Page 75 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 5

To my distress, I came to realize that I had been given the task because, as a new gradu-
ate, I could still remember how to manipulate such equations. I quickly came to the
realization that none of the senior engineers had used such formalities in many years.
They designed more by something I can best describe as enlightened instinct. As such, they
had somehow reprogrammed parts of their brains to envision the control process in a
way that they could not describe on paper!
Having failed miserably to find a way out, I took a breadboarding system to the simula-
tor room where I could excite my design with the inputs from a huge analog simulator of
the aircraft. I threw out all the stages that appeared to be relatively less significant, and
eventually discovered a configuration with a mere three operational amplifiers that could
produce output traces nearly identical to those desired. It passed initial testing, but my
relief was short lived. My next assignment was to produce a mathematical report for the
Navy showing how the configuration accomplished the desired function!

At this point I reverted to the techniques I had honed in engineering school during labo-
ratory exercises. I fudged. I manipulated the equations of the specification and those of
the desired results to attempt to show that the difference (caused by my removal of 80%
of the circuitry) was mathematically insignificant. In this I completely failed, so when I
had the two ends stretched as close to each other as possible, I added the phrase “and
thus we see that” for the missing step.
A few months later my report was returned as “rejected.” Knowing I had been exposed, I
began planning for a new carrier in telemarketing. I opened the document with great
apprehension. I found that the objections had to do with insufficient margins and im-
proper paragraph structures. I was, however, commended for my clear and excellent
mathematical explanation!

Basic PID controls

At the simple extreme of the world of controls is the humble PID control. PID
stands for Proportional, Integral, and Derivative. It is a purely reactive control as it
only responds to the system error (the gap between the rabbit and the hound). PID
controls were first introduced for industrial functions such as closed loop tempera-
ture control, and were designed using analog components. Amazingly, to this day,
there are still a very significant number of analog PID controls sold every year. Be-
cause of its simplicity, many robot designers have adapted software PID controls for
servo motor applications. Figure 5.1 shows a simplified block diagram of a PID

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