Page 49 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

24 MOTION PLANNING—INTRODUCTION

software would try to reproduce it. In conclusion, in spite of a long history (in
relative terms of the robotics field), the robot teaching methods can still be said
to be in their infancy.
The data “massaging” techniques mentioned above are widely used in manu-
facturing robot systems. These include, for example,

• Path smoothing
• Straight line interpolation
• Achieving a uniform velocity path
• Manipulating velocity/acceleration profiles along the path

Path smoothing is usually done to improve the system performance. Smoothing
the first and second derivatives of the robot path will help avoid jerky motion
and sharp turns.
Straight-line interpolation is something different. Many applications—for
example, welding two straight line beams along their length—require a straight-
line path. Arms with revolute joints, such as in Figure 1.2, tend to move along
curved path segments, so approximating a straight-line path takes special care.
This is a tedious job, and we will consider it further in the next chapter. The
human arm has a similar problem, though we often are not aware of this: Humans
are not good in producing straight lines, even with the powerful feedback control
help of one’s vision.
A uniform velocity path may be needed for various purposes. For a quality
weld in continuous welding, the robot has to move the gun with the uniform
speed. In the example above with the painting robot, a nonuniform velocity of
the painting gun will produce streaks of thinner and thicker paint on the surface
that is being painted. Furthermore, note that the meaning of “uniform velocity”
in this example must refer not to the velocity at the painting gun endpoint, but to
the velocity at an imaginary point in space where paint meets the painted surface.
That is the gun aiming point (say, 20 cm away from the gun’s endpoint) that has
to move with the uniform velocity. This may coincide with the gun endpoint
moving sometimes faster and sometimes slower, and sometimes even stopping,
with the gun rotating in space.
Manipulating velocity/acceleration profiles presents an extension of the veloc-
ity control. Some tasks may require control of the robot linear or angular accel-
eration—for example, to ascertain a certain pattern of starting and finishing a
motion. A good robot system will likely include software that allows creating
various profiles of robot velocity and acceleration.

1.2.7 Motion Planning
Motion planning is the single unique defining core of the field of robotics—same
as computation is the single unique defining core of the field of computers. Many
components and disciplines contribute to producing a good robot—the same is
true for a good computer—but it is motion planning that makes a robot a robot.