Abstract:
Methods and apparatuses for compensating for changes in delivery pressure and protection of a printhead against increased ink flow resistance caused by air trapped in the felt or foam are described. In an exemplary embodiment, ink ejection flow rates are adjusted to keep delivery pressures safely at or below the maximum sustainable delivery pressure required to protect a micro-fluid ejection device of a printhead assembly.

Description:
FIELD OF THE INVENTION 
   The present invention relates to ink jet printing, and, more particularly, to methods and apparatuses for protecting a micro-fluid ejection device against changes in fluid delivery pressures caused by air trapped in felt or foam. 
   BACK GROUND OF THE INVENTION 
   An imaging apparatus, such as an ink jet printer, forms an image on a print medium, such as paper, by applying ink to the print medium. The ink may be contained in one or more replaceable supply cartridges. Examples of such replaceable supply cartridges include a replaceable ink tank and an ink jet printhead cartridge. An ink jet printhead cartridge, for example, includes both an ink tank and a printhead (e.g., an ink jet micro-fluid ejection device) in a unitary device. In contrast, a replaceable ink tank is indirectly coupled via a fluid interface to a separate micro-fluid ejection device, and wherein the micro-fluid ejection device forms part of a printhead assembly that is separately attached to the printhead carrier. 
   Each supply cartridge used by an ink jet printer will have a certain ink volume. Continued printing beyond the intended delivery volume causes delivery pressures to increase dramatically. These high delivery pressures inhibit ink flow to the nozzles of the printhead, and instead of ink flow, air will be ingested into the printhead through the nozzles. As a result, the life of the printhead may be drastically shortened. 
   One such ink jet printer includes an ink tank system, and mounts a plurality of ink tanks, with each ink tank containing a supply of a particular color of ink, e.g., black, cyan, magenta, and yellow. Each ink tank is mounted to a micro-fluid ejection device that is separately mounted to the printhead carrier, and is commonly referred to as an on-carrier ink tank system. In an on-carrier ink tank system, for example, the ink is transferred from the ink tank to the micro-fluid ejection device through as series of fluid interfaces, e.g., a felt ink retaining member located in the ink tank and a wick located on the printhead assembly. 
   A typical ink tank includes a free ink chamber separated from a felt chamber by a dividing wall. The felt chamber has inserted therein the felt ink retaining member. The divider wall between the free ink chamber and the felt chamber has an ink communication port, sometimes referred to in the art as a “bubbler window”, to allow transfer of air and ink between the two chambers. The term “bubbling” refers to the process of air and liquid exchange through the communication port, aka “bubbler window”. Air enters the free ink chamber, which in turn allows ink from the free ink chamber to move into the felt chamber. 
   The felted chamber is used to maintain a constant pressure while the free ink drains from the free ink chamber. Typically speaking, an ink tank has reached its end of life when the free ink is completely drained from the free ink chamber. However, even after the free ink is out, a deliverable reserve of ink remains in the felt. This reserve is depleted when the delivery pressure equals the maximum pressure the printhead can sustain without ingesting air. Utilizing this reserve has advantages and disadvantages. If the free ink is depleted in the middle of a print job, the reserve can be used to complete the job. However, when the reserve is used the felt naturally ingests air as the ink drains. This air ingestion is not a concern if the current ink tank is replaced by a new ink tank. However, this ingesting of air may pose a problem when a user opts to refill the tank in lieu of purchasing a new tank. 
   The addition of new ink into an ink tank complicates ink flow, especially if air was ingested into the felt. Experiments have shown that the majority of this air remains trapped in the felt after new ink is added. The air trapped in the felt increased ink flow resistance through the felt and jeopardizes the micro-fluid ejection printhead. 
   SUMMARY OF THE INVENTION 
   Methods and apparatuses for compensating for changes in delivery pressure and protection of a printhead against increased ink flow resistance caused by air trapped in the felt or foam are described. In an exemplary embodiment, ink ejection flow rates are adjusted to keep delivery pressures safely at or below the maximum sustainable delivery pressure required to protect a micro-fluid ejection device of a printhead assembly. 
   In one exemplary embodiment, a method is described that includes starting a print job; detecting whether free ink is present in a supply cartridge; if free ink is detected, and a memory device associated with the supply cartridge indicates no free ink is available, then designating the supply cartridge as having had new ink added; reducing a print speed from a normal print speed associated with the original fill to a new print speed required to protect the printhead; printing a page of the print job at the adjusted print speed; again detecting whether free ink is present in a supply cartridge; and if no free ink is detected, utilizing a reserve amount of ink that remains in an ink suspension body of the supply cartridge to continue printing the print job at the adjusted print speed. 
   The invention, in another form thereof, is directed to an imaging apparatus. The imaging apparatus includes a print engine having a printhead carrier. A printhead assembly is configured to be mounted to the printhead carrier. A removable ink tank is configured to be mounted to the printhead assembly. The removable ink tank includes a free ink chamber and a suspended ink chamber. The suspended ink chamber has an ink output port and contains an ink suspension body. The suspended ink chamber is separated from the free ink chamber by a divider wall. The divider wall has an ink communication port to facilitate fluid communication between the free ink chamber and the suspended ink chamber. The output port is in fluid communication with the printhead assembly. A memory is associated with the removable ink tank. A controller is communicatively coupled to the print engine, the printhead assembly, and the memory. The controller executes program instructions for determining whether the removable ink tank has had new ink added, wherein: if the removable ink tank has had ink added, then printing is performed at a normal ink ejection rate, and if the removable ink tank has had new ink added, then printing is performed at an adjusted ink ejection rate that protects the micro-fluid ejection device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a diagrammatic depiction of an imaging system embodying the present invention. 
       FIG. 2  is a perspective view of the printhead carrier of  FIG. 1 , with the printhead assembly and ink tanks uninstalled. 
       FIG. 3  is a sectional view of one of the removable ink tanks of  FIG. 2  taken along line  3 - 3 . 
       FIG. 4  is a graph that plots volume delivered (X-axis) to delivery pressure (Y-axis) for three different conditions. 
       FIG. 5  is a general flowchart of a method for compensating for a refill of a supply cartridge, such as an ink tank, in accordance with an embodiment of the present invention. 
       FIGS. 6A and 6B  form a flowchart of a method for compensating for a refilled supply cartridge for printing, associated with another implementation of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , there is shown a diagrammatic depiction of an imaging system  10  embodying the present invention. Imaging system  10  may include a host  12  and an imaging apparatus  14 . Imaging apparatus  14  communicates with host  12  via a communications link  16 . Communications link  16  may be established by a direct cable connection, wireless connection or by a network connection such as for example an Ethernet local area network (LAN). 
   Alternatively, imaging apparatus  14  may be a standalone unit that is not communicatively linked to a host, such as host  12 . For example, imaging apparatus  14  may take the form of an all-in-one, i.e., multifunction, machine that includes standalone copying and facsimile capabilities, in addition to optionally serving as a printer when attached to a host, such as host  12 . 
   Host  12  may be, for example, a personal computer including an input/output (I/O) device, such as keyboard and display monitor. Host  12  further includes a processor, input/output (I/O) interfaces, memory, such as RAM, ROM, NVRAM, and a mass data storage device, such as a hard drive, CD-ROM and/or DVD units. During operation, host  12  may include in its memory a software program including program instructions that function as an imaging driver, e.g., printer driver software, for imaging apparatus  14 . Alternatively, the imaging driver may be incorporated, in whole or in part, in imaging apparatus  14 . 
   In the embodiment of  FIG. 1 , imaging apparatus  14  includes a controller  18 , a print engine  20  and a user interface  22 . 
   Controller  18  includes a processor unit and associated memory, and may be formed as an Application Specific Integrated Circuit (ASIC). Controller  18  communicates with print engine  20  via a communications link  24 . Controller  18  communicates with user interface  22  via a communications link  26 . Communications links  24  and  26  may be established, for example, by using standard electrical cabling or bus structures, or by wireless connection. 
   Print engine  20  may be, for example, an ink jet print engine configured for forming an image on a sheet of print media  28 , such as a sheet of paper, transparency or fabric. Print engine  20  may include, for example, a reciprocating printhead carrier  30 . 
     FIG. 2  shows in a perspective view printhead carrier  30 , with a printhead assembly  32  and a plurality of removable ink tanks  34  in an uninstalled state. Printhead carrier  30  is mechanically and electrically configured to mount and carry at least one printhead assembly  32  that includes at least one printhead, e.g., ink jet micro-fluid ejection device  36 , and is communicatively coupled to controller  18  via communications link  24 . Printhead assembly  32  is mounted into position to printhead carrier  30  by inserting printhead assembly  32  into a cavity  38  in printhead carrier  30 , and is latched in position by a mounting lever  40 . Printhead carrier  30  transports printhead assembly  32 , and in turn ink jet micro-fluid ejection device  36 , in a reciprocating manner in a bi-directional main scan direction, i.e., axis,  42  over an image surface of the sheet of print media  28  during a printing operation. 
   Printhead assembly  32  is configured to mount and carry the plurality of removable ink tanks  34 , and to facilitate an ink transfer from one or more of the plurality of removable ink tanks  34  to micro-fluid ejection device  36 . The plurality of removable ink tanks  34  may be made, for example, from plastic. The plurality of ink tanks  34  are individually identified as ink tanks  34 - 1 ,  34 - 2 ,  34 - 3  and  34 - 4 , and may include a monochrome ink tank containing black ink, and three color ink tanks containing cyan, magenta, and yellow inks. Micro-fluid ejection device  36  may include an ink jet nozzle array for each color of ink. 
   In the present embodiment, each of ink tanks  34 - 1 ,  34 - 2 ,  34 - 3  and  34 - 4  form a respective supply cartridge that is removably mounted to printhead assembly  32 . Those skilled in the art, however, will recognize that a unitary supply cartridge may be formed by the combination of the ink tank(s) with the printhead assembly to form an ink jet printhead cartridge. As used herein, the term “supply cartridge” includes both an ink tank that is separable from a printhead assembly, as well as a unitary ink jet printhead cartridge that integrally combines the ink tank and printhead as a non-separable unit. 
   Printhead assembly  32  includes a printhead body  44  and a filter cap  46 . Those skilled in the art will recognize that some printhead assemblies may not include a filter cap. Micro-fluid ejection device  36  is attached to a snout portion of printhead body  44 . Filter cap  46  is attached to printhead body  44  via a hermetic seal, such as by welding or adhesive attachment. Filter cap  46  has a filter cap body  48  configured with a plurality of ink receiving devices  50 , individually identified as ink receiving device  50 - 1 , ink receiving device  50 - 2 , ink receiving device  50 - 3 , and ink receiving device  50 - 4 . Each ink receiving device  50 - 1 ,  50 - 2 ,  50 - 3 , and  50 - 4  includes a respective wick  52 - 1 ,  52 - 2 ,  52 - 3 , and  52 - 4  that operably engages and facilitates fluid communication with the respective ink output ports of ink tanks  34 - 1 ,  34 - 2 ,  34 - 3  and  34 - 4 , respectively. Each of wicks  52 - 1 ,  52 - 2 ,  52 - 3 , and  52 - 4  may be constructed from a porous material, such as for example, from a porous felt material or a porous foam material. Also, those skilled in the art will recognize that some printhead assemblies may not include a wick. 
   Associated with each of ink tanks  34 - 1 ,  34 - 2 ,  34 - 3  and  34 - 4  is a respective memory device  56 - 1 ,  56 - 2 ,  56 - 3 ,  56 - 4 , such as for example, a memory chip or an RFID circuit, that is communicatively coupled to controller  18  via communications link  24  (see  FIG. 1 ). 
   Ink tanks  34 - 1 ,  34 - 2 ,  34 - 3  and  34 - 4  are individually mounted to printhead assembly  32  via individual ink tank latches  54 - 1 ,  54 - 2 ,  54 - 3  and  54 - 4 . Actuating, e.g., deflecting, a respective ink tank latch  54 - 1 ,  54 - 2 ,  54 - 3  and  54 - 4 , releases a respective ink tank  34 - 1 ,  34 - 2 ,  34 - 3 ,  34 - 4  to allow removal of the respective ink tank  34 - 1 ,  34 - 2 ,  34 - 3 ,  34 - 4  from printhead assembly  32 , and more particularly from printhead body  44 . 
     FIG. 3  is a section view taken along line  3 - 3  of one of the removable ink tanks  34 , and in particular, ink tank  34 - 1  in this example. Each of removable ink tanks  34  are similar in design, varying only in size in the present embodiment. Accordingly, for convenience and ease of discussion, the following description will specifically reference ink tank  34 - 1 , hut those skilled in the art will recognize that the description may be applied equally to each of ink tank  34 - 2 , ink tank  34 - 3 , and ink tank  34 - 4 . 
   Ink tank  34 - 1  includes a free ink chamber  58  and a suspended ink chamber  60 . Associated with free ink chamber  58  is an ink sensor  59 . Ink sensor  59  may be, for example, an optical sensor. Free ink chamber  58  includes a free-flowing supply of ink FI, referred to herein as free ink, and is positioned adjacent to suspended ink chamber  60 . Free ink chamber  58  is separated from suspended ink chamber  60  by a divider wall  62 . Divider wall  62  has an ink communication port, i.e., bubbler window,  64  to provide fluid communication between free ink chamber  58  and suspended ink chamber  60 . 
   Ink tank  34 - 1  has a floor  66 , and a plurality of side walls  68 , for example, a first side wall  68 - 1  and a second side  68 - 2 , extending upwardly away from floor  66 . Side wall  68 - 2  is separated from side wall  68 - 1 , with divider wall  62  being interposed between and connected to each of side wall  68 - 1  and side wall  68 - 2 . In the present embodiment, ink communication port, i.e., bubbler window,  64  is located in a lower portion of divider wall  62  near floor  66 . 
   Floor  66  includes a first floor portion  66 - 1  and a second floor portion  66 - 2 . Free ink chamber  58  is located over first floor portion  66 - 1  of floor  66 . Suspended ink chamber  60  is located over second floor portion  66 - 2  of floor  66  around an ink output port  70  formed through second floor portion  66 - 2  of floor  66 . Ink output port  70  facilitates fluid communication with printhead assembly  32  when ink tank  34 - 1  is installed on printhead assembly  32 . 
   Positioned in suspended ink chamber  60  is an ink suspension body  72  that provides a restriction to prevent a free-flow of ink through suspended ink chamber  60  to ink output port  70  and produce a negative pressure. In the present embodiment, ink suspension body  72  may include, for example, a lower ink suspension body  74  and an upper ink suspension body  76 . In this example, lower ink suspension body  74  is positioned adjacent to floor  66 . Upper ink suspension body  76  is positioned in suspended ink chamber  60  adjacent to and above lower ink suspension body  74 . Each of lower ink suspension body  74  and upper ink suspension body  76  may be constructed from a porous material, such as for example, from a porous felt material or a porous foam material. Lower ink suspension body  74  has a porous ink transfer surface  78  positioned above ink output port  70 , which is engaged and deflected by ink receiving device  50 - 1  and its associated wick  52 - 1  when ink tank  34 - 1  is installed in printhead assembly  32 . 
   In the present embodiment, lower ink suspension body  74  and an upper ink suspension body  76  may be configured with materials having different porosities. Alternatively, ink suspension body  72  may be formed from a single unitary porous material, if desired. 
     FIG. 4  is a graph that plots ink volume delivered (in cubic centimeters (cc); X-axis) to delivery pressure (in centimeters of water column (cmH 2 O); Y-axis) for three different conditions. The first condition is represented by plot  80 , and is associated with the original fill of ink tank  34 - 1  at an ink ejection rate of 5 milligrams per second (mg/sec). The second condition is represented by plot  82 , and represents a refill of ink tank  34 - 1  at an ink ejection rate of 5 mg/sec. Plot  84  represents the same refill of ink tank  34 - 1 , but at an ink ejection rate of 1.5 mg/sec. The ink ejection rate is the rate at which ink is expelled through micro-fluid election device  36  of printhead assembly  32 . The ink ejection rate is determined, at least in part, on the print speed of imaging apparatus  14 , such as for example, the velocity (speed) at which printhead carrier  30  reciprocates along bi-directional main scan direction (axis)  42  during printing. 
   As used herein, the term “normal ink ejection rate” is the ink ejection rate of an ink tank and associated printhead assembly, e.g., ink tank  34 - 1  and printhead assembly  32 , with the ink tank containing the original fill of ink. The term “refill ink ejection rate” is the ink ejection rate of an ink tank and associated printhead assembly, e.g., ink tank  34 - 1  and printhead assembly  32 , with the ink tank having been refilled with ink to replenish the ink supply in the ink tank after the original fill has been significantly depleted. 
   Plot  80  demonstrates that the maximum sustainable delivery pressure for ink tank  34 - 1  with the original fill is 10 cmH 2 O at a 5 mg/sec ink ejection rate. However, as demonstrated by plot  82 , the same ink tank  34 - 1  after refill will exceed the maximum sustainable delivery pressure 10 cmH 2 O at a 5 mg/sec ink ejection rate, e.g., will only drain from ink suspension body  72  at 5 mg/sec ink ejection rate since the flow resistance from the free ink chamber  58  to ink output port  70  is too high, thus in effect blocking the flow from free ink chamber  58  into suspended ink chamber  60 . As demonstrated by plot  84 , equivalent delivery pressures to those of plot  80 , i.e., at the maximum sustainable delivery pressure of 10 cmH 2 O, are not experienced unless the flow rate is reduced to 1.5 mg/sec. In the present example, the ratio of ink ejection rate reduction is 1.5 to 5, or 30 percent of the ink ejection rate of the original fill of ink tank  34 - 1 . 
     FIG. 5  is a general flowchart of a method for compensating for a refilled supply cartridge, such as ink tank  34 - 1 , for printing, in accordance with an embodiment of the present invention. The method associated with the flowchart of  FIG. 5  may be implemented, for example, as program instructions executed by controller  18 . 
   At act S 100 , it is determined whether the supply cartridge, e.g., ink tank  34 - 1 , has been refilled. 
   For example, the memory device on the supply cartridge, e.g., memory device  56 - 1  of ink tank  34 - 1 , may be used to record ink usage information relating to the depletion of the ink supply contained in the supply cartridge from full to its end of life. For example, by controller  18  counting the number of ink drops ejected from ink tank  34 - 1 , and knowing the nominal ink drop volume and total original fill ink volume of ink tank  34 - 1 , an amount of ink remaining in ink tank  34 - 1  may be calculated by controller  18  and stored as ink usage information in memory device  56 - 1 . Also, the ink usage information may include a bit in memory device  56 - 1  that is designated to be set if the amount of ink in the original ink fill of ink tank  34 - 1  has been significantly depleted, i.e., ink tank  34 - 1  has been emptied. 
   Also, in embodiments wherein ink sensor  59  is an optical sensor, for example, optical methods implemented as program instructions executed by controller  18  may be used to detect whether there is free ink in free ink chamber  58 . For example, ink sensor  59  may be in the form of an optical sensor positioned adjacent a window formed in a side wall of free ink chamber  58 , and based on the optical characteristics detected, may indicate a presence or absence of free ink in free ink chamber  58 . 
   If the ink usage information stored in memory device  56 - 1  indicates that ink tank  34 - 1  has been emptied, i.e., the ink supply has been significantly depleted, and ink sensor  59  does not detect free ink in free ink chamber  58 , then ink tank  34 - 1  is assumed to have not been refilled, and any pending print job would not start since free ink chamber  58  is empty. However, if the ink usage information stored in memory device  56 - 1  indicates that ink tank  34 - 1  has been emptied, i.e., the ink supply has been significantly depleted, but ink sensor  59  detects free ink in free ink chamber  58 , then ink tank  34 - 1  is assumed to have been refilled. 
   If the determination at act S 100  is NO, then at act S 102  the printing is performed at the normal ink ejection rate, e.g., at a 5 mg/sec ink ejection rate, and then the process ends. The normal ink ejection rate is a rate correlated to the normal print speed of imaging apparatus  14 , such as for example, the normal velocity (speed) at which printhead carrier  30  reciprocates along bi-directional main scan direction (axis)  42 . Thus, when printhead carrier  30  reciprocates at a normal printhead carrier velocity, the rate of ink ejection is at the normal ink ejection rate. 
   If the determination at act S 100  is YES, then at act S 104  the printing is performed at the refill ink ejection rate, i.e., the ink ejection rate is reduced from the normal ink ejection rate to a predetermined refill ink ejection rate. The amount of reduction of the ink ejection rate with respect to the normal ink ejection rate may be determined empirically (see, for example, the graphical plots of  FIG. 4 ) to keep delivery pressures safely at or below the maximum sustainable delivery pressure to protect micro-fluid ejection device  36  of printhead assembly  32  (see, e.g.,  FIG. 4 ). The refill ink ejection rate is a rate correlated to a predetermined refill print speed of imaging apparatus  14 , such as for example, the predetermined refill velocity (speed) at which printhead carrier  30  reciprocates along bi-directional main scan direction (axis)  42 . The refill print speed is slower than the normal print speed. Thus, when printhead carrier  30  reciprocates at a refill printhead carrier velocity, the rate of ink ejection is at the refill ink ejection rate. 
   For example, the ink ejection rate for ink tank  34 - 1  after a refill, e.g., the refill ink ejection rate, may be reduced to a predetermined percentage, e.g., 30 percent, of the normal ink ejection rate of ink tank  34 - 1  at the original fill. This reduction in ink ejection rate to 30 percent of the normal ink ejection rate corresponds to a reduction in print speed to 30 percent of the normal print speed associated with the normal ink ejection rate. Thus, in the present example, the ink ejection rate will be reduced from the original ink ejection rate of 5 mg/sec to the refill ink ejection rate of 1.5. For the refilled ink tank  34 - 1 , limiting the refill ink ejection rate to 30 percent of the normal (i.e., original fill) ink ejection rate helps to assure that the delivery pressures do not exceed the maximum sustainable delivery pressure (e.g., 10 cmH 2 O) and thereby provides protection for micro-fluid ejection device  36  of printhead assembly  32  against excessive delivery pressures, and to helps prevent air ingestion through the ink jetting nozzles of micro-fluid election device  36 . 
     FIGS. 6A and 6B  form a flowchart of a method for compensating for a refilled supply cartridge for printing, associated with another implementation of the present invention. 
   At act S 200 , a print job is started. The print job may be started, for example, by sending print data from host  12  to imaging apparatus  14 . Initially, the print speed is set to the normal print speed. 
   At act S 202 , it is determined whether an ink sensor, e.g., ink sensor  59 , detects the presence of free ink in the supply cartridge, e.g., ink tank  34 - 1 . 
   If the determination at act S 202  is NO, then the process proceeds to act S 204 . 
   At act S 204  a hit is set in the memory device associated with the supply cartridge, e.g., memory device  56 - 1  of ink tank  34 - 1 , to indicate that the supply cartridge is empty. The process continues to act S 224 . An “OUT OF INK” message is displayed, e.g., at user interface  22 , after which the process ends. In other words, the print job is cancelled since there is no free ink available to complete the print job. 
   If the determination at act S 202  is YES, indicating the presence of free ink in the supply cartridge, then the process proceeds to act S 206 . 
   At act S 206 , it is determined whether the bit in the memory device, e.g., memory device  56 - 1 , indicating that the supply cartridge is empty is set, even though the presence of ink was detected at act S 202 . 
   If the determination at act S 206  is YES, then the process proceeds to act S 208 . 
   At act S 208  the supply cartridge, e.g., ink tank  34 - 1 , is designated as having been refilled. 
   At act S 210 , with the supply cartridge having been determined to have been refilled, the print speed is reduced from a normal print speed to a refill print speed. In other words, the print speed is reduced from the normal print speed associated with the original fill to a refill print speed that is associated with the refilling of the supply cartridge. The print speed is reduced by an amount so as to reduce the ink ejection rate so as to not exceed the maximum sustainable delivery pressure, thereby protecting micro-fluid ejection device  36  of printhead assembly  32  against excessive delivery pressures, and reducing the possibility of air ingestion through the ink jetting nozzles of micro-fluid ejection device  36 . The process then proceeds to act S 212 , with the print speed being at the refill print speed. In the previous example, the refill print speed is about 30 percent of the normal print speed used with the original fill of the supply cartridge. 
   If the determination at act S 206  is NO, then the process proceeds to act S 212 , with the print speed being at the normal print speed. 
   At act S 212 , a page of the print job is printed at the selected print speed, e.g., at the refill print speed in the case of the supply cartridge being determined to have been refilled. 
   At act S 214 , it is determined whether the print job is complete. 
   If the determination at act S 214  is YES, then the process ends. 
   If the determination at act S 214  is NO, then the process proceeds to act S 216 . 
   At act S 216 , it is determined whether the ink sensor, e.g., ink sensor  59 , detects the presence of free ink in the supply cartridge, e.g., ink tank  34 - 1 . While act S 216  will be performed at some point for each print job, the frequency at which act S 216  is performed may be optional. For example, one may choose to check the ink sensor, e.g., ink sensor  59 , after every page, or alternatively, for example, after every 5 pages, or only at the end of the print job. 
   If the determination at act S 216  is YES, then the process returns to act S 212  to print the next page at the selected print speed, e.g., at the refill print speed in the case of the supply cartridge being determined to have been refilled. 
   If the determination at act S 216  is NO, then the process proceeds to act S 218 . 
   At act S 218 , the bit is set in the memory device associated with the supply cartridge, e.g., memory device  56 - 1  of ink tank  34 - 1 , to indicate that the supply cartridge is empty. However, even though the ink sensor, ink sensor  59 , now detects the absence of ink in the supply cartridge, e.g., ink tank  34 - 1 , a reserve amount of suspended ink remains in ink suspension body  72  (e.g., felt) of suspended ink chamber  60 . By experimentation, the reserve amount of ink may be represented in terms of a drop count, i.e., the number of ink drops remaining, and stored in the associated memory, e.g., memory device  56 - 1 . 
   At act S 220 , the next print swath is printed, and the drop count is decremented based on the number of ink drops ejected as the print swath is printed. 
   At act S 222 , it is determined whether the print job is ended. 
   If the determination at act S 222  is YES, then the process proceeds to act S 224 . 
   At act S 224 , an “OUT OF INK” message is displayed, e.g., at user interface  22 , and the process ends. 
   If the determination at act S 222  is NO, then the process proceeds to act S 226 . 
   At act S 226 , it is determined whether the number of drops remaining equals zero. 
   If the determination at act S 226  is NO, then the process returns to act S 220  for printing the next print swath. 
   If the determination at act S 226  is YES, then the process proceeds to act S 224 , wherein the “OUT OF INK” message is displayed, e.g., at user interface  22 , and the process ends. 
   While this invention has been described with respect to embodiments of the invention, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.