Facsimile and static presentation processing – Static presentation processing – Position or velocity determined
Reexamination Certificate
1999-04-14
2002-06-11
Evans, Arthur G. (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Position or velocity determined
C358S001180
Reexamination Certificate
active
06404507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to control of a printer carriage in an ink jet printer which prints by reciprocal scans of a print head. In particular, the present invention relates to control of such a printer so as to accommodate speed non-uniformities and image degradation that result from high speed movement of an ink jet head.
2. Description of the Related Art
Ink jet printers have become increasingly popular for printing text, continuous data such as non-color graphics, and color images from a host computer onto recording media. In addition, ink jet print heads increasingly are used in devices other than printers, such as copying machines. The demand for faster ink jet printing techniques has grown along with this increased prevalence of ink jet printing.
One technique for increasing the speed of ink jet printing is to increase the speed at which an ink jet print head scans across a recording medium, for example by using a faster motor to drive an ink cartridge receptacle that holds an ink jet cartridge having the print head. However, faster motors tend to suffer from greater speed non-uniformities than slower motors, particularly at the start of a scan operation. These speed non-uniformities can result in rippled or otherwise degraded image formation.
Another technique for increasing the speed of ink jet printing is to use bi-directional printing, in which ink is ejected from a print head during both forward and reverse scans across a recording medium. However, in bi-directional printing, speed non-uniformity occurs on opposite sides of a recording medium from scan line to scan line. As a result, distortions caused by speed non-uniformity at a start of each scan line become more noticeable by proximity to vertically-adjacent non-distorted ends of previous and subsequent scan lines.
In addition, high-speed bi-directional printing can exacerbate a satelliting effect that can occur when ink is ejected from a print head. When a main droplet of ink is ejected from an ink jet print head so as to record a pixel, a small satellite droplet often is also ejected. Ink jet print heads typically are angled slightly with respect to a recording medium so that the satellite droplet overlaps the main droplet when the print head is scanned across a recording medium in a forward direction. However, in the reverse direction, this angling tends to cause the satellite droplet to land near an edge of or even outside of the main droplet, resulting in a small satellite being recorded next to each recorded pixel during a reverse scan.
Furthermore, as carriage scanning speed increases, the satellite droplet tends to travel farther from the main droplet before striking the recording medium, resulting in satellites appearing farther from each pixel. As a result, the satellites tend to become more noticeable, particularly in the case that continuous images are recorded. Thus, increased scanning speed tends to increase image degradation caused by the satelliting effect.
Accordingly, what is needed is a way to address image degradation and satelliting effects that result when using faster carriage motors in an ink jet printer that can exhibit increased speed non-uniformity.
SUMMARY OF THE INVENTION
The invention addresses motor speed non-uniformity at a start of a scan line by printing with a lateral scan process that does not use a critical zone for printing at edges in a lateral scan of the print head. This critical zone is a zone in which printing of continuous images (e.g., non-color graphics such as tables or charts) with speed non-uniformity can result in noticeable ripple effects and image degradation.
In one embodiment, the lateral scan process inserts a margin into a scan line so as to allow a print head to traverse the critical zone before ejection of ink begins. As a result, speed non-uniformities tend to dissipate to less noticeable levels before printing a scan line. The margin preferably is not added to scan lines for isolated (e.g., text) scan lines, because ripple effects from speed non-uniformity are less noticeable in text. Thus, a balance is achieved between image quality and a time needed for a print head to traverse scan lines.
Accordingly, in one aspect the invention is a method for printing on a recording medium by lateral scans of a print head in accordance with print data. In this aspect, a content of print data is determined. Then, the print data is printed either with a first lateral scan process using a critical zone at edges in a lateral scan of the print head for printing, or with a second lateral scan process that does not use the critical zone for printing. The first or second lateral scan process is selected based on the print data.
The critical zone is an unstable zone for moving the print head in a lateral scan. Preferably, the critical zone is sized in correspondence with ramp up non-uniformities of a print carriage on which the print head is mounted, so as to accommodate a distance between a point where print degradation due to speed non-uniformities are noticeable to a point where print degradation due to speed non-uniformities are no longer noticeable.
The second lateral scan process preferably is a process in which a predetermined margin is inserted into the first lateral scan process. The second lateral scan process is used if print data for a current scan and print data for a previous scan, in at least the critical zone, are continuous print data, thereby alleviating ripple effects for the continuous data. In a case where the print data for the current scan and the print data for the previous scan are not continuous print data, the print data preferably is printed using the first lateral scan process.
By virtue of the foregoing, ripple of continuous images due to speed non-uniformity is alleviated through use of an inserted margin, while faster printing speed is maintained for non-continuous data.
Preferably, it is determined whether or not print data for a current scan and print data for a previous scan, in at least the critical zone, are continuous print data. The current scan is printed in a direction opposite to that of the previous scan by the first lateral scan process in a case that the print data for the current scan and the print data for the previous scan are not continuous print data. The current scan is printed in a same direction as that of the previous scan by the second lateral scan process in a case that the print data for the current scan and the print data for the previous scan are continuous print data.
By virtue of the foregoing, bi-directional printing that includes printing in the critical zone is used for isolated (e.g., text) scan lines, where distortion from speed non-uniformity is less noticeable, thereby improving printing speed. Unidirectional printing that does not include printing in the critical zone is used for scan lines of continuous images, thereby alleviating image distortion from speed non-uniformity where such distortion is most noticeable.
In another aspect, the invention concerns a method for forward and reverse printing on a recording medium by reciprocal forward and reverse scans of a print head in accordance with print data. According to this aspect, print data is printed in one direction of the reciprocal forward and reverse scans of the print head, and print data is printed in another direction of the reciprocal forward and reverse scans so that the printed data in the other direction is laterally shifted a predetermined distance as compared to printing where each pixel printed in the other direction vertically matches each pixel printed in the one direction. Preferably, the predetermined distance is a distance corresponding to one fourth of a printed pixel. This lateral shift tends to mask satelliting effects, particularly in the case of printing continuous image data.
In yet other aspects, the invention concerns a printer driver and an apparatus that utilize the foregoing methods for reducing image degradation.
This brief summary has been provided so that the nature
Hamamoto Akihiko
Hirabayashi Hiromitsu
Kanemitsu Shinji
Masumoto Kazuyuki
Noyes Steven
Canon Kabushiki Kaisha
Evans Arthur G.
Fitzpatrick ,Cella, Harper & Scinto
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