Moog Crossbow GNAV540 - Manual (Page 28)

Page 28
GNAV540 User Manual
7430‐0808‐01 Rev. B
Setting Default Value Comments
Freely
Integrate OFF The Freely Integrate setting allows configuring the unit into a free gyroscope. In
free gyroscope mode, the roll, pitch and yaw are computed exclusively from
angular rate with no Kalman filter based corrections of roll, pitch, or yaw. When
turned on, there is no coupling of acceleration based signals into the roll and
y with pitch. As a result, the roll, pitch, and yaw outputs will drift roughly linearl
time due to sensor bias.
For best performance, the Freely Integrate mode should be used after the
algorithm has initialized. This allows the Kalman Filter to estimate the roll and
pitch e rate sensor bias prior to entering the free gyroscope mode. Exiting the fre
scope mode (OFF), causes one of the following behaviors to occur:
•
gyro
If the unit has been in freely integrate mode for less than sixty seconds, the
algorithm will resume operation at normal gain settings.
If the unit has been in freely integrate mode for greater than sixty seconds,
the algorithm will force a reset and reinitialize with high gains automatically.
•
Restart On
Over Range
OFF This setting forces an algorithm reset when a sensor over range occurs, i.e., a
rotational rate on any of the three axes exceeds the maximum range. The default
setting is OFF. Algorithm reset returns the unit to a high gain state, where the
unit rapidly estimates the gyroscope bias and uses the accelerometer feedback
heavily. This setting is recommended when the source of over‐range is likely to
be sustained and potentially much greater than the rate sensor operating limit.
Large and sustained angular rate over‐ranges result in unrecoverable errors in
roll and pitch outputs. An unrecoverable error indicates the EKF cannot stabilize
the resulting roll and pitch reading. If the over‐ranges are expected to be of
m operating
turned off.
short duration (<1 sec) and a modest percentage over the maximu
range, it is recommended that the restart on over range setting be
Han
g an inertial rate se dlin nsor over‐range is controlled with the
rtOnOverRange resta switch.
• If restartOnOverRange is off, the system will flag the overRange status flag
and continue to operate through it.
• If restartOnOverRange is on, the system will flag a masterFail error during an
over‐range condition and continue to operate with this flag until a quasi‐
static condition is met to allow for an algorithm restart.
The quasi‐static condition required is that the absolute value of each low‐pass
ill filtered rate sensor falls below 3 deg/sec to begin initialization. The system w
then attempt a normal algorithm start.
Dynamic
Motion ON The default setting is ON. Turning off the dynamic motion setting results in a
higher gain state that uses the accelerometer feedback heavily. During periods of
d off time when there is known low dynamic acceleration, this switch can be turne
to allow the attitude estimate to quickly stabilize.
Turn Switch
threshold 10.0 deg/sec With respect to centripetal or false gravity forces from turning dynamics (or
coordinated turn), the unit monitors the yaw‐rate. If the yaw rate exceeds a given
turn switch threshold, the feedback gains from the accelerometer signals for
attitude correction are reduced because they are likely corrupted.