Printing device and printing method

Abstract

To suppress density unevenness corresponding to position errors between nozzle rows.SOLUTION: A printing device comprises: a printing head that has a first nozzle row in which a plurality of first nozzles that can discharge dots of liquid to a medium are arranged in a first direction and a second nozzle row in which a plurality of second nozzles are arranged in the first direction, in which the first nozzle row and the second nozzle row are arranged in parallel in a second direction crossing the first direction; a conveying part that executes relative movement of the medium and the printing head in the second direction; and a control part that controls discharging of the dots by the nozzles in accordance with print data, so that raster lines on which the dots are arranged in the second direction can be formed on the medium. In a printing process of forming the plurality of raster lines in parallel on the medium in a third direction crossing the second direction, the control part forms a first area in which two or more raster lines are continuously formed by the first nozzles and a second area in which two or more raster lines are continuously formed by the second nozzles, alternately in the third direction.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] 2. Description of the Related Art Inkjet printers are known that perform printing using a print head that has a plurality of nozzles capable of ejecting dots of liquid onto a medium.

[0003] Also, a full line printer has been disclosed in which nozzles are arranged in a staggered pattern alternately on the upstream and downstream sides of the transport direction of the medium, forming a long head by connecting multiple nozzle groups consisting of an upstream nozzle row and a downstream nozzle row in a direction perpendicular to the transport direction (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-29146 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to document 1, by making the distance in the transport direction between two nozzle rows within a nozzle group and the distance in the transport direction between the nozzle groups all equal, streaky density unevenness that occurs due to the difference in landing time of dots on the medium depending on the distance between the nozzle rows is suppressed.

[0006] However, if there is an error in the positional relationship between nozzle rows in the direction in which the nozzles that make up the nozzle rows are aligned, a misalignment will occur between the raster lines recorded by different nozzle rows, which can result in streaky density unevenness in the print result. Therefore, improvements are needed to suppress density unevenness that corresponds to such positional errors between nozzle rows. [Means for solving the problem]

[0007] The printing device has a first nozzle row in which a plurality of first nozzles, which are nozzles capable of ejecting dots of liquid onto a medium, are arranged in a predetermined first direction, and a second nozzle row in which a plurality of second nozzles, which are the same nozzles, are arranged in the first direction, a print head in which the first nozzle row and the second nozzle row are arranged in a second direction intersecting the first direction, a transport unit that performs relative movement between the medium and the print head in the second direction, and a control unit that is capable of forming raster lines on the medium in which the dots are arranged in the second direction by controlling the ejection of the dots by the nozzles in accordance with print data, and in a printing process in which the control unit forms a plurality of the raster lines on the medium by arranging them in a third direction intersecting the second direction, a first region in which two or more consecutive raster lines formed by the first nozzles and a second region in which two or more consecutive raster lines formed by the second nozzles are alternately formed in the third direction.

[0008] a printing method for performing printing using a print head having a plurality of nozzles capable of ejecting dots of liquid onto a medium, the print head having a first nozzle row in a predetermined first direction, and a second nozzle row in a plurality of second nozzles in the first direction, the first nozzle row and the second nozzle row being aligned in a second direction intersecting the first direction, the method comprising: a printing step for forming on the medium a plurality of raster lines in which the dots are aligned in the second direction, arranged in a third direction intersecting the second direction, by relative movement between the medium and the print head in the second direction and controlling the ejection of the dots by the nozzles in accordance with print data, the printing step forming a first region in which two or more successive raster lines formed by the first nozzles and a second region in which two or more successive raster lines formed by the second nozzles alternate in the third direction. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a simplified device configuration. [Diagram 2] FIG. 2 is a simplified diagram showing the relationship between a print head and a medium as viewed from above. [Diagram 3] 4 is a flowchart showing a printing process according to the embodiment. [Figure 4] FIG. 11 is a diagram showing an example of a print result in step S120 after step S110. [Diagram 5] FIG. 13 is a diagram showing a conventional printing result. [Figure 6] FIG. 13 is a diagram showing an example of the print result obtained in step S120 after step S110, in which an attachment error has occurred in part of the print head. [Figure 7] FIG. 13 is a diagram showing a conventional print result when an installation error occurs in part of the print head. [Figure 8] FIG. 11 is a diagram for explaining a first modified example. [Figure 9] FIG. 13 is a diagram showing an example of a first modified example in which the overlapping pixel ratio on a specific raster line is reduced. [Figure 10] 13 is a flowchart showing a printing process according to a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that each drawing is merely an example for explaining the present embodiment. Since each drawing is an example, the ratio, shape, and shading may not be accurate, may not match each other, and some parts may be omitted.

[0011] 1.Outline of the device: 1 shows a simplified configuration of a printing device 10 according to this embodiment. The printing method of this embodiment is executed by the printing device 10. The printing device 10 includes a control unit 11, a display unit 13, an operation reception unit 14, a communication IF 15, a storage unit 16, a transport unit 17, a print head 18, and the like. IF stands for interface. The control unit 11 includes one or more ICs having a CPU 11a as a processor, a ROM 11b, a RAM 11c, and the like, and other non-volatile memories, and the like.

[0012] In the control unit 11, a processor, i.e., a CPU 11a, executes arithmetic processing according to a program 12 stored in a ROM 11b or other memory, using a RAM 11c or the like as a work area. The processor is not limited to a single CPU, and may be configured to perform processing using multiple CPUs or a hardware circuit such as an ASIC, or may be configured to perform processing in cooperation with a CPU and a hardware circuit.

[0013] The display unit 13 is a means for displaying visual information, and is configured, for example, by a liquid crystal display, an organic electroluminescence display, or the like. The display unit 13 may be configured to include a display and a drive circuit for driving the display. The operation reception unit 14 is a means for receiving operations by a user, and is realized, for example, by a physical button, a touch panel, a mouse, a keyboard, or the like. Of course, the touch panel may be realized as one function of the display unit 13. The display unit 13 and the operation reception unit 14 may be collectively referred to as the operation panel of the printing device 10. The display unit 13 and the operation reception unit 14 may be part of the configuration of the printing device 10, or may be peripheral devices externally attached to the printing device 10.

[0014] The communication IF 15 is a general term for one or more IFs that allow the printing device 10 to communicate with an external device (not shown) via wired or wireless communication in accordance with a predetermined communication protocol including a known communication standard. Examples of the external device include a personal computer, a server, a smartphone, a tablet terminal, a scanner, etc.

[0015] The storage unit 16 is, for example, a hard disk drive, a solid state drive, or other memory-based storage means. A part of the memory of the control unit 11 may be regarded as the storage unit 16. The storage unit 16 may be regarded as a part of the control unit 11.

[0016] In a so-called line printer, the transport unit 17 is a means for transporting the medium in a predetermined "transport direction" under the control of the control unit 11, and includes, for example, rollers (not shown) that rotate to transport the medium and a motor for driving the rollers. In a serial printer, the transport unit 17 is a means for relatively moving the medium and the print head 18 in the "transport direction" under the control of the control unit 11, and includes, for example, rails (not shown) for moving the print head 18 and a motor for moving the print head 18 along the rails. The medium is typically paper, but may be a medium made of a material other than paper as long as it is a medium that can be printed with liquid. The transport direction corresponds to the "second direction" as described below, and the transport unit 17 executes the relative movement between the medium and the print head 18 in the second direction.

[0017] The print head 18 is a mechanism that ejects liquid such as ink by a so-called inkjet method to print on a medium. The print head 18 has a plurality of nozzles 19 capable of ejecting dots of liquid, and ejects dots from each nozzle 19 onto a medium transported by the transport unit 17 under the control of the control unit 11. Alternatively, while the transport unit 17 moves the print head 18 relative to the medium in the transport direction D2, the print head 18 ejects dots from each nozzle 19 under the control of the control unit 11. The print head 18 may be called a liquid ejection head, a recording head, a print head, an inkjet head, or the like.

[0018] Printing device 10 may be a single inkjet printer, but may also be a printing system consisting of multiple devices connected to each other so that they can communicate with each other. For example, the printing system may include an information processing device that corresponds to control unit 11, and a printer that has transport unit 17 and print head 18 and is controlled by the information processing device.

[0019] Figure 2 shows a simplified view of the relationship between the print head 18 and the medium 30 from an above perspective. In Figure 2 and other figures, each nozzle 19 is represented by a white circle, and the predetermined "first direction" in which the multiple nozzles 19 are aligned is indicated by the symbol D1. In this specification, the first direction D1 is also referred to as the "nozzle alignment direction D1." Furthermore, the symbol D2 indicates the second direction D2 that intersects with the first direction D1, that is, the transport direction D2. A "nozzle row" is formed by lining up the multiple nozzles 19 along the nozzle alignment direction D1.

[0020] In FIG. 2, the reference symbol D3 indicates a "third direction D3" that intersects with the transport direction D2. In this specification, the third direction D3 is also referred to as a "width direction D3." In FIG. 2, the transport direction D2 and the width direction D3 are perpendicular to each other. The width direction D3 can be interpreted as the longitudinal direction of the print head 18. The length in the width direction D3 is simply referred to as the width. The nozzle row of the print head 18 has a width equal to or greater than the width of the medium 30. The printing device 10 having such a print head 18 corresponds to a so-called line printer. In the example of FIG. 2, the nozzle arrangement direction D1 and the width direction D3 are parallel. The distance between the nozzles 19 in the nozzle arrangement direction D1 is referred to as the nozzle pitch. In other words, a row in which a plurality of nozzles 19 are arranged at a constant nozzle pitch is a nozzle row.

[0021] The print head 18 has a "first nozzle row 20a" in which a plurality of "first nozzles 19a" that are nozzles 19 are arranged, and a "second nozzle row 20b" in which a plurality of "second nozzles 19b" that are nozzles 19 are arranged. The first nozzle row 20a and the second nozzle row 20b are arranged in the transport direction D2. The positions of the first nozzle row 20a and the second nozzle row 20b in the width direction D3 are aligned by design. The first nozzle 19a and the second nozzle 19b are nozzles 19 that eject ink of the same color, for example, black (K) ink. Therefore, there is no substantial difference between the first nozzle 19a and the second nozzle 19b, but for convenience, they are called different names.

[0022] 2, the first nozzle row 20a is configured by connecting a plurality of small nozzle rows 20a1, 20a2, and 20a3, each of which has a predetermined number of first nozzles 19a, in the nozzle arrangement direction D1. Similarly, the second nozzle row 20b is configured by connecting a plurality of small nozzle rows 20b1, 20b2, and 20b3, each of which has the same predetermined number of second nozzles 19b, in the nozzle arrangement direction D1. Needless to say, the number of small nozzle rows constituting each of the first nozzle row 20a and the second nozzle row 20b is not limited to three.

[0023] The control unit 11 can form a "raster line" on the medium 30 in which dots are arranged in the transport direction D2 by controlling the ejection of dots by each nozzle 19 according to the print data. That is, the control unit 11 prints the image on the medium 30 by making each nozzle 19 eject or not eject dots based on the print data expressing the image to be printed. Note that the term "raster line" does not only refer to the result formed on the medium 30, but is also used in the state of the print data. In the state of the print data, the raster line is a pixel row in which a plurality of pixels are arranged corresponding to the transport direction D2. A certain first nozzle 19a belonging to the first nozzle row 20a and a second nozzle 19b of the second nozzle row 20b, which corresponds to the position of the first nozzle 19a in the width direction D3, can form a raster line at the same position in terms of design. That is, one raster line 31 illustrated in FIG. 2 can be formed by one first nozzle 19a, and can also be formed by one second nozzle 19b.

[0024] In the example of FIG. 2, the nozzle arrangement direction D1 is parallel to the width direction D3, but in the viewpoint of FIG. 2, the nozzle arrangement direction D1 may be inclined obliquely with respect to the width direction D3. It is known that the printing resolution of the print head 18 in the width direction D3 can be improved by inclining the nozzle arrangement direction D1 with respect to the width direction D3. Even if the nozzle arrangement direction D1 is inclined with respect to the width direction D3, the nozzle arrangement direction D1 and the transport direction D2 intersect. Furthermore, each raster line formed by each nozzle 19 of the nozzle row will naturally be aligned in the width direction D3. When the nozzle arrangement direction D1 is parallel to the width direction D3 as shown in FIG. 2, the first direction D1 and the third direction D3 are naturally interpreted as being the same direction. As mentioned above, "the first nozzle row 20a is configured by connecting a plurality of small nozzle rows 20a1, 20a2, 20a3, each of which has a predetermined number of first nozzles 19a arranged in the nozzle arrangement direction D1," but if the nozzle arrangement direction D1 is obliquely inclined with respect to the width direction D3, this may be read as "the first nozzle row 20a is configured by connecting a plurality of small nozzle rows 20a1, 20a2, 20a3, each of which has a predetermined number of first nozzles 19a arranged in the width direction D3."

[0025] Needless to say, the print head 18 can eject ink of other colors, such as cyan (C), magenta (M), and yellow (Y), in addition to K ink. The print head 18 may also be a product capable of ejecting liquids of other colors than ink. Although omitted in FIG. 2 for space reasons, the print head 18 has a first nozzle row and a second nozzle row for ejecting liquids of colors and types other than K ink in the same manner as the first nozzle row 20a and the second nozzle row 20b.

[0026] 2, the print head 18 is stationary on the transport path of the medium 30, and the print head 18 ejects liquid onto the medium 30 transported by the transport unit 17 from upstream to downstream in the transport direction D2. However, the relative movement between the medium 30 and the print head 18 may at least include the movement of the print head 18. In other words, a mechanism may be adopted in which the print head 18 ejects liquid onto the medium 30 while moving from downstream to upstream in the transport direction D2 by a carriage (not shown), thereby forming a raster line on the medium 30 and achieving printing. In this case, the carriage corresponds to at least a part of the transport unit that executes the relative movement between the medium 30 and the print head 18.

[0027] 2.Printing method: 3 is a flowchart showing the printing process executed by the control unit 11 in accordance with the program 12. As the printing process, the control unit 11 forms a plurality of raster lines aligned in the width direction D3 on the medium 30. The description of this flowchart will serve as the description of the printing method of this embodiment. In step S100, the control unit 11 generates print data. First, the control unit 11 acquires image data expressing an image to be printed, which is the source of the print data. The image data is transmitted, for example, from an external device, and the control unit 11 acquires the image data from the external device via the communication IF 15. Alternatively, the image data is selected by a user's operation via the operation acceptance unit 14. The control unit 11 acquires the image data selected by the user from a storage location for the image data, for example, the storage unit 16.

[0028] The control unit 11 generates print data from image data. The control unit 11 generates print data by performing various image processing such as resolution conversion processing, color conversion processing, halftone processing, etc. on the image data. The print data is data that specifies the ejection or non-ejection of dots for each pixel and for each type of liquid. The type of liquid may be interpreted as the color of ink. The ejection of dots is also called dot-on, and the non-ejection of dots is also called dot-off.

[0029] In step S110, the control unit 11 assigns each raster line constituting the print data to each nozzle 19 of the print head 18 according to its position in the width direction D3. Specifically, the control unit 11 assigns each group of N consecutive raster lines in the width direction D3 as one unit alternately to the first nozzle row 20a and the second nozzle row 20b. N is an integer of 2 or more. More preferably, N is 2 or more and 4 or less.

[0030] In step S120, the control unit 11 outputs data of each pixel constituting each raster line of the print data to each nozzle 19 of the print head 18 according to the allocation in step S110, and causes the print head 18 to execute printing based on the print data. Step S120 corresponds to a "printing step" in which a plurality of raster lines are formed on the medium 30 in the width direction D3 by the relative movement between the medium 30 and the print head 18 in the transport direction D2 and the control of the ejection of dots by the nozzles 19 according to the print data. According to step S120, a "first region" in which two or more consecutive raster lines formed by the first nozzle 19a are formed and a "second region" in which two or more consecutive raster lines formed by the second nozzle 19b are formed alternately in the width direction D3. Each of the first region and the second region is a group of N raster lines that are consecutive in the width direction D3.

[0031] Figure 4 is a diagram illustrating a printing result in step S120 after step S110, and shows the print head 18 and a part of the medium 30. Figure 4 should be viewed in substantially the same way as Figure 2. Also, Figures 5, 6, and 7, which will be described later, should be viewed in the same way as Figure 4. In FIG. 4, each long area along the transport direction D2 shown in the medium 30 simply represents each raster line. In FIG. 4, among these raster lines, the raster lines formed by dot ejection from the first nozzle 19a of the first nozzle row 20a are shown in white, and the raster lines formed by dot ejection from the second nozzle 19b of the second nozzle row 20b are shown in gray. Of course, these white and gray colors are used for convenience to distinguish between raster lines and areas, and are unrelated to the color of the actual image represented by the print data. In addition, since an actual image is represented by dot-on and dot-off of each pixel in the print data, even if it is called one raster line, the dots are not necessarily completely connected along the transport direction D2, and naturally, the dots may be interrupted along the way.

[0032] 4 shows an example where N=2. That is, a region where two consecutive raster lines formed by the first nozzle 19a in the width direction D3 is a first region 32, and a region where two consecutive raster lines formed by the second nozzle 19b in the width direction D3 is a second region 33. Thus, according to this embodiment, the first regions 32 and the second regions 33 are formed alternately in the width direction D3, and an image is reproduced on the medium 30.

[0033] Fig. 5 is a comparative example to Fig. 4, and shows a print result by a conventional printing process. In the conventional printing process, as shown in Fig. 5, white raster lines, i.e., raster lines formed by the first nozzle 19a, and gray raster lines, i.e., raster lines formed by the second nozzle 19b, are alternately formed in the width direction D3 to reproduce an image on the medium 30.

[0034] FIG. 6 shows a printing result by step S120 after step S110, and shows an example different from FIG. 4. According to FIG. 6, an installation error not shown in FIG. 4 occurs in a part of the configuration of the print head 18. Specifically, the installation position of the small nozzle row 20b2, which is a part of the second nozzle row 20b, is shifted downward by a distance D in the width direction D3 from the viewpoint of FIG. 6. Note that the upper side along the width direction D3 in FIG. 6 and FIG. 7 and FIG. 8 from the same viewpoint as FIG. 6 will be referred to as one side, and the lower side will be referred to as the other side. It is also possible that the entire second nozzle row 20b is shifted in the width direction D3 relative to the first nozzle row 20a. Such installation errors of the nozzle row and the small nozzle row can occur during product manufacturing, and the presence or absence and degree of the error differ for each individual product.

[0035] When printing in step S120 after step S110 is performed using a print head 18 that includes such an installation error, the second region 33, which is composed of N consecutive raster lines assigned to the second nozzles 19b in the small nozzle row 20b2 of the second nozzle row 20b, is formed on the medium 30 shifted from the ideal position shown in FIG. 4. According to the example of FIG. 6, the second region 33, which is composed of N consecutive raster lines formed by the second nozzles 19b in the small nozzle row 20b2, is formed shifted to the other side in the width direction D3, and as a result, a gap E is generated between one side of the second region 33 and the first region 32 on one side, and the other side of the second region 33 overlaps with a part of the first region 32 on the other side. Such gaps E and overlaps can be visually recognized by a user as streaky density unevenness along the transport direction D2.

[0036] Fig. 7 is a comparative example of Fig. 6, and shows the print result by the conventional printing process as in Fig. 5. Fig. 7 differs from Fig. 5 only in that an error occurs in the mounting position of the small nozzle row 20b2 as in Fig. 6. According to Fig. 7, the raster line assigned to the second nozzle 19b in the small nozzle row 20b2 is formed shifted to the other side in the width direction D3 from the ideal position as shown in Fig. 5, and as a result, a gap E occurs between the raster line assigned to the first nozzle 19a on one side, and an overlap occurs between the raster line assigned to the first nozzle 19a on the other side.

[0037] Comparing FIG. 6 with FIG. 7, FIG. 6, in which the first region 32 and the second region 33 are alternately formed, has fewer locations where such gaps E and overlaps occur. In particular, when the print result is visually confirmed, the gaps E are visually recognized as streaky density unevenness that is lighter in color than the rest, and are likely to lower the image quality evaluation. According to this embodiment, by reducing the number of locations where the gaps E and overlaps occur compared to the conventional case, it is possible to suppress the deterioration of image quality due to density unevenness. The larger the value of N, the more likely it is that the number of locations where the gaps E and overlaps occur can be reduced.

[0038] 3. Summary: Thus, according to this embodiment, the printing device 10 has a first nozzle row 20a in which a plurality of first nozzles 19a, which are nozzles 19 capable of ejecting dots of liquid onto a medium 30, are arranged in a predetermined first direction D1, and a second nozzle row 20b in which a plurality of second nozzles 19b, which are nozzles 19, are arranged in the first direction D1, a print head 18 in which the first nozzle row 20a and the second nozzle row 20b are arranged in a second direction D2 that intersects with the first direction D1, a transport unit 17 that performs relative movement between the medium 30 and the print head 18 in the second direction D2, and a control unit 11 that is capable of forming a raster line in which dots are arranged in the second direction D2 on the medium 30 by controlling the ejection of dots by the nozzles 19 in accordance with printing data. In a printing process in which multiple raster lines are arranged on a medium 30 in a third direction D3 that intersects with the second direction D2, the control unit 11 alternately forms a first region 32 having two or more consecutive raster lines formed by the first nozzle 19a and a second region 33 having two or more consecutive raster lines formed by the second nozzle 19b in the third direction D3.

[0039] According to the above configuration, even if an error occurs in the positional relationship between the first nozzle row 20a and the second nozzle row 20b in a direction intersecting the transport direction D2, the control unit 11 can suppress the occurrence of streaky density unevenness more than before by alternately forming the first region 32 and the second region 33 in the width direction D3 in the printing process in which multiple raster lines are arranged in the width direction D3 and formed on the medium 30.

[0040] The control unit 11 may set the number of raster lines constituting each first region 32 and the number of raster lines constituting each second region 33 to be equal to or greater than 2 and equal to or less than 4. In other words, N may be defined as being equal to or greater than 2 and equal to or less than 4. Since the first nozzle row 20a used to form the first region 32 and the second nozzle row 20b used to form the second region 33 are separated in the second direction D2, a density difference between the first region 32 and the second region 33 may be visible at the boundary between the two regions due to a difference in landing time of dots on the medium 30. If the first region 32 and the second region 33 are large, the difference between the first region 32 and the second region 33 becomes more clearly visible. In other words, while each of the first region 32 and the second region 33 needs to be an area in which multiple raster lines formed by the nozzles 19 of the same nozzle row are continuous as explained in the comparison between FIGS. 6 and 7, if many raster lines formed by the nozzles 19 of the same nozzle row are continuous, the image quality may be deteriorated. Based on this viewpoint, the optimal number of raster lines constituting each of the first region 32 and the second region 33 was examined, and it was found that N is preferably set to 2 to 4. Some modifications included in this embodiment will be described below.

[0041] 4. First variant: The control unit 11 may form at least one of the raster lines adjacent to the boundary where the first region and the second region switch in the third direction D3, by both the first nozzle 19a and the second nozzle 19b.

[0042] 8 is a diagram for explaining the first modified example, in which the upper part of the diagram shows a part of the print data 40, and the lower part of the diagram shows the print result on the medium 30 based on the print data 40. In the print data 40, each rectangle is a pixel, and a pixel row in which a plurality of pixels are arranged corresponding to the transport direction D2 is a raster line. For convenience of explanation, in FIG. 8, raster numbers such as #n-1, #n, #n+1... are sequentially assigned to each raster line of the print data 40 along the width direction D3.

[0043] In step S110, the control unit 11 assigns each raster line of the print data 40 to the first nozzle 19a of the first nozzle row 20a or the second nozzle 19b of the second nozzle row 20b. As described above, when N=2, the control unit 11 assigns two consecutive raster lines as a unit to the first nozzle row 20a and the second nozzle row 20b alternately. In the print data 40, the symbol "A" indicates a pixel to be assigned to the first nozzle 19a, and the symbol "B" indicates a pixel to be assigned to the second nozzle 19b. That is, in the example of FIG. 8, the control unit 11 assigns each of the raster lines of raster numbers = #n-1, #n to two consecutive first nozzles 19a, each of the raster lines of raster numbers = #n+1, #n+2 to two consecutive second nozzles 19b, and each of the raster lines of raster numbers = #n+3, #n+4 to two consecutive first nozzles 19a. The explanation of FIG. 8 so far is the same as that of this embodiment.

[0044] Here, the boundary between the raster line with raster number = #n and the raster line with raster number = #n+1 can be said to be one of the boundaries where the first area and the second area switch in the width direction D3. Therefore, in step S110 of the first modified example, the control unit 11 assigns at least one of the raster lines adjacent to this boundary, for example, the raster line with raster number = #n+1, not only to the second nozzle 19b to which it should be assigned, but also to the first nozzle 19a. Such a raster line adjacent to the boundary and to be formed by both the first nozzle 19a and the second nozzle 19b is called a "specific raster line."

[0045] Since it is at least one of the raster lines adjacent to the boundary, not only the raster line with raster number = #n+1 but also the raster line with raster number = #n may be the specific raster line. Here, the explanation will be continued for the case where the raster line with raster number = #n+1 is the specific raster line. In the print data 40, "A & B" in a pixel means that the pixel is assigned to both the first nozzle 19a and the second nozzle 19b whose positions in the width direction D3 correspond. "The positions correspond in the width direction D3" means that the positions in the width direction D3 match when the installation error in the width direction D3 is assumed to be 0.

[0046] The print result by step S120, which is executed after such allocation of each raster line of the print data 40, is shown in the lower part of Fig. 8. Naturally, dots are formed on the medium 30, but in the lower part of Fig. 8, in order to easily show that the print data 40 is printed, pixels of the print data 40 are arranged on the medium 30 instead of dots. Also, in the lower part of Fig. 8, it is assumed that an attachment error such as that shown in Fig. 6 has occurred in the second nozzle row 20b, and pixels for which dots are formed on the medium 30 by the first nozzle 19a are shown by solid lines, and pixels for which dots are formed on the medium 30 by the second nozzle 19b are shown by dashed lines.

[0047] 8, the raster line with raster number = #n+1 is assigned not only to the second nozzle 19b but also to the first nozzle 19a. As a result, the gap E between the raster line with raster number = #n formed by the first nozzle 19a and the raster line with raster number = #n+1 formed by the second nozzle 19a is substantially filled by the raster line with raster number = #n+1 formed by the first nozzle 19a. In other words, according to the first modified example, even if an error occurs in the positional relationship between the first nozzle row 20a and the second nozzle row 20b in the direction intersecting the transport direction D2, the gap E caused by such an error, that is, streaky density unevenness, can be more accurately suppressed.

[0048] Note that when a specific raster line is said to be formed by both the first nozzle 19a and the second nozzle 19b, it does not only refer to a mode in which all pixels of the specific raster line are assigned to both the first nozzle 19a and the second nozzle 19b as in the example of Fig. 8. It also includes a mode in which some pixels of the specific raster line are assigned to both the first nozzle 19a and the second nozzle 19b, and a mode in which pixels of the specific raster line are assigned to the first nozzle 19a and the second nozzle 19b at a predetermined assignment ratio, for example, a ratio of 50% to 50%.

[0049] Here, when the dot formation rate indicated by the print data is low, the coverage rate of the dots on the medium 30 is low, so that even in places where the dots are sparse, such as the gap E, density unevenness is unlikely to occur. Conversely, by forming a specific raster line using both the first nozzle 19a and the second nozzle 19b, a dot that would normally be one becomes two dots, so that the color becomes darker than necessary at the dot overlapping area, and the graininess of the print result may deteriorate. From this viewpoint, in the first modified example, the control unit 11 may lower the ratio of pixels where the dots discharged by the first nozzle 19a and the dots discharged by the second nozzle 19b overlap in the raster line adjacent to the boundary where the first region and the second region switch in the width direction D3 and formed using the first nozzle 19a and the second nozzle 19b, as the dot formation rate indicated by the print data is low.

[0050] The dot formation rate indicated by the print data can be calculated as the ratio of the number of dot-on pixels to the number of pixels of the print data. The control unit 11 may calculate one dot formation rate for the entire image represented by the print data, or may calculate the dot formation rate for each area by dividing the image into several areas. The ratio of pixels in a specific raster line where dots discharged by the first nozzle 19a and dots discharged by the second nozzle 19b overlap (hereinafter, overlap pixel ratio) is the ratio of pixels of "A&B" to the number of pixels of the raster line of raster number = #n+1, which is the specific raster line of the print data 40, with reference to FIG. 8. In the example of FIG. 8, the overlap pixel ratio in the raster line of raster number = #n+1 is 100%, but the control unit 11 can reduce the overlap pixel ratio to less than 100% by changing at least a part of the pixels of "A&B" in the print data 40 to pixels of "A" or "B". As described above, in a mode in which the pixels of a specific raster line are allocated to the first nozzle 19a and the second nozzle 19b at a predetermined allocation ratio, for example, a ratio of 50% to 50%, the overlap pixel ratio is 0%.

[0051] In step S110, the control unit 11 assigns each pixel to the first nozzle 19a and the second nozzle 19b by lowering the overlapping pixel ratio in the specific raster line according to the dot formation rate of the entire image represented by the print data or the dot formation rate of the area to which the specific raster line belongs, as the formation rate decreases. As a result, problems such as deterioration of graininess and deterioration of image quality due to overlapping dots in an image with a low dot formation rate can be suppressed.

[0052] FIG. 9 is a diagram for explaining the first modified example, and shows an example in which the overlapping pixel ratio in a specific raster line is reduced to 50%. FIG. 9 can be viewed in the same way as FIG. 8. According to the upper part of FIG. 9, 50% of the pixels in the raster line with raster number = #n+1, which is a specific raster line of the print data 40, are pixels of "A & B", and the remaining pixels are pixels of "B". Therefore, as shown in the lower part of FIG. 9, in the print result by step S120 after step S110, the number of pixels of the raster line with raster number = #n+1 formed by the first nozzle 19a, which fills the gap E between the raster line with raster number = #n formed by the first nozzle 19a and the raster line with raster number = #n+1 formed by the second nozzle 19a, is half that of FIG. 8. As an example, when the dot formation rate is 20% or less, control unit 11 sets the overlapping pixel ratio in a specific raster line lower than when the dot formation rate exceeds 20%. In this way, control unit 11 may have in advance a plurality of threshold values ​​for the dot formation rate for changing the overlapping pixel ratio in a specific raster line.

[0053] 5. Second variant: The control unit 11 has a plurality of printing modes for printing processing. As at least a part of such printing modes, a "first printing mode" in which the first region 32 and the second region 33 are alternately formed in the width direction D3 as described above, and a "second printing mode" in which the raster lines formed by the first nozzle 19a and the raster lines formed by the second nozzle 19b are alternately formed in the width direction D3 as described with reference to Figs. 5 and 7 can be executed. In addition, the control unit 11 can have various printing modes, such as a mode in which printing is completed using only either the first nozzle 19a or the second nozzle 19b, and a mode in which each raster line is so-called overlap-printed using the first nozzle 19a and the second nozzle 19b.

[0054] In the second variant, the control unit 11 executes a first printing mode when printing on a "first medium" which is medium 30 and a "second medium" which is more susceptible to liquid bleeding than the first medium, and executes a second printing mode when printing on a second medium. Fig. 10 is a flowchart showing a printing process according to a second modified example, which is executed by the control unit 11 in accordance with the program 12. Fig. 10 differs from the flowchart in Fig. 3 in that it includes steps S105 and S115.

[0055] In step S105, the control unit 11 determines whether the medium 30 used by the printing device 10 for printing is a first medium. Here, it is assumed that various media that can be used by the printing device 10 are classified in advance as either a first medium or a second medium. A medium that is relatively resistant to bleeding of liquids such as ink is classified as a first medium, and a medium that is relatively resistant to bleeding of liquids such as ink is classified as a second medium. Information on the classification of the first medium and the second medium is stored in advance in the storage unit 16 or the like.

[0056] The control unit 11 acquires the type of medium 30 to be used. Then, by referring to the classification information, if the type of medium 30 corresponds to the first medium classification, the control unit 11 judges "Yes" in step S105 and proceeds to step S110, and if the type of medium 30 corresponds to the second medium classification, the control unit 11 judges "No" in step S105 and proceeds to step S115. The control unit 11 may appropriately acquire the type of medium 30 to be used from print settings input by the user, print instructions transmitted from an external device, etc. The timing of the judgment in step S105 may be after step S100 as shown in FIG. 10, but may also be before step S100 or simultaneously with step S100.

[0057] According to FIG. 10, the flow of printing on the first medium in step S120 through step S110 corresponds to the execution of the first print mode. On the other hand, the flow of printing on the second medium in step S120 through step S115 corresponds to the execution of the second print mode. In step S115, the control unit 11 alternately assigns each raster line constituting the print data to the first nozzle 19a of the first nozzle row 20a and the second nozzle 19b of the second nozzle row 20b for each raster line according to the position in the width direction D3. In step S120 after step S115, the control unit 11 outputs data of each pixel constituting each raster line of the print data to each nozzle 19 of the print head 18 according to the assignment in step S115, and causes the print head 18 to perform printing based on the print data.

[0058] If the medium 30 is one on which the liquid easily spreads, the gap E described above is easily filled by the dots that land on it, so there is little need to employ a printing method in which the first region 32 and the second region 33 are alternately formed as in the first printing mode. Also, if there is no error in the mounting position of the nozzle row as described above, it is easier to homogenize the image quality when viewed as a whole image by using the first nozzle 19a and the second nozzle 19b at as small a period as possible. From this perspective, in the second modified example, the first printing mode and the second printing mode are switched depending on the tendency of the liquid to spread on the medium 30. This makes it possible to obtain a high-quality print result by taking into account the characteristics of the medium 30. It goes without saying that the first modified example can be adopted in the first printing mode.

[0059] 6.Other notes: Although only some of the combinations of claims are described in the claims, this embodiment naturally includes within its scope not only one-to-one combinations of independent claims and dependent claims, but also various combinations of multiple dependent claims. In addition to the printing device 10, the present embodiment also discloses a method and a program 12 for implementing the method in cooperation with a processor. According to a printing method in which printing is performed using a print head 18 having a plurality of nozzles 19 capable of ejecting dots of liquid onto a medium 30, the print head 18 has a first nozzle row 20a in which a plurality of first nozzles 19a, which are nozzles 19, are arranged in a predetermined first direction D1, and a second nozzle row 20b in which a plurality of second nozzles 19b, which are nozzles 19, are arranged in the first direction D1, and the first nozzle row 20a and the second nozzle row 20b are arranged in a second direction D2 that intersects the first direction D1. The method includes a printing process for forming, on the medium 30, multiple raster lines in which dots are arranged in the second direction D2, arranged in a third direction D3 intersecting the second direction D2, by relative movement between the medium 30 and the print head 18 in the second direction D2 and controlling the ejection of dots by the nozzles 19 in accordance with print data, and in the printing process, a first region 32 in which two or more consecutive raster lines formed by the first nozzles 19a and a second region 33 in which two or more consecutive raster lines formed by the second nozzles 19b are alternately formed in the third direction D3.

[0060] The liquid ejected by the first nozzles 19a of the first nozzle row 20a and the liquid ejected by the second nozzles 19b of the second nozzle row 20b may be inks of different colors. In other words, two nozzle rows that eject inks of different colors can be considered as a first nozzle row and a second nozzle row. [Explanation of symbols]

[0061] 10...printing device, 11...control unit, 12...program, 13...display unit, 14...operation reception unit, 15...communication IF, 16...storage unit, 17...transport unit, 18...print head, 19...nozzle, 19a...first nozzle, 19b...second nozzle, 20a...first nozzle row, 20b...second nozzle row, 30...medium, 32...first area, 33...second area, 40...print data

Claims

1. a print head having a first nozzle row in a predetermined first direction, the first nozzles being nozzles capable of ejecting dots of liquid onto a medium, and a second nozzle row in a predetermined first direction, the second nozzles being nozzles being nozzles, the first nozzle row and the second nozzle row being arranged in a second direction intersecting the first direction; a transport unit that performs relative movement between the medium and the print head in the second direction; a control unit capable of forming a raster line in which the dots are aligned in the second direction on the medium by controlling the ejection of the dots from the nozzles in accordance with print data; The printing device is characterized in that, in a printing process in which a plurality of the raster lines are arranged on the medium in a third direction intersecting the second direction, the control unit alternately forms a first region in which two or more consecutive raster lines are formed by the first nozzle and a second region in which two or more consecutive raster lines are formed by the second nozzle in the third direction.

2. 2. The printing device according to claim 1, wherein the control unit forms at least one of the raster lines adjacent to the boundary where the first area and the second area switch in the third direction using both the first nozzles and the second nozzles.

3. 2. The printing device according to claim 1, wherein the control unit sets the number of raster lines constituting each of the first regions and the number of raster lines constituting each of the second regions to between 2 and 4, respectively.

4. The control unit is a first printing mode in which the first areas and the second areas are alternately formed in the third direction, and a second printing mode in which the raster lines formed by the first nozzles and the raster lines formed by the second nozzles are alternately formed in the third direction, A printing device as described in claim 1, characterized in that, when printing on a first medium, which is a first medium and a second medium which is more susceptible to bleeding of the liquid than the first medium, the first printing mode is executed, and when printing on the second medium, the second printing mode is executed.

5. The printing device described in claim 2, characterized in that the control unit reduces the ratio of pixels in the raster line adjacent to the boundary where the dots ejected by the first nozzles and the dots ejected by the second nozzles overlap, in the raster line formed using the first nozzles and the second nozzles, as the dot formation rate indicated by the print data becomes lower.

6. A printing method for performing printing using a print head having a plurality of nozzles capable of ejecting dots of liquid onto a medium, comprising: the print head has a first nozzle row in which a plurality of first nozzles, which are the nozzles, are aligned in a predetermined first direction, and a second nozzle row in which a plurality of second nozzles, which are the nozzles, are aligned in the first direction, the first nozzle row and the second nozzle row being aligned in a second direction intersecting the first direction; a printing step of forming, on the medium, a plurality of raster lines in which the dots are arranged in the second direction, in a third direction intersecting the second direction, by controlling relative movement between the medium and the print head in the second direction and ejection of the dots by the nozzles in accordance with print data; a printing method characterized in that, in the printing process, a first region in which two or more consecutive raster lines are formed by the first nozzle and a second region in which two or more consecutive raster lines are formed by the second nozzle are alternately formed in the third direction.

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