Underwater Robots - Gianluca Antonelli.pdf

86 4. Fault Detection/Tolerance Strategies for AUVs and ROVs
de-activated and the information obtained by abackup sensor able to recover
the vehicle. Nodynamic simulations are provided.
In [100], the wavelet theory is used to detect the fault in the vehicle’s
navigation angle fault.
Finally, [258] developed asoftware tool to test intelligent controllers for
AUVs. This is done by using learning techniques from the artificial intelligence
theory.
4.4 Fault Tolerant Schemes
Most of the fault tolerant controllers developed for thruster-driven underwater
vehicles are based onasuitable inversion of the TCM in eq. (2.48). It is
self-evident that, if the matrix islow rectangular itisstill possible to turn
off the broken thruster and to control the vehicle in all the 6DOFs. When
the vehicle becomes underactuated, or when it is driven by control surfaces,
the problem is mathematically more complex. In this case only few solutions
to specific set-up have been developed.
The work in [52, 61] reports afault tolerantapproachfor ROMEO, athruster
redundant ROV with 8thrusters. The strategy, experimentally verified,
simply consists indeleting the column corresponding tothe broken thruster
from the TCM. The mapping from the vehicle force/moment tothe thrusters’
forces thus, does not concern the failed component. Asimilar approach
is used in [306, 307] by exploiting the thruster redundancy of ODIN, an AUV
developed at the Autonomous Systems Laboratory (ASL) of the University
of Hawaii, HI, USA. The proposed approach is sketched in Figure 4.5 where
the subscript d denotes the desired trajectory, V m is the motor input voltage
and Ω the propeller angular velocity ofthe thrusters.
η d
˙η d
¨η d
Vehicle
Controller &
Fault Tolerant
Strategy
u d
Thruster
V m Thruster
Controller Dynamics
η , ˙η
Ω
Direct
Kinematics
u
TCM
τ Vehicle
Dynamics
Fig. 4.5. Fault tolerance strategy proposed by K.S. Yang, J. Yuhand S.K. Choi
In [232, 233, 234, 236, 251], atask-space-based, fault tolerant control
for vehicles with redundant actuation isproposed. The control law is model
η
ν