Underwater Robots - Gianluca Antonelli.pdf

7.2 Feedforward Decoupling Control 145
The experiment isconducted under some assumptions: the vehicle does
not influence the manipulator dynamic due toits small movements; the desired
joint acceleration are used instead ofthe measured/filtered ones; there
is no current and the lift forces are small compared to the in-line forces. For
this specific experiment, moreover, the control ofthe vehicle is obtained by
resorting to PID-like actions at the 6DOFs independently. Inview of these
assumptions it is:
τ v = τ PID + ˆτ m ( q , ˙q , ¨q d ) .
Figure 7.2 reports some experimental results of the end-effector error commanded
to aperiodic motion. In the top-left plot the vehicle is not controlled
at all; the influence of the arm on the vehicle can be observed. In the top-right
and the bottom-left plots the sole decoupling force and vehicle feedback are
considered. Finally, inthe bottom-right plot the benefit of considering the
proposed control strategy can be fully appreciated.
distance [m]
distance [m]
2
1.5
1
0.5
0
0 5 10
time [s]
Decoupling Control Only
2
1.5
1
0.5
No Vehicle Control
0
0 5 10
time [s]
distance [m]
2
1.5
1
0.5
0
0 5 10
time [s]
Feedback with Decoupling Control
2
distance [m]
1.5
1
0.5
Feedback Control Only
0
0 5 10
time [s]
Fig. 7.3. Feedforward Decoupling control. End-effector step response. Top-left:
without vehicle control; top-right: with the sole decoupling action; bottom-left: with
the sole vehicle feedback control; bottom-right: the proposed approach (courtesy of
T. McLain, Brigham Young University)