JP5157703B2 - Liquid ejecting apparatus and raster line forming method - Google Patents

Description

  The present invention relates to a liquid ejection apparatus and a raster line forming method.

  As one of liquid ejecting apparatuses, an ink jet printer that performs printing by ejecting liquid (ink) onto various media such as paper, cloth, and film is known. This printer includes a head in which a plurality of nozzles that discharge liquid onto a medium are arranged in a first direction (sub-scanning direction), and the head is in a second direction (main scanning direction) that intersects the first direction. The liquid is discharged while moving.

The above-described printer performs, for example, so-called overlap printing from the viewpoint of improving image quality. That is, the printer moves the head alternately in the second direction and the first direction a plurality of times, and forms one raster line by discharging liquid to two or more different nozzles.
International Publication No. 01/03930 Pamphlet

  Meanwhile, some printers include a head unit having a plurality of the heads along the first direction from the viewpoint of increasing the printing speed. In this case, for example, it is conceivable that the width of the head unit in the first direction is larger than the width of the medium in the first direction so that the liquid is ejected all over the entire width of the medium. However, in such a configuration, when the total movement amount of the head unit in the first direction during printing is large, the liquid is ejected at once over the entire width of the medium during the movement in the second direction. In order to achieve this, it is necessary to increase the width of the head unit in the first direction.

  It is also known that the liquid ejection characteristics differ depending on the individual differences of the heads. For example, one head has a characteristic of easily ejecting liquid, and the other head has a characteristic of hardly ejecting liquid. For this reason, when a plurality of heads constituting the head unit eject liquid, so-called density unevenness or the like occurs due to a difference in ejection characteristics of each head, and as a result, image quality may be deteriorated.

  The present invention has been made in view of the above problems, and an object thereof is to suppress an increase in the width of the head unit in the first direction and to suppress deterioration in image quality.

In order to solve the above problems, the main present invention is:
(A) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction along the first direction so that there are overlap nozzles between the adjacent heads; A head unit that ejects the liquid while moving relative to the medium in a second direction intersecting with one direction,
A head unit in which the width in the first direction of the head unit is larger than the width in the first direction of the medium;
(B) a moving mechanism for moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times;
(C) While moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times, the raster line is transferred to the two or more different nozzles. A control unit for forming a raster line group by discharging
The total amount of movement of the head unit in the first direction when the head unit has moved relatively a plurality of times,
A value obtained by adding one half of the number of overlapping nozzles of the plurality of nozzles to the number of non-overlapping nozzles of the plurality of nozzles arranged in the first direction in one head. When,
Moving the head unit relative to the moving mechanism to be smaller than the product of the nozzle spacing in the first direction ,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. A control unit for forming the raster line group so as to be equal to or less than the number of the raster lines;
A liquid ejecting apparatus comprising (d).

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

(A) A plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction are provided along the first direction, and the second direction intersecting the first direction is directed to the medium. A head unit that discharges the liquid while relatively moving;
A head unit in which the width in the first direction of the head unit is larger than the width in the first direction of the medium;
(B) a moving mechanism for moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times;
(C) While moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times, the raster line is transferred to the two or more different nozzles. A control unit for forming a raster line group by discharging
In the moving mechanism, the total moving amount of the head unit in the first direction when the head unit is relatively moved a plurality of times is smaller than the effective nozzle width of the one head in the first direction. Relatively moving the head unit;
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. A control unit for forming the raster line group so as to be equal to or less than the number of the raster lines;
A liquid ejection apparatus comprising (d). According to such a liquid ejecting apparatus, it is possible to suppress an increase in the width of the head unit in the first direction and to suppress deterioration in image quality.

In addition, such a liquid ejection device,
When the number of movements of the head unit in the second direction when the head unit is relatively moved a plurality of times is m times,
It is desirable that all the heads eject the liquid during the m movements. In such a case, a raster line group can be formed with a minimum number of heads while reducing the total amount of movement of the head unit.

In addition, such a liquid ejection device,
When the number of times of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times is n times,
It is desirable that the movement amounts of the n movements have the same size. In such a case, deterioration of image quality can be effectively suppressed.

In addition, (a) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction are arranged in the first direction, and the medium is arranged in the second direction intersecting the first direction. A head unit that discharges the liquid while moving relative to the head unit, wherein the width of the head unit in the first direction is larger than the width of the medium in the first direction;
By forming each raster line by ejecting the liquid to two or more different nozzles while moving relative to the medium alternately in the second direction and the first direction a plurality of times, a raster line is formed. A raster line forming method for forming a group,
(B) The total amount of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times is smaller than the effective nozzle width of the one head in the first direction. Move the head unit relatively,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. The raster line forming method, wherein the raster line group is formed so as to be equal to or less than the number of raster lines. According to such a raster line forming method, it is possible to suppress an increase in the width of the head unit in the first direction and to suppress deterioration in image quality.

== Configuration example of inkjet printer ==
An ink jet printer (hereinafter referred to as “printer 1”), which is an example of a liquid ejection device, is attached to a strip-shaped printing tape T, which is an example of a medium, on a unit image to be cut out later, for example, a wrap film of fresh food A seal-like printed matter is printed by an inkjet method. Here, the printing tape T is roll paper (continuous paper) with release paper, and images to be printed are continuously printed in a direction in which the printing tape T continues.

<< Configuration of Printer 1 >>
FIG. 1 is a block diagram of the overall configuration of the printer 1. FIG. 2A is a schematic sectional view of the printer 1, and FIG. 2B is a schematic top view of the printer 1. FIG. 3 shows the nozzle arrangement on the lower surface of the head unit 40.

  When the printer 1 receives the print data, the controller 10 which is an example of a control unit controls each unit (conveyance unit 20, drive unit 30, and head unit 40) to form an image on the print tape T. The state in the printer 1 is monitored by the detector group 50, and the controller 10 controls each unit based on the detection result.

  The transport unit 20 transports the print tape T from the upstream side to the downstream side in the direction in which the print tape T continues (hereinafter referred to as the transport direction). The transport unit 20 includes a feed roller 21, a feed roller 22, a suction table 23, and the like. The feed roller 21 feeds the roll-shaped printing tape T before printing to the suction table 23 which is a printing area. The suction table 23 vacuums the printing tape T from below and holds the printing tape T. The delivery roller 22 delivers the printed printing tape T from the printing area. The printing tape T sent out from the printing area is wound up in a roll shape by a winding mechanism.

  The drive unit 30 is a moving mechanism that freely moves the head unit 40 in a main scanning direction corresponding to the transport direction and a sub-scanning direction corresponding to the width direction of the printing tape T. The drive unit 30 includes, for example, an X movement table that moves the head unit 40 in the main scanning direction, a Y movement table that moves the X movement table holding the head unit 40 in the sub scanning direction, and a motor that moves them. (Not shown).

  The head unit 40 forms a dot row (raster line) on the printing tape T by ejecting ink while moving in the main scanning direction. Since the collection of dot rows forms an image, the image is printed by forming the dot rows. The head unit 40 has ten heads 41, and the ten heads 41 are arranged in a staggered manner in the width direction (sub-scanning direction). The head unit 40 can be ejected over the entire width of the printing tape T by one movement in the main scanning direction, that is, the width of the head unit 40 in the sub-scanning direction is larger than the width of the printing tape T. Ten heads are arranged to be larger.

  Further, on the lower surface of each head 41, a nozzle row Y for discharging yellow ink, a nozzle row M for discharging magenta ink, a nozzle row C for discharging cyan ink, and a nozzle row K for discharging black ink are formed. Has been. In each nozzle row, 360 nozzles are arranged at a constant interval (360 dpi) in the width direction. Of the two heads adjacent to each other in the width direction (here, the head 41 (1) and the head 41 (2) will be described as examples) The two nozzles # 359 and # 360 and the innermost nozzles # 1 and # 2 of the front head 41 (2) are located on the same line (that is, the nozzles overlap). In this embodiment, the sub-scanning direction corresponds to the first direction, and the main scanning direction corresponds to the second direction.

<< Moving Mode of Head Unit 40 During Printing >>
FIG. 4A to FIG. 4I are schematic diagrams for explaining the movement mode of the head unit 40 during printing. The printer 1 forms each dot row (raster line) by moving the head unit 40 four times in the main scanning direction. At the time of printing, the printing tape T is held on the suction table 23 without being conveyed.

  The head unit 40 before printing stands by at the home position (position shown in FIG. 4A). At the time of printing, first, the head unit 40 is moved from the downstream side to the upstream side in the main scanning direction by the drive unit 30 (FIG. 4B). During this movement (pass 1), ink is ejected from each nozzle of the head unit 40 over the entire width of the print tape T, and a dot row of pass 1 is formed on the print tape T. The head unit 40 moved in the main scanning direction is moved from the back side to the front side in the sub scanning direction by the drive unit 30 (FIG. 4C), and then the head unit 40 is again moved from the upstream side to the downstream side in the main scanning direction. While moving (pass 2) (FIG. 4D), ink is ejected from the nozzles over the entire width of the print tape T, and a dot row of pass 2 is formed. Here, “pass” means that the head unit 40 moves once in the main scanning direction, and the number after the pass indicates the order in which the pass is performed.

  As described above, the head unit 40 moves in the main scanning direction of the head unit 40 for dot formation (FIGS. 4B, 4D, 4F, and 4H) and moves in the sub-scanning direction of the head unit 40 (FIG. 4C). 4E and 4G) are alternately performed. Thereby, a plurality of dot rows (raster line groups) are formed over the entire width of the printing tape T. Then, after the fourth movement in the main scanning direction (pass 4, FIG. 4H) is completed, the head unit 40 moves to the back side in the sub-scanning direction (FIG. 4I) and is positioned at the home position shown in FIG. 4A. . This completes a series of movements of the head unit 40 during printing.

== Density unevenness due to difference in ejection characteristics of each head 41 ==
It is known that ink ejection characteristics vary depending on individual differences of the heads 41. For example, while ink is likely to be ejected from the nozzle of one head 41, it may be difficult to eject ink from the nozzle of another head 41. For this reason, when printing is performed by the head unit 40 having ten heads 41 having individual differences, so-called density unevenness may occur due to the difference in ejection characteristics of the heads 41.

  Here, among the ten heads 41, the head 41 (3), the head 41 (4), and the head 41 (5) will be described as an example. Temporarily, the head 41 (3) has a characteristic that it is difficult to eject ink (the amount of ink ejected is less than the proper amount), and the head 41 (4) ejects ink normally (the amount of ink ejected is appropriate). The head 41 (5) has a characteristic that it is easy to eject ink (the amount of ink ejected is larger than an appropriate amount). For this reason, if it is necessary to form a dot with an appropriate discharge amount (hereinafter referred to as a medium dot), the head 41 (3) has a dot (hereinafter referred to as a small dot) with a smaller discharge amount than the appropriate amount. The head 41 (4) forms a medium dot, and the head 41 (5) forms a dot whose discharge amount is larger than an appropriate amount (hereinafter referred to as a large dot). It should be noted that most of the other heads 41 out of the ten heads 41 form medium dots in the same manner as the head 41 (4).

  5A and 5B are diagrams for explaining density unevenness due to a difference in ejection characteristics of the heads 41. FIG. The dot rows shown in FIGS. 5A and 5B are formed in two passes, FIG. 5A shows the dot row after pass 1, and FIG. 5B shows the dot row after pass 2.

  In the first dot row of the five dot rows, pass 1 and pass 2 are formed by the head 41 (3). Therefore, only small dots are arranged in the first dot row. In the second dot row, pass 1 is formed by the head 41 (3), and pass 2 is formed by the head 41 (4). For this reason, in the second dot row, small dots and medium dots are alternately arranged. In the third dot row, pass 1 and pass 2 are formed by the head 41 (4), and only medium dots are arranged. In the fourth dot row, pass 1 is formed by the head 41 (4) and pass 2 is formed by the head 41 (5), and medium dots and large dots are alternately arranged. The fifth dot row is formed by the head 41 (5) in pass 1 and pass 2, and only large dots are arranged.

  In such a case, the first dot row is formed with only small dots, and appears lighter than a dot row formed with medium dots (dots with an appropriate discharge amount). That is, it is recognized as density unevenness. Similarly, the fifth dot row is formed of only large dots and looks darker than a dot row formed of medium dots. That is, it is recognized as density unevenness. When the number of the first dot row and the fifth dot row increases, the density unevenness becomes conspicuous and the image quality further deteriorates.

  On the other hand, since the third dot row is formed with only medium dots, it has an appropriate density. Further, since the second and fourth dot rows occupy half of the medium dots, even if small dots and large dots are included, the density is neutralized as a whole and is difficult to be recognized as density unevenness.

  As described above, in a configuration in which a dot row is formed using a plurality of heads 41 having different ink ejection characteristics, the dot row is formed by only one head 41 (the head 41 (3) and the head 41 (5) described above). When it is formed, there may be a problem that the density unevenness becomes remarkable.

== Relationship between total sub-scanning amount of head unit and width of head unit during printing ==
The printer 1 according to the present embodiment is configured such that ink is ejected over the entire width of the printing tape T during four movements in the main scanning direction (pass 1 to pass 4). This is because the resolution of the image (for example, the resolution in the sub-scanning direction is 720 dpi) is finer than the nozzle pitch (360 dpi), and the head unit 40 is moved in the sub-scanning direction in units of 720 dpi. This is to form dot rows with fine spacing.

  On the other hand, the head unit 40 moves three times in the sub-scanning direction during four passes of pass 1 to pass 4 (FIGS. 4C, 4E, and 4G). In order to cause ink to be ejected over the entire width of the printing tape T in pass 1 to pass 4, depending on the total movement amount of the three movements (hereinafter also referred to as total sub-scanning amount). The width of the head unit 40 in the sub-scanning direction is different. This point will be described with reference to FIGS. 6A and 6B.

  FIG. 6A shows the width of the head unit 40 when the total sub-scanning amount is increased. FIG. 6B shows the width of the head unit 40 when the total sub-scanning amount is reduced. 6A and 6B is in the state immediately before the first movement in the main scanning direction (pass 1), and the right head unit 40 shown by the solid line is the fourth head unit 40. It is in a state immediately before the movement in the scanning direction (pass 4). Therefore, the amount of deviation in the sub-scanning direction between the dotted head unit 40 and the solid head unit 40 is the total sub-scanning amount of the head unit 40.

  As can be seen from FIGS. 6A and 6B, the larger the total sub-scanning amount, the larger the width in the sub-scanning direction of the head unit 40 so that ink is ejected over the entire width of the printing tape T. That is, the number of heads 41 constituting the head unit 40 increases. When the width of the head unit 40 is increased, the printer 1 may be increased in size in order to secure an installation space for the head unit 40.

== Print processing according to the present embodiment ==
In order to suppress the above-described problem, that is, the density unevenness and the width of the head unit 40 in the sub-scanning direction are suppressed, the printer 1 executes a printing process described below.

  In this printing process, (1) the drive unit 30 is configured so that the total amount of movement of the head unit 40 in the sub-scanning direction during printing is smaller than the effective nozzle width (described later) of one head 41 in the sub-scanning direction. The head unit 40 is moved, and (2) the number of raster lines (dot rows) formed by ejecting ink only to the nozzles of one head 41 in the raster line group (a plurality of dot rows) is two. The raster line group is formed so as to be equal to or less than the number of raster lines formed by ejecting ink to the nozzles of the head 41 described above.

  Various operations of the printer 1 when the printing process is executed are mainly realized by the controller 10. In particular, this embodiment is realized by the CPU 12 processing a program stored in the memory 13. And this program is comprised from the code | cord | chord for performing the various operation | movement demonstrated below.

  FIG. 7 is a flowchart for explaining the printing process. The flowchart shown in FIG. 7 starts when the controller 10 receives print data from the computer 90 (FIG. 1) via the interface 11.

In this printing process, first, the controller 10 sends the printing tape T to the printing area by the transport unit 20 (step S2). That is, the feed roller 21 feeds the printing tape T before printing to the suction table 23 that is a printing area.
Next, the controller 10 causes the drive unit 30 to eject the ink from the nozzles while moving the head unit 40 in the main scanning direction (FIG. 4B) (step S4). That is, the controller 10 forms a dot row of pass 1 on the printing tape T held on the suction table 23. Since the image ( printed material ) is formed by four passes, when the dot row of pass 1 is formed, the controller 10 moves the head unit 40 to the drive unit 30 by a certain amount of sub-scanning in the sub-scanning direction (FIG. 4C (Step S6: No, Step S8).
Then, the controller 10 forms a dot row with the movement of the head unit 40 in the main scanning direction (FIGS. 4D, 4F, and 4H) and moves the head unit 40 in the sub-scanning direction until the dot formation process is completed. (FIGS. 4E and 4G) are alternately performed (steps S4 to S8). In this embodiment, so-called overlap printing is performed.

  Here, the overlap printing according to the present embodiment will be described. Overlap printing is a printing method in which one dot row (raster line) is formed by two or more nozzles. Specifically, one nozzle intermittently forms a dot row every several dots in the main scanning direction. Then, dot rows are formed so as to complement the intermittent dot rows already formed by other nozzles.

  8 and 9 are diagrams for explaining overlap printing according to the present embodiment. However, for simplicity of explanation, only the nozzle row C of the four nozzle rows (nozzle row Y, nozzle row M, nozzle row C, nozzle row K) of each head 41 is shown, and the number of nozzles of each head 41 is also shown. Reduced to 16. For this reason, FIG. 8 shows the positions in the pass 1 to pass 4 of the nozzle row C of the heads in the sub-scanning direction (head 41 (1), head 41 (2), etc.) among the ten heads 41. FIG. 9 shows the state of dot formation, and FIG. 9 shows the positions in pass 1 to pass 4 of nozzle row C of the head (head (10), head 41 (9), etc.) on the front side in the sub-scanning direction. The state of dot formation is shown. 8 and 9, dots formed by the nozzles of the head 41 (1) and the head 41 (7) are indicated by white circles (◯), and the nozzles of the head 41 (2) and the head 41 (8) are formed. The dots to be formed are indicated by black circles (●), the dots formed by the nozzles of the head 41 (3) and the head 41 (9) are indicated by white triangles (Δ), and the nozzles of the head 41 (4) and the head 41 (10) are The dots to be formed are indicated by black triangles (▲).

  In pass 1 to pass 4, dots are formed in the pixels in the print area by the nozzles in the nozzle row C. Here, the “pixel” refers to a grid on a grid virtually defined on the printing tape T in order to regulate the positions where dots are formed. Further, in order to specify and describe the pixels, the pixels arranged in the main scanning direction are represented by “rows”, and the pixels arranged in the sub scanning direction are represented by “columns”. Note that the pixels shown in FIGS. 8 and 9 are arranged at an interval of 720 dpi in both the main scanning direction and the sub-scanning direction.

  First, in pass 1, ink is ejected from the nozzles of each head 41. Then, the dot rows are formed in the pixels in the odd rows (1 · 3 · 5...) Shown in FIG. 8 and in the odd rows (1 · 3 · 5...). For example, ink is ejected from the nozzle # 1 of the head 41 (1), and dots are formed on the pixels in the odd-numbered columns of the first row. Similarly, ink is ejected from the nozzle # 2 of the head 41 (1), and dots are formed on the pixels in the odd-numbered columns of the third row. In this way, each nozzle forms a dot every other pixel in the main scanning direction in each row corresponding to each position.

  Note that the ink ejection method of the overlapping nozzles of two heads adjacent in the width direction (here, the head 41 (1) and the head 41 (2) will be described as an example) is a non-overlapping nozzle (for example, This is different from the method of ejecting ink from the nozzle # 1) of the head 41 (1). That is, in pass 1, the nozzle # 15 and the nozzle # 16 of the head 41 (1) on the back side in the width direction form a dot row on the 3 × 7 × 11 × pixels, and the front side head 41 (2 No. # 1 and No. # 2 form dot rows on the 1 × 5 × 9 rows of pixels. In this way, the nozzles of the two adjacent heads 41 eject ink alternately to form dot rows in odd-numbered pixels.

After the end of pass 1, the head unit 40 moves as the first movement in the sub-scanning direction during printing.
It moves by a predetermined sub-scanning amount F (specifically, 7/720 dpi) from the back side to the front side in the sub-scanning direction.

  In pass 2 after the movement of the head unit 40, dot rows are formed in pixels in even-numbered rows (8, 10, 12,...) And even-numbered columns (2, 4, 6,...). For example, ink is ejected from the nozzle # 1 of the head 41 (1), and dots are formed in the pixels in the even-numbered columns of the eighth row. Similarly, ink is ejected from the nozzle # 2 of the head 41 (1), and dots are formed in pixels in even-numbered columns of the tenth row. In the second pass, nozzle # 15 and nozzle # 16 of the head 41 (1) on the back side in the width direction of adjacent heads form dot rows in pixels of 4, 8, 12,. Nozzle # 1 and nozzle # 2 of the head 41 (2) on the front side form a dot row on the 2 · 6 · 10... Row of pixels. That is, as in the first pass, the nozzles of two adjacent heads 41 alternately discharge ink to form dots in even-numbered pixels (the same applies to the third pass and the fourth pass described later). is there).

  After the end of pass 2, the head unit 40 moves by a predetermined sub-scanning amount F (7/720 dpi) as the second movement in the sub-scanning direction.

  Similarly, in pass 3, dot rows are formed in pixels in odd rows (15, 17, 19,...) And even columns (2, 4, 6,...). As a result, for example, the dot row on the 23rd row is completed by pass 1 and pass 3.

  After the end of pass 3, the head unit 40 moves by a sub-scanning amount F (7/720 dpi) having the same magnitude as the first and second sub-scanning amounts as the third movement in the sub-scanning direction. Thus, each movement amount F of the three movements of the head unit 40 in the sub-scanning direction has the same magnitude. Further, the total of the three sub-scanning amounts (total sub-scanning amount 3F) of the head unit 40 is smaller than the effective nozzle width of one head 41 described below.

  First, the effective nozzle will be described. About an effective nozzle, a view differs according to the presence or absence of the overlap nozzle (above-mentioned) between the adjacent heads 41. FIG. When there is no overlap nozzle, the effective nozzles of each head 41 are all the nozzles in the nozzle row (see FIG. 11). On the other hand, when there are overlap nozzles, the effective nozzles of each head 41 are determined in consideration of the overlap nozzles. Specifically, the effective nozzles of the head 41 include nozzles that do not overlap in the nozzle row of the head 41 and nozzles that distribute the overlap nozzles of the head 41 evenly in relation to the other heads 41. Become.

  Here, how the overlap nozzles are evenly distributed will be described. For example, in FIG. 8, nozzle # 15 and nozzle # 16 of the head 41 (1) overlap with nozzle # 1 and nozzle # 2 of the head 41 (2). In this case, nozzle # 15 of nozzle # 15 and nozzle # 16 is included in the effective nozzle of head 41 (1), and nozzle # 2 of nozzle # 1 and nozzle # 2 is the head. The overlap nozzles are evenly distributed so as to be included in the effective nozzles 41 (2). Thus, half of the overlapping nozzles of the head 41 are distributed to the head 41 so as to be included in the effective nozzles.

  The ten heads 41 of the present embodiment each have an overlap nozzle, and the effective nozzles of each head 41 are as follows. The effective nozzles of the head 41 (1) are the nozzles # 1 to # 14, the nozzle # 1 of the head 41 (2), the nozzle # 15 that overlaps the nozzle # 2, and the nozzle # 15 of the nozzle # 16. 15 nozzles. On the other hand, the effective nozzles of the head 41 (2) are the nozzle # 15 of the head 41 (1), the nozzle # 1 overlapping the nozzle # 16, the nozzle # 2 of the nozzle # 2, and the nozzle # 3 to the nozzle # 3. 14 nozzles # 1 of the head 41 (3), nozzle # 15 overlapping nozzle # 2 and nozzle # 15 of nozzle # 16. The effective nozzles of the head 41 (3) to the head 41 (9) are the nozzle # 2 to the nozzle # 15, similarly to the head 41 (2). On the other hand, the effective nozzles of the head 41 (10) are fifteen nozzles # 1 and # 2 of the nozzle # 1 and nozzle # 2 that overlap the nozzle of the head 41 (9), and nozzles # 3 to # 16. Nozzle.

  Next, the effective nozzle width determined from the above-described effective nozzle will be described. The effective nozzle width is a width of effective nozzles in the sub-scanning direction (the effective nozzles are arranged at intervals of 2/720 dpi in the sub-scanning direction). In this embodiment, the effective nozzle width of the head 41 (1) and the head 41 (10) is 30/720 dpi because there are 15 effective nozzles. On the other hand, the effective nozzle width of the head 41 (2) to the head 41 (9) is 28/720 dpi because there are 14 effective nozzles. In the printer 1, the total sub-scanning amount 3F (21/720 dpi) at the time of printing by the head unit 40 is set to be smaller than the smaller effective nozzle width (28/720 dpi) of the two effective nozzle widths. Has been.

  Continue explaining overlap printing. In pass 4, dot rows are formed in pixels in even-numbered rows (22, 24, 26,...) And in odd-numbered rows (1, 3, 5,...). As a result, for example, the 22nd dot row is completed by pass 2 and pass 4. As described above, in the overlap printing of this embodiment, one dot row is formed by two different nozzles.

  Here, the nozzles of which heads 41 form the dot rows (raster lines) in the print area will be considered. Here, the dot row in the print area refers to a dot row that is completed like the dot row of the 22nd row, and in this embodiment, refers to the dot rows from the 22nd row to the Lth row (FIG. 9).

  First, attention is paid to 28 dot rows (raster lines) from 22 lines to 49 lines. These dot rows are formed by the nozzles of the head 41 (1) and the head 41 (2). If it sees in detail, ten dot rows of the 22nd line-28th line, the 30th line, the 32nd line, and the 34th line are formed by two different nozzles of the head 41 (1), and two dots on the 47th line and the 49th line. This dot row is formed by only two nozzles having different heads 41 (2). On the other hand, of the 28 dot rows, the other dot rows (16 dot rows) are formed by the nozzles of both the head 41 (1) and the head 41 (2). Thus, in the dot rows from 22 to 49, the number (12) of dot rows formed only by the nozzles of one head 41 is the number of dot rows formed by the nozzles of the two heads 41. Less than the number (16).

  Next, attention is paid to 28 dot rows from 50 rows to 77 rows. The reason for paying attention to every 28 dot rows is that the sub-scanning amount F (7/720 dpi) of the head unit 40 is 1/4 times the effective nozzle width (28/720 dpi), so This is because the rows are repeatedly formed with 28 dot rows as one cycle (in other words, the combination of nozzles for forming each dot row is determined for every 28 dot rows). That is, similarly to the 28 dot rows from the 50th row to the 77th row, the subsequent 28 dot rows (for example, the dot row from the 78th row to the 105th row) are also 28 rows from the 22nd row to the 49th row. Are formed in the same manner as the dot rows.

  The dot rows from the 50th row to the 77th row are formed by the nozzles of the head 41 (1), the head 41 (2), and the head 41 (3). In detail, eight dot columns of 51 rows, 53 rows to 56 rows, 58 rows, 60 rows and 62 rows are formed by two different nozzles of the head 41 (2), and 75 rows and 77 rows of 2 are formed. Each dot row is formed by two different nozzles of the head 41 (3). On the other hand, of the 28 dot rows, the other dot rows (18 dot rows) are nozzles of two heads of the head 41 (1), the head 41 (2), and the head 41 (3). Is formed by.

  Thus, only the nozzles of one head 41 in the dot rows from 50 rows to 77 rows (that is, 28 dot rows corresponding to one cycle when the combination of the used nozzles is periodically repeated). The number of dot rows formed by (10) is smaller than the number of dot rows formed by the nozzles of the two heads 41 (18). In this printing process, the number of dot rows formed only by the nozzles of one head 41 in the dot rows included in the print area is the number of dot rows formed by the nozzles of the two heads 41. Less than.

The overlap printing according to the present embodiment has been described above. Returning to the flowchart shown in FIG. 7, the description of the print processing will be continued. When the dot formation process is completed by forming the dot row of pass 4 (step S6: Yes), in other words, when a printed matter (image) is printed on the printing tape T, the controller 10 causes the drive unit 30 to the head unit 40. Is moved in the sub-scanning direction (FIG. 4I) and is positioned at the home position (step S10).
Next, the controller 10 sends out the printing tape T on which dots are formed (printed printing tape T) from the printing area by the transport unit 20 (step S12). That is, the delivery roller 22 delivers the printed printing tape T from the printing area.
If there is further print data to be printed (step S14: Yes), the controller 10 repeats the above-described operation (steps S2 to S12) to print on the print tape T. On the other hand, when there is no print data (step S14: No), the controller 10 ends the print processing.

<< Effectiveness of this printing process >>
In the printing process described above, the controller 10 has the total sub-scanning amount 3F (21/720 dpi) in the sub-scanning direction of the head unit 40 smaller than the effective nozzle width (28/720 dpi) of one head 41 in the sub-scanning direction. As described above, by moving the head unit 40, it is possible to suppress an increase in the width of the head unit 40 in the sub-scanning direction.

  That is, as described above, the larger the total sub-scanning amount of the head unit 40, the larger the width of the head unit 40 in the sub-scanning direction (see FIG. 6). Therefore, by making the total sub-scanning amount of the head unit 40 smaller than the effective nozzle width of one head 41, overlap printing can be realized while reducing the total sub-scanning amount of the head unit 40 (FIGS. 8 and 9). ). As a result, even when ink is ejected over the entire width of the printing tape T in each pass of overlap printing, it is possible to suppress an increase in the width of the head unit 40 (the number of heads 41 increases).

  In addition, the controller 10 has two raster lines formed by ejecting ink only to the nozzles of one head 41 in the raster line group (raster lines in the print area of FIGS. 8 and 9). By forming a raster line group so that the number of raster lines formed by ejecting ink to the nozzles of the head 41 is less than or equal to that, deterioration in image quality can be suppressed.

  That is, as described above, the raster line formed by only the nozzles of one head 41 (the head 41 (3) having a small discharge amount and the head 41 (5) having a large discharge amount as described in FIG. 5). As the number increases, density unevenness tends to become more prominent (see FIG. 5). Therefore, by reducing the number of raster lines formed only by the nozzles of one head 41 to the number of raster lines formed by the nozzles of two or more heads 41, one head 41 (10 heads). 41, the ratio of raster lines (raster lines with density unevenness) formed only by nozzles of the head 41 having a small ejection amount and the head 41 having a large ejection amount to the raster line group can be reduced (FIG. 8, FIG. 9). For this reason, it is possible to suppress the density unevenness from becoming remarkable, and as a result, it is possible to suppress the deterioration of the image quality.

  In addition, by making the total sub-scanning amount 3F smaller than the effective nozzle width of one head 41, it is possible to suppress the density unevenness due to the joint between adjacent heads 41 from becoming significant. That is, since the head unit 40 is formed by connecting ten heads 41 in the sub-scanning direction, it is known that density unevenness occurs due to the low positional accuracy of the joints. When an image is formed by a plurality of passes, for example, if the joint in pass 1 and the joint in pass 2 match in the sub-scanning direction, density unevenness caused by the joint becomes noticeable. On the other hand, by making the total sub-scanning amount 3F smaller than the effective nozzle width of one head 41 as in this printing process, as shown in FIGS. Since the joints are dispersed, it is possible to suppress the density unevenness from becoming remarkable.

  Therefore, according to the printing process described above, it is possible to suppress an increase in the width of the head unit 40 in the sub-scanning direction and to suppress deterioration in image quality.

  In the above printing process, the controller 10 ejects ink from all the heads 41 in four passes (corresponding to m movements) of pass 1 to pass 4. Thereby, overlap printing can be realized with the minimum number of heads 41 while reducing the total sub-scanning amount of the head unit 40.

  Further, in the above printing process, the controller 10 has the same amount of movement (sub-scanning amount F) when the head unit 40 moves three times in the sub-scanning direction (corresponding to n movements). I have to. For this reason, dot rows are periodically formed, density unevenness occurrence positions are regularly dispersed, and it is possible to effectively suppress density unevenness.

== Second Embodiment ==
FIG. 10 shows a head unit 40 according to the second embodiment. Unlike the head unit 40 according to the first embodiment shown in FIG. 3, the head unit 40 does not have an overlap nozzle. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  Also in the second embodiment, the controller 10 (1) drives so that the total movement amount of the head unit 40 in the sub-scanning direction during printing is smaller than the effective nozzle width of one head 41 in the sub-scanning direction. The head unit 40 is moved to the unit 30, and (2) the number of raster lines formed by ejecting ink only to the nozzles of one head 41 in the raster line group corresponds to the nozzles of two or more heads 41. A raster line group is formed so as to be equal to or less than the number of raster lines formed by ejecting ink.

  FIG. 11 is a diagram for explaining overlap printing according to the second embodiment. In FIG. 11, as in FIG. 8, only the nozzle row C is shown, and the number of nozzles of each head 41 is also 14. The dots formed by the nozzles of the head 41 (1) are indicated by white circles (◯), the dots formed by the nozzles of the head 41 (2) are indicated by black circles (●), and the nozzles of the head 41 (3) are formed. The dots are indicated by white triangles (Δ), and the dots formed by the nozzles of the head 41 (4) are indicated by black triangles (▲). The effective nozzles of each head 41 shown in FIG. 11 are 14 nozzles # 1 to # 14, and the effective nozzle width of each head 41 is equal to 28/720 dpi.

  As shown in FIG. 11, the single sub-scanning amount F of the head unit 40 is 7/720 dpi as in the first embodiment (FIG. 8), and the total sub-scanning amount 3F is 21/720 dpi. The total sub-scanning amount 3F (21/720 dpi) is smaller than the effective nozzle width (28/720 dpi). For this reason, as in the first embodiment, it is possible to suppress an increase in the width of the head unit 40 in the sub-scanning direction.

  Unlike FIG. 8, in FIG. 11, the number of raster lines formed by ejecting ink only to the nozzles of one head 41 is the number of raster lines formed by ejecting ink to the nozzles of two or more heads 41. Equal to the number of lines. This is due to the absence of an overlap nozzle in the second embodiment.

  First, attention is paid to 28 dot rows from 22 rows to 49 rows. The ten dot columns of the 22nd to 28th, 30th, 32th, and 34th rows are formed only by the nozzles of the head 41 (1), and the four rows of 43th, 45th, 47th, and 49th rows are formed. The dot row is formed only by the nozzles of the head 41 (2). That is, 14 dot rows are formed by only the nozzles of one head 41. On the other hand, of the 28 dot rows, the other dot rows (14 dot rows) are formed by the nozzles of both the head 41 (1) and the head 41 (2). Similarly, in 28 dot rows from 50 rows to 77 rows, the number of dot rows formed by one head 41 is 14, and the number of dot rows formed by two heads 41 is 14. is there.

  Thus, the number of raster lines formed by ejecting ink only to the nozzles of one head 41 is less than the number of raster lines formed by ejecting ink to the nozzles of two or more heads 41. By forming the raster line group, as in the first embodiment, only the nozzles of one head 41 (the head 41 having a small ejection amount and the head 41 having a large ejection amount as described in FIG. 5) are formed. The ratio of the raster lines to the raster line group can be reduced. For this reason, even if there is a raster line formed only by the nozzles of one head 41, the number of raster lines that cause density unevenness can be reduced, and as a result, the density unevenness can be suppressed from becoming significant.

== Third Embodiment ==
Next, overlap printing according to the third embodiment will be described. FIG. 12 is a diagram for explaining overlap printing according to the third embodiment.

  Also in the third embodiment, as shown in FIG. 12, one raster line is completed in four passes (overlap printing). That is, during four passes, ink is ejected from each head to complete one raster line. Specifically, the dots in the first and fifth rows are formed in the first pass, the dots in the second and sixth rows are formed in the second pass, and the dots in the third and sixth rows are 3 Formed in the second pass, the dots in the fourth and eighth rows are formed in the fourth pass. FIG. 12 shows dots up to the eighth row, but in reality, dots are formed in more rows.

  In addition, the head unit 40 of this embodiment is the same as the head unit 40 (FIG. 3) of 1st embodiment. That is, there are overlap nozzles in two adjacent heads 41. The nozzle pitch of each nozzle is 1/360 dpi.

  By the way, the raster line interval shown in FIG. 12 is 1/720 dpi (refer to FIGS. 8 and 11) in the first and second embodiments, but is 2/720 dpi (= 1/1 /). 360 dpi) (ie, the same size as the nozzle pitch). For this reason, in the third embodiment, unlike the first and second embodiments, interlaced printing is not performed. Here, interlaced printing means a printing method in which raster lines that are not formed are sandwiched between raster lines that are formed in one pass, as shown in FIGS. 8 and 11.

  Further, in FIG. 12, as in FIG. 8, only the nozzle row C is shown, and the number of nozzles of each head 41 is also 16. Here, for convenience of explanation, the head unit 40 will be described as having three heads 42 (1) to 42 (3). The dots formed by the nozzles of the head 41 (1) are indicated by white circles (◯), the dots formed by the nozzles of the head 41 (2) are indicated by black circles (●), and the nozzles of the head 41 (3) are formed. The dots are indicated by white triangles (Δ).

  Further, the effective nozzles of each head 41 shown in FIG. 12 are as follows, as in the first embodiment. The effective nozzles of the head 41 (1) are fifteen nozzles # 1 to # 15, and the effective nozzle width is 30/720 dpi. The effective nozzles of the head 41 (2) are 14 nozzles # 2 to # 15, and the effective nozzle width is 28/720 dpi. The effective nozzles of the head 41 (3) are 15 nozzles # 2 to # 16. The effective nozzle width is 30/720 dpi.

  In the third embodiment, the single sub-scanning amount F of the head unit 40 is 8/720 dpi, and the total sub-scanning amount 3F in the four passes is 24/720 dpi. In the third embodiment, the total sub-scanning amount 3F (24/720 dpi) is set to be smaller than the smaller effective nozzle width (28/720 dpi) of the two effective nozzle widths. For this reason, it can suppress that the width | variety of the subscanning direction of the head unit 40 becomes large similarly to 1st embodiment.

  Here, consider which nozzle of each head 41 forms each raster line in the print area. Here, as shown in FIG. 12, the raster lines in the printing area in the present embodiment indicate the raster lines from the R1 line to the R30 line.

  First, the R1 to R3 rows of raster lines are formed only by the nozzles of the head 41 (1). The raster lines in the R4 to R15 rows are formed by the nozzles of the head 41 (1) and the head 41 (2). The raster lines of the R16 and R17 rows are formed only by the nozzles of the head 41 (2). R18 line to R29 line raster lines are formed by the nozzles of the head 41 (2) and the head 41 (3). The R30 row raster line is formed only by the nozzles of the head 41 (3).

  Further, when viewed within the range of the effective nozzle width (28/720 dpi) described above (here, a raster line of R4 to R27 lines will be described as an example), ink is applied only to the nozzles of one head 41. The number of raster lines formed by ejecting is 12 from R4 to R15, and the number of raster lines formed by ejecting ink to the nozzles of the two heads 41 is 2 in R16 and R17. It is a piece.

  Thus, the number of raster lines formed by ejecting ink only to the nozzles of one head 41 is smaller than the number of raster lines formed by ejecting ink to the nozzles of two or more heads 41. As a result, as in the first embodiment, even if there are raster lines formed only by the nozzles of one head 41, the number of raster lines that cause density unevenness can be reduced. As a result, density unevenness becomes noticeable. Can be suppressed.

  In the above description, the sub-scanning amount F for each pass when performing four passes is 8/720 dpi having the same size, but the sub-scanning amount for each pass may be different. In the above, the first row (5th row) dots are formed in the first pass, the second row (6th row) dots are formed in the second pass, and the third row (7th row). The dots are formed in the third pass and the dots in the fourth row (eighth row) are formed in the fourth pass. However, the present invention is not limited to this. It is sufficient that at least dots in adjacent rows are formed by different passes.

  Furthermore, in the above description, one raster line is formed by four passes, but the present invention is not limited to this. One raster line may be formed by at least two passes (passes of integer number of 2 or more). For example, one raster line may be formed by three passes (first embodiment and second embodiment). Is the same).

== Other Embodiments ==
The liquid ejection device and the like according to the present invention have been described above based on the above embodiment. However, the above-described embodiment is intended to facilitate understanding of the present invention and is intended to limit the present invention. is not. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof.

  In the above embodiment, the liquid ejection device is embodied as an ink jet printer. However, the present invention is not limited to this, and other liquids (for example, a liquid material in which particles of functional material are dispersed, a flow such as a gel, etc.) are used. The present invention can also be embodied in a liquid discharge device that discharges (injects) a shape. For example, a liquid material ejecting apparatus that ejects a liquid material in the form of dispersed or dissolved materials such as electrode materials and color materials used in the manufacture of liquid crystal displays, color filters, EL (electroluminescence) displays, and surface emitting displays, It may be a liquid ejecting apparatus for ejecting a bio-organic material used for biochip manufacturing, or a liquid ejecting apparatus for ejecting a liquid as a sample used as a precision pipette. In addition, a transparent resin liquid such as UV curable resin is used to form a liquid ejection device that ejects lubricating oil pinpoint to precision machines such as watches and cameras, and micro hemispherical lenses (optical lenses) used in optical communication elements. A liquid discharge device that discharges a liquid onto the substrate, a liquid discharge device that discharges an etching solution such as acid or alkali to etch the substrate, and a fluid discharge device that discharges gel. The present invention can be applied to any one of these discharge devices.

  In the above embodiment, the raster line is formed by moving the head unit 40 four times in the main scanning direction and three times in the sub-scanning direction while the printing tape T is stopped (see FIGS. 8 and 8). 9) However, the present invention is not limited to this. For example, the raster line may be formed by moving the head unit 41 only in the main scanning direction and the printing tape T moving in the sub-scanning direction. Also, the head unit 41 does not move and the printing tape T is not moved. A raster line may be formed by moving in the main scanning direction and the sub-scanning direction. That is, the raster line may be formed by the head unit 40 moving relative to the printing tape T in the main scanning direction and the sub-scanning direction.

In the above embodiment, the overlapping nozzles of adjacent heads 41 (for example, nozzle # 15 of head 41 (3) and nozzle # 1 of head 41 (4)) alternately eject ink. Although one raster line is formed (that is, both of the two overlapping nozzles eject ink), the present invention is not limited to this.
For example, only one of the overlapping nozzles of the adjacent heads 41 may eject ink. Specifically, for the head 41 (3), ink is ejected from the nozzles # 1 and # 2 of the overlap nozzles (nozzles # 1, # 2, # 15, and # 16), and the nozzles # 15 and # 2 are ejected. No ink may be ejected from 16. Similarly, for the head 41 (4), ink is ejected from nozzles # 1 and # 2 of the overlapping nozzles (nozzles # 1, # 2, # 15, and # 16), and the nozzles # 15 and # 16 The ink may not be ejected. In such a case, the number of effective nozzles (14) of each head 41 is equal.
In the above case, since the nozzles (mainly overlap nozzles) at the joints between adjacent heads 41 are used in the same manner, raster lines corresponding to the joints between the heads 41 are also formed at equal intervals. (That is, regularly formed) can suppress density unevenness caused by the joint.

1 is an overall configuration block diagram of a printer 1. FIG. FIG. 2A is a schematic sectional view of the printer 1, and FIG. 2B is a schematic top view of the printer 1. The nozzle arrangement on the lower surface of the head unit 40 is shown. FIG. 4A to FIG. 4I are schematic diagrams for explaining the movement mode of the head unit 40 during printing. 5A and 5B are diagrams for explaining density unevenness due to a difference in ejection characteristics of the heads 41. FIG. FIG. 6A shows the head unit 40 when the total sub-scanning amount is increased. FIG. 6B shows the head unit 40 when the total sub-scanning amount is reduced. 6 is a flowchart for explaining the printing process. It is a figure for demonstrating the overlap printing concerning a present Example. It is a figure for demonstrating the overlap printing concerning a present Example. The head unit 40 which concerns on 2nd embodiment is shown. It is a figure for demonstrating the overlap printing which concerns on 2nd embodiment. It is a figure for demonstrating the overlap printing which concerns on 3rd embodiment.

Explanation of symbols

1 printer,
10 controller, 11 interface, 12 CPU, 13 memory,
14 unit control circuit, 20 transport unit, 21 feed roller,
22 delivery roller, 23 suction table, 30 drive unit,
40 head units, 41 heads, 50 detector groups,
90 computers

Claims (6)

(A) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction along the first direction so that there are overlap nozzles between the adjacent heads; A head unit that ejects the liquid while moving relative to the medium in a second direction intersecting with one direction,
A head unit in which the width in the first direction of the head unit is larger than the width in the first direction of the medium;
(B) a moving mechanism for moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times;
(C) While moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times, the raster line is transferred to the two or more different nozzles. A control unit for forming a raster line group by discharging
The total amount of movement of the head unit in the first direction when the head unit has moved relatively a plurality of times,
A value obtained by adding one half of the number of overlapping nozzles of the plurality of nozzles to the number of non-overlapping nozzles of the plurality of nozzles arranged in the first direction in one head. When,
Moving the head unit relative to the moving mechanism to be smaller than the product of the nozzle spacing in the first direction ,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. A control unit for forming the raster line group so as to be equal to or less than the number of the raster lines;
A liquid ejection apparatus comprising (d). (A) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction along the first direction so that there is no overlap nozzle between the adjacent heads; A head unit that ejects the liquid while moving relative to the medium in a second direction intersecting with one direction,
A head unit in which the width in the first direction of the head unit is larger than the width in the first direction of the medium;
(B) a moving mechanism for moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times;
(C) While moving the head unit relative to the medium alternately in the second direction and the first direction a plurality of times, the raster line is transferred to the two or more different nozzles. A control unit for forming a raster line group by discharging
The total amount of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times is the number of the plurality of nozzles arranged in the first direction and the first direction in one head. Relative movement of the head unit to the moving mechanism so as to be smaller than the product of the nozzle interval ,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. A control unit for forming the raster line group so as to be equal to or less than the number of the raster lines;
A liquid ejection apparatus comprising (d). The liquid ejection device according to claim 1 or 2 , wherein
When the number of movements of the head unit in the second direction when the head unit is relatively moved a plurality of times is m times,
All the heads eject the liquid during the m times of movement. A liquid ejection apparatus according to any one of claims 1 to 3 ,
When the number of times of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times is n times,
The amount of movement of the n times of movement is the same size. (A) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction along the first direction so that there are overlap nozzles between the adjacent heads; A head unit that discharges the liquid while moving relative to the medium in a second direction that intersects one direction, wherein a width of the head unit in the first direction is greater than a width of the medium in the first direction. A larger head unit,
By forming each raster line by ejecting the liquid to two or more different nozzles while moving relative to the medium alternately in the second direction and the first direction a plurality of times, a raster line is formed. A raster line forming method for forming a group,
(B) The total amount of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times,
A value obtained by adding one half of the number of overlapping nozzles of the plurality of nozzles to the number of non-overlapping nozzles of the plurality of nozzles arranged in the first direction in one head. When,
Moving the head unit relative to the moving mechanism to be smaller than the product of the nozzle spacing in the first direction ,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. The raster line forming method, wherein the raster line group is formed so as to be equal to or less than the number of raster lines. (A) a plurality of heads in which a plurality of nozzles that discharge liquid to the medium are arranged in the first direction along the first direction so that there is no overlap nozzle between the adjacent heads; A head unit that discharges the liquid while moving relative to the medium in a second direction that intersects one direction, wherein a width of the head unit in the first direction is greater than a width of the medium in the first direction. A larger head unit,
By forming each raster line by ejecting the liquid to two or more different nozzles while moving relative to the medium alternately in the second direction and the first direction a plurality of times, a raster line is formed. A raster line forming method for forming a group,
(B) The total amount of movement of the head unit in the first direction when the head unit is relatively moved a plurality of times is the number of the plurality of nozzles arranged in the first direction in the one head The head unit is relatively moved so as to be smaller than the product of the nozzle interval in one direction ,
In the raster line group, the number of raster lines formed by discharging the liquid only to the nozzles of one head is formed by discharging the liquid to the nozzles of two or more heads. The raster line forming method, wherein the raster line group is formed so as to be equal to or less than the number of raster lines.

Images