Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-05-21
2001-09-18
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06290316
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates to a method of printing and more particularly to a method of printing utilising a print head of the so called ink jet kind, although the invention may be applied to a method of printing having other kinds of print head comprising a plurality of printing elements which may be actuated independently to print on a substrate.
In one kind of ink jet printer, there is provided an array of printing elements e.g. arranged in a linear or substantially linear array, and each of which may create a jet of ink and propel the ink towards a substrate. The jets may be created by, for example, passages in the print head which are caused to constrict by piezzo electric means, to squeeze ink therefrom or by other similar means.
The design and manufacturing tolerances of such print heads is demanding and it will be appreciated by those skilled in the art, that the performance of the individual printing elements will in practice vary, such that print heads tend to be imperfect. This variation in performance of the printing elements leads to print image irregularities. Where the variation in performance of the individual printing elements is too great, the print head has to be rejected.
The variation in performance may mean that the amount of ink and/or the velocity of the ink in the created jet is not constant for all of the printing elements. The latter of these produces the result that the ink in one or more jets reaches the substrate at a different time to ink from others of the jets, even where the jets travel substantially the same distance from the print head to the substrate. In general, in a printer of this kind, during printing there is relative movement between the substrate and the print head, and consequently, the quality of the image is impaired by an amount proportional to the velocity variation.
SUMMARY OF THE INVENTION
According to a first aspect of the invention we provide a method of printing utilising a print head comprising a plurality of printing elements which may be actuated independently to print on a substrate, and a control means which produces control signals for the printing elements for independently addressing and controlling the printing elements so that the print head may print a desired character, wherein the method comprises analysing the performance of the individual printing elements to determine the printing characteristic of the print head and to produce control data, feeding the control data to the control means which utilises the control data to compensate for variations in the performance of the individual printing elements whereby the control means produces modified control signals for the printing elements so as to adjust the printing characteristic of the print head, and wherein the control means uses the control data to compensate for variation in performance of the printing elements by actuating one or more of the printing elements at a different time to others of the printing elements.
Thus, in an ink jet type printer as described above, when printing a row of image the ink from all of the jets reaches the substrate at the same time. Additionally, the control means may use the control data to compensate for variation in performance of the printing elements by providing a control signal to one or more of the printing elements at a power different to others of the printing elements.
In each case, the variation in performance of the printing elements is compensated for so that the quality of the resultant image is improved.
The characteristic of the print head may be determined at least in part by causing the print head to print a test print, and electronically examining the test print to produce a control data input to the control means but other analysing steps may be canied out for a particular kind of print head.
Where the printing elements each comprise means to create a jet of ink and to propel the ink to the substrate, the characteristic of the print head may be determined, at least in part by deriving for each printing element, a measure of the velocity of ink drops in the ink jet created thereby to produce the control data, using for example an electronic imaging means which provides a control data input to the control means.
According to a second aspect of the invention we provide a printing apparatus comprising a print head comprising a plurality of printing elements which may be actuated independently to print on a substrate, and a control means which produces control signals for the printing elements for independently addressing and controlling the printing elements so that the print head may print a desired character, characterised in that means are provided for analysing the performance of the individual printing elements to determine the printing characteristic of the print head and to produce control data, means to feed the control data to the control means which utilises the control data to compensate for variations in the performance of the individual printing elements whereby the control means produces modified control signals for the printing elements so as to adjust the printing characteristic of the print head.
The apparatus may have a print head of the kind in which the printing elements each comprise means to create a jet of ink and to propel the ink to the substrate and the means which analyses the performance of the individual printing elements, measures for each printing element, the velocity of ink drops in the ink jet created thereby to produce the control data, using an electronic imaging means which provides a control data input to the control means.
REFERENCES:
patent: 5285220 (1994-02-01), Suzuki et al.
patent: 5343231 (1994-08-01), Suzuki
patent: 5483265 (1996-01-01), Kneezel et al.
patent: 5610637 (1997-03-01), Sekiya et al.
patent: 0 605 216 B1 (1994-07-01), None
patent: 0 665 105 A1 (1995-08-01), None
patent: 0 709 192 A2 (1996-05-01), None
Patent Abstracts of Japan, JP 01 299049 A (Fuji Xerox Co Ltd), Dec. 1989.
European Search Report.
Barlow John
Fish & Richardson P.C.
Markem Technologies Limited
Stewart Jr. Charles W.
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