Patent Application
20100201764
This disclosure relates generally to phase change ink jet imaging devices, and, in particular, to methods and devices for reducing foam in printheads used in such imaging devices.
Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and the ink sticks are pushed or slid along the feed channel by a feed mechanism and/or gravity toward a solid ink melting assembly. The melting assembly melts the solid ink into a liquid that is delivered to a melted ink container. The melted ink container is configured to hold a quantity of melted ink and to communicate the melted ink to one or more printhead reservoirs located proximate at least one printhead of the printer as needed. This melted ink container could be located on the melting assembly between it and the printhead(s) or could be part of the head reservoir.
In some printing systems, the remote ink containers are configured to communicate melted phase change ink held therein to the printhead reservoirs through an ink delivery conduit or tube that extends between the ink containers and the printhead reservoir(s). The ink is transmitted through the ink delivery conduit by introducing a positive pressure in the ink container which causes the ink in the containers to enter the delivery conduit and travel to the printhead reservoir(s). Once the pressurized ink reaches the printhead reservoir, it is typically passed through a filter before reaching an on-board chamber or tank where the ink is held and delivered as needed to the ink jets of the printhead.
One difficulty faced in using pressurized ink delivery to communicate melted phase change ink to the printhead reservoirs is foam formation in the printhead reservoirs. For example, when the printer is turned off or enters a sleep mode, the molten ink that remains in the ink containers, conduits, and printhead reservoirs can solidify, or freeze. When the printer is subsequently powered back on or wakes from the sleep mode, air that was once in solution in the ink can come out of solution to form air bubbles or air pockets in the ink containers, conduits, and printhead reservoirs. During pressurized ink delivery, air trapped in the ink containers, conduits, and printhead reservoirs may be forced through printhead reservoir filters along with molten ink creating foam. The foam poses three problems: 1) it can completely fill the volume above the nominal maxim liquid ink level in the on-board ink tanks of the printhead and lead to color mixing and/or clogged vent lines, 2) it can create a false “full” reading at the level sense probes because it occupies a larger volume than liquid ink, and 3) it can potentially become entrained in the ink flow path to the ink jets and cause ink jetting malfunction, typically termed Intermittent Weak and Missing jets (IWM's).
In order to reduce the foam that may form in a printhead reservoir as a result of pressurized ink delivery through a filter wetted by ink, an additional feature in a reservoir assembly for use in a phase change ink imaging device is provided. In one embodiment, the reservoir assembly includes a back plate having an ink input port configured to receive liquid ink under pressure from an ink source and a front plate including an ink tank configured to hold ink received from the ink source and to communicate the ink to a printhead. A first plate is bonded to the back plate. The first plate and the back plate enclose a filter chamber therebetween. The filter chamber is configured to receive ink via the ink input port and to direct the received ink to an ink supply path opening in the first plate having a first cross-sectional area. The filter chamber includes at least one filter positioned between the ink input port and the ink supply path opening in the first plate. A second plate is bonded between the first plate and the front plate. The second plate includes an ink supply path opening that aligns with the ink supply path opening in the first plate. The ink supply path opening in the second plate has a second cross-sectional area, the second cross-sectional area being less than the first cross-sectional area.
In another embodiment, a reservoir assembly for use in a phase change ink imaging device includes a back plate including an ink input port configured to receive liquid ink from an ink source; and a front plate including an ink tank configured to hold ink received from the ink source and to communicate the ink to a printhead. A foam plate is positioned between the front plate and the back plate. The foam plate and the back plate enclose a filter chamber therebetween. The filter chamber is configured to receive ink via the ink input port, the foam plate including a thin channel exiting at a slit configured to constrict a flow of ink foam from the filter chamber to the ink tank thus collapsing a majority of the bubbles. The filter chamber includes at least one filter positioned between the ink input port and the slit in the foam plate.
The foregoing aspects and other features of the present disclosure are explained in the following description, taken in connection with the accompanying drawings, wherein:
For a general understanding of the present embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements.
As used herein, the term “imaging device” generally refers to a device for applying an image to print media. “Print media” can be a physical sheet of paper, plastic, or other suitable physical media or substrate for images, whether precut or web fed. The imaging device may include a variety of other components, such as finishers, paper feeders, and the like, and may be embodied as a copier, printer, or a multifunction machine. A “print job” or “document” is normally a set of related sheets, usually one or more collated copy sets copied from a set of original print job sheets or electronic document page images, from a particular user, or otherwise related. An image generally may include information in electronic form which is to be rendered on the print media by the marking engine and may include text, graphics, pictures, and the like.
The ink jet printing apparatus includes an ink delivery system (not shown in
The remote ink containers 51-54 are configured to communicate melted phase change ink held therein to the on-board ink reservoirs 61-64. In one embodiment, the remote ink containers 51-54 may be selectively pressurized, for example by compressed air that is provided by a source of compressed air 67 via a plurality of valves 81, 82, 83, 84. The flow of ink from the remote containers 51-54 to the on-board reservoirs 61-64 can be under pressure or by gravity, for example. Output valves 91, 92, 93, 94 may be provided to control the flow of ink to the on-board ink reservoirs 61-64.
The on-board ink reservoirs 61-64 may also be selectively pressurized, for example by selectively pressurizing the remote ink containers 51-54 and pressurizing an air channel 75 via a valve 85. Alternatively, the ink supply channels 71-74 can be closed, for example by closing the output valves 91-94, and the air channel 75 can be pressurized. The on-board ink reservoirs 61-64 can be pressurized to perform a cleaning or purging operation on the printhead 20, for example. The on-board ink reservoirs 61-64 and the remote ink containers 51-54 can be configured to contain melted solid ink and can be heated. The ink supply channels 71-74 and the air channel 75 can also be heated.
The on-board ink reservoirs 61-64 are vented to atmosphere during normal printing operation, for example by controlling the valve 85 to vent the air channel 75 to atmosphere. The on-board ink reservoirs 61-64 can also be vented to atmosphere during non-pressurizing transfer of ink from the remote ink containers 51-54 (i.e., when ink is transferred without pressurizing the on-board ink reservoirs 61-64).
As schematically depicted in
Once pressurized ink reaches an on-board reservoir of a printhead, it is typically passed through a filter prior to being collected in a chamber or tank in the on-board reservoir that is configured to communicate the ink to the ink jets for ejection onto a print medium (
In order to reduce or eliminate foam formation in the printhead reservoir caused by pressurized ink delivery through the reservoir filter, the present disclosure proposes a reservoir assembly that may be used to implement the on-board reservoirs 61, 62, 63, 64 that provides a series of foam reducing passages, openings, or paths within the on-board reservoirs between the reservoir filters and the ink tanks or chambers of the on-board reservoirs that are designed to collapse, compress, stretch, and/or shear the air bubbles that make up the foam before the foam enters the ink tanks of the reservoir assembly. The foam reducing paths may be formed by features in the plates that make up the reservoir assembly between the filters and the ink tanks of the on-board reservoirs that have at least one characteristic that enable the paths to collapse, compress, stretch, and/or shear air bubbles that make up foam that enter the ink supply path prior to the foam reaching the reservoir tanks. Examples of characteristics that enable the foam reducing paths to collapse and or shear air bubbles in foam that enters the paths include changes in aspect ratio, reduction in the cross-sectional area of the paths as the ink/foam travels along the paths, and relatively sharp edges along the path. In addition, although the present discussion is directed primarily to the utilization of foam reducing ink passages in printhead reservoir assemblies of phase change ink imaging devices, such foam reducing passages may be utilized to reduce or prevent foam formation in printheads that utilize other forms of marking material, such as, for example, aqueous inks, oil based inks, UV curable inks, and the like. Therefore, references to phase change ink and phase change ink printheads utilized herein should not be taken to limit the present disclosure in any manner.
The heater 110 includes heating elements that may be in the form of a resistive heat tape, traces, or wires that generate heat in response to an electrical current flowing therethrough. The heating elements may be covered on each side by an electrical insulation having thermal properties that enable the generated heat to be transferred to the plates of the reservoir assembly in adequate quantities to maintain or heat the phase change ink contained therein to an appropriate temperature. In one embodiment, the heater 110 is a Kapton heater made in a manner described in more detail below. Alternate heater materials and constructions, such as a silicone heater, may be used for different temperature environments, or to address cost and geometry issues for the construction of other embodiments of umbilical assemblies.
The back plate 104, the first heater plate 114, the second heater plate 118, the filter assembly 120, and the front plate 108 may each be formed a thermally conductive material, such as stainless steel or aluminum, and may be bonded or sealed to each other in any suitable manner, such as by, for example, a pressure sensitive adhesive or other suitable adhering or bonding agent. The heater 110 includes heating elements that may be in the form of a resistive heat tape, traces, or wires that generate heat in response to an electrical current flowing therethrough. The heating elements may be covered on each side by an electrical insulation material, such as polyimide, having thermal properties that enable the generated heat to be transferred to the plates of the reservoir assembly in adequate quantities to maintain or heat the phase change ink contained therein to an appropriate temperature. In one embodiment, the heater is configured to generate heat in a uniform gradient to maintain ink in the reservoir assembly within a temperature range of about 100 degrees Celsius to about 140 degrees Celsius. The heater 110 may also be configured to generate heat in other temperature ranges. The heater 110 is capable of generating enough heat to enable the reservoir assembly to melt phase change ink that has solidified within the passages and chambers of the reservoir assembly, as may occur when turning on a printer from a powered down state.
To keep the heater 110 from self-destructing from high localized heat, the heater may be coupled to a thermally conductive strip to improve thermal uniformity along the heater length. The thermal conductor may be a layer or strip of aluminum, copper, or other thermally conductive material that is placed over at least one side of the electrically insulated heating traces. The thermal conductor provides a highly thermally conductive path so the thermal energy is spread quickly and more uniformly over the mass. The rapid transfer of thermal energy keeps the trace temperature under limits that would damage, preventing excess stress on the traces and other components of the assembly. Less thermal stress results in less thermal buckling of the traces, which may cause the layers of the heater to delaminate.
After the heater 110 has been constructed, the first heat distribution plate 114 is adhered or bonded to one side of the heater 110. The first heat distribution plate 114 may be adhesively bonded to the heater using a double-sided pressure sensitive adhesive (PSA). Likewise, the second heat distribution plate 118 of the reservoir assembly is adhered or bonded to the other side of the heater 110. This construction enables a single heater to be used to generate heat in the substantially the entire reservoir assembly to maintain the ink within the reservoirs at a desired temperature. In one embodiment, the heater is configured to generate heat in a uniform gradient to maintain ink in the reservoir assembly within a temperature range of about 100 degrees Celsius to about 140 degrees Celsius. The heater 110 may also be configured to generate heat in other temperature ranges. The heater is capable of melting phase change ink that has solidified within the passages and chambers of the reservoir assembly, as may occur when turning on a printer from a powered down state.
Generally, the ink travels from the rear plate 104 towards the front plate 108. The rear panel includes input ports 171, 172, 173, 174 that are respectively connected to the supply channels 71, 72, 73, 74 to receive ink therethrough from the associated remote ink containers 51-54 (
In the embodiment of
The foam reducing ink supply paths formed by the openings in the heater and first and second heater plates guide ink received in the filter chambers 124 to an associated reservoir, or tank, 61-64 incorporated into the front panel 108, referred to herein as a tank plate. As depicted in
During pressurized ink delivery to the reservoir assembly, ink will fill a respective filter chamber 124, pass through the filter(s) 120 positioned in the filter chamber 124, and be directed to the foam reducing ink supply path opening in the first heater/weir plate. The position of the ink supply path openings 271-274 in the first heater plate 114 act as a weir over which the ink travels into the corresponding reservoir 61-64 in the front plate 108. The openings 271-274 in the first heater plate 114 act to constrict or reduce the cross-section of flow from the filter chamber 124 toward the ink tanks 61-64 which enables the first heater plate openings 271-274 to collapse or shear many of the largest air bubbles that make up any foam that may have formed.
The openings 271-274 in the first heater plate may have any suitable shape and/or size such as circles, squares, ellipses, and rectangles, may have rounded or straight edges, and may be regularly or irregularly shaped. The ability of the ink supply path openings in the first heater plate to collapse or shear air bubbles as they enter the ink supply paths corresponds to the dimensions of the openings. The openings in the first heater plate may be provided with a shape or aspect ratio that enhances the ability of the openings to collapse or shear foam bubbles. For example, ink supply path openings in the first heater plate may be provided with elongated slot-like shapes such as elongated circles, ellipses or rectangles.
After ink and/or foam have passed through the foam reducing opening in the first heater, the flow is directed through the opening 374 in the heater. The openings 371-374 in the heater are typically larger than the openings 271-274 in the first and second 471-474 heater plates by design for manufacturing processes. The flow of ink foam then continues along the respective foam reducing ink supply path where it is directed through the openings 474 in the second heater plate. In order to further reduce or eliminate foam that enters the ink supply paths through the ink supply path openings in the first heater plate, the second heater plate 118 comprises a foam plate having openings 471-474 that are smaller in at least one dimension or aspect than the ink supply path openings 271-274 in the first heater plate 114 in order to further reduce the cross-section of flow along the paths. The reduction in the cross-section of flow through the second heater/foam plate acts to collapse or shear more of the air bubbles of the foam that were permitted to pass through the openings in the first heater plate prior to the foam reaching the tanks.
In the embodiment of
To further enhance the ability of the foam reducing openings 471-474 in the foam plate 118 to collapse or shear bubbles passing therethrough, the foam plate may be provided as a thin or narrow plate so that the edges (
Foam plates may be incorporated into other embodiments of printhead reservoirs to reduce foam that may be formed during pressurized ink delivery through a filter. For example,
Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. Therefore, the following claims are not to be limited to the specific embodiments illustrated and described above. The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
