Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-06-07
2002-01-08
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S040000
Reexamination Certificate
active
06336703
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a technology for expanding the area in which an image is printed by a printer that uses interlaced printing to print images by forming dots while effecting sub-scanning.
DESCRIPTION OF THE RELATED ART
In order to increase the printing speed of printers that use a dot printing head to form raster lines while performing sub-scanning at right-angles to the raster lines, most such printers are equipped with an array of nozzles arrayed in the sub-scanning direction. This is particularly true in the case of inkjet printers. In recent years, to achieve higher speeds, there has been a trend toward increasing the number of nozzles in the sub-scanning direction, increasing the size of nozzle arrays.
The interlaced printing system disclosed by U.S. Pat. No. 4,198,642 is one technology that is used to improve the quality of printing by such printers.
FIG. 18
illustrates an example of interlaced printing. In this example, the number N of dot-formation nozzles is three. The pitch k of the raster lines laid down by the nozzles, that is, the spacing between nozzle raster line centers, is two raster lines. In the sub-scanning direction, the paper is fed in length L increments of three raster lines. In
FIG. 18
, the two-digit number in each circle denote the position at which each dot is printed. With further respect to the two-digit numbers, the digit on the left is the number of the nozzle used to print the dot, while the digit on the right indicates the number of the main scanning unit pass during which the dot is printed.
In the example of
FIG. 18
, during the first pass, dot raster lines are formed by the second and third nozzles, and the first nozzle is not used. The paper is then advanced by an amount corresponding to three raster lines, and the second main scanning unit is performed, during which a raster line is printed by each of the three nozzles. The image is printed by repeating this process of raster line formation and paper advance. The first nozzle is not used to form a raster line during the first pass to enable it to be used to form adjoining raster lines therebelow, during the second and subsequent passes.
Interlaced printing enables the effect of variations in nozzle pitch, sub-scan feed precision, ink emission properties and the like to be diffused, thereby enabling the image quality to be improved by reducing the deviation in dot position caused by such factors. Interlaced printing can be implemented using various paper feed amounts according to the number of scanning passes to complete dot formation on each raster line, the number of nozzles, nozzle pitch and so forth.
However, a problem with interlaced printing is that at the lower end of the paper there is an area in which printing cannot be accomplished. This is shown by
FIG. 19
, which illustrates an example of interlaced printing using a print head having seven nozzles disposed at a pitch corresponding to four raster lines. The paper is fed in the sub-scan direction in set increments of seven raster lines each. The circles represent the position of the head in the sub-scanning direction, during each main scanning unit pass. The numbers in the circles are the nozzle numbers.
FIG. 19
shows seven main scanning unit passes, from L−6 to L, at the lower end of the page being printed. In this explanation, nozzle number
7
in main scanning unit pass L is taken to be at the lower limit at which a nozzle can be positioned during printing. As can be seen, interlaced printing gives rise to a blank raster line, a raster line on which dots are not printed, shown here as the raster line adjoining the lower end of the area A. This means that printing cannot be effected in the 18-raster line area that extends from the area A down to the lower limit.
The greater the number of nozzles there are in the array, the larger the unprintable area becomes. The growing size of nozzle arrays in recent years has made it impossible to ignore this unprintable area. A large such area reduces the value of a printer. Moreover, with the demand being for higher print quality and faster speeds, reducing the size of the unprintable area at the expense of print quality is unacceptable.
SUMMARY OF THE INVENTION
This invention was accomplished to overcome the foregoing problems of the related art and has as its object to provide a technology which, during interlaced printing, ensures an adequate printable area without any excessive loss of print quality.
The present invention provides a printer having the following configuration.
In accordance with the present invention, there is provided a printer that prints an image on a print medium by using a print head to form raster lines in a primary direction and scan in a sub-scan direction at right-angles to the raster lines. The printer comprising:a print head having a plurality of dot formation elements disposed in a sub-scanning direction at a prescribed spacing that is not less than two dots, and dot formation elements for forming dots of a different type, disposed separately in the sub-scanning direction; a first transport unit that effects sub-scanning by transporting at a first precision at least one selected from the print head and the print medium;a second transport unit that, when sub-scanning cannot be effected by the first transport unit, effects sub-scanning by transporting at a second precision that is lower than the first precision at least one selected from the print head and the print medium;a data supply unit that assigns to the dot formation elements raster data for forming raster lines for printing the image, supplies the data to the print head, and also performs masking of dot formation elements where there are no raster lines to be formed;a raster line formation unit that drives the print head to form each raster line in accordance with the data supplied by the data supply unit; and a sub-scanning unit that performs sub-scanning by a preset feed amount when there arises a condition in which, in sequential usage of the first and second transport unit, an area is formed in which raster lines formed during sub-scanning effected by the second transport unit are included between raster lines formed during sub-scanning effected by the first transport unit. This is intended for printers with print heads having formation elements for different types of dots arrayed in the main scanning unit direction, such as a multicolor printer having a print head in which the elements for forming the dots of each color are arrayed in the main scanning unit direction.
Printers usually have a unit for effecting high-precision sub-scanning during printing, and a unit of ejecting the paper after the printing is finished. In the case of the printer of this invention, the first transport unit is used as the former and the second transport unit as the latter. Moreover, when sub-scanning by the first transport unit is no longer possible, printing continues using the second transport unit to effect sub-scanning. As explained above, when printing by the interlaced method, although sub-scanning may be effected down to the lower limit with respect to nozzle position, below that is an unprintable area. In this respect, the second transport unit of the printer of this invention enables the lower limit of sub-scanning to be extended, thereby increasing the area that can be printed using interlaced printing.
In addition, sub-scanning by the printer of this invention produces an area that includes raster lines formed by the second transport unit between raster lines formed by the first transport unit. The first and second transport unit are used sequentially, so printed images are comprised of an area printed by the first transport unit (hereinafter also referred to as “high-precision area”), an area comprised of raster lines formed by both the first and second transport unit (hereinafter also referred to as “mixed-raster line area”), and an area printed by the second transport unit (hereinafter also referred to as “low-precision area”), in that order, or the re
Le N.
Nguyen Lamson D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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