Patrice Minotti

High-performance load-adaptive speed control for ultrasonic motors

Abstract High-performance servo-control schemes using ultrasonic motors (USMs) as new actuators have not yet been applied in practice in modern industry and office-automation systems, because the dynamic and steady-state modelling of USMs is extremely difficult from the theoretical point of view. In the first part of this paper, the rotational speed-control characteristics of a circular travelling wave motor are theoretically analysed and experimentally explored by using an experimental measuring system. In the second part, a newly-developed servo-control system using two feedback control loops based on a sensorless technique is described. This technique, using strategies for both instantaneous control and average value control, is based upon control of both the load-adaptive resonant frequency and a constant velocity. These control schemes are considered theoretically, and experimental results are demonstrated and evaluated in practice.

CONTROL OF A MULTIDEGREE OF FREEDOM STANDING WAVE ULTRASONIC MOTOR DRIVEN PRECISE POSITIONING SYSTEM

A newly developed positioning system incorporating a multidegree of freedom standing wave ultrasonic motor (SWUM) is presented and its advantageous features, operating principles, and some experimental results are described. The principle of motorization is based on the conversion, through frictional contact, of a stationary bending vibration sustained in a slotted metallic resonator, into rigid body displacements. A small autonomous multidegree of freedom nanopositioner using a SWUM motor is presented for fine positioning in scanning tunneling microscopy. The positioning system is achieved via the simultaneous operation of two identical pulse width modulation servo-control systems, each having a laser vibrometer position feedback loop. The closed loop position schemes are theoretically considered and their results are demonstrated and evaluated in practice. Evaluations of experimental tests indicate that a positioning resolution less than 100 nm are successfully achieved for an unlimited X−Y travel range...

Design and Characterization of High-Torque/Low-Speed Silicon Based Electrostatic Micromotors Using Stator/Rotor Contact Interactions

Capabilities of future direct-drive electrostatic actuators are investigated through the mechanical characterization of annular-type polysilicon micromotors. Contact interactions are provided at the stator/rotor interface in order to allow high integrated speed reduction to be performed. The driving torque is therefore considerably amplified, as a consequence of the torque/speed duality. Direct torque measurements are performed through a self-adjustable torque sensor that is integrated in the polysilicon rotor. The first experimental results presented here give rise to the expectations of numerous direct drive applications down to the micrometer scale.

Micromachined Traveling Wave Motors: Three Dimensional Mechanical Optimization and Miniaturization Limits Evaluation.

This paper concerns a physical limits evaluation with respect to the miniaturization of traveling wave type ultrasonic motors (TWUM) down to the millimeter scale. According to present knowledge in research dedicated to centimeter scale TWUM, two different prototypes, whose external diameters are 5 mm and 2 mm, have previously been designed through numerical calculations, and fabricated using watch making technologies. An experimental characterization has been carried out in order to identify the main physical and technological limitations specific to millimeter scale traveling wave motors. The very first numerical results presented in this paper show important outcomes related to the miniaturization of TWUM. In particular, the limits of current mechanical assumptions such as those related to the two-dimensional mechanical behavior of the stator/rotor interface and also to the rotors rigidity are clearly shown by a three dimensional finite element calculation. New design rules are thus given in order to allow the mechanical architecture of TWUM to be optimized. The corresponding results indicate that powerful torque/speed characteristics can be expected, and therefore show the adequacy of traveling wave ultrasonic motors for direct-drive actuation down to the millimeter scale.

Toward Standard Method for Microelectromechanical Systems Material Measurement through On-Chip Electrostatic Probing of Micrometer Size Polysilicon Tensile Specimens

Polysilicon deposited by low pressure chemical vapor deposition is the most widely used structural material for surface-micromachined microelectromechanical systems. Thus, investigations are still needed in order to identify polysilicon mechanical characteristics as a function of the deposition conditions. The following work focuses on new micrometer size monolithic test cells combining polysilicon tensile specimens and ultra-high driving force electrostatic actuators fabricated from a common process flow. The proposed approach allows intrinsic material properties such as polysilicon tensile fracture to be measured through electrostatic probing, using on-chip micrometer size uniaxial tensile test cells.

Three dimensional active microcatheter combining shape memory alloy actuators and direct-drive tubular electrostatic micromotors

This paper investigates 3D active microcatheters having millimeter size outer diameters. The proposed architectures combine mechanical cells which involve new direct-drive tubular electrostatic micromotors and conventional shape memory alloy actuators. The tubular electrostatic motors are actuated by silicon surface micromachined flexible stators. The polysilicon stators integrate up to several thousands of direct-drive electrostatic microactuators. However, they have been designed in order to provide a gap compensation at the rotor/motor frame interface. Multiple stator/rotor contact interactions involve a significant speed reduction that allow a large torque amplification, as a consequence of the torque/speed duality. These mechanical interactions allow the rotor to be moved with respect to the motor frame through direct-drive contact mechanisms, therefore allowing high torque/low speed characteristics to be performed. In such a way to get a 3D behavior, the microcatheter combines tubular electrostatic motors having flexible rotors. The rotors integrate Ti-Ni shape memory alloy wires which actuate a 2D bending motion on each mechanical cell. The 3D global behavior of the catheter is provided by the relative rotation of each cell, with respect to the other ones. The proposed architecture is particularly convenient with respect to the electric power supply which is, usually, the major problem in designing active microcatheters. A (Phi) 1 mm 3D active catheter is given as an example, but external diameters less than one millimeter can be easily expected, opening therefore numerous applications in the near future.

Toward Smart Surfaces Using High-Density Arrays of Silicon-Based Mechanical Oscillators

Computer chips and other electronics have been getting faster and cheaper for a long time. But, often overlooked, they are also getting smaller and therefore allowing wearable high-technology to be developed on the near future. Current miniaturization and integration trends will result in the need to assemble ever-smaller systems and to handle smaller and smaller chips and other components that will be too small for humans to manipulate and assemble. As a consequence, the automation infrastructure of the future electronics assembly industry will have to scale with the technology, using fully and entirely automated micromachines such as manipulators and intelligent conveyance systems. The paper investigates, consequently, rapid and accurate positioning systems that will allow very small chips and components to be conveyed and automatically sorted. High-density arrays of silicon-based electrostatic actuators particularly are analyzed, according to their ability to move parts locally with high speed and sub-micrometer positioning accuracy. Actuator densities as high as 1000 actuators/mm are investigated, therefore allowing micrometer silicon based components to be manipulated. Lower densities involving larger actuation cells are also investigated in order to move millimeter size components on a few cm square motive surface. Very first design steps toward future smart surfaces are finally discussed. The paper shows how arrayed silicon based sensors, that can be easily distributed along with arrayed actuators, may provide tactile information from the external world, therefore allowing intelligent conveyance systems to be realized on the near future.

Toward New Cylindrical Electrostatic Micromotors Using Tubular Combination of Arrayed Direct-Drive Actuators

A new generation of electrostatic micromotors is investigated using cooperation of arrayed direct-drive actuators. Electrostatic scratch-drive actuators (SDAs), which combine active frictional contact mechanisms with electrostatic actuation are particularly analyzed. A prototype of a cylindrical micromotor, whose external diameter and length are, respectively, 1 mm and 2 mm, has been realized through the insertion of a flexible active polysilicon sheet at the rotor/motor-frame interface. The sheet, which acts as a stator, is fabricated by the surface micromachining process and then released automatically from the silicon wafer. One thousand four hundred thirty actuators are integrated on a 6 mm2 polysilicon sheet surface, leading to high-driving-torque characteristics.

On-Chip Investigation of Torque/Speed Characteristics on New High-Torque Micrometer-Size Polysilicon Electrostatic Actuators

In this study, we investigate new-generation high-torque/low-speed electrostatic micromotors as well as original on-chip testing methods for the mechanical characterization of silicon-based microactuators. Torque/speed characteristics of micrometer-size electrostatic actuators are measured for the first time using real-time elastic braking video analysis of polysilicon rotors that are monolithically coupled with elastic mechanical sensors. Loading characteristics measured through on-chip electrostatic probing indicate the potentialities of emerging actuator design methodologies involving frictional stator/rotor contact interactions on the micrometer scale.

Direct-Drive Electrostatic Micromotors Using Flexible Polysilicon Rotors

This paper is devoted to the design, the fabrication and the characterization of a new generation of direct-drive silicon based electrostatic micromotors. The following work points out the main torque limitations that occur in the design of conventional electrostatic actuators using electrostatic field interactions. Stator/rotor contact interactions are then considered, in order to provide larger external torque. Distributed motion systems are also investigated, because of significant driving forces that are expected through cooperative arrayed microactuators. According to this analysis, annular-type micromotors having a (500 Atm external diameter are proposed. The motor actuation involves stator/rotor contact interactions by using a flexible polysilicon rotor which combines arrayed elementary bending actuators. Moreover, the rotor integrates a self-adjusted torque sensor that allows the driving torque to be directly measured. Experimental characteristics point out the relevance of the proposed design rules. Unusual driving torque, one thousand times higher than ones obtained using conventional electrostatic wobble motors, have been already measured. Rotation speed ranging from 0.001 up to 750 rpm is also reported, according to the driving voltage frequency which was tuned from 1 Hz up to 500 kHz.