Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-09-20
2003-05-20
Hsieh, Shih-wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S019000
Reexamination Certificate
active
06565185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for printing images by recording dots on the surface of a printing medium by ejecting ink droplets from a plurality of nozzles, and more particularly to a printing technique that utilizes a nozzle test for testing whether or not ink droplets are ejected from each nozzle.
2. Description of the Related Art
Ink jet printers print images by ejecting ink droplets from a plurality of nozzles. Numerous nozzles are provided to the printing head of an ink jet printer, but there are instances when of some the nozzles become clogged and are unable to eject ink droplets due to an increase in the viscosity of the ink, the admixture of bubbles, or another such cause. In particular, if an ink jet printer is left for an extended period without printing anything, the viscosity of the ink can increase to the point that ink droplets can no longer be ejected from the nozzles. When a nozzle becomes clogged, dots will be missing in the image, which adversely affects image quality. In this Specification, a test of the nozzles is also referred to as a “missing dot test.”
In order to clear the nozzles of clogging, a cleaning mechanism is ordinarily provided to an ink jet printer. The user can press a button on the printer and clean the nozzles whenever desired. Also, to deal with situations when the printer is left unused for extended periods as above, the printer itself is sometimes designed so that it automatically performs cleaning whenever a specific length of time has elapsed from a predetermined point in time.
However, although some measures in the cleaning sequence and in the construction of the cleaning mechanism are taken and vary rare, there are cases rarely in which a nozzle that had not been clogged before cleaning becomes clogged as a result of cleaning. In such a case, cleaning in an attempt to eliminate clogged nozzles can actually increase the likelihood of creating nozzle clogging.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to reduce the likelihood of generating nozzle clogging.
In order to attain at least part of the above and other objects, there is provided a printer comprising a printing head having a plurality of nozzles for ejecting ink droplets, a cleaning mechanism for cleaning the plurality of nozzles, and a test unit for testing whether each of the plurality of nozzles can eject ink droplets. When the cleaning mechanism performs cleaning for a specific inducement other than the detection by the test unit of at least a specific number of non-operating nozzles unable to eject ink droplets, automatically carrying out the testing of the nozzles by the test unit before and/or after this cleaning. The following description will be divided into two cases: when the testing is conducted before cleaning, and when the testing is conducted after cleaning.
(1) Test After Cleaning:
In one embodiment, when the cleaning mechanism performs cleaning for the specific inducement other than the detection by the test unit of non-operating nozzles unable to eject ink droplets, the testing of the nozzles can be automatically carried out by the test unit after this cleaning. This makes it possible to ascertain whether the nozzles are clogged when there is the possibility that nozzle clogging will not be cleared by cleaning. Therefore, the reduction in image quality can be ameliorated by choosing a suitable printing operation according to whether there is any clogging after cleaning.
When a non-operating nozzle is detected by the testing of the nozzles after cleaning, and a nozzle array to be used for printing can be made up of just operating nozzles, it is preferable for the printing to be carried out using a nozzle array made up of just operating nozzles. If this is done, then even if there are some non-operating nozzle, normal printing can still be carried out with just the operating nozzles.
When a non-operating nozzle is detected by a test of the nozzles after cleaning, and a nozzle array to be used for printing can be made up of not just operating nozzles but with the non-operating nozzle, it is preferable for the printing to be carried out according to a printing operation including a supplemental operation in which dots on a main scanning line to be recorded by the non-operating nozzle in the nozzle array are recorded using one of the operating nozzles. If this is done, the dots that are supposed to be recorded by the non-operating nozzle can be recorded by the other operating nozzles, thereby preventing a decrease in image quality.
The cleaning may include an operation in which ink is drawn out of the plurality of nozzles by suction. With cleaning such as this, there is believed to be a likelihood that some nozzles which were not clogged prior to cleaning will be clogged after cleaning, although some measures in the cleaning sequence and in the construction of the cleaning mechanism are taken. Therefore, the above-mentioned effect will be particularly great if a nozzle test is conducted after such cleaning. Furthermore, conducting a test of the nozzles after cleaning makes it possible to simplify the complex cleaning mechanism.
(2) Test Before Cleaning:
In one embodiment, when the cleaning mechanism performs cleaning for the specific inducement other than the detection by the test unit of at least a specific number of non-operating nozzles unable to eject ink droplets, the testing of the nozzles can be automatically carried out by the test unit before this cleaning.
This makes it possible to ascertain whether the nozzles are clogged before cleaning. There is also the possibility that nozzles which are not clogged will become clogged when cleaned. If the above procedure is followed, however, it can be ascertained whether the nozzles are clogged prior to cleaning, so a decision not to clean can be made according to the number of clogged nozzles, thereby lowering the potential for new clogging to occur.
The excluded inducement, “the detection of at least a specific number of non-operating nozzles,” may be “the detection of one or more non-operating nozzles.” The nozzle test may also be performed both before and after cleaning. Specifically, it can be performed before cleaning, after cleaning, or both.
It is preferable to cancel the cleaning if the number of non-operating nozzle detected by the testing of the nozzles before cleaning is less than a first threshold. Even in this case, however, flushing (blowing out the ink) may be performed. The phrase “if the number of non-operating nozzle is less than a first threshold” as used here encompasses “less than one,” that is, “if no non-operating nozzles are detected.”
The above procedure more effectively lowers the probability that the cleaning of nozzles which are not clogged will result in new clogging and non-operating nozzles. Furthermore, if the amount of ink consumed in the cleaning of the nozzles is greater than the amount of ink consumed in the testing of the nozzles, ink consumption can be kept lower than when cleaning is carried out directly by choosing whether or not to execute the cleaning as above.
The cleaning for the specific inducement preferably includes timer cleaning carried out automatically by the printer when at least a specific amount of time has elapsed since a specified event.
If a printer of the type that ejects ink droplets from nozzles is left for an extended period without printing anything, the viscosity of the ink can increase to the point that ink droplets can no longer be ejected from the nozzles. If the nozzles are automatically cleaned after a specific length of time has elapsed since printing or nozzle cleaning as above, however, this blocked ejection caused by the thickening of the ink can be effectively prevented.
Furthermore, in the above embodiment, this automatic cleaning will not be performed if the number of non-operating nozzles detected by the nozzle test before cleaning is less than a first threshold, so the likelihood that non-operating nozzles will result from the cleaning
Hsieh Shih-wen
Seiko Epson Corporation
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