JP6171916B2 - Printing method and printing apparatus - Google Patents

Description

  The present invention relates to a printing method and a printing apparatus that perform printing by ejecting ink droplets from ink nozzles.

  In a printing apparatus that performs printing by ejecting ink from an ink nozzle, an ink nozzle that does not eject ink for a certain period of time becomes clogged due to evaporation of moisture from the nozzle tip, increasing the viscosity of the ink. For this reason, ink cannot be normally ejected from ink nozzles with low ejection frequency, and print quality may be deteriorated. Therefore, a maintenance unit is provided in the printing apparatus, and flushing is performed to discharge ink toward the maintenance unit, thereby preventing or eliminating clogging of the ink nozzles. Patent Document 1 discloses this type of printing apparatus (inkjet recording apparatus).

  In Patent Document 1, in order to suppress an increase in ink consumption and a decrease in throughput during printing due to performing flushing at regular intervals, control is performed so as not to perform flushing according to the contents of printing. For example, the time when printing is not performed for each nozzle is measured, and only the nozzles for which the time equal to or greater than the reference value has passed is flushed. However, even if such control is performed, although the frequency of flushing is reduced, the reduction in throughput due to flushing cannot be completely eliminated. Therefore, flushing that discharges ink onto a recording medium (so-called flushing on paper) is performed without using a maintenance unit to prevent or eliminate clogging of the ink nozzles. Patent Document 2 discloses this type of printing apparatus (droplet discharge apparatus).

  In Patent Document 2, a pattern in which dots are irregularly arranged (dummy jet discharge data) is stored in a memory in advance, or such a pattern is generated each time, and this pattern is combined with image data to be printed. By combining and printing, flushing is performed on the recording medium. In this way, it is not necessary to interrupt printing when performing flushing. Therefore, it is possible to prevent a decrease in print quality due to clogging of the ink nozzles without reducing the throughput.

JP 11-192729 A JP 2007-136722 A

  In Patent Document 2, in order to perform flushing on paper for ejecting ink onto a recording medium, a pattern in which dots are irregularly arranged (that is, a flushing pattern) is stored in advance, or based on a random number. Each time a flushing pattern is generated. However, if the flushing pattern is stored in advance, it is necessary to store the flushing pattern corresponding to the maximum print size in the memory, which increases the necessary storage capacity. Further, when generating a pattern each time based on a random number, it is necessary to store such a processing program.

  SUMMARY OF THE INVENTION In view of such problems, it is an object of the present invention to reduce the storage capacity of data necessary for performing flushing in a printing method and printing apparatus that perform flushing by ejecting ink toward a recording medium.

In order to solve the above-described problem, the printing method of the present invention intersects the reference flushing pattern of n columns × m rows (n and m are integers of 2 or more) including flushing dots with the conveyance direction of the recording medium. A first printing dot pattern generated based on first printing data and a first printing dot pattern synthesized based on the first printing data are arranged in a column direction and a row direction that is the transport direction, and are determined. and of generating a composite dot pattern, ejection and ink from the print head based on the first synthesized dot pattern, it performs the conveyance of the recording medium, the second print data following the first print data When printing, the last line of the print flushing pattern synthesized with the first print dot pattern is k lines (k <m) of the flushing pattern. ), The first line of the print flushing pattern to be combined with the second print dot pattern generated based on the second print data is set to the k + 1 line of the flushing pattern, and the second combined dot pattern is generated, the ejection of ink from the print head based on the second synthesized dot pattern, and performs the conveyance of the recording medium.

  The printing apparatus of the present invention includes a reference head flushing of a print head having ink nozzles, a transport mechanism for transporting a recording medium, and n columns × m rows (n and m are integers of 2 or more) including flushing dots. A storage unit that stores a pattern; a flushing pattern determination unit that generates a print flushing pattern by arranging the reference flushing pattern in a column direction intersecting a conveyance direction of the recording medium and a row direction that is the conveyance direction; A print dot pattern generation unit that generates a first print dot pattern based on the print data and a second print dot pattern based on the second print data; When the print data of 2 is printed, the first print dot pattern and the last row are k rows (k <m A first composite dot pattern is generated by combining the print flushing pattern that is an integer), and the second print dot pattern is combined with the print flushing pattern in which the first line is k + 1 lines of the flushing pattern. A flushing pattern synthesis unit that generates a second synthesized dot pattern; and a print control unit that ejects ink from the ink nozzles based on the first synthesized dot pattern and the second synthesized dot pattern. It is characterized by that.

  As described above, the printing apparatus and the printing method of the present invention can repeatedly form the reference flushing pattern to form a print flushing pattern having the same size as the print data. Therefore, the size of the reference flushing pattern can be reduced, and there is no need to prepare a different reference flushing pattern for each print data. Accordingly, it is possible to reduce the storage capacity of data necessary for the on-paper flushing. Further, when printing a plurality of print data, the last line of the print flushing pattern when combining with the first print data and the first line of the print flushing pattern when combining with the second print data are the reference flushing pattern. The print flushing pattern is determined so as to be a continuous line in the. As a result, when a plurality of print data are continuously printed, the occurrence frequency of the flushing dots can be maintained at the occurrence frequency determined by the reference flushing pattern. Therefore, even when printing on a plurality of print areas, flushing on paper can be performed with a certain frequency. Therefore, clogging of the ink nozzles can be prevented or eliminated with a small storage capacity and without reducing the throughput during printing.

  In the present invention, when the printer has a maintenance unit that receives ink discharged from the ink nozzles of the print head, the print head is opposed to the maintenance unit, and ink is discharged to the maintenance unit at a preset timing. It is desirable to perform flushing. In this way, even when printing is performed without using ink nozzles outside the print area, such as when printing in a print area narrower than the maximum print width with a line-type print head, periodic flushing is performed. Ink nozzle clogging can be prevented or eliminated.

  In the present invention, it is preferable that the reference flushing pattern includes one flushing dot in one row. As described above, the size of the reference flushing pattern can be minimized by setting the size of the reference flushing pattern in the column direction to the print size of one flushing cycle. Therefore, the necessary storage capacity can be reduced.

FIG. 2 is a schematic block diagram illustrating a control system of a printer to which the present invention is applied. FIG. 2 is an explanatory diagram schematically illustrating a print head, a maintenance unit, and a print sheet of the printer of FIG. 1. It is explanatory drawing which shows the conversion process from input data to head drive data. It is explanatory drawing of a reference | standard flushing pattern. It is explanatory drawing of a printing flushing pattern. It is explanatory drawing which shows the condition where the printing flushing pattern and the printing dot pattern were offset for each ink color and superimposed. It is explanatory drawing of an offset position information table. It is explanatory drawing of the synthetic | combination method of a printing flushing pattern and a printing dot pattern. It is explanatory drawing of the flushing dot composition table.

  Hereinafter, embodiments of a printing apparatus and a printing method to which the present invention is applied will be described with reference to the drawings. In the following embodiments, the present invention is applied to an ink jet printer. However, the present invention is also applicable to a printing apparatus having functions such as a scanner and a facsimile. In addition, although the following embodiment includes a line head type print head, the present invention is also applicable to a printing apparatus including a serial head type print head.

(printer)
FIG. 1 is a schematic block diagram showing a control system of a printer to which the present invention is applied, and FIG. 2 is an explanatory diagram schematically showing a print head, a maintenance unit, and printing paper of the printer of FIG. As shown in FIGS. 1 and 2, the printer 1 includes a print head 2 that ejects ink droplets of four colors of cyan ink C, magenta ink M, yellow ink Y, and black ink Bk, and printing by the print head 2. A transport mechanism 3 that transports the printing paper P (recording medium) along a transport path that passes through the position, a maintenance unit 4, a control unit 5 that controls the print head 2, the transport mechanism 3, the maintenance unit 4, and the like, and printing. A communication unit 6 that receives target input data (image data, document data, etc.) is provided. In this embodiment, as the printing paper P, a label paper on which a label is attached to a long mount at a predetermined interval is used. In the case of label paper, the entire area of the label or a predetermined area on the label is the print area P1. Note that as the printing paper P, a continuous paper or a cut sheet without a label may be used.

  The print head 2 is a line-type inkjet head, and includes four sets of inkjet heads 2C, 2M, 2Y, and 2Bk arranged at a predetermined interval along the conveyance direction A of the printing paper P as shown in FIG. . Inkjet heads 2C, 2M, 2Y, and 2Bk all have a length in the paper width direction B that intersects the transport direction A longer than the maximum width of the printing paper P, and print by ejecting ink onto the printing paper P. Do. The inkjet head 2Bk arranged at the uppermost stream in the transport direction A of the printing paper P ejects black ink Bk, and the downstream inkjet head 2C ejects cyan ink C. The inkjet head 2M disposed on the downstream side of the inkjet head 2C ejects magenta ink M, and the downstream inkjet head 2Y ejects yellow ink Y.

  The ink jet heads 2C, 2M, 2Y, and 2Bk include four head units 21 to 24 that are arranged in the paper width direction B that intersects the transport direction A. The four head units 21 to 24 are arranged so that adjacent head units move back and forth in the transport direction A. The four head units 21 to 24 include two ink nozzle rows in which a plurality of ink nozzles 25 are arranged at a predetermined nozzle pitch in the paper width direction B. The nozzle pitch is set to 300 dpi, for example. The two ink nozzle rows are arranged by shifting the position in the paper width direction B by a dimension that is ½ of the distance between the adjacent nozzles (nozzle pitch). Further, the head units 21 and 22 adjacent in the paper width direction B are arranged so that the ink nozzles 25 at the end portions overlap when viewed in the transport direction A. Similarly, the head units 22 and 23 and the head units 23 and 24 adjacent in the paper width direction B are also arranged so that the ink nozzles 25 at the end portions overlap when viewed in the transport direction A.

  The maintenance unit 4 is disposed at a standby position of the print head 2, for example, outside in the width direction of the transport path. The print head 2 is moved to a position facing the printing paper P on the transport path and a position facing the maintenance unit 4 by a head moving mechanism (not shown). In the standby state in which printing is not performed, the nozzle surface of the print head 2 is capped by the maintenance unit 4. In addition, periodic flushing is performed in which the print head 2 is moved to a position facing the maintenance unit 4 at a predetermined timing such as when printing is started or during printing standby, and ink is ejected from the ink nozzles 25 toward the maintenance unit 4. To be implemented. In this embodiment, as will be described later, flushing (so-called flushing on paper) is performed during printing, in which ink droplets are periodically ejected from the ink nozzles 25 located at a position facing the printing region P1 in parallel with the printing operation. To do. In the regular flushing, flushing is performed on all ink nozzles 25 including the ink nozzles 25 that are not used at the time of printing, for example, the ink nozzles 25 located outside the print region P1 in the paper width direction B. Therefore, flushing can be performed also on the ink nozzles 25 located outside the printing region P1, and the clogging can be prevented or eliminated.

(Control system)
As shown in FIG. 1, the control system of the printer 1 is configured around a control unit 5 including a CPU and the like. A communication unit 6 is connected to the input side of the control unit 5. Input data (image data, document data, etc.) to be printed is supplied to the control unit 5 from an external device such as a computer via the communication unit 6. On the other hand, to the output side of the control unit 5, a print head 2, a transport mechanism 3, a maintenance unit 4 and the like are connected. The transport mechanism 3 is a known mechanism such as a paper feed roller pair that transports the printing paper P, a transport motor that is rotated by a control signal from the control unit 5, and a driving force transmission mechanism that transmits the rotation of the transport motor to the paper feed roller pair. It has.

  The control unit 5 includes a storage unit 51, a rendering unit 52, a color conversion processing unit 53, a binarization processing unit 54, a flushing pattern determination unit 55, a flushing pattern synthesis unit 56, a print control unit 57, and the like. In addition, the control unit 5 controls the transport mechanism 3 to transport the printing paper P at a specified speed (not shown), and to periodically eject ink from the ink nozzles 25 toward the maintenance unit 4. A flushing execution unit (not shown) for controlling the execution of flushing is provided.

  The storage unit 51 stores a color conversion lookup table 61, an SML table 62, a reference flushing pattern 63, an offset position information table 64, a flushing dot composition table 65, and the like.

(Conversion process from input data to head drive data)
FIG. 3 is an explanatory diagram showing a conversion process from input data to head drive data. The rendering unit 52 performs rendering processing for converting the input data 10 (print data) to be printed into image data 11 having the number of pixels corresponding to the designated print size and resolution. Specifically, the input data 10 is enlarged or reduced to a designated print size, and decomposed into pixels so as to have a designated resolution. The pixels of the image data 11 after the rendering processing are RGB color system color data (RGB multivalued data).

  The color conversion processing unit 53 (a part of the print dot pattern generation unit) refers to the pixel (RGB multi-valued data) of the image data 11 after the rendering process with reference to the color conversion lookup table 61, C, Y, M , Bk, the color conversion process for separating the ink amount data 12 (12Bk, 12C, 12M, 12Y) of the four colors. In the color conversion lookup table 61, ink amount data of four colors C, Y, M, and Bk is stored with respect to RGB multi-value data (a combination of R, G, and B) that is RGB color system color data. It is associated. The ink amount data of C, Y, M, and Bk is represented by, for example, an 8-bit gradation value (256 gradations).

  The binarization processing unit 54 (a part of the print dot pattern generation unit) forms pixel ink amount data with the ink nozzles 25 for the ink amount data 12 (12Bk, 12C, 12M, 12Y) after the color conversion processing. A process of converting into dot data of possible four gradations is performed. In the SML table 62, gradation values of C, M, Y, and Bk ink amount data are associated with the occurrence rates of four types of dots including blank dots. The four types of dots are Null (blank dots), S (small dots), M (medium dots), and L (large dots). First, the binarization processing unit 54 refers to the SML table 62 and performs a dot ratio determination process for converting the ink amount data of the pixel into the incidence data of the four types of dots. Halftone processing is performed to determine the presence or absence for each dot size. As a result, a print dot pattern 13 (13Bk, 13C, 13M, 13Y) in which any one of four types of print dots including a blank dot is designated with respect to the pixel position for each ink color is generated.

  The flushing pattern determination unit 55 performs a flushing pattern determination process for determining the print flushing pattern 66 based on the reference flushing pattern 63 and the print size of the input data 10. The print flushing pattern 66 is a pattern for designating the ink nozzles 25 for ejecting ink droplets and the timing thereof when performing on-paper flushing for ejecting ink droplets onto the print region P1 in parallel with the printing of the input data 10. Specific configurations of the reference flushing pattern 63 and the print flushing pattern 66 will be described later.

  The flushing pattern synthesis unit 56 performs a flushing pattern synthesis process for synthesizing the print dot pattern 13 (13Bk, 13C, 13M, 13Y) after the halftone process and the print flushing pattern 66. As will be described later, the flushing pattern synthesis process is performed with reference to the offset position information table 64 (see FIG. 7) and the flushing dot synthesis table 65 (see FIG. 9).

  The print control unit 57 assigns each dot of the combined dot pattern 14 (14Bk, 14C, 14M, 14Y) after combining the print flushing pattern 66 to the ink nozzles 25 of the inkjet heads 2C, 2M, 2Y, 2Bk. Then, a head drive data generation process for generating head drive data 15 used for driving the print head 2 is performed. Then, the ejection of ink from the print head 2 is controlled based on the generated head drive data. Here, the ink nozzles 25 for each color overlap in the transport direction A at the end portions of the four head units 21 to 24 as described above. For this reason, in the head drive data generation process, a mask process for assigning dots to one of the overlapping ink nozzles 25 of the head unit is performed. In this mask process, when the dots assigned to the ink nozzles 25 overlapping in the transport direction A are dots for the purpose of flushing on paper (a flushing dot Df described later) or a dot obtained by combining this with a print dot. The dots are assigned to both of the overlapping ink nozzles 25.

(Reference flushing pattern)
FIG. 4 is an explanatory diagram of the reference flushing pattern 63. As shown in this figure, the reference flushing pattern 63 is a dot matrix pattern of n columns × m rows, and is composed of blank dots and flushing dots Df. In FIG. 4, for the sake of simplicity, an example of a dot matrix pattern of 10 columns × 10 rows is shown, but a dot matrix pattern having a different number of rows and columns may be used. In the following description, “column alignment direction” is referred to as “column direction”, and “row alignment direction” is referred to as “row direction”. That is, as shown in FIG. 4, the reference flushing pattern 63 is a dot matrix pattern in which n columns are arranged in the column direction V and m rows are arranged in the row direction H.

  The column direction V of the reference flushing pattern 63 corresponds to the arrangement direction of the ink nozzles 25. The four sets of inkjet heads 2C, 2M, 2Y, and 2Bk included in the print head 2 have the same number of arrays of ink nozzles 25 in the paper width direction B, and the number of columns in the paper width direction B is 3200 in this embodiment. The number of dot arrangements in the row direction V (that is, the number of rows n) in the reference flushing pattern 63 is set to be smaller than the number of arrangements (3200) in the paper width direction B of the ink nozzles 25 in the print head 2.

  The row direction H of the reference flushing pattern 63 corresponds to the flushing execution timing. The size in the row direction H (that is, the number of rows m) of the reference flushing pattern 63 is obtained by replacing the flushing execution cycle (that is, the generation cycle of the flushing dots Df) with the number of dots. For example, when flushing is performed once in 0.1 sec, the number of dots printed in this period (0.1 sec) (that is, the number of lines m) depends on the setting of the printing speed and resolution, but is 1000 to 10,000. The number is within the dot range. For example, when the generation period of the flushing dot Df is 5000 dots, the number of rows m is set to 5000. Note that the number of rows m may be an integral multiple of the generation cycle of the flushing dots Df, but in order to reduce the size of the reference flushing pattern 63, the number of rows m is set to the generation cycle of the flushing dots Df.

  Here, when the resolution is constant and the printing speed is slow, the number of dots in one cycle decreases. Also, when the printing speed is constant and the resolution changes, the number of dots in one cycle is reduced. The printing speed is a dimension printed in a unit time (length in the transport direction A), and a value such as 300 mm / sec is applied, for example. Since the size of the reference flushing pattern 63 in the row direction H is the number of dots in one flushing cycle, it is increased or decreased in proportion to the printing speed and resolution. That is, when the printing speed is low, the size of the reference flushing pattern 63 in the row direction H can be reduced. Further, when the resolution is slow, the size of the reference flushing pattern 63 in the row direction H can be reduced.

  Since the reference flushing pattern 63 is a flushing pattern of one cycle, it includes one flushing dot Df in one row. The flushing execution timing is designated by the position of the flushing dot Df in each row. The positions of the flushing dots Df are the same in some of the n columns and are different from each other in the other columns. For example, in the example of FIG. 4, the flushing dot Df is arranged in the first row in the third and tenth columns of the reference flushing pattern 63. On the other hand, in the other eight columns, the positions of the flushing dots Df are distributed in different rows (8 rows of 2 to 7 rows and 9 to 10 rows). Note that the flushing dots Df may be arranged in the same row in three or more of the n columns.

(Print flushing pattern)
FIG. 5 is an explanatory diagram of the print flushing pattern 66. An example of a plurality of print flushing patterns 66 used when a plurality of input data 10 are continuously printed on a plurality of print areas P1 arranged on the print paper P at a predetermined pitch. Is shown. As shown in FIG. 5, the non-printing area is arranged on the printing paper P between the adjacent printing areas P1. The first input data 10 (1) is printed in the first print area P1 (1), and then the second input data 10 (2) is printed in the second print area P1 (2). . When three or more input data 10 are continuously printed, similarly, the input data 10 (i) is continuously printed up to the i-th (i ≧ 3) print area P1 (i).

  At this time, the flushing pattern determining unit 55 applies the print flushing pattern 66 (66 (1) of the size corresponding to the print size to the input data 10 ((1), 10 (2)... 10 (i)). ), 66 (2)... 66 (i)) are formed. That is, the first print flushing pattern 66 (1) having the same size as the print size of the first input data 10 (1) and the second print flushing having the same size as the print size of the second input data 10 (2). A pattern 66 (2) is generated. Similarly, a print flushing pattern 66 (i) having the same size as the print size of the i-th input data 10 (i) is generated. The print flushing pattern 66 (66 (1), 66 (2)... 66 (i)) is input to the input data 10 (10 (1), 10 (2). ) And the printed dot pattern 13 (13 (1), 13 (2)... 13 (i)) generated from the above.

  The print size of the input data 10 (10 (1), 10 (2)... 10 (i)) is the size of the image data 11 after the rendering process described above, and more specifically, the pixels are printed dots. Is the size of the printed dot pattern 13 replaced with. The printing flushing pattern 66 (66 (1), 66 (2)... 66 (i)) matches the row direction H of the reference flushing pattern 63 with the transport direction A and the column direction V with the paper width direction B. The reference flushing patterns 63 are generated by being arranged in the row direction H (transport direction A) and the column direction V (paper width direction B). For example, in the print flushing pattern 66 (1), the reference flushing pattern 63 is repeatedly arranged in the row direction H and the column direction V a plurality of times. In this way, a print flushing pattern 66 having the same size as an arbitrary print size is generated from the reference flushing pattern 63 which is a flushing pattern of one cycle.

  In the example shown in FIG. 5, the first row of the first print flushing pattern 66 (1) is the first dot row of the reference flushing pattern 63. On the other hand, the last row of the first print flushing pattern 66 (1) is the k-th (k <m) dot column of the reference flushing pattern 63. Thus, when the print size in the transport direction A of the first input data 10 (1) is not an integral multiple of the size in the row direction H of the reference flushing pattern 63, the last row of the first print flushing pattern 66 (1). (K row) is a dot column different from the last row (m row) of the reference flushing pattern 63.

  When the first printing flushing pattern 66 (1) ends in the middle of the reference flushing pattern 63, that is, in a row before the m-th row, the flushing pattern determination unit 55 uses the second flushing pattern used in the next printing. The first line of the print flushing pattern 66 (2) is determined in consideration of the last line of the first print flushing pattern 66 (1) used immediately before. Specifically, the first line of the second print flushing pattern 66 (2) is set to the line (k + 1 line) next to the last line (k line) of the first print flushing pattern 66 (1). Similarly, the first line of the i-th print flushing pattern 66 (i) is defined as the line (j + 1 line) next to the jth line (j <m) which is the last line of the immediately preceding print flushing pattern 66 (i-1). To do.

  Thus, in the case of continuous printing, the position of the reference flushing pattern 63 is offset and arranged based on the last line of the immediately preceding print flushing pattern 66 to generate the next print flushing pattern 66. As a result, the flushing dots Df are arranged so that the flushing frequency determined by the reference flushing pattern 63 is maintained over the two print flushing patterns 66 that are used continuously. Thus, the arrangement of the flushing dots Df is determined so that the flushing frequency determined by the reference flushing pattern 63 is maintained in all the steps of continuous printing on the plurality of print regions P1.

(Composition of printing flushing pattern)
FIG. 6 is an explanatory diagram showing a situation in which the printing flushing pattern 66 and the printing dot pattern 13 (13Bk, 13C, 13M, 13Y) are offset and overlapped for each ink color. FIG. 7 is an explanatory diagram of the offset position information table 64. As shown in FIG. 7, the offset position information table 64 includes, for each of four ink colors C, Y, M, and Bk, color combinations that are combinations of the offset amount Dh in the row direction H and the offset amount Dv in the column direction V. Offset amounts (Dh, Dv) are associated with each other. The color-specific offset amounts (Dh, Dv) are, for example, (0, 0), (4, 1), (6, 3), (5, 5) in the order of Bk, C, M, Y. Set to The color-specific offset amount is not limited to the value shown in FIG. 7 as long as one or both of Dh and Dv are different from each other.

  In the synthesis process of the print flushing pattern 66 and the print dot pattern 13 (13Bk, 13C, 13M, 13Y), first, the same print flushing pattern is applied to the four print dot patterns 13 (13Bk, 13C, 13M, 13Y). 66 are shifted and overlapped by the specified color-specific offset amounts (Dh, Dv). Specifically, as shown in FIG. 6A, the print flushing pattern 66 is superimposed on the print dot pattern 13Bk without offset based on the color-specific offset amount (0, 0). Similarly, as shown in FIG. 6B, in the print dot pattern 13C, the print flushing pattern 66 is 4 dots in the row direction H and 1 dot in the column direction V based on the color-specific offset amount (4, 1). They are superimposed and shifted. Further, as shown in FIG. 6C, in the print dot pattern 13M, the print flushing pattern 66 is shifted by 6 dots in the row direction H and 3 dots in the column direction V based on the offset amount by color (6, 3). Are superimposed. As shown in FIG. 6D, in the print dot pattern 13Y, the print flushing pattern 66 is shifted by 5 dots in the row direction H and 5 dots in the column direction V based on the color-specific offset amount (5, 5). Are superimposed.

  As shown in FIG. 6E, the print flushing pattern 66 is superimposed with the offset position shifted depending on the ink color, and synthesized with the print dot pattern 13 (13Bk, 13C, 13M, 13Y). That is, the print dot pattern 13Bk and the print flushing pattern 66 are combined based on the offset amount (0, 0) for black ink, and the print dot pattern 13C and the print flushing pattern 66 are based on the offset amount (4, 1) for cyan ink. The print dot pattern 13M and the print flushing pattern 66 are synthesized based on the offset amount (6, 3) with respect to the magenta ink, and the print dot pattern 13Y and the print flushing pattern 66 are offset with respect to the yellow ink (5, 5). Is synthesized based on In this way, by shifting the offset position depending on the ink color, it is possible to avoid the positions of the flushing dots Df overlapping for a plurality of ink colors. Thereby, it is possible to make the change in the printing result due to the on-paper flushing (that is, the addition of dots by the flushing and the change of the dot size) inconspicuous. Accordingly, it is possible to suppress a decrease in print quality due to the flushing performed on the print area. Further, by shifting the offset position, the same printing flushing pattern 66 can be used for a plurality of ink nozzle groups that eject a plurality of ink colors. Therefore, the processing load can be reduced and the storage capacity can be reduced.

  FIG. 8 is an explanatory diagram of a method for synthesizing the print flushing pattern 66 and the print dot pattern 13 (13Bk, 13C, 13M, 13Y), and shows a change in dot size at the position where the flushing dot Df is superimposed. FIG. 9 is an explanatory diagram of the flushing dot composition table 65. In the flushing dot composition table 65, the final dot size that is finally adopted when the flushing dot Df overlaps is associated with the dot sizes of the four gradations in the print dots. 8 and 9 illustrate a case where the dot size of the flushing dot Df is set to M.

  The flushing dot composition table 65 is set to adopt the larger dot size as the final dot size when the flushing dot Df overlaps the print dot. Specifically, as shown in FIG. 9, when the flushing dot Df overlaps the printing dots D (Null) and D (S) having a size smaller than M, the dot size is corrected to M dots, and the final dot Dt (M) is adopted. On the other hand, when the flushing dot Df overlaps the M or L size print dots D (M) and D (L), the dot size of the original print dot is applied as it is, and the final dot Dt (M) or Dt ( L) is adopted. By referring to the flushing dot composition table 65, as shown in FIG. 8, the composite dot pattern 14 (14Bk, 14C, 14M) is formed from the print dot pattern 13 (13Bk, 13C, 13M, 13Y) on which the print flushing pattern 66 is superimposed. , 14Y) is generated. As described above, when dots of different sizes are overlapped, an increase in the viscosity of the ink in the vicinity of the nozzle surface can be suppressed by adopting a dot having a large size, that is, an ink discharge amount. Further, in such a composition method, it is possible to minimize the change in the print target data associated with the composition of the flushing dot Df as compared with the method of simply adding the flushing dot Df.

(Printing method)
When the control unit 5 of the printer 1 receives input data 10 (print data) such as image data or document data via the communication unit 6, the rendering processing, color conversion processing, and 2 described above are performed on the input data 10. A value conversion process (dot ratio determination process and halftone process) is performed, and a determination process of the above-described print flushing pattern 66 and a combination process with the print dot pattern 13 (13Bk, 13C, 13M, 13Y) are performed. 14, the head drive data 15 is generated.

  On the other hand, the control unit 5 performs a cueing operation for transporting the printing paper P toward the printing head 2 and positioning the leading portion of the printing area P1 of the printing paper P at the printing position by the printing head 2. When the cueing operation is completed, a pulse of a voltage applied to the piezoelectric element corresponding to the ink nozzle 25 is generated as a drive signal based on the generated head drive data 15 and supplied to the print head 2. As a result, the print head 2 is driven, ink droplets are ejected from the ink nozzles 25 of the ink jet heads 2C, 2M, 2Y, and 2Bk, and the contents designated by the input data 10 are printed. The control unit 5 performs an operation of driving the print head 2 based on the head drive data 15 to eject ink onto the printing paper P and an operation of transporting the printing paper P.

  Since the print flushing pattern 66 is combined with the head drive data 15, by driving the print head 2 according to the head drive data 15, the ink dot forming operation for printing the input data 10 and the flushing of the ink nozzle 25 are performed. An ink dot forming operation is performed. That is, printing of an image or a document on the print area P1 and flushing (paper flushing) on the print area P1 are performed.

  As described above, in the printer 1 of the present embodiment, the printing operation of the input data 10 to the printing area P1 and the flushing on paper are performed. Therefore, the clogging of the ink nozzles 25 can be prevented or eliminated without reducing the throughput during printing, and the deterioration of the printing quality can be suppressed. In particular, in this embodiment, a print flushing pattern 66 having a size corresponding to an arbitrary print size can be generated using the reference flushing pattern 63 having a size corresponding to one flushing cycle. Therefore, the print flushing pattern 66 can be generated from the reference flushing pattern 63 having a small size by a simple process. For this reason, the storage capacity of data required for the on-paper flushing is small, and the image processing load is small.

  In the present embodiment, when printing a plurality of input data 10, the print flushing pattern 66 can be generated so as to keep the occurrence frequency of the flushing dot Df for each ink nozzle 25 at the occurrence frequency determined by the reference flushing pattern 63. Specifically, when the last row of the first print flushing pattern 66 (1) is k rows (k <m) of the reference flushing pattern 63, the second print flushing pattern 66 (2) used subsequently. The print flushing pattern 66 (2) is determined so that the first line of () starts from the (k + 1) th line of the reference flushing pattern 63. In this way, by considering the last line of the print flushing pattern 66 (1) generated immediately before, the first line of the next print flushing pattern 66 (2) is determined, so that printing in a plurality of print regions P1 is performed. Even when it is performed, flushing on paper can be performed at a certain frequency. Therefore, clogging of the ink nozzles 25 can be prevented or eliminated with a small storage capacity and without reducing the throughput during printing.

DESCRIPTION OF SYMBOLS 1 ... Printer (printing apparatus), 2 ... Print head, 2Bk, 2C, 2M, 2Y ... Inkjet head, 3 ... Conveyance mechanism, 4 ... Maintenance unit, 5 ... Control part, 6 ... Communication part, 10 ... Input data (printing) Data), 11 ... Image data, 12 (12Bk, 12C, 12M, 12Y) ... Ink amount data, 13 (13Bk, 13C, 13M, 13Y) ... Print dot pattern, 14 (14Bk, 14C, 14M, 14Y) ... Composition Dot pattern, 15 ... head drive data, 21-24 ... head unit, 25 ... ink nozzle, 51 ... storage unit, 52 ... rendering unit, 53 ... color conversion processing unit (part of print dot pattern generation unit), 54 ... Binarization processing unit (part of print dot pattern generation unit), 55... Flushing pattern determination unit, 56. 57: Print control unit, 61: Color conversion lookup table, 62 ... SML table, 63 ... Reference flushing pattern, 64 ... Offset position information table, 65 ... Flushing dot synthesis table, 66 ... Print flushing pattern, A ... Conveyance Direction, B ... paper width direction, D ... printing dot, Df ... flushing dot, Dt ... final dot, H ... row direction, V ... column direction, P ... printing paper (recording medium), P1 ... printing area

Claims (6)

N columns × m lines containing flushing dot (n, m are both an integer of 2 or more) are arranged in the row direction is a column direction and the transport direction intersecting the transport direction of the reference flushing pattern recording medium, first Generating a first print flushing pattern having a size corresponding to the print size of one print data ;
The dot size in overlapping position with the first print dot pattern and the first printing flushing pattern generated based on the first print data,
When the size of the print dots included in the first print dot pattern at the overlapping position is less than a predetermined size, the first composite dot pattern is generated by correcting to a predetermined size,
When the size of the print dot at the overlapping position is equal to or larger than the predetermined size, the size of the print dot at the overlapping position is applied to generate the first composite dot pattern,
Performing ejection of ink from the print head based on the first synthetic dot pattern and conveyance of the recording medium;
When printing the second print data subsequent to the first print data, if the last row of the first print flushing pattern is k rows of the reference flushing pattern (k <m is an integer),
The second print flushing pattern having a size corresponding to the print size of the second print data is generated by setting the first line of the second print flushing pattern to k + 1 lines of the reference flushing pattern. Printing method.   The printing method according to claim 1, wherein flushing is performed by ejecting ink to the maintenance unit at a preset timing with the print head facing the maintenance unit.   The printing method according to claim 1, wherein the reference flushing pattern includes one flushing dot in one row. A print head having ink nozzles;
A transport mechanism for transporting the recording medium;
A storage unit for storing a reference flushing pattern of n columns × m rows (n and m are each an integer of 2 or more) including flushing dots;
The first flushing pattern having a size corresponding to the print size of the first print data is generated by arranging the reference flushing pattern in a column direction intersecting with the conveyance direction of the recording medium and a row direction that is the conveyance direction. and, the first dot size in a position overlapping with the first print dot pattern generated based on the print data and the first print flushing pattern of the first print dot pattern in the overlap position If the size of the print dots included in the image is less than the predetermined size, the first composite dot pattern is generated by correcting to a predetermined size, and the size of the print dots at the overlapping position is the predetermined size. If the size is greater than or equal to the size, the size of the print dot at the overlapping position is applied to generate the first composite dot pattern. And, based on the generated first synthesis dot pattern and a control unit for ejecting ink from the ink nozzles,
The controller is
When printing the second print data subsequent to the first print data, if the last row of the first print flushing pattern is k rows of the reference flushing pattern (an integer of k <m) , the first line of the second printing flushing pattern in the k + 1 line of the reference flushing pattern, characterized that you to generate the second print flushing pattern of size corresponding to the print size of the second print data Printing device. A maintenance unit for receiving ink ejected from the ink nozzles of the print head;
The printing apparatus according to claim 4, further comprising: a flushing execution unit that causes the print head to face the maintenance unit and causes the maintenance unit to perform flushing that discharges ink at a preset timing.   The printing apparatus according to claim 4, wherein the reference flushing pattern includes one flushing dot in one row.

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