Vibratory MEMS Gyroscopes

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Contents 1 Introduction to Vibratory MEMS Gyroscopes 2 Operating Principle of MEMS vibratory gyros[1] 2.1 The role of mechanical resonance in vibratory gyros 3 Types of Resonating MEMS Gyroscopes[2] 4 Resources 4.1 Notes

Introduction to Vibratory MEMS Gyroscopes

See Also

MEMS Gyro Modeling Simplified Lumped Parameter MEMS Tuning Fork Gyroscope Model

All MEMS gyroscopes currently use vibrating proof masses. Those masses typically vibrate at a high frequency. As the sensor housing rotates in inertial space a Coriolis force is induced on the proof mass. The Coriolis force causes a vibration in an orthogonal plane and the amplitude of the orthogonal motion can be measured.

Operating Principle of MEMS vibratory gyros^[1]

A simplified model of vibratory gyros is shown in Figure 1. The system has 2 orthogonal vibration modes; one mode corresponds to the vibration of the mass in the x-direction, the other the y-direction. The vibration frequency of the x-axis is ω_x and the equivalent for the y-axis is ω_y. Typically ω_x is almost equal to ω_y.

When powered on, the mass is driven in the x-direction with a driving frequency ω_d which is close to ω_y. When the entire MEMS gyro is rotated about the z-axis (out of the plane of the screen), an alternating force in the y-direction is caused by the Coriolis force. The amplitude of this vibration in the y-direction is used as a measure of the angular rate.

All MEMS gyroscopes use the Coriolis effect.

where:

is the force of the proof mass,

is the proof mass,

is the velocity of the mass, and

is the angular velocity of the reference frame (or sensor housing).

The role of mechanical resonance in vibratory gyros

The Coriolis force is typically weak. As a result mechanical resonance is used to amplify the motion and thus keep the signal to noise ratio high over the desired bandwidth. The driving frequency, ω_d, and the 2 resonance frequencies, ω_x and ω_y, must be designed carefully.

Types of Resonating MEMS Gyroscopes^[2]

All MEMS gyros require a resonating mass. The most common types of resonating MEMS gyros are

• Tuning Fork Gyros (TFG)
• Hemispherical Resonating Gryo (HRG) or Wine Glass Resonator Gyro
• Vibrating-Wheel Gyros
• Foucault Pendulum Gyros

Resources

• SensorMag site on the basics of MEMS sensors
• Mohite, S., Patil, N., Pratap, R., "Design, modeling and simulation of vibratory micromachined gyroscopes.", Journal of Physics: Conference Series 34 (2006), pp. 757-763.
• Thermoelastic Damping and Engineering for High Q MEMS Resonators
• Boa, M. 2004 Micro Mechanical Transducers. 2nd. Elsevier. ISBN 044450558X
• Gaura, E., and Newman, R 2006 Smart MEMS and Sensor Systems. 1st. Imperial College Press. ISBN 1860944930

Notes

1. ↑ Boa, pp. 16-19
2. ↑ Sensormag