Abstract:
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.

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an ink transport system for a printer. 
         FIG. 2  is a schematic view of an ink transport system for a multi-printhead printer. 
         FIG. 3  is a schematic view of another ink transport system for a multi-printhead printer. 
         FIG. 4  is a process diagram of a process for transporting ink in a printer. 
     
    
    
     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. 1  is a schematic diagram of an ink transport system  100  installed in a printer. The ink transport system  100  includes an external reservoir  104 , a printhead  140 , a thermally conductive tube  124 , which fluidly connects the external reservoir to the printhead  140 , and a controller  180 . The external reservoir  104  is configured to store a volume of liquid ink  160 , and includes a heater (not shown) to enable ink in the external reservoir  104  to 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 printhead  140  includes an internal reservoir  144  and an ink level sensor  148 . The internal reservoir  144  is fluidly connected to a plurality of inkjets that terminate in apertures on a faceplate of the printhead  140  to enable the internal reservoir  144  to supply liquid phase change ink to the inkjets for ejection through the apertures or nozzles onto an image receiving surface. The ink level sensor  148  is operatively connected to the internal ink reservoir  144 , and is configured to detect the amount of ink in the internal reservoir  144  and generate an electrical signal corresponding to the amount of ink detected. The ink level sensor  148  can be any suitable sensor for determining the amount of ink in the internal reservoir  144 , 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 tube  124  is operatively connected to the external and internal ink reservoirs to fluidly connect the reservoirs. The tube  124  includes a thermoelectric device  120  and a pressure source  108 . In the embodiment of  FIG. 1 , the pressure source is a pump configured to move the liquid ink through the tube  124 , 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 device  120  is 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 device  120  to pull heat from one side of the device and expel heat from the other side of the thermoelectric device  120  when an electric current is applied through the device  120 . The heat flow in the thermoelectric device  120  is reversible, such that reversing the direction of the current applied to the device  120  switches the direction of heat flow through the device  120 . By controlling the direction of electrical current through the device  120 , the device  120  can selectively heat or cool the surface to which it is attached. The thermoelectric device  120  is positioned to enable one side to contact the thermally conductive tube  124 , while the other side of the device  120  is attached to a heat sink to enable the device  120  to dissipate heat. Thus, application of an electric current having a first polarity through the thermoelectric device  120  removes heat from the heat sink and heats the thermally conductive tube  124 , while application of an electric current having an opposite polarity to the first polarity removes heat from the thermally conductive tube  124  and 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 controller  180  is operatively connected to the ink level sensor  148 , the thermoelectric device  120 , and the pressure source  108 . The controller  180  receives the electrical signal generated by the ink level sensor  148 , and, based on the level of ink detected by the sensor  148 , the controller  180  is configured to determine the direction or polarity of the current to be supplied to the thermoelectric device  120 . For example, when the ink level in the internal reservoir is low, the controller  180  operates the thermoelectric device  120  to heat the tube, melting the ink in the tube  124 . The controller is further configured to activate the pressure source  108  while the ink in the tube  124  is in a liquid state to urge the liquid ink  160  from the external reservoir  104  through the tube  124  to the internal reservoir  144  of the printhead  140 . Once the reservoir is full, the controller is configured to reverse the polarity of the power supplied to the thermoelectric device  120  to remove heat from the thermally conductive tube  124 , solidifying the ink in the tube  124  and blocking the flow of ink from the external reservoir  104  to the internal reservoir  144 . 
     In operation, the amount of ink in the printhead internal reservoir  144  decreases as the printhead  140  ejects ink onto image receiving members or performs maintenance operations that use ink. The ink level sensor  148  generates a signal corresponding to the amount of ink in the internal reservoir  144  at predetermined intervals, and delivers the signal to the controller  180 . Once the sensor detects that the ink level in the internal reservoir  144  is below a lower threshold, the controller activates the thermoelectric device  120  to apply heat to the thermally conductive tube  124 , melting solid ink  164  that is in the thermally conductive tube  124 . The controller activates the pressure source  108  to urge the liquid ink  160  from the external reservoir, through the thermally conductive tube  124 , where ink has been liquefied by the thermoelectric device  120 , and into the internal reservoir  144  of the printhead  140 . When the ink level sensor  148  detects that the ink level in the internal reservoir  144  is above an upper threshold, the controller  180  deactivates the pressure source  108  and reverses the polarity of the electric power supplied to the thermoelectric device  120 , which then removes heat from the thermally conductive tube  124 . In response, the phase change ink  164  in the thermally conductive tube  124  solidifies, blocking the flow of ink through the tube  124 . 
       FIG. 2  is a schematic diagram of an ink transport system  200  for a printer having multiple printheads. The ink transport system  200  includes an external reservoir  204 , four printheads  240 A-D, four thermally conductive tubes  224  A-D, and a controller  280 . While the embodiment of  FIG. 2  includes 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 reservoir  204  is configured to store a volume of liquid ink  260 , and includes a heater (not shown) to enable ink in the external reservoir  204  to remain in a liquid state. In the embodiment of  FIG. 2 , the external reservoir  204  includes a pressure source  208 , for example, an air compressor to pressurize the air inside the external reservoir  204  and enable the ink to flow from the external reservoir  204  toward the printheads  240 A-D. 
     Each of the printheads  240 A-D includes an internal reservoir  244 A-D and an ink level sensor  248 A-D. The internal reservoirs  244 A-D are each fluidly connected to a plurality of inkjets located in apertures on a faceplate of the corresponding printhead  240 A-D to enable the internal reservoirs  244 A-D to supply ink to the inkjets for ejection onto an image receiving surface. Each ink level sensor  248 A-D is operatively connected to one of the internal ink reservoirs  244 A-D, and is configured to detect the amount of ink in the corresponding internal reservoir  244 A-D and generate an electrical signal indicative of the amount of ink in the internal reservoir  244 A-D. 
     The thermally conductive tubes  224 A-D fluidly connect the external ink reservoir  204  with internal ink reservoirs  244 A-D, respectively. The thermoelectric devices  220 A-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 devices  220 A-D are reversible, such that reversing the direction of the current applied to the devices  220 A-D reverses the direction of heat flow through the device  220 A-D. The thermoelectric devices  220 A-D are positioned to enable one side to contact the corresponding thermally conductive tube  224 A-D, while the other side of the device  220 A-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 devices  220 A-D removes heat from the heat sink and heats the corresponding thermally conductive tube  224 A-D, while application of an electric current having a polarity opposite to the first polarity removes heat from the thermally conductive tubes  224 A-D and expels heat into the heat sink. 
     The controller  280  is operatively connected to the ink level sensors  248 A-D, the thermoelectric devices  220 A-D, and the pressure source  208 . The controller  280  receives the electrical signal generated by each of the ink level sensors  248 A-D, and, based on the level of ink detected by the sensors  248 A-D, individually and independently determines the polarity of the power to supply to each of the thermoelectric devices  220 A-D. When the controller  280  operates any of the thermoelectric devices  220 A-D to heat one of the thermally conductive tubes  224 A-D, the controller  280  is configured to activate the pressure source  208  and generate an elevated air pressure in the external reservoir  204  to enable flow of the liquid ink  260  from the external reservoir  204  toward the internal reservoirs  244 A-D. The controller can be configured to activate the pressure source  208  immediately, 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 source  208  can 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 reservoirs  244 A-D decreases as the corresponding printhead  240 A-D ejects ink onto image receiving surface(s) or performs maintenance operations that use ink. The amount of ink in each of the reservoirs  244 A-D decreases at differing rates, depending on the amount of ink ejected by each printhead  240 A-D, necessitating individual and independent control of the ink supplied to each printhead reservoir  244 A-D. Each of the ink level sensors  248 A-D generates a signal corresponding to the amount of ink in the corresponding internal reservoir  244 A-D at predetermined intervals, and the signals are delivered to the controller  280 . When one of the sensors  248 A-D detects that the ink level in the corresponding internal reservoir  244 A-D is below a lower threshold, the controller activates the corresponding thermoelectric device  220 A-D to apply heat to the thermally conductive tube  224 A-D and melt solid ink present in the corresponding thermally conductive tube  224 A-D. The controller activates the pressure source  208  to urge the liquid ink  260  from the external reservoir  204 , through the thermally conductive tube(s)  224 A-D where ink has been liquefied by the heated thermoelectric device  220 A-D, and into the internal reservoir  244 A-D that the sensor  248 A-D indicated as being low. When the ink level sensor  248 A-D corresponding to the heated thermoelectric device  220 A-D detects that the ink level in the internal reservoir  244 A-D is above an upper threshold, the controller  280  reverses the polarity of the electric power supplied to the heated thermoelectric device  220 A-D, which then begins cooling the corresponding thermally conductive tube  224 A-D. The phase change ink in the cooled thermally conductive tube  224 A-D solidifies, blocking the flow of ink through the tube and terminating the refill process. 
       FIG. 3  is a schematic diagram of an ink transport system  300  for a printer having multiple printheads that does not use a pressure source to urge ink through the tubes to the printheads. The ink transport system  300  includes an external reservoir  304 , four printheads  340 A-D, four thermally conductive tubes  324  A-D, and a controller  380 . The external reservoir  304  is configured to store a volume of liquid ink  360 , and includes a heater (not shown) to enable ink in the external reservoir  304  to remain in a liquid state. 
     Each of the printheads  340 A-D includes an internal reservoir  344 A-D and an ink level sensor  348 A-D. The internal reservoirs  344 A-D are each fluidly connected to a plurality of inkjets located in apertures on a faceplate of the corresponding printhead  340 A-D to enable the internal reservoirs  344 A-D to supply ink to the inkjets for ejection onto an image receiving surface. Each ink level sensor  348 A-D is operatively connected to one of the internal ink reservoirs  344 A-D, and is configured to detect the amount of ink in the corresponding internal reservoir  344 A-D and generate an electrical signal indicative of the amount of ink in the internal reservoir  344 A-D. 
     The thermally conductive tubes  324 A-D fluidly connect the external ink reservoir  304  with the corresponding internal ink reservoirs  344 A-D. Each tube  324 A-D includes a thermoelectric device  320 A-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 devices  320 A-D are positioned to enable one side to contact the corresponding thermally conductive tube  324 A-D, while the other side of the device  320 A-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 devices  320 A-D removes heat from the heat sink and applies heat to the corresponding thermally conductive tube  324 A-D, while application of an electric current having a polarity opposite to the first polarity removes heat from the thermally conductive tube  324 A-D and transfers heat to the heat sink. 
     The controller  380  is operatively connected to the ink level sensors  348 A-D and the thermoelectric devices  320 A-D. The controller  380  receives the electrical signals generated by the ink level sensors  348 A-D, and, based on the level of ink detected by the sensors  348 A-D, individually determines the polarity of the power supplied to each of the thermoelectric devices  320 A-D. 
     In operation, the amount of ink in the printhead internal reservoirs  344 A-D decreases as the corresponding printhead  340 A-D ejects ink onto image receiving members or performs maintenance operations that use ink. The amount of ink in each of the reservoirs  344 A-D decreases at differing rates, depending on the amount of ink ejected by each printhead  340 A-D, necessitating individual control of the ink supplied to each printhead reservoir  344 A-D. Each of the ink level sensors  348 A-D generates a signal at predetermined intervals corresponding to the amount of ink in the corresponding internal reservoir  344 A-D, and the signals are delivered to the controller  380 . When one of the sensors  348 A-D detects that the ink level in the corresponding internal reservoir  344 A-D is below a lower threshold, the controller  380  activates the corresponding thermoelectric device  320 A-D to apply heat to the thermally conductive tube  224 A-D, melting solid ink that is in blocking the corresponding thermally conductive tube  324 A-D. In the embodiment shown in  FIG. 3 , the external ink reservoir  304  is positioned above the printheads  340 A-D to enable gravity and fluid pressure to urge the liquid ink  360  to flow from the external reservoir  304 , through any of the thermally conductive tubes  324 A-D that are not blocked by solid ink, and into the corresponding internal reservoirs  344 A-D. When the ink level sensor  348 A-D corresponding to a heated thermoelectric device  320 A-D detects that the ink level in the corresponding internal reservoir  344 A-D is above an upper threshold, the controller  380  reverses the polarity of the electric power supplied to the heated thermoelectric device  320 A-D, which cools the corresponding thermally conductive tube  324 A-D. The phase change ink in the cooled thermally conductive tubes  324 A-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. 4  depicts a process  400  for transporting ink to refill a printhead reservoir in a phase change ink printer. The process refers to a controller, such as the controllers  180 ,  280 , and  380  described 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 process  400  is 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 process  400  begins with the controller receiving a signal from the sensor in the internal reservoir indicating an amount of ink in the internal reservoir (block  410 ). The controller then determines whether the amount of ink in the internal reservoir is below the lower threshold (block  420 ). If the amount is below the lower threshold, then the controller activates the thermoelectric device to generate heat in the tube (block  430 ), 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 of  FIG. 2  described 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 block  410 . 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 (block  440 ). If the amount of ink is above the upper threshold, then the controller activates the thermoelectric device to remove heat from the tube (block  450 ), stopping flow of ink to the internal reservoir, and the process repeats from block  410 . 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 (block  460 ). 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 block  410 . 
     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 or applications. 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.