D. Piyabongkarn, A. S. Sezen, R. Rajamani and B.J. Nelson
Funding : National Science Foundation


MEMS gyroscopes are typically designed to measure angular rate of rotation. A measurement of the angle itself is useful in many applications but cannot be obtained by integrating the angular rate due to the presence of bias errors which cause a drift. This project develops an innovative design for a vibrating gyroscope that can directly measure both angle and angular rate. The design is based on the principle of measuring the angle of free vibration of a suspended mass with respect to the casing of the gyroscope. Several critical challenges have to be handled before the theoretical sensing concept can be converted into a reliable practical sensor. These include compensating for the presence of dissipative forces, mismatched springs, cross-axis stiffness and transmission of rotary torque. These challenges are addressed by the development of a composite nonlinear feedback control system that compensates for each of the above effects and ensures that the mass continues to behave as a freely vibrating structure. Theoretical analysis and simulation results show that the gyroscope can accurately measure both angle and angular rate for low bandwidth applications.

A MEMS embodiment of the developed design has been fabricated using bulk micromachining to obtain a high aspect ratio device. The device utilizes electrostatic comb actuation and capacitive sensing for position measurement. A control system to enable angle measurement is currently being implemented on the MEMS device.

 

[Above] Fabricated MEMS Absolute Angle Device, [Top Right] DRIE Fabrication Steps, [Right] MEMS Device on PCB

PUBLICATIONS

ACC 2002     Development of a MEMS Gyroscope for Measurement of Absolute Angle

IROS 2002     A Novel Dual Axis Electrostatic Microactuation System for Micromanipulation

Sensors and Actuators A     A High Aspect Ratio Two-Axis Electrostatic Microactuator with Extended Travel Range

 

MOVIES

	No coupling between the two axes
		This movie shows the two axes (x and y) of the gyroscope. X-axis is actuated by a sinusoidal voltage of 6V @2 Hz. There is no visible coupling between the x- and y axes since y axis does not move under the influence of the motion in x.
	A frequency sweep between 1-20 Hz
		This movie shows the open loop response of one of the axes of the gyroscope under a sinusoidal frequency sweep from 1 to 20 Hz.
	Two axis performance
		This movie shows a close-up shot of the comb drives on both of the axes. The frequencies of oscillation for the two axes are different and being changed through the movie having values ranging from 1 - 8 Hz. Again there is no coupling.
	Bird's Eye View
		Here is a movie shot by using a smaller magnification lens so it gives a better view of the whole device itself.
	Springs and Mass
		This movie shows the movement of the springs and the mass at a corner of the device. Two axes are first actuated at the same frequency and the horizontal axis then abrubtly dropped to 1 Hz.

ANGLE RATE GYROSCOPE

To learn about the working of a typical angle rate gyroscope, click here