Patent Publication Number: US-10328703-B2

Title: Inkjet recording apparatus, inkjet recording method

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2017-028699 filed on Feb. 20, 2017, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an inkjet recording apparatus and an inkjet recording method. 
     In an inkjet recording apparatus that forms an image by an inkjet system, ink may be ejected from a nozzle to a sheet when a voltage is applied to a piezoelectric element that corresponds to the nozzle. In addition, in the inkjet recording apparatus, an amount of ink ejected from the nozzle may vary due to increase in viscosity of the ink caused by drying of ink. This reduces the image quality of the print output from the inkjet recording apparatus. With regard to this problem, there is known, as a related technology, an inkjet recording apparatus that ejects ink from the nozzle before the execution of the print process. 
     SUMMARY 
     An inkjet recording apparatus according to an aspect of the present disclosure includes a nozzle, a piezoelectric element, an extraction processing portion, and a drive control portion. From the nozzle, ink is ejected. The piezoelectric element is provided in correspondence with the nozzle, and upon input of a predetermined first drive signal, causes the ink to be ejected from the nozzle. The extraction processing portion, when a continuous print process is executed, extracts a non-ejection period during which a non-ejection state continues for more than a predetermined reference time period, from an execution period of the continuous print process based on a plurality of pieces of image data that are printed in the continuous print process, the non-ejection state being a state in which the ink is not ejected from the nozzle. The drive control portion inputs a predetermined second drive signal to the piezoelectric element during a partial or a whole period of the non-ejection period extracted by the extraction processing portion, the second drive signal causing the piezoelectric element to stir the ink in the nozzle and causing the piezoelectric element not to eject the ink from the nozzle. 
     An inkjet recording method according to another aspect of the present disclosure is executed in an inkjet recording apparatus that includes a nozzle from which ink is ejected, and a piezoelectric element provided in correspondence with the nozzle, and configured to, upon input of a predetermined first drive signal, cause the ink to be ejected from the nozzle. The inkjet recording method includes: when a continuous print process is executed, extracting a non-ejection period during which a non-ejection state continues for more than a predetermined reference time period, from an execution period of the continuous print process based on a plurality of pieces of image data that are printed in the continuous print process, the non-ejection state being a state in which the ink is not ejected from the nozzle; and inputting a predetermined second drive signal to the piezoelectric element during a partial or a whole period of the non-ejection period extracted by the extraction processing portion, the second drive signal causing the piezoelectric element to stir the ink in the nozzle and causing the piezoelectric element not to eject the ink from the nozzle. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of an inkjet recording apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a diagram showing a configuration of a recording portion of the inkjet recording apparatus according to the embodiment of the present disclosure. 
         FIG. 3  is a block diagram showing a configuration of a control portion of the inkjet recording apparatus according to the embodiment of the present disclosure. 
         FIG. 4  is a diagram showing an example of table data used in the inkjet recording apparatus according to the embodiment of the present disclosure. 
         FIG. 5  is a diagram for explaining content of processing performed by a signal processing portion of the inkjet recording apparatus according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes an embodiment of the present disclosure with reference to the accompanying drawings for the understanding of the present disclosure. It should be noted that the following embodiment is an example of a specific embodiment of the present disclosure and should not limit the technical scope of the present disclosure. 
     [Outlined Configuration of Inkjet Recording Apparatus  10 ] 
     First, a description is given of an outlined configuration of an inkjet recording apparatus  10  according to an embodiment of the present disclosure, with reference to  FIG. 1  to  FIG. 3 . Here,  FIG. 1  is a schematic cross-sectional view showing a configuration of the inkjet recording apparatus  10 .  FIG. 2  is a plan view showing a configuration of a recording portion  3 . It is noted that in  FIG. 3 , a flow of image data is represented by an arrow line, and a flow of control signal is represented by a two-dot chain line. 
     The inkjet recording apparatus  10  is a printer that can form an image by an inkjet system. It is noted that the present disclosure is applicable to other types of inkjet recording apparatuses such as a facsimile apparatus, a copier, and a multifunction peripheral. 
     As shown in  FIG. 1 , the inkjet recording apparatus  10  includes a sheet feed cassette  1 , a sheet feed portion  2 , a recording portion  3 , an ink container portion  4 , a conveyance unit  5 , a sheet discharge portion  6 , and a control portion  7 . 
     The sheet feed cassette  1  stores sheets that are print targets in the inkjet recording apparatus  10 . For example, the sheets stored in the sheet feed cassette  1  are sheet-like materials such as sheets of paper, sheets of coated paper, postcards, envelopes, and OHP sheets. 
     The sheet feed portion  2  supplies sheets stored in the sheet feed cassette  1  one by one to the recording portion  3 . As shown in  FIG. 1 , the sheet feed portion  2  includes a pickup roller  21 , a conveyance roller  22 , a conveyance path  23 , a registration roller  24 , a manual feed tray  25 , and a sheet feed roller  26 . The pickup roller  21  picks up, one by one, the sheets stored in the sheet feed cassette  1 . The conveyance roller  22  conveys the sheet picked up by the pickup roller  21  to the registration roller  24 . The conveyance path  23  is a moving passage of the sheet from the sheet feed cassette  1  and the manual feed tray  25  to the recording portion  3 . The registration roller  24  conveys the sheet to the recording portion  3  at a predetermined conveyance timing (image writing timing). The manual feed tray  25  and the sheet feed roller  26  are used to supply sheets from outside. 
     The recording portion  3  records an image on a sheet supplied from the sheet feed portion  2 . As shown in  FIG. 1 , the recording portion  3  includes line heads  31 ,  32 ,  33 , and  34  and a head frame  35  supporting the line heads, wherein the line heads  31  to  34  respectively correspond to colors of black, cyan, magenta, and yellow. The head frame  35  is supported by a housing  11  of the inkjet recording apparatus  10 . It is noted that the number of line heads mounted in the recording portion is not limited to 4 (four), but may be 1 (one) or 2 (two) or more excluding 4. 
     The line heads  31  to  34  are so-called line-head-type recording heads. That is, the inkjet recording apparatus  10  is a so-called line-head-type inkjet recording apparatus. The line heads  31  to  34  are elongated in a width direction D 2  perpendicular to a sheet conveyance direction D 1  (see  FIG. 2 ). Specifically, each of the line heads  31  to  34  has a length that corresponds to the width of a sheet of the maximum size among sheets that can be stored in the sheet feed cassette  1 . The line heads  31  to  34  are fixed to the head frame  35  at regular intervals along the sheet conveyance direction D 1 . 
     As shown in  FIG. 2 , each of the line heads  31  to  34  includes a plurality of recording heads  30 . The recording heads  30  eject ink toward a sheet conveyed by the conveyance unit  5 . Specifically, a lot of nozzles  30 B for ejection of ink are provided on a facing surface  30 A of each of the recording heads  30  (see  FIG. 1 ), each of the nozzles  30 B having an opening, the facing surface  30 A facing the sheet conveyed by the conveyance unit  5 . Each of the recording heads  30  includes pressurizing chambers (not shown), piezoelectric elements  302  (see  FIG. 3 ), and communication flow passages (not shown), the pressurizing chambers respectively corresponding to the nozzles  30 B, the piezoelectric elements  302  respectively corresponding to the pressurizing chambers, the communication flow passages being respectively communicated with the pressurizing chambers. Upon input of a predetermined first drive signal, each of the piezoelectric elements  302  causes ink to be ejected from the nozzle  30 B. For example, the first drive signal is a clock signal having predetermined voltage, frequency, and duty ratio. Specifically, each of the piezoelectric elements  302  pressurizes ink stored in the pressurizing chamber so that the ink is ejected from the nozzle  30 B. 
     As shown in  FIG. 3 , each of the recording heads  30  includes a drive portion  301 . The drive portions  301  are provided respectively in correspondence with the piezoelectric elements  302 . The drive portion  301  generates a drive signal for driving the piezoelectric element  302 , based on image data input from the control portion  7 , and inputs the generated drive signal to the piezoelectric element  302 . 
     In the present embodiment, three recording heads  30  are arranged in zigzag along the width direction D 2 . In addition, in each of the other line heads  32  to  34 , as in the line head  31 , three recording heads  30  are arranged in zigzag along the width direction D 2 . It is noted that  FIG. 2  shows a state where the recording portion  3  is viewed from the upper side of  FIG. 1 . 
     The ink container portion  4  includes ink containers  41 ,  42 ,  43 , and  44  that respectively store black, cyan, magenta, and yellow ink. The ink containers  41 ,  42 ,  43 , and  44  are respectively connected to the line heads  31  to  34  of the same color, via an ink supply portion (not shown). 
     The conveyance unit  5  is disposed below the line heads  31  to  34 . The conveyance unit  5  conveys the sheet in such a state where the sheet faces the facing surfaces  30 A of the recording heads  30 . As shown in  FIG. 1 , the conveyance unit  5  includes a sheet conveyance belt  51  on which the sheet is placed, stretching rollers  52  to  54 , and a conveyance frame  55 , the sheet conveying belt  51  being stretched over the stretching rollers  52  to  54 , the conveyance frame  55  supporting these members. It is noted that the interval between the sheet conveyance belt  51  and the facing surfaces  30 A is adjusted so that during an image recording, the interval between the sheet and the facing surfaces  30 A becomes, for example, 1 (one) mm. 
     The stretching roller  52  is coupled with a rotation shaft of a motor (not shown). When the motor is driven and the stretching roller  52  is rotated counterclockwise, the sheet conveyance belt  51  moves rotationally so as to convey the sheet in the conveyance direction D 1 . As the sheet conveyance belt  51  moves rotationally in such a manner, the sheet supplied from the sheet feed portion  2  is conveyed through the recording portion  3  toward the sheet discharge portion  6 . It is noted that the conveyance unit  5  also includes a suction unit (not shown) for sucking air through a lot of through holes formed in the sheet conveyance belt  51  so that the sheet is attracted by the sheet conveyance belt  51 . In addition, a pressure roller  56  is provided positioned to face the stretching roller  53  so as to press the conveyed sheet against the sheet conveyance belt  51 . 
     The sheet discharge portion  6  is provided downstream of the recording portion  3  in the conveyance direction D 1 . As shown in  FIG. 1 , the sheet discharge portion  6  includes a drying device  61 , a conveyance path  62 , a sheet discharge roller  63 , and a sheet discharge tray  64 . The drying device  61  dries the ink that has been fixed to the sheet, by, for example, blowing air to the sheet. The sheet dried by the drying device  61  is fed to the conveyance path  62 , and is discharged onto the sheet discharge tray  64  by the sheet discharge roller  63 . 
     Meanwhile, in the inkjet recording apparatus  10 , an amount of ink ejected from the nozzle  30 B may vary due to increase in viscosity of the ink caused by drying of ink. This reduces the image quality of the print output from the inkjet recording apparatus  10 . With regard to this problem, there is known an inkjet recording apparatus that ejects ink from the nozzles  30 B before the execution of the print process. 
     However, even during the execution of the print process, the ink may be dried and the amount of ink ejected from the nozzle  30 B may vary if a non-ejection state continues, the non-ejection state being a state where the ink is not ejected from the nozzle  30 B. On the other hand, as described below, the inkjet recording apparatus  10  according to the embodiment of the present disclosure can improve the image quality of the print. 
     In the following, the control portion  7  is described with reference to  FIG. 3 . As shown in  FIG. 3 , the control portion  7  includes a main control portion  71  and a plurality of signal processing portions  72 . The signal processing portions  72  are provided to correspond to the piezoelectric elements  302  that correspond to the nozzles  30 B. 
     The main control portion  71  comprehensively controls the inkjet recording apparatus  10 . Specifically, the main control portion  71  includes control equipment such as CPU, ROM, and RAM that are not shown. The CPU is a processor that executes various calculation processes. The ROM is a nonvolatile storage device in which various information such as control programs for causing the CPU to execute various processes are stored in advance. The RAM is a volatile storage device that is used as a temporary storage memory (working area) for the various processes executed by the CPU. In the main control portion  71 , the CPU executes the various control programs stored in advance in the ROM. This allows the inkjet recording apparatus  10  to be controlled comprehensively by the main control portion  71 . 
     As shown in  FIG. 3 , the main control portion  71  includes a conversion processing portion  711  and a generation processing portion  712 . Specifically, the main control portion  71  functions as the conversion processing portion  711  and the generation processing portion  712  when it executes the control programs stored in the ROM. 
     The conversion processing portion  711  converts each of a plurality of pieces of pixel data included in the image data that is printed by the inkjet recording apparatus  10 , to either ejection pixel data or non-ejection pixel data, wherein the ejection pixel data corresponds to ejection of ink from a nozzle  30 B that corresponds to a position of the piece of pixel data in the image data in the main scanning direction, and the non-ejection pixel data corresponds to non-ejection of ink from the nozzle  30 B that corresponds to the position of the piece of pixel data in the image data in the main scanning direction. 
     Here, the ejection pixel data corresponds to the first drive signal that causes the piezoelectric element  302  to eject the ink from the nozzle  30 B. In addition, the non-ejection pixel data corresponds to the third drive signal that does not cause the piezoelectric element  302  to eject the ink from the nozzle  30 B. 
     The generation processing portion  712 , when a continuous print process of sequentially printing a plurality of pieces of image data is executed, generates print data in which the plurality of pieces of image data printed in the continuous print process are aligned in order of printing via one or more pieces of inter-paper data that correspond to intervals between the plurality of pieces of image data. 
     Specifically, the generation processing portion  712  generates print data in which a plurality of pieces of image data converted by the conversion processing portion  711  are aligned in order of printing via one or more pieces of inter-paper data. Here, the inter-paper data is composed of the non-ejection pixel data. It is noted that the inter-paper data may include: data that is added to upstream, in a sub scanning direction, of a piece of image data that is printed first in the continuous print process; and data that is added to downstream, in the sub scanning direction, of a piece of image data that is printed last in the continuous print process. 
     The generation processing portion  712  outputs each piece of pixel data included in the generated print data, to a signal processing portion  72  that corresponds to a position of the piece of pixel data in the print data in the main scanning direction. Specifically, the generation processing portion  712  outputs each piece of pixel data in the print data in order from the upstream to the downstream in the sub scanning direction. 
     In addition, when a single print process of printing a piece of image data is executed, the generation processing portion  712  regards a piece of image data converted by the conversion processing portion  711  as the print data, and outputs each piece of pixel data included in the print data, to a signal processing portion  72  that corresponds to a position of the piece of pixel data in the print data in the main scanning direction. 
     The signal processing portion  72  controls driving of the piezoelectric element  302  based on the pixel data input from the generation processing portion  712 . In addition, the signal processing portion  72  causes the piezoelectric element  302  to execute a flashing during a partial period of a non-ejection period during which a non-ejection state continues for more than a predetermined reference time period, the non-ejection period being extracted from the execution period of the continuous print process or the single print process, the flashing causing the ink in the nozzle  30 B to be stirred, the non-ejection state being a state in which the ink is not ejected from the nozzle  30 B. 
     Specifically, each of the signal processing portions  72  is composed of an electronic circuit such as an integrated circuit (ASIC, DSP). As shown in  FIG. 3 , each of the signal processing portions  72  includes a first buffer  721 , an extraction processing portion  722 , a setting processing portion  723 , a second buffer  724 , and a drive control portion  725 . In the signal processing portion  72 , the pixel data output from the generation processing portion  712  is input to both the first buffer  721  and the second buffer  724 . 
     The first buffer  721  outputs each piece of pixel data included in the print data input from the generation processing portion  712 , to the extraction processing portion  722 . Specifically, the first buffer  721  outputs each piece of pixel data included in the print data, in order from the upstream in the sub scanning direction at predetermined intervals. Here, the predetermined interval is a driving interval in the drive portion  301 , and is a time period required for the conveyance unit  5  to convey the sheet such that an ink ejection position (a pixel recording position), namely a position on the sheet at which the nozzle  30 B ejects the ink, moves toward the downstream in the sub scanning direction by one pixel. 
     The second buffer  724  outputs each piece of pixel data included in the print data input from the generation processing portion  712 , to the drive control portion  725 . Specifically, the second buffer  724  outputs each piece of pixel data included in the print data, in order from the upstream in the sub scanning direction at the predetermined intervals. In addition, the second buffer  724  delays the output of each piece of pixel data included in the print data to the drive control portion  725 , by a predetermined delay time compared to the first buffer  721 . 
     For example, as shown in  FIG. 3 , the second buffer  724  includes a delay circuit  724 A. The delay circuit  724 A outputs each piece of pixel data to the drive control portion  725  after an elapse of a time (the delay time) that is obtained by multiplying the predetermined interval by a specific number. That is, the delay circuit  724 A delays the output of the pixel data by the number of pixels that corresponds to the specific number. For example, the specific number may be 1000. In that case, in the signal processing portion  72 , the first piece of pixel data is input from the delay circuit  724 A to the drive control portion  725  at a timing when the 1001 st  piece of pixel data is input from the first buffer  721  to the extraction processing portion  722 . It is noted that the specific number may be an arbitrary number other than 1000. 
     When the continuous print process is executed, the extraction processing portion  722  extracts the non-ejection period from the execution period of the continuous print process, based on a plurality of pieces of image data that are printed in the continuous print process. 
     In addition, when the single print process is executed, the extraction processing portion  722  extracts the non-ejection period from the execution period of the single print process, based on a piece of image data that is printed in the single print process. 
     Specifically, the extraction processing portion  722  extracts, as the non-ejection period, a period during which a non-ejection pixel sequence is output, wherein the non-ejection pixel sequence is composed of non-ejection pixels that continue in the print data exceeding a reference number that corresponds to the reference time period, the non-ejection pixels corresponding to non-ejection of the ink in the print data. For example, the reference number may be 999. In that case, the reference time period is obtained by multiplying the predetermined interval by 999. It is noted that the reference number may be an arbitrary number other than 999. 
     More specifically, the extraction processing portion  722  counts the continuous inputs of non-ejection pixels from the first buffer  721 , and determines whether or not a continuous set of non-ejection pixels is a non-ejection pixel sequence, based on a result of counting the continuous inputs of non-ejection pixels at a time when an ejection pixel is input from the first buffer  721 , wherein the ejection pixel corresponds to an ejection of the ink. That is, the extraction processing portion  722  determines that a continuous set of non-ejection pixels is a non-ejection pixel sequence in a case where the result of counting the continuous inputs of non-ejection pixels exceeds the reference number at the time when an ejection pixel is input from the first buffer  721 . 
     For example, as shown in  FIG. 3 , the extraction processing portion  722  includes a counter  722 A. The counter  722 A counts the continuous inputs of non-ejection pixels from the first buffer  721 . Specifically, each time a piece of pixel data is input from the first buffer  721 , the counter  722 A determines whether or not the input piece of pixel data is a piece of non-ejection pixel data. Upon determining that a piece of pixel data input from the first buffer  721  is a piece of non-ejection pixel data, the counter  722 A increments the count value. In addition, upon determining that a piece of pixel data input from the first buffer  721  is a piece of ejection pixel data, the counter  722 A notifies the extraction processing portion  722  of the count value at that time, and resets the count value to 0 (zero). It is noted that the extraction processing portion  722  resets the count value of the counter  722 A to 0 before the continuous print process or the single print process is executed. 
     Upon receiving the notification of the count value from the counter  722 A, the extraction processing portion  722  determines whether or not the notified count value exceeds the reference number. In a case where the notified count value exceeds the reference number, the extraction processing portion  722  determines that the continuous set of non-ejection pixels is a non-ejection pixel sequence, and notifies the setting processing portion  723  of the notified count value. In addition, in a case where the notified count value is equal to or less than the reference number, the extraction processing portion  722  determines that the continuous set of non-ejection pixels is not a non-ejection pixel sequence. 
     That is, in the inkjet recording apparatus  10 , the following period is extracted as the non-ejection period: a period from a timing at which the piezoelectric element  302  is driven based on a piece of pixel data that is input when the counter  722 A starts to be incremented, to a timing at which the piezoelectric element  302  is driven based on a piece of pixel data that is input when the count value of the counter  722 A is reset after the count value exceeds the reference number. 
     It is noted that the extraction processing portion  722  may measure the time during which non-ejection pixels are continuously input from the first buffer  721 , instead of counting the continuous inputs of non-ejection pixels from the first buffer  721 . 
     The setting processing portion  723  sets a start timing at which to start the flashing in the non-ejection period, based on the length of the non-ejection period. Specifically, the setting processing portion  723  sets the start timing based on the number of continuous inputs of non-ejection pixels counted by the extraction processing portion  722  in a case where the extraction processing portion  722  determines that the continuous set of non-ejection pixels is a non-ejection pixel sequence. 
     For example, as shown in  FIG. 3 , the setting processing portion  723  includes a storage portion  723 A. The storage portion  723 A stores table data X 10  in which various lengths of the non-ejection period (the count value of the counter  722 A notified from the extraction processing portion  722 ) are associated with start timings.  FIG. 4  shows an example of the table data X 10 . 
     Upon receiving a notification of the count value of the counter  722 A from the extraction processing portion  722 , the setting processing portion  723  obtains a start timing based on the notified count value and the table data X 10 . Subsequently, the setting processing portion  723  sets the start timing by notifying the drive control portion  725  of the obtained start timing. 
     It is noted that the signal processing portion  72  may not include the setting processing portion  723 . 
     The drive control portion  725  inputs a predetermined second drive signal to the piezoelectric element  302  during a partial period of the non-ejection period extracted by the extraction processing portion  722 , wherein the second drive signal causes the piezoelectric element  302  to stir the ink in the nozzle  30 B and causes the piezoelectric elements  302  not to eject the ink from the nozzle  30 B. 
     Specifically, the drive control portion  725  inputs the second drive signal to the piezoelectric element  302  during a period in the non-ejection period from the start timing set by the setting processing portion  723  to the end of the non-ejection period. It is noted that in a case where the signal processing portion  72  does not include the setting processing portion  723 , the drive control portion  725  may input the second drive signal to the piezoelectric element  302  during a period from a predetermined start timing to the end of the non-ejection period. 
     In addition, the drive control portion  725  replaces each piece of non-ejection pixel data, included in the non-ejection pixel sequence, that corresponds to a period from the start timing set by the setting processing portion  723  to the end of the non-ejection period, with specific pixel data that corresponds to the second drive signal. Specifically, the drive control portion  725  replaces each piece of pixel data that is input from the second buffer  724  during the period from the start timing set by the setting processing portion  723  to an input of a piece of ejection pixel data, with the specific pixel data. Subsequently, the drive control portion  725  inputs the second drive signal to the piezoelectric element  302  by inputting the specific pixel data to the drive portion  301 . 
     For example, as shown in  FIG. 3 , the drive control portion  725  includes a counter  725 A. When the start timing is set by the setting processing portion  723 , the counter  725 A counts the remaining number of pixels until a piece of ejection pixel data is input from the second buffer  724 . In other words, the counter  725 A counts the number of pixels that corresponds to the remaining time until the end of the non-ejection period. Specifically, when the start timing is set by the setting processing portion  723 , the counter  725 A sets the count value to the specific value (1000). Subsequently, the counter  725 A decrements the count value each time a piece of pixel data is input from the second buffer  724 . 
     For example, before the start timing is set by the setting processing portion  723 , the drive control portion  725  holds the pixel data input from the delay circuit  724 A, for a time period that corresponds to the predetermined interval, and then outputs the pixel data to the drive portion  301  of the recording head  30 . It is noted that in the inkjet recording apparatus  10 , the start timing is set on the condition that the number of continuous pieces of non-ejection pixel data exceeds the number of pixels ( 1000 ) delayed by the delay circuit  724 A. As a result, in the inkjet recording apparatus  10 , output of pixel data from the delay circuit  724 A is started before the setting processing portion  723  sets the start timing. 
     In addition, after the setting processing portion  723  sets the start timing, the drive control portion  725  determines, based on the count value of the counter  725 A, whether or not the start timing has come. Specifically, the drive control portion  725  determines that the start timing has come in a case where the count value of the counter  725 A is equal to or less than the value of the start timing set by the setting processing portion  723 . 
     Here, upon determining that the start timing has come, the drive control portion  725  replaces the pixel data held therein to the specific pixel data, and outputs the specific pixel data to the drive portion  301  of the recording head  30 . On the other hand, upon determining that the start timing has not come, the drive control portion  725  outputs the pixel data held therein to the drive portion  301  of the recording head  30  as it is. The drive control portion  725  determines whether or not the start timing has come, each time a piece of pixel data is input from the second buffer  724  and the count value of the counter  725 A is decremented. In addition, when the count value of the counter  725 A has become 0 (zero), the drive control portion  725  outputs the pixels data input from the second buffer  724 , to the drive portion  301  of the recording head  30  as it is, during a period until the start timing is set by the setting processing portion  723 . 
     The drive portion  301  drives the piezoelectric element  302  based on pixel data that has been subject to a replacement process performed by the drive control portion  725 . That is, when a piece of pixel data input from the drive control portion  725  is a piece of ejection pixel data, the drive portion  301  inputs the first drive signal to the piezoelectric element  302 . In addition, when a piece of pixel data input from the drive control portion  725  is the specific pixel data, the drive portion  301  inputs the second drive signal to the piezoelectric element  302 . Furthermore, when a piece of pixel data input from the drive control portion  725  is a piece of non-ejection pixel data, the drive portion  301  inputs the third drive signal to the piezoelectric element  302 . 
     With the above-described operation, a piece of image data or a plurality of pieces of image data included in the print data are printed. In addition, the non-ejection period during which the non-ejection state continues for more than the reference time period is extracted from the execution period of the print process (the continuous print process or the single print process), and the flashing is performed to stir the ink in the nozzle  30 B during a partial period of the extracted non-ejection period, wherein the non-ejection state is a state in which the ink is not ejected from the nozzle  30 B. 
     The following describes the content of processing performed by the signal processing portion  72  with reference to  FIG. 5 . It is noted that in  FIG. 5 , all pieces of pixel data from the first piece to the 5000 th  piece of pixel data input to the extraction processing portion  722  are non-ejection pixel data G 1 . In addition, the 5001 st  piece of pixel data input to the extraction processing portion  722  is ejection pixel data G 2 . 
     First, at timing t 1 , the first piece of pixel data is input from the first buffer  721  to the extraction processing portion  722 . The counter  722 A of the extraction processing portion  722  determines whether or not the input piece of pixel data is non-ejection pixel data. The pixel data input to the extraction processing portion  722  at timing t 1  is non-ejection pixel data G 1 . As a result, the counter  722 A increments the count value. Consequently, the count value of the counter  722 A becomes 1 (one). 
     On the other hand, at timing t 1 , no piece of pixel data is input from the second buffer  724  to the drive control portion  725 . 
     Next, at at timing t 2 , the 1001 st  piece of pixel data is input from the first buffer  721  to the extraction processing portion  722 . The counter  722 A determines whether or not the input piece of pixel data is non-ejection pixel data. The pixel data input to the extraction processing portion  722  at timing t 2  is non-ejection pixel data G 1 . As a result, the counter  722 A increments the count value. Consequently, the count value of the counter  722 A becomes 1001. 
     On the other hand, at timing t 2 , the first piece of pixel data is input from the second buffer  724  to the drive control portion  725 . At timing t 2 , the setting processing portion  723  has not set the start timing yet. As a result, the drive control portion  725  holds the first piece of pixel data for a time period that corresponds to the predetermined interval, and then outputs the pixel data to the drive portion  301  of the recording head  30 . 
     Subsequently, at timing t 3 , the 5001 st  piece of pixel data is input from the first buffer  721  to the extraction processing portion  722 . The counter  722 A determines whether or not the input piece of pixel data is non-ejection pixel data. The pixel data input to the extraction processing portion  722  at timing t 3  is ejection pixel data G 2 . As a result, the counter  722 A notifies the extraction processing portion  722  of the count value at that time, and resets the count value to 0 (zero). The extraction processing portion  722  determines whether or not the count value notified from the counter  722 A exceeds the reference number ( 999 ). The count value of the counter  722 A at timing t 3  is 5000. As a result, the extraction processing portion  722  notifies the setting processing portion  723  of the count value notified from the counter  722 A. 
     Upon receiving a notification of the count value of the counter  722 A from the extraction processing portion  722  at timing t 3 , the setting processing portion  723  obtains the start timing based on the notified count value and the table data X 10 . Here, the start timing corresponding to the count value 5000 is 500 (see  FIG. 4 ). As a result, at timing t 3 , the setting processing portion  723  sets the start timing by notifying the drive control portion  725  of the obtained start timing. The counter  725 A of the drive control portion  725  sets the count value to the specific value (1000) in response to the setting of the start timing by the setting processing portion  723 . 
     On the other hand, at timing t 3 , the 4001 st  piece of pixel data is input from the second buffer  724  to the drive control portion  725 . At timing t 3 , the setting processing portion  723  sets the start timing by notifying the drive control portion  725  of the start timing. As a result, the drive control portion  725  determines whether or not the start timing has come, based on whether or not the count value of the counter  725 A is equal to or less than the value of the start timing. At timing t 3 , the count value of the counter  725 A is 1000, and the set start timing is 500. Accordingly, the drive control portion  725  determines that the start timing has not come, and holds the 4001 st  piece of pixel data for the time period that corresponds to the predetermined interval, and then outputs the pixel data to the drive portion  301  of the recording head  30 . In addition, the counter  725 A decrements the count value each time a piece of pixel data is input from the second buffer  724 . 
     Next, at timing t 4 , the 4501 st  piece of pixel data is input from the second buffer  724  to the drive control portion  725 . The drive control portion  725  determines whether or not the count value of the counter  725 A is equal to or less than the value of the start timing. At timing t 4 , the count value of the counter  725 A is 500, and the set start timing is 500. As a result, the drive control portion  725  determines that the start timing has come, replaces the 4501 st  piece of pixel data with specific pixel data G 3 , and outputs the specific pixel data G 3  to the drive portion  301  of the recording head  30 . 
     Subsequently, at timing t 5 , the 5001 st  piece of pixel data is input from the second buffer  724  to the drive control portion  725 . At timing t 5 , the count value of the counter  725 A is 0. As a result, the drive control portion  725  holds the 5001 st  piece of pixel data for the time period that corresponds to the predetermined interval, and then outputs the pixel data to the drive portion  301  of the recording head  30 . 
     As described above, in the inkjet recording apparatus  10 , in a case where the continuous print process or the single print process is executed, the non-ejection period during which the non-ejection state continues for more than the reference time period is extracted from the execution period of the print process, wherein the non-ejection state is a state in which the ink is not ejected from the nozzle  30 B. Furthermore, upon extraction of the non-ejection period, the flashing is performed to stir the ink in the nozzle  30 B during a partial period of the extracted non-ejection period. With this configuration, in a situation where the image quality of the print would be reduced due to increase in viscosity of the ink caused by drying of ink, the image quality of the print is prevented from being reduced even during an execution of a print process (the continuous print process or the single print process). This makes it possible to improve the image quality of the print. 
     In addition, the inkjet recording apparatus  10  includes the first buffer  721  and the second buffer  724  individually, wherein the second buffer  724  outputs the print data that is to be input to the recording heads  30 , and the first buffer  721  outputs the same print data as the second buffer  724  before the second buffer  724  outputs the print data. In addition, the extraction process of extracting the non-ejection period is executed based on the data that is output from the first buffer  721  earlier than the second buffer  724 , and the replacement process of replacing the non-ejection pixel data with the specific pixel data is executed based on the execution result of the extraction process, and the data after the replacement process is input to the recording head  30 . As a result, compared to a configuration where the extraction process and the replacement process are executed on the print data stored in memory, the memory for storing the print data is not necessary. It is thus possible to reduce the capacity of memory provided in the inkjet recording apparatus  10 . 
     It is noted that the signal processing portion  72  may include control equipment such as CPU, ROM, and RAM, and function as the extraction processing portion  722 , the setting processing portion  723 , and the drive control portion  725  by executing programs that are stored in advance in the ROM. 
     In the above-described case, the drive control portion  725  may input the second drive signal to the piezoelectric element  302  during the whole non-ejection period extracted by the extraction processing portion  722 . In addition, the drive control portion  725  may input the second drive signal to the piezoelectric element  302  during a period from the start of the non-ejection period extracted by the extraction processing portion  722  or from a start timing that is set in advance, to an end timing that is set in advance. In addition, the drive control portion  725  may input the second drive signal to the piezoelectric element  302  by transmitting to the drive portion  301  a control signal that instructs inputting the second drive signal, instead of performing the process of replacing the non-ejection pixel data with the specific pixel data. 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.