Patent Publication Number: US-2022234357-A1

Title: Liquid ejection apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2021-011064 filed Jan. 27, 2021. The entire content of the priority application is incorporated herein by reference. 
     BACKGROUND 
     As an example of a liquid ejection apparatus that ejects liquid from a nozzle, a printer that ejects ink from a nozzle and records on paper is known. This printer performs, when a particular time set in advance has come, a maintenance operation including a purge for forcibly discharging ink from a head by driving a pump and applying pressure. 
     SUMMARY 
     According to one aspect, this specification discloses a liquid ejection apparatus. The liquid ejection apparatus includes a liquid ejection head, a signal output circuit, a recovery device, a memory, and a controller. The liquid ejection head has a nozzle configured to eject liquid. The signal output circuit is configured to, when inspection driving is performed by the liquid ejection head, output a determination signal indicating whether the nozzle is an abnormal nozzle. The inspection driving is driving the liquid ejection head to eject liquid from the nozzle for checking whether the nozzle is the abnormal nozzle. The recovery device is configured to perform a recovery operation of discharging liquid from the nozzle. The controller is configured to: in response to receiving a first signal, perform the inspection driving and, in response to determining that the determination signal transmitted from the signal output circuit indicates that the abnormal nozzle exists, store flag information in the memory, the flag information indicating that the recovery operation needs to be performed; and in response to receiving a second signal different from the first signal and determining that the memory stores the flag information, control the recovery device to perform the recovery operation. 
     In a case where the inspection driving is performed when the first signal is received and the determination signal indicates that an abnormal nozzle exists, if the recovery operation is immediately performed and if the period from the reception of the first signal to the reception of the second signal is long, the viscosity of the liquid in the liquid ejection head may increase during this period. In this case, it is necessary to perform the recovery operation again when the second signal is received, and as a result, the discharge of the liquid by the recovery operation performed when the first signal is received is wasted. 
     In this disclosure, when the first signal is received, the inspection driving is performed, and when the determination signal indicates that an abnormal nozzle exists, the flag information is stored. Then, when the second signal is received and the flag information is stored, the recovery operation is performed. With this process, even when the period from the reception of the first signal to the reception of the second signal is long, the wasteful liquid discharge as described above is not performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments in accordance with this disclosure will be described in detail with reference to the following figures wherein: 
         FIG. 1  is a schematic configuration diagram of a printer; 
         FIG. 2  is a diagram for explaining a detection electrode arranged in a cap and a connection relationship among the detection electrode, a high-voltage power supply circuit, and a determination circuit; 
         FIG. 3A  is a diagram showing a change in a voltage value of the detection electrode when ink is ejected from a nozzle; 
         FIG. 3B  is a diagram showing a change in the voltage value of the detection electrode when ink is not ejected from the nozzle; 
         FIG. 4  is a block diagram showing an electrical configuration of the printer; 
         FIG. 5A  is a flowchart showing a flow of processing in a state where power is supplied to at least a controller and a clock; 
         FIG. 5B  is a table for explaining information on stored temperature ranges; 
         FIG. 6  is a flowchart showing a flow of a process A in  FIG. 5A ; 
         FIG. 7  is a flowchart showing a flow of a process B in  FIG. 5A ; 
         FIG. 8  is a flowchart showing a flow of processing at the time of recording; 
         FIG. 9  is a flowchart similar to  FIG. 5A ; and 
         FIG. 10  is a flowchart similar to  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     The above printer performs the maintenance operation when a particular time set in advance has come as described above. However, if a period from the particular time until the printer performs recording on a sheet is long, viscosity of ink in the head may increase during this period, and the maintenance operation may have to be performed again immediately before the recording on the sheet. In this case, as a result, the ink ejection due to the maintenance operation when the particular time has come is wasted. 
     In view of the foregoing, an aspect of an object of this disclosure is to provide a liquid ejection apparatus configured to suppress wasteful liquid ejection. 
     Hereinafter, an embodiment of this disclosure will be described. 
     &lt;Overall configuration of printer&gt; 
     As shown in  FIG. 1 , a printer  1  according to the embodiment (“liquid ejection apparatus” of this disclosure) includes a carriage  2 , a sub tank  3 , an inkjet head  4  (“liquid ejection head” of this disclosure), a platen  5 , conveyance rollers  6  and  7 , a maintenance unit  8 , and so on. 
     The carriage  2  is supported by two guide rails  11  and  12  extending in a scanning direction. The carriage  2  is connected to a carriage motor  86  (see  FIG. 4 ) via a belt and so on (not shown). When the carriage motor  86  is driven, the carriage  2  moves in the scanning direction along the guide rails  11  and  12 . In the following, the right side and the left side in the scanning direction are defined as shown in  FIG. 1  for description. 
     The sub tank  3  is mounted on the carriage  2 . Here, the printer  1  includes a cartridge holder  13 , and four ink cartridges  14  are detachably attached to the cartridge holder  13 . The four ink cartridges  14  are arranged in the scanning direction, and store ink (“liquid” of this disclosure) of black, yellow, cyan, and magenta from the one arranged at the right side in the scanning direction. The sub tank  3  is connected to the four ink cartridges  14  mounted on the cartridge holder  13  via four tubes  15 . With this configuration, ink of the above four colors is supplied from the four ink cartridges  14  to the sub tank  3 . 
     The inkjet head  4  is mounted on the carriage  2  and connected to the lower end of the sub tank  3 . The inkjet head  4  is supplied with ink of the above four colors from the sub tank  3 . The inkjet head  4  ejects ink from a plurality of nozzles  10  formed on a nozzle surface  4   a  which is the lower surface of the inkjet head  4 . More specifically, the plurality of nozzles  10  are arranged in a conveyance direction perpendicular to the scanning direction to form nozzle arrays  9 , and four nozzle arrays  9  are arranged in the scanning direction on the nozzle surface  4   a . Ink of black, yellow, cyan, and magenta is ejected from the plurality of nozzles  10  from those forming the nozzle array  9  at the right side in the scanning direction. 
     The platen  5  is arranged below the inkjet head  4  and faces the plurality of nozzles  10 . The platen  5  extends over the entire width of a recording sheet P (“medium” of this disclosure) in the scanning direction and supports the recording sheet P from below. The conveyance roller  6  is arranged upstream of the inkjet head  4  and the platen  5  in the conveyance direction. The conveyance roller  7  is arranged 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  (see  FIG. 4 ) via a gear (not shown) and so on. When the conveyance motor  87  is driven, the conveyance rollers  6  and  7  rotate, and the recording sheet P is conveyed 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 arranged at the right side of the platen  5  in the scanning direction. When the carriage  2  is located at a maintenance position at the right side of the platen  5  in the scanning direction, the plurality of nozzles  10  face the cap  71 . 
     The cap  71  is configured to be raised and lowered by a cap elevating mechanism  88  (see  FIG. 4 ). When the cap  71  is raised by the cap elevating mechanism  88  in a state where the plurality of nozzles  10  face the cap  71  by positioning the carriage  2  at the maintenance position, the upper end of the cap  71  is in close contact with the nozzle surface  4   a  and the plurality of nozzles  10  are covered with the cap  71 . The cap  71  is not limited to a cap covering the plurality of nozzles  10  by being in close contact with the nozzle surface  4   a . The cap  71  may be a cap that cover a plurality of nozzles  10  by, for example, being in close contact with a frame (not shown) arranged at the periphery of the nozzle surface  4   a  of the inkjet head  4 . 
     The suction pump  72  is a tube pump and so on, and is connected to the cap  71  and the waste liquid tank  73 . In the maintenance unit  8 , when the suction pump  72  is driven in a state where the plurality of nozzles  10  are covered by the cap  71  as described above, ink in the inkjet head  4  is discharged from the plurality of nozzles  10 , which is so-called suction purge. The ink discharged by the suction purge is stored in the waste liquid tank  73 . 
     In the present embodiment, one of a plurality of types of suction purges having different ink discharge amounts is selectively performed. The amount of ink discharged differs among the plurality of types of suction purges, for example, because at least the driving time of the suction pump  72  or the rotation speed of the suction pump  72  is different. 
     Here, for convenience, it is assumed that the cap  71  covers all the nozzles  10 , and the ink in the inkjet head  4  is discharged from all the nozzles  10  in the suction purge. However, the method is not limited to this. For example, the cap  71  may separately include a portion covering the plurality of nozzles  10  constituting the rightmost nozzle array  9  for ejecting black ink, and a portion covering the plurality of nozzles  10  constituting the left three nozzle arrays  9  for ejecting color ink (yellow, cyan, magenta ink), and may be configured to selectively discharge either black ink or color ink in the inkjet head  4  in the suction purge. Alternatively, for example, a cap may be provided individually for each nozzle array  9 , so that ink is discharged from the nozzles  10  individually of each nozzle array  9  in the suction purge. 
     As shown in  FIG. 2 , a detection electrode  76  having a rectangular planar shape is arranged in the cap  71 . The detection electrode  76  is connected to a high-voltage power supply circuit  77  via a resistor  79 . A particular positive potential (for example, approximately 600 V) is applied to the detection electrode  76  by the high-voltage power supply circuit  77  at the time of determination driving described later. The inkjet head  4  is held at the ground potential. As a result, a particular potential difference is generated between the inkjet head  4  and the detection electrode  76 . A determination circuit  78  is connected to the detection electrode  76 . The determination circuit  78  compares the potential of a signal output from the detection electrode  76  with a threshold value Vt, and outputs a signal according to the result. 
     More specifically, since a potential difference is generated between the inkjet head  4  and the detection electrode  76 , ink ejected from the nozzle  10  is charged. When ink is ejected from the nozzle  10  toward the detection electrode  76  in a state where the carriage  2  is located at the maintenance position, as shown in  FIG. 3A , the charged ink approaches the detection electrode  76  and, until the ink lands on the detection electrode  76 , the potential of the detection electrode  76  drops from a potential Va at the time when the inkjet head  4  is not driven, and reaches a potential Vb lower than the potential Va. Then, after the charged ink lands on the detection electrode  76 , the potential of the detection electrode  76  gradually rises and returns to the potential Va. That is, the potential of the detection electrode  76  changes during a driving period Td of the inkjet head  4 . 
     When ink is not ejected from the nozzle  10 , as shown in  FIG. 3B , the potential of the detection electrode  76  is almost unchanged from the potential Va during the driving period Td of the inkjet head  4 . Thus, in the determination circuit  78 , a threshold value Vt (Va&gt;Vt&gt;Vb) is set in order to distinguish these states. Then, the determination circuit  78  compares the lowest potential of the voltage signal output from the detection electrode  76  with the threshold value Vt during the driving period Td of the inkjet head  4 , and outputs a determination signal according to the determination result. In the present embodiment, the combination of the detection electrode  76 , the high-voltage power supply circuit  77 , the resistor  79 , and the determination circuit  78  serves as the “signal output circuit” of this disclosure. This signal output circuit outputs a determination signal depending on whether the nozzle  10  is an abnormal nozzle in which ink is not ejected. This determination of whether the nozzle  10  is an abnormal nozzle is performed individually for each nozzle. 
     Here, the high-voltage power supply circuit  77  applies a positive potential to the detection electrode  76 . Alternatively, the high-voltage power supply circuit  77  may apply a negative potential (for example, approximately −600 V) to the detection electrode  76 . In this case, contrary to the above, when ink is ejected from the nozzle  10  toward the detection electrode  76  in a state where the carriage  2  is located at the maintenance position, the charged ink approaches the detection electrode  76  and the potential of the detection electrode  76  rises from the potential Va until the ink lands on the detection electrode  76  and, after the ink lands on the detection electrode  76 , the potential of the detection electrode  76  gradually decreases and returns to the potential Va. 
     &lt;Electrical Configuration of Printer&gt; 
     Next, the electrical configuration of the printer  1  will be described. As shown in  FIG. 4 , the printer  1  includes a controller  80 . The controller  80  includes a CPU (Central Processing Unit)  81 , a ROM (Read Only Memory)  82 , a RAM (Random Access Memory)  83 , a flash memory  84 , an ASIC (Application Specific Integrated Circuit)  85 , and so on. The controller  80  controls the operations of the carriage motor  86 , the inkjet head  4 , the conveyance motor  87 , the cap elevating mechanism  88 , the suction pump  72 , the high-voltage power supply circuit  77 , a driver IC  89 , and so on. In the present embodiment, the controller  80  controls the inkjet head  4  by controlling the driver IC  89 . Further, a determination signal is input to the controller  80  from the determination circuit  78 . 
     In addition to the configuration described above, the printer  1  includes a display  69 , an operation interface  70 , a clock  68 , a temperature sensor  67 , and a battery  66 . The display  69  is, for example, a liquid crystal display provided on the housing of the printer  1 . The controller  80  controls the display  69  to display information and so on necessary for the operation of the printer  1 . The operation interface  70  is, for example, a button provided on the housing of the printer  1 , a touch panel provided on the display  69 , and so on. By operating the operation interface  70 , the user inputs a signal to the controller  80 . 
     In the present embodiment, the operation interface  70  includes a power switch (not shown). By operating the power switch, the user switches the power of the printer  1  on and off. When the user operates the power switch of the operation interface  70  to turn on the power of the printer  1 , the operation interface  70  outputs a power-on signal indicating that the power of the printer  1  has been turned on (“second signal” of this disclosure), and the controller  80  receives this power-on signal. 
     The clock  68  measures the time, and the controller  80  receives a time signal indicating the time (“first signal” of this disclosure) from the clock  68 . The temperature sensor  67  detects, for example, the temperature of the inkjet head  4 . The controller  80  receives a temperature signal indicating the temperature from the temperature sensor  67 . 
     The battery  66  is connected to at least the controller  80  and the clock  68 . Power is supplied to the printer  1  from an outlet (not shown), at which time the battery  66  is charged. In a state where the printer  1  is unplugged, power is supplied from the battery  66  to at least the controller  80  and the clock  68 . 
     In the controller  80 , only the CPU  81  may perform various processes, only the ASIC  85  may perform various processes, or the CPU  81  and the ASIC  85  may cooperate with each other to perform various processes. Further, in the controller  80 , one CPU  81  may perform processing independently, or a plurality of CPUs  81  may share the processing. Further, in the controller  80 , one ASIC  85  may perform the processing independently, or a plurality of ASICs  85  may share the processing. 
     &lt;Control During Standby&gt; 
     The control by the controller  80  during standby when recording on the recording sheet P is not performed in the printer  1  will be described. In the printer  1 , the controller  80  performs processing according to the flow of  FIG. 5A  during the standby. The flow of  FIG. 5A  is started, for example, when the plug is first inserted in the printer  1  and the power supply to the printer  1  is started, and is continued (that is, repeatedly executed) while power is supplied from the plug or the battery  66  to the controller  80  and the clock  68 . 
     The flow of  FIG. 5A  will be described in more detail. The controller  80  is in the standby state while the time signal received from the clock  68  does not indicate a particular time (S 101 : NO), the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is the same as the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when inspection driving described later is performed last time (S 102 : NO), and the power-on signal is not received (S 103 : NO). 
     For example, information of temperature ranges 1 to 4 as shown in  FIG. 5B  is stored in the flash memory  84 . Temperatures T 1 , T 2 , and T 3  in  FIG. 5B  have a magnitude relationship of T 1 &lt;T 2 &lt;T 3 . The controller  80  stores, in the flash memory  84 , the information of the temperature T indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed. The controller  80  makes the determination of S 102  based on the temperature T indicated by the temperature signal received from the temperature sensor  67 , the temperature range information of  FIG. 5B  stored in the flash memory  84 , and the temperature T stored during the inspection driving. 
     In the present embodiment, among the temperature ranges shown in  FIG. 5B , the temperature range including the temperature T indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed corresponds to “first temperature range”. In the present embodiment, when the temperature T indicated by the temperature signal received from the temperature sensor  67  thereafter falls in another temperature range different from the first temperature range, the other temperature range corresponds to “second temperature range”. 
     When the time signal received from the clock  68  indicates that the time is a particular time (S 101 : YES), the controller  80  executes a process A (S 102 ). In the present embodiment, the time signal indicating that the time is a particular time corresponds to “first signal”. 
     The controller  80  also executes the process A (S 104 ) when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  differs from the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving was performed last time (S 102 : YES). When the power-on signal is received (S 103 : YES), the controller  80  executes the process B (S 105 ). 
     &lt;Process A&gt; 
     The process A will be described. As shown in  FIG. 6 , in the process A, the controller  80  first executes an inspection process (S 201 ). In the inspection process, the controller  80  transmits a drive signal to the driver IC  89  for performing inspection driving for driving the inkjet head  4  so as to eject ink sequentially from the plurality of nozzles  10 . 
     Subsequently, the controller  80  determines whether the inspection driving has been actually performed by the inspection process of S 201  (S 202 ). The case where the inspection driving is actually performed by the inspection process is, for example, a case where a plug is inserted and the inkjet head  4  is ready to be driven for inspection by the electric power supplied from the plug. The case where the inspection driving is not actually performed by the inspection process is, for example, the case where the plug is unplugged and the inkjet head  4  is not ready to be driven for inspection. 
     If the inspection driving is not actually performed by the inspection process (S 202 : NO), the flow returns to the flow of  FIG. 5A . When the inspection driving is actually performed by the inspection process (S 202 : YES), the controller  80  updates inspection history information (S 203 ). More specifically, the flash memory  84  stores the inspection history information, which is information on the time when the inspection driving was performed last time. In S 203 , the controller  80  updates the information of the time when the inspection driving was performed last time, which is stored in the flash memory  84 , based on the time signal from the clock  68 . 
     Subsequently, the controller  80  resets the variable C to 0 (S 204 ). The variable C corresponds to the number of recording sheets P on which recording has been performed since the inspection driving was performed last time. 
     Subsequently, when the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle does not exist (S 205 : NO), the flow returns to the flow of  FIG. 5A . When the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle exists (S 205 : YES), the controller  80  stores flag information indicating that an abnormal nozzle exists in the flash memory  84  (S 206 ). 
     Subsequently, the controller  80  stores, in the flash memory  84 , the type information indicating the type of suction purge to be performed (S 207 ). The processing will be described in detail. In S 207 , the controller  80  stores a type of suction purge in the flash memory  84  as the type information such that a larger amount of ink is discharged in the suction purge as the determination signal output from the determination circuit  78  during the inspection driving indicates that a larger number of nozzles  10  are abnormal nozzles. 
     One example will be described. The inkjet head  4  has 100 nozzles. Of the 100 nozzles, 80 nozzles are designated as inspection nozzles to be inspected. For the 80 nozzles, determination of whether a nozzle is an abnormal nozzle is performed one by one. Of the 80 inspection nozzles, the result may be that 5 nozzles are abnormal nozzles, or 20 nozzles are abnormal nozzles, for example. If the result is 5 abnormal nozzles which is smaller than or equal to a threshold (for example, 10 abnormal nozzles), small suction purge is performed (that is, a small amount of ink is discharged). If the result is 20 abnormal nozzles which is larger than the threshold, large suction purge is performed (that is, a large amount of ink is discharged). 
     Subsequently, the controller  80  executes a flushing process (S 208 ) and returns to the flow of  FIG. 5A . In the flushing process, the controller  80  controls the driver IC  89  to cause the inkjet head  4  to perform flushing to discharge ink from the nozzle  10 . At this time, the controller  80  may discharge ink only from the abnormal nozzle or may discharge ink from all the nozzles  10  of the inkjet head  4  including the abnormal nozzle. 
     &lt;Proces s B&gt; 
     The process B will be described. As shown in  FIG. 7 , in the process B, first, based on the above-mentioned inspection history information, it is determined whether the inspection driving is performed at the last particular time before the power is turned on (S 301 ). 
     When the inspection driving is performed at the last particular time before the power is turned on (S 301 : YES), the controller  80  subsequently determines whether the flag information is stored in the flash memory  84  (S 302 ). 
     If the flag information is not stored in the flash memory  84  (S 302 : NO), the process returns to the flow of  FIG. 5A . When the flag information is stored in the flash memory  84  (S 302 : YES), the controller  80  determines the type of suction purge based on the type information (S 303 ) and executes the purge process (S 304 ). In the purge process of  5304 , the controller  80  performs the suction purge determined in  5303 . After the purge process of  5304  is completed, the controller  80  deletes the flag information stored in the flash memory  84  (S 305 ), and returns to the flow of  FIG. 5A . 
     When the inspection driving is not performed at the last particular time before the power is turned on (S 301 : NO), the controller  80  subsequently executes the inspection process similar to S 201  (S 306 ), updates the inspection history information (S 307 ), and resets the variable C to 0 (S 308 ) similarly to S 203  and S 204 . The process B is a process performed when the power is turned on, that is, a process performed in a state where power is supplied from the plug. Thus, when the inspection process of S 306  is executed, inspection driving is performed in the inkjet head  4 . 
     Subsequently, when the determination signal output from the determination circuit  78  during the inspection driving performed by the inspection process of S 306  indicates that an abnormal nozzle does not exist (S 309 : NO), the controller  80  returns to the flow of  FIG. 5A . 
     When the determination signal indicates that an abnormal nozzle exists (S 309 : YES), the controller  80  subsequently determines the type of suction purge to be performed based on the determination signal output from the determination circuit  78  during the inspection driving performed by the inspection process of S 306  (S 310 ). In S 310 , the controller  80  determines the type of suction purge to be performed such that, as the determination signal indicates that a larger number of nozzles  10  are abnormal nozzles, a larger amount of ink is discharged in the suction purge. 
     Subsequently, the controller  80  executes a flushing process as in S 208  (S 311 ), and then executes a purge process (S 312 ). In the purge process of S 312 , the controller  80  performs the suction purge determined in S 310 . After the purge process of S 312  is completed, the flow returns to the flow of  FIG. 5A . 
     In the present embodiment, the inkjet head  4  for flushing and the maintenance unit  8  for performing the suction purge correspond to “recovery device” In the present embodiment, the combination of flushing and suction purge corresponds to “recovery operation”, and among them, the flushing corresponds to “first part of the recovery operation”, and the suction purge corresponds to “second part of the recovery operation excluding the first part”. 
     &lt;Control During Recording&gt; 
     Next, the control when the printer  1  performs recording on the recording sheet P will be described. When the printer  1  receives a recording instruction (“ejection instruction”) instructing to perform recording on the recording sheet P, the controller  80  performs processing according to the flow of  FIG. 8 . 
     The flow of  FIG. 8  will be described in more detail. The controller  80  first executes a sheet feeding process (S 401 ). In the sheet feeding process, the controller  80  controls a sheet feeding mechanism (not shown) and the conveyance motor  87  to supply the recording sheet P to the sheet feeding mechanism, and controls the conveyance rollers  6  and  7  to convey the recording sheet P to a position where an area in which an image is recorded in the first recording pass of the recording sheet P faces the plurality of nozzles  10  of the inkjet head  4 . 
     Subsequently, the controller  80  executes a recording pass process (S 402 ). In the recording pass process, the controller  80  controls the carriage motor  86  to move the carriage  2  in the scanning direction, and controls the driver IC  89  to drive the plurality of driving elements  22   a , thereby performing a recording pass of causing the inkjet head  4  to eject ink from the plurality of nozzles  10  toward the recording sheet P. 
     Subsequently, when the recording on one recording sheet P is not completed (S 403 : NO), the controller  80  executes a conveyance process (S 404 ) and returns to S 402 . In the conveyance process, the controller  80  controls the conveyance motor  87  to cause the conveyance rollers  6  and  7  to convey the recording sheet P by a particular distance. 
     When the recording of an image on one recording sheet P is completed (S 403 : YES), the controller  80  executes a sheet discharging process (S 405 ) and increments the value of the variable C by one (S 406 ). In the sheet discharging process of S 405 , the controller  80  controls the conveyance motor  87  to cause the conveyance rollers  6  and  7  to discharge the recording sheet P for which recording has been completed. 
     When recording data for recording on the next recording sheet P exists (S 407 : YES), the process returns to S 401 . If no recording data exists (S 407 : NO) and the value of the variable C is less than a particular value Ct (S 408 : NO), the process ends. 
     When the value of the variable C is larger than or equal to the particular value Ct (S 408 : YES), the controller  80  executes the processes of S 409  to S 415  as in S 306  to S 312 , and ends the process. 
     &lt;Effects&gt; 
     Here, a case will be considered in which, when the inspection driving is performed in response to receiving a time signal indicating that the time is a particular time, and the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle exists, the recovery operation is immediately performed. In this case, if the period elapsed from the reception of the time signal indicating that the time is the particular time to the reception of the power-on signal is long, the viscosity of ink in the inkjet head  4  may increase during this period. In this case, it is necessary to perform the recovery operation again when the power-on signal is received, and as a result, the ink is wastefully discharged by the recovery operation performed when the time signal indicating that the time is the particular time is received. 
     In the present embodiment, when the time signal indicating that the time is the particular time is received, the inspection driving is performed, and the flag information is stored when the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle exists. After that, when the power-on signal is received, the recovery operation is performed when the flag information is stored. As a result, even when the period elapsed from the reception of the time signal indicating that the time is the particular time to the reception of the power-on signal is long, the wasteful ink discharge as described above is not performed. 
     When the inspection driving is performed at a particular time, for example, the particular time is desirably a time zone such as nighttime when the user is unlikely to use the printer  1 . However, even a small sound is noisy at night, so if the recovery process is executed immediately after the inspection driving, it may become noisy. Thus, the noise problem is solved by performing the recovery process at the timing when the power-on signal is received when the user uses the printer  1 , without performing the recovery process immediately after the inspection driving. 
     In the present embodiment, when the time signal indicating that the time is the particular time is received, the inspection driving is performed, and the type information of suction purge is stored based on the determination signal output from the determination circuit  78  during the inspection driving. After that, when the power-on signal is received, if the flag information is stored, the suction purge of the stored type information is performed. As a result, an appropriate suction purge is performed depending on the number of abnormal nozzles and so on. 
     In the present embodiment, when a time signal indicating that the time is the particular time is received, the inspection driving is performed, and the flushing which is a part of the recovery operation is performed when the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle exists. After that, when the power-on signal is received, the suction purge, which is the second part of the recovery operation excluding the first part, is performed. As a result, the time required for the recovery operation performed when the power-on signal is received is shortened. 
     As described above, when the particular time is set in a time zone such as nighttime, the user may feel noise even if the sound is small. When comparing purging that drives the suction pump  72  and flushing that does not drive the suction pump  72  as a recovery operation, the purging that drives the suction pump  72  is louder than the flushing that does not drive the suction pump  72 . Thus, only flushing is performed at a particular time (immediately after the inspection driving). As a result, the user is less likely to feel noise. 
     In the present embodiment, since the inspection driving is performed at a particular time, for example, the inspection driving is performed at a time when the user does not frequently use the printer  1 . The time when the user does not use the printer  1  frequently is, for example, nighttime, lunch break time, early morning, and so on. The user may set the particular time according to the usage cycle. 
     When recording is performed on a large number of recording sheets P, paper dust generated from the recording sheets P may gather in the nozzle  10  and an abnormal nozzle may occur. In the present embodiment, the inspection driving is performed again when the number of recording sheets P recorded by the inkjet head  4  reaches a particular number after the last inspection driving is performed last time (when C≥Ct is satisfied). As a result, an abnormal nozzle is accurately grasped. 
     In the present embodiment, when the number of recording sheets P recorded by the inkjet head  4  reaches a particular number during recording on a plurality of recording sheets P, the inspection driving is performed again after the recording on all the plurality of sheets P is completed. As a result, recording is not interrupted even if the number of recording sheets P recorded by the inkjet head  4  reaches the particular number during recording on a plurality of recording sheets P. 
     When the temperature of the inkjet head  4  changes greatly, the viscosity of the ink in the nozzle  10  may change, and the state of whether the nozzle is abnormal may change. Thus, in the present embodiment, the inspection driving is performed again when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is different from the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving was performed last time. As a result, the abnormal nozzle is accurately grasped. 
     When the printer  1  is unplugged at a particular time and power is supplied from the battery  66  to the controller  80 , the inspection process is executed, but the inspection driving is not performed. When the battery  66  is out of power, the inspection process is not executed even at the particular time, and naturally, the inspection driving is not performed. 
     Thus, in the present embodiment, at the time of reception of the power-on signal, in a case where the inspection driving is not performed at the last particular time before the reception of the power-on signal, the inspection driving is performed. As a result, an abnormal nozzle is grasped and the necessary recovery operation is performed. 
     &lt;Modifications&gt; 
     While the disclosure has been described in detail with reference to the above aspects thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the claims. 
     In the above-described embodiment, the controller  80  executes the process B when the power-on signal is received in the standby state, but this disclosure is not limited to this. 
     In a first modification shown in  FIG. 9 , the controller  80  stands by while the time signal received from the clock  68  does not indicate a particular time (S 101 : NO), the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is the same as the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed last time (S 102 : NO), and a recording instruction is not received (S 501 : NO). 
     As in the above-described embodiment, the controller  80  executes the process A (S 104 ) when the time signal received from the clock  68  indicates that the time is the particular time (S 101 : YES), or when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is different from the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed last time (S 102 : YES). 
     When the recording instruction is received (S 501 : YES), and the received recording instruction is the recording instruction received first after the process A including the inspection process is executed in response to reception of the time signal indicating that the time is the particular time (S 502 : YES), the process B is executed (S 105 ) similarly to the above-described embodiment, and then the recording process is executed (S 503 ). If the received recording instruction is not the recording instruction received first after the process A including the inspection process is executed in response to reception of the time signal indicating that the time is a particular time (S 502 : NO), the recording process is executed (S 503 ) without executing the process B. The recording process of S 503  is the same process as S 401  to S 415  of the above-described embodiment. 
     In the first modification, the time signal indicating that the time is the particular time corresponds to the “first signal”, as in the above-described embodiment. In the first modification, the recording instruction received first after the process A including the inspection process is executed in response to receiving the time signal indicating that the time is a particular time corresponds to the “second signal”. 
     In the first modification, since the suction purge is performed immediately before recording on the recording sheet P, ink will not be wastefully discharged even if the period elapsed from the reception of the time signal indicating that the time is the particular time to the reception of the recording instruction is long. 
     When the printer  1  is unplugged at a particular time and power is supplied from the battery  66  to the controller  80 , the inspection process is executed, but the inspection driving is not performed. When the battery  66  is out of power, the inspection process is not executed even at a particular time, and naturally, the inspection driving is not performed. 
     Thus, in this modification, at the time of reception of the recording instruction, in a case where the inspection driving is not performed at the last particular time before the reception of the recording instruction, the inspection driving is performed. As a result, an abnormal nozzle is grasped. 
     In a second modification shown in  FIG. 10 , the controller  80  stands by while the power-on signal is not received (S 601 : NO), the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is the same as the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed last time (S 102 : NO), and a recording instruction is not received (S 501 : NO). 
     The controller  80  executes the process A (S 104 ) when the power-on signal is received (S 601 : YES), or when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is different from the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed last time (S 102 : YES). When the recording instruction is received (S 501 : YES), the processes of S 502 , S 105 , and S 503  are executed as in the first modification. 
     In the second modification, ink will not be wastefully discharged even if the period elapsed from the reception of the power-on signal to the reception of the recording instruction is long. 
     In the second modification, the power-on signal corresponds to the “first signal”. In the second modification, as in the first modification, the recording instruction received first after the process A including the inspection process is executed in response to receiving the time signal indicating that the time is a particular time corresponds to the “second signal”. 
     In the first and second modifications, the controller  80  executes the process B when the recording instruction is received first after the process A including the inspection process is executed in response to receiving the first signal (the time signal indicating that the time is a particular time of the first modification and the power-on signal of the second modification). This disclosure is not limited to this. For example, the printer  1  may selectively perform either low image quality recording or high image quality recording, and the process B may be executed when a recording instruction instructing to perform high image quality recording is first received after the process A including the inspection process is executed in response to the first signal. 
     In the above-described embodiment, the process A is also executed when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  is different from the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  when the inspection driving is performed last time. This disclosure is not limited to this. The process A may not be executed when the temperature range including the temperature indicated by the temperature signal received from the temperature sensor  67  has changed. 
     In the above-described embodiment, during recording on a plurality of recording sheets P, in a case where the number of recorded recording sheets P after the last inspection driving reaches a particular number (C≥Ct) after recording on all the recording sheets P is completed, the inspection driving is performed. This disclosure is not limited to this. 
     For example, when a relationship C≥Ct is satisfied in the middle of recording on a plurality of recording sheets P, the recording may be interrupted and the inspection driving may be performed. 
     Alternatively, the inspection driving based on the number of recording sheets P recorded after the last inspection driving was performed may not be performed. 
     In the above-described embodiment, flushing is performed as a part of the recovery operation when the determination signal output from the determination circuit  78  during the inspection driving that is performed at a particular time indicates that an abnormal nozzle exists. After that, when the power is turned on, suction purge is performed as the second part excluding the first part of the recovery operation. However, this disclosure is not limited to this. 
     For example, when the recovery operation is suction purge and the determination signal output from the determination circuit  78  during the inspection driving that is performed at a particular time indicates that an abnormal nozzle exists, a part of the suction purge may be performed as a part of the recovery operation. After that, when the power is turned on, the remaining part of the suction purge may be performed as the second part excluding the first part of the recovery operation. 
     Alternatively, when the recovery operation is flushing and the determination signal output from the determination circuit  78  during the inspection driving that is performed at a particular time indicates that an abnormal nozzle exists, a part of the flushing may be performed as a part of the recovery operation. After that, when the power is turned on, the remaining part of flushing may be performed as the second part excluding the first part of the recovery operation. 
     When the determination signal output from the determination circuit  78  during the inspection driving that is performed at a particular time indicates that an abnormal nozzle exists, a part of the recovery operation may not be performed. For example, when the determination signal output from the determination circuit  78  during the inspection driving that is performed at a particular time indicates that an abnormal nozzle exists, a part of the recovery operation may not be performed, and then the entirety of the recovery operation (flushing and/or purge) may be performed when the power is turned on. 
     In the above-described embodiment, the type information of suction purge is stored in the flash memory  84  and the type of suction purge is determined based on the determination signal output from the determination circuit  78  during the inspection driving, but this disclosure is not limited to this. For example, when the determination signal output from the determination circuit  78  during the inspection driving indicates that an abnormal nozzle exists, a single (one type) suction purge may be performed in the subsequent purge process. 
     In the above-described embodiment and the first modification, when the inspection driving is not performed when the process A including the inspection process is executed in response to receiving the time signal indicating that the time is a particular time, the inspection driving is subsequently performed in the process B that is executed when the power-on signal is received. In the second modification, in a case where the inspection driving is not performed when the process A including the inspection process is executed in response to receiving the power-on signal, the inspection process is subsequently executed in the process B that is executed when the recording instruction is received. However, this disclosure is not limited to this. 
     In a case where the inspection driving is not performed when the inspection process is executed in response to receiving the first signal (the time signal indicating that the time is a particular time in the above-described embodiment and the first modification and the power-on signal in the second modification), the inspection process may not be subsequently executed in response to receiving the second signal (the power-on signal in the above-described embodiment and the first modification and the recording instruction in the second modification). In this case, since the flag information is not stored in the flash memory  84  when the second signal is received, the recovery operation is not performed. 
     In the above-described embodiment, all the nozzles  10  of the inkjet head  4  are driven for inspection, but this disclosure is not limited to this. For example, the inspection driving may be performed only on some nozzles  10  of the inkjet head  4  such as every other nozzles  10  in each nozzle array  9 , and it may be estimated for the other nozzles  10  whether it is an abnormal nozzle based on the determination signal output from the determination circuit  78  during the inspection driving. 
     The controller  80  stores the information itself indicating the type of suction purge to be performed as the type information in the flash memory  84 , but this disclosure is not limited to this. For example, information for determining the type of suction purge, such as the number of abnormal nozzles and the positions of abnormal nozzles, may be stored as the type information. 
     In the above-described embodiment, the determination circuit  78  outputs a signal indicating whether the nozzle  10  is an abnormal nozzle depending on the potential of the detection electrode  76  when ink is ejected from the nozzle  10  toward the detection electrode  76 . However, the method is not limited to this. 
     For example, a detection electrode extending in the vertical direction may be arranged, and a determination circuit may output a signal indicating whether the nozzle is an abnormal nozzle depending on the potential of the detection electrode when ink is ejected from the nozzle  10  so as to pass through the region facing the detection electrode. Alternatively, an optical sensor (“signal output circuit” of this disclosure) for detecting the ink ejected from the nozzle  10  may be provided, and the optical sensor may output a signal indicating whether the nozzle is an abnormal nozzle. 
     Alternatively, for example, as described in Japanese Patent No. 4929699, a voltage detection circuit for detecting a change in voltage when ink is ejected from a nozzle (“signal output circuit” of this disclosure) may be connected to a plate of the inkjet head in which nozzles are formed, and the voltage detection circuit may output, to the controller  80 , a signal indicating whether the nozzle is an abnormal nozzle. 
     Alternatively, for example, as described in Japanese Patent No. 6231759, the control board of the inkjet head may be provided with a temperature detection element (“signal output circuit” of this disclosure). After applying a first applied voltage to drive the heater for ink ejection, a second applied voltage may be applied to drive the heater so that ink is not ejected, and thereafter a signal indicating whether the nozzle  10  is an abnormal nozzle may be output based on the change in temperature detected by the temperature detection element until a particular time elapses. 
     In the above example, the nozzle  10  from which ink is not ejected is determined to be an abnormal nozzle, but the present disclosure is not limited to this. For example, a signal output circuit for outputting a signal indicating whether the ink ejection direction from the nozzle  10  is normal may be provided, and a nozzle  10  having an abnormality in the ejection direction may be determined to be an abnormal nozzle based on the signal from the signal output circuit. 
     In the above example, a suction purge is performed in the purging process, but the present disclosure is not limited to this. For example, a pressure pump may be provided in the middle of the tube  15  that connects the sub tank  3  and the ink cartridge  14 . Alternatively, the printer may be provided with a pressure pump connected to an ink cartridge. In a state where the plurality of nozzles  10  are covered with the cap  71 , the pressure pump may be driven to pressurize ink in the inkjet head  4  and discharge the ink in the inkjet head  4  from the nozzles  10 , which is so-called a pressure purge. 
     Further, in the purge process, both suction by the suction pump  72  and pressurization by the pressure pump may be performed. 
     In the above example, the present disclosure is applied to a printer provided with a so-called serial head, which ejects ink from a plurality of nozzles while moving in the scanning direction together with the carriage, but the present disclosure is not limited to this. For example, this disclosure may be applied to a printer provided with a so-called line head extending over the entire length of the recording sheet P in the scanning direction. 
     In the above example, the present disclosure is applied to a printer that ejects ink from nozzles and records on a recording sheet P, but the present disclosure is not limited to this. This disclosure may also be applied to a printer that records an image on a recording medium other than a recording sheet, such as a T-shirt, a sheet for outdoor advertising, a case of a mobile terminal such as a smartphone, a corrugated cardboard, and a resin member. This disclosure may also be applied to a liquid ejection apparatus that ejects liquid other than ink, for example, a liquefied resin or metal.