This paper discusses the development of a low-cost, redundant, strapdown inertial measurement unit (IMU). The unit comprises four ceramic vibrating structure gyroscopes and four QLC 400 acceleromet...

A Low-Cost, Redundant Inertial Measurement Unit for Unmanned Air Vehicles:

The preliminary design of a redundant strapdown navigation system for integrated flight-control/navigation use is presented. Based on tuned-gimbal gyros, a compact configuration (13 in. x 13 in. x 14 in.) has been achieved for fail-operational/fail-operational redundancy. Hardware and software design of a four-channel system configuration is given. The system consists of four gyros, eight accelerometers, and four processors. Compact packaging into four identical chassis is based on the symmetry properties of an octahedron. The design matrix for least-squares combinations of n two-degree-of-freedom gyros is derived, and general parity equations are shown for extracting errors from measurements. A limitation on the amount of sensed information for failure isolation of some second-gyro failures is described, and system failure probability is calculated from hardware failure rate, channel interconnection, and signal-to-noise ratio. Test data are presented for skewed, dual-redundant strapdown inertial measurement units, including typical parity equation responses during physical motion, simulated gyro and accelerometer failures, and a 180-deg turn with a 20-deg roll angle. Fault detection and isolation time for various failure amplitudes and likelihood of false alarms for the assumed error detection amplitudes are given.

J. G. Mark

Papers

Redundant Integrated Flight-Control/Navigation Inertial Sensor Complex