JP2010036423A - Liquid ejecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an image quality degradation. <P>SOLUTION: A plurality of heads each having a main nozzle group in which nozzles are arranged in a predetermined direction at predetermined intervals, a sub nozzle group in which nozzles of a smaller number than that of the nozzles possessed by the main nozzle group are arranged in the predetermined direction at the predetermined intervals, and driving elements set correspondingly to the respective nozzles to make the liquid ejected from the corresponding nozzles when a drive signal is inputted are arranged in the predetermined direction. Each of the heads has a first input part in which the drive signal for driving the driving elements corresponding to the nozzles that belong to the main nozzle group is inputted, and a second input part in which the drive signal for driving the driving elements corresponding to the nozzles that belong to the sub nozzle group is inputted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus.

As a liquid ejecting apparatus, an ink jet printer that performs printing by ejecting ink from nozzles onto a medium such as paper or cloth is known. Among ink jet printers, a line head printer in which a large number of nozzles are arranged at predetermined intervals over the width of the paper sheet enables high-speed printing. However, it is difficult to arrange the nozzles in the paper width length with one long head due to manufacturing problems and the like. Therefore, a head row in which a plurality of heads are arranged so that the nozzle row is along the paper width direction is provided on one side and the other side in the transport direction intersecting the paper width direction, and the end nozzle of the head on one side and the other side A line head printer has been proposed in which the heads are arranged so that the interval between the end nozzles of the head in the paper width direction becomes the nozzle pitch of the nozzle row (see, for example, Patent Document 1).
JP-A-10-95113

However, in the printer described in Patent Document 1, when an image is printed without adjusting the drive signal for ejecting liquid from the nozzles, the dot rows are shifted to one side and the other side in the transport direction, and the image quality deteriorates. End up.
An object of the present invention is to suppress image quality deterioration.

  A main invention for achieving the above object is that a main nozzle group in which nozzles are arranged at predetermined intervals in a predetermined direction and a number of nozzles smaller than the number of nozzles of the main nozzle group are the predetermined intervals in the predetermined direction. A plurality of heads each having a sub nozzle group arranged in a row and a driving element provided corresponding to each of the nozzles, wherein the driving element discharges liquid from the corresponding nozzle when a driving signal is input. The heads are arranged in the predetermined direction, and each head belongs to the sub-nozzle group, and a first input unit to which the driving signal for driving the driving element corresponding to the nozzle belonging to the main nozzle group is input. And a second input unit to which the driving signal for driving the driving element corresponding to the nozzle is input.

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

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

That is, a main nozzle group in which nozzles are arranged at predetermined intervals in a predetermined direction, and a sub nozzle group in which a smaller number of nozzles than the number of nozzles of the main nozzle group are arranged in the predetermined direction at the predetermined intervals; A plurality of heads arranged corresponding to each of the nozzles, each having a driving element that discharges liquid from the corresponding nozzle when a driving signal is input, are arranged in the predetermined direction. The head includes: a first input unit to which the driving signal for driving the driving element corresponding to the nozzle belonging to the main nozzle group is input; and the driving element corresponding to the nozzle belonging to the sub nozzle group. And a second input unit to which the driving signal for driving is input.
According to such a liquid ejecting apparatus, the first input is performed when the liquid ejecting characteristics of the main nozzle group and the sub nozzle group are different or the main nozzle group and the sub nozzle group are shifted in a direction intersecting the predetermined direction. By adjusting the drive signals input to the unit and the second input unit, it is possible to adjust the liquid discharge amount and the liquid discharge timing of the main nozzle group and the sub nozzle group, and to suppress image quality deterioration.

In this liquid ejection apparatus, the drive signal that is input to the first input unit by one drive signal generation unit and the drive signal that is input to the second input unit by another drive signal generation unit To generate.
According to such a liquid ejection device, the drive signals input to the first input unit and the second input unit can be adjusted, respectively, and the liquid ejection amount and the liquid ejection timing of the main nozzle group and the sub nozzle group can be adjusted. It can be adjusted and image quality degradation can be suppressed.

In this liquid ejection apparatus, the drive signal generated in the other drive signal generation unit is input to the second input units of the plurality of heads.
According to such a liquid ejection apparatus, the number of drive signal generation units can be reduced, and the cost can be reduced.

In this liquid ejection apparatus, the generation timing of the drive pulse included in the drive signal input to the first input unit, the generation timing of the drive pulse included in the drive signal input to the second input unit, To adjust.
According to such a liquid ejection apparatus, the timing of liquid ejection from the main nozzle group and the sub nozzle group can be adjusted.

In this liquid ejection apparatus, the shape of the drive pulse included in the drive signal input to the first input unit and the shape of the drive pulse included in the drive signal input to the second input unit are adjusted. To do.
According to such a liquid discharge apparatus, the liquid discharge amount from the main nozzle group and the sub nozzle group can be adjusted.

In this liquid ejection apparatus, the drive signal generated by one drive signal generation unit is input to the first input unit, and the drive signal generated by the one drive signal generation unit is input to a delay circuit. And the drive signal output from the delay circuit is input to the second input unit.
According to such a liquid ejection apparatus, the timing of liquid ejection from the main nozzle group and the sub nozzle group can be adjusted.

A main nozzle group in which nozzles are arranged at predetermined intervals in a predetermined direction; and a sub nozzle group in which a smaller number of nozzles than the number of nozzles of the main nozzle group are arranged in the predetermined direction at the predetermined intervals; A plurality of heads each having a driving element provided corresponding to each of the nozzles, each having a driving element that discharges liquid from the corresponding nozzle when a driving signal is input, are arranged in the predetermined direction, and The drive signal input to the drive element corresponding to the nozzle belonging to the nozzle group is different from the drive signal input to the drive element corresponding to the nozzle belonging to the sub-nozzle group. A liquid ejection device;
According to such a liquid ejection apparatus, when the liquid ejection characteristics of the main nozzle group and the sub nozzle group are different, or when the main nozzle group and the sub nozzle group are shifted in a direction crossing the predetermined direction, the main nozzle group By adjusting the drive signal input to the drive element corresponding to the nozzle belonging to and the drive signal input to the drive element corresponding to the nozzle belonging to the sub nozzle group, the liquid discharge amount of the main nozzle group and the sub nozzle group The timing of liquid discharge can be adjusted, and image quality deterioration can be suppressed.

=== About Line Head Printers ===
In the present embodiment, a “line head printer” in an ink jet printer will be described as an example of the “liquid ejecting apparatus”. First, a line head printer (hereinafter, printer 1) will be described.

  FIG. 1 is a block diagram of the overall configuration of the printer 1. FIG. 2A is a cross-sectional view of the printer 1. FIG. 2B is a diagram illustrating a state in which the printer 1 transports the paper S (medium). The printer 1 that has received print data from the computer 50, which is an external device, controls each unit (conveyance unit 20, head unit 30) by the controller 10, and forms an image on the paper S. Further, the detector group 40 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result. The detector group 40 includes, for example, a sensor that detects the paper S during paper feeding, a rotary encoder that transports the paper S by a predetermined transport amount, and the like.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 50 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing the program of the CPU 12 and a work area. The CPU 12 controls each unit with a unit control circuit 14 according to a program stored in the memory 13.

  The transport unit 20 feeds the paper S to a printable position, and transports the paper S by a predetermined transport amount in the transport direction during printing. The paper feed roller 23 is a roller for automatically feeding the paper S inserted into the paper insertion opening onto the transport belt 22 in the printer 1. Then, the ring-shaped transport belt 22 is rotated by the transport rollers 21A and 21B, and the sheet S on the transport belt 22 is transported. The sheet S is electrostatically adsorbed or vacuum adsorbed on the transport belt 22.

  The head unit 30 is for ejecting ink onto the paper S, and has a plurality of heads 31 arranged in the transport direction. The head 31 (chip) has a plurality of nozzles that are ink ejection portions. Each nozzle is provided with a pressure chamber containing ink (liquid) and a drive element (piezo element) for changing the volume of the pressure chamber to eject ink. Ink is ejected from the nozzles by applying a voltage (driving pulse) to the driving element to expand and contract the pressure chamber. However, the present invention is not limited thereto, and a heating element (corresponding to a driving element) may be provided in the pressure chamber. In this case, a voltage (driving pulse) is applied to the heating element to generate heat, and bubbles are generated in the pressure chamber by the generated heat. By doing so, the liquid is discharged from the nozzle by the generated bubbles.

  In such a printer 1, the controller 10 that has received the print data first rotates the paper feed roller 23 to send the paper S to be printed onto the transport belt 22. Thereafter, the sheet S is transported on the transport belt 22 without stopping at a constant speed, and is transported under the head unit 30. While the sheet S is conveyed under the head unit 30, ink is intermittently ejected from each nozzle. As a result, a dot row composed of a plurality of dots along the transport direction is formed on the paper S, and an image is printed.

<About nozzle arrangement>
FIG. 3A shows the arrangement of the heads 31 on the lower surface of the head unit 30, and FIG. 3B shows the nozzle arrangement at the joint portion of the heads 31. A line head printer in which nozzles are arranged at predetermined intervals over the width of the paper enables high-speed printing. However, it is difficult to form a nozzle array over the paper width in one head due to manufacturing problems (yield and the like). Therefore, in the present embodiment, as shown in FIG. 3A, a plurality of short heads 31 are arranged side by side in the paper width direction (corresponding to a predetermined direction) on the lower surface of the head unit 30. For the sake of explanation, young numbers are assigned in order from the left head 31 in the paper width direction.

  As shown in FIG. 3B, the nozzles of each head 31 are classified into a main nozzle group and a sub nozzle group having a smaller number of nozzles than the number of nozzles of the main nozzle group. The sub nozzle group is located at the left end of the head 31 in the paper width direction, and the main nozzle group is located from the right side of the sub nozzle group to the right end of the head 31. Each of the main nozzle group and the sub nozzle group is composed of a yellow ink nozzle row Y, a magenta ink nozzle row M, a cyan ink nozzle row C, and a black ink nozzle row K. The nozzle row of the sub nozzle group is shifted to the downstream side in the transport direction by one row with respect to the nozzle row of the main nozzle group. Therefore, for example, the yellow nozzle row Y of the sub nozzle group and the magenta ink nozzle row M of the main nozzle group are aligned in the paper width direction. Further, in the sub nozzle group, the number of nozzles is smaller in the upstream nozzle row (for example, the yellow nozzle row Y) in the transport direction, and conversely, in the main nozzle group, the upstream nozzle row in the transport direction is the same. The number of nozzles increases. Therefore, as a result, the number of nozzles in each nozzle row is equal in one head 31.

  The nozzles of each nozzle row are arranged at an interval of 800 dpi (predetermined interval) in the paper width direction, and “nozzle pitch = 800 dpi”. Further, in the nozzle rows of the same color of the adjacent heads 31 (1) and 31 (2), the right end nozzle (yellow nozzle row Y) of the main nozzle group of the left head 31 (1) in the paper width direction. Nozzle #N) and the left end nozzle (nozzle # 1 of yellow nozzle row Y) in the sub nozzle group of the right head 31 (2) are “800 dpi”. In the same color nozzle rows of the same head 31 (2), the right end nozzle (nozzle #n of the yellow nozzle row) in the sub nozzle group and the left end nozzle (in the main nozzle group) ( The distance from the nozzle # 1) in the yellow nozzle row is “800 dpi”. That is, the nozzles are arranged at intervals of 800 dpi in the paper width direction over the paper width. Since the positions of the end portions of the nozzle rows in the transport direction are not aligned, as shown in FIG. 3A, the range in which the nozzles of all the nozzle rows exist is the maximum printing range.

  Normally, as shown in FIG. 3B, the distance between the edge of the head 31 and the end of the nozzle row is wider than the nozzle pitch (800 dpi). Therefore, by simply arranging the heads having nozzle rows in which the nozzles are arranged in the paper width direction, the paper width direction of the end nozzle of one head and the end nozzle of the other head at the joint portion of the head. Is wider than the nozzle pitch. Therefore, in the present embodiment, as described above, by shifting the nozzle row of the sub nozzle group in the transport direction with respect to the nozzle row of the main nozzle group, even at the joint portion of the heads 31, It is possible to set the interval of the partial nozzles in the paper width direction to the nozzle pitch (800 dpi). As a result, the nozzles can be arranged at a predetermined nozzle pitch over the paper width.

In order to arrange the nozzles at a predetermined interval in the paper width direction, as in Patent Document 1 (Japanese Patent Laid-Open No. 10-95113), a nozzle group having the same number of nozzles (a head consisting of nozzle rows having the same length). Are shifted in the medium conveyance direction and arranged in the paper width direction (when arranged in a staggered manner), the head unit becomes longer in the conveyance direction, and the printing apparatus becomes larger.
Therefore, in this embodiment, as shown in FIG. 3, the main nozzle groups of the heads 31 are arranged in the paper width direction without being shifted in the medium transport direction, and the sub nozzle groups located at the joints of the heads 31 are the main nozzle groups. Are shifted in the medium transport direction. By doing so, the interval in the paper width direction of the nozzles located at the joints of the heads 31 can be made constant, and the length of the head unit 30 in the medium conveyance direction can be reduced, thereby preventing an increase in the size of the printing apparatus. it can. Further, the number of sub nozzle groups can be reduced as compared with the main nozzle group.

  Moreover, since the nozzles of the main nozzle group to which many nozzles belong among the nozzles of the head unit 30 are arranged in a straight line in the nozzle row direction, the deviation adjustment of the landing positions of the dots discharged from the nozzles of the main nozzle group is adjusted. The amount is small. If the main nozzle groups are arranged so as to be shifted in the medium transport direction as in Patent Document 1, the amount of dot landing position adjustment for each main nozzle group is increased, and the time for shifting the printing timing is also increased. As a result, the print data must be stored in the buffer for the time to shift the print timing. Further, the amount of deviation in the medium conveyance direction between the sub nozzle group and the main nozzle group is equal to the amount of deviation between adjacent nozzle rows in the head 31, and is smaller than that of the above-mentioned Patent Document 1. Therefore, in the main nozzle group and the sub nozzle group, the time for shifting the print timing is short, and the time for storing the print data in the buffer can be shortened.

=== Regarding Adjustment of Liquid Discharge from Main Nozzle Group and Sub Nozzle Group ===
FIG. 4 is a diagram illustrating how dots are formed when the drive signal for ejecting liquid from the main nozzle group and the sub nozzle group is not adjusted. Hereinafter, for the sake of explanation, attention is focused on one color nozzle row (black nozzle row K). The black nozzle row K of the sub-nozzle group is shifted from the black nozzle row K of the main nozzle group on the downstream side in the transport direction. Therefore, when liquid is simultaneously ejected from the black nozzle rows K of the main nozzle group and the sub nozzle group, the dot row formed in the sub nozzle group is more transported than the dot row formed in the main nozzle group, as shown in the figure. Formed on the downstream side. That is, it is necessary to adjust the timing at which the liquid is discharged from each nozzle group so that the dot rows formed in the main nozzle group and the dot rows formed in the sub nozzle group are aligned in the paper width direction. Otherwise, the image quality will deteriorate.

  The number of nozzles that the sub nozzle group has is smaller than the number of nozzles that the main nozzle group has, and the nozzle row of the sub nozzle group is shifted from the nozzle row of the main nozzle group to the downstream side in the transport direction. For this reason, the main nozzle group and the sub nozzle group, for example, have different shapes of components for ejecting liquid from the nozzles, or how ink is supplied from the common ink supply port to the pressure chambers corresponding to the nozzles. It ’s different. The sub nozzle group is concentrated on the end of the head 31. Therefore, it is considered that the liquid ejection characteristics from the main nozzle group and the liquid ejection characteristics from the sub nozzle group may be different. For example, if the liquid discharge speed is different between the main nozzle group and the sub nozzle group, the dot positions formed in the main nozzle group and the dot positions formed in the sub nozzle group are shifted, and the image quality is deteriorated. Also, if the liquid discharge amount is different between the main nozzle group and the sub nozzle group, the dot size formed in the main nozzle group and the dot size formed in the sub nozzle group are different as shown in FIG. Then, the density difference between the image portion formed in the sub nozzle group and the image portion formed in the main nozzle group is conspicuous, and the image quality deteriorates.

  Thus, the number of nozzles is different between the main nozzle group and the sub nozzle group, and the nozzle position is also shifted in the transport direction. Therefore, the drive signal for discharging the liquid from the main nozzle group and the drive signal for discharging the liquid from the sub nozzle group are adjusted, and the timing at which the liquid is discharged from the nozzle and the amount of liquid discharged from the nozzle are adjusted. There is a need. Otherwise, the image quality will deteriorate. Therefore, an object of the present embodiment is to suppress image quality degradation caused by a difference in nozzle positions and liquid ejection characteristics between the main nozzle group and the sub nozzle group.

  Therefore, in this embodiment, the printer 1 prints a test pattern, and based on the test pattern result, a drive signal for ejecting liquid from the main nozzle group and a drive signal for ejecting liquid from the sub nozzle group are provided. adjust. Thus, the deviation of the landing positions of the liquid ejected from the main nozzle group and the sub nozzle group and the density difference between the images formed in the main nozzle group and the sub nozzle group are adjusted.

  By the way, in the head 31 of this embodiment, the number of nozzles of the sub nozzle group is smaller than that of the main nozzle group. That is, in the nozzles that discharge the same liquid, a large number of nozzles belonging to the main nozzle group are arranged in a straight line in the paper width direction, and a small number of nozzles belonging to the sub nozzle group are shifted from the main nozzle group in the transport direction. Become. As described above, since the main nozzle group and the sub nozzle group are arranged so as to be shifted in the transport direction, it is necessary to adjust the timing of discharging the liquid from each nozzle group. Therefore, in the head 31 of this embodiment, the number of sub-nozzle groups is smaller than that of the main nozzle group so that dots are aligned in the paper width direction without adjusting the ejection timing of as many nozzles as possible. By doing so, image quality deterioration can be further suppressed. When ink (liquid) discharged from the nozzles reaches the paper, the paper expands and contracts due to the solvent component (water) of the ink. In the main nozzle group and the sub nozzle group, the liquid is discharged to the same area in the transport direction on the paper, so the number of sub nozzle groups is smaller than the main nozzle group, and as many nozzles as possible (main nozzles). When the liquid is simultaneously discharged from the (group), the number of nozzles (sub nozzle groups) that are affected by the expansion and contraction of the paper due to the liquid previously discharged from the nozzles can be reduced, and image quality deterioration can be further suppressed.

  In addition, since each head 31 of this embodiment has four nozzle rows for each color, the main nozzle group and the sub nozzle group each have four nozzle rows, but the present invention is not limited to this. For example, when the head has a nozzle row that ejects one type of ink, the nozzle row having a large number of nozzles corresponds to the main nozzle group in the head, and is shifted from the main nozzle group in the transport direction and has a small number of nozzles. The nozzle row corresponds to the sub nozzle group.

=== About Test Patterns ===
FIG. 5 is a diagram showing a test pattern for adjusting the positional deviation of dots formed in the main nozzle group and the sub nozzle group. In the head 31 of the present embodiment, in order to align the nozzles at a predetermined interval in the paper width direction, the nozzle row of the sub nozzle group is arranged to be shifted downstream in the transport direction with respect to the nozzle row of the main nozzle group. . Therefore, in order to form a dot row along the paper width direction, it is necessary to adjust the timing of ejecting liquid from the main nozzle group and the sub nozzle group. Specifically, since the nozzle row of the sub nozzle group is located downstream in the transport direction with respect to the nozzle row of the main nozzle group, the liquid discharge from the sub nozzle group is more than the liquid discharge from the main nozzle group. Need to delay.

  Here, as shown in FIG. 4, the amount of deviation in the transport direction in the design between the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group is defined as “interval D”. Therefore, in terms of design, if the liquid is discharged from the main nozzle group and the sheet S is conveyed by the length of the interval D and then the liquid is discharged from the sub nozzle group, the dot rows and the sub lines formed in the main nozzle group The dot rows formed in the nozzle group are aligned on the straight line in the paper width direction. However, in practice, the dot rows are not always formed according to the design calculation due to various factors such as the transport error of the transport unit 20 and the nozzle manufacturing error.

  Therefore, the test pattern as shown in FIG. 5 is printed on the printer 1 to adjust the liquid ejection timing of the main nozzle group and the sub nozzle group. The test pattern is composed of dot rows in which the way of shifting the liquid ejection timing of the main nozzle group and the sub nozzle group is changed. The characters shown above the test pattern indicate the amount of deviation between the dot row of the sub nozzle group and the dot row of the main nozzle group in the design. For example, if the character described in the test pattern is “0”, the dot row described below is designed in the transport direction of the dot row of the sub nozzle group and the dot row of the main nozzle group. The dot rows are printed by adjusting the liquid ejection timing from the main nozzle group and the sub nozzle group so that the positions are equal. That is, the dot row described under “0” is a dot row formed by ejecting liquid from the sub nozzle group after the liquid is ejected from the main nozzle group and the sheet is conveyed for the length of the interval D. It is.

  In addition, dot rows in which the liquid discharge timings of the main nozzle group and the sub nozzle group are shifted are described. For example, the dot row described below the letter “D / 3” is designed so that the dot row of the sub nozzle group is “interval D / 3” on the downstream side in the transport direction from the dot row of the main nozzle group. It is a dot row printed by adjusting the liquid ejection timing from the main nozzle group and the sub nozzle group so as to be shifted by as much as possible. On the other hand, the dot row described below the character “−D / 3” is designed so that the dot row of the sub nozzle group is located at the “interval D / D” upstream of the dot row of the main nozzle group in the transport direction. This is a dot row printed by adjusting the liquid ejection timing from the main nozzle group and the sub nozzle group so as to be shifted by 3 ”.

  In this way, by forming a dot row in which the liquid discharge timings from the main nozzle group and the sub nozzle group are changed, the liquid discharge timing from the main nozzle group and the liquid discharge timing from the sub nozzle group are shifted by how much. You can judge whether it is okay. In design, the dot rows described below the character “0” should be aligned in the paper width direction. However, in the test pattern of FIG. 5, the dot rows described under “D / 3” are aligned in the paper width direction. For this reason, the liquid is discharged from the main nozzle group, and the liquid is discharged from the sub nozzle group after the sheet S is transported in the transport direction by a length of “2D / 3 (= D−D / 3)”. Thus, it can be seen that the positions of the dot rows of the main nozzle group and the dot rows of the sub nozzle group coincide with each other.

  Thus, based on the result of the test pattern, the timing of liquid ejection from the main nozzle group and the sub nozzle group is adjusted so that the positions of the dot rows of the main nozzle group and the dot rows of the sub nozzle group coincide with each other. be able to. As a result, it is possible to prevent the image quality from deteriorating due to the dot row of the main nozzle group and the dot row of the sub nozzle group being shifted in the transport direction. Note that the timing adjustment amount of the liquid ejection from the main nozzle group and the sub nozzle group calculated based on the test pattern result may be stored in the memory 13 of the printer 1 or the like. By doing so, each drive signal for ejecting liquid from the main nozzle group and the sub nozzle group can be adjusted based on the adjustment amount stored in the memory 13.

  FIG. 6 is a diagram illustrating a test pattern for adjusting a density difference between an image formed in the main nozzle group and an image formed in the sub nozzle group. The head 31 of this embodiment may have different liquid discharge characteristics from the main nozzle group and the sub nozzle group, for example, because the nozzle row of the sub nozzle group is displaced in the transport direction with respect to the nozzle row of the main nozzle group. There is. For example, due to the difference in liquid ejection characteristics, as shown in FIG. 4, more liquid is ejected from the sub nozzle group than the main nozzle group even if the same amount of liquid is ejected from the main nozzle group and the sub nozzle group. Let's say. Then, the dot size formed in the sub nozzle group becomes larger than the dot size formed in the main nozzle group. As a result, the image formed in the sub-nozzle group is viewed darker than the image formed in the main nozzle group, and the difference in image density causes density unevenness, which causes image quality deterioration. Therefore, it is necessary to adjust so that the image density formed in the main nozzle group is equal to the image density formed in the sub nozzle group. As an adjustment method, in order to adjust the amount of liquid ejected from the main nozzle group or sub nozzle group at a time, a method of adjusting a drive signal (details will be described later) for ejecting liquid from the nozzle, or the entire image In order to adjust the amount of liquid discharged, there is a method of adjusting the dot generation rate and the like by adjusting the density (command gradation value) indicated by the print data.

  Therefore, a test pattern as shown in FIG. 6 is printed by the printer 1 and adjusted so that the image density formed in the main nozzle group matches the image density formed in the sub nozzle group. The test pattern includes an image in which the density of the image formed in the sub nozzle group is changed with respect to the image formed in the main nozzle group. For example, if the character shown in the test pattern is “± 0%”, the image formed in the main nozzle group and the image formed in the sub nozzle group are printed when instructed to print at the same density. It is an image. In addition, in the image described under “+ 5%”, the image formed in the sub nozzle group is higher in density by 5% than the image formed in the main nozzle group. This is an image printed when an instruction is issued. On the contrary, the image described under “−5%” instructed that the image formed in the sub nozzle group is lower in density by 5% than the image formed in the main nozzle group. In this case, the image is printed.

  If the amount of liquid ejected from the main nozzle group and the sub nozzle group is equal, there should be no density difference between the image of the main nozzle group and the image of the sub nozzle group described under “± 0%”. However, in the image described under “± 0%” of the test pattern in FIG. 6, the image of the sub nozzle group is printed darker than the image of the main nozzle group, and is below “−5%”. In the described image, there is no density difference between the image of the main nozzle group and the image of the sub nozzle group. From this, it can be seen that even if an instruction is given to print at the same density, the image formed in the sub nozzle group is printed darker than the image formed in the main nozzle group. That is, in order to print the image of the main nozzle group and the image of the sub nozzle group at the same density, the density of the image formed on the sub nozzle group is 5% lighter than the density of the image formed on the main nozzle group. You can make adjustments so that printing is done with. It should be noted that the density comparison between the image formed in the main nozzle group and the image formed in the sub nozzle group may be performed by visual observation or by a reading result obtained by causing the scanner to read a test pattern.

  In this way, a test pattern is formed by changing a plurality of image densities (command gradation values) formed in the sub nozzle group with respect to image densities (command gradation values) formed in the main nozzle group. By doing so, it is possible to know how light or how dark the image formed in the sub nozzle group is printed with respect to the image formed in the main nozzle group based on the result of the test pattern, The image density formed in the main nozzle group and the image density formed in the sub nozzle group can be adjusted to be equal. As a result, it is possible to prevent unevenness in the density of the image formed in the main nozzle group and the image formed in the sub nozzle group, and to suppress deterioration in image quality. Note that the density adjustment values of the image formed in the main nozzle group and the image formed in the sub nozzle group may be stored in the memory 13 of the printer 1.

=== About Adjustment Method of Drive Signal ===
Based on the test pattern results described above, how much the liquid discharge timing of the main nozzle group and the sub nozzle group should be shifted, and how to adjust the density of the image formed in the main nozzle group and the image formed in the sub nozzle group You can see how much you should do. In order to discharge liquid from each nozzle as one of methods for adjusting the liquid discharge timing of the main nozzle group and the sub nozzle group and adjusting the density of each image formed in the main nozzle group and the sub nozzle group There is a method of adjusting the drive signal. Therefore, first, a mechanism in which liquid is ejected from the nozzle by a drive signal will be described.

<About the head controller HC>
FIG. 7 is an electronic circuit diagram showing that the drive element PZT belonging to a certain nozzle row of a certain head 31 is operated by the drive signal generating unit 32 and the head control unit HC, and FIG. 8 is a timing chart of each signal. is there. The head unit 30 includes a head controller HC and a drive signal generator 32 (described later). The head controller HC includes the first shift register 33, the second shift register 34, the switch SW, and the latch circuit group corresponding to the number of nozzles of one head 31 (n sub nozzle groups + N main nozzle groups). 35 and a data selector 36. The head controller HC drives the piezo elements PZT corresponding to the nozzles belonging to one head 31 based on the serially transmitted print signal PRT, and discharges ink from the nozzles. The head controller HC is provided for each head 31 and each nozzle row.

  The print signal PRT (i) is a signal corresponding to pixel data assigned to one pixel assigned to the nozzle #i. Here, the print signal PRT (i) is a signal having 2-bit information per pixel. First, when print signals PRT (i) for the number of nozzles are serially transmitted to the first shift register 33 and the second shift register 34 of the head controller HC, the print signal PRT (i) is converted into parallel data. . When the rising pulse of the latch signal LAT is input to the latch circuit group 35, the data of each shift register is latched in the latch circuit group 35. At the same time, the data selector 36 is in an initial state.

  The data selector 36 converts the print signal PRT (i), which is 2-bit data latched in the latch circuit group 35, into the switch control signal prt (i) before the next latch signal LAT is input. , Output to each switch SW (i). The drive signal COM from the drive signal generation unit 32 is also input to the switch SW. As shown in FIG. 8, the drive signal COM has two drive pulses W1 and W2 within a repetition period T. When the level of the switch control signal prt (i) is “1”, the switch SW (i) passes the drive pulse W corresponding to the drive signal COM as it is. On the other hand, when the level of the switch control signal prt (i) is “0”, the switch SW (i) blocks the drive pulse W corresponding to the drive signal COM. Therefore, strictly speaking, the drive pulse W included in the drive signal COM for ejecting the liquid from the nozzle is input to the drive element (piezo element) corresponding to each nozzle. It is also said that the drive signal COM is input to the drive element.

  When the drive pulses W1 and W2 are applied to the piezo element PZT (i), the piezo element PZT (i) is deformed. Accordingly, the elastic film (side wall) that partitions a part of the pressure chamber filled with ink is deformed, and the ink in the pressure chamber is ejected from the nozzle #i. Therefore, the shapes of the drive pulses W1 and W2 are determined according to the amount of ink ejected from the nozzles. That is, dots having different sizes can be formed due to the difference in the shape of the drive pulse W.

  In the present embodiment, it is assumed that one pixel is represented by four gradations. As shown in FIG. 8, when the switch control signal prt (i) is “11”, a pulse W1 that drives the piezo element PZT (i). And W2 are applied to form a large dot. Similarly, when the switch control signal prt (i) is “10”, the first drive pulse W1 is applied to the piezo element PZT (i), a medium dot is formed, and the switch control signal prt (i) is “01”. In this case, the second drive pulse W2 is applied to the piezo element PZT (i) to form a small dot, and no dot is formed when the switch control signal prt (i) is “00”.

<About Drive Signal Generation Unit 32>
FIG. 9A is a diagram illustrating the drive signal generation unit 32, and FIG. 9B is a diagram for explaining the operation of the waveform generation circuit 70. The drive signal generation unit 32 includes a waveform generation circuit 70 and a current amplification circuit 60.

  The DAC value is sequentially output from the controller 10 to the waveform generation circuit 70 every update period τ. In the example of FIG. 9B, the DAC value corresponding to the voltage V1 is output at the timing t (n) defined by the clock CLK. Thereby, the voltage V1 is output from the waveform generation circuit 70 in the cycle τ (n). Until the update period τ (n + 4), the DAC value corresponding to the voltage V1 is sequentially input from the controller 10 to the waveform generation circuit 70, and the voltage V1 is continuously output. Further, at the timing t (n + 5), the DAC value corresponding to the voltage V <b> 2 is input from the controller 10 to the waveform generation circuit 70. Thereby, the output of the waveform generation circuit 70 drops from the voltage V1 to the voltage V2 in the cycle τ (n + 5). Similarly, at the timing t (n + 6), the DAC value corresponding to the voltage V3 is input from the controller 10 to the waveform generation circuit 70, and the output drops from the voltage V2 to the voltage V3. Similarly, since the DAC value is sequentially input to the waveform generation circuit 70, the output voltage gradually decreases. Then, at the period τ (n + 10), the output of the waveform generation circuit 70 drops to the voltage V4. By such a method, the potential waveform signal COM ′ is output from the waveform generation circuit 70 to the current amplification circuit 60.

  Then, the current amplification circuit 60 amplifies the current of the potential waveform signal COM ′ input from the waveform generation circuit 70 and outputs it as a drive signal COM. The current amplifier circuit 60 amplifies current in order to drive a large number of piezoelectric elements. The output of the current amplification circuit 60 is fed back to the current amplification circuit 60.

  The current amplifier circuit 60 includes a rising transistor Q1 (NPN type transistor) that operates when the potential of the drive signal COM rises, and a lowering transistor Q2 (PNP type transistor) that operates when the potential of the drive signal COM decreases. When the raising transistor Q1 is turned on by the potential waveform signal COM 'from the waveform generation circuit 70, the drive signal COM rises and the piezo element PZT is charged. On the other hand, when the lowering transistor Q2 is turned on by the potential waveform signal COM ', the driving signal COM is lowered and the piezo element PZT is discharged.

<About the adjustment method of the drive signal>
By the way, in the head 31 of this embodiment, since the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group are shifted in the transport direction, it is necessary to adjust the liquid ejection timing from the main nozzle group and the sub nozzle group. . Further, as described above, the liquid is ejected from each nozzle by applying the driving pulses W1 and W2 included in the driving signal COM to the driving elements (piezo elements and heating elements) corresponding to the nozzles. That is, by adjusting the timing at which the driving pulse is applied to the driving element corresponding to each nozzle, the timing at which the liquid is ejected from each nozzle can be adjusted.

  Therefore, in this embodiment, the timing at which the driving pulses W1, W2 are applied to the driving elements of the nozzles belonging to the main nozzle group and the timing at which the driving pulses W1, W2 are applied to the driving elements belonging to the sub nozzle group are shifted. The timing of liquid ejection from the nozzle group and the sub nozzle group is adjusted. Thus, adjustment is made so that the dot rows formed in the main nozzle group and the dot rows formed in the sub-nozzle group are aligned in a straight line in the paper width direction, and image quality deterioration is suppressed.

  As shown in FIG. 8, the drive signal COM generates drive pulses W1 and W2 for each repetition period T. That is, the time period during which the conveyed paper S and one nozzle face each other is the repetition period T. Note that the liquid ejection timing can be adjusted by shifting the timing of applying the drive pulse W to the drive element corresponding to each nozzle in units of the repetition period T. In this case, the drive signal COM input to the drive element of the main nozzle group and the drive signal COM input to the drive element of the sub nozzle group can be made common, and the drive signal generating unit 32 is provided in the main nozzle group and the sub nozzle group. Can be shared. However, if the drive signal COM input to the drive element of the main nozzle group and the drive signal COM input to the drive element of the sub nozzle group are made common, the liquid discharge is performed only at the repetition period T, that is, every other pixel. The timing cannot be adjusted. When the interval D (FIG. 4) in the transport direction between the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group is relatively narrow and shorter than the length of one pixel, or when the liquid is discharged at a timing shorter than the repetition period T When it is desired to adjust the dot position, it becomes impossible to adjust the shift of the dot formation position due to the shift of the nozzle rows of the main nozzle group and the sub nozzle group.

  Therefore, as shown in FIG. 7, each head 31 of the present embodiment has a first input unit 371 to which a drive signal COM1 for driving a drive element corresponding to each nozzle belonging to the main nozzle group is input, A second input unit 372 to which a drive signal COM2 for driving a drive element corresponding to each nozzle belonging to the nozzle group is input. The drive signal COM1 input to the first input unit 371 and the drive signal COM2 input to the second input unit 372 are made different. That is, the drive signal COM1 input to the nozzle drive elements belonging to the main nozzle group (switch SW and the terminal portion of the head controller HC) is different from the drive signal COM2 input to the nozzle drive elements belonging to the sub nozzle group. Make it. Hereinafter, for the sake of explanation, the drive signal input to the drive element of the main nozzle group is referred to as “COM1”, and the drive signal input to the drive element of the sub nozzle group is referred to as “COM2”.

  FIG. 10 is a diagram illustrating a difference between the drive signal COM1 input to the drive element of the main nozzle group and the drive signal COM2 input to the drive element of the sub nozzle group. As shown in the figure, the repetition cycle T of the drive signal COM1 for the main nozzle group starts from time t0, whereas the repetition cycle T of the drive signal COM2 for the sub nozzle group starts from time t1. That is, liquid is discharged from the main nozzle group from time t0 to time t0 + T, and liquid is discharged from the sub nozzle group from time t1 to time t1 + T. The difference between the time t0 and the time t1 is a deviation amount of the liquid ejection timing between the main nozzle group and the sub nozzle group. As described above, the generation timing of the drive pulse W included in the drive signal COM1 input to the first input unit 371 and the generation timing of the drive pulse W included in the drive signal COM2 input to the second input unit 372 are adjusted. To do.

  When the deviation amount of the liquid discharge timing is larger than the repetition period T, the deviation amount larger than the repetition period T among the deviation amounts of the liquid discharge timing is adjusted in units of the repetition period T (see FIG. 7). The switch control signal SW ′ is adjusted), and the remaining shift amount may be adjusted by the difference between the start times of the drive signal COM1 of the main nozzle group and the drive signal COM2 of the sub nozzle group, or the shift of the liquid discharge timing All of the amounts may be adjusted by the amount of deviation of the start of the drive signals COM1 and COM2.

  For example, in the test pattern example shown in FIG. 5, liquid is ejected from the main nozzle group, and after the sheet S is transported a length of “2D / 3” in the transport direction, the liquid is ejected from the sub nozzle group. Thus, the dot row of the main nozzle group and the dot row of the sub nozzle group can be arranged in a straight line in the paper width direction. In such a case, the time during which the sheet S is conveyed by a length of 2D / 3 corresponds to the difference between the time t0 and the time t1.

  In this way, by making the drive signal COM1 input to the drive element of the main nozzle group different from the drive signal COM2 input to the drive element of the sub nozzle group, while the liquid is being discharged from the main nozzle group, the sub signal is output. It is possible to start discharging liquid from the nozzle group. Therefore, even if the adjustment amount of the liquid discharge timing between the main nozzle group and the sub nozzle group is small (one pixel, repetition period T, narrower), the liquid discharge timing of the main nozzle group and the sub nozzle group is adjusted. it can. As a result, the dot rows formed in the main nozzle group and the dot rows formed in the sub nozzle group can be aligned on the straight line in the paper width direction, and image quality deterioration can be suppressed.

  Further, the liquid ejection characteristics of the main nozzle group and the sub nozzle group may be different. Then, even if the same liquid amount is instructed, that is, even if the same drive pulse W is applied to the drive element, different liquid amounts may be ejected. For example, according to the example of the test pattern shown in FIG. 6, it can be seen that the image formed in the sub nozzle group is viewed darker than the image formed in the main nozzle group. This is because the amount of liquid discharged from the sub nozzle group at a time is larger than the amount of liquid discharged from the main nozzle group at a time. In the present embodiment, since the drive signal COM1 input to the drive element of the main nozzle group and the drive signal COM2 input to the drive element of the sub nozzle group are made different, the amount of liquid discharged from the main nozzle group and the sub signal are reduced. The shape of the drive pulse included in each drive signal COM1, COM2 can be adjusted so that the amount of liquid ejected from the nozzle group at the same time is the same.

  For example, the larger the voltage change amount of the driving pulse W, the more the pressure chamber filled with the liquid is deformed, and more liquid is ejected from the nozzle. Therefore, when the amount of liquid ejected from the sub nozzle group is larger than that of the main nozzle group, as shown in FIG. 10, the voltage difference Vh from the intermediate voltage Vc to the maximum voltage of the drive pulse W1 of the main nozzle group is larger. The voltage difference Vh ′ from the intermediate voltage Vc to the maximum voltage of the drive pulse W1 ′ of the sub nozzle group may be reduced. That is, the shape of the drive pulse W included in the drive signal COM1 input to the first input unit 371 and the shape of the drive pulse W included in the drive signal COM2 input to the second input unit 372 are adjusted. By doing so, a larger amount of liquid was discharged from the sub nozzle group than the main nozzle group before adjustment, but the same amount of liquid can be discharged from the main nozzle group and the sub nozzle group. As a result, it is possible to prevent unevenness in the density of the image formed in the main nozzle group and the image formed in the sub nozzle group, and to suppress deterioration in image quality.

  As described above, in order to make the drive signals COM1 and COM2 input to the drive elements of the main nozzle group and the sub nozzle group different from each other, in this embodiment, the drive signal COM1 ( Drive signal input to the first input unit 371), and the other drive signal generation unit 32 generates a drive signal COM2 for the sub nozzle group (drive signal input to the second input unit 372).

  Incidentally, the number of drive elements that can be driven by the drive signal COM generated by one drive signal generation unit 32 is limited due to power problems. Therefore, normally (in a printer different from this embodiment), one drive signal generation unit 32 is provided for one nozzle row of one head. That is, a common drive signal COM is input to the drive elements of the nozzle rows from which the same liquid is ejected from the same head. By doing so, it is possible to generate the drive signal COM in accordance with the difference in properties depending on the variation in the ejection characteristics of each head and the type of liquid to be ejected. However, the heads 31 of this embodiment belong to the same head 31, and even if they are nozzles that discharge the same liquid, the nozzles belonging to the main nozzle group and the nozzles belonging to the sub nozzle group are input to the respective drive elements. The drive signal COM needs to be different.

  Here, for example, one drive signal generation unit 32 is provided for the drive elements of the nozzles belonging to the main nozzle group in a nozzle row of a head 31, and the same nozzle row (the same liquid is ejected from the same head 31). It is assumed that one drive signal generation unit 32 is provided for the drive elements belonging to the sub nozzle group of the nozzles. In this case, a drive signal generation unit of “the number of heads 31 of the printer 1 × the number of nozzle rows × 2” is required. That is, since one drive signal generation unit 32 is provided for at least one nozzle row of one sub nozzle group, such as the sub nozzle group, the printer 1 must include a large number of drive signal generation units. Don't be. Doing so is costly.

  Therefore, in this embodiment, even if the nozzles belong to different heads 31, a common drive signal is input to the drive elements of the nozzles that belong to the sub nozzle group and eject the same liquid. That is, liquid is ejected from nozzles belonging to a plurality of sub nozzle groups by a drive signal generated by one drive signal generation unit. By doing so, the number of drive signal generation units (in this embodiment, compared to the case where one drive signal generation unit 32 is provided for each drive element belonging to the sub nozzle group for each head 31 and each nozzle row ( “The number of heads 31 of the printer 1 × the number of nozzle rows + 4”) is approximately halved, and costs can be reduced.

  Note that in one head 31 having a main nozzle group and a sub nozzle group, nozzles (nozzle rows) that are arranged in the medium transport direction and eject different types of ink are provided by one drive signal generation unit 32 for each nozzle group. It may be driven by the generated drive signal. For example, in one head 31, each YMCK nozzle (nozzle row) of the main nozzle group is driven by the drive signal generated by one drive signal generation unit 32, and each YMCK nozzle (nozzle row) of the sub nozzle group. May be driven by a drive signal generated by one drive signal generator 32. In this case, the YMCK nozzles (nozzle rows) driven by the drive signal generated by one drive signal generation unit 32 can adjust the liquid ejection timing only in units of pixels, that is, in units of the repetition period T. However, there is no problem because the positional deviation between the color dots is not noticeable.

  FIG. 11 is a schematic diagram of a circuit diagram of the drive signal generation unit 32 and the head control unit HC in the printer 1 of the present embodiment. For the sake of simplicity, the relationship between the drive signal generation unit 32 and the head control unit HC for one nozzle row of the four nozzle rows of the head is shown. In the drawing, for the sake of explanation, the symbol of the drive signal generator that generates the drive signal COM1 of the main nozzle group is “32-1”, and the symbol of the drive signal generator that generates the drive signal COM2 of the sub nozzle group is “ 32-2 ". One drive signal generator 32-1 is provided for each color nozzle row of the main nozzle group of each of the heads 31 (1) to 31 (i), and is generated by the drive signal generator 32-1. The drive signal COM1 is input to the first input unit 371 of the head control unit HC corresponding to each head 31. One drive signal generator 32 for the main nozzle group in one nozzle row of one head 31 due to the limitation on the number of drive elements that can be driven by the drive signal COM generated by one drive signal generator 32. Is provided. Therefore, even in the main nozzle groups that discharge the same liquid, the liquid discharge timing and the liquid discharge amount can be adjusted according to the characteristic difference of the head 31, as shown in FIG. As a result, it is possible to suppress image quality deterioration due to variations among heads.

  On the other hand, a common drive signal generation unit 32-2 is provided for a certain color nozzle row of the sub nozzle group of each head 31 (1) to 31 (i), and the drive signal generation unit 32- 2 is input to the second input unit 372 of the head control unit HC of all the heads 31 (1) to 31 (i). Since all the heads 31 (1) to 31 (i) have the same structure, the shift direction of the transport direction of the sub nozzle group with respect to the main nozzle group is the same. Therefore, the shift amount of the liquid discharge timing of the sub nozzle group with respect to the liquid discharge from the main nozzle group is the same in all the heads 31 (1) to 31 (i). In addition, it can be said that the difference in the liquid discharge characteristics (liquid discharge amount) of the sub nozzle group with respect to the liquid discharge characteristics (liquid discharge amount) of the main nozzle group is common to all the heads 31 (1) to 31 (i). Therefore, even if the nozzles belong to different heads 31, as long as the nozzles belong to the sub nozzle group that discharges the same liquid, there is no problem even if the drive signal COM <b> 2 input to the drive elements of these nozzles is shared.

  Further, since the number of nozzles of the sub nozzle group is smaller than the number of nozzles of the main nozzle group, each sub nozzle group of the plurality of heads 31 is driven by the drive signal generated by one drive signal generation unit 32. Can do.

Next, a method for adjusting the liquid discharge timing and the method for adjusting the liquid discharge amount of the main nozzle group and the sub nozzle group will be specifically described based on the above test pattern results.
12 to 14 are diagrams showing examples of test patterns for adjusting the amount of deviation of the dot formation position of the sub nozzle group with respect to the main nozzle group. For simplicity of explanation, test pattern results formed by four heads 31 (1) to 31 (4) are shown. In the test pattern example shown in FIG. 5 described above, among the dot rows formed by changing a plurality of liquid discharge timings of the main nozzle group and the sub nozzle group, the dot row described under “D / 3” The dot rows of the nozzle group and the dot rows of the sub nozzle group are aligned on the paper width direction. However, in an actual test pattern, when the dot rows of the main nozzle group of each head 31 and the dot rows of the sub-nozzle group of each head 31 are all aligned on the straight line in the paper width direction due to the influence of the characteristic difference of each head 31 and the like. Is not limited. Therefore, a dot row having the smallest deviation amount in the transport direction between the dot row of the main nozzle group and the dot row of the sub nozzle group is selected from a plurality of dot rows formed as test patterns, and the main nozzle group and the sub nozzle group are selected accordingly. The liquid ejection timing of the nozzle group may be adjusted. The dot rows shown in FIGS. 12 to 14 are dot rows in which the shift amount in the transport direction of the dot row of the main nozzle group and the dot row of the sub nozzle group among the dot rows formed as a plurality of test patterns is the smallest.

  In the test pattern result example of FIG. 12, the dot rows formed in the sub nozzle groups of the four heads 31 (1) to 31 (4) are formed substantially in a straight line in the paper width direction. The dot rows formed in the main nozzle groups 31 (1) to 31 (4) are slightly shifted in the transport direction. As shown in FIG. 11 described above, in this embodiment, one common drive signal generation unit 32-2 is provided for the sub nozzle groups of all the heads 31. On the other hand, for the drive elements of the main nozzle group, one drive signal generation unit 32-1 is provided for each main nozzle group of each head 31. Therefore, the drive signal COM1 input to the drive element of the main nozzle group can adjust the liquid ejection timing for each head 31. However, since the drive signal COM2 input to the drive element of the sub nozzle group is a drive signal common to the sub nozzle groups of all the heads 31, the liquid discharge timing cannot be adjusted for each head 31. In order to use the common drive signal COM2 for the sub nozzle group of each head 31, the drive pulse W generated at each repetition period T is input to the drive element of the sub nozzle group by the switch control signal prt (FIG. 7). It is only possible to adjust the liquid ejection timing for each nozzle belonging to the sub nozzle group only depending on whether or not. That is, it is possible to adjust the timing for ejecting the liquid only every other pixel (every repetition period T).

  Therefore, as shown in the result of the test pattern in FIG. 12, the dot rows formed in the sub nozzle group are formed substantially in a straight line in the paper width direction, but the dot rows formed in the main nozzle group are shifted in the transport direction. In this case, adjustment is made so that the dot row of the main nozzle group is formed at the position in the transport direction where the dot row of the sub nozzle group is formed. In other words, the dot formation position of the main nozzle group that can finely adjust the timing of ejecting the liquid from the nozzle (adjustable at intervals smaller than one pixel) is matched with the dot formation position of the sub nozzle group. That is, in the test pattern result, each of the liquids ejected from the main nozzle group of each head 31 is based on the position in the transport direction (direction intersecting the predetermined direction) of the dot row ejected from the sub nozzle group. Adjust the position of the dot row in the transport direction. For this purpose, the drive signal COM1 input to the drive element of the main nozzle group for each head 31 may be adjusted to adjust the timing for discharging the liquid from the main nozzle group.

  For example, since the dot row formed in the main nozzle group of the head 31 (1) is formed on the upstream side in the transport direction with respect to the dot row of the sub nozzle group, liquid is supplied from the main nozzle group of the head 31 (1). The drive signal COM1 may be adjusted so that the discharge timing is advanced. On the contrary, since the dot row formed in the main nozzle group of the head 31 (3) is formed on the downstream side in the transport direction with respect to the dot row of the sub nozzle group, the dot row from the main nozzle group of the head 31 (3) The drive signal COM1 may be adjusted so that the timing of ejecting the liquid is delayed. By doing so, as many dot rows as possible can be arranged in a straight line in the paper width direction, and image quality deterioration can be further suppressed.

  In the test pattern result example of FIG. 13, the dot rows formed in the main nozzle groups of the heads 31 (1) to 31 (4) and the dot rows formed in the sub nozzle groups are shifted in the transport direction. As described above, since the main nozzle group can adjust the liquid discharge timing more finely than the sub nozzle group, the direction of transport of the dot row formed in the main nozzle group with respect to the dot row formed in the sub nozzle group Adjust the position. However, in the test pattern result of FIG. 13, the dot rows formed in the sub nozzle groups of the heads 31 (1) to 31 (4) are shifted in the transport direction. In such a case, the dot formation position by the main nozzle group is adjusted based on the average position of the dot row formed in the sub nozzle group adjacent to the main nozzle group of the head 31 in the paper width direction. Good.

  For example, the main nozzle group of the head 31 (1) is adjacent to the sub nozzle group of the same head 31 (1) and the sub nozzle group of the head 31 (2) adjacent in the paper width direction. Here, the difference in the transport direction between the dot rows formed in the sub nozzle group of the head 31 (1) and the dot rows formed in the sub nozzle group of the head 31 (2) is defined as “X”. In this case, it is conveyed from the position of the dot row of the sub nozzle group of the head 31 (1) by “X / 2” downstream in the carrying direction, that is, from the position of the dot row of the sub nozzle group of the head 31 (2). Adjustment is made so that the dot row of the main nozzle group of the head 31 (1) is formed at a position upstream by "X / 2" in the direction. By doing so, the amount of deviation in the conveyance direction of the dot rows of the main nozzle group of the head 31 (1) with the dot rows of two sub nozzle groups adjacent in the paper width direction can be made as small as possible. As a result, the boundary portion between the image formed by the main nozzle group and the image formed by the sub nozzle group becomes inconspicuous and image quality deterioration can be further suppressed.

Further, not limited to this, when the dot rows formed in the sub nozzle groups of the heads 31 (1) to 31 (4) are shifted in the transport direction, as shown in FIG. (1)
Even if the dot formation positions by the main nozzle groups of all the heads 31 (1) to 31 (4) are adjusted based on the average position in the transport direction of the dot rows formed in the sub nozzle groups of No. 31 to (4). Good. By doing so, it is possible to reduce the shift amount in the transport direction between the dot rows formed in the main nozzle group of each head and the dot rows formed in the sub nozzle group of each head, and it is possible to suppress image quality deterioration.

  Similarly, in the test pattern result of FIG. 6, there is a density difference in each image formed in the main nozzle group of each head 31, or there is a density difference in each image formed in the sub nozzle group of each head 31. Even in this case, the image density (liquid ejection amount) of the main nozzle group that can adjust the drive signal COM for each head 31 may be adjusted based on the image density (liquid ejection amount) formed in the sub nozzle group. For this purpose, the voltage displacement of the drive pulse W included in the drive signal COM1 input to the drive element of the main nozzle group for each head 31 may be adjusted. By doing so, the density difference between the image of the main nozzle group and the image of the sub nozzle group can be reduced more accurately.

=== Variation of Adjustment Method of Driving Signal ===
FIG. 15 is a diagram illustrating a test pattern in the modification. In the above-described embodiment (the test pattern of FIG. 5), the deviation amount D in the conveyance direction between the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group in the design and the deviation amount due to the conveyance error are adjusted together. ing. Thereafter, the dot row with the smallest positional deviation in the transport direction of each dot row of the main nozzle group and the sub nozzle group is selected from the test pattern result (FIG. 5), and the liquid discharge timing deviation between the main nozzle group and the sub nozzle group is selected. The amount is calculated, and the drive signal COM2 common to all the sub nozzle groups is determined. Then, the shift amount in the transport direction of the main nozzle group and the sub nozzle group for each head is corrected by adjusting the drive signal COM1 for the main nozzle group of each head 31, as shown in FIGS.

  However, the present invention is not limited to this, and when the test pattern is formed, a shift in the transport direction interval between the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group in design may be eliminated. According to such a test pattern, it is possible to determine how much the conveyance error amount and the deviation amount for each head 31 are. For example, in the test pattern of FIG. 15, in the dot row described under “± 0”, liquid is ejected from the main nozzle group, and the sheet is conveyed by the interval D in the conveyance direction between the main nozzle group and the sub nozzle group. And a dot row formed by discharging liquid from the sub nozzle group. Therefore, when there is no deviation between the dot row of the sub nozzle group described below “± 0” and the dot row of the main nozzle group, it can be determined that no transport error or the like occurs. On the other hand, the dot row described under “+ y” is a dot row formed so that the dot row of the sub nozzle group is shifted by “y” to the downstream side in the transport direction from the dot row of the main nozzle group. . That is, in the dot row described under “+ y”, the liquid is ejected from the main nozzle group, and the liquid is ejected from the sub nozzle group after the sheet is transported by “design deviation amount D−y” in the transport direction. It is a dot row formed by being ejected. On the other hand, in the dot row described under “−y”, the liquid is ejected from the main nozzle group, and the liquid is ejected from the sub nozzle group after the sheet S is transported by the “design deviation amount D + y” in the transport direction. Is a dot row formed by ejecting.

  In the test pattern example of FIG. 15, it is assumed that there is no displacement of the head 31 in the dot row of the sub nozzle group for the sake of simplicity. On the other hand, it is assumed that each dot row formed in the main nozzle group is shifted in the transport direction due to the characteristics of each head 31. In the present embodiment, the drive signal generation unit 32 that generates a drive signal to be input to the drive element of the sub nozzle group is common to all the sub nozzle groups, but the drive signal to be input to the drive element of the main nozzle group. Is different for each head 31 (for each main nozzle group). Therefore, the shift amount of the dot row for each head 31 (for each main nozzle group) in the transport direction may be adjusted by adjusting the drive signal input to the drive element for the main nozzle group based on the dot row for the sub nozzle group.

  For example, the dot row formed in the main nozzle group of the head 31 (1) is a dot row of “± 0”, and the deviation amount in the transport direction from the dot row of the sub nozzle group is “zero (or minimum)”. Become. Therefore, it is preferable to input a drive signal in which only the design shift amount D of the main nozzle group and the sub nozzle group is adjusted to the drive element of the main nozzle group of the head 31 (1). On the other hand, the dot row of the main nozzle group of the head 31 (2) is a dot row of “+ y”, and the amount of deviation in the transport direction from the dot row of the sub nozzle group is “zero”. For this reason, the main nozzle group discharges the liquid faster than the drive signal in which only the design shift amount D of the main nozzle group and the sub nozzle group is adjusted so that the paper advances the distance of “+ y”. The drive signal of the nozzle group may be adjusted.

=== Variation of Driving Circuit of Head 31 ===
FIG. 16 is a diagram illustrating a modification of the drive circuit of the head 31 (corresponding relationship between the head 31, the drive signal generation unit 32, and the head control unit HC). For simplicity of illustration, the number of heads 31 is reduced, and only the drive signal generation unit 32 corresponding to one nozzle row is drawn. Up to this point, in order to reduce the number of drive signal generation units 32 and reduce the cost, the second input units 372 (each drive element of the sub nozzle group) of all the heads 31 as shown in FIG. The common drive signal COM2 is input. That is, one drive signal generation unit 32-1 is provided for the sub nozzle group of all the heads 31. However, it is not limited to this.

  For example, as shown in FIG. 16, a common drive signal generation unit 32 may be provided for the main nozzle group and the sub nozzle group belonging to one head 31. In this case, the shift amount of the dot formation position due to the shift in the transport direction of the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group is adjusted by the delay circuit when the drive signal COM is input to the drive element of the sub nozzle group. It is good to adjust.

  In the head 31 of this embodiment, the nozzle row of the sub nozzle group is located on the downstream side in the transport direction with respect to the nozzle row of the main nozzle group. Therefore, the drive signal COM1 generated by the drive signal generation unit 32 (corresponding to one drive signal generation unit) is input to the first input unit 371 as it is for the drive elements of the main nozzle group, and is input to the main nozzle group. The drive element corresponding to the nozzle to which it belongs is driven by the drive signal COM1. On the other hand, the drive signal COM1 generated by the drive signal generation unit 32 (corresponding to one drive signal generation unit) is input to the delay circuit, and the delay circuit generates a drive whose generation timing of the drive pulse W is delayed from the drive signal COM1. The signal COM2 is input to the second input unit 372, and the drive elements corresponding to the nozzles belonging to the sub nozzle group are driven by the drive signal COM2. By doing so, the liquid discharge timing from the nozzles of the sub nozzle group can be delayed from the liquid discharge timing from the nozzles of the main nozzle group, and the nozzle row of the sub nozzle group is transported in the transport direction more than the nozzle row of the main nozzle group Even if it is located on the downstream side, the dot rows formed in the main nozzle group and the dot rows formed in the sub nozzle group can be aligned on the straight line in the transport direction. In this case, a delay circuit is required, but the number of drive signal generation units 32 can be halved compared to the case where one drive signal generation unit 32 is provided for the sub nozzle group of each head 31. Note that the timing of the drive signal COM input to the drive elements of the main nozzle group may be adjusted.

  In FIG. 16, one drive signal generation unit 32 corresponding to one nozzle row (the nozzle row of the main nozzle group and the nozzle row of the sub nozzle group that discharges the same liquid) is depicted. Since there are four nozzle rows, four drive signal generators 32 are provided for each head 31 and four delay circuits are provided, but this is not restrictive. The four nozzle rows of the main nozzle group and the four nozzle rows of the sub nozzle group are shifted in the transport direction at the same interval. For example, since the interval between the black nozzle row of the main nozzle group and the black nozzle row of the sub nozzle group is equal to the interval between the cyan nozzle row of the main nozzle group and the cyan nozzle row of the sub nozzle group, the main nozzle group and the sub nozzle group A delay circuit for adjusting the liquid ejection timing may be shared, and one delay circuit may be provided for one head 31.

  As described above, when the liquid discharge timing of the main nozzle group and the sub nozzle group is adjusted by the delay circuit, it is generated by the common drive signal generation unit for the drive elements of the main nozzle group and the sub nozzle group. The timing at which the drive pulse W having the same shape included in the drive signal COM is input to the drive element of the main nozzle group and the timing of input to the drive element of the sub nozzle group are adjusted. By doing so, the dot formation position of the main nozzle group and the dot formation position of the sub nozzle group are adjusted. Therefore, the density difference of the image due to the difference in the liquid ejection characteristics between the main nozzle group and the sub nozzle group is adjusted by adjusting the amount of liquid ejected from each nozzle at one time (that is, the voltage change amount of the drive pulse W is adjusted). It cannot be resolved). Therefore, the density (command gradation value) indicated by the print data assigned to the main nozzle group and the density (command gradation value) indicated by the print data assigned to the sub nozzle group are adjusted to form the main nozzle group. The image density and the image density formed in the sub nozzle group can be adjusted to be equal. As a result, image quality deterioration can be suppressed.

=== Other Embodiments ===
The above-described embodiment is mainly described for a printer. Among them, a printing apparatus, a recording apparatus, a liquid ejection apparatus, a printing method, a recording method, a liquid ejection method, a printing system, a recording system, and a computer system are included. Needless to say, the disclosure includes a program, a storage medium storing the program, a method for producing a printed material, and the like.

  Moreover, although the printer etc. as one embodiment were demonstrated, said embodiment is for making an understanding of this invention easy, and is not for limiting and interpreting this 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 liquid ejection device>
In the above-described embodiment, the ink jet printer is exemplified as the liquid ejecting apparatus (part) for performing the liquid ejecting method, but is not limited thereto. If it is a liquid ejection device, it can be applied to various industrial devices, not a printer (printing device). For example, a textile printing device for patterning a fabric, a display manufacturing device such as a color filter manufacturing device or an organic EL display, a DNA chip manufacturing device for manufacturing a DNA chip by applying a solution in which DNA is dissolved in a chip, a circuit board manufacturing The present invention can be applied even to an apparatus or the like.
The liquid discharge method may be a piezo method that discharges liquid by applying voltage to the drive element (piezo element) to expand and contract the ink chamber, or generates bubbles in the nozzle using a heating element. It is also possible to use a thermal method in which liquid is discharged by the bubbles.

  In the above-described embodiment, the line head printer that conveys the medium under the nozzles arranged in the paper width direction is described as an example, but the present invention is not limited to this. For example, a printing apparatus that forms an image while moving a plurality of heads arranged in the nozzle row direction in a direction intersecting the nozzle row direction with respect to the medium, or a plurality of heads arranged in the nozzle row direction intersecting the nozzle row direction The printing apparatus may alternately repeat an operation of forming an image while moving the head and the medium in a moving direction and a transporting operation of moving the head and the medium relatively in the nozzle row direction.

<About Drive Signal Generation Unit 32>
In the above-described embodiment, one drive signal generation unit 32 is provided for the sub-nozzle group of all the heads 31 in order to reduce the cost, but this is not restrictive. For example, one drive signal generation unit 32 may be provided for the sub nozzle group of each head. By doing so, although it costs, the drive signal COM matched with the sub nozzle group of each head 31 can be produced | generated like the main nozzle group, and the dispersion | variation by the characteristic difference for every head 31 can be correct | amended. As a result, image quality deterioration can be further suppressed. In addition, since there is a limit to the number of drive elements that can be driven by the drive signal COM generated by one drive signal generation unit, a plurality of sub-nozzle groups are provided for all sub-nozzle groups according to the number of sub-nozzle groups. A drive signal generation unit may be provided.

  Further, the drive signal generation unit 32 of the above-described embodiment inputs the DAC value to the waveform generation circuit 70 (D / A converter), and the waveform generation circuit 70 outputs the DAC value to the potential waveform signal COM ′ that is analog data. Although the current of the potential waveform signal COM ′ is amplified by the current amplification circuit 60 including the transistors Q1 and Q2 and is input to the drive element, this is not restrictive. For example, a potential waveform signal obtained by converting a DAC value (digital signal) into an analog signal by a D / A converter is pulse-modulated, the pulse-modulated modulation signal is power-amplified by a digital amplifier, and the power-amplified signal is smoothed. It may be smoothed by a filter and input to the drive element.

1 is a block diagram of an overall configuration of a printer. FIG. 2A is a cross-sectional view of the printer, and FIG. 2B is a diagram illustrating how a sheet is conveyed. FIG. 3A shows the arrangement of the heads, and FIG. 3B is a diagram showing the nozzle arrangement at the joint portion of the heads. FIG. 4 is a diagram illustrating how dots are formed when the drive signal for ejecting liquid from the main nozzle group and the sub nozzle group is not adjusted. It is a figure which shows the test pattern for adjusting the position shift of a dot. It is a figure which shows the test pattern for adjusting the density difference of an image. It is an electronic circuit diagram which shows that a drive element operate | moves. It is a timing chart of each signal. FIG. 9A is a diagram illustrating a drive signal generation unit, and FIG. 9B is a diagram illustrating a waveform generation circuit. It is a figure which shows the difference in a drive signal. It is the schematic of the circuit diagram of a drive signal production | generation part and a head control part. It is a figure which shows the example of the test pattern for adjusting the deviation | shift amount of a dot formation position. It is a figure which shows the example of the test pattern for adjusting the deviation | shift amount of a dot formation position. It is a figure which shows the example of the test pattern for adjusting the deviation | shift amount of a dot formation position. It is a figure which shows the test pattern in a modification. It is a figure which shows the modification of the drive circuit of a head.

Explanation of symbols

1 printer, 10 controller, 11 interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 21A-21B transport roller, 22 transport belt,
23 paper feed roller, 30 head unit, 31 head, 32 drive signal generator,
33 first shift register, 34 second shift register, 35 latch circuit group,
36 data selector, 371 first input section, 372 second input section,
40 detector groups, 50 computers, 60 current amplification circuits, 70 waveform generation circuits,
HC head controller

Claims (7)

A main nozzle group in which nozzles are arranged at predetermined intervals in a predetermined direction, a sub nozzle group in which a smaller number of nozzles than the number of nozzles of the main nozzle group are arranged in the predetermined direction at the predetermined intervals; A plurality of heads arranged corresponding to the nozzles, each having a drive element that discharges liquid from the corresponding nozzle when a drive signal is input;
Each of the heads includes a first input unit to which the driving signal for driving the driving element corresponding to the nozzle belonging to the main nozzle group is input, and the driving corresponding to the nozzle belonging to the sub nozzle group. A second input unit to which the drive signal for driving the element is input,
A liquid discharge apparatus characterized by the above. The liquid ejection device according to claim 1,
A liquid ejection apparatus that generates the drive signal input to the first input unit by one drive signal generation unit and generates the drive signal input to the second input unit by another drive signal generation unit. The liquid ejection device according to claim 2,
The liquid ejection apparatus, wherein the drive signal generated by the other drive signal generation unit is input to the second input units of the plurality of heads. The liquid ejection device according to claim 2 or 3, wherein
A liquid ejection apparatus that adjusts a generation timing of a drive pulse included in the drive signal input to the first input unit and a generation timing of a drive pulse included in the drive signal input to the second input unit. The liquid ejection apparatus according to any one of claims 2 to 4, wherein
A liquid ejection apparatus that adjusts a shape of a drive pulse included in the drive signal input to the first input unit and a shape of a drive pulse included in the drive signal input to the second input unit. The liquid ejection device according to claim 1,
The drive signal generated by one drive signal generation unit is input to the first input unit, and the drive signal generated by the one drive signal generation unit is input to a delay circuit and output from the delay circuit. The liquid ejection device, wherein the drive signal is input to the second input unit. A main nozzle group in which nozzles are arranged at predetermined intervals in a predetermined direction, a sub nozzle group in which a smaller number of nozzles than the number of nozzles of the main nozzle group are arranged in the predetermined direction at the predetermined intervals; A plurality of heads arranged corresponding to the nozzles, each having a drive element that discharges liquid from the corresponding nozzle when a drive signal is input;
Differentiating the drive signal input to the drive element corresponding to the nozzle belonging to the main nozzle group and the drive signal input to the drive element corresponding to the nozzle belonging to the sub-nozzle group;
A liquid discharge apparatus characterized by the above.