The Output Nonlinear Mechanism and the Compensation Method of Digital Closed-Loop Quartz Flexible Accelerometer

Quartz flexible accelerometers (QFAs) have been widely utilized in inertial navigation systems (INS) due to their low cost, compact structure, and relatively high accuracy. However, the indicated QFAs do have high-order nonlinear parameters, which have a significant impact on the navigation performance of the INS, particularly in high-g input environments. Therefore, the suppression of the output nonlinearity is of great importance to enhance the performance of QFA. The digital closed-loop QFA (DigitalQFA) provides a convenient solution to compensating for such nonlinear error without altering the header structure by means of the digital control processor. In this article, a method based on the maximum likelihood estimate is proposed to compensate for the output nonlinearity of Digital-QFA. The mechanism of the output nonlinearity has been analyzed based on the pendulous unbalancing and elastic properties of the pendulum component. A revised model equation is derived to describe the total output nonlinear errors. The precision centrifuge test for Digital-QFA has been conducted to verify the effectiveness of the proposed method. The experiments show that the output linearity of Digital-QFA could be improved effectively. The maximum output nonlinear error is restricted from over 2% to about 0.1% within an acceleration range of +/- 50 g, which is of great assistance to enhance the performance of Digital-QFA under high-g input environments.