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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. [Display omitted] • Simultaneous sensing of force and displacement at the tip of the piezoelectric bender. • Complete hysteresis modeling for piezoelectric actuators under voltage and force excitations. • Force sensing improved with two hysteresis compensation strategies. • Closed-loop displacement control is possible, attributed to the accurate displacement sensing. • Applications to in vivo skin measurements. [ABSTRACT FROM AUTHOR]

Highlights • Typically, transverse modes are used. This article explores the validity of using longitudinal modes. • A design is proposed to compare the performance of longitudinal modes and compare them to transverse modes. • To do this a device is designed. To produce the motion, piezoelectric ceramics are used. • Closed loop amplitude control of the vibration is implemented. • Longitudinal modes perform better than transverse modes at higher amplitudes. [Display omitted] 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. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • The development of a diagnostic sensor for skin mechanical impedance is presented. • Results for a test of reproducibility of the measurements are analysed. • Tests show the device developed can distinguish skin mechanics in different sites. • Measurements of skin hydration are made and crossed with the acoustical mechanical impedance. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A new stimulation principle to render haptic feedback. • A closed loop controller that synchronizes the vibration of 2 plate's modes. • An original methodology to estimater system's parameters. • A theory that is confirmed by experimental measurement. [ABSTRACT FROM AUTHOR]

Highlights: [•] The design and the fabrication of a haptic knob. [•] The presentation of a position sensor based on force measurements with 3.6° accuracy. [•] The modeling and the control of the vibration amplitude. [•] The psychophysical experiment showing how haptic can increase user's accuracy in a pointing task. [ABSTRACT FROM AUTHOR]

Abstract: 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 25kHz, 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 (0.5mm) at the minimal frequency of 25kHz. 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]