Inkjet printing device

Abstract

To appropriately correct a discharging timing, by suppressing tension of a printing medium and adverse effect of variation in conveyance speed.SOLUTION: In an inkjet printing device 1 according to the embodiment, an Mavgi calculating part 51 calculates one sided movement average value of distances calculated by an Mi calculating part 51, and a di+1 calculating part 51 calculates a correction amount on the basis of the movement average value. A discharging control part 57 controls a discharging timing for a printing head 27W, on the basis of the correction amount. Since the correction amount calculated by the di+1 calculating part 51 is equal to the movement average value, the correction amount can be smoothed even if variation of a detected distance between pages is detected. This can suppress tension of a film WF for soft packaging and adverse effect of variation in conveyance speed to appropriately suppress misregister between images to be printed on each page.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an inkjet printing device that prints by ejecting ink droplets onto a print medium being transported in a predetermined transport direction, and in particular to a technology for suppressing misregistration in the transport direction when printing using inkjet heads arranged at a distance in the transport direction. [Background technology]

[0002] Conventionally, this type of device includes a conveying unit, a first ejection unit, a detection unit, and a second ejection unit (see, for example, Patent Document 1).

[0003] The transport unit transports the long print medium in a predetermined transport direction. The first and second ejection units are spaced apart in the transport direction. The detection unit detects the distance from a predetermined origin for a plurality of predetermined marks printed on the print medium by the first ejection unit for each page. The detection unit calculates an average value of the difference between the detection value detected by the detection unit and a set value based on a theoretical value corresponding to the detection value. The second ejection unit performs ejection by correcting the ejection timing based on the distance between the first and second ejection units and the transport speed of the print medium by adding the calculated average value. This suppresses misregistration in the transport direction due to detection error by the detection unit. In addition, by taking the difference (error) from the set value based on the theoretical value, the effect of elongation in the transport direction due to swelling of the print medium caused by ink droplets is suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-168833 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional example having such a configuration has the following problems. That is, conventional devices detect the marks printed on each page and perform correction based on the difference between the detected value and a set value based on a theoretical value corresponding to the detected value, that is, the average value of the error. Therefore, the device may be adversely affected by fluctuations in the tension of the transported print medium and the transport speed. For example, the device may be affected by local or temporary fluctuations when the detection unit detects the mark, or by long-period fluctuations that exceed the entire length of multiple marks on a page. In other words, correction based on a simple average value of the error may not be able to properly correct the ejection timing. Therefore, misregistration may not be properly corrected.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide an inkjet printing device that can suppress the adverse effects of fluctuations in printing medium tension and transport speed, and appropriately suppress misregistration. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention has the following configuration. That is, the invention described in claim 1 is an inkjet printing device that prints by ejecting ink droplets onto a long printing medium, the inkjet printing device comprising: a transport unit that transports the printing medium in a predetermined transport direction along a predetermined transport path; a first print head that prints an image on multiple pages at a predetermined position on the transport path and prints a predetermined mark indicating a printing start position of the image on the multiple pages in the transport direction; a detection unit that detects the mark at a detection position downstream of the first print head on the transport path; a second print head that prints an image on the multiple pages with an ejection timing based on the mark detected by the detection unit at the predetermined position on the transport path; a distance detection unit that detects the distance over which the printing medium is transported in accordance with detection by the detection unit; a distance calculation unit that calculates the distance between the marks as a mark distance based on the detection by the detection unit and the distance detected by the distance detection unit; a calculation unit that calculates a moving average value of the mark distance for each page calculated by the distance calculation unit and calculates a correction amount based on the moving average value; and a control unit that controls the ejection timing of the second print head based on the correction amount.

[0008] [Actions and Effects] According to the invention described in claim 1, the calculation unit calculates a moving average value of the mark distance calculated by the distance calculation unit, and calculates a correction amount based on this moving average value. The control unit controls the ejection timing of the second print head based on this correction amount. Since the correction amount calculated by the calculation unit is a moving average value, even if the mark distance between pages fluctuates and is detected, it is smoothed out. Therefore, it is possible to suppress the adverse effects of fluctuations in the tension and transport speed of the printing medium, and appropriately suppress misregistration between images printed on each page by the first print head and the second print head.

[0009] In the present invention, it is preferable that the calculation unit calculates the moving average value by a one-sided moving average (claim 2).

[0010] The calculation unit calculates the moving average value by one-sided moving average (also called backward moving average). Since the calculation is performed using only the current value and past value of the mark distance for each page, the calculation load of the calculation unit can be reduced.

[0011] In the present invention, it is preferable that the calculation unit calculates the moving average value by a two-sided moving average (claim 3).

[0012] The calculation unit calculates the moving average value by a two-sided moving average (also called a median moving average). Therefore, the phase delay caused by the one-sided moving average can be eliminated. As a result, even if the range of the variation in the mark distance for each page falls outside a certain range, the ejection timing can be appropriately corrected.

[0013] In the present invention, it is preferable that the calculation section sets the moving average value to a predetermined initial setting value in calculating the moving average value until the number of pages reaches the moving average number (claim 4).

[0014] The moving average value cannot be calculated until the number of pages reaches the moving average number, which is the number of pages for which the moving average value is calculated. In this case, the moving average value is set to a predetermined initial setting value. This makes it possible to prevent an inappropriate correction amount from being obtained even when the moving average value cannot be calculated.

[0015] In the present invention, it is preferable that the moving average number is an odd number (claim 5).

[0016] This is suitable for calculating a two-sided moving average.

[0017] In the present invention, the moving average number is preferably 7 (claim 6).

[0018] This is suitable for calculating a two-sided moving average. Furthermore, it can absorb long-term fluctuations in the mark distance compared to when the value is less than 7. It can reflect fluctuations in the mark distance more quickly compared to when the value is 8 or more.

[0019] In the present invention, it is preferable that the second print head is farther away from the first print head in the transport direction than an arrangement distance in the transport direction between the second print head and the detection unit (claim 7).

[0020] The second print head is separated from the first print head on which the mark is printed. Therefore, when the mark is detected by the detection unit, it is easily affected by tension, etc. Therefore, this is suitable for such a configuration. Effect of the Invention

[0021] In the inkjet printing device according to the present invention, the calculation unit calculates a moving average value of the mark distance calculated by the distance calculation unit, and calculates a correction amount based on this moving average value. The control unit controls the ejection timing of the second print head based on this correction amount. Because the correction amount calculated by the calculation unit is a moving average value, even if the mark distance between pages fluctuates and is detected, it is smoothed out. Therefore, it is possible to suppress the adverse effects of fluctuations in the tension and transport speed of the printing medium, and appropriately suppress misregistration between images printed on each page by the first print head and the second print head. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic configuration diagram showing the entire inkjet printing apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a front view showing a detailed configuration of a printing unit. [Diagram 3] FIG. 2 is a schematic diagram illustrating a print area and a cue mark. [Figure 4] 4 is a time chart for explaining a detection unit signal and a print signal. [Diagram 5] 1A to 1C are schematic diagrams illustrating detection errors and misregistration of cue marks. [Figure 6] 11A and 11B are schematic diagrams illustrating the amount of correction for correcting misregistration. [Figure 7]FIG. 2 is a functional block diagram illustrating details of a control unit according to the first embodiment. [Figure 8] FIG. 10 is a diagram illustrating a correction amount according to the second embodiment. [Figure 9] FIG. 11 is a functional block diagram illustrating details of a control unit according to a second embodiment. [Figure 10] 13 is a graph showing misregistration without correction. [Figure 11] 13 is a graph showing misregistration in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Each embodiment of the present invention will be described below. EXAMPLES

[0024] A first embodiment of the present invention will be described below with reference to the drawings.

[0025] FIG. 1 is a schematic diagram showing the overall configuration of an inkjet printing apparatus according to a first embodiment.

[0026] The inkjet printing apparatus 1 includes a paper feed section 3, a coating section 5, a printing section 7, a main drying section 9, a paper discharge section 11, and a control section 13.

[0027] The left-right direction in Fig. 1 is the transport direction X. The left side of the transport direction X is the downstream side, and the right side is the upstream side. The direction toward the front of the paper surface in Fig. 1 is the width direction Y. The up-down direction in Fig. 1 is the height direction Z. The paper feed unit 3, coating unit 5, printing unit 7, main drying unit 9, and paper discharge unit 11 are arranged in that order toward the downstream side in the transport direction X.

[0028] The paper feed unit 3 supplies the flexible packaging film WF to be printed to the coating unit 5. The paper feed unit 3 holds the long flexible packaging film WF in a roll shape so that it can rotate around a horizontal axis. The flexible packaging film WF is long in the conveying direction X. The paper feed unit 3 unrolls the flexible packaging film WF with the printing surface facing upward relative to the coating unit 5. The material of the flexible packaging film WF is, for example, a hydrophobic base material that has low absorbency of aqueous ink. Examples of the flexible packaging film WF include plastic films such as polypropylene resin, vinyl chloride resin, and polyimide resin.

[0029] The flexible packaging film WF corresponds to the "printing medium" in the present invention.

[0030] The coating unit 5 applies a primer to the flexible packaging film WF to form a primer layer. The primer layer is also called a pretreatment layer, an ink permeation layer, or an ink receiving layer. The primer is a coating liquid, and is also called an undercoat liquid or a base adjustment liquid. Specifically, the coating unit 5 includes a pan 15, a gravure roller 17, and a conveying unit 19.

[0031] The pan 15 stores the primer. The gravure roller 17 has a lower portion partially immersed in the primer stored in the pan 15, and when the gravure roller 17 rotates, the upper portion supplies the primer to the printing surface of the flexible packaging film WF. The conveying section 19 unwinds the flexible packaging film WF from the paper feed section 3 and conveys the flexible packaging film WF to the gravure roller 17. In the region where the primer is supplied by the gravure roller 17, the conveying direction X of the flexible packaging film WF and the rotation direction of the circumferential surface of the gravure roller 17 are opposite. The primer is applied to the flexible packaging film WF by a so-called reverse kiss method. The conveying section 19 conveys the flexible packaging film WF from the application section 5 to the printing section 7 in a position where the printing surface of the flexible packaging film WF to which the primer has been applied faces upward.

[0032] The printing unit 7 includes a color printing unit 21 , a pre-drying unit 23 , a detection unit 25 , a white printing unit 27 , an upper drying unit 29 , and a transport unit 31 .

[0033] The color printing unit 21 prints a color image, for example, by ejecting multiple color inks onto the printing surface of the flexible packaging film WF on which the primer layer has been applied.

[0034] The pre-drying section 23 pre-dries the printed surface of the flexible packaging film WF on which color printing has been performed. The detection section 25 detects a mark indicating the page of the flexible packaging film WF. The mark will be described later. The white printing section 27 ejects white ink onto the printed surface of the flexible packaging film WF on which color printing has been performed to print a white image. The upper drying section 29 dries the printed surface of the flexible packaging film WF on which the white image has been printed. The conveying section 31 conveys the flexible packaging film WF from the above-mentioned color printing section 21 to the upper drying section 29. The printing section 7 will be described in detail later.

[0035] The main drying section 9 dries both the printed surface and the opposite surface of the flexible packaging film WF printed in the printing section 7. Specifically, the main drying section 9 includes a first drying section 33, a second drying section 35, a third drying section 37, a first conveying section 39, a second conveying section 41, and a third conveying section 43. The first drying section 33 dries the printed surface of the flexible packaging film WF conveyed downstream in the conveying direction X by the first conveying section 39. The second drying section 35 dries both sides of the flexible packaging film WF conveyed upstream in the conveying direction X by the second conveying section 41. The third drying section 37 dries both sides of the flexible packaging film WF conveyed downstream in the conveying direction X by the third conveying section 43. The first drying section 33, the second drying section 35, and the third drying section 37 discharge gas heated to a predetermined temperature onto the flexible packaging film WF, thereby drying the image printed on the printing surface of the flexible packaging film WF.

[0036] The paper discharge section 11 winds up the flexible packaging film WF that has been dried by the main drying section 9 around a horizontal axis.

[0037] The control unit 13 comprehensively controls the coating unit 5, the printing unit 7, and the main drying unit 9. The control unit 13 includes a CPU, a memory, a communication unit, and the like. The control unit 13 is connected to a host computer (not shown). An image to be printed on the flexible packaging film WF is provided to the control unit 13 from the host computer as print data.

[0038] The inkjet printing device 1 according to this embodiment performs printing by so-called reverse printing, for example, using the reverse side of the flexible packaging film WF as the printing surface. In the reverse printing printed matter, the reverse side, which is the printing surface, is attached to a member, and the image is visually recognized from the front side of the transparent flexible packaging film WF.

[0039] The above-mentioned printing unit 7 will now be described in detail with reference to Fig. 2. Fig. 2 is a front view showing the detailed configuration of the printing unit.

[0040] The printing unit 7 takes in the flexible packaging film WF from the coating unit 5 from the lower side in the height direction Z and the upstream side in the conveying direction X by the conveying unit 31 having a plurality of conveying rollers 45 including a drive roller. The flexible packaging film WF taken in by the printing unit 7 is redirected upward in the height direction Z at the most downstream of the printing unit 7, and then redirected to the upstream side in the conveying direction X at the upper side. The flexible packaging film WF is once redirected downward in the height direction Z, and is conveyed to the downstream side in the conveying direction X so as to draw an arc upward. The color printing unit 21 is arranged on the conveying path that draws an arc. Here, the conveying path refers to the path that the conveyed flexible packaging film WF follows.

[0041] The color printing unit 21 includes a plurality of (e.g., four) print heads 21K, 21C, 21M, and 21Y. Each of the print heads 21K, 21C, 21M, and 21Y ejects, for example, water-based ink by an inkjet method. Each of the print heads 21K, 21C, 21M, and 21Y ejects, for example, color inks of different colors.

[0042] In this example, color ink means ink other than white. For example, color ink includes cyan (C), magenta (M), yellow (Y), black (K), etc. Print head 21K ejects black ink. Print head 21C ejects cyan ink. Print head 21M ejects magenta ink. Print head 21Y ejects yellow ink. The color printing unit 21 prints a color image on the printing surface of the flexible packaging film WF by ejecting color ink from each of print heads 21K, 21C, 21M, and 21Y onto the printing surface of the flexible packaging film WF.

[0043] The above-mentioned print head 21K corresponds to the "first print head" in the present invention.

[0044] The color-printed flexible packaging film WF is turned downward in the height direction Z, and then conveyed upstream in the conveying direction X. A pre-drying section 23 is disposed in this region. The pre-drying section 23 includes a plurality of gas discharge sections (e.g., nine gas discharge sections). The gas discharge sections discharge dry gas onto the printed surface of the flexible packaging film WF.

[0045] After passing through the pre-drying section 23, the flexible packaging film WF is redirected upward in the height direction Z on the upstream side in the conveying direction X. Above that, the flexible packaging film WF is redirected downstream in the conveying direction X. A white printing section 27 is disposed in the redirected region. The white printing section 27 includes one print head 27W. The print head 27W is, for example, an inkjet nozzle. The print head 27W ejects white (W) ink to print a white image on the printing surface of the flexible packaging film WF on which the color image is printed.

[0046] The above-mentioned print head 27W corresponds to the "second print head" in this invention.

[0047] A conveying roller 45 is disposed upstream of the white printing section 27 at a position where the flexible packaging film WF is changed to a horizontal position. The conveying roller 45 is equipped with an encoder 47. The encoder 47 detects the rotation of the conveying roller 45. The encoder 47 outputs a pulse-shaped signal (a line number signal is generated by appropriately multiplying the signal) in synchronization with the rotation of the conveying roller 45. By counting the signal, the distance conveyed by the flexible packaging film WF can be obtained based on the outer circumferential length of the conveying roller 45.

[0048] The above-mentioned detection unit 25 is attached to the conveying roller 45 to which the encoder 47 is attached. The detection unit 25 detects a predetermined mark (a cue mark CM described later) printed on the flexible packaging film WF being conveyed. The detection unit 25 detects the predetermined mark printed on the flexible packaging film WF in a non-contact manner.

[0049] The above-mentioned encoder 47 corresponds to the "distance detection unit" in the present invention.

[0050] The detection unit 25 and the print head 27W of the white print unit 27 are disposed on the transport path at a distance AL between them. The print head 27W of the white print unit 27 is disposed on the transport path at a distance greater than the distance AL between the print head 21K of the color print unit 21. The print head 27W is disposed at a distance from the print head 21K that is greater than the distance between the print heads 21K, 21C, 21M, and 21Y.

[0051] The flexible packaging film WF that has passed through the white printing unit 27 is redirected toward the downstream side in the conveying direction X. The upper drying unit 29 is disposed in the area where the flexible packaging film WF is in a horizontal position. The upper drying unit 29 is equipped with a plurality of nozzles. Each nozzle sprays air from above toward the printing surface of the flexible packaging film WF being conveyed. The upper drying unit 29 dries the white image printed by the white printing unit 27.

[0052] The control unit 13 comprehensively controls the coating unit 5, the printing unit 7, and the main drying unit 9. The control unit 13 is composed of a CPU, a memory, a communication unit, etc. The control unit 13 is connected to a host computer (not shown). An image to be printed on the flexible packaging film WF is provided to the control unit 13 from the host computer as print data. The control unit 13 will be described in detail later.

[0053] Please refer to Fig. 3. Fig. 3 is a schematic diagram for explaining the print area and the cue mark.

[0054] The flexible packaging film WF is printed while being transported in the transport direction X under the control of the control unit 13 based on predetermined printing conditions. The printing conditions include, for example, the transport speed of the flexible packaging film WF and tension at each section. The control unit 13 causes the color printing unit 21 and the white printing unit 27 to print an image based on print data in the printing area IA of the flexible packaging film WF. For example, a plurality of printing areas IA are set consecutively in the transport direction X of the flexible packaging film WF. Each printing area IA corresponds to a page. The printing areas IA are numbered from the upstream side in the transport direction X as the first page, the second page, ..., the nth page.

[0055] The control unit 13 causes the color printing unit 21 to print a cue mark CM outside the printing area IA of the flexible packaging film WF. The cue mark CM is printed, for example, by the print head 21K of the color printing unit 21. The cue mark CM is formed by ejecting black ink from the print head 21K. The cue mark CM is printed for each printing area IA. The cue mark CM is printed at a position indicating the beginning of the start area of ​​the printing area IA in the transport direction X. In other words, the cue mark CM indicates the start position of the printing area IA. The cue mark CM indicates the start position of each page in a plurality of pages that are continuous in the transport direction X on the flexible packaging film WF.

[0056] The above-mentioned cue mark CM corresponds to the "mark" in the present invention.

[0057] Please refer to Fig. 4. Fig. 4 is a time chart for explaining the detection unit signal and the print signal. The horizontal axis in Fig. 4 is the count value of the signal (encoder pulse) output by the encoder 47.

[0058] The detection unit 25 detects the cue mark CM. For example, the detection unit 25 outputs a signal when it detects the cue mark CM. When the detection unit 25 detects the cue mark CM, it outputs a pulsed signal. In other words, the detection unit 25 outputs a signal for timing printing. In response to the signal output from the detection unit 25, the control unit 13 applies a print signal to the print head 27W after a predetermined delay distance D according to the arrangement position AL and the printing conditions has elapsed. For example, the control unit 13 outputs a print signal according to the delay distance D from the falling edge of the pulsed signal output from the detection unit 25.

[0059] In other words, the control unit 13 gives a print signal to the print head 27 when the flexible packaging film WF is transported a predetermined distance from the detection unit 25 based on a signal from the detection unit 25. The control unit 25 starts printing by the white printing unit 27 in response to a signal from the detection unit 25 detecting the cue mark CM. The control unit 25 controls the ejection timing of the print head 27W based on the cue mark CM and the detection unit 25. In other words, the white printing unit 27 prints an image at an ejection timing based on the cue mark CM detected by the detection unit 25. This allows the image to be printed by the print head 27W so that the relative position in the transport direction X is aligned with the image in the printing area IA by the color printing unit 21, ideally.

[0060] However, since the flexible packaging film WF is particularly thin, it is easily affected by fluctuations in tension and conveying speed during conveyance, so the detection unit 25 may detect the cue mark CM at a timing that is shifted from the actual position of the cue mark CM in the conveyance direction X.

[0061] Now, reference is made to Fig. 5. Fig. 5 is a schematic diagram for explaining the detection error of the cue mark CM and misregistration. The misregistration here refers to the deviation of the print position in the transport direction X. The misregistration refers to the position deviation in the transport direction X.

[0062] A method for preventing misregistration between printing in print area IA by print head 21K and printing in print area IA by print head 27W will be described below.

[0063] 5, the first, second, third, and fourth pages are printed while being transported in transport direction X. The hatched rectangle to the right indicated by the symbol K is an image of print area IA printed by print head 21K. The white rectangle to the right indicated by the symbol W is an image of print area IA printed by print head 27W.

[0064] The symbols in FIG. 5 have the following meanings. R: KW misregistration. This is the misregistration in the transport direction X between the black image (K) (i.e., the image in print area IA by print head 21K) and the white image (W) (i.e., the image in print area IA by print head 21W). On the first page, the misregistration is zero (R=0). This is the misregistration in the transport direction X when printing in order from the first page. It represents the average value within the page. L: The true value of the distance between adjacent cue marks CM. This value is a theoretically correct value, but is an unknown value. M: the detected distance between adjacent cue marks CM. This distance M is calculated by the detection unit 25 and the encoder 47. This distance M may be detected as being shifted from the actual distance L between the cue marks CM due to the conveyance state of the flexible packaging film WF and the detection operation of the detection unit 25. This distance M may be detected as fluctuating even if the actual distance is constant.

[0065] For the first page, printing starts without any misregistration, so R1 = 0. For the second page, R2 = M1 - L1. For the third page, R3 = M1 + M2 - (L1 + L2). For the fourth page, R4 = M1 + M2 + M3 - (L1 + L2 + L3). From these relationships, the misregistration amount R for the i+1th page is i+1 is the amount of deviation when detecting the cue mark CM up to the i-th page (M i -L i )

[0066] Furthermore, the true value L of the distance between the cue marks CM is calculated by subtracting the deviation (detection error) from the actual distance M between the cue marks CM calculated by the detector 25 and the encoder 47, and the deviation is calculated by subtracting the deviation from the actual distance M. i If we approximate it by Mavg, the writing position deviation can be expressed by formula (1) in Figure 5. i is the two-sided moving average. In other words, equation (1) becomes:

[0067] R n+1 ≒R n +M n -Mavg n ……(1)

[0068] However, the above two-sided moving average uses the positional deviation amount of the page before it is printed. To calculate the correction amount of the page to be printed, the positional deviation amount of the page downstream of the page to be printed is required. Therefore, formula (1) cannot be calculated in real time.

[0069] From formula (1) in FIG. 5, the position shift of the printing start of white (W) caused by the detection error of the cue mark CM by the detection unit 25 can be predicted.

[0070] Here, reference is made to Fig. 6. Fig. 6 is a schematic diagram illustrating the amount of correction for correcting misregistration. The horizontal axis of the time chart in the upper part of Fig. 6 represents the count value of the signal (encoder pulse) output by the encoder 47.

[0071] The delay distance D is corrected so as to absorb the detection error in the detection unit 25. When the bilateral moving average in Equation (1) is replaced with a unilateral moving average, the equation for obtaining the correction amount for correcting the delay distance D becomes as shown in Equation (2) below Figure 6. That is, Equation (2) is as follows. Here, the symbol i represents a page.

[0072] d i+1 =d i -M i +Mavg i ……(2) However, d1 = d init

[0073] Mavg i is the moving average value of n points from M i-1 to M i When i < n, Mavg i It is preferable to calculate the moving average value from 1 to i. Or, it is preferable to set it to a predetermined initial setting value. The relationship of each value at this time is as shown in the upper part of Figure 6.

[0074] Each symbol in the mathematical formula in Figure 6 shown here has the following meaning. M i : The distance between the queue marks CM between i and i + 1. It is also the number of lines (output signal number) of the encoder 47. Mavg i : The moving average value of n points of M i-n to M i d i : The delay distance D on the i-th page d init : The initial setting value of the delay distance D (a constant value when there is no correction)

[0075] Here, refer to Figure 7. Figure 7 is a functional block diagram showing the details of the control unit 13 according to the first embodiment. Each function of the control unit 13 shown in Figure 7 is realized by the CPU of the control unit 13 executing data processing according to a program stored in the memory.

[0076] The control unit 13 is M i ​A calculation unit 51, a delay distance storage unit 52, and Mavg i A moving average calculation unit 53 and d i+1 It includes a calculation unit 55 and a discharge control unit 57 .

[0077] M i The calculation unit 51 calculates the distance M between the cue marks CM based on the signals from the detection unit 25 and the encoder 47. i Calculate Mavg i The calculation unit 51 is M i The distance M calculated by the calculation unit 51 i Based on the one-sided moving average Mavg i The delay distance storage unit 52 stores the delay distance D of each page. i+1 The calculation unit 55 calculates the delay distance D of the i-th page output by the delay distance storage unit 52 and the distance M i and one-sided moving average Mavg i Based on this, the correction amount d i+1 The discharge control unit 57 calculates the actual delay distance D by a correction amount d i+1 In other words, the discharge control unit 57 corrects the delay distance D when there is no detection error in the distance between the cue marks CM by a correction amount d i+1 The discharge timing is controlled by the distance M i , delay distance D, one-sided moving average Mavg i , and the correction amount d i+1 etc. are lengths in units of the number of pulses of the encoder 47.

[0078] According to the inkjet printing apparatus 1 of this embodiment, Mavg i The calculation unit 51 is M i The calculation unit 51 calculates a one-sided moving average value of the distances, and calculates d based on this moving average value. i+1 The calculation unit 51 calculates the correction amount. The ejection control unit 57 controls the ejection timing of the print head 27W based on the correction amount. i+1The correction amount calculated by the calculation unit 51 is a moving average, so even if the detected distance between pages fluctuates, it is smoothed out. Therefore, it is possible to suppress the adverse effects of fluctuations in the tension and conveying speed of the flexible packaging film WF, and appropriately suppress misregistration between the images printed on each page by the print head 21K and the print head 27W.

[0079] In addition, the present embodiment calculates the correction value by the moving average, which is different from the method of using the moving average only when a specific condition is satisfied. Since the present embodiment always calculates the correction value by the moving average, the correction value can be calculated stably.

[0080] In addition, the above-mentioned M i The calculation unit 51 corresponds to the "distance calculation unit" in the present invention, and d i+1 The calculation unit 55 corresponds to the "calculation unit" in the present invention, and the discharge control unit 57 corresponds to the "control unit" in the present invention. EXAMPLES

[0081] Next, a second embodiment of the present invention will be described with reference to the drawings.

[0082] 8 is a diagram for explaining the correction amount according to the embodiment 2. Note that since the overall configuration is the same as that of the above-mentioned embodiment 1, the same reference numerals are used and detailed description will be omitted.

[0083] The distance between the cue marks CM may change due to disturbances such as temperature changes. In the configuration of the above-mentioned first embodiment, a one-sided moving average is used to calculate the correction amount, which causes a delay in the correction amount. In this embodiment, the correction amount is calculated to eliminate this delay.

[0084] Here, the ideally time-free average value on the i-th page is the two-sided moving average value (where the number of moving average points n is an odd number) M' i One-sided moving average Mavg i is the two-sided moving average M' i The value Mavg delayed by k=(n-1) / 2 from i+kTherefore, the error that occurs on the i-th page is e' i is expressed by the formula shown in the upper part of Figure 8. In other words, the error e' i is expressed as follows:

[0085] e' i =M' i -Mavg i =Mavg i+k -Mavg i

[0086] This error e' i occurs for each page. Therefore, the error e' on the i-th page i is the sum of them. Let e i Then, the error e' i Since it can be calculated on the i+kth page, the error e' i The correction amount for the (i+1)th page that cancels out the accumulation of is expressed by equation (3) in Fig. 8. That is, equation (3) becomes as follows.

[0087] f i+1 = (d i +Mavg i -M i )+(e i +Mavg i -Mavg i-k )……(3)

[0088] Correction amount f i+1 Since moving averages are used, if the number of moving averages n is small, the effect of reducing variation is small. Also, if the number of moving averages n is large, the effect of delays in the moving average cannot be absorbed by the correction term e. Therefore, based on the results of desk calculations and verification using an actual machine, n = 7 is preferable.

[0089] Here, reference is made to Fig. 9. Fig. 9 is a functional block diagram illustrating details of a control unit according to the second embodiment.

[0090] The calculation of the correction amount using the two-sided moving average in this manner is performed by the control unit 13A.

[0091] The control unit 13A is iA calculation unit 51, a delay distance storage unit 52, and Mavg i A moving average calculation unit 53 and d i+1 A calculation unit 55, a holding unit 61, and e i+1 An error calculation unit 63, f i+1 It includes a calculation unit 65 and a discharge control unit 57 .

[0092] M i The calculation unit 51 calculates the distance M between the cue marks CM as described above. i The delay distance storage unit 52 stores the delay distance D of each page. Mavg i The moving average calculation unit 53 calculates the distance M i Calculate the one-sided moving average based on d i+1 The calculation unit 51 calculates the correction amount d i+1 The storage unit 61 calculates Mavg i The one-sided moving averages calculated by the moving average calculation unit 53 are sequentially stored and held. i+1 The error calculation unit 63 reads the moving average stored in the storage unit 61 and calculates the error. i+1 The calculation unit 65 calculates the correction amount f based on the formula (3). i+1 The discharge control unit 57 calculates the discharge timing by a correction amount f i+1 The discharge control unit 57 corrects the discharge timing according to the distance obtained by the detection unit 25 and the encoder 31 by a correction amount f i+1 Correct with.

[0093] This embodiment 2 has the same effect as the above-mentioned embodiment 1. Furthermore, since this embodiment 2 uses a two-sided moving average, it is possible to eliminate the phase delay caused by the one-sided moving average. As a result, even if the range of the distance fluctuation for each page is outside a certain range, the correction is unlikely to be delayed, and the ejection timing can be appropriately corrected.

[0094] Reference is now made to Figs. 10 and 11. Fig. 10 is a graph showing misregistration without correction. Fig. 11 is a graph showing misregistration in Example 2. In Figs. 10 and 11, the upper side of the vertical axis is positive, and the lower side of the vertical axis is negative. Positive indicates that the white (W) ink was deposited earlier. Negative indicates that the white (W) ink was deposited later. The vertical distance between adjacent horizontal lines is the average misregistration on the page. Arrows are attached to areas of significant misregistration.

[0095] In detail, FIG. 10 shows the M i The result is shown in FIG. 1, where the ejection control unit 57 controls the ejection timing of the print nozzles 27W based on the distance calculated by the calculation unit 51. In this case, M i The distance calculated by calculation unit 51 includes a fluctuating error, and the error accumulates. As a result, the average value of misregistration (positional deviation) within a page (page length is 1.1 m) becomes larger, as shown by the up and down arrows.

[0096] On the other hand, when printing is performed using this Example 2, the average misregistration (positional deviation) within a page is much smaller than without correction, as indicated by the up and down arrows, as shown in Figure 11. Although the results of the above-mentioned Example 1 are not shown, the average misregistration is smaller than the conventional example.

[0097] The present invention is not limited to the above-described embodiment, but can be modified as follows.

[0098] (1) In the above-mentioned first and second embodiments, the case where misregistration between the color printing unit 21 (print head 21K) and the white printing unit 27 (print head 27W) is corrected has been described as an example. However, the present invention is not limited to this form. In other words, the present invention can also be applied to misregistration between any of the other print heads 21C, 21M, and 21Y of the color printing unit 21 and the white printing unit 27 (print head 27W).

[0099] (2) In the above-mentioned first and second embodiments, the inkjet printing device 1 using the flexible packaging film WF as a printing medium has been described as an example. However, the present invention can also be applied to a case where the printing medium is paper.

[0100] (3) In the above-mentioned first and second embodiments, the inkjet printing device 1 is configured so that printing is completed on the flexible packaging film WF by the printing unit 7. However, the present invention is not limited to this configuration. For example, the present invention can be applied to a double-sided printing device that performs printing using two printing units, such as a front unit that prints on the front side of the printing medium and also prints a cue mark CM, and a rear unit downstream detects the cue mark CM and uses this as a reference to print on the back side of the printing medium.

[0101] (4) In the above-described embodiments, the print head 27W is located farther away from the print head 21K than the transport direction arrangement distance AL between the detection unit 25 and the encoder 47. However, the present invention is also applicable to positions other than this. [Explanation of symbols]

[0102] 1 … Inkjet printing device 3 … Paper feed section 5 … Application section 7 … Printing department 9 … Main drying section 11 ... Paper ejection section 13, 13A … Control section X … Transport direction WF: Flexible packaging film 21 … Color Printing Department 21K, 21C, 21M, 21Y ... Print head 25 … Detector 27 … White printing section 27W ... Print head CM... Cue mark 45 ... Transport roller 47 ... Encoder AL … Placement distance IA … Print area D … Delay distance R … KW misalignment L … The true distance between the cue marks CM M … the actual distance between the cue marks CM Mavg i …moving average 51 … M i Calculation section 52 ... Delay distance maintenance section 53 … Mavg i Moving average calculation section 55 … d i+1 Arithmetic section 57 ... Discharge control section e' i … error 63 … e i+1 Error calculation section 65 … f i+1 Arithmetic section

Claims

1. In an inkjet printing device that prints by ejecting ink droplets onto a long print medium, a transport unit that transports the print medium along a predetermined transport path in a predetermined transport direction; a first print head that prints an image on a plurality of pages at a predetermined position on the transport path and prints a predetermined mark that indicates a print start position of the image on the plurality of pages in the transport direction; a detection unit that detects the mark at a detection position downstream of the first print head on the transport path; a second print head that prints images on the plurality of pages at ejection timing based on the mark detected by the detection unit at a predetermined position on the transport path; a distance detection unit that detects a distance that the print medium is transported in response to the detection by the detection unit; a distance calculation unit that calculates a distance between the marks as a mark distance based on the detection by the detection unit and the distance detected by the distance detection unit; a calculation unit that calculates a moving average value of the mark distance for each page calculated by the distance calculation unit, and calculates a correction amount based on the moving average value; a control unit that controls the ejection timing of the second print head based on the correction amount; An inkjet printing apparatus comprising:

2. 2. The inkjet printing apparatus of claim 1, The inkjet printing apparatus, wherein the calculation unit calculates the moving average value by a one-sided moving average.

3. 2. The inkjet printing apparatus of claim 1, The inkjet printing apparatus, wherein the calculation unit calculates the moving average value by a two-sided moving average.

4. 2. The inkjet printing apparatus of claim 1, The inkjet printing apparatus according to claim 1, wherein the calculation unit sets the moving average value to a predetermined initial setting value in calculating the moving average value until the number of pages reaches the moving average number.

5. 2. The inkjet printing apparatus of claim 1, The inkjet printing apparatus according to claim 1, wherein the moving average number is an odd number.

6. 6. The inkjet printing apparatus according to claim 5, The inkjet printing apparatus according to claim 1, wherein the moving average number is seven.

7. 7. The inkjet printing apparatus according to claim 1, an inkjet printing device, wherein the second print head is located farther from the first print head in the transport direction than an arrangement distance between the second print head and the detection unit in the transport direction.

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