Patent Description:
Inkjet printers employing Memjet® technology are commercially available for a number of different printing formats, including small-office-home-office ("SOHO") printers, label printers, digital inkjet presses and wideformat printers. Memjet® printers typically comprise one or more stationary inkjet printheads, which are user-replaceable. For example, a desktop printer may comprise a single user-replaceable multi-colored or monochrome printhead, a high-speed digital press may comprise a plurality of user-replaceable monochrome printheads aligned along a media feed direction, and a wideformat printer may comprise a plurality of user-replaceable printheads in a staggered overlapping arrangement so as to span across a wideformat pagewidth.

Ink is supplied to an inkjet printhead via an ink delivery system, which is designed primarily for delivering ink to the printhead at a predetermined hydrostatic pressure. Ink delivery systems also typically include an ink filter for filtering particulates from the ink.

An example of fluid distribution system for a printhead is given in <CIT>.

Air bubbles are a perennial problem in inkjet printers. Air bubbles that reach inkjet nozzles can block nozzles and cause catastrophic deprime events. Air bubbles can also reduce the efficacy of ink filters in the ink delivery system by blocking microscopic pores in the filter material. Air bubbles can also affect the operation of ink level sensors, for example, by sticking to a float sensor and increasing its buoyancy, thereby resulting in a potential false ink level reading.

To some extent, the problems associated with air bubbles can be mitigated through the use of degassed ink in a closed ink delivery system. However, such ink delivery systems are not immune to the problems of air bubbles even when degassed ink is employed. For example, air may be intentionally introduced into the ink delivery system via printhead depriming operations when air is drawn through the printhead so that the printhead can be replaced with minimal ink fouling. This introduced air can circulate around the ink delivery system and cause problems, such as blocking an ink filter. If the ink filter becomes catastrophically blocked with air bubbles, it will require replacement by the user which is both inconvenient and time-consuming.

In some ink delivery systems described in the prior art, the ink filter is connected to a de-aeration pump, which removes air from the filter chamber housing the filter material. The de-aeration pump ensures that any air bubbles trapped in the ink filter can escape to atmosphere without causing long-term problems through continuous build-up of air bubbles. However, de-aeration pumps add to the cost and complexity of ink delivery systems.

<CIT> describes an ink filter which passively de-aerates via an air-permeable tube under positive ink pressure.

It would therefore be desirable to provide an ink tank having an integrated filter, which minimizes ingress of air bubbles into the filter. It would further be desirable to provide an ink tank, which allows efficient removal of air bubbles. It would further be desirable to provide an ink tank having an ink level sensor whose operation is not affected by air bubbles in the ink.

In a first aspect, there is provided an ink tank for an ink delivery system comprising:.

The housing has an upper section and a lower section, the upper section having a greater cross-sectional area than the lower section, the lower section having an ink inlet port and an ink outlet port.

Preferably, the upper section has a greater volume than the lower section.

Preferably, the ink outlet port is positioned in a base of the housing and the filter comprises a filter drum positioned over the ink outlet port.

Preferably, the baffle plate extends from the base of the housing towards a roof of the ink tank.

Preferably, in use, the baffle plate extends into a headspace of the ink tank.

Preferably, the ink inlet port is positioned above the baffle opening.

Preferably, the ink tank further comprises an ink level sensor, wherein the baffle plate is positioned between the ink level sensor and the ink inlet port.

Preferably, the ink level sensor comprises a float level sensor having a stem extending into the ink tank and one or more floats movable along the stem.

Preferably, the air vent communicates with a labyrinthine channel defined in a roof of the ink tank.

In a second aspect, there is provided an ink delivery system for an inkjet printer comprising:.

Preferably, the printhead comprises a printhead outlet port in fluid communication with the ink tank via an ink return line.

Preferably, the ink return line is connected to the ink supply line.

Preferably, the ink delivery system further comprises a pump and an air intake for depriming the printhead.

Preferably, air enters the ink tank via the ink inlet port during printhead depriming and/or printhead priming.

Preferably, the control system is configured to control a height of ink in the ink tank.

Preferably, the control system controls a supply pump in the ink supply line in response to feedback from one or more ink level sensors in the ink tank.

As used herein, the term "ink" is taken to mean any printing fluid, which may be printed from an inkjet printhead. The ink may or may not contain a colorant. Accordingly, the term "ink" may include conventional dye-based or pigment based inks, infrared inks, UV inks, fixatives (e.g. pre-coats, primers, finishers etc.), 3D printing fluids, biological fluids, functional printing fluids (e.g. solar inks, biosensing inks etc.) and the like.

As used herein, the term "printer" refers to any printing device, such as conventional desktop printers, label printers, duplicators, copiers, digital inkjet presses, 3D printers and the like. The printer may be, for example, a sheet-fed or web-fed printing device.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawing, in which:.

A gravity-feed ink delivery system is described hereinbelow as one exemplary use of the ink tank according to the first aspect. However, it will be appreciated that the ink tank according to the first aspect is equally suitable for use in any circulating ink delivery system incorporating an ink filter.

Referring to <FIG>, there is shown schematically a printer <NUM> having an ink delivery system for supplying ink to a printhead <NUM>. The ink delivery system is a gravity-feed system, which is similar in function to those described in <CIT> and <CIT>.

The ink delivery system comprises an ink tank <NUM> having an ink outlet port <NUM> connected to a printhead inlet port <NUM> of a printhead <NUM> via a first ink delivery line <NUM>. An ink inlet port <NUM> of the ink tank <NUM> is connected to a printhead outlet port <NUM> of the printhead <NUM> via an ink return line <NUM>. Hence, the ink tank <NUM>, the ink delivery line <NUM>, the printhead <NUM> and the ink return line <NUM> together form a closed fluidic loop. Typically, the ink delivery line <NUM> and the ink return <NUM> are comprised of lengths of flexible tubing, which may be of the same or different diameters. In some embodiments, the ink return line <NUM> has a smaller diameter than the ink delivery line <NUM> for efficient air bubble removal, as described in <CIT> and <CIT>.

The ink tank <NUM> additionally contains an integrated filter <NUM> positioned over the ink outlet port <NUM> for filtering ink delivered to the printhead <NUM>, and a baffle plate <NUM> positioned between the ink inlet port <NUM> and the filter <NUM>. The function of the baffle plate <NUM> is described in further detail below.

The printhead <NUM> is user-replaceable by means of a first coupling <NUM> releasably interconnecting the printhead inlet port <NUM> and the first ink line <NUM>; and a second coupling <NUM> releasably interconnecting the printhead outlet port <NUM> and the second ink line <NUM>. The printhead <NUM> is typically a pagewide printhead and may be, for example, a printhead as described in <CIT> or <CIT>.

Ink <NUM> contained in the ink tank <NUM> is open to atmosphere via an air vent <NUM> positioned in roof thereof. Accordingly, during normal printing, ink is supplied to the printhead <NUM> at a negative hydrostatic pressure ("backpressure") under gravity. In other words, gravity-feeding of ink from the ink tank <NUM>, which is positioned below the printhead <NUM>, provides a pressure-regulating system for supplying ink to the printhead at a predetermined negative hydrostatic pressure. The amount of backpressure experienced at a nozzle plate <NUM> of the printhead <NUM> is determined by the height h of the nozzle plate above a level of ink <NUM> in the ink tank <NUM>.

Ink is supplied to the ink inlet port <NUM> of the ink tank <NUM> from a bulk ink reservoir comprising a collapsible ink bag <NUM> housed by an ink cartridge <NUM>. The ink cartridge <NUM> is open to atmosphere via a cartridge vent <NUM> so that the collapsible ink bag <NUM> can collapse as ink is consumed by the system. The collapsible ink bag <NUM> is typically an air-impermeable foil bag containing degassed ink, which is supplied to the ink inlet port <NUM> via an ink supply line <NUM> connected to the ink return line <NUM>. The ink cartridge <NUM> is typically user-replaceable and connected to the ink supply line <NUM> via a suitable ink supply coupling <NUM>. The ink supply line <NUM> may comprise an inline ink filter (not shown) for filtering ink before it reaches the ink tank <NUM>.

A control system is used to maintain a substantially constant level of ink in the ink tank <NUM> and, therefore, a constant height A and corresponding backpressure. As shown in <FIG>, a supply pump <NUM> is positioned in the ink supply line <NUM> and controls a flow of ink from the cartridge <NUM> into the ink tank <NUM>. The supply pump <NUM> is operated under the control of a first controller <NUM>, which receives feedback from an ink level sensor <NUM> having 'high' and 'low' float sensors <NUM> and <NUM> (e.g. magnetic float sensors) positioned in the ink tank <NUM>. When the level of ink <NUM> falls below the 'low' sensor <NUM>, the first controller <NUM> signals the supply pump <NUM> to pump ink into the ink tank <NUM>, and when the level of ink reaches the 'high' sensor <NUM>, the first controller signals the supply pump to stop pumping. In this way, the level of ink <NUM> in the ink tank <NUM> can be maintained relatively constant.

The closed fluidic loop, incorporating the ink tank <NUM>, the ink delivery line <NUM>, the printhead <NUM> and the ink return line <NUM>, facilitates priming, de-priming and other required fluidic operations. The ink return line <NUM> includes a reversible peristaltic pump <NUM> for circulating ink around the fluidic loop. By way of convention only, the "forward" direction of the pump <NUM> corresponds to pumping ink from the ink outlet port <NUM> to the return port <NUM> (i.e. clockwise as shown in <FIG>), and the "reverse" direction of the pump corresponds to pumping ink from the return port <NUM> to the ink outlet port <NUM> (i.e. anticlockwise as shown in <FIG>).

The pump <NUM> cooperates with a pinch valve arrangement <NUM> to coordinate various fluidic operations. The pinch valve arrangement <NUM> comprises a first pinch valve <NUM> and a second pinch valve <NUM>, and may take the form of any of the pinch valve arrangements described in, for example, <CIT>; <CIT>; and <CIT>.

The first pinch valve <NUM> controls a flow of air through an air conduit <NUM>, which is branched from the ink delivery line <NUM>. The air conduit <NUM> terminates at an air filter <NUM>, which is open to atmosphere and functions as an air intake for the closed fluidic loop.

By virtue of the air conduit <NUM>, the ink delivery line <NUM> is divided into a first section 10a between the ink outlet port <NUM> and the air conduit <NUM>, and a second section 10b between the printhead inlet port <NUM> and the air conduit <NUM>. The second pinch valve <NUM> controls a flow of ink through the first section 10a of the ink delivery line <NUM>.

The pump <NUM>, the first pinch valve <NUM> and the second pinch valve <NUM> are controlled by a second controller <NUM>, which coordinates various fluidic operations. From the foregoing, it will be appreciated that the ink delivery system shown in <FIG> provides a versatile range of fluidic operations. Table <NUM> describes various pinch valve and pump states for some example fluidic operations used in the printer <NUM>. Of course, various combinations of these example fluidic operations may be employed.

During normal printing ("PRINT" mode), the printhead <NUM> draws ink from ink tank <NUM> at a negative backpressure under gravity. In this mode, the peristaltic pump <NUM> may either pump ink forwards around the fluidic loop or alternatively be switched off and function as a shut-off valve. The first pinch valve <NUM> is closed and the second pinch valve <NUM> is open to allow ink flow from the ink outlet port <NUM> to the printhead inlet port <NUM>. During printing, ink is supplied to the ink inlet port <NUM> of the ink tank <NUM>, under the control of the first controller <NUM>, to maintain a relatively constant ink level <NUM> and, consequently, a relatively constant backpressure for the printhead <NUM>.

During printhead priming or flushing ("PRIME" mode), ink is circulated around the closed fluidic loop in the forward direction (i.e. clockwise as shown in <FIG>) with the supply pump off. In this mode, the peristaltic pump <NUM> is actuated in the forward pumping direction whilst the first pinch valve <NUM> is closed and the second pinch valve <NUM> is open to allow ink flow from the ink outlet port <NUM> to the ink inlet port <NUM> via the printhead <NUM>. Priming in this manner may be used to prime a deprimed printhead with ink, flush air bubbles from the printhead <NUM> and/or filter particulates from the ink.

In the "STANDBY" mode, the pump <NUM> is switched off whilst the first pinch valve <NUM> is closed and the second pinch valve <NUM> is open. Usually, the printhead is capped in the standby mode to minimize evaporation of ink from the nozzles (see, for example, <CIT>).

In order to ensure each nozzle of printhead <NUM> is fully primed with ink and/or to unblock any nozzles which have become clogged, a "PULSE" mode may be employed. In the "PULSE" mode, the first and second pinch valves <NUM> and <NUM> are closed, while the pump <NUM> is actuated in a reverse direction (i.e. anticlockwise as shown in <FIG>) to force ink through nozzles in the nozzle plate <NUM> of the printhead <NUM>. The supply pump <NUM> is off during pulse priming and the ink tank <NUM> provides a reservoir of ink required for pulse priming. Alternatively, nozzles may be primed using external suction at the nozzle plate <NUM>, as described in, for example, <CIT> ("Method and System for Priming Dry Printheads").

In order to replace a spent printhead <NUM>, it is necessary to de-prime the printhead before it can be removed from the printer. In the "DEPRIME" mode, the first pinch valve <NUM> is open, the second pinch valve <NUM> is closed and the first pump <NUM> is actuated in the forward direction to draw in air from atmosphere via the air conduit <NUM>. Depriming displaces ink in the printhead <NUM> with air and introduces air bubbles into the ink tank <NUM> via the ink inlet port <NUM>. Once the printhead <NUM> has been deprimed of ink, the printer is set to "NULL" mode, which isolates the printhead from the ink supply, thereby allowing safe removal thereof with minimal ink spillages.

In a circulatory ink delivery system employing degassed ink, introducing air into the system for printhead depriming and replacement is potentially problematic. Dissolved air is problematic since it may outgas in the printhead, losing the inherent advantages of using degassed ink. Furthermore, non-dissolved air bubbles behave similarly to particulates and can cause blockages in the ink delivery system. Ideally, non-dissolved air bubbles need to be removed from the system before they cause problems such as blocked nozzles in the printhead <NUM> or blocked ink filters.

Referring now to <FIG> and <FIG>, the ink tank <NUM> is designed to facilitate pressure regulation, ink circulation, filtration and removal of air bubbles from the ink delivery system. The ink tank <NUM> comprises a housing <NUM>, typically formed of molded plastics, which defines an upper section <NUM> and a lower section <NUM> of the ink tank.

The lower section <NUM> includes a truncated cylindrical portion <NUM> for accommodating the filter <NUM>, which takes the form of a cylindrical filter drum <NUM>. The filter drum <NUM> is positioned over the ink outlet port <NUM> at a base of the housing <NUM> for delivering filtered ink to the printhead <NUM>.

The ink inlet port <NUM> is positioned at a sidewall of the lower section <NUM>, such that all ink entering the ink tank <NUM> via the ink inlet port is filtered by the filter <NUM> before exiting the ink tank via the ink outlet port <NUM>. (An additional connection port <NUM>, which is capped in <FIG> and <FIG>, is provided for the option of fluidically connecting multiple ink tanks <NUM> together if required).

A lid <NUM> is fastened to an upper part of the housing <NUM> to define a roof of the ink tank <NUM>. The lid <NUM> defines the air vent <NUM> communicating with a headspace of the ink tank <NUM> as well as a labyrinthine channel <NUM> connected to the air vent. A vent port <NUM> open to atmosphere extends downwardly from the lid <NUM> and communicates with the headspace of the ink tank <NUM> via the labyrinthine channel <NUM> and the air vent <NUM>. The labyrinthine channel <NUM> functions to minimize evaporation of water from the ink tank <NUM> whilst allowing air to vent therethrough.

The baffle plate <NUM> extends upwards from the base of the ink tank <NUM> towards the lid <NUM> and is positioned between the ink inlet port <NUM> and the filter <NUM>. Typically, the baffle plate <NUM> is an insert slidably received in the molded housing <NUM>. The baffle plate <NUM> effectively partitions the ink tank <NUM> into a first side <NUM> having the ink inlet port <NUM> and a second side <NUM> having the filter <NUM> and the ink outlet port <NUM>.

A lower portion of the baffle plate <NUM> defines a baffle opening <NUM> which allows the passage of ink from the ink inlet port <NUM> at the first side <NUM> towards the filter <NUM> at the second side <NUM> via the lower section <NUM> of the ink tank <NUM>. The ink inlet port <NUM> is positioned above the baffle opening <NUM> such that any air bubbles entering the ink tank <NUM> via the ink inlet port do not pass through the baffle opening into the second side <NUM> of the ink tank <NUM>. Instead, air bubbles entrained in ink pumped into the ink tank via the ink inlet port <NUM> tend to strike the baffle plate <NUM> above the baffle opening <NUM> and float upwards into the headspace of the ink tank, where they can vent to atmosphere via the air vent <NUM>. The baffle plate <NUM> therefore protects the filter <NUM> from air bubbles entering the ink tank <NUM> via the ink inlet port <NUM>. (To the extent that a minimal number of air bubbles reach the filter <NUM>, these can float upwards towards the air vent). The baffle plate <NUM> additionally protects the float sensors <NUM> and <NUM> from air bubbles, as will be explained further below.

When fresh degassed ink from the ink reservoir enters the ink tank <NUM> via the ink inlet port <NUM>, this ink flows through the baffle opening <NUM> towards the filter <NUM> via the lower section <NUM> of the ink tank. The baffle plate <NUM> extends into a headspace of the ink tank <NUM> such that ink contained in the upper section <NUM> cannot pass from the first side <NUM> of the ink tank to the second side <NUM>. Since aerated ink in the upper section <NUM> is relatively immobile and separated (in height) from ink in the lower section <NUM>, this aerated ink diffuses only very slowly towards the lower section <NUM>. Therefore, during normal printing, degassed ink in the lower section <NUM> remains degassed when replenished with fresh degassed ink from the ink reservoir. The design of the ink tank <NUM> therefore provides an effective diffusion barrier between the upper and lower sections <NUM> and <NUM>, making it suitable for gravity control of backpressure at the printhead <NUM> whilst enabling the use of degassed inks.

The ink level sensor <NUM> takes the form of a magnetic float sensor having a stem <NUM> fastened to the lid <NUM> and extending into the ink tank <NUM>. 'High' and 'low' float sensors <NUM> and <NUM> are movable along the stem <NUM> between respective fixed stops <NUM>. Each float sensor contains a magnet, which actuates a respective reed switch (not shown) in the stem <NUM> to indicate a 'high' or 'low' level of ink in the ink tank <NUM>. As described above, the supply pump <NUM> is actuated or deactuated depending on the level of the float sensors <NUM> and <NUM> and the corresponding state of the reed switches. The ink level sensor <NUM> is positioned at the second side of the ink tank <NUM> and is thereby protected from air bubbles by the baffle plate <NUM>. Protection of the float sensors <NUM> and <NUM> from air bubbles advantageously minimizes false ink level signals from the ink level sensor <NUM> by avoiding disturbances to the sensitive float sensors.

From the foregoing, it will be appreciated that the ink tank <NUM> achieves multiple functions: (<NUM>) protection of the filter from air bubbles; (<NUM>) protection of the ink level sensor from air bubbles; (<NUM>) efficient removal of air bubbles from an ink delivery system; and (<NUM>) gravity control of ink pressure in an ink delivery system supplied with degassed ink. These and other advantages will be readily apparent to the person skilled in the art.

Claim 1:
An ink tank (<NUM>) for an ink delivery system comprising:
a housing (<NUM>) having an upper section (<NUM>) and a lower section (<NUM>), the upper section having a greater cross-sectional area than the lower section, the lower section having an ink inlet port (<NUM>) and an ink outlet port (<NUM>);
an air vent (<NUM>) communicating with a headspace of the ink tank;
a filter (<NUM>) positioned in the housing for filtering ink supplied from the ink tank via the ink outlet port; and
a baffle plate (<NUM>) positioned in the housing between the ink inlet port and the filter, the baffle plate being configured for directing air bubbles entering the ink tank via the ink inlet port towards the headspace of the ink tank,
wherein the baffle plate has a baffle opening positioned towards a base of the ink tank, thereby allowing ink to flow from the ink inlet port towards the ink outlet port via the baffle opening.