Patent Publication Number: US-11046094-B2

Title: Liquid discharge apparatus and method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-030771, filed on Feb. 22, 2019 in the Japan Patent Office, the entire disclosures of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure relate to a liquid discharge apparatus and a method thereof. 
     Related Art 
     A liquid discharge apparatus includes a liquid discharge head to discharge a liquid onto a medium. The liquid discharge apparatus discharges the liquid from the liquid discharge head while scanning the liquid discharge head. A liquid to be discharged from the liquid discharge head includes a curable liquid having a property of being cured by irradiation of light of a specific wavelength. The liquid discharge apparatus that discharges the curable liquid includes a light irradiator that irradiates the curable liquid discharged onto the medium with the light such as ultraviolet rays. 
     The liquid discharge apparatus periodically performs a maintenance operation (maintenance recovery operation) to ensure the liquid discharge head continues to stably discharge. The maintenance operation prevents clogging of a nozzle of the liquid discharge head and stabilizes a state of liquid discharge of the liquid discharge head. In the maintenance operation, the liquid discharge apparatus performs a discharge operation (dummy-discharge operation) at a position different from a position at which the medium is placed. The liquid discharge apparatus includes a container (dummy-discharge receptacle) at a position at which the dummy-discharge operation is performed. The dummy-discharge receptacle collects the liquid discharged by the dummy-discharge operation. The dummy-discharge receptacle may collect the curable liquid. 
     SUMMARY 
     In an aspect of this disclosure, a novel liquid discharge apparatus is described that includes a liquid discharge head configured to discharge a liquid onto a medium, a carriage mounting the liquid discharge head configured to move the liquid discharge head in a main scanning direction, a dummy-discharge receptacle to receive a dummy-discharge liquid discharged from the liquid discharge head in a dummy-discharge operation, a light irradiator to irradiate the dummy-discharge liquid in the dummy-discharge receptacle with a light and circuitry. The circuitry sets a plurality of dummy-discharge areas virtually dividing an interior of the dummy-discharge receptacle, moves the carriage in the main-scanning direction to a first dummy-discharge area among the plurality of dummy-discharge areas, drives the liquid discharge head to discharge the dummy-discharge liquid onto the first dummy-discharge area in the dummy-discharge receptacle, irradiates the dummy-discharge liquid in the first dummy-discharge area in the dummy-discharge receptacle with the light, determines whether a number of dummy-discharge operations exceeds a threshold value, and moves the carriage to a second dummy-discharge area different from the first dummy-discharge area among the plurality of dummy-discharge areas if the number of dummy-discharge operations exceeds the threshold value. 
     In another aspect of this disclosure, a novel method of performing a dummy-discharge operation in a liquid discharge apparatus is described. The method includes setting a plurality of dummy-discharge areas virtually dividing an interior of a dummy-discharge receptacle, moving a carriage in a main scanning direction to a first dummy-discharge area among the plurality of dummy-discharge areas, driving a liquid discharge head to discharge a dummy-discharge liquid onto the first dummy-discharge area in the dummy-discharge receptacle, irradiating the dummy-discharge liquid in the first dummy-discharge area in the dummy-discharge receptacle with a light, determining whether a number of dummy-discharge operations exceeds a threshold value, and moving the carriage to a second dummy-discharge area different from the first dummy-discharge area among the plurality of dummy-discharge areas if the number of dummy-discharge operations exceeds the threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic plan view of a main part of a printer as an embodiment of a liquid discharge apparatus according to the present disclosure; 
         FIG. 2  is a schematic front view of the main part of the printer; 
         FIG. 3  is a schematic plan view of the main part of the printer; 
         FIG. 4  is a schematic front view of the main part of the printer illustrating a dummy-discharge operation of the printer; 
         FIG. 5  is a schematic front view of the main part of the printer illustrating the dummy-discharge operation of the printer; 
         FIG. 6  is a schematic plan view of the main part of the printer illustrating the dummy-discharge operation of the printer; 
         FIG. 7  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 8  is a schematic cross-sectional view of the dummy-discharge receptacle illustrating another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 9  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating still another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 10  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating still another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 11  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating still another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 12  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating still another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 13  is a schematic front view of the main part of the printer illustrating the dummy-discharge operation according to the present embodiment; 
         FIG. 14  is a graph illustrating a correlation between a number of dummy discharges in the dummy-discharge operation and a height of accumulated dummy-discharge liquids; 
         FIG. 15  is a schematic cross-sectional view of a dummy-discharge receptacle illustrating still another example of a state of accumulated dummy-discharge liquids by the dummy-discharge operation in the present embodiment; 
         FIG. 16  is a functional block diagram of a controller that controls an operation of the printer; and 
         FIG. 17  is a flowchart of a flow of the dummy-discharge operation in the printer. 
     
    
    
     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 have the same function, 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. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Hereinafter, embodiments of a liquid discharge apparatus according to the present embodiment is described with reference to the drawings. The liquid discharge apparatus according to the present embodiment discharges a curable liquid having a property of being cured by irradiation of a light (curing ray) having a specific wavelength. The liquid discharge apparatus has a characteristic of periodically performing a dummy-discharge operation to maintain an operation of the liquid discharge head and to recover a state of operation of the liquid discharge head. The liquid discharge apparatus further has a characteristic in a process of collecting the curable liquid discharged during the dummy-discharge operation. 
     [Structure of Liquid Discharge Apparatus] 
       FIG. 1  is a schematic plan view of an example of a configuration of a printer  100  as an embodiment of a liquid discharge apparatus.  FIG. 2  is a schematic front view of an example of a configuration of the printer  100 . A schematic configuration of the printer  100  is described with reference to  FIGS. 1 and 2 . 
     The printer  100  includes a stage  101 , a carriage  102 , a head device  103 , a light irradiator  104 , maintenance units  105   a  and  105   b , a drive motor  111 , a dummy-discharge receptacle  112 , a capping unit  113 , a carriage stay  114 , a controller (circuitry)  120 , and the like. 
     The controller  120  includes a computer that performs arithmetic processing to control all operations of the printer  100 , for example. Details of the controller  120  are given below. 
     The stage  101  includes a mounting surface on which a medium used for image formation is mounted. The stage  101  temporary fixes a conveyed medium on the mounting surface, and maintains a state in which the liquid discharged from the head device  103  is adhered onto the medium. The printer  100  includes an image forming area  106  previously set inside the stage  101 . The printer  100  discharges the liquid inside the image forming area  106  to form an image on the medium. The printer  100  includes a suction mechanism  107  at a position corresponding to the image forming area  106 . The suction mechanism  107  temporarily fixes the medium at a predetermined position in the image forming area  106 . 
     The printer  100  includes the suction mechanism  107  on a back side (lower side in  FIG. 2 ) of the mounting surface  101   a . The stage  101  includes a plurality of suction holes  108  communicating the mounting surface  101   a  and a back surface  101   b  of the stage  101  in a region corresponding to the image forming area  106  of the stage  101 . The suction mechanism  107  operates fans  109  that generate airflow flowing through the suction holes  108  of the stage  101  from the mounting surface  101   a  to the back surface  101   b  of the stage  101 . 
     Specifically, the air above the mounting surface  101   a  is vacuumed from the suction holes  108  toward the back surface  101   b  of the stage  101  by the fans  109 . Thus, the medium is attracted to and temporarily stuck to the mounting surface  101   a  of the stage  101  by the airflow generated by the fans  109  of the suction mechanism  107 . The suction mechanism  107  is not limited to a configuration using the airflow as described above but may also be a configuration using electrostatic suction. 
     The carriage  102  is slidably held at a predetermined height above the mounting surface  101   a  of the stage  101 . A carriage stay  114  holds the carriage  102 . The carriage stay  114  is an elongated bar-shaped member having a length longer than a width of the stage  101 . Each longitudinal end of the carriage stay  114  is held by a support  110 . Further, the drive motor  111  slidably moves the carriage stay  114  and the carriage  102  in a depth direction of the stage  101 . The depth direction is along a sub-scanning direction of the carriage  102 . 
     The drive motor  111  drives the carriage  102  held by the carriage stay  114  to reciprocally move in a width direction of the stage  101  along the carriage stay  114 . The width direction of the stage  101  is in a main-scanning direction of the carriage  102  along which the carriage  102  reciprocally moves. Thus, the carriage stay  114  and the drive motor  111  scans the carriage  102  in two dimensions parallel to the mounting surface  101   a  of the stage  101 . In the following description, a direction of movement of the carriage  102  along a longitudinal direction of the carriage stay  114  is referred to as the “main-scanning direction” as indicated by arrow “MSD” in  FIGS. 1 and 2 . Further, a direction of movement of the carriage  102  on the carriage stay  114  in the depth direction of the stage  101  by the drive motor  111  is referred to as the “sub-scanning direction” indicated by arrow “SSD” in  FIG. 1 . 
     The carriage  102  mounts a head device  103  including a plurality of the liquid discharge heads  119  to individually discharge liquids of a plurality of colors. Each of the head devices  103  discharges, for example, liquids colored white, cyan, magenta, yellow, black, clear, and primer (treatment liquid). The liquid discharged by the head device  103  according to the present embodiment is a curable liquid having a property of being cured when irradiated with light having a specific wavelength. Thus, the head device  103  can discharge the curable liquid and the processing liquid of each color. Thus, the controller  120  controls the head device  103  to discharge the curable liquid to a predetermined position in the medium temporarily stuck to the stage  101  while scanning the head device  103  in the main-scanning direction MSD and sub-scanning direction SSD by the driving force from the drive motor  111 . 
     Thus, a head scanner includes the drive motor  111 , the carriage  102 , and the carriage stay  114 . 
     The maintenance units  105   a  and  105   b , the dummy-discharge receptacle  112 , and the capping unit  113  are disposed outside the stage  101  in a scanning range (movable range) of the carriage  102  along the carriage stay  114 . 
     The maintenance unit  105   a  includes webbing  131 , for example, to clean the nozzles  130  in the liquid discharge head  119  of the head device  103 . With movement of the head device  103  above the maintenance unit  105   a  to face the maintenance unit  105   a , the maintenance unit  105   a  can clean the nozzles  130  of the liquid discharge head  119  with the webbing  131  to maintain the head device  103  to stably discharge the curable liquid and the processing liquid. 
     The maintenance unit  105   b  includes the dummy-discharge receptacle  112  within the scanning range of the carriage  102  outside the stage  101  (see  FIG. 1 ). The dummy-discharge receptacle  112  includes a container having a space to receive the liquid discharged by the “dummy-discharge operation” that is one of the maintenance operations of the head device  103 . The dummy-discharge receptacle  112  is, for example, a container having a concave shape in cross-section with an opening facing upward to the head device  103  (carriage  102 ). The dummy-discharge receptacle  112  is installed outside the stage  101 . The dummy-discharge receptacle  112  is replaceable with a new dummy-discharge receptacle  112  when full of the liquid related to the dummy-discharge operation. 
     The capping unit  113  includes caps  113   a  that protects nozzles  130  (see  FIG. 3 ) to prevent the nozzles  130  from drying when the liquid discharge head  119  of the head device  103  does not perform a discharge operation. Thus, the maintenance unit  105   b  includes the dummy-discharge receptacle  112  and the capping unit  113 . 
     The carriage  102  mounts light irradiators  104  that configure light irradiators. Each of the light irradiators  104  includes a light source that emits light having a specific wavelength to cure the curable liquid discharged from the head device  103 . The light irradiators  104  include, for example, an ultraviolet lamp (UV lamp) that radiates ultraviolet rays  117  (see  FIG. 5 ) as a light having a specific wavelength. The light irradiator  104  may irradiate an electron beam to cure the curable liquid. The light irradiators  104  irradiate, with ultraviolet rays  117 , the curable liquid discharged onto the medium on the stage  101  and the dummy-discharge receptacle  112 . As illustrated in  FIGS. 1 and 2 , the light irradiators  104  may be installed on both sides of the carriage  102  in the main-scanning direction MSD, or may be installed on only one side of the carriage  102  in the main-scanning direction MSD. The light irradiator  104  moves with the movement of the carriage  102 . 
     [Overview of Maintenance Operation] 
     The printer  100  having a configuration as described-above maintains stable discharge of the nozzles  130  in each of the liquid discharge heads  119  of the head device  103 . The printer  100  performs the maintenance operation to prevent the liquid in the nozzles  130  from drying and to prevent dust from entering the nozzles  130 . The maintenance units  105   a  and  105   b  perform the maintenance operation. The maintenance unit  105   b  includes the capping unit  113  that includes the caps  113   a  to cap the nozzle surfaces  119   a  (see  FIG. 4 ). The maintenance units  105   a  and  105   b  may include a wiper  132  (also referred to as a wiper blade, a wiping blade, a blade, or the like) installed in the maintenance units  105   a  and  105   b . The wiper  132  wipes and cleans the nozzle surface  119   a  of the liquid discharge head  119  (recording head). 
     When the printer  100  performs the maintenance operation, the controller  120  moves the head device  103  to the maintenance unit  105   b  and performs a recovery operation such as wiping the nozzle surface  119   a  of the liquid discharge head  119  with the wiper  132  to form a nozzle meniscus in each of the nozzles  130 . Then, the capping unit  113  of the maintenance unit  105   b  caps the nozzle surfaces  119   a  of the liquid discharge heads  119  with caps  113   a  until the next discharge operation. 
     Further, the printer  100  performs the dummy-discharge operation at a predetermined timing as one of the maintenance operations. The dummy-discharge operation is a discharge operation performed by moving the head device  103  to the dummy-discharge receptacle  112 . 
     [Head Device  103  and Dummy-Discharge Receptacle  112 ] 
     Next, the relation between the head device  103  and the dummy-discharge receptacle  112  is described below using  FIG. 3 . 
       FIG. 3  is a partial enlarged plan view of the carriage  102  and the dummy-discharge receptacle  112 . In  FIG. 3 , “MAIN-X1” indicates a dimension of one liquid discharge head  119  (recording head) in the head device  103  in the main-scanning direction MSD. Further, “SUB-Y1” in  FIG. 3  indicates a dimension in the sub-scanning direction SSD of one liquid discharge head  119  (recording head) in the head device  103 . 
     In  FIG. 3 , “MAIN-X” indicates a dimension of the dummy-discharge receptacle  112  in the main-scanning direction MSD. Further, “SUB-Y” in  FIG. 3  indicates a size of the dummy-discharge receptacle  112  in the sub-scanning direction SSD. 
     As illustrated in  FIG. 3 , the dummy-discharge receptacle  112  has an opening larger than a size of one liquid discharge head  119  (recording head) mounted on the head device  103  so that relations of MAIN-X1&lt;MAIN-X and SUB-Y1&lt;SUB-Y are satisfied. Thus, the dummy-discharge receptacle  112  has a dimension “MAIN-X” longer than the dimension “MAIN-X1” of the liquid discharge head  119  in the main scanning direction MSD. Further the dummy-discharge receptacle  112  has a dummy-discharge receiving area  115  corresponding to the dimension of “SUB-Y1” of the liquid discharge head  119  in the sub scanning direction SSD. Thus, when the liquid discharge head  119  (recording head) moves above the dummy-discharge receptacle  112  and performs the dummy-discharge operation, the liquid discharged as the dummy-discharge liquid  116  (see  FIG. 4 ) is reliably stored and stacked in the dummy-discharge receptacle  112 . 
     [Interference Between Dummy-Discharge Liquid  116  and Head Device  103 ] 
     As illustrated in  FIG. 4 , when the head device  103  moves above the dummy-discharge receptacle  112  and performs the dummy-discharge operation to the dummy-discharge receptacle  112 , the dummy-discharge liquid  116  discharge by the dummy-discharge operation are stored and accumulated inside the dummy-discharge receptacle  112 . When a height of accumulated dummy-discharge liquids  116  reaches “a certain height”, the accumulated dummy-discharge liquids  116  interfere (contact) with the carriage  102  and the liquid discharge head  119  (recording head). Here, “a certain height” refers to, for example, a distance (height Z) from an upper end of the dummy-discharge receptacle  112  to the nozzle surface  119   a  of the liquid discharge head  119  (recording head) or a bottom surface of the carriage  102 . Thus, when the dummy-discharge liquids  116  accumulate to the height Z, the dummy-discharge liquids  116  may hinder the scanning movement of the carriage  102 . The printer  100  according to the present embodiment can prevent such interference beforehand and efficiently collect the dummy-discharge liquid  116 . 
     [Light (Ultraviolet) Irradiation of Dummy-Discharge Liquids  116 ] 
     As illustrated in  FIG. 5 , the light irradiator  104  as the light irradiator irradiates the dummy-discharge liquid  116  stored in the dummy-discharge receptacle  112  with ultraviolet rays  117  to cure the dummy-discharge liquids  116  in an interior of the dummy-discharge receptacle  112 . Thus, the printer  100  can prevent generation of odor due to volatilization of the dummy-discharge liquid in the dummy-discharge receptacle  112 . 
       FIG. 5  is a cross-sectional partial front view of the printer  100 .  FIG. 5  illustrates an irradiation operation in which the light irradiator  104  irradiates the dummy-discharge liquid  116  in the dummy-discharge receptacle  112  with the ultraviolet rays  117  when the light irradiator  104  passes above a landing position of the dummy-discharge liquid  116  in the dummy-discharge receptacle  112  during scanning movement of the carriage  102  in the main-scanning direction MSD in the dummy-discharge operation. 
     The controller  120  controls irradiation timing, duration of irradiation, and output (irradiation amount) of the light irradiator  104  during the dummy-discharge operation. The light irradiator  104  also irradiates the liquid discharged to the image forming area  106  with the light (ultraviolet rays). The controller  120  controls the irradiation timing, duration of irradiation, and the output during irradiation (irradiation amount) of the light (ultraviolet rays). 
     The carriage  102  mounts the light irradiators  104  at both ends of the carriage  102  in the main scanning direction MSD. Thus, the light irradiator  104  installed on a left side of the carriage  102  irradiates the ultraviolet rays  117  on the dummy-discharge liquid  116  in the dummy-discharge receptacle  112  when the carriage  102  moves right side in a front view in  FIG. 5 . Conversely, the light irradiator  104  installed on a right side of the carriage  102  irradiates the ultraviolet rays  117  on the dummy-discharge liquid  116  in the dummy-discharge receptacle  112  when the carriage  102  moves left side in a front view in  FIG. 5 . Further, both of the light irradiators  104  may operate to irradiate the dummy-discharge liquid  116  with the light (ultraviolet rays) during the dummy-discharge operation. 
     Further, the light irradiator  104  may change an irradiation amount of the light (ultraviolet rays) onto the dummy-discharge liquid  116  according to a droplet size of the dummy-discharge liquid  116  discharged by the dummy-discharge operation when the discharge operation on the image forming area  106  and a discharge amount of liquid (size of liquid droplet) in the dummy-discharge operation are changed. 
       FIG. 6  is a partial plan view of the printer  100  in a state of the dummy-discharge receptacle  112  after performing the dummy-discharge operation. As illustrated in  FIG. 6 , the dummy-discharge liquid  116  is landed on a side close to the stage  101  in the dummy-discharge receiving area  115  that is the interior of the dummy-discharge receptacle  112  and is cured at the landing position by irradiation of the liquid with the light (radiation) such as the ultraviolet rays  117 . 
     As illustrated in  FIG. 6 , the liquid discharge head  119  (recording head) discharges the dummy-discharge liquid  116  from the nozzles  130  to the dummy-discharge receptacle  112  at a position above a specific position of the dummy-discharge receptacle  112 . The nozzles  130  are arrayed in the sub-scanning direction SSD in each of the liquid discharge head  119  as illustrated in  FIG. 6 . During the dummy-discharge operation, either only a specific liquid discharge head  119  (recording head) may discharge the dummy-discharge liquid  116 , or plurality of the liquid discharge heads  119  (recording heads) may discharge the dummy-discharge liquid  116 . As a result of the dummy-discharge operation, the cured dummy-discharge liquid  116  inside the dummy-discharge receptacle  112  is arranged in the sub-scanning direction SSD (see  FIG. 6 ). 
     [Example of Dummy-Discharge Receptacle  112  after Dummy-Discharge Operation] 
       FIG. 7  is a schematic cross-sectional view of the dummy-discharge receptacle  112  that is a container having a concave shape in cross-section with the opening facing upward to the carriage  102 . First, when the dummy-discharge operation is first performed from a state in which the dummy-discharge operation is not performed, the controller  120  performs the dummy-discharge operation at a position along an inner wall surface of the dummy-discharge receptacle  112  parallel to a side surface of the stage  101 . Thus, the dummy-discharge liquids  116  are landed at positions along the inner wall surface of the dummy-discharge receptacle  112  in the sub-scanning direction SSD. 
     As illustrated in  FIG. 7 , a virtually divided “dummy-discharge areas” are set in the interior of the dummy-discharge receptacle  112 . The controller  120  performs a virtual setting of the dummy-discharge areas. An example illustrated in  FIG. 7  is an example in which eight dummy-discharge areas (areas A to H) are set. 
     A plurality of dummy-discharge areas are virtually set in the dummy-discharge receptacle  112  according to the present embodiment. The controller  120  determines to which of the dummy-discharge area the dummy-discharge operation is performed. Thus, the controller  120  determines a size (width) of the dummy-discharge area in the main-scanning direction MSD based on a physical size of the dummy-discharge receptacle  112 , the size of the dummy-discharge liquid  116  discharged by the dummy-discharge operation, and the size of the dummy-discharge liquid  116  after the dummy-discharge liquid  116  is cured. Further, the controller  120  controls the scanning movement of the head device  103  to the dummy-discharge area based on the above-described virtual setting. 
     As illustrated in  FIG. 7 , when the dummy-discharge liquids  116  are accumulated (stacked) to reach the specific height Z (see  FIG. 4 ), the dummy-discharge liquids  116  may interfere with (contact) the carriage  102 . Here, the dummy-discharge liquids  116  may be accumulated (stacked) higher than a side wall  112 W of the dummy-discharge receptacle  112  as indicated by solid line in  FIG. 7  unless the height of accumulated dummy-discharge liquids  116  is lower than the height Z. Thus, the height Z may be set higher than the side wall  112 W of the dummy-discharge receptacle  112 . 
     Therefore, the controller  120  controls to move the position of the carriage  102  to change the dummy-discharge area based on an accumulated (stacked) height of the dummy-discharge liquids  116  in the dummy-discharge receptacle  112 . For example, the controller  120  may perform the dummy-discharge operation in another area (an area C, for example) as a second dummy-discharge area after performing the dummy-discharge operation for a predetermined number in an area A (first dummy-discharge area). 
     [First Example of Setting of Dummy-Discharge Area] 
       FIG. 8  is a schematic cross-sectional view of the dummy-discharge receptacle  112 .  FIG. 8  illustrates an example of setting the dummy-discharge area for the dummy-discharge operation. As illustrated in  FIG. 8 , first, the dummy-discharge operation is performed in the area A. A height of accumulated (stacked) dummy-discharge liquids  116  in one dummy-discharge operation can be calculated based on a size of a dummy-discharge liquid  116  discharged by one dummy-discharge operation. Further, the controller  120  controls a number of the dummy-discharge operations performed in one maintenance operation. Thus, the controller  120  controls the head device  103  to perform the dummy-discharge operation to the dummy-discharge area until the height of accumulated (stacked) dummy-discharge liquids  116  in the dummy-discharge area at time of a current setting exceeds a predetermined threshold value. 
     That is, the controller  120  calculates the height of accumulated (stacked) dummy-discharge liquids  116  in the dummy-discharge area of the dummy-discharge receptacle  112  based on an accumulated number of dummy-discharge operations, a height of cured dummy-discharge liquid  116  at one dummy-discharge operation, and the size of the dummy-discharge liquid  116  discharged by one dummy-discharge operation. Further, the controller  120  determines whether the height of the accumulated (stacked) dummy-discharge liquids  116  exceeds a predetermined threshold. When the controller  120  determines that the height of accumulated (stacked) dummy-discharge liquids  116  becomes equal to or greater than a first threshold value, the controller  120  sets another dummy-discharge area (second dummy-discharge area). In an example illustrated in  FIG. 8 , the controller  120  sets the area C as the dummy-discharge area for the next dummy-discharge operation. 
     The controller  120  according to the present embodiment sets the first threshold value using a number of dummy-discharge operations successively performed until the height of accumulated (stacked) dummy-discharge liquids  116  reaches the height Z. Then, the controller  120  changes the setting of the dummy-discharge area using the first threshold value as described above. 
     When the number of the dummy-discharge operations on the area C exceeds the first threshold value, the controller  120  sets the area B as the next dummy-discharge area. When the dummy-discharge operation on the area B exceeds the first threshold, the controller  120  next sets the area E as the next dummy-discharge area. Similarly, the controller  120  next sets an area D as the next dummy-discharge area. 
     That is, as illustrated in  FIG. 8 , the controller  120  sets a dummy-discharge area (area C, etc.) not adjacent to a current dummy-discharge area (area A, etc.) as the next dummy-discharge area when the height of accumulated (stacked) dummy-discharge liquid  116  exceeds the first threshold value as a result of the dummy-discharge operation on a certain dummy-discharge area (area A, etc.). In the above-described case, the controller  120  sets the next dummy-discharge area using the dummy-discharge area (area C, etc.) not adjacent to the current dummy-discharge area (area A, etc.). 
     Specifically, the controller  120  sets the dummy-discharge area (area C, etc.) adjacent to the dummy-discharge area (area B, etc.) that is adjacent to the current dummy-discharge area (area A, etc.) that is, a dummy-discharge area corresponding to a next adjacent dummy-discharge area. Then, the controller  120  sets the next dummy-discharge area using the dummy-discharge area (area B, etc.) adjacent to both the previous dummy-discharge area (area A, etc.) and the current dummy-discharge area (area C, etc.) when the height of accumulated (stacked) dummy-discharge liquids  116  exceeds the first threshold value as a result of the dummy-discharge operation on the current dummy-discharge area (area C, etc). 
     [Second Example of Setting of Dummy-Discharge Area] 
     Further, as illustrated in  FIG. 9 , the controller  120  can set the next dummy-discharge area in an order of area A, area C, area E, area G, area B, area D, area F, and area H. In the above-described case, the controller  120  sets the next dummy-discharge area using the dummy-discharge area (areas C, E, G, etc.) not adjacent to the current dummy-discharge area (areas A, C, E, etc.) when the height of accumulated (stacked) dummy-discharge liquids  116  exceeds the first threshold value as a result of the dummy-discharge operation on a certain (current) dummy-discharge area (areas A, C, E, etc.). That is, the controller  120  sets the next dummy-discharge area using a dummy-discharge area (area C, etc.) not adjacent to the current dummy-discharge area (area A, etc). Specifically, the next dummy-discharge area (area C, etc.) is adjacent to the dummy-discharge area (area B, etc) adjacent to the current dummy-discharge area (area A, etc.) that is the dummy-discharge area corresponding to the next adjacent dummy-discharge area. 
     Then, the controller  120  sets the next dummy-discharge area (area E, etc.) that is the next adjacent dummy-discharge area when the height of accumulated (stacked) dummy-discharge liquids  116  exceeds the first threshold value as a result of the dummy-discharge operation on the current dummy-discharge area (area C, etc.). Then, the controller  120  sets the next dummy-discharge area using the dummy-discharge area (area B, etc.) between the dummy-discharge areas (areas A and C, etc.), onto which the dummy-discharge liquids  116  has already been accumulated (stacked), and has not been used for the dummy-discharge operation when a position of the current dummy-discharge area (area G, etc.) reaches a position corresponding to a width (MAIN-X) of the dummy-discharge receiving area  115  in the dummy-discharge receptacle  112  (see  FIG. 3 ). 
     As described above, the controller  120  sets the area A that is a (one) dummy-discharge area among a plurality of dummy-discharge areas as the next dummy-discharge area to perform the dummy-discharge operation, and performs the dummy-discharge operation on the area A. The controller  120  continuously performs the dummy-discharge operations on the area A as the current dummy-discharge area until an amount (height) of stored (accumulated or stacked) dummy-discharge liquids  116  in the area A reaches a predetermined amount (predetermined height Z). Here, the “amount of dummy-discharge liquids  116  in the area A” refers to the “height of accumulated (stacked) dummy-discharge liquids  116  in the area A”. 
     Further, “the amount of dummy-discharge liquids  116  in the area A reaches a predetermined amount” means that the number of dummy-discharge operations reaches the first threshold value so that the height of accumulated (stacked) dummy-discharge liquids  116  in the area A becomes equal to or higher than the height Z, at which point the accumulated (stacked) dummy-discharge liquids  116  interferes with (contacts) the carriage  102  (i.e., the number of dummy-discharge operations exceeds a predetermined number of times (first threshold value)). Thus, the controller  120  changes the next dummy-discharge area according to a dummy-discharge operation immediately before the number of dummy-discharge operations exceeds a predetermined number of times (first threshold value). 
     Further, the controller  120  sets the area C as the next dummy-discharge area when the amount of the dummy-discharge liquids  116  stored (accumulated or stacked) in the area A reaches a predetermined amount. The area C is another dummy-discharge area (second dummy-discharge area) not adjacent to the area A (first dummy-discharge area). Thus, the second dummy-discharge area is separate from the first dummy-discharge area. 
     Then, the controller  120  sets the area B between the area A and the area C as the next dummy-discharge area when an amount (height) of dummy-discharge liquids  116  stored (accumulated or stacked) in the area C reaches a predetermined amount (predetermined height Z). 
     Note that, if the dummy-discharge areas are set in an order from an end of the dummy-discharge receptacle  112 , such as an area A, an area B, an area C, an area D, an area E, an area F, an area G, and an area H, the dummy-discharge liquids  116  in one dummy-discharge area may adhere to the dummy-discharge liquids  116  accumulated (stacked) in the adjacent dummy-discharge area by surface tension. Thus, the amount (height) of accumulated (stacked) dummy-discharge liquids  116  in one dummy-discharge area may exceed the first threshold value with an amount of the dummy-discharge liquid  116  smaller than a capacity of accumulated (stacked) dummy-discharge liquids  116  accommodatable in one dummy-discharge area in the dummy-discharge receptacle  112 . 
     In each of the areas A to H, the dummy-discharge liquids  116  stored (accumulated) in the dummy-discharge receptacle  112 , amount of which reaches the predetermined amount, are irradiated with the light (ultraviolet rays, etc.) at a predetermined timing to be cured. Thus, the dummy-discharge liquids  116  cured in the dummy-discharge receptacle  112  becomes partition walls to partition an interior of the dummy-discharge receptacle  112  into multiple separate areas. Thus, if the controller  120  sets the next dummy-discharge area in an order of the area A, the area C, and the area B, the dummy-discharge liquids  116  discharged by the dummy-discharge operation performed on the area B flow into a gap formed between the dummy-discharge liquids  116  accumulated (stacked) in each of the areas A and C. Thus, the printer  100  can efficiently fill a storage area of the dummy-discharge receptacle  112  with the dummy-discharge liquids  116 . 
     [Another Example of the Dummy-Discharge Receptacle  112 ] 
     Note that the dummy-discharge receptacle  112  is not limited to a container having a concave shaped cross-section as illustrated in  FIG. 7  and the like, but may also be a planar member such as the dummy-discharge receptacle  112   a  as illustrated in  FIG. 10 . In the dummy-discharge receptacle  112   a  in  FIG. 10 , the dummy-discharge liquids  116  accumulated (stacked) in the dummy-discharge area (area A) by the first dummy-discharge operation form a partition wall in the dummy-discharge receptacle  112 . The partition wall partitions the interior of the dummy-discharge receptacle  112 . Thus, the controller  120  sets a dummy-discharge area (area C) not adjacent to the area A (first dummy-discharge area) as the next (second) dummy-discharge area. Thus, the second dummy-discharge area (area C) is separated from the first dummy-discharge area (area A). 
     [Third Example of Setting of Dummy-Discharge Area] 
     As illustrate in  FIG. 11 , the controller  120  can set separate dummy-discharge areas for each of the liquid discharge heads  119  (recording heads) performing a dummy-discharge operation. Thus, the controller  120  sets the area A as a dummy-discharge area for dummy-discharge liquids  116 W of white color as illustrated in  FIG. 11 . Thus, the dummy-discharge liquids  116 W of white color are accumulated (stacked) in the area A in the dummy-discharge receptacle  112 . Further, the controller  120  sets the area C as a dummy-discharge area for dummy-discharge liquids  116 C of cyan color. Thus, the dummy-discharge liquids  116 C of cyan color are accumulated (stacked) in the area C in the dummy-discharge receptacle  112 . Further, the controller  120  sets the area B as a dummy-discharge area for dummy-discharge liquids  116 M of magenta color. Thus, the dummy-discharge liquids  116 M of magenta color are accumulated (stacked) in the area B in the dummy-discharge receptacle  112 . 
     As described above, the controller  120  sets the next dummy-discharge area for each color of the dummy-discharge liquids  116  (for each of the liquid discharge heads  119  (recording heads)). Thus, the printer  100  can prevent mixing of colors in the dummy-discharge receptacle  112  even when the dummy-discharge liquids  116  rebounds to the liquid discharge head  119  because a color of the dummy-discharge liquid  116  rebounding to the liquid discharge head  119  and a color of the liquid discharge head  119  is the same. In  FIG. 11 , the controller  120  previously irradiates the dummy-discharge liquids  116  with the light such as ultraviolet rays to cure the dummy-discharge liquids  116  discharged by a previous dummy-discharge operation. 
     The plurality of dummy-discharge areas respectively accommodates a plurality of dummy-discharge liquids  116  of respective colors. 
     Further, the printer  100  may respectively include a plurality of dummy-discharge receptacles  112  for a plurality of types (colors) of dummy-discharge liquids  116  to prevent mixing of colors in the dummy-discharge receptacle  112 . 
     [Fourth Example of Setting of Dummy-Discharge Area] 
     The controller  120  can set a size of liquid droplet of the dummy-discharge liquid  116  to be small (small droplets) to increase a number of dummy-discharge areas even for the dummy-discharge receptacle  112  of the same size. For example, the controller  120  may set sixteen dummy-discharge areas as illustrated in  FIG. 12 . The controller  120  controls a size of each of the dummy-discharge areas. Since the controller  120  can control the size of each of the dummy-discharge liquids  116  discharged by the dummy-discharge operation, the size of each of the dummy-discharge areas is set in conjunction with the control of the size of each of the dummy-discharge liquids  116 . 
     As illustrated in  FIG. 12 , the controller  120  can change the size of the dummy-discharge area. Particularly, the controller  120  reduces the setting (size) of the dummy-discharge area. Thus, a gap between the partition walls formed by the cured dummy-discharge liquids  116  becomes small when the dummy-discharge liquids  116  discharged to each dummy-discharge area are cured by the light such as ultraviolet rays. Thus, the printer  100  can use every corner of an accommodation area of the dummy-discharge receptacle  112 . Further, the controller  120  reduces the size of each of the dummy-discharge liquids  116  during the dummy-discharge operation so that an amount of liquid consumed in the dummy-discharge operation can be reduced. Thus, inefficient liquid consumption can be reduced. 
     Further, the controller  120  may measure a number of discharge operations (discharge history) for image formation for each liquid discharge heads  119  (for each color). Thus, the controller  120  reduce a number of the dummy-discharge operation and an amount of the dummy-discharge liquids  116  discharged per one time of the dummy-discharge operation for the liquid discharge head  119  (recording head) that performs more discharge operations than other liquid discharge heads  119 . 
     [Medium Thickness and Dummy-Discharge Operation] 
     Next, a dummy-discharge operation performed in a state in which a substrate  118  as a medium is placed on the stage  101 . 
       FIG. 13  is a partial front view of the printer  100  in a state in which the substrate  118  is placed on the stage  101 . As illustrated in  FIG. 13 , the controller  120  changes a size of a gap between an upper surface of the stage  101  and the nozzle surface  119   a  of the liquid discharge head  119  on the carriage  102  according to a thickness of the substrate  118 . The printer  100  includes a carriage lift  133  to raise or lower the carriage  102  as indicated by vertical arrow in  FIG. 13 . The carriage lift  133  moves the carriage  102 , the head device  103 , the light irradiator  104 , and the carriage stay  114  in a vertical direction to change the size of the gap between the nozzle surface  119   a  and the upper surface of the stage  101 . 
     Conversely, the stage  101  and the maintenance unit  105   b  may be vertically movable relative to the carriage  102  and the head device  103 . Therefore, the controller  120  may change (correct) the first threshold value according to the thickness of the substrate  118  even when the first threshold value is used to change the setting of the dummy-discharge area during the dummy-discharge operation. More specifically, the controller  120  changes a height position of the carriage  102  by setting a thickness of the substrate  118  in the controller  120 . For example, as illustrated in  FIG. 13 , the carriage  102  is raised (larger gap) when the substrate  118  is thicker, and the carriage  102  is lowered (smaller gap) when the substrate  118  is thinner. The controller  120  may correct the first threshold value based on the changed height position of the carriage  102 . 
     [Size of Dummy-Discharge Liquid of Dummy-Discharge Operation and First Threshold Value] 
       FIG. 14  is a graph of correlation between a number of dummy discharge in the dummy-discharge operation and the height of accumulated (stacked) dummy-discharge liquids  116 . A solid line in  FIG. 14  illustrates an example in which the size of the dummy-discharge liquid  116  in the dummy-discharge operation is a “large droplet”. Conversely, a broken line in  FIG. 14  illustrates an example in which the size of the dummy-discharge liquid  116  in the dummy-discharge operation is “small droplet”. As illustrated in  FIG. 14 , the height of accumulated dummy-discharge liquids  116  of the large droplet is higher than the height of accumulated dummy-discharge liquids  116  of the small droplet for the same number of dummy-discharge operations. 
     Further,  FIG. 14  illustrates the difference of the “height Z” between the nozzle surface  119   a  of the liquid discharge head  119  (recording head) and the top surface of the stage  101  by a difference in the thickness of the substrate  118  by dash-single-dot lines. As illustrated in  FIG. 13 , the carriage  102  is raised (larger gap) when the substrate  118  is thick, and the carriage  102  is lowered (smaller gap) when the substrate  118  is thin. As illustrated in  FIG. 14 , the “height Z” increases when the thickness of the substrate  118  is “thick”. If the height Z is large, the height of accumulated dummy-discharge liquids  116  needed for interfering (contacting) the carriage  102  (nozzle surface  119   a ) increases. Conversely, the “height Z” decreases when the thickness of the substrate  118  is “thin”. If the height Z is small, the height of accumulated dummy-discharge liquids  116  needed for interfering (contacting) the carriage  102  (nozzle surface  119   a ) decreases. 
     As described above, the controller  120  raises the carriage  102  to increase the “height Z” when the thickness of the substrate  118  increases. Thus, the height of accumulated dummy-discharge liquids  116  needed to interfere (contact) the carriage  102  (nozzle surface  119   a ) increases (clearance increases) even if the number of dummy-discharge operations in one dummy-discharge area increases. The “clearance” is a gap between the nozzle surface  119   a  of the liquid discharge head  119  and a top of the accumulated dummy-discharge liquids  116 . Further, the controller  120  reduces the size of the dummy-discharge liquid  116  during the dummy-discharge operation to further increase the number of dummy-discharge operations in one dummy-discharge area. 
     [Setting of Dummy-Discharge Operation and First Threshold Value] 
     The printer  100  according to the present embodiment can also determine the timing of performing the dummy-discharge operation based on the number of the discharge operations for the image formation. For example, the controller  120  may cumulatively add a number of discharge operations for each liquid discharge heads  119  (recording heads), that is, for each discharged colors. 
     Then, the controller  120  may perform the maintenance operation (dummy-discharge operation) on only the liquid discharge head  119  (recording head) when a cumulatively added value of the number of discharge operations equals or exceeds a predetermined value (first threshold value). Hereinafter, the “cumulatively added value” is also referred to as an “integrated value” or a “cumulative number”. In the above-described case, the controller  120  may perform the maintenance operation (dummy-discharge operation) for all the liquid discharge heads  119  (recording heads) when a condition of the maintenance operation for one liquid discharge head (recording head) is satisfied. 
     Further, the controller  120  may change the integrated value of the number of dummy-discharge operations according to whether the size of dummy-discharge liquid  116  is the “large droplet” or the “small droplet”. For example, the controller  120  may use the integrated value of twice as large as the discharge operation of the “small droplet” for the discharge operation of the “large droplet”. In other words, the controller  120  uses the integrated value of the discharge operation of the “small droplet” as half of the integrated value of the discharge operation of the “large droplet”. 
     Further, the controller  120  may change the size of the dummy-discharge liquid  116  during the dummy-discharge operation according to the size of the discharged liquid in a previous discharge operation when the controller  120  controls to perform the dummy-discharge operation for the liquid discharge head  119  (recording head), the number of discharge operations of which exceeds a predetermined number of discharge operations. For example, the controller  120  uses “large droplet” during the dummy-discharge operations when the liquid discharge head  119  performs a large number of the discharge operations using the “large droplet”. 
     Conversely, the controller  120  uses “small droplet” during the dummy-discharge operations when the liquid discharge head  119  performs a large number of the discharge operations using the “small droplet”. In any case, the controller  120  may change variation of the dummy-discharge operation to effectively improve the discharge stability of the liquid discharge head  119  (recording head) and prevent clogging of the nozzles  130 . Thus, the controller  120  can perform maintenance operation in a state close to the discharge operation for the image formation. 
     Further, the controller  120  may change the size of the dummy-discharge liquids  116  during the dummy-discharge operation for every dummy-discharge operations. For example, as illustrated in  FIG. 15 , the number of the “small droplets” is counted as half of the number of the “large droplets”. Thus, the controller  120  sets a coefficient of the “small droplet” to be smaller than a coefficient of the “large droplet” in counting the number of the dummy-discharge operations. Then, the printer  100  can perform further larger number of the dummy-discharge operations for one dummy-discharge area. Thus, the printer  100  can efficiently use the dummy-discharge receptacle  112  and reduce the amount liquids that becomes the dummy-discharge liquids  116  in the dummy-discharge receptacle  112 . 
     [Functional Blocks of Controller  120 ] 
     Next, functional blocks of the controller  120  according to the present embodiment are described below. 
     As described above, the controller  120  is a computer that controls all operations of the printer  100  and a control software executed by using hardware resources of the computer to execute the functional blocks illustrated in  FIG. 16 . 
     As illustrated in  FIG. 16 , the controller  120  includes an image forming processor  121 , a discharge number counter  122 , a maintenance timing determiner  123 , a dummy-discharge area setter  124 , a dummy-discharge operation controller  125 , a dummy-discharge area changing determiner  126 , a light irradiation-amount setter  127 , and a light irradiation controller  128 . 
     The image forming processor  121  scans the carriage  102  in the main-scanning direction MSD and the sub-scanning direction SSD based on data (image forming data) input from outside the printer  100 . The image forming processor  121  further controls the discharge operation of the liquid discharge head  119  of the head device  103  that discharges the curing liquid. That is, the image forming processor  121  drives the drive motor  111  to scan the carriage  102  in the main-scanning direction MSD and in the sub-scanning direction SSD based on the image forming data. 
     Further, the image forming processor  121  moves the head device  103  (liquid discharge head  119 ) to a predetermined position, sets the size of the discharge droplet and the number of discharge operations of the curing liquid to be discharged from the liquid discharge head  119 , and controls the discharge operation of the liquid discharge head  119  based on the above-described setting. Further, the image forming processor  121  instructs the light irradiation controller  128  to irradiate the curing liquid discharged onto the stage  101  with the light such as ultraviolet rays. 
     The discharge number counter  122  counts the number of discharge operations in the image forming processor  121  and cumulatively adds the counted numbers of discharge operations to obtain an integrated value. The discharge number counter  122  calculates an integrated value of each of the liquid discharge heads  119  (recording heads) based on the number of discharge operations of each of the plurality of liquid discharge heads  119  (recording heads) and the size of liquid droplet discharged in each discharge operations. The integrated value is sequentially notified to the maintenance timing determiner  123 . 
     The maintenance timing determiner  123  determines whether the integrated value notified from the discharge number counter  122  exceeds a predetermined threshold value as a condition to start the dummy-discharge operation. If the integrated value exceeds the predetermined threshold value, the maintenance timing determiner  123  starts the dummy-discharge operation. The maintenance timing determiner  123  may start the dummy-discharge operation for all liquid discharge heads  119  (recording heads) when the integrated value of a certain liquid discharge head  119  (recording head) exceeds the predetermined threshold value. Further, the maintenance timing determiner  123  may start the dummy-discharge operation for the liquid discharge head  119  (recording head), the integrated value of which exceeds the predetermined threshold value. 
     The dummy-discharge area setter  124  sets the dummy-discharge area according to a preset order, and notifies the dummy-discharge operation controller  125  of the dummy-discharge area set by the dummy-discharge area setter  124 . Further, the dummy-discharge area setter  124  sets a new dummy-discharge area based on a notification from the dummy-discharge area changing determiner  126 , and notifies the dummy-discharge operation controller  125  of the new dummy-discharge area set by the dummy-discharge area setter  124 . 
     The dummy-discharge operation controller  125  performs the dummy-discharge operation on the notified dummy-discharge area, and counts a cumulative number of dummy-discharge operations during the dummy-discharge operation. 
     The dummy-discharge area changing determiner  126  determines whether a count result of the cumulative number of dummy-discharge operations in the dummy-discharge operation controller  125  equals or exceeds a preset first threshold value. If the dummy-discharge area changing determiner  126  determines that the count result of the cumulative number of dummy-discharge operations equals or exceeds the preset first threshold value, the dummy-discharge area changing determiner  126  instructs the dummy-discharge area setter  124  to change the dummy-discharge area. 
     The light irradiation-amount setter  127  sets an intensity of the light (ultraviolet rays) irradiated from the light irradiator  104  and a duration of irradiation of the light (ultraviolet rays) from the light irradiator  104 . 
     The light irradiation controller  128  determines whether the count result in the dummy-discharge operation controller  125  is equal to or larger than a second threshold value that is a predetermined number of dummy-discharge operations. If the count result equals or exceeds the second threshold value, the light irradiator  104  irradiates a currently set dummy-discharge area with the light (ultraviolet rays) based on the setting set by the light irradiation-amount setter  127 . Thus, the printer  100  can cure the dummy-discharge liquids  116  in a predetermined dummy-discharge area and can efficiently use the capacity of the dummy-discharge receptacle  112 . The second threshold value is set smaller than the first threshold value. 
     [Process Flow of Dummy-Discharge Operation] 
     Next, a process flow of the dummy-discharge operation according to the present embodiment is described below with referring to  FIG. 17 . 
       FIG. 17  is a flowchart of the dummy-discharge operation performed by the controller  120  including the above-described functional blocks. First, the maintenance timing determiner  123  determines whether the integrated value calculated by the image forming processor  121  and the discharge number counter  122  exceeds a predetermined threshold value (S 1701 ). If the integrated value does not exceed the predetermined threshold value, the maintenance timing determiner  123  ends a determination process (S 1701 /NO). 
     If the integrated value exceeds the predetermined threshold value (S 1701 /YES), the dummy-discharge operation controller  125  starts the dummy-discharge process. First, the dummy-discharge operation controller  125  refers to the dummy-discharge area setter  124  and moves carriage  102  mounting the liquid discharge head  119  (recording head) in the main-scanning direction MSD toward the dummy-discharge area virtually set in the dummy-discharge receptacle  112  (S 1702 ). 
     Next, the dummy-discharge operation controller  125  starts the dummy-discharge operation on the dummy-discharge area at which the liquid discharge head  119  faces (S 1703 ). Here, the dummy-discharge operation controller  125  integrates the number of the dummy-discharge operations using any of variations described above for each time of the dummy-discharge operations. For example, the dummy-discharge operation controller  125  may calculate the cumulative number by integrating the number of the dummy-discharge operations for each liquid discharge head  119  and further multiplying integrated value with a coefficient based on the size of the dummy-discharge liquid  116  discharged during the dummy-discharge operation. 
     The information used for calculating the cumulative number in the step S 1703  is information indicating a state of the liquid discharge operation for image formation. Further, the cumulative number calculated by the dummy-discharge operation controller  125  may indicate a number of the dummy-discharge operations actually performed. Further, the cumulative number calculated by the dummy-discharge operation controller  125  may be a value calculated using various coefficients so that the dummy-discharge operation is performable at an appropriate timing during the performance of the maintenance operation of the liquid discharge head  119  (recording head). 
     The dummy-discharge operation controller  125  updates the cumulative number for each dummy-discharge operations, and notifies an updated value to the dummy-discharge area changing determiner  126  and the light irradiation controller  128 . 
     Next, the light irradiation controller  128  determines whether the cumulative number notified from the dummy-discharge operation controller  125  exceeds the second threshold value (S 1704 ). If the cumulative number exceeds the second threshold value (S 1704 /YES), the light irradiator  104  irradiates the dummy-discharge liquid  116  with a light (curing light) such as ultraviolet rays (S 1705 ). The second threshold value is also used as a threshold value to adjust an amount of irradiation according to a degree of curing of the dummy-discharge liquid  116 . For example, the second threshold value may be set to radiate the light (ultraviolet rays) for each one dummy-discharge operation. 
     Further, the second threshold value may be set so that a next light irradiation is performed after a predetermined dummy-discharge operation that is performed after one light irradiation. Further, the second threshold value may be set to control timing of the next light irradiation according to elapsed time after performance of one light irradiation. If the cumulative number does not exceed the second threshold value (S 1704 /NO), the irradiation step (S 1705 ) is omitted. 
     Next, the dummy-discharge area changing determiner  126  determines whether the cumulative number of dummy-discharge operations for the current dummy-discharge area exceeds the first threshold value using the various variations as described-above (S 1706 ). Here, if the cumulative number of dummy-discharge operations on the dummy-discharge area exceeds the first threshold value (S 1706 /YES), the dummy-discharge area changing determiner  126  instructs the dummy-discharge area setter  124  to change and set the next dummy-discharge area according to a predetermined rule as described above. 
     Then, the dummy-discharge area changing determiner  126  notifies the dummy-discharge operation controller the next dummy-discharge area (S 1707 ). If the cumulative number does not exceed the first threshold value (S 1706 /NO), the step of changing the dummy-discharge area (S 1707 ) is omitted. A condition of “the cumulative number exceeds the first threshold value” in S 1706  includes a condition of “the cumulative number of the dummy-discharge operation equals or exceeds the first threshold value”. In other words, if the cumulative number of dummy-discharge operations is less than the first threshold value, the step of changing the dummy-discharge area (S 1707 ) is omitted. 
     Next, the dummy-discharge operation controller  125  determines completion of the dummy-discharge operation (S 1708 ). If the dummy-discharge operation controller  125  determines that it is not time to terminate the dummy-discharge operation (S 1708 /NO), the dummy-discharge operation controller  125  returns to the dummy-discharge operation (S 1703 ). If the dummy-discharge operation controller  125  determines that it is time to terminate the dummy-discharge operation (S 1708 /YES), the dummy-discharge operation controller  125  ends the dummy-discharge operation. 
     The dummy-discharge operation controller  125  determines time to terminate the dummy-discharge operation according to various conditions, such as whether the dummy-discharge liquids  116  accumulated in the dummy-discharge receptacle  112  exceeds the capacity of the dummy-discharge receptacle  112 , or whether the dummy-discharge operation has been performed a sufficient number of times as the maintenance operation, for example. 
     If the dummy-discharge operation controller  125  ends the dummy-discharge operation by a determination of the condition of the dummy-discharge liquids  116  accumulated in the dummy-discharge receptacle  112  exceeding the capacity of the dummy-discharge receptacle  112 , the dummy-discharge operation controller  125  may notify and prompts replacement of the dummy-discharge receptacle  112 . 
     The present disclosure is not limited to specific embodiments described above, and numerous additional modifications and variations are possible in light of the teachings within the technical scope of the appended claims. It is therefore to be understood that, the disclosure of this patent specification may be practiced otherwise by those skilled in the art than as specifically described herein, and such, modifications, alternatives are within the technical scope of the appended claims. Such embodiments and variations thereof are included in the scope and gist of the embodiments of the present disclosure and are included in the embodiments described in claims and the equivalent scope thereof. 
     Each of the functions of the described embodiments performed by the controller  120  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), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions. 
     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 is 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.