Applanix POS MV V5, Инструкция по установке и эксплуатации

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POS MV V5 Installation and Operation Guide
Theory
of Operation
Copyright © Applanix Corporation, 2017
B-8
This action gives the platform stability in the
inertial reference frame
. In this condition, to an
observer on the surface of the Earth the platform would appear to rotate at the Earth rate of
15°/hour relative to a locally level navigation frame.
To remove this apparent rotation, the control system makes the platform locally level by adding to
the respective feedback signals, reference signals that cause the three gimbals axis to rotate at
the Earth rate plus the transport rate.
• With the INS housing fixed to the vessel and the platform north aligned and locally level, the INS
can measure the roll, pitch and heading of the vessel directly from the gimbals angles of the INS
platform. It takes these measurements from angular resolvers in each gimbals axis.
The accelerometers are also mounted orthogonally on the platform to sense accelerations in the
x
,
y
and
z
directions relative to the surface of the Earth. When the platform is aligned and level
with respect to the Earth surface, its
x-axis
points in a known direction, usually towards true north.
With the platform aligned and maintained locally both stable and level, the accelerometers align
to a geographic navigation frame. In this orientation, the accelerometer array measures specific
forces that the INS experiences relative to the inertial reference frame, and resolves them in the
geographic navigation frame.
From these measurements, the INS computes its accelerations with respect to the surface of the
Earth, also resolved in the geographic navigation frame. The INS integrates these accelerations
in the navigation frame to obtain velocity and changes in position.
Strap-Down INS
A strap-down INS has its rate gyros and accelerometers fixed to the INS or IMU housing. This housing is
fixed to the vessel. The inertial sensor array therefore moves and rotates with the vessel. This is the
inertial navigator mechanization used by POS MV.
The accelerometers sense specific forces with respect to the inertial frame. These are resolved in the IMU
body frame defined by the orthogonal accelerometer and gyro arrangement.
Similarly, the gyros sense all angular rates with respect to the inertial frame. These too are resolved in the
inertial sensor frame.
The INS uses the sensed angular rates, the computed Earth rate and transport rates to update a
Direction Cosine Matrix (DCM), which describes the mathematical transformation from the IMU body
frame to a mathematically defined geographic navigation frame.
Following transformation of the measured specific forces into the geographic navigation frame, the
navigation computations are the same as those for the INS platform.