JP2007196490A - Printing system, program, and printing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing system which prevents occurrence of banding and improves the image quality of a print image, and to provide a program and a printing device. <P>SOLUTION: The printing system is formed of (A) a moving body, (B) a conveying mechanism, and (C) a controller. The moving body moves a head for ejecting ink droplets, in a moving direction. The conveying mechanism conveys a medium in a conveying direction. The controller alternately carries out an ejection operation of ejecting an ink droplet from the head according to pixel data indicative of a gradation of a pixel, and shooting the ink droplet to the pixel on the medium, corresponding to the image data, and a conveying operation of conveying the medium by the conveying mechanism. Further when the pixel data indicates a specific gradation, the controller adjusts relative shooting locations of the first and second ink droplets, by shooting the first ink droplet to the pixel on the medium, corresponding to the image data in one ejecting operation, while shooting the second ink droplet to the pixel on the medium, corresponding to the image data in another ejection operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing system, a program, and a printing apparatus.

  In a printing apparatus such as an ink jet printer, a dot forming process that forms dots by ejecting ink droplets from a head that moves in a moving direction, and a transport that transports a medium (for example, paper, cloth, OHP paper, etc.) in the transport direction The processing is alternately repeated to print a print image composed of innumerable dots on the medium.

The image data for forming the dots is usually composed of pixel data indicating the gradation of each pixel arranged in a grid pattern. Conventionally, a print image is formed by arranging a plurality of dot rows arranged in a straight line in the movement direction in accordance with the pixels arranged in a grid pattern in the conveyance direction.
Japanese Patent Laid-Open No. 6-183033

However, if the dot row is composed of a plurality of dots arranged in a straight line in the moving direction, the image quality of the printed image may be deteriorated.
An object of the present embodiment is to suppress the occurrence of banding and improve the quality of a printed image.

  The main inventions for achieving the above object are: (A) a moving body that moves a head that discharges ink droplets in the movement direction; (B) a conveyance mechanism that conveys a medium in the conveyance direction; and (C) a pixel floor. An ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating a tone and landing the ink droplets on pixels on the medium corresponding to the pixel data; and a transport operation for transporting the medium to the transport mechanism When the pixel data indicates a specific gradation, a first ink droplet is landed on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and another controller A controller that adjusts the relative landing position of the first ink droplet and the second ink droplet by causing the second ink droplet to land on the pixel on the medium corresponding to the pixel data in the ejection operation. Characterized in that it comprises and La, the.

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

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

(A) a moving body that moves a head that discharges ink droplets in a moving direction;
(B) a transport mechanism for transporting the medium in the transport direction;
(C) an ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data; A controller that alternately repeats a transport operation for transporting a medium,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A controller for adjusting a relative landing position of the first ink droplet and the second ink droplet;
A printing system comprising (C).
According to such a printing system, the image quality of the printed image can be improved.

  In this printing system, it is preferable that the controller shifts a relative landing position of the first ink droplet and the second ink droplet in the transport direction. In addition, it is preferable that the controller adjusts a relative landing position of the first ink droplet and the second ink droplet by adjusting a conveyance amount of the medium by the conveyance mechanism. Thereby, the landing positions of the first ink droplet and the second ink droplet can be relatively shifted in the transport direction.

  In such a printing system, in the ejection operation before and after the transport operation, when the first ink droplet or the second ink droplet is landed on a reference position serving as a reference in the transport direction, the controller In the operation, the medium is transported by the transport mechanism with a reference transport amount serving as a reference, and in the discharge operation before and after the transport operation, in one discharge operation, the reference position, and in the other discharge operation, the reference position. When the first ink droplet or the second ink droplet is landed on the adjustment position shifted in the transport direction, the controller moves the transport mechanism to the transport mechanism with a transport amount different from the reference transport amount. It is desirable to transport the medium. Thereby, the landing positions of the first ink droplet and the second ink droplet can be relatively shifted in the transport direction.

  In this printing system, when the pixel data indicates a gradation different from the specific gradation, the controller applies an ink droplet to the pixel on the medium corresponding to the pixel data in one ejection operation. A dot of a predetermined size is formed by landing, the dot of the predetermined size is formed during a certain discharge operation for a certain pixel, and the predetermined dot is formed during a different discharge operation for another pixel It is desirable to form sized dots. Thereby, the image quality of the printed image formed with the dots of the predetermined size can be improved.

  In this printing system, the controller forms the dot of the predetermined size during the certain ejection operation for the pixel having the same position in the transport direction as the certain pixel, For the pixels having the same position in the transport direction, it is desirable to form the dots of the predetermined size during the another ejection operation. Thereby, the distance between dots of a predetermined size becomes uniform.

  In such a printing system, the controller forms a dot of the predetermined size during the another ejection operation for a pixel adjacent to the certain pixel, and applies to the pixel adjacent to the other pixel. Therefore, it is desirable to form dots of the predetermined size during the certain ejection operation. Thereby, the graininess of a printed image formed with dots of a predetermined size is improved.

  In this printing system, it is preferable that the dots formed by the ink droplets landing on the medium have an elliptical shape having a major axis in the movement direction. This is particularly effective in such a case.

  In this printing system, it is preferable that the controller shifts a relative landing position of the first ink droplet and the second ink droplet in the moving direction. The controller preferably adjusts the relative landing position of the first ink droplet and the second ink droplet by adjusting the ejection timing of the ink droplet from the head. In this way, the image quality of the printed image can be improved.

A moving body that moves a head that discharges ink droplets in a moving direction;
A transport mechanism for transporting the medium in the transport direction;
A printing apparatus comprising:
An ejection operation for ejecting ink droplets from the head according to pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data, and transporting the medium to the transport mechanism And the transfer operation to be repeated alternately,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A program for adjusting a relative landing position of the first ink droplet and the second ink droplet.
According to such a program, it is possible to cause the printing apparatus to print a high-quality print image.

(A) a moving body that moves a head that discharges ink droplets in a moving direction;
(B) a transport mechanism for transporting the medium in the transport direction;
(C) an ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data; A controller that alternately repeats a transport operation for transporting a medium,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A controller for adjusting a relative landing position of the first ink droplet and the second ink droplet;
A printing apparatus comprising (C).
According to such a printing apparatus, the image quality of the printed image can be improved.

=== Configuration of Printing System ===
Next, an embodiment of a printing system will be described with reference to the drawings. However, the description of the following embodiments includes embodiments relating to a computer program and a recording medium on which the computer program is recorded.

  FIG. 1 is an explanatory diagram showing an external configuration of a printing system. The printing system 100 includes a printer 1, a computer 110, a display device 120, an input device 130, and a recording / reproducing device 140. The printer 1 is a printing apparatus that prints an image on a medium such as paper, cloth, or film. The computer 110 is communicably connected to the printer 1 and outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image.

  A printer driver is installed in the computer 110. The printer driver is a program for causing the display device 120 to display a user interface and converting image data output from the application program into print data. This printer driver is recorded on a recording medium (computer-readable recording medium) such as a flexible disk FD or a CD-ROM. Alternatively, the printer driver can be downloaded to the computer 110 via the Internet. This program is composed of codes for realizing various functions.

  The “printing apparatus” means an apparatus that prints an image on a medium, and corresponds to the printer 1, for example. The “printing control device” means a device that controls the printing device, for example, a computer in which a printer driver is installed. The “printing system” means a system including at least a printing apparatus and a printing control apparatus.

=== Printer driver ===
<About the printer driver>
FIG. 2 is a schematic explanatory diagram of basic processing performed by the printer driver. The components already described are given the same reference numerals, and the description thereof is omitted.

  In the computer 110, computer programs such as a video driver 112, an application program 114, and a printer driver 116 operate under an operating system installed in the computer. The video driver 112 has a function of displaying, for example, a user interface on the display device 120 in accordance with display commands from the application program 114 and the printer driver 116. The application program 114 has a function of performing image editing, for example, and creates data related to an image (image data). The user can give an instruction to print an image edited by the application program 114 via the user interface of the application program 114. Upon receiving a print instruction, the application program 114 outputs image data to the printer driver 116.

  The printer driver 116 receives image data from the application program 114, converts the image data into print data, and outputs the print data to the printer. Here, the print data is data in a format that can be interpreted by the printer 1, and is data having various command data and pixel data. Here, the command data is data for instructing the printer to execute a specific operation. The pixel data is data relating to pixels constituting an image to be printed (printed image). For example, data relating to dots formed at positions on the paper corresponding to a certain pixel (such as dot color and size). Data).

  The printer driver 116 performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, and the like in order to convert image data output from the application program 114 into print data. Hereinafter, various processes performed by the printer driver 116 will be described.

  The resolution conversion process is a process of converting image data (text data, image data, etc.) output from the application program 114 into a resolution for printing on paper. For example, when the resolution for printing an image on paper is specified as 720 × 720 dpi, the image data received from the application program 114 is converted into image data having a resolution of 720 × 720 dpi. Note that the image data after the resolution conversion process is multi-gradation (for example, 256 gradations) RGB data represented by an RGB color space. Hereinafter, RGB data obtained by performing resolution conversion processing on image data is referred to as RGB image data.

  The color conversion process is a process for converting RGB data into CMYK data represented by a CMYK color space. The CMYK data is data corresponding to the ink color of the printer. This color conversion processing is performed by the printer driver 116 referring to a table (color conversion lookup table LUT) in which gradation values of RGB image data and gradation values of CMYK image data are associated with each other. Through this color conversion process, RGB data for each pixel is converted into CMYK data corresponding to the ink color. The data after the color conversion processing is CMYK data with 256 gradations represented by the CMYK color space. Hereinafter, CMYK data obtained by performing color conversion processing on RGB image data is referred to as CMYK image data.

  The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. For example, data representing 256 gradations is converted into 1-bit data representing 2 gradations or 2-bit data representing 4 gradations by halftone processing. In the halftone process, pixel data is created by using a dither method, γ correction, error diffusion method, or the like so that the printer can form dots dispersedly. When performing halftone processing, the printer driver 116 refers to a dither table when performing a dither method, refers to a gamma table when performing γ correction, and refers to a diffused error when performing an error diffusion method. Refer to the error memory for storage. The data subjected to the halftone process has a resolution (for example, 720 × 720 dpi) equivalent to the RGB data described above. The halftoned data is composed of 1-bit or 2-bit data for each pixel, for example.

  The rasterizing process is a process of changing matrix (grid-like) image data in the order of data to be transferred to the printer. The rasterized data is output to the printer as pixel data included in the print data.

<About printer driver settings>
FIG. 3 is an explanatory diagram of the user interface of the printer driver. The user interface of this printer driver is displayed on the display device via the video driver 112. The user can make various settings of the printer driver using the input device 130.

  The user can select a print mode from this screen. For example, the user can select the high-speed print mode or the fine print mode as the print mode. Then, the printer driver converts the image data into print data so as to have a format corresponding to the selected print mode.

  Further, the user can select the printing resolution (dot interval when printing) from this screen. For example, the user can select 720 dpi or 360 dpi as the print resolution from this screen. Then, the printer driver performs resolution conversion processing according to the selected resolution, and converts the image data into print data.

  Further, the user can select a printing paper used for printing from this screen. For example, the user can select plain paper or glossy paper as the printing paper. If the paper type (paper type) is different, the ink bleeding and drying methods are also different, so the ink amount suitable for printing also differs. Therefore, the printer driver converts the image data into print data according to the selected paper type.

  As described above, the printer driver converts the image data into print data according to the conditions set via the user interface. The user can make various settings of the printer driver from this screen, and can also know the remaining amount of ink in the cartridge.

=== Configuration of Printer ===
<Inkjet printer configuration>
FIG. 4 is a block diagram of the overall configuration of the printer 1. FIG. 5A is a schematic diagram of the overall configuration of the printer 1. FIG. 5B is a cross-sectional view of the overall configuration of the printer 1. Hereinafter, a basic configuration of the printer will be described.

  The printer 1 of this embodiment includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, and a printer-side controller 60. The printer 1 that has received print data from the computer 110, which is an external device, controls each unit (conveyance unit 20, carriage unit 30, head unit 40) by the printer-side controller 60. The printer-side controller 60 controls each unit based on the print data received from the computer 110 and prints 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 printer-side controller 60. The printer-side controller 60 controls each unit based on the detection result output from the detector group 50.

  The transport unit 20 is for transporting a medium (for example, paper S) in a predetermined direction (hereinafter referred to as a transport direction). 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 feeding the paper inserted into the paper insertion slot into the printer. The transport roller 23 is a roller that transports the paper S fed by the paper feed roller 21 to a printable area, 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 paper S to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area.

  The carriage unit 30 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 and is driven by a carriage motor 32. Further, the carriage 31 detachably holds an ink cartridge that stores ink.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 includes a head 41 having a plurality of nozzles. Since the head 41 is provided on the carriage 31, 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, dot lines (raster lines) along the moving direction are 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 being fed. The optical sensor 54 detects the presence or absence of paper 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 while being moved by the carriage 31 to detect the width of the paper. The optical sensor 54 also detects the leading end (the end on the downstream side in the transport direction, also referred to as the upper end) and the rear end (the end on the upstream side in the transport direction, also referred to as the lower end) depending on the situation. it can.

  The printer-side controller 60 is a control unit (control unit) for controlling the printer. The printer-side 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 which 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 a program of the CPU 62, a work area, and the like, and includes storage elements 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 nozzle>
FIG. 6 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 nozzle (# 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 driving each nozzle to eject ink droplets. Further, the optical sensor 54 is substantially at the same position as the nozzle # 180 on the most upstream side with respect to the position in the paper transport direction.

<About printing operation>
FIG. 7 is a flowchart of processing during printing. Each process described below is executed by the printer-side 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 printer-side 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 printer-side controller 60 analyzes the contents of various commands included in the received print data, and performs the following paper feed processing / conveyance processing / dot formation processing using each unit.

  Paper Feed Process (S002): The paper feed process is a process for supplying paper to be printed into the printer and positioning the paper at a print start position (also referred to as a cue position). The printer-side controller 60 rotates the paper feed roller 21 and sends the paper to be printed to the transport roller 23. Subsequently, the printer-side controller 60 rotates the transport roller 23 to position 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 Forming Process (S003): The dot forming process is a process for forming dots on paper by intermittently ejecting ink from a head that moves in the moving direction. The printer-side controller 60 drives the carriage motor 32 to move the carriage 31 in the movement direction. The printer-side controller 60 ejects ink from the head based on the print data while the carriage 31 is moving. When ink droplets ejected from the head 41 land on the paper, dots are formed on the paper. Since ink is intermittently ejected from the moving head 41, a dot row (raster line) composed of a plurality of dots along the moving direction is formed on the paper.

  Conveyance process (S004): The conveyance process is a process of moving the paper relative to the head in the conveyance direction. The printer-side controller 60 drives the carry motor and rotates the carry roller to carry the paper in the carrying 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 printer-side 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 printer-side controller 60 alternately repeats dot formation processing and conveyance processing 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 printer-side 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.

  Determination of printing end (S007): Next, the printer-side 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.

Meanwhile, the printer-side controller 60 controls each unit based on the print data received from the printer driver. For example, the printer-side controller 60 causes the transport unit 20 to perform a transport process according to the transport amount indicated by the command data included in the print data. Further, the printer-side controller 60 causes the head unit to eject ink droplets in the order of the pixel data included in the print data.
For this reason, it can also be said that the printer driver that generates the print data controls the printer via the print data. In this way, it can be said that the computer 110 on which the printer driver is installed and the printer-side controller 60 control the printing operation of the entire printing system. Therefore, the computer 110 in which the printer driver is installed and the printer-side controller 60 are collectively referred to as a “controller”.

=== Basic printing operation ===
<Interlaced printing>
8A and 8B are explanatory diagrams of interlaced printing. FIG. 8A shows the position of the head (or nozzle row) and the state of dot formation in pass 1 to pass 4, and FIG. 8B shows the position of the head and the state of dot formation in pass 1 to pass 6. .

  For convenience of explanation, only one nozzle row of a plurality of nozzle rows is shown, and the number of nozzles in the nozzle row is also reduced (here, 8). The nozzles indicated by black circles in the figure are nozzles that can eject ink. On the other hand, nozzles indicated by white circles are nozzles that cannot eject ink. For convenience of explanation, the head (or nozzle row) is depicted as moving with respect to the paper, but this figure shows the relative position of the head and the paper. The paper is moved in the transport direction. Also, for convenience of explanation, each nozzle is shown as having only a few dots (circles in the figure), but in reality, ink droplets are ejected intermittently from nozzles that move in the direction of movement. Therefore, a large number of dots are arranged in the moving direction. This row of dots is also called a raster line. A dot indicated by a black circle is a dot formed in the last pass, and a dot indicated by a white circle is a dot formed in a previous pass. Note that “pass” refers to an operation (dot formation operation) in which ink is ejected from a moving nozzle to form dots. Each pass is alternately performed with an operation (conveying operation) for conveying the paper in the conveying direction.

  “Interlaced printing” means a printing method in which k is 2 or more and a raster line that is not recorded is sandwiched between raster lines that are recorded in one pass. For example, in the printing method in FIGS. 8A and 8B, three raster lines are sandwiched between raster lines formed in one pass.

  In interlace printing, each time the paper is transported in the transport direction by a constant transport amount F, each nozzle records a raster line immediately above the raster line recorded in the immediately preceding pass. In order to perform recording with a constant carry amount in this way, (1) the number N (integer) of nozzles that can eject ink is relatively prime to k, and (2) the carry amount F is N · The condition is that it is set to D.

  In the figure, the nozzle row has eight nozzles arranged along the transport direction. Since the nozzle pitch k of the nozzle array is 4, in order to satisfy the condition for performing interlaced printing, “N and k are relatively prime”, all the nozzles are not used and seven nozzles (nozzles # 1 to # 1) are used. Nozzle # 7) is used. Further, since seven nozzles are used, the paper is transported with a transport amount of 7 · D. As a result, dots are formed on the paper at a dot interval of 720 dpi (= D) using a nozzle row having a nozzle pitch of 180 dpi (4 · D). Since the actual number of nozzles (90) is greater than 7, the actual transport amount (89 · D) is greater than 7 · D.

  In the case of interlace printing, k passes are required to complete a raster line having a continuous nozzle pitch width. For example, in order to complete four raster lines that are continuous at a dot interval of 720 dpi using a nozzle row having a nozzle pitch of 180 dpi, four passes are required. According to the figure, continuous raster lines are formed at dot intervals D upstream of the raster line (raster line indicated by the arrow in the figure) formed by nozzle # 2 in pass 3 in the transport direction. It has been shown.

<Overlap printing>
9A and 9B are explanatory diagrams of overlap printing. FIG. 9A shows the head position and dot formation in pass 1 to pass 8, and FIG. 9B shows the head position and dot formation in pass 1 to pass 11.

  “Overlap printing” means a printing method in which a raster line is formed by a plurality of nozzles. For example, in the printing method in FIGS. 9A and 9B, each raster line is formed by two nozzles.

In overlap printing, each time the paper is transported at a constant transport amount F in the transport direction, each nozzle intermittently forms dots every few dots. In another pass, by forming dots so that the intermittent dots already formed by other nozzles are complemented (filling between the dots), one raster line is formed by a plurality of nozzles. It is formed. When one raster line is formed in M passes in this way, it is defined as “overlap number M”.
In FIG. 9A and FIG. 9B, since each nozzle forms dots intermittently every other dot, dots are formed in odd-numbered pixels or even-numbered pixels for each pass. Since one raster line is formed by two nozzles, the overlap number M = 2.

In overlap printing, in order to perform recording with a constant conveyance amount, (1) N / M is an integer, (2) N / M is relatively prime to k, (3) The condition is that the carry amount F is set to (N / M) · D.
9A and 9B, the nozzle row has eight nozzles arranged along the transport direction. However, since the nozzle pitch k of the nozzle row is 4, not all nozzles can be used in order to satisfy “N / M and k are relatively prime”, which is a condition for performing overlap printing. Therefore, overlap printing is performed using six of the eight nozzles. Further, since six nozzles are used, the paper is transported with a transport amount of 3 · D. As a result, for example, using a nozzle row with a nozzle pitch of 180 dpi (4 · D), dots are formed on the paper at a dot interval of 720 dpi (= D).

  When one raster line is formed by M nozzles, k × M passes are required to complete a raster line for the nozzle pitch. For example, in FIG. 9A and FIG. 9B, since one raster line is formed by two nozzles, eight passes are required to complete four raster lines. According to the figure, continuous raster lines are dots upstream of the raster line (raster line indicated by the arrow in the figure) formed by nozzle # 4 in pass 3 and nozzle # 1 in pass 7 in the transport direction. It is shown that they are formed at a distance D.

  9A and 9B, in pass 1, each nozzle forms dots on odd pixels, in pass 2, each nozzle forms dots on even pixels, and in pass 3, each nozzle forms dots on odd pixels. In 4, each nozzle forms a dot at an even pixel. That is, in the first four passes, dots are formed in the order of odd pixel-even pixel-odd pixel-even pixel. In the latter four passes (pass 5 to pass 8), dots are formed in the reverse order of the first four passes, and dots are formed in the order of even pixel-odd pixel-even pixel-odd pixel. . The dot formation order after pass 9 is the same as the dot formation order from pass 1.

<Overprint printing>
10A and 10B are explanatory diagrams of overprinting. 10A shows the position of the head and the state of dot formation in pass 1 to pass 8, and FIG. 10B shows the position of the head and the state of dot formation in pass 1 to pass 11.

  “Overprint printing” means a printing method in which when a predetermined dot is formed on a certain pixel, ink droplets are landed on the pixel twice. In FIGS. 10A and 10B, dots formed by ink droplets landing twice are indicated by double circles. Further, in the figure, the dot on which the second ink droplet is landed in the last pass is shown with the circle inside the double circle being a black circle.

  In the printing method shown in the figure, a transport operation similar to the above-described overlap printing is performed. However, in the above-described overlap printing, each time the carriage 31 moves 1/360 inch in each pass, ink droplets are ejected from each nozzle to form dots in odd pixels or even pixels. Each time the carriage 31 moves 1/720 inch (the same interval as the pixels) in each pass, ink droplets are ejected from each nozzle.

  In this overprinting, there are two opportunities to land the ink droplets ejected from the nozzle on each pixel. For example, the ink droplets ejected from the nozzle # 4 in pass 3 and the ink droplets ejected from the nozzle # 1 in pass 7 land on the pixels of the dots forming the raster line indicated by the arrow in FIG. 10A. Is possible.

FIG. 11 is a diagram for explaining the drive signal COM and the applied signal applied to the piezo element.
The drive signal COM is repeatedly generated every repetition period T. The repetition period T is a period required for the carriage 31 to move 1/720 inch, in other words, a period required for the carriage 31 to cross one pixel.

  Within each repetition period T, it can be divided into four sections T1 to T4. The first section signal SS1 including the driving pulse PS1 is generated in the first section T1, the second section signal SS2 including the driving pulse PS2 is generated in the second section T2, and the driving pulse PS3 is generated in the third section T3. A third section signal SS3 including the driving pulse PS4 is generated in the fourth section T4.

  The waveforms of the drive pulses PS1 to PS4 are determined based on the operation to be performed by the piezo element. When the drive pulse PS1 is applied to the piezo element, pressure fluctuations that do not eject ink occur in the ink, and the ink meniscus (the free surface of the ink exposed at the nozzle portion) slightly vibrates. When the drive pulses PS2 and PS3 are applied to the piezo elements, 14 pl (picoliter) ink droplets are ejected. When the driving pulse PS3 is applied to the piezo element, a 3 pl ink droplet is ejected.

  An application signal corresponding to pixel data is applied to the piezo elements corresponding to the nozzles capable of ejecting ink (black circle nozzles in FIGS. 10A and 10B) at each repetition period T.

There are two timings at which ink droplets are ejected toward pixels on paper corresponding to certain pixel data.
When the pixel data indicates that no dot is formed at the first timing of the two times, the first interval signal SS1 is applied to the corresponding piezoelectric element of the pixel data, and the piezoelectric element is driven to drive pulse PS1. The ink meniscus vibrates slightly without being ejected. Further, when the pixel data indicates that a small dot is formed at the first timing, the third interval signal SS3 is applied to the corresponding piezo element of the pixel data, and the piezo element is driven by the drive pulse PS3. A 3 pl ink droplet lands on a pixel on paper corresponding to the pixel data. When the pixel data indicates that a medium dot is to be formed at the first timing, the second interval signal SS2 and the fourth interval signal SS4 are applied to the corresponding piezoelectric element of the pixel data, and the piezoelectric element is driven to drive pulses. Driven by PS2 and drive pulse PS4, a total of 14 pl ink droplets land on pixels on the paper corresponding to the pixel data. Further, when the pixel data indicates that a large dot is formed at the first timing, the second interval signal SS2 and the fourth interval signal are applied to the piezo element as in the case where the pixel data indicates that a medium dot is formed. SS4 is applied, the piezo element is driven by the drive pulse PS2 and the drive pulse PS4, and a total of 14 pl ink droplets land on the pixels on the paper corresponding to the pixel data.

  When the pixel data indicates that no dot is formed at the second timing of the two timings, the first interval signal SS1 is applied to the corresponding piezoelectric element of the pixel data, and the piezoelectric element is driven by a driving pulse. Driven by PS1, the ink meniscus vibrates slightly without ejecting ink droplets. In addition, when the pixel data indicates that a small dot or medium dot is formed at the second timing, the first interval signal SS1 is applied to the piezo element as in the case where the pixel data indicates that no dot is formed. Then, the piezo element is driven by the drive pulse PS1, and the ink meniscus slightly vibrates without ejecting ink droplets. Further, when the pixel data indicates that a large dot is formed at the second timing, the second section signal SS2 and the fourth section signal SS4 are applied to the corresponding piezoelectric element of the pixel data, and the piezoelectric element is driven. Driven by the pulses PS2 and PS4, a total of 14 pl ink droplets land on the pixels on the paper corresponding to the pixel data.

  Therefore, when the pixel data indicates that no dot is formed, the first interval signal SS1 is applied to the piezo element at both timings, and no dot is formed on the pixel on the paper corresponding to the pixel data. When the pixel data indicates that a small dot is to be formed, a 3 pl ink droplet is landed on the paper pixel corresponding to the pixel data at the first timing, and the ink droplet is not landed at the second timing. Small dots are formed by 3 pl ink drops. When the pixel data indicates that a medium dot is to be formed, a 14 pl ink droplet lands on the paper pixel corresponding to the pixel data at the first timing, and the ink droplet does not land at the second timing. A medium dot is formed by a total of 14 pl ink droplets. When the pixel data indicates that a large dot is to be formed, a 14 pl ink droplet is landed at the first timing and a 14 pl ink droplet is landed at the second timing. However, a large dot is formed by a total of 28 pl ink droplets. In other words, a large dot is formed by overlapping two medium dots with the same pixel.

=== Description of Reference Example ===
FIG. 12A is an explanatory diagram when large dots are formed on all the pixels in the positions of the dots of the reference example. Here, it is assumed that large dots are formed with a resolution of 720 dpi × 720 dpi. For convenience of explanation, dots constituting the upper two raster lines in the figure are numbered sequentially from the left.

Ink droplets are ejected from nozzles that move in the moving direction, and the ink droplets land on the paper to form dots. Therefore, the dots are elliptical with the moving direction of the carriage 31 as the major axis.
When large dots are formed with a normal size, dots are formed without gaps as shown in the figure. However, since the dots are elliptical with a long axis in the movement direction, the dots adjacent in the transport direction do not overlap much compared to the dots adjacent in the movement direction.

FIG. 12B is an explanatory diagram when a large dot becomes small.
One of the causes of dot reduction is the effect of paper. Glossy paper having an ink absorbing layer on the surface has higher ink absorbability than plain paper, so ink droplets that have landed on the paper are likely to penetrate without bleeding. For this reason, the dots formed on glossy paper are smaller than those on plain paper.
Another cause of dot reduction is head manufacturing error. For example, the ink amount of ink droplets ejected from the nozzle may be reduced due to the influence of the processing accuracy of the nozzle opening. When the ink amount of the ejected ink drops is reduced, the large dots formed by the ink drops are also reduced.
When the large dot becomes small, as shown in the figure, the dots adjacent in the transport direction are separated from each other, and a gap is generated. When a black filled image is included in the print image, a black filled image is formed with large dots, but when the large dots are small, it becomes impossible to spread the dots without gaps, as shown in the image data There is a possibility that a black filled image cannot be formed on paper.

  Further, when a raster line is formed by small large dots, as shown in the drawing, the gap extends in the moving direction, and a light white stripe is formed in the printed image. This white streak is called “banding” and causes deterioration in the image quality of the printed image.

=== Dot Arrangement of the Present Embodiment ===
FIG. 13A is an explanatory diagram when large dots are formed in all pixels in the present embodiment. For convenience of explanation, dots constituting the upper two raster lines in the figure are numbered sequentially from the left.

  As will be described later, two ink droplets are displaced and landed per pixel. Since one ink droplet has the same 14 pl ink amount as that for forming a medium dot, in the following description, an ink mark formed by one ink droplet is referred to as a “medium dot”. In the following description, the pixels are counted in order from the left. For example, the leftmost pixel is referred to as “the first pixel”. Further, two medium dots respectively formed on the pixels in the uppermost row in the figure are given the pixel numbers, and one middle dot number is marked with a dash to distinguish them. For example, “1” is attached to the medium dot formed in the first pixel. Further, in the following description, the medium dot formed in the first pixel is referred to as “the first medium dot” or “the first medium dot”. In the following description, the large dot formed in the first pixel is referred to as “the first large dot”. That is, “the first large dot” is composed of “the first medium dot” and “the first medium dot”. The pixel data corresponding to the first pixel is also referred to as “first pixel data”.

  In the present embodiment, the “first medium dot” causes the ink droplet to land at the same position as the first dot in FIG. 12A described above. However, in this case, a total of 28 pl ink droplets land at this position, but in this embodiment, a total of 14 pl ink droplets land (hence this position in this embodiment). In this case, no large dots are formed and medium dots are formed). Hereinafter, the position of the medium dot without a dash added to the number is referred to as “reference position”.

  “No. 1 medium dot” is formed at a position shifted from the reference position with respect to “No. 1 medium dot”. In this embodiment, the “1 ′ middle dot” is formed with a shift of 1/2880 inches in the moving direction from the reference position (formed on the right side in the drawing), and is upstream in the transport direction (the lower end side of the paper). ) By 1/2880 inches (formed on the lower side in the figure). Hereinafter, the position of the middle dot with a dash added to the number is referred to as an “adjustment position”.

  FIG. 13B is an explanatory diagram in the case where the dots become smaller in the dot arrangement of the present embodiment. Here, for the sake of explanation, not only the top raster line but also the dots constituting the second raster line from the top are numbered.

  In the above-described reference example (FIG. 12B), when the dots become small, it becomes difficult to spread the dots without a gap. On the other hand, in this embodiment, since the middle dot (medium dot with a dash added to the number) of the adjustment position is formed to fill the gap between the middle dot of the reference position (middle dot without a dash added to the number), As shown in the image data, a black filled image can be formed on the paper.

  As the dots become smaller, the “first medium dot” of raster lines adjacent to each other in the transport direction are separated from each other as in the case of this embodiment (FIG. 12B). However, in the present embodiment, the “1 ′ middle dot” is formed so as to be shifted upstream in the transport direction from the reference position. Therefore, this “1 ′ middle dot” is adjacent to the upstream in the transport direction. This is formed by approaching the “first medium dot” of the raster line. As a result, the “1 ′ middle dot” is formed so as to fill in the space between the “first middle dots” of the raster lines adjacent in the transport direction, and the banding is less visible.

  As described above, in this embodiment, when large dots are formed in overprinting, image quality deterioration is suppressed by forming one medium dot at an adjustment position that is shifted from the reference position.

=== Printing Operation of this Embodiment ===
FIG. 14 is an explanatory diagram of the printing operation of this embodiment. FIG. 15 is an explanatory diagram of how dots are formed in the area indicated by the dotted line in FIG.

  On the left side of FIG. 15, a nozzle that is not hatched is a nozzle that forms a medium dot for forming a large dot at a reference position. On the other hand, the nozzles indicated by hatching with hatching are nozzles that form medium dots for forming large dots at the adjustment positions. Further, on the right side of FIG. 15, the hatched hatched dots are medium dots formed at the reference position. On the other hand, the dots indicated by hatching are medium dots formed at the adjustment position. For example, the large dot constituting the raster line of raster number 1 is composed of a medium dot at the reference position formed by nozzle # 4 in pass 3 and a medium dot at the adjustment position formed by nozzle # 1 in pass 7. Is done. The large dot constituting the raster line of raster number 2 is composed of a medium dot at the adjustment position formed by nozzle # 5 in pass 2 and a medium dot at the reference position formed by nozzle # 2 in pass 6. Is done.

<About deviation in the transport direction>
The printing method of the present embodiment differs in the conveyance amount in the conveyance process performed between passes as compared to the printing method of FIGS. 10A and 10B described above. In the printing method of FIGS. 10A and 10B, the carry amount F is constant. In the printing method of this embodiment, the adjustment value C is added to or subtracted from the carry amount F according to the interval between passes. Yes. For example, in the printing method of FIGS. 10A and 10B, the conveyance amount in the conveyance process performed between pass 1 and pass 2 is F, but in the printing method of the present embodiment, between the pass 1 and pass 2. The conveyance amount in the conveyance process to be performed is F + C.

  The adjustment value C is 1/2800 inch. As will be described later, the value of the adjustment amount C is set according to the type of paper to be printed. In this embodiment, since the adjustment value C is 1/2880 inch, the middle dot at the adjustment position for forming a large dot is shifted by 1/2880 inch upstream in the transport direction with respect to the middle dot at the reference position. It is formed.

  When dots are formed at the reference position in a certain pass and dots are formed at the adjustment position in the next pass, in the carrying process performed between these passes, the carry amount is set to the normal carry amount F with an adjustment value C. It becomes the addition. Thereby, dots at the adjustment position are formed at positions upstream of the reference direction dot in the transport direction by 1/2880 inches on the upstream side in the transport direction. For example, in the transport process performed between pass 1 and pass 2, the transport process performed between pass 3 and pass 4, the transport process performed between pass 6 and pass 7, and the like, However, the adjustment value C is larger than the normal transport amount F.

  Also, when dots are formed at the adjustment position in a certain pass and dots are formed at the reference position in the next pass, the carry amount is adjusted to the normal carry amount F in the carry process performed between these passes. Subtract C. As a result, the dot at the reference position is formed at a position downstream of the adjustment direction by 1/2880 inches with respect to the position in the conveyance direction of the dot. For example, in the transport process performed between pass 2 and pass 3, the transport process performed between pass 5 and pass 6, the transport process performed between pass 7 and pass 8, and the like, However, the adjustment value C is smaller than the normal transport amount F.

  If dots are formed at the reference position in a certain pass and dots are formed at the reference position in the next pass, the transport amount of the transport process performed between these passes is the normal transport amount F. For example, although not shown, in the conveyance process performed between pass 8 and pass 9, the conveyance amount becomes the normal conveyance amount F. Similarly, when a dot is formed at the adjustment position in a certain pass and a dot is formed at the adjustment position in the next pass, the carrying amount of the carrying process performed between these passes is a normal carrying amount F. For example, in the conveyance process performed between pass 4 and pass 5, the conveyance amount becomes the normal conveyance amount F.

<About displacement in the moving direction>
The printing method of the present embodiment is different from the dot arrangement of the reference example of FIG. 12A described above in the movement direction positions of the two medium dots constituting the large dot. In the dot arrangement of the reference example of FIG. 12A, the two medium dots constituting the large dot are formed at the same position, whereas in the printing method of the present embodiment, the two medium dots move in the moving direction by the adjustment value C. It is shifted to.

  When a medium dot is formed at a reference position in a certain pass, ink droplets are ejected from each nozzle at normal ejection timing. As a result, the ink droplet lands on the reference position, and a medium dot is formed at the reference position.

  On the other hand, when forming a medium dot at the adjustment position in a certain pass, ink droplets are ejected from each nozzle at a different ejection timing than usual. In FIG. 15, when a middle dot is formed at the adjustment position in a pass in which the nozzle moves from left to right, at a timing after the carriage 31 has further moved by 1/2880 inches from the position of the carriage 31 at the normal ejection timing. An ink droplet is ejected from each nozzle (at a delayed timing). Further, in FIG. 15, when forming a middle dot at the adjustment position in the pass in which the nozzle moves from right to left, the carriage reaches 1/2880 inches before (on the right side) the position of the carriage 31 at the normal ejection timing. The ink droplets are ejected from each nozzle at the timing (early timing). As a result, the ink droplet lands with a shift of 1/2880 inch to the right in the movement direction from the reference position, and a medium dot is formed at the adjustment position.

=== Arrangement of Small Dots in this Embodiment ===
In the description of FIG. 11 described above, when the pixel data indicates that a small dot is to be formed, an ink droplet lands on the pixel on the paper corresponding to the pixel data at the first timing, and the ink is printed at the second timing. The drop has not landed. That is, in the description of FIG. 11 described above, all small dots are formed in the first pass.
However, if a small dot is formed in the first pass during the printing operation of the present embodiment, the image quality may deteriorate as described below.

  FIG. 16A is an explanatory diagram when a small dot is formed in the first pass while performing the printing operation of the present embodiment. This figure is an explanatory diagram of how dots are formed in the region indicated by the dotted line in FIG. 14, as in FIG. 15.

  If small dots are formed in the first pass, the small dots of any raster line are formed in any one of pass 1 to pass 4. For example, the small dot of the raster line with raster number 1 is formed by nozzle # 4 in pass 3, and the small dot of the raster line with raster number 2 is formed by nozzle # 5 in pass 2. On the other hand, in pass 1 and pass 3, a small dot is formed at the reference position, and in pass 2 and pass 3, a small dot is formed at the adjustment position.

  As a result, the distance between adjacent raster lines is different. For example, the distance between the raster lines with raster numbers 1 and 2 is increased, but the distance between the raster lines with raster numbers 2 and 3 is reduced. Specifically, the distance between the raster lines of raster numbers 1 and 2 is 2/2880 inches farther than the distance between the raster lines of raster numbers 2 and 3.

  When the distance between the raster lines is increased, the portion of the raster line in the printed image is visually recognized lightly. Further, when the distance between the raster lines is increased, the portion of the raster line in the printed image is visually recognized darkly. For this reason, there is a possibility that unevenness in density occurs in the printed image.

  Also, in a portion composed of small dots in a print image, small dots are often formed sparsely without forming small dots on all pixels as shown in FIG. 16A. However, even when sparsely formed small dots are formed in this way, there are portions where small dots are densely formed and portions where they are coarsely formed, so that it is not possible to form small dots uniformly. The graininess of the image may be deteriorated.

FIG. 16B is an explanatory diagram of a first improved example of the arrangement of small dots.
In the first improved example, small dots are formed in a pass in which dots are formed at the reference position. Here, small dots are formed in pass 1, pass 3, pass 6 and pass 8. As a result, in the first improved example, small dots are not necessarily formed in the first pass. For example, the small dot of the raster line with raster number 2 is formed in pass 6 instead of pass 2.
As described above, as a result of forming the small dots at the reference position, the distance between the raster lines becomes uniform. Thereby, the unevenness of the printed image is eliminated, and the granularity of the printed image is improved.

FIG. 16C is an explanatory diagram of a second improved example of the arrangement of small dots.
In the second improved example, small dots are alternately formed at the reference position and the adjustment position. For example, when forming a raster line of raster number 1, small dots are formed at the reference position for odd pixels, and small dots are formed at the adjustment position for even pixels. When forming a raster line with raster number 2 adjacent to raster number 1, a small dot is formed at the reference position for even pixels, and a small dot is formed at the adjustment position for odd pixels. ing.
Thus, as a result of alternately forming small dots at the reference position and the adjustment position, small dots are formed sparsely, and the graininess of the printed image is improved.

=== Setting of Adjustment Value C ===
As already described, the size of the dot changes depending on the paper type. Since the gap between the dots changes according to the size of the dots, the occurrence of banding and the ease of visual recognition differ depending on the paper type. On the other hand, if banding is unlikely to occur, the adjustment value C may be small. If banding is likely to occur, increasing the adjustment value C makes it difficult to visually recognize the banding. Therefore, in this embodiment, since the paper type is selected by the setting of the printer driver (see FIG. 3), the adjustment value C is determined according to the selected paper type.

FIG. 17 is an explanatory diagram of a table showing the relationship between the paper type and the adjustment value C. In this table, the paper type and the adjustment value C are associated with each other.
Since glossy paper has an ink absorbing layer on its surface, the dots formed on the glossy paper have a clearer shape (contour) than plain paper. For this reason, glossy paper is easier to recognize banding than plain paper. Therefore, the adjustment value C for glossy paper is larger than the adjustment value for plain paper. Also, printing on plain paper does not require higher image quality than glossy paper. Also, since printing is performed at a lower resolution than glossy paper, the dots used are large and banding is difficult to recognize. In such a case, the adjustment value is set to zero.
Thus, the adjustment value of the table is a value corresponding to the required image quality, the shape of the dots formed on the paper, and the banding.

  The printer driver has such a table in advance. Then, at the time of printing, the printer driver acquires information on the paper type selected by the printer driver setting, refers to the table based on this paper type, and determines an adjustment value C corresponding to the paper type.

  The printer driver generates print data by attaching command data for instructing the conveyance amount and ejection timing according to the determined adjustment value C to the pixel data after the rasterization process, and transmits the print data to the printer. . When the printer 1 receives the print data, the printer-side controller 60 controls the transport unit 20 based on the command data in the print data and manages the ejection timing based on the command data in the print data, Ink droplets are ejected from each nozzle of the head 41 based on the pixel data. In this way, the printer-side controller 60 realizes the printing operation of the present embodiment by controlling each unit based on the print data.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating 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 nozzle row>
In the above-described embodiment, the nozzle pitch of the nozzle row was 1/180 inch. However, it is not limited to this. If the nozzle pitch is 1/2880 inches, dots can be formed as follows.
FIG. 18 is an explanatory diagram of dot formation using a nozzle row having a nozzle pitch of 1/2880 inches.
In this embodiment, the nozzle for ejecting ink droplets changes according to the position of the head in the moving direction. For example, when forming dots at the reference position, every fourth nozzle of nozzle # 1, nozzle # 5, nozzle # 9,... Ejects ink droplets, and when forming dots at the adjustment position. , Nozzle # 2, nozzle # 6, nozzle # 10... Ejects ink droplets every fourth nozzle. Thereby, it is possible to form dots with the same dot arrangement as in the above-described embodiment in one pass.
However, in this embodiment, the amount of shifting the dot depends on the nozzle pitch. On the other hand, in the above-described embodiment, the amount of shifting the dots can be adjusted by the carry amount, so that it does not depend on the nozzle pitch.

<About the adjustment position>
In the above-described embodiment, the adjustment position is deviated from the reference position in both the movement direction and the conveyance direction. However, it is not limited to this. Even when the adjustment position is shifted only in the transport direction with respect to the reference position, an effect of suppressing deterioration in image quality can be obtained. However, if the amount of deviation in the transport direction in the adjustment direction with respect to the reference position is the same, the dots are formed without gaps when the medium dots formed at the adjustment position are also shifted in the movement direction, compared to the case where they are not shifted in the movement direction. This is advantageous when printing a black-filled image.

  Even when the adjustment position is shifted only in the moving direction with respect to the reference position, an effect of suppressing deterioration in image quality can be obtained. However, when the dot has an elliptical shape with a long axis in the movement direction, even if the adjustment position is shifted only in the movement direction with respect to the reference position, the obtained effect is less than when the dot is shifted only in the transport direction.

<About nozzle>
In the above-described embodiment, ink is ejected using a piezoelectric element. However, the method for discharging the liquid is not limited to this. For example, other methods such as a method of generating bubbles in the nozzle by heat may be used.

=== Summary ===
(1) The printing system 100 described above includes a carriage 31, a transport unit 20, a computer in which a printer driver is installed, and a printer-side controller 60 (see FIGS. 1 to 5). The carriage 31 is a moving body that moves the head 41 that ejects ink droplets in the movement direction. The transport unit 20 is a transport mechanism that transports a medium such as paper, cloth, or OHP paper in the transport direction. The computer on which the printer driver is installed and the printer-side controller 60 are controllers that alternately repeat a pass and a conveyance operation. In each pass, the controller causes ink droplets to be ejected from the head 41 in accordance with pixel data indicating the gradation of the pixels, and causes the ink droplets to land on the pixels on the paper corresponding to the pixel data. In the transport operation, the controller causes the transport unit 20 to transport the paper.

  By the way, in the above-described overprinting, when the pixel data indicates the formation of a large dot, the controller causes ink droplets to land on a pixel on the paper corresponding to the pixel data in one pass and ink droplets in another pass. Let it land. However, if the landing positions of the two ink droplets are the same, as shown in FIG. 12B, the deterioration of the image quality increases when the large dot becomes small.

  Therefore, in the overprinting of the present embodiment, the controller relatively shifts the landing positions of the two ink droplets (see FIGS. 13A and 13B). Thereby, degradation of image quality can be suppressed.

(2) The controller described above shifts the landing positions of the two ink droplets in the transport direction. Thereby, it is possible to prevent the dots adjacent in the transport direction from separating from each other, and to improve dot filling when forming a filled image.

(3) The controller described above shifts the landing positions of the two ink droplets in the transport direction by adjusting the paper transport amount by the transport unit 20 (see FIGS. 14 and 15). Specifically, the printer driver transmits print data including command data instructing the conveyance amount according to the adjustment value C to the printer 1, and the printer-side controller 60 controls the conveyance unit 20 according to the command data. By adjusting the transport amount, the landing positions of the two ink droplets are shifted in the transport direction. As a result, it is possible to land the ink droplet on the adjustment position.
However, as shown in FIG. 18, the landing positions of the two ink droplets can be shifted in the transport direction without adjusting the transport amount.

(4) In the above-described embodiment, when the ink droplets are landed at the reference position in the pass before and after the transport operation, the controller causes the transport unit 20 to transport the paper with the normal transport amount F in the transport operation. On the other hand, in the passes before and after the transport operation, when ink droplets are landed at the reference position in one pass and at the adjustment position in the other pass, the controller sets the adjustment value C to the normal transport amount F in the transport operation. The paper is transported to the transport unit 20 by the transport amount obtained by adding or subtracting (see FIGS. 14 and 15). As a result, it is possible to land the ink droplet on the adjustment position.

(5) In the above-described overprinting, when pixel data indicates the formation of small dots, small dots are formed in one pass (see FIG. 11). However, if small dots are formed in the first pass, the image quality of a printed image formed with small dots may be deteriorated. Therefore, in the above-described embodiment, small dots are formed in a first pass for a certain pixel, and small dots are formed in a second pass for another pixel.

(6) For example, in FIG. 16B, the small dot of the raster line with raster number 1 is formed in the first pass, and the small dot of the raster line with raster number 2 is formed in the second pass. As a result, the distance between the raster lines becomes uniform, the density unevenness of the printed image is eliminated, and the graininess of the printed image is improved.

(7) Further, for example, in the raster line of raster number 1 in FIG. 16C, odd-numbered small dots are formed in the first pass, and even-numbered small dots are formed in the second pass. Further, paying attention to the odd-numbered pixels in FIG. 16C, the odd-numbered raster line small dots are formed in the first pass, and the even-numbered raster line small dots are formed in the second pass. Thereby, small dots are formed sparsely, and the graininess of the printed image is improved.

(8) In the above-described embodiment, when the ink droplet lands on the paper, a long-axis elliptical dot is formed in the movement direction. When the dots have such a shape, shifting the adjustment position in the transport direction rather than shifting the adjustment position in the transport direction contributes to improving the image quality because the dots can be formed without gaps.

(9) However, even if the adjustment position is shifted only in the movement direction with respect to the reference position, an effect of suppressing the deterioration of the image quality can be obtained. In particular, when the amount of shift in the transport direction in the adjustment direction with respect to the reference position is the same, the dots are formed without gaps when the medium dots formed at the adjustment position are also shifted in the movement direction, compared with the case where they are not shifted in the movement direction This is advantageous when printing a black-filled image.

(10) The controller described above shifts the landing positions of the two ink droplets in the transport direction by adjusting the ejection timing of the ink droplets from the head (see FIG. 15). Specifically, the printer driver transmits print data including command data instructing the ejection timing according to the adjustment value C to the printer 1, and the printer-side controller 60 removes ink droplets from the head 41 according to the command data. By adjusting the ejection timing for ejection, the landing positions of the two ink droplets are shifted in the transport direction. As a result, it is possible to land the ink droplet on the adjustment position.

(11) If all the above-described configurations are provided, all the effects can be achieved, which is desirable. However, it is needless to say that not all configurations are necessary.

(12) The above-described printer driver is a program for generating print data, and is also a program for controlling the printer via print data by transmitting the print data to the printer.
Such a printer driver can cause the printer to execute the above-described overprint printing, and thus can cause the printer to print a high-quality print image.

(13) The printer itself may have the printer driver function described above. In other words, the printer itself may have the functions of the entire printing system.

It is explanatory drawing of the whole structure of a printing system. FIG. 10 is an explanatory diagram of processing performed by a printer driver. 3 is an explanatory diagram of a user interface of a printer driver. FIG. 1 is a block diagram of an overall configuration of a printer 1. FIG. FIG. 5A is a schematic diagram of the overall configuration of the printer 1. FIG. 5B is a cross-sectional view of the overall configuration of the printer 1. It is explanatory drawing which shows the arrangement | sequence of a nozzle. It is a flowchart of the process at the time of printing. 8A and 8B are explanatory diagrams of interlaced printing. 9A and 9B are explanatory diagrams of overlap printing. 10A and 10B are explanatory diagrams of overprinting. It is a figure for demonstrating the drive signal COM and the applied signal applied to a piezoelectric element. It is explanatory drawing at the time of forming a large dot in all the pixels in the dot arrangement of a reference example. FIG. 12B is an explanatory diagram when a large dot becomes smaller in the dot arrangement of the reference example. FIG. 13A is an explanatory diagram when large dots are formed in all pixels in the present embodiment. FIG. 13B is an explanatory diagram in the case where the dots become smaller in the dot arrangement of the present embodiment. It is explanatory drawing of the printing operation of this embodiment. It is explanatory drawing of a mode of formation of the dot of the area | region shown with a dotted line in FIG. FIG. 16A is an explanatory diagram when a small dot is formed in the first pass while performing the printing operation of the present embodiment. FIG. 16B is an explanatory diagram of a first improved example of the arrangement of small dots. FIG. 16C is an explanatory diagram of a second improved example of the arrangement of small dots. It is explanatory drawing of the table which shows the relationship between the paper type and adjustment value C. It is explanatory drawing of dot formation using the nozzle row whose nozzle pitch is 1/2880 inches.

Explanation of symbols

1 printer,
20 transport unit, 21 paper feed roller, 22 transport motor (PF motor),
23 transport roller, 24 platen, 25 discharge roller,
30 Carriage unit, 31 Carriage,
32 Carriage motor (CR motor),
40 head units, 41 heads,
50 detector groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Optical sensor,
60 printer-side controller, 61 interface unit, 62 CPU,
63 memory, 64 unit control circuit 100 printing system 110 computer,
112 video drivers, 114 application programs,
116 Printer Driver 120 Display Device, 130 Input Device, 140 Recording / Reproducing Device

Claims (13)

(A) a moving body that moves a head that discharges ink droplets in a moving direction;
(B) a transport mechanism for transporting the medium in the transport direction;
(C) an ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data; A controller that alternately repeats a transport operation for transporting a medium,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A controller for adjusting a relative landing position of the first ink droplet and the second ink droplet;
A printing system comprising (C). The printing system according to claim 1,
The printing system, wherein the controller shifts a relative landing position of the first ink droplet and the second ink droplet in the transport direction. The printing system according to claim 2,
The printing system, wherein the controller adjusts a relative landing position of the first ink droplet and the second ink droplet by adjusting a conveyance amount of the medium by the conveyance mechanism. The printing system according to claim 3,
In the ejection operation before and after the transport operation, when the first ink droplet or the second ink droplet is landed on a reference position serving as a reference in the transport direction, the controller performs a reference transport that is a reference in the transport operation. The medium is transported by the transport mechanism in an amount,
In the discharge operation before and after the transport operation, the first ink droplet or the second ink is positioned at the reference position in one discharge operation and the adjustment position shifted in the transport direction with respect to the reference position in the other discharge operation. When the ink droplets are landed, the controller causes the transport mechanism to transport the medium by a transport amount different from the reference transport amount in the transport operation. The printing system according to claim 3 or 4, wherein
When the pixel data indicates a gradation different from the specific gradation, the controller causes an ink droplet to land on a pixel on the medium corresponding to the pixel data in a single ejection operation to generate a dot of a predetermined size. Form the
The dot of the predetermined size is formed during a certain ejection operation for a certain pixel, and the dot of the predetermined size is formed during a different ejection operation for another pixel. Printing system. The printing system according to claim 5, wherein
The controller is
For the pixel having the same position in the transport direction with the certain pixel, the dot of the predetermined size is formed during the certain ejection operation,
The printing system is characterized in that dots having the predetermined size are formed in the different ejection operation for the pixels having the same position in the transport direction as the other pixels. The printing system according to claim 5, wherein
The controller is
For the pixel adjacent to the certain pixel, the dot of the predetermined size is formed during the separate ejection operation,
A printing system characterized in that, for a pixel adjacent to the other pixel, the dot of the predetermined size is formed during the certain ejection operation. The printing system according to claim 3, wherein:
The dots formed when the ink droplets land on the medium have an elliptical shape having a major axis in the movement direction. A printing system according to any one of claims 1 to 8,
The printing system, wherein the controller shifts a relative landing position of the first ink droplet and the second ink droplet in the moving direction. The printing system according to claim 9,
The printing system, wherein the controller adjusts a relative landing position of the first ink droplet and the second ink droplet by adjusting a discharge timing of the ink droplet from the head. (A) a moving body that moves a head that discharges ink droplets in a moving direction;
(B) a transport mechanism for transporting the medium in the transport direction;
(C) an ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data; A controller that alternately repeats a transport operation for transporting a medium,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A controller for adjusting a relative landing position of the first ink droplet and the second ink droplet;
A printing system comprising (C),
(D) The controller adjusts a relative landing position of the first ink droplet and the second ink droplet by adjusting a conveyance amount of the medium by the conveyance mechanism;
(E) In the ejection operation before and after the transport operation, when the first ink droplet or the second ink droplet is landed on a reference position serving as a reference in the transport direction, the controller uses the reference in the transport operation as a reference. Transporting the medium to the transport mechanism with a reference transport amount of
In the discharge operation before and after the transport operation, the first ink droplet or the second ink is positioned at the reference position in one discharge operation and the adjustment position shifted in the transport direction with respect to the reference position in the other discharge operation. When the ink droplets are landed, the controller causes the transport mechanism to transport the medium with a transport amount different from the reference transport amount in the transport operation,
(F) When the pixel data indicates a gradation different from the specific gradation, the controller causes an ink droplet to land on a pixel on the medium corresponding to the pixel data in a single ejection operation to determine a predetermined value. Forming dots of size,
For a certain pixel, the dot of the predetermined size is formed during the certain ejection operation, and for another pixel, the dot of the predetermined size is formed during the another ejection operation,
(G) The controller
For the pixel having the same position in the transport direction with the certain pixel, the dot of the predetermined size is formed during the certain ejection operation,
For the pixel having the same position in the transport direction as the other pixel, the dot of the predetermined size is formed during the another ejection operation,
(H) The dots formed by the ink droplets landing on the medium have an elliptical shape having a major axis in the moving direction;
(I) The controller adjusts the relative landing position of the first ink droplet and the second ink droplet by adjusting the ejection timing of the ink droplet from the head. system. A moving body that moves a head that discharges ink droplets in a moving direction;
A transport mechanism for transporting the medium in the transport direction;
A printing apparatus comprising:
An ejection operation for ejecting ink droplets from the head according to pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data, and transporting the medium to the transport mechanism And the transfer operation to be repeated alternately,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A program for adjusting a relative landing position of the first ink droplet and the second ink droplet. (A) a moving body that moves a head that discharges ink droplets in a moving direction;
(B) a transport mechanism for transporting the medium in the transport direction;
(C) an ejection operation for ejecting ink droplets from the head in accordance with pixel data indicating pixel gradation and landing the ink droplets on pixels on the medium corresponding to the pixel data; A controller that alternately repeats a transport operation for transporting a medium,
When the pixel data indicates a specific gradation, the medium corresponding to the pixel data is caused to land on a pixel on the medium corresponding to the pixel data in a certain ejection operation, and the pixel data corresponds to the pixel data in another ejection operation. Land the second ink drop on the upper pixel,
A controller for adjusting a relative landing position of the first ink droplet and the second ink droplet;
A printing apparatus comprising (C).

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