Printing method and printing device

Abstract

To provide a technology that can readily control temperature of ink by feed forward control of a heater even when a flow rate of ink varies.SOLUTION: An FF control unit 911 generates an FF control value CV1 on the basis of a first temperature Tt1 of ink before being heated by a heater 351. A gain inference unit 914 performs reinforcement learning for inferring a gain G1 used for correcting the FF control value CV1 on the basis of an equivalent amount in accordance with an amount of ink discharged from a discharge head 21. A control value correction part 913 corrects the FF control value CV1 on the basis of the gain G1 that has been inferred by the gain inference unit 914.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a printing method and a printing device. [Background technology]

[0002] Conventionally, there is known a printing device that forms an image on a substrate by ejecting ink from an ejection head onto the surface of the substrate while transporting the substrate in a continuous form using a roll-to-roll method. In this type of printing device, ink viscosity control is generally important.

[0003] For example, if the temperature of the ink drops, the viscosity increases, causing uneven ejection, which can lead to problems such as misalignment of the ink landing position or the occurrence of streaks. For this reason, a mechanism for heating the ink is sometimes provided to keep the ink temperature constant.

[0004] For example, in Patent Document 1, ink is circulated in a circulation path connected to a discharge head, and the ink flowing through the circulation path is heated by a hot water unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2016-055501 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, the amount of ink consumed by the ejection head can fluctuate from time to time depending on the print pattern printed on the substrate. Therefore, the temperature of the ink sent from the ink tank storing unused ink to the ejection head can fluctuate irregularly depending on the ink flow rate. Therefore, simply heating the ink in the ejection head uniformly results in a large fluctuation in ink temperature. Therefore, it is necessary to appropriately control the heater power.

[0007] Feedback (FB) control is often used as a heater control method, but with FB control, temperature control is performed after detecting a change in flow rate, so it can be difficult to respond quickly to temperature changes. For this reason, it is possible to apply feedforward (FF) control.

[0008] In FF control, a gain is set to correct the FF control value that controls the heater. However, the gain must be readjusted every time the environment changes, which requires a lot of work. For this reason, it has not been easy to regulate the ink temperature using FF control.

[0009] An object of the present invention is to provide a technique that can easily adjust the temperature of ink by feedforward control of a heater even when the ink flow rate fluctuates. [Means for solving the problem]

[0010] In order to solve the above problem, a first aspect is a printing method, comprising: a) ejecting ink from an ejection head onto a surface of a long strip-shaped substrate while transporting the substrate along a predetermined transport path; Discharge The method includes the steps of: supplying an amount of ink corresponding to the amount of ink ejected from the head from an ink tank capable of storing the ink to the ejection head; and c) controlling a heater that heats the ink, wherein the step c) includes: c-1) measuring a first temperature of the ink before being heated by the heater; c-2) generating a feedforward control value based on the first temperature; c-3) performing reinforcement learning of an inference device that infers a gain that corrects the feedforward control value based on the equivalent amount; and c-4) controlling the heater based on the feedforward control value corrected by step c-3).

[0011] A second aspect is the printing method of the first aspect, Memorandum The logic device further infers the gain based on the first temperature.

[0012] A third aspect is the printing method of the first or second aspect, wherein the first temperature is a temperature of the ink at an inlet of the heater.

[0013] A fourth aspect is the printing method of the first or second aspect, wherein the first temperature is the temperature of the ink in the ink tank.

[0014] A fifth aspect is a printing method according to any one of the first to fourth aspects, wherein the step c) further comprises: c-5) measuring a second temperature of the ink heated by the heater; and c-6) feedback-controlling the heater based on the second temperature.

[0015] The sixth aspect is , th 5 states Dear In a printing method, the second temperature is a temperature of the ink at an outlet of the heater.

[0016] The seventh aspect is 5 Aspects or Sixth state Dear In the printing method, the second temperature sensor measures the temperature of the ink in a reservoir included in the ejection head.

[0017] An eighth aspect is a printing device comprising: an ejection head that ejects ink; an ink tank capable of storing the ink; a supply unit that supplies an amount of ink corresponding to the amount of ink ejected from the ejection head from the ink tank to the ejection head; a heater that heats the ink; a first temperature sensor that measures a first temperature of the ink before being heated by the heater; and a control unit that controls the heater, wherein the control unit has a feedforward control unit that generates a feedforward control value for feedforward control of the heater based on the first temperature; a gain inference unit that performs reinforcement learning to infer a gain used to correct the feedforward control value based on the equivalent amount; and a control value correction unit that corrects the feedforward control value based on the gain inferred by the gain inference unit.

[0018] A ninth aspect is a printing device of the eighth aspect, further comprising a second temperature sensor that measures a second temperature of the ink heated by the heater, and the control unit further has a feedback control unit that generates a feedback control value for feedback controlling the heater based on the second temperature, and the control unit controls the heater based on the feedback control value output by the feedback control unit. [Effects of the Invention]

[0019] According to the printing method of the first aspect, even if the ink flow rate changes, the feedforward control value is corrected with a gain corresponding to the flow rate. This enables feedforward control that reflects the actual situation. This allows the ink temperature to be appropriately controlled, reducing printing defects and suppressing unnecessary consumption of ink and substrate.

[0020] According to the printing method of the second aspect, the temperature of the ink before it is heated by the heater can be reflected in the feedforward control.

[0021] According to the printing device of the third aspect, the temperature of the ink immediately before it is heated by the heater can be reflected in the feedforward control.

[0022] According to the printing device of the fourth aspect, the temperature of the ink stored in the ink tank can be reflected in the gain.

[0023] According to the printing method of the fifth aspect, the heater is further feedback-controlled, so that the ink temperature can be brought closer to the target temperature.

[0024] According to the printing method of the sixth aspect, the temperature of the ink at the outlet of the heater can be reflected in the feedback control.

[0025] According to the printing method of the seventh aspect, the temperature of the ink at the ejection position can be reflected in the feedback control.

[0026] According to the printing device of the eighth aspect, even if the ink flow rate changes, the feedforward control value is corrected using a gain that corresponds to the flow rate. This enables feedforward control that reflects the actual situation. This allows the ink temperature to be appropriately controlled, reducing printing defects and suppressing unnecessary consumption of ink and substrate.

[0027] According to the printing device of the ninth aspect, the temperature of the ink can be adjusted more appropriately by feedback control. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a printing apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing connections between a control unit and each unit of the printing device. [Figure 3] FIG. 2 is a diagram showing a control block for controlling a heater. [Figure 4] FIG. 10 is a diagram showing the change over time in outlet temperature before and after gain adjustment. [Figure 5] FIG. 10 is a diagram showing a first reinforcement learning flow executed by a gain inference unit. [Figure 6] FIG. 10 is a diagram illustrating a second reinforcement learning process performed by the gain inference unit. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the components described in the embodiment are merely examples and are not intended to limit the scope of the present invention. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0030] <1. Embodiment> FIG. 1 is a diagram showing the configuration of a printing device 1 according to an embodiment. The printing device 1 is a device that performs printing using an inkjet method. More specifically, the printing device 1 records an image on the surface of a long strip-shaped substrate W by ejecting ink from multiple ejection heads 21-24 onto the substrate W while transporting the substrate W using multiple transport rollers 12. The substrate W is, for example, a flexible medium, such as printing paper, a resin film, cardboard, or a thin metal film.

[0031] As shown in FIG. 1, the printing apparatus 1 includes a transport mechanism 10, a printing unit 20, a supply unit 30, an encoder 60, a camera 70, a plurality of various sensors 80, and a control unit 9.

[0032] The transport mechanism 10 transports the base material W along a predetermined transport path in a transport direction that is along the longitudinal direction of the base material W. The transport mechanism 10 has an unwinding roller 11, multiple transport rollers 12, and a winding roller 13. The base material W is stretched across these rollers. The base material W is unwound from the unwinding roller 11 and transported along the predetermined transport path while being supported by the multiple transport rollers 12. Each transport roller 12 rotates about an axis extending perpendicular to the transport direction, thereby guiding the base material W to the downstream side of the transport path. The base material W transported by the multiple transport rollers 12 is wound up by the winding roller 13. Tension is applied to the base material W in the transport direction. This prevents the base material W from sagging or wrinkling during transport.

[0033] The transport mechanism 10 further includes a motor 14 that rotates some of the rollers (hereinafter referred to as "drive rollers"). The transport mechanism 10 may include multiple motors 14. The motors 14 are electrically connected to the control unit 9. When the motors 14 are driven, the control unit 9 inputs a command value to each motor 14 to drive the motor 14 to rotate. The motor 14 then drives in accordance with the command value, causing the drive roller to rotate. As a result, the substrate W is transported from the unwinding roller 11 toward the winding roller 13.

[0034] The printing unit 20 is a processing unit that ejects ink droplets (hereinafter referred to as "ink droplets") onto the substrate W transported by the transport mechanism 10. The printing unit 20 has multiple (four in this example) ejection heads 21-24. The ejection heads 21-24 have the same structure. The ejection heads 21-24 are arranged at intervals along the transport direction of the substrate W. The substrate W moves below the multiple ejection heads 21-24, approximately parallel to the arrangement direction of the multiple ejection heads 21-24. At this time, the surface (printing surface) of the substrate W faces upward (toward each ejection head 21-24).

[0035] Each of the ejection heads 21-24 has an internal space capable of storing ink and a plurality of nozzles (not shown). The plurality of nozzles are arranged parallel to the width direction of the substrate W on the underside of each of the ejection heads 21-24. Each of the plurality of nozzles has a piezoelectric element (not shown) as a pressure-generating element and an ejection port communicating with the internal space of each of the ejection heads 21-24. When ejecting ink, ink flows down from the internal space to the vicinity of the ejection port. Then, the action of the piezoelectric element pressurizes the ink near the ejection port, causing droplets of ink to be ejected from the ejection port. The ink ejection method may be a so-called thermal method, in which a heater is used as a pressure-generating element to heat the ink near the ejection port and generate bubbles.

[0036] Each of the ejection heads 21-24 ejects ink droplets of each color—K (black), C (cyan), M (magenta), and Y (yellow)—that constitute the color components of a multicolor image from multiple nozzles toward the upper surface of the substrate W. That is, the ejection head 21 ejects K ink droplets as a treatment material onto the upper surface of the substrate W at a first printing position P1, which is a processing position on the transport path. The ejection head 22 ejects C ink droplets as a treatment material onto the upper surface of the substrate W at a second printing position P2, which is a processing position downstream from the first printing position P1. The ejection head 23 ejects M ink droplets as a treatment material onto the upper surface of the substrate W at a third printing position P3, which is a processing position downstream from the second printing position P2. The ejection head 24 ejects Y ink droplets as a treatment material onto the upper surface of the substrate W at a fourth printing position P4, which is a processing position downstream from the third printing position P3.

[0037] In this embodiment, the first printing position P1, the second printing position P2, the third printing position P3, and the fourth printing position P4 are arranged at equal intervals along the transport direction of the substrate W. The ejection heads 21-24 each record a single-color image on the upper surface of the substrate W by ejecting ink droplets. Then, a multi-color image is formed on the upper surface of the substrate W by superimposing the four single-color images. Each ejection head 21-24 can also print on the upper surface of the substrate W by ejecting ink droplets.

[0038] The supply unit 30 is a unit that supplies ink to the ejection heads 21-24. The supply unit 30 has multiple (four in this example) ink supply systems 31. The multiple ink supply systems 31 are connected to the ejection heads 21-24 respectively, and supply ink of the corresponding color to the ejection heads 21-24 respectively. The ink supply system 31 that supplies ink to the ejection head 21 will be described below.

[0039] The ink supply system 31 includes an ink tank 311 , a pipe 321 , a pump 331 , a flow meter 341 , a heater 351 , an inlet temperature sensor 361 , an outlet temperature sensor 371 , and a liquid level sensor 381 .

[0040] The ink tank 311 is capable of storing unused ink. One end of the pipe 321 is connected to the internal space of the ejection head 21. The other end of the pipe 321 is connected to the ink tank 311. The pump 331 is installed in the pipe 321. The pump 331 operates based on a drive value input from the control unit 9. It generates a flow of ink from the ink tank 311 to the ejection head 21. The pump 331 is, for example, a pump equipped with a brushless motor. The pipe 320 and the pump 331 are an example of a "supply unit" that supplies ink from the ink tank 311 to the ejection head 21. Note that the ink in the ink tank 311 may be sent to the ejection head 21 by a pressurizing mechanism that pressurizes the inside of the ink tank 311. In this case, the pressurizing mechanism functions as the "supply unit."

[0041] A primary tank that supplies ink to the ink tank 311 may be provided upstream of the ink tank 311. Ink may be supplied from the primary tank in response to a decrease in the amount of ink stored in the ink tank 311, for example.

[0042] The flow meter 341 is installed in the pipe 321. The flow meter 341 measures the flow rate of the ink flowing in the pipe 321. The flow meter 341 transmits a signal indicating the measured flow rate value to the control unit 9.

[0043] When ink droplets are ejected from the ejection head 21 toward the substrate W, the amount of ink in the ejection head 21 decreases. The control unit 9 inputs a drive value to the pump 331 in accordance with the decrease in the amount of ink in the ejection head 21. As a result, the pump 331 is driven in accordance with the drive value, and an amount of ink corresponding to the amount of ink that has decreased in the ejection head 21 (an amount equivalent to the amount of ink) is supplied from the ink tank 311 to the ejection head 21. As with the ejection head 21, ink is also supplied to the other ejection heads 22-24 from the corresponding ink supply systems 31.

[0044] The heater 351 heats the ink supplied from the ink tank 311 to the ejection head 21 by the pump 331. The heater 351 is installed in the pipe 321. The heater 351 is located between the pump 331 and the flow meter 341. The heater 351 heats the ink flowing through the pipe 321.

[0045] The inlet temperature sensor 361 is located in a piping section of the piping 321 between the ink tank 311 and the heater 351. The inlet temperature sensor 361 is disposed at the inlet of the heater 351. The inlet temperature sensor 361 transmits a signal indicating the measured temperature to the control unit 9. The inlet temperature sensor 361 is an example of a "first temperature sensor" that measures the temperature of ink flowing from the ink tank 311 to the heater 351.

[0046] The outlet temperature sensor 371 is installed in the pipe 321. The outlet temperature sensor 371 is located between the heater 351 and the ejection head 21. The outlet temperature sensor 371 measures the temperature of the ink flowing from the heater 351 to the ejection head 21 via the pipe 321. In this example, the outlet temperature sensor 371 is provided near the outlet of the heater 351. Therefore, the outlet temperature sensor 371 measures the temperature of the ink immediately after passing through the heater 351. However, the outlet temperature sensor 371 may be located closer to the ejection head 21 than the heater 351. The outlet temperature sensor 371 transmits a signal indicating the measured temperature to the control unit 9. The outlet temperature sensor 371 is an example of a "second temperature sensor" that measures the temperature (second temperature) of the ink flowing from the heater 351 to the ejection head 21, 22, 23, or 24.

[0047] The liquid level sensor 381 is a sensor for measuring the amount of ink in the ejection head 21, and measures the height of the ink liquid surface in the ejection head 21. The liquid level sensor 381 is, for example, a non-contact sensor that detects the height of the liquid surface using ultrasonic waves. The liquid level sensor 381 transmits a signal indicating the measured liquid level to the control unit 9.

[0048] The supply unit 30 has an outside air temperature sensor 39. The outside air temperature sensor 39 is located outside the ink tank 311 and measures the outside air temperature outside the ink tank 311.

[0049] The encoder 60 is attached to the shaft core of one of the plurality of conveying rollers 12 (in the example of FIG. 1, the conveying roller 121). The encoder 60 detects the rotation of the conveying roller 121 and outputs a continuous pulse signal synchronized with the rotation of the conveying roller 121 to the control unit 9. The continuous pulse signal is data reflecting a change over time in the conveying speed of the substrate W conveyed by the plurality of conveying rollers 12 including the conveying roller 121.

[0050] The camera 70 is an imaging device that captures an image of the printed surface (front surface) of the substrate W that has passed through the printing unit 20. The camera 70 is disposed facing the printed surface of the substrate W at an imaging position P5 that is downstream of the four ejection heads 21-24 on the conveyance path. The camera 70 has, for example, a line sensor in which a plurality of imaging elements, such as CCD or CMOS, are arranged in the width direction. While the substrate W is being conveyed by the conveyance mechanism 10, the camera 70 captures images of the printed surface of the substrate W at predetermined intervals, thereby acquiring image data of the printed substrate W. The camera 70 transmits the obtained image data to the control unit 9.

[0051] The multiple sensors 80 are measuring instruments that measure the transport state of the substrate W in addition to those listed above. The multiple sensors 80 are provided at multiple measurement points on the transport path of the substrate W. The sensors 80 acquire measurement values ​​at each measurement point. Measurement items of the sensors 80 may include, for example, the vertical displacement of the substrate W (the amount of displacement in a direction perpendicular to the substrate W), the tension applied to the substrate W, and the widthwise position of the edge of the substrate W. Note that the sensors 80 that measure the same item may be disposed at multiple positions on the transport path. While the substrate W is transported by the transport mechanism 10, the multiple sensors 80 constantly measure the state at each measurement point. The sensors 80 then transmit signals indicating the obtained measurement values ​​to the control unit 9.

[0052] 2 is a block diagram showing the connections between the control unit 9 and each unit of the printing device 1. The control unit 9 controls the operation of the printing device 1. The control unit 9 has a processor 91 formed of a CPU or the like, and a storage unit 93 formed of a RAM, a hard disk, or the like. The storage unit 93 stores a program 90P and various data.

[0053] The program 90P is provided by a recording medium M. The program 90P is recorded on the recording medium M so as to be readable by a control unit 9, which is a computer. The recording medium M is, for example, a USB (Universal Serial Bus) memory, an optical disk such as a DVD (Digital Versatile Disc), or a magnetic disk.

[0054] The control unit 9 is communicatively connected to the motor 14 of the transport mechanism 10, the ejection heads 21-24 of the printing unit 20, the pump 331 of the supply unit 30, the flow meter 341, the heater 351, the inlet temperature sensor 361, the outlet temperature sensor 371, the liquid level sensor 381, and the outside air temperature sensor 39. The control unit 9 is also communicatively connected to the encoder 60, the camera 70, and various sensors 80.

[0055] The control unit 9 controls the heater 351 so that the temperature of the ink supplied to the ejection heads 21-24 becomes a predetermined target temperature. The ejection control unit 910, feedforward (FF) control unit 911, feedback (FB) control unit 912, control value correction unit 913, and gain inference unit 914 shown in Fig. 2 are functions realized by the processor 91 executing the program 90P.

[0056] The ejection control unit 910 controls the ejection of ink from the ejection heads 21-24 based on a print pattern that indicates an image to be printed on the substrate W. The FF control unit 911 and the FB control unit 912 generate control values ​​for controlling the heater 351. The functions of the FF control unit 911, the FB control unit 912, the control value correction unit 913, and the gain inferrer 914 will be described with reference to FIG. 3.

[0057] <Heater control> 3 is a diagram showing a control block for controlling the heater 351. The following explanation will mainly focus on the case where the heater 351 of the ink supply system 31 connected to the ejection head 21 is controlled. The same control as that shown in FIG. 3 is also performed in the ink supply system 31 connected to the ejection heads 22-24.

[0058] The FF control unit 911 performs FF control on the heater 351. The FF control unit 911 generates an FF control value CV1. The FF control value CV1 is, for example, a value indicating the power value applied to a heat source (e.g., a heating wire) in the heater 351. The FF control unit 911 outputs the FF control value CV1 based on a difference value (temperature difference ΔT1) between the target temperature Ttg and an inlet temperature Tt1 measured by the inlet temperature sensor 361, and a flow rate FR1 measured by the flow meter 341. The FF control value CV1 output by the FF control unit 911 is input to the control value correction unit 913. As described above, the pump 331 is controlled to supply, to the ejection head 21, an amount of ink corresponding to the amount of ink ejected by the ejection head 21. Therefore, the flow rate FR1 measured by the flow meter 341 corresponds to the equivalent amount of ink.

[0059] The FB control unit 912 performs FB control on the heater 351 so that the temperature of the ink measured by the outlet temperature sensor 371 becomes a preset target temperature Ttg. The FB control is preferably PID control or PI control. The FB control unit 912 generates an FB control value CV2. The FB control value CV2 is, for example, a value indicating the power value applied to a heat source (e.g., a heating wire) in the heater 351. The FB control unit 912 outputs the FB control value CV2 based on the difference value (temperature difference ΔT2) between the target temperature Ttg and the outlet temperature Tt2 measured by the outlet temperature sensor 371.

[0060] The control value corrector 913 calculates a corrected FF control value CV1 (modified FF control value CV1a) by multiplying the FF control value CV1 by a gain G1.

[0061] 3, the control unit 9 inputs a heater command value CV3 obtained by adding the corrected FF control value CV1a and the FB control value CV2 to the heater 351. In this way, the heater 351 is controlled.

[0062] FIG. 4 is a diagram showing changes over time in outlet temperature Tt2 before and after adjustment of gain G1. In FIG. 4, the horizontal axis represents time, and the vertical axis represents outlet temperature Tt2. Also in FIG. 4, graph gr1 represents temperature changes before adjusting gain G1, and graph Gr2 represents temperature changes after adjusting gain G1. As graph Gr1 shows, when gain G1 is not adjusted, outlet temperature Tt2 is higher than the target temperature guideline (here, 32°C), and outlet temperature Tt2 decreases over time. In contrast, by adjusting gain G1, it becomes possible to maintain outlet temperature Tt2 near the target temperature guideline, as shown by graph gr2.

[0063] 3, the gain inference unit 914 has a function of inferring an appropriate gain G1 by executing reinforcement learning. Specifically, the gain inference unit 914 uses the temperature difference ΔT1, the temperature difference ΔT2, the flow rate FR1, and the gain G1 currently used by the control value corrector 913 as input variables, and the new gain G1 as an output variable.

[0064] The new gain G1 output by the gain inferrer 914 is input to the control value corrector 913. As a result, the control value corrector 913 used in the control value corrector 913 is replaced with the new gain G1.

[0065] FIG. 5 is a diagram showing the flow of the first reinforcement learning executed by the gain inference unit 914. The first reinforcement learning starts when the printing process in the printing device 1 starts. In this reinforcement learning, the gain inference unit 914 evaluates the performance of the gain G1 held by the control value correction unit 913 (evaluation step S11). The performance evaluation of the gain G1 is performed, for example, using the temperature fluctuation range within a predetermined evaluation interval. The temperature fluctuation range is, for example, the difference between the maximum and minimum values ​​of the outlet temperature Tt2 during one heating on / off cycle of the heater 351. Note that in the evaluation step S11, the temperature fluctuation range may be evaluated based on the standard deviation.

[0066] After the evaluation step S11, the gain inference unit 914 determines whether the printing process has ended (determination step S12). If the printing process has not ended (No in the determination step S12), the gain inference unit 914 outputs a new gain G1 calculated by reinforcement learning based on the evaluation in the evaluation step S11 to the control value correction unit 913. As a result, the gain G1 of the control value correction unit 913 is replaced with the new gain G1 (replacement step S13). Then, the gain inference unit 914 executes the evaluation step S11 again. If the printing process has ended (Yes in the determination step S12), the gain inference unit 914 ends the reinforcement learning. In this way, from the start of the printing process until the end of the printing process, the gain inference unit 914 repeatedly replaces (updates) the gain G1 of the control value correction unit 913 by reinforcement learning.

[0067] The initial value of the gain G1 may be a value determined in advance through a preliminary experiment, or may be a randomly assigned value. In either case, the gain G1 is automatically adjusted to an appropriate value as reinforcement learning progresses.

[0068] FIG. 6 is a diagram illustrating the second reinforcement learning executed by the gain inference unit 914. The second reinforcement learning illustrated in FIG. 6 is executed based on the temperature fluctuation range. Specifically, when the temperature fluctuation range increases during the printing process and exceeds a predetermined tolerance, the second reinforcement learning illustrated in FIG. 6 is started. In the second reinforcement learning, the gain inference unit 914 determines whether the gain G1 satisfies predetermined performance based on the evaluation result of the evaluation step S11 (determination step S21). If the predetermined performance is satisfied (Yes in the determination step S21), the gain inference unit 914 terminates the processing. If the predetermined performance is not satisfied (No in the determination step S21), the gain inference unit 914 executes the replacement step S13. Then, upon completion of the replacement step S13, the gain inference unit 914 executes the evaluation step S11 again. In this way, each time the temperature fluctuation range exceeds the predetermined tolerance, the gain G1 held by the control value correction unit 913 is repeatedly replaced based on the reinforcement learning until the temperature fluctuation range becomes equal to or less than the predetermined tolerance.

[0069] As described above, in the printing device 1 of this embodiment, the gain inferrer 914 updates the gain G1 through reinforcement learning based on the sensor information detected by each sensor. This allows the gain G1 to be automatically adjusted to an appropriate value based on the actual operating environment. Therefore, even if the environment of the device changes, the effort of readjusting the gain G1 can be eliminated. This allows ink temperature adjustment through FF control of the heater 351 to be performed appropriately and easily.

[0070] Furthermore, by controlling the heater 351 using a combination of feedforward control and feedback control, it is possible to bring the ink closer to the target temperature while reducing the temperature fluctuation range of the ink.

[0071] <2. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0072] For example, in the above embodiment, the gain inferor 914 is configured to perform reinforcement learning. However, the learning algorithm may also be deep reinforcement learning, which combines reinforcement learning with deep learning.

[0073] In the above embodiment, the flow rate value FR1 measured by the flow meter 341 is used as an input to the FF control unit 911 and the gain inferrer 914. However, instead of the flow rate value FR1, a drive control value for the pump 331 (for example, a drive voltage of the pump) may be used.

[0074] In the above embodiment, the control unit 9 controls one heater 351 using the heater command value CV3 obtained by adding the corrected FF control value CV1a and the FB control value CV2. However, the corrected FF control value CV1a and the FB control value CV2 may be separated and used to control two heaters, respectively.

[0075] Furthermore, in the above embodiment, the inlet temperature Tt1 near the inlet of the heater 351 is used as an input to the FF control unit 911 and the gain inferrer 914. However, instead of the inlet temperature Tt1, for example, the ink temperature inside the ink tank 311 may be used. Also, a temperature sensor may be provided that measures the temperature of the ink inside the ink tank 311. In this case, the temperature of the ink stored in the ink tank 311 can be reflected in the FF control.

[0076] In the above embodiment, the outlet temperature Tt2 near the outlet of the heater 351 is used as an input to the FB control unit 912. However, instead of the outlet temperature Tt2, the ink temperature inside the ejection heads 21-24 or the ink temperature inside a reservoir (not shown) provided in the ejection heads 21-24 may be used. In this case, the ink temperature at the ink ejection position can be reflected in the FB control.

[0077] In the above embodiment, ink is supplied in one direction from the supply unit 30 to each of the ejection heads 21-24. However, a circulation path for circulating ink between the supply unit 30 and each of the ejection heads 21-24 may be provided. Also, a circulation path for circulating ink within the ejection heads 21-24 may be provided. Also, a heater for heating ink may be provided on the circulation path, and the control unit 9 may control the heater.

[0078] Although the present invention has been described in detail, the above description is merely illustrative in all respects and does not limit the present invention. It is understood that countless variations not illustrated can be envisioned without departing from the scope of the present invention. The configurations described in the above embodiments and variations can be combined or omitted as appropriate as long as they are not mutually inconsistent. [Explanation of symbols]

[0079] 1 Printing device 9 Control Unit 21 Discharge head 910 Discharge control section 911 FF control unit 912 FB control unit 913 Control value correction unit 914 Gain Inferor 311 Ink Tank 331 Pump (supply section) 341 Flowmeter 351 Heater 361 Inlet temperature sensor (first temperature sensor) 371 Outlet temperature sensor (second temperature sensor) W Base material

Claims

1. 1. A printing method comprising: a) ejecting ink from an ejection head onto a surface of a long strip-shaped substrate while transporting the substrate along a predetermined transport path; b) supplying the ink from an ink tank capable of storing the ink to the ejection head in an amount corresponding to the amount of the ink ejected from the ejection head; c) controlling a heater that heats the ink; Including, The step c) c-1) measuring a first temperature of the ink before being heated by the heater; c-2) generating a feedforward control value based on the first temperature; c-3) performing reinforcement learning of an inference device that infers a gain that corrects the feedforward control value based on the corresponding amount; c-4) controlling the heater based on the feedforward control value corrected in step c-3); A printing method including:

2. 2. The printing method according to claim 1, The printing method, wherein the inferrer further infers the gain based on the first temperature.

3. 3. The printing method according to claim 1, further comprising: The printing method, wherein the first temperature is a temperature of the ink at an inlet of the heater.

4. 3. The printing method according to claim 1, further comprising: A printing method, wherein the first temperature is a temperature of ink in the ink tank.

5. 3. The printing method according to claim 1, further comprising: The step c) c-5) measuring a second temperature of the ink heated by the heater; c-6) feedback-controlling the heater based on the second temperature; A printing method comprising:

6. 6. The printing method according to claim 5, The printing method, wherein the second temperature is a temperature of the ink at an outlet of the heater.

7. 6. The printing method according to claim 5, A printing method, wherein the second temperature is the temperature of the ink in a reservoir of the ejection head.

8. 1. A printing device, comprising: an ejection head that ejects ink; an ink tank capable of storing the ink; a supply unit that supplies the ink from the ink tank to the ejection head in an amount corresponding to the amount of ink ejected from the ejection head; a heater for heating the ink; a first temperature sensor that measures a first temperature of the ink before being heated by the heater; a control unit that controls the heater; Equipped with The control unit a feedforward control unit that generates a feedforward control value for feedforward controlling the heater based on the first temperature; a gain inferrer that performs reinforcement learning to infer a gain used to correct the feedforward control value based on the corresponding amount; a control value correcting unit that corrects the feedforward control value based on the gain inferred by the gain inferrer; A printing device comprising:

9. 9. The printing device according to claim 8, a second temperature sensor for measuring a second temperature of the ink heated by the heater; Furthermore, the control unit further includes a feedback control unit that generates a feedback control value for feedback-controlling the heater based on the second temperature; The control unit controls the heater based on a feedback control value output by the feedback control unit.

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