JP2016182717A - Liquid discharge device, and liquid discharge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the irregularity of the density of a picture image.SOLUTION: A liquid discharge device comprises: a discharge head for discharging a liquid from a nozzle; a scanning part for performing a main scan to move the discharge head in a main scanning direction relatively to a printing medium while discharging the liquid from the nozzle and a sub-scan to move the discharge head in a sub-scanning direction relatively to the printing medium; and a control part for controlling the discharge head and the scanning part in a manner to form a plurality of first raster lines containing the maximum of a nozzle using ratio or a using ratio of the nozzle, and for controlling the discharge head and the scanning part in a manner to form a second raster line between a plurality of first raster lines. The total value of the nozzle using rate at the time of forming the second raster lines is larger than the total value of the nozzle using ratio at the time of forming the first raster lines.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a liquid discharge technique for discharging liquid from a nozzle of a discharge head onto a print medium.

  2. Description of the Related Art A printing apparatus that has a nozzle row in which a plurality of nozzles are arranged in the sub-scanning direction and includes a discharge head that discharges liquid from each nozzle onto a print medium is generally known. In such a printing apparatus, main scanning for ejecting liquid from the nozzle while moving the ejection head in the main scanning direction relative to the printing medium, and movement of the ejection head in the sub scanning direction relative to the printing medium. In some cases, printing is performed on a print medium by executing sub-scanning.

  In such a printing apparatus, if an error occurs in the movement distance of the ejection head with respect to the print medium in the sub-scanning, an unnecessary streak pattern may occur at the boundary between two images formed adjacent to each other by different main scanning. In order to suppress the occurrence of the streak pattern, in Patent Document 1, control is performed such that the ends of two images formed adjacent to each other by different main scans are overlapped. Further, in order to prevent the amount of ink in the overlapping portion from becoming excessive, the amount of ink per unit area is gradually increased from 0% to 100% from the end of the ejection head toward the center.

JP 11-245384 A

  Changing the amount of liquid discharged per unit area in this way corresponds to changing the number of times that the nozzle performs liquid discharge per unit area, that is, changing the discharge frequency. By the way, the discharge amount of the liquid from the nozzle changes depending on the discharge frequency of the liquid from the nozzle. Therefore, by performing the control to change the discharge frequency as described above, the discharge amount of the nozzles between which the discharge frequency is between these (for example, intermediate) is smaller than the discharge amount of each nozzle that has the minimum or maximum discharge frequency. In some cases, the density of the printed image is reduced and unevenness occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of suppressing density unevenness of a printed image by discharging liquid from nozzles of a discharge head.

  In order to achieve the above object, a liquid discharge apparatus according to the present invention has a nozzle row in which a plurality of nozzles are arranged, a discharge head that discharges liquid from the nozzles to a print medium, and printing while discharging liquid from the nozzles Use of nozzles and a scanning unit that performs main scanning for moving the ejection head in the main scanning direction relative to the medium and sub-scanning for moving the ejection head in the sub-scanning direction relative to the print medium The ejection head and the scanning unit are controlled so as to form a plurality of first raster lines including the maximum value of the nozzle usage rate, which is a ratio, and ejection is performed so as to form a second raster line between the plurality of first raster lines. A control unit that controls the head and the scanning unit, and the total value of the nozzle usage rate when forming the second raster line is greater than the total value of the nozzle usage rate when forming the first raster line And wherein the hearing.

  In order to achieve the above object, the liquid ejection method according to the present invention performs main scanning on the ejection head relative to the print medium while ejecting liquid from the nozzles of the ejection head having a nozzle row in which a plurality of nozzles are arranged. Performing a main scan to move in the direction to form a plurality of first raster lines, a step to perform a sub-scan to move the ejection head in the sub-scan direction relative to the print medium, and a main scan to And a step of forming a second raster line between the plurality of first raster lines, and the ejection head discharges liquid to the nozzles in a plurality of areas constituting the raster line. The nozzle usage rate, which is the ratio of the area that permits printing), discharges liquid from the nozzles to the print medium based on the mask defined for each nozzle, and the first raster line is the highest nozzle usage rate. Contains the value, the total value of the nozzle usage rate in forming the second raster line, and greater than the sum of the nozzle usage rate in forming the first raster line.

  In the present invention (liquid ejection device, liquid ejection method), the total nozzle usage rate when forming the second raster line is larger than the total nozzle usage rate when forming the first raster line. Therefore, the decrease in image density in the second raster line relative to the image density in the first raster line can be made inconspicuous, and unevenness in the image density can be suppressed.

  Further, the liquid ejecting apparatus may be configured such that the total value of the nozzle usage rates when forming the second raster line is greater than 100%. Such a configuration can suppress a decrease in image density on the second raster line, and contributes to suppression of unevenness in image density.

  Further, the liquid ejection device may be configured such that the total value of the usage rates of the nozzles when forming the first raster line is 100% or less. Such a configuration contributes to suppression of uneven image density by suppressing the difference between the image density on the first raster line and the image density on the second raster line.

  In addition, liquid ejection is performed so that the nozzle usage rate of at least one nozzle out of two or more nozzles that eject liquid to the second raster line is an intermediate value between the maximum nozzle usage rate and the minimum nozzle usage rate. An apparatus may be configured.

  In addition, a mask having a nozzle usage rate defined for each nozzle is provided, and the mask is configured to apply liquid to the second raster line in the main scan that is performed first among the plurality of main scans that discharge liquid to the second raster line. The liquid ejection device may be configured so that the nozzle usage rate of the nozzles that eject ink is defined to be larger than the nozzle usage rate of the nozzles that eject liquid to the second raster line in other main scans. By performing the liquid discharge by the nozzle having a large nozzle usage rate first, it is possible to ensure the drying time of the liquid discharged by the nozzle and to execute the drying reliably.

  In addition, a mask having a nozzle usage rate defined for each nozzle is provided, and the mask is configured to apply liquid to the second raster line in the main scan that is performed first among a plurality of main scans that discharge liquid to the second raster line. The liquid ejection device may be configured so that the nozzle usage rate of the nozzles that eject ink is defined to be smaller than the nozzle usage rate of the nozzles that eject liquid to the second raster line in other main scans.

  In addition, the control unit sets the nozzle usage rate of the nozzle that discharges the liquid to the second raster line in the first main scan to be performed among the plurality of main scans that discharge the liquid to the second raster line. And the second raster in the first main scan to be performed among the plurality of main scans for discharging the liquid to the second raster line and the mask that defines the nozzle usage rate larger than the nozzle usage rate of the nozzle that discharges the liquid to the second raster line. The mask that defines the nozzle usage rate of the nozzle that discharges the liquid to the line to be smaller than the nozzle usage rate of the nozzle that discharges the liquid to the second raster line in other main scans is used depending on the range of the print medium. A liquid discharge apparatus may be configured. In such a configuration, it is possible to limit a region where control for increasing the nozzle usage rate is performed, and it is possible to reduce the burden on the ejection head in order to eject liquid from the nozzle at a high nozzle usage rate.

  Further, the nozzle that discharges the liquid to the first raster line is located in the middle of the nozzles at both ends of the nozzle row in the sub-scanning direction, and the distance for moving the discharge head relative to the print medium in the sub-scanning is The liquid ejecting apparatus may be configured to be half the distance between the nozzles at both ends of the nozzle row in the sub-scanning direction.

1 is a perspective view showing a printer according to an embodiment of a liquid ejection apparatus of the present invention. FIG. 2 is a perspective view schematically showing an internal mechanism of the printer shown in FIG. 1. FIG. 2 is a block diagram showing an electrical configuration of the printer shown in FIG. 1. FIG. 6 is a schematic diagram illustrating a scanning line in which an ejection head ejects ink in two main scans. The figure for demonstrating the discharge duty which a mask prescribes | regulates. FIG. 6 is a diagram schematically illustrating a relationship between an ejection duty and an ink ejection amount Iw. The figure which shows typically the relationship between discharge duty and dot duty. The figure which shows typically the relationship between discharge duty and dot duty. The figure which shows typically the relationship which the mask of 1st Embodiment prescribes | regulates. The figure which shows the case where main scanning is performed using the mask of 1st Embodiment. The figure which shows typically the relationship which the mask of 2nd Embodiment prescribes | regulates. The figure which shows the case where main scanning is performed using the mask of 2nd Embodiment. The figure which shows typically the relationship which the mask of 3rd Embodiment prescribes | regulates. The figure which shows the case where main scanning is performed using the mask of 3rd Embodiment.

  FIG. 1 is a perspective view showing an appearance of a printer according to an embodiment of the liquid ejection apparatus of the present invention. FIG. 2 is a perspective view schematically showing an internal mechanism of the printer shown in FIG. FIG. 3 is a block diagram showing an electrical configuration of the printer shown in FIG. The printer 1 receives print data from a host computer 100 that is an external device, and based on the print data, drops (hereinafter referred to as “ink droplets”) of an ink composition (hereinafter simply referred to as “ink”) on a print medium RM. Is discharged). As a result, an image (including information such as characters) corresponding to the print data is printed on the print medium RM. As the print medium RM, for example, a large single sheet such as JIS standard A1 size, paper such as roll paper having the same paper width as the single sheet, or a resin film may be used.

  As shown in FIG. 1, the printer 1 includes a housing 10 formed by combining three types of box members, that is, an upper box member 10 a, a lower box member 10 b, and a small box member 10 c, and a leg portion 12 that supports the housing 10. And have. The upper box member 10a and the lower box member 10b are stacked in the vertical direction. An operation panel 14 is provided on the front right side of the upper box member 10a. The operation panel 14 includes, for example, a liquid crystal display, an organic EL display, an LED lamp, and the like, and includes a display unit (not shown) for displaying various messages and an operation unit (not shown) including various switches. I have. A cartridge holder 16 for loading an ink cartridge 20 containing ink is provided on the front left side of the lower box member 10b.

  Although not shown in FIG. 1, a spindle is horizontally provided at the rear portion (back side in FIG. 1) of the lower box member 10 b, and a roll is attached to the spindle. The roll is obtained by winding a long print medium RM before printing, and the print medium RM can be drawn from the roll between the upper box member 10a and the lower box member 10b. Then, the transport unit 31 of the internal mechanism 30 sends the print medium RM pulled out from the roll to the front side, and the head unit 32 of the internal mechanism 30 prints an image on the print medium RM. The print medium RM printed in this way is further sent to the front side of the casing 10 (the front side in FIGS. 1 and 2) by the transport unit 31 and hangs downward due to its own weight.

  Next, the internal mechanism 30 will be described with reference to FIG. The internal mechanism 30 includes a scanning unit 33 for moving the head unit 32, a cap unit 34, a flushing unit 35, and the like in addition to the transport unit 31 and the head unit 32 described above.

  The transport unit 31 includes a transport motor (not shown), a transport drive roller 311, a transport driven roller (not illustrated), a suction platen 312, and the like. The transport driving roller 311 and the suction platen 312 are arranged in this order along the sub-scanning direction S that is the transport direction of the print medium RM. The transport driving roller 311 is accommodated in the upper box member 10a. On the other hand, the suction platen 312 is accommodated in the lower box member 10b. When the transport motor operates in response to a control command from the unit controller 42 (FIG. 3) of the controller 40 that controls the entire apparatus, the transport drive roller 311 that is rotationally driven by the transport motor presses the print medium RM. Rotate and feed onto the front suction platen 312.

  The suction platen 312 has a horizontal and flat surface, and supports the print medium RM fed from the transport driving roller 311 from below. The suction platen 312 has a large number of suction holes on the surface that communicate with a reduced pressure source such as a suction fan, and sucks the print medium RM. As a result, the suction platen 312 holds the print medium RM with the curl flat under the head unit 32. In addition, a smooth guide surface 312a is formed at the front end of the suction platen 312 and smoothly guides the print medium RM to be sent out downward.

  As shown in FIG. 3, the head unit 32 has an ejection head 320. As will be described later, the ejection head 320 has a plurality of nozzles arranged in the sub-scanning direction S, and is driven from the unit control unit 42 while being moved by the scanning unit 33 in the main scanning direction M (FIG. 2). Ink droplets are ejected intermittently from each nozzle in accordance with the command. Thereby, dot lines (raster lines) along the main scanning direction M are formed on the print medium RM.

  As shown in FIG. 2, the scanning unit 33 includes a guide rail 331, a carriage 332, a carriage motor 333, and the like. The guide rail 331 is provided in the upper box member 10a so as to extend horizontally in the longitudinal direction. The carriage 332 is supported by the guide rail 331 and can reciprocate (scan) horizontally along the guide rail 331 in the main scanning direction M perpendicular to the sub-scanning direction S. The carriage 332 carries the head unit 32 and moves together with the head unit 32.

  A timing belt 335 hung on a pair of pulleys 334 is disposed behind the guide rail 331. One of the pulleys 334 is connected to a rotation shaft (not shown) of the carriage motor 333. Between the pulleys 334, the timing belt 335 can travel in parallel with the guide rail 331. A part of the timing belt 335 is coupled to the carriage 332. Therefore, the carriage 332 moves in the main scanning direction M when the carriage motor 333 is actuated in accordance with a control command from the unit controller 42.

  A linear scale 336 is arranged in parallel to the main scanning direction M. The linear scale 336 has a transparent main body and a light shielding band formed at a constant period along the main scanning direction M. Then, the unit control unit 42 recognizes the amount of movement of the carriage 332 based on the result of detecting the light shielding body by the sensor mounted on the carriage 332.

  On the outside of the suction platen 312 in the main scanning direction M, a flushing part 35 and a cap part 34 are arranged side by side in the main scanning direction M as maintenance units. The head motor 32 can be moved to the flushing part 35 or the cap part 34 by operating the carriage motor 333 in accordance with a control command from the unit control part 42. For example, the carriage 332 (head unit 32) is moved to the flushing section 35, and ink is ejected from a predetermined nozzle to perform flushing. On the other hand, the flushing part 35 absorbs the ejected ink. By such a flushing process, the thickened ink can be removed from the head unit 32. Further, the cap unit 34 hermetically seals the lower surface of the head unit 32 during the period when the printer 1 is at rest, and prevents the ink from being thickened or solidified in the head unit 32.

In the printer 1 configured as described above, the controller 40 controls each unit of the printer 1 based on the print data received from the host computer 100 and prints an image corresponding to the print data on the print medium RM. The controller 40 includes a unit control unit 42, an interface unit 44, and a memory 46. The unit controller 42 is a computer configured with a CPU (Central Processing Unit) or the like. The interface unit 44 transmits and receives data between the host computer 100 which is an external device and the printer 1. The memory 46 includes a RAM (Random Access Memory), an EEPROM (Electrically
Erasable Programmable Read-Only Memory) and the like, and has an area for storing the program of the unit controller 42, a work area, and the like. Further, the memory 46 stores a mask 5 used for ink ejection control of the ejection head 320 described in detail later. Here, in the present embodiment, the mask 5 is stored in the printer 1, but the present invention is not limited to this. For example, it may be stored in the host computer 100 or in a memory other than the host computer 100 and the printer 1. In other words, any location that can be accessed by the controller 40 is acceptable.

  Then, the unit controller 42 executes the printing program stored in the memory 46, thereby alternately executing main scanning and sub-scanning, and prints an image on the printing medium RM. Here, the main scanning is an operation of moving the ejection head 320 in the main scanning direction M relative to the print medium RM while ejecting ink from the nozzles of the ejection head 320. The sub-scan is an operation for moving the ejection head 320 in the sub-scanning direction S relative to the print medium RM. In the present embodiment, main scanning is performed by moving the ejection head 320 in the main scanning direction M integrally with the carriage 332, and sub-scanning is performed by conveying the print medium RM in the sub-scanning direction S. Incidentally, the main scanning is executed in each of the forward path and the backward path of the ejection head 320 that reciprocally moves in the main scanning direction M, and the sub-scanning print medium RM on one side (arrow side) in the sub-scanning direction S. It is executed by conveying.

  FIG. 4 is a diagram schematically illustrating scanning lines in which the ejection head ejects ink in each of the two main scans executed in succession. 4A shows a scanning line that is an ink discharge destination of the discharge head 320 in the I-th main scan (I is an integer of 1 or more), and FIG. 4B shows the I-th main scan ( FIG. 4C shows a state in which the ejection head 320 moves in the sub-scan executed between the (I + 1) th main scan, and FIG. 4C shows the ink ejection destination of the ejection head 32 in the (I + 1) -th main scan. The above-described scanning line is shown superimposed on the scanning line in the I-th time. Here, the scanning line is a virtual line in which a plurality of pixels are arranged in a line in the main scanning direction M. Incidentally, as described above, the sub-scanning is executed by moving the print medium RM to the arrow side in the sub-scanning direction S. Therefore, in FIG. 4, the ejection head 320 is shown to move to the opposite side of the arrow in the sub scanning direction S (that is, the upstream side in the sub scanning direction S) in the sub scanning.

  As shown in FIG. 4A, in the ejection head 320, a nozzle row Nr is composed of a plurality of nozzles N arranged in a row at an equal pitch in the sub-scanning direction S. In the main scanning, each of the plurality of nozzles N ejects ink while moving along the scanning line L to form dots. Therefore, dots can be formed collectively along the plurality of scanning lines L by one main scanning. Here, the scanning line L is a line that virtually represents a path when the nozzle scans in the main scanning direction, and is not a line that can be visually recognized on an actual medium.

  In addition, by performing sub-scanning between successive main scans and moving the ejection head 320 by the movement distance Ds in the sub-scanning direction S, the main scanning target range W is moved in the sub-scanning direction S and the main scanning is performed. A scan can be performed. That is, when the I-th main scan is completed, the sub-scan is performed as shown in FIG. 4B, and the ejection head 320 moves in the sub-scanning direction S by the moving distance Ds. As a result, as shown in FIG. 4C, the target range W (I) for the I-th main scan and the target range W (I + 1) for the (I + 1) -th main scan move in the sub-scanning direction S. It is shifted by the distance Ds. At this time, the target ranges W (I) and W (I + 1) of the main scans that are successively executed partially overlap in the sub-scanning direction S. Then, along each scanning line L belonging to these overlapping portions Δw, ink is ejected in both the I-th main scanning and the (I + 1) -th main scanning.

  That is, in the I-th main scanning, the J-th nozzle N (J is an integer of 1 or more) counted in the sub-scanning direction S (arrow direction) in the nozzle row Nr is sub-scanning direction S in the target range W (I). Ink is ejected along the J-th scanning line L (I, J). Subsequently, when the sub-scan is executed, the nozzle N (J + K) in the nozzle row Nr counting from the nozzle N (J) in the sub-scanning direction S to the K-th (K is an integer equal to or greater than 1) nozzle N (J + K) J). In the (I + 1) -th main scan, the nozzle N (J + K) ejects ink along the scan line L (I, J). That is, along the scanning line L (I, J), the nozzle N (J) ejects ink in the I-th main scanning, and the nozzle N (J + K) ejects ink in the (I + 1) -th scanning.

  In particular, the sub-scan is executed such that half of the target range W (I + 1) of the (I + 1) -th main scan in the sub-scanning direction S becomes the overlapping portion Δw. Accordingly, in the target range W (I + 1) of the (I + 1) th main scanning, the scanning line L to which no ink is attached is arranged in the upstream half of the sub-scanning direction S, and the downstream side in the sub-scanning direction S. In half, the scanning lines L to which ink from the I-th main scanning is attached are arranged. In the (I + 1) -th main scan, ink is ejected along these scanning lines L belonging to the target range W (I + 1). Thus, ink is ejected to each scanning line L by two main scans executed successively.

  Specifically, in the example shown in FIG. 4, such sub-scanning is realized by setting the movement distance Ds to half the width Dn of the target range W of each main scanning (Dn = 2 × Ds). Here, the width Dn corresponds to the distance between the centers of the nozzles N at both ends of the nozzle row Nr in the sub-scanning direction S, and in the sub-scanning direction S of the scanning line L positioned at both ends of the main scanning target range W. It corresponds to the distance.

  In such a configuration, in each main scan, each nozzle N ejects ink while moving along the opposing scan line L. At this time, the unit control unit 42 causes the nozzle N to eject ink at a timing according to the print data, thereby causing the nozzle N to land on a predetermined pixel along the scanning line L. Specifically, the unit control unit 42 generates raster data indicating the presence or absence of dots for each pixel by rasterizing print data received from the host computer 100. In each main scan, the unit control unit 42 executes control for causing each nozzle N to eject ink at a timing when the nozzle N faces a pixel whose raster data indicates that there is a dot. As a result, dots can be formed on each pixel whose raster data indicates that there is a dot, and an image corresponding to the print data can be printed on the print medium RM.

  By the way, as described above, two main scans are performed for one scanning line L. In such a configuration, both the nozzle N positioned on the scanning line L in the first main scanning and the nozzle N positioned on the scanning line L in the second main scanning cause ink to be applied to the pixels along the scanning line L. Can be discharged. Therefore, for one pixel along the scanning line L, if at least one of the two nozzles N assigned to the scanning line L in different main scans ejects ink, a dot is applied to the one pixel. Can be formed. Therefore, the unit controller 42 (FIG. 3) causes at least one of the two nozzles N assigned to the scanning line L to which the one pixel belongs to perform ejection of ink to at least one of the nozzles. Execute control. Specifically, the unit controller 42 specifies a discharge duty for each nozzle N, which is a ratio of pixels that allow the nozzle N to discharge ink among a plurality of pixels configured along the scanning line L. 5 controls the ejection of ink from the nozzle N.

  FIG. 5 is a schematic diagram for explaining the discharge duty defined by the mask. In the table shown in the figure, a plurality of pixels P1, P2,..., P12,... Arranged in a line in the main scanning direction M along one scanning line L, and each pixel P1,. The relationship with whether or not ink can be ejected is shown. As shown in the figure, among all the pixels configured along the scanning line L, ink ejection is permitted for the number of pixels indicated by the ejection duty, and the number of pixels of the ratio obtained by subtracting the ejection duty from 100%. Ink ejection is prohibited for the pixel. Incidentally, in FIG. 5, the cases of 0%, 25%, 50%, 75% and 100% are illustrated, but the same applies to other values. In addition, the arrangement pattern of the pixels for which ink ejection is permitted and the pixels forbidden shown in FIG. 5 is an example, and can be changed as appropriate. Therefore, it is not always necessary to arrange these pixels regularly as shown in FIG.

  In the mask 5, such an ejection duty is defined for each nozzle N, and the unit control unit 42 ejects ink only to pixels in which the logical product of the raster data and the data of the mask 5 is “1”. Each nozzle N is controlled. In other words, each nozzle N is a pixel whose raster data indicates dot formation, and the corresponding ejection duty ejects ink only to pixels that permit ink ejection, and does not eject ink to other pixels. .

  This mask 5 increases the ejection duty of the nozzle N from 0% to 100% as it goes from the nozzle N at the end of the nozzle row Nr toward the center in the sub-scanning direction S. That is, the nozzle N having the minimum discharge duty (0%) located at the end of the nozzle row Nr has the maximum discharge duty (100%) located at the center of the nozzle row Nr (in the middle of the nozzles N at both ends). Until the nozzle N is reached, the discharge duty of the nozzle N increases.

  Then, by alternately executing main scanning and sub-scanning while using this mask 5, the total value of the ejection duty of the two nozzles N that eject ink along different scanning lines along one scanning line L. Is controlled to be 100% or more. Thus, the two main scans for one scanning line L complementarily execute ink ejection to a plurality of pixels configured along the scanning line L. That is, for the pixels for which ink ejection is prohibited in one main scanning, ink ejection is permitted in other main scanning, and along these scanning lines L, these two main scannings are performed. Ink can be discharged to all of the plurality of configured pixels.

  Incidentally, the amount Iw of ink that can be ejected by the nozzle N at a time varies depending on the driving frequency of the nozzle N, that is, the ejection duty (FIG. 6). FIG. 6 is a diagram schematically illustrating the relationship between the ejection duty and the ink ejection amount Iw. The relationship shown in the figure is an example schematically described for explanation, and may actually be different from that shown in FIG. In the example shown in FIG. 6, the discharge amount Iw (solid line) of a predetermined intermediate region (hereinafter simply referred to as “intermediate region” as appropriate) between the minimum discharge duty and the maximum discharge duty is the ideal discharge amount (two points). It is less than the chain line). As a result, as described below, there is a possibility that unevenness occurs in the density of the image printed on the print medium RM.

  FIG. 7 is a diagram schematically showing the relationship between the discharge duty and the dot duty of each nozzle. In the left graph of FIG. 7, the discharge duty defined for each nozzle N is shown. In the graph on the right, the dot duty of each nozzle N is shown. Here, the dot duty of the nozzle N is a case where the nozzle N discharges ink to all the pixels for which the discharge duty of the nozzle N permits ink discharge, and dots are formed along one scanning line L. Further, this corresponds to the area ratio of all the dots along the scanning line L. Therefore, ideally, the dot duty is the same as the ejection duty, as indicated by the one-dot chain line in the left graph of FIG.

  In the example of the figure, the mask 5 linearly increases the discharge duty of the nozzle N from 0% to 100%. However, in the intermediate region, the ink discharge amount Iw of the nozzle N decreases, so the dot duty is lower than the discharge duty. As a result, when one main line is formed by executing two main scans as described above, the image density of the raster line including the ink ejected by the nozzle N having the ejection duty in the intermediate region becomes light.

  FIG. 8 is a diagram schematically showing the relationship between the ejection duty and the dot duty when two main scans are executed. The left graph in the same figure shows the ejection duty, and the right graph in the same figure. Shows the dot duty. As shown in the left graph, ink is applied to each scanning line L in the overlapping portion Δw of the target range W (I) of the I-th main scan and the target range W (I + 1) of the (I + 1) -th main scan. The total discharge duty of the two nozzles N that discharge is uniformly 100%.

  However, the total dot duty of the overlapping portion Δw is partially below 100%. That is, the total value of the dot duty is 100% in each scanning line Le in which the raster line is formed by the ink ejected by the nozzle N having the maximum ejection duty and the nozzle N having the minimum ejection duty. On the other hand, in each scanning line Lc in which a raster line is formed with ink ejected by each nozzle N having a middle area ejection duty, the total value of the dot duty is less than 100%. As a result, the image density is reduced near the center of the overlapping portion Δw, and density unevenness occurs in the entire image. In order to cope with this, the present embodiment has the following configuration.

  FIG. 9 is a diagram schematically showing the relationship between the discharge duty and the dot duty of each nozzle defined by the mask of the first embodiment. In the left graph of FIG. 9, the relationship is defined for each nozzle N. The discharge duty is shown, and in the right graph of the figure, the dot duty of each nozzle N is shown. FIG. 9 is the same as FIG. 7 in that the discharge duty of the nozzle N increases from 0% to 100% from the nozzle N at the end of the nozzle row Nr toward the center in the sub-scanning direction S.

  However, as shown in the left graph of FIG. 9, the mask 5 according to the present embodiment has a discharge duty in the intermediate region as compared with a one-dot chain line pattern that linearly increases the discharge duty of the nozzle N from 0% to 100%. Is increasing. Accordingly, compared to the graph on the right side of FIG. 7, in the graph on the right side of FIG. 9, the dot duty of the nozzle N in the intermediate region is increased and corrected, and the discharge duty of the nozzle N increases linearly from 0% to 100%. doing. As a result, when a raster line is formed by executing two main scans, the occurrence of a problem that the image density becomes light near the center of the overlapping portion Δw and density unevenness occurs in the entire image is suppressed.

  FIG. 10 is a diagram schematically showing the relationship between the ejection duty and the dot duty when two main scans are executed using the mask of the first embodiment. In the left graph of FIG. 10, the ejection duty is shown. The dot duty is shown in the graph on the right side of the figure. As shown in the left graph, ink is applied to each scanning line L in the overlapping portion Δw of the target range W (I) of the I-th main scan and the target range W (I + 1) of the (I + 1) -th main scan. The total discharge duty of the two nozzles N that discharge is 100% or more.

  More specifically, the nozzle N having the maximum discharge duty and the nozzle N having the minimum discharge duty discharge ink along the scanning line Le located at both ends of the overlapping portion Δw, and the total value of these discharge duties is 100%. That is, the raster line (first raster line) formed on the scanning lines Le at both ends of the overlapping portion Δw is formed by the ink ejected by the nozzle N having the maximum ejection duty, in other words, the maximum value of the ejection duty. including.

  On the other hand, the total value of the ejection duties of the two nozzles N that eject ink along each scanning line Lc located between the scanning lines Le at both ends of the overlapping portion Δw is greater than 100%. That is, the total discharge duty of the two nozzles N that discharge ink to the raster line (second raster line) formed between the raster lines formed along the scanning lines Le at both ends of the overlapping portion Δw is: Greater than 100%. As a result, as shown in the graph on the right side of FIG. 10, in the overlapping portion Δw, the total dot duty of the two nozzles N that eject ink along each scanning line L is uniformly 100%. Yes.

  That is, in this embodiment, the total value of the discharge duty when forming the second raster line with the nozzle N having the discharge duty in the intermediate region is the discharge duty when forming the first raster line with the nozzle N having the maximum discharge duty. Is greater than the sum of Therefore, the decrease in image density in the second raster line relative to the image density in the first raster line can be made inconspicuous, and unevenness in the image density can be suppressed.

  Further, the total value of the discharge duty when forming the second raster line is larger than 100%. Such a configuration can suppress a decrease in image density on the second raster line, and contributes to suppression of unevenness in image density.

  Further, the total usage rate of the nozzles when forming the first raster line is 100% or less. Such a configuration contributes to suppression of uneven image density by suppressing the difference between the image density on the first raster line and the image density on the second raster line.

  Thus, in the present embodiment, the printer 1 corresponds to an example of the “liquid discharge device” of the present invention, the discharge head 320 corresponds to an example of the “discharge head” of the present invention, and the scanning unit 33 corresponds to the present invention. The unit controller 42 corresponds to an example of the “control unit” of the present invention, the mask 5 corresponds to an example of the “mask” of the present invention, and the printing duty corresponds to the “scan unit” of the present invention. The nozzle corresponds to an example of “nozzle usage rate”, the pixel corresponds to an example of “region” of the present invention, the ink corresponds to an example of “liquid” of the present invention, and a raster line formed along the scanning line Le The raster line formed along the scanning line Lc corresponds to an example of the “first raster line” of the present invention, and the raster line formed along the scanning line Lc corresponds to an example of the “second raster line” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, in the above embodiment, the maximum discharge duty is 100% and the minimum discharge duty is 0%, but these values may be changed as appropriate. Specifically, the maximum discharge duty may be 75% and the minimum discharge duty may be 25%.

  Alternatively, the target for increasing the total value of the discharge duty as compared with the raster line constituted by the discharge ink of the nozzle N having the maximum discharge duty can be appropriately changed. For example, a raster line composed of ink ejected by nozzles N whose ejection duty is equal to or higher than a first predetermined value (for example, 40%) and equal to or lower than a second predetermined value (for example, 60%) is targeted. Also good. In this case, the total value of the discharge duty at the time of forming the raster line composed of the discharge ink of the nozzle N having the discharge duty of the first predetermined value or more and the second predetermined value or less is the discharge ink of the nozzle N having the maximum discharge duty. It becomes larger than the total value of the discharge duty when forming the constituted raster line. On the other hand, the total value of the ejection duty when forming the raster line composed of the ejection ink of the nozzle N that is smaller than the first predetermined value or larger than the second predetermined value is the ejection ink of the nozzle N having the maximum ejection duty. It becomes equal to the discharge duty at the time of forming the constituted raster line.

  Incidentally, it can be assumed that the decrease in the discharge amount Iw shown in FIG. 6 is relatively significant at a discharge duty near the middle between the minimum discharge duty and the maximum discharge duty. Therefore, these predetermined values may be set so that an intermediate value between the minimum discharge duty and the maximum discharge duty is included between the first predetermined value and the second predetermined value.

  Furthermore, the pattern for changing the ejection duty in accordance with the position of the nozzle N in the sub-scanning direction S as shown in FIGS. 9 and 10 can be changed as appropriate. FIG. 11 is a diagram schematically showing the relationship between the discharge duty and the dot duty of each nozzle defined by the mask of the second embodiment. FIG. 12 is a diagram schematically showing the relationship between the ejection duty and the dot duty when two main scans are executed using the mask of the second embodiment. Note that the notation in FIG. 11 is the same as in FIG. 9, and the notation in FIG. 12 is the same as in FIG.

  The second embodiment shown in FIGS. 11 and 12 differs from the first embodiment shown in FIGS. 9 and 10 in that the discharge duty is increased from the nozzle N of the nozzle row Nr toward the center side in the sub-scanning direction S. Is a range (duty change range). That is, as shown in FIG. 11, in the second embodiment, the duty change range is provided only for a part of both end portions in the sub-scanning direction S, and the discharge duty is uniform in the central portion in the sub-scanning direction S. 100%. Then, as shown in FIG. 12, the duty change range in the I-th main scan and the (I + 1) -th duty change range overlap to form an overlapping portion Δw, so that the ejection head 320 in the sub-scan is formed. The travel distance is set.

  Also in the second embodiment, the nozzle N having the maximum discharge duty and the nozzle N having the minimum discharge duty discharge ink to the scanning lines Le located at both ends of the overlapping portion Δw, and these discharges The total value of the duty is 100%. That is, the raster line (first raster line) formed on the scanning lines Le at both ends of the overlapping portion Δw is formed by the ink ejected by the nozzle N having the maximum ejection duty, in other words, the maximum value of the ejection duty. including.

  On the other hand, the total ejection duty of the two nozzles N that eject ink to each scanning line Lc located between the scanning lines Le at both ends of the overlapping portion Δw is greater than 100%. That is, the total discharge duty of the two nozzles N that discharge ink to the raster line (second raster line) formed between the raster lines formed on the scanning lines Le at both ends of the overlapping portion Δw is 100%. Greater than. As a result, as shown in the graph on the right side of FIG. 12, in the overlapping portion Δw, the total dot duty of the two nozzles N that eject ink to each scanning line L is uniformly 100%.

  That is, also in the second embodiment, the total value of the discharge duty when the second raster line is formed by the nozzle N having the discharge duty in the intermediate region is the same as that when the first raster line is formed by the nozzle N having the maximum discharge duty. It is larger than the total value of the discharge duty. Therefore, the decrease in image density in the second raster line relative to the image density in the first raster line can be made inconspicuous, and unevenness in the image density can be suppressed.

  Alternatively, the pattern for changing the ejection duty in accordance with the position of the nozzle N in the sub-scanning direction S may be configured asymmetrically. FIG. 13 is a diagram schematically illustrating the relationship between the ejection duty and the dot duty of each nozzle defined by the mask of the third embodiment. FIG. 14 is a diagram schematically showing the relationship between the ejection duty and the dot duty when two main scans are executed using the mask of the third embodiment. Note that the notation in FIG. 13 is the same as in FIG. 9, and the notation in FIG. 14 is the same as in FIG.

  In the third embodiment, the change pattern of the discharge duty is asymmetric between the upstream half and the downstream half in the sub-scanning direction S. That is, in the upstream half in the sub-scanning direction S, the discharge duty of the nozzle N is α% (α is greater than 50%, for example, 60%) from the nozzle N at the upstream end of the nozzle row Nr toward the center side. To 100% (maximum discharge duty). On the other hand, in the downstream half of the sub-scanning direction S, the discharge duty of the nozzle N increases from 0% (minimum discharge duty) to α% as it goes from the nozzle N at the downstream end of the nozzle row Nr toward the center. Therefore, in the sub-scanning direction S, the discharge duty of each nozzle N in the upstream half of the nozzle row Nr is larger than the discharge duty of the nozzle N in the downstream half of the nozzle row Nr. The center nozzle N in the nozzle row Nr belongs to the upstream half and has a discharge duty of 100%.

  In the third embodiment, the nozzle N having the maximum discharge duty and the nozzle N having the minimum discharge duty are arranged along the scanning line Le located at one end of the overlapping portion Δw (downstream end in the sub-scanning direction S). Ejects ink, and the total value of these ejection duties is 100%. That is, the raster line (first raster line) formed along the scanning line Le at one end of the overlapping portion Δw is formed by the ink ejected from the nozzle N having the maximum ejection duty, in other words, the ejection duty. Includes maximum value.

  On the other hand, by repeating the main scan, the total ejection duty of the two nozzles N that eject ink along each scanning line Lc located between the scanning lines Le at one end of each overlapping portion Δw aligned in the sub-scanning direction S. The value is greater than 100%. That is, the total discharge duty of the two nozzles N that discharge ink onto a raster line (second raster line) formed between the raster lines formed along the scanning line Le at one end of each overlapping portion Δw. Is greater than 100%. As a result, as shown in the right graph of FIG. 14, in the overlapping portion Δw, the total dot duty of the two nozzles N that eject ink along each scanning line L is uniformly 100%. Yes.

  That is, also in the third embodiment, the total value of the discharge duty when forming the second raster line with the nozzle N having the discharge duty in the intermediate region is the same as that when the first raster line is formed with the nozzle N having the maximum discharge duty. It is larger than the total value of the discharge duty. Therefore, the decrease in image density in the second raster line relative to the image density in the first raster line can be made inconspicuous, and unevenness in the image density can be suppressed.

  Furthermore, according to the mask 5 of the third embodiment, the nozzle that ejects ink in the previous main scan out of the two main scans that eject ink to the raster line (second raster line) along the scan line Lc. The ejection duty of N (upstream half nozzle N) is larger than the ejection duty of the nozzle N (downstream half nozzle N) that ejects ink in the subsequent main scan. As described above, the ink is ejected by the nozzle N having a large ejection duty first, so that the drying time of the ink ejected by the nozzle N can be secured and the drying can be surely performed.

  Incidentally, the mask 5 may have a configuration opposite to that of the third embodiment. That is, the discharge duty of the nozzle N (upstream half nozzle N) that discharges ink in the main scan that is executed first is the same as the nozzle N (downstream half nozzle N) that discharges ink in the main scan that is executed later. The mask 5 can also be configured to be smaller than the discharge duty of the fourth embodiment (fourth embodiment).

  Further, the mask 5 of the third embodiment and the mask 5 of the fourth embodiment may be properly used depending on the range of the print medium RM. In such a configuration, it is possible to limit a region where the control for increasing the ejection duty is executed, and it is possible to reduce a burden on the ejection head 320 (for example, a burden on the piezoelectric element) for ejecting ink from the nozzle N with a high ejection duty. .

  In the above embodiment, the total value of the dot duty at the overlapping portion Δw is uniformly 100%, but the specific value of the total value is not limited to this. For example, the total value of the dot duty at the overlapping portion Δw may be slightly changed depending on the position in the sub-scanning direction S in the range of 100% or more.

  In the above embodiment, the case where the present invention is applied to a so-called large format printer has been described as an example. However, the application target of the present invention is not limited to this, and the present invention can also be applied to, for example, a sheet-fed desktop printer.

  Various specific methods for ejecting ink from the nozzles N are also conceivable. Therefore, either a piezo-type or a thermal-type nozzle N can be used.

  Various types of ink are also conceivable, and either water-based ink or non-water-based ink may be used. Examples of non-aqueous inks include, for example, ultraviolet curable inks that are cured by irradiation with ultraviolet rays.

  DESCRIPTION OF SYMBOLS 1 ... Printer, 320 ... Discharge head, 33 ... Scanning part, 42 ... Unit control part, 5 ... Mask

Claims (9)

A nozzle row having a plurality of nozzles, and a discharge head for discharging liquid from the nozzles onto a print medium;
Main scanning for moving the discharge head in the main scanning direction relative to the print medium while discharging liquid from the nozzle, and moving the discharge head in the sub-scanning direction relative to the print medium A scanning unit that performs sub-scanning;
The ejection head and the scanning unit are controlled so as to form a plurality of first raster lines including the maximum value of the nozzle usage rate, which is the usage rate of the nozzles, and a second raster is provided between the plurality of first raster lines. A control unit that controls the ejection head and the scanning unit to form a line;
With
The liquid ejection apparatus according to claim 1, wherein a total value of the nozzle usage rates when forming the second raster line is larger than a total value of the nozzle usage rates when forming the first raster line.   The liquid ejecting apparatus according to claim 1, wherein a total value of the nozzle usage rates when forming the second raster line is greater than 100%.   The liquid ejection apparatus according to claim 1, wherein a total value of the usage rates of the nozzles when forming the first raster line is 100% or less.   The nozzle usage rate of at least one of the two or more nozzles that discharges liquid to the second raster line is an intermediate value between the maximum nozzle usage rate and the minimum nozzle usage rate. Item 4. The liquid ejection device according to any one of Items 1 to 3. The nozzle usage rate comprises a mask defined for each nozzle,
The mask includes the nozzle usage rate of the nozzle that discharges liquid to the second raster line in the main scan that is first performed among the plurality of main scans that discharge liquid to the second raster line. 5. The liquid ejection apparatus according to claim 1, wherein the liquid ejection device is defined to be larger than the nozzle usage rate of the nozzle that ejects the liquid to the second raster line in the other main scanning. 6. The nozzle usage rate comprises a mask defined for each nozzle,
The mask includes the nozzle usage rate of the nozzle that discharges liquid to the second raster line in the main scan that is first performed among the plurality of main scans that discharge liquid to the second raster line. 5. The liquid ejection apparatus according to claim 1, wherein the liquid ejection device is defined to be smaller than the nozzle usage rate of the nozzles that eject the liquid to the second raster line in the other main scanning. 6. The controller is
Of the plurality of main scans that discharge liquid to the second raster line, the nozzle usage rate of the nozzle that discharges liquid to the second raster line in the main scan that is executed first is set to the other main scan. The mask defining greater than the nozzle usage rate of the nozzles for discharging liquid to the second raster line in scanning;
Of the plurality of main scans that discharge liquid to the second raster line, the nozzle usage rate of the nozzle that discharges liquid to the second raster line in the main scan that is executed first is set to the other main scan. The mask defining less than the nozzle usage rate of the nozzle for discharging liquid to the second raster line in scanning;
The liquid ejection device according to claim 1, wherein the liquid ejection device is selectively used depending on the range of the print medium. Nozzles that discharge liquid to the first raster line are located in the middle of the nozzles at both ends of the nozzle row in the sub-scanning direction,
The distance by which the ejection head is moved relative to the print medium in the sub-scan is half of the distance between the nozzles at both ends of the nozzle row in the sub-scan direction. The liquid ejection apparatus according to any one of the above. A first raster line is formed by performing a main scan for moving the discharge head in the main scan direction relative to the print medium while discharging liquid from the nozzle of the discharge head having a nozzle row in which a plurality of nozzles are arranged. Forming a plurality of
Performing sub-scanning for moving the ejection head in the sub-scanning direction relative to the print medium;
Performing the main scan to form a second raster line between the plurality of first raster lines;
With
The first raster line includes a maximum value of the nozzle usage rate, which is a usage rate of the nozzle,
The liquid ejection method according to claim 1, wherein a total value of the nozzle usage rates when forming the second raster line is larger than a total value of the nozzle usage rates when forming the first raster line.

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