Subsumption Architecture - LEGO MINDSTORMS Robots Manual

Subsumption Architecture

The traditional approach to robot programming has been to emulate human thought processes. First, the robot processes its sensor data. Based on the sensor data, the robot constructs or updates a
model of the world. Then it decides how to act. This deliberative approach is very complicated; it requires heavy-duty processing power and may not work properly anyway.
Overview
Subsumption architecture is a radically different paradigm for robot programming developed by Rodney Brooks at MIT in the late 1980s. In this reactive approach, several robot behaviors run at
the same time. Input from sensors is used to determine which behavior controls the robot at any given time. Depending on the sensor values, higher-level behaviors completely take over control of
the robot, subsuming (replacing) lower-level behaviors. As you'll see, subsumption architecture is simple enough to be implemented on inexpensive hardware, including the RCX.
A basic example will clarify the concept. Imagine a robot that has a bumper (a touch sensor) on its front. When the robot bumps into something, it should back up and turn around. With
subsumption architecture, the robot will use two behaviors. The first behavior is cruise and simply moves the robot forward. Figure 9-1 shows a diagram of this behavior. It controls the motors
to make the robot move forward.
To avoid obstacles, the robot needs another behavior, avoid. This behavior will become active when it detects a bump on the touch sensor. It will completely take
Page 180
Figure 9-1.
Cruise, a simple robot behavior
over control of the robot. Figure 9-2 shows a diagram with both the cruise and avoid behaviors. The circle with an ''S" indicates that the avoid behavior can take control of the motors from
the cruise behavior.