Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-11-28
2003-04-29
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000, C347S014000
Reexamination Certificate
active
06554386
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of printing a receiving material using an ink jet printer provided with a print head having at least one print element, said print head being fixed on a support element, the method comprising heating the print head to a working temperature higher than room temperature, moving the support element with respect to the receiving material in a main scanning direction and in a sub-scanning direction, and image-wise actuation of the print element so that ink drops are ejected from the print head in the direction of the receiving material. The invention also relates to an ink jet printer suitable for performing this method.
A method and ink jet printer of this kind are known from U.S. Pat. No. 6,086,194. In this method, an ink jet printer is used which has four print heads fixed on a support element. Each of the print heads comprises a row of print elements disposed parallel to the sub-scanning direction. The print heads themselves are distributed over a row extending parallel to the main scanning direction. Each of the print heads contains a hot melt or phase change ink of a different colour, namely cyan, magenta, yellow and black. During the printing of an image, each of the print heads will print a sub-image in the corresponding colour. By arranging the support element to make a number of scanning passes in the main scanning direction and conveying the receiving material in the sub-scanning direction it is possible to print the entire receiving material with the relatively small print heads. At the back the support element is provided with an active heating means divided up into twelve heating zones made up of four rows in the main scanning direction and three in the sub-scanning direction. The heating zones have a smaller heating power the closer they are to the centre of the support element. The object of this configuration is to heat the print heads uniformly. This is important, because the printing properties of each of the print elements depends greatly on the local temperature of the print head of which the relevant print element forms part.
The known method has one significant disadvantage. It has been found that when this method is used all kinds of print artefacts may form depending on the circumstances during the printing of the receiving material, particularly the type of image printed, the printer settings and the ambient conditions. For example, it has been found that the subimages printed with each of the print heads and together forming the intended image on the receiving material, do not always adjoin one another accurately. There may also be disturbing patterns forming in the image. These and other print artefacts are visible particularly in the case of photographs or similar graphic images and full-colour pictures.
The object of the invention is to provide a method with which print artefacts are avoided are far as possible, and to provide a printer with which this method can be performed. To this end, a method has been discovered according to the preamble of claim 1, which is characterised in that the method further comprises guaranteeing that the position that the print head occupies with respect to a fixed point on the support element during the printing of the receiving material, is substantially a predetermined position. In addition, an ink jet printer has been invented according to the preamble of claim 5, which is characterised in that the printer comprises a guarantee means to gurantee that the position that the print head occupies with respect to a fixed point of the support element during the printing of the receiving material is substantially a predetermined position.
The invention is based on the recognition of the problem that the print head, depending on circumstances, occupies a different position with respect to a fixed point of the support element. Since the print element in turn occupies a fixed position in the print head, the result of this problem is that the position occupied by the print element with respect to the receiving material during the printing thereof is not unambiguously determined. This can be considered as follows. During the printing of the receiving material, a fixed point of the support element (for example a marker which may or may not in turn form part of a carriage) is used to determine the location of the print head at any time. The time when a print element is to be actuated is then derived from this in order to ensure that the corresponding ink drop precisely reaches the correct location on the receiving material. However, with the known actuation, no consideration is given to the fact that the position of the print head on the support element is itself dependent on the instantaneous circumstances. The result is that the ink drop, as soon as the position of the print head with respect to the fixed point on the support element deviates from a normal position, reaches a different location on the receiving material. If this deviation is sufficiently large, it is visible to the human eye and will therefore lead to print artefacts.
Research by the Applicants has shown that the said position dependent upon the circumstances can specifically be related to expansion and shrinkage of the support element. It has been found that in the method known from the above-mentioned patent, the support element assumes a temperature deviating from the set value, at least locally, depending on the circumstances. As a result, the dimensions, and in this case the geometry of the support element and hence also the position occupied by the print head on the support element with respect to the fixed point, undergo changes. This uncertain position can then lead to visible print artefacts because the position of the print element has also become uncertain as a result.
The fact that the known method can give rise to a deformation of the support element of this kind can be understood from the following. The known method is aimed at heating the print heads uniformly. For this purpose the above-mentioned heating zones are disposed at the back of the support element, each of the zones having a fixed heating power. In addition, the heating of the print heads is controlled by feeding to the print heads hot ink of a preset temperature. By measuring both the temperature of the support element and the temperature of the ink, and adjusting these two temperatures to a predetermined set temperature through the agency of independent heating means, the method is intended to ensure that the print heads and hence also the support element are uniformly heated. However, this objective does not appear to be achieved in all circumstances. If, for example, much less printing is carried out with one of the print heads than with each of the other print heads, it has been found that the support element no longer assumes a uniform temperature. This situation occurs, for example, if a full-colour image is printed in which there is little black. Each of the four print heads will lose heat by convection, radiation and conduction. To some extent this is compensated by the supply of new ink which has a temperature equal to the set temperature of the print heads. To another extent it will be compensated by the heating means disposed at the back of the support element. Since, however, the black print head hardly receives a supply of hot ink, this head will therefore miss one of the two heat flows and accordingly cool off with respect to the other print heads. The temperature sensor will not pick up this cooling with respect to the other heads. After all, the temperature of the support element is measured at the colour heads which will cool off to a much less degree as a result of the printing, for the reasons described above. Even by measuring the temperature of the black ink supply it will not be possible to detect the cooling of the black head because this ink supply is kept at the set temperature by independent heating means. The result of the relative cooling of the black print head, which is extra intense bec
Boerstal Hendricus Gerardus Josef
Classens Wilhelmus Peter Johannes
Nguyen Lamson
Oce--Technologies B.V.
Stewart Jr. Charles W.
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