Incremental printing of symbolic information – Ink jet – Ejector mechanism
Patent
1992-05-11
1996-03-05
Grimley, A. T.
Incremental printing of symbolic information
Ink jet
Ejector mechanism
347 78, 347 94, B41J 2085
Patent
active
054971772
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to ink jet printers with multiple ink jets or channels. More particularly, the invention relates to a method of compensating for crosstalk between charging electrodes in such an ink jet printer.
In an ink jet printer, ink drops are applied to a printing surface to jointly form a picture, a text, etc. To provide such a print, ink jet printers with multiple continuous ink Jets have a printing head comprising a nozzle with a number of orifices distributed in one or more rows and communicating with a liquid container accommodating an electrically conductive liquid. The liquid is forced by pressure through each nozzle orifice in the form of separate continuous printing jets which are decomposed into drops, i.e. each printing jet is transformed into a drop train.
A multiple jet ink printer further comprises, immediately adjacent the drop formation point of each printing jet, a separate charging electrode associated with the printing jet and adapted to generate a charge field for selectively charging the drops of the corresponding drop train. Drop charge-controlling electrode potentials are applied selectively to each charging electrode to charge the drops when these are being formed at the drop formation points. In other words, each continuous printing jet is transformed into a drop train consisting of drops with selectively controlled charges.
The drop trains with their selectively charged drops pass from the drop formation points through a deflection field which is associated with the printer and in which charged drops are deflected and uncharged drops pass in undeflected paths. The printing surface, for example a paper on a rotating roller may be adapted, depending upon the printer construction, to receive either the undeflected or the deflected drops.
During start-up of an ink jet printer of this type, the pressure in the liquid container is increased for a short but by no means negligible time during which the paths of the printing jets and the drop trains are unpredictable and the drop formation process is not fully developed. This unstable function lasts until the correct operating pressure has been attained in the liquid container.
Conditions are essentially the same upon shut-down of the printer. When the pressure in the liquid container decreases and the liquid flow through the nozzle orifices is reduced, the printing jets and the drop trains become unstable and difficult to control.
During start-up and shut-down of an ink jet printer there is, therefore, a considerable risk that liquid will be deposited on the charging electrodes, causing physical obstacles to the printing jets and/or the drops, and this again may result in an erroneous text or no text at all. Also during normal operation, there may occur, for various reasons, an undesired deposition of drops on the charging electrodes. For the reasons stated below, this phenomenon is especially pronounced in multiple jet printers. In a system with multiple printing jets positioned relatively close to one another, the electric field from a charging electrode (the charge field) may affect the drop charge of several printing jets, besides the jet associated with that particular charging electrode, i.e. crosstalk between different channels may occur. To reduce such crosstalk, it is conventional to arrange the separate charging electrodes in the manner shown in FIG. 1 of the accompanying drawings. One such electrode structure is described in, for example, IBM Technical Disclosure Bulletin, Vol. 20, No. 1, June 1977 and IBM Technical Disclosure Bulletin, Vol. 19, No. 8, January 1977.
FIG. 1 shows a broken-away part of a charging electrode means 10 in an ink jet printing head with multiple printing jets 12. The electrode means 10 has, for each printing jet 12, a rectangular recess or slit in which a separate charging electrode 14 is formed. The shielded U profile thus imparted to each charging electrode 14 reduces the crosstalk between the separate charge fields. Furthermore, FIG. 1 illustrates schematically how a pri
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Grimley A. T.
Lee Shuk Y.
Plotcon HB
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