INERTIAL NAVIGATION SYSTEM By Lochana and Karthick
Different Forms of Navigation
Introduction INS is a navigation aid that uses a computer, motion sensors and rotation sensors. The motion sensors such as accelerometers. The rotational sensors such as gyroscopes. It calculates the position, orientation, and velocity of a moving object. Inertial navigation is a self-contained navigation technique. The INS is initially provided with its position and velocity from another source such as: GPS satellite receiver, etc. It is the only form of navigation that does not depend on external references. It is used on vehicles such as ships, aircraft, submarines, guided missiles, and spacecraft.
Basic Components of INS • A stable platform oriented to maintain the accelerometers horizontal to the Earth and to provide azimuth orientation. • The accelerometers arranged on the stable platform to supply specific components of acceleration. • The integrators to receive the output from the accelerometers and to calculate velocity by integrating acceleration once and integrating again to calculate the distance. • A computer to receive the signals from the integrators and to change to distance travelled into latitude and longitude.
Accelerometers • The basic principles upon which the accelerometers operate are related to Newton's laws regarding motion. • Linear accelerometers measure object’s linear acceleration and therefore detect direction of object’s movement. • Most accelerometers can measure acceleration along one axis. • In an inertial navigation system, two or three accelerometers are used. • One will measure the aircraft’s accelerations in the North-South directions. • Second one will measure the aircraft’s accelerations in the East-West directions. • The third accelerometer, if fitted, will measure vertical displacement.
Gyroscopes • Gyroscopes are rotational sensors that measure the angular velocity or orientation of a device. • Gyros can be used as rate gyros or integrating gyros. • There are different types of gyroscopes such as :Mechanical, Optical and MEMS gyroscopes.
Mechanical Gyroscopes • A conventional gyroscope consists of a spinning wheel mounted on two gimbals which allow it to rotate in all three axes. • Conventional gyroscope measures orientation. ➢ Disadvantages of Mechanical gyroscopes • It contains moving parts. • Moving parts cause friction, which in turn causes the output to drift over time. • To minimize friction high-precision, bearings and special lubricants are use. • Mechanical gyroscopes also require a few minutes to warm up, which is not ideal in many situations.
Optical Gyroscopes • It is based on Sagnac Effect. • Two beams from a laser are injected into the same fiber but in opposite directions. Due to the Sagnac effect, the beam travelling against the rotation experiences a slightly shorter path delay than the other beam. The resulting differential phase shift is measured through interferometry, thus translating one component of the angular velocity into a shift of the interference pattern which is measured photometrically.
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- Spring '19
- Global Positioning System, Inertial navigation system, Gyroscope, Ring laser gyroscope