System for transporting phase change ink using a thermoelectric device

An ink transport system for a phase change ink printer has been developed that enables accurate control of refilling a second ink reservoir from a first ink reservoir with minimal moving parts. The system includes a thermoelectric device that is operatively connected to a thermally conductive tube, which fluidly connects the first and second ink reservoirs. The thermoelectric device is operated by a controller to heat phase change ink in the thermally conductive tube and enable flow of ink from the first reservoir to the second reservoir, and to remove heat from the phase change ink in the thermally conductive tube to solidify ink in the tube and disable flow of ink from the first reservoir to the second reservoir.

TECHNICAL FIELD

This disclosure relates generally to phase change ink printers, and, in particular, to ink transport systems within phase change ink printers.

BACKGROUND

In general, inkjet printers include at least one printhead configured with an array of inkjet ejectors that are operated to eject drops of liquid ink onto an image receiving surface. A phase-change inkjet printer employs phase change inks that are solid at ambient temperature, but transition to a liquid phase at an elevated temperature. The melted ink can then be ejected by the inkjet ejectors in a printhead to form an ink image on the image receiving surface. The image receiving surface may be an intermediate imaging member, such as a rotating drum or belt, on which a layer of release agent has been applied. After the ink image is formed on the release agent layer, the image is then transferred to an image receiving substrate, such as a sheet of paper, as the substrate passes through a nip formed between a transfix roller and the intermediate imaging member. In other printing systems, the ink can be ejected directly onto printing media as the media moves past the printheads.

As already noted above, phase change ink is loaded into a printer in solid form, transported to a melting device, and melted to produce liquid ink. The melted ink can be stored in a reservoir that can be either internal or external to a printhead. Some printers include both internal and external reservoirs, with the reservoir internal to the printhead(s) refilling from the external reservoir when the ink in the internal reservoir is low.

In phase change inkjet printers having multiple printheads, the ink is used at varying rates by each printhead. These varying rates of use necessitate independent refilling of the internal ink reservoir of each printhead. Previous printers used a series of ball valves, flapper valves, solenoids, pressure sources, and other mechanical hardware to enable individual refilling of each internal reservoir from the external reservoir. However, the mechanical ink transport systems can be slow at responding to changes in ink levels in the internal reservoirs, and the mechanical transport systems have a large number of parts that can malfunction. Thus, improved transport of liquid ink in a phase change ink printer is desirable.

SUMMARY

In one embodiment an ink transport system enables accurate refilling of a second ink reservoir from a first ink reservoir with minimal moving parts. The ink transport system comprises a thermally conductive tube, a thermoelectric device, and a controller. The thermally conductive tube has a first end that is fluidly connected to a first ink reservoir and a second end that is fluidly connected to a second ink reservoir to enable transport of melted phase change ink between the first ink reservoir and the second ink reservoir. The thermoelectric device is operatively connected to the thermally conductive tube and the controller is operatively connected to the thermoelectric device. The controller is configured to selectively operate the thermoelectric device to heat the thermally conductive tube to melt phase change ink within the tube to enable the phase change ink to flow from the first ink reservoir to the second ink reservoir, and to remove heat from the thermally conductive tube to solidify the melted phase change ink within the tube to disable flow of the phase change ink from the first ink reservoir to the second ink reservoir.

In another embodiment an ink transport system enables accurate refilling of ink reservoirs internal to a plurality of printheads from a first ink reservoir with minimal moving parts. The ink transport system comprises a first ink reservoir, a plurality of printheads, a plurality of thermally conductive tubes, a plurality of thermoelectric devices, and a controller. The first ink reservoir configured to hold a supply of phase change ink, while each printhead in the plurality of printheads includes at least one internal ink reservoir. Each tube in the plurality of thermally conductive tubes has a first end that is fluidly connected to the first ink reservoir to enable melted phase change ink from the first reservoir to enter each tube in the plurality of thermally conductive tubes. Each tube in the plurality of thermally conductive tubes further includes a second end that is fluidly connected to only one of the at least one internal ink reservoir in the plurality of printheads. Each second end of each thermally conductive tube is connected to a different internal ink reservoir than the other second ends of the other thermally conductive tubes in the plurality of thermally conductive tubes to enable each tube in the plurality of thermally conductive tubes to supply melted phase change ink to only one internal ink reservoir of one printhead in the plurality of printheads. Each thermoelectric device in the plurality of thermoelectric devices is operatively connected to only one of the thermally conductive tubes and each thermoelectric device is operatively connected to a thermally conductive tube that is different than the thermally conductive tubes to which the other thermoelectric devices in the plurality of thermoelectric devices are operatively connected. The controller is operatively connected to each thermoelectric device in the plurality of thermoelectric devices. The controller is configured to selectively operate each thermoelectric device independently of the other thermoelectric devices in the plurality of thermoelectric devices to heat independently each thermally conductive tube to melt phase change ink within each tube to enable melted phase change ink to flow from the first ink reservoir to the internal ink reservoir to which the tube is fluidly connected, and to remove heat independently from each thermally conductive tube to solidify the melted phase change ink within the tube to disable flow of the phase change ink from the first ink reservoir to the internal ink reservoir to which the tube is fluidly connected.

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 terms “printer,” “printing device,” or “imaging device” generally refer to a device that produces an image with one or more colorants on print media and may encompass any such apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, or the like, which generates printed images for any purpose. Phase change ink printers use phase change ink, also referred to as a solid ink, which is in a solid state at room temperature but melts into a liquid state at a higher operating temperature.

The term “printhead” as used herein refers to a component in the printer that is configured with an array of inkjet ejectors that are operated by firing signals to eject ink drops onto an image receiving surface. The firing signals operate actuators in the inkjet ejectors to expel ink through the nozzles of the inkjet ejectors. In some embodiments, the inkjets in an array of inkjets 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. Some printer embodiments include a plurality of printheads arranged in a print zone. An image receiving surface, such as a print medium or the surface of an intermediate member that enables formation of an ink image, moves past the printheads in a process direction through the print zone. The inkjets in the printheads eject ink drops in rows in a cross-process direction, which is perpendicular to the process direction across the image receiving surface.

FIG. 1is a schematic diagram of an ink transport system100installed in a printer. The ink transport system100includes an external reservoir104, a printhead140, a thermally conductive tube124, which fluidly connects the external reservoir to the printhead140, and a controller180. The external reservoir104is configured to store a volume of liquid ink160, and includes a heater (not shown) to enable ink in the external reservoir104to remain in a liquid state. In some embodiments, the external reservoir can be configured to receive melted ink from an ink melt plate, which melts solid ink sticks or pellets inserted into an ink delivery system of the printer, to supply the external reservoir with liquid phase change ink. In other embodiments, the external reservoir can be positioned to enable solid phase change ink to be delivered directly to the external reservoir, where the ink melts in the heated reservoir.

The printhead140includes an internal reservoir144and an ink level sensor148. The internal reservoir144is fluidly connected to a plurality of inkjets that terminate in apertures on a faceplate of the printhead140to enable the internal reservoir144to supply liquid phase change ink to the inkjets for ejection through the apertures or nozzles onto an image receiving surface. The ink level sensor148is operatively connected to the internal ink reservoir144, and is configured to detect the amount of ink in the internal reservoir144and generate an electrical signal corresponding to the amount of ink detected. The ink level sensor148can be any suitable sensor for determining the amount of ink in the internal reservoir144, for example, a float sensor, an optical sensor, a capacitive sensor, a pressure transducer, an electrical resistance sensor, a thermistor, or a thermocouple.

The thermally conductive tube124is operatively connected to the external and internal ink reservoirs to fluidly connect the reservoirs. The tube124includes a thermoelectric device120and a pressure source108. In the embodiment ofFIG. 1, the pressure source is a pump configured to move the liquid ink through the tube124, although any suitable pressure source capable of urging the liquid ink from the external reservoir through the thermally conductive tube to the internal reservoir can be used. The thermoelectric device120is a thermoelectric cooler (“TEC”), also known as a Peltier device, which includes alternating P-type and N-type semiconductors electrically connected in series in a manner known in the art to enable the device120to pull heat from one side of the device and expel heat from the other side of the thermoelectric device120when an electric current is applied through the device120. The heat flow in the thermoelectric device120is reversible, such that reversing the direction of the current applied to the device120switches the direction of heat flow through the device120. By controlling the direction of electrical current through the device120, the device120can selectively heat or cool the surface to which it is attached. The thermoelectric device120is positioned to enable one side to contact the thermally conductive tube124, while the other side of the device120is attached to a heat sink to enable the device120to dissipate heat. Thus, application of an electric current having a first polarity through the thermoelectric device120removes heat from the heat sink and heats the thermally conductive tube124, while application of an electric current having an opposite polarity to the first polarity removes heat from the thermally conductive tube124and expels heat into the heat sink. In other embodiments, the side of the thermoelectric device not coupled to the thermally conductive tube can be open to atmosphere or thermally connected to an ink reservoir to enable the thermoelectric device to supply heat to the ink reservoir while cooling the tube.

The controller180is operatively connected to the ink level sensor148, the thermoelectric device120, and the pressure source108. The controller180receives the electrical signal generated by the ink level sensor148, and, based on the level of ink detected by the sensor148, the controller180is configured to determine the direction or polarity of the current to be supplied to the thermoelectric device120. For example, when the ink level in the internal reservoir is low, the controller180operates the thermoelectric device120to heat the tube, melting the ink in the tube124. The controller is further configured to activate the pressure source108while the ink in the tube124is in a liquid state to urge the liquid ink160from the external reservoir104through the tube124to the internal reservoir144of the printhead140. Once the reservoir is full, the controller is configured to reverse the polarity of the power supplied to the thermoelectric device120to remove heat from the thermally conductive tube124, solidifying the ink in the tube124and blocking the flow of ink from the external reservoir104to the internal reservoir144.

In operation, the amount of ink in the printhead internal reservoir144decreases as the printhead140ejects ink onto image receiving members or performs maintenance operations that use ink. The ink level sensor148generates a signal corresponding to the amount of ink in the internal reservoir144at predetermined intervals, and delivers the signal to the controller180. Once the sensor detects that the ink level in the internal reservoir144is below a lower threshold, the controller activates the thermoelectric device120to apply heat to the thermally conductive tube124, melting solid ink164that is in the thermally conductive tube124. The controller activates the pressure source108to urge the liquid ink160from the external reservoir, through the thermally conductive tube124, where ink has been liquefied by the thermoelectric device120, and into the internal reservoir144of the printhead140. When the ink level sensor148detects that the ink level in the internal reservoir144is above an upper threshold, the controller180deactivates the pressure source108and reverses the polarity of the electric power supplied to the thermoelectric device120, which then removes heat from the thermally conductive tube124. In response, the phase change ink164in the thermally conductive tube124solidifies, blocking the flow of ink through the tube124.

FIG. 2is a schematic diagram of an ink transport system200for a printer having multiple printheads. The ink transport system200includes an external reservoir204, four printheads240A-D, four thermally conductive tubes224A-D, and a controller280. While the embodiment ofFIG. 2includes four printheads, the reader should appreciate that the ink transport system can be used in a printer including any number of printheads. In addition, multiple ink transport systems can be installed in a single printer, for example, one transport system for each color of ink printed by the printer. In one embodiment, a printer has four printheads, each of which has four internal ink reservoirs, one for each CMYK (cyan, magenta, yellow, and black) color. The printer also has four ink transport systems, each having four thermoelectric devices and four thermally conductive tubes to convey each CMYK color to the appropriate internal ink reservoir of each printhead. Each transport system thus enables ink of a single color to be delivered to one reservoir in each of the four printheads corresponding to the color of the external reservoir coupled to the particular transport system.

The external reservoir204is configured to store a volume of liquid ink260, and includes a heater (not shown) to enable ink in the external reservoir204to remain in a liquid state. In the embodiment ofFIG. 2, the external reservoir204includes a pressure source208, for example, an air compressor to pressurize the air inside the external reservoir204and enable the ink to flow from the external reservoir204toward the printheads240A-D.

Each of the printheads240A-D includes an internal reservoir244A-D and an ink level sensor248A-D. The internal reservoirs244A-D are each fluidly connected to a plurality of inkjets located in apertures on a faceplate of the corresponding printhead240A-D to enable the internal reservoirs244A-D to supply ink to the inkjets for ejection onto an image receiving surface. Each ink level sensor248A-D is operatively connected to one of the internal ink reservoirs244A-D, and is configured to detect the amount of ink in the corresponding internal reservoir244A-D and generate an electrical signal indicative of the amount of ink in the internal reservoir244A-D.

The thermally conductive tubes224A-D fluidly connect the external ink reservoir204with internal ink reservoirs244A-D, respectively. The thermoelectric devices220A-D of the illustrated embodiment are thermoelectric coolers, also known as Peltier devices, which include alternating P-type and N-type semiconductors electrically connected in series in a manner known in the art to enable the devices to pull heat from one side of the device and expel the heat from the other side of the thermoelectric device when an electric current is applied through the device. The thermoelectric devices220A-D are reversible, such that reversing the direction of the current applied to the devices220A-D reverses the direction of heat flow through the device220A-D. The thermoelectric devices220A-D are positioned to enable one side to contact the corresponding thermally conductive tube224A-D, while the other side of the device220A-D is connected to a heat sink. As noted above, in some configurations, the thermoelectric devices can be connected to the ink reservoir or open to ambient air on the other side of the device. Thus, application of an electric current having a first polarity through the thermoelectric devices220A-D removes heat from the heat sink and heats the corresponding thermally conductive tube224A-D, while application of an electric current having a polarity opposite to the first polarity removes heat from the thermally conductive tubes224A-D and expels heat into the heat sink.

The controller280is operatively connected to the ink level sensors248A-D, the thermoelectric devices220A-D, and the pressure source208. The controller280receives the electrical signal generated by each of the ink level sensors248A-D, and, based on the level of ink detected by the sensors248A-D, individually and independently determines the polarity of the power to supply to each of the thermoelectric devices220A-D. When the controller280operates any of the thermoelectric devices220A-D to heat one of the thermally conductive tubes224A-D, the controller280is configured to activate the pressure source208and generate an elevated air pressure in the external reservoir204to enable flow of the liquid ink260from the external reservoir204toward the internal reservoirs244A-D. The controller can be configured to activate the pressure source208immediately, or the controller can be programmed to delay before activating the pressure to enable the ink in the tube to melt before activating the pressure source. In another embodiment, the pressure source208can be active at all times when the printer is on. In some embodiments, the pressure source can be a fluid pressure source, for example, a gear pump, to urge ink from the external reservoir toward the internal reservoirs.

In operation, the amount of ink in the printhead internal reservoirs244A-D decreases as the corresponding printhead240A-D ejects ink onto image receiving surface(s) or performs maintenance operations that use ink. The amount of ink in each of the reservoirs244A-D decreases at differing rates, depending on the amount of ink ejected by each printhead240A-D, necessitating individual and independent control of the ink supplied to each printhead reservoir244A-D. Each of the ink level sensors248A-D generates a signal corresponding to the amount of ink in the corresponding internal reservoir244A-D at predetermined intervals, and the signals are delivered to the controller280. When one of the sensors248A-D detects that the ink level in the corresponding internal reservoir244A-D is below a lower threshold, the controller activates the corresponding thermoelectric device220A-D to apply heat to the thermally conductive tube224A-D and melt solid ink present in the corresponding thermally conductive tube224A-D. The controller activates the pressure source208to urge the liquid ink260from the external reservoir204, through the thermally conductive tube(s)224A-D where ink has been liquefied by the heated thermoelectric device220A-D, and into the internal reservoir244A-D that the sensor248A-D indicated as being low. When the ink level sensor248A-D corresponding to the heated thermoelectric device220A-D detects that the ink level in the internal reservoir244A-D is above an upper threshold, the controller280reverses the polarity of the electric power supplied to the heated thermoelectric device220A-D, which then begins cooling the corresponding thermally conductive tube224A-D. The phase change ink in the cooled thermally conductive tube224A-D solidifies, blocking the flow of ink through the tube and terminating the refill process.

FIG. 3is a schematic diagram of an ink transport system300for a printer having multiple printheads that does not use a pressure source to urge ink through the tubes to the printheads. The ink transport system300includes an external reservoir304, four printheads340A-D, four thermally conductive tubes324A-D, and a controller380. The external reservoir304is configured to store a volume of liquid ink360, and includes a heater (not shown) to enable ink in the external reservoir304to remain in a liquid state.

Each of the printheads340A-D includes an internal reservoir344A-D and an ink level sensor348A-D. The internal reservoirs344A-D are each fluidly connected to a plurality of inkjets located in apertures on a faceplate of the corresponding printhead340A-D to enable the internal reservoirs344A-D to supply ink to the inkjets for ejection onto an image receiving surface. Each ink level sensor348A-D is operatively connected to one of the internal ink reservoirs344A-D, and is configured to detect the amount of ink in the corresponding internal reservoir344A-D and generate an electrical signal indicative of the amount of ink in the internal reservoir344A-D.

The thermally conductive tubes324A-D fluidly connect the external ink reservoir304with the corresponding internal ink reservoirs344A-D. Each tube324A-D includes a thermoelectric device320A-D configured to remove heat from one side of the device and expel heat from the other side of the device when current is applied through the thermoelectric device. The thermoelectric devices320A-D are positioned to enable one side to contact the corresponding thermally conductive tube324A-D, while the other side of the device320A-D is coupled to a heat sink. As noted above, in some configurations, the thermoelectric devices can be connected to the ink reservoir or open to ambient air on the other side of the device. Application of an electrical current having a first polarity through the thermoelectric devices320A-D removes heat from the heat sink and applies heat to the corresponding thermally conductive tube324A-D, while application of an electric current having a polarity opposite to the first polarity removes heat from the thermally conductive tube324A-D and transfers heat to the heat sink.

The controller380is operatively connected to the ink level sensors348A-D and the thermoelectric devices320A-D. The controller380receives the electrical signals generated by the ink level sensors348A-D, and, based on the level of ink detected by the sensors348A-D, individually determines the polarity of the power supplied to each of the thermoelectric devices320A-D.

In operation, the amount of ink in the printhead internal reservoirs344A-D decreases as the corresponding printhead340A-D ejects ink onto image receiving members or performs maintenance operations that use ink. The amount of ink in each of the reservoirs344A-D decreases at differing rates, depending on the amount of ink ejected by each printhead340A-D, necessitating individual control of the ink supplied to each printhead reservoir344A-D. Each of the ink level sensors348A-D generates a signal at predetermined intervals corresponding to the amount of ink in the corresponding internal reservoir344A-D, and the signals are delivered to the controller380. When one of the sensors348A-D detects that the ink level in the corresponding internal reservoir344A-D is below a lower threshold, the controller380activates the corresponding thermoelectric device320A-D to apply heat to the thermally conductive tube224A-D, melting solid ink that is in blocking the corresponding thermally conductive tube324A-D. In the embodiment shown inFIG. 3, the external ink reservoir304is positioned above the printheads340A-D to enable gravity and fluid pressure to urge the liquid ink360to flow from the external reservoir304, through any of the thermally conductive tubes324A-D that are not blocked by solid ink, and into the corresponding internal reservoirs344A-D. When the ink level sensor348A-D corresponding to a heated thermoelectric device320A-D detects that the ink level in the corresponding internal reservoir344A-D is above an upper threshold, the controller380reverses the polarity of the electric power supplied to the heated thermoelectric device320A-D, which cools the corresponding thermally conductive tube324A-D. The phase change ink in the cooled thermally conductive tubes324A-D solidifies, blocking the flow of ink through the tube and terminating the refill process.

Operation and control of the various components and functions of the ink transport system are performed with the aid of the controller. The controller can be implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions are stored in memory associated with the processors or controllers. The processors, their memories, and interface circuitry configure the components of the system to perform the functions described above and the processes described below. The controller components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits.

FIG. 4depicts a process400for transporting ink to refill a printhead reservoir in a phase change ink printer. The process refers to a controller, such as the controllers180,280, and380described above, executing programmed instructions stored in a memory operatively connected to the controller to cause the controller to operate one or more components of the system to perform the specified function or action described in the process. The process400is illustrated for a system having a single internal reservoir. However, the reader will appreciate that the process can be performed in parallel for multiple thermoelectric devices in a printer with multiple internal reservoirs.

The process400begins with the controller receiving a signal from the sensor in the internal reservoir indicating an amount of ink in the internal reservoir (block410). The controller then determines whether the amount of ink in the internal reservoir is below the lower threshold (block420). If the amount is below the lower threshold, then the controller activates the thermoelectric device to generate heat in the tube (block430), melting the ink in the tube and enabling ink to flow from the external reservoir to the internal reservoir, as described above. In the embodiment ofFIG. 2described above, this processing also includes operation of the pressure source to urge melted ink through the tube to the printhead. The process then repeats from block410. If the amount of ink in the internal ink reservoir is not below the lower threshold, then the controller determines if the amount of ink in the internal reservoir is above the upper threshold (block440). If the amount of ink is above the upper threshold, then the controller activates the thermoelectric device to remove heat from the tube (block450), stopping flow of ink to the internal reservoir, and the process repeats from block410. If the internal ink reservoir is neither above the upper threshold nor below the lower threshold, then the controller does not change the operation of the thermoelectric device (block460). Thus, when the reservoir is between the lower and upper thresholds, the controller allows the reservoir to continue depleting until reaching the lower threshold or filling until reaching the upper threshold. In some embodiments, the controller is configured to deactivate the thermoelectric device after the ink in the tube has solidified, and the thermoelectric device remains off until the amount of ink in the internal reservoir falls below the lower threshold. The process then repeats from block410.