G M'boungui

B Lemaire-Semail

F Giraud

Piezoelectric actuator for a force-feedback application: preliminary evaluation

Keywords: piezoelectric actuator, force feedback, electro-active lubrication, psychophysical evaluation

As a solution to the lack of compactness and simplicity often encountered in haptic interfaces, we propose a device based on friction coefficient control principle. This device includes polarised piezoceramics well adjusted and glued to a 64x38x3 mm copper-beryllium plate supported by four legs. Then, properly energised around a resonant frequency, with legs at antinodes, a stationary wave is created in the plate. Variable friction forces between the legs and the plane substrate are created by the control of the wave amplitude, according to electro-active lubrication. So the user obtains force feedback by holding the plate, and moving it on a plane substrate, as he could do with a mouse interface. Preliminary psychophysical evaluation trends to assess the validity of the device as a force feedback interface.

INTRODUCTION

Many of the tasks in our daily life may be performed with greater efficiency and speed with haptic (tactile and force feedback rendering) assistance. Consequently, the use of force feedback to enhance interactive graphics has often been discussed since it's an area of growing interest from the research community and various devices of this field have been developed for many years. Nevertheless force feedback interfaces available are generally complex using a broad range of technologies, especially DC motors. So, as a motivation, in our research we aimed to design a compact and simple force feedback device.

This work presents design and implementation of our proposal which is a passive 2Dof device able to provide different resistant feeling sensations when a user moves it. To realise such a system, we chose to use active lubrication effect [START_REF] Garbuio | Piezoelectric Thrust Bearing For Severe Environments[END_REF] induced by piezoelectric actuator. We also introduce preliminary evaluation of the system in use toward its qualification for force feedback rendering.

The actuator will first be described: it's based on a vibrating plate fitted with four legs. Then, the principle of active lubrication is reminded in that specific case which leads to a global control of adjustable friction coefficient between the plate and its plan support. This effect is underlined through simulation and experimental results about reactive force obtained with the device. At last, a psychophysical test is described and its results presented. On the opposite side (fig. 1), four built in feet support the plate despite of hyperstaticity it implies. Previously some studies closed to this structure [START_REF] Pigache | Modelling and identification of a planar standing wave ultrasonic motor. Identification of a planar actuator[END_REF][3] were carried out. As a difference our plate will only move normally. Indeed, as we will see later, this particular structure is not V V supposed to move by itself along the tangential direction. It is a passive device.

DEVICE

Operating principle

As explained above, feet are positioned exactly at antinodes of the standing wave induced in the plate and they are in contact with a plan steel substrate for example. Therefore, when no voltage is applied to ceramics and if users move the actuator, they can feel the classical Coulomb friction force acting at the interface feet/substrate. When voltage is applied to ceramics electrode, however, standing wave (fig. 3) is generated and we can decrease friction between feet and substrate: this happens according to amplitude vibration control. As a matter of fact, from given amplitude an intermittent contact may occur at the interface. Consequently, we create transitions between stick or slip conditions at the contact level and the global friction force changes.

Stick/slip generation condition

From [START_REF] Desai | Cyclinc Testing and Modelling of Interface[END_REF] micro-slip is defined as "Small relative tangential displacement in a contacting area at an interface, when the remainder of the interface in the contacting area is not relatively displaced tangentially" which means the existence of a region where surfaces are said to adhere or to stick. In our case user's action leads two surfaces in contact to slide against each other: an elastic (micro-slip) and plastic deformation may occur before macro-slip takes place. Therefore our principle to generate stick-slip conditions will be based on the consideration that for small displacements, foot/substrate contact presents stick and partial slip zones under a normal load Rn. Furthermore, it is shown on figure 2 that the plate deformation scale is in micrometer, so we can use an approach based on Coulomb-Orowan model (fig. 4) to interpret friction coefficient variations.

µ C µ 0 0 δ critique δ (µm)
Figure 4 depicts friction coefficient as a function of tangential displacement and the plot is divided approximately in two parts. The first part which relies to tangential stiffness of the contact is linear and describes the partial slip. Then, from a critical displacement (δcritic) corresponding to total slip, µ is constant.

We define δ critic from the following relationship after prior identification of tangential stiffness of the foot kt:

t n n crit k R R C . . . 0 0 µ µ δ = = (1)
With C (m/N), the compliance and µ 0 , the maximum friction coefficient at the interface.

From now, we are able to obtain µ(t) during foot/substrate contact time limited by tc and td which are respectively contact and separation instant during one period of our vibrating device.

So we can write

: if ] [ d c t t t , ∈ and δ < δ c then C t) ( δ µ = , if ] [ d c t t t , ∈ and δ > δ c then 0 µ µ = , (2)
The displacement δ(t) is computed from the tangential speed integration.

Variation of normal and tangential forces

This actuator (at last one part) can be modelled as a mass-spring system as shown in figure 5. On the figure 5, Mext represents the load applied on the top of the device to assume pre-stress. This load lies on an elastic element whose stiffness km is low so that the force Fn due to Mext is considered constant. The mass of the vibrating plate is noted m and the number of feet, n. The foot mass is too low to be considered and its normal stiffness is kn. Finally the displacement w A (t) is imposed by plate vibrations.

Applying general laws of dynamic to the system, we have:

) ( .. .. t R g n m n F w n m z n m n n A A + - - = (3) Rn Rt Where, during contact, . )) ( ( ) ( G n A n n z d t z h k t R - - = (4) And during separation, 0 ) ( = t R n (5)
The knowledge of instantaneous reaction Rn(t) by solving numerically equation 3 allows us to deduce the tangential force Rt(t). For that aim we use Coulomb's law

n t R t R ) ( µ = .
It may be noted that µ is a function of time because we use the modelling described in figure 4, and δ is a function of time according to vibration period. Rt mean value is obtained by integration on a vibrating period.

EFFECTIVENESS OF FRICTION FORCE VARIATIONS

This section is concerned with outlining friction force characteristics obtained before a preliminary device evaluation in use, in order to precise the perception limitation and to know the range for which it is available for force feedback rendering. We first need of course to illustrate the effectiveness of friction force variation controlling the excitation of the device displaced by a user.

Simulations results: So, the previous modelling has been simulated using Matlab-Simulink software®. We practised some simulations and the plots below give an overview of friction force variations. Figure 6 shows the friction force for a fixed normal pre-load equal to 20 N and different tangential speeds. It is noticeable that from a given vibration amplitude value, friction decreases suddenly. This amplitude value is due to an intermittent contact between the foot and the substrate which occurs above this given amplitude. A glass substrate (µ0=.08) was used for these trials. We continue our investigation and plot the graph of figure 7 observing that tangential force rises, at exploration speed of 5 cm/s with pre-load addition and decreases when the vibratory amplitude increases. We can notice that faster the plate is displaced by a user, lower friction force reduction is.

Experimental results: To compare these theoretical results to experimental one the following set-up was realised to measure friction force value. The set up consists on a cable-driven pulley system used to pull the actuator by mean of DC motor ®Maxon at a defined controlled speed. Measuring current in the DC motor, we evaluate the developed torque and then the force pulling the plate. Also, varying actuator supply voltage amplitude is equivalent to change vibratory amplitude W around 40.7 kHz. An optical encoder is mounted on the rotating shaft to count motor speed and the set up is controlled by a dSPACE DS1104. Under these conditions, figure 9 and 10 finally show some results: in particular, we have a friction force reduction which can reach 61.41 % (from .71 N to .274 N for 3 N at 1 cm/s).

Presented results enable us to see that theoretical and experimental results are close together, which tends to validate our model. More over, it may be noted that friction force is a function of the vibration amplitude. So, the vibration amplitude has to be controlled. We can also remark that this variation depends on the tangential speed imposed by the user and there will be a limitation of the effect for high speeds.

PRELIMINARY DEVICE EVALUATION

Principle of pattern simulation

The evaluation method of a haptic device is often determined by the application the device is dedicated to. And these applications highly depend on the capabilities of the haptic device. For devices working on the principle of friction reduction, typical evaluations have been performed especially in the range of cutaneous feelings rendering. From the famous Watanabe's experience [START_REF] Watanabe | a method for controlling tactile sensation of surface roughness using ultrasonic vibration[END_REF], tactile interface designers in particular gave illusion of gratings exploration according to sliding and blocking effect alternance. For instance, inspired by this experience, M. Biet and L. Winfield [START_REF] Biet | Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays[END_REF][7] used friction variation of a surface to simulate various textures. Indeed it can be shown that under given conditions of frequency and vibratory amplitude there's an overpressure (squeeze effect) in the air gap between two plates, one of the plates vibrating. In the works mentioned above, this principle has been used replacing one plate by the finger, the other one assuming the function of tactile device. In accordance with Watanabe's experience, vibratory amplitude was correlated with friction reduction level between the fingertip and the plate. At last, moving his finger on the vibrating plate, the user feels a sliding sensation whilst without any vibration of the plate, a sticky sensation is perceived. Then, to simulate thin textures, the idea is to control the vibration amplitude as a function of the finger position. This temporal amplitude modulation induces sliding and blocking feeling alternatively, which may be perceived as a texture [START_REF] Biet | Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays[END_REF].

As our device is also working on the principle of friction reduction but is dedicated to render reaction force on the hand, we follow the same idea to create periodic shapes. Such a result is in accordance with V. Hayward and Robles-De-La-Torre [START_REF] Robles-De-La-Torre | Force can overcome object geometry in the perception of shape through active touch[END_REF] who identify shape characteristics through force cues.

First we tried a simple temporal modulation of the friction coefficient at the foot/substrate interface: as expected, the result was more a vibratory sensation rather than a texture feeling. Then we replaced the temporal modulation by a spatial one to feel a sensation close to texture perception. Like M. Biet and L. Winfield for tactile devices we chose to simulate space fixed patterns shown in figure 11, which means a relationship between exploration speed and texture pattern.

To create anything like notches above, the idea is to generate alternatively sliding and blocking sensations tuning the vibrating wave amplitude. For that, it's necessary to impose the wave amplitude reference as a function of the plate position moved by the user and measured by the optical encoder of the experimental set up. Therefore a spatial-temporal transformation allows the control of sliding region apparition times, following the kind of profiles highlighted in figure 11.

Plate Rt Optical

Spatio-temporal Amplitude encoder transformation modulation W calculation Space period reference Fig. 12: wave amplitude control structure to achieve pattern simulation a practical point of view, to achieve this control, we modulate the amplitude of the power supply voltage with a low frequency signal on the principle schematically represented fig.12. Thus the wave amplitude modulation is controlled according to the plate position. As a result, the modulation of the vibration amplitude creates in turn a modulation of the sliding effect.

Experiments

As there is no standard for meaningful hatpic devices assessment, their evaluation implies specific tasks. It also needs to be simple enough to be easily applied while taking all important attributes of haptic interaction into account [START_REF] Samur | Generic and systematic Evaluation of Haptic Interfaces Based on Testbeds[END_REF]. . We still simulate virtual gratings depicted fig. 11 generated by the device along a given distance of 87 mm, modifying spatial frequency (number of cycles) and vibration amplitude (sliding effect). The maximum number of cycles is equal to 28, that means a minimum spatial period equal to 3.1 mm. The idea is to count the spatial periods felt by the user. This procedure is quite similar to that used by West and Cutkosky [START_REF] West | Detection of real and virtual fine surface features with a haptic interface and stylus[END_REF] who asked users to count the number of 1-D sinusoidal cycles on a real and virtual surfaces, with almost the same numbers of spatial periods.

In the same time, as the device effectively provides a variable reacting force in movement, it was an opportunity to check the users ability to hold the plate, as he could do with a familiar mouse, to sense in the future the 1D boundaries or changes in form of an object displayed in a virtual environment.

But before we are going to impose vibration amplitude steps on the device. It is useful to check its wave amplitude response time. From fig. 13 we can see that the preloaded plate response time of the preloaded plate is about 1 ms. Considering the typical speed with which the plate is displaced by a user, in the context of exploration, the corresponding frequency limit will never be reached.

Task and stimuli

The task required participants to move the plate on the steel substrate along the fixed distance (87 mm) and to identify the number of cycles (space frequency on fig. 11) present. Two groups (respectively two and five) of graduate students were chosen to perform the experiment. Results obtained with the first group were examined before conducting additional tests with the second group. One of the subjects was female. The experimental set up was the one described fig. 8 but the user took the place of the motor to move in forward or backward directions the device. First of all, after presenting the "mobile" on "rails", subjects performed self directed displacement of the plate towards and backward to familiarise with the manipulation. Next, they were instructed to grasp the pre-load plate and to move it without voltage supply. After that the plate was excited at their unknown.

From that moment they said they recognise a kind of jolts. Thereafter they were told the task consisted on counting the number of cycles present between the material limits of the displacement. We conducted some additional trials before starting the task. This preliminary stage took around 5 mns. Participants used their dominant hand and made some comments at the end of the experiment. At last, the duration of the experiment was about 30 minutes per participant.

Psychophysical results

To analyse the average results of the two groups of participants tested we present the average number of cycles (or spatial period) present for each test. We consider the result in terms of absolute value of an average error rate (DER) defined as follows [START_REF] West | Detection of real and virtual fine surface features with a haptic interface and stylus[END_REF],

cycles actual ected cycles cycles actual DER _ ) det _ _ ( - = (6)
It's important to notice that the wave amplitude in our experiment didn't represent the deep of a notch, although it was the case in experiment from West and Cutkosky [START_REF] West | Detection of real and virtual fine surface features with a haptic interface and stylus[END_REF].

Experimental results

The average results obtained for both groups of subjects are graphically presented in fig. 14. We have plotted average number of cycles detected for each given couple vibratory amplitude/ frequency. The symbol in the legend denotes the actual number of cycles present for the corresponding test. Each curve plots the results for a particular wave frequency (number of cycles present inside departure and arrival lines) with different points along the curve corresponding to different wave amplitudes. Fig. 15 shows the average DER which globally isn't greater than 12 % except at one point.

Discussion

An experiment of counting features in a given distance was conducted using the proposed device. Since some experimental parameters and the material differ from the one used by West and Cutkosky, we can't directly compare our results to theirs.

Nevertheless the approach is similar and some conclusions too. We also used the DER to interpret our results. They considered that a DER of 50 % or more means that subjects are unable to count features accurately. These researchers found the arbitrary limit of 50 % to correlate well from the comments from subjects about their perceived ability to count features. They also compare the results obtained with real features. In the same manner, from us, for the range of frequencies and wave amplitudes we displayed, the DER is globally less than 12 % and participants comments didn't vary much. Also, an examination of the standard deviation of the average error rate which, in general, is lower for the tests with higher wave amplitude consolidates the idea that participants have good perception of the patterns. As a matter of the fact, almost all the participants spontaneously stated firmly to feel a "strong" sensation for the highest vibratory amplitude (.65 µm). So we can assess that the proposed device can reach physical conditions (vibration amplitude in particular) allowing accurate counting of notches.

CONCLUSION

In this paper we propose to use the principle of active lubrication to design a 2Dof passive haptic feedback device. The device is first described and its operating principle is explained as well.

Then some details are given on the modelling of the device, leading to the expression of tangential force. Simulations are performed in order to check the effectiveness of friction control According to an experimental set-up, those simulations results are successfully compared with the simulated ones. So, it is possible to control the friction force in a range available for force feedback rendering, even if this force highly depends on normal pre-load and tangential speed. Preliminary Psycho-physic studies have been conducted to evaluate this device in use. As preliminary evaluation it trends to assess the validity of the interface for 1D low force feedback application such as assisting users for sensing the boundaries of virtual objects.

For future works and evaluation purpose, several experiments may be run to check the ability of this interface for discrimination tasks between similar Spatial Periods like in [START_REF] Biet | Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays[END_REF]: also, the shape recognition has to be investigated, according to different values of friction coefficient.

Figure 1 Fig. 1 :Fig. 2 :

 112 Figure 1 schematically shows the proposed structure. A set of PZT polarised piezo-ceramics of 12x12mm are glued on the upside of a cupper-beryllium substrate whose size is 64x38x3 mm. Considering this polarisation, piezo-ceramics electrode are conveniently supplied by a sinusoidal voltage of some ten Volts to create a standing wave using the piezoelectricity inverse effect with 40.7 kHz as driving frequency (resonant frequency). As a result, fig.2 shows an experimental mapping of the standing waveform obtained. "+"

Fig. 3 :

 3 Fig.3: Stationary wave and foot trajectory

Fig. 4 :

 4 Fig.4: Coulomb-Orowan for the friction coefficient

Fig. 5 :

 5 Fig. 5: Equivalent mechanical scheme and forces acting on one foot

Fig. 6 :

 6 Fig. 6: Friction force on the plate at a fixed preload (simulation).

Fig. 7 :

 7 Fig. 7: Friction force on the plate at a fixed speed (simulation).

Fig 8 :Fig 9 :

 89 Fig 8: Experimental set up.

Fig. 10 :

 10 Fig. 10: Theoretical and experimental results on steel surface; preload 3 N, speed 1, 2 and 5 cm/s.

"

  Fig.11: texture patterns and corresponding "blocking" and "sliding" feelings.

Fig. 13 :

 13 Fig.13: system wave amplitude response time

Finally

  , fig.16deals with standard deviation of DER and its interpretation in fig.17 which shows the tendency to the decrease of answer range when vibratory amplitude increases.

FigFig. 17 :

 17 Fig. 14: average number of cycles detected

Acknowledgements

This work has been carried out within the framework of INRIA Alcove project and is supported by IRCICA (Institut de recherche sur les composants logiciels et matériels pour l' information et la communication avancée).


Alain Bouscayrol
email: alain.bouscayrol@univ-lille1.fr

Philippe Delarue

Fréderic Giraud

Xavier Guillaud

Xavier Kestelyn

Betty Lemaire-Semail

Walter Lhomme

Teaching drive control using Energetic Macroscopic Representationexpert level

Keywords: Education methodology, Control of Drive, Wind energy, Energetic Macroscopic Representation

The Energetic Macroscopic Representation (EMR) has been developed in 2000 to develop control of electric drives. Since 2002 this graphical tool has been introduced to teach drive control in France, then Canada, Switzerland and China. The University of Lille proposes two drive control units using EMR for students in electrical engineering: initiation level and expert level. A first paper has described the initiation level with the simulation of an electric vehicle. This second paper deals with the content of the expert level unit and describes the simulation project of a wind energy conversion system using a MPPT (Maximal Power Point Tracking) strategy.

Introduction

Nowadays, drive control is of main interest in electrical engineers teaching [START_REF] Blaabjerg | An industry/university collaboration in power electronics and drives[END_REF]- [START_REF] Gambôa | Modern Technologies for Experimental Education in Industrial Electronics and Electric Drives[END_REF]. But it requires skills in various scientific fields such as power electronics, electrical machines, automatic control, mechanics and control electronics. Causal Ordering Graph (COG) has been introduced ten years ago [START_REF] Hautier | The Causal Ordering Graph[END_REF] [START_REF] Hautier | The causal ordering graph -A tool for modelling and control law synthesis[END_REF] to describe power electronics and electrical machines for developing their control. This graphical description exclusively uses integral causality [START_REF] Iwasaki | Causality and model abstraction[END_REF] [START_REF] Rubin | The development of vehicular powertrain system modeling methodologies: philosophy and implementation[END_REF] on the contrary as the well-known Bond-Graph [START_REF] Paynter | Analysis and design of engineering systems[END_REF]. The inversion of this graph yields the control structure of the system with measurements and controllers. Energetic Macroscopic Representation (EMR) has been introduced in 2000 for research development in complex electromechanical drives as multi-drives systems [START_REF] Bouscayrol | Multimachine Multiconverter System: application for electromechanical drives[END_REF]. EMR is based on action reaction principle, which organizes the system according to the integral causality. An inversion of this description leads to macro-control blocs. These both descriptions have been successfully used for control of various applications [START_REF] Barrre | Inversion-based control of electromechanical systems using causal graphical descriptions[END_REF]- [START_REF] Bouscayrol | Power strategies for Maximum Control Structure of a wind energy conversion system with a synchronous machine[END_REF]. COG has been used in teaching since 1996 at University of Lille and engineering schools of Lille (Arts et Métiers ParisTech (ex ENSAM),, Ecole Centrale and Polytech'Lille). EMR has been introduced in 2002 in the common Master degree of these university establishments. Both graphical tools are used in some other French universities and also at University of Québec Trois Rivières (Canada) since 2004, Ecole Polytechnique Fédérale de Lausanne (Switzerland) since 2005 and University of Tsinghua (China) since 2008. Indeed these graphical descriptions enable a unified way for causal description of the components of electromechanical systems. Moreover simple inversion rules lead to easily deduce the control structure of the studied system. It is then a very useful intermediary step for students to develop control of electrical drives. The Master degree of University of Lille proposes two teaching units for drive control based on Energetic Macroscopic Representation. The first unit is devoted to an initiation level for developing basic knowledge on drive control and to connect this to other scientific fields. The second unit consists of an expert level to control more complex drives by using more advanced control methodologies. A first paper has been presented on the initiation level with the simulation of an electric vehicle [START_REF] Bouscayrol | Teaching drive control using Energetic Macroscopic Representation -initiation level[END_REF]. In this paper, the expert level is presented. The simulation project is now focused on a Wind Energy Conversion System (WECS) using a Maximum Power Point Tracking (MMPT).

EMR fundamentals

Interaction principle

The system is decomposed in basic subsystems in interactions (Table 1): energy sources (green ovals), accumulation elements (orange rectangles), conversion element without energy accumulation (various orange pictograms) and coupling elements for energy distribution (orange overlapped pictograms). Purple pictograms are devoted to estimation bocks. All the elements are connected according to the action and reaction principle using exchange variable (arrows). The product of action and reaction variables between two elements leads to the instantaneous power exchanged.

Causality principle

As in COG [START_REF] Hautier | The causal ordering graph -A tool for modelling and control law synthesis[END_REF], only the integral causality is considered in EMR. This property leads to define accumulation elements by a time-dependant relationship between its variables: its output is an integral function of its inputs. Other elements are described using relationships without time dependence. In order to respect the integral causality specific association rules are defined, but there are taught only in the expert level unit.

Inversion principle

The inversion based control theory has been initiated by COG [START_REF] Hautier | The causal ordering graph -A tool for modelling and control law synthesis[END_REF]. The control structure of a system is considered as an inversion of the system modelling: the control has to define the inputs to apply to the system from the desired output (Fig. 1). In this method, relationships without time-dependence are directly inverted (with neither control nor measurement). Because the derivative causality is forbidden, a direct inversion of time-dependence relationships is not possible. An indirect inversion is thus made using a controller and measurements. These inversion rules have been extended to EMR (blue pictograms, see Table 1): conversion elements are directly inverted and accumulation elements are inverted using controller. It is another way to located controllers and measurements.

y(t) u(t) System y ref (t)

EMR and initiation to drive control

A specific unit "Control of electrical drives using EMR" has been introduced in the Master degree of University of Lille. This unit concerns an initiation to drive control using such a graphical tool. The students can improve their skills by choosing a complementary unit "Advanced control of electric systems using EMR". This unit deals with more complex systems (wind energy conversion systems, multi-motor traction systems, hybrid electric vehicles, power systems…) for an expert level. Each unit is associated with 5 ECTS (European Credit Transfer System). Only the expert level is considered in this paper.

The unit is composed of 12 h of lecture on EMR, 20 h of seminars on industrial applications, and 24 h for a simulation project. Each group of student has to simulate different systems. Only a wind energy conversion system is considered in this paper.

The lecture is composed of the following sections:

• Notions of systemic (different description of systems, systemic, internal description and causality, external description and interaction) • Causal Ordering Graph (basic elements, modeling graphs, inversion-based control methodology, control graphs) • Energetic Macroscopic Representation (basic elements, elementary conversion between two energy sources, association rules, electromechanical conversion systems) • Inversion-based control deduced from EMR (inversion of EMR elements, maximum control structure, practical control structures, strategy level) • Extension to multimachine systems (concept of multimachine systems, coupling elements, inversion of coupling elements)

Seminar on industrial applications illustrate the different concepts:

• EMR and inversion-based control of an automatic subway (performed by an engineer of Siemens Transportation Systems)

• EMR and inversion-based control of a Wind Energy Conversion System (WECS) • EMR and inversion-based control of a Flexible AC Transmission Systems (FACTS) • EMR and inversion-based control of a Hybrid Electric Vehicle (HEV) • EMR and inversion-based control of a ship propulsion system

The studied systems are real industrial applications with different subsystems interconnected. Indeed, this expert level is focused on the associations of sub-systems and the use of ac drives with their control. At the end of the unit the students must be able to model and decompose the system in a physical causal way, and to deduce the control structure of the system by locating controller and measurements or estimations to do.

EMR for the simulation of a wind energy conversion system (WECS) Studied WECS

The studied system is composed of a rotor blade, a gearbox, a squirrel cage induction machine and a 3leg voltage source inverter and an equivalent DC bus (Fig. 2) [START_REF] Bouscayrol | Power strategies for Maximum Control Structure of a wind energy conversion system with a synchronous machine[END_REF]. In this project, the dc bus is assumed to be constant. In another project, the connection to the grid is studied.

Modeling of the WECS

During the WECS seminar, the students learn about the WECS modelling. The following relationships are provided. An EMR is derived from the mathematical models (upper part of Fig. 4).

Blades -

The wind imposes the wind velocity v wind on the blades. The torque T blade produced by the blades depends on the wind velocity: where S is the area swept by the blades, ρ the air density, β the orientation blade and R the blade radius. The torque coefficient C T [START_REF] Bouscayrol | Power strategies for Maximum Control Structure of a wind energy conversion system with a synchronous machine[END_REF] is a non-linear function of the tip-slip ratio λ which depends on the wind velocity and the rotation speed Ω shaft :

wind shaft v RΩ λ = ( 2 )
The torque coefficient also depends on the blade orientation β (Fig. 3).

C T λ β=8°β =6°β =4°β =2°β =0°
Fig. 3: Torque coefficient versus tip-slip ratio of the WECS Mechanical power train -Using an equivalent shaft [START_REF] Bouscayrol | Power strategies for Maximum Control Structure of a wind energy conversion system with a synchronous machine[END_REF] we can deduce the rotation speed Ω shaft from the blade and gearbox torques, T blade and T gear :

shaft blade gear shaft f T T dt d J Ω Ω - + - = ( 3 )
where J and f are the inertia and the friction coefficient of the equivalent shaft respectively. The gearbox yields the rotation speed Ω gear and torque T gear as a function of the gearbox ratio k gear and the induction machine torque T im :

⎪ ⎩ ⎪ ⎨ ⎧ = = im gear gear shaft gear gear T k T k Ω Ω ( 4
)
Induction machine -Classical (d,q) dynamic modelling is used to describe the induction machine [START_REF] Vas | Vector control of ac machines[END_REF]. First, the transformation [T(θ d/s )] expresses stator voltages u rect and currents i im in the (d,q) frame:

[ ] [ ] ⎪ ⎩ ⎪ ⎨ ⎧ = = - sdq 1 s / d im rect s / d sdq i ) ( ' T i u ) ( T u θ θ ( 5 )
where θ d/s is the rotor flux position with respect to the stator stationary frame, since we have chosen to orient the d axis on the rotor flux for a classical field oriented control. In this (d,q) frame, the equivalent stator windings impose the stator currents i sdq =[i sd ,i sq ] t as state variables in terms of the stator voltages u sdq =[u sd ,u sq ] t and the e.mf. e sdq =[e sd ,e sq ] t :

sdq s sdq sdq sdq s i R e u i dt d L - - = ( 6 )
where R s and L s are the resistance and cyclic inductance of the stator winding respectively. The electromechanical conversion yields the machine torque T im and the e.m.f from the current and the rotation speed Ω shaft :

) , , i ( f e i k T rd s / d sdq sdq sq rd 1 im ⎪ ⎩ ⎪ ⎨ ⎧ = = φ θ φ ( 7
)
The rotor flux φ rd is given in terms of the d axis current i sd :

rd sd 3 rd 2 i k dt d k φ φ + = ( 8 )
The transformation phase θ d/s is deduced as follows:

p i k dt d shaft sq rd 4 s / d Ω φ θ + = ( 9 )
where p is the pole pair number. In the previous equations, the coefficients k i are combinations of machine parameters. Fig. 4: EMR and inversion-based control of the studied WECS

Voltage-source-converter -

The VSC induces a modulated voltage vector u rect =[u rect13 , u rect23 ] t , from the dc voltage u cap and the switching order vector s vsc =[s rc11 , s rc21 , s rc31 ] t . Note that only two stator voltages are used because the third one is a linear combination of the two others. The converter supplies the machine, which reacts via a circulating current vector i im =[i im1 ,i im2 ] t . These currents are also modulated to produce the current i rect . A modulation vector m vsc =[m 1 , m 2 ] t can be introduced to define the modulation ratio between all variables [START_REF] Delarue | Generic control method of multi-leg voltage-source-converters for fast practical implementation[END_REF]:

i m i u m u im t vsc rect cap vsc rect ⎪ ⎩ ⎪ ⎨ ⎧ = = with vsc vsc s 1 1 0 1 0 1 m ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ - - = ( 10 )

Inversion-based control of the WECS

Due to the exclusive integral causality, a maximum control structure is deduced from the EMR using inversion-based rules. First, all variables are considered measurable, which yields a control with the greatest number of measurements and controllers. In the second step, simplifications and estimations of non-measured variables are made. Finally, a strategy element is added to define physical references from the power objective [START_REF] Bouscayrol | Power strategies for Maximum Control Structure of a wind energy conversion system with a synchronous machine[END_REF].

First a tuning chain (Fig. 5) is defined, which begins at the tuning variable that acts on the system (the switching vector s vsc ) and which ends at the variables that have to be controlled (the machine torque T im and flux φ rd ). We assume that the blade orientation is an external operation. A control scheme is obtained from EMR using inversion rules (lower part of Fig. 4). At this stage all variables are assumed measurable. Then the tuning chain is inverted step by step. Two kinds of inversion are considered.

For conversion element (without energy accumulation), direct inversions are used (simple parallelograms): neither controller nor measurement are required. For inversion of accumulation elements, a controller is required (crossed parallelograms) and some measurements are also needed.

For example, the inversion of ( 6) requires a flux controller to provide the current i sd_ref from the reference flux φ rd-ref and the measured (or estimated) flux φ rd-mesq :

[ ] mes _ rd ref _ rd ref _ sd C i φ φ - = ( 11 )
where C[X ref -X mes ] is a controller, which could be PI or other controllers.

In another example, the inversion of ( 7) leads to the reference current i sq_ref from the reference torque T im-ref and φ rd-ref :

T k 1 i im_ref ref _ rd 1 sq_ref φ = ( 12 )

Simulation of the WECS

The simulation project is composed of 5 sessions of 4h each in a simulation room. A supervisor is available only 1 h per session. An oral presentation including a simulation demonstration has to be done at the end of the unit. Only the WECS application is presented in this paper. Matlab-Simulink TM is chosen as simulation software. The students have three programs at their disposal: an initialisation program containing the WECS parameters (blade, gearbox, IM parameters…), and a Simulink library containing the EMR basic elements. The objective of the project is to study the WECS using a Maximum Power Point Tracking (MPPT) strategy to extract power from the wind. The students have to build the simulation model of the WECS including the induction machine and the 3-leg voltage source inverter. They have also to determine the whole control structure of the WECS, to tune all controllers and to implement the control part in the simulation software. A field-oriented control can be used for the induction machine. The power electronics is simulated using average values. The MMPT strategy is provided.

In order to organise their simulation, the students are invited to describe EMR of the system and the deduced control. Most of the students (80 %) develop the whole Simulink program (Fig. 6). It may be noted that the EMR scheme of Fig. 4 looks like the Simulink scheme. This is helpful for the students for accurately organising their simulation. Different wind profiles are then used (Fig. 7) and power extraction can be studied for different winds and different blade orientation (Fig. 8). For more advanced student (10 %), the simulation can be improved by comparisons of different controllers, simulation of the converter using instantaneous values with PWM, or simulation of flux weakening. Moreover, best students can validate their control scheme in real-time using the Hardware-In-the-Loop simulation platform of the Laboratory [START_REF] Bouscayrol | Energetic Macroscopic Representation and inversion-based control illustrated on a wind energy conversion systems using Hardware-in-the-loop simulation[END_REF].

Conclusion

The use of EMR is an efficient methodology to develop student skills on drive control. A unified and physical modelling is developed, and inversion rules are used to find the control scheme. By using this intermediary step, they can easily connect other scientific fields such as power electronics, electrical machines, mechanics and automatic control. In the expert level, complex systems are studied to develop scientific skills on drive control. Evaluations of the unit have shown a very good acquisition of fundamentals on drive control. Because of the attractive graphical description, some students choose a final training period in drive control using EMR, both in industry or in academic laboratory. such as in [START_REF] Djani | Extension of Energetic Macroscopic Representation to time-varying systems, applications to winder tension control[END_REF], [START_REF] Verhille | Torque tracking strategy for anti-slip control in railway traction systems with common supplies[END_REF].

Fig. 1 :

 1 Fig. 1: Inversion-based control principle

Fig. 2 :

 2 Fig. 2: Studied Wind Energy Conversion System

Fig. 5 :

 5 Fig. 5: Tuning chain of the WECS

Fig. 6 : 15 Fig. 7 :Fig. 8 :

 61578 Fig. 6: Matlab-Simulik TM model of the studied WECS and its control

Table 1 :

 1 Elements of EMR and of control

	Source of energy	Element with
		energy accumulation
	Electrical converter	Control block
	(without energy accumulation)	without controller
	Mechanical converter (without	Control block
	energy accumulation)	with controller
	Electromechanical converter	Strategy block
	(without energy accumulation)
	Coupling devices (for energy	Estimation block
	distribution)


Kirsi Hyytinen
email: kirsi.hyytinen@vtt.fi

Sampsa Ruutur
email: sampsa.ruutu@vtt.fi

Mika Nieminen
email: mika.nieminen@vtt.fi

Faïz Gallouj
email: faiz.gallouj@univ-lille1.fr

Marja Toivonen
email: marja.toivonen@vtt.f

Hyytinen, Senior Scientist, Kirsi

Sampsa

Ruutu

Faïz

Gallouj

XXIV. International RESER Conference: Evaluation of services linked to the sustainability: a dynamic and multi-criteria approach

The purpose of this paper is to study the challenge of the evaluation in the context of the services in the sector of environment and energy. Because of the specific nature of service innovation the traditional evaluation methods and measures are not able to capture neither the diversity of the innovations nor the multifaceted dimensions of performance. This paper aims to contribute to the need for a more diverse evaluation approach. We study the use of multi-criteria and system dynamic perspectives in the evaluation of services, and we develop a new type of methodology to evaluate their dynamics and multifaceted performance. (10 lines max)

Introduction

The focus in the definition and the evaluation of innovations has typically been on traditional S-T indicators orienting highly towards their technological and economic aspects. This approach has been criticized in the service studies (e.g. [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013;[START_REF] Toivonen | Different types of innovation processes in services and their organizational implications[END_REF][START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]. Because of the specific nature of services, especially their immaterial and interactive dimension, the traditional evaluation methods and measures are not able to capture neither the diversity of the innovations nor the multifaceted dimensions of performance in the sector [START_REF] Djellal | The Productivity in services: measurement and strategic perspectives[END_REF]).

The increasing "servitization" of society has also put pressure to develop a more advanced approach to evaluation and in some recent studies (e.g. [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013;[START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]), both the "plurality of methods" [START_REF] Dyehouse | A comparison of linear and systems thinking approaches for program evaluation illustrated using Indiana Interdisciplinary GK-12[END_REF]Williams & Imam 2007) and the basics for new evaluation criteria have been suggested. According to them, impacts should be assessed on the basis of a multidimensional approach to take into account their aspects of quality, reputation, social innovation and social value [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013;[START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]).

Systems thinking have often been applied hand in hand with these views. Reasoning is rooted in the modern "broad view on innovation" that highlights the interactivity (including multiple sources and actors in it), complexity and uncertainty of development and implementation of innovations. These arguments and perspectives affect both to the definition of innovations and to the evaluation of their effects and impacts (e.g. [START_REF] Kline | An Overview of Innovation[END_REF][START_REF] Lundvall | National Systems of Innovation: Towards a Theory of Innovation and Interactive Learning[END_REF][START_REF] Freeman | Networks of innovators: A synthesis of research issues[END_REF][START_REF] Nelson | Technical Innovation and National Systems[END_REF][START_REF] Dosi | Some notes on national systems of innovation and production, and their implications for economic analysis[END_REF]. And it directs to consider the dynamic nature, interrelationships and feedbacks between multiple actors within the process [START_REF] Smith | Innovation as a systemic phenomenon: Rethinking the role of policy[END_REF][START_REF] Edquist | Reflections on the systems of innovation approach[END_REF][START_REF] Cabrera | Systems thinking[END_REF].

The evaluation challenge concerns especially services that are linked to the sustainability and environmental issues. In such services, the technological perspective (especially "end-of-pipe" technologies) typically dominates discussions. However, the most urgent problems in the present society cannot be solved via the development of individual technologies or services. Instead, the focus is in service solutions which can be characterised as complex innovations integrating technological, nontechnological and service-based elements and developed and implemented in the interaction with various actors (e.g. [START_REF] Djellal | How public-private innovation networks in services (ServPPINs) differ from other innovation networks: what lesson for theory?[END_REF]. The emerging role of service solutions is not sufficiently taken into account [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013) in the current evaluation approaches.

This paper aims to contribute to the above described need for a more diverse evaluation approach. The objective in this paper is firstly to study the system perspective and the evaluation challenge in the context of service innovation and secondly to develop a new type of dynamic multi-criteria evaluation approach. Suggested approach integrates the multi-criteria perspective [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013) and system dynamic modelling [START_REF] Sterman | Business dynamics: Systems thinking and modeling for a complex world[END_REF]). In the methodology multi-criteria perspective describes the various impacts by giving insight to different societal spheres and their principles and values in the sens of Economics of Convention [START_REF] Gadrey | Les quatre "mondes" des économies de services développées[END_REF][START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013). System dynamic modelling pays attention to the interaction of various actors and their values in the evaluation situation (cf. [START_REF] Giddens | Social Theory and Modern Sociology[END_REF]) and provides information how the system structure creates complex dynamic behaviour over time. It helps to explain the role of feedback loops between different actors and factors that promote or hinder the emergence of impacts.

The following research questions are guiding our work:

-How and by what means should the outcomes and impacts be evaluated in order to take into account the multifaceted and dynamic nature of service innovations in the sector of environment and energy?

-What are the dynamic impacts of service innovations in the sector of environment and energy?

As a result of our study we provide a two dimensional approach to evaluate the impacts of services. The focus is in understanding the dynamics of service creation in the environmental sector and the use of evaluation methods and indicators in it. At more detailed level, our study provides analytical material about complementarities and contradiction between different indicators. The results will illustrate how the technical and non-technical aspects of service innovations interact in the area of sustainability.

This paper is divided into three sections. The second section after this introduction is based on literature and discusses the current evaluation challenges in services. The third section presents the two main perspectives that we apply in our framework to evaluate the services. In the fourth section our case study context and methodology are described. In the fifth section we present the application of our frameworks and present the main results of our study. Final section sums up the discussion and makes the concluding remarks.

Theoretical background

System approach to services

The current social, economic, and environmental challenges are too big to be solved via individual product and service innovations created in individual organizations.

Conversely, the challenges require various innovations and simultaneous development of organizations, technologies, services and multiple network relationships [START_REF] Gallouj | Economie de l'innovation dans les services, Editions L'Harmattan, Logiques. Économiques[END_REF][START_REF] Gallouj | Innovation in the service economy: The new wealth of nations[END_REF][START_REF] Windrum | A neo-Schumpeterian model of health services innovation[END_REF][START_REF] Harrison | Social innovation, social enterprise and services[END_REF][START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]. A crucial question is how to combine various innovations effectively and disseminate them rapidly on the basis of continuous interaction of different organizations. In other words, examining and developing innovations at the systemic level has come to the fore.

While innovations are increasingly combinations of many technologies, organizational changes and services, they are also embedded in a wider social environment which supports or restrains the development of new innovations. This wider context could be described as socio-technical system in which radical changes take place only rarely due to such phenomena as "path-dependency" and "lock-ins". These concepts refer to the fact that past decisions and choices may steer and restrain new developments. Wide socio-technical change based on radical innovations becomes possible only if system faces e.g. a performance crisis which is not possible to solve with incremental improvements. In essence, a wide change requires complex interaction between actors, resources, institutionalised practises and regulation in a system. [START_REF] Geels | Typology of sociotechnical transition pathways[END_REF][START_REF] Geels | From sectoral systems of innovation to socio-technical systems. Insights about dynamics and change from sociology and institutional theory[END_REF][START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: a multi-level perspective and a case-study[END_REF] This means that we need a more systemic view and system oriented methods when we are assessing the dynamics and performance of the system. The focus on separate service or technological innovations needs to be replaced by a wider view taking into account the context and its complex interactions.

This kind of view is emphasized in recent studies on innovation ecosystems. The idea of innovation ecosystem emphasizes the idea of a system of various actors with mutual dependencies and causal linkages. For some writers the concept means innovator-distributor-retailer-end customer relationships and how the innovator/producer is dependent on other firms in its innovation and market activity (e.g. [START_REF] Adner | The Wide Lens. A New Strategy for Innovation[END_REF]). Some other writers replace the whole concept of innovation system with the concept of innovation ecosystem (e.g. [START_REF] Heller | The Russian Innovation Ecosystem 2013[END_REF]). The more elaborated versions of the concept refer to systems theory and use such concepts as coevolution, co-specialization and co-opetition [START_REF] Carayannis | Mode3 and Quadruple Helix: Toward a 21st century fractal innovation ecosystem[END_REF]. In here we suggest that an ecosystem is a multi-actor and co-evolving system of private and public actors working together to create economic and societal advantage.

Evaluation challenge in services

For two decades, service studies and specifically the studies on service innovation have argued that the traditional tools, indicators and measures do not capture the performance, innovativeness and impacts in services [START_REF] Sundbo | The theory of innovation: entrepreneurs, technology and strategy[END_REF]Metcalfe & Miles 2000). A central background reason for the existence of the gap is the "assimilation" perspective adopted in the early service research [START_REF] Coombs | New industrial financial services : what distinguishes winners[END_REF][START_REF] Gallouj | Economie de l'innovation dans les services, Editions L'Harmattan, Logiques. Économiques[END_REF]). This perspective analyzed services innovation as an imitation of technological and manufacturing innovations. The perspective was based on the traditional definition of innovation as an invention which results from an R&D project [START_REF] Howells | Innovation, consumption and services: encapsulation and the combinatorial role of services[END_REF]). The linear, stage-gate model of an innovation process, which was raised to the position of a norm and marketed as a prerequisite for success (e.g. Cooper & de Brentani 1991), increased the bias.

These arguments and perspectives have been developed in the context of service innovations. However, they are strongly rooted in general innovation theories basing on the Schumpeter"s definition of innovation that has afterwards been regenerated to "the neo-Schumpeterian" theory of innovation or a broader view of innovation (Lundvall 2007;[START_REF] Toivonen | Starting points for the comparison of SDL and neo-Schumpeterian views on innovation[END_REF]). These traditions are interlinked by several common aspects that affect both the definition of innovations and evaluation of their effects and impacts. Important cornerstones are complexity and uncertainty of innovation process, intangible nature of innovation (focus in new solutions and processes) and systemic view of innovation encompassing multiple sources and actors taking part into the innovation process. [START_REF] Kline | An Overview of Innovation[END_REF][START_REF] Lundvall | National Systems of Innovation: Towards a Theory of Innovation and Interactive Learning[END_REF][START_REF] Freeman | Networks of innovators: A synthesis of research issues[END_REF][START_REF] Nelson | Technical Innovation and National Systems[END_REF][START_REF] Dosi | Some notes on national systems of innovation and production, and their implications for economic analysis[END_REF]. Also from the perspective of general innovation literature conclusion has been parallel: current practices in defining innovation and evaluating them do still follow the mainstream linear innovation thinking which simplifies too much the innovation process as well as the complex dynamics between actors contributing innovation (e.g. [START_REF] Smith | Innovation as a systemic phenomenon: Rethinking the role of policy[END_REF][START_REF] Arnold | Evaluating research and innovation policy: a systems world needs systems evaluations[END_REF][START_REF] Edquist | Reflections on the systems of innovation approach[END_REF][START_REF] Smits | The rose of systemic instruments in innovation policy[END_REF][START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013;[START_REF] Patton | Developmental evaluation: Applying complexity concepts to enhance innovation and use[END_REF]).

In addition to the narrow view on innovation, the dominating view on performance is also mechanical and narrow. It is usually linked to the concept of productivity which refers to the linear and mechanistic input-output function (e.g. Djellal andGallouj 2010, 2013;Kellog foundation 2004;[START_REF] Patton | Developmental evaluation: Applying complexity concepts to enhance innovation and use[END_REF]. Its" traditional definition is unable to recognize the "hidden performance" concerning the societal aspects of services and innovations like equality, ecological sustainability and societal well-being. It also often excludes the aspect of social innovation (e.g. [START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]. [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF] have described the interaction between performance and innovation by referring to the visible vs. invisible nature of this phenomenon. Whereas technology-based innovations are visible, non-technological innovations are invisible. As regards performance, the authors link the visible-invisible dichotomy to short-term vs. long-term influences. Both in scientific and the managerial discussions, short-term influences of performance are often analyzed in terms of productivity and growth. Longer-term influences are increasingly analyzed in terms of environmental or social sustainability. There are four possibilities in the relationship between innovation and performance as Figure 1 illustrates (ibid., 668). The most apparent relation is between visible innovation and visible performance, but visible innovation may also lead to invisible performance by promoting the long term ecological sustainability or societal well-being. Correspondingly, invisible innovation may be a source of visible performance, i.e. growth and productivity, or promote sustainability.

The idea of "double gap" has been noticed to cause significant implications to public policies, which are still very technologist oriented and do not take into account the innovation and performance gap included. Thus, the invisible innovation and performance remain invisible in the policy making, causing problemsnot only in the performance measurement as suchbut also in target setting, and in steering and policy planning. In order to improve the situation, both the visible and invisible aspects in innovation and performance has to be included in an integrative way [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF].

Opening the specific characteristics of service innovation and performance

After the realization of the narrowness of the assimilation view, two alternatives have gained ground. The first is the differentiation perspectivealso known as the demarcation perspective [START_REF] Coombs | New industrial financial services : what distinguishes winners[END_REF][START_REF] Gallouj | Economie de l'innovation dans les services, Editions L'Harmattan, Logiques. Économiques[END_REF]). It focuses on the specific characteristics of service innovation and has highlighted the difficulty of recognizing "newness" and its creator in the service context [START_REF] Preissl | Service Innovation: What makes it different? Empirical Evidence from Germany[END_REF]. The second alternative is an integrative or synthesis perspective (Cooms and Miles 2000;[START_REF] Gallouj | Innovation in the service economy: The new wealth of nations[END_REF]) which has become increasingly relevant due to the blurring lines between goods and services. It highlights the production and consumption that focus on integrated solutions and systems. The role of integrative services is emerging especially in the area of environment and energy (e.g. [START_REF] Hyytinen | Future energy services: empowering local communities and citizens[END_REF].

Recently, these approaches have also been applied when searching better indicators for innovation and performance in services. The peculiar characteristics of services that specifically have been pointed out in this context are intangibility and the central role of interaction; the latter refers to the central role of co-production between the provider, customers and partners. An important implication of intangibility is the difficulty of defining the "unit of output" and differentiating the product from the process. These aspects challenge the definition of innovation and quality improvements in it.

Interactivity increases the complexity of the development of services innovations [START_REF] Gallouj | Public-private innovation networks in services[END_REF]. Ignoring these complex and dynamic relationships (cf. Arnold 2004) is often linked to the traditional technologic measures and the linear innovation model [START_REF] Smith | Innovation as a systemic phenomenon: Rethinking the role of policy[END_REF]Edqvist 2005;[START_REF] Ahrweiler | Innovation in Complex Social Systems[END_REF]). It may lead to the oversimplification of the reality and to the biased understandingnot only of the impacts of services and innovationsbut also of their drivers and dynamics [START_REF] Arnold | Evaluating research and innovation policy: a systems world needs systems evaluations[END_REF]).

New aspects in the analysis are inclusion of the time factor and the social nature of services [START_REF] Djellal | The Productivity in services: measurement and strategic perspectives[END_REF]. Time highlights the dynamic nature of services, focusing to their evolution over time. Considering time as a dynamic factor leads to the differentiation of short-term outputs from medium and long-term effects. The social nature of services derives from the fact that the value and benefit of services is always defined by users. This means that different actors have different values, and it is just this multiplicity of values which makes it necessary to include various criteria in evaluation. In addition to immediate users, it is important to take into account the multiple values of indirect users as well as those of different actors participating in the development, [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013). Thus, in service innovation boundary lines are blurringnot only between products and processesbut also organizations often change simultaneously [START_REF] Preissl | Service Innovation: What makes it different? Empirical Evidence from Germany[END_REF]. These kinds of combinatory innovations and their broader socio-economic impacts cannot be tackled on the basis of the traditional linear and industrialist models.

3.

New framework for the evaluation of services 3.1.

Multi-criteria approach to diversify the perspectives of evaluation

These above described challenges in measurement and evaluation of services intend to assess the performance and impacts on the basis of a multidimensional approach which takes into account the special characteristics of services as well as their aspects of quality and social value [START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF][START_REF] Adner | The Wide Lens. A New Strategy for Innovation[END_REF][START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF]. Like writers have argued one potential and diversified way of analyzing the various impacts is by giving insight to different societal spheres "worlds of services" and their principles and values in the sens of Economics of Convention [START_REF] Gadrey | Les quatre "mondes" des économies de services développées[END_REF][START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013).

In that model the outcomes are evaluated from the perspective of different goals encompassing both the traditional measures and the modern evaluation criteria taking into account the needs of knowledge society. In addition to the different target areas the model takes into account the long time-scale in the generation of impacts by dividing outcomes into the direct, short-term outputs and indirect, long term-outcomes (or impacts). The table 1 below illustrates the different worlds given the specific justification criteria related to the each of the worlds [START_REF] Gallouj | Innovation in the service economy: The new wealth of nations[END_REF][START_REF] Djellal | The Productivity in services: measurement and strategic perspectives[END_REF].

Compared to original model, we have made some minor modifications into it. Referring to the recent literature, the concepts concerning the aspects of social innovation, sustainability and responsibility should be taken more clearly into the consideration in the analysis of impacts [START_REF] Rubalcaba | Shaping, Organizing and Rethinking Service innovation: A multidimensional Framework[END_REF][START_REF] Djellal | The Productivity in services: measurement and strategic perspectives[END_REF]. Our modifications concern especially the aspect of "the civic world" that originally was focused to social relations characterized by the ethical issues such as equal treatment and fairness. In this model we suggest to integrate the concept of societal value and responsibility into the idea of civic world and also rename it "responsible world". By the addition our aim is to better take into the account the aspects concerning the social innovations, environmental sustainability and societal well-being.

In the original model also the word of innovation (referring to creativity and inspiration) is differentiated. Because in our study the focus is in analysing service innovations, the specific perspective of innovation world is excluded from our table. Instead we clarify the different elements of innovation by adding that perspective horizontally to the table and by analyzing these aspects in the light of each world.

Performance related

Analysing the impacts from the perspective of different worlds makes visible the multifaceted nature of service innovations. However, analytical table remains static and does not increase understanding of their dynamic and complex nature. It does not show how the different impact criteria are mutually interlinked and may reinforce or contradict each other. This perspective in our framework is considered with the system dynamic modelling tools more carefully described in the following sub-chapter.

System dynamic modelling to evaluate the dynamics of services

One key insight behind systems thinking is that interlinkages between different elements in a system can create complex behaviour. This complex behaviour and nonlinear nature in the evaluation of impacts can remain unnoticed if each component, such as the elements in the table above, is analysed separately.

Systemic problems cannot be identified directly because systems involve several characteristics that make them counter-intuitive. The following features are important to take into account in particular [START_REF] Sterman | Business dynamics: Systems thinking and modeling for a complex world[END_REF]):

-Systems are tightly coupled, i.e. the actors interact with another and with the outside world. Feedback is a central characteristic of systems: decisions of the actors trigger others to act, which again alters the next decisions of the original actors.

-The central position of feedback makes systems history-dependent: taking one path precludes many others.

-Systems are non-linear, i.e. effect is not proportional to cause. It is also difficult to identify immediate cause-effect relationshipsinstead of that cause and effect are often distant in space and time.

-Systems are constantly changing at many scales that interact. They are also self-organizing and adapting: small, random perturbations are often amplified by feedback, and capabilities of actors change as a result of learning.

-Systems are policy-resistant: the complexity makes it difficult to understand the system and as a result many seemingly obvious solutions to problems fail. Time delays in feedback often mean that long-run response of the system is different from the short-run.

System dynamics (e.g. [START_REF] Sterman | Business dynamics: Systems thinking and modeling for a complex world[END_REF]) is a methodology that focuses on the underlying feedback structure of a system. System dynamics models incorporate causal connections between system elements that can be mapped using causal loop diagrams. Simulation modelling is used to understand how the interaction of various feedback loops creates certain dynamic behaviour (i.e. change over time in variables of interest). Even though the role of simulation is emphasized in the system dynamics methodology, even qualitative diagrams that show the interactions and feedback loops in a system can increase understanding of a system.

Case context and methodology

In our empirical analysis the focus is in service innovations in the area of environment and sustainability. According to some recent studies (e.g. Djellal andGallouj 2010, 2013) the technologist perspective dominates typically the discussion of sustainable innovations although the role of integrative services is emerging especially in that area.

In this paper the focus is in analyzing the complex combinatory innovations. By that we mean that they all encompasses both technological and non-technological ingredients and are developed in the collaboration between multiple actors. As regards their targets they are aiming to tackle with prominent societal challenges, among which the environmental sustainability is primary. Specific service innovation we are interested in is Environmental data platform that aims to be a comprehensive platform to support continuous data gathering and real-time environmental monitoring, analysis and reporting.

Innovation has been developed in research and development program built on public-private innovation network that aim to promote systemic change in the field of environmental measurement in Finland. The program is carried out by a Strategic Centre for Science, Technology and Innovationa new Finnish innovation policy instrument. The centres (abbreviated "SHOK") operate in various industrial and service sectors as limited companies and are built on public-private partnerships. SHOKs can be characterized as public and private innovation networks generating complex and architectural services and innovations [START_REF] Djellal | How public-private innovation networks in services (ServPPINs) differ from other innovation networks: what lesson for theory?[END_REF]).

We have applied the case study methodology and qualitative approach in our study.

The main method in data gathering in our study was face-to-face interviews (30 in total). The interviews were gathered between February and June 2013. We applied snowball sampling in the identification of interviewees: the first respondents were Managing Director of Cleen Ltd and the Program Managers. Based on their suggestions, we thereafter selected the other interviewees among the members of the program consortiums. The final sample represented actors in the area of sustainable energy in a versatile way. It consisted of representatives of private companies (e.g. energy companies, companies developing environmental and industrial measurement), and universities and other public research organizations. All interviewees were managers or experts in their organizations and had a significant role in the research programs. Typically they were acting as a work package leaders or leading the service demonstration development.

For the data gathering we applied a semi-structured interview method: the topics were decided beforehand but within them the respondents were given a great deal of freedom [START_REF] Bryman | Business Research Methods[END_REF]. The main topics focused on the manifestations of new innovative solutions within the programs, factors that promote or slow down their generalization, impacts of the innovations and their evaluation. The duration of the interviews ranged from one and half to three hours. All interviews were recorded and transcribed. Documentary data on the general development of energy technologies and markets were used as supplementary material.

In the analysis and interpretation of empirical data we applied the modified multicriteria and system dynamic perspectives. We started the analysis by studying how the environmental data platform is impacting in a short and long term from the perspective of different worlds of services. In the analysis we are reflecting impacts both from the traditional and modern perspectives. Thereafter we moved to system dynamics modelling that aims to increase understanding of the dynamics in the system that results from interactions between the parts of the systemincluding reinforcing and balancing feedback loops.

Research results

Environmental data platform (table 2) is from an industrial perspective a prototype platform to gather and share environmental data. As a short term output it integrates real-time data sources (e.g. measured data of water quality and satellite data concerning environment and atmosphere) and provides visualized maps based on the data. In a long-term the goal is to integrate multiple data sources in it and provide "cloud-based comprehensive solution" to produce and share environmental data. Cloud-based solution would make the access to big data possible. In addition the architecture for real-time monitoring, analyzing and reporting will be created to improve the quality and reliability of environmental information, weather forecasts and warnings. New architecture helps in developing new end-user applications and thus accelerates business start-ups generation. Our respondents highlighted that services are in the central role in the development of comprehensive solution and new information architecture.

In the market world the main characteristic of the innovation is economically free access to the multiple data sources and especially to public sectors data. According to our interviewees free access to data is considered to be an important social goal and also a starting point for the development of data platform. In a long term goal is in opening new markets based on environmental analysis and in creation of new export possibilities.

Preferences and valuation principles in the relational world highlight the interaction between multiple actors and a role of end users is the development and use of service. Central innovative aspect here is the connectivity via one mediator to multiple data sources. As an output goal trust in the public-private innovation networks is enhanced. From the performance viewpoint enhances actors" connectivity and consolidates the networks. Long-term goal is to integrate citizens to the data provision, to better take into account the specific users" needs and requirements and hence provide personalized environmental data. That affects in a long term to users ability to be integrated part of the environmental data generation. Like our interviewees highlighted that development removers the clear distinction between the production and use of data: citizens are becoming data producers. That has been considered as a prerequisite for a systemic change in the sector.

From the perspective of responsible world overall sustainability is highlighted as a central value in development of new solution. The other value based aspects highlighted are transparency and the citizens" equal rights to participate to the data provision. Innovative aspect relates to the open and equal access to public sector data. As a short term goal platform enhances transparency, availability and multifaceted us of public data. As a long-term goal respondents have considered the possibilities to apply new end-user applications for example to the game and school worlds to support the environmental education and thus increase the awareness of environmental issues from the early age. From the performance viewpoint that may increase responsibility as a value in decision making in individual, firm and policy level. Finally in the world of reputation innovation is analyzed from the perspective of brand and image effect. From a short and long term the aim is in analyzing how the innovation impact to the attractiveness of different actors. The aspects concerning the image and brand needs to be analyzed from the perspective of specific actors and are thus analyzed in details in the following sub-chapter.

To summarize the central findings from the perspective of different type of evaluation criteria following aspects have been recognized. According to our interviews services have important role in renewing the environment sector. To solve the most urgent societal problems, like sustainability, there is need to develop technologies and services as systemic wholes instead of individual technologies or services. The emergence of comprehensive service solutions in renewing the environment and energy technologies can be perceived by traditional measures. However the focus from the perspective of industrial and financial world is on technical characteristics of the concepts and solutions, not so much in their social and systemic nature.

To capture the interactive and social nature of service development as well as its" interlinks to the social goals and system level changes the other criteria are needed.

Like our example show, relational and responsible worlds are particularly important to make these aspects visible. Like our respondents highlighted the changing roles of data users and producers ("from user to producer") plays a central role in the renewal and a system level change in a sector. That can be perceived only from the perspective of relational world. In addition our example shows that impacts generated in the different worlds are often interdependent and complementary to each other. Some factors in relational and responsible worlds can be seen as a prerequisite to effects generated from the viewpoint of technical and financial worlds. For example for the development of environmental data platform the transparency and open access to public sector data is seen as a precondition. However, the dynamic nature and interlinkages between different justification criteria are not comprehensible for readers because the analytical table remains. It does not show how the different impact criteria are mutually interlinked and may reinforce or contradict each other. This perspective in our framework is considered in the analysis carried out with the system dynamic modelling tools.

From the systems perspective (Figure 2) free access to data increases open and equal access to data, which creates new connections between actors. This in turn increases the ability to process multiple data sources quickly and efficiently and creates new market openings and new end user applications. An increased number of end user applications increases people"s awareness of environmental issues, due to which new actors start producing data. These new actors then create more demand for transparency of data and political pressure to provide even more access to data.

(Reinforcing feedback R1 "new connections between actors"). Increasing free access to data also leads to new market openings because of the reduced costs of sharing and providing data (reinforcing feedback R2 "reduced costs"). As already noted, an increased awareness of environmental issues leads to citizens becoming active in producing data. This raises awareness even more (reinforcing feedback R3 "awareness raising"). An increased number of new actors producing data also leads to more data and personalized data being produced, which can lead to new market openings (reinforcing feedbacks R4 and R5: "amount of data" and "personalized data").

There are also balancing feedback loops in the system. Once the number of actors producing data grows, data quality may become an issue and can decrease the ability to process multiple data sources efficiently (balancing feedback B1 "data quality"). However, a low data quality that creates a need for data verification can lead to new criteria for data gathering, which then improves the quality of data (balancing feedback B2: "new criteria for data gathering"). The development of an environmental data platform can also be started in order to improve the ability to process multiple data sources (balancing feedback B3 "platform development").

Concluding remarks

The purpose of this paper is to study the challenge of the evaluation in the context of the services. Because of their specific natureespecially immaterial and interactive dimensionthe traditional evaluation methods and measures are not able to capture neither the diversity of the innovations nor the dynamic nature and multifaceted dimensions of performance in the sector. This paper aims to contribute to the need for a more diverse and dynamic evaluation approach. We focus on the context of service innovation in the area of environmental measurement in which we develop further multi-criteria and system dynamic perspectives. Multi-criteria framework describes the impacts of new sustainable services and system perspective analyses dynamic impacts of service innovation.

As a result we identified that services have an important role in renewing the services in environmental measurement. To solve the most urgent societal problems, like sustainability, there is need to develop technologies and services as systemic wholes instead of individual technologies or services. Furthermore the collaborative interaction between societal fields and multiple actors (including citizens) is extremely important.

The emergence of new technologies and new solutions in environmental measurement can be perceived with traditional measures. However the focus from the perspective of industrial and financial world is in technical characteristics of the concepts and solutions. From this traditional perspective neither the role of new solutions in renewing sector (social and value based aspects) nor the importance of interactivity in developing new solutions ca be captured. To perceive and make visible the societal goals of the new solutions as well as their interactive nature relational and responsible worlds are particularly important. In addition relational world also focuses for example to the changing role of end users ("from user to producer"). That can be seen as an enabling factor for the systemic change in the sector and thus a central goal in renewing the sector.

Our analysis also shows that impacts generated in the different worlds are often interdependent and complementary to each other. Some factors in relational and responsible worlds can be seen as a prerequisite to effects generated from the viewpoint of technical and financial worlds. For example cornerstone and reinforcing feedback in developing new service innovations for environmental measurement relates to the free access of data (the perspective of market world). To attain it political decisions to open of public sector data sources (perspective of responsible world) are required. That development facilitates the equal access to the data for multiple types of actors and thus enhances the creation of new connections and provides the new type of collaboration between actors (relational world). This development supports the emergence of new market opening and the development of new end user applications. Like example shows, the relational and responsible aspects are needed to generate long-term technological and economic impacts.

The complex dynamics, interrelationships and multiple feedbacks between the different impact criteria remain invisible without systemic perspective. By integrating multicriteria and system dynamic perspectives we aim to offer a dynamic alternative to create understanding of development and impacts of service solutions.

Regarding to the further studies more studies would be useful to test the generalizability of our results. Furthermore to go deeper to the dynamic relations studying the role (and impacts) of different actors in service ecosystem could be the next step. In addition generating indicators based on these findings would be both interesting and useful.

Figure 1 .

 1 Figure 1. Innovation and performance gap in measurement of services (Source Djellal & Gallouj 2010)

Figure 2 .

 2 Figure 2. Systems perspective to environmental data platform

Table 1 .

 1 Different justification criteria to evaluate outputs and outcomes of services (modified from[START_REF] Djellal | The Innovation gap and the performance gap in the service economies: a problem for public policy[END_REF], 2013)

	Worlds	Industrial	and	Market	and	Relational and	Responsible word	Reputational
			technical world		financial world	domestic word		world
	Innovation		Central aspects of the innovation from the perspective of each world
	Output	(di-
	rect,	short
	term)
	Performance related Outcome (indirect, long	Volumes, flows and technical operations	Value and monetary and financial trans-actions	Interpersonal and organiza-tional relations, trust, quality of	Values like sustaina-ble development, responsibility, equal treatment, fairness and justice	Brand, image
	term)						relationship

Table 2 .

 2 A multi-criteria framework to analyse the impacts of environmental data platform

		Industrial and technological	Market and financial	Relational	Responsible	Reputation
	Innovation/Input	A prototype platform for environ-	Free access to public sector data	Connectivity via one mediator	Open and equal access to public	Image as an innovation to
		mental data gathering and sharing		to multiple data sources and	sector data	enhance sustainability
		(integrating real-time data sources &		end-users
		data storage)
	Output (direct, short	Varied measured and satellite data	Economical of free access to	New connections and actor	Transparency of public data; Easy	Short term image
	term)	concerning environment and atmos-	multiple environmental data	networks created (via new	access
		phere (e.g Weather radar visualised	sources	solution)
		on the map)
	Performance related to	Ability to process increasing amount	Reduced cost of sharing data	Increased connectivity between	Increased transparency of public	Improvement/change in
	output	of environmental data more quickly		multiple actors	data	reputation and image
		and more effectively	Reduced cost of providing data
					Increased availability and better
					use of public data
	Outcome (indirect,	"Cloud-based comprehensive solu-	New market opening based on	Integrating citizens and citi-	Equality in sharing information	Long-term reputation and
	longterm)	tion" for producing and sharing	environmental monitoring	zens' requirements to the data	(data)	image
		environmental data		provision
			New opening export possibilities		Quality controlled data
		Architecture for real time environ-		"Users as a data providers"
		mental monitoring, analysing and		(Social innovation)	Platforms applied e.g. in educa-
		reporting, bid data			tion: environmental education and
				Personalised environmental	awareness
		New end-user applications created		data
		New start-ups crated; new jobs		Trust
	Performance related to	Improvements in weather forecasts,	Improvements in the generation	Increased usability of environ-	Increased awareness of environ-	Long-term improve-
	outcome	environmental information and	of various types of revenues	mental data /knowledge	mental issues	ment/change of reputation
		warnings	based on environmental data			and image
				Increased trust	Increased responsibility in deci-
		Increased quality and reliability of			sion making (individual, firm and
		environmental data			policy level)
		Increasing number of business start-
		ups based on environmental data;
		Increasing number of new jobs