Patent Publication Number: US-9409410-B2

Title: Image forming apparatus and non-transitory computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application Nos. 2014-209418, filed on Oct. 10, 2014, and 2015-081781, filed on Apr. 13, 2015, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     Aspects of this disclosure relate to an image forming apparatus and a non-transitory computer readable medium storing a program to cause a computer to execute a process for the image forming apparatus. 
     2. Description of the Related Art 
     An image forming apparatus may have a liquid discharge head (droplet discharge head) serving as a recording head to discharge droplets and a main tank (e.g., ink cartridge) to store liquid supplied to the liquid discharge head. Such an image forming apparatus may permit post-end printing using residual liquid in the head tank after it is determined that the main tank is in an end state. 
     However, for example, in a configuration in which post-end printing in an end state of an ink cartridge is allowable by a user&#39;s operation, post-end printing may be started even when the amount of ink remaining in a head tank of a recording head is not sufficient. 
     SUMMARY 
     In an aspect of this disclosure, there is provided an image forming apparatus that includes a recording head, a head tank, a main tank, and a controller. The recording head includes nozzles to discharge liquid droplets. The head tank includes a liquid containing part to contain liquid supplied to the recording head. The main tank contains the liquid supplied to the head tank. The controller controls, after detection of an end state of the main tank, post-end printing using the liquid remaining in the head tank corresponding to the main tank in the end state. The controller permits the post-end printing when an amount of the liquid remaining in the head tank to which the liquid is supplied from the main tank in the end state is a predetermined threshold remaining amount or greater. 
     In another aspect of this disclosure, there is provided a non-transitory computer readable medium that stores a program to cause a computer to execute a process for an image forming apparatus including a liquid discharge head including nozzles to discharge liquid droplets, a head tank including a liquid containing part to contain liquid supplied to the liquid discharge head, and a main tank to contain the liquid supplied to the head tank. The process includes controlling, after detection of an end state of the main tank, post-end printing using the liquid remaining in the head tank corresponding to the main tank in the end state, and permitting the post-end printing when an amount of the liquid remaining in the head tank to which the liquid is supplied from the main tank in the end state is a predetermined threshold remaining amount or greater. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is an outer perspective view of an example of an image forming apparatus according to an embodiment of this disclosure; 
         FIG. 2  is a side view of an example pf a mechanical section of the image forming apparatus of  FIG. 1 ; 
         FIG. 3  is a partial plan view of the mechanical section of  FIG. 2 ; 
         FIG. 4  is a plan view of an example of a head tank of the image forming apparatus; 
         FIG. 5  is a front view of the head tank of  FIG. 4 ; 
         FIG. 6  is an illustration of a liquid supply-and-discharge system of the image forming apparatus. 
         FIG. 7  is a schematic view of an example of a pressure detector and a nearby portion; 
         FIG. 8  is an illustration of the pressure detector of  FIG. 7 ; 
         FIG. 9  is an illustration of a change in pressure between a main tank and a liquid feed pump; 
         FIGS. 10A and 10B  are illustrations of operation of the pressure detector; 
         FIG. 11  is a block diagram of a controller according to an embodiment of this disclosure; 
         FIG. 12  is a flow chart of an example of a process flow of filling liquid from a main tank to a head tank executed by the controller; 
         FIG. 13  is a flow chart of a first example of a reverse feeding process (first control process) of  FIG. 12 ; 
         FIG. 14  is a flow chart of a second example of the reverse feeding process (first control process); 
         FIG. 15  is a flow chart of an example pf a post-end printing process (second control process) executed by the controller; 
         FIGS. 16A, 16B, and 16C  are illustrations of a determination process of a remaining amount of liquid in a post-end printing control process; 
         FIG. 17  is a flow chart of a first example of a post-end printing process of  FIG. 15 ; 
         FIG. 18  is a flow chart of a second example of the post-end printing process; 
         FIG. 19  is a flow chart of a reverse feeding process (first control process) according to a second embodiment of this disclosure; 
         FIG. 20  is a flow chart of a reverse feeding process (first control process) according to a third embodiment of this disclosure; and 
         FIG. 21  is a flow chart of a post-end printing process according to a fourth embodiment of this disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Hereinafter, embodiments of the present disclosure are described with reference to the attached drawings. First, an example of an image forming apparatus according to an embodiment of this disclosure is described with reference to  FIG. 1 .  FIG. 1  is an outer perspective view of an image forming apparatus according to an embodiment of this disclosure, in which a second waste liquid container is not mounted. 
     Hereinafter, embodiments of the present disclosure are described with reference to the attached drawings. First, an example of an image forming apparatus according to an embodiment of this disclosure is described with reference to  FIG. 1 .  FIG. 1  is an outer perspective view of an image forming apparatus  1000  according to this embodiment. 
     In this embodiment, the image forming apparatus  1000  is a serial-type image forming apparatus. A cover  101  is disposed at an upper face side of an apparatus body  1  to be openable and closable. Opening the cover  101  allows access to a mechanical section in the apparatus body  1 . At a front side of the apparatus body  1  are disposed a sheet feed tray  2  and a sheet ejection tray  3 . 
     A cartridge cover  104 , which is openable and closable, is disposed at one lateral side of a front face of the apparatus body  1 . Opening the cartridge cover  104  allows mounting and unmounting of main tanks (also referred to as cartridges) serving as liquid cartridges relative to a cartridge holder  4  of the apparatus body  1 . 
     Next, an example of a print mechanical section of the image forming apparatus  1000  is described with reference to  FIGS. 2 and 3 .  FIG. 2  is a side view of the print mechanical section.  FIG. 3  is a plan view of a portion of the print mechanical section. 
     A main guide rod  31  and a sub-guide rod  32  serving as guides are laterally bridged between side plates  21 A and  21 B of the apparatus body  1  to support a carriage  33  slidably in a main scanning direction indicated by arrow MSD in  FIG. 2 . A main scanning motor  554  reciprocally moves the carriage  33  in the main scanning direction MSD in  FIG. 2 . 
     The carriage  33  mounts recording heads  34   a  and  34   b  serving as liquid ejection heads. The recording heads  34   a  and  34   b  are collectively referred to as “recording heads  34 ” unless distinguished (and other multiple components are referred in the same manner). The recording heads  34   a  and  34   b  discharge droplets of different colors, e.g., yellow (Y), cyan (C), magenta (M), and black (K). 
     In this embodiment, each of the recording heads  34  includes two nozzle rows. For example, one of the nozzle rows of the recording head  34   a  discharges droplets of black (K) and the other discharges droplets of cyan (C). In addition, one of the nozzle rows of the recording head  34   b  discharges droplets of magenta (M) and the other discharges droplets of yellow (Y). 
     In some embodiments, as the recording head  34 , a recording head is used that has a nozzle face of one recording head (liquid discharge head) in which multiple rows, each including multiple nozzles, are arrayed to discharge droplets of respective colors. 
     The carriage  33  mounts head tanks  35   a  and  35   b  (collectively referred to as “head tanks  35 ” unless distinguished) to supply the respective color inks to the corresponding nozzle rows of the recording heads  34 . The head tanks  35   a  and  35   b  are paired tanks corresponding to the nozzle rows of each of the recording heads  34   a  and  34   b . That is, the carriage  33  includes multiple head tanks. 
     Main tanks  10   y ,  10   m ,  10   c , and  10   k  (collectively referred to as main tanks  10  unless distinguished) corresponding to Y, M, C, and K colors, respectively, are detachably mounted to the cartridge holder  4 . A liquid feed pump  241  supplies the respective color inks from the main tanks  10  to head tanks  35  via supply tubes (liquid supply passages)  36  for the respective colors. 
     The image forming apparatus  1000  further includes a sheet feeder to feed sheets  42  stacked on a sheet stacker  41  of the sheet feed tray  2 . The sheet feeder further includes a sheet feed roller  43  and a separation pad  44 . The sheet feed roller  43  separates and feeds the sheets  42  sheet by sheet from the sheet stacker  41 . The separation pad  44  is disposed opposing the sheet feed roller  43 . 
     To feed a sheet  42  fed from the sheet feeder to below the recording heads  34 , the image forming apparatus  1000  includes a first guide  45  to guide the sheet  42 , a counter roller  46 , a conveyance guide  47 , and a pressing member  48  including a leading-edge press roller  49 . The image forming apparatus  1000  also includes a conveyance belt  51  serving as a conveyor to electrostatically attract the sheet  42  thereon and convey the sheet  42  to a position opposing the recording heads  34 . 
     The conveyance belt  51  is an endless belt entrained around a conveyance roller  52  and a tension roller  53  to circulate in a belt conveyance direction (sub-scanning direction) indicated by arrow SSD in  FIG. 2 . The image forming apparatus  1000  also has a charging roller  56  serving as a charger to charge a surface of the conveyance belt  51 . The charging roller  56  is disposed to contact a surface layer of the conveyance belt  51  and rotate with circulation of the conveyance belt  51 . The conveyance roller  52  is rotated by a sub scanning motor via a timing belt, so that the conveyance belt  51  circulates in the belt conveyance direction. 
     The image forming apparatus  1000  further includes a sheet ejector to eject the sheet  42  on which an image has been formed by the recording heads  34 . The sheet ejector includes a separation claw  61  to separate the sheet  42  from the conveyance belt  51 , a first ejection roller  62 , a spur roller  63  serving as a second ejection roller, and the sheet ejection tray  3  disposed at a position lower than the first ejection roller  62 . 
     A duplex unit  71  is detachably mounted on a rear face portion of the apparatus body  1 . When the conveyance belt  51  rotates in reverse to return the sheet  42 , the duplex unit  71  receives the sheet  42 . Then the duplex unit  71  reverses and feeds the sheet  42  to a nipping portion between the counter roller  46  and the conveyance belt  51 . A bypass tray  72  is formed at an upper face of the duplex unit  71 . 
     As illustrated in  FIG. 2 , a maintenance assembly (maintenance and recovery assembly)  81  is disposed in a non-printing area (non-recording area) at one end in the main scanning direction MSD of the carriage  33 . The maintenance assembly  81  maintains and recovers nozzle conditions of the recording heads  34 . 
     The maintenance assembly  81  includes, for example, a suction cap  82   a , a moisture-retention cap  82   b  (the suction cap  82   a  and the moisture-retention cap  82   b  are also referred to as caps  82  unless distinguished), and a wiper (wiper blade)  83 . The suction cap  82   a  caps the nozzle face of any one of the recording heads  34  to suck ink from the nozzles. The suction cap  82   a  also caps the nozzle face of any one of the recording heads  34  for moisture retention. The moisture-retention cap  82   b  caps the nozzle face of any one of the recording heads  34  for moisture retention. The wiper  83  wipes the nozzle face of the recording head  34 . 
     The maintenance assembly  81  further includes a first dummy-discharge receptacle  84  and a carriage lock  87 . The first dummy-discharge receptacle  84  receives droplets discharged by dummy discharge in which droplets not contributing to image recording are discharged to remove thickened recording liquid. The carriage lock  87  locks the carriage  33 . Below the maintenance assembly  81 , a waste liquid tank  100  is removably mounted to the apparatus body  1  to store waste ink or liquid discharged by the maintenance and recovery operation. 
     As illustrated in  FIG. 2 , a second dummy-discharge receptacle  88  is disposed at a non-printing area on the opposite end in the main scanning direction MSD of the carriage  33 . The second dummy-discharge receptacle  88  receives droplets discharged, e.g., during recording (image forming) operation by dummy discharge in which droplets not contributing to image recording are discharged to remove viscous recording liquid. The second dummy-discharge receptacle  88  has openings  89  arranged in parallel to the nozzle rows of the recording heads  34 . 
     In the image forming apparatus  1000  having the above-described configuration, the sheets  42  are separated sheet by sheet from the sheet feed tray  2 , fed in a substantially vertically upward direction, guided along the first guide  45 , and conveyed while being sandwiched between the conveyance belt  51  and the counter roller  46 . Further, a leading edge of the sheet  42  is guided by the conveyance guide  47  and is pressed against the conveyance belt  51  by the leading-edge press roller  49  to turn a conveyance direction of the sheet  42  by approximately 90°. 
     At this time, the conveyance belt  51  is charged in alternating charge voltage pattern with the charging roller  56 . When the sheet  42  is fed onto the conveyance belt  51  charged, the sheet  42  is attracted onto the conveyance belt  51  and conveyed in the sub-scanning direction SSD by circulation of the conveyance belt  51 . 
     By driving the recording heads  34  in accordance with image signals while moving the carriage  33 , ink droplets are discharged onto the sheet  42 , which is stopped below the recording heads  34 , to form one line of a desired image. Then, the sheet  42  is fed by a certain distance to prepare for the next operation to record another line of the image. Receiving a recording end signal or a signal indicating that the rear end of the sheet  42  has arrived at the recording area, the recording operation finishes and the sheet  42  is output to the sheet ejection tray  3 . 
     Next, an example of the head tank  35  is described with reference to  FIGS. 4 and 5 .  FIG. 4  is a schematic upper plan view of the head tank.  FIG. 5  is a schematic front view of the head tank of  FIG. 4 . 
     The head tank  35  has a tank case  201  including a liquid containing part  202  to contain ink and having an opening at one lateral side. In this embodiment, as described above, a pair of two head tanks  35  are disposed to supply different color liquids to the respective nozzle rows of each of the recording heads  34 . 
     The opening of the tank case  201  is sealed with a film  203  serving as a flexible member to form the liquid containing part  202 . The film  203  is constantly urged outward by a restoring force of a spring  204  serving as an elastic member disposed in the tank case  201 . 
     Thus, since the restoring force of the spring  204  acts on the film  203  of the tank case  201 , a decrease in the remaining amount of liquid in the liquid containing part  202  of the tank case  201  creates a negative pressure. 
     At the exterior of the tank case  201  is disposed a displacement member (hereinafter, may also be referred to as simply “feeler”)  205  formed with a feeler having one end swingably supported by a shaft  206 . 
     The displacement member  205  is urged toward the tank case  201  by a spring  210  and pressed against the film  203 . Accordingly, the displacement member  205  displaces with movement of the film  203 . 
     The displacement member  205  is detected with, e.g., a body sensor  301  serving as a body-side detector disposed at the apparatus body  1 , thus allowing detection of the remaining amount of liquid or negative pressure in the head tank  35 . 
     A supply port portion  209  is disposed at an upper portion of the tank case  201  and connected to a supply tube  36  to supply liquid from the main tank  10 . At one lateral side of the tank case  201 , an air releaser  207  serving as an air releaser is disposed to release the interior of the head tank  35  to the atmosphere. 
     The air releaser  207  includes, for example, an air release passage  207   a  communicating with the interior of the head tank  35 , a valve body  207   b  to open and close the air release passage  207   a , and a spring  207   c  to urge the valve body  207   b  into a closed state. An air release solenoid  302  is disposed at the apparatus body  1 , and the valve body  207   b  is pushed by the air release solenoid  302  to open the air release passage  207   a , thus causing the interior of the head tank  35  to be opened to the atmosphere (in other words, causing the interior of the head tank  35  to communicate with the atmosphere). 
     The head tank  35  are provided with electrode pins  208   a  and  208   b  (also referred to as electrode pins  208 ) serving as a liquid level detector to detect a liquid level of liquid in the head tank  35 . Since liquid has electric conductivity, when the liquid level reaches the electrode pins  208   a  and  208   b , electric current flows between the electrode pins  208   a  and  208   b  and the resistance values of the electrode pins  208   a  and  208   b  change. Such a configuration can detect that the liquid level has decreased to a threshold level or lower. 
     Next, a liquid supply-and-discharge system of the image forming apparatus according to this embodiment is described with reference to  FIG. 6 .  FIG. 6  is a schematic view of the liquid supply-and-discharge system in this embodiment. 
     A liquid feed pump  241  serving as a liquid feeder supplies liquid from the main tank  10  to the head tank  35  via the supply tube  36 . 
     The liquid feed pump  241  is a reversible pump (reversible liquid feeder), e.g., a tube pump, capable of performing normal feed operation to supply liquid from the main tank  10  to the head tank  35  and reverse feed operation to return liquid from the head tank  35  to the main tank  10 . 
     The maintenance assembly  81  includes the suction cap  82   a  to cap a nozzle face of any one of the recording heads  34  and a suction pump  812  connected to the suction cap  82   a . The suction pump  812  is driven with the nozzle face capped with the suction cap  82   a  to suck liquid from the nozzles via a suction tube  811 , thus allowing liquid to be sucked from the head tank  35 . Waste liquid sucked from the head tank  35  is discharged to a waste liquid tank  100 . 
     The air release solenoid  302  serving as a pressing member to open and close the air releaser  207  of the head tank  35  is disposed at the apparatus body  1 . By activating the air release solenoid  302 , the air releaser  207  can be opened. 
     The liquid supply-and-discharge system also includes a pressure detector  571  to detect that the pressure of the liquid supply passage (supply tube  36 ) between the main tank  10  and the head tanks  35  is a threshold value or lower. In this embodiment, the pressure detector  571  is disposed between the main tank  10  and the liquid feed pump  241 . 
     The liquid supply-and-discharge system further includes a temperature sensor  572  serving as a temperature detector to detect a temperature near the head tank  35  and a humidity sensor  573  to detect humidity near the head tank  35 . 
     A controller  500  performs drive control of the liquid feed pump  241 , the air release solenoid  302 , and the suction pump  812  and control of post-end printing. 
     Next, an example of the pressure detector is described with reference to  FIGS. 7 and 8 .  FIG. 7  is a schematic view of the pressure detector and a nearby portion.  FIG. 8  is an illustration of the pressure detector. 
     A pressure detector  571  in this example includes a pressure detection part  701  intervening a liquid supply passage (supply tube  36 ) and a sensor  702  to detect that an internal pressure of the liquid supply passage detected with pressure detection part  701  is a predetermined pressure or lower. 
     The pressure detection part  701  is communicated with a main tank  10  via a hollow needle  703  and includes a channel formation member  711  forming a channel  710  communicated with the liquid feed pump  241  via the supply tube  36 . A portion of the channel  710  is formed of a deformable elastic member  712 . The elastic member  712  is connected to a rod  713 , and a spring  714  urges the rod  713  outward of the channel formation member  711 . 
     The sensor  702  is formed of, e.g., a transmissive photosensor to detect a detection piece (feeler)  715  mounted on the rod  713 . When the pressure of the channel  710  of the channel formation member  711  decreases and the rod  713  is drawn into a predetermined position in the channel formation member  711 , the sensor  702  detects the detection piece  715 . 
     Operation of the pressure detector  571  thus configured is described with reference to  FIGS. 9 and 10 .  FIG. 9  is an illustration of a change in pressure between a main tank and the liquid feed pump.  FIGS. 10A and 10B  are illustrations of operation of the pressure detector. 
     In normal liquid feeding in which a certain amount of liquid remains in a main tank  10  as illustrated in  FIG. 10A  (the main tank  10  is not in the end state), as illustrated in  FIG. 9 , a channel between the main tank  10  and the liquid feed pump  241  only pulsates even when liquid is supplied with the liquid feed pump  241 . 
     By contrast, when liquid is supplied with the liquid feed pump  241  in the end state of the main tank  10  as illustrated in  FIG. 10B , as illustrated in  FIG. 9 , the pressure in the channel between the main tank  10  and the liquid feed pump  241  rapidly falls (the negative pressure in the channel rapidly increases). 
     Accordingly, when the main tank  10  is not in the end state, as illustrated in  FIG. 10A , the detection piece  715  of the rod  713  is placed at a position not opposing the sensor  702 . 
     By contrast, when the main tank  10  turns into in the end state and the pressure in the channel between the main tank  10  and the liquid feed pump  241  decreases, the elastic member  712  is introduced into the channel  710  and the rod  713  displaces in a direction indicated by arrow C. As a result, the detection piece  715  is placed as a position opposing the sensor  702 . 
     Accordingly, the sensor  702  detects the detection piece  715 , thus allowing detection of the end state of the main tank  10 . 
     Next, an outline of a controller of the image forming apparatus  1000  is described with reference to  FIG. 11 .  FIG. 7  is a block diagram of the controller  500  of the image forming apparatus. 
     The controller  500  includes a central processing unit (CPU)  501 , a read-only memory (ROM)  502 , a random access memory (RAM)  503 , a non-volatile random access memory (NVRAM)  504 , and an application-specific integrated circuit (ASIC)  505 . The CPU  501  manages the control of the entire image forming apparatus  1000 . The ROM  502  stores fixed data, such as various programs including programs executed by the CPU  501 , and the RAM  503  temporarily stores image data and other data. 
     The NVRAM  504  is a rewritable memory capable of retaining data even when the apparatus is powered off The ASIC  505  processes various signals on image data, performs sorting or other image processing, and processes input and output signals to control the entire apparatus. 
     The controller  500  also includes a print control  508  and a head driver (driver integrated circuit)  509 . The print control  508  includes a data transmitter and a driving signal generator to drive and control the recording heads  34 . The head driver  509  drives the recording heads  34  mounted on the carriage  33 . 
     The controller  500  further includes a main scanning motor  554 , a sub-scanning motor  555 , and a motor driver  510 . The main scanning motor  554  moves the carriage  33  for scanning, and the sub-scanning motor  555  circulates the conveyance belt  51 . The motor driver  510  drives a maintenance motor  556  of the maintenance assembly  81  to move the caps  82  and the wiper  83  of the maintenance assembly  81  or suck ink with the suction pump  812 . 
     The controller  500  further includes an alternating-current (AC) bias supply  511  and a supply-system driver  512 . The AC bias supply  511  supplies AC bias to the charging roller  56 . The supply-system driver  512  drives liquid feed pumps  241  of the supply pump unit  24 . 
     The controller  500  is connected to a control panel  514  serving as an input unit to input and a notifier to display information necessary to the image forming apparatus  1000 . 
     The controller  500  includes a host interface (I/F)  506  for transmitting and receiving data and signals to and from a printer driver  601  of a host  600 , such as an information processing device (e.g., personal computer), an image reading device, or an image pick-up device, via a cable or network. 
     The CPU  501  of the controller  500  reads and analyzes print data stored in a reception buffer of the I/F  506 , performs desired image processing, data sorting, or other processing with the ASIC  505 , and transfers image data from the print control  508  to the head driver  509 . 
     The print control  508  transfers the above-described image data as serial data and outputs to the head driver  509 , for example, transfer clock signals, latch signals, and control signals required for the transfer of image data and determination of the transfer. 
     In addition, the print control  508  includes the driving signal generator including, e.g., a digital/analog (D/A) converter (to perform digital/analog conversion on pattern data of driving pulses stored on the ROM  502 ), a voltage amplifier, and a current amplifier. The print control  508  outputs a driving signal containing one or more driving pulses from the driving signal generator to the head driver  509 . 
     In accordance with serially-inputted image data corresponding to one line recorded by the recording heads  34 , the head driver  509  selects driving pulses of a driving waveform transmitted from the print control  508  and applies the selected driving pulses to the pressure generator to drive the recording heads  34 . Thus, the recording heads  34  are driven. At this time, by selecting a part or all of the driving pulses forming the driving waveform or a part or all of waveform elements forming a driving pulse, the recording heads  34  can selectively discharge dots of different sizes, e.g., large droplets, medium droplets, and small droplets. 
     The I/O unit  513  obtains information from the pressure detector  571 , a temperature sensor  572 , a humidity sensor  573 , a cartridge-cover sensor  574  to detect opening of the cartridge cover  104 , and various types of sensors  515  mounted in the image forming apparatus  1000 . The I/O unit  513  also extracts information necessary for controlling the image forming apparatus  1000  and uses such information to perform various controls. 
     Next, a process flow of filling liquid from a main tank to a head tank executed by the controller according to an embodiment of this disclosure is described with reference to  FIG. 12 .  FIG. 12  is a flow chart of an example of a process flow of filling liquid from a main tank to a head tank executed by the controller. 
     The liquid filling process is started when liquid filling from a main tank  10  to a head tank  35  is needed. 
     Here, the phrase “when liquid filling from a main tank  10  to a head tank  35  is needed” means, for example, when a displacement member  205  displaces in a direction to decrease the remaining amount of liquid in the head tank  35  and passes through a predetermined filling start position, when the consumption amount of liquid in the head tank  35  is a predetermined threshold amount or greater, and when the air releaser  207  is opened and liquid is supplied until electrode pins  208  detect a liquid level (liquid surface). 
     With the start of the filling process, at S 101  the liquid feed pump  241  rotates forward and starts feeding (forward rotation feeding) of liquid to the head tank  35 . 
     At S 102 , the controller  500  determines whether the filling operation is completed. The completion of the filling operation can be determined based on, for example, 1) whether the displacement member  205  has displaced in a direction to increase the remaining amount of liquid in the head tank  35  and has arrived at a predetermined filling full position, 2) whether the drive time of the liquid feed pump  241  has reached a threshold time, 3) whether the number of rotation of the liquid feed pump  241  has reached a threshold number of rotation, and 4) whether the liquid surface is detected with the electrode pins  208 . 
     When the controller  500  determines that the filling operation is completed (YES at S 102 ), at S 103  the controller  500  finishes the forward rotation operation of the liquid feed pump  241  and finishes the forward rotation feeding. 
     By contrast, when the controller  500  determines that the filling operation is not completed (NO at S 102 ), at S 104  the controller  500  determines whether the pressure in the liquid supply passage is a threshold value or lower, in other words, whether the main tank  10  is in an end state, based on a detection result of the pressure detector  571 . 
     When the controller  500  determines that the pressure in the liquid supply passage is higher than a threshold value (NO at S 104 ), the controller  500  continues the filling operation (and the process goes back to S 102 ). 
     By contrast, when the controller  500  determines that the pressure in the liquid supply passage is the threshold value or lower, based on the detection result of the pressure detector  571  (YES at S 104 ), at S 105  the process shifts to a reverse feeding process (first control process) to return liquid from the head tank  35  to the main tank  10 . 
     Next, a first example of the reverse feeding process (first control process) is described with reference to  FIG. 13 .  FIG. 13  is a flow chart of the first example of the reverse feeding process (first control process). 
     When the controller  500  detects with the pressure detector  571  that the pressure in the liquid supply passage is the threshold value or lower (the main tank  10  is in the end state) (YES at S 104 ), liquid filling into the head tank  35  is not performed. Accordingly, it is assumed that the remaining amount of liquid in the head tank  35  is relatively small (the negative pressure in the head tank  35  is relatively large). In addition, since liquid is not fed from the main tank  10 , it is assumed that the supply tube  36  of the liquid feed pump  241  and the negative pressure in the pressure detector  571  are relatively large. 
     At this time, if replacement of the main tank  10  is performed without releasing the negative pressure, air may be introduced from an upstream side (main tank side) of the liquid supply passage by action of the negative pressure in the liquid supply passage. If such air is introduced into the liquid supply passage, the following failure may arise. 
     For example, when liquid is fed into the head tank  35 , air bubbles might hamper accurate detection of the liquid surface with the electrode pins  208 . When barmy liquid leaks from the air releaser  207  into the inside of the image forming apparatus and adheres to an electric circuit, an electric board might be damaged and the inside of the image forming apparatus might be contaminated. Such barmy liquid might also act as a pressure damper and cause ejection failure. 
     Hence, when the reverse feeding process starts, at S 201  the air releaser  207  of the head tank  35  is opened. After the inside of the head tank  35  is opened to an ambient atmosphere to release the negative pressure, at S 202  the air releaser  207  is closed. 
     At S 203 , the liquid feed pump  241  is driven for reverse rotation to feed a threshold amount (first threshold amount) of liquid in reverse from the head tank  35  to the main tank  10  to release the negative pressure in the liquid feed pump  241  and the pressure detector  571 . 
     At S 204 , the controller  500  determines whether the reverse rotation operation is completed. 
     Here, the completion of the reverse rotation operation can be determined based on, for example, 1) whether the reverse rotation feeding has been performed for a threshold time period and 2) whether the liquid feed pump  241  has been rotated a threshold number of times. 
     When the reverse rotation operation is completed (YES at S 204 ), at S 205  the controller  500  stops driving of the reverse rotation of the liquid feed pump  241  to finish the reverse rotation feeding (reverse feeding). Thus, the reverse feeding process ends. 
     Next, a second example of the reverse feeding process (first control process) is described with reference to  FIG. 14 .  FIG. 14  is a flow chart of the second example of the reverse feeding process (first control process). 
     Like the above-described first example, when the reverse feeding process starts, at S 301  the air releaser  207  of the head tank  35  is opened. After the inside of the head tank  35  is opened to an ambient atmosphere to release the negative pressure, at S 302  the air releaser  207  is closed. 
     At S 303 , the carriage  33  is moved to a position at which the displacement member (feeler)  205  of the head tank  35  is detectable with the apparatus sensor  301 . 
     At S 04 , the liquid feed pump  241  is driven for reverse rotation to feed a threshold amount (first threshold amount) of liquid in reverse from the head tank  35  to the main tank  10  to release the negative pressure in the liquid feed pump  241  and the pressure detector  571 . 
     At S 305 , the controller  500  determines whether the displacement member  205  of the head tank  35  is detected with the apparatus sensor  301 . 
     When the displacement member  205  of the head tank  35  is detected with the apparatus sensor  301  (YES at S 305 ), at S 306  the controller  500  stops driving of the reverse rotation of the liquid feed pump  241  to finish the reverse rotation feeding. Thus, the reverse feeding process ends. 
     Note that, since the reverse rotation feeding operation is performed after the air releaser  207  is opened and closed, the reverse rotation feeding operation also serves as a negative pressure forming operation of the head tank  35 . Accordingly, the controller  500  can shift to a subsequent post-end printing control process (second control process) without performing an additional operation. 
     Next, an example pf the post-end printing process (second control process) executed by the controller is described with reference to  FIG. 15 .  FIG. 15  is a flow chart of an example pf the post-end printing process. 
     The post-end printing is a printing method in which, for example, when a color ink other than black ink is in an end state, the controller  500  permits only monochromatic printing. In such a case, for a recording head for a non-black color ink, only dummy discharge and other maintenance operation to maintain normal performance of nozzles is permitted and printing is not permitted for the recording head for the non-black color ink. 
     When black ink is in the end state, monochromatic printing in composite black using three types of non-black color inks can be permitted. 
     Such a configuration allows monochromatic printing even when a new main tank (cartridge) is not readily available for replacement. 
     In other words, the post-end printing is a printing operation accompanying consumption of a residual liquid of a head tank corresponding to a main tank determined to be in the end state. Note that the term “corresponding” means that the head tank is a head tank to be fed from the main tank in the end state. However, it does not necessary means that liquid is fed from the main tank to the head tank in the post-end printing. 
     For the post-end printing in this embodiment, residual liquid in the head tank corresponding to the main tank determined to be in the end state is not used for image formation and is used only for operation to maintain nozzle conditions. Image formation is performed using liquid of a head tank supplied from a main tank not determined to be in the end state. 
     In the post-end printing process, after the reverse feeding process is performed, at S 401  the controller  500  determines whether the remaining amount of liquid in the head tank  35  is a predetermined threshold remaining amount (second threshold amount). 
     When the remaining amount of liquid is the threshold remaining amount or greater (YES at S 401 ), at S 402  the controller  500  permits post-end printing. 
     At S 403  the controller  500  determines whether post-end printing is instructed from a user. When post-end printing is instructed (YES at S 403 ), at S 404  the controller  500  shifts to a post-end printing mode. When post-end printing is not instructed (NO at S 403 ), at S 406  the controller  500  prompts the user to replace cartridges and finishes the post-end printing process. 
     By contrast, when the remaining amount of liquid is smaller than the threshold remaining amount (NO at S 401 ), at S 405  the controller  500  does not permit post-end printing. 
     At S 406  the controller  500  prompts the user to replace cartridges (main tanks) and finishes the post-end printing process. 
     As described above, the controller  500  permits only when the remaining amount of liquid in a head tank is a threshold remaining amount or greater, the controller  500  permits post-end printing. Such a configuration prevents post-end printing from being permitted, executed, and stopped uncompleted even when the remaining amount of liquid in the head tank is an amount at which post-end printing is not available. 
     In other words, for example, when a non-black color ink is in the end state and post-end printing only permitting monochromatic printing is performed, the non-black color ink is in the end state and is not used for printing in a sense of discharging to a sheet. However, if the non-black color ink is not discharged at all, nozzle failure may arise in the nozzles for the non-black color ink. Hence, in this embodiment, only a regular operation to maintain the nozzle conditions. e.g., dummy discharge is permitted. The regular dummy discharge includes, for example, a pre-printing dummy discharge to discharge liquid before printing, an in-printing dummy discharge to discharge liquid at regular intervals during printing, and a post-leaving dummy discharge to discharge liquid after liquid is not discharged from a head tank for a long time period. 
     Here, if monochromatic printing causes the remaining amount of a non-black color ink to be smaller than the second threshold amount required for dummy discharge, sufficient dummy discharge would not be performed even when the process shifts to post-end printing. Hence, in this embodiment, when the remaining amount of a non-black color ink is not greater than the second threshold amount, the controller  500  does not permit post-end printing in the end state of the non-black color ink. 
     Next, a determination process of the remaining amount of liquid in the above-described post-end printing control process is described with reference to  FIGS. 16A, 16B , and  16 C. 
     A remaining amount of liquid V HT  remaining in the head tank  35  illustrated in  FIG. 16B  is obtained by subtracting an amount of air V air  introduced by opening and closing of the air releaser  207  in the reverse feeding process and an amount of liquid V rev fed by the reverse rotation feeding from a volume of liquid V fill  fully filled in the head tank  35 . The remaining amount of liquid V HT  remaining in the head tank  35  is expressed by the following Formula 1:
 
 V   HT   =V   fill   −V   air   −V   rev   (1).
 
     Here, the remaining amount of liquid V HT  is a threshold remaining amount V EM  or greater as illustrated in  FIG. 16C , the controller  500  permits post-end printing. The threshold remaining amount V EM  is obtained by subtracting an amount of liquid V rev  fed by the reverse rotation feeding and a tolerance amount of liquid V tol  from an amount of liquid V dis  dischargeable from an air release state. The threshold remaining amount V EM  is expressed by the following Formula 2:
 
 V   EM   =V   dis   −V   air   −V   tol   (2).
 
     Examples of the tolerance amount V tol  are as follows. 
     1) Amount of liquid needed for printing one page In a configuration in which, e.g., an amount of liquid at which post-end printing is executable is constantly monitored during printing, if the remaining amount of a head tank becomes lower than the amount of liquid at which post-end printing is executable, the controller would determine that liquid cannot be discharged at that time and stop printing. To prevent such a situation, in this embodiment, the tolerance amount V tol  is subtracted in advance from the threshold remaining amount V EM . 
     In other words, depending on a recording mode or an environment, even when only dummy discharge is performed, the consumption amount (usage) of liquid by the dummy discharge during post-end printing might exceed the second threshold amount. For example, in a configuration in which the controller constantly monitors the consumption amount of liquid by dummy discharge during printing and determines the end of post-end printing, if the consumption amount of liquid by dummy discharge exceeds the second threshold amount during printing a sheet, the post-end printing might be finished without printing the sheet completely. Hence, a threshold amount is set so that printing on the first sheet can be completed even if post-end printing ends during printing a second sheet. 
     2) Margin A predetermined amount is subtracted in advance as a margin to secure stable discharge. 
     To stably perform dummy discharge and maintenance during post-end printing, the remaining amount of liquid V HT  remaining in the head tank  35  is, preferably, sufficiently greater than the threshold remaining amount V EM  required for dummy discharge operation in the post-end printing. 
     Note that, if the remaining amount of liquid V HT  remaining in the head tank  35  is smaller than the threshold remaining amount V EM  required for dummy discharge operation in the post-end printing, liquid discharge (dummy discharge) would not be performed during post-end printing. As a result, an abnormal image might be output when normal printing is performed after replacement of the main tank  10 . Additionally, maintenance might be needed to recover an abnormal state, causing a failure, such as an increase in wasteful liquid consumption or waiting time. 
     Next, a first example of the post-end printing process is described with reference to  FIG. 17 .  FIG. 17  is a flow chart of the first example of the post-end printing process. 
     When the post-end printing process starts, at S 501  the controller  500  starts post-end printing and, as described above, continues printing using liquid of a head tank  35  other than a head tank  35  corresponding to a main tank  10  in the end state. 
     For the head tank  35  corresponding to the main tank  10  in the end state, at S 502  the controller  500  determines whether the usage of liquid used to maintain nozzle conditions by, e.g., dummy discharge or maintenance during the post-end printing is a threshold usage or greater. Note that the threshold usage is the above-described threshold remaining amount (second threshold amount). 
     When the consumption amount of liquid during post-end printing is the threshold usage or greater (YES at S 502 ), at S 503  the controller  500  finishes the post-end printing. At S 504 , the controller  500  finishes the post-end printing mode, stops the image forming apparatus  1000 , and displays (notifies) the end state on, e.g., the control panel  514  serving as a notifier to prompt replacement of the main tank  10  (cartridge). 
     In other words, after the process shifts to the post-end printing mode, the controller  500  prohibits discharge for printing using liquid of a color in the end state and permits only dummy discharge and maintenance to perform minimum maintenance of nozzle conditions. 
     At this time, the controller  500  records the amount of liquid used for dummy discharge and maintenance as a usage of liquid during post-end printing. During printing, the controller  500  monitors the usage of liquid during post-end printing and the threshold usage (second threshold amount) and determines whether post-end printing is executable. 
     Note that the monitoring of the usage of liquid and the threshold usage during post-end printing may be, for example, constant monitoring or monitoring per one scanning or page, and the unit of monitoring is not particularly specified. The usage of liquid during post-end printing is stored onto, for example, the NVRAM  504 . 
     With such a configuration, printing can be continued while the remaining amount of liquid is the amount of liquid at which post-end printing is executable. Accordingly, urgent printing can be continued until a user replaces a main tank (cartridge) in the end stage. Additionally, by monitoring the consumption of liquid, the controller can prompt a user to replace the main tank (cartridge) before the negative pressure in a head tank rises and a nozzle failure occurs. 
     Next, a second example of the post-end printing process is described with reference to  FIG. 18 .  FIG. 18  is a flow chart of the second example of the post-end printing process. 
     When the post-end printing mode starts, at S 601  the controller  500  starts post-end printing. At S 602 , the controller  500  determines whether an elapsed time period from the start of the post-end printing is a predetermined threshold time period or greater. 
     When the elapsed time period from the start of the post-end printing is the threshold time period or greater (YES at S 602 ), at S 5603  the controller  500  finishes the post-end printing. At S 604 , the controller  500  finishes the post-end printing mode, stops the image forming apparatus  1000 , and displays the end state on, e.g., the control panel  514  to prompt replacement of the main tank  10  (cartridge). 
     In other words, like the post-end printing process described in the above-described second embodiment, after the process shifts to the post-end printing mode, the controller  500  prohibits discharge for printing using liquid of a color in the end state and permits only dummy discharge and maintenance to perform minimum maintenance of nozzle conditions. 
     At regular timings, such as before printing, during printing, after printing, when the image forming apparatus is powered on, before maintenance, and after maintenance, the controller monitors whether the elapsed time from when the process shifts to the post-end printing is a threshold time period (for example, a specified date and time) or greater. 
     Only minimum dummy discharge and maintenance are performed during post-end printing. If such a state continues over a long period of time, an abnormal image is likely to be output after cartridge replacement. To prevent such a failure, in this example, the controller  500  sets a time limit and stops permission of the post-end printing when the elapsed time from the start of the post-end printing exceeds the threshold time period. 
     Note that the time (date and time) of the start of the post-end printing is stored onto the NVRAM  504 . 
     With such a configuration, printing can be continued while the remaining amount of liquid is the amount of liquid at which post-end printing is executable. Accordingly, urgent printing can be continued until a user replaces a main tank (cartridge) in the end stage. Additionally, by monitoring the elapsed time from when the process shifts to the post-end printing, the controller can prompt a user to replace the main tank (cartridge) before nozzle abnormality, e.g., a nozzle failure due to thickening of liquid in nozzles occurs. 
     Next, a reverse feeding process (first control process) according to a second embodiment of this disclosure is described with reference to  FIG. 19 .  FIG. 19  is a flow chart of the reverse feeding process in the second embodiment. 
     In this embodiment, when the reverse feeding process starts, at S 701  the air releaser  207  of the head tank  35  is opened. After the inside of the head tank  35  is opened to an ambient atmosphere to release the negative pressure, at S 702  the air releaser  207  is closed. 
     At S 703 , the controller  500  checks the cartridge-cover sensor  574  and determines whether the cartridge cover  104  is open. 
     When the cartridge cover  104  is open (YES at S 703 ), at S 709  the controller  500  does not permit post-end printing and at S 710  prompts a user to replace a main tank (cartridge)  10 . Thus, the reverse feeding process ends. 
     By contrast, when the cartridge cover  104  is not open (NO at S 703 ), like the above-described first embodiment, at S 704  the liquid feed pump  241  is driven for reverse rotation to feed a threshold amount (first threshold amount) of liquid in reverse from the head tank  35  to the main tank  10  to release the negative pressure in the liquid feed pump  241  and the pressure detector  571 . 
     At S 705 , the controller  500  determines whether the reverse rotation operation is completed. 
     When the reverse rotation operation is completed (YES at S 705 ), at S 706  the controller  500  stops driving of the reverse rotation of the liquid feed pump  241  to finish the reverse rotation feeding (reverse feeding). Thus, the reverse feeding process ends. 
     When the reverse rotation operation is not completed (NO at S 705 ), at S 707  the controller  500  determines whether the cartridge cover  104  is open. 
     When the cartridge cover  104  is not open (NO at S 707 ), the controller  500  returns to S 705  and determines whether the reverse rotation operation is completed. 
     By contrast, when the controller  500  detects that the cartridge cover  104  is open before the reverse rotation operation is completed (YES at S 707 ), the controller  500  finishes the reverse rotation feeding at S 708 , does not permit post-end printing at S 709  and prompts a user to replace a main tank (cartridge)  10  at S 710 . Thus, the reverse feeding process ends. 
     In other words, in the reverse feeding process (first control process) to feed liquid in reverse from the head tank  35  to the main tank  10  on detection of the end state, when the controller  500  determines that the post-end printing is not executable, the controller  500  does not shift to the post-end printing control process (second control process) and displays (notifies) a prompt for cartridge replacement on, e.g., the control panel  514 . 
     Depending on the conditions in the image forming apparatus  1000 , post-end printing may not be executable. 
     For example, if the cartridge cover  104  is opened before or during the reverse rotation feeding, the main tank  10  might be removed from the cartridge holder  4  and liquid might be ejected. Hence, the controller  500  stops reverse rotation of the liquid feed pump  241 . 
     In such a case, since the reverse rotation of the liquid feed pump  241  has not been performed normally, the negative pressure in the liquid feed pump  241  and the pressure detector  571  may not be released. Therefore, the controller  500  does not permit post-end printing. 
     When the cartridge cover  104  is opened, the controller  500  also determines that the main tank  10  has been removed. Therefore, it is preferable to assume that air has been introduced into the liquid supply passage and perform a proper maintenance operation for recovering abnormality after cartridge replacement. 
     For example, normal rotation supply with the liquid feed pump  241  and suction with the suction cap  82   a  are alternately repeated to feed such air introduced into the liquid supply passage to the head tank  35  and eliminate bubbles. 
     As described above, even if the cartridge cover  104  is opened during the reverse feeding process, the controller  500  can treat the opening as an abnormal state. Accordingly, 
     the controller  500 , though cannot perform post-end printing, can perform proper maintenance after cartridge replacement to restore a normal state. 
     Next, a reverse feeding process (first control process) according to a third embodiment of this disclosure is described with reference to  FIG. 20 .  FIG. 20  is a flow chart of the reverse feeding process in the third embodiment. 
     In this embodiment, when the reverse feeding process starts, at S 801  the air releaser  207  of the head tank  35  is opened. After the inside of the head tank  35  is opened to an ambient atmosphere to release the negative pressure, at S 802  the air releaser  207  is closed. 
     At S 803 , like the above-described first embodiment, the liquid feed pump  241  is driven for reverse rotation to feed a threshold amount (first threshold amount) of liquid in reverse from the head tank  35  to the main tank  10  to release the negative pressure in the liquid feed pump  241  and the pressure detector  571 . 
     At S 804 , the controller  500  determines whether the reverse rotation operation is completed. When the reverse rotation operation is completed (YES at S 804 ), at S 805  the controller  500  stops driving of the reverse rotation of the liquid feed pump  241  to finish the reverse rotation feeding (reverse feeding). 
     At S 806 , the controller  500  determines whether the electrode pins  208  has detected air before the start of the preceding filling operation. 
     When the electrode pins  208  has detected air (YES at S 806 ), at S 807  the controller  500  prompts a user to replace a main tank (cartridge)  10 . Thus, the first control process ends. 
     When the electrode pins  208  has not detected air (NO at S 806 ), the first control process directly ends. 
     In other words, when the electrode pins  208  has detected air before the start of the preceding filling operation, the volume of liquid V fill  fully filled in the head tank  35  is not a proper full volume. Consequently, the relation of V HT &gt;V EM  might not be satisfied. 
     In such a case, since liquid consumption by the threshold remaining amount V EM  required for post-end printing cannot be secured, the controller  500  does not permit post-end printing. 
     Next, a control process according to a fourth embodiment of this disclosure is described with reference to  FIG. 21 .  FIG. 21  is a flow chart of the control process in the fourth embodiment. 
     In this embodiment, after the reverse feeding process is performed, at S 901  the controller  500  starts the post-end printing process (second control process) and determines whether the remaining amount of liquid in the head tank  35  is a threshold remaining amount or greater. 
     When the remaining amount of liquid is the threshold remaining amount or greater (YES at S 901 ), at S 902  the controller  500  permits post-end printing. 
     At S 903 , the controller  500  displays a prompt for cartridge replacement on, e.g., the control panel  514  and notifies a user that post-end printing is available. 
     At S 904  the controller  500  determines whether post-end printing is instructed from a user. When post-end printing is instructed (YES at S 904 ), at S 905  the controller  500  shifts to a post-end printing mode. When post-end printing is not instructed (NO at S 904 ), at S 907  the controller  500  prompts the user to replace cartridges and finishes the post-end printing process. 
     When the remaining amount of liquid is smaller than the threshold remaining amount (NO at S 901 ), at S 906  the controller  500  does not permit post-end printing. 
     At S 907 , the controller  500  prompts the user to replace cartridges and finishes the post-end printing process. 
     Thus, a case in which the process cannot go to post-end printing can be reliably eliminated. By contrast, when the process goes to post-end printing, the user can securely select whether to perform the post-end printing or cartridge replacement. 
     In the above-described embodiments, post-end printing is described with examples in which printing is continued using liquid of a head tank(s) not in the end state, and liquid remaining in a head tank supplied from a main tank in the end state is used only for maintaining nozzle conditions. However, post-end printing may be applied to a case in which printing is performed using the liquid remaining in the head tank in the end state. 
     Programs causing a computer to execute control of the post-end printing executed by the controller in the above-described embodiments are stored in, e.g., the ROM  502 . 
     For example, in this disclosure, the term “sheet” used herein is not limited to a sheet of paper and is anything to which liquid droplets can be attached. The term “sheet” is used as a generic term including a recorded medium, a recording medium, a recording sheet, and a recording sheet of paper. The terms “image formation”, “recording”, “printing”, and “image printing” are used herein as synonyms for one another. 
     The term “image formation”, which is used herein as a synonym for “recording” or “printing”, includes providing not only meaningful images, such as characters and figures, but meaningless images, such as patterns, to the medium (in other words, the term “image formation” includes only causing liquid droplets to land on the medium). 
     The term “image” used herein is not limited to a two-dimensional image and includes, for example, an image applied to a three dimensional object and a three dimensional object itself formed as a three-dimensionally molded image. 
     The term “image forming apparatus” includes both serial-type image forming apparatus and line-type image forming apparatus. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC) and conventional circuit components arranged to perform the recited functions. 
     The present invention can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software. The present invention may be implemented as computer software implemented by one or more networked processing apparatuses. The network can comprise any conventional terrestrial or wireless communications network, such as the Internet. The processing apparatuses can compromise any suitably programmed apparatuses such as a general purpose computer, personal digital assistant, mobile telephone (such as a WAP or 3G-compliant phone) and so on. Since the present invention can be implemented as software, each and every aspect of the present invention thus encompasses computer software implementable on a programmable device. The computer software can be provided to the programmable device using any storage medium for storing processor readable code such as a floppy disk, hard disk, CD ROM, magnetic tape device or solid state memory device. 
     The hardware platform includes any desired kind of hardware resources including, for example, a central processing unit (CPU), a random access memory (RAM), and a hard disk drive (HDD). The CPU may be implemented by any desired kind of any desired number of processor. The RAM may be implemented by any desired kind of volatile or non-volatile memory. The HDD may be implemented by any desired kind of non-volatile memory capable of storing a large amount of data. The hardware resources may additionally include an input device, an output device, or a network device, depending on the type of the apparatus. Alternatively, the HDD may be provided outside of the apparatus as long as the HDD is accessible. In this example, the CPU, such as a cache memory of the CPU, and the RAM may function as a physical memory or a primary memory of the apparatus, while the HDD may function as a secondary memory of the apparatus.