EP1105297B1 - Direct printing machine by ink jet on a medium - Google Patents

Abstract

The invention concerns a direct printing machine by ink jet on a medium, including one or several printing heads with a spray nozzle, each head being dedicated to one shade. The invention is characterized in that the heads are borne by a pen carriage on the medium along three orthogonal axes X, Y and Z. Each of the heads is provided with a surge tank borne by the pen carriage, the surge tanks being supplied from one or several fixed tanks, the heads and the surge tanks are maintained in low pressure and the surge tanks are supplied with ink from the fixed tanks.

Description

The present invention relates to a direct printing machine by projection of ink drops on a support.

The inkjet technique is known (see eg. FR-A-2 707 919).

It makes use of piezoelectric ceramic print heads, one chamber of which by deformation projects the ink at the outlet of the nozzles onto a support.
The projection of the ink can also be obtained, for certain types of ink, by heating generating the formation of a gas bubble whose expulsion causes the ink jet.

These techniques are associated with microprocessor control systems allowing the production by ink projection of the desired image which can be, for example example, an alphabetical sign or letter or any representation. These techniques are more particularly used in office automation equipment.

In these materials, the relative displacements of the print head by ink jets and of the support to be printed are of small amplitude, which does not harm the quality of the print, the vacuum necessary at the output of the projection nozzles n not being affected by small displacements.
These technologies are however only suitable for certain specific types of inks and are not suitable for the projection of inks with high corrosive power, the use of which is sought after for the quality of the impression obtained and for its unalterable adhesion on the support or for inks revealing by ultraviolet rays.

The invention aims to produce a machine which can be used for direct printing, with corrosive inks, that is to say based on solvents or ultraviolet, on small or very large formats and on any type of support, especially rigid, flat or shaped.
The realization of such a machine meeting this definition goes through the control of a number of problems.

Corrosive inks cannot be loaded into known dispensing cartridges of the HEWLETT PACKARD (registered trademark) or LEXMARK (registered trademark) type, it is necessary to design a specific ink supply system with devices making it possible to maintain a vacuum of 4 millibars at the level of the projection nozzles without pressure variation detrimental to a good impression, regardless of the technical data according to which the relative movements between the heads and projection nozzles must be very rapid.
By way of example, the heads and nozzles can be subjected to displacement speeds of 800 millimeters per second and to accelerations of 5000 millimeters per second squared, which generates a pressure variation at the level of the nozzles.

In addition, the nozzles operating in slight depression, with the above-mentioned variations, are likely, during displacement in dynamic operation, to suck in air bubbles.
This generates a degradation of their functioning: projection stop, deflected jet, etc ...
The present invention aims to provide a solution to this problem in the production of a direct printing machine.

• la ou les têtes est ou sont portées par un équipage mobile au-dessus du support à imprimer suivant les trois axes X, Y et Z orthogonaux dans l'espace voir eg. EP-A-754 555 ;
• chacune des têtes est dotée d'un réservoir tampon porté par l'équipage mobile
• la ou les têtes et leur réservoir tampon sont maintenus en dépression et les réservoirs tampons sont alimentés en pression à partir d'un ou des réservoirs à poste fixe.

Suivant une autre caractéristique de l'invention, l'équipage mobile amène cycliquement les têtes et les buses sur un système de nettoyage et d'entretien des têtes qui, par succion, nettoie les buses et les amorce, par raclage évacue les gouttes excédentaires et qui permet de maintenir les buses en situation de bon fonctionnement.To this end, the machine according to the invention for direct printing operating by spraying drops of ink onto a support, by one or more heads with projection nozzles, said machine being of the type with relative movements between the support to print and projection heads, each head being preferably dedicated to a color or a tint is essentially characterized in that:

• the head (s) is or are carried by a mobile assembly above the support to be printed along the three axes X, Y and Z orthogonal in space see eg. EP-A-754,555;
• each head has a buffer tank carried by the moving part
• the head or heads and their buffer tank are kept under vacuum and the buffer tanks are supplied with pressure from one or more stationary tanks.

According to another characteristic of the invention, the moving assembly cyclically brings the heads and the nozzles to a system for cleaning and maintaining the heads which, by suction, cleans the nozzles and the primers, by scraping removes the excess drops and which keeps the nozzles in good working order.

According to yet another characteristic of the invention, the internal volume of each on-board buffer tank is divided to reduce the amplitude of the waves produced by the displacement of tanks.

• la figure 1 est une vue schématique en plan d'une machine selon l'invention
• la figure 2 est une représentation schématique du système hydraulique de la machine selon l'invention
• la figure 3 est une vue schématique des réservoirs tampons avec têtes de projection
• les figures 4 et 5 sont des vues en plan et en coupe de l'insert diviseur introduit dans chacun des réservoirs.
• la figure 6 représente en plan le système de nettoyage et d'entretien des têtes et buses de projection qui est raccordé au circuit hydraulique
• la figure 7 est une vue en coupe du dispositif représenté à la figure 6
• la figure 8 représente schématiquement le cycle d'entretien
• la figure 9 représente en coupe un réservoir tampon et un réservoir additionnel.

Other advantages and characteristics of the invention will appear on reading the following description of an embodiment of the invention given by way of non-limiting example and illustrated by the accompanying drawings in which

• Figure 1 is a schematic plan view of a machine according to the invention
• Figure 2 is a schematic representation of the hydraulic system of the machine according to the invention
• Figure 3 is a schematic view of the buffer tanks with spray heads
• Figures 4 and 5 are plan views and in section of the divider insert inserted into each of the tanks.
• FIG. 6 shows in plan the cleaning and maintenance system for the spray heads and nozzles which is connected to the hydraulic circuit
• Figure 7 is a sectional view of the device shown in Figure 6
• Figure 8 schematically shows the maintenance cycle
• Figure 9 shows in section a buffer tank and an additional tank.

As shown diagrammatically, in plan view in FIG. 1, the machine according to the invention comprises a rectangle table 1 comprising a flat, horizontal plate, of rectangle shape on which the support intended to receive the print is disposed.
A transverse gantry 2 is movable in the X direction on the table.

On the gantry 2 is mounted an on-board crew 3 mobile by any known means along the Y axis and the Z axis; the X, Y and Z axes being orthogonal in space. The mobile crew can therefore move in any direction on the table 1 and in height along Z relative to the latter. Its movements are controlled by a control and command unit comprising a microprocessor with associated equipment. The position of the moving assembly, particularly in height, with respect to the table, is adjusted by any known type of detection system

Laterally at the table is arranged, at a fixed position, one or more tanks 4 receiving the inks used and supplying, via lines 7, the tank or tanks 6 of the moving assembly 3, these tanks 6 being located lower than the tank or tanks 4.

A fixed station, on table 1, is arranged a system 5 for cleaning heads and plates projection nozzles.

The on-board crew 3 is shown in more detail in FIG. 2 with the system hydraulic.

The high-speed mobile on-board crew includes one or more buffer tanks 6.
In the example of FIG. 2, four buffer tanks 6 are represented, each of them being dedicated to an ink color or to an ink tint used to compose a color, each of them is connected by a line of line 7 to the stationary tank 4, which includes as many chambers and lines as there are buffer tanks.

One or two spray heads correspond to each buffer tank downstream piezoelectric or other system ink, each head feeding its projection nozzles carried by a nozzle plate. According to the preferred embodiment each buffer tank 6 supplies one projection head and only one. Furthermore, the buffer tanks 6 are independent of each other and are removably mounted on the moving element. This provision, by authorizing the individual replacement of each tank, facilitates the maintenance of the whole. In the same spirit, a similar provision will be made for projection heads and associated nozzles. Another advantage in the removability of tanks 6 and projection heads lies in the improvement of the flexibility of use of the machine printing. Thus each reservoir 6 and associated projection head can now be assigned to a single color and a single ink category, this avoids the obligation of a complete cleaning of tanks and heads before replacing ink justified by chemical and / or physical incompatibility issues that may exist between inks of different categories and / or different colors.

The mark 8 indicates the connections of each of the heads which are supplied by a servo solenoid valve 9 downstream of each of the buffer tanks 6. The distributors 9 are individually controlled by the control and command unit. By ordering solenoid valves is interrupted or communication between the buffer tanks and the associated projection heads and therefore the ink supply of the spray nozzles. These solenoid valves are controlled independently of each other other.

Upstream of each of the buffer tanks 6, on each of the supply lines 7 a stationary solenoid valve 10 controlled by the stationary reservoir 4 the control and command unit. By controlling each of these solenoid valves is established or interrupted the communication between the associated tanks 4 and 6 and therefore whether or not the reservoir 6 is supplied with ink.

In order to detect the ink level in the tank and control the supply of ink when the level is at minimum and interrupt this supply when the level is at most, tank 6 is associated with a level detector capable of delivering two signals separate electrics, one of which is representative of a minimum level and the other of which is representative of a maximum level. This level detector is electrically connected to the unit of control and command to deliver to the latter the minimum level signals and maximum level.

As can be seen in Figure 2, the buffer tanks 6 can be maintained in depression by a common line 11 with means of depression 12, said line being connected to a compressor 13. This means of depressurization is advantageously constituted by a venturi effect device. Such a device, known per se, comprises a first channel internal provided at one of its ends with a compressed air inlet mouth and according to its other end of a compressed air outlet. In this internal channel radially the end of a second channel connected by its other end to line 11. By passage of an air flow in the first channel is created in the second a suction effect generator of depression.

Line 11 is provided, between the compressor 13 and the venturi effect device 12, with control and adjustment means, such as filter, regulator and pressure gauge of known types and which are not described.

A branch 14 connected to line 11 is connected, by means of a controlled shutter 15, to a venturi effect device 16 which puts a reservoir 17 with vacuum valve 18 under vacuum.
The vacuum tank 17 is connected by a solenoid valve 19 to the system 5 for cleaning and maintaining the ink spray nozzles.
The venturi effect device 12 on line 11 maintains the buffer tank in depression.

According to another embodiment, each buffer tank 6 is equipped with its own means of depression. This means of depression is made up advantageously by a venturi effect device 12 like that previously described. The suction mouth of this venturi effect device is connected directly by its mouth of suction through a through hole made in the upper wall of the buffer tank 6. Thus a depression is created in the upper part of the tank 6, above the level ink.

According to a first embodiment, the buffer tanks are supplied with ink through lines 7, the ink supply pressure being of the order of 0.1 to 0.2 bar.

According to a second embodiment each buffer tank 6 is supplied with ink by its own additional reservoir 34, the additional reservoir 34 being connected to the corresponding pipe 7 by the corresponding solenoid valve 10. This tank additional, for example of cylindrical shape, comprises a bottom wall, an envelope wall standing vertically on the back wall and a shutter cover coming to rest on the shore horizontal top of the envelope wall to close the opening which delimits said wall at this level. The additional tank 34 receives the level detector device and is connected to the buffer tank 6 via a lower pipe 34a located below the minimum level ink and by an upper line 34b located above the ink level allowing respectively the ink supply to the buffer tank 6 and the balance of air pressures in both tanks. Preferably, the pipes 34a and 34b provide a connection rigid mechanical between the buffer tank 6 and the additional tank 34. Thus these two tanks 6 and 34 both constitute a removable assembly in one piece.

As can be seen in Figure 9, the lower part of the shell wall of the tank additional has a through hole to which the outlet outlet of the the solenoid valve 10. This additional tank is therefore supplied from below; we avoid thus during the ink supply, the formation of waves and shock waves, generating ink pressure variations in the additional tank 34 and in the buffer tank 6.

The level detector is advantageously constituted by a float 35 and by a float position sensor 36, this sensor electrically connected to the control and control, being capable of delivering to said unit a minimum level signal and a signal maximum level. This detector is carried by the cover of the additional tank 34.

The projection heads operate at slight depression. It is necessary for the regularity of impression that this depression remains constant around minus 4 millibars or undergo as few variations as possible, a variation of minus four to minus eight millibars being acceptable.

It is necessary that there is in each of the buffer tanks 6, independently of the variations in ink level and of the movement of the latter in each tank due to the movement of the on-board crew carrying them, a minimum of change of vacuum to avoid variations in vacuum at the outlet of the nozzles, which would generate printing disorders.
For this purpose, each buffer tank 6 is divided to avoid the formation of waves.
Figure 3 shows a sectional view of a buffer tank among the four on-board buffer tanks 6.

Each buffer tank 6 is preferably a cylindrical volume, the top of which is closed and the base 20 of which towards the solenoid valve and the head is restricted.
To this end, the bottom wall 21 of each buffer tank has a cylindrical volume of small height and of smaller diameter than that of the tank with an outlet nozzle 22.
In the cylindrical volume of each of the buffer tanks 6 is introduced a dividing device 23 which breaks it down into several small tanks and fulfills a wave breaker damping function.

As shown in Figures 4 and 5, the dividing device is a block of section corresponding to that of the internal volume of the buffer tank which is provided from top to bottom with parallel channels 24 defining as many small tanks.
Advantageously, the divider has at its base a recess 25 facilitating the circulation of the ink.
It goes without saying that any other system performing a division and partitioning of the tank can be adapted.

Buffer tanks 6 and additional, dividers and covers are made of suitable materials, resistant to the solvents of the inks used.

The device for cleaning the nozzle plates and for maintaining the nozzles connected to the compressor by the branch 14 (FIG. 2) and shown diagrammatically in position in FIG. 1 is shown in detail in FIGS. 6 and 7.
It consists of a plate 26 of rectangular shape.
On this plate are reservations of rectangular shape 27. In each of the reservations 27 open two channels 28 and 29 connected by pipes to the reservoir 17 in depression.
The reservations 27 are aligned and offset at an angle relative to their alignment axis.
The reservations 27 each receive a plate made of a flexible material, for example silicone.
The plate has two oblong parallel oblique lights.
A first short lumen 30 corresponds to a nozzle of the duct 28. The lumen 30 is provided with two lips 31 of low height.
A second oblong opening 32 corresponds to the duct 29. This opening 32 has a scraping lip 33.

The maintenance cycle for heads and nozzles is shown in Figure 8 in solid lines, the different stages of the cycle and the movement of the head or heads being identified by the letters A, B, C, D, E, F and G .
In A the projection head is brought to a speed V1 above the lips 31 of the light 30.
At B the head is lowered at a speed V2 onto the lips 31.
In C the depression at the head is interrupted; the suction is put into operation by action of the venturi effect device 16 for a time T1.
In D the head is raised by a value of 2 millimeters above the lips 31, the suction is stopped, the depression is restarted.
At E the head is moved at a speed V2 above the scraper lip 33.
At F the head is raised to a speed V3.
In G the head is brought above the maintenance zone and the light 32, the spitting of the frames, that is to say of an amount of ink during a time T, is triggered.
This maintenance cycle makes it possible to clean the nozzles and nozzle plates and to prime the heads and the nozzles both while avoiding clogging thereof, for example by evaporation of the solvents.

Finally to avoid the migration of inks between the different areas printed on the support is carried out a prepolymerization. For this purpose behind the projection heads the machine is equipped with a means capable of causing polymerization of the ink affixed to the support, this means possibly consisting of a source of ultraviolet light radiation oriented towards the support. Any other suitable means may be used.

Claims (14)

1. A machine for "direct to substrate" printing on a table (1) by one or more heads with spray nozzles, said machine being of the type displaying relative movement between the substrate to be printed and the spray heads, each head preferably being dedicated to one colour or one shade, the head(s) being carried by a moving element (3), above the substrate to be printed, along the three spatial, orthogonal axes X, Y and Z, characterised in that each of the heads is equipped with a removable buffer reservoir (6), separable from the head, carried by the moving element and in that the head(s) and their buffer reservoir(s) (6) are maintained at a negative pressure to ensure operation of said head(s).
2. A machine according to claim 1, characterised in that the moving element (3) brings the heads and nozzles cyclically to a cleaning and maintenance system (5) which, by suction, cleans the nozzles and primes them and, by scraping, removes the excess drops and which allows the nozzles to be kept in such a state that they operate well.
3. A machine according to claim 1, characterised in that the interior space of each fitted buffer reservoir (6) is divided to reduce the amplitude of the waves produced by reservoir displacement.
4. A machine according to claim 1 or claim 2, characterised in that a compressor (13) connected by a line (11) to each buffer reservoir (6) comprises at least one venturi device (12) for lowering the pressure of said buffer reservoirs which are supplied with ink via lines (7) from the reservoir(s) (4) and in that a branch (14) of the line (11) is connected via a venturi effect device (16) to the device (5) for cleaning the heads and nozzles.
5. A machine according to claim 1 and claim 4, characterised in that a reservoir (17) is set to negative pressure between the venturi effect device (16) and the cleaning device (5).
6. A machine according to claim 4 or claim 5, characterised in that each buffer reservoir (6) is provided with its own venturi effect device (12).
7. A machine according to any one of the preceding claims, characterised in that each buffer reservoir (6) is supplied with ink by an additional reservoir (34) provided with a level detector device, this reservoir (34) is connected to the buffer reservoir (6) by a lower duct situated below the minimum ink level and by an upper duct situated above the ink level, respectively allowing the buffer reservoir (6) to be supplied with ink and the air pressure in the two reservoirs (6) and (34) to be balanced.
8. A machine according to claim 1 and claim 2, characterised in that the cleaning system comprises, for each head and/or nozzle plate, an oblong suction slot (30) and an oblong array purging slot (32).
9. A machine according to claim 1, claim 2 and claim 8, characterised in that the suction slot (30) is equipped with lips (31).
10. A machine according to claim 1, claim 2, claim 8 and claim 9, characterised in that the slot (32) is equipped with a scraping lip (33).
11. A machine according to claim 1 and claims 2, 8, 9, characterised in that, in the maintenance cycle, each head passes through the array suction, scraping and purging stage.
12. A machine according to claim 1 and claim 3, characterised in that the interior space of each fitted reservoir accommodates a divider device.
13. A machine according to any one of the preceding claims, characterised in that, downstream of the spray heads, it is provided with a means capable of causing polymerisation of the ink affixed to the substrate.
14. A machine according to any one of the preceding claims, characterised in that the buffer reservoirs (6) are supplied with ink from one or more stationary reservoirs (4) by supply lines (7), on each of which is mounted a servo-driven solenoid valve (10) actuated by the control and actuation unit, actuation of each of these solenoid valves establishing or interrupting communication between the associated reservoirs (4 and 6) and thus supply or non-supply of the reservoir (6) with ink.

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