This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

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Micromachined inertial sensors

Survey of advanced suspension developments and related optimal control applications

The accomplishments to date on the development of automatic vehicle control technology in the Program on Advanced Technology for the Highway (PATH) at the University of California, Berkeley, are summarized. The basic principles and assumptions underlying the PATH work are identified, and the work on automating vehicle lateral (steering) and longitudinal (spacing and speed) control is explained. For both lateral and longitudinal control, the modeling of plant dynamics is described, and the development of the additional subsystems needed (communications, reference/sensor systems) and the derivation of the control laws are presented. Plans for testing on vehicles in both near and long term are discussed. >

Automated vehicle control developments in the PATH program

The paper presents an overview and reports the recent progress of research on squeeze film air damping in MEMS. The review starts with the governing equations of squeeze film air damping: the nonlinear isothermal Reynolds equation and various reduced forms of the equation for different conditions. After the basic effects of squeeze film damping on the dynamic performances of micro-structures are discussed based on the analytical solutions to parallel plate problems, recent research on various aspects of squeeze film air damping are reviewed, including the squeeze film air damping of perforated and slotted plate, the squeeze film air damping in rarefied air and the squeeze film air damping of torsion mirrors. Finally, the simulation of squeeze film air damping is reviewed. For quick reference, important equations and curves are included.

Squeeze film air damping in MEMS

We present a new electric equivalent circuit for the forces created by a squeezed gas film between vertically moving planar surfaces. The model is realized with frequency-dependent resistors and inductors. Circuit analysis tools are applied to calculate the response of a micromechanical silicon capacitive accelerometer in both the frequency and the time domains. The simulations are shown to match the measured frequency responses in an excellent way. We utilize the circuit model to calculate the effective viscosity in a narrow gap between the moving surfaces. The results are compared with different slip-flow equations discussed in the literature. We present a simple approximate equation of the pressure-dependent viscosity that is valid for both viscous and molecular damping regions, and has 5% accuracy.

Equivalent-circuit model of the squeezed gas film in a silicon accelerometer

A Study of Fluid Squeeze-Film Damping

The fundamental lateral performance capabilities of rubber-tired automated guideway transit (AGT) vehicles operating under automatic steering control on exclusive guideways are discussed. Control is achieved by steering the front wheels in response to signals derived from the position errors between the vehicle and a guideway-based reference containing random irregularities. Optimal control techniques are used to synthesize controllers which minimize a performance index consisting of mean square lateral acceleration and tracking error, defining a frontier which limits the performance of steering controllers. Simple single-sensor proportional steering controllers are found to offer performance comparable to the optimum for a typical AGT vehicle. The degradations in performance arising from dynamic lags in the steering actuator and operation at off-design speeds are shown.

Steering controller design for automated guideway transit vehicles

The importance of elevated guideway/vehicle dynamics to the design of advanced ground transportation systems is discussed and the general vehicle-suspension-guideway interaction problem is outlined. Simplifying assumptions valid for many practical beam-type elevated guideway systems are described including the Bernoulli-Euler beam assumptions, support conditions, and simplified vehicle models. The theoretical and experimental literature on beam-guideway/vehicle dynamics is reviewed and recent computer-based analytical techniques (lumped mass, finite difference and modal analysis) are discussed. Available simulation programs are described and published results for wheeled, air cushion and magnetically levitated vehicles operating over beam-elevated guideways are reviewed. The influences of critical system parameters on guideway deflection and vehicle vibrational acceleration (ride comfort) are illustrated through simple limiting case analyses. Low ratios of vehicle-suspension to guideway natural frequency and distribution of vehicle weight over finite pressure pads as in air or magnetic suspensions reduce guideway structural requirements for specified ride comfort. Continuous guideway beams on simple supports provide lower static deflection and greater dynamic range than simply supported single or multiple span beams. Severe resonance problems which may occur in synchronous vehicle systems are illustrated using a point-force vehicle model.

Transportation Vehicle/Beam-Elevated Guideway Dynamic Interactions: A State-of-the-Art Review

A Preliminary Study of Whirl Instability for Pressurized Gas Bearings

The optimum linear suspension which minimizes a linear combination of vehicle heave acceleration (a passenger comfort index) and suspension-guideway displacement (a measure of required suspension strike length) is synthesized using a Wiener-Hoepf technique. This optimum suspension, which is independent of specific mechanical, magnetic, or fluid methods of implementation, is used to determine the form of active control required to make the performance of a flexible-skirted air cushion suspension approach the optimum performance. The optimally compensated suspension acceleration, flexible base, and gap height excursions are computed and compared with those of optimum passive suspensions.

H. H. Richardson

Papers

A Study of Fluid Squeeze-Film Damping

Steering controller design for automated guideway transit vehicles

Transportation Vehicle/Beam-Elevated Guideway Dynamic Interactions: A State-of-the-Art Review

A Preliminary Study of Whirl Instability for Pressurized Gas Bearings

Active Control of Vehicle Air Cushion Suspensions