A Stepwise Decoupling Self-Calibration for Attitude Demodulation Errors in Dual-Axis RINS

The attitude accuracy of dual-axis rotational inertial navigation systems (RINS) is often degraded by periodic oscillations stemming from attitude demodulation errors. A primary cause, largely unaddressed by conventional static models, is the dynamic precession of the rotation axes. To address this, this paper proposes a systematic, stepwise decoupling selfcalibration scheme to identify and compensate for these complex errors. The core of this method is an innovative timevarying error model that describes non-orthogonal axes as a superposition of constant and angle-dependent sinusoidal terms, accurately capturing the axis precession effects. The calibration scheme first resolves grating measurement errors (both functional and sampling asynchrony) and then uses single-axis rotations to isolate the non-orthogonal axis errors. These are estimated using a Recursive Least Squares (RLS) algorithm that fuses multi-source data from gyroscopes and accelerometers . Simulation and prototype experiment results demonstrate that the proposed method effectively suppresses the second-harmonic oscillations missed by traditional techniques. For instance, experiments showed a reduction in peakto-peak pitch oscillation from 8 to 2 arcseconds during outer gimbal rotation, restoring attitude accuracy to the theoretical level determined by sensor noise. This work provides both a practical compensation strategy and a diagnostic tool for evaluating the mechanical quality of RINS indexing mechanisms.