Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1996-12-26
2003-02-18
Nghiem, Michael (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06520623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for printing, in which a detect of an image due to faulty nozzle causing fluctuation or failure in ejection, can be complemented.
2. Description of the Related Art
An ink-jet type printing method is adapted to form an image of a printing medium by directly ejecting ink droplets onto the printing medium through a printing head located in opposition to the printing medium with a predetermined clearance. Different from electrophotographic or laser printing method or so forth, there are much lesser process and/or components required in formation of the image. Therefore, desired image can be stably obtained.
However, in the ink-jet printing method, there is an instability factor for formation of an image by ejecting fine ink droplets through ends (ejection openings) of a plurality of fine nozzles of a printing head. A phenomenon representative of such instability is fluctuation or failure in ejection for example. Failure of ejection can be caused by stopping the flow in the nozzle due to dust, ink of increased viscosity and so forth, breakage of heater in the nozzle, covering of the ejection opening of the nozzle by the ink droplet and so forth. Therefore, if ejection failure is caused in a part of the nozzles among a plurality of nozzles in the printing head, when the printing head is driven in a primary scanning direction with respect to the printing medium, a white line extending in the primary scanning direction should appear at the position of the printing medium corresponding to the faulty nozzles not ejecting the ink. Conventionally, once failure of ejection is caused in the printing head, it has been not possible to obtain an image having no defect.
The possibility of occurrence of failure in ejection is progressively increased in proportion to an increasing number of nozzles. Therefore, when the number of nozzles is increased to be several hundreds or several thousands for the purpose of speeding of printing, possibility of occurrence of the faulty nozzle is proportionally.increased. This makes it difficult to achieve high speed printing without causing defect on the printed image,
On the other hand, in viewpoint of manufacturing of the printing head, conventionally, it is inherently required to produce the defect free printing heads, all of the nozzle of which are in normal condition. Thus, increasing of number of nozzles to be provided in one printing head should result in increasing of possibility of defects in the printing head and thus inherently results in lowering of yield in manufacturing. This inherently raises production cost of the printing head.
Furthermore, even when a defect free printing head is successfully produced, if failure of the nozzle is caused during use to.make ink ejection through such faulty nozzle unstable to degrade the obtained image. Therefore, such printing head with faulty nozzle becomes not possible to use and has to be exchanged. On the other hand, in four to eight color ink-jet printing apparatus employing four to eight printing heads, each having several thousands of nozzles, if failure is caused in one or more nozzles, defective print is produced at every time of occurrence of failure. Furthermore, at every occurrence of failure, the printing head has to be exchanged to inherently stop the overall printing apparatus. Therefore, the apparatus becomes not possible to operate stably.
As a solution for this, the applicant has proposed a printing method and a printing apparatus which can perform complementing printing for obtaining complete printing products even in presence of the faulty nozzle in the printing head, in Japanese Patent Application Laying-open No. 25700/1996. Namely, the proposed printing method performs auxiliary scanning for the printing medium by an auxiliary scanning means for a magnitude smaller than an arrangement length of printing elements (nozzles) in the printing head after completion of primary printing scan by a primary scanning means with shifting of the printing head relative to the printing medium, so that the complemental printing for the printing region where printing has not been performed in the preceding primary scanning cycle due to failure of the printing element with other printing element during returning of the printing head to an initial position for the next primary scanning operation.
With such innovative printing method, the non-printed portion can be complementally printed so that a complete printing product can be obtained even when the faulty nozzle is present in the printing head.
However, such printing method still maintains rooms for improvement as claimed below.
(1) It is inherent to change flow of complemental printing when non-printing failure is caused on the nozzle located at certain positions among a plurality of nozzles in the printing head. For instance, when the faulty nozzle is located at a lower end of an array of a plurality nozzles in the auxiliary scanning direction, complemental print for a complementally printing defect caused by such faulty nozzle cannot be performed by a flow for complementally printing adapted for shifting in the downstream side in the auxiliary scanning direction. Therefore, in such case, the flow has to be changed to a flow for causing shift in the upstream side.
(2) On the other hand, the width of the image corresponding to the width of the array of the nozzles in the printing head is varied. The auxiliary scanning width for complementally printing is also varied. Therefore, the data unit of the image to be handled is varied.
(3) Since feeding amount in the auxiliary scanning direction for complementally printing is not constant.
(4) There are the foregoing problems in the items (1) to (3) which are mutually correlated to obtain satisfactory or complete complemental function, when the principle of complemental printing is applied for a color printing apparatus having a plurality of printing heads.
(5) It is difficult to accurately perform auxiliary scan of the printing medium in the extent corresponding to one or several pixels. Particularly, in case of a large scale apparatus, such as a printing apparatus performing textile printing in ink-jet system, in which a construction for transporting a cloth as the printing medium with an endless belt of about 1.8 m width becomes necessary. It is quite difficult or even impossible to provide a fine shift in the extent of several tens &mgr;m corresponding to one pixel. If overrunning is caused by excessive shift of the printing medium, it has been necessary to stop at the target position by several times of reciprocating shift, or to shift in large extent back to the original position to again shift for one pixel to reach the target position. Thus, feeding operation for complementing printing becomes too complicate.
SUMMARY OF THE INVENTION
In a first aspect of the present invention, there is provided a printing apparatus, comprising:
primary scanning means for performing primary scan of a printing head relative to a printing medium, the printing head having a plurality of printing elements arranged;
printing head driving means for driving the printing elements of the printing head, during primary scan of the printing head by the primary scanning means, to form an image on the printing medium;
auxiliary scanning means for performing auxiliary scanning of the printing head in a direction substantially perpendicular to the scanning direction of the primary scanning means, relative to the printing medium; and
printing control means, at a printing region of the printing medium corresponding to the printing element of the printing head which cannot perform printing in a forward direction of the primary scan, for performing complementally printing by another printing element in a condition where the printing head and the printing medium are relatively shifted in the direction of auxiliary scan at least a pitch between the printing elements of the printing head, and then performing next printing in a condi
Katsuma Makoto
Miyake Hiroyuki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nghiem Michael
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