Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-17
2001-10-23
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S012000
Reexamination Certificate
active
06305781
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to alignment errors in bi-directional printing.
2. Description of Related Art
Image recording devices such as, for example, inkjet printers, fire drops of recording fluid from rows of nozzles of a print head. The nozzles are usually fired sequentially in groups beginning at one end of the head and continuing to the other end of the head. While the nozzles are being fired, the head moves at a rate designed to advance it by a resolution distance before the next firing sequence begins. As an example, for a 300 dot per inch (dpi) resolution with a firing frequency of 5.5 KHz, the print head moves 84.7 &mgr;m across the page in 182 &mgr;sec. If, for example, the velocity of the drop of recording fluid is 7 m/sec and the distance from the print head to the paper is 1.1 mm, the drop will require 157 &mgr;sec to reach the paper. During this time, the drop will drift sideways by 73 &mgr;m due to the motion of the print head. If the nozzles are not fired simultaneously, the row of nozzles is usually tilted so that drops fired from all nozzles land in a substantially vertical column.
It is often desirable to operate the print head bi-directionally to enhance productivity. The sideways drift of the print head between the location of the drop of recording fluid being fired and the location of the dot on the paper results in a bi-directional misalignment of two drops, one in each printing direction, fired at the same print head location. In the example given above, where the sideways drift is 73 &mgr;m in the direction the printhead is moving, this misalignment would be 146 &mgr;m for bi-directional printing. To compensate for this misalignment, the drops fired while the print head is moving in the reverse direction should be fired before the print head reaches the location at which the drop in the forward direction was fired. This firing lead time should be twice as long as the time required for a drop to reach the paper. In the above example, this would be 314 &mgr;sec (2×157 &mgr;sec).
The appropriate amount of lead time is determined by the printer, typically by means of a test pattern where the user is allowed to choose from the best aligned of a series of vertical lines. This procedure works relatively well where all of the nozzles fire drops at the same velocity.
SUMMARY OF THE INVENTION
The drops will tend to fire at the same velocity for a monochrome print head. In contrast, a multicolor print head can have drops that fire at significantly different velocities.
In a multicolor print head, different colored fluids are often fired at different velocities due to, for example, different colors having different drop volumes for optimum print quality. Because two drops of fluid fired from the print head at different velocities require a different amount of time between firing and hitting the paper, the drift of the print head between firing the drop and the drop hitting the paper is different for each different velocity. In a print head moving at 84.7 &mgr;m in 182 &mgr;sec, as described above, fluid fired at 7 m/sec results in a 73 &mgr;m drift of the print head. For the same print head, fluid fired at 9 m/sec results in a 57 &mgr;m drift. In this example, a drop fired at 7 m/sec and a drop fired at 9 m/sec would be separated by 16 &mgr;m on the paper. This would result in a bi-directional misalignment of 32 &mgr;m (2×16 &mgr;m). If the vertical alignment test discussed above fires jets of only one color or type of fluid, having a first velocity, the bi-directional misalignment for jets firing a second color or type of fluid having a different velocity will not be eliminated or reducted.
In order to eliminate or reduce this bi-directional misalignment of the drops having different velocities, the systems and methods according to this invention time delay firing drops of fluid that are fired at a higher velocity in order to compensate for the different duration of time required for different velocity drops to travel between the print head and the paper. Similarly, the firing of drops of fluid fired at a lower velocity could be advanced.
For ease of discussion, as an example of one type of print head, the systems and methods according to this invention will be described using a print head having one row of nozzles. The fluid, for example ink, is fired from the nozzles sequentially beginning at one end of the row and ending at the other end of the row. Such a sequential firing is called a stroke. In each stroke, only certain ones of the nozzles are fired as required by the image being printed. In the case of a color printer, one stroke could contain drops of a first colored ink and drops of a second colored ink, each colored ink being fired at a different velocity. In one exemplary embodiment of the systems and methods according to this invention, the bi-directional alignment is improved by relatively delaying a drop of a higher velocity ink from one stroke to a subsequent stroke in order to partially compensate for the decreased time required for the higher velocity drop of fluid to hit the paper.
Depending on the different velocities of the fluids being fired, the relative firing delay of the higher velocity fluid can be implemented in either or both printing directions.
These and other features and advantages of the invention are described in or are apparent from the following detailed description of the exemplary embodiments.
REFERENCES:
patent: 4386358 (1983-05-01), Fischbeck
patent: 4523364 (1985-06-01), Bain et al.
patent: 4528576 (1985-07-01), Koumura et al.
patent: 5570118 (1996-10-01), Rezanka et al.
patent: 5675365 (1997-10-01), Becerra et al.
patent: 5949451 (1999-09-01), Takagi
patent: 5956055 (1999-09-01), Gibson et la.
Le N.
Nguyen Lamson D.
Oliff & Berridge PLC.
Xerox Corporation
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