Patent Publication Number: US-9889667-B2

Title: Maintenance device used in liquid discharge head, liquid discharge device, and liquid discharge apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2016-053043 filed, on Mar. 16, 2016, and 2016-144397 filed, on Jul. 22, 2016, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to a maintenance device used in a liquid discharge head, a liquid discharge device, and a liquid discharge apparatus. 
     Description of the Related Art 
     Currently, image forming apparatuses used to output information in the form of electronic data or copy documents are widely used. Inkjet printers, one type of image forming apparatuses, discharge ink from a nozzle of a liquid discharge head onto recording media to perform printing. 
     In such inkjet printers, if ink droplets are not discharged from the nozzle for a while, solvent of ink inside the nozzle evaporates, and the ink in the nozzle dries. Then, the viscosity of ink increases, or the meniscus of ink inside the nozzle may be broken. As a result, the nozzle may be clogged, or bubbles may enter the nozzle, and desirable printing is inhibited. 
     To prevent such inconveniences, for example, a nozzle face is capped to keep the nozzle face and the adjacent area at a constant vapor pressure, thereby inhibiting the ink from drying or the meniscus from being broken. 
     Additionally, after ink is discharged, scattering ink may adhere to the liquid discharge head or the nozzle face. If the adhering ink is left as it is, the ink dries to solidify. As the dried ink accumulates, solidified ink may hang from the liquid discharge head or the nozzle face, or the nozzle face may become dirty. 
     If inkjet printers perform printing in such a state, the hanging ink may contact the recording medium or a conveyor such as a conveyance roller, causing defective printing, or the ink solidified on the nozzle faces may hinder discharge of ink droplets. 
     Accordingly, there are inkjet printers that remove ink adhering to the liquid discharge head or the nozzle face as maintenance. 
     SUMMARY 
     An embodiment of this disclosure provides a maintenance device used in a liquid discharge head includes a first cap to seal a nozzle face of the liquid discharge head, a second cap disposed outside the first cap, and a humidity conditioner disposed outside the first cap and inside the second cap. The second cap seals the first cap and at least a contact portion between the nozzle face of the liquid discharge head and the first cap. The humidity conditioner adjusts humidity in a space between the first cap and the second cap. 
     In another embodiment, a liquid discharge device includes a liquid discharge head and the above-described maintenance device, to perform maintenance of the liquid discharge head. 
     In yet another embodiment, a liquid discharge apparatus includes a liquid discharge head; and the above-described maintenance device, to perform maintenance of the liquid discharge head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic side view of an inkjet printer according to an embodiment; 
         FIG. 2  is a penetrative view, from above, of the inkjet printer illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic block diagram of a hardware configuration and a functional configuration of an inkjet printer according to an embodiment; 
         FIG. 4  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 5  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 6  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 7  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 8  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 9  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 10  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 11  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 12  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 13  is a cross-sectional view of the inkjet printer illustrated in  FIG. 1 , as viewed in the sub-scanning direction; 
         FIG. 14  is a cross-sectional view of a comparative inkjet printer, as viewed in the sub-scanning direction; 
         FIG. 15  is a bottom view of a nozzle plate in the comparative inkjet printer, as viewed from below; 
         FIG. 16  is a cross-sectional view of an inkjet printer including a head cap (a second cap) according to an embodiment, as viewed in the sub-scanning direction; 
         FIG. 17  is a top view of a nozzle cap and the head cap in the inkjet printer illustrated in  FIG. 16 ; 
         FIG. 18  is a cross-sectional view of the inkjet printer illustrated in  FIG. 16 , as viewed in the sub-scanning direction; 
         FIG. 19  is a top view of the nozzle cap and the head cap in the inkjet printer illustrated in  FIG. 16 ; 
         FIG. 20  is a cross-sectional view of the nozzle cap and the head cap in the inkjet printer illustrated in  FIG. 16 , as viewed in the sub-scanning direction; 
         FIG. 21  is a top view of the nozzle cap and the head cap in the inkjet printer illustrated in  FIG. 16 ; 
         FIG. 22  is a cross-sectional view of the nozzle cap and the head cap in the inkjet printer illustrated in  FIG. 16 , as viewed in the sub-scanning direction; 
         FIG. 23  is a top view of a nozzle cap and a head cap in an inkjet printer according to a variation; 
         FIG. 24  is a top view of a nozzle cap and a head cap in an inkjet printer according to another variation; 
         FIG. 25  is a graph of changes in relative humidity inside the head cap (i.e., head cap interior) when the liquid discharge head is capped with the head cap illustrated in  FIG. 16 ; 
         FIG. 26  is a graph of changes in moisture content in residual ink while the liquid discharge head is capped with the head cap illustrated in  FIG. 16 ; 
         FIG. 27  is a graph of changes with time of probability of malfunction caused by residual ink in the inkjet printer illustrated in  FIG. 16 ; 
         FIG. 28  illustrates a graph of relative humidity changes of the head cap interior moisturized by a humidity conditioner according to an embodiment and a graph of relative humidity changes of the head cap interior moisturized by a comparative humidity conditioner; 
         FIG. 29  is a table illustrating relations among relative humidity, types of saturated salt solutions, and temperature in a sealed space; 
         FIG. 30  illustrates graphs of relative humidity of the head cap interior attained by different saturated salt solutions according to an embodiment; 
         FIG. 31  is a cross-sectional view of the inkjet printer as viewed in the sub-scanning direction and illustrates a location of the humidity conditioner according to an embodiment; 
         FIG. 32  is a graph of changes in moisture content in the residual ink while the liquid discharge head is capped with the head cap, in the arrangement illustrated in  FIG. 31 ; 
         FIG. 33  is a cross-sectional view of an inkjet printer including a head cap cover (a sealed-state retainer) according to an embodiment, as viewed in the sub-scanning direction; 
         FIG. 34  illustrates a graph of relative humidity changes of the head cap interior when the liquid discharge head is capped with the head cap, in the structure illustrated in  FIG. 33 ; 
         FIG. 35  is a cross-sectional view of an inkjet printer according to an embodiment, as viewed in the sub-scanning direction; 
         FIG. 36  is a cross-sectional view of an inkjet printer according to an embodiment, as viewed in the sub-scanning direction; 
         FIG. 37  is a cross-sectional view of an inkjet printer including a stirrer according to an embodiment, as viewed in the sub-scanning direction; and 
         FIG. 38  illustrates a graph of relative humidity changes of the head cap interior when the liquid discharge head is capped with the head cap, in the structure illustrated in  FIG. 37 . 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to  FIG. 1 , descriptions are given below of an inkjet printer including a carriage and a liquid discharge head mounted on the carriage, according to an embodiment of the present invention. 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. 
     It is to be noted that the suffixes y, m, c, and k attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary. 
     The inkjet printer serves as a liquid discharge apparatus including a liquid discharge head or a liquid discharge device. The liquid discharge apparatus is configured to drive the liquid discharge head to discharge liquid. The term “liquid discharge apparatus” used here includes, in addition to apparatuses to discharge liquid to materials to which the liquid can adhere, apparatuses to discharge liquid into gas (air) or liquid. 
     The term “liquid discharge head” in this disclosure means a single function unit to discharge liquid and corresponds to a liquid discharge head  34  in the present embodiment. Examples of source to generate energy to discharge liquid include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs a thermoelectric conversion element, such as a thermal resistor, and an electrostatic actuator including a diaphragm and opposed electrodes. The terms “image formation”, “recording”, “printing”, “image printing”, and “molding” used in the present disclosure are synonymous with each other. 
     The term “liquid discharge device” means a structure including the liquid discharge head and a functional part(s) or mechanism integrated or united thereto. That is, “liquid discharge device” is an assembly of parts relating to liquid discharge. For example, “liquid discharge device (or unit)” includes a combination of the liquid discharge head and at least one of a head tank, the carriage, a supply unit, a maintenance device (or a maintenance unit), and a main-scan moving mechanism. 
     Herein, the terms “integrated” or “united” mean attaching the liquid discharge head and the functional parts (or mechanism) to each other by fastening, screwing, binding, or engaging and holding one of the liquid discharge head and the functional parts movably relative to the other. The liquid discharge head may be detachably attached to the functional part(s) or unit(s) s each other. 
     For example, “liquid discharge unit” includes the liquid discharge head and the head tank united to each other. Alternatively, the liquid discharge head and the head tank are coupled to each other via, e.g., a tube. Here, a unit including a filter may be added between the head tank and the liquid discharge head in the liquid discharge device. In yet another example, the liquid discharge head and the carriage may be united as “liquid discharge device”. 
     In still another example, in the liquid discharge device, the liquid discharge head is movably held by a guide that is a portion of a main-scan moving mechanism, so that the liquid discharge head and the main-scan moving mechanism are united together. The liquid discharge device may be an integrated unit in which the liquid discharge head, the carriage, and the main-scan moving mechanism are united into a single unit. 
     In another example, the cap that is a portion of the maintenance device is secured to the carriage mounting the liquid discharge head so that the liquid discharge head, the carriage, and the maintenance device are integrated or united into the liquid discharge device. 
     Further, in another example, a tube is coupled to the liquid discharge head to which either the head tank or a channel member is attached, so that the liquid discharge head and the supply unit are united into a single unit. 
     The main-scan moving mechanism may be a guide only. The supply unit may be a tube(s) only or a loading portion only. 
     The liquid discharge apparatus may include at least one of devices to feed, convey, and eject the material to which liquid can adhere. The liquid discharge apparatus may further include at least one of a pretreatment apparatus and a post-treatment apparatus. 
     As the liquid discharge apparatuses, for example, there are image forming apparatuses to discharge ink onto sheets to form images and three-dimensional apparatuses to discharge molding liquid to a powder layer in which powder is molded into a layer-like shape, so as to form three-dimensional articles. 
     The liquid discharge apparatus is not limited to an apparatus to discharge liquid to visualize meaningful images, such as letters or figures. For example, the liquid discharge apparatus may be an apparatus to form meaningless images, such as meaningless patterns, or fabricate three-dimensional images. 
     The above-mentioned term “material to which liquid can adhere” represents a material to which liquid is at least temporarily adhere, a material to which liquid adhere to solidify thereon, or a material into which liquid permeates. Examples of “material to which liquid can adhere” include paper sheets, recording media such as recording paper, recording sheets, film, and cloth; electronic components such as electronic substrates and piezoelectric elements; and media such as powder layers, organ models, and testing cells. The term “material to which liquid can adhere” includes any material to which liquid adheres, unless particularly limited. 
     Examples of materials to which liquid can adhere include any material to which liquid can adhere even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic. 
     The term “liquid” is not limited to a particular liquid as long as the liquid has a viscosity or surface tension to be discharged from the liquid discharge head. However, preferably, the viscosity of the liquid is not greater than 30 mPa·s under ordinary temperature and ordinary pressure, or heated or cooled to 30 mPa·s or lower than 30 mPa·s. Examples of the liquid include a solution, a suspension, or an emulsion including, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, and an edible material, such as a natural colorant. Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink, surface treatment solution, a liquid for forming components of electronic element or light-emitting element or a resist pattern of electronic circuit, or a material solution for three-dimensional fabrication. 
     Although the liquid discharge apparatus is generally an apparatus in which the liquid discharge head and a material to which liquid can adhere move relative to each other, the liquid discharge apparatus is not limited thereto. For example, the liquid discharge apparatus may be a serial head apparatus that moves the liquid discharge head or a line head apparatus that does not move the liquid discharge head. 
     Examples of the liquid discharge apparatus further include a treatment liquid coating apparatus to discharge a treatment liquid to a sheet to coat the sheet with the treatment liquid to reform the sheet surface and an injection granulation apparatus to eject a composition liquid including a raw material dispersed in a solution from a nozzle to mold particles of the raw material. 
     The inkjet printer according to the present embodiment discharges ink droplets from a nozzle formed in a liquid discharge head while moving a carriage in a main scanning direction relative to a recording medium, thereby forming an image portion corresponding to one or multiple lines with a single stroke of the carriage in the main scanning direction. Then, the inkjet printer according to the present embodiment forms another image portion on the subsequent line in a sub-scanning direction on the recording medium and repeats this operation to perform printing. 
     Referring to  FIGS. 1 and 2 , descriptions are given below of an internal structure and mechanism of an inkjet printer  1  according to the present embodiment. In the accompanying drawings, a front side of the inkjet printer  1  is the side on which an output tray  3  is disposed.  FIG. 1  is an internal view of the inkjet printer  1  as viewed in the main scanning direction. 
     As illustrated in  FIG. 1 , the inkjet printer  1  according to the present embodiment includes a sheet feeding tray  2 , the output tray  3 , a carriage support rod  31 , a stay  32 , a carriage  33 , a sheet table  41  on which a sheet  42  is mounted, a sheet feeding roller  43 , a separation pad  44 , a guide  45 , a counter roller  46 , a conveyance guide  47 , a pressing member  48 , an end pressing roller  49 , a conveyor belt  51 , a conveyance roller  52 , a tension roller  53 , a charging roller  56 , a recording guide  57 , a stripping claw  61 , an ejection roller  62 , an ejection roller  63 , a sheet reversing unit  71 , a bypass feeding tray  72  (a manual sheet feeding tray), and a sheet sensor  95 . 
     As illustrated in  FIG. 2 , the inkjet printer  1  further includes a cartridge mount  4 , ink cartridges  10   k ,  10   c ,  10   m , and  10   y  (collectively “ink cartridges  10 ”), a frame  21 , a wire harness  22 , a supply pump unit  24 , a latch  25 , an ink supply tube  36 , a maintenance device  81  for standby time, serving as a maintenance device (i.e., a maintenance-and-recovery unit) for the liquid discharge head, a maintenance device  88  for recording time, and the sheet sensor  95 . 
     The frame  21  includes a left frame  21 A, a right frame  21 B, and a back frame  21 C. The maintenance device  81  for standby time includes nozzle caps  82  (first caps), a wiper blade  83 , and a dummy discharge receptacle  84 . The maintenance device  88  for recording time includes dummy discharge receptacles  89   k ,  89   c ,  89   m , and  89   y  (collectively “dummy discharge receptacles  89 ”). The carriage  33  includes the liquid discharge head  34  and a sub tank including sub tanks  35   k ,  35   c ,  35   m , and  35   y.    
     The nozzle caps  82  include nozzle caps  82   k ,  82   c ,  82   m , and  82   y . As illustrated in  FIG. 2 , the nozzle caps  82  serving as the first caps correspond to a plurality of ink cartridges  10 , respectively. That is, the inkjet printer  1  includes a plurality of nozzle caps  82 . 
     Regarding the internal structure and mechanism of the inkjet printer  1 , descriptions about recording on sheets and descriptions about sheet conveyance are separately given below with reference to  FIGS. 1 and 2 . 
     Initially, descriptions are given of operation of the inkjet printer  1  for recording on sheets. The ink cartridge  10   y  for yellow, the ink cartridge  10   c  for cyan, the ink cartridge  10   m  for magenta, and the ink cartridge  10   k  for black are mounted in the cartridge mount  4  for supply of ink of each color. 
     The carriage support rod  31  is a guide member laterally bridging the left frame  21 A and the right frame  21 B. The carriage support rod  31  supports the carriage  33  slidably in the main scanning direction illustrated in  FIG. 2 . The carriage  33  is supported slidably in the main scanning direction illustrated in  FIG. 2  by the carriage support rod  31  and the stay  32  and is driven by a main scanning motor  500  via a main scanning belt. On the carriage  33 , the liquid discharge head  34  including liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  to discharge ink droplets of yellow (Y), cyan (C), magenta (M), and black (K) is mounted. 
     Each of the four liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  is oriented perpendicular to the main scanning direction of the carriage  33  illustrated in  FIG. 2 . The four liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  are lined parallel to the main scanning direction illustrated in  FIG. 2  and oriented to eject ink droplets downward. 
     The carriage  33  includes the sub tank  35  to supply the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  of the liquid discharge head  34  with the respective color inks. The sub tank  35  includes the sub tanks  35   k ,  35   c ,  35   m , and  35   y  corresponding to the respective colors of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k.    
     To each of the sub tanks  35   k ,  35   c ,  35   m , and  35   y , the ink is supplied from the ink cartridge  10  of the corresponding color, mounted in the cartridge mount  4 , through the ink supply tube  36 . The cartridge mount  4  is provided with the supply pump unit  24  to supply the ink from the ink cartridge  10  through the ink supply tube  36  to the sub tank  35 . The ink supply tube  36  is held, at a position midway in a route of laying inside the inkjet printer  1 , by the latch  25  secured to the back frame  21 C. 
     The maintenance device  81  maintains or recovers conditions of the nozzles of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  in idle time or standby time (non-recording time). In the present embodiment, the maintenance device  81  is disposed in a non-print area on the side of the right frame  21 B as illustrated in  FIG. 2 . 
     The maintenance device  81  includes the nozzle caps  82  ( 82   k ,  82   c ,  82   m , and  82   y ) to cap the nozzle faces of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k , respectively, the wiper blade  83  that is a blade to wipe the nozzle faces, and the dummy discharge receptacle  84  onto which excessive recording liquid that has thickened is discharged. Each nozzle cap  82  caps space adjacent to the nozzle face, which is hereinafter referred to as a nozzle cap interior  106  (illustrated in  FIG. 4 ) to seal the nozzle cap interior  106  in order to keep the nozzle cap interior  106  at a constant atmosphere or almost constant atmosphere. 
     The nozzle caps  82   k ,  82   c ,  82   m , and  82   y  correspond to the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k , respectively, and are lined in the same direction as the arrangement direction of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k , at widths identical or similar to the widths of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k.    
     The maintenance device  81  further includes suction tubes  85  (illustrated in  FIG. 4 ) for the four colors and a moisturizing and absorbing agent  86  (illustrated in  FIG. 4 ) for each color. The suction tubes  85  are used to suck in the thickened recording liquid and air bubbles from inside the nozzles in a state in which each nozzle face of the liquid discharge head  34  is covered with the nozzle cap  82 . The moisturizing and absorbing agent  86  moisturizes the ink inside the nozzles and absorb excessive ink from the nozzles. 
     The waste recording liquid generated by maintenance operation by the maintenance device  81 , the ink discharged into the nozzle caps  82 , and the ink discharged into the dummy discharge receptacle  84  are collected in a waste liquid container. The ink adhering to the wiper blade  83  is cleaned by a wiper cleaner (e.g., a wiper scraper  97 ) and is discharged to the waste liquid container. 
     With this structure, in the inkjet printer  1  according to the present embodiment, suction and moisturizing of the nozzles of the liquid discharge head  34  are performed during standby time or idle time, thereby inhibiting defective ink discharge caused by the dried ink and bubbles inside the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k . Thus, ink discharging performance can be kept reliable. 
     The maintenance device  88  maintains or recovers conditions of the nozzles of the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  at the start of recording or during recording. In the present embodiment, the maintenance device  88  is disposed in a non-print area on the side of the left frame  21 A as illustrated in  FIG. 2 . The maintenance device  88  includes the dummy discharge receptacles  89  onto which thickened excessive ink is discharged. 
     Next, referring to  FIG. 3 , descriptions are given below of a hardware configuration and a functional configuration of the inkjet printer  1  according to the present embodiment.  FIG. 3  is a schematic block diagram of the hardware configuration and the functional configuration of the inkjet printer  1  according to the present embodiment. It is to be noted that, in  FIG. 3 , solid liens represent electrical connections. Further, elements identical or corresponding to those illustrated in  FIG. 1 or 2  are given identical or similar reference characters, and descriptions thereof are omitted. 
     As illustrated in  FIG. 3 , the inkjet printer  1  according to the present embodiment includes the carriage  33 , the conveyor belt  51 , the charging roller  56 , a printer driver  100 , a controller  200 , a control panel  300 , a head driver  400 , the main scanning motor  500 , a linear encoder  600 , a sub-scanning motor  700 , and a wheel encoder  800 . 
     The printer driver  100  generates print data in a data processing terminal such as a personal computer (PC), an image reading device such as an image scanner, and a host device such as an imager (e.g., a digital camera). 
     The controller  200  includes a central processing unit (CPU)  201 , a read only memory (ROM)  202 , a random access memory (RAM)  203 , a nonvolatile RAM (NVRAM)  204 , an application specific integrated circuit (ASIC)  205 , an input/output (I/O)  206 , a host interface (I/F)  207 , a head controller  208 , a main scanning motor driver  209 , an alternating-current (AC) bias supplier  210 , and a sub-scanning motor driver  211 . 
     The CPU  201  is a computation device and controls actions of the entire inkjet printer  1 . That is, the CPU  201  controls operations relating to sheet conveyance and movement of the liquid discharge head  34 . The ROM  202  is a non-volatile memory dedicated to reading out and stores programs such as firmware. The RAM  203  is a volatile memory capable of high-speed data reading and writing. The RAM  203  is used as workspace when the CPU  201  processes data. The NVRAM  204  is a non-volatile storage medium capable of data reading and writing, and an operating system (OS), various types of control programs, application programs, and the like are stored therein. 
     In the above-described hardware configuration, the CPU  201  executes computation according to programs loaded in the RAM  203  from the ROM  202 , the NVRAM  204 , or recording media such as an optical disc. Then, control software is implemented. With the implemented control software and the above-described hardware in combination, a function block to execute the capabilities of the inkjet printer  1  is constructed. 
     The ASIC  205  incorporates various types of interfaces to control the entire inkjet printer  1 , an image processing circuit, and a circuit to control input and output of image data. The ASIC  205  is controlled by the CPU  201 . That is, the ASIC  205  performs processing of various types of signals relating to image data, image processing including sorting of image data, and processing of input signals to control the entire inkjet printer  1 . 
     The I/O  206  inputs, to the controller  200 , detection pulses from the linear encoder  600  and the wheel encoder  800  and detection signals from the sheet sensor  95  and other sensors. The host I/F  207  transmits and receives data to and from the host device via the network or a universal serial bus (USB) cable. The linear encoder  600  detects the position of the carriage  33  in the main scanning direction, and the wheel encoder  800  detects the position of the conveyor belt  51  in the sub-scanning direction. 
     The head controller  208  generates a drive waveform to drive the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  and outputs, to the head driver  400 , the image data to selectively drive a pressure generator for the liquid discharge head  34  and various types of data relating thereto. The main scanning motor driver  209  drives the main scanning motor  500 . The AC bias supplier  210  supplies an AC bias to the charging roller  56 . The sub-scanning motor driver  211  drives the sub-scanning motor  700 . 
     The control panel  300  is a visual user interface for users to check a status of the inkjet printer  1 . The control panel  300  serves as both of an output interface to visually display the state of the inkjet printer  1  and an input interface such as a touch panel for users to directly operate the inkjet printer  1  or input data into the inkjet printer  1 . That is, the control panel  300  has a capability to display images to accept user operation. 
     Based on image data (dot pattern data) serially input for one line recorded by the liquid discharge head  34 , the head driver  400  selects a driving voltage corresponding to the drive waveform given by a drive waveform generator of the head controller  208  (including a single drive pulse or a plurality of drive pulses). Then, the head driver  400  applies the selected driving voltage to the pressure generators for the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k  to drive the liquid discharge heads  34   y ,  34   c ,  34   m , and  34   k.    
     The main scanning motor  500  moves the carriage  33  along the carriage support rod  31  via the main scanning belt, according to signals from the main scanning motor driver  209 . The sub-scanning motor  700  drives the conveyance roller  52  via a sub-scanning belt according to signals from the sub-scanning motor driver  211 , thereby rotating the conveyor belt  51  in the sub-scanning direction (the belt conveyance direction) illustrated in  FIG. 2 . 
     With this configuration, in the inkjet printer  1  according to the present embodiment, the CPU  201  reads and analyzes print data received in a reception buffer of the host I/F  207 . Then, the ASIC  205  performs necessary image processing, data rearrangement, and the like and transfers the processed image data to the head controller  208 . The head controller  208  outputs the image data and the drive waveform to the head driver  400  at a predetermined timing. 
     In the inkjet printer  1  described above, as the ink is discharged, scattering ink may adhere to the nozzle face or the liquid discharge head  34 . If the adhering ink is left as it is, the ink dries to solidify. As the dried ink accumulates, solidified ink may hang from the liquid discharge head  34  or the nozzle face, or the nozzle face may become dirty. 
     If inkjet printers perform printing in such a state, the hanging ink may contact the recording medium or a conveyor such as a conveyance roller, causing defective printing, or the ink solidified on the nozzle face may hinder discharge of ink droplets. 
     Accordingly, in the inkjet printer  1  according to the present embodiment, the adhering ink is wiped off from the liquid discharge head  34  and the nozzle face. 
     Descriptions are given below of wiping of the nozzle face of the liquid discharge head  34  in the inkjet printer  1  according to the present embodiment, with reference to  FIGS. 4 through 13 .  FIGS. 4 through 13  are cross-sectional views of the inkjet printer  1  according to the present embodiment, as viewed in the sub-scanning direction. 
     As illustrated in  FIGS. 4 through 13 , the liquid discharge head  34  according to the present embodiment further includes a nozzle plate  37  and nozzle covers  38 . Additionally, as illustrated in  FIGS. 4 through 12 , the inkjet printer  1  according to the present embodiment includes, as the maintenance device  81 , the wiper blade  83 , a cleaner roller  87 , the wiper scraper  97 , and a passage  98  leading to a waste liquid container, at least a portion of which serves as a liquid remover. 
     The nozzle plate  37  includes a nozzle face  37 N in which the nozzle is formed. The nozzle cover  38  covers and protects the nozzle plate  37 . The cleaner roller  87  presses the wiper blade  83  against the wiper scraper  97 . The wiper scraper  97  scrapes off ink  39  adhering to the wiper blade  83 . The ink scraped by the wiper scraper  97  is transported through the passage  98  and collected in the waste liquid container. 
     It is to be noted that the nozzle caps  82 , the wiper blade  83 , the suction tubes  85 , and the cleaner roller  87  are driven by an identical driver and are configured to operate at respective timings in conjunction with each other. 
     Before the inkjet printer  1  starts wiping of the nozzle face  37 N of the liquid discharge head  34 , as illustrated in  FIG. 4 , the nozzle face  37 N of the nozzle plate  37  is capped with the nozzle caps  82 . 
     To perform the wiping of the liquid discharge head  34 , the inkjet printer  1  initially lowers the nozzle cap  82  in the direction of gravity as illustrated in  FIG. 5  and lifts the wiper blade  83  in the direction of gravity as illustrated in  FIG. 6 . 
     Then, as illustrated in  FIGS. 7 and 8 , the inkjet printer  1  moves the liquid discharge head  34  in the main scanning direction. With this movement, the wiper blade  83  wipes the nozzle face  37 N of the nozzle plate  37  to transfer the ink  39  adhering the nozzle face  37 N to the wiper blade  83 . 
     Subsequently, while the cleaner roller  87  presses the wiper blade  83  against the wiper scraper  97  as illustrated in  FIG. 9 , the inkjet printer  1  lowers the wiper blade  83  in the direction of gravity as illustrated in  FIG. 10 . With this movement, the ink  39  adhering to the wiper blade  83  is transferred to the wiper scraper  97 . 
     After returning the cleaner roller  87  to a home position as illustrated in to  FIG. 11 , the inkjet printer  1  returns the liquid discharge head  34  to a home position (a capped position) as illustrated in  FIG. 12 . At that time, the ink adhering to the wiper scraper  97  falls under the gravity along the passage  98  and is collected in the waste liquid container. 
     Subsequently, after the liquid discharge head  34  moves to the capped position, as illustrated in  FIG. 13 , the inkjet printer  1  lifts the nozzle caps  82  in the direction of gravity to cap the nozzle face  37 N of the nozzle plate  37 . 
     The actions described above are performed in wiping of the nozzle face  37 N of the liquid discharge head  34  in the inkjet printer  1 . 
     In the inkjet printer  1  according to the present embodiment, the ink  39  adhering to the liquid discharge head  34  and the nozzle face  37 N is wiped away by such a wiping operation. 
     However, it is difficult to fully wipe away the ink  39  from the nozzle face  37 N, with the wiping of the nozzle face  37 N of the nozzle plate  37  of the liquid discharge head  34 . Accordingly, it is possible that the remaining ink  39  (hereinafter also “residual ink”) dries to solidify and accumulates. Then, the solidified ink  39  may hang from the end of the liquid discharge head  34  (e.g., the end of the nozzle plate  37 ) as illustrated in  FIG. 14 , or the contact portion (e.g., a contact portion  37 C in  FIG. 16 ) between the nozzle plate  37  and the nozzle cap  82  may be smeared with the solidified ink  39  as illustrated in  FIG. 15 . Accordingly, there is a risk of defective printing or defective liquid discharge even if the nozzle face  37 N of the liquid discharge head  34  are wiped. 
       FIG. 14  is a cross-sectional view of a comparative inkjet printer, as viewed in the sub-scanning direction.  FIG. 15  is a bottom view of the nozzle plate  37  in the comparative inkjet printer. The above-described inconveniences are less likely to occur in the portion of the nozzle plate  37  corresponding to the space inside the nozzle cap  82  since the space capped by the nozzle cap  82  is moisturized. 
     In view of the foregoing, as illustrated n  FIGS. 16 and 17 , in the inkjet printer  1  according to the present embodiment, the maintenance device  81  further includes a head cap  99  (a second cap) disposed outside the nozzle cap  82  and designed to cover the nozzle face  37 N of the liquid discharge head  34  entirely to the end. For example, in the structure illustrated in  FIG. 16 , the head cap  99  is disposed outside the nozzle plate  37  to cover the nozzle plate  37  entirely to the end. The head cap  99  seals the space including the contact portion  37 C between the nozzle plate  37  and the nozzle cap  82  and the end (lower end in  FIG. 16 ) of the liquid discharge head  34 , which is hereinafter referred to as “head cap interior  107 ” (second space). The head cap  99  moisturizes the head cap interior  107 . As illustrated in  FIGS. 16 and 17 , the head cap  99  according to the present embodiment includes an outside-air shutter  101  and a humidity conditioner  102 . Since a plurality of ink cartridges  10  is mounted in the inkjet printer  1  as described above, the inkjet printer  1  includes a plurality of nozzle plates  37 . In the inkjet printer  1 , the nozzle plates  37 , one of which is illustrated in  FIG. 15 , are arranged in the lateral direction in  FIG. 15 . 
       FIG. 16  is a cross-sectional view of the inkjet printer  1  according to the present embodiment, as viewed in the sub-scanning direction.  FIG. 17  is a top view of the nozzle cap  82  and the head cap  99  in the inkjet printer  1  according to the present embodiment. 
     The outside-air shutter  101  is disposed in tight contact with end of the liquid discharge head  34  on the side of the nozzle face  37 N (hereinafter “nozzle formation side”) to shut off the head cap interior  107  from outside air. The outside-air shutter  101  is made of a material including, for example, urethane rubber, silicon, or polyvinylidene chloride (PVDC). 
     The humidity conditioner  102  keeps the head cap interior  107  at a constant or almost constant humidity. In other words, the humidity conditioner  102  keeps the amount of vapor in the head cap interior  107  (hereinafter “vapor amount”) at a constant amount. Specifically, the relative humidity (RH) of air in thermal equilibrium with a saturated aqueous solution of salt such as sodium chloride is determined by the type of the salt and the temperature of the solution. Accordingly, when the saturated solution of given salt is disposed in the head cap interior  107 , the head cap interior  107  can be kept at a constant humidity. The term “vapor” generally represents a substance in a gas phase, and “vapor” in this disclosure represents steam, that is, water in gas phase. The term “vapor amount” represents the amount (e.g., mass, weight, number of moles, or the like) of vapor in a unit volume. The humidity conditioner  102  is contained in a container having a plurality of slits or a plurality of holes to generate vapor to adjust the humidity therearound. 
     With this structure, in the state in which the liquid discharge head  34  is capped with the head cap  99 , the contact portion between the nozzle plate  37  and the nozzle cap  82  and the end (nozzle formation side) of the liquid discharge head  34  are moisturized. It is to be noted that one head cap  99  serving as the second cap can be configured to cap the plurality of nozzle caps  82 . That is, the maintenance device  81  includes a single head cap  99 . Alternatively, each of the nozzle caps  82  can be capped with one of a plurality of head caps  99 . 
     Accordingly, the inkjet printer  1  according to the present embodiment can inhibit the residual ink from drying to solidify, and the ink remaining after the nozzle face  37 N of the liquid discharge head  34  is wiped can be kept at a low viscosity. Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     Additionally, this structure facilitates the maintenance of the liquid discharge head  34  with a simple structure and a low cost. 
     Further, as illustrated in  FIG. 16 , an impact absorber  103  is disposed below the head cap  99 . The impact absorber  103  absorbs impact caused by vibration of the inkjet printer  1  so that the head cap  99  is not shaken to create a gap between the head cap  99  and the liquid discharge head  34  as the inkjet printer  1  vibrates. As illustrated in  FIG. 18 , the head cap  99  moves in conjunction with the nozzle cap  82 .  FIG. 18  is a cross-sectional view of the inkjet printer  1  according to the present embodiment, as viewed in the sub-scanning direction. 
     Next, descriptions are given below of sealing of the head cap interior  107  by the outside-air shutter  101 , with reference to  FIGS. 19 through 22 .  FIGS. 19 and 21  are top views of the nozzle cap  82  and the head cap  99  in the inkjet printer  1  according to the present embodiment.  FIGS. 20 and 22  are cross-sectional views of the nozzle cap  82  and the head cap  99  in the inkjet printer  1  according to the present embodiment, as viewed in the sub-scanning direction. 
     As illustrated in  FIGS. 19 through 22 , the outside-air shutter  101  includes two shutter halves  101 A that approach to each other from two sides (upper side and lower side in  FIG. 19 ), toward the nozzle plate  37  (the nozzle face  37 N) of the liquid discharge head  34 , and tightly contact the end (the nozzle formation side) of the liquid discharge head  34 . Thus, the head cap interior  107  is sealed such that the nozzle formation side of the liquid discharge head  34  is covered entirely to the end. 
     Alternatively, as illustrated in  FIGS. 23 through 24 , the outside-air shutter  101  may include four pieces (shutter pieces  101 B 1  and  101 B 2 ) that approach to each other from four sides, toward the end (e.g., the nozzle plate  37 ) of the liquid discharge head  34 , and tightly contact the nozzle formation side of the liquid discharge head  34 .  FIGS. 23 and 24  are top views of the nozzle cap  82  and the head cap  99  in the inkjet printer  1  according to the present embodiment. 
     Next, descriptions are given below of effect attained by the inkjet printer  1  according to the present embodiment, with reference to  FIGS. 25 through 27 . 
       FIG. 25  illustrates a graph of changes in the relative humidity (RH) of the head cap interior  107  while the liquid discharge head  34  is capped with the head cap  99 . 
       FIG. 25  includes, for comparison, the graph of relative humidity in a configuration in which the head cap  99  is not provided. Specifically, in  FIG. 25 , the solid line represents the graph of relative humidity in the configuration including the head cap  99 , and broken lines represent the graph of relative humidity in the configuration in which the head cap  99  is not provided. The graphs in  FIG. 25  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
       FIG. 26  illustrates a graph of changes in moisture content in the residual ink while the liquid discharge head  34  is capped with the head cap  99 . 
       FIG. 26  includes, for comparison, the graph of moisture content in the configuration in which the head cap  99  is not provided. Specifically, in  FIG. 26 , the solid line represents the graph of moisture content in the configuration including the head cap  99 , and broken lines represent the graph of moisture content in the configuration in which the head cap  99  is not provided. The graphs in  FIG. 26  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
       FIG. 27  illustrates changes with time of probability of malfunction caused by the residual ink in the inkjet printer  1  according to the present embodiment. 
       FIG. 27  includes, for comparison, the graph of probability of malfunction in the configuration in which the head cap  99  is not provided. Specifically, in  FIG. 27 , the solid line represents the graph in the configuration including the head cap  99 , and broken lines represent the graph in the configuration in which the head cap  99  is not provided. 
     As illustrated in  FIG. 25 , while the liquid discharge head  34  is capped with the head cap  99  according to the present embodiment, the relative humidity of the head cap interior  107  increases with elapse of time and then becomes stable. By contrast, in the configuration in which the head cap  99  is not provided, the relative humidity remains identical or similar to the humidity inside the inkjet printer  1  with elapse of time. 
     Thus, the inkjet printer  1  according to the present embodiment can moisturize the nozzle formation side (lower end in  FIG. 22 ) of the liquid discharge head  34  entirely in the state in which the liquid discharge head  34  is capped with the head cap  99 . 
     Additionally, since the relative humidity inside the inkjet printer  1  is low as illustrated in  FIG. 25 , the moisture content in the residual ink decreases for a time immediately after the liquid discharge head  34  is capped with the head cap  99  according to the present embodiment, as illustrated in  FIG. 26 . However, as the relative humidity inside the inkjet printer  1  increases, the moisture content increases and becomes stable. By contrast, in the configuration in which the head cap  99  is not provided, since the moisture in the residual ink keeps evaporating, the moisture content keeps decreasing as well. 
     Thus, the inkjet printer  1  according to the present embodiment can inhibit the residual ink from drying to solidify, and, after the nozzle face  37 N of the liquid discharge head  34  is wiped, the remaining ink can be kept at a low viscosity. Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     Further, as illustrated in  FIG. 27 , according to the present embodiment, the probability of malfunction caused by the residual ink is kept at a relatively low rate with the improved wiping capability. By contrast, in the configuration in which the head cap  99  is not provided, the remaining ink  39  can dry, solidify, and accumulate. Then, the probability of malfunction keeps rising as the solidified ink  39  hangs from the end of the liquid discharge head  34  as illustrated in  FIG. 14 , or the contact portion between the nozzle plate  37  and the nozzle cap  82  is smeared with the solidified ink  39  as illustrated in  FIG. 15 . Thus, the inkjet printer  1  according to the present embodiment can prevent or reduce the occurrence of malfunction. 
     Next, descriptions are given below of a main ingredient of the humidity conditioner  102  in the inkjet printer  1  according to the present embodiment, with reference to  FIG. 28 .  FIG. 28  illustrates graphs of changes in the relative humidity of the head cap interior  107  while the liquid discharge head  34  is capped with the head cap  99 . 
     In  FIG. 28 , the solid graph represents the relative humidity in a case where the main ingredient of the humidity conditioner  102  is a saturated salt solution, and the dotted graph represents the relative humidity in a case where the main ingredient of the humidity conditioner  102  is either identical to the main ingredient of ink or glycerin. In  FIG. 28 , for comparison, the case where the head cap  99  is not provided is also illustrated. That is, the broken lines represent the graph in the configuration in which the head cap  99  is not provided. The graphs in  FIG. 28  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
     As illustrated in  FIG. 28 , when the main ingredient of the humidity conditioner  102  is a saturated salt solution, a constant (or almost constant) humidity is maintained for a long time compared with the case where the main ingredient is identical to the main ingredient of ink or glycerin. Accordingly, when the saturated salt solution is used as the main ingredient of the humidity conditioner  102 , the interior of the head cap  99  covering the liquid discharge head  34  can be moisturized better. However, the ingredient of ink or glycerin can be used. 
     The term “saturated salt solution” used here means a mixture of at least one powdered salt and at least one saturated aqueous solution of salt. 
     In the saturated salt solution used in the present embodiment, powdered salt is soaked in a saturated aqueous solution to maintain the shape of the humidity conditioner  102 . Accordingly, in the present embodiment, the humidity conditioner  102  can be disposed at a given position regardless of the direction of gravity. 
     Additionally, in the present embodiment, the humidity conditioner  102  is disposed to avoid direct contact with a metal portion of the inkjet printer  1 . When the container of the humidity conditioner  102  is made of a nonmetal material, corrosion of the container can be prevented. These features facilitate maintenance of the inkjet printer  1 . 
     Next, descriptions are given below of the relative humidity of the head cap interior  107  capped with the head cap  99  when the main ingredient of the humidity conditioner  102  is a saturated salt solution, with reference to  FIGS. 29 and 30 . 
       FIG. 29  is a table illustrating relations between relative humidity maintained by different types of saturated salt solutions and temperature in a sealed space.  FIG. 30  illustrates graphs of changes in the relative humidity of the head cap interior  107  while the liquid discharge head  34  is capped with the head cap  99 . 
       FIG. 30  illustrates a graph for each of the different saturated salt solutions presented in  FIG. 29 , used as the main ingredient of the humidity conditioner  102 . That is, in  FIG. 30 , Graph G 1  (solid line) corresponds to the case where potassium sulfate is used for the saturated salt solution, Graph G 2  (alternate long and short dashed lines) corresponds to the case where potassium chloride is used for the saturated salt solution, Graph G 3  (long broken lines) corresponds to the case where sodium chloride is used for the saturated salt solution, Graph G 4  (alternate long line and dot) corresponds to the case where sodium bromide is used for the saturated salt solution, and Graph G 5  (chain double-dashed line) corresponds to the case where potassium carbonate is used for the saturated salt solution. 
     In  FIG. 30 , for comparison, the case where the head cap  99  is not provided is also illustrated. That is, Graph G 6  (broken lines) represent the case where the head cap  99  is not provided. Additionally,  FIG. 30  also presents the case where the main ingredient of the humidity conditioner  102  is identical to the main ingredient of ink or glycerin for comparison. That is, Graph G 7  (dotted graph) corresponds to the case where the main ingredient of the humidity conditioner  102  is identical to the main ingredient of ink or glycerin. The graphs in  FIG. 30  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
     Although potassium sulfate, potassium chloride, sodium chloride, sodium bromide, and potassium carbonate are presented as example salts for the saturated salt solution in  FIGS. 29 and 30 , the salt for the saturated salt solution is not limited thereto as long as the salt can keep the sealed space at or above a given relative humidity. 
     Use of a salt capable of keeping the relative humidity of a sealed space equal to or higher than 40% is advantageous in moisturizing the space of the liquid discharge head  34  capped with the head cap  99 . The saturated salt solutions presented in  FIG. 29  satisfy this condition. Preferably, the salt used for the saturated salt solution is environmentally friendly and imposes fewer effects on human body. For example, sodium chloride is preferable. 
     The location of the humidity conditioner  102  is not limited to the bottom of interior of the head cap  99  illustrated in  FIG. 16 , as long as the location is inside the head cap  99 . For example, the humidity conditioner  102  can be disposed opposing an end portion of the liquid discharge head  34  on the nozzle formation side as illustrated in  FIG. 31 . That is, the humidity conditioner  102  is disposed on a side face  99 A of the head cap  99 .  FIG. 31  is a cross-sectional view of the inkjet printer  1  according to the present embodiment, as viewed in the sub-scanning direction. 
     When the humidity conditioner  102  is disposed on the side face  99 A of the head cap  99  as illustrated in  FIG. 31 , the following advantage is available. In such an arrangement, the humidity conditioner  102  is close to the end of the liquid discharge head  34  and the contact portion between the nozzle plate  37  and the nozzle cap  82 , in which the ink tends to remain after the nozzle face  37 N is wiped. 
     Accordingly, with such an arrangement, as illustrated in  FIG. 32 , the moisture content at the above-mentioned end or the above-mentioned contact portion can be higher than the moisture content maintained in the arrangement in which the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99 . 
     Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge.  FIG. 32  is a graph of changes in moisture content in the residual ink while the liquid discharge head  34  is capped with the head cap  99 . 
     In  FIG. 32 , the solid line represents the graph in the arrangement in which the humidity conditioner  102  is disposed on the side face  99 A of the head cap  99 , and broken lines represent the graph in the arrangement in which the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99 . The graphs in  FIG. 32  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
     Referring to  FIG. 32 , the moisture content of the residual ink decreases for a time immediately after the liquid discharge head  34  is sealed with the head cap  99  since the relative humidity inside the inkjet printer  1  is low as illustrated in  FIG. 25 . Then, in the arrangement in which the humidity conditioner  102  is disposed on the side face  99 A of the head cap  99 , the moisture content increases and becomes stable earlier, compared with the arrangement in which the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99 . 
     Accordingly, in the arrangement in which the humidity conditioner  102  is disposed on the side face  99 A of the head cap  99 , the moisture content at the end of the liquid discharge head  34  or the contact portion between the nozzle plate  37  and the nozzle cap  82  can be kept higher compared with the arrangement in which the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99 . Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     However, when the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99  as illustrated in  FIG. 16 , the entire head cap interior  107  can be moisturized uniformly compared with the arrangement in which the humidity conditioner  102  is disposed on the side face  99 A of the head cap  99  as illustrated in  FIG. 31 . 
     In a variation, the humidity conditioner  102  is disposed at the bottom of interior of the head cap  99  as illustrated in  FIG. 16 , and another humidity conditioner  102  is disposed on the side face  99 A of the head cap  99  as illustrated in  FIG. 31 . With such an arrangement, while the moisture content at the end of the liquid discharge head  34  or the contact portion between the nozzle plate  37  and the nozzle cap  82  can be kept at a higher content, the entire head cap interior  107  can be moisturized uniformly. 
     During printing, wiping, and the maintenance operation such as dummy discharge, the head cap  99  is disengaged from the liquid discharge head  34 , exposing the interior of the head cap  99 . As time elapses with the interior of the head cap  99  left unsealed, the relative humidity thereof continues to decrease. 
     In view of the foregoing, as illustrated in  FIG. 33 , the inkjet printer  1  can further include a head cap cover  104  (a sealed-state retainer) to seal the head cap interior  107  when the head cap  99  is removed from the liquid discharge head  34  (the liquid discharge head  34  is not capped).  FIG. 33  is a cross-sectional view of the inkjet printer  1 , as viewed in the sub-scanning direction. 
     This structure can suppress changes in relative humidity of the head cap interior  107  when the head cap  99  is disengaged from the liquid discharge head  34 . 
     Accordingly, this structure can moisturize the residual ink promptly after the liquid discharge head  34  is changed to the capped state from the unsealed state. Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     Descriptions are given below of changes in relative humidity of the head cap interior  107  when the head cap cover  104  covers the head cap  99 , with reference to  FIG. 34 .  FIG. 34  illustrates graphs of changes in the relative humidity of the head cap interior  107  while the liquid discharge head  34  is capped with the head cap  99 . 
       FIG. 34  includes, for comparison, the case where the interior of the head cap  99  is not sealed with the head cap cover  104 . That is, in  FIG. 34 , the solid graph corresponds to the case where the interior of the head cap  99  is sealed with the head cap cover  104 , and the dotted graph corresponds to the case where the interior of the head cap  99  is not sealed with the head cap cover  104 . 
     In  FIG. 34 , for comparison, the case where the head cap  99  is not provided is also illustrated. That is, in  FIG. 34 , the broken straight graph represents the relative humidity in the configuration in which the head cap  99  is not provided. The graphs in  FIG. 34  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. In  FIG. 34 , the head cap  99  is removed at the start of printing at Time T 1 , and the liquid discharge head  34  is covered with the head cap  99  at Time T 2  at which printing ends. At Time T 3  at which maintenance operation starts, the head cap  99  is removed, and the liquid discharge head  34  is covered with the head cap  99  at Time T 4  at which the maintenance operation ends. 
     As illustrated in  FIG. 34 , changes in the relative humidity of the head cap interior  107  can be suppressed by sealing the head cap interior  107  with the head cap cover  104  when the head cap  99  is disengaged from the liquid discharge head  34 . By contrast, in the case where the head cap interior  107  is not sealed with the head cap cover  104  when the head cap  99  is disengaged from the liquid discharge head  34 , the relative humidity of the head cap interior  107  continues to decrease from when the liquid discharge head  34  is uncapped until when the liquid discharge head  34  is capped again. 
     Accordingly, this structure can moisturize the residual ink promptly after the liquid discharge head  34  is changed to the capped state from the unsealed state. Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     In the inkjet printer  1 , the residual ink can adhere to, not only the liquid discharge head  34  and the nozzle face  37 N, but also the wiper blade  83 , the cleaner roller  87 , and the wiper scraper  97 . Accordingly, the wiping capability may be degraded as the ink adhering to the wiper blade  83 , the cleaner roller  87 , or the wiper scraper  97  dries to solidify and accumulates. 
     Therefore, the inkjet printer  1  can be configured such that the outside-air shutter  101  seals the space including, not only the liquid discharge head  34 , but also the wiper scraper  97  as illustrated in  FIG. 35 , or the space further including the wiper blade  83  and the cleaner roller  87  as illustrated in  FIG. 36 . In performing head cleaning, the outside-air shutter  101  moves in either the main scanning direction or the sub-scanning direction to expose the upper side of the wiper blade  83 . For example, a motor such as an electric motor can be used to move the outside-air shutter  101 .  FIGS. 35 and 36  are cross-sectional views of the inkjet printer  1 , as viewed in the sub-scanning direction. 
     This structure can moisturize the space including the wiper blade  83 , the cleaner roller  87 , and the wiper scraper  97  and inhibit the residual ink adhering thereto from drying to solidify and accumulating. Thus, the wiping capability of the inkjet printer  1  according to the present embodiment is enhanced, thereby inhibiting defective printing and defective liquid discharge. 
     Further, as illustrated in  FIG. 37 , the inkjet printer  1  as an embodiment of this disclosure can further include a stirrer  105  (e.g., a fan or a propeller) to stir air in the head cap interior  107  to shorten the time period from when the head cap interior  107  is sealed until the head cap interior  107  is filled with steam and the relative humidity is stabilized.  FIG. 37  is a cross-sectional view of the inkjet printer  1 , as viewed in the sub-scanning direction. 
     Referring to  FIG. 38 , descriptions are given below of changes in relative humidity of the head cap interior  107  when the stirrer  105  stirs air inside the head cap interior  107  after the head cap interior  107  is sealed.  FIG. 38  illustrates graphs of changes in the relative humidity of the head cap interior  107  while the liquid discharge head  34  is capped with the head cap  99 . 
     In  FIG. 38 , for comparison, the case where stirring by the stirrer  105  is not performed is also illustrated. That is, in  FIG. 38 , the solid graph corresponds to the case where stirring by the stirrer  105  is performed, and the dotted graph corresponds to the case where stirring by the stirrer  105  is not performed. For comparison, the graphs in  FIG. 38  are on the assumption that the interior of the inkjet printer  1  is kept at a constant humidity. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.