the friction contrast is laid down; it gives consistent output for 10 participants out of 12 having different biomechanical parameters of the skin.

A realistic keyclick sensation is a serious challenge for haptic feedback since vibrotactile rendering faces the limitation of the absence of contact force as experienced on physical buttons. It has been shown that creating a keyclick sensation is possible with stepwise ultrasonic friction modulation. However, the intensity of the sensation is limited by the impedance of the fingertip and by the absence of a lateral force component external to the finger. In our study, we compare this technique to rendering with an ultrasonic travelling wave, which exerts a lateral force on the fingertip. For both techniques, participants were asked to report the detection (or not) of a keyclick during a forced choice one interval procedure. In experiment 1, participants could press the surface as many time as they wanted for a given trial. In experiment 2, they were constrained to press only once. The results show a lower perceptual threshold for travelling waves. Moreover, participants pressed less times per trial and exerted smaller normal force on the surface. The subjective quality of the sensation was found similar for both techniques. In general, haptic feedback based on travelling ultrasonic waves is promising for applications without lateral motion of the finger.

Inclure un nouveau type de retour d'informations dans les interfaces homme-machine peut-être intéressant pour les utilisateurs. En plus du retour audiovisuel, l'intégration d'un retour tactile sur un clavier virtuel par exemple permet d'augmenter la vitesse de frappe et la précision des utilisateurs. Il existe une méthode permettant de produire des sensations tactiles localisées sur une plaque mince en excitant les modes de la structure. Pour cela, il est nécessaire d'assurer un régime transitoire bien précis pour chacun des modes contrôlés, ceci en dépit des différentes sources de perturbation. L'objectif de cette thèse est d'améliorer la robustesse de ce type de dispositif à retour tactile grâce au contrôle en boucle fermée. La méthodologie proposée dans cette thèse consiste donc à commander en boucle fermée l'amplitude et la phase d'un mode de vibration en utilisant un contrôle par modulation-démodulation. Nous proposons un modèle dynamique d'un mode de vibration dans la base démodulée et nous établissons une approche systématique pour le calcul des gains du contrôleur en nous basant sur la commande Linéaire Quadratique. Nous développons une méthode basée sur le filtrage modal pour la généralisation du contrôle par modulation-démodulation pour le cas d'un contrôle multimodal. Cette méthode de filtrage consiste à exploiter les propriétés spatiales et fréquentielles des modes pour reconstruire les coordonnées modales des différents modes contrôlés, où chaque mode possède son propre bloc de contrôle par modulation-démodulation. Nous appliquons et validons expérimentalement les techniques proposées sur le cas d'une poutre et puis nous étendons le concept sur le cas d'une plaque mince.