Page 99 - Dynamic Vision for Perception and Control of Motion

3.4 Behavioral Capabilities for Locomotion 83

Learning parameters of generic steering maneuvers: Performing this “lane
change maneuver” several times at different speeds and memorizing the parameters
as well as the real outcome constitutes a learning process for car driving. This will
be left open for future developments. The essential point here is that knowledge
about these types of maneuvers can trigger a host of useful (even optimal) behav-
ioral components and adaptations to real-world effects depending on the situation
encountered. Therefore, the term “maneuver” is very important for subjects: Its
implementation in accordance with the laws and limits of physics provides the be-
havioral skills of the subject. Its compact representation with a few numbers and a
symbolic name is important for planning, where only the (approximate) left and
right boundary values of the state variables, the transition time, and some extreme
values in between (quasi-static parameters) are sufficient for decision-making. This
will be discussed in Section 3.4.4.1.
Effects of maneuvers on visual perception: The final effects to be discussed here
are the centrifugal forces in curves and their influence on measurement data, in-
cluding vision. The
b Tr
centrifugal forces pro- F Cf = F Fr + F Fl
b Tr F Cf = F Fr + F Fl
portional to curvature
Bank (roll)
of the trajectory C·V² Bank (roll) cg angle
cg angle ĭ
may be thought to at- ǻH cg ĭ
-F Cf -F Cf
tack at the center of H cg H cg
gravity. The counter-
acting forces keeping F Fl F Fr F Fl F Fr
the vehicle on the road
Figure 3.14. Vehicle banking in a curve due to centrifugal
occur at the points forces ~ C·V²; influence of elevation of cg
where the vehicle
touches the ground.
Figure 3.14 shows the balance of forces and torques leading to a bank angle ĭ of
the vehicle body in the outward direction of the curve driven. Therefore, the eleva-
tion H cg of the cg above the ground is an important factor determining the inclina-
tion to banking of a vehicle in curves. Sports utility vehicles (SUV) or vans (Figure
3.14 right) tend to have a higher cg than normal cars (left) or even racing cars.
Their bank angle ĭ is usually larger for the same centrifugal forces; as a conse-
quence, speed in curves has to be lower for these types of vehicles. However, sus-
pension system design allows reducing this banking effect by some amount.
Critical situations may occur in dynamic maneuvering when both centrifugal
and braking forces are applied. In the real world, the local friction coefficients at
the wheels may be different. In addition, the normal forces at each wheel also dif-
fer due to the torque balance from braking and curve steering. Figure 3.15 shows a
qualitative representation in a bird’s-eye view. Unfortunately, quite a few accidents
occur because human drivers are not able to perceive the environmental conditions
and the inertial forces to be expected correctly. Vehicles with autonomous percep-
tion capabilities could help reduce the accident rate. A first successful step in this
direction has been made with the device called ESP (electronic stability program or
similar acronym, depending on the make). Up to now, this unit looks just at the
yaw rate (maybe linear accelerations in addition) and the individual wheel speeds.
If these values do not satisfy the conditions for a smooth curve, individual braking