Page 72 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

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CHAPTER

Closed Loop Controls,

Rabbits and Hounds

Any good athlete will tell you that the key to an exceptional performance is to ima-
gine the task ahead and then to practice until the body can bring this imagined
sequence into reality. Similarly, generals create “battle plans,” and business people
create “business plans” against which they can measure their performance. In each
case there is a master plan, and then separate plans for each component. An athlete
has a script for each limb, the general for each command, and so forth. All of these
plans must be kept in synchronization.

Controlling a robot or other complex intelligent machine requires that it have a
plan or model of what it expects to accomplish. Like all such plans, it is quite likely
to require modification within moments of the beginning of its execution, but it is
still essential.

Like the commander or executive who must modify a plan to allow for changing si-
tuations, a robot must also be able to modify its plan smoothly, continuously, and on
the fly. If circumstances cause one part of the plan to be modified, then the plans for
all other parts must be capable of adjusting to this.

For the plan to have any meaning, physical hardware will need to track to the plan
to the best of its ability. Thus we trespass into the fiefdom of Controls. This subject is
deep and broad, and engineers spend their entire careers mastering it. In short, it is a
great subject to trample on. The fact is that it is quite possible to create decent con-
trols for most applications using little more than common sense algorithms.
The purpose of a control system is to compare the plan to reality, and to issue com-
mands to the servos or other output devices to make reality follow the plan. The
desired position of the robot or one of its servos is often referred to as the rabbit and

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