CONFIDENTIAL

26.10.2012 Slide 1

CONFIDENTIAL

Model Based Design for Embedded Control Systems

Koenraad Rombaut

Coordinator applied physics & systems

Koenraad.rombaut@verhaert.com

Michiel De Paepe

Consultant applied physics & systems

Michiel.depaepe@verhaert.com

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26.10.2012 Slide 2

Model Based Design in general:

• What ?

• Why ?

• How ?

A model based design case study:

• Case study

• Models

• Conclusions & demonstration

Content

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26.10.2012 Slide 3

What ? Model driven engineering ?

Model based development ?

Build model Plant / Process

Product design

Design Concepts

Verification

Implement Product code

Testing

Mo

del s

pace

C

od

e s

pace

Model = system + control + environment + stimuli

Multi-domain = control + system behaviour

Coupling / transformations models design

requirements design implementation test scenario

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26.10.2012 Slide 4

Why ?

Why ?

• Cheaper & faster

• Higher reliability

• Better definition

When ?

• Complex processes / designs Complex control strategies

• High reliability

• Early validation

• Fast developments

• Changing requirements

Outputs:

• design inputs

• insights

• derisk

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26.10.2012 Slide 5

Why : definition

Communication

between disciplines,

with customer & subcontractors,

over project phases

Re-use of subsystems

Safety factor for (sw) budget &

schedule

Needs Requirements Specs Design Implementation Documentation

Needs (what do we want) vs.

specifications (how do we define)

Specifying new (innovating) products

and subsystems

Changing requirements

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26.10.2012 Slide 6

Why simulation : early validation

Benefits

• More and faster iterations

• Parallel hw & sw development

• Multiple off-nominal and fault

testing (non feasible tests)

• Early full system validation

and risk mitigation without hw

• Less real-life testing

(= the poor man’s approach)

• More optimal system design

by sw-physics co-simulation

• Improved communication &

design specification

=> time & cost reduction

Traditional:

• sequential = lengthy

• validation on hw = late

Model based:

• Parallel = fast

• validation on model = early

Device

Requirements

System

Design

Subsystem

requirements

Detailled

Design

Functional

Test

Component

Test

Device

Validation

System

Verfication

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26.10.2012 Slide 7

Why early: cost vs. freedom

• Design & test

freedom

• Unlimited

measurements

in simulation

• Lots of risks

• Cost (project,

build,

measurement,

change)

• Real world

representation

• Number of

people

involved

Lab

model

Field

model Virtual

model

Ris

k / E

ffo

rt

Time

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26.10.2012 Slide 8

Re-use proven tools from high reliability

domains?

• Space, aeronautics, nuclear, automotive,

chemical plants

• Domain specific tools

• Tool cost not an issue

• Long learning curve, less flexibility

Need for a new toolchain

• affordable

• flexible, scalable

for generic developments

• easy learning (graphical ?)

• open (no vendor lock-in)

• automatic transformations

How ?

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26.10.2012 Slide 9

How: examples

Multi domain tools:

• Matlab/Simulink +

SimMech+StateFlow

+ RTW + AutoSar

• Dymola / Modelica

• LabView

• SysML / Raphsody

Some research projects

• Modelisar: Modelica +

Autosar

• Destecs: co-sim CT + DE

• Deploy: B for dependable

sw

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26.10.2012 Slide 10

How : Modelisar / Autosar ?

Application sw

Hardware

standardized

HW-specific

Customer needs

Adaptive Cruise Control

Lane Departure

Warning

Advanced Front

Lighting System

Using standards

Communication Stack

OSEK

Diagnostics

CAN, FlexRay

Autosar =

Automotive

hw interface

Modelica =

Plant modelling

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26.10.2012 Slide 11

Case study : excavator with Destecs

Complex

• manual operations

• => inherent fault tolerant design

• 3D dynamic motion, digging map & boundaries

• unknown soil conditions

• multidomain: hydraulics, mechanics, sw

Well known case

• Manual operator as a reference

• Scalable & testable

Destecs differentiators:

• discrete event (sw) & continuous time (physics)

• fault injection & error checking

• open

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26.10.2012 Slide 12

Model Based Design in general:

• What ?

• Why ?

• How ?

A model based design case study:

• Case study introduction

• Models

• Scale model

• Continuous time model

• Discrete event model

• Conclusions & demonstration

Content

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26.10.2012 Slide 13

DESTECS inspiration

• Inspiration

• Use collaborative multidisciplinary design of Embedded Systems

• Rapid construction and evaluation of system models

• Evaluated on industrial applications

• Need because of Embedded Systems

• More demanding functional & non-functional requirements

• Reliability, Fault Tolerance

• Increasingly distributed

• More design possibilities, and faults

• Communication between physics and control

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26.10.2012 Slide 14

DESTECS approach

• Methods and Open tools

• Model-based approach for collaborative design of ECS

• Co-simulation

• Different tools, reflecting relevant aspects of design

• Rapid, consistent analysis & comparison of models

• Advances needed in

• Continuous time modeling

• Discrete event modeling

• Fault modeling and fault tolerance

• Open tool frameworks

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26.10.2012 Slide 15

Dredging

• Dredging

= Underwater excavation

• No visual

• Introducing semi automated control

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26.10.2012 Slide 16

Scale model

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26.10.2012 Slide 17

Actuators

Full scale Hydraulic pistons

vs.

Scale model Electric linear actuators

12V full speed out

0V no movement

-12V full speed retract

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26.10.2012 Slide 18

Sensors

Incremental encoders

2 shifted square waves

Step and direction information

Driving step counter (up and down)

1 index pulse / revolution

Absolute positioning

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26.10.2012 Slide 19

Continuous Time model

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26.10.2012 Slide 20

3D Model

• STL-files for visualisation

• Mass & Inertia

• Dimmensions

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26.10.2012 Slide 21

Discrete Event model

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26.10.2012 Slide 22

Excavator model

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26.10.2012 Slide 23

Operator

• Joystick inputs (from CSV files)

• Pressing buttons

• Power on

• Start/Stop

• Manual/Assisted mode

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26.10.2012 Slide 24

Safety unit

• Redundant system

• In normal circumstances, no action

• Overrules controller at controller failure Software bug,

unforeseen situation,

hardware failure

• If triggered, 3 actions: Trigger emergency state on controller

Overrule output and thereby stop all motion

Cut off power to the motors (unimplemented, slows down CT)

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26.10.2012 Slide 25

Controller

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26.10.2012 Slide 26

Operation modes

Direct mode Assisted mode

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26.10.2012 Slide 27

Assisted mode

Boom encoder

Stick encoder

Bucket encoder

X-joystick

Y-joystick

Scoop-joystick

Kinematics Inverse

kinematics

Angular velocities:

Boom, Stick,

Bucket

Actuator velocities:

Boom, Stick,

Bucket Boom linear actuator

Stick linear actuator

Bucket linear actuator

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26.10.2012 Slide 28

Conclusions

• Ability to implement large level of complexity at both sides:

Physics and Controller

• Currently it’s an academic tool, not mature.

• Steep learning curve, only for large and complex projects

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26.10.2012 Slide 29

Excavator : current practice

Mechanics

• 3D CAD

System design

• requirements doc

• architecture doc

• design specs doc

Electronics

• schematic

Hydraulics

• 1D model

control sw

• C-code

Detailed design

Build &

Integration

Final product

• Test & verification

sensor

actuator

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26.10.2012 Slide 30

20sim

• continuous time

• multi-disciplinary

• graphical

• open libraries with

validated components

• from high level to detailed

Co-Sim IF

• version tracking

• co-sim solver

• design space exploration

• fault injection

VDM++

• discrete event

• inherent condition checking

• formal

• graphical (via UML)

• support for sw methods

• C-code generation

Excavator : with DESTECS

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26.10.2012 Slide 31

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Time for a demonstration

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26.10.2012 Slide 32

Any questions?

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26.10.2012 Slide 33

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