Liquid ejection head maintenance method

Abstract

To suppress occurrence of abnormalities in ejection characteristics after completion of a maintenance method. [Solution] A maintenance method for a liquid ejection head having a first ejection section group including a plurality of first ejection sections, a second ejection section group including a plurality of second ejection sections, and a common liquid supply flow path communicating with the first ejection section group and the second ejection section group, wherein after starting a first ejection process to eject liquid from the first ejection section group, a second ejection process to eject liquid from the second ejection section group is started, and the amount of liquid ejected from the first ejection section group per unit period during a first start period from the start of the first ejection process is less than the amount of liquid ejected from the first ejection section group per unit period during a first high ejection period that starts after the first start period.

Description

[Technical Field]

[0001] The present invention relates to a maintenance method for a liquid ejection head. [Background technology]

[0002] In a liquid ejection head that ejects a liquid such as ink from nozzles onto a recording medium such as printing paper to form an image on the recording medium, for example, thickening of the liquid due to evaporation of water contained in the liquid can be a problem. For example, Patent Document 1 discloses a maintenance method for a liquid ejection head having two nozzle rows. In this maintenance method, while one of the two nozzle rows performs an idle ejection operation in which a liquid that does not contribute to image formation is ejected from the other nozzle row, the idle ejection operation is not performed from one nozzle row, and while the other nozzle row performs an idle ejection operation, the one nozzle row is not performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-208870 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional maintenance method, abnormalities in the ejection characteristics may occur after the maintenance method is completed. [Means for solving the problem]

[0005] A preferred aspect of the present disclosure provides a maintenance method for a liquid ejection head having a first ejection section group including a plurality of first ejection sections, a second ejection section group including a plurality of second ejection sections, and a common liquid supply flow path communicating with the first ejection section group and the second ejection section group, wherein after starting a first ejection process to eject liquid from the first ejection section group, a second ejection process to eject liquid from the second ejection section group is started, and the amount of liquid ejected from the first ejection section group per unit period during a first start period from the start of the first ejection process is less than the amount of liquid ejected from the first ejection section group per unit period during a first high ejection period that starts after the first start period. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the configuration of an inkjet printer 100. [Figure 2] FIG. 1 is a block diagram showing an example of the configuration of an inkjet printer 100. [Figure 3] FIG. 2 is a schematic partial cross-sectional view of the head chip 111, in which the head chip 111 is cut so as to include a discharge portion D. [Figure 4] FIG. 10 is a plan view showing the flow paths when the head chip 111 is viewed in the Z2 direction. [Figure 5] FIG. 10 is an enlarged cross-sectional view of the vicinity of a piezoelectric element 111F. [Figure 6] FIG. 2 is a block diagram showing an example of the configuration of a liquid ejection head HU. [Figure 7] FIG. 10 is a diagram for explaining the phenomenon in which printing unevenness occurs in a comparative example. [Figure 8] FIG. 4 is a diagram for explaining a head flushing process in the first embodiment. [Figure 9] FIG. 4 is a diagram for explaining a first emission amount change mode. [Figure 10] FIG. 10 is a diagram for explaining a second emission amount change mode. [Figure 11] FIG. 10 is a diagram for explaining a third emission amount change mode. [Figure 12] FIG. 4 is a diagram for explaining the effect of the first embodiment. [Figure 13] FIG. 10 is a diagram for explaining a head flushing process in the second embodiment. [Figure 14] FIG. 10 is a diagram for explaining the effect of the second embodiment. [Figure 15] FIG. 10 is a diagram for explaining a head flushing process in the third embodiment. [Figure 16] FIG. 10 is a diagram for explaining a second emission amount change mode in the first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part are appropriately different from those of the actual parts. Furthermore, since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are applied, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0008] A. First embodiment A1. Overview of Inkjet Printer 100 FIG. 1 is a schematic diagram illustrating an example of the configuration of an inkjet printer 100. FIG. 2 is a block diagram illustrating an example of the configuration of the inkjet printer 100. The inkjet printer 100 is a liquid ejection device that ejects ink, an example of a liquid. The inkjet printer 100 performs recording on the recording medium PP using an inkjet method, i.e., by ejecting ink onto the recording medium PP. By performing recording on the recording medium PP, an image is formed on the recording medium PP. Hereinafter, the process of forming an image on the recording medium PP by ejecting ink onto the recording medium PP may be referred to as a "printing process." In the following explanation, mutually orthogonal X, Y, and Z axes are assumed. A direction along the X axis as viewed from an arbitrary point is referred to as the X1 direction, and a direction opposite to the X1 direction is referred to as the X2 direction. Similarly, mutually opposite directions along the Y axis from an arbitrary point are referred to as the Y1 direction and the Y2 direction, and mutually opposite directions along the Z axis from an arbitrary point are referred to as the Z1 direction and the Z2 direction.

[0009] The inkjet printer 100 is a serial-type liquid ejection device that moves a liquid ejection head HU back and forth along the X axis. Specifically, as shown in FIG. 1, the inkjet printer 100 performs a printing process in which the recording medium PP is transported in the Y1 direction, which is the sub-scanning direction, and the liquid ejection head HU is moved in the X1 and X2 directions, which are main scanning directions, while ejecting ink from the nozzles N to form an image on the recording medium PP. In the following description, one movement of the liquid ejection head HU in the main scanning direction is referred to as one pass. The inkjet printer 100 forms an image on the recording medium PP by repeating a process of moving the liquid ejection head HU during one pass to form a partial image on the recording medium PP corresponding to one pass, and a process of transporting the recording medium PP by the distance corresponding to one pass.

[0010] As shown in FIGS. 1 and 2, the inkjet printer 100 includes a liquid ejection head HU, a liquid container 120, a moving mechanism 130, a transport mechanism 140, a maintenance mechanism 145, a memory circuit 160, and a control circuit 170.

[0011] The liquid ejection head HU is an assembly having a head chip 111 , a drive circuit 112 , a power supply circuit 183 , and a drive signal generation circuit 184 .

[0012] 2, the liquid ejection head HU has a head chip 111 and a drive circuit 112. Note that a part or all of the control module 180 may be incorporated into the liquid ejection head HU. The control module 180 includes a power supply circuit 183 and a drive signal generation circuit 184.

[0013] Head chip 111 ejects ink toward recording medium PP. FIG. 2 representatively illustrates some of the 2M ejection units D that are part of the components of head chip 111. In this embodiment, M is an integer greater than or equal to 2. One ejection unit D includes one nozzle N. An example of the details of head chip 111 will be described later with reference to FIG. 3.

[0014] 2, the liquid ejection head HU has one head chip 111, but the number of head chips 111 may be two or more. One or more head chips 111 are arranged so that a plurality of nozzles N are distributed across a portion of the X axis, which is the width direction of the recording medium PP.

[0015] In FIG. 1, the outlines of the nozzles N and the head chip 111 are shown with dashed lines to indicate the arrangement of the nozzles N. The head chip 111 has 2M nozzles N arranged in the direction along the Y axis. The 2M nozzles N are divided into two rows spaced apart from each other in the direction along the X axis. Hereinafter, a set of nozzles N arranged in a certain line may be referred to as a "nozzle row Ln." Furthermore, below, as shown in FIG. 1, the nozzle row Ln located in the X2 direction of the head chip 111 of the liquid ejection head HU may be referred to as a "nozzle row La," and the nozzle row Ln located in the X1 direction may be referred to as a "nozzle row Lb."

[0016] In this embodiment, as shown in FIG. 2, the 2M discharge units D are divided into a first discharge unit group GDa of M discharge units whose nozzles N belong to nozzle row La, and a second discharge unit group GDb of M discharge units whose nozzles N belong to nozzle row Lb. As shown in FIG. 2, the discharge units D belonging to the first discharge unit group GDa may be referred to as discharge units Da, and the discharge units D belonging to the second discharge unit group GDb may be referred to as discharge units Db. In this embodiment, the number of discharge units Da belonging to the first discharge unit group GDa and the number of discharge units Db belonging to the second discharge unit group GDb are the same, but they may be different. Note that the discharge units Da are an example of a "first discharge unit," and the discharge units Db are an example of a "second discharge unit."

[0017] Hereinafter, to distinguish between the 2M discharge units D provided on one head chip 111, they may be referred to in order as 1st row, 2nd row, ..., 2Mth row. Furthermore, a discharge unit D that is divided into nozzle rows Ln and corresponds to row m may be referred to as discharge unit D[m], where m is an integer between 1 and M. Furthermore, when a component or signal of the liquid discharge head HU corresponds to the nozzle row Ln and row number m of the discharge unit D[m], the subscript [m] indicating that the component or signal corresponds to the nozzle row Ln and row number m may be added to the symbol representing the component or signal.

[0018] The liquid ejection head HU has the same number of drive circuits 112 as the head chips 111. In the example of FIG. 2, the liquid ejection head HU has one head chip 111 and therefore one drive circuit 112. The drive circuit 112 includes a switching circuit 115. Under the control of the control circuit 170, the switching circuit 115 switches whether or not to supply the drive signal Com output from the drive signal generation circuit 184 to each of the 2M ejection sections D included in the head chip 111 connected to the drive circuit 112. The switching circuit 115 includes, for example, a group of switches such as transmission gates for this switching.

[0019] The power supply circuit 183 receives power from a commercial power supply (not shown) and generates various predetermined potentials. The generated potentials are supplied to each section of the inkjet printer 100 as appropriate. In the example shown in FIG. 2, the power supply circuit 183 generates a power supply potential VHV and an offset potential VBS. The offset potential VBS is supplied to the head chip 111 and the like. The power supply potential VHV is also supplied to the drive signal generation circuit 184 and the like.

[0020] 1, a liquid container 120 that stores ink is installed in the inkjet printer 100. For example, the liquid container 120 may be a cartridge that can be attached to or detached from the inkjet printer 100, a bag-shaped ink pack made of flexible film, or an ink tank that can be refilled with ink.

[0021] The movement mechanism 130 and the transport mechanism 140 move the relative positions of the recording medium PP and the liquid ejection head HU under the control of the control circuit 170. Moving the relative positions may involve moving the liquid ejection head HU while keeping the position of the recording medium PP fixed, or moving the recording medium PP while keeping the position of the liquid ejection head HU fixed. In this embodiment, in the direction along the X axis, which is the main scanning direction, the liquid ejection head HU is moved in the direction along the X axis while keeping the position of the recording medium PP fixed on the X axis, and in the Y1 direction, which is the sub-scanning direction, the recording medium PP is moved in the Y1 direction while keeping the position of the liquid ejection head HU fixed in the direction along the Y axis.

[0022] The movement mechanism 130 reciprocates the liquid ejection head HU along the X axis under the control of the control circuit 170. As shown in Fig. 1, the movement mechanism 130 includes a substantially box-shaped carriage 131 that houses the liquid ejection head HU, and an endless belt 132 to which the carriage 131 is fixed. Note that a configuration in which the liquid container 120 is mounted on the carriage 131 together with the liquid ejection head HU may also be employed.

[0023] The transport mechanism 140 transports the recording medium PP in the Y1 direction under the control of the control circuit 170. Specifically, the transport mechanism 140 includes a transport roller (not shown) whose rotation axis is parallel to the X axis, and a motor (not shown) that rotates the transport roller under the control of the control circuit 170.

[0024] The storage circuitry 160 stores various programs and various data executed by the control circuitry 170. The storage circuitry 160 includes, for example, one or more volatile memories such as RAM and one or more nonvolatile memories such as ROM, EEPROM, or PROM. The storage circuitry 160 may be configured as a part of the control circuitry 170.

[0025] The control circuit 170 has the function of controlling the operation of each part of the inkjet printer 100 and the function of processing various types of data. The control circuit 170 includes, for example, one or more processors such as CPUs. Note that the control circuit 170 may include a programmable logic device such as an FPGA instead of or in addition to a CPU.

[0026] The control circuit 170 executes the programs stored in the memory circuit 160 to control the operation of each part of the inkjet printer 100. Here, the control circuit 170 generates signals such as control signals Sk1, Sk2, Sk3, print signal SI, and waveform designation signal dCom as signals for controlling the operation of each part of the inkjet printer 100.

[0027] The control signal Sk1 is a signal for controlling the driving of the movement mechanism 130. The control signal Sk2 is a signal for controlling the driving of the transport mechanism 140. The control signal Sk3 is a signal for controlling the maintenance mechanism 145. The print signal SI is a signal for controlling the driving of the drive circuit 112. Specifically, the print signal SI specifies for each drive cycle Tu whether the drive circuit 112 will supply the drive signal Com from the drive signal generation circuit 184 to the discharge unit D. One or more drive cycles Tu are included in the operating period of the inkjet printer 100. The amount of ink discharged from the head chip 111, etc., is specified by specifying whether the drive signal Com will be supplied to the discharge unit D. The waveform specification signal dCom is a digital signal for defining the waveform of the drive signal Com generated by the drive signal generation circuit 184.

[0028] The control circuit 170 first stores print data Img supplied from the host computer in the memory circuit 160. Next, based on various data such as the print data Img stored in the memory circuit 160, the control circuit 170 generates various control signals, such as a print signal SI, a waveform designation signal dCom, a signal for controlling the transport mechanism 140, and a signal for controlling the movement mechanism 130. Based on the various control signals and the various data stored in the memory circuit 160, the control circuit 170 controls the transport mechanism 140 and the movement mechanism 130 to change the relative position of the recording medium PP with respect to the liquid ejection head HU, while also controlling the liquid ejection head HU to drive the ejection unit D. In this way, the control circuit 170 adjusts whether or not ink is ejected from the ejection unit D, the amount of ink ejected, the timing of ink ejection, and the like, and controls the execution of a printing process to form an image corresponding to the print data Img on the recording medium PP.

[0029] Furthermore, the inkjet printer 100 according to this embodiment uses the maintenance mechanism 145 to perform maintenance processing to recover from the ejection failure of the ejection section D having the ejection failure. The inkjet printer 100 performs maintenance processing before, during, and after the printing process.

[0030] The maintenance processes include a flushing process that discharges ink from the discharge unit D, a wiping process that uses a wiper 147 to wipe away foreign matter such as paper dust adhering near the nozzles N of the discharge unit D, and a pumping process that uses a tube pump to suck out ink, air bubbles, and the like from within the discharge unit D. The flushing process forcibly removes thickened ink and air bubbles mixed in the ink by repeatedly driving the discharge unit D with a flushing process drive signal Com. The maintenance mechanism 145 includes a cap 146 that covers the liquid discharge head HU to seal the nozzles N, a wiper 147, a tube pump (not shown) that sucks out ink, air bubbles, and the like, and a discharged ink receiving unit (not shown) that receives discharged ink when discharging ink. The maintenance mechanism 145 is located in an area that does not overlap with the recording medium PP when viewed in the Z-axis direction. Therefore, the flushing process discharges ink from the liquid discharge head HU to a position that does not overlap with the recording medium PP in the Z-axis direction. The inkjet printer 100 may also perform a flushing process between printing processes.

[0031] Fig. 3 is a schematic partial cross-sectional view of the head chip 111, in which the head chip 111 is cut so as to include the ejection portion D. Fig. 4 is a plan view showing the flow paths when the head chip 111 is viewed in the Z2 direction. However, Fig. 3 also shows a drive circuit 112 in addition to the head chip 111. Furthermore, Fig. 3 also schematically shows an in-head supply flow path HSR that supplies ink to the first ejection portion group GDa and the second ejection portion group GDb.

[0032] As shown in FIG. 3, head chip 111 has flow path substrate 111A, pressure chamber substrate 111B, nozzle plate 111C, vibration absorber 111D, diaphragm 111E, 2M piezoelectric elements 111F, protective plate 111G, case 111H, and wiring substrate 111I.

[0033] In the following description, among the elements of the head chip 111, elements related to the first discharger group GDa may be suffixed with "a," and elements related to the second discharger group GDb may be suffixed with "b." Furthermore, when there is no need to distinguish between elements related to the first discharger group GDa and elements related to the second discharger group GDb, the suffixes "a" and "b" are not used.

[0034] The flow path substrate 111A and the pressure chamber substrate 111B are stacked in this order in the Z1 direction to form a flow path for supplying ink to 2M nozzles N. In an area positioned further in the Z1 direction than the stack consisting of the flow path substrate 111A and the pressure chamber substrate 111B, a diaphragm 111E, 2M piezoelectric elements 111F, a protective plate 111G, a case 111H, and a wiring substrate 111I are provided. On the other hand, in an area positioned further in the Z2 direction than the stack, a nozzle plate 111C and a vibration absorber 111D are provided. Each element of the head chip 111 is roughly a plate-like member that is elongated in the Y direction, and is joined to one another by, for example, an adhesive. Each element of the head chip 111 will be described in order below.

[0035] The nozzle plate 111C is a plate-like member having M nozzles N for each of the nozzle arrays La and Lb. Specifically, the nozzle plate 111C has M nozzles Na for the nozzle array La and M nozzles Nb for the nozzle array Lb. Each of the M nozzles N is a through-hole that allows ink to pass through. The surface of the nozzle plate 111C facing the Z2 direction is the nozzle surface FN. The nozzle plate 111C is manufactured by processing a silicon single crystal substrate using semiconductor manufacturing techniques such as dry etching or wet etching. However, other known methods and materials may also be used as appropriate for manufacturing the nozzle plate 111C. The cross-sectional shape of the nozzle N is typically circular, but is not limited thereto and may be non-circular, such as polygonal or elliptical.

[0036] The flow path substrate 111A is provided with a space R1, 2M supply flow paths RA, and 2M communication flow paths NA for each of the nozzle array La and nozzle array Lb provided on the head chip 111. Specifically, as shown in FIGS. 3 and 4, the flow path substrate 111A is provided with a space R1a, M supply flow paths RAa, and M communication flow paths NAa for the nozzle array La, and a space R1b, M supply flow paths RAb, and M communication flow paths NAb for the nozzle array Lb. The space R1 is an elongated opening extending in the direction along the Y axis in a plan view seen in the direction along the Z axis. Each of the supply flow paths RA and the communication flow paths NA is a through hole formed for each nozzle N. Each supply flow path RA communicates with the space R1.

[0037] The pressure chamber substrate 111B is a plate-like member provided with 2M pressure chambers CV, referred to as cavities, for each of the nozzle arrays La and Lb provided in the head chip 111. Specifically, as shown in FIGS. 3 and 4, the pressure chamber substrate 111B is provided with M pressure chambers CVa for the nozzle array La and M pressure chambers CVb for the nozzle array Lb. The 2M pressure chambers CV are arranged in a direction along the Y axis. Each pressure chamber CV is formed for each nozzle N and is an elongated space extending in a direction along the X axis in a plan view. Like the nozzle plate 111C described above, the flow path substrate 111A and the pressure chamber substrate 111B are manufactured by processing a silicon single crystal substrate using, for example, semiconductor manufacturing technology. However, other known methods and materials may be used as appropriate to manufacture the flow path substrate 111A and the pressure chamber substrate 111B.

[0038] The pressure chamber CV is a space located between the flow path substrate 111A and the vibration plate 111E. 2M pressure chambers CV are arranged in the direction along the Y axis for each of the nozzle array La and the nozzle array Lb provided on the head chip 111. The pressure chambers CV are also connected to the communication flow path NA and the supply flow path RA. Specifically, the pressure chamber CVa is connected to the communication flow path NAa and the supply flow path RAa, and the pressure chamber CVb is connected to the communication flow path NAb and the supply flow path RAb. Therefore, the pressure chamber CV is connected to the nozzle N via the communication flow path NA, and to the space R1 via the supply flow path RA.

[0039] A diaphragm 111E is disposed on the surface of the pressure chamber substrate 111B facing the Z1 direction. The diaphragm 111E is a plate-like member that can vibrate elastically. The diaphragm 111E has, for example, a first layer and a second layer, which are stacked in this order in the Z1 direction. The first layer is, for example, an elastic film made of silicon oxide. The elastic film is formed, for example, by thermally oxidizing one surface of a silicon single crystal substrate. The second layer is, for example, an insulating film made of zirconium oxide. The insulating film is formed, for example, by forming a zirconium layer by sputtering and then thermally oxidizing the layer. Note that the diaphragm 111E is not limited to a configuration in which the first and second layers are stacked together, and may be, for example, a single layer or three or more layers.

[0040] On the surface of the vibration plate 111E facing the Z1 direction, 2M piezoelectric elements 111F are arranged, each corresponding to a nozzle N, for each of the nozzle array La and the nozzle array Lb. Specifically, on the surface of the vibration plate 111E facing the Z1 direction, M piezoelectric elements 111Fa are arranged for the nozzle array La, and M piezoelectric elements 111Fb are arranged for the nozzle array Lb. Each piezoelectric element 111F is a passive element that deforms when a drive signal Com is supplied. Each piezoelectric element 111F has an elongated shape extending in the direction along the X-axis in a plan view. The 2M piezoelectric elements 111F are arranged in the direction along the Y-axis so as to correspond to the 2M pressure chambers CV. The piezoelectric elements 111F overlap the pressure chambers CV in a plan view. The piezoelectric elements 111F are an example of a "drive element."

[0041] Fig. 5 is an enlarged cross-sectional view of the vicinity of the piezoelectric element 111F. However, in Fig. 5, the protective plate 111G is omitted to avoid cluttering the drawing. Hereinafter, the signal of the drive signal Com that is actually supplied to the piezoelectric element 111F may be referred to as the supplied drive signal Vin.

[0042] 5, the piezoelectric element 111F is a laminated body in which a piezoelectric body Zm is interposed between an upper electrode Zu to which an offset potential VBS is supplied and a lower electrode Zd to which a supply drive signal Vin is supplied. When viewed from the Z1 direction, for example, the piezoelectric element 111F is a portion where the lower electrode Zd, the upper electrode Zu, and the piezoelectric body Zm overlap. A pressure chamber CV is provided in the Z2 direction of the piezoelectric element 111F. While the first embodiment illustrates a configuration in which the offset potential VBS is supplied to the upper electrode Zu and the supply drive signal Vin is supplied to the lower electrode Zd, it is also possible to employ a configuration in which the supply drive signal Vin is supplied to the upper electrode Zu and the offset potential VBS is supplied to the lower electrode Zd.

[0043] 3 and 4. The protective plate 111G is a plate-like member placed on the surface of the diaphragm 111E facing the Z1 direction, and protects the plurality of piezoelectric elements 111F and reinforces the mechanical strength of the diaphragm 111E. The plurality of piezoelectric elements 111F are housed between the protective plate 111G and the diaphragm 111E. The protective plate 111G is made of, for example, a resin material.

[0044] The case 111H is a member for storing ink to be supplied to the multiple pressure chambers CV. The case 111H is made of, for example, a resin material. The case 111H is provided with a space R2 for each of the nozzle row La and the nozzle row Lb. Specifically, a space R2a is provided for the nozzle row La, and a space R2b is provided for the nozzle row Lb. The space R2 is a space that communicates with the above-mentioned space R1, and together with the space R1, functions as a reservoir R that stores ink to be supplied to the multiple pressure chambers CV. As shown in FIG. 3, the spaces R1a and R2a function as reservoirs Ra, and the spaces R1b and R2b function as reservoirs Rb. The case 111H is provided with an inlet IH for supplying ink to each reservoir R. Specifically, the case 111H is provided with an inlet IHa for supplying ink to the reservoir Ra and an inlet IHb for supplying ink to the reservoir Rb. The ink in each reservoir R is supplied to the pressure chamber CV via each supply channel RA.

[0045] The wiring board 111I is mounted on the surface of the diaphragm 111E facing the Z1 direction, and is a mounting component for electrically connecting the head chip 111 with the drive circuit 112, the control module 180, etc. The wiring board 111I is a flexible wiring board such as COF, FPC, or FFC. The above-mentioned drive circuit 112 is mounted on the wiring board 111I of this embodiment. COF is an abbreviation for Chip On Film. FPC is an abbreviation for Flexible Printed Circuit. FFC is an abbreviation for Flexible Flat Cable.

[0046] 3, one ejection section D includes one piezoelectric element 111F, one pressure chamber CV, and one nozzle N. That is, the 2M piezoelectric elements 111F correspond one-to-one to the 2M pressure chambers CV. When a supply drive signal Vin is supplied to the piezoelectric element 111F based on a print signal SI, the ejection section D ejects ink from the pressure chamber CV from the nozzle N by driving the piezoelectric element 111F with the supply drive signal Vin.

[0047] The nozzle N included in the ejection section Da is an example of a "first nozzle," the pressure chamber CV included in the ejection section Da is an example of a "first pressure chamber," and the piezoelectric element 111F included in the ejection section Da is an example of a "first driving element."

[0048] As illustrated in FIG. 3, the in-head supply channel HSR is formed by a member of the liquid ejection head HU other than the head chip 111. The in-head supply channel HSR communicates with the internal space of the connection pipe HSA provided on the surface of the liquid ejection head HU facing the Z1 direction. The in-head supply channel HSR also communicates with the inlet port IH. Therefore, ink supplied to the in-head supply channel HSR is supplied to the reservoir R via the inlet port IH. The ink in the reservoir R is then supplied to the first ejector group GDa and the second ejector group GDb.

[0049] 3, the reservoir Ra, the in-head supply channel HSR, and the reservoir Rb function as a common liquid supply channel CSR, which communicates with the first discharge part group GDa and the second discharge part group GDb.

[0050] A2. Configuration of the liquid ejection head HU The configuration of the liquid ejection head HU will be described below with reference to FIG.

[0051] Fig. 6 is a block diagram showing an example of the configuration of the liquid ejection head HU. Fig. 6 shows a head chip 111 and a drive circuit 112 provided in the liquid ejection head HU. In addition to the head chip 111 and the drive circuit 112, the liquid ejection head HU also includes an internal wiring LHA to which a drive signal Com is supplied from a drive signal generation circuit 184, and an internal wiring LHD to which an offset potential VBS is supplied.

[0052] 6, the switching circuit 115 includes 2M switches SW and a connection state designation circuit 116 that designates the connection state of each switch. The 2M switches SW are switches SWa[1] to SWa[M] connected to the piezoelectric element 111Fa and switches SWb[1] to SWb[M] connected to the piezoelectric element 111Fb. Each switch may be, for example, a transmission gate.

[0053] The connection state designation circuit 116 generates connection state designation signals SLa[1] to SLa[M] that designate the on / off states of the switches SWa[1] to SWa[M], and connection state designation signals SLb[1] to SLb[M] that designate the on / off states of the switches SWb[1] to SWb[M], based on at least some of the signals of the print signal SI, the latch signal LAT, and the change signal CH supplied from the control circuit 170. When m1 is any integer between 1 and M, the switch SWa[m1] switches between electrical continuity and non-conduction between the internal wiring LHA and the lower electrode Zd of the piezoelectric element 111Fa[m1] in accordance with the connection state designation signal SLa[m1]. For example, the switch SWa[m1] is turned on when the connection state designation signal SLa[m1] is high level and turned off when the connection state designation signal SLa[m1] is low level. When electrical continuity is established between the internal wiring LHA and the lower electrode Zd of the piezoelectric element 111Fa[m1], the drive signal Com is supplied to the piezoelectric element 111Fa[m1] as the supply drive signal Vina[m1]. When m1 is any integer between 1 and M, the switch SWb[m1] switches between electrical continuity and non-conduction between the internal wiring LHA and the lower electrode Zd of the piezoelectric element 111Fb[m1] in accordance with the connection state designation signal SLb[m1]. For example, the switch SWb[m1] is turned on when the connection state designation signal SLb[m1] is high level and turned off when the connection state designation signal SLb[m1] is low level. When electrical continuity is established between the internal wiring LHA and the lower electrode Zd of the piezoelectric element 111Fb[m1], the drive signal Com is supplied to the piezoelectric element 111Fb[m1] as the supply drive signal Vinb[m1].

[0054] A3.Specific examples of flushing processing The flushing process can be performed before and during the printing process. Therefore, if the time required for the flushing process is long, the time from when the user of the inkjet printer 100 issues an instruction to execute the printing process to when the recording medium PP with an image formed on it is obtained will also be long, so it is preferable to shorten the time required for the flushing process.

[0055] Simultaneous flushing of two nozzle rows Ln can result in problems such as exceeding the ink supply capacity of the liquid container 120. Therefore, a possible configuration is one in which, while a flushing process is being performed on one of the two nozzle rows Ln with the maximum discharge amount per unit period for the other nozzle row Ln, a flushing process is not being performed on the other nozzle row Ln, and, while a flushing process is being performed on the other nozzle row Ln with the maximum discharge amount per unit period for the other nozzle row Ln, a flushing process is not being performed on the other nozzle row Ln. Hereinafter, this configuration may be referred to as a "comparative configuration." The unit period is, for example, an integral multiple of the drive cycle Tu. However, in the comparative configuration, after flushing of the two nozzle rows Ln is completed, abnormalities in the ejection characteristics may occur. More specifically, printing unevenness may occur from the nozzles N constituting the other nozzle row Ln. The phenomenon of printing unevenness will be described with reference to FIG. 7.

[0056] FIG. 7 is a diagram illustrating the phenomenon of print unevenness occurring in a comparative example. The pressure fluctuation characteristic PaR in graph g1 shown in FIG. 7 represents the pressure fluctuation characteristic of ink in nozzle Nb in the comparative example. The horizontal axis of graph g1 represents time, and the vertical axis of graph g1 represents pressure [kPa]. The example in FIG. 7 assumes that flushing processing is performed on nozzle row La from time tf1 to time tf2, and flushing processing is performed on nozzle row Lb from time tf2 to time tf3.

[0057] Furthermore, the nozzle N in the comparative example and the present embodiment is a nozzle with a two-stage structure, as shown in Fig. 7. The nozzle N has a first nozzle portion NP1 that opens to the nozzle surface FN, and a second nozzle portion NP2 that has a diameter longer than the diameter of the first nozzle portion NP1 and is located upstream of the first nozzle portion NP1. Although Fig. 7 shows the shape of the nozzle Nb, the nozzle Na is also a nozzle with a two-stage structure, like the nozzle Na.

[0058] 7 shows the state of the vicinity of nozzle Nb before, during, and after the flushing process. Time t1, which precedes time tf1, is the time before the flushing process. Specifically, time t1 is the time before the flushing process is performed on nozzle row La. At time t1, the meniscus MN, which is the liquid surface in nozzle N, is stationary and located at approximately the same position as the nozzle surface FN on the Z axis. At time t1, thickened ink InT is present in nozzle N.

[0059] Time t2, between time tf1 and time tf2, is a time during the flushing process. Specifically, at time t2, the flushing process for nozzle array La is being performed, and ink is not being ejected from each nozzle Nb of nozzle array Lb. As shown by the pressure fluctuation characteristic PaR, a sudden fluctuation in flow rate occurs when the flushing process for nozzle array La begins at time tf1. Because the first ejector group GDa and the second ejector group GDb are connected via the common liquid supply channel CSR, pressure vibrations occur due to a water hammer effect caused by the flow rate fluctuations that occur when the flushing process begins, generating strong negative pressure in the nozzle array Lb. Hereinafter, these pressure vibrations may be referred to as "pressure vibrations at the start of flushing." Time t2 is the time when the negative pressure reaches its maximum during the flushing process, in other words, when the negative pressure reaches its peak value. Due to this negative pressure, the meniscus MN of each nozzle Nb of nozzle array Lb is pulled in the Z1 direction and resides within the second nozzle portion NP2, as shown in FIG. 7. Viscosity ink InT is also present inside the second nozzle portion NP2. This state of the meniscus MN in the nozzle Nb at time t2 differs from the state assumed by the manufacturer of the liquid ejection head HU. In the following description, the manufacturer of the liquid ejection head HU may be referred to as the "head manufacturer." After time t2, the pressure oscillation of the ink in the intra-head supply channel HSR converges to a constant negative pressure in response to the supply of ink from the liquid container 120 to the intra-head supply channel HSR and the inherent pressure oscillation of the common liquid supply channel CSR. After this, ink is supplied from the intra-head supply channel HSR to the reservoir Ra at a stable pressure.

[0060] As shown by the pressure fluctuation characteristic PaR, pressure oscillations occur during a period TC2 starting at time tf2 when the target of the flushing process is switched from nozzle row La to nozzle row Lb. Hereinafter, these pressure oscillations may be referred to as "flushing switching pressure oscillations." At time tf2, when switching from nozzle row La to nozzle row Lb, there is a momentary period during which ink droplets are not ejected from either nozzle row La or nozzle row Lb, causing the negative pressure in the intra-head supply channel HSR to weaken. Subsequently, pressure oscillations occur due to a water hammer effect caused by fluctuations in the ink flow rate caused by the start of ink droplet ejection from nozzle row Lb. However, because ink has already flowed from the liquid container 120 to the intra-head supply channel HSR due to the previous flushing process for nozzle row La, the amplitude of the pressure oscillations is smaller during period TC2 than during period TC1, and the generated negative pressure is also weaker.

[0061] Time t3, between time tf2 and time tf3, is a time between flushing processes. Specifically, at time t3, the flushing process is being performed on nozzle row Lb, and ink is not being ejected from each nozzle Na of nozzle row La. At time t3, the meniscus MN that was retracted into the second nozzle portion NP2 at time t2 is retracted in the Z1 direction and exists inside the second nozzle portion NP2. The meniscus MN that was retracted into the second nozzle portion NP2 at time t2 cannot eject ink normally, even if each piezoelectric element 111F of the second ejection portion group GDb is driven. Therefore, even if the flushing process is performed on nozzle row Lb, the thickened ink InT in the nozzle Nb cannot be ejected.

[0062] Time t4, which follows time tf3, is the time after the flushing process for nozzle row Lb has been performed. As shown by the pressure fluctuation characteristic PaR, when the flushing process for nozzle row Lb is completed, a pressure oscillation occurs in the opposite direction to the pressure oscillation at the start of flushing during period TC3. This pressure oscillation is sometimes referred to as the "pressure oscillation at the end of flushing." At time tf3, ink droplet ejection from nozzle row La and nozzle row Lb stops, but the flow of ink supply from the liquid container 120 to the in-head supply channel HSR continues for a while. Therefore, the ink pressure in the in-head supply channel HSR increases temporarily. Thereafter, the pressure repeatedly increases and decreases in response to the inherent pressure oscillation of the common liquid supply channel CSR, eventually converging to a predetermined pressure. Due to the pressure oscillation at the end of flushing, the meniscus MN, which was drawn into the second nozzle portion NP2 in nozzle Nb at time t2, returns to approximately the same position on the Z axis as the nozzle face FN. However, at time t4, the thickened ink InT remains in the nozzle Nb. Although the ink itself is ejected from the nozzle Nb during the printing process after the flushing process, the ejection characteristics deviate from those expected by the head manufacturer, resulting in uneven printing. The inventors' experiments and experience also revealed that the pressure fluctuations caused by the flushing process depend on the pressure oscillations of the common liquid supply channel CSR. The period TC1 in graph g1 corresponds to 1 / 2 the period of the inherent pressure oscillations of the common liquid supply channel CSR. The period TC1 is the period from time tf2 to time t2. The period TC1 is, for example, 5 milliseconds. While FIG. 7 illustrates a configuration in which the nozzle N has a two-stage structure, the phenomenon shown in FIG. 7 can occur even when the nozzle N has other configurations.

[0063] One way to suppress the phenomenon shown in FIG. 7 is to reduce the pressure oscillations at the start of flushing. Reducing the amount of ink discharged per unit period during the flushing process would be sufficient to reduce the pressure oscillations at the start of flushing. However, simply reducing the amount of ink discharged would lengthen the time required for the flushing process. Therefore, in the first embodiment, the amount of ink discharged per unit period during the flushing process for nozzle row La is gradually increased. In the following description, the flushing process for nozzle row La in this embodiment may be referred to as the "first flushing process," and the flushing process for nozzle row Lb may be referred to as the "second flushing process." Furthermore, the flushing process for all nozzle rows Ln of the liquid ejection head HU, including the first and second flushing processes, may be referred to as the "head flushing process." The head flushing process discharges more ink than the head manufacturer expects.

[0064] The first flushing process is an example of a “first discharge process,” and the second flushing process is an example of a “second discharge process.” The head flushing process will be described below with reference to FIG.

[0065] A4. Head flushing process Figure 8 is a diagram illustrating the head flushing process in the first embodiment. As shown in Figure 8, the inkjet printer 100 executes a first flushing process as the head flushing process, and after the first flushing process is completed, starts a second flushing process. Specifically, the inkjet printer 100 starts the second flushing process immediately after the first flushing process is completed. As shown in Figure 8, the period TH required for the head flushing process is divided into a period TF1 required for the first flushing process and a period TF2 required for the second flushing process, in that order.

[0066] The period TF1 is divided into a first start period Ts1, a first high discharge period Th1, and a first end period Te1, in that order. The period TF2 is divided into a second start period Ts2, a second high discharge period Th2, and a second end period Te2, in that order. However, as described above, the amplitude of the pressure vibration is smaller during the period TC2 than during the period TC1, and the generated negative pressure is also weaker. Therefore, the period TF1 does not need to include the first end period Te1. Similarly, the period TF2 does not need to include the second start period Ts2. As can be seen from FIG. 8, during the period TF1 when the first flushing process is being performed, ink is not discharged from the second discharger group GDb, and during the period TF2 when the second flushing process is being performed, ink is not discharged from the first discharger group GDa. That is, in the head flushing process, the second ejection part group GDb does not eject ink during the period when the first ejection part group GDa ejects ink, and the first ejection part group GDa does not eject ink during the period when the second ejection part group GDb ejects ink.

[0067] The first start period Ts1 is the period from the start of the first flushing process to the start of the first high discharge period Th1. The first high discharge period Th1 starts after the first start period Ts1, specifically, from the end of the first start period Ts1. The first end period Te1 starts from the end of the first high discharge period Th1.

[0068] The first start period Ts1 and the first end period Te1 preferably have a length equivalent to at least half a period of the inherent pressure oscillation of the common liquid supply channel CSR caused by the start of the first flushing process. The first start period Ts1 and the first end period Te1 preferably have a length of at least 5 milliseconds. In other words, the first start period Ts1 and the first end period Te1 are preferably longer than the period TC1.

[0069] The first high discharge period Th1 is preferably longer than the first start period Ts1. Specifically, the ratio of the first high discharge period Th1 to the period TF1 is preferably 50% or more. Similarly, the second high discharge period Th2 is preferably longer than the second start period Ts2. Specifically, the ratio of the second high discharge period Th2 to the period TF2 is preferably 50% or more.

[0070] The second start period Ts2 is the period from the start of the second flushing process to the start of the second high discharge period Th2. The second high discharge period Th2 starts after the second start period Ts2, specifically, from the end of the second start period Ts2. The second end period Te2 starts from the end of the second high discharge period Th2.

[0071] The second start-up period Ts2 is preferably equal to or longer than 5 milliseconds.

[0072] The ink discharge amount per unit period of the first high discharge period Th1 and the second high discharge period Th2 is greater than the ink discharge amount per unit period of the first start period Ts1, the first end period Te1, the second start period Ts2, and the second end period Te2. For example, the ink discharge amount per unit period of the first high discharge period Th1 and the second high discharge period Th2 is twice the ink discharge amount per unit period of the first start period Ts1, the first end period Te1, the second start period Ts2, and the second end period Te2. The ink discharge amount per unit period of the first high discharge period Th1 and the second high discharge period Th2 may be the same or different from each other. Similarly, the ink discharge amount per unit period of the first start period Ts1, the first end period Te1, the second start period Ts2, and the second end period Te2 may be the same or different from each other. In this way, by making the ink discharge amount per unit period during the first start period Ts1 and the second start period Ts2 less than the ink discharge amount per unit period during the first high discharge period Th1 and the second high discharge period Th2, it is possible to suppress the negative pressure caused by water hammer during the first start period Ts1 and the second start period Ts2 while causing ink to flow from the liquid container 120 to the in-head supply channel HSR, thereby making it possible to suppress the negative pressure caused by water hammer even if the ink discharge amount per unit period during the first high discharge period Th1 and the second high discharge period Th2 is large. Also, by making the ink discharge amount per unit period during the first end period Te1 and the second end period Te2 less than the ink discharge amount per unit period during the first high discharge period Th1 and the second high discharge period Th2, it is possible to suppress the amplitude of the inherent pressure oscillation of the common liquid supply channel CSR after discharge from the first discharger group GDa and the second discharger group GDb has stopped.

[0073] The following describes the discharge amount change modes that change the amount of ink discharged per unit period during the first start period Ts1 and the first high discharge period Th1. There are three discharge amount change modes: In response to instructions from the control circuit 170, the liquid ejection head HU discharges ink during the first start period Ts1 and the first high discharge period Th1 in accordance with at least one of the three discharge amount change modes.

[0074] 9 is a diagram illustrating a first discharge amount change mode. In the first discharge amount change mode, the number of discharge sections Da that discharge ink in the first start period Ts1 is smaller than the number of discharge sections Da that discharge ink in the first high discharge period Th1. The example in FIG. 9 is based on the assumption that M is an even number. Under the instruction of the control circuit 170, the liquid discharge head HU discharges ink from odd-numbered discharge sections Da out of the M discharge sections Da in the first start period Ts1, and discharges ink from all M discharge sections Da in the first high discharge period Th1.

[0075] 10 is a diagram illustrating a second discharge amount change mode. In the second discharge amount change mode, the number of first flushing pulses FP1 included per unit period in the supply drive signal Vin supplied to the piezoelectric element 111Fa during the first start period Ts1 is smaller than the number of first flushing pulses FP1 included per unit period in the supply drive signal Vin supplied to the piezoelectric element 111Fa during the first high discharge period Th1.

[0076] 10, the control circuit 170 outputs a latch signal LAT having a pulse PlsL to the drive circuit 112. The control circuit 170 defines a drive period Tu as the period from the rising edge of one pulse PlsL to the rising edge of the next pulse PlsL. Furthermore, the control circuit 170 outputs a change signal CH having a pulse PlsC to the drive circuit 112. The control circuit 170 divides one drive period Tu into two control periods Tbu1 and Tbu2 by the pulse PlsC.

[0077] 10, the drive signal generation circuit 184 generates a drive signal Com in which two first flushing pulses FP1 are provided in one drive period Tu. One of the two first flushing pulses FP1 is provided in a control period Tbu1, and the other first flushing pulse FP1 is provided in a control period Tbu2.

[0078] The first flushing pulse FP1 drives the piezoelectric element 111F to apply a pressure fluctuation to the ink in the pressure chamber CV so as to eject the ink from the nozzle N. The first flushing pulse FP1 is an example of an "ejection pulse."

[0079] The first flushing pulse FP1 has a first expansion element EF1, a first contraction element ET1, and a second expansion element EF2, in this order. The first expansion element EF1 changes the potential so as to expand the pressure chamber CV. Specifically, the first expansion element EF1 changes the potential from a reference potential V0, which is the starting potential of the first flushing pulse FP1, to a minimum potential VL1. The first contraction element ET1 changes the potential so as to contract the pressure chamber CV. Specifically, the first contraction element ET1 changes the potential from the minimum potential VL1 to a maximum potential VH1. The first expansion element EF1 and the first contraction element ET1 are connected by a potential maintaining element EM1, which maintains the minimum potential VL1. The second expansion element EF2 changes the potential so as to expand the pressure chamber CV. Specifically, the second expansion element EF2 changes the potential from the maximum potential VH1 to the reference potential V0. The first contraction element ET1 and the second expansion element EF2 are connected via a potential maintaining element EM2 that maintains the maximum potential VH1. Hereinafter, the maximum potential change width of one pulse, i.e., the potential difference between the maximum and minimum potentials of one pulse, may be referred to as the potential difference ΔVh. The potential difference ΔVh in the first flushing pulse FP1 is the potential difference ΔVh1, which is the potential difference between the maximum potential VH1 and the minimum potential VL1. Increasing the potential difference ΔVh allows for the amount of ink discharged from the nozzle N to be increased.

[0080] During the i-th drive period Tu[i], where Tu[i] is an integer greater than or equal to 1, within the first start period Ts1, the control circuit 170 outputs to the drive circuit 112 a print signal SI that specifies only the first flushing pulse FP1 provided during the control period Tbu1 for all M ejection sections Da. Therefore, a supply drive signal Vin having one first flushing pulse FP1 per drive period Tu is supplied to all M ejection sections Da. As a result, during the first start period Ts1, each ejection section Da of the first ejection section group GDa ejects ink once per drive period Tu.

[0081] During the jth drive period Tu[j], where Tu[j] is an integer greater than or equal to 1 and is greater than i, within the first high discharge period Th1, the control circuit 170 outputs a print signal SI to the drive circuit 112, specifying a first flushing pulse FP1 provided in the control period Tbu1 and a first flushing pulse FP1 provided in the control period Tbu2, for all M discharge sections Da. Therefore, a supply drive signal Vin having two first flushing pulses FP1 in one drive period Tu is supplied to all M discharge sections Da. As a result, during the first start period Ts1, each discharge section Da of the first discharge section group GDa discharges ink twice in one drive period Tu.

[0082] In the second discharge amount change mode, the drive signal Com output by the drive signal generation circuit 184 is the same during the first start period Ts1 and the first high discharge period Th1, and the number of first flushing pulses FP1 supplied to the discharge section Da by the print signal SI is changed, but this is not limited to this. For example, the second discharge amount change mode can also be achieved by changing the drive signal Com output by the drive signal generation circuit 184 during the first start period Ts1 and the first high discharge period Th1. Specifically, the control circuit 170 may cause the drive signal generation circuit 184 to output a drive signal Com having one first flushing pulse FP1 per drive cycle Tu during the first start period Ts1, and to output a drive signal Com having two first flushing pulses FP1 per drive cycle Tu during the first high discharge period Th1.

[0083] Alternatively, the second discharge amount change mode can be achieved by changing the length of the drive period Tu between the first start period Ts1 and the first high discharge period Th1. Specifically, the control circuit 170 makes the drive period Tu during the first start period Ts1 longer than the drive period Tu during the first high discharge period Th1. For example, the control circuit 170 sets the drive period Tu during the first start period Ts1 to twice the drive period Tu during the first high discharge period Th1. This allows the number of first flushing pulses FP1 included per unit period in the supply drive signal Vin supplied to the discharge section Da during the first start period Ts1 to be set to half the number of first flushing pulses FP1 included per unit period in the supply drive signal Vin supplied to the discharge section Da during the first high discharge period Th1.

[0084] 11 is a diagram illustrating a third discharge amount change mode. In the third discharge amount change mode, the potential difference ΔVh2 of the second flushing pulse FP2 supplied to the piezoelectric element 111Fa of the discharge section Da during the first start period Ts1 is smaller than the potential difference ΔVh1 of the first flushing pulse FP1 supplied to the piezoelectric element 111Fa of the discharge section Da during the first high discharge period Th1.

[0085] In the example of FIG. 11, the control circuit 170 outputs a latch signal LAT and a change signal CH to the drive circuit 112, similarly to the example of FIG.

[0086] 11, the drive signal generation circuit 184 generates a drive signal Com in which one first flushing pulse FP1 and one second flushing pulse FP2 are provided in one drive period Tu. One second flushing pulse FP2 is provided in a control period Tbu1, and one first flushing pulse FP1 is provided in a control period Tbu2.

[0087] The second flushing pulse FP2 has a third expansion element EF3, a second contraction element ET2, and a fourth expansion element EF4, in this order. The third expansion element EF3 changes the potential to expand the pressure chamber CV. Specifically, the third expansion element EF3 changes the potential from a reference potential V0, which is the starting potential of the second flushing pulse FP2, to a minimum potential VL2. The minimum potential VL2 is higher than the minimum potential VL1. The second contraction element ET2 changes the potential to contract the pressure chamber CV. Specifically, the second contraction element ET2 changes the potential from the minimum potential VL2 to a maximum potential VH2. The maximum potential VH2 is lower than the maximum potential VH1. The third expansion element EF3 and the second contraction element ET2 are connected by a potential maintaining element EM3, which maintains the minimum potential VL2. The fourth expansion element EF4 changes the potential to expand the pressure chamber CV. Specifically, the fourth expansion element EF4 changes the potential from the highest potential VH2 to the reference potential V0. A potential maintaining element EM4, which maintains the highest potential VH2, is connected between the second contraction element ET2 and the fourth expansion element EF4. The potential difference in the second flushing pulse FP2 is a potential difference ΔVh2, which is the potential difference between the highest potential VH2 and the lowest potential VL2. The potential difference ΔVh2 is smaller than the potential difference ΔVh1.

[0088] The second flushing pulse FP2 is also an example of an “ejection pulse.” In the following description, the first flushing pulse FP1 and the second flushing pulse FP2 may be referred to as the flushing pulse FP without distinction.

[0089] In the i-th drive cycle Tu[i] within the first start period Ts1, for all of the M discharge sections Da, the control circuit 170 outputs a print signal SI that specifies only the second flushing pulse FP2 provided in the control period Tbu1 to the drive circuit 112. Therefore, a supply drive signal Vin having one second flushing pulse FP2 in one drive cycle Tu is supplied to all of the M discharge sections Da.

[0090] In the j-th drive cycle Tu[j] within the first high discharge period Th1, the control circuit 170 outputs a print signal SI specifying the first flushing pulse FP1 provided in the control period Tbu2 to the drive circuit 112 for all of the M discharge sections Da. Therefore, a supply drive signal Vin having one first flushing pulse FP1 per drive cycle Tu is supplied to all of the M discharge sections Da.

[0091] As described above, the potential difference ΔVh2 of the second flushing pulse FP2 is smaller than the potential difference ΔVh1 of the first flushing pulse FP1, and therefore the ink discharge amount in the first start period Ts1 is smaller than the ink discharge amount in the first high discharge period Th1.

[0092] In the third discharge amount change mode, the drive signal Com output by the drive signal generation circuit 184 is the same during the first start period Ts1 and the first high discharge period Th1, and the magnitude of the potential difference ΔVh of the flushing pulse FP supplied to the discharge section Da by the print signal SI is changed, but this is not limited to this. For example, the third discharge amount change mode can also be achieved by changing the drive signal Com output by the drive signal generation circuit 184 between the first start period Ts1 and the first high discharge period Th1. Specifically, the control circuit 170 may output the drive signal Com having one second flushing pulse FP2 per drive cycle Tu during the first start period Ts1, and output the drive signal Com having one first flushing pulse FP1 per drive cycle Tu during the first high discharge period Th1.

[0093] The liquid ejection head HU may eject ink during the first start period Ts1 and the first high discharge period Th1 by combining two or more of the three discharge amount change modes described above under instructions from the control circuit 170. For example, as a mode combining the first discharge amount change mode and the second discharge amount change mode, the liquid ejection head HU may make the number of ejection units Da that eject ink during the first start period Ts1 less than the number of ejection units Da that eject ink during the first high discharge period Th1, and may make the number of first flushing pulses FP1 included per unit period of the first start period Ts1 less than the number of first flushing pulses FP1 included per unit period of the first high discharge period Th1.

[0094] Although not explained here, the liquid ejection head HU also ejects ink during the first end period Te1, the second start period Ts2, and the second end period Te2 in the same discharge amount change manner as the first start period Ts1. Furthermore, the liquid ejection head HU also ejects ink during the second high discharge period Th2 in the same discharge amount change manner as the first high discharge period Th1.

[0095] FIG. 12 is a diagram for explaining the effects of the first embodiment. Graph g2 shown in FIG. 12 shows the pressure fluctuation characteristics in the comparative embodiment and the first embodiment. The horizontal axis of graph g2 is time [s], and the vertical axis of graph g2 is pressure [kPa]. [s] represents seconds. Pressure fluctuation characteristics PaR1 shown in graph g2 show the pressure fluctuation characteristics in the comparative embodiment. The period TC1 shown in pressure fluctuation characteristics PaR1 is the same as the period TC1 shown in graph g1, and corresponds to 1 / 2 the period of the inherent pressure oscillation of the common liquid supply channel CSR. Pressure fluctuation characteristics PaC1 shown in graph g2 show the pressure fluctuation characteristics in the first embodiment.

[0096] In the example of FIG. 12, as shown by the pressure fluctuation characteristic PaR1, in the comparative embodiment, the negative pressure caused by water hammer reduces the pressure to approximately -4.55 kPa. On the other hand, as shown by the pressure fluctuation characteristic PaC1, in the first embodiment, the negative pressure caused by water hammer reduces the pressure to approximately -2.15 kPa. That is, in the first embodiment, the peak value of the negative pressure is reduced by approximately 2.4 kPa compared to the comparative embodiment. Thus, in the first embodiment, by gradually increasing the ink discharge amount per unit period, the magnitude of the negative pressure caused by water hammer can be reduced compared to the comparative embodiment. By reducing the magnitude of the negative pressure, the meniscus of the nozzle N that is connected to the same common liquid supply channel CSR and is not undergoing a flushing process is prevented from being drawn in the Z1 direction, thereby preventing thickened ink from remaining in the nozzle Nb.

[0097] A5. Summary of the first embodiment According to the first embodiment, this can be defined as a maintenance method for a liquid ejection head HU including a first ejector group GDa including a plurality of ejectors Da, a second ejector group GDb including a plurality of ejectors Db, and a common liquid supply channel CSR communicating with the first ejector group GDa and the second ejector group GDb. In response to instructions from the control circuit 170, the liquid ejection head HU starts a first flushing process to eject ink from the first ejector group GDa, and then starts a second flushing process to eject ink from the second ejector group GDb. The amount of ink ejected from the first ejector group GDa per unit period during a first start period Ts1 from the start of the first flushing process until a first predetermined period has elapsed is less than the amount of ink ejected from the first ejector group GDa per unit period during a first high discharge period Th1 that starts after the first start period Ts1. According to the first embodiment, by gradually increasing the amount of ink discharged per unit period, the magnitude of the negative pressure caused by the water hammer effect can be reduced, which prevents the meniscus of the nozzle N that has not undergone the flushing process from being drawn in the Z1 direction, and prevents thickened ink from remaining in the nozzle N. As a result, the inkjet printer 100 can prevent abnormalities from occurring in the ejection characteristics after the head flushing process is completed.

[0098] The first start period Ts1 preferably has a length equivalent to at least half the period of the inherent pressure oscillation of the common liquid supply channel CSR caused by the start of the first flushing process. Furthermore, the first start period Ts1 preferably has a length of at least 5 milliseconds. In other words, the first start period Ts1 preferably has a length equal to or greater than the period TC1. As can be seen from graphs g1 and g2, the ink pressure in the nozzles Nb increases in the negative direction during the period TC1, and the ink pressure shifts to the positive direction after the period TC1. Therefore, by making the first start period Ts1 longer than the period TC1, the magnitude of the negative pressure applied to the ink in the nozzles Nb during the period TC1 can be reduced compared to a mode in which the first high discharge period Th1 is entered during the period TC1.

[0099] During the execution of the first flushing process, ink is not discharged from the multiple discharge sections Db, and after the execution of the first flushing process is completed, the second flushing process is started, and during the execution of the second flushing process, ink is not discharged from the multiple discharge sections Da.

[0100] In addition, the amount of ink discharged from the second ejection group GDb per unit period during the second start period Ts2 from the start of the second flushing process is less than the amount of ink discharged from the second ejection group GDb per unit period during the second high discharge period Th2 that starts from the end of the second start period Ts2. As shown by the pressure fluctuation characteristic PaR in FIG. 7, switching the target of the flushing process from nozzle row La to nozzle row Lb causes pressure oscillations in period TC2. If the amplitude of the pressure oscillations increases, the likelihood of the meniscus MN breaking increases. If the meniscus MN breaks, the likelihood of air bubbles getting into the nozzles N increases. If air bubbles get into the nozzles N, ejection abnormalities may occur. Therefore, according to the first embodiment, the amplitude of the pressure oscillations when switching flushing can be suppressed compared to a mode in which there is no second start period Ts2.

[0101] Furthermore, the second start period Ts2 is preferably equal to or longer than 5 milliseconds. According to the first embodiment, the magnitude of the amplitude of the pressure vibration at the time of switching to flushing can be suppressed compared to the aspect in which the second start period Ts2 is shorter than 5 milliseconds.

[0102] In addition, in the second flushing process, the amount of ink discharged from the second ejection group GDb per unit period during the second end period Te2, which starts from the end of the second high discharge period Th2, is less than the amount of ink discharged from the second ejection group GDb per unit period during the second high discharge period Th2, which starts from the end of the second start period Ts2 from the start of the second flushing process. As shown by the period TC3 of the pressure fluctuation characteristic PaR, pressure fluctuations at the end of flushing occur in the comparative example. Similar to pressure fluctuations at the start of flushing, pressure fluctuations at the end of flushing can also be a cause of ejection abnormalities. Therefore, according to the first embodiment, compared to the example without the second end period Te2, the flow rate of ink supplied from the liquid container 120 to the in-head supply channel HSR during the second end period Te2 can be reduced, thereby suppressing the magnitude of pressure fluctuations at the end of flushing.

[0103] In the first flushing process, the amount of ink discharged from the first ejection group GDa per unit period during the first end period Te1, which starts from the end of the first high discharge period Th1, is less than the amount of ink discharged from the first ejection group GDa per unit period during the first high discharge period Th1. According to the first embodiment, compared to a configuration in which the first end period Te1 is not present, the flow rate of ink supplied from the liquid container 120 to the supply flow path HSR inside the head during the first end period Te1 can be reduced, thereby suppressing the amplitude of the pressure vibration when switching to flushing.

[0104] Furthermore, the first end period Te1 preferably has a length equivalent to at least 1 / 2 the period of the inherent pressure oscillation of the common liquid supply channel CSR that occurs when the first flushing process is started. Like the pressure vibration at the start of flushing, the pressure vibration at the time of flushing switching is also affected by the pressure vibration of the ink in the common liquid supply channel CSR. Therefore, according to the first embodiment, the magnitude of the amplitude of the pressure vibration at the time of flushing switching can be suppressed compared to an aspect in which the first end period Te1 is less than half the period of the inherent pressure vibration of the common liquid supply channel CSR that occurs when the first flushing process starts.

[0105] Moreover, the first end period Te1 is preferably 5 milliseconds or longer. According to the first embodiment, the magnitude of the amplitude of the pressure vibration at the time of switching to flushing can be suppressed compared to the aspect in which the first end period Te1 is shorter than 5 milliseconds.

[0106] Furthermore, in the first discharge amount change mode, the number of discharge units Da that discharge ink in the first start period Ts1 is smaller than the number of discharge units Da that discharge ink in the first high discharge period Th1. Furthermore, in the second discharge amount change mode, each of the multiple discharge units Da includes a nozzle N that discharges ink, a pressure chamber CV that communicates with the nozzle N, and a piezoelectric element 111F that applies pressure fluctuations to the ink in the pressure chamber CV in response to a supplied drive signal Com. The drive signal Com includes a flushing pulse FP that drives the piezoelectric element 111Fa to apply pressure fluctuations to the ink in the pressure chamber CV so as to discharge ink from the nozzle N. The number of flushing pulses FP included per unit period of the drive signal Com supplied to the piezoelectric element 111Fa in the first start period Ts1 is smaller than the number of flushing pulses FP included per unit period of the drive signal Com supplied to the piezoelectric element 111Fa in the first high discharge period Th1. In the third discharge amount change mode, the potential difference ΔVh2 of the second flushing pulse FP2 supplied to the piezoelectric element 111Fa in the first start period Ts1 is smaller than the potential difference ΔVh1 of the first flushing pulse FP1 supplied to the piezoelectric element 111Fa in the first high discharge period Th1. Comparing the three discharge amount change modes, in the third discharge amount change mode, the potential difference ΔVh2 of the second flushing pulse FP2 is smaller than the potential difference ΔVh1 of the first flushing pulse FP1, so if the ink has a high viscosity, there is a risk that ink will not be ejected during the first start period Ts1. In other words, compared to the third discharge amount change mode, the first discharge amount change mode and the second discharge amount change mode are applicable even when the ink has a high viscosity. Furthermore, while the first discharge amount change mode has ejection sections Da that do not eject ink during the first start period Ts1, the second discharge amount change mode and the third discharge amount change mode allow ink to be ejected evenly from the M ejection sections Da during the first start period Ts1.

[0107] B. Second embodiment In the first embodiment, the ink discharge amount per unit period of the flushing process is increased in stages to reduce the pressure oscillations at the start of flushing, but the method for reducing the pressure oscillations at the start of flushing is not limited to this. Specifically, the magnitude of the peak of the pressure oscillations at the start of flushing can be reduced by switching the target of the flushing process from nozzle row La to nozzle row Lb before the pressure oscillations at the start of flushing reach a peak negative pressure value. A second embodiment will now be described.

[0108] B1. Head Flushing Process in the Second Embodiment FIG. 13 is a diagram illustrating the head flushing process in the second embodiment. As shown in FIG. 13, the period THA required for the head flushing process in the second embodiment coincides with the period TF1A required for the first flushing process in the second embodiment. The first flushing process in the second embodiment differs from the first flushing process in the first embodiment in that the second flushing process in the second embodiment is executed after the first start period Ts1A and before the first high discharge period Th1A. In other words, during the first high discharge period Th1A, after the second flushing process in the second embodiment is completed, ink is discharged from the first discharger group GDa without being discharged from the second discharger group GDb.

[0109] The period TF1A required for the first flushing process in the second embodiment is divided into a first start period Ts1A, a period TF2A required for the second flushing process in the second embodiment, a first high discharge period Th1A, and a first end period Te1A, in that order. The period TF2A is divided into a second high discharge period Th2A and a second end period Te2A, in that order. The second flushing process in the second embodiment differs from the second flushing process in the first embodiment in that it does not have a second start period Ts2. As in the first embodiment, in the head flushing process in the second embodiment, the second discharger group GDb does not discharge ink during the period in which the first discharger group GDa discharges ink, and the first discharger group GDa does not discharge ink during the period in which the second discharger group GDb discharges ink.

[0110] The first high discharge period Th1A is longer than the first start period Ts1A. As in the first embodiment, the ratio of the first high discharge period Th1A to the period TF1A minus the period TF2A is preferably 50% or more. Similarly, the ratio of the second high discharge period Th2A to the period TF2A is preferably 50% or more.

[0111] As described in the first embodiment, the period during which the pressure oscillation at the start of flushing reaches the negative pressure peak corresponds to half the period of the inherent pressure oscillation of the common liquid supply channel CSR. Therefore, the first start period Ts1A is less than half the period of the inherent pressure oscillation of the common liquid supply channel CSR. For example, the first start period Ts1A is 5 milliseconds long.

[0112] FIG. 14 is a diagram for explaining the effects of the second embodiment. Graph g3 in FIG. 14 shows the pressure fluctuation characteristics in the comparative embodiment and the second embodiment. The horizontal axis of graph g3 is time [s], and the vertical axis of graph g3 is pressure [kPa]. [s] represents seconds. Pressure fluctuation characteristic PaR2 shown in graph g3 shows the pressure fluctuation characteristics in the comparative embodiment. More specifically, pressure fluctuation characteristic PaR2 shows the characteristics when a flushing process for nozzle array La is performed for 100 milliseconds, and then a flushing process for nozzle array Lb is performed 100 milliseconds later. The period TC1 shown in pressure fluctuation characteristic PaR2 is the same as the period TC1 shown in graph g1, and corresponds to 1 / 2 the period of the inherent pressure oscillation of the common liquid supply channel CSR. Pressure fluctuation characteristic PaC2 shown in graph g3 shows the pressure fluctuation characteristics in the second embodiment.

[0113] In the example of FIG. 14 , as shown by the pressure fluctuation characteristic PaR2, in the comparative example, the negative pressure caused by water hammer reduces the pressure to approximately -5.6 kPa. On the other hand, as shown by the pressure fluctuation characteristic PaC1, in the second embodiment, the negative pressure caused by water hammer reduces the pressure to approximately -4.9 kPa. In other words, in the second embodiment, the negative pressure caused by water hammer stops the ejection from the first ejection part group GDa to the extent that the meniscus MN in the nozzle Nb of the second ejection part group GDb, which does not eject ink, is not pulled in to a state that causes a malfunction. That is, in the second embodiment, the peak value of the negative pressure is reduced by approximately 0.7 kPa compared to the comparative example. Thus, in the second embodiment, the target of the flushing process is switched from nozzle row La to nozzle row Lb before the pressure oscillation at the start of flushing reaches the negative pressure peak, thereby reducing the magnitude of the negative pressure caused by water hammer compared to the comparative example. Furthermore, it is preferable to schedule the start of discharge from the nozzles Nb of the second discharger group GDb at time t4, when the inherent pressure oscillation of the common liquid supply channel CSR is shifting to a positive pressure. This offsets the negative pressure caused by the water hammer resulting from discharge from the nozzles Nb of the second discharger group GDb with the shift in the inherent pressure oscillation of the common liquid supply channel CSR to a positive pressure, preventing the meniscus MN in the nozzles Na of the first discharger group GDa from being drawn in to a state that would cause a malfunction. Therefore, a predetermined period from the start of the second high discharge period Th2A can be set in which no ink is discharged from either the first discharger group GDa or the second discharger group GDb. The amount of ink discharged per unit period during the first start period Ts1A and the amount of ink discharged per unit period during the first high discharge period Th1A may be equal to or different from each other. However, it is preferable that the total discharge amount from the first discharge part group GDa in the period TF1A is equal to the total discharge amount from the second discharge part group GDb in the period TF2A. Furthermore, the period TF2A does not necessarily have to include the second end period Te2A. In that case, it is preferable to set the start of discharge from the nozzles Na of the first discharger group GDa to the time when the inherent pressure oscillation of the common liquid supply channel CSR is changing to the positive pressure side. By doing so, the negative pressure caused by the water hammer resulting from discharge from the nozzles Na of the first discharger group GDa is offset by the change in the inherent pressure oscillation of the common liquid supply channel CSR to the positive pressure side, preventing the meniscus MN in the nozzles Nb of the second discharger group GDb, which are not discharging, from being drawn in to a state that causes a malfunction. Therefore, a predetermined period from the start of the first high discharge period Th1A can be set in which ink is not discharged from either the first discharger group GDa or the second discharger group GDb.

[0114] B2. Summary of the second embodiment As described above, in the second embodiment, during the first start period Ts1A, ink is discharged from the first discharger group GDa without being discharged from the second discharger group GDb. The second flushing process, which occurs after the first start period Ts1A, discharges ink from the second discharger group GDb without being discharged from the first discharger group GDa. The first high discharge period Th1A is a period during which ink is discharged from the discharger Da without being discharged from the discharger Db after the second flushing process is performed, and the first high discharge period Th1A is longer than the first start period Ts1A. According to the second embodiment, similar to the first embodiment, it is possible to prevent abnormalities in the ejection characteristics from occurring after the head flushing process is completed. Comparing the second embodiment with the first embodiment, the second embodiment does not have the second start period Ts2, thereby shortening the period required for the head flushing process compared to the first embodiment. Meanwhile, the number of times the target of the flushing process is switched is one in the first embodiment and two in the second embodiment. Therefore, the first embodiment switches the target of the flushing process less frequently than the second embodiment, making it easier to control the control circuit 170.

[0115] C. Third embodiment In the third embodiment, the nozzle row Ln that is the target of the flushing process, which is performed in the second embodiment, is repeatedly switched. The third embodiment will be described below.

[0116] C1. Head Flushing Process in the Third Embodiment Figure 15 is a diagram illustrating the head flushing process in the third embodiment. As shown in Figure 15, the inkjet printer 100 starts a first flushing process as a head flushing process, and then starts a second flushing process during a first start period Ts1B of the first flushing process. As shown in Figure 15, the period THB required for the head flushing process in the third embodiment is divided into a period TF1B required for the first flushing process in the third embodiment, and a second high-discharge period Th2B and a second end period Te2B within a period TF2B required for the second flushing process in the third embodiment, in that order.

[0117] The period TF1B is divided into a first start period Ts1B, a first high discharge period Th1B, and a first end period Te1B, in this order. The first start period Ts1B is divided into a discharge period Ts11, a non-discharge period Ts12, a discharge period Ts13, and a non-discharge period Ts14, in this order. The discharge period Ts11 and the discharge period Ts13 are periods during which ink is discharged from the first discharger group GDa. The non-discharge period Ts12 and the non-discharge period Ts14 are periods during which ink is not discharged from the first discharger group GDa.

[0118] The period TF2B is divided into a second start period Ts2B, a second high discharge period Th2B, and a second end period Te2B, in this order. The second start period Ts2B is divided into a discharge period Ts21, a non-discharge period Ts22, a discharge period Ts23, and a non-discharge period Ts24, in this order. The discharge period Ts21 and the discharge period Ts23 are periods during which ink is discharged from the second discharge section group GDb. The non-discharge period Ts22 and the non-discharge period Ts24 are periods during which ink is not discharged from the second discharge section group GDb. The discharge period Ts21 is the same period as the non-discharge period Ts12. The non-discharge period Ts22 is the same period as the discharge period Ts13. The discharge period Ts23 is the same period as the non-discharge period Ts14. The non-discharge period Ts24 is the same period as the period obtained by connecting the first high discharge period Th1B and the first ending period Te1B.

[0119] Furthermore, as can be seen from Figure 15, similar to the first and second embodiments, in the head flushing process in the third embodiment, the second ejection unit group GDb does not eject ink during the period when the first ejection unit group GDa ejects ink, and the first ejection unit group GDa does not eject ink during the period when the second ejection unit group GDb ejects ink.

[0120] The discharge period Ts11 may be the same length as or shorter than the discharge period Ts13. The amount of ink discharged per unit period during the discharge period Ts11 may be the same as or shorter than the amount of ink discharged per unit period during the discharge period Ts13. Similarly, the discharge period Ts21 may be the same length as or shorter than the discharge period Ts23. The amount of ink discharged per unit period during the discharge period Ts21 may be the same as or shorter than the amount of ink discharged per unit period during the discharge period Ts23. The discharge period Ts11 may be the same length as or different from the non-discharge period Ts12. Similarly, the discharge period Ts13 may be the same length as or different from the non-discharge period Ts14. For example, the discharge period Ts11 is 1 millisecond long, the non-discharge period Ts12 is 3 milliseconds long, the discharge period Ts13 is 5 milliseconds long, and the non-discharge period Ts14 is 10 milliseconds long. Furthermore, it is preferable to set the start of discharge from the nozzles Nb of the second discharger group GDb during the discharge period Ts21 and the discharge period Ts23 to a time when the inherent pressure oscillation of the common liquid supply channel CSR is changing to a positive pressure. This offsets the negative pressure caused by the water hammer resulting from discharge from the nozzles Nb of the second discharger group GDb with the change in the inherent pressure oscillation of the common liquid supply channel CSR to a positive pressure, preventing the meniscus MN in the nozzle Na of the first discharger group GDa from being drawn in to a state that would cause a malfunction. Therefore, it is possible to provide a predetermined period from the start of the discharge period Ts21 and a predetermined period from the start of the discharge period Ts23 in which ink is not discharged from either the first discharger group GDa or the second discharger group GDb. Similarly, it is preferable to set the start of discharge from the nozzles Na of the first discharger group GDa during the discharge period Ts13 and the first high discharge period Th1B to a time when the inherent pressure oscillation of the common liquid supply channel CSR is changing to a positive pressure. By doing so, the negative pressure caused by the water hammer effect resulting from discharge from the nozzle Na of the first discharge part group GDa is offset by the change in the inherent pressure vibration of the common liquid supply flow path CSR to the positive pressure side, preventing the meniscus MN in the nozzle Nb of the second discharge part group GDb that is not discharging from being drawn in to a state that would cause a malfunction.The ink discharge amount per unit period during each of the discharge period Ts11, discharge period Ts13, and first high discharge period Th1B may be equal to or different from each other. Similarly, the ink discharge amount per unit period during each of the discharge period Ts21, discharge period Ts23, and second high discharge period Th2B may be equal to or different from each other. However, it is preferable that the total discharge amount from the first discharger group GDa during period TF1B is equal to the total discharge amount from the second discharger group GDb during period TF2B.

[0121] Furthermore, in the third embodiment, the period in which ink is discharged out of the first start period Ts1B and the second start period Ts2B is divided into two, but the number of divisions is not limited to two and may be three or more.

[0122] Similar to the first and second embodiments, the third embodiment can also prevent abnormalities from occurring in the ejection characteristics after the head flushing process is completed.

[0123] D. Variations The above-described embodiments can be modified in various ways. Specific modifications that can be applied to the above-described embodiments are exemplified below. Two or more embodiments arbitrarily selected from the following examples can be combined as appropriate to the extent that they are not mutually contradictory.

[0124] D1. First modified example In the second discharge amount change mode described above, the potential difference ΔVh of the flushing pulse FP supplied to the piezoelectric element 111F in the first start period Ts1 may be larger than the potential difference ΔVh of the flushing pulse FP supplied to the piezoelectric element 111F in the first high discharge period Th1. A specific example will be described with reference to FIG.

[0125] Fig. 16 is a diagram for explaining a second discharge amount change manner in Modification 1. In the example of Fig. 16, the control circuit 170 divides one drive cycle Tu into four control periods Tbu1, Tbu2, Tbu3, and Tbu4 using pulses PlsC.

[0126] 16, the drive signal generation circuit 184 generates a drive signal Com in which one first flushing pulse FP1 and three second flushing pulses FP2 are provided in one drive cycle Tu. One first flushing pulse FP1 is provided in control period Tbu1, the first of the three second flushing pulses FP2 is provided in control period Tbu2, the second second flushing pulse FP2 is provided in control period Tbu3, and the third second flushing pulse FP2 is provided in control period Tbu4.

[0127] In the i-th drive cycle Tu[i] within the first start period Ts1, for all of the M discharge sections Da, the control circuit 170 outputs a print signal SI that specifies only the first flushing pulse FP1 provided in the control period Tbu1 to the drive circuit 112. Therefore, a supply drive signal Vin having one first flushing pulse FP1 in one drive cycle Tu is supplied to all of the M discharge sections Da.

[0128] In the j-th drive cycle Tu[j] within the first high discharge period Th1, for all of the M discharge sections Da, the control circuit 170 outputs a print signal SI specifying three second flushing pulses FP2 provided in control periods Tbu2, Tbu3, and Tbu4 to the drive circuit 112. Therefore, a supply drive signal Vin having three second flushing pulses FP2 in one drive cycle Tu is supplied to all of the M discharge sections Da.

[0129] 16, in the first modified example, the number of flushing pulses FP included per unit period in the first start period Ts1 is smaller than the number of flushing pulses FP included per unit period in the first high discharge period Th1. Also, in the first modified example, the potential difference ΔVh1 of the first flushing pulse FP1 supplied to the piezoelectric element 111F in the first start period Ts1 is larger than the potential difference ΔVh2 of the second flushing pulse FP2 supplied to the piezoelectric element 111F in the first high discharge period Th1.

[0130] During the first start period Ts1, thickened ink accumulates inside the nozzles N, and a large force may be required to eject the ink. Meanwhile, if ink is ejected during the first high discharge period Th1 using a flushing pulse FP with a large potential difference ΔVh, there is a risk that the negative pressure of the ink in the nozzles Nb that are not ejecting ink will become too large. As described above, according to the first modified example, during the first start period Ts1, thickened ink can be more easily ejected by increasing the potential difference ΔVh, and during the first high discharge period Th1, the negative pressure in the nozzles Nb that are not ejecting ink can be prevented from becoming too large.

[0131] D2. Second variant In the first discharge amount change mode, the liquid discharge head HU may, under the instruction of the control circuit 170, repeatedly discharge ink from the odd-numbered discharge sections Da among the M discharge sections Da and discharge ink from the even-numbered discharge sections Db during the first start period Ts1.

[0132] D3. Third variant In each of the above-described aspects, the nozzle row Ln that is the target of the flushing process may be switched over for a short period of time, for example, every 5 milliseconds.

[0133] D4. Fourth Variation In each of the above-described aspects, the nozzles Na of the first ejector group GDa are nozzles Na belonging to the nozzle row La, and the nozzles Nb of the second ejector group GDb are nozzles Nb belonging to the nozzle row Lb. In other words, the flushing process is performed for each nozzle row Ln, but this is not limited to this. For example, the flushing process may be performed by setting the ejector D to which the nozzles N of one nozzle row Ln that are closer to the Y1-direction end of the head chip 111 than the Y2-direction end belong as the first ejector group GDa, and setting the ejector D to which the nozzles N of the head chip 111 that are closer to the Y2-direction end than the Y1-direction end belong as the second ejector group GDb.

[0134] D5. Fifth Variation In each of the above-described embodiments, the liquid ejection head HU has a piezoelectric element 111F, but may have a heating element instead of the piezoelectric element 111F. The heating element generates bubbles in the pressure chamber CV by heating the ink in the pressure chamber CV. In the fifth modification, the heating element is an example of a "driving element."

[0135] D6. Sixth Variation In the above-described embodiments, a manufacturing method for a serial-type inkjet printer 100 in which the liquid ejection head HU is moved back and forth in the direction along the X axis has been exemplified, but the present disclosure is not limited to such embodiments. The inkjet printer 100 may also be a line-type liquid ejection device in which multiple nozzles N are distributed across the entire width of the recording medium PP.

[0136] D7. Other variations The inkjet printer 100 described above can be used in various devices, such as facsimile machines and copiers, as well as devices dedicated to printing. However, the use of the recording device of the present invention is not limited to printing. For example, a recording device that ejects a solution of color material is used as a manufacturing device for forming color filters for liquid crystal display devices. Furthermore, a recording device that ejects a solution of conductive material is used as a manufacturing device for forming wiring and electrodes for wiring substrates. [Explanation of symbols]

[0137] 100... inkjet printer, 111... head chip, 111A... flow path substrate, 111B... pressure chamber substrate, 111C... nozzle plate, 111D... vibration absorber, 111E... vibration plate, 111Fa, 111Fb... piezoelectric element, 111G... protective plate, 111H... case, 111I... wiring board, 112... drive circuit, 115... switching circuit, 116... connection state designation circuit, 120... liquid container, 130... movement mechanism, 131... carriage, 132... endless belt, 140... conveyance mechanism, 145... maintenance mechanism, 146... cap, 147... wiper, 160... memory circuit, 170... control circuit, 180...control module, 183...power supply circuit, 184...drive signal generation circuit, CH...change signal, CSR...common liquid supply flow path, CVa, CVb...pressure chamber, Com...drive signal, Da, Db...discharge portion, EF1...first expansion element, EF2...second expansion element, EF3...third expansion element, EF4...fourth expansion element, EM1, EM2, EM3, EM4...potential maintenance elements, ET1...first contraction element, ET2...second contraction element, FN...nozzle surface, FP1...first flushing pulse, FP2...second flushing pulse, GDa...first discharge portion group, GDb...second discharge portion group, HSA...connecting pipe, HSR ...supply flow path in head, HU...liquid ejection head, IHa, IHb...inlet, Img...print data, InT...viscous ink, LAT...latch signal, LHA, LHD...internal wiring, La, Lb, Ln...nozzle array, MN...meniscus, NAa, NAb...communicating flow path, NP1...first nozzle portion, NP2...second nozzle portion, Na, Nb...nozzle, PP...recording medium, PaC1, PaC2, PaR, PaR1, PaR2...pressure fluctuation characteristics, PlsC, PlsL...pulse, R...reservoir, R1, R1a, R1b, R2, R2a, R2b...space, RA, RAa, RAb...supply flow path, R a, Rb... reservoir, SI... printing signal, SLa, SLb... connection status designation signal, SW, SWa, SWb... switch, Sk1, Sk2, Sk3... control signal, TC1, TC2, TC3, TF1, TF1A, TF1B, TF2, TF2A, TF2B, TH, THA, THB... period, Tbu1, Tbu2, Tbu3, Tbu4... control period, Te1, Te1A, Te1B... first end period, Te2, Te2A, Te2B... second end period, Th1, Th1A, Th1B... first high discharge period, Th2, Th2A, Th2B... second high discharge period, Ts1... first start period, Ts11,Ts13, Ts21, Ts23...discharge period, Ts12, Ts14, Ts22, Ts24...non-discharge period, Ts1A, Ts1B...first start period, Ts2...second start period, Ts2B...second start period, Tu...drive period, V0...reference potential, VBS...offset potential, VH1, VH2...highest potential, VHV...power supply potential, VL1, VL2...lowest potential, Vina, Vinb...supplied drive signal, Zd...lower electrode, Zm...piezoelectric body, Zu...upper electrode, dCom...waveform designation signal, g1, g2, g3...graph, m...number of stages, ΔVh1, ΔVh2...potential difference.

Claims

1. a first ejection part group including a plurality of first ejection parts; a second ejection part group including a plurality of second ejection parts; a common liquid supply flow path communicating with the first discharge part group and the second discharge part group; A maintenance method for a liquid ejection head, comprising: after starting a first discharge process for discharging liquid from the first discharge part group, starting a second discharge process for discharging liquid from the second discharge part group; an amount of liquid discharged from the first discharge part group per unit period during a first start period from the start of the first discharge process is less than an amount of liquid discharged from the first discharge part group per unit period during a first high discharge period that starts after the first start period; A maintenance method for a liquid ejection head.

2. the first start period has a length corresponding to at least half a cycle of the inherent pressure oscillation of the common liquid supply channel that occurs upon start of the first discharge process; 2. The method for maintaining a liquid ejection head according to claim 1.

3. the first initiation period is greater than or equal to 5 milliseconds in length; 2. The method for maintaining a liquid ejection head according to claim 1.

4. During the first discharge process, liquid is not discharged from the second discharge units, After the first discharge process is completed, the second discharge process is started. During the second discharge process, liquid is not discharged from the plurality of first discharge units.

2. The method for maintaining a liquid ejection head according to claim 1.

5. an amount of liquid discharged from the second discharge part group per unit period during a second start period from the start of the second discharge process is less than an amount of liquid discharged from the second discharge part group per unit period during a second high discharge period starting from the end of the second start period; 5. The maintenance method for a liquid ejection head according to claim 4.

6. the second initiation period is greater than or equal to 5 milliseconds in length; 6. A maintenance method for a liquid ejection head according to claim 5.

7. In the second discharge process, the amount of liquid discharged from the second discharge part group per unit period in a second end period starting from the end of a second high discharge period starting from the end of a second start period from the start of the second discharge process is less than the amount of liquid discharged from the second discharge part group per unit period in the second high discharge period.

5. The maintenance method for a liquid ejection head according to claim 4.

8. the first start period is a period in which liquid is discharged from the first discharge part group without being discharged from the second discharge part group; the second discharge process discharges liquid from the second discharge part group without discharging liquid from the first discharge part group after the first start period; the first high discharge period is a period during which, after the second discharge process is completed, liquid is discharged from the first discharge unit without being discharged from the second discharge unit, the first high discharge period is longer than the first start period; 2. The method for maintaining a liquid ejection head according to claim 1.

9. In the first discharge process, the amount of liquid discharged from the first discharge part group per unit period in a first end period that starts from the end of the first high discharge period is less than the amount of liquid discharged from the first discharge part group per unit period in the first high discharge period.

2. The method for maintaining a liquid ejection head according to claim 1.

10. the first end period has a length corresponding to at least half a period of the inherent pressure oscillation of the common liquid supply channel that occurs upon the start of the first discharge process; 10. The maintenance method for a liquid ejection head according to claim 9.

11. the first termination period is greater than or equal to 5 milliseconds in length; 10. The maintenance method for a liquid ejection head according to claim 9.

12. the number of first discharge units among the plurality of first discharge units that discharge liquid in the first start period is smaller than the number of first discharge units among the plurality of first discharge units that discharge liquid in the first high discharge period; 2. The method for maintaining a liquid ejection head according to claim 1.

13. each of the plurality of first ejection units includes a first nozzle that ejects liquid, a first pressure chamber that communicates with the first nozzle, and a first drive element that applies a pressure fluctuation to the liquid in the first pressure chamber in response to a supplied drive signal; the drive signal includes an ejection pulse that drives the first drive element to impart a pressure fluctuation to the liquid in the first pressure chamber so as to eject the liquid from the first nozzle, the number of ejection pulses included per unit period of the drive signal supplied to the first drive element in the first start period is smaller than the number of ejection pulses included per unit period of the drive signal supplied to the first drive element in the first high discharge period; 2. The method for maintaining a liquid ejection head according to claim 1.

14. a maximum potential change width of the ejection pulse supplied to the first driving element in the first start period is greater than a maximum potential change width of the ejection pulse supplied to the first driving element in the first high discharge period; 14. The maintenance method for a liquid ejection head according to claim 13.

15. each of the plurality of first ejection units includes a first nozzle that ejects liquid, a first pressure chamber that communicates with the first nozzle, and a first drive element that applies a pressure fluctuation to the liquid in the first pressure chamber in response to a supplied drive signal; the drive signal includes an ejection pulse that drives the first drive element to impart a pressure fluctuation to the liquid in the first pressure chamber so as to eject the liquid from the first nozzle, a maximum potential change width of the ejection pulse supplied to the first driving element in the first start period is smaller than a maximum potential change width of the ejection pulse supplied to the first driving element in the first high discharge period; 2. The method for maintaining a liquid ejection head according to claim 1.

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