Printing apparatus and corresponding method

Abstract

A printing apparatus on a print support includes a print head to print on said print support a print material; a feed device to feed the print material to the print head; and a recirculating unit to generate a recirculation of the print material through the print head and having a first container of the print material placed upstream of the print head, a second container of the print material placed downstream of the print head, a first recirculating sub-unit to generate a first flow of the print material from the first container to the print head and the second container, and a second recirculating sub-unit to transfer the print material from the second container to the first container, wherein the first and second containers are both maintained under two distinct negative pressures.

Claims

1. A printing apparatus comprising: a print head adapted to print a print material; a feed device to feed said print material to said print head; and a recirculating unit to generate a recirculation of said print material through said print head, said recirculating unit comprising: (a) a first container of said print material placed upstream of said print head; (b) a second container of said print material, placed downstream of said print head; (c) a first recirculating sub-unit to generate a first flow of said print material from said first container to said print head and said second container; and (d) a second recirculating sub-unit to transfer said print material from said second container to said first container, wherein said first container and second container are both maintained under two distinct negative pressures, and wherein the feed device for refilling ink into the recirculation unit comprises a pipe feeding the ink to the first container of the recirculation unit and a pumping device for picking ink from an accumulation tank and feeding the ink to the first container, the pipe having an outlet opening which is placed at a predetermined depth inside the first container, said depth being lower than a predetermined minimum level of the ink inside the first container and/or inside the second container.

2. The printing apparatus according to claim 1, wherein said recirculating unit comprises two members generating negative pressures, connected to said first container and respectively to said second container.

3. The printing apparatus according to claim 2, further comprising in a negative pressure sensor, wherein said recirculating unit comprises protection members to prevent said print material contained in one or both of said first container or said second container from entering into said members generating negative pressure in the negative pressure sensor.

4. A printing method performed with the printing apparatus according to claim 1, comprising: feeding, through the feed device, the print material to the print head for printing said print material, and recirculating, at least during printing, the print material through the print head, through the recirculating unit, by performing the following steps: feeding said print material through said feed device to the first container of said recirculating unit, generating the first flow of said print material through the first recirculating sub-unit from said first container to said print head and to the second container of said recirculating unit, and transferring through the second recirculating sub-unit said print material from said second container to said first container, wherein said first container and second container of said print material are maintained under two distinct negative pressures, further comprising the steps of setting a predetermined minimum level of the print material in the first container and delivering the print material through the feed device inside the first container at a depth which is below the predetermined minimum level.

5. The printing method according to claim 4, wherein said first and said second print material containers are maintained under positive pressure for performing a cleaning cycle of said print head when said printing apparatus is not printing.

6. The printing method according to claim 4, wherein feeding the print material to the first container is carried out in a pulsed manner by feeding in an alternate manner predetermined amounts of the print material with a predetermined repetition cycles and with a predetermined duration of feeding and non-feeding.

7. The printing method according to claim 4, further comprising the steps of setting the predetermined minimum level of print material inside the first container and/or inside the second container, and delivering the print material recirculated by the second recirculating sub-unit in the first container at a depth which is lower than the predetermined minimum level inside the said first and/or the second container.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and properties of the present invention are disclosed in the following description, in which exemplary embodiments of the present invention are explained in detail based on the drawing:

(2) FIG. 1 is a schematic representation of an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(3) FIG. 1 shows an embodiment of a printing apparatus 10 according to the present invention, to print a print material on a (not shown) support.

(4) The print material can comprise an ink, a paint or an enhancing material suitable to confer, for example, a shiny or opaque effect or other graphic effects, such as glitter, sequins or the like, conferred for example by respective paints.

(5) The print support can be made for example of a material chosen from paper, cardboard, textile materials, metal materials, wood materials, plastic materials, mineral materials or ceramic materials, although other types of material can also be used, and are not relevant for the purposes of the present invention.

(6) According to an embodiment, the printing apparatus 10 comprises a feed device 11 to feed the print material toward a recirculating unit 15, which in its turn generates, in a print head 13, a continuous recirculation of the print material. For the sake of convenience, in the description the recirculating unit 15 is subdivided into two recirculating subunits, a first recirculating subunit 16 and a second recirculating subunit 17.

(7) The print head 13 can be selectively controlled, in a substantially known way, to deposit the print material on a (not shown) print support according to a prefixed pattern.

(8) According to a preferred embodiment, the feed device 11 comprises an accumulation tank 12 into which the print material is deposited before printing, and a first pumping device 22 to transfer the print material from the accumulation tank 12 toward the recirculating unit 15.

(9) Said accumulation tank 12 is connected to a filtering device 21 through a pipe 41. The pumping device 22 takes the print material from the accumulation tank 12 through a first suction pipe 41, and channels it to the recirculating unit 15 through a second pipe 42.

(10) In an embodiment, the feed device 11 further comprises a mixing device 30 to periodically or continuously mix the print material contained in the accumulation tank 12.

(11) On the first pipe 41 and/or on the second pipe 42 a filtering device 21 can be interposed, e.g. in the form of a filter or the like.

(12) According to an embodiment a control unit 33 may be provided which drives the pumping device 22 in a pulsed way, such as to feed the ink for refilling the first tank 14 of the recirculation unit 15 with small ink amounts in an alternate manner.

(13) According to a first variant embodiment, the control unit 33 is configured in order to set predetermined repetition frequencies of the on/off deriving cycles of the pumping device 22. Variant embodiments may provide a control unit configured to set the time duration of the on and off phases of the pumping device 22.

(14) According to an embodiment, the control unit 33 is provided with a user interface allowing to input data relating to the repetition frequency and to the duration of the on and off phases of the pumping device 22.

(15) According to still a further embodiment one or more of the above parameters may be set in an automatic way by measuring the level of the ink inside at least the first container 14 by an ink level sensor 56 and by setting at least one of the repetition frequency and to the duration of the on and off phases of the pumping device 22 needed for refilling the ink in the tank in order the level of the ink falls below a minimum level L1.

(16) The algorithm of calculating and setting the above parameters, either manually or automatically is preferably determined in an empirical, especially experimental manner, as a function of the constructive parameters of the system, particularly of the feeding device 11 of the refilling system and of the kind of ink either in house by the system producer or at the system user.

(17) The said algorithm can be in the form of a program in which the instructions are coded for carrying out the algorithm by the control unit 33.

(18) Said recirculating unit comprises a first container 14 for print material connected to the feed device 11. The first container 14 is connected to the accumulation tank 12 through pipe 42. The first container 14 is upstream a respective print head 13 to which is connected through a first pipe 43a. In a preferred embodiment, the first pipe 43a is connected in correspondence to a lower portion, or bottom, of the first container 14. The connection of the first pipe 43a in the lower part of the first container 14 allows preventing the forming of air bubbles in the print material contained in the first container 14.

(19) According to still another feature of the present invention, the second pipe 42 connecting the output of the pumping device with the first container 14 of the recirculating unit 15, has an outlet 142 which is placed at a depth inside the said first container 14 which depth is lower than a predetermined minimum ink level L1 inside the said first container 14.

(20) The recirculating unit further comprises a second container 18 for print material, coming from the print head 13 through pipe 43b. In a preferred embodiment, the second pipe 43b is connected in correspondence to a lower portion, or bottom, of the second container 18. The connection of the second pipe 43b in the lower part of the second container 18 allows preventing the forming of air bubbles in the print material contained in the second container 18.

(21) Print material first container 14 and second container 18 lie on the same plane, and can contain two distinct levels of print material.

(22) The recirculating unit is of pneumatic type and comprises a pair of members 19, 20 (in the form of a series of solenoid valves) for generating negative pressure connected to said print material first container 14 and second container 18. In particular, said members 19, 20 are configured for generating a negative pressure, or depression, inside first container 14 and second container 18. The difference of negative pressure between the first container 14 and the second container 18 leads the print material to shift from the first container 14 to the second container 18, passing through the print head 13.

(23) The members 19, 20 for generating negative pressure comprise a series of solenoid valves assembled on a mechanical block configured to exploit Venturi effect. In particular, the member 19 generates negative pressure in the first container 14, and the member 20 generates negative pressure in the second container 18; the two negative pressures are different between the said print material containers 14 and 18.

(24) Typically, the value of the negative pressure in the print material first container 14 is −4 Kilopascal (kPa), while the value in the print material second container 18 is −10 kPa. This difference in the negative pressures activates the shifting of print material from the first container 14 to the second container 18 passing through the print head 13.

(25) Controlling the two members 19 and 20 for generating negative pressure, the negative pressure in said two print material containers 14 and 18 can be varied. Indicatively, the values of negative pressure which can be obtained range 0 to −50 Kilopascal.

(26) Different print heads and different print materials require the fine-tuning of the negative pressures in print material first container 14 and second container 18.

(27) The detection of negative pressure values is performed by a pressure sensor 50 detecting the negative pressure values in print material containers 14 and 18. The detected values are then transmitted to a control unit 33 controlling the members 19 and 20 so that the desired negative pressure values are obtained.

(28) Moreover, the members 19 and 20 generating negative pressure have a further valve enabling the cleaning of the print head 13 under positive pressure, modifying the pressure inside print material containers 14 and 18. Obviously, cleaning cycles, which implies feeding the print head 13 under positive pressure, are performed when the printing apparatus is not printing.

(29) Moreover, there are provided two overflow tanks 25a, 25b, which are interposed between print material first container 14 and second container 18, e.g. in an intermediate position between a first connecting pipe 46 and a second connecting pipe 47.

(30) In particular, in the tank 25a, connected to the first container 14, air is kept in a condition of negative pressure, and in the tank 25b, connected to the second container 18, a condition of negative pressure is generated, too.

(31) Said overflow tanks 25a and 25b can be provided with (not shown) discharge valves, for discharging possible condensation, or print material that could be present inside them. Moreover, said tanks 25a, 25b can be provided with sensors detecting print material. If such sensors are activated, they control or provide a signal for deactivating said members 19, 20 for generating negative pressure. In this way damages to the members 19, 20 generating negative pressure can be prevented.

(32) In an embodiment of the present invention, the recirculating unit 15 comprises a second recirculating sub-unit 17 too, to transfer the print material from the second container 18 to the first container 14.

(33) The second recirculating subunit 17 comprises a pumping device 23 connected, through a pipe 28, to the first container 14 and second container 18, to shift the print material from the second container 18 to the first container 14. In a preferred embodiment, the suction pipe 28 is connected with one of its end to the lower portion, or bottom, of the second container 18. This allows preventing that air is suctioned through suction pipe 28.

(34) The pipe 28 connects the pumping device 23 to print material second container 18, while a pipe 45 connects the pumping device 23 to the first container 14 for print material. In a preferred embodiment, the pipe 45 is connected with one of its end to the lower portion, or bottom, of the second container 18. This allows preventing that air is suctioned through suction pipe 28.

(35) In an embodiment, at least the delivery pipe 45 is provided with a filtering device 59 for filtering the print material stream that from the second container 18 enters in the first container 14. Moreover, should the pumping device 23 membrane break, the presence of the filtering device 59 prevents the entrance of undesired particles into the print material first container 14, and from there to the print head 13, with ensuing possible damages to the print head.

(36) According to an embodiment of the present invention, at least the delivery pipe 45 connecting the output of the pumping device 23 with the first container 14 of the recirculating unit 17, has an outlet which is placed at a depth inside the said first container 14 which depth is lower than a predetermined minimum ink level L1 inside the said first container 14.

(37) In a further embodiment, also the pipe 28 connecting the second container 18 with the input of the pumping device 23 of the recirculating unit 17, has an inlet which is placed at a depth inside the said first container 14 which depth is lower than a predetermined minimum ink level L1 inside the said first container 14.

(38) In an embodiment, there are provided detection devices, which comprise a first level sensor 56a to detect the level of print material in the first container 14, and a second level sensor 56b to detect the level of print material in the second container 18.

(39) The first level sensor and the second level sensor can be chosen from a group comprising optical sensors, magnetic sensors, inductive sensors, capacitive sensors, floating members, or possible combinations thereof.

(40) In the present embodiment, there are provided new dynamic level sensors, which allow, with respect to the previous on/off sensors, a more accurate control of print material level in the feed tank of the print heads, improving their management.

(41) In an embodiment, the recirculating unit 15 comprises conditioning devices connected to at least one of either the first container 14 or the second container 18 and configured to modify in a desired way the physical characteristics (e.g. temperature, viscosity) of the print material that circulates through the print head 13.

(42) The conditioning devices can comprise a system to regulate the temperature, for example obtained with a heat-carrying circuit, able to modulate the temperature of the print material contained in at least one of either the first container 14 or the second container 18, for example by heating and/or cooling action.

(43) The conditioning devices comprise e.g. a heating member 52 mounted outside at least one of either the first container 14 or the second container 18 to heat the print material contained in the latter according to pre-set modes.

(44) The heating member comprises e.g. an electric resistance 52 as shown in FIG. 1, a heat conditioning circuit or other device suitable to the purpose.

(45) In a further embodiment, the conditioning devices comprise a cooling member 61 to induce in at least one of either the first container 14 or the second container 18 a cooling of the print material contained therein, and to adjust its temperature to the temperature of use by the print head 13. In an embodiment, the cooling member 61 comprises a fluid-dynamic conditioning circuit that exploits the principles of a cooling cycle.

(46) The printing apparatus comprises a control unit 33, in this case a PLC, configured to monitor and manage at least the functioning mode of the first recirculating subunit 16 and the second recirculating subunit 17. In particular, depending on the signals detected by the first level sensor and the second level sensor, the control unit 33 can suitably manage the activation of the first pumping device 22 and of the pumping device 23, in order to maintain in the first container 14 and the second container 18 a predetermined level of print material, so as to ensure the correct supply to the print head 13.

(47) In an embodiment, the control unit 33 is connected to the components of the apparatus 10 to be controlled and managed through electric connections (not shown), such as electric cables or electric tracks, in the case where the control device comprises integrated boards or PCB.

(48) In a further embodiment, the control unit 33 can be served by user interface devices 34 to allow a human user to selectively set some print parameters and monitor alarms and anomalies.

(49) In an embodiment, the interface devices 34 are external to the printing apparatus 10, for example made by means of an electronic calculator such as a PC, or similar device.

(50) Even if the present invention was described with reference to a printing apparatus 10 comprising one print head 13 only, an application of the invention to a printing apparatus with more than one print head 13 is possible.

(51) In an embodiment, for each print head 13 it is necessary to provide its own feed device 11 and its own recirculating unit 15, like in the description above

(52) In an alternative embodiment, the recirculating unit 15 according to the present invention can feed a plurality of print heads, typically up to four.

(53) According to a variant embodiment of the apparatus of FIG. 1, the first and the second container 14 and 18 for the print material are provided with a dedicated print material level sensor 56a and 56b. Each of the two sensors monitors the level of the print material in the corresponding container 14 and 18 separately. The sensors react to a maximum print material L2 level in the respective container 14 and 18 and the signal generating by each sensor, separately, is transmitted to the control unit 33 which controls the members for generating negative pressure 19 and 20. When the level of the print material in at least one of the two containers 14, 18, reaches the maximum level L2, the signal of the sensor triggers the stop of the members generating negative pressure allowing the atmospheric pressure to build up into both the containers 14 and 18 and causing the print material to evacuate the containers. Evacuation takes place through the nozzles of the print head 13, since in absence of the flow through the print head no retain force is applied to the meniscus of print material in each of the nozzles and the print material flows down into a recovery tank 62.

(54) From this tank, the print material can be again pumped into the system. This can be carried out automatically by providing sensors of the print material in the tank 62, such as level sensors or other kind of sensors which controls a pump for transferring the print material from tank 62 to the containers 14 and 18. Obviously the transfer of the print material from the retrieval tank 62 into the containers 14 and/or 18 can also be carried out by a manual control of the pump.

(55) When the ink level in the containers reaches a minimum level indicated by L1 the level sensors 56a and/or 56b signals this condition and triggers the activation of the members 19, 20 generating the negative pressure in the containers 14 and 18 and the system starts again its normal operation.

(56) The above system for controlling the level of the print material in the containers 14 and 18 is particularly relevant when considering that a negative pressure is applied to each of the containers 14 and 18 and since this negative pressures apply a suction action on the print material if the system fails in maintaining the correct balances of the pressures it easily may happen that the level of the print material in one of the two containers or in both rises in an uncontrolled manner leaving the container and filling up the apparatus. Monitoring the level of the print material allows directing the print material exciding a certain level along a controlled path to a retrieve tank avoiding the flow of rising print material flooding all-over the apparatus causing damages and requesting long lasting recovery interventions.

(57) While the invention has been described in connection with the above described embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the scope of the invention. Further, the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and the scope of the present invention is limited only by the appended claims.

LIST OF REFERENCE NUMBERS

(58) 10 printing apparatus 11 feed device 12 accumulation tank 13 print head 14 first print material container 15 recirculating unit 16 first recirculating sub-unit 17 second recirculating sub-unit 18 second print material container 19 member for generating negative pressure 20 member for generating negative pressure 21 filtering device 22 pumping device 23 pumping device 25a first overflow tank 25b second overflow tank 28 pipe 30 mixing device 33 control unit 34 interface device 41 pipe 42 pipe 142 pipe outlet 43a pipe 43b pipe 45 delivery pipe 46 pipe 47 pipe 50 pressure sensor 52 heating member 56 detection device 59 filtering device 61 cooling member 62 print material retrieve tank L1 print material minimum level L2 print material maximum level