Ink tank

Abstract

An ink tank for an inkjet printer, the ink tank comprising: a tank floor defining a bottom surface of the tank during normal use; tank walls defining side surfaces of the tank; a tank bottom defining the lowest point within the tank; a bulk region configured to store most of the ink within the ink tank, the bulk region having a tank floor that is horizontal or slopes toward the tank bottom during normal use; and a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by the tank walls.

Description

[Technical Field]

[0001] The present invention relates to inkjet printing, and more particularly to an ink storage tank and mixing system for storing and mixing ink. The ink may be a pigmented ink for use in inkjet printers, such as continuous inkjet printers. [Background technology]

[0002] In inkjet printing systems, the print material consists of individual ink droplets that are generated at a nozzle and propelled towards a substrate. Two main systems exist: drop-on-demand systems, in which ink droplets are produced as and when needed for printing, and continuous inkjet printing systems, in which ink droplets are produced continuously, with only selected droplets directed towards the substrate and the rest recycled to the ink supply.

[0003] A continuous ink jet printer supplies pressurized ink to a drop generator in a printhead, where a continuous jet or stream of ink emerging from a nozzle is stimulated, for example by a vibrating piezoelectric element, to form individual, regular droplets. The droplets are directed past charging electrodes, which selectively and individually impart a predetermined charge to them, and then pass through a transverse electric field, which may be established across a pair of deflection plates. Each charged droplet is deflected by the electric field by an amount dependent on the magnitude of its charge before striking the substrate, while uncharged droplets proceed undeflected and are collected in a gutter, from which they are recycled to the ink supply for reuse. Charged droplets bypass the gutter and strike the substrate at a location determined by the charge on the droplet and the position of the substrate relative to the printhead. Typically, the substrate is moved in one direction relative to the printhead, and the droplets are deflected in a direction generally perpendicular to the substrate, although the deflector plates can be oriented at an angle to a vertical position to compensate for the velocity of the substrate (movement of the substrate relative to the printhead means that the droplet line does not extend completely perpendicular to the direction of substrate movement during the droplet arrival).

[0004] In continuous inkjet printing, characters can be printed from a matrix with a regular array of potential drop positions. Each matrix has multiple columns (strokes), and each column is defined by a line with multiple potential drop positions (e.g., seven) determined by the charge applied to the drop and various other influencing factors. Thus, each available drop is charged according to its intended position within the stroke. If a particular drop is not used, it is not charged and is collected in a gutter for recirculation. This cycle is repeated for all strokes in the matrix, then begins again for the next character matrix.

[0005] Ink is delivered to the printhead under pressure by an ink supply system typically housed in a sealed compartment of a cabinet that also contains separate compartments for the control circuitry and user interface panel. The system includes a main pump that draws ink from an ink storage tank in the ink supply system through a filter and delivers it under pressure to the printhead. As ink is consumed, the tank is replenished as needed from replaceable ink cartridges that are detachably connected to the tank by supply conduits. Ink is pumped from the tank to the printhead through flexible supply conduits. Unused ink droplets collected in a gutter are recirculated by the pump back to the tank through a return conduit. The flow of ink in each conduit is typically controlled by a solenoid valve and / or other similar component.

[0006] Because reliable droplet generation (by jet break-off) depends on the ink having substantially non-viscous properties, the ink in the ink tank is preferably diluted. The ink recirculated from the gutter is solvent-depleted due to solvent evaporation. Therefore, the ink (storage) tank is intermittently adjusted with replenishment solvent from a replaceable solvent cartridge to ensure that the ink drawn from the ink tank has an acceptable viscosity.

[0007] Various types of inks can be used in continuous inkjet printers. The inks can contain organic solvents selected from C1-C4 alcohols, C4-C8 ethers, C3-C6 ketones, C3-C6 esters, and mixtures thereof. The inks can contain different types of colorants. Dye-based inks are used in some situations. This is typically the case when the substrate being printed on is relatively light in color, so that the dyes contained in the ink color the light reflected from the surface, creating a pattern visible to the user. On the other hand, pigment inks may be preferred when the surface being printed on is dark and therefore less reflective. In such situations, the pigments contained in the ink reflect light of a specific color, thereby making the printed image visible to the user. Of course, both dye-based and pigment inks can be used to print on some substrates, while pigment inks can be used on light surfaces and dye-based inks on dark surfaces. One specific subgroup of pigment inks is known as hard pigment inks. The pigments in these inks are typically hard particles such as titanium dioxide, resulting in highly opaque printed marks.

[0008] When pigmented inks are used, the ink consists of a suspension of colorant (i.e., pigment) particles in a solvent. The ink composition may also include various other ingredients or additives (such as surfactants or dispersants). Ink compositions can vary depending on various characteristics, such as the color required, the surface to be printed on, the solvent suitable for the particular application environment, and many other factors.

[0009] During operation, the contents of the ink tank are subject to a certain degree of agitation due to the operation of the ink supply system and reflux from the gutter, which means that the pigment particles remain in relatively uniform suspension.

[0010] While continuous ink jet printers typically operate continuously, it is desirable to shut down the printer during events such as weekends and holidays. This is due to safety concerns, as continuous ink jet printers combine highly flammable fluids with high voltage power connections, and continuous operation also shortens the life of the pump. Therefore, it is not recommended to leave a continuous ink jet printer running unattended.

[0011] However, it should be understood that during such printer idle periods, pigment particles (especially hard pigments) may settle under gravity in the ink tank, forming a sediment layer on the bottom of the tank. Sedimentation may also occur in other components of the printer or ink supply system, such as in filters for filtering the ink and in ink supply lines. Sedimentation is accelerated in the ink tank because the substantially non-viscous mixture offers little resistance to pigment settling. The sediment layer may be characterized as a dense, densified layer of pigment with semi-solid properties, which may cause blockage of the ink supply path if the sediment layer enters the printer's internal fluid circuitry. Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present invention to provide an improved ink tank for use with ink jet printers, particularly continuous ink jet printers, which overcomes one or more of the problems associated with the use of pigmented inks, inks containing sediment and / or solid deposits, whether or not specified above. [Means for solving the problem]

[0013] According to a first aspect disclosed in this specification, there is provided an ink tank for an inkjet printer, comprising a tank floor defining a bottom surface of the tank and tank walls defining sides of the tank during normal use, the tank comprising: a tank bottom defining a lowest point in the tank; a bulk region configured to store most of the ink in the ink tank, wherein the tank floor within the bulk region is horizontal or slopes toward the tank bottom during normal use; and a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by the tank walls.

[0014] Providing a mixing region between the bulk region and the tank bottom (i.e., the global lowest point of the tank) promotes gradual movement of ink sediment across the bottom of the bulk region, preventing compaction of the sediment. Meanwhile, the mixing region can be provided with mixing elements or other mixing devices that can disperse compacted sediment. In this way, compaction of sediment in one small area can be more easily addressed than if the sediment were distributed over a larger area. Furthermore, providing a large bulk region with a less steeply sloping floor allows for a larger tank volume for a given overall height, since the floor is less steep than in a conventional conical tank.

[0015] The tank further comprises a tank ceiling defining a top wall of the tank, the tank floor, tank walls and tank ceiling together enclosing an interior volume of the tank.

[0016] In the mixing region, the tank walls may also function in part as the tank floor, i.e., in at least some portions of the mixing region, the sloping walls may function to define both the lower surface and the sides of the tank, while in other portions of the mixing region, the lower surface is provided by the tank bottom.

[0017] The terms "wall" and "floor" are used herein to refer to different portions of a tank wall that may be of continuous construction (e.g., formed as a single component). Generally, if the component slopes less than 45 degrees from horizontal, the area will be referred to as a "floor," whereas if the component slopes more than 45 degrees from horizontal, the area will be referred to as a "wall."

[0018] The mixing region may have a circular cross section when viewed from above.

[0019] In some embodiments, the seam between the mixing zone and the bulk zone can be considered the point where the tank wall transitions into the tank floor, i.e., the point where the wall / floor slope angle is less than 45 degrees from horizontal.

[0020] Alternatively, the top of the mixing region can be determined based on the width of the mixing region, for example, the top of the mixing region can be considered to be the point in the tank where the width (or diameter) of the tank exceeds a predetermined value (e.g., 50 mm).

[0021] However, it should be understood that the mixing region can be defined in many ways, and the sizes and shapes of the mixing region and bulk region can vary significantly. Thus, the benefits of providing a mixing region at the bottom of the tank with steeper sidewalls than the bulk region can be realized in a variety of ways.

[0022] The tank walls surrounding the mixing region between the tank bottom and the bulk region may be vertical or have a steeper slope than the tank floor in the bulk region.

[0023] Providing the mixing zone with vertical walls or walls that are steeper than the floor of the bulk zone provides a convenient structural configuration while providing the desired floor and wall profile, i.e., a less steep bulk zone is separated from the tank bottom by a steeper-sided mixing zone.

[0024] The tank walls surrounding the mixing region can be vertical or can slope towards the tank bottom.

[0025] The slope of the floor within the bulk area may be at least 2 degrees from a nominal horizontal reference line.

[0026] The slope of the floor within the bulk area may be at least 5 degrees from a nominal horizontal reference line.

[0027] The slope of the tank wall within the mixing area may be no more than 85 degrees from the nominal horizontal reference line.

[0028] The nominal horizontal reference line may be defined as the line that is horizontal when the ink tank is oriented in its normal use configuration and when the ink tank is mounted in a printer supported on a horizontal surface. Of course, it should also be understood that during use, the printer may be operated when supported on a surface that is not strictly horizontal, causing the nominal horizontal reference line to deviate from the horizontal plane. Reference to the nominal horizontal reference line is intended to provide a convenient frame of reference for other components of the printer, rather than to restrict orientation by strict adherence.

[0029] In view of the above, it should be understood that when describing the slope of the tank walls in the mixing area as being less than 85 degrees from a nominal horizontal reference line, it is intended that in use the tank walls in the mixing area will be close to vertical (e.g., 85 degrees), but may vary depending on usage due to the printer being placed on an uneven surface.

[0030] The tank may have a vertical depth of at least 15 mm from the bottom of the tank to the lowest point of the bulk area.

[0031] The ink tank may have a lateral width of at least 18 mm at a vertical distance of 10 mm from the bottom of the tank.

[0032] The ink tank may have a width of 40 mm or less at a vertical distance of 10 mm from the bottom of the tank.

[0033] Providing a relatively narrow mixing zone (e.g., less than 40 mm wide) can facilitate mixing because less mixing force is needed to disperse any sediment that settles within the mixing zone, whereas a mixing zone that is too narrow (e.g., less than 18 mm wide) may require the mixing zone to be excessively tall to provide sufficient volume to accommodate a sufficient amount of pigment.

[0034] The width of the mixing area shall be defined by defining the horizontal width at a distance of 10 mm from the bottom of the tank.

[0035] The tank width in the bulk zone can be significantly greater than the width in the mixing zone, for example, the tank width in the bulk zone can be about 100-200 mm.

[0036] The mixing region may have a volume that is less than 5% of the total liquid volume of the tank.

[0037] The total liquid volume of a tank comprises the volume enclosed by the tank floor and tank walls below the maximum fill level (in its normal operating orientation). Of course, it is understood that it is possible to overfill a tank beyond this level, but many tanks nevertheless have a maximum or normal recommended fill level.

[0038] The ink tank may further comprise a transition region between the bulk region and the mixing region, the transition region having a slope greater than that of the bulk region floor, and the transition region having a slope less than that of the mixing region wall.

[0039] The slope of the transition region need not be constant; that is, the transition region can provide a gradual transition between the steeper sides of the mixing region and the flatter bed slope of the bulk region.

[0040] In some embodiments, the transition region may have a more complex profile (eg, an inflection point, etc.).

[0041] The addition of a transition region can slow the formation of high viscosity ink in a settling region at the bottom of the bulk region bed before it reaches the mixing region.

[0042] The transition region may have a vertical depth of at least 15 mm from the highest point of the mixing region to the lowest point of the bulk region.

[0043] The transition region may have a vertical depth at least as large as the vertical depth of the mixing region.

[0044] The transition region may have a volume that is at least 5% of the total liquid volume of the tank.

[0045] The ink tank may further comprise a header region, which may be located above the bulk region of the tank and may be separated from the tank floor by at least the bulk region, and which may extend from the maximum liquid fill level of the tank to the tank ceiling.

[0046] The ink tank may further include a level sensor including a float and a float chamber, and the float chamber may be fluidly connected to the mixing tank via at least an upper connection and a lower connection, the upper connection being located at a position above the maximum liquid fill level of the tank, and the lower connection being located at a position above the upper limit of the mixing area.

[0047] The lower connection may be provided in the transition region.

[0048] The level sensor may be configured to generate a low level signal when the liquid level in the tank falls below a minimum fill level.

[0049] The level sensor may be configured to generate a high level signal when the liquid level in the tank exceeds a liquid maximum fill level.

[0050] The ink tank may further include a mixing device disposed within the mixing region, and the mixing device may include a plurality of fluid ports, each with a respective opening, and the plurality of fluid ports may be configured to direct fluid away from the mixing device into the mixing region and toward a tank wall surrounding the mixing region.

[0051] The ink tank may further include a mixing device disposed within the mixing region, and the mixing device may include a plurality of fluid ports, each with a respective opening, and the plurality of fluid ports may be configured to direct fluid away from the mixing device into the mixing region and toward the bottom of the tank.

[0052] The plurality of fluid ports can be configured to direct fluid away from the mixing device into the mixing region, toward a tank wall surrounding the mixing region, and / or toward the tank bottom.

[0053] By providing a mixing device within the mixing region, any sediment formed within the mixing region can be disturbed by a jet of ink from the fluid port.

[0054] According to a second aspect disclosed herein, there is provided an ink tank for an inkjet printer, comprising a tank floor defining a bottom surface of the tank and tank walls defining sides of the tank during normal use, the tank comprising: a tank bottom defining a lowest point within the tank; a mixing device provided adjacent the tank bottom, the mixing device comprising a plurality of fluid ports each having a respective opening, the plurality of fluid ports configured to direct fluid away from the mixing device and into an area of ​​the tank surrounding the mixing device; and a fluid supply conduit configured to supply fluid to the plurality of fluid ports of the mixing device, the fluid supply conduit configured to deliver fluid to the mixing device from below the mixing device.

[0055] Locating the fluid supply conduit delivering fluid to the mixing device from below the mixing device reduces the risk of sediment forming in the fluid ports as a result of settling in the supply conduit, and locating the fluid supply in this manner eliminates the need for conduits in the upper (e.g., bulk) region of the tank.

[0056] This type of (i.e., bottom-fed) mixing device can be combined with a tank having a mixing zone (as detailed above) or can be provided within a conventional tank (e.g., a tank with a conical bottom, flat bottom, or gently sloping bottom).

[0057] The following optional features may be combined with either the first or second aspect disclosed herein.

[0058] The plurality of fluid ports can be configured to direct fluid from the mixing device in a plurality of directions, where each of the plurality of directions can have a horizontal component and a vertically downward component, and / or at least one of the plurality of directions can have a non-radial component.

[0059] The use of a non-radial horizontal component allows the fluid to flow in a circular fashion around the mixing region, improving mixing performance.

[0060] The plurality of fluid ports may be configured to direct fluid radially outward from the mixing device.

[0061] The plurality of fluid ports may be configured to direct fluid circumferentially around the tank bottom.

[0062] By being directed around the bottom of the tank, the fluid flow is deflected by the floor and walls of the tank and then recirculates through the mixing area, disturbing the settled pigment and maximizing the mixing effect.

[0063] Each of the plurality of openings may be vertically oriented, i.e., at least partially downwardly oriented.

[0064] Each of the plurality of apertures may have a diameter of at least 1 mm.

[0065] Each of the plurality of openings may have a diameter of 2 mm or less.

[0066] Positioning the openings in this manner reduces the likelihood of sediment falling into the openings.

[0067] The ports may be tapered outwardly toward the opening or may be straight.

[0068] The plurality of fluid ports may comprise at least three fluid ports.

[0069] The plurality of fluid ports may comprise 10 fluid ports or less, preferably 7 fluid ports or less.

[0070] Providing at least three fluid ports allows mixing over a large area around the mixing device, while providing seven or fewer fluid ports maintains a convenient minimum flow rate through each port, thereby reducing the risk of clogging when using a large number of ports.

[0071] The central axes of the plurality of fluid ports may be positioned at a vertical distance of at least 3 mm from the bottom of the tank.

[0072] Each of the plurality of openings may be located at a horizontal distance of 15 mm or less from the tank wall.

[0073] By providing a relatively small horizontal distance, ink released from the openings can easily reach the side walls, so that effective mixing can be provided even with a relatively low power pump.

[0074] Each of the plurality of openings may be spaced horizontally from the tank wall by at least 4 mm. If the horizontal spacing is too small, blockages may occur, making mixing difficult.

[0075] The reservoir may further comprise a mixing pickup configured to pick up ink fluid from the ink reservoir for mixing the inks. The mixing pickup may be provided in the bulk region.

[0076] By supplying ink for mixing from within the bulk region, the likelihood of blockages occurring within the mixing assembly is reduced as the bulk region is less likely to accumulate large amounts of sediment.

[0077] The mixed pickup may also perform other functions, for example, it may also function as an ink return line (e.g., allowing ink to flow from the printhead gutter to the ink tank), or it may have a separate mixed pickup port.

[0078] The tank may further comprise a fluid supply conduit configured to supply fluid to the plurality of fluid ports, and the fluid supply conduit may be configured to deliver fluid to the mixing device from below the mixing device.

[0079] Locating the fluid supply conduit in this manner reduces the risk of sediment forming in the fluid ports as a result of precipitation in the supply conduit, and locating the fluid supply conduit in this manner eliminates the need for a conduit in the upper (e.g., bulk) region of the tank.

[0080] The fluid supply conduit can include a vertical portion configured to deliver fluid to the mixing device from below the mixing device and a side portion configured to deliver fluid to the vertical portion, and the side portion can slope upwardly away from a junction between the vertical portion and the side portion.

[0081] Providing an inclined feed conduit in this manner reduces the risk of settling within the feed conduit as any pigment that does settle will gradually move along the lower surface of the conduit rather than clumping along the bottom of the conduit.

[0082] The side portion may be angled upwardly away from the junction between the vertical portion and the side portion at an angle of at least 2 degrees relative to the horizontal.

[0083] The fluid supply conduit may further include a sump tank at the junction between the vertical section and the side section, the sump tank being configured to receive sediment from the side section.

[0084] After the rest period, when fluid is first pumped along the side toward the mixing device, any sediment that has formed in the side can be pushed toward the sump tank, reducing the risk of this sediment blocking the fluid port. The sump tank can have a volume of approximately 1 ml.

[0085] The tank may further comprise a fluid supply conduit configured to supply fluid to the plurality of fluid ports, and the fluid supply conduit may be configured to deliver fluid to the mixing device from above the mixing device.

[0086] The fluid supply conduit can include a vertical portion directly above the mixing device and a side portion configured to deliver fluid to the vertical portion, and the side portion can be sloped upwardly away from the junction between the vertical portion and the side portion.

[0087] The fluid supply conduit above the mixing device may comprise a straight vertical pipe.

[0088] The fluid supply conduit above the mixing device may comprise a spirally wound pipe.

[0089] By providing a spirally wound pipe when delivering fluid from the top of the mixer, a gentle slope is introduced into the pipe rather than a (predominantly) vertical orientation, which causes any sediment to move slowly along the bottom of the pipe, reducing the risk of sediment blocking the mixer fluid ports.

[0090] According to a third aspect disclosed herein, there is provided an ink system comprising an ink tank according to the first or second aspect and a mixing device configured to mix the inks in a mixing region.

[0091] The mixing apparatus can be a mechanical stirrer or other form of stirring device.

[0092] The mixing device may have multiple outlets. The mixing device may comprise a single port.

[0093] A pump may be provided to supply ink to the outlet or ports.

[0094] According to a fourth aspect disclosed herein, there is provided an ink system comprising an ink tank according to the first or second aspect, and a pump configured to supply fluid to a mixing region.

[0095] The pump can be configured to supply ink to a plurality of outlets disposed within the mixing region.

[0096] According to a fifth aspect disclosed herein, there is provided an ink system comprising an ink tank according to the first or second aspect, and a pump configured to supply fluid to a mixing region to mix the inks.

[0097] The pump (in any of the third to fifth aspects) may be configured to pump ink from the ink tank through the mixing pickup and to supply the pumped ink to the mixing device to mix the inks.

[0098] The inking system (according to any of the third to fifth aspects) may be configured to eject ink into the ink tank during shutdown operations, and the inking system may be configured to mix ink in the ink tank during startup operations. The inking system may be configured to mix ink in the ink tank during periods of idle operation.

[0099] Mixing the inks can include flowing the inks out of a port in a mixing device (eg, a mixing apparatus), if present.

[0100] Draining the ink may include allowing the ink to flow into the reservoir under gravity and / or pumping the ink into the reservoir.

[0101] According to a sixth aspect disclosed herein, there is provided a continuous ink jet printer comprising the ink system of any of the third, fourth or fifth aspects, further comprising: a drop generator configured to receive ink from the ink system and generate ink jets for printing; a gutter configured to receive portions of the jets not required for printing; and a gutter line connected to the gutter and configured to return unprinted ink to an ink tank.

[0102] The continuous ink jet printer may further comprise a printhead operable to receive ink from the ink system for printing, the printhead comprising a drop generator and a gutter.

[0103] The jet of ink may be a modulated jet of ink configured to form a stream of individual droplets.

[0104] The continuous ink jet printer may be an electrostatic deflection continuous ink jet printer configured to selectively charge ink droplets within an ink jet and deflect the charged droplets in an electrostatic field.

[0105] The droplets can be selectively, and possibly variably, charged, with the charge of each particular droplet being determined based on the pattern to be printed.

[0106] The continuous ink jet printer may further include at least one charging electrode configured to induce an electric charge in the ink droplets and at least one deflection electrode configured to generate an electrostatic field.

[0107] The printhead may include a charge electrode. The printhead may include at least one deflection electrode. The printhead may include two deflection electrodes.

[0108] A continuous ink jet printer can be configured to deflect the charged droplets by an amount so that they strike the substrate at a desired print location to print the printed pattern.

[0109] A continuous ink jet printer can be configured so that uncharged droplets are transferred to a gutter, and unprinted ink droplets can be recycled back into the ink system.

[0110] The printer may include an ink supply line configured to transport ink from an ink reservoir to a drop generator.

[0111] According to a seventh aspect disclosed in the present specification, there is provided a method for mixing pigment ink, the method including the steps of storing ink in an ink tank, the ink tank having a tank floor that defines a bottom surface of the tank during normal use and tank walls that define sides of the tank, the tank having a tank bottom that defines a lowest point in the tank, a bulk region configured to store most of the ink in the ink tank, the tank floor within the bulk region being horizontal or sloping towards the tank bottom, and a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by the mixing region tank walls; and mixing the ink in the mixing region.

[0112] Providing a mixing region between the bulk region and the tank bottom (i.e., the global lowest point of the tank) promotes gradual movement of ink sediment across the bottom of the bulk region, preventing compaction of the sediment. When mixing occurs, only a relatively small volume of the mixing region needs to be mixed. This mixing helps to disperse compacted sediment. In this way, compaction of sediment in one small region is more easily addressed than if the sediment were distributed over a larger region. Furthermore, providing a large bulk region with a less steep floor allows for a larger tank volume for a given overall height, since the floor is less steep than in a conventional conical tank.

[0113] The method may further include supplying the fluid to a mixing device disposed within the mixing region and directing the fluid away from the mixing device into the mixing region through a plurality of fluid ports, each of the plurality of fluid ports of the mixing device having a respective opening.

[0114] The ink tank may further include a mixing device disposed within the mixing region.

[0115] The method may further comprise supplying the fluid to a mixing device.

[0116] The method may further include directing fluid away from the mixing device into the mixing region, toward the mixing region tank wall and / or toward the tank bottom, by a plurality of fluid ports for mixing the inks, each with a respective opening.

[0117] According to an eighth aspect disclosed herein, there is provided a method for mixing pigmented ink, the method including the steps of storing ink in an ink tank, the ink tank having a tank floor defining a bottom surface of the tank during normal use and tank walls defining sides of the tank, the tank having a tank bottom defining a lowest point in the tank, and a mixing device disposed proximate to the tank bottom, supplying fluid to the mixing device from below the mixing device via a fluid supply conduit, and directing the fluid away from the mixing device and into a region of the tank surrounding the mixing device by a plurality of fluid ports, each of the plurality of fluid ports having a respective opening. The method further includes directing the fluid away from the mixing device and into a region of the tank surrounding the mixing device by the plurality of fluid ports, each of the plurality of fluid ports having a respective opening.

[0118] The mixing device may be located within a mixing area of ​​the tank.

[0119] It should be understood that features described in connection with one embodiment may be combined with other embodiments described herein. For example, features described above in connection with an ink tank may also be applied to a continuous ink jet printer including such an ink tank, or to a method of operating such an ink tank, or to a method of manufacturing an ink tank, or to a kit of parts. In particular, it should be understood that features of the ink tank of the first embodiment may be combined with features of the ink tank of the second embodiment, features of the ink system of the fifth embodiment may be combined with the ink system of the third embodiment and / or the fourth embodiment, features of the continuous ink jet of the sixth embodiment may be combined with the ink tank of the first or second embodiment, the ink systems of the third through fifth embodiments, and the methods of the seventh and eighth embodiments, features of the seventh and eighth embodiments may be combined with features of the first through sixth embodiments, and features of the first through eighth embodiments may be combined.

[0120] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0121] [Figure 1] 1 shows a schematic diagram of a continuous ink jet printer. [Figure 2] 2 shows a schematic diagram of the ink circuit of the continuous ink jet printer shown in FIG. 1; [Figure 3] 2 shows a schematic cross-section of an ink storage tank used in the continuous ink jet printer shown in FIG. 1; [Figure 4] 2 shows a schematic representation of an alternative embodiment of an ink storage tank for use in the continuous ink jet printer shown in FIG. 1; [Figure 5] 1 shows a schematic of a mixing device having a bottom-mounted fluid supply conduit. [Figure 6A] 10A and 10B show schematic diagrams of an alternative mixing device having a top-mounted fluid supply conduit with side sections; [Figure 6B]10A and 10B show schematic diagrams of an alternative mixing device having a top-mounted fluid supply conduit without side sections; [Figure 7] 10A and 10B show schematic diagrams of another alternative mixing device having a helical top-mounted fluid supply conduit; DETAILED DESCRIPTION OF THE INVENTION

[0122] In the figures, like parts are designated by like reference numerals. It should be understood that the drawings are for illustrative purposes only and may not be drawn to scale.

[0123] Figure 1 shows a schematic diagram of a continuous ink jet printer 101. The printer 101 comprises a printer body 103 connected to a print head 105 by an umbilical cable 107. The printer body 103 comprises an ink supply system and a printer controller, and may have a display 109 (e.g., a touch screen) for use by an operator. The print head 105 is positioned to print on a substrate, such as the surface of an article 111, moving along a production line 113.

[0124] Referring now to FIG. 2, a simplified schematic diagram of a possible fluid system for the inkjet printer of FIG. 1 is shown. The inkjet printer 101 includes an ink supply system 115 housed within the printer body 103. The ink supply system 115 includes an ink tank 117 for storing ink. A mixing device 123 is located below the liquid level of the ink tank 117 and is connected to an ink pickup line 119, which is itself connected to a pump 121. Thus, fluid within the ink tank 117 is in fluid communication with the pump 121, and ink also passes through the mixing device 123. The pump 121 has an outlet connected to a 3:2 valve 122. The 3:2 valve is operable to connect the pump 121 to a filter 126 to enable ink to be supplied from the ink tank 117 to the printhead 105 (described in more detail below). The 3:2 valve also connects the pump to a mixing pickup 120 located within the ink tank 117.

[0125] The pump 121 can be operated in a forward or reverse direction. When the pump 121 is operated in a forward direction and the 3:2 valve 122 is configured to connect the pump outlet to the filter 126, the fluid system is said to be in a forward configuration. In the forward configuration, ink is drawn by the pump 121 from the ink tank 117 through the mixing device 123 and the ink pickup line 119 towards the 3:2 valve 122. The pump delivers the ink from the 3:2 valve 122 to the filter 126. The filter 126 has an outlet connected to the damper 125.

[0126] A damper 125 is provided after the filter 126 to reduce fluctuations in ink pressure within the ink supply. A pressure sensor 129 is provided at the damper outlet and configured to monitor the pressure at the damper 125 outlet. A valve 127 is provided downstream of the pressure sensor 129. An ink supply line 128 is configured to transport ink from the ink supply system 15 along the umbilical 7 to the printhead 5. The ink supply line 128 is connected to the ink pickup line 119 via the pump 121, the 3:2 valve 122, the filter 126, the damper 125, and the valve 127. Thus, in the forward configuration, ink is drawn from the ink tank 117 toward the printhead 105. The valve 127 is configured to control the supply of ink to the printhead 105.

[0127] The ink supply system 115 also includes an ink cartridge connection 131 connectable to an associated ink cartridge 133 and a solvent cartridge connection 135 connectable to an associated solvent cartridge 137. The ink cartridge 133 and the ink cartridge connection 131 are connected to an ink refill line 141, allowing ink to be drawn through a valve 143 by a pump 145 (e.g., a diaphragm pump) and delivered to the ink tank 117.

[0128] Similarly, the solvent cartridge 137 and solvent cartridge connection 135 are connected to a solvent refill line 149, and the suction of the pump 145 allows solvent to be delivered to the ink tank 117 through a valve 151. Each valve 143, 151 can be operated independently, allowing either ink or solvent to be delivered to the ink delivery tank independently under the control of the pump 145.

[0129] In some configurations, ink and / or solvent reservoirs (not shown) may be provided for temporary storage of ink or solvent between the cartridges 133, 137 and their respective refill lines 141, 149.

[0130] To function properly, the ink supplied to the printhead 115 must be within a specific viscosity range. The ink tank 117 acts as a premixed ink reservoir so that any ink drawn from it meets the viscosity specification. The precise mixture of ink and solvent is maintained by the controlled flow of ink and solvent from the ink cartridge 133 and solvent cartridge 137.

[0131] As described above, in use, ink is pumped along ink pickup line 119 and ink supply line 128 through umbilical 107 to printhead 105. Within printhead 105, ink is supplied to drop generator 155. The ink is supplied under pressure (under the influence of pump 121) to the drop generator and forced through a nozzle of drop generator 155 to form an ink jet 157. Ink jet 157 begins as a steady stream of ink and, under the influence of surface tension and vibrations applied within drop generator 155 (e.g., by a piezoelectric oscillator), gradually breaks up into a series of ink droplets 159 that continue in the direction of ink jet 157.

[0132] In some printers (such as the printer shown in FIG. 2 ), a purge line 158 is connected to the droplet generator. The purge line 158 can be connected to a purge port on the droplet generator 155. The droplet generator 155 can be part of a droplet generator assembly that includes a droplet generator body with known acoustic characteristics and a piezoelectric oscillator. The purge port can be provided by the body or by a separate component connected to the body. The purge line 158 allows ink to exit the droplet generator through a purge opening without passing through the nozzles, cleaning the droplet generator. The purge line 158 extends from the droplet generator 155 along the umbilical 107 and returns ink (or solvent) to the ink delivery tank 117 depending on the stage of operation. One or more valves (not shown) can be provided in the purge line 158. It should be understood that the purge line is not required and can be omitted in some printers. Additionally, additional fluid lines can be provided to support certain printer operations. For example, a solvent supply line may be provided to supply clean solvent to the printhead for cleaning purposes.

[0133] The ink jet 157 passes through a charging electrode 161 immediately after emerging from the nozzle of the drop generator 155. The point at which the continuous ink jet 157 breaks into droplets 159 is positioned within the charging electrode 161. Ink is a conductive liquid, and the drop generator is conventionally held at a fixed potential (e.g., ground potential). A variable voltage is applied to the charging electrode 161, inducing a charge in the continuous stream of ink extending from the ink drop generator 155 toward the charging electrode 161. When the continuous stream of ink (i.e., the ink jet 157) breaks into droplets 159, the charge induced in the ink within the droplets is trapped at the moment the individual droplets break off from the main stream of ink 157. In this way, each ink droplet within the ink drop stream 159 can be imparted with a variable charge.

[0134] The stream of ink droplets 159 then continues through the electrostatic field from the charged electrode 161. In the illustrated example, the stream of ink droplets 159 passes between deflection electrodes 163, 165. A first one of the deflection electrodes 163 is held at a first voltage, while a second one of the deflection electrodes 165 is held at a second voltage, establishing a large potential difference (e.g., 8-10 kilovolts) between the deflection electrodes 163, 165. In some systems, one electrode can be maintained at ground potential, while the other electrode is held at a high (positive or negative) voltage (relative to ground). In other systems, one electrode is held at a negative voltage (relative to ground), while the other electrode is held at a positive voltage (relative to ground). The electric field established between the deflection electrodes 163, 165 deflects the charged droplets (i.e., droplets charged by the charged electrode 161). In this manner, droplets 159 can be selectively (and variably) directed from the path of ejection from the nozzle of droplet generator 155 based on the variable charge applied by electrode 161 .

[0135] Droplets that pass through the deflection field without being deflected proceed to a gutter 167. The gutter 167 comprises an orifice through which the droplets enter. The gutter 167 is connected to a gutter line 169 that extends from the gutter to the ink supply system 115. Optionally, a valve 171 is provided in the gutter line 169 to allow the line to be opened and closed. Suction is applied to the gutter line 169 by a suction system to draw ink along the line from the gutter towards the ink supply system 115.

[0136] In many inkjet printers, suction is provided by a suction system that includes a venturi 173 (sometimes called a jet pump). The venturi 173 is located within the ink supply system 115 and is configured to receive a pressurized flow of ink from the ink pump 121 through a venturi supply line 175 that is connected to a second outlet of the filter 126. After passing through the venturi 173, the ink flowing from the venturi supply line 175 through the venturi 173 is returned to the ink delivery tank 117 via an ink return line 177.

[0137] A venturi comprises a conduit with a converging then diverging cross section. A venturi uses a constriction to create a localized high velocity, low pressure flow region. The high velocity, low pressure region is in communication with suction port 178. In use, gutter line 169 is connected to venturi 173 via suction port 178. In this manner, the low pressure region created within venturi 173 is used to apply suction to gutter line 169.

[0138] Any ink that flows into the gutter 167 is forced to flow along the gutter line 169 and is eventually sucked into the venturi 173 (through the suction port 78), exits the venturi, and travels along the return line 177 before returning to the ink delivery tank 117.

[0139] By using the venturi in this manner (i.e., as a jet pump), it is possible to design a system in which the main system ink pump 121 can generate both positive pressure (e.g., to supply ink to the printhead) and negative vacuum pressure (e.g., to provide gutter suction).

[0140] The ink tank 117 is vented by a vent 179 to prevent excessive pressure buildup within the ink tank 117. However, it should be understood that venting air through the vent 179 may result in solvent vapors being vented to the external environment, which may be undesirable (e.g., because the solvent would need to be replaced and may be harmful to the environment). In some embodiments, a collection system 180 may be connected to the vent 179 to collect the solvent from the vented air. The collection system 180 may include a condenser. The collected solvent may be returned to another location within the ink supply system 115, such as the ink feed tank 117. The collection system 180 may be connected to the pump 145.

[0141] Filter 126 has been described above as filtering ink delivered to the printhead via ink supply line 128 as well as ink delivered to venturi 173 via venturi supply line 175. However, it should be understood that in alternative configurations, separate filters may be used. That is, a first filter may be provided to finely filter the relatively small amount of ink delivered to the printhead, while a second filter may be provided to more coarsely filter the larger amount of ink delivered to venturi 173.

[0142] It should be understood that the ink cartridge 133 and solvent cartridge 137 are replaced periodically (depending on ink and solvent usage) to replenish the ink and solvent within the printer. Additionally, other components of the printer 101 may be removable to facilitate periodic cleaning or replacement. For example, the ink tank 117 may be a removable module to allow for periodic replacement. Accordingly, various fluid ports into (and out of) the ink tank 117 may be provided with one or more connection interfaces.

[0143] In the following description, reference will be made to the x-axis, y-axis, and z-axis, with the reader being directed to the axes as presented in Figures 3 through 7. It should also be noted that during normal use of the printer, the z-axis is consistently defined such that the (positive) z-axis is defined anti-parallel to the direction of gravity.

[0144] 3, an ink tank 200 is shown in schematic cross section with connection ports omitted except for a vent 202 and a mixing device 204. The ink tank may contain ink 117 for supply to the printer 101. The ink tank 200 includes a tank floor 206 that defines the bottom surface of the tank during normal use, a tank ceiling 208 that defines the top surface of the tank, and tank walls 211 that define the tank sides. The tank floor 206, tank ceiling 208, and tank walls 211 together define an interior volume for containing ink.

[0145] The interior volume defined by the tank comprises a large bulk region 212, a transition region 214, and a relatively small mixing region 216. The locations of each region are shown in Figure 3. The bottom of bulk region 212 is adjacent to the top of transition region 214. The bottom of transition region 214 is adjacent to the top of mixing region 216.

[0146] The tank floor 206 comprises a bulk zone floor 206a (i.e., the tank floor adjacent to the bulk zone 212) and a tank bottom 206b. The tank bottom 206b defines the lowest point within the tank and is adjacent the bottom of the mixing zone 216.

[0147] The tank wall 211 comprises a bulk region wall 211a and a mixing region wall 211b. The bulk region wall 211a and the mixing region wall 211b partially surround the bulk region 4 and the mixing region 6, respectively. While Figure 3 shows a schematic cross section of the ink tank, it should be understood that the tank wall 211 will define a three-dimensional container for storing ink.

[0148] The bulk region 212 is configured to store most of the ink in the ink tank. The bulk region floor (i.e., the tank floor in the bulk region) 206a slopes toward the tank bottom 206b at an angle θ≧0. Furthermore, the mixing region wall 211b slopes steeply toward the tank bottom. Therefore, the tank bottom 206b can be referred to as the lowest point.

[0149] The transition region 214 is partially bounded by a section of the ink tank's interior surface that has a slope intermediate the slope of the bulk region floor and the slope of the mixing region wall.

[0150] The mixing device 204 is located within the mixing region 216. In the illustrated embodiment, the mixing device 204 is connected to the tank bottom 206b. The mixing pickup 120 (see FIG. 2) can be located within the ink tank 200 at a position within the bulk region 212. That is, it may be preferable to locate the mixing pickup at a position above the mixing region 216 and the transition region 214 (if present).

[0151] In the example shown in FIG. 3 , ink is stored within the ink tank and extends from the tank bottom 206 b to a maximum liquid fill level 219. The region of the ink tank's interior volume between the maximum liquid fill level 219 and the tank ceiling 208 may be referred to as a header region 218. The tank ceiling may further include a vent 202. The vent 202 places the header region 218 in fluid communication with the external environment, allowing pressure equalization between the ink tank interior and the external environment. Such equalization prevents the creation of pressure differentials, such as a pressure buildup within the header region 218, which could increase demands on a pump attached to the fluid circuit. For example, a net inflow of gas from the gutter line into the ink tank 200 would result in a pressure buildup.

[0152] In the mixing region 216 and the transition region 214, the tank walls may also function in part as the tank floor. That is, in at least some portions of the mixing and transition regions, the sloping walls may function to define both the lower surface and the sides of the tank. In other portions of the mixing region, the lower surface is provided by the tank bottom.

[0153] As mentioned above, during extended periods of printer inactivity (e.g., extended shutdown), the pigment particles in hard pigment inks will begin to sink and settle under gravity. Thus, after an extended period of time, a significant positive concentration gradient of pigment particles will develop in the negative Z direction, as shown in Figure 3. A layer of densified sediment with semi-solid properties may form at the bottom of the tank.

[0154] However, if there is a lowest point on the tank floor 206 and no regions of positive gradient (i.e., slope away from the lowest point), particles adjacent to the tank floor will not settle. Instead, particles adjacent to the floor will undergo a biased random walk due to Brownian motion toward the local lowest point. This is true even if there is a perfectly horizontal, localized region of the lowest point.

[0155] By providing a steeper mixing region 216 between the bulk region 212 and the tank bottom 206b (i.e., the only tank lowest point), the concentrated pigment particles are encouraged to move gradually across the bulk region floor 206a, preventing sediment from forming outside the tank bottom 206b. As a result, sedimentation is substantially localized to a small mixing region, limiting the volume of sediment that requires dispersion.

[0156] The mixing area 216 may include a mixer, such as mixer 204, or other mixing device. The mixer can disperse any compacted sediment. In this way, compaction of sediment in one small area can be more easily handled than if the sediment were distributed over a larger volume. Furthermore, by providing a large bulk area with a less steeply sloping floor, the tank volume can be increased for a given overall height because the floor is less steep than in a conventional conical tank.

[0157] In some embodiments, the transition region 214 can be omitted. In other embodiments, the transition region 214 can be considered part of a larger mixing region. However, without the transition region, pigment particles in the bulk region 212 would randomly walk directly into the mixing region 216. This could lead to increased settling pressure within the mixing region 216, which could accelerate sediment formation. If the size of the transition region 214 is appropriate, it is highly unlikely that pigment particles from the bulk region 212 would reach the mixing region 216 during the period during which the printer is typically idle. However, it should be understood that a transition region is not required if the expected idle period is short or if the bulk and mixing regions are sized appropriately.

[0158] When the inkjet printer resumes operation after an extended period of inactivity, any ink precipitate present in the mixing region can be dispersed using the mixing device 204. The mixing device 204 is operable to expel fluid. One of the key parameters determining the effectiveness of mixing is volumetric power input. A smaller volume mixing region requires less overall power input (due to agitation) for effective mixing than a larger volume mixing region. Therefore, the limited amount of precipitate that needs to be dispersed within the mixing region 216 results in a lower mixing power input required by the mixing device. For agitation by fluid jets, the mixing power input is roughly proportional to the flow rate. Therefore, it is possible to use a less expensive, lower flow rate pump or operate a high flow rate pump at a lower flow rate to extend its life. Furthermore, the limited amount of precipitate that needs to be dispersed reduces the mixing time for a given agitation power input.

[0159] The structure and operation of the mixer 204, and its supporting structure, are described in more detail below.

[0160] FIG. 4 illustrates another embodiment of an ink tank. The ink tank 200′ is substantially similar to the ink tank 200 described above with reference to FIG. 3. However, the ink tank 200′ further includes a level sensor 220. Additionally, the geometry of the tank floor of the ink tank 200′ differs from that of the ink tank 200 in that the outline includes an inflection point A1 and the mixing region 216 and transition region 214 are off-center relative to the bulk region 212. The inflection point A1 is provided to increase the effective volume of the transition region 214. An additional advantage is that the volume of the ink tank 200′ can be increased relative to the height occupied by the ink tank.

[0161] The level sensor 220 comprises a (magnetic) float 222 and a float chamber 224. The float chamber is in fluid communication with the mixing tank via at least an upper connection 224a and a lower connection 224b. The upper connection is located above the maximum liquid fill level 219 of the tank. The lower connection is located in the transition area 214. The float moves with the ink level as long as it floats in the ink.

[0162] The float 222 is magnetic and activates an external Hall Effect sensor (not shown) to provide an indication of the float position and therefore the ink level in the tank (shown as maximum liquid fill level 219).

[0163] In use, the level sensor 220 is configured to generate a low level signal when the liquid level in the tank falls below the minimum fill level 226. The level sensor 220 is also configured to generate a high level signal when the liquid level in the tank is equal to or exceeds the liquid maximum fill level 219.

[0164] In practice, the minimum fill level 226 is significantly higher than the point at which the printer will fail, e.g., 300%. This is preferable to provide some additional tolerance as well as a "buffer" time to allow an operator to prepare and insert a new ink and / or solvent cartridge upon receiving a low level signal. Furthermore, because floats exhibit some delay, or hysteresis, in their level indication, additional tolerance is required for the minimum fill level 226. While 300% of the level at which printer failure occurs is given as an example, this may vary between printer systems and / or ink and solvent cartridges.

[0165] The upper connection may be at the maximum liquid fill level 219. The lower connection may be positioned at or above the upper limit of the mixing region. In the embodiment of Figure 4, the lower connection 224b is located in the transition region 214, which has the advantage of lowering the float's position relative to the rest of the ink storage tank.

[0166] Given that magnetic floats tend to have significant dimensions and high densities, the floats will be significantly submerged ("low") in the liquid when in buoyant equilibrium. By locating the lower connection 224b in the transition region, sufficient fluid depth can be provided to allow the magnetic float 222 to float at the lowest level that requires sensing. As noted above, to accurately sense liquid level, the magnetic float 222 must be in buoyant equilibrium, and therefore, locating the lower connection in a deeper section of the tank, such as the mixing or transition region, is advantageous for sensing very low ink levels.

[0167] One advantage of off-center positioning of the mixing area 216 is that it facilitates positioning the float-type level sensor closer to the tank wall, allowing the magnetic float 222 to better interact with an external Hall effect device to indicate ink level.

[0168] It should be understood that the level sensor is described merely by way of example and may be configured differently or omitted entirely in some embodiments.

[0169] 3 and 4, it should be understood that the terms "wall" and "floor" are used herein to refer to different portions of a tank wall that may be a continuous structure (e.g., formed as a single component). Generally, if the component slopes less than 45 degrees from horizontal, the area will be referred to as a "floor," whereas if the component slopes more than 45 degrees from horizontal, the area will be referred to as a "wall."

[0170] Since there are significant similarities between the embodiments of Figures 3 and 4, their geometric details will be described in common.

[0171] However, it should be understood that certain features of the tank may be omitted. For example, in some embodiments, the transition region 214 may be omitted, and the mixing region may extend from the tank bottom to the bulk region. Similarly, the bulk region floor slope may be omitted so that the floor is horizontal (i.e., θ=0). Additionally, the tank ceiling 208 may be omitted. Additionally, the mixing device 204 may be omitted. Thus, embodiments may be provided that have any combination of some, all, or none of these features.

[0172] In practical use cases, perfect ink tank alignment cannot be guaranteed, so the bulk area floor 206a can be sloped toward its overall lowest point, as indicated by the angle θ in FIGS. 3 and 4. For example, this slope can be at least 2° from a nominal horizontal plane, the xy plane in FIGS. 3 and 4. The slope of the bulk area floor 206a creates some tolerance for tank orientation, but with a 2-degree slope, accidental tilting of the ink tank between ±2 degrees does not substantially affect the function of the ink tank. In the worst case scenario, a portion of the bulk area floor 206a will be horizontal, yet still promote particle movement along the tank floor.

[0173] In practice, users may find it difficult to orient a printer system housing the ink tanks to within ±2 degrees horizontally. Therefore, the bulk area floor 206a may have a slope greater than this amount. For example, in some embodiments, a slope of 5 degrees or more (e.g., 6 degrees) from a nominal horizontal plane may be preferred.

[0174] The angular geometry of the tank wall 211 can also be varied depending on the conditions of use. The tank wall (i.e., mixing zone wall) 211b that surrounds the mixing zone between the tank bottom 206b and the bulk zone 212 can be vertical or have a steeper slope than the tank floor in the bulk zone 206a.

[0175] Providing the mixing zone with vertical walls, or walls 211b that are steeper than the bulk zone floor, provides a convenient structural configuration while also providing the desired floor and wall profile: the less steep bulk zone is separated from the tank bottom 206b by the steeper-sided mixing zone 216.

[0176] The tank walls surrounding the mixing region 211b can be vertical or can slope towards the tank bottom.

[0177] Additionally, the angle of the tank wall within the mixing region, designated φ in Figures 3 and 4, can be limited to 85 degrees from the nominal horizontal plane at any point.

[0178] It should be understood that the term "nominal horizontal plane" refers to an imaginary plane defined relative to the ink tank that would be perpendicular to the direction of gravity under its exact designed orientation. Of course, it should also be understood that during use, the printer may operate when supported on a surface that is not exactly horizontal, causing the nominal horizontal plane to deviate from horizontal. Reference to the nominal horizontal plane is intended to provide a convenient frame of reference for other components of the printer, rather than to restrict orientation by strict adherence.

[0179] In view of the above, it should be understood that when describing the slope of the tank walls in the mixing area as being 85 degrees or less from a nominal horizontal reference line, it is intended that in use the tank walls in the mixing area will be close to vertical (e.g., 85 degrees), but may vary in use due to the printer being placed on an uneven surface.

[0180] All figures presented are not to scale and the exact geometry of the ink tank 1 may vary depending on end-user requirements such as space and volume requirements or ink properties.

[0181] In one example, the ink tank may have a vertical depth 216h from the tank bottom 206b to the lowest part of the bulk region 212 of at least 15 mm.

[0182] In some embodiments, the juncture between the mixing region 216 and the bulk region 212 (if the transition region is omitted) can be considered the point where the tank wall transitions into the tank floor, i.e., the point where the wall / floor slope angle is less than 45 degrees from horizontal.

[0183] Alternatively, the top of the mixing region 216 can be determined based on the width of the mixing region 216. For example, the top of the mixing region 216 can be considered to be the point in the tank where the width (or diameter) of the tank exceeds a predetermined value (e.g., 50 mm). It should be understood that the width of the mixing region may vary (e.g., gradually increase) from the tank bottom 206b to the top of the mixing region.

[0184] It should be understood that the extent of the mixing region 216 can be defined in a variety of ways, and the sizes and shapes of the mixing region 216 and the bulk region 212 can vary significantly. Thus, the advantage of providing a mixing region 216 at the bottom of the tank with steeper sidewalls than the bulk region 212 can be realized in a variety of ways.

[0185] Additionally, the width 216w of the mixing region (defined, for example, as the horizontal width at a vertical distance of 10 mm from the tank bottom 206b) can be controlled to promote enhanced mixing. Specifically, providing a relatively narrow mixing region (e.g., less than 40 mm wide) can promote better mixing because a lower mixing force is required to disperse any sediment that settles within the mixing region than with a wider width. On the other hand, if the mixing region is too narrow (e.g., less than 18 mm wide), the mixing region may need to be excessively tall to provide sufficient volume to accommodate a sufficient amount of pigment.

[0186] Of course, it should be understood that the dimensions described herein are based on the particular mixer 204 and mixing zone 216 combination. Thus, a mixer 204 having a larger diameter can be used in combination with a mixing zone 216 having a larger diameter, and vice versa.

[0187] The tank width of the bulk region 212 can be significantly larger than the width of the mixing region, for example, the tank width of the bulk region can be about 100-200 mm.

[0188] It should be understood that the vertical depth and lateral width can vary as dictated by the settling rate of the particular ink and design requirements regarding typical maximum dwell periods.

[0189] In some systems, the maximum period a printer can be left idle is approximately eight weeks. This is because if the printer is idle for more than eight weeks, other components within the printer are more likely to fail. For example, some ink pumps are known to seize if left idle for more than eight weeks. With this in mind, the ink tanks in such systems can be designed to accommodate eight weeks of accumulated sediment. Of course, systems can be designed to accommodate longer idle periods, but in some situations, longer periods may be unnecessary due to other potential causes of failure.

[0190] In another example, the volume of the mixing zone 216 can be less than 5% of the total liquid volume of the tank. This choice can be advantageous in that it can limit the amount of densified sediment within the mixing zone. Any subsequent dispersion will require less mixing power input and / or will proceed more quickly. In fact, in some embodiments, the volume of the mixing zone can be significantly less than 5%. Furthermore, providing a small volume mixing zone can increase the tank capacity relative to the total volume footprint.

[0191] On the other hand, providing a larger volume mixing region 216 will increase the amount of time that sediment will be contained solely in the mixing region, i.e., the period of time that the printer can be left in its normal dormant state.

[0192] It should be understood that the total liquid volume of the tank includes the volume enclosed by the tank bottom 206 and tank walls 211 (in its normal operating orientation) below the maximum fill level 219. It will of course be understood that it is possible to overfill the tank beyond this level, but many tanks nevertheless have a maximum or normal recommended fill level.

[0193] The volume of the header region 218 is provided to accommodate bubbles generated by the introduction of air from the gutter (see ink return line 177 in FIG. 2). The volume of the header region 218 may be, for example, at least equal to the air introduction volume of the attached inkjet printer over one minute. In one example, this may be approximately 180 ml for an inkjet printer with an expected maximum air intake volume rate of 180 ml / min. Of course, bubble formation and collapse rates will vary between different ink supply systems and different inks. Therefore, the volume of the header region 218 may vary depending on the requirements of a particular application.

[0194] Another geometric parameter of the mixing tank is its xy, or cross-sectional, geometry. Figures 3 and 4 show cross-sections in the xz plane. The ink tank can have any of a number of xy plane cross-sectional geometries. For example, the xy plane cross-sectional geometry of the mixing region 216 can be circular, polygonal, or oval.

[0195] As described above, the height and volume of the mixing region 216 can be determined based on a specified height or a ratio of the volume to the total ink tank volume. Preferably, the average xy-plane cross-section of the mixing region 216 can be limited so that its opening is located at a horizontal separation distance 216s from the mixing region tank wall 211b. The horizontal separation distance 216s can be a specified distance, e.g., 15 mm or less. Advantageously, such geometrical restrictions promote effective mixing by dissipating the mixing jet (in terms of energy and thus dispersion) over a longer length scale. Limiting the distance from the mixer at which precipitate forms can ensure effective dispersion for a given pump. Therefore, the maximum specified spacing between the mixing region tank wall 211b and the port of the mixer 204 will depend on specific system characteristics, such as the ink properties, the fluid flow rate from the mixer, and the geometry of the mixer and tank.

[0196] In some circumstances, a lower limit may be applied to reduce the likelihood of blockages occurring, for example, horizontal separation distance 216s may be at least 4 mm.

[0197] In a particular embodiment, the mixing device may have a width of about 15 mm and the mixing region 216 may have a width of about 27 mm at a vertical height adjacent the port (e.g., 3 mm from the tank bottom), providing a separation distance of about 6 mm between each side of the mixing device 204 and the mixing region tank wall 211 b.

[0198] While the mixing region is shown centrally in Figure 3, the mixing region can also be positioned off-center as described with respect to Figure 4, or immediately adjacent to the tank wall (e.g., so that a portion of the mixing region wall 211b is continuous with a portion of the bulk region wall 211a). An advantage of locating the mixing region wall 211a adjacent to the bulk region wall 211b is that a magnetic float level sensor (e.g., 220 in Figure 4) can be located in the deeper transition region 214 or mixing region 216 of the ink tank. However, a centrally located mixing region can increase the liquid volume of the ink tank relative to its total footprint.

[0199] The exact xy plane geometry can vary depending on the use case, particularly spatial compatibility with surrounding equipment within an inkjet printer.

[0200] Additionally, the size and geometry of transition region 214 can be tailored to better suit the needs of an application. For example, transition region 214 can have a vertical depth at least as deep as the vertical depth of mixing region 216. In this manner, pigment particles in bulk region 212 will fall into the transition region, and the elapsed time in settling down the depth of the transition region will match or exceed the specified maximum dwell period. As a result, pigment particles in bulk region 212 of a device configured as described herein will not reach mixing region 216 within the specified maximum dwell period.

[0201] For example, the transition region 214 may have a vertical depth, from the highest point of the mixing region 216 to the lowest point of the bulk region 212, of at least 15 mm.

[0202] The volume of the transition region 214 can be specified to complement the properties of the ink contained in the ink tank. In one embodiment, it may be advantageous to have a transition region that can accommodate all of the pigment contained in the ink tank. This is advantageous because it ensures that the pigment does not become concentrated to a solid phase density that would cause it to settle at the bottom of the transition region 214 or at the bottom of the bulk region 212.

[0203] For example, if the volume fraction of pigment in the ink is 5%, the volume of the transition region 214 may have at least 5% of the total liquid volume of the tank.

[0204] The transition region 214, if present, can have a variety of geometries, the selection of which will be optimized according to the constraints discussed above and / or any spatial considerations imposed by the inkjet components surrounding the ink tank.

[0205] The ink tank described in connection with FIGS. 3 and 4 includes a mixing device 204 provided within the mixing region 216. The mixing device 204 may be secured by fasteners, welding, or an interference fit of cooperating mechanical features. The mixing device 204 may be connected to a pump within the fluid supply system via a fluid delivery circuit. The fluid delivery circuit may be synonymous with, for example, the ink pickup line 19 described in connection with FIG. 2. However, it should be understood that a mixing device of the type described may be omitted entirely, and an alternative mixing device may be provided. Examples of other mixing arrangements include a mechanical agitator, other forms of agitation device, or a single fluid port. A further alternative may include multiple fluid ports provided within the tank wall and arranged around the periphery of the mixing region.

[0206] The combination of the mixing device and associated fluid delivery circuitry may be referred to as a mixing assembly.

[0207] One example of a possible mixing assembly is shown in axial cross section in Figure 5A. A mixing device 250 is shown in situ within the mixing region 216 and connected to the tank bottom 206b. The mixing device includes multiple fluid ports 252, each including an opening 254. In the illustrated embodiment, the lower edges of the openings are spaced a distance h from the tank bottom 206b. The fluid ports 252 are configured to direct fluid away from the mixing device (as a jet) and into the mixing region 216 in multiple directions, or with a jet vector J. The fluid ports 252 can be configured to direct fluid away from the mixing device toward the tank wall 211b surrounding the mixing region 216 and / or toward the tank bottom 206b.

[0208] Each jet vector J includes a horizontal component (x, y) and a vertically downward component (negative z). The fluid ports are configured to direct fluid around the periphery of the tank bottom 206b, which is defined by the junction between the mixing region wall 211b and the tank bottom 206b.

[0209] The direction of fluid flow during operation is indicated by the arrows presented in FIG.

[0210] The mixing device 250 of Figure 5A is also shown in radial cross section in Figure 5B. The dashed lines indicate the horizontal (xy) contours of the fluid supply conduits 256a and fluid ports 252. Because the fluid ports 252 are radially arranged in a horizontal plane, the resulting jet vector J has a substantially radial horizontal component.

[0211] Fluid delivery circuit 255 includes a fluid supply conduit 256 configured to supply fluid to a plurality of fluid ports 252 of the mixing device, with fluid supply conduit 256 configured to deliver fluid to the mixing device from below mixing device 250. Positioning the fluid supply in this manner avoids the risk of sediment forming in fluid ports 252 as a result of settling in supply conduit 256. Positioning the fluid supply in this manner also eliminates the need for conduits in the upper (e.g., bulk) region of the tank.

[0212] The fluid supply conduit 256 includes a vertical section 256a configured to deliver fluid to the mixing device from below the mixing device and a side section 256b configured to deliver fluid to the vertical section. The side section 256b preferably slopes upwardly away from the junction between the vertical and side sections. The fluid supply circuit further includes a sump tank 258 at the junction between the vertical and side sections 256a and 256b.

[0213] Providing such a sloped supply conduit reduces the risk of settling within the supply conduit. The slope, denoted by α, induces settling pigment to gradually move along the lower surface of the conduit rather than solidifying along the bottom of the conduit. The settling pigment is received in sump tank 258. As a result, subsequent flow can bypass any settling within the fluid delivery system.

[0214] The sump tank 258 can be sized to contain any sediment that is expected to accumulate between maintenance cycles during which it is replaced. In one example, the sump tank 258 has a capacity of approximately 1 ml. Advantageously, this means that the mixing assembly does not need to be cleaned periodically.

[0215] In one example, side portion 256b can be angled upwardly away from the junction between vertical portion 256a and side portion 256b at an angle of at least 2 degrees relative to the horizontal. Advantageously, this means that side portion 256b will have some slope toward sump tank 258 even in situations where the printer is not perfectly horizontally oriented.

[0216] After the rest period, when fluid is first pumped along side 256b toward the mixing device, any sediment that has formed within the side is pushed toward the sump tank, reducing the risk of this sediment blocking fluid port 252.

[0217] In use, fluid is pumped through fluid delivery circuit 255 and out fluid port 252, creating multiple jets directed toward the mixing area walls and tank bottom. The erosive action of each jet digs channels through the sediment, causing the sediment to become entrained and / or break down into the moving fluid jet, achieving thorough mixing at moderate flow rates.

[0218] Other layouts for the fluid delivery circuit of the mixing device are possible.

[0219] 6A illustrates an alternative mixing arrangement 260. A fluid delivery circuit 265 is provided that includes a fluid supply conduit 266 configured to supply fluid to a plurality of fluid ports 252, each port defining an opening 254. The fluid supply conduit 266 is configured to deliver fluid to the mixing device from above the mixing device. The fluid supply conduit includes a vertical portion 266a directly above the mixing device and a side portion 266b configured to deliver fluid to the vertical portion 266a, with the side portion 266b sloping upwardly away from the junction between the vertical portion 266a and the side portion 266b.

[0220] It should be understood that the side 266b of the fluid supply conduit is optional and the fluid supply conduit can be completely vertical. Such an alternative configuration is shown in Figure 6B, which is a straight, completely vertical flow path member 266'.

[0221] 7 shows another alternative mixing assembly comprising a mixing device 270 and a fluid delivery circuit 275 with a fluid supply conduit 276 above the mixing device, the supply conduit itself comprising a spirally wound pipe. The fluid supply conduit 276 is configured to supply fluid to a plurality of fluid ports 252, each port defining an opening 254.

[0222] It should be understood that a straight vertical pipe could be used instead of the helical pipe 276 (as shown in FIG. 6B), which unfortunately exposes the internal spaces (i.e., the internal spaces of the fluid supply conduits and fluid ports) directly to the settling pressure, increasing the risk of blockage.

[0223] By providing a spirally wound pipe 276 when delivering fluid from the top of the mixer, a gentle slope is introduced into the pipe rather than a (predominantly) vertical orientation. This gentle slope causes any sediment to move slowly along the bottom of the pipe, reducing the rate at which it reaches the fluid ports 252. Thus, the risk of sediment blocking the fluid ports of the mixer is greatly reduced. Alternatively or additionally, the time before a sediment blockage occurs is greatly increased.

[0224] Top-feeding, as shown in Figures 6A, 6B, or 7, can be advantageous when height constraints exist. Bottom-feeding, as described in connection with Figure 5, increases the overall height of the tank due to the sump tank and other fluid delivery components located below the tank bottom.

[0225] The jet-generating portions of the mixing devices described with reference to Figures 5A, 5B, 6A, 6B and 7 are substantially similar and therefore their geometric details will be commonly described.

[0226] In some embodiments, the horizontal component of the fluid port direction can be entirely radial, as illustrated with respect to FIG. 5B.

[0227] In other embodiments, the fluid ports 252 may have a non-radial horizontal component relative to the vertical central axis CC. The use of a non-radial horizontal component can induce a circulatory flow in the mixing region, improving mixing performance.

[0228] The size and orientation of the fluid port openings 254 can vary depending on the intended application and characteristics of the operating environment.

[0229] For example, each of the plurality of openings 254 can be oriented vertically, i.e., at least partially downward. That is, the normal to the plane defined by the plurality of openings 254 can be horizontal or partially vertical (and downward). Such an arrangement is advantageous because it provides an "overhang" that hides the opening from sediment, reducing the likelihood that sediment will fall into the opening.

[0230] Each of the plurality of apertures 254 may have a diameter of at least 1 mm. Such an aperture size may provide a large enough aperture with an acceptably low risk of blockage.

[0231] Each of the plurality of openings 254 may have a diameter of 2 mm or less. Such opening size may be small enough to promote a jet velocity sufficient to disperse sediment.

[0232] Such an opening size represents a good compromise between being small enough to provide sufficient jet velocity to disperse sediment, and being large enough with an acceptably low risk of clogging.

[0233] The fluid ports 252 can have a constant cross-sectional area. This cross-sectional area and / or diameter can also vary within the fluid port. For example, the ports 252 can taper outward toward the opening. Advantageously, tapered fluid ports can facilitate the removal of precipitated blockages.

[0234] The plurality of fluid ports 252 may include 3 to 10 fluid ports 252, and preferably 7 or fewer fluid ports 252.

[0235] Providing at least three fluid ports 252 allows mixing over a large area around the mixing device, while providing seven or fewer fluid ports 252 maintains a convenient minimum flow rate through each port, thereby reducing the risk of clogging when using a large number of ports.

[0236] The plurality of openings 254 may be separated by a vertical distance from the tank bottom to the opening of at least 3 mm, i.e., the central axis of the port (or opening) may be at least 3 mm from the tank bottom.

[0237] It should be understood that the mixing devices described above are not limited to use with any one type of ink tank, such as, for example, the ink tanks 200 and 200' described with respect to Figures 3 and 4, respectively. Indeed, any of the mixing devices described above may be provided with, for example, conical or cylindrical ink tanks, or tanks having flat or gradually sloping floors.

[0238] Illustratively, the ink tank 200 of FIG. 3 can be connected to the fluid circuit using ports, valves, or connections located within the ink tank 200.

[0239] As mentioned above, during normal printing operations, properly mixed ink is continuously drawn from an ink reservoir tank to the printhead. This can be accomplished with a port in the tank that allows fluid communication with the printhead. As mentioned above, a portion of the ink ejected from the nozzles of the printhead is returned to the printer through a gutter under suction. Thus, in operation, there is a fluid loop that includes the ink reservoir, the printhead, and one or more pumps (e.g., pump 121 and venturi 173) that cause the flow. This gutter flow is returned to the ink reservoir tank through a port in the reservoir. There may also be one or more ports for refilling the ink and / or solvent levels in the ink reservoir when they are low.

[0240] To perform a printer shutdown, the equipment within the printer can be emptied, with residual ink being substantially drained into the ink tank. By collecting the fluid in the tank, only one remix solution is required for the entire system when inkjet operation is resumed. Transferring ink held outside the ink tank to the ink tank can be accomplished by running the ink pump in the fluid supply system in reverse. Illustratively, in FIG. 2, running pump 119 in reverse, with 3:2 valve 122 configured to connect the pump outlet to filter 126, will draw ink from the rest of the system into the ink tank.

[0241] When the printer is shut down, the printhead-ink tank fluid loop stops flowing and the ports cease to facilitate fluid flow.

[0242] Upon resumption of inkjet operation (e.g., during start-up operation or sequence), the contents of the tank are agitated by flow through the mixer, as described above in connection with Figures 3-7. The contents of the tank may also be agitated by flow through the mixer during periods of idle operation (i.e., when no printing is occurring).

[0243] Thus, the ink tank may have ports to provide (printhead) ink pick-up, gutter return, mixer pick-up, in addition to vent and mixer ports. A number of porting schemes are possible.

[0244] For the purposes of the following discussion, the mixer port will be treated as one port.

[0245] In one example, the ink tank may have three ports. The ports may include a combined mixing device and ink pickup port, a gutter return port, and a vent. During operation, ink for the printhead is drawn or picked up through the mixing device. The pickup flow is induced by a pump (e.g., pump 121). During resumption of inkjet operation after an extended period of inactivity, the mixing device flow initially results from residual fluid in the mixing device, which is driven back by the pickup pump. A properly connected ink return line located below the ink surface in the tank 117 (e.g., in the bulk region) can be used to supply ink to the mixing device 204 for mixing. This configuration allows the mixing pickup (in this case, the ink return line) to pick up and mix ink from the bulk region of the ink tank, enabling ink mixing operations even when the mixing region and / or transition region contain sediment.

[0246] In another example, the ink tank may have four ports. Additional ports can be added to the above configuration by adding a separate mixing pickup port to supply agitating fluid for use during mixing. That is, there can be another mixing pickup port for use during reverse operation.

[0247] In yet another example, the ink tank may have five ports, which may include a dedicated mixing device (as described in detail above), a separate main ink pickup port (to supply ink to the printhead), a separate mix pickup port (to supply ink to the mixing device during mixing), a gutter return port, and a vent.

[0248] In either the four-port or five-port configuration, the mix pickup port (e.g., mix pickup 120 in FIG. 2) can be located within the bulk region of the tank, i.e., above the mixing region and transition region (if present). This configuration allows the mix pickup to pick up and mix ink from the bulk region of the ink tank, thereby enabling ink mixing even when the mixing region and / or transition region contain sediment. That is, the ink pump can pump ink from the ink tank through the mix pickup and deliver it to the mixing device to mix the inks.

[0249] The above five-port configuration may be useful when the pump cannot be operated in reverse. Potentially, this may allow the use of a cheaper one-way pump. The five-port configuration may also be applicable to ink supply systems with two ink pumps. For example, the ink supply system may have one low-pressure, high-flow pump and one high-pressure, low-flow pump.

[0250] In practice, the gutter return will contain air-fluid multiphase flow. Therefore, it may be advantageous to provide a weir plate for the tank above the maximum liquid fill level. During use, the gutter return flow can flow over the weir plate, advantageously enhancing air bubble removal from the flow. This configuration involves some increased complexity compared to, for example, a gutter return port provided below the fluid level.

[0251] Of course, various other port configurations are possible. Indeed, the ink flow circuit described above in connection with FIG. 2 is provided by way of example and can be modified in various ways. The ink tank 117 of FIG. 2 has a port configuration that roughly corresponds to the four-port configuration described above, including (i) a mixing structure and ink pickup port, (ii) a mixing pickup port, (iii) a gutter return port, and (iv) a vent. Additionally, there are ports that serve roles not considered in the three-port / four-port / five-port scheme. The ink tank 117 has a port that connects to a purge line 158 and a port 144 that receives ink and solvent from the respective cartridges labeled 133 and 137.

[0252] Various modifications and alternatives to the above-described embodiments may be provided. For example, although the ink tanks described above are described in connection with a continuous ink jet printer, they may also be provided independently. Such ink tanks may be provided as removable modules of the ink jet printer. Similarly, ink tanks having a mixing region may be provided without a mixing device of the type described, and mixing devices of the type described herein may be provided in ink tanks that do not have a dedicated mixing region.

[0253] The above embodiments are exemplary in nature and are not intended to limit or define the scope of protection, which is defined by the claims.

[0254] Additionally or alternatively, the following examples are provided. Features described in any of the following examples may be used in combination with any of the other examples described herein. [Example]

[0255] An ink tank for an inkjet printer, comprising a tank floor defining the bottom surface of the tank during normal use, and tank walls defining the sides of the tank, the ink tank further comprising: a tank bottom defining the lowest point in the tank; a bulk region configured to store most of the ink in the ink tank, the bulk region having a tank floor that is horizontal or slopes toward the tank bottom during normal use; and a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by the tank walls. [Example]

[0256] 10. The ink storage tank of example 1, further comprising a mixing device disposed within the mixing region, the mixing device comprising a plurality of fluid ports, each of the plurality of fluid ports having a respective opening, the plurality of fluid ports configured to direct fluid away from the mixing device into the mixing region, toward a tank wall surrounding the mixing region, and / or toward a tank bottom. [Example]

[0257] 3. The ink storage tank of any one of claims 1 to 2, wherein the tank wall surrounding the mixing region between the tank bottom and the bulk region is vertical or has a steeper slope than the tank floor in the bulk region. [Example]

[0258] 4. The ink tank of any one of Examples 1 to 3, wherein the slope of the floor within the bulk region is at least 2 degrees from a nominal horizontal reference line. [Example]

[0259] 5. The ink tank of any one of Examples 1 to 4, wherein the slope of the tank wall within the mixing region is 85 degrees or less from a nominal horizontal reference line. [Example]

[0260] 6. The ink tank of any one of Examples 1 to 5, wherein the tank has a vertical depth of at least 15 mm from the bottom of the tank to the lowest part of the bulk region. [Example]

[0261] An ink tank according to any one of Examples 1 to 6, wherein the ink tank has a width of at least 18 mm at a vertical distance of 10 mm from the bottom of the tank, and / or the ink tank has a width of 40 mm or less at a vertical distance of 10 mm from the bottom of the tank. [Example]

[0262] 8. An ink tank according to any one of Examples 1 to 7, wherein the mixing region has a volume of less than 5% of the total liquid volume of the tank. [Example]

[0263] 9. The ink tank of any one of Examples 1 to 8, further comprising a transition region between the bulk region and the mixing region, the transition region having a slope greater than the slope of the bulk region floor and less than the slope of the mixing region wall. [Example]

[0264] 10. The ink tank of example embodiment 9, wherein the transition region has a vertical depth of at least 15 mm from the highest point of the mixing region to the lowest point of the bulk region. [Example]

[0265] 11. The ink tank of any one of Examples 9 and 10, wherein the mixing region has a volume that is less than 5% of the total liquid volume of the tank. [Example]

[0266] 12. The ink tank of any one of Examples 1 to 11, further comprising a header region disposed above the bulk region of the tank, separated from a tank floor by at least the bulk region, and extending from a maximum liquid fill level of the tank to a tank ceiling. [Example]

[0267] An ink tank as described in any one of Examples 1 to 12, further comprising a level sensor including a float and a float chamber, the float chamber being fluidly connected to the mixing tank via at least an upper connection portion and a lower connection portion, the upper connection portion being located at a position above the maximum liquid fill level of the tank, and the lower connection portion being located at a position above the upper limit of the mixing area. [Example]

[0268] The ink tank according to Examples 13 and 8, wherein the lower connection portion is provided in the transition region. [Example]

[0269] An ink tank as described in Example 13 or 14, wherein the level sensor is configured to generate a low level signal when the liquid level in the tank falls below a minimum fill level, and / or the level sensor is configured to generate a high level signal when the liquid level in the tank exceeds a maximum liquid fill level. [Example]

[0270] 16. The tank of any one of Examples 1 to 15, further comprising a fluid supply conduit configured to supply fluid to the plurality of fluid ports, the fluid supply conduit configured to deliver fluid to the mixing device from above the mixing device. [Example]

[0271] 17. The tank of example 16, wherein the fluid supply conduit comprises a vertical portion directly above the mixing device and a side portion configured to deliver fluid to the vertical portion, the side portion sloping upwardly away from a junction between the vertical portion and the side portion. [Example]

[0272] 17. The tank of example 16, wherein the fluid supply conduit above the mixing device comprises a straight vertical pipe. [Example]

[0273] 17. The tank of example 16, wherein the fluid supply conduit above the mixing device comprises a spirally wound pipe. [Example]

[0274] 16. The ink tank of any one of Examples 1 to 15, further comprising a fluid supply conduit configured to supply fluid to a plurality of fluid ports of the mixing device, the fluid supply conduit configured to deliver fluid to the mixing device from below the mixing device. [Example]

[0275] An ink tank for an inkjet printer, comprising: a tank floor defining a bottom surface of the tank during normal use; and tank walls defining the sides of the tank, the tank bottom defining the lowest point within the tank; a mixing device provided adjacent the tank bottom, the mixing device comprising a plurality of fluid ports each having a respective opening, the plurality of fluid ports configured to direct fluid away from the mixing device and into a region of the tank surrounding the mixing region; and a fluid supply conduit configured to supply fluid to the plurality of fluid ports of the mixing device, the fluid supply conduit configured to deliver fluid to the mixing device from below the mixing device. [Example]

[0276] 22. The tank of claim 20 or 21, wherein the fluid supply conduit comprises a vertical section configured to deliver fluid to the mixing device from below the mixing device and a side section configured to deliver fluid to the vertical section, the side section sloping upward away from a junction between the vertical section and the side section. [Example]

[0277] 23. The tank of claim 22, wherein the fluid supply conduit further comprises a sump tank at a junction between the vertical section and the side section, the sump tank configured to receive sediment from the side section. [Example]

[0278] 24. The tank of any one of Examples 1 to 23, wherein the plurality of fluid ports are configured to direct fluid from the mixing device in a plurality of directions, each of the plurality of directions having a horizontal component and a vertically downward component, and / or at least one of the plurality of directions having a non-radial horizontal component. [Example]

[0279] 25. The tank of any one of examples 1 to 24, wherein the plurality of fluid ports are configured to direct fluid circumferentially around the tank bottom. [Example]

[0280] 26. The tank of any one of Examples 1 to 25, wherein each of the plurality of openings is directed vertically or at least partially downward, and / or each of the plurality of openings has a diameter of at least 1 mm, and / or each of the plurality of openings has a diameter of 2 mm or less. [Example]

[0281] 27. The tank of any one of Examples 1 to 26, wherein the plurality of fluid ports comprises at least three fluid ports, and / or the plurality of fluid ports comprises no more than 10 fluid ports, preferably no more than 7 fluid ports. [Example]

[0282] 28. The tank of any one of Examples 1 to 27, wherein the central axes of the plurality of fluid ports are positioned at a vertical separation distance of at least 3 mm from the bottom of the tank. [Example]

[0283] 29. The tank of any one of Examples 1 to 28, wherein each of the plurality of openings is located at a horizontal distance of 15 mm or less from the tank wall. [Example]

[0284] 30. The tank of any one of Examples 1 to 29, further comprising a mixing pickup configured to pick up ink fluid from the ink tank to mix the ink, the mixing pickup being provided in the bulk region. [Example]

[0285] An ink system comprising the ink tank according to any one of Examples 1 to 30 and a mixing device configured to mix the inks in a mixing region. [Example]

[0286] An ink system comprising: an ink tank according to any one of Examples 1 to 30; and a pump configured to supply fluid to a mixing region. [Example]

[0287] An ink system comprising: an ink tank according to any one of Examples 1 to 30; and a pump configured to supply fluid to a mixing device to mix the inks. [Example]

[0288] 34. An ink system according to any one of Examples 31 to 33, wherein the pump is configured to pump ink from the ink tank through the mixing pickup and supply the pumped ink to the mixing device to mix the ink. [Example]

[0289] An ink system described in any one of Examples 31 to 34, wherein the ink system is configured to eject ink into the ink tank during shutdown operation, and the ink system is configured to mix ink in the ink tank during startup operation or during idling operation. [Example]

[0290] 36. A continuous ink jet printer comprising the ink system of any one of Examples 31 to 35, further comprising: a droplet generator configured to receive ink from the ink system and generate ink jets for printing; a gutter configured to receive a portion of the ink jet not needed for printing; and a gutter line connected to the gutter and configured to return unprinted ink to the ink tank. [Example]

[0291] 37. The continuous ink jet printer of example 36, further comprising a printhead operable to receive ink from the ink system for printing, the printhead comprising a drop generator and a gutter. [Example]

[0292] 38. The continuous ink jet printer of claim 36 or 37, wherein the continuous ink jet printer is an electrostatic deflection continuous ink jet printer configured to selectively charge ink droplets in an ink jet and deflect the charged droplets in an electrostatic field. [Example]

[0293] 1. A method for mixing pigment inks, the method comprising: storing ink in an ink tank; the ink tank having a tank floor defining a bottom surface of the tank during normal use and tank walls defining sides of the tank; a tank bottom defining a lowest point in the tank; a bulk region configured to store most of the ink in the ink tank, the tank floor within the bulk region being horizontal or sloping toward the tank bottom; and a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by the mixing region tank walls; and mixing the ink in the mixing region. [Example]

[0294] 39. The method of claim 39, wherein the tank comprises a mixing device disposed within the mixing region, and the method further comprises supplying fluid to the mixing device and directing the fluid away from the mixing device into the mixing region, toward the mixing region tank wall and / or toward the tank bottom, by a plurality of fluid ports for mixing the inks, each having a respective opening. [Example]

[0295] A method for mixing pigment inks, comprising the steps of storing ink in an ink tank, the ink tank having a tank floor defining a bottom surface of the tank during normal use and tank walls defining sides of the tank, the tank having a tank bottom defining a lowest point in the tank, and a mixing device located adjacent to the tank bottom, the method comprising the steps of supplying fluid to the mixing device from below the mixing device via a fluid supply conduit, and directing fluid away from the mixing device and into an area of ​​the tank surrounding the mixing device by a plurality of fluid ports to mix the inks.

Claims

1. An ink tank for an inkjet printer, the ink tank comprising: a tank floor that defines a bottom surface of the ink tank during normal use; and a tank wall that defines a side surface of the ink tank, the ink tank comprising: a tank bottom defining the lowest point in the ink tank; a bulk region configured to store a majority of the ink in the ink tank, the tank floor within the bulk region being horizontal or sloping toward the tank bottom during normal use; a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by a tank wall; a mixing device disposed within the mixing region; Equipped with an ink tank, the mixing device comprising a plurality of fluid ports, each of the plurality of fluid ports comprising a respective opening, the plurality of fluid ports configured to direct fluid away from the mixing device into the mixing region, toward the tank wall surrounding the mixing region and / or toward the tank bottom;

2. 2. The ink storage tank of claim 1, wherein the tank wall surrounding the mixing region between the tank bottom and the bulk region is vertical or has a steeper slope than the tank floor within the bulk region.

3. 3. The ink tank of claim 1, wherein the slope of the tank floor within the bulk region is at least 2 degrees from a nominal horizontal reference line.

4. 4. The ink tank according to claim 1, wherein the mixing region has a volume that is less than 5% of the total liquid volume of the ink tank.

5. further comprising a transition region between the bulk region and the mixed region; the transition region has a slope greater than the slope of the bulk region floor; 5. An ink tank according to claim 1, wherein the transition region has a slope that is less than the slope of the mixing region wall.

6. 6. The ink tank of claim 5, wherein said transition area has a volume of at least 5% of the total liquid volume of said tank.

7. 7. The ink tank of claim 1, further comprising a header region disposed above the bulk region of the ink tank, separated from the tank floor by at least the bulk region, and extending from a maximum liquid fill level of the ink tank to a tank ceiling.

8. a level sensor including a float and a float chamber; the float chamber is in fluid communication with the mixing tank via at least an upper connection and a lower connection; the upper connection is located at a position above the maximum liquid fill level of the tank; 8. The ink tank according to claim 1, wherein the lower connection portion is located at a position equal to or higher than an upper limit of the mixing area.

9. 9. The ink tank of claim 1, further comprising a fluid supply conduit configured to supply fluid to the plurality of fluid ports, the fluid supply conduit configured to deliver fluid to the mixing device from above the mixing device.

10. the fluid supply conduit comprises a vertical portion directly above the mixing device and a side portion configured to deliver fluid to the vertical portion, the side portion sloping upwardly away from a junction between the vertical portion and the side portion; or the fluid supply conduit above the mixing device comprises a straight vertical pipe; or 10. The ink tank of claim 9, wherein the fluid supply conduit above the mixing device comprises a spirally wound pipe.

11. 9. The ink tank of claim 1, further comprising a fluid supply conduit configured to supply fluid to the plurality of fluid ports of the mixing device, the fluid supply conduit configured to deliver fluid to the mixing device from below the mixing device.

12. An ink tank for an inkjet printer, the ink tank comprising: a tank floor that defines a bottom surface of the ink tank during normal use; and a tank wall that defines a side surface of the ink tank, the ink tank comprising: a tank bottom defining a lowest point within the tank; a mixing device disposed adjacent the bottom of the tank, the mixing device including a plurality of fluid ports, each having a respective opening, the plurality of fluid ports configured to direct fluid away from the mixing device and into a region of the ink tank surrounding the mixing device; a fluid supply conduit configured to supply fluid to the plurality of fluid ports of the mixing device, the fluid supply conduit configured to deliver fluid to the mixing device from below the mixing device; An ink tank comprising:

13. the fluid supply conduit comprises a vertical section configured to deliver fluid to the mixing device from below the mixing device and a side section configured to deliver fluid to the vertical section; the side portions slope upwardly away from the junction between the vertical portion and the side portions; and optionally 13. An ink tank according to claim 11 or 12, wherein the fluid supply conduit further comprises a sump tank at a junction between the vertical section and the side section, the sump tank being configured to receive sediment from the side section.

14. the plurality of fluid ports are configured to direct fluid from the mixing device in a plurality of directions; each of the plurality of directions comprises a horizontal component and a vertically downward component; and / or 14. An ink tank according to any preceding claim, wherein at least one direction of the plurality of directions comprises a non-radial component.

15. 15. The ink tank of claim 1, wherein the plurality of fluid ports are configured to direct fluid around the periphery of the tank bottom.

16. each of the plurality of openings is oriented vertically or at least partially downwards; and / or each of the plurality of apertures has a diameter of at least 1 mm; and / or 16. An ink tank according to claim 1, wherein each of the plurality of openings has a diameter of 2 mm or less.

17. the plurality of fluid ports comprises at least three fluid ports; and / or the plurality of fluid ports comprises 10 fluid ports or less, preferably 7 fluid ports or less; and / or the central axes of the fluid ports are spaced vertically apart from the bottom of the tank by at least 3 mm; and / or 17. An ink tank according to claim 1, wherein each of said plurality of openings is provided at a horizontal distance of 15 mm or less from said tank wall.

18. 18. An ink tank according to claim 1 or any one of claims 2 to 17 that cites claim 1, further comprising a mixing pickup configured to pick up ink fluid from the ink tank to mix the inks, the mixing pickup being provided within the bulk region.

19. 19. An ink system comprising an ink tank according to any one of claims 1 to 18 and a pump configured to supply fluid to the mixing device to mix the inks.

20. 20. The ink system of claim 19, wherein the ink tank is the ink tank of claim 18, and the pump is configured to pump ink from the ink tank through the mixing pickup and supply the pumped ink to the mixing device to mix the inks.

21. 20. The ink system of claim 18 or 19, wherein the ink system is configured to eject ink into the ink tank during shutdown operation, and wherein the ink system is configured to mix ink within the ink tank during start-up or idling operation.

22. A continuous ink jet printer comprising an ink system according to any one of claims 19 to 21, a drop generator configured to receive ink from the inking system and generate ink jets for printing; a gutter configured to receive a portion of the ink jet not required for printing; a gutter line connected to the gutter and configured to return unprinted ink to the ink tank; A continuous ink jet printer further comprising:

23. 23. The continuous ink jet printer of claim 22, further comprising a printhead operable to receive ink from said ink system for printing, said printhead comprising said drop generator and said gutter.

24. 24. A continuous ink jet printer according to claim 22 or 23, wherein the continuous ink jet printer is an electrostatic deflection continuous ink jet printer configured to selectively charge ink droplets in the ink jet and deflect the charged droplets in an electrostatic field.

25. 1. A method of mixing pigment inks, comprising: a step of storing ink in an ink tank, the ink tank having a tank floor defining a bottom surface of the ink tank during normal use and a tank wall defining a side surface of the ink tank, the ink tank comprising: a tank bottom defining the lowest point in the ink tank; a bulk region configured to store a majority of the ink in the ink tank, the tank floor within the bulk region being horizontal or sloping toward the tank bottom; a mixing region between the tank bottom and the bulk region, the mixing region being partially surrounded by a tank wall; a mixing device disposed within the mixing region; Equipped with The method comprises: supplying a fluid to the mixing device; directing fluid from a plurality of fluid ports for mixing the inks, each having a respective opening, away from the mixing device into the mixing area, toward the mixing area tank wall and / or toward the tank bottom; A method for providing

26. 1. A method of mixing pigment inks, comprising: a step of storing ink in an ink tank, the ink tank having a tank floor defining a bottom surface of the ink tank during normal use, and tank walls defining side surfaces of the ink tank, the ink tank having a tank bottom defining a lowest point in the ink tank, and a mixing device provided adjacent to the tank bottom; supplying fluid to the mixing device via a fluid supply conduit from below the mixing device; 10. The method of claim 9, further comprising: directing fluid from a plurality of fluid ports away from the mixing device and into a region of the tank surrounding the mixing device to mix the inks, wherein each of the plurality of fluid ports has a respective opening.

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