Overview

Practical inertial navigation systems may take a variety of forms. These forms generally fall into one of two basic categories,

• stable platform systems;

• strapdown systems.

Although the two types of system are very different, both physically and computationally, it must be stressed that the underlying principles and functionality of the two types of system are identical.

Stable Platform Systems

The original applications of inertial navigation technology used stable platform techniques. At that time, neither sensors with the necessary dynamic range nor sufficiently powerful computers were available to allow strapdown systems to be produced. At the core of such a system is a structure, called the platform, on which inertial sensors are mounted. This platform is 'isolated' from the rotational motion of the vehicle using a number of gimbals arranged to provide at least three degrees of rotational freedom and so minimise the angular coupling between the vehicle and the platform. Generally, three gimbals are used.

Figure C.1 shows a schematic representation of a three gimbal stabilised platform system. The platform containing the inertial sensors is supported by three gimbals. The gimbals are mechanical frames, each of which is free to rotate about a single-axis which is nominally perpendicular to the free axis of its neighbouring gimbal(s). Torque motors are used to rotate the gimbals with respect to...