System for removing condensation from printhead assembly

Abstract

A printer includes: a platen; a printhead assembly having an inkjet printhead operatively positioned opposite the platen; a feed mechanism for feeding a web of print media over the platen and along a printing feed path; and a diverter configured for periodically diverting a portion of the web towards the printhead assembly and along a maintenance feed path. The portion of the web diverted along the maintenance feed path wipes part of the printhead assembly and removes condensation.

Claims

1. A printer comprising: a platen comprising a plenum chamber having an apertured platen surface; a printhead assembly comprising at least one inkjet printhead operatively positioned opposite the platen; a feed mechanism for feeding a web of print media over the platen and along a printing feed path; and a gas source connected to the plenum chamber; a controller configured for periodically providing a pulse of positive gas pressure from the gas source to the plenum chamber, thereby periodically diverting a portion of the web towards the printhead assembly and along a maintenance feed path, wherein the portion of the web diverted along the maintenance feed path wipes part of the printhead assembly.

2. The printer of claim 1, wherein the feed mechanism continuously feeds the web past the printhead when the portion of the web is diverted along the maintenance feed path.

3. The printer of claim 1, wherein the portion of the web fed along the maintenance feed path contacts a lowermost part of the printhead assembly.

4. The printer of claim 3, wherein the lowermost part of the printhead assembly comprises an encapsulant material immediately downstream of a respective printhead, the encapsulant material encapsulating data and power connectors for the printhead.

5. The printer of claim 1, wherein the portion of the web fed along the maintenance feed path does not contact a nozzle plate of the printhead.

6. The printer of claim 1, further comprising a vacuum source connected to the plenum chamber.

7. The printer of claim 6, wherein the controller is configured for periodically interrupting a vacuum pressure in the plenum chamber with the pulse of positive gas pressure.

8. The printer of claim 1, wherein the controller is configured for providing the pulse of positive gas pressure with a predetermined pulsewidth and/or frequency.

9. The printer of claim 8, wherein the pulsewidth and/or frequency is dependent on one or more of: a type of print media; a speed of printing; an image to be printed; an ambient humidity; an ambient temperature; and a type of ink supplied to the printhead.

10. The printer of claim 8, wherein the pulsewidth is in the range of 0.05 to 0.8 seconds.

11. The printer of claim 1, wherein the vacuum source and the gas source are connected to the plenum chamber via a multiway valve, the controller controlling the valve to connect either the vacuum source or the gas source to the plenum chamber.

12. A method of wiping part of a printhead assembly, the method comprising the steps of: feeding a web of print media over a platen having an aperture plenum surface, the printhead assembly comprising at least one inkjet printhead positioned opposite the platen; and applying a pulse of positive gas pressure to the plenum chamber so as to lift a portion of the web away from the platen surface and divert the portion of the web along a maintenance feed path, wherein the portion of the web diverted along the maintenance feed path wipes part of the printhead assembly.

13. The method of claim 12 wherein the portion of web removes condensation from part of the printhead assembly.

14. The method of claim 12, wherein the wiped part of the printhead assembly is immediately downstream of a respective printhead.

15. The method of claim 12, wherein the web is moving when the positive gas pressure is applied to the plenum chamber.

16. The method of claim 12, wherein the pulse of positive gas pressure lifts the web from the platen surface by a distance in the range of 0.2 to 1 mm.

17. The method of claim 12, wherein the pulse of positive gas pressure interrupts a vacuum pressure in the plenum chamber.

18. The method of claim 12, wherein the web is continuously fed past the printhead assembly at a speed of at least 30 inches per second.

19. A printer comprising: a platen; a printhead assembly comprising at least one inkjet printhead operatively positioned opposite the platen; a feed mechanism for feeding a web of print media over the platen and along a printing feed path; and a diverter configured for periodically diverting a portion of the web towards the printhead assembly and along a maintenance feed path, wherein the portion of the web diverted along the maintenance feed path wipes part of the printhead assembly but does not contact a nozzle plate of the printhead.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A specific embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of a printer according to the present invention during normal printing;

(3) FIG. 2 is the printer shown in FIG. 1 during wiping; and

(4) FIG. 3 is a partial perspective view of a plenum chamber.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to FIG. 1, there is shown schematically a printer 1 comprising a plenum chamber 5 having an apertured platen surface 6 and a printhead assembly 12. The printhead assembly comprises a printhead 7, which is operatively positioned opposite the platen surface 6 for printing. The printhead assembly 12 may take the form of a replaceable printhead cartridge, such as the Memjet® printhead cartridge described in U.S. Pat. No. 8,025,383, the contents of which are herein incorporated by reference. Furthermore, a plurality of printhead cartridges (e.g. monochrome printhead cartridges) may be positioned opposite the platen surface 6, as described in U.S. Pat. No. 8,616,678. Plenum chambers are well known in the inkjet printing art and typically take the form of a vacuum platen. By way of completeness, U.S. Pat. No. 8,616,678 describes a suitable plenum chamber having an apertured upper platen surface and one or more ports for connection to a vacuum source. FIG. 3 also shows an example of a suitable plenum chamber 5 for use in the present invention.

(6) A feed mechanism, comprising rollers 18 positioned at either side of the plenum chamber 5, feeds the web 3 of print media over the platen surface 6 of the plenum chamber 5 in the direction indicated by arrow D. During normal printing of an image, a gas port 21 of the plenum chamber 5 is connected to a vacuum pump 20 via a three-way valve 22. Accordingly, the web 3 normally experiences a suction force through the apertured platen surface 6 of the plenum chamber 5 during printing, which positionally stabilizes the web relative to the printhead 7 for high quality printing. The web 3 is fed over the platen surface 6 along a printing feed path during normal printing.

(7) As explained above, ink droplets ejected from the printhead 7 create a region 10 of relatively high humidity immediately downstream of the printhead. Water vapor in this region 10 tends to condense on relatively cool surface(s) of the printhead assembly 12. In the case of the printer 1, the relatively cool surface is predominantly the lower surface of an encapsulant material 14, which protects wirebonds supplying power and data to the printhead 7. Condensed water droplets 13 collect on the lower surface of the encapsulant material 14 over time during printing and may migrate onto a nozzle plate 15 of the printhead 7 via capillary forces. These water droplets 13 have a deleterious effect on print quality, especially if they reach the nozzle plate 15, by dilution of ink in inkjet nozzle chambers.

(8) Turning now to FIG. 2, the printer 1 is shown in a configuration for removing condensation. A controller 24 controlling the three-way valve 22 has now connected the plenum chamber 5 to an air compressor 26 such that the apertured platen surface 6 experiences a positive air pressure. The positive air pressure lifts a portion of the web 3 away from the platen surface 6 so that the portion of the web is diverted along a maintenance feed path, whereby the web wipes a lower surface of the encapsulant material 14. Accordingly, the controller 24, air compressor 26 and plenum chamber 5 cooperate to function as a diverter for diverting the web along the maintenance feed path.

(9) The web 3 may lightly contact the encapsulant material 14, or the web may be lifted in sufficient proximity to collect water droplets without actually contacting the encapsulant material.

(10) When the web is lifted from the platen surface 6, as shown in FIG. 2, the condensed water droplets 13 accumulated on the encapsulant material 14 are wiped away. The positive air pressure is provided in the form of a relatively short pulse (e.g. less than about 0.8 seconds). Furthermore, interruption of the vacuum pressure with the pulse of positive air pressure is usually timed such that the portion of the web 3 contacting the water droplets 13 does not contain part of a printed image. Switching from a vacuum pressure to a positive air pressure is performed with sufficient frequency to minimize any unpredictable deterioration in image quality (e.g. streaks) caused by the condensed water droplets 13. For example, the positive air pressure may be applied every 50 feet of printing for about 0.1 seconds when printing at 55 inches per second. Optimum timing of the positive air pressure may be determined empirically depending on, for example, the print speed, the type of print media (e.g. weight, porosity etc), the image to be printed (e.g. high density or low density image), an ambient humidity, an ambient temperature or the type of ink supplied to the printhead.

(11) As shown in FIG. 2, the positive air pressure is controlled so that it is sufficient to lift the web 3 into contact with the encapsulant material 14, but insufficient to lift the web into potentially damaging contact with the nozzle plate 15 of the printhead 7. The optimum amount of positive of air pressure required may depend, for example, on the weight and porosity of the print media.

(12) Once the web 3 has been lifted from the platen surface 6 to wipe the condensed water droplets 13 from the encapsulant material 14, the controller 24 configures the three-way valve 22 so that the vacuum pump 20 is re-connected to the plenum chamber 5. Thus, the web 3 lowers back into contact with the platen surface 6 (FIG. 1) and printing of the image may resume.

(13) From the foregoing, it will be appreciated that the present invention provides a highly effective means for wiping condensation from a printhead assembly without requiring intervention from a dedicated maintenance assembly, and without requiring the web 3 to be broken or stopped. Simply by apportioning predetermined breaks in the printed image for web-wiping as described above (e.g. a 5 to 30 inch break in the printed image for every 30 to 200 feet of printing), the deleterious effects of condensation can be readily ameliorated. In practice, images printed onto the web 3 have natural breaks for cutting the web; therefore, incorporating somewhat extended breaks in the image for web-wiping, as described above, has minimal practical impact on most print jobs.

(14) It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.