The present invention relates to an integrated proc- ess for the control, centering and regulation of the camber of a metallic strip in process lines.

In a production line of metallic strips, one of the most important requisites consists in the possibility of keeping the strip "centered" with respect to the central line in the processing area. Obviously, the higher the centering, the higher the parameters such as the repeatability and accuracy of the processings will be, whereas other such as the wear and maintenance costs will be reduced. In other words, the quality of the final product and production cost depend to a large extent on the centering which can be obtained on the widest range of strips under processing.

For the above reasons, line producers, as also producers of the components relating thereto, have always paid great attention to the systems which govern the trajectory of the strip i.e. the development of monitoring and centering systems for correcting its position.

Trajectory defects of the strip, which can be found in practical cases, can be classified in two categories (or a mixture of the two): offset, i.e. side translations of the axis of the strip with respect to the centre of the line, and deviations caused by cambers, i.e. long- radius curvatures in the lying plane and radius orthogonal to the axis.

The latter defect can be considered as being the most dangerous from both a geometrical and more precisely metallurgical point of view.

From a geometrical point of view, in fact, correction means can translate the strip for centering its po- sition in various points of the line but the correction is generally limited to the transversal position of the strip (near the positioning sensor) . A curvature of the moving strip, on the other hand, causes a misalignment (even if remaining in the same plane as the strip) be- tween the axis of the line and the axis of the strip and, in the transients, between the vectors of the project rate and actual rate: as a result, the defect therefore propagates beyond the correction means. In practice, a snakering or meandering is formed which propagates along the whole line. This obviously causes errors in the processing (for example a longitudinal cut, deposition processes or rolling into coils) which can also significantly affect the quality of the end-product.

From a metallurgical point of view, the formation of a snakering inside ovens or in high-temperature areas of the strip can cause plasticizations affecting the ends of the strip which, in turn, can create undulations orthogonal to its plane. Excessive curvatures, together with drastic corrective interventions can cause the material to yield and, at times, cause defects such as excessive elongations at the edges or cracks which lead to the discarding of a part of the roll. It is interesting to note, in fact, that once formed and if not corrected with adequate means, cambers tend to make all downstream proc- esses critical .

The most widely-used centralizers which can be found distributed along a process line for strips and, for example, at the outlet of a thermal section, consist of one or more rolls assembled on frames capable of rotating (even if in a limited manner) , with respect to the main axes of the ingoing strip. The following types of centralizers can be distinguished, for the function they exert :

- purely proportional: i.e. suitable for moving the out- going branch of the strip with respect to the ingoing branch (offset corrections) , normally by means of a rotation β (see Figure la) of the roll around an axis parallel to the plane on which the ingoing branch of strip is lying (for example that described in the Paradine patent US3774831 or in US4322060) . This type is not capable of acting on the ingoing branch and the maximum correction is limited to the mechanical run of the centralizer itself in relation to the diameter of the roll (i.e. if the system is composed of two or more rolls, the distance be- tween the interaxes) . It should be noted that the system remains for the most part unvaried, as effects, with respect to different arrangements of the rotation pins provided they are lying on a plane orthogonal to the ingoing strip and passing through the centre of the line. This arrangement allows an effective opposing action against offset faults to be rapidly and safely established. The correction takes place only on the outgoing strip and, if the axis coincides with that of the centre line, its entity can be calculated, in quite a simple way, by taking into account the diameter of the roll, the possible in- teraxis (if the system is composed of more than one roll) , the winding angle and sine of the β deflection angle. In this way, it is therefore possible to introduce automatic control methods of the strip, but limited to the outgoing branch and correction of offset errors alone .

- purely integral: i.e. suitable for creating a steering angle γ (see Figure lb) of the roll with respect to an axis perpendicular to the plane of the ingoing branch of the strip and arranged on the centre of the line; this type causes a strong asymmetry of the pull of the strip between the motor-side edge and the operator-side edge of the line. In the case of strips having a reduced thickness or made of a material having a low resistance (in particular for branches of strip coming from thermal treatment sections) , a yielding of the material can be caused with consequent possible damage or deterioration of the qualitative characteristics. A typical example of the group of purely integral centralizers is illustrated in figure 6 of the patent of Somitomo Ind. JP7001022 (Ni- shino Ken) which shows the corrective effect of the roll for a camber present on the branch upstream (ingoing) . It should be pointed out that the intervention is limited to the ingoing branch and that it can cause a consistent offset on the outgoing branch due to the "steered" orientation of the outgoing branch or, in some cases, abnormal tensions on the edges of the strip. This offset must, in turn, be corrected by a proportional system situated on this branch, adding further components to the line, i.e. complicating it. It should also be noted that the corrective effect of the "steering" imposed by the integral centering roll is not immediate and attempts at automating the control system have been opposed by oscillation effects of the position of the strip. At times, these ef- fects are not stabilized and therefore require a reduc- tion in the return of the centering regulator, thus jeopardizing its effect.

- proportional-integral : these are a combination of the two types indicated above and are those most commonly used as they are capable of effecting corrections on both branches (ingoing and outgoing) .

From what has been previously specified with respect to "pure" correction systems, it is evident that each arrangement of the pins, with axes oriented differently from what is indicated, creates mixed effects, i.e. a total behaviour which can be divided into a pure proportional correction marked by an effective β) and an integral correction (marked by a γ) .

Considerations based on cost or simplicity aspects of the mechanical devices and control systems substantially reduce the choice of possible applicable configurations. In practice, that which is most commonly applied is obtained by means of a fixed frame and a mobile frame on which the rolls are housed (1, 2 or more rolls) . The mobile frame generates a rotation trajectory around an axis tilted by an angle a with respect to the plane of the ingoing branch so as to have a component of the rotation vector parallel to the plane of the ingoing branch (see figure lc) combined with a component perpendicular to the plane itself. The mixing of the two effects (pro- portional and integral) is therefore commonly obtained by tilting the frames by the angle a (as shown in Figure lc) in a fixed mode. It should be pointed out that practically all the systems currently in use do not envisage the continuous modification of the angle which is normally defined in the project phase and blocked during the line commissioning. Consequently, the integral action cannot be modulated in relation to the type of strip, the residual tensioning conditions or form and nature of the material.

The selection of a is, therefore, a compromise selected by the line designer and is not always suitable for the conditions of the inlet material (for example limited a values produce modest correction possibilities upstream, high a values produce excessive tensions/deformations in the material, with possible stretchings of an edge or breakage of the material itself) .

An example of this configuration is indicated in the patent Posco KR20010042781 (Ju Gap Sik) where mention is made of the inclination with respect to the progress of the ingoing strip.

A general objective of the present invention is to solve the drawbacks mentioned above of the known art in an extremely simple, economical, and particularly func- tional way.

Another objective is to provide a centering process which combines all the advantages of the three known types, attempting to reduce the drawbacks to the minimum.

A further objective is to provide a process which, by effecting an optimal centering, controls and regulates the camber of the strip in all types of strip process lines, in the presence of various kinds of defects.

In view of the above objectives, according to the present invention, an integrated control, centering and regulation process has been conceived, of the camber of the metallic strip in process lines having the characteristics specified in the enclosed claims.

The structural and functional characteristics of the present invention and its advantages with respect to the known art will appear more evident from the following description, referring to the enclosed drawings, which also show an embodiment of an integrated control, centering and regulation process of the camber of the metallic strip in process lines obtained according to the same invention.

More specifically, in the drawings:

figure la is a schematic plan view from above, which shows a pure proportional centering device of the known art ; figure lb is a schematic plan view from above, which shows a pure integral centering device of the known art ;

figure lc is a schematic plan view from above, which shows a combined proportional -integral centering device of the known art;

figure 2 is a schematic block arrangement of an integrated control, centering and regulation process of the camber of the metal strip in process lines obtained according to the invention.

An integrated process for the control, centering and regulation of the camber of the metallic strip in process lines according to the invention, essentially consists, as a whole, of three components: a measuring group of the position of a strip 14 and camber, which can be schematized in 11, a group of centering rolls (for example one or more rolls positioned on a frame) schematized in 12, and a management unit, which acquires data, drives active elements and registers the status of the line, schema- tized in 13.

More specifically, in the control system 11, the measuring group of the position of the strip consists of a form and position analyzer of the strip 14, capable of defining the geometrical status of the strip 14, moment by moment, in order to be able to detect the onset of possible defects and take the necessary corrective measurements .

In a non-limiting embodiment, the form analyzer acts as monitoring system which comprises optical methods in which the strip 14 reveals its position by intercepting part of a light emitted by a source. The source is situated in front of a detector, subject to geometrical constraints of the line, in order to obtain its curvature. The presence is advantageously required of a minimum of two of these optical monitoring systems, such as those schematized in fig. 2 and indicated with 15, 16 and 17. Sensors 15 of the inductive or capacitive type schematically shown in fig. 2, can also be used.

More innovative and less traditional systems, based, for example, on "image processing" can also be effective. In this case, the basis is represented by image recognition, as shown in figure 2, using at least one video camera 16 or 17 and an algorithm capable of extracting the geometrical information from the acquired frames. Alter- natively, apparatuses can be used equipped with traversable or fixed laser devices. There is no necessary constraint for the positioning of the form detection systems. As the feed-back times for the reduction in the camber defect are relatively long, the selection of the positioning of the acquisition systems of the form of the strip (either first that 17 or after that 16 of a roll control system 18, or in both positions) only has limited implications on the algorithm used for the control.

A group of centering rolls 12, which determines the mechanical control of the position and curvature of the strip 14, is envisaged according to the invention in association with this first group 11. For this purpose, in an embodiment, rolls 19 are envisaged, assembled on a double frame, fixed 20 and movable 21. Between the frames, the reference frame 20, fixed with respect to the line, and the movable frame 21 carrying the rolls 19 which determines the control, active and passive means are present, such as hydraulic or electromagnetic pistons 22, 23, ball bearings (not shown), etc.. These means are capable of guaranteeing the motion of the steering frame by simultaneously, autonomously and continuously varying the traditional angles a and β which determine, as mentioned in the premises, the integral and proportional action .

An integral part of the control system, relating to hot lines where the strip 14 passes through an oven 24 and leaves the same, consists of a set of flow-regulating valves 25 of a cooling fluid capable of operating on the cooling rate of the strip 14 in a differentiated way with respect to its width (between the operator-side edge and the motor-side edge) . The integral mechanical control (by introducing non-constant stress on the width) therefore allows a differentiated operation on the strip 14 at the outlet of the cooling section 26, by selectively and de- liberately "stretching" only one edge of the strip 14. In practice, selective deformations are introduced, calculated for (partially) recuperating possible metallurgical or geometrical defects and of residual tensioning (preexisting and/or induced by the present processing cycle) capable of significantly modifying the qualitative state of the final product.

In the system of the present invention, an electronic control centre 13 is envisaged, which is the core of the system. The following functions are exerted therein: ac- quisition of the general data in 31 of the strip 14 being treated; reception of the offset data in 32 and curvature data in 33 obtained from the system 11; calculation of the corrective interventions and management of the control rolls of the group 12 (indicated as 34 for the in- tervention on β - proportional - and as 35 for the modifications in a - mixed integral/proportional) and communication in 36 to an automation system of the line 37 of information relating to the strip being treated. The algorithm, in particular, is based on the evaluation of the offset 32 and curvature 33 (observed by the monitoring system 11) to define the variation in real time of the proportional angles β and integral angles a to be implemented on the control cylinders 19. The algorithm used by the controller has a form of the following type:

for the correction of the proportional portion in β:

Up = Kp * Ep

wherein Up is the intervention to be effected on β for the correction, Ep expresses the positioning error of the strip (as revealed by the sensors) and Kp is a dimen- sional parameter which expresses the gain and translation to β of the offset reading.

Analogously, for the integral part in a

Ui = Ki * Ei

wherein Ui is the intervention to be effected on a for the correction, Ei expresses the camber error of the strip (as revealed by the sensors) and Ki is a dimensional parameter which englobes the gain and translation to a of the curvature parameters revealed.

In practice, for a given positioning error Ep = e, a Up is generated on β, equal to the entire total correction predicted, i.e.:

Up = e * Kp

Correspondingly, there is a camber error Ei = e' with which the integral correction (steering γ) must be calcu- lated, which is calculated and established through the present tilt a and β the gain must be regulated to be lower than 1 (complete correction of the camber) using, for example, the "Ziegler-Nichols" method, 50% of the total correction intervention is adopted, i.e.:

Ui = e' * Ki/2

The regulator, once the integral correction has been effected (by correcting the angle α) , waits for the "flight time" calculated in relation to the distance of the area at the maximum temperature in the oven and rate, after which it re-analyzes the camber by comparing the reading obtained with the expected value (50% of the initial value) .

At this point, the regulator effects a recalculation based on the new parameters (present β, a and camber er- ror, residual Ei) and recycles determining the new value of Ui (intervention on a) .

In hot lines, a further set of signals indicated with 38 can be used for selectively modifying the parti- alization of the cooling fluid in the areas of the strip 14, typically three areas (outer operator side, central and outer motor side) . This action is preferably obtained by modifying the ejection flow-rate of the cooling fluids insufflated in 39 on the three areas of the cooling section 26.

As already indicated, the algorithm must take into account the position of the sensors and centering device with respect to the area with the highest temperature in the oven 24 (in the case of the centering device at the oven exit) or the length of the branch of entry free strip (in the generic case of a centering device operating in a cold area) , but the most significant aspect of the calculation consists in the graduality of the intervention: an instantaneous action and complete correction on the part of the centering roll would exert excessive stress on the edges of the strip in addition to an unstable and divergent response on its trajectory. It should be noted that, from an energy point of view, the integral action acts by increasing the potential energy of the system for a quantity proportion to the elastic modulus of the material multiplied by the square of the deformation imposed, it is therefore extremely sensitive to differential variations (between the edges) in the trajectory. From a dynamic point of view, the strip reaches the new condition of minimum energy by passing, without slid- ing, on the roll, wherein, with the same steering angle γ the deformation ε and tension σ on the edges of the strip deriving from the stress generated by the "pulling" difference between the two edges are inversely proportional to the length of the free span of the ingoing branch.

The response times of a system of this type to an "integral" correction are not instantaneous but the shift (for a steering angle) continues to grow (hence the term "integral") until the angle γ is reversely modified.

It is evident that this type of intervention (in particular for oven outlet centering devices) can be unstable, rebounding between levels which are energetically similar but in opposite positions with respect to the line centre.

In practice, the strategy recommended herein con- sists in establishing an integral γ correction lower than what is necessary for totally eliminating the camber defect of the ingoing strip for thermal lines or position of the ingoing strip for cold branches giving the system the possibility of perfectly correcting the outgoing po- sition thanks to the so-called "proportional" action (β rotation) . The total correction of the camber can be obtained by means of a series of consecutive and cumulative interventions also acting on the cooling system. In this way, the overall correction time is compatible with the passage time of cambers already present or induced by the thermal cycle, making their correction possible. In order to avoid the onset of subsidence or deformations which could be dangerous for the product, in addition to the dynamic parameters, the entity of each intervention is also calculated on the basis of metallurgic considera- tions .

An alternative control method consists in the use, initially, of pre-established corrective parameters, inferred from the geometrical and compositional character- istics of the strip. These parameters are then optimized during the process, by comparing the actual and expected behaviour. Methods of this type can be used for both running the control rolls alone (i.e. in a cold process line) and also in more complex systems such as, for exam- pie those in which, in addition to rolls, there are also differentiated cooling means (modulating the flow of the cooling fluid) . As far as the feedback signal on these thermal systems is concerned, the algorithm is based on the fact that greater cooling gradients and a consequent higher thermal contraction of the fibres involved, correspond to different flow-rates or severe cooling conditions (if different cooling systems are used, such as, for example, mist or nebulized air) of the cooling fluid. The result is that, when the cooling action is increased, an increase in tension is obtained in the oven 24 with a consequent extension of the fibres. The correlation between cooling gradient and fibre elongation can be calculated analytically or with models with respect to the finished elements. The ultimately most complex charac- terization of the cooling is simulated by means of calcu- lation models with respect to the finished elements or finished and refined differences, in order to consider the specific characteristics of the line, by adjustments in the commissioning phase.

Important but less innovative functions for this control centre 13 consist of interconnections with the computer and informative system of the steelworks 37 for the acquisition of physical and chemical parameters in 31 of the roll under processing and the transfer, at the outlet, of the descriptive parameters of the processing effected in 36, possibly equipped with the analytical calculation of the shape defects. A direct interexchange function of data with the treatment oven 24 and the quenching section (non represented) can also be imple- mented.

It should be pointed out, in particular, that, in a cold line section (which does not include thermal sections) , the centering system is equipped with proportional action plus integral action (determined by the means 22 and 23), the latter adjustable according to the feedback signals coming from the main sensor 15 of the position of the strip 14 (normally positioned downstream of the centering rolls 12) , from the position sensor of the frame (linear transducer normally used in common cen- tering devices) and, when possible, from additional posi- tion sensors 16 and 17 situated so as to allow the calculation of the camber of the strip 14, by means of specific electronic equipment 40 or line automation 41. The integral action is therefore regulated in relation to the camber measured and characteristics of the strip (thickness, width, and yield point of the material) 31.

In a line section which comprises thermal sections 24, 26, the correction system is typically situated at the outlet of the cooling section 26 of a thermal treat- ment oven 24. The roll centering system 12 has proportional action (in 22) plus integral action (in 23) , the latter adjustable in relation to the feedback signals 32 coming from the position sensor of the main strip 15 (normally positioned downstream of the centering roll group) , from the position sensor of the frame and from the additional position sensors and/or planarity and camber measurers (for example 16 and/or 17) , arranged so as to allow the calculation of the camber of the strip by means of specific electronics 40 or line automation 41.

The integral action is regulated (in 40) in relation to the camber measured and characteristics of the strip (thickness, width, yield point of the material at the operating temperature of the oven, provided in 31) to obtain, in addition to the proportional action immediately operating in the exit branch following the centering movement, a correction of the form of the ingoing branch. With suitable expedients (for example, by avoiding the introduction of deflections around rolls, which would homogenize the load) , it is possible to extend the effect of the differential stress induced by the steering as far as the inside of the oven 24. In this way, it is possible to exploit the plastic characteristics of the high- temperature metal by correcting the defect directly inside the oven 24. From what has just been said, it is evident that this effect can be further improved with a suitable control of the cooling unit 26. By being able to operate with different cooling severity profiles (longitudinally and transversally with respect to the strip) it is therefore possible to further homogenize the stress condition inside the oven 24 in order to recuperate, at least partially, the camber defect (whether it be preexisting or generated by the same thermal treatment) .

An example is proposed hereunder of the functioning principle of the embodiment described above, referring to the previous figure 2.

In this functioning the starting situation is:

the centering device is equipped with a fixed frame 20 and a mobile frame 21 on which the rolls 19 (1, 2 or more rolls) are housed, the mobile frame. 21 generates a trajectory (rotation around an axis B of Fig. la or rota- tion around an instantaneous rotational axis A of Fig. lc, if the motion is obtained with other mechanisms) ;

the centering device has a tilt angle (a) of the rotation axis (A of Fig. lc) with respect to the plane on which the ingoing branch lies (congruent with the angle of the plane on which the rotation is effected of the mobile frame with respect to the plane perpendicular to the inlet branch of the strip) ;

the strip 14 has a shift equal to X cm with respect to the centre line on the position sensor 15 and a camber with curve radius of Y m (as observed by the sensors 16 and/or 17) determining a long and a short side.

A first action of the centering device is therefore effected (corresponding to the behaviour of a classical proportional integral centering device) as follows:

on the basis of the measurements effected by the measuring system 11 (15, 16 and/or 17) the control unit 13 calculates the first proportional corrections and transmits the shift to be effected as angle β, to the ac- tuator 22;

the rotation β of the frame 21 (around the rotation axis B of Fig. la) generates a proportional correction (with a shift calculated as X + ε cm wherein ε is a further correction effected to take into account the shift due to the camber defect Y m of the outlet branch of the strip) which centres the strip with respect to the sensor 15. The rotation β is always subjected to continuous regulation based on the use of the position feedback of the strip leaving the centering device (sensor 15) in or- der to maintain the position of the outgoing strip within the position tolerance range (for ex. ± 5 mm) ;

the strip 14 tends to reposition itself in central position (centre of line) on the sensor 15 at the outlet of the centering device 12 ,- - as a result of the tilt angle a of the centering device 12 (suitably calculated on the basis of the geometrical data of the plant) , an integral action (equivalent to a steering of the roll of an angle γ around the axis G of Fig. lb) starts contemporaneously with the propor- tional action, on the inlet branch of the strip 14, with a consequent increase in the "traction" on one of the two edges of the strip itself 14.

A second action of the centering device is also effected, according to the present invention, as follows:

- thanks to the measurement sensors of the camber (a non-limiting example can be one or more video camera (s) 16 and/or 17 or 2 or more sensors, in succession, of the type 15) the result of the action effected is measured by updating the geometrical situation of the strip; on the basis of the new situation, the integral action of the centering device 12 is modulated by- modifying the angle a through the actuator 23, by means of a control algorithm for calculating the optimal a, schematized in 42, of the inclination of the frame 20, in order to correct the position of the ingoing branch. In the calculation of the entity of the intervention, the algorithm in 42 also takes into consideration, in addition to the entity of the defect, the thickness and the width of the strip and the yield point of the material;

the integral intervention effected is dosed so as to operate on the inlet branch with a quantity which is lower than that required for the total recovery of the form defect. In this phase, the system 13 reanalyzes the geometrical status (position and camber) of the strip 14 (through the sensors 11) and compares the actual effects with what has been predicted by the model. In the case of discrepancies, if the camber and the position of the strip are within an admitted tolerance range, the regulation obtained (angle a) is maintained, otherwise the system 13 modifies the calculation parameters in order to fall within the expected tolerance.

The third action of the centering device is also ef- fected according to the present invention, as follows: thanks to the measurement sensors of the camber (a non- limiting example can be one or more video camera (s) 16 and/or 17 or 2 or more sensors, in succession, of the type 15) the result of the action effected is measured by updating the geometrical situation of the strip;

if the centering device is downstream of a thermal section (24 and 26) , the algorithm schematized in 43, calculates the optimal situation for transferring the differential load (between the edges) , generated by the integral fraction of the intervention effected, on the hot material (and therefore plastic) present in the oven 24. To do this, the algorithm 43 acts in the cooler 26 by modulating the streams passing through the nozzles 25 by means of the signals 38, therefore aiming at eliminating the causes which have generated the camber defect.

Following the modifications applied, the system effects another correction cycle using the new calculation parameters. In practice, the cycle starts from the first action listed herein and is reiterated until the conclusion of the strip being processed.

The present invention consequently consists of an integrated innovative system for centering and/or control- ling/regulating the camber of the strip, which can be optimized and adapted to practically all strip process lines, to all defects which can be encountered in normal production routines and to all types of strip processed in a steelworks .

The invention consists of a centering device (with one or more rolls) with a proportional action (shifting of the exit branch with respect to the inlet branch) and integral (progressive action during the steering time of the roll with respect to the ingoing strip advance direction) of an on-line measuring system of the camber and an electronic control system capable of regulating the quantity of integral action of the centering system in relation to the curve angle detected by the camber measurer and on the basis of the physical characteristics of the material (coming from the line automation system) .

The modulation of the integral effect is effected by means of hydraulic or electro-mechanical actuators capable of modifying the tilt angle a of the rotation axis of the roll(s) so as to be able to vary the ratio between the integral action and proportional action, by adjusting the line response to the actual conditions of the strip.

The invention is characterized in that, in order to be able to express its specific application elasticity, it must be capable of simultaneously controlling both the angle β and the angle a (and consequently also γ) through a calculation algorithm capable of dosing its intervention in extension and time.

A further characteristic of the invention, in lines equipped with a thermal treatment oven, consists in the application of the calculation algorithm for a contemporaneous and simultaneous control of the driving roll (by exploiting the "traction" asymmetry induced by γ) and cooling step at the oven exit (through dosage valves of the cooling flow, which control the cooling allowing more or less time for establishing the plastic deformation) . By using this combined system, it is therefore possible to effect a controlled deformation of the strip which can be used for attenuating the camber avoiding the formation of metallurgical defects induced by the excessive deformation of the edges (with an improvement in the quality conditions of the strip) .

With respect to the reduction in the entity of the camber, results have shown an improvement in the defects present in particular when the centering device is downstream of a thermal section. The certainty of the improvement is due to the fact that, by trying when the ovens are switched off, the divergences in the parts of the line downstream increase in frequency. By using a angles over the calculated values, an excessive correction was obtained with a consequent unstable behaviour (oscillation between engine-side corrections and operator-side corrections) . Due to the serious operative limitations, the result is particularly valid.

The objective mentioned in the preamble of the description has therefore been achieved.

The forms of the structure for the embodiment of the invention, as also the material and assembly modes, can naturally differ from those shown for purely illustrative and non-limiting purposes in the drawings.

The protection scope of the invention is therefore delimited by the enclosed claims.