1. Behaviour Based approaches to robotics Jeremy Wyatt School of Computer Science University of Birmingham

2. Shakey outline Planex Strips ILAs LLAs Hardware World Model central representation logic based error recovery at several levels communication through model

3. Shakey: key ingredients A mix of planning using logic and planning using geometric information ILAs did simple error recovery internally (reactive controllers) e.g. push(box1, (14.1 22.3)) Major error recovery done by updating the world model e.g. if the robot is uncertain about its position it takes a camera fix and updates the world model. World model based on First Order Predicate Logic (FOPL)

4. Criticisms Modelling the world too hard and slow Non-linear planning intractable (NP-complete) Feedback through world model cumbersome Single chain mapping sensing to action Very general poor at lots of tasks Passing representations between modules is slow PerceptionPlanningExecution

5. Turn the problem on its head Don’t build world models Don’t plan Use short feedback loops Create many chains that map sensing to action Very specific good at one or two tasks Don’t pass representations between modules “There are no general purpose animals… why should there be general purpose robots?” D. MacFarland

6. Behaviour Based Control Overall controller composed of two parts –Task achieving controllers –Arbitrating controller (also task specific) Controllers: –Are reactive (map perception to action) –Have no models, no planning –Are only capable of performing one task each

7. A comparison PerceptionPlanningExecution Push Go through door Approach object Follow a wall Arbitration

8. Eye, Brain, Hand: Rules Eyes: Shout “Stop!” if Hand is in danger. (i.e. Hand might trip up or hit something). Otherwise you can answer: (i) Yes/No questions e.g. Is there a box on the floor (ii) How many? e.g. How many boxes in the room? (iii) Spatial relationship questions e.g. “Where is the nearest box to hand?” – “3 metres in front of hand”

9. Eye, Brain, Hand: Rules Brain: Build a tower out of three boxes on the table at the front of the lecture room. You may: (i) Give instructions to Hand (ii) Ask questions (yes/no, how many, how far, where) of Eyes

10. Eye, Brain, Hand: Rules Hand: If Eyes shout “Stop!” then stop: something dangerous is about to happen. Otherwise do brain tells you.

11. Behaviour Based System: Rules Agent 1: (Box finder) Rule 1: if another agent is holding a box then look for boxes on the table Rule 2: If no other agent is holding a box look for boxes on the floor Rule 3: Go to the box you are looking at and stand next to it. Raise your hand if it is on the floor. Rule 4: When there are no boxes left to look for return to your seat.

12. Behaviour Based System: Rules Agent 2: (Box Getter) Rule 1: Find and follow agent 1 Rule 2: If agent 1 is stationary with hand raised, pick up the object near agent 1’s feet. Rule 3: If agent 1 is stationary and hand is down, hold out the object you are carrying to the other agent (not 1) nearby. Rule 4: If agent 1 sits down return to your seat.

13. Behaviour Based System: Rules Agent 3: (Box Stacker) Rule 1: Stand by the table until the other agents are seated. Rule 2: When the other agents are seated return to your seat. Rule 3: If another agent offers you an object take it. Rule 4: If you are holding an object, place it carefully on top of the object(s) in front of you.

14. Behaviour Based System: assumptions Each agent has the relatively simple perceptual and physical talents to perform its task easily The difficulties of the classical system are not just due to natural language We were able to decompose the task into appropriate sub-tasks

15. Interacting behaviours: Vestibular Occular Reflex

16. Some early Behaviour Based Robots

17. The colony architecture M1 M2 M3 M4 M5 s s s s I P1 P2 P3 P1 P2 P4 P2 A1 A2 M – Behavioural Modulessupression nodes P – Perceptual informationinhibition nodes A – actuators s I

18. The colony architecture: features Only one module can have control over a particular actuator There are no direct channels between behavioural modules Modules send packets of information along wires There is some pre and post processing

19. Herbert: a can collector