Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-07-31
2001-10-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000, C347S023000
Reexamination Certificate
active
06302511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to multi-pass ink-jet printing. More particularly, the invention relates to a method and system for detecting one or more failed ink jets and thereafter compensating for the one or more failed ink jets with the remaining operational ink jets.
2. Description of the Related Technology
Multi-pass printing is a technique used to reduce banding in ink-jet printing. Dots of ink, when still in liquid form, tend to run together due to surface tension. This is referred to as coalescence. To print a high quality image it is important to print individual round dots. But to achieve full saturated colors, the dots must overlap to completely cover the paper. By only printing a portion of the image data so as to avoid simultaneously printing adjacent dots during each printing cycle, coalescence may be largely avoided. Additionally, by avoiding all horizontal adjacencies, the transverse speed of the printing mechanism can be increased up to two times the rated print speed of the printhead.
Multi-pass printing is accomplished by filtering the image data using a print mask to determine which dots are to be printed in each swath. A swath is defined as a region, or portion, of a recording medium which is printed upon by a given portion, or print zone, of a printhead cartridge having a specified number of ink jets, as the printhead cartridge passes over the recording medium. The swath successively advances through each print zone after each pass of the printhead and is partially printed in each print zone. The printing of a swath is completed after it has successively advanced through each print zone.
In multi-pass printing, each jet of a printhead is assigned the role of ejecting ink, as necessary, onto pre-specified areas or “dots” on a raster line which is currently in the jet's respective print zone. However, a jet sometimes fails either due to being clogged or electrical problems in its firing circuitry. When this occurs, the pre-specified areas which are assigned to the failed jet in accordance with a respective jet mask, are not printed upon. Therefore, if one or more jets fail and there are many areas in which intended ink drops are not deposited, the quality of the printed image may significantly suffer.
Prior art methods have dealt with this problem by utilizing auxiliary jets in the printhead which are assigned the task of replacing failed jets. However, this method is inefficient because these auxiliary jets are inactive during periods when there are no jet failures. Therefore, the auxiliary jets represent printhead resources which are not fully utilized to their maximum potential. Additionally, in order to safeguard against situations in which multiple jets simultaneously fail, not just one but a bank of multiple auxiliary jets are set aside in the printhead for taking the place of failed jets. Although printheads having multiple auxiliary printheads improve the reliability and quality of the images produced by the printer, these printheads are more costly, larger and, therefore, require more space in a printer than those printheads without auxiliary jets.
SUMMARY OF THE INVENTION
The invention provides a multi-pass printing compensation scheme which detects nonfunctional ink jets in a jet group and utilizes any remaining jets of the jet group to compensate for the one or more failed jets in that jet group, without the utilization of otherwise idle auxiliary jets. The method and system of the invention accomplishes this task by assigning new replacement jet masks to the remaining jets of the jet group such that all areas, or dots, on a respective raster line are accounted for. Furthermore, these replacement jet masks avoid forming horizontally and vertically adjacent dots during a single pass of the printhead over the recording medium.
In one embodiment of the invention, a system for compensating for defective ink jets in an ink jet printer includes: a printhead having a plurality of print zones and a plurality of ink jets in each print zone, each ink jet being assigned to print respective dots on a respective raster line of a recording medium, wherein the plurality of ink jets are divided into a plurality of jet groups, each jet group having at least one ink jet in each print zone; a plurality of jet group masks corresponding to a respective one of said plurality of jets groups, wherein each jet group mask allocates the printing of dots on a respective raster line to each of the ink jets of a respective jet group; and a replacement jet group mask which replaces the jet group mask for a jet group having one or more nonfunctional ink jets, wherein the replacement jet group mask allocates the printing of dots to the remaining functional ink jets of the jet group having one or more nonfunctional ink jets. As a result, the remaining functional ink jets of the jet group compensate for the one or more nonfunctional ink jets in that jet group. In a preferred embodiment, the above-described system of the invention does not utilize auxiliary jets which are idle during times of normal operation. Therefore, the resources of the printhead are maximized.
In another embodiment, an ink-jet printer includes: a printhead having a plurality of ink jets, each ink jet being assigned to print respective dots on a respective raster line of a recording medium in accordance with a print mask, wherein when an ink jet is detected as being defective, at least a portion of said print mask is replaced with a replacement print mask such that one or more of the remaining ink jets of the plurality of ink jets compensates for the defective ink jet. In a preferred embodiment, the above-described ink jet printer does not utilize auxiliary jets which are idle during times of normal operation. Therefore, the resources of the printhead are maximized.
In a further embodiment, in the printer described above, when an ink jet in a jet group is detected as being non-functional during a printing process, the replacement jet masks assigned to the remaining functional ink jets in that jet group successively replace the original jet masks of each respective ink jet in that jet group one print zone at a time, per pass of the printhead over the recording medium, so as to provide a gradual transition from the original jet group mask to the replacement jet group mask.
As described above, if one or more defective jets are detected during the printing process, the method and system of the invention successively updates the portions of the print mask corresponding to only one print zone at a time. For example, if a defective jet is detected during printing, then prior to the next pass of the printhead over the recording medium, the jet masks corresponding to print zone
1
are updated and the printhead is then allowed to make another pass over the recording medium. Prior to the next pass, the jet masks corresponding to print zone
2
are updated, and so on. In this way, if a defective or nonfunctional jet is detected during the middle of a printing job, a smooth transition from the original jet group mask to the replacement jet group masked is achieved.
In another embodiment, in the printer described above, the plurality of replacement jet masks are sequentially numbered and assigned to respective remaining functional ink jets of the first jet group based upon the print zone numbers of the remaining functional ink jets such that ascending replacement jet mask numbers correlate with ascending print zone numbers; and when said first jet group is adjacent to said second jet group, the plurality of replacement jet masks are assigned to respective remaining functional ink jets of the second jet group based on a rotation scheme such that the order of assignment of the plurality of replacement jet masks to respective functional ink jets in the second jet group is rotated when compared to the order of assignment of the plurality of replacement jet masks to respective functional ink jets in the first jet group so as to avoid the assignment of identical replacement j
Free Warren
Hoang Loan M.
Neese David A.
Barlow John
Encad, Inc.
Knobbe Martens Olson & Bear LLP
Stewart Jr. Charles W.
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