Underwater Robots - Gianluca Antonelli.pdf

156 7. Dynamic Control of UVMSs
[m]
1
0
−1
x 10−3
2
y
x
z
−2
0 5 10 15
time [s]
N
0
−100
−200
−300
−400
−500
X
Y
−600
0 5 10 15
tim
Fig. 7.5. Sliding mode control. Left: vehicle positions. Right: vehicle control forces
Figure 7.5 shows that, as expected, the vehicle position is affected by the
manipulator motion; however, the displacements are small and the target
position is recovered after atransient. It can be recognized that at steady
state the force along z is non null; this happens because the manipulator is
not neutrally buoyant.
Figure 7.6 shows that the dynamic coupling ismostly experienced along
the roll direction because of the chosen UVMS structure. This effect was
intentional in order to test the control robustness. It can be recognized that
vehicle control moments are zero at steady state; this happens because the
center of gravity and the center of buoyancy of vehicle body and manipulator
links are all aligned with the z -axis of the earth-fixed frame at the final system
configuration.
[deg]
0.05
0
−0.05
−0.1
φ
−0.15
0 5 10 15
time [s]
50
0
−50
−100
−150
−200
−250
0 5 10 15
tim
Fig. 7.6. Sliding mode control. Left: vehicle attitude in terms of Euler angles.
Right: vehicle control moments
Figure7.7 shows the time histories of manipulator jointerrors andtorques.
It is worth noting that the initial value of the joint torques is non null because
Nm
K
Z