JP2016013645A - Ink jet printing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet printing device, in which the image degradation is prevented by making the wind ripple irregularity of a half-tone region unapparent.SOLUTION: In the case where a resolution of image data contained in a printing job is high and where densities of individual pixels in the image data are identical and within a predetermined range, on the basis of a self air stream indicating an occurrence degree of a self air stream to cause ink discharged from a nozzle to flow straight against transportation air stream of a printer sheet of the nozzle per unit time, thereby to discharge inks from the individual nozzles so that the densities of the individual pixels in the image data may increase.

Description

  The present invention relates to an inkjet printing apparatus.

  A line-type inkjet printing apparatus performs printing by ejecting ink droplets onto a sheet conveyed by a conveyance belt by using a plurality of inkjet heads arranged in a direction orthogonal to the sheet conveyance direction.

  In such a line-type ink jet printing apparatus, due to various factors, a landing position shift may occur in droplets ejected from the ink jet head, which may cause image degradation.

  In Patent Document 1, the distance between the ejection surface of a liquid ejection head formed with a plurality of droplet ejection openings and the recording surface is grasped, and the amount of landing position deviation on the recording surface is specified based on the distance. A technique relating to an image recording apparatus that corrects image data in accordance with the specified amount of landing position deviation and performs halftone processing has been proposed.

JP 2007-21807 A

  However, the image recording apparatus described in Patent Document 1 does not take into account the influence of the self-airflow described later. For this reason, it has not been possible to cope with a case where image degradation occurs due to the influence of the self-stream. A specific description will be given below.

  In the line-type ink jet printing apparatus, an air current is generated by the paper conveyed directly under the head. Further, when ink is continuously ejected from the nozzle provided on the upstream side in the transport direction, the ink droplets are ejected with a self-air stream, and thus act as a wall that blocks the air stream by transport (hereinafter referred to as this formation). The simulated pseudo wall is called the ink wall).

  Then, the air flow generated by the conveyed paper may collide with the ink wall, and the air flow may be complicated. Due to this turbulent air flow, there may be a deviation from the position where the ink should be ejected and landed, which may cause density unevenness called so-called wind ripple unevenness.

  It has been found that this wind ripple unevenness is most noticeable when it occurs in a halftone region that is a halftone that is neither dark nor thin. When the wind pattern unevenness occurs in the high density region where the density is high, the ink of the adjacent pixels is blurred and fills the portion where the wind pattern unevenness is generated, so that it becomes less noticeable. On the other hand, when wind pattern unevenness occurs in a low-density area with low density, the original image has many colorless pixels, which makes it less noticeable. As a result, it becomes most noticeable when the unevenness of the wind pattern occurs in the halftone area, and it has been anxious to make the unevenness of the wind pattern inconspicuous in the halftone area.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink jet printing apparatus that makes a wind pattern unevenness in a halftone area generated due to the influence of a self-air flow inconspicuous.

  In order to achieve the above object, a first feature of an ink jet printing apparatus according to the present invention is that a plurality of nozzle rows are arranged in an ink jet head disposed above a transport path in a transport direction of a print sheet transported on the transport path. When the ink jet head prints on the printing paper by ejecting ink from each nozzle of each nozzle row based on the print job, the inkjet head has the first resolution or the first resolution. An inkjet printing apparatus capable of printing at a higher second resolution, wherein the resolution of image data included in the print job is the second resolution, and the density of each pixel in the image data is the same. Prints the ink ejected from the nozzle, calculated based on the ink ejection amount of the nozzle per unit time when it is within the predetermined range The resolution of the image data is converted to the first resolution based on the degree of self-airflow indicating the degree of self-airflow that goes straight against the paper conveyance airflow, and the density of each pixel in the image data is increased. Thus, there is provided control means for ejecting ink from each nozzle.

In order to achieve the above object, a second feature of the ink jet printing apparatus according to the present invention is that the image data includes self-airflow based on the self-airflow degree, and image data included in the print job. Determining means for determining whether or not the resolution is the second resolution, and whether or not the image data is control target image data in which the density of each pixel in the image data is the same and within a predetermined range;
A distance variable means capable of changing a distance between the inkjet head and the transport path, and the control means, when the distance between the inkjet head and the transport path is a predetermined value or more, The determination process is performed by the determination unit.

  In order to achieve the above object, a third feature of the ink jet printing apparatus according to the present invention is a storage unit that stores a determination table for determining whether or not the image data is the control target according to the type of printing paper. And determining processing by the determination unit based on the type of printing paper to be printed based on the print job with reference to the determination table.

  According to the first feature of the ink jet printing apparatus according to the present invention, the resolution of the image data included in the print job is the second resolution, and the density of each pixel in the image data is the same and within a predetermined range. In this case, based on the self-airflow degree, which is calculated based on the ink discharge amount of the nozzle per unit time, and indicates the degree of self-airflow that causes the ink discharged from the nozzle to go straight against the conveyance airflow of the printing paper. Then, the resolution of the image data is converted to the first resolution, and ink is ejected from each nozzle so as to increase the density of each pixel in the image data. Specifically, self-airflow is generated, and the half-tone image data in which the density of each pixel is the same and within a predetermined range is supported by the wraparound airflow that is generated by bypassing the airflow generated by the conveyance of printing paper. Wind pattern unevenness is easily noticeable in the print area. For this reason, the resolution of the image data is converted to the first resolution, the number of pixels to be ejected is reduced to reduce the self-flow rate, and the ink is applied to each nozzle so as to increase the density of each pixel in the image data. It is possible to reduce the landing deviation caused by the sneak current. As a result, the ink droplets ejected from the ink jet head become heavier and are less susceptible to the influence of the transport airflow generated by the transport of the paper, so that the amount of landing position deviation is reduced and the wind pattern unevenness is less noticeable.

  According to the second feature of the ink jet printing apparatus according to the present invention, when the distance between the ink jet head and the transport path is equal to or greater than a predetermined value, the image data generates self air flow based on the self air flow degree. In addition, it is determined whether or not the resolution of the image data included in the print job is the second resolution and the density of each pixel in the image data is the same as the control target image data within a predetermined range. The larger the interval between the inkjet head and the conveyance path for conveying the paper, the more likely to cause wind ripple unevenness. Therefore, the determination process is executed only when the interval is wide, and printing is performed at the first resolution when the determination condition is satisfied. As a result, it is possible to obtain a high effect with respect to wind ripple unevenness without reducing the resolution as much as possible.

  According to the second feature of the ink jet printing apparatus according to the present invention, a determination table for determining whether or not the image data is control target is stored according to the type of paper, and the determination table is referred to. The determination unit performs determination processing based on the type of printing paper to be printed based on the print job. Since the method of bleeding when ink droplets land on the paper differs depending on the type of paper, for example, the number of drops per pixel for determining the halftone density for each type of paper is determined in advance in the determination table, By determining the halftone density according to the type of paper, printing can be performed at a low resolution when the unevenness of the wind pattern is conspicuous depending on the paper.

It is a block diagram which shows the structure of the inkjet printing apparatus which is Example 1 of this invention. It is a top view of the ink jet unit with which the ink jet printer which is Example 1 of the present invention is provided. It is the figure which showed typically the droplet discharged from the nozzle of the inkjet head with which the inkjet printing apparatus which is Example 1 of this invention is provided, and the produced | generated air flow. (A) is the figure seen from the conveyance direction (subscanning direction) upstream of the paper P, (b) is a perspective view. It is explanatory drawing explaining the state of a wind ripple nonuniformity. (A) shows the wind pattern unevenness in the high density area, (b) shows the wind pattern unevenness in the halftone area, and (c) shows the wind pattern unevenness in the low density area. It is the figure which showed the function structure of the inkjet printing apparatus which is Example 1 of this invention. It is the figure which showed an example of the condition determination table memorize | stored in ROM of the control part with which the inkjet printing apparatus which is Example 1 of this invention is provided. (A) is a figure showing an example of a condition judgment table corresponding to mat paper, and (b) is a figure showing an example of a condition judgment table corresponding to plain paper. It is the flowchart which showed the process sequence of the inkjet printing apparatus which is Example 1 of this invention. It is explanatory drawing which showed typically the conversion process of the resolution and discharge amount of step S140 of the flowchart of FIG. 8 in the inkjet printing apparatus which is Example 1 of this invention. (A) shows the drop data of the control target image data included in the received print job, and (b) shows the ink droplet when the wind pattern unevenness occurs when printing based on the drop data. (C) is a diagram showing the landing position where ink droplets land when printing is performed based on the drop data obtained by converting the resolution in the sub-scanning direction and the ejection amount. FIG. 6D is a diagram showing a state where the ink oozes on the paper when the ink droplet has landed at the landing position shown in FIG. It is explanatory drawing which showed typically the conversion process of the resolution and discharge amount of step S140 of the flowchart of FIG. 8 in the inkjet printing apparatus which is Example 1 of this invention. (A) shows the drop data of the control target image data included in the received print job, and (b) shows the ink droplet when the wind pattern unevenness occurs when printing based on the drop data. (C) shows the landing position where ink droplets land when printing is performed based on drop data obtained by converting the resolution and discharge amount in the main scanning direction and sub-scanning direction. (D) is a diagram showing a state in which ink oozes on paper when ink droplets have landed at the landing positions shown in (c).

  Hereinafter, an ink jet printing apparatus according to a first embodiment of the present invention will be described with reference to the drawings. In addition, the inkjet printing apparatus 1 of Example 1 which concerns on this invention demonstrated below is an example of the inkjet printing apparatus which concerns on this invention to the last, and can be suitably changed within the range of the technical idea of this invention.

<Overall configuration of inkjet printing apparatus>
In Embodiment 1 of the present invention, an inkjet head having an inkjet head arranged in a direction (main scanning direction) orthogonal to the conveyance direction of the sheet is used based on image data with respect to the sheet conveyed on the conveyance path. A line-type inkjet printing apparatus that prints by discharging ink from the nozzles will be described as an example.

  FIG. 1 is a configuration diagram illustrating a configuration of an inkjet printing apparatus 1 that is Embodiment 1 of the present invention.

  As shown in FIG. 1, the inkjet printing apparatus 1 includes a side paper feed unit 10, an internal paper feed unit 20, a printing unit 30, a paper discharge unit 40, and a reversing unit 50.

  The side paper feeder 10 includes a paper feeder 11 on which paper P is stacked, a primary paper feeder 12 that conveys only the uppermost paper P from the paper feeder 11 onto the paper feed conveyance path FR, And a secondary paper feeding unit 14 for carrying the paper P conveyed by the primary paper feeding unit 12 onto the circulation conveyance path CR.

  The internal paper feeder 20 includes a paper feeder 21a on which the paper P is stacked, a primary paper feeder 22a that conveys only the uppermost paper P from the paper feeder 21a onto the paper feed conveyance path FR, and paper A sheet feeding table 21b on which P is stacked, a primary sheet feeding unit 22b that conveys only the uppermost sheet P from the sheet feeding table 21b onto the sheet feeding conveyance path FR, and a sheet feeding table on which the sheet P is stacked. 21c, a primary paper supply unit 22c that conveys only the uppermost paper P from the paper supply table 21c onto the paper supply conveyance path FR, a paper supply table 21d on which the paper P is stacked, and the paper supply table 21d. And a primary paper feed unit 22d for transporting only the uppermost sheet P onto the paper feed transport path FR.

  As described above, the paper P is transported to the secondary paper feeder 14 from the side paper feeder 10 and the internal paper feeder 20, and further, the paper P is transported from the reversing unit 50 described later.

  Therefore, in front of the secondary paper feeding unit 14 in the transport direction, a joining point where the transport path of the fed paper P and the path on which the paper on which one side is printed is circulated and joined is merged Exists. Based on this merging point, the path on the paper feed mechanism side is referred to as a paper feed conveyance path FR, and the other path is referred to as a circulation conveyance path CR.

  The printing unit 30 includes an inkjet unit 31 in which a plurality of print heads are incorporated, and an annular conveyance belt 133 provided on the opposite surface of the inkjet unit 31, and is fed by the secondary sheet feeding unit 14. The paper P is sucked on the transport belt 133 by the suction fan 131 installed in the annular transport belt 133 corresponding to the back surface of the transport path of the paper, and is transported at a predetermined transport speed from the inkjet unit 31. Printing is performed on the paper P by the discharged ink.

  The paper P printed by the printing unit 30 is conveyed on the circulation conveyance path CR in the housing by a conveyance roller or the like disposed on the circulation conveyance path CR. On the circulation conveyance path CR, a switching mechanism 43 that switches between guiding the paper P conveyed on the circulation conveyance path CR to the paper discharge unit 40 or recirculating on the circulation conveyance path CR is provided. .

  The switching mechanism 43 switches the paper P in order to guide the paper P to one of a paper discharge unit 40 and a reversing unit 50 described later.

  The paper discharge unit 40 includes a tray-shaped paper discharge table 41 protruding from the casing of the inkjet printing apparatus 1 and a pair of paper discharge rollers 42 that guide the paper P to the paper discharge table 41. Then, the paper P guided to the paper discharge unit 40 by the switching mechanism 43 is transported to the paper discharge table 41 by the paper discharge roller 42 and stacked on the paper discharge table 41 with the printing surface down.

  The reversing unit 50 includes a reversing table 51 for reversing the paper P, and a reversing roller 52 that transports the paper P from the circulation conveyance path CR to the reversing table 51 or conveys the paper P from the reversing table 51 onto the circulation conveyance path CR. It has.

  The sheet P guided to the reversing unit 50 by the switching mechanism 43 is transported from the circulation transport path CR to the reversing table 51 by the reversing roller 52, and is transported from the reversing table 51 to the circulation transport path CR after a predetermined time. The front and back are reversed with respect to the circulation conveyance path CR. The sheet P with the front and back reversed is conveyed toward the printing unit 30 on the circulation conveyance path CR by a plurality of rollers such as a conveyance roller 53 provided on the circulation conveyance path CR.

  Moreover, it has the control part 80 which controls the whole inkjet printing apparatus 1. FIG. The control unit 80 executes the printing process based on the image data by controlling the side paper feeding unit 10, the internal paper feeding unit 20, the printing unit 30, the paper discharge unit 40, and the reversing unit 50. To do.

  FIG. 2 is a plan view of the ink jet unit 31 provided in the ink jet printing apparatus 1 according to the first embodiment of the present invention.

  The inkjet unit 31 includes a plurality of line-type inkjet heads 110, 112, and 114 in which two rows of nozzles are arranged in the main scanning direction, that is, the direction orthogonal to the conveyance direction of the paper P.

  Printing is performed by ejecting ink from the plurality of inkjet heads 110, 112, and 114 while the sheet P is conveyed in the sub-scanning direction (the conveyance direction of the sheet P) below the inkjet unit 31.

  The inkjet unit 31 stores inkjet heads 110a to 110f storing black (K) ink, inkjet heads 112a to 112f storing cyan (C) and magenta (M) ink, and yellow (Y) ink. Inkjet heads 114a to 114f. The ink jet heads 110a to 110f, the ink jet heads 112a to 112f, and the ink jet heads 114a to 114f have the same physical structure, although different ink colors are ejected.

  The inkjet heads 110a to 110f have an upstream nozzle row 121 in which nozzles are arranged at a pitch interval that realizes a resolution of 300 dpi and a pitch interval that realizes a resolution of 300 dpi so as to be parallel to the main scanning direction. A downstream nozzle row 123 in which nozzles are arranged is arranged. The two nozzle rows 121 and 123 are provided with the positions of the nozzles shifted in the main scanning direction, and the same color (here, black) ink is ejected from the two nozzle rows 121 and 123. , 600 dpi resolution is realized.

  The ink jet heads 110a to 110f are provided with an ink chamber for storing black (K) ink, and a piezo element is disposed in the ink chamber. Then, a drive voltage for ejecting ink is applied to the piezo element based on the supplied drive signal, whereby black (K) ink is ejected in units of drops from nozzles communicating with the ink chamber. Although not shown, each of the inkjet heads 110a to 110f is provided with a thermometer for measuring the temperature of the ink.

  Thus, by ejecting black (K) ink from the nozzle rows 121 and 123 arranged in two rows in the main scanning direction, printing can be performed with a resolution of 600 (dpi). By ejecting black (K) ink from any one of the 123, printing can be performed with a resolution of 300 (dpi). That is, printing can be performed with the resolution switched to 600 (dpi) or 300 (dpi) depending on whether the nozzle rows to be ejected are two or one.

  On the other hand, the inkjet heads 112a to 112f include an upstream nozzle row 124 that discharges cyan (C) ink with nozzles arranged at a pitch interval that realizes a resolution of 300 dpi so as to be parallel to the main scanning direction. , Nozzles are arranged at a pitch interval that realizes a resolution of 300 dpi, and a downstream nozzle row 125 that discharges magenta (M) ink is arranged one by one.

  Each of the inkjet heads 112a to 112f is provided with an ink chamber for storing cyan (C) ink and an ink chamber for storing magenta (M) ink. Piezo elements are disposed in the ink chamber. Has been placed. Then, a drive voltage for ejecting ink is applied to the piezo element based on the drive signal, whereby cyan (C) and magenta (M) from the nozzles communicating with the respective ink chambers of cyan (C) and magenta (M). Each ink is ejected in units of drops. Although not shown, each of the inkjet heads 112a to 112f is provided with a thermometer for measuring the temperature of the ink.

  As described above, of the nozzle rows 124 and 125 arranged in two rows in the main scanning direction, cyan (C) ink is ejected from the upstream nozzle row 124 and magenta (M) is ejected from the downstream nozzle row 125. By ejecting this ink, cyan (C) and magenta (M) are each printed at a resolution of 300 (dpi).

  In the inkjet heads 114a to 114f, nozzle rows in which nozzles are arranged at a pitch interval that realizes a resolution of 300 dpi are arranged in two rows so as to be parallel to the main scanning direction, and yellow ( A nozzle row 127 for discharging ink Y) is arranged, and a nozzle row 128 for preliminary ink is arranged on the downstream side.

  The ink jet heads 114a to 114f are provided with an ink chamber for storing yellow (Y) ink and an ink chamber for storing spare ink, and a piezo element is disposed in the ink chamber. Then, by applying a drive voltage for ejecting ink to the piezo element based on the drive signal, the nozzles communicating with the ink chambers of yellow (Y) and the preliminary ink colors respectively output yellow (Y) and the preliminary ink colors. Ink is ejected in units of drops.

  As described above, of the nozzle rows arranged in two rows in the main scanning direction, yellow (Y) ink is ejected from the upstream nozzle row 127 and preliminary ink is ejected from the downstream nozzle row 128. Thus, yellow (Y) and preliminary ink colors are printed at a resolution of 300 (dpi).

  The spare ink may be cyan (C), magenta (M), yellow (Y), black (K), light cyan (LC), or light magenta (LM).

  In addition, as described above, the inkjet heads 110a to 110f, the inkjet heads 112a to 112f, and the inkjet heads 114a to 114f have different physical colors, but have the same physical structure. When ink of the same color is accommodated in one inkjet head, the resolution in the main scanning direction can be switched to 600 (dpi) or 300 (dpi), and printing can be performed when ink of different colors is accommodated in one inkjet head. It is possible to print with two different colors of ink at a resolution of 300 (dpi).

<Description of landing position shift due to airflow>
FIG. 3 is a diagram schematically illustrating droplets discharged from the nozzles of the inkjet head included in the inkjet printing apparatus 1 according to the first embodiment of the present invention and the generated airflow. (A) is the figure seen from the conveyance direction (subscanning direction) upstream of the paper P, (b) is a perspective view.

  As shown in FIGS. 3A and 3B, it is assumed that ink droplets D are continuously ejected from the three upstream nozzle rows 121 at the center in the main scanning direction of the inkjet head 110a. At this time, since the ink droplet D is ejected with a self-airflow, it acts like a wall that blocks the airflow caused by the conveyance and forms a pseudo ink wall.

  The self-air flow is stronger than the fact that a plurality of nozzles that are continuous in the main scanning direction eject ink. In addition, the self-air flow becomes high when ink is repeatedly ejected to dots of a plurality of lines in which the same nozzle is continuous. That is, if there is a region where the ink discharge amount of each nozzle is high per unit time, the degree of occurrence of self-air flow that causes the ink discharged from the nozzle to go straight against the conveyance air flow of the printing paper in that region increases. .

  On the other hand, when the paper P is transported in the sub-scanning direction, transport airflows F1 to F6 are generated along with the transport. Among them, the carrier airflows F3 and F4 flowing through the central portion in the main scanning direction collide with an ink wall (self-airflow) formed by continuous ejection of the ink droplets D. As a result, the transport airflows F3 and F4 form a flow that wraps around the formed ink wall, and the circulated transport airflows F3 and F4 affect or wrap around the transport airflows F2 and F5. The airflows F3 and F4 may collide with each other and the airflow may be complicated. Due to this turbulent air flow, there may be a deviation from the position where the ink should be discharged and landed, which may cause density unevenness called so-called wind ripple unevenness.

  Further, it has been found that this wind pattern unevenness is most noticeable when it occurs in a halftone region that is a halftone that is neither high density nor low density.

  FIG. 4 is an explanatory diagram for explaining the state of wind ripple unevenness. (A) shows the wind pattern unevenness in the high density area, (b) shows the wind pattern unevenness in the halftone area, and (c) shows the wind pattern unevenness in the low density area. In this figure, the image data included in the received job received by the inkjet printing apparatus 1 is high-resolution data, and so-called solid images are continuously ejected at regular intervals in this image data. It is assumed that a continuous discharge area is included.

  In other words, in the image data, self-airflow is generated, the resolution of the image data included in the print job is high, and the density of each pixel in the image data is the same and within a predetermined range. The target image data is included. In the case of (b), the predetermined range is a halftone density range.

  As shown in FIG. 4A, the image data 201 converted into drop data is image data of a high-density continuous ejection region, and an image printed based on the image data 201 is a print image 211. . At this time, since the image data 201 is image data of a high-density continuous ejection region, as shown in the enlarged image data 201a, pixels ejected at a high density are arranged at an interval of b1. When ejected based on the image data, as shown in the landing position 211a, a landing position shift of the ink droplet occurs, and an interval b2 is left between the landing pixels.

  However, as shown in the landing pixel 211b, when the ink droplet lands on the paper, the ink droplet bleeds on the paper, so that the distance from the adjacent landing pixel is shortened (in the example shown in the landing pixel 211b, contact or overlap). For this reason, even if wind ripple unevenness occurs in the high-density continuous ejection region, it becomes inconspicuous due to blurring of the landing pixels.

  On the other hand, as shown in FIG. 4B, the image data 202 converted into the drop data is halftone continuous discharge area image data, and an image printed based on the image data 202 is a print image 212. It is. In the printed image 212, a wind-pattern uneven area 212e where the wind-pattern unevenness is generated is formed so as to be conspicuous.

  Since the image data 202 is image data of a halftone continuous ejection region, pixels ejected at a medium density are arranged as shown in the enlarged image data 202a. When the ink is ejected based on the image data, as shown in the landing position 212a, a landing position shift of the ink droplet occurs, and an interval b4 is provided between the landing pixels.

  As shown in the landing pixel 212b, when ink droplets land on the paper, the ink droplets bleed on the paper, but the landing pixels ejected at a medium density have an interval b5. For this reason, in the halftone continuous ejection region, when the unevenness of the wind ripples occurs, the shading unevenness region 212e becomes conspicuous because the shading becomes more conspicuous.

  As shown in FIG. 4C, the image data 203 converted into drop data is image data of a low-density continuous ejection region, and an image printed based on the image data 203 is a print image 213. It is. At this time, since the image data 203 is image data of a low-density continuous ejection region, as shown in the enlarged image data 203a, pixels ejected at a low density are arranged at intervals of b7. When ejected based on the image data, as shown in the landing position 213a, an ink droplet landing position shift occurs, and an interval b8 is provided between the landing pixels.

  As shown in the landing pixel 213b, as with the landing pixel 211b and the landing pixel 212b, the ink droplet bleeds on the paper when it hits the paper, so the distance between the adjacent landing pixels becomes short. However, when landing at a low density, the original pixel interval b7 is wide, so even if the landing position interval is b8 due to the occurrence of wind ripple unevenness and the landing pixel 213b interval is b9, the apparent density is Has little effect. Therefore, in the low-density continuous ejection region, even if wind ripple unevenness occurs, it becomes inconspicuous due to the wide interval between the landing pixels.

  Therefore, in the inkjet printing apparatus 1 that is Embodiment 1 of the present invention, the print pattern uneven area 212e generated in the print image 212 of FIG. 4B is printed so as not to be noticeable.

<Functional Configuration of Inkjet Printing Apparatus 1>
Next, a functional configuration of the inkjet printing apparatus 1 that is Embodiment 1 of the present invention will be described.

  FIG. 5 is a diagram illustrating a functional configuration of the inkjet printing apparatus 1 that is Embodiment 1 of the present invention.

  As shown in FIG. 5, the inkjet printing apparatus 1 includes a side paper feed unit 10, an internal paper feed unit 20, a printing unit 30, a paper discharge unit 40, a reversing unit 50, an operation panel unit 70, and a control. Part 80. Among these configurations, the side paper feeding unit 10, the internal paper feeding unit 20, the printing unit 30, the paper discharge unit 40, and the reversing unit 50 have been described above, and a description thereof will be omitted.

  The control unit 80 is transmitted by the CPU 81, the ROM 82 storing the operation program of the CPU 81 and various tables, the image data read by the image reading unit (not shown), the computer device (not shown), and the like. The RAM 83 stores image data and a print job including various printing conditions from the operation panel unit 70 or a computer device (not shown).

  FIG. 6 is a diagram illustrating an example of a condition determination table stored in the ROM 82 of the control unit 80 included in the inkjet printing apparatus 1 according to the first embodiment of the present invention. (A) is a figure showing an example of a condition judgment table corresponding to mat paper, and (b) is a figure showing an example of a condition judgment table corresponding to plain paper. As will be described later, this condition determination table is a table for determining whether or not the image data is control target according to the type of printing paper in order to make the unevenness of the wind pattern inconspicuous.

  6 (a) and 6 (b), the number of pixels that are continuous at regular intervals in the main scanning direction, the time for continuous ejection, the interval between pixels in the sub-scanning direction determined by the transport belt 133, and the number of drops per unit area are associated. Is remembered. The number of pixels that are continuous at regular intervals in the main scanning direction indicates the density of pixels in the main scanning direction, the interval between pixels in the sub scanning direction indicates the density of pixels in the sub scanning direction, and the resolution of the image data is high. This is a condition for determining whether or not there is. In addition, it is a condition for determining whether or not the degree of occurrence of self-airflow is high, and a condition for determining whether or not it is a halftone area, based on the continuous discharge time and the number of drops per unit time. ing. As will be described later, this condition determination table is used to determine whether or not to switch to a low resolution in order to make the wind pattern unevenness inconspicuous. This condition determination table is obtained experimentally in advance.

  Returning to FIG. 5, the CPU 81 executes the operation program stored in the ROM 82, so that the entire apparatus, that is, the side paper feed unit 10, the internal paper feed unit 20, the printing unit 30, and the paper discharge unit 40 are displayed. The operation of the reversing unit 50 and the operation panel unit 70 is controlled. The CPU 81 also includes a determination unit 81a and an ink ejection control unit 81b.

  The determination unit 81a determines whether the image data to be printed is the control target image data for each page to be printed. Specifically, the determination unit 81a generates a self-airflow based on the self-airflow degree, and the resolution of the image data included in the print job is high resolution. It is determined whether or not the control target image data has the same density of each pixel in the data and a predetermined range.

  When the determination unit 81a determines that the image data is to be controlled, the ink discharge control unit 81b discharges ink by increasing the number of drops per pixel while maintaining the same total number of drops for the image data. In addition, when the inkjet heads 110, 112, and 114 are controlled to print at a low resolution, and the determination unit 81a determines that the image data is not the above-described control target image data, printing is performed at a resolution specified based on the image data. Thus, the inkjet heads 110, 112, and 114 are controlled.

<Operation of Inkjet Printing Apparatus 1>
Next, a detailed processing procedure of the inkjet printing apparatus 1 that is Embodiment 1 of the present invention will be described.

  FIG. 7 is a flowchart showing a processing procedure of the inkjet printing apparatus 1 according to the first embodiment of the present invention.

  As shown in FIG. 7, first, when the CPU 81 of the control unit 80 receives a print job (step S100 “YES”), the image data converted into the drop data included in the received job is 600 (dpi). Determine whether it is bitmapped at high resolution for printing at x600 (dpi) or bitmapped at low resolution for printing at 300 (dpi) x 300 (dpi) ( Step S105).

  If it is determined in step S105 that the image data is a low-resolution bitmap (NO), the ink ejection control unit 81b of the CPU 81 of the control unit 80 does not convert the resolution in step S100. Print processing is executed based on the drop data included in the received print job (step S160).

  On the other hand, when it is determined that the image data is a high-resolution bitmap (YES), the CPU 81 acquires the image data and paper type converted into drop data for each page from the received print job. (Step S110).

  Next, the determination unit 81a of the CPU 81 determines whether or not a gap, which is an interval between the inkjet unit 31 and the annular conveyance belt 133 provided on the opposite surface of the inkjet unit 31, is equal to or greater than a predetermined value (step S120). . Since the paper to be printed is different in thickness of the paper itself and the shape of the paper such as an envelope, a gap is set according to the paper type so that the paper can be printed appropriately without contacting the inkjet unit 31. . Therefore, the determination unit 81a determines a gap based on the paper type acquired in step S110, and determines whether the determined gap is equal to or greater than a predetermined value. Here, the wider the gap, the easier the landing position deviation occurs, and the more likely the wind ripple unevenness is.

  Therefore, if it is determined in step S120 that the gap is less than the predetermined value ("NO"), the landing position deviation is unlikely to occur, so the ink ejection control unit 81b is included in the print job received in step S100. A print process is executed based on the drop data (step S160).

  On the other hand, when it is determined that the gap is equal to or larger than the predetermined value (step S120 “YES”), the determination unit 81a determines whether there is control target image data based on the print job (step S130). Specifically, the determination unit 81a extracts a condition determination table corresponding to the sheet type acquired in step S110 from the condition determination table for each sheet type stored in the ROM 82, and adds the condition determination table to the drop data included in the print job. Based on this, if any one of C, M, Y, and K satisfies the condition of the extracted condition determination table, it is determined that there is control target image data. For example, when the paper type is “plain paper”, when a pixel that ejects K2 or more ink in the main scanning direction is continuously ejected by K ink for Y2 hours or more, a solid area of K single color is formed. It will be. When the pixel interval in the sub-scanning direction is V2 or more and the number of drops per unit area is “3” to “6” (drop), the K solid region is a halftone region. In such a case, it can be determined as control target image data.

  In step S130, when it is determined that there is control target image data (“YES”), the ink ejection control unit 81b converts the resolution and the ejection amount (step S140). Specifically, the ink ejection control unit 81b ejects ink by increasing the number of drops per pixel while maintaining the same total number of drops for the image data, and the resolution of the drop data in the sub-scanning direction is set. Conversion from 600 (dpi) to 300 (dpi). Thereby, the drop data converted in resolution and discharge amount is drop data having a resolution of 600 (dpi) × 300 (dpi).

  The CPU 81 executes a printing process based on the drop data generated in step S140 (step S160).

  FIG. 8 is an explanatory view schematically showing the resolution and discharge amount conversion processing in step S140 of the flowchart of FIG. 8 in the inkjet printing apparatus 1 which is Embodiment 1 of the present invention. (A) shows the drop data of the control target image data included in the received print job, and (b) shows the ink droplet when the wind pattern unevenness occurs when printing based on the drop data. (C) is a diagram showing the landing position where ink droplets land when printing is performed based on the drop data obtained by converting the resolution in the sub-scanning direction and the ejection amount. FIG. 6D is a diagram showing a state where the ink oozes on the paper when the ink droplet has landed at the landing position shown in FIG.

As shown in FIG. 8A, the drop data of the control target image data included in the received print job is 600 (dpi) × 600 (dpi) image data in the main scanning direction and the sub-scanning direction. The pixels are arranged so that they are printed with a constant tone density,
Then, when printing is performed based on the drop data shown in FIG. 8A, the ink droplet lands at a slightly shifted position as shown in FIG. 8B due to the influence of the turbulence of the airflow. . As described above, due to the deviation of the landing position of the ink droplet, a wide space such as a1 is left between the pixels, and this is recognized by the user as wind pattern unevenness.

  At this time, if the resolution in the sub-scanning direction is converted from 600 (dpi) to 300 (dpi) and the number of drops per pixel is increased while maintaining the same total number of drops for the control target image data, Compared with the case of discharging at the resolution, the degree of occurrence of the self-airflow can be reduced, and the increase in the number of drops makes the ink droplets heavier and less affected by the airflow. Therefore, as shown in FIG. 8C, when the ink droplets are landed in a state where the pixels in the sub-scanning direction are thinned in half and the number of drops is increased, it becomes difficult to be affected by the transport airflow. Ink droplets land at an interval a2 that is narrower than the interval a1 shown in FIG.

  Specifically, in the example of the drop data shown in FIG. 8A, if the number of drops per pixel is 2 drops, 8 columns in the main scanning direction and 4 columns in the sub scanning direction are arranged. Therefore, the total number of drops for this control target image data is “64” drops.

  In the example shown in FIG. 8C, since the pixels in the sub-scanning direction are thinned out in half, eight columns in the main scanning direction and two columns in the sub-scanning direction are arranged. In order to set the total number of drops to “64” drops for this control target image data, the number of drops per pixel is set to “4” drops.

  In this way, the number of drops per pixel is increased to “4” drops, thereby making it less susceptible to the influence of the carrier airflow.

  Further, as shown in FIG. 8D, since the number of drops is increased, the landed ink droplets are likely to spread and spread on the paper, and the distance between the pixels is shortened as an interval a3. As a result, it is difficult for the user to recognize the wind pattern unevenness. That is, the wind pattern unevenness is less noticeable.

  As described above, according to the ink jet printing apparatus 1 that is Embodiment 1 of the present invention, the ink ejection control unit 81b has the resolution of the image data included in the print job, and each of the image data in the image data When the pixel density is the same and within the specified range, self-air flow is generated based on the amount of ink ejected from the nozzle per unit time, causing the ink ejected from the nozzle to go straight against the paper transport air current Since the resolution of the image data is converted to a lower resolution based on the degree of self-flow indicating the degree, and the ink is ejected from each nozzle so as to increase the density of each pixel in the image data, the ejected ink droplets Since it becomes difficult to be affected by the air flow generated by ink ejection or paper conveyance, the amount of landing position deviation is reduced, and the unevenness of the wind pattern is less noticeable.

  Further, in the first embodiment of the present invention, in order to increase the number of drops per pixel while keeping the same total number of drops for the control target image data, the pixels in the sub-scanning direction are thinned in half. However, the thinning may be performed in half of the main scanning direction and the sub-scanning direction.

  In order to change the resolution in the main scanning direction from 600 (dpi) to 300 (dpi), as described above, as shown in the inkjet heads 110a to 110f, the same color ink is stored in one inkjet head. In this case, printing can be performed by switching the resolution to 600 (dpi) or 300 (dpi) by controlling the ink to be ejected from either the upstream or downstream nozzle row. That is, by converting the main scanning direction and the sub-scanning direction to low resolution, 600 (dpi) × 600 (dpi) drop data can be changed to 300 (dpi) × 300 (dpi) drop data.

  FIG. 9 is an explanatory view schematically showing the resolution and discharge amount conversion processing in step S140 in the flowchart of FIG. 8 in the inkjet printing apparatus 1 that is Embodiment 1 of the present invention. (A) shows the drop data of the control target image data included in the received print job, and (b) shows the ink droplet when the wind pattern unevenness occurs when printing based on the drop data. (C) shows the landing position where ink droplets land when printing is performed based on drop data obtained by converting the resolution and discharge amount in the main scanning direction and sub-scanning direction. (D) is a diagram showing a state in which ink oozes on paper when ink droplets have landed at the landing positions shown in (c).

As shown in FIG. 9A, the drop data of the control target image data included in the received print job is 600 (dpi) × 600 (dpi) image data in the main scanning direction and the sub-scanning direction. The pixels are arranged so that they are printed with a constant tone density,
Then, when printing is performed based on the drop data shown in FIG. 9A, the ink droplets land at a slightly shifted position as shown in FIG. 8B due to the influence of the turbulence of the airflow. . As described above, due to the deviation of the landing position of the ink droplet, a wide space such as a1 is left between the pixels, and this is recognized by the user as wind pattern unevenness.

  At this time, the resolution in the main scanning direction and the sub-scanning direction is converted from 600 (dpi) to 300 (dpi), and the number of drops per pixel is increased while maintaining the same total number of drops for the control target image data. Then, compared with the case where the resolution is converted to 300 (dpi) only in the sub-scanning direction, the generation degree of the self-airflow is further reduced, and the ink droplets become heavy and are not easily affected by the airflow. Therefore, as shown in FIG. 9C, when the ink droplets are landed in a state where the pixels in the main scanning direction and the sub-scanning direction are thinned in half and the number of drops is increased, FIG. The ink droplets land at an interval a5 that is narrower than the indicated interval a4.

  Specifically, in the example of drop data shown in FIG. 9A, if the number of drops per pixel is 2 drops, 8 columns in the main scanning direction and 4 columns in the sub scanning direction are arranged. Therefore, the total number of drops for this control target image data is “64” drops.

  In the example shown in FIG. 9C, since the pixels in the main scanning direction and the sub-scanning direction are thinned out in half, four columns in the main scanning direction and two columns in the sub-scanning direction are arranged. In order to set the total number of drops to “64” drops for this control target image data, the number of drops per pixel is set to “8” drops.

  Thus, by increasing the number of drops per pixel to “8” drops, it is further less susceptible to the influence of the transport airflow.

  Further, as shown in FIG. 9 (d), since the number of drops is increased to “8” drops, the landed ink droplets are more likely to spread on the paper and further expand, and there is an interval a6 between the pixels. As a result, it becomes difficult for the user to recognize the wind pattern unevenness. That is, the wind pattern unevenness is less noticeable.

  As described above, according to the inkjet printing apparatus 1 that is Embodiment 1 of the present invention, the number of drops per pixel is increased while the number of drops is the same for the control target image data, and ink is ejected. In addition, since the inkjet heads 110, 112, and 114 are controlled so as to print at a low resolution in the main scanning direction and the sub-scanning direction, the discharged ink droplets are less susceptible to the influence of the conveying airflow, so that the landing position The amount of deviation is reduced, and the unevenness of the wind pattern is less noticeable.

  In the first exemplary embodiment of the present invention, when the control target image data includes a single color solid image, the ink discharge control unit 81b converts the resolution and the discharge amount. However, the present invention is not limited to the single color solid image, and a plurality of inks are used. Even if it is a solid region, if there is control target image data, the unevenness of the wind pattern can be made inconspicuous by converting the resolution and the discharge amount for the control target image data.

  In Embodiment 1 of the present invention, in order to increase the number of drops per pixel while keeping the same total number of drops for the control target image data, the pixels in the sub-scanning direction are thinned in half, or the main scanning is performed. Although the pixels in the direction and the sub-scanning direction are thinned out in half, the pixels may be thinned out in half only in the main scanning direction, and the thinning out is not limited to half, so that it becomes 2/3 or 1/3. Pixels may be thinned out.

  In the first embodiment of the present invention, the inkjet heads are arranged in a direction (main scanning direction) orthogonal to the paper transport direction, and the paper transported on the transport path is based on image data. The line-type inkjet printing apparatus that prints by ejecting ink from the nozzles of the inkjet head has been described as an example, but the present invention is not limited to this.

  A serial type printer that has an inkjet head that moves in a direction (main scanning direction) orthogonal to the paper transport direction, and that prints by ejecting ink from the nozzles of the inkjet head based on image data on the transported paper. An ink jet printing apparatus may be used.

  In a serial-type inkjet printing apparatus, a plurality of nozzles are parallel to a paper transport direction (sub-scanning direction) on one ink jet head that moves in a direction (main scanning direction) orthogonal to the paper transport direction. The rows are arranged, and the positions of the nozzles in the sub-scanning direction are shifted for each of the plurality of nozzle rows, and while the conveyed paper is stopped, the inkjet head is moved in the main scanning direction, Ink is ejected from at least one nozzle row of the plurality of nozzle rows on the paper.

  Even in the case of such a serial type ink jet printing apparatus, when it is determined that the image data has high resolution and the control target image data is present in the image data, the ink ejection control unit 81b adds the control target image data to the control target image data. In contrast, the number of drops per pixel is increased while the number of all drops is the same, and ink is ejected, and the inkjet heads 110, 112, and 114 are controlled so as to print at a low resolution, thereby reducing the influence of the air flow. It is possible to reduce the wind pattern unevenness.

  That is, the inkjet head may be configured such that a plurality of nozzle rows are arranged in parallel and eject ink from the nozzle rows while moving relative to the paper P.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printing apparatus 10 ... Side paper feed part 11 ... Paper feed stand 12 ... Primary paper feed part 14 ... Secondary paper feed part 30 ... Printing part 31 ... Inkjet unit 40 ... Paper discharge part 50 ... Inversion part 70 ... Operation Panel unit 80 ... Control unit 81 ... CPU
81a: determination unit 81b: ink ejection control unit 82: ROM
83 ... RAM
110, 112, 114 ... inkjet head

Claims (3)

A plurality of nozzle rows are arranged in the inkjet head arranged above the conveyance path so as to be shifted in the conveyance direction of the printing paper conveyed on the conveyance route, and from each nozzle of each nozzle row based on the print job The ink jet head is an ink jet printing apparatus capable of printing at a first resolution or a second resolution higher than the first resolution when each ink is ejected and printed on printing paper,
When the resolution of the image data included in the print job is the second resolution, and the density of each pixel in the image data is the same and within a predetermined range, the ink ejection amount of the nozzle per unit time The resolution of the image data is calculated based on the self-airflow degree, which indicates the degree of self-airflow that causes the ink ejected from the nozzles to advance straightly against the airflow of the printing paper. An ink jet printing apparatus comprising a control unit that converts ink into a resolution and ejects ink from each nozzle so as to increase the density of each pixel in the image data. The image data has a self-airflow based on the self-airflow degree, the resolution of the image data included in the print job is the second resolution, and the density of each pixel in the image data Determining means for determining whether or not the image data is control target image data that is the same and within a predetermined range;
A distance variable means capable of varying the distance between the inkjet head and the transport path;
2. The inkjet printing apparatus according to claim 1, wherein the control unit performs a determination process by the determination unit when a distance between the inkjet head and the transport path is a predetermined value or more. Storage means for storing a determination table for determining whether the image data is the control target image data according to the type of printing paper;
The inkjet printing apparatus according to claim 2, wherein the determination process is performed by the determination unit based on a type of print paper printed based on the print job with reference to the determination table.