Method for minimizing power consumption of a drying unit

Abstract

A method for controlling a drying unit having a controllable fan and an air recirculation loop is disclosed. Given the usual parameters of the associated printing unit, including the ink properties in the print coverage, the method sets the fan speed, the air recirculation rate and the temperature accordingly and achieves a lower power consumption than using a standard parameter set.

Description

Technical Field

[0001] This invention relates to a method for configuring a printing press to minimize its power consumption. The method is particularly suitable for rotary in-line printing presses, where a drying unit follows each printing or coating unit, responsible for drying the ink before applying new ink to the next printing unit. Furthermore, the invention is applicable to coating machines, where coating units are used to effectively "print" coating material onto a substrate. It is worth noting that we will use the same terminology and consider the coating machine as "printing" coating material. In this context, the coating units are managed similarly to printing units, although they have different parameter values ​​and operating guidelines. Background Technology

[0002] The power consumption of a printing (or coating) machine is primarily affected by the printing speed and the ventilation power of the drying unit. Power consumption tends to decrease at high speeds, while the maximum printing speed is often limited by the maximum drying capacity of the drying unit. Given a substrate type, ink, and print coverage, the printing speed is mainly limited by the drying unit's capacity.

[0003] The fundamental metric for a drying unit's capability is its ability to evaporate solvent within a specific timeframe. This capability is influenced by various factors, including solvent type, ink or coating material type, substrate type, and thickness. Furthermore, it depends on the airflow within the drying unit, which is determined by the unit's fan. The amount of solvent that must be evaporated per unit surface area is determined by the ink's basis weight and its drying percentage. Therefore, when considering surface area, in addition to the ink's basis weight and drying percentage, the amount of solvent to be evaporated also depends on the substrate width, printing speed, and print coverage. Summary of the Invention

[0004] To determine the maximum printing speed of a complete printing or coating press, we need to determine the maximum speed of each printing unit and select the speed based on the slowest printing unit. The maximum printing speed between units can vary due to different printing jobs, the presence of coating units, variations in ink volume for different pattern colors (each unit prints a single color), and the presence of drying units with greater capacity for faster drying. Typically, some presses have a more powerful drying unit in the last printing unit to print a white background with full ink coverage.

[0005] The purpose of this invention is to provide a method for controlling the power consumption of a drying unit used in a printing or coating unit.

[0006] The printing unit has a drying unit. It can also be a coating unit instead of a printing unit, where a coating material replaces the ink. The drying unit has a controllable fan and air recirculation loop.

[0007] This method involves setting a set of global printing parameters, which include: Printing speed, The type, width, and thickness of the substrate to be printed. The type of ink or coating material, The type of solvent, Print coverage, basis weight, and drying percentage. Solvent refers to the solvent used in the ink or coating material. Basis weight is the basis weight of ink or coating material per unit surface area on the substrate. Drying percentage is the percentage of ink or coating material that has dried. By considering print coverage, basis weight, and drying percentage, along with the printing speed and substrate width, the amount of solvent that must be extracted from the substrate per unit time can be determined. Therefore, this method sets the fan speed, air recirculation rate, and temperature of the drying unit to evaporate the stated amount of solvent. The values ​​to be set are determined according to a predetermined formula and / or a lookup table. This produces a set of unit-specific drying parameters. Once these values ​​are set, the substrate is processed using the printing or coating unit according to these parameters.

[0008] Therefore, after setting the global printing parameters of the printing press and before processing the substrate, the appropriate fan speed, air recirculation rate (most of the time), and temperature of the drying unit are calculated using formulas and set according to the results of these formulas. For example, the formula calculates the amount of solvent that needs to be removed from the substrate per unit time, depending on the type of solvent used. Thus, unit-specific drying parameters are pre-set before the substrate is processed by the printing or coating unit, and these parameters are applicable to the previously set global printing parameters. At least one, but preferably all, of the unit-specific drying parameters, consisting of the fan speed, air recirculation rate, and temperature of the drying unit, depends on the global printing parameters. Therefore, the unit-specific drying parameters are parameters of the drying unit.

[0009] Preferably, the air recirculation rate is set by a damper located on the air recirculation loop. The damper removes a portion of the air from the air recirculation loop and replaces it with fresh air. The damper regulates the air recirculation rate so that the solvent in the air recirculation loop reaches a concentration that meets predefined safety specifications while reaching the maximum permissible level. While the air recirculation rate has a smaller direct impact on drying capacity compared to fan speed or temperature, it plays a crucial role in ensuring safety (by reducing the risk of explosion) and supporting sustainability. Attached Figure Description

[0010] Embodiments of the present invention are illustrated by way of example in the accompanying drawings, wherein reference numerals denote the same or similar elements, and wherein: Figure 1An example of a printing or coating machine connected to a remote computer is shown, illustrating a winding machine, an unwinding machine, and elements for controlling the speed and tension of the substrate. Figure 2 An example of a printing press with multiple printing units is shown, in which the method according to the invention can be applied. Figure 3 An example of a printing or coating unit with its drying unit according to the present invention is shown. Figure 4 A method for calculating the printing speed of a printing or coating machine is shown. Figure 5 A method for setting unit-specific drying parameters in each printing or coating unit is shown. Figure 6 A general method for setting parameters for a printing or coating machine is shown; Figure 7 Examples of possible printing speeds for a given ink and substrate, in relation to drying temperature, are shown. Detailed Implementation

[0011] The printing press 1 includes multiple printing units 2. The printing press 1 can also be a coating press 1 having one or more coating units 2. The methods disclosed herein for a printing press can also be applied to a coating press. The substrate 4 moves from one printing or coating unit 2 to the next. Each printing or coating unit 2 is associated with a drying unit 6, which is located downstream of the printing or coating unit 2 as it travels along the path of the substrate 4. The printing speed 8 is the same for all printing or coating units 2.

[0012] To minimize the power consumption of the printer 1, we calculated the maximum printing speed of each printing or coating unit 2 to be 108. The printing speed is limited by the capability of the drying unit 6.

[0013] Given a printing speed, set specific drying parameters per unit. The drying unit 6 has an internal air recirculation loop 10 powered by a controllable fan 12. Air circulates in the loop 10 due to the push of the fan 12 and the heating of the heater 14. The temperature 15 in the loop is measured by a thermometer. The air flows toward the substrate 4, causing the solvent mixed with the ink on the substrate to evaporate. The air and solvent mixture 18 then reaches a damper 22, which recirculates a portion of the air and solvent mixture 18, removing some of the mixture 18 from the loop 10 and replacing the missing mixture with fresh air from the outside. The proportion of solvent in the mixture is measured by a sensor 20, which is preferably located on the loop 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 maintained within a certain range: it must be hot enough to have good drying capacity and cold enough to prevent explosion. The damper 22 determines the proportion of air circulating in the air recirculation loop 10 and the proportion replaced by fresh air. Therefore, by setting the position of damper 22, we set the air recirculation rate 23. Some air must be replaced with fresh air to prevent the air in the loop from becoming saturated with solvent. The maximum permissible amount of solvent is given by the device's safety specifications. Excessive solvent may cause an explosion, but solvent recovery (outside the drying unit) is only feasible when the solvent concentration is sufficiently high. Furthermore, fresh air must be heated before reaching the loop, thus consuming more energy. Therefore, an optimal recirculation ratio needs to be set. This optimal value is achieved by setting the solvent concentration to its maximum permissible level. When referring to the "maximum permissible level," we specify a threshold that ensures it does not exceed the limits specified by the safety specifications. This consideration takes into account the natural variation in this value, which stems from inherent inaccuracies present in all components that contribute to the setup (damper, sensors, and the system's real-time responsiveness). The proportion of solvent in the air recirculation loop 10 is measured by sensor 20. The set of parameters measured by sensor 20, including temperature 15 and fan speed 13, constitutes the core of the unit-specific drying parameters 40. Preferably, the air recirculation rate 23 can also be a core part of the unit-specific drying parameter 40, as it is typically set along with fan speed and temperature, but its significance lies in the fact that it does not directly affect print quality. It impacts safety and sustainability.

[0014] To set the temperature, we can use Figure 7 The data is as follows. The temperature must be maintained between two boundaries: the lower boundary is the ink profile, and the upper boundary is the substrate profile. Temperatures above the ink profile ensure that the solvent (or water) evaporates from the ink, while temperatures below the substrate profile ensure that the substrate is not damaged by excessive heat. Type A substrates are rigid substrates, while Type D substrates are stretchable substrates. Types B and C are substrates with properties between the two. Table 1 provides examples of ink and substrate types:

[0015] Table 1: Classification of Inks and Substrates Within the range given by the two curves, a high temperature can be determined to reduce the risk of improperly drying printed materials, or a low temperature can be determined to reduce the risk of substrate deformation while saving some energy. Therefore, the input temperature can be specified as the risk to be emphasized, with the default value located in the middle of the two curves.

[0016] To set the fan speed 13, i.e., the unit-specific drying parameter, this method calculates the amount of solvent removed from the substrate per unit time. This amount is derived by multiplying the amount of ink passing through the drying unit by the percentage of solvent in the ink (i.e., 1 minus the drying percentage). The ink amount is obtained by multiplying the basis weight by the print coverage and the print speed 8. Then, based on the amount of solvent per unit time, the unit-specific drying parameter 40 is set according to the type of solvent used. These final parameters are provided by the solvent manufacturer and / or determined empirically.

[0017] In practice, we can calculate the empirical dryer capacity index K, which equals the percentage of solvent (or water) in the ink divided by the percentage of solid material in the ink multiplied by the ink's basis weight (i.e., the amount of ink per unit substrate surface). Then, multiply the result by the printing speed (i.e., the substrate's running speed) and divide by the dryer hood length. K = Solvent volume / Solid volume * Gram weight * (Speed ​​ / Shield length) * K_solv.

[0018] K is expressed in kg / (m 2 · hours) is used to indicate.

[0019] K_solv is a solvent-dependent parameter. For standard solvents, K_solv = 1. If the solvent is water, in other words, if we are using water-based inks, we use K_solv = 3 to obtain K.

[0020] K is an estimate of dryness; the lower the value, the better the drying. Let's call K_dry the K value when the print is completely dry. The parameter K_dry often depends on the printing press. On our press, K_dry = 36.

[0021] For a given printed cell, if the value of K is less than K_dry, we can consider reducing the fan speed. For example, we can set the fan speed as a percentage of its nominal speed using the following formula: fan_speed = (K / K_dry)^0.33 * 100 [%]. For instance, if K is approximately half of K_dry, we would set the fan speed to 80% of its nominal speed, thus achieving 50% of the fan power consumption. We can reduce this percentage to avoid reaching a value close to 0, as this rough estimate is too approximate (the dryness formula using the value K is a rough estimate of the actual drying process).

[0022] To calculate the parameter K_dry for any printing press, we need to know the conditions under which the job is printed and dried. These conditions are given by the printing press manufacturer for a specific combination of ink and substrate, or they can be measured using the first successfully printed job. We can then calculate the parameter K under these conditions for the most critical drying unit, deriving the K_dry value. Similarly, we can calculate the K value for each drying unit and set K_dry to the maximum of these values.

[0023] Therefore, once the printing speed 8 is given, the drying unit sets the unit-specific drying parameters 40 (i.e., the drying unit's fan speed 13, air recirculation rate 23, or temperature 15) to values ​​that depend on the printing speed 8 and minimizes power consumption.

[0024] In practice, if the drying unit is a new piece of equipment in the product line, or if the substrate or ink is not well-known, the drying unit can only operate in two modes: Full mode and ECO mode. In Full mode, the fan speed is set to its maximum value, and in ECO mode, the fan speed is set to 80% of the maximum speed, which halves its power consumption (there is a cubic relationship between fan speed and power consumption). ECO mode is selected for each printing unit where K / K_dry is less than or equal to 50%. Simplifying to only Full and ECO modes provides the benefit of clarity, making it easier to pinpoint problems if the printing drying deviates from specifications. Once sufficient data is collected regarding the drying unit, substrate, and ink combination, the fan speed can be determined more precisely, for example, using the fan_speed formula. Calculate the maximum allowable substrate speed of the drying unit. The maximum permissible printing speed 108 of the printing or coating unit 2 is limited by the maximum speed of the printing rollers and the maximum permissible speed of the drying unit, with the maximum permissible speed of the drying unit being the limiting factor most of the time. To calculate the maximum permissible printing speed 108 from the perspective of the drying unit, the fan 12 of the drying unit 6 is set to its maximum (recommended) value, while the heater 14 and damper 22 are set to values ​​that maximize solvent evaporation while remaining within safe limits. 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 permissible temperature. This gives the amount of solvent that can be removed from the substrate per unit time. Since this amount is equal to the amount of ink passing through the drying unit multiplied by the percentage of solvent in the ink, we can calculate the maximum permissible printing speed 108. Alternatively, if the printing press has been well-characterized, we can calculate the maximum printing speed (i.e., the maximum printing speed allowed by the dryer) by setting K / K_dry = 100% and solving for the printing speed.

[0025] Fine-tuning the drying unit parameter model To improve the efficiency of unit-specific drying parameters 40, drying unit 6 needs to accurately estimate the impact of each settable unit-specific drying parameter 40 on the drying process. In this way, it can set unit-specific drying parameters 40 to successfully operate the drying process while minimizing power consumption. To improve the model estimating the impact of each parameter on the drying process (i.e., Table 1, the fan_speed formula, and...), further research is needed. Figure 7 The machine is connected to a remote computer 7, and the model's accuracy can be improved due to the feedback process. The method works as follows: For a predefined drying unit model, the operator sets unit-specific drying parameters 40 (including fan speed 13, air recirculation rate 23, and temperature 15) with the aim of producing at maximum speed and / or consuming very little power (i.e., attempting to set a minimum fan speed 13, low temperature 15, and high air recirculation rate 23). Alternatively, an initial set of parameters is proposed by the remote computer based on a predefined parameter model of the printing press. The printing press is running, and the operator checks the print quality and ensures that the solvent concentration remains below explosion safety limits. The operator "processes" the parameters until the quality is good. Then, the operator accepts the settings, and the job runs.

[0026] Once the settings are accepted, the printing press records the unit-specific drying parameters 40, printing parameters 30, and the brand 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 and 40 to a remote computer 7. The remote computer creates entries in a database 79 and builds a lookup table for each drying unit model. In other words, the remote computer establishes a correspondence between the global printing parameters 30, the unit-specific drying parameters 40, and the power consumption. For example, we can calculate the K_solv value for each ink-solvent combination and the K_dry value for each type of printing unit. If sufficient data is available, we can select all printing jobs with the same printing unit configuration, the same ink, and the same solvent, and interpolate or select among the parameter sets that lead to successful jobs.

[0027] The remote computer is preferably connected to multiple printing presses around the world. Therefore, when a printing press begins a new job, if it lacks the data or knowledge required to set the printing and / or drying parameters 30, 40, it can send a request to the remote computer. The calculation is a two-step process performed on the remote computer: first, it determines the maximum printing speed 108 for each printing or coating unit 2, then selects a compatible printing speed 8—preferably the maximum printing speed 108 of the slowest printing unit—and then, considering the printing speed 8, it determines the unit-specific drying parameters 40 for each printing unit with the aim of minimizing power consumption. Therefore, the remote computer searches for the model of the printing press / drying unit in database 79, and considers… - The type, width, and thickness of the substrate 32 to be printed. - The type of ink or coating material 34, - Solvent type 36 - Print coverage, grammage, and drying percentage: 38. (That is, excluding the global printing parameter 30 which is the printing speed 8), and calculate the maximum printing speed 108 for each printing unit.

[0028] Then, it selects a printing speed 8 compatible with each printing or coating unit 2 and adds it to the global printing parameters 30. Therefore, according to - The type, width, and thickness of the substrate 32 to be printed. - The type of ink or coating material 34, - Solvent type 36 - Print coverage, grammage, and drying percentage: 38. - Printing speed 8, The remote computer 7 calculates the unit-specific drying parameters 40 for each printing or coating unit 2 to consume as little energy as possible. It then sends the unit-specific drying parameters 40 for each printing unit and the (global) printing speed 8 back to the printing press 1.

[0029] In practice, once the remote computer 7 has collected enough data for a given drying unit model, it can construct a parametric model based on global printing parameters 30, including printing speed 8. Figure 5 and Figure 6 (As shown) to calculate drying parameters, and build another model to consider global printing parameters 30 (such as) that do not include printing speed 8. Figure 4 The maximum printing speed of 108 is calculated using the figure shown. This model can be calculated by fitting statistical data between a group of global printing parameters 30 and unit-specific drying parameters 40, or by interpolation using machine learning techniques.

[0030] When data is missing (e.g., if the substrate is new), the remote computer works by analogy: it finds a known material with the most similar properties and sets the printing press according to the parameters associated with that material. For example, if a new plastic substrate is used, the remote computer will find another plastic in the list. If a new metal substrate is used, the remote computer will use the parameters of another metal substrate in the list. Furthermore, when setting tension-related parameters for a new material, the remote computer will use data from substrates with similar Young's modulus. These parameters are provided as initial parameters, and if the result does not produce a print that meets specifications, the operator will correct them.

[0031] Over time, whenever quality control is performed and verified, the printing press can send information about drying parameters, printing or coating parameters, the brand and model of the drying unit, and a quality label. The quality label indicates whether the print conforms to specifications or not. Note that the printing press can send this information even if the quality is deemed non-compliant. This information, once collected over time, will improve the accuracy of determining the set of global printing parameters 30 and unit-specific drying parameters 40.

[0032] Preferably, the parameter model of the printing press or drying unit is learned based on an empirical model of the printing press with corrections. Therefore, the system learns the differences to apply to the parameter set in consideration of a predetermined parameter model. The predetermined parameter model is based on experience and historical knowledge of the printing press.

[0033] Set printing machine parameters Once the printing speed 8 is determined, the control unit 9 of the printing press 1 sets some minor parameters for the control substrate speed and tension of the printing press, and sets parameters in each printing press unit.

[0034] The substrate is stored on reel 50 and unwound by unwinder 60. This is followed by an unwinder traction group 62 that controls the substrate tension. The substrate is then processed by this group of printing units, passed through a rewinder traction group 72 (also used to control substrate tension), and finally rewound in rewinder 70 to complete the process 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 are all parameters that can be added to the global printing parameters. Adding these parameters to the global printing parameters provides a more complete printing press control model, allowing for the collection of a complete set of parameters for producing compliant printed materials.

[0035] Set up printing unit Within each printing unit, the printing press control system sets the unit impression (Nip) pressure 82, doctor blade pressure 84, doctor blade oscillation speed 86, ink pump speed and pressure 88, ink roller speed 90 (depending on the substrate speed), and ink roller pressure 92. These parameters can be added to the global printing parameters. Adding these parameters to the global printing parameters provides a more complete printing unit control model, allowing for the collection of a complete set of parameters for producing compliant printed materials.

Claims

1. A method for controlling a printing or coating unit (2) having a drying unit (6), said drying unit (6) comprising a controllable fan (12) and an air recirculation loop (10), said method comprising: a) A group for setting the global printing parameters (30) of the printing or coating unit (2), defined as a parameter group including the following parameters: - Printing speed (8). - The type, width, and thickness of the substrate (32) to be printed, - The type of ink or coating material (34), - The type of solvent (36) for the ink or coating material (34), - Print coverage of ink or coating material (34) on the substrate to be printed (32), weight of ink or coating material (34) on the substrate to be printed (32), and drying percentage of ink or coating material (34) (38). b) Set the fan speed (13) and temperature (15) of the drying unit (6) according to a predetermined formula and / or according to a lookup table to obtain a group of unit-specific drying parameters (40) for the drying unit (6), the group consisting of the fan speed (13) and temperature (15) of the drying unit (6), wherein each of the unit-specific drying parameters (40) in the group is set according to the printing parameters (30); c) Then, the substrate (4) is processed using the printing or coating unit (2) according to the settings set in a) and b). The fan speed (13) and the temperature (15) are set based on the calculated amount of solvent (36) removed from the substrate per unit time, wherein the amount of solvent (36) to be removed is calculated by multiplying the amount of ink passing through the drying unit by the percentage of solvent in the ink, wherein the amount of ink is calculated by multiplying the weight by the printing coverage and the printing speed (8).

2. The method of claim 1, wherein step (b) of setting the unit-specific drying parameter (4) includes setting an air recirculation rate (23) as a part of the unit-specific drying parameter (40), and wherein the air recirculation rate (23) is set based on a calculated amount of solvent (36) removed from the substrate per unit time.

3. The method according to claim 2, wherein the air recirculation rate (23) is set by a damper (22) located on the recirculation loop (10) of the drying unit (6), the damper (22) removing a portion of the air in the air recirculation loop (10) and replacing it with fresh air, and wherein the damper (22) adjusts the air recirculation rate (23) to achieve a concentration of solvent in the air recirculated from the ink or coating material (34) into the air recirculation loop (10) such that the concentration meets predetermined safety specifications while reaching the maximum permissible level.

4. The method according to any one of the preceding claims, for a printing or coating unit connected to a remote computer (7), the method further comprising measuring the power consumption (100) or the printing or coating unit (2), wherein, The global printing parameters (30), the unit-specific drying parameters (40), the power consumption (100), and the brand and model of the drying unit are sent to the remote computer (7).

5. A printing or coating unit (1) including a drying unit (6), said drying unit (6) comprising - Air recirculation loop (10). - A fan with controllable speed (12). - Thermometer (16). - The area configured to receive the running substrate (4), - Sensor (20), configured to measure the concentration of solvent evaporated from ink or coating material (34) into the air recirculated in the air recirculation loop (10), and - Damper (22), which is connected to air inlet (24) and air outlet (26). The printing or coating unit (2) includes a control unit (9) configured to implement the method according to any one of the preceding claims.

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