Master Thesis Design and Construction of the Shutter ...€¦ · Demonstrator Model for the Mercury Radiometer and Thermal Infrared Spectrometer Dipl.-Ing. (FH) ... I Geometrical

Master Thesis

Design and Construction of the Shutter

Demonstrator Model for the Mercury Radiometer

and Thermal Infrared Spectrometer

Dipl.-Ing. (FH) Andreas Hurni

from Bern, Switzerland

Thesis submitted in partial fulfillment of the requirementsfor the degree of Master of Science (M.Sc.)

University of Applied Sciences Munich

Department of Precision- and Micro-Engineering, Engineering Physics

Master’s program Micro- and Nanotechnology

Examiner: Prof. Dr. rer. nat. Rolf Heilmann

Second examier: Prof. Dr.-Ing. Rainer Froriep

Supervisor: Dr.-Ing. Thomas Zeh, Kayser-Threde GmbH Munich

Day of submission: July 31, 2008

Munich 2008

We verify that this thesis satisfies the requirements of the graduate school as approved

by the graduate faculty.

——————————————— ———————————————

Prof. Dr. rer. nat. Rolf Heilmann Prof. Dr.-Ing. Rainer Froriep

Acknowledgements

Writing a thesis about a self conceived mechanism once flying to an orbit of another

planet is an amazing fortune, when I thinking about my unbroken fascination of space

flight since childhood. Furthermore, to combine it with the attained knowledge of the

basic studies in microtechnology, and improve it to culminate in a degree of Master of

Science in micro- and nanotechnology causes a big satisfaction, which I like to share

with all concerned persons.

First of all I like to thank Dr. Thomas Zeh to make this topic possible for writing

my master thesis. His support and cooperativeness was exceptionally positive during

whole the work. Special thanks go to Hans-Georg Preißler, Marion Rost, Dr. Michael

Leininger, Markus Manhart and many others from Kayser-Threde GmbH for their

design-engineering support and the profitable discussions.

Of course I like to express my gratitude to the examiners Prof. Dr. rer. nat. Rolf

Heilmann and Prof. Dr.-Ing. Rainer Froriep for their support on the part of the

University of Applied Sciences Munich.

For the discussions about the mechanical optimizations and the sometimes exhausting

encouragements to finish this work, I don’t want to miss to thank Thomas Wenger.

And of course, Anna, thank you very much for the time with you besides working on

this thesis for gaining new energy everytime.

Andreas Hurni

Munich

July 2008

i

Abstract

Exploring Mercury, the planet closest to the Sun, can offer valuable clues to the forma-

tion of the solar system and the Earth itself. However, accurate investigations must be

performed locally. This encouraged the ESA to launch the BepiColombo mission. The

on-board infrared spectrometer MERTIS will thereby globally map the mineralogical

surface. To substract disturbing radiation from the wanted spectrum, a shutter is re-

quired inside the instrument. The goal of this master thesis is to design and construct

the demonstrator model of this shutter.

Based on the results of a precedent shutter actuation principle study, just a voice

coil driven shutter guided with a flexible hinge structure can fulfill all requirements.

Besides the definition of the mechanical design, a helmholtz coil shaped setup was

determined for the voice coil actuator after theoretical analyses.

A power amplifier with a contol circuit was designed for reaching the required switching

mode of the shutter blade. Test measurements with the manufactured demonstrator

model in the closed loop system showed, that the requirements can be fulfilled with

the selected design. When the verification tests of the complete instrument will show

positive results as well, the flight model of the shutter shall finally be built based on

this demonstrator.

ii

Zusammenfassung

Durch seine Nahe zur Sonne kann die Erforschung des Merkurs Aufschlusse uber die

Entstehung des Sonnensystems und damit auch der Erde geben. Genauere Unter-

suchungen mussen hierfur jedoch vor Ort gemacht werden, was die ESA dazu veran-

lasst hat, die BepiColombo Mission ins Leben zu rufen. Das mitfliegende Infrarot-

spektrometer MERTIS wird dabei den Merkur auf mineralogischer Ebene kartieren.

Dazu ist ein Kameraverschluss notwendig, um Storstrahlungen zu messen, damit das

Nutzspektrum kalibriert werden kann. Ziel dieser Masterarbeit ist die Entwicklung

und Konstruktion des Demonstrator Modells dieses sogenannten Shutters.

Die Entwicklung basiert auf den Resultaten einer im Vorfeld durchgefuhrten Studie

uber anwendbare Shutterprinzipien. Dabei hat sich als einzige Losung, welche allen

gestellten Anforderungen gerecht werden kann, ein Voice-Coil-Antrieb gefuhrt von

einer Festkorpergelenkstruktur herausgestellt. Nach theoretischen Analysen wurde

neben der Festlegung des Mechanik-Designs eine helmholtzartige Spulenanordnung

fur den Voice-Coil-Antrieb definiert.

Zum Erreichen des geforderten Schaltzyklus wurde einhergehend mit der Endstufe eine

Regelelektronik entworfen und aufgebaut. Messungen mit dem gefertigten Demonstra-

tor Model des Shutters, eingebaut im Regelkreis, zeigten als Resultat, dass die An-

forderungen mit dem gewahlten Design erfullt werden konnen. Bei positiven Testergeb-

nissen nach dem Einbau im Instrument soll zu einem spateren Zeitpunkt aufbauend

auf diesem Demonstrator letztendlich das Flugmodel gebaut werden konnen.

iii

Abbreviations

AlNiCo Aluminum Nickel Cobalt

DM Demonstrator Model

EDM Electrical Discharge Machining

FEM Finite Element Method

FH Flexible Hinge

MEOP MERTIS Entrance Optics

MERTIS Mercury Radiometer and Thermal Infrared Spectrometer

MMO Mercury Magnetospheric Orbiter

MPO Mercury Planetary Orbiter

MRAD MERTIS Radiometer Focal Plate and Slit

MSOP MERTIS Spectrometer Optics

MSTS MERTIS Short Term Shutter

NdFeB Neodymium Iron Boron

OPAMP Operational Amplifier

SmCo Samarium Cobalt

VCA Voice Coil Actuator

iv

Notations

aFH Aspect Ratio of the Flexible Hinge

B Magnet Field

BHmax Maximum Magnetic Energy Product

b Width of the Flexible Hinge

c Spring Constant

cH Heat Capacity

D Damping Ratio

d Helmholtz VCA Clearance

DC Coil Diameter

dC Coil Wire Diameter

dL Magnet Length

dM Magnet Diameter

E Young’s Modulus

e Error Signal

EV CA Total VCA Energy

F Dynamic Force

v

f Deflection of the Flexible Hinge

f(1)eig 1st Eigenfrequency

fres Resonant Frequency

FV CA Lorentz Force

GFH(s) Transfer Function of the Mechanical Part

GV CA(s) Transfer Function of the Electromagnetic Part

h Thickness of the Flexible Hinge

hC Coil Winding Height

I Geometrical Moment of Inertia

IC Coil Current

KF Force Factor

k Attenuation Constant

L Coil Inductance

l Length of the Flexible Hinge

LC Coil Wire Length

lC Coil Length

M Bending Moment

m Mass

N Number of Windings of the Coil

Nc Buckling Load

P Force applied on the Flexible Hinge

PC Power Dissipation of the Coil

vi

RC Coil Resistance

r Feedback Variable

S ′e Endurance Strength

TC Curie Temperature

UC Coil Voltage

w Set Point

x Control Variable

y Actuating Variable

z Disturbance Variable

∆ Oscillation Amplitude

δ Logarithmic Decrement

ε Thermal Efficiency

ζ Glue Thickness

λT Thermal Conductivity Coefficient

µ0 Vacuum Permeability

ξ Ratio of the Necked Down Flexure

ρ Mass Density

ρC Electrical Resitivity

τL Time Constant of the Inductance

χ Magnet Clearance

vii

Contents

page

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 BepiColombo Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 About the Mission . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.2 Technological Challenges . . . . . . . . . . . . . . . . . . . . . . 2

1.2 MERTIS Instrument . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Scientific Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.2 Instrument Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.3 Short Term Shutter . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Shutter Actuation Principles . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 Shutter Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2 Study Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1 Statics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.1.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1.4 Wire-Cut EDM . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

viii

Contents

4.1.5 Stage with two Parallel Blades . . . . . . . . . . . . . . . . . . . 15

4.1.6 Technological Limitations . . . . . . . . . . . . . . . . . . . . . 18

4.1.7 Linear Stage with Necked Down Flexures . . . . . . . . . . . . . 18

4.2 Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.2.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.3 Electromagnetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.3.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.3.3 Coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.3.4 Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.3.5 Cylindric Single Coil VCA . . . . . . . . . . . . . . . . . . . . . 23

4.4 Interaction Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.5 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.5.2 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5 Analysis, Calculations and Experiments . . . . . . . . . . . . . . . . . 30

5.1 Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.2 Finite Element Calculations . . . . . . . . . . . . . . . . . . . . . . . . 33

5.2.1 Electromagnetic FEM . . . . . . . . . . . . . . . . . . . . . . . 33

5.2.2 Mechanical FEM . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.3 Cylindric Single Coil VCA Experiments . . . . . . . . . . . . . . . . . . 34

5.4 Flexible Hinge Experiments . . . . . . . . . . . . . . . . . . . . . . . . 35

5.5 Parallel Blade Stage VCA . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.6 Helmholtz VCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

6 MERTIS Short Term Shutter Demonstrator Model . . . . . . . . . . 46

6.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

6.2 Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

6.2.1 MSTS FH Structure . . . . . . . . . . . . . . . . . . . . . . . . 48

6.2.2 Mounting Part . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6.3 Electromagnetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

ix

Contents

6.4 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

6.4.1 Static Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 51

6.4.2 Dynamic Measurement . . . . . . . . . . . . . . . . . . . . . . . 51

7 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.1 Control Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.1.1 Power Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

7.1.2 Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.1.3 Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

7.2 Control Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

8 Conclusions, Status and Open Work . . . . . . . . . . . . . . . . . . . 58

APPENDIX

A Deviation of the Logarithmic Decrement . . . . . . . . . . . . . . . . . 61

B MSTS DM Design Drawing . . . . . . . . . . . . . . . . . . . . . . . . . 63

C MSTS DM Breadboard Electronics Circuit Diagram . . . . . . . . . 65

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

x

Chapter 1

Introduction

1.1 BepiColombo Mission

1.1.1 About the Mission

BepiColombo1, an ESA mission in cooperation with Japan, will explore Mercury, the

planet closest to the Sun. Europe’s space scientists have identified the mission as one of

the most challenging long-term planetary projects, because Mercury’s proximity to the

Sun makes it difficult for a spacecraft to reach and survive in the harsh environment.

The scientific interest to go to Mercury lies in the valuable clues that such a mission

can provide in understanding the planet itself as well as the formation of our Solar

System—clues which cannot be obtained with distant observations from Earth.

Only NASA’s Mariner 10 and MESSENGER have visited Mercury so far. Mariner

10 provided the first-ever close-up images of the planet when it flew past three times

in 1974 - 1975. En route to its final destination in orbit around Mercury in 2011,

MESSENGER flew past the planet on January the 14th, 2008, providing new data

and images. The information gleaned, when BepiColombo arrives in 2019, will throw

light not only on the composition and history of Mercury, but also on the history and

formation of the inner planets in general, including the Earth.

The mission will consist of two separate spacecrafts that will orbit the planet. ESA is

building one of the main spacecraft, the Mercury Planetary Orbiter (MPO) and the

1 Named after Giuseppe Colombo (October 2, 1920 - February 20, 1984), Italian scientist, math-ematician and engineer. He is best known for his orbit calculations on planet Mercury.

1

1 – INTRODUCTION

Figure 1.1: Emblem of the BepiColombo mission.

Japanese space agency ISAS/JAXA will contribute the other, the Mercury Magneto-

spheric Orbiter (MMO). The MPO will study the surface and internal composition

of the planet and the MMO will study Mercury’s magnetosphere, the region of space

around the planet that is dominated by its magnetic field.

1.1.2 Technological Challenges

With two spacecrafts, BepiColombo is a large and costly mission, one of the corner-

stones in ESA’s long-term science programme. The mission presents enormous, but

exciting challenges. All of ESA’s previous interplanetary missions have been to rela-

tively cold parts of the solar system. BepiColombo will be the agency’s first experience

of sending a spacecraft to hot regions.

The journey from Earth to Mercury will also be a first. After launch into a geo-

stationairy transfer orbit, the Mercury composite spacecraft will be boosted to the

phasing orbit using chemical propulsion. From here the spacecraft will be set on its

interplanetary trajectory through a flyby of the Moon. On its way to Mercury, the

spacecraft must brake against the Sun’s gravity, which increases with proximity to the

Sun, rather than accelerate away from it, as is the case with journeys to the outer Solar

System. BepiColombo will accomplish this by making clever use of the gravity of the

Earth, Venus and Mercury itself and by using solar electric propulsion. This innovative

combination of low thrust space propulsion and gravity assist has been demonstrated

by ESA’s technology mission SMART-1.

When approaching Mercury, the spacecraft will use the planet’s gravity plus con-

ventional rocket engines to insert itself into a polar orbit. A special weak stability

boundary capturing technique is employed. This gives flexibility and is more robust

2

1 – INTRODUCTION

against failures compared to using the more traditional “big kick” approach (single

burn capture). The MMO will be released into its operational orbit, then the sunshield

and the MMO interface structure will be separated while the chemical propulsion sys-

tem will bring the MPO to its lower orbit. Observations from orbit will continue for

one Earth year2.

1.2 MERTIS Instrument

1.2.1 Scientific Goals

The scientific goal of the Mercury Radiometer and Thermal Infrared Spectrometer

(MERTIS) is to provide detailed information about the mineralogical composition of

Mercury’s surface layer by measuring the spectral emittance of different locations.

Knowledge of the mineralogical composition is crucial for choosing the best of several

competing theories, and thus for selecting the valid model for origin and evolution

of the planet. MERTIS has four main scientific objectives, building on the general

science objectives of the BepiColombo mission:

• study of Mercury‘s surface composition,

• identification of rock-forming minerals,

• global mapping of the surface mineralogy and

• study of surface temperatures and the thermal inertia.

The instrument covers the range from 7− 14µm at a high spectral resolution of up to

90 nm which can be adapted depending on the actual surface properties to optimize

the signal-to-noise ratio (S/N). MERTIS will globally map the planet with a spatial

resolution of 500 m and a S/N of at least 100. The flexibility of the instrumental setup

will allow to study the composition of the radar bright polar deposits for an assumed

surface temperature of 200 K.

2 http://www.esa.int/esaSC/120391_index_0_m.html accessed on June 4, 2008.

3

http://www.esa.int/esaSC/120391_index_0_m.html

1 – INTRODUCTION

1.2.2 Instrument Setup

The MERTIS instrument (fig. 1.2) is an IR-imaging spectrometer based on the push-

broom principle which is located on the MPO. It is based on an uncooled micro-

bolometer array providing spectral separation and spatial resolution according to its

two-dimensional shape. The operation concept principle is characterized by interme-

diate scanning of the planet surface and three different calibration targets—free space

and two on-board black body sources. Sharing the same optical path, a pushbroom

radiometer is implemented according an in-plane separation arrangement. The general

instrument architecture showed in figure 1.3 comprises two separate parts—the sensor

head (SH) including optics, detector and proximity electronics and the electronics unit

(EU) containing sensor control and driving electronics, as well as the power supply.

This highly integrated measurement system is completed by a pointing device which

orients the optical path to the planet and the calibration targets.

1.2.3 Short Term Shutter

For spectrometer data acquisitions a reference signal representing the instruments

background ratiation is necessary for on-board data processing and for on-ground cali-

bration. This is performed by periodical acquisitions without the targets scene/planet

radiation. Therefore a shutter is foreseen, the MERTIS Short Term Shutter (MSTS),

covering the optical slit by closing the MSTS. The designated integration position of

the MSTS in the MERTIS instrument is indicated with the red dashed ellipse in figure

1.2.

Within this master thesis, the Demonstrator Model (DM) of the MSTS shall be de-

signed and constructed, which finally shall prove its functionality after integration in

the MERTIS instrument.

4

1 – INTRODUCTION

Figure 1.2: MERTIS instrument model with the MSTS integration position indicatedwith the red dashed ellipse [12].

BepiColomboMERTIS

Reference:Issue:Date:Page:

MER-DLR-TN-007 Draft Rev: 1 25.05.20072

MERTIS Overall Concept MSBA Radiator IF Design Consideration

The main parameters of the instrument are given in table Table 2.2-1

Fig. 2.2-1 MERTIS structure block diagram

Space View

SH

EU

MBOL

MSOP

MB

B3

MREDMEOPMPOI

MHAR MBB7 MICU

MPSU S/C

Inst

rum

ent P

anel

(TR

P)

-20

…+4

0°C

±5K

/ Orb

it

S/C Radiator

Planet View

MRBA

MBEL

S/C

MLI

MSTS MLTS

MB

EL /

MH

KE

MRAD

MSHS

MOST

MSBA

Space View

SH

EU

MBOL

MSOP

MB

B3

MREDMEOPMPOI

MHAR MBB7 MICU

MPSU S/C

Inst

rum

ent P

anel

(TR

P)

-20

…+4

0°C

±5K

/ Orb

it

S/C Radiator

Planet View

MRBA

MBEL

S/C

MLI

MSTS MLTS

MB

EL /

MH

KE

MRAD

MSHS

MOST

MSBA

Parameter Unit Spectrometer Radiometer (µRAD) Focal length F 50 mm F – number F# 2.0 Optical efficiency opt 0.54 Microbolometer array detector

illuminated pixels

µRAD thermopile line array

pixels 160 x 120 @ 35 µm 100 spatial 80 spectral

2 x 15 @ 250 µm Spectral channel width 90 nm / pixel Spectral resolution / 78 – 156 Spectral range 7 – 14 m 7 – 40 µm Detectivity D* 0.95 109 cm Hz1/2 W -1 7 108 cm Hz1/2 W -1

Instantaneous field of view IFOV 0.7 mrad 5 mrad Ground sample distance

Periherm 400 km Apoherm 1500 km

GSD 280 - 1400 m (M = 1- 5) 1050 m

2000 m 7500 m

Dwell time Periherm 400 km

Apoherm 1500 km 109 ms 784 ms

775 ms 5597 ms

Field of view FOV 4° ACT, 0° ALT 4° ACT, 1° ALT Swath width 28 km Instrument overall dimensions + ext. Baffles

180 x 180 x 130 mm³ 200 x ø75 & 90 x ø75 mm³

Instrument total mass incl. 20% margin 3.3 kg

Figure 1.3: MERTIS instrument block diagram [12].

5

Chapter 2

Boundary Conditions

2.1 Requirements

A first requirement compilation for the MSTS was proposed from the MERTIS instru-

ment team at the German Aerospace Center (DLR) in spring 2007. Table 2.1 lists the

reviewed requirements annotated with priorities. Further boundary conditions which

must be considered are summarized in the experiment interface documents [11] and

[12].

The shutter blade must cover the slit periodically as expressed in figure 2.1. Hereby,

the required velocities and accelerations of the blade can be estimated and used for

the selection of an applicable shutter actuation principle presented in the following

chapter.

Lifetime and fail safe are quoted as most important requirements. When multiplying

the lifetime of two years with one closing and one opening stoke in a period of 109 ms,

a total number of cycles of 1.577 · 109 results [5]. A required security factor of 1.25

for moving mechanical components [11] increases the number of cycles to around two

billion. If the MSTS will fail, the shutter blade shall never cover the infrared light

beam to guarantee at least resticted operation of the instrument. Therefore, a fail safe

mechanism shall be foreseen in the MSTS design.

It must be mentioned, that several requirements and priorities had changed during

the design phase. Some of them had to be discussed due to installation interferences

with other MERTIS components. However, table 2.1 lists the requirements which were

valid during the shutter actuation principle study.

6

2 – BOUNDARY CONDITIONS

MERTIS

MERTIS Shutter Study

MER-KTM-TN-005 Issue 1 draft c

September 05, 2007 Page 2-6

C:\Dokumente und Einstellungen\Andreas Hurni\Desktop\MSTS\Papers & Presentations\MER-KTM-TN-005-Issue-1 Draft_c_Shutter_Study_05.09.2007.doc This document is proprietary. Any dispatch or disclosure of content is authorized only after written authorization by Kayser-Threde. Kayser-Threde GmbH, Wolfratshauser Str. 48, 81379 Munich, Germany, Tel.:+49 (0) 89 / 72495-0, E-Mail: [email protected], www.kayser-threde.com

Mechanical robustness

nominal as specified in Section 3.2.3.4 in the EID-A [AD3]

nominal as specified in Section 3.2.3.4 in the EID-A [AD3]

3

EMC properties low conducted and radiative emission (sensor systems)

low conducted and radiative emission (near bolometer)

2

Operation temperature range

-30 … 50 °C without heater 0 … 50 °C with heater

-30 … 50 °C without heater 0 … 50 °C with heater

Non operation temperature range

-30 … 50 °C -30 … 50 °C

Space qualification (e.g. out gassing, radiation, vacuum)

yes yes 3

Fail-safe integration

yes, fail open yes, fail open 3

Position feedback yes, closed / open yes, closed / open 2

Temperature feedback

yes yes 3

Applicability for IR 7 – 14 μm 7 – 14 μm 3

Technology if possible the same for LTS if possible the same for STS 2

Contrast ratio tbd tbd

Reflector surface properties (e.g. max. radiation power, absorption)

tbd tbd

Switching mode

T = 109 ms, f = 9,2 Hz

T = 20 s, f = 0,05 Hz

Table 2-1: STS and LTS requirements

19,8 s 99 ms 200 ms 10 ms

close

open

close open

Figure 2.1: Shutter blade switching mode.

2.2 Integration

As indicated in figure 1.3, the MSTS shall be integrated between the MERTIS En-

trance Optics (MEOP) and the MERTIS Spectrometer Optics (MSOP). The light

beam escapes from the MEOP and then passes the MERTIS Radiometer Focal Plate

and Slit (MRAD) before it will be blocked by the MSTS blade during its closed phase.

The blade shall be placed with a distance of 0.5 mm to MRAD in direction of the beam

propagation.

The MRAD consists of a tiny silicon plate without providing space for furter mounting

screws. Therefore, the MSTS shall be mounted at the MSOP housing. Figure 2.2 shows

a bird’s eye view of the MSTS integration space.

When considering the slit dimensions (tab. 2.1), it is reasonable that the blade stroke

shall be oriented across the slit width for fast operation. Enough space for mounting

the MSTS on the MSOP housing is provided at the right side of the window (fig. 2.2).

All boundary conditions had to be considered for the study and the ultimate selection

of the shutter actuation principle.

7

2 – BOUNDARY CONDITIONS

Figure 2.2: Bird’s eye view of the MSTS integration space between the MEOP (grey)and MSOP (light blue). The MSTS shall be placed in front of the MSOP windowclose to the MRAD (wine red).

Property Value Priority

Weight 25 g 3Dimensions max. 20× 20× 5 mm3 2Frequency (fig. 2.1) worst case 10 Hz, 2

depends on operationClose time max. 6 ms 2Open time max. 6 ms 2Close area slit area: ca. 1.5× 5 mm incl. 3

overlapLifetime 2 years 3Power consumption average 0.6 W at 3.3 V (3 W peak) 2Control 3.3 V digital 1Mechanical robustness nominal as specified in section 3

3.2.3.4 in [11]EMC properties low conducted and radiative 2

emissionOperation temperature range −30 . . . 50 C without heater, 2

0 . . . 50 C with heaterNon operation temperature range −30 . . . 50 C 2Space qualification yes 3(e.g. out gassing, radiation, vacuum)Fail safe integration yes, fail open 3Position feedback yes, closed / open 2Temperature feedback yes 3Applicability for IR 7− 14µm 3

Table 2.1: MSTS requirements and their design priorities weighted from 1 (lowestpriority) to 3 (highest priority).

8

Chapter 3

Shutter Actuation Principles

3.1 Shutter Study

In a preliminary phase of the MSTS design, common shutter actuation principles and

mechanisms were studied and summarized in [5]. Already space qualified or even flown

actuators were particularly investigated. However, no one of these shutter mechanisms

can fulfill all boundary conditions listed in table 2.1. Nevertheless, a lot of information

about actuation principles and control electronics designs could be gathered.

The investigated actuation principles comprise

• motor driven shutters,

• electromagnetic field driven shutters,

• piezo actuator driven shutters and

• piezo motor driven shutters.

The actuation principles of these four shutters are sketched in figure 3.1. Termed as

non applicable principles for the MSTS, but listed for the sake of completeness are

• opaque fluid based optical shutters and

• liquid crystal optical shutters.

The most promising and withal space qualified shutter design considered in [5] is

the Laser Chopper Mechanism (LCM) included in the ALADIN instrument for the

ADM-Aeolus satellite which will be launched in 2009 [9]. This voice coil based shutter

mechanism persisted > 6 · 109 cycles in the testing phase.

9

3 – SHUTTER ACTUATION PRINCIPLES

VCA

Fail safe spring

Shutter blade

Fail safe spring

Shutter blade

Piezo motor

Piezo actuator

Rotary tubular shutter

DC motor

a)

Shutter blade

c)

b)

d)

Figure 3.1: Investigated shutter actuation principles: a) DC motor rotary tubularshutter, b) piezo actuator driven shutter, c) piezo motor driven shutter and d) voicecoil actuator linear shutter.

3.2 Study Results

As result of the study, the piezo actuator driven shutter and the voice coil actuator

linear shutter were valuated as predestinated to fulfill all the requirements listed in

table 2.1. However, piezo actuators need high driving voltages and cannot achieve long

strokes. Designing the MSTS DM based on the Voice Coil Actuator (VCA) principle

was therefore concluded as best solution in every sense.

The shutter study was closed with the insight of combining a debris free guidance with

a fail safe mechanism in terms of a Flexible Hinge (FH) structure driven by a VCA.

10

Chapter 4

Fundamentals

4.1 Statics

4.1.1 Introduction

As a result of the shutter study presented in the previous chapter, the MSTS mechan-

ical part shall be designed using a flexible hinge structure due to the lifetime and fail

safe requirements. To consider the basics of flexible hinges and to discuss applicable

materials and machining technologies is important for the design of the MSTS FH

structure.

A FH generally works like a spring in the elastic range described by Hooke’s law,

but additionally performs frictionless guiding and stroke amplification. Although a

FH underlies that simple mechanical principle, conception methods for their usage in

micro- and even nanotechnology just came up in the end of the 20th century. Powerful

computers for calculations with the Finite Element Method (FEM) and improved per-

formances of the Electrical Discharge Machining (EDM) are essential for designing and

manufacturing flexible hinges in the micro- and nanotechnological range. MEMS1 ac-

celerator sensors, today manufactured in lot of millions, contain flexible hinges etched

in silicon with lengths below one millimeter2.

Flexible hinges are generally characterized by regions of reduced bending stiffness in

one ore more directions. They have a lot of advantages for microsystems compared to

1 Microelectromechanical systems.2 http://www.panasonic-electric-works.de/pewde/en/html/23405.php? accessed on June 4,

2008.

11

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4 – FUNDAMENTALS

bush and ball bearings or other bearing systems e.g. magnetic, hydrostatic, hydrody-

namic and air guidings [4]. But they also have some disadvantages which are listed in

the following compilation.

Advantages DisadvantagesFrictionless guiding Limited strokesNo wear and therefore no wear debris Restoring forcesNo galling Complex geometriesNo lubricationHigh transversal rigidityNo playMonolithic piece

A conclusion of this valuation shows, that flexible hinges are ideal for the MSTS

application due to the frictionless, lubrication and wear debris free guiding3. The

reachable stroke will be determined by the design analysis discussed in chapter 5.4.

Different translational and rotatory FH designs are presented with formulas in [4]

and [6] with improvements of the general designs in [10] and [13]. Figure 4.1 shows

three patterns of flexible hinges for getting a first impression in which direction the

design of the MSTS FH structure tends. These designs have different advantages and

disadvantages. For instance, the circular notch hinge features the highest precision due

to its stationary rotation center. However, high forces must be applied for reaching

adequate deflections.

4.1.2 Theory

The formulas for calculating the forces and deflections, presented in the above men-

tioned papers, are exclusively deduced form the fundamental theory of structural me-

chanics

y′′ =M(x)

EI(x)+

(η

GA(x)

∂F (x)

∂x

). (4.1)

This equation describes approximately the curvature of a beam implementing the

bending moment M , Young’s modulus E and the geometrical moment of inertia I.

The term in the brackets describes the shearing, which won’t be further considered

due to its small influence on the deflection [4].

3 Applying lubricants in spacecraft mechanisms is generally problematic, especially inside opticalinstruments. As well as wear debis, they can contaminate the optical components.

12

4 – FUNDAMENTALS

a) b) c)

Figure 4.1: General designs of flexible hinges: a) leaf spring hinge, b) circular notchhinge and c) elliptical notch hinge [6].

The mathematical description in (4.1) bases on three assumptions named continu-

ity, homogeneity and isotropy. Parts of the MSTS FH structure can possibly reach

dimensions where some of these assumptions loose validity due to very thin waists.

Therefore, a good knowledge about the material properties and the accuracy of the

FEM calculations is required for the MSTS FH design.

4.1.3 Materials

A lot of materials, preferably metals, are applicable for flexible hinges. Thereby,

different properties like

• density,

• Young’s modulus,

• endurance strength,

• thermal conductivity,

• space qualification and

• radiation degradation

must be evaluated.

The range of applicable materials is not only limited to metals as already shown with

the mentioned MEMS sensor. Also ceramics like silicon nitride (Si3N4) or composits

13

4 – FUNDAMENTALS

containing carbon fiber show good performances for FH structures. However, a com-

parison of the above listed properties with the requirements (tab. 2.1) obviate their

usage, what reduces the range of applicable materials for the MSTS FH.

For a further confinement, the endurance strength is regarded as most important cri-

terion due to the high required number of cycles of the MSTS. Some metals have an

endurance strength limit, what means that the number of cycles until a loaded FH

breaks, tends to infinity, when a certain stress limit will never be exceeded. The en-

durance strength of a metal depends on its crystal system. Metals with body-centered

cubic systems have an endurance strength limit, whereas metals with face-centered cu-

bic systems do not. The S-N curve4 characterizes the magnitude of an applied cyclical

stress against the logarithmic scale of cycles until failure [8]. This fatigue test with

structural damage divides the applicable metals for the MSTS in two groups, which

are listed in table 4.1.

Beryllium copper, titanium alloys and cobalt alloys have been classified as best candi-

dates for the MSTS FH structure. Beryllium copper (CuBe) is an excellent alloy for

springs and is space qualified. However, the high density and the missing endurance

strength limit exclude its applicability. Furthermore, the toxicity of Beryllium is a

problem during the wire-cut EDM due to emerging vapours.

NIVAFLEX R© 45/18, basically used in the watch industry, is designed especially for

long term cyclical stressed springs5. Thus, it has an endurance strength limit. A

high elastic force is required according to the high Young’s modulus, which possibly

cannot be generated with the VCA. Missing space qualification and minimum deliv-

ery quantities of several 100 kg avoid the usage of NIVAFLEX R© for the MSTS FH

structure.

As most commonly used titanium alloy for space applications, Ti-6Al-4V shows ideal

properties like an existing endurance strength limit [3], a low density and a low

Young’s modulus. The influence of these properties for the MSTS FH structure

design will be discussed in chapter 5.4.

Figure 4.2 shows a collection of S-N curves of Ti-6Al-4V samples with different milling

axes and surface finishes respectively. Obviously the endurance limit depends on

the surface finish. Thus, it is crucial for the MSTS FH design, that the maximum

stress which occurs in the flexible hinges never exceeds the endurance strength limit.

4 Also known as Wohler curve.5 http://www.vacuumschmelze.de accessed on June 4, 2008.

14

http://www.vacuumschmelze.de

4 – FUNDAMENTALS

Otherwise, a nondestructive operation cannot be guaranteed over several billion cycles.

For the most demanding applications e.g. aerospace, lifetime and fatigue tests must

be perforemd at any rate [2].

Alloy ρ / kgm3 E / GPa S ′e / MPa λT / W

Km

Ti-6Al-4V 4420 114 ≈ 350 7.2NIVAFLEX R© 45/5 8500 220 n/a n/a

Beryllium Copper (CuBe) 8260 131 - 106

Table 4.1: Properties of the investigated materials for the MSTS FH structure. Listedare the mass density ρ, the Youngs’s modulus E, the endurance strength S ′e and thecoefficient of thermal conductivity λT . The table is separated in two parts character-ized by the endurance strength limit.

4.1.4 Wire-Cut EDM

EDM allows very high precision and arbitrary shaped machining of electrical conduc-

tive materials. There are two main types of EDM called sinker EDM and wire-cut

EDM. Flexible hinges with one degree of freedom will be ideally machined by wire-cut

EDM. Reasons for selecting this method are the simpler machine setup, because no

special matrices must be prepared, and the lower costs.

A maximum precision of 5µm and an average roughness height of Ra ≈ 0.18µm are

obtainable by wire-cut EDM [4]. The average roughness height has an influence on

the endurance strength limit as shown in figure 4.2. Thus, a roughness measurement

on the surface of the manufactured MSTS FH structure should be performed before

the flight model will be constructed. The wire diameters are generally in the range of

a few hundred microns. The MSTS FH design must be optimized for the applied wire

diameter. For example, with a diameter of 0.2 mm no radii smaller than 0.3 mm can

be cut. Repeated passages with reduced cutting velocities improve the surface finish,

but increase the machining costs [4].

4.1.5 Stage with two Parallel Blades

Since the movement of the shutter blade will be performed just in one direction, a

FH structre variant called stage with two parallel blades presented in [4] should be

discussed in detail.

15

4 – FUNDAMENTALS

700

600

500500

400a

300σ/ M

P

200

100

0104 105 106 107

Number of Cycles

0

Figure 4.2: Ti-6Al-4V fatigue tests [4].

Figure 4.3 (left) shows the main principle of the stage with two parallel blades. The

formulas for calculating the deflection, the rigidity and the buckling load for this FH

structure are deduced in [4] using the approximated Euler-Bernoulli beam theory.

The formula for the deflection f thereby follows to

f =Pl3

2Ebh3. (4.2)

It is obvious that the length l and the thickness h have the highest significance for

the blade dimensioning, because they raise to the power of three. P characterizes the

force applied on the FH and is reasonably equal to the force generated by the VCA,

which will be introduced in chapter 4.3. The rigidity, which is represented by the

spring constant c, can be calculated with

c =24EI

l3, (4.3)

and the buckling load Nc with

Nc =8π2EI

l2. (4.4)

16

4 – FUNDAMENTALS

S. Henein, Slide 3.8

P

B

A

f

b

hl

λ

Mobile Block

l/2d

e

Parallel Spring StageParabolic Translation (1 Degree-of-Freedom (DOF))

S. Henein, Slide 3.23

Linear stage with necked down flexures

f

bh

l

l c

P

l/2d

A

B

Bloc mobile

Bloc de base

e

P

lλ

fN

C

M

llc2

=ξ 10 ≤< ξ1=ξ

0→ξ

Mobile block

Fixed base

For a given stroke f and given outer dimensions l and b,

what is the optimal hinge length lc ?

Figure 4.3: Stage with two parallel blades (left) and linear stage with necked downflexures (right) [4].

Figure 4.4: Occuring blade deflections during the wire-cut EDM process limit themaximum aspect ratio aFH = l/h [4].

17

4 – FUNDAMENTALS

4.1.6 Technological Limitations

When estimating the parameters in (4.2) for the MSTS design, it becomes obvious,

that especially the thickness h of the FH blades can achieve very small dimensions.

Therefore, it is reasonable to check the technological limitations of the applied manu-

facturing methode.

Wire-cut EDM is a swarf-free machining method, because the electric discharges melt

and vaporize the metal for cutting. Nevertheless, vibrations occur due to electrical

arcs and busts, electrostatic forces and due to the jet of the dielectric fluid for rinsing.

This limits the aspect ratio of machined blades and therefore affects the MSTS FH

structure design. A maximum aspect ratio of aFH= l/h ≈ 60 was defined for steel

based on manufacturing experiments [4]. Figure 4.4 sketches occuring blade deflections

during the wire-cut EDM process due to the above mentioned disturbances.

The minimum notch thickness depends on the material and the EDM quality. Circular

notch hinges can reach values of a few microns. For blades as in leaf spring hinges,

a minimum thickness of at least 50µm is reasonable. In this dimension range no

violation of the three basic assumptions noted in subsection 4.1.2 shall occur.

4.1.7 Linear Stage with Necked Down Flexures

To avoid the technological limitations for extending the dimensioning range of the FH

structure shown in figure 4.3 (left), an improved variant called linear stage with necked

down flexures is presented in [4]. As sketched in figure 4.3 (right), both blades carry

a segment considered as infinitely rigid. A parameter ξ defines the ratio between the

flexible and rigid parts to

ξ =2lcl

with 0 < ξ ≤ 1. (4.5)

A multidimensional optimization including the rigidity, the blade thickness and the

critical load yields an ideal ratio for the necked down flexure of ξopt ≈ 0.3 [4].

An adequate aspect ratio shall be optained for the MSTS FH stucture design using

ξopt. The required force in this setup will be higher due to the augmented translational

rigidity, but increases as well the eigenfrequencies, what is highly desired for the control

as discussed in section 4.5.

The formula for the deflection can be deduced to

f =Pl3ξ(3− 3ξ + ξ2)

2Ebh3. (4.6)

18

4 – FUNDAMENTALS

Analogously follows for the rigidity

c =2bh3E

ξ(3− 3ξ + ξ2)l3(4.7)

and the buckling load

Nc =8π2EI

ξ2l2. (4.8)

4.2 Dynamics

4.2.1 Introduction

The design of the MSTS FH structure shall be optimized in terms of dimensions and

weight to achieve the requirements listed in table 2.1. To fulfill the shutting frequency

and especially the maximum open/close time, an optimization in consideration of the

MSTS dynamics is essential.

4.2.2 Theory

A mathematical model for the MSTS FH structure design as proposed in figure 4.3 is

required to optimize the mentioned parameters. The sketch 4.10 (left) allows to deduce

the mathematical description for a driven damped spring-mass system satisfying the

equation

md2x

dt2+ k

dx

dt+ cx = F (x, t), (4.9)

whereas m is the mass, k the attenuation constant, c the spring constant and F the

applied dynamic force.

The mass and the spring constant are coupled with the system’s first eigenfrequency

f(1)eig =

1

2π

√c

m. (4.10)

The parameters in (4.10) can be determined by means of FEM calculations. How-

ever, determing the attenuation constant is virtually impossible with simple calcula-

tion methods. Measurements at a manufactured FH structure must be performed for

disclosing the attenuation constant.

The required open/close time is in the range of a few milliseconds. A relatively high

first eigenfrequency of the FH structure shall therefore be achieved to guarantee fast

19

4 – FUNDAMENTALS

shutting. Furthermore, controlling a mechanical system is much simpler in a frequency

range considerably below its first resonant peak. The system’s resonant frequency fres

and its eigenfrequency nearly coincide for weakly damped mechanical systems. They

are coupled with the damping ratio D to fres = f(1)eig

√1−D2.

Analog to (4.10), the first eigenfrequency can be written in terms of

f(1)eig =

k

4πDm. (4.11)

Dynamical step response measurements of the mechanical system allow to determine

the damping ratio.

Weakly damped systems show approximately PT2 behaviour in words of the control

theory. Thus, several decaying oscillations occur before reaching a stationary state

after a step or Dirac delta excitation respectively. Neighboring amplitudes ∆ of

these oscillations peaks define the logarithmic decrement6 δ to

δ = ln∆i

∆i+1

. (4.12)

Hereafter, D can be calculated with

D =δ√

π2 + δ2. (4.13)

In the verification phase of the MERTIS project, the MSTS shall persist several shaking

tests simulating the launch phase. It is appropriate to maximize the damping ratio

for avoiding high resonant peaks, which can destroy the MSTS. However, a high first

eigenfrequency is required for fast shutting. These parameters obviously interact in

an reciprocal manner when analyzing (4.11).

The force generated by the VCA is equal to the dynamic force F in (4.9) and must

counteract the totalized acceleration force, attenuation force and spring force. The

goal for the MSTS FH design is therefore to minimize these forces by finding adequate

values for the parameters m, k and c.

6 Consider the associatied graphic and the mathematical derivation of the logarithmic decrementfor unknown stationary amplitudes presented in appendix A.

20

4 – FUNDAMENTALS

4.3 Electromagnetics

4.3.1 Introduction

As applicable actuation principle, a voice coil actuator was disclosed in the shutter

study. This electromagnetic actuator is capable to perform linear or rotary movements

comparable to electric motors. The configuration of a VCA is in general a cylindric

coil, which plunges into a setup of a centered magnet surrounded by a ferrite ring, like

it can be found in conventional loudspeakers. The application of rotary VCAs is well

established in hard disk drive heads.

4.3.2 Theory

To introduce the relevant electromechanic parameters, a loudspeaker VCA shall be

considered as shown in fig. 4.5 (left). The stroke of the coil will be generated by the

Lorentz force FV CA induced by the coil current IC and the magnet field B of the

centered permanent magnet. The Lorentz force can be written as

~FV CA =

∫ICd~LC × ~B, (4.14)

whereas d~LC indicates the differential of the coil wire cross section normal.

The right hand grip rule defines the direction of ~FV CA. Due to the axisymmetric setup

of the considered VCA, ~B is always perpendicular to d~LC . Therefore (4.14) can be

simplified to

FV CA = ICLCB. (4.15)

When assuming a homogeneous magnetic field within the coil region, a force factor

KF can be determined written as

KF =FV CA

IC= LCB, (4.16)

which characterizes every VCA7. Loudspeaker VCAs usually have a heavy magnet

setup compared to the coil’s mass. So, it is obvious that normally the coil is moved for

optaining high accelations. However, moving the magnet has significant advantages

when its mass is in the same range as the mass of the coil. Here, the coil’s power leads

do not move and possibly break after a high number of performed cycles. Thus, two

VCA concepts can be deduced and will be named as

7 www.beikimco.com accessed on June 4, 2008.

21

www.beikimco.com

4 – FUNDAMENTALS

FVCA

dLC B

x, VCAFr

yz

Figure 4.5: Loudspeaker VCA model with the indicated vectors of the Lorentzforce ~FV CA, the magnet field ~B and the coil wire cross section normal d~LC buildingan orthonormal system (left). Cylindric single coil VCA model with some indicatedmagnet field lines (right).

• moving coil concept and

• moving magnet concept.

This concepts shall be evaluated for the MSTS application. However, when reminding

the lifetime requirement, it must be said, that the selection shall tend towards the

moving magnet concept to avoid a power lead breakage.

4.3.3 Coil

An axisymmetric coil setup allows to generate the highest possible FV CA due to the

cross product identity d~LC × ~B =⇒ max when d~LC ⊥ ~B. Since the induced field in

the coil does not remarkably influence the magnet field B, FV CA mainly depends on

the current IC and the coil wire length LC . Ohm’s law couples these parameters in a

reciprocal way to

RC =UC

IC=

8ρCLC

d2Cπ

, (4.17)

whereas RC represents the coil resistance, ρC the electrical resistivity, UC the applied

coil voltage and dC the coil wire diameter8. RC shall be minimized due to the low

supply voltage (tab. 2.1). However, to maximize the Lorentz force a high LC is

required.

8 Note that dC is considered as the the overall wire diameter including its isolation, whereby thecalculated RC is smaller than the measured value.

22

4 – FUNDAMENTALS

4.3.4 Magnet

Nowadays several new combinations of materials are used for permanent magnets,

which replace more and more the common ferrite magnets. They mainly differ in

terms of the maximum magnetic energy product BHmax.

Three permanent magnet materials can be taken into account for the MSTS VCA

known as

• Aluminum Nickel Cobalt (AlNiCo),

• Samarium Cobalt (SmCo) and

• Neodymium Iron Boron (NdFeB).

SmCo and NdFeB are rare earth element magnets with the today highest possible

energy products. The theoretical maximum of NdFeB amounts to 64 MGOe [1]. Table

4.2 lists the most important parameters of these materials.

Material ρ / kgm3 BHmax / MGOe TC / C

AlNiCo 7300 7.5 - 9.0 ≈ 800SmCo 8000 - 8500 28 700 - 800NdFeB† 7400 64 310 - 370

Table 4.2: Properties of the investigated permanent magnet materials. Listed arethe mass density ρ, the maximum magnetic energy product BHmax and the Curietemperature TC . † www.ndfebmagnets.de accessed on June 4, 2008.

The restricted MSTS dimension requirements ask for applying a NdFeB magnet due

to its high BHmax. The VCA concept in terms of moving magnet or moving coil has

a direct influence to the magnet selection concerning its dimensions and mass. Fur-

thermore, the Curie temperature TC must be well above the operating temperature

of the MSTS to avoid demagnetization.

4.3.5 Cylindric Single Coil VCA

VCAs generally consist of a cylindric permanent magnet and an ambiant cylindric coil.

An optional ferrite ring, which is directly coupled to the magnet, encases the coil to

concentrate the magnetic field lines for achieving higher Lorentz forces.

23

www.ndfebmagnets.de

4 – FUNDAMENTALS

Figure 4.5 (right) shows a model of a cylindric single coil VCA without ferrite ring.

The x-axis indicates the direction of the translational movement and coincides with~FV CA, which follows with (4.15) to

FV CA(x) = ICLCBx(x). (4.18)

The coil’s magnet field Bx(x) induced by the current shows the same distribution like

the field of the permanent magnet (fig. 4.6). Thus, the Lorentz force pushes or pulls

the coil9 on the x-axis depending on the current flow direction. It is reasonable that no

force will be generated when the axial centers of the magnet and the coil conincides,

because the magnet fields cannot cause a magnetic attraction or repulsion respectively.

An axial displacement of this two components is necessary for optaining a functional

cylindric single coil VCA.

The magnet field distribution on the x-axis of a cylindric coil can be derived to

BxC(x) =µ0N

2lC

lC2− x√(

lC2− x)2

+(

DC

2

)2 +lC2

+ x√(lC2

+ x)2

+(

DC

2

)2 , (4.19)

whereas µ0 indicates the vacuum permeability, N the number of windings of the coil,

lC the coil length and DC the coil diameter.

Due to the same field line distribution, the magnet’s field BxM(x∗) will be defined

analogously to (4.19) with the translation x∗ = x+ a. Note that x = x− a. The force

distribution of a cylindric single coil VCA can now be calculated with the superposition

of the two B-fields depending on the shifting parameter a, to

FV CA(x, a) = ICLC(BxC(x)−BxM(x∗)). (4.20)

Anticipating to the following chapter, figure 4.7 shows a calculated force distribution

for arbitrary defined values, which won’t be discussed here. In fact, the characteristic

of the FV CA curve interests in terms of the optimal coil positioning relative to the

magnet. The goal is to maximize the VCA force. The two optimal displacement

positions can be calculted using the first derivative

∂FV CA(x, a)

∂x= 0. (4.21)

It must be noted, that the this displacement optimization must be considered dy-

namically due to the stroke, which the VCA shall perform for operation. Further

investigations will be presented in chapter 5.

9 Evidentially, the magnet will be pushed or pulled when applying the moving magnet concept.

24

4 – FUNDAMENTALS

−5 −4 −3 −2 −1 0 1 2 3 4 50

0.5

1

1.5

x / a.u.

Bx /

a.u.

Figure 4.6: Calculated |Bx(x)| distribution of a cylindric single coil.

−8 −6 −4 −2 0 2 4 6 8

x 10−3

−0.2

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

x / m

F /

N

Figure 4.7: Calculated Lorentz force distribution of a cylindric single coil VCA.

25

4 – FUNDAMENTALSInteraction Map

Electro-magnetic Magnet properties

Coil propertiesBack-EMF damping

Mechanical ThermalMechanical Thermal

FH ti Heat conductionFH properties Heat conduction

EigenfrequenciesShutter installation

Thermal radiationGlue heat conductivity

DIVISION Science & Earth Observation31.10.20071 Short Term Shutter and Long Term Shutter

Figure 4.8: Map of the physical interactions separated in the mechanical, electromag-netic and thermal branches.

4.4 Interaction Map

In the previous sections, the mechanical and electromagnetic basics for the MSTS

design were discussed. However, no introduction in the thermal basics is given due to

its reduced significance for the DM during the preliminary design phase. Nevertheless,

a thermal analysis, which served its purpose, was performed and will be discussed in

chapter 5.1.

As a summary of the physical interactions, which lead the MSTS design, figure 4.8

shows an interaction map with indicated parameters of the concerning physical branches.

This figure shall point the designing difficulties for fulfilling all requirements. Recip-

rocal relations of different parameters in the electromechanical equations do not allow

a straightforward design approach, but rather require good optimizations.

26

4 – FUNDAMENTALS

4.5 Control

4.5.1 Introduction

A shutter blade switching mode with a maximum close/open time for the MSTS

movement is defined in table 2.1. Thus, an adequate electronics which controls the

blade stroke is required to achieve this mode.

Applicable fundamentals of the control theory will be introduced here in view of defin-

ing the control parameters, which must be finally converted into electric resistances

and capacitances respectively.

Controller

z

x y e w

-

Control Path

Figure 4.9: Standard closed loop system [7].

Figure 4.9 shows the standard closed loop system subdivided in the controller, the con-

trol path and its characterizing feedback comparator. The parameters are well known

as

x control variable,

w set point,

e error signal,

y actuating variable and

z disturbance variable.

The electronics shall perform all parts of the standard closed loop system excepting

the control path, which is composed by the FH and the VCA.

27

4 – FUNDAMENTALS

4.5.2 Theory

The first step in control theory is to build a physical model of the control path and then

to describe it mathematically. For simplifying the physical model of an electromechan-

ical system, the mechanical and electrical part shall be considered separately. Their

models are sketched in figure 4.10, whereof the applicable formulas can be deduced.

k m c

x

UR UL

UC

IC

RC L

Figure 4.10: Models of the FH as a spring mass system (left) and the VCA as a RLcircuit (right).

The mathematical model of the mechanics and its Laplace transform follow to

mx+ kx+ cx = FV CA(x, t) (4.22)

s2mX(s) + skX(s) + cX(s) = FV CA(s). (4.23)

Thereof, the transfer function for the mechanical part GFH(s) can be described as

GFH(s) =X(s)

FV CA(s)=

1

s2m+ sk + c. (4.24)

Analogously follows for the mathematical model of the electric circuit and its Laplace

transform the equations

uR + uL − uC = 0 (4.25)

RCiC + LdiCdt

= uC (4.26)

RCIC(s) + sLIC(s) = UC(s). (4.27)

28

4 – FUNDAMENTALS

Thus, the transfer function of the electromagnetic part GV CA(s) results in

GV CA(s) =IC(s)

UC(s)=

1

sL+RC

. (4.28)

Since the VCA drives the FH, the mechancial part can be considered as connected in

series to the electromagnetical part. Thus, a multiplication of the transfer functions

results in the frequency domain. As interconnecting part, the force factor KF derived

in (4.16) must be taken into account, whereof its Laplace transformation can be

denoted by KF KF (s) = FV CA(s)/IC(s). The extracted control path is shown in

figure 4.11.

Note that this description must be considered as a first approximation, what corre-

sponds to the general path of modeling in control theory. Obviously, no distrubance

variable appears in figure 4.11. But when the MPO once arrives in Mercury’s orbit

and the MSTS starts working, no disturbances should occur anymore.

GVCA(s)

UC

KF(s)

GFH(s)

IC FVCA x

Figure 4.11: Model of the control path consisting of a serial connection of the transferfunctions GV CA(s), KF (s) and GFH(s).

29

Chapter 5

Analysis, Calculations and Experiments

5.1 Thermal Analysis

It is a fact, that a thermal analysis must be performed for every component once

reaching the outer space due to the hash conditions and, of course, the missing air.

Thus, no convection occurs which normally supports the heat dissipation mainly of

electronic components.

Two VCA concepts were presented in section 4.3.2 named as moving coil and moving

magnet. One of theses concepts shall eventually be selected with help of a thermal

analysis to proceed the MSTS design.

Figure 5.1 shows the thermal networks for the two concepts consisting of six nodes, each

coupled by heat conduction and thermal radiation respectively. The applied physical

parameters of the nodes are listed in table 5.1. They are defined in all conscience at

this project stage. The ESATAN software was applied for the calculations.

The node Housing (No. 6) shown in figure 5.1 was set to a constant temperature of

45 C acting as a boundary condition. Fixing the mangnet does obviously not allow

an efficient heat dissipation of the moving coil by conduction, but just by radiation.

This was taken into account for the definition of the thermal networks. As variables,

the temperature of the electronic board, whereof the coil will be supplied, and the

length of its power leads were defined for the moving coil concept. Analogous, the

glue thickness between the fixed coil and its mounting structure was altered for the

calculations of the moving magnet concept.

30

5 – ANALYSIS, CALCULATIONS AND EXPERIMENTS

5Housing

4Moving

part

3Fixedpart

2Magnet

1Coil

6EL board

5Housing

4Moving

part

3Fixedpart

1Coil

2Magnet

6EL board

Figure 5.1: Thermal networks for the moving magnet concept (left) and moving coilconcept (right). Connecting lines indicate conductive couplings and thunder linesindicate radiative couplings between the thermal nodes. The electronics board is ab-breviated with EL board.

Figure 5.2 shows the calculated coil temperatures for both VCA concepts for a maxi-

mum allowed average power consumption of 0.6 W (tab. 2.1) and a maximum housing

temperature1 of 45 C. On the abscissa, the temperature of the electronics board is

plotted as undependent variable. The glue thickness is fixed to 0.1 mm and the lenght

of the power leads amounts to 40 mm.

With the moving magnet concept, the coil does apparently not heat up to temperatures

of > 50 C, whereas the coil reaches temperatures of > 110 C with the moving coil

concept. A relatively big gluing area between the fixed coil and the mounting structure

allows a high conductive heat dissipation. This can furthermore be improved when

reducing the glue thickness.

With this analysis, the design progress has definitely turned in direction of the moving

magnet concept for the MSTS VCA, what furthermore supports the postulation about

the power lead breakage discussed in section 4.3.2. Now the mass of the magnet must

be defined as small as possible to achieve the required shutter blade’s open/close time.

1 The preliminary thermal calculations of the whole MERTIS instrument show a maximum tem-perature for the MSOP housing of 45 C at Mercury’s subsolar point.

31


Component Node Material cH / JkgK

λT / WmK

m / kg ε / -

Coil 1 Cu 385 393 0.2 · 10−3 0.6Magnet 2 NdFeB 9† 502‡ 0.31 · 10−3 0.5Fixed part 3 Steel 444 67 6 · 10−3 0.5Moving part 4 Steel 444 67 4 · 10−3 0.5

Table 5.1: Thermal and material properties of the nodes 1 to 4 of the thermal networkconfiguration (fig. 5.1). Listed are the heat capacity cH , the coefficient of thermalconductivity λT , the mass m and the defined thermal efficiency ε.† www.johnsonmag.com, ‡ www.shnfb.com accessed on June 8, 2008.

30 40 50 60 70 80 9040

50

60

70

80

90

100

110

120

Electronic Board Temperature / °C

Coi

l Tem

pera

ture

/ °C

Figure 5.2: Thermal analysis curves of the moving coil concept (red) and the movingmagnet concept (blue). The average power dissipation of the coil is set to PC = 0.6 Wand a MSOP temperature to 45 C.

32

www.johnsonmag.com

www.shnfb.com


5.2 Finite Element Calculations

5.2.1 Electromagnetic FEM

First estimations of FV CA for the coil dimensioning were performed with (4.15). How-

ever, force measurements of different loadspeaker VCAs and voice coil motors showed,

that this simple mathematical model cannot be applied for the dimensioning of the

MSTS VCA. As a powerful tool, the FEMM2 electromagnetic simulation software was

used for the design progress. FEMM solves planar and axisymmetric problems for

electro- and magnetostatic setups. The results of the FEM calculations are in good

agreement with the performed test measurements.

The left part of figure 5.3 shows a cylindic single coil VCA setup meshed with triangles.

Since FEMM solves axisymmetric problem in 2D, just the half of a cylindrical VCA’s

cross section must be sketched. The parameters of the magnet, the coil and the

surrounding air3 are directly indicated inside of the corresponding countours. As result

of the calculation, the right part of the figure shows the field lines and the magnet

field distribution represented with graded colors. The generated Lorentz force will

be determined by integrating the coil area and results as a planar vector.

5.2.2 Mechanical FEM

Applying the mathematical model for the mechanical deflection calculation presented

in (4.2) shows results, which are in a good agreement with the FEM calculations

performed with NASTRAN. Therefore, this formula was mainly applied for the di-

mensioning of the FH structure.

For experimenting with more complicated FH shapes, the calculations must be per-

formed with FEM. The mechanical FEM model was generally meshed with tetrahe-

drons of an adequate mesh size for reducing the calculation time.

2 The Finite Element Methode Magnetics (FEMM) solver is a freeware tool an can be downloadedat http://femm.foster-miller.net accessed on June 8, 2008.

3 Air must be defined as surrounding medium for the DM. The permeability and permittivity ofair and vacuum (space condition) almost conicide, that this fact practically can be disregarded forthe flight model.

33

http://femm.foster-miller.net


NdFeB 40 MGOeAir

0.125mm[Coil:500]

Density Plot: |B|, Tesla

1.082e+000 : >1.139e+0001.025e+000 : 1.082e+0009.679e-001 : 1.025e+0009.110e-001 : 9.679e-0018.540e-001 : 9.110e-0017.971e-001 : 8.540e-0017.402e-001 : 7.971e-0016.832e-001 : 7.402e-0016.263e-001 : 6.832e-0015.694e-001 : 6.263e-0015.124e-001 : 5.694e-0014.555e-001 : 5.124e-0013.986e-001 : 4.555e-0013.416e-001 : 3.986e-0012.847e-001 : 3.416e-0012.278e-001 : 2.847e-0011.708e-001 : 2.278e-0011.139e-001 : 1.708e-0015.696e-002 : 1.139e-001<2.415e-005 : 5.696e-002

Figure 5.3: A meshed cylindrical single coil VCA (left) and the corresponding FEMMcalcualtion result (right). The left vertical border of both images indicates the rotationaxis of the half of the cross section. Integrating the magnet field in the green coil areaand multiplying it with the defined current results in the Lorentz force.

5.3 Cylindric Single Coil VCA Experiments

As first performed experiments, three test VCAs with different self wound coils were

constructed and measured for verifying the calculations and simulations. A single

point load cell with strain gauges4 was applied for the force measurement after cal-

ibrating it with reference weights. Fixed on a linear positioning table, the load cell

carried the magnet, which penetrated into the fixed coil on its x-axis. First of all,

the linear force to displacement characteristic FV CA(x) ∝ x was verified by linearly

augmenting the coil current IC . A good correlation was established for currents up to

IC = 500 mA. However, during the steady state with IC > 0.5 A, the coil was heating

up to temperatures of > 100 C. This caused unlinearities in the FV CA(x) relation due

to the coil resistance changement.

For all VCA setups, the static force distribution FV CA(x) along the coil axis was

measured and compared with the simulations. Figure 5.4 shows the measurement

results of a VCA setup with the parameters listed in table 5.2. The cruxes in the

negativ x-domain in the mentioned figure indicate the measured values. Due to the

test setup, no forces for x > −1.5 mm could be measured. However, when considering

4 www.vishay.com/docs/12002/1004.pdf accessed on June 8, 2008.

34

www.vishay.com/docs/12002/1004.pdf


(4.20) and its curve plotted in figure 4.7, the characteristic for the positive x-domain

can be anticipated. Therefore, the curve in figure 5.2 is rotational symmetric mirrored

for easier interpretation. All measurement results are in good agreement with the

analytic and FEM calculations.

Coil Magnet

Material MULTOGAN† Material NdFeBdC 0.1 mm dM 2 mmhC 1.75 mm dL 3 mmlC 4.2 mm BHmax 38 MGOeN 500IC 0.2 A

Table 5.2: Parameters of the test VCA setup for the static measurements, whereas hC

represents the coil winding height, dM the magnet diameter and dL the magnet length(see fig. 6.2). † www.isodraht.de/MHflachd.pdf accessed on June 8, 2008.

The MSTS switching mode characterized in figure 2.1 allows to estimate the induced

voltage in the coil, which depends on the magnet’s velocity expressed as

Uind ∝ −Bx(x)x. (5.1)

High induction voltage peaks possibly disturbe the power supply and furthermore

complicates the control of the MSTS. However, as an advantage of the induction, the

transient period of a weakly damped spring-mass system can be shortened due to the

eddy current brake effect. This damping effect shall be utilized during the launch by

short-circuiting the coil for achieving lower FH deflections forced by structure shakings.

5.4 Flexible Hinge Experiments

The calculations and measurements of the test VCAs confined the range of generate-

able Lorentz forces to FV CA ≈ 130 mN. This value was applied for estimating the

FH dimensions starting with a blade thickness of h = 50µm. Its width was defined to

b = 5 mm according to the maximum dimension requirement. The following calcula-

tion shows the necessary FH blade length of a stage with two parallel blades presented

in section 4.1.5. At this stage, Ti-6Al-4V was definitely selected for the MSTS FH

structure. Thus, with its Young’s modulus, the required deflection of f = 1.5 mm

35

www.isodraht.de/MHflachd.pdf


and the equality FV CA = P , the resulting FH length can be calculated with (4.2) to

l = h3

√2fEb

P≈ 13 mm. (5.2)

This length does not exceed the MSTS dimension requirement. But the defined thick-

ness reaches the limit for blades manufactured by wire-cut EDM. Considering the

technological limitations, the aspect ratio for l ≈ 13 mm follows to

aFH =l

h≈ 260. (5.3)

However, this ratio distinctly exceeds the maximum allowed ratio of aFH ≈ 60 dis-

cussed in section 4.1.6. The MSTS design shall therefore be progressed in terms of the

linear stage with necked down flexures.

5.5 Parallel Blade Stage VCA

Based on the presented calculations, a test shutter consisting of a cylindrical single

coil VCA and a stage with two parallel blades was constructed. The VCA parameters

correspond to the values listed in table 5.2. As FH structure, a steel band with a

thickness of 50µm was cutted, folded and glued. Figure 5.5 shows the test shutter,

where the cylindric magnet can be identified on the right side of the coil.

The performed static measurements confirmed the calculated parameters. Further-

more, the damping ratio could be measured, which is laborious to determine by means

of FEM calculations. The test shutter setup shows a very weak damping ratio. This

causes dozens of decaying oscillations of the FH structure when measuring the step

response. So, a control electronics with well adjusted parameters will be inevitable for

the MSTS.

Albeit the simple construction of this test shutter, a lot of useful measurement data

could be gathered and used for the MSTS design progress. Furthermore, the study an

analysis results in terms of using a flexible hinge structure driven by a moving magnet

VCA could be physically proved.

A necessary step of improvement is to increase the first eigenfrequency for achiev-

ing the required switching mode by broadening the blade thickness. Therefore, a

higher Lorentz force will be needed for reaching an adequate stroke. Optimizing the

different VCA parameters however rapidly voilated the requirements and boundary

conditions. Thus, an alternative to the single coil VCA had to be found for the MSTS.

36


−6 −4 −2 0 2 4 6−50

−40

−30

−20

−10

0

10

20

30

40

50

FV

CA /

mN

x / mm

Figure 5.4: Result of the single coil VCA force distribution measurement. A maximumLorentz force of FV CA ≈ 43 mN can be generated with IC = 0.2 A. The magnet’saxial center must therefore be displaced to x ≈ ±2 mm relative to the coil’s axialcenter (x = 0).

Figure 5.5: Photo of the test shutter consisting of a cylindrical single coil VCA and astage with two parallel blades.

37


5.6 Helmholtz VCA

A first idea for optimizing the VCA based on the well known Helmholtz coil setup.

The goal there is to elongate the magnet field’s peak for achieving an extended region

with a constant field along the x-axis (compare fig. 4.6). This can be realized by two

axially oriented coils separated in a particular distance. The reason for experimenting

with a Helmholtz coil setup was the fact, that the generated force no longer depends

on the magnet’s position expressed as

FV CA(x) ∝ Bx(x)⇒ FV CA ∝ Bx. (5.4)

Since it was clear that the magnet’s and the coil’s axial origins must be displaced

for a cylindric single coil VCA, its optimal positions had to be figured out for the

Helmholtz VCA. This was mainly performed with means of the FEMM simulation

software.

Obviously, four variants are possible for wiring and coupling the coils of the Helmholtz

VCA named as

1. serial – equal coupled,

2. serial – anti-coupled,

3. parallel – equal coupled,

4. parallel – anti-coupled.

The terms serial and parallel point to the electrical wiring of the coils. Equal coupled

and anti-coupled define, whether the coils are wound in the same or in the opposite

orientation relative to the x-axis. Elongating the constant B-field will be optained with

an equal coupled setup. The two coils thereby act as a long cylindric coil. But since it

was clear, that the required coil lenght must exceed the magnet length for generating

the required Lorentz force, no improvements can be achieved with a equal coupled

Helmholtz coil compared to a single coil setup. However, the simulation shows, that

an anti-coupled setup is capable to augment the generated force by approximately 80 %

compared to a corresponding equal coupled coil. The |Bx(x)| distribution of an equal

coupled Helmholtz coil has a behaviour comparable to that of a single coil with an

extended summit. But for the anti-coupled Helmholtz coil, the |Bx(x)| distribution

corresponds to the curve shown in figure 4.7.

38


Coils Magnet

Material MULTOGAN Material NdFeBdC 0.125 mm dM 2 mmhC 1.8 mm dL 3 mmlC 2.1 mm BHmax 40 MGOeN 2× 250IC 0.5 A

Table 5.3: Parameters of the Helmholtz VCA simulation.

A formula for calculating the force can be deduced using (4.20). However, the force can

be directly determined with the FEMM software. A free parameter of a Helmholtz

VCA is the clearance d between the coils. The figures 5.6 to 5.8 show the simulated

curves for three different clearances comparing the forces of an equal coupled VCA

(blue) and an anti-coupled VCA (red) with the parameters listed in table 5.3.

The maximum force of the anti-coupled VCA will be reached when the magnet is

precisely positioned in the middle of the coils. Compared to the maximum force of the

equal coupled VCA, an absolute augmentation of 80 % can be achieved in the best case.

This can be explaned when considering each coil as a single magnet. One pushes the

permanent magnet and the other one pulls it respectively. The maximum force depends

on the clearance when considering the negative peaks of the red curves5. Figure 5.9

shows the simulation result of Fmax(d). The optimal clearance was calculated with the

Taylor approximation to dopt ≈ 1.3 mm.

The highest mechanical force appears at the maximum deflection of the FH structure

due to the spring force F (x) = cx according to (4.9). Therefore, it is reasonable that

the axial magnet center shall then coincide with Fmax of the anti-coupled Helmholtz

VCA. However, high acceleration forces occur during the deflection phase because of

the fast switching mode requirement. These forces may exceed the spring force. Hence,

an optimization of the total VCA energy EV CA was performed in terms of

EV CA =

∣∣∣∣∣∣x2∫

x1

FV CA(x)dx

∣∣∣∣∣∣ . (5.5)

The required stroke for the MSTS amounts to f = 1.5 mm. Two cases of the magnet’s

end points were analyzed for optimizing EV CA . For the first, Fmax shall be achieved

5 The negative force peak results of the magnet’s B-field orientation defined in the simulation.Thus, the magnet must be correctly oriented in the MSTS to achieve the desired movement.

39


Coils Magnet

Material MULTOGAN Material NdFeBdC 0.1 mm dM 1.5 mmhC 2.0 mm dL 5.0 mmlC 2.2 mm BHmax 38 MGOed 1.7 mmN 2× 400IC 0.15 A

Table 5.4: Parameters of the Helmholtz VCA test setup.

at the full stoke expressed in (5.6). For the second, Fmax shall be achieved at the half

stroke expressed in (5.7).

Fmax = FV CA(f) ⇒ EV CA =

∣∣∣∣∣∣1.5 mm∫0 mm

FV CA(x)dx

∣∣∣∣∣∣ (5.6)

Fmax = FV CA

(f

2

)⇒ EV CA =

∣∣∣∣∣∣0.75 mm∫

−0.75 mm

FV CA(x)dx

∣∣∣∣∣∣ (5.7)

The optimization curves in relation to the coil clearance are shown in figure 5.10. A

coil energy improvement of around 22 % will be optained for the second case (blue)

compared to the first case (red). Furthermore, the maximum coil energy occurs approx-

imately at dopt like in the maximum force simulation of the anti-coupled Helmholtz

VCA shown in figure 5.9.

The same static measurement as described in subsection 5.3 was performed for a

Helmholtz VCA setup with the parameters listed in table 5.4. The current was

set to a low value to suppress the coil heating. The test setup did also not allow to

measure the force at x > −1.5 mm. Figure 5.11 shows the measured force distribution,

whereas the curves in the positive x-domain are rotational symmetric mirored as well.

The measured curve characteristics are in good agreement with the simulated results

plotted in figure 5.7.

With the same Helmholtz VCA setup, several dynamic measurements were per-

formed to gain conculsions about the eddy current brake effect and the induction with

the different coil wirings and couplings. The magnet was thereby moved along the

x-axis inside the fixed coils driven by a loudspeaker VCA, which was excited with

different shaped signals.

40


Considering the step response measurements showed in figure 5.12, distinct statements

about the different wiring of the coils can be made. The anti-coupled setup shows a

considerably better damping behaviour and smaller induction voltage peaks. Due to

the same winding number of the coils and the opposite axial orientation, the induction

peaks will be almost completely suppressed. Furthermore, the eddy current brake

effect occurs in both movement directions, what can be deduced from the falling edge

of the upper curve in figure 5.12 (right). Thus, this measurement results confirm the

selection of the favoured Helmholtz VCA setup for applying it in the MSTS.

41


−5 −4 −3 −2 −1 0 1 2 3 4 5−250

−200

−150

−100

−50

0

50

100

150

x / mm

F /

mN

Figure 5.6: Helmholtz VCA simulation with d = 0.5 mm.

−5 −4 −3 −2 −1 0 1 2 3 4 5−250

−200

−150

−100

−50

0

50

100

150

x / mm

F /

mN


42


−5 −4 −3 −2 −1 0 1 2 3 4 5−250

−200

−150

−100

−50

0

50

100

150

x / mm

F /

mN


0 0.5 1 1.5 2 2.5 3−210

−205

−200

−195

−190

−185

−180

−175

−170

d / mm

Fm

ax /

mN

Figure 5.9: Maximum force to clearance characteristic of the simulated HelmholtzVCA.

43


0 0.5 1 1.5 2 2.5 3190

200

210

220

230

240

250

260

270

280

290

300

d / mm

EC

oil /

µ J

Figure 5.10: Helmholtz VCA energy optimization curves.

−10 −8 −6 −4 −2 0 2 4 6 8 10−50

−40

−30

−20

−10

0

10

20

30

x / mm

F /

mN

Figure 5.11: Result of the Helmholtz VCA force distribution measurement withd = 1.7 mm.

44


Figure 5.12: Step response oscillograms of the equal coupled (left) and the anti-coupled(right) Helmholtz VCA. The upper curves show the magnet’s step responses of thestroke x measured with a capacitve sensor in USensor = 2 V/DIV and the lower curvesshow the induction voltages measured in Uind = 10 mV/DIV. The abscissa is measuredin t = 20 ms/DIV.

45

Chapter 6

MERTIS Short Term Shutter Demonstrator Model

6.1 Design

This chapter discloses the finally realized MSTS DM design with its mechanical and

electromagnetic components. To highlight the parameters and their interactions sum-

marized in figure 4.8 shall make this design solution comprehensible.

The MSTS design had to bear several requirement adaptions during the work period.

Here, the clearance between the MSOP and the MEOP structure (fig. 2.2), where

the MSTS will be embedded, shall be mentioned. The dimension requirement firstly

allowed an overall width of 5 mm. Due to calculation corrections of the optical path,

the width was eventually confined to 4.5 mm. This influenced the MSTS FH design,

which had to be adapted several times.

6.2 Mechanics

The mechanical part can be devided in two parts, even when it is monolithically

manufactured. These are the moving FH structure and the non moving mounting

part discussed in the following sections. Figure 6.1 shows the CAD model of the

MSTS mechanics with the mounted coils and magnet. Table 6.1 lists the defined

and calculated mechanical parameters. A comparison of these parameters with the

manufactured MSTS test sample is essential for the construction of the Engineering

Model (EM) and, ultimately, the Flight Model (FM). The design drawing of the MSTS

DM can be found in appendix B.

46

6 – MERTIS SHORT TERM SHUTTER DEMONSTRATOR MODEL

Figure 6.1: MSTS DM CAD model which shows the mechanical part (grey), themounted coils (green), the magnet (red) and the support pin (voilet).

Parameter Value

Material Ti-6Al-4Vl 20 mmb 4 mmh 80µmm 1.782 gρ 4430 kgm−3

E 113.8 GPac 83.0 Nm−1

f(1)eig 110.4 Hz

Table 6.1: Defined and calculated design parameters of the MSTS DM mechanicalpart.

47


6.2.1 MSTS FH Structure

The maximum force generated from the Helmholtz VCA and the required first

eigenfrequency determined by the switching mode (fig. 2.1) define the dimension

parameters of the FH. They result from the FEM simulations to FV CA= 124 mN and

f(1)eig = 110.4 Hz. The leaf width was defined to b = 4 mm and its length1 to l = 20 mm.

For reaching an adequate spring constant c, the leaf thickness amounts to h = 80µm.

Thus, a necked down flexures design is necessary. With ξ = 0.5, the length of the

flexible hinges results to lc = 5 mm for each leaf. With a thickness of 0.5 mm, the rigid

part is around 250 times stiffer than the leafs.

The parallel stage avoids canting and rotary movements of the magnet and increases

the eigenfrequency due to the higher stiffness. However, this will be counteracted by

the higher mass, what forced the implementation of three mass reducing cavities in

the rigid parts.

The infrared light beam exits the slit with a divergence of ≈ 30 and passes the

MSOP window afterwards. So, the blade will be placed as close as possible to the slit

for reducing the blade width.

The force should be induced in the middle of the FH structure to avoid tensile and

compressive stress in the leafs [4]. This would require an additional rigid bar and a

changement of the VCA positioning. But FEM calculations showed maximum stress

amplitudes in the leafs far below the endurance strenght limit when inducing the

force at the bottom of the FH structure. Thus, the Helmholtz VCA is positioned

centered to the half round magnet mounting area (fig. 6.1). Since the magnet must

be placed axially centered between the coils, an additional support pin with the same

diameter and a resulting length of 4.7 mm is required to connect the magnet with the

FH structure. Aluminum was selected as material to keep down the moving mass.

6.2.2 Mounting Part

The MSTS DM will be fixed at the MSOP structure with two M2 screws. The MSOP

window and the milling slot for the grating adjustment screws (fig. 2.2) restrict the

bore placement for the MSTS screws. Because the VCA must be placed towards the

grating and, therefore, interfere with its screw, an additional knob at the MSOP is

1 The height of the MSTS obviously exceeds the dimension requirement with the defined leaflength. However, this was approved by the instrument prime.

48


Coils Magnet

Material MULTOGAN Material NdFeBdC 0.1 mm dM 2 mmhC 1.75 mm dL 3 mmlC 3.85 mm χ 0.15 mmd 1.3 mm BHmax 38 MGOeN 2× 232ζ 0.1 mm

Table 6.2: Electromagnetic parameters of the MSTS DM design.

necessary. The bores are designed as long holes for adjusting the shutter blade relative

to the light beam. The mounting part supports the coils of the Helmholtz VCA.

Due to the coils’ diameter of ≈ 6 mm, a slot must be milled in the MSOP to let insert

the MSTS VCA support.

6.3 Electromagnetics

As confirmed with test constructions, the Helmholtz VCA is capable to achieve an

around 1.8 times higher FV CA than a VCA with an equivalent coil, without necessi-

tating more installation space. Listed in table 6.2 are the magnet and coil parameters.

Figure 6.2 shows the VCA cross section with the corresponding dimension parameters.

A glue thickness of ζ= 0.1 mm was defined.

The coils were hand-crafted and glued with epoxy after every winding layer to optain

self-supporting air-core coils. The magnet was glued on the support pin, which itself

was glued on the junction of the FH structure. A small vertical displacement of the

magnet relative to the coils occurs at maximum deflection because of the parallel FH

structure setup. However, the displacement for the required stroke of f = 1.5 mm

amounts to approximately 56µm. With a magnet clearance of χ= 0.15 mm, enough

space between the magnet and the coils is foreseen, even for longer strokes possibly

provoked by launch shakings.

6.4 Measurements

Static and dynamic measurements were performed with the constructed MSTS DM to

determine the mechanical and electromagnetic parameters, which are required for the

49


Coil Dimension

ζεδ

+++=++=

=

=

=

CM

SC

tot

D

C

D

C

hrRllL

mnNdl

m

dh

n

222

Boundary Conditions

)(15.0)(1.0

)(3)(9

)(25.0)(3.1

clearancemagnetmmthicknessgluemm

conditionboundarymmRconditionboundarymmL

clearanceadjustmentmmonoptimizatiduemmlS

======

εζ

δ

Coil wire diameter dD with insulation and copper thickness of 0.15mm.

1. single coating 2. double coating fine 3. double coating thick

No. dD / mm ⎣n⎦ ⎡m⎤ Ntot Rtot / Ω Imax / mA Fmax / mN P / W 1 0.164 10 22 440 5.46 495 127.9 1.34 2 0.174 10 21 420 5.21 518 127.8 1.4 3 0.185 9 20 360 4.47 604 127.7 1.63

Comments

• UC=2.7V as maximum output voltage of an applicable H-bridge amplifier. • Increasing the wire thickness lowers the resistance, thus increases the force and, however, the dissipated

power.

NdFeB

lC lC d 2

χ

hC

ζ

lM

Figure 6.2: Helmholtz VCA dimension parameters shown in the axisymmetric crosssection.

Figure 6.3: Photo of the MSTS DM.

50


Parameter Value

fres 109.1 Hzm 194.6 mgc 91.46 Nm−1

k 1.652 · 10−3 kgs−1

RC 1.712 ΩL 38µH

Table 6.3: Measured mechanical and electromagnetic parameters of the MSTS DM.Note that the spring constant c was not measured for the MSTS DM, but was deducedfrom the step response and, therefore, slightly differs to the value listed in table 6.1

design of the control electronics. Since the MSTS builds a electromechanical system,

the calculated parameters resulting from the separated considerations discussed in the

previous sections must slightly differ to the measured parameters. Table 6.3 lists the

measured parameters of the MSTS DM.

6.4.1 Static Measurement

The spring constant can be determined by a force measurement at static deflections.

Figure 6.4 shows the resulting linear characteristic of the MSTS FH structure, whereas

its slope corresponds to the spring constant, which can be calculated to c = 82.3 Nm−1.

This value almost coincides with the simulated value (tab. 6.1). Thus, it can be con-

cluded, that the leafs of MSTS FH structure were accurately cut by the manufacturer.

6.4.2 Dynamic Measurement

Figure 6.5 shows the measured step response of the MSTS DM VCA excited by a

symmetric rectangular signal with f = 0.9 Hz. Due to the weak damping ratio D, the

highest peak reaches almost the double value of the steady state amplitude. The sys-

tem’s resonant frequency can be determined to fres= 109.1 Hz. With (4.11) to (4.13),

the attenuation constant can be calculated to k = 1.652·10−3 kgs−1. When considering

this measurement result, it becomes obvious, that the MSTS control electronics must

be very well adjusted to reach the required open/close time.

The spring mass can be calculated with (4.10) to m = 194.6 mg considering the mea-

sured spring constant c and the attenuation constant k. These values will be used to

define the experimental model of the control path.

51


0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

20

40

60

80

100

120

140

f / mm

P /

mN

Figure 6.4: Static force measurement of the MSTS FH structure which results in aspring constant of c = 82.3 Nm−1.

0 0.5 1 1.5 2 2.5-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

t / s

f / m

m

Figure 6.5: Measured step response of the MSTS DM VCA. The VCA was excited bya symmetric rectangular signal with f = 0.9 Hz. Because of the weak damping ratioD, the transient period is relatively long.

52

Chapter 7

Electronics

7.1 Control Electronics

7.1.1 Power Amplifier

The design of the control electronics for the DM was mainly driven by the selection

of an adequate power amplifier for the Helmholtz VCA. Two possibilities were dis-

cussed named as

• push pull Operational Amplifier (OPAMP) and

• bridge amplifier.

Due to the small attenuation constant of the FH structure and the resulting blade

oscillations, relatively high braking currents are required to guarantee the switching

mode (fig. 2.1). Therefore, the power amplifier must drive currents in both directions

through the coil, which can be realized by a push pull OPAMP. The low required

supply voltage of 3.4 V allows maximum driving voltages of ±1.5 V even with rail-to-

rail amplifiers1. Thus, the coil resistance must be kept small for reaching high driving

currents. The coils can favorably be connected in parallel in the Helmholtz VCA

setup, which halves the total coil resistance.

With the MSTS DM’s Helmholtz coil resistance of RC= 1.712 Ω (tab. 6.3) and the

minimum driving current of IC= 1.2 A, a minimum driving voltage of UC = 2.05 V

results. Therefore, it is necessary to select a bridge amplifer for the MSTS DM control

1 Note that the supply voltage requirement (tab. 2.1) was changed to 3.4 V during the designphase.

53

7 – ELECTRONICS

Sensor

r

y

w

P

P

I

D

+

_

x

Figure 7.1: Functional schematic of the control electronics. The operational ampli-fier compares w with the feedback variable r. Directly implemented in the OPAMPcircuit are the P-, I- and D-contributions indicated with dashes rectangles. A secondP-contribution is implemented in the bridge amplifier, which consists of two power am-plifiers. The position of the MSTS DM, replaced by the coil symbol, will be contactlessmeasured with the sensor and returned as feedback signal to the comparator.

electronics, because a push pull OPAMP circuit cannot reach this minimum driving

voltage.

7.1.2 Controller

When considering the measured step response of the MSTS DM (fig. 6.5), it is rea-

sonable to define PT2 behaviour for the control path. For the DM, a classical PID

controller based on an operational amplifier as shown in [7] was applied. Since no sen-

sor was definitly selected for the position feedback, the controller had to be designed

for fulfilling all wiring possibilities of the P-, I- and D-contributions. Figure 7.1 shows

the functional schematic of the realized control electronics. This figure is leaned on the

standard closed loop system (fig. 4.9). An operational amplifier compares w with x,

which is conditioned with an additional circuit. The control contributions are directly

implemented in the OPAMP circuit indicated with dashed rectangles.

In the circuit diagram (appendix C), the feedback signal conditioning circuit consists

of three additional OPAMPs to compensate the offset, adjust the gain and invert the

signal if needed. This circuit diagram shows the breadboard electronics design, which

offers a large range for adaption.

54

7 – ELECTRONICS

7.1.3 Sensor

The laser triangulator optoNCDT 1700 from MICRO-EPSILON2 was applied as

position measuring sensor for the static and dynamic measurements. Furthermore,

it was used as feedback sensor for the control electronics breadboard, whereas the

conditioning circuit was adjusted to compensate the sensor’s output signal range of

0 . . . 10 V. It must be mentioned that the optoNCDT 1700 causes a dead time of

1.2 . . . 1.6 ms due to the internal analog-to-digital conversion. However, this seems to

be useful at the first glance and will be discussed in the following section.

A sensor for the position feedback must be found which is

• small,

• lightweight,

• shows a linear input to output characteristic,

• operates with a maximum supply voltage of +3.4 V and

• causes virtually no dead time.

Different sensor systems were evaluated e.g. inductive, capacitive, optical and Hall

effect sensors. Thereby, the latter turned out as most promising because of the already

existing moving magnet in the MSTS VCA, which can directly stimulate the sensor.

An applicable space qualified sensor was not found up to the day of submission of this

thesis, but is to be determined for the further project phase.

7.2 Control Results

For closing the design and construction part within this thesis, the first achieved results

of the controlled MSTS DM presented in figure 7.2 will be discussed. When focussing

on the lower curve in the right part of this figure, it becomes clear, that the switching

mode requirement can be satisfied with the controlled MSTS DM. The open/close time

can be measured to < 5 ms and is therefore shorter than the value listed in table 2.1.

In the right part of figure 7.2, a switching period of ≈ 100 ms is identifiable. Note the

almost entirely suppression of the decaying oscillations, which otherwise occur in the

2 http://www.me-us.com/laser-sensor/ accessed on July 5, 2008.

55

http://www.me-us.com/laser-sensor/

7 – ELECTRONICS

step response measurement of the uncontrolled MSTS (fig. 6.5). The stroke amplitude

amounts to f ≈ 1.2 mm and is slightly below the required stroke. Therefor a peak

current of IC ≈ 1.3 A must be applied, what can be deduced from the upper curve.

As stimulus, a rectangular LVTTL signal was applied with a frequency of 10 Hz and a

duty cycle of 20 %. The controller only consists of a P-contribution, what surprises at

the first glance when considering the stroke measurements. Now the fact of the dead

time in the feedback path, caused by the laser triangulator, must be discussed. This

dead time is directly discoverable as the time shift of the two measured curves. There-

fore, the set point (IC) spurts to around the half amplitude and then stays constant

for ≈ 2 ms until the feedback signal reaches the comparator. The time constant of

the Helmholtz coil can be calculated to τL= L/R ≈ 22µs and has an insignificant

influence to the blades open/close time.

The control variable x, which corresponds to the blade stroke f , shall follow the set

point as accurate as possible to reduce the error signal e to a minimum. Here, just a

proportional controller3 was applied, what typically does not suffices for well control-

ling a control path with PT2 behaviour. Hence, undetermined capacitives occuring in

the whole control loop optimize the controller, that the required behaviour just can

be achieved. Further investigations must be performed for the controller design when

an adequate sensor will be applied.

3 Note that the P-contribution was manually adjusted with help of a potentiometer until therequired behaviour was achieved.

56

7 – ELECTRONICS

MERTIS MSTS P-Control 25.05.2008

H:\MERTIS_HUA\MSTS DM Control Electronics\Measurements\P-Control.doc 5 - 5

MERTIS MSTS P-Control 25.05.2008

H:\MERTIS_HUA\MSTS DM Control Electronics\Measurements\P-Control.doc 4 - 5

Figure 7.2: Results of the controlled MSTS DM, which fulfills the required switchingmode. The left part shows one cycle measured in t = 20 ms/DIV, whereas the rightpart is zoomed in to t = 5 ms/DIV. The lower curves of both parts show the stroke ofthe blade measured with the optoNCDT 1700 represented in f = 0.4 mm/DIV. Theupper curves show the controlled current IC measured in 0.5 A/DIV.

57

Chapter 8

Conclusions, Status and Open Work

A voice coil actuator driven shutter based on a flexible hinge structure was concluded

in the study [5] for the design of the MERTIS short term shutter. Within this master

thesis, it could be showed, that the implementation of this selection is capable to fulfill

all requirements. The electromagnetic and mechanical parts were designed with help

of analytic and FEM calculations in view of harmonizing all parameters and resulted in

the construction of the MSTS DM. To reach this goal, investigations in the fundamen-

tals of material properties, flexible hinges and electromagnetics had to be performed.

The parameters were adjusted to minimize the power consumption, the dimensions

and the mass of the MSTS DM. However, this couldn’t be performed staightforward

due to reciprocal relations, what rather caused a parameter optimization.

The mechanical structure with the flexible hinges was deviated from a the linear stage

with necked down flexures presented in [4]. But for the voice coil actuator, an uncon-

ventional design based on two anti-coupled coil was proposed, realized and labeled

as Helmholtz VCA. This VCA design shows an improvement of the generated

Lorentz force of around 80 % compared to an equivalent single coil VCA. Theoretic

considerations of this electromagnetic design let assume a lot of advantages, which

could be proved with adequate measurements.

The low damping ratio of the MSTS DM is a result of the force reducing sanctions for

fulfilling the power and open/close time requirements. Therefore, a control electronics

was designed to achieve the required blade switching mode. A laser triangulator was

applied as feedback sensor, whereby satisfying results of the closed loop system could

be optained.

58

8 – CONCLUSIONS, STATUS AND OPEN WORK

As a result from the MERTIS shutter study, life time and fail safe are quoted as

most important requirements, which can be met with the designed and constructed

MSTS DM. Up to the day of submission of this thesis, the constructed MSTS DM

performed almost 50 million cycles without identifiable damage. However, this must

be investigated in regard to occuring microcracks in the thin FH blades. Detailed

material and lifetime tests must be noted as open work, as well as the definition of a

space qualified sensor and control electronics.

Albeit the MSTS DM must be sligthly adpated for the ultimate integration in the

MERTIS instrument due to continual structur and optics changements, a solid base

was achieved with the presented construction, whereon the following engineering and

flight models can be built.

It is still a long way to go until the scheduled launch of BepiColombo in 2013. So, let’s

use the time for upgradings and—as free side effect—to learn from every performed

step.

59

APPENDIX

60

Appendix A

Deviation of the Logarithmic Decrement

Calculating the logarithmic decrement δ is important for the determination of the

damping ratio D of a mechanical system. The formulas presented in [7] allow to

calculate D when the stationary amplitude x0 is known, to which ∆1 and ∆2 can be

related. When the system cannot reach a steady state due to a periodical excitation,

the amplitude of a third peak is required for calculating δ. In the following part, the

required formulas will be derivated refering to figure A.1.

With

δ =∆1

∆2

=∆2

∆3

(A.1)

and a simple geometrical consideration follows

∆1∆3 = ∆22 (A.2)

∆1 + ∆2 = x1 − x2 (A.3)

x3 = x2 + ∆2 + ∆3. (A.4)

When substituting (A.2) with (A.3), the quadratic equation

∆22 + ∆2∆3 −∆3(x1 − x2) = 0 (A.5)

results with the roots

∆2(1,2) =−∆3 ±

√∆2

3 + 4∆3(x1 − x2)

2. (A.6)

(A.4) can now be written as

2x3 = 2x2 + (−∆3 ±√

∆23 + 4∆3(x1 − x2)) + 2∆2 (A.7)

61

A – DEVIATION OF THE LOGARITHMIC DECREMENT

t / a.u.

x / a

.u.

T0

Δ3

x3

Δ2

x2

x1 Δ1

Figure A.1: Step response function with the indicated parameters.

and solved to

∆3 =−x2

3 + 2x2x3 − x22

2x2 − x3 − x1

. (A.8)

Finally a set of three reqursive formulas can be defined for the calculation of the

logarithmic decrement with three absolute peak amplitudes to

∆3 = − (x2 − x3)2

2x2 − x3 − x1

(A.9)

∆2 = x3 − x2 −∆3 (A.10)

∆1 = x1 − x2 −∆2. (A.11)

62

Appendix B

MSTS DM Design Drawing

63

Appendix C

MSTS DM Breadboard Electronics Circuit

Diagram

65

MERTIS

20.03.08 HUA

MSTS DM Control Electronics

1HUA05.03.08First Issue1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

L

K

I

H

G

F

E

D

C

B

A

16151413121110987654321

A

B

C

D

E

F

G

H

I

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Rev Änderungs-Nr. Tag Name

Bearb.

Gepr.

Tag Name

Benennung

Zeichnungs-Nr.

MSTS_DM_V1_0

zu Gerät

zu Anlage

1/1 02.04.2008 11:46:29 Blatt

+

Signal Conditioning

Control

EmergencyBridge Amplifier

Header D-Sub

(U10)

(U30)

LVTTL Stabilization

Vref

LVTTL Stabilization

Constant Current Regulator

(U20) (U10)

(U70)

Ur

(U21) (U70)

R22

R21

R23

2

31

U10A

6

57

U10B9

108

U10C

13

1214

U10D

411

R102

C102

C40

R97

R95R14

R100

C100

R12

R43

2

31

U70A6

57

U70B

9

108

U70C

13

1214

U70D

411

R72 R73

R74

R75

R88R85

12345678

9101112131415

X10

R60

D60R15

8

9

14 6

2

125

3

U20

8

9

146

2

125

3

U21

R30

123456789

SV10

161

K60

O1S1

P1

K60

O2S2

P2

K60ADJ

IN OUT

U30

R56Q50

R55

R57

R54A

CR VR50

R50

C41

C42

R20

R25

R24

R51

R52

R53

ACR VR40R40

R41

R42

R13

C43

R70

R71

R17

R18R19

R16

R93

R94 R96

R92

R90

R91R98

R58

R61

R101 R103

C101 C103

C44 C45

R82

R81

R86

R89

R83

R84

R87

T60

SENSOR_OUT

SENSOR_OUT

SENSOR_OUT

MSTS_CLOSE_NOM

MSTS_CLOSE_NOM

LVTTL_GND LVTTL_GND

MSTS_POS_DIG

MSTS_POS_DIG

STS_+3V4

RTN_+3V4RTN_+3V4

MSTS_CLOSE_EME

MSTS_CLOSE_EME

COIL_NOM+

COIL_NOM+

COIL_NOM-

COIL_NOM-

COIL+

COIL+

COIL-

COIL-

MSTS_CLOSE_STAB

MSTS_CLOSE_STAB

+1V5

+1V5

+1V5

+1V5

MSTS_POS_ANA_MAIN

MSTS_POS_ANA_MAIN

SENSOR_MOD

SENSOR_MOD

+2V5

+2V5

+3V0+3V0

+3V0

+3V0

+1V0

+1V0

MSTS_TEMP_MAIN+MSTS_TEMP_MAIN-

MSTS_TEMP_RED+MSTS_TEMP_RED-

1k

1k

STS_+3V4STS_+3V4

6.8k

RTN_+3V4

TLV2764

TLV2764 TLV2764 TLV2764

RTN_+3V4

220uF

0R

RTN_+3V4

TLV2764TLV2764

TLV2764TLV2764

10k

MLC1N4148

RTN_+3V4

STS_+3V4

STS_+3V4

OPA567 OPA567

RTN_+3V4

1R / 2W

G6A-274P-ST_US

LT1086

10kBSS123

7.5k

10k

10k

TL431

10R

RTN_+3V4

STS_+3V4

RTN_+3V4

RTN_+3V4

100nF

100nF

2k2

1k

6.8k

20k

10k

20k

RTN_+3V4

RTN_+3V4

TL431220R

56R

RTN_+3V4

10R

STS_+3V4STS_+3V4

RTN_+3V4

100nF

RTN_+3V4

STS_+3V4

RTN_+3V4

RTN_+3V4

RTN_+3V4RTN_+3V4

1k

0R

RTN_+3V4

RTN_+3V4

100nF 100nF

RTN_+3V4RTN_+3V4

STS_+3V4 STS_+3V4

BFS20

List of Figures

Figure page

1.1 BepiColombo emblem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 MERTIS instrument model . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 MERTIS instrument block diagram . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Shutter blade switching mode . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 MSTS integration space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Shutter actuation principles . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.1 Flexible hinge patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Ti-6Al-4V fatigue tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.3 Parallel blade stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.4 Technological limitations of wire-cut EDM . . . . . . . . . . . . . . . . . . 17

4.5 VCA models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.6 Calculated magnet field distribution of a cylindric single coil . . . . . . . . 25

4.7 Calculated Lorentz force distribution of a single coil VCA . . . . . . . . . 25

67

List of Figures

4.8 Interaction map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.9 Standard closed loop system . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.10 Models of the spring mass system and the RL circuit . . . . . . . . . . . . 28

4.11 Model of the control path . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5.1 Thermal networks for moving coil and moving magnet . . . . . . . . . . . 31

5.2 Thermal analysis curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.3 FEMM meshing and calculation result . . . . . . . . . . . . . . . . . . . . 34

5.4 Single coil VCA force distribution measurement result . . . . . . . . . . . 37

5.5 Photo of the test shutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.6 Helmholtz VCA simulation with d = 0.5 mm . . . . . . . . . . . . . . . . . 42



5.9 Maximum force to clearance of the simulated Helmholtz VCA . . . . . . . 43

5.10 Helmholtz VCA energy optimization . . . . . . . . . . . . . . . . . . . . . 44

5.11 Helmholtz force dirstribution measurement . . . . . . . . . . . . . . . . . 44

5.12 Step responses of the equal coupled and the anti-coupled Helmholtz VCA 45

6.1 MSTS DM CAD model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

6.2 Helmholtz VCA dimension parameters . . . . . . . . . . . . . . . . . . . . 50

6.3 Photo of the MSTS DM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6.4 Static force measurement of the MSTS FH structure . . . . . . . . . . . . 52

68

List of Figures

6.5 Measured step response of the MSTS DM VCA . . . . . . . . . . . . . . . 52

7.1 Control electronics principle . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.2 Results of the controlled MSTS DM . . . . . . . . . . . . . . . . . . . . . 57

A.1 Step response function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

69

List of Tables

Table page

2.1 MSTS requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.1 FH material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.2 Magnet material properties . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.1 Thermal model properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.2 Test VCA parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.3 Helmholtz VCA simulation parameters . . . . . . . . . . . . . . . . . . 39

5.4 Helmholtz VCA test setup parameters . . . . . . . . . . . . . . . . . . . 40

6.1 MSTS DM mechanical design parameters . . . . . . . . . . . . . . . . . . 47

6.2 MSTS DM electromagnetic design parameters . . . . . . . . . . . . . . . . 49

6.3 Measured MSTS DM mechanical and electromagnetic parameters . . . . . 51

70

Bibliography

[1] U. S. Deshpande. Recent Advances in Materials for use in Permanent Magnet

Machines - A Review. Electric Machines and Drives Conference, 2003.

[2] S. Henein et al. Fatigue Failure of thin Wire-EDM Machined Flexible Hinges.

Proc. SPIE Int. Symp. on Intelligent Systems & Adv. Manufacturing, 2002.

[3] E. Goodin, A. Kallmeyer, and P. Kurath. Multiaxial Fatigue Evaluation of Ti-

6Al-4V under Simulated Mission Histories. Journal of Engineering Materials and

Technology, 2002.

[4] S. Henein. Conception des guidages flexibles. Presses Polytechniques et Universi-

taires Romandes, 2004.

[5] A. Hurni. MERTIS Shutter Study. Kayser-Threde MER-KTM-TN-005, 2007.

[6] U. Jungnickel. Miniaturisierte Positioniersysteme mit mehreren Freiheitsgraden

auf der Basis monolithischer Strukturen. PhD thesis, TU Darmstadt, 2004.

[7] H. Mann, H. Schiffelgen, and R. Froriep. Einfuhrung in die Regelungstechnik.

Carl Hanser Verlag Munchen, 2003.

[8] L. Susmel and P. Lazzarin. A bi-parametric Wohler curve for high cycle multiaxial

fatigue assessment. Fatigue & Fracture of Engineering Materials and Structures,

2002.

[9] G. S. Szekely and F. Henzelin. Design and Qualification of the Mechanisms for

the ALADIN Instrument. Proceedings of the 11th European Space Mechanisms

and Tribology Symposium, ESMATS 2005, Lucerne, Switzerland.

71

Bibliography

[10] B. P. Trease, Y.-M. Moon, and S. Kota. Design of Large-Displacement Compliant

Joints. Journal of Mechanical Design, 2005.

[11] J. van Casteren et al. Experiment Interface Document Part A. ESTEC BC-EST-

RS-01140, 2007.

[12] J. van Casteren et al. Experiment Interface Document Part B. ESTEC BC-EST-

RS-02521, 2007.

[13] Z. J. Zhang and Y. B. Yuan. Research of a Novel Flexure Hinge. Journal of

Physics, 2006.

72

Name Andreas Hurnigeb. 30.11.1982Matr. Nr. 8376608801706MNM im SS 2008

Erklarunggemaß § 13 Abs. 5 RaPO

Hiermit erklare ich, dass ich die Masterarbeit selbstandig verfasst, noch nicht ander-

weitig fur Prufungszwecke vorgelegt, keine anderen als die angegebenen Quellen oder

Hilfsmittel benutzt sowie wortliche und sinngemaße Zitate als solche gekennzeichnet

habe.

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Master Thesis Design and Construction of the Shutter ...€¦ · Demonstrator Model for the Mercury Radiometer and Thermal Infrared Spectrometer Dipl.-Ing. (FH) ... I Geometrical