Patent Publication Number: US-2021170751-A1

Title: Image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon, and claims the benefit of priority from, corresponding Japanese Patent Application No. 2019-221149 filed in the Japan Patent Office on Dec. 6, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Field of the Invention 
     The present disclosure relates to an image forming apparatus that discharges ink and performs printing. 
     Description of Related Art 
     An ink jet type image forming apparatus discharges ink and performs printing. The ink jet type image forming apparatus may measure ink consumption. 
     An image forming apparatus may include a plurality of control boards (controller). In a large image forming apparatus or a multifunctional image forming apparatus, it may be difficult to control all members with only one control board. In such an image forming apparatus, a plurality of control boards are often provided. A CPU and a memory are provided in each control board. Each control board has a different role and a different process. For example, a control board in charge of ink discharge control and a control board (control board in charge of management) for calculating ink consumption are provided separately. 
     Conventionally, the actual number of ink discharges of a head is counted, and the number of counted discharges is multiplied by the amount of ink per discharge to obtain ink consumption. When the control board in charge of ink discharge control and the control board for calculating the ink consumption are different, in order to obtain the ink consumption on the basis of the count value of the actual number of discharges, a large amount of data must be frequently exchanged between the control boards for each page. However, there is data to be exchanged other than the data for calculating the ink consumption. Frequent exchange of many data has the problem that it may interfere with high-speed processing. For example, communication between control boards may be delayed and a print process may take a long time. 
     SUMMARY 
     An image forming apparatus according to the present disclosure includes a head, a first controller, and a second controller. The head includes a plurality of nozzles. The head discharges ink from the nozzle. The first controller manages a print job using the head. The first controller calculates the amount of the ink used in the print job. The second controller controls ink discharge at the head on a basis of an instruction of the first controller. When calculating the amount of the ink used, the first controller obtains an estimated number of discharges, which is the number of dots of the ink to be discharged, on a basis of print image data which is image data used for printing, without using information on an actual number of discharges of the ink at the head. The first controller obtains a print usage on a basis of a value obtained by multiplying the obtained estimated number of discharges by a discharged droplet amount per ink discharge. The print usage is the amount of the ink discharged onto a paper for printing each page of the print job 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of an image forming apparatus according to an embodiment; 
         FIG. 2  is a diagram illustrating an example of the image forming apparatus according to the embodiment; 
         FIG. 3  is a diagram illustrating an example of the image forming apparatus according to the embodiment; 
         FIG. 4  is a flowchart illustrating an example of calculation of an amount of ink used in the image forming apparatus according to the embodiment; 
         FIG. 5  is a flowchart illustrating an example of calculation of a print usage according to the embodiment; 
         FIG. 6  is a diagram illustrating an example of a mechanism for performing maintenance of the image forming apparatus according to the embodiment; and 
         FIG. 7  is a flowchart illustrating an example of calculation of a purge usage according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an image forming apparatus  100  according to an embodiment of the present disclosure will be described with the use of  FIGS. 1 to 7 . The image forming apparatus  100  described later is a printer. The image forming apparatus  100  may be, for example, a multifunction peripheral. The image forming apparatus  100  performs printing using ink. 
     (Overview of Image Forming Apparatus  100 ) 
     First, the overview of an image forming apparatus  100  according to an embodiment will be described with the use of  FIGS. 1 to 3 .  FIGS. 1 to 3  are diagrams illustrating an example of the image forming apparatus  100  according to the embodiment. 
     The image forming apparatus  100  performs printing on a paper. The image forming apparatus  100  performs printing using ink. The image forming apparatus  100  includes a controller  1  (corresponding to the first controller), a storage unit  2 , an engine controller  3 , a video controller  4  (corresponding to the second controller), an operation panel  5 , a paper feeder  6 , a paper conveyer  7 , an image former  8 , and a communicator  12 . The controller  1 , the engine controller  3 , and the video controller  4  are, for example, boards. 
     The controller  1  issues an operation instruction for each component of the image forming apparatus  100 . That is, the controller  1  manages a print job using a line head  80 . For example, at the time of a print job, the controller  1  issues an instruction for paper feeding and paper conveyance to the engine controller  3 . The engine controller  3  controls the operations of the paper feeder  6  and the paper conveyer  7  on the basis of this instruction. At the time of the print job, the controller  1  generates print image data i 1 . and generates ink discharge image data i 2  on the basis of the print image data i 1 . The controller  1  transmits the print instruction and the ink discharge image data i 2  to the video controller  4 . The video controller  4  discharges ink from the line head  80  on the basis of the ink discharge image data i 2 . 
     The controller  1  is a board including a control circuit  10  and an image processing circuit  11 . For example, the control circuit  10  is a CPU. The control circuit  10  performs calculations and processing on the basis of the control program and control data stored in the storage unit  2 . The storage unit  2  includes a non-volatile storage device such as a ROM and a storage (an HDD, a flash ROM). In addition, the storage unit  2  includes a volatile storage device such as a RAM. The image processing circuit  11  performs image processing of the image data used for printing (print image data i 1 ). Moreover, the controller  1  obtains the amount of ink consumed by one print job for each calculation item (the details will be described later). 
     The engine controller  3  includes an engine control circuit  30  and an engine memory  31 . The engine control circuit  30  is, for example, a CPU. The engine memory  31  stores programs and data related to paper feed control and paper conveyance control. 
     The video controller  4  is a board or a chip. The video controller  4  includes a video control circuit  40  and a second image memory  41 . The video control circuit  40  performs image processing and controls the ink discharge of the line head  80 . The second image memory  41  is a memory for storing the data required for image processing and ink discharge. The second image memory  41  is, for example, a DRAM. 
     The operation panel  5  includes a display panel  51  and a touch panel  52 . The controller  1  causes the display panel  51  to display a setting screen and information. The display panel  51  displays an operation image such as a key, a button, and a tab. The touch panel  52  detects a touch operation on the display panel  51 . The controller  1  recognizes an operated operation image on the basis of the output of the touch panel  52 . The controller  1  recognizes a setting operation performed by a user. 
     The paper feeder  6  accommodates a bundle of paper. The paper feeder  6  includes a paper feed roller  61 . The paper feed roller  61  contacts the highest-level paper among the papers set in the paper feeder  6 . A paper feed motor (not illustrated) for rotating the paper feed roller  61  is provided. At the time of a print job, the engine controller  3  rotates the paper feed motor to rotate the paper feed roller  61 . As a result, a paper is fed from the paper feeder  6  to the paper conveyer? (first conveyer  7   a ). A separate paper feed device (not illustrated) can be installed to the side surface of the image forming apparatus  100  (on the right side in  FIG. 1 ). The connected paper feed device can accommodate a large amount of paper and feeds the paper to the first conveyer  7   a.    
     The paper conveyer  7  conveys a paper. The paper conveyer  7  includes the first conveyer  7   a  and a second conveyer  7   b . The first conveyer  7   a  conveys the paper supplied from the paper feeder  6  toward the image former  8 . The second conveyer  7   b  conveys the paper that has passed through the image former  8  (line head  80 ) toward an ejection tray  101 . A separate post-processing device (not illustrated) can be installed to the side surface of the image forming apparatus  100  (left side in  FIG. 1 ). When the post-processing device is installed, the image forming apparatus  100  can feed a printed paper to the post-processing device. In this case, the controller  1  causes the post-processing device to perform post-processing. 
     The engine controller  3  conveys the paper supplied from the paper feeder  6  to the first conveyer  7   a  toward the image former  8 . As illustrated in  FIG. 1 , the first conveyer  7   a  includes a first conveyance roller pair  71 , a reading unit  8   a  and a light source  8   b , a resist sensor  72 , a resist roller pair  73 , a paper sensor  74 , and a conveyance unit  75  in this order from the upstream side in the paper conveyance direction. 
     A plurality of first conveyance roller pairs  71  are provided. In order to rotate each first conveyance roller pair  71 , a first conveyance motor (not illustrated) is provided. At the time of a print job, the engine controller  3  rotates the first conveyance motor. In addition, a resist motor  76  is provided to rotate the resist roller pair  73 . The engine controller  3  controls the rotation of the resist motor  76  to control the rotation of the resist roller pair  73 . 
     The resist sensor  72  is provided in the more upstream side than the resist roller pair  73  in the paper conveyance direction. The output level of the resist sensor  72  changes depending on whether the presence of a paper is detected. The output of the resist sensor  72  input to the engine controller  3 . The engine controller  3  recognizes that, the front edge of the paper has reached the resist sensor  72 , on the basis of the output. The engine controller  3  recognizes that the rear edge of the paper has passed through the resist sensor  72 . 
     When the paper reaches the resist roller pair  73 , the engine controller  3  has stopped the resist roller pair  73 . For example, when the rear edge of the paper passes through the resist sensor  72 , the engine controller  3  stops the resist roller pair  73 . On the other hand, the engine controller  3  rotates the first conveyance roller pair  71  which is in one more upstream side than the resist roller pair  73 . The front edge of the paper hits the resist roller pair  73 . The hit paper bends, and the front edge of the paper follows the nip of the resist roller pair  73 . The skew of the paper is corrected. When a specified bend creation time elapses after recognizing the arrival of the front edge of the paper on the basis of the output of the resist sensor  72 , the engine controller  3  rotates the resist roller pair  73 . This causes the paper to be fed toward the conveyance unit  75 . 
     The conveyance unit  75  includes a conveyance belt  77 , a drive roller  78 , and a driven roller  79 . The conveyance belt  77  is hung around the drive roller  78  and the driven roller  79 . A belt motor  710  is provided to rotate the drive roller  78 . During a print job, the engine controller  3  rotates the belt motor  710  and causes the conveyance belt  77  to go around. The conveyance belt  77  sucks a paper. For example, a plurality of holes are opened in the conveyance belt  77 . A suction device that sucks air from the holes is provided (not illustrated). The position of the paper on the belt can be fixed by suction. 
     The reading unit  8   a  reads a conveyed paper.  FIG. 1  illustrates an example in which the reading unit  8   a  and the light source  8   b  are provided between the first conveyance roller pair  71  and the resist sensor  72 . The reading unit  8   a  includes a conveyance image sensor. The conveyance image sensor is a line sensor. The conveyance image sensor includes a plurality of light receiving elements. The plurality of light receiving elements are lined up in the main scanning direction (the direction perpendicular to the paper surface in  FIG. 1 , and the direction perpendicular to the paper conveyance direction). The conveyance image sensor reads the conveyed paper. 
     A plurality of second conveyance roller pairs  711  are provided in the second conveyer  7   b . A second conveyance motor (not illustrated) is provided to rotate each second transport roller pair  711 . At the time of a print job, the engine controller  3  rotates the second conveyance motor. 
     In this way, the engine controller  3  controls the operations of the paper feeder  6  and the paper conveyer  7 . For example, the engine control circuit  30  controls the rotation of the resist motor  76  and the belt motor  710 . In addition, the engine control circuit  30  recognizes the paper transfer status on the basis of the outputs of the resist sensor  72  and the paper sensor  74 . 
     The engine control circuit  30  notifies the video controller  4  that, for example, the paper sensor  74  has detected the arrival of the front edge of a paper. When a preliminarily specified waiting time elapses from the notification, the video controller  4  (video control circuit  40 ) starts printing a page (drawing a first line). The waiting time is, for example, a time obtained by dividing the distance from the paper sensor  74  to the nozzle of the line head  80  by an ideal (on-specification) paper conveyance speed. 
     The image former  8  performs printing on a conveyed paper. The image former  8  discharges ink to the conveyed paper. As illustrated in  FIG. 1 , the image former  8  includes four line heads  80 . A line head  80 Bk discharges black ink. A line head  80 Y discharges yellow ink. A line head  80 C discharges cyan ink. A line head  80 M discharges magenta ink. Each line head  80  is fixed. Each line head  80  is provided above the conveyance unit  75  (conveyance belt  77 ). A certain gap is provided between each line head  80  (nozzle on the lower surface) and the conveyance belt  77 . A paper passes through this gap. 
     The line head  80  includes a plurality of nozzles. The nozzles are aligned in the direction perpendicular to the paper conveyance direction (main scanning direction) (the direction perpendicular to the paper surface in  FIG. 1 ). The opening of each nozzle faces the conveyance belt  77 . That is, the nozzle faces downward. The controller  1  supplies the ink discharge image data i 2  to the video controller  4 . The video controller  4  causes the line head  80  to perform ink discharge from the nozzle to the conveyed paper on the basis of this ink discharge image data i 2 . The ink lands on the conveyed paper and an image is recorded (formed). 
     The controller  1  is connected to the communicator  12 . The communicator  12  includes a communication connector, a communication control circuit, and a communication memory. The communication memory stores communication software. The communicator  12  communicates with a computer  200 . The computer  200  is, for example, a PC or a server. The controller  1  receives print job data from the computer  200 . The print job data includes print settings and print content. For example, the print job data includes data written in a page description language. The controller  1  (image processing circuit  11 ) analyzes the received (input) print job data. The controller  1  generates raster data (print image data i 1 ) on the basis of the analysis result of the print job data. 
     The image processing circuit  11  applies, to the generated print image data i 1 , image processing according to the print settings. The image processing circuit  11  eventually performs the halftone processing of the print image data it and generates the ink discharge image data i 2 . The ink discharge image data i 2  is data in which the value of each pixel indicates the discharge or non-discharge of the ink of each nozzle (each pixel). For example, the image processing circuit  11  generates the ink discharge image data i 2  for each color. The controller  1  stores the generated ink discharge image data i 2  in the first image memory  21 . The storage unit  2  includes the first image memory  21 . The first image memory  21  is, for example, a DRAM. 
     The controller  1  transmits the ink discharge image data i 2  of the first image memory  21  to the second image memory  41  for each color. The second image memory  41  stores the received ink discharge image data i 2 . In addition, the video control circuit  40  generates mask data i 3  on the basis of the conveyed read image data obtained by reading by the reading unit  8   a . The mask data i 3  is data for preventing ink discharge to a part where a paper is not present. The video control circuit  40  edits the ink discharge image data i 2  on the basis of the mask data i 3 . Specifically, the video control circuit  40  changes the pixel value of the pixel of the ink discharge image data i 2 , that discharges ink to the outside of a paper, so that the value indicates non-discharge. The video control circuit  40  generates and edits the ink discharge image data i 2  for each color. The video controller  4  supplies the edited ink discharge image data i 2  to the line head  80 . The line head  80  discharges ink on the basis of the received ink discharge image data i 2  (ink discharge image data i 2  edited in a mask process). 
     The video controller  4  (video control circuit  40 ) can count the number of ink discharges from the nozzle for each line head  80 . For example, the video controller  4  can count the number of ink discharges on a page-by-page basis (the number of dots of discharged ink). For example, the video controller  4  counts the number of discharges, such as 500,000 times and 1 million times. 
     (Calculation of Amount of Ink Used) 
     Next, the overview of the calculation of an amount of ink used in the image forming apparatus  100  according to the embodiment will be described with the use of  FIG. 4 .  FIG. 4  is a flowchart illustrating an example of the calculation of the amount of ink used in the image forming apparatus  100  according to the embodiment. 
     Each time a print job is performed, the controller  1  obtains the amount of ink consumed by the print job (amount of ink used). That is, the controller  1  obtains the amount of ink used as a unit of one job. When obtaining the amount of ink used, the controller  1  does not acquire the information on the number of ink discharges from the video controller  4 . The controller  1  obtains the amount of ink used only by calculation. 
     The controller  1  obtains the amount of ink used for each preliminarily specified calculation item. For example, the calculation item is a normal print usage, an error print usage, and a purge usage. The details of each usage will be described later. Items other than the above may be added as a calculation item. The controller  1  outputs data (one job usage file) that summarizes the values of each calculated item. The one job usage file is data that summarizes the values obtained for each color for each calculation item. The user can check the one job usage file. By checking, the user can grasp how much ink is consumed for each calculation item. 
     The start in  FIG. 4  is the time when a print job is started. The controller  1  starts the calculation of the usage for each color and each calculation item (step # 11 ). Eventually, the print job ends (step # 12 ). When the print job ends, the controller  1  generates one job usage file (step # 13 ). Then, the controller  1  causes the communicator  12  to transmit the one job usage file to the computer  200  (step # 14  to END). 
     The destination of the one job usage file may be fixed. For example, the computer  200  for managing the image forming apparatus  100  or the shared server can be defined as the destination. In this case, the address of the computer  200  that transmits the one job usage file is preset. For example, the operation panel  5  accepts the setting of the address of the computer  200 . The controller  1  non-volatilely stores the set address in the storage unit  2 . When transmitting the one job usage file, the controller  1  refers to the stored address. In addition, the controller  1  may transmit the one job usage file to the computer  200  that has transmitted the print job data. 
     The user can check the content of the one job usage file on the computer  200 . For example, when the one job usage file is opened, the computer  200  displays the content of the one job usage file on the display of the computer  200 . By checking the content, the user can grasp how much ink has been used on which calculation item. It is possible to check whether there is a problem with the amount of ink used. It is possible to grasp various information on the basis of the one job usage file. 
     (Normal Print Usage and Error Print Usage) 
     Next, an example of calculation of the normal print usage and the error print usage according to the embodiment will be described with the use of  FIG. 5 .  FIG. 5  is a flowchart illustrating an example of calculation of the normal print usage and error print usage according to the embodiment. 
     The control circuit  10  or the image processing circuit  11  may calculate the normal print usage and the error print usage. The start in  FIG. 5  is the time when the calculation of amount of ink used starts with the start of a print job. First, the controller  1  selects the first page of the print job (step # 21 ). The controller  1  obtains the estimated number of discharges of the selected page for each color, on the basis of the print image data i 1  of the selected page (step # 22 ). 
     The estimated number of discharges is an estimated value of the number of dots discharged when printing on the basis of the print image data i 1  of the selected page. The print image data i 1  used to calculate the estimated number of discharges is the image data before halftone processing (dot processing). In other words, the controller  1  calculates the estimated number of discharges with the use of the image data before conversion to the ink discharge image data i 2 . The image data before conversion to the format supplied to the video controller  4  can be used. For example, the controller  1  calculates the estimated number of discharges with the use of the image data obtained by converting the image data generated by a rasterizing process into a CMYK format. 
     Specifically, the controller  1  calculates the estimated number of discharges with the use of a primary conversion table. The storage unit  2  non-volatilely stores the conversion table. In the conversion table, the number of discharges (number of dots) corresponding to the pixel values (a density value, a gradation value) of the pixels of the print image data i 1  is defined. For example, the higher the pixel value, the larger the defined number of discharges. The lower the pixel value, the smaller the defined number of discharges. For example, the number of discharges corresponding to a pure white pixel value is zero. The conversion table may be prepared for each color. The controller  1  converts all the pixels of the print image data i 1  of one page into the number of discharges. The controller  1  obtains the total number of discharges converted for each color. The controller  1  uses the obtained total value as the estimated number of discharges. The estimated number of discharges may be obtained by an other method. 
     Next, the controller  1  recognizes a discharged droplet amount on the printing of the selected page (step # 23 ). The discharged droplet amount from the line head  80  has multiple stages. The video controller  4  can control the discharged droplet amount by making different the signal waveform and the amplitude of the waveform of the voltage applied to the piezo element attached to each nozzle. The video controller  4  can change the amount of ink used per discharge (the discharged droplet amount) depending on the type of paper used for printing. 
     For example, the video controller  4  increases the discharged droplet amount for an ink jet mat paper compared to an ink jet plain paper. Since the mat paper absorbs ink better than the plain paper and tends to have a low concentration. For a paper (an other paper) that is neither an ink jet mat paper nor an ink jet plain paper, the video controller  4  may set the discharged droplet amount to be less than that of the ink plain paper. 
     The operation panel  5  accepts the setting of the type of paper used for printing (a paper set in the paper feeder  6 ). The controller  1  recognizes the type of a printing paper on the basis of the output of the operation panel  5 . The controller  1  recognizes the amount of ink used (the discharged droplet amount) ejected for one discharge when the video controller  4  performs printing. The controller  1  sets the discharged droplet amount to a value according to the paper used for printing. 
     Then, the controller  1  obtains the print usage of the selected page (step # 24 ). Specifically, the controller  1  obtains the print usage on the basis of the following formula 1. 
       print usage=discharged droplet amount×estimated number of discharges÷adjustment value  (Formula 1)
 
     The adjustment value is a value for matching the resolution of the print image data i 1  to the print resolution of the line head  80 . In some cases, due to the specifications, the resolution of the print image data i 1  generated by the image processing circuit  11  may be fixed. In addition, the print resolution of the line head  80  is determined by the pitch of the nozzle. If the resolution of the print image data i 1  and the print resolution are different, the print usage cannot be calculated correctly. Accordingly, the estimated number of discharges is adjusted with the use of the adjustment value. 
     For example, the resolution of the print image data i 1  is 1200 dpi. The print resolution of the line head  80  is 600 dpi. It is necessary to match the estimated number of discharges (dots) counted on the basis of 1200 dpi to 600 dpi. If the vertical 1200 dpi is 600 dpi and the horizontal 1200 dpi is 600 dpi, the number of dots will be 1/2×1/2=1/4. In this case, the controller  1  divides the estimated number of discharges by the adjustment value “4”. 
     Next, the controller  1  confirms whether the selected page is the last page of the print job (step # 25 ). When the selected page is not the last page (No in step # 25 ), the controller  1  selects the next page (step # 26 ). Then, the controller  1  executes step # 22  (returns to the step # 22 ). In this way, the controller  1  calculates the print usage for each page. When the selected page is the last page of the print job, the controller  1  obtains the normal print usage and the error print usage (step # 27 ). Then, the controller  1  ends this flowchart (END). 
     The normal print usage is the total of the print usage of the pages ejected to the ejection tray  101  without an error. In the print job, even if an error occurs, error processing is performed, and finally all the pages are ejected to the ejection tray  101 . Therefore, the controller  1  may use the total print usage of all pages as the normal print usage. The error print usage is the total print usage of the pages that have not been ejected to the ejection tray  101  by an error. If no error occurs, the error print usage will be zero. 
     The engine controller  3  can recognize the occurrence of a paper conveyance error (paper jam error). In addition to the resist sensor  72  and paper sensor  74 , a sensor that detects the arrival and passage of a paper is installed in the paper conveyance path (not illustrated). The engine controller  3  detects the paper transport error on the basis of the outputs of these sensors. When there is a sensor that should detect the paper arrival but cannot detect the paper arrival beyond an allowable time, the engine controller  3  determines that a paper conveyance error has occurred. When there is a sensor that should detect paper passage but cannot detect paper passage beyond an allowable time, the engine controller  3  determines that a paper conveyance error has occurred. 
     When determining that a paper conveyance error has occurred, the engine controller  3  stops the paper conveyance. In addition, the image forming apparatus  100  includes an ejection sensor  32  in the paper ejection port to the ejection tray  101  (see  FIGS. 1 and 3 ). The engine controller  3  recognizes whether the paper has been ejected on the basis of the output of the ejection sensor  32 . The engine controller  3  grasps which page has been ejected normally. The engine controller  3  grasps which page has not been ejected to the ejection tray  101  due to the paper conveyance error. When the paper conveyance is stopped by the paper conveyance error, the user performs work to eliminate the error. For example, the user removes the paper remaining in the machine. After removal, the engine controller  3  resumes paper conveyance, and the video controller  4  resumes ink discharge to the paper. 
     When determining that a paper conveyance error has occurred, the engine controller  3  notifies the controller  1  and the video controller  4  that the engine controller  3  has determined that the paper conveyance error has occurred. In response to this notification, the video controller  4  stops the ink discharge from the line head  80 . In addition, the engine controller  3  notifies the controller  1  of the pages that have not been ejected to the ejection tray  101  among the pages on which ink has been discharged. The controller  1  uses the total print usage of the notified page as the error print usage. 
     (Purge Usage) 
     Next, an example of calculation of a purge usage according to the embodiment will be described with the use of  FIGS. 1, 6 and 7 .  FIG. 6  is a diagram illustrating an example of a mechanism for performing maintenance of the image forming apparatus  100  according to the embodiment.  FIG. 7  is a flowchart illustrating an example of calculation of a purge usage according to the embodiment. 
     For example, when printing a printed matter with margins consecutively, the ink is not discharged from the nozzle facing the margins. The ink components (solvent) are volatilized (evaporated) from the ink surface of a nozzle. For a nozzle that does not discharge ink for a long time, the viscosity of the ink increases due to the volatilization of the components. For a nozzle with a high viscosity, it becomes difficult for the ink to be discharged. If the viscosity continues to increase, the nozzle may eventually become clogged and the ink may not be discharged. 
     Therefore, the controller  1  causes the image former  8  (line head  80 ) to perform a purge process every certain time after the start of printing. The purge process is a process of discharging ink from the line head  80  to prevent clogging. The purge process is one of the processes for maintenance. In the purge process, printing is interrupted. During the purge process, the engine controller  3  does not feed or convey a paper. 
     The image forming apparatus  100  includes a maintenance unit  9  for the maintenance of the line head  80 . As illustrated in  FIG. 1 , the maintenance unit  9  is provided below the line head  80 . As illustrated in  FIG. 6 , the maintenance unit  9  includes a tray unit  90 , a first moving mechanism  91 , a second moving mechanism  92 , and a third moving mechanism  93 . 
     The tray unit  90  includes an ink receiving tray  94  and a cap tray  95 . The ink receiving tray  94  is a tray for receiving and collecting the ink discharged from the line head  80  (nozzle). The cap tray  95  is provided with an anti-drying cap. The anti-drying cap can be fitted to the nozzle surface (lower surface) of the line head  80 . The nozzle surface of the line head  80  can be sealed. By fitting the anti-drying cap, evaporation of an ink component can be prevented. 
     The first moving mechanism  91  moves the conveyance unit  75  in the horizontal direction (the direction perpendicular to the paper surface in  FIG. 1 ). When printing, the first moving mechanism  91  moves and positions the conveyance unit  75  so as to be below the line head  80 . When performing the purge process or fitting the anti-drying cap, the controller  1  moves the conveyance unit  75  to the first moving mechanism  91  toward a retracted position. The retracted position of the conveyance unit  75  is a position that is deviated from positions below the line head  80 . 
     The second moving mechanism  92  moves the tray unit  90  in the up-down direction (vertical direction). When performing the purge process or fitting the anti-drying cap, after moving the conveyance unit  75  to the retracted position, the controller  1  raises the tray unit  90  to the second moving mechanism  92 . This causes the tray unit  90  to move toward the lower surface of the line head  80 . The second moving mechanism  92  moves the tray unit  90  to a position below the line head  80 . When the purge process is completed, or when the anti-drying cap is not fitted, the controller  1  causes the second moving mechanism  92  to move the tray unit  90  to a lower limit position. After the lowering, the controller  1  moves the conveyance unit  75  to the first moving mechanism  91  toward the lower side of the line head  80 . 
     The third moving mechanism  93  is a mechanism for exchanging the tray facing the lower surface (nozzle surface) of the line head  80 . At the time of a purge process, the third moving mechanism  93  positions the ink receiving tray  94  below the line head  80 . When fitting the anti-drying cap, the third moving mechanism  93  positions the cap tray  95  below the line head  80 . 
     For the movement of units and trays, the first moving mechanism  91 , the second moving mechanism  92 , and the third moving mechanism  93  include mechanical elements such as motors, gears, belts, pulleys, belts, and wires. The controller  1  controls the rotation of the motors and controls the operation of the maintenance unit  9 . 
     For a purge process, the image forming apparatus  100  also includes a pump  96 . During the purge process, the controller  1  operates the pump  96 . The pump  96  is a device that presses ink in the direction of feeding to each line head  80 . As a result, the ink oozes out from all the nozzles. The ink is pushed out from the nozzles. By applying this pressure, viscosity-increased ink can be discharged to the outside of the nozzles. 
     The controller  1  performs a purge process at an execution interval preliminarily specified. The execution interval is, for example, about several tens of minutes to 60 minutes. The operation panel  5  may accept the setting of the execution interval. In this case, the controller  1  performs a purge process on all four color line heads  80  at the set execution interval. When the execution interval elapses from the start of a print job or a previous purge process, the controller  1  pauses printing, performs a purge process, and resumes printing after the purge process. 
     An example of calculation of a purge usage will be described with the use of  FIG. 7 . The start in  FIG. 7  is the time when a print job is started. First, the controller  1  (control circuit  10 ) measures the required time for the job (step # 31 ). The required time for the job is the time from the start to the end of printing. The controller  1  divides the required time for the job by a purge interval to obtain the number of purge executions (step # 32 ). For example, the controller  1  truncates the fractional part of the number of purge executions. Next, the controller  1  calculates the purge usage by multiplying the obtained number of purge executions by the amount of ink used in one purge process (step # 33 ). The controller  1  obtains the purge usage for each color. This makes it possible to obtain the amount of ink used in the purge process during one print job. 
     The amount of ink used in one purge process is preliminarily specified (for example, 1000 to several thousand μl). The amount is common to each color. The controller  1  multiplies the amount of ink used and the number of executions. When a purge process occurs for all four colors at the same time, the purge usage is the same for all colors. 
     In this way, the image forming apparatus  100  according to the embodiment includes a head (line head  80 ), a first controller (controller  1 ), and a second controller (video controller  4 ). The head includes a plurality of nozzles. The head discharges ink from the nozzle. The first controller manages a print job using the head. The first controller calculates the amount of ink used in the print job. The second controller controls the ink discharge at the head on the basis of an instruction of the first controller. When calculating the amount of ink used, the first controller obtains the estimated number of discharges, which is the number of dots of ink to be discharged, on the basis of print image data it which is image data used for printing, without using the information on the actual number of ink discharges at the head. The first controller obtains a print usage on the basis of a value obtained by multiplying the obtained estimated number of discharges by a discharged droplet amount per ink discharge. The print usage is the usage of ink discharged onto a paper for printing each page of the print job. 
     It is possible to accurately calculate the amount of ink used (print usage) without acquiring the data of the actual number of ink discharges from the second controller. An amount of ink used can be calculated accurately while reducing the amount of data exchanged between the first controller and the second controller so as not to interfere with high-speed processing other than the calculation of the amount of ink used. 
     The first controller performs the halftone processing of the print image data it to generate the ink discharge image data i 2 . The first controller transmits the generated ink discharge image data i 2  to the second controller. The first controller obtains the estimated number of discharges on the basis of the print image data i 1  before the halftone processing. The print usage can be calculated on the basis of the image data (print image data i 1 ) before the halftone processing. The calculation of the print usage can be started without waiting for the progress of image processing. The print usage can be calculated at high speed. 
     The second controller changes the discharged droplet amount in accordance with the type of paper used for printing. The first controller sets the discharged droplet amount multiplied to the estimated number of discharges to be a value according to the type of paper used for printing. The discharged droplet amount to be used for calculation can be matched with the discharged droplet amount in actual printing. The print usage can be calculated accurately. 
     When calculating the print usage, the first controller obtains, as the print usage, a value obtained by multiplying the value obtained by dividing the estimated number of discharges by the adjustment value for adjusting the resolution of the print image data it to the print resolution of the head and the discharged droplet amount. The estimated number of discharges can be adjusted to a value according to the print resolution (nozzle pitch) of the line head  80 . The print usage can be calculated accurately. 
     The first controller calculates the amount of ink consumed by one print job for each preliminarily specified calculation item. One calculation item is a normal print usage. The normal print usage is the total of the print usage on pages for which a paper is ejected to the outside of a machine without an error. The first controller outputs one job usage file. The one job usage file is data that summarizes the amount of ink used obtained for each calculation item for one print job. It is possible to calculate the amount of ink used in one print job for each item (by use). The user can easily grasp what kind of use and how much ink has been used in one print job on the basis of the one job usage file. 
     One calculation item is an error print usage. The error print usage is the total of the print usage of pages that have not been ejected to the outside of the machine by an error. It is possible to calculate the amount of ink used on a paper with an error. The user can grasp the amount of ink used in printing a paper with an error on the basis of the one job usage file. 
     One calculation item is a purge usage. The purge usage is an amount of ink used in a purge process performed in the middle of a print job. The purge process is a process for discharging ink from a nozzle to prevent clogging. It is possible to calculate the amount of ink used in the purge process (process to prevent nozzle clogging). The user can grasp the amount of ink used in the purge process during a print job on the basis of the one job usage file. 
     The first controller measures the time required for the job from the start to the end of a print job. The execution interval of the purge process and the amount of ink used in one purge process are preliminarily specified. The first controller obtains the number of purge executions on the basis of a value obtained by dividing the time required for the job by the execution interval. The first controller obtains the purge usage by multiplying the obtained number of purge executions by the amount of ink used in one purge process. The number of purge executions can be calculated accurately. The amount of ink used in the purge process can be calculated accurately. 
     While the embodiment of the present disclosure has been described, the scope of the present disclosure is not limited to the embodiment, and various variations can be practiced without departing from the spirit of the disclosure. 
     The present disclosure can be used for an image forming apparatus that performs printing using ink.