Underwater Robots - Gianluca Antonelli.pdf

84 4. Fault Detection/Tolerance Strategies for AUVs and ROVs
u
ψ
EKF
nominal
model
EKF
left th. fault
model
EKF
right th. fault
model
residual
evaluation
residual
evaluation
residual
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Fig. 4.3. Fault detection strategy for one of the horizontal thruster failure proposed
by A. Alessandri, M.Caccia and G. Verrugio
ments afault detection strategy based onfive rule-based systems that monitor
all the subsystems. The five systems concern the Navigation, the Power/Propulsion,
the Direction Control and the Communication; they are coordinated
byaGlobal Diagnoser that avoid contradictory actions. Aspecific
attention has been given at the hardware reliability: as amatter of fact the
AUVC is distributed on aredundantnetwork of 18 loosely coupledprocessors.
AUVC has been also used to test the approach proposed in [222], aredundancy
management technique based on CLIPS expert system shell to identify
faults affecting depth and heading control. In [308] an architecture developed
for the vehicle ARICS with fault detection/tolerant capabilities ispresented.
Asoftware developed for ROVs tohelp the remote operator that integrates
some elementary fault detection algorithms is presented in [279]. The paper
in [177] describes the first results on the development ofalong endurance
AUV that iscurrently ongoing atthe MBARI (Monterey Bay Aquarium Research
Institute, California, USA). The fault detection approach ismainly
ported from the MIT (Massachusetts Institute of technology, Massachusetts,
USA) vehicle Odyssey (I and II) [46] and it is based onthe Layered Control
Architecture. The software architecture isbased onC++, QNX-based modules,
whichoffers multi-tasking capabilities suited for fault-tolerantoperations.
Asingle thread suppression and restart can be implemented to recover from
software failure. Short-duration operations inopen sea and long-duration
operations inthe lab proved the effectiveness ofthis approach.
In [143] amodel-based observer is used to generate residual between the
sensor measured behavior and the predicted one. The model also takes into
account the presence ofwaves incase of operations near the surface. When
the residual is larger than agiven threshold aFuzzy Inference System isin
charge of isolate the source of this mismatching (see sketch in Figure 4.4). A
FD