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Unified Control Design for Autonomous Vehicle 299

Y
Following vehicle

P f
P b
y
l
P r pg
d
Leading vehicle f
P d
u
X
x

FIGURE 8.2 Backward tracking configuration.

where

1 for forward tracking
f =
−1 for backward tracking
Vehicle tracking motion is defined as the collective motions of both vehicles
as well as the relative distance and orientation angle between two vehicles.
A good performance of tracking maneuvers is ensured only if the follower
vehicle can follow the leader vehicle at a specified spacing and with a tracking
error bounded or going to zero.

8.3 A UNIFIED TRACKING CONTROLLER

The objective of tracking control is to drive the follower vehicle automatically to
follow the leader vehicle and maintain a predetermined intervehicular spacing.
In this section, a nonlinear output feedback controller is developed. The idea is
motivated by what a human driver does in car following maneuvers. The driver
keeps his eye focused on the leader vehicle at a comfortable distance. He drives
the vehicle so that his eye focus point is able to follow the leader vehicle with
the same distance. With this motivation, we develop a look-ahead controller for
forward tracking maneuver and a look-behind controller for backward tracking.
In the following, these two controllers are developed as a unified nonlinear
controller.
The focus point P r is defined l meters away from the vehicle with l being
the desired spacing between two vehicles (P f P r = l in forward tracking and

© 2006 by Taylor & Francis Group, LLC

FRANKL: “dk6033_c008” — 2006/3/31 — 16:43 — page 299 — #5