Method for aligning a printed pattern on a printed medium and printing apparatus
The method enhances printing apparatus alignment by using optical detection units to adjust alignment marks on the outer edge regions, achieving precise color registration with minimized waste through reduced mark widths and efficient alignment corrections.
Patent Information
- Application Number
- JP2025525401
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-11
- Filing Date
- 2023-07-04
- Publication Date
- 2025-07-28
AI Technical Summary
Existing printing apparatuses face challenges in achieving precise alignment of color planes while minimizing waste generated by alignment marks that are cut off after printing, which affect print quality and increase material loss.
A method involving multiple printing units with optical detection units, where alignment marks are printed on the outer edge regions of the printing medium, allowing for high-precision alignment adjustments through vertical and horizontal corrections, and skew detection, reducing the width of alignment marks on subsequent units to minimize waste.
Enables high-precision alignment of printing patterns with reduced waste by optimizing alignment mark widths and using optical detection units, ensuring accurate color registration without increasing the overall size of the alignment marks.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for aligning a plurality of printing patterns on a printing medium in a printing apparatus, and a printing apparatus including at least two printing units. Specifically, the present invention relates to a gravure printing machine, a flexographic printing machine, or an offset printing machine.
Background Art
[0002] Printing apparatuses typically have a plurality of printing units for printing different color planes. The printing medium passes successively through the different printing units.
[0003] The alignment of the color planes must be very accurate. In particular, color misregistration exceeding 50 microns has a significant impact on print quality. Therefore, it is necessary to control the alignment of the printing units with respect to horizontal and vertical alignment and skewing.
[0004] It is known to print alignment marks in the outer edge region of the printing medium to facilitate alignment control. However, the area with the alignment marks does not contribute to the final print and needs to be cut off at the end of the printing process.
Summary of the Invention
Problems to be Solved by the Invention
[0005] Therefore, an object of the present invention is to enable sufficient alignment of printing patterns on a printing medium in a printing apparatus while reducing the waste generated.
Means for Solving the Problems
[0006] This object is achieved by a method of aligning a printing pattern on a printing medium in a printing apparatus having at least a first printing unit and a second printing unit, each printing unit having a printing roller, the second printing unit having an optical detection unit, the printing medium having a first outer edge region and a second outer edge region opposite the first outer edge region, and moving longitudinally from the first printing unit to the second printing unit. One method step includes printing a first alignment mark on the first outer edge region and a second alignment mark on the second outer edge region using the first printing unit. Further method steps include determining the horizontal and vertical positions of the first alignment mark in the first outer edge region using the detection unit, and adjusting the vertical and / or horizontal alignment based on the position of the first alignment mark. Another method step includes, after adjusting the vertical and / or horizontal alignment based on the position of the first alignment mark, printing a third alignment mark on the first outer edge region of the printing medium and a fourth alignment mark on the second outer edge region by the second printing unit. The maximum widths of the second and fourth alignment marks on the second outer edge region are smaller than the maximum widths of the first and third alignment marks on the first outer edge region.
[0007] Since the width of the alignment mark on the second outer edge region is smaller than the width of the alignment mark on the first outer edge region, the space on the printing medium can be increased, and as a result, waste can be reduced. Specifically, the width of the alignment mark on the second outer edge region can be made smaller because the horizontal alignment is adjusted based on the position of the first alignment mark printed on the first outer edge region by the first printing unit, and the horizontal position of the alignment mark printed by the second printing unit is already clearly defined. Therefore, it has been confirmed that the alignment mark printed on the second outer edge region by the second printing unit crosses the sensing area of the optical detection unit despite its small size. However, with the method of the present invention, high-precision alignment is still possible.
[0008] The width of the alignment mark on the second outer edge region is, for example, between one-third and two-thirds of the width of the alignment mark on the first outer edge region.
[0009] Vertical alignment can be adjusted by temporarily changing the rotational speed of the printing roller of the second printing unit.
[0010] Horizontal alignment can be adjusted by displacing the printing roller of the second printing unit along its axis of rotation, specifically using a dedicated shifting device.
[0011] According to one aspect, the alignment mark on the first outer edge region is a two-dimensional alignment mark, and the alignment mark on the second outer edge region is a one-dimensional or two-dimensional alignment mark. A two-dimensional alignment mark is a mark that can measure two positions, specifically the horizontal and vertical positions of the mark, using a single sensor such as an optical photocell. A one-dimensional alignment mark is a mark that can measure only one position, specifically the vertical position.
[0012] For example, the alignment mark on the first outer edge region has a horizontal edge and an edge inclined with respect to the horizontal edge. The horizontal edge enables detection of the vertical position of the alignment mark, and the inclined edge enables measurement of the horizontal position. Due to the inclined edge, the detected length of the alignment mark varies depending on the horizontal position of the alignment mark.
[0013] For example, the trigger code is printed on the first outer edge region by the first printing unit, and the first alignment mark printed on the first outer edge region by the first printing unit is printed after the trigger code with respect to the moving direction of the printing medium. The trigger code enables measurement of the mark without prior knowledge of where the mark is located in the longitudinal direction. Specifically, the trigger code is used to set the zero position of the alignment system.
[0014] Preferably, the trigger code is printed on the second outer edge area by the first printing unit, and the second alignment mark printed on the second outer edge area by the first printing unit is printed after the trigger code with respect to the moving direction of the printing medium. In addition to the advantages described above with respect to the trigger code on the first outer edge area, the trigger code on the second outer edge area allows the alignment mark on the second outer edge area to be placed at any vertical position in comparison with the alignment mark on the first outer edge area. Therefore, the printing pattern of the alignment mark becomes more flexible.
[0015] The vertical distance to the reference point of the third alignment mark printed on the first outer edge area by the second printing unit is measured, and the vertical distance to the reference point of the fourth alignment mark printed on the second outer edge area by the second printing unit is measured. Based on the measured distances, skewing between the first printing unit and the second printing unit can be detected. In this way, the skewing deviation can be detected in a simple manner.
[0016] The reference point can be the trigger code, the alignment mark printed by the first printing unit, or another mark whose distance from the third alignment mark and the fourth alignment mark is defined respectively.
[0017] According to one embodiment, the vertical distance between the alignment marks printed by the first printing unit and the second printing unit on the first outer edge region is measured, and the vertical distance between the alignment marks printed by the first printing unit and the second printing unit on the second outer edge region is measured. In order to detect the skewing between the first printing unit and the second printing unit, the vertical distances between the alignment marks can be compared. Specifically, the skewing can be detected based on the comparison of the two measured vertical distances. If the two detected vertical distances are equal, there is no skewing. However, if the two measured vertical distances are different from each other, the printing unit needs to be adjusted with respect to the skewing.
[0018] For example, the degree of skewing between the first printing unit and the second printing unit is determined, and the skewing is adjusted by rotating a skewing roller disposed between the printing roller of the first printing unit and the printing roller of the second printing unit. Thereby, the skewing deviation is corrected.
[0019] The horizontal position of the second alignment mark printed by the first printing unit on the second outer edge region can be measured, and the horizontal alignment can be adjusted again based on the position of the second alignment mark on the second outer edge region. Thereby, the alignment of the color planes can be performed more accurately. Specifically, the adjustment in the horizontal direction can be improved by averaging the measured values of the first and second alignment marks.
[0020] The object of the present invention is further solved by a printing device configured to perform the method and skew adjustment of the present invention, at least two printing units being arranged successively with respect to each other, each printing unit comprising a printing roller and a skew roller, the second printing unit arranged following the first printing unit comprising an optical detection unit, the optical detection unit preferably comprising first and second photocells arranged downstream of the printing roller, the first photocell being able to detect a registration mark in a first outer edge region of the printing medium, and the second photocell being able to detect a registration mark in a second outer edge region of the printing medium.
[0021] The second photocell preferably has a sensing area with a smaller width than the first photocell. The second photocell can be of the same type and model as the first photocell, but may have a different orientation.
[0022] The rotation axis of the skew roller is, for example, movable on one side and fixed on the opposite side. Thereby, the skew parameter can be adjusted. As another embodiment, both sides of the skew roller can be movable.
[0023] Further features and advantages will become apparent from the following description and the accompanying drawings.
Brief Description of the Drawings
[0024]
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Embodiments for Carrying Out the Invention
[0025] FIG. 1 schematically shows a printing apparatus 10.
[0026] The printing apparatus includes an unwinder 12, a preheating unit 14, a first printing unit 16, and a second printing unit 18 arranged following the first printing unit 16. However, the printing apparatus 10 can include three or more printing units.
[0027] For example, the printing apparatus 10 is a heptachrome printing apparatus having seven printing units.
[0028] It should be noted that the first printing unit 16 is not necessarily the first printing unit of the printing apparatus. There may be a printing unit before the first printing unit 16 that does not require precise alignment. Also, the second printing unit 18 can be any printing unit arranged after the first printing unit, but it does not necessarily have to be continuous with the first printing unit 16.
[0029] A dryer 20 is arranged after each of the printing units 16, 18.
[0030] Each of the printing units 16, 18 includes skew rollers 21, 22 and printing rollers 24, 25.
[0031] The second printing unit 18, also visualized in FIG. 2, further includes an optical detection unit 26 arranged downstream of the printing roller 25.
[0032] The detection unit 26 can include two photocells 28, 29.
[0033] The photocells 28, 29 are, for example, monochromatic photocells.
[0034] Alternatively, the optical detection unit 26 can also be composed of two cameras 28, 29.
[0035] The printing medium 30 advances through the printing apparatus 10 along the moving direction indicated by the arrow 32.
[0036] In order to ensure high print quality, the printing units 16, 18 need to be aligned with high precision in the horizontal direction, the vertical direction, and with respect to skewing.
[0037] The vertical direction corresponds to the moving direction of the printing medium 30.
[0038] The horizontal direction is lateral with respect to the moving direction of the printing medium 30.
[0039] In order to adjust the horizontal displacement of the printing units 16, 18, the printing rollers 24, 25 move along their rotation axes.
[0040] In order to adjust the vertical displacement of the printing units 16, 18, the angular positions of the printing rollers 24, 25 are adjusted by adjusting the phase of the printing rollers before printing, that is, before bringing the printing rollers 24, 25 into contact with the printing medium 30. This can be done by temporarily changing the rotational speed of the printing roller 24.
[0041] Skewing is corrected by pivoting the skew rollers 21, 22, for example, by moving one side of the skew rollers 21, 22 along the direction indicated by the arrow 23 in FIG. 2 and leaving the other side fixed.
[0042] A method for detecting the displacement of different color planes is described with respect to FIGS. 3 to 5.
[0043] A color plane is a pattern printed by one of the printing units 16, 18.
[0044] First, a trigger code 34 is printed on the first outer edge region 35 of the printing medium 30 by the first printing unit 16. In the figure, the first outer edge region 35 is on the left side of the printing medium 30.
[0045] Further, the first printing unit 16 prints a trigger code 36 on a second outer edge region 37 opposite to the first outer edge region 35 of the printing medium 30, which is on the right side of the printing medium 30 in the figure.
[0046] The trigger codes 34, 36 are codes having distinct symbols along the vertical direction and include marks having horizontal edges.
[0047] The trigger codes 34, 36 on the first and second outer edge regions 35, 37 are arranged at intervals perpendicular to each other with respect to the moving direction 32 of the printing medium 30.
[0048] In the figure, the marks printed by one printing unit are shown with the same hatching. In reality, the marks printed by one printing unit have the same color.
[0049] Further, the first printing unit 16 prints a first alignment mark 38 on the first outer edge region 35 and a second alignment mark 40 on the second outer edge region 37.
[0050] The first and second alignment marks 38, 40 are printed following the trigger codes 34, 36. Therefore, the alignment marks 38, 40 are arranged at a distance perpendicular to the trigger codes 34, 36.
[0051] The distances between the first and second alignment marks 38, 40 and the respective trigger codes 34, 36 are defined.
[0052] Figure 4 shows an enlarged view of the first alignment mark 38 printed on the first outer edge region 35.
[0053] The first alignment mark 38 has a horizontal edge 42 and an edge 44 inclined with respect to the horizontal edge 42. In the illustrated embodiment, the first alignment mark 38 is a right triangle.
[0054] In addition, in FIG. 4, the sensor paths of the respective photocells 28 are indicated by broken lines.
[0055] The width of the first alignment mark 38 printed on the first outer edge region 35 is such that it covers the maximum lateral error in the position of the print medium 30.
[0056] For example, the first alignment mark 38 has a width w of 6 mm.
[0057] In an embodiment, the second alignment mark 40 on the second outer edge region 37 has the same shape as the first alignment mark 38 on the first outer edge region 35.
[0058] Both the first and second alignment marks 38, 40 are two-dimensional alignment marks.
[0059] However, the second alignment mark 40 on the second outer edge region 37 can also be a one-dimensional alignment mark such as a square or a rectangle.
[0060] When the print medium 30 moves along the moving direction and the section having the trigger codes 34, 36 enters the second printing unit 18, while the second printing unit 18 is not printing, that is, while the printing roller 24 is not in contact with the print medium 30, the trigger codes 34, 36 are read by the detection unit 26.
[0061] By reading the trigger codes 34, 36, the alignment process is started.
[0062] After reading the trigger code 34, the detection unit 26 detects the first alignment mark 38 on the first outer edge region 35.
[0063] When the first alignment mark 38 moves along the respective photocells 28, the vertical position of the first alignment mark 38 can be determined by detecting the position of the horizontal edge 42.
[0064] As shown in FIG. 4, the horizontal position of the first alignment mark 38 can be determined by detecting the length l of the first alignment mark 38. The detected length l is specific to the horizontal position of the first alignment mark 38 due to the fact that the edge 44 is inclined with respect to the horizontal edge 42. Preferably, the edge 44 is inclined at an angle between 40° and 50°, specifically 45°, with respect to the horizontal edge 42. An angle within this range ensures high accuracy.
[0065] After determining the horizontal and vertical positions of the first alignment mark 38 on the first outer edge region 35, the vertical and / or horizontal alignment is adjusted based on the position of the first alignment mark 38.
[0066] After adjusting the vertical and / or horizontal alignment based on the position of the first alignment mark 38, the third alignment mark 46 is printed on the first outer edge region 35 by the second printing unit 18, and the fourth alignment mark 48 is printed on the second outer edge region 37 of the printing medium 30.
[0067] The shapes of the third and fourth alignment marks 46, 48 printed by the second printing unit 18 correspond to the shapes of the first and second alignment marks 38, 40 printed by the first printing unit 16. However, different shapes are also possible.
[0068] Due to the previous adjustment, the horizontal and vertical positions of the third and fourth alignment marks 46, 48 printed by the second printing unit 18 are already clearly defined.
[0069] Since the position is clearly defined, a monochromatic photocell can determine which printing unit created the alignment mark based on that position.
[0070] In the next step, the vertical distance v1 between the first alignment mark 38 and the third alignment mark 46 printed by the first and second printing units 16, 18 on the first outer edge region 35 is measured, and the vertical distance v2 between the second alignment mark 40 and the fourth alignment mark 48 printed by the first and second printing units 16, 18 on the second outer edge region 37 is measured. The vertical distances v1 and v2 between the alignment marks are compared to detect skewing between the first and second printing units 16, 18.
[0071] Specifically, if the distances v1 and v2 are different from each other, skewing correction is required.
[0072] The degree of skewing between the first printing unit 16 and the second printing unit 18 is determined, and the skewing is adjusted by rotating a skewing roller 22 disposed between the printing roller 24 of the first printing unit 16 and the printing roller 25 of the second printing unit 18.
[0073] In an alternative embodiment, to detect skewing, the vertical distances of the alignment marks 46, 48 can be measured relative to the trigger codes 34, 36 respectively or relative to other reference points.
[0074] In an optional method step, the horizontal and / or vertical position of the second alignment mark 40 printed by the first printing unit 16 on the second outer edge region 37 is measured, and based on the position of the second alignment mark 40 on the second outer edge region 37, vertical and / or horizontal alignment is adjusted again. Thereby, the alignment of the color planes can be made even more accurate.
[0075] The method steps described with respect to the first printing unit 16 and the second printing unit 18 can be repeated with respect to subsequent printing units of the printing apparatus.
[0076] The maximum widths of the second and fourth alignment marks 40, 48 on the second outer edge region 37 are smaller than the maximum widths of the first and third alignment marks 38, 46 on the first outer edge region 35, and more specifically, are between one-third and two-thirds of the widths of the first and third alignment marks 38, 46 on the first outer edge region 35.
[0077] For example, on both sides of the medium 35、37 when using the same photocells 28, 29 in the same orientation, the maximum widths of the alignment marks 40, 48 on the second outer edge region 37 are 4 mm. In another example, when using a photocell 29 having a narrower sensing area along the horizontal direction, the maximum widths of the alignment marks 40, 48 on the second outer edge region 37 are 2 mm.
[0078] After the first alignment, the maximum lateral error decreases, allowing for a smaller width. Also, the vertical positions of the alignment marks 40, 48 on the second outer edge region 37 are measured, but the horizontal positions are not necessarily measured. This also contributes to making the possible widths of the alignment marks 40, 48 on the second outer edge region 37 smaller.
[0079] Thereby, waste generated in the printing process is reduced.
[0080] More specifically, the outer edge regions 35, 37 having the alignment marks do not contribute to the final printed matter and are cut after the printing process.
[0081] FIG. 5 visualizes the sensor paths of the photocells 28, 29 of the detection unit 26, and more specifically, the paths of the sensing areas of the photocells 28, 29.
[0082] The sensing areas of the photocells 28, 29 are rectangular.
[0083] For example, the sensing area of the photocell is 2 mm × 1 mm.
[0084] FIG. 5 shows that the second photocell 29 has a smaller width than the first photocell 28.
[0085] For example, although the photocells 28, 29 are identical, the second photocell 29 is rotated by approximately 90° with respect to the first photocell 28. Specifically, the photocell 28 is used in a horizontal orientation on the larger alignment marks 38, 46 of the first outer edge region, and the second photocell 29 is used in a vertical orientation on the smaller marks 40, 48 of the second outer edge region.
[0086] In another embodiment, the photocells 28, 29 are different, and the second photocell 29 has a smaller sensing area than the first photocell 28.
[0087] Due to the lateral error in the position of the printing medium 30, a first Outer edge region The width of the alignment marks 38, 46 of 35 needs to be at least slightly larger than the tolerance range of the initial lateral position error, thereby ensuring that the marks cross the sensing area of the photocell 28. The width of the alignment marks 38, 46 is preferably at least the same size as the width of the sensing area of the photocell 28 in order to ensure that the alignment marks 38, 46 completely cross the sensing area of the photocell 28. Therefore, the width of the alignment marks 38, 46 is preferably slightly larger than the width of the sensing area of the photocell 28. The same applies to the second Outer edge region 37 of the medium, i.e., the alignment marks 40, 48 and the photocell 29. However, Second outer edge region The lateral error tolerance value on 37 is applied after the first lateral alignment based on the marks on the First outer edge region 35 of the medium, so it is smaller, and the size of the marks on the Second outer edge region 37 of the medium can be made smaller.
[0088] Since the horizontal positions of the second and fourth alignment marks 40, 48 are already set according to the positions of the first and third alignment marks 38, 46 on the first outer edge region 35, the horizontal position error is within the range of 1 mm.
Claims
1. In a printing apparatus (10) comprising at least a first printing unit (16) and a second printing unit (18), a method for aligning a printing pattern on a printing medium (30), wherein each of the printing units (16, 18) comprises a printing roller (24, 25), the second printing unit (18) comprises an optical detection unit (26), the printing medium (30) comprises a first outer edge region (35) and a second outer edge region (37) opposite to the first outer edge region (35), and the printing medium (30) moves longitudinally from the first printing unit (16) to the second printing unit (18), printing a first alignment mark (38) on the first outer edge region (35) and a second alignment mark (40) on the second outer edge region (37) using the first printing unit (16); printing a third alignment mark (46) on the first outer edge region (35) of the printing medium (30) and a fourth alignment mark (48) on the second outer edge region (37) by the second printing unit (18); determining the horizontal position and the vertical position of the first alignment mark (38) in the first outer edge region (35) using the detection unit (26); determining the horizontal position of the third alignment mark (46) in the first outer edge region (35) using the detection unit (26); adjusting the horizontal alignment of the second printing unit (18) based on the relative horizontal positions of the first alignment mark (38) and the third alignment mark (46); comprising a method in which the maximum widths of the second and fourth alignment marks (40, 48) on the second outer edge region (37) are smaller than the maximum widths of the first and third alignment marks (38, 46) on the first outer edge region.
2. determining the vertical position of the first alignment mark (38) in the first outer edge region (35) using the detection unit (26); determining the vertical position of the third alignment mark (46) in the first outer edge region (35) using the detection unit (26); Adjusting the vertical alignment of the second printing unit (18) based on the relative vertical positions of the first alignment mark (38) and the third alignment mark (46); The method according to claim 1, comprising the above.
3. The first and second alignment marks (38, 46) on the first outer edge region (35) are two-dimensional alignment marks, and the second and fourth alignment marks (40, 48) on the second outer edge region (37) are one-dimensional or two-dimensional alignment marks. The method according to claim 1 or 2.
4. The alignment marks (38, 46) on the first outer edge region (35) have a horizontal edge (42) and an edge (44) inclined with respect to the horizontal edge (42). The method according to claim 1.
5. A trigger code (34) is printed on the first outer edge region (35) by the first printing unit (16), and the first alignment mark (38) printed on the first outer edge region (35) by the first printing unit (16) is printed after the trigger code (34) with respect to the moving direction of the printing medium (30). The method according to claim 1.
6. A trigger code (36) is printed on the second outer edge region (37) by the first printing unit (16), and the second alignment mark (40) printed on the second outer edge region (37) by the first printing unit (16) is printed after the trigger code (36) with respect to the moving direction of the printing medium (30). The method according to claim 1.
7. The vertical distance to the reference point of the third alignment mark (46) printed by the second printing unit (18) on the first outer edge region (35) is measured, and the vertical distance to the reference point of the fourth alignment mark (48) printed by the second printing unit (18) on the second outer edge region (37) is measured. When the measured distances are different, skewing between the first printing unit and the second printing unit (16, 18) is detected based on the measured distances. The method according to claim 1.
8. The vertical distance (v1) between the alignment marks (38, 46) printed by the first and second printing units (16, 18) on the first outer edge region (35) is measured, and the vertical distance (v1, v2) between the alignment marks (40, 48) printed by the first and second printing units (16, 18) on the second outer edge region (37) is measured. The vertical distances (v1, v2) between the alignment marks (38, 40, 46, 48) are compared to detect skewing between the first and second printing units (16, 18). The method according to claim 7.
9. The degree of skewing between the first printing unit (16) and the second printing unit (18) is determined, and skewing is adjusted by rotating a skewing roller (22) disposed between the printing roller (24) of the first printing (16) unit and the printing roller (25) of the second printing unit (18). The method according to claim 7.
10. The horizontal positions of the second alignment mark (40) and the fourth alignment mark (48) on the second outer edge region (37) are measured, and horizontal alignment is adjusted again based on the positions of the second alignment mark (40) and the fourth alignment mark (48) on the second outer edge region (37). The method according to claim 1. Printing apparatus (10) configured to perform the method according to claim 8, wherein at least two printing units (16, 18) are arranged in succession with respect to one another, each of said printing units (16, 18) comprising a printing roller (24, 25) and a skew roller (21, 22), said second printing unit (18) arranged following said first printing unit (16) comprising an optical detection unit (26), said optical detection unit (26) comprising first and second photocells (28, 29) arranged downstream of said printing roller (25), said first photocell (28) being able to detect said first and second alignment marks (38, 46) in said first outer edge region (35) of said printing medium (30), said second photocell (29) being able to detect said second and fourth alignment marks (40, 48) in said second outer edge region (37) of said printing medium (30). Printing apparatus.
12. The printing apparatus according to claim 11, wherein said second photocell (29) has a smaller width than said first photocell (28).