Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-01-16
2003-12-23
Tran, Huan Huu (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C358S001100
Reexamination Certificate
active
06666535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to ink jet printers, and more particularly to method and apparatus for preventing banding defects caused by satellite drops ejected by a print head.
2. Description of Related Art
When a main drop of an ink drop is ejected at a speed greater than certain values (e.g., approximately 5 m/sec), the main drop is accompanied by one or more small sub-drops called satellite drops.
Satellite drops are usually smaller than the main drop and travel at a lower speed than the main drop. As a result, satellite drops can land on different locations of the image receiving member (e.g., a sheet of paper) relative to the main drop during printing when the drop ejector and the image receiving member are moving relative to each other. Another factor that can cause satellite drops to land at different locations than the main drop is that satellite drops generally have a velocity vector that is slightly different from that of the main drop. This satellite drop misplacement can increase or decrease with increasing print head speeds and with an increased gap between the print head and the image receiving member.
Because satellite drops occasionally travel in slightly different directions relative to the main drop, the effect of satellite drops on the image quality can differ based on a traveling direction of the print head. In one example of a conventional printer, the print head transfers ink onto the image receiving member as the print head travels from right-to-left and left-to-right relative to the image receiving member, i.e., a bi-directional printer. Furthermore, while in a stationary position, the nozzles of this print head create satellite drops having velocity vectors which direct satellite drops to land slightly to the left of a main drop on the image receiving member.
As the print head passes from right-to-left and transfers ink onto the image receiving member, the velocity vector of the print head in conjunction with the velocity vectors of the satellite drops cause the satellite drops to land farther away from the main drop on the image receiving member relative to that of the satellite drops of the print head when stationary. In other words, the satellite drops will lag even farther behind the main drop due to the additional print head velocity vector.
On a return swath, as this print head moves from left-to-right and transfers ink onto the image receiving member, the velocity of the print head causes the satellite drops to land closer to, or possibly within, the main drop on the image receiving member. The differing positions of the satellite drops relative to the main drop cause variations in the appearance between swaths formed by a left-to-right pass versus swaths formed by a right-to-left pass. Accordingly, this effect causes bi-directional banding in the final image because the patterns formed by drops printed in one direction are different from those printed in the other direction. In particular, the percentage coverage of the recording medium will differ depending on the swath direction.
SUMMARY OF THE INVENTION
The invention addresses the problems set forth above. Aspects of this invention relate to method and apparatus for preventing image defects caused by satellite induced banding in a single pass bidirectional ink jet printer.
According to one aspect of the invention, a method and apparatus prevents satellite induced banding caused in bidirectional printing in which a print head alternatively moves in a first printing direction and in a second printing direction opposite to the first printing direction. The ink jet printer includes a controller that performs at least one of (i) selectively removing pixels in the first printing direction in order to lighten an image, and (ii) selectively adding pixels in the second printing direction in order to darken the image.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of various exemplary embodiments.
REFERENCES:
patent: 5369428 (1994-11-01), Maze et al.
Markham Roger G.
Xie Yonglin
Oliff & Berridg,e PLC
Tran Huan Huu
Xerox Corporation
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