DESCRIPTION The present invention relates to a cleaning head for inkjet printing apparatus, particularly but not exclusively inkjet printing apparatus of the type having a printhead assembly within which there is provided a plurality of printing heads.

The use of inkjet printing apparatus of the type including a plurality of printing heads is well known in the art. Each printing head includes a nozzle plate on which there is defined an exterior nozzle orifice surface having a row of nozzle orifices through which ink is ejected under a microprocessor control.

It is well-appreciated that inkjet printing apparatus of the present type require regular maintenance and cleaning. In use, droplets of ink become airborne as they are ejected and can adhere to the nozzle surface adjacent to and within the nozzle orifices. The build-up of ink and debris subsequently affects the ink injection performance to the extent that print quality reduces.

The present invention is particularly directed to cleaning effectively the orifices and orifice surfaces of a nozzle plate without causing physical wear to the orifice surface while effecting efficient cleaning and reducing the need for additional maintenance. It will be understood by the skilled addressee that the terms ‘printing head’ and

'printhead' are interchangeable and the terms are not intended to be limiting and should be interpreted broadly to incorporate any common inkjet delivery device requiring a regime of maintenance and cleaning such as that described hereinafter.

It has been noted that in the prior art the term ‘wiping’, as applied to cleaning a surface with an elastomeric blade or with a material mop, has been used synonymously with ‘scraping’ which often implies the use of a rigid edge, however, is also used more broadly to describe the action of an ‘air-knife’ where a narrow blade of high velocity air is angularly directed onto a surface to remove debris therefrom. In the description that follows, the term ‘scrape’ is also used to denote an action where high shear forces are brought to bear against a surface with the intended purpose of removing ink and/or debris from the subject surface.

It will be appreciated by the skilled addressee that the term ‘ink’ as used herein may comprise water-based inks, solvent based inks and inks having specialised characteristics relating to curing, such as ultraviolet UV radiation curing inks, and related to security features, most commonly, radiating under UV light.

The present applicant has appreciated the need for an improved cleaning head capable of overcoming or at least alleviating the disadvantages associated with prior art. In accordance with a first aspect of the present invention, there is provide a cleaning head for cleaning an exposed exterior nozzle orifice surface of a nozzle plate of an inkjet print head, the cleaning head comprising: a body defining a vacuum port configured to be coupled to a vacuum source, the body having an exterior surface profiled to deflect the trajectory of air drawn into the vacuum port against the exposed exterior nozzle orifice surface of the nozzle plate as the nozzle plate moves relative to the cleaning head along a path substantially parallel to a longitudinal axis of the body so as to dislodge ink and accumulated debris from the exposed exterior nozzle orifice surface, said ink and debris dislodged from the orifice surface being drawn into the vacuum port (e.g. for collection in a fluid trap for disposal); wherein the body comprises: a nozzle portion; and a base portion supporting the nozzle portion.

In one embodiment, the vacuum port comprises an inlet slot (e.g. horizontal inlet slot) extending laterally between opposed first and second laterally spaced side walls of the nozzle portion.

In one embodiment, the nozzle portion defines: a tapered nozzle body defining an external airflow guide surface; and a nozzle tip surrounding the inlet slot.

In one embodiment, the nozzle tip is a tapered nozzle tip.

In one embodiment, the tapered nozzle body has an uppermost tapered section inclined to vertical at a steeper taper angle than a corresponding taper angle of a lowermost tapered section of the tapered nozzle tip.

In this way, a cleaning head is provided in which a nozzle with an inlet slot and an airflow guide surface is combined with an inclined droplet collection surface configured to both guide airflow towards the nozzle orifice surface and collect droplets attempting to travel down the sides of the nozzle. Advantageously, the proposed nozzle geometry has been found to allow a reduction in area of the inlet slot and increase in vacuum flow rate resulting in more effective cleaning and reduced cleaning head maintenance.

In one embodiment, the cleaning head is a contactless cleaning head (i.e. no part of the cleaning head makes physical contact with the inkjet printing head). In one embodiment, the body comprises first and second opposed inclined end walls

(e.g. leading and trailing inclined end walls relative to a forward direction).

In one embodiment, the body comprises first and second opposed inclined side walls.

In one embodiment, the uppermost tapered section of the tapered nozzle body has a taper angle (e.g. mean taper angle) A. In one embodiment, the lowermost tapered section of the tapered nozzle tip has a taper angle (e.g. mean taper angle) B.

For the purposes of the present disclosure, the or each taper angle is an acute angle, measured from vertical (i.e. the smaller the value of the angle, the steeper the inclination of the taper). In one embodiment, A <B (i.e. taper angle A is steeper than taper angle B).

In one embodiment, the tapered nozzle tip has a substantially constant taper angle (e.g. a constant taper angle B).

In one embodiment, taper angle A = 25-37°.

In one embodiment, taper angle A is substantially 31°. In one embodiment, taper angle B = 39-59°.

In one embodiment, taper angle B is substantially 49°.

In one embodiment, the tapered nozzle body comprises first and second opposed nozzle body end walls.

In one embodiment, the tapered nozzle body comprises first and second opposed nozzle body side walls.

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body end walls are inclined relative to vertical.

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body side walls are inclined relative to vertical.

In one embodiment, the nozzle tip comprises first and second opposed nozzle tip end walls.

In one embodiment, the nozzle tip comprises first and second opposed nozzle tip side walls.

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip end walls are inclined relative to vertical.

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip side walls are inclined relative to vertical. In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body end walls have an uppermost tapered section inclined by a first taper angle (e.g. first mean taper angle) Ai.

In one embodiment, taper angle Ai = 25-37°.

In one embodiment, taper angle Ai is substantially 31°. In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body side walls have an uppermost tapered section inclined by a second taper angle (e.g. second mean taper angle) A2.

In one embodiment, Ai > A2.

In one embodiment, taper angle A2 = 17-25°. In one embodiment, taper angle A2 is substantially 21°.

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip end walls are inclined by a first taper angle (e.g. first mean taper angle) Bi.

In one embodiment, taper angle Bi = 39-59°.

In one embodiment, taper angle Bi is substantially 49°. In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip side walls are inclined by a second taper angle (e.g. second mean taper angle) B2.

In one embodiment, Bi _> B2.

In one embodiment, taper angle B2 = 27-41°.

In one embodiment, taper angle B2 is substantially 34°. In one embodiment, the uppermost tapered section of the tapered nozzle body is contiguous with the lowermost tapered section of the tapered nozzle tip.

In one embodiment, the tapered nozzle body and the tapered nozzle tip are formed as a single component. In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body side walls have a concave curved surface profile (e.g. with an angle of inclination to vertical which increases with increase distance from the bottom of the base portion).

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle body end walls have a concave curved surface profile (e.g. with an angle of inclination to vertical which increases with increase distance from the bottom of the base portion).

In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip side walls have a concave curved surface profile (e.g. with an angle of inclination to vertical which increases with increase distance from the bottom of the base portion). In one embodiment, one or more (e.g. both) of the first and second opposed nozzle tip end walls have a concave curved surface profile (e.g. with an angle of inclination to vertical which increases with increase distance from the bottom of the base portion).

In one embodiment, the nozzle portion defines a passageway defining a tapered internal chamber section and an elongate entrance section connecting the inlet slot to the tapered internal chamber section.

In one embodiment, the base portion defines a vacuum source connection chamber and the tapered internal chamber section connects the elongate entrance section to the vacuum source connection chamber.

In one embodiment, the tapered internal chamber section is profiled to act as an internal airflow guide surface (e.g. to smoothly transition airflow passing from the elongate entrance section to the vacuum source connection chamber).

In one embodiment, the internal tapered chamber section comprises first and second opposed internal end walls.

In one embodiment, the internal tapered chamber section comprises first and second opposed internal side walls.

In one embodiment, one or more (e.g. both) of the first and second opposed internal end walls have a convex curved surface profile (e.g. with an angle of inclination to vertical which increases with increased distance from the bottom of the base portion).

In one embodiment, one or more (e.g. both) of the first and second internal side walls have a convex curved surface profile (e.g. with an angle of inclination to vertical which increases with increased distance from the bottom of the base portion).

In one embodiment, the inlet slot has a slot length S _L (e.g. extending in the lateral direction) and a slot width Sw (e.g. extending in the longitudinal direction). In one embodiment, the ratio of the slot length S _L to the slot width Sw is > 20 (e.g. 20- 30).

In one embodiment, the slot length S _L is substantially 27x slot width Sw.

In one embodiment, the print head nozzle plate has an exposed exterior nozzle orifice surface width Pw and the slot length S _L is greater than or substantially equal to Pw (e.g. substantially equal to Pw) _.

In one embodiment, the inlet slot has a cross-sectional area SA < 2.6 mm ² (e.g. < 2.0 mm ² , e.g. < 1.8 mm ² ).

In one embodiment, SA is substantially 1.63 mm ² . In accordance with a second aspect of the present invention, there is provided an inkjet printing apparatus having a printhead assembly, movable between a printing position and a maintenance position, comprising a plurality of printing heads each of the type having a nozzle plate on which there is defined an exposed exterior nozzle orifice surface, the orifice surface being formed with a row of nozzle orifices through which ink is ejected under microprocessor control; wherein the printing apparatus includes, at the maintenance position of the printhead assembly, a cleaning station comprising a plurality of laterally spaced cleaning heads (e.g. separated by longitudinally extending channels); and at least one vacuum source in communication with the plurality of cleaning heads; wherein each cleaning head is a cleaning head in accordance with the first aspect of the present invention (e.g. in accordance with any embodiment of the first aspect of the present invention).

In one embodiment, the inlet slot has a vacuum flow rate (Fs) >13 litres/min (e.g. >20 litres/min, e.g. substantially 26 litres/min).

In one embodiment, spacing between an uppermost surface of the cleaning head and the exposed exterior nozzle orifice surface of the nozzle plate is in the range of 0.145mm - 0.435mm (e.g. 0.18mm - 0.27mm, e.g. substantially 0.225mm).

In one embodiment, the at least one vacuum source is a non-pulsatile vacuum pump.

In one embodiment, the at least one vacuum source is a constant-velocity vacuum pump (e.g. positive displacement pump or momentum transfer pump).

In one embodiment, the at least one vacuum source is a rotary vane vacuum pump. In one embodiment, the at least one vacuum source has a vacuum source inlet flow rate

(Fi) > 18 litres/min (e.g. > 29 litres/min, e.g. substantially 36 litres/min).

In one embodiment, the inkjet printing apparatus includes a plurality of vacuum sources (e.g. as previously defined) and each of the plurality of cleaning heads is connected to a respective one of the plurality of vacuum sources.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1A is a schematic perspective view of inkjet printing apparatus in accordance with an embodiment of the present invention including a printhead assembly and a cleaning station with the printhead assembly shown in a printing position;

Figure IB is a schematic perspective view of the inkjet printing apparatus of Figure 1 A with the printhead assembly shown in a maintenance position;

Figure 2A is a schematic side view of the cleaning station and printhead assembly of the inkjet printing apparatus of Figure 1 A when the printhead assembly is in the maintenance position;

Figure 2B is a schematic partial perspective underside view of the printhead assembly and cleaning station of Figure 2A;

Figure 2C is a schematic diagram illustrating a fluid circuit of the cleaning station of the inkjet printing apparatus of Figure 1A;

Figure 3 is a schematic perspective view of components of the cleaning station of Figure 1A;

Figure 4A is a schematic perspective view of a cleaning head of the cleaning station of Figure 1A; Figure 4B is a schematic plan view of the cleaning head of Figure 4A;

Figure 4C is a schematic cross-sectional view of the cleaning head of Figure 4A along line A-A showing external angles and internal geometry thereof;

Figure 4D is a schematic cross-sectional view of the cleaning head of Figure 4A along line B-B showing external angles and internal geometry thereof; Figure 4E is a schematic cross-sectional view of the cleaning head of Figure 4A along line A-A showing external dimensions thereof;

Figure 4F is a schematic cross-sectional view of the cleaning head of Figure 4A along line B-B showing external dimensions thereof;

Figure 4G is a schematic cross-sectional view of the cleaning head of Figure 4A along line A-A showing internal dimensions thereof;

Figure 4H is a schematic cross-sectional view of the cleaning head of Figure 4A along line B-B showing internal dimensions thereof; and

Figure 5 is diagrammatic perspective view of the cleaning head of Figure 4A showing flow trajectories of ambient air drawn into the vacuum port of the cleaning head and the pressure levels encountered.

Figures 1 A and IB show inkjet printing apparatus 10 comprising an inkjet printhead assembly 20 movable across a print media on which ink for printing is to be applied. The inkjet printhead assembly 20 comprises a plurality of inkjet printing heads 30, each having a reservoir for ink fed from ink supply lines 40 and, as described hereinbelow, a printing surface comprising a nozzle plate 50 having an exposed exterior nozzle orifice surface 52 defining an array of orifices through which ink is ejected under microprocessor control.

The printhead assembly 20 is also movable from its printing position (Figure 1 A) to a maintenance position (Figure IB) where purging and cleaning processes are performed. The maintenance position is defined by a purge tray 60 within which there is provided a contactless cleaning station 70 over which the inkjet printhead assembly 20 is moved reciprocally.

As shown in figure 2A, the cleaning station 70 comprises an array of cleaning heads 80 mounted on an array block 90, the array of cleaning heads 80 being positioned to receive in close proximity respective printing heads 30 of the inkjet printhead assembly 20 during a cleaning cycle. Each cleaning head 80 includes a quick-connect coupling 82 provided for connecting a respective vacuum source to the cleaning head 80.

Figure 2B shows a cleaning head 80 in juxtaposition to a nozzle plate 50 of an inkjet printing head 30. The inkjet printing head 30 includes a peripheral nozzle plate guard 32 configured to protect the nozzle plate 50 to be cleaned as the inkjet printing head 30 is moved progressively over the cleaning station 70. The exposed exterior nozzle orifice surface 52 corresponds to the visible part of the nozzle plate 50.

As detailed in Figure 2C, vacuum source connecting pipes 72 (which pass through a side wall of the purge tray 60) connect to respective ones of the cleaning heads 80 via quick- connect couplings 82. Each of the cleaning heads 80 of the cleaning array is connected via its vacuum source connecting pipe 72 through a fluid trap 74 (via an air filter 73) to a respective vacuum source 75 of the cleaning station 70 (for simplicity only a single vacuum source and its associated parts are shown). Each fluid trap 74 is, in turn, connected to a common waste collection tank 77 via an ink separator drain pump 79. The waste outlet pipe 62 from the purge tank 60 also feeds to the common waste collection tank 77. Typically each vacuum source 75 is a non-pulsatile, constant- velocity vacuum pump with sufficient rotor inertia to deal with vacuum pressure increases for short periods of time without dropping flowrate. For example, each vacuum source 75 may be a rotary vane vacuum pump. In one example, the vacuum source 75 is set provide a vacuum source inlet (Fi) flowrate of substantially 36 litres/min in order to generate a flow rate at the inlet slot (Fs) of 26 litres/min at its respective cleaning head 80. Figures 3 and 4A-H show the array of cleaning heads 80 of the cleaning station 70 in more detail.

With reference to Figures 4A-H, each cleaning head 80 comprises a body 110 (formed as a single component, e.g. by 3D printing) having a longitudinal axis “A”. Body 110 defines a nozzle portion 120 featuring a vacuum port 130 configured to be coupled to vacuum source 75 via quick-connect couplings 82, and a base portion 140 supporting the nozzle portion 120.

Nozzle portion 120 comprises: a tapered nozzle body 150 defining an external airflow guide surface 150A; and a tapered nozzle tip 160 surrounding a horizontal inlet slot 132 of the vacuum port 130 that extends laterally between opposed first and second laterally spaced side walls 122A, 122B of the nozzle portion 120. Tapered nozzle body 150 comprises inclined first and second opposed nozzle body side walls 152A, 152B having a first concave curved surface profile and inclined first and second opposed nozzle body end walls 154A, 154B (e.g. leading and trailing inclined nozzle body end walls relative to a forward direction) having a second concave curved surface profile.

Tapered nozzle tip 160 comprises inclined first and second opposed substantially triangular nozzle tip side walls 162A, 162B and inclined first and second opposed substantially trapezoidal nozzle tip end walls 164A, 164B (e.g. leading and trailing inclined nozzle tip end walls relative to a forward direction). The first and second opposed nozzle tip end walls 164A, 164B are inclined by a first taper angle Bi and the first and second opposed nozzle tip side walls 162A, 162B are inclined by a second taper angle B2, wherein Bi > B2. The tapered nozzle body 150 has an uppermost tapered section 150’ inclined to vertical at a steeper taper angle than a corresponding taper angle of the corresponding adjacent section of the tapered nozzle tip 160. In particular, the first and second opposed nozzle body end walls 154A, 154B have an uppermost tapered section 155A, 155B contiguous with tapered nozzle tip end walls 164A, 164B, the uppermost tapered sections 155A, 155B being inclined by a first taper angle Ai. The first and second opposed nozzle body side walls 152A, 152B have an uppermost tapered section 153 A, 153B contiguous with tapered nozzle tip side walls 162A, 162B, the upper most tapered sections 153 A, 153B being inclined by a second taper angle A2, wherein Ai > A2. With reference to Figures 4C and 4D, in the illustrated embodiment taper angle Ai = 31°, taper angle A2 = 21°, taper angle Bi = 49° and taper angle B2 = 34°.

As illustrated in Figures 4E and 4F, the inlet slot has a slot length SL (e.g. extending in the lateral direction) and a slot width Sw (e.g. extending in the longitudinal direction). In this example, the slot length SL =“a” and slot Sw width =0.037a so SL is 27x slot width Sw. The external dimensions of cleaning head 80 may be determined with reference to the slot inlet length “a” as illustrated. In the specific illustrated embodiment, a = 6.5mm and hence slot length SL = 6.5 mm and slot Sw width = 0.25mm resulting in an inlet slot with a cross-sectional area SA of 1.63 mm ² . The value “a” is dependent upon the lateral width of the exposed exterior nozzle orifice surface 32 and is generally at least equal to this lateral width.

With reference to Figures 4C and 4D, nozzle portion 120 defines a passageway 134 defining a tapered internal chamber section 134A and an elongate entrance section 134B connecting the inlet slot 132 to the tapered internal chamber section 134A.

Base portion 140 defines a vacuum source connection chamber 142 and the tapered internal chamber section 134A connects the elongate entrance section 134B to the vacuum source connection chamber 142.

As illustrated, tapered internal chamber section 134A is profiled to act as an internal airflow guide surface to smoothly transition airflow passing from the elongate entrance section to the vacuum source connection chamber and comprises first and second opposed internal side walls 136A, 136B with a first convex curved surface profile and first and second opposed internal end walls 138A, 138B with a second convex curved surface profile. The internal flow path of chamber section 134A is sculpted by 3D printing to reduce turbulence at the inlet slot 132 and to ensure more constant air velocity at the inlet slot 132.

The cross-sectional area SA of inlet slot 132 is extremely small compared to the internal cross-sectional area of its respective vacuum source connecting pipe 72 (approximately 3% of the internal area of the pipe 72) resulting in high air velocity at the inlet. This helps to create a large shear force at the printhead nozzle plate 50 to “scrape” the ink from the nozzle plate 50. The ink is pulled into the cleaning nozzle completely. It effectively works like an air knife, but in reverse (using negative vacuum pressure rather than positive pressure).

The gap between the uppermost surface of the cleaning head 80 and the exposed exterior nozzle orifice surface of the nozzle plate 50 is maintained at all times at this constant distance (as set by a gauge block 100), ideally in the region of 0.145mm - 0.435mm and most preferably maintained at substantially 0.225mm. Within this range ensures that the negative pressure normal to the print head nozzle plate 50 is below the value that would pull ink out of the print head, whilst close enough to make the airflow into the inlet slot 132 shear the nozzle plate of the print head with a very high shear force. This distance is set using a high tolerance machined gauge block 100 (with a +/- 0.025mm height tolerance), which sets the nozzle height off the print head. Gauge block 100 is removed once the height is set, resulting in a completely contact-free assembly.

The tapered nozzle body 150 is designed such that no ink is allowed to escape the cleaning nozzle inlet slot. If ink were to run down the outer face of the nozzle body 150 then it would cure on them and the print head cleaning would degrade over time due to the surface roughness of the cleaning nozzle changing, effecting ink wettability and airflow, possibly even blocking up the cleaning nozzle orifice eventually. A run of over 4000 cycles (5 year accelerated test) was conducted in testing and the cleaning nozzles remained clean throughout. This is in stark contrast to known cleaning systems which require manually nozzle cleaning at regular intervals.

When a cleaning procedure is required, the inkjet printhead assembly 20 is moved from the printing position to the maintenance position passing over the cleaning station 70 to initiate a purge cycle above the purge tray 60.

As the printhead assembly 20 moves over the cleaning station 70, the vacuum source 75 is engaged to each cleaning head 80 of the cleaning station 70 and the inkjet printhead assembly 30 stops over the purge tray 60 to commence the purge cycle.

Ink is initially flushed from within each printing head 30 out through the nozzle orifices of the exposed exterior nozzle orifice surface 52 into the purge tray. Ink that falls into the purge tray 60 is fed under gravity to a waste outlet pipe 62. When flushing is complete, a period is allowed to facilitate withdrawal of the ink meniscus back into the nozzle orifices 52 so that siphoning is prevented during the cleaning phase. The printhead assembly 20 is then traversed rearwardly (in the direction of the printing position) to the location where the cleaning heads 80 are mounted such that the exposed exterior nozzle orifice surfaces 52 of the respective printing heads 50 are brought into close proximity with the upper surface of the cleaning heads 80.

Each printing head 30 is progressively moved passed its respective cleaning head 80 so that each nozzle orifice of the nozzle plate 50 is exposed to the high shear forces generated at the inlet slot 132 which act to scrape ink from the nozzle plate without the cleaning head 80 physically contacting the printing head 30. The removed ink and debris is drawn under vacuum through the vacuum port 130 and into respective fluid traps 74 where, once the level of accumulated ink has reached a sufficient volume, is pumped to the waste collection tank 77. According to the type or characteristic of the ink used for printing, the flushing step is recommenced once the printing head has moved over the purge tray. The number of repeats is predetermined according to the characteristic of the inks in use.

Figure 6 is a diagrammatic illustration of fluid flow trajectories of ambient air under influence of the vacuum, generated via the vacuum port 130, around the cleaning head 80. First and second nozzle body end walls 154A, 154B are designed to deflect the air flow trajectory generated by vacuum port 130 upwardly against the nozzle plate 50 to generate sufficient shear forces to remove ink droplets and debris accumulated thereon. The curved profile of nozzle body end walls 154A, 154B are configured to smoothly guide airflow to an optimum angle for this purpose. In the case of a nozzle body including curved opposed body end walls 154A, 154B, the first and second opposed nozzle body side walls 152A, 152B act to supplement the airflow generated by end walls 154A, 154B.

First and second nozzle tip end walls 164A, 164B and first and second nozzle tip side walls 162 A, 162B are designed to provide an inclined support surface for supporting ink droplets as they are drawn into inlet slot 132 of the vacuum port 130. The first and second nozzle tip end walls 164 A, 164B and first and second nozzle tip side walls 162 A, 162B are configured to discourage droplets from falling down the sides of the tapered nozzle body 150 whilst at the same time providing minimal disruption to the upward flow generated by nozzle body end walls 154A, 154B and nozzle body side walls 152A, 152B.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the appended claims.