Patent Grant
8020980
The present invention relates to printers and in particular the fluidic architecture of inkjet printers.
The following application has been filed by the Applicant simultaneously with the present application:
The disclosure of this co-pending application is incorporated herein by reference.
Various methods, systems and apparatus relating to the present invention are disclosed in the following US patents/patent applications filed by the applicant or assignee of the present invention:
The disclosures of these applications and patents are incorporated herein by reference.
Inkjet printing is a popular and versatile form of print imaging. The Assignee has developed printers that eject ink through MEMS printhead IC's. These printhead IC's (integrated circuits) are formed using lithographic etching and deposition techniques used for semiconductor fabrication.
The micro-scale nozzle structures in MEMS printhead IC's allow a high nozzle density (nozzles per unit of IC surface area), high print resolutions, low power consumption, self cooling operation and therefore high print speeds. Such printheads are described in detail in U.S. Ser. No. 10/160,273 filed Jun. 4, 2002 and U.S. Ser. No. 10/728,804 filed on Dec. 8, 2003 to the present Assignee. The disclosures of these documents are incorporated herein by reference.
The small nozzle structures and high nozzle densities can create difficulties with color mixing between nozzles of different color. During periods of prolonged inactivity (or ‘standby mode’) the separate fluidic lines for each ink color can undergo slight pressure changes relative to each other. Different rates of heating and outgassing in different ink lines will generate a slight pressure differential. If paper dust or ink residue on the nozzle face extends between nozzles of the different ink lines, the dust or residual ink can forge a fluid connection between the two ink lines. The ink lines try to equalize the pressure difference between them and this drives an ink from the higher pressure line to the lower pressure line. If left unchecked, the ink contamination in the lower pressure ink line can extend to the ink tank. In this case, the contaminated ink supply is irretrievable and needs replacement before the ink lines are flushed through to the nozzles.
The ink tanks can be isolated from the printhead by a shut off valve upstream of the printhead. This protects the tanks from contamination during standby, but there is a risk that the tank and the printhead will generate a pressure difference during the standby period. If this happens, the sudden pressure equalization causes a pulse through the ink line which floods the nozzle plate.
Accordingly, the present invention provides an inkjet printer comprising:
a printhead for printing onto a media substrate;
a reservoir for containing a quantity of ink, the reservoir having a lower portion for holding ink and an upper portion defining a headspace of air above the ink;
a fluid connection extending between the printhead and the reservoir; and,
a pump for drawing air from the headspace into atmosphere.
The invention uses a fluidic system that controls the air pressure in the headspace of an ink reservoir to control the hydrostatic pressure of the ink at the key points along the ink line. Controlling the ink pressure in one of the ink reservoirs (either the ink tank supplying the printhead or the ink sump collecting waste ink) can maintain a more consistent negative pressure (i.e. a hydroststatic pressure less than atmospheric) at the printhead nozzles. The negative pressure at the printhead nozzles prevents, or at least reduces color mixing by ensuring that the ink meniscus at each nozzle is drawn inwards. An inwardly drawn meniscus significantly reduces the chance that paper dust or residual ink can establish a fluid connection between nozzles of different color. Drawing air from the headspace in the sump helps to equalize the pressure in the different ink lines as the sump headspace is common to all the color channels. By the same token, it is a simple matter to use a single pump to connect the respective headspaces for each ink tank. In this way, the air pressure in each ink tank is equal and so the hydrostatic pressure of the ink at the nozzles will only vary by the variations in the ink levels of the ink tanks. In a normal usage profile, the ink levels remain roughly the same for each ink tank. To further minimize variations, the tanks can have a wide and squat shape to reduce the change in hydrostatic pressure from full to empty. With equal pressures (or at least very nearly equal pressures) in each ink line, there is no pressure differential to drive a color mixing process other than diffusion. As the fluid connection across the nozzle is so small, mixing by diffusion is negligible.
Preferably, the reservoir is a sump that collects waste ink drained from the printhead.
Preferably, the reservoir is an ink tank for supplying ink to the printhead. In a further preferred form, the printer is a color printer for printing a plurality of differently colored inks, each of the differently colored inks being stored in a respective ink tank for supplying the printhead, the headspace of each of the tanks is connected to the pump such that they are in fluid communication with each other.
Preferably, the reservoir has a vent for venting the headspace to atmosphere, and for allowing a throttled flow of air into the headspace as the pump is drawing air out of the headspace. In a further preferred form, the vent has a filter for removing particulate contaminants from the throttled air flow into the headspace.
Preferably, the printing further comprises an upstream valve positioned upstream of the printhead. In a further preferred form, the printer further comprises a downstream valve positioned downstream of the printhead.
Preferably, the pump is reversible such that it can increase the air pressure in the headspace and force ink towards the printhead. In a further preferred form, the pump is used to prime the printhead. In another preferred form, the pump is used to purge ink from the nozzles and flood the printhead.
Preferably, the printhead has a distribution manifold and a plurality of printhead integrated circuits mounted to the distribution manifold such that priming the distribution manifold with ink also primes the printhead integrated circuits. In some embodiments, the printer further comprises a maintenance station having a capper and blotter for the printhead integrated circuits. In specific embodiments, the pump is in fluid communication with the maintenance station and the sump such that ink collected by the maintenance station can be transferred to the sump by running the pump in one direction and air drawn from the headspace by running the pump in the other direction. In a particularly preferred form, the printhead is provided as a user removable and replaceable cartridge which is fluidly detachable from the printer via the upstream and the downstream valves.
Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which:
Referring to
The fluidic system shown in
The printhead has a maintenance station 22 for capping and blotting the nozzles. A drain line 16 connects the maintenance station 22 to the sump 28.
The printhead 2 is an assembly of an ink distribution manifold 4 on which a series of printhead integrated circuits (ICs) 6 are mounted. The printhead ICs 6 define the nozzle arrays which eject the ink to the media substrate. The nozzles are MEMS devices which can be thermally actuated such as those described in U.S. Ser. No. 11/482,953 filed on Jul. 10, 2006 or mechanically actuated such as those disclosed in U.S. Ser. No. 10/160,273 filed Jun. 4, 2002.
The ink distribution manifold 4 is an LCP molding with a system of large channels feeding a network of smaller channels to supply the ink to many points along the length of each printhead IC 6. An embodiment of the distribution manifold 4 and the printhead ICs 6 is disclosed in detail in the U.S. Ser. No. 11/688,863 filed Mar. 21, 2007 reference listed above. This document also details the manner in which the printhead is primed with ink or, if necessary, purged of ink to correct any cross channel color contamination and/or bubble removal.
In standby mode, the air pump 30 draws air from the headspace 32 in the tank 8. The air pressure in the headspace drops and air is drawn back into the headspace 32 through the filtered vent 40. The air constriction from the vent 40 is carefully controlled to create a predetermined negative air pressure. The tubing 38 fluidly connects the headspaces 34 and 36 in tanks 10 and 12 such that all the headspaces are at the same air pressure. Tanks 10 and 12 can have their own vents to atmosphere (not shown) but the system will operate with a single vent.
With the headspaces 32, 34, and 36 at the same pressure, the hydrostatic pressure in the ink is very early equal. The hydrostatic pressure of the ink at the nozzles will only vary by the variations in the ink levels of the ink tanks. Normal usage is designed to keep the ink levels roughly the same in each ink tank. To further minimize variations, the tanks can have a wide and squat shape to reduce the change in hydrostatic pressure from full to empty. With equal pressures (or at least very nearly equal pressures) in each ink line, there is no pressure differential to drive a color mixing process other than diffusion. As the fluid connection across the nozzle is so small, mixing by diffusion is negligible.
The pump 30 is reversible so it can be used to pressurize the headspaces 32, 34 and 36 in order to prime the printhead 2 or purge ink through the printhead ICs 6. Priming requires the upstream and downstream shut off valves 18 and 26 to be open. Ink from the tanks 8, 10 and 12 is forced down the upstream ink line 20, through the distribution manifold 4 and into the sump 28 via the downstream ink line 24. The printhead ICs 6 prime by capillary action from the ink in the distribution manifold.
To purge the printhead ICs 6 (to recover dried nozzles, outgassing bubble blockages etc) the down stream valve 26 is closed as the pump 30 pressurizes the headspace 32. Ink is forced from the nozzles and the resulting flood on the nozzle plate is cleared with the maintenance station 22.
It will be appreciated that the pump 30 operates during a power up standby mode. That is, during periods of inactivity between print jobs, but the printer is still plugged in and connected to a power supply. During a power off standby, the shut off valve 18 and 26 are closed to isolate the printhead and prevent mixing. When the printer powers up again, the pump 30 can be used to ready the printhead by priming or purging (if necessary) as discussed above.
With the pump 30 connected to the sump 28, the upstream shut off valve 18 is closed during power down standby. The negative air pressure in the headspace 32 draws on the column of ink hanging from the printhead 2. This ensures that a sufficiently negative pressure is maintained at the nozzles. More importantly, the negative pressure in the nozzles of each color is the same. As discussed above, this removes the mechanism that drives the color mixing process.
The pump 30 is marginally more complex in that it needs to be able to handle an ink/air mixture. It is in the drain line 16 from the maintenance assembly 22 to the sump 28 to assist the transfer of blotted ink to the sump 28 but needs to be able to draw air from the headspace 32 or from atmosphere through the filter 42.
In this embodiment, priming requires the upstream valve 18 to be open and the pump 30 to create a low pressure in the sump 28 to draw the ink from the tank 8 down the upstream ink line 20, through the distribution manifold 4 and into the downstream ink line 24. Again the printhead ICs 6 prime by capillarity.
To purge, the upstream valve 18 is closed and the pump 30 creates a positive pressure in the headspace 32 to force the ink in the down stream ink line 24 and the distribution manifold 4 to flood the printhead ICs 6.
The invention has been described by way of example only. Ordinary workers in this field will readily recognize any variations and modifications which do not depart from the spirit and scope of the broad inventive concept.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4419678 | Kasugayama et al. | Dec 1983 | A |
| 4476472 | Aiba et al. | Oct 1984 | A |
| 4494124 | Piatt et al. | Jan 1985 | A |
| 4555712 | Arway et al. | Nov 1985 | A |
| 5583544 | Stamer et al. | Dec 1996 | A |
| 5980034 | Tsai et al. | Nov 1999 | A |
| 6302516 | Brooks et al. | Oct 2001 | B1 |
| 6991313 | Sasa | Jan 2006 | B2 |
| 7798600 | Karppinen et al. | Sep 2010 | B2 |
| 20060132554 | Ota et al. | Jun 2006 | A1 |
| 20070206050 | Morgan et al. | Sep 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 0082272 | Jun 1985 | EP |
| 2005-125669 | May 2005 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20090096846 A1 | Apr 2009 | US |
