Launcher position controlfor ECRH feedback control on magnetic is-

lands in a tokamak

E.M.M. Demarteau

DCT.2008.124

Report of Master traineeship

Supervisory committee:

Prof. Dr. Ir. M. Steinbuch 1

Dr. Ir. P.W.J.M. Nuij 1

B.A. Hennen MSc. 2

Dr. M de Baar 2

1 EINDHOVEN UNIVERSITY OF TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING

CONTROLS SYSTEMS TECHNOLOGY GROUP

2 FOM INSTITUTE FOR PLASMA PHYSICS RIJNHUIZEN

TOKAMAK PHYSICS GROUP

ON DETACHMENT AT FORSCHUNGSZENTRUM JÜLICH

Eindhoven, June 2008

Abstract

Nuclear fusion is the power source of the universe. It is the energy source of the sun and

enabler of all energy sources presently available on earth. A lot of research is focussed

on realizing the application of this almost inexhaustible energy source on earth. Fusion

experiments that include reactions similar to those that occur in the core of the sun, can

be safely conducted in a tokamak device. In a tokamak electrical coils are used to confine a

donut shaped plasma by means of poloidal and toroidal magnetic fields.

In the plasma, where the fusion reaction takes place, a number of Magneto Hydro

Dynamic (MHD) instabilities occur. One set of instabilities, the so-called Neo-classical

Tearing Modes (NTMs) or magnetic islands have shown to be suppressible through early

detection and radio wave (ECRH/ECCD) actuation. This gives rise to the control problem

to stabilize and suppress magnetic islands.

At the TEXTOR tokamak an integrated detection and suppression system has been

developed. This system consists of an Electro Cyclotron Emission detector, that provides

multiple local temperature profiles from the plasma, allowing the detection of an islands

location, spinning frequency and phase. The system further consists of a gyrotron, i.e. a

high power (800kW) ECRH/ECCD actuator and a 2 Degree Of Freedom (DOF) focus mir-

ror also referred to as launcher. By adjusting the launcher rotation the toroidal coordinate

of the ECRH/ECCD beam can be adjusted and a change in the elevation angle corresponds

to a radial position in the poloidal plane. Hence the deposition of the ECRH power can be

focussed exactly at the islands O-point.

To asses and improve the performance of the motion controller of the launcher, a mockup

ii

system has been made. This is a copy of the system dynamics and one driven DOF. The

mockup system provides a sandbox environment in which a motion controller can be

developed and tested, to be included in the larger island suppression control scheme. The

work reported in chapter 3 focusses primarily on the setting up of the mockup. To safely

operate the mockup a two level safety system has been applied, making use of both soft

and hard limit switches. Furthermore attention is paid to the setup and connection from

the existing electronics to the controller rapid prototyping environment Matlab&Simulink.

The dynamics of the launcher system have been modeled by making use of Frequency

Response Function (FRF) identification and estimation techniques. A feedback PID

controller has been designed and tested on the system to be stable and meet the demands

on speed and accuracy. This controller is expected to remain stable if transferred to the

real launcher system at TEXTOR, allowing the inclusion into the larger feedback loop on

magnetic island suppression.

Finally, in appendix G, this report presents a list of problems and errors encountered during

the work on the mockup system, together with possible solutions to the problems described.

Samenvatting

Nucleaire fusie is de energiebron van het universum. Het is de drijvende kracht achter ons

zonlicht en daarmee de oorsprong van alle energiebronnen die er momenteel op aarde te

vinden zijn. Veel onderzoek is gericht op het realiseren van deze vrijwel onuitputtelijke

energiebron voor aardse toepassingen. Een veilig fusie-experiment, met reacties zoals

die plaats hebben in het centrum van de zon, kan worden gedaan in een tokamak. In

een tokamak worden elektrische spoelen gebruikt om een donut-vormig plasma vast te

houden; door middel van toroïdale en poloïdale magneetvelden.

In het plasma waar de daadwerkelijke fusiereacties plaats hebben, kunnen een aantal Mag-

neto Hydro Dynamische (MHD) instabiliteiten optreden. Een groep van instabiliteiten,

de zogenaamde "Neo-classical Tearing Modes" (NTMs) of magnetische eilanden kan

worden onderdrukt door bestraling met hoog vermogen radio golven (ECRH/ECCD). Dit

vormt de basis voor het regelprobleem om deze eilanden te stabiliseren en te onderdrukken.

Voor de TEXTOR tokamak is een geïntegreerd detectie en suppressie systeem ontwikkeld.

Dit systeem bestaat uit een Electron Cyclotron Emissie (ECE) detector, waarmee meerdere

locale temperatuurprofielen in het plasma kunnen worden gemeten. Deze zes profielen

maken detectie van de eiland locatie, draai-frequentie en fase mogelijk. Verder bestaat

het systeem uit een hoog vermogen gyrotron (800 kW), dat de ECRH/ECCD actuatie

verzorgt en een in twee vrijheidsgraden (2 DOF) verstelbare richtspiegel; ook wel launcher

genoemd. Door de rotatiehoek van de launcher aan te passen kan de toroïdale coördinaat

van de ECRH/ECCD bundel worden ingesteld en een verandering in de elevatiehoek

correspondeert met een radiale positieverandering in het poloïdale vlak. Zo kan het

depositiepunt van het ECRH/ECCD vermogen precies worden gericht op het O-punt van

iv

een eiland.

Om de prestatie van de bewegingsregelaar te beoordelen en te verbeteren, is er een mockup

van het systeem gemaakt. Dit is een kopie van de systeemdynamica met één aangedreven

vrijheidsgraad. Dit systeem fungeert als testomgeving waarin een bewegingsregelaar

kan worden ontwikkeld en getest, om vervolgens te worden opgenomen in de grotere

regellus voor eiland onderdrukking. Het werk waarover in hoofdstuk 3 van dit verslag

wordt bericht richt zich hoofdzakelijk op het opzetten van deze mockup. Om de mockup

veilig te bedrijven is er een dubbellaags veiligheidssysteem toegepast met zachte en harde

eindschakelaars. Verder is er aandacht voor het opzetten en verbinden van de snelle

ontwikkel omgeving Matlab&Simulink met de bestaande elektronica.

De dynamica van het launcher systeem zijn vervolgens gemodelleerd door gebruik te

maken van Frequentie Respons Functie (FRF) identificatie en benader technieken. Een

teruggekoppelde PID regelaar is ontworpen en getest op het systeem. Deze regelaar voldoet

aan de stabiliteitscriteria en tevens aan de gestelde eisen ten aanzien van snelheid en

nauwkeurigheid. Verwacht wordt dat deze karakteristieken behouden blijven bij toepassing

op het echte launcher systeem van TEXTOR, waardoor deze kan worden opgenomen in de

grotere regellus voor eiland onderdrukking.

Als laatste, in appendix G, toont dit verslag een lijst met problemen en fouten die tijdens

het werk op het mockup systeem zijn geïdentificeerd. Voor elk beschreven probleem valt

ook een mogelijke oorzaak en oplossing te lezen.

Contents

Abstract i

Samenvatting iii

1 Introduction 2

1.1 Nuclear fusion at a glimpse . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Starting the Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 That twist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.4 Tearing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.5 Internship goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.6 This report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2 The tokamak 11

2.1 TEXTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.1 Ohmic Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.2 Neutral Beam Injection . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.3 Radio Frequency Heating . . . . . . . . . . . . . . . . . . . . . . . . 14

2.3.4 ECRH Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.4 ECRH installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

CONTENTS vi

3 The mockup 19

3.1 Actuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2 Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3 Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.4 Livewiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.5 TUeDACS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.6 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.7 Safety system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4 System identification and model deduction 27

4.1 FRF Identification technique . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2 Open loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.3 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.4 Model fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5 Controller design 33

5.1 Controller theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.2 Loop shaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5.3 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.4 Homing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.5 Comparison to the ’real’ launcher . . . . . . . . . . . . . . . . . . . . . . . . 36

6 Conclusions and outlook 39

A Appendix A: Technical data servo actuator 42

B Appendix B: Servostar connector layout 44

C Appendix C: Servostar operational connections 45

D Appendix D: Electronics to connect the Servostar to the TUeDACS MicroGiant 46

E Appendix E: Cable wiring 47

F Appendix F: Simulink model for the homing of the launcher 49

G Appendix G: Errors and possible solutions 56

G.1 Encoder signal and motor design . . . . . . . . . . . . . . . . . . . . . . . . 56

CONTENTS 1

G.2 Motor phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

G.3 EnDAT encoder connection . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

G.4 Terminal commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

G.5 Warnings and practical remarks . . . . . . . . . . . . . . . . . . . . . . . . . 58

G.5.1 Linux OS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

G.5.2 Servostar Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

G.5.3 Matlab & Simulink . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

G.5.4 Simulink library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

G.5.5 Electronics box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

G.5.6 TUeDACS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Bibliography 63

CHAPTER ONE

Introduction

1.1 Nuclear fusion at a glimpse

The sun has been the power source of generations. At the very beginning of human history,

it was lightning ignited fire that kept us warm and kept the carnivore animals at distance.

Burning leafs were considered as a precious, even divine gift from the sky. Both fuel (leafs

full of carbohydrates) and ignition (lightning discharges caused by temperature differences

in the air) were provided by the sun.

Present day energy supplies show remarkable resemblance with this rudimentary power

source. We have managed the chemistry of ignition, but the largest part of our energy

consumption still draws from carbohydrates bounded by photosynthesis. Either present as

’young’ biofuels or as ’old’ charcoal, essentially they are all condensed solar energy.

The world wide energy situation, with ever increasing demand on the one hand and the

staggering oil prices, CO2 emission certificates and governmental intentions to reduce

greenhouse gas emissions on the other, demands for the development of alternative en-

ergy sources. What better energy generation can there be, than that of the ultimate source:

the sun itself. Nuclear fusion provides the possibility to have a virtually unlimited energy

source, based on reactions that also occur in the core of stars like the sun. With raw mate-

1 Introduction 3

rials, i.e. two liter of water and the equivalent amount of lithium found in three ordinary

rocks, a fusion reactor would be able to cover the yearly energy consumption of a typical

household in the Netherlands [1].

Figure 1.1 / It seems incredible, but these rocks and 2 liter of water can supply a typical

Dutch household with enough energy for one year.

Unfortunately such a reactor does not exist yet. The factory layout however exists already

in the mind of fusion physicians and engineers, and a number of experimental reactors

have already been built to understand and manage the fusion reactions. The basic idea of

such a reactor is to use the fusion reaction between deuterium (D) and tritium (T) to form a

helium atom. Both deuterium and tritium are isotopes of hydrogen, where deuterium has

two neutrons in its core and tritium three. After the reaction, the final helium atoms have

a mass m which is slightly less than the sum of its building blocks deuterium and tritium.

(∆m = m+D +m+

T − (m+4He +mn) = 3.1 · 10−29 kg) On the basis of Einsteins theorem on the

equivalence of mass and energy E = mc2 (where E is energy,m is mass and c ≈ 3 ·108 m/s

is the speed of light in a vacuum), one can conclude that an energy of 17.6 MeV (= 2.8 pJ)

is released with this reaction.

In the foreseen reactor, plain water can be brought in and converted to hydrogen and

oxygen through an electrolysis process. Hydrogen naturally contains about 154 PPM (=

0.015 %vol.) deuterium which we can extract relatively easy due to the mass difference. We

now have the raw material for a first fusion reaction. First of all the fuel is heated until

it becomes a plasma, which is the fourth state of matter. The reactor will start up with

a deuterium plasma; the deuterium-deuterium (D-D) reaction is not the easiest fusion

reaction, but this reaction will produce the first neutrons, which can be used in order to

produce tritium in the breeding layer just outside of the main reactor. Here, a reaction

1 Introduction 4

Most of what is now called fusion research aims at exploiting deuteronbreak-up by letting deuterium react with itself, with tritium, or with 3He. Thelatter are produced in d–d reactions, but may also be supplied as fuel alongwith the deuterium. The reactions in question are:

dþ d" tþ pþ 4:0MeV

dþ d"3Heþ nþ 3:3MeV

dþ t"4Heþ nþ 17:6MeV

dþ 3He"4Heþ pþ 18:3MeV

of which the first and second have approximately equal probability (figure1.2). The high cross-section and the high energy yield of the d–t reactionmake it the favourite candidate for terrestrial fusion.

To confuse the terminology still further, even a fission, or spallationreaction like

11Bþ p" 3 4Heþ 8:7 MeV

has been labelled ‘fusion’, which must now be understood to include allenergy-producing reactions between light nuclei.

Figure 1.2. Cross-section, f, for the d–d, d–t and d–3He fusion reactions as a function of

kinetic energy, E, of the relative motion of the colliding nuclei. The curve marked d–d

indicates the total cross-section for the two reactions dþ d mentioned in the text.

The scientific roots 5

Copyright © 2002 IOP Publishing Ltd.

Figure 1.2 / Reaction rate <σ> as a function of the particle energy.

between lithium and the neutrons from the plasma will form the required tritium.

Once enough tritium has been produced, the deuterium-tritium (D-T) reaction can be

started. As we can see in figure 1.1, where the average reaction rate <σ> is given as a

function of the particle energy, the reaction rate is highest for the D-T reaction at low par-

ticle energies. Hence, this reaction is the preferred nuclear fusion reaction for an energy

generation process [2]. The subsequent fusion reactions for this scheme read:

in the vessel

D +D → 3He(0.82MeV ) + n(2.45MeV ) (1.1)

D +D → T (1.01MeV ) +H(3.02MeV ) (1.2)

D + T → 4He(3.50MeV ) + n(14.1MeV ) (1.3)

D +3 He → 4He(3.60MeV ) +H(14.7MeV ) (1.4)

in the breeding layer7Li+ n → 4He+ T + n− 2.47MeV (1.5)6Li+ n → 4He(2.05MeV ) + T (2.73MeV ) (1.6)

The net result of this reaction scheme is a release of energy, however the fusion conditions

for initiation of this reaction scheme are among the extremest on earth. The nuclei from

the fusion fuel all have a positive charge, which makes it extremely difficult to bring them

close enough together to make them fuse. In order to start the fusion reaction we need

particle energies up to 10,000 eV, which corresponds to a high pressure and a temperature

of more than 100 million degrees Celsius - which is about seven to ten times larger than

1 Introduction 5

the core temperature of the sun [3]. A general measure for the required conditions on a net

energy release by a fusion plasma, can be formulated as the Lawson criterion. The criterion

is noted as [4]:

n · T · τE > K (1.7)

where n is the density in particles per cubic meter, T the temperature in keV and τE the

confinement time in seconds. The confinement time is the ratio between the stored energy

in the plasma and the input power. It is a measure for the thermal transport in the plasma.

Now for a fusion powerplant it holds that the constant K should be larger than 3 · 1021

m-3 keV s for a break-even operation and should increase to 5 · 1021 m-3 keV s for sustained

’burning’ of the plasma.

The working conditions that follow from the Lawson criterion impose particulary challeng-

ing design requirements on a fusion reactor. In general it holds that for a higher efficiency

we need higher pressures and higher temperatures, and hence larger plasma volumes, and

additional heating systems.

Figure 1.3 / Layout of an energy producing fusion plant.

1.2 Starting the Fusion

For the confinement of a hot plasma, we need a mechanism that holds the particles

together and prevents them from melting the walls or cooling down so much that the

1 Introduction 6

reaction stops. Two branches of fusion research have developed: inertial and magnetic

confinement. Inertial confinement comes down to providing a lot of energy during a very

short period of time to a small pellet of deuterium-tritium fuel. In practice this is achieved

with high energy lasers or particle beams during a billionth of a second [3]. This results in a

compression and ignition of the fuel pellet, without immediately destroying the containing

vessel, so that the released energy can be converted into a useful carrier.

A second branch of research focusses on magnetic confinement and is based on the mag-

netic and current conducting properties of a plasma. Since a plasma consists of charged

particles, it can be confined by applying electrical and magnetic fields. This implies that

one can use an external magnetic field to shape the plasma and compress the medium in

the vessel.

Several machine designs have been tested, both linear and toroidal devices. Linear devices

suffer from large edge effects, due to their discontinuous geometry. A solution was found

in connecting the two ends of a linear device together, resulting in a toroidal device where

a continuous plasma shape is achieved. The required magnetic field Bθ is of a toroidal

shape, but dependant of major radius R: Strongest on the inside (major radius R0 − a)

and weakest at the outside (major radius R0 + a), as a result of the geometric positioning

of the coils around the torus. These coils will hold the plasma in a torus shape, but do

not stabilize the plasma. Due to the divergence of the toroidal magnetic field along the

major radius, an electrical field is created which forces the negative charged electrons to

the bottom of the plasma and the positive ions to the top. This polarization will give rise to

position instabilities. In order to stabilize the plasma, we could think of a second magnetic

field Bφ, which superpositions a twist to the toroidal magnetic field. This twist short

circuits the positive and negative charged particles, up and down. When this situation is

achieved a Pfirsch-Schlüter current will start to flow through the plasma which provides

full stabilization of the plasma shape.

During the cold war (mid 1940’s until early 1990’s) the fusion research was mainly

carried out in the United States of America and Russia. While the American scientist

worked mainly on stellarators, their Russian colleagues focussed on a different design,

the tokamak. A stellarator is a device in which the plasma is confined by means of a set

of external toroidal coils and external helix shaped coils that fold around the plasma. The

resulting magnetic field has the desired helix shape that can stabilize the plasma shape and

keep it from touching the wall. The main detriment to progress of stellarator research is

their extremely complex and expensive construction and the precise coil alignment which

1 Introduction 7

is needed to generate the correct magnetic fields.

The Russian scientists in the meanwhile developed the ’TOroidalnaya KAmera

MAgnitnymi Katuskami’, abbreviated as tokamak. The ease of construction and promising

high temperatures reported by the physicists from the Kurchatov institute in the late

1960’s, set the stage for present day fusion research which is concentrated on tokamaks.

1.3 That twist

The main difference between the tokamak design versus the stellarator can be found in

the way the poloidal field is generated. Instead of a dedicated set of coils, the plasma

creates its own magnetic field in poloidal direction. This is done by making use of the

conducting properties of the plasma and a large transformer core around the plasma

vessel. By providing a current ramp to the transformers primary winding, the change of

the magnetic field will induce a current in the plasma, which serves as secondary winding

of the transformer. This technique has proven to be a very robust way of generating a

poloidal magnetic field. A drawback to this technique is that it is impossible to sustain this

poloidal field for a long time since the plasma current is induced by a ramped current in

the primary winding, which cannot grow to infinity.

1 Introduction 8

1.4 Tearing Modes

The magnetic structure of a tokamak in operation, comprises an infinite set of nested

toroidal magnetic surfaces; also called flux surfaces. On these surfaces the plasma pres-

sure is constant and each magnetic field line stays on its according surface. The transport

of heat and mass perpendicular to a flux surface (in poloidal direction) is zero in theory.

The surfaces and the overall magnetic configuration can be described by the flux number

or safety factor q, which is the – device specific – ratio between the toroidal and poloidal

field strength, or number of toroidal twists a field line has to make for a single poloidal

turn. In a circular tokamak, q is approximated by [5]

q =r ·Bφ

R0 ·Bθ

(1.8)

where r is the minor radius, R0 the major radius, both in m, Bφ the poloidal magnetic field

strength and Bθ the toroidal magnetic field strength, both in T.

tO OX

rrs

0

Te

ΔTe

Figure 1.4 / Image of the flattened electron temperature profile around an island. At two

sides of the island, a temperature over time signal from a rotating plasma is

depicted, indicating the O-point and the X-point.

On rational values of q, the so-called resonance surfaces, instabilities have a seed to grow.

Here the magnetic flux surfaces start to detach along the separatrix and a Neo-classical

Tearing (NTM) mode can occur. The magnetic configuration is changed, which is referred

to as a magnetic island. Typically NTMs occur at surfaces with q-values of q = m/n = 3/2

or 2/1 [6]. If an island has emerged, the surfaces no longer nest inside each other but

start to drift periodically. This results in an enhanced thermal transport perpendicular to

the original flux surface. The temperature profile is flattened over the island width and

confinement of energy is decreased. Remark that the width of an island changes as a

1 Introduction 9

function of the toroidal coordinate. This means that the island is widest at the so-called

O-point and at a minimum at the X-point; so at the X-point, the original q-profile and flux

surfaces still hold the original shape. In figure 1.4 the temperature is plotted as a function

of the radius, and the effect of island presence for temperature can clearly be seen.

Islands have shown to destabilize if the plasma pressure passes a certain threshold and are

therefore likely to occur in large future devices [7, 8].

1.5 Internship goals

Control of the island width is possible by heating up the center of the magnetic island

by means of Electro Cyclotron Resonance heating (ECRH) and Electro Cyclotron Current

Drive (ECCD). Active control schemes and several control concepts are presently being

designed and developed for this application [9, 10]. At the TEXTOR tokamak, where this

internship has taken place, the ECRH/ECCD feedback system consists of an actuator to

direct and focus a high power radio beam. The same actuator is used to measure the

temperature profile and detect magnetic islands in the plasma. An integrated control

scheme for feedback control on magnetic islands has been designed.

One part of the feedback system is the 2 rotational degrees of freedom (DOF) steerable

mirror, the so-called launcher. The dynamics of this instrument have been measured and

modeled in terms of Frequency Response Function (FRF) estimation and equations of

motion. Based on these characterizations a cascaded control strategy has been designed

and implemented in a simulation environment to improve the launchers performance in

terms of motion control. This controller meets the requirements of 10 rotation in 100 ms,

with a positioning accuracy of 1, which is based on a typical island growth rate of 10 ms or

more [6].

In continuation of previous projects, the improved controller should be implemented

on the real launcher system. In order to avoid safety risks, an experimental test facility

(launcher mockup) has been built that provides a safe sandbox environment to conduct

experiments for verification and improve the control performance.

The first goal is to perform a characterization of the mockup system in terms of FRF mea-

surements and compare these results to the earlier verified dynamics of the real launcher.

1 Introduction 10

This will also require the gain of insight in all technical details of the electromechanical

actuators and the corresponding servo amplifiers. Secondly this knowledge enables the

assessment of possibilities for implementation of the control strategies on the launcher

system and advise on improvements on the system. For example on the position sensing

side there are several possible sensors. A choice has to be made between potentiometers,

encoders or accelerometers.

In the end the goal is to have a motion controller which can be implemented in the overall

feedback loop to stabilize the NTMs in the TEXTOR tokamak. The TEXTOR tokamak

which is an acronym for ’Tokamak Experiment for Technology Oriented Research is

a medium sized tokamak and is owned by the Forschungszentrum (FZ) Jülich and is

operated within the Institut für Energie Forschung 4 (IEF-4), that researches plasma and

fusion physics together with FOM institute for plasma physics ’Rijnhuizen’ and the École

Royale Militaire de Bruxelles.

Research at TEXTOR and other tokamaks (i.e. JET, JT-60 and DIII-D) around the world is

focussed on the ITER tokamak that is being designed and built at the moment of writing

and which will be the first tokamak in the world dedicated to energy production, rather than

plasma physics only. This machine is expected to come into operation in 2018.

1.6 This report

This report was written as an introduction to fusion, based on personal new insights in the

topic of nuclear fusion and with a focus on the TEXTOR tokamak. Secondly this report is

a summary of the FRF identification and controller design work that has been done for the

TEXTOR launcher mockup system; this can be used as a manual for the operation of the

launcher, and as a kick start document for future work on the launcher or the mockup. Ad-

ditionally a number of problems and other system specific topics will be treated in appendix

G, together with possible solutions.

CHAPTER TWO

The tokamak

2.1 TEXTOR

The TEXTOR tokamak was built around 1980. The toroidal field is generated by 16 toroidal

field coils around the vessel. The plasma current is induced by an iron core transformer. It

has six yokes and an Ohmic coil wound around the central leg. There are two vertical field

coils, that compensate hoop forces, and four position coils, that can be used to position

the plasma with controlled fields, both in horizontal and vertical direction. Further details

about the TEXTOR tokamak can be found in table 2.1 [11].

A rather unique set of coils that is available at TEXTOR is the Dynamic Ergodic Diveror

(DED). These coils can be used to superposition a predefined distortion field on the

plasma. Although initially designed to focus the heat load of the plasma onto the wall and

to test surface material for ITER, these coils proved to be especially appropriate to excite

specific Magneto Hydro Dynamics (MHD) modes in the plasma. If the coils are supplied

with an AC voltage source, the tearing mode instabilies in the plasma, tend to phase lock

to the DED frequency. This phenomena is useful to set up special experiments on NTM

stabilization and control.

2 The tokamak 12

Table 2.1 / TEXTOR parameters

Parameter Value Unit

Major radius R0 1.75 [m]

Minor radius a 0.47 [m]

Toroidal magnetic field BT <3 [T]

Plasma current Ip <800 [kA]

Pulse length <10 [s]

Total auxiliary heating power 8 [MW]

Maximum NBI power two beams with 1.5 MW each

Maximum ECRH power two gyrotrons: 800 kW or 350 kW

Maximum ICRH power 4 [MW]

Typical central plasma temperature (electron/ion) 1 [keV]

Typical central density ne 3·1019 m-3

2.2 Performance

To address tokamak performance, the ratio between external magnetic pressure and inter-

nal plasma pressure is used. This ratio β is a measure for confinement and can be expressed

as

β =< p >

< B2/2µ0 >=< nI · k · TI > + < ne · k · Te >

< B2/2µ0 >(2.1)

where <> denotes the averaging over particles of all velocities and subscripts I and e de-

note respectively the ions and electrons in the plasma. Constant k denotes the Boltzmann

constant in eVK-1 and µ0 the magnetic permeability of a vacuum in Hm-1. The performance

of a reactor can be expressed with β and the confinement time (see also equation 1.7).

Due to fundamental plasma properties the theoretical limit for beta lies around 6% for

a tokamak. For TEXTOR the experimental βmax is about 1.6% [12]. The best performing

tokamaks (i.e JET) establish beta values up to 4.5%.

Enhancing tokamak performance requires operation in higher beta regimes. This drives the

equilibria of a plasma, further towards instability. Modes that come into play in high per-

formance tokamaks are for instance sawtooth instabilities, Edge Localized Modes (ELMs)

and Neo-classical Tearing Modes (NTMs) or magnetic islands. These instabilities can ulti-

mately trigger a disruption, which is a rapid decrease of confinement and puts a huge force

and thermal load on the vessel walls. A disruption in a large device such as ITER, can have

disastrous effects and may destroy the machine.

2 The tokamak 13

2.3 Heating

2.3.1 Ohmic Heating

As soon as a discharge occurs and a plasma current starts to flow, the plasma begins to heat

up due to this current and its own resistance. The so-called Ohmic heating can only heat up

the plasma to a limited temperature. With increasing temperature, the resistance drops, so

this heating can heat the plasma up to 1.7 - 2.6 keV, which is far below the desired plasma

temperature for an appropriate fusion for energy scenario. Additional heating systems are

needed to further ramp up the temperature and realize the desired plasma temperatures.

Several heating systems are available, each with their own specific benefits.

2.3.2 Neutral Beam Injection

Neutral beam injector is a system that consists of a linear accelerator for ionized gas

particles. Particles are accelerated to a high energy level and led into a neutralizer or gas

cell where about 50% of the particles are neutralized by transferring their energy to the

gas in the cell, which can be H2, D2, 3He or 4He. The remaining ions are deflected by a

magnetic field and collected. The beam is then led through an aperture into the plasma

under an angle such that the beam is tangential to the toroidal radius. By adjusting the

aperture opening the beam power can be regulated. Since the injected atom particles are

chargeless, they are not influenced by the magnetic field in the vessel and can penetrate

deeply into the plasma, where they can transfer their energy via collisions with the plasma

particles. By choosing the appropriate neutral particles, NBI can be used also to fuel the

fusion reactions in the plasma.

Often the system is installed in duplo, to regulate the momentum transferred to the

plasma, which directly influences the plasma rotation. One NBI injector is installed in

the same direction as the plasma current (co-current), a second system is installed in

counter-current direction. If both beams balance their power output, the net momentum

applied to the plasma is equal to zero.

2 The tokamak 14

2.3.3 Radio Frequency Heating

Another way of heating the plasma, is by means of radio waves. There are several fre-

quencies available, each with specific characteristics concerning propagation through the

plasma and absorption by plasma particles (ions or electrons). They are usually referred

to as Ion Cyclotron Resonance Heating (ICRH), Electron Cyclotron Resonance Heating

(ECRH) and lower hybrid heating. ECRH has the advantage that it has a very localized

absorption, hence for local temperature control (and instable islands), this is the most

appropriate actuator and will have focus in this report.

2.3.4 ECRH Heating

Electron cyclotron resonance heating and Electron Cyclotron Current Drive (ECCD, the in-

duce of a local current) is based on the principle that energy can be transferred to the elec-

trons in a magnetically confined plasma through radio waves. The electrons gyrate around

a magnetic field line, against the direction of the magnetic field. They gyrate at the electron

frequency ωce, which is given by [11]

ωce =e ·Bme

(2.2)

where e is the electron charge and me the mass of an electron. So fce = ωce/2π ≈28 · B GHz, if B is given in T. At this frequency and its higher harmonics n · ωce the

electron emits electromagnetic radiation, but it also absorbs energy from an electromag-

netic radiowave [13]. This absorption frequency depends only on the magnetic field and as

stated before, in a tokamak the magnetic field has a 1/R dependency. This implies that an

electromagnetic beam of a certain frequency ω, corresponds to a specific radial position in

the plasma

R =n · e ·B0 ·R0

me · ω(2.3)

An ECRH/ECCD installation makes use of this relation to deposit energy locally. The

system comprises of a gyrotron that generates a high power radio wave. Through a quasi

optical transmission line the beam is led into the plasma where the energy is absorbed

at the corresponding radius. Often the system includes a steerable mirror (launcher) at

the end of the wave guide. By adjusting the (poloidal) elevation angle (θ) of the beam,

the spot where the power is deposited can be adjusted along the fixed plane at posi-

tion R(ω). By adjusting the (toroidal) rotation angle (φ) of the launcher, the radio beam is

set co or counter-current with respect to the plasma current (and plasma rotation direction).

2 The tokamak 15

By changing the rotation angle φ, the ratio between heating (ECRH) and current drive

(ECCD) is influenced. These two effects are coupled, but in general a co-current launch

angle leads to more heating, where as a counter-current launch angle induces a larger

current drive component. In general the complete system is referred to as ECRH.

2.4 ECRH installation

At TEXTOR the ECRH installation consists of two gyrotrons; one 110 GHz gyrotron

(350 kW, 200 ms) and a 140 GHz gyrotron (800 kW, 10 s). The radio beam is led through

a quasi optical transmission line (meaning that the radio wave is transmitted through air

as if it was a light ray) to a Chemical Vapor Deposition (CVD) diamond window, where the

wave enters the tokamak [14]. At the inside of the tokamak the beam is conducted to the

desired plasma position by the launcher.

Figure 2.1 / An overview of the complete ECE feedback system and all of its components.

The same launcher mirror is used to pick up the ECE emission from the plasma. This

signal is led back through the same transmission line to an optics box, where the reflected

signal is separated from the high power 140 GHz beam that comes from the gyrotron. The

separation is done by means of a dielectric plate which has a very low reflection coefficient

at frequencies 140 ± n · 3 GHz and a high reflection coefficient at 141.5 ± n · 3 GHz.

This allows a frequency selective decoupling of the two beams. The high power 140 GHz

beam goes right through the dielectic plate whereas the low power ECE signal is led into a

2 The tokamak 16

horn antenna and once more filtered by a radio Notch filter at the gyrotron frequency of

140 GHz. The final signal consists of six radio channels that translates into the tempera-

tures at six radial positions on the beam line [15].

Largest benefit of this system is that the detection and actuation on magnetic islands, stay

within the same metrology frame. The use of an absolute position coordinate is abundant.

This enables the direct use of these signals for feedback control. Alternative systems that

depend on different diagnostics, have to translate the measured position into the desired

actuator position. Often this is done with Mirnov coils (flux measurement coils around

the vessel) [16]. To get an exact position of the island center a reconstruction of the plasma

equilibrium has to be made, which requires very complex calculations, that have to be made

in real-time to enable timely feedback corrective actions.

Island suppression has shown to be possible through early detection and ECRH actuation

[9, 10, 17]. In order to achieve a feedback controller that stabilizes the 2/1 NTM, we need

to position the launcher accurately and fast. The underlying idea is to search for an island,

by sweeping the line of sight through the plasma. The measured ECE channels show

six ’temperature’ signals, corresponding to six positions in the plasma. So over time we-0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5

t(s)

EC

E c

hann

els

1-6

[A.U

.]

(a)

132.5 GHz135.5 GHz138.5 GHz141.5 GHz144.5 GHz147.5 GHz141 GHz EC11

1.500 1.502 1.504 1.506 1.508 1.510 t(s)

EC

E c

hann

els

1-6

[A.U

.]

(b) 132.5 GHz

135.5 GHz138.5 GHz141.5 GHz144.5 GHz147.5 GHz141 GHz EC11

Figure 2.2 / Raw ECE measurements show the temperature profiles at different radial posi-

tions. It is clear that the channels swap phase as they ’pass’ an island and that

the maximum amplitude is found at the widest point of the island. In this case

the island is located around the radial position, that corresponds to 135.5 GHz.

2 The tokamak 17

see six complete circular profiles of the temperatures in the plasma. In an ideal plasma

without islands, the temperature profiles are flat. If an island prevails, the signals become

sinusoidal. If the island grows, the signal amplitude increases due to the larger temperature

fluctuations near the island. Considering all six channels, the largest amplitude is found,

near the spatial edge or separatrix of the island. This is due to the fact that the temperature

throughout the island is more or less constant and the edge of the island shows the largest

temperature distortion. This also implies that the temperature profiles of the channels that

are located further towards the outside of the plasma, with respect to the island center

have a minimum temperature, whereas the plasma center side channels have a maximum

temperature. By looking at the phase information of the channels, the signal shifts 180

degrees in phase if it surpasses the island center.

The exact location of an island center can be found by interpolating the two channel

frequencies, in between which the phase shift has occurred. This frequency corresponds to

a position, relative to the launcher angle. The launcher can now be steered to the position

such that the gyrotron frequency (140 GHz) overlays the chord where X- and O-point can

be found. The next step is to synchronize the island period and the passing of the O-point,

with the firing of the gyrotron. Hence we can heat up just the O-point, which leads to a

more efficient island suppression [18, 19].

CHAPTER THREE

The mockup

The mockup system is a reduced copy of the TEXTOR launcher system with only one

Degree of freedom (DOF). It consists of a mechanical part, one actuator, 380V power

supply, a servo amplifier, two personal computers, for control and monitor tasks, a safety

electronics box and a TUeDACS system for data acquisition and DA/AD conversion. The

mechanics, actuator, power supply and servo amplifier are identical to the TEXTOR system.

At the start of the internship the mockup consisted of the actuator, the servo controller

and two actuator cables for power supply and data transport. A part of the workload was to

assemble everything and construct a working setup.

3.1 Actuator

A linear servo actuator, type MA408F from the firm Danaher Motion Kollmorgen was

chosen as the actuator for the launcher. It is a six poled (three phase) brushless rotational

spindle actuator. Under the hood there is a rotational servomotor that drives a linear 10mm

pitch spindle. From the outside it looks like a regular pneumatic or hydraulic actuator and

it is intended for precision motion tasks with high loads. It has a DC powered brake, which

3 The mockup 19

Electronicsbox

Servostar

Relay

380V CEE stekker

TUeDACS

PC

Launcher

MotorHard and softlimit switches

Homing switch

Figure 3.1 / An overview of the components in the mockup system.

is released on a high signal. This is also failsafe in case of a power loss.

To drive such a motor, a PWM regulated AC voltage is applied in three phases to two (six

poles/three phases) of the motor windings at a time. The motor encompasses six sinu-

soidally distributed stator windings and a rotor with permanent magnets. In alternating

sequence the windings are actuated. The biggest advantage of such a motor is that it has a

ripple-less torque output and a very large operating range [20].

Furthermore the motor is equipped with a high resolution Heidenhain R© EQN-1325

encoder, for position measurement. This encoder has 2048 lines per revolution which

comes down to a rotation accuracy of 10’33” and a linear accuracy of 4.88µm. This encoder

is of the sincos type, which means that it sends out a sine and a cosine channel. Because of

the 90 degrees phase difference between both channels it is possible to derive the rotation

direction of the encoder, and a quadrature counter would know to increase or decrease the

position. The EQN-1325 encoder sends out the position in two formats. The raw sincos

signal (differential) and an absolute position up to 4096 distinguishable turns. The latter

signal is presented in the EnDat 2.2 format [21].

3 The mockup 20

47

Parameters and Memory AreasThe encoder provides several memory areas for parameters. These can be read from by the subsequent electronics, and some can be written to by the encoder manufacturer, the OEM, or even the end user. Certain memory areas can be write-protected.

The parameters, which in most cases are set by the OEM, largely defi ne the function of the encoder and the EnDat

interface. When the encoder is exchanged, it is therefore essential that its parameter settings are correct. Attempts to confi gure machines without including OEM data can result in malfunctions. If there is any doubt as to the correct parameter settings, the OEM should be consulted.

Parameters of the encoder manufacturer

This write-protected memory area contains all information specifi c to the encoder, such as encoder type (linear/angular, singleturn/multiturn, etc.), signal periods, position values per revolution, transmission format of position values, direction of rotation, maximum speed, accuracy dependent on shaft speeds, warnings and alarms, ID number and serial number. This information forms the basis for automatic

confi guration. A separate memory area contains the parameters typical for EnDat 2.2: Status of additional information, temperature, acceleration, support of diagnostic and error messages, etc.

Absolute encoder Subsequent

electronics

Absolute position value

Operating parameters

Operating status

Parameters of the OEM

Parameters of the encoder manufacturer for

EnDat 2.1 EnDat 2.2

EnD

at in

terf

ace

Monitoring and Diagnostic

FunctionsThe EnDat interface enables comprehensive monitoring of the encoder without requiring an additional transmission line. The alarms and warnings supported by the respective encoder are saved in the “parameters of the encoder manufacturer” memory area.

Error message

An error message becomes active if a malfunction of the encoder might result in incorrect position values. The exact cause of the disturbance is saved in the encoder’s “operating status” memory.Interrogation via the “Operating status error sources” additional information is also possible. Here the EnDat interface transmits the error 1 and error 2 error bits (only with EnDat 2.2 commands). These are group signals for all monitored functions and serve for failure monitoring. The two error messages are generated independently from each other.

Warning

This collective bit is transmitted in the status data of the additional information.It indicates that certain tolerance limits

of the encoder have been reached or exceeded—such as shaft speed or the limit of light source intensity compensation through voltage regulation—without implying that the measured position values are incorrect. This function makes it possible to issue preventive warnings in order to minimize idle time.

Online diagnostics

Encoders with purely serial interfaces do not provide incremental signals for evaluation of encoder function. EnDat 2.2 encoders can therefore cyclically transmit so-called valuation numbers from the encoder. The valuation numbers provide the current state of the encoder and ascertain the encoder’s “functional reserves.” The identical scale for all HEIDENHAIN encoders allows uniform valuation. This makes it easier to plan machine use and servicing.

Cyclic Redundancy Check

To ensure reliability of data transfer, a cyclic redundancy check (CRC) is performed through the logical processing of the individual bit values of a data word. This 5-bit long CRC concludes every transmission. The CRC is decoded in the receiver electronics and compared with the data word. This largely eliminates errors caused by disturbances during data transfer.

Incremental signals *)

*) Depends on encoder

» 1 VPP A*)

» 1 VPP B*)

Parameters of the OEM

In this freely defi nable memory area, the OEM can store his information, e.g. the “electronic ID label” of the motor in which the encoder is integrated, indicating the motor model, maximum current rating, etc.

Operating parameters

This area is available for a datum shift, the confi guration of diagnostics and for instructions. It can be protected against overwriting.

Operating status

This memory area provides detailed alarms or warnings for diagnostic purposes. Here it is also possible to initialize certain encoder functions, activate write protection for the OEM parameter and operating parameter memory areas, and to interrogate their status. Once activated, the write protection

cannot be reversed.

Figure 3.2 / Working principle of an encoder: A circular ruler with accurate position incre-

ments is moved along a stationary enlighten grid, two receiving photo diodes

(90 phase shifted) collect the interference signals and transmit a sinusoidal

channel as a function of the displaced angle. 1Vpp means 1 Volt peak to peak.

Channel A is sine, channel B cosine.

3.2 Controller

The controller/amplifier used for this actuator is a digital servo amplifier of the type

ServoStarTM

600 (Kollmorgen Seidel R©). This controller has an internal control loop to sup-

ply the three phases of the motor with a current, such that the torque output is regulated. It

has an internal control structure that can be addressed with the Microsoft R© WindowsTM

soft-

ware ’drive’ [22]. The controller has an internal EEPROM memory that can be programmed

with the drive software. In this memory the motor characteristics will be stored and a

simple motion task can be preprogrammed. Furthermore this controller has a hardware

safety circuit (ready to operate switch BTB/RTO and a hardware enable input), it has

several digital and analog inputs, different connectors for communication to a PC or to

another Servostar, connections for a resolver or an encoder, a 24V supply voltage and

the connections from the mains and to the drive. For an overview of the connections see

appendices B and C.

3 The mockup 21

3.3 Mechanics

The launcher mockup mechanics only comprise the two driverods for the rotational

actuation, which pivot around two rotational joints. The mirror is suspended on the end

of these rods by two spherical bearings. The elevation movement is unconstrained since

the according rod is not connected. The conversion from the two translational movements

x1 and x2 in m, into the rotation α and elevation β in radians, is possible through the

following goniometric relations

from x1 , x2 to α , β

α = arccos

(A2

1 − (C2 + x21)−B2

−2 ·√C2 + x2

1 ·B

)+ arctan

(C

x1

)− π

2(3.1)

β = arctan

(−C1x2 cosα− sign(E) ·

√C2E2 + E2x2

2 cos2 α− E4

x22 cos2 α− E2

)(3.2)

and from α , β to x1 , x2

x1 =√A2

1 − (B1 − C)2 −√A2

1 − (B1 cosα− C)2 +B1 sinα (3.3)

x2 =√A2

2 − (B2 − C)2 +B2 sin β cosα−√A2

2 − (B2 cos β − C)2 − (B2 sin β sinα)2 (3.4)

where

x1 = x1 +√A2

1 − (B1 − C1)2

x2 = x2 −√

22 − (B2 − C)2

D =√

(A22 −B2

2 − C2)

E =x2

2 −D2

2B2

and geometric constants

A1 = 255 · 10−3m, A2 = 215 · 10−3m, B1 = 62 · 10−3m,

B2 = 60 · 10−3m, C = 57 · 10−3m

3.4 Livewiring

In order to livewire the launcher in a safe way, a power supply unit is set up. This power

supply connects to a CEEform, 16A three phase power supply. Internally each phase goes

3 The mockup 22

−0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8−0.05

−0.04

−0.03

−0.02

−0.01

0

0.01

0.02

0.03

0.04

0.05position of the rotation rod

α [rad]

x 1 [m]

Figure 3.3 / x1 only depends on the rotational angle α, whereas x2 depends on both α and

β. This degree of freedom however is not connected in the mockup. The small

circle indicates a maximum in the position derivative, where the largest posi-

tion errors can be expected.

through a safety fuse and one phase is tapped to feed the 24V source. The 24V supplies the

Servostar amplifier and if the Servostar has booted up, the ready to operate signal is led, via

the safety system to the mains contactor. Also the signals from the emergency system enter

the box and if one of these signals falls off (failsafe for cable break) the mains contactor

disconnects all three phases. If the system is secure, a 24V line is contacted as well, which

is connected to the hardware enable of the Servostar. For a more detailed overview of the

connections please see Appendix C.

The Servostar is capable of supervising a simple control structure. It has an internal

controller that monitors the movements of the spindle and it can be steered by a preset

trajectory or by CAN communication.

The idea is to develop an external motion controller that can be integrated into the ECE

detection system and is apart of the feedback on the magnetic islands. This system can be

connected to input a number of sensor signals to use in the controller, i.e. ECE data and

Mirnov coils. This system should also control the launcher angles, by means of a position

feedback controller. It must be a seamless part of the whole controller.

3 The mockup 23

3.5 TUeDACS

As a rapid prototyping environment for the mockup motion controller the Linux version

of Matlab R© & Simulink R© (version R2006b, MathworksTM

2006) is used. The complete

operating system and the software was installed to the harddisk of a test computer from

the TUeDAX Linux live DVD, v. 3.2.7. Within this environment we can target the real-

time application interface (RTAI) that communicates with the TUeDACS hardware for data

acquisition, digital I/O, A/D and D/A conversions. Note that for a good performance the

TUeDACS should be connected through a USB 2.0 port (not 1.1, check the control led at

the frontpanel of the TUeDACS). In this way the position control of launcher angles can be

taken out of the Servostar into the more flexible Simulink environment and integrated into

the larger control loop. The Servostar has to be configured as a current amplifier, which

can be steered by the analog input (X3 - 4,5). The encoder position information has to be

forwarded to the X5 output. These configuration alterations can be made within the drive

software.

3.6 Electronics

To read out the safety system states, an electronics box has been designed, that conducts

the safety states into the TUeDACS. This box has four overload protected 24V LEMO-

connectors and two unprotected 5V LEMO-connectors at the front. The box is supplied

with both a 24V voltage and a 5V voltage.

Each connector consists of two pins for supply (green) and return (white) and a ground at

the housing. These can be used to connect a safety or homing switch. The common pole

(comm) should be connected to the return pin, the normally closed (NC) pole should be

connected to the supply and the normally open (NO) to the ground. The connection to the

ground is crucial. If this pole is not connected, the voltages start to float and tends to stay

high, due to the electronic internal inversion and pull up circuit. These signals are now

routed to both the TUeDACS (inverted) and the Servostar.

3 The mockup 24

Figure 3.4 / A picture of the fully wired mockup.

3.7 Safety system

The safety system that supervises the system is set up in two different levels. The ’soft’

safety system consists of the launchers first line limit switches. The signals are via the

electronics box transferred to the Servostar and the TUeDACS. On the Servostar a limit

switch signal activates the software based internal emergency system. The velocity observer

from the Servostars internal control loop downramps the velocity profile to zero and in less

than a second the system is halted. Note that the system may have some overshoot before

it is completely at rest.

In some cases the velocity is so high that after the first safety stop the system cannot be

halted within the small overshoot range and a second line safety switch is activated. This

’hard’ switch directly disconnects the 380V power relay and the ’hardware enable’ input

on the Servostar. If this system has been triggered, the 24V supply to the motor release-

brake is disconnected and the brake immediately halts the complete launcher. If the ’hard’

safety system is activated, the system needs to be reset manually. To reset the system first

disconnect the TUeDACS controller (in Matlab), than the switches have to be manually

pulled back (this may require dismounting them), which reactivates the power relay. Now

3 The mockup 25

the Servostar can be reset from the Drive software. To do this click on the warning/error

button and choose reset amplifier.

CHAPTER FOUR

System identification and model deduction

In order to properly design a motion controller for the mockup system, a model of

the dynamics is made. This model is obtained by making use of Frequency Response

Function (FRF) identification and estimation techniques. Since the mockup system is

non-continuous, meaning that there are constraints to the motion in both directions, a

closed loop identification is used to deduct a model of the launcher.

4.1 FRF Identification technique

Control related system identification often makes use of FRF estimation techniques. The

frequency response function is defined as the gain and phase response of the to be iden-

tified system or plant (G). For a Single Input, Single Output system (SISO) the formal

description reads:

y(t) =

∫ ∞−∞

x(τ)h(t− τ)dτ (4.1)

where x (or u) is the input to the system, y is the output and h(τ) is the impulse response of

the system. If we now change from the time domain to the frequency domain, calculating

the fourier transform of these signals we derive:

Y (f) = H(f)X(f) (4.2)

4 System identification and model deduction 27

We call H(f) the frequency response function that relates gain and phase of a harmonic

excitation to the harmonic system output.

In practice a broadband input signal with energy content at all frequencies is used to excite

the system, for instance a white noise signal. By looking at the power of a signal instead

of the real signal in the frequency domain, internal noise and non linearities have a low

correlation with the input signal and will not show up in the transfer function.

For cross power techniques it is needed to simultaneously measure both input and output

signal. For this reason, we feed through the D/A output signal of the TUeDACS directly to

one of the A/D input channels. In this way we will have at the same time a measurement

for both in- and output of the system.

Now the cross power spectrum (Sxy) and the auto power spectrum (Sxx) can be calculated

by

Sxx(f) =1

TX∗(f)X(f) (4.3)

Sxy(f) =1

TX∗(f)Y (f) (4.4)

And the frequency response follows from

H(f) =SxySxx

(4.5)

If the powerspectra are known, than also the coherence can be calculated; a measure for

the linearity of input and output and the influence of the input signal on the output. The

definition for the coherence reads

Cxy =|Sxy|2

Sxx(f)Syy(f)(4.6)

This is a number between one and zero and if the coherence for a specific frequency is

close to one this means that there exists a strong linear relationship between input and

output.

In Matlab these routines are automated in the functions tfestimate and mscohere.

Both of these functions accept input parameters that allow the averaging over a num-

ber of Fast Fourier Transform (FFT) blocks. The input arguments are: WINDOW, to take

a smooth window instead of a block, NOVERLAP, defines the number of samples overlap

between the blocks (this has to be smaller than the blocksize), NFFT, is the block size

4 System identification and model deduction 28

Output1Servostar & Mockup (G)

White Noise

u y

Figure 4.1 / A scheme for open loop measurements

Output1

White noise

Reference profileGenerator

Servostar & Mockup (G)Controller (K)ew

u y

Figure 4.2 / A scheme for a closed loop system identification

or the number of samples the FFT is calculated with, (Of course this should be smaller

than the length of your sample), Fs, is the sample frequency (set in the configuration

parameters window in Simulink). Note that a longer sample block enhances the resolu-

tion on the frequency axis. If you take for instance Fs/0.25 samples (resembles 4 sec-

onds of data), the frequency resolution is 0.25 Hz, however if the resolution is increased

too much there is less averaging. For the conducted experiments these parameters were

set to [WINDOW, NOVERLAP, NFFT, Fs] = [hanning(T*Fs), 0.5*T*Fs, T*Fs, Fs],

where Fs is 16,000 and T is 1/0.25. This resembles a frequency resolution of 0.25 Hz and

sample blocks of 4 seconds.

4.2 Open loop

After the mockup setup has been livewired and the first tests showed a system responding

to the input signals, the system identification could commence.

A first open loop (OL) test was performed in order to see how the system responds to

the input. A sinusoidal signal was applied to the input and by very slowly increasing the

amplitude the system started to move. Now to calculate the transfer function from input to

output, qadscope (Matlab command qs_usb) has been used.

4 System identification and model deduction 29

10−1

100

101

102

103

−180

−160

−140

−120

−100

−80

−60

−40

−20

Servostar & Mockup (G)A

mpl

itude

[dB

]

10−1

100

101

102

103

−300

−200

−100

0

100

Pha

se [d

egre

e]

Frequency [Hz]

Figure 4.3 / Closed loop identified frequency response function for the Servostar and the

launcher mockup.

4.3 Closing the loop

Since the system has two limit stops we would like to close the loop as soon as possible, in

order to prevent the system from running off into the limit switches. In a first attempt the

system was closed, using a very low gain proportional controller, based on the first open

loop FRF identification.

After a first test, the system shows to be stable and subsequently a control scheme has been

set up for closed loop identification. In this scheme we add a white noise signal w to the

controller output uC . So the total input becomes u = uC + w. We have to make sure that

u and w are of the same magnitude, otherwise the summing point is not balanced, which

will give an incorrect relation from w to u. The last signal we need is the error e, which is

the difference between the reference signal and the system output.

4 System identification and model deduction 30

To reconstruct the plant from these signals we need the following calculations.

S =u

w=

1

1 +KG(4.7)

PS =−yw

=e

w=

−G1 +KG

(4.8)

G =−PSS

=y

u(4.9)

With Matlab we calculate the tfestimate and mscohere from w to u for the sensitivity

and from w to e for the process sensitivity (using the same FFT blocksize and other

parameters). Afterwards the two signals are element wise divided to obtain the plant

G=-1*PS./S.

During the measurement a weak feedback gain was applied and the reference input was set

to a low frequent, large amplitude sine, so the system is never operating in the non-linear

stick-slip friction regime. Now a band limited white noise up to 4,000 Hz is injected after

the controller output as disturbance w and we save the signals w, u and e. The derived

frequency response functions are depicted in figure 4.3.

100

101

102

103

104

105

−200

−150

−100

−50

0

50

100

150

200

Frequency [rad/s]

Pha

se [d

egre

e]

100

101

102

103

104

105

10−10

10−8

10−6

10−4

10−2

100

Mag

nitu

de [−

]

Plant data (solid) & estimated fit (dash)

Figure 4.4 / FRF data and the fitted model.

4 System identification and model deduction 31

4.4 Model fitting

Now with the FRF data it is possible to fit a transfer function in the frequency domain

onto this data. This is done with the frsfit tool from the DIET toolbox. The input

parameters for this function read [num,den] = frsfit(fr,hz,struc), where num and

den will be the output arguments, which are the numerator an denominator coefficients

for the transfer function in laplace variable s. Furthermore fr stands for the frequency

response data vector and hz for the frequency vector, both produced by tfestimate. struc

Denotes a vector with three elements[nden, nnom, nint], where nden is the order of the

denominator, nnom the order of the nominator and nint the number of integrators in the

transfer function.

The model has been fitted with the parameters [nden, nnom, nint] = [6,4,2] with a

larger weight on the first, smooth part of the FRF and the estimated function is depicted in

figure 4.4. This fit will serve as a basis to further controller design for the mockup launcher.

CHAPTER FIVE

Controller design

Based on the fitted frequency response data a controller is designed that stabilizes the

system up to a high bandwidth. For this reason we would like to have a small loop gain for

all frequencies, so that the disturbance rejection is high.

5.1 Controller theory

Various control techniques are thinkable, but for simplicity we follow a loop shaping ap-

proach which is sufficient for this SISO plant. The controllers at disposal for this task are

a Proportional Derivative (PD) controller and a lead/lag filter in combination with a con-

troller gain. Additionally an integrator (I) action may be added for extra performance at low

frequencies [23]. Written in terms of the Laplace variable s these equations read:

CPD = KP +Kvs (5.1)

Clead/lag = Kc

1 + 12πτ1s

1 + 12πτ2s

(5.2)

CI =KI

s(5.3)

Where KP is the proportional gain, Kv the derivative gain, KC is controller gain of the

lead lag filter and τ1 and τ2 are the parameters to adjust the frequency of the lead/lag start

5 Controller design 33

(τ1) and the lead/lag end (τ2). The ratio γ = τ1τ2

defines if the filter adds a phase lead or

lag. If γ > 1 the filter adds a phase lead and if γ < 1, the filter adds a phase lag. KI is the

influencing parameter for the integrator action and defines the maximum frequency up to

which the integrator contributes.

In essence both controllers are the same, although the PD controller has an increasing gain

for higher frequencies. So to prevent the amplification of noise we always use a second

order low pass filter to prevent this noise amplification.

2nd Order low pass filter:

Clowpass =1

s2

ω2co

+ 2β sωco

+ 1(5.4)

where ωco is the cutoff frequency and β the damping of the resonance at the cutoff

frequency, or a measure for how sharp, the cutoff needs to be.

5.2 Loop shaping

Using Shapeit as a loop shaping tool for the fitted plant, two controllers have been derived

[24]. One based on a PD controller and another on a lead controller. The parameters for

both controllers are given in table 5.1. The bode plots for open loop characteristics with

Table 5.1 / Controller parameters

Lead/lag Controller PD Controller

τ1 = 6 [Hz] KP = 47

τ2 = 300 [Hz] Kv = 2

ωco = 300 [Hz] ωco = 300 [Hz]

β = 0.5 β = 0.5

both controllers are depicted in figure 5.1. As shown in figure 5.1, the controller based on a

PD control scheme has a slightly better performance. It has a bandwidth of 15 Hz, meaning

that any signal up to 15 Hz can be tracked by the controller, against a 10 Hz bandwidth for

the lead controller, based on the lead/lag filter. Furthermore all stability criteria are met, i.e.

a gain margin of 6 dB and a phase margin larger than 30 .

5 Controller design 34

100

101

102

103

−150

−100

−50

0

Mag

nitu

de [d

B]

Bode plot for both controllers

100

101

102

103

−200

−150

−100

−50

0

50

100

150

200

Frequency [Hz]

Pha

se [d

egre

es]

lead/lag controllerPD controller

−4 −3 −2 −1 0 1 2−3

−2

−1

0

1

2

3

Re

Im

Nyquist plot for both controllers

Gain margin

lead/lag controller

minus one point

PD controller

Figure 5.1 / Two controllers for the Mockup

5.3 Performance

The PD controller has been implemented in the real setup and its performance has been

checked to meet the requirements as stated in section 1.5. To see if the controller satisfies

the demand of a rotation of 10 in 100 ms, we look at the step response in figure 5.2.

This trajectory shows that the overshoot for the lead/lag based controller is about 42.4%

whereas the overshoot for the PD based controller is about 33.5%. After 100 ms the error is

13.8% (which corresponds to 1.38 deviation) for the lead controller and only 5.1% (= 0.51

deviation) for the PD controller and decaying rapidly. This meets the set requirements to

speed and accuracy.

To asses error rejecting performance, the sensitivity function for the open loop is plotted

in the right part of figure 5.2. It can be seen that there is a good error rejection up until

8.5 Hz for the lead controller and for the PD controller errors up to 15 Hz are rejected. This

means that motions on a timescale as small as 83 ms can be tracked. This also is in line

with expectations to the launchers motion control system.

5.4 Homing

For an accurate positioning of the mirror angles the linear motions of the actuator have to

be translated into rotation and elevation angles. Since there is a non-linear relation between

these states a reproducible zero position has to be set every time the launcher is started.

5 Controller design 35

1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.50

0.5

1

1.5Step response for both controllers

lead/lag controllerPD controller

10−2

10−1

100

101

102

103

−100

−80

−60

−40

−20

0

Mag

nitu

de [d

B]

Sensitivity plot for both controllers

10−2

10−1

100

101

102

103

−200

−150

−100

−50

0

50

100

150

200

Frequency [Hz]

Pha

se [°

]

lead/lag controllerPD controller

Figure 5.2 / Step response and sensitivity of the system showing both controllers.

To achieve this, a homing procedure has been designed that is automatically executed at

the start of an experiment. The Simulink model for the homing procedure, makes use of

several discrete events, to detect a trigger from the home switch, reset the actual position to

zero and move the system to a fixed offset, from where the motion tracking task can start.

The model has been set up in such a way that a separate homing controller is used, so that

full freedom is maintained for controller improvements. The complete system is masked in

Simulink and resembles the inputs and outputs as if it was the ordinary launcher system.

The difference being, that during the homing procedure the controller is not working.

Under the mask the homing controller is found. This homing procedure is based on three

discrete states: state one is the slowly moving of the launcher to ’find’ the home switch and

set this position to the zero position, during state two the mirror is moved away from the

zero point to a safe starting distance and in state three the complete control is given to the

’normal’ control loop, that can be found in the top level of the Simulink model.

The Simulink model can be found in appendix F.

5.5 Comparison to the ’real’ launcher

The question now is: To what extent can the mockup dynamics be considered as a

representation of the real launcher system in TEXTOR? The launcher mockup has no stiff

suspension to the real world. It is mounted on an ordinary office desk and allows a lot of

vibrations. These however are not seen in the systems frequency response. Furthermore

5 Controller design 36

the friction experienced in the mockup is much higher than the friction in the real system.

There is a strong belief that, the real system, which is much better suspended and has less

friction, will perform better than the mockup system. Resonances that are present in both

the mockup and the real launcher will manifest themselves at higher frequencies at the

real system than at the mockup.The reduced friction will only increase the stability of the

controller. It should be no problem to copy the controller from the mockup to the TEXTOR

launcher.

CHAPTER SIX

Conclusions and outlook

Enhanced tokamak performance can be achieved by operating in higher beta regimes.

This requires MHD disturbances to be rejected or kept as small as possible. Localized

ECRH injection has shown to be a suitable way of suppressing NTM (magnetic island)

disturbances in the plasma. The performance of an NTM suppressing control system,

based on ECCD/ECRH actuation, is dictated by the accuracy of the beam directing and

the time to first actuation. A well tuned motion controller should align the ECCD/ECRH

deposition location precisely and well timed onto the O-point of the island.

To set up a motion controller for the TEXTOR launcher, a mockup of the system has been

made. This mockup served as a safe sandbox environment to develop and optimize the

position control for the launcher in real-time experiments. The mockup system consists of

a copy of the dynamics, the electronic actuator and the servo amplifier; however during the

presented experiments only 1DOF (rotation) was driven. The implemented position control

loop is based on a high resolution differential encoder whereas the original launcher

uses linear potentiometers for an absolute position measurement. By choosing encoders

over potentiometers, the precision has been enhanced which permitted the use of a high

bandwidth feedback controller. Additionally a homing procedure has been implemented to

retain an absolute position measure.

The requirements on the position controller demand a fast response and high accuracy.

Based on typical grow rates of magnetic islands in a plasma, a 10 step should be possible

6 Conclusions and outlook 38

within 100 ms and the static positioning error should be less than 1. A PD controller

has been developed to meet these demands. With the designed controller the launcher is

capable of executing a 10 sweep within 100 ms where after a settling time of 200 ms

a static error of less than 0.01 remains. The performance may be further enhanced by

using feed forward techniques, steering on the moment of inertia and on the friction in

the stick-slip regimen. Measurements have shown a good congruence in the mockup and

original system dynamics, allowing the controller design to be mapped to the TEXTOR

launcher system.

To transfer the controller to the original system, the high resolution encoder signals are

preferred over the potentiometer signals and should be made available to the control loop.

Once this has been changed, a homing switch has to be added to each motor guidance to

obtain an absolute position measure. The control loop based on the combined TUeDACS

and Servostar system can than be set up in the same way as was done for the mockup.

One remaining difficulty in closing the positioning control loop, lies in the generation of

real-time (higher order) setpoints for the positioning controller.

Alternatively the TEXTOR launcher can be controlled from an integrated, more powerful

and faster controller based on a National Instruments Field-Programmable Gate Array

(FPGA), which allows a seamless integration of the motion control in the larger island

suppression control loop. This will, in the end, be the preferable option since this allows

a more flexible control layout. A disadvantage would be that the motion controller has to

be rewritten in National Instruments’ LabView (visual) code to be implemented into the

FPGA controller.

If a working island suppression setup can be realized at TEXTOR this will be a proof of

the concept, that inline ECE feedback and real-time launcher actuation is a feasible way of

NTM control. This will provide possibilities for application of these methods in the ITER

tokamak, where NTMs should be controlled in order to enhance the operational stability,

extend the plasma pulse length and avoid disruptions. Especially in larger tokamaks,

such as the ITER tokamak, disruptions invoke huge forces on the device and should be

avoided at all time. Besides the control of magnetic islands, ECRH/ECCD can also be

employed to influence sawtooth instabilities. Because of its ability to manipulate these

MHD characteristics in a tokamak accurately and very-well localized, ECRH/ECCD is

expected to play an important roll in the start-up of plasmas in ITER and will be crucial to

achieve better operational modes with higher confinement, which should ultimately result

in a so-called ’burning’ plasma, where the fusion process is self-sustaining and applicable

for fusion as an energy generator.

6 Conclusions and outlook 39

Appendix A

Table A.1 / Technical data servo actuator

Description Parameter Value [Unit]

Voltage of intermediate circuit of converter UDC 330 [V]

Standstill values

Standstill torque M0 3 [Nm]

Standstill current I0 4.2 [A]

Torque constant kM 0.727 [Nm/A]

Rated values of the motor

Rated voltage UNMOT 145 [V]

Rated torque MN 2.52 [Nm]

Rated current IN 3.62 [A]

Rated speed nN 3000 [min-1]

Rated power output PN 792 [W]

Voltage constant KE 44 [Vmin/1000]

Voltage constant kE 0.420 [Vs/rad]

Overload capacity at rated speed

Overloading capacity at rated speed M0 8.2 [Nm]

Max. overloading capacity at rated speed M0/MN 3.24 [-]

A Appendix A: Technical data servo actuator 41

Description Parameter Value [Unit]

Values of the motor at max. supply voltage U1

Max. values of the motor

Max. torque Mmax 12.9 [Nm]

Max. current Imax 20 [A]

Max. speed nmech 9000 [min-1]

Limit point

Current Ic 20 [A]

Breakdown torque Mc 12.08 [Nm]

Speed nc 2309 [min-1]

Max. utilizable parameters for S1

Max. utilizable speed nnutz 4023 [min-1]

Max. utilizable torque Mnutz 2.36 [Nm]

Max. utilizable power output Pnutz 994 [W]

No-loading running (IandM = 0)

No-load speed n0 4318 [min-1]

Technical features

Number of poles p 6 [-]

Resistance of winding RU−V 2.61 [Ω]

Inductance of winding LU−V 6.54 [mH]

Moment of inertia J 0.16 [kgm2/1000]

Mass m 4.6 [kg]

Axial load FA 114 [N]

Radial load FR 404 [N]

Average speed nmitt 1500 [min-1]

Mechanical values of the motor

Static friction torque Mr 0.05 [Nm]

Damping constant kD 1.8 [Nm·min·10-5]

Mechanical time constant Tm 1.18 [ms]

Thermal values of the motor

Thermal resistance (winding-ambient atm.)

Thermal resistance (frame-ambient atm.) Rth(RU) 0.71 [K/W]

Thermal time constant Tth 30.2 [min]

Appendix B

Figure B.1 / Connectors available on the Servostar, with their according pin layout.

Appendix C

EmergencyStop

HardP-Stop

HardN-Stop Mains

contactor

To BTB/RTO+24V Continuous

+24V overmains contactor

+24V continuous

for TUeDACsMains

contactor

SERVOSTAR S600

Heidenhain EQN 1325

Figure C.1 / Livewiring connections to the Servostar and the safety circuit.

Appendix D

7/1/2008 3:44:30 PM C:\Documents and Settings\emile\My Documents\eagle\New_Project\schakeling01.sch (Sheet: 1/1)

LEM

O 1

LEM

O 2

LEM

O 3

LEM

O 4

LEM

O 5

EN

AB

LE1

PS

TOP

1N

STO

P1

PS

TOP

2N

STO

P2

EN

AB

LE2

LEM

O 6

A B C D E F G H I

12

34

56

78

910

1112

A B C D E F G H I

12

34

56

78

910

1112

Con

nect

ion

box

from

Ser

vost

ar a

nd la

unch

er to

TU

eDA

cs

01 J

ULY

200

81

1/1

scha

kelin

g01.

sch

R1

1 234

OP

TO_C

OU

PLE

R1

1 234

OP

TO_C

OU

PLE

R2

23 1

P-S

TOP

_SW

ITC

H1

1 2

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15

X1

R3

1 234

OP

TO_C

OU

PLE

R3

1 234

OP

TO_C

OU

PLE

R4

23 1

N-S

TOP

_SW

ITC

H1

1 2

R2

23 1

P-S

TOP

_SW

ITC

H2

1 2

23 1

N-S

TOP

_SW

ITC

H2

1 2R

4

23 1

HO

ME

_SW

ITC

H1

1 2

23 1

HO

ME

_SW

ITC

H2

1 2

1 2 3 4

X2

5 6

R5

LED

1

R6

LED

2

R7

LED

3

R8

LED

4

R10

LED

6

R11

LED

5

24V

0V

5V

2K2

LTV

816

LTV

816

Dig

ital I

/O

GN

D

GN

D

GN

D

2K2

LTV

816

LTV

816

GN

D

GN

D2K

2

GN

D

GN

D

GN

D2K

2

GN

D

GN

D

GN

D

Ser

vost

ar c

onne

ctio

n

1K7

1K7

1K7

1K7

1K7

GN

D

1K7

GN

D

Figure D.1 / Electronic circuit, to transfer the signals from the Servostar to the TUeDACS

Appendix E

DIGITAL I/O1 2 3 4 5 6 7 8

1514131211109

Enab

le

PSTO

P

NST

OP

GR

OU

ND

24V

5V

24V 24V 24V 24V 5V 5V

1 3 4 5 62

ELECTRONICS BOX (FRONT)ELECTRONICS BOX (BACK)

- +

- +

MicroGiant

QUAD CNT 15 4 3 2 1

9 8 7 6

QUAD CNT 2

PWM 11 2 3 4 5

6 7 8 9

PWM 21 2 3 4 5

6 7 8 9

ADC 1 ADC 2 DAC 1 DAC 2

8 7 6 5 4 3 2 1

9101112131415

DIGITAL I/O5 4 3 2 1

9 8 7 6

1 2 3 4 5

6 7 8 9

ServostarEncoder out (X5)

8 7 6 5 4 3 2 1

9101112131415

ServostarEncoder in (X1)

E

121110

15

1617 14

13

9

87

65

1

4

3

2

Encoder connectionon actuator MA408F

Figure E.1 / Overview of all the used connectors, and their according pin numbering.

Note:

• The servostar output X5 is single ended TTL, meaning that the A- and B- signals are

zero and the signal is fully transmitted over A+ and B+, as 5V pulses.

• On the Electronics box, the LEMO input connectors 1 to 4 are intended for 24V limit

switches and connectors 5 and 6 are intended for 5V home switches.

E Appendix E: Cable wiring 46

Table E.1 / Cable connections from the actuator side (17 poled round connector) to the Ser-

vostar encoder input (X1)

Actuator MA408F, 17pol. Servostar X1

pin signal name symbol pin

1 Sense supply voltage (for long cables) Up sense 12

2 not connected

3 not connected

4 Sense supply ground 0V sense 10

5 Thermal switch (normally closed) θ+ 14

6 Thermal switch return θ- 7

7 Supply voltage Up 4

8 Clock signal for encoder CLOCK 8

9 Inverted clock signal CLOCK 15

10 Supply ground 0V 2

11 Inside shield - -

12 Cosine encoder signal B+ 9

13 Inverted cosine encoder signal B- 1

14 Data channel to/from the encoder DATA 5

15 Sine encoder signal A+ 11

16 Inverted sine encoder signal A- 3

17 Inverted data channel to/from the encoder DATA 13

Table E.2 / Cable connections from Servostar to TUeDACS

Servostar X6 MicroGiant QUAD CNT1

pin signal name symbol pin

4 Inverted sine A- 5

5 Sine A+ 9

6 Cosine B+ 8

7 Inverted cosine B- 4

Appendix F

Simulink model for the homing of the

launcher.

ST

AT

EE

XP

LAN

AT

ION

:st

ate

1=

mov

ing

tow

ards

the

hom

esw

itch

stat

e2

=ho

med

,set

posi

tion

to0.

08m

stat

e3

=re

ady

e5w4u3enc12

adc11

stat

usin

puts

enc1

_sco

pe

adc1

_sco

pe

Laun

cher

dac1

dac2

adc1

adc2

enc1

enc2

stat

usi/o

Sta

te

Got

o1

[B]

Got

o

[A]

GN

D1

Fro

m2

[B]

Fro

m

[A]

Dis

play

1

CO

NT

RO

LLE

R

Enc

oder

posi

tion

u w e

prin

ted

12-J

ul-2

008

12:0

8pa

ge1/

7

ho

min

g06

G:\l

aunc

her\

hom

ing\

hom

ing0

6.m

dl

F Appendix F: Simulink model for the homing of the launcher 48

e3

w2

u1

posi

tion_

setp

oint

pos_

erro

r_sc

ope

Sig

nal

Gen

erat

or

Sat

urat

ion

Off20

Off1-C

-

Man

ualS

witc

h1

Man

ualS

witc

h

Gai

n3

1

Gai

n2

1

Con

trol

ler

Inpu

tO

utpu

t

Ban

d-Li

mite

d

Whi

teN

oise

Enc

oder

posi

tion

1

Err

or

prin

ted

12-J

ul-2

008

12:0

8pa

ge2/

7

ho

min

g06

/CO

NT

RO

LL

ER

G:\l

aunc

her\

hom

ing\

hom

ing0

6.m

dl

F Appendix F: Simulink model for the homing of the launcher 49

Sta

te6

stat

usi/o

5

enc24

enc13

adc22

adc11

outp

utst

ate

swtc

h

inpu

tsta

tesw

itch

inpu

t

hom

ing

enco

der

data

Sta

te

posi

tion

Sta

tedi

spla

y

Saf

ety

dist

ance

set

Sta

te:s

witc

hon

2O

ut1

Laun

cher

hard

war

e

dac1

dac2

adc1

adc2

enc1

enc2

stat

usi/o

Inita

lizat

ion

cont

rolle

r

erro

ru

Hom

ing

ram

p

dac22

dac11

prin

ted

12-J

ul-2

008

12:0

8pa

ge3/

7

ho

min

g06

/Lau

nch

er

G:\l

aunc

her\

hom

ing\

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Appendix G

Errors and possible solutions

G.1 Encoder signal and motor design

If the connection scheme from appendix E is followed, the Servostar and TUeDACS are

correctly connected. However it could look like there is no (or a very weak) encoder signal

if the actuator spindle is turned. Always remember the design of this actuator. Inside the

actuator a rotating bolt is driven by the motor and the spinde only makes a translational

movement! So if you turn the spindle (while the motor brake is holding the bolt presum-

ably), you only measure the eccentricity of the spindle, which does produce a small signal,

but this is too weak to be picked up by the Servostar or the MicroGiants quadrature counter

and is not to be interpreted as a real signal produced by the encoder.

G.2 Motor phase

Once during the experimental work it happened that the motor phase was reversed. The

sequence in which the three phases are sent out from the Servostar has to be correct at all

times. Otherwise even the Servostars internal control loops are unstable.

It was observed that the Servostar, as soon as it touched the limit switches forcefully pushed

the launcher further into the limit switch and finally the second limit switch had to power

off the complete system.

After several telephone calls with the Danaher support department (+49(0)203-99 79-0)

they found the solution by reconfiguring the motor phase. This is an internal variable,

and should never change during the operation, so it is unclear how this phase change has

occurred.

A solution to this problem can be found in resetting the motor phase through the terminal

window. The procedure is as follows: Open the terminal window in Drive (one of the icons

in the top bar) and enter MPHASE. This command retreives the stored value of the motor

phase from Servostar. If this value is different from 172, we have to set it to this value.

Enter MPHASE 172, which resets the motor phase to 172, the correct value for the MA408F

actuator we have.

G Appendix G: Errors and possible solutions 55

It is quite strange however to have a motor phase that is not around zero, which is the

standard value. The Servostar is usually preset at a motor phase of zero and most motors

have a motor phase around zero.

G.3 EnDAT encoder connection

The first time the encoders were connected to the Servostar, the drive software was not able

to use the EnDAT signal from the encoders. This is the digital encoder connection, that

allows absolute position data, which can be useful in setting a software limit switch, just

before the real limit switch.

To activate the EnDAT encoder data, open the terminal window and enter HSAVE. This saves

all the necessary data to the Heidenhain encoder EEPROM.

G.4 Terminal commands

Table G.1 / Some other useful terminal commands

HDUMP Displays all the relevant encoder parameters

HSAVE Saves all the necessary parameters to the encoders EEPROM.

MDUMP Displays the currently valid motor parameters.

MPHASE The motor phase is saved in the serial EEPROM of the encoder

(HSAVE command) and is read out from the encoder after every

power-on of the amplifier. So if an encoder is exchanged, the

MPHASE setting goes with the encoder. When a new encoder

is fitted, the MPHASE value must be re-established and stored

in the encoder (HSAVE command).

SAVE Saves the current configuration to the Servostar EEPROM.

This can also be done with the save to EEPROM button in

Drive.

ZERO ZERO starts the automatic commutation angle measurement.

G Appendix G: Errors and possible solutions 56

G.5 Warnings and practical remarks

G.5.1 Linux OS

The lab PC has been installed to dual boot with Windows and Linux. To work with the

launcher mockup, the Linux OS should be selected at the boot loader, username and pass-

word are launcher and emile as standard user and for the root user root and launcher.

To acces files, either Simulink models or data files, the transfer disk can be used. This

disk is formatted as FAT32 and is accessible, both from windows and Linux. In Windows

this drive is accessible at E:, and in Linux the address reads /home/launcher/FAT/. Note

that running Simulink files created under Windows may lead to unexpected behavior

in Linux. This may be due to different Matlab versions or differences in continuous vs.

digital blocks. From Linux it is possible to connect to the Forschungszentrums X-Box

through FUSE. The FUSE program is installed on the computer, although the mounting

command is not working properly all the time. For completion the command is given:

sshfs username@sftp.ipp.kfa-juelich.de:/ /home/launcher/xbox. After this, the

system asks for your password and you can acces the X-box at /home/launcher/xbox.

G.5.2 Servostar Drive

It has been tried to setup the drive software for the Servostar from Linux using the WINE

Windows emulator. The win32 executable can be started with WINE, however is not able

to connect to the Servostar. Even after setting the symbolic links from the COM port to the

Linux equivalent /dev/ttyS0, the software was not able to contact the Servostar on the COM

port.

G.5.3 Matlab & Simulink

The Matlab program can be started from the desktop or from a console window with

the command ml. Simulink can be started by executing simulink from the command

line or opening any of the .mdl files in the Matlab startup subdirectories launcher/test

or launcher/homing. In Simulink the TUeDACS connections are represented by the

td_inports and td_outports blocks. The underlying S-function communicates over the

RTAI target to the hardware. This S-function is written in C code and uses functions from

the TUeDACS device library. Small changes are made to the original S-functions in order

G Appendix G: Errors and possible solutions 57

to configure all eight available i/o bits as input bits. These input bits are normally high

(corresponds to a digital low), and the best way to switch these, is by pulling down the

bit to the digital grounds. This results in a digital true signal, available in the Simulink

environment. Please note that without the proper bit configuration to input bits in the

S-functions, you can destroy the electronics.

Now the first files originate from the preset file PATO01.mdl, which incorporates all the

Simulink Real Time Workshop (RTW) settings. The only thing that may be altered in

the configuration parameters, is the sample time, which can be set in the menu Simu-

lation > Configuration Parameters > Solver in the field Sample time properties. A

minimum value for this field is 1/16,000.

G.5.4 Simulink library

Opening the Simulink library and and the sublibrary sources will cause Matlab to crash.

It is not clear why the program crashes, but is must have something to do with one of the

blocks in the sources library. To add source blocks to a model one can try to create the file

under Windows and try to open it under Linux, although this is no guarantee for succes,

since there are incompatibilities or different results on both platforms. The best option is

to open other models and copy the source blocks from these files.

G.5.5 Electronics box

Make sure that for the electronics box the power supply lines for the 24V and the 5V are

connected, before connecting to the mains. In this way it is ensured that there can be no

incidental connection of the 24V supply to the 5V supply connector. (this could be the case

since the 5V connector is much larger in size than the 24V connector.

G.5.6 TUeDACS

Opening the TUeDACS

The TUeDACS was opened for inspection, after a short circuit and the 5V voltage regulator

and the fan wiring were broken by demounting the backplane of the TUeDACS. The

G Appendix G: Errors and possible solutions 58

voltage regulator has been replaced by another IC of the same type: Motorola MC7805A

and the fan wires have been replaced by longer ones, allowing the demounting of the

backplane in the future.

Please remark that the plastic screw on the backplane has to be released at all times before

demounting the plane. For a normal TUeDACS Microgiant all possible screws have to be

unscrewed before taking off the backplane!

Supply voltage

This specific TUeDACS MicroGiant is altered for the TU/e Robocup team to operate on a

5V supply voltage. It is recognizable by the plastic mount hooks and the thick white tape

on the top of the box. Do not replace the adjusted power supply, which also has a connector

for the 5V electronics box, for a different one. The information regarding input voltage

(9V) on the TUeDACS back panel is incorrect!

Limit vs. home switches

The limit switches are intended for use as Servostar inputs and are connected at 24V,

whereas the home switches are intended for use in the digital domain, so they are con-

nected at 5V. Please make sure these are connected at the corresponding LEMO connector

at the electronics box. Also make sure that the homing switch is switched first and secondly

the limit switch and finally the emergency limit switch. Note as well that the home switch

should be mounted to the actuator side, not on the mirror side. Otherwise the home switch

will never be found or the mirror angles are incorrectly calculated.

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