Solid ink printer with magnetic ink mixing

A phase change inkjet printer is equipped with an agitator to prevent settling of metal particles in melted magnetic phase change ink. The agitator operates to agitate the melted magnetic phase change ink as the ink enters the printhead to maintain the metal particles in suspension within the melted ink.

TECHNICAL FIELD

This disclosure relates generally to inkjet printers that utilize magnetic ink, and more particularly, to devices that help keep magnetic particles suspended in the magnetic ink used in such printers.

BACKGROUND

Solid ink or phase change ink printers conventionally receive ink in a solid form, sometimes known as solid ink sticks. The solid ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a melt reservoir. The melt reservoir maintains the ink in a melted state and delivers the ink to a printing system of the printer for ejection onto an image receiving surface. The image receiving surface can be the surface of media, such as paper, or a liquid layer of release agent supported by an intermediate imaging member, such as a metal drum or belt.

Currently, efforts are underway to use phase change inks in magnetic character ink recognition (MICR) printing. MICR printing uses aqueous magnetic inks to print characters on financial documents to enable character recognition technology that detects the characters with magnetic detectors. This technology is used primarily in the banking industry to facilitate the processing of checks. The technology allows magnetic readers to read information, such as routing numbers and account numbers, from printed documents. Unlike barcodes or similar technologies, however, MICR codes can also be easily read by humans.

MICR printing ink typically includes a suspension of metal particles, such as iron oxide, which enable the magnetic readers to recognize the printed characters. In MICR solid ink, the metal particles are suspended in a phase change medium. When MICR solid ink is melted and in a liquid state, the metal particles can be pulled downwardly by gravity and collect in the lower regions of melted ink containers and passageways in a printer. The metal particles settling out of the ink can degrade the uniform distribution of magnetic particles in the ink that can make characters printed with the non-uniform ink difficult to detect.

Uniform distribution of metal particles in phase change ink is more difficult than maintaining such distribution in aqueous inks because the viscosity of the phase change ink and the ability of the ink to change phase affects the flow dynamics of the ink. Consequently, previously known methods of maintaining a uniform distribution of metal particles in aqueous inks are not as effective or robust with phase change inks. Thus, a need exists for devices and methods that help maintain a uniform distribution of metal particles in phase change ink as the ink is used in an inkjet printer.

SUMMARY

In accordance with one embodiment, a printer that ejects magnetic phase change ink comprises a printhead configured to eject drops of melted phase change ink having metal particles. The printhead includes an inlet for receiving melted phase change ink and an onboard reservoir fluidly connected to the inlet to hold a quantity of melted phase change ink received through the inlet. An agitator is configured to produce turbulence in the melted phase change ink entering the inlet of the printhead to maintain the metal particles in suspension within the melted phase change ink as the melted phase change ink enters the printhead.

In accordance with another embodiment, a method of operating a printing apparatus comprises transporting melted ink through a heated conduit to an inlet of an onboard reservoir of a printhead of a phase change ink printer, the melted ink having metal particles; and producing turbulence in the melted magnetic ink melted phase change ink entering the inlet of the printhead with an agitator to maintain the metal particles in suspension within the melted phase change ink as the melted ink enters the inlet of the onboard reservoir.

In accordance with yet another embodiment, a printer configured to eject melted magnetic phase change ink comprises a printhead configured to eject drops of melted phase change ink having metal particles. The printhead includes an inlet for receiving the melted phase change ink and an onboard reservoir fluidly connected to the inlet to hold a quantity of melted phase change ink received through the inlet. A heated conduit is fluidly connected to the inlet for delivering melted phase change ink to the onboard reservoir from a source of melted phase change ink. An agitator is mechanically coupled to one of the heated conduit and the onboard reservoir. The agitator is configured to produce turbulence in the melted ink to maintain the metal particles in suspension within the melted phase change ink.

DETAILED DESCRIPTION

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 “printer” generally refers to an apparatus that produces an ink image on print media and can encompass any such apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc., which performs a printing function for any purpose.

As used herein, the term “inkjet printer” generally refers to a device that produces ink images on print media by ejecting ink onto an image receiving surface. “Print media” can be a physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed. A printer can include a variety of other components, such as finishers, paper feeders, and the like, and can be embodied as a copier or a multifunction machine. Image data generally includes digital data which is rendered for use to operate inkjet ejectors in printheads to form ink images on an image receiving surface and can include text, graphics, pictures, and the like.

As used herein, the term “ink” refers to a colorant that is liquid when applied to an image receiving surface. For example, ink can be aqueous ink, ink emulsions, solvent based inks and phase change inks. “Phase change ink” refers to inks that are in a solid or gelatinous state at room temperature and change to a liquid state when heated to an operating temperature for application or ejection onto an image receiving surface. The phase change inks return to a solid or gelatinous state when cooled on the print media after the printing process. As used herein, the term “magnetic ink” refers to an ink that includes a suspension of magnetic particles, such as iron oxide, in a liquid or phase-change medium.

The term “printhead” as used herein refers to a component in the printer that is configured to eject ink drops onto an image receiving surface. A typical printhead includes a plurality of inkjet ejectors that are configured to eject ink drops of one or more ink colors onto the print media. The inkjet ejectors are arranged in an array of one or more rows and columns. In some embodiments, the inkjet ejectors are arranged in staggered diagonal rows across a face of the printhead. Various printer embodiments include one or more printheads that form ink images on an image receiving surface.

FIG. 1is a simplified schematic view of a portion of a phase change ink, or solid ink, printer10. The printer10includes a solid ink loader14, an ink melter18, an ink melt reservoir20, and a printhead24. The ink loader14, ink melter18, melt reservoir20, and a printhead24are configured to utilize a magnetic solid ink, and in particular, a magnetic solid ink that is suitable for use in Magnetic Ink Character Recognition (MICR) printing.

The ink loader14is configured to receive magnetic solid ink, such as blocks of ink28, which are commonly called ink sticks. The ink loader14includes feed channels30into which ink sticks28are inserted. Although a single feed channel30is depicted inFIG. 1, the ink loader14can include a separate feed channel30for each type, color or shade of ink stick28used in the printer10.

Each feed channel30guides ink sticks28to an ink melter18where the sticks are heated to a phase change ink melting temperature to melt the solid ink into a liquid. Any suitable melting temperature can be used depending on the solid ink formulation of the ink sticks. In one embodiment, the solid ink melting temperature is approximately 80° C. to 130° C.

The melted ink is directed gravitationally or by pressurizing devices from the ink melter18to an ink melt reservoir or tank20. A separate melt reservoir20can be provided for each ink color, shade, or composition used in the printer10. Alternatively, a single reservoir housing can be compartmentalized to contain the differently colored inks. Each melt reservoir20can include a heating element (not shown) operable to heat the ink contained in the corresponding reservoir to a temperature suitable for melting the ink and/or maintaining the ink in liquid form, at least during appropriate operational states of the printer10.

Melted ink is transported from the melt reservoir20to the printhead24by at least one heated conduit or tube, such as heated conduit34. The heated conduit34includes an inlet end36which is fluidly connected to an ink source, such as the melt reservoir20, and an outlet end38that is fluidly connected to an inlet46of a printhead40. A lumen within the conduit enables ink to flow from the reservoir20to the printhead24. The printhead24can be a single printhead having a width that enables most or all of a width of an image receiving surface to be printed by the printhead. Alternatively, a plurality of printheads24, each of which covers only a portion of the width of the image receiving member, can be arranged in a known manner to cover most or all of the width of the image receiving member. Each printhead24includes a housing40in which a plurality of inkjet ejectors44and an onboard reservoir42are provided.

The onboard reservoir42includes at least one inlet46that is fluidly coupled to the heated conduit34to receive melted ink from the melt reservoir. The onboard reservoir42maintains a quantity of melted ink for the ejectors44. The ejectors44receive the melted ink from the reservoir42and eject drops of melted ink onto the ink receiving surface50in response to receiving firing signals from the control system54.

FIG. 2depicts an embodiment of a printhead assembly64, referred to herein as a print box unit (PBU), in which a plurality of printheads24is mounted. The PBU includes a plurality (e.g., four inFIG. 2) of printheads24that are arranged in a linear array and secured to a support housing66. The PBU64is secured to the frame (not shown) of a printer with the printheads24extending across the width of the media pathway (not shown) of the printer. The PBU64can be installed and removed from the printer as a unit which facilitates customization as well as maintenance of the printer.

FIG. 3depicts the ink transport system of the PBU64without the housing66and printheads24. As depicted inFIG. 3, the PBU64includes a manifold68, which receives melted ink from the melt reservoir (FIG. 1). The manifold includes a plurality of ink injectors70for supplying melted ink to the printheads. Each injector70is fluidly connected to the onboard reservoir of the one of the printheads by a heated conduit74. The heated conduits74ofFIG. 3are supported by a conduit support78.

The printer10ofFIG. 1may be configured as a direct or an indirect printer. In a direct printer, the ejectors44are configured to eject drops of ink directly onto print media. In an indirect printer, the ink receiving surface50comprises the surface of an intermediate member, such as a rotating drum or belt. The melted ink is ejected onto the surface of the intermediate member, and then print media is pressed against the surface of the intermediate member on top of the ink to transfer the ink to the print media (not shown).

A control system54(FIG. 1) aids in operation and control of the various subsystems, components, and functions of the printer10. The control system54includes a controller56, electronic storage or memory58, and a user interface (UI)60. The controller56comprises 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 image data received from image sources, such as scanners or network computers (not shown), to generate signals for operating the inkjet ejectors of one or more printheads24.

The controller56is configured to execute programmed instructions that are stored in the memory58. The controller56executes these instructions to operate the components and subsystems of the printer10. Any suitable type of memory or electronic storage can be used. For example, the memory58can 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)60comprises a suitable input/output device located on the printer10that enables operator interaction with the control system54. For example, UI60can include a keypad and display (not shown).

MICR solid ink contains a suspension of metal particles that enable a magnetic reader to recognize characters printed with the ink. The characters are most easily and accurately recognized when the metal particles are uniformly distributed within the ink. The metal particles, however, can settle in the lower regions of melted ink containers and passageways and disrupt the uniform distribution of the particles within the ink. The metal particles settling out of the ink degrades the magnetic properties of the ink and can make it unsuitable for its intended purpose. To address the difficulties posed by the settling of metal particles in magnetic solid ink, an ink agitator100is configured to help maintain the uniform distribution of the melted particles within the melted ink. As shown inFIG. 1, the agitator100is positioned to produce turbulence in the melted ink contained in the heated conduit34proximate the inlet46of the onboard reservoir42of the printhead24.

In one embodiment, the agitator100is positioned inline between the melt reservoir20and the printhead reservoir42in one of the printheads to act on the melted ink being transported by the heated conduit34to the printhead40. As depicted inFIGS. 3 and 4, for example, the inline agitator100is attached to the conduit support78and operatively connected to the heated conduit74at the end of each conduit74proximate the printhead(s)24. The conduit support78provides a surface for mounting the agitators100and includes electrical terminals (not shown) for electrically connecting the agitators100to power and control wiring (not shown).

FIGS. 5-8depict various embodiments of inline agitators100A-100D that can be incorporated into the printer10. In the embodiments ofFIGS. 5 and 6, the agitator100A,100B is configured to act on the ink directly to produce turbulence in the ink whereas in the embodiments ofFIGS. 7 and 8, the agitator100C,100D is configured to act on the heated conduit34to produce turbulence in the ink.

Referring toFIG. 5, the agitator100A comprises a rotating drum102that has an interior cavity104with an inlet106and an outlet108. The inlet106is fluidly connected to receive melted ink from the melt reservoir20(or manifold68) via heated conduit34. The outlet108is fluidly connected to the inlet of the onboard reservoir of the printhead by a portion of the heated conduit. The drum102is operatively connected to an actuator110, such as a motor, that is configured to rotate the drum102at one or more predetermined rates. The motor110in turn is operatively connected to the controller56in control system54for selectively controlling the activation and deactivation of the agitator100A.

The axis of rotation A of the drum102is aligned with the longitudinal axis of the heated conduit. The rotating drum102therefore works similar to a cement mixer by turning the melted ink over as it moves from the inlet106to the outlet108of the drum. The rate of rotation of the drum102does not have to be high to maintain the metal particles in suspension, and in one embodiment is approximately 6 rpm although any suitable rate of rotation can be utilized. The rate of rotation can be constant or can be varied based on various factors, such as operating state, print rate, type of print job, and the like.

In the embodiment ofFIG. 5, agitation is caused by the movement of the drum or housing102of the agitator. The agitator100B ofFIG. 6includes a housing114that has an interior cavity116with an inlet118and an outlet120similar toFIG. 5. The agitator100B includes mixers122,124, which are configured in the interior cavity116for rotation, as indicated in the figure, to produce turbulence in the ink sufficient to maintain the distribution of the metal particles in the ink. In the embodiment ofFIG. 6, the mixers122,124are in the form of counter rotating fingers, such as intermeshing gears, which are rotatably mounted in the interior cavity116of the housing114.

In one embodiment, the fingers are driven to rotate by the flow of melted ink through the agitator. For example, the first set of fingers rotate in response to the ink entering the cavity from the inlet. The second set of fingers is connected to the first set of fingers by meshed gears to rotate in the opposite direction from the first set of fingers. In alternative embodiments, the mixers can be operatively connected to an actuator, such as actuator110, which drives the mixers to rotate with or without the aid of the flowing ink.

InFIGS. 5 and 6, the agitator includes a housing, which receives melted ink from a heated conduit, such as conduit34or conduit74, and directs melted ink back into the heated conduit34or74connected to the outlet. InFIGS. 7 and 8, the agitator100C,100D at least partially surrounds a portion of the lumen130of the heated conduit34or74to provide turbulence in the melted phase change ink being transported in the heated conduit. In the embodiments ofFIGS. 7 and 8, the energy that is used to agitate the melted ink is transmitted to the melted ink through the lumen130of the heated conduit.

In the embodiment ofFIG. 7, the agitator100C comprises at least one magnetic ring placed around a portion of the outer surface of the conduit34or74. The magnetic ring100C includes a pass-through opening134through which the conduit34or74extends and is configured to have an alternating ring of North-South magnetic fields. The magnetic ring100C is operatively connected to the controller56and is pulsed on and off at suitable frequencies by the controller56to generate magnetic fields136that act on the metal particles in the ink to cause turbulence.

FIG. 8depicts an embodiment of an agitator100D that comprises an oscillating mechanism configured to vibrate the conduit and thereby agitate the ink. The oscillator100D is mechanically connected to the conduit so that the energy is transmitted to the ink in the lumen130. In one embodiment, the oscillator100D comprises an ultrasonic plate transducer that at least partially surrounds the outer surface of the conduit34or74. The ultrasonic transducer is operatively connected to the controller56. The controller56is configured to activate the ultrasonic plate to oscillate at one or more ultrasonic or near ultrasonic frequencies.

As an alternative to coupling an ultrasonic transducer to the conduit adjacent to the printhead, an ultrasonic transducer100F can be incorporated into the onboard reservoir42of the printhead as depicted inFIG. 9. The ultrasonic transducer100F comprises a plate that is mechanically coupled onto one of the walls of the housing40of a printhead24. For example, as shown inFIG. 9, the transducer100F is mechanically coupled to the floor138of the reservoir42. Alternatively, the transducer100F can be embedded in a wall of the housing40during casting.

The ultrasonic transducer100F is operatively connected to the controller56. The controller56is configured to cycle the transducer100F on when the printer is idle and to cycle the transducer off during active printing. Otherwise, the vibration induced by the transducer into the printhead reservoir may affect the accuracy of the ink drops ejected from the ejectors in the printhead. In one embodiment, the controller56can be configured to activate the transducer100F only after a certain amount of time has elapsed after an idle state has commenced. For example, in one embodiment, the controller56can be configured to activate the transducer100F after an hour has elapsed the idle state was entered. The use of the transducer100F in the onboard reservoir42is also capable of removing air and gas bubbles from the ink prior to entering the ejectors44and dislodging debris and contaminants from the passages of the printhead so it can be cleared through the ejectors.

FIGS. 10 and 11depict an embodiment of an agitation system100G that is configured to utilize a Venturi device or pump150to siphon a portion of the magnetic ink out of the bottom of the onboard reservoir42of the printhead and mix it with the ink that is being delivered to the printhead. As depicted inFIGS. 10 and 11, the agitation system100G includes a return conduit140having an inlet end142and an outlet end144. The inlet end142of the return conduit140is fluidly connected to an outlet opening146provided in the base or bottom138of the onboard reservoir142. The outlet end of the return conduit is fluidly connected to an inlet148in the Venturi device150.

The Venturi device150fluidly connects the heated conduit34or74and the return conduit140to the inlet46of the onboard reservoir42. The Venturi device150is configured to generate a vacuum pressure in the return conduit140in response to the flow of ink toward the inlet of the onboard reservoir42. Thus, whenever ink flows into the printhead, a portion of the ink from the onboard reservoir, including the metal particles that have settled out of the mixture, are re-circulated and mixed in with the incoming ink flow. As an alternative to the use of a Venturi device, a pump can be used to generate the pressure drop in the return conduit. Use of a pump requires a power input during standby or sleep mode, but provides the ability to mix the ink at periodic intervals when the machine is not printing.