JP2004306617A - Printer and printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer and a method for color printing which improve both print quality and throughput under a scanning system in which main scanning and subscanning are simply and alternately performed. <P>SOLUTION: Nozzle arrays to eject inks of black, cyan, magenta, and yellow are arranged on a printhead. Each nozzle array has N nozzles 191, 192, ..., and 19N arranged in a subscanning direction at the interval k times the dot pitch of a print image. The nozzles 191, 192, ..., and 19N are driven at an intermittent timing while the printhead is performing main scanning, thereby forming dots at the interval s times the dot pitch. When main scanning is finished, subscanning is performed by a specified distance. The subscanning distance L is set to meet a following formula: L=N/(s×D×k), wherein S is an arbitrary integer of 2 or above and a divisor of N; k is an arbitrary integer of 2 or above in a prime relation with N/s; and D is the number of the nozzles per unit distance in the subscanning direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a serial scan type or drum scan type printer that performs printing while a print head scans the surface of a print medium, and in particular, to an improvement in a method of driving and scanning a head to improve print image quality and throughput. About.

  As one of techniques for improving the image quality of this type of printer, particularly an ink jet printer, there is an invention called "interlace method" disclosed in U.S. Pat. No. 4,198,642 and JP-A-53-2040. This interlacing method is characterized by the configuration of the inkjet nozzle array on the print head and the sub-scanning method. That is, the nozzle array is composed of N nozzles arranged in the sub-scanning direction. The center point interval (nozzle pitch) between adjacent nozzles is set to k times the pixel pitch D of the print image. k is selected as an integer having a relatively prime relationship. The distance of the sub-scan performed after each main scan is set to ND.

  This interlace method has an effect of improving print image quality by dispersing variations in nozzle pitch, ink ejection characteristics, and the like on a print image.

  Further, as another technique for improving the image quality of a color ink jet printer, there is a technique called "singling" or "multi-scan" disclosed in Japanese Patent Application Laid-Open No. Hei 3-207665 and Japanese Patent Publication No. Hei 4-19030. This shingling uses a print head in which a plurality of nozzle arrays that eject different color inks are arranged in parallel in the main scanning direction, and in one main scan, the nozzle arrays are driven at intermittent timings. Dots are formed every fixed number of dots in the scanning direction, and each nozzle array forms dots at different dot positions. By repeating such main scanning a plurality of times with the nozzle drive timing shifted each time, the formation of all dots on a line continuous in the main scanning direction is completed.

  In this shingling, since the ink dots of different colors are not formed at the same position in the same main scan, the so-called ink bleed problem that the dots of different color inks are united to deteriorate the image quality is caused. Be improved.

  In order to obtain high image quality in a color printer, it is necessary to prevent the image quality from deteriorating due to variations in nozzle pitch and ejection characteristics, and to prevent ink bleed between dots of different colors. Conventionally, an interlace method is known for the former request, and shingling is known for the latter request.

  However, when the conventional interlacing method and the conventional shingling are simply combined, the following problem occurs.

  The first problem is a decrease in throughput. That is, in order to reliably prevent ink bleeding, it is desirable to prevent different color dots from being formed not only at the same dot position but also at adjacent dot positions in the same main scanning. However, if this is to be realized by the conventional shingling, it is necessary to repeat main scanning four or more times to complete printing at all dot positions. Therefore, even if bidirectional printing is performed, in which printing is performed on both the forward path and the return path of main scanning, it is necessary to repeat two or more round trips. Without bidirectional printing, four or more round trips are repeated. There must be. As a result, the printing speed decreases and the throughput decreases.

  The second problem is that scanning control becomes complicated.

  That is, if the main scanning reciprocation is repeated two or more times to reliably prevent ink bleed as described above, the sub-scanning is not performed during this reciprocating repetition, and the sub-scanning is performed at the stage when this repetition is completed. Will do. As a result, a simple scanning method for alternately performing the main scanning and the sub-scanning cannot be adopted, and the scanning control becomes complicated. In addition, such a scanning method may cause band-like unevenness in a printed image.

  A third problem is that it cannot be used in a drum scan type printer. That is, the drum scan type printer adopts a scanning method in which the print head runs at a constant speed while rotating the drum at a constant speed, thereby realizing high throughput and high image quality. This scanning method is the same as the method in which the main scanning and the sub-scanning are simply performed alternately from the viewpoint of the relative relationship between the head and the medium. Further, in the drum scan printer, bidirectional printing cannot be performed due to the above-described scanning method.

  Under these circumstances, the drum scanning type printer cannot employ the conventional shingling. This is because if shingling is performed under conditions where bidirectional printing is not possible, the main scan must be repeated a plurality of times between sub-scans. This means that a method in which the main scanning and the sub-scanning are simply repeated alternately cannot be adopted, that is, the method does not conform to the above-described scanning method of the drum scan type printer.

  Accordingly, an object of the present invention is to provide a printing apparatus and method capable of realizing both improvement in print image quality and improvement in throughput under a scanning method in which main scanning and sub-scanning are performed simply and alternately.

  The printing apparatus and method of the present invention use a print head having a dot forming element array in which N dot forming elements (for example, inkjet nozzles) for forming dots of the same color are arranged at a constant pitch in the sub-scanning direction. Thus, the main scanning and the sub scanning of the print head are alternately performed. In one or both of the forward scan period and the return scan period of the main scan, the dot element array of the print head is driven to form dots on the print medium. The sub-scan is always performed for a fixed distance.

  Here, the distance of one sub-scan is the sub-scanning pitch L, the number of repetitions of the main scanning required to print a continuous line in the main scanning direction is the number of scanning repetitions s, and the distance between the center points of the dot forming elements is printed. A value represented by a multiple of the dot pitch of the image is defined as an element pitch k, and the number of the dot forming elements existing per unit distance in the dot forming element array is defined as an element density D.

  In the apparatus and method of the present invention, an arbitrary integer less than 2 or less than N is selected as the number of scan repetitions s, and an arbitrary integer less than 2 or less than N having a relatively prime relationship with N / s as the element pitch k. A value that satisfies the relational expression L = N / (sDk) is selected as the sub-scanning pitch L.

  According to the present invention, if the dot forming element array is driven at an intermittent timing during the main scanning, dots separated from each other in both the main scanning direction and the sub-scanning direction are formed by the same dot forming element. That is, adjacent dots are formed by different dot forming elements. As a result, variations in the dot forming characteristics of the nozzles and the like are dispersed in both the main scanning direction and the sub-scanning direction, and the image quality of a printed image is improved.

  One preferable mode of the driving at the intermittent timing is to drive the dot forming element array at an intermittent timing corresponding to (s-1) every other dot. Expressing this preferred mode more generally, different dots in the dot matrix of s dots in the main scanning direction and k dots in the sub-scanning direction are different in different main scans in successive s × k main scan repetitions. That is, the dot forming element array is driven at a timing selected for each main scan so as to be formed.

  In the apparatus and method of the present invention, the separation distance (value converted into the number of dot pitches) of dots formed by the same dot forming element in the main scanning direction can be determined in proportion to the number of scan repetitions s, and The resolution and the separation distance in the sub-scanning direction (value converted into the number of dot pitches) can be determined in proportion to the nozzle pitch k. Therefore, as the number of scan repetitions s and the nozzle pitch k are set to larger values, the resolution and image quality of the image are improved. Therefore, if a plurality of print modes are prepared and different values are selected for each print mode as the number of scan repetitions s or the nozzle pitch k, an appropriate resolution and image quality can be selected according to the application, and for the user, It is convenient.

  When a plurality of print modes are prepared as described above, the throughput decreases as the number of scan repetitions s and the nozzle pitch k increase. Therefore, if the main scanning speed is increased as the number of scan repetitions s increases, a decrease in throughput due to an increase in the number of scan repetitions s can be suppressed.

  By setting the number of scan repetitions s and the nozzle pitch k to be appropriately large, it is possible to prevent dots of different colors from being formed not only at the same position but also at adjacent positions in the same main scanning in the case of color printing. . As a result, ink bleeding is extremely effectively prevented, and the image quality is further improved.

  The preferred embodiment includes four dot-forming element arrays for forming dots of four colors, black, cyan, magenta, and yellow, wherein dots of different colors are formed at different dot positions during one main scan. Thus, these four sets of dot forming element arrays are driven at different timings. This can prevent ink bleed during color printing. In this case, a higher throughput can be obtained than in a case where a similar bleed prevention effect is obtained by a conventional shingling.

  Further, in this embodiment, both the number of scan repetitions s and the nozzle pitch k are selected to be even numbers. As a result, when bidirectional printing is performed, one line in the main scanning direction is always printed only in the forward path or in the return path of the main scanning, so that image quality deterioration in bidirectional printing hardly appears remarkably.

  Further, the present invention can be applied to a case where one pixel is represented by a plurality of dots in order to represent multiple gradations. In this case, one pixel can be represented by a dot matrix of s dots in the main scanning direction × k dots in the sub-scanning direction, and printing of one pixel can be completed in s × k times of main scanning. As a result, different dots in one pixel are formed by different dot forming elements, so that variations in dot forming characteristics of the dot forming elements can be absorbed to improve image quality.

  FIG. 1 shows a mechanical configuration of a main part of a serial scan type color inkjet printer according to an embodiment of the present invention.

  As shown in FIG. 1, a printing paper 1 is taken up from a paper stacker 2 by a paper feed roller 3 driven by a step motor, and is fed on the surface of a platen plate 5 in the sub-scanning direction. The carriage 7 is pulled by a pulling belt 11 driven by a step motor 9 and moves along a guide rail 13 in a main scanning direction perpendicular to the sub-scanning direction.

  A print head 15K having black (K) ink and a print head 15CMY having three color inks of cyan (C), magenta (M), and yellow (Y) are mounted on the carriage 7. I have. These print heads 15K and 15CMY are arranged in the main scanning direction as a whole. The color ink print head 15CMY may be configured as a separate print head for each color ink.

  FIG. 2 is a plan view showing an array of inkjet nozzles arranged on a surface of the print heads 15K and 15CMY facing the paper 1. FIG.

  A nozzle array 17K that ejects K ink is provided on the print head 15K, and nozzle arrays 17C, 17M, and 17Y that eject Y ink, M ink, and C ink, respectively, are provided on the print head 15CMY. . These four nozzle arrays 17K, 17C, 17M, and 17Y are arranged in parallel in the main scanning direction as a whole, with their positions in the sub-scanning direction completely coincident with each other.

  Each of the nozzle arrays 17K, 17C, 17M, 17Y has a large number of ink nozzles 191, 192,... Arranged in a zigzag pattern at a constant pitch (hereinafter, referred to as a nozzle pitch) k along the sub-scanning direction. .

  In the above configuration, as the scanning method, a method in which main scanning and sub-scanning are simply repeated alternately is adopted. That is, in the case of unidirectional printing, while the print heads 15K and 15CMY reciprocate once in the main scanning direction, they are driven only on the outward path to form dots on the surface of the sheet 1, and each reciprocation is completed. Each time, the sheet 1 is fed by a certain distance in the sub-scanning direction. In the case of bidirectional printing, while the print heads 15K and 15CMY reciprocate once in the main scanning direction, they are driven on both the forward path and the return path to form dots, and each forward path is completed. The sheet 1 is fed by a fixed distance each time and each time the return travel is completed.

  Here, a distance L (hereinafter, referred to as a sub-scanning pitch) for one paper feed is set so as to satisfy the following equation (1).

L = N / (sPk) (1)
Here, N is the total number of nozzles of one nozzle array. In addition, s is the number of repetitions of the main scanning required to completely print one continuous line in the main scanning direction (hereinafter, referred to as the number of scan repetitions), and is an arbitrarily selected integer less than N and equal to or greater than 1. . k is the distance between the center points of two nozzles adjacent in the sub-scanning direction, that is, the nozzle pitch. This nozzle pitch k is expressed using a multiple of the dot pitch of the print image, and its value is an arbitrarily selected integer less than N and not less than 1 and relatively prime to N / s. D is the nozzle density, that is, the number of nozzles included in one inch in the sub-scanning direction of the nozzle array. In the description of the present specification, the nozzle density D is expressed in units of npi (nozzle / inch), and therefore, the sub-scanning pitch L is expressed in inches (i).

  Table 1 shows specific examples of the parameters of the above equation (1).

  The example of Table 1 is a specific example when N = 30 [nozzles] and D = 180 [npi]. Four types of printing modes, "high speed", "standard", "high quality", and "ultra high quality" are prepared, and a unique value of each parameter is set for each mode.

  The “standard mode” of the print mode aims at printing with the most standard image quality, and the image resolution (the density of dots on the print image) is set to the standard 360 dpi (dot / inch). The “high-speed mode” aims to print at a higher speed than the standard mode, and the resolution is set to 180 dpi, which is １ ／ of the standard mode. The “high-quality mode” is intended to print with higher image quality than the standard mode, and the resolution is set to 720 dpi which is twice the standard mode. The “ultra-high quality mode” aims to print with even higher image quality, and the resolution is set to 1440 dpi, which is four times the standard mode.

The meaning of each parameter shown in Table 1 is as follows. The meanings of “the number of scan repetitions s” and “nozzle pitch k” have already been described. Although the meaning of “sub-scanning pitch L” has already been described, the numerical value of the denominator shown in Table 1 indicates the image resolution, and the numerical value of the numerator indicates that the sub-scanning pitch L is the dot pitch (the distance between adjacent dots). It shows how many times it corresponds. The “relative main scanning speed” is a value obtained by expressing the traveling speed of the head in each mode as 1 in the standard mode and expressed as a relative ratio. “Head frequency” is the frequency of a clock signal that drives each nozzle of the head. “Relative printing speed” is the number of pages (throughput) that can be printed on a sheet of a certain size within a certain period of time, expressed as a relative ratio, with that in a standard mode being one.
The “number of relative data” represents a relative ratio where the amount of data (= in proportion to the square of the resolution) that can be printed on paper of a certain size is set to 1 in a standard mode.

  Hereinafter, parameter settings in each print mode and their meanings will be described with reference to Table 1.

  In the high-speed mode, the number of scan repetitions s = 1, the nozzle pitch k = 1, and the sub-scanning pitch L = 30/180 [i]. When the number of scan repetitions is s = 1, the nozzles 191, 192,... Are driven at continuous timings corresponding to all dots during the main scan, and a continuous line in the main scan direction is formed by one main scan. Means completely printed. The nozzle pitch k = 1 means that the nozzle pitch is equal to the dot pitch, that is, the image resolution is 180 dpi equal to the nozzle density D. The sub-scanning pitch L = 30/180 [i] means that one sub-scanning distance is equivalent to 30 (= N / s) dots of a 180 dpi image.

  In the high-speed mode, in short, in one main scan, the band area traversed by the nozzle array is completely printed during the main scan, and when the main scan is completed, the sub-scan is performed for the width of the band area. The most orthodox printing operation is performed. In this mode, therefore, no special operation for improving the image quality such as interlace or shingling is performed.

  In the standard mode, the number of scan repetitions s = 2, the nozzle pitch k = 2, and the sub-scanning pitch L = 15/360 [i]. The number of scan repetitions s = 2 means that the nozzles 191, 192,... Are driven at intermittent timings corresponding to every other (= s−1) dots during the main scan. Therefore, in order to completely print a continuous line in the main scanning direction, 2 (= s) main scanning repetitions are required. The nozzle pitch k = 2 means that the nozzle pitch is twice the dot pitch, that is, the image resolution is 360 dpi, which is twice the nozzle density D (= 180 dpi). The sub-scanning pitch L = 15/360 [i] means that one sub-scanning distance is equivalent to 15 (= N / s) dots of a 360 dpi image.

  A specific printing operation in the standard mode performed under such parameter settings will be described with reference to FIG.

  FIG. 3 schematically shows positions of individual nozzles in one nozzle array in the sub-scanning direction and positions of dots formed by the nozzles. However, since it is difficult to show all 30 nozzles 191 to 1930, only a part of the nozzles necessary for the explanation is extracted and shown. In the figure, the nozzle positions and dot positions indicated by circles marked with numerals 1, 2, 3,... Correspond to the first main scan, the second main scan, the third main scan,. It shows the position and the position of the dot that it forms.

  As understood from FIG. 3, in the first main scan, the nozzles 191 to 1930 are intermittently driven at one-dot intervals to form dots at every other dot position indicated by the numeral 1. When the first main scan is completed, sub-scan is performed for a distance of 15 dots. Here, the distance of 15 dots corresponds to the distance of 7 nozzles plus 1 dot. By this sub-scanning, the nozzles 191 to 1930 move to the positions marked with the numeral 2, that is, intermediate positions between the nozzle positions during the first main scanning. Subsequently, a second main scan is performed, and the nozzles 191 to 1930 are intermittently driven at exactly the same timing as in the first main scan. As a result, a new dot is formed at a position (numeral 2) adjacent to the dot in the first main scan on the lower side in the figure.

  When the second main scan is completed, the sub-scan for 15 dots is performed again, and the nozzles 191 to 1930 move to the positions marked with the numeral 3, that is, the positions overlapping the nozzle positions of the first main scan. I do. Subsequently, a third main scan is performed. In this case, the nozzles 191 to 1930 are intermittently driven at timings inverted from the timings of the first and second main scans. Thereby, a new dot is formed at a position (numeral 3) adjacent to the dot position of the first main scanning in the main scanning direction.

  After the third main scan, the sub-scan for 15 dots is performed again. Subsequently, a fourth main scan is performed, and the nozzles 191 to 1930 are intermittently driven at the same timing as that during the third main scan. Thereby, a new dot is formed at a position (numeral 4) adjacent to the dot position of the second main scanning in the main scanning direction.

  By the above operation, it is understood that each dot is formed by a different nozzle during a different main scan in a dot matrix of 2 (= s) dots in the main scanning direction × 2 (= k) dots in the sub-scanning direction.

  The above operation is performed for one nozzle array. Then, the nozzle arrays 17K, 17C, 17M, and 17Y of the four colors execute the above-described operations at mutually different drive timings. For example, in the first to fourth main scans, the nozzle array 17K forms dots in the dot sequence of numbers 1 → 2 → 3 → 4 in FIG. 3, and the nozzle array 17C forms dots in the order of numbers 2 → 3 → 4 → 1. The dots are formed in the dot order, the nozzle array 17M forms dots in the order of the numbers 3 → 4 → 1 → 2, and the nozzle array 17Y forms dots in the order of the numbers 4 → 1 → 2 → 3. In this way, the dots are formed so that the four color dots do not overlap at the same position in the same main scan.

  Next, the high-quality mode will be described with reference to Table 1 again.

  In the high quality mode, the number of scan repetitions s = 2, the nozzle pitch k = 4, the sub-scanning pitch L = 15/720 [i], and the relative main scanning speed = 2. Since the number of scan repetitions s = 2, the nozzles 191, 192,... Are driven at intermittent timings corresponding to every other dot, as in the standard mode described above. The nozzle pitch k = 4 means that the nozzle pitch is four times the dot pitch, that is, the image resolution is 720 dpi which is four times the nozzle density D (= 180 dpi). The sub-scanning pitch L = 15/720 [i] means that one sub-scanning distance is equivalent to 15 (= N / s) dots of a 720 dpi image. The relative main scanning speed = 2 means that the head runs at twice the speed of the standard mode.

  A specific printing operation in the high-quality mode under this setting will be described with reference to FIG.

  FIG. 4 also shows, as in FIG. 3, a part of the nozzles necessary for the description extracted from one nozzle array, and schematically shows the positions in the sub-scanning direction and the positions of the dots formed by the nozzles. Things. The nozzle positions and dot positions indicated by circles marked with numerals 1, 2, 3,... Are formed by the positions of the nozzles in the sub-scanning direction in the first main scan, the second main scan, the third main scan,. This shows the position of the dot.

As shown in FIG. 4, in the first main scan, the nozzles 191 to 1930 are driven every other dot at intermittent timing to form dots at the dot positions marked with the numeral 1. When the first main scan is completed, sub-scan is performed for a distance of 15 dots.
Here, the distance for 15 dots corresponds to the distance for 3 nozzles plus 3 dots. By this sub-scanning, the nozzles 191 to 1930 move to the positions marked with the numeral 2, that is, positions shifted by one dot upward in the drawing from the nozzle positions at the time of the first main scanning. Subsequently, a second main scan is performed, and the nozzles 191 to 1930 are driven at exactly the same intermittent timing as that of the first main scan, so that a dot position (numerical) adjacent to the dot in the first main scan In 2), a new dot is formed.

  When the second main scan is completed, the sub-scan for 15 dots is performed again, and the nozzles 191 to 1930 are positioned one dot above the position marked with the numeral 3, that is, one dot above the nozzle position in the second main scan. Move to the position shifted only by. Subsequently, the third main scan is performed, and the nozzles 191 to 1930 are driven at exactly the same timing as in the first and second main scans. As a result, a new dot is formed at a dot position (numeral 3) adjacent to the dot in the second main scan above.

  Subsequently, the sub-scan for 15 dots is performed, and the nozzles 191 to 1930 are shifted upward by one dot from the nozzle position of the third main scan, that is, to a position lower than the nozzle position of the first main scan. Move to a position shifted by one dot. Then, the fourth main scanning is performed, and the nozzles 191 to 1930 are driven at the intermittent timing whose phase is inverted from the driving timing at the time of the first to third main scanning. As a result, a new dot is formed at a dot position (numeral 4) adjacent to the dot position of the first main scan in the lower right diagonal direction in the figure.

  In the subsequent sub-scanning, the nozzles 191 to 1930 move to positions overlapping with the position in the first main scanning, and the fifth main scanning is performed, and the nozzles 191 to 1930 at the same timing as the fourth main scanning. Is driven. Thereby, a new dot is formed at a dot position (numeral 5) adjacent to the dot of the first main scanning in the main scanning direction.

  In the sixth main scan, the nozzles 191 to 1930 are driven at the same timing as in the fourth and fifth main scans, and the nozzles 191 to 1930 are moved to the dot positions (numeral 6) adjacent to the dot positions in the second main scan in the main scan direction. New dots are formed. Thereafter, although not shown, in the seventh main scan, the dot position adjacent to the dot in the third main scan in the main scanning direction, and in the eighth main scan, the dot position in the fourth main scan. New dots are respectively formed at dot positions adjacent to each other in the main scanning direction.

  By the above operation, it is understood that each dot is formed by a different nozzle at a different main scan in a dot matrix of 2 (= s) dots in the main scanning direction × 4 (= k) dots in the sub-scanning direction.

  The above operation is performed for one nozzle array. Then, the nozzle arrays 17K, 17C, 17M, and 17Y for the four colors execute the above-described operations at drive timings that are out of phase with each other. As a result, dots of four colors are formed at different positions in the same main scan, and dots of different colors are not formed at the same position.

  Next, the super high quality mode will be described with reference to Table 1 again.

  In the ultra high quality mode, the number of scan repetitions s = 4, the nozzle pitch k = 8, the sub-scanning pitch L = 7/720 [i], and the relative main scanning speed = 4. In this mode, of the 30 nozzles in each nozzle array, only continuous 28 nozzles are used. When the number of scan repetitions is s = 4, the nozzles 191, 192,... Are driven at intermittent timings corresponding to every third dot, so that a line continuous in the main scanning direction in four main scans is completely formed. It means to print. The nozzle pitch k = 8 means that the nozzle pitch is eight times the dot pitch, that is, the image resolution is 1440 dpi which is eight times the nozzle density D. The sub-scanning pitch L = 7/1440 [i] means that one sub-scanning distance corresponds to 7 (= N / s) dots of a 1440 dpi image. The relative main scanning speed = 4 means that the head runs at four times the speed of the standard mode.

  Although the printing operation in the ultra high quality mode is not shown, as can be understood from the operations in the standard mode and the high quality mode shown in FIGS. It is understood that in the dot matrix of 8 (= k) dots in the sub-scanning direction, each dot is formed by a different nozzle during a different main scan.

  The four-color nozzle arrays 17K, 17C, 17M, and 17Y operate at drive timings that are out of phase with each other in each main scan, and form four-color dots at different positions in the same main scan. .

  As can be seen from the above description of the standard mode, the high-quality mode, and the ultra-high-quality mode, by setting the number of scan repetitions s and the nozzle pitch k to two or more values according to the present invention, the main scan and the sub-scan can be performed. , A new printing operation in which the conventional interlacing method and shingling are harmoniously integrated can be performed under a scanning method in which is simply repeated.

  Focusing on the operation of the one-color nozzle array in this new printing operation, each dot in the dot matrix of s dots in the main scanning direction × k dots in the sub-scanning direction is formed by different nozzles during different main scanning. Thus, in the main scanning direction and the sub-scanning direction, variations in the ejection characteristics of the nozzles and the like are dispersed on the image, and as a result, the image quality is improved. This image quality improvement effect becomes more remarkable as s and k are set larger. Incidentally, the conventional interlace method can only disperse the variation in the nozzle discharge characteristics and the like only in the main scanning direction, and cannot disperse it in the sub scanning direction as in the present embodiment.

  Focusing on the mutual relationship between the operations of the nozzle arrays of different colors, by shifting the phase of the drive timing of each nozzle array, the same main scan can be performed at different dot positions in the s × k dot matrix. It can be seen that dots of different colors are formed. Therefore, dots of different colors are not formed at the same position in the same main scanning. In particular, when s = 2 or more and k = 2 or more, all four dots of K, C, M, and Y usually used for color printing can be formed at different positions. Ink bleeding can be prevented well. This also means that the possibility of using a low-permeability ink for all four color inks arises, in which case the density is higher than with a super-penetrable ink. Further, since an image with high saturation can be printed, further improvement in image quality can be expected. By the way, in the conventional shingling, in order to form four-color dots at different positions, the number of scans must be set to four or more, and the throughput becomes s = 2 (standard mode, high (Quality mode).

  Further, for example, when a slow permeable ink is used for the K ink and a super permeable ink is used for the CMY color ink, the slow permeable K ink and the super permeable color ink are It is desirable that the scans do not overlap. Therefore, in the standard mode shown in FIG. 3, for example, the K ink dot is formed at the dot position of numeral 1 in the first main scan, the color ink dot is formed at the dot position of numeral 4, and the K ink dot is formed in the second main scan. A color ink dot is formed at a dot position of a numeral 3 at a dot position of a numeral 2, a K ink dot is formed at a dot position of a numeral 3, and a color ink dot is formed at a dot position of a numeral 2 in the third main scan. In this manner, two types of ink dots can be formed separately at diagonal positions. With this configuration, the distance between the two types of dots is larger than when two types of dots are formed at adjacent positions in the main scanning direction or the sub-scanning direction, so that ink bleeding can be more effectively prevented. By the way, if the same thing is to be realized by the conventional shingling, the number of scans must be set to four or more, and the throughput is lower than in the standard mode.

  Further, by setting s or k to a larger value, it is also possible to form dots of four colors at positions not adjacent to each other in the same main scanning. For example, in the super high quality mode, s = 4 and k = 8 are set, so that four color dots can be formed at different dot positions in a 4 × 8 dot matrix in the same main scan. . Therefore, it becomes possible to form these four color dots at positions separated from each other by two dots or more. In addition, it is possible to change the timing at which different color dots are formed at the same position by two or more main scans. Therefore, ink bleeding can be completely prevented.

  In the present embodiment, since the main scanning speed is increased with an increase in the number of scan repetitions s or the resolution as in the case from the standard mode to the ultra high quality mode, for example, the number of scan repetitions s and the increase in the resolution are increased. Also, there is a merit that a decrease in throughput due to is small.

By the way, as described above, unidirectional printing and bidirectional printing can be selected.
In unidirectional printing, the head is driven only during the outward travel of the head to form dots. In bidirectional printing, the head is driven during both the forward and backward passes of the head travel to form dots. Accordingly, the throughput of the bidirectional printing is almost twice as high as that of the unidirectional printing, but on the other hand, there is a possibility that the dot formation positions on the forward path and the backward path are slightly shifted, and the image quality is deteriorated. This is because the flying speed of the ink from the ink jet head or the elongation speed of the wire from the wire impact head is finite. In order to solve this problem, a correction that slightly changes the drive timing of the head between the forward path and the return path can be performed by the control device, but it is still difficult to completely solve the above problem. This problem of bidirectional printing may be remarkable particularly when one line in the main scanning direction is printed separately for the forward pass and the return pass. For example, in FIG. 3, if the dot printed with the number 1 is printed on the outward path and the dot marked with the number 3 is printed on the return path, the dot 1 and the number 1 are printed due to the displacement of the dot formation positions on the forward path and the return path. There is a possibility that the distance from the dot 3 is not constant and the image quality is reduced.

  In order to make the above-described problem of bidirectional printing as inconspicuous as possible, in the printing operation of the present invention, it is desirable to always print one line in the main scanning direction only on the outward path or only on the return path. For example, when bidirectional printing is performed in the high quality mode shown in FIG. 3, dots marked with odd numbers are printed on the forward path, and dots marked with even numbers are printed on the backward path. Only on the return path or on the return path. The same can be said for the super high quality mode shown in FIG. As described above, a condition necessary for printing one line only in the forward pass or in the return pass only is to set both the scan repetition count s and the nozzle pitch k to an even number.

  FIG. 5 shows a configuration of a control circuit of the printer for performing the above printing operation.

  In FIG. 5, the printer driver of the external host computer 51 determines the parameter values as shown in Table 1 based on the print mode specified by the user, and based on this, prints suitable for printing in that print mode. Generate data and transfer it to the printer. The transferred data is temporarily stored in the reception buffer memory 53.

  In the printer, the system controller 55 reads the print data from the reception buffer memory 53, and sends control signals to the main scanning driver 57, the sub-scanning driver 61, and the head driver 69 based on the read data.

  The gate array 65 reads the print data from the reception buffer memory 53, creates K, C, M, and Y image data based on the print data, and writes the image data into the image buffer 67 for each color. Then, the head drive driver 65 reads each color image data from the image buffer 67 in accordance with the control signal from the system controller 55, and drives each color nozzle array 17K, 17C, 17M, 17Y.

  The main scanning driver 57 and the sub-scanning driver 61 drive the carriage motor 59 and the paper feed motor 63, respectively, in accordance with control signals from the system controller 55.

  FIG. 6 shows a flow of the entire operation by the configuration of FIG.

  First, the printer driver of the host computer 51 processes the image data according to the print mode specified by the user (S1), and transfers the print data of the processing result to the reception buffer 53 of the printer (S2). In the printer, the gate array 65 reads the print data from the reception buffer 53 (S3), creates K, C, M, and Y print image data based on the print data and writes the image data into the image buffer (S4). Next, under the control of the system controller 55, the carriage motor 59, the paper feed motor 63, and the nozzle arrays 17K, 17C, 17M, and 17Y for each color are driven to execute printing (S5).

  The above operation is repeated until the printing is completed. When the printing is completed (S6), it is checked whether or not a change of the print mode is input by the user at the host computer 51 (S7). If there is a change, the above series of processing is re-executed in the changed print mode.

  FIG. 7 shows a flow of the image data processing (FIG. 6, S1) by the printer driver of the host computer 51.

  First, the selection of the print mode from the user is received (S11), and the parameter values such as the number of scan repetitions s and the nozzle pitch k listed in Table 1 are determined according to the selected print mode (S12). Next, scaling is performed, that is, the original image data created by the application is converted into image data having a resolution corresponding to the selected print mode (S13).

  Next, an ink reduction process is performed, that is, a duty limit is imposed on the image data according to the type of printing paper selected by the user, based on the restriction on the amount of ink received on the paper (S14). Next, the image data (generally, 256 gradations for each color in RGB expression) is subjected to color correction and binarization processing, and converted into CMY expression binary data (S15).

  Next, it is checked whether or not the image data after the above processing is optimal (S16). If the image data is not optimal, the process is repeated from the selection of the print mode, and if the image data is optimal, the formation of each color dot according to the print mode is performed. The image data is rearranged so as to conform to the order (S17), and the image data processing ends.

  FIG. 8 shows a flow of scanning and printing processing (FIG. 6, S5) performed under the control of the system controller 55.

  First, the print head and the printing paper are aligned so that printing can be started from the first print line (S21). Next, image data of each color is read from the image buffer 67 (S22), and printing is performed by driving each color nozzle according to the image data while running the carriage (S23). When the main scanning is completed, the printing paper is moved by the sub-scanning pitch L (S24). Steps S22 to S24 are repeated until printing of one page is completed.

  The above processing is repeated until the printing of the previous page is completed, and when it is completed (S25), the above scanning and printing processing ends.

  The preferred embodiment of the present invention has been described above, but the present invention can be implemented in various modes other than this embodiment. For example, the present invention is applicable not only to color printing but also to monochrome printing. Further, the present invention can be applied to printing in which one pixel is expressed by a plurality of dots to express multiple gradations. Further, the present invention can be applied to a drum scan printer. In a drum scan printer, the drum rotation direction is the main scanning direction, and the carriage traveling direction is the sub scanning direction.

FIG. 1 is a perspective view showing a mechanical configuration of a main part of a serial scan type color inkjet printer according to an embodiment of the present invention. FIG. 3 is a plan view showing an array of inkjet nozzles arranged on a surface of the print heads 15K and 15CMY facing the paper 1 of the embodiment. FIG. 4 is a schematic diagram illustrating a specific dot formation in a standard mode. FIG. 3 is a schematic diagram showing a specific dot formation in a high quality mode. FIG. 2 is a block diagram showing a configuration of a control circuit of the embodiment. 5 is a flowchart illustrating the flow of the entire operation of the control circuit. 5 is a flowchart showing the flow of image data processing by a printer driver of a host computer 51. 9 is a flowchart showing the flow of scanning and printing processes performed under the control of the system controller 55.

Explanation of reference numerals

Reference Signs List 1 printing paper 7 carriage 15 print head 17 nozzle array 19 inkjet nozzle 51 host computer 55 system controller 65 gate array

Claims (14)

In an apparatus in which a print head performs printing on the surface of the print medium by performing main scanning and sub-scanning on the surface of the print medium,
A dot forming element array formed by arranging N dot forming elements for forming dots of the same color at a constant pitch in the sub-scanning direction at a position of the print head facing the print medium;
Main scanning drive means for performing main scanning of the print head;
A head driving unit that drives the dot forming element array during the main scanning; and a sub-scanning driving unit that performs the sub-scanning by a fixed distance every time the main scanning is completed.
The distance of one sub-scan is the sub-scan pitch L, the number of repetitions of the main scan required to print a continuous line in the main scanning direction is the number of scan repetitions s, and the distance between the center points of the dot forming elements is the dot of the printed image. When a value expressed by a multiple of the pitch is defined as an element pitch k, and the number of the dot forming elements existing per unit distance in the dot forming element array is defined as an element density D,
An arbitrary integer less than N and equal to or greater than 2 is selected as the number of scan repetitions s,
As the element pitch k, an arbitrary integer less than N and not less than 2 which is relatively prime to N / s is selected, and
A printing apparatus characterized in that a value satisfying a relational expression of L = N / (sDk) is selected as the sub-scanning pitch L. The device of claim 1,
A print mode selecting unit for selecting one print mode from a plurality of print modes in which different values are selected in at least one of the scan repetition count s and the element pitch k. apparatus. The device according to claim 2,
The main scanning drive unit may vary the main scanning speed according to the number of scan repetitions s selected by the print mode selection unit so that the main scanning speed increases as the number of scan repetitions s increases. Characteristic printing device. The device of claim 1,
A printing apparatus, wherein the head driving means drives the dot forming element array at intermittent timings corresponding to (s-1) dot intervals during the main scanning. The device according to claim 4,
The head driving unit forms different dots in a dot matrix of s dots in the main scanning direction and k dots in the sub-scanning direction in different main scans in successive s × k main scan repetitions. A printing apparatus for driving the dot forming element array. The device of claim 1,
Comprising a plurality of dot forming element arrays for forming dots of different colors,
A printing apparatus, wherein the head driving means drives the plurality of dot forming element arrays at different timings so that dots of different colors are formed at different dot positions during the main scanning. The device of claim 1,
The head driving unit drives the dot forming element array in both the forward pass period and the return pass period of the main scanning,
The sub-scanning drive unit performs the sub-scanning by a fixed distance each time the forward path period and the return path period end, and both the scan repetition count s and the nozzle pitch k are selected to be even numbers. A printing device characterized by the above-mentioned. In a method of printing on the surface of a print medium using a print head having a dot forming element array formed by arranging N dot forming elements for forming dots of the same color at a constant pitch in the sub-scanning direction,
Performing a main scan of the print head;
Driving the dot forming element array during the main scan;
Each time the main scanning is completed, a process of performing the sub-scanning of the print head by a fixed distance, and repeating the main scanning required to print a continuous line in the main scanning direction by setting the distance of one sub-scanning to the sub-scanning pitch L. The number of scans is the number of scan repetitions s, the distance between the center points of the dot forming elements is a multiple of the dot pitch of the print image, the element pitch k, and the dots present per unit distance in the dot forming element array. When the number of forming elements is defined as element density D, respectively,
Selecting the scan repetition count s to be an integer less than N and equal to or greater than 2;
A step of selecting an arbitrary integer less than N and not less than 2 which is relatively prime to N / s as the element pitch k;
Selecting a value satisfying a relational expression of L = N / (sDk) as the sub-scanning pitch L. 9. The method of claim 8, wherein
Further comprising a step of selecting any of a plurality of print modes prepared in advance,
The step of selecting the number of scan repetitions s includes the step of selecting a first value according to the selected print mode as the number of scan repetitions s,
The step of selecting the element pitch k includes the step of selecting a second value corresponding to the selected print mode as the element pitch k.
A printing method characterized in that: The method of claim 9,
Performing the main scanning,
A printing method, comprising: varying the main scanning speed according to the selected first value so that the larger the first value is, the faster the main scanning speed is. 9. The method of claim 8, wherein
Driving the dot forming element array,
A printing method, comprising a step of driving the dot forming element array at intermittent timings corresponding to (s-1) every other dot during the main scanning. The method of claim 11, wherein
Driving the dot forming element array,
The dot forming element array is formed such that different dots in a dot matrix of s dots in the main scanning direction and k dots in the sub-scanning direction are respectively formed in different main scans in s × k main scan repetitions. A printing method comprising a step of driving. 9. The method of claim 8, wherein
Driving the dot forming element array,
A printing method comprising: driving a plurality of dot forming element arrays for forming dots of different colors at different timings so that dots of different colors are formed at different dot positions. 9. The method of claim 8, wherein
Driving the dot-forming element array includes driving the dot-forming element array during both the forward path and the return path of the main scanning,
Performing the sub-scan includes performing the sub-scan for a fixed distance each time the forward pass period and the return pass period end,
The step of selecting the number of scan repetitions includes the step of selecting a first even number as the number of scan repetitions s,
The printing method, wherein the step of selecting the nozzle pitch includes a step of selecting a second even number as the nozzle pitch k.