Ink jet printer, preliminary ejection method and program

Abstract

To provide an ink jet printer, a preliminary ejection method and a program that can suppress an image formed on a printing medium through preliminary ejection from being conspicuous.SOLUTION: Respective head modules 26 of an ink jet head 21 have a plurality of nozzles which are arrayed vertically and discharge ink to a printing medium. A control part controls the ink jet head 21 to perform preliminary ejection in which respective nozzles 27 of each nozzle group of each head module 26 of the ink jet head 21 discharge ink based upon pattern image data 34 if the time for which at least one nozzle 27 of the nozzle group discharges no ink reaches a predetermined time.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an inkjet printing apparatus, a preliminary ejection method, and a program. [Background technology]

[0002] In an inkjet printing device, if the nozzle surface of the inkjet head is left open, the ink near the nozzles may dry out and thicken, causing ejection defects such as disturbances in the ejection direction of the ink from the nozzles or failure to eject the ink. Even during printing operations, ink may dry out and thicken during periods when the ink is not being ejected from the nozzles, causing ejection defects.

[0003] In response to this, a technology is known that reduces the above-mentioned ink ejection defects by performing a preliminary ejection (also called a spit or blank ejection) in which ink that does not contribute to printing the image to be printed is ejected from nozzles where ejection has been suspended for a long period of time during printing operation.

[0004] Regarding such preliminary ejection, Patent Document 1 discloses a technology in which white pixels are formed by preliminary ejection of white ink on top of colored pixels formed on a white printing medium by preliminary ejection, thereby making the image (dot) formed by the preliminary ejection less noticeable. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-205622 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the print medium is non-white, such as cardboard, it is difficult to make the images (dots) produced by the preliminary ejection inconspicuous even when the technique of Patent Document 1 is used.

[0007] Furthermore, when the printing resolution is relatively low, even if the technique of Patent Document 1 is used, the dots produced by the preliminary ejection may be relatively large and therefore noticeable.

[0008] The present invention has been made in view of the above, and has an object to provide an inkjet printing apparatus, a preliminary ejection method, and a program that can prevent an image formed on a printing medium by preliminary ejection from being conspicuous. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided an inkjet printing device comprising: an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium; and a control unit that controls the inkjet head so that at least some of the plurality of nozzles, a plurality of nozzles that are consecutive in the nozzle arrangement direction, including nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, perform a preliminary ejection of ink based on pattern image data for printing an image that mimics the pattern of a foreign object contained in the printing medium.

[0010] According to another aspect of the present invention, there is provided a preliminary ejection method for an inkjet printing device equipped with an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction and ejecting ink onto a printing medium, the preliminary ejection method comprising controlling the inkjet head so that a plurality of nozzles that are consecutive in the nozzle arrangement direction, including at least a portion of the plurality of nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, perform a preliminary ejection in which ink is ejected based on pattern image data for printing an image that mimics the pattern of a foreign matter contained in the printing medium.

[0011] According to another aspect of the present invention, there is provided a program for causing a processing unit of an inkjet printing device equipped with an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium to execute a process of controlling the inkjet head so that a plurality of nozzles that are consecutive in the nozzle arrangement direction, including at least a portion of the plurality of nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, perform a preliminary ejection of ink based on pattern image data for printing an image that mimics the pattern of a foreign matter contained in the printing medium. Effect of the Invention

[0012] According to the present invention, it is possible to prevent an image formed on a printing medium by preliminary ejection from being conspicuous. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a configuration of an inkjet printing apparatus according to an embodiment; [Diagram 2] 2 is a perspective view showing a schematic configuration of a transport unit, a printing unit, and an image reading unit of the inkjet printing apparatus shown in FIG. [Diagram 3] 2 is a schematic configuration diagram of a head module of the inkjet printing apparatus shown in FIG. [Figure 4] FIG. 11 is an explanatory diagram of an operation for generating pattern image data. [Diagram 5] FIG. 11 is a diagram showing an example of pattern image data. [Figure 6] 13 is a flowchart of a preliminary ejection process. [Figure 7] 11A and 11B are diagrams illustrating an example of a preliminary ejection process. [Figure 8] 11A and 11B are diagrams illustrating an example of a preliminary ejection process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0015] The following embodiments are examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0016] Fig. 1 is a block diagram showing a configuration of an inkjet printing device according to an embodiment of the present invention. Fig. 2 is a perspective view showing a schematic configuration of a transport unit, a printing unit, and an image reading unit of the inkjet printing device shown in Fig. 1. Fig. 3 is a schematic configuration diagram of a head module of the inkjet printing device shown in Fig. 1. In the following description, the up / down, left / right, front / rear directions indicated by arrows in Fig. 2 are defined as up / down, left / right, front / rear directions. The up / down direction is the vertical direction, and the left / right direction and front / rear direction are mutually orthogonal, and are all orthogonal to the up / down direction and parallel to the horizontal direction.

[0017] As shown in FIG. 1, an inkjet printing apparatus 1 according to this embodiment includes a transport unit 2, a printing unit 3, an image reading unit 4, a storage unit 5, and a control unit 6.

[0018] The transport unit 2 transports a print medium 11 on which printing is to be performed in the inkjet printing device 1 .

[0019] Here, the printing medium 11 is made of a material having foreign matter such as fibrous impurities on the surface. For example, the printing medium 11 is made of cardboard, craft paper, cardboard, straw paper, wood, etc. In this embodiment, the printing medium 11 is a rectangular box-shaped medium such as a cardboard box.

[0020] The printing unit 3 performs printing by ejecting ink onto the print medium 11 transported by the transport unit 2. As shown in Figures 1 and 2, the printing unit 3 includes inkjet heads 21K, 21C, 21M, and 21Y, and a head holder 22. Note that the alphabetical suffixes of the reference numerals of the inkjet heads 21K, 21C, 21M, and 21Y may be omitted to collectively represent the heads.

[0021] Here, the printing unit 3 can print on the right side of the printing medium 11 by ejecting ink in a horizontal direction with the inkjet head 21 facing the right side of the printing medium 11 as shown in FIG. 2. The printing unit 3 can also be set to a state in which the inkjet head 21 faces the upper surface of the printing medium 11 by rotating about a rotation axis (not shown) parallel to the front-rear direction, and in this state, it is also possible to eject ink downward to print on the upper surface of the printing medium 11. The printing medium 11 is not limited to a box-shaped one, and it is also possible to eject ink downward to print on the printing medium 11 made of a sheet of printing paper or the like. In this embodiment, unless otherwise specified, the printing unit 3 is set in the state shown in FIG. 2 and prints on the right side of the printing medium 11.

[0022] Inkjet head 21 ejects ink onto print medium 11. Inkjet heads 21K, 21C, 21M, and 21Y eject black (K), cyan (C), magenta (M), and yellow (Y) ink, respectively. Inkjet heads 21K, 21C, 21M, and 21Y are arranged in parallel in the transport direction (sub-scanning direction) of print medium 11 from the rear side to the front side. Inkjet heads 21K, 21C, 21M, and 21Y have the same configuration, except for the colors of ink they eject.

[0023] The inkjet head 21 includes a plurality of head modules 26. In this embodiment, the inkjet head 21 includes six head modules 26. In the inkjet head 21, the head modules 26 are arranged in a staggered manner along the up-down direction. That is, in the inkjet head 21, the six head modules 26 arranged along the up-down direction are arranged with their positions shifted alternately in the front-rear direction.

[0024] As shown in Fig. 3, the head module 26 has a plurality of nozzles 27. Here, Fig. 3 is a diagram of the head module 26 as viewed from the left side. The nozzles 27 eject ink stored in the head module 26. The nozzles 27 open in a nozzle surface 26a. The nozzle surface 26a is the left side surface of the head module 26. In the nozzle surface 26a, the plurality of nozzles 27 are arranged along a main scanning direction (corresponding to the nozzle arrangement direction) that is parallel to the up-down direction.

[0025] The head holder 22 holds the inkjet heads 21K, 21C, 21M, and 21Y.

[0026] The image reading unit 4 reads the surface of the print medium 11 .

[0027] The storage unit 5 stores various programs executed by a CPU (Central Processing Unit) of the control unit 6. The storage unit 5 also stores a plurality of pattern image data 34, which will be described later. The storage unit 5 is configured with a hard disk or the like.

[0028] The control unit 6 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 6 includes a CPU, a RAM, a ROM, and the like.

[0029] Specifically, the control unit 6 controls the inkjet heads 21K, 21C, 21M, and 21Y to eject ink onto the printing medium 11 to print the original image based on original data for printing the original image, while causing the conveying unit 2 to convey the printing medium 11.

[0030] Furthermore, the control unit 6 executes a preliminary ejection process during the printing operation. The preliminary ejection process is a process for controlling the inkjet head 21 so that, when at least any one of the nozzles 27 in each nozzle group of each head module 26 of the inkjet head 21 has not ejected ink for a predetermined period of time or longer during the printing operation, each nozzle 27 in the nozzle group performs preliminary ejection to eject ink based on the pattern image data 34.

[0031] Here, the above-mentioned nozzle groups are formed by dividing all the nozzles 27 of the head module 26 into a plurality of groups. Each nozzle group includes a plurality of nozzles 27 that are continuous in the main scanning direction.

[0032] Next, the operation of generating the pattern image data 34 in the inkjet printing apparatus 1 will be described with reference to FIG.

[0033] The operation of generating this pattern image data 34 is performed prior to the printing operation for printing an original image on the printing medium 11 in the inkjet printing device 1. The pattern image data 34 is image data for printing an image imitating the pattern of a foreign matter contained in the printing medium 11. The pattern image data 34 is used for preliminary ejection for each nozzle group in the preliminary ejection process.

[0034] In the operation of generating pattern image data 34, first, the control unit 6 causes the conveying unit 2 to convey an unprinted printing medium 11 of the same type as the printing medium 11 on which the original image will be printed in the printing operation, while causing the image reading unit 4 to read at least a portion of the surface of the printing medium 11.

[0035] When the image reading unit 4 reads at least a portion of the surface of the print medium 11, the image reading unit 4 generates read image data 31 (see FIG. 4) and outputs it to the control unit 6.

[0036] When the control unit 6 acquires the read image data 31 from the image reading unit 4, the control unit 6 binarizes the read image data 31 as shown in FIG.

[0037] Next, the control unit 6 performs morphological operations to shrink and expand black pixels in the binarized image data 32, thereby removing isolated points that become noise.

[0038] Next, the control unit 6 extracts image data 33a of the foreign matter from the image data 33 after the isolated points have been removed, and performs thinning to generate pattern image data .

[0039] In the pattern image data 34 shown in Fig. 4, one square represents one pixel, and squares filled with black represent pixels from which ink is ejected. The pattern image data 34 has the same number of pixels in the main scanning direction as the number of nozzles in the nozzle group described above. The pattern image data 34 includes one or more pixels from which ink is ejected in each line along the main scanning direction and each line along the sub-scanning direction. In this embodiment, the pattern image data 34 is image data with 12 pixels in each of the main scanning direction and the sub-scanning direction, as shown in Fig. 4.

[0040] 4 shows image data 33a of one foreign object extracted from image data 33 after isolated points are removed and its corresponding pattern image data 34, but the control unit 6 extracts image data 33a of a plurality of foreign objects and generates pattern image data 34 from each of them. For example, the control unit 6 generates pattern image data 34A, 34B, ... shown in FIG.

[0041] The control unit 6 also generates pattern image data 34 by transforming each pattern image data 34, thereby increasing the variety of pattern image data 34. For example, as shown in Fig. 5, the control unit 6 generates pattern image data 34Aa by horizontally inverting pattern image data 34A using affine transformation, pattern image data 34Ab by inverting pattern image data 34A up and down, and pattern image data 34Ac by inverting pattern image data 34A up and down and left and right (rotating 180 degrees). Similarly, the control unit 6 generates pattern image data 34Ba to 34Bc, 34Ca to 34Cc, ... from pattern image data 34B, 34C, ....

[0042] As described above, the control unit 6 generates a plurality of pattern image data 34 for printing images with different patterns. Then, the control unit 6 stores the generated plurality of pattern image data 34 in the storage unit 5. This completes the series of operations.

[0043] Next, the operation of the inkjet printing apparatus 1 during printing will be described.

[0044] When the control unit 6 is instructed to start printing, it controls the inkjet heads 21K, 21C, 21M, and 21Y to print on the print medium 11 based on the document data while causing the transport unit 2 to transport the print medium 11.

[0045] During this printing operation, the control unit 6 executes the above-mentioned preliminary ejection process. This preliminary ejection process will be described.

[0046] Fig. 6 is a flowchart of the preliminary ejection process. The preliminary ejection process is performed by the CPU of the control unit 6 executing a program stored in the storage unit 5. The process of the flowchart in Fig. 6 is performed for each nozzle group of each head module 26 of each inkjet head 21.

[0047] 6, when starting a printing operation, the control unit 6 sets the non-ejection count value of all nozzles 27 in the nozzle group to "0." Here, the non-ejection count value of a nozzle 27 is a value indicating the number of pixels in the sub-scanning direction into which the nozzle 27 has not ejected ink since the last time the nozzle 27 ejected ink during a printing operation. Also, the non-ejection count value of a nozzle 27 is a value indicating the number of pixels in the sub-scanning direction into which the nozzle 27 has not ejected ink from the start of printing until the nozzle 27 ejects ink for the first time after the start of printing.

[0048] Next, in step S2, the control unit 6 sets "1" to a variable 1 indicating the line number of a line along the main scanning direction in the document data.

[0049] Next, in step S3, the control unit 6 causes each nozzle 27 to print the lth line based on the manuscript data corresponding to the color of ink ejected by the nozzle group (the inkjet head 21 to which the nozzle group belongs). Here, if pattern image data 34 is combined with the manuscript data as described below, the control unit 6 causes the lth line to be printed based on the combined manuscript data.

[0050] Next, in step S4, the control unit 6 determines whether the variable l is "L" which indicates that this is the last line in the manuscript data.

[0051] If it is determined that l=L is not true (step S4: NO), then in step S5, the control unit 6 sets the non-ejection count value of the nozzles 27 that ejected ink in printing the lth line to "0", and adds "1" to the non-ejection count value of the nozzles 27 that did not eject ink (see Figures 7 and 8 described below).

[0052] Next, in step S6, the control unit 6 determines whether or not the maximum value of the non-ejection count value in the nozzle group is equal to or greater than a predetermined threshold value.

[0053] Here, the above-mentioned threshold value is a value for determining whether the time during which the nozzles 27 are not ejecting ink is equal to or longer than a predetermined time. In other words, when the maximum value of the non-ejection count value in a nozzle group is equal to or greater than the threshold value, it means that the time during which at least any of the nozzles 27 in the nozzle group is not ejecting ink during a printing operation is equal to or longer than a predetermined time.

[0054] Meanwhile, the control unit 6 randomly changes the above-mentioned threshold value (predetermined time). For example, the control unit 6 subtracts or adds a small random value from the threshold value at a predetermined cycle. The control unit 6 changes the threshold value within a range in which the non-ejection period of ink corresponding to the threshold value does not exceed the lower limit of the time during which poor ink ejection from the nozzles 27 may occur due to drying or thickening of the ink. The possible range of the threshold value (predetermined time) is set in advance based on experiments, etc. This process of randomly changing the threshold value is performed for each nozzle group.

[0055] If it is determined that the maximum non-ejection count value in the nozzle group is equal to or greater than the threshold value (step S6: YES), then in step S7, the control unit 6 combines the pattern image data 34 with the original data (see FIGS. 7 and 8, described later).

[0056] Specifically, the control unit 6 randomly selects one pattern image data 34 from the multiple pattern image data 34 stored in the storage unit 5. Then, the control unit 6 combines the selected pattern image data 34 with the manuscript data so that ink ejection (preliminary ejection) based on the pattern image data 34 is performed from the (l+1)th line.

[0057] 6, in step S8, the control unit 6 sets the non-ejection count values ​​of all nozzles 27 in the nozzle group to "0." This prevents the pattern image data 34 from being continuously combined with the document data in the sub-scanning direction.

[0058] Next, in step S9, the control unit 6 adds "1" to the variable 1. After that, the control unit 6 returns to step S3.

[0059] In step S6, when it is determined that the maximum value of the non-ejection count value in the nozzle group is less than the threshold value (step S6: NO), the control unit 6 skips steps S7 and S8 and proceeds to step S9.

[0060] In step S4, when it is determined that l=L (step S4: YES), the control unit 6 ends the preliminary ejection process.

[0061] Next, an example of the above-mentioned preliminary ejection process will be described with reference to FIGS.

[0062] In this embodiment, one nozzle group is made up of 12 nozzles 27. As shown in Figures 7 and 8, the nozzle numbers within a nozzle group are numbered 1 (#1), 2 (#2), ..., 12 (#12).

[0063] 7 and 8, the threshold value of the maximum non-ejection count value is set to "999." As shown in Fig. 7, no ink is ejected from the first line to the 999th line in all nozzles 27, numbered 1 to 12, in the nozzle group, and the non-ejection count value of each nozzle 27 is incremented by "1" for each line (step S5 in Fig. 6). Therefore, in the 999th line, the maximum non-ejection count value in the nozzle group reaches the threshold value of "999" (step S6 in Fig. 6: YES).

[0064] Moreover, the pattern image data 34C is selected as the pattern image data 34 to be combined with the document data. Therefore, the pattern image data 34C is combined with the document data so that ink ejection (preliminary ejection) based on the pattern image data 34C is performed from the 1000th line (step S7 in FIG. 6).

[0065] As a result, the first line of the pattern image data 34C is printed on the 1000th line (step S3 in FIG. 6). Here, because the maximum value of the non-ejection count value in the nozzle group reaches the threshold value on the 999th line, the non-ejection count values ​​of all nozzles 27 in the nozzle group are reset to "0" (step S8 in FIG. 6). After this, in printing the 1000th line, the non-ejection count values ​​of nozzles 27 No. 1 and No. 4 to No. 9, which did not eject ink based on the pattern image data 34C, are set to "1" (step S5 in FIG. 6).

[0066] Printing is performed from the 1000th line to the 1011th line based on the pattern image data 34C, and ink is ejected (preliminary ejection) onto at least one pixel from each nozzle 27. The non-ejection count value of the nozzle 27 that performed the preliminary ejection is set to "0" (step S5 in FIG. 6).

[0067] In the situation of Fig. 8 after printing based on the pattern image data 34C of Fig. 7, nozzles 27 nos. 1 to 6 on the kth line are ejecting ink to print an original image based on the original data, and the non-ejection count values ​​of these nozzles 27 are set to "0" (step S5 of Fig. 6). Then, on the (k+3)th line, the non-ejection count value of nozzle no. 7 27 has reached "999." Therefore, on the (k+3)th line, the maximum non-ejection count value within the nozzle group has reached the threshold value of "999" (step S6 of Fig. 6: YES).

[0068] Here, the pattern image data 34Ca is selected as the pattern image data 34 to be combined with the document data. Therefore, the pattern image data 34Ca is combined with the document data so that ink ejection (preliminary ejection) based on the pattern image data 34Ca is performed from the (k+4)th line (step S7 in FIG. 6).

[0069] As a result, the first line of the pattern image data 34Ca is printed on the (k+4)th line (step S3 in FIG. 6). Here, because the maximum value of the non-ejection count value in the nozzle group reaches the threshold value on the (k+3)th line, the non-ejection count values ​​of all nozzles 27 in the nozzle group are reset to "0" (step S8 in FIG. 6). After this, in printing the (k+4)th line, the non-ejection count values ​​of each of nozzles 27, nos. 1 to 9 and 12, which did not eject ink based on the pattern image data 34Ca, are set to "1" (step S5 in FIG. 6).

[0070] Printing is performed from the (k+4)th line to the (k+15)th line based on the pattern image data 34Ca, and ink is ejected (preliminary ejection) onto at least one pixel from each nozzle 27. The non-ejection count value of the nozzle 27 that performed the preliminary ejection is set to "0" (step S5 in FIG. 6).

[0071] As described above, in the inkjet printing device 1, when the time during which at least any of the nozzles 27 in each nozzle group of each head module 26 of the inkjet head 21 does not eject ink during a printing operation reaches or exceeds a predetermined time, the control unit 6 executes a preliminary ejection process for controlling the inkjet head 21 to perform preliminary ejection in which each nozzle 27 in the nozzle group ejects ink based on the pattern image data 34. As a result, the image formed on the printing medium 11 by the preliminary ejection becomes an image that imitates a pattern caused by foreign matter present on the printing medium 11. This makes it possible to prevent the image formed on the printing medium 11 by the preliminary ejection from being conspicuous.

[0072] In addition, by performing the preliminary ejection process for each nozzle group obtained by dividing all the nozzles 27 of the head module 26 into a plurality of nozzle groups, it is possible to prevent an image with an excessively large pattern from being printed by the preliminary ejection. This makes it possible to further prevent the image formed on the print medium 11 by the preliminary ejection from being conspicuous.

[0073] Furthermore, the control unit 6 controls the inkjet head 21 to perform preliminary ejection in each nozzle group based on pattern image data 34 randomly selected from a plurality of pattern image data 34 for printing images with different patterns. This allows the image formed by the preliminary ejection to resemble a natural pattern, thereby making it possible to further prevent the image formed on the printing medium 11 by the preliminary ejection from being conspicuous.

[0074] In addition, the control unit 6 randomly changes the above-mentioned predetermined time for each nozzle group. This makes it possible to prevent the images formed by the preliminary ejection of each nozzle group from being close to each other in the sub-scanning direction, even when printing is performed based on document data that has a large area where ink is not ejected. As a result, it is possible to further prevent the images formed on the printing medium 11 by the preliminary ejection from being conspicuous.

[0075] In the above-described embodiment, the pattern image data 34 is generated from the image data 33a of the foreign matter extracted from the read image data obtained by reading the surface of the unprinted print medium 11. However, this is not limiting, and for example, the pattern image data 34 may be generated by regularly or randomly deforming an arc or parabola resembling a foreign matter extracted from the read image data obtained by reading the surface of the unprinted print medium 11.

[0076] In the embodiment described above, the pattern image data 34 generated in advance from an unprinted printing medium 11 of the same type as the printing medium 11 used for printing is used for preliminary ejection. However, a plurality of pattern image data 34 generated respectively from a plurality of types of printing medium 11 may be stored in the storage unit 5 in advance, and different pattern image data 34 may be used depending on how foreign objects are seen on the printing medium 11 used for printing.

[0077] Furthermore, the number of nozzles constituting a nozzle group may be set according to the size of foreign matter on the print medium 11 used for printing.

[0078] In addition, when the printing medium 11 used for printing is one in which the majority of foreign matter on the surface is isolated dot-like and there is almost no fibrous foreign matter, preliminary ejection may be performed using pattern image data 34 of fibrous foreign matter generated from another type of printing medium 11.

[0079] In the above-described embodiment, the preliminary ejection process described in the flowchart of Fig. 6 was performed for each nozzle group of each head module 26 of each inkjet head 21. However, it is also possible to calculate the maximum non-ejection count value for each of the four color nozzle groups in each inkjet head 21 that print the same area in the main scanning direction, and perform preliminary ejection based on the pattern image data 34 in all of the four color nozzle groups when the calculated maximum value reaches a threshold value. In this case, the four colors of ink are ejected in an overlapping manner onto each pixel where ink in the pattern image data 34 is ejected.

[0080] 6, the inkjet head 21Y that ejects yellow ink, which is difficult to see, may be configured to perform preliminary ejection in which ink is randomly ejected from each nozzle 27. In this case, the other inkjet heads 21K, 21C, and 21M may be configured to calculate the maximum non-ejection count value for each of the three color nozzle groups that print the same area in the main scanning direction, and when the calculated maximum value reaches a threshold value, the three color nozzle groups may perform preliminary ejection based on the pattern image data 34. In this case, the three colors of ink are ejected in an overlapping manner onto each pixel where ink in the pattern image data 34 is ejected.

[0081] Furthermore, when the document data is to be printed in black and white using only the inkjet head 21K, the above-described preliminary ejection process may be omitted for the inkjet heads 21C, 21M, and 21Y.

[0082] In the preliminary ejection process of the embodiment described above, all the nozzles 27 of the head module 26 are divided into a plurality of nozzle groups, and the preliminary ejection process is performed for each nozzle group. However, instead of dividing into nozzle groups, the time during which ink is not ejected may be counted for each nozzle 27, and preliminary ejection based on the pattern image data 34 may be performed by a plurality of nozzles 27 that are consecutive in the main scanning direction, including a nozzle 27 that has not ejected ink for a predetermined time or more. It is sufficient that at least a portion of the nozzles 27 of the inkjet head 21, a plurality of nozzles 27 that are consecutive in the main scanning direction, including a nozzle 27 that has not ejected ink for a predetermined time or more during a printing operation, perform preliminary ejection based on the pattern image data 34.

[0083] In the above embodiment, the inkjet head 21 is configured to include a plurality of head modules 26. However, the inkjet head 21 may be a single long head module.

[0084] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[0085] [Note] This application discloses the following inventions.

[0086] (Appendix 1) an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium; a control unit that controls the inkjet head so that a plurality of nozzles that are continuous in the nozzle arrangement direction, including at least a portion of the plurality of nozzles that has not ejected ink for a predetermined period of time or more during a printing operation, perform preliminary ejection of ink based on pattern image data for printing an image that imitates a pattern of a foreign object contained in a printing medium; An inkjet printing apparatus comprising:

[0087] (Appendix 2) The inkjet printing device described in Appendix 1, characterized in that the control unit controls the inkjet head to perform the preliminary ejection based on pattern image data randomly selected from a plurality of pattern image data for printing images with different patterns.

[0088] (Appendix 3) The inkjet printing device described in Appendix 1 or 2, characterized in that the control unit controls each nozzle of a plurality of nozzle groups, each of which includes a plurality of the nozzles arranged consecutively in the nozzle arrangement direction, to perform the preliminary ejection when the time during which at least any of the nozzles in the nozzle group is not ejecting ink during a printing operation reaches or exceeds the predetermined time.

[0089] (Appendix 4) 4. The inkjet printing apparatus according to claim 3, wherein the control unit randomly changes the predetermined time for each of the nozzle groups.

[0090] (Appendix 5) A preliminary ejection method for an inkjet printing device having an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction and ejecting ink onto a printing medium, comprising: a preliminary ejection method for ejecting ink from at least a portion of the plurality of nozzles, the plurality of nozzles being consecutive in the nozzle arrangement direction, including nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, the method comprising controlling the inkjet head so that the plurality of nozzles ejects ink based on pattern image data for printing an image that mimics the pattern of a foreign object contained in a printing medium.

[0091] (Appendix 6) A processing unit of an inkjet printing device including an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium, A program for executing a process of controlling the inkjet head so that at least a portion of the plurality of nozzles, including a plurality of nozzles that are consecutive in the nozzle arrangement direction and that include nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, perform a preliminary ejection of ink based on pattern image data for printing an image that mimics the pattern of a foreign object contained in a printing medium. [Explanation of symbols]

[0092] 1 Inkjet printing device 2. Conveyor section 3 Printing Department 4 Image reading section 5 Storage section 6. Control Unit 11 Print media 21, 21K, 21C, 21M, 21Y Inkjet Head 22 Head Holder 26 Head Module 26a Nozzle surface 27 Nozzle 34, 34A, 34B, ... Pattern image data 34Aa~34Ac, 34Ba~34Bc,… Pattern image data

Claims

1. an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium; a control unit that controls the inkjet head so that a plurality of nozzles that are continuous in the nozzle arrangement direction, including at least a portion of the plurality of nozzles that has not ejected ink for a predetermined period of time or more during a printing operation, perform preliminary ejection of ink based on pattern image data for printing an image that imitates a pattern of a foreign object contained in a printing medium; An inkjet printing apparatus comprising:

2. The inkjet printing device according to claim 1 , wherein the control unit controls the inkjet head to perform the preliminary ejection based on pattern image data randomly selected from a plurality of pattern image data for printing images with different patterns.

3. 3. The inkjet printing device according to claim 1, wherein the control unit controls each nozzle of a plurality of nozzle groups, each of which includes a plurality of the nozzles arranged consecutively in the nozzle arrangement direction, to perform the preliminary ejection when the time during which at least any of the nozzles has not ejected ink during a printing operation reaches or exceeds the predetermined time.

4. The inkjet printing apparatus according to claim 3 , wherein the control unit randomly changes the predetermined time for each of the nozzle groups.

5. A preliminary ejection method for an inkjet printing device having an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction and ejecting ink onto a printing medium, comprising: a preliminary ejection method for ejecting ink from at least a portion of the plurality of nozzles, the plurality of nozzles being consecutive in the nozzle arrangement direction, including nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, the method comprising controlling the inkjet head so that the plurality of nozzles ejects ink based on pattern image data for printing an image that mimics the pattern of a foreign object contained in a printing medium.

6. A processing unit of an inkjet printing device including an inkjet head having a plurality of nozzles arranged in a nozzle arrangement direction for ejecting ink onto a printing medium, A program for executing a process of controlling the inkjet head so that at least a portion of the plurality of nozzles, including a plurality of nozzles that are consecutive in the nozzle arrangement direction and that include nozzles that have not ejected ink for a predetermined period of time or more during a printing operation, perform a preliminary ejection of ink based on pattern image data for printing an image that mimics the pattern of a foreign object contained in a printing medium.

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