JP2007296748A - Printer and method for printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cost and a size of a printer without degrading quality of an image when performing the printing in overlapping. <P>SOLUTION: This printer comprises the prescribed number of first nozzles each for ejecting ink in a first color, second nozzles having the number less than that of the first nozzles and being adapted to eject ink in a second color different from the first color, and a controller that prints on a medium a print image consisting of a plurality of dot rows such that the medium, the first nozzles and the second nozzles are relatively moved in a prescribed direction and the ink is ejected from the first and second nozzles to form on the medium the dot rows having the dots arranged in the prescribed direction. The controller forms each dot row of the first color by two or more different first nozzles and each dot row of the second color by the second nozzles with the number smaller than that of the first nozzles for forming each dot row of the first color when the dots are formed corresponding to all the pixels. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a printing apparatus and a printing method.

  In a printing apparatus such as an ink jet printer, there is a printing method in which one raster line is formed by one nozzle (such as band printing). In the printing method, when there is a defective nozzle, streaks appear in the printed image.

In order to improve the image quality, an overlap printing method in which one raster line is formed by two or more nozzles has been proposed. (For example, refer to Patent Document 1) Further, when performing overlap printing, the printing speed is increased by increasing the number of nozzles. (For example, see Patent Document 2)
JP 2006-15596 A Japanese Patent Laid-Open No. 10-323978

  When performing overlap printing, increasing the number of nozzles to increase the printing speed increases the cost and the size of the apparatus.

  Therefore, the present embodiment aims to reduce the cost and the size of the apparatus without substantially reducing the image quality.

(1) a predetermined number of first nozzles for discharging the first color ink;
(2) discharging ink of a second color different from the first color, the number of second nozzles being less than the predetermined number;
(3) a moving mechanism that relatively moves the medium, the first nozzle, and the second nozzle in a predetermined direction;
(4) A dot row in which dots are arranged in the predetermined direction by ejecting ink from the first nozzle and the second nozzle while relatively moving the medium, the first nozzle, and the second nozzle in the predetermined direction. A controller that prints a print image composed of a plurality of the dot rows on the medium,
When forming dots on all pixels,
Each dot row of the first color is formed by two or more different first nozzles;
A controller that forms each of the dot rows of the second color with a smaller number of the second nozzles than the number of the first nozzles forming each of the dot rows of the first color;
A printing apparatus having (5).

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

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

That is, (1) a predetermined number of first nozzles that eject ink of the first color;
(2) discharging ink of a second color different from the first color, the number of second nozzles being less than the predetermined number;
(3) a moving mechanism that relatively moves the medium, the first nozzle, and the second nozzle in a predetermined direction;
(4) A dot row in which dots are arranged in the predetermined direction by ejecting ink from the first nozzle and the second nozzle while relatively moving the medium, the first nozzle, and the second nozzle in the predetermined direction. A controller that prints a print image composed of a plurality of the dot rows on the medium,
When forming dots on all pixels,
Each dot row of the first color is formed by two or more different first nozzles;
A controller that forms each of the dot rows of the second color with a smaller number of the second nozzles than the number of the first nozzles forming each of the dot rows of the first color;
(5) A printer having (5) can be realized.
In such a printing apparatus, the cost and the size of the apparatus can be suppressed by reducing the second nozzle number rather than the first nozzle number.

In this printing apparatus, the printing apparatus includes a transport mechanism that moves the medium in a direction perpendicular to the predetermined direction with respect to the first nozzle and the second nozzle.
The moving mechanism is a moving mechanism that moves the first nozzle and the second nozzle in the predetermined direction with respect to the medium,
The predetermined number of the first nozzles are arranged in a direction perpendicular to the predetermined direction at regular intervals;
A smaller number of the second nozzles than the predetermined number are arranged in a direction perpendicular to the predetermined direction at the predetermined interval.
In such a printing apparatus, the cost and the size of the apparatus can be suppressed by reducing the second nozzle number rather than the first nozzle number.

In this printing apparatus, the predetermined number of the first nozzles constitute a plurality of first nozzle rows arranged in a direction perpendicular to the predetermined direction,
The number of the second nozzles smaller than the predetermined number constitutes a number of the second nozzle rows smaller than the plurality of numbers arranged side by side in a direction perpendicular to the predetermined direction,
The first nozzle row and the second nozzle row are arranged side by side in the predetermined direction.
In such a printing apparatus, the cost and the size of the apparatus can be suppressed by reducing the second nozzle number rather than the first nozzle number.

In this printing apparatus, the printing apparatus includes a transport mechanism that moves the medium in a direction perpendicular to the predetermined direction with respect to the first nozzle and the second nozzle.
The movement mechanism moves the first nozzle and the second nozzle in the predetermined direction with respect to the medium, and the transport mechanism moves the medium in the predetermined direction with respect to the first nozzle and the second nozzle. Alternate movements in the vertical direction.
In such a printing apparatus, the cost and the size of the apparatus can be suppressed by reducing the second nozzle number rather than the first nozzle number.

In this printing apparatus, the moving mechanism is a transport mechanism that moves the medium in the predetermined direction with respect to the first nozzle and the second nozzle.
In such a printing apparatus, the cost and the size of the apparatus can be suppressed by reducing the second nozzle number rather than the first nozzle number. Further, since the operation of moving the medium, the first nozzle, and the second nozzle in a direction perpendicular to a predetermined direction is not performed, the printing speed is increased.

In such a printing apparatus, when forming dots in all pixels,
The controller is configured so that the number of pixels assigned to form dots by the first nozzle is less than the number of pixels assigned to form dots by the second nozzle. Ink is ejected from the first nozzle and the second nozzle.
In such a printing apparatus, the number of the second nozzles can be reduced from the number of the first nozzles, and the cost and the size of the apparatus can be suppressed.

In this printing apparatus, the size of the first pixel assigned so that the first nozzle forms a dot in the predetermined direction is assigned so that the second nozzle forms a dot. The controller causes ink to be ejected from the first nozzle and the second nozzle so as to be smaller than the size of two pixels in the predetermined direction.
In such a printing apparatus, the number of pixels assigned so that the first nozzle forms dots is the same as the number of pixels assigned so that the second nozzle forms dots.

Such a printing apparatus,
Drive that generates each drive signal so that the waveform of the drive signal used when the first nozzle forms a dot and the waveform of the drive signal used when the second nozzle forms a dot are the same. Having a signal generation circuit.
In such a printing apparatus, the number of gradations of dots formed by the first nozzle is the same as the number of gradations of dots formed by the second nozzle.

In this printing apparatus, each drive is performed so that the waveform of the drive signal used when the first nozzle forms dots and the waveform of the drive signal used when the second nozzle forms dots are different. A driving signal generating circuit for generating a signal;
In such a printing apparatus, the printing speed can be increased.

Such a printing apparatus,
A drive signal generation circuit configured to generate a drive signal for forming one dot in the second pixel while the first nozzle crosses the plurality of first pixels;
In such a printing apparatus, even if the sizes of the first pixel and the second pixel are different, a drive signal can be generated without reducing the printing speed.

Such a printing apparatus,
The first color is magenta or cyan;
The second color is yellow.
In such a printing apparatus, when the second color is a low visibility color such as yellow, the cost and the size of the apparatus can be suppressed without substantially reducing the image quality.

A predetermined number of first nozzles for discharging the first color ink;
Discharging a second color ink different from the first color, and having a number of second nozzles less than the predetermined number;
A transport mechanism for moving a medium in a predetermined direction with respect to the first nozzle and the second nozzle;
While moving the medium in the predetermined direction with respect to the first nozzle and the second nozzle, ink is ejected from the first nozzle and the second nozzle, and a dot row in which dots are arranged in the predetermined direction is added to the medium. A controller that forms and prints a print image composed of a plurality of dot rows on the medium,
When forming dots on all pixels,
Each dot row of the first color is formed by two or more different first nozzles;
Each dot row of the second color is formed by a smaller number of the second nozzles than the number of the first nozzles forming each of the dot rows of the first color;
The size in the predetermined direction of the first pixel assigned so that the first nozzle forms a dot is the size in the predetermined direction of the second pixel assigned so that the second nozzle forms a dot. A controller for discharging ink from the first nozzle and the second nozzle so as to be smaller than the size;
The predetermined number of the first nozzles includes a plurality of nozzle rows arranged in a direction perpendicular to the predetermined direction,
The number of the second nozzles smaller than the predetermined number includes a number of nozzle rows smaller than the plurality of nozzles arranged in a direction perpendicular to the predetermined direction.
Drive that generates each drive signal so that the waveform of the drive signal used when the first nozzle forms a dot and the waveform of the drive signal used when the second nozzle forms a dot are the same. A signal generation circuit;
The first color is magenta or cyan;
The second color is yellow;
Printing device.
According to such a printing apparatus, almost all of the effects described above can be obtained, so that the object of the present invention can be achieved most effectively.

=== Configuration of Inkjet Printer ===
FIG. 1 is an overall configuration block diagram of a printer 1 (inkjet printer) of the present embodiment. FIG. 2 is a schematic diagram of the overall configuration of the printer 1 of the present embodiment. FIG. 3 is a cross-sectional view of the overall configuration of the printer 1 of this embodiment.

Hereinafter, a basic configuration of the printer 1 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 controller 60. The printer 1 that has received the print data from the computer 110 as 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 the medium S (hereinafter referred to as paper). The situation in the printer 1 is monitored by a detector group 50, and the detector group 50 outputs a detection result to the controller 60. The controller 60 that receives the detection result from the detector group 50 controls each unit based on the detection result.

  The transport unit 20 feeds the paper to a printable position and transports the paper by a predetermined transport amount F in a predetermined direction (hereinafter referred to as a transport direction) during printing. That is, the transport unit 20 also functions as a transport mechanism (transport means) that transports paper. 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. However, in order for the transport unit 20 to function as a transport mechanism, all of these components are not necessarily required. The paper feed roller 21 is a roller for automatically feeding the paper inserted into the paper insertion slot into the printer 1. The transport motor 22 is a motor for transporting paper in the transport direction. The transport roller 23 is a roller that transports the paper 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 being printed. The paper discharge roller 25 is a roller for discharging the printed paper to the outside of the printer 1. The paper discharge roller 25 rotates in synchronization with the transport roller 23.

  The carriage unit 30 is for moving (also referred to as “scanning”) the head 41 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 movement direction (the head moves along the movement direction). Further, the carriage 31 detachably holds an ink cartridge 90 that stores ink. The carriage motor 32 is a motor for moving the carriage 31 in the movement direction.

  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. Each nozzle is provided with a piezo element (not shown) which is a drive element for driving each nozzle to eject ink droplets. 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, dot rows (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 is for detecting the position of the carriage 31 in the moving direction. The rotary encoder 52 is for detecting the rotation amount of the transport roller 23. The paper detection sensor 53 is for detecting the position of the leading edge of the paper to be printed. The paper detection sensor 53 is provided at a position where the position of the leading edge of the paper can be detected while the paper feed roller 21 feeds the paper toward the transport roller 23. The optical sensor 54 is attached to the carriage 31. The optical sensor 54 detects the presence or absence of paper by the light receiving unit detecting reflected light of light irradiated on the paper from the light emitting unit. The optical sensor 54 detects the position of the edge of the paper while being moved by the carriage 31.

  The controller 60 is a control unit (control means) for controlling the printer 1. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 is for transmitting and receiving 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 1. 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 has a unit control circuit 64 according to a program stored in the memory 63 and controls each unit.

  Note that the printer 1 of this embodiment performs four-color printing (yellow, cyan, magenta, black).

=== About printing operation ===
FIG. 4 is a processing flow during printing.
Each process described below is executed by the controller 60 controlling each unit in accordance with a program 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 processing, transport processing, ink ejection processing, and the like using each unit.

  Paper Feed Process (S002): The paper feed process is a process for supplying paper to be printed into the printer 1 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 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 face the paper.

  Dot Formation Process (S003): The dot formation process is a process for forming dots on paper by intermittently ejecting ink from a head that moves in the moving direction. The controller 60 drives the carriage motor 32 to move the carriage 31 in the movement direction. Then, the controller 60 ejects ink from the nozzles based on the print data while the carriage 31 is moving. When ink droplets ejected from the nozzles land on the paper, dots are formed on the paper. Since ink is intermittently ejected from the moving head, a dot row consisting of a plurality of dots along the moving direction is formed on the paper.

  Transport Process (S004): The transport process is a process of moving the paper relative to the head 41 in the transport direction. The controller 60 drives the carry motor 22 and rotates the carry roller 23 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 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.

  Determination of printing end (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 Printing Method and Image Degradation ===
<Comparative Example 1: Band printing>
FIG. 5 is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head 41. The head 41 is used when performing band printing in Comparative Example 1. On the lower surface of the head 41, a yellow ink nozzle row Y, a cyan ink nozzle row C, a magenta ink nozzle row M, and a black ink nozzle row K are formed. Each nozzle row includes 180 nozzles that are ejection openings for ejecting ink of each color. Out of the 180 nozzles, the lower nozzles are assigned with lower numbers (# 1 to # 180).

  Further, the nozzles of each nozzle row are aligned at regular intervals (nozzle pitch: k · D) along the transport direction. Here, D is the minimum dot pitch in the transport direction. k is an integer of 1 or more. 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 transport direction.

  FIG. 6 is an explanatory diagram of band printing using the head 41. However, for simplification of explanation, only the cyan ink nozzle row C is shown among the four nozzle rows in the head 41 of FIG. 5, and the number of nozzles in the nozzle row is also reduced to eight. FIG. 6 shows the position of the cyan ink nozzle row C and the state of dot formation from pass 1 to pass 2. Dots formed in pass 1 are indicated by white circles, and dots formed in pass 2 are indicated by black circles. Here, “pass” means that the carriage 31 (cyan ink nozzle row C in FIG. 6) moves once in the movement direction. The number after the path indicates the order in which the path is performed.

  By the way, in the printer 1, the paper is intermittently conveyed by the predetermined conveyance amount F by the conveyance unit, and the carriage 31 moves in the moving direction during the intermittent conveyance. During the movement of the carriage 31, ink is ejected from each nozzle. However, in FIG. 6, for convenience of explanation, the cyan ink nozzle row C is illustrated as moving in the transport direction with respect to the paper, but actually the paper moves in the transport direction. Further, the movement in the moving direction of the cyan ink nozzle row C coincides with the operation of the printer 1. Similarly to FIG. 6, the following explanatory diagrams (FIGS. 7, 8, 9, 11, 13, 15) of the printing method are also drawn.

  For the sake of explanation, it is assumed that dots are formed in all the pixels in FIG. 6 by each nozzle of the cyan ink row C. Here, the “pixel” refers to a square on a grid virtually defined on paper in order to define a position where a dot is recorded. Further, in order to identify and describe the pixels, the pixels aligned in the movement direction are represented by “rows”, and the pixels aligned in the transport direction are represented by “columns”. Rows are assigned a lower number in the left column in the moving direction. Rows are assigned lower numbers in the downstream side in the transport direction.

Hereinafter, the flow of band printing using the head 41 by the printer 1 will be described.
First, in pass 1, the carriage 31 moves from the right side to the left side in the movement direction. During the movement, ink is ejected from each nozzle, and dots are formed in the pixels in the first to eighth rows. For example, ink is ejected from nozzle # 1 to form a first dot row. The second dot row is formed by nozzle # 2, and the third dot row is formed by nozzle # 3. In this way, each nozzle forms a dot column in each row of pixels corresponding to each position. That is, a dot row (hereinafter referred to as a raster line) along one movement direction is formed by one nozzle.

  After pass 1, the paper is transported by a predetermined transport amount F by the transport unit. The carry amount F is determined by the following method. In band printing, dots are formed at the same interval as the nozzle pitch k · D. That is, the nozzle pitch k · D is equal to the minimum dot pitch D, and k = 1. If the number of nozzles that can be used in one pass is N, the transport amount F = N · k · D, that is, F = N · D. In FIG. 6, since the number of nozzles that can be used in one pass is 8, the transport amount F = 8 · D.

After the paper is transported, in pass 2, the carriage 31 moves from the left side to the right side in the moving direction. The carriage 31 moves in the direction of movement opposite to the previous pass. During the movement, dots are formed on the pixels in the 9th to 16th rows. For example, ink is ejected from the nozzle # 1, and the ninth dot row is formed. The tenth dot row is formed by nozzle # 2, and the eleventh dot row is formed by nozzle # 3. In pass 2, as in pass 1, one raster line is formed by one nozzle.
The raster line forming operation and the paper conveying operation are continued until there is no more data to be printed.

  That is, band printing is a printing method in which an image having a length in the transport direction is the nozzle row length and a length in the movement direction is the paper width is completed in one pass. Therefore, the carry amount F is F = N · D. One raster line is formed by one nozzle.

<Image degradation>
FIG. 7 is an explanatory diagram of image deterioration when ink is not ejected from the nozzle # 7 in the cyan ink nozzle row C to an appropriate position. This is the same as FIG. 6 except that ink is not ejected from the nozzle # 7 indicated by diagonal lines to an appropriate position, and shows the position of the cyan ink nozzle row C and the state of dot formation by band printing. The fact that the ink is not ejected from the nozzle to an appropriate position means that the nozzle is clogged due to an original manufacturing defect, ink thickening, dust, or the like, and the ink is not ejected. Further, ink may be ejected to an inappropriate position due to defective manufacturing of the nozzle position.

  In FIG. 7, ink is not ejected from nozzle # 7. Then, the dot row of cyan ink is not formed on the pixels in the seventh row and the fifteenth row where the nozzle # 7 should have formed a dot row. In other words, since the cyan ink is not mixed with the ink of other colors in the pixels in the 7th and 15th rows, a dot row different from the print data is formed. Alternatively, no dot row is formed. As a result, dot lines different from the print data such as the 7th and 15th lines appear in the printed image as a streak.

  That is, in band printing, since one raster line is formed by one nozzle, if there is a defective nozzle, it appears as a streak in the printed image and image degradation occurs.

<Comparative Example 2: Overlap printing with one head>
FIG. 8 is an explanatory diagram of overlap printing by one head. Also in the comparative example 2, the head 41 (FIG. 5) is used. However, for the sake of simplicity of explanation, only the cyan ink nozzle row C in the head 41 is shown as in FIG. 6, and the number of nozzles in the nozzle row is also reduced to eight. Then, the position of the cyan ink nozzle row C and the state of dot formation in pass 1 to pass 4 are shown. Dots formed in pass 1 are indicated by triangles, dots formed in pass 2 are indicated by white circles, dots formed in pass 3 are indicated by black circles, and dots formed in pass 4 are indicated by crosses.

Hereinafter, the flow of overlap printing by one head 41 will be described.
First, in pass 1, the carriage 31 moves from the left side to the right side in the movement direction. During the movement, ink is ejected from each nozzle. Then, dots are formed in pixels in even-numbered columns (2 · 4 · 6...) From the first row to the fourth row. For example, ink is ejected from nozzle # 5, and dots are formed in pixels in even-numbered columns in the first row. The even-numbered dots in the second row are formed by the nozzle # 6, and the even-numbered dots in the third row are formed by the nozzle # 7. That is, each nozzle forms a dot every other pixel in the movement direction in each row corresponding to each position.

After pass 1, the paper is transported by a predetermined transport amount F by the transport unit. In FIG. 8, the carry amount F = 4 · D. The carry amount F will be described later.
In pass 2 after the paper is transported, dots are formed in the pixels in the odd-numbered columns (1 · 3 · 5...) Of the first to eighth rows while the carriage 31 moves from the right side to the left side. As a result, dots are formed in the odd-numbered pixels in the first to fourth rows where no dots are formed in pass 1. Then, the first to fourth dot columns are completed. That is, the dot column in each row is completed in two passes.

Similarly, in pass 3 after paper conveyance, dots are formed in even-numbered columns from the fifth row to the twelfth row. Then, the fifth to eighth dot columns are completed. The paper is transported after pass 3, and in pass 4, dots are formed in odd columns from the 9th row to the 16th row. Then, the 9th to 12th dot columns are completed.
The raster line forming operation and the paper conveying operation are continued until there is no more data to be printed.

By the way, the even-numbered dots in the first row are formed by the nozzle # 5 in pass 1, and the odd-numbered dots in the first row are formed by the nozzle # 1 in pass 2. That is, one raster line is formed by two different nozzles.
In summary, overlap printing is a printing method in which one raster line is formed by two or more nozzles. Each nozzle forms a dot row intermittently every several dots in the movement direction. Then, dot rows are formed so as to complement the intermittent dot rows already formed by other nozzles.

When one raster line is formed by M passes, the overlap number is M. In other words, if the number of nozzles required to form one raster line is M, the overlap number is M. In FIG. 8, each nozzle forms a dot every other dot and forms a dot row of one row in two passes, so the overlap number M = 2.
In addition, in overlap printing, in order to perform recording with a constant carry amount F,
(1) N / M is an integer
(2) N / M is relatively prime with k
(3) The transport amount F is set to (N / M) · D.

  In FIG. 8, dots are formed at the same interval as the nozzle pitch k · D. That is, the nozzle pitch k · D is equal to the minimum dot pitch D, and k = 1. Then, since the number of nozzles that can be used in one pass N = 8 and the number of overlaps M = 2, N / M = 4, which is an integer, satisfies the condition (1). N / M = 4 and k = 1 are relatively prime, and the condition (2) is also satisfied. (3) Conveyance amount F = (N / M) · D = 4 · D.

  By the way, in band printing, since one raster line is formed by one nozzle, it has been described that when there is a defective nozzle, streaks appear in the printed image and image degradation occurs. FIG. 9 is an explanatory diagram of image deterioration when ink is not ejected from the nozzle # 7 in the cyan ink nozzle row C to an appropriate position in overlap printing. 8 is the same as FIG. 8 except that ink is not ejected from one nozzle to an appropriate position.

  In FIG. 9, ink is not ejected from the nozzle # 7 indicated by diagonal lines. Then, cyan ink dots are not formed on the pixels in the even-numbered rows of the third row and the eleventh row and the odd-numbered rows of the seventh row and the fifteenth row where the nozzle # 7 should form a dot row. However, nozzles # 3 form dots of cyan ink in the odd-numbered columns in the third row and the eleventh row, and the pixels in the even-numbered rows in the seventh row and the fifteenth row. That is, dots different from the print data are formed at every other pixel arranged in the moving direction.

In other words, in overlap printing, one raster line is formed by two or more nozzles, so that even if a defective nozzle intermittently forms dots different from the print data in one row, the other nozzles complement each other. The dots are formed according to the print data. That is, a dot row in which dots different from the print data and dots as printed are mixed is completed. Therefore, when there is a defective nozzle, overlap printing can alleviate image deterioration compared to band printing in which streaks appear in the printed image.
However, the carry amount F = N / M · D for overlap printing is smaller than the carry amount F = N · D for band printing, and printing time is required.

<Comparative Example 3: Overlap printing with two heads>
FIG. 10 is a diagram illustrating the arrangement of nozzles on the lower surface of the carriage 31 having two heads. The two heads are arranged side by side in the movement direction. A head located on the right side in the moving direction is referred to as a first head 411, and a head located on the left side is referred to as a second head 412. 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 on the lower surface of each head. Each nozzle row includes 180 nozzles. The nozzle pitch is k · D, and each nozzle is provided with a piezo element. The configurations of the first head 411 and the second head 412 are the same except that only the first head has the optical sensor 54.

  FIG. 11 is an explanatory diagram of overlap printing by two heads (first head 411 and second head 412). The positions of the cyan ink nozzle row (hereinafter referred to as the first cyan ink nozzle row C1) of the first head 411 and the cyan ink nozzle row (hereinafter referred to as the second cyan ink nozzle row C2) of the second head 412 in pass 1 to pass 2 The state of dot formation is shown. The dots formed by the first cyan ink nozzle row C1 are indicated by black circles, and the dots formed by the second cyan ink nozzle row C2 are indicated by white circles.

Hereinafter, the flow of overlap printing by the two heads (the first head 411 and the second head 412) will be described.
First, in pass 1, the carriage 31 moves from the right side to the left side. During the movement, the first cyan ink nozzle row C1 forms dots on even-numbered pixels from the first row to the eighth row, and the second cyan ink nozzle row C2 has odd-numbered rows from the first row to the eighth row. Dots are formed on the pixels. For example, the first dot row is formed by the nozzle # 1 of the first cyan ink nozzle row C1 in pass 1 and the nozzle # 1 of the second cyan ink nozzle row C2 in pass 1. That is, one raster line is formed by two different nozzles in one pass.

After pass 1, the paper is transported by a predetermined transport amount F by the transport unit. Since FIG. 11 shows the state of overlap printing, the carry amount is F = (N / M) · D. F = 8 · D because the number of nozzles N = 16 and the number of overlaps M = 2 that can be used to form one row of dot columns in one pass.
In pass 2 after paper conveyance, during the movement of the carriage 31 from the left side to the right side, the first cyan ink nozzle row C1 forms dots on pixels in even-numbered rows from the 9th row to the 16th row. Then, the second cyan ink nozzle row C2 forms dots on the pixels in the odd rows from the 9th row to the 16th row.
The raster line forming operation and the paper conveying operation are continued until there is no more data to be printed.

By the way, in the overlap printing by the two heads in FIG. 11, one raster line is formed by two different nozzles. Therefore, when there is a defective nozzle, image degradation can be alleviated compared to band printing.
Further, in Comparative Example 3, the number of nozzles is twice that of Comparative Example 2. Therefore, the carry amount F = 8 · D of Comparative Example 3 is larger than the carry amount F = 4 · D of Comparative Example 2, and the printing speed is increased.
That is, when performing the overlap printing, increasing the number N of nozzles that can eject ink increases the printing speed. However, as the number N of nozzles increases, the cost increases and the apparatus becomes larger.
Therefore, the present embodiment aims to reduce the cost and the size of the apparatus without substantially reducing the image quality.

=== Printing with a head with reduced yellow nozzles ===
Hereinafter, usage examples of the printing method in the present embodiment will be described.

<Use Example 1: Printing with one head>
FIG. 12 is a diagram illustrating an arrangement of nozzles on the lower surface of the third head 413. On the lower surface of the third head 413, four rows of a third yellow ink nozzle row Y3, a third cyan ink nozzle row C3, a third magenta ink nozzle row M3, and a third black ink nozzle row K3 are formed. Yes. The nozzle row of cyan, magenta, and black ink has 180 nozzles. On the other hand, the number of nozzles of the third yellow ink nozzle row Y3 is 90, half of the other nozzle rows. The most downstream nozzle # 1 among the nozzles of the third yellow ink nozzle row Y3 is aligned with the nozzle # 91 of the third cyan ink nozzle row C3 in the moving direction. That is, the third head 413 and the head 41 (FIG. 5) have the same configuration except that the number of nozzles in the third yellow ink nozzle row Y3 is 90.

  FIG. 13 is an explanatory diagram of printing by the third head 413. The positions of the third cyan ink nozzle row C3 and the third yellow ink nozzle row Y3 in pass 1 to pass 3 and how dots are formed are shown. For the sake of simplicity, only the third cyan ink nozzle row C3 and the third yellow ink nozzle row Y3 of the third head 413 in FIG. 12 are shown, and the number of nozzles is also reduced. For the sake of explanation, it is assumed that one dot of cyan ink and one dot of yellow ink are formed on all the pixels in FIG. The dots formed by the third cyan ink nozzle row C3 in pass 1 are indicated by white circles, the dots formed by the third cyan ink nozzle row C3 are indicated by black circles in pass 2, and the third cyan ink nozzle row C3 is formed in pass 3 Dots are indicated by white circles. The dots formed by the third yellow ink nozzle row Y3 in pass 1 to pass 3 are indicated by crosses.

Hereinafter, the flow of printing by the third head 413 will be described.
First, in pass 1, the carriage 31 moves from the left side to the right side. During the movement, the nozzles # 5 to # 8 of the third cyan ink nozzle row C3 form dots in the odd-numbered pixels from the first row to the fourth row, and the third yellow ink nozzle row Y3 is the first row. To dots in both the odd and even columns in the fourth row. As a result, the first to fourth yellow ink dot columns are completed.
After pass 1, the paper is transported by a predetermined transport amount F by the transport unit. In FIG. 13, the carry amount F = 4 · D. The carry amount F will be described later.

  In pass 2 after paper conveyance, during the movement of the carriage 31 from the right side to the left side, the third cyan ink nozzle row C3 forms dots in the pixels of the even-numbered rows from the first row to the eighth row, and the third yellow The ink nozzle row Y3 forms dots in both the odd-numbered and even-numbered pixels of the fifth to eighth rows. As a result, the first to fourth cyan ink dot columns are completed. Then, the yellow ink dot rows in the 5th to 8th rows are completed. To summarize up to pass 2, for example, the dot row of cyan ink in the first row is the nozzle # 5 of the third cyan ink nozzle row C3 of pass 1 and the nozzle # 1 of the third cyan ink nozzle row C3 of pass 2. It is formed. The first yellow ink dot row is formed by the nozzle # 1 of the third yellow ink nozzle row Y3 in pass 1. That is, the raster line for cyan ink is formed by two different nozzles, while the raster line for yellow ink is formed by one nozzle. In other words, the cyan ink raster lines are formed according to overlap printing, while the yellow ink raster lines are formed according to band printing rather than overlap printing.

In pass 3 after paper transport, the third cyan ink nozzle row C3 forms dots in the odd rows from the 5th row to the 12th row, and the third yellow ink nozzle row Y3 takes the odd numbers from the 9th row to the 12th row. Dots are formed on the pixels in both the even and even columns. As a result, the cyan ink dot columns in the fifth to eighth rows are completed. Then, the yellow ink dot rows in the 9th to 12th rows are completed.
The raster line forming operation and the paper conveying operation are continued until there is no more data to be printed.

  Incidentally, it is described above that the carry amount F in FIG. 13 is F = 4 · D. Since the third cyan ink nozzle row C3 is overlap-printed, the carry amount is F = (N / M) · D. Since the number of nozzles that can be used in one pass N = 8 and the number of overlaps M = 2, F = 4 · D. On the other hand, since the third yellow ink nozzle row Y3 is band-printed, the carry amount F = N · k · D. The nozzle pitch k · D is equal to the minimum dot pitch D, and k = 1. Since the number of nozzles that can use yellow ink is four, the carry amount F = 4 · D. That is, the third cyan ink nozzle row C3 and the third yellow ink nozzle row Y3 are different printing methods, but the number of nozzles and the like are set so that the carry amount F is equal.

  To summarize the usage example 1, the raster line of cyan ink is formed according to overlap printing. On the other hand, the raster line of yellow ink is formed according to band printing. Although not shown in FIG. 13, raster lines of magenta ink and black ink are also formed according to overlap printing. That is, even when there are defective nozzles in the cyan, magenta, and black nozzle rows of the third head 413, no streaks appear in the printed image and image degradation is alleviated. On the other hand, when there is a defective nozzle in the third yellow ink nozzle row Y3, a dot row of yellow ink is not formed on the pixels in the row to which the defective nozzle is assigned. However, yellow is generally known as a low visibility color compared to cyan, magenta, and black. Therefore, even when there are defective nozzles in the third yellow ink nozzle row Y3, the printed image does not appear to have streaks to the human eye.

  In other words, the usage example 1 is compared with the comparative example 2 (compare FIG. 5 and FIG. 12), and the number of yellow ink nozzles is reduced from 180 to 90, and the cost and size are reduced. Is not felt by human eyes.

<Usage example 2: Printing with two heads>
FIG. 14 is a diagram showing an arrangement of nozzles on the lower surface of the carriage 31 having two heads. The two heads are arranged side by side in the movement direction. A head located on the right side in the moving direction is referred to as a first head 411, and a head located on the left side is referred to as a fourth head 414. The configuration of the first head 411 in FIGS. 10 and 14 is the same. That is, four rows of the first yellow ink nozzle row Y1, the first cyan ink nozzle row C1, the first magenta ink nozzle row M1, and the first black ink nozzle row K1 are formed on the lower surface of the first head 411. Has been. On the other hand, three rows of the fourth cyan ink nozzle row C4, the fourth magenta ink nozzle row M4, and the fourth black ink nozzle row K4 are formed on the lower surface of the fourth head 414. That is, the first head has a yellow ink nozzle row, whereas the fourth head 414 does not have a yellow ink nozzle row. Each nozzle row includes 180 nozzles.

  FIG. 15 is an explanatory diagram of printing by the first head 411 and the fourth head 414. The positions of the first cyan ink nozzle row C1, the first yellow ink nozzle row Y1 and the fourth cyan ink nozzle row C4 and the state of dot formation in pass 1 to pass 2 are shown, and the number of nozzles is also reduced. For the sake of simplicity, only the first cyan ink nozzle row C1 and the first yellow ink nozzle row Y1 of the first head 411 and the fourth cyan ink nozzle row C4 of the fourth head 414 are shown in FIG. For the sake of explanation, it is assumed that one dot of cyan ink and one dot of yellow ink are formed on all the pixels in FIG. The dots formed by the first cyan ink nozzle row C1 are indicated by black circles, the dots formed by the first yellow ink nozzle row Y1 are indicated by crosses, and the dots formed by the fourth cyan ink nozzle row C4 are indicated by white circles.

Hereinafter, the flow of printing by the first head 411 and the fourth head 414 will be described.
First, in pass 1, the carriage 31 moves from the right side to the left side. During the movement, the first cyan ink nozzle row C1 forms dots on even-numbered pixels from the first row to the eighth row, and the fourth cyan ink nozzle row C4 moves to the odd-numbered rows from the first row to the eighth row. Dots are formed on the pixels. The first yellow ink nozzle Y1 forms dots in both the odd-numbered and even-numbered pixels in the first to eighth rows. That is, the dot row of cyan ink in the first row is formed by the nozzle # 1 of the first cyan ink nozzle row C1 in pass 1 and the nozzle # 1 of the fourth cyan ink nozzle row C4 in pass 1. The yellow ink dot row in the first row is formed by the nozzle # 1 of the first yellow ink nozzle row Y1 in pass 1. That is, the raster line for cyan ink is formed by two different nozzles, while the raster line for yellow ink is formed by one nozzle. In other words, cyan ink raster lines are formed according to overlap printing, while yellow ink raster lines are formed according to band printing.

  After pass 1, the paper is transported by a predetermined transport amount F by the transport unit. Since the cyan ink raster line is formed in accordance with the overlap printing, the transport amount is F = (N / M) · D. Since the number of nozzles that can be used in one pass N = 16 and the number of overlaps M = 2, F = 8 · D. On the other hand, since the raster line of yellow ink is formed according to band printing, the carry amount F = N · k · D. The nozzle pitch k · D is equal to the minimum dot pitch D, and k = 1. Since the number of nozzles that can be used for yellow ink is 8, it is the same as the transport amount of the cyan ink nozzle row, and F = 8 · D.

In pass 2 after paper conveyance, during the movement of the carriage 31 from the left side to the right side, the first cyan ink nozzle row C1 forms dots in the pixels in the even-numbered rows from the 9th row to the 16th row, and the fourth cyan The ink nozzle column C4 forms dots at pixels in the odd columns from the 9th row to the 16th row. Then, the first yellow ink nozzle row Y1 forms dots in both the odd-numbered and even-numbered pixels of the 9th to 16th rows.
The raster line forming operation and the paper conveying operation are continued until there is no more data to be printed.

  To summarize Usage Example 2, cyan ink raster lines are formed according to overlap printing. On the other hand, the raster line of yellow ink is formed according to band printing. Although not shown in FIG. 15, raster lines of magenta ink and black ink are also formed according to overlap printing. That is, even when there are defective nozzles in the cyan, magenta, and black ink nozzle rows of the first head 411 and the nozzle row of the fourth head, no streaks appear in the printed image and image degradation is alleviated. On the other hand, when there is a defective nozzle in the first yellow ink nozzle row Y1, a yellow dot row is not formed in the pixel of the row to which the defective nozzle is assigned. However, yellow is generally known as a low visibility color compared to cyan, magenta, and black. Therefore, even when there are defective nozzles in the first yellow ink nozzle row Y1, the printed image does not appear to have streaks to the human eye.

  In other words, compared with Comparative Example 3 (Comparing FIGS. 10 and 14), Usage Example 2 reduces the number of yellow ink nozzle rows by one and reduces the cost and size. There is no feeling.

<Usage example 3: Printing method with different resolutions depending on the nozzle array>
The head used in Usage Example 1 (FIG. 12) has fewer yellow nozzles than the head used in Comparative Example 2 (FIG. 5). Further, the head used in Usage Example 2 (FIG. 14) has fewer yellow nozzles than the head used in Comparative Example 3 (FIG. 10). Therefore, in usage example 1 and usage example 2, each of the cyan, magenta, and black ink nozzle rows forms a dot every other pixel in the moving direction, whereas the yellow ink nozzle row is all aligned in the moving direction. Dots are formed on the pixels. That is, the number of dots formed by the yellow ink nozzle row is twice the number of dots formed by the nozzle rows of other inks.

  Therefore, in this usage example 3, overlap printing by the head (third head 413) used in usage example 1 or overlap printing by the heads (first head 411 and fourth head 414) used in usage example 2 is performed. When performing, a printing method is performed in which the number of dots formed by the yellow ink nozzle row is equal to the number of dots formed by the nozzle rows of other inks.

  Therefore, the size in the moving direction of the pixel Y where the yellow ink dots are formed is set to be twice the size in the moving direction of the pixel C where the cyan, magenta, and black ink dots are formed. For example, if the size of the pixel C is 1/180 inch × 1/180 inch (moving direction × transport direction), the size of the pixel Y is 1/90 inch × 1/180 inch (moving direction × transport direction). It becomes. The resolution of the raster lines of cyan, magenta, and black that form dots on the pixel C is 180 dpi. The resolution of the raster line of yellow that forms dots on the pixel Y is 90 dpi.

  FIG. 16 shows how the cyan ink nozzle row C forms dots on the pixel C. This cyan ink nozzle row C forms a dot every other pixel C arranged in the moving direction. In FIG. 16, the nozzle # 1 of the cyan ink nozzle row C forms three dots in one pass. Although not shown in FIG. 16, the magenta and black ink nozzle rows also form dots in the same manner as the cyan ink nozzle row C.

  FIG. 17 shows how the yellow ink nozzle row Y forms dots on the pixel Y. The yellow ink nozzle row Y forms dots on all the pixels Y arranged in the movement direction. In FIG. 17, the nozzle # 1 in the yellow ink nozzle row forms three dots in one pass.

  In summary, in usage example 3, the number of dots formed by the yellow ink nozzle row is equal to the number of dots formed by the other ink nozzle rows, but the resolution of the yellow raster line is the raster line of the other color. Half the resolution.

=== About Head Unit 40 ===
Usage example 1 to usage example 3 show the nozzle arrangement and printing method of this embodiment. From here, it shows about the ink discharge operation | movement in this embodiment. First, the head unit 40 will be described.

  FIG. 18 is an electronic circuit diagram showing that each piezo element PZT belonging to a certain nozzle row is operated by the drive signal generation circuit 43 and the head drive circuit 42. The numbers in parentheses in the figure indicate the number of the nozzle to which the member or signal corresponds.

  Here, the head unit 40 includes a head 41, a head drive circuit 42 that drives the head 41 to eject ink from the nozzles, and a drive signal generation circuit 43 that generates a drive signal DRV. The head drive circuit 42 includes 180 first shift registers 421, 180 second shift registers 422, a latch circuit group 423, a data selector 424, and 180 switches 44. The head drive circuit 42 is provided for each nozzle row. The head 41 includes a nozzle row for each color, piezo elements PZT for the number of nozzles, and pressure chambers (not shown) provided in the piezo elements PZT. The drive signal DRV will be described later.

  Hereinafter, a flow from when the print signal PRT is input to the head drive circuit 42 until ink is ejected will be described.

  First, the print signal PRT is serially transmitted to the head drive circuit 42. The print signal PRT (i) is a signal corresponding to the pixel data assigned to one pixel assigned to the nozzle #i. The print signal PRT (i) is a signal having 2-bit information for each pixel in which dots are formed. That is, the print signal PRT is 180 pieces of 2-bit data. However, the third yellow ink nozzle row Y3 of Usage Example 1 has 90 nozzles (FIG. 12). Therefore, the print signal PRT transmitted to the head drive circuit 42 corresponding to the third yellow ink nozzle row Y3 is 90 pieces of 2-bit data. The number of first shift registers 421, second shift registers 422, and switches 44 is also 90.

  The serially transmitted print signal PRT is input to 180 first shift registers 421. Thereafter, the signals are input to 180 second shift registers 422.

  Next, when the rising pulse of the latch signal LAT is input to the latch circuit 423, 360 data of each shift register is latched by the latch circuit 423. Thus, the latch signal LAT has a pulse indicating the timing at which the print signal PRT changes.

  When the rising pulse of the latch signal LAT is input to the latch circuit group 423, the rising pulse of the latch signal LAT is also input to the data selector 424. The data selector 424 is in an initial state when the latch signal LAT is input. The data selector 424 that has entered the initial state selects the print signal PRT that is 180 pieces of 2-bit data from the latch circuit group 423 before the next latch, and selects the switch control signal SW (according to the print signal PRT (i). i) is output to each of the switches 44 (i).

  The switch control signal SW indicates the timing when the switch 44 is turned on or off. The on / off operation of the switch 44 inputs or blocks the drive signal DRV to the piezo element PZT. For example, when the level of the switch control signal SW (i) is “1”, the switch 44 (i) is turned on, the drive pulse included in the drive signal DRV is allowed to pass through, and the drive pulse is input to the piezo element. On the other hand, when the level of the switch control signal SW (i) is “0”, the switch 44 (i) is turned off, and the drive pulse included in the drive signal DRV is cut off. The drive signal DRV is supplied in common to 180 piezo elements PZT belonging to a certain nozzle row.

  Then, based on the print signal PRT (i), after the drive signal DRV (i) is input to the piezo element PZT (i), the piezo element PZT (i) according to the voltage change of the drive pulse included in the drive signal DRV (i). ) Is deformed. When the piezo element PZT (i) is deformed, the elastic film (side wall) defining a part of the pressure chamber is deformed, and ink in the pressure chamber is ejected from the nozzle #i.

From here, the drive signal DRV and the dot size will be described.
FIG. 19 is a timing chart of each signal. The period T from the rising pulse to the next rising pulse of the latch signal LAT is set as a repetition period T. Within this repetition period T, the drive signal DRV has a first drive pulse W1 and a second drive pulse W2. The rising pulse of the change signal CH indicates the timing at which the first drive pulse W1 is switched to the second drive pulse W2.

By the way, the piezo element PZT is deformed according to the drive pulse of the drive signal DRV, and ink is ejected from the nozzle. The shape of the drive pulse is determined in advance according to the amount of ink to be ejected. That is, dots having different sizes can be formed depending on the difference in driving pulse. For example, when the switch control signal SW (i) is “11”, the first drive pulse W1 and the second drive pulse W2 are input to the piezo element PZT (i), and a large dot is formed. When the switch control signal SW (i) is “10”, the first drive pulse W1 is input to the piezo element PZT (i), and a medium dot is formed. When the switch control signal SW (i) is “01”, the second drive pulse W2 is input to the piezo element PZT (i), and a small dot is formed. When SW (i) is “00”, no drive pulse is input to the piezo element PZT (i), so no dot is formed.
That is, the first drive pulse W1 and the second drive pulse W2 can express four gradations of large dots, medium dots, small dots, and no dots for one pixel.

=== About the Drive Signal DRV ===
Hereinafter, examples of drive signals corresponding to the printing methods of Usage Example 1 to Usage Example 3 will be described.

<Drive signal example 1>
FIG. 20 is a diagram illustrating drive pulses included in each drive signal of the drive signal example 1.
In the drive signal example 1, two types of signals of the first drive signal DRV1 and the second drive signal DRV2 are used. These two types of drive signals are properly used for each nozzle row. A period in which each nozzle row crosses the distance of one pixel is a period Ta. FIG. 20 shows drive pulses during a period in which the nozzle row crosses the distance of two pixels. The drive signal example 1 is applied to the use example 1 and the use example 2 described above.

First, the first drive signal DRV1 and the second drive signal DRV2 will be described.
The nozzle row in which the first drive signal DRV1 is used forms dots every other pixel in the movement direction. That is, the first drive signal DRV1 is used for the nozzle rows of cyan, magenta, and black ink in the first and second usage examples.

  The repetition period T (1) of the first drive signal DRV1 is a period Ta1 in which the nozzle array forms dots within the period Ta (hereinafter referred to as dot formation period Ta1), and the nozzle array forms dots within the period Ta. This is the total period of the period Ta0 that is not performed (hereinafter referred to as the dotless period Ta0). The first drive pulse W1 and the second drive pulse W2 are present within the dot formation cycle Ta1. With these two drive pulses (W1 and W2), it is possible to represent four gradations of large dots, medium dots, small dots, and no dots for one pixel (described above). The dotless cycle Ta0 does not have a driving pulse and maintains a constant voltage. Therefore, the print signal PRT corresponding to the first drive signal DRV1 has 2-bit information for each nozzle in the period 2Ta (Ta1 + Ta0).

  The nozzle row in which the second drive signal DRV2 is used forms dots at all the pixels arranged in the movement direction. That is, the second drive signal DRV2 is used for the yellow ink nozzle rows of Usage Example 1 and Usage Example 2. Further, the repetition period T (2) of the second drive signal DRV2 is the dot formation period Ta1. There are also a first drive pulse W1 and a second drive pulse W2 within this dot formation cycle Ta1.

  In summary, all of the pixels assigned to the nozzle row that uses the first drive signal DRV1 and the pixels assigned to the nozzle row that uses the second drive signal DRV2 are expressed in four gradations. Therefore, the print signal PRT corresponding to the second drive signal DRV2 has 4-bit information for each nozzle in the period 2Ta (Ta1 + Ta1).

Next, a period during which the nozzle row crosses the distance of one pixel will be described for the period Ta.
A period in which the voltage of the first drive pulse changes is a period T1, and a period in which the voltage of the second drive pulse changes is a period T2. In addition, a stable period Ts is provided between the period T1 and the period T2. This is because the meniscus immediately after ink ejection (the free surface of the ink exposed at the nozzle) vibrates, and if the next ink is ejected before the vibration is subtracted, an ink amount different from the prescribed ink amount is ejected. This is because there is a risk of it.
That is, the period Ta includes a period T1 in which the voltage of the first drive pulse W1 changes, a stable period Ts after ink ejection by the first drive pulse W1, a period T2 in which the voltage of the second drive pulse W2 changes, and the second period. This is a total period of the stable period Ts after ink ejection by the drive pulse W2.

<Drive signal example 2>
FIG. 21 is a diagram illustrating drive pulses included in each drive signal of the drive signal example 2. FIG. 21 also shows the second drive signal DRV2 of the drive signal example 1 for comparison.
In the drive signal example 2, two types of signals of the third drive signal DRV3 and the fourth drive signal DRV4 are used. These two types of drive signals are properly used for each nozzle row. A period in which each nozzle row crosses the distance of one pixel is defined as a period Tb. FIG. 21 shows drive pulses during a period in which the nozzle row crosses the distance of two pixels. The drive signal example 2 is applied to the use example 1 and the use example 2 described above.

First, the third drive signal DRV3 and the fourth drive signal DRV4 will be described.
The nozzle row using the third drive signal DRV3 forms dots every other pixel in the movement direction. That is, the third drive signal DRV3 is used for the nozzle rows of cyan, magenta, and black ink in usage example 1 and usage example 2.

  The repetition period T (3) of the third drive signal DRV3 includes a period Tb1 in which the nozzle array forms dots within the period Tb (hereinafter referred to as dot formation period Tb1), and a nozzle array forms dots within the period Tb. It consists of a total period of non-period Tb0 (hereinafter referred to as dotless period Tb0). The first drive pulse W1 and the second drive pulse W2 are present within the dot formation period Tb1. With these two drive pulses (W1 and W2), four gradations can be expressed for one pixel (described above). The dotless cycle Tb0 does not have a driving pulse and maintains a constant voltage. Therefore, the print signal PRT corresponding to the third drive signal DRV3 has 2 bits of information per nozzle in the period 2Tb (Tb1 + Tb0).

  The nozzle row in which the fourth drive signal DRV4 is used forms dots at all the pixels arranged in the movement direction. In other words, the fourth drive signal DRV4 is used for the yellow ink nozzle rows of Usage Example 1 and Usage Example 2. Further, the repetition period T (4) of the fourth drive signal DRV4 is the dot formation period Tb1. There is a first drive pulse W1 within this dot formation period Tb1. Therefore, a two-tone expression with medium dots or no dots is obtained for one pixel. Therefore, the print signal PRT corresponding to the fourth drive signal DRV4 has 2-bit information for each nozzle in the period 2Tb (Tb1 + Tb1). That is, the fourth drive signal DRV4 has a lower number of gradations per pixel than the second drive signal DRV2 of the drive signal example 1, but instead, the print signal PRT has a smaller number of information.

  That is, the pixels assigned to the nozzle row in which the third drive signal DRV3 is used are expressed in four gradations, but the pixels assigned to the nozzle row in which the fourth drive signal DRV4 is used are expressed in two gradations. Is done. As a result, the image quality of the drive signal example 2 is lower than that of the drive signal example 1 in which all the pixels are expressed in four gradations. However, if the dot expressed in two gradations is a color with low visibility such as yellow, the image quality does not deteriorate significantly.

Next, a period in which the nozzle row crosses the distance for one pixel will be described for the period Tb.
The period Tb in the third drive signal DRV3 includes a period T1 in which the voltage of the first drive pulse W1 changes, a stable period Ts after ink ejection by the first drive pulse W1, and a period in which the voltage of the second drive pulse W2 changes. It is a period of totaling T2. The period Tb does not include the stable period Ts after ink ejection by the second drive pulse W2. In the dotless cycle Tb0, the meniscus after ink ejection by the second drive pulse W2 is stabilized. That is, this period Tb is shorter than the period Ta of the drive signal example 1 by the stable period Ts.

  Further, the period Tb in the fourth drive signal DRV4 is a period obtained by summing the period T1 in which the voltage of the first drive pulse W1 changes, the period T0 in which the constant voltage before and after the voltage change of the first drive pulse is maintained, and the period T3. It becomes. The lengths of the period Tb in the third drive signal DRV3 and the period Tb in the fourth drive signal DRV4 are equal.

  In summary, the drive signal example 2 is lower in image quality than the drive signal example 1, but the printing speed is increased. Further, the driving signal example 2 requires less information than the driving signal example 1 has in the print signal PRT. That is, both of the driving signal example 1 and the driving signal example 2 are applied to the usage example 1 and the usage example 2, but it is possible to select which one is used according to the application.

<Drive signal example 3>
FIG. 22 is a diagram illustrating drive pulses included in each drive signal of the drive signal example 3.
The drive signal example 3 includes two types of signals, a third drive signal DRV3 and a fifth drive signal DRV5. These two types of drive signals are properly used for each nozzle row. A period in which the nozzle row corresponding to the third drive signal DRV3 crosses the distance of one pixel is defined as a period Tb. A period in which the nozzle row corresponding to the fifth drive signal crosses the distance of one pixel is a period 2Tb that is twice the period Tb. In other words, the size of the movement direction of the pixels assigned to the nozzle row using the fifth drive signal DRV5 is twice the size of the movement direction of the pixels assigned to the nozzle row using the third drive signal DRV3. It becomes. That is, the drive signal example 3 is applied to the use example 3 described above.

First, the third drive signal DRV3 and the fifth drive signal DRV5 will be described.
The third drive signal DRV3 is also used in the drive signal example 2. That is, the third drive signal DRV3 is used for the nozzle row of cyan, magenta, and black ink in the third use example. Also, four gradations can be expressed for one pixel assigned to the nozzle row in which the third drive signal DRV3 is used (described above).

  In the nozzle row in which the fifth drive signal DRV5 is used, dots are formed in all the pixels arranged in the movement direction. That is, the fifth drive signal DRV5 is used for the nozzle row of yellow ink in the third use example.

  In the fifth drive signal DRV5, there are three third drive pulses W3 within the period 2Tb. Large dots are formed by three third drive pulses W3, medium dots are formed by two third drive pulses W3, and small dots are formed by one third drive pulse W3. Therefore, four gradations can be expressed for one pixel to which the nozzle row corresponding to the fifth drive signal DRV5 is assigned. Therefore, the print signal PRT corresponding to the fifth drive signal DRV5 has 2-bit information for each nozzle within the period 2Tb. That is, the fifth drive signal DRV5 requires less information than the second drive signal DRV2 of the drive signal example 1 in the print signal PRT.

  That is, the pixels assigned to the nozzle row in which the third drive signal DRV3 is used and the pixels assigned to the nozzle row in which the fifth drive signal DRV5 is used are expressed in four gradations. However, the resolution of the raster line formed by the nozzle row using the fifth drive signal DRV5 is half the resolution of the raster line formed by the nozzle row using the third drive signal DRV3.

  By the way, the size of the pixels assigned to the nozzle row that uses the third drive signal DRV3 and the nozzle row that uses the drive signal example 1 (the first drive signal DRV1 and the second drive signal DRV2) are assigned. The size of the pixels is equal. That is, the resolution of the raster line formed by the nozzle row using the fifth drive signal DRV5 is half the resolution of the raster line formed by the nozzle row used for the second drive signal DRV2. Therefore, the image quality of the drive signal example 3 is lower than that of the drive signal example 1. However, if the nozzle row in which the fifth drive signal is used is a nozzle row of a low visibility color such as yellow, the image quality does not deteriorate significantly.

Next, a period in which the nozzle row corresponding to each drive signal crosses the distance for one pixel will be described.
A period Tb in which the nozzle row in which the third drive signal DRV3 is used crosses the distance of one pixel includes a period T1 in which the voltage of the first drive pulse W1 changes and a stable period Ts after ink ejection by the first drive pulse W1. Then, the period T2 during which the voltage of the second drive pulse W2 changes is a total period. That is, this period Tb is equal to the period Tb shown in the drive signal example 2 and is shorter than the period Ta of the drive signal example 1 by the stable period Ts.

In summary, the drive signal example 3 is lower in image quality than the drive signal example 1, but the printing speed is increased.
Further, the drive signal example 3 requires less information than the drive signal example 1 in the print signal PRT. In other words, it is possible to select which one of the printing method of the usage example 1 using the driving signal example 1 and the usage example 3 using the driving signal example 3 is used according to the application.

=== Other Embodiment 1 ===
<Configuration of line head printer>
FIG. 23 is an overall configuration block diagram of a printer 2 (line head printer) according to another embodiment 1 of the present invention. FIG. 24 is a cross-sectional view of the printer 2. FIG. 25 is a diagram showing how the printer 2 transports a medium S (hereinafter referred to as paper).

Hereinafter, a basic configuration of the printer 2 will be described.
The printer 2 includes a transport unit 70, a head unit 80, a detector group 50, and a controller 60. The printer 2 that has received the print data from the computer 110, which is an external device, controls each unit 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 detector group 50 monitors the situation in the printer 2, and the controller 60 controls each unit based on the detection result.

  The transport unit 70 is for feeding paper to a printable position and transporting the paper in a predetermined direction during printing (hereinafter referred to as a transport direction). Further, the transport unit 70 includes a paper feed roller 73, a transport motor (not shown), two transport rollers 71 </ b> A and 71 </ b> B, and a belt 72. The paper feed roller 73 is a roller for automatically feeding the paper inserted into the paper insertion slot into the printer 2. The paper fed by the paper feed roller 73 is conveyed by a belt conveyor system. The belt conveyor system is a system in which a ring-shaped belt 72 is rotated by transport rollers 71A and 71B to transport a transported material (here, paper) on the belt. Further, the transport rollers 71A and 71B are driven by the transport motor 22.

  The head unit 70 has a head provided with a plurality of nozzles that are ink ejection portions. A plurality of heads are arranged in a staggered manner in the paper width direction (perpendicular to the transport direction). The nozzles of the respective colors are arranged in the paper width direction over at least the same width as the maximum printable paper width. Therefore, unlike the printer 1, the printer 2 does not need to form dots while the head is moved in the paper width direction (the moving direction in the printer 1) by the carriage. Therefore, since the dots are formed from the nozzles at a constant cycle without stopping the conveyance of the paper, the printing speed is increased. Each nozzle is provided with a drive element and a piezo element for driving each nozzle to eject ink droplets.

The detector group 50 and the controller 60 have the same configuration as the printer 1 and perform the same function.
The printer 2 performs four-color printing (yellow, cyan, magenta, black).
Hereinafter, a printing method by the printer 2 will be described.

<Head unit comparison example 1: normal printing>
FIG. 26 shows an arrangement of nozzles on the lower surface of the head unit 80. The head unit 80 has six fifth heads 415. The six fifth heads 415 are arranged in a staggered manner in the paper width direction. In addition, the fifth head 415 on the left side in the paper width direction has a younger number in parentheses. A yellow ink nozzle row Y, a cyan ink nozzle row C, a magenta ink nozzle row M, and a black ink nozzle row K are formed on the lower surface of the fifth head 415, and each nozzle row includes 180 nozzles. Yes. Of the 180 nozzles, the left nozzle is assigned a smaller number (# 1 to # 180). The nozzles of each nozzle row are aligned at a constant interval D (nozzle pitch D) in the paper width direction. The fifth heads 415 are also arranged at regular intervals in the paper width direction. Of the two fifth heads 415 arranged in the paper width direction, each fifth head is arranged such that the distance between the nozzle # 180 of the left fifth head 415 and the nozzle # 1 of the right fifth head 415 is D. 415 is arranged. This interval D is the minimum dot pitch in the paper width direction.

  FIG. 27 is an explanatory diagram of normal printing by the head unit 80. However, for simplicity of explanation, only two fifth heads 415 in the head unit 80 of FIG. 26 are shown. Furthermore, only the cyan ink nozzle row C among the four nozzle rows of each fifth head 415 is shown. The number of nozzles in each nozzle row is also reduced to eight. For the sake of explanation, it is assumed that dots are formed in all pixels. In order to identify and describe the pixels, the pixels arranged in the paper width direction are represented by “rows”, and the pixels arranged in the transport direction are represented by “columns”. Rows are assigned with lower numbers on the left side in the paper width direction. Rows are given lower numbers in the upstream side in the transport direction.

Next, the flow of normal printing by the head unit 80 will be described.
The paper is conveyed from the upstream side to the downstream side at a constant speed without stopping. Then, ink is ejected from the nozzles at a constant cycle onto the conveyed paper. The paper transport speed is determined by the ink ejection cycle and the resolution of dot rows (hereinafter referred to as raster lines) along the transport direction.

In FIG. 27, the fifth cyan ink nozzle array C5 (1) forms dots on the pixels in the first to eighth columns with black circles. A white circle indicates that the fifth cyan ink nozzle row C5 (2) forms dots on the 9th to 16th pixels. For example, the first dot row is formed by the nozzle # 1 of the fifth cyan ink nozzle row C5 (1).
That is, one raster line is formed by one nozzle. Therefore, when there is a defective nozzle, the printed image appears as a streak and image degradation occurs.

<Head unit comparison example 2: overlap printing with two heads>
FIG. 28 shows the arrangement of nozzles on the lower surface of the first head unit 801. The first head unit 801 has six sets, each including two fifth heads 415 arranged in the transport direction. The six sets are arranged in a staggered pattern in the paper width direction. The head on the left side in the paper width direction has a young number in parentheses. Of the two fifth heads arranged in the transport direction, A is attached to the downstream head and B is attached to the upstream head. For example, the leftmost head of the first head unit 801 and the downstream head is the fifth head 415 (1A).

  FIG. 29 is an explanatory diagram of overlap printing by the first head unit 801. However, for simplification of explanation, only four fifth cyan ink nozzle rows (C5 (1A), C5 (1B), C5 (2A), C5 (2B)) are shown. For the sake of explanation, it is assumed that dots are formed in all pixels.

Next, the flow of overlap printing by the first head unit 801 will be described.
The paper is conveyed at a constant speed without stopping. Ink is ejected from each nozzle onto the conveyed paper. In FIG. 29, a white circle indicates that the fifth cyan ink nozzle column C5 (1A) forms dots on pixels in even-numbered rows from the first column to the eighth column. A black circle indicates that the fifth cyan ink nozzle row C5 (1B) forms dots on the pixels in the odd-numbered rows from the first row to the eighth row. For example, the first dot row is formed by the nozzle # 1 of the fifth cyan ink nozzle row C5 (1A) and the nozzle # 1 of the fifth cyan ink nozzle row C5 (1B).
Similarly, white circles indicate that the fifth cyan ink nozzle C5 (2A) forms dots on pixels in even-numbered rows from the ninth column to the sixteenth column. A state in which the fifth cyan ink nozzle column C5 (2B) forms dots on pixels in odd-numbered rows from the 9th column to the 16th column is indicated by black circles.

That is, in this head unit comparative example 2, one raster line is formed by two different nozzles. In other words, raster lines are formed according to overlap printing. Therefore, when there is a defective nozzle, image deterioration can be alleviated compared to head unit comparative example 1.
In the head unit comparative example 2, since each nozzle forms a dot every other pixel in the transport direction, the printing speed is faster than in the head unit comparative example 1. However, as the number N of nozzles increases, the cost increases and the apparatus becomes larger.

  Therefore, in the first embodiment, a printing method that suppresses the cost and the size of the apparatus without substantially reducing the image quality will be described below.

<Head unit usage example 1: Printing with two heads>
FIG. 30 shows an arrangement of nozzles on the lower surface of the second head unit 802. The second head unit 802 has six fifth heads 415 and six sixth heads 416. The fifth head 415 is arranged on the downstream side, and the sixth head 416 is arranged on the upstream side, aligned in the conveyance direction. Further, the fifth head 415 and the sixth head 416 arranged in the transport direction are arranged in a staggered manner in the paper width direction. The head on the left side in the paper width direction has a young number in parentheses.

  The fifth head 415 has four nozzle rows of yellow, cyan, magenta, and black ink, whereas the sixth head 416 has three nozzle rows of cyan, magenta, and black ink. Each nozzle row includes 180 nozzles.

  FIG. 31 is an explanatory diagram of printing by the second head unit 802. However, for the sake of simplicity, two fifth cyan ink nozzle rows C5 (1) and C5 (2), two sixth cyan ink nozzle rows C6 (1) and C6 (2), and two fifth Only the yellow ink nozzle rows Y5 (1) and Y5 (2) are shown. For the sake of explanation, it is assumed that dots are formed in all pixels. The number of nozzles in each nozzle row is also reduced to eight.

Next, the flow of printing by the second head unit 802 will be described. The paper is conveyed at a constant speed without stopping. Ink is ejected from each nozzle onto the conveyed paper. In FIG. 31, the fifth cyan ink nozzle column C5 (1) shows dots formed on the odd-numbered pixels in the first to eighth columns by black circles. A state in which the sixth cyan ink nozzle column C6 (1) forms dots on pixels in even-numbered rows from the first column to the eighth column is indicated by white circles. The fifth yellow ink nozzle row Y5 (1) forms dots on the odd-numbered and even-numbered pixels in the first to eighth columns with crosses.
That is, one raster line of cyan ink is formed by two different nozzles. On the other hand, one raster line of yellow ink is formed by one nozzle.

Although not shown in FIG. 31, each raster line of magenta ink ink and black ink is also formed by two different nozzles.
As a result, when there are defective nozzles in the cyan, black, and magenta ink nozzle rows, no streaks appear in the printed image and image degradation is alleviated. On the other hand, when there is a defective nozzle in the yellow ink nozzle row, a yellow dot row is not formed on the pixels in the row to which the defective nozzle is assigned. However, yellow is generally known as a low visibility color compared to cyan, magenta, and black. Therefore, even if there are defective nozzles in the yellow ink nozzle row, the printed image does not appear to have streaks to the human eye.

  In other words, head unit usage example 1 has fewer yellow ink nozzle rows and lowers cost and size compared to head unit comparative example 2 (compare FIG. 28 and FIG. 30). Don't let me feel it.

  Further, in the head unit usage example 1, the driving signal example 1 or the driving signal example 2 described above is used. When the drive signal example 1 is used, the first drive signal DRV1 is used for the cyan, magenta, black, and ink nozzle arrays, and the second drive signal DRV2 is used for the yellow ink nozzle array. When the drive signal example 2 is used, the third drive signal DRV3 is used for the cyan, magenta, and black ink nozzle rows, and the fourth drive signal DRV4 is used for the yellow ink nozzle row.

<Head unit usage example 2: Printing method with different resolutions depending on the nozzle array>
The second head unit 802 (FIG. 30) used in the head unit usage example 1 has fewer yellow nozzle rows than the first head unit 801 (FIG. 28) used in the head unit comparative example 2. Therefore, in the head unit usage example 1, each nozzle row of cyan, magenta, and black ink forms a dot every other pixel in the transport direction, whereas the yellow ink nozzle row has all the pixels arranged in the transport direction. Dots are formed on the pixels. That is, the number of dots formed by the yellow ink nozzle row is twice the number of dots formed by the nozzle rows of other inks.

Therefore, in this head unit usage example 2, when overlap printing is performed by the second head unit 802 used in the head unit usage example 1, the number of dots formed by the yellow ink nozzle row and the nozzle rows of other inks are determined. A printing method in which the number of dots to be formed is equal is performed.
For this purpose, the size of the pixel Y in which the yellow ink dots are formed is doubled in the conveyance direction of the pixel C in which the cyan, magenta, and black ink dots are formed.

  FIG. 32 is an explanatory diagram of printing according to the head unit usage example 2. For simplification of description, two fifth cyan ink nozzle rows C5 (1) and C5 (2) and two sixth cyan ink nozzle rows C6 (1) and C6 (2) in the second head unit 802 are provided. Only two fifth yellow ink nozzle rows Y5 (1) and Y5 (2) are shown. For the sake of explanation, it is assumed that dots are formed in all pixels. The number of nozzles in each nozzle row is also reduced to eight.

  In FIG. 32, the fifth cyan ink nozzle row C5 (1) forms dots on the pixels C in the odd-numbered rows from the first row to the eighth row by crosses. A state in which the sixth cyan ink nozzle column C6 (1) forms dots on pixels C in even-numbered rows from the first column to the eighth column is indicated by crosses. That is, the fifth cyan ink nozzle row C5 (1) and the sixth cyan ink nozzle row C6 (1) form dots every other pixel C in the transport direction. In FIG. 32, the nozzle # 1 of the fifth cyan ink nozzle row C5 (1) forms three dots in the transport direction. Similarly, the nozzle # 1 of the sixth cyan ink nozzle row C6 (1) forms three dots in the transport direction. Although not shown in FIG. 32, the magenta and black ink nozzle rows in the second head unit 802 also form dots in the same manner as the cyan ink nozzle rows.

  On the other hand, a state in which the fifth yellow ink nozzle row Y5 (1) forms dots on the pixels Y in the first to eighth rows is indicated by an ellipse. The fifth yellow ink nozzle row Y5 (1) forms dots on all the pixels Y arranged in the transport direction. In FIG. 32, nozzle # 1 in the fifth yellow ink nozzle row Y5 (1) forms three dots in the transport direction.

In other words, in the head unit usage example 2, the number of dots in the transport direction formed by the yellow ink nozzle row is equal to the number of dots in the transport direction formed by the other nozzle rows of other inks, but the resolution of the raster line of the yellow ink Is half the resolution of the other ink raster lines.
Further, in the head unit use example 2, the above-described drive signal example 3 is used. The third drive signal DRV3 is used for the cyan, black, and magenta ink nozzle rows, and the fifth drive signal DRV5 is used for the yellow ink nozzle row.

=== Other Embodiment 2 ===
Each of the embodiments described above mainly describes a printing system having an ink jet printer and a printing system having a line head printer, but includes disclosure of head arrangement, nozzle arrangement on the lower surface of the head, drive signals, and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About colors with few nozzles>
In the above-described embodiment, yellow is taken as an example of a color that hardly deteriorates image quality even if dots are not formed according to overlap printing. An example of a head in which the number of yellow nozzles is smaller than the number of nozzles of other colors is shown, but the present invention is not limited to this. The color with a smaller number of nozzles than the other colors may be, for example, the color of special color ink (light cyan, light magenta, etc.) used when printing four or more colors (cyan, yellow, black, magenta).
Also, when performing overlap printing, the number of black nozzles may be smaller than the number of nozzles of other colors. This is because a raster line can be formed from black ink dots and black dots formed by mixing cyan, magenta and yellow inks.

<About the nozzle arrangement>
In the third head 413 of the above-described embodiment, the yellow ink nozzle row has half the number of downstream nozzles compared to the other ink nozzle rows, but is not limited thereto. For example, in the yellow ink nozzle row, the number of upstream nozzles may be reduced by more than half compared to the nozzle row of other inks.
The nozzles of the heads of the above-described embodiments are aligned at regular intervals in the transport direction (or paper width direction) for each color, but the present invention is not limited to this. For example, in order to increase the resolution in the transport direction (or the paper width direction), the nozzles of each color may be arranged in a staggered pattern in the transport direction (or the paper width direction).

<Ink ejection cycle>
In the above-described embodiment, the nozzle row of cyan, magenta, and black ink forms dots (discharges ink) every other pixel in the movement direction (or transport direction), but is not limited thereto. For example, dots may be formed every two pixels in the movement direction (or conveyance direction).

<About pixels>
In the usage example 3 (or head unit usage example 2) of the above-described embodiment, the size of the pixel Y in which the yellow ink dot is formed is changed in the moving direction (or transport direction), and the cyan, magenta, and black ink dots are set. Although the size of the pixel C to be formed is twice as large as the moving direction (or transport direction), the present invention is not limited to this. For example, the size of the moving direction (or transport direction) of the pixel Y may be three times the size of the moving direction (or transport direction) of the pixel C.

<About drive signal DRV>
Although four gradations (or two gradations) can be expressed for one pixel by the drive signal DRV of the above-described embodiment, the present invention is not limited to this. For example, eight gradations may be expressed for one pixel.

<About drive elements>
In the above-described embodiment, ink is ejected using the piezo element PZT. However, the present invention is not limited to this. A driving element other than the piezoelectric element, for example, a heating element or a magnetostrictive element may be used.

<About ink>
Since the above-described embodiment is an embodiment of the printer 1 and the printer 2, the liquid dye ink or pigment ink is ejected from the nozzle, but the present invention is not limited to this. If it is liquid, it can be discharged from the nozzle.

<About the printer configuration>
In the above-described embodiment, the configurations of the printer 1 (inkjet printer) and the printer 2 (line head printer) have been described. However, the configurations are not necessarily the same. For example, although the printer 2 feeds paper by the belt conveyor system, the paper may be fed by winding the paper around a platen.

FIG. 2 is a block diagram of an overall printer configuration. 1 is a schematic diagram of an overall configuration of a printer. 1 is a sectional view of the overall configuration of a printer. It is a flowchart of the process at the time of printing. It is explanatory drawing which shows the arrangement | sequence of the nozzle in the lower surface of a head. It is explanatory drawing of the band printing using a head. It is explanatory drawing of image degradation when an ink is not discharged to the appropriate position from the nozzle in a cyan ink nozzle row. It is explanatory drawing of the overlap printing by one head. It is explanatory drawing of image degradation when an ink is not discharged to the appropriate position from the nozzle in a cyan ink nozzle row. It is a figure which shows the arrangement | sequence of the nozzle in the carriage which has two heads and the two heads. It is explanatory drawing of the overlap printing by two heads (1st head and 2nd head). It is a figure which shows the arrangement | sequence of the nozzle in the lower surface of a 3rd head. It is explanatory drawing of the overlap printing by a 3rd head. It is a figure which shows the arrangement | sequence of the nozzle in the carriage which has two heads and the two heads. It is explanatory drawing of the overlap printing by a 1st head and a 4th head. A state in which the cyan ink nozzle row forms dots on the pixel C is shown. A state in which the yellow ink nozzle row forms dots in the pixel Y is shown. It is an electronic circuit diagram showing that each piezo element belonging to a certain nozzle row is operated by a drive signal generation circuit and a head drive circuit. It is a timing chart figure of each signal. It is a figure which shows the drive pulse which each drive signal of the drive signal example 1 has. It is a figure which shows the drive pulse which each drive signal of the drive signal example 2 has. It is a figure which shows the drive pulse which each drive signal of the drive signal example 3 has. FIG. 10 is a block diagram illustrating the overall configuration of a printer according to another embodiment. It is sectional drawing of a printer. It is a figure which shows a mode that a printer conveys paper. An arrangement of nozzles on the lower surface of the head unit is shown. It is explanatory drawing of normal printing by a head unit. The arrangement | sequence of the nozzle of the lower surface of a 1st head unit is shown. It is explanatory drawing of the overlap printing by a 1st head unit. The arrangement | sequence of the nozzle of the lower surface of a 2nd head unit is shown. It is explanatory drawing of the overlap printing by a 2nd head unit. It is explanatory drawing of the printing by the head unit usage example 2. FIG.

Explanation of symbols

1 printer, 2 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,
40 head units, 41 heads, 42 head drive circuits,
43 drive signal generation circuit, 44 switch,
50 detector groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Optical sensor,
60 controller, 61 interface unit, 62 CPU,
63 memory, 64 unit control circuit,
70 transport unit, 71A / 71B transport roller,
72 belts, 73 paper feed rollers,
80 head unit, 801 first head unit, 802 second head unit,
90 ink cartridges, 110 computers,
411 1st head, 412 2nd head, 413 3rd head,
414 4th head, 421 1st shift register, 422 2nd shift register,
423 latch circuit group, 424 data selector,
Y yellow ink nozzle row, C cyan ink nozzle row,
M magenta ink nozzle row, K black ink nozzle row,
DRV drive signal, PZT piezo element, PRT print signal,
LAT latch signal, CH change signal, SW switch control signal,
W1 first drive pulse, W2 second drive pulse,
T repetition period, Ts stabilization period, S medium (paper, etc.), F transport amount

Claims (12)

(1) a predetermined number of first nozzles for discharging the first color ink;
(2) discharging ink of a second color different from the first color, the number of second nozzles being less than the predetermined number;
(3) a moving mechanism that relatively moves the medium, the first nozzle, and the second nozzle in a predetermined direction;
(4) A dot row in which dots are arranged in the predetermined direction by ejecting ink from the first nozzle and the second nozzle while relatively moving the medium, the first nozzle, and the second nozzle in the predetermined direction. A controller that prints a print image composed of a plurality of the dot rows on the medium,
When forming dots on all pixels,
Each dot row of the first color is formed by two or more different first nozzles;
A controller that forms each of the dot rows of the second color with a smaller number of the second nozzles than the number of the first nozzles forming each of the dot rows of the first color;
A printing apparatus having (5). The printing apparatus according to claim 1,
A transport mechanism for moving the medium in a direction perpendicular to the predetermined direction with respect to the first nozzle and the second nozzle;
The moving mechanism is a moving mechanism that moves the first nozzle and the second nozzle in the predetermined direction with respect to the medium,
The predetermined number of the first nozzles are arranged in a direction perpendicular to the predetermined direction at regular intervals;
A smaller number of the second nozzles than the predetermined number are arranged in a direction perpendicular to the predetermined direction at the predetermined interval.
Printing device. The printing apparatus according to claim 1,
The predetermined number of the first nozzles constitute a plurality of first nozzle rows arranged in a direction perpendicular to the predetermined direction,
The number of the second nozzles smaller than the predetermined number constitutes a number of the second nozzle rows smaller than the plurality of numbers arranged side by side in a direction perpendicular to the predetermined direction,
The first nozzle row and the second nozzle row are arranged side by side in the predetermined direction,
Printing device. The printing apparatus according to claim 3,
A transport mechanism for moving the medium in a direction perpendicular to the predetermined direction with respect to the first nozzle and the second nozzle;
The movement mechanism moves the first nozzle and the second nozzle in the predetermined direction with respect to the medium, and the transport mechanism moves the medium in the predetermined direction with respect to the first nozzle and the second nozzle. Alternately moving in the vertical direction,
Printing device. The printing apparatus according to claim 3,
The moving mechanism is a transport mechanism that moves the medium in the predetermined direction with respect to the first nozzle and the second nozzle.
Printing device. The printing apparatus according to any one of claims 1 to 5,
When forming dots on all pixels,
The controller is configured so that the number of pixels assigned to form dots by the first nozzle is less than the number of pixels assigned to form dots by the second nozzle. Discharging ink from the first nozzle and the second nozzle;
Printing device. The printing apparatus according to any one of claims 1 to 5,
The size in the predetermined direction of the first pixel assigned so that the first nozzle forms a dot is the size in the predetermined direction of the second pixel assigned so that the second nozzle forms a dot. The controller causes ink to be ejected from the first nozzle and the second nozzle so as to be smaller than the size.
Printing device. The printing apparatus according to any one of claims 1 to 6,
Drive that generates each drive signal so that the waveform of the drive signal used when the first nozzle forms a dot and the waveform of the drive signal used when the second nozzle forms a dot are the same. A signal generation circuit;
A printing apparatus. The printing apparatus according to any one of claims 1 to 6,
Drive signal generation for generating each drive signal so that the waveform of the drive signal used when the first nozzle forms dots differs from the waveform of the drive signal used when the second nozzle forms dots Circuit,
Printing apparatus having The printing apparatus according to claim 7, wherein
A drive signal generation circuit that generates a drive signal for forming one dot in the second pixel while the first nozzle crosses the plurality of first pixels;
Printing apparatus having The printing apparatus according to any one of claims 1 to 10,
The first color is magenta or cyan;
The second color is yellow;
Printing device A predetermined number of first nozzles for discharging the first color ink;
Discharging a second color ink different from the first color, and having a number of second nozzles less than the predetermined number;
A transport mechanism for moving a medium in a predetermined direction with respect to the first nozzle and the second nozzle;
While moving the medium in the predetermined direction with respect to the first nozzle and the second nozzle, ink is ejected from the first nozzle and the second nozzle, and a dot row in which dots are arranged in the predetermined direction is added to the medium. A controller that forms and prints a print image composed of a plurality of dot rows on the medium,
When forming dots on all pixels,
Each dot row of the first color is formed by two or more different first nozzles;
Each dot row of the second color is formed by a smaller number of the second nozzles than the number of the first nozzles forming each of the dot rows of the first color;
The size in the predetermined direction of the first pixel assigned so that the first nozzle forms a dot is the size in the predetermined direction of the second pixel assigned so that the second nozzle forms a dot. Discharging ink from the first nozzle and the second nozzle so as to be smaller than the size;
Have a controller,
The predetermined number of the first nozzles includes a plurality of nozzle rows arranged in a direction perpendicular to the predetermined direction,
The number of the second nozzles smaller than the predetermined number includes a number of nozzle rows smaller than the plurality of nozzles arranged in a direction perpendicular to the predetermined direction.
Drive that generates each drive signal so that the waveform of the drive signal used when the first nozzle forms a dot and the waveform of the drive signal used when the second nozzle forms a dot are the same. A signal generation circuit;
The first color is magenta or cyan;
The second color is yellow;
Printing device.

Images