EP0262004B1 - Ink jet print head and industrial recorder equipped with same - Google Patents

Description

The invention relates to an ink jet print head; it relates more particularly to its applications to industrial tracers.

The latter come in various forms, but are all composed of a part supporting the sheets (supports) to be traced, of another part supporting one or more styli, these two parts being set in relative movement, either by displacement of the sheets, either by moving the styli, or by a combination of the two methods.

On these industrial plotters, the pens depositing the ink are often either ballpoint pens, or felt tips, or hollow tips with special inks of the Chinese ink type.

These styli have several drawbacks, among which one may cite the need for necessary contact, during printing, between the printed medium and the stylus. However, depending on the stylus technology and the quality of the surface of the printed support, the quality of the tracing is not constant and is not always the best, especially when the support to be printed is abrasive on the surface (paper ... ), which often results in a very short lifespan of the stylus, whatever its technology.

Another drawback lies in the fact that the absence of printing when the printed medium is moved requires the stylus to be lifted, which results in a significant loss of time in the execution of the plot. In addition, when resuming a trace, the ink of the stylus does not always flow instantly, hence marks appearing at the start of the trace.

A difficulty also arises in terms of the compatibility between the ink, the technology of the stylus, and the quality of the support to be printed which is not obvious, which has the consequence of greatly limiting the quality and duration of life of the track on its support. In general, for each type of support (different qualities of paper, mylar, polyester film, etc.), a different type of stylus should be used (ballpoint pens, felt tip pens, hollow tubes, etc.).

• . la figure 1 illustre schématiquement la technique classique du jet d'encre;
• . la figure 2 est une illustration des épaisseurs de traits variables qui peuvent être obtenues par la technique du jet d'encre;
• . la figure 3a et la figure 3b illustrent schématiquement et respectivement une tête d'impression conforme à l'invention vue de face, et les plaques de déflexion de ladite tête vue de dessus;
• . les figures 4a, 4b et 4c illustrent le fonctionnement du jeu de plaques de déflexion de cette première variante de réalisation conforme à l'invention;
• . la figure 5 représente un tracé sur un support avec des orientations de la trame de points différents;
• . la figure 6 illustre la trajectoire relative tête-support corrigée, en fonction du rayon de rotation de la trame de points;
• . les figures 7a et 7b illustrent respectivement vue de face une seconde variante de réalisation d'une tête d'impression conforme à l'invention et, vue de dessus, la combinaison du jeu de plaques de déflexion coopérant avec une gouttière de récupération à configuration adaptée;
• . la figure 8 illustre le trajet des gouttes dans cette seconde variante;
• . les figures 9a, 9b, 9c et 9d illustrent le fonctionnement des plaques de déflexion de cette seconde variante;
• . la figure 10 illustre la fonction jouée par la gouttière de récupération adaptée;
• . la figure 11 illustre une troisième variante de réalisation d'un jeu de plaques de déflexion selon l'invention;
• . la figure 12 est un exemple de circuit électronique de commande des tensions de déflexion;

• les figures 13 et 14 sont des diagrammes illustrant les paramètres de commande de ces tensions.

The object of the invention makes it possible to avoid all of the drawbacks listed above, by proposing an alternative solution to existing styli, by a continuous inkjet print head, adapted to the needs of the industrial layout. . The invention relates to a continuous ink jet printhead of calibrated ink drops in which, at the level of the break of the jet leaving the ejection nozzle, the drops are electrostatically charged by means of electrodes. load to be then deflected by means of deflection electrodes which are at least three in number, the first two of which are face to face and parallel to each other and the third of which is perpendicular and juxtaposed with the first two, the supply at the top voltage of each of the three deflection plates being controlled by an electronic circuit to create an electric field whose module is constant and the direction is variable from 0 ° to 180 ° in a plane perpendicular to the deflection electrodes so as to ensure the deflection of the drops of a frame at an angle which can vary from 0 ° to 180 °, so that the thickness of the lines determined by the number of drops forming the frame remains constant whatever the relative displacement of the medium to be printed and whatever the direction of this displacement.
The invention will be better understood with the aid of the explanations which follow and of the appended figures among which:

• . Figure 1 schematically illustrates the conventional inkjet technique;
• . FIG. 2 is an illustration of the variable line thicknesses which can be obtained by the inkjet technique;
• . FIG. 3a and FIG. 3b schematically and respectively illustrate a print head according to the invention seen from the front, and the deflection plates of said head seen from above;
• . Figures 4a, 4b and 4c illustrate the operation of the set of deflection plates of this first alternative embodiment according to the invention;
• . FIG. 5 represents a plot on a support with orientations of the frame of different points;
• . FIG. 6 illustrates the corrected relative head-support trajectory, as a function of the radius of rotation of the dot grid;
• . FIGS. 7a and 7b respectively illustrate a front view of a second alternative embodiment of a print head according to the invention and, seen from above, the combination of the set of deflection plates cooperating with a recovery gutter with suitable configuration ;
• . FIG. 8 illustrates the path of the drops in this second variant;
• . Figures 9a, 9b, 9c and 9d illustrate the operation of the deflection plates of this second variant;
• . FIG. 10 illustrates the function played by the adapted recovery gutter;
• . FIG. 11 illustrates a third alternative embodiment of a set of deflection plates according to the invention;
• . FIG. 12 is an example of an electronic control circuit deflection voltages;

• Figures 13 and 14 are diagrams illustrating the control parameters of these voltages.

For clarity, the same elements are given the same references in all the figures.

Figure 1 is a figure of the known art which illustrates the ink jet printing technique concerned.

This consists of making a continuous jet of calibrated drops (I) supplied by a modulation system (8) connected to an ink supply device (80). At the level of the break of the jet leaving the ejection nozzle (81), the drops are electrostatically charged by means of charging electrodes (7). Deflection plates (35) create an electric field deflecting them from their path. All of these modulation, ejection, load and deflection means constitute the print head (T). If the support (S) on which one wishes to write and the print head (T) are in relative movement, one obtains the formation of a printing matrix. In the example described, it is an "M". All unused drops are collected in a gutter (1) before being recycled into the ink circulation system (2).

As shown in Figure 2, different line thicknesses can be obtained by juxtaposing several drops. Lines of thickness e = 0.1; 0.2; 0.3; 0.4; 0.5 were represented. They are respectively composed of a number of drops (nb) varying from 1 to 5 creating on the support an impact of the order of 130 µm in diameter.

We therefore see on the one hand that there is no support point between the print head and the support, which eliminates the major drawbacks linked to this contact, drawbacks that are encountered in machines where the '' a stylus is used to trace on a support. It can also be seen that a single printhead makes it possible to obtain lines of different thicknesses while each thickness requires the use of a suitable stylus in the case of conventional plotting machines.

This description therefore shows the advantage of replacing the marking members generally used in industrial marking machines with an ink jet print head; this is an application indisputably interesting from the inkjet technique to the field of industrial tracing.

The present invention also relates to a new print head particularly suitable for this application as is now described. It turns out that, in the conventional inkjet technique, and as illustrated by means of FIG. 1, the jet prints columns of dots. On an industrial layout machine, the support can move in all directions relative to the stylus. However, in the known technique of the deflected continuous jet, printing columns of dots (screens), these are always located in the same plane which is, in general, perpendicular to the direction of movement of the object to be marked (see Figure 1 ).

One of the important characteristics of the invention therefore resides in the fact that, thanks to a new arrangement of the deflection plates, an orientable electric field of deflection of the drops is obtained. Under these conditions, it becomes possible to maintain the column of points (1 to 5 points in the example of Figure 2), composed of a set of deflected drops (weft) in a plane always perpendicular to the relative direction of movement of the media to print and whatever it is. An electronic control circuit cooperates with this new set of deflection plates according to the invention, a circuit which will be described later. In addition, in certain variant embodiments, an adaptation of the shape of the gutter contributes to the success of the process.

A first variant embodiment of a print head according to the invention is shown, seen from above, in FIG. 3a while FIG. 3b illustrates the new set of deflection plates for this head, seen from above.

There is a modulation body (8) receiving the pressurized ink comprising an ink ejection nozzle forming the ink jet, a drop charge electrode associated with a detector (6) for passing the drops, a gutter (1) for recovering the ink drops not used for printing, associated with a recovery pipe (2) for the ink placed under vacuum (arrow f).

According to the invention, this print head comprises a combination of three deflection plates (3,4,5) in order to create an electric field of deflection of the charged drops, orientable by an angle which can vary from 0 ° to 180 °. Two of these plates (3) and (5) are parallel to each other and the third (4) is located in a plane perpendicular to the previous ones. According to another characteristic of the invention, this set of three deflection electrodes (3,4,5) cooperates with a particular structure of recovery gutter (1), allowing the orientation of the deflected drops from 0 ° to 180 °. The drops fall into a circular orifice (1a) produced in a narrowed extension (1b) of the flat reservoir forming the gutter (1). This orifice is located in the axis of the head (T).

$\text{β = 45°;}$

$\text{β = 180°.}$

FIGS. 4a, 4b and 4c illustrate by way of example three angles of deflection of the drops, namely:

$\text{β = 0 °;}$

$\text{β = 45 °;}$

$\text{β = 180 °.}$

Each deflection angle corresponds to an electric field (E) created by combining the high voltage supply from each of the three plates.

For an angle β of 0 °, only the plate (5) is supplied.

For an angle β of 45 °, the plates (4) and (5) are fed simultaneously.

For an angle β of 180 °, only the plate (3) is supplied.

These examples of oriented deflections are made in FIGS. 4a, 4b and 4c, with a frame (t) of 4 drops, the non-deflected jet being represented by a white point (x) in the gutter (1). By changing the number of drops in the frame, as explained in Figure 2, it is then possible to draw a line by choosing the thickness of the line. This line thickness is preserved whatever the direction of travel of the support, by orientation of the deflection field. This is oriented perpendicular to the direction of travel of the support relative to the tracing head.

In FIG. 5 is shown a line (100) on a support (not shown) with orientations of the frame of different points, so as to keep a constant line thickness (β = 180 °, 135 °, 90 °, 45 ° , 0 °).

With respect to a fixed point on the print head, depending on the deflection angle of the moment, the dot pattern does not fall in the same place. Also, it is necessary to make a trajectory correction in the relative movement of the print head relative to the support to be printed as a function of the angle retained in the deflection of the dot frame.

In Figure 6 is shown, depending on the radius of rotation (R) of the plot of points around the axis of the gutter, the relative corrected head-support trajectory (tr), for a given curve plot (tc). This variant of the inkjet drawing printhead requires a curve drawing trajectory correction program taking into account the deflection radius of the dot frame used for drawing.

A second alternative embodiment of a print head according to the invention is illustrated by means of FIGS. 7a and 7b, of FIG. 8 and of FIGS. 9a, 9b, 9c and 9d. As previously, FIG. 7a schematically represents the print head viewed from the front and FIG. 7b, the set of deflection plates seen from above with the recovery gutter (1) having an original shape and suitable for this application. The number of deflection plates is here again equal to three. We find the same elements as in the previous variant. In this solution, only change the shape of the gutter as well as the way of using the drops for printing. In fact, the drops not used for printing are this time systematically deflected in the gutter (1) which, according to a characteristic of the invention, comprises a semicircular reception chute (111). The drops used for printing are, in turn, deflected so that the center of the screen of printed dots, whatever the number, is in the axis of the head, and therefore in the center of the semicircular chute (111) of the gutter (1). The example is given in FIG. 8 with a grid of five points, a figure in which only appear the modulation system and the gutter (1) with its semicircular trough (111).

In FIGS. 9a, 9b, 9c and 9d are shown schematically several orientations of the deflection field, respectively 0 °, 45 °, 90 ° and 180 °, with a frame of four points. The drops not used for printing are deflected and represented by the white spot (x) in the chute (111) of the recovery gutter (1).

The advantage of this architecture is the possibility of making a line, with programmable line thickness, by playing on the number of drops, and this while retaining this line thickness whatever the relative trajectory of the head and of the printed medium, without having to use a correction of the relative trajectory of the head relative to the support as was the case in the previous variant (Figure 6).

Another advantage of this second variant lies in the fact that the print head can withstand significant accelerations thanks to at the special disposal of the recovery gutter (1). Indeed, during a phase of acceleration (and deceleration) of the head in the direction of the vector (V₀) represented in FIG. 10, that is to say perpendicular to the plane of deflection of the drops; these are slightly offset in the axis of the vector (V₁) (Figure 10) during their trajectory. There is therefore a risk for drops not intended for printing that they will no longer be able to fall into the recovery gutter. The arrangement of the gutter proposed in the variant of FIGS. 7 to 10 overcomes this drawback insofar as the arc of a circle formed by the chute (111) offers in the direction of (V₁) a very large gutter dimension compared to the other solutions.

The two advantages of this second variant, namely the uselessness of a correction of a trajectory and the possibility of supporting strong accelerations, make it an interesting solution for applications where the speed of the tracing is important.

FIG. 11 illustrates a third alternative embodiment of a print head according to the invention. In this configuration, four deflection plates (3,4,5,9) are provided. The plate (9) is parallel to the plate (4) and perpendicular to the other two (3,5). An example has been shown in which the plates (4,5) are under tension. The calculation of the distances (a) and (b) between the plates will be explained later. For maintenance purposes of the print head, the fourth plate (9) is provided retractable.

In accordance with the invention and as already stated above, a control circuit (C) for the high deflection voltages cooperates with a directional deflection printing head according to the invention.

The role of the control circuit (C) for the high deflection voltages is therefore to bring the three electrodes (3), (4) and (5) of FIG. 3 (or the three or four deflection electrodes (3) to the appropriate potentials. ), (4), (5), (9) in the variants of FIGS. 7 and 11, so that the plane of deflection of the drops is perpendicular at all times to the axis of the relative movement of the printed medium with respect to the head The electrode voltages are noted respectively (V₃, V₄, V₅, V₉).

In a particular embodiment shown in FIG. 12, the angle (β) of the relative movement of the printed support with respect to the print head is transmitted to a control device (200). These measures command (200) searches at all times in a memory (30) the values of the voltages (V₃, V₄, V₅, V₉) that it is necessary to apply to the electrodes to obtain the orientation of the frame according to the desired angle (β). The same circuit (200) permanently controls the devices (201) for supplying voltage to the deflection electrodes. These voltages are characteristic of a given print head. An example of calculation of the values of these voltages is given below.

The voltages of the deflection electrodes are adjusted so as to create a resulting electric field (E) at the droplets, of a given intensity, and oriented in the plane perpendicular to the axis of the relative movement of the printed medium with respect to the printhead.

The calculation of the voltages (V₃, V₄, V₅, V₉) depends on the geometry of the head considered and strictly requires the resolution of the physical problem of the distribution of the electrical potential in the print head, taking into account the geometric details of the head. This resolution can be done by various methods, including digital computer resolution methods. When the position of the drops is centered with respect to the electrodes and the size of the electrodes is large compared with that of the frame, it is possible to obtain an approximate value of the deflection voltages necessary to obtain the electric field of value (E) oriented as follows the desired angle (β).

$\text{et tan (β) = Ey/Ex ;}$

les valeurs de (Ex) et (Ey) étant calculées à l'aide des formules données ci-après.

et:

The following formulas are used in this case:

$\text{and tan (β) = Ey / Ex;}$

the values of (Ex) and (Ey) being calculated using the formulas given below.

and:

In a particular example of application of the variant illustrated by means of FIG. 11, the distances between the electrodes are a = b = 5 mm, and the electrode (9) is at the potential 0 volts. Figure 13 gives the necessary relation between the values of the voltages (V₃), (V₄) and (V₅) so that the value of the electric field resulting at the point (j) located on the axis of the non deflected jet, is: E = 0.25 MV / m.

In practice and by way of illustration, for an angle (β) = 60 °, FIG. 14 gives (V₅) = 750 volts and (V₃) = 0 volt. Figure 13 then gives (V₄) = 1300 volts. The value of the resulting field is, under these conditions, equal to 0.25 MV / m.

Other voltage combinations can be envisaged to obtain this result. These combinations follow from the same equations.

In the example given, the ink ejection nozzle has an internal diameter of 25 microns, and the voltages applied to the charging electrode are of the order of 150 volts maximum to obtain the desired line widths (0.1 to 0.4 mm).

As has already been said previously, a preferred application of a continuous jet print head and more particularly of a print head with orientable deflection plates is found in the field of industrial plotters. Any contact between the marking member and the support to be marked is avoided with all the advantages that this brings. In addition, the thickness of the line can be chosen and kept constant whatever the axis of the relative movement of the head relative to the support. Finally, even during acceleration (deceleration), recovery of unused ink drops is possible thanks to the installation of a recovery gutter with suitable geometry.

Claims (13)

1. Printing head with a continuous ink jet of measured drops of ink, in which, at the level of the break point of the jet leaving the ejection nozzle (81), the drops are charged electrostatically by means of charging electrodes (7) and are then deflected by means of deflection electrodes which are at least three in number, the first two (3) and (5) of which face each other and are parallel to each other and the third (4) of which is perpendicular to and positioned alongside the first two, the high voltage supply to each of the three deflection electrodes (3, 4, 5) being controlled by an electronic circuit (C) in order to create an electrical field (E), the modulus of which is constant and the direction of which can be varied between 0° and 180° in a perpendicular plane to the deflection electrodes so as to ensure the deflection of the drops of a pattern according to an angle (β) which can vary between 0° and 180°, so that the thickness of the lines, which is determined by the number of drops forming the pattern, remains constant whatever the relative displacement of the medium for printing and whatever the direction of this displacement.
2. Printing head according to claim 1, characterised in that it further comprises a fourth electrode (9) which is parallel to the third electrode (4) and faces it so that the electrical field (E) has a direction which can vary between 0° and 360°.
3. Printing head according to claim 2, characterised in that the said fourth electrode (9) can be retracted.
4. Printing head according to one of the preceding claims, characterised in that the function of the control circuit (C) is to bring the electrodes (3, 4, 5, 9) to suitable potentials so that the plane of deflection of the charged drops is perpendicular at all times to the relative movement of the printing medium in relation to the printing head.
5. Printing head according to claim 4, characterised in that the said value (E) = constant = 0.25 Mv/m for the electrodes, which are equidistant from each other at a distance of approximately 5 mm.
6. Printing head according to claim 4, characterised in that, from a first graph giving the change in the voltage (V₃) in dependence upon (β) and the change in the voltage (V₅) in dependence upon (β), there is determined, for a chosen angle (β), the value of one of the voltages (V₃) or (V₅) under consideration, and, this value having been obtained, the value of the voltage to be applied to the third deflection plate (V₄) is derived from a second graph giving, for (E) = constant 0.25 Mv/m, the change in the voltage (V₄) in dependence upon (V₃) and the change in the voltage (V₅) in dependence upon (V₄).
7. Printing head according to claim 6, characterised in that, for an angle (β) = 60°, (V₅) is equal to 750 volts, (V₃) is equal to 0 volt and (V₄) is equal to 1,300 volts.
8. Printing head according to one of the preceding claims, characterised in that the recovery gutter (1) has a circular aperture (1a) centred on the axis of the head.
9. Printing head according to one of claims 1 to 8, characterised in that the recovery gutter (1) has a semicircular trough (111) for receiving unused drops deflected towards this trough, while the centre of the patterns of drops serving for printing is located on the axis of the head, which is in turn centred relative to the axis of the semicircular trough (111).
10. Industrial tracer comprising a tracing medium and a marking element, these two parts being set in relative motion, characterised in that this marking element is a printing head according to one of the preceding claims.
11. Industrial tracer according to claim 10, characterised in that the said printing head comprises a set of deflection electrodes (3, 4, 5, 9) arranged and polarized so that the deflection field (E) can be oriented in dependence upon the orientation of the axis of relative displacement of the medium in relation to the head.
12. Industrial tracer according to one of claims 10 and 11, characterised in that the gutter (1) for recovery from the printing head comprises a circular aperture (1a) centred relative to the axis of the head.
13. Industrial tracer according to one of claims 10 and 11, characterised in that the recovery gutter (1) comprises a trough (111) in a semicircular shape, the unused drops being deflected into the said trough (111) while the centre of the patterns of drops used for marking is located on the axis of the head, which is in turn centred relative to the axis of this trough (111).

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