The present disclosure relates to a cleaning system, more particularly to a cleaning system for the print head of an inkjet printer.

In inkjet printing, a print head delivers ink in drops from nozzles to pixel positions in a grid of rows and columns of closely spaced pixel positions or other organized or randomized patterns.

In domestic inkjet printers, the print head is moved relative to a substrate to be printed upon, typically paper, in two dimensions, with a scanning motion along the width of the paper and paper motion along its length between scans.

Inkjet heads or arrays of inkjet heads can, however, be made as wide as (or wider than) an area to be printed to allow single-pass printing. Such heads are commonly found in industrial inkjet printers. In single-pass printing, the head is held in a fixed position while the substrate to be printed upon is moved along its length in an intended printing direction. All print lines along the length of the substrate are printed in one pass.

In such industrial single-pass inkjet printers it is common that nozzles will remain unused for periods of time, for example, when a substrate narrower than the print head is printed or when the image to be printed in a run does not use all of the nozzles in the nozzle array on the print head. This can be problematic, since ink within the nozzles can dry in situ blocking the nozzles.

To counteract the problem of blocked nozzles, the print head may be purged periodically by pushing ink through the nozzles under positive pressure. Following the purge, the print head must be manually wiped to clear away excess ink remaining on the print head. This is time consuming and often ineffective, leading to further problems.

Blocked nozzles can also occur during machine downtimes. When solvent or water based inks are used, ink drying leading to nozzle blocking occurs by evaporation. When UV curable inks are used, this problem can be exacerbated by the inks curing under the effect of ambient light.

The present invention arose in a bid to provide an improved cleaning mechanism for an inkjet print head; and to provide a solution to the problem of UV curable inks drying out during machine down times.

According to the present invention, in a first aspect, there is provided a cleaning mechanism for an inkjet print head, comprising a cleaning head that is provided with a cleaning element that is arranged to be drawn across the print head to clean nozzles in the print head, wherein the cleaning head is arranged such that the portion of the cleaning element that is in contact with the print head is constantly changed as the cleaning element is drawn across the print head.

According to the present invention, in a further aspect, there is provided a purge tray for an inkjet printer comprising an opening, for receiving ink from nozzles of print heads that are supported by a print head plate, and at least one gasket arranged around the periphery of the opening, wherein the gasket is configured to engage the print head plate when the purge tray and print head plate are brought into contact with one another and to prevent the passage of light from outside the purge tray and the print head plate to the nozzles whilst allowing the passage of air from outside the purge tray and the print head plate to the nozzles.

Further, preferable features of the cleaning mechanism and the purge tray are presented in the dependent claims.

According to the present invention is another aspect, there is provided a cleaning mechanism as described above in combination with a purge tray as described above.

According to the present invention in a final aspect, there is provided an inkjet printer comprising a cleaning mechanism as described above and/or a purge tray as described above. Non-limiting embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view from below of the cleaning mechanism;

Figure 2 shows a side view of the cleaning mechanism of Figure 1;

Figure 3 shows a perspective view of the cleaning head of the cleaning mechanism of Figure 1; and

Figure 4 shows a perspective view from above of the purge tray.

Referring to Figures 1 to 3, there is shown a partial view of an inkjet printing mechanism 1, which comprises a print head plate 2, which is substantially rectangular and supports a plurality of print heads 3, each of which is provided with a plurality of nozzles. The faces of the print heads that are provided with the nozzles are substantially flush with the lower face of the print head plate. The nozzles in each of the print heads extend in rows in the X-direction. The print heads, and thereby the rows of nozzles, are provided side by side in the Y-direction.

The print head plate is supported by wheels, which engage guide tracks in a frame 4 which supports the print head plate and allows for planar movement of the print head plate, and thereby the print heads, back and forth in the X-direction. In the depicted arrangement a piston 5 is provided to effect the back and forth movement of the print head. By such planar movement the print head plate may be moved between a printing position (not shown), a cleaning position and a purging/storage position.

It will be readily appreciated by those skilled in the art that numerous other support and movement mechanisms may be provided to effect planar movement of the print head plate. Moreover, arrangements will be possible where the position of the print head plate is fixed and the other described elements are moved to the print head plate instead.

Figure 1 additionally shows a cleaning mechanism 6, which is provided for cleaning the print heads 3, and a purge tray 7. The cleaning mechanism 6 comprises a cleaning head 8 that is provided with a cleaning element (cloth 9) that is arranged, in use, to be drawn across the print heads to clean the nozzles in the print heads. The cloth is preferably a lint free cloth. The cleaning head is mounted to a cleaning head support structure 14.

The cloth 9 is held on a first roller 10 and is taken up by a second roller 11. The first roller 10 may be considered to be a feed roller, supplying clean cloth to the cleaning head, and the second roller 11 may be considered to be a take up roller, receiving dirty cloth following cleaning. A pair of guide rollers 12 may further be provided between the first and second rollers, one either side of the cleaning head, as shown. Alternative roller

arrangements will, however, be possible. The rollers are rotatably mounted to the cleaning head support structure and have their axes perpendicular to the rows of nozzles in the print heads. Alternative arrangements are possible where the axes are parallel to the rows of nozzles although the present perpendicular arrangement is preferred, since multiple print heads may be cleaned simultaneously without any risk of the ink from one print head being drawn across face of another print head of a different colour. One or more motors (not shown) are provided to rotate the first and/or second rollers.

The cleaning head 8 has a tapered upper surface which supports the cloth as it passes from the first roller to the second roller. The upper surface is fixed against rotational movement. The cloth slides over the fixed upper surface as it travels between the rollers. In the present arrangement, the tapered upper surface is curved. The cleaning head has a greater width than the cloth in the Y-direction. The cleaning head is arranged to clean multiple print heads at once and the cloth is therefore wider than the combined width of the print heads in the Y-direction. The width of the print head and the cloth will be configured in dependence of the combined width of the print heads to be cleaned and may be varied accordingly. The cleaning head may comprise a nylon block.

The cleaning head is resiliently biased by one or more springs, which urge the cleaning head towards the print head plate in the Z-direction (i.e. the printing head is urged upwards, as viewed in the figures). It will be readily appreciated that alternative biasing means may be utilized, however. During cleaning of the print head, the portion of the cloth at the apex of the curved surface of the cleaning head is held in contact with the surface of the print head under the biasing force of the spring(s). The cloth is sandwiched between the print head and the cleaning head. The portion of the cloth that is at the apex of the curved surface of the cleaning head, and is thereby in contact with the print head, is constantly changed, by rotation of the rollers 10, 11, as the cleaning element is drawn across the print head, as described in more detail below.

It should be noted that the tapered upper surface of the cleaning head need not be curved but may take alternative forms, such as but not limited to a wedge shape. In further alternatives the upper surface of the cleaning head may be flat. In all cases the portion of the cloth that is in contact with the print head will be constantly changed as the cleaning head is drawn across the print head.

It is preferable that the leading edge of the cleaning head, which is brought into contact with the print head as the print head and cleaning head are translated towards one another is curved or sloped, i.e. provided at an oblique angle to the bottom face of the print head plate and thereby the print heads, such that the cleaning head is easily urged downwards against the biasing force of the spring(s) to pass under the print head.

A spray head 13 is preferably provided, which is arranged to spray solvent, or other cleaning fluid, which may also be water, on the cloth. The spray head comprises a tube provided with a plurality of nozzles along its length. The spray head is positioned between the first roller and the cleaning head so that solvent may be applied to the cloth prior to the cloth contacting the print head during a cleaning operation.

The cleaning head support structure is mounted on pistons 15, which are arranged to raise and lower the cleaning head support structure, and thereby the cleaning head. It will be readily appreciated by those skilled in the art, however, that alternative mechanisms may be implemented to allow the print head support structure to be raised and lowered. In alternative arrangements the height of the print head support structure may be fixed. A cleaning operation using the cleaning mechanism will now be described:

The print head plate is moved along the X-axis towards the cleaning head (in the direction of arrow A in Figure 1).

At this time or before, the cleaning head support structure 14 is moved into the position in the Z-direction shown in Figures 1 and 2 by actuation of the pistons, so that the apex of the curved surface of the cleaning head, which supports the cleaning cloth, is at a predetermined height above that of the planar face of the print head plate.

With continued travel of the print head plate along the X-axis (in the direction of arrow A in Figure 1), the print head plate is brought into contact with the cleaning head, and thereby the cleaning cloth. With contact of the cleaning head and the print head plate, the cleaning head is deflected downwards against the biasing force of the spring(s), wherein the biasing force of the spring(s) apply a counterforce upwards, which acts to urge the print head, and thereby the cleaning cloth, against the print head plate and the print heads supported thereby as the print head plate travels over the print head in the direction of arrow A.

As contact is made between the cleaning head and the print head plate, or immediately before contact is made, the motor(s) are activated to rotate the rollers so that the cleaning cloth is pulled over the face of the cleaning head as the cleaning head and the print head plate are moved relative to one another by the movement of the print head plate over the cleaning head (in the direction A in Figure 1). Note that the position of the cleaning head is static in the X-direction whilst the cleaning cloth travels in the X-direction.

The cloth travels in the same direction (the direction of arrow B in Figure 1) as the direction in which the cleaning head, and thereby the cloth, is drawn across the print head plate by the movement of the print head plate over the cleaning head (in the direction A in Figure 1). Note that the speed at which the cleaning head is drawn across the print head plate corresponds directly to the speed at which the print head plate is moved in the X- direction (in the direction of arrow A in Figure 1). By virtue of the movement of the cloth over the cleaning head, as described, whilst the cleaning head and the print head plate are translated relative to one another, the portion of the cloth at the apex of the cleaning head, which contacts the print head, is constantly changed and thereby the portion of cloth contacting (wiping) the cleaning head is always clean.

The speed at which the print head and the cleaning head are moved relative to one another may be considered to be the cleaning head speed, since this is the speed at which the cleaning head is drawn across the face of the print head plate. The speed at which the cloth travels over the cleaning head may be considered the cloth speed.

The cloth speed is governed by the absorption speed of the ink into the cloth. As ink from the nozzles is absorbed by the cloth it will spread (bleed). Absorbed ink is always drawn forward into the direction of the dirty nozzles. The cloth speed is configured such that clean cloth only is drawn onto the clean nozzles. The cloth speed may be faster than the print head speed to compensate for the spread of ink in the cloth.

The cloth speed will preferably be at a minimum to conserve the rolls. The cleaning head speed will preferably be balanced to be as fast as possible to allow for quick cleaning whilst being slow enough to ensure suitable absorption of ink from the nozzles and thereby sufficient cleaning. The cloth and print head speeds will be balanced with one another to ensure that clean cloth is presented to every nozzle to be cleaned whilst the amount of cloth used in minimized and the cleaning speed is maximized.

It should be noted that whilst in the present arrangement, the print head plate is moved in the X-direction and the cleaning head is static in the X-direction, in alternative arrangements, the print head plate may remain static in the X-direction with the cleaning head moved in the X-direction. The print heads may be purged prior to cleaning. Furthermore, the cloth may be treated with solvent, water, or any other suitable cleaning fluid using the spray head 13 as the cloth is moved over the cleaning head.

The purge tray 7 comprises an opening 16, for receiving ink from the nozzles of the print heads that are supported by the print head plate, a lower opening 31, which is in fluid communication with a fluid reservoir 17 for collecting ink for extraction and disposal, and side walls 18 extending between the openings.

The purge tray is provided with a gasket 19 arranged around the periphery of the opening. The gasket is shown in Figure 4. The gasket is configured to engage the print head plate when the purge tray and print head are brought into contact with one another and to prevent the passage of light from outside the purge tray and the print head plate to the nozzles whilst allowing the passage of air from outside the purge tray and the print head plate to the nozzles. The gasket provides a labyrinth seal. The gasket is preferably foam.

The purge tray 7 is sized such that the opening 16, and thereby the gasket, surrounds all of the print heads supported by the print head plate with the gasket contacting the planar bottom face of the print head plate to form the required seal. Whilst the purge tray is shown to be rectangular, it need not be and may take numerous other forms, as will be readily appreciated by those skilled in the art.

The gasket of the present arrangement is formed in two parts 19a, 19b, wherein each gasket part is substantially U-shaped. The gasket parts oppose one another and provide first and second channels 20, 21, which are open to atmosphere at their ends. The channels allow air to flow from outside of the print head plate and the purge tray when the print head plate and purge tray are brought into contact with one another and the gasket contacts the planar bottom face of the print head plate to create a seal.

It must be noted that whilst an arrangement with two gasket parts is shown, in alternative arrangements the gasket may be of single piece construction. In such an arrangement, a single channel may be provided and/or the channel(s) may be formed by grooves in the gasket, which do not extend through the thickness of the gasket. Furthermore, the gasket need not be of rectangular form. Additional suitable alternative arrangements will be readily appreciated by those skilled in the art.

In the present arrangement, the purge tray has a longitudinal dimension and a transverse dimension. Each gasket part has a pair of parallel spaced longitudinal limbs that are joined at one end by a transversely extending limb. The first gasket part 19a has its transversely extending limb 22 extending along a transversely extending edge 23 of the purge tray and the second gasket part 19b has its transversely extending limb 24 extending along the opposite transversely extending edge 25 of the purge tray. The transversely extending limb of the second gasket part is narrower in the transverse direction than the transversely extending limb of the first gasket part. The longitudinally extending limbs 26 of the second gasket part are shorter than the longitudinally extending limbs 27 of the first gasket part. The longitudinally extending limbs of the first gasket part extend along respective longitudinally extending side edges 28, 29 of the purge tray and have their ends aligned with the outer edge of the transversely extending limb of the second gasket part. The longitudinal extending limbs 26 of the second gasket part are each spaced inwardly from a respective one of the longitudinally extending limbs of the first gasket part and have their ends spaced from the inner edge of the transversely extending limb 22 of the first gasket part, which they extend towards.

The purge tray is of particular benefit for storage of the print heads during down times of the inkjet printer when UV curable inks are used, wherein the purge tray may be maintained in sealing engagement with the print head plate when the printer is not being used to block the passage of light to the nozzles and prevent the curing of the ink therein. The benefit of not providing an air tight seal is that pressure is normalized and problems with meniscuses in the nozzles are avoided.

The purge tray is supported on pistons 40, in the same manner as the cleaning head support structure discussed above. The pistons allow the purge tray to be raised into engagement with the print head plate (by travel upwards in the Z-direction) once the print head plate has been brought into alignment with the purge tray by appropriate translation in the X-direction. Again, alternative means of bringing the purge tray and the print head plate into engagement with one another will be readily appreciated by those skilled in the art.