Behavior-Behavior-Based Based

ApproachesApproaches

Finishing up robotic architecture

Reactive control Motor Schemas Subsumption

OverviewOverviewRobot architecture from the bottom up

Getting around

Perceiving the world

OverviewOverviewReasoning

representing space

motion planning

OverviewOverviewHandling uncertainty sensor fusion

building maps

localization

OverviewOverviewVision -- just another sensor ?

OverviewOverview• Sonar Sound Navigation and Ranging

– Sonar provides useful information about objects very close to the robot and is often used for fast emergency collision avoidance.

• Camera data– machine vision– structured light sensors– cross beam sensors– parallel-beam sensors

ARCHITECTURESARCHITECTURES

• How the job of generating actions from percepts is organized

• Concerned to Autonomous mobile robot in dynamic environments

• The design of robot architectures is essentially the same agent design problem that was discussed

Classical architectureClassical architecture• Shakey 1969, demonstrated the importance of

experimental research in bringing to light unsuspected difficulties

– difficulties of general problem solving• integrating geometric and symbolic representation of the

world

– low level actions– macro-operators– error detection – recovery capabilities

Situated automataSituated automata• Since the mid 1980s , a significant minority of AI

and robotics researchers have begun to question the “classical” view of intelligent agent design based on representation and manipulation of explicit knowledge

• In robotics, the principal drawback of the classical view is that explicit reasoning about the effects of low-level actions is too expensive to generate real time behavior

Situated automataSituated automata• Finite state machine whose inputs are provided

by sensors connected to the environment and whose outputs are connected to effectors

• Situated automata provide a very efficient implementation of reflex agents with state

Rosenschein’s basic designRosenschein’s basic design

Theorem:Theorem:• Any finite-state machine can be implemented as

a state register together with a feed-forward circuit that updates the state based on the sensor inputs and the current state, and another circuit that calculates the output given the state register

• Execution time for each decision cycle is small

CONFIGURATIONCONFIGURATION SPACES: SPACES: A FRAMEWORK FOR ANALYSISA FRAMEWORK FOR ANALYSIS

• Both the configuration of the robot’s body and the locations of the objects in physical space are defined by real-valued coordinates.

– It is therefore impossible to apply standard search algorithms in any straightforward way because the number of states and actions are infinite.

• The configuration space is mathematical tool for design and analyzing motion planning algorithms.

Robot ArchitecturesRobot Architectureshow much / how do we represent the world internally ?

None.

Just what we need.

Just the current world.

As much as possible.

1

2

3

4

Purely Reactive Control

Absolute Control

SPA architecture

Subsumption paradigm

Motor Schema

how much / how do we represent the world internally ?

Just the current world.2 Purely Reactive Control

• Decision-making based only on the current sensor readings.

• For the survivor robot assignment (A, part 1):

int computeRotationalVelocity(…)

Robot ArchitecturesRobot Architectures

One view of reactive controlOne view of reactive controlControl is a function of the sensed data.

Case 1: If sonars 12, 13, or 14

•Look at the front nine sonar values -- which are closest ?

Turn left at 20 deg./sec

Case 2: If sonars 15, 0, or 1 Turn left at 40 deg./sec

Case 3: If sonars 2, 3, or 4 Turn right at 20 deg./sec

012

3

4

1514

13

12

Another view of reactive controlAnother view of reactive control

Direct mapping from the environment to a control signal

goal-seeking behaviorobstacle-avoiding behavior

Robot ArchitectureRobot Architecturehow much / how do we represent the world internally ?

Just what we need.3Subsumption paradigm

Motor Schema

• Motor schemas compose simple reactions by adding

the outputs that each would send to the robot.

• Individual schemas may contain state

Ron Arkin @ Georgia Tech

Behavior SummerBehavior Summer

vector sum of the avoid and goal motor schemas

path taken by a robot controlled by the resulting

field

Additional primitivesAdditional primitives

Direct mapping from the environment to a control signal

go! schemacorridor-centering schema

A more complex taskA more complex taskDirect mapping from the environment to a control signal

larger composite task

Another primitiveAnother primitiveDirect mapping from the environment to a control signal

larger composite task random motion schema

Local minimaLocal minimaNoise allows a system to “jump out” of local minima.

the problem a solution

Bigger deadends...Bigger deadends...How to get out of larger wells ?

uses memory of where the robot has been

past-avoiding motor schema

Bigger deadends...Bigger deadends...

Another exampleAnother exampleKeeping away from past locations...

InspirationInspiration

Study of how animals react to different stimuli

Toads (Arbib 87)Vowels

Rodents (Hull 1934)

InspirationInspiration

Beyond subsumptionBeyond subsumption

......1995

Polly Navlab & ALVINN

PollyPollyIan Horswill @ MIT