Patent Publication Number: US-8534793-B2

Title: Liquid discharge apparatus and maintenance system for liquid discharge apparatus and method of manufacturing liquid discharge apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-18955, filed on Jan. 31, 2011, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a liquid discharge apparatus which includes a discharge outlet through which a liquid is discharged and to a maintenance system for a liquid discharge apparatus and to a method of manufacturing a liquid discharge apparatus. 
     BACKGROUND OF THE INVENTION 
     There has been proposed a technique to let a space inside a cap which airtightly seals a nozzle surface (i.e., a discharge surface) which is opened through nozzles and a water reservoir (i.e., a humidifier liquid reservoir) which contains water (i.e., a humidifier liquid) communicate with each other in order to prevent an increase in viscosity of ink in an inkjet head. With this technique, the cavity inside the cap is filled with air that is humidified with the water contained in the water reservoir. 
     In the technique described above, if a non-volatile component (e.g., an antiseptic agent) is included in the water replenished in the water reservoir, an amount of the non-volatile component in water reservoir increases during repeated evaporation and replenishment of water in the water reservoir. Therefore, the concentrated non-volatile component in the water reservoir causes deterioration in a steam generating function and, as a result, it becomes impossible to produce humidified air efficiently. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a liquid discharge apparatus that can prevent deterioration in humidifying function caused by an increased amount of non-volatile component in a humidifier liquid reservoir. 
     A liquid discharge apparatus according to the present invention includes a liquid discharge head which includes a discharge surface forming a plurality of discharge outlets for discharging a liquid. A discharge space is defined as facing the discharge surface. A cap unit is configured to be in a sealed state in which the cap unit seals the discharge space to an external space, and a non-sealed state in which the cap unit does not seal the discharge space to the external space. A humidification mechanism comprises: a humidifier liquid reservoir configured to store an externally supplied humidifier liquid including a non-volatile component, and a humidified air supply unit configured to supply humidified air humidified by a humidifier liquid stored in the humidifier liquid reservoir to the discharge space when it is in the sealed state. A determination unit is configured to determine whether an amount of the non-volatile component in the humidifier liquid stored in the humidifier liquid reservoir is greater than a predetermined amount. 
     A maintenance system for a liquid discharge apparatus according to the present invention includes a liquid discharge head which includes a discharge surface forming a plurality of discharge outlets for discharging a liquid. A discharge space is defined as facing the discharge surface. A cap unit is configured to be in a sealed state in which the cap unit seals the discharge space to an external space, and a non-sealed state in which the cap unit does not seal the discharge space to the external space. A humidification mechanism comprises: a humidifier liquid reservoir configured to store an externally supplied humidifier liquid including a non-volatile component, and a humidified air supply unit configured to supply humidified air humidified by a humidifier liquid stored in the humidifier liquid reservoir to the discharge space when it is in the sealed state. A determination unit is configured to determine whether an amount of the non-volatile component in the humidifier liquid stored in the humidifier liquid reservoir is greater than a predetermined amount. 
     A method of manufacturing a liquid discharge apparatus according to the present invention comprising: providing a liquid discharge head which includes a discharge surface, the discharge surface including a plurality of discharge outlets for discharging a liquid, a discharge space being defined facing the discharge surface; providing a cap unit configured to be in a sealed state in which the cap unit seals the discharge space to an external space, and a non-sealed state in which the cap unit does not seal the discharge space to the external space; providing a humidification mechanism comprising: configuring a humidifier liquid reservoir to store an externally supplied humidifier liquid including a non-volatile component; and configuring a humidified air supply unit to supply humidified air humidified by a humidifier liquid stored in the humidifier liquid reservoir to the discharge space when it is in the sealed state; configuring a determination unit to determine whether an amount of the non-volatile component in the humidifier liquid stored in the humidifier liquid reservoir is greater than a predetermined amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates, in a schematic side view, an internal structure of an inkjet printer according to an embodiment of the present invention; 
         FIG. 2  illustrates, in a plan view, a channel unit and an actuator unit of an inkjet head incorporated in a printer of  FIG. 1 ; 
         FIG. 3  illustrates, in an enlarged view, an area III defined by a dash-dot line in  FIG. 2 ; 
         FIG. 4  is a fragmentary sectional view along line IV-IV line of  FIG. 3 ; 
         FIG. 5  illustrates, in a schematic diagram, a head holder and a humidification mechanism incorporated in the printer of  FIG. 1 ; 
         FIG. 6  illustrates, in a fragmentary sectional view, an area VI defined by a dash-dot line in  FIG. 5 ; 
         FIG. 7  illustrates, in a schematic diagram, connecting of all the heads and the humidification mechanism incorporated in the printer of  FIG. 1 ; 
         FIG. 8  illustrates, in a functional block diagram, a controller incorporated in the printer of  FIG. 1 ; 
         FIG. 9  illustrates, in a flowchart, method steps of the inkjet printer according to the embodiment of the present invention; 
         FIG. 10  illustrates, in a functional block diagram, a modification of the present invention; 
         FIG. 11  illustrates, in a flowchart, method steps of the inkjet printer according to a modification of the present invention; 
         FIG. 12  illustrates, in a functional block diagram, another modification of the present invention; 
         FIG. 13  illustrates, in a schematic block diagram, another modification of the present invention; 
         FIG. 14  illustrates, in a schematic block diagram, a further modification of the present invention; and 
         FIG. 15  illustrates, in a schematic block diagram, an even further modification of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. 
     An entire configuration of an inkjet printer (hereinafter, “printer”)  1  according to an embodiment of the present invention will be described. 
     As illustrated in  FIG. 1 , the printer  1  includes a rectangular parallelepiped-shaped housing  1   a . A paper sheet discharge unit  31  is provided above a top plate of the housing  1   a . An inner cavity of the housing  1   a  is divided into cavities A, B and C in this order from the top. A paper sheet conveyance path connecting to the paper sheet discharge unit  31  is formed in the cavities A and B. Ink cartridges  39  are placed in the cavity C as ink supply sources to the inkjet head (hereinafter, “head”)  10 . 
     Four heads  10 , a conveyance unit  21  which conveys a paper sheet P, a guide unit which guides the paper sheet P, a humidification mechanism  50  used for humidification maintenance (see  FIG. 5 ) and other components are placed in the cavity A. A controller  1   p  which controls operations of the components of the printer  1  and manages an operation of the printer  1  is placed in an upper position in the cavity A. 
     The controller  1   p  controls, in accordance with image data supplied from external device(s), a conveyance operation of the paper sheet P by each component of the printer  1 , an ink discharge operation in synchronization with the conveyance of the paper sheet P, a maintenance operation relating to recovery and maintenance of discharge performance, and other operations. The maintenance operation includes flushing, purging, wiping, humidification maintenance, water reservoir cleaning. Flushing is an operation in which actuator(s) of any or all heads  10  are driven in accordance with flushing data that is different from image data so as to compulsorily discharge ink through the discharge outlet  14   a . Purging is an operation in which ink in the head  10  is pressurized by, for example, a pump so as to compulsorily discharge ink through all the discharge outlets  14   a . Wiping is an operation in which foreign substances on the discharge surfaces  10   a  are removed with a wiper after the flushing or purging. Humidification maintenance is an operation in which humidified air is supplied to a discharge space S 1  (see  FIG. 5 ) which faces the discharge surfaces  10   a . Water reservoir cleaning will be described below. 
     The conveyance unit  21  includes a platen  9  and conveyance nip rollers  5  and  6  placed on both sides of the platen  9  in the conveying direction. The conveyance nip rollers  5  and  6  each include a pair of roller members; the roller members face each other to hold the paper sheet P from above and below. The conveyance nip rollers  5  and  6  apply conveying force to the paper sheet P such that the paper sheet P which is being held is conveyed in the conveying direction. The paper sheet P to which conveying force is applied by the conveyance nip roller  5  located in conveying direction upstream is conveyed in the conveying direction while being supported on an upper surface of the platen  9 . The conveyance nip roller  6  applies conveying force to the paper sheet P which has passed the upper surface of the platen  9  and conveys the paper sheet P in conveying direction downstream of the platen  9 . 
     An inversion mechanism  7  is placed under the four heads  10 . The platen  9  and a glass table  8 , which are opposing to each other, are fixed to the inversion mechanism  7 . The inversion mechanism  7  moves in a manner that either of the platen  9  or the glass table  8  faces (discharge surfaces  10   a ) of the four heads  10 . For example, the inversion mechanism  7  lets the platen  9  face the discharge surfaces  10   a  during printing operation (see  FIG. 1 ). When humidification maintenance or water reservoir cleaning, described below, is carried out in this state, the inversion mechanism  7  moves downward to avoid interference between the platen  9  or the glass table  8  and the discharge surfaces  10   a , then rotates such that the glass table  8  faces the discharge surfaces  10   a  (see  FIGS. 5 and 6 ) and, after that, moves upward. 
     Each of the heads  10  is a linear head of substantially rectangular parallelepiped shape extending along the main scanning direction. Each of the heads  10  has the discharge surface  10   a  on a lower surface thereof. Many discharge outlets  14   a  (see  FIGS. 3 and 4 ) are formed on the discharge surfaces  10   a . During printing operation, black, magenta, cyan and yellow ink is discharged from each one of the discharge surfaces  10   a  of the four heads  10 . The four heads  10  are arranged at predetermined intervals along the sub-scanning direction and are supported by the housing  1   a  via a head holder  3 . The head holder  3  supports the heads  10  in a manner that the discharge surfaces  10   a  face the platen  9  and that predetermined space suitable for the printing operation is defined between the discharge surfaces  10   a  and the platen  9 . The head holder  3  includes ring-shaped caps  40  each of which surrounds an outer periphery of the discharge surface  10   a  of the head  10 . Structures of the heads  10  and the head holder  3  will be described in more detail below. The sub-scanning direction is parallel to the conveying direction in which the paper sheet P is conveyed by the conveyance unit  21 . The main scanning direction is parallel to the level surface and is perpendicular to the sub-scanning direction. 
     The guide unit includes an upstream-side guide unit and a downstream-side guide unit placed on both sides of the conveyance unit  21 . The upstream-side guide unit includes two guides  27   a  and  27   b , and a pair of feed rollers  26 . The guide unit connects a paper feed unit  1   b  (described later) and the conveyance unit  21 . The downstream-side guide unit includes two guides  29   a  and  29   b , and two pairs of feed rollers  28 . The guide unit connects the conveyance unit  21  and the paper sheet discharge unit  31 . 
     The paper feed unit  1   b , which can be removed from and replaced in the housing  1   a , is placed in the cavity B. The paper feed unit  1   b  includes a paper sheet feed tray  23  and a paper sheet feed roller  25 . The paper sheet feed tray  23  is an upwardly open box-shaped tray which holds paper sheets P of several sizes. The paper sheet feed roller  25  sends the uppermost paper sheet P held in the paper sheet feed tray  23  out and feeds it to the upstream-side guide unit. 
     As described above, the paper sheet conveyance path extending from the paper feed unit  1   b  to the paper sheet discharge unit  31  via the conveyance unit  21  is formed in the cavities A and B. In response to a print command received from an external device, the controller  1   p  drives a paper sheet feed motor (not illustrated) for the paper sheet feed roller  25 , a feed motor (not illustrated) for the feed roller of each guide unit, a conveying motor, and other components. The paper sheet P sent out from the paper sheet feed tray  23  is fed to the conveyance unit  21  by the feed rollers  26 . When the paper sheet P passes below each head  10  in the sub-scanning direction, ink is discharged sequentially from the discharge surfaces  10   a  to form a color image on the paper sheet P. The paper sheet P is then conveyed upward by the two feed rollers  28 . The paper sheet P is outputed onto the paper sheet discharge unit  31  from an upper opening  30 . 
     An ink unit  1   c  which can be removed from and replaced in the housing  1   a  is placed in the cavity C. The ink unit  1   c  includes a cartridge tray  35 , four cartridges  39  placed in parallel on the cartridge tray  35  and a water reservoir  54  (not illustrated; see  FIG. 5 ). Each cartridge  39  supplies ink to a corresponding head  10  via an ink tube (not illustrated). 
     Next, the structure of the head  10  will be described with reference to  FIGS. 2 to 4  and  7 . In  FIG. 3 , pressure chambers  16  and apertures  15  formed below actuator units  17  are illustrated by a solid line which should actually be a dotted line. 
     As illustrated in  FIGS. 2 to 4 , the head  10  includes vertically arranged reservoir units  11  (not shown in  FIGS. 2 to 4 , see  FIG. 6 ) and channel units  12 , eight actuator units  17  fixed to upper surfaces  12   x  of the channel units  12 , and FPCs connected to each of the actuator units  17 . An ink channel including a reservoir which temporarily keeps ink supplied from the cartridges  39  (see  FIG. 1 ) is formed in the reservoir unit  11 . An ink channel extending from openings  12   y  on an upper surface  12   x  to each discharge outlet  14   a  on a lower surface (i.e., the discharge surface  10   a ) is formed in the channel unit  12 . Each actuator unit  17  includes piezoelectric actuators each corresponding to each of the discharge outlets  14   a.    
     Projections and recesses are formed on the lower surface of the reservoir unit  11 . The projections are affixed to the upper surface  12   x  of the channel unit  12  at areas in which no actuator unit  17  is provided (i.e., areas defined by dash-dot-dot lines including the openings  12   y  as illustrated in  FIG. 2 ). An end surface of each projection includes an opening connected to the reservoir and facing each opening  12   y  of the channel unit  12 . Thus the reservoir and an individual ink channel  14  communicate with each other via the opening described above. The recesses face the upper surface  12   x  of the channel unit  12  and the surface of the actuator unit  17  with a slight gap therebetween. 
     The channel unit  12  is a layered product of nine rectangular metal plates  12   a ,  12   b ,  12   c ,  12   d ,  12   e ,  12   f ,  12   g ,  12   h  and  12   i  of substantially the same size affixed to each other. The ink channel of the channel unit  12  includes a manifold channel  13  which includes the opening  12   y  at an end, a sub-manifold channel  13   a  branched from the manifold channel  13 , and an individual ink channel  14  extending from an outlet of the sub-manifold channel  13   a  to the discharge outlet  14   a  via a pressure chamber  16 . As illustrated in  FIG. 4 , the individual ink channel  14  is formed for each discharge outlet  14   a  and includes an aperture  15  used for channel resistance adjustment. In the adhesive area of each actuator unit  17  on the upper surface  12   x , substantially diamond-shaped openings are arranged in a matrix so as to expose the pressure chambers  16 . In areas which face the adhesive area of each actuator unit  17  on the lower surface (i.e., the discharge surface  10   a ), the discharge outlets  14   a  are arranged in a matrix in the same arrangement pattern as in the pressure chambers  16 . 
     As illustrated in  FIG. 2 , the actuator units  17  each has a trapezoidal shape and are arranged in two rows of alternate pattern on the upper surface  12   x  of the channel unit  12 . Each actuator unit  17  covers the multiple openings of the pressure chambers  16  of formed in the adhesive areas of the actuator unit  17  as illustrated in  FIG. 3 . Although not illustrated, the actuator unit  17  includes a plurality of piezoelectric layers extending across the multiple pressure chambers  16  and electrodes which hold the piezoelectric layer from above and below in the thickness direction. The electrode includes individual electrodes each corresponding to each of the pressure chambers  16  and a common electrode common to the pressure chambers  16 . The individual electrodes are formed on a surface of the uppermost piezoelectric layer. 
     Various drive signals generated by a control substrate and a driver IC (not illustrated) provided in each head  10  are transferred to the actuator units  17  under the control of the controller  1   p  (see  FIG. 1 ). 
     Next, a structure of head holder  3  will be described with reference to  FIGS. 2 ,  5  and  6 . The head holder  3  is, for example, a metal frame. The cap  40  provided in each head  10  and a pair of joints  51  are attached to the head holder  3 . 
     As illustrated in  FIG. 5 , a pair of joints  51  form one end and the other end of a circulation channel of the humidification mechanism  50 . One of the pair of joints  51  is located near one end of the corresponding head  10  and the other is located near the other end of the corresponding head  10  along the main scanning direction. In humidification maintenance, air is collected through an opening (i.e., an exhaust outlet)  51   a  on the lower surface of one of the joints  51  (i.e., the left one in  FIG. 5 ) and humidified air is supplied through an opening (i.e., an inlet)  51   b  on the lower surface of the joint  51  of another side (i.e., the right one in  FIG. 5 ). A valve  52   a  which opens and closes the opening  51   a  is provided near the opening  51   a  and a valve  52   b  which opens and closes the opening  51   b  is provided near the opening  51   b  (see  FIG. 8 ). 
     As illustrated in  FIG. 6 , the joint  51  is substantially cylindrical in shape and includes a base end  51   x  and an end  51   y  extending from the base end  51   x . A hollow cavity  51   z  is formed to extend in a vertical direction from the base end  51   x  to the end  51   y . The base end  51   x  and the end  51   y  are different in outer diameter: the outer diameter of the base end  51   x  is larger than that of the end  51   y , but the hollow cavity  51   z  has a constant diameter along the vertical direction. The end  51   y  includes a cut portion along an outer periphery of an upper end surface thereof, and is thus tapered. With this, the tubes  55  and  57  are easily connected, at one end thereof, to the end  51   y.    
     The joint  51  is fixed to the head holder  3  in a state in which the end  51   y  is inserted in a through-hole  3   a  of the head holder  3 . The through-holes  3   a  are formed at positions at which the joint  51  is fixed to the head holder  3 , i.e., both main scanning direction ends of the head  10 . The outer diameter of the end  51   y  is slightly smaller than the diameter of the through-hole  3   a , and therefore a slight gap is formed between an outer peripheral surface of the end  51   y  and a wall surface which defines the through-hole  3   a  of the head holder  3 . The gap is sealed by filling, for example, a sealant during fixation of the joint  51  to the head holder  3 . 
     The cap  40  is formed in a ring shape, when seen in a plan view, which surrounds the outer periphery of the discharge surface  10   a  of the head  10 . The cap  40  includes an elastic body  41  supported by the head holder  3  via a fixing unit  41   c  and a movable member  42  which can be raised and lowered. 
     The elastic body  41 , formed by an elastic material such as rubber, includes a base  41   x , a protrusion  41   a , a fixing unit  41   c  and a connecting unit  41   d . The protrusion  41   a  is triangular in shape when seen in sectional view and protrudes downward from the lower surface of the base  41   x . The fixing unit  41   c  is T-shaped when seen in a sectional view and is fixed to the head holder  3 . The connecting unit  41   d  connects the base  41   x  and the fixing unit  41   c . The elastic body  41 , which includes the above components, is formed as a ring which surrounds the outer periphery of the discharge surface  10   a  of the head  10  when seen in a plan view. An upper end of the fixing unit  41   c  is fixed to the head holder  3  by, for example, an adhesive. The fixing unit  41   c  is held between the head holder  3  and the base end  51   x  of each joint  51  near each through-hole  3   a . The connecting unit  41   d  extends outward (in a direction away from the discharge surface  10   a  when seen in a plan view) from the lower end of the fixing unit  41   c  in a curved manner and connects to the lower end of the base  41   x . The connecting unit  41   d  has flexibility sufficient to be deformed accompanying raising and lowering of the movable member  42 . A recess  41   b  which fits the lower end of the movable member  42  is formed on the upper surface of the base  41   x.    
     The movable member  42  is formed from a rigid material and is formed as a ring which surrounds the outer periphery of the discharge surface  10   a  of the head  10  when seen in a plan view as in the elastic body  41 . The movable member  42  is supported by the head holder  3  via the elastic body  41  and is, at the same time, movable in the vertical direction relative to the head holder  3 . In particular, the movable member  42  is connected to a plurality of gears  43  and, under the control of the controller  1   p , is raised or lowered accompanying rotation of the gears  43  driven by a raising and lowering motor  44  (see  FIG. 8 ). In this state, since the recess  41   b  of the elastic body  41  fits the lower end of the movable member  42 , the base  41   x  is also raised or lowered together with the movable member  42 . In the elastic body  41 , when the movable member  42  is raised or lowered, the base  41   x  including the protrusion  41   a  is raised or lowered together with the movable member  42  in a state in which the fixing unit  41   c  is fixed to the head holder  3 . Thus, relative positions between the end  41   a   1  of the protrusion  41   a  and the discharge surface  10   a  change along the vertical direction. 
     The protrusion  41   a  is selectively located at a contact position and at a separated position accompanying the raising and lowering of the movable member  42 . In the contact position, the end  41   a   1  is in contact with a support surface  8   a  of the glass table  8  (i.e., is positioned by the inversion mechanism  7  to face the discharge surface  10   a ) (see  FIG. 5 ). In the separated position, the end  41   a   1  is separated from the support surface  8   a  (see  FIG. 6 ). As illustrated in  FIG. 5 , when the protrusion  41   a  is in the contact position, the discharge space S 1  formed between the discharge surface  10   a  and the support surface  8   a  is separated from the external space S 2 : the capped (sealed) state. As illustrated in  FIG. 6 , when the protrusion  41   a  is in the separated position, the discharge space S 1  communicates with the external space S 2 : the non-capped (non-sealed) state. 
     The protrusion  41   a  is separated from the discharge surface  10   a  along the entire outer periphery of the discharge surface  10   a  (i.e., the lower surface of the head  10  illustrated in  FIG. 2 ) when seen in a plan view. The protrusion  41   a  has a substantially rectangular shape and surrounds the discharge surface  10   a  when seen in a plan view. 
     Next, a structure of the humidification mechanism  50  will be described with reference to  FIGS. 5 and 7 . 
     The humidification mechanism  50  includes joints  51 , tubes  55 ,  56  and  57 , a humidification pump  53 , a water reservoir  54  and a replenishing mechanism  59  as illustrated in  FIG. 5 . A pair of joints  51  (i.e., two joints) are provided to each head  10 . The heads  10  in a printer  1 , i.e., four heads  10  share a single humidification pump  53  and a water reservoir  54  as illustrated in  FIG. 7 . The tubes  55  and  57  each includes main portions  55   a  and  57   a  shared by four heads  10 , and four branch units  55   b  and  57   b  branched from the main portion  55   a  and  57   a  and extending to the joints  51 . Note that the humidification pump  53  and the water reservoir  54  may be provided in each of the four heads  10 . 
     One end of the tube  55  (i.e., an end of each branch unit  55   b ) fits the end  51   y  of one of the joints  51  (left one in  FIG. 5 ) of each head  10  and the other end (i.e., an end opposite to the branch unit  55   b  of the main portion  55   a ) is connected to the humidification pump  53 . That is, the tube  55  connects the hollow cavity  51   z  in one of the joints  51  provided in each head  10  to the humidification pump  53  to provide communication therebetween. The tube  56  connects the humidification pump  53  and the water reservoir  54  to provide communication therebetween. One end of the tube  57  (i.e., an end of each branch unit  57   b ) fits the end  51   y  of the other joint  51  (right one in  FIG. 5 ) of each head  10  and the other end (i.e., an end opposite to the branch unit  57   b  of the main portion  57   a ) is connected to the water reservoir  54 . That is, the tube  57  connects the hollow cavity  51   z  of the other joint  51  in each head  10  to the water reservoir  54  to provide communication therebetween. 
     The water reservoir  54  stores water in a lower space and air in a upper space; the air is humidified by the water in the lower space. The tube  56  is connected to the water reservoir  54  at a position below the water surface; i.e., the tube  56  communicates with the lower space of the water reservoir  54  via an upstream outlet  54   a . The upstream outlet  54   a  is formed near the bottom surface of the water reservoir  54 . The tube  57  is connected to the water reservoir  54  at a position above the water surface; i.e., the tube  57  communicates with the upper space of the water reservoir  54 . In humidification maintenance, the humidification pump  53  is driven to rotate forward in the capped state, whereby air in the discharge space S 1  is collected through the opening  51   a . Air collected through the opening  51   a  reaches the humidification pump  53  via the hollow cavity  51   z  of the joint  51 , and the cavity in the tube  55 , and then reaches the water reservoir  54  via the cavity in the tube  56 . The air is supplied to the lower space (i.e., below the water surface) of the water reservoir  54  via the upstream outlet  54   a . Supplied air is humidified with water in the water reservoir  54  to become humidified air. The humidified air leaves the upper space of the water reservoir  54  through a downstream outlet  54   b  and, via the cavity in the tube  57 , flows into the discharge space S 1  through the opening  51   b . Thus, the tubes  55 ,  56  and  57  form a circulation channel through which humidified air circulates. During stop or forward rotation, the humidification pump  53  functions as a check valve which prevents water in the water reservoir  54  flowing in the direction opposite to that of arrow. 
     The replenishing mechanism  59  is in communication with a water level sensor  59   a  which detects an amount of remaining water stored in the water reservoir  54  and, when amount of remaining water detected by the water level sensor  59   a  decreases to or below a predetermined amount, the replenishing mechanism  59  replenishes water to the water reservoir  54 . 
     An antiseptic agent which prevents reduction in water quality is added to water to be replenished in the water reservoir  54 . For example, as for the antiseptic agent, Ehydroacetic acid, Docosahexaenoic acid, Potassium benzoate, 2-Pyridinethiol, 1-Oxide sodium, 1,2-Benzisothiazol-3-one, etc. correspond. Since the antiseptic agent includes a non-volatile component, an amount of the non-volatile component in the water reservoir  54  increases during repeated evaporation and replenishment of water. Therefore, the concentrated non-volatile component in the water reservoir  54  causes deterioration in a steam generating function and, as a result, it becomes impossible to produce humidified air efficiently. To avoid this phenomenon, when the amount of the non-volatile component in the antiseptic agent included in the water reservoir  54  increases to a prescribed amount (“prescribed amount”) or greater, water reservoir cleaning is performed to remove the non-volatile component in the antiseptic agent included in the water reservoir  54 . The prescribed amount is smaller than an amount at which the concentrated non-volatile component causes deterioration in steam generating function. In water reservoir cleaning, after the state is shifted to the capped state, the humidification pump  53  is driven to rotate forward. Thus, water is agitated by the air compulsorily supplied to the water reservoir  54  and the non-volatile component in the antiseptic agent deposited on the bottom surface starts floating. Then, the humidification pump  53  is driven to rotate backward to cause the non-volatile component in the antiseptic agent is exhausted with water into the discharge space S 1  through the opening  51   a . The water reservoir  54  is emptied in the present embodiment. However, in an alternative embodiment, a certain amount of water may be exhausted so that the rest of water remains in the water reservoir  54 . After water is exhausted, the replenishing mechanism  59  replenishes water in the water reservoir  54 . 
     A recovering mechanism  80  is provided on the glass table  8 . The recovering mechanism  80  includes a waste liquid reservoir  81 , tubes  82  and  83  and a recovery pump  84 . The tubes  82  and  83  are each connected to the waste liquid reservoir  81  and the glass table  8  so that the waste liquid reservoir  81  and the discharge space S 1  communicate with each other. The recovery pump  84  is provided in the tube  82 . In water reservoir cleaning, after the water exhausted through the opening  51   a  is collected in the discharge space S 1 , the recovery pump  84  is driven such that the water liquid collected in the discharge space S 1  is collected in the waste liquid reservoir  81  via the tube  82 . At this time, air in the waste liquid reservoir  81  is supplied to the discharge space S 1  via the tube  83 . Therefore, the waste liquid collected in the discharge space S 1  can be recovered smoothly. 
     Next, the controller  1   p  will be described. The controller  1   p  includes a central processing unit (CPU), non-volatile memory and random access memory (RAM). Programs executed by the CPU and data used by the programs are rewritably stored in the non-volatile memory. During the execution of the program, data is temporarily stored in the RAM. Each of the function units of the controller  1   p  is cooperatively formed by the hardware and the software in the non-volatile memory. As illustrated in  FIG. 8 , the controller  1   p  includes an image data memory unit  61 , a head control unit  62 , a maintenance control unit  64  and a conveyance control unit  65 . 
     The image data memory unit  61  stores image data representing an image to be printed on the paper sheet P. The conveyance control unit  65  controls the conveyance unit  21  such that the paper sheet P is conveyed along the conveying path at a predetermined speed. The head control unit  62  controls the head  10  such that the image related to the image data stored in the image data memory unit  61  is printed on the paper sheet P which is conveyed by the conveyance unit  21  and that flushing is performed in the maintenance operation. 
     The maintenance control unit  64  controls the inversion mechanism  7 , the humidification pump  53  of the humidification mechanism  50 , the raising and lowering motor  44  which raises and lowers the movable member  42  (i.e., the end  41   a   1  of the protrusion  41   a ) and the recovery pump  84 , and the valves  52   a  and  52   b  such that humidification maintenance or water reservoir cleaning is performed. When the amount of remaining water detected by the water level sensor  59   a  decreases to or below a predetermined amount, the maintenance control unit  64  controls the replenishing mechanism  59  such that water is replenished to the water reservoir  54 . 
     The humidification maintenance, in which humidified air is supplied to the discharge space S 1  in a capped state, is started when predetermined time elapsed since the latest printing operation is completed. 
     When the humidification maintenance is started, the maintenance control unit  64  controls the inversion mechanism  7  such that the support surface  8   a  of the glass table  8  faces the discharge surfaces  10   a . The movable member  42  is then moved downward by the rotation of the gears  43 . The protrusion  41   a  is in the separated position (see  FIG. 6 ) during the printing operation and, is moved to the contact position accompanying downward movement of the movable member  42  (see  FIG. 5 ). Therefore, the discharge space S 1  is sealed and the state is shifted to a capped state (YES at S 1  in  FIG. 9 ). In a standby state or idle state in which no printing operation is carried out, the maintenance control unit  64  moves the protrusion  41   a  to a contact position and the state is shifted to a capped state. The maintenance control unit  64  then opens the openings  51   a  and  51   b  with the valves  52   a  and  52   b.    
     Subsequently, the maintenance control unit  64  drives the humidification pump  53  (S 2 ) and collects air in the discharge space S 1  through the opening  51   a  of one of the joints  51 . Here, air collected through the opening  51   a  reaches the humidification pump  53  via the hollow cavity  51   z  of the joint  51  and the cavity in the tube  55 , and then reaches the water reservoir  54  via the cavity in the tube  56 . The air is supplied to the lower space (i.e., below the water surface) of the water reservoir  54  through the upstream outlet  54   a . The humidified air humidified by the water in the water reservoir  54  is exhausted from the upper space of the water reservoir  54  through the downstream outlet  54   b . At this time, humidity of humidified air exhausted from upper space of water reservoir  54  serves as value near 100%. The humidified air is supplied to the discharge space S 1  via the cavity in the tube  57  and through the opening  51   b  of the other of the joints  51 . Black arrows in  FIG. 5  represent the flow of air before the humidification and white arrows represent the flow of air after the humidification. The maintenance control unit  64  controls switch valves (not illustrated) provided in the branch units  55   b  and  57   b  illustrated in  FIG. 7  in addition to the driving of the humidification pump  53  so as to selectively adjust the flow of air in the branch units  55   b  and  57   b.    
     When the humidified air is thus supplied to the discharge space S 1  through the opening  51   b , humidity in the discharge space S 1  increases and, as a result, viscosity of the concentrated ink at the discharge outlet  14   a  decreases. In a balanced state, it is only necessary that humidity of the humidified air is equal to or greater than the ambient humidity; and it is preferred that humidity of air is, in a balanced state, is equivalent to or greater than the proper humidity at which ink viscosity at the discharge outlet  14   a  is suited to discharging ink. At the completion of supply of the humidified air (S 3 ), feed time (equivalent to driving time of the humidification pump  53 ) is stored in a humidification history storage unit  64   a  (S 4 ). Now, the humidification maintenance is completed. 
     Upon reception of a print command, the maintenance control unit  64  drives the gears  43  to move the movable member  42  upward and thereby the protrusion  41   a  are moved to the separated position from the contact position. Then, the maintenance control unit  64  controls the inversion mechanism  7  such that the platen  9  faces the discharge surfaces  10   a . Now the printer  1 , it is ready for printing. In a standby state or idle state after the printing operation is completed, the maintenance control unit  64  controls the inversion mechanism  7  such that the support surface  8   a  of the glass table  8  faces the discharge surface  10   a , and then lets the movable member  42  move downward to thereby move the protrusion  41   a  to the contact position from the separated position, whereby the state is shifted to the capped state. 
     Water reservoir cleaning is performed to exhaust the non-volatile component in the water reservoir  54  with water after the exhaust determination unit  64   b  determines that the amount of the non-volatile component in the antiseptic agent stored in the water reservoir  54  is greater than a prescribed amount and immediately before replenishment of water is started by the replenishing mechanism  59  in response that the amount of remaining water in the water reservoir  54  decreases to or below a predetermined amount (preferably ¼, 1/10, and so on of the total capacity of the water reservoir  54 , S 6 ). The exhaust determination unit  64   b  determines, with reference to the humidification history storage unit  64   a , that the amount of the non-volatile component in the water is greater than a prescribed amount each time a predetermined amount (predetermined time) of humidified air is supplied (S 5 ). Moisture in the humidification air is absorbed into the ink in a discharge outlet  14   a . Therefore, the driving time of the humidification pump  53  and the amount of consumption of the water in the water reservoir  54  (equivalent to the amount of supply of water to the water reservoir  54 ) is proportionally related. The predetermined time is set to reflect when the amount of the non-volatile component in the water is greater than a prescribed amount. 
     When the water reservoir cleaning is started (S 7 ), the maintenance control unit  64  controls the inversion mechanism  7  as in the humidification maintenance such that the support surface  8   a  of the glass table  8  faces the discharge surfaces  10   a , and then drives the gears  43  to rotate so as to move the movable member  42  downward, whereby the state is shifted to the capped state. The maintenance control unit  64  drives the humidification pump  53  to rotate forward. Thus, water is agitated by the air compulsorily supplied to the water reservoir  54  and the non-volatile component deposited on the bottom surface starts floating. Subsequently, the opening  51   a  is opened by the valve  52   a  and the opening  51   b  is closed by the valve  52   b , and the humidification pump  53  is driven to rotate backward. Therefore, the total amount of the non-volatile component in the water reservoir  54  is exhausted into the discharge space S 1  through the opening  51   a  with water. Water exhausted through the opening  51   a  is recovered by the recovering mechanism  80 . The maintenance control unit  64  lets the valve  52   a  close the opening  51   a  after the exhaust of water through the opening  51   a  is completed. Now, water reservoir cleaning is completed. During water reservoir cleaning, the water liquid reservoir  81 , the water reservoir  54  or other liquid paths are made to communicate with ambient air, thereby promoting movement of water. After water reservoir cleaning is completed, the feed time which is stored in a humidification history storage unit  64   a  is reset (S 8 ), and replenishment of water is performed by the replenishing mechanism  59  (S 9 ). 
     As described above, water stored in the water reservoir  54  is exhausted when the amount of the non-volatile component is greater than a prescribed amount. Therefore, the printer  1  according to the present embodiment can prevent deterioration in humidifying function caused by an increased amount of non-volatile component in the water reservoir  54 . 
     The exhaust determination unit  64   b  determines, with reference to the humidification history storage unit  64   a , that the amount of the non-volatile component in the antiseptic agent included in the water is greater than a prescribed amount each time a predetermined amount of humidified air is supplied. Thereby, it is determined whether the amount of the non-volatile component is greater than a prescribed amount. 
     Water reservoir cleaning is started after the exhaust determination unit  64   b  determines that the amount of the non-volatile component is greater than a prescribed amount and immediately before replenishment of water by the replenishing mechanism  59  is started in response that the amount of the remaining water in the water reservoir  54  decreases to or below the predetermined amount. As a result, water is exhausted with the concentrated non-volatile component and is then replenished. Therefore, waste of replenished water can be reduced. 
     In addition, water stored in the water reservoir  54  is exhausted through the upstream outlet  54   a  provided near the bottom surface of the water reservoir  54 , whereby water in the water reservoir  54  is exhausted efficiently. 
     In humidification maintenance, the circulation channel through which the humidified air circulates is formed, whereby water consumption is reduced. 
     In addition, humidified air can be produced in a simple structure in which air is supplied compulsorily through the upstream outlet  54   a  which is in contact with water in the water reservoir  54 . 
     In water reservoir cleaning, the humidification pump  53  is driven to rotate forward immediately before the non-volatile component is exhausted with water, and thus water is agitated by the air compulsorily supplied to the water reservoir  54  so that the non-volatile component deposited on the bottom surface starts floating. As a result, the non-volatile component deposited on the bottom surface can be exhausted efficiently. 
     Modification 
     In the present embodiment, the exhaust determination unit  64   b  determines, with reference to the humidification history storage unit  64   a , that the amount of the non-volatile component included in water is greater than a prescribed amount each time a predetermined amount of the humidified air is supplied; however, whether the amount of the non-volatile component included in water is greater than a prescribed amount may be determined by other methods. For example, as illustrated in  FIG. 9 , when the amount of remaining water detected by the water level sensor  59   a  decreases to or below a predetermined amount (YES at S 21  in  FIG. 11 ), a maintenance control unit  164  controls the replenishing mechanism  59  such that water is replenished to the water reservoir  54  (S 22 ). The amount of water replenished in the water reservoir  54  by the replenishing mechanism  59  is stored in a replenishment history storage unit  164   a  (S 23 ). An exhaust determination unit  154   b  may determine, with reference to the replenishment history storage unit  164   a , whether the amount of the non-volatile component is greater than a prescribed amount in accordance with the total amount of water replenished in the water reservoir  54  (YES at S 24 ). Therefore, the amount of the non-volatile component can be detected correctly. Water reservoir cleaning is performed to exhaust the non-volatile component in the water reservoir  54  with water after the exhaust determination unit  64   b  determines that the amount of the non-volatile component is greater than a prescribed amount in accordance with the total amount of water replenished in the water reservoir  54  (S 25 ). After water reservoir cleaning is completed, the amount of water replenished which is stored in a replenishment history storage unit  164   a  is reset (S 26 ), and replenishment of water is performed by the replenishing mechanism  59  (S 27 ). 
     Also, when the amount of remaining water detected by the water level sensor  59   a  decreases to or below a predetermined amount, a maintenance control unit  164  controls the replenishing mechanism  59  such that a predetermined amount of water is replenished to the water reservoir  54 . The number of water replenishments of the water reservoir  54  by the replenishing mechanism  59  is stored in a replenishment history storage unit  164   a . An exhaust determination unit  154   b  may determine, with reference to the replenishment history storage unit  164   a , whether the amount of the non-volatile component is greater than a prescribed amount in accordance with the total amount of water replenished in the water reservoir  54 . Therefore, the amount of the non-volatile component can be detected correctly. 
     Another Modification 
     In the present embodiment, water reservoir cleaning is performed to exhaust the non-volatile component in the water reservoir  54  with water after the exhaust determination unit  64   b  determines that the amount of the non-volatile component in the antiseptic agent stored in the water reservoir  54  is greater than a prescribed amount; however, the controller  1   p  may output a message which indicates the amount of the non-volatile component is greater than the predetermined amount before water reservoir cleaning is performed. For example, as illustrated in  FIG. 12 , when the exhaust determination unit  64   b  determines that the amount of the non-volatile component is greater than a prescribed amount in accordance with the total amount of water replenished in the water reservoir  54 , an output unit  164   d  output a message to a display  91  which is fixed on the housing  1   a . Information on the printer which needs the water reservoir cleaning is included in the message, such that a user looking at the message displayed on the display can know the reason or necessity for the water reservoir cleaning. And the user can perform the water reservoir cleaning by operating an exhaust valve  257  (see  FIG. 13 ) manually. In addition, when there is no exhaust valve  257 , the user removes the water reservoir  54  and can perform the water reservoir cleaning. 
     Although preferred embodiments of the present invention have been described above, the present invention is not limited to the same. Various design changes may be made. For example, in the embodiments described above, water reservoir cleaning is started after it is determined that the amount of the non-volatile component is greater than a prescribed amount and immediately before replenishment of water by the replenishing mechanism  59  is started in response that the amount of the remaining water in the water reservoir  54  decreases to or below a predetermined amount. However, water reservoir cleaning may be started at any time once it is determined that the amount of the non-volatile component is greater than a prescribed amount. For example, water reservoir cleaning may be started immediately after it is determined that the amount of the non-volatile component is greater than a prescribed amount. Alternatively, water reservoir cleaning may be started after a certain period of time elapsed after it is determined that the amount of the non-volatile component is greater than a prescribed amount (for example, at the next water supply event). 
     In the embodiments described above, the exhaust determination unit  64   b  ( 164   c ) determines, with reference to the humidification history storage unit  64   a  or the replenishment history storage unit  164   a , that the amount of the non-volatile component included in water is greater than a prescribed amount. However, the amount of the non-volatile component included in the water may be measured by measuring directly a refractive index or a electrical resistance of the water in the water reservoir  54  by a sensor for determining the amount of the non-volatile component. In this case, the exhaust determination unit  64   b  ( 164   c ) unit determines that the amount of the non-volatile component included in water is greater than a prescribed amount, when the concentration of the non-volatile component included in water is greater than a prescribed concentration value. 
     In the embodiments described above, water in the water reservoir  54  is exhausted through the upstream outlet  54   a ; but water in the water reservoir  54  may be exhausted through an exhaust passage  256  formed in the water reservoir  54  as illustrated in  FIG. 10 . In this case, an exhaust valve  257  provided in the exhaust passage  256  is controlled by the maintenance control unit  64  and water in the water reservoir  54  is exhausted into a waste water reservoir  281  through an opening exhaust valve  257 . 
     In the embodiments described above, the upstream outlet  54   a  is provided near the bottom surface of the water reservoir  54 ; but the upstream outlet may be provided at any other position as long as it is in contact with water. 
     In the embodiments described above, the total amount of the non-volatile component in the water reservoir  54  is exhausted, because the water reservoir  54  is emptied. However, alternatively, an amount of water may be exhausted so that there is remaining water in the water reservoir  54  which is taken into consideration by the exhaust determination unit  64   b.    
     In the embodiments described above, a circulating channel through which the humidified air circulates is formed for humidification maintenance; but it is not always necessary to let humidified air exhausted into the discharge space circulate. 
     In the embodiments described above, the tube  83  is in communication with the discharge space S 1 ; but it is not always necessary to provide the tube  83 . In this case, the discharge space S 1  is made to communicate with ambient air at the recovery of the exhausted water to thereby achieve suitable recovery of exhausted water. 
     In the embodiments described above, humidified air is produced by compulsorily supplying air through the upstream outlet  54   a  which is in contact with water in the water reservoir  54 ; but humidified air may be produced by other mechanisms. For example, humidified air may be produced by heating water with a heater. That is, humidified air may be produced by any mechanisms with which the non-volatile component deposits on the water reservoir  54 . 
     It is not always necessary that the protrusion  41   a  is movable as in the embodiments described above. For example, the protrusion may be fixed to a head holder in a non-movable manner and a relative position of the end of the protrusion to the discharge surface may be constant. In this case, the protrusion may be selectively located at a contact position and a separated position by raising or lowering the head holder or the support surface of a medium support so as to change the relative position of the protrusion to the discharge surface. 
     As illustrated in  FIG. 11 , the cap  340  may be provided separately from the head  10 . In this case, the cap  340  may be located at a position at which it faces the discharge surfaces  10   a  after the conveyance unit is moved downward. A seamless conveyor belt may be used in the conveyance unit. The cap  340  may be selectively located at a contact position and a separated position by raising or lowering at least one of the head  10  and the cap  340 : at the contact position, an end  341   a  of the cap  340  is in contact with the discharge surfaces  10   a ; at the separated position, the end  341   a  is separated from the discharge surfaces  10   a . When cap  340  is at the contact position, the discharge space S 201  is sealed by the cap  340  (a capped state). When the cap  340  is at the separated position, the discharge space S 201  is opened (a non-capped state). In the structure of  FIG. 11 , the humidification mechanism  50  may be provided at the cap  340 . In this case, when the humidification pump  53  is driven to rotate backward to exhaust water stored in the water reservoir  54  into the cap  340 , the exhausted water easily flows into the tube  57 . Thus, the opening  51   b  is effectively closed. In this case, interference in driving of the humidification pump  53  at the time that the humidification pump  53  is driven to rotate backward should be prevented by, for example, opening an ambient air communication valve (not illustrated) provided at an upper position of the water reservoir  54  and introducing ambient air to replace the air exhausted from the water reservoir  54  with. 
     In the embodiments described above, in water reservoir cleaning, the humidification pump  53  is driven to rotate forward immediately before the non-volatile component is exhausted with water such that air is compulsorily supplied to the water reservoir  54  and agitates water. It is also possible to agitate water by an agitating mechanism  454   c , such as a propeller, which is provided inside the water reservoir  54  as illustrated in  FIG. 12 . According to this, water can be agitated reliably. 
     The inlet and the outlet of the circulation channel may be of any shape and may be located at any position as long as they are formed at the head, the head holder or the cap and communicate with the discharge space. For example, one of the inlet and the outlet may be formed at the head and the other may be formed at the head holder. The inlet or the outlet may be formed at the protrusion of the cap. It is also possible that no recess  3   x  is formed on a surface of the head or the head holder, but the inlet and/or outlet of the circulation channel may be located on the same level as the discharge surfaces  10   a . The inlet and outlet may be located at positions on both sides of the discharge surfaces  10   a  (or a group of discharge outlets if the inlet and/or outlet is formed at the head) along the sub-scanning direction when seen in a plan view. Alternatively, the inlet and outlet may be located at positions on the same sides of the discharge surfaces  10   a  (i.e., positions on the same sides with respect to the discharge surface  10   a ) which does not sandwich when seen in a plan view. 
     In the embodiment described above, a component in an antiseptic agent is described as an example of the non-volatile component; but any type of non-volatile components may be used as long as they are deposited in the water reservoir  54  and cause deterioration in humidifying function. 
     The present invention is applicable to a line printer and a serial printer, and is also applicable to a facsimile machine, a copy machine and other devices. The apparatus of the present invention may discharge any liquid other than ink.