P. Le Moal

Optimization of travelling wave ultrasonic motors using a three-dimensional analysis of the contact mechanism at the stator–rotor interface

Abstract The present paper investigates optimization rules and new design methodologies dealing with the contact mechanics in rotative travelling wave ultrasonic motors (TWUM). The proposed approaches focus on the design of the rotor, including the friction layer that is usually deposited onto its lower surface, while the stator is supposed to be preliminary designed. Contact aspects such as the transmission of mechanical power as well as the wear mechanism of the friction layer are investigated, according to the analysis of the stator–rotor contact mechanics in both hoop and radial directions. Considering a classical wear criterion in a preliminary step, a contact ratio, that allows the mechanical power to be optimized, is pointed out in the hoop direction. In a further step, the contact conditions in the radial direction are improved through the elastic fitting of the stator and rotor radial deflexions, therefore allowing the materials wear to be decreased. Some experimental tests, that have been recently performed, give a comparison of wear marks, which occur onto optimal and non-optimal rotor geometries. A first mechanism synthesis is finally proposed in such a way to allow the mechanical architecture of the rotor (including the friction layer) to be automatically designed according to a given set of mechanical constraints.

Evaluation of creep compliances of unidirectional fibre-reinforced composites

Abstract In this paper, a method is proposed for the determination of the viscoelastic behaviour of unidirectional fibre-reinforced composites. The method is based on the model of Laws and McLaughlin. The interface problem is taken into account by using anisotropic elastic coefficients for the fibre. The non-linearity of the matrix is also considered and integrated in the model. Comparisons with experimental data are performed on glass/epoxy materials.

New multi-degree of freedom piezoelectric micromotors for micromanipulator applications

The authors have developed new multidegrees of freedom (d.o.f.) piezoelectric micromotors using both stationary bending modes and traveling wave technology. These devices are respectively based on the conversion, through frictional contact, of bending vibrations sustained in one or several vibrators into rigid body displacements of a moving element. They have allowed the design and the development of a micromanipulator with five degrees of freedom composed of stationary wave type linear translators (2 d.o.f.) and traveling wave type spherical micromotors (3 d.o.f.). These two motors can be driven reversibly in both directions with linear speeds between one mm. s/sup -1/ and few cm. s/sup -1/. The paper shows however that micrometer steps can be activated for micropositioning applications without displacement limitations.

Realization and Control of Autonomous Microconveyors with Piezoelectric Actuators

Abstract This paper deals with the development of centimeter size robots for tasks of conveying and positioning. Their advantages are their multi-degrees of freedom, their nanometer range of positioning. The displacements of the robot are realized with a system of piezoelectric resonator. The directions of displacement depend on the frequency of the input voltage and the characteristics of the mechanical structure. The major difficulty to steer the nanopositioner is to control the direction of the movement. To realize this operation, we have to control the input frequency by using the PZT modules as actuator and sensor

Dynamic characteristics of circular CMUTs with air-filled cavities

Our work deals with the study of the dynamic characteristics of a single circular CMUT transducer under squeeze film damping effect. A simplified analytical approach is developed for parallel plate approximation for the electromechanical behavior and the squeeze film damping. Analytically calculated results demonstrates, that trends of resonant frequency with bias voltage are defined by the ratio of air spring constant to mechanical spring constant. At the same time FEM multiphysics model is built to define the influence of membrane flexibility and venting boundary conditions to the dimensionless viscous and elastic damping forces. FEM study shows the presence of viscous loss in the sealed air-filled cavity and the insensitivity of squeeze film damping forces to the type of lateral venting boundary conditions in high squeeze number region which is typical for CMUT operation. Finally, the experimental dynamic characterization is conducted on CMUT with 67 μm - 167 μm radii fabricated utilizing an anodic bonding technology. Experimental data are in a good agreement with the results of multiphysics FEM calculation, which take into account bias voltage, initial plate deflection, radiation loss and squeeze film damping.

A Two-Degrees of Freedom Speed Control of a Revolving Travelling Wave Piezomotor

Abstract A newly-developed servo-control system using two feedback control loops based on sensorless technique have been demonstrated by the authors. The schemes using an instantaneous control and average value control processing strategies are based upon loadadaptative resonant frequency and constant velocity amplitude schemes. Its control schemes are theoretically considered and its experimental results are demonstrated and evaluated in practice.