Shape Memory Alloy actuators in robotsand composites.

Piet Schreurs28th February 2002

Technische Wetenschappen

Title Shape Memory Alloy actuators in robots and composites.

Dutch title Shape Memory Alloy actuatoren in robots en composieten.

Applicants Prof.dr. H. Nijmeijer (Project leader)Dynamics and Control Technologytel.: 040 - 2473203E-mail : h.nijmeijer@tue.nl

Prof.dr.ir. H.E.H. MeijerMaterials Technologytel. : 040 - 2474827E-mail : h.e.h.meijer@tue.nl

Dr.ir. P.J.G. Schreurs (Contact person)Materials Technologytel. : 040 - 2472778E-mail : p.j.g.schreurs@tue.nl

Eindhoven University of TechnologyDepartment of Mechanical EngineeringPostbox 513, 5600 MB EindhovenTel. (040)2472851 ; Fax. (040)2447355

Embedding Engineering Mechanics (EM)Dutch Institute of Systems and Control (DISC)Netherlands Institute for Metals Research (NIMR)Dutch Polymer Institute (DPI)

Keywords Shape Memory Alloys (SMA), actuators, robots, adaptivecomposites, shape control, vibration control

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1 Summaries

1.1 Research

This research focuses on the application of Shape Memory Alloys (SMAs) wires as actuators1. in robots to prescribe their position and movement (trajectory control).2. in composite parts to change their geometry (shape control) and their dynamic char-

acteristics (vibration control).To realise the desired behaviour of robot or composite, the actuators must be driven by acontrol algorithm. For this proposal our attention is focused on two separate but relatedapplication fields in the following projects :

1. Concerning the SMA robot, attention will be given to the control of systems withhysteresis, a characteristic feature of SMA actuators. With more degrees of freedomof the robot, the number of SMA actuators will grow and the control becomes moreinvolved. The redundancy of a robot with more then two degrees of freedom allowsthe development of efficient feedback and feedforward controllers. A miniature more-then-two-degrees-of-freedom robot will be build to evaluate the controller design.

2. An SMA composite is a continuous system (plate). The numerical model – neededfor feedback and feedforward control – is therefore complex (finite element model). Asimple model has to be developed, however, for online (real-time) analysis. Measur-ing deformation – needed for feedback control – has to be done using optical fibresintegrated in the composite material (distributed sensing). It has to be investigatedwhether the mechanical behaviour of the composite material is influenced by the SMAwires and the glass fibres – stress concentrations – and the necessary periodic temper-ature increase of the SMA wires.

The projects have the characteristic features of SMA actuators,e.g. hysteresis, in common.The feasibility of the project follows from an earlier PhD project at the Materials Technologygroup [12], in which preliminary steps towards the realization of the above goals were made.

1.2 Utilisation

This research may contribute to fundamental knowledge for a number of applications. Dutchindustries (NLR, Memory Metal Holland, AMC, Philips CFT and Philips PMS) have alreadyexpressed their interest.

For project 1 (SMA actuators in robots) these applications are :

Robotics- Trajectory control in miniaturized positioning systems with high accuracy.Space technology- Trajectory and vibration control in space structures.Medical technology- Trajectory control in flexible catheters with dirigible tips.- Trajectory control in active prostheses.

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For project 2 (Materials with integrated SMA actuators) possible applications are :

Medical technology- Vibration control of thin-walled structures (MRI tubes).Aircraft and energy industry- Vibration control of thin-walled structures (fuselage).- Shape control of wing and rotor blade profiles.

Besides the above-mentioned possible applications, knowledge and algorithms for the controlof systems with redundancy, hysteresis and distributed actuators will be valuable for not-SMAapplications as well.

This also applies to the knowledge and techniques which must be developed for the localmeasurement of strains with glass fibre technology.

1.3 Summaries in Dutch

1.3.1 Onderzoek

De doelstelling van het onderzoek is de toepassing van geheugenmetaal (Eng.: Shape MemoryAlloy (SMA)) als actuatoren1. in robots voor het voorschrijven van positie en beweging (trajectory control).2. in composietmaterialen voor het onder gebruiksomstandigheden doelgericht veranderen

van de vorm van constructiedelen (shape control) en van de dynamische karakteristieken(vibration control).

Om het gewenste gedrag van robot of composietmateriaal te realiseren moeten de actuatorenworden aangestuurd d.m.v. een regelprocedure. In dit voorstel wordt de aandacht gericht optwee verschillende toepassingen in de volgende projecten :

1. M.b.t. de SMA robot zal de aandacht uitgaan naar het regelen van systemen met hys-terese, een kenmerkende karakteristiek van SMA actuatoren. Bij toenemend aantalvrijheidsgraden van de robot neemt ook het aantal SMA actuatoren toe en wordt deregeling belangrijker. De redundantie van een robot met meer dan twee graden vanvrijheid biedt de mogelijkheid om efficiente feedback en feedforward regelaars te on-twikkelen. Een minirobot met meer dan twee graden van vrijheid zal worden gebouwdom de regeling experimenteel te testen.

2. Een SMA composiet is een continu materiaal (een plaat). Het numerieke model – t.b.v.feedback en feedforward regeling – is hierdoor gecompliceerd. Een eenvoudig modelmoet echter worden ontwikkeld voor online (real time) berekeningen. Het meten vandeformaties – t.b.v. feedback regeling – moet gebeuren m.b.v. in het composietmate-riaal geıntegreerde optische vezels (distributed sensing). Onderzocht moet worden ofhet mechanisch gedrag van het composietmateriaal niet nadelig wordt beınvloed doorde aanwezigheid van SMA draden en glasvezels – spanningsconcentraties – en door denoodzakelijke periodieke temperatuurverhoging van de SMA draden.

In de twee projecten komen de karakteristieke eigenschappen van SMA actuatoren, bv.hysteresis, naar voren. In een voorafgaand promotieonderzoek, uitgevoerd binnen de groep

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Materials Technology [12], zijn de eerste stappen gezet ter realisering van bovenstaande doel-stellingen. De resultaten van dit onderzoek waren zodanig dat mag worden verwacht dat hetvoorgestelde onderzoek succesvol zal zijn.

1.3.2 Utilisatie

De resultaten van dit onderzoek kunnen resulteren in een aantal toepassingen. Nederlandsebedrijven en instellingen (NLR, Memory Metal Holland, AMC, Philips CFT and Philips PMS)hebben van hun belangstelling blijk gegeven.

Voor project 1 (SMA actuatoren in robots) zijn de mogelijke toepassingen :

Robot systemen- Trajectory control in geminiaturiseerde robotsystemen met hoge positioneringsnauw-keurigheid.Ruimtevaart technologie- Trajectory en vibration control van ruimte constucties.Medische technologie- Trajectory control van flexibele catheters met bestuurbare tips.- Trajectory control bij actieve prothesen.

Van project 2 (Materialen met geıntegreerde SMA actuatoren) zijn de mogelijke toepassingen :

Medische technologie- Vibration control van dunwandige constructies (MRI buizen).Luchtvaart en energie industrie- Vibration control van dunwandige constructies (vliegtuigromp).- Shape control van vleugel en rotorblad profielen.

Behalve de bovenstaande mogelijke toepassingen, kunnen de verworven kennis en de on-twikkelde algoritmen voor het regelen van systemen met redundantie, hysteresis en continuverdeelde actuatoren van belang zijn voor niet-SMA toepassingen.

Dit geldt ook voor de kennis en technieken, die verkregen c.q. ontwikkeld moeten wordenvoor het meten van lokale rekken met glasvezel technologie.

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2 The research group

2.1 The current research group

The proposed research will be supervised and supported by staff of the Eindhoven Universityin the groups Dynamics and Control Technology and Materials Technology. Support fromothers is garanteed as well, as is described in section 4 on ”Utilisation”.

The next table lists names of TUE staff and the expected time they will spend for super-vision and support (indicative !).

Prof.dr. H. Nijmeijer Dynamics and Control Technology (TUE/W)040-2473203; h.nijmeijer@tue.nl

2 h/w

Prof.dr.ir. H.E.H. Meijer Materials Technology (TUE/W)040-2474827; h.e.h.meijer@tue.nl

2 h/w

Dr.ir. P.J.G. Schreurs Materials Technology (TUE/W)040-2472778; p.j.g.schreurs@tue.nl

6 h/w

Dr.ir. L.E. Govaert Materials Technology (TUE/W)040-2472838; l.e.govaert@tue.nl 4 h/w

Dr.ir. F.E. Veldpaus Systems and Control (TUE/W)040-2472796; frans@wfw.wtb.tue.nl

4 h/w

Dr.Ing. A.A.J.M. Peijs QMWC University of LondonDepartment of MaterialsMile End Road, London E1 4NS, UK+44 (0)1719755281; T.Peijs@qmul.ac.uk

2 h/w

Laboratory and workshop personel of both research groups are available when needed. As-sistance can also be acquired from Central Service Facilities like the ”GemeenschappelijkeTechnische Dienst” and the Computer Centre.

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3 Scientific description

3.1 The research projects

In this subsection two research projects are described. First however, in §3.1.1, the character-istic properties of Shape Memory Alloys and their application as actuators are summarized.

3.1.1 General description of Shape Memory Alloys and their application as ac-tuators

Properties of adaptive materials can be changed at will during their use and optimized forchanging external circumstances. Well-known and widely applied are the piezoelectric ceram-ics and polymers. Displacements (strains) which can be realized with these materials are verysmall (µm-range), which confines their spectrum of application. Less used, partly due to highcosts, are the electro- and magnetoreological fluids.

Much attention is currently focused onto the Shape Memory Alloys (see also [48]). Theadaptive properties of SMAs results from a change of their microstructure, more specifically aphase transformation [14, 15, 16, 18]. The much used Nickel-Titanium (NiTi) alloys, which aredescribed here, are completely martensitic – martensite fraction m = 1 – at low temperature,typically θ = 15o C. The figure below shows how the completely martensitic (M : m =1), unconstrained material is transformed into austenitic (A : m = 0) material when thetemperature is raised.

MA

θθafθasθmsθmf

m

1

0

AM

Fig. 1 : Temperature driven phase transformation of unconstrained SMA

The martensitic-austenitic (MA) transformation starts at temperature θas and is completedat temperature θaf . The phase transformation is reversible : cooling of the material givesrise to an austenitic-martensitic (AM) transformation, which starts at θms and is completedat θmf . As can be seen in the figure, the MA and AM trajectories do not coincide : anhysteresis loop is observed.

The limit temperatures – θas, θaf , θms and θmf – are determined by the composition ofthe alloy and can be fixed very accurately. Because the phase transformations, which are theresult of a change in lattice, are volume invariant, the material will not show any deformation.

The phase transformation in SMAs can also be provoked by stress. The figure below showstwo tensile curves at two different temperatures θ1 > θ2 > θaf .

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σms

σmf

θ1 > θaf

ε

AM

MA

AM

σ

σmf

σms

θ2 > θaf

σas

σ

ε

σaf

Fig. 2 : Stress-strain curves

As indicated in the figure an AM transformation starts at σms and is finished at σmf . Atunloading, the MA transformation starts for θ1 at σas and is finished at σaf . The strainrange is typically 5-8%. As can be seen the stiffness varies considerably : typically 20 GPa(m = 0), 5 GPa (m = 1) and 1 GPa (0 < m < 1). The hysteresis loop is indicative for thehigh energy dissipation in the material. The phenomenon is denoted as superplasticity due tothe large reversible deformation.

For the lower temperature θ2, the MA transformation does not take place at unloading,and the material stays completely austenitic. A permanent deformation remains. However,this can be eliminated by raising the temperature of the material. To understand this, thefigure below shows a three-dimensional plot of the σ − ε − θ behaviour of the SMA, wherevarious parts of the tensile curves are modelled with straight lines.

1

43

2

σ

θ

ε

Fig. 3 : σ − ε − θ behaviour of SMA

The two former tensile curves can be recognised. The next indicated trajectory reveals theactuator property of the SMA :

1 → 2 loading m = 0 → m = 1 θ1 = θ2 > θaf

2 → 3 unloading m = 1 θ3 = θ2 = θ1

3 → 4 heating m = 1 → m = 0 θ3 → θ4 > θ3

4 → 1 cooling m = 0 θ4 → θ1

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The property that a permanent deformation can be eliminated is denoted as pseudoplasticity.When deformation is constrained, material stresses may become very high and care must

be taken to prevent permanent plastic deformation or fracture.The characteristic thermomechanical properties of SMAs are employed to fabricate prod-

ucts with shape memory. They are produced by plastic deformation (m = 0 → m = 1)and subsequently heated at constrained deformation (m = 1 → m = 0). After cooling andrenewed plastic deformation the initial shape can be retrieved by simply heating the product.

Until now SMAs are mainly used as on-off actuators (m = 0 ↔ m = 1). The associatedhigh strains (5 - 8 %) have led to fixation applications in technology [29, 14] and medicine[16]. Combining SMA components with eg. springs, has led to their use in switches for valves,windows, fire alarms, etc.. Due to their high internal energy dissipation SMAs are also usedin safety belts and armour.

The hysteresis loop in the stress-strain curve can also be traversed intermediately (AM→ MA at 0 < m < 1) as is indicated in Fig. 2. This allows application as temperaturecontrolled force/displacement actuator. For such applications a control system is needed tomeasure deformation or stress and control the heating of the material. In the PhD researchof Dr. Van der Wijst such applications of SMAs are developed and realised where NiTi wiresare used as actuators to control the motion of robot arms and the shape of composite beams.

Two control procedures were used : feedback and feedforward. The (elementary) feed-back design is based on the difference between the measured system response and the desiredresponse. Using PID controllers this difference can in principle be minimized using the tem-perature controlled SMA wire-actuators.

In the feedforward or open loop approach the behaviour of the system is simulated andpredicted and the actuator action is calculated. The simulation can be done off-line (notreal time) or on-line (real time). An accurate model of the complete system must be madeconsisting of the mathematical equations of motion, the thermal heat transfer equations andmaterial models, among which that of the SMA, describing its complex thermomechanicalbehaviour. Due to model errors, feedforward control alone has proven to be too inaccurate.Combination of feedforward and PID feedback has led to the best results sofar.

The promising results of the above-mentioned research have inspired us to formulate twonew research projects, described in the following two sections.

3.1.2 Project 1 : SMA actuators in robots

Manipulation robots are used very much and are generally controlled by electric motors. Forsome applications these motors pose a problem regarding their dimension and weight. SMAwire actuators do not have this disadvantage : they are very light-weight and small. In factthey can be easily integrated in other components of the device [45, 46]. Controlling the SMAactuators is readily accomplished with electric current, which gives rise to the desired heating.Coordinated action of a set of actuators allows the so-called end-effector (a selected point) ofthe robot to follow a predefined trajectory.

In the PhD research of Van der Wijst a miniaturised manipulation robot has been build[6, 12]. It consists of a stationary segment to which an assembly of two rotational segments areconnected (see Fig. 4). The maximum rotation angle of each segment is 150o. The rotationis realised by SMA wires in the stationary and the first rotational segment.

8

E

77

77

95FSMA1 FSMA2

Fig. 4 : Two-segment robot with SMA actuators (measures in mm)

The rotation angles were prescribed as a function of time such that the end of the secondrotational segment – the end-effector E – followed a desired trajectory in a two-dimensionalplane. For this two-segment robot the position of the end-effector is determined unambigu-ously by the two segment angles.

The SMA feedback current (for heating) can be determined by a PID controller based onthe difference between the actual and the desired segment angle. Measurement of the anglesis done with potentiometers in the rotation points. The best results – smallest deviationbetween realised and desired trajectory – have been achieved by using a feedforward controllerin combination with PID feedback.

In view of the above-mentioned promising results it is believed that further research willlead to more and better results which will be interesting both from a scientific point of viewand for future applications.

Attention should be focused onto the following aspects :

1. It is expected that the control procedures which were used, can be improved consid-erably. PID controllers can be optimized as is the case for the model-based controlstrategies. A wide variety of suitable control algorithms have been designed for stan-dard rigid robots : computed torque controllers, passivity based controllers and adaptiveversions of these to compensate for uncertainties in system parameters. An overview ofa number of these controllers can be found in [27] and [26] and in the references giventhere.

It will be a challenge to control the intrinsic hysteresis loop, which is characteristicfor SMAs, based on a model-based procedure. Results of these investigations are ofimportance for the control of all systems with hysteresis.

As is also described in [26], model-based controllers use an estimator/observer forthe angular velocity. It remains an essential question how a suitable observer (andcontroller/observer combination) can be designed for an SMA controlled robot.

2. Measurement of the segment angles must be improved. Friction in the potentiometers,which have been used until now, lead to inaccuracies in the feedback control procedure.

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It is also necessary to investigate whether there exist accurate and feasable methodsto measure the temperature of the SMA actuators.

3. An obvious strategy for the control of an SMA actuated robot is to avoid as much aspossible the complete martensitic state of the SMA wires. In this way the intrinsictime delay from the hysteresis loop can be avoided and the control may be expected tobe simplified. A possible way to achieve this, is by making the two-dimensional robotredundant with a third segment in the two-dimensional plane. Making the end-effectorto follow a desired trajectory is then redundant, as the necessary torques applied to thethree segments are no longer uniquely determined. This provides the possibility to stayaway from the complete martensitic states of the SMA wires.

3.1.3 Project 2 : Materials with integrated SMA actuators

Fibre reinforced (polymer) materials are widely used. Such composites can be given desiredanisotropic properties (stiffness, strength) by specific selection of fibre material, fibre volumeand fibre direction.

SMA wires can be placed at both surfaces of composite plates. Heating of these integratedSMA actuators results in shrinkage of the wires and bending of the plate [2, 3]. Such anapplication of SMAs is denoted as shape control.

Van der Wijst has investigated some preliminary steps towards the possibilities of shapecontrol [13, 12]. Beams have been made of Polypropylene (PP), acting as a thermoplasticmatrix, in which SMA wires were placed at both beam surfaces (see Fig. 5). The wires wereprestrained (3.5%) to make them completely martensitic. Heating the wires at one of thebeam surfaces makes them shrink, leading to bending of the beam. Bending in the otherdirection can be realised by heating the SMA wires at the opposite beam surface.

Four of such beams are combined to a square frame (see Fig. 5). The goal has been torealise a desired curvature of the beams as a function of time, by heating selected SMA wireswith electric current. The required current has been determined with a control system.

For feedback control the realised curvatures have to be measured. This has been doneusing an optical system and image analysis software [7]. Markers have been placed on eachbeam and their three-dimensional position is measured. Therefor, two images of the markershad to be recorded with a CCD camera and a mirror system. To get good quality images ofthe markers, the SMA-beam-frame, the mirror and the camera were mounted on a large (± 3m long) stable structure. The calculated three-dimensional position of the markers resultedin the curvature of the beams. The difference between the realised (= measured) and desiredbeam curvatures has been used by a PID controller to calculate the electric current for theSMA wires.

10

1.6

115

7

0.10.7

CCD camera

SMAbeamstructure

marker

mirror

Fig. 5 : SMA beam structure and optical deformation measurement (measures in mm)

Application of feedforward (open loop) control requires the analysis of an accurate model ofthe complete system. For the 4-beam system a finite element model has been made, whichcould not be analysed in real time (on-line). Feedforward control can then only be appliedwhen the desired system behaviour is known in advance.

It has been shown that the best results could be realised by using a combination of feedbackand feedforward control.

In this proposed follow-up research project attention must be focused onto the followingtopics :

1. To improve the accuracy of the feedforward (open loop) control the system model mustbe improved.

2. Special attention must be given to the heat exchange between SMA wires and thethermoplastic matrix and between the matrix and the environment. Relevant materialparameters (film coefficients) must be determined experimentally. In this context itwould be worthwhile to investigate the use of other (than PP) matrix materials. Agood candidate seems to be a PSF/epoxy mixture, which shows reaction-induced phaseseparation at interfaces with solid substructures, such as fibres.

3. It is necessary to investigate whether the system model can be simplified without com-promising its accuracy. A less complicated model may be analysed in real time, whichcould be important for many applications.

4. Measuring the shape of a composite (plate) needs serious attention. The used opticaltechnique is obviously not feasable for practical applications as the complete measure-ment system was large and bulky. It is necessary to measure the local deformation ofthe system with sensors which are integrated in the material.

Literature reveals that this is possible with glass fibre technology. It is possible tomeasure strain [17], but also temperature [80] as a function of the position along thefibre, a technique known as distributed sensing. Local damage detection of the basematerial (matrix) is also feasable, which is also of eminent importance for not-SMAcomposites and can lead to a more efficient use of material.

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5. Applying SMA wires as actuators in composites is only possible when the adhesionbetween wires and matrix is good. This has proven to be no problem for short-termapplications. Survey into this is needed for long-term applications [79]. Optical fibres –for measurement – must also adhere well to the matrix. Coatings on these fibres mustnot hamper this adhesion and may not be damaged during production.

The influence of SMA wires and optical fibres on the mechanical behaviour of thecomposite must be investigated [40, 43, 51, 52, 62]. It is a question whether the peri-odic temperature increase of the SMA wires will influence the properties of the matrixmaterial. The thickness of the optical fibres is about 250 µm. It must be investigatedwhether stress concentrations introduced by their presence, will initiate fatigue damage.Finally, precautions may have to be taken to circumvent measurement errors, causedby the internal composite geometry.

6. Dynamic properties – eigen frequencies, eigen modes – of thin-walled structures arehighly influenced by their stiffness. This is determined by the intrinsic material prop-erties and the geometry of structural components. Using fibre reinforced compositesprovides the possibility to choose fibre volume and fibre orientation to realise desiredlocal stiffness in specified directons.

Integrated SMA wires may introduce compressive stresses in the matrix material dueto the constrained shrinkage. These stresses change the stiffness of the composite mate-rial. In this way local dynamic properties may be changed during service [21, 22, 23, 32].Changing the dynamic properties is mostly needed to shift eigen frequencies and/ormodes to avoid excitation frequencies. Such applications of SMA wires are denoted asvibration control. For efficient control of the SMA action the dynamic properties mayhave to be measured locally.

Increasing temperature of the SMA wires provokes compressive prestraining of thecomposite material and thus lowers the eigen frequencies. This downward shift can bevery fast as heating is almost instantaneous. Cooling of the SMA wires on the contraryis very slow. Fast actuation is therefore not possible with SMA wires. However, for theapplications described in section 4 this small bandwidth poses no serious disadvantage.

3.2 Results and scientific relevance

The proposed research will lead to :1. an increase of knowledge about SMAs and related materials;2. development of numerical material models for SMAs and related materials;3. development of control procedures for SMA actuator driven systems;4. development of new materials eg. SMA-fibre reinforced composites with embedded glass-

fibre strain sensors;5. design of SMA-actuator driven systems for mechanical and biomedical application.

In the first project an important part of the research effort will be directed towards thedevelopment of strategies for improved and optimal control. The redundance resulting fromthe application of many actuators is a general feature of Multi-Input-Single-Output systemsand is still an open problem, a topic of worldwide research.

It is a challenge to control the intrinsic hysteresis loop, resulting from the SMA behaviour,with a model-based algorithm. This research is – to our knowledge – new and generallyimportant for controlling systems with hysteresis.

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The second project is interesting with regard to the control of distributed systems. Thecontrol design in this case is extremely challenging given the forementioned hysteresis in SMAwires, in combination with the boundary control of the plate.

An essential part of the second project is the modelling of an SMA composite and its nu-merical simulation in a feed forward (open loop) control algorithm. This is a so-called inverseproblem : given the desired output (= dynamic characteristics or shape) the input (= temper-ature increase of the SMA fibres) has to be determined [44]. The coupled thermomechanicalbehaviour complicates such simulations. Much attention must be given to the reduction (→simplification) of the numerical model allowing fast, maybe on-line analysis.

Feedback control requires the local measurement of dynamic characteristics and/or shape.Glass fibres, with Bragg gratings can be embedded in the composite material. Light from abroad-banded source (LED) is transmitted through the fibre and analysed at the fibre-endusing a bandpass filter. The deformation of the Bragg gratings can be measured resulting inthe local strain of the composite material. Several aspects of the above techniques have to beinvestigated and developed, among which efficient data aquisition and processing.

3.3 Personnel and equipment

Each of the two research projects will be carried out by a PhD student. These two re-searchers will be contracted for a four-year period. Each project will be evaluated after twoyears and only continued when it shows good progress.

Subsection 3.5 describes the existing infrastructure of the groups Dynamics and ControlTechnology and Materials Technology at Eindhoven University of Technology. Although thecurrent facilities are good, some additional equipment is needed, some of which is specificfor the proposed research. Also some existing facilities will have to be extended to preventoverload and queueing. The additional hard- and software are listed below. Costs can befound in section 6.4 on ”Investments”.

• Silicon Graphics Workstation (server) + software: compilers (C,C++,F77,F90) / Mat-lab

• optical fibre measurement system : LED transmitter plus beam splitter + optical fibreswith Bragg gratings + spectrum analyser (bandpass filter)

3.4 Schedules and tasks

The two research projects have to be carried out within a four-year period. For each projecta number of tasks are formulated. Task description and duration (in month) are listed below.A graphical time schedule is also provided.

Although ”transfer of knowledge” is included as an individual task, it is obvious that duringthe course of the research there will be (in)formal contacts with potential users. Results willalso be published in journals as soon as possible.

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Project 1 Totaltask 1 Literature search. 6 6task 2 Revitalisation of (existing) experimental setup : two-

segment robot with SMA actuators.Investigation of improved control algorithms.

6 12

task 3 Realisation of new experimental setup : three-segment robotwith SMA actuators.

12 24

decision whether programme is to be continuedtask 4 Implementation of control algorithms for redundant system. 6 30task 5 Transfer of knowledge and expertise to one or more user

applications.12 42

task 6 Writing the PhD thesis. 6 48

Project 2 Totaltask 1 Literature search. 6 6task 2 Manufacturing of SMA fibre embedded composite material

with integrated glass fibres for strain measurement. Buyingand deploying glass fibre measurement system.

6 12

task 3 Realisation of experimental setup : SMA & glass fibre em-bedded composite plate for shape control.

12 24

decision whether programme is to be continuedtask 4 Implementation of model-based feedforward control algo-

rithm (inverse problem) for distributed system.6 30

task 5 Transfer of knowledge and expertise to one or more userapplications.

12 42

task 6 Writing the PhD thesis. 6 48

p1.t2p1.t1

p1.t3p1.t4p1.t5p1.t6

p2.t1p2.t2p2.t3p2.t4p2.t5p2.t6

6 mnd 6 mnd 6 mnd 6 mnd 6 mnd 6 mnd 6 mnd 6 mnd

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The two PhDs will work in close cooperation and discuss their work on a regular basis withthe supervisors and the users-committee.

3.5 Current infrastructure

The research will be carried out at the Eindhoven University of Technology in the groupsDynamics and Control Technology and Materials Technology. The supervising and supportingpersons are staff members within these groups and are listed in section 2.1.

Laboratory facilities, relevant for the proposed research projects, are available amongwhich : tensile machines with various measurement ranges, composite production facilities,contactless deformation measuring systems, damage detection equipment and microscopy (op-tical, AFM, ESEM). A local computer network includes Silicon Graphics computers, work-stations and servers, PC’s and a 64-node Beowulf cluster.

As will be described in section 3.6, there are contacts with other research groups. Especiallynoteworthy is the cooperation with the group at the University of London. It is without doubtthat the researchers can use the London facilities when needed.

3.6 Relation with other research

As will be clear from the project description, the proposed research has a highly multidisci-plinary character. Concepts and methods from system control, material science and mechan-ical modelling have to be combined. In each project numerical and experimental techniqueshave to be employed. Because material and system modelling is an essential part of all re-search within the groups Dynamics and Control Technology and Materials Technology, theproposed projects will fit nicely into the complete picture. It is also important to mentionthat both groups cooperate within research schools and institutes e.g. EM, DISC, NIMR andDPI.

Cooperation with third parties

In The Netherlands and neighbouring countries several groups are carying out or startingresearch related to the projects described in this proposal. The Eindhoven groups havecontacts with groups listed below. Close cooperation and exchange of knowledge and evenpersonnel may be expected within the framework of the proposed research.

• Queen Mary and Westfield College (QMWC) of the University of London.

Dr.ir. T. Peijs, Reader at QMWC, is starting research projects aiming towards the devel-opment of SMA composites. The characterisation of their thermomechanical propertiesand long-term behaviour is an important topic. Dr. Peijs is also working on a parttimebasis within the Dutch Polymer Institute (DPI) at the Eindhoven University, so closecooperation is garanteed. Exchange of MSc and PhD students for shorter periods willbe part of the cooperation between TUE and QMWC. It is also worth mentioning thatProf. M.P. Cartwell of QMWC is carying out a project ”Control of vibration by SmartSMA-embedded composite structures”, which is funded by EPSRC.

• Philips Centre for Fabrication Technology (CFT).

There are rather close contacts between the Dynamics and Control Technology groupand Philips CFT concerning the research on the control of robotic systems.

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Activities in the world

Widespread application of adaptive materials and structures is not yet realised. However,interest from both companies and scientific institutes is growing fast. In recent years two newjournals have been launched [81, 82] for publication about such topics.

Research groups investigating actuators and sensors for adaptive materials and structuresare listed below together with references to publications of these groups.

• Smart Materials and Structures Laboratory; Mechanical Engineering DepartmentVirginia Polytechnic Institute and State UniversityBlacksburg, Virginia 24061, U.S.A. [56, 57, 69, 70]

• Department of Mechanical Engineering; Massachusetts Institute of TechnologyCambridge, MA 02139, USA [19]

• Mechanical Engineering Department; Northwestern University2145 Sheridan Road, Evanston, Illinois 60208 [34, 35]

• Mechanical Engineering Department; The Catholic University of AmericaWashington, DC 20064, U.S.A. [21, 22, 23]

• Physikalische Ingenieurwissenschaft; TU Berlin [20, 28, 61]

• Laboratoire de Technologie des Composites et Polymeres;Ecole Polytechnique Federale de Lausanne1015 Lausanne, Switzerland [31, 32]

• Dept. of Metall. and Mat. Eng.; KU LeuvenDe Croylaan 2, B-3030 Heverlee, Leuven, Belgium [59, 64, 66, 67, 48, 72, 65]

• Department of Aerospace Engineering; Tokyo Metropolitan Institute of TechnologyAsahigaoka 6-6, J-191 Hino/Tokyo, Japan [76, 77]

• Optoelectronic Research Centre, Southampton University

• DLR, Institut fur Struktur Mechanik;Lilienthalplatz 7, D-38108 Braunschweig

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4 Utilisation

Discussions with companies and research institutes have revealed a great interest for theproposed research. Possible applications of the results in various companies are described insubsection 4.1. Names of persons, willing to be part of the proposed user committee, aregiven in subsection 4.2.

Results of the research are almost certainly also important for other applications, notdescribed here. Especially the knowledge concerning the use of glass fibres as sensors seemsto be useful for a broad range of applications.

4.1 Practical applications

4.1.1 Robotics

Many companies use robots in their production processes. With ongoing miniaturisation,positioning accuracy is important especially in the manufacturing of electronic devices [24,54, 58].

The Philips Centre for Fabrication Technology (CFT) is interested in the results of theproposed research projects regarding the application to professional (nanometer precision)positioning systems. Another application is the reduction of vibration problems in lasertracking systems of optical storage devices in consumer electronics. Especially the knowledgeabout control strategies is essential for the above applications.

4.1.2 Space technology

The astronautical industry is interested in trajectory control, shape control and vibrationcontrol. Space structures are subjected to large temperature changes. Due to their light-weight construction they are apt to be influenced by dynamic loads. Positioning and shapeaccuracy must however be very high.

At the International Astronautical Conference, which is held each year, one session is de-voted to ”Smart Materials and Adaptable Structures” [8], while the use of integrated actuatorsin space structures is an increasingly important issue.

More than 100 Dutch companies are involved in space programmes. The governmentspends yearly 100 million C= on astronautical research, of which 75% is given to ESA, theEuropean Space Association. More than 10 million C= is spend on research in Dutch companiesand institutes. The supervision of this research is with the NIVR1. The TUE has worked incooperation with some companies eg. Bradford Engineering.

4.1.3 Medical Technology

NiTi is a biocompatible material [37, 74]. This alloy has been successfully applied in cathetersand stents [42, 47, 41, 16]. A catheter tip made from SMA can be guided to insure easyinsertion. SMA stents are used to widen veins and ureters. The thin SMA stent can beguided to a certain position after which increasing temperature unfolds the stent wideningthe conduct permanently.

1NIVR = Nederlands Instituut voor Vliegtuigontwikkeling en Ruimtevaart (Netherlands Agency forAerospace Programmes)

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SMAs are used as fixation devices in orthopedics. In orthodontology they are used moreand more as a denture correction expedient, because the stiffness hardly changes over a largestrain range.

Finally the active prostheses have to be mentioned here [16, 65], where SMA wires act assmall, light-weight actuators and replace the normaly used bulky and heavy electric motors.

Engineering company Memory Metal Holland (Ir. P. Besselink) [29, 30] produces NiTi wiresof various diameter and composition. They also develop devices for technical and medicaluse.

4.1.4 Aircraft and energy industry

Possible application of shape and vibration control of composites is highly important for thissector of industry. We can think of the adaptation of shape and/or dynamic characteristicsof aircraft wings and wind mill rotor blades to the flight- or wind speed allowing efficientoperation of wing or rotor over a large (wind) speed range. Moreover lifetime and (foraircraft) comfort will be increased. The research group at QMWC (see §3.6) has facilitiesto fabricate prototypes of SMA composites and test their aerodynamic properties in a windtunnel.

The NLR2 (Dr. L. Velterop) is interested in application of SMA composites in aircraftparts (wings, fuselage).

4.1.5 System Dynamics

External dynamic loading may give rise to undesired vibrations. Especially thin-walled struc-tures, eg. aircraft fuselages, housing for motors, pumps, transformers and parts of vehicles[73], may be seriously affected. Proper design must preclude the coincidence of the structuraleigen frequencies and the frequencies of the external loads. Using integrated SMA wires, thestiffness of composite materials can be changed (locally) to prevent undesired vibrations.

These applications could be important for the design of MRI3 scanners. The fast switchingof strong magnetic fields induces vibrations in the scanner casing, which may be reduced withembedded SMA fibres. Because the NiTi alloy is not magnetic, these will not influence thegenerated MR fields.

Philips Medical Systems and Philips Centre for Fabrication Tehnology (Dr.ir. B. Roozen)have shown interest in this application for vibration control. It would also be worthwile tobuild SMA actuated supports for the scanner tube to prevent the transduction of vibrationsto the environment.

4.2 Users

It has become clear from the Utilisation section that members of the user group may befound in the aircraft and space industry, the energy sector, medical system businesses andcompanies working in the field of mass production (machinery).

Meetings and discussions have learned that the following persons and the companies orinstitutions which they represent, agree that the proposed research is important and thatthey are interested in the results. They have been found prepared to be part of the usercommittee, supervising the progress of the research projects.

2NLR = National Aerospace Laboratory (Nationaal Lucht- en Ruimtevaartlaboratorium)3MRI = Magnetic Resonance Imaging

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Dr. L. Velterop NLR ; Structures Technology DepartmentPostbus 153, 8300 AD Emmeloordtel: 0527-248735

Ir. P. Besselink Memory Metal HollandGronausestraat 1220, 7534 AT Enschedetel.: 053-4614947 ; fax.: 053-4611730

Dr.ir. B. Roozen Philips Centre for Fabrication TechnologyAcoustics and Control ; Mechatronics ResearchP.O.Box 218, 5600 MD Eindhoventel.: 040-2739213 ; fax.: 040-2733201

Ir. P. Limpens Philips Medical Systems Nederland B.V.P.O. Box 10.000, 5680 DA Best, The Netherlandstel. 040-2763220; fax 040-2763771

Prof.dr.mr.dr B. de Mol AMC ; Hfd. Afd. Cardio-thoracale ChirurgiePostbus 22660, 1100 DD Amsterdamtel.: 020-5666088

4.3 Implementation

The implementation of both projects will at first be in the Mechanical Engineering laboratoryat the Eindhoven University of Technology. Of course, close contact with the users-committeemay give useful directions in the development of the robot and composite plate. On theother hand the main results of the two applications should lie in a successful design of afully actuated three-degrees-of-freedom robot and a deformable plate. Specific industrialapplications likely require further specializations. The projects should provide insight in thefeasibility of the use of SMAs in industrial applications. To the best of our knowledge, noother research groups are studying applications of SMAs in the way we are proposing.

4.4 Past performance

As mentioned before, the proposed research can be seen as a follow-up of the PhD research ofDr.ir. Van der Wijst. This indicates that within the current research group there is alreadya lot of experience with SMA materials and their use as actuators.

In the (recent) past the Dynamics and Control Technology and Materials Technologygroups have been involved in many research projects. Research programmes, publicationsand theses of both groups can be found on the websites http://www.wfw.wtb.tue.nl/dyna/and http://www.mate.tue.nl/ respectively.

5 Knowledge management

5.1 Contracts

There are no contracts with relation to the proposed research.

5.2 Patents

As far as we are aware of no patents exist that prohibit the here proposed applications.

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6 Budget

The research of Van der Wijst was financed by Eindhoven University (eerste geldstroom),because of its explorative character. The follow-up research is more focused on extension ofthe method and its application to some specific areas of technology and medicine. Universityfunding is not feasible therefore. Funding from companies (derde geldstroom) is also not anoption, as the possible applications will demand a lot of basic research and development. Thisis why we expect the funding to be typically ”tweede geldstroom”.

The research will be supported heavily by the Eindhoven University of Technology. Alsocooperation with other groups will be of much help. All this support will comprise personnel(§3.3) and infrastructure (§3.5).

6.1 Personnel

The following table lists the personnel, which has to be contracted to carry out the proposedresearch.

PhD student project 1 4 year fulltime

PhD student project 2 4 year fulltime

Table 1 : Research personnel

6.2 Materials

It will be necessary that the researchers visit collegues at home and abroad for personal(bilateral) discussions and at conferences and symposia. The rather low costs of day-trips inThe Netherlands (and in neighbouring countries) are listed in the table below. The higherexpenses of travel abroad are listed in §6.3.

The proposed investigations will require specific equipment and tools, which cannot becharacterised as ”Investments” (§6.4). Computer hardware is generally written off during afour-year period. Specific laboratory facilities and tools will have to be purchased or made inhouse. Material for experiments will have to be ordered from manufacturers.

The table below lists the expected costs, excluded VAT. The workshop costs are based onexperiences from other research projects.

2 × ”extended” PC KC= 2.5 /proj KC= 5

Work shop costs KC= 25 /proj KC= 50

Materials (incl. travel at home) KC= 15 /proj KC= 30

Table 2 : Tools and materials

6.3 Travel abroad

It is to be expected that the two PhD’s will visit a research group, collegues and a conferenceabroad once a year. This will cost approximately KC= 20 in total. The following table lists anumber of conferences in this field of research :

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SPIE Annual Symposium on Smart Materials

Int. Conf. on Composite Materials (ICCM)

IEEE Conference on Control Applications

Table 3 : International Conferences

6.4 Investments

The research projects can be carried out within the infrastructure (computers, computernetworks, laboratories) of the groups Dynamics and Control Technology and Materials Tech-nology. Although the current facilities are good (see §3.5), some additional investments areneeded for the following specific equipment (costs are indicative and excl. VAT) :

Silicon Graphics Workstation KC= 20

Software: compilers (C,C++,F77,F90), Matlab KC= 5

Optical fibre measurement system KC= 30

specification :

LED transmitter plus beam splitter KC= 5

optical fibres with Bragg gratings KC= 20

spectrum analyser (bandpass filter) KC= 5

Table 4 : Investments

6.5 User contributions

Some users have already indicated that they will support the research not only with theirexperience and knowledge but also by providing facilities and materials. Especially the appli-cation in MRI scanners (and other medical equipment) will be facilitated by Philips concerningpossible experimental setups.

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6.6 Budget summary

The table below shows a summary of the total budget for the proposed research projects. Inthis table we have indicated which part of the costs are to be expected at the start of theprojects – initial costs (I) – and which would be needed later – continuation costs (C) –.

Personnel I C

PhD project 1 4 fte

PhD project 2 4 fte

Materials

2 × ”extended” PC 5 5

Work shop costs 50 20 30

Materials (incl. travel at home) 30 15 15

Total Materials 85

Travel abroad

Conferences 20 10 10

Total Travel abroad 20

Investments

Silicon Graphics Workstation 20 20

Software 5 5

Optical fibre measurement system 30 20 10

Total Investments 55

Total 160 95 65

Table 5 : Budget summary (in KC= excl. VAT)

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7 References

7.1 Publications of the research group related to SMA actuators

[1] Banens, J.. Documentation on TCE moduls. Technical report WFW 94.050, EindhovenUniversity of Technology, 1994.

[2] Giurgiutiu, V.; Rogers, C.A.; Zuidervaart, J. Design and preliminary tests of an SMAactive composite tab. Proc. of the SPIE’s 4th annual symposium on Smart Materials,paper 3041-17, 1997.

[3] Giurgiutiu, V.; Zuidervaart, J.; Rogers, C.A.. Incrementally adjustable rotor-blade tracking tab using SMA composites. Proceedings of the 38th Proc. of 31stAIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conf.,Paper 97-1387, 1997.

[4] Heuvel, P.W.J. van den; Peijs, T.; Young, R.J. Analysis of stress concentrations inmulti-fibre microcomposites by means of Raman spectroscopy. J. Mater. Sci. Lett., 15,pp 1908-1911, 1996.

[5] Meurs, P.F.M.; Schreurs, P.J.G.; Peijs, T.; Meijer, H.E.H. Characterization of inter-phase conditions in composite materials. Composites, 27A(9), pp 781-786, 1996.

[6] Moens, M.T.R.. A Shape Memory Alloy actuated Manipulator. Master’s thesis MT97.003, Eindhoven University of Technology, The Netherlands, 1997.

[7] Peters, G.. Tools for the measurement of stress and strain fields in soft tissue. PhD.Thesis, Eindhoven University of Technology, The Netherlands, 1987.

[8] Schreurs, P.; Wijst, van der M.; Zuidervaart, J. SMA actuators for shape control ofstructures and materials. Paper presented at the 48th International Astronautical Con-ference, Turijn, october 1997.

[9] Wijst, M.W.M. van der. The numerical modelleing of a smart structure with ShapeMemory Alloys. Technical report WFW 93.080, Eindhoven University of Technology,The Netherlands, 1993.

[10] Wijst, M.W.M. van der; Schreurs, P.; Veldpaus, F.E.. Application of computed phasetransformation power to control shape memory alloy actuators. Smart Materials andStructures, Vol. 6, pp. 190-198, 1997.

[11] Wijst, M.W.M. van der; Zuidervaart, J.; Peijs, T.; Schreurs, P.J.G.. Active shape con-trol of Shape Memory Alloy composite structures. Proc. 11th Int.Conf. on CompositesMaterials (ICCM/11), Vol. IV, ed. M.L. Scott, Gold Coast, Queensland, Australia, pp.561-570, 1997.

[12] Wijst, M.W.M. van der. Shape Control of Structures and Materials with Shape MemoryAlloys. PhD. Thesis, Eindhoven University of Technology, The Netherlands, 1998.

[13] Zuidervaart, J. Active shape control of composites using Shape Memory Alloy embed-ded actuators. Master’s thesis MT 97.015, Eindhoven University of Technology, TheNetherlands, 1997.

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