Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-03-24
2002-08-06
Hallacher, Craig A. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S010000, C347S037000
Reexamination Certificate
active
06428138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that creates dots to print an image on a printing medium. More specifically the invention pertains to a printing apparatus that enables adjustment of the positions of dot formation in the respective pixels in the main scanning direction.
2. Description of the Related Art
A variety of printers have been used widely to print multi-color, multi-tone images as the output device of the computer and the digital camera. One of such printers is an ink jet printer that causes several color inks to be ejected from a plurality of nozzles formed on a print head, so as to create dots and record an image. In order to attain the high quality printing in this printer, it is desirable to form dots without any significant positional misalignment.
The ink jet printer generally has a print head with a large number of nozzles for the purpose of the improvement in printing speed.
FIG. 4
shows one example of the applicable print head. In the example of
FIG. 4
, a plurality of nozzle arrays, each including a plurality of nozzles Nz arranged at fixed intervals in the sub-scanning direction, are disposed in the main scanning direction. The print head often has a plurality of nozzle rows with regard to each color ink to allow the closely packed arrangement of nozzles. In the example of
FIG. 4
, each color ink, for example, yellow (Y) ink, has two nozzle rows, that is, a 0
th
nozzle row and a 1
st
nozzle row.
FIG. 27
shows a process of printing with a print head having a plurality of nozzle rows. In the example of
FIG. 27
, a print head HD having two nozzle rows, that is, a 0
th
nozzle row and a 1
st
nozzle row, is shifted in a predetermined direction to carry out printing. Symbols A and B respectively represent the positions of the print head HD in the main scanning direction at preset timings. Rectangles P
1
and P
2
respectively denote pixels. An ink droplet Ip is ejected from a nozzle included in the 0
th
nozzle row at the preset timing A, so that one dot is formed in the pixel P
1
. The print head HD then moves in the predetermined direction. At the preset timing B after elapse of a predetermined time period, a nozzle included in the 1
st
nozzle row reaches the position that has been occupied by the nozzle of the 0
th
nozzle row at the preset timing A. An ink droplet Ip is ejected from the nozzle included in the 1
st
nozzle row at the preset timing B, so that another dot is formed in the pixel P
1
.
In the printer with the print head HD having the plurality of nozzle rows, the timings of ejecting ink droplets from the respective nozzle rows are varied according to an interval D of the adjoining nozzle rows and a moving speed Vc of the print head HD, so that dots are created in each pixel. Namely dots are formed in each pixel by outputting driving signals, which cause the nozzles Nz to eject ink droplets Ip, at a preset time difference between the respective nozzle rows.
In the prior art printer, however, there may be a positional misalignment of dots in the main scanning direction formed by the plurality of nozzle rows, due to reasons discussed below. The positional misalignment results in the poor picture quality. For example, the interval D between the adjoining nozzle rows may be varied, due to an error in the manufacturing process. In another example, the respective nozzles may have varying ink ejection characteristics, that is, ink ejection speed and direction. In the prior art printer, these variations may cause a positional misalignment of dots in the main scanning direction.
FIG. 28
shows the effects of a positional misalignment of dots in the main scanning direction on the picture quality. The open circles represent the dots formed by the 0
th
nozzle row shown in
FIG. 27
, whereas the closed circles represent the dots formed by the 1
st
nozzle row. The left column of
FIG. 28
shows an ideal alignment of dots to be formed. The right column of
FIG. 28
, on the other hand, shows a positional misalignment of dots in the main scanning direction formed by the respective nozzle rows. The positional misalignment is recognized as undesirable bents of a straight line and thereby deteriorates the printing quality. With the development of the high-resolution, high-quality printers, the deterioration of the picture quality due to the positional misalignment of dots in the main scanning direction is not negligible.
In order to cancel the positional misalignment of dots in the main scanning direction, one applicable method regulates the dot formation timings with regard to each nozzle row. This method provides separate driving waveform generation circuits and delay circuits with regard to the respective nozzle rows for regulating the output timings of driving waveforms and individually regulates the dot formation timings with regard to the respective nozzle arrays, in order to prevent the positional misalignment of dots in the main scanning direction. Unlike the prior art printer that ejects ink at a fixed timing preset for each nozzle row, this arrangement enables the regulation of the dot formation timings according to the ink ejection characteristics of each nozzle row.
This method, however, requires the additional circuits to regulate the dot formation timings with regard to the respective nozzle rows. In order to attain the richer tone expression, the printer often uses inks of different densities for some colors. This increases the number of different color inks and thereby the number of nozzle rows on the print head. The additional circuits provided for the respective nozzle rows thus cause a significant increase in manufacturing cost of the printer.
The printing method that forms dots both in the forward pass and in the backward pass of the main scan (hereinafter referred to as the bi-directional printing) has been proposed recently to improve the printing speed. In the case of the bi-directional printing, there may be a positional misalignment of dots in the main scanning direction formed in the forward pass and formed in the backward pass, due to the backlash of the mechanism carrying out the main scan or other causes. Namely the bi-directional printing has the same problem as that occurring in the structure having a plurality of nozzle rows in the main scanning direction.
The positional misalignment of dots is the problem commonly arising when there are two or more different conditions with regard to the dot formation timing, for example, a difference in position in the main scanning direction between adjoining nozzle rows and a difference in moving direction of the print head in the course of dot formation. This problem is found not only between a plurality of nozzle rows with regard to one color ink but between nozzle rows of different color inks. The problem is not restricted to the print head having the arrangement of nozzles shown in
FIG. 4
, but arises in any print head having nozzles disposed at different positions in the main scanning direction. The problem is found not only in the ink jet printer but a variety of other printing apparatuses that create dots to print an image.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique of preventing a positional misalignment of dots in the main scanning direction and thereby improving the picture quality of the resulting printed image without causing a significant expansion of the circuit structure for driving a print head in a printing apparatus that prints an image with the print head.
At least part of the above and the other related objects is attained by a printing apparatus with a print head having a dot forming element, which creates a dot in response to a driving signal. The printing apparatus carries out main scan, which moves the print head forward and backward relative to a printing medium in a predetermined direction of the printing medium, and creates different dots, which have different dot forming conditions with regard to an ejection timing of ink into each pixel
Asauchi Noboru
Otsuki Koichi
Hallacher Craig A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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