Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-02-21
2004-07-06
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S082000
Reexamination Certificate
active
06758555
ABSTRACT:
The present invention relates to the domain of printing heads for printers. It relates in particular to an improvement of electrostatic deflection electrodes for electrically charged ink drops. It also concerns an ink jet printer equipped with this improved head.
STATE OF PRIOR ART
Ink jet printers can be divided into two major technological families, a first constituted of “request drop” printers and a second constituted of continuous jet printers:
The “request drop” printers are essentially office printers, intended for printing a text and graphics, in black and white or in colour.
The “request drop” printers generate directly and uniquely the ink drops needed for the printing of the motives required. The printing head of these printers comprises a plurality of ink ejection nozzles, usually aligned following an alignment axis of the nozzles and each addressing a unique printing support point. When the injection nozzles are sufficient in number, the printing is obtained by simple displacement of the printing support under the head, perpendicularly to the alignment axis of the nozzles. Otherwise, a supplementary sweep of the support relative to the printer head is indispensable.
The continuous ink jet printers are usually used for industrial applications for marking and coding.
The typical function of a continuous ink jet printer can be described as follows. Electrically conducting ink maintained under pressure escapes from a calibrated nozzle, thus forming an ink jet. Under the action of a periodic stimulation device, the ink jet thus formed splits at regular time intervals at a point unique in space. This forced fragmentation of the ink jet is usually induced at a said jet break point by periodic vibrations of a piezoelectric crystal, placed in the ink and upstream of the nozzle. Starting from the break point, the continuous jet transforms into a series of identical ink drops, regularly spaced. Next to the break point a first group of electrodes is placed, called “charge electrodes”, whose function is to transfer selectively, and for each drop of the series of drops, a predetermined quantity of electric charge. The group of drops of the jet then crosses a second arrangement of electrodes called “deflection electrodes” forming an electric field which will modify the trajectory of the charged drops.
In a first variant, for printers called deviated continuous ink jet printers, the quantity of charge transferred to the drops of the jet is variable and each drop registers a deflection proportional to the electric charge which has previously been attributed to it. The point of the printing support reached by a drop is a function of this electric charge. The non-deflected drops are recuperated by a gutter and recycled towards an ink circuit.
Those skilled in the art also know that a specific device is required to ensure constant synchronisation between the instants when the jet is broken and the application of the charge signals of the drops. It is to be noted that this technology, thanks to its multiple levels of deflection, makes it possible for a single nozzle to print the integrality of a motive by successive segments, that is to say by lines of points of a given width. The passage from one segment to another takes place by a continuous relative displacement of the substrate compared to the printing head, perpendicular to said segments. For applications requiring a printing width slightly wider than the width of an isolated segment, several mono-nozzle printing heads, typically from 2 to 8, can be grouped together within the same housing.
A second variant of deviated continuous ink jet printers called binary continuous jet printers differ mainly from the above in that a single deflection level is created for the drops. The printing of letters or motives therefore needs the use of multi-nozzle printing heads. The centre distance between the nozzles coincides with that of the impacts on the printing support. It is to be noted that generally the drops destined for printing are the non-deflected drops. The binary continuous jet printers are intended for high speed printing applications such as addressing or personalisation of documents.
It should be emphasised that the continuous jet technique requires pressurisation of the ink, thus allowing a printing distance, that is to say the distance between the lower face of the printing head and the printing support, able to reach 20 mm, or ten to twenty times greater than the printing distances of request drop printers.
Those skilled in the art insist on optimising the performances of the layout of the deflection electrodes following two techniques.
These techniques are shown diagrammatically in
FIGS. 1
to
4
in the appendix.
The first deflection technique, so-called equipotential, is the oldest. It consists of using two metallic electrodes with surfaces facing each other—called active surfaces—. The series of drops crosses the space comprised between the active surfaces. Each of the active surfaces, relative to the jet, is raised to a constant and uniform electric potential. Two embodiments are used in particular.
The first embodiment is shown in FIG.
1
.
A printer comprises a reservoir
111
containing electrically conductive ink
110
which is distributed by a distribution channel
113
towards a drop generator
116
. The drop generator
116
, using the ink under pressure contained in the distribution channel
113
, forms an ink jet and splits this jet into a series of drops. These drops are electrically charged in a selective way by means of a charge electrode
120
fed by a voltage generator
121
. The charged drops pass across a space comprised between two deviation electrodes
2
,
3
. According to their charge, they are more or less deviated. The drops which are least deviated or non-deviated are directed towards an ink recuperation unit or gutter
6
while the other deviated drops are directed towards a substrate
27
carried locally by a support
13
. The successive drops from a burst reaching the substrate
27
can thus be deviated towards a low end position, an high end position, and successive intermediary positions. The drops of the burst as a whole form a line of width &Dgr;X perpendicular to an advanced position Y relative to the printing head and the substrate. The printing head is formed by the means
116
for generating and slitting the ink jet into drops, the charge electrode
120
, the deviation electrodes
2
,
3
, and the gutter
6
. This head is generally enclosed in a housing, not shown. The time between the first and second drop of a burst is very short. The result is that despite continuous movement between the printing head and the substrate, it can be considered that the substrate has not moved relative to the printing head during the time of a burst. The bursts are fired at regularly spaced intervals. The combination of the relative movement of the head and the substrate, and the selection of the drops of each burst directed towards the substrate make it possible to print any motive such as that shown as
28
in FIG.
1
. In the following description only the deviation electrodes of the drops of series
1
of drops formed from an ink jet exiting from the nozzle will be considered.
Concerning the deviation of said drops, it is a matter of forming a very strong electric field Ed, by application of a voltage Vd, which is constant between the two electrodes
2
,
3
formed by two parallel plates
2
,
3
. The value of the electric field Ed created between the active surfaces of the electrodes
2
,
3
is called optimal when this value is slightly lower, by subtracting a security margin, compared to that of the breakdown field corresponding to the space e between the active surfaces.
Such a concept is characterised by its simplicity but also by numerous inconveniences:
a high value of e, typically 5 mm, is indispensable for allowing the printing of very wide segments at the usual printing distances. Such a spacing implies the use of a very high value of Vd, about 8 kV, which cannot be generated within the pri
Feggins K.
Imaje (SA)
Nguyen Lamson
Pearne & Gordon LLP
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