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Navigation Mechanism
MAYA Electronics
MAYA electronics consist of the main controller
(a small PC running Linux) and vehicle payloads
(AHRS, GPS, DVL and UHF modem) interfaced through
serial ports. Other nodes like the Thruster node
with pressure sensor, the Fins & Rudder node,
the Sonar node and the Battery monitoring
node are interfaced by a CAN 2.0B network. A separate
science node acquires data from scientific sensors
(CTD, Oxygen, Fluorometer and Optical Radiometer)
and talks to the main controller through a serial
port.
Organization of functional blocks
Software architecture
MAYA software is designed as two processes: one
a server communicating with the control PC and
other doing data acquisition, Control, Navigation,
Guidance and Safety loops on the embedded Linux
OS. The two processes communicate through a shared
memory block. The GUI software on the control
PC is a client to the server running on MAYA.
The navigation, guidance and control mechanism
Navigation, Guidance, and Control Systems: Reference
path following
Navigation block: estimates of vehicle position
from measurements.
Guidance block : Calculates the desired path and
outputs references to control block.
Control block : Generates commands to the actuator
nodes to move vehicle to desired position.
Distributed control network
Graphical User Interface (GUI)
The GUI is used to control MAYA and upload/download
data. The current position of MAYA gets updated
on the map in the display panel. A compass dial
indicates the direction of the vehicle orientation
to helps the user to locate MAYA.
Data logging of science payloads
Mission based nose cones with payload sensors
Sensor payloads of Dissolved Oxygen (DO) , Fluorometer
(Chlorophyll, Turbidity) Conductivity, Temperature,
Depth (CTD) and Optical Radiometer are interfaced
to a Rabbit Core micro-controller through RS 232
serial ports. The data records of each sensors
are stamped with date, time, and position values
which are transmitted from the MZ 104 main controller.
Method used for navigation control
Navigation is the method to determine present
AUV position which is important for the safe operation
and recovery of the vehicle. The measured position
Pm is calculated from the from the GPS position
with reference to origin position in (x,y). The
measured velocity Vm is the Doppler Velocity Log
(DVL) velocity transformed to inertial frame from
body referenced frame using rotation matrix.
A single track guidance mission was carried out
to test the performance of the complementary filter
output with reference to the GPS position.
Surface navigation using complementary
filter and GPS
Underwater navigation
using complementary filter (DVL underwater and
GPS on surface)
Obstacle avoidance
Maya's underwater navigation would be aided by
obstacle avoidance mechanism. This system is based
on sanning/imaging sonar that generates an acoustic
view ahead of the vehicle. From the view, possible
obstacle are identified and the information is
fed into the obstacle avoidance algorithm that
generates necessary warnings commands that can
be implemented by the Maya. The sonar for this
application is Tritech's micron sonar which is
a very small scanning sonar. It consumes a low
4.5 VA at 24 VDC. As this sonar is fully under
the control of sonar node implemented using a
microcontroller, modifying the operation and algorithm
from various experimental results can be easily
done relatively.
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