JP2020121420A - Inkjet printing device - Google Patents

Abstract

To provide an inkjet printing device configured to prevent density unevenness in a joint between adjacent inkjet heads and a line from thickening or thinning.SOLUTION: The inkjet printing device comprises: a line head which has a plurality of head rows in which an inkjet heads having a plurality of nozzles for discharging ink to a printing medium arranged therein are arranged with respect to a direction orthogonal to a carrying direction of the printing medium, where the plurality of head rows are arranged in the carrying direction and ranges of some nozzles of the inkjet heads adjacent to each other in the direction orthogonal to the carrying direction are overlappingly arranged side by side with respect to the carrying direction; and a control part that controls the line head so that printing processing is applied to the printing medium. The control part dynamically changes a position of a joint J between the adjacent inkjet heads, in an overlapped range R of the nozzles of the adjacent inkjet heads, on the basis of characteristics of image data on an input object to be printed.SELECTED DRAWING: Figure 9

Description

The present invention relates to an inkjet printing apparatus including a line head in which a plurality of inkjet heads are arranged in a staggered pattern.

Conventionally, an inkjet printing apparatus has been proposed which performs a printing process by ejecting ink from an inkjet head onto a print medium that is transported on a transport path.

As such an ink jet printing apparatus, a line type ink jet printing apparatus has been proposed in which a plurality of ink jet heads are arranged in a direction orthogonal to the transport direction of a print medium, and the plurality of ink jet heads perform printing for one line. ..

In a line-type inkjet printing apparatus, a configuration in which inkjet heads are arranged in a staggered manner is common, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-242242. In the line-type inkjet printing apparatus having such a configuration, since printing is performed without gaps in all areas, some inkjet heads that are adjacent to each other in the direction orthogonal to the transport direction of the print medium overlap some nozzles (overlap). Be arranged). In this overlapped portion, if it is printed as it is, the ink density is doubled. Therefore, a joint is set between adjacent inkjet heads, and the printing range is distributed with the joint as a boundary. As a result, an image having a width of A3 or more can be printed with a short inkjet head.

JP 2004-154950 A

However, at the time of actually assembling the inkjet heads, the installation positions of the inkjet heads are displaced (errors) in units of microns. Due to this shift, unintended density unevenness occurs at the joint between adjacent inkjet heads. In order to prevent this, joint correction is performed in which the print density is distributed by the nozzles near the joint.

Regarding this joint correction, conventionally, in the actual assembly process, the displacement amount of the installation position of the inkjet head was measured, the nozzle position (joint) suitable for the correction was specified from that value, and then the joint correction was performed at that position. Do it statically. Most image data do not bother with the joints in this method, but problems occur with specific image data.

For example, in an image composed of thin lines such as a spreadsheet chart, if there is a ruled line portion at the joint, if the two nozzle positions of the joint are separated or too close, the ruled line looks thick or thin. Therefore, there is a problem in image reproducibility at the joint. Further, when the image data includes a solid image having a relatively low density, there is a problem that density unevenness occurs due to the distance between the two nozzle positions at the joint.

In view of the above circumstances, it is an object of the present invention to provide an inkjet printing apparatus capable of preventing density unevenness and thickening or thinning of lines at the joints between adjacent inkjet heads.

In an inkjet printing apparatus of the present invention, an inkjet head in which a plurality of nozzles for ejecting ink to a print medium are arranged has a plurality of head rows arranged in a direction orthogonal to a transport direction of the print medium, A line head in which a plurality of head rows are arranged in the transport direction, and some nozzle ranges of the inkjet heads that are adjacent to each other in the direction orthogonal to the transport direction are arranged side by side in the transport direction in an overlapping manner. And a control unit for performing a printing process on a print medium by controlling, based on the characteristics of the input image data of the print target, within the range of overlapping nozzles of adjacent inkjet heads, Dynamically change the position of the joint.

According to the inkjet printing apparatus of the present invention, the position of the joint is dynamically changed within the range of the overlapping nozzles of the adjacent inkjet heads based on the characteristics of the input image data of the printing target. It is possible to prevent uneven density and thickening or thinning of lines at the joints between adjacent inkjet heads.

The figure which shows the schematic structure of one Embodiment of the inkjet printing apparatus of this invention. Top view of head unit Block diagram showing a schematic configuration of a control system of the inkjet printing apparatus shown in FIG. An example of inkjet heads arranged in a staggered manner (A) and an enlarged view of an overlapping portion of adjacent inkjet heads (B). An enlarged view (A) of an overlapping portion of adjacent ink jet heads and an enlarged view (B) near a joint. Diagram for explaining the case where a seam exists on a thin line included in image data FIG. 3 is a diagram for explaining a case where a seam exists in a solid area of low density included in image data. The figure which shows an example of the image data which has the characteristic that the position of a joint needs to be changed. FIG. 8 is an enlarged view of a range A in FIG. 8 and a view showing a nozzle for printing the range A. FIG. 8 is an enlarged view of the range D in FIG. 8 and a view showing a nozzle for printing the range D. Diagram showing an example of the error diffusion table The figure which shows an example of the number of the nozzle in an overlap range. Diagram showing an example of nozzles assigned to each section FIG. 8 is an enlarged view of a range C in FIG. 8 and a view showing a nozzle for printing the range C. FIG. 8 is an enlarged view of the range B in FIG. 8 and a view showing a nozzle for printing the range B. Flowchart for explaining the position change process of the joint The figure for demonstrating the case where one of the adjacent inkjet heads is installed incliningly.

Hereinafter, an embodiment of an inkjet printing apparatus of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus according to the present embodiment is characterized by the method of setting the joint between adjacent inkjet heads. First, the overall configuration will be described. FIG. 1 is a diagram showing a schematic configuration of an inkjet printing apparatus 1 of this embodiment. The up, down, left, and right directions shown in FIG. 1 are the up, down, left, and right directions of the inkjet printing apparatus 1 of this embodiment.

As shown in FIG. 1, the inkjet printing apparatus 1 of the present embodiment includes a side paper feed unit 10, an internal paper feed unit 20, a print processing unit 30, a paper discharge unit 40, a reversing unit 50, and a control unit. 60 and an operation panel 70.

The print processing unit 30, the internal paper feeding unit 20, and the control unit 60 are housed and installed in a housing made of metal or resin. In addition, the side paper feed unit 10, the paper discharge unit 40, and the reversing unit 50 are installed in a state where a part of the side paper feed unit 10, the paper discharge unit 40, and the reversing unit 50 are housed inside the housing and part of the housing protrudes outside the housing.

The side paper feed unit 10 is a paper feed tray 11 on which the print medium P is placed, and a primary paper feed unit that feeds out only the uppermost print medium P from the paper feed tray 11 and conveys it onto the paper feed conveyance path FR. 12 and a secondary paper feed unit 14 that carries the print medium P carried by the primary paper feed unit 12 onto the circulation carrier path CR.

The internal paper feeding section 20 is a primary paper feeding section 21a on which the printing medium P is placed, and a primary paper feeding section for feeding only the uppermost printing medium P from the paper feeding table 21a and carrying it to the paper feeding path FR. 22a, a paper feed table 21b on which the print medium P is placed, a primary paper feed section 22b for feeding only the uppermost print medium P from the paper feed table 21b and carrying it to the paper feed path FR, The paper feed table 21c on which the medium P is placed, the primary paper feed section 22c for feeding only the uppermost print medium P from the paper feed tray 21c and carrying it to the paper feed carrying path FR, and the print medium P are placed. It is provided with a paper feed table 21d to be placed and a primary paper feed section 22d for feeding out only the uppermost print medium P from the paper feed table 21d and carrying it to the paper feed path FR.

As described above, the print medium P is conveyed from the side paper feed unit 10 or the internal paper feed unit 20 to the secondary paper feed unit 14, and the print medium P is further carried from the reversing unit 50 described later.

Therefore, in front of the secondary paper feed unit 14 in the transport direction, the transport path of the print medium P fed from the internal paper feed unit 20 and the print medium P on which one surface transported from the reversing unit 50 is printed. There is a confluence point where the transportation route of the vehicle merges. With reference to this confluence point, the path on the side of the paper feed mechanism is called the paper feed conveyance path FR, and the other paths are called the circulation conveyance path CR.

The print processing unit 30 includes a head unit 31 and an annular transport belt 133 provided so as to face the head unit 31.

The conveyor belt 133 is formed of an annular endless belt and has a large number of suction holes. The print medium P fed from the secondary paper feed unit 14 is conveyed to the circular conveyance belt 133. Then, the print medium P is adsorbed onto the conveyor belt 133 by the suction of the suction fans 131 and 132 installed on the back side of the conveyor road surface of the conveyor belt 133, and is conveyed at a predetermined conveying speed. Then, while the print medium P is being transported by the transport belt 133, ink is ejected from the head unit 31 to the print medium P, whereby the print process is performed on the print medium P.

The head unit 31 includes four line heads 32a, 32b, 32c, 32d and a head holder 33 in which the four line heads 32a, 32b, 32c, 32d are installed.

Each of the line heads 32 a to 32 d extends in a direction orthogonal to the transport direction of the print medium P and ejects ink onto the print medium P transported by the transport belt 133. As shown in FIG. 1, the four line heads 32a to 32d are arranged at predetermined intervals along the conveyance path of the print medium P. The four line heads 32a to 32d eject ink of different colors (for example, black, cyan, magenta, and yellow).

The head holder 33 is a member on which the inkjet head 34 included in each of the line heads 32a to 32d is installed. FIG. 2 is a top view of a state in which the inkjet head 34 of each of the line heads 32a to 32d is installed in the head holder 33 as seen from above.

The head holder 33 is composed of a box-shaped support member, and the bottom surface of the head holder 33 is formed with a plurality of installation holes into which the respective inkjet heads 34 are fitted and installed. The installation hole is a through hole, and is formed so that the ink ejection surface of each inkjet head 34 is exposed outside the bottom surface of the head holder 33.

The dotted line rectangles shown in FIG. 2 indicate the ranges in which the six inkjet heads 34 of each of the line heads 32a to 32d are arranged.

As shown in FIG. 2, each of the line heads 32a to 32d has a head row in which three inkjet heads 34 are arranged at equal intervals in a direction (front-back direction) orthogonal to the transport direction of the print medium P. Each of the line heads 32a to 32d has two head rows, and the two head rows are arranged in the transport direction. Further, the two head rows of each of the line heads 32a to 32d are arranged such that the ranges of some nozzles of the inkjet heads 34 that are adjacent to each other in the direction orthogonal to the transport direction are aligned and overlap in the transport direction. There is. That is, the inkjet heads 34 in the two rows of heads are arranged in a staggered manner such that the inkjet heads 34 adjacent to each other in the direction orthogonal to the transport direction overlap by a predetermined number of nozzles.

Then, printing is performed by the inkjet heads 34 of the two head rows of each of the line heads 32a to 32d to form a print image of one line.

The print medium P that has been subjected to the print processing by the print processing unit 30 is transported on the circulation transport path CR by transport rollers or the like arranged on the circulation transport path CR. A switching mechanism 43 for switching between guiding the print medium P transported on the circulation transport route CR to the paper discharge unit 40 or recirculating on the circulation transport route CR is provided on the circulation transport route CR. There is. The switching mechanism 43 specifically switches between the transport path on the side of the paper discharge unit 40 and the transport path on the side of the reversing unit 50.

The paper discharge unit 40 has a tray-shaped paper discharge base 41 protruding from the housing of the inkjet printing apparatus 1, and a pair of paper discharge rollers 42 for discharging the print medium P onto the paper discharge base 41. Then, the print medium P guided by the switching mechanism 43 to the transport path on the side of the paper discharge unit 40 is discharged onto the paper discharge tray 41 by the paper discharge rollers 42.

The reversing unit 50 conveys the print medium P from the circulation conveyance route CR to the reversal stage 51, and the reversal table 51 for reversing the print medium P, and the print medium P conveyed to the reversal stage 51 on the circulation conveyance route CR. And a reversing roller 52 for returning to.

The print medium P guided to the reversing unit 50 by the switching mechanism 43 is conveyed from the circulation conveyance path CR to the reversal table 51 by the reversal roller 52, and is returned from the reversal table 51 to the circulation conveyance path CR again so that the front and back are reversed. In this state, it is conveyed on the circulation conveyance path CR. Then, the print medium P whose front and back are reversed is again conveyed toward the print processing unit 30 by a plurality of rollers such as the conveyance roller 53 provided on the circulation conveyance path CR.

The operation panel 70 is composed of a touch panel having a liquid crystal display, displays various setting input screens, and receives various setting inputs such as a print start instruction input.

FIG. 3 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus 1 of this embodiment.

The control unit 60 controls the entire inkjet printing apparatus 1, and includes an FPGA (Field-Programmable Gate Array), a semiconductor memory, a hard disk, and the like. The control unit 60 controls the operation of each unit of the inkjet printing apparatus 1 by operating the FPGA and other electric circuits. Although the FPGA is used in the present embodiment, the present invention is not limited to this, and the control unit 60 includes a CPU (Central Processing Unit) and causes the CPU to execute a program stored in advance in a semiconductor memory or a hard disk. By doing so, the operation of each unit of the inkjet printing apparatus 1 may be controlled.

Further, the control unit 60 communicates with the control unit 90 of the print job output device 2 and receives the print job output from the control unit 90. Then, the control unit 60 controls each inkjet head 34 of the head unit 31 of the print processing unit 30 based on the image data of the print target included in the input print job. At this time, the control unit 60 is orthogonal to the transport direction. The connection correction between the adjacent inkjet heads 34 in the direction is performed. Hereinafter, this joint correction will be described in detail.

First, in the present embodiment, as described above, each of the line heads 32a to 32d has two head rows, and the ink jet heads 34 are arranged in a staggered manner in the two head rows. Then, as shown in FIG. 4A, the inkjet heads 34 that are adjacent to each other in the direction orthogonal to the transport direction of the print medium P are arranged so as to overlap each other by a predetermined number of nozzles, and the print head P moves in the transport direction. Along with this, the print images are printed without gaps. Since FIG. 4A is a schematic diagram, only four inkjet heads 34 are shown. The row of nozzles 35 of each inkjet head 34 is indicated by a straight line.

FIG. 4B is an enlarged view of the overlapping portion of the adjacent ink jet heads 34 shown by the dotted squares in FIG. 4A. In FIG. 4B, the inkjet head 34_1 and the inkjet head 34_2 are adjacent to each other, and the overlapping region of these inkjet heads (corresponding to the range of the overlapping nozzles of the adjacent inkjet heads of the present invention) is indicated by R. ..

In the overlap region R, the joint J is set in advance so that the print range of the inkjet head 34_1 and the print range of the inkjet head 34_2 do not overlap. Then, with the joint J as a boundary, the mask range mr1 of the inkjet head 34_1 and the mask range mr2 of the inkjet head 34_2 are set, and the control unit 60 controls the ink from the nozzles 35 included in the mask range mr1 and the mask range mr2. Is controlled so as not to discharge. The joint J is set in advance by acquiring a displacement amount from the designed installation position of the inkjet head 34 by printing a test pattern or the like.

5A is a view similar to the enlarged view shown in FIG. 4B, and FIG. 5B is an enlarged view near the joint J in FIG. 5A. Even when the joint J is set as described above, on the joint J, when the printing range of the nozzle 35_1 of the inkjet head 34_1 and the printing range of the nozzle 35_2 of the inkjet head partially overlap and ink is ejected as usual, The concentration becomes high.

Therefore, the control unit 60 controls the nozzles 35x_1 of the inkjet head 34_1 and the nozzles 35x_2 of the inkjet head 34_2 so as to eject the ink amount of 100% of the ink amount according to the image data. The nozzles 35_1 and the nozzles 35_2 are controlled so that the ink amount of 50% of the ink amount corresponding to the image data is ejected, and the nozzles 35_1 and the nozzles 35_2 form one dot Dt. As a result, it is possible to prevent the density unevenness that occurs at the joints for most image data.

However, depending on the characteristics of the image data, an appropriate print image may not be obtained even if the above-described joint correction is performed. Specifically, for example, when a straight line extending in the transport direction is printed by the two nozzles 35 on the joint J, as shown by a dotted ellipse in FIG. Unable to get print image.

Further, when a solid area having a relatively low density is printed, the density of the portion printed by the two nozzles 35 on the joint J becomes high as shown by a dotted ellipse in FIG. 7, and density unevenness occurs. The solid area is an area formed by continuously ejecting ink from the nozzles 35 of the inkjet head 34 in the transport direction and in a direction orthogonal to the transport direction.

Therefore, the control unit 60 of the present embodiment changes the position of the joint J based on the characteristics of the image data to be printed included in the input print job. Hereinafter, the change of the position of the joint J will be described in detail.

FIG. 8 is a diagram showing an example of image data having a feature that the position of the joint J needs to be changed. First, a case where a preset joint J exists in a range A shown by a dotted ellipse in FIG. 8 will be described. FIG. 9 is an enlarged view of the range A of FIG. 8 and a view showing the nozzle 35 for printing the range A.

As shown in FIG. 9, when the seam J exists in a solid area having a relatively low density (corresponding to the low density area of the present invention), density unevenness may occur on the seam J as described above. Therefore, the control unit 60 changes the joint J existing in the solid area having the relatively low density to the area having the relatively high density existing in the overlap area R. P1 and P2 shown in FIG. 9 are nozzles on the joint J before the change, and Pn1 and Pn2 are nozzles on the joint after the change.

That is, the control unit 60 includes a solid area whose image data is equal to or less than a preset first density threshold value, a preset joint J exists in the solid area, and an overlap area R is preset. If there is a high-density area that is equal to or higher than the set second density threshold, the joint is changed to the high-density area.

As described above, by changing the joint from the low density area to the high density area, the seam can be made inconspicuous, and the occurrence of density unevenness in the low density area can be prevented.

When the joint J exists in the solid area where the density is low as described above, the high density area may not exist in the overlap area R. Specifically, when the preset joint J exists in the range D indicated by the dotted ellipse in FIG. 8, there is no high-density region in the vicinity thereof. FIG. 10 is an enlarged view of the range D of FIG. 8 and a view showing the nozzle 35 for printing the range D. As shown in FIG. 10, since there is no high-concentration region in the overlap region R in the range D, the joint J as described above cannot be changed.

Therefore, when a preset joint J exists in a low-density area such as the range D shown in FIG. 8, the control unit 60 sets the low-density area in the overlap area R for each line to be printed. Change the position of the joint.

That is, the control unit 60 extends in the direction orthogonal to the transport direction when the image data includes a solid area having a density threshold equal to or lower than a preset density threshold and the preset joint J exists in the solid area. The position of the joint is changed in the overlap region R for each line.

In this case, all the nozzles 35 (nozzles shown by diagonal lines) existing in the overlap region R shown in FIG. 10 can be nozzles on the joint. The control unit 60 randomly changes the position of the joint for each line from a plurality of joint candidates that can be set in the overlap region R, for example. As a method of randomly determining the position of the joint, a known method can be used, and for example, an error diffusion method can be used. Hereinafter, a method of determining the joint position using the error diffusion method will be described.

First, the control unit 60 acquires one row of image data extending in the transport direction at the position corresponding to the joint J before the change. The one row of image data may be one row of image data from the leading edge to the trailing edge of the low density area in the transport direction, or may be one column of image data from the leading edge to the trailing edge of the print medium P in the transport direction. .. Here, it is assumed that the control unit 60 acquires one row of image data from the leading end to the trailing end in the transport direction of the low density region. Further, it is assumed that the control unit 60 acquires the pixel data D1 to DN as one row of image data. D1 is the pixel data at the leading end of the image data of one column, DN is the pixel data at the trailing end, and 1 to N mean the numbers of each line of the image data extending in the direction orthogonal to the carrying direction. .. In addition, each pixel data D1 to DN is assumed to be an integer value of 0 to 255. For example, when the joint of the line including the pixel data D1 is the joint J before the change shown in FIG. 10, the pixel data D1 is distributed to the nozzles P1 and P2 and printed by the two nozzles P1 and P2.

Next, the control unit 60 performs error diffusion processing on the image data composed of the pixel data D1 to DN. Specifically, the control unit 60 first compares the pixel data D1 with the reference pixel data L0=127.

Then, the control unit 60 sets D1 to 1 when L0<D1 and sets D1 to zero when D1≦L0. For example, the error diffusion table shown in FIG. Spread. Specifically, when the target pixel TP is D1 and L0<D1, the control unit 60 adds (D1-255)×5/16 to the pixel data D2, and D1≦L0. In this case, D1×5/16 is added to the pixel data D2.

Then, as a result of adding a value according to the error diffusion table to the pixel data D2, the pixel data D2 becomes a value having a small number portion such as 128.13. The control unit 60 acquires this minority portion and holds it as a2=0.13.

Next, the control unit 60 compares the pixel data D2 to which the error has been added with the reference pixel data L0, and adds the value corresponding to the error diffusion table to the next pixel data D3 based on the comparison result. Then, a small part of the pixel data D3 after the addition is acquired and held as a3. After that, the control unit 60 repeatedly performs the above-described calculation for the pixel data D3 to DN, and acquires and holds the minority portions a4 to aN. That is, the control unit 60 acquires and holds a1 to aN corresponding to the pixel data D1 to DN of one column. Note that a1 is a constant zero. Finally, although D1 to DN are 0 or 1, this value is a value obtained in the above-described error diffusion calculation process and is not used in the print process.

On the other hand, the control unit 60 divides the range of 0 to 1 into 6 equal parts to set 6 sections, and sets the nozzles on the joints corresponding to the respective sections. For example, when the nozzles in the overlap region R are numbered as shown in FIG. 12, the control unit 60 selects (P11, P21) as the nozzle on the joint with respect to the first section as shown in FIG. Set, (P12, P22) is set for the second division, (P13, P23) is set for the third division, and (P14, P24) is set for the fourth division. , (P15, P25) are set for the fifth division, and (P16, P26) are set for the sixth division.

Then, the control unit 60 determines which of the first to sixth sections the values of a1 to aN included in the low concentration area belong to, and the lines 1 to N of the low concentration area are determined. The position of the joint of each line 1-N is determined by determining the nozzle on the joint at. Specifically, for example, when the value of a1 belongs to the first section, the control unit 60 specifies the nozzle P11 and the nozzle P21 as the nozzles on the joint of the line 1, and these two nozzles P11. , P21 to distribute pixel data to print one dot, and when the value of a2 belongs to the third section, the nozzles P13 and P23 are specified as nozzles on the joint of line 2, Pixel data is distributed to the two nozzles P13 and P23 to print one dot. Accordingly, the control unit 60 can randomly determine the position of the joint for each line.

Although the above description is an example using the error diffusion method, for example, using random numbers, (P11, P21), (P12, P22), (P13, P23), (P14, P24) shown in FIG. , (P15, P25) and (P16, P26) may be determined as the nozzle on the joint. However, the method using the above-described error diffusion method can arrange the joints according to the characteristics of the image.

By randomly determining the seams for each line in this manner, the seams can be made inconspicuous, and density unevenness in a solid area of low density can be suppressed.

Next, a case where a preset joint J exists on a line extending in the transport direction will be described. FIG. 14 is an enlarged view of the range C in FIG. 8 including a line extending in the transport direction and a view showing the nozzle 35 for printing the range C. As shown in FIG. 14, when the joint J exists on the line extending in the transport direction, the line may become thick or thin as described above.

Therefore, the control unit 60 changes the joint J existing on the line to a range other than the line in the overlap region R. P1 and P2 shown in FIG. 14 are nozzles on the joint J before the change, and Pn1 and Pn2 are nozzles on the joint after the change. The control unit 60 sets, for example, the nozzles Pn1 and Pn2 adjacent to the nozzles P1 and P2 on the joint J before the change as new nozzles on the joint.

That is, when the image data includes a line extending in the transport direction and a preset joint exists on the line, the control unit 60 changes the joint to a range other than the line. Regarding the method of detecting the line included in the image data, for example, the line may be detected by scanning the image data in a direction orthogonal to the transport direction for each line and detecting the density peak. You may make it detect using a filter.

By changing the position of the joint in this way, it is possible to prevent thickening or thinning of the lines included in the image data.

Note that, for example, when the preset joint J exists on the line extending in the direction orthogonal to the transport direction, the control unit 60 does not change the preset joint J. FIG. 15 is an enlarged view of the range B in FIG. 8 including a line extending in the direction orthogonal to the transport direction and a view showing the nozzle 35 for printing the range B. In this case, the control unit 60 leaves the nozzles on the joint J as the nozzles P1 and P2 without changing the joint J.

The control unit 60 of the present embodiment determines whether or not the position of the joint J described above needs to be changed for each line of image data, and changes the position of the joint for each line as necessary.

The above is the description of the change of the position of the joint by the control unit 60 of the present embodiment.

Returning to FIG. 3, the print job output device 2 is composed of a computer. The print job output apparatus 2 is installed with a document creation application for creating image data to be printed and a printer driver for creating a print job including the image data. The print job output device 2 generates a print job based on the image data created by the document creation application and print conditions such as the number of print copies set on the printer driver, and outputs the print job to the inkjet printing device 1.

Next, the process for changing the position of the joint of the inkjet printing apparatus 1 according to the above embodiment will be described with reference to the flowchart shown in FIG.

First, a print job is output from the print job output device 2 and accepted by the control unit 60 of the inkjet printing device 1 (S10).

The control unit 60 associates the image data included in the input print job with the preset position of the joint J (S12). For example, the control unit 60 calculates a feature amount such as a low-density region, a high-density region, and a line extending in the transport direction, which will be described later, included in the image data, and associates the feature amount with a preset position of the joint J. Attach. In the present embodiment, the control unit 60 sequentially receives the image data for each line, and sequentially performs the position changing process of the joint for each line.

First, the control unit 60 confirms whether or not the preset joint J exists in the low-density area included in the image data (S14). When the joint J exists in the low density area (S14, YES), the control unit 60 confirms whether or not the high density area exists in the overlap area R including the seam J (S16). ).

When there is a high density area in the overlap area R (S16, YES), the control unit 60 changes the preset joint J to a seam in the high density area (S18).

On the other hand, when it is confirmed in S14 that the joint J is not in the low density region (S14, NO), the controller 60 confirms whether or not the joint J exists on the line extending in the transport direction. (S20). Then, the control unit 60, when confirming that the joint J is on the line extending in the transport direction (S20, YES), changes the joint to a range other than the line in the overlap area including the joint J ( S22).

Further, when it is confirmed in S16 that the high density region does not exist in the overlap region R (S16, NO), the control unit 60 selects among the plurality of joint candidates that can be set in the overlap region R. Then, the joints are randomly changed (S24).

If the joint J does not exist in the low-concentration region (S14, NO) and does not exist on the line extending in the transport direction (S20, NO), the controller 60 does not change the joint J (S26). ).

Then, the control unit 60 repeats the processing from S12 to S26 until the joints of all the lines of the image data are confirmed (S28, NO), and when the joints of all the lines are confirmed, the position of the joints is determined. The change process ends (S28, YES).

According to the inkjet printing apparatus 1 of the above embodiment, the position of the joint is dynamically changed within the range of the overlapping nozzles of the adjacent inkjet heads based on the characteristics of the input image data of the print target. Therefore, it is possible to prevent density unevenness and thickening or thinning of lines at the joints between adjacent inkjet heads.

Further, according to the inkjet printing apparatus 1 of the above-described embodiment, the control unit 60 automatically changes the position of the joint based on the characteristics of the image data, which saves the user the trouble of resetting the joint. it can.

In addition, in the inkjet printing apparatus 1 of the above embodiment, when the position of the joint is changed, a new joint is set in the overlap region R. However, in the region narrower than the overlap region R, the new joint is set. May be set. That is, the control unit 60 may set a prohibition region in the overlap region R in which a new joint cannot be set.

Specifically, for example, when the adjacent inkjet heads 34 are appropriately installed in the head holder 33 and the nozzle rows of each inkjet head 34 are arranged in parallel in the direction orthogonal to the transport direction, the overlap region R is formed. There is no problem even if a new joint is set in, but, for example, as shown in FIG. 17, when one ink jet head 34 is installed at an inclination and its nozzle row and the nozzle row of the other ink jet head 34 are not parallel. When the new joint is set at the end of the overlap area, the gap d between the nozzle 35_1 and the nozzle 35_2 on the joint is too wide, and the joint correction limit is exceeded. For this reason, the density of the dots formed by the two nozzles may not be the desired density, and density unevenness may occur.

Therefore, it is preferable that the control unit 60 changes the joint in a region narrower than the overlap region R. As a result, it is possible to prevent the distance between the two nozzles on the joint from being too wide, and it is possible to suppress uneven density.

Further, in the inkjet printing apparatus 1 of the above-described embodiment, the position changing process of the joint is performed for each line of the image data, but it is, for example, color image data, and the same line is printed in two or more different colors. In this case, the joints may be shifted for each color. That is, in this case, the control unit 60 may change the joint to a different position for each of the line heads 32a to 32d. As a result, it is possible to further suppress density unevenness and thickening of thin lines due to overlapping of the positions of joints for each color.

Further, in the inkjet printing apparatus 1 according to the above-described embodiment, the image data for each line is sequentially received, and the position changing process of the joint is sequentially performed for each line. After accepting the whole, the position change process of the joint may be performed for each line. In that case, the control unit 60 does not necessarily have to perform the position changing process of the joints for all the lines. For example, in the case of image data of only characters and lines that do not include a solid area, every other line, or You may make it perform the position change process of the joint of every several lines set up beforehand. Thereby, the processing time can be shortened.

Further, in the inkjet printing apparatus 1 of the above-described embodiment, the position of the joint is changed in order to prevent the density unevenness from occurring when the seam J exists in the low density area. The degree of occurrence varies depending on the type of print medium P. Specifically, for example, the print medium P on which ink does not easily bleed is more likely to cause uneven density. It should be noted that the print medium P on which the ink is easily bleeding has a less blank area due to the bleeding of the ink and becomes closer to a solid image of high density, so that density unevenness is less noticeable.

Therefore, the control unit 60 may receive the information about the type of the print medium P and change the density threshold when determining the low density area based on the information. For example, the control unit 60 may increase the density threshold for the print medium P that is less likely to cause ink bleeding, and increase the low-density area that is the target of the joint position changing process. The information on the type of the print medium P may be set in the print job, or the user may set and input using the operation panel 70.

Regarding the inkjet printing apparatus of the present invention, the following additional notes are disclosed.
(Appendix)

In the inkjet printing apparatus of the present invention, the control unit changes the joint to a range other than the line when the image data includes a line extending in the transport direction and a preset joint exists on the line. be able to.

Further, in the inkjet printing apparatus of the present invention, the control unit, when the image data includes a low density region of a preset density threshold or less, and when there is a preset joint in the low density region, The seam can be changed within the range of overlapping nozzles for each line extending in the direction orthogonal to the transport direction.

Further, in the inkjet printing apparatus of the present invention, the control unit can change the density threshold when determining the low density area based on the information on the type of print medium.

Further, in the above-described inkjet printing apparatus of the present invention, the control unit can randomly change the position of the joint for each line from among the plurality of joint candidates that can be set in the overlapping nozzle range.

Further, in the inkjet printing apparatus of the present invention, the control unit includes a low density area of the image data having a preset first density threshold or less, and a preset joint exists in the low density area, In addition, when there is a high-density region equal to or higher than the second density threshold value set in advance within the range of overlapping nozzles, the joint can be changed to the high-density region.

Further, in the above-described inkjet printing apparatus of the present invention, the control unit can change the joint in an area narrower than the area of the overlapping nozzles.

Further, the inkjet printing apparatus of the present invention may have a plurality of line heads that eject ink of different colors, and the control unit may change the joint at different positions for each line head.

1 Inkjet Printing Device 2 Print Job Output Device 10 Side Paper Feeding Unit 11 Paper Feeding Stand 12 Primary Paper Feeding Section 14 Secondary Paper Feeding Section 20 Internal Paper Feeding Sections 21a to 21d Paper Feeding Tables 22a to 22d Primary Paper Feeding Section 30 Print processing unit 31 Head units 32a to 32d Line head 33 Head holder 34 Inkjet head 35 Nozzle 40 Paper discharging unit 41 Paper discharging table 42 Paper discharging roller 43 Switching mechanism 50 Reversing unit 51 Reversing table 52 Reversing roller 53 Conveying roller 60 Control unit 70 Operation panel 90 Control units 131, 132 Suction fan 133 Conveying belt CR Circulating conveying path FR Paper feeding conveying path J Joint P Print medium P1 Nozzle P2 Nozzle Pn1 Nozzle Pn2 Nozzle R Overlap area d Interval mr1 Mask range mr2 Mask range

Claims (5)

An inkjet head in which a plurality of nozzles for ejecting ink to a print medium are arranged has a plurality of head rows arranged in a direction orthogonal to the transport direction of the print medium, and the plurality of head rows are A line head that is arranged in the transport direction, and a range of some nozzles of the inkjet heads that are adjacent to each other in the direction orthogonal to the transport direction is arranged side by side in the transport direction.
A control unit that controls the line head to perform a print process on the print medium,
Inkjet printing in which the control unit dynamically changes the position of the joint between the adjacent inkjet heads within the range of overlapping nozzles of the adjacent inkjet heads based on the characteristics of the input image data to be printed. apparatus. The control unit changes the joint to a range other than the line when the image data includes a line extending in the transport direction and a preset joint exists on the line. Inkjet printing device. In the case where the control unit includes a low density area where the image data is equal to or lower than a preset density threshold value, and a preset joint exists in the low density area, a direction orthogonal to the transport direction is set. The inkjet printing apparatus according to claim 1, wherein the joint is changed within the range of the overlapping nozzles for each extending line. The inkjet printing apparatus according to claim 3, wherein the control unit randomly changes the position of the joint for each line from among a plurality of joint candidates that can be set in the overlapping nozzle range. The control unit includes a low density area of the image data that is equal to or lower than a preset first density threshold, and a preset joint exists in the low density area, and is within the range of the overlapping nozzles. The ink jet printing apparatus according to claim 1, wherein when there is a high-density area having a second density threshold value equal to or higher than a preset second density threshold value, the seam is changed to the high-density area.