IofT 1910 W Fall 2006 Week 3 Plan for today:  discuss questions asked for the writeup  talk about Brooks’ approach and compare it with other approaches  talk about the lab on Thursday

Questions for writeup 1.What is the difference between a suppressor and an inhibitor? Why are both needed? 2.Explain in your own words what the modules in level 0 do. 3.What would be the effect of removing module runaway? 4.Explain how Level 1 is added to Level 0.

Decomposition of control From R. Brooks, “A robust layered control system for a mobile robot,” IEEE JRA, Vol 2, N 1, 1986 Traditional architecture Brooks’ layered architecture

1. Suppressors and inhibitors From R. Brooks, “A robust layered control system for a mobile robot,” IEEE JRA, Vol 2, N 1, 1986

Answer: How do suppressors and inhibitors work?  There are two ways in which a signal can be suppressed: Suppress the original signal and do not replace it. This is what an Inhibitor does when applied to an output. Suppress the original signal and replace it with a different signal. This is what a Suppressor does when applied to an input. This is used when a higher-level module wants to inject its signal into a lower level module

2. Modules in level 0 From R. Brooks, “A robust layered control system for a mobile robot,” IEEE JRA, Vol 2, N 1, 1986 This figure is from an older version of the paper and is slightly different

Answer: what do modules in level 0 do?  sonar: takes sonar readings, filters out outliers, and produces a robot-centric map in polar coordinates.  feelforce: adds vectors of virtual forces computed from each sonar distance as (1/distance 2 ).  runaway: monitors if force is above threshold and then sends heading to turn.  collide: sends halt command if it detects a close object in front of the robot.  turn and forward: communicate with the robot to turn and move. When the robot stops moving forward sends the shaft-encoder readings to turn and resets turn for the next motion.

3. Effect of removing module runaway?

Answer: Effect of removing module runaway  runaway makes the robot to move towards a place where the force on it is null (i.e. equidistant from all obstacles) when the force is above a threshold. This prevents the robot from jiggling. Without runaway the force vector will always be passed directly to turn.

4. How is Level 1 added to Level 0? From R. Brooks, “A robust layered control system for a mobile robot,” IEEE JRA, Vol 2, N 1, 1986

Answer: How is Level 1 added to Level 0 wander avoid From R. Brooks, “A robust layered control system for a mobile robot,” IEEE JRA, Vol 2, N 1, 1986 S/20 avoid gets force from level 0, combines it with desired heading from wander, and suppresses input from runaway into motor injecting its own heading.

Compare Brooks’ approach to others: Traditional model  In the traditional model cognition mediates between perception and actions.  Actions affect the world  Perception gets information from the world to feed cognition Perception CognitionAction World

Action Brooks’ model  Cognition is in the eye of the observer.  Perception and action do all the work.  The world is its own best model. Perception World Cognition

Lab on Thursday  Where: in EE/CS  You need your U card to get in.  We’ll continue using MEdit to write simple programs to get the AIBO to move.  You can bring your laptop and get help in setting up the software on your laptop.