JP2013144415A - Liquid discharge device and liquid discharge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve image quality by obscuring density unevenness at a joint.SOLUTION: The liquid discharge device is provided with a control unit for forming an image on a medium by repeating a discharge operation to form a band with a plurality of dots arranged in a moving direction and a conveyance direction by discharging liquid from each nozzle while moving a nozzle string in the moving direction, and a conveyance operation to convey the medium in the conveyance direction in a conveyance amount shorter than the length of the nozzle string. The device includes a storage unit which stores a plurality of mask patterns for forming a joint of each band separately in a first area using a nozzle on one end side of the nozzle string and a second area using a nozzle on the other end side of the nozzle string. The first area and second area are different in shape.The boundary between the first area and second area has a boundary line at least oblique relative to the conveyance direction and moving direction. The control unit uses, in forming the image, different mask patterns of the plurality of mask patterns for a first joint and a second joint.

Description

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

  As a liquid ejecting apparatus that forms an image on a medium by ejecting the liquid onto the medium, for example, an ink jet printer is known. Also, as such a printer, band printing is performed by repeating a transport operation for transporting a medium in the transport direction and a discharge operation for ejecting a liquid from the head while moving the head in a moving direction intersecting the transport direction. It has been known. In such a printer, there is a possibility that density unevenness such as white stripes along the moving direction may occur at the joints (band joints) of the image formed by each ejection operation due to the ejection characteristics of the printer. Therefore, in order to suppress the occurrence of density unevenness, there has been proposed one in which a band is partially overlapped with each other and the joint is formed in a complementary manner in each band (for example, patent document). 1).

JP-A-8-244253

The tendency of uneven density as described above is not the same at each joint. For example, when skew (skew) occurs in which the medium is transported while being inclined with respect to the transport direction, the magnitude of the shift amount may change within the surface of the medium (each joint). That is, even if a joint pattern (a mask pattern described later) corresponding to a specific deviation is determined, it is difficult to suppress density unevenness within the surface of the medium.
An object of the present invention is to improve image quality by making the density unevenness of a joint inconspicuous.

The main invention for achieving the above object is to provide a transport mechanism for transporting a medium in the transport direction, a nozzle array in which a plurality of nozzles for discharging liquid are arranged in the transport direction, and a movement that intersects the nozzle array with the transport direction. A moving mechanism for moving the nozzle in the direction, and by controlling the moving mechanism to move the nozzle row in the moving direction and discharging the liquid from each nozzle in the nozzle row, dots are formed in the moving direction and the transport direction. An ejection operation for forming a plurality of bands arranged in a row and a transport operation for controlling the transport mechanism to transport the medium in the transport direction with a transport amount shorter than the length of the nozzle array are repeated. A liquid ejecting apparatus comprising: a control unit that forms a first region that uses a nozzle on one end side in the transport direction of the nozzle row; A plurality of mask patterns formed separately in a second region using a nozzle on the other end side in the transport direction of the row, wherein the shapes of the first region and the second region are different from each other, and A storage section storing a plurality of mask patterns having boundary lines at least oblique to the transport direction and the movement direction at a boundary between the first area and the second area; and the control section includes the image In forming the liquid crystal, a different mask pattern of the plurality of mask patterns is used at the first joint and the second joint different from the first joint. It is.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram of an overall configuration of a printer. FIG. 2A is a schematic diagram of the overall configuration of the printer. FIG. 2B is a cross-sectional view of the overall configuration of the printer. It is a flowchart of the process at the time of printing. FIG. 4A is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head. FIG. 4B is a diagram illustrating a nozzle row for one color. It is explanatory drawing which showed the printing state to paper for every hand. 6A is an explanatory diagram showing the shape of a band joint in Comparative Example 1. FIG. 6B and 6C are explanatory diagrams in the case where there is a shift in the transport direction in Comparative Example 1. FIG. FIG. 7A is an explanatory diagram showing the shape of a band joint in Comparative Example 2. 7B and 7C are explanatory diagrams in the case where there is a shift in the transport direction. FIG. 7D is an explanatory diagram when there is a shift in the movement direction. FIG. 8A is an explanatory diagram showing the shape of a band joint in Comparative Example 3. 8B and 8C are explanatory diagrams in the case where there is a shift in the transport direction. FIG. 8D is an explanatory diagram when there is a shift in the movement direction. It is explanatory drawing of the joint formed with the mask patterns M1-M3 of this embodiment. It is a flowchart for demonstrating the process at the time of the mask pattern setting in this embodiment. It is explanatory drawing of the test pattern in this embodiment. 12A and 12B are explanatory diagrams of the print shape of the joint.

At least the following matters will become clear from the description of the present specification and the accompanying drawings.
A transport mechanism that transports the medium in the transport direction, a nozzle array in which a plurality of nozzles that discharge liquid are arranged in the transport direction, a moving mechanism that moves the nozzle array in a moving direction that intersects the transport direction, and the moving mechanism Discharge operation to form a band in which a plurality of dots are arranged in the moving direction and the transport direction by discharging the liquid from each nozzle of the nozzle row while controlling the nozzle row in the moving direction, A liquid ejector comprising: a controller that controls the transport mechanism to transport the medium in the transport direction with a transport amount shorter than the length of the nozzle row, and repeatedly forms an image on the medium. The apparatus includes a first region that uses a nozzle on one end side in the transport direction of the nozzle row and a nozzle on the other end side in the transport direction of the nozzle row. A plurality of mask patterns formed separately in the second region, wherein the shapes of the first region and the second region are different, and at the boundary between the first region and the second region, A storage unit storing a plurality of mask patterns having at least oblique boundary lines with respect to the transport direction and the moving direction, and the control unit, when forming the image, the first joint, A liquid ejection apparatus characterized by using a different mask pattern of the plurality of mask patterns at a second joint different from the first joint is clarified.
According to such a liquid ejecting apparatus, an optimal mask pattern can be determined for each joint. Therefore, density unevenness due to skew (skew) or the like can be made inconspicuous at each joint, thereby improving image quality.

In this liquid ejection apparatus, the control unit arranges a plurality of patches for confirming misalignment between the first area and the second area at each joint before forming the image on the medium. It is desirable to print a pattern and select a mask pattern to be used for each joint based on the print result of the test pattern.
According to such a liquid ejecting apparatus, since an optimal mask pattern can be selected from each test pattern print result, density unevenness at each joint when an image is actually formed on the medium can be more reliably suppressed. Can do.

In the liquid ejection apparatus, it is preferable that the control unit selects a mask pattern to be used at each joint according to the amount of skew of the medium when the medium is transported.
According to such a liquid ejecting apparatus, it is possible to suppress image quality deterioration due to skew.

In this liquid ejection apparatus, the plurality of mask patterns may have different inclinations of the boundary lines.
According to such a liquid ejecting apparatus, even when there is skew, the density unevenness of each joint can be made inconspicuous, and the image quality can be improved.

  In addition, by moving the nozzle row in which a plurality of nozzles for discharging the liquid are arranged in the conveyance direction of the medium in the movement direction intersecting the conveyance direction, the liquid is discharged from each nozzle of the nozzle row, thereby moving the movement direction and An image is formed on the medium by repeating a discharge process for forming a band in which a plurality of dots are arranged in the transport direction and a transport process for transporting the medium in the transport direction with a transport amount shorter than the length of the nozzle row. In the liquid ejection method, a second region that uses a nozzle on one end side in the transport direction of the nozzle row and a nozzle on the other end side in the transport direction of the nozzle row in a joint of each band. A plurality of mask patterns formed separately into regions, each having a different shape in the first region and the second region, and at a boundary between the first region and the second region; A plurality of mask patterns having at least slanted boundary lines with respect to the transport direction and the moving direction are prepared, and when forming the image, the first joint and the first joint are different from the first joint. The liquid ejection method is characterized by using a different mask pattern of the plurality of mask patterns at the second joint.

  In the following embodiments, an ink jet printer (hereinafter also referred to as a printer 1) will be described as an example of the liquid ejection device.

=== About the outline of the printer ===
<About printer configuration>
FIG. 1 is a block diagram of the overall configuration of the printer of this embodiment. FIG. 2A is a schematic diagram of the overall configuration of the printer of this embodiment. FIG. 2B is a cross-sectional view of the overall configuration of the printer of this embodiment. Hereinafter, the basic configuration of the printer of this embodiment will be described.

  The printer of this embodiment includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, and a controller 60. The printer 1 that has received print data from the computer 110 that is an external device controls each unit (the conveyance unit 20, the carriage unit 30, and the head unit 40) by the controller 60. The controller 60 controls each unit based on the print data received from the computer 110 and forms an image on paper. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 receiving the detection result from the detector group 50 controls each unit based on the detection result.

  A transport unit 20 (corresponding to a transport mechanism) feeds a medium (for example, paper S) to a printable position and transports the paper by a predetermined transport amount in a predetermined direction (hereinafter referred to as a transport direction) during printing. Is for. The transport unit 20 includes a paper feed roller 21, a transport motor 22 (also referred to as a PF motor), a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for automatically feeding the paper inserted into the paper insertion slot into the printer. The paper feed roller 21 has a D-shaped cross section, and the length of the circumferential portion is set to be longer than the transport distance to the transport roller 23. 23 can be conveyed. The transport motor 22 is a motor for transporting paper in the transport direction, and is configured by a DC motor. The transport roller 23 is a roller that transports the paper S fed by the paper feed roller 21 to a printable region, and is driven by the transport motor 22. The platen 24 supports the paper S being printed. The paper discharge roller 25 is a roller for discharging the printed paper S to the outside of the printer. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

  The carriage unit 30 (corresponding to a moving mechanism) is for moving (also referred to as “scanning”) the head in a predetermined direction (hereinafter referred to as a moving direction). The carriage unit 30 includes a carriage 31 and a carriage motor 32 (also referred to as a CR motor). The carriage 31 can reciprocate in the moving direction. (Thus, the head moves along the moving direction.) The carriage 31 detachably holds an ink cartridge that stores ink. The carriage motor 32 is a motor for moving the carriage 31 in the movement direction, and is constituted by a DC motor.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 has a head 41. The head 41 has a plurality of nozzles that are ink discharge portions, and discharges ink intermittently from each nozzle. The head 41 is provided on the carriage 31. Therefore, when the carriage 31 moves in the movement direction, the head 41 also moves in the movement direction. Then, by intermittently ejecting ink while the head 41 is moving in the moving direction, a row of dots (raster lines) along the moving direction is formed on the paper.

  The detector group 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, an optical sensor 54, and the like. The linear encoder 51 detects the position of the carriage 31 in the moving direction. The rotary encoder 52 detects the rotation amount of the transport roller 23. The paper detection sensor 53 detects the position of the leading edge of the paper S to be printed. The optical sensor 54 detects the presence or absence of the paper S by a light emitting unit and a light receiving unit attached to the carriage 31. The optical sensor 54 can detect the position of the edge of the paper S while being moved by the carriage 31, and can detect the width of the paper S. The optical sensor 54 also has a leading edge (an end on the downstream side in the transport direction, also referred to as an upper end) and a rear end (an end on the upstream side in the transport direction, also referred to as the lower end) of the paper S depending on the situation. It can be detected.

  The controller 60 is a control unit for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing the program of the CPU 62, a work area, and the like, and has storage means such as a RAM and an EEPROM. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

<About printing operation>
FIG. 3 is a flowchart of processing during printing. Each process described below is executed by the controller 60 controlling each unit in accordance with a program stored in the memory 63. This program has a code for executing each process.

  Print command reception (S001): First, the controller 60 receives a print command from the computer 110 via the interface unit 61. This print command is included in the header of print data transmitted from the computer 110. Then, the controller 60 analyzes the contents of various commands included in the received print data, and performs the following paper feed process, transport process, ink ejection process, and the like using each unit.

  Paper Feed Process (S002): The paper feed process is a process for supplying a medium to be printed (here, paper) into the printer and positioning the paper at a print start position (also referred to as a cue position). The controller 60 rotates the paper feed roller 21 and sends the paper to be printed to the transport roller 23. The controller 60 rotates the transport roller 23 and positions the paper fed from the paper feed roller 21 at the print start position. When the paper is positioned at the print start position, at least some of the nozzles of the head 41 are opposed to the paper.

  Dot formation process (S003): The dot formation process (corresponding to the ejection operation) is a process of intermittently ejecting ink from the head moving in the moving direction to form dots on the paper. The controller 60 drives the carriage motor 32 to move the carriage 31 in the movement direction. Then, the controller 60 discharges ink from the head based on the print data while the carriage 31 is moving. When ink droplets ejected from the head land on the paper, dots are formed on the paper. Since ink is intermittently ejected from each nozzle of the moving head, a plurality of dot rows (raster lines) composed of a plurality of dots along the movement direction are formed side by side in the transport direction on the paper. In the following description, such dot formation processing is also referred to as “pass”. An image printed in one pass (a plurality of dots formed side by side in the movement direction and the conveyance direction) is also referred to as a “band”.

  Conveyance process (S004): The conveyance process (corresponding to the conveyance operation) is a process of moving the paper relative to the head along the conveyance direction. The controller 60 drives the transport motor 22 and rotates the transport roller to transport the paper in the transport direction. By this carrying process, the head 41 can form dots at positions different from the positions of the dots formed by the previous dot formation process.

  Paper discharge determination (S005): The controller 60 determines whether or not to discharge the paper being printed. If data to be printed remains on the paper being printed, no paper is discharged. Then, the controller 60 alternately repeats the dot formation process and the conveyance process until there is no more data to be printed, and gradually prints an image composed of dots on paper.

  Paper Discharge Process (S006): When there is no more data to be printed on the paper being printed, the controller 60 discharges the paper by rotating the paper discharge roller. The determination of whether or not to discharge paper may be based on a paper discharge command included in the print data.

  Print end determination (S007): Next, the controller 60 determines whether or not to continue printing. If printing is to be performed on the next paper, printing is continued and the paper feeding process for the next paper is started. If printing is not performed on the next paper, the printing operation is terminated.

== About the configuration of the head ===
FIG. 4A is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head 41. On the lower surface of the head 41, a black ink nozzle row K, a cyan ink nozzle row C, a magenta ink nozzle row M, and a yellow ink nozzle row Y are formed. Each nozzle row includes a plurality of nozzles (180 in this embodiment) that are ejection openings for ejecting ink of each color.
The plurality of nozzles in each nozzle row are aligned at a constant interval (nozzle pitch: k · D) along the transport direction. Here, D is the minimum dot pitch in the carrying direction (that is, the interval at the highest resolution of dots formed on the paper S). K is an integer of 1 or more. For example, when the nozzle pitch is 180 dpi (1/180 inch) and the dot pitch in the transport direction is 720 dpi (1/720), k = 4.
The nozzles in each nozzle row are assigned a lower number in the downstream side in the transport direction (# 1 to # 180). That is, the nozzle # 1 is located downstream of the nozzle # 180 in the transport direction. Each nozzle is provided with a piezo element (not shown) as a drive element for ejecting ink droplets.

  FIG. 4B is a diagram showing nozzle rows for one color. As shown in the figure, for a plurality of nozzles in the nozzle row, a predetermined number of nozzles on the downstream side in the transport direction are used as downstream nozzle portions 43a, and a predetermined number of nozzles on the upstream side in the transport direction are used as upstream side nozzles 43c. A nozzle between the downstream nozzle portion 43a and the upstream nozzle portion 43c is a central nozzle portion 43b. In the present embodiment, the transport amount of the medium in each transport process (transport operation) is an added value of the length of the upstream nozzle portion 43a (or the downstream nozzle portion 43c) and the length of the central nozzle portion 43b. That is, the transport amount of the medium by the transport operation is shorter than the length of the nozzle row, and therefore the positions of the downstream nozzle portion 43a and the upstream nozzle portion 43c (positions in the movement direction) overlap during successive passes. become.

=== About the printing method ===
FIG. 5 is an explanatory diagram showing the printing state on the paper S for each hand. As described above, a band is an image (a plurality of dots formed side by side in the conveyance direction and the movement direction) printed in one pass. Here, an image is formed using the nozzle row for one color shown in FIG. 4B.

  As shown in the figure, areas R01 to R03 on the paper S are printed in the first pass (first band). Here, the region R01 is a region printed by the downstream nozzle unit 43a, the region R02 is a region printed by the central nozzle unit 43b, and the region R03 is a region printed by the upstream nozzle unit 43c. It is. In the second pass (second band), regions R03 to R05 on the paper S are printed. In the second pass, the region R03 is a region printed by the downstream nozzle portion 43a, the region R04 is a region printed by the central nozzle portion 43b, and the region R05 is printed by the upstream nozzle portion 43c. It is an area to be done. That is, a part of the region R03 is printed by the upstream nozzle part 43c when the first band is printed, and the remaining part is printed by the downstream nozzle part 43a when the second band is printed. On the other hand, the region R02 or the region R04 is printed only by the central nozzle portion 43b. Printing in such a manner that a part of the transport direction overlaps between the bands is called “partial overlap printing”, and an area formed by a plurality of bands is called “overlap area”. For example, in the figure, regions R03 to R05 correspond to one band, and regions R03 and R05 each correspond to an “overlap region”. That is, the joint of each band is an overlap region.

  Similarly, regions R05 to R07 on the paper S are printed in the third pass (third band). In the third pass, the region R05 is a region printed by the downstream nozzle portion 43a, the region R06 is a region printed by the central nozzle portion 43b, and the region R07 is printed by the upstream nozzle portion 43c. It is an area to be done. Here again, the regions R05 to R07 correspond to one band, and the regions R05 and R07 each correspond to an “overlap region”. However, the area printed by the downstream nozzle section 43a when the first band is printed on the paper S and the area printed by the upstream nozzle section 43c when the last band is printed are only one time. It will be printed with a pass.

=== Band joints ===
As described above, in this embodiment, the joint portion of the band is formed by two passes. In the following description, the first path of the two paths forming each joint is also referred to as a preceding path, and the next path is also referred to as a subsequent path.
For this reason, a nozzle that ejects ink in each pass (preceding pass and subsequent pass) and a nozzle that does not eject so that the joint of the band (for example, the region R03 in FIG. 5) is formed in two passes. A predetermined mask pattern is used. This mask pattern is stored in advance in the memory 63, for example. Then, when printing the joint portion in each pass, the controller 60 selectively ejects ink from each nozzle of the downstream nozzle portion 43a or the upstream nozzle portion 43c based on the mask pattern.
Hereinafter, printing of band joints using a mask pattern will be described.

<Comparative Example 1>
6A is an explanatory diagram showing the shape of a band joint (for example, a region R03 in FIG. 5) in Comparative Example 1. FIG. In other words, FIG. 6A shows the shape of the mask pattern. In the drawing, the region Ra is a region printed by the upstream nozzle portion 43c during the preceding pass, and the region Rb is a region printed by the downstream nozzle portion 43a during the subsequent pass. That is, in the preceding pass, ink is ejected to the region Ra using the downstream half nozzles of the upstream nozzle portion 43c, and in the subsequent pass, the upstream half of the downstream nozzle portion 43a. Ink is ejected to the region Rb using the nozzle. In Comparative Example 1, the controller 60 uses such a mask pattern to discharge ink from the corresponding nozzle in each pass to form an image of the joint portion.

  6B and 6C are explanatory diagrams in the case where there is a shift in the transport direction in Comparative Example 1. FIG. For example, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 6B due to a transport error by the transport unit 20, a blank portion that is not printed is generated between the region Ra and the region Rb along the movement direction. (It becomes a white stripe). On the other hand, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 6C, a part of the region Ra and a part of the region Rb are formed overlapping each other. In this case, since the density of the overlapping portion is high, density unevenness occurs in the moving direction. As described above, in Comparative Example 1, density unevenness such as white stripes may occur along the moving direction. When such density unevenness occurs, image quality deterioration is easily noticeable.

<Comparative example 2>
FIG. 7A is an explanatory diagram showing the shape of a band joint in Comparative Example 2. In the figure, a part of the joint shape along the moving direction is shown. In an actual joint, a plurality of shapes in the figure are formed side by side in the moving direction.
In the drawing, the region Ra is a region printed by the upstream nozzle portion 43c during the preceding pass, and the region Rb is a region printed by the downstream nozzle portion 43a during the subsequent pass. In Comparative Example 1, the boundary between the region Ra and the region Rb is parallel to the moving direction (perpendicular to the transport direction), but in the case of this Comparative Example 2, the boundary between the region Ra and the region Rb is moved. It forms so that it may become diagonal with respect to a direction and a conveyance direction, respectively. By using such a mask pattern, the controller 60 forms a plurality of regions Ra (or regions Rb) having the shape of FIG. 7A in the moving direction at the joint portion of each pass. That is, in Comparative Example 2, the boundary between the portion formed by the preceding pass and the portion formed by the subsequent pass becomes zigzag with respect to the movement direction.

  7B and 7C are explanatory diagrams in the case where there is a shift in the transport direction. Also in Comparative Example 2, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 7B, a blank portion that is not printed is generated between the region Ra and the region Rb along the movement direction. On the other hand, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 7C, a part of the region Ra and a part of the region Rb are formed overlapping each other. However, in Comparative Example 2, white stripes (blank portions) and density unevenness are not parallel (straight line) to the moving direction, but oblique (zigzag), so that the frequency component becomes high and image quality deterioration is conspicuous compared with Comparative Example 1. It becomes difficult.

  FIG. 7D is an explanatory diagram when there is a shift in the movement direction. In FIG. 7D, the formation position of the region Rb is shifted to one end side (right side in the drawing) in the movement direction with respect to the formation position of the region Ra. In this case, an unprinted blank portion is generated at the left boundary portion, and the region Ra and the region Rb are overlapped and printed at the right boundary portion. On the other hand, in the mask pattern of Comparative Example 1, blank portions and density unevenness do not occur even when shifted in the movement direction. Therefore, in the second comparative example, when the movement direction is deviated, the deterioration in image quality is more conspicuous than in the first comparative example.

<Comparative Example 3>
FIG. 8A is an explanatory diagram showing the shape of a band joint in Comparative Example 3. In the drawing, the region Ra is a region printed by the upstream nozzle portion 43c during the preceding pass, and the region Rb is a region printed by the downstream nozzle portion 43a during the subsequent pass. In the case of the comparative example 3, an oblique boundary (hereinafter also referred to as an uneven portion) is further added to the oblique boundary portion of the comparative example 2.

  8B and 8C are explanatory diagrams in the case where there is a shift in the transport direction. Also in Comparative Example 2, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 8B, a blank portion that is not printed is generated between the region Ra and the region Rb along the movement direction. On the other hand, when the formation positions of the region Ra and the region Rb are shifted in the transport direction as shown in FIG. 8C, a part of the region Ra and a part of the region Rb are formed overlapping each other. However, in Comparative Example 3, since there are uneven portions, the shape of blank portions and density unevenness is more complicated than in Comparative Example 2. For this reason, blank portions and density unevenness are less noticeable than in the case of Comparative Example 2.

  FIG. 8D is an explanatory diagram when there is a shift in the movement direction. In FIG. 8D, the formation position of the region Rb is shifted to one end side (right side in the drawing) in the movement direction with respect to the formation position of the region Ra. In this case, an unprinted blank portion is generated at the left boundary portion, and the region Ra and the region Rb are overlapped and printed at the right boundary portion. However, compared with the case of the comparative example 2 (FIG. 7D), the printed part appears in the comparative example 3 overlapping with the blank part in a shorter cycle. That is, in Comparative Example 3, the displacement in the moving direction (density unevenness) is less noticeable than in Comparative Example 2.

<This embodiment>
As described above, when the shape of the joint is the same as that in Comparative Example 3, density unevenness due to a shift in the transport direction and the movement direction can be made inconspicuous. However, even in the case of Comparative Example 3, there is a possibility that density unevenness may occur at the joint. For example, the medium (paper S) may be transported obliquely with respect to the transport direction. As described above, the conveyance of the paper S inclined with respect to the conveyance direction is also referred to as skew. If skew occurs during the conveyance of the paper S, the tendency of the amount of deviation may change at each joint between the bands. For example, even if the shape of the joint is as shown in FIG. 8A, density unevenness may be noticeable when the skew is large.

  Therefore, in this embodiment, a plurality of mask patterns (three mask patterns described later) are prepared, and the mask pattern to be used for each joint is changed according to the print result of printing the test pattern. .

  FIG. 9 is an explanatory diagram of joints formed by the mask patterns M1 to M3 of the present embodiment. The left side of the figure is a diagram showing the shape of a joint formed by each mask pattern, and the right side of the figure is a schematic explanatory diagram when a skew occurs when printing using each mask pattern.

  In the mask patterns M1 to M3 used in the present embodiment, the shape of the region Ra and the shape of the region Rb are different. Specifically, the mask patterns M1 to M3 are different in the shape of the uneven portion. The mask pattern M1 is the same as the mask pattern of Comparative Example 3.

  When skew occurs when printing using each of these mask patterns, as shown on the right side of the figure, a portion that is printed overlapping with a blank portion due to a shift in the position of the region Ra and the formation position of the region Rb Occurs. However, as can be seen from the figure, the size of the blank portion and the portion to be printed overlapping differ depending on the pattern. For example, in the mask pattern M1, when there is a skew, a blank part or a duplicated part is most noticeable (most susceptible to the influence of the skew). On the other hand, in the mask pattern M3, when there is a skew, a blank portion or a portion that is printed redundantly is most inconspicuous (is hardly affected by the skew).

  In the present embodiment, such three mask patterns M1 to M3 are stored in advance in the memory 63 or the like. Then, a test pattern for skew detection is printed on the paper S, and a mask pattern to be used for each joint is set according to the printing result.

FIG. 10 is a flowchart for explaining processing at the time of setting a mask pattern in the present embodiment.
First, the controller 60 controls the transport unit 20 and the head unit 30 to print a test pattern for skew detection on the paper S (S101).

  FIG. 11 is an explanatory diagram showing an example of a test pattern in the present embodiment. In the test pattern of the present embodiment, a plurality of rectangular patches P1 and P2 are formed along the moving direction at the joint portion of the band. The patch P1 is a patch formed by the upstream nozzle portion 43c in the nozzle row during the preceding pass. The patch P2 is a patch formed by the downstream nozzle 43a in the nozzle row during the subsequent pass. By confirming the formation positions (position shifts) of the patches P1 and P2 at each joint, it is possible to detect the occurrence of skew for each joint. For example, if there is a uniform skew when transporting the paper S, the difference between the positions where the patch P1 and the hatch P2 are formed on the one end side and the other end side in the moving direction of the joint increases as the upstream side in the transport direction. . In addition, when there is a local skew, the difference in displacement between the formation positions of the patch P1 and the hatch P2 at one end side and the other end side of the joint portion of the local portion becomes large, and the movement direction at the other joint portion. The difference in displacement between the formation positions of the patch P1 and the hatch P2 on the one end side and the other end side becomes small.

  After the test pattern as shown in FIG. 11 is printed on the paper S, the controller 60 causes the test pattern to be read by a colorimeter or a sensor (not shown) (S102). Then, the controller 60 selects any one of the three mask patterns M1 to M3 for each band joint according to the reading result (S103). For example, the mask pattern M3 that is not easily affected by the skew is set to be used at a portion (joint) where the amount of deviation due to the skew is large. On the contrary, the mask pattern M1 is set to be used at a portion (joint) where the amount of deviation due to skew is small.

12A and 12B are explanatory diagrams of the print shape of the joint.
FIG. 12A is an explanatory diagram for printing a joint having a large skew. The controller 60 selects, for example, the mask pattern M3 at the joint where the skew is large from the test pattern printing result of FIG. Then, in each pass when printing the joint, the joint is printed using the mask pattern M3.

  FIG. 12B is an explanatory diagram for printing a joint with a small skew. The controller 60 selects, for example, the mask pattern M1 at the joint with a small skew from the test pattern printing result of FIG. Then, in each pass when printing the joint, the joint is printed using the mask pattern M1.

  As described above, the printer 1 according to the present embodiment includes the transport unit 20 that transports the paper S in the transport direction, the head 31 having a nozzle row in which nozzles that eject ink are arranged in the transport direction, and the head 31. The carriage unit 30 is moved in the moving direction.

  The controller 60 moves the head 31 (in other words, the nozzle row) in the movement direction, and ejects ink from each nozzle of the nozzle row to form a band in which a plurality of dots are arranged in the movement direction and the conveyance direction, and a nozzle An image is formed on the paper S by repeatedly performing a transport process for transporting the paper S in the transport direction with a transport amount shorter than the length of the row. In the memory 63 of the printer 1, mask patterns M <b> 1 to M <b> 3 are formed by dividing the band joints into a region Ra that uses the downstream nozzle portion 43 a of the nozzle row and a region Rb that uses the upstream nozzle portion 43 c. Is remembered. The mask patterns M1 to M3 are different in the shape of the region Ra and the region Rb (the shape of the concavo-convex portion), respectively, and at the boundary between the region Ra and the region Rb, at least an oblique boundary line with respect to the transport direction and the moving direction. Have.

  The controller 60 prints a test pattern before forming an image on the paper S, and selects an optimal mask pattern for each joint according to the printing result. When an image is printed on the paper S, the image is formed using the mask pattern selected for each joint.

  By doing so, density unevenness can be made inconspicuous even when skew occurs during conveyance of the paper S and the amount of shift (skew amount) differs at each joint. Therefore, the image quality can be improved.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is 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 printer>
In the above-described embodiment, the printer is described as an example of the liquid device, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional modeling machine, liquid vaporizer, organic EL manufacturing apparatus (particularly polymer EL manufacturing apparatus), display manufacturing apparatus, film formation The same technology as that of the present embodiment may be applied to various liquid ejection devices to which inkjet technology such as a device and a DNA chip manufacturing device is applied.

<Discharge method>
In the above-described embodiment, ink is ejected using a piezoelectric element (piezo 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.

<About mask pattern>
In the embodiment described above, the prepared mask pattern has a complicated shape having an uneven portion at an oblique boundary portion between the region Ra and the region Rb. However, the present invention is not limited to this, and at least the transport direction and movement It is only necessary to include an oblique boundary line in the direction. For example, a plurality of mask patterns having different slopes of the boundary lines (oblique boundary lines) between the region Ra and the region Rb are prepared, and the mask pattern to be used for each joint is changed according to the test pattern printing result. It may be. Even in this case, even if there is a skew, it is possible to make the density unevenness inconspicuous at each joint and to improve the image quality.

  In the above-described embodiment, the number of mask patterns prepared in advance is three. However, the number of mask patterns is not limited to this, and may be two or four or more. That is, it is only necessary to prepare a plurality of mask patterns and select them according to the test pattern printing result. As the number of mask patterns increases, a more optimal pattern can be selected according to the magnitude of the skew.

<About print processing>
In the above-described embodiment, one band is formed by one pass (ejection operation). However, the present invention is not limited to this, and one band may be formed by a plurality of passes. For example, a dot row (raster line) in which dots are arranged in the moving direction using odd-numbered nozzles in a path to one end side (outward path) in the moving direction is formed, and transport processing is not performed. A dot row (raster line) in which dots are arranged in the moving direction may be formed by using even-numbered nozzles in the pass to the other end side (return pass). In this case, one band is formed by two passes.

1 printer, 20 transport unit, 21 paper feed roller,
22 transport motor, 23 transport roller, 24 platen, 25 paper discharge roller,
30 Carriage unit, 31 Carriage, 32 Carriage motor,
40 head unit, 41 head, 43a downstream nozzle part,
43b central nozzle part, 43c upstream nozzle part,
50 detector groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Optical sensor,
60 controller, 61 interface, 62 CPU,
63 memory, 64 unit control circuit,
110 computer

Claims (5)

A transport mechanism for transporting the medium in the transport direction;
A nozzle row in which a plurality of nozzles for discharging liquid are arranged in the transport direction;
A moving mechanism that moves the nozzle row in a moving direction that intersects the transport direction;
Discharging to form a band in which a plurality of dots are arranged in the moving direction and the transport direction by discharging the liquid from each nozzle of the nozzle row while controlling the moving mechanism to move the nozzle row in the moving direction A controller for controlling the transport mechanism and transporting the medium in the transport direction with a transport amount shorter than the length of the nozzle row to repeatedly form an image on the medium; and
A liquid ejection device comprising:
A plurality of joints formed by dividing each band into a first region using a nozzle on one end side in the transport direction of the nozzle row and a second region using a nozzle on the other end side in the transport direction of the nozzle row. Each having a different shape in the first area and the second area, and at least a boundary between the first area and the second area with respect to the transport direction and the moving direction. A storage unit storing a plurality of mask patterns having oblique boundary lines;
The control unit uses a different mask pattern of the plurality of mask patterns at a first joint and a second joint different from the first joint when forming the image.
A liquid discharge apparatus characterized by that. The liquid ejection device according to claim 1,
The controller prints a test pattern in which a plurality of patches for confirming misalignment between the first area and the second area are arranged at each joint before forming the image on the medium, and the test pattern Select the mask pattern to be used for each joint based on the printing results of
A liquid discharge apparatus characterized by that. The liquid ejection device according to claim 1 or 2,
The control unit selects a mask pattern to be used at each joint according to the amount of skew of the medium when transporting the medium.
A liquid discharge apparatus characterized by that. The liquid ejection device according to any one of claims 1 to 3,
The liquid ejecting apparatus according to claim 1, wherein the plurality of mask patterns have different boundary line inclinations. The movement direction and the conveyance are performed by discharging the liquid from each nozzle of the nozzle row while moving a nozzle row in which a plurality of nozzles for discharging the liquid are arranged in the movement direction intersecting the conveyance direction. Liquid discharge for forming an image on a medium by repeating a discharge process for forming a band in which a plurality of dots are arranged in a direction and a transport process for transporting the medium in the transport direction with a transport amount shorter than the length of the nozzle row A method,
A plurality of joints formed by dividing each band into a first region using a nozzle on one end side in the transport direction of the nozzle row and a second region using a nozzle on the other end side in the transport direction of the nozzle row. Each having a different shape in the first area and the second area, and at least a boundary between the first area and the second area with respect to the transport direction and the moving direction. A plurality of mask patterns having oblique boundary lines are prepared,
When forming the image, a different mask pattern of the plurality of mask patterns is used at a first joint and a second joint different from the first joint.
A liquid discharge method.

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