Page 134 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

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CHAPTER

Live Reckoning

It is ironic that the most central precept of autonomous navigation is often viewed
disparagingly, especially by laypersons. Perhaps this is because the term dead reckon-
ing was adopted to describe this precept, and most people have a preformed view of
what this entails. The very name dead reckoning seems to imply doomed guesswork.
At best, the term conjures up images of Charles Lindbergh flying across the Atlantic
Ocean with little more than a compass heading for navigation.

If we announce that our robot has excellent dead reckoning, many in our audience
will think this means that our robot has no true navigation at all! At the very least,
they will tend to think that our robot, like Lindbergh, travels long distances between
updates of its position. For the purposes of this discussion, we will surrender to this
view, and use the new term live reckoning to describe what we want to accomplish. To
under-stand live reckoning, we should first discuss dead reckoning a bit.
The truth is that dead reckoning was invented by nature long before man coined the
term, and this is just the first of many of nature’s techniques that will be useful to us.
One of the Zen aspects of mobile robot design is the fact that we will continually
come to these same concepts whether we attempt to copy nature or not!
In mammals, dead reckoning is accomplished primarily by signals from the inner ear.
We may think we find our way across a room by visual navigation, but the fact is that
without our inner ear we couldn’t even stand up and walk. Other senses, such as the
feeling of pressure on the soles of our feet, play into our navigation next, and finally
our vision is used to correct these estimates.

Inertial navigation uses accelerometers and gyroscopes as inputs to its calculations,
but is in the end a form of dead reckoning. On the other hand, if the position and

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