JP2025011551A - Inkjet recording apparatus and inkjet recording method - Google Patents

Abstract

An inkjet recording apparatus and an inkjet recording method are provided that are capable of improving the image quality of printed matter by reducing ink ejection defects caused by drying of ink without performing preliminary ejection of ink.
[Solution] The inkjet recording device comprises a recording head 30 having a nozzle from which ink is ejected and a piezoelectric element 302, a dot counting unit 713 that counts the number of ejected pixels based on the image data printed in a printing process, an extraction processing unit 722 that extracts non-ejection periods based on the image data, a drive control unit 725 that inputs a predetermined second drive signal to the piezoelectric element 302, and a setting processing unit 723 that sets the start timing of input of the second drive signal based on the length of the non-ejection period, and the setting processing unit 723 sets the start timing corresponding to the number of pixels based on the length of the non-ejection period.
[Selected figure] Figure 3

Description

The present invention relates to an inkjet recording device and an inkjet recording method.

In an inkjet recording device that forms images using the inkjet method, ink is ejected from the nozzles onto a sheet by applying a voltage to a piezoelectric element that is 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 as the ink dries. In this case, the image quality of the printed matter printed by the inkjet recording device decreases.

In addition, in an inkjet recording device, if the nozzles continue to fail to eject ink even during printing, the ink may dry out and change the viscosity of the ink, causing a change in the amount of ink ejected from the nozzles. Conventionally, inkjet recording devices have been disclosed that are capable of changing the minimum number of preliminary ejections required depending on the head temperature of the recording head (see, for example, Patent Document 1).

JP 2006-168041 A

However, when printing an image that requires a large amount of ink ejection, the amount of heat generated by the recording head itself and the head driver installed in the recording head increases during the printing process, causing the temperature to rise in the areas around the nozzles and in the flow paths leading to the nozzles, accelerating the drying of the ink in the nozzles and resulting in poor ink ejection.

The object of the present invention is to provide an inkjet recording device and an inkjet recording method that can improve the image quality of printed matter by reducing ink ejection defects caused by an increase in ink viscosity due to ink drying, without performing preliminary ink ejection.

The inkjet recording device according to one aspect of the present invention includes a recording head having a nozzle from which ink is ejected and a piezoelectric element that is provided corresponding to the nozzle and ejects the ink from the nozzle in response to input of a predetermined first drive signal; a pixel number counting unit that counts the number of ejection pixels corresponding to the ejection of the ink in the image data based on the image data printed in the printing process when a printing process for printing one image data is executed; an extraction processing unit that extracts a non-ejection period during the execution period of the printing process during which a non-ejection state in which the ink is not ejected from the nozzle continues beyond a predetermined reference time based on the image data printed in the printing process; a drive control unit that inputs a predetermined second drive signal to the piezoelectric element that can stir the ink in the nozzle and cannot eject the ink from the nozzle; and a setting processing unit that sets the start timing of the input of the second drive signal during the non-ejection period based on the length of the non-ejection period, and the setting processing unit sets the start timing according to the number of pixels counted by the pixel number counting unit based on the length of the non-ejection period.

An inkjet recording method according to another aspect of the present invention is an inkjet recording method executed by an inkjet recording device equipped with a recording head having nozzles from which ink is ejected and piezoelectric elements provided corresponding to the nozzles and ejecting the ink from the nozzles in response to input of a predetermined first drive signal. The inkjet recording method includes, when a printing process for printing one image data is executed, counting the number of ejection pixels corresponding to the ejection of the ink in the image data based on the image data printed in the printing process, extracting a non-ejection period during the execution period of the printing process during which a non-ejection state in which the ink is not ejected from the nozzle continues beyond a predetermined reference time based on the image data printed in the printing process, inputting a predetermined second drive signal capable of stirring the ink in the nozzle and disabling the ink from the nozzle to the piezoelectric element, and setting the start timing of input of the second drive signal during the non-ejection period according to the number of pixels based on the length of the non-ejection period.

According to the present invention, it is possible to reduce ink ejection failures caused by ink drying and improve the image quality of printed matter without performing preliminary ink ejection.

FIG. 1 is a diagram showing the configuration of an inkjet recording apparatus according to an embodiment of the present invention. 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. FIG. 3 is a block diagram showing the configuration of a control unit of the inkjet recording apparatus according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of table data used in the inkjet printing apparatus according to the embodiment of the present invention. FIG. 5 is a diagram for explaining the processing contents in the signal processing section of the inkjet printing apparatus according to the embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the attached 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.

[Schematic configuration of inkjet recording apparatus 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 Figures 1 to 3. Here, Figure 1 is a schematic cross-sectional view showing the configuration of the inkjet recording apparatus 10. Also, Figure 2 is a plan view showing the configuration of the recording unit 3. In Figure 3, the flow of image data is indicated by arrows, and the flow of control signals is indicated by dashed lines.

The inkjet recording device 10 is a printer capable of forming images using an inkjet method. The present invention may also be applied to inkjet recording devices such as facsimile machines, copy machines, and multifunction machines capable of forming images using an inkjet method.

As shown in FIG. 1, the inkjet recording device 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.

The paper feed cassette 1 contains sheets to be printed by the inkjet recording device 10. For example, the sheets contained in the paper feed cassette 1 are sheet materials such as paper, coated paper, postcards, envelopes, and overhead projector sheets.

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 sheets picked up by the pickup roller 21 to the registration roller 24. The transport path 23 is a path along which the sheets move from the paper feed cassette 1 and the manual feed tray 25 to the recording unit 3. The registration roller 24 transports the sheets 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.

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 the housing 11 of the inkjet recording device 10. The number of line heads included in the recording unit 3 may be one, or multiple, excluding four.

The line heads 31 to 34 are so-called line head type recording heads. In other words, the inkjet recording device 10 is a so-called line head type inkjet recording device. The line heads 31 to 34 are long in the 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 that corresponds to the width of the largest size sheet that can be accommodated in the paper feed cassette 1. Each of the line heads 31 to 34 is fixed to the head frame 35 at a predetermined distance apart along the sheet transport direction D1.

As shown in FIG. 2, each of the line heads 31 to 34 has a plurality of recording heads 30. The recording head 30 has nozzles 30B from which ink is ejected and piezoelectric elements 302 (see FIG. 3) provided corresponding to the nozzles 30B. The recording head 30 ejects ink toward a sheet transported by the transport unit 5. Specifically, a number of nozzles 30B having openings for ejecting ink are provided on the surface 30A (see FIG. 1) of the recording head 30 facing the sheet transported by the transport unit 5. The recording head 30 also has a plurality of pressure chambers (not shown) corresponding to each of the nozzles 30B, a plurality of piezoelectric elements 302 (see FIG. 3) provided corresponding to each of the pressure chambers, and a communication flow path (not shown) communicating with each of the pressure chambers. The piezoelectric elements 302 eject ink from the nozzles 30B in response to the input of a predetermined first drive signal. For example, the first drive signal is a clock signal having a predetermined voltage, frequency, and duty ratio. Specifically, the piezoelectric element 302 pressurizes the ink contained in the pressure chamber, causing the ink to be ejected from the nozzle 30B.

As shown in FIG. 3, the recording head 30 also includes a head driver 301 (an example of a drive unit of the present invention). The head driver 301 is provided corresponding to each of the piezoelectric elements 302. The head driver 301 generates a drive signal for driving the piezoelectric element 302 based on pixel data input from the control unit 7, and controls the drive of the piezoelectric element 302 by inputting the generated drive signal to the piezoelectric element 302. Examples of the drive signal are the first drive signal, the second drive signal, and the third drive signal described below.

In this embodiment, the line head 31 has three recording heads 30 arranged in a staggered pattern 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 pattern along the width direction D2. Note that FIG. 2 shows the recording unit 3 as viewed from above in FIG. 1.

The ink container section 4 includes ink containers 41, 42, 43, and 44 that contain ink corresponding to the colors 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 section (not shown).

The transport unit 5 is disposed below the line heads 31 to 34. The transport unit 5 transports the sheet while facing the facing surface 30A of the recording head 30. As shown in FIG. 1, the transport unit 5 includes a paper transport belt 51 on which the 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 facing surface 30A is adjusted so that the gap between the surface of the sheet and the facing surface 30A during image recording is, for example, 1 mm.

The tension roller 52 is connected to the rotating shaft of a motor (not shown). When the tension roller 52 is rotated counterclockwise by the drive of the motor, the paper transport belt 51 rotates in a direction that allows the sheet to be transported in the transport direction D1. As a result, the sheet supplied from the paper feed section 2 is transported by the rotation of the paper transport belt 51 through the recording section 3 toward the paper discharge section 6. The transport unit 5 is also provided with a suction unit (not shown) that sucks air through a number of through holes formed in the paper transport belt 51 to adsorb the sheet to the paper transport belt 51. In addition, a pressure roller 56 is provided opposite the tension roller 53 to press the sheet against the paper transport belt 51 for transport.

The paper discharge unit 6 is provided downstream of the recording unit 3 in the transport direction D1. As shown in FIG. 1, 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 the 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.

However, in the inkjet recording device 10, the amount of ink ejected from the nozzle 30B may change due to an increase in the viscosity of the ink caused by the drying of the ink. In this case, the image quality of the printed matter printed by the inkjet recording device 10 decreases. Furthermore, when printing an image that ejects a large amount of ink, the amount of heat generated by the recording head 30 itself and the head driver 301 provided in the recording head 30 increases during the printing process, causing the temperature of the area around the nozzle 30B and the communicating flow path to rise, accelerating the drying of the ink in the nozzle 30B. In this case, the viscosity of the ink increases further, which may lead to poor ink ejection in the recording head 30.

In contrast, in the inkjet recording device 10 according to this embodiment, as described below, it is possible to reduce ink ejection failures caused by dried ink and improve the image quality of printed matter without performing preliminary ink ejection even during printing processing.

The control unit 7 will be described below with reference to FIG. 3. As shown in FIG. 3, the control unit 7 includes a main control unit 71 and multiple signal processing units 72. The signal processing units 72 are provided corresponding to each of the multiple piezoelectric elements 302 corresponding to the multiple nozzles 30B. Note that while FIG. 3 shows one signal processing unit 72, in reality the control unit 7 includes multiple signal processing units 72 corresponding to each of the multiple piezoelectric elements 302.

The main control unit 71 comprehensively controls the inkjet recording device 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 control programs 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 the various processes executed by the CPU. In the main control unit 71, the CPU executes the various control programs pre-stored in the ROM. As a result, the inkjet recording device 10 is comprehensively controlled by the main control unit 71.

3, the main control unit 71 includes a conversion processing unit 711, a generation processing unit 712, a dot count unit 713, and a table selection processing unit 714. Specifically, the main control unit 71 functions as the conversion processing unit 711, the generation processing unit 712, the dot count unit 713, and the table selection processing unit 714 by executing the control program stored in the ROM.

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 the position in the main scanning direction of the pixel data in the image data, or non-ejection pixel data corresponding to the non-ejection of ink from nozzle 30B corresponding to the position in the main scanning direction of the pixel data.

Here, the ejection pixel data is data corresponding to the first drive signal that can cause the piezoelectric element 302 to eject ink from the nozzle 30B. The non-ejection pixel data is data corresponding to the third drive signal that cannot cause the piezoelectric element 302 to eject ink from the nozzle 30B.

When a continuous printing process is executed to sequentially print a plurality of the image data, the generation processing unit 712 generates print data in which each of the image data to be printed in the continuous printing process is arranged in printing order via sheet spacing data corresponding to the sheet spacing between the image data.

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 that is added upstream in the sub-scanning direction from the image data that is printed first in the continuous printing process, and data that is added downstream in the sub-scanning direction from the image data that is printed last in the continuous printing process.

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.

In addition, when a single printing process is executed to print one 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 of the pixel data included 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.

The dot count unit 713 is an example of a pixel count unit of the present invention. When a process for printing one page of the print data is executed, the dot count unit 713 counts the number of ejected pixels (pixel count) in the print data for one page based on the print data for one page before the print process is executed. Here, the ejected pixels are pixels corresponding to the ejection of ink from the nozzle 30B. The dot count unit 713 stores the counted pixel count in the RAM of the main control unit 71. The dot count unit 713 may count the pixel count based on the print data generated by the generation processing unit 712, or may count the pixel count based on the image data after the conversion processing by the conversion processing unit 711.

The table selection processing unit 714 selects table identification information according to the number of pixels. For example, when there are table identification information X11 and table identification information X12 as the table identification information indicating each of the two table data X (X11, X12) shown in FIG. 4, the table selection processing unit 714 selects either the table identification information X11 or the table identification information X12 based on the number of pixels. Specifically, the table selection processing unit 714 selects the table identification information X11 when the number of pixels is equal to or greater than a predetermined threshold. Also, the table selection processing unit 714 selects the table identification information X12 when the number of pixels is less than a predetermined threshold. The threshold is set to a value that can be evaluated as the temperature of the recording head 30 or the like being higher than a predetermined set temperature when printing an image with a large amount of ink ejection (an image with a large number of pixels) in the printing process.

The table selection processing unit 714 outputs the selected table identification information to a setting processing unit 723 (described later) included in the signal processing unit 72. The table identification information and the table data X (X11, X12) will be described later.

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. The signal processing unit 72 also causes the piezoelectric element 302 to execute flushing to stir the ink in the nozzle 30B during a portion of the non-ejection period during which the non-ejection state in which ink is not ejected from the nozzle 30B continues beyond a predetermined reference time during the execution period of the continuous printing process or the single printing process. In this case, the stirring operation is an operation that only stirs the ink in the nozzle 30B without ejecting ink.

Specifically, the signal processing unit 72 is composed of electronic circuits such as integrated circuits (ASIC, DSP). As shown in FIG. 3, the signal processing unit 72 includes a first buffer 721, an extraction processing unit 722, a setting processing unit 723, a second buffer 724, and a drive control unit 725. 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.

The first buffer 721 outputs each of the pixel data included in the print data input from the generation processing unit 712 to the extraction processing unit 722. Specifically, the first buffer 721 outputs each of the pixel data included in the print data at predetermined time intervals, starting from the upstream side in the sub-scanning direction. Here, the time interval is the driving 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.

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. In addition, the second buffer 724 outputs 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.

For example, as shown in FIG. 3, the second buffer 724 includes a delay circuit 724A. The delay circuit 724A outputs each of the pixel data to the drive control unit 725 after a time (the delay time) obtained by multiplying the time interval by a predetermined specific number has elapsed. That is, the delay circuit 724A delays the output of the pixel data by the number of pixels corresponding to the specific number. For example, the specific number is 1000. In this case, in the signal processing unit 72, the first pixel data is input from the delay circuit 724A to the drive control unit 725 at the timing when the 1001st pixel data is input from the first buffer 721 to the extraction processing unit 722. Note that the specific number may be any number other than 1000.

When the continuous printing process is executed, the extraction processing unit 722 extracts the non-ejection period during the execution period of the continuous printing process based on each of the image data printed in the continuous printing process.

In addition, when the single print process is executed, the extraction processing unit 722 extracts the non-ejection period during the execution period of the single print process based on the image data printed in the single print process.

Specifically, the extraction processing unit 722 extracts the output period of a non-ejection pixel row identified based on each of the pixel data input from the first buffer 721 as the non-ejection period. Here, the non-ejection pixel row refers to a pixel row in which non-ejection pixels corresponding to non-ejection of ink in the print data input from the generation processing unit 712 continue for more than a reference number corresponding to the reference time. The reference number is, for example, 999. In this case, the time obtained by multiplying the time interval by 999 is the reference time. Note that the reference number may be any number other than 999.

More specifically, the extraction processing unit 722 counts the number of consecutive non-ejection pixels input from the first buffer 721, and determines whether the consecutive non-ejection pixels are the non-ejection pixel row based on the result of counting the consecutive number when an ejection pixel corresponding to ink ejection is input from the first buffer 721. That is, the extraction processing unit 722 determines that the consecutive non-ejection pixels are the non-ejection pixel row when the result of counting the consecutive number when the ejection pixel is input from the first buffer 721 exceeds the reference number.

For example, the extraction processing unit 722 includes a counter 722A as shown in FIG. 3. The counter 722A counts the number of consecutive inputs of the non-ejection pixels from the first buffer 721. Specifically, the counter 722A determines 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 each time the pixel data is input from the first buffer 721. Then, when the pixel data input from the first buffer 721 is the non-ejection pixel data, the counter 722A counts up the count value in the count memory (not shown) of the counter 722A. When the pixel data input from the first buffer 721 is the ejection pixel data, the counter 722A notifies the extraction processing unit 722 of the count value counted up to that point (i.e., the number of consecutive non-ejection pixels). In the following, the count value notified to the extraction processing unit 722 from the counter 722A may be referred to as the first count value. After notifying the first count value, the counter 722A resets the count memory of the counter 722A to 0. The extraction processing unit 722 also resets the count memory of the counter 722A to 0 when the continuous printing process or the single printing process is executed.

When the extraction processing unit 722 is notified of the first count value from the counter 722A, the extraction processing unit 722 determines whether the notified first count value exceeds the reference number. If the first count value exceeds the reference number, the extraction processing unit 722 determines that the series of non-ejection pixels is the non-ejection pixel row, and notifies the setting processing unit 723 of the first count value. Furthermore, if the first count value is equal to or less than the reference number, the extraction processing unit 722 determines that the series of non-ejection pixels is not the non-ejection pixel row.

In other words, in the inkjet recording device 10, the extraction processing unit 722 extracts, as the non-ejection period, the period from the timing when the piezoelectric element 302 is driven based on the pixel data input when the counter 722A starts counting up to the timing when the piezoelectric element 302 is driven based on the pixel data input when the count value of the counter 722A is reset after the count value exceeds the reference number.

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

The setting processing unit 723 sets the start timing for starting the flushing during the non-ejection period based on the length of the non-ejection period. In this embodiment, the setting processing unit 723 sets the start timing according to the number of pixels counted by the dot counting unit 713 based on the length of the non-ejection period.

The length of the non-ejection period is the result of counting the number of consecutive non-ejection pixels by the extraction processing unit 722 when the extraction processing unit 722 determines that the series of non-ejection pixels is the non-ejection pixel row (i.e., the first count value that exceeds the reference number notified by the extraction processing unit 722). That is, the setting processing unit 723 sets the start timing according to the number of pixels based on the count value notified by the extraction processing unit 722.

For example, as shown in FIG. 3, the setting processing unit 723 includes a memory unit 723A. The memory unit 723A stores table data X (X11, X12) in which the length of the non-ejection period (the first count value exceeding the reference number notified from the extraction processing unit 722) is associated with a value indicating the start timing. FIG. 4 shows table data X11 and table data X12 as an example of the table data X. Note that, hereinafter, identification information indicating the table data X11 may be referred to as the table identification information X11, and identification information indicating the table data X12 may be referred to as the table identification information X12.

Here, the numerical value of the start timing indicated in the table data X (X11, X12) is a numerical value that is compared with the count value of the counter 725A by the drive control unit 725.

The table data X11 is an example of the first table data of the present invention. The table data X11 is table data selected by the setting processing unit 723 when the number of pixels is equal to or greater than the threshold value. The table data X11 is table data in which a value indicating a first start timing that is earlier than a second start timing described below is defined. In the table data X11, a plurality of first start timings corresponding to a plurality of first count values are defined. In the table data X11, the values "100, 200, 300, ..." indicating the first start timings are numerical values to be compared with the count value after counting down by the counter 725A described below. The specific numerical values of the first start timings are merely examples and can be set arbitrarily.

The table data X12 is an example of the second table data of the present invention. The table data X12 is table data selected by the setting processing unit 723 when the number of pixels is less than the threshold value. The table data X12 is table data in which a second start timing that is later than the first start timing is defined. In the table data X12, a plurality of second start timings corresponding to the plurality of first count values are defined. In the table data X12, the values "70, 140, 210, ..." indicating the second start timing are values that are compared with the count value after counting down by the counter 725A described later. The specific values of the second start timing are merely examples, and can be set arbitrarily as long as they are shorter than the first interval.

When the setting processing unit 723 is notified of the first count value by the extraction processing unit 722, it obtains the start timing based on the notified first count value and the table data X.

In this embodiment, the setting processing unit 723 selects the table data X indicated by the table identification information output from the table selection processing unit 714 from the storage unit 723A, and refers to the table data X to obtain the value of the start timing corresponding to the first count value from the table data X. Note that the table data X selected here is table data corresponding to the number of pixels.

For example, when the table identification information X11 is input from the table selection processing unit 714 to the setting processing unit 723, the setting processing unit 723 selects the table data X11 corresponding to the table identification information X11 from the memory unit 723A, and obtains the value of the first start timing corresponding to the first count value from the table data X11.

In addition, when the table identification information X12 is input from the table selection processing unit 714 to the setting processing unit 723, the setting processing unit 723 selects table data X12 corresponding to the table identification information X12 from the memory unit 723A, and obtains the value of the second start timing corresponding to the first count value from the table data X12.

Then, the setting processing unit 723 notifies the drive control unit 725 of the acquired value of the second start timing, thereby setting the start timing.

The drive control unit 725 inputs a predetermined second drive signal from the head driver 301 to the piezoelectric element 302. In this embodiment, the drive control unit 725 inputs the second drive signal from the head driver 301 to the piezoelectric element 302 during a portion of the non-ejection period extracted by the extraction processing unit 722. Here, the second drive signal is a drive signal that can stir the ink in the nozzle 30B but cannot eject ink from the nozzle 30B.

Specifically, the drive control unit 725 inputs the second drive signal to the piezoelectric element 302 during the non-ejection period from the time when the start timing set by the setting processing unit 723 arrives to the time when the end of the non-ejection period arrives. Note that, if the signal processing unit 72 does not include the setting processing unit 723, the drive control unit 725 may input the second drive signal to the piezoelectric element 302 during the time when the start timing set in advance arrives to the time when the end of the non-ejection period arrives.

The drive control unit 725 also replaces each of the non-ejection pixel data included in the non-ejection pixel row, which corresponds to the period from the start timing set by the setting processing unit 723 to the end of the non-ejection period, with specific pixel data corresponding to the second drive signal. Specifically, the drive control unit 725 replaces each of the non-ejection pixel data input from the second buffer 724 during the period from the start timing set by the setting processing unit 723 to the input of the ejection pixel data, with the specific pixel data. The drive control unit 725 then inputs the specific pixel data to the head driver 301, thereby causing the head driver 301 to input the second drive signal to the piezoelectric element 302.

For example, as shown in FIG. 3, the drive control unit 725 includes a counter 725A. When the start timing is set by the setting processing unit 723, the counter 725A counts the number of remaining pixels until the ejection pixel data is input from the second buffer 724. In other words, the counter 725A counts the number of pixels corresponding to the remaining time until the end of the non-ejection period. Specifically, when the start timing is set by the setting processing unit 723, the counter 725A sets the initial value of the count value by the counter 725A to the same value as the specific number (1000). Then, each time the pixel data is input from the second buffer 724, the counter 725A counts down the count value in the count memory (not shown) of the counter 725A from the initial value. In the following, the count value by the counter 725A may be referred to as the second count value.

For example, before the start timing is set by the setting processing unit 723, the drive control unit 725 holds the pixel data input from the delay circuit 724A for a time corresponding to the time interval, and then outputs it to the head driver 301 of the recording head 30. Note that in the inkjet recording device 10, the condition for setting the start timing is a continuation of the non-ejection pixel data equal to or greater than the number of delayed pixels (1000) by the delay circuit 724A. Therefore, in the inkjet recording device 10, the output of the pixel data from the delay circuit 724A begins before the start timing is set by the setting processing unit 723.

When the start timing is set by the setting processing unit 723, the drive control unit 725 determines whether the start timing has arrived based on the second count value of the counter 725A. Specifically, the drive control unit 725 determines that the start timing has arrived when the second count value of the counter 725A is equal to or less than the value of the start timing set by the setting processing unit 723.

Here, when the drive control unit 725 determines that the start timing has arrived, it replaces the held pixel data with the specific pixel data and outputs it to the head driver 301 of the recording head 30. On the other hand, when the drive control unit 725 determines that the start timing has not arrived, it outputs the held pixel data as is to the head driver 301 of the recording head 30. The drive control unit 725 determines whether the start timing has arrived each time the pixel data is input from the second buffer 724 and the count value of the counter 725A is counted down. In addition, when the second count value of the counter 725A becomes 0, the drive control unit 725 outputs the pixel data input from the second buffer 724 as is to the head driver 301 of the recording head 30 until the start timing is set again by the setting processing unit 723.

The head driver 301 drives the piezoelectric element 302 based on the pixel data after the replacement process by the drive control unit 725. That is, the head driver 301 inputs the first drive signal to the piezoelectric element 302 when the pixel data input from the drive control unit 725 is the ejection pixel data. Furthermore, the head driver 301 inputs the second drive signal to the piezoelectric element 302 when the pixel data input from the drive control unit 725 is the specific pixel data. Furthermore, the head driver 301 inputs the third drive signal to the piezoelectric element 302 when the pixel data input from the drive control unit 725 is the non-ejection pixel data.

As a result, one image data or multiple image data included in the print data is printed. Also, during the period during which the continuous printing process or the single printing process is being performed, during a portion of the non-ejection period during which a non-ejection state in which ink is not ejected from nozzle 30B continues beyond the reference time, the flushing is performed to agitate the ink in nozzle 30B but not eject ink.

As described above, when the number of pixels is equal to or greater than the threshold value, the table data X11 is referenced to obtain the value of the first start timing, which is earlier than the second start timing, so that the flushing time interval is relatively short even when printing an image with a large amount of ink ejection (an image with the number of pixels equal to or greater than the threshold value) in the printing process. This eliminates the problem of the recording head 30 overheating and accelerating the drying of the ink, and reduces ink ejection defects associated with drying of the ink, resulting in improved image quality of the printed matter.

The processing contents in the signal processing unit 72 will be described below with reference to FIG. 5. Note that in FIG. 5, the pixel data between the first pixel data input to the extraction processing unit 722 and the 5000th pixel data input to the extraction processing unit 722 are all non-ejection pixel data G1. The 5001st pixel data input to the extraction processing unit 722 is ejection pixel data G2.

First, at timing t1, the first pixel data is input from the first buffer 721 to the extraction processing unit 722. The counter 722A of the extraction processing unit 722 determines whether the input pixel data is the non-ejection pixel data. The pixel data input to the extraction processing unit 722 at timing t1 is non-ejection pixel data G1. Therefore, the counter 722A counts up. As a result, the count value of the counter 722A becomes 1.

On the other hand, at timing t1, the pixel data has not yet been input from the second buffer 724 to the drive control unit 725.

Next, at timing t2, the 1001st pixel data is input from the first buffer 721 to the extraction processing unit 722. The counter 722A determines whether the input pixel data is the non-ejection pixel data. The pixel data input to the extraction processing unit 722 at timing t2 is non-ejection pixel data G1. Therefore, the counter 722A counts up. As a result, the count value in the counter 722A becomes 1001.

On the other hand, at timing t2, the first pixel data is input from the second buffer 724 to the drive control unit 725. At timing t2, the setting processing unit 723 has not yet set the start timing. Therefore, the drive control unit 725 holds the input first pixel data for a period of time corresponding to the time interval, and then outputs it to the head driver 301 of the recording head 30.

Next, at timing t3, the 5001st pixel data is input from the first buffer 721 to the extraction processing unit 722. The counter 722A judges whether the input pixel data is the non-ejection pixel data. The pixel data input to the extraction processing unit 722 at timing t3 is the ejection pixel data G2. Therefore, the counter 722A notifies the extraction processing unit 722 of the count value at that time and resets the count value to 0. The extraction processing unit 722 also judges whether the count value notified from the counter 722A exceeds the reference number of 999. The count value of the counter 722A at timing t3 is 5000. Therefore, the extraction processing unit 722 notifies the setting processing unit 723 of the count value notified from the counter 722A.

The setting processing unit 723, which is notified of the count value "5000" of the counter 722A by the extraction processing unit 722 at timing t3, acquires the value of the start timing based on the notified count value and the selected table data X. Here, it is assumed that table data X11 has been selected in the setting processing unit 723. In this case, the value of the start timing corresponding to the count value "5000" is 500 (see table data X11 in FIG. 4). Therefore, at timing t3, the setting processing unit 723 notifies the drive control unit 725 of the acquired value of the start timing and sets the start timing. The counter 725A of the drive control unit 725 sets the initial setting value of the count value to the same numerical value (1000) as the specific number, in accordance with the setting of the start timing by the setting processing unit 723.

On the other hand, at timing t3, the 4001st pixel data is input from the second buffer 724 to the drive control unit 725. At timing t3, the setting processing unit 723 sets the start timing to the drive control unit 725. Therefore, the drive control unit 725 judges whether the start timing has arrived based on whether the count value of the counter 725A is equal to or less than the value of the start timing. At timing t3, the initial setting value of the counter 725A is 1000, the count value of the counter 725A is 1000, and the set value of the start timing is 500. Therefore, since the count value has not decreased to the value of the start timing, the drive control unit 725 judges that the start timing has not arrived, and holds the input 4001st pixel data for a time corresponding to the time interval, and then outputs it to the head driver 301 of the recording head 30. Also, the counter 725A counts down the count value each time the pixel data is input from the second buffer 724.

Next, at timing t4, the 4501st pixel data is input from the second buffer 724 to the drive control unit 725. The drive control unit 725 determines whether the count value of the counter 725A is equal to or less than the value of the start timing. At timing t4, the count value of the counter 725A has decreased to 500, and the set start timing is 500. Therefore, the drive control unit 725 determines that the start timing has arrived, replaces the input 4501st pixel data with specific pixel data G3, and outputs the replaced specific pixel data G3 to the head driver 301 of the recording head 30.

Next, at timing t5, the 5001st pixel data is input to the drive control unit 725. At timing t5, the count value of the counter 725A is decreased from the initial setting value to 0. Therefore, the drive control unit 725 holds the input 5001st pixel data for a time corresponding to the time interval, and then outputs it to the head driver 301 of the recording head 30.

As described above, in the inkjet recording device 10, when the continuous printing process or the single printing process is executed, the non-ejection period during which the non-ejection state in which ink is not ejected from the nozzle 30B continues beyond the reference time is extracted from the execution period of the continuous printing process or the single printing process. Then, the flushing is executed to stir the ink in the nozzle 30B during a portion of the extracted non-ejection period. This suppresses the deterioration of the image quality of the printed matter caused by the increase in the viscosity of the ink due to the drying of the ink, even during the execution of the continuous printing process or the single printing process. Therefore, it is possible to improve the image quality of the printed matter.

Also, when the number of pixels is equal to or greater than the threshold value, it can be said that the heat generation amount of the head driver 301 is equal to or greater than a certain level. In this case, the recording head 30 becomes hot, and the drying of the ink in the nozzle 30B is promoted. In this case, the setting processing unit 723 selects the table data X11 having a relatively short interval between the start timings, and based on the selected table data X11 and the counter value notified from the extraction processing unit 722, the first start timing earlier than the second start timing is acquired from the table data X11. Then, the drive control unit 725 compares the start timing thus acquired with the count value of the counter 725A to determine whether the start timing has arrived, and when it is determined that the start timing has arrived, replaces the held pixel data with the specific pixel data and outputs it to the head driver 301 of the recording head 30. As a result, when the recording head 30 becomes hot, the flushing for stirring the ink in the nozzle 30B is performed at short time intervals. In other words, the stirring interval from the previous stirring to the next stirring can be shortened. As a result, the ink drying rate can be reduced, and ink ejection defects can be reduced. If the number of pixels is smaller than the threshold, it can be said that the amount of heat generated by the head driver 301 is less than a certain level. In this case, the table data X12 is selected, and the second start timing, which is later than the first start timing indicated in the table data X11, is obtained from the table data X12 based on the selected table data X12 and the counter value notified from the extraction processing unit 722. In this case, since the recording head 30 is not at a high temperature, there is no need to shorten the stirring interval.

In addition, in the inkjet recording device 10, a first buffer 721 is provided that outputs the same data as the print data output from the second buffer 724 prior to the second buffer 724, in addition to the second buffer 724 that outputs the print data input to the recording head 30. Then, the extraction process of the non-ejection period is executed based on the data output from the first buffer 721 in advance, and the data output from the second buffer 724 is replaced with the specific pixel data based on the result of the extraction process, and the data after the replacement process is input to the recording head 30. Therefore, compared to a configuration in which the extraction process and the replacement process are executed on the print data stored in a memory, the memory capacity provided in the inkjet recording device 10 can be reduced by the amount that a memory for storing the print data is not required.

The signal processing unit 72 may include control devices such as a CPU, a ROM, and a RAM, and may function as an extraction processing unit 722, a setting processing unit 723, a drive control unit 725, etc., by executing a program pre-stored in the ROM.

In this case, the drive control unit 725 may input the second drive signal to the piezoelectric element 302 for the entire period of the non-ejection period extracted by the extraction processing unit 722. The drive control unit 725 may also input the second drive signal to the piezoelectric element 302 from the start of the non-ejection period extracted by the extraction processing unit 722 or from the time when the preset start timing arrives to the time when the preset end timing arrives. The drive control unit 725 may also input the second drive signal to the piezoelectric element 302 by sending a control signal to the head driver 301 to instruct the input of the second drive signal, instead of replacing the non-ejection pixel data with the specific pixel data.

In the above embodiment, a processing example using two pieces of table data X is illustrated, but the processing example may be, for example, a processing example using three or more pieces of table data X provided according to the number of pixels.

In the above embodiment, a processing example in which the table data X12 is selected when the number of pixels is equal to or greater than the threshold value has been described, but the present invention is not limited to such a processing example. For example, it is also conceivable that the table data X to be selected in the setting processing unit 723 is initially set to the table data X11. In this case, the setting processing unit 723 may select the initially set table data X11 unless the table identification information X12 is input from the table selection processing unit 714, and may select the table data X12 only when the table identification information X12 is input.

Furthermore, the setting processing unit 723 may maintain the initial setting of the table data X11 until a determination result is input that the pixel count has been equal to or greater than the threshold value for a predetermined number of consecutive pages (e.g., the table identification information X12 has been input a predetermined number of times in succession), and may change the initial setting of the selected table data X from the table data X11 to the table data X12 when the determination result is input. In this case, the setting processing unit 723 may select the changed table data X12 unless the table identification information X11 is input from the table selection processing unit 714, and may select the table data X11 only when the table identification information X11 is input.

[Notes on the invention]
The following will provide an overview 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 in any desired manner.

<Appendix 1>
a recording head having nozzles from which ink is ejected and piezoelectric elements provided corresponding to the nozzles and for ejecting the ink from the nozzles in response to input of a predetermined first drive signal;
a pixel number counting unit that, when a print process for printing one image data is executed, counts the number of ejection pixels corresponding to the ejection of the ink in the image data based on the image data to be printed in the print process;
an extraction processing unit that extracts a non-ejection period during which a non-ejection state in which the ink is not ejected from the nozzles continues beyond a predetermined reference time during an execution period of the printing process based on the image data printed in the printing process;
a drive control unit that inputs a predetermined second drive signal to the piezoelectric element, the second drive signal being capable of stirring the ink in the nozzle but not capable of ejecting the ink from the nozzle;
a setting processing unit that sets a start timing of input of the second drive signal during the non-ejection period based on a length of the non-ejection period,
The setting processing unit sets the start timing according to the number of pixels counted by the pixel number counting unit, based on a length of the non-ejection period.

<Appendix 2>
A storage unit is further provided for storing a plurality of table data in which the length of the non-ejection period and the start timing are associated with each other,
The plurality of table data are
The method includes: first table data in which a predetermined first start timing is defined; and second table data in which a second start timing that is later than the first start timing is defined;
The setting processing unit:
and setting the first start timing corresponding to the length of the non-ejection period by referring to the first table data selected when the number of pixels is equal to or greater than a predetermined threshold value;
The inkjet recording apparatus according to claim 1, further comprising: setting the second start timing corresponding to the length of the non-ejection period by referring to the second table data selected when the number of pixels is less than the threshold value.

<Appendix 3>
the recording head has a plurality of nozzles and a plurality of piezoelectric elements provided corresponding to each of the nozzles,
The extraction processing unit extracts the non-ejection period for each of the nozzles,
The drive control unit inputs the second drive signal to each of the plurality of piezoelectric elements.
3. The inkjet recording apparatus according to claim 1 or 2.

<Appendix 4>
the extraction processing unit extracts, as the non-ejection period, an output period of a non-ejection pixel string in which non-ejection pixels corresponding to the non-ejection of ink from the nozzles in the image data printed in the printing process continue for more than a reference number corresponding to the reference time,
the drive control unit replaces each of the non-ejection pixels included in the non-ejection pixel row, which corresponds to a period from the start timing set by the setting processing unit to the end of the non-ejection period, with a specific pixel corresponding to the second drive signal, and inputs the specific pixel as the second drive signal to the piezoelectric element;
4. The inkjet recording apparatus according to claim 1, further comprising a drive section that drives the piezoelectric element based on the image data after the replacement process by the drive control section.

<Appendix 5>
a first buffer that outputs each pixel included in the image data to the extraction processing unit in sequence from an upstream side in a sub-scanning direction of the image data at each drive interval of the drive unit;
a second buffer that outputs the same pixel as the pixel output from the first buffer to the drive control unit after delaying the pixel by a predetermined delay time from the first buffer,
the extraction processing unit counts a number of consecutive inputs of the non-ejection pixels from the first buffer, and determines whether or not the consecutive non-ejection pixels are the non-ejection pixel row based on a result of counting the number of consecutive inputs when the ejection pixels are input from the first buffer;
the setting processing unit sets the start timing using the counting result of the number of consecutive pixels by the extraction processing unit when the extraction processing unit has determined that the consecutive non-ejection pixels are the non-ejection pixel row and the table data selected according to the number of pixels;
The inkjet recording device described in Appendix 4, wherein the drive control unit replaces each of the non-ejection pixels input from the second buffer between the time when the start timing set by the setting processing unit arrives and the time when the ejection pixel is input with the specific pixel.

<Appendix 6>
1. An inkjet recording method executed by an inkjet recording apparatus including a recording head having nozzles from which ink is ejected and piezoelectric elements provided corresponding to the nozzles and causing the ink to be ejected from the nozzles in response to input of a predetermined first drive signal, comprising:
counting the number of ejection pixels corresponding to the ejection of the ink in the image data based on the image data printed in the printing process when a printing process for printing one image data is executed;
extracting a non-ejection period during which a non-ejection state in which the ink is not ejected from the nozzles continues for more than a predetermined reference time during an execution period of the printing process based on the image data printed in the printing process;
inputting a predetermined second drive signal to the piezoelectric element, the second drive signal being capable of stirring the ink in the nozzle but not capable of ejecting the ink from the nozzle;
an input start timing of the second drive signal during the non-ejection period, the input start timing corresponding to the number of pixels being set based on a length of the non-ejection period.

7: Control unit 10: Inkjet recording device 30: Recording head 30A: Opposing surface 30B: Nozzles 31-34: Line head 71: Main control unit 72: Signal processing unit 301: Head driver 302: Piezoelectric element 711: Conversion processing unit 712: Generation processing unit 713: Dot count unit 714: Table selection processing unit 721: First buffer 722: Extraction processing unit 722A: Counter 723: Setting processing unit 723A: Memory unit 724: Second buffer 724A: Delay circuit 725: Drive control unit 725A: Counter

Claims (6)

a recording head having nozzles from which ink is ejected and piezoelectric elements provided corresponding to the nozzles and for ejecting the ink from the nozzles in response to input of a predetermined first drive signal;
a pixel number counting unit that, when a print process for printing one image data is executed, counts the number of ejection pixels in the image data corresponding to the ejection of the ink based on the image data to be printed in the print process;
an extraction processing unit that extracts a non-ejection period during which a non-ejection state in which the ink is not ejected from the nozzles continues beyond a predetermined reference time during an execution period of the printing process based on the image data printed in the printing process;
a drive control unit that inputs a predetermined second drive signal to the piezoelectric element, the second drive signal being capable of stirring the ink in the nozzle but not capable of ejecting the ink from the nozzle;
a setting processing unit that sets a start timing of input of the second drive signal during the non-ejection period based on a length of the non-ejection period,
The setting processing unit sets the start timing according to the number of pixels counted by the pixel number counting unit, based on a length of the non-ejection period. A storage unit is further provided for storing a plurality of table data in which the length of the non-ejection period and the start timing are associated with each other,
The plurality of table data are
The method includes: first table data in which a predetermined first start timing is defined; and second table data in which a second start timing that is later than the first start timing is defined;
The setting processing unit:
and setting the first start timing corresponding to the length of the non-ejection period by referring to the first table data selected when the number of pixels is equal to or greater than a predetermined threshold value;
The inkjet recording apparatus according to claim 1 , further comprising: a step of: setting the second start timing corresponding to the length of the non-ejection period by referring to the second table data selected when the number of pixels is less than the threshold value. the recording head has a plurality of nozzles and a plurality of piezoelectric elements provided corresponding to each of the nozzles,
The extraction processing unit extracts the non-ejection period for each of the nozzles,
The drive control unit inputs the second drive signal to each of the plurality of piezoelectric elements.
3. The inkjet recording apparatus according to claim 1 or 2. the extraction processing unit extracts, as the non-ejection period, an output period of a non-ejection pixel string in which non-ejection pixels corresponding to the non-ejection of ink from the nozzles in the image data printed in the printing process continue for more than a reference number corresponding to the reference time,
the drive control unit replaces each of the non-ejection pixels included in the non-ejection pixel array corresponding to a period from the start timing set by the setting processing unit to the end of the non-ejection period with a specific pixel corresponding to the second drive signal, and inputs the specific pixel as the second drive signal to the piezoelectric element;
The inkjet recording apparatus according to claim 2 , further comprising a drive section that drives the piezoelectric element based on the image data after the replacement process by the drive control section. a first buffer that outputs each pixel included in the image data to the extraction processing unit in sequence from an upstream side in a sub-scanning direction of the image data at each drive interval of the drive unit;
a second buffer that outputs the same pixel as the pixel output from the first buffer to the drive control unit after delaying the pixel by a predetermined delay time from the first buffer,
the extraction processing unit counts a number of consecutive inputs of the non-ejection pixels from the first buffer, and determines whether or not the consecutive non-ejection pixels are the non-ejection pixel row based on a result of counting the number of consecutive inputs when the ejection pixels are input from the first buffer;
the setting processing unit sets the start timing using the counting result of the number of consecutive pixels by the extraction processing unit when the extraction processing unit has determined that the consecutive non-ejection pixels are the non-ejection pixel row and the table data selected according to the number of pixels;
The inkjet recording device according to claim 4 , wherein the drive control unit replaces each of the non-ejection pixels input from the second buffer during the period from the time when the start timing set by the setting processing unit arrives until the ejection pixel is input with the specific pixel. 1. An inkjet recording method executed by an inkjet recording apparatus including a recording head having nozzles from which ink is ejected and piezoelectric elements provided corresponding to the nozzles and causing the ink to be ejected from the nozzles in response to input of a predetermined first drive signal, comprising:
counting the number of ejection pixels corresponding to the ejection of the ink in the image data based on the image data printed in the printing process when a printing process for printing one image data is executed;
extracting a non-ejection period during which a non-ejection state in which the ink is not ejected from the nozzles continues for more than a predetermined reference time during an execution period of the printing process based on the image data printed in the printing process;
inputting a predetermined second drive signal to the piezoelectric element, the second drive signal being capable of stirring the ink in the nozzle but not capable of ejecting the ink from the nozzle;
an input start timing of the second drive signal during the non-ejection period, the input start timing corresponding to the number of pixels being set based on a length of the non-ejection period.

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