JP2009119665A - Liquid jetting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid jetting device capable of suppressing concentration irregularity. <P>SOLUTION: The liquid jetting device includes a nozzle to jet a liquid, a conveying mechanism to convey a medium in such a state that the medium is sucked to a conveying belt by a suction mechanism through-holes provided on the conveying belt, and a control part to control the nozzle to jet the liquid by an amount in accordance with a command data to a center area of the medium and the nozzle to jet the liquid from the nozzle by an amount corrected to be smaller than the amount in accordance with the command data to a peripheral area of the medium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus.

  As one of liquid ejecting apparatuses, an ink jet printer that performs printing by ejecting ink from nozzles onto various media such as paper, cloth, and film is known.

Among inkjet printers, there is a printer that has a conveyance mechanism in which a belt is stretched between two rollers and conveys a medium on the belt by the rotation of the belt. In such a transport mechanism, air is sucked from the lower side of the belt by a suction fan or the like through a plurality of holes provided in the belt so that the position of the medium does not shift during transport, and the medium is adsorbed on the belt. A method has been proposed. (For example, see Patent Document 1)
JP 2005-280192 A

However, when the above-described transport mechanism is used, the ink ejected toward the peripheral area of the paper is affected by the suction force from the hole near the paper. Therefore, for example, when a satellite is generated after ink is ejected from the nozzle, the landing positions of the main ink droplet and the satellite are shifted, and a plurality of dots are formed. As a result, the peripheral portion of the paper is printed darker than the density instructed by the print data, and density unevenness occurs.
Therefore, an object is to suppress uneven density.

  A main invention for solving the above problems is a transport mechanism for transporting the medium in a state in which the medium is adsorbed to the transport belt by a suction mechanism via a nozzle for discharging a liquid and a hole provided in the transport belt. And a controller that discharges an amount of liquid corresponding to the command data from the nozzle to the central area of the medium, and less than the amount corresponding to the command data for the peripheral area of the medium. And a controller that discharges a corrected amount of liquid from the nozzle.

  Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, with respect to a transport mechanism for transporting the medium and a central region of the medium in a state in which the medium is adsorbed to the transport belt by a suction mechanism through a hole provided in the transport belt and a hole provided in the transport belt. A control unit that discharges an amount of liquid corresponding to the command data from the nozzle, and corrects an amount of liquid corrected to be smaller than the amount corresponding to the command data from the nozzle to the peripheral area of the medium. And realizing a liquid ejection apparatus having a control section for ejection.
According to such a liquid ejecting apparatus, the liquid (main liquid and satellite) ejected toward the peripheral area of the sheet is affected by the suction force from the hole of the transport belt that is not covered by the sheet. The main liquid and the satellite land at a position apart from each other, and a plurality of dots are formed, so that it is possible to suppress the peripheral area of the paper from being displayed darker than the command data. Further, uneven density in the peripheral area and the central area of the paper can be suppressed.

In this liquid ejection apparatus, the liquid ejection apparatus forms a test pattern for specifying the peripheral region in which main dots and sub dots are formed apart by one liquid ejection, and the test pattern is Sub-dots formed by one liquid discharge and main dots formed by another liquid discharge are formed so as not to overlap.
According to such a liquid ejecting apparatus, it is possible to reliably specify a region where the main dot and the sub dot are formed apart from each other. As a result, it is possible to reliably perform correction for the region that is darker than the command data, and to further suppress density unevenness.

In this liquid ejection apparatus, the control unit thins out dots to be formed in the peripheral area.
According to such a liquid ejecting apparatus, it is possible to eject an amount of liquid corrected to be smaller than the amount according to the command data to the peripheral region.

In such a liquid ejection apparatus, the control unit corrects a command gradation value indicated by some pixels belonging to the peripheral region.
According to such a liquid ejecting apparatus, it is possible to eject an amount of liquid corrected to be smaller than the amount according to the command data to the peripheral region.

In this liquid ejecting apparatus, the control unit causes the nozzle to eject an amount of liquid that is corrected to be smaller than the amount corresponding to the command data as the end of the medium is approached in the peripheral region. thing.
According to such a liquid ejecting apparatus, as it approaches the edge of the medium, it is easily affected by the suction force from the hole of the conveyor belt, and the degree of darkness is higher than the command data. Can be suppressed.

In this liquid ejection apparatus, the peripheral region is specified based on a positional relationship between an end portion of the medium and the hole that is not covered by the medium among the holes provided in the transport belt. .
According to such a liquid ejection device, it is possible to reliably identify a region that is affected by the suction force from the hole of the transport belt. As a result, it is possible to reliably perform correction for the region that is darker than the command data, and to further suppress the density unevenness.

In this liquid ejecting apparatus, the control unit specifies, on the medium, an area where a distance to the hole that is not covered by the medium is within a threshold value as the peripheral area.
According to such a liquid ejection device, it is possible to reliably identify a region that is affected by the suction force from the hole of the transport belt.

In the liquid ejecting apparatus, the control unit is configured to correct the amount in the peripheral region that is corrected to be smaller than the amount corresponding to the command data in a region closer to the hole that is not covered with the medium. Discharging liquid from the nozzle;
According to such a liquid ejecting apparatus, the density unevenness can be further suppressed because the degree of darker expression than the command data increases as the distance to the hole of the conveyor belt is approached.

In this liquid ejecting apparatus, the liquid ejecting apparatus is capable of ejecting liquid to a plurality of sizes of media, and the control unit varies the peripheral area based on the size of the media.
According to such a liquid ejecting apparatus, since the positional relationship between the medium and the hole differs depending on the size of the medium, it is possible to reliably specify the region affected by the suction force from the hole of the transport belt.

In this liquid ejection apparatus, the liquid ejection apparatus has a sensor upstream of the nozzle in the conveyance direction of the medium, and the control unit detects the position of the medium detected by the sensor and the medium The peripheral region is made different based on a positional relationship with the position of the hole not covered with the surface.
According to such a liquid ejecting apparatus, since the positional relationship between the medium and the hole differs depending on the position at which the medium is supplied to the transport belt, the region affected by the suction force from the hole of the transport belt is surely specified. be able to.

=== Line Head Printer ===
Hereinafter, an embodiment will be described by taking a liquid ejection apparatus as an ink jet printer and a line head printer (printer 1) in the ink jet printer as an example.

  FIG. 1 is a block diagram showing the overall configuration of the printer 1 according to this embodiment. FIG. 2A is a cross-sectional view of the printer 1. FIG. 2B is a diagram illustrating a state in which the printer 1 transports the paper S (medium). The printer 1 that has received print data from the computer 50, which is an external device, controls each unit (conveyance unit 20, head unit 30) by the controller 10, and forms an image on the paper S. Further, the detector group 40 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 50 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing the program of the CPU 12 and a work area. The CPU 12 controls each unit by a unit control circuit 14 according to a program stored in the memory 13.

The transport unit 20 includes transport rollers 21A and 21B, a transport belt 22, and a suction mechanism 24. The transport unit 20 feeds the paper S to a printable position, and transports the paper S at a predetermined transport speed in the transport direction during printing. . The paper feed roller 23 is a roller for automatically feeding the paper S inserted into the paper insertion opening onto the transport belt 22 in the printer 1. The sheet S on the transport belt 22 is transported by the rotation of the annular transport belt 22 by the transport rollers 21A and 21B.
FIG. 3A is a view of the conveyor belt 22 as viewed from above. The transport belt 22 is provided with a plurality of holes 25 (for example, a diameter of 10 mm). The holes are arranged on the conveyance belt 22 at predetermined intervals (for example, 30 mm) in the conveyance direction and the paper width direction. As shown in FIG. 2A, a suction mechanism 24 is provided between the annular transport belts 22. The suction mechanism 24 sucks a sheet from below through a hole 25 provided in the conveyance belt 22 and causes the sheet to be vacuum-adsorbed to the conveyance belt 22. By doing so, it is possible to prevent the positional deviation of the paper during printing (during conveyance).
Note that the printer 1 performs “bordered printing” and does not perform “borderless printing”. When performing borderless printing, ink is usually ejected toward an area wider than the paper in preparation for positional deviation of the paper with respect to the nozzles. For this reason, if the printer 1 that transports the paper by the transport belt 22 tries to perform borderless printing, ink is ejected onto the transport belt 22 beyond the paper, and the transport belt 22 and the paper are soiled. Therefore, it is assumed that the printer 1 performs only bordered printing.

  The head unit 30 is for ejecting ink onto paper, and has a plurality of heads 31. On the lower surface of the head 31, a plurality of nozzles that are ink ejection portions are provided. Each nozzle is provided with a pressure chamber (not shown) containing ink and a drive element (piezo element) for changing the volume of the pressure chamber to eject ink. When the drive signal is applied to the drive element, the drive element is deformed, and the pressure chamber expands / contracts along with the deformation, and ink is ejected.

  FIG. 3B shows the nozzle arrangement on the lower surface of the head unit 30. Each head unit 30 includes a plurality (n) of heads 31. The plurality of heads 31 are arranged in a staggered manner in the paper width direction intersecting the transport direction. A yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, and a black ink nozzle row K are formed on the lower surface of the head 31, and each nozzle row includes 180 nozzles. The nozzles of each nozzle row are aligned at a constant interval of 180 dpi in the paper width direction. Of the two heads 31 arranged in the paper width direction, the rightmost nozzle of the left head (example: # 180 of 31 (1)) and the leftmost nozzle of the right head (example: 31 (2)). Each head 31 is arranged so that the distance from # 1) is 180 dpi. That is, in the head unit 30, four color nozzles (YMCK) are arranged in the paper width direction at intervals of 180 dpi.

  In such a line head printer, when the controller 10 receives print data, the controller 10 first rotates the paper feed roller 23 to send the paper S to be printed onto the conveyor belt 22. The sheet S is conveyed on the conveyor belt 22 without stopping at a constant speed, and passes under the head unit 30. While the sheet S passes under the head unit 30, ink is intermittently ejected from each nozzle. As a result, a dot row composed of a plurality of dots along the transport direction is formed on the paper S, and an image is printed.

=== About uneven density ===
In the printer 1 of this embodiment, the paper S is sucked by the suction mechanism 24 from the hole 25 of the transport belt 22 and transported in a state where the paper S is adsorbed to the transport belt 22. As shown in FIG. 2A, the suction mechanism 24 is located between the upstream side conveyance roller 21A and the downstream side conveyance roller 21B, and is located from the left end to the right end of the conveyance belt 22 in the paper width direction.

  FIG. 4A is a diagram illustrating the sheet S on the transport belt 22. As shown in the figure, the hole appearing on the upper surface of the transport belt is divided into a hole covered with the paper and a hole not covered with the paper, depending on the size of the paper to be printed and the position of the paper on the transport belt. The hole covered with the paper sucks the paper, but the hole not covered with the paper sucks the air on the conveyance belt. That is, the air around the hole that is not covered by the paper is sucked. The peripheral area of the paper is surrounded by a hole that is not covered by the paper, as shown. Therefore, air on the peripheral area of the paper is also sucked.

  FIG. 4B is a diagram illustrating the state of the ink ejected toward the paper. In the drawing, nozzle 1, nozzle 2, and nozzle 3 are sequentially arranged from the downstream side in the transport direction. Ink is ejected from the nozzle 1 toward pixels near the leading edge of the paper S, ink is ejected from the nozzle 2 toward pixels closer to the center of the paper than the nozzle 1, and ink is ejected from the nozzle 3 than the nozzle 2. Further, ink is ejected toward the pixels on the center side of the paper.

  After a large ink droplet (hereinafter referred to as a main ink droplet) is ejected from a nozzle, a minute ink droplet (hereinafter referred to as a satellite) as shown in FIG. 4B may occur. For example, when the speed of the main ink droplet ejected from the nozzle is too slow, a part of the main ink droplet is separated, and a part of the separated ink is generated as a satellite. Even when the residual vibration of the meniscus after the main ink droplet is discharged is large, satellites are discharged separately from the main ink droplet. That is, when the main ink droplet is ejected once from the nozzle, a plurality of ink droplets (main ink droplet and satellite) may land on the medium. Such satellites are likely to occur particularly in a high temperature environment where the viscosity of the ink is lowered.

  Ink is ejected from the nozzle 3 shown in FIG. 4B to pixels that are relatively far from the leading edge of the paper. Therefore, neither the main ink droplet nor the satellite bends with respect to the paper without being affected by the suction force from the hole 25 of the transport belt 22 that is not covered by the paper (hereinafter referred to as a suction hole). Without falling vertically. As a result, the main ink droplet and the satellite land at substantially the same position, and are formed as one dot in the pixel defined by the print data.

  On the other hand, ink is ejected from the nozzle 1 to the pixels near the leading edge of the paper. For this reason, satellites that are light in weight are affected by the suction force from the suction holes, and they tend to bend toward the leading edge of the paper when dripping, and the satellites land at a position closer to the leading end than the main ink droplet. End up. As a result, the main ink droplet and the satellite land at a distant position, and a plurality of dots are formed.

  The nozzle 1 ejects ink to pixels closer to the front end of the paper than the nozzle 2. That is, the ink droplet ejected from the nozzle 1 is more susceptible to the suction force from the hole not covered by the paper than the ink droplet ejected from the nozzle 2. Therefore, for example, as shown in the figure, when two satellites are generated from the nozzle, only one satellite generated from the nozzle 2 lands on a position separated from the main ink droplet, whereas the satellite generated from the nozzle 1 Both can land at a position away from the main ink drop. That is, the closer to the edge of the paper, the more satellites land at positions away from the main ink droplet.

  In summary, in a printer that transports a medium while adsorbed to the transport belt by the suction mechanism 24 through the hole 25 provided in the transport belt 22, the main ink droplets ejected toward the peripheral area of the paper When satellites are generated, the satellites are affected by the suction force from the suction holes (holes in the vicinity of the paper) and land at positions away from the main ink droplets. That is, a plurality of dots are formed by one main ink droplet ejection from the nozzle. Further, the closer to the edge of the paper, the more satellites land at positions away from the main ink droplets.

  FIG. 5A is a diagram showing dots formed from the leading edge to the trailing edge of the paper, and FIG. 5B is a diagram showing how density unevenness occurs. The dots shown in FIG. 5A are the results of ejecting main ink droplets from the nozzles on paper (A3 size paper having a length of 420 mm in the conveyance direction). Small dots (hereinafter referred to as sub-dots) formed by satellites are formed in the vicinity of large dots (hereinafter referred to as main dots) in the leading and trailing edge regions of the paper. Also, at the beginning (front end area) of the paper, sub dots are formed on the front end side (upper side) with respect to the main dots. ). From this, it can be seen that the satellite is affected by the suction force from the hole located near the edge of the paper and lands on the edge of the paper with respect to the main ink droplet. On the other hand, only large dots (main dots) are formed in the central area of the paper, and it can be seen that the main ink droplet and the satellite landed at substantially the same position.

  That is, by ejecting the main ink droplet from the nozzle once, one dot is formed in the central area of the paper, whereas a plurality of dots are formed in the peripheral area of the paper. This means that the area of the ink spreading on the surface of the paper is larger in the peripheral area of the paper than in the central area for the same amount of ink ejection. That is, even if ink is ejected in the same manner on the central area and the peripheral area of the paper, the peripheral area of the paper is printed darker than the central area. In other words, while the central area is printed at the density specified by the print data, the peripheral area is printed darker than the density specified by the print data. As a result, density unevenness occurs in the peripheral area and the central area. For example, even if an image is printed at a constant density over the entire surface of the paper, the peripheral area of the paper is printed darker than the central area, as shown in FIG. 5B.

  Further, the closer to the edge of the paper, the more easily affected by the suction force from the holes not covered by the paper, and the number of satellites that land at positions away from the main ink droplets increases. For example, when attention is paid to a pixel row in which a plurality of pixels are arranged in the paper width direction, the number of pixels that have landed away from the main ink droplet and the satellite increases as the pixel row is closer to the leading edge of the paper. For this reason, it can be said that the degree of printing darker than the density instructed by the print data increases as it approaches the edge of the paper. Therefore, it can be said that uneven density occurs not only in the central area and the peripheral area of the paper but also in the peripheral area.

  Therefore, in the present embodiment, the landing position of the main ink droplet and the satellite is determined by a printer that transports the medium while adsorbing the medium to the transport belt 22 by the suction mechanism 24 through the hole 25 provided in the transport belt 22. The object is to suppress density unevenness caused by deviation.

  Hereinafter, the landing positions of the main ink droplet and the satellite are shifted, and the area of the paper that is printed darker than the density instructed by the print data (the main dot and the sub dot are formed apart by one liquid discharge). Area) is called a “peripheral area”, and an area where the landing positions of the main ink droplet and the satellite are substantially the same position is called a “central area”.

For the sake of explanation, dots formed by main ink droplets are called “main dots”, and dots formed by satellites separately from main dots are called “sub dots”. A dot formed by landing the main ink droplet and the satellite at the same position in the central region is also referred to as a “main dot”. A sub dot formed by a satellite landed at a position away from the main ink droplet is referred to as a “main dot sub dot”.
Actually, the main ink droplets ejected toward the peripheral area may land slightly closer to the edge of the sheet than the position instructed by the print data, although not as much as the satellite. However, here, it is assumed that the main ink droplet lands at a position designated by the print data.

=== Embodiment 1: Regarding the suppression of uneven density ===
FIG. 6 is a flow for suppressing density unevenness. In the present embodiment, before the printer 1 is shipped, a test pattern is actually printed for each printer or each printer model (S001). Then, based on the result of the test pattern, the “peripheral area (area where the landing positions of the main ink droplet and satellite are shifted)” is specified (S002). Next, the peripheral area information is stored in the memory 13 (or printer driver) of the printer 1 (S003), and then the printer 1 is shipped to the user. When the user executes printing, the area corresponding to the central area on the paper to be printed is printed at the density indicated by the print data (corresponding to the command data) (the amount of liquid corresponding to the command data is The area corresponding to the peripheral area on the paper is printed lighter than the density instructed by the print data (an amount of liquid corrected to be smaller than the amount corresponding to the command data is discharged). (Ii) Density correction is performed and printing is performed (S004). It is assumed that the printer driver or controller 10 (corresponding to a control unit) performs density correction. By doing so, density unevenness between the peripheral area printed darker than the print data and the central area printed according to the print data is suppressed, and deterioration in image quality is suppressed. In the first embodiment, the paper size that can be printed by the printer 1 is one type, and the test pattern is printed on paper that can be printed by the printer 1. In addition, it is assumed that the sheet is fed so that the positional relationship (distance) between each end of the sheet (front end, rear end, left and right ends) and the suction hole not covered by the sheet is always constant.

  First, what kind of test pattern is printed and the peripheral area is specified will be described with a specific example.

<Test pattern: first example>
FIG. 7A is a diagram illustrating a first example of a test pattern. In the test pattern of the first example, main dots are formed at predetermined intervals (for example, 1/90 inch) in the paper width direction and the transport direction. Therefore, ink is simultaneously ejected from nozzle rows arranged at intervals of 1/90 inch in the paper width direction, and every time the paper is conveyed by 1/90 inch, it is arranged at intervals of 1/90 inch in the previous paper width direction. Ink is again ejected from the nozzle array simultaneously. In the printer 1, the heads 31 are arranged in a staggered manner in the paper width direction (FIG. 3B), but it is assumed that the nozzles are arranged on one straight line for the sake of simplicity. Further, the nozzles that form dot rows arranged at intervals of 1/90 inch in the paper width direction are fixed (for example, the black ink nozzle row K) so that the test pattern results are not easily affected by the characteristics of each nozzle.

  As a result, on the paper, as shown in FIG. 7A, dot rows (hereinafter referred to as raster lines) in which main dots are arranged at intervals of 1/90 inch in the paper width direction are arranged at intervals of 1/90 inch in the transport direction. Formed side by side. Here, the first raster line, the second raster line,. In addition, the first dot, second dot,... J dot in order from the left end of the paper. In FIG. 7A, for the sake of explanation, the dot diameter and the dot interval are drawn larger than the paper size.

  After printing the test pattern, the test pattern is read by a scanner or a microscope is used to check whether the landing positions of the main ink droplet and the satellite are shifted. Then, the landing positions of the main ink droplet and the satellite are shifted, and the area where the sub dot is formed in the vicinity of the main dot is specified as the “peripheral area” on the test pattern. For example, in the test pattern shown in FIG. 7A, sub dots are formed in the vicinity of main dots belonging to the first raster line to the tenth raster line. From this, the peripheral area is specified from the leading edge of the sheet to the area where the tenth raster line is formed. The area from the area where the I-9 raster line is formed to the rear end of the paper is also identified as a peripheral area because subdots are formed in the vicinity of the main dot. Similarly, the area where the second dot is formed from the left end of the sheet and the area where the J-1th dot is formed from the right end of the sheet are also specified as the peripheral area. That is, the area inside the dotted line enclosure shown in FIG. 7A becomes the “center area” on the test pattern, and the area outside (end side) the dotted line enclosure becomes the “peripheral area” on the test pattern.

  An intermediate point between a dot row (for example, the 10th raster line) in which the landing positions of the main ink droplet and the satellite are shifted and a dot row (for example, the 11th raster line) in which the landing position is not shifted is defined as a boundary between the central region and the peripheral region. To do. In addition, if a dot row in which dots are arranged in the carrying direction or a sub dot is formed in the vicinity of at least one main dot constituting a raster line, a dot row or raster line arranged in the carrying direction is formed. This area is a peripheral area.

  In this test pattern, with respect to each main dot, in order to confirm whether or not the main ink droplet and the satellite have landed at a position separated from each other, a predetermined interval (in the figure, the main dots are not overlapped). Main dots are formed every 1/90 inch. Further, the main dots are sub-dots (sub-dots formed by discharging one liquid) and the main dots are spaced at predetermined intervals so that they do not overlap with other main dots (main dots formed by discharging another liquid). Is formed. If the main dots overlap each other, or if a sub dot of one main dot overlaps with another main dot, check whether the main ink droplet and satellite landed on each main dot. Can not do it. As a result, it becomes impossible to specify the peripheral area on the test pattern.

  Therefore, in the test pattern of the first example, the main dots are not overlapped with each other, and the sub-dots of one main dot and another main dot are not overlapped with each other in the paper width direction and the conveyance direction interval for forming the main dots. To form a test pattern. By doing so, it is possible to reliably detect the sub-dots formed by landing with the satellites shifted from the main ink droplets among the dots formed in the test pattern. As a result, the peripheral area on the test pattern can be accurately specified.

  FIG. 7B is a diagram illustrating a positional relationship between main dots (thick lines) and sub dots (thin lines) in the test pattern. In order to prevent the main dots from overlapping each other, the distance X1 between the centers of the main dots adjacent in the transport direction and the paper width direction may be set to a length equal to or greater than the diameter D of the main dots (X1 ≧ D). That is, the test pattern is printed so that the distance X1 between the pixel forming the main dot and the pixel forming the main dot adjacent to the main dot in the transport direction or the paper width direction is equal to or larger than the diameter D of the main dot. Create print data for printing.

  In order to prevent a sub-dot of a main dot from overlapping with another main dot, the outer periphery of a sub-dot of a certain main dot may not overlap with the outer periphery of another main dot. Specifically, the distance X1 between the centers of the main dots adjacent in the transport direction and the paper width direction is set to a maximum dot interval X2 (for example, 720 dpi) between a certain main dot and a sub dot of a certain main dot, and the radius R2 of the sub dot. It is sufficient that the length is equal to or longer than the length including the radius R1 of the main dot (X1 ≧ (X2 + R1 + R2)). That is, the test pattern is printed such that the distance X1 between the pixel forming the main dot and the pixel forming the main dot adjacent to the main dot in the transport direction or the paper width direction is equal to or longer than the length “X2 + R1 + R2”. Create print data for printing. In the test pattern shown in FIG. 7, the interval between the adjacent main dots in the paper width direction and the conveyance direction is made equal, but this is not limiting, and the interval between the adjacent main dots in the paper width direction and the conveyance direction is different. Also good.

  FIG. 7C is a diagram illustrating another positional relationship between the main dots and the sub dots on the test pattern. Up to this point, it has been described that the test pattern is formed so that a sub dot of a certain main dot and another main dot do not overlap, but this is not restrictive. If the sub-dot of one main dot and another main dot do not overlap completely, even if the parts overlap each other as shown in FIG. 7C, it is confirmed whether or not the satellite has landed out of the main ink droplet. can do. Therefore, the distance X3 between the center of a certain main dot and the outer periphery of another main dot adjacent to the main dot in the carrying direction and the paper width direction is set to be longer than the length of the maximum dot interval X2 between the certain main dot and the sub dot. (X3 ≧ X2).

<Test pattern: second example>
FIG. 8 is a diagram illustrating a second example of the test pattern. In this second example, print data is set so that the entire area of the paper is printed at a constant density (command gradation value), and a test pattern is printed. The main ink droplets and satellites ejected toward the periphery of the paper are landed at distant positions due to the suction force from the holes of the conveyor belt not covered by the paper. As a result, even if a test pattern is to be printed at a constant command density, the peripheral portion of the test pattern is printed darker than the central portion as shown in FIG. In the second example, an area printed darker than the central portion in the printed test pattern is specified as a “peripheral area”. For this purpose, for example, a test pattern result may be read by a scanner, and an area having a reading gradation value higher than the reading gradation value at the center may be specified as a “peripheral area”.

  In other words, in the test pattern of the first example described above, the peripheral area is specified depending on whether or not a sub dot is formed in the vicinity of the main dot, whereas in the second example, printing is performed at a constant command density. When the test pattern is viewed macroscopically, the peripheral region on the test pattern is specified by the density difference between the central portion and the peripheral portion.

  In the test pattern of the second example, it is possible to know how much density unevenness occurs due to the difference between the density of the peripheral area actually printed and the density of the central area with respect to the command density of the print data. . For example, when a tense pattern is read by a scanner, the ratio of the average read gradation value of the peripheral area and the average read gradation value of the central area may be calculated. Further, according to the test pattern of the second example, it is possible to know how dark the peripheral area is printed with respect to the command density. Therefore, it is possible to calculate how lightly the printing should be performed with respect to the command density when density correction is performed on the peripheral area.

  If the command density (command gradation value) for printing the test pattern is set too high (so-called solid printing), the main dots are formed to overlap each other. Then, another main ink droplet lands on the satellite (subdot) landed at a position away from a certain main ink droplet. Even if a certain amount or more of ink lands on a certain area, the surface area of the ink spreading on the surface of the paper does not change much, and the density at which the area is expressed does not change. That is, if the command density for printing the test pattern is set too high, the degree to which the peripheral area is printed darker than the command density is reduced. For this reason, it is difficult to specify the peripheral region due to the density difference between the peripheral region and the central region.

  Therefore, in the second example, as in the test pattern of the first example, the main dots do not overlap each other, and the test pattern is printed without overlapping the sub-dots of one main dot and another main dot. In this manner, the command density (command gradation value) for printing the test pattern is set. Then, since the density difference between the peripheral region and the central region is clear in the test pattern result, the peripheral region on the test pattern can be reliably specified. In addition, as shown in FIG. 7C, even if a test pattern is printed with a sub-dot of one main dot overlapping with a part of another main dot, a density difference occurs between the peripheral area and the central area. The peripheral area can be specified.

<Test pattern: modification>
9A to 9C are modification examples of the test pattern. FIG. 9A is a modified example of the test pattern of the first example, and FIG. 9B is a modified example of the test pattern of the second example, in which no dot is formed at the center of the test pattern. This is because it is known in advance that the landing positions of the main ink droplet and satellite do not shift at the center of the paper, so there is no problem in identifying the peripheral area without forming dots at the center of the paper. It is. Then, by specifying the peripheral region by such a test pattern, it is possible to reduce the ink consumption and the printing time.

  In the test pattern of FIG. 9C, instead of printing an image with a constant command density on the entire area of the paper as in the test pattern of the second example, small patterns are formed at predetermined intervals. Each small pattern is printed at a constant command density. As a result, the small pattern at the periphery of the sheet is printed darker than the small pattern at the center of the sheet. Therefore, an area where a small pattern printed with a higher density than the small pattern formed in the center is located is specified as a “peripheral area”. For example, the test pattern may be read by a scanner, the read gradation values of the small patterns may be compared, and the area where the small pattern having a high read gradation value is printed is specified as the peripheral area. According to such a test pattern, the ink consumption can be reduced and the printing time can be shortened as compared with the test pattern of the second example.

As described above, when the “peripheral area” on the test patterns of the first example (FIG. 7), the second example (FIG. 8), and the modified example (FIG. 9) is specified, information on the peripheral area (size of the peripheral area) ) Is stored in the memory 13 of the printer 1 or the printer driver. For example, when the peripheral area is specified as shown in FIG. 7A, based on the stored peripheral area information, a range extending from the left end of the paper actually printed under the user to the right side in the paper width direction over the length dx1, and A range extending from the right end of the paper to the left side in the paper width direction over the length dx2, a range extending from the front end of the paper to the rear end side in the transport direction over the length dy1, and a range extending from the rear end of the paper toward the front end side in the transport direction over the length dy2. The peripheral area is specified (note that the paper size on which the test pattern is printed is equal to the paper size on which the user prints). Then, the density correction is performed so that the peripheral area defined on the paper to be printed is printed lighter than the density instructed by the print data. In the first embodiment, the paper is fed so that the positional relationship between the paper and the hole on the conveyor belt is always constant. Therefore, the range affected by the suction force from the suction hole, that is, the size of the peripheral region is always constant regardless of the paper.
Next, a density correction method for the peripheral area will be described.

<Density correction example 1>
FIG. 10A is a diagram showing a dot thinning pattern in the peripheral area of the paper S. FIG. The small squares in the figure are defined as one pixel, dots are formed in the pixels indicated by the dark color, and the dots of the pixels indicated by the white color are thinned out. A pixel belonging between the leading edge of the sheet and the position I1 in the transport direction and a pixel belonging between the position I2 and the trailing edge of the sheet are used as a peripheral region, and between the left edge of the sheet and the position J1 in the paper width direction. And the pixels belonging to between the position J2 and the right edge of the paper are defined as peripheral areas. For example, it is assumed that the print data instructs all pixels to form dots so that an image with a constant density is printed over the entire area of the paper. However, if dots are formed on all the pixels in the peripheral area according to the print data, printing is performed darker than the print data in the peripheral area.

  Therefore, in density correction example 1, even if the print data of some pixels belonging to the peripheral region is “form dots”, it is rewritten to “do not form dots”. That is, printing is performed by thinning out dots in the peripheral area. By doing so, it is possible to suppress the peripheral area from being printed darker than the command density, and it is possible to suppress density unevenness between the peripheral area and the central area. For example, as shown in FIG. 10A, no dot is formed on the outer pixel closest to the paper edge (white portion), a dot is formed on the inner pixel (dark portion), and the inner pixel Dots are not formed on the pixels, and so on. In the peripheral area, dots are formed every other pixel. In this way, even if some dots belonging to the peripheral area do not form dots against the print data, the landing of the main ink droplets and satellites ejected toward other pixels belonging to the peripheral area Since the position is shifted and a plurality of dots are formed by one main ink droplet ejection, the density of the pixels where dots are not formed is compensated, and the peripheral area is printed at the command density (or close to the command density). Is done.

  10B to 10E are diagrams illustrating modifications of the density correction example 1. FIG. Of the pixels belonging to the peripheral area, the pixels (white portions) set to “not form dots” regardless of the print data are set every other line (each pixel aligned in the paper width direction) as shown in FIG. 10B, for example. Alternatively, as shown in FIG. 10C, it may be set every other row (for each pixel arranged in the transport direction). Further, it is assumed that dots may be formed in a staggered manner as shown in FIGS. 10D and 10E.

  Note that the process of rewriting the print data of some pixels belonging to the peripheral area to “data that does not form dots” may be performed by the printer driver on the print data created by the printer driver or transmitted to the printer 1. The controller 10 in the printer 1 may perform the print data that has been printed.

<Density correction example 2>
Here, print data creation processing by the printer driver in the computer 50 will be described. When the printer driver receives image data from various application software, first, the resolution of the image data is converted to a resolution (printing resolution) for printing by the printer. Then, color conversion processing is performed by matching the image data represented in the RGB space with the ink (YMCK) of the printer. At this time, one pixel is represented by 256 gradations, and the lower the gradation value, the lighter the density expressed. Thereafter, the high gradation number data (256 gradations) are converted into gradation values that can be printed by the printer (for example, two gradation data depending on whether or not dots are formed) (halftone processing). The matrix-like image data formed by these processes is rearranged in the order of data to be transferred to the printer 1, and is sent from the printer driver to the printer 1 together with command data corresponding to the printing method.

  In density correction example 2, it is assumed that the printer driver performs density correction processing while print data is being created by the printer driver. After the color conversion process, the printer driver corrects the gradation value (command gradation value) indicated by the pixels belonging to the peripheral area to a low gradation value while maintaining the gradation values indicated by the pixels belonging to the central area. Then, halftone processing is performed based on the corrected gradation value, and the presence or absence of dot formation is determined. As a result, in print data that has been subjected to halftone processing with a corrected tone value, compared to print data that has been subjected to halftone processing with a tone value before correction, dots formed in the peripheral region The number decreases (or the dot size decreases). However, the landing positions of the main ink droplets and satellites ejected toward the peripheral area are shifted, and a plurality of dots are formed by one main ink droplet ejection, so the density corresponding to the reduced number of dots is compensated. . As a result, it is possible to suppress the peripheral area from being printed darker than the command density, and to suppress density unevenness between the central area and the peripheral area.

  As described above, the density correction example 1 and the density correction example 2 describe a method for printing lighter than the density instructed by the print data in the peripheral area. Next, a density correction method for varying the density correction amount in the peripheral area in order to further suppress density unevenness will be described.

<Density correction example 3>
FIG. 11 is a diagram illustrating a state in which the peripheral area is divided into a plurality of areas. A portion surrounded by diagonal lines of the paper is defined as a central region, and a region around the central region is defined as a peripheral region. By the way, in the peripheral area of the paper, not only the density instructed by the print data is printed, but also, as it approaches the edge of the paper, it approaches the suction hole that is not covered by the paper. Also, the degree of printing darkly becomes high. For this reason, when the same density correction is performed on the entire peripheral area (when the printing density is lighter than the command density), density unevenness also occurs in the peripheral area.

  Therefore, in this density correction example 3, the density correction amount is varied also in the peripheral area, and the degree of printing lighter than the command density is higher as it approaches the end of the paper (in the direction of the arrow in the figure). (The amount of liquid corrected to be smaller than the amount corresponding to the command data is discharged). As for the area near the corner of the paper, as indicated by the arrow in the figure, the closer to the corner of the paper, the higher the degree of printing lighter than the command density.

  For example, the peripheral area is divided into three areas, which are designated as a first area, a second area, and a third area in order from the area near the edge of the sheet. The first area is printed with a higher degree of printing lighter than the command density than the second area, and the second area is printed with a higher degree of printing lighter than the command density than the third area.

  As in the density correction example 1, when a part of the pixels belonging to the peripheral region is “no dot (no dot is formed)” regardless of the print data, for example, half of the pixels in the first region closest to the paper edge In the second area farther from the paper edge than the first area, one of the three pixels is made dotless, and in the third area farthest from the paper edge, one of the four pixels Make no dot. Further, as in the density correction example 2, when the command gradation value indicated by the pixels belonging to the peripheral area is corrected to a low gradation value during the creation of the print data, the instruction gradation value indicated by the pixels belonging to the first area is changed. The gradation value is corrected to 70%, the instruction gradation value indicated by the pixel belonging to the second area is corrected to 80% gradation value, and the instruction gradation value indicated by the pixel belonging to the third area is 90%. Correct to key value.

  By performing the density correction in this way, not only the density unevenness between the central area and the peripheral area but also the density unevenness within the peripheral area is suppressed, and a higher quality image can be obtained.

  In addition, the peripheral area close to the central area (third area) is printed darker than the central area compared to the peripheral area close to the end (first area). For this reason, if the same density correction is performed on the peripheral area close to the central area as in the peripheral area close to the end, the peripheral area close to the central area may be printed lighter than the command density. Then, the peripheral area close to the central area is printed lighter than the central area, and the boundary between the central area and the peripheral area becomes conspicuous. Therefore, as in the density correction example 3, the boundary between the central area and the peripheral area may be made inconspicuous by correcting the density so that the degree of printing is lighter than the command density as it approaches the edge of the sheet. it can.

<Density correction example 4>
12A is a diagram illustrating a positional relationship between the upper left corner of the sheet S and the hole 25 on the conveyance belt, and FIG. 12B is a diagram illustrating a state in which the peripheral region is divided into a plurality of regions. As shown in FIG. 12B, the peripheral area includes a corner area (upper left area / upper right area / lower left area / lower right area) and other end areas (front end area / rear end area / left end area / right end area) Divide into The one end region is affected by either the suction holes arranged along the transport direction or the suction holes arranged along the paper width direction. On the other hand, as shown in FIG. 12A, the corner area is affected by both suction holes arranged along the transport direction and suction holes arranged along the paper width direction. That is, since the corner region is affected by more suction holes than the one end region, the number of satellites that land at a position away from the main ink droplet increases. Therefore, in the corner area, the number of dots formed with respect to the same ink discharge amount increases as compared with the one end area, and the degree of printing darker than the command density increases. Therefore, when the same density correction is performed on the one end region and the corner region, density unevenness occurs in the one end region and the corner region. Therefore, in this density correction example 4, the corner area is subjected to density correction so that the degree of printing is lighter than the command density than the one end area. As a result, density unevenness in the corner region and the one end region is suppressed. In addition to making the density correction amount different between the corner area and the one end area, as in the density correction example 3, the density correction amount is increased toward the end of the sheet in the one end area, and the end area is set to the sheet. By increasing the density correction amount as it approaches the corner, the density unevenness of the entire sheet is suppressed.

<Density correction example 5>
By the way, when printing the test pattern of the second example, if the command density (command gradation value) for printing the test pattern is set too high, the main ink droplet different from the satellite generated by the discharge of a certain main ink droplet is used. As described above, since the peripheral area is printed at the same position, the degree to which the peripheral area is printed darker than the command density is reduced. That is, as the command gradation value of the pixels belonging to the peripheral area increases, the influence of satellites that land away from the main ink droplet in the peripheral area decreases, and the density unevenness between the peripheral area and the central area decreases.

  Therefore, the test pattern of the second example is printed at a relatively high command density (command tone value), and a threshold value (tone value / density) that eliminates the density difference between the central area and the peripheral area is set. When printing is performed under the user, if the peripheral area is printed with a gradation value (command density) equal to or higher than the threshold value, it is printed lighter than the command density in the peripheral area. It is assumed that density correction is not necessary.

=== Embodiment 2: Suppression of density unevenness with different paper sizes ===
As shown in FIG. 3A, the holes 25 provided in the transport belt 22 are formed at predetermined intervals in the transport direction and the paper width direction. Therefore, when the paper is fed at a distance from the suction hole to the paper edge, even if the distance from the paper edge is the same region (pixel), the influence of the suction hole is different. That is, even if the distance from the edge of the paper is the same region, the main ink droplet and the satellite land on the same position depending on the position where the paper is fed, or land on the same position.

  FIG. 13 is a diagram illustrating a state in which three types of sizes of paper are fed onto the transport belt 22. In the second embodiment, the printer 1 can print on three types of paper, A4 size paper, B5 size paper, and postcard. The printer 1 also feeds the paper with the right end along the fixed guide rail and the left end with the movable guide rail. For this reason, the right ends of the respective sheets are aligned, but the left ends of the sheets of different sizes are not aligned. For this reason, the distance between the left end of the paper and the suction hole (thick line) closest to the left end of the paper among the holes that are not completely covered by the paper differs depending on the paper size. In FIG. 13, the distance between the left end of each sheet and the suction hole (thick line) is shortened in the order of A4 size paper, B5 size paper, and postcard.

  The positional relationship between the paper edge and the suction hole 25 not covered by the paper is different depending on the paper size, and the distance between the paper edge and the suction hole is different. That is, the size of the peripheral region is different. Therefore, even if the distance from the paper edge is the same area (pixel), the area belongs to the peripheral area or the central area. For example, the postcard shown in FIG. 13 is closer to the left edge of the paper and the suction hole than the A4 size paper, and the range affected by the suction hole is widened. That is, the size of the peripheral area in the vicinity of the left end portion (left end area in FIG. 12B) of the postcard is larger than that of A4 size paper. Similarly, the size of the peripheral region in the vicinity of the left end is larger for B5 size paper than for A4 size paper. Thus, in a printer that prints a plurality of sizes of paper, a peripheral area corresponding to the positional relationship between the edge of the paper and the suction hole 25 not covered by the paper is specified for each paper size, and the size of each paper size is different. It is necessary to perform density correction on the region (peripheral region).

  Therefore, as in the first embodiment, in the method of printing a test pattern on a sheet of paper to be actually printed and specifying the size of the peripheral area from the printed test pattern result, a plurality of patterns are matched to the sheet size. A test pattern must be printed, which takes processing time. Therefore, when specifying the peripheral area in a printer that prints paper of multiple sizes, specify the size of the peripheral area according to each paper size based on the distance from the edge of the paper and the suction hole 25 not covered by the paper. (Peripheral area varies depending on paper size).

  FIG. 14 is a diagram showing the positional relationship between the edge of the sheet on which the test pattern is printed and the suction holes 25. The test pattern (for example, FIG. 8) described in the first embodiment is printed on paper (A4 size paper) of a size that can be printed by the printer 1, and a peripheral area on the test pattern is specified. Then, based on the peripheral area specified from the test pattern result and the positional relationship between the suction hole and the edge of the paper when the test pattern is printed, the suction hole around the paper affects which range on the paper. A threshold value can be calculated.

  For example, in FIG. 14, the distance from the suction hole (bold line) near the left edge of the paper to the left edge of the paper is Z11, and the distance from the left edge of the paper to the boundary between the peripheral area and the central area is Z11. Z12. From this, it can be seen that the range affected by the suction hole in the vicinity of the left end of the sheet is the length Z1 (= Z11 + Z12) obtained by adding the two distances Z11 and Z12. Then, this length Z1 is used as a threshold value for specifying the peripheral region. Similarly, a range (threshold value) in which the suction holes in the vicinity of the right end, the front end, and the rear end of the sheet are affected is also calculated.

  It is assumed that the paper is fed so that the positional relationship between each edge of the paper and the suction holes not covered by the paper is always constant for each paper size (for example, the positional relationship shown in FIG. 13). For this reason, the peripheral area does not change depending on the paper as long as the paper has the same size. For A4 size paper, a test pattern is actually printed in order to calculate the threshold of the range in which the suction hole affects, and the peripheral area (size) of A4 size paper can be specified. ing. Therefore, the peripheral area (size) of other size paper (postcard / B5 size paper) is specified based on the threshold of the range in which the suction hole affects.

  FIG. 15A is a diagram illustrating a state in which a peripheral region of a postcard is specified, and FIG. 15B is a diagram illustrating a state in which a peripheral region of B5 size paper is specified. A small square is defined as one pixel, a hatched area is a peripheral area, and the other area is a central area. Here, it is determined whether or not each pixel row along the transport direction is a peripheral region.

The range affected by the suction hole is a region away from the center of the suction hole by the threshold value Z1, and the range from the center of the suction hole to the threshold value Z1 is specified as the peripheral region. The length from the left end of the postcard to the suction hole is defined as length Z2. Therefore, the pixel column belonging to the range from the threshold value Z1 to the length (Z1-Z2) obtained by subtracting the length Z2 from the left end of the postcard is specified as the peripheral region. As a result, the area from the left end of the sheet to the third pixel column is specified as the peripheral area.
On the other hand, the length from the left end of the B5 size paper to the suction hole 25 is defined as a length Z3. Therefore, the pixel column belonging to the range from the threshold value Z1 to the length (Z1-Z3) with the left end of the B5 size paper as the base point is specified as the peripheral region. As a result, the area from the left end of the paper to the second pixel column is specified as the peripheral area, and the third pixel array from the left end is specified as the central area.
Even the same third pixel from the left edge of the paper is specified as a peripheral area on a postcard and specified as a central area on B5 size paper. Thus, since the distance from the suction hole to the left end of the paper is shorter in the postcard than in the B5 size paper, the number of pixel columns specified as the peripheral region increases.

  FIG. 15C is a diagram illustrating a state in which a peripheral region is specified for each pixel. In FIG. 15A and FIG. 15B described above, it is determined whether or not each pixel row along the transport direction is a peripheral region, and the peripheral region is specified. However, the present invention is not limited to this, and a peripheral region may be specified for each pixel. For example, as shown in FIG. 15C, a pixel that is located on the upper right side with respect to the suction hole 25 and whose distance Z3 from the suction hole is longer than the threshold value Z1 is specified as a pixel belonging to the central region, and A pixel located at the lower right and having a distance Z4 from the suction hole shorter than the threshold is specified as a pixel belonging to the peripheral region. That is, the pixel in which the center of the pixel is located in the range (within the dotted line in the figure) within the radius Z1 from the center of the suction hole 25 is specified as the peripheral region. Thus, by specifying whether or not each pixel is a peripheral region, the peripheral region can be specified more accurately, and as a result, density unevenness can be further suppressed. However, if it is specified for each pixel whether or not it is a peripheral region, the processing time becomes long, so even if it is specified for each region composed of a plurality of pixels whether or not it is a peripheral region Good.

  Then, not only the peripheral area due to the influence from the suction hole near the left end of the sheet, but also the peripheral area due to the influence from the suction hole near the other end of the paper (right end, front end, rear end) is specified. Thus, based on the test pattern formed on the A4 size sheet, the threshold value of the range affected by the suction hole (threshold value whether or not to specify the peripheral region) is calculated. Based on the threshold value, the peripheral area (size) of the other size paper (B5 size / postcard) is specified by the distance between the paper edge and the suction hole. In this manner, by specifying an area on the paper where the distance to the suction hole is within the threshold as the peripheral area, the printer 1 can print each paper size for each paper size without printing all the test patterns of the paper size that can be printed. The peripheral area can be specified. Conversely, the positional relationship between the edge of the paper and the suction hole differs depending on the paper size, but the peripheral area is specified as the peripheral area because the area affected by the suction force from the suction hole is specified. Can do.

  As described above, when the peripheral area is specified for each paper size, information on the peripheral area for each paper size (size of the peripheral area) is stored in the printer memory 13 or the printer driver. Then, when printing is performed by the user, an area corresponding to the peripheral area on the paper to be printed is determined based on the stored peripheral area information, and the print is lighter than the density instructed by the print data. As shown, density correction is performed. The density correction method is the same as that in the first embodiment.

  In the above-described density correction example 3, the density correction amount is increased in the region closer to the paper edge (paper corner). This is because the region closer to the end of the sheet (the corner of the sheet) is closer to the suction hole and is therefore strongly influenced by the suction hole. However, as in the second embodiment, when the positional relationship between the suction hole and the paper edge varies depending on the paper size, even if the distance from the paper edge is the same region (pixel), it is darker than the command density. The degree of printing is different. For example, the first pixel column from the left end of the postcard in FIG. 15A is printed darker than the command density than the first pixel column from the left end of the B5 size paper in FIG. 15B. Therefore, it is necessary to increase the density correction amount. That is, the density correction amount may be increased in a region closer to the suction hole (a liquid having a corrected amount smaller than the amount corresponding to the command data is discharged).

  Further, in the process before shipment of the printer 1, all the peripheral areas of the paper size that can be printed by the printer 1 may be specified, and the information on the peripheral area may be stored in the memory, but this is not limitative. For example, when the density correction is performed by storing the threshold value (Z1) of the range in which the suction force from the suction hole affects, and the positional relationship between the paper edge and the suction hole when each size of paper is fed. The peripheral area on the paper may be specified according to the paper size to be printed. In this case, the processing time before printing becomes longer, but the memory capacity can be reduced.

  Further, since the printer 1 feeds the right edge of the paper along the fixed guide rail and the left edge of the paper along the movable guide rail, the positional relationship between the right edge of the paper and the suction hole is the paper size. Regardless of whether it is constant or not (FIG. 13). Therefore, the peripheral area near the right edge of the sheet (the right edge area in FIG. 12B) is constant regardless of the sheet size, and there is no need to calculate for each sheet size.

  Then, unlike the printer 1, it is not necessary to feed the paper along the fixed guide rail. For example, in the case of a printer that can change the paper feed position in the paper width direction depending on the paper size, the distance between the right edge of the paper and the suction hole near the right edge, and the suction near the left edge and the left edge of the paper. It is preferable to feed paper so that the distance from the hole is equal. By doing so, the size of the peripheral area near the left edge of the paper (left edge area in FIG. 12B) and the peripheral area near the right edge of the paper (right edge area) can be made equal, and density unevenness is visually recognized. It becomes difficult. Similarly, even when the paper is fed so that the size of the peripheral area (front end area) near the front end of the paper and the peripheral area (rear end area) near the rear end of the paper is equal, uneven density is less likely to be visually recognized. .

=== Embodiment 3: Suppression of density unevenness by position detection ===
FIG. 16 is a diagram illustrating a difference in the positional relationship between the sheet edge and the suction hole 25 in the sheets S1 and S2 having different sheet feeding positions. In the first and second embodiments described above, since the paper is fed along the guide rail, the positional relationship between the paper edge and the suction hole in the paper width direction is as long as the paper size to be fed is the same. It is constant. However, in the third embodiment, it is assumed that the position in the paper width direction where the paper is fed is not constant, and the paper feeding position in the paper width direction is different for each paper.

  For example, as shown in the drawing, the paper S1 (solid line) is fed to the left side by a length Z5 in the paper width direction with respect to the same size paper S2 (dotted line), and is fed in the vicinity of the left edge and the left edge of the paper S1. Assume that the distance Z6 to the suction hole (thick line) is longer than the distance Z7 between the left end of the sheet S2 and the suction hole (thick line) in the vicinity of the left end. In this case, the area near the left end of the sheet S1 is narrower than the area near the left end of the sheet S2. That is, the peripheral area near the left end of the sheet S1 is smaller than the peripheral area near the left end of the sheet S2. That is, if the paper feed position in the paper width direction differs for each paper, the distance between the paper edge and the suction hole near the edge differs for each paper, so the size of the peripheral area also differs.

  As in the third embodiment, when the position in the paper width direction in which the paper is fed is not constant, the positional relationship between the paper edge and the suction holes near the edge is detected for each fed paper. The surrounding area must be specified. Therefore, in the third embodiment, a CCD line sensor 41 (corresponding to a sensor) is provided on the upstream side of the conveyor belt 22. The CCD line sensor 41 detects the position of the paper fed on the transport belt 22. Then, the controller 10 that has received the detection result calculates the distance between the sheet edge and the suction hole near the edge. Further, not only in the paper width direction but also when the paper line is fed with the positional relationship between the leading and trailing edges of the paper and the suction holes being different for each paper, the CCD line sensor 41 has four edge portions (leading edges) of the paper. The controller 10 calculates the distances between the four ends of the sheet and the suction holes near the ends. Since the positions of the suction holes in the paper width direction are fixed, the distance between the left and right edges of the paper and the suction holes can be calculated by detecting the positions of the left and right edges of the paper in the paper width direction. On the other hand, since the position of the suction hole in the transport direction changes with time, the position of the suction hole in the transport direction is managed by an encoder or the like that controls the number of rotations of the transport roller 21, so that the front and rear ends of the paper and the suction hole What is necessary is just to calculate a distance.

  Then, the peripheral area is specified according to the distance between the four end portions of the sheet and the suction hole (peripheral areas are made different). The peripheral region specifying method is the same as that of the above-described second embodiment, and as shown in FIG. 15, based on the threshold value stored in the memory 13 (the range in which the suction force from the suction hole affects), An area on the sheet extending from the suction hole to the threshold length is specified as the peripheral area.

  When the peripheral area on the fed paper is specified, the controller 10 performs density correction so that the peripheral area is printed lighter than the command density. The density correction method is the same as the method shown in the first embodiment. For example, as in the density correction example 1 (FIG. 10), the data of some pixels belonging to the peripheral area may be rewritten to “no dots” and the dots may be thinned out for printing. Further, in the third embodiment, in order to perform density correction after specifying the peripheral area based on the positional relationship between the fed paper and the hole, as in the density correction example 2, the printer driver is creating print data. In the method of correcting the density with respect to the command gradation value, printing takes time.

  Thus, by specifying the peripheral area based on the positional relationship between the position where the paper is fed and the hole of the conveying belt, the positional relationship between the edge of the sheet and the hole of the conveying belt is always constant. No need to feed paper to Even if an error occurs when the paper is fed along the guide rail and the paper is fed out of a predetermined position, the positional relationship between the edge of the fed paper and the suction hole is different. Based on this, the peripheral area is specified, so that the peripheral area can be specified more accurately.

=== Other Embodiments ===
Each of the above embodiments has been described mainly for a printing system having an ink jet printer, but includes disclosure of a method for suppressing density unevenness. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About paper types>
In the case of a liquid ejecting apparatus that ejects liquid onto various types of media having different weights, the medium may be conveyed by changing the suction force of the suction device according to the type of the medium. In this case, since the suction force from the suction hole differs depending on the type of the medium, the probability that the main ink droplet and the satellite will land with a deviation when the liquid is ejected on a heavy medium increases, so that the peripheral region Increases, and the degree of darkness is higher than the command density. Therefore, the size and density correction amount of the area specified as the peripheral area may be varied depending on the type of medium.

<About liquid ejection device>
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus (part) for performing the liquid ejecting method, but is not limited thereto. If it is a liquid ejection device, it can be applied to various industrial devices, not a printer (printing device). For example, a textile printing device for patterning a fabric, a display manufacturing device such as a color filter manufacturing device or an organic EL display, a DNA chip manufacturing device for manufacturing a DNA chip by applying a solution in which DNA is dissolved in a chip, a circuit board manufacturing The present invention can be applied even to an apparatus or the like. When ejecting a transparent liquid, the peripheral area of the medium is not always expressed with a higher density than the command data, but the liquid coverage area (dot surface area) in the peripheral area of the medium is indicated by the command data. It is also included in the fact that it becomes larger than the covered area of the liquid, which is expressed by a concentration higher than the command data.

  The liquid discharge method may be a piezo method that discharges liquid by applying voltage to the drive element (piezo element) to expand and contract the ink chamber, or generates bubbles in the nozzle using a heating element. It is also possible to use a thermal method in which liquid is discharged by the bubbles.

  When the controller 10 in the printer 1 performs density correction processing on the peripheral region, the controller 10 corresponds to a control unit, and the printer alone corresponds to a liquid ejection device. On the other hand, when the printer driver in the computer 50 performs density correction processing on the peripheral area, the computer 50 corresponds to a control unit, and a system in which the printer 1 and the computer 50 are connected corresponds to a liquid ejecting apparatus.

<About line head printer>
In the above-described embodiment, a line head printer in which nozzles are arranged in the paper width direction intersecting the medium conveyance direction is described as an example, but the present invention is not limited to this. For example, in the case of a printer that transports a medium while adsorbing the medium from under the transport belt provided with holes, an image that forms an image while one head moves in a moving direction that intersects the transport direction of the medium. A serial printer that alternately performs a forming operation and a conveying operation for conveying a medium may be used.

1 is an overall configuration block diagram of a printer according to an embodiment. 2A is a cross-sectional view of the printer, and FIG. 2B is a diagram in which the printer transports paper. FIG. 3A is a top view of the conveyor belt, and FIG. 3B shows the nozzle arrangement. FIG. 4A is a diagram illustrating a sheet on the conveyance belt, and FIG. 4B is a diagram illustrating a state of ink ejected toward the sheet. It is a figure which shows the dot formed on the paper. It is a figure which shows generation | occurrence | production of density unevenness. This is a flow for suppressing uneven density. FIG. 7A is a first example of a test pattern, FIG. 7B is a diagram showing the positional relationship between main dots and sub-dots in the test pattern, and FIG. 7C is another positional relationship between main dots and sub-dots on the test pattern. FIG. It is a figure which shows the 2nd example of a test pattern. 9A to 9C are variations of the test pattern. FIG. 10A is a diagram illustrating a dot thinning pattern in the peripheral region, and FIGS. 10B to 10E are diagrams illustrating modifications of the density correction example 1. FIG. It is a figure which shows a mode that the peripheral area | region was divided | segmented into the several area | region. FIG. 12A is a diagram illustrating the positional relationship between the upper left corner of the sheet and the hole, and FIG. 12B is a diagram illustrating a state in which the peripheral region is divided into a plurality of regions. FIG. 6 is a diagram illustrating a state in which three types of sizes of paper are fed onto a conveyance belt. It is a figure which shows the positional relationship of the edge part of the paper with which the test pattern was printed, and a suction hole. 15A is a diagram for specifying a peripheral region of a postcard, FIG. 15B is a diagram for specifying a peripheral region of B5 size paper, and FIG. 15C is a diagram for specifying the peripheral region for each pixel. FIG. 6 is a diagram illustrating a difference in positional relationship between a sheet edge and a suction hole at different sheet feeding positions.

Explanation of symbols

1 printer, 10 controller, 11 interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 21 transport roller, 22 transport belt,
23 feeding roller, 24 suction mechanism, 25 holes,
30 head units, 31 heads, 40 detector groups,
41 CCD line sensor, 50 computers

Claims (10)

A nozzle for discharging liquid;
A transport mechanism for transporting the medium in a state in which the medium is adsorbed to the transport belt by a suction mechanism through a hole provided in the transport belt;
A control unit that discharges an amount of liquid corresponding to command data from the nozzle to the central region of the medium, and corrects the peripheral region of the medium to be less than the amount corresponding to the command data A controller for discharging a quantity of liquid from the nozzle;
A liquid ejection apparatus having The liquid ejection device according to claim 1,
The liquid ejection device forms a test pattern for specifying the peripheral region in which main dots and sub dots are formed apart by a single liquid ejection,
The test pattern is formed so that sub-dots formed by one liquid discharge and main dots formed by another liquid discharge do not overlap.
Liquid ejection device. The liquid ejection device according to claim 1 or 2, wherein
The control unit is a liquid ejection apparatus that thins out dots to be formed in the peripheral area. The liquid ejection device according to claim 1 or 2, wherein
The liquid ejection device that corrects a command gradation value indicated by a part of pixels belonging to the peripheral area. The liquid ejection device according to any one of claims 1 to 4,
In the peripheral area, the control unit discharges, from the nozzle, an amount of liquid that is corrected to be smaller than the amount corresponding to the command data as it approaches the end of the medium. The liquid ejection device according to claim 1,
A liquid ejection apparatus that identifies the peripheral region based on a positional relationship between an end portion of the medium and the hole that is not covered by the medium among the holes provided in the transport belt. The liquid ejection device according to claim 6,
The liquid ejecting apparatus, wherein the control unit specifies an area on the medium where a distance to the hole that is not covered by the medium is within a threshold value as the peripheral area. The liquid ejection device according to claim 6 or 7, wherein
In the peripheral area, the control unit is configured to discharge liquid from the nozzle in a corrected amount that is smaller than the amount corresponding to the command data in a region closer to the hole that is not covered by the medium. Discharge device. The liquid ejection device according to any one of claims 1 to 8,
The liquid ejection device is capable of ejecting liquid to a plurality of sizes of media,
The control unit varies the peripheral area based on the size of the medium.
Liquid ejection device. The liquid ejection device according to any one of claims 1 to 8,
The liquid ejection device has a sensor on the upstream side in the conveyance direction of the medium from the nozzle,
The control unit varies the peripheral region based on a positional relationship between the position of the medium detected by the sensor and the position of the hole not covered with the medium.
Liquid ejection device.