Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-11
2002-08-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S010000, C347S011000
Reexamination Certificate
active
06435672
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of increasing the reliability of an inkjet printer, containing at least one pressure chamber provided with a nozzle, wherein ink drops are jetted from the nozzle and a disturbance is detected in the pressure chamber, whereafter the jetting of the ink drops is interrupted. The present invention also relates to an inkjet printer suitable for use with this method.
This method is known from U.S. Pat. No. 4,625,220 and is used to remove disturbances in the pressure chamber which influence the operation of the pressure chamber. In a printer of this kind, a pressure pulse is generated in the pressure chamber by means of a pulse generator. This results in a pressure wave in the ink in the pressure chamber and an ink drop is jetted from the nozzle. Disturbances in the pressure chamber, e.g. a gas bubble or an unwanted solid particle, result in generated pressure waves in the pressure chamber having a deviation from the standard pressure wave, i.e. the pressure wave which precedes the jetting of a regular (on average good) ink drop. Thus a disturbance may result in ink drops having a volume different from the volume of a regular ink drop. It is also possible that a disturbance may result in the presence of one or more disturbing satellite drops at each jetted ink drop. In an extreme case, a disturbance may even result in the breakdown of the pressure chamber, so that it is subsequently impossible to jet ink drops from the nozzle. The method proposes detecting a disturbance in the pressure chamber whereafter the jetting is temporarily interrupted so that print artefacts can be obviated. During the interruption, an active restoration operation is performed, in which the pressure chamber is flushed with new ink so that the old ink, including the disturbance, is removed from the pressure chamber. After the restoration operation has been carried out, ink jetting is resumed.
An important disadvantage of this method is that flushing the pressure chamber with new ink is accompanied by a considerable loss of expensive ink, since after the flushing operation the ink is frequently discharged to a waste container. Although there are methods known to collect the ink with which the pressure chamber has been flushed out and return it to the ink supply of the inkjet printer, these methods are combined with complex cap constructions since care must be taken at all times to prevent dirt, dust, air or other impurities reaching the ink from the exterior, since they can in turn result in disturbances in the pressure chamber. Moreover, in the latter case a return system is required, which is complex particularly in the case of meltable inks, since these inks solidify shortly after they have left the (heated) pressure chamber. In addition, due to the miniaturization of the print heads of inkjet printers, the caps are often many times larger than the dimensions of one nozzle, so that when one pressure chamber is flushed a number of nozzles of any pressure chambers in the vicinity are also flushed with ink, and this means a further waste.
Another significant disadvantage of such active restoration operations is that the entire print head to which the pressure chamber belongs cannot be used for printing substrates during the flushing operation, so that the inkjet printer productivity is under considerable pressure if high reliability is required.
SUMMARY OF THE INVENTION
The method according to the present invention is intended to obviate these disadvantages. To this end, a method has been developed in which the jetting is interrupted for a predetermined time. During this time no active restoration operations are carried out to remove the disturbance, and the pressure chamber is simply left to itself. After the predetermined time has elapsed, jetting of the ink drops from the nozzle of the pressure chamber is resumed. This method is based on the recognition that practically all disturbances disappear by themselves if the pressure chamber is not activated for a specific time. This method has the considerable advantage that there is no need to flush the pressure chamber with new ink in order actively to remove the disturbance from the pressure chamber. As a result no ink is wasted in removing the disturbance. Another important advantage is that any other pressure chambers in the print head need not interrupt the jetting, so that a print job started can be continued.
The temporary non-activation of the pressure chamber in which a disturbance is present may lead to very small artefacts in a printed image, which are practically invisible to the observer, and if considered necessary they can be intercepted in the manner known to the skilled man, for example in the manner known from Japanese Patent 60-104335. By the use of such a method there is practically no negative effect on the inkjet printer productivity and the temporary interruption of the jetting of the pressure chamber is prevented from resulting in print artefacts in the printed image. Another advantage of the method according to the present invention is that it is already known in advance—i.e. directly prior to the actual interruption of jetting—when jetting will be resumed, since resumption is not dependent on an active restoration operation being completed. This advantage can be used, inter alia, in determining the most optimal print strategy.
In a preferred embodiment, directly prior to the disturbance, a predetermined number of pressure pulses is generated following the detection of a previous disturbance. It has been found that most of the pressure waves which differ from the standard pressure wave do not lead to visible print artefacts. If jetting of the pressure chamber were temporarily interrupted after the occurrence of such a disturbance, it would result in an unnecessary fall-off in the inkjet printer productivity. Consequently, it is advantageous to determine which disturbances form a risk to the operation of the pressure chamber, and to interrupt the jetting of that chamber only when such disturbances are present.
It has now been found that a disturbance practically certainly leads to visible print artefacts if the disturbance does not disappear during the jetting of a specific number of ink drops from said pressure chamber. The reason why most disturbances disappear spontaneously during the jetting of a specific number of ink drops and that a small number of the disturbances increases precisely during said jetting is not completely clear. It may be that most disturbances are small gas bubbles which dissolve spontaneously in the ink before they reach a size such as to be accessible to growth under the influence of the pressure pulses. Another reason might be that disturbances occur mainly in the neighborhood of the nozzle with which they are jetted with the ink drops from the pressure chamber before they can lead to perceptible print artefacts. In this preferred embodiment, after it has been found that a disturbance is present in the pressure chamber, a specific number of pressure waves is generated in the associated pressure chamber in order to jet ink drops, whereafter it is determined whether there is still a disturbance present. If not, then the disturbance has obviously disappeared and there is no further acute risk to the operation of the pressure chamber. If the disturbance is still present, then there is a considerable chance that the last detected disturbance has or will have a perceptible negative effect on the function of the pressure chamber, so that visible print artefacts will occur in a printed image. To obviate this, jetting is temporarily interrupted and the pressure chamber is left to itself for a specific time.
In another preferred embodiment, a maximum of 100 pressure pulses is generated in the pressure chamber between the previous and the later disturbance. By making the number of pressure pulses not more than 100, the disturbance is prevented from becoming too large, so that it would take too long before it disappears when jetting is interrupted. In ano
Gröninger Mark Alexander
Reinten Hans
Simons Johannes Mathieu Marie
Barlow John
Birch & Stewart Kolasch & Birch, LLP
Do An H.
OCE Technologies BV
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