The apparatus and method described below relates to devices for heating phase change ink, and more particularly to using immersed heaters in an ink reservoir to melt solidified ink.
Inkjet printers eject drops of liquid ink from inkjet ejectors to form an image on an image receiving surface, such as an intermediate transfer surface, or a media substrate, such as paper. Full color inkjet printers use a plurality of ink reservoirs to store a number of differently colored inks for printing. A commonly known full color printer has four ink reservoirs. Each reservoir stores a different color ink, namely, cyan, magenta, yellow, and black ink, for the generation of full color images.
Phase change inkjet printers utilize ink that remains in a solid phase at room temperature, often with a waxy consistency. After the ink is loaded into a printer, the solid ink is transported to a melting device, which melts the solid ink to produce liquid ink. The liquid ink is stored in a reservoir that may be either internal or external to a printhead. The liquid ink is provided to the inkjet ejectors of the printhead as needed. If electrical power is removed from the printer to conserve energy or for printer maintenance, the melted ink begins to cool and may eventually return to the solid form. In this event, the solid ink needs to be melted again before the ink can be ejected by a printhead. Consequently, the time taken to melt the ink impacts the availability of a solid ink printer for printing operations. Therefore, improvements to the devices in a printer that heat and store melted ink are desirable.
A volumetric container for storage of ink in a solid inkjet printer has been developed. The container includes a housing comprised of thermally insulating material having a volume of space internal to the housing, the volume of space having a height, a width, and a depth, and a heater element positioned within the volume of space of the housing to melt ink uniformly across the width of the volume of space. The heater element is configured to have a surface area that is greater than an area defined by the height and width of the volume of space.
The description below and the accompanying figures provide a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method. In the drawings, like reference numerals are used throughout to designate like elements. The word “printer” as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc. which performs a print outputting function for any purpose. While the specification focuses on a system that controls the melting of solid ink in a solid ink reservoir, the apparatus for melting ink in a reservoir may be used with any device that uses a phase-change fluid that has a solid phase. Furthermore, solid ink may be called or referred to herein as ink, ink sticks, or sticks. The term “parametric volume” refers to a volume defined by an envelope around the form of an object, such as a heater element, that may include gaps and cavities. Thus, the parametric volume of an object includes open spaces within the object as well as the volume of material forming the object. Parametric volume as used in this document means an interior volume of a tight fitting, multi-sided box into which the heater fits. Similarly, the term “parametric thickness” refers to a thickness of an object, such as a heater element, that may include openings or gaps. For example, a corrugated object has a parametric thickness extending from the top of one corrugation to the bottom of another corrugation.
In more detail, the ink handling system 12, which is also referred to as an ink loader, is configured to receive phase change ink in solid form, such as blocks of ink 14, which are commonly called ink sticks. The ink loader 12 includes feed channels 18 into which ink sticks 14 are inserted. Although a single feed channel 18 is visible in
The printing system 26 includes at least one printhead 28 including a printhead reservoir 27 having inkjets arranged to eject drops of melted ink onto an intermediate surface 30. Printhead reservoir 27 receives molten ink from reservoir 24 via a conduit 25. Printhead reservoir 27 contains a heater element, as shown in further detail below. One printhead is shown in
The intermediate surface 30 comprises a layer or film of release agent applied to a rotating member 34 by the release agent application assembly 38, which is also known as a drum maintenance unit (DMU). The rotating member 34 is shown as a drum in
The media supply and handling system 48 of device 10 is configured to transport recording media along a media path 50 defined in the device 10 that guides media through the nip 44, where the ink is transferred from the intermediate surface 30 to the recording media 52. The media supply and handling system 48 includes at least one media source 58, such as supply tray 58 for storing and supplying recording media of different types and sizes for the device 10. The media supply and handling system includes suitable mechanisms, such as rollers 60, which may be driven or idle rollers, as well as baffles, deflectors, and the like, for transporting media along the media path 50.
The media path 50 may include one or more media conditioning devices for controlling and regulating the temperature of the recording media so that the media arrives at the nip 44 at a suitable temperature to receive the ink from the intermediate surface 30. For example, in the embodiment of
A control system 68 aids in operation and control of the various subsystems, components, and functions of the imaging device 10. The control system 68 is operatively connected to one or more image sources 72, such as a scanner system or a work station connection, to receive and manage image data from the sources and to generate control signals that are delivered to the components and subsystems of the printer. Some of the control signals are based on the image data, such as the firing signals, and these firing signals operate the printheads as noted above. Other control signals cause the components and subsystems of the printer to perform various procedures and operations for preparing the intermediate surface 30, delivering media to the transfix nip, and transferring ink images onto the media output by the imaging device 10.
The control system 68 includes a controller 70, electronic storage or memory 74, and a user interface (UI) 78. The controller 70 comprises a processing device, such as a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) device, or a microcontroller. Among other tasks, the processing device processes images provided by the image sources 72. The one or more processing devices comprising the controller 70 are configured with programmed instructions that are stored in the memory 74. The controller 70 executes these instructions to operate the components and subsystems of the printer. Any suitable type of memory or electronic storage may be used. For example, the memory 74 may be a non-volatile memory, such as read only memory (ROM), or a programmable non-volatile memory, such as EEPROM or flash memory.
User interface (UI) 78 comprises a suitable input/output device located on the imaging device 10 that enables operator interaction with the control system 68. For example, UI 78 may include a keypad and display (not shown). The controller 70 is operatively coupled to the user interface 78 to receive signals indicative of selections and other information input to the user interface 78 by a user or operator of the device. Controller 70 is operatively coupled to the user interface 78 to display information to a user or operator including selectable options, machine status, consumable status, and the like. The controller 70 may also be coupled to a communication link 84, such as a computer network, for receiving image data and user interaction data from remote locations.
The controller 70 generates control signals that are output to various systems and components of the device 10, such as the ink handling system 12, printing system 26, media handing system 48, release agent application assembly 38, media path 50, and other devices and mechanisms of the imaging device 10 that are operatively connected to the controller 70. Controller 70 generates the control signals in accordance with programmed instructions and data stored in memory 74. The control signals, for example, control the operating speeds, power levels, timing, actuation, and other parameters, of the system components to cause the imaging device 10 to operate in various states, modes, or levels of operation, that are denoted in this document collectively as operating modes. These operating modes include, for example, a startup or warm up mode, shutdown mode, various print modes, maintenance modes, and power saving modes.
Housing 204 is a volumetric container that is primarily composed of a thermally insulating material that is compatible with various phase change inks in both the solid and molten phases. Various plastics, including thermoplastics, and elastomeric materials are suitable for use in the housing 204. Additionally, housing 204 may comprise one or more layers of both thermally insulating and thermally conductive materials. The materials of housing 204 are configured to provide at least moderate heat retention within reservoir volume 208. Reservoir volume 208 has an internal height 252, width 256 (extending through the page), and depth 260. The upper liquid level for a volume of ink within the reservoir may be well below the upper reservoir confinement. such a configuration enables ink to be retained even when the product is tipped at an angle. The reservoir may be vented, partially open or fully open at the top.
The exemplary heater element 212 includes multiple heating members, such as vane-like heating member 220, that extend substantially across the width 256 of the reservoir volume 208. The shape of heater element 212 provides a surface area exposed to ink 210 that is greater than a surface area defined by the height 252 and width 256 of reservoir volume 208. Heater element 212 occupies a position in reservoir volume 208 that is proximate to conduit 248 to expedite melting of ink near the conduit, and the heater element extends from the bottom of reservoir volume 208 toward the top of reservoir volume 208. The parametric volume of heater element 212 is greater than 50% of the total volume of reservoir volume 208 up to the upper liquid volume level 268. The upper liquid volume level limits the volume of ink in reservoir 200 to enable a portion of reservoir volume 208 to remain unfilled during operation. Heater element 212 extends below a low limit fluid level, shown by dashed line 264. As used herein, the term “low limit fluid level” refers to a minimum level of a fluid, such as ink, held in a fluid reservoir during operation. As the fluid level in a reservoir reaches the low limit fluid level, the printer may suspend operation or take other actions to ensure that the fluid level in reservoir volume 208 exceeds the low limit fluid level.
In one embodiment, the heater element 212 is formed from a positive thermal coefficient (PTC) material and may be a modified shape PTC thermistor. A PTC material exhibits an increased resistance to a flow of electrical current in response to an increase in temperature of the material. The PTC material, which may be a ceramic like substance, may be formed into a heater and coated, as appropriate or required, for chemical compatibility with the ink or other material being heated. Electrical leads 206 extend from the heater element 212 through the top of housing 204. In the embodiment of
As seen in
Referring again to
In another mode of operation, ink 210 occupies reservoir volume 208 in a solid phase. Controller 236 may deactivate electrical power source 244 to allow the ink 210 to cool and solidify according to various energy saving programs and techniques that are known to the art. Controller 236 is typically an electronic control system and may be embodied by the controller 70 described above. Ink 210 may also solidify when a printing device is removed from electrical power for a time period sufficient to allow the ink to cool to or below the solidification point. When electrical power supply 244 activates the heater element 212, the solid ink 210 in areas proximate to the heater element 212 begin to melt first. Molten ink flows through gaps, such as gap 216 provided between individual elements of heater element 212, and enters conduit 248 from outlet 224. The location of heater element 212 at a position proximate to outlet 224 enables melted ink to flow through the conduit 248 quickly after the heater 212 begins to heat. While ink melts uniformly along the width 256 of reservoir volume 208, ink located near the wall of housing 204 opposite conduit 248 is positioned farther from the heater element 212, and may melt more slowly than ink closer to the heater element 212. Thus, melted ink may flow through conduit 248 to printhead 250 even if other portions of the ink 210 in the reservoir volume remain solid or at a temperature lower than the elevated operational temperature.
During both modes of operation described above, a portion of heater element 212, shown as portion 214 in
Housing 304 is primarily composed of a thermally insulating material that is compatible with various phase change inks in both the solid and molten phases. Housing 304 is a volumetric container having an internal volume, seen here as reservoir volume 308, having a height 352, width 356, and depth 360. Reservoir volume 308 holds ink received from ink reservoir 402 through conduit 448 and inlet 346. Various plastics, including thermoset plastics, thermoplastics, and elastomeric materials compatible with reservoir operational temperatures are suitable for use in the housing 304 where any of these materials provides at least a moderate degree of thermal insulation, such as a material that provides at least 20 times more thermal insulation than an aluminum housing as traditionally used. Additionally, housing 304 may comprise one or more internal voids or layers of thermally insulating materials. As shown in
As shown in
Referring again to
Controller 336 may be an electronic control device, such as controller 70 from
In an operating mode where ink 310 is maintained in a molten state, controller 336 selectively opens and closes switch 340 in response to the reservoir temperature detected by temperature sensor 340. When the signal generated by the temperature sensor 340 indicates that the ink temperature is below a predetermined lower temperature threshold, controller 336 closes switch 340 to enable electric current from electrical power supply 344 to flow through heater element 312. The temperature of heater element 312 increases in response to the electrical current, heating ink in the ink reservoir 308. When the temperature of ink 310 reaches an upper threshold temperature that is higher than the lower threshold temperature, controller 336 opens switch 340 to remove electric current from the heater element 312. Alternatively, a more precise control method may use a temperature change rate or predetermined temperatures approaching offsets from the lower or upper temperature set points to initiate a change in the current delivered to the heater and/or on/off cycling frequency. One form of this type of “switch” is a PID controller. Lower and upper temperature thresholds for some embodiments of phase change ink that may be used are 110° C. and 125° C., respectively.
In another mode of operation, ink 310 occupies reservoir volume 308 in a solid phase. Controller 336 may open switch 340 to allow the ink 310 to cool and solidify according to various energy saving programs and techniques that are known to the art. Ink 310 may also solidify when a printing device is disconnected from electrical power for a time period sufficient to allow the ink to cool to the freezing point. When melting solidified ink, controller 336 closes switch 340 to enable electrical current from electrical power source 344 to flow through leads 306 and heater element 312. Heater element 312 applies heat uniformly across width 356 of reservoir volume 308. Due to the proximity of heater element 312 to inkjet ejectors 416, ink 310 near the ejectors 416 melts more quickly than ink in portions of the reservoir volume 308 that are farther from the inkjet ejectors 416. Thus, the ejectors 416 receive melted ink in a uniform manner across the width of the printhead and melted ink is available for ejection through the plurality of ejectors even if a portion of the ink 310 remains solid.
The embodiments described above are merely illustrative and are not limiting of alternative embodiments. For example, the PTC heater elements of
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.