JP2008213221A - Liquid ejection apparatus, liquid ejection method, and program - Google Patents

Abstract

Disclosed is a method for ejecting a liquid agent used to alleviate deformation of a medium by an amount corresponding to the ejection amount of a liquid droplet forming an image by a smaller number of nozzles than the nozzles for forming an image.
A first liquid ejection unit that ejects a first liquid droplet onto a medium and a second liquid ejection unit that ejects a second liquid droplet to alleviate deformation of the medium caused by the first liquid droplet. And a second liquid ejection unit that ejects a larger liquid droplet than the largest liquid droplet ejected by the first liquid ejection unit.
[Selection] Figure 3

Description

  The present invention relates to a liquid ejection apparatus, a liquid ejection method, and a program.

  There is a liquid ejecting apparatus that ejects liquid onto a medium to form an image. When such an apparatus forms an image, a cockling phenomenon in which the medium becomes wrinkled due to the moisture of the liquid droplets may occur in an area where many liquid droplets have landed. In such a case, transparent liquid droplets are also ejected to areas on the medium where many liquid droplets have not landed, and liquid droplets equivalent to the liquid amount per unit area of the image land in all areas. To do. By doing so, the occurrence of the cockling phenomenon can be reduced.

When an image is formed, the liquid droplets that form the image are ejected while the liquid droplet ejection unit and the medium are relatively moved. When the image is expressed in color, for example, liquid droplets of three primary colors and black are ejected. Then, a plurality of nozzles are used so as to eject liquid droplets for at least four colors. On the other hand, in order to alleviate the cockling phenomenon, it may be necessary to eject transparent liquid droplets in an amount corresponding to the ejection amount per unit area of the liquid droplets for four colors. Then, it is considered that the same number of nozzles for discharging transparent liquid droplets are required.
JP-A-9-300619

  Transparent liquid droplets are used to mitigate the occurrence of cockling phenomenon and do not require gradation expression as much as colored liquid droplets. Therefore, by roughening the gradation expression of transparent liquid droplets, the amount of liquid droplets that form an image is close to the discharge amount per unit time with fewer nozzles than the number of nozzles that discharge colored liquid droplets. In some cases, it can be discharged.

  The present invention has been made in view of such circumstances, and the number of nozzles is smaller than the number of nozzles for forming an image, and the medium is deformed by an amount corresponding to the discharge amount of the liquid droplets that form the image. It aims at discharging the liquid agent used in order to ease.

The main invention for achieving the above object is:
A first liquid ejection unit that ejects a first liquid droplet onto the medium;
A second liquid ejection unit that ejects a second liquid droplet to relieve deformation of the medium caused by the first liquid droplet, the liquid droplet being larger than the largest liquid droplet ejected by the first liquid ejection unit A second liquid discharger capable of discharging
It is a liquid discharge apparatus provided with.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A first liquid ejection unit that ejects a first liquid droplet onto the medium;
A second liquid ejection unit that ejects a second liquid droplet to relieve deformation of the medium caused by the first liquid droplet, the liquid droplet being larger than the largest liquid droplet ejected by the first liquid ejection unit A second liquid discharger capable of discharging
A liquid ejection apparatus comprising:
By doing so, the liquid agent used to relieve the deformation of the medium by an amount corresponding to the discharge amount of the liquid droplets forming the image is discharged by a smaller number of nozzles than the nozzles for forming the image. can do.

  In this liquid ejection apparatus, the first liquid ejection unit includes a first nozzle for ejecting the first liquid droplet, and the second liquid ejection unit is a second for ejecting the second liquid droplet. It is preferable that the number of the second nozzles is smaller than the number of the first nozzles. Further, it is desirable that the second nozzle can eject the second liquid droplet in an amount corresponding to the total amount of liquid ejected from a plurality of the first nozzles to one pixel. It is desirable that the number of gradations that can be expressed by the first liquid droplet ejected from the first nozzle is equal to the number of gradations that can be expressed by the second liquid droplet ejected from the second nozzle. The hole size of the second nozzle is preferably larger than the hole size of the first nozzle.

Further, it is desirable that the second liquid ejection unit ejects the second liquid droplet so as to have a liquid amount corresponding to a liquid amount per unit area of the first liquid droplet forming the image. The second liquid droplet is preferably ejected on the same surface as the surface on which the first liquid droplet is ejected. In addition, it is preferable that the second liquid droplet be ejected onto a surface opposite to the surface from which the first liquid droplet is ejected. In addition, it is desirable to further include a reversing mechanism for reversing the medium in order to eject the second liquid droplet to the opposite surface.
By doing so, the liquid agent used to relieve the deformation of the medium by an amount corresponding to the discharge amount of the liquid droplets forming the image is discharged by a smaller number of nozzles than the nozzles for forming the image. can do.

Ejecting a first liquid drop onto a medium to form dots;
Discharging a second liquid drop to alleviate deformation of the medium caused by the first liquid drop, discharging a second liquid drop larger than the maximum size of the first liquid drop;
A liquid ejection method comprising:
By doing so, the liquid agent used to relieve the deformation of the medium by an amount corresponding to the discharge amount of the liquid droplets forming the image is discharged by a smaller number of nozzles than the nozzles for forming the image. can do.

A program for operating a liquid ejection device,
Ejecting a first liquid drop onto a medium to form dots;
Discharging a second liquid drop to alleviate deformation of the medium caused by the first liquid drop, discharging a second liquid drop larger than the maximum size of the first liquid drop;
A program for causing the liquid ejection apparatus to perform
By doing so, the liquid agent used to relieve the deformation of the medium by an amount corresponding to the discharge amount of the liquid droplets forming the image is discharged by a smaller number of nozzles than the nozzles for forming the image. can do.

=== Embodiment ===
<About the overall configuration>
FIG. 1 is a schematic diagram of the overall configuration of the printer 1. FIG. 2 is a block diagram of the overall configuration of the printer 1. Hereinafter, a basic configuration of the printer 1 will be described.

  The printer 1 includes a transport unit 20, a hydrator unit 30, a head unit 40, a detector group 50, a controller 60, a reversing unit 70, and an interface 80. The printer 1 that has received print data from the computer 110, which is an external device, controls each unit (the conveyance unit 20, the hydrator unit 30, the head unit 40, and the reversing unit 70) by the controller 60. Then, the controller 60 prints an image on a sheet. The situation in the printer 1 is monitored by a detector group 50, and the detector group 50 outputs a detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

  The transport unit 20 is for transporting a medium such as the paper S in a predetermined direction (referred to as a transport direction). The transport unit 20 includes a driven roller 21, a pressing roller 22, a driving roller 23, a tensioner 24, a belt 25, and a suction unit 26. The driving roller 23 is driven by rotating a driving motor (not shown) under the control of the controller 60. Since the belt 25 is also stretched over the driven roller 21 and the tensioner 24, when the driving roller 23 is rotated, the belt 25 moves in the transport direction. The tensioner 24 is for adjusting the tension of the belt 25 and ensuring the frictional force between the belt 25 and the driving roller 23.

  The belt 25 is a belt having a predetermined width, and the sheet S is transported when the sheet S is placed on the belt 25. The belt 25 has holes that are uniformly distributed. The suction unit 26 generates a negative pressure and sucks the paper S from the hole formed in the belt 25. By doing so, the paper S is attracted onto the belt 25 and is conveyed along with the movement of the belt 25.

  The hydrator unit 30 is for ejecting transparent liquid droplets onto the paper S. The hydrator unit 30 has a head 31 having a plurality of nozzles. The amount of liquid droplets discharged from each nozzle is controlled by the controller 60. The arrangement of the nozzles of the hydrator unit 30 will be described later. The head 31 of the hydrator unit 30 is included in a second liquid discharge unit that discharges transparent liquid droplets in order to mitigate the occurrence of the cockling phenomenon.

  The head unit 40 is for ejecting ink droplets onto the paper S. The head unit 40 includes a head 41 having a plurality of nozzles. The ink droplets ejected from the head unit are colored ink droplets. For example, liquid droplets of yellow Y, magenta M, cyan C, and black K are ejected. By ejecting these ink droplets, an image is formed on the paper S. The head 41 of the head unit 40 is included in a first liquid ejection unit that ejects color ink droplets onto the paper S.

  The arrangement of the nozzles of the hydrator unit 30 and the head unit 40 will be described later.

  The detector group 50 includes, for example, a rotary encoder attached to a driving roller. Then, the output from the rotary encoder is input to the controller 60, and is used for control such as paper conveyance.

  The controller 60 is a control unit for controlling the printer 1. The controller 60 includes a processing unit and a memory. The processing unit is an arithmetic device for controlling the entire printer. The memory has a storage area for storing programs executed by the processing unit and data. The controller 60 controls each unit by executing a program stored in the memory by the processing unit.

  The reversing unit 70 opens and closes the open / close gates 72 and 73 to pull the paper S on which the front surface has been printed into the reversing unit 71. After that, it has a function of transporting the paper and feeding it again. In this way, the back side of the paper can be printed.

  The interface 80 is an interface such as a USB interface for connecting to the computer 110. By connecting to the interface 80 and connecting to the computer 110, print data can be acquired from the computer 110. The print data will be described later. Note that although a wired interface is used here, an interface capable of transmitting and receiving print data by applying wireless technology can also be employed.

  The computer 110 creates and transmits print data for an image to be printed by the printer 1. A printer driver is installed in the computer 110. When image data to be printed is sent from an application running on the OS of the computer 110, the printer driver converts the data into print data necessary for print processing to be described later. The print data includes pixel data indicating what size dot each nozzle of the printer 1 forms for each pixel on the paper.

<About the configuration of the head>
FIG. 3 is a diagram for explaining the arrangement of the heads in the head unit 40 and the hydrator unit 30. In the figure, the printer 1 is viewed from above. Originally, the nozzle hole of the head is obstructed by other elements and cannot be seen from above, but here it is drawn so that the state of the nozzle hole can be observed from above for convenience of explanation.

  The head unit 40 is classified into four units: a yellow head unit Y, a magenta head unit M, a cyan head unit C, and a black head unit K. Each head unit includes four heads 41. Each head has four nozzle rows. In each nozzle row, 180 nozzles are formed at intervals of 180 dpi. The papers are arranged so as to be shifted from each other by 720 dpi in the paper width direction (perpendicular to the transport direction). By doing so, an image can be formed with a resolution of 720 dpi in the width direction of the paper.

  The hydrator unit 30 also includes four heads. Similarly, each head has four nozzle rows. In each nozzle row, 180 nozzles are formed at intervals of 180 dpi. Then, by disposing each other by 720 dpi in the paper width direction, transparent liquid droplets can be ejected at a resolution of 720 dpi in the paper width direction.

  Each nozzle of the head included in the head unit 40 and the hydrator unit 30 is provided with an elastic plate and a piezoelectric element, which will be described later. The elastic plate is vibrated by driving the piezo element so that ink droplets can be ejected from the nozzles. Note that the number of heads 31 included in the hydrator unit 30 is ¼ of the number of heads 41 included in the head unit 40. That is, the number of nozzles included in the hydrator unit 30 is ¼ that of the nozzles included in the head unit 40 and is small. On the other hand, each nozzle of the head 31 of the hydrator unit 30 is configured to eject a liquid amount four times the amount of liquid contained in the dots formed by the nozzles of the head 41 of the head unit 40.

  For example, the amount of liquid contained in the small dots formed by the nozzles of the head 31 of the hydrator unit 30 includes a liquid amount four times that of the small dots formed by the nozzles of the head 41 of the black head unit K. . Similarly, the amount of liquid contained in the medium dots formed by the nozzles of the head 31 includes four times the amount of liquid as the medium dots formed by the nozzles of the head 41, and includes the large dots formed by the nozzles of the head 31. The liquid amount includes a liquid amount four times as large as the large dots formed by the nozzles of the head 41. The configuration of the head capable of ejecting four times the amount of liquid will be described later.

<About the head>
FIG. 4 is a diagram for explaining the structure of the heads 31 and 41. In the figure, a nozzle Nz, a piezo element PZT, an ink supply path 402, a nozzle communication path 404, and an elastic plate 406 are shown.

  The ink supply path 402 is supplied with ink drops or transparent liquid drops from an ink tank (not shown). These ink droplets and the like are supplied to the nozzle communication path 404. A drive pulse described later is applied to the piezo element PZT. When the drive pulse is applied, the piezo element PZT expands and contracts according to the signal of the drive pulse and vibrates the elastic plate 406. An amount of liquid droplets corresponding to the amplitude of the drive pulse is ejected from the nozzle Nz.

  The basic structure of the head is substantially the same for the ink droplet and the transparent liquid droplet. However, the diameter of the nozzle Nz and the like are changed according to the required discharge amount of the liquid droplets.

<About drive signal>
FIG. 5 is a diagram for explaining a drive signal. As shown in the figure, the drive signal COM is repeatedly generated every repetition period T. The drive signal includes a drive pulse PS1 in the period T1, a drive pulse PS2 in the period T2, a drive pulse PS3 in the period T3, and a drive pulse PS4 in the period T4. The drive pulse PS1 is applied to a piezo element PZT of the head, which will be described later, thereby ejecting a liquid droplet for forming a medium dot. When the driving pulse PS2 is applied to the piezo element PZT, the meniscus (the free surface of the ink exposed at the nozzle portion) is slightly vibrated. The drive pulse PS3 is applied to the piezo element PZT, thereby ejecting a liquid droplet for forming a small dot. The drive pulse PS4 is applied to the piezo element PZT, thereby ejecting a liquid droplet for forming a large dot.

  These drive pulses are selectively applied to the piezo element PZT to form dots in pixels to be described later. A drive signal including these drive pulses is generated by a drive signal generation circuit (not shown) included in the controller 60.

<When the distribution of liquid droplets that land on the medium is biased (reference example)>
FIG. 6 is a diagram for explaining the cockling phenomenon. In the figure, a sheet S is shown, and further a view of the sheet S viewed from the side and a view of the sheet S viewed from below are shown. An image A is formed on a portion of the paper S. The image A is printed with a high amount of liquid per unit area for explaining the cockling phenomenon. For example, the image A is formed by high density printing such as solid printing.

  When such printing is performed, a large amount of ink droplets adhere to the area of the image A. Then, the fibers of the paper S absorb the moisture of the ink droplets and expand. On the other hand, since the fibers do not expand in other regions, the portion where the ink droplets land is deformed into a raised shape as compared with the other regions. Then, wrinkles are formed on the paper S. Such a phenomenon is called a cockling phenomenon (cockle).

  Such deformation is caused by a large amount of ink droplets adhering only to a specific location. Therefore, it is considered that not only the area of the image A but also the ink droplets are landed on other areas, so that the fibers in the other areas are similarly expanded and the deformation of the paper S can be reduced. It is done. In this case, transparent liquid droplets are landed on other areas so as not to affect the expressed image.

  The hydrator unit 30 included in the printer 1 is provided to eject the above-described transparent liquid droplets onto the paper S. For example, when an image as shown in FIG. 6 is formed, the hydrator unit 30 discharges a transparent liquid droplet to a place other than the place where the image A is formed. By doing in this way, the fiber of the whole paper S expand | swells, Therefore A cockling phenomenon can be relieved.

  In order to make the expansion amount of the fiber of the entire sheet S the same as the expansion amount of the fiber in the place where the image is formed, the water amount per unit area of the place where the image is formed is almost the same. It is necessary to be able to eject transparent liquid droplets. The printer 1 forms an image while the paper S is being conveyed. Therefore, the hydrator unit 30 that discharges transparent liquid droplets is required to have a discharge capability that can discharge the same amount of liquid droplets as the amount of ink droplets that form an image per unit time. In order to do this, it is conceivable that substantially the same head unit as the head unit 40 is used as a hydrator unit, and transparent ink droplets are ejected from the same number of nozzles as the head unit 40.

  FIG. 7 is a diagram when the same head unit 40 is used as the hydrator unit 30 ′. In this way, the number of heads 31 ′ of the hydrator unit 30 ′ is made the same as the number of heads for all colors, and the same amount of liquid droplets as the ink discharge amount of the head unit 40 per unit time are discharged. Can be done.

  FIG. 8 is a diagram when large dots are formed in all colors when the number of heads 31 ′ of the hydrator unit 30 ′ is the same as the number of heads of each color. In the figure, yellow Y, magenta M, cyan C, and black K ink droplets are sequentially ejected onto one pixel. Here, ink droplets are formed such that each color forms a large dot in one pixel. In the figure, since ink droplets are ejected to the same pixel, the ink droplets of these colors are shown superimposed. On the other hand, in the figure, a nozzle H for discharging a transparent liquid droplet is shown. Again, transparent liquid droplets that form large dots from four nozzles H in one pixel are ejected. In this way, the same amount of transparent liquid as that of the color ink can be discharged per unit time.

  Since the hydrator unit 30 ′ is equivalent to the head unit 40, the hydrator unit 30 ′ has gradation expression power equivalent to that expressed by the ink droplets ejected from the head unit 40. For example, when the nozzle of the head unit 40 can form no dots, small dots, medium dots, and large dots, the nozzles of the hydrator unit 30 ′ have the same size for the small dots, medium dots, and large dots, respectively. Can be formed.

  However, since the transparent liquid is used to alleviate the occurrence of the cockling phenomenon, it does not require the gradation expression power that the colored ink droplets express. Therefore, by roughening the gradation expression of transparent liquid droplets, the number of nozzles is smaller than the number of nozzles that eject ink droplets, and the amount of liquid is almost the same as the ejection amount per unit time of liquid droplets that form images. The droplets can be discharged to reduce the occurrence of the cockling phenomenon.

  In the embodiment described below, transparent liquid droplets of an amount close to the ejection amount per unit time of ink droplets forming an image are ejected with a smaller number of nozzles than the number of nozzles ejecting ink droplets.

  Note that although it is a “transparent liquid”, the substance that affects the deformation of the paper S is moisture. Therefore, this transparent liquid may be pure water. However, in order to discharge more stably from the nozzle, it is preferable that the transparent liquid has as close physical properties as ink. Therefore, in the embodiment described below, a mixture of an organic solvent for preventing moisture from drying on the nozzle surface, a surfactant that affects the penetration into the paper, and water is used as a transparent liquid. However, the composition is not limited to this.

<Discharge amount of transparent liquid drops>
FIG. 9A is a diagram for explaining a configuration in which the number of heads 31 of the hydrator unit 30 is smaller than the number of heads 41 included in the head unit 40. In the figure, nozzles of four colors from yellow Y to black K are arranged toward the downstream side in the sheet conveyance direction. Further, a nozzle H for ejecting transparent liquid droplets is disposed on the downstream side in the transport direction. Again, YMCK ink droplets are ejected in sequence on one pixel. The amount of ink droplets ejected here is also such an amount that each nozzle forms a large dot. In contrast, the nozzle H for ejecting transparent liquid droplets ejects liquid droplets of an amount corresponding to four large dots to one pixel with one nozzle.

  FIG. 9B is a diagram for explaining the amount of liquid droplets that can be ejected by the nozzles of the hydrator unit 30. In the upper diagram, the amount of liquid droplets that can be ejected by the nozzles of the head unit 40 is shown for comparison. In order from the left, a state of landing on a sheet with a liquid amount for forming small dots, a liquid amount for forming medium dots, and a liquid amount for forming large dots is shown. On the other hand, in the lower diagram, the amount of liquid droplets that can be discharged from the nozzles of the hydrator unit 30 is shown. From left to right, the amount of liquid to form a small dot in a transparent liquid drop, the amount of liquid to form a medium dot in a transparent liquid drop, and the amount of liquid to form a large dot in a transparent liquid drop It shows how it landed on the paper.

  Here, the liquid amount for forming the small dots in the transparent liquid droplet is a liquid amount four times the liquid amount for forming the small dots ejected from the head unit 40. Similarly, the liquid amount for forming the medium dots in the transparent liquid droplet is four times the liquid amount for forming the medium dots ejected from the head unit 40. Further, the liquid amount for forming large dots in the transparent liquid droplet is four times the liquid amount for forming the large dots ejected from the head unit 40. By doing so, it is possible to eject transparent liquid droplets in an amount corresponding to the total amount of ink ejected from one color nozzle of the head unit 40 to one pixel.

  In order to eject transparent liquid droplets in such an amount, in this embodiment, the diameter of each nozzle of the hydrator unit 30 is made larger than the diameter of each nozzle of the head unit 40 (FIG. 3). Further, in order to eject a transparent liquid droplet in such an amount, the drive signal is also different from that for ejecting a color ink droplet.

  FIG. 10 is a diagram illustrating a drive signal for ejecting a transparent liquid droplet. The drive signal COM ′ applied to the piezo element PZT included in the hydrator unit 30 is different from the drive signal for ejecting ink droplets, and the amplitude of the drive pulse applied to the piezo element PZT is , Larger than that for ejecting ink droplets. For example, the maximum amplitude hs 'of the drive pulse PS3' for small dots of transparent liquid droplets is larger than the maximum amplitude hs of the drive pulse PS3 for small dots of ink droplets. Similarly, the maximum amplitude hm 'of the drive pulse PS1' for medium dots in a transparent liquid droplet is larger than the maximum amplitude hm of the drive pulse PS1 for medium dots of an ink droplet. Further, the maximum amplitude hl 'of the driving pulse PS4' for large dots of transparent liquid droplets is larger than the maximum amplitude hl of the driving pulse PS4 for large dots of ink droplets.

  Note that the maximum amplitudes hs ′, hm ′, and hl ′ are determined in consideration of the nozzle diameter of the head 31 and can eject liquid droplets four times as large as the ink droplets of the nozzles of the head unit 40, respectively. It is decided so.

<Pixel data>
The printer 1 ejects ink droplets and transparent liquid droplets based on the pixel data. Here, the pixel data will be described. The method for generating pixel data for color ink droplets will be described in the section “Pixel data generation processing”, and the method for generating pixel data for transparent liquid droplets is described in “Processing for generating pixel data for transparent liquid droplets”. This will be described in the section.

  Pixel data is data relating to pixels of an image to be printed. Here, the pixel is a square grid virtually defined on the paper, and indicates a region where dots are formed. The pixel data in the print data is data relating to dots formed on the paper. In this embodiment, the pixel data includes data “00” corresponding to no dot, data “01” corresponding to a small dot, data “10” corresponding to a medium dot, and data “10” corresponding to a large dot. 11 ”. These data are prepared for each color (YMCK) and transparent liquid. Pixel data corresponding to the dot size is set for each pixel. Based on this, either no dot, small dot, medium dot, or large dot is ejected to each pixel.

  As described above, the dot sizes that can be formed for each color (YMCK) ink droplet and the transparent liquid droplet are different, but each color (YMCK) and the transparent liquid droplet can be expressed for one pixel. The logarithm is the same for all four gradations.

  Pixel data is included in the print data. The print data is data in a format that can be interpreted by the printer 1, and is data having various command data and pixel data. The command data is data for instructing the printer 1 to execute a specific operation. The command data includes, for example, command data for a paper feed instruction, a conveyance amount instruction, a paper discharge instruction, and a paper reversal instruction.

<Pixel data generation processing>
FIG. 11 is a flowchart for explaining pixel data generation processing. Here, a method for creating pixel data for color ink application will be described with reference to this flowchart.

  First, the printer driver performs resolution conversion processing based on the sent image data (S1102). The resolution conversion process is a process of converting image data (text data, image data, etc.) to a resolution for printing an image on the paper S.

  Next, the printer driver performs color conversion processing based on the image data converted to the print resolution (S1104). The color conversion process is a process of converting each RGB pixel data of the RGB image data into data having gradation values in multiple levels (256 levels in this embodiment) represented by the YMCK color space. This color conversion processing is performed by referring to a table (color conversion lookup table) in which RGB gradation values and YMCK gradation values are associated with each other.

  Next, the printer driver performs halftone processing based on the YMCK tone value data (S1104). The halftone process is a process of converting gradation value data having multi-stage gradation values into small-stage pixel data that can be expressed by the printer 1. A technique such as a dither method is used for the halftone process. By halftone processing, 2-bit pixel data indicating four gradation values is obtained from data indicating 256 gradation values.

<Transparent Liquid Drop Pixel Data Generation Processing>
Here, a description will be given of pixel data generation processing in which a transparent liquid droplet is ejected to a place where no image is formed. Then, how the transparent liquid droplet ejection amount corresponding to the ink droplet ejection amount is determined will be described.

FIG. 12 is a flowchart for explaining pixel data generation processing of a transparent liquid droplet. Hereinafter, pixel data generation processing of a transparent liquid drop will be described according to this flowchart.
In the printing process described later, the pixel data generation process described above is performed before the pixel data generation process for the transparent liquid droplet is performed. Then, pixel data for color ink droplets in each pixel is generated. Here, the ink amount for each pixel is calculated based on the pixel data (S1202).

  FIG. 13 is a diagram for explaining how the paper S is divided in units of pixels. Here, for ease of explanation, the description will be divided into 12 pixels, but an actual pixel is 1/720 inch × 1/720 inch square and is extremely small. Therefore, in practice, the paper S is divided into much more pixels.

  In this case, the ink amount of 100% is defined as the time when ink droplets of all four colors have landed on one pixel. Therefore, each large dot has a 25% ink amount. Each medium dot has an ink amount of 18.75%. Each small dot of each color has an ink amount of 12.5%. Then, an ink amount for each pixel is obtained based on these ink amount standards. For example, when yellow Y is a medium dot, magenta M is a large dot, cyan C is a small dot, and black K is no dot, the ink amount is 18.75% + 25% + 12.5% + 0% = 56.25%. It is assumed that it has landed on one pixel.

  FIG. 14 is a table for explaining the ink amount in each pixel. The table shows an example of what size dot is formed for each color corresponding to each pixel number. And the ink amount calculated | required by the above-mentioned reference | standard for every pixel number is shown.

  Next, the printer driver obtains an average ink amount of pixels from which ink droplets are ejected (S1204). Referring to FIG. 14 again, the ink droplets are ejected from the pixel numbers 4 to 9. Therefore, the average value of the ink amounts of the pixel numbers 4 to 9 is obtained. Here, the total value of the ink amounts from pixel number 4 to pixel number 9 was 443.75%. By dividing this by 6 of the number of pixels from which the liquid droplets are ejected, an average value is obtained. Here, the average value is 74.0%.

  Next, the printer driver generates pixel data of a transparent liquid droplet based on the obtained average value (S1206). The pixel data of the transparent liquid droplet is set so that the transparent liquid droplet is ejected to the pixel from which the ink droplet is not ejected. Therefore, here, the pixel data is set so that transparent liquid droplets are ejected to the pixels of pixel numbers 1 to 3 and pixel numbers 10 to 12. In pixel numbers 1 to 3 and pixel numbers 10 to 12, pixel data of transparent liquid droplets is set so that dots selected as follows are formed.

  FIG. 15 is a table for obtaining pixel data of a transparent liquid drop. The table shows the average value of the ink amount and the corresponding dot size of the transparent liquid droplet. The pixel data corresponding to the dot size is shown in parentheses. With reference to this table, pixel data of transparent liquid droplets corresponding to the average value obtained in the above is determined.

  In the above description, the average value of the ink amount was 74.0%. Referring to the table, the medium dot (10) corresponds to this. Therefore, the pixel data is set so that a transparent liquid droplet that forms a medium dot is ejected to a pixel to which no ink droplet is ejected. Specifically, “10” is set as pixel data of a transparent liquid droplet to a pixel from which no ink droplet is ejected. That is, “10” is set as pixel data of transparent liquid droplets in pixel numbers 1 to 3 and pixel numbers 10 to 12 of the transparent liquid droplets. On the other hand, “00” is set as pixel data of transparent liquid droplets in pixel numbers 4 to 9 of the pixels from which ink droplets are ejected.

  Here, the ink amount is 100% when all four colors (YMCK) form a large dot in one pixel. On the other hand, a transparent liquid droplet can discharge four times as many liquid droplets as a color ink droplet for each dot. Therefore, by ejecting transparent liquid droplets based on the pixel data generated in this way, the liquid amount per unit area that is close to the liquid amount per unit area of the ink droplet that forms the image is transparent. Liquid droplets can be ejected. In addition, the amount of liquid distributed on the paper S can be made substantially uniform, and the occurrence of the cockling phenomenon can be alleviated.

<Print processing>
FIG. 16 is a flowchart for explaining the printing process in the present embodiment. Hereinafter, the printing process will be described with reference to this flowchart.

  When printing is executed in an application running on the computer 110, image data is sent to the printer driver. Then, the printer driver generates pixel data for color ink droplets ejected from the head 41 of the head unit 40 based on the image data (S1602). The generation of pixel data for color ink droplets is performed by the above-described pixel data generation process.

  When the pixel data generation processing is completed, the printer driver next performs pixel data generation processing for transparent liquid droplets (S1604). Since this “transparent liquid droplet pixel data generation process” has already been described, a description thereof will be omitted.

  Next, the printer driver generates print data so as to include pixel data of color ink droplets and pixel data of transparent liquid droplets (S1606). The generation of the print data includes a process of changing the pixel data of the ink droplet and the pixel data of the transparent liquid droplet in the order of data to be transferred to the printer 1 and including the command data in the print data. The generated print data is output to the printer 1.

  The printer 1 performs printing based on the print data (S1608). At this time, transparent liquid droplets are ejected from the portion on the paper S where ink droplets are not ejected by the above-described configuration. Since the transparent liquid droplets are ejected in the above-described configuration, it is possible to eject the transparent liquid droplets in an amount corresponding to the ejection amount of the color ink droplets with a smaller number of nozzles than the nozzles for forming an image. it can.

=== Other Embodiments ===
<When forming dots with multiple drive pulses>
In the above-described embodiment, for ease of explanation, one liquid droplet is ejected by applying one drive pulse. Each dot of each color is formed by one liquid droplet ejected by one drive pulse. However, the number of drive pulses used to form one dot is not limited to one. For example, a plurality of drive pulses may be applied to the piezo element PZT within one repetition period T, and various dots may be formed in one pixel by ejecting a plurality of liquid droplets. Also at this time, since the largest liquid droplet ejected from the head 31 of the hydrator unit 30 is larger than the liquid droplet ejected from the head 41 of the head unit 40, a dot larger than the largest dot formed by the head unit 40 is obtained. The hydrator unit 30 can be formed.

<When used for curling measures>
FIG. 17A is a diagram for describing an image that causes a curl phenomenon. Here, a case where an image is formed only on one side (front side) of a sheet will be described.

  In the figure, a sheet S is shown, and an image A is formed so as to occupy most of the sheet. The image A is printed with a large amount of liquid per unit area to explain the curl phenomenon. For example, the image A is formed by high density printing such as solid printing.

  When such printing is performed, a large amount of ink droplets adhere to the area of the image A. Then, the fibers of the paper S absorb the moisture of the ink droplets and expand. Here, when a large amount of ink droplets adhere to the front surface, the fibers on the front surface of the paper expand. Image A is an image that occupies most of the area of the paper. Then, the fiber in the portion where the image is formed expands, and the entire sheet curls so that the front surface is outside the circumference.

  FIG. 17B is a diagram for explaining the principle of occurrence of the curl phenomenon. As can be seen from the figure, the fibers on the front surface of the paper are expanded, and the paper is curled so as to spread the front surface.

  Such deformation occurs due to many ink droplets adhering to many portions on one side of the paper S. Therefore, by causing many liquid droplets to land on many parts of the other side (back side) of the paper S, the fibers on the other side also expand in the same manner, and the deformation of the paper S can be mitigated. It is considered a thing. In this case, a transparent liquid droplet is landed on the other surface so as not to affect the expressed image.

  Such a curling phenomenon is caused by the fact that the head 31 of the hydrator unit 30 ejects transparent liquid droplets and the ink droplets and transparent liquid droplets adhere to the entire front surface of the paper S in the above-described embodiment. It is thought that it is also generated by. Therefore, in this case as well, it is considered that the occurrence of the curling phenomenon of the paper S can be alleviated by landing many transparent liquid droplets on many portions of the other surface (back surface). At this time, a transparent liquid droplet is ejected to the entire back surface so as to eject a liquid droplet of a corresponding size based on the average amount of ink droplets and liquid droplets on the front surface.

  The reversing unit 70 included in the printer 1 is provided for discharging the above-described transparent liquid droplets onto the back surface of the paper S. For example, when an image as shown in FIG. 17A is formed on the front surface, the sheet is reversed by the reversing unit 70, and a transparent liquid droplet is ejected on the back surface by the hydrator unit 30. In the present embodiment, since a transparent liquid droplet larger than the color ink droplet can be ejected, it is possible to eject a transparent liquid droplet on the back surface at a high speed.

<Others>
In the present embodiment, the “image” is not limited to an image formed on a sheet, but includes a pattern used during a semiconductor manufacturing process. The technology described above can be applied to various industrial apparatuses other than a printing method in which printing is performed by ejecting ink onto paper or the like. The main products are a textile printing apparatus (method) for patterning a fabric, a circuit board manufacturing apparatus (method) for forming a circuit pattern on a circuit board, and a DNA solution by applying a solution of DNA to a chip. Examples include a DNA chip manufacturing apparatus (method) for manufacturing a chip, a display manufacturing apparatus (method) such as an organic EL display, and the like.

  The above-described embodiments are for facilitating the 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 the head>
In the above-described embodiment, ink is ejected using a piezoelectric element. However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.
In the above-described embodiment, the head does not move relative to the printer 1. However, the printer may be of a type in which the head forms an image while moving in the paper width direction of the paper inside the printer.

=== Summary ===
(1) The liquid ejection device in the above-described embodiment includes a first liquid ejection unit and a second liquid ejection unit. The first liquid ejection unit includes the head 41 of the head unit 40 and a controller 60 including a drive signal generation circuit. The second liquid ejection unit includes a head 31 of the hydrator unit 30 and a controller 60 including a drive signal generation circuit.

The head 41 of the head unit 40 ejects paper S color ink droplets. The head 31 of the hydrator unit 30 ejects transparent liquid droplets in order to alleviate deformation (cockling phenomenon) of the paper S caused by color ink droplets. The transparent liquid droplets ejected by the head 31 can eject liquid droplets larger than the largest color ink droplet ejected by the head 41.
By doing so, it is possible to eject transparent liquid droplets in an amount corresponding to the ejection amount of the color ink droplets that form an image with a smaller number of nozzles than the nozzles that eject the color ink droplets.

(2) The head unit 40 includes a nozzle for discharging a color ink droplet, and the hydrator unit 30 includes a nozzle for discharging a transparent liquid droplet. The number of nozzles of the hydrator unit 30 is smaller than the number of nozzles of the head unit 40.
By doing in this way, the part which discharges a transparent liquid drop in the printer 1 can be made compact.

(3) Further, the nozzles of the hydrator unit 30 can eject transparent liquid droplets in an amount corresponding to the total amount of liquid ejected from a plurality of nozzles of the head unit 40 to one pixel.
By doing so, the hydrator unit 30 can eject an amount of liquid close to the amount of liquid that the head unit 40 can eject.

(4) The number of gradations that can be expressed by the color ink droplets ejected from the nozzles of the head unit 40 is equal to the number of gradations that can be expressed by the transparent liquid droplets ejected from the nozzles of the hydrator unit 30.
By doing so, it is possible to discharge transparent liquid droplets while using a structure similar to the structure for discharging color ink droplets.

(5) The size of the nozzle hole of the hydrator unit 30 is larger than the nozzle hole of the head unit 40.
By doing in this way, the nozzle of the hydrator unit 30 can discharge a transparent liquid droplet larger than the color ink droplet.

(6) Further, the nozzle of the hydrator unit 30 ejects transparent liquid droplets having a liquid amount per unit area corresponding to the liquid amount per unit area of the color ink droplets forming the image.
By doing so, the liquid droplets are ejected almost uniformly over the entire surface of the paper, and the occurrence of the cockling phenomenon can be mitigated.

(7) Moreover, the hydrator unit 30 discharges a transparent liquid drop. By doing so, the occurrence of the cockling phenomenon or the curling phenomenon can be mitigated.

(8) Further, the transparent liquid droplet is ejected on the same surface as the surface on which the color ink droplet is ejected.
By doing so, the occurrence of the cockling phenomenon can be mitigated.

(9) Further, the transparent liquid droplet is ejected to the surface opposite to the surface from which the color ink droplet is ejected.
By doing so, the occurrence of the curl phenomenon can be mitigated.

(10) Further, a reversing mechanism for reversing the paper S in order to discharge a transparent liquid droplet onto the opposite surface is further provided.
In this way, even when the head unit 40 and the hydrator unit 30 are configured to eject liquid droplets from the same direction, it is possible to eject transparent liquid droplets also to the back surface of the paper S.

(11) Needless to say, there are the following liquid ejection methods. That is, in this liquid discharge method, first, color ink droplets are discharged onto the paper S. Then, a transparent liquid droplet is ejected to alleviate the cockling phenomenon of the paper S caused by the color ink droplet, but a transparent liquid droplet larger than the maximum size of the color ink droplet is ejected.
By doing so, it is possible to eject transparent liquid droplets corresponding to the ejection amount of the color ink droplets that form an image with a smaller number of nozzles than the nozzles that eject the color ink droplets.

(12) Needless to say, there is a program for causing the above-described liquid discharge apparatus to perform the above-described liquid discharge method.

1 is a schematic diagram of an overall configuration of a printer 1. FIG. 1 is a block diagram of an overall configuration of a printer 1. FIG. FIG. 4 is a diagram for explaining the arrangement of heads in the head unit 40 and the hydrator unit 30. It is a figure for demonstrating the structure of the heads 31 and 41. FIG. It is a figure for demonstrating a drive signal. It is a figure for demonstrating a cockling phenomenon. It is a figure when the same thing as the head unit 40 is used as a hydrator unit 30 '. It is a figure when all the colors form a large dot when the number of heads 31 'of the hydrator unit 30' is the same as the number of heads of each color. FIG. 9A is a diagram for explaining a configuration in which the number of heads 31 of the hydrator unit 30 is smaller than the number of heads 41 included in the head unit 40, and FIG. It is a figure for demonstrating the quantity of an appropriate liquid drop. It is a figure which shows the drive signal for discharging a transparent liquid drop. It is a flowchart for demonstrating pixel data generation processing. It is a flowchart for demonstrating the pixel data generation process of a transparent liquid drop. It is a figure for demonstrating a mode that the paper S was divided | segmented per pixel. It is a figure for demonstrating the ink amount in each pixel. It is a table | surface for calculating | requiring the pixel data of a transparent liquid drop. 6 is a flowchart for explaining printing processing in the present embodiment. FIG. 17A is a diagram for explaining an image that causes a curl phenomenon, and FIG. 17B is a diagram for explaining a generation principle of the curl phenomenon.

Explanation of symbols

1 printer, 20 transport unit, 21 driven roller, 22 pressure roller,
23 drive roller, 24 tensioner, 25 belt, 26 suction unit,
30 hydrator units, 31 heads, 40 head units, 41 heads,
50 detector groups, 60 controllers, 70 reversing units, 80 interfaces,
110 computers

Claims (12)

A first liquid ejection unit that ejects a first liquid droplet onto the medium;
A second liquid ejection unit that ejects a second liquid droplet to relieve deformation of the medium caused by the first liquid droplet, the liquid droplet being larger than the largest liquid droplet ejected by the first liquid ejection unit A second liquid discharger capable of discharging
A liquid ejection apparatus comprising:   The first liquid ejection unit includes a first nozzle for ejecting the first liquid droplet, and the second liquid ejection unit includes a second nozzle for ejecting the second liquid droplet, and the second nozzle 2. The liquid ejection apparatus according to claim 1, wherein the number of is less than the number of the first nozzles.   3. The liquid ejection apparatus according to claim 2, wherein the second nozzle is capable of ejecting an amount of the second liquid droplet corresponding to a total amount of liquid ejected from a plurality of the first nozzles to one pixel.   4. The gradation number that can be expressed by the first liquid droplet ejected from the first nozzle is equal to the gradation number that can be expressed by the second liquid droplet ejected from the second nozzle. The liquid discharge apparatus according to 1.   The liquid ejecting apparatus according to claim 2, wherein a size of the hole of the second nozzle is larger than that of the first nozzle.   The said 2nd liquid discharge part discharges the said 2nd liquid drop so that it may become the liquid amount corresponding to the liquid amount per unit area of the said 1st liquid drop which forms an image. The liquid discharge apparatus according to 1.   The liquid ejection apparatus according to claim 1, wherein the second liquid ejection unit ejects a transparent liquid droplet as the second liquid droplet.   The liquid ejecting apparatus according to claim 1, wherein the second liquid droplet is ejected on the same surface as the surface on which the first liquid droplet is ejected.   The liquid ejection apparatus according to claim 1, wherein the second liquid droplet is ejected to a surface opposite to a surface from which the first liquid droplet is ejected.   The liquid ejecting apparatus according to claim 9, further comprising a reversing mechanism that reverses the medium in order to eject the second liquid droplet to the opposite surface. Discharging a first liquid drop onto a medium;
Discharging a second liquid drop to alleviate deformation of the medium caused by the first liquid drop, discharging a second liquid drop larger than the maximum size of the first liquid drop;
A liquid ejection method comprising: A program for operating a liquid ejection device,
Discharging a first liquid drop onto a medium;
Discharging a second liquid drop to alleviate deformation of the medium caused by the first liquid drop, discharging a second liquid drop larger than the maximum size of the first liquid drop;
A program for causing the liquid ejection apparatus to perform