INK SUPPLY SYSTEM FOR DIGITAL PRINTING DEVICE AND DIGITAL PRINTING DEVICE COMPRISING SAID SYSTEM

Abstract

Ink supply system (1) for digital printing device comprising: a supply tank (9) suitable for containing ink; a delivery tank (2), in fluid connection with said supply tank (9), suitable for containing ink; one or more delivery conduits (4) suitable for connecting said delivery tank (2) to one or more print heads (100) associatable with said supply system (1); first pressure adjusting means (10) suitable for controlling the pressure inside the delivery tank (2); a supply pump (6) suitable for moving ink from said supply tank (9) to said delivery tank (2); a first level sensor (7) suitable for performing the continuous reading of the level variations inside the delivery tank (2); wherein said supply pump (6) is continuously feed-back controlled on the basis of the reading of said first level sensor (7) for keeping a pre-defined level inside said delivery tank (2).

Claims

1. An ink supply system for digital printing device comprising: a supply tank suitable for containing ink; a delivery tank suitable for containing ink, in fluid connection with said supply tank; one or more delivery conduits suitable for connecting said delivery tank to one or more print heads associatable with said supply system; first pressure adjusting means suitable for controlling the pressure inside the delivery tank; a supply pump suitable for moving ink from said supply tank to said delivery tank; a first level sensor suitable for continuously acquiring a level signal of the ink inside the delivery tank; wherein said supply pump is continuously feed-back controlled on the basis of the level signal acquired by the first level sensor for keeping a pre-defined level inside said delivery tank; and wherein said first level sensor is an analog sensor.

2. Supply system according to claim 1, wherein the feed-back control of said supply pump on the basis of the signal acquired by said first level sensor comprises at least a proportional action.

3. Supply system according to claim 1, further comprising: a return tank, suitable for containing ink, in connection with the supply tank; one or more return conduits, suitable for connecting the one or more print heads to said return tank, the delivery conduits and the return conduits defining an ink path through said one or more print heads; second pressure adjusting means, suitable for controlling the pressure inside the return tank; a re-circulating pump, suitable for moving ink from said return tank to said supply tank; a second level sensor, suitable for continuously acquiring a level signal of the ink inside the return tank; wherein said re-circulating pump is continuously feed-back controlled on the basis of the level signal acquired by the second level sensor for keeping a pre-defined level inside said return tank.

4. Supply system according to claim 3, wherein both the first and the second level sensor are analog sensors.

5. Supply system according to claim 4, wherein both the feed-back control of said supply pump on the basis of the signal of said first level sensor and the feed-back control of said re circulating pump on the basis of the signal of said second level sensor comprise at least a proportional action.

6. Supply system according to claim 5, further comprising two PID controllers for the feed-back control of the supply pump and of the re-circulating pump.

7. Supply system according to claim 3, wherein said first pressure adjusting means and said second pressure adjusting means allow the independent control of the pressure inside the delivery tank and inside the return tank.

8. Supply system according to claim 7, wherein both the first pressure adjusting means and the second pressure adjusting means are suitable for taking the pressure inside the delivery tank inside the return tank respectively both to values inferior to the atmospheric pressure and to values superior to the atmospheric pressure.

9. Supply system according to claim 8, wherein said first and/or second pressure control means comprise a compressor and an inversion valve, wherein the compressor's action defines a compression of a gaseous phase within the delivery tank and/or return tank when the inversion valve is in a first configuration, an expansion of said gaseous phase when the inversion valve is in a second configuration.

10. Supply system according to claim 9, wherein said first and/or second pressure control means further comprise a pressure control line with an initial section communicating with the delivery tank and/or return tank, a final section communicating with an outlet to the atmosphere, and a ring-shaped intermediate section intercepted by said compressor and provided with an inlet and an outlet, wherein the inversion valve respectively connects the inlet and the outlet of the intermediate section to the final section and to the initial section of the pressure control line if in first configuration, and viceversa if in second configuration.

11. Supply system according to claim 10, wherein the initial section of the pressure control line comprises an expansion tank on which a pressure sensor is provided for, the signal detected by said pressure sensor being employed for the feed-back control of the pressure.

12. Supply system according to claim 8, wherein said first and/or said second pressure control means comprise a proportional valve connected to a compressed air circuit.

13-14. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0054] FIG. 1 shows a scheme of an ink supply system according to a first embodiment of the present invention;

[0055] FIG. 2 shows a scheme of an ink supply system according to a second embodiment of the present invention;

[0056] FIG. 3 shows an enlargened detail of the scheme of FIG. 1, relative to the pressure adjusting means;

[0057] FIG. 4 shows an enlargened detail of the scheme of FIG. 2, relative to the pressure adjusting means.

MODES FOR CARRYING OUT THE INVENTION

[0058] With reference to the annexed FIG. 1, we generically identify with 1 an ink supply system for digital printing device according with a first embodiment of the present invention.

[0059] We note that such a supply system 1 is generally integrated in a digital printing device, namely in a device arranged for the digital printing of a printing support.

[0060] Such printing device, known per se, preferably comprises a fixed bridge under which the printing support is dragged, which can be of various nature. One or more print heads 100, supplied by the supply device 1, provide for the delivery of ink on the printing support that transits under the bridge, realizing an image, a motif, a decoration, or any desired graphic element.

[0061] Alternatively, the device can comprise a mobile print module that transits over a fixed printing support (for example: plotter).

[0062] The supply device 1, of the ink recirculating type, comprises a delivery tank 2 and a return tank 3 provided with one or more delivery conduits 4 and return conduits 5 that close themselves on the print heads 100, realizing the desired ink circulation.

[0063] Ink comes from a supply tank 9 above, which in turn is connected to a main tank 23 with interposition of a conditioning chamber 24. Ink coming from the main tank 23 is preliminarily heated in said conditioning chamber 24 to be taken to a homogeneous temperature with ink circulating in the circuit of the supply device 1.

[0064] A level sensor 25 of the supply tank 9 indicates the emptying of such volume, enabling the recall of more ink from the main tank 23.

[0065] On the supply tank 9 are also provided for, on the one hand, an ink conditioning system, which allows both the heating and the cooling thereof, and on the other hand, a temperature sensor 28, which allows the control of such variable of the fluid.

[0066] The presence of a conditioning system with refrigerating means as well as heating means appears to be particularly advantageous within the context of the invention, since it allows to cancel the heating effects of ink due to the circulation in the heads.

[0067] The supply tank 9 is connected to the delivery tank 2 through a line intercepted by a supply pump 6, which encourages the movement of ink from said supply tank 9 to said delivery tank 2.

[0068] Said line is also interrupted by an intermediate degassing device 26, from which an evacuation line 27 of the excess air departs.

[0069] A line is also provided for that takes ink from the return tank 3 to the supply tank 9, on which a recirculating pump 12 works. Such line is intercepted by a non-return valve 29, which impedes the passage of ink when the circuit is closed.

[0070] In use, ink is therefore re-circulated through the circuit described above:

[0071] from the supply tank 9 to the delivery tank 2, through the delivery conduits 4 to the heads 100, through the return conduits 5 to the return tank 3 and from here again to the supply tank 9.

[0072] Also the line that connects the return tank 9 to the supply tank 9 is intercepted by a non-return valve 31, which impedes the passage of ink when the circuit is idle.

[0073] The delivery tank 2 provides for a conditioning system of the ink that allows the heating thereof and a temperature sensor 30 for the control of such variable.

[0074] The delivery tank 2 and the return tank 3 are provided with a first level sensor 7 and a second level sensor 8 respectively, of analog type, destined to perform the continuous reading of the variations of the level of ink inside the chambers.

[0075] Both the first level sensor 7 and the second level sensor 8 send the level signal acquired to a controller, preferably of PID type, which operates the supply pump 6 and the re-circulating pump 12 respectively for keeping a level setpoint inside the delivery tank 2 and the return tank 3.

[0076] The setpoint is preferably represented by a constant ink level, and the use of the continuous feed-back control allows to avoid sensitive variations in time, unlike what happens in the realizations of the background art, wherein the filling up and the emptying of the tanks is executed only when the minimum and the maximum thresholds are reached.

[0077] The delivery tank 2 and the return tank 3 are both pressurized, and are provided for respective first adjusting means 10 and second adjusting means 11, independent from one another.

[0078] The first and the second adjusting means 10, 11 are of the same type.

[0079] With reference to FIG. 3, the following are described here: first adjusting means 10 acting on the delivery tank 2; the same description applies, mutatis mutandis, also to the second adjusting means 11 acting on the return tank 3.

[0080] The adjusting means 10, 11 comprise an expansion tank 16, directly connected to the upper part of the respective delivery tank 2 or return tank 3 through a first portion 18a of a pressure control line.

[0081] At the expansion tank 16 a pressure sensor 17 is provided for, which allows to acquire a signal indicative of the pressure inside the expansion tank 16, substantially equal to the pressure within the delivery tank 2 or return tank 3 directly connected to it.

[0082] On the expansion tank 16 an overflow sensor 19 is also provided for, suitable for identifying a maximum allowable liquid threshold inside the volume.

[0083] From the upper part of the expansion tank 16 a second portion 18b, 18c, 18d branches off of the pressure control line; thanks to the control executed by the overflow sensor 19 the absence of liquid in such line portion is guaranteed.

[0084] The second portion comprises an initial section 18b, a ring-shaped intermediate section 18c, and a final section 18d that flows into an outlet to the atmosphere 15. On the intermediate section 18c a compressor 13 acts, while an inversion valve 14, specifically a two-position electrovalve, allows to invert the connections between the two outlets of the intermediate section 18c and the initial section 18b and final section 18d.

[0085] When the inversion valve 14 is in a first configuration, the connection of the intermediate section 18c with the initial section 18b and final section 18d is such that the action of the compressor 13 takes air from the outlet to the atmosphere 15 to the expansion tank 16. In this case, the gas present in the expansion tank 16 compresses and the pressure measured by the pressure sensor 17 increases.

[0086] When the inversion valve 14 is in a second configuration (represented in FIG. 3), the connection of the pressure control line is inverted and the compressor 13 acts as an air expulsion fan, defining a gas expansion and a pressure fall in the expansion tank 16.

[0087] It is noted that, thanks to the action of the compressor 13 and of the inversion valve 14, the respective pressurized tank 2, 3 can be taken both to pressure and to depression.

[0088] The adjusting means 10 preferably act with feed-back control on the variable of pressure measured by the pressure sensor 17, following a pressure setpoint set by the operator.

[0089] With reference to FIG. 2, an ink supply system for digital printing device according to a second embodiment of the present invention is generically identified with reference 1′.

[0090] It is noted that the second embodiment differs from the preceding one only in the realization of the first and of the second pressure control means 10′, 11′.

[0091] For the other components of the device, integral reference is therefore made to the previous description.

[0092] The first adjusting means 10′ and second adjusting means 11′, as in the case of the first embodiment, are independent one from another and are of the same type.

[0093] With reference to FIG. 4, below are described the first adjusting means 10′ acting on the delivery tank 2; the same description applies, mutatis mutandis, also to the second adjusting means 11′ acting on the return tank 3.

[0094] The adjusting means 10′, 11′ comprise also in this case an expansion tank 16′, directly connected to the upper part of the respective delivery tank 2 or return tank 3 through a first portion 22a of a pressure control line.

[0095] At the expansion tank 16′ a pressure sensor 17′ is provided for, which allows to acquire a signal indicative of the pressure inside the expansion tank 16′, substantially equal to the pressure within the delivery tank 2 or return tank 3 directly connected to it.

[0096] On the expansion tank 16′ an overflow tank 19′ is also provided for, suitable for identifying a maximum allowable liquid threshold inside the volume.

[0097] From the upper part of the expansion tank 16 a second portion 18b, 18c, 18d branches off of the pressure control line; thanks to the control executed by the overflow sensor 19 the absence of liquid in such line portion is guaranteed.

[0098] The second portion 22b connects the expansion tank 16′ with a proportional valve 20, connected to a compressed air circuit 21 provided with a vaccumm branch 21a and with a high pressure branch 21a.

[0099] It is noted that the compressed air circuit 21 is preferably shared between the first adjusting means 10′ and the second adjusting means 11′.

[0100] Thanks to the proportional valve 20, it is possible to modify the pressure in the expansion tank 16′ and in the respective delivery tank 2/return tank 3, modifying the reading of the pressure sensor 17′.

[0101] Also in this embodiment, the delivery tank 2/return tank 3 can be taken both to positive pressures and to negative pressures.

[0102] The adjusting means 10′ preferably act with feed-back control on the variable of pressure measured by the pressure sensor 17′, following a pressure setpoint set by the operator.

[0103] The systems described above, thanks to the double feed-back control on the pressure and on the level, allow an unusual stability of the pressure values in the delivery tank 2 and return tank 3, avoiding or anyway minimizing the printing errors due to changes in the ink pressure.

[0104] The systems described above also allow a wide range of adjustments for the ink flowrate and for the meniscus pressure in the heads 100, being possible to independently adjust the incoming Pin pressure and the outcoming Pout pressure, defined by the pressure in the delivery chamber 2 and in the return chamber 3 respectively.

[0105] Further, always thanks to the above-mentioned adjustment faculty, it is possible to execute a flow inversion (reverse flow), or else a purge operation of the heads 100 automatically.

[0106] Naturally, to the description made here, in order to satisfy contingent and specific needs, a skilled person will be able to devise further modifications and variants, all however contained in the scope of protection of the invention as defined by the following claims.