Patent Application
20100271424
This disclosure relates generally to printheads of an ink jet imaging device, and, in particular, to maintenance methods for use with such printheads.
Solid ink or phase change ink printers conventionally receive ink in a solid form, sometimes referred to as solid ink sticks. The solid ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a printhead assembly for jetting onto a recording medium. In the direct printing architecture, the recording medium is typically paper, while for an offset printing architecture, the ink is printed onto a liquid layer supported by an intermediate imaging member, such as a metal drum or belt.
A printhead assembly of a phase change ink printer typically includes one or more printheads each having a plurality of ink jets from which drops of melted solid ink are ejected towards the recording medium. The ink jets of a printhead receive the melted ink from an ink supply chamber, or manifold, in the printhead which, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each ink jet includes a channel having one end connected to the ink supply manifold. The other end of the ink channel has an orifice, or nozzle, for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture, or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators in the ink jets to expel drops of fluid from the ink jet nozzles onto the recording medium. By selectively activating the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
One difficulty faced by fluid ink jet systems is partially or completely blocked ink jets. Partially or completely blocked ink jets may be caused by a number of factors including contamination from dust or paper fibers, dried ink, etc. In addition, when the solid ink printer is turned off, the ink that remains in the print head can freeze. When the printer is turned back on and warms up, the ink thaws in the print head. Air that was once in solution in the ink can come out of solution to form air bubbles or air pockets that can become lodged in the ink pathways of the print head. Partially or completely blocked ink jets can lead to ink jet malfunctions or failures resulting in missing, undersized or misdirected drops on the recording media that degrade the print quality.
Some partially or completely blocked ink jets may be recovered by performing a printhead maintenance action. Print head maintenance generally includes purging ink through the ink pathways and nozzles of a print head assembly in order to clear contaminants, air bubbles, dried ink, etc. from the print head assembly and/or wiping the nozzle plate of the print head assembly. Previously known purging methods required that ink be purged through each ink jet in the printhead regardless of the number or location of non-functional jets in the printhead. If a printhead is purged to recover a single jet, ink is currently moved through all of the jets which requires a larger amount of ink, most of which does not contribute to the recovery of the weak or missing jets. There are currently no means to limit the purging of ink jets to a particular location or number of jets.
The present disclosure proposes the selective purging of jets such that more (or all) of the ink flowed during purge is used in the specific jet which required recovery. This is done to either increase the efficiency of jet recovery or reduce the amount of ink used for jet recovery (or both). This is done by either using surface energy and wetting characteristics of the aperture plate of a printhead as a valve or by using methods and mechanisms to control which portions and/or jets of the head are purged. In one particular embodiment, a method of performing maintenance on a printhead of an imaging device includes the detection of at least one contaminated ink jet in a printhead. A first pressure is applied to ink in the printhead in response to the detection of the at least one contaminated ink jet. The first pressure is configured to prevent ink from entering a plurality of apertures in an aperture plate of the printhead and to prevent ink from drooling from the plurality of apertures unless the apertures are wiped by a wiper blade. A first portion of apertures in the plurality of apertures in the aperture plate is wiped with a wiper blade while leaving a second portion of the apertures untouched by the wiper blade while the first pressure is applied to the ink in the printhead. The wiping of the first portion of apertures enables ink to drool from the first portion of apertures. The first portion of apertures includes at least one of the contaminated ink jet(s).
In another embodiment, a method of performing printhead maintenance includes the detection of at least one contaminated ink jet in a printhead. A first pressure is applied to ink in the printhead in response to the detection of the at least one contaminated ink jet. The first pressure is configured to prevent ink from entering a plurality of apertures in an aperture plate of the printhead and to prevent ink from drooling from the plurality of apertures when ink jets of the printhead are not actuated. At least one detected contaminated ink jet is then actuated while the first pressure is being applied to the printhead to enable ink to drool from the at least one detected contaminated ink jet.
In yet another embodiment, a method of performing maintenance on a printhead of an imaging device includes detecting at least one contaminated ink jet in a printhead. A first pressure is applied to ink in the printhead in response to the detection of the at least one contaminated ink jet. The first pressure is configured to prevent ink from entering a plurality of apertures in an aperture plate of the printhead and to prevent ink from drooling from the plurality of apertures. A wiper blade is moved into contact with the aperture plate in front of the at least one detected contaminated jet to cause ink to drool from the first portion of the apertures in the aperture plate. The first portion of apertures includes the at least one detected contaminated ink jet. The wiper blade is configured to catch or divert ink drooled from the first portion of the apertures and to prevent drooled ink from reaching apertures in the aperture plate below the first portion of apertures.
The foregoing aspects and other features of the present disclosure are explained in the following description, taken in connection with the accompanying drawings, wherein:
For a general understanding of the present embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements.
As used herein, the term “imaging device” generally refers to a device for applying an image to print media. “Print media” may be a physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed. The imaging device may include a variety of other components, such as finishers, paper feeders, and the like, and may be embodied as a copier, printer, or a multifunction machine. A “print job” or “document” is normally a set of related sheets, usually one or more collated copy sets copied from a set of original print job sheets or electronic document page images, from a particular user, or otherwise related. An image generally may include information in electronic form which is to be rendered on the print media by the marking engine and may include text, graphics, pictures, and the like. As used herein, the process direction is the direction in which an image receiving surface, e.g., media sheet or web, or intermediate transfer drum or belt, onto which the image is transferred moves through the imaging device. The cross-process direction, along the same plane as the image receiving surface, is substantially perpendicular to the process direction.
Although not depicted in
The remote ink containers 51-54 are configured to communicate melted phase change ink held therein to the on-board ink reservoirs 61-64. In one embodiment, the remote ink containers 51-54 may be selectively pressurized, for example by compressed air that is provided by a pressure 67 via a plurality of valves 81, 82, 83, 84. The flow of ink from the remote containers 51-54 to the on-board reservoirs 61-64 may be under pressure or by gravity, for example. Output valves 91, 92, 93, 94 may be provided to control the flow of ink to the on-board ink reservoirs 61-64. The pressure source may be configured to deliver air under pressure to the on-board reservoir at a plurality of different pressure levels. The plurality of pressure levels may be provided by using a variable speed air pump and/or by controlling valve 85 to bleed off pressure from the pressure supplied by the air pump until a desired pressure level is reached. As explained below, the plurality of pressure levels include at least a purge pressure and an assist pressure.
The on-board ink reservoirs 61-64 may also be selectively pressurized, for example by selectively pressurizing the remote ink containers 51-54 and pressurizing an air channel 75 via a valve 85. Alternatively, the ink supply channels 71-74 may be closed, for example by closing the output valves 91-94, and the air channel 75 may be pressurized. The on-board ink reservoirs 61-64 may be pressurized to perform a cleaning or purging operation on the printhead 20, for example. The on-board ink reservoirs 61-64 and the remote ink containers 51-54 may be configured to contain melted solid ink and may be heated. The ink supply channels 71-74 and the air channel 75 may also be heated.
The on-board ink reservoirs 61-64 are vented to atmosphere during normal printing operation, for example by controlling the valve 85 to vent the air channel 75 to atmosphere. The on-board ink reservoirs 61-64 may also be vented to atmosphere during non-pressurizing transfer of ink from the remote ink containers 51-54 (i.e., when ink is transferred without pressurizing the on-board ink reservoirs 61-64).
As schematically depicted in
Once pressurized ink reaches a printhead via an ink supply channel, it is collected in the on-board reservoir. The on-board reservoir is configured to communicate the ink to a jet stack 100 that includes a plurality of ink jets (not shown) for ejecting the ink onto a print medium (
One difficulty faced by fluid ink jet systems is ink jet contamination, also referred to herein as contaminated jets. As used herein, the term “contaminated jets” is used to refer to ink jets that are partially or completely blocked as a result of contamination, such as paper dust and debris particles, in and around the corresponding apertures in the aperture plate. In order to recover from and/or prevent contaminated jets, imaging devices may include a maintenance system for periodically performing a maintenance procedure on the printhead(s). Maintenance procedures typically include purging ink through apertures of the printhead, also referred to as burping, and wiping the aperture plate to remove ink and debris from the surface of the aperture plate. In order to purge ink from the printhead of
The wiper blade and/or the printhead may include a positioning system (not shown) that enables the wiper blade and/or the printhead to be moved with respect to each to perform a wiping procedure. As used herein, the term “wiping procedure” or “wiping” with respect to the aperture plate refers to the process of moving the wiper into contact with the aperture plate at a first location, e.g., above the apertures in the aperture plate, and drawing the wiper blade across the surface of the aperture plate to a second location on the aperture plate, e.g., below the apertures in the aperture plate. To enable a wiping procedure, either or both of the wiper blade and the printhead may be configured for movement so that the wiper blade 108 may be moved toward and away from the aperture plate 104 along an axis B substantially normal to the aperture plate into and out of contact with the aperture plate. In addition, the positioning system enables relative movement of the wiper along an axis A substantially parallel to the front surface of the aperture plate so that the wiper may be moved into and out of contact with the aperture plate. The wiper may be moved into and out of contact with the aperture plate at a plurality of locations along the axis A to enable dabbing procedures. As used herein, the term “dabbing” or “dabbing procedure” refers to the process of moving the wiper blade into and out of contact with an aperture plate of a printhead in an effort to remove debris particles from the wiper blade. Wiper dabbing may be performed at any suitable time such as before and/or after a wiping procedure. The wiper blade may be dabbed against the aperture plate at any suitable location on the aperture plate, such as below the apertures.
The positioning system is also configured to move the wiper blade into and out of contact with the aperture plate at a plurality of locations along the axis A to enable partial wiping of the aperture plate as well as the formation of a purge dam that may be used to facilitate selective purging of certain ink jets. As used herein, the terms “partial wiping,” “partial wipe,” and equivalents thereof refers to the process of performing a wiping procedure on a select portion of the aperture plate. A partial wiping procedure may be utilized to wipe, for example, as few as one or two rows of nozzles, or half of aperture plate or more. The term “purge dam” refers to the process of moving the wiper blade into contact with the aperture plate at a predetermined location in front of the apertures of the aperture plate for a predetermined duration. As explained below, the wiper blade used as a purge dam catches ink drooled from select apertures while preventing drooled ink from reaching apertures in the aperture plate below the select apertures.
To prevent ink and debris from being pushed back into the printhead via the apertures during wiping, the pressure source 67 may also be configured to deliver a low pressure assist (i.e., “LPA” or “assist”) pressure to the on-board reservoir 61 of the printhead. As used herein, an assist pressure is a pressure applied to the ink in an on-board reservoir that is configured to maintain the meniscus of ink at the apertures during a wiping procedure thus preventing ink from being sucked into the apertures during a wiping procedure. The assist pressure may be any suitable pressure level capable of impeding the flow of ink into the apertures. In one embodiment, the assist pressure is approximately about 0.25 to about 1.5 inches of water.
Previously known purging methods required that ink be purged through each ink jet in the printhead. Often, however, printheads may have only one or a few contaminated jets at any given time. While purging ink through each ink jet aperture may be effective in recovering contaminated ink jets, the ink mass moved through uncontaminated jets, i.e., jets that are working as intended, does not contribute to the recovery of the contaminated jets and is effectively wasted. Therefore, the efficiency of contaminated jet recovery may be increased if the total number of jets purged can be reduced. Accordingly, as an alternative to purging each and every ink jet of a printhead during a purge procedure, the present disclosure proposes the selective purging of ink jets to increase the efficiency of jet recovery for a given amount of purged ink by either using surface energy and wetting characteristics as a valve or by using methods and mechanisms to control which portions and/or jets of the head are purged.
According to one embodiment, a selective purging method involves controlling the jets which expel ink by controlling the pressure to the head and the portion of the head which is wiped prior to the purge. Tests have shown that under some pressures, printheads may drool ink from the apertures during or after being wiped, but not before the wipe. As used herein, the term “selective purge pressure” is a pressure applied to the ink in a printhead that is configured to prevent ink from escaping or being emitted from the apertures prior to performing a wiping procedure and to enable ink to escape or be emitted from the apertures after the apertures are wiped by the wiper blade. In one embodiment, the selective purge pressure is approximately 1.5 in H2O although the selective purge pressure may be any suitable pressure level. The selective purge pressure may be applied to ink in the on-board printhead reservoir 61 using the pressure source 67 and controlling valve 85. Once the printhead is pressurized at the selective purge pressure level, the ink jets of the printhead may be selectively purged by controlling which apertures or locations on the aperture plate are wiped by the wiper blade. As mentioned above, the wiping system is configured to perform a partial wiping procedure that may include a wipe of as few as one or two rows of nozzles or apertures in the apertures plate.
Once at least one contaminated ink jet has been detected, the selective purge pressure may be applied to the ink in the printhead (block 504). As mentioned, the selective purge pressure is configured to prevent ink from entering a plurality of apertures in an aperture plate of the printhead during a wiping procedure and to prevent ink from drooling from the plurality of apertures unless the apertures are wiped by a wiper blade. Once the selective purge pressure has been applied to the ink in the printhead, a partial wiping procedure may be performed to wipe a first portion of the aperture plate with the wiper blade while leaving a second portion of the apertures untouched by the wiper blade (block 508). The first portion of the aperture plate includes the at least one detected contaminated ink jet. The wiping of the first portion of apertures enables ink to drool from the first portion of apertures (including the contaminated jet(s)) while the apertures in the second portion of the aperture plate do not drool. The partial wipe may be performed on at least one row of apertures in the aperture plate that include the at least one detected contaminated ink jet. In one embodiment, the partial wipe is performed on two rows of apertures in which the contaminated jet(s) is/are located. Once the partial wipe has been performed, the selective purge pressure may be removed (block 510) and a partial or full wiping procedure may be performed on the aperture plate without the selective purge pressure applied to the ink in the printhead (block 514).
According to another embodiment, a selective purging method involves controlling the jets which expel ink by applying the selective purge pressure to the ink in the printhead and using the wiper blade as a purge dam to cause ink to drool from select apertures in the aperture plate.
According to another embodiment, a selective purging method involves controlling the jets which expel ink by pressurizing a printhead and actuating select jets while the head is pressurized to augment the process of wetting the surface around a specific aperture or apertures to cause ink to drool from the select apertures. Pressurization of the printhead and select actuation of jets enables the purging of a specific bad jet or a very few number of jets. In this embodiment, the pressure applied to the printhead may correspond to the assist pressure described above that is configured to deter ink from entering through the aperture plate. By actuating certain jets with an assist pressure applied to the ink in the printhead, the actuated jets emit ink which wets the aperture enabling the actuated jets to begin to drool ink.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
