Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-02
2002-09-03
Nguyen, Lamson D. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S019000, C347S014000
Reexamination Certificate
active
06443556
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for printing text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to a scanning thermal-inkjet machine and method that construct text or images from individual ink spots created on a printing medium, in a two-dimensional pixel array. The invention employs print-mode techniques to optimize image quality.
BACKGROUND OF THE INVENTION
(a) Orientation—Printmasks are used to determine the pass number in which a halftone dot is formed by an inkjet on the paper. Modern inkjet printers have the capability to detect defective nozzles on-line. In order to compensate for the defective nozzle the printmask has to be redesigned, or at least modified.
Currently applied methods either redesign a printmask on-line, or replace the defective nozzle with a predetermined backup nozzle. Those methods compromise the quality of the printmask, either globally (in the former), or locally.
A final stage of the inkjet printing pipeline consists of determining the pass number in which inkdrops allocated by the halftoning stage will be laid on the paper. The goal is, usually, to make sure that neighboring dots are laid as distant on the time axis, as is made possible by the number of passes allocated to the print-mode.
One reason for this time separation is that nearby liquid inkdrops might coalesce, thereby creating pigment density fluctuations on the paper. If, on the other hand, by the time a dot is laid down all its previously laid neighbors are already dry, no coalescence occurs.
The pass-number allocation is technically achieved using an integer matrix of pass numbers, called “printmask,” which is placed in a periodically repetitive manner on the halftone pattern (FIG.
4
). This way, every halftone location corresponds to a pass number from the printmask. An inkdrop, if allocated by the halftoning stage, is laid down at the corresponding pass number.
Modern inkjet printers have on-line nozzle quality-checking capabilities. Having detected a defective nozzle a printer should relieve that nozzle from part of its duties, or simply stop using it at all.
All this may be done by redesigning or modifying the printmask. For every line in the printmask there is a mapping between pass numbers and nozzles. Thus forbidding a certain nozzle is achieved by prohibiting predetermined pass numbers in certain lines of the printmask.
The problem of compensating for damaged nozzles is thus transformed to a problem of designing new printmasks with the appropriate constraints. Since the number of nozzles is too large to save a different printmask optimized for the possibility that a each different nozzle may be damaged, the design has to be performed on-line on the printer. Factory-created printmask patterns are carefully designed to use the tradeoff between various technical and print-quality requirements, whose optimization of which is too complicated for an on-line routine. Nevertheless, fast alternatives with reasonably good quality have been used.
Three mask creations methods in use are the following.
1. Handmade masks—These allow very good control over placement of each drop, and also help with considering interactions between printheads in an easy way. The main drawback of handmade masks comes from the fact that they are very small, therefore tending when tiled throughout an image to produce banding or regular patterns.
Handmade masks also do not allow good management of nozzle usage. Any error-hiding policy that is attempted here requires some amount of hardcoded mask replacement.
2. Redesign—A new printmask is designed on-line. The time and hardware constraints dictate a suboptimal design, which reduces the overall quality of the printmask. Furthermore, this method is limited to printers with enough computation power to support it, and might require a noticeable time duration to be performed. In this method the burden of the damaged nozzle is partitioned equally between the available nozzles.
3. Backup Nozzle—Every nozzle has a backup nozzle. When a nozzle is damaged, its backup is activated. The printmask does not change, only the mapping between pass numbers and nozzles.
Thus, at the lines where the damaged nozzle was not employed, the print quality is not altered; however, at the damaged-nozzle locations, the application of a backup nozzle results usually in poor quality due to possible breaches of printmask design requirements. In addition, the double duty of the backup nozzle might shorten its life span. This procedure requires no significant computation.
(b) Automated and semiautomated generation of print-masks—Joan Manel Garcia-Reyero, in U.S. utility-patent applications Ser. No. 09/150,321 through '323, has introduced a fundamental advance in printmask generation. His system and method express all needed considerations for use in preparing a mask—and test criteria as well—in a generalized form and accordingly are able to produce at each attempt a usable mask of high quality.
In some circumstances, however, the Garcia approach in its purest form is subject to undesired limitations such as excessive time consumption for use in the field. It is accordingly susceptible to refinement for mitigation of these limitations.
Because Garcia's invention in particular addresses issues of controlling the randomness (or granularity) of printmasks and resulting images, he dubbed it “Shakes”. For brevity and convenience, this document too will refer to his invention by that nickname.
Nozzle weighting is a technique first described in Joan Manel Garcia-Reyero's document about Shakes, consisting of specifying a certain percentage of usage per nozzle. That is, a single nozzle will not only be used or not, but the number of times it will appear in a mask description can be specified.
The interesting thing is that this nozzle weighting is also dependent on the printhead status in a given moment. Algorithms to determine this weighting have also been disclosed.
It was later discovered that they could easily support Variable Paper Advance Printmodes, Pass-Dependent Nozzle Weighting and Multilevel Printing. They also provide an easy way to install printmodes into the printer, even through the Internet.
(c) Classical Shakes with Nozzle Weighting—Shakes is a tool that automatically generates fuzzy masks, given a set of rules determined by the engineer that is designing the masks. Therefore, the designer must “explain” to Shakes how he/she wants the mask, and let it do it.
The main advantage is that masks can be generated that are far larger than handmade ones, and noisy enough to build banding robustness. Nozzle weighting is much easier now, but it still requires a significant number of CPU cycles.
On the other hand, if the resulting mask is not good enough for the designer's needs, the “explanation” must be reformulated, which turns into a recursive process. The complexity of the process increases, as more regular masks are sought.
In summary, Shakes is optimal for masks that have a certain degree of randomness (i.e., the fuzzy masks), but there seems to be a discontinuity when trying to move to more regular masks.
The Shakes process allows Nozzle Weighting in two senses. One Nozzle-Weighting process is what is called “List”. This was already implemented inside a product (Shakesmall), but there was a very poor correlation between the input weight and the actual nozzle usage.
The other Nozzle-Weighting option offered by Shakes is called “NozzDist”. It requires two rounds of calculation for a given mask, the second round being much slower than the first one. This option was discarded for Shakesmall because the throughput hit was unacceptable.
(d) Encad Error Hiding Method Using a Backup Matrix—In this competitive system a different backup nozzle was used for each location. A basic drawback: it was for binary printing (only one drop per pixel) and only supported Error Hiding (a nozzle is either used or not).
A single nozzle, on a binary pipeline (that is, one drop per ce
Baharav Izhak
Garcia Joan Manuel
Garcia-Reyero Santiago
Gil Miquel Antoni
Shaked Doron
Ashen & Lippman
Hewlett--Packard Company
Nguyen Lamson D.
LandOfFree
Automated and semiautomated printmask generation for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automated and semiautomated printmask generation for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automated and semiautomated printmask generation for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2856244