POS MV V5 Installation and Operation Guide
Theory
of Operation
Copyright © Applanix Corporation, 2017
B-7
INS Platform
An INS platform is one that has its accelerometers mounted on a mechanically gimballed platform. The
platform is stabilized so that it always remains level relative to the local geographic navigation frame.
Note:
POS MV does
not
use a mechanically stabilized platform of the type described in this subsection.
This explanation is included because it may be easier to visualise an inertial navigation system based on
a mechanical platform than one based on a strap-down INS arrangement.
Note:
POS MV uses a strap-down INS of the type described in Strap-Down INS on page B-8.
Figure 82 on page B-7 represents a simplified INS platform suspended by three gimbals. The platform
defines a locally level navigation frame as long as it maintains a level orientation with respect to the
surface of the Earth, in spite of any motion applied externally.
Feedback systems and a servomechanism maintain platform stability in each axis of suspension:
•
An arrangement of three gyros senses any angular rate of motion of the platform about each axis.
The arrangement places each of the gyros orthogonally so that each responds to rotations in one
axis only.
Figure 82: Gimballed INS Platform Structure
•
A servomotor in each axis receives the amplified signals from its complementary gyro and rotates
the gimbals axis to correct for the measured rate of rotation. In an ideally configured and
compensated INS platform, the net angular rotation of the platform is almost entirely removed.
G=Gyro
A=Accelerometer
X-axis
Y-axis
Z-axis
Z-axis
Y-axis
X-axis
Outer gimbal
Middle gimbal
Inner gimbal
Angular resolver