Error analysis and directional frequency response estimation for design and error compensation of dynamically tuned strapdown gyroscope

Abstract

Dry, dynamically tuned gyroscope (DTG) for strapdown use, which is mounted directly on vehicles, is a two-degree-of-freedom angular velocity sensor. For comparable overall performance to floated device, DTG has several advantages. It is of simple structure, not necessitating fluid to support, low in cost per axis, small in size, and amenable to thermal modeling. The development of a modern DTG gives attention to the technology of low drift and high dynamic range. Drifts are the inherent errors in the output signal of gyro, which are generated owing to the dynamic characteristics of DTG and its rebalance loop, and the imperfection in manufacturing. Recently, as the environmental condition becomes severer than ever, resulting in a higher rate input to a gyro up to a thousand degrees per second, it becomes necessary to design the DTG so that it has a high acceleration capability. In addition, the size of DTG tends to become smaller than twice the size of a match box. These design tendencies adversely lead to high drift, and result in the significant growth of the previously neglected effects of the gimbal moments of inertia, the asymmetries of flexures stiffness and rotor moments of inertia, and the higher order terms related with misalignments. Consequently, in order to lower the drift error in a modern DTG, it becomes necessary to re-investigate such effects so that proper countermeasures can be established. In this work, the drift errors to constant and harmonic rotational rate inputs are fully derived for the dynamically tuned strapdown gyroscopes with the single gimbal and the orthogonally placed double gimbals. To account for recent design tendencies, the analytic expressions for the drift errors, which newly include the influences of gimbal moments of inertia, asymmetries of flexures stiffnesses and rotor moments of inertia, and higher order terms related with misalignments, are presented. The drift errors are classified according to the sources, and thei...