Gilles Bourbon

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.

Dynamic electro-thermo-mechanical modelling of a U-shaped electro-thermal actuator

In this paper, we develop original analytical electro-thermal and thermo-mechanical models for the U-shaped electro-thermal actuator. The dynamics of the temperature distribution and displacement are obtained as a direct relationship between the systems dimensions, material properties and electrical input. The electro-thermal model provides an exact solution of the hybrid partial differential equations that describe the electro-thermal behaviour for each of the actuators three connected arms. The solution is obtained using a new calculation method that allows the representation of an integrable function by a hybrid infinite sum of sine and cosine functions. The displacement at the actuators tip is then calculated using a quasi-static model based on the superposition and virtual works principles. The obtained temperature and displacement solutions are then discussed and compared with finite element method simulations via ANSYS® and experimental results. Comparisons showed good agreement making the proposed modelling a reliable alternative which paves the way for improving the design and optimising the dimensions of U-shaped micro-actuators.

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.

Modeling and Stress Analysis of a Pre-Shaped Curved Beam: Influence of High Modes of Buckling

In this paper, we investigate the effect of high modes of buckling on the mechanical behavior of a pre-shaped curved beam. In a first stage, the presented modeling develops further the snapping forces solution and bistability conditions in order to include high modes of buckling. In a second stage, we develop the analytical solution of the stresses inside the beam during deflection between the two sides of buckling. The buckling with or without mechanical conditions on antisymmetric modes, the force characteristics, bistability conditions and stresses are described in this paper based on mathematical approach in order to provide a clear physical understanding of the curved beam behavior and its design parameters. The accurate knowledge of the design parameters is important in order to achieve the best integration of the curved beam in a complete microstructure. The analytical results are compared with and without considering high modes of buckling and have shown to be in excellent agreement with FEM simulations. The results show the importance of the high modes in calculating stresses and snapping forces.

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.

Mechanical stop mechanism for overcoming MEMS fabrication tolerances

A mechanical stop mechanism is developed in order to compensate MEMS fabrication tolerances in discrete positioning. The mechanical stop mechanism is designed to be implemented on SOI wafers using a common DRIE etching process. The various fabrication tolerances obtained due to the etching process are presented and discussed in the paper. The principle and design of the mechanism are then presented. Finally, experiments on microfabricated positioning prototypes show accurate steps unaffected by the fabrication tolerances.

Design optimization of bistable modules electrothermally actuated for digital microrobotics

This article deals with the optimization of the main element of a digital microrobot, which is a bistable module. the bistable module consists of curved beams and electrothermal actuators. A design study of the curved beam and the electrothermal actuator is presented in order to achieve the limits in line with miniaturization. Finally, An optimization for the dimensions is proposed respect to microfabrication and elastic limits.

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.