Method for building a model of a printing or coating machine and minimizing its power consumption by using a remote computer

Abstract

A Method for controlling the power consumption of a drying unit using a remote computer. The method is about using the data from several drying units spread around the world to gain knowledge about how to set the drying unit, namely how to set the fan speed, the recirculation rate, and the temperature to achieve a good drying performance while reducing the power consumption of the unit.

Description

[0001] Method for building a model of a printing or coating machine and minimizing its power consumption by using a remote computer

[0002] Field of the invention

[0003] The present invention pertains to a method for configuring a printing machine's settings with the aim of minimizing its power consumption and / or maximizing the printing speed, i.e. the volume of production. This method applies particularly to rotary in-line printing machines, where each printing or coating unit is succeeded by a drying unit responsible for drying the ink before the next printing unit applies fresh ink. The invention also applies to a coating machine, where the coating material is effectively "printed" onto a substrate using a coating unit. We will employ the same vocabulary and treat the coating machine as if it were "printing" the coating material. In this context, a coating unit is managed similarly to a printing unit, albeit with distinct parameter values and operational guidelines.

[0004] Technical background

[0005] The power consumption of a printing (or coating) machine is mainly affected by the printing speed and the ventilation power of the drying unit. The power consumption tends to be reduced at high speed, while the maximum printing speed tends to be limited by the maximum drying capacity of the drying unit. The printing speed is limited mainly by the drying unit capacity given the substrate type, ink and print coverage.

[0006] The essential measure of drying unit capacity is its ability to evaporate solvent within a specific timeframe. This capacity is influenced by various factors, including the solvent type, ink or coating material type, substrate type, and thickness. Furthermore, it hinges on the drying unit's airflow, which is determined by the drying unit fan(s). The quantity of solvent that must be evaporated per unit of surface area is determined by both the ink's grammage and its dry percentage. Consequently, when considering the surface area, the amount of solvent to be evaporated is contingent upon the substrate's width, printing speed, and print coverage, in addition to the grammage and dry percentage of the ink.

[0007] CONFIDENTIAL Summary of the Invention

[0008] To determine the maximum printing speed of a complete printing or coating machine, we need to determine the maximum speed of each printing unit and choose the speed according to the slowest printing unit. The maximum printing speed may differ between units due to varying print jobs, due to the presence of a coating unit, due to varying ink amounts for different pattern colors (each unit prints a single color), and due to some units having a drying unit with a larger capacity for faster drying. Typically, some printing machines have a stronger drying unit in the last printing unit to print a white background with full ink coverage.

[0009] It is an object of the invention to provide a method for controlling the power consumption of a drying unit for a printing or coating unit using a remote computer.

[0010] The principle uses the multitude of installed machines, and the experience of the operators that drive these machines and builds upon widely collecting trial-and- error information to gain insight into the behaviour of the different parts of the printing machines and build a parametric model. In particular, the method comprises, for a printing job, a) Setting a set of global printing or coating parameters comprising

[0011] - a printing speed,

[0012] - a type, width, and thickness of a substrate to be printed,

[0013] - a type of ink or type of coating material,

[0014] - a type of solvent,

[0015] - a print coverage, grammage, and dry percentage; b) Setting drying parameters including a fan speed, optionally an air recirculation rate, and a temperature of the drying unit by any suitable method, resulting in a set of unit-specific drying parameters, and checking the quality of the print at the output of the drying or coating unit,

[0016] If the quality of the print is out of specification, correct the unitspecific drying parameters including the fan speed, optionally the air recirculation rate, and the temperature of the drying unit until the quality reaches an acceptable quality; c) Recording said set of global printing parameters and unit-specific drying parameters during the printing job;

[0017] CONFIDENTIAL d) Measuring the power consumption of the printing unit for performing the printing job; e) Sending the set of recorded parameters comprising the global printing parameters and unit-specific drying parameters as well as the power consumption to a remote computer; f) Repeating steps 1 .a) to e) for several printing jobs; g) With the remote computer, building a link between the set of global printing parameters, unit-specific drying parameters and the power consumption, resulting in a parametric model of a dryer. h) For a following printing job, from a new set of printing or coating parameters,

[0018] - applying the parametric model of the dryer to compute a new set of unit-specific drying parameters including the fan speed, optionally the air recirculation rate, and the temperature of the drying unit,

[0019] - and applying said new set of unit-specific drying parameters to the dryer for running said following printing job.

[0020] A parametric model of the dryer is created based on the drying parameters and global printing parameters that have been set, as well as the print quality and power consumption of corresponding multiple printing jobs. This parametric model can then be applied to new subsequent printing jobs to determine new unit-specific parameters that result in good print quality at lower power consumption. By applying this model, the optimum global printing parameters and unit-specific drying parameters can be determined for subsequent printing jobs with good printing quality and a low energy consumption.

[0021] Brief description of the figures

[0022] Embodiments of the present invention are illustrated by way of example in the accompanying drawings in which reference numbers indicate the same or similar elements and in which:

[0023] CONFIDENTIAL Figure 1 shows an example of a printing or coating machine connected to a remote computer, where the winder, the unwinder and the elements for controlling the substrate speed and tension are illustrated,

[0024] Figure 2 shows an example of a printing machine with several printing units, where the method according to the invention can be applied,

[0025] Figure 3 shows an example of a printing or coating unit with its drying unit, according to the invention,

[0026] Figure 4 shows a method for computing the printing speed of the printing or coating machine,

[0027] Figure 5 shows a method for setting the unit-specific drying parameters in each printing or coating unit,

[0028] Figure 6 shows the overall method for setting the printing or coating machine parameters,

[0029] Figure 7 shows an example of possible printing speeds for a given ink and substrate in relation to the drying temperature.

[0030] Detailed description of the invention and of some of its embodiments

[0031] A printing machine 1 comprises several printing units 2. The printing machine 1 could also be a coating machine 1 with one or several coating units 2. The method disclosed here for a printing machine may also be applied to a coating machine. A substrate 4 runs from one printing or coating unit 2 to the next. Each printing or coating unit 2 is associated with a drying unit 6 located downstream from the printing or coating unit 2 when following the path of the substrate 4. The printing speed 8 is the same for all the printing or coating units 2.

[0032] To minimize the power consumption of the printing machine 1 we compute the maximum printing speed 108 of each printing or coating unit 2. The printing speed is limited by the drying unit 6 capacity.

[0033] Setting the unit-specific drying parameters given the printing speed

[0034] The drying unit 6 has an internal air recirculation circuit 10 powered by a controllable fan 12. The air is circulated in the circuit 10 by being pushed by the fan 12 and heated by a heater 14. The temperature 15 is measured in the circuit

[0035] CONFIDENTIAL by a thermometer. The air flows toward the substrate 4 and causes an evaporation of the solvent, which is mixed with ink on the substrate. The air and solvent mixture 18 then reach a damper 22 that recirculates a proportion of the air and solvent mixture 18, removes some of the mixture 18 from the circuit 10, and replaces the missing mixture with fresh air from outside. The proportion of solvent in the mixture is measured by a sensor 20, which is preferably located on the circuit 10, between the substrate 4 and the damper 22. The speed 13 of the fan 12 can be set by the machine’s control unit 9. Its maximum speed defines the maximum drying capacity of the drying unit 6. The temperature 15 must be kept within a range: it must be hot enough to have a good drying capacity, and cold enough to prevent an explosion. The damper 22 determines the proportion of air that loops in the air recirculation circuit 10, and the proportion that gets replaced by fresh air. Thus, by setting the damper 22 position, we set the air recirculation rate 23. Some of the air must be replaced by fresh air to avoid saturating the air in the circuit with solvent. The maximum amount of solvent allowed is given by the safety specification of the setup. Too much solvent might cause an explosion but recycling the solvent (outside of the drying unit) is only doable if the solvent concentration is high enough. Also, fresh air must be heated before reaching the circuit, thus consuming more energy. Consequently, there is an optimal recirculation proportion to be set. This optimum is reached by setting the solvent concentration to its maximum allowable level. When referring to the 'maximum allowable level,' we are specifying a threshold that is assured not to exceed the limit defined by the safety specification. This consideration takes into account the natural variability in this value stemming from the inherent inaccuracies present in all components contributing to the setting (the damper, the sensor, and the reactivity of the system in time). The proposition of solvent in the air recirculation circuit 10 is measured by a sensor 20. The set of parameters comprising the temperature 15 measured by the sensor 20 and the fan speed 13 constitutes the core of the unit-specific drying parameters 40. Preferably, the air recirculation rate 23 may also be part of the core of the unit-specific drying parameters 40, because it is generally set with the fan speed and temperature but it is particular in the sense that it does not directly impact the quality of the print. It impacts safety and sustainability.

[0036] To set the temperature, we can use the data in Figure 7. The temperature must be kept between two boundaries: it is lower bounded by an ink curve, and upper

[0037] CONFIDENTIAL bounded by a substrate curve. Being above the ink curve ensures that the solvent (or water) is evaporated from the ink, and being under the substrate curve ensures that the substrate doesn’t get damaged by an excessive temperature. Type A substrates are rigid substrates while type D substrates are extendable substrates. Type B and C are substrates whose properties lie in-between. Examples of inks and substrate types are given in Table 1 :

[0038] Table 1 : categorization of inks and substrates

[0039] Within the margin given by the two curves, one may decide for a high temperature to reduce the risk of not drying the print correctly, or for a low temperature to reduce the risk of deforming the substrate while saving some energy. Thus, the input temperature could be specified as which risk to emphasize, with a default value that lies in the middle of the two curves.

[0040] To set the fan speed 13, i.e. a unit-specific drying parameter, the method computes the amount of solvent to be removed from the substrate per unit of time. This amount is given by the amount of ink that crosses the drying unit multiplied by the percentage of solvent in the ink (i.e., one minus the dry percentage). The amount of ink is given by multiplying the grammage by the print coverage and the printing speed 8. Then, from the amount of solvent per unit of time, the unit-specific drying parameters 40 are set depending on the type of solvent used. These last parameters are given by the solvent manufacturers and / or determined on an empirical basis.

[0041] In practice, we can compute an empirical dryer capacity index K, which is equal to the percentage of solvent (or water) in the ink divided by the percentage of solid material in the ink multiplied by the grammage of the ink, i.e. the amount of ink per

[0042] CONFIDENTIAL unit surface of the substrate. The result is then multiplied by the printing speed (i.e. the running speed of the substrate) divided by the dryer hood length:

[0043] K = amount of solvent / amount of solid * grammage * (speed / hood length) * K_solv.

[0044] K is expressed in kg / (m2■ hours)

[0045] K_solv is a parameter which depends on the solvent. For a standard solvent, K_solv = 1 . If the solvent is water, in other words, if we use water-based inks, we use K_solv = 3 to obtain K.

[0046] K is an estimator of the drying goodness, the lower the value the better the drying. Let’s call K_dry the value of K at which the print is well-dried. The parameter K_dry tends to depend on the press. On our machines K_dry = 36.

[0047] For a given printing unit, if the value ok K is smaller than K_dry, we may consider reducing the fan speed. For example we may set the fan speed, in percentage to its nominal speed with the formula: fan_speed = (K / K_dry)A0.33 *100 [%]. For example, if K is about half of K_dry, we set the fan speed to 80% of its nominal speed, and thereby gain 50% of the power consumption of the fan. We may lowerbound this percentage to avoid reaching a value close to 0 where this rough estimate would be too approximate (the formula of drying goodness using value K is a rough estimate of the real drying process).

[0048] To compute the parameter K_dry for any presses, we need to know under which conditions the job can be printed and dried. These conditions are given for a particular combination of ink and substrate by the press manufacturer or can be measured using the first successfully printed job. We then compute parameter K under these conditions for the most critical drying unit, which results in the value K_dry. Equivalently, we may compute the K value for each drying unit and set K_dry as the maximum of these values.

[0049] Thus, once the printing speed 8 is given, the drying unit sets unit-specific drying parameters 40, i.e. the fan speed 13, the air recirculation rate 23, or the temperature 15 of the drying unit, to a value that depends on said printing speed 8 and minimizes the power consumption.

[0050] In practice, if the drying unit is new in a product line, or if the substrate or ink is not well known, the drying unit may be operated in only two modes: a FULL mode,

[0051] CONFIDENTIAL with the fan speed set at its maximum value, and an ECO mode, where the fan speed is set to 80% of its maximum speed, which reduced its power consumption by half (there is a cubic relationship between fan speed and power consumption). ECO mode is selected in each printing unit where K / K_dry is smaller or equal to 50%. Simplifying to just FULL mode and ECO mode offers the benefit of ease and clarity, making it easier to pinpoint issues if the print drying deviates from specifications. Once enough data is collected about the drying unit and substrate and ink combination, the fan speed can be determined more in a more precise way, for example using the fan_speed formula

[0052] Computing the maximum substrate speed allowed by the drying unit

[0053] The maximum allowable printing speed 108 of a printing or coating unit 2 is limited by the maximum speed of the printing rollers and the maximum speed allowed by the drying unit, which is most of the time the limiting factor. To compute the maximum allowable printing speed 108 from the drying unit’s perspective, the fan 12 of the drying unit 6 is set to its maximum (recommended) value, while the heater 14 and the damper 22 at set to a value to maximize the solvent evaporation while staying within the safety specification. Most of the time, this is achieved by opening the damper 22 to replace the air with fresh air and setting the heater 14 to reach the maximum allowable temperature. This gives the amount of solvent that can be removed from the substrate per unit of time. Since this amount is equal to the amount of ink that crosses the drying unit multiplied by the percentage of solvent in the ink, we can compute the maximum allowable printing speed 108. Alternatively, If the printer is already well-characterized, we can compute the maximum print speed (i.e. the maximum printing speed allowed by the dryer) by setting K / K_dry = 100% and solving for the printing speed.

[0054] Fine-tuning the drying unit parametric model

[0055] To improve the efficiency of the unit-specific drying parameters 40, the drying unit 6 needs to precisely estimate the influence that each of the settable unitspecific drying parameters 40 has on the drying process. In this way, it can set the unit-specific drying parameters 40 to successfully run the drying process while minimizing power consumption. To improve the model that estimates the effect of each parameter on the drying process, i.e. Table 1 , the fan_speed formula and figure 7, the machine is connected to a remote computer 7, and thanks to a

[0056] CONFIDENTIAL feedback process, the precision of the model can be improved. The method works as follows: For a predefined drying unit model, an operator sets the unit-specific drying parameters 40 (including the fan speed 13, the air recirculation rate 23 and the temperature 15), with the aim of producing at maximum speed and / or consuming little power (i.e. trying to set the minimal fan speed 13, a low temperature 15 and a high air recirculation rate 23). Alternatively, the initial parameter set is proposed by the remote computer based on a predefined parametric model of the printer. The printer is running, and the operator checks the print quality and checks that the solvent concentration remains under the explosion safety limit. The operator “plays” with the parameters until the quality is good. Then, the operator accepts the settings, and the job is run.

[0057] When the settings are accepted, the printing machine records the unit-specific drying parameters 40, the printing parameters 30, and the make and model of the drying unit. It then measures the power consumption of the drying unit 6 and sends this complete set of parameters 30,40 to the remote computer 7. The remote computer creates an entry in a database 79 and builds a lookup table for each drying unit model. In other words, the remote computer builds a link between the set of global printing parameters 30, unit-specific drying parameters 40, and power consumption. For example, we may compute a K_solv value for each ink-solvent combination and a K_dry value for each type of printing unit. If enough data is available, we may select all the print jobs with the same printing unit configuration, the same ink and the same solvent and interpolate or choose between the set of parameters that led to successful jobs.

[0058] The remote computer is preferably connected to several printing machines throughout the world. Thus, when a printing machine starts a new job, if it does not have the required data or knowledge to set up the printing and / or drying parameters 30, 40, the printer may send a request to the remote computer. The computation is a two-step process that runs in the remote computer: first, it determines the maximum printing speed 108 of every printing or coating unit 2, then chooses a compatible printing speed 8— which is preferably the maximum printing speed 108 of the slowest printing unit— and then, given that printing speed 8, it determines the unit-specific drying parameters 40 for every printing unit with the aim to minimize power consumption. Thus, the remote computer searches the database 79 for that printer / drying unit model and given,

[0059] CONFIDENTIAL - The type, width, and thickness of a substrate to be printed 32,

[0060] - The type of ink or type of coating material 34,

[0061] - The type of solvent 36,

[0062] - The print coverage, grammage, and dry percentage 38

[0063] (i.e., the global printing parameters 30 excluding the printing speed 8) and computes the maximum printing speed 108 for every printing unit.

[0064] Then it chooses a printing speed 8 compatible with every printing or coating unit 2, and adds it to the global printing parameters 30. Thus, from

[0065] - The type, width, and thickness of a substrate to be printed 32,

[0066] - The type of ink or type of coating material 34,

[0067] - The type of solvent 36,

[0068] - The print coverage, grammage, and dry percentage 38

[0069] - The printing speed 8

[0070] The remote computer 7 computes the unit-specific drying parameters 40 for every printing or coating unit 2 that will consume the least possible energy. It then sends the unit-specific drying parameters 40 for each printing unit and the (global) printing speed 8 back to the printing machine 1.

[0071] In practice, once the remote computer 7 has collected enough data for a given drying unit model, it may build a parametric model to compute the drying parameters from the global printing parameters 30 including the printing speed 8 (shown in Figures 5 and 6) and another model that computes the maximum printing speed 108 given the global printing parameters 30 excluding the printing speed 8, shown in Figure 4. This model may be computed by interpolating between the set of global printing parameters 30 and unit-specific drying parameters 40, by statistical data fitting, or by machine learning techniques.

[0072] When data is missing, for example, if the substrate is now, the remote computer works by analogy: it finds the known material with the most similar properties and sets up the printer according to the parameters linked to said material. For example, if a new plastic substrate is used, then the remote computer finds another plastic in the list. If a new metal substrate is used, then the remote computer uses the parameters of another metal substrate in the list. Also, when setting the tension-related parameters for a new material, the remote computer will use the

[0073] CONFIDENTIAL data of a substrate having a similar young modulus. These parameters are provided as initial parameters that will be corrected by the operator if the result does not produce a print according to specifications.

[0074] Over time, the printing machines may send information about the drying parameters, the printing or coating parameters, the make and model of the drying unit, and a quality tag whenever quality control is performed and validated. The quality tag specifies if the print was within- or out of- specifications. Please note that the printing machine may send this information even when the quality is deemed out of specification. This information, once collected over time improves the precision of the global printing parameter 30 and unit-specific drying parameter 40 set determination.

[0075] Preferably, the parametric model of the printer or drying unit is learnt based on an empirical model of the printer to which a correction is added. Thus, the system learns the difference to apply to the parameters set given a predetermined parametric model. The predetermined parametric model is based on empirical and historical knowledge of the printer.

[0076] Setting up the printer parameters

[0077] Once the printing speed 8 is determined, the control unit 9 of the printing machine 1 sets some side parameters of the printer which control the substrate speed and tension and sets the parameters in each of the printer units.

[0078] The substrate is stored on a reel 50, and unwound by the unwinder 60. Then follows an unwinder draw group 62 that controls the tension of the substrate. The substrate is then processed by the set of printing units, goes through a rewinder draw group 72, which is also used to control the substrate tension and is finally rewound in a rewinder 70 to finish in the processed substrate reel 51. In practice, the unwinder tension 61 and speed 66, the unwinder group tension 63 and speed 68, the rewinder tension 71 and speed 76 and the rewinder group tension 73 and speed 78. These parameters may be added to the global printing parameters. Adding these parameters to the global printing parameters allows for a more complete model of the printer control, and thus allows the collection of a whole set of parameters that are producing prints according to specification.

[0079] CONFIDENTIAL Setting up the printing unit

[0080] In each printing unit, the control system of the printer sets the unit Nip pressure 82, the Doctor Blade pressure 84, the doctor blade oscillating speed 86, the ink pump speed pressure 88, the ink roll speed 90 (according to the speed of the substrate) and the ink roll pressure 92. These parameters may be added to the global printing parameters. Adding these parameters to the global printing parameters allows for a more complete model of the printing unit control, and thus allows the collection of a whole set of parameters that are producing prints according to specification.

[0081] Assessing the Quality of the print

[0082] The Quality can be specified and / or measured in various ways, using a set of criteria. Here is a list of criteria, which can be measured as a numerical value, and compared to a predefined threshold. If the value has passed the threshold, then the quality of the print is out of specification:

[0083] 1 . The print repeat length

[0084] The print repeat length is the distance variation between two identical patterns that result from a complete rotation of a printing cylinder. For example, the distance between two register marks. This distance may vary if the web tensions varies. Thus, typically, a print job will have a tolerance in percent of the print repeat length. It can be measured by controlling the rotation of the printing roller in relation to the timing of detection of the register marks, or just by measuring the distance between two consecutive register marks along the print direction.

[0085] 2. Substrate dimensional stability (shrinkage)

[0086] When the web tension is large, the substrate (i.e. the web) tends to stretch, thus becoming less wide. The stretch can be measured when placing register marks on both sides of the web, along the transversal direction, and measuring the distance between said marks. Typically, web tension, material characteristics, and drying temperature greatly influence this value.

[0087] 3. Color-to-Color Registration Accuracy

[0088] CONFIDENTIAL Determined by calculating the deviation between reference marks of successive colors, expressed in microns.

[0089] 4. Color Fidelity

[0090] Evaluated by comparing printed color values against target specifications using standardized colorimetric methods, for example using an inline spectrophotometer, on a set of spot colors printed on the side of the web, compared to their specified value. The result is expressed in deltaE, a standard colorimetric metric.

[0091] 5. Ink Transfer Completeness

[0092] Verified on chosen spot colors with low color density, in the same way as color fidelity,

[0093] 6. Number of Printing Defects

[0094] Verified through visual or automated inspection to ensure no streaks, pinholes, or missing ink. Verified inline using an imaging system, or offline by scanning a portion of the print.

[0095] 7. Uniformity of Ink Density and Coverage

[0096] Assessed by sampling multiple points across the printed area to detect variations beyond defined tolerances. Usually performed offline on a scan or visually by an operator.

[0097] 8. Absence of Printing Defects

[0098] Verified on text portions where small details may be missing, for example, the dot above letter “i”, and / or by reading any printed barcode if there are any. A Missing thin line on a barcode generates an error in barcode reading; every barcode must be readable. This can be performed inline a camera or offline on a scan.

[0099] 9. Print sharpness

[0100] The sharpness of printed images can be assessed using a camera and computing the sharpness of sharp edges on text or on printed images. If the print is not dry, smearing may appear, resulting in the blurring of edges or text. This can be measured in-line if a camera records the printing process or offline on a scan.

[0101] CONFIDENTIAL 10. Ink Film Thickness

[0102] Measured offline using gravimetric or optical methods to confirm uniformity and adherence to specifications.

[0103] 11 . Residual Solvent Content

[0104] Measured offline through chemical analysis to confirm compliance with regulatory and safety limits.

[0105] 12. Drying Performance

[0106] Evaluated offline by determining solvent evaporation rate and ink set characteristics under standard process conditions.

[0107] The number of criteria might vary from one job to the next. For example, the ink film thickness or residual solvent content might not be measured for every print job. Also, not every criterion applies to coating (for example, color fidelity only applies to printing).

[0108] Prints that meet inline quality criteria but fail offline specifications are flagged by rejecting their parameter set through the printer interface and recorded on the remote computer as negative samples. These negative samples are used to delineate the boundary between valid and invalid parameter sets.

[0109] The criteria that can be evaluated inline enable the printing or coating machine to correct the unit-specific drying parameters in real time until reaching an acceptable quality, i.e., a quality within specification according to said predefined threshold and list of criteria. For example, we can raise the fan speed, raise or lower the temperature (raise the temperature if drying is an issue, lower the temperature if stretch is an issue, etc), until the print becomes within specification. In another example, we could lower the fan speed until the print goes out of specification, and choose the last setting within specification to minimize the power consumption.

[0110] The set of parameters recorded on the remote computer preferably includes the set of quality parameters that were computed or measured to ensure that the quality is within specification.

[0111] CONFIDENTIAL

Claims

Claims1. Method for controlling the power consumption (100) of a drying unit for a printing or coating unit (1) using a remote computer (7), the method comprising, for a printing job, a) Setting a set of global printing parameters (30) defined as a set of parameters comprising- a printing speed (8),- a type, width, and thickness of a substrate (4) to be printed (32),- a type of ink or type of coating material (34),- a type of solvent (36) of the ink or coating material (34),- a print coverage of the ink or coating material (34) on the substrate (4) to be printed (32), grammage of the ink or coating material (34) on the substrate (4) to be printed (32), and dry percentage (38) of the ink or coating material (34); b) Setting drying parameters including a fan speed (13), and a temperature (15) of the drying unit (6), resulting in a set of unit-specific drying parameters (40) of the drying unit (6), and checking a quality of a print on the substrate (4) at the output of the drying unit, and,- if the quality of the print is out of specification, correct the unitspecific drying parameters (40) including the fan speed (13), the air recirculation rate (23), and the temperature (15) of the drying unit (6) until the quality reaches an acceptable quality; c) Recording said set of global printing parameters (30) and unit-specific drying parameters (40) during the printing job; d) Measuring the power consumption (100) of the printing unit (2) for performing the printing job; e) Sending the global printing parameters (30), the unit-specific drying parameters (40) and the measured power consumption (100) to the remote computer (7); f) Repeating steps a) to e) for several printing jobs; g) With the remote computer (7), generating a relation between the set of global printing parameters (30), unit-specific drying parameters (40) and the power consumption (100), resulting in a parametric model of a dryer (6);CONFIDENTIALh) For a following printing job, with a new set of global printing parameters (30),- applying the parametric model of the dryer to compute a new set of unit-specific drying parameters (40) including the fan speed (13), and the temperature (15) of the drying unit (6) that minimizes the power consumption (100),- and applying said new set of unit-specific drying parameters (40) to the drying unit (6) for running said following printing job.

2. The method according to claim 1 , wherein the unit-specific drying parameters (40) comprise an air recirculation rate (23) which is set in step b) and computed in step h).

3. The method according to claim 1 or 2, wherein the remote computer (7) collects the global printing parameters (30), the unit-specific drying parameters (40) and the measured power consumption (100) along with the drying unit model (39) and builds a database (79) with an entry for each set of recorded parameters.

4. Method according to claim 3, wherein if the quality of the print is out of specification, the method further comprises the steps of collecting the global printing parameters (30) and the unit-specific drying parameters (40) and sending them to the remote computer (7)global, and wherein the remote computer (7) adds an entry into the database (79) for each set of global printing parameters (30) and unit-specific drying parameters (40), wherein said entry comprises the information that the global printing parameters (30) and unit-specific drying parameters (40) produce a quality of the print that is out of specification.

5. Method according to claim 3 or 4, wherein the remote computer (7) builds, for each drying unit model (39), a parametric model for calculating the maximum printing speed (108) that the drying unit (6) can process to produce a printing result within specifications, based on the global printing parameters (30) excluding the printing speed (8)..

6. Method according to claim 3 or 4, wherein the remote computer (7) builds, for each drying unit model (39), a parametric model for calculating the lowest possible power consumption (100) and a printing result within specification, basedCONFIDENTIAL- 17 - on the global printing parameters (30) excluding the printing speed (8), the unitspecific drying parameters (40) and the printing speed (8).

7. Method according to any one of claim 3-6, wherein the parametric model is built, for each drying unit model (39), by interpolating between the entries of the database (79) that are associated with said drying unit model (39).

8. Method according to any one of claim 3-6, wherein the parametric model is built for each drying unit model by fitting a parametric model to the entries of the database (79) that are associated with said drying unit model (39).

9. Method according to any one of claim 3-6, wherein the parametric model is built for each drying unit model (39) as a correction to be applied on top of a predetermined empirical model of the drying unit (6).

10. Method according to claim 8, wherein the parametric model is a multilayer artificial neural network.

11. Method according to any preceding claims, for controlling the power consumption of a printing or coating machine (1) comprising several printing or coating units (2), comprising applying the method according to any one of the preceding claims for each printing or coating unit (2) or the printing or coating machine (1), thereby obtaining a parametric model of the printing or coating machine (1).

12. Method according to the preceding claim, wherein an unwinder tension (61), an unwinder group tension (63), a rewinder tension (71) and a rewinder group tension (73) of an unwinder or a rewinder are added to the global printing parameters (30).

13. Method according to the preceding claim, wherein a unit Nip pressure (82), a Doctor Blade pressure (84), a doctor blade oscillating speed (86), a ink pump pressure (88), a ink roll speed (90) and a ink roll pressure (92) of each printing or coating unit (2) are added to the global printing parameters (30)CONFIDENTIAL

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