Page 32 - Introduction to Autonomous Mobile Robots

17
Locomotion
that implement desired kinematic and dynamic properties. Locomotion and manipulation
thus share the same core issues of stability, contact characteristics, and environmental type:

• stability
- number and geometry of contact points
- center of gravity
- static/dynamic stability
- inclination of terrain
• characteristics of contact
- contact point/path size and shape
- angle of contact
- friction
• type of environment
- structure
- medium, (e.g. water, air, soft or hard ground)

A theoretical analysis of locomotion begins with mechanics and physics. From this start-
ing point, we can formally define and analyze all manner of mobile robot locomotion sys-
tems. However, this book focuses on the mobile robot navigation problem, particularly
stressing perception, localization, and cognition. Thus we will not delve deeply into the
physical basis of locomotion. Nevertheless, the two remaining sections in this chapter
present overviews of issues in legged locomotion [33] and wheeled locomotion. Then,
chapter 3 presents a more detailed analysis of the kinematics and control of wheeled mobile
robots.

2.2 Legged Mobile Robots

Legged locomotion is characterized by a series of point contacts between the robot and the
ground. The key advantages include adaptability and maneuverability in rough terrain.
Because only a set of point contacts is required, the quality of the ground between those
points does not matter so long as the robot can maintain adequate ground clearance. In addi-
tion, a walking robot is capable of crossing a hole or chasm so long as its reach exceeds the
width of the hole. A final advantage of legged locomotion is the potential to manipulate
objects in the environment with great skill. An excellent insect example, the dung beetle, is
capable of rolling a ball while locomoting by way of its dexterous front legs.
The main disadvantages of legged locomotion include power and mechanical complex-
ity. The leg, which may include several degrees of freedom, must be capable of sustaining
part of the robot’s total weight, and in many robots must be capable of lifting and lowering
the robot. Additionally, high maneuverability will only be achieved if the legs have a suf-
ficient number of degrees of freedom to impart forces in a number of different directions.