Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-02-23
2003-05-06
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S030000
Reexamination Certificate
active
06557969
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a printing apparatus and suction recovery control method, and more particularly, to a printing apparatus employing a printhead which performs printing in accordance with an ink-jet printing method, and suction recovery control method.
BACKGROUND OF THE INVENTION
A printing apparatus, employed in a printer or a printer unit of a copy machine or facsimile apparatus or the like, prints an image based on inputted image data by forming dot patterns on a print medium, e.g., paper, thin plastic sheet, fabric or the like.
Such printing apparatus can be categorized according to printing methods, e.g., ink-jet method, wire dot method, thermal-transfer method, laser-beam method and so on.
Among these printing apparatuses, the type employing ink-jet printing method which performs printing by discharging ink from a printhead to a print medium is advantageous, not only because printing can be performed with high precision at high speed, but because printing can be performed with low noise by virtue of the non-impact method, and color images can easily be printed with multiple colors of ink.
Furthermore, according to a bubble-jet method of the ink-jet printing method, ink is heated to cause film boiling and ink is discharged by pressure of bubbles generated by the film boiling. The bubble-jet method is known to realize high resolution printing and high speed printing even more easily.
An ink-jet printing apparatus, using ink as a recording material for printing, attributes importance to reliability maintenance for the ink discharge function of a printhead, in order to prevent negative influence on printing, caused by ink evaporation or bubble mixture in ink.
More specifically, while an ink-jet printing apparatus is performing printing operation or is not in use, bubbles are gradually generated inside the ink discharge nozzles of the printhead or in the inserted portion of the printhead. This may disable ink discharge (no discharge) or cause discharge failure, disabling normal print operation. In order to eliminate these bubbles, the ink-jet printing apparatus comprises a cap for capping the printhead, and a head recovery unit having a suction pump for sucking ink inside the cap. The ink discharge surface of the printhead is capped at the position where the printhead faces against the cap, and the suction pump sucks bubbles inside the printhead. The suction recovery processing is an important technique for reliability maintenance of the ink-jet printing apparatus.
However, even if a suction condition is determined so as to make full use of the bubble-eliminating capability of the head recovery unit, in reality, volumes of bubbles vary in different suction operations. Therefore, the same bubble-eliminating performance cannot always be achieved. In view of this, in order to maintain excellent bubble-eliminating performance, the conventional ink-jet printing apparatus counts the number of times of discharge, or times the non-printing state period of the apparatus, or executes both, so that the suction is performed while the bubble volume is as constant as possible, and then controls suction operation in accordance with the counted values. More specifically, the timing of suction operation of the printhead is determined based on the point of time whichever earlier: at which a predetermined time has elapsed from an initial point of time, or at which a predetermined amount of printing is completed from the initial point of time.
Japanese Patent Application Laid-Open (KOKAI) No. 6-238914 proposes a method of determining timing of suction operation of a printhead based on the number of times of discharge, non-printing state period of the printer, and temperature of the printhead, taking into account a difference in the bubble generation amount in the head caused by a temperature rise inside the printhead.
However, the reliability maintenance employed in the conventional ink-jet printing apparatus does not consider the number of times of discharge per unit printing area of a printhead (e.g., actual number of times of discharge while an image corresponding to one line is printed on A4-size paper. Hereinafter referred to as a print image duty). Therefore, depending on a print image duty, suction operation is unnecessarily performed, causing to reduce the throughput of the printing apparatus or increase the amount of wasted ink, or causing discharge failure by bubbles before suction operation is performed.
Particularly, the bubble-jet method employs a method of locally heating ink to cause film boiling to generate ink discharge energy. According to this method, the internal temperature of the printhead gradually rises as printing operation is performed, and as a result of the temperature rise, the generation state or growth rate of bubbles changes. In view of this, as described above, the conventional example proposes a method of determining the timing of suction operation of the printhead based on the number of times of discharge, non-printing state period of the printer, and printhead temperature.
However, this method has the following problems.
(1) The temperature rise of a printhead varies for each head.
(2) Temperature detection accuracy of a printhead varies, making accurate control difficult.
(3) The internal temperature of a printhead differs depending on a pattern of a printing image.
Hereinafter, these three problems are described further in detail.
The following facts have been discovered as a result of careful study of causes and mechanism of bubble generation in a printhead which causes discharge failure.
In a case where printing operation is performed by a printhead employing an ink-jet printing method, small bubbles are first generated in the printhead, and then these bubbles are coalesced to grow into large bubbles. After the bubbles are first generated, if ink is not discharged from the printhead, these bubbles melt in the ink and disappear. Therefore, it is considered that the condition for small bubbles to coalesce and grow into large bubbles is to repeat ink discharge from the printhead within a predetermined time period before small bubbles disappear. In other words, if the printhead performs many times of ink discharge within a unit time period, bubbles coalesce and grow before disappearing, thus causing discharge failure.
FIG. 10
shows a relation between the number of lines printed by a printhead before discharge failure occurs, and a print time duty. Note that the print time duty is the number of print dots per unit time (dot/second).
As can be apparent from
FIG. 10
, as the number of print dots per unit time increases, discharge failure occurs at the smaller number of line, i.e., discharge failure occurs in the earlier stage.
If the internal temperature of the printhead is further taken into consideration, the case where the number of print dots per unit time is large and the internal temperature is low is more likely to cause discharge failure than the case where the number of print dots per unit time is small and the internal temperature is high.
As described above, mere detection of a printhead temperature is not sufficient for determining suction operation timing. Particularly when an ink-jet printing apparatus is in a print stand-by state during print data transfer, growth of bubbles, i.e., occurrence of discharge failure, is more highly correlated with the number of print dots per unit time than the printhead temperature, as is apparent from the aforementioned study. Furthermore, in a case where an ink-jet printing apparatus executes control (hereinafter referred to as temperature rise detection) such that printing is allowed only when the printhead temperature is lower than a predetermined temperature, discharge failure occurs depending on the print time duty rather than the printhead temperature.
In other words, mass-produced ink-jet printheads differ in various printing characteristics. Therefore, even in a case where the same print data is inputted to print the same image, consideration must be given in that the
Inui Toshiharu
Murakami Shuichi
Touge Yoshiyuki
Uetsuki Masaya
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Huan
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