Patent Publication Number: US-8991970-B2

Title: Printing device, discharge test device and discharge test method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority under 35 U.S.C. §120 on, U.S. application Ser. No. 13/759,668, filed Feb. 5, 2013, which claims priority under 35 U.S.C. §120 on U.S. application Ser. No. 12/917,098, filed Nov. 1, 2010, now U.S. Pat. No. 8,388,089, which claims priority under 35 U.S.C. §119 on Japanese patent application no. 2009-259689, filed Nov. 13, 2009. The content of each such related application is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a printing device, a discharge test device and a discharge test method. 
     2. Related Art 
     Ink jet printers, which discharge ink and form an image on a medium, are used. Such printers form an image by discharging ink from nozzles. However when ink is not normally discharged from the nozzles, a desired image cannot be obtained. 
     JP-A-2003-53949 is an example of related art. 
     To prevent ink from not being discharged normally from nozzles, it may be determined whether or not there are abnormal nozzles in advance. In this determination, if erroneous determination occurs, a nozzle restore operation is performed and ink may be discharged and thrown away from nozzles erroneously determined to be abnormal. Therefore, it is desired that a nozzle test is not performed in an environment where erroneous determination occurs. On the other hand, even in an environment where erroneous determination occurs, there is a case in which ink can be discharged to perform printing. Because of the above, it is desirable to appropriately control the nozzle test and liquid discharge in accordance with the environment. 
     SUMMARY 
     An advantage of some aspects of the invention is to control the nozzle test and the liquid discharge in accordance with the environment. 
     According to aspects of the invention, a printing device or a discharge test device includes: 
     (A) a head that includes a nozzle discharging liquid to a medium, 
     (B) a temperature obtaining section that obtains a temperature related to the head, 
     (C) a missing-dot detecting section that detects whether or not the liquid is discharged from the nozzle, and 
     (D) a control section that controls the head and the missing-dot detecting section so that: 
     (d1) when the temperature obtained by the temperature obtaining section is within a first temperature range, the head is configured to discharge the liquid to the medium and whether or not the liquid is discharged from the nozzle is detected, 
     (d2) when the temperature obtained by the temperature obtaining section is outside the first temperature range and within a second temperature range, the head is configured to discharge the liquid to the medium and whether or not the liquid is discharged from the nozzle is not detected, and 
     (d3) when the temperature obtained by the temperature obtaining section is outside the second temperature range, the liquid is not discharged to the medium and whether or not the liquid is discharged from the nozzle is not detected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1A  is a block diagram for explaining a printing system including a printer and a computer CP, and  FIG. 1B  is a perspective view of the printer. 
         FIG. 2A  is a cross-sectional view of a head, and  FIG. 2B  is a diagram showing an array of nozzles (Nz) provided in a nozzle plate. 
         FIGS. 3A to 3C  are diagrams showing a positional relationship between the head and a cap mechanism during a restore operation. 
         FIG. 4  is a view of the cap seen from the above. 
         FIG. 5A  is a diagram for explaining a missing-dot detector, and  FIG. 5B  is a block diagram for explaining a detection controller. 
         FIG. 6A  is a diagram showing an example of a drive signal COM used in a discharge test,  FIG. 6B  is a diagram for explaining a voltage signal SG outputted from an amplifier when ink is discharged from a nozzle by the drive signal COM, and  FIG. 6C  is a diagram showing the voltage signal SG that is a result of the discharge test of a plurality of nozzles. 
         FIG. 7  is a flowchart for explaining print processing according to an embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     At least the following item will be clarified by the description of this specification and the accompanying drawings. 
     A discharge test device including: 
     (A) a head that includes a plurality of nozzles discharging liquid to a medium, 
     (B) a temperature obtaining section that obtains a temperature related to the head, 
     (C) a detection electrode that faces the head with a predetermined distance therebetween, 
     (D) an identification section that applies a predetermined voltage to the detection electrode and identifies an abnormal nozzle on the basis of voltage change of the detection electrode generated by liquid discharge from the nozzles, and 
     (E) a control section that controls the head and the identification section so that: 
     (e1) when the temperature obtained by the temperature obtaining section is within a first temperature range, the head discharges the liquid to the medium after the identification section identifies the abnormal nozzle, 
     (e2) when the temperature obtained by the temperature obtaining section is outside the first temperature range and within a second temperature range that is larger than the first temperature range, the head discharges the liquid to the medium without the abnormal nozzle being identified by the identification section, and 
     (e3) when the temperature obtained by the temperature obtaining section is outside the second temperature range, the abnormal nozzle is not identified and the liquid is not discharged to the medium. 
     In this way, it is possible to appropriately control the nozzle test and the liquid discharge in accordance with the environment. 
     In the discharge test device, it is desired that, when the control section identifies the abnormal nozzle, the control section discharges the liquid to an object other than the medium from the abnormal nozzle and performs an operation to restore the abnormal nozzle to a normal nozzle. It is desired that the identification section detects the voltage change of the detection electrode generated by the liquid discharge from the nozzles and identifies a nozzle where the voltage change of the detection electrode is smaller than or equal to a predetermined value as an abnormal nozzle. It is desirable to determine that the temperature obtaining section fails when the temperature obtained by the temperature obtaining section is outside the second temperature range. It is desired that, when the temperature obtained by the temperature obtaining section is within the first temperature range, the control section further performs a mechanical abnormality check of the discharge test device, and when there is a mechanical abnormality, the control section does not identify the abnormal nozzle and does not discharge the liquid to the medium. 
     It is desired that, when the temperature obtained by the temperature obtaining section is within the first temperature range, the control section performs an electrical abnormality check of the discharge test device, and when there is the electrical abnormality, the control section does not identify the abnormal nozzle and does not discharge the liquid to the medium. When the temperature obtained by the temperature obtaining section is outside the second temperature range, it is desirable to display a warning indicating that there is a risk that the liquid is not normally discharged from the head. 
     In this way, it is possible to appropriately control the nozzle test and the liquid discharge in accordance with the environment. 
     A discharge test method including: 
     obtaining a temperature related to a head including a plurality of nozzles that discharge liquid to a medium, 
     applying a predetermined voltage to a detection electrode when the temperature is within a first temperature range, and discharging liquid from the head to a medium after identifying an abnormal nozzle on the basis of voltage change of the detection electrode generated by liquid discharge from the nozzles, 
     discharging liquid from the head to the medium without identifying the abnormal nozzle when the temperature is outside the first temperature range and within a second temperature range that is larger than the first temperature range, and 
     identifying no abnormal nozzle and discharging no liquid to the medium when the temperature is outside the second temperature range. 
     In this way, it is possible to appropriately control the nozzle test and the liquid discharge in accordance with the environment. 
     About Ink Jet Printer 
     An embodiment will be described using an ink jet printer (hereinafter, printer  1 ) as an example. 
       FIG. 1A  is a block diagram for explaining a printing system including the printer  1  and a computer CP, and  FIG. 1B  is a perspective view of the printer  1 . The printer  1  discharges ink that is a kind of liquid to a medium such as a paper sheet, a cloth, or a film. The computer CP is communicably connected to the printer  1 . The computer CP transmits print data of an image to the printer to cause the printer  1  to print the image. Printer  1  includes a paper transport mechanism  10 , a carriage moving mechanism  20 , a head unit  30 , a drive signal generating circuit  40 , a missing-dot detector  50 , a cap mechanism  60 , a detector group  70 , and a controller  80 . 
     The paper transport mechanism  10  transports a paper sheet in a transport direction. The carriage moving mechanism  20  moves a carriage  21  on which the head unit  30  is mounted in a movement direction (perpendicular to the transport direction). 
     The head unit  30  includes a head  31  and a head controller HC. The head  31  discharges ink to a paper sheet. The head controller HC controls the head  31  on the basis of a head control signal from the controller  80 . 
       FIG. 2A  is a cross-sectional view of the head  31 . The head  31  includes a case  32 , a flow path unit  33 , and a piezoelectric element unit  34 . The case  32  is a member for holding and fixing a piezoelectric element PZT and the like, and for example, made of a non-conductive resin material such as an epoxy resin. 
     The flow path unit  33  includes a flow path forming substrate  33   a , a nozzle plate  33   b , and a vibration plate  33   c . The nozzle plate  33   b  is bonded to one surface of the flow path forming substrate  33   a  and the vibration plate  33   c  is bonded to the other surface of the flow path forming substrate  33   a . Voids and channels that form a pressure chamber  331 , an ink supply path  332 , and a common ink chamber  333  are formed on the flow path forming substrate  33   a . The flow path forming substrate  33   a  is made of, for example, a silicon substrate. A nozzle group including a plurality of nozzles Nz is provided in the nozzle plate  33   b . The nozzle plate  33   b  is made of a conductive plate member, for example, a thin metal plate. The nozzle plate  33   b  is connected to a ground line and has a ground potential. A diaphragm section  334  is provided to a portion on the vibration plate  33   c  corresponding to each pressure chamber  331 . The diaphragm section  334  is deformed by the piezoelectric element PZT and changes the volume of the pressure chamber  331 . The piezoelectric element PZT and the nozzle plate  33   b  are electrically insulated by the vibration plate  33   c , a bonding layer, and the like lying therebetween. 
     The piezoelectric element unit  34  includes a piezoelectric element group  341  and a fixed plate  342 . The piezoelectric element group  341  has a comb teeth shape. Each of the comb teeth is the piezoelectric element PZT. The top surface of each piezoelectric element PZT is bonded to an island section  335  included in the corresponding diaphragm section  334 . The fixed plate  342  supports the piezoelectric element group  341  and is a mounting portion of the case  32 . The piezoelectric element PZT is a kind of an electromechanical conversion element, and when the drive signal COM is applied, the piezoelectric element is expanded or contracted in the longitudinal direction and provides a pressure change to the liquid in the pressure chamber  331 . The pressure change is generated in the liquid in the pressure chamber  331  owing to a volume change of the pressure chamber  331 . By using this pressure change, an ink droplet can be discharged from the nozzle Nz. 
     A thermistor  710  (included in the detector group  703 ) is attached to an upper portion of the head  31 . The thermistor  710  is connected to the controller  80 , so that the controller  80  can obtain a temperature of the head  31 . 
       FIG. 2B  is a diagram showing an array of nozzles (Nz) provided in the nozzle plate  33   b . In the nozzle plate, a plurality of nozzle rows, each of which includes 180 nozzles (# 1  to # 180 ) arranged at an interval of 180 dpi along the transport direction of a paper sheet, are provided. Each nozzle row discharges ink of a color different from each other, and four nozzle rows are provided in the nozzle plate  33   b . Specifically, the nozzle rows include a black ink nozzle row K, a cyan ink nozzle row C, a magenta ink nozzle row M, and a yellow ink nozzle row Y. 
     The drive signal generating circuit  40  generates the drive signal COM. When the drive signal COM is applied to the piezoelectric element PZT, the piezoelectric element is expanded or contracted, so that the volume of the pressure chamber  331  corresponding to each nozzle Nz changes. Therefore, the drive signal COM is applied to the head  31  when performing a printing operation, a missing-dot test (described below), and a flushing operation that is a restore operation of a nozzle causing a missing dot. 
     The missing-dot detector  50  detects whether or not ink is discharged from each nozzle Nz. The cap mechanism  60  suppresses the evaporation of ink solvent from the nozzle Nz and performs a sucking operation to suck in ink from each nozzle Nz so as to recover a discharge capability of the nozzle Nz. The detector group  70  includes a plurality of detectors for monitoring the status of the printer  1 . The detection results of the detectors are outputted to the controller  80 . 
     The controller  80  performs an entire control of the printer  1 , and includes an interface section  80   a , a CPU  80   b , and a memory  80   c . The interface section  80   a  transmits and receives data to and from the computer CP. Memory  80   c  secures an area to store a computer program, a work area, and the like. The CPU  80   b  controls each component to be controlled (the paper transport mechanism  10 , the carriage moving mechanism  20 , the head unit  30 , the drive signal generating circuit  40 , the missing-dot detector  50 , the cap mechanism  60 , and the detector group  70 ) in accordance with the computer program stored in the memory  80   c.    
     In the printer  1 , dot forming processing to form dots on a paper sheet by intermittently discharging ink from the head  31  moving along the movement direction of the carriage, and transport processing to transport the paper sheet in the transport direction are repeatedly performed. As a result, dots are formed in a position different from the position where dots are formed by the previous dot forming processing, so that a two-dimensional image is formed on the medium. 
     Discharge Test and Restore Operation 
     The nozzle may be clogged if ink (liquid) is not discharged from the nozzle for a long time or a foreign object such as paper powder is attached to the nozzle. If the nozzle is clogged, ink is not discharged when the ink should be discharged from the nozzle, and thus a phenomenon (missing dot) in which a dot is not formed at a position where the dot should be formed occurs. When the “missing dot” occurs, image quality deteriorates. Therefore, in this embodiment, when a nozzle of missing-dot is detected as a result of “discharge test” performed by the missing-dot detector  50 , “restore operation” is performed so that ink is normally discharged from the nozzle of missing dot. 
     It is preferable that the missing-dot test is performed immediately after the printer  1  is turned on, or when the printer  1  receives print data from the computer CP and starts printing. Or, the missing-dot test may be performed every predetermined time in long time printing. Hereinafter, the restore operation of the nozzle of missing dot will be described, and then the discharge test will be described. 
     Restore Operation 
       FIGS. 3A to 3C  are diagrams showing a positional relationship between the head  31  and the cap mechanism  60  during the restore operation. First, the cap mechanism  60  will be described. The cap mechanism  60  includes a cap  61  and a slider member  62  that supports the cap  61  and can move in an obliquely vertical direction. The cap  61  includes a rectangular bottom section (not shown in the figures) and a side wall section  611  standing on peripheral edges of the bottom section, and has a thin box shape whose upper surface facing the nozzle plate  33   b  is open. A sheet-shaped moisture retaining member made of a porous material such as felt or sponge is disposed in a space surrounded by the bottom section and the side wall section  611 . 
     As shown in  FIG. 3A , when the carriage  21  is apart from a home position (here, right in the movement direction), the cap  61  is located sufficiently lower than the surface of the nozzle plate  33   b  (hereinafter, also referred to as nozzle surface). As shown in  FIG. 3B , when the carriage  21  moves toward the home position, the carriage  21  comes into contact with a contact section  63  provided on the slider member  62 , and the contact section  63  moves toward the home position along with the carriage  21 . When the contact section  63  moves toward the home position, the slider member  62  rises along a guiding long hole  64 , and the cap  61  also rises along with the slider member  62 . Finally, as shown in  FIG. 3C , when the carriage  21  is located at the home position, the side wall section  611  (porous material) of the cap  61  is closely attached to the nozzle plate  33   b . Therefore, it is possible to suppress the evaporation of ink solvent from the nozzle by positioning the carriage  21  at the home position when the printer  1  is turned off or not used for a long time. 
     Next, the restore operation will be described. There is “flushing operation” as one of restore operations of a nozzle of missing dot. As shown in  FIG. 3B , the flushing operation is an operation in which an ink droplet is forcibly and continuously discharged from each nozzle and clogs in the nozzles are removed when there is a certain gap between the nozzle surface and opening edges of the cap  61 . 
     A waste liquid tube  65  is disposed in a space between the bottom surface of the cap  61  and the side wall section  611 , and a suction pump (not shown in the figures) is connected to a halfway portion of the waste liquid tube  65 . As one of the other restore operations, “pump suction” is performed when the opening edges of the cap  61  are in contact with the nozzle surface as shown in  FIG. 3C . If the suction pump is operated when the side wall section  611  of the cap  61  is in contact with the nozzle surface, the space in the cap  61  can be under negative pressure. In this way, it is possible to suck ink from the head  31  along with thickened ink and paper powder, so that the nozzle of missing dot can be restored. 
     As another restore operation, by moving the carriage  21  in the movement direction while the cap mechanism  60  is held in the position shown in  FIG. 3B , ink droplets and foreign objects attached to the nozzle surface are removed by a wiper  66  protruded upward from the side wall section  611  of the cap  61 . As a result, ink can be normally discharged from nozzles that were clogged by foreign objects. 
     About Missing-Dot Detector  50   
       FIG. 4  is a view of the cap  61  seen from the above,  FIG. 5A  is a diagram for explaining the missing-dot detector  50 , and  FIG. 5B  is a block diagram for explaining a detection controller  57 . The missing-dot detector  50  actually discharges ink from each nozzle, checks whether the ink is discharged normally or not, and thus detects a nozzle of missing dot. First, a configuration of the missing-dot detector  50  will be described. As shown in  FIG. 5A , the missing-dot detector  50  includes a high voltage power supply unit  51 , a first limiting resistance  52 , a second limiting resistance  53 , a detecting capacitor  54 , an amplifier  55 , a smoothing capacitor  56 , and a detection controller  57 . 
     When missing-dot detection is performed, as shown in  FIGS. 3B and 5A , the nozzle surface and the cap  61  face each other with a predetermined gap d therebetween. As shown in  FIG. 4 , in a space surrounded by the side wall section  611  of the cap  61 , a moisture retaining member  612  and a wire-shaped detection electrode  613  are arranged. When the missing-dot detection is performed, the detection electrode  613  shows a high voltage of about 600 V to 1 kV. The detection electrode  613  illustrated in  FIG. 4  includes a frame section having a double-line rectangular shape, a diagonal section connecting opposing corners of the frame section, and a cross section connecting the centers of each side of the frame section. Based on this structure, the detection electrode  613  is electrostatically charged uniformly over a large area. The ink solvent of this embodiment is a liquid (for example, water) having electrical conductivity, and when a high voltage is applied to the detection electrode  613  while the moisture retaining member  612  is wet, the surface of the moisture retaining member  612  shows the same voltage. Because of this, an area to which ink is discharged from the nozzles is electrostatically charged uniformly over a large area. 
     The high voltage power supply unit  51  is a kind of power supply that applies a predetermined voltage to the detection electrode  613  in the cap  61 . The high voltage power supply unit  51  according to this embodiment includes a DC power supply of around 600 V to 1 kV, and an operation of the high voltage power supply unit  51  is controlled by a control signal from the detection controller  57 . 
     The first limiting resistance  52  and the second limiting resistance  53  are arranged between an output terminal of the high voltage power supply unit  51  and the detection electrode  613 , and limit an electric current flowing between the high voltage power supply unit  51  and the detection electrode  613 . In this embodiment, the first limiting resistance  52  and the second limiting resistance  53  have the same resistance value (for example, 1.6 MΩ), and the first limiting resistance  52  and the second limiting resistance  53  are connected in series. As shown in  FIG. 5 , one terminal of the first limiting resistance  52  is connected to the output terminal of the high voltage power supply unit  51 , the other terminal of the first limiting resistance  52  is connected to one terminal of the second limiting resistance  53 , and the other terminal of the second limiting resistance  53  is connected to the detection electrode  613 . 
     The detecting capacitor  54  is an element for extracting a voltage change component of the detection electrode  613 . One conductor of the detecting capacitor  54  is connected to the detection electrode  613 , and the other conductor of the detecting capacitor  54  is connected to the amplifier  55 . By disposing the detecting capacitor  54  between the detection electrode  613  and the amplifier  55 , it is possible to eliminate a bias component (DC component) of the detection electrode  613  and facilitate handling of the signal. In this embodiment, the capacitance of the detecting capacitor  54  is 4700 pF. 
     The amplifier  55  amplifies a signal (voltage change) appearing at the other terminal of the detecting capacitor  54  and outputs the amplified signal. The amplifier  55  according to this embodiment has a gain of 4000. Based on this, the voltage change component can be obtained as a voltage signal having amplitude of around 2 to 3 V. A pair of the detecting capacitor  54  and the amplifier  55  corresponds to a kind of detector, and detects an electrical change which is generated in the detection electrode  613  when an ink droplet is discharged. 
     The smoothing capacitor  56  suppresses an abrupt change of voltage. One terminal of the smoothing capacitor of this embodiment is connected to a signal line connecting the first limiting resistance  52  and the second limiting resistance  53 , and the other terminal is connected to the ground. The capacitance of the smoothing capacitor  56  is 0.1 μF. 
     The detection controller  57  is a section for controlling the missing-dot detector  50 . As shown in  FIG. 5B , the detection controller  57  includes a register group  57   a , an AD converter  57   b , a voltage comparator  57   c , and a control signal output section  57   d . The register group  57   a  includes a plurality of registers. A determination result of each nozzle Nz and a voltage threshold value for determination are stored in the registers. The AD converter  57   b  converts the amplified voltage signal (analog values) outputted from the amplifier  55  into digital values. The voltage comparator  57   c  compares a value of amplitude based on the amplified voltage signal with the voltage threshold value. The control signal output section  57   d  outputs a control signal for controlling the high voltage power supply unit  51 . 
     About Discharge Test 
     In the printer  1 , the nozzle plate  33   b  is connected to the ground and the ground voltage is applied to the nozzle plate  33   b , and a high voltage of about 600 V to 1 kV is applied to the detection electrode  613  disposed in the cap  61 . The ink droplet discharged from the nozzle is set to the ground voltage by the nozzle plate of the ground voltage. The nozzle plate  33   b  and the detection electrode  613  are faced each other with a predetermined gap d therebetween (refer to  FIG. 5A ), and an ink droplet is discharged from the nozzle where the voltage change will be detected. The detection controller  57  obtains an electrical change generated in the detection electrode  613  owing to the discharge of the ink droplet via the detecting capacitor  54  and the amplifier  55  as a voltage signal SG. The detection controller  57  determines whether or not the ink droplet is discharged normally from the nozzle where the voltage change will be detected on the basis of the amplitude value (voltage change) of the voltage signal SG. 
     The principle of the detection is based on the fact that the nozzle plate  33   b  and the detection electrode  613  are arranged with a predetermined gap d therebetween, so that the nozzle plate  33   b  and the detection electrode  613  behave as if they were a capacitor. As shown in  FIG. 5A , the ink elongated into a columnar shape (ink column) from the nozzle Nz comes into contact with the nozzle plate  33   b  connected to the ground, so that the ink column is set to the ground voltage. The elongation of the ink changes the electrostatic capacitance of the capacitor. Specifically, when the ink is discharged from the nozzle, the ink of the ground voltage and the detection electrode  613  constitute a capacitor, and the electrostatic capacitance changes. 
     When the electrostatic capacitance decreases, an amount of charge that can be accumulated between the nozzle plate  33   b  and the detection electrode  613  decreases. Therefore, surplus charge moves from the detection electrode  613  to the high voltage power supply unit  51  through the limiting resistances  52  and  53 . In other words, an electric current flows toward the high voltage power supply unit  51 . On the other hand, when the electrostatic capacitance increases or the decreased electrostatic capacitance returns to the original state, the charge moves from the high voltage power supply unit  51  to the detection electrode  613  through the limiting resistances  52  and  53 . In other words, an electric current flows toward the detection electrode  613 . When such electric currents (for convenience, also referred to as discharge test current If) flow, the voltage of the detection electrode  613  changes. The voltage change of the detection electrode  613  also appears as a voltage change of the other conductor (conductor connected to the amplifier  55 ) of the detecting capacitor  54 . Therefore, it is possible to determine whether or not an ink droplet is discharged by monitoring the voltage change of the other conductor. 
       FIG. 6A  is a diagram showing an example of the drive signal COM used in the discharge test,  FIG. 6B  is a diagram for explaining the voltage signal SG outputted from the amplifier  55  when ink is discharged from a nozzle by the drive signal COM, and  FIG. 6C  is a diagram showing the voltage signal SG that is a result of the discharge test of a plurality of nozzles (# 1  to # 10 ). The drive signal COM includes a plurality of drive waveforms W (for example, 24 drive waveforms) for discharging ink from a nozzle in the first half period TA of a repetition period T, and a certain voltage is maintained at a medium voltage level in the second half period TB. The drive signal generating circuit  40  repeatedly generates the plurality of drive waveforms W (24 drive waveforms) every repetition period T. The repetition period T corresponds to the time required to perform a test of one nozzle. 
     The drive signal COM is applied to a piezoelectric element corresponding to a certain nozzle among the nozzles to be tested over the repetition period T. Then, ink droplets are continuously discharged from the nozzle to be tested in the first half period TA (for example, 24 shots are discharged). In this way, the voltage of the detection electrode  613  changes, and the amplifier  55  outputs the voltage change to the detection controller  57  as the voltage signal SG (sine curve) shown in  FIG. 6B . Since the amplitude of the voltage signal SG obtained with one shot of ink droplet is small, ink droplets are continuously discharged from the nozzle, so that the voltage signal SG having sufficient amplitude to perform the test can be obtained. 
     The detection controller  57  calculates a maximum amplitude Vmax (difference between a maximum voltage VH and a minimum voltage VL) from the voltage signal SG of the nozzle to be tested during the test period (T), and compares the maximum amplitude Vmax and a predetermined threshold value TH. When ink is discharged from the nozzle to be tested in accordance with the drive signal COM, the voltage of the detection electrode  613  changes and the maximum amplitude Vmax of the voltage signal SG becomes greater than the threshold value TH. On the other hand, if ink is not discharged from the nozzle to be tested due to clogs or the like, or if an amount of discharged ink is small, the voltage of the detection electrode  613  does not change, or the voltage change is small, so that the maximum amplitude Vmax of the voltage signal SG becomes smaller than or equal to the threshold value TH. 
     After the drive signal COM is applied to a piezoelectric element corresponding to a certain nozzle, the drive signal COM is applied to a piezoelectric element corresponding to the next nozzle to be tested over the repetition period T. In such a way, for every nozzle to be tested, the drive signal COM is applied to a piezoelectric element corresponding to the nozzle over the repetition period T. As a result, as shown in  FIG. 6C , the detection controller  57  can obtain the voltage signal SG in which a voltage change of sine curve occurs for each repetition period T. 
     For example, from the result of  FIG. 6C , the detection controller  57  determines that the nozzle # 5  is a missing-dot nozzle (abnormal nozzle) because the maximum amplitude Vmax of the voltage signal SG corresponding to the test period of the nozzle # 5  is smaller than the threshold value TH. The detection controller  57  determines that the other nozzles (# 1  to # 4 ,  6  to # 10 ) are normal nozzles because the maximum amplitudes Vmax of the voltage signal SG corresponding to the test periods of the other nozzles are greater than or equal to the threshold value TH. 
       FIG. 7  is a flowchart for explaining print processing according to this embodiment. 
     When the discharge test starts, first, it is determined whether or not a cover (not shown in the figures) of the printer is open (S 102 ). The reason why it is determined whether or not the cover is open is because a high voltage is applied to the electrode in the discharge test as described above, and in such a time if the cover is open, a user may touch the high voltage electrode. A sensor not shown in the figures is provided in the printer  1  so as to determine whether or not the cover of the printer  1  is open. 
     In step S 102 , the determination is not limited to whether or not the cover is open. For example, in step S 102 , it may be determined whether or not a waste liquid tank is open, whether or not a cartridge lever that fixes an ink cartridge is released, whether or not the printer  1  is turned off, whether or not an error occurs in a program operating the printer  1 , and so on. 
     The determination whether or not the cover of the printer  1  is open, the determination whether or not the waste liquid tank is open, and the determination whether or not the cartridge lever is released as described above correspond to a determination with respect to mechanical abnormality. The determination whether or not the printer  1  is turned off and the determination whether or not an error occurs in the program operating the printer  1  correspond to a determination with respect to electrical abnormality. 
     In step S 102 , when a mechanical abnormality or an electrical abnormality occurs, the discharge test cannot be performed, and thus the process ends. 
     On the other hand, in step S 102 , when a mechanical abnormality and an electrical abnormality do not occur, a head temperature is obtained (S 104 ). The temperature of the head  31  is obtained by the controller  80  connected to the above-mentioned thermistor  710 . 
     Next, it is determined whether or not the obtained temperature of the head  31  is within a range of stable operation of the head  31  (S 106 ). Here, the range of stable operation of the head  31  is set to a range of temperature that is higher than or equal to 10° C. and lower than 40° C. When the obtained temperature of the head  31  is higher than or equal to 10° C. and lower than 40° C., the nozzle discharge test is performed (S 108 ). The discharge test has been described above, so that the description will be omitted. 
     After the discharge test is performed, whether or not there are abnormal nozzles is determined (S 110 ). When the there is at least one abnormal nozzle, the nozzle restore operation (S 114 ) is performed. The method of the nozzle restore operation has been described above, so that the description will be omitted. After the nozzle restore operation (S 114 ) is performed, printing is performed (S 112 ). 
     On the other hand, when the there is no abnormal nozzle in step S 110 , printing is performed (S 112 ). 
     In this way, when the there are abnormal nozzles, it is possible to perform printing after performing the nozzle restore operation to restore abnormal nozzles to normal nozzles. 
     In step S 106 , when the obtained temperature of the head  31  is outside the range of stable operation (specifically, higher than or equal to 10° C. and lower than 40° C.), it is further determined whether or not the temperature of the head  31  is within an operable range (S 116 ). Here, the operable range is a range of temperature that is higher than or equal to 0° C. and lower than 10° C. and a range of temperature that is higher than or equal to 40° C. and lower than 50° C. When the obtained temperature of the head  31  is within the operable range, a warning is displayed on the printer  1  (S 118 ). 
     The warning displayed here is a warning indicating that, for example, although ink can be discharged, it cannot be guaranteed that ink droplets of an appropriate size are discharged. After such a warning is displayed, the printing is performed (S 112 ). In this way, it is possible to perform printing while notifying a user that ink can be discharged, but print quality is out of guarantee. 
     When the temperature of the head  31  is out of the operable range (specifically, lower than 0° C., or higher than or equal to 50° C.) in step S 116 , the process ends without performing printing. When the head temperature is out of the operable range, it is very difficult to discharge ink from the head  31 . Thus, by doing the above operation, a useless printing operation can be avoided. When it is determined that the temperature of the head  31  is out of the operable range in step S 116 , it may be determined that the thermistor  710  that obtains the temperature of the head  31  fails. 
     By the way, the discharge test described above is a test in which ink is discharged from the head  31  and it is determined whether or not a nozzle is an abnormal nozzle in accordance with a degree of discharge. Therefore, if the discharge test is performed when the head  31  is outside the range of stable operation and ink may not be appropriately discharged from the head  31 , a normal nozzle may be determined to be an abnormal nozzle. In other words, the discharge test may make a false determination. However, in this embodiment, as described above, when the head  31  is outside the range of stable operation, the discharge test is not performed, so that the discharge test does not make a false determination. 
     If the restore operation is performed under a situation in which a normal nozzle may be erroneously determined to be an abnormal nozzle, the restore operation may be performed on a normal nozzle and waste ink. However, in this embodiment, the discharge test is performed only when the temperature of the head  31  is within the range of stable operation, and then the restore operation is performed, so that the discharge test is performed in a situation in which there is no false determination, and thus ink can be prevented from being wasted. 
     In this way, it is possible to appropriately control the discharge test and printing in accordance with the environment. 
     Other Embodiments 
     Although the printer  1  is described as the discharge test device in the above embodiment, the embodiment is not limited to this, and the discharge test device may be incorporated in a liquid discharge device that ejects or discharges fluid other than ink (liquid, a liquid body in which functional material particles are dispersed, and a fluid body such as gel). For example, the same technique as that of the above embodiment may be applied to various devices to which an ink jet technique is applied. Such devices include a color filter manufacturing device, a dyeing device, a microprocessing device, a semiconductor manufacturing device, a surface processing device, a three-dimensional molding device, a vaporizer, an organic EL manufacturing device (particularly, a polymer EL manufacturing device), a display manufacturing device, a deposition device, and a DNA chip manufacturing device. Methods and manufacturing methods performed in such devices are also within the scope of application of the invention. 
     The above embodiments are intended for easier understanding of the invention and do not limit the interpretation of the invention. Needless to say, the invention may be modified and improved without departing from the scope of the invention and the invention includes equivalents thereof.