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A nonreciprocal system composed of a one-dimensional piezoelectric phononic crystal whose periodic electrical conditions are modulated in time is presented. One-way longitudinal wave propagation is studied experimentally and compared to finite element temporal simulations. The modulation is performed by prescribing grounded or floating potential conditions on a periodic set of electrodes through external circuits. This approach makes it possible to consider a wide range of modulation speeds, and the large number of unit cells of the phononic crystal allows us to characterize experimentally the full dispersion curves of the system. This permits to observe the presence of directional bandgaps and to follow the shift in frequencies of these bandgaps as a function of the modulation speed. The experiments show the linear evolution of the central position of the bandgaps with the increase in the modulation speed, as well as their progressive closure, over a wide range of frequencies. Experiments are also used to estimate the evolution of bandgaps in a dispersive system, a problem discussed in several theoretical works but never observed experimentally. This work may constitute the foundation for experimental analysis of Floquet acoustic metamaterials, accelerated-modulation space-time metamaterials, or acoustic analog of the event horizon.

Texture, a fundamental object attribute, is perceived through multisensory information including touch and auditory cues. Coherent perceptions may rely on shared texture representations across different senses in the brain. To test this hypothesis, we delivered haptic textures coupled with a sound synthesizer to generate real-time textural sounds. Participants completed roughness estimation tasks with haptic, auditory, or bimodal cues in an MRI scanner. omatosensory, auditory, and visual cortices were all activated during haptic and auditory exploration, challenging the traditional view that primary sensory cortices are sense-specific. Furthermore, audio-tactile integration was found in secondary somatosensory (S2) and primary auditory cortices. Multivariate analyses revealed shared spatial activity patterns in primary motor and somatosensory cortices, for discriminating texture across both modalities. This study indicates that primary areas and S2 have a versatile representation of multisensory textures, which has significant implications for how the brain processes multisensory cues to interact more efficiently with our environment.

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 paper describes an electromechanical handheld probe dedicated to skin biomechanics characterization. This probe is composed of two piezoelectric bending actuators that control tip displacement. Simultaneous force and displacement sensing is achieved by integrating two pairs of resistive strain gauge sensors. Piezoelectric hysteresis, however, compromises the accuracy of force sensing. To improve force sensing, a hysteresis model is introduced. The hysteresis behavior of piezoelectric actuators is usually described between the input voltage and output displacement. The influence of external force is rarely discussed. Considering the combined effects of the electric field and the external stress, we model hysteresis with the instantaneous displacement relying on the Bouc–Wen model. Experimental and simulation results show that the hysteresis model can predict bender behavior even driven by multi-harmonic voltages. Based on this hysteresis model, the hysteresis compensation strategy is validated at no load and loaded conditions (a spring load). However, to simplify the compensation process, another original strategy is proposed, relying on a closed-loop displacement control. Results demonstrate that the second approach also improves the accuracy of force sensing. Finally, preliminary measurements performed on the real skin show promising results.

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.

Friction reduction using ultrasonic longitudinal surface vibration can modify the user perception of the touched surface and induce the perception of textured materials. In the current paper, the mechanisms of friction reduction using longitudinal vibration are analyzed at different finger exploration velocities and directions over a plate. The development of a non-Coulombic adhesion theory based on experimental results is evaluated as a possible explanation for friction reduction with vibrations that are non-collinear with the finger displacement. Comparison with experimental data shows that the model adequately describes the reduction in friction, although it is less accurate for low finger velocities and depends on motion direction.

The design and closed loop control of a device able to produce both longitudinal mode and transverse mode vibration, at about the same resonance frequency (60 kHz) are presented in this article. The structure uses an array of piezo-ceramics. A dynamic analysis is performed on the obtained modes, and their dynamic lumped parameters are identified. A closed loop control is performed to maintain the desired vibration amplitude in the presence of a finger. Longitudinal and transverse motion cartographies show that the objective of achieving and controlling pure modes independently has been achieved. Using this device, tribological, psychophysical and energetic analyses are carried out. The analyses show that in terms of friction measurements and perception, both modes produce equivalent results. In terms of active power losses, an advantage of the longitudinal mode over the transverse mode is observed due to the interaction with the finger.

Combining multisensory sources is crucial to interact with our environment, especially for older people who are facing sensory declines. Here, we examined the influence of textured sounds on haptic exploration of artificial textures in healthy younger and older adults by combining a tactile device (ultrasonic display) with synthetized textured sounds. Participants had to discriminate simulated textures with their right index while they were distracted by three disturbing, more or less textured sounds. These sounds were presented as a real-time auditory feedback based on finger movement sonification and thus gave the sensation that the sounds were produced by the haptic exploration. Finger movement velocity increased across both groups in presence of textured sounds (Rubbing or Squeaking) compared to a non-textured (Neutral) sound. While young adults had the same discrimination threshold, regardless of the sound added, the older adults were more disturbed by the presence of the textured sounds with respect to the Neutral sound. Overall, these findings suggest that irrelevant auditory information was taken into account by all participants, but was appropriately segregated from tactile information by young adults. Older adults failed to segregate auditory information, supporting the hypothesis of general facilitation of multisensory integration with aging.

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.

Teleoperation of unmanned ground vehicles (UGVs), particularly for inspection of unstructured and unfamiliar environments still raises important challenges from the point of view of the operator interface. One of these challenges is caused by the fact that all information available to the operator is presented to the operator through a computer interface, providing only a partial view of the robot situation. The majority of existing interfaces provides information using visual, and, less frequently, sound channels. The lack of situation awareness (SA), caused by this partial view, may lead to an incorrect and inefficient response to the current UGV state, usually confusing and frustrating the human operator. For instance, the UGV may become stuck in debris while the operator struggles to move the robot, not understanding the cause of the UGV lack of motion.

In the field of tactile feedback, researchers try to generate localized stimulations on screens. Some solutions such as time reversal or phased array use vibration induced in the screen equipped with piezoelectric ceramics. We propose to use the modal basis to reproduce a specified velocity field on such devices. We explain the theory and propose a methodology to practically synthesize the voltages to achieved a controlled focusing in a given time. Experiments on a simple demonstrator are in good agreement with the theory for various velocity fields and a reduced number of modes.

In this paper, we address the problem of pull out and stalling of the vector control of the piezo-actuator drive. The model presented reveals the similarities with synchronous machine and therefore we propose the vector control to solve the problem and to enhance its performances. The implementation using a position sensor is tested. Experimental results show that the vector control avoids pull out and reduces dramatically the voltage applied to achieve the same performances. Speed up to 2.5 times the maximum rated speed at full load could be achieved without loss of synchronization.

This paper presents the implementation of a novel vibration amplitude control and resonant frequency tracking for Piezoelectric Transducers (PT) and Ultrasonic Motors (USM). It is based on a generalization of the Vector Control Method (VCM) to PT and USM that is explained in the first part. We show that two independent controllers with similar structure are required : one tracks the resonant frequency and the second controls the amplitude.We then present the implementation into a low cost DSP controller with a 200μsec sampling period. Experimental results on a Langevin Transducer achieved a time response of 20msec approximately, and the generality of the method is further demonstrated on a 2D Tactile stimulator at the end of the paper.

Ultrasonic vibration is employed to modify the friction of a finger pad in way that induces haptic sensations. A combination of intermittent contact and squeeze film levitation has been previously proposed as the most probable mechanism. In this paper, in order to understand the underlying principles that govern friction modulation by intermittent contact, numerical models based on finite element (FE) analysis and also a spring-Coulombic slider are developed. The physical input parameters for the FE model are optimized by measuring the contact phase shift between a finger pad and a vibrating plate. The spring-slider model assists in the interpretation of the FE model and leads to the identification of a dimensionless group that allows the calculated coefficient of friction to be approximately superimposed onto an exponential function of the dimensionless group. Thus, it is possible to rationalize the computed relative reduction in friction being (i) dependent on the vibrational amplitude, frequency, and the intrinsic coefficient of friction of the device, and the reciprocal of the exploration velocity, and (ii) independent of the applied normal force, and the shear and extensional elastic moduli of the finger skin provided that intermittent contact is sufficiently well developed. Experimental validation of the modelling using real and artificial fingertips will be reported in part 2 of this work, which supports the current modelling.

This work demonstrates the ability of a torsion-based shear-mode energy harvester to power a sensor module by integrating a temperature sensor circuit with a purpose developed piezoelectric energy harvester. A 10-cm3 energy harvester was developed for this application and was found to produce over 200 µW of maximum power through an optimal load resistance under 0.25 gpk acceleration excitation at its resonant frequency of 237 Hz. This harvester was then tested with two interface circuits: a standard interface diode bridge rectifier and a nonlinear synchronous electrical charge extraction circuit that were compared for their suitability in powering the sensor module. Through this, the synchronous electrical charge extraction nonlinear conditioning circuit was found to have superior performance when charging a capacitor and with DC loads at low voltages and was capable of providing a maximum power output of 37 µW under 0.25 gpk acceleration at 237 Hz. This output power was then used to successfully power a temperature sensor module consisting of a temperature sensor, a microcontroller, and a radio-frequency identification memory chip at a sensing frequency of 0.5 Hz.

In Variable Friction Tactile Displays, an ultrasonic standing wave can be used to reduce the friction coefficient between a user’s finger sliding and a vibrating surface. However, by principle, the effect is limited by a saturation due to the contact mechanics, and very low friction levels require very high vibration amplitudes. Besides, to be effective, the user’s finger has to move. We present a device which uses a travelling wave rather than a standing wave. We present a control that allows to realize such a travelling wave in a robust way, and thus can be implemented on various plane surfaces. We show experimentally that the force produced by the travelling wave has two superimposed contributions. The first one is equal to the friction reduction produced by a standing of the same vibration amplitude. The second produces a driving force in the opposite direction of the travelling wave. As a result, the modulation range of the tangential force on the finger can be extended to zero and even negative values. Moreover, the effect is dependant on the relative direction of exploration with regards to the travelling wave, which is perceivable and confirmed by a psycho-physical study.

This paper describes the control in a (d-q) frame of the vibration amplitude of a tactile stimulator based on ultrasonic vibrations. The goal is to fulfil simultaneously two objectives: maintain a constant level of vibration amplitude and excite the system at the resonance frequency. A new modelling approach is presented in order to facilitate the control and to fulfil the two objectives simultaneously. Then, thanks to an experimental setup, the validation of the new model is performed. Finally, the result of the closed loop control over a wide range of disturbing factors is presented.

RÉSUMÉ L’électrovibration et l’effet squeeze film produit par vibration ultrasonique sont deux principes de stimulation tactile permettant de modifier la sensation de toucher d’un utilisateur explorant une surface plane. Le présent article s’attache à démontrer leur compatibilité sur un même stimulateur tactile lors d’une utilisation concomitante. Une description du principe physique et des spécificités de chacun des phénomènes sera entreprise et les résultats expérimentaux obtenus lors de leur association seront par ailleurs présentés. ABSTRACT Electrovibration and squeeze film effect are two different principles, which modify the user’s perception of a surface. The first one is generated by the polarization of a finger approaching a high voltage supplied plate, and the latter by the ultrasonic vibration of a plate. Their compatibility on the same stimulator will be presented in this paper and their concomitant use will be proven. A parametric study on electrovibration in function of the material choice and a first experimental investigation of the validity of the squeeze film effect hypothesis are performed. A description of the physical principle and the characteristics of each effect will be proposed and force measurements of their coupling will be presented.

Tactile interfaces are intuitive but lack of haptic feedback. One method to provide tactile feed- back is to change the friction coefficient of the touch surface. Several small-size tactile devices have been developed to provide programmable friction coefficient based on the squeeze air film effect. This effect is produced by ultrasonic vibration of the tactile plate thanks to piezoceramics. In order to design larger embedded tactile feedback areas, a key issue is the power consumption. In this paper, we present the power analysis of a tactile device which is based on the squeeze film effect. We first investigate the source of power consumption by a series of measurements. Then, an analytical model is developed to estimate the power, which gives the conclusion that, when the vibration amplitude is constant, the power consumption is not related to the number of piezoelectric actuators. According to this result, we design a large area (198 mm × 138 mm) tactile plate with only eight piezoelectric actuators. Experimental results show that the power consumption of the large tactile plate is less than 2 W. Moreover, we also find that the power consumption of the large tactile plate was predictable with the measurement results from small plates with an average error of less than 10%.

Stimulating the human hand with a tactile device in order to simulate pile fabric touch is a challenge. The stimulation has to be designed from the friction characteristics of the investigated pile surfaces, i.e. velvet fabrics. The tactile illusion of pile is given when touching the smooth plate of the tactile stimulator STIMTAC by modulating the coefficient of friction between the plate and the finger during an active movement. In a preliminary study, five tribological features as velvet fabric character- istics were identified, used for the design of the stimulator’s control signal, and validated via psychophysical studies where real and simulated fabrics were compared. But a specific tribological feature described and expected by individuals was missing. Then, a tribological investigation has been done in order to obtain this tribological feature, with the five previous ones, by changing experimental conditions: slider shape, texture, and joint stiffness. The obtained results show that a rounded shape of the slider has an influence only on the friction force level, but a texture of the slider close to fingerprints and a joint stiffness is crucial to obtain the missing characteristic and therefore for the pile surface tribological characterization. The role of the fingerprints in touching grooved surfaces has been pub- lished before but not for pile surfaces.

Two different principles are available to modulate the user perceived roughness of a surface: electrovibration and ultrasonic vibration of a plate. The former enhances the perceived friction coefficient and the latter reduces it. This paper will highlight the independence of the two effects on the physical and perceptual point of view to confirm the increased range of sensation and stimulation that can be supplied by the two coupled techniques to the users. Firstly, a tribometric analysis of the induced lateral force on the finger by the two coupled effects will be presented, then a study on the dynamic of the two effects will be reported. In the end, a psychophysical experiment on the perception of the two coupled techniques will be shown.

When the frequency of the source of vibration of a piezolectric generator is significantly different from its eigenfrequency, the dielectric power losses become prominent and decrease the amount of power which is practically harvested. For off-resonance vibrating frequencies, the optimal operating conditions can be obtained with a Maximum Power Point Tracking method. This paper introduces complex phasors in the study of power conversion for piezoelectric generators. These complex phasors are used to describe three strategies which help simplify the tracking of the optimal generator output power for vibration frequencies which are away from resonance. Experimental results obtained on a prototype illustrate and confirm the approach with the phasor approaches illustrate and confirm the success of the proposed optimal power tracking strategies. Finally, we show that the efficiency results of each strategy depend on whether they are used inside or outside a frequency bandwidth around the eigenfrequency, and that the length of this bandwidth depends on the excitation amplitude.

A simple device based on friction coefficient control was designed as a solution to the lack of compact- ness and simplicity encountered in the number of force feedback interfaces. The structure comprises a 64 × 38 × 3 mm copper-beryllium plate on which well-adjusted polarized piezoceramics are glued. The plate stands on four legs, each of which has a spherical end. By controlling the drive voltage, friction force may be varied as required by a user who moves the device on a flat surface, as he or she would do with a normal mouse. This adds the possibility of rendering simulated forces from objects manipulated on a PC screen. Friction forces obtained using Hertz contact theory compare well with the ones measured on an experimental setup, which demonstrate the validity of the approach with regard to force feedback application.

In the field of e-commerce or virtual prototyping of textile fabrics and garments, tactile stimulators could be very pertinent and useful tools for the industry. The challenge is to stimulate the human hand using a tactile device in order to simulate the textile fabric touch. The principle of the tactile device is described. The kinds of fabrics investigated are pile fabrics, such as velvet. In this study, the illusion of pile is given when touching the smooth plate of the tactile device by modulating the coefficient of friction between the plate and the finger during an active movement. The control signal is qualitatively designed from some tribological features identified in this study as velvet fabric characteristics. The influence of each tribological feature on the tactile rendering is studied via psychophysical studies comparing real and simulated fabrics. The best rendering needs a simulation with three specific features: a coefficient of friction, which depends on the finger movement direction; a transition phase for the change of movement direction; and small amplitude variations of the coefficient of friction with about one millimeter wavelength.

This paper presents the closed-loop control of exciters to produce a traveling wave in a finite beam. This control is based on a dynamical modeling of the system established in a rotating reference frame. This method allows dynamic and independent control of the phase and amplitude of two vibration modes. The condition to obtain the traveling wave is written in this rotating frame, and requires having two vibration modes with the same amplitude, and imposing a phase shift of 90?? between them. The advantage of the method is that it allows easy implementation of a closed loop control that can handle parameter drift of the system, after a temperature rise, for example. The modeling is compared with measurement on an experimental test bench which also implements real-time control. We managed to experimentally obtain a settling time of 250 ms for the traveling wave, and a standing wave ratio (SWR) of 1.3.

—Haptic perception of curvature depends largely on the kind of touch. An active and dynamic touch is considered to be the most natural way of exploring. In this study, we have designed and evaluated a kinematic platform for curvature perception through active and dynamic touch. This platform can independently orient, elevate, and translate a flat plate; by exploring forward and backward along the flat plate with a finger, users can achieve curvature feeling of extruded objects. The mechanism of platform and the way of touch have maximally respected the cues for curvature perception, especially the slip cue. Psychophysical evaluation demonstrated that the discrimination threshold of curvature for virtual shapes is close to that for real shapes, and the virtual shape is felt equally curved as the real one. The curvature perception of mono-convex surfaces was then expanded to perception of more complex surfaces: large textures, which have a sinusoidal profile. The evaluation has accessed the correspondence between the virtual and real large textures.

Introducing haptic into tactile input interfaces allow users to really feel their action on the device they control by this way. In this paper, we achieve tactile stimulation by using the squeeze film effect. It is applied on a haptic knob, as those which control an MP3 player for example. We present our design procedure of the active surface and of the position sensor based on force measurement which achieves a resolution of 3.6 deg. We also show that stimuli are damped by fingertip, and a specific control loop with a response time of 2.5 ms has been achieved to tackle this problem. Finally, a psychophysical experiment was conducted showing how the haptic feedback can increase user’s accuracy in a pointing task.

A piezoelectric generator converts mechanical energy into electricity and is used in energy harvesting devices. In this paper, synchronisation conditions in regard to the excitation vibration are studied. We show that a phase shift of ninety degrees between the vibration excitation and the bender’s displacement provides the maximum power from the mechanical excitation. However, the piezoelectric material is prone to power losses; hence the bender’s displacement amplitude is optimised in order to increase the amount of power which is converted into electricity. In the paper, we use active energy harvesting to control the power flow, and all the results are achieved at a frequency of 200 Hz which is well below the generator’s resonant frequency.

This paper deals with the control and experimentation of a one degree of freedom haptic stick, actuated by a travelling wave ultrasonic motor. This type of actuator has many interesting properties such as low speed operation capabilities and a high torque-to-weight ratio, making it appropriate for haptic applications. However, the motor used in this application displays non linear behaviour due to the necessary contact between its rotor and stator. Moreover, due to its energy conversion process, the torque applied to the end -- effector is not a straightforward function of the supply current or voltage. This is why a force-feedback control strategy is presented, which includes an online parameter estimator. Experimental runs are then presented to examine the fidelity of the interface.

Le projet REACTIVE a pour objectif de développer un outil de rééducation en réalité virtuelle pour les personnes cérébrolésées et notamment héminégligentes. Plusieurs scénarios paramétrables ont été développés ainsi que des interfaces permettant aux patients d’interagir avec le système.

The Tactile plate consists of piezoceramics glued on a copper-beryllium resonator. Its purpose is to create programmable tactile sensations, which give the illusion of finely textured surfaces. The illusion originates from the variable friction between a finger and the vibrating resonator, caused by the squeeze film effect. In order to obtain a maximal deflection of the plate for a minimal supply voltage, an optimization is carried out of the length, thickness, and width of both the resonator and the ceramics. Constraints are realistic geometrical dimensions, a resonance frequency of at least 25 kHz, and a low supply voltage. The plate is modelled by both an analytical and a numerical model. The maximal dynamical deflection per volt was achieved with thin piezoceramics (0.5 mm) at the minimal frequency of 25 kHz. A high deflection can be obtained in a wide range of the resonator length. With increasing length, the optimal resonator thickness increases too. The plate width seems to have little influence. Experiments are carried out on two plates with different geometry.

Using piezoelectric actuators can reduce the bulk size of servomechanisms; they are thus very useful in avionics applications. However, mechanical overload on the shaft of a traveling-wave ultrasonic motor often results in the motor suddenly stalling. To avoid this drawback, one can increase the supply voltage or add a control loop in the rotating reference frame of the traveling wave. The consequences are extra power losses or lower dynamic performances. The proposed method combines the advantages of classical controls and controls in a rotating frame: Both stability and dynamic performances are obtained at low supply-voltage levels. Experimental runs are presented.

This paper describes implementation and initial evaluation of variable friction displays. We first analyse a device that comprises a stator of an ultrasonic motor supplied by only one channel. In this way, the stator does not induce any rotative movement but creates a slippery feeling on the stator’s surface. Considering the range of frequency and amplitude needed to obtain this phenomenon, we interpret it as the squeeze film effect, which may be the dominant factor causing an impression of lubrication. This effect is thus able to decrease the friction coefficient between the fingertip and the stator as a function of the vibration amplitude. Moreover, if we add a position sensor, we can create a textured surface by generating alternatively sliding and braking sensations by tuning the vibration amplitude of the wave. Then, based on the principle of the first device, another device is proposed in order to enable a free exploration of the surface, according to ergonomic requirements.

Most tactile displays currently built rely on pin based arrays. However, this kind of tactile device is not always appropriate when we need to give the illusion of finely textured surfaces. In this paper, we describe the squeeze film effect between a plate and a finger, and we use this effect to design an ultrasonic tactile plate. The plate is actuated by piezoelectric ceramics. Ultrasonic vibrations are thus produced and are capable of generating the squeeze film effect. This enables us to simulate variable friction on the surface of the plate. In order to identify the squeeze film phenomenon, this study considers the case where a finger, with a planar bottom surface and with epidermal ridges, is placed on a rapidly vibrating plate. The overpressure is calculated and the result enables us to assess the relative coefficient of friction as a function of the vibration amplitude of the plate. Based on this principle, and using both analytic and FE method studies, and given ergonomic and stimulation (squeeze film) requirements, we show that it is possible to suggest a method of designing a tactile plate which is capable of giving programmable tactile sensations. We conclude by comparing the results obtained from our simulations with experimental results.

Precise position control of a Travelling Wave Ultrasonic Motor is achieved, avoiding the traditional drawbacks attributable to non-linear torque generation: overshoot or slow response time. For that purpose, a behavior model control is proposed and presented. With this control law, a quick and precise response is obtained. In this article, we present a position control scheme of an inertial load. The guideline used for this control was a rotation of 90° in a response time of about 200ms with a position error of 0,6mrad, targeting a typical application for avionics. In the paper, a shinsei USR30 is used, but the method can be applied to other Ultrasonic Motors.

Depending on its electrical to mechanical energy conversion process, the torque on a Travelling Wave Ultrasonic Motor(TWUM)’s shaft is not directly proportional to a measurable electrical variable, such as current or voltage, but is derived from a complicated process at the stator/rotor interface. The load torque is thus quite unknown, and this can be a disadvantage in applications where a torque limitation is required or a torque measurement is needed. The aim of this article is to come up with a straightforward torque estimator on a TWUM. For that purpose, the motor is modelled, this modelling leads to different estimator strategies. More specifically, we chose a strategy for which a speed sensor is useless, relying only on the stator’s resonant behavior. The parameters of the motor needed for the estimator are measured afterwards while some non linearities are identified and taken into account. Several experimental trials are then carried out to check the performance of the estimator. Finally, a claw actuated by a TWUM is presented, because this is a typical application where the knowledge of the torque helps guarantee the safety of the device.

The aim of this paper is to define a linear model of a planar standing wave ultrasonic motor (SWUM). First, the analytical approach using the variational formulation is presented. An identification method is deduced to find the parameters of a vibrating rectangular plate. Non-linearities are also emphasized and verified by the experimental measurements. Secondly, the mechanical energy conversion of the actuator is identified, using an average behavior modelling and a linear approach for the contact interaction. Finally, a complete modelling of the actuator is presented, using the Causal Ordering Graph formalism.

An original modeling of a traveling-wave ultrasonic motor is established in order to provide a new torque control law for this category of actuators. In particular, self-driving is implemented, avoiding the classical drawbacks of frequency control, i.e., pull-out phenomenon. With such a robust control, force feedback application is available. Experimental results are obtained on an active haptic stick.

This paper deals with the causal modeling of a Traveling Wave Ultrasonic Motor; the aim of the study is to build an approach which may take into account the physical contact responsible for the pull-out phenomenon, but straightforward enough to be useful for control. As the parameters available for the modeling can not be obtained following the well known electromechanical equivalent scheme identification, a new identification method is proposed. In this purpose, the model of the motor is expressed in the traveling wave rotating frame.

Cet article propose une modélisation entièrement paramétrable d’un moteur à onde progressive. Le formalisme de représentation choisi est celui du graphe informationnel causal (GIC), adapté à l’établissement d’un modèle de commande. L’originalité de la démarche réside en la construction d’un modèle intermédiaire entre le schéma électromécanique équivalent et l’approche lagrangienne. En particulier, ce modèle ne se base pas sur une description fine du contact stator-rotor, généralement trop complexe pour être prise en compte lors d’une commande. Pour valider le modèle mis en place, les résultats sont confrontés à ceux issus d’un modèle de référence considérant la loi de Coulomb au niveau du contact.

L’intérêt des dispositifs à retour tactile dans les domaines de la conception, la communication, l’aide à la personne, donne lieu actuellement à de nombreuses recherches qui débouchent sur un large spectre de propositions technologiques. Les potentialités, et la structure de ces interfaces sont également très variées. Dans cet article nous traitons plus particulièrement des dispositifs tactiles basés sur l’exploitation du frottement variable, et dédiés à la reconstitution de textures fines. Cette variation du coefficient de frottement est obtenue grâce à la mise en vibration ultrasonore de la surface touchée, générant un phénomène de « squeeze film ». Après un état de l’art sur le retour tactile par action sur le frottement, ce phénomène physique est présenté et justifié dans le cas d’une plaque vibrante en contact avec le doigt. Les conditions portant sur l’amplitude et la fréquence des vibrations sont explicitées. La mise en oeuvre de ces conditions à l’aide d’une excitation piézo-électrique permet de mettre en évidence, par des essais expérimentaux et des tests psychophysiques, l’effet de diminution du frottement. Enfin, par le contrôle de ce frottement selon la position du doigt, nous montrons qu’il est possible de simuler le rendu de surfaces finement texturées.

While much research has been conducted on multisensory interactions in passive touch, research on how active touch influences how the senses interact remains scarce. Using a haptic surface based on ultrasonic vibrations, we investigated the perception of synchronization of audio-tactile stimuli in active touch. Tactile stimuli were delivered upon sliding the finger, and auditory stimuli followed with a delay ranging from 0-700 ms. In this simultaneity judgment task, two visual conditions were employed: (i) a visual cue showing the location of the active zone on the screen; (ii) a black picture on the screen. We also consider two sliding directions: (i) right-to-left (RTL); (ii) left-to-right (LTR). We estimated the psychometric function (threshold and slope) of the ability to judge whether the auditory and tactile stimuli were temporally synchronous. We found a threshold of 201.26 and 211.73 ms for LTR and 233.3 and 207.23 ms for RTL with and without visual cues, respectively. We translated temporal delays into distances (mm) using the finger sliding velocity measured for each trial. The results indicate that the simultaneity judgment was independent of sliding velocity. Our results provide insights into participants’ sensitivity in perceiving simultaneous audio-tactile feedback generated during active touch exploration.

La recherche a montré que l’interaction avec les surfaces peut bénéficier de l’ajout de retour haptique. La perception de cette retour haptique est influencée par d’autres modalités, telles que visuelles et auditives, ce qui permet de le renforcer ou de l’enrichir. Cependant, l’effet des textures 3D dans la réalité augmentée (AR), comme le rendu stéréoscopique et la déformation de surface, sur la perception tactile des textures n’a pas encore été étudié, en particulier dans une condition tactile active. Dans cet article, nous étudions l’interaction perceptuelle entre la stéréoscopie, la déformation de surface et la retour haptique dans un état actif. La retour haptique a été mise en oeuvre en utilisant une modulation par friction basée sur des vibrations à ultrasons, tandis que la retour visuelle a été implémentée avec une paire de lunettes 3D en AR. L’étude expérimentale est une exploration visuelle-tactile d’une texture virtuelle. Notre objectif est de comprendre l’interaction d’une modalité sur l’autre pour la rugosité et la perception de la profondeur. Nous avons demandé aux participants de porter des jugements de rugosité de texture visuelle et tactile et d’estimer la profondeur de la déformation de la texture sous leurs doigts. Nos résultats suggèrent que : 1) la rugosité tactile perçue peut être modifiée en ajoutant un rendu stéréoscopique et / ou une déformation de surface visuelle mais uniquement pour les textures tactiles lisses. 2) La rugosité visuelle perçue peut être modifiée en augmentant la rugosité tactile. 3) La rugosité globale (visuel + tactile) est principalement impactée par la perception tactile.

Research has shown that interaction with tactile surfaces can benefit from the addition of haptic feedback. The perception of this feedback is influenced by other modalities, visual and auditory, making it possible to reinforce or enrich it. However, the effect of visual depth cues, such as stereoscopic rendering and surface deformation, on the tactile perception of textures has not been studied yet, especially in an active touch condition. In this paper, we investigate the perceptual interaction between stereoscopy, surface deformation, and haptic feedback in the condition of active touch implemented using friction modulation based on ultrasonic vibrations. The experimental study is based on a Visual-Tactile exploration of a virtual texture. Our objective is to understand the interaction of one modality over the other for roughness and depth perception. Participants were asked to make visual and tactile texture roughness judgments and to estimate the depth of deformation of the texture below their fingers. Our results suggest that: 1) perceived tactile roughness can be modified by adding stereoscopic rendering and/or visual surface deformation but only for smooth tactile textures, 2) perceived visual roughness can be modified by increasing the tactile roughness, 3)the overall roughness (Visual + Tactile) is mainly impacted by the tactile perception.

Active touch (AT) is defined as the action of touching, implying voluntary, self-generated movement. While much research has been conducted on multisensory interactions in passive touch, research on how AT influences how the senses interact remains scarce. Using a haptic surface (HS) based on ultrasonic vibrations, we investigated the perception of synchronization of audio-tactile stimuli in AT. Tactile stimuli were delivered upon sliding the finger over the tactile zone of the HS. Auditory stimuli (a white noise burst) followed the tactile stimuli with a delay ranging from 0 to 700 ms. Participants reported whether the two stimuli were perceived as coinciding in time or not. Two conditions were employed for the discrimination task: (i) either with a visual clue showing the location of the tactile zone on the screen; (ii) or with a black screen below the HS. Time delays (ms) between the tactile-auditory inputs were converted in displacement (mm), depending on the sliding velocity of the participant’s finger across the HS, to calculate spatial distances at which the two stimuli were perceived as coinciding or not with the same probability. The average distance was 5.87mm with visual cues and 5.63mm without a visual cue. No significant difference was found between the two visual conditions suggesting performance is not affected by the presence of a visual cue regarding the location of the tactile stimulus. Our results provide insights into the sensitivity of participants in perceiving spatiotemporal differences between tactileauditory stimuli generated during AT exploration.

Mechanical properties of skin are a clue for the diagnostic of pressure ulcers (PU) [1]. This project proposes a low- frequency ultrasound (LFU) device to identify the mechanical impedance (MI) of skin in different sites. The device’s goal is to identify the evolution of MI of skin over time and link it with the development of PU. In literature, studies involving LFU and PU focus on debridement through LFU cavitation [2]–[3]. Use of LFU on PU often present reduced pain and faster recovery. Although LFU for PU treatment is widely documented, the use of LFU for diagnosis is unexplored. Thus, a Langevin transducer (LT), with 60kHz of resonance frequency is proposed for PU detection. It is a high efficiency LFU device, based on the piezoelectric effect.

This paper presents an integrated probe, designed to measure the rheological properties of the skin in situ. It includes two piezoelectric bender actuators and strain gauges as sensors. The advantage of the proposed probe is that the measurements of tip force and displacement are accomplished without external devices. A feedback voltage control is applied to control the vibration amplitude of the piezoelectric benders. Through feedback from integrated strain gauges, the displacement control is achieved. As shown in the simulation, the closed-loop system is robust to disturbance and uncertainty. The proposed probe may be used to measure skin mechanical impedance.

When the finger interacts with a surface where a purely lateral ultrasonic vibration occurs, a vibration attenuation is produced. An added force is therefore needed in order to maintain the vibration amplitude in closed loop control. In this article we explore whether the friction reduction in lateral ultrasonic surface haptic devices may be predicted using static measurements of this additional force.

Friction attenuation using ultrasonic lateral surface haptic devices (ULSHD) can modify the user perception of the touched surface and induce the perception of textured materials. In the current paper, the mechanisms of friction attenuation using lateral vibration are analyzed at different finger exploration velocities and directions over a plate. A development of a non-Coulombic friction function based on experimental results is proposed and evaluated.

The study of skin mechanical impedance is a clue to analyse its health. We use a Langevin Transducer at 60kHz to excite the skin. In return we observe the acoustic forces generated by the interaction. To achieve that, the system is identified and presented in the rotating reference frame, and we describe the design of two PI controllers that accurately control the vibration velocity. However, in vivo analysis can be tricky when it comes to safety and duration of tests. Thus, phantom tissues are used as substitute to simulate skin behaviour. Due to its mechanical properties similar to skin, and its simple manipulation, Dragon Skin ®, a silicone rubber type of phantom, was chosen. The paper presents the characterisation of the mechanical impedance of three silicon phantoms with different properties based on force observation. The results show that the phantoms can be indeed identified based on this method.

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.

In this paper, we propose a new device in order to produce normal and lateral ultrasonic vibrations in a plate, using an array of piezoelectric ceramics. This setup serves to continue the comparative analysis between the two vibration modes for tactile feedback rendering, by including an energetic characterization. With the help of a tribological analysis, this study will help to examine the energy performance of each vibration mode in terms of active power consumption against friction contrast (which is linked to perception). Using a simplified second order plate model, the energetic results are analyzed. The results show a better energy efficiency for the lateral vibration for low exploration speeds. The tribological analysis helps as well to evaluate the effect of frequency increase in terms of friction reduction vs. vibration amplitude for both vibration modes

Recent studies have shown that a button click sensation could be simulated thanks to ultrasonic vibrations. In this context, a travelling wave may enhance the simulation because it creates internal lateral stresses that are released during the stimulation. However, this solution is difficult to integrate on plates. We present 2MoTac, a method which superpose a longitudinal and a bending mode simultaneously on a plate, in order to create a pseudo-travelling wave. We present the design, and a psychophysical study to deduce the optimal ratio between the bending and longitudinal mode amplitudes, in terms of detection threshold and robustness.

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.

The influence of the vibration frequency on the friction reduction of an ultrasonic haptic surface has been reported in the literature. The models predict that increasing the frequency of the vibration leads to higher friction reduction at constant vibration amplitude, but this has not been reported experimentally. In this paper, we study the friction reduction on a prototype which can vibrate at low (66kHz) and high (225kHz) frequency. By estimating the Point of Subjective Equivalence between a standard at low frequency with a sample at high frequency, we have found that high frequencies can indeed reduce the friction, with the advantage of much smaller vibration amplitude. Moreover, we show that the invariant between the two frequency conditions is not the vibration amplitude. Our conclusion is that the invariant could be the acceleration instead.

Alongside questions of how to create haptic effects on displays via alternative hardware, recent work has explored rendering options with respect to haptic effects, i.e. when and where to provide haptic feedback. In particular, recent work by Zhang and Harrison for electrostatic haptic feedback noted that the optimal technique for haptic feedback during interaction is the Fill technique, where haptic effects are rendered at all times when a user's finger is within the bounds of the target. In this paper, we explore whether this result generalizes to an alternative haptic rendering technology that uses ultrasonic vibrations to create haptic sensations, a technique called the “Squeeze Film Effect”. In contrast to prior work, our results indicate that positioning the haptic feedback as a discrete linear stimulus centred on the target provides an optimal trade-off between speed, accuracy, and user preference. We highlight the implications of this work to the generalizability of haptic feedback: Haptic feedback can improve time, errors, and user satisfaction during interaction, but only if the correct form of feedback is used for the specific haptic effect generated by the hardware.

The multimodal control of a 2D controlled-Friction Device is presented. We use the Vector control method because the phase and amplitude of two vibration modes at a same frequency can be precisely set. The closed loop response time of 10msec is achieved. The device is then associated with a finger position sensor. The algorithm of the multimodal approach is then tested. In spite of the inevitable limitations of the system - saturation of amplifiers, low sampling frequency of the sensor - low friction could be imposed under one finger and high friction on a second one in the same time. This confirms the validity of the modal approach to create multi touch interactions.

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}.

Tactile devices with ultrasonic vibrations (based on squeeze film effect) using piezoelectric actuators are one of the existing haptic feedback technologies. In this study we have performed two psychophysical experiments on an ultrasonic haptic tablet, in order to find the minimum size of a tactile element on which all the users are able to perfectly identify different types of textures. Our results show that the spatial resolution of the tactile element on haptic touchscreen actually varies, depending on the number and types of tactile feedback information. A first experiment exhibits three different tactile textures, chosen as being easily recognized by users. We use these textures in a second experiment, and evaluate minimal spatial area on which the chosen set of textures can be recognized. Among other, we find the minimal size depends on the texture nature.

In this study, we develop and implement a method for superimposing two vibration modes in order to produce different tactile stimuli on two fingers located in different positions. The tactile stimulation is based on the squeeze film effect which decreases the friction between a fingertip and a vibrating plate. Experimental test have been conducted on a 1D tactile device. They show that it is possible to continuously control the friction on two fingers moving independently. Then, we developed the design of a 2D device based on the same principle, which gives rise to the design of a two-fingers tactile display. Evaluations were conducted using a modal analysis with experimental validation.

Ultrasonic vibrations of a plate can modify the perception of the friction between a surface and a sliding finger. This principle, coupled with modern position sensing techniques, is able to reproduce textured materials. In this paper, an open loop control through model inversion of the friction force between the finger and the plate is presented. The device incorporating the control system is described, and two different reproduction strategies are formalized to address the reproduction of objects and textures. In the end, a psychophysical experiment evaluating the two control strategies is described.

Among human senses, touch is much less understood than hearing or sight. However, today, new emerging technologies are placing tactile interaction at the heart of the communication with smart devices (smartphones, tablets,…). Hence, studying the sense of touch is now very important, in order to better understand the mechanisms induced from the mechanical excitation of skin to the feeling experienced by a user. Also, being able to detect and measure tactile disabilities, and to propose rehabilitation is a challenge; otherwise, numerous people can drift away from these objects as they can't be used easily by them. In the paper, we present Dtact, a device which stimulates the finger pulp with a calibrated stimulation. It is designed to be used during experimental studies aiming at recording nerves and brain activity of a user touching its surface. It will be used to detect tactile disabilities …

The PAD motor has remarkable abilities for ultra-precise positioning at very low speed. Recent works have shown the possibility to extend its speed range, but some challengess remain such as pull-off. This paper proposes a model that highlights the parameters of the voltage supply that act on the torque and the contact, and can be used for control. Experimental results demonstrate the role of higher vibration modes, and show that typical signature of the imminence of pull-off can be detected thanks to some of the harmonic of the displacement of the actuators, giving some indications on means to address this problem.

In this paper, the control of the vibration amplitude of a Langevin transducer is obtained simultaneously with the tracking of its resonant frequency. Vector control method is applied to achieve this. The result of this study is illustrated with experimental and simulation results.

The present study investigates the implementation of a closed loop control in a new smart tactile stimulator called “SMARTTAC”. This haptic device is able to stimulate the fingertip in order to simulate the texture perception of different real surfaces such as gratings. Two closed loop control are implemented to ensure both a stable vibration amplitude despite of external disturbances and accurate control of the friction coefficient using the new design of the tactile stimulator. Experimental measurements give satisfactory results both on dynamics and robustness points of view.

This paper presents a method to control ultrasonic waves on a beam, allowing to obtain a Multi-touch ultrasonic tactile stimulation in two points, to give the sensation to two fingers, from two piezoelectric transducers. The multi-modal approach and the vector control method are used to regulate the vibration amplitude, in order to modulate the friction coefficient with the fingers. An analytical modelling is presented, with experimental validation. Finally a psychophysical experiment shows that a multi-touch ultrasonic tactile stimulation is possible.

The control of the vibration amplitude, and the resonance frequency tracking for ultrasonic transducer have been established. However, some applications require to control the vibration amplitude and its relative phase at a fixed frequency as the generation of travelling wave. In this paper, the transducer is modelled in rotating frame, and the decoupling according to two-axis allows to obtain a double independent closed loop control to address this issue. It is possible to control the transducer vibration amplitude and its relative phase, in steady state even in transient by acting on the amplitude of the supply voltage. Thanks to vector control method. This approach will be confirmed with experimental and simulation results.

Ultrasonic vibrating devices are able to modulate the friction of a finger sliding on them. The underlying principles of the friction reduction are still unclear, and this work is carried out to investigate the influence of the ambient pressure on the friction modulation. A specific tactile stimulator has been used for this purpose and the friction between the finger sliding on the device has been recorded for an ambient pressure of 0.5 and 1 atm showing a significant difference for comparable experimental conditions. A comparison with the model proposed in literature is performed underlying that the squeeze film interaction can be present but not the only responsible of the friction modulation in this kind of devices.

This paper presents a new method to produce and control the vibration amplitude and direction of a travelling wave in a finite beam, using multi-modal approach. A closed loop control of the transducer vibration is applied using vector control method. the modelling in rotating frame and the decoupling according to two-axis allows to obtain a double independent closed loop control. This allows to regulate the vibration amplitude of the travelling wave directly. An analytical modelling is presented, with experimental validation, showing good performances even in the presence of perturbations.

Electrostatic attraction, may be used to modulate the apparent friction coefficient between two surfaces. Applied to the human finger and a polarized interface, the principle can modify the user perception of the interface surface. Especially, the feeling is relevant when electrovibration occurs, which is a dy- namic excitation of the surface. In this paper, the different steps towards the modelling of the electrovibration phenomenon are developed. An investigation on the current modelling will be carried on, with a focus on the temporal evolu- tion and frequency dependence of the stimulus. Thus, an improvement of the modelling will be proposed to take into account this major effect. Then, this new modelling is checked with an experimantal set-up.

This paper presents a method for controlling the vibration amplitude of a tactile stimulator used to give the sensation to the fingertip that it touches a texture. The active surface of the stimulator is excited by an ultrasonic vibration frequency in order to modulate the friction coefficient with the fingertip. Due to the large size of the tactile display, two types of perturbations may affect the vibration amplitude which are the finger pressure and the temperature variation. We tackle these problems by coupling the control of the vibration amplitude and the tracking of the resonance frequency. This work is validated by plotting the vibration amplitude response with closed loop control and with a psychophysical test.

The paper presents a serial architecture of an actuated manipulator which uses an ultrasonic motor. The serial architecture allows to modify the kinetic relationship between user’s input and a tool. The design of the device is presented. A load, which exhibits fine details, is used in order to show how a zooming effect of its haptic rendering can be achieved with the haptic magnifier. Finally, the design is validated through an experimental analysis.

Friction reduction based tactile devices use an ultrasonic vibration to create an overpressure between a user’s fingertip and the vibrating surface. This phenomenon is called "the squeeze film effect". This is an emerging technology to produce a haptic feedback on the touchscreen of handheld electronic devices. In this paper, we present the technology and the main technological issues to be improved.

We study the effect of feedback on an energy harvester for broadband applications. Using modal analysis we show that it has an influence on modal shape as a side effect of the resonance shifting. We show that the piezoelectric coupling can thus be reduced. Experimental results are in agreement and also reveal that non-linear effects are promoted in some cases.

This paper deals with an one-dimensional semi-analytical modelling of the vibratory behaviour of a rectangular beam excited by several piezoelectric ceramics glued on its lower face. The establishment of the equations of motion is guaranteed by the application of Hamilton’s principle. From this approach, it results an accurate knowledge on the mode shape in function of the geometry, the structure and the positions of the piezoelectric actuators. This approach deployed on a simple case falls within a general process of the tactile surfaces optimization. This article shows that there is a trade-off between the optimization of the homogeneity of the tactile stimulation and the electromechanical coupling factor.

This paper presents a new powder transportation system that uses a high frequency flexural stationary wave coupled with a low frequency horizontal displacement of a beam to produce the transport of the powder. The ultrasonic wave is produced with the help of piezoelectric cells glued under the beam and is used to decrease the friction coefficient between the powder and the beam surface. The powder transport mechanism has been described using a simplified mathematical model.

This paper deals with the control of a haptic device which is used in a generator mode to produce electricity from a user’s walking movements in a handheld device, like a mobile phone for instance. We first present the design principle of such a device. Then, a design is presented, which allows haptic feedback and energy harvesting to be produced with a same device. It is based on a piezoelectric plate actuator. A causal modelling of the system is then developed, and inverted in order to obtain the key control algorithms. Compared to other energy harvesting system, HarTic is characterized by some interesting features like the accelerometer which is now embedded into most mobile phones, and its measurement can be used in the energy harvesting strategy. Our simulations show that 2mW can be harversted in our case study.

In this paper, we propose a power supply for piezoelectric actuators that can generate arbitrary waveforms at frequencies ranging from low to medium frequency. The actuators are used in a forging process and require high voltage. The converter is based on an original combination of a boost DC-DC converter and a rectifier circuit, thus reducing the number of components needed. Moreover, no transformer is required. Experimental results on a single and three phase version are presented and validate the proposed converter.

Electrovibration and squeeze film effect can modify the perception a user has of a flat surface. These two stimulation principles are compatible, which means that they can be used at the same time on the same tactile stimulator. This paper first highlights the differences between the two principles, then gives experimental results obtained when merging, with specific conditions, these two stimulation principles.

This paper presents a new powder transportation system that uses a high frequency flexural stationary wave coupled with a low frequency horizontal displacement of a beam to produce the transport of the powder. The ultrasonic wave is produced with the help of piezoelectric cells glued under the beam and is used to decrease the friction coefficient between the powder and the beam surface.

This paper presents a study about a tactile stimulator based on the “squeeze film air bearing”, and which could be used in a hand-held device. First, we analyze power consumption of tactile feedback provided with our stimulator, since battery life of hand-held device is critical. Then, we present a new design of a transparent tactile device which allows co-localized operations.

This paper presents the design of a transparent tactile stimulator, based on the friction reduction between the fingertip and the active surface. With such a design, the ratio between the useful area (i.e. the active display and the tactile area) and the device face is equal to 0.7, while the touched area’s size is 93mm×65mm. Key design procedure is given, and experimental results are presented.

Haptic perception of curvature can be achieved by passive or active finger touch. In this study we proposed a new curvature perception haptic device that can independently orient, elevate and translate a flat plate. By exploring it with a finger through active touch, we can render a curved shape. According to the characteristics of this device, two curvature rendering motion models were analyzed: motion model without compensation and motion model with position compensation. Two experiments were then executed. Experiment 1 has verified that our device is able to produce distinct curvatures. Experiment 2 has compared the performances obtained with each motion model during the tasks of curved shape discrimination.

This paper presents a haptic interface actuated by a Traveling Wave Ultrasonic Motor (TWUM). First, we detail a one degree of freedom force-feedback device on which control laws are tested. Then the control strategy is presented. It relies on a modeling of the motor which is inverted in order to reach the control laws. We present a strategy to attain good behavior when the lever rotates at low rotational speed. Moreover, a virtual environment is described. It is is made of a spring and walls. A specific way to simulate walls which takes advantage of TWUM is shown. Finally, experimental results are presented.

This article shows that using a piezoelectric motor in a mecatronic system, the thermal management is not an issue, as for conventional electromagnetic motors. We then show that choosing a motor on the maximal velocity or force/torque required in the application is not sufficient,and the motor selected may not be able to perform the motion profile. We then propose a selection procedure based on the maximal mechanical power required for the application.

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This paper describes design improvements of a friction reduc- tion based tactile device, which yields to reduction of the supply power. We rst evaluated the power consumption of four dierent plates. We found that a convenient design could cut the power losses down by 90%. To explain these changes we propose a modelling of the dielectric losses in the piezoelectric actuators and of the vibration amplitude.

In the domain of haptics, the sensation of touch is normally classed into two types: tactile and kinesthetic. Correspondingly, the haptic display can also be divided into two categories: tactile display and kinesthetic display. The two aspects are commonly addressed separately, but life experience has shown that this is not intuitive and not effective. Therefore, it is a significant work to couple the tactile display and the kinesthetic display. In this paper, we propose a new design of haptic display coupling tactile and kinesthetic feedback for rendering spatial texture (tactile) and haptic shape (kinesthetic).

In this paper, we propose an actuator of 64x38x3 mm comprising polarised piezoceramics glued on a copper-beryllium plate supported by four feet. By controlling the drive voltage, we vary friction force perceived by a user who displaces the device, as he could do with a usual mouse. This adds the possibility to render simulated force from objects manipulated on a PC screen. Results from a psychophysical study conducted as preliminary evaluation demonstrate the availability of the proposed device for force feedback application.

This article presents the design of a new tactile stimulator which is able to make a user feeling the sensation that he’s touching a programmable textured surface. In a first section, the principle of the interaction between the device and the finger is presented. Then, we describe the design of the stimulator which is made up with a layer of piezo-ceramic bonded on a copper plate. Experimental run are presented.

Piezo-electric actuators provide interesting properties accounting for their high torque-weight ratio, and low speed operating modes. Nevertheless, their control is difficult to achieve and it is then necessary to develop an accurate modelling of the physical phenomena involved. This paper focuses on a typical TWUM USR 30 from Shinsei®. After a physical analysis, the causal ordering graph of the actuator is established, taking into account mechanical non linearity’s. Then, according to the principle of inversion, the control structure is deduced. Simulation and experimental results are compared and show the accuracy of the proposed modelling.

In this paper, we investigate the use of friction based tactile displays for the simulation of finely textured surfaces, as such displays offer a promising way for the development of devices with co-located vision and tactile feedback. The resolution of the textures rendered with such devices and their matching to real textures have never been investigated. The paper first contributes to the evaluation of the texture resolution of friction based tactile displays. In a controlled experiment, we investigate the differential thresholds for square gratings simulated with a friction based tactile device by dynamic touch. Then we compare them to the differential thresholds of real square wave gratings. We found that theWeber fraction remains constant across the different spatial period at 9%, which is close to the Weber fraction found for corresponding real square gratings. This study inclines us to conclude that friction based tactile displays offers a realistic alternative to pin based arrays and can be used for co-located vision and tactile rendering. From the results of the experiment, we also give the design guidelines to improve the perception of textures on friction based tactile displays.

Using Piezo electric actuators can reduce bulk size of servomechanisms; they are thus very interesting in avionics applications. But mechanical overload on shaft of a traveling Wave Ultrasonic Motor often results in a sudden stop and stalling of the motor. To avoid this drawback, one can increase the supply voltage or add a control loop in the rotating reference frame of the traveling wave. The consequences are extra power losses or lower dynamic performances. The proposed method takes advantage of classical control and in a rotating frame one : stability and dynamic performances are obtained at low supply voltage level. Experimental runs are presented.

The Energetic Macroscopic Representation (EMR) has been developed in 2000 to develop control of systems with several drives. Since 2002 this graphical tool has been introduced to teach drive control in France, then Canada and Switzerland. The University of Lille proposes two drive control units for students in electrical engineering: initiation level and expert level unit. This first paper deals with the content of the initiation level unit and describes the simulation project of an electrical vehicle using EMR.

Ultrasonic transducers can be used to control friction. In case of a haptic texture actuated and explored simultaneously with the bare finger, this technology allows to reduce perceived roughness. In this article, we investigate its use to understand determinants of friction at contact. In the literature, a researcher recently suggested that microtexture perception was mainly determined by an interaction determinant: the commensurability of its asperities with epidermal ridges. In this paper, we levitate the skin with an air gap and thus cancel shear forces at contact. Results show that more important amplitude of vibration of the actuator is necessary to suppress friction at contact area when a directed movement is done along the epidermal ridges than across. This suggests that tactile perception of texture really depends on the bearing forces exerted by the surface on the skin.

Properties of the travelling Wave Ultrasonic Motor (TWUM)-among which we find a high-torque to mass ratio, locking without supply, ultrasonic operation - are very attractive for embedded application, such as human prothesis for example. But unfortunately, its control for high precision or high dynamic motion is not easy to achieve because of many non linearities induced by its particular energy conversion process. This is why this paper deals with the modelling of a TWUM, based on a physical causal approach. According to the inversion principle, control strategies are deduced as well as a novel torque estimation structure. A mechanical claw control using this torque estimator is then achieved and experimental results check the accuracy of the proposed control scheme.

A travelling Lamb wave tactile display has been developed. To indicate smooth or braking sensation, the device is controlled in order to impose the relative speed between the finger and the wave, so that a variable shear force appears on the fingerpulp. Moreover, at low frequency, an amplitude modulation of the travelling Lamb wave is achieved so as to excite alternatively shear forces on the surface of the substrate; according to the finger’s speed. Using a stator of a travelling wave motor (Shinei USR60) with a linear position sensor, users can enjoy various textures. A comparison test has been carried out and shows good percentage of correct recognition for specific rough textures.

This article presents basic force feedback operations with a travelling Wave Ultrasonic Motor. First, we show how to simulate low stiffness springs. Then, we propose a new method to simulate walls that profits from the holding torque of TWUM. Experimental results are presented on a 1dof test device.

Piezo-electric travelling Wave Ultrasonic Motors have a high torque to mass ratio compared to classical electromagnetic motors. This is why they fit well in applications where a high torque at low speed is required since they don’t need speed reducer. Using them in force feedback devices is an issue but can provide significant reduction of bulk size of the system by removing pulleys and belts. However, the non linearity of the motors ?mostly located at the stator/rotor interface ?complicate matters; an improved control scheme is then necessary to achieve the required performances of the device.

This work concerns the design of piezoelectric travelling wave actuators for haptic application. The approach presented here deals with the design of a tactile device based on the creation of lateral stretch under the fingerpulp. With a first device, it is shown how the Lamb wave tactile display can produce several distinct sensations according to the finger’s speed. To indicate smooth or braking sensation, the device is controlled in order to impose the relative speed between the finger and the wave, so that a variable shear force appears on the fingerpulp. Moreover, at low frequency, an amplitude modulation of the travelling Lamb wave is achieved so as to excite alternatively shear forces on the surface of the substrate according to the finger’s speed. Then, a linear travelling wave actuator, whose dimensions are adapted to touch gesture in active touch condition, is designed considering the previous study.

A precise position control of a Travelling Wave Ultrasonic Motor is achieved, avoiding the traditional drawbacks attributable to the non-linear torque generation: overshoot or slow response time. For that purpose, a behavior model control is proposed and presented. With this control law, a quick and precise response is obtained. In this article, we present a position control scheme of an inertial load. The guidelines to that control was a rotation of 90° in a response time of about 300ms with a position error of 0.6mrad, targeting a typical application for avionics. In the paper, a shinsei USR30 is used, but the method can be applied to other Ultrasonic Motors.

Travelling Wave Ultrasonic Motors are piezo-electric actuators that can produce high torque at low rotational speed. But because of the contact between stator and rotor, the torque on the shaft is not easy to impose: speed or position control are difficult to achieve, especially when a load torque is applied. The aim of this article is to set down a robust position control besides the external load torque. The scheme relies on a modelling already detailed, which parameters are first identified.

An original modelling of a travelling wave ultrasonic motor is established in order to provide a new torque control law for this kind of actuator. Especially, self-control is implemented, avoiding the classical drawbacks of frequency control, that is pull-out phenomenon. With such a robust control, force feedback application is available. Experimental results are obtained on an active haptic stick.

Even thought Travelling Wave Ultrasonic Motors use an other way of energy conversion than electromagnetic machines, the inversion of the Causal Ordering Graph of a simplified modelling, based on the assumption of the “ideal rotor”, highlights the need of a self driving of the actuator, in the same way of the classical synchronous machine. This self driving is then experimentally tested on a force feedback stick, because this application needs high torque and low rotational speed.

The aim of the present communication concerns the motorization of an electro-active artificial hand (motorization of the wrist and grasping capacities). The study presented here deals with the feeding and control of a rotating mode motor which ensures the necessary mobility of the prosthesis.

The paper proposes a model of a piezoelectric TWUM adapted to its control. The model described by a Causal Ordering Graph is first established using the amplitudes of the two stationary waves. Transient operations and steady state points check the validity of the model. A control scheme is then proposed in a rotating reference frame.

Pressure ulcers are a concern not only for the patients who suffer from them, but also for public health. Its costs to the quality of life of patients and to the public finances can be reduced with an early diagnostic. Several efforts have been made to find a solution for this diagnostic, for example by analysing the hydration or the electrical impedance of the skin. So far, no method is sufficiently reliable. In this context, a low-frequency ultrasound device is proposed, with the aim of offering an alternative that can be reliable and non-invasive. The Langevin transducer is a highly efficient device that can provide a measurement of the mechanical characteristics of the skin. Initial results show that mechanical impedance can discriminate the skin according to the location of the measurement.

Ultrasonic vibrations are used to modulate the friction coefficient between a sliding surface and the vibrating object. In this paper an ultrasonic travelling wave is used to modulate the friction accordingly to the direction of motion of the finger. In its propagation direction, the travelling wave applies a net force on the sliding body reducing the friction whereas in the other increases it. The ability to obtain an asymmetric friction coefficient in function of the motion direction has made possible to induce different sensation on the finger accordingly to the controlled direction of travelling wave.

L’électrovibration et l’effet squeeze film produits respectivement par un champ électrostatique et par vibration ultrasonique, sont deux principes de stimulation tactile permettant de modifier la sensation de toucher d’un utilisateur explorant une surface plane. Le présent article s’attache à démontrer leur compatibilité sur un même stimulateur tactile lors d’une utilisation concomitante. Une description du principe physique et des spécificités de chacun des phénomènes sera entreprise et les résultats expérimentaux obtenus lors de leur association seront par ailleurs présentés.

Résumé Tactile stimulation is used in the rehabilitation of damage to the central or peripheral nervous system and in brain injury recovery. Tactile deficits of the hand are currently diagnosed through the evaluation of pain thresholds, spatial discrimination, vibration sensitivity and by using filaments or tuning forks, without truly established protocols. The global goal of the COSTaM project is to develop a tactile stimulator to identify tactile disorders and allow specific rehabilitation. The first step is to study the response of healthy individuals to complex textures in different ways: perceptive discrimination, study of friction and vibration between textures and the finger and the response of each kind of cutaneous mechanoreceptor. Three kinds of real textures have been chosen: relief, braking and fibrous. The use of a tactile stimulator, based on the modulation of the coefficient of friction.

L’objectif est de proposer un effecteur tactile capable, dans le futur, de simuler le rendu tactile de surfaces complexes et multi-échelles type textiles. Une surface textile est particulièrement difficile à simuler du fait de la présence d’une pilosité de surface. Quatre critères tribologiques relatifs aux étoffes velours ont été identifiés. Quatre signaux de commande de l’effecteur tactile ont donc été générés prenant en compte de un aux quatre critères tribologiques. Ces simulations ont été proposées à des sujets humains et il ressort que la simulation qui prend en compte les quatre critères est la plus proche de la surface d’un velours. L’énergie que peut transmettre au doigt la pilosité par retour élastique lors d’un changement de direction ainsi que l’enfoncement dans la surface ne sont pas encore considérés.

Cet article montre dans un premier temps que le décalage des ondes stationnaires d’un moteur piézoélectrique à onde progressive n’est pas obtenu systématiquement par le décalage des tensions d’alimentation. Dans un deuxième temps, un contrôle de ces tensions d’alimentation est proposé qui aboutit au décalage souhaité des ondes stationnaires.

Dans cet article, nous présentons un dispositif capable de stimuler la pulpe du doigt de manière paramétrable. Ce dispositif exploite le « squeeze film air bearing », qui modifie l’interaction entre le doigt et la surface en contact du stimulateur. Un modèle de l’interaction doigt-surface est d’abord présenté. Il permet de déterminer des recommandations de design nécessaires à la conception du dispositif. Puis nous montrons la méthode de dimensionnement, et des tests psychosensoriels permettent de valider l’approche.

Dans cet article, nous présentons la conception d’un amplificateur linéaire à bon rendement pour l’alimentation d’un moteur piézo-électrique en laboratoire.

L’étude présentée traite de la commande en couple et en vitesse d’un moteur ultrasonique à onde progressive. La stratégie de commande découle d’une analyse du modèle ici présenté à l’aide du formalisme des graphes informationnels causaux ( GIC ). Compte tenu des informations disponibles sur le moteur, une commande en phase est alors élaborée et mise en oeuvre. Des résultats expérimentaux viennent illustrer la démarche.

L’étude présentée traite de la commande en couple et vitesse d’un moteur ultrasonique à onde progressive. La stratégie de commande découle d’une analyse du modèle ici présenté à l’aide du formalisme des graphes informationnels causaux (GIC). Compte tenu des informations disponibles sur le moteur, une commande en phase est élaborée, des résultats de simulation et expérimentaux sont présentés.

The invention relates to a touch interface comprising, on the one hand, an interfacial surface able to generate a haptic-feedback effect in response to a touch of said surface by a user, and, on the other hand, at least one piezoelectric actuator configured to generate, in said interfacial surface, at least one wave of ultrasonic frequency able to endow the particles of this surface with an elliptical movement having a movement component tangential to said surface, which component is denoted ut(t), and a movement component normal to said surface, which component is denoted un(t), wherein said wave of ultrasonic frequency is chosen so that the amplitude Ut of the tangential component ut(t) and the amplitude Un of the normal component un(t) are substantially equal.

A system includes sensor-actuator units fixed onto a plate to be actuated according to at least one predetermined vibratory mode, each sensor-actuator unit having an electromechanical actuator and a deformation or vibratory speed sensor, wherein the electromechanical actuator and the sensor are colocated on the surface, that is to say that the measurement by the sensor is performed in immediate proximity to the electromechanical actuator, this proximity being such that the actuator and the sensor can respectively actuate and measure the same predetermined vibratory mode.

Procédé pour générer au moins un motif tactile avec un dispositif à retour tactile (70) ayant un espace actif au sein duquel un utilisateur peut déplacer son doigt (F) pour ressentir le motif tactile, la perception du motif étant provoquée par la modulation de l’excitation mécanique de la pulpe du doigt par un élément excitateur, le procédé comportant les étapes consistant à : - détecter la position du doigt (F) dans l’espace actif; - calculer la vitesse du doigt, - déterminer pour chaque position du doigt détectée un taxtel associé au sein d’une grille de taxtels prédéfinie, chaque taxtel ayant une valeur de texture associée qui dépend du motif tactile à reproduire, chaque taxtel étant de plus grande dimension inférieure ou égale à 8 mm, - générer en fonction de la valeur de texture associée à ce taxtel un signal de commande de l’élément excitateur, ce signal d’excitation étant dépendant de la vitesse du doigt au moins pour les motifs tactiles les plus denses à reproduire.

L’interface tactile (1) comporte : - une structure vibrante (2) comprenant une plaque (20) dont l’une (20a) des faces forme la surface de contact vibrante de l’interface destinée à être en contact avec le doigt d’un utilisateur, et une couche piézoélectrique (21) fixée contre l’autre face de ladite plaque, et - des moyens d’alimentation électrique qui sont connectés à la couche piézoélectrique (21). La plaque (20), la couche piézoélectrique (21) et les moyens d’alimentation électrique sont adaptés pour générer dans la structure vibrante (2) des ondes de Lamb stationnaires ayant une direction de propagation suivant au moins un axe rectiligne. L’interface tactile permet de reproduire tactilement des textures ou rugosités très fines, en modifiant la sensation tactile de toucher de la surface de contact (20a), et en modulant l’effet « Squeeze film ».

Dispositif pour la création de sensations haptiques sur une surface à l’aide d‘ondes ultrasonores produisant des mouvements elliptiques

Causal Ordering Graph and Energetic Macroscopic Representation are graphical descriptions to model electromechanical systems using integral causality. Inversion rules have been defined in order to deduce control structure step-by-step from these graphical descriptions. These two modeling tools can be used together to develop a two-layer control of system with complex parts. A double-drive paper system is taken as an example. The deduced control yields good performances of tension regulation and velocity tracking.

This chapter presents a preliminary overview of the state-of-the art in the field of piezoelectric actuators. Starting from the material, and describing its manufacturing process, we present several ways to exploit the energy conversion in order to obtain the displacement of a mechanical load. The basic principles of some widely used piezoelectric actuators and motors are presented, and illustrated with typical applications. The chapter also discusses the variability of the operating point of the piezoelectric actuators, and explains why a closed-loop control is needed. The chapter ends with the basics of the control theory, which are used in later chapters to design controllers.

Classical synchronous motors are the most effective device to drive industrial production systems and robots with precision and rapidity. However, numerous applications require efficient controls in non-conventional situations. Firstly, this is the case with synchronous motors supplied by thyristor line-commutated inverters, or with synchronous motors with faults on one or several phases. Secondly, many drive systems use non-conventional motors such as polyphase (more than three phases) synchronous motors, synchronous motors with double excitation, permanent magnet linear synchronous motors, synchronous and switched reluctance motors, stepping motors and piezoelectric motors. This book presents efficient controls to improve the use of these non-conventional motors.

Les moteurs piézo-électriques à onde progressive, grâce à leur caractéristique fort couple – basse vitesse et leur faible encombrement, proposent une alternative intéressante aux machines électromagnétiques dans les systèmes automatisés. Cependant, leur structure vibrante et les caractéristiques tribologiques complexes à l’interface stator-rotor les rendent difficiles à commander. C’est afin de déterminer les lois de commande adaptées que nous avons d’abord modélisé de manière causale le moteur. Nous avons discuté de la pertinence de ce modèle, soit par comparaison avec un modèle plus complexe et plus précis, soit expérimentalement par des relevés sur un moteur commercialisé. Cette modélisation a conduit d’une part à l’élaboration d’un protocole d’identification des paramètres du moteurs insensible aux non linéarités inhérentes aux matériaux piézo-électriques. D’autre part, le Graphe Informationnel Causal, utilisé pour la représentation du modèle, a permis, par son inversion, l’établissement des lois de commande. Nous avons alors été capables d’établir plusieurs stratégies d’autopilotage originales; nous n’en avons retenu qu’une, qui a été mise en oeuvre sur un banc expérimental. Cette commande a été testée sur un dispositif à retour d’effort, application à très basse vitesse pour laquelle un contrôle précis du couple est nécessaire.