TWI881379B - A method for aligning a print pattern on a print medium and a printing device - Google Patents

Abstract

A method for aligning a print pattern on a print medium (30) in a printing device (10) with at least a first printing unit (16) and a second printing unit (18), wherein each printing unit (16, 18) comprises a printing roller (24, 25) and wherein the second printing unit (18) comprises an optical detection unit (26), wherein the print medium (30) comprises a first lateral edge region (35) and a second lateral edge region (37) opposed to the first lateral edge region (35) and travels along a longitudinal direction from the first printing unit (16) to the second printing unit (18). One method step comprises printing a first register mark (38) on the first lateral edge region (35) and a second register mark (40) on the second lateral edge region (37) being opposed to the first lateral edge region (35) of the print medium (30) by a first printing unit (16). A further method step comprises determining the horizontal and vertical position of the first register mark (38) at the first lateral edge region (35) using the detection unit (26) and adjusting a vertical and/or horizontal register based on the position of the first register mark (38). Another method step comprises, after adjusting the vertical and/or horizontal register based on the position of the first register mark (38), printing a third register mark (46) on the first lateral edge region (35) and a fourth register mark (48) on the second lateral edge region (37) of the print medium (30) by the second printing unit (18). The maximum width of the second and fourth register marks (40, 48) on the second lateral edge region (37) is smaller than the maximum width of the first and third register marks (38, 46) on the first lateral edge region (35). Moreover, a printing device (10) is provided.

Description

Method for aligning printed patterns on printing medium and printing device

The present invention relates to a method for aligning a plurality of printed patterns on a printing medium in a printing device, and to a printing device having at least two printing units. Specifically, the present invention relates to a rotary gravure printing machine, a flexographic printing machine or a letterpress printing machine.

A printing device usually has several printing units for printing different color planes. The print medium then passes through the different printing units.

The alignment of the color planes must be extremely accurate. Specifically, color misalignment of more than 50 microns will significantly affect the print quality. Therefore, it is necessary to control the registration of the print units with respect to horizontal and vertical alignment as well as with respect to skew.

It is known that printing registration marks in the lateral edge areas of the print media can help with alignment control. However, the area with the registration marks does not contribute to the final print and must be cut off at the end of the printing process.

Therefore, the object of the present invention is to enable the printed pattern to be fully aligned on the print medium in the printing device while reducing the waste generated.

This object is achieved by a method for aligning a print pattern on a print medium in a printing device, the printing device having at least a first printing unit and a second printing unit, wherein each printing unit comprises a print roller and wherein the second printing unit comprises an optical detection unit, wherein the print medium comprises a first lateral edge region and a second lateral edge region opposite to the first lateral edge region and travels from the first printing unit to the second printing unit along a longitudinal direction. A method step comprises printing a first registration mark on the first lateral edge region and printing a second registration mark on the second lateral edge region by the first printing unit. Another method step includes using a detection unit to determine the horizontal and vertical position of the first registration mark at the first lateral edge region, and adjusting the vertical and/or horizontal registration based on the position of the first registration mark. Another method step includes printing a third registration mark on the first lateral edge region of the print medium and printing a fourth registration mark on the second lateral edge region by a second printing unit after adjusting the vertical and/or horizontal registration based on the position of the first registration mark. The maximum width of the second and fourth registration marks on the second lateral edge region is less than the maximum width of the first and third registration marks on the first lateral edge region.

Since the width of the registration mark on the second lateral edge region is smaller than the width of the registration mark on the first lateral edge region, it is possible to gain space on the print medium and thus reduce waste. Specifically, the width of the registration mark on the second lateral edge region can be reduced because the horizontal registration is based on the position adjustment of the first registration mark printed on the first lateral edge region by the first printing unit, so that the horizontal position of the registration mark printed by the second printing unit is clearly defined. Therefore, it is ensured that the registration mark printed on the second lateral edge region by the second printing unit passes over the sensitive area of the optical detection unit regardless of its size reduction. However, the method of the present invention still achieves highly accurate alignment.

The width of the registration mark on the second lateral edge region is, for example, between one third and two thirds of the width of the registration mark on the first lateral edge region.

Vertical registration can be adjusted by temporarily varying the rotation speed of the print roller of the second print unit.

The horizontal registration can be adjusted by shifting the print roller of the second printing unit along its rotation axis (in detail, by a dedicated shifting device).

According to one aspect, the registration mark on the first lateral edge region is a two-dimensional registration mark, and the registration mark on the second lateral edge region is a one-dimensional or two-dimensional registration mark. A two-dimensional registration mark is a mark that allows two positions (in detail, the horizontal and vertical positions of the mark) to be measured using a single point sensor (e.g., an optical photocell). A one-dimensional registration mark is a mark that allows only one position (in detail, the vertical position) to be measured.

For example, a registration mark on the first lateral edge region has a horizontal edge and an edge inclined to the horizontal edge. The horizontal edge allows the vertical position of the registration mark to be detected, while the inclined edge allows the horizontal position to be measured. Due to the inclined edge, the detected length of the registration mark differs depending on the horizontal position of the registration mark.

For example, a trigger code is printed by the first printing unit on the first lateral edge area, wherein the first registration mark printed by the first printing unit on the first lateral edge area is printed after the trigger code with respect to the travel direction of the print medium. The trigger code allows the mark to be measured without knowing the longitudinal position of the mark in advance. In detail, the zero position of the registration system is set using the trigger code.

Preferably, the trigger code is printed on the second lateral edge area by the first printing unit, and the second registration mark printed on the second lateral edge area by the first printing unit is printed after the trigger code relative to the travel direction of the printing medium. In addition to the advantages already mentioned about the trigger code on the first lateral edge area, the trigger code on the second lateral edge area also allows the registration mark to be placed at any vertical position on the second lateral edge area compared to the registration mark on the first lateral edge area. Therefore, the printing pattern of the registration mark is more flexible.

The vertical distance between the third registration mark printed on the first lateral edge area by the second printing unit and the reference point can be measured, and the vertical distance between the fourth registration mark printed on the second lateral edge area by the second printing unit and the reference point can be measured, and the skew between the first and second printing units can be detected based on the measured distances. This allows skew misalignment to be detected in a simple manner.

The reference point can be a trigger code, a registration mark printed by the first printing unit, or another mark having a defined distance from the third registration mark and the fourth registration mark, respectively.

According to one embodiment, the vertical distance between registration marks printed by the first and second printing units on the first lateral edge region is measured, and the vertical distance between registration marks printed by the first and second printing units on the second lateral edge region is measured, and the vertical distances between the registration marks can be compared to detect the skew between the first and second printing units. Specifically, the skew can be detected based on the comparison of the two measured vertical distances. If the two detected vertical distances are equal, no skew exists, but if the two measured vertical distances are different from each other, the printing units must be adjusted for the skew.

For example, the degree of skew between the first printing unit and the second printing unit is determined, and the skew is adjusted by pivoting the skew roller between the print roller of the first printing unit and the print roller of the second printing unit. In this way, the skew misalignment is corrected.

The horizontal position of the second registration mark printed by the first printing unit on the second lateral edge region can be measured, and the horizontal registration can be adjusted again based on the position of the second registration mark on the second lateral edge region. Thereby, the alignment of the color plane can be even more accurate. In detail, the horizontal adjustment can be improved by averaging the measurement of the first and second registration marks.

The object of the present invention is further achieved by a printing device configured to perform the method and skew adjustment of the present invention, wherein at least two printing units are arranged in sequence, wherein each printing unit comprises a printing roller and a skew roller, and the second printing unit arranged after the first printing unit comprises an optical detection unit, which preferably comprises a first and a second photocell arranged downstream of the printing roller, so that the first photocell can detect a registration mark in a first lateral edge region of the printing medium, and the second photocell can detect a registration mark in a second lateral edge region of the printing medium.

The second photocell preferably has a sensitive area that is smaller in width than the first photocell. The second photocell may be of the same type and model as the first photocell, but oriented in a different way.

The rotation axis of the deflection roller can be movable on one side and fixed on the opposite side, for example. This allows the deflection parameter to be adjusted.

As an alternative, the deflection roller can be moved on both sides.

10: Printing device

12: Unwinding machine

14: Preheating unit

16: First printing unit

18: Second printing unit

20: Dryer

21,22: Deflection roller

23: Arrow

24,25: Printing roller

26: Optical detection unit/detection unit

28,29: Photocell/Camera

30: Printing media

32: Arrow/direction of travel

34,36: Trigger code

35: First lateral edge area

37: Second lateral edge area

38: The first set of standard symbols

40: The second set of standard symbols

42: Horizontal edge

44: Edge

46: The third set of standard symbols

48: The fourth set of standard symbols

l: Length

v ₁ ,v ₂ : vertical distance

w: width

Other features and advantages will become apparent from the following description and the accompanying drawings. In the drawings: - [FIG. 1] schematically shows a printing device of the present invention, - [FIG. 2] shows a printing unit of the printing device of FIG. 1, - [FIG. 3] shows a printed pattern, - [FIG. 4] shows a registration mark, and - [FIG. 5] shows a sensor path.

FIG1 schematically shows a printing device 10.

The printing device includes an unwinder 12, a preheating unit 14, a first printing unit 16, and a second printing unit 18 disposed after the first printing unit 16. However, the printing device 10 may include more than two printing units.

For example, the printing device 10 is a heptachrome printing device having seven printing units.

Please note that the first printing unit 16 is not necessarily the first printing unit of the printing device. There may be a printing unit that does not require precise registration before the first printing unit 16. In addition, the second printing unit 18 can be any printing unit arranged after the first printing unit but not necessarily connected to the first printing unit 16.

After each printing unit 16, 18, a dryer 20 is arranged.

Each printing unit 16, 18 includes a deflection roller 21, 22 and a printing roller 24, 25.

The second printing unit 18 (which is also visualized in FIG. 2 ) further comprises an optical detection unit 26 arranged downstream of the printing roller 25 .

The detection unit 26 may include two photocells 28, 29.

For example, photocells 28 and 29 are monochromatic photocells.

As an alternative, the optical detection unit 26 may be composed of two cameras 28, 29.

The print medium 30 moves in the printing device 10 along the direction of travel indicated by the arrow 32.

In order to ensure high print quality, the print units 16, 18 must be aligned with high accuracy in the horizontal and vertical directions as well as with respect to skew.

The vertical direction corresponds to the traveling direction of the printing medium 30.

The horizontal direction is transverse to the traveling direction of the printing medium 30.

To adjust the horizontal misalignment of the printing units 16 and 18, the printing rollers 24 and 25 move along their rotation axes.

To adjust the vertical misalignment of the printing units 16 and 18, the angular position of the printing rollers 24 and 25 is adjusted by adjusting the phase of the printing rollers 24 and 25 before printing, that is, before the printing rollers 24 and 25 contact the printing medium 30. This can be done by temporarily changing the rotation speed of the printing roller 24.

The skew is corrected by pivoting the skew rollers 21, 22, for example by moving one side of the skew rollers 21, 22 in the direction indicated by arrow 23 in FIG. 2 while keeping the other side fixed.

A method for detecting misalignment of different color planes is described with respect to FIGS. 3 to 5 .

The color plane is a pattern printed by a single printing unit 16, 18.

First, the trigger code 34 is printed on the first lateral edge area 35 of the printing medium 30 by the first printing unit 16. In the figure, the first lateral edge area 35 is on the left side of the printing medium 30.

In addition, the trigger code 36 is printed on the second lateral edge area 37 opposite to the first lateral edge area 35 of the printing medium 30 by the first printing unit 16. In the figure, the second lateral edge area is on the right side of the printing medium 30.

Trigger codes 34 and 36 are codes having different signatures along the vertical direction and including marks having horizontal edges.

The trigger codes 34, 36 on the first lateral edge region 35 and the second lateral edge region 37 are positioned at a vertical distance from each other relative to the travel direction 32 of the print medium 30.

In the drawings, marks printed by one printing unit are indicated by the same shading. Actually, marks printed by one printing unit have the same color.

The first printing unit 16 also prints a first registration mark 38 on the first lateral edge region 35 and a second registration mark 40 on the second lateral edge region 37.

The first registration mark 38 and the second registration mark 40 are printed after the trigger codes 34 and 36. Therefore, the registration marks 38 and 40 are positioned to be vertically spaced apart from the trigger codes 34 and 36.

Defines the distance between the first registration mark 38 and the second registration mark 40 and the respective trigger codes 34 and 36.

FIG. 4 shows the first registration mark 38 printed on the first lateral edge region 35 in an enlarged view.

The first alignment mark 38 has a horizontal edge 42 and an edge 44 that is inclined toward the horizontal edge 42. In the depicted embodiment, the first alignment mark 38 is a right triangle.

Furthermore, the sensor paths of the individual photocells 28 are visualized in FIG. 4 by means of dashed lines.

The width of the first registration mark 38 printed on the first lateral edge area 35 covers the maximum lateral error of the position of the print medium 30.

For example, the first registration mark 38 has a width w of 6 mm.

In an embodiment, the second registration mark 40 on the second lateral edge region 37 has the same shape as the first registration mark 38 on the first lateral edge region 35.

Both the first registration mark 38 and the second registration mark 40 are two-dimensional registration marks.

However, the second registration mark 40 on the second lateral edge region 37 may also be a one-dimensional registration mark, such as a square or a rectangle.

When the print medium 30 moves along the travel direction and the section with the trigger codes 34, 36 enters the second print unit 18, the trigger codes 34, 36 are read by the detection unit 26, and the second print unit 18 does not print, which means that the print roller 24 does not contact the print medium 30.

The alignment process starts by reading the trigger codes 34 and 36.

After reading the trigger code 34, the detection unit 26 detects the first registration mark 38 on the first lateral edge area 35.

As the first set of alignment marks 38 travels along the respective photocells 28, the vertical position of the first set of alignment marks 38 can be determined by detecting the position of the horizontal edge 42.

The horizontal position of the first registration mark 38 can be determined by detecting the length l of the first registration mark 38, as indicated in FIG4. The detected length l is specific to the horizontal position of the first registration mark 38 due to the inclination of the edge 44 toward the horizontal edge 42. Preferably, the angle at which the edge 44 inclines toward the horizontal edge 42 is between 40° and 50°, specifically 45°. Angles in this range ensure high accuracy.

After determining the horizontal and vertical positions of the first registration mark 38 on the first lateral edge region 35, the vertical and/or horizontal registration is adjusted based on the position of the first registration mark 38.

After adjusting the vertical and/or horizontal registration based on the position of the first registration mark 38, the second printing unit 18 prints the third registration mark 46 on the first lateral edge area 35 of the print medium 30 and prints the fourth registration mark 48 on the second lateral edge area 37.

The shapes of the third registration mark 46 and the fourth registration mark 48 printed by the second printing unit 18 correspond to the shapes of the first registration mark 38 and the second registration mark 40 printed by the first printing unit 16. However, different shapes are also possible.

Due to the previous adjustment, the horizontal and vertical positions of the third registration mark 46 and the fourth registration mark 48 printed by the second printing unit 18 are clearly defined.

Due to the clearly defined position, the monochrome photocells can determine which print unit generates the registration mark based on their position.

In the next step, the vertical distance v1 between the first registration mark 38 and the third registration mark 46 printed on the first lateral edge area 35 by the first printing unit 16 and the second printing unit 18 is measured, and the vertical distance _v2 between the second registration mark 40 and the fourth registration mark 48 printed on the second lateral edge area 37 by the first printing unit 16 and the second printing unit ₁₈ is measured. The vertical distances _v1 and _v2 between the registration marks are compared to detect the skew between the first printing unit 16 and the second printing unit 18.

In particular, if the distances _v1 and _v2 are different from each other, a deflection correction is necessary.

Determine the degree of skew between the first printing unit 16 and the second printing unit 18, and adjust the skew by pivoting the skew roller 22 between the print roller 24 of the first printing unit 16 and the print roller 25 of the second printing unit 18.

In an alternative embodiment, the vertical distances of the registration marks 46, 48 relative to the trigger codes 34, 36, respectively, or relative to other reference points may be measured to detect skew.

In a method step which is optionally used, the horizontal and/or vertical position of the second registration mark 40 printed by the first printing unit 16 on the second lateral edge region 37 is measured, and the vertical and/or horizontal registration is adjusted again based on the position of the second registration mark 40 on the second lateral edge region 37. As a result, the alignment of the color plane can be even more accurate.

The method steps described with respect to the first printing unit 16 and the second printing unit 18 may be repeated for subsequent printing units of the printing device.

The maximum width of the second registration mark 40 and the fourth registration mark 48 on the second lateral edge region 37 is smaller than the maximum width of the first registration mark 38 and the third registration mark 46 on the first lateral edge region 35, specifically, between one third and two thirds of the width of the first registration mark 38 and the third registration mark 46 on the first lateral edge region 35.

For example, when using the same photocells 28, 29 with the same orientation on both sides of the medium, the maximum width of the registration marks 40, 48 on the second lateral edge region 37 is 4 mm. In another example, when using a photocell 29 with a narrower sensitive area along the lateral direction, the maximum width of the registration marks 40, 48 on the second lateral edge region 37 is 2 mm.

A smaller width is possible because the maximum lateral error is reduced after the first alignment. In addition, the horizontal position of the registration marks 40, 48 on the second lateral edge region 37 is measured, but the vertical position does not need to be measured. This also contributes to a smaller possible width of the registration marks 40, 48 on the second lateral edge region 37.

This reduces waste generated during the printing process.

In detail, the lateral edge areas 35, 37 with registration marks do not contribute to the final printing and are cut off after the printing process.

FIG5 shows the sensor paths of the photocells 28 and 29 of the detection unit 26, specifically, the paths of the sensitive areas of the photocells 28 and 29.

The sensitive area of photocells 28 and 29 is rectangular.

For example, the sensitive area of a photocell is 2mm x 1mm.

Figure 5 shows that the width of the second photocell 29 is smaller than that of the first photocell 28.

For example, the photocells 28, 29 are identical, but the second photocell 29 is rotated approximately 90° relative to the first photocell 28. Specifically, the photocell 28 is used in a horizontal orientation on the larger registration marks 38, 46 on the first lateral edge region, and the second photocell 29 is used in a vertical orientation on the smaller marks 40, 48 on the second lateral edge region.

In another example, the photocells 28, 29 are different, wherein the second photocell 29 has a smaller sensitive area than the first photocell 28.

Due to the lateral error in the position of the print medium 30, the width of the registration marks 38, 46 on the first lateral edge region 35 of the medium 30 added to the width of the sensitive area of the photocell 28 must be at least slightly larger than the initial lateral position error tolerance to ensure that the marks pass over the sensitive area of the photocell 28. The width of the registration marks 38, 46 is preferably at least as large as the width of the sensitive area of the photocell 28 to ensure that the registration marks 38, 46 completely pass over the sensitive area of the photocell 28. Therefore, the width of the registration marks 38, 46 is preferably slightly larger than the width of the sensitive area of the photocell 28. The same applies to the second lateral edge region 37 of the medium, i.e., the registration marks 40, 48 and the photocell 29. However, since the lateral error tolerance on the second lateral edge region 37 is smaller, this is because it is applied after the initial lateral alignment of the marks on the first lateral edge region 35 of the medium, which can make the size of the marks on the second lateral edge region 37 of the medium smaller.

Since the horizontal positions of the second registration mark 40 and the fourth registration mark 48 have been set according to the positions of the first registration mark 38 and the third registration mark 46 on the first lateral edge area 35, the error in the horizontal position is within the range of 1 mm.

30: Printing medium 32: Arrow/travel direction 34, 36: Trigger code 35: First lateral edge area 37: Second lateral edge area 38: First alignment mark 40: Second alignment mark 46: Third alignment mark 48: Fourth alignment mark v ₁ , v ₂ : Vertical distance

Claims (12)

A method for aligning a print pattern on a print medium (30) in a printing device (10), the printing device having at least a first print unit (16) and a second print unit (18), wherein each print unit (16, 18) comprises a print roller (24, 25) and wherein the second print unit (18) comprises an optical detection unit (26), wherein the print medium (30) comprises a first lateral edge region (35) and a second lateral edge region (37) opposite to the first lateral edge region (35) and travels from the first print unit (16) to the second print unit (18) along a longitudinal direction, the method comprising The first printing unit (16) prints a first registration mark (38) on the first lateral edge region (35) and a second registration mark (40) on the second lateral edge region (37), The second printing unit (18) prints a third registration mark (46) on the first lateral edge region (35) of the printing medium (30) and a fourth registration mark (48) on the second lateral edge region (37), The detection unit (26) is used to determine the horizontal and vertical positions of the first registration mark (38) at the first lateral edge region (35), The detection unit (26) is used to determine the horizontal position of the third registration mark (46) at the first lateral edge region (35), and a horizontal registration of the second printing unit (18) is adjusted based on the relative horizontal positions of the first registration mark (38) and the third registration mark (46), wherein the maximum width of the second and fourth registration marks (40, 48) on the second lateral edge region (37) is less than the maximum width of the first and third registration marks (38, 46) on the first lateral edge region. A method as claimed in claim 1, wherein the method comprises: using the detection unit (26) to determine the vertical position of the first registration mark (38) at the first lateral edge region (35); using the detection unit (26) to determine the vertical position of the third registration mark (46) at the first lateral edge region (35); adjusting a vertical registration of the second printing unit (18) based on the relative vertical positions of the first registration mark (38) and the third registration mark (46). A method as claimed in claim 1 or 2, wherein the first and third registration marks (38, 46) on the first lateral edge region (35) are two-dimensional registration marks, and the second and fourth registration marks (40, 48) on the second lateral edge regions (37) are one-dimensional or two-dimensional registration marks. A method as claimed in claim 1 or 2, wherein the registration marks (38, 46) on the first lateral edge region (35) have a horizontal edge (42) and an edge (44) inclined towards the horizontal edge (42). A method as claimed in claim 1 or 2, wherein a trigger code (34) is printed on the first lateral edge area (35) by the first printing unit (16), and wherein the first registration mark (38) printed on the first lateral edge area (35) by the first printing unit (16) is printed after the trigger code (34) relative to the travel direction of the printing medium (30). A method as claimed in claim 1 or 2, wherein a trigger code (36) is printed on the second lateral edge area (37) by the first printing unit (16), and the second registration mark (40) printed on the second lateral edge area (37) by the first printing unit (16) is printed after the trigger code (36) relative to the travel direction of the printing medium (30). A method as claimed in claim 1 or 2, wherein a vertical distance between the third registration mark (46) printed on the first lateral edge area (35) by the second printing unit (18) and a reference point is measured, and a vertical distance between the fourth registration mark (48) printed on the second lateral edge area (37) by the second printing unit (18) and a reference point is measured, and when the measured distance changes, a deflection between the first and second printing units (16, 18) is detected based on the measured distance. A method as claimed in claim 7, wherein a vertical distance ( _v1 ) between the registration marks (38, 46) printed on the first lateral edge area (35) by the first and second printing units (16, 18) is measured, and a vertical distance (v2) between the registration marks (40, 48) printed on the second lateral edge area (37) by the first and second printing units (16, 18) is measured, and wherein the vertical distances ( _v1 , _v2 ) between the registration marks (38, 46, 40, ₄₈ ) are compared to detect the skew between the first and second printing units (16, 18). A method as claimed in claim 7, wherein the degree of skew between the first printing unit (16) and the second printing unit (18) is determined, and the skew is adjusted by pivoting a skew roller (22) between the print roller (24) of the first printing unit (16) and the print roller (25) of the second printing unit (18). A method as claimed in claim 1 or 2, wherein a horizontal position of the second registration mark (40) and the fourth registration mark (48) on the second lateral edge region (37) is measured, and the horizontal registration is again adjusted based on the position of the second registration mark (40) and the fourth registration mark (48) on the second lateral edge region (37). A printing device (10) is configured to perform any one of claims 1 to 10 and in addition to the method of claim 8, wherein at least two printing units (16, 18) are arranged in sequence, wherein each printing unit (16, 18) includes a printing roller (24, 25) and a deflection roller (21, 22), and the second printing unit (18) arranged after the first printing unit (16) includes an optical detection unit (26) The unit (26) includes a first and a second photocell (28, 29) arranged downstream of the print roller (25), so that the first photocell (28) can detect the first and third registration marks (38, 46) in the first lateral edge area (35) of the print medium (30), and the second photocell (29) can detect the second and fourth registration marks (40, 48) in the second lateral edge area (37) of the print medium (30). A printing device as claimed in claim 11, wherein the second photocell (29) has a smaller width than the first photocell (28).