This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 02079712.2 filed in Europe on Nov. 6, 2002, which is herein incorporated by reference.
The present invention relates to a method of printing, in particular to a method of bi-directional printing. More in particular, the present invention relates to a method of printing using an ink-jet or laserjet printer having a resolution which is at least twice the resolution of the input image.
Methods are known for allowing a 600 dpi printer to print a 300 dpi bitmap. In printing, a droplet discharged from a print head nozzle to form a pixel has a ball-shaped leading portion and an elongated tail portion. During falling this tail portion may divide itself into two or more droplet parts. Due to the fact that the print head performs a continuous movement during a printing stroke, the ball portion will reach the printing surface, in particular paper, before the tail or other droplet parts will do so. The ball portion hits the paper at the desired location according to a grid based on the higher resolution of the printer to form a pixel. However, the remaining portions of the droplet will hit the paper at locations spaced from the center of the pixel in the direction of movement of the print head and form small satellite pixels.
According to a known method of printing, double pixels for a e.g., 600 dpi resolution are printed using a reciprocating print head having two rows of nozzles arranged perpendicular to the direction of travel, in which, as seen in the direction of travel, the leading row of nozzles is activated for discharging ink droplets to form the pixel located at the trailing side of the double-pixel to be formed. As a result, satellites will hit the paper at the downstream sides of the pixels. The images resulting from this process are blurred or have created vague edges which is unacceptable for 600 dpi printing.
This effect is even more noticeable when printing is performed according to a two pass bi-directional mode, in which, in a first swath, a first part of the leading row of nozzles is activated and in the adjacent, second swath, an adjacent, second part of the trailing row of nozzles is activated. The satellites will appear along the edges of the row of double-pixels in the first swath only, resulting in more or less step-like edges which intensifies the irregular appearance of the edges of the image.
In an attempt to find a solution to this problem it has been proposed to lower the speed of travel of the print head so as to decrease the distance between the location of the center of the pixel formed by the ball portion of the droplet and the location where the tail portion(s) of the droplets hit(s) the paper. In this solution, however, the printing time would increase resulting in less printing efficiency.
An object of the present invention is to improve on the known methods.
A further object of the present invention is to provide a method of printing double or multiple pixels having sharp edges on both sides.
Yet another object of the invention is to provide a method of two pass bi-directional printing at a high frequency resulting in a high resolution image with sharp edged double or multiple pixels.
From one aspect according to the present invention, these and other objects are realized by a method of printing pixel images on a sheet or web of paper using an ink-jet or laserjet printer, wherein the printer has means for storing an input image corresponding to the pixel image in the form of a first grid of imaginary lines according to a first resolution, and the printer is adapted to print the pixel image in the form of a second grid of imaginary lines according to a second resolution which is a plurality of the first resolution. The printer has a print head with at least one nozzle and is provided with control means which operates the print head in accordance with the input image recorded in the storing means. The print head reciprocates across the sheet or web of paper along a first path in a first direction and along a second path in a second, opposite direction, wherein the pixel image has first pixels located at a first edge which forms an upstream edge with respect to the movement of the print head in the first direction and second pixels located at a second edge which forms an upstream edge with respect to the movement of the print head in the second direction. All first pixels at the first edge are printed through activation of the print head nozzle by the control means to discharge an ink droplet at a line of the second grid which coincides with the first edge at that location when moving in the first direction, and all second pixels at the second edge are printed through activation of the print head nozzle by the control means to discharge an ink droplet at a line of the second grid which coincides with the second edge at that location when moving in the second direction.
From a second aspect, the present invention provides a method of printing pixel images on a sheet or web of paper using an ink-jet or laserjet printer, wherein the printer has a resolution which is a plurality of the resolution of the input image, the printer has a print head which reciprocates across the sheet or web of paper along a first path in a first direction and along a second path in a second, opposite direction, the pixel images consist of a plurality of pixels located adjacent to each other as viewed in said first and second directions, including first and second pixels to be placed at the leading or upstream edges of the image in question as considered in the first and second directions, and wherein the print head is controlled to discharge an ink droplet for forming the first and second pixels only when moving in the first and second directions, respectively.
In the method according to the present invention, the satellites will always hit the paper at a location which is within the intended area of the double or multiple pixel, in other words in the area which is indeed to be covered by ink. As a result, the edges of the printed image will be sharp, without requiring the printing speed to be decelerated.
In a further embodiment, the second or printer resolution is twice the first or input image resolution, in particular 600 dpi.
In an advantageous embodiment of the method according to the present invention, use is made of a print head having a first and a second row of nozzles arranged according to lines transverse to said first and second directions, wherein said first row of nozzles is located at the downstream side of the print head when moving in the first direction, and the second row of nozzles is located at the downstream side of the print head when moving in the second direction, the first pixels are printed by activating the first row of nozzles and the second pixels are printed by activating the second row of nozzles.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
In
In
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When the printer head 1 is moved in the direction A, the —not shown-control system of the printer activates the nozzles 10a-h to discharge ink droplets 2 such that the ball portion 3 of the ink droplets will hit the paper sheet 5 at line 7a of the grid 6. The tail parts 4a, 4b or satellites will hit the paper sheet 5 at the down stream side of the ball portions 3.
In the return stroke, depictured in
In
The present invention is described with an inkjet head having two rows of nozzles (10a-h; 11a-h) but also a head having a single row can be used for the present invention.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included with the scope of the following claims.
Number | Date | Country | Kind |
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02079712.2 | Nov 2002 | EP | regional |