Institut für Regelungs- und Automatisierungstechnik 1 Michael Hofbaur Modular Machines Modular Machines - reconfigurable mobile robots for research and

Institut für Regelungs- und Automatisierungstechnik

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Michael Hofbaur Modular Machines

Modular Machines-

reconfigurable mobile robots for research and education

Michael Hofbaur

Institut für Regelungs- und AutomatisierungstechnikTechnische Universität Graz


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Motivation

Robot drives with diverse wheel-geometry and drive-functionality

Teaching• Hands-on experience with diverse drives• Verify and understand robot kinematics

Research• Investment costs / re-usable hardware• Novel, but still generic drive concepts

Industrial Application• Easy configuration • Fault tolerance


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Motivation



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Motivation



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Motivation



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Modular Mobile Robot

Goal: quickly build/configure diverse wheeled robot drives

Innovative Design: – 6-edge honey-comb prism– Module-in-Module design


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Application: Teaching & Research

Toolbox for diverse robots/applications

• cost-effective starter-kit• expandable• re-usable• versatile configurations for

research & education• new perspectives & coole ideas


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Robot Control

How do we operate / control robots with diverse wheel configurations and geometries?

Keyword: kinematics / inverse kinematics

RxRy

R 1 1

2 2

3 3

,R

R R

R

x

y

Drive Command Wheel Setpoints


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Robot Control

How do we operate / control robots with diverse wheel configurations and geometries?

Keyword: kinematics / inverse kinematics

1 1

2 2

3 3

,R

R R

R

x

y

Drive Command Wheel Setpoints

VIDEOwheel_view_of_gamepad_drive_short.avi


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Model-programmed Robot Drive Control

instead of using the (manually) derived inverse-kinematics for a drive we:

• specify a model that captures the drive‘s geometry and functionality • analyze the kinematics and deduce the inverse-kinematics

on-line during operation of the robot


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Complete Architecture

• Kinematics Reasoning

• Monitoring & Diagnosis

• Coordinated Control

• Model / autom. Modelling

higher-level Robot Control - Path and Task Planning & Execution OR Robot Cluster Control

Coordinated Control Unit

Kinematics Reasoning Unit

Hybrid Monitoring& Estimaton Unit

AutomatedHybrid

ModellingUnit

Drive UnitHandler

Drive UnitHandler

Drive UnitHandler

.......... Drive FrameHandler

Drive Unit1

Drive Unit2

Drive Unitn

RobotSensors

Drive Unit Network

higher-level Robot Network


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Complete Architecture

• Kinematics Reasoning

• Monitoring & Diagnosis

• Coordinated Control

• Model / autom. Modelling

higher-level Robot Control - Path and Task Planning & Execution OR Robot Cluster Control

Coordinated Control Unit


Hybrid Monitoring& Estimaton Unit

AutomatedHybrid

ModellingUnit

Drive UnitHandler

Drive UnitHandler

Drive UnitHandler

.......... Drive FrameHandler

Drive Unit1

Drive Unit2

Drive Unitn

RobotSensors

Drive Unit Network

higher-level Robot Network


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MODEL:• specifies the drive‘s geometry and functionality


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Kinematics Analysis

Wheel geometry & functionality constrains the possible movements of the robot: it defines its Kinematics

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R

R R

R

x

y B

Example 1: omnidirectional 3-wheel robot

admissible & controllable movements B


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Kinematics Analysis

3

R

R R

R

x

y B

Example 2: differential-drive robot with steered front wheel




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Kinematics Analysis


3R

R R

R

x

y B




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Kinematics Analysis





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Kinematics Analysis


Example 3: robot with two standard wheels and a steered front wheel



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on-line kinematics solver that computes B and allows:

• variable robot geometry– geometry & number of wheels can change during operation

• variable drive functionality– operational- and fault modes

• self-awareness– drive explicitely knows the space of

possible movements for the drive (B)

– validate a drive command from higher level control

– reconfiguration

?R B

*R R


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on-line solver for robot kinematics:assumption: drive with unsteered wheels

[sin( ) cos( ) cos( )] 0

[cos( ) sin( ) sin( )] 0

i i i i i i R i i R i i

i i

Ti

i i i RT

i R i

l r r

l

j

c

rolling constraint for wheel i:

sliding constraint for wheel i:


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1 2

1

roll : 0

slide: 0

R

R

J

C

J

Combination of the constraints for all wheels:



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admissible movements:

controllable movements:

admissible & controllable movements:


1( )Z Kern C

1( ), ( )T

S Kern S Kern JS

B Z S

Z

SB

Z S


1 2

1

roll : 0

slide: 0

R

R

J

C

J



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1( )Z Kern C

1( ), ( )T

S Kern S Kern JS

B Z S

Z

SB

Z S


1 2

1

roll : 0

slide: 0

R

R

J

C

J


How can we apply this line of reasoning to steered wheels, faults, etc.


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Qualitative rolling & sliding constraints for steered wheels

B Z S

1 1Mode

sin( ) sin( / 2)

OK cos( ) cos( / 2) 0 0 0

cos(0) cos( / 2)

cos( ) cos( / 2)

rot. stuck 0 0 0 sin( ) sin( / 2)

sin(0) sin( / 2)

free spinning 0 0 0 0 0 0

T Tq

T

T

q

l l

l l

j c

1q( )Z Kern C

1q( ), ( )T

S Kern S Kern JS


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(Re)Configuration & Control

Example: Eye-Catcher Task

desired behaviour

Fault-szenario (blocked steering in one wheel)with reconfiguration

VIDEOeye-catcher_wo_fault.avi

VIDEOeye-cather_w_cool_reconf.avi


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Virtual rekonfiguration of the drive geometry

Coordinated control of Multi-Robot Systems

Basis for control is a model ofthe drive geometry that can changeduring operation of the robot

(Re)Configuration & Control

VIDEOdrivemovie1.avi


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Drive modules as wheel-units for an automated guided vehicle:

• flexible – easy configuration of mechanics & control

• costs - standard-units

• robust - modules replaceable

• new perspectives– multi-robot transport

– direkt objekt transport

Application: Automated Guided Vehicles


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Modular Machines - Summary

Hardware

• Patent-pending modular robot design to realize wheeled robots with diverse drive geometries

• Module-in-module design – extend your robots with additional modules to meet demanding research requirements

• Multi-robot (re)configuration

Software / Control

• Model-programmed self-configuring kinematics control • Real-time kinematics analysis• Health monitoring/diagnosis for fault tolerant operation

Documents

Institut für Regelungs- und Automatisierungstechnik 1 Michael Hofbaur Modular Machines Modular Machines - reconfigurable mobile robots for research and