TECHNICAL FIELD

The present invention relates to a device and method for cleaning ink-jet printing heads.

In particular reference is made, for example, to a device and a method for cleaning ink-jet printing heads for printers used in the ceramic sector, for decorating tiles or the like.

PRIOR ART

As is known, printers for use in the ceramic sector exhibit one or more printing bars on which are normally fixedly mounted one or more printing heads. The manufactured items to be . decorated slide below the heads, resting on a conveyor belt, and the heads expel small droplets of ink from the nozzles in synchrony with the movement of the conveyor belt, decorating the items with the desired fantasy patterns.

The ink used in ceramic printing is constituted by suspensions of solids finely suspended in a liquid. For this reason, with the aim of preventing blockage of the nozzles, the printing heads, usually piezoelectric, include an internal recycling of the ink which is supplied by means of an inlet and an outlet predisposed on the head. To improve the fluidity of the ink, the head can also include a heater which acts on the ink when it circulates in the head.

The recycling of the ink reduces the natural tendency to separation/sedimentation of the solid particulate present in the ink.

However, the recycling and heating are not sufficient to prevent blockage of the heads. At present, when the owners of inkjet printers notice a decaying in the performance of the inkjet printing heads, especially heads used for printing in the central zone of the product, first they move those printing heads to the sides of the bar, where the defect generated thereby is less perceptible to the naked eye, and then they replace the heads which progressively get blocked. To prevent too-frequent replacement of the heads, it is possible to proceed to some cleaning operations which at present are carried out manually once the heads have been demounted from the printer.

DESCRIPTION OF THE INVENTION

An aim of the present invention is to provide a device which enables carrying out cleaning of the blocked printing heads automatically, in a way that is clean, fast and safe, without fouling and preventing useless waste of washing liquid.

This and other aims are attained by a device realised according to the technical teaching of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will emerge from a reading of the description that follows, provided by way of non-limiting example, with the aid of the figures of the accompanying tables, in which: figure 1 is a perspective view of the device of the invention, where some parts have been omitted for simplicity of description;

figure 2 is a frontal view of the device of the invention, and in this view too some parts have been omitted for simplicity of description;

figure 3 is a lateral view of the device of figure 2; and

figure 4 is a schematic view of a supply line and a collecting line of a washing liquid which are part of the device of the present invention.

BEST WAY OF CARRYING OUT THE INVENTION

With reference to the figures, a device for cleaning heads of inkjet printers is illustrated, denoted in its entirety by reference numeral 1.

The device 1 comprises a frame 2 to which a plurality of walls 2A and doors 2B are fixed (in the drawings, for the sake of simplicity only some are shown) which delimit the external casing of the device, internally of which a washing tub 200 is included for the external part of the head and a collecting tub 119 of a purging liquid.

The tubs are fixed to a work plane 260 also fixed to the frame 2. The work plane 260 is positioned such as to be accessible from a front part 1A of the device and a vertical wall 261 extends therefrom which separates the front part from the rear part of the device 1 B, where the plants and systems necessary for correct functioning thereof are housed.

A support 130 is accessible from the front part A of the device, above the two tubs 1 19, 200, which support 130 is provided with removable fixing of a head 108 destined to be cleaned. The fixing means are of a conventional type and are for example the same as used for fixing the head to the printer, for example by means of threaded organs. The head can be of the piezoelectric type and includes an inlet 109A and an outlet 1 11A which, when the head is on the printer, are connected to appropriate ink tubing with which ink is supplied to the head and recycled internally thereof.

The support 130 includes movement and guide means between the first operating position in which the support 130 is positioned at the washing tub 200, and a second operating position in which it is positioned at the collecting tub 1 19.

The washing tub 200, during use, is filled with a second washing liquid 204 (for example solvents and/or organic or non-organic dilutants, such as for example the product commercially known as "flus sp" produced by the company Triangle Inc., i.e. a vinyl-based solvent, and/or the product known by the commercial name of SM1620 produced by the company Smaltochimica, i.e. a solvent based on a mixture of glycols, also suitable for cleaning solvent-based inks) which is injected therein in a known and appropriate way, for example by pouring it through the opening of the washing tub 200, or via known tubings that are not illustrated. It also exhibits a drain (not shown) which enables evacuating one or both the washing tubs 200 and the collecting tub 1 19 when necessary. It can further exhibit an ultrasound generator 300 associated thereto and/or a heater 301 of the liquid internally thereof.

More precisely, the support 130, when in the first operating position, is internal of the washing tub 200 and positioned such that when the support 130 supports the head 108, the head 08 is at least partly immersed in the second washing liquid 204 present internally of the washing tub 200. When on the other hand the support 130 is in the second operating position it is positioned above the collecting tub 119, or at least partly internally thereof, so that a first washing liquid draining from the head 108, and specifically from the nozzles thereof, is completely collected internally thereof.

With the aim of moving the support 13 as described above, the guide and movement means thereof include a plate structure 206 which is positioned above the tubs 119, 120 and fixed to the vertical wall 261. The plate structure 206 supports a first guide 207 on which a carriage 208 is slidable. The carriage 208 is constrained to a transmission belt 209 stretched between an idle pulley 210B and a drive pulley 210A drawn in rotation by a motor 205 which can function as the only movement means of the whole structure.

The carriage 208 includes, realised internally thereof, a second guide 211 which in this case is formed by two through-holes internally of which bearings are positioned which cooperate with a pair of stems 212 reciprocally joined by a first plate 213 and by a second profiled plate 214.

The first profiled plate 213 is appropriately fixed to the support and to the stems 212. The second profiled plate 214 is also fixed to the stems 212 and includes a wheel 216 mounted idle thereon. The wheel 216 is rested on a profiled guide 218 fixed to the vertical wall 216. In this way the wheel 216 unloads the weight of the stems 212 on the guide, the support 130 and the plates 213 and 214.

The profiled guide 218 has a camel-hump conformation, with the vertex 218A positioned between the two tubs 119, 200 and above the tubs 199, 200, and with a first and a second trough respectively aligned with the centre of the washing tub and the collecting tub 119. Of note is the fact that in proximity of both the troughs and the vertex the profiled guide 218 can include substantially horizontal portions.

When the carriage 208 is vertically aligned to the vertex 218A of the profiled guide the wheel 2 6 is in proximity thereof and therefore the support 130 is in a rest position, raised above the tubs and easily accessible by an operator for the fixing operations thereto of the head 108 about to be cleaned. When on the other hand the carriage 208 is vertically aligned to a trough, the wheel 216 is in the corresponding trough and therefore the support 30 is lowered internally of the corresponding tub 119, 120.

What is described herein above is an example of how a single actuator can advantageously move the support 130 along two mutually-inclined axes, given that mechanical means are present (i.e. the profiled guide 218 and the wheel 26 sliding thereon) which correlate the movement along the first axis with the movement along the second axis. In fact it is sufficient to move the carriage 208 so as to obtain a corresponding movement of the support 130. The device of the invention also comprises a supply line 240 and a collecting line 250 of a first washing liquid, which are not visible in figures 2 and 3 as they are positioned in the rear part 1 B of the device 1. Both are connectable to the head 108 by means of an end part 110, 102 thereof formed by flexible tubes which can be grouped together by a common support 107. In this way the tubes do not hamper the movement of the head when it is associated to the support.

More precisely, the supply line 240 is connected to the head by means of a flexible supply tube 120, provided with coupling means 109 to the inlet 109A of the head.

These coupling means 109 can be rapid connections, threads or other means enabling a sealed coupling between the flexible tubes and the inlet 109A and the outlet 111A of the head 108.

The supply line 240 can comprise, opportunely connected by tubes 103 and connections 104, a pressure-raising means (for example a pump 102) with a delivery supplying a filter 118 downstream of which a serpentine 103A (or another suitable means) is located for heating the first washing fluid. The pressure of the supply line is detected by a pressure transducer 05 located thereon, preferably downstream of the filter 1 8 and the serpentine 103A. The presence of the serpentine 103A and the filter 118 is optional, as is the presence of the pressure transducer 113.

The pump 102 aspiration is in communication, via an appropriate tubing 115 possibly also flexible, with a source of the first washing fluid which can be a tank 116 external of the device or a reservoir internally thereof. As in the preceding case, the collecting line 250 is connected to the head 108 by means of a flexible collecting tube 110, connected to the outlet 111 A of the head, also by coupling means 111.

The collecting line 250 also includes appropriate tubing 103 and connections 104 and a solenoid valve 113 which intercepts the line. A container 114 is included downstream of the solenoid valve 113, for the waste liquid, which in this case too can be integrated into the device or an external tank.

In conclusion it is stressed that a control unit 101 is provided for managing the guide and movement means, the pump 102 and the solenoid valve 113. The control unit 101 can also manage the serpentine 103A, the pressure transducer 105 on the basis of the reading of which it can command the pump 102 so as to obtain a desired pressure value, and all the other electronic devices present in the device or not explicitly described here.

The functioning of the invention is clear to the technical expert in the field from what is described in the foregoing and is substantially the following.

First an operator takes a printing head to be cleaned, fixes it to the support 130 appropriately; the inlet 109A and the outlet 11A are connected to the head, by means of the flexible tubes, respectively to the supply line 240 and the collecting line 250.

In this step the support is in the rest position, illustrated in figure 2, i.e. between a tub and another so as to be easily accessible to the operator. When the preliminary operations have been completed, and once the first and the second liquid have reached the desired temperature (which can be suitably detected by the control unit 01 using sensors placed respectively on the supply line 240 downstream of the serpentine 103A and directly in the washing tub 200, the control unit 101 activates the pump 102 so as to cause the first washing liquid internally of the head 108. The pressure at which the fluid is supplied to the head is regulated by the control unit 101 with an appropriate activation of the pump 102, based on the reading of the pressure transducer 105, which can vary according to the model of head 108 inserted in the circuit. During this washing step of the recycling, the solenoid valve 1 13 is open and the first washing liquid transiting internally of the head 108 is drained into the container 1 14. This step enables removing any traces of sediment from the internal part of the head 108 normally involved in the recycling of the ink. Note that during this step there is no outlet of the first washing liquid from the nozzles of the head 108 since the pressure internal of the head is not sufficient to cause the liquid to exit therefrom (the solenoid valve 13 being open).

With the aim of reducing the times necessary for the cleaning of the heads 108, during this step the control unit 101 displaces/positions the support 130 into the first working position. In this way the head 108 is immersed in the second washing liquid present in the washing tub 200, and, possibly with the aid of ultrasounds created by the ultrasound generator 300 associated to the tub, is cleaned meticulously with regard to the external surface thereof.

Following the step of external cleaning, the duration of which is regulated by the control unit 101 according to preset parameters, the support 130 is extracted from the washing tub 200 and brought into the rest position or into the second operating position.

Note that the duration of the external washing step and the recycling washing step can lead to various situations. For example when the support is extracted from the washing tub 200, i.e. when the external washing step has been concluded, the recycling washing step can also be terminated or might still be in operation. If the recycling washing step is still in operation, it can be completed either internally of the washing tub 200, possibly by deactivating the ultrasounds 300 so as to save energy, or by bringing the support 300 into the rest position or by bringing the support 130 directly into the second operating position. The latter solution is more advantageous as the second washing liquid present externally of the head 108 falls directly into the collecting tub without fouling other parts of the device.

Once both the external cleaning step and the recycling cleaning step are terminated, the control unit 101 closes the solenoid valve, the control unit 101 closes the solenoid valve 113 and, by activating the pump 102 (in this case too at a controlled pressure) the nozzle-cleaning step is initiated.

In this case the pressure that is created internally of the head 108 causes the expulsion of the first washing liquid from the nozzles (see figure 4). The liquid expelled in the form of droplets 303 optimally cleans the nozzles (for example the internal channels of the nozzles) and is collected in the collecting tub 119. In practice, a sort of rain is created where the liquid, which exits from the nozzles of the head 108, flows in a cascade and pours into the collecting tub 119 (producing a kind of comb-tooth appearance as it falls).

The cleaning step of the nozzles also has a predetermined duration controlled by the control unit 101. In this step, the management of the inlet pressure of the first liquid internally of the head 108 is crucial. In fact, a too- high pressure would lead to the breaking of the nozzles, which a too-low pressure would not enable a complete and homogeneous cleaning thereof. Therefore during the step it is very important for a pressure transducer 105 to be present to enable the control unit 101 to carry out a precise calibration of the pressure injected into the head 108 on the basis of pre-set values.

Note that the temperature of the first washing liquid is also advantageously controlled by the control unit 101 so that it falls within the required parameters according to the type of washing liquid used and the respective viscosity/density of the washing liquid used.

When the cleaning step has been completed, an external cleaning of the head 108 can be newly carried out, placing it in the first operating position and activating the ultrasounds, or the head 108 can be returned into the rest position so that it is immediately available for an operator who disconnects it from the device 1.

In practice the cleaning step of the nozzles of the head 108 can be totally managed by the control unit 101 , which enables personalizing the washing cycles described above, by programming and using planned procedures and set or settable times in line with the user's requirements, for example so as to be able to memorise, in the control unit 101 , a list of specific cleaning cycles for any model of head 108 and ink used. Various embodiments of the invention have been described, but others might be conceived using the same innovative concept.