JP6710116B2 - Inkjet printer - Google Patents

Description

The present invention relates to an inkjet printing apparatus that prints by ejecting ink from an inkjet head.

In an inkjet printing apparatus, ink mist in which the ink is atomized is generated by ejecting ink from nozzles of an inkjet head (for example, refer to Patent Document 1). The ink mist may adhere to the print medium and stain the printed matter. In addition, the ink mist also causes stains inside the device.

The ink mist is formed by dividing the ink ejected from the nozzle into a slender column in the ejection direction before the ink landing on the print medium due to the influence of the transport wind generated when transporting the print medium. appear.

Here, in a multi-drop type inkjet head, when a plurality of ink droplets are ejected to one pixel, the ink droplets coalesce during flight. Therefore, the more ink droplets are ejected for one pixel, the thicker the ink liquid column becomes, and the more difficult it is to divide the ink liquid column, so that ink mist is less likely to occur. That is, as the number of ink droplets ejected per pixel is small, ink mist is likely to occur. In particular, when only one drop is ejected for one pixel, ink mist is likely to occur.

On the other hand, it is known that ink mist is reduced by performing so-called 1-dropless processing, in which ejection of only 1 drop per pixel is not performed.

JP, 2014-172389, A

However, if the above-described one-dropless process is performed, the number of gradations decreases, which leads to deterioration in print image quality.

The present invention has been made in view of the above, and an object of the present invention is to provide an inkjet printing apparatus capable of reducing ink mist while suppressing deterioration of print image quality.

In order to achieve the above-mentioned object, a first feature of the inkjet printing apparatus according to the present invention is to include a plurality of nozzles arranged along a main scanning direction orthogonal to a carrying direction of a printing medium to be carried, in the carrying direction. A plurality of nozzle rows arranged in parallel with each other, the nozzles of each nozzle row are arranged so as to be displaced in the main scanning direction with respect to the nozzles of another nozzle row, An ink jet head that ejects ink of the same color onto a print medium and ink is ejected line by line in the main scanning direction from the nozzles of the plurality of nozzle rows based on image data indicating the ink ejection amount for each pixel, and printing is performed. Thus, the control unit controls the inkjet head, and in the control unit, among the pixels whose ink ejection amount based on the image data is less than or equal to a threshold value and not 0, a nozzle that ejects ink to the pixel is in the transport direction. Based on the image data of at least one of the nozzles in the predetermined area of the end of the inkjet head in the main scanning direction of the most upstream nozzle row, and adjacent pixels on both sides of the pixel in the main scanning direction. The ink discharge amount for a pixel whose ink discharge amount is equal to or less than the maximum ink discharge amount per pixel minus the threshold value is stopped, and the ink discharge amount for the pixel stopped is the uppermost nozzle row. It is to add to the ink ejection amount of any of the adjacent pixels on both sides of the pixel in the main scanning direction by the nozzles of the nozzle rows other than the above.

A second feature of the inkjet printing apparatus according to the present invention is that, in the controller, among the pixels whose ink ejection amount based on image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is the transporting unit. Direction is the nozzle in the predetermined area at the end of the inkjet head in the main scanning direction of the most upstream nozzle row in the direction, and both adjacent pixels on both sides of the pixel in the main scanning direction are image data. The ink ejection amount based on the above is larger than the amount obtained by subtracting the threshold value from the maximum ink ejection amount per pixel, and the ink ejection amount is added so that the ink ejection amount for the pixel becomes larger than the threshold value. The additional amount of the ink ejection amount is to be reduced from the ink ejection amount by the nozzle of the nozzle row other than the most upstream nozzle row to any of the adjacent pixels on both sides of the pixel in the main scanning direction.

A third feature of the inkjet printing apparatus according to the present invention is that a plurality of nozzles are arranged in parallel in the carrying direction, each of the nozzles including a plurality of nozzles arranged along a main scanning direction orthogonal to a carrying direction of a print medium to be carried. A nozzle row, the nozzles of each nozzle row are arranged so as to be displaced in the main scanning direction with respect to the nozzles of another nozzle row, and ink of the same color is applied from the nozzles of each nozzle row to a print medium. The inkjet head is controlled so that ink is ejected from the nozzles of the plurality of nozzle rows for each line in the main scanning direction to perform printing based on the inkjet head that ejects the ink and the image data indicating the ink ejection amount for each pixel. A control unit, wherein the control unit is configured such that, among pixels whose ink ejection amount based on image data is less than or equal to a threshold value and is not 0, a nozzle that ejects ink to the pixel is a most upstream nozzle row in the transport direction, The ink ejection amount based on the image data of at least one of the adjacent pixels on the both sides in the main scanning direction of the pixel, which is a nozzle in a predetermined region of the end portion of the inkjet head in the main scanning direction, is equal to or more than the threshold value. The ink ejection amount for a pixel is added so that the ink ejection amount is larger than the threshold value, and the additional amount of the ink ejection amount for the pixel is calculated by the nozzles of the nozzle row other than the most upstream nozzle row. It is to reduce the ink ejection amount from any one of the adjacent pixels on both sides in the main scanning direction.

According to the first aspect of the inkjet printing apparatus of the present invention, the control unit determines that among the pixels whose ink ejection amount based on the image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is in the transport direction. Ink ejection based on the image data of at least one of the adjacent pixels on both sides in the main scanning direction of the pixel which is a nozzle in a predetermined region of the end of the inkjet head in the main scanning direction Ink ejection is stopped for pixels whose amount is less than or equal to the amount obtained by subtracting the threshold amount from the maximum ink ejection amount per pixel. In addition, the control unit controls the ink ejection amount corresponding to the ejection stopped for the pixel to be ejected to any one of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzles of the nozzle row other than the most upstream nozzle row. Add to quantity.

As a result, the amount of ink ejected from the nozzles in the area where the air volume of the air flow generated by the transportation of the print medium is large is reduced, which is less than the threshold value at which the ink mist is likely to occur, so that the ink mist can be reduced. Further, since the ink ejection amount corresponding to the ejection stopped in the most upstream nozzle row is added to adjacent pixels in the nozzle rows other than the most upstream nozzle row and ejected, a change in density in the print image is suppressed. .. Therefore, deterioration of print quality can be suppressed. Therefore, according to the first feature of the inkjet printing apparatus of the present invention, it is possible to reduce ink mist while suppressing deterioration of print image quality.

According to the second aspect of the inkjet printing apparatus of the present invention, the control unit determines that among the pixels whose ink ejection amount based on the image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is in the transport direction. The nozzles in the uppermost stream of nozzles in a predetermined area at the end of the inkjet head in the main scanning direction, and both adjacent pixels in the main scanning direction of the pixel are both the ink discharge amount based on the image data. Is larger than the maximum ink discharge amount per pixel minus the threshold value, the ink discharge amount is added so that the ink discharge amount for a pixel becomes larger than the threshold value. Further, the control unit reduces the additional amount of the ink ejection amount for the pixel from the ink ejection amount for any of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle of the nozzle row other than the most upstream nozzle row. To do.

As a result, the amount of ink ejected from the nozzles in the region where the air volume of the transport air is large is smaller than the threshold value at which ink mist is likely to occur, and thus the amount of ink mist can be further reduced. In addition, since the ink ejection amount added in the most upstream nozzle row is reduced from the ink ejection amount ejected to the adjacent pixel in the nozzle rows other than the most upstream nozzle row, the density change in the print image is not changed. It can be suppressed. Therefore, deterioration of print quality can be suppressed. Therefore, according to the second feature of the inkjet printing apparatus of the present invention, it is possible to further reduce the ink mist while suppressing the deterioration of the print image quality.

According to the third aspect of the inkjet printing apparatus of the present invention, the control unit determines that among the pixels whose ink ejection amount based on the image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is in the transport direction. Ink ejection based on the image data of at least one of the adjacent pixels on both sides in the main scanning direction of the pixel which is a nozzle in a predetermined region of the end of the inkjet head in the main scanning direction The ink ejection amount is added so that the ink ejection amount for a pixel whose amount is greater than or equal to the threshold is greater than the threshold. Further, the control unit reduces the additional amount of the ink ejection amount for the pixel from the ink ejection amount for any of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle of the nozzle row other than the most upstream nozzle row. To do.

As a result, the amount of ink ejected from the nozzles in the region where the air volume of the transport air is large is reduced to a small ejection amount equal to or less than the threshold value at which ink mist is likely to occur, and thus the ink mist can be reduced. In addition, since the ink ejection amount added in the most upstream nozzle row is reduced from the ink ejection amount ejected to the adjacent pixel in the nozzle rows other than the most upstream nozzle row, the density change in the print image is not changed. It can be suppressed. Therefore, deterioration of print quality can be suppressed. Therefore, according to the third aspect of the inkjet printing apparatus of the present invention, it is possible to reduce ink mist while suppressing deterioration of print image quality.

FIG. 3 is a block diagram showing the configuration of the inkjet printing apparatus according to the first embodiment. It is a schematic block diagram of a conveyance part and a printing part of the inkjet printing apparatus shown in FIG. FIG. 2 is a plan view of a transport unit and a printing unit of the inkjet printing apparatus shown in FIG. 1. FIG. 3 is an explanatory diagram of nozzle rows in the inkjet head of the inkjet printing apparatus shown in FIG. 1. 6 is a flowchart of an ink mist countermeasure process according to the first embodiment. 9 is a flowchart of an ink mist countermeasure process according to the second embodiment. 9 is a flowchart of an ink mist countermeasure process in the third embodiment.

Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts or components are designated with the same or equivalent reference numerals.

The embodiments described below exemplify devices and the like for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, arrangement, etc. of each component. Is not specified below. The technical idea of the present invention can be modified in various ways within the scope of the claims.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of an inkjet printing apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a transport unit and a printing unit of the inkjet printing apparatus shown in FIG. FIG. 3 is a plan view of the transport unit and the printing unit of the inkjet printing apparatus shown in FIG. FIG. 4 is an explanatory diagram of nozzle rows in the inkjet head of the inkjet printing apparatus shown in FIG.

In the following description, the direction orthogonal to the paper surface of FIG. 2 is the front-back direction, and the paper surface front direction is the front. Further, the up, down, left and right of the paper surface in FIG. In addition, the direction from left to right in FIG. 2 is the conveyance direction of the paper PA that is the print medium. Upstream and downstream in the following description mean upstream and downstream in the conveyance direction of the paper PA.

As shown in FIG. 1, the inkjet printing apparatus 1 according to the first embodiment includes a transport unit 2, a printing unit 3, and a control unit 4.

The transport unit 2 transports the sheet PA fed from a sheet feeding unit (not shown). As shown in FIGS. 1 and 2, the transport unit 2 includes a transport belt 11, a drive roller 12, driven rollers 13, 14, and 15, a transport motor 16, and a fan 17.

The conveyance belt 11 sucks and holds the sheet PA and conveys it. The conveyor belt 11 is an annular belt that is stretched around the driving roller 12 and the driven rollers 13 to 15. The conveyor belt 11 is formed with a plurality of belt holes (not shown) that are through holes for sucking and holding the paper PA. The conveyance belt 11 sucks and holds the sheet PA by the suction force generated in the belt hole by the air suction by the fan 17. The conveyance belt 11 rotates clockwise in FIG. 2 to convey the suction-held sheet PA to the right.

The drive roller 12 rotates the conveyor belt 11 in the clockwise direction in FIG.

The driven rollers 13 to 15 support the conveyor belt 11 together with the drive roller 12. The driven rollers 13 to 15 are driven to rotate by the drive roller 12 via the conveyor belt 11. The driven roller 13 is arranged at the same height as the driving roller 12 and to the left of the driving roller 12. The driven rollers 14 and 15 are disposed below the drive roller 12 and the driven roller 13 in the left-right direction and at the same height.

The carry motor 16 rotationally drives the drive roller 12.

The fan 17 produces a downward airflow. As a result, the fan 17 sucks air through the belt hole of the conveyor belt 11 to generate a negative pressure in the belt hole, and adsorbs the paper PA on the conveyor belt 11. The fan 17 is arranged in a region surrounded by the conveyor belt 11.

The printing unit 3 prints an image on the sheet PA conveyed by the conveying unit 2. The printing unit 3 is arranged above the transport unit 2. The printing unit 3 includes line heads 21C, 21K, 21M, 21Y. In the following description, the subscripts (C, K, M, Y) of the alphabet in the reference numerals of the line heads 21C, 21K, 21M, 21Y may be omitted and collectively described.

The line head 21 ejects ink onto the paper PA conveyed by the conveyor 2. The line heads 21C, 21K, 21M, and 21Y eject cyan (C), black (K), magenta (M), and yellow (Y) inks, respectively. The line heads 21C, 21K, 21M, and 21Y are arranged above the transport unit 2 in parallel in the sub-scanning direction (horizontal direction) that is the transport direction of the paper PA. The line heads 21C, 21K, 21M, and 21Y each include six inkjet heads 26.

In each line head 21, the six inkjet heads 26 are arranged in a staggered manner. That is, in each line head 21, the six inkjet heads 26 are arranged along the main scanning direction (front-back direction) orthogonal to the transport direction (sub-scanning direction) of the paper PA, and every other sub-scanning. The positions in the direction (left-right direction) are shifted.

As shown in FIG. 4, the inkjet head 26 has two nozzle rows 27A and 27B. The nozzle rows 27A and 27B are arranged in parallel at intervals in the left-right direction. The nozzle rows 27A and 27B each have a plurality of nozzles 28. The nozzle rows 27A and 27B eject ink of the same color from the nozzles 28.

The nozzle 28 opens on the ejection surface 26a, which is the lower surface of the inkjet head 26, and ejects ink downward. In the inkjet head 26, the number of drops of ink ejected from one nozzle 28 to one pixel (the number of drops) can be changed, and the density is expressed by the ink ejection amount according to the number of drops. Gradation printing is performed.

In each of the nozzle rows 27A and 27B, the plurality of nozzles 28 are arranged at regular intervals at a predetermined pitch P along the main scanning direction (front-back direction). The nozzles 28 of the upstream nozzle row 27A and the nozzles 28 of the downstream nozzle row 27B are arranged so as to be offset by a half pitch (P/2) in the main scanning direction. This enhances the resolution in the main scanning direction.

The control unit 4 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 4 includes a CPU, a RAM, a ROM, a hard disk, and the like.

Specifically, the control unit 4 drives the transport unit 2 and ejects ink from the nozzles 28 of the nozzle rows 27A and 27B for each line in the main scanning direction based on the image data, and the transport unit 2 transports the ink. The inkjet head 26 is controlled to print on the paper PA to be printed.

In the control of each inkjet head 26, the control unit 4 first causes the nozzles 28 of the upstream nozzle row 27A to eject ink for one line in the main scanning direction. Thereafter, the control unit 4 forms the dots on the same line as the dots formed by the ink ejected from the nozzles 28 of the upstream nozzle row 27A, and the nozzles of the downstream nozzle row 27B. Ink is ejected from. As a result, on one line in the main scanning direction, dots formed by the ink discharged from the nozzles 28 of the downstream nozzle row 27B are formed between dots formed by the ink discharged from the nozzles 28 of the upstream nozzle row 27A. Can be formed. By repeating this, a print image is formed on the conveyed paper PA for each line in the main scanning direction.

The image data described above is data indicating the number of ink drops for each pixel. Printing is performed using image data corresponding to each color of cyan (C), black (K), magenta (M), and yellow (Y). The number of drops per pixel in the image data is set within the range of 0 to 7 drops, for example. The maximum number of drops per pixel (corresponding to the maximum ink ejection amount in the claims) Dm (eg, 7 drops) is determined according to the paper type.

At the time of printing, the control unit 4 stops the ejection of ink to pixels that satisfy the following conditions (1) to (3).

(1) The number of drops of the pixel based on the image data is less than or equal to the threshold value Dt and is not 0.

(2) The nozzle 28 that ejects ink to the pixel is the nozzle 28 in the strong wind area (corresponding to the predetermined area in the claims) A of the upstream nozzle row 27A.

(3) The number of drops based on the image data of at least one of the adjacent pixels on both sides of the pixel in the main scanning direction is less than or equal to the number of drops obtained by subtracting the threshold value Dt from the maximum number of drops Dm.

In addition, the control unit 4 determines the number of drops for which ejection is stopped for the pixel satisfying the conditions (1) to (3) by the nozzle 28 of the nozzle array 27B on the downstream side on both sides of the pixel in the main scanning direction. Add to the number of drops for any of the pixels.

The condition (1) described above is a condition for determining whether or not the number of drops of the pixel based on the image data is the number of drops in which ink mist is likely to occur. The drop number threshold Dt is a threshold value for determining whether or not the number of drops is likely to cause ink mist. As the number of drops per pixel is smaller, ink mist is more likely to occur. The threshold value Dt is set in advance based on experimental results and the like.

The condition (2) is a condition for determining whether or not the nozzle 28 that ejects ink to the pixel is located at a position where ink mist is likely to occur due to the influence of the conveyance wind generated by the conveyance of the paper PA.

The strong wind area A is an area in which the air volume of the transport air generated by the transportation of the paper PA is equal to or larger than the reference air volume and the ink mist is easily generated. Specifically, as shown in FIG. 4, the strong wind area A is set at the ends (front end and rear end) of the inkjet head 26 in the main scanning direction. This is because, at the end portion of the inkjet head 26 in the main scanning direction, the transport air is easily blown from the outside, so that the air volume of the transport air is likely to be larger than that at the central portion. The size (width) of the strong wind area A is determined according to the arrangement of the inkjet head 26, the transport speed of the paper PA, etc., and is set in advance based on the results of simulations and experiments.

Here, even in the strong wind region A, at the position of the nozzle row 27B on the downstream side, the air volume is smaller than the position of the nozzle row 27A on the upstream side, which is on the windward side of the transport wind, and ink mist is relatively less likely to occur. Therefore, the condition (2) includes the nozzle 28 of the upstream nozzle row 27A.

The condition (3) is that when the ejection of the ink of the number of drops equal to or less than the threshold value Dt from the nozzle 28 of the upstream nozzle row 27A is stopped, the nozzle of the downstream nozzle row 27B adjacent to the nozzle 28 in the main scanning direction. 28 is a condition for judging whether or not alternative ejection is possible.

Next, the operation of the inkjet printing apparatus 1 will be described.

When printing with the inkjet printing apparatus 1, first, the control unit 4 performs an ink mist countermeasure process on the image data to be printed. This ink mist countermeasure process will be described with reference to the flowchart of FIG. Here, it is assumed that the threshold value Dt for determining whether or not the number of drops in which ink mist is likely to occur is “1”. The process of the flowchart of FIG. 5 is performed for each image data of each color.

In step S1 of FIG. 5, the control unit 4 sets “1” in the variable l indicating the line number of the line in the main scanning direction in the image data.

Next, in step S2, the control unit 4 sets "1" to the variable m indicating the pixel number on the line.

Next, in step S3, the control unit 4 determines whether or not the target pixel, which is the m-th pixel on the l-th line, is the ejection target pixel of the upstream nozzle row 27A. Here, in each line, the ejection target pixels of the upstream nozzle row 27A and the ejection target pixels of the downstream nozzle row 27B are alternately arranged.

When it is determined that the target pixel is not the ejection target pixel of the upstream nozzle row 27A, that is, the target pixel is the ejection target of the downstream nozzle row 27B (step S3: NO), the control unit 4 will be described later. To step S10.

When it is determined in step S3 that the target pixel is the pixel of the ejection target of the upstream nozzle row 27A (step S3: YES), the control unit 4 determines in step S4 that the target pixel is the nozzle 28 in the strong wind region A. It is determined whether or not the pixel is a pixel to be ejected. Here, the fact that the target pixel is the pixel to be ejected from the nozzle row 27A on the upstream side and the pixel to be ejected from the nozzle 28 in the strong wind area A means that the above condition (2) is satisfied. To do.

When it is determined that the pixel of interest is not the pixel to be ejected from the nozzle 28 in the strong wind area A (step S4: NO), the control unit 4 proceeds to step S10.

When it is determined that the target pixel is the pixel to be ejected from the nozzle 28 in the strong wind area A (step S4: YES), the control unit 4 determines in step S5 whether the number of drops of the target pixel is “1”. To judge. Here, since the threshold value Dt is “1”, the number of drops of the target pixel is “1” means that the number of drops of the target pixel is equal to or less than the threshold value Dt and not zero. That is, this means that the above-mentioned condition (1) is satisfied.

When it is determined that the number of drops of the target pixel is not "1" (step S5: NO), the control unit 4 proceeds to step S10.

When it is determined that the number of drops of the pixel of interest is "1" (step S5: YES), the controller 4 determines in step S6 that the number of drops of adjacent pixels on both sides of the pixel of interest in the main scanning direction is the maximum number of drops. It is determined whether or not it is Dm. Adjacent pixels on both sides of the target pixel are the (m-1)th pixel on the 1st line and the (m+1)th pixel on the 1st line. Here, since the threshold value Dt is “1”, the number of drops of adjacent pixels on both sides of the target pixel is the maximum drop number Dm, which means that the number of drops of both adjacent pixels on both sides of the target pixel is the maximum drop number. It is larger than the number of drops obtained by subtracting the threshold value Dt from the number Dm.

When it is determined that the numbers of drops of the adjacent pixels on both sides of the target pixel are both the maximum number of drops Dm (step S6: YES), the control unit 4 maintains the number of drops of the target pixel as "1" in step S7. To do. After that, the control unit 4 proceeds to step S10.

When it is determined in step S6 that the number of drops of at least one of adjacent pixels on both sides of the target pixel is not the maximum number of drops Dm (step S6: NO), the control unit 4 determines the number of drops of the target pixel in step S8. Is changed from "1" to "0".

Here, since the threshold value Dt is “1”, the fact that the number of drops of at least one of the adjacent pixels on both sides of the target pixel is not the maximum drop number Dm means that the number of drops of at least one of the adjacent pixels on both sides of the target pixel is not. It means that the number is less than or equal to the number of drops obtained by subtracting the threshold value Dt from the maximum number of drops Dm. That is, this means that the above-mentioned condition (3) is satisfied. Further, changing the number of drops of the pixel of interest from “1” to “0” means stopping the ejection of ink to this pixel of interest.

Next, in step S9, the control unit 4 adds “1” to the number of drops of adjacent pixels on both sides of the target pixel. Here, when the number of drops of one of the adjacent pixels on both sides of the target pixel is the maximum number of drops Dm, the control unit 4 adds “1” to the number of drops of the other adjacent pixel. After that, the control unit 4 proceeds to step S10.

Here, adding “1” to the number of drops of any of the adjacent pixels on both sides of the pixel of interest adds the number of drops for which ejection of the pixel of interest is stopped to the number of drops of any of the adjacent pixels of both sides of the pixel of interest. Means to do. The pixel of interest here is a pixel to be ejected from the nozzle row 27A on the upstream side, and adjacent pixels on both sides of the pixel of interest are pixels to be ejected from the nozzle row 27B on the downstream side.

In step S10, the control unit 4 determines whether or not the variable m is M indicating the last pixel in one line.

When it is determined that m=M is not satisfied (step S10: NO), the control unit 4 adds "1" to the variable m in step S11. After that, the control unit 4 returns to step S3.

When it is determined that m=M (step S10: YES), in step S12, the control unit 4 determines whether or not the variable 1 is L indicating the last line.

When it is determined that 1=L is not satisfied (step S12: NO), the control unit 4 adds “1” to the variable l in step S13. Then, the control unit 4 returns to step S2.

When it is determined that 1=L (step S12: YES), the control unit 4 ends the ink mist countermeasure process.

When the ink mist countermeasure process ends, the control unit 4 starts driving the carry motor 16. As a result, the rotation of the conveyor belt 11 is started. The control unit 4 also starts driving the fan 17. When the sheet PA is fed from a sheet feeding unit (not shown), the sheet PA is transported by the transport unit 2. The control unit 4 causes the inkjet heads 26 of the line heads 21C, 21K, 21M, and 21Y to eject ink on the paper PA transported by the transport unit 2 based on the image data of each color after the ink mist countermeasure process. As a result, the image is printed on the paper PA.

Here, as a result of the above-described ink mist countermeasure process, ink ejection to the pixels satisfying the conditions (1) to (3) is stopped. That is, among the pixels to be ejected by the nozzles 28 in the strong wind region A of the nozzle row 27A on the upstream side, and the number of drops based on the image data is “1”, the pixels on both sides of the pixel in the main scanning direction are adjacent. Ink ejection is stopped for a pixel whose drop number based on image data of at least one of adjacent pixels is not the maximum drop number Dm. Then, “1” is added to the number of drops for any of the adjacent pixels on both sides of the pixel for which ink ejection has been stopped, and for this adjacent pixel, one drop is made from the nozzle 28 of the nozzle row 27B on the downstream side. Ink is ejected for the added number of drops.

That is, in the nozzles 28 in the strong wind area A of the nozzle row 27A on the upstream side, ejection of only one drop per pixel may be stopped. As a result, it is possible to reduce ink mist generated during printing.

Also, since one drop is added to any of the adjacent pixels on both sides of the pixel for which the ejection of one drop of ink has been stopped, the change in density in the printed image can be suppressed. Therefore, deterioration of print quality can be suppressed.

When the printing based on the image data is completed, the control unit 4 stops the carry motor 16 and the fan 17. This completes a series of operations.

As described above, in the inkjet printing apparatus 1, the control unit 4 stops the ink ejection for the pixels that satisfy the conditions (1) to (3). That is, the control unit 4 determines that among the pixels whose drop number based on the image data is less than or equal to the threshold value Dt and is not 0, the nozzle 28 that ejects ink to the pixel is the nozzle 28 in the strong wind region A of the upstream nozzle row 27A. And that the number of drops based on the image data of at least one of the adjacent pixels on both sides in the main scanning direction of the pixel is less than or equal to the number of drops obtained by subtracting the threshold value Dt from the maximum number of drops Dm, the ink ejection is stopped. .. At the same time, the control unit 4 sets the number of drops corresponding to the ejection stopped for the pixel to the number of drops of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle 28 of the nozzle row 27B on the downstream side. to add.

As a result, ink ejection of a small number of small drops equal to or less than the threshold value Dt at which ink mist is likely to occur from the nozzles 28 in a region where the air volume of the transport air is large is reduced, so that the ink mist can be reduced.

Further, since the number of drops corresponding to the ejection stopped in the upstream nozzle row 27A is added to adjacent pixels in the downstream nozzle row 27B and ejected, the change in the density in the print image is suppressed. Therefore, deterioration of print quality can be suppressed.

Therefore, according to the inkjet printing apparatus 1, it is possible to reduce ink mist while suppressing deterioration of print image quality.

(Second embodiment)
Next, a second embodiment in which the ink mist countermeasure process of the above-described embodiment is changed will be described.

In the second embodiment, the control unit 4 stops the ink ejection to the pixels that satisfy the conditions (1) to (3), as in the first embodiment. At the same time, the control unit 4 sets the number of drops corresponding to the ejection stopped for the pixel to the number of drops of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle 28 of the nozzle row 27B on the downstream side. to add.

In addition, in the second embodiment, the control unit 4 adds the number of drops so that the number of drops for a pixel satisfying the above-mentioned conditions (1) and (2) and the following condition (4) becomes larger than the threshold value Dt.

(4) The number of drops based on the image data is larger than the number of drops obtained by subtracting the threshold value Dt from the maximum number of drops Dm of both adjacent pixels on both sides of the pixel in the main scanning direction.

Further, the control unit 4 uses the nozzles 28 of the nozzle array 27B on the downstream side on both sides of the pixel in the main scanning direction by the addition of the number of drops for the pixel satisfying the conditions (1), (2), and (4). The number of drops for any of the adjacent pixels is reduced.

The above-mentioned condition (4) is a case where the number of drops discharged from the nozzles 28 of the upstream nozzle row 27A is added to a pixel that satisfies the conditions (1) and (2) but does not satisfy the condition (3). In addition, it is a condition for determining whether or not the additional amount can be reduced from the number of drops in the nozzle 28 of the downstream nozzle row 27B adjacent to the nozzle 28 in the main scanning direction.

Next, the ink mist countermeasure process in the second embodiment will be described with reference to the flowchart in FIG. Here, similarly to the description of the ink mist countermeasure process in the first embodiment described above, the threshold value Dt will be described as "1".

The processing of steps S11 to S16 of FIG. 6 is the same as the processing of steps S1 to S6 of FIG. 5 described above.

When it is determined in step S16 that the numbers of drops of adjacent pixels on both sides of the target pixel are both the maximum number of drops Dm (step S16: YES), the control unit 4 sets the number of drops of the target pixel to “1” in step S17. Is added.

Here, since the threshold value Dt is “1”, the number of drops of adjacent pixels on both sides of the target pixel is the maximum drop number Dm, which means that the number of drops of both adjacent pixels on both sides of the target pixel is the maximum drop number. It is larger than the number of drops obtained by subtracting the threshold value Dt from the number Dm. That is, this means that the above-mentioned condition (4) is satisfied.

Further, in step S17, adding “1” to the number of drops of the target pixel which is “1” in the original image data means adding the number of drops so that the number of drops of the target pixel becomes larger than the threshold value Dt. means. Note that the number of drops added to the pixel of interest here is not limited to “1”, but in order to suppress changes in the density of the print image, it may be the minimum number of drops within the range in which the number of drops of the pixel of interest is larger than the threshold value Dt. preferable. Therefore, the number of drops added to the pixel of interest is set to "1".

Next, in step S18, the control unit 4 subtracts "1" from the number of drops of adjacent pixels on both sides of the target pixel. After that, the control unit 4 proceeds to step S21.

Here, subtracting “1” from the number of drops of any of the adjacent pixels on both sides of the target pixel means reducing the number of drops of any of the adjacent pixels of both sides by the addition of the number of drops for the target pixel. Means

When determining in step S16 that the number of drops of at least one of the adjacent pixels on both sides of the target pixel is not the maximum number of drops Dm (step S16: NO), the control unit 4 proceeds to step S19.

The processing of steps S19 to S24 is the same as the processing of steps S8 to S13 of FIG. 5 described above. When it is determined in step S23 that l=L (step S23: YES), the control unit 4 ends the ink mist countermeasure process.

At the time of printing based on the image data after the ink mist countermeasure process in the second embodiment, ink ejection to the pixels satisfying the conditions (1) to (3) is stopped as in the first embodiment. Then, “1” is added to the number of drops for any of the adjacent pixels on both sides of the pixel for which ink ejection has been stopped, and for this adjacent pixel, one drop is made from the nozzle 28 of the nozzle row 27B on the downstream side. Ink is ejected for the added number of drops.

In addition, “1” is added to the number of drops for pixels that satisfy the conditions (1), (2), and (4), and ink ejection is performed. Then, the number of drops ejected from the nozzle 28 of the nozzle row 27B on the downstream side is reduced by "1" with respect to any of the adjacent pixels on both sides of the pixel to which the drop number is added.

That is, in the nozzles 28 in the strong wind region A of the nozzle row 27A on the upstream side, in addition to stopping the ejection of only one drop per pixel, the ejection may be changed to two drops. As a result, it is possible to further reduce the ink mist generated during printing.

In addition, one drop is added to any of the adjacent pixels on both sides of the pixel for which the ejection of one drop of ink has been stopped, and any of the adjacent pixels on both sides of the pixel changed from the ejection of one drop to the ejection of two drops. One drop is reduced in or. As a result, changes in the density of the printed image can be suppressed. Therefore, deterioration of print quality can be suppressed.

As described above, in the second embodiment, the control unit 4 stops the ink ejection for the pixels that satisfy the conditions (1) to (3). At the same time, the control unit 4 sets the number of drops corresponding to the ejection stopped for the pixel to the number of drops of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle 28 of the nozzle row 27B on the downstream side. to add.

Further, the control unit 4 adds the number of drops so that the number of drops for pixels satisfying the conditions (1), (2), and (4) becomes larger than the threshold value Dt. That is, the control unit 4 determines that among the pixels whose drop number based on the image data is less than or equal to the threshold value Dt and is not 0, the nozzle 28 that ejects ink to the pixel is the nozzle 28 in the strong wind region A of the upstream nozzle row 27A. And the number of drops for both adjacent pixels in the main scanning direction of the pixel is such that the number of drops based on the image data is larger than the number of drops obtained by subtracting the threshold value Dt from the maximum number of drops Dm. The number of drops is added so that is greater than the threshold value Dt. At the same time, the control unit 4 reduces the additional drop number for the pixel from the drop number for any of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle 28 of the nozzle row 27B on the downstream side.

As a result, the number of small drops of ink that are less than the threshold value Dt at which ink mist is likely to occur is reduced from the nozzles 28 in the region where the air volume of the transport air is large, and thus the ink mist can be further reduced.

Further, the number of drops corresponding to the ejection stopped in the upstream nozzle row 27A is added to the adjacent pixel in the downstream nozzle row 27B and ejected. Further, the number of drops added in the upstream nozzle row 27A is reduced from the number of drops ejected to the adjacent pixel in the downstream nozzle row 27B. As a result, changes in the density of the printed image can be suppressed. Therefore, deterioration of print quality can be suppressed.

Therefore, according to the second embodiment, the ink mist can be further reduced while suppressing the deterioration of the print image quality.

(Third Embodiment)
Next, a third embodiment in which the ink mist countermeasure process of the above-described embodiment is changed will be described.

In the second embodiment, the control unit 4 adds the number of drops so that the number of drops for a pixel satisfying the above conditions (1) and (2) and the following condition (5) is larger than the threshold value Dt.

(5) The number of drops based on the image data of at least one of the adjacent pixels on both sides of the pixel in the main scanning direction is equal to or larger than the threshold value Dt.

In addition, the control unit 4 uses the nozzles 28 of the nozzle array 27B on the downstream side to add the number of drops corresponding to the pixels satisfying the conditions (1), (2), and (5) to both sides of the pixel in the main scanning direction. The number of drops for any of the adjacent pixels is reduced.

The above condition (5) reduces the number of drops added to the nozzle 28 of the upstream nozzle row 27A from the number of drops of the nozzle 28 of the downstream nozzle row 27B adjacent to the nozzle 28 in the main scanning direction. This is a condition for determining whether or not it is possible.

Next, the ink mist countermeasure process in the third embodiment will be described with reference to the flowchart in FIG. Here, similarly to the description of the ink mist countermeasure process in the first embodiment described above, the threshold value Dt will be described as "1".

The processing of steps S31 to S35 of FIG. 7 is the same as the processing of steps S1 to S5 of FIG. 5 described above.

When it is determined in step S35 that the number of drops of the target pixel is “1” (step S35: YES), in step S36, the control unit 4 determines that the number of drops of adjacent pixels on both sides of the target pixel in the main scanning direction is the same. It is determined whether both are "0". Here, since the threshold value Dt is “1”, the number of drops of the adjacent pixels on both sides of the target pixel is “0”, which means that the number of drops of both the adjacent pixels on both sides of the target pixel is less than the threshold value Dt. It means small.

When it is determined that the numbers of drops of adjacent pixels on both sides of the target pixel are both “0” (step S36: YES), the control unit 4 maintains the number of drops of the target pixel at “1” in step S37. .. After that, the control unit 4 proceeds to step S40.

When it is determined in step S36 that the number of drops of at least one of the adjacent pixels on both sides of the target pixel is not “0” (step S36: NO), the control unit 4 proceeds to step S38.

Here, since the threshold value Dt is “1”, it means that the number of drops of at least one of the adjacent pixels on both sides of the target pixel is not “0”, that is, at least one of the adjacent pixels on both sides of the target pixel in the main scanning direction. It means that the number of drops based on the image data is not less than the threshold value Dt. That is, this means that the above-mentioned condition (5) is satisfied.

The processing of steps S38 and S39 is the same as the processing of steps S17 and S18 of FIG. 6 described above. After step S39, the control unit 4 proceeds to step S40.

The processing of steps S40 to S43 is the same as the processing of steps S10 to S13 of FIG. 5 described above. When it is determined in step S42 that l=L (step S42: YES), the control unit 4 ends the ink mist countermeasure process.

At the time of printing based on the image data after the ink mist countermeasure process in the third embodiment, “1” is added to the number of drops for the pixels satisfying the conditions (1), (2) and (5), and ink is ejected. .. Then, the number of drops ejected from the nozzle 28 of the nozzle row 27B on the downstream side is reduced by "1" with respect to any of the adjacent pixels on both sides of the pixel to which the drop number is added.

That is, in the nozzles 28 in the strong wind area A of the nozzle row 27A on the upstream side, the ejection of only one drop per pixel may be changed to the ejection of two drops. As a result, it is possible to reduce ink mist generated during printing.

Further, one drop is reduced in any of the adjacent pixels on both sides of the pixel changed from the one-drop ejection to the two-drop ejection. As a result, changes in the density of the printed image can be suppressed. Therefore, deterioration of print quality can be suppressed.

As described above, in the third embodiment, the control unit 4 adds the number of drops so that the number of drops for the pixels satisfying the conditions (1), (2), and (5) becomes larger than the threshold value Dt. That is, the control unit 4 determines that among the pixels whose drop number based on the image data is less than or equal to the threshold value Dt and is not 0, the nozzle 28 that ejects ink to the pixel is the nozzle 28 in the strong wind region A of the upstream nozzle row 27A. And the drop number is added so that the drop number for a pixel whose drop number based on the image data of at least one of the adjacent pixels on both sides in the main scanning direction of the pixel is greater than or equal to the threshold Dt is greater than the threshold Dt. .. At the same time, the control unit 4 adds the additional drop number to the pixels satisfying the conditions (1), (2), and (5) on both sides of the pixel by the nozzle 28 of the nozzle row 27B on the downstream side in the main scanning direction. From the number of drops for any of the adjacent pixels of.

As a result, ink ejection of a small number of small drops equal to or less than the threshold value Dt at which ink mist is likely to occur from the nozzles 28 in a region where the air volume of the transport air is large is reduced, so that the ink mist can be reduced.

Further, since the number of drops added in the upstream nozzle row 27A is reduced from the number of drops ejected to adjacent pixels in the downstream nozzle row 27B, the change in density in the print image can be suppressed. Therefore, deterioration of print quality can be suppressed.

Therefore, according to the third embodiment as well, it is possible to reduce ink mist while suppressing deterioration in print image quality.

(Other embodiments)
As described above, the present invention has been described by the first to third embodiments, but it should not be understood that the description and drawings forming a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be apparent to those skilled in the art.

In the above-described first to third embodiments, the case where the inkjet head 26 has a configuration having two nozzle rows 27A and 27B has been described. However, the inkjet head may have three or more nozzle rows, and the nozzles of each nozzle row may be arranged to be displaced in the main scanning direction with respect to the nozzles of the other nozzle rows. In this case, the “upstream nozzle row” of condition (2) may be replaced with the “upstream nozzle row”.

In the configuration in which the inkjet head has three or more nozzle rows as described above, any pixel other than the most upstream nozzle row is adjacent to the adjacent pixel in the main scanning direction of the pixel to be ejected by the nozzle of the most upstream nozzle row. Ink is ejected by the nozzles of the nozzle row. For this reason, when the ink mist countermeasure processing of the first and second embodiments is applied, the number of drops for which ejection is stopped in the most upstream nozzle row is any other than the most upstream nozzle row. It is added to adjacent pixels in the nozzle row and ejected. In addition, when the ink mist countermeasure processing of the second and third embodiments is applied, the number of drops added in the most upstream nozzle row is the number of drops added in any nozzle row other than the most upstream nozzle row. It is reduced from the number of drops ejected to adjacent pixels.

In the above-described first to third embodiments, the configuration in which the multi-drop type inkjet head 26 is used and the ink ejection amount for each pixel is set by the number of ink drops has been described. However, the ink ejection amount for each pixel may be set according to the size of the ink droplet. Even in this case, as the ejected ink droplet (ink ejection amount) is smaller, the ink liquid column is more likely to be divided and the ink mist is more likely to occur, so that the present invention can be applied.

In the above-described first to third embodiments, the configuration has been described in which the plurality of inkjet heads 26 arranged in a staggered manner covers the printing area in the main scanning direction, but a single inkjet head covers the printing area in the main scanning direction. May be

In the above-described first to third embodiments, the case where printing is performed on the sheet PA that is the cut sheet (sheet) conveyed by the conveyor belt 11 has been described, but roll paper (continuous paper) is continuously conveyed. The present invention can be applied even when printing is performed.

As described above, it goes without saying that the present invention includes various embodiments and the like not described here. Therefore, the technical scope of the present invention is defined only by the matters specifying the invention according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Conveying section 3 Printing section 4 Control section 21, 21C, 21K, 21M, 21Y Line head 26 Inkjet head 27A, 27B Nozzle row 28 Nozzle A Strong wind area

Claims (3)

It has a plurality of nozzle rows that are arranged in parallel in the transport direction and that each include a plurality of nozzles that are disposed along the main scanning direction that is orthogonal to the transport direction of the print medium that is transported, and the nozzles of each of the nozzle rows are An inkjet head that is arranged to be displaced in the main scanning direction with respect to the nozzles of another nozzle row, and that ejects ink of the same color from the nozzles of each nozzle row onto a print medium,
A control unit that controls the inkjet head to print by ejecting ink for each line in the main scanning direction from the nozzles of the plurality of nozzle rows based on image data indicating an ink ejection amount for each pixel,
The control unit is
Among the pixels whose ink ejection amount based on the image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is the end portion of the inkjet head in the main scanning direction of the most upstream nozzle row in the transport direction. Of the nozzle in the predetermined area of the pixel and the ink discharge amount based on the image data of at least one of the adjacent pixels on both sides of the pixel in the main scanning direction is subtracted from the maximum ink discharge amount per pixel by the threshold value. Stop ejecting ink to pixels that are less than
The ink ejection amount of the ejection stopped for the pixel is added to the ink ejection amount of any of the adjacent pixels on both sides in the main scanning direction of the pixel by the nozzle of the nozzle row other than the most upstream nozzle row. An inkjet printing device characterized by the above. The control unit is
Among the pixels whose ink ejection amount based on image data is less than or equal to the threshold value and not 0, the nozzle that ejects ink to the pixel is the end of the inkjet head in the main scanning direction of the most upstream nozzle row in the transport direction. Of the nozzles in the predetermined area of the same portion, and both adjacent pixels in the main scanning direction of the pixel in question, the ink ejection amount based on image data is equal to the threshold value from the maximum ink ejection amount per pixel. The ink ejection amount for a pixel that is larger than the subtracted amount is added so that it becomes larger than the threshold value.
An additional portion of the ink ejection amount for the pixel is reduced from the ink ejection amount for any of the adjacent pixels on both sides of the pixel in the main scanning direction by the nozzle of the nozzle row other than the most upstream nozzle row. The inkjet printing device according to claim 1. It has a plurality of nozzle rows that are arranged in parallel in the transport direction and that each include a plurality of nozzles that are disposed along the main scanning direction that is orthogonal to the transport direction of the print medium that is transported, and the nozzles of each of the nozzle rows are An inkjet head that is arranged to be displaced in the main scanning direction with respect to the nozzles of another nozzle row, and that ejects ink of the same color from the nozzles of each nozzle row onto a print medium,
A control unit that controls the inkjet head to print by ejecting ink for each line in the main scanning direction from the nozzles of the plurality of nozzle rows based on image data indicating an ink ejection amount for each pixel,
The control unit is
Among the pixels whose ink ejection amount based on the image data is equal to or less than the threshold value and is not 0, the nozzle that ejects ink to the pixel is the end portion of the inkjet head in the main scanning direction of the most upstream nozzle row in the transport direction. Is a nozzle within a predetermined area of the pixel, and the ink ejection amount for a pixel whose ink ejection amount based on image data of at least one of adjacent pixels on both sides in the main scanning direction of the pixel is equal to or more than the threshold is Add the amount of ink to be discharged,
An additional portion of the ink ejection amount for the pixel is reduced from the ink ejection amount for any of the adjacent pixels on both sides of the pixel in the main scanning direction by the nozzle of the nozzle row other than the most upstream nozzle row. Inkjet printing device.