Inkjet recording device and flushing condition determination method

Abstract

To provide an inkjet recording device which enables reduction of waste of an ink during flushing, and to provide a flushing condition determination method.SOLUTION: A control unit 7 of an inkjet recording device counts a number of discharge with a discharge number count part (S11), counts a non-discharge time with a non-discharge time count part (S12), and determines whether or not the non-discharge time is shorter than a predetermined first reference time t1 (S13). When it is determined that the non-discharge time is shorter than the first reference time t1, the control unit sets a gradation level of a corresponding nozzle 30B to a gradation level: 3 (S16).SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an inkjet recording apparatus and a method for determining flushing conditions. [Background technology]

[0002] In an inkjet recording device that forms an image by the inkjet method, ink is ejected from the nozzles onto a sheet by applying a voltage to a piezoelectric element provided corresponding to the nozzle. In addition, in an inkjet recording device, the amount of ink ejected from the nozzles may change due to an increase in the viscosity of the ink caused by drying of the ink. In this case, the image quality of the printed matter printed by the inkjet recording device decreases.

[0003] Furthermore, in an inkjet recording device, if the non-ejection state of the ink in the nozzles continues even during the execution of a printing process, the viscosity of the ink may change due to the ink drying, and the amount of ink ejected from the nozzles may change. Conventionally, an inkjet recording device has been disclosed that determines the conditions for blank ejection (flushing) based on the ejection history of the recording head (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-114494 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional inkjet recording devices, flushing ejection conditions are determined uniformly for all nozzles in a recording head, so flushing is performed under the same ejection conditions even for nozzles that do not require flushing or nozzles that do not require a large amount of ink ejected during flushing, which can result in unnecessary consumption of ink.

[0006] An object of the present invention is to provide an inkjet printing apparatus and a flushing condition determination method that are capable of reducing wasteful consumption of ink during flushing. [Means for solving the problem]

[0007] An inkjet recording device according to one aspect of the present invention comprises a recording head having a plurality of nozzles from which ink is ejected and piezoelectric elements provided corresponding to each of the plurality of nozzles and causing the ink to be ejected from the nozzles; a flushing control unit that controls a flushing process that ejects a predetermined amount of ink from the nozzles during a non-printing period during which a first print process is executed to print predetermined first image data; a non-ejection time acquisition unit that acquires, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzles continues during the execution period of the first print process based on the first image data; an ejection count acquisition unit that, when the first print process is executed, acquires, for each of the plurality of nozzles, the number of ejections at which the ink is ejected from the nozzles during the execution period of the first print process based on the first image data; and a flushing condition determination unit that determines execution conditions of the flushing process for each of the plurality of nozzles based on both or either one of the non-ejection time and the ejection count.

[0008] A flushing condition determination method according to another aspect of the present invention is a flushing condition determination method executed by an inkjet recording device equipped with a recording head having a plurality of nozzles from which ink is ejected and piezoelectric elements provided corresponding to each of the plurality of nozzles and causing the ink to be ejected from the nozzles. The flushing condition determination method includes the steps of: acquiring, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzle continues during an execution period of a first printing process in which the first image data is printed, based on predetermined first image data; acquiring, for each of the plurality of nozzles, a number of ejections at which the ink is ejected from the nozzle during an execution period of the first printing process, based on the first image data, when the first printing process is executed; and determining, for each of the plurality of nozzles, an execution condition for a flushing process in which a predetermined amount of ink is ejected from the nozzle during a non-printing period during the execution period of the first printing process, based on both or either one of the non-ejection time and the number of ejections. Effect of the Invention

[0009] According to the present invention, it is possible to reduce wasteful consumption of ink during flushing. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the configuration of an inkjet recording apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the configuration of a printing unit of an inkjet printing apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram showing the configuration of a printing unit of an inkjet printing apparatus according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the configuration of a paper transport belt of an inkjet recording apparatus according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a block diagram showing the configuration of a control unit of an inkjet recording apparatus according to an embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart showing an example of the procedure of a flushing condition determination process executed by the control unit of the inkjet recording apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings to facilitate understanding of the present invention. Note that the following embodiment is an example of the present invention and does not limit the technical scope of the present invention.

[0012] [Schematic configuration of the inkjet recording device 10] First, the schematic configuration of an inkjet recording apparatus 10 according to an embodiment of the present invention will be described with reference to Figs. 1 to 4. Fig. 1 is a cross-sectional view showing the configuration of the inkjet recording apparatus 10. Fig. 2 is a plan view showing the configuration of the recording unit 3. Fig. 3 is a cross-sectional view showing the configuration of the recording unit 3. Fig. 4 is a schematic view showing the configuration of a paper transport belt 51.

[0013] The inkjet recording apparatus 10 is a printer capable of forming images by an inkjet system. The present invention may be applied to inkjet recording apparatuses such as facsimile machines, copy machines, and multifunction machines capable of forming images by an inkjet system.

[0014] As shown in FIG. 1, the inkjet recording apparatus 10 includes a paper feed cassette 1, a paper feed section 2, a recording section 3, an ink container section 4, a transport unit 5, a paper discharge section 6, and a control section 7.

[0015] The paper feed cassette 1 accommodates sheets to be printed in the inkjet recording apparatus 10. For example, the sheets accommodated in the paper feed cassette 1 are sheet materials such as paper, coated paper, postcards, envelopes, and overhead projector sheets.

[0016] The paper feed unit 2 supplies the sheets stored in the paper feed cassette 1 to the recording unit 3. As shown in FIG. 1, the paper feed unit 2 includes a pickup roller 21, a transport roller 22, a transport path 23, a registration roller 24, a manual feed tray 25, and a paper feed roller 26. The pickup roller 21 picks up sheets one by one from the paper feed cassette 1. The transport roller 22 transports the sheet picked up by the pickup roller 21 to the registration roller 24. The transport path 23 is a path along which the sheet moves from the paper feed cassette 1 and the manual feed tray 25 to the recording unit 3. The registration roller 24 transports the sheet to the recording unit 3 at a predetermined transport timing (image writing timing). The manual feed tray 25 and the paper feed roller 26 are used to supply sheets from the outside.

[0017] The recording unit 3 records an image on a sheet supplied from the paper feed unit 2. As shown in Fig. 1, the recording unit 3 includes line heads 31, 32, 33, and 34 corresponding to the colors black, cyan, magenta, and yellow, respectively, and a head frame 35 that supports these. The head frame 35 is supported by a housing 11 of the inkjet recording device 10. The number of line heads included in the recording unit 3 may be one or more.

[0018] The line heads 31 to 34 are so-called line head type recording heads. That is, the inkjet recording device 10 is a so-called line head type inkjet recording device. The line heads 31 to 34 are long in a width direction D2 (see FIG. 2) perpendicular to the sheet transport direction D1. Specifically, each of the line heads 31 to 34 has a length in the width direction D2 corresponding to the width of the largest size sheet among the sheets that can be accommodated in the paper feed cassette 1. Each of the line heads 31 to 34 is fixed to a head frame 35 at a predetermined distance apart along the sheet transport direction D1.

[0019] As shown in Fig. 2, each of the line heads 31 to 34 has a plurality of recording heads 30. The recording heads 30 have nozzles 30B from which ink is ejected, and piezoelectric elements 302 (see Fig. 5) provided corresponding to the nozzles 30B. The recording heads 30 eject ink toward a sheet transported by a paper transport belt 51 of the transport unit 5. Specifically, a large number of nozzles 30B having openings for ejecting ink are provided on a surface 30A (see Fig. 1) of the recording heads 30 facing the sheet transported by the transport unit 5.

[0020] The recording head 30 also includes a plurality of pressure chambers (not shown) corresponding to the respective nozzles 30B, a plurality of piezoelectric elements 302 (see FIG. 5) provided corresponding to the respective pressure chambers, and a communication flow path (not shown) communicating with the respective pressure chambers. The piezoelectric elements 302 eject ink from the nozzles 30B in response to input of a predetermined drive signal (control signal). For example, the drive signal is a clock signal having a predetermined voltage, frequency, and duty ratio. Specifically, the piezoelectric elements 302 pressurize the ink contained in the pressure chambers to eject ink from the nozzles 30B.

[0021] In the inkjet recording device 10 of this embodiment, during printing processing of an image on a sheet, the control unit 7 outputs a drawing drive signal (control signal) for causing the piezoelectric element 302 to eject ink to a head driver 301 (see Figure 5) described below, thereby causing the nozzle 30B to eject ink for drawing at a predetermined drawing position on the sheet.

[0022] Furthermore, in this embodiment, the control unit 7 outputs a flushing drive signal (control signal) to the head driver 301 (see FIG. 5) described below for causing the piezoelectric element 302 to eject a predetermined specified amount (ink ejection amount) of ink at a timing different from that during the printing process of the image, and executes a process (flushing process) for ejecting the specified amount of ink from the nozzle 30B toward the opening group 512 (see FIG. 4) described below. In this way, by performing the flushing process at a timing different from that during the printing process, clogging of the nozzle 30B due to drying of ink is eliminated.

[0023] The recording head 30 includes a head driver 301 (see FIG. 5). The head driver 301 is provided corresponding to each of the piezoelectric elements 302. The head driver 301 generates the drive signal for controlling the operation of the piezoelectric elements 302 based on pixel data input from the control unit 7, and controls the drive of the piezoelectric elements 302 by inputting the generated drive signal to the piezoelectric elements 302. Examples of the drive signal are the drawing drive signal and the flushing drive signal.

[0024] 2, in this embodiment, the line head 31 has three recording heads 30 arranged in a staggered manner along the width direction D2. Similarly to the line head 31, each of the other line heads 32 to 34 also has three recording heads 30 arranged in a staggered manner along the width direction D2. Note that FIG. 2 shows the recording unit 3 as viewed from above in FIG. 1.

[0025] The ink container unit 4 includes ink containers 41, 42, 43, and 44 that accommodate inks corresponding to the respective colors of black, cyan, magenta, and yellow. The ink containers 41 to 44 are connected to the line heads 31 to 34 of the same color via an ink supply unit (not shown).

[0026] The transport unit 5 is disposed below the line heads 31 to 34. The transport unit 5 transports the sheet while aligning the recording surface (upper surface) of the sheet with the facing surface 30A of the recording head 30.

[0027] 3, the transport unit 5 includes a paper transport belt 51 on which a sheet is placed, tension rollers 52 to 54 that tension the paper transport belt 51, and a transport frame 55 that supports these. The gap between the paper transport belt 51 and the opposing surface 30A is adjusted so that the gap between the recording surface of the sheet and the opposing surface 30A during image recording is 1 mm, for example.

[0028] The paper transport belt 51 is an endless circular belt. The tension rollers 52 to 54 are disposed on the inside of the paper transport belt 51.

[0029] The tension roller 52 is connected to a rotating shaft of a motor (not shown). When the tension roller 52 is rotated counterclockwise by the drive of the motor, the paper conveying belt 51 rotates in a direction capable of conveying the sheet in the conveying direction D1. As a result, the sheet supplied from the paper feed section 2 is conveyed toward the paper discharge section 6 via the recording section 3 by the rotation of the paper conveying belt 51. The conveying unit 5 is also provided with a suction unit (not shown) that sucks air from a number of through holes formed in the paper conveying belt 51 in order to make the sheet adhere to the paper conveying belt 51. In addition, a pressure roller 56 is provided at a position opposite the tension roller 53 to press the sheet against the paper conveying belt 51 for conveying.

[0030] 1, the paper discharge unit 6 is provided downstream of the recording unit 3 in the transport direction D1. The paper discharge unit 6 includes a drying device 61, a transport path 62, paper discharge rollers 63, and a paper discharge tray 64. The drying device 61 dries ink adhering to the sheet, for example, by blowing air onto the sheet. The sheet dried by the drying device 61 is then sent to the transport path 62 and discharged to the paper discharge tray 64 by the paper discharge rollers 63.

[0031] As shown in FIG. 3, the conveying unit 5 is provided with a sheet sensor 81. The sheet sensor 81 is provided downstream of the registration roller 24 in the conveying direction D1 and upstream of the recording unit 3 in the conveying direction D1. The sheet sensor 81 is disposed above the paper conveying belt 51 so as to be able to detect the sheet conveyed by the paper conveying belt 51. The sheet sensor 81 is a sensor that detects the position of the sheet conveyed by the paper conveying belt 51. The control unit 7 controls the rotation of the registration roller 24 based on a detection signal received from the sheet sensor 81, and sends out the sheet toward the conveying unit 5 at a predetermined timing in accordance with the ink ejection timing from the recording head 30. The control unit 7 also controls the ejection of ink from the nozzles 30B to the sheet that has reached a position facing each of the recording heads 30 of each color by the paper conveying belt 51.

[0032] The transport unit 5 is also provided with belt sensors 82 and 83. The belt sensor 82 is disposed downstream of the recording unit 3 in the transport direction D1 and above the paper transport belt 51. The belt sensor 83 is disposed inside the paper transport belt 51. The belt sensor 83 is disposed downstream of the pressure roller 56 in the transport direction D1 and upstream of the recording unit 3 in the transport direction D1. The belt sensors 82 and 83 are sensors for detecting the position of an opening group 512 (see FIG. 4), which is a collection of a plurality of openings 511 (described later) provided in the paper transport belt 51.

[0033] 4, the paper transport belt 51 has a plurality of openings 511 penetrating from the front to the back. The openings 511 are through holes through which ink ejected from the recording heads 30 passes during flushing. The plurality of openings 511 are formed at positions and with sizes corresponding to the plurality of recording heads 30. A plurality of openings 511 (for example, three openings) are grouped together to form an opening group 512.

[0034] In this embodiment, the multiple opening groups 512 are arranged at equal intervals at predetermined intervals in the transport direction D1. On the paper transport belt 51, a sheet to be printed is arranged in a space between adjacent opening groups 512 in the transport direction D1. When a flushing process is performed by the control unit 7, the control unit 7 ejects ink from the nozzles 30B of the recording head 30 toward the opening groups 512 located between the sheets (between the sheets) on the paper transport belt 51. The ejected ink passes through one of the openings 511 of the opening groups 512 and is discharged into an ink receiver 84 described later.

[0035] 3, the inkjet recording device 10 is provided with a plurality of ink receivers 84. The ink receivers 84 are disposed below the recording heads 30 and on the inner side of the paper transport belt 51. The ink receivers 84 receive ink that has passed through the openings 511 of the paper transport belt 51 during flushing.

[0036] 4, when sheets S are conveyed in order in conveying direction D1 by paper conveying belt 51, control unit 7 executes a preset flushing process at a predetermined timing for opening group 512 immediately before sheet S, and then executes an image printing process for sheet S upstream of opening group 512. For example, when control unit 7 executes a predetermined flushing process for opening group 512A immediately before sheet S1, it executes an image printing process for sheet S1 upstream of opening group 512A.

[0037] However, conventional inkjet recording devices perform flushing processing under uniformly determined ejection conditions for all nozzles in a recording head. Therefore, flushing processing is performed under uniformly determined ejection conditions even for nozzles that do not require flushing processing or nozzles that do not mind a small amount of ink ejected during flushing processing. This can result in unnecessary consumption of ink.

[0038] In contrast, in the inkjet recording device 10 according to this embodiment, as described below, ejection conditions are determined for each nozzle, making it possible to reduce unnecessary consumption of ink during flushing that is performed while the printing process is being executed.

[0039] The control unit 7 will be described below with reference to FIG. In FIG. 5, the flow of image data is indicated by solid arrows, and the flow of control signals is indicated by dashed arrows. As shown in FIG. 5, the control unit 7 includes a main control unit 71 and a plurality of signal processing units 72. The signal processing units 72 are provided corresponding to the plurality of piezoelectric elements 302 corresponding to the plurality of nozzles 30B. Although FIG. 3 shows one signal processing unit 72, the control unit 7 actually includes a plurality of signal processing units 72 corresponding to the plurality of piezoelectric elements 302. Furthermore, in FIG. 3, the recording head includes one head driver 301 and one piezoelectric element 302, but in reality, the recording head 30 includes a plurality of head drivers 301 and one piezoelectric element 302 corresponding to each of the nozzles 30B.

[0040] The main control unit 71 comprehensively controls the inkjet recording apparatus 10. Specifically, the main control unit 71 includes control devices such as a CPU, a ROM, and a RAM (not shown). The CPU is a processor that executes various arithmetic operations. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile storage unit used as a temporary storage memory (work area) for various processes executed by the CPU. In the main control unit 71, the CPU executes various control programs previously stored in the ROM. As a result, the inkjet recording apparatus 10 is comprehensively controlled by the main control unit 71.

[0041] 5, the main control unit 71 includes a conversion processing unit 711, a generation processing unit 712, and an ejection number counting unit 713 (an example of an ejection number acquiring unit of the present invention). Specifically, the main control unit 71 functions as the conversion processing unit 711, the generation processing unit 712, and the ejection number counting unit 713 by executing the control program stored in the ROM.

[0042] The conversion processing unit 711 converts each pixel data included in the image data printed by the inkjet recording device 10 into either ejection pixel data corresponding to the ejection of ink from nozzle 30B corresponding to a position in the main scanning direction in the image data of the pixel data, or non-ejection pixel data corresponding to non-ejection of ink from nozzle 30B corresponding to a position in the main scanning direction of the pixel data.

[0043] Here, the ejection pixel data is data corresponding to the drawing drive signal (hereinafter referred to as a first drive signal) that can cause the piezoelectric element 302 to eject ink from the nozzle 30B during image printing processing. Also, the non-ejection pixel data is data corresponding to the drawing drive signal (hereinafter referred to as a second drive signal) that cannot cause the piezoelectric element 302 to eject ink from the nozzle 30B during image printing processing.

[0044] When a continuous printing process is executed to sequentially print multiple pieces of the image data, the generation processing unit 712 generates print data in which each piece of image data to be printed in the continuous printing process is arranged in printing order via paper spacing data corresponding to the paper spacing between the image data.

[0045] Specifically, the generation processing unit 712 generates the print data in which each of the image data after conversion processing by the conversion processing unit 711 is arranged in printing order via the sheet-to-sheet data. Here, the sheet-to-sheet data is data composed of the non-ejection pixel data. Note that the sheet-to-sheet data may include data added upstream in the sub-scanning direction from the image data printed first in the continuous printing process, and data added downstream in the sub-scanning direction from the image data printed last in the continuous printing process.

[0046] The generation processing unit 712 outputs each of the pixel data included in the generated print data to the signal processing unit 72 corresponding to the position of the pixel data in the main scanning direction in the print data. Specifically, the generation processing unit 712 outputs each of the pixel data in order from the upstream side to the downstream side in the sub-scanning direction in the print data.

[0047] In addition, when a single printing process is executed to print one piece of the image data, the generation processing unit 712 outputs the image data after conversion processing by the conversion processing unit 711 as the print data, and each piece of pixel data contained in the print data to the signal processing unit 72 corresponding to the position of the pixel data in the main scanning direction in the print data.

[0048] When a process for printing one page of the print data (an example of a first print process) is executed, the discharge count unit 713 executes a process of acquiring the number of times ink is discharged from each nozzle 30B during the execution period of the print process for each nozzle 30B. For example, the discharge count unit 713 counts the number of discharged pixels (number of pixels) corresponding to each nozzle 30B based on the print data for which the print process has been executed. Here, the discharged pixels are pixels corresponding to the discharge of ink from the nozzle 30B. The number of pixels corresponding to each nozzle 30B is, in other words, the number of discharges of each nozzle 30B when printing one page of the print data. In this case, the discharge count unit 713 stores the counted number of pixels for each nozzle 30B as the number of discharges in the RAM of the main control unit 71 or the like.

[0049] In addition, the ejection count counting unit 713 may count the number of pixels as the number of ejections based on the print data generated by the generation processing unit 712, or may count the number of pixels as the number of ejections based on the image data after conversion processing by the conversion processing unit 711.

[0050] Furthermore, the ejection counting section 713 may use an internal counter to count the number of times the first drive signal is output to the piezoelectric element 302 of each nozzle 30B during the execution period of the process of printing one page of the print data as the ejection number.

[0051] The discharge counting unit 713 does not have to be provided in the main control unit 71, and may be provided in each signal processing unit 72 corresponding to each nozzle 30B. For example, the discharge counting unit 713 is provided in a drive control unit 725 described later, and an internal counter of the discharge counting unit 713 counts the number of times the first drive signal is output to the piezoelectric element 302 of the nozzle 30B as the discharge number.

[0052] The signal processing unit 72 controls the driving of the piezoelectric element 302 based on the pixel data input from the generation processing unit 712 .

[0053] Specifically, the signal processing unit 72 is composed of electronic circuits such as integrated circuits (ASIC, DSP). As shown in Fig. 5, the signal processing unit 72 includes a first buffer 721, a non-ejection time counting unit 722 (an example of a non-ejection time acquiring unit of the present invention), a flushing condition determining unit 723 (an example of a flushing condition determining unit of the present invention), a second buffer 724, and a drive control unit 725 (an example of a flushing control unit of the present invention). In the signal processing unit 72, the pixel data output from the generation processing unit 712 is input to both the first buffer 721 and the second buffer 724.

[0054] The first buffer 721 outputs each of the pixel data included in the print data input from the generation processing unit 712 to the non-ejection time counting unit 722. Specifically, the first buffer 721 outputs each of the pixel data included in the print data at predetermined time intervals in order from the upstream side in the sub-scanning direction. Here, the time interval is a drive interval in the head driver 301, and is the time it takes for the ink ejection position (pixel recording position) by the nozzle 30B on the sheet to move by one pixel downstream in the sub-scanning direction by the transport unit 5.

[0055] The second buffer 724 outputs each of the pixel data included in the print data input from the generation processing unit 712 to the drive control unit 725. Specifically, the second buffer 724 outputs each of the pixel data included in the print data at the time intervals in order from the upstream side in the sub-scanning direction. Note that the second buffer 724 may output each of the pixel data included in the print data to the drive control unit 725 with a delay of a predetermined delay time from the first buffer 721, as necessary.

[0056] The non-ejection time counting unit 722 performs a process of acquiring the non-ejection time during the execution period of a process (an example of a first print process) for printing one page of the print data. Here, the non-ejection time is a time interval during the execution period of the print process during which a non-ejection state in which ink is not ejected from nozzle 30B continues. In this embodiment, when a print process for printing the print data is executed, the non-ejection time counting unit 722 counts the non-ejection time from the last time ink was ejected from nozzle 30B during the execution of the print process.

[0057] Specifically, the non-ejection time counting unit 722 extracts, as the non-ejection time, the output time of a non-ejection pixel row identified based on each of the pixel data input from the first buffer 721. Here, the non-ejection pixel row refers to a pixel row in which non-ejection pixels corresponding to the non-ejection of ink in the print data input from the generation processing unit 712 continue.

[0058] More specifically, the non-ejection time counting unit 722 counts the number of consecutive inputs of the non-ejection pixels from the first buffer 721. For example, when an ejection pixel corresponding to the ejection of ink is input from the first buffer 721, the non-ejection time counting unit 722 resets the count value and counts the number of consecutive inputs of the non-ejection pixels again. Furthermore, when the printing process ends without an ejection pixel corresponding to the ejection of ink being input from the first buffer 721, the non-ejection time counting unit 722 outputs the count value of the number of consecutive inputs of the non-ejection pixels that it has counted to the flushing condition determination unit 723 as the non-ejection time.

[0059] Note that, for example, when the count value of the consecutive number exceeds a predetermined reference number, the non-ejection time counting section 722 may output the count value to the flushing condition determination section 723 as the non-ejection time.

[0060] For example, as shown in Fig. 5, the non-ejection time counting unit 722 includes a counter 722A. The counter 722A counts the number of consecutive inputs of the non-ejection pixels from the first buffer 721. Specifically, each time the pixel data is input from the first buffer 721, the counter 722A judges whether the input pixel data is the non-ejection pixel data indicating the non-ejection pixel or the ejection pixel data indicating the ejection pixel. If the pixel data input from the first buffer 721 is the non-ejection pixel data, the counter 722A counts up a count value in a count memory (not shown) of the counter 722A. If the pixel data input from the first buffer 721 is the ejection pixel data, the counter 722A resets the count value (i.e., the number of consecutive non-ejection pixels) counted up to that point.

[0061] When the pixel data of the final line is input from the first buffer 721 and it is the non-ejection pixel data, the non-ejection time counting unit 722 counts up the count value in the count memory (not shown) of the counter 722A and then outputs the count value up to that point to the flushing condition determination unit 723 as the non-ejection time.

[0062] In addition, the non-ejection time counting unit 722 may measure the time during which the non-ejection pixel data is continuously input from the first buffer 721 as the non-ejection time, instead of counting the number of consecutive inputs of the non-ejection pixel from the first buffer 721.

[0063] The flushing condition determination unit 723 performs a process of determining the execution conditions of the flushing process (hereinafter referred to as flushing conditions) for each of the nozzles 30B based on both or either one of the non-ejection time and the number of ejections corresponding to the nozzles 30B that perform the flushing process. Here, the flushing conditions are conditions that are determined for each nozzle 30B, such as whether or not to perform the flushing process, the specified amount in the flushing process, etc.

[0064] In this embodiment, the flushing condition determination unit 723 determines whether or not to execute the flushing process for each of the plurality of nozzles 30B based on either or both of the non-ejection time and the number of ejections.

[0065] Furthermore, the flushing condition determination unit 723 determines the specified amount that defines the amount of ink ejected when the flushing process is performed for each of the multiple nozzles 30B, based on either or both of the non-ejection time and the number of ejections.

[0066] Specifically, the flushing condition determination unit 723 determines whether or not to execute the flushing process based on the number of ejections when the non-ejection time is equal to or longer than a predetermined reference time. The reference time can be determined arbitrarily depending on the type and specifications of the ink used, or the environmental conditions in which the inkjet recording apparatus 10 is used.

[0067] Furthermore, the flushing condition determination unit 723 determines not to execute the flushing process when the number of ejections is equal to or greater than a predetermined reference number, and determines to execute the flushing process when the number of ejections is less than the reference number. The reference number can be arbitrarily determined according to the type and specifications of the ink used, the environmental conditions in which the inkjet recording apparatus 10 is used, and the like.

[0068] Furthermore, when the non-ejection time is less than a predetermined reference time, the flushing condition determination unit 723 determines the specified amount based on the non-ejection time. For example, the flushing condition determination unit 723 increases the specified amount as the non-ejection time is longer, and decreases the specified amount as the non-ejection time is shorter.

[0069] Then, the flushing condition determination unit 723 outputs the determined flushing condition to the drive control unit 725 .

[0070] The drive control unit 725 inputs the predetermined drive signal from the head driver 301 to the piezoelectric element 302, causing ink to be ejected from the nozzle 30B.

[0071] When an image printing process is performed on a sheet, the drive control unit 725 outputs the drawing drive signal corresponding to the pixel data input from the second buffer 724 to the head driver 301. For example, when the ejection pixel data is input, the drive control unit 725 outputs the first drive signal to the head driver 301, and when the ejection pixel data is input, the drive control unit 725 outputs the second drive signal to the head driver 301.

[0072] Furthermore, when the flushing process is performed during the execution of the printing process, the drive control unit 725 outputs the flushing drive signal for ejecting a predetermined amount of ink from the nozzle 30B during a non-printing period when the printing process is not performed on the sheet to the head driver 301. This allows the flushing process to be performed during the execution of the printing process.

[0073] Here, the non-printing period is a period during which the opening group 512 (see FIG. 4) on which no sheet is placed on the paper transport belt 51 passes over the facing surface 30A of the recording head 30. The fact that the opening group 512 has reached the facing surface 30A is determined by the main control unit 71 based on information such as signals from the belt sensors 82 and 83, the belt transport speed, the elapsed time from detection, and the distance from each sensor. A flushing timing signal indicating that the opening group 512 has reached the facing surface 30A is input from the main control unit 71 to the drive control unit 725.

[0074] In this embodiment, the drive control unit 725 generates specific pixel data corresponding to the flushing drive signal based on the flushing condition input from the flushing condition determination unit 723 and the flushing timing signal input from the main control unit 71, and outputs the specific pixel data to the head driver 301. In this embodiment, the drive control unit 725 generates the specific pixel data when the flushing timing signal is input.

[0075] The specific pixel data corresponds to the flushing drive signal and is generated based on the flushing conditions. For example, when the following four gradation levels (levels 0 to 4) are set as an index indicating the specified amount, the specific pixel data is pixel data of a density corresponding to each gradation level. Here, "gradation level: 0" is a gradation level indicating that the specified amount is zero. "gradation level: 1" is a gradation level indicating that the specified amount is small. "gradation level: 2" is a gradation level indicating that the specified amount is medium. "gradation level: 3" is a gradation level indicating that the specified amount is sufficient for nozzle maintenance. The pixel data of the gradation level "0" is pixel data having no density. Note that the gradation levels as an index indicating the specified amount are not limited to the four levels illustrated, and may be set to at least two levels.

[0076] The head driver 301 generates a precursor drive signal (the drawing signal, the flushing drive signal) for driving the piezoelectric element 302 based on the pixel data from the drive control unit 725 , and outputs it to the piezoelectric element 302 .

[0077] That is, when the pixel data input from the drive control unit 725 is the ejection pixel data, the head driver 301 generates the first drive signal (the drawing signal) corresponding to the ejection pixel data, and inputs the first drive signal to the piezoelectric element 302. In addition, when the pixel data from the drive control unit 725 is the non-ejection pixel data, the head driver 301 inputs the second drive signal (the drawing signal) to the piezoelectric element 302.

[0078] As a result, the image data or the image data included in the print data is printed.

[0079] In addition, when the pixel data input from the drive control unit 725 is the specific pixel data, the head driver 301 generates the flushing drive signal corresponding to the specific pixel data and inputs the flushing drive signal to the piezoelectric element 302.

[0080] As a result, during the non-printing period, the flushing process is executed based on the flushing conditions determined for each nozzle 30B.

[0081] Hereinafter, an example of the procedure of the process for determining the flushing conditions (flushing condition determination process) executed in the inkjet recording apparatus 10 will be described with reference to the flowchart of Fig. 6, and the flushing condition determination method of the present invention shown in the flowchart of Fig. 6 will be described. In this embodiment, the processes from steps S11 to S19 are performed for each nozzle 30B.

[0082] First, in step S11, the number of ejections is counted by the ejection number counter 713, and in the next step S12, the non-ejection time is counted by the non-ejection time counter 722.

[0083] In the next step S13, the control unit 7 determines whether the non-ejection time is less than a predetermined first reference time t1. Here, the first reference time t1 is set to, for example, a count value of the number of consecutive inputs of the non-ejection pixels, "200."

[0084] If it is determined in step S13 that the non-ejection time is less than the first reference time t1, the control unit 7 sets the gradation level of the corresponding nozzle 30B to "gradation level: 3" (S16).

[0085] If it is determined in step S13 that the non-ejection time is equal to or longer than the first reference time t1, the control unit 7 determines in the next step S14 whether the non-ejection time is shorter than a predetermined second reference time t2, where the second reference time t2 is set to, for example, a count value of the number of consecutive inputs of the non-ejection pixels, "100".

[0086] If it is determined in step S14 that the non-ejection time is less than the second reference time t2, the control unit 7 sets the gradation level of the corresponding nozzle 30B to "gradation level: 2" (S17).

[0087] If it is determined in step S14 that the non-ejection time is equal to or longer than the second reference time t2, the control unit 7 determines in the next step S15 whether the number of ejections is equal to or longer than a predetermined reference number c1. Here, the reference number c1 is set to, for example, "2000 times."

[0088] If it is determined in step S15 that the number of ejections is equal to or greater than the reference number c1, the control unit 7 sets the gradation level of the corresponding nozzle 30B to "gradation level: 1" (S18). On the other hand, if it is determined in step S15 that the number of ejections is less than the reference number c1, the control unit 7 sets the gradation level of the corresponding nozzle 30B to "gradation level: 0" (S19).

[0089] Once the gradation level has been set for each of the nozzles 30B, the control unit 7 then executes a flushing process in which the specified amount of ink corresponding to the set gradation level is ejected from the corresponding nozzle 30B on condition that the flushing timing signal has been input (S20). Note that for nozzles 30B for which the gradation level is set to "0", the specified amount is zero, so no ink is ejected.

[0090] As described above, in the embodiment of the present invention, the flushing condition determination process is performed, so that the flushing conditions are not uniformly determined for the multiple nozzles 30B, but are determined for each nozzle 30B according to the number of times each nozzle 30B has previously ejected and the length of non-ejection time. As a result, the flushing process is not performed for nozzles 30B that do not require the flushing process, and the flushing process is performed only for nozzles 30B that require the flushing process. In addition, the amount of ink ejected during the flushing process is also determined for each nozzle 30B, so that a small amount of ink is ejected for nozzles 30B that do not require a small amount of ink ejection, and a relatively large amount of ink is ejected for nozzles 30B that require a sufficient amount of ink ejection. As a result, it is possible to reduce wasteful consumption of ink during the flushing process performed during the execution of the printing process.

[0091] [Notes on the invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0092] <Appendix 1> a recording head having a plurality of nozzles from which ink is ejected, and piezoelectric elements provided corresponding to each of the plurality of nozzles and for ejecting the ink from the nozzles; a flushing control unit that controls a flushing process for ejecting a predetermined amount of ink from the nozzles during a non-printing period during an execution period of a first printing process that prints predetermined first image data; a non-ejection time acquisition unit that acquires, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzles continues during an execution period of the first printing process based on the first image data; an ejection count acquisition unit that acquires, when the first printing process is executed, an ejection count of the number of times the ink is ejected from the nozzles during an execution period of the first printing process for each of the plurality of nozzles based on the first image data; a flushing condition determination unit that determines an execution condition of the flushing process for each of the plurality of nozzles based on either or both of the non-ejection time and the number of ejections.

[0093] <Appendix 2> The inkjet recording apparatus according to claim 1, wherein the flushing condition determination unit determines whether or not to execute the flushing process for each of the nozzles based on either or both of the non-ejection time and the number of ejections.

[0094] <Appendix 3> 3. The inkjet recording apparatus according to claim 1, wherein the flushing condition determination unit determines the specified amount for each of the plurality of nozzles based on either or both of the non-ejection time and the number of ejections.

[0095] <Appendix 4> The flushing condition determination unit 4. The inkjet recording apparatus according to claim 1, further comprising: a step of: determining whether or not to execute the flushing process based on the number of ejections when the non-ejection time is equal to or longer than a predetermined reference time.

[0096] <Appendix 5> The flushing condition determination unit An inkjet recording apparatus according to any one of claims 1 to 4, wherein the inkjet recording apparatus determines not to perform the flushing process when the number of ejections is equal to or greater than a predetermined reference number, and determines to perform the flushing process when the number of ejections is less than the reference number.

[0097] <Appendix 6> The flushing condition determination unit 6. The inkjet recording apparatus according to claim 1, wherein, when the non-ejection time is shorter than a predetermined reference time, the specified amount is determined based on the non-ejection time.

[0098] <Appendix 7> The inkjet recording apparatus according to any one of claims 1 to 6, wherein the flushing condition determination unit increases the specified amount as the non-ejection time is longer, and decreases the specified amount as the non-ejection time is shorter.

[0099] <Appendix 8> 1. A method for determining a flushing condition executed in an inkjet recording apparatus having a recording head having a plurality of nozzles from which ink is ejected, and piezoelectric elements provided corresponding to each of the plurality of nozzles and causing the ink to be ejected from the nozzles, comprising: acquiring, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzles continues during an execution period of a first print process for printing the first image data based on predetermined first image data; when the first printing process is executed, acquiring, for each of the plurality of nozzles, the number of times that the ink is ejected from the nozzle during an execution period of the first printing process, based on the first image data; and determining, for each of the plurality of nozzles, execution conditions for a flushing process that causes a predetermined amount of ink to be ejected from the nozzle during a non-printing period during execution of the first printing process, based on both or either one of the non-ejection time and the number of ejections. [Explanation of symbols]

[0100] 5: Transport unit 7: Control section 10: Inkjet recording device 30: Recording head 30A: Opposite surface 30B: Nozzle 31: Line Head 32: Line Head 33: Line Head 34: Line Head 35: Head frame 51: Paper conveyor belt 55: Transport frame 56: Pressure roller 71: Main control section 72: Signal processing section 81: Sheet sensor 82: Belt sensor 83: Belt sensor 84: Ink receiver 301: Head driver 302: Piezoelectric element 511 :Aperture 512:Aperture group 711: Conversion processing section 712: Generation processing unit 713: Discharge count unit 721: First buffer 722: Non-ejection time counter 723: Flushing condition determination section 724: Second buffer 725: Drive control unit

Claims

1. a recording head having a plurality of nozzles from which ink is ejected, and piezoelectric elements provided corresponding to each of the plurality of nozzles and for ejecting the ink from the nozzles; a flushing control unit that controls a flushing process for ejecting a predetermined amount of ink from the nozzles during a non-printing period during an execution period of a first printing process for printing predetermined first image data; a non-ejection time acquisition unit that acquires, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzles continues during an execution period of the first printing process based on the first image data; an ejection count acquisition unit that acquires, when the first printing process is executed, an ejection count of the ink ejected from the nozzle during an execution period of the first printing process for each of the plurality of nozzles based on the first image data; a flushing condition determination unit that determines an execution condition of the flushing process for each of the plurality of nozzles based on either or both of the non-ejection time and the number of ejections.

2. The inkjet recording apparatus according to claim 1 , wherein the flushing condition determination unit determines whether or not to execute the flushing process for each of the plurality of nozzles based on either or both of the non-ejection time and the number of ejections.

3. The inkjet recording apparatus according to claim 1 , wherein the flushing condition determination unit determines the specified amount for each of the plurality of nozzles based on either or both of the non-ejection time and the number of ejections.

4. The flushing condition determination unit The inkjet recording apparatus according to claim 1 , wherein when the non-ejection time is equal to or longer than a predetermined reference time, it is determined whether or not to execute the flushing process based on the number of ejections.

5. The flushing condition determination unit 5. The inkjet recording apparatus according to claim 4, wherein the flushing process is determined not to be executed when the number of ejections is equal to or greater than a predetermined reference number, and the flushing process is determined to be executed when the number of ejections is less than the reference number.

6. The flushing condition determination unit The inkjet recording apparatus according to claim 1 , wherein, when the non-ejection time is less than a predetermined reference time, the specified amount is determined based on the non-ejection time.

7. The inkjet recording apparatus according to claim 6 , wherein the flushing condition determination unit increases the specified amount as the non-ejection time is longer, and decreases the specified amount as the non-ejection time is shorter.

8. 1. A method for determining flushing conditions executed in an inkjet recording apparatus having a recording head having a plurality of nozzles from which ink is ejected, and piezoelectric elements provided corresponding to each of the plurality of nozzles and causing the ink to be ejected from the nozzles, comprising: acquiring, for each of the plurality of nozzles, a non-ejection time during which a non-ejection state in which the ink is not ejected from the nozzles continues during an execution period of a first print process for printing the first image data based on predetermined first image data; when the first printing process is executed, acquiring, for each of the plurality of nozzles, the number of times that the ink is ejected from the nozzles during an execution period of the first printing process based on the first image data; and determining, for each of the plurality of nozzles, execution conditions for a flushing process that causes a predetermined amount of ink to be ejected from the nozzle during a non-printing period during execution of the first printing process, based on both or either one of the non-ejection time and the number of ejections.

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