Experiences with an Architecture for Intelligent Reactive Agents

By R. Peter Bonasso, R. James Firby, Erann Gat, David Kortenkamp, David P Miller, Marc G Slack

Presented By Tony Morelli 9/16/2004

Abstract● 3T Robot Architecture● 3 Levels of abstraction

– Variety of software tools have been created to implement this on multiple real robots

– Has been implemented on several different robot systems with different processors, operating systems, effectors, and sensors.

Introduction● Three interacting layers

– Dynamically reprogrammable set of reactive skills cooridnated by a skill manager

– Sequencer that controls skills to accomplis a specific task. Use the Reactive Action Packages (RAP)

– Deliberative planner that reasons in depth about goals, resources and timing constraints. Use the Adversarial Planner (AP)

Software Tools for Arcitechture Implementation

● A number of tools were developed for integrating the three tiers together and providing the user with a paradigm for developing robotic applications

Skills

● Input and Out Specification – Each skill must provide a description of the inputs it expects and the outputs it generates

● Computational Transform – The actual work● Initialization Routine – What to do on power up● An Enable Function● A Disable Function

Sequencing

● Accomplish routinely performed tasks● Task is dependent upon the robot's knowledge of

the situation.● Replies are through skills called events.

– Events take inputs from other skills– Events notify the sequencer when a desired state has

been detected.● Lacks the foresite to achieve global behavior

Planning

● Operates at the highest level of abstraction to make its problem space as small as possible

● Using the AP planner– Multiagent control (robots usually have interaction

with either people or other robots)– Robots need to be able to work together– CounterPlanning --- Need to do change plans when

something an uncontrolled agent enters the picture.

Applications of the Architecture

● Discuss the robot.● Describe the task, the skills, the RAPs, and the

plans● Give results and lessons learned of the

architecture

A Mobile Robot that Recognizes People

● Search for a particular color shirt● Crop the face and identify the person● Skills – Searching and tracking colors,

cropping the face, recognizing the face, and obstacle avoidance.

● 20 RAPs to disable/enable skill sets and recover from errors.

● Did not use the planning tier of the architecture

A Mobile Robot that Recognizes People - Skill Network

A Trash Collecting Mobile Robot

● Named Chip● Skills – Moving while avoiding obstacles, face a

particular direction, finding an object visually, tracking an object, and reaching towards an object.

● Middle tier combined low level RAPs to make higher level RAPs

● No upper tier● Successful in their experiments

A Mobile Robot that Navigates Office Buildings

● Use sonar data for obstacle avoidance and laser scanner with bar coded tages for landmark recognition.

● Skills – Watching for landmarks, moving to landmarks, and moving through doorways.

● RAPs for moving to a landmark or moving through a set of connecting spaces.

● Planner can plan a new path if the hallway is blocked.

A Mobile Robot that Navigates Office Buildings

Space Station Robots

● Plans are made by humans and sent to the planner● The planner creates a series of RAPs.● Simple failures are handled at the RAP level● Drastic failures will could cause the planner to

abandon all plans● Implemented on a simulator prior to real life.● Differences were in the interfaces and the level of

autonomy. The planner and the RAPs were basically unchanged.

Allocating Knowledge Across the Architecture

● Time – Skill level has time in milliseconds, sequencer in tenths of a second, and the planning level in seconds.

● Bandwidth – Skills are high bandwidth (image transferring). Between skill system and the RAP is small (enable/disable).

● Task Requirements – A RAP should be broken down into skills. If a RAP starts doing look ahead, it should be considered an AP.

Allocating Knowledge Across the Architecture (2)

● Modifiability – Skills are compiled into runtime events. RAP and planner are based on interpreters and their behavior can be changed by changing RAP descriptions and planning operators.

Comparison With Other Work

● 2 Categories of autonomous agents– Control physically embedded agents– Explore issues in general intelligence

● 3T an example of the first

Robot ArchitecturesSubsumption

● Subsumption – Decomposes robot control by task, rather than function.

● No architectural support for abstraction, planning or resource management.

Robot ArchitecturesSSS

● Three layer architecture● Subsumption is the middle layer● Only been demonstrated on tasks involving pure

navigation

Robot ArchitecturesTask Control Architecture

● No tiers● Cumbersome to have a general planner● All failures are lumped together

– 3T handles failures at all three levels

Non-robotic Agent Architectures

● Guardian – Similar to 3T but with sequencing and deliberation performed by the same mechanism– Decision making can be faster

● Cypress – Their version of RAPs were difficult to integrate as they were not designed to allow integration with conventional AI planners

Future Work and Conclusions

● Division of labor permits the generalization of knowledge across multiple projects.

● 3T can ease the development of software control code.

● 3T use in non-robotic control systems– WWW Robot (retrieves maps to fight fires)– Closed Ecological Life Support Systems

● Determine the planting cycles of various crops

Questions?