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324 Autonomous Mobile Robots

5

0

y (m) – 5

Leading
l=– 1 m
– 10
l=– 2.5 m
l=– 4 m
l=– 5.5 m
– 15
– 50 – 40 – 30
x (m)

FIGURE 8.18 Vehicle trajectories (x, y) with different values of l.

8.4.2.2 Influence of parameter l
The parameter p is fixed at p =−1 and several values of l in the range
[−1m, −8m) are tested, with results shown in Figure 8.18 to Figure 8.22.
The tracking performance in the look-behind case is also influenced by para-
meter l the same way as that in forward tracking. When l takes larger values,
the tracking vehicle takes the “corner-cutting” way to follow the leader vehicle.
With smaller absolute values of l, the tracking performance is better in terms
of smaller tracking error. However, the steering angle might rise to high values.
It is because we are tracking the front point of the leader vehicle which is sup-
posed to be less steady than the back point. Again, the selection of the desired
spacing l is subject to the requirement in an application.

8.5 CONCLUSIONS
Many applications such as in outdoor industrial settings and logistics envir-
onments require autonomous mobile robot vehicles to carry out frequent and
tight turnings, as well as forward and backward maneuvers. The unified non-
linear tracking controller, presented in this chapter, is able to work for both
forward and backward maneuvers as well as driving and steering. The design is
based on either kinematics or dynamics using an output function as the interve-
hicular connection. Design parameters of desired intervehicular spacing l and

© 2006 by Taylor & Francis Group, LLC

FRANKL: “dk6033_c008” — 2006/3/31 — 16:43 — page 324 — #30