Frictionless electrostatic rotary stepper micromotor for microrobotic applications

We present the modeling and experimental characterization of a monolithic 3-phase rotary stepper micromotor which employs a flexure suspension to guide the rotor. The monolithic structure avoids any frictional contact during operation, providing a precise, repeatable and reliable bidirectional stepping motion without feedback control. We have performed finite element analysis (FEA) simulations of the mechanical static and dynamic properties. These studies are consistent with the extensive experimental characterization performed in the quasi-static, transient, and dynamic regimes. Dynamic nonlinearities have been observed and compared to a complete mathematical model including the electrostatic actuation and the mechanical properties of the system. The analytic model is consistent with the simulations and the experiments. The monolithic 3-phase rotary stepper micromotor has been modified to increase its torque and we have included a differential capacitive angular sensor. The implementation of this micromotor in a microgripper has also been studied and designed. These designs have been fabricated in a single-crystal silicon, using a simple single-mask process, based on standard Silicon-On-Insulator technology. The fabrication was performed in the cleanroom of the EPFL Center of MicroNanoTechnology (CMi) and has conducted to the preliminary experimental characterization of prototypes which validated the single-mask process

Subpixel translation of MEMS measured by discrete Fourier transform analysis of CCD images

We present a straightforward method for measuring in-plane linear displacements of microelectromechanical systems (MEMS) with a subnanometer resolution. The technique is based on Fourier transform analysis of a video recorded with a Charge-Coupled Device (CCD) camera attached to an optical microscope and can be used to characterize any device featuring periodic patterns along the direction of motion. Using a digital microscope mounted on a vibration isolation table, a subpixel resolution better than 1/100 pixel could be achieved, enabling quasi-static measurements with a resolution of 0.5 nm

Modal analysis and modeling of a frictionless electrostatic rotary stepper micromotor

We present the design, modeling and characterization of a 3-phase electrostatic rotary stepper micromotor. The proposed motor is a monolithic device fabricated using silicon-on-insulator (SOI) technology. The rotor is suspended with a frictionless flexural pivot bearing and reaches an unprecedented rotational range of 30° (+/- 15°) at 65 V. We have established a mechanical model of the deformation structure and performed finite element analysis (FEA) simulations of the dynamic properties. These studies are consistent with the extensive experimental characterization performed in the quasi-static, transient, and dynamic regimes

High-angular-range electrostatic rotary stepper micromotors fabricated with SOI technology

Flexible bearings are advantageous for microelectromechanical systems as they enable precise, accurate, repeatable, and reliable motion without frictional contact. Based on the principle of a rotary folded-beam suspension, we have designed, fabricated, modeled, and characterized an electrostatic rotary stepper micromotor in silicon. Using 3-D finite-element analysis simulations that were corroborated by extensive characterizations performed in quasi-static, transient, and dynamic regimes, we could establish a consistent electromechanical model of the motor. In particular, dynamic nonlinearities such as superharmonic and subharmonic resonances are well described by the proposed model. Two prototypes of monolithic three-phase stepper motors have been fabricated with standard silicon-on-insulator (SOI) technology, using either a two-mask or a single-mask process. The two-mask SOI motor has a rotor diameter of 1.4 mm and has an angular range of 30°(+/- 15°) for a 65-V (130 Vpp) sinusoidal actuation. The single-mask SOI motor has a rotor diameter of 1.8 mm and incorporates a differential capacitive sensor for angular position measurement. It reaches a maximum angular speed of 1°/ms and has an angular range of 30° for a 23-V (46 Vpp) sinusoidal actuation. The exceptional performance of the motor and the demonstration of successful capacitive sensing make it suitable for use as an active joint module in future microrobotic application

Temporally aliased video microscopy: an undersampling method for in-plane modal analysis of microelectromechanical systems

A simple optical method is proposed for performing in-plane experimental modal analysis of micromachined structures with a conventional charge-coupled device (CCD) camera. The motion of a micromechanical device actuated by high frequency sinusoidal forces (kHz range) is recorded at the fixed sampling rate of a camera (typically 28 frames/sec.) which is configured with a short shutter aperture time (1/5000 s). Provided a CCD sensor with sufficient sensitivity, lots of information are contained in the video on the dynamics of the vibrating system despite the limited frame rate. Taking advantage of the theory of undersampling, we show that the dynamics of systems with several kHz bandwidth can be retrieved very easily. For demonstration purposes, we first study a push-pull electrostatic comb- drive actuator, which is a well-known damped harmonic oscillator system. Then, we show that our measurement method also provides useful information on the behavior of nonlinear systems. In particular, we can characterize systems' superharmonic and subharmonic resonances in a straightforward way