30
2010-05/MU/ROVINS-001-B
31
2010-05/MU/ROVINS-001-B
MORE…
The previous steps consist only of the basic configuration of your ROVINS system. You will find hereafter a list of other
possible configurations. Details on these configurations can be found in the ROVINS User Guide.
ROVINS TO VEHICLE MISALIGNMENT
ROVINS measures heading and attitude with respect to its reference frame defined by the 3 axes X1, X2 and X3 (see Figure
1). ROVINS reference frame may not be parallel to the vehicle reference frame. In such case, heading and attitude outputs
can be compensated for angular misalignments of ROVINS relative to the vehicle reference frame so that ROVINS outputs
heading and attitude of the vehicle.
This is done by setting misalignment bias for the three reference axis. These biases are the Euler angles which relate
ROVINS and vehicle reference frame. Vehicle reference frame is depicted on Figure 2.
Figure 2 - Vehicle Reference Frame
For more details about the misalignment bias, refer to Part 2 of the ROVINS User Guide.
STEP 4. NAVIGATING WITH ROVINS
As soon as ROVINS is powered on, it starts its alignment phase with the manually input position stored into ROVINS
PROM.
•
During the first five minutes after powering-on, ROVINS performs its coarse alignment: ROVINS inertial sensor data
(accelerometers and gyrometers) are computed to estimate heading, roll and pitch angles. At sea it is recommended
that the system is kept as steady as possible during coarse alignment: oscillations around a mean position are
permitted but accelerations should be avoided. Leaving the vessel adrift for 5 minutes would lead to satisfactory
conditions for coarse alignment.
•
After the first fine minutes long coarse alignment phase, ROVINS switches to the “fine alignment” phase to improve
the accuracy of roll, pitch and heading estimations. Such improved accuracy is useful if data from external sensors are
not available right at the beginning of the mission. Any movement is allowed during the fine alignment. 90 degrees
rotations are even recommended so that the Kalman filter assesses the sensors bias on different axes. The fine
alignment is ended automatically by ROVINS when the heading covariance is below 0.1degree.
•
At the end of the fine alignment process, ROVINS is ready for navigation with optimal performances.
Heading &
Attitude
Invalid output
Reliable output
Full accuracy output
Position
= Position given by the
GPS
Reliable output
Full accuracy output
Flag in the System
status area
Alignement
Fine Alignement
System ready
Navigation = Static or
max speed
<
3 knot
Navigation with large
heading variations
(
>
90°)
When heading standard
deviation
<
0.1
Time in minutes
0
5
