Recorders – Performance of multiple functions of steam and gas engines – Pressure responsive element
Patent
1990-05-15
1992-06-30
Fuller, Benjamin R.
Recorders
Performance of multiple functions of steam and gas engines
Pressure responsive element
346140R, 36446402, 271276, 271195, B41J 1312
Patent
active
051267535
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an ink-jet printing assembly for printing on rapidly moving articles of correspondence, especially in a cancelling, franking or more generally stamping machine.
Such an assembly known, for example, from the document GB-A-2,110,854 comprises printing heads equipped with ink emission nozzles, means for guiding and driving the article or support to be printed in front of the said nozzles and means for detecting the advance of the support, triggering the emission of ink by the said nozzles.
In a cancelling machine, it is desirable to print a standardized postal impression of the dimensions 80 mm.times.25 mm in the upper right-hand corner of the postal consignments In a franking machine, the width of the zone to be printed can assume a higher value, without this in any way changing the conditions and solutions presented hereafter. The processing speed must be capable of reaching a plurality of meters per second, and in this respect the printing heads employing the "drops on demand" technique with a piezoelectric actuator make it possible to reach a linear speed which can attain 2 m/s with a writing density of 4 to 6 dots per mm [that is to say 100 to 150 dpi (where dpi is the abbreviation of "dots per inch")].
To function correctly with a high-performance ink jet, it is necessary to control accurately: paper. order to prevent image distortions.
This latter condition must be satisfied at all events, but with even greater accuracy with printing systems in which the spacing of the nozzles is greater than the spacing of the dots, thus making it necessary to incline the line of the nozzles in relation to the direction of movement of the paper.
It will be appreciated that, under these conditions, the emission moments of the various nozzles must be staggered in order to compensate their spatial stagger attributable to the inclination. This spatial stagger is of the order of approximately one hundred elementary steps (the distance between two adjacent drops), and to prevent visible distortion the relative error in the stagger must be less than one per cent.
In order to control the distance between the nozzles and the paper, one idea was to use a bearing plate for the flat articles, projecting slightly relative to the nozzles, and a system of belts retaining the article on its rear face and laying it against the bearing plate; such a system has two disadvantages: there is a high risk of smudging, irregularities which impair the printing quality.
In order to adjust the emission of the drops exactly, the document GB-A-2,110,854 envisages detecting the passage of the article at a given point, for example by detecting its front edge, and subsequently triggering a time base adjusting the emission of the drops. This solution is unsuitable because it then makes it necessary to regulate the speed of the paper with a tolerance impossible to achieve in practice. There must therefore be a device which is coupled closely to the advance of the paper and which generates the moments of release of the successive drops. For this purpose, there was the idea of using a mechanical pulse transmitter coupled to the flat article. Such a system can consist of a driving roller which drives the article of correspondence without slip and on which is mounted a pulse generator connected in terms of rotation, or of a roller connected to a pulse generator mounted loosely in terms of rotation and pressed by a spring arm against the article of correspondence or against the means of driving the article (roller or belt); such systems function well with articles of uniform thickness. In contrast, when the articles are letters filled unevenly, it is troublesome to compress them between two rollers, and this can cause local deformations of the paper which impair the printing quality.
The object of the invention is to provide a satisfactory solution to these two fundamental problems.
According to a first aspect of the invention, the means for guiding and driving the printing assembly comprise a device for maintaining the article at a
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Chevillon Francis
Martin Claude
DeVito Victor
Fuller Benjamin R.
SECAP
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