Patent Publication Number: US-9409400-B2

Title: Image forming apparatus configured to include nozzle face capping control

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2013-006851, filed on Jan. 18, 2013, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     Exemplary embodiments of this disclosure relate to an image forming apparatus and more specifically to an image forming apparatus including a recording head to eject liquid droplets. 
     2. Description of the Related Art 
     Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multifunction devices having two or more of the foregoing capabilities. As one type of image forming apparatuses employing a liquid-ejection recording method, for example, inkjet recording apparatuses are known that use a recording head(s) for ejecting droplets of liquid (e.g., ink). 
     Such image forming apparatuses may have a maintenance unit (maintenance-and-recovery unit) including caps to cap nozzle faces of recording heads. When the image forming apparatus is on standby for printing or a cover is opened to open the inside of an apparatus body to the outside, the caps cap and protect the nozzle faces of the recording heads. 
     To facilitate maintenance work of a service person, for example, JP-2000-326525-A proposes an inkjet recording apparatus that allows a service person to forcefully replace ink cartridges and conduct maintenance work when the service person turns the power on with a maintenance switch turned on. 
     For such an inkjet-type image forming apparatus, for example, when the apparatus is left unused for a long time, ink may firmly adhere to the nozzle faces of the recording heads, thus causing skewed ejection or non-ejection of droplets. Hence, for example, a wet cleaner may be provided to clean the nozzle faces and remove such firmly-adhering ink. 
     However, for the above-described inkjet recording apparatus, as described above, the nozzle faces are capped with the caps during standby and so forth, thus hampering a service person from easily checking and cleaning the nozzle faces of the recording heads. 
     BRIEF SUMMARY 
     In at least one exemplary embodiment of this disclosure, there is provided an image forming apparatus including an apparatus body, a recording head, a maintenance unit, a cover, and a controller. The recording head has a nozzle face and nozzles in the nozzle face to eject droplets of liquid. The maintenance unit has a cap to protect the nozzle face of the recording head. The cover opens an interior of the apparatus body to an outside of the apparatus body. The controller performs a normal control to cap the nozzle face of the recording head with the cap on opening of the cover and a special control to expose the nozzle face of the recording head to an area opened by the cover on receipt of an external instruction. 
    
    
     
       BRIEF DESCRIPTION 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 a side view of a mechanical section of an image forming apparatus according to exemplary embodiments of this disclosure; 
         FIG. 2  is a side view of the image forming apparatus of  FIG. 1  in a state in which a front cover is open; 
         FIG. 3  is a plan view of the image forming apparatus of  FIG. 1 ; 
         FIG. 4  is a back view of the image forming apparatus of  FIG. 1 ; 
         FIGS. 5A and 5B  are side views of movement of a carriage and a maintenance unit in exemplary embodiments of this disclosure; 
         FIGS. 6A and 6B  are side views of movement of a supply unit in exemplary embodiments of this disclosure; 
         FIG. 7  is a side view of movement of the supply unit; 
         FIGS. 8A and 8B  are plan views of movement of the supply unit; 
         FIG. 9  is a plan view of movement of the supply unit; 
         FIGS. 10A and 10B  are back views of movement of the supply unit; 
         FIG. 11  is a back view of movement of the supply unit; 
         FIG. 12  is a schematic block diagram of a controller of an image forming apparatus in exemplary embodiments of this disclosure; 
         FIG. 13  is a front view of an apparatus body in a special control mode according to an exemplary embodiment of this disclosure; 
         FIG. 14  is a flowchart of a procedure of processing in a special control mode according to an exemplary embodiment of this disclosure; 
         FIG. 15  is a flowchart of a procedure of processing in a special control mode according to an exemplary embodiment of this disclosure; 
         FIG. 16  is a flowchart of a procedure of processing in a special control mode according to an exemplary embodiment of this disclosure; 
         FIG. 17  is a flowchart of a procedure of processing in a special control mode according to an exemplary embodiment of this disclosure; and 
         FIG. 18  is a schematic view of an example of an operation panel to instruct shift to and canceling of a special control mode in exemplary embodiments of this disclosure. 
     
    
    
     The accompanying drawings are intended to depict exemplary 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 OF EXEMPLARY EMBODIMENTS 
     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. 
     For example, in this disclosure, the term “sheet” used herein is not limited to a sheet of paper and includes anything such as OHP (overhead projector) sheet, cloth sheet, glass sheet, or substrate on which ink or other liquid droplets can be attached. In other words, the term “sheet” is used as a generic term including a recording medium, a recorded medium, a recording sheet, and a recording sheet of paper. The terms “image formation”, “recording”, “printing”, “image recording” and “image printing” are used herein as synonyms for one another. 
     The term “image forming apparatus” refers to an apparatus that ejects liquid on a medium to form an image on the medium. The medium is made of, for example, paper, string, fiber, cloth, leather, metal, plastic, glass, timber, and ceramic. The term “image formation” 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” also includes only causing liquid droplets to land on the medium). 
     The term “ink” is not limited to “ink” in a narrow sense, unless specified, but is used as a generic term for any types of liquid usable as targets of image formation. For example, the term “ink” includes recording liquid, fixing solution, DNA sample, resist, pattern material, resin, and so on. 
     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. 
     Although the exemplary embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and all of the components or elements described in the exemplary embodiments of this disclosure are not necessarily indispensable to the present invention. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, exemplary embodiments of the present disclosure are described below. 
     First, an image forming apparatus according to exemplary embodiments of this disclosure is described with reference to  FIGS. 1 to 4 . 
       FIG. 1  is a side view of a mechanical section of an image forming apparatus according to exemplary embodiments of this disclosure.  FIG. 2  is a side view of the image forming apparatus of  FIG. 1  in a state in which a front cover is opened.  FIG. 3  is a plan view of the image forming apparatus of  FIG. 1 .  FIG. 4  is a back view of the image forming apparatus of  FIG. 1 . 
     The image forming apparatus illustrated in  FIGS. 1 to 4  is a serial-type image forming apparatus and includes, e.g., an image forming device  2  serving as an image forming unit and a conveyance assembly  5  serving as a conveyance unit inside an apparatus body  1 . The image forming apparatus also has a feed tray  4  serving as a sheet feeder to load sheets  10  serving as recording media at a lower side of the apparatus body  1 . It is to be noted that the sheet feeder is not limited to the feed tray  4  illustrated in  FIGS. 1 to 4 . In some embodiments, the sheet feeder is, for example, a sheet feed cassette. 
     When a sheet  10  is fed from the feed tray  4 , the conveyance assembly  5  receives the sheet  10 . While the sheet  10  is intermittently conveyed in a vertical direction by the conveyance assembly  5 , the image forming device  2  horizontally ejects liquid droplets to record a desired image on the sheet  10 . The sheet  10  having the desired image formed thereon is further conveyed upward through an output conveyance unit  6 , and discharged onto an output tray  7  serving as an output unit. 
     For duplex printing (double-face printing), after printing on one face (front face) ends, a reverse unit  8  receives the sheet  10  from the output conveyance unit  6 . While conveying the sheet  10  in the opposite direction (downward direction), the conveyance assembly  5  turns around and feeds the sheet  10  toward the image forming device  2  again so that the image forming device  2  can print on the other face (back face) of the sheet  10 . After printing on the other face (back face) ends, the output conveyance unit  6  outputs the sheet  10  to the output tray  7 . 
     In the image forming device  2 , a carriage  23  mounting at least one recording head  24  is movably supported by a main guide member  21  and a sub guide member extending between a left side plate  101 L and a right side plate  101 R. A main scanning motor  25  of a carriage moving assembly moves the carriage  23  for scanning in a main scanning direction via a timing belt looped between a driving pulley and a driven pulley. 
     The carriage  23  mounts, for example, recording heads  24   a  and  24   b  (referred to as “recording heads  24 ” unless distinguished) serving as liquid ejection heads to eject ink droplets of different colors, e.g., yellow (Y), magenta (M), cyan (C), and black (K). 
     The recording heads  24   a  and  24   b  having nozzle rows are mounted on the carriage  23  so that multiple nozzles forming each of the nozzle rows are arrayed in line in a sub scanning direction perpendicular to the main scan direction and ink droplets are horizontally ejected from the nozzles. In other words, the image forming apparatus employs a horizontal ejection method in which a nozzle face having multiple nozzles in each recording head  24  is oriented in the vertical direction to horizontally eject liquid droplets. 
     Each recording head  24  has, for example, two nozzle rows, each of which multiple nozzles are arrayed in line to eject liquid droplets. For example, the recording head  24   a  ejects droplets of yellow (Y) from one of the nozzle rows and droplets of magenta (M) from the other of the nozzle rows. In addition, the recording head  24   b  ejects droplets of black (K) from one of the nozzle rows and droplets of cyan (C) from the other of the nozzle rows. 
     The carriage  23  mounts head tanks  29  to supply the respective color inks to the corresponding nozzle rows of the recording heads  24 . 
     A supply unit  200  is disposed at a back face side of the carriage  23  to supply inks to the head tanks  29 . The supply unit  200  has a cartridge unit  201  to replaceably accommodate ink cartridges  100  serving as liquid cartridges and a supply pump  202  to deliver ink stored in the ink cartridges  100 . The supply pump  202  delivers ink to the recording heads  24  via a supply tube  203 . 
     A maintenance unit  9  is disposed below the image forming device  2  and the supply unit  200  at a position opposite a position of the conveyance assembly  5  via the image forming device  2 . The maintenance unit  9  serves as a maintenance device to perform maintenance operations to maintain and recover good conditions of the recording heads  24 . 
     The sheets  10  in the feed tray  4  are separated by a sheet feed roller (half-moon-shaped roller)  43  and a separation pad  44  and fed sheet by sheet into the apparatus body  1 . The sheet  10  is sent along a conveyance guide member  45  to between a conveyance belt  51  and a regulation roller  48 , and attached to and conveyed by the conveyance belt  51 . 
     The conveyance assembly  5  includes, e.g., the conveyance belt  51 , a conveyance roller  52 , a driven roller  53 , and a charging roller  54 . The conveyance belt  51  has an endless shape and is looped around the conveyance roller  52 , serving as a driving roller, and the driven roller  53 . The charging roller  54  charges the conveyance belt  51 . The conveyance assembly  5  also has a platen member  55 , a conveyance roller  56 , and a spur wheel  58 . The platen member  55  is disposed at a position opposing the image forming device  2  to maintain flatness of the conveyance belt  51 . The conveyance roller  56  is disposed opposing the spur wheel  58 . 
     The conveyance roller  52  is rotated by a sub-scanning motor via a timing belt and a timing pulley. By rotation of the conveyance roller  52 , the conveyance belt  51  is moved for circulation in a belt conveyance direction (also referred to as sub-scanning direction or sheet conveyance direction). 
     The output conveyance unit  6  includes an output guide member  61 , an output conveyance roller  62 , a spur wheel  63 , an output conveyance roller  66 , a spur wheel  67 , an output roller  64 , and a spur wheel  65 . The output conveyance unit  6  discharges the sheet  10  having an image formed, from between the output roller  64  and the spur wheel  65  onto the output tray  7  in a face-down manner. 
     The reverse unit  8  sends the sheet  10 , which is partially discharged to the output tray  7 , back to between the conveyance belt  51  and the regulation roller  48  while turning the sheet  10  upside down in a switchback manner. The reverse unit  8  has a switching claw  81  to switch between an output passage and a reverse passage, a reverse guide member  82 , a conveyance roller  83 , and a spur wheel  84  serving as a reverse roller. 
     The reverse unit  8  also has an auxiliary conveyance roller  85  opposing the driven roller  53  and an auxiliary conveyance roller  87  opposing the conveyance roller  52 . The reverse unit  8  also has a bypass guide member  86 . When the sheet  10  is separated from between an opposite conveyance area of the conveyance belt  51  (in which the sheet  10  is conveyed in a direction opposite the sheet conveyance direction) and the auxiliary conveyance roller  87 , the bypass guide member  86  guides the sheet  10  to between the conveyance belt  51  and the regulation roller  48 . 
     In the image forming apparatus having the above-described configuration, the sheet  10  is separately fed from the feed tray  4 , is electrostatically attached onto the conveyance belt  51  charged by the charging roller  54 , and conveyed in the vertical direction by the circulation of the conveyance belt  51 . By driving the recording heads  24  in accordance with image signals while moving the carriage  23 , ink droplets are ejected onto the stopped sheet  10  to form one line of a desired image. The sheet  10  is fed by a certain distance to prepare for recording another line of the image. After the recording of the image is completed, the sheet  10  is discharged to the output tray  7 . 
     For duplex printing, a first face of a sheet  10  is printed in the same manner as described above. When a rear edge of the sheet  10  passes a branching part (switching claw  81 ) of the reverse unit  8 , the output roller  64  is rotated in reverse to switch the sheet  10  back. Further, the sheet  10  is guided toward the reverse guide member  82 , conveyed to between the conveyance roller  83  and the spur wheel  84 , and sent into between the opposite conveyance area of the conveyance belt  51  and the auxiliary conveyance roller  85 . 
     As a result, the sheet  10  is attached onto the conveyance belt  51  by static electricity, conveyed by the circulation of the conveyance belt  51 , separated from the conveyance belt  51  at the conveyance roller  52 , guided by the bypass guide member  86 , and sent into between the normal conveyance area of the conveyance belt  51  and the regulation roller  48 . Then, the sheet  10  is adhered onto the conveyance belt  51  and conveyed again to an image formation area in which image formation is performed by the recording heads  24 . After a second face of the sheet  10  is printed, the sheet  10  is output to the output tray  7 . 
     Next, an opening configuration of a conveyance unit of the image forming apparatus according to an exemplary embodiment of this disclosure is described below. 
     At a front face side of the apparatus body  1 , the front cover  101  serving as an opening and closing cover is disposed so as to be openable and closable around a support shaft  102  serving as a fulcrum disposed at a lower end of the front cover  101 . On the front cover  101  are mounted a guide member  103  to form a reverse passage, the conveyance roller  83 , and the auxiliary conveyance rollers  85  and  87 . 
     The conveyance belt  51 , the conveyance roller  52 , the driven roller  53 , the conveyance roller  56 , and the platen member  55  are integral parts of a conveyance unit  300 . The conveyance unit  300  is openable and closable (swingable) around a support shaft  52   a  of the conveyance roller  52  serving as a fulcrum. 
     Thus, by opening the front cover  101  and the conveyance unit  300 , an opening  301  is formed at the front face side in the apparatus body  1 . The ink cartridges  100  are inserted into and extracted from the cartridge unit  201  through the opening  301 . 
     Next, a maintenance configuration according to an exemplary embodiment of this disclosure is described with reference to  FIGS. 5A and 5B . 
       FIGS. 5A and 5B  are side views of the carriage and the maintenance unit in movement. 
     In  FIGS. 5A and 5B , the maintenance unit  9  is disposed below the image forming device  2  and at a position opposite a position of the conveyance assembly  5  via the image forming device  2 . The maintenance unit  9  serves as a maintenance device to perform maintenance operations to maintain and recover good conditions of the recording heads  24 . 
     The feed tray  4  (feed unit)  4  is disposed below the apparatus body  1  to feed a recording medium (sheet  10 ). At an upper portion of the apparatus body  1  is disposed the output tray  7  serving as the output unit onto which the recording medium having an image formed by the image forming device  2  is discharged. The image forming device  2  and the maintenance unit  9  are disposed in a space surrounded by the feed tray  4 , the output tray  7 , and the conveyance assembly  5 . The maintenance unit  9  is disposed below the image forming device  2 . 
     The maintenance unit  9  has a frame  90  provided with caps  91  to cap nozzle faces  124  of the recording heads  24  and a wiping member (wiping blade)  94  to wipe the nozzle faces  124  of the recording heads  24 . The maintenance unit  9  also has, e.g., a suction pump  97  serving as a suction device connected to the caps  91  and a waste liquid tank  98  connected to the suction pump  97 . 
     The carriage  23  mounting the recording heads  24  of the image forming device  2  is displaceable between an image forming position indicated by a broken line in  FIG. 5A  and a maintenance position indicated by a solid line in  FIGS. 5A and 5B . The recording heads  24  horizontally eject liquid droplets at the image forming position and are opposable to the maintenance unit  9  at the maintenance position. 
     In the configuration of  FIGS. 5A and 5B , since the maintenance unit  9  is disposed lower than the image forming device  2 , the recording heads  24  are rotated by substantially 90 degrees downward from the image forming position to the maintenance position so that the nozzle faces  124  are directed downward. 
     The driving motor (main scanning motor) moves the carriage  23  for scanning in the main scanning direction. Driving force of the main scanning motor is transmitted via a clutch assembly to rotate the carriage  23 , thus resulting in a reduced number of components. 
     The maintenance unit  9  is movable between a maintenance position indicated by the solid line in  FIG. 5B  and a retracted position indicated by a solid line in  FIG. 5A  (i.e., a broken line in  FIG. 5B ). The caps  91  cap the nozzle faces  124  of the recording heads  24  at the maintenance position. The maintenance unit  9  is retracted from the maintenance position to the retracted position. 
     The driving motor (sub-scanning motor) moves the conveyance belt  51  in the sub-scanning direction. Driving force of the sub-scanning motor is transmitted via a clutch assembly to move the maintenance unit  9 , thus resulting in a reduced number of components. 
     Next, movement of the carriage  23  and the maintenance unit  9  is described below. 
     For example, when nozzles of the recording heads  24  are clogged or when negative pressure in the head tanks  29  is not maintained and thus menisci of nozzles are broken, cleaning operation (maintenance operation) is performed. The cleaning operation includes, e.g., sucking operation, wiping operation, and dummy ejection operation. The sucking operation is performed, for example, in an order of capping, ink suction, decapping, and suction of the interior of the caps. 
     As illustrated in  FIG. 5A , the carriage  23  is rotated by substantially 90 degrees in a direction indicated by an arrow B from the image forming position indicated by the broken line to the maintenance position indicated by the solid line. Thus, the nozzle faces  124  are moved so as to direct downward. 
     Then, as illustrated in  FIG. 5B , the maintenance unit  9  is moved obliquely upward in a direction indicated by an arrow C from the retracted position to the maintenance position, to cap the nozzle faces  124  of the recording heads  24  with the caps  91 . Alternatively, in some embodiments, after the maintenance unit  9  is moved vertically upward, the maintenance unit  9  is horizontally moved. 
     The suction pump  97  is driven to suck a predetermined amount of liquid (ink) from the nozzles of the recording heads  24  into the caps  91 , thus discharging liquid into the caps  91 . 
     The maintenance unit  9  is moved to a position at which the caps  91  are placed away (decapped) from the nozzle faces  124  of the recording heads  24 . 
     The suction pump  97  is activated again to suck residual waste liquid remaining in the caps  91  to discharge the waste liquid into the waste liquid tank  98 . 
     Then, the wiping member  94  is moved to a wipable position at which the wiping member  94  can wipe the nozzle faces  124  of the recording heads  24 , and starts to wipe the nozzle faces  124 . A wiping direction of the wiping member  94  may be any of a longitudinal direction and a lateral direction relative to the nozzle rows. 
     After the wiping member  94  wipes the nozzle faces  124 , the caps  91  are placed under the nozzle faces  124  of the recording heads  24  and the recording heads  24  perform dummy ejection to eject droplets to the inside of the caps  91 . After the dummy ejection, the suction pump  97  is activated to suck waste liquid from the inside of the caps  91  and discharge the waste liquid into the waste liquid tank  98 . 
     The maintenance unit  9  is moved obliquely downward to the retracted position indicated by the solid line in  FIG. 5A . 
     As described above, the maintenance unit  9  is disposed within the space surrounded by the feed tray  4 , the output tray  7 , and the conveyance assembly  5  and at a side opposite the conveyance assembly  5  via the image forming device  2  (a side opposite the droplet ejected direction with respect to the recording heads  24 ). Such a configuration reduces the size of the apparatus body in the width direction, thus allowing downsizing. 
     In addition, the caps  91  of the maintenance unit  9  are directed upward. Such a configuration prevents liquid from leaking from the caps  91  even when liquid is discharged into the caps  91 . 
     In other words, if, with the nozzle faces  124  held in a vertical state and capped with caps, liquid is discharged into the caps, waste liquid would drip down from the caps when the caps are decapped from the nozzle faces  124 . Hence, for example, it is conceivable to provide the caps with air release valves to release liquid from the inside of the caps and then open the inside of the caps relative to the atmosphere. After the inside of the caps is opened to the atmosphere, waste liquid remaining in the caps is sucked and discharged by the suction pump, and then the caps are decapped from the nozzle faces. Consequently, the configuration and operation are complicated and, even when waste liquid in the caps is discharged by suction, residual waste liquid might remain in the caps, thus resulting in dropping of waste liquid from the caps. 
     By contrast, in the above-described configuration, liquid is discharged into the caps  91  with the caps  91  directed upward, thus preventing waste liquid from dropping from the caps. 
     Next, a normal action conducted (or controlled by a first controller) when the openable cover is opened is described with reference to  FIGS. 6A to 11B . 
       FIGS. 6A, 6B, and 7  are side views of an image forming apparatus according to exemplary embodiments of this disclosure.  FIGS. 8A, 8B, and 9  are plan views of the image forming apparatus.  FIGS. 10A, 10B, and 11  are plan views of the image forming apparatus. 
     As illustrated in  FIG. 6A ,  FIG. 8A , and  FIG. 10A , when a user opens the front cover  101  in a direction indicated by an arrow D, a front-cover opening-and-closing sensor  400  serving as a cover sensor detects that the front cover  101  is opened and the conveyance unit  300  is opened. 
     When the front cover  101  is opened and the conveyance unit  300  is opened, the opening  301  is formed at the front side of the apparatus body  1 . 
     Then, as illustrated in  FIG. 8A , the carriage  3  is moved toward the maintenance unit  9  (to the home position). 
     As illustrated in  FIG. 6B , the carriage  3  is rotated by substantially 90 degrees in the direction indicated by the arrow B and moved so as to direct the nozzle faces  124  downward (see also  FIGS. 8B and 10B ). 
     Next, as illustrated in  FIG. 7 , the maintenance unit  9  is moved obliquely upward in the direction indicated by the arrow C to cap the nozzle faces  124  of the recording heads  24  (see also  FIGS. 9 and 11 ). 
     Next, a controller of the image forming apparatus in exemplary embodiments of this disclosure is described with reference to  FIG. 12 . 
       FIG. 12  is a block diagram of a controller  500  of the image forming apparatus according to exemplary embodiments of this disclosure. 
     The controller  500  includes a central processing unit (CPU)  501 , a read-only memory (ROM)  502 , a random access memory (RAM)  503 , a rewritable non-volatile random access memory (NVRAM)  504 , and an application specific integrated circuit (ASIC)  505 . The CPU  501  controls the entire image forming apparatus. The ROM  502  stores programs, including programs causing the CPU  501  to perform control processing according to exemplary embodiments described below, and other fixed data. The RAM  503  temporarily stores image data or other data. 
     The rewritable non-volatile memory  504  retains data even while the apparatus is powered off. The ASIC  505  processes image data signals, performs image processing, e.g., sorting, or processes input and output signals for controlling the entire image forming apparatus. 
     The controller  500  also includes a print controller  508 , a head driver (driver IC)  509 , a motor driver  510 , a motor driver  511 , and an alternating current (AC) bias supplier  512 . The print controller  508  includes a data transmitter and a driving signal generator to drive and control the recording heads  24  in accordance with print data. The head driver  509  drives the recording heads  24  mounted on the carriage  23 . 
     The motor driver  510  drives the main scanning motor  25  for moving the carriage  23 , and the motor driver  511  drives the sub-scanning motor  151  for circulating the conveyance belt  51 . The AC bias supplier  512  supplies AC bias to the charging roller  54 . 
     The controller  500  further includes a carriage rotation driver  521 , a maintenance-unit driver  522 , and a cartridge-unit driver  523 . The carriage rotation driver  521  drives a carriage rotating assembly  401  to rotate the carriage  3  around the main guide member  21 . The maintenance-unit driver  522  drives a maintenance-unit moving assembly  402  to move the maintenance unit  9 . The cartridge-unit driver  523  drives a cartridge-unit moving assembly  403  to move the cartridge unit  201 . 
     The controller  500  is connected to an operation unit  514  (e.g., operation panel) to input and display information necessary to the image forming apparatus. The operation unit  514  forms part of an instruction unit to instruct shift to special control according to exemplary embodiments of this disclosure. 
     The controller  500  includes an interface (I/F)  506  to transmit and receive data and signals to and from a host  600 , such as an information processing device (e.g., personal computer) 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 transmits image data to the head driver  509 . It is to be noted that dot-pattern data for image output may be created by a printer driver  601  of the host  600 . 
     The print controller  508  transmits 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 transmission of print data and determination of the transmission. The print controller  508  further includes a driving signal generator including, e.g., a digital/analog (D/A) converter to convert pattern data of driving pulses stored in the ROM  502  from digital to analog, a voltage amplifier, and a current amplifier. From the driving signal generator, driving signals of one or more driving pulses are output to the head driver  509 . 
     In accordance with serially-input image data corresponding to one line of a desired image recorded by the recording heads  24 , the head driver  509  selectively applies driving pulses constituting a driving signal transmitted from the print controller  508 , to the recording heads  24  to drive the recording heads  24 . At this time, by selecting driving pulses constituting the driving signal, liquid droplets of different liquid amounts, such as large-size droplets, medium-size droplets, and small-size droplets, can be selectively ejected to form different sizes of dots. 
     The I/O unit  513  obtains information from a group of sensors  515  mounted on a main scanning encoder, a sub-scanning encoder, and other devices. Information for controlling devices is extracted and used to control the print controller  508 , the motor driver  510  and  511 , and the AC bias supplier  512 . 
     The I/O unit  513  also obtains information from the front-cover opening-and-closing sensor  400  to detect opening and closing of the front cover  101 , a sheet-on-belt sensor  410  (serving as a media sensor) to detect whether a sheet is placed on the conveyance belt  51 , and a cartridge remaining-amount sensor  411  to detect an amount of ink remaining in the ink cartridges  100 . Information for controlling devices is extracted and used to control, e.g., the carriage rotation driver  521 , the maintenance-unit driver  522 , and the cartridge-unit driver  523 . 
     The group of sensors  515  includes, for example, a sheet sensor to detect a sheet, a thermistor to monitor temperature and/or humidity in the apparatus body  1 , and a voltage sensor to monitor the voltage of the conveyance belt charged. The I/O unit  513  processes information from such various types of sensors. 
     The controller  500  also serves as a control unit according to exemplary embodiments of this disclosure. When the image forming apparatus is on standby or the front cover  101  is open as described above, the controller  500  normally controls operation (referred to as normal operation) of capping the nozzle faces of the recording heads  24  with the caps  91  of the maintenance unit  9 . When the front cover  101  is opened during printing, the carriage  23  is moved to the maintenance unit  9  (home position) to cap the nozzle faces of the recording heads  24  with the caps  91 . 
     As described above, when the front cover  101  is opened, normally, the nozzle faces of the recording heads  24  are capped with the caps  91 , thus hampering a service person from touching or checking the nozzle faces. 
     By contrast, when the controller  500  receives an instruction from outside, the controller  500  performs control (referred to as special control) to expose the nozzle faces of the recording heads  24  to an area (the opening  301 ) opened by the front cover  101 . A state in which the image forming apparatus is under the special control is referred to as “special control mode”. 
     In the special control mode, as illustrated in  FIG. 13 , the caps  91  are detached (decapped) from the nozzle faces  124  of the recording heads  24 . By rotating the carriage  23 , the controller  500  controls the nozzle faces  124  of the recording heads  24  to face an area from the opening  301  to the front side of the apparatus body. 
     Then, by opening the front cover  101 , the nozzle faces  124  of the recording heads  24  are exposed to the opening  301  (see  FIG. 7 ), thus facilitating a service person to check and clean the nozzle faces  124 . 
     As described above, in this exemplary embodiment, the image forming apparatus has a controller to perform special control to expose the nozzle faces of the recording heads to an area opened by the openable cover when the controller  500  receives an external instruction, thus facilitating cleaning work of the nozzle faces of the recording heads. 
     Next, a processing procedure of the special control mode according to an exemplary embodiment of this disclosure is described with reference to  FIG. 14 . 
     When a certain operation key of the operation unit  514  is turned on (YES at S 101 ), at S 101  the controller  500  determines whether or not the nozzle faces  124  of the recording heads  24  are capped (i.e., the image forming apparatus is on standby). 
     If the image forming apparatus is not on standby (NO at S 101 ), at S 103  the controller  500  continues current operation until the image forming apparatus turns into a standby state. For example, during printing, the controller  500  waits until the current print job ends, or during occurrence of an error, the controller  500  waits until the error is cleared. 
     When the image forming apparatus is on standby or turns into the standby state (YES at S 101 ), at S 102  the controller  500  starts the special control and shifts to the special control mode (turns on the special control mode). 
     As described above, by handling the certain operation key on the operation unit  514 , the image forming apparatus can be turned into the special control mode, thus reducing the operation time with a simple configuration. It is to be noted that the certain operation key to instruct the special control may be preferably a combination of keys not used in the normal mode or the special control may be instructed by pushing the certain key for a long seconds. 
     At S 104 , the controller  500  determines whether or not the front cover  101  is opened in the special control mode. 
     When the front-cover opening-and-closing sensor  400  detects that the front cover  101  is opened (YES at S 104 ), at S 105  the controller  500  controls the maintenance unit  9  to move to the retracted position and release capping of the nozzle faces  124  with the caps  91  (decapping). At S 106 , the controller  500  rotates the carriage  23  to expose the nozzle faces  124  of the recording heads  24  to the area from the opening  301  to the front side of the apparatus body  1 . 
     In such a state, at S 107 , a service person can check and clean the nozzle faces  124  of the recording heads  24 . 
     When the front cover  101  is closed at S 108  and the certain key on the operation unit  514  is operated (turned off) at S 109 , at S 110  the controller  500  causes the carriage  23  to move to the home position. 
     At S 111 , the controller  500  causes the carriage  23  to rotate. At S 112 , the controller  500  causes the maintenance unit  9  to move to the maintenance position and cap the nozzle faces  124  with the caps  91 . 
     At S 113 , the controller  500  cancels the special control mode (turns off the special control mode). 
     To cancel the special control mode, the same key as the certain key to instruct the start of the special control mode may be employed or a power key may be employed. In the case of using the power key, the controller  500  do not power off hardware until the processing of the special control mode ends. 
     In addition, when a print job is received (i.e., printing is instructed) during execution of the special control mode, the controller  500  preferably starts the print job after the special control mode is canceled. Such a configuration prevents a conveyance error that might be otherwise caused by conveying a sheet with the front cover  101  including the conveyance assembly  5  open, and also prevents ink droplets from being ejected from the nozzle faces  124  exposed the area from the opening  301  to the front side of the apparatus body  1 . 
     Next, a processing procedure of the special control mode according to an exemplary embodiment of this disclosure is described with reference to  FIG. 15 . 
     For this exemplary embodiment illustrated in  FIG. 15 , in the above-described exemplary embodiment described with reference to  FIG. 14 , when the special control mode is turned on, the controller  500  displays on a display part (e.g., display part  514   a  in  FIG. 18 ) of the operation unit  514  an indication that the image forming apparatus is in the special control mode. When the special control mode is canceled, the controller  500  turns off the indication that the image forming apparatus is in the special control mode. 
     Specifically, in this exemplary embodiment illustrated in  FIG. 15 , the processing of 
     S 201  to S 203  is conducted in the same manner as that of S 101  to  103  in the above-described exemplary embodiment described with reference to  FIG. 14 . When the special control mode is turned on at S 202 , at S 204  the controller  500  displays, on the display part of the operation unit  514 , the indication that the image forming apparatus is in the special control mode. The processing from S 205  to  213  is conducted in the same manner as S 104  to  112 , respectively. At S 214 , the controller  500  turns off the indication on the display part that the image forming apparatus is in the special control mode. At S 215 , the controller  500  cancels the special control mode. 
     As described above, displaying on the display part the indication that the image forming apparatus is in the special control mode prevents a user from accidentally touching the nozzle faces as the user forgets canceling the special control mode. 
     Next, a processing procedure of the special control mode according to an exemplary embodiment of this disclosure is described with reference to  FIG. 16 . 
     For this exemplary embodiment illustrated in  FIG. 16 , in the above-described exemplary embodiment described with reference to  FIG. 15 , when the front-cover opening-and-closing sensor  400  detects that the front cover  101  is closed, the controller  500  cancels the special control mode. Specifically, in this exemplary embodiment illustrated in  FIG. 16 , the processing of S 301  to S 308  is conducted in the same manner as that of S 201  to  208  in the above-described exemplary embodiment described with reference to  FIG. 15 . When, at S 309 , the front-cover opening-and-closing sensor  400  detects that the front cover  101  is closed (YES at S 309 ), the controller  500  performs the processing from S 310  to  312  in the same manner as S 211  to  213  of  FIG. 15 , respectively. At S 313 , the controller  500  turns off the indication on the display part that the image forming apparatus is in the special control mode. At S 314 , the controller  500  cancels the special control mode. 
     Such a configuration obviates pushing the certain key on the operation unit  514  again in canceling the special control mode. Thus, such a configuration allows easier operation of a service person and prevents a user from accidentally touching the nozzle faces as the user forgets canceling the special control mode. 
     Next, a processing procedure of the special control mode according to an exemplary embodiment of this disclosure is described with reference to  FIG. 17 . 
     For this exemplary embodiment illustrated in  FIG. 17 , in the above-described exemplary embodiment described with reference to  FIG. 16 , when the controller  500  cancels the special control mode after the front cover  101  is closed, the controller  500  performs cleaning operation and then capping operation. Specifically, in this exemplary embodiment illustrated in  FIG. 17 , the processing of S 401  to S 411  is conducted in the same manner as that of S 301  to  311  in the above-described exemplary embodiment described with reference to  FIG. 16 . After the controller  500  causes the maintenance unit  9  to move to the maintenance position at S 412 , at S 413  the controller  500  causes the wiper member  94  to clean the nozzle faces  124  of the recording heads  24 . At S 414 , the controller  500  causes the caps  91  to cap the nozzle faces  124  of the recording heads  24 . At S 415 , the controller  500  turns off the indication on the display part that the image forming apparatus is in the special control mode. At S 416 , the controller  500  cancels the special control mode. 
     Such a configuration prevents occurrences of ejection failure and non-ejection nozzles that might be otherwise caused by drying of nozzles due to exposure of the nozzle faces during the special control mode. 
     Next, an example of the operation panel  514  to instruct shift to or canceling of the special control mode in the above-described exemplary embodiments is described with reference to  FIG. 18 . 
     In the example illustrated in  FIG. 18 , the operation panel  514  includes a display part  514   a  and operation keys. The display part  514   a  displays various types of information. The operation keys include, for example, a power key  514   b , a menu key  514   c , an upward key  514   d , a downward key  514   e , an enter key  514   f , a back key  514   g , a print cancel key  514   h , and a forceful sheet output  514   i.    
     In this exemplary embodiment, the operation panel  514  also includes, e.g., a special control mode key  514   j  to instruct shift to and canceling of the above-described special control mode. In such a case, as described above, a combination of operation buttons may be used to instruct shift to and canceling of the above-described special control mode. 
     In the above-described exemplary embodiments, the image forming apparatus has a configuration in which liquid droplets are horizontally ejected to from an image on a sheet. It is to be noted that the image forming apparatus is not limited to the above-described configuration. In some embodiments, for example, the image forming apparatus may have a configuration in which liquid droplets are ejected vertically downward to form an image on a sheet. 
     In the configuration in which liquid droplets are horizontally ejected, the nozzle faces of the recording heads are horizontally directed. Accordingly, as described above, by opening the openable cover, the nozzle faces of the recording heads are opened and exposed to the outside. 
     By contrast, in the configuration in which liquid droplets are ejected vertically downward, the nozzle faces of the recording heads are normally directed downward. Accordingly, the recording heads are rotated to expose the nozzle faces to an area opened by the openable cover. 
     The direction in which droplets are ejected is not limited to the horizontal or vertically downward direction. For example, liquid droplets may be ejected upward, obliquely downward, or obliquely upward. 
     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 above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.