Patent Publication Number: US-2022234352-A1

Title: Liquid ejection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2021-011068 filed on Jan. 27, 2021, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects of the disclosure relate to a liquid ejection apparatus that ejects liquid from nozzles. 
     BACKGROUND 
     Examples of a known liquid ejection apparatus that ejects liquid from nozzles include a printer that records images by ejecting ink from nozzles. The known printer drives a pump at a predetermined time appointed in advance to apply pressure, performing a maintenance operation including purging for forcibly discharging ink from a head. 
     SUMMARY 
     According to an aspect of the disclosure, a liquid ejection apparatus includes a liquid ejection head having a plurality of nozzles, a determination circuit, a clock, and a controller. The determination circuit is configured to output a determination signal in response to ejection of liquid from a nozzle of the plurality of nozzles. The determination signal indicates whether the nozzle is a defective nozzle. The controller is configured to determine whether the clock is in an on or off state. In response to determining that the clock is in an on state, the controller is configured to perform an inspection process at a first time. In the inspection process, the controller is configured to drive the liquid ejection head to eject liquid from the nozzle of the plurality nozzles and receive a determination signal that is output from the determination circuit in response to ejection of liquid from the nozzle of the plurality of nozzles. In response to determining that the clock is in an off state, the controller is configured to perform the inspection process at a predetermined time that is a time after the clock is returned to an on state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a general configuration of a printer according to an illustrative embodiment. 
         FIG. 2  illustrates a detection electrode disposed in a cap, a connection relationship between the detection electrode and a high-voltage power supply circuit, and a connection relationship between the detection electrode and a determination circuit. 
         FIG. 3A  is a graph showing changes in potential of the detection electrode in a case where ink has been ejected from a nozzle. 
         FIG. 3B  is a graph showing no change in potential of the detection electrode in a case where ink has not been ejected from a nozzle. 
         FIG. 4  is a block diagram illustrating an electrical configuration of the printer. 
         FIG. 5  is a flowchart of a process performed when power is supplied from a plug or a battery. 
         FIG. 6  is a flowchart of a process performed when power is supplied from the plug. 
         FIG. 7  is a flowchart according to a first modification, corresponding to  FIG. 6 . 
         FIG. 8  is a flowchart according to a second modification, corresponding to  FIG. 6 . 
         FIG. 9  is a flowchart according to a third modification, corresponding to  FIG. 5 . 
         FIG. 10  is a flowchart according to the third modification, corresponding to  FIG. 6 . 
         FIG. 11  is a flowchart according to a fourth modification, corresponding to  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     In the known printer described above, the maintenance operation is performed at a predetermined time. However, when the printer is not powered, that is, when the plug is disconnected and a built-in battery runs out, its internal clock does not keep time. Hereinafter, this state will be referred to as that “the clock is in an off state”. In this case, even if the plug is inserted and the power supply to the printer is resumed thereafter, the clock cannot keep accurate time, and the maintenance operation cannot be performed at an appropriate time. 
     To solve the above problem, it is an object of the disclosure to provide a liquid ejection apparatus configured to perform a maintenance operation appropriately even when a clock is in an off state. 
     Hereinafter, an illustrative embodiment will be described with reference to the accompanying drawings. 
     General Configuration of Printer 
     As illustrated in  FIG. 1 , a printer  1  as an example of a liquid ejection apparatus includes a carriage  2 , a sub tank  3 , an inkjet head  4  as an example of a liquid ejection head, a platen  5 , conveyance rollers  6  and  7 , a maintenance unit  8 , and a plug  19 . 
     The carriage  2  is supported by two guide rails  11  and  12  each extending in a scanning direction (e.g., a right-left direction). The carriage  2  is configured to reciprocate in the scanning direction along the guide rails  11  and  12 . The carriage  2  is connected to a carriage motor  86  (in  FIG. 4 ) via a belt. In response to the carriage motor  86  being driven, the carriage  2  moves in the scanning direction along the guide rails  11  and  12 . The scanning direction corresponds to a right-left direction as illustrated in  FIG. 1 . 
     The sub tank  3  is mounted on the carriage  2 . The printer  1  further includes a cartridge holder  13 . The cartridge holder  13  accommodates a plurality of, for example, four, ink cartridges  14  that are detachable. The four ink cartridges  14  arranged in the scanning direction store ink (as an example of liquid) of different colors, from right to left, black, yellow, cyan, and magenta, respectively. The sub tank  3  is connected via four tubes  15  to the four ink cartridges  14  attached to the cartridge holder  13 . Such a configuration thus enables supply of ink of the four colors to the sub tank  3  from the four ink cartridges  14 . 
     The inkjet head  4  is mounted on the carriage  2  and connected to a lower end of the sub tank  3 . The inkjet head  4  is supplied with ink of the four colors from the sub tank  3 . The inkjet head  4  has an array of nozzles  10  defined in a nozzle surface  4   a  that is its lower surface. The inkjet head  4  is configured to eject ink from the nozzles  10 . Specifically, for example, the nozzles  10  are arranged in rows extending in a conveyance direction orthogonal to the scanning direction to form nozzle rows  9 . The nozzle surface  4   a  has a plurality of, for example, four, nozzle rows  9  next to each other in the scanning direction. In the inkjet head  4 , black ink is ejected from the nozzles  10  constituting the rightmost nozzle row  9  in the scanning direction. Yellow ink is ejected from the nozzles  10  constituting the nozzle row  9  to the left of the black nozzle row  9 . Cyan ink is ejected from the nozzles  10  constituting the nozzle row  9  to the left of the yellow nozzle row  9 . Magenta ink is ejected from the nozzles  10  constituting the nozzle row  9  to the left of the cyan nozzle row  9 . 
     The platen  5  is disposed below the inkjet head  4  and faces the nozzles  10 . The platen  5  extends in the scanning direction to have a dimension covering the entire width of a recording sheet P to be conveyed. The recording sheet P is an example of a recording medium. The platen  5  is configured to support from below a recording sheet P being conveyed. The conveyance roller  6  is disposed upstream of the inkjet head  4  and the platen  5  in the conveyance direction. The conveyance roller  7  is disposed downstream of the inkjet head  4  and the platen  5  in the conveyance direction. The conveyance rollers  6  and  7  are connected to a conveyance motor  87  (in  FIG. 4 ) via gears. In response to the conveyance motor  87  being driven, the conveyance rollers  6  and  7  rotate to convey a recording sheet P in the conveyance direction. 
     The maintenance unit  8  includes a cap  71 , a suction pump  72 , and a waste liquid tank  73 . The cap  71  is disposed to the right of the platen  5  in the scanning direction. When the carriage  2  is located in a maintenance position, the nozzles  10  face the cap  71 . The maintenance position is further to the right than the platen  5  in the scanning direction. 
     The cap  71  is movable upward and downward selectively by control of a cap up-and-down mechanism  88  (in  FIG. 4 ). The carriage  2  is moved to stop at the maintenance position so that the nozzles  10  and the cap  71  face each other. In such a state, in response to the cap  71  being moved upward by the cap up-and-down mechanism  88 , an upper end of the cap  71  fully contacts the nozzle surface  4   a  of the inkjet head  4  to cover the nozzles  10 . At this time, the cap  71  that covers the nozzles  10  is in a capping state, and the nozzles  10  capped by the cap  71  are in a capped state. The cap  71  is not limited to have such a configuration that the upper end fully contacts the nozzle surface  4   a  to cover the nozzles  10 . The cap  71  may be structured such that that the upper end fully contacts a frame surrounding the nozzle surface  4   a  of the inkjet head  4  to cover the nozzles  10 . 
     The suction pump  72  may be a tube pump. The suction pump  72  is connected to the cap  71  and the waste liquid tank  73 . The maintenance unit  8  uses the suction pump  72  to perform suction purging in which, in response to the suction pump  72  being driven with the nozzles  10  in the capped state, ink in the inkjet head  4  is pumped out or discharged from the nozzles  10 . Ink discharged from the inkjet head  4  through suction purging is collected in the waste liquid tank  73 . 
     For the sake of convenience, in this embodiment, the cap  71  covers all the nozzles  10  of the inkjet head  4  and suction purging is performed to discharge ink in the inkjet head  4  from all the nozzles  10 . In some embodiments, the maintenance unit  8  may include a plurality of caps  71 , one for covering the nozzles  10  constituting the rightmost nozzle row  9  from which black ink is discharged, and the other for covering the nozzles  10  constituting the remaining three nozzle rows  9  from which respective color inks (e.g., yellow, cyan, and magenta inks) are discharged. Such a configuration may enable suction purging to discharge black ink or color inks selectively in the inkjet head  4 . Alternatively, for example, the maintenance unit  8  may include a plurality of caps  71  for respective nozzle rows  9 . Such a configuration may enable ink to be discharged from the nozzles  10  of the inkjet head  4  on a nozzle row  9  basis. 
     As illustrated in  FIG. 2 , a detection electrode  76  having a rectangular planar shape is disposed within the cap  71 . The detection electrode  76  is connected to a high-voltage power supply circuit  77  via a resistor  79 . The detection electrode  76  receives a predetermined positive potential (e.g., 600 v) from the high-voltage power supply circuit  77  during an ejection determination process described later. In contrast, the inkjet head  4  is maintained at the ground potential. This causes a potential difference between the inkjet head  4  and the detection electrode  76 . The detection electrode  76  is connected to a determination circuit  78 . The determination circuit  78  compares a potential of a signal outputted from the detection electrode  76  with a threshold value Vt, and outputs a signal responsive to a comparison result. 
     As the detection electrode  76  and the inkjet head  4  have a potential difference therebetween, ink becomes charged when ejected from the nozzles  10 . When the carriage  2  is at the maintenance position, the inkjet head  4  is driven to eject ink from a nozzle  10  toward the detection electrode  76 . As illustrated in  FIG. 3A , until the charged ink approaches and reaches the detection electrode  76 , the potential of the detection electrode  76  lowers from a potential Va at which the inkjet head  4  is not driven to eject ink, and reaches a potential Vb, which is lower than the potential Va. After the charged ink reaches the detection electrode  76 , the potential of the detection electrode  76  gradually rises to the potential Va. In other words, the potential of the detection electrode  76  changes in a driving period Td during which the inkjet head  4  is driven to eject ink. 
     In contrast, in a case where ink is not ejected from a nozzle  10  while the inkjet head  4  is driven, as illustrated in  FIG. 3B , the potential of the detection electrode  76  does not change substantially from the potential Va in the driving period Td of the inkjet head  4 , for example, less than the difference between Va and Vt. The determination circuit  78  uses the threshold value Vt satisfying an equation Vb&lt;Vt&lt;Va to discriminate whether ink is ejected or not ejected from a nozzle  10 . In the driving period Td of the inkjet head  4 , the determination circuit  78  compares a maximum potential of a voltage signal outputted from the detection electrode  76  with a threshold value Vt, and outputs a determination signal responsive to a comparison result. In this embodiment, a combination of the detection electrode  76 , the high-voltage power supply circuit  77 , the resistor  79 , and the determination circuit  78  is an example of a determination circuit. The determination circuit outputs a determination signal responsive to whether a nozzle  10  is a defective nozzle having an abnormal condition in ink ejection. Specifically, a defective nozzle in this case is a nozzle from which ink is not ejected. 
     The high-voltage power supply circuit  77  may apply a negative potential (e.g., −600 V) to the detection electrode  76  instead of a positive potential. In this case, when the carriage  2  is at the maintenance position and ink is ejected from a nozzle  10  toward the detection electrode  76 , the potential of the detection electrode  76  rises from the potential Va until the charged ink approaches and reaches the detection electrode  76 , and gradually lowers to the potential Va after the charged ink reaches the detection electrode  76 . 
     The plug  19  is connectable to the electricity supply. The printer  1  is supplied with power from the plug  19  when the plug  19  is inserted in a wall outlet and connected to the electricity supply. When the plug  19  is disconnected from the electricity supply, the supply of power from the plug  19  is stopped. 
     Electrical Configuration of Printer 
     Hereinafter, a description will be provided on an electrical configuration of the printer  1 . As illustrated in  FIG. 4 , the printer  1  includes a controller  80 . The controller  80  includes a CPU  81 , a ROM  82 , a RAM  83 , a flash memory  84 , and an ASIC  85 . The controller  80  controls the carriage motor  86 , the inkjet head  4 , the conveyance motor  87 , the cap up-and-down mechanism  88 , the suction pump  72 , and the high-voltage power supply circuit  77 . The controller  80  receives a determination signal from the determination circuit  78 . 
     The printer  1  includes a display  69 , an operation device  70 , a clock  68 , and a battery  67 . The display  69  is, for example, a liquid crystal display provided in a housing of the printer  1 . The controller  80  controls the display  69  to display information necessary for the operations of the printer  1 . The operation device  70  includes buttons provided on the housing of the printer  1  and a touch screen provided on the display  69 . When the user operates the operation device  70 , a signal is input to the controller  80 . 
     In this embodiment, the operation device  70  includes a power switch. The user operates the power switch to switch the power of the printer  1  on and off. When the user turns on the power of the printer  1  by operating the power switch of the operation device  70 , the controller  80  receives a power-on signal (as an example of a “predetermined signal”) from the operation device  70 . The power-on signal indicates that the power of the printer  1  has been turned on. The clock  68  measures time, and the controller  80  receives a time signal indicating a time from the clock  68 . 
     The battery  67  is connected to at least the controller  80  and the clock  68 . While the printer  1  is supplied with power from the plug  19 , the battery  67  is charged. When the printer  1  is not supplied with power from the plug  19 , which is disconnected from the electricity supply, but the battery  67  is alive, the battery  67  supplies power to at least the controller  80  and the clock  68 . 
     In the controller  80 , only the CPU  81  or the ASIC  85  may perform all processing or a combination of the CPU  81  and the ASIC  85  may perform all processing. Alternatively, the controller  80  may include a single CPU  81  that may perform all processing or include a plurality of CPUs  81  that may share all processing. Alternatively, the controller  80  may include a single ASIC  85  that may perform all processing or include a plurality of ASICs  85  that may share all processing. 
     Processing During Power Supply from Plug or Battery 
     Next, a description will be given of processing performed when electric power is supplied from the plug  19  or the battery  67  to the control device  80  and the clock  68  in the printer  1 . 
     The controller  80  performs a process in accordance with the flowchart of  FIG. 5 . The process of  FIG. 5  is started when the plug  19  is connected to the electricity supply, for example, with the battery  67  dead and power supply to the printer  1  is started. The process is repeated until the plug  19  is disconnected and the battery  67  runs out. 
     Specifically, as to the process of  FIG. 5 , the controller  80  determines whether power-loss flag information is stored in the flash memory  84  in S 101 . The flash memory  84  is as an example of storage. The power-loss flag information indicates that the clock  68  is in an off state because the power supply to the clock  68  is stopped due to the plug  19  being disconnected and the battery  67  running out. 
     In response to determining that the power-loss flag information is not stored in the flash memory  84  (S 101 : NO), the controller  80  determines whether the battery  67  runs out in S 102 . In S 102 , for example, when the plug  19  is removed and the state of charge of the battery  67  is less than a predetermined threshold value, the controller  80  determines that the battery  67  runs out. Further, in S 102 , for example, when the plug  19  is inserted and the state of charge of the battery  67  is equal to or higher than the predetermined threshold value, the controller  80  determines that the battery  67  does not run out or is alive. 
     When the controller  80  determines that the battery  67  does not run out or is alive (S 102 : NO), the process returns to S 101 . In response to determining that the battery  67  runs out (S 102 : YES), the controller  80  stores the power-loss flag information in the flash memory  84  in S 103  and the process returns to S 101 . 
     In response to determining that the power-loss flag information is stored in the flash memory  84  (S 101 : YES), the controller  80  determines whether it has received a power-on signal, a time setting signal, or a recording instruction including the time information in S 104 , S 105 , and S 106 . If the controller  80  has received none of them (S 104 : NO, S 105 : NO, S 106 : NO), the process returns to S 101 . 
     The power-on signal is a signal that is input when the user operates the power switch of the operation device  70  or disconnects the plug  19  without turning off with the power switch and then reconnects the plug  19  with the power switch in the on position. The power-on signal is a signal and that indicates an instruction to turn the power of the printer  1  on. The time setting signal is a signal for setting a time that is input when the user operates the power switch of the operation device  70 . The recording instruction including time information is, for example, a recording instruction including transmission time information input to the printer  1  from an external device such as a PC, which is connected to the printer  1 . 
     In response to receipt of a power-on signal (S 104 : YES), the controller  80  determines whether the clock  68  is measuring a temporary time in S 107 . The clock  68  measuring a temporary time refers to a state where the clock  68  is working but measuring time different from the actual time. 
     When the controller  80  determines that the clock  68  is measuring a temporary time (S 107 : YES), the process returns to S 101 . In response to determining that the clock  68  is not measuring a temporary time (S 107 : NO), the controller  80  sets current time information to a second time and causes the clock  68  to start measuring the temporary time from the second time in S 108 , and the process returns to S 101 . The second time is time reset when the controller  80  receives the power-on signal, for example, 0:00. The second time is time for the controller  80  to perform an inspection process described later. The controller  80  determines the clock  68  as measuring the temporary time unless and until the controller  80  receives a time setting signal or a recording instruction including time information. 
     In response to receipt of a time setting signal (S 105 : YES) or a recording instruction including time information (S 106 : YES), the controller  80  sets the clock  68  to the time included in the time setting signal or the time information, and causes the clock  68  to start measuring time from the set time in S 109 . The controller  80  erases the power-loss flag information stored in the flash memory  84  in S 110  and the process returns to S 101 . 
     Processing During Power Supply from Plug 
     Next, a description will be given of processing performed when electric power is supplied from the plug  19 . The controller  80  performs a process in accordance with the flowchart of  FIG. 6 . The process of  FIG. 6  is started when the plug  19  is connected to the electricity supply. The process is repeated until the plug  19  is disconnected and the battery  68  runs out. When electric power is supplied from the plug  19 , the controller  80  performs the process shown in the flowchart of  FIG. 5  and the process shown in the flowchart of  FIG. 6  in parallel. 
     Specifically, as to the process of  FIG. 6 , the controller  80  determines whether power-loss flag information is stored in the flash memory  84  in S 201 . In response to determining that the power-loss flag information is not stored in the flash memory  84  (S 201 : NO), the controller  80  determines whether the time the clock  68  indicates is a first time in S 202 . The first time is time for the controller  80  to perform the inspection process, and is stored in advance in the flash memory  84 . 
     In response to determining that the power-loss flag information is stored in the flash memory  84  (S 201 : YES), the controller  80  determines whether the temporary time the clock  68  indicates is the second time in S 203 . In response to determining that, in S 202 , the time the clock  68  indicates is not the first time (S 202 : NO) and, in S 203 , the temporary time the clock  68  indicates is not the second time (S 203 : NO), the controller  80  determines whether it has received a recording instruction in S 204 . In response to the controller  80  not receiving the recording instruction (S 204 : NO), the process returns to S 201 . 
     In response to determining that the power-loss flag information is not stored in the flash memory  84  (S 201 : NO) and the time the clock  68  indicates is the first time (S 202 : YES), the controller  80  performs an inspection process in S 205 . In the inspection process, the controller  80  drives the inkjet head  4  to perform inspection driving to eject ink from each nozzle  10  sequentially. The controller  80  receives a determination signal output from the determination circuit  78  during the inspection driving. 
     The controller  80  determines whether the nozzles  10  of the inkjet head  4  include a defective nozzle in accordance with a determination signal received during the inspection process in S 206 . If the nozzles  10  do not include a defective nozzle (S 206 : NO), the process returns to S 201 . 
     In response to determining that the nozzles  10  include a defective nozzle (S 206 : YES), the controller  80  stores recovery flag information in the flash memory  84  in S 207 . The recovery flag information indicates a need to perform a recovery operation to discharge ink from the nozzles  10  to recover the defective nozzle. The controller  80  performs a flushing process in S 208  and the process returns to S 201 . In the flushing process at S 208 , the controller  80  drives the inkjet head  4  to perform flushing to discharge ink from the nozzles. In this flushing, ink may be discharged from a defective nozzle only, or from at least a group of the nozzles  10  that are not defective in addition to the defective nozzle. 
     In response to determining that the power-loss flag information is stored in the flash memory  84  (S 201 : YES) and the time the clock  68  indicates is the second time (S 203 : YES), the controller  80  performs steps S 205  to S 208 . 
     In response to receipt of the recording instruction (S 204 : YES), the controller  80  determines whether the received recording instruction is an initial recording instruction only after the inspection process is performed in S 209 . If the received recording instruction is not an initial recording instruction only after the inspection process is performed (S 209 : NO), the process proceeds to S 213 . In response to determination that the received recoding instruction is the initial recording instruction only after the inspection process is performed (S 209 : YES), the controller  80  determines whether the recovery flag information is stored in the flash memory  84  (S 210 ). In response to determining that the recovery flag information is not stored in the flash memory  84  (S 210 : NO), the process proceeds to S 213 . 
     In response to determining that the recovery flag information is stored in the flash memory  84  (S 210 : YES), the controller  80  performs a purging process in S 211 , and erases the recovery flag information stored in the flash memory  84  in S 212 , and then the process proceeds to S 213 . 
     In S 213 , the controller  80  performs a recording process. In the recording process, the controller  80  controls the carriage motor  86  and the conveyance motor  87  to alternately perform a recording pass and a conveyance operation. In the recording pass, the inkjet head  4  ejects ink from the nozzles  10  toward a sheet P while the carriage  2  is moved in the scanning direction. In the conveyance operation, the conveyance rollers  6  and  7  convey the recording sheet P for a predetermined distance. After the recording process, the process returns to S 201 . 
     In this embodiment, the inkjet head  4  that performs flushing and the maintenance unit  8  that performs suction purging correspond to “recovery means”. A combination of flushing and suction purging corresponds to the “recovery operation”. In the combination, flushing corresponds to a part of the recovery operation, and suction purging corresponds to the remaining part of the recovery operation. 
     Effects 
     In this embodiment, in response to determining that the clock  68  is in an on state in which the clock  69  keeps actual time (in other words, the power-loss flag information is not stored in the flash memory  84 ), the controller performs the inspection process when the time the clock  68  indicates is the first time. This enables the liquid ejection apparatus to check whether the nozzles include a defective nozzle at a desired time, such as in a period of time during which the user is not using the liquid ejection apparatus. In response to determining that the clock  68  is in an off state, the controller sets time when the power is turned on to the second time, and causes the clock  68  to measure a temporary time from the second time. Thereafter, the controller  80  performs the inspection process every time the temporary time indicated by the clock  68  is the second time of next and subsequent days until the battery  67  runs out. This enables the controller  80  to perform the inspection process periodically even if the clock  68  has been switched to an off state. 
     In this embodiment, when the clock  68  returns from an off state to an on state, time to perform the inspection process is returned to time at which the time the clock  68  indicates is the first time. After the clock  68  returns to the on state, the inspection process can be performed at a timing desired by the user. 
     In this embodiment, the controller  80  stores the power-loss flag information in the flash memory  84  when the battery  67  runs out. This enables the controller  80  to determine whether the clock is in an off state depending on whether the power-loss flag information is stored in the flash memory  84 . 
     Unlike this embodiment, if the recovery operation is performed immediately after a determination signal, which is output during the inspection driving, indicates a defective nozzle and the time interval between the inspection driving and receipt of a recording instruction is increased, the liquid in the inkjet head  4  may be thickened. In this case, the recovery operation would be necessarily performed when the recording instruction is received. This would eventually lead to wasteful discharge of ink at the recovery operation performed immediately after the inspection driving. 
     In this embodiment, however, when a determination signal output during the inspection driving indicates a defective nozzle, the flash memory  84  is used to store the recovery flag information. When an initial recording instruction is received only after the inspection driving and the recovery flag information is stored in the flash memory  84 , a recovery operation is performed. This eliminates needless ink discharge described above even if the period of time between the inspection driving and receiving of the initial recording instruction is long. 
     In this embodiment, when a determination signal output during the inspection driving indicates a defective nozzle, flushing, which is a part of the recovery operation, is performed immediately after the inspection driving. Then, when the initial recording instruction is received only after the inspection driving, suction purging, which is a remaining part of the recovery operation is performed before the recording process. This can reduce the time it takes to perform the recovery operation before the recording process. 
     Modifications 
     While the disclosure has been described in detail with reference to the specific embodiment thereof, this is merely an example, and various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure. 
     In the above-described embodiment, when the power-loss flag information is stored in the flash memory  84  (S 201 : YES) and the temporary time indicated by the clock  68  becomes the second time (S 203 : YES), the steps S 205  to S 208  are performed. In some embodiments, these steps may be omitted or different steps may be performed. 
     In a first modification, the controller  80  performs a process in accordance with the flowchart of  FIG. 7  instead of the process in accordance with the flowchart of  FIG. 6  of the above-described embodiment. The process of  FIG. 7  is obtained by replacing S 203  in the flowchart of  FIG. 6  with S 301 . 
     In S 301 , the controller  80  determines whether the temporary time indicated by the clock  68  is a third time that is earlier than the second time. The third time is time for the controller  80  to perform the inspection process, and is stored in advance in the flash memory  84 . If the temporary time indicated by the clock  68  is not the third time (S 301 : NO), the process proceeds to S 204 . In response to determining that the temporary time indicated by the clock  68  is the third time (S 301 : YES), the controller  80  performs steps S 205  to S 208 . 
     In the first modification, if the clock  68  is in an off state when power is turned on, the controller  80  assumes the time at which the power is turned on as the second time and causes the clock  68  to measure a temporary time. Thereafter, the controller  80  performs the inspection process every time the temporary time indicated by the clock  68  is the third time, which is earlier than the second time, of next and subsequent days until the battery  67  runs out. The controller  80  thus performs the inspection process periodically even if the clock  68  has been switched to an off state. Normally, the user turns on the power of the printer when using the printer. Probably, the user will not use the printer between the second time and the third time that is earlier than the second time. Thus, the inspection process can be performed when the temporary time indicated by the clock  68  is the third time before the second time. 
     In this embodiment and the first modification, when the clock  68  returns from an off state to an on state, time to perform the inspection process is returned to time at which the time the clock  68  indicates is the first time. However, the inspection process may be performed at a different time from the above. For example, even after the clock  68 , which was in an off state, returns to the on state in which it keeps actual time, the inspection process may be performed at time different from the first time, such as the second time or the third time. 
     Further, the present invention is not limited to a configuration in which, when the clock  68  is in an off state, the clock  68  is caused to measure a temporary time and an inspection process is performed based on the temporary time. 
     In a second modification, the controller  80  performs a process in accordance with the flowchart of  FIG. 8  instead of the process in accordance with the flowchart of  FIG. 6  of the above-described embodiment. In the process of  FIG. 8 , in response to determining that the power-loss flag information is not stored in the flash memory  84  (S 201 : NO) and that the time indicated by the clock  68  is not the first time (S 202 : NO), the controller  80  determines whether it has received a power-on signal in S 401 . If the controller  80  has not received the power-on signal (S 401 : NO), the process proceeds to S 204 . 
     In response to receipt of the power-on signal (S 401 : YES), the controller  80  performs a return process in S 402 . In the return process, the controller  80  controls at least some of the components of the printer  1  to perform a return operation for returning the printer  1  to a state in which recording on the recording sheet P is feasible. The return operation refers to, for example, an operation for adjusting an original positions of the carriage  2  or the cap  71 . 
     In accordance with a time signal received from the clock  68 , the controller  80  determines whether an elapsed time T from when the power of the printer  1  was turned off to when the power is turned on again is longer than a predetermined time Th in S 403 . If the elapsed time T is shorter than or equal to the predetermined time Th (S 403 : NO), the process proceeds to S 204 . When the elapsed time T is longer than the predetermined time Th (S 403 : YES), the process proceeds to S 205 . 
     In response to determining that the power-loss flag information is stored in the flash memory  84  (S 201 : YES), the controller  80  determines whether it has received a power-on signal in S 404 . 
     If the controller  80  has not received the power-on signal (S 404 : NO), the process proceeds to S 204 . In response to receipt of the power-on signal (S 404 : YES), the controller  80  performs a return process similar to that in S 402  in S 405 , and the process proceeds to S 205 . 
     In the second modification, when the clock  68  is in an off state, the controller  80  performs the inspection process at a timing after the return operation when the power is turned on. When the battery becomes exhausted, the printer  1  cannot keep track of the elapsed time since the power was turned off. In the second modification, however, the inspection process is performed at a timing after the return operation. The printer  1  can thus keep track of whether a nozzle  10  is defective, and subsequently perform the recovery operation only when necessary. This reduces or eliminates unnecessary consumption of ink. 
     In the second modification, the inspection process is performed at a time after the return operation. In some embodiments, the inspection process may be performed at a different timing. In the second modification, the inspection process may be performed at a time within a period from when the power is turned on to when the return operation is started, for example, immediately before S 402  or S 405  is started. 
     In a third modification, the controller  80  performs a process in accordance with the flowchart of  FIG. 9 or 10  instead of the process in accordance with the flowchart of  FIG. 5 or 6  of the above-described embodiment. 
     The process of  FIG. 9  does not include steps S 104 , S 107 , and S 108  of the process of  FIG. 5 . When the controller  80  determines that the power-loss flap information is stored in the flash memory  84  in S 101  (S 101 : YES), the process proceeds to S 105 . 
     In the process of  FIG. 10 , in response to determining that the power-loss flag information is stored in the flash memory  84  (S 201 : YES), the controller  80  determines whether it has received a power-on signal in S 501 . 
     If the controller  80  has not received the power-on signal (S 501 : NO), the process proceeds to S 204 . In response to receipt of the power-on signal (S 501 : YES), the controller  80  waits until a predetermined time elapses (S 502 : NO), and when the predetermined time has elapsed (S 502 : YES), the process proceeds to S 205 . 
     In the third modification, even if the clock  68  is in an off state, the controller  80  performs the inspection process at the conclusion of a predetermined time elapsed since the power was turned on. The user is likely to use the printer immediately after the power is turned on, whereas, as described in the third modification, the user is unlikely to use the printer after a predetermined time elapsed since the power was turned on. Thus, the inspection process may be performed at the timing when the predetermined time has elapsed since the power was turned on. 
     In a fourth modification, the controller  80  performs a process in accordance with the flowchart of  FIG. 11  instead of the process in accordance with the flowchart of  FIG. 6  of the above-described embodiment. 
     In the process of  FIG. 11 , when the power-loss flag information is stored in the flash memory  84  (S 201 : YES) or is not stored in the flash memory  84  (S 201 : NO) and the time indicated by the clock  68  is not the first time (S 202 : NO), the process proceeds to S 204 . 
     In S 204 , when the controller  80  determines that the recording instruction has not been received (S 204 : NO), the process returns to S 201 . In response to determining that the recording instruction has been received in the S 204  (S 204 : YES), the controller  80  determines whether the received recording instruction is an initial recording instruction received only after receipt of the power-on signal in S 601 . Here, “an initial recording instruction received only after receipt of the power-on signal” refers to a recording instruction received only after the power supply of the printer  1  is turned on with the clock  68  losing time. 
     If the received recording instruction is not an initial recording instruction received only after receipt of the power-on signal (S 601 : NO), the process proceeds to S 213 . When the received recording instruction is an initial recording instruction received only after receipt of the power-on signal (S 601 : YES), the controller  80  stores, in the flash memory  84 , recording flag information indicating that recording is to be performed in S 602 , and the process proceeds to S 205 . 
     In the fourth modification, when it is determined that the nozzles do not include a defective nozzle in S 206  (S 206 : NO) or after the flushing process is performed in S 208 , the controller  80  determines whether the recording flag information is stored in the flash memory  84  in S 603 . When the recording flag information is not stored in the flash memory  84  (S 603 : NO), the process returns to S 201 . In response to determining that the recording flag information is stored in the flash memory  84  (S 603 : YES), the controller  80  erases the recording flag information stored in the flash memory  84  in S 604 , and then the process proceeds to S 210 . 
     In the fourth modification, even when the clock  68  is in an off state, the controller  80  performs the inspection process before image recording on a sheet P only after the power is turned on. 
     In the above embodiment, when a determination signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, flushing, which is a part of the recovery operation, is performed. In response to a receipt of a recording instruction only after the inspection driving, suction purging is performed as a remaining part of the recovery operation. However, the timing to perform suction purging is not limited to the above. 
     For example, the printer  1  may be selectable between recording with low image quality and recording with high image quality, and perform steps S 210  to S 213  upon receiving a recording instruction to perform recording with high image quality only after the inspection driving. 
     Suction purging, which is a remaining part of the recovery operation, may be performed except when a recording instruction is received. For example, suction purging may be performed when a specified signal except for a recording instruction is received. 
     The recovery operation is not limited to the combination of flushing and suction purge. 
     For example, the recovery operation may be suction purge. When a detection signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, suction purge may be performed as a part of the recovery operation. Thereafter, when a predetermined signal is received, suction purging may be performed as a remaining part of the recovery operation. 
     Alternatively, for example, the recovery operation may be flushing. When a detection signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, flushing may be performed as a part of the recovery operation. Thereafter, when a predetermined signal is received, flushing may be performed as a remaining part of the recovery operation. 
     When a determination signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, maintenance is not limited to performing a part of the recovery operation. When a predetermined signal is received, maintenance is not limited to performing a remaining part of the recovery operation. 
     For example, when a detection signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, the recovery operation may not be performed. Thereafter, when a predetermined signal is received, the entire recovery operation may be performed. 
     Alternatively, for example, when a detection signal output from the determination circuit  78  during the inspection driving indicates a defective nozzle, the entire recovery operation may be performed immediately. Thereafter, when a predetermined signal is received, the recovery operation may not be performed. 
     In the above-described embodiment, the inspection driving is performed for each of the nozzles  10  of the inkjet head  4 . For example, inspection driving may be performed only for some of the nozzles  10  of the inkjet head  4 , such as every other nozzle  10  in each nozzle row  9 . Remaining nozzles  10  may be estimated as to whether or not a nozzle is defective based on the determination signal output from the determination circuit  78  during the inspection driving. 
     The above-described embodiment shows, but is not limited to, that the determination circuit  78  outputs a signal responsive to whether a nozzle  10  is defective in accordance with a potential of the detection electrode  76  when ink is ejected from the nozzle  10  toward the detection electrode  76 . However, ink ejected from the nozzle  10  may not be directed toward the detection electrode  76 . 
     For example, instead of the detection electrode  76 , a detection electrode elongated vertically may be disposed such that ink ejected from the nozzle  10  may pass an area parallel to the elongated detection electrode, and a signal responsive to whether a nozzle is a defective nozzle may be output from the determination circuit. Alternatively, an optical sensor may be disposed to detect ink ejected from a nozzle  10 , and the determination circuit is configured to output a signal responsive to whether a nozzle is a defective nozzle based on a signal from the optical sensor. 
     Alternatively, a known technique for outputting a determination signal may be adopted. For example, a printer may include a voltage detection circuit connected to a nozzle plate of an inkjet head. In response to the inkjet head being driven for ejecting ink from a nozzle, the voltage detection circuit may detect changes in voltage at the voltage detection circuit and output a signal responsive to whether the nozzle is a defective nozzle to the controller  80 . The voltage detection circuit is another example of the determination circuit. 
     Alternatively, another known technique for outputting a determination signal may be adopted. For example, a substrate of an inkjet head may include a temperature detection element. In such a case, a first voltage may be applied to a heater to allow the inkjet head to eject ink from a nozzle. Then, a second voltage may be applied to the heater to prevent the inkjet head from ejecting ink from the nozzle. The determination circuit will output a signal responsive to whether the nozzle  10  is a defective nozzle based on changes in temperature detected by the temperature detection element during a certain time period since the application of the second voltage. 
     In the above embodiment and modifications, a nozzle  10  from which ink is not ejected is determined as a defective nozzle. However, a defective nozzle is not limited to such a nozzle. For example, a determination circuit may be used to output a signal responsive to whether ink is ejected from a nozzle  10  in an intended direction. Based on the signal, a nozzle  10  from which ink is ejected in an unintended direction may be determined as a defective nozzle. 
     In the above-described embodiment, suction purging for discharging a predetermined amount of ink is performed in the purging process. However, purging is not limited to suction purging. For example, the maintenance unit  8  may be configured to selectively perform any one of a plurality of types of suction purging each for discharging a different amount of ink. The plurality of types of suction purging may each have a different amount of ink to be discharged, for example, by changing at least one of the driving time or the rotation speed of the suction pump  72 . In the purging process, for example, suction purging may be performed with larger amount of ink to be discharged the number of defective nozzles is. 
     In the above description, suction purging is performed in the purging process. However, the purging process is not limited to suction purging. For example, a booster pump may be disposed in portions of the tubes  15  connecting the sub tank  3  and the ink cartridges  14 . Alternatively, the printer may include the booster pump to be connected to the ink cartridges. The booster pump may be driven with the nozzles  10  covered by the cap  71  to increase the pressure of ink in the inkjet head  4 , thereby causing the inkjet head  4  to discharge ink from the nozzles  10 . This is what is called pressurized purging. 
     Alternatively, both of suction by the suction pump  72  and pressurization by the booster pump may be performed in the purging process. 
     In the above-described examples, the printer includes the battery that supplies power to the clock, and the clock stops keeping the actual time when the power supply from the plug to the printer is stopped and the battery runs out. In some embodiments, for example, the printer may not include a battery that supplies power to the clock. In this case, the clock may stop keeping the actual time when the supply of power from the plug to the printer is stopped. 
     The disclosure has been applied to a printer including a serial head that moves in the scanning direction together with a carriage. However, the disclosure may also be applied to a printer including, for example, a line head extending over the entire length of a recording sheet P in the scanning direction. 
     The disclosure has been applied to a printer that ejects ink from nozzles to record an image on a recording sheet P. However, the disclosure may also be applied to another printer that may record an image on a recording medium other than a recording sheet. Examples of the recording media include a T-shirt, a sheet for outdoor advertisement, a casing of a mobile terminal such as a smartphone, a cardboard, and a resin member. Further, the disclosure may also be applied to a liquid ejection apparatus that may eject liquid other than ink such as liquid resin or liquid metal.