Processor for an inertial measurement unit

TLDR: In this paper, a processor for an inertial measurement unit which computes its angular velocity and translational acceleration in terms of dynamic variables chosen because they uniquely define the motion of the inertial measurements.

Abstract: A processor is provided for an inertial measurement unit which computes its angular velocity and translational acceleration in terms of dynamic variables chosen because they uniquely define the motion of the inertial measurement unit in terms of linear combinations of the outputs of the transducers used in the inertial measurement unit. In one embodiment, the processor includes a demodulator for obtaining d.c., in-phase and quadrature sets of signals from the outputs of the transducers, a combining circuit for deriving some of the dynamic variables from the in-phase and quadrature sets of signals, and a microprocessor for transforming the dynamic variables into angular velocity and translational acceleration vectors. The processor is used with a small rugged, precise inertial measurement unit in which vector components are measured by the use of accelerometers fixed in a spinning rotor, at least one of which is off-set from the rotor axis and has a sensitive axis parallel to that of the rotor. This off-set/parallel accelerometer permits obtaining the signs of the angular velocities in addition to their magnitudes such that complete vector components are obtained. In an alternative embodiment, two orthogonally oriented rotor systems are utilized which permits all a.c. signal processing, thereby eliminating the necessity of d.c. measurements. Error isolation and correction are easily accomplished in a specialized combining circuit which simplifies initial alignment of the instrument. Another alternative embodiment employs three rotors and provides complete redundancy.