Patent Publication Number: US-11654688-B2

Title: Printing apparatus, and ink residual amount control method

Description:
The present application is based on, and claims priority from JP Application Serial Number 2020-048929, filed Mar. 19, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a printing apparatus, and an ink residual amount control method. 
     2. Related Art 
     In the related art, a printing apparatus controls a residual amount of ink retained in an ink retaining unit such as an ink cartridge, and outputs a warning when an ink residual amount is reduced. 
     For example, an ink residual amount detection device of an inkjet printer disclosed in JP 6-320751 A, upon starting dot formation, counts up the number of times of discharging ink from an inkjet head. When the inkjet head stops after the termination of the dot formation, the ink residual amount detection device calculates an ink consumption amount by integrating an ink consumption amount for one dot and the count up number of times of discharging ink together. 
     Unfortunately, when ink clogging occurs in a nozzle that discharges ink, the ink is not discharged from the nozzle in which the ink clogging occurred. As a result, there is an issue in that a correct control of ink residual amount cannot be achieved. 
     SUMMARY 
     An aspect of resolving the above-described issue is a printing apparatus that includes an ink retaining unit, a head including a nozzle row formed by a plurality of nozzles arranged side by side, and configured to discharge ink from the nozzles based on image data to form an image on a printing medium, the ink being supplied from the ink retaining unit, an ink residual amount control unit configured to control a residual amount of the ink retained in the ink retaining unit, a nozzle inspection unit configured to inspect nozzle clogging of the nozzle, a discharged dot count unit configured to count a number of times a discharge signal is transmitted to the nozzle, provided that a discharge signal is transmitted to the nozzle once corresponding to one dot of the image data transmitted, and a storage unit configured to store ink residual amount-related information containing an ink consumption amount for one dot and used to calculate the residual amount of the ink retained in the ink retaining unit, in which the ink residual amount control unit is configured to calculate an ink consumption amount based on the number of times the discharge signal is transmitted counted by the discharged dot count unit and the ink consumption amount for one dot, to update the residual amount of the ink retained in the ink retaining unit, and to remove a nozzle determined to be clogged in the inspection of the nozzle clogging by the nozzle inspection unit, from nozzles for which the ink consumption amount is calculated nozzle determined to be clogged. 
     Another aspect of resolving the above-described issue is an ink residual amount control method for a printing apparatus configured to discharge ink supplied from an ink retaining unit from a nozzle based on image data to form an image on a printing medium, the method including a control step for controlling a residual amount of the ink retained in the ink retaining unit, and an inspection step for inspecting whether nozzle clogging occurred in the nozzle, in which the control step includes counting, provided that a discharge signal is transmitted to the nozzle once corresponding to one dot of the image data, a number of times the discharge signal is transmitted to the nozzle corresponding to one dot of the image data, calculating an ink consumption amount based on the counted number of times the discharge signal is transmitted and an ink consumption amount for one dot, updating the residual amount of the ink retained in the ink retaining unit, and removing the nozzle determined to be clogged by the inspection of the nozzle clogging by the inspection step from the nozzles targeted for calculating the ink consumption amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating a configuration of a printing apparatus in a first embodiment. 
         FIG.  2    is a view illustrating a configuration of a printing head. 
         FIG.  3    is a flowchart illustrating an operation of a printing apparatus. 
         FIG.  4    is a block diagram illustrating a configuration of a printing apparatus in a second embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure are described with reference to the accompanying drawings. 
       FIG.  1    is a block diagram illustrating a configuration of a printing apparatus  1 . 
     The printing apparatus  1  is communicatively connected to a host computer and implements a print job received from the host computer. The print job is a group of data that include commands instructing printing on the printing apparatus  1  and data of images and texts to be printed. The printing apparatus  1  generates print data based on the received print job, and performs printing of an image based on the generated print data on a printing medium P illustrated in  FIG.  2   . 
     The printing apparatus  1  includes a communication unit  3 , an operation unit  5 , a display  7 , a printing unit  10 , an ink retaining unit  60 , a head driver  70 , a nozzle inspection unit  80 , a motor driver  90 , and a control unit  100 . 
     The communication unit  3  executes, in accordance with a control of the control unit  100 , data communication with the host computer in accordance with a predetermined communication standard, and receives the print job. The communication unit  3  outputs the received print job to the control unit  100 . The control unit  100 , upon being input with the print job, generates print data in a storage unit  110  based on the input print job. The control unit  100  outputs the generated print data to the head driver  70 . 
     The operation unit  5  is an acceptance unit that accepts a user operation. The operation unit  5  includes an operation switch, an operation button, and the like, and outputs an operation signal corresponding to the operation switch and the operation button that are operated to the control unit  100 . 
     The display  7  includes a display screen such as a liquid crystal panel, and displays various types of information in accordance with the control of the control unit  100 . The display  7  corresponds to a user interface of the present disclosure. 
     The printing unit  10  includes a carriage  20 , a discharged dot count unit  30 , a scanning motor  40 , and a transport motor  50 . 
       FIG.  2    is a view schematically illustrating a nozzle face  13  of a printing head  25  and the printing medium P. 
     The carriage  20  is attached to a non-illustrated guide shaft extending in a main scanning direction D 1  that is a width direction of the printing medium P. The carriage  20  also reciprocally moves, by a power of the scanning motor  40 , in the main scanning direction D 1  that is a direction in which the guide shaft extends. The printing head  25  is mounted on the carriage  20 , and as the carriage  20  moves, the printing head  25  also moves in the main scanning direction D 1 . 
     In the printing head  25 , four nozzle rows  11 K,  11 C,  11 M, and  11 Y in each of which a plurality of nozzles are formed side by side are arranged side by side in a sub scanning direction D 2 . In the first embodiment, four color inks of black, cyan, magenta, and yellow are discharged from the nozzle rows  11 K,  11 C,  11 M, and  11 Y, respectively. These four nozzle rows  11 K,  11 C,  11 M, and  11 Y are formed at the nozzle face  13  of the printing head  25 . A plurality of nozzles  15  constituting the respective nozzle rows of the nozzle rows  11 K,  11 C,  11 M, and  11 Y are arranged at predetermined intervals in the main scanning direction D 1 . 
     The printing head  25  discharges, based on image data, ink supplied from the ink retaining unit  60  from the nozzles  15  to form an image on the printing medium P. The nozzle  15  included in the printing head  25  includes a discharge element such as a piezoelectric element. The discharge element allows pressure to be generated inside the nozzle  15  to cause ink inside the nozzle  15  to be discharged. 
     The discharged dot count unit  30  counts the number of ink droplets discharged from the nozzles  15  included in the printing head  25 . Specifically, the discharged dot count unit  30  counts discharge signals output from the head driver  70  to the printing head  25 , to count the number of the ink droplets discharged from each of the nozzles  15 . The discharge signal is a pulse signal that drives the discharge element provided inside the nozzle  15 . The head driver  70  outputs, based on the image data, the discharge signal to the nozzle  15  that discharges the ink droplets. The nozzle  15  is input with the discharge signal from the head driver  70 , then the discharge element is driven to discharge the ink droplets. The discharged dot count unit  30  counts the number of times the discharge signal is input to the nozzle  15  for each of the nozzles  15  provided that the discharge signal is transmitted to the nozzle  15  once corresponding to one dot of the image data. 
     The scanning motor  40  drives the carriage  20  to cause the carriage  20  to scan in the main scanning direction D 1 . The transport motor  50  transports the printing medium P in the sub scanning direction D 2 . 
     The ink retaining unit  60  accommodates a reservoir  61  that retains ink from an ink tank, an ink cartridge, and the like. The ink retaining unit  60  supplies the ink retained in the reservoir  61  to the printing head  25 . The ink supplied from the ink retaining unit  60  is four color ink of cyan, magenta, yellow, and black, for example. The ink retaining unit  60  in the first embodiment does not support ink replenishment, and the reservoir  61  accommodated in the ink retaining unit  60  is replaced when whole of the ink retained in the reservoir  61  is consumed. 
     The head driver  70  is input with the print data. The head driver  70  selects the nozzle  15  that discharges ink based on the input print data, and outputs the discharge signal to the selected nozzle  15 . 
     The nozzle inspection unit  80  inspects whether nozzle clogging has occurred. 
     For example, the printing apparatus  1  is provided with a nozzle inspection mechanism that detects whether the nozzle clogging has occurred. The nozzle inspection mechanism includes an electrode that charges ink discharged from the nozzles  15 . The nozzle inspection mechanism also includes a conductive material in which the ink discharged from the nozzles  15  lands. The nozzle inspection mechanism is also configured such that an electrical signal flowing through the conductive material is output to a predetermined signal processing circuit. Under such a configuration described above, the nozzle inspection unit  80  allows the nozzle  15  targeted to be detected whether the nozzle clogging has occurred to discharge a predetermined amount of ink particles. The discharged ink particles are charged with a predetermined amount of charge by an electrode, to land in the conductive material. In accordance with the landing of the ink particles, a state of a current in the conductive material changes, and a signal indicating an amount of the change is output to the nozzle inspection unit  80  via the predetermined signal processing circuit. When a value indicated by the input signal exceeds a predetermined threshold value, the nozzle inspection unit  80  determines that the nozzle clogging has not occurred for the nozzle on the supposition that an assumed amount of ink has been normally discharged. On the other hand, when the value indicated by the input signal falls below the predetermined threshold value, the nozzle inspection unit  80  determines that the nozzle clogging has occurred for the nozzle on the supposition that the assumed amount of ink has not been normally discharged due to some reasons. 
     Note that a method for detecting whether the nozzle clogging has occurred is not limited to the method described above. For example, ink may be discharged from the target nozzle  15  to form a dot, and the formed dot may be optically read to determine whether the nozzle clogging has occurred in the target nozzle  15 . Also, signal waveforms of a control signal and the like that drive an actuator may be monitored to determine whether the nozzle clogging has occurred. That is, a detection of errors may be implemented using any method as long as the detection whether the nozzle clogging has occurred for each of the nozzles  15  is possible. 
     In addition to the nozzle clogging, the nozzle inspection unit  80  may also inspect nozzle omission that is a state where ink is not normally discharged from the nozzles  15  due to dried ink staying in the nozzle  15 , contamination in the nozzle  15 , or the other reasons. 
     The motor driver  90  drives the scanning motor  40  and the transport motor  50  in accordance with the control of the control unit  100 . 
     The control unit  100  is a computer that includes the storage unit  110  and a processor  130 . The storage unit  110  includes memories such as a ROM and a RAM, and a storage device such as an HDD or an SSD. The processor  130  is configured by a CPU or an MPU. The ROM is an abbreviation for Read Only Memory. The RAM is an abbreviation for Random Access Memory. The HDD is an abbreviation for Hard Disk Drive. The SSD is an abbreviation for Solid State Drive. The CPU is an abbreviation for Central Processing Unit. The MPU is an abbreviation for Micro-Processing Unit. 
     The storage unit  110  stores ink residual amount-related information  115 . 
     The ink residual amount-related information  115  contains an ink initial value and an ink consumption amount for one dot. The ink initial value is an initial value of the ink retained in the reservoir  61 . That is, the ink initial value is an amount of the ink retained in the reservoir  61  that is not yet used. In addition, the ink consumption amount for one dot indicates a weight (ng) of ink per one dot, for example. Further, the ink consumption amount for one dot indicates an average value of sizes of the ink droplets. For example, supposing that the sizes of the ink droplets discharged from the printing head  25  have three sizes that are large, medium and small, the ink consumption amount for one dot is an average value of these three ink droplets of large, medium and small. 
     The control unit  100  materializes various types of functional configurations by the processor  130  executing a computer program stored in the storage unit  110 . The control unit  100  includes, as the functional configurations, an ink residual amount control unit  131 , a flushing control unit  133 , a drive control unit  135 , and a UI control unit  137 . When the detection whether the nozzle clogging has occurred is performed by monitoring the signal waveforms of the control signal and the like that drive the actuator, the control unit  100  may include the nozzle inspection unit  80 . 
     The ink residual amount control unit  131  controls an ink residual amount in the reservoir  61 , and updates the ink residual amount-related information  115  stored in the storage unit  110  based on the ink residual amount. 
     The ink residual amount control unit  131  calculates the ink residual amount in the reservoir  61  by a calculation method A described below. 
     The ink residual amount control unit  131  calculates, by the calculation method A, the ink residual amount in the reservoir  61  according to Formula (1) set out below.
 
Ink Residual Amount=Ink Initial Value−Ink Consumption Amount per One Dot×Cumulative Count Value of Number of Times of Discharging  (1)
 
     The cumulative count value of the number of times of discharging is a count value of the discharged dot count unit  30 , and is a value obtained by cumulating a count value obtained by counting the number of times of discharging from a start of use of the ink in the reservoir  61  after the reservoir  61  that is not yet used is accommodated in the ink retaining unit  60 , until the present time. 
     The ink residual amount control unit  131  also excludes a count value of the nozzles  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80  from a target for calculating an ink consumption amount. That is, the cumulative count value of the number of times of discharging in Formula (1) does not include the count value of the nozzles  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80 . The ink residual amount control unit  131  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred from the count value of all of the nozzles counted by the discharged dot count unit  30  to calculate the number of times of discharging. 
     The ink residual amount control unit  131  may also exclude the nozzle  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80  from a target for counting the discharge signals by the discharged dot count unit  30 . The ink residual amount control unit  131  notifies the discharged dot count unit  30  of information about the nozzle  15  determined that the nozzle clogging has occurred. The discharged dot count unit  30  does not count the discharge signal input to the nozzle  15  notified from the ink residual amount control unit  131 . 
     In addition, the method for calculating the ink residual amount may be a calculation method B or C described below. 
     In the calculation method B, the ink initial value, the ink consumption amount for one dot, and a cumulative ink discharge amount are stored as the ink residual amount-related information  115  in the storage unit  110 . The cumulative ink discharge amount is a value calculated by the ink residual amount control unit  131 , and is calculated by the Formula (2) set out below.
 
Cumulative Ink Discharge Amount=Ink Consumption Amount per One Dot×Cumulative Count Value of Number of times of Discharging  (2)
 
     The ink residual amount control unit  131  allows the storage unit  110  to store the calculated cumulative ink discharge amount as the ink residual amount-related information  115 . 
     As described above, the cumulative count value of the number of times of discharging is a value obtained by cumulating the count value obtained by counting the number of times of discharging from the start of use of the ink in the reservoir  61 , until the present time. Also, as in the calculation method A, the cumulative count value of the number of times of discharging does not include the count value of the nozzles  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80 . The ink residual amount control unit  131  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred from the count value of all of the nozzles counted by the discharged dot count unit  30  to calculate the number of times of discharging. 
     The ink residual amount control unit  131  calculates the ink residual amount based on the ink residual amount-related information  115  stored in the storage unit  110 . The ink residual amount control unit  131  subtracts the cumulative ink discharge amount from the ink initial value to calculate the ink residual amount in the reservoir  61 . 
     That is, the ink residual amount is calculated, by the calculation method B, according to Formula (3) set out below.
 
Ink Residual Amount=Ink Initial Value−Cumulative Ink Discharge Amount  (3)
 
     This calculation method B may also be a modified example described below. In this modified example, a differential ink discharge amount that is a cumulative ink discharge amount from the previous update time is stored as the ink residual amount-related information  115  in the storage unit  110 . The update time is an update time of updating the ink residual amount displayed on a display screen of the display  7 . In the modified example of the calculation method B, the count value of the discharged dot count unit  30  is reset when updating the ink residual amount displayed on the display screen. First, the ink residual amount control unit  131  calculates a differential ink discharge amount. The differential ink discharge amount is calculated according to Formula (4) set out below.
 
Differential Ink Discharge Amount=Ink Consumption Amount per One Dot×Count Value of Number of times of Discharging  (4)
 
     In the above-described Formula (4), the count value of the number of times of discharging is a count value from the time after resetting the discharged dot count unit  30 , until the present time. Also, as in the calculation method A, the count value of the number of times of discharging does not include the count value of the nozzles  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80 . The ink residual amount control unit  131  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred from the count value of all of the nozzles counted by the discharged dot count unit  30  to calculate the number of times of discharging. 
     In addition, in this modified example, the ink residual amount control unit  131  calculates the cumulative ink discharge amount according to Formula (5) set out below.
 
Cumulative Ink Discharge Amount=Cumulative Ink Discharge Amount at Previous Update Time+Differential Ink Discharge Amount  (5)
 
     The cumulative ink discharge amount at the previous update time is the ink residual amount-related information  115  that is stored as the cumulative ink discharge amount in the storage unit  110 . Further, the differential ink discharge amount is a value that is calculated by Formula (4). 
     In this modified example, the ink residual amount control unit  131  calculates the ink residual amount according to Formula (6) set out below.
 
Ink Residual Amount=Ink Initial Value−Cumulative Ink Discharge Amount at Previous Update time−Differential Ink Discharge Amount  (6)
 
     In the calculation method C, the ink residual amount and the ink consumption amount for one dot are stored as the ink residual amount-related information  115  in the storage unit  110 . The ink residual amount is an ink residual amount calculated by the ink residual amount control unit  131 , and the ink residual amount is an ink initial value when the reservoir  61  is not used. 
     The ink residual amount control unit  131  calculates the ink residual amount according to Formula (7) set out below.
 
Ink Residual Amount=Ink Residual Amount at Previous Update Time−Ink Consumption Amount per One Dot×Count Value of Number of times of Discharging  (7)
 
     In the calculation method C as well, the count value of the discharged dot count unit  30  is reset when updating the ink residual amount displayed on the display screen. Thus, the count value of the number of times of discharging is a count value from the time of resetting the count value of the discharged dot count unit  30 , until the present time. Also, as in the calculation method A, the count value of the number of times of discharging does not include the count value of the nozzles  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80 . The ink residual amount control unit  131  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred from the count value of all of the nozzles counted by the discharged dot count unit  30  to calculate the number of times of discharging. 
     The flushing control unit  133  implements a flushing operation every time a predetermined period of time has elapsed or every time an implementation of a preset operation has been completed. The flushing operation is performed to prevent clogging in the nozzle  15  of the printing head  25 . In the flushing operation, the flushing control unit  133  drives the printing head  25  to discharge a predetermined amount of ink from the nozzles  15  of the printing head  25 . Also, the preset operation includes a receiving operation of the print job and a printing operation. The flushing control unit  133 , upon receiving the print job, implements the flushing operation before a start of printing. The flushing control unit  133 , upon completion of the printing of an image by a preset amount of one page, one row, or the like, also implements the flushing operation. 
     When the flushing control unit  133  executes the flushing operation, the ink residual amount control unit  131  causes the nozzle inspection unit  80  to implement the nozzle inspection to detect the nozzle  15  in which the ink clogging has occurred. Subsequently, when the printing is started, the ink residual amount control unit  131  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred from the count value of all of the nozzles counted by the discharged dot count unit  30  to calculate the number of times of discharging. The ink residual amount control unit  131  then calculates the ink residual amount according to any one of the calculation methods A, B, and C described above. 
     In addition, when the nozzle  15  in which the nozzle clogging had occurred is determined that the nozzle clogging has not occurred by the nozzle inspection after the flushing operation, the ink residual amount control unit  131  adds the nozzle  15  in which the nozzle clogging has been resolved to a target for counting the number of times of discharging. The ink residual amount control unit  131  adds the nozzle  15  in which the nozzle clogging has been resolved to the target for counting the number of times of discharging. 
     The drive control unit  135  controls the head driver  70  to allow the printing head  25  to operate. The drive control unit  135  also controls the motor driver  90  to allow the scanning motor  40  and the transport motor  50  to operate. 
     The UI control unit  137  allows the display screen of the display  7  to display the ink residual amount calculated by the ink residual amount control unit  131 . The UI control unit  137  also updates the ink residual amount displayed on the display screen of the display  7  every time a printing of an image by an amount of one row, an amount of a plurality of rows, or an amount of one page is completed. The UI control unit  137  may also update the ink residual amount displayed on the display screen of the display  7  when an operation instructing display of the ink residual amount is accepted by the operation unit  5 , or when the ink residual amount that has been detected becomes not greater than a preset amount of ½, ¼, or the like, or may update the ink residual amount in real time. 
       FIG.  3    is a flowchart illustrating an operation of the control unit  100 . 
     The operation of the control unit  100  will be described with reference to the flowchart illustrated in  FIG.  3   . 
     First, the control unit  100  determines whether the print job has been received from the host computer (step S 1 ). The control unit  100 , when not receiving the print job (step S 1 /NO), waits for a start of the process until receiving the print job. Alternatively, the control unit  100 , when receiving the print job (step S 1 /YES), causes the flushing operation to be implemented before printing is started, and causes the nozzle inspection unit  80  to inspect the nozzle clogging (step S 3 ). 
     The control unit  100  also implements the flushing operation (step S 4 ) and an inspection of the nozzle clogging (step S 5 ) before moving the carriage  20  in the main scanning direction to perform printing. The control unit  100  implements the flushing operation (step S 4 ) and the inspection of the nozzle clogging (step S 5 ) every time an image for one reciprocating operation is printed. 
     The control unit  100 , after implementing the flushing operation (step S 4 ) and the inspection of the nozzle clogging (step S 5 ), moves the carriage  20  in the forward direction of the main scanning and causes the printing medium P to print an image (step S 6 ). 
     Next, the control unit  100  determines whether the printing of the image by the amount of one page has been completed (step S 7 ). When the printing of the image by the amount of one page has not been completed (step S 7 /NO), the control unit  100  proceeds to a processing of step S 12 . 
     Alternatively, when the printing of the image by the amount of one page has been completed (step S 7 /YES), the control unit  100  acquires the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  (step S 8 ). The control unit  100  also subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred in the inspection of step S 5  from the number of times the discharge signal is transmitted. The control unit  100  then calculates, in accordance with Formula (1) described above, an integrated value by integrating the cumulative count value of the number of times of discharging and the ink consumption amount for one dot together, and subtracts the calculated integrated value from the ink initial value to calculate the ink residual amount (step S 9 ). The control unit  100  allows the display  7  to display the calculated ink residual amount (step S 10 ). 
     Next, the control unit  100  determines whether the print job has been terminated (step S 11 ). When the print job has been terminated (step S 11 /YES), the control unit  100  terminates this process flow. Alternatively, when the print job has not been terminated (step S 11 /NO), the control unit  100  proceeds to the processing of step S 12 . Further, in step S 7 , the control unit  100 , when determining that the printing of the image by the amount of one page has not been completed (step S 7 /NO), also proceeds to the processing of step S 12 . 
     In step S 12 , the control unit  100  moves the carriage  20  in the back direction of the main scanning, and causes the printing medium P to print an image (step S 12 ). The control unit  100  then determines whether the printing of the image by the amount of one page has been completed (step S 13 ). When the printing of the image by the amount of one page has been completed (step S 13 /YES), the control unit  100  acquires the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  (step S 14 ). 
     The control unit  100  subtracts the count value of the nozzles  15  determined that the nozzle clogging has occurred in the inspection of step S 5  from the number of times the discharge signal is transmitted acquired in step S 14  to calculate the ink residual amount in accordance with Formula (1) described above (step S 15 ). The control unit  100  allows the display  7  to display the calculated ink residual amount (step S 16 ). Subsequently, the control unit  100  determines whether the print job has been terminated. 
     When the print job has not been terminated (step S 17 /NO), or when the printing of the image by the amount of one page has not been completed in step S 13  (step S 13 /NO), the control unit  100  proceeds to a processing of step S 4  to implement the flushing operation. 
     Alternatively, when the print job has been terminated (step S 17 /YES), the control unit  100  terminates this process flow. 
     In the flowchart described above, steps S 8  and S 9 , steps S 14  and S 15  correspond to the control steps of the present disclosure. Further, steps S 3  and S 5  correspond to the inspection steps of the present disclosure. 
     As described above, the printing apparatus  1  in the first embodiment includes the ink retaining unit  60 , the printing head  25 , the ink residual amount control unit  131 , the nozzle inspection unit  80 , and the storage unit  110 . 
     The printing head  25  includes a nozzle row  11  in which the plurality of nozzles  15  are formed side by side, and is configured to discharge, from the nozzles  15 , the ink supplied from the ink retaining unit  60  based on the image data to form an image on the printing medium P. 
     The ink residual amount control unit  131  is configured to control a residual amount of the ink retained in the ink retaining unit  60 . 
     The nozzle inspection unit  80  is configured to inspect nozzle clogging of the nozzle  15 . 
     The discharged dot count unit  30  is configured to count the number of times the discharge signal is transmitted to the nozzle  15 , provided that the discharge signal is transmitted to the nozzle  15  once corresponding to one dot of the image data. 
     The storage unit  110  is configured to store the ink residual amount-related information  115  containing the ink consumption amount for one dot and used to calculate the residual amount of the ink retained in the ink retaining unit  60 . 
     The ink residual amount control unit  131  is configured to calculate the ink consumption amount based on the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  and the ink consumption amount for one dot, and to update the residual amount of the ink retained in the ink retaining unit  60 . 
     The ink residual amount control unit  131  is also configured to remove the nozzle  15  determined that the nozzle clogging has occurred by the inspection of the nozzle clogging by the nozzle inspection unit from the nozzles  15  targeted for calculating the ink consumption amount. 
     This makes it possible to enhance an accuracy of calculating the ink consumption amount, and to more accurately control the ink residual amount of the ink retaining unit  60 . 
     The discharged dot count unit  30  is configured, when the nozzle inspection unit  80  inspects the nozzle clogging, to count the number of times the discharge signal is transmitted, excluding the nozzle  15  determined that the nozzle clogging has occurred by the inspection of the nozzle clogging from the nozzles  15  targeted for counting the number of times of the discharge signals. 
     This makes it possible to accurately calculate the number of times of the discharge signals with which the ink has been consumed, enhancing the accuracy of calculating the ink consumption amount. 
     The ink residual amount control unit  131  is configured to subtract the number of times of the discharge signals transmitted to the nozzle determined that the nozzle clogging has occurred from the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  to calculate the number of times the discharge signal is transmitted. 
     This makes it possible to accurately calculate the number of times of the discharge signals with which the ink has been consumed, enhancing the accuracy of calculating the ink consumption amount. 
     The discharged dot count unit  30  is configured, when the nozzle  15  determined that the nozzle clogging has occurred by the nozzle inspection unit  80  and excluded from a target for counting the discharge signals is determined that the nozzle clogging has not occurred by the nozzle inspection unit  80 , to add the nozzle  15  to the target for counting the discharge signals. 
     Thus, even the nozzle  15  once determined that the nozzle clogging has occurred is added to the target for counting the discharge signals when the nozzle clogging is resolved, thus making it possible to accurately calculate the number of times of the discharge signals with which the ink has been consumed. This makes it possible to enhance the accuracy of calculating the ink consumption amount. 
     The nozzle inspection unit  80  is configured to inspect the nozzle clogging before printing is started. 
     This makes it possible to enhance the accuracy of determining the nozzle  15  that cannot be used in printing. 
     The printing apparatus  1  also includes the flushing control unit  133  configured to cause the printing head  25  to discharge the ink to execute flushing processing of the head. 
     The nozzle inspection unit  80  is configured to inspect the nozzle clogging every time the flushing control unit  133  executes the flushing processing. 
     This makes it possible to detect the nozzle  15  in which the nozzle clogging has been resolved by flushing. 
     The printing apparatus  1  includes the display  7  configured to display the residual amount of the ink retained in the ink retaining unit  60 , and the UI control unit  137  configured to update display information of the display  7  based on the ink residual amount-related information  115 . 
     The UI control unit  137  is configured to update the display information of the display  7  every time printing for one page is completed. 
     This enables the display  7  to display a ink residual amount at every time the printing for one page is completed. 
     The ink residual amount-related information  115  contains information indicating the residual amount of the ink retained in the ink retaining unit  60 . The ink residual amount control unit  131  is configured to subtract the ink consumption amount calculated based on the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  and the ink consumption amount for one dot, from the residual amount of the ink retained in the ink retaining unit  60  indicated by the ink residual amount-related information  115 , and to update the residual amount of the ink retained in the ink retaining unit  60 . 
     This makes it possible to accurately calculate the ink consumption amount by a simple operation, to update the ink residual amount. 
     The ink residual amount-related information  115  also contains an initial value of an amount of the ink retained in the ink retaining unit  60 , and a cumulative value of the ink consumption amount from a start of use of the ink retaining unit  60 . 
     The ink residual amount control unit  131  is configured to add the ink consumption amount calculated based on the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  and the ink consumption amount for one dot, and to the cumulative value of the ink consumption amount from the start of use of the ink retaining unit  60 . This makes it possible to update the cumulative value of the ink consumption amount from the start of use of the ink retaining unit  60 . 
     The ink residual amount control unit  131  is also configured to subtract the updated cumulative value of the ink consumption amount from the start of use of the updated ink retaining unit  60  from the initial value of the amount of the ink retained in the ink retaining unit  60 , and to update the residual amount of the ink retained in the ink retaining unit  60 . 
     This makes it possible to accurately calculate the ink consumption amount by a simple operation, to update the ink residual amount. 
     The ink residual amount-related information  115  further contains the initial value of the amount of the ink retained in the ink retaining unit  60 . 
     The ink residual amount control unit  131  is configured to subtract the ink consumption amount calculated based on the number of times the discharge signal is transmitted counted by the discharged dot count unit  30  and the ink consumption amount for one dot, from the initial value of the amount of the ink retained in the ink retaining unit  60  indicated by the ink residual amount-related information  115 , and to update the residual amount of the ink retained in the ink retaining unit  60 . 
     This makes it possible to accurately calculate the ink consumption amount by a simple operation, to update the ink residual amount. 
     Second Embodiment 
     The second embodiment of the present disclosure is described below with reference to the accompanying drawings. 
       FIG.  4    is a block diagram illustrating a configuration in the second embodiment. 
     The second embodiment is configured to refill the ink in the reservoir  61  of the ink retaining unit  60 , and the other configurations are the same as those in the first embodiment. 
     The ink retaining unit  60  in the second embodiment includes a refill port to which an ink refill container  65  can be coupled. The ink refill container  65  is coupled to the refill port so that the ink filled inside the ink refill container  65  is refilled in the reservoir  61  of the ink retaining unit  60 . When the ink refill container  65  is used to refill the ink in the reservoir  61 , the ink is refilled so that an ink amount in the reservoir  61  becomes fully filled. 
     As in the first embodiment, the storage unit  110  in the second embodiment stores the ink initial value and the ink consumption amount for one dot as the ink residual amount-related information  115 , where the ink initial value in the second embodiment indicates an ink amount when the ink amount in the reservoir  61  is fully filled. 
     The ink residual amount control unit  131  in the second embodiment also calculates the ink residual amount by the calculation method A described in the first embodiment. When the reservoir  61  is refilled with the ink, the control unit  100  resets the count value of the discharged dot count unit  30 , and changes the ink initial value to the ink amount when the reservoir  61  is fully filled. 
     The ink residual amount control unit  131  in the second embodiment can also calculate the ink residual amount by the calculation method B described in the first embodiment. In this case as well, when the ink refill container  65  is used to refill the ink retaining unit  60 , the ink is refilled so that the ink amount in the reservoir  61  becomes fully filled. 
     In the calculation method B, the information stored as the ink residual amount-related information  115  in the storage unit  110  contains the ink initial value, the ink consumption amount for one dot, and the cumulative ink discharge amount. The ink residual amount control unit  131  resets the cumulative ink discharge amount and the count value of the discharged dot count unit  30  when the ink has been refilled in the ink retaining unit  60 . In addition, the control unit  100  changes the ink initial value to the ink amount when the reservoir  61  is fully filled. 
     The ink residual amount control unit  131  in the second embodiment can also calculate the ink residual amount by the calculation method C described above. In this case as well, when the ink refill container  65  is used to fill the ink retaining unit  60 , the ink is refilled so that the ink amount in the reservoir  61  becomes fully filled. 
     When the ink is refilled in the ink retaining unit  60 , the control unit  100  resets the count value of the discharged dot count unit  30  stored as the ink residual amount-related information  115  in the storage unit  110 . The control unit  100  also changes the ink residual amount stored as the ink residual amount-related information  115  in the storage unit  110  to the ink amount when the reservoir  61  is fully filled. 
     Also, when the ink refill container  65  is used to refill the ink, the amount of the ink to be refilled may be optionally changed. In this case, an ink refill port of the ink retaining unit  60  is provided with a detection unit  63  configured to detect a refill amount of the ink refilled from the ink refill container  65 , to thus detect an amount of the ink refilled by the detection unit  63 . The detection unit  63  is configured to detect a refilled ink amount based on a coupling time during which the ink refill container  65  is coupled to the refill port, for example. The detection unit  63  may also include a rotation body at a flow path coupling the ink refill container  65  with the ink retaining unit  60 , and may be configured to detect a rotation amount of the rotation body to detect the refilled ink amount. Alternatively, the ink retaining unit  60  may not be provided with the detection unit  63  or the like, and the user may operate the operation unit  5  to input the ink amount that has been refilled in the ink retaining unit  60 . Further, a timing of refilling the ink to the ink retaining unit  60  includes various timings, such as a timing when the printing apparatus  1  waits for printing or when the ink residual amount becomes zero during printing. The detection unit  63  corresponds to a refill amount acquisition unit of the present disclosure. 
     For example, when the ink residual amount is calculated by the calculation method C, the control unit  100 , when detecting that the ink residual amount becomes zero, allows the display  7  to display a guide notifying that the ink residual amount becomes zero. The control unit  100  also changes the ink residual amount stored as the ink residual amount-related information  115  in the storage unit  110  to zero. Subsequently, when the ink refill container  65  is used to refill the ink, the control unit  100  adds the refilled ink amount to the ink residual amount stored in the storage unit  110 , and stores the calculated value in the storage unit  110 . 
     Thus, even when the ink is refilled in the ink retaining unit  60 , the residual amount of the ink retained in the ink retaining unit  60  can be calculated with high accuracy. 
     Each of the embodiments described above merely illustrates a specific example to which the present disclosure is applied. The present disclosure is not limited to the configurations in the embodiments described above, and can be implemented in various aspects without departing from the gist of the disclosure. 
     For example, in the flowchart illustrated in  FIG.  3   , the ink residual amount is displayed on the display  7  at a timing at which the printing of the image for one page is completed, and the ink residual amount is updated as well. In addition, the timing of the display and the update of the ink residual amount may also be a timing at which one print job is terminated, or a timing at which the ink residual amount is reduced to an amount not greater than a preset amount after an operation of powering off a power source is input, immediately after the printing apparatus  1  is powered on, for example. 
     For example, each of the components of the printing apparatus  1  illustrated in  FIG.  1    is an example, and specific implementation aspects are not particularly limited. That is, hardware that individually corresponds to each of the components is not necessarily implemented, and a configuration is possible as a matter of course in which a single processor executes a program to enable function of each of the components. In addition, in the above-described embodiments, some of the functions enabled by software may be enabled by hardware, or some of the functions enabled by the hardware may be enabled by the software. 
     Further, a step unit in the flowchart illustrated in  FIG.  4    is obtained by dividing processing in accordance with a main processing content in order to facilitate the understanding of the operations of the printing apparatus  1 . Thus, the present disclosure is not limited by a method for dividing the processing into processing units and a name. The processing may be divided into more step units depending on a processing content. Also, one step unit may be divided so as to contain furthermore processings. Further, the order of the steps may be transposed as appropriate in a range where the gist of the present disclosure is not hindered.