1. Field of the Invention
The present invention relates to an inkjet printer and inkjet printing method, in particular, it relates to an inkjet printer and inkjet printing method for printing small droplet of ink at a high density and high frequency.
2. Description of the Related Art
Small droplet, high density nozzles and high driving frequencies have been promoted in inkjet printers. Under such circumstances, there has recently arisen a new problem called “end-deviation.”
The “end-deviation” is generally easily checked as the ejection volume becomes small, the ejecting frequency is high and the arrangement density of the ejection ports is high, in particular, it becomes apparent when the ejection volume is not more than 10 pl.
Regarding the “end-deviation” as described above, various countermeasures have been proposed. For example, a constitution is disclosed that an amount of the ink droplets ejected from the ejection ports positioned at the further end is set large in advance in arranging a plurality of ejection ports in the printing head. Thus, an inertia weight of the ink droplets from the end can be increased, and the airflow in the vicinity of the end hardly has influence on the ink droplets. However, making the ink droplets lager prevents an image having high definition and high gradation from being formed. In the inkjet printer having the advantage of performing printing with small droplets of ink at a high definition, increasing the ejection volume although partially is not suitable as a solving method of the end-deviation.
On the other hand, Japanese Published Unexamined Patent Application No. 2003-145775 discloses a printing head in which ejection ports positioned at the end are arranged at pitches larger than that of the center. For example, ejection ports positioned in the vicinity of the end are arranged at larger intervals than 21.2 μm in anticipation of the print position deviation, so that dots are printed on the print medium at pitches of 21.2 μm even if the end-deviation arises. However, even when a low duty image, in which the end deviation can hardly arise, is formed with the printing head having such a constitution, a print position of the ink droplets ejected from the ejection ports positioned at the end is deviated further outward. Accordingly, in this case, an area arises in which the connecting part between the print scans excessively overlap with each other, and there is a risk that black streaks become conspicuous.
The “end-deviation” arises under conditions with a small ejection volume, a high ejecting frequency, and a high print density. Accordingly, if any one of the conditions is removed, the “end-deviation” can be reduced. However, these conditions are all essential for printing an image having a high resolution and high quality at a high speed. Accordingly, a reducing method of the “end-deviation” without removing the conditions is demanded.
Japanese Patent Laid-Open Nos. 2002-096455 and 2002-292910 disclose a reducing method of the “end-deviation” adverse effects by providing a mask pattern to be used in performing a multi-pass printing method with features.
However, in the multi-pass printing method, printing is not performed for all printable pixels by only one print scanning. For example, in the two-pass type multi-pass printing, printing is performed for approximately half of all printable pixels via the ejection ports positioned at the lower half part of the printing head 1200 in a first print scanning. When the first print scanning is performed, the print medium is conveyed by a length corresponding to half of a print width of the printing head 1200 in a sub-scanning direction in
In the following second print scanning, printing is performed for the remaining pixels via the ejection ports positioned at the upper half part of the printing head 1200 in the image area where the printing has already been performed for approximately half of all pixels by the first print scanning. In addition, in the second print scanning, the lower half part of the printing head 1200 performs printing for the pixels of approximately half of the blank area adjacent to the image area. When the second print scanning ends, the print medium is further conveyed by the length corresponding to half of the print width of the printing head 1200 in the sub-scanning direction in
In the two-pass type multi-pass printing method, the image is formed in stages by alternately repeating the above print main scanning to half of all pixels and the sub-scanning of the length corresponding to half of the print width. According to the multi-pass printing method, the image is formed in the identical image area on the print medium by a plurality of print scannings via the ejection port groups different from each other in the printing head. Accordingly, even if there are variations in the ejecting direction and the ejection volume of the ejection ports, and even if there are some variations in conveying amount of the print medium, it is possible to make adverse effects due to the variations inconspicuous. Furthermore, although the two-pass type multi-pass printing method for completing an image by the two print main scannings is described above with reference to
When the above-described multi-pass printing method is employed, a mask pattern, in which permission or non-permission of printing is determined, is frequently used in order to determine pixels for which the printing is to be performed by each print main scanning. Various image quality items other than uniformity can be improved by providing such a mask pattern with various features.
FIG. 6 is disclosed in Japanese Patent Laid-Open No. 2002-096455, and is a view showing mask patterns which are improved to avoid the end-deviation. Here, a printing head having 768 ejection ports is employed, and mask patterns used for performing four-pass type multi-pass printing is shown. The size of the mask pattern is 768 are as corresponding to the number of ejection ports in a vertical direction, and 256 are as in a horizontal direction. An area shown by black is a print permission pixel, and an area shown by white is a print non-permission pixel. The print permission or print non-permission of each pixel is determined so that the four mask patterns corresponding to four ejection port groups respectively are complementary to each other.
As shown in
Japanese Patent Laid-Open No. 2002-96455 discloses that a bias is provided between the numbers of print permission pixels in accordance with positions of ejection ports. Furthermore, Japanese Patent Laid-Open No. 2002-96455 discloses that it is effective to lower the print permission rate of the ejection port positioned at the end compared with that of the ejection port positioned at the center as shown in FIG. 6 to reduce the “end-deviation.”
However, currently when reduction in the ejection volume is being further promoted, as the inventors carried out a diligent examination, they confirmed that only droplet ejected from the ejection port at the end are not always deflected toward the center.
In
Even if an image is formed by using the mask patterns (FIG. 6) disclosed in Japanese Patent Laid-Open No. 2002-096455 for the printing head in such a print state, the density unevenness is not reduced. If the mask patterns shown in FIG. 6 are used which extremely reduce the print permission rate of the end area having few deviations and raises the print permission rate of the area having many deviations, adverse effects due to the density unevenness becomes more conspicuous.
In order to solve the above problems, the present invention has been made. An object of the present invention is that an image having a high quality is output, in which density unevenness due to a deflection in an ejecting direction is reduced, in an inkjet printer for forming an image by ejecting small droplets of ink at a high frequency and high density.
The first aspect of the present invention is an inkjet printer for printing an image on a print medium by ejecting ink from a printing head having an ejection port array based on a print permission rate determined in advance for the ejection port array while moving the printing head with respect to the print medium, wherein respective print permission rates of respective ejection ports positioned at both ends of the ejection port array are higher than that of a ejection port positioned at the center of the ejection port array.
The second aspect of the present invention is an inkjet printer for printing an image on a print medium by ejecting ink from a printing head having first ejection port array and second ejection port array based on a print permission rates determined in advance for the respective first and second ejection port arrays while moving the printing head with respect to the print medium, wherein respective print permission rates of respective ejection ports positioned at both ends of the first ejection port array are higher than that of a ejection port positioned at the center of the first ejection port array, and respective print permission rates of respective ejection ports positioned at both ends of the second ejection port array are lower than that of a ejection port positioned at the center of the second ejection port array.
The third aspect of the present invention is an inkjet printer for printing an image on a print medium by moving a printing head comprising a plurality of ejection port arrays each having an arrangement of ejection ports for ejecting ink with respect to the print medium comprising: means for completing an image to be printed in an identical area in the print medium by printing an image in accordance with a mask pattern in each of a plurality of movements of the printing head, the mask pattern having a print permission rate determined for every ejection port, wherein in the mask pattern corresponding to at least one of the ejection port arrays among the plurality of ejection port arrays, respective print permission rates of respective ejection ports positioned at both ends of the ejection port array are set higher than those of respective ejection ports positioned at the other parts of the ejection port array.
The forth aspect of the present invention is an inkjet printing method for printing an image on a print medium by ejecting ink from a printing head having an ejection port array composed of an arrangement of ejection ports for ejecting the ink based on a print permission rate determined in advance for the ejection port array while moving the printing head with respect to the print medium in a direction crossing the arrangement direction of the ejection ports, wherein respective print permission rates of respective ejection ports positioned at both ends of the ejection port array are higher than that of a ejection port positioned at the center of the ejection port array.
The fifth aspect of the present invention is an inkjet printing method for printing an image on a print medium by ejecting ink from a printing head having first ejection port array and second ejection port array based on a print permission rates determined in advance for the respective first and second ejection port arrays while moving the printing head with respect to the print medium, wherein respective print permission rates of respective ejection ports positioned at both ends of the first ejection port array are higher than that of a ejection port positioned at the center of the first ejection port array, and respective print permission rates of respective ejection ports positioned at both ends of the second ejection port array are lower than that of a ejection port positioned at the center of the second ejection port array.
The sixth aspect of the present invention is an inkjet printing method for printing an image on a print medium by moving a printing head having a plurality of ejection port arrays each having an arrangement of ejection ports for ejecting ink with respect to the print medium comprising the step of: completing an image to be printed in an identical area in the print medium by printing an image in accordance with a mask pattern in each of a plurality of movements of the printing head, the mask pattern having a print permission rate determined for every ejection port, wherein in the mask pattern corresponding to at least one of the ejection port array among the plurality of ejection port arrays, respective print permission rates of respective ejection ports positioned at both ends of the ejection port array are set higher than those of respective ejection ports positioned at the other parts of the ejection port array.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
An embodiment of the present invention will be described below citing a serial type inkjet printer having printing heads provided with a plurality of ejection port arrays as an example.
The ink of four colors are printable via the printing head 1, and cyan ink, magenta ink, yellow ink and black ink are respectively supplied from the ink tanks. The printing head 1 is positioned and changeably mounted on the carriage 502, a connector holder (electrical connecting part), in which a driving signal, etc., is transmitted to the printing head 1 via a connector, is provided on the carriage 502.
The carriage 502 moves along a guide shaft 503 provided in an apparatus main body while being guided and supported in a main scanning direction. Driving force of a main scanning motor 504 is transmitted to a motor pulley 505, a following pulley 506 and a timing belt 507, and thus the carriage 502 moves, and a position and a movement amount thereof are controlled.
A print medium 508 such as a sheet of paper or plastic thin plate is conveyed so as to pass through a position (print part) opposite a ejection port surface of the printing head 1 by rotation of two sets of conveying rollers (509 and 510, and 511 and 512). Moreover, the back side of the print medium 508 is supported by a platen (not shown) so that the print medium 508 can form into a flat printing surface in the print part. The ejection port surface of the printing head 1 mounted on the carriage 502 is projected downward from the carriage 502 and held between the two sets of conveying rollers (509 and 510, and 511 and 512) so as to be kept parallel with the print medium 508.
Electric thermal converters (heater) 26, which are thermal energy generating means, are arranged on a substrate 24 at pitches of 600 dpi in a sub-scanning direction, on both sides in a longitudinal direction of the ink supplying port 20. Furthermore, the two heater arrays are arranged so as to deviate from each other by a half pitch in the sub-scanning direction.
A coated resin layer 29 for introducing the ink into each heater is adhered to the substrate 24. Flow paths 27 and the ink supplying port 20 are formed in the coated resin layer 29, the flow paths 27 each being formed at the position corresponding to the heater, and the ink supplying port 20 being capable of evenly supplying the ink to each flow path 27. A tip of each flow path 27 forms into an ejection port 28 for ejecting ink droplets cased by a film boiling effect by the heater 26.
In the above constitution, a voltage is applied to each heater at a predetermined timing while the printing head is moved in a main scanning direction, and thus the ink droplets supplied from the same ink supplying port 20 can be printed at a resolution of 1200 dpi in the sub-scanning direction.
One kind of ink is supplied to one ink supplying port 20. A plurality of ink supplying ports 20 are juxtaposed on the substrate 24, and various kinds of ink can be respectively ejected from the ink supplying ports 20.
The host device 704 connected to the exterior of the printer is a supplying source of the image data. However, the device 704 may be a computer for preparing and processing data such as an image to be printed, a reading part for reading the image, etc. Image data, other commands, status signals, etc., are transmitted/received to/from the controller 700 via an interface (I/F) 712.
An operating part 705 is a switch group for receiving an instruction input from an operator, and includes: a power source switch 706; a print switch 707 for instructing the controller to start printing operation; and a recovery switch 708 for instructing the controller to start maintenance processing for the printing head.
A head driver 709 is a driver for driving the electric thermal converters 26 of the printing head 1 in accordance with print data, etc. The head driver 709 includes: a shift register for making the print data align in accordance with the positions of the electric thermal converters 26; a latch circuit for latching at a proper timing; a logic circuit element for operating the electric thermal converters 26 in synchronization with a driving timing signal; a timing setting part for suitably setting a driving timing (ejecting timing) for dot formation positioning; etc.
A sub-heater 712 is provided in the printing head 1. The sub-heater 712 performs a temperature adjustment for stabilizing ink ejecting features. Although the sub-heater 712 may be formed on the substrate 24 of the printing head together with the electric thermal converter 26, this may be attached to a main body of the printing head 1.
A motor driver 711 is a driver for driving the main scanning motor 504, and a motor driver 713 is a driver for driving a sub-scanning motor 714 for generating force for rotating the conveying rollers.
In a first print scanning, printing is performed for pixels of approximately 50% in forward direction via the 128 ejection ports of each color positioned at the lower half part of the printing head 1. When the first print scanning ends the print medium is conveyed by a length corresponding to half of a print width of the printing head 1 in the sub-scanning direction in
In the following second print scanning, printing is performed for the remaining pixels of 50% in backward direction in the image area, where the printing has already been performed for the pixels of approximately 50% by the first print scanning, via the 128 ejection ports positioned at the upper half part of the printing head 1. In addition, in the second print scanning, the lower half part of the printing head 1 performs printing for pixels of approximately 50% of a blank area adjacent to the image area. When the second print scanning ends, the print medium is further conveyed in the sub-scanning direction in
As printing conditions in the embodiment, the moving speed of the carriage in the print scanning was 25 inch/sec, and 100% printing was performed by the printing head for the pixels arranged at pitches of 1200 dpi, and the distance between the print medium and ejection port surface was fixed at 1.0 mm. If the two-pass type multi-pass printing is performed with generally used random mask patterns under such conditions, the print position deviation arises having a tendency as shown in
On the other hand, when printing is performed with the mask patterns shown in FIG. 6 disclosed in Japanese Patent Laid-Open No. 2002-096455, the density unevenness is further increased.
As described referring
However, if the two-pass type multi-pass printing is performed with the mask pattern of
When the multi-pass printing is performed with mask patterns 1400 and 1401 in which the print permission rates of the ejection ports at both ends are thus set higher than those of the ejection ports positioned at the other parts, the print position deviation shown in
Furthermore, although the ejection port arrays 1302 to 1305 for four colors are arranged in the printing head of the embodiment, the mask patterns shown in
In addition, the print permission rate of ejection ports positioned at the both end and at the center is not limited to the combination of 75% and 25%. The print permission rate of ejection ports positioned at the both end and at the center may be a combination of 90% and 10% or a combination of 60% and 40%, for example. If a mask pattern in which the print permission rates of the ejection ports positioned at both ends are set higher than those of the ejection ports positioned at the other parts (for example, center parts) is provided, the mask pattern may have applicability to this invention.
A second embodiment of the present invention will be described hereinafter. The inkjet printer and inkjet printing head as described with reference to
When an image is thus formed in a plurality of stages of ejection volume regarding one color, print data is adjusted for every ejection port array in accordance with an input density signal.
In the embodiment, the mask pattern 1400 or 1401, in which the print permission rate of the end is higher than that of the center, shown in
According to the embodiment as described above, when an image is printed with a printing head having a plurality of ejection port arrays corresponding to ejection volumes of a plurality of stages, a mask pattern, in which the print permission rates of both ends are set higher than those of the other parts, is made to correspond to the ejection port array having a smaller ejection volume. Thus, the image can be obtained which has no end-deviation and density unevenness and has high definition.
Furthermore, although the two-pass type multi-pass printing is cited in the above embodiments, the present invention is not limited thereto. In this case, when the number of passes is changed, a substantial ejecting frequency of the printing head is also changed. Accordingly, even in the case where the same printing head is used, it can be assumed that the tendency of the print position deviation is changed by changing the number of passes. That is, although the tendency of the print position deviation as shown in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Laid-Open No. 2006-130790, filed May 9, 2006, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2006-130790 | May 2006 | JP | national |
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Number | Date | Country |
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2002-96455 | Apr 2002 | JP |
2002-292910 | Oct 2002 | JP |
2003-145775 | May 2003 | JP |
Number | Date | Country | |
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20070285450 A1 | Dec 2007 | US |