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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.

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.

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.

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.

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.

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.

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.

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.

Les dispositifs à retour tactile sont utilisés pour créer un retour sensoriel à leurs utilisateurs. Par exemple, il est possible de reproduire sous le doigt l'illusion de surfaces texturées par le contrôle de la friction entre une surface mise en vibration et le doigt de l'utilisateur parcourant la dalle. Pour la plupart de ces dispositifs, le principe de base consiste à utiliser un mode de résonance dont la fréquence et la forme sont imposées par la nature du matériau et la géométrie du dispositif. Le mode est sélectionné pour réaliser une stimulation homogène, et de ce fait elle est indifférenciée sur l'ensemble de la surface. En regard de certaines applications demandant une information plus variée, c'est un facteur limitant. On propose dans ce travail de thèse une nouvelle approche, basée sur la superposition de plusieurs modes de vibration. Les modes sont excités simultanément pour réaliser des déformées plus complexes et modulables, afin de générer une simulation à retour tactile multitouch. Cette approche a été validée pour le cas d'une poutre où deux modes de vibration ont été superposés pour générer une simulation tactile différenciée sous deux doigts, grâce au contrôle vectoriel de deux actionneurs piézoélectriques. Un système de suivi a été implémenté pour donner une illusion multitouch en fonction de la position des deux doigts. Cette approche multimodale a été ensuite étendue au cas d'une plaque mince où différentes distributions spatiales du déplacement ont été imposées, ce qui provoque différents coefficients de frottement sur toute la surface de la structure. L'approche développée dans ce travail nous a permis également de générer et de contrôler une onde progressive en amplitude et en direction. Pour cette raison, nous avons évalué l'intérêt des ondes progressives dans les interfaces tactiles. Les résultats ont montré la possibilité d'obtenir deux sensations différentes selon la direction contrôlée de l'onde progressive. Les évaluations psychophysiques des dispositifs proposés montrent clairement l'intérêt d'exploiter plusieurs modes de vibration pour une simulation à retour tactile.