A New IMU with a Digitally Controlled PZT CVG
A. Dorian Challoner, Jeremy D. Popp, Peter W. Bond, InertialWave, Inc.; Jose Beitia, Innalabs, LLC.; Rongsheng (Ken) Li, The Boeing Company
Location: Big Sur
This paper presents a new Inertial Measurement Unit featuring digital control of a symmetric, piezoelectrically-transduced Coriolis Vibratory Gyro (CVG) with improved performance and design for compact ASIC implementation in terrestrial and space environments. Previously a metallic PZT transduced cylindrical resonator with simple analog control electronics resulted in a successful low noise rate gyro produced by Innalabs [1, 2] for stabilization and targeting applications and satellite pointing. This work details key benefits of applying a very low noise digital control and demodulation approach that extends InertialWave’s previous work on generalized feedback control of capacitive CVG’s . This was first demonstrated at breadboard level to further reduce rate noise toward the very low, 60 micro-deg/rt-h mechanical thermal noise (MTN) inherent in its massive 23 mm, high quality resonator and pointing to a clear path for achieving navigation grade performance in a mass producible CVG and compact three-axis IRU or IMU assembly. InertialWave Inc. has integrated three of Innalabs CVG resonators and three accelerometers with its own compact digital control electronics into a very compact 25 in^3 IMU design and is testing it with Boeing’s support in its inertial test facilities. Based on already measured breadboard ARW of 0.00033deg/rt-h and in-run bias stability of 0.021 deg/h, navigation grade performance is anticipated with our co-located digital electronics and our IMU compact mechanical design.
Piezoelectric transduction has a number of practical advantages for a Coriolis Vibratory Gyroscope (CVG) including low electrical noise leading to low rate sense noise with a simple voltage buffer and the absence of small mechanical gaps around the CVG resonator. The latter reduces manufacturing complexity and the need for high vacuum packaging to preserve high resonator quality. Piezoelectrically-transduced tuning fork CVGs with open loop control electronics have been successfully applied to low cost, low performance applications. Symmetric high quality symmetric CVGs with piezoelectric transduction have much higher performance potential due to low thermal mechanical noise (MTN) and closed loop tuned operation. However, current state of the art symmetric tuned CVGs with piezoelectric transduction control electronics [1,2] have analog demodulators or modulators in the loop with baseband analog rate output and so far have not met their full potential. Baseband control with analog demodulation and modulation has electronic dynamic range limitations and exhibits undesirable 1/f or flicker noise limiting high performance.
What is needed is control electronics for a tuned CVG with piezoelectric transduction that does not require analog demodulation to baseband. Our Inertial Wave Angle Gyroscope (IWAG) electronics with generalized feedback control [3, 4] obviates analog demodulation or modulation in a number of ways. In this paper digital position and velocity feedback control at baseband within the IWAG DSP avoids baseband analog rate output and analog to digital conversion. In radiation hard ASIC form our IWAG digital electronics operating Innalabs production piezoelectric CVG resonators enables a low-cost, compact, high performance 3-axs Inertial Reference Units (IRU) for near-term space applications.
This paper presents this new compact InertialWave IMU design and the latest inertial test results.
 J. Beitia, et al, “High-grade CVG for Stabilisation Control Systems and Tactical Grade Systems”, Inertial Sensors and Systems Symposium (ISS), 2013
 J. Beitia, et al, “Low Cost CVG for High Grade North Finders and Targeting Systems”, Inertial Sensors and Systems Symposium (ISS), 2014
 A.D. Challoner, J. D. Popp, P. Bond, “A universal electronics approach for Rate Integrating Gyroscopes”, Inertial Sensors and Systems Symposium (ISS), 2017
 Parsa, A.D. Challoner, et. al., “A new electronic feedback compensation method for rate integrating gyroscopes”, Inertial Sensors and Systems Symposium (ISS), 2017