Feedforward Ins Aiding: an Investigation of Maneuvers for In-flight Alignment

Navigation in autonomous vehicles involves integrating measurements from on–board inertial sensors and external data collected by various sensors. In this paper, the computer–frame velocity error model is augmented with a random constant model of accelerometer bias and rategyro drift for use in a Kalman filter–based fusion of a lowcost rotating inertial navigation system (INS) with external position and velocity measurements. The impact of model mismatch and maneuvers on the estimation of misalignment and inertial measurement unit (IMU) error is investigated. Previously, the literature focused on analyzing the stripped observability matrix that results from applying piece-wise constant acceleration segments to a stabilized, gimbaled INS to determine the accuracy of misalignment, accelerometer bias, and rate-gyro drift estimation. However, its validation via covariance analysis neglected model mismatch. Here, a vertically undamped, three channel INS with a rotating IMU with respect to the host vehicle is simulated. Such IMU rotation does not require the accurate mechanism of a gimbaled INS (GINS) and obviates the need to maneuver away from the desired trajectory during in-flight alignment (IFA) with a strapdown IMU. In comparison with a stationary GINS at a known location, IMU rotation enhances estimation Revista Controle & Automação/Vol.18 no.4/Outubro, Novembro e Dezembro 2007 459 of accelerometer bias, and partially improves estimation of rate-gyro drift and misalignment. Finally, combining IMU rotation with distinct acceleration segments yields full observability, thus significantly enhancing estimation of rategyro drift and misalignment.