Page 94 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

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CHAPTER

Communications and Control

In mobile robot design, there are few decisions more critical than deciding how
communications will be performed. The method in which the data is encoded in a
message is called the protocol. There are thousands of different protocols floating
around the world. Some protocols are concerned only with piping data from one
place to another without regard to what it means, while other protocols are con-
cerned with actual meaning of the data.

Some protocols have layers for each of these purposes and more. A protocol or layer
of a protocol that concerns itself with the meaning of the data is usually called the
application layer or application protocol. This is the protocol we need to decide upon.
While this protocol may ride on other protocols, it is still the native interface lan-
guage of the machine.

As an example, on the internet the most common application protocol for browsers
is HTML. This hypertext markup language acts to convey the way a page should ap-
pear and respond to the recipient’s mouse actions. The actual transmission of HTML
is accomplished by other protocols such as TCP. We need a similar, and equally
flexible, protocol that meets the needs of controlling and monitoring our machine.
Before getting into the requirements of a robot’s application protocol, it is useful to
briefly consider the network technology that will be carrying our messages.

Popular networks
In the past, the natural choice for inter-robot communications was ASCII, com-
monly at RS-232, RS-485, and RS-422 levels. ASCII was designed for point-to-
point communications, but could be easily adapted to master-slave networking.

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