Printhead cleaning cap

Abstract

A printhead maintenance cap for attachment to a printhead, the cap comprising: a main body defining a chamber into which rinse fluid passes from the printhead during a cleaning cycle; a seal for engagement with the printhead prior to a cleaning cycle starting; and a venting system for equalizing the pressure in the chamber and the surrounding atmosphere.

Claims

1. A printhead maintenance cap for attachment to a printhead, the cap comprising: a main body defining a chamber into which rinse fluid passes from the printhead during a cleaning cycle; a seal for engagement with the printhead prior to a cleaning cycle starting; and a venting system for equalising the pressure in the chamber and the surrounding atmosphere; wherein the venting system includes one or more baffles which are configured to allow equalising of pressure in the chamber and the surrounding atmosphere while preventing the escape of rinse fluid through the venting system.

2. A printhead maintenance cap according to claim 1, further comprising means for, in use, bringing the seal into engagement with the printhead.

3. A printhead maintenance cap according to claim 1, wherein the engagement means includes a clamp and/or a pneumatically operated mechanism.

4. A printhead maintenance cap according to claim 1, wherein the one or more baffles are formed from a single piece component.

5. A printhead maintenance cap according to claim 1, further comprising one or more drains for draining fluid from the cap in use.

6. A printhead maintenance cap according to claim 1, further comprising one or more additional seals to permit the cap to be used with a multi-head printhead.

7. A printhead maintenance cap according to claim 1, further comprising a movable spray head for providing one or more jets of rinse fluid within the cap.

8. A printhead maintenance cap according to claim 1, further comprising a drive mechanism for moving the cap into and out of engagement with the printhead.

9. A printhead maintenance cap according to claim 8, further comprising an interlock for preventing movement of the cap when in a sealed engagement with the printhead.

10. A printhead maintenance cap according to claim 1, further comprising a vacuum wiper.

11. A printhead maintenance cap according to claim 10, wherein the vacuum wiper is pivotable relative to the cap main body.

12. A printhead maintenance cap according to claim 11, wherein the vacuum wiper is biased towards the intended location of the printhead.

13. An electrostatic printhead having a plurality of ejection tips and an intermediate electrode, the printhead further comprising a maintenance cap according to claim 1.

14. A printhead according to claim 13 further comprising an interlock for preventing movement of the cap when in a sealed engagement with the printhead, wherein the vacuum wiper does not contact the intermediate electrode.

Description

DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the invention will now be described with reference to the attached figures in which:

(2) FIG. 1 is a perspective view of a printhead according to the present invention;

(3) FIG. 2 is an exploded view of the printhead illustrated in FIG. 1;

(4) FIG. 3 is a sectional view of a manifold block that directs cleaning fluids to different parts of the printhead;

(5) FIG. 4 is a sectional view in of the printhead showing the passages that direct cleaning fluids to the tip region of the printhead;

(6) FIG. 5 is a detailed cross-sectional view of the ejection region of the printhead illustrated in FIG. 1

(7) FIG. 6 is a three-dimensional close-up illustration of the ejection region of the printhead illustrated in FIG. 1

(8) FIG. 7 is the same view as FIG. 4, but with fluid flow paths indicated;

(9) FIG. 8 shows one example of a maintenance cap for use in the cleaning method;

(10) FIG. 9 shows an end view of the maintenance cap of FIG. 8, and the various fluid connections;

(11) FIG. 10 shows a schematic view of some of the internal components of the maintenance cap;

(12) FIGS. 11A and 11B show one arrangement of baffles in the venting system on the maintenance cap;

(13) FIG. 12 shows an example of a printhead module outer casing with which the maintenance cap engages; and

(14) FIG. 13 is a flow chart describing the stages of the cleaning process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(15) The printhead 100 of the present invention comprises a two-part main body consisting of an inflow block 101 and an outflow block 102, between which are located a prism 202 and a central tile 201, the latter having the ejector array formed along its front edge. At the front of the printhead, an intermediate electrode plate 103 is mounted on to a datum plate 104, which in turn is mounted onto the main body of the printhead. A gasket 208 is provided between the datum plate 104 and the inflow and outflow blocks.

(16) Referring to FIGS. 2, 3, 4, 5 and 6, the main body of the printhead comprises the inflow block 101 and the outflow block 102, sandwiched between which are the prism 202 and the central tile 201. The central tile 201 has an array of ejection locations or tips 403 along its front edge and an array of electrical connections 203 along its rear edge. Each ejection location 403 comprises an upstand 400 with which an ink meniscus interacts (in a manner well known in the art). On either side of the upstand 400 is an ink channel 404 that carries ink past both sides of the ejection upstand 400. In use, a proportion of ink is ejected from the ejection locations 403 to form, for example, the pixels of a printed image. The ejection of ink from the ejection locations 403 by the application of electrostatic forces is well understood by those of skill in the art and will not be described further herein.

(17) The prism 202 comprises a series of narrow channels 411, corresponding to each of the individual ejection locations 403 in the central tile 201. The ink channels of each ejection location 403 are in fluid communication with the respective channels of the prism 202, which are, in turn, in fluid communication with a front portion 407 of the inlet manifold formed in the inflow block 101 (said inlet manifold being formed on the underside of the inflow block 101 as it is presented in FIG. 2 and thus not shown in that view). On the other side of the ejection locations 403, the ink channels 404 merge into a single channel 412 per ejection location 403 and extend away from the ejection locations 403 on the underside (as drawn in FIG. 5) of the central tile 201 to a point where they become in fluid communication with a front portion 409 of the outlet manifold 209 formed in the outflow block 102.

(18) The ink is supplied to the ejection locations 403 by means of an ink supply tube 220 in the printhead 100 which feeds ink into the inlet manifold within the inflow block 101. The ink passes through the inlet manifold and from there through the channels 411 of the prism 202 to the ejection locations 403 on the central tile 201. Surplus ink that is not ejected from the ejection locations 403 in use then flows along the ink channels 412 of the central tile 201 into the outlet manifold 209 in the outflow block 102. The ink leaves the outlet manifold 209 through an ink return tube 221 and passes back into the bulk ink supply.

(19) The channels 411 of the prism 202 which are connected to the individual ejection locations 403 are supplied with ink from the inlet manifold at a precise pressure in order to maintain accurately controlled ejection characteristics at the individual ejection locations 403. The pressure of the ink supplied to each individual channel 411 of the prism 202 by the ink inlet manifold is equal across the entire width of the array of ejection locations 403 of the printhead 100. Similarly, the pressure of the ink returning from each individual channel 412 of the central tile 201 to the outlet manifold 209 is equal across the entire width of the array of ejection locations 403 and precisely controlled at the outlet, because the inlet and the outlet ink pressures together determine the quiescent pressure of ink at each ejection location 403.

(20) The printhead 100 is also provided with an upper 204 and a lower 205 cleaning fluid manifold. The upper and lower cleaning fluid manifolds have respective inlets 105a, 105b through which rinse/cleaning fluid can be supplied to the printhead 100. The inflow 101 and outflow 102 blocks are both provided with cleaning fluid passages 401. The passages in the inflow block 101 are in fluid communication with upper cleaning fluid manifold 204 and those passages in the outflow block 102 are in fluid communication with the lower cleaning fluid manifold 205. Fluid connectors 206 link the cleaning fluid manifolds to the respective cleaning fluid passages.

(21) The cleaning fluid passages 401 within the inflow and outflow blocks end at cleaning fluid outlets 207. The pathway to the ejection locations 403 continues along enclosed spaces 405 defined by the V-shaped cavity 402 in the datum plate 104 and the outer surfaces of the inflow 101 and outflow 102 blocks, until the point at which the ejection locations 403 themselves lie within the cavity 402. The two sides of the V-shaped cavity are, in this example, at 90 degrees to each other.

(22) As can be seen in FIG. 7, arrows A show the fluid pathways taken by the rinse/cleaning fluid and/or air during cleaning of the printhead. Regions B show the pathways taken by the ink through the inlet and outlet manifolds and along ink channels 411 and 412. During normal operation a flow of ink exists around the tips 403 from the inlet side (inlet block 201) to the outlet side (outflow block 202). In normal use, there is no flow of cleaning fluidindeed no cleaning fluid is present in the printhead. However, during a cleaning operation, ink flow is stopped and the ink is withdrawn slightly from the tips to the position indicated above and in FIG. 7, as described below. This withdrawal of the ink means that, when cleaning fluid is supplied through passages 401 and into cavity 402, the cleaning fluid does not mix substantially with the ink in the printhead, but can clean the tips 403. When cleaning is complete, the printhead can be primed easily by moving the ink back to the ejection locations 403 so that it can resume a constant flow around the ejection locations 403 from the inflow to the outflow side of the printhead.

(23) An example of a maintenance cap that can be used during cleaning of the ejection tips is shown in FIGS. 8 to 10.

(24) The maintenance cap 800 includes a printhead engaging section 801 and an engagement section 802, which in this example is a clamping engagement. The printhead engaging section 801 includes a base section 803 and upstanding side walls 804. The side walls include linear key way bearings 805 which engage with a corresponding profile 902 on a printhead module outer casing 901 (FIG. 12). The side walls could be replaced with, or used together with, other means of mounting the cap 800 on the printhead. This is especially true, if multiple printheads are provided and the same cap is used to cover more than one of the printheads at the same time. The cap may also provided with a fitting handle 814 to help with the initial installation of the cap in the printer (although thereafter the cap is controlled automatically).

(25) The base section 803 includes a tank 806 on which a printhead seal 807 is mounted. The tank has an opening 808 into which, in use, rinse fluid is drained from the printhead through the slot in the IE 103, the opening defining a cavity within the tank 806. The opening 808 is surrounded by the seal 807. In the figures, the printhead to be cleaned is placed above the tank, in engagement with the seal 807. Beneath the seal 807, on the opposite side of the opening 808, a movable spray head 809 is provided, mounted on a pair of spray head guides 810 (one is visible in FIG. 10). The function of the spray head 809 is to clean the outer face of the IE 103 by directing fine jets of rinse fluid thereon.

(26) In operation, the maintenance cap is inserted across the front of the printhead and clamped or otherwise fastened against the outer face of the intermediate electrode forming a fluid-tight seal. The printhead ink pathways remain filled with ink during the cleaning process, except for the very tip region as the ink is caused to retreat from tips by a pressure differential at the tips. The cleaning action is therefore confined to the tip-IE region of the printhead. The cap collects and drains rinse fluid from the printhead during a cleaning operation, the fluid preferably being drained to a tank in the fluid management system remote from and lower than the printhead. Because of the seal, the draining action from the maintenance cap could create a partial vacuum in the maintenance cap that would draw the ink out of the printhead. A further preferred feature is a baffled venting system, see FIG. 11, which can prevent this. The system includes one or more, in this case two, air vents 813, and these vents allow equalisation of air pressure between the inside of the maintenance cap and the surrounding atmosphere, and prevents the escape of rinse fluid through the vent by incorporating a series of baffles 843, 844.

(27) The maintenance cap, in a preferred embodiment, has a pneumatically actuated clamp to clamp to the face of the intermediate electrode. This is preferably achieved using a pair of bidirectional pin cylinder actuators 811 acting directly on a pair of cam strips 812, which are moved, longitudinally in this example, to cause the upward clamping motion of the maintenance cap base section 803 to the printhead. The cylinders 811 are pneumatically driven in parallel from switched compressed air sources that connect to two pneumatic connectors respectively as shown in FIG. 9: seal-unclamp 818 and seal-clamp 819.

(28) When sealed to the printhead, it is important that no attempt is made to withdraw the cap, causing it to rub across the printhead, potentially damaging the seal, the drive, or the printhead itself. Similarly the cap must not be inserted across the face of the printhead while in a clamped state. To guard against these eventualities, the coupling of the cap to a linear drive mechanism (not shown) that inserts and withdraws the cap is preferably interlocked to the clamp state of the cap, by use of a third pneumatic pin cylinder 815 that may be fed from the same switched compressed air source as the cylinders 811 that actuate the clamping mechanism. The cylinder 815 engages the drive with the cap when the cap is unclamped and disengages it when clamped, thereby interlocking the cap drive to the clamp state. In the example shown, the linear drive mechanism is continuously engaged with the drive engagement block 816 via four drive engagement pins 817, which locate in the moving part of the linear drive mechanism. When actuated, the pin of the cylinder 815 locates into the socket of the drive engagement block 816. In this state, the entire maintenance cap is coupled to the linear drive for insertion and withdrawal under the printhead. The switched compressed air source that actuates the cylinder 815 is the same source that actuates the unclamped state of the clamping cylinders 811, these all being linked by pneumatic tubing to the seal-unclamp pneumatic connector 818. Hence, when the unclamped state is actuated, the linear drive mechanism engages with the entire cap assembly.

(29) When in the clamped state, the linear drive mechanism engages with the moveable spray head 809 only. The spray head 809 is moveable along the length of the opening 808, its motion guided centrally by the guides 810. Rinse fluid is supplied to the spray head via a rigid tube 830 that connects the spray head with the spray head connection 831. The tube 830 also mechanically couples the spray head 809 to the drive engagement block 816, the tube 830 passing through an O-ring seal in the tank wall that allows movement of the tube through the seal without losing fluid from the tank 806. When in the clamped state, the spray head 809 may thereby be moved along the length of the printhead spraying rinse, air, or a mixture thereof, when required by the cleaning operation.

(30) Vacuum Wiper

(31) In a preferred embodiment a vacuum wiper 820 is located at one end of the base section 803. The vacuum wiper 820 comprises a narrow slot 821 in the upper face of a wiper body 822 which is in fluid communication via a pair of tubes 810 (rigid tubes that also act as the spray head guides in this example) and connectors 823 to a pair of vacuum wiper connections 825 via short lengths of flexible tubing (not shown). The wiper body is pivoted at its point of attachment to the base section 803 and is sprung upwards towards the printhead. Two rollers 824 attached to the wiper body 822 roll against the face of the printhead several millimeters either side of the ejection region as the maintenance cap is inserted or withdrawn, the rollers serving to control the spacing between the wiper slot and the face of the IE to approximately 0.2 mm. When the connections 825 are connected to a source of vacuum, air is drawn into the slot 821. Applying vacuum in this way as the maintenance cap is withdrawn from the printhead after a cleaning operation draws any drips or residual rinse fluid from the face of the IE into the wiper and may be used to dry the outer face of the IE. It has been found to be more effective at drying the IE than a conventional wiper because the vacuum will draw fluid out of the slot between the two blades of the IE more effectively. The vacuum wiper described above also has no rubbing contact with the IE, and therefore minimises the risk of wearing or otherwise damaging the precision IE component, or of pushing foreign material into the IE slot.

(32) Baffle System

(33) Fluid that enters the tank 806 is drained from one or both cap drain connectors 832. The provision of two cap drains allows the cap to be employed on printheads mounted in a variety of orientations, in each case the lower of the two drains is used and the upper one is plugged. The cap drain connectors 832 are mounted in a baffled venting block 840, which allows equalisation of air pressure between the inside of the maintenance cap and the surrounding atmosphere while preventing the escape of rinse fluid through the vents 813 by incorporating a series of internal baffles 843, 844. The venting block comprises a hollow body 842 with two downward projecting sections, one on each side. Each of these has at its base a channel 845 that carries rinse fluid that drains from the cap back to a tank in the remote fluid management system. The channels 845 are open to the hollow interior of the venting block within which a series of downward-sloping baffles 843, 844 inhibit the passage of rinse up through the body 842 from splashing, etc, while allowing air to pass between the vents 813 and the channels 845. The combination of rinse and air used in the printhead cleaning process is such that the flow of rinse from the tank 806 to the venting block 840 along short tubes (not shown) connecting the tank drains 834 to the venting block inlets 833 is discontinuous, allowing sufficient passage of air between the venting block 840 and the tank 806 to maintain pressure in the tank 806 close to that of the surrounding atmosphere. Furthermore, when the printhead and cap are operated in an orientation other than vertical, the higher of the two channels 845 will generally be free of rinse and will serve as a continuous air connection with the tank 806 to maintain atmospheric pressure therein.

(34) The maintenance cap described above is capable of operating vertically as depicted in FIGS. 8 to 10 or at any angle as indicated in FIG. 9 of up to 75 degrees from vertical, and so is suitable for use in printing machines in which the printheads are mounted in this range of orientations.

(35) Description of the one example of the cleaning process is shown in FIG. 13 and is described as follows:

(36) 1. START: When a printhead cleaning operation is called for, either through automatic scheduling or operator intervention, printing is stopped, the printhead moved away from the substrate (or the substrate moved depending on the type of printer), and a maintenance cap, such as that described in FIGS. 8 to 10, presented to the face of the printhead.

(37) 2. The maintenance cap is sealed to the face of the printhead.

(38) 3. Ink flow around the printheada constant feature of the printhead in its normal operating state, controlled by difference in ink pressures between the inlet and outlet ports of the printheadis stopped by setting equal pressures at the inlet and outlet ports, at the mid-point of the normal operating pressures.

(39) 4. Air under slight positive pressure is supplied to the cleaning fluid inlets 105a and 105b via an external control valve. The air passes through the upper and lower cleaning fluid manifolds 204, 205, where it is distributed via fluid connectors 206 to eight passages 401 spaced evenly across the width of the printhead: four on the upper side and four on the lower side. It emerges from cleaning fluid outlets 207 into the cavity 402 near the front of the printhead in close proximity to the ejection tips 403 and the inner face of the intermediate electrode 103. The air pressure near the tips is slightly higher than that of the atmosphere external to the printhead or in the maintenance cap because the narrow slot in the IE presents a restriction to the flow of air out of the printhead. The higher air pressure is not sufficient to force the ink backwards out of the printhead, but causes it to retreat from the tip region enough to expose the ejection tips 403.

(40) 5. A rinse-air mixture is periodically directed through the cleaning fluid passages 401 in short bursts, controlled via an external control valve. Typical timings are: air 2 s; rinse & air 3 s; air 2 s; rinse & air 3 s; air 2 s; rinse & air 3 s; air 2 s. The timings have been found to provide effective cleaning whilst minimising the amount of rinse that enters the ink channels. Rinse fluid flows from the cavity 402 through the open slot in the centre of the intermediate electrode 103 into the maintenance cap from where it is drained.

(41) 6. Air is turned off and the maintenance cap released, allowing a wiper to be drawn across the outside face of the intermediate electrode 103 to remove any drips. The cap is re-sealed to the printhead.

(42) 7. The air supply is turned on again to start drying the internal faces of the printhead. Air flows through the spaces 405 and the cavity 402 and into the maintenance cap from where it is vented.

(43) 8. Ink flow around the printhead is re-established by raising the ink pressures to bring the ink forwards to the tips again and setting a pressure difference between the inlet and outlet ports of the printhead. Flow is established in the forward direction (inlet to outlet) for 30 s, then reversed by swapping the pressures at the inlet and outlet ports, which has the effect of expelling any air trapped in the ink channels from the cleaning process.

(44) 9. In this state, the maintenance cap is released again and the outside face of the intermediate electrode wiped again to remove residual drips of rinse, and the maintenance cap withdrawn completely from the printhead.

(45) 10. There follows a further drying phase of 150 s in total, after 120 s of which the ink flow is restored to the forward direction. The air is then turned off.

(46) 11. The pressures are controlled such that the ink pressure at the tips is just below that of the atmosphere surrounding the tips so that the ink flow is confined in the channels 404 each side of the ejection tips and the ink meniscus pins to the tips and edges of the channels 404.

(47) 12. END

(48) The whole sequence is complete in under 5 minutes, around a quarter that of earlier methods.

(49) It will be appreciated that many of the steps described above are not essential to the invention as describedindeed, the present invention is defined in the broadest terms by the claims filed herewith.