Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-11-09
2003-04-15
Nguyen, Judy (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C358S001900
Reexamination Certificate
active
06547355
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to a printing apparatus and printing method for printing images through formation of monochrome or multi-color dots on a recording medium during main scanning.
BACKGROUND ART
An inkjet printer is used as a device for outputing images processed by a computer or images captured by a digital camera. An inkjet printer forms dots by ejection of ink of various colors such as cyan, magenta, yellow and black, for example. Dots of each color are typically ejected from a print head while the print head is moving in a main scanning direction. If the positions at which the dots of each color are formed are misaligned, it would cause a problem of reduced image quality.
This problem of image quality deterioration due to dot formation misalignment occurs in both uni-directional recording and bi-directional recording. Here, uni-directional recording refers to a recording method in which, where the print head moves back and forth along the main scanning passes, the dots are ejected only when the print head is moving along one of the passes. Bi-directional printing refers to a recording method in which dots are ejected when the print head is moving along both of the main scanning passes. While the problem of dot position misalignment typically occurs with respect to dots of different colors in uni-directional printing, it occurs in bi-directional printing with respect to dots of the same color formed during forward and reverse passes.
In the conventional printer, the dot position misalignment may be reduced by adjusting the formation positions of color dots in the main scanning direction while using black dots as a reference, for example. This type of dot position misalignment adjustment is realized by a head drive circuit that supplies drive signals to the print head while changing the output timing of the drive signals.
However, the above-described conventional dot position misalignment adjustment method has various inherent limitations. For example, because the drive signal timing can be changed only for the entire print head in a typical printer, dot position misalignment adjustment is limited to what can be achieved by the timing change.
The present invention was made in order to resolve the abovementioned problem with the conventional art, and an object thereof is to provide the technique that reduces the dot position misalignment in the main scanning direction using a means other than changing the drive signal output timing from the head drive circuit, thereby improving image quality.
DISCLOSURE OF THE INVENTION
In order to attain the above object, in the present invention, while performing main scanning in which a head having a plurality of nozzles that eject ink is moved in prescribed forward and reverse directions relative to a print medium, sub-scanning is carrying out in which the print medium is forwarded in a sub-scanning direction perpendicular to the main scanning direction relative to the head. The head is driven in accordance with print data along at least one of the forward or reverse scanning passes. Dots are formed in at least some of the a plurality of pixels aligned in the main scanning direction. The dot formation position misalignment for each nozzle in the main scanning direction are corrected using image pixel value data indicating a dot formation status regarding image pixels that constitute images, as well as adjustment pixel value data that indicates existence of adjustment pixels in which dots are not formed and are used to adjust positions of the image pixels in the main scanning direction. In this arrangement, as dots are formed in accordance with the print data, the misalignment of the formation positions of the dots from each nozzle in the main scanning direction is corrected using (i) image pixel value data indicating the dot formation status in image pixels that comprise the image, and (ii) adjustment pixel value data indicating the existence of adjustment pixels in which dots are not formed and which are used to adjust positions of the image pixels in the main scanning direction. Various aspects of the present invention will be explained below.
(1) Allocation of Adjustment Pixels at Either End of Main Scanning Direction
First, the allocation of the adjustment pixels are set to one or both ends of the image pixel value data so that the amount of the dot formation position misalignment is corrected. Here, the ‘allocation of adjustment pixels to one or both ends’ may include the case in which adjustment pixels are not allocated at one end. Raster data is generated from the image pixel value data and the allocation of the adjustment pixels. The raster data has the image pixel value data and the adjustment pixel value data placed at least one side of the image pixel value data. The print data including the raster data is then generated. The head is thereafter driven in accordance with the print data while main scanning is being performed.
According to this aspect of the present invention, the misalignment of the dot formation positions can be corrected and high-quality printing can be realized by giving the following characteristics to the print data for driving the head. Typically, print data includes those multi-level data for each of pixels arrayed in a predetermined number, which are converted from image tone values. This multi-level data corresponds to the image pixel data in the present invention. The print data in the present invention contains, in addition to the image pixel data, data regarding a prescribed number of adjustment pixels in the main scanning direction. The adjustment pixel data represent the blank left and right margins in the main scanning direction.
Through the use of print data having this structure, the printing apparatus of the present invention can correct dot formation position misalignment within the range attained by the adjustment pixels. An example will be described in which main scanning is performed from left to right. Assume that the head includes a nozzle that forms dots to the left of the target pixel position due to its ink expulsion characteristic. In the printing apparatus of the present invention, the amount of dot formation misalignment attributable to the nozzle is stored beforehand. Here, the amount of misalignment is assumed to be one pixel. In the present invention, the position at which a dot is formed by this nozzle is shifted in accordance with this stored misalignment amount, and print data is generated accordingly. In other words, print data is generated in which a dot is formed at a position that is shifted to the right by one pixel from the target pixel position. This is equivalent to setting the adjustment pixel allocation such that the number of adjustment pixels on the right side is reduced by one and the number of adjustment pixels on the left side is increased by one in the main scanning direction, relative to those in the case in which the dot could be formed at the correct position. When ink is ejected from this nozzle based on this print data, the abovementioned dot formation shift occurs, and a dot is formed at the pixel on which it should be.
In the printing apparatus of the present invention, dot formation position misalignment may be corrected in pixel-width increments based on this principle. In recent years, pixel width in the main scanning direction has become extremely small, and it has become possible to sufficiently correct for dot formation position misalignment for each nozzle by shifting the dot formation position in pixel-width increments. Therefore, high-quality printing may be attained with the printing apparatus of the present invention. Moreover, because the present invention does not require new hardware for the head driving mechanism in order to carry out the above correction, it is possible to reduce the degree of dot formation position misalignment with relative ease.
In the present invention, the print data may be generated in various steps. For example, print data may be generated in two steps comprising a first step wherein basi
Hayashi Toshihiro
Kanaya Munehide
Otsuki Koichi
Shimada Kazumichi
Mouttet Blaise
Nguyen Judy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
LandOfFree
DOT formation position misalignment adjustment performed... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DOT formation position misalignment adjustment performed..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DOT formation position misalignment adjustment performed... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3054035