The subject matter of the present invention is a supply system for a printer that uses a jet of ink, commonly known as an inkjet printer. Specifically, but not exclusively, the supply system finds application in supplying inkjet printers that use inks with high solids content, the solids essentially being constituted by pigments reduced to fine particles.
The nature of such inks, constituted by suspensions of solids finely divided in a liquid, is the root of the main problem that the present invention intends to solve. The problem consists of the possibility of sedimentation of the solid parts that naturally tend to separate from the liquid in which they are suspended. This phenomenon has two main negative effects: it alters the physical-chemical properties of the suspension, thus influencing the quality of the inkjet printing and it can cause clogging of the print head nozzles.
The document
Other examples of prior art ink supply system are disclosed in
Therefore, the principal aim of the present invention is to provide an adequate solution to the problem consisting of possible sedimentation, thereby overcoming the negative consequences described above.
An additional aim of the invention is to provide a simple means of control of the working conditions of the print heads that ensures a high level of constancy of operation.
An additional aim of the invention is that of rendering the operation of the (single) heads independent of the recirculation system so as to maximize the performance of both.
An advantage of the invention lies in the fact that it allows for a rapid stabilizing of the pressures throughout the circuit supplying the heads whenever, owing to the inevitable variations caused by corresponding variations in the flows required by some of the same heads, pressure imbalances occur, negatively affecting the regular operation of the printer. Another advantage can definitely be found in the fact that the supply system permits regular operation even in the event of a temporary shutdown of some parts of the system, such as the pumps that produce circulation of the ink for example.
Further characteristics and advantages of the present invention will become more apparent from the detailed description herein below of several embodiments of the invention, which are illustrated by way of non-limiting example in the attached figures, wherein:
With reference to the above-mentioned
The print head 1 is part of a printing unit 2 that proves to be made up of one or more print heads 1 with ink recirculation and that forms a "bar of colour" or a printing unit 2 of an extension suited to the size to be printed. The print heads that make up the "bar of colour" or printing unit 2 work with the same ink, that is, with the same colour.
The print heads 1 forming the said "bar of colour" are supplied by an ink supply system, which comprises: a line for supply-distribution of the ink, indicated in its entirety by the number 3, and a line for recirculation 4 of the ink.
In particular, the supply-distribution line 3 originates from a reservoir 5, has a plurality of short connecting branches 30 for supplying the print heads 1 and empties into the same reservoir 5.
The line for recirculation 4 of the ink is made up of a plurality of short channels 40 originating from the print heads 1 - in the case represented, a short channel 40 originates from each print head - and converging into a collection manifold 41, which empties into the reservoir 5.
The ink supply-distribution line 3 comprises a distribution tube 31, from which the short connecting branches 30 directly branch off for the supply of the print heads 1 in a number at least equal to the number of print heads 1 to be supplied.
At least the distribution tube 31 is shaped and proportioned so as to reduce to a minimum head loss of the liquid circulating therein.
This means for example that the distribution tube 31 has a larger diameter than that of the tubing making up the remaining part of the entire supply-distribution line 3. The distribution tube 31 empties directly into the reservoir 5.
There is provided a first means suitable for producing the circulation of the ink in the supply-distribution line 3.
This first means serves the function of producing the circulation of the ink in the supply-distribution line 3 and comprises a circulation pump 32 located upstream of the distribution tube 31.
Also upstream of the distribution tube 31, and downstream of the circulation pump 32, there is provided an equipment, indicated in its entirety by the number 33, containing a filtering device and a device for deaeration of the ink.
The supply-distribution line 3 is subject to a set of control means, the function of which is that of controlling the pressure in the said supply-distribution line and particularly in the distribution tube 31.
These means comprise a first pressure sensor 34 suitable for measuring the pressure existing in the distribution tube 31 of the supply-distribution line 3, for comparing said pressure value with a preset pressure value and, based on the difference found, for commanding the activation of an apparatus 50 suitable for maintaining the pressure inside the reservoir 5 in keeping with the said preset value.
The apparatus 50 keeps the reservoir 5 under vacuum conditions, creating therein the said preset vacuum value, which is determined and regulated to enable the proper timed operation of the print head nozzles, thus realizing the ejection of ink only on command and in the amount foreseen, without the occurrence of conditions giving rise to the possibility for example of undesired spontaneous ejection.
The ink level pre-established for proper functioning of the printing unit is automatically maintained in the reservoir 5 by means of a simple device that comprises an ink level sensor 51, which automatically activates a refiller pump 52. The latter provides for replenishment of the liquid until the pre-established level is reached.
The ink recirculation line 4 is made up of a plurality of short channels 40 originating from the print heads 1 and converging into a collection manifold 41, which empties by converging into the reservoir 5.
A second means suitable for producing the circulation of the ink in the collection manifold 41 comprises a suction-pumping device, which is preferably constituted by a pump 43 that is commanded to suction the ink from the collection manifold 41 and re-introduce it into the reservoir 5.
As an alternative, instead of the pump 43, there may be provided an apparatus made up of a reservoir, in which a pre-established vacuum degree is maintained through a vacuum pump or a Venturi for the purpose of generating suction and thus the circulation of the ink in the recirculation line 4.
A specific control means is provided for controlling the pressure in the recirculation line 4 and particularly in the collection manifold 41, thus controlling the system in this manner.
In particular, a pressure sensor 42 is provided for measuring the pressure existing in the recirculation line 4, for comparing of said pressure value with a preset pressure value and, based on the difference found, for commanding the activation of a suction-pumping device consisting of a pump 43 suitable for maintaining the pressure in keeping with the said preset value.
In practice, the apparatus 50 controls the pressures inside the heads 1 by controlling the pressure in the reservoir 5.
For this purpose, as regards the realization, there may be provided a sort of safety circuit, which for example makes it possible to prevent undesired discharge of ink from the heads 1, when supply voltage to the electrical equipments for activation of the system is not present. The system may consist of a circuit comprising a valve 46, a Venturi tube 47 and a pressure gauge or pressure indicator 48. A compressed air circuit 49 passes through the pressure gauge 48, the valve 46 and the Venturi tube 47, thereby realizing in the Venturi tube a vacuum that is transmitted by means of a channel 55 to the reservoir 5.
The electrically commanded valve 46 is of a type that is normally open when electrical voltage is present. Therefore, when it is energized, it closes, preventing the passage of air. The electrical command of the valve is directly connected to the voltage generator of the machine. In the event of an electrical power failure, the apparatus 50 stops working, the valve goes out of control, opening instantly and permitting the compressed air to reach the Venturi tube 47. The vacuum created by the Venturi tube 47 is transmitted to the reservoir 5 by means of the channel 55. The pressure gauge or pressure indicator 48 is regulated in such a manner as to have the necessary flow of air pass into the Venturi tube for the purpose of generating the proper vacuum level inside the reservoir 5, which makes it possible to maintain the ink in equilibrium inside the heads 1.
The special structure of the supply system that is the subject matter of the invention described creates an operating condition of the printing unit 2, which substantially renders the operation of the individual head 1 independent of that of the others making up the printing unit 2, thereby permitting a considerable reduction of the possibility of sedimentation of solid particles. This is afforded by the possibility of keeping considerable amounts of ink in constant movement, in a manner substantially independent of the absorption of the individual heads. In fact, the constant movement and the considerable flows counteract the risk of sedimentation very effectively. The flow of ink drawn by the individual heads is independent of the "external" flow that takes place in the distribution tube 31, which closes the supply-distribution line 3 in a loop on the reservoir 5.
The flow is drawn by the individual head 1 through the short connecting branches 30, thus being fractionated in two parts: the first, which is ejected on command from the nozzles so as to realize the printing, or decoration in the case of ceramic tiles 10, the second, which is recirculated through the short channel 40 and directed into the collection manifold 41, which provides for channelling it into the-reservoir 5.
In the event of a temporary zeroing of the first fraction of the flow, internal recirculation of the second fraction of the flow takes place in any case, this latter fraction being recirculated in its entirety through the short channel 40.
The control system implemented as a whole by the described control means, which operates by monitoring the pressure in the distribution tube 31 and in the collection manifold 41, makes it possible to carry out the adjustments needed so as to maintain the operation of the system constantly aligned with the required parameters in the presence of variability of the situations involving the demand for ink on the part of the various print heads.
The flow rate of the ink realized by the system can be set as desired, and this is an advantage of the system. In particular, it can also be set at a value higher than the maximum supply value and simultaneously for all the heads 1 in the printing unit 2. This makes it possible to have ink flow into the heads, always under the best conditions, for example being highly deaerated by the system 33. In addition, the present solution also makes it possible to exclude the circulation pump 32 or the equipment 33 temporarily for short periods of time, without impairing the regular operation of the same heads.
The pump 43 is of a type capable of realizing, on command, reversal of the flow of the fluid pumped, for the purpose of carrying out internal recirculation in the heads 1 in a direction opposite the usual direction for carrying out internal cleaning.
The reversal of the flow is important for removing contaminating particles that may be present inside the individual head and that can obstruct the head, or also simply for washing out the heads.
The reversal of the flow is realized by means of the reversal of the motion of the pump 43 that draws the ink from the reservoir 5 and sends it to the heads. The stabilization inside the heads is realized by regulating the pressure in the reservoir 5. The external recirculation through the distribution tube 31 returns the ink to the reservoir 5.
In the event that electrical reversal cannot be realized, the same results of the reversal of flow can be achieved with an auxiliary circuit 14 such as the one shown in
This auxiliary circuit can be obtained by means of the insertion, on the collection manifold 41, of two three-way valves 14a and 14b, located, respectively, upstream and downstream of the pump 43 so that there is a direct connection of the downstream valve 14b with the reservoir 5.
There are also provided a direct connection of the upstream valve 14a with the reservoir 5 by means of a first channel 14c, and a direct connection of the downstream valve 14b by means of a second channel 14d, to the collection manifold 41 in a point located upstream of the upstream valve 14a.
The reversal of the flow in the collection manifold 41 can thus be realized very simply, by activating the valves 14a and 14b so that the ink is collected from the reservoir 5 through the first channel 14c and pushed by the pump 43 so as to re-enter the collection manifold 41 through the second channel 14d.
Normal operation of the supply system is achieved by commanding the valves 14a and 14b so as to enable the passage of fluid solely along the collection manifold 41.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.