TECHNICAL FIELD

The present invention relates to a system and a method for controlling a flow regulating valve in a filling machine for filling composite packages with a pourable food product .

BACKGROUND ART

As is known, many liquid or pourable food products , such as fruit j uice , UHT (ultra-high-temperature treated) milk, wine , tomato sauce , etc . , are distributed and marketed in composite packages made of a multilayer composite packaging material .

A typical example is the parallelepiped-shaped package for pourable food products known as Tetra Brik Aseptic™, which is made by sealing and folding a laminated strip packaging material . The packaging material has a multilayer structure comprising a carton and/or paper base layer, covered on both sides with layers of heat-seal plastic material , e . g . polyethylene . In the case of aseptic packages for long-storage products , the packaging material also comprises a layer of oxygen-barrier material , e . g . an aluminum foil , which is superimposed on a layer of heat-seal plastic material , and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product . Composite packages of this sort are normally produced within fully automatic filling (or, also denoted as, packaging) plants, which at least form the composite packages starting from a web of multilayer composite packaging material (wound from a reel) and fill the composite packages with the pourable food product.

A typical packaging plant comprises at least a filling machine, which forms the composite packages from the multilayer composite packaging material and fills the composite packages with the pourable food product. Additionally, packaging plants may also comprise downstream treatment equipment, receiving the composite packages from the filling machine and executing additional treatments on the composite packages; the downstream treatment equipment may for example comprise one or more of a buffer unit for temporarily buffering the composite packages; an application unit for applying e.g. straws on the composite packages; a grouping unit, e.g. a palletizer unit, for grouping a plurality of composite packages together in a storing unit (such as a pallet) .

With reference to Figure 1, a filling machine 1, sometimes also referred to as a packaging machine, is generally illustrated by way of example, being in particular a roll-fed filling machine used for filling liquid or pourable food products in multilayer composite packages 2.

Multilayer composite packaging material may comprise at least a layer of fibrous material, such as e.g. a paper or cardboard layer, and at least two layers of heat-seal plastic material , e . g . polyethylene , interposing the layer of fibrous material in between one another . One of these two layers of heat-seal plastic material defines an inner face of the composite packages 2 eventually contacting the pourable food product packaged within the same composite packages 2 .

Multilayer composite packaging material may also comprise a layer of gas- and light-barrier material , e . g . aluminum foil or ethylene vinyl alcohol (EVOH) film, in particular being arranged between one of the layers of the heat-seal plastic material and the layer of fibrous material . Preferentially, multilayer composite packaging material may also comprise a further layer of heat-seal plastic material being interposed between the layer of gas- and light-barrier material and the layer of fibrous material .

In particular, the multilayer composite packaging material is provided in the form of a web, in particular being wound up on a packaging material reel 3 , from which it is fed through the filling machine 1 in a web feeding direction A; a tube 4 is formed in the filling machine 1 from the web by producing a longitudinal sealing .

The liquid food product is fed into the tube 4 via a pipe 5 and a regulating valve 6 is used for regulating a flow of the liquid food product through the pipe 5 , reaching the tube 4 and filling the packages 2 . In particular, the regulating valve 6 couples the pipe 5 to a processing line 7 , which is configured to process ( in any known manner ) the liquid food product before its packaging ( the processing line 7 being also coupled to a tank or similar storage element 7 ' ) .

A lower end 8 of the tube 4 is fed into a folding device 9 , in which a transversal sealing is produced, the tube 4 being folded according to folding lines , also referred to as weakening lines , and then cut of f such that the composite packages 2 filled of the liquid food product are formed .

As shown in the same Figure 1 , the filling machine 1 can further comprise a sterili zation device S , e . g . a hydrogen peroxide bath or an LVEB ( Low-Voltage Electron Beam) station, for ensuring that the web is free from unwanted microorganisms , before the formation of the tube 4 .

The filling machine 1 further comprises a control unit 10 , which ( in addition to other functions , here not illustrated, for managing operation of the filling machine 1 ) is operatively coupled to the regulating valve 6 and configured to provide to the same regulating valve 6 a control signal S _c to modulate its position and thereby regulate the flow of liquid through the pipe 5 and into the tube 4 .

The control unit 10 for example includes a PLC ( Programmable Logic Controller ) or any suitable processing and computing unit , configured to execute a computer program designed to generate the above control signal S _c for the regulating valve 6 .

European patent application No . 21180243 filed on 18 / 06/2021 in the name of the present Applicant , di scloses an advantageous and ef fective solution for controlling the regulating valve 6 by the control unit 10 .

In particular, according to this solution, the filling machine 1 further compri ses a pressure sensor 14 for determining an inlet pressure measurement PIN of the liquid food product fed from the processing line 7 towards the pipe 5 in the same filling machine 1 . The determined inlet pressure measurement PIN is provided to the control unit 10 ( in a wired or wireless manner ) .

In particular, the pressure sensor 14 is arranged upstream of the regulating valve 6 , with respect to the direction of flow of the liquid food product towards the pipe 5 into the filling machine 1 .

The filling machine 1 further comprises a flow meter 16 and a level detector 18 .

The flow meter 16 determines an inlet product flow measurement FIN of the liquid food product fed from the processing line 7 to the filling machine 1 ; and the level detector 18 determines a product level measurement LM of the liquid food product that is fed from the pipe 5 into the tube 4 for filling of the packages 2 .

The determined product flow and level measurements FIN, LM are also provided to the control unit 10 (again, in a wired or wireless manner) .

In particular, the flow meter 16 is also arranged upstream of the regulating valve 6, with respect to the direction of flow of the liquid food product into the filling machine 1; and the level detector 18 is arranged in any suitable manner (e.g. in proximity of the tube 4) , so as to detect the level of fluid inside the same tube 4 (e.g. in a non-contact manner, via an electromagnetic- type measurement) .

The inlet pressure, product flow and product level measurements may be referred to as filling control parameters, based on which the control unit 10 controls the regulating valve 6 and generates the corresponding control signal S _c .

As disclosed in the above-mentioned patent application No. 21180243 (and as will also be detailed in the following) , the control unit 10 is configured to implement a flow proportional-integral-derivative (PID) module, receiving at its input a flow set point and the inlet product flow measurement FIN. An output of the flow PID module is indicative of a difference between a real flow, measured by means of the flow meter 16, and a desired flow, represented by the flow set point.

The control unit 10 is further configured to implement a flow feed-forward (FF) module, receiving at its input the inlet pressure measurement PIN from the pressure sensor 14 and the flow set point. The flow feed forward module generates a direct control output as a function of the flow set point and inlet pressure measurement PIN , using fluid-dynamic maps , which are a result of characteri zation of the regulating valve 6 in a test condition .

The outputs of the flow proportional-integral- derivative ( PID) module and the flow feed- forward module (both indicative of a position of the regulating valve 6 ) are combined in the control unit 10 , to generate the control signal S _c for the regulating valve 6 , which is therefore adj usted as a function of the combined outputs .

Use of the inlet pressure measurement PIN as an input of the flow feed forward control module is particularly advantageous , since it allows to adj ust the regulating valve 6 also based on real-time pressure measurements from the processing line 7 , so that the same regulating valve 6 can quickly adapt to pressure changes and fluctuations in the same processing line 7 . For instance , in case of a pressure drop in the processing line 7 , for example due to product line disturbances , the regulating valve 6 may be adj usted to compensate for this pressure drop .

A fast reaction to disturbances is therefore achieved and a stable operation for the filling machine 1 is provided, with reduced packaging material and product waste with respect to known control solutions (without the above discussed pressure sensor 14 ) .

The control unit 10 may further comprise an outer level PID control module , receiving at its inputs a level set point and the product level measurement LM and generating an output being indicative of a di f ference between a real product level , measured by means of the level detector 18 , and a desired level , represented by the level set point , that is used to provide the above discussed flow set point .

The control unit 10 implements in this case a double PID control loop for an even more accurate control action, based on the pressure and level measurements , in order to adj ust the flow through the regulating valve 6 .

The present Applicant has reali zed that , although advantageous , the above-discussed control solution may be improved .

In particular, the predetermined fluid-dynamic maps stored and used in the flow feed- forward control module are based on a characteri zation of the flow regulating valve 6 performed in a test rig ( i . e . with the same valve separated from the filling machine 1 ) , with a predefined liquid, in particular water, as the liquid flowing therethrough . Therefore , only a pressure drop on the regulating valve 6 and water viscosity properties may be taken into account in the model of the flow regulating valve 6 represented by the fluid-dynamic maps .

The present Applicant has reali zed that , when the filling machine 1 is supposed to handle products with higher viscosity, or in the presence of high pressure drop in the filling line due to the corresponding capacity/volume , the predetermined fluid-dynamic maps may need to be adj usted in that the regulating valve 6 may be initially set to a slightly of fset position . As a consequence , the control unit 10 may be slower to react to pressure disturbances ( in this case , mainly through the action of the flow PID control module , which, as is known, is slower to compensate for the same disturbances ) .

Even though known filling machines operate satis fyingly well , the present Applicant has therefore reali zed that a need is felt for an improved solution for controlling the related flow regulating valve , which adj usts the flow of the liquid food product filling the packages being formed .

DISCLOSURE OF INVENTION

It is therefore an obj ect of the present solution to provide an improved system and method for controlling the flow regulating valve , which allow to satis fy, at least in part , the above-mentioned need .

According to the present solution, a control method and system are therefore provided, as defined in the appended claims .

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings , in which :

- Figure 1 is a schematic representation of a known filling machine with a control unit for controlling a corresponding flow regulating valve ;

Figure 2 is a schematic block diagram of the control unit of the filling machine , according to a possible embodiment;

- Figures 3-5 show plots of quantities related to the operation of the control unit of Figure 2;

- Figure 6 is a flow chart of operations performed in the control unit of Figure 2;

- Figures 7A and 7B are schematic block diagrams of the control unit of the filling machine according to different embodiments; and

Figure 8 is a schematic block diagram of the control unit of the filling machine according to yet a different embodiment. BEST MODE FOR CARRYING OUT THE INVENTION

Figure 2 (where elements similar to those discussed above with reference to Figure 1 are denoted with the same references) shows a schematic block diagram of a control unit 10, for controlling a flow regulating valve 6 in a filling machine 1 (the same filling machine 1 being e.g. arranged and configured as previously disclosed with reference to Figure 1) .

The control unit 10 is configured to receive the above discussed filling control parameters, and in particular: the inlet pressure measurement, PIN, from the pressure sensor 14; and the inlet product flow measurement, FIN, from the flow meter 16.

The control unit 10 comprises: a flow feed-forward (FF) control module 20, receiving at its input the inlet pressure measurement PIN from the pressure sensor 14 and, moreover, a flow set point, FSP; and a flow feedback control module 22 , receiving at its input the same flow set point FSP and the inlet product flow measurement FIN from the flow meter 16 ( in the example being arranged and operating in parallel to the flow feedforward control module 20 ) .

The flow set point FSP is indicative of a target flow of product through the regulating valve 16 and into the pipe 5 towards the tube 4 . The flow set point FSP may be determined as a function of one or more of a start flow percentage , a nominal flow percentage , a machine speed flow percentage , a level set point and/or a product level ( as measured by level detector 18 ) .

In a possible embodiment , the flow feedback control module 22 is implemented by a proportional-integral- derivative ( FID) module , which generates at its output a first control contribution Ci, based on a di f ference between the inlet product flow measurement FIN measured by means of the flow meter 16 ( and representing a real flow) and the flow set point FSP ( representing a desired flow) , according to proportional , integrative and derivative control actions ( in any known manner, here not discussed in detail ) .

As shown in the same Figure 2 , the above di f ference between the inlet product flow measurement FIN and the flow set point FSP is performed in a summing block 23 , whose output represents the input of the flow feedback control module 22 .

The flow feed- forward control module 20 generates at its output a second control contribution C2 , as a function of the flow set point FSP and the inlet pressure measurement PIN , using the pre-set fluid-dynamic maps , which are a result of characteri zation of the flow regulating valve 6 in a test condition, as previously discussed .

The first and second control contributions Ci, C2 are combined ( in particular, added) in a summing block 24 , which generates at the output the control signal S _c for the flow regulating valve 6 of the filling machine 1 , for modulating its position ( the position of the valve ranging from a closed position to a fully open position) and thereby adj usting the flow of the liquid food product passing therethrough into the pipe 5 and then into the tube 4 for the formation of the filled packages 12 .

Figure 3 shows exemplary graphs related to the fluiddynamic maps implemented in the flow feed- forward control module 20 to determine the second control contribution C2 to the controlled position of the flow regulating valve 6 .

In the representation of Figure 3 , these graphs plot the flow ( in the y axis ) versus the valve position ( in the x axis ) , each graph referring to a di f ferent pressure value . In particular, given the value of the inlet pressure measurement PIN ( and thus the corresponding graph) and a flow set point FSP, the position of the flow regulating valve 6 (representing the above discussed second control contribution C2 by the feed-forward control module 20) can be found in the same corresponding graph.

Figure 4 shows a different representation for the same fluid-dynamic maps implemented in the flow feedforward control module 20, where a combination variable Cd, which is determined as a function of both flow and pressure values, is introduced:

Cd ⁼ <P(FIN>PIN)-

Again, given the values of the inlet pressure measurement PIN and the flow set point FSP (and thus a resulting value Cd' of the combination variable Cd) , the working point, i.e. the position of the flow regulating valve 6 according to the above discussed second control contribution C2, may be determined in the graph.

As previously discussed, the fluid-dynamic maps stored and implemented in the flow feed-forward control module 20 are pre-determined, e.g. obtained by a characterization of the flow regulating valve 6 (or being set by design) . Therefore, the same maps do not take into account different properties of the filling food product, e.g. in terms of its viscosity, and/or different operating conditions of the filling machine 1, e.g. in terms of a high volume/capacity, high pressure drop or high speed.

In this respect, Figure 5 shows different plots relating to the actual model of the flow regulating valve 6, in case of different products (denoted with Pl, P2, P3) and different operating conditions (e.g. a high-speed condition) of the filling machine. It is evident that the predetermined map stored in the flow feed-forward control module 20 may not be ideal in modelling the system in case of different products and/or different operating conditions, so that the position of the flow regulating valve 6 determined by the same flow feed-forward control module 20 may bring the system to a less than ideal initial working point or offset position.

As a consequence, the flow feedback control module 22, implemented by the proportional-integral-derivative (PID) module, has to compensate the offset position with the first control contribution Ci, determining a slower overall response by the control system.

In order to solve this issue, and according to an aspect of the present solution, the flow feed-forward control module 20 is configured to use the fluid dynamics maps in a dynamically adaptive manner, depending on the different operating characteristics of the filling machine 1 (and the related liquid food product) , thereby adapting to these different characteristics.

As will be detailed in the following, according to a possible embodiment, the flow feed-forward control module

20 is configured to dynamically adapt the pre-stored fluid dynamics maps to the above different characteristics of the filling machine and related product.

In more details, and with reference to Figure 6, according to an aspect of the present solution, a dynamic adaptation procedure is implemented in the control unit 10 during an adaptation time interval, e.g. when the filling machine 1 starts a new production (which may imply a different liquid food product and/or different operating parameters and conditions for the same filling machine 1) •

In a first step, denoted with 30, the control unit 10 may wait for stabilization of the filling operations.

As shown at step 31, operating signals indicative of the filling machine operation are then acquired for a defined period of time, in particular: the inlet product flow and pressure FIN, PIN (provided by the flow meter 16 and, respectively, the pressure sensor 14) ; the (actual) position of the flow regulating valve 6 (e.g. determined by the position of a corresponding driving servomotor) ; the value of the second control contribution C2 generated by the flow feed-forward control module 20.

The control unit 10 then process the received data, as shown at step 32, in order to adapt to the (possibly different) operating conditions of the filling machine 1 and related product; according to a possible embodiment, a dynamically adapted fluid-dynamic map is determined, to be implemented in the flow feed-forward control module 20, in order to adapt to the filling machine behaviour.

In particular, a theoretical pressure value is determined, corresponding to an inlet pressure that would be required as an input to the flow feed-forward module 20 in order to match the (actual) position of the flow regulating valve 6 with the value of the second control contribution C2 generated at the output of the same flow feed-forward control module 20.

In a possible embodiment, as shown starting from step 33, it is considered that the maps are expressed by means of a matrix, which represents a relation between the above discussed variable Cd and the position of the flow regulating valve 6 (see above Figure 4) , Cd being a function of inlet product pressure and flow.

From the determined position of the flow regulating valve 6, e.g. indirectly measured by means of a corresponding driving servomotor, the correspondent Cd value is therefore computed, by means of the reverse Cd- valve position matrix.

At step 34, from the computed Cd value, as a function of inlet product flow and pressure, the theoretical pressure value is obtained.

As shown at step 35, by computing the difference between the measured inlet product pressure PIN and this theoretical pressure, a delta pressure (AP) value is obtained .

This AP value is then used to determine the adjustment associated with the fluid dynamic maps used in the flow feed-forward module 20, in order to adapt to the different operating conditions of the filling machine 1, at step 36.

In more details, as shown at step 36' and as also shown schematically in Figure 7A, the computed AP value can be added to the measured inlet product pressure value PIN and the sum can be used as the input to the flow feedforward module 20, in order to identify the correct working point on the pre-stored fluid dynamic maps. This has the effect of actually "shifting" the standard, prestored, fluid dynamic map (and in particular the value of the variable Cd) of a "AC " quantity, based on the AP value, thereby obtaining the final map, adapted to the actual operating conditions of the filling machine 1 (e.g. to the liquid food product viscosity and/or the machine operating conditions, e.g. the corresponding speed) .

As shown at step 36", in a corresponding manner, instead of adding the AP value to the input of the flow feed-forward module 20, the control unit 10 may actually compute the "shifted" or dynamically adapted fluid dynamic maps, as a function of the above AC quantity (in other words, computing a different, "shifted", matrix representing the relation between the variable Cd and the position of the flow regulating valve 6 , by means of the above expression ( 1 ) considering the sum of the inlet product pressure PIN and the AP value ) .

As shown schematically in Figure 7B, this " shi fted" or dynamically adapted fluid dynamic map is then used in the flow feed- forward module 20 , receiving in this case at the input the "raw" inlet product pressure measurement PIN ( as provided by the pressure sensor 14 ) .

As shown at step 38 , the control unit 10 , after the above discussed determination of the adapted fluiddynamic map, may start a transition period from the standard, pre-stored, map to the adapted map by means of a pressure ramp ( starting from a fixed initial value and arriving to the above discussed sum of the inlet product pressure value PIN and the AP value ) .

At the end of the transition period, the value of the second control contribution C2 generated at the output of the flow feed- forward control module 20 wil l thus substantially match the position required for the flow regulating valve 6 based on the speci fic filling machine/product system . Therefore , it will be possible to compensate the contribution of the ( slower ) flow feedback control module 22 , with the ( faster ) flow feed- forward control module 20 representing the main contribution to the determination of the position control signal for the flow regulating valve 6 ( thus achieving the desired responsiveness of the control unit 10 to possible pressure disturbances ) .

The new fluid-dynamic map may be used until the next production stop is requested; when the filling machine 1 is restarted, the adaptation procedure may be performed again .

As shown in Figure 8 , according to a possible embodiment , the control unit 10 may further comprise a level feedback control module 42 , implemented by a respective proportional-integral-derivative ( PID) module , which generates at its output a control contribution CSP indicative of the flow set point FSP , based on a di f ference between the product level measurement LM received from the level detector 18 ( representing a real product level ) and a level set point LSP ( representing a desired product level ) , according to proportional , integrative and derivative control actions ( in any known manner, here not discussed in detail ) .

As shown in the same figure 8 , the above di f ference between the product level measurement LM and the level set point LSP is performed in a summing block 43 , whose output represents the input of the level feedback control module 42 .

The control unit 10 implements in this case a double PID control loop, based on the pressure and level measurements , in order to adj ust the flow through the regulating valve 6 with an additional control action based on the product level ( so as to achieve an even more stable operation of the filling machine 1 ) .

The control contribution CSP may represent the actual flow set point FSP , provided at the input of the flow feedback control module 22 .

In the embodiment shown in Figure 8 , the control contribution CSP is selectively provided, via a first switch 43a, to a summing block 44 , which generates at the output the flow set point FSP and further receives at the input a machine flow contribution CM .

In particular, this machine flow contribution CM is generated by a multiplier block 46 , which receives at its inputs : a machine speed percentage ; and, selectively, either a nominal flow percentage (via a second switch 43b ) , or a start flow percentage (via a ramp generator 45 and a third switch 43c ) .

In a known manner, the machine f low contribution CM represents a contribution to the flow set point FSP used at the start of the filling machine 1 .

The advantages of the discussed solution will be clear from the foregoing description .

In any case , it is underlined again that the improved control action implemented by the control unit 10 allows to achieve a more stable operation of the filling machine 1 , with a more stable level of product in the filled packages , reducing waste of product and of the same packages .

The discussed solution allows to promptly adapt to the operating characteristics of the filling machine ( and product ) , e . g . at the start of any new production or at any other suitable time .

In particular, thanks to the adaptation of the fluid dynamic maps to the filling system, the feed forward action determines the main contribution to the position of the flow regulating valve 6 , with the PID action load being reduced ( thus achieving a faster response to pressure disturbances ) .

Clearly, changes may be made to what described herein without , however, departing from the scope of protection as defined in the accompanying claims .

In particular, it is underlined that the discussed solution may be applied for any packaging or filling machine and for any kind of pourable food product .