A Hardware Platform for Tuning of MEMS Devices Using Closed-Loop Frequency Response Michael I. Ferguson, Jet Propulsion Laboratory, Michael.I.Ferguson@jpl.nasa.gov MS 3031300,4800 Oak Grove Dr., Pasadena, CA 91 109,s18-393-6967 Eric MacDonald -University of Texas at El Paso, emac@utep.edu 500 West University Dr., El Paso, TX 79968-0523, 915-747-5969 David Foor - Texas A&M - Kingsville, quatro@ieee.org 7 19 W Kleberg, Kingsville, TX 78363, 36 1-549-6338. Abstract-We report on the development of a hardware platform for integrated tuning and closed-loop operation of MEMS gyroscopes. The platform was developed and tested for the second generation JPLIBoeing Post-Resonator MEMS gyroscope. The control of this device is implemented through a digital design on a Field Programmable Gate Array (FPGA). A sofhvare interface allows the user to configure, calibrate, and tune the bias voltages on the microgyro. The interface easily transitions to an embedded solution that allows for the miniaturization of the system to a single chip. errors in the MEMS devices in order to produce a navigation-grade gyroscope for spaceflight with the form- factor available with these devices. The end result of using the microgyro in these non-conventional environments will reduce size, mass and power while maintaining control of the remote system. Typical applications that would benefit from this technology include: the detection of angular rotation in all axes of a robotic arm, integration of the device in a planetary rover or lunar or planetary sample return missions that have a premium on weight because of the cost of lifting mass off the remote surface. TABLE OF CONTENTS As a corollary to the advancement of technology, the 1. INTRODUCTION ...................................... 1 .......... 2. MECHANICS OF THE MEMS MICROGYRO 2 ........................... 3. CONTROL OF THE MICROGYRO 2 ................................. 4. GYRO DIGITAL SUBSYSTEM 3 5. FUTURE MODIFICATIONS ..................................... 5 6. SUMMARY AND DISCUSSION ................... .. ........ 5 ......................................... 7. ACKNOWLEDGEMENTS 5 ............................................................. REFERENCES 5 BIOGRAPHY ......................................................... 6 The JPLIBoeing MEMS gyroscope, or microgyro, is a type of post resonator gyroscope (PRG) that detects the coriolis precession of an oscillating silicon post to determine angular rate of rotation. MEMS PRGs all suffer from degradations in performance due to manufacturing imperfections which errors such as zero-rate drift, or a measured rotation of a stationary gyro. Competing designs such as spinning-mass gyroscopes typically have orders of magnitude higher volume, size and power, so there is a great incentive among the aerospace community to develop lighter, more compact and less power consuming gyroscopes. Other small gyroscope designs have been proposed which measure effects on light passing through a fiber-optic cable [12], however, fibers are notorious for becoming cloudy when exposed to radiation. This adds incentive to correct for the microgyro suffers, before calibration, from a decrease in accuracy and precision with respect to the larger, spinning- mass types. This is a characteristic passed down by the several parts of the manufacturing process that leads to asymmetry in the silicon structure. This will be explained fbrther in Section 2. The result of the inherent asymmetry results in the existence of a non-degeneracy in the modes of oscillation along the X- and Y-axes. This causes a reduction in the microgyro's sensitivity and zero-rate drift--or the ability of the microgyro to detect no rotation when it is in a static state. Two general solutions exist for the problem of decreased sensitivity. (1) By increasing the accuracy in the manufacturing process, the microgyro will be more symmetric. This, however, would be expensive and impractical in light of another solution. (2) Corrections can be applied to the system post-fabrication. The corrections are by far more cost effective and take several forms. One option is to apply a transformation to the vibration for both axes of rotation [6]. Unfortunately this method requires a careful characterization of the covariance matrix, which is a numeric measurement of the coupling between the X- and Y-axes. Another method is to adapt the resonant frequency of the gyroscope by applying feedback, a closed-loop approach 1.51. A third approach is change the sensing pickoff frame by creating weighted sums of the pickoff signals to decouple the dynamics El]. The third approach 1 0-7803-8 155-6/041$17.0002004 IEEE