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tracktheposition,velocityandorientationoftheobjectwithrespecttoastartingpoint.

INS consists of inertial measurement unit (IMU) and a navigation processor. IMU

consists of three orthogonally placed gyroscopes to measure angular rate and three

orthogonally placed accelerometers to measure the linear acceleration. INS gives

the position without taking any external signals. Hence it is called self-contained

system and it is not influenced by external factors [4]. Inertial navigation system has

a wide range of applications in aircrafts, missiles, guidance systems, launch vehi-

cles, space-crafts, submarines, ships, intelligent transport system and autonomous

navigation.

INS usually fall into the following two categories of implementation:

a.

Gimbaled or stable platform system

b.

Strapdown system.

a.

Gimbaled or Stable platform system

INS technology includes inertial sensors mounted on stable platforms. These are

mechanically isolated with rotational motion of the moving vehicle by gimbals.

Gimbal is a rigid frame having rotational bearings for isolating a frame from another

frame due to rotations, about bearing axes (pitch, roll and yaw). Such arrangement

helps it to rotate freely in all the three axes. A minimum of three gimbals are needed

to isolate the subsystems from the rotations of the vehicle about three axes. In INS,

the gimbals are mounted one inside the other. The torque servos and gimbals are

helpful in nullifying the rotation of stable platform where the inertial sensors are

placed as shown in Fig. 13.1. Gimbal platform systems are used in order to estimate

the accurate navigational data of ships and submarines.

b.

Strapdown system

In the Strapdown system inertial sensors are mounted or attached to the host vehicle

as shown in Fig. 13.2. In place of gimbals, computers are used to simulate frame

transformation and calculate position, velocity and attitude of the moving vehicle

[5]. Strapdown systems are small in size, low cost, reliable, flexible and low power

consumption compared with stable platform. The Strapdown Inertial Navigation

Systems (SINS) are becoming more popular with their advantages. Different types

of accelerometers and gyroscopes like Fiber Optic Gyroscopes (FOG) and Ring Laser

Gyroscopes (RLG) are available to use in strapdown navigation systems.

Accelerometers

Accelerometers are used to measure the acceleration in three directions. Accelerom-

eters can broadly be classified as either a mechanical or a solid-state device. In

this section these two types of accelerometers are described including MEMS

accelerometers.