Liquid discharge head

Abstract

To provide a liquid discharge head capable of further adjusting discharge speed of droplets by making a width of a discharge waveform shorter than a half-period of parasitic vibration when continuously discharging the plurality of droplets.SOLUTION: A liquid discharge head includes: a nozzle plate; a pressure chamber; an actuator; and a drive circuit. A drive signal includes a plurality of discharge waveforms for discharging a plurality of droplets from a nozzle. At least one of discharge waveforms of the drive signal is an arbitrarily shaped waveform that is continuous twice. The drive circuit cancels vibration of an acoustic resonance frequency in a frequency region higher than a main acoustic resonance frequency of liquid in the pressure chamber caused by a change in potential difference by at least one time or more of potential difference changes to be performed after the change in potential difference. The intervals of the plurality of discharge waveforms are substantially the same as a period of the main acoustic vibration frequency.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a liquid ejection head. [Background technology]

[0002] Conventionally, liquid ejection heads that eject liquid have been able to express gradations of ink density on the media by continuously ejecting multiple droplets, thereby increasing the dot diameter when the droplets land on the media. In addition, when multiple droplets are continuously ejected, the width of the ejection pulse for each droplet is adjusted to adjust the ejection speed of each droplet.

[0003] Even when ejecting multiple droplets continuously using an inkjet head that has parasitic vibrations in addition to the main acoustic vibration, the ejection speed of each droplet can be adjusted by adjusting the width of the ejection pulse for each droplet while canceling out the parasitic vibrations using a stepped ejection pulse that is timed to half the period of the parasitic vibrations.

[0004] However, since the width of the ejection waveform cannot be made shorter than half the period of the parasitic vibration, there is a problem in that there is a limit to the adjustment of the ejection speed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-045797 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a liquid ejection head that can further adjust the droplet ejection speed when ejecting multiple droplets continuously by making the width of the ejection waveform (Dp width) shorter than half the period of the parasitic vibration. [Means for solving the problem]

[0007] The liquid ejection head of the embodiment includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate includes a nozzle that ejects liquid. The pressure chamber is in communication with the nozzle. The actuator varies the volume of the pressure chamber in response to a drive signal. The drive circuit generates the drive signal that drives the actuator. The drive signal includes multiple ejection waveforms that cause multiple droplets to be ejected from the nozzle. At least one of the ejection waveforms of the drive signal is a waveform of an arbitrary shape that occurs twice consecutively. The drive circuit cancels out vibrations of an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency of the liquid in the pressure chamber, which are generated by a change in potential difference, by changing the potential difference at least once after the change in potential difference. The interval between the multiple ejection waveforms is approximately the same as the period of the main acoustic vibration frequency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view showing the configuration of a liquid ejection head according to the embodiment, with some parts omitted. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a liquid ejection head according to the embodiment, with some parts omitted. [Figure 3] FIG. 2 is a block diagram schematically illustrating the configuration of a drive circuit of the liquid ejection head according to the embodiment. [Figure 4] FIG. 1 is an explanatory diagram showing the configuration of a liquid ejection apparatus using a liquid ejection head according to an embodiment. [Figure 5] FIG. 1 is a block diagram showing an example of the configuration of a liquid ejection apparatus according to an embodiment. [Figure 6] 5A and 5B are explanatory diagrams showing examples of drive waveforms including ejection waveforms and cancellation waveforms of the liquid ejection head according to the embodiment. [Figure 7] 10A and 10B are explanatory diagrams showing an example of a drive waveform including an ejection waveform and a cancellation waveform of a liquid ejection head according to a comparative example. [Figure 8] 5A and 5B are explanatory diagrams showing examples of drive waveforms and acoustic vibrations of the liquid ejection head according to the embodiment. [Figure 9] 5A and 5B are explanatory diagrams showing the relationship between a drive waveform and ejected droplets in an example of a liquid ejection head according to an embodiment. [Figure 10]3A and 3B are explanatory diagrams showing an example of droplets ejected from a liquid ejection head according to an embodiment. [Figure 11] FIG. 10 is an explanatory diagram showing an example of frequency analysis of a liquid ejection head according to a comparative example. [Figure 12] 10A and 10B are explanatory diagrams showing an example in which the main acoustic vibration and the parasitic vibration of a liquid ejection head according to a comparative example are combined. [Figure 13] FIG. 10 is an explanatory diagram showing an example of frequency analysis of a liquid ejection head according to a comparative example. [Figure 14] 6A and 6B are explanatory diagrams showing an example of a driving waveform and acoustic vibration of a liquid ejection head according to a comparative example. [Figure 15] 6A and 6B are explanatory diagrams showing an example of a driving waveform and acoustic vibration of a liquid ejection head according to a comparative example. [Figure 16] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 17] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 18] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 19] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 20] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 21] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The configuration of a liquid ejection head 1 according to an embodiment and a liquid ejection device 100 using the liquid ejection head 1 will be described below with reference to FIGS. 1 to 5. FIG. 1 is a cross-sectional view showing the configuration of the liquid ejection head 1 according to an embodiment with some parts omitted, and FIG. 2 is a cross-sectional view showing the configuration of the liquid ejection head 1 with some parts omitted. FIG. 3 is a block diagram schematically showing the configuration of a drive circuit 70 for the liquid ejection head 1. FIG. 4 is an explanatory diagram showing the configuration of a liquid ejection device 100 using the liquid ejection head 1 according to an embodiment, and FIG. 5 is a block diagram showing an example of the configuration of the liquid ejection device 100. Note that in each drawing, the configuration is enlarged, reduced, or omitted as appropriate for ease of explanation.

[0010] 1 and 2, the liquid ejection head 1 includes a base 10, an actuator 20, a vibration plate 30, a flow path plate 40, a nozzle plate 50 having a plurality of nozzles 51, and a drive circuit 70.

[0011] The base 10 is formed in the shape of, for example, a rectangular plate. The actuator 20 is joined to the base 10.

[0012] The actuator 20 is a piezoelectric member including, for example, a plurality of piezoelectric pillars 21 and non-driven piezoelectric pillars 22 arranged alternately with the plurality of piezoelectric pillars 21. The actuator 20 is formed in a comb shape by arranging the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 in one direction at predetermined intervals. For example, such an actuator 20 is formed by dicing a stacked piezoelectric member bonded to the base 10 from the end face opposite the base 10 side to form a plurality of rectangular pillar-shaped piezoelectric elements at predetermined intervals for each piezoelectric member. The formed plurality of piezoelectric elements are then provided with electrodes or the like to form a plurality of piezoelectric pillars 21 and a plurality of non-driven piezoelectric pillars 22 arranged alternately as piezoelectric elements. That is, the actuator 20 is divided into a plurality of parts at one end side (closer to the vibration plate 30) by the formed plurality of grooves, and the other end side (closer to the base 10) is connected.

[0013] For example, the laminated piezoelectric member that constitutes the actuator 20 is formed by stacking and sintering sheet-like piezoelectric materials. As a specific example, as shown in FIGS. 1 and 2, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 are, for example, laminated piezoelectric bodies serving as driving elements. The piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 each include a plurality of stacked piezoelectric layers, a plurality of internal electrodes formed on the main surfaces of each piezoelectric layer, and a plurality of external electrodes. Note that, as an example, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 have the same configuration.

[0014] The piezoelectric layers are thin plates made of piezoelectric materials such as PZT (lead zirconate titanate) or lead-free KNN (potassium sodium niobate). The multiple piezoelectric layers are stacked in the thickness direction and bonded by sintering. The stacking direction of the multiple piezoelectric layers is perpendicular to the arrangement direction of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22.

[0015] The internal electrodes are conductive films made of a sinterable conductive material such as silver-palladium and formed in a predetermined shape. The internal electrodes are formed in predetermined regions on the main surfaces of the piezoelectric layers. The multiple internal electrodes are configured with alternate polarities in the arrangement direction.

[0016] The external electrodes are formed on the surfaces of the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22, and are configured by collecting the ends of the internal electrodes. The external electrodes are formed by depositing films of Ni, Cr, Au, or the like using a known method such as plating or sputtering. The plurality of external electrodes are arranged on different side surfaces of the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22, respectively, and are configured to have different polarities. Note that the external electrodes of different polarities may be routed around different regions of the same side surface of the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22.

[0017] In this embodiment, as an example, the external electrodes include individual electrodes formed on each of the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22, and a common electrode formed continuously with the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22. The individual electrodes formed on each of the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22 are arranged independently of one another. The common electrode is, for example, grounded.

[0018] These external electrodes are connected to, for example, a drive circuit 70. For example, each external electrode is connected by wiring to a control unit 150 as a drive unit via a driver 723 (described later) of the drive circuit 70, and is configured to be drive-controllable by control by a processor 151.

[0019] When a voltage is applied to the internal electrodes via the external electrodes, the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22 vibrate longitudinally along the stacking direction of the piezoelectric layers. The longitudinal vibration here refers to, for example, "vibration in the thickness direction defined by the piezoelectric constant d33." For example, as shown in FIG. 2, every other piezoelectric pillar 21 is arranged corresponding to the pressure chambers 46 across the vibration plate 30, and the remaining non-driven piezoelectric pillars 22 are arranged in positions facing the partition wall 42 across the vibration plate 30.

[0020] When a voltage is applied, the piezoelectric pillars 21 vibrate longitudinally, displacing the vibration plate 30. That is, the piezoelectric pillars 21 deform the pressure chambers 46. The non-driven piezoelectric pillars 22 are disposed in positions facing the partition wall portions 42. No voltage is applied to the non-driven piezoelectric pillars 22. That is, each piezoelectric pillar 21 constitutes an actuator that deforms the pressure chambers 46 when driven, and each non-driven piezoelectric pillar 22 constitutes a support pillar. That is, the piezoelectric pillars 21 expand and contract the pressure chambers 46, thereby varying the volume of the pressure chambers.

[0021] The vibration plate 30 is bonded to one side in the stacking direction of the piezoelectric layers of the multiple piezoelectric pillars 21, 22, i.e., to the surface on the nozzle plate 50 side. The vibration plate 30 is deformed, for example, by driving the piezoelectric pillars 21. The vibration plate 30 is bonded to the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22 of the actuator 20.

[0022] The vibration plate 30 is, for example, a flat plate arranged so that the thickness direction coincides with the stacking direction of the piezoelectric layers. The surface direction of the vibration plate 30 extends in the direction in which the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22 are arranged. The vibration plate 30 is, for example, a metal plate. The vibration plate 30 has multiple vibration parts 301 that face each pressure chamber 46 and are individually displaceable. The vibration plate 30 is formed by integrally connecting the multiple vibration parts 301.

[0023] For example, the vibration plate 30 is configured as a single flat plate, and the regions joined to the piezoelectric pillars 21 are displaced individually. The vibration plate 30 is configured from, for example, a stainless steel plate. The vibration plate 30 may have folds or steps formed in the regions adjacent to the vibration portion 301 or between adjacent vibration portions 301, so that the multiple vibration portions 301 can be easily displaced.

[0024] The vibration plate 30 expands and contracts the pressure chamber 46 by displacing the part of the vibration plate 30 opposite the piezoelectric pillar 21 due to the expansion and compression of the piezoelectric pillar 21 caused by the longitudinal vibration of the piezoelectric pillar 21, thereby varying the volume of the pressure chamber 46.

[0025] One main surface of the vibration plate 30 is bonded to the actuator 20, and the other main surface is bonded to the flow path plate 40. A pressure chamber 46 capable of containing ink is formed between the vibration plate 30 and the flow path plate 40.

[0026] One main surface of the vibration plate 30 faces the piezoelectric pillars 21 and 22, and the other main surface faces the pressure chamber 46 and the partition wall 42, respectively.

[0027] The flow path plate 40 is bonded to the vibration plate 30. The flow path plate 40 is disposed between the nozzle plate 50 and the vibration plate 30. The flow path plate 40 has a plurality of partition walls 42. The flow path plate 40 also forms predetermined flow paths 45. The flow path plate 40 forms the plurality of partition walls 42 and the predetermined flow paths 45 by, for example, stacking a plurality of plates 401, each of which has an opening.

[0028] A plurality of partition walls 42 are arranged in the arrangement direction of the plurality of piezoelectric pillars 21, 22, and face the non-driven piezoelectric pillars 22 via the vibration plate 30. The partition walls 42 separate a plurality of pressure chambers 46 (described later) of a predetermined flow path 45, as well as a plurality of individual flow paths 47.

[0029] The predetermined flow path 45 includes a plurality of pressure chambers 46 separated by partition walls 42 of the flow path plate 40, a plurality of individual flow paths 47 separated by partition walls 42, and a common flow path 48 communicating with the plurality of individual flow paths 47.

[0030] The multiple pressure chambers 46 are aligned in the alignment direction of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22, and face the multiple piezoelectric pillars 21 via the vibration plate 30. The multiple pressure chambers 46 aligned in one direction are separated by partition walls 42. The multiple partition walls 42 arranged between the multiple pressure chambers 46 face the multiple non-driven piezoelectric pillars 22 via the vibration plate 30. The multiple pressure chambers 46 are formed by closing one side of the flow path plate 40 with the vibration plate 30 and closing the other side with the nozzle plate 50 in the stacking direction of the piezoelectric layers. Furthermore, nozzles 51 formed in the nozzle plate 50 are arranged in the pressure chambers 46.

[0031] The multiple pressure chambers 46 communicate with a common flow path 48 via individual flow paths 47. The pressure chambers 46 hold liquid supplied from the common flow path 48 through the individual flow paths 47, and are deformed by vibration of the vibration plate 30 that forms part of the pressure chambers 46, thereby ejecting the liquid from the nozzles 51. The individual flow paths 47 connect the common flow path 48 and the pressure chambers 46. The same number of individual flow paths 47 are provided as the pressure chambers 46. The cross-sectional shape of the individual flow paths 47 is different from the cross-sectional shape of the pressure chambers 46. The cross-sectional area of ​​the individual flow paths 47 is smaller than the cross-sectional area of ​​the pressure chambers 46. The common flow path 48 is fluidly connected to the multiple individual flow paths 47, and communicates with the pressure chambers 46 through each individual flow path 47.

[0032] The nozzle plate 50 is made of a metal such as SUS or Ni, or a resin material such as polyimide. The nozzle plate 50 is bonded to the flow path plate 40 and covers the multiple pressure chambers 46. The nozzle plate 50 has multiple nozzles 51 formed in positions facing the multiple pressure chambers 46 and penetrating through the thickness direction. The multiple nozzles 51 form a nozzle row.

[0033] As shown in Fig. 5, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data in chronological order for each of the piezoelectric pillars 21 and 22. The decoder 722 controls the driver 723 for each of the piezoelectric pillars 21 and 22 based on the print data stored in the data buffer 721. The driver 723 outputs drive signals that operate each of the piezoelectric pillars 21 and 22 under the control of the decoder 722. The drive signals are voltages that are applied to each of the piezoelectric pillars 21 and 22.

[0034] 1, the drive circuit 70 includes a wiring film 71 having one end connected to an external electrode, a driver IC 72 mounted on the wiring film 71, and a printed wiring board mounted on the other end of the wiring film 71. For example, the driver IC 72 includes a data buffer 721, a decoder 722, and a driver 723. Note that the driver IC 72 may include some of the data buffer 721, the decoder 722, and the driver 723, and the remaining parts may be included in the printed wiring board or the like.

[0035] The drive circuit 70 applies a drive voltage to the external electrode by the driver IC 72 to drive the piezoelectric pillar 21 , vary the volume of the pressure chamber 46 , and eject droplets from the nozzle 51 .

[0036] The wiring film 71 is connected to the plurality of individual electrodes and the common electrode. For example, the wiring film 71 is an anisotropic conductive film (ACF) that is fixed to the connection portions of the external electrodes by thermocompression bonding or the like. The wiring film 71 is, for example, a COF (chip on film) on which a driver IC 72 is mounted.

[0037] The driver IC 72 is connected to the external electrodes via the wiring film 71. The driver IC 72 may be connected to the external electrodes by other means such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste) instead of the wiring film 71.

[0038] The driver IC 72 generates control signals and drive signals to be applied to each piezoelectric pillar 21, 22 to operate the piezoelectric pillars 21. The driver IC 72 generates control signals for controlling the timing of ink ejection and the selection of the piezoelectric pillars 21 to eject ink, according to an image signal input from the control unit 150 of the liquid ejection device 100. The driver IC 72 also generates a voltage, i.e., a drive signal (electrical signal), to be applied to the piezoelectric pillars 21 according to the control signal. When the driver IC 72 applies a drive signal to the piezoelectric pillars 21, the piezoelectric pillars 21 are driven by displacing the diaphragm 30 to vary the volume of the pressure chambers 46, expanding and contracting. This causes pressure vibrations in the ink filled in the pressure chambers 46. The pressure vibrations cause ink to be ejected from the nozzles 51 provided in the pressure chambers 46. The liquid ejection head 1 may be configured to achieve gradation expression by changing the amount of ink droplets that land on each pixel. The liquid ejection head 1 may also be configured to change the amount of ink droplets that land on each pixel by changing the number of ink ejections. In this way, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pillar 21.

[0039] Next, an example of the drive circuit 70 will be described as shown in Fig. 3. The drive circuit 70 includes, for example, a voltage control unit 724 and voltage switching units 725 in the same number as the pressure chambers 46 within a driver IC 72. However, Fig. 3 illustrates two voltage switching units 725, and does not illustrate the other voltage switching units 725.

[0040] The drive circuit 70 is connected to a first voltage source 81, a second voltage source 82, and a third voltage source 83. The drive circuit 70 applies the voltage supplied from the first voltage source 81 to each wiring electrode 726. The drive circuit 70 also selectively applies the voltages supplied from the first voltage source 81, the second voltage source 82, and the third voltage source 83 to each wiring electrode 727. Here, if the actuator 20 is a laminated PZT, application of voltages of both polarities tends to cause deterioration, so the voltages supplied by the first voltage source 81, the second voltage source 82, and the third voltage source 83 are set to a ground voltage and one of positive and negative polarities with respect to the ground voltage.

[0041] The output voltage of the first voltage source 81 is, for example, a ground voltage, and its voltage value is V0 (V0=0 [V]). The voltage value indicated by the output voltage of the second voltage source 82 is V1. The voltage value V1 is a voltage higher than V0. The voltage value indicated by the output voltage of the third voltage source 83 is, for example, V2. For example, the voltage value V2 is a voltage higher than V0 and lower than V1.

[0042] The wiring electrode 726 is connected to a common electrode serving as a ground electrode of the actuator 20. The plurality of wiring electrodes 727 are connected to individual electrodes serving as non-ground electrodes of the actuator 20, respectively.

[0043] The voltage control unit 724 is connected to each of the multiple voltage switching units 725. The voltage control unit 724 outputs to each voltage switching unit 725 a command indicating which voltage source to select from the first voltage source 81, the second voltage source 82, and the third voltage source 83. For example, the voltage control unit 724 receives an image signal from the control unit 150 and determines the timing of switching the voltage source in each voltage switching unit 725. Then, the voltage control unit 724 outputs a command to the voltage switching unit 725 to select one of the first voltage source 81, the second voltage source 82, and the third voltage source 83 at the determined switching timing. The voltage switching unit 725 switches the voltage source connected to the wiring electrode 727 in accordance with the command from the voltage control unit 724.

[0044] The voltage switching unit 725 is configured by, for example, a semiconductor switch. Under the control of the voltage control unit 724, the voltage switching unit 725 connects one of the first voltage source 81, the second voltage source 82, and the third voltage source 83 to the wiring electrode 727. Therefore, the internal electrodes of different polarities of the piezoelectric pillar 21 are connected to the wiring electrode 726 and the wiring electrode 727 via the external electrodes (common electrode and individual electrode).

[0045] Such a drive circuit 70 switches the connection wiring between voltage sources 81, 82, and 83 and the actuator 20 using a switching circuit configured with a voltage control unit 724 and multiple voltage switching units 725, thereby inputting drive waveforms having at least three types of potential differences as drive signals between the electrodes of the actuator 20. Here, the drive waveforms are ejection waveforms that eject droplets when the actuator 20 is driven. In this embodiment, potential differences other than the largest and smallest potential differences are called intermediate potential differences.

[0046] The printed wiring board is a PWA (Printing Wiring Assembly) on which various electronic components and connectors are mounted. The printed wiring board is connected to a control unit 150 of the liquid ejection device 100.

[0047] Next, an example of a liquid ejection device 100 including the liquid ejection head 1 will be described with reference to Figures 4 and 5. The liquid ejection device 100 is, for example, an inkjet recording device. The liquid ejection device 100 includes a housing 111, a medium supply unit 112, an image forming unit 113, a medium ejection unit 114, and a conveying device 115. The liquid ejection device 100 also includes a control unit 150.

[0048] The liquid ejection device 100 is a liquid ejection device that performs an image formation process on paper P by ejecting a liquid such as ink while transporting the paper P as a printing medium, which is the ejection target, along a predetermined transport path A that runs from a medium supply section 112 through an image forming section 113 to a medium ejection section 114.

[0049] The housing 111 constitutes the outer shell of the liquid ejection device 100. The housing 111 has an outlet at a predetermined location for ejecting the paper P to the outside.

[0050] The medium supply unit 112 includes a plurality of paper feed cassettes, and is configured to be able to hold a stack of multiple sheets of paper P of various sizes.

[0051] The medium discharge unit 114 includes a paper discharge tray configured to be able to hold the paper P discharged from the discharge port.

[0052] The image forming section 113 includes a support section 117 that supports the paper P, and a plurality of head units 130 that are disposed above the support section 117 and face each other.

[0053] The support section 117 includes a conveyor belt 118 that is looped in a predetermined area where image formation is performed, a support plate 119 that supports the conveyor belt 118 from the back side, and a plurality of belt rollers 120 that are provided on the back side of the conveyor belt 118.

[0054] During image formation, the support unit 117 supports the paper P on a holding surface, which is the upper surface of the conveyor belt 118, and conveys the paper P downstream by moving the conveyor belt 118 at a predetermined timing by the rotation of the belt roller 120.

[0055] The head unit 130 includes a liquid ejection head 1, a plurality of ink tanks 132 as liquid tanks each mounted on the liquid ejection head 1, a connection flow path 133 connecting the liquid ejection head 1 and the ink tanks 132, and a supply pump 134.

[0056] In this embodiment, a plurality of head units 130 are provided. Each head unit 130 uses a different color ink. For example, the plurality of head units 130 includes liquid ejection heads 1 of four colors, cyan, magenta, yellow, and black, and ink tanks 132 that respectively store ink of each color. The ink tanks 132 are connected to the common flow path 48 of the liquid ejection heads 1 by connection flow paths 133.

[0057] A negative pressure control device such as a pump (not shown) is connected to the ink tank 132. The negative pressure control device controls the negative pressure inside the ink tank 132 in accordance with the head value between the liquid ejection head 1 and the ink tank 132, thereby causing the ink supplied to each nozzle 51 of the liquid ejection head 1 to form a meniscus of a predetermined shape.

[0058] The supply pump 134 is a liquid transfer pump constituted by, for example, a piezoelectric pump. The supply pump 134 is provided in a supply flow path. The supply pump 134 is connected to the control unit 150 by wiring and is controlled by the control unit 150. The supply pump 134 supplies liquid to the liquid ejection head 1.

[0059] The conveying device 115 conveys the paper P along a conveying path A that runs from the medium supply unit 112 through the image forming unit 113 to the medium discharge unit 114. The conveying device 115 includes a plurality of guide plate pairs 121 and a plurality of conveying rollers 122 that are arranged along the conveying path A.

[0060] Each of the guide plate pairs 121 includes a pair of plate members arranged opposite each other with the paper P being conveyed therebetween, and guides the paper P along the conveying path A.

[0061] The conveying rollers 122 are driven to rotate under the control of the control unit 150, thereby sending the paper P downstream along the conveying path A. Note that sensors for detecting the conveying status of the paper are arranged at various points along the conveying path A.

[0062] The control unit 150 is, for example, a control board, and includes a processor 151, a ROM (Read Only Memory) 152, a RAM (Random Access Memory) 153, an I / O port 154 which is an input / output port, and an image memory 155.

[0063] The processor 151 is a processing circuit such as a CPU (Central Processing Unit) that is a controller. The processor 151 controls the head unit 130, drive motor 161, operation unit 162, various sensors 163, and the like that are provided in the liquid ejection device 100 through an I / O port 154. The processor 151 transmits print data stored in an image memory 155 to the drive circuit 70 in the order of drawing.

[0064] ROM 152 stores various programs and the like. RAM 153 temporarily stores various variable data, image data, and the like. Note that ROM 152 and RAM 153 are examples of storage media, and other storage media may be used as long as they are capable of storing various programs, data, and the like. I / O port 154 is an interface unit that inputs data from the outside, such as an externally connected device 200, and outputs data to the outside. Print data from the externally connected device 200 is sent to control unit 150 via I / O port 154 and saved in image memory 155.

[0065] The characteristics of the liquid ejection head 1 used in the liquid ejection device 100 according to this embodiment and the drive waveform of the liquid ejection head 1 (ejection waveform of the drive signal) will be described below.

[0066] First, the drive waveform of the liquid ejection head 1 of this embodiment will be described with reference to FIGS. 6 to 15. FIG. 6 is an explanatory diagram showing an example of a drive waveform including a multi-drop ejection waveform and a cancel waveform for the liquid ejection head 1, which continuously ejects multiple droplets. FIG. 7 is an explanatory diagram showing an example of a drive waveform including a multi-drop ejection waveform and a cancel waveform for the liquid ejection head 1 of a comparative example, which is compared with the liquid ejection head 1 of this embodiment. FIG. 8 is an explanatory diagram showing an example of one ejection waveform and acoustic vibration of the liquid ejection head 1 of this embodiment. FIG. 9 is an explanatory diagram showing the relationship between the ejection waveform and ejected droplets in an example of the liquid ejection head 1. FIG. 10 is an explanatory diagram showing an example of ejected droplets from the liquid ejection head 1. FIGS. 11 to 15 are drawings explaining a conventional liquid ejection head as a comparative example. FIG. 11 is an explanatory diagram showing an example of a frequency analysis of pressure vibrations of the liquid ejection head of the comparative example. FIG. 12 is an explanatory diagram showing an example in which the main acoustic vibration and parasitic vibration of FIG. 11 are combined. FIG. 13 is an explanatory diagram showing an example of frequency analysis of a liquid ejection head according to a comparative example, FIG. 14 is an explanatory diagram showing an example of a drive waveform and acoustic vibration of a liquid ejection head according to a comparative example, and FIG. 15 is an explanatory diagram showing an example of a drive waveform and acoustic vibration of a liquid ejection head according to a comparative example.

[0067] First, conventional liquid ejection heads use a driving method known as pull-and-shoot, which increases the ejection force by driving the piezoelectric pillars 21 in sync with the half-period AL of the main acoustic vibration of the pressure chamber. However, as shown in the example of frequency analysis of nozzle pressure vibration in Figure 11, when the liquid ejection head (actuator) is driven to eject droplets from the nozzle, in addition to the main acoustic vibration caused by the fluid vibration of the ink, parasitic vibrations may occur in the pressure chamber in a frequency range higher than the main acoustic vibration.

[0068] When the actuator is driven to eject droplets from the nozzle, if parasitic vibrations with a higher frequency than the main acoustic vibration occur, the pressure in the pressure chamber will produce pressure peaks with a shorter period than the half period of the main acoustic vibration, as shown in Figure 12. In other words, the composite wave of the main acoustic vibration and the parasitic vibration has a sharp initial vibration. The short-period pressure peak increases the ejection speed of the leading edge of the ejected droplet, but does not persist until the end of the ejection, decreasing the ejection speed of the trailing edge of the ejected droplet. As a result, as shown in the upper diagram (a) of Figure 10, when a droplet is ejected, the volume of the satellite increases relative to the leading edge droplet, resulting in a deterioration of print quality. Here, satellites are droplets that follow the leading edge droplet and are ejected with a gap between them when the piezoelectric pillar 21 is driven and the pressure chamber is deformed, causing liquid to be ejected from the nozzle.

[0069] Furthermore, for example, in a conventional liquid ejection head similar to the liquid ejection head 1 of this embodiment, in addition to the main acoustic vibration, a parasitic vibration that is approximately three times (for example, 2.8 times) the main acoustic vibration occurs, as shown in the frequency analysis of Fig. 13. Here, the following are thought to be the causes of the parasitic vibration having a higher frequency than the main acoustic vibration occurring in the pressure chamber of the liquid ejection head.

[0070] One example of the cause is an odd multiple vibration of three or more in the liquid column vibration of a closed tube. An example of such a liquid ejection head is an end shooter, as shown in Figure 13, which has an opening at the connection point with a common flow path, similar to the liquid ejection head 1 of the embodiment.

[0071] Another example of a cause is vibrations that are integer multiples of two or more in the liquid column vibration of an open tube. An example of such a liquid ejection head is a side shooter, whose open end is the connection point with a common flow channel, as shown in Figure 14. Note that, in the main acoustic vibration of an open tube, the amplitude of the pressure vibration is greatest at the center of the open tube, so nozzles are located near the center of the open tube. As shown in Figure 14, when vibrations that are even multiples of two or more in the liquid column vibration of an open tube occur, the center of the open tube becomes a vibration node with a small amplitude of the pressure vibration. Therefore, when a nozzle is located near the center of the open tube, the shape of the ejected droplets is less affected by vibrations that are even multiples of two or more. Therefore, when a nozzle is located near the center of an open tube, vibrations that are odd multiples of three or more are more likely to increase the volume of satellites and degrade print quality than vibrations that are even multiples of two or more.

[0072] Another example of the cause is vibration caused by reflection of pressure vibrations when the pressure chamber and the individual flow paths have different flow path cross sections, which changes the speed of sound in each flow path.

[0073] Another example of a cause is vibration caused by a pressure vibration node occurring between the pressure chamber and the less rigid flow path when the wall or part of the wall of the individual flow path has lower rigidity than the pressure chamber, as the pressure generated in the pressure chamber is reduced in the less rigid flow path. This occurs, for example, when the installation range of an actuator (piezoelectric pillar 21) such as a PZT shown by the two-dot chain line in Figure 1 is offset from the range of the vibration plate on the wall of the pressure chamber due to manufacturing errors, as in the actuator (piezoelectric pillar 21) shown by the solid line in Figure 1, and the area of ​​the pressure chamber wall that is only supported by the vibration plate and is not supported by the actuator is relatively large. 11 and 13 show the graphs of the results of a frequency analysis of the pressure vibration in the nozzle when a simulation was performed in which the head in which only the diaphragm in the upper right of the pressure chamber in Figure 1 is used and the unsupported area of ​​the actuator is set to a range slightly less than 30% of the longitudinal length of the pressure chamber (the width of pressure chamber 46 in Figure 1) was used. The simulation involved structural analysis of the deformation of the PZT and pressure chamber, compressive fluid analysis of the liquid behavior in the flow path, and fluid surface analysis of the droplet ejection from the nozzle. It is also possible to investigate the main acoustic vibration and parasitic vibration by inputting a step-like drive waveform to the actuator, measuring the time change in the velocity and position of the nozzle meniscus, and performing frequency analysis, or by ejecting droplets with a square wave as shown in Figure 15, and measuring the change in ejection velocity when the time width of the square wave is changed.

[0074] As shown in Figure 15, when the rectangular wave width UL of the ejection waveform is set to AL, the third harmonic vibration AI caused by the advance expansion of the pressure chamber before ejection (rising waveform) and the third harmonic vibration AII of the liquid column vibration caused by the contraction of the pressure chamber during ejection (falling waveform) reinforce each other, resulting in a short-period pressure peak caused by the third harmonic vibration, which leads to a deterioration in print quality.

[0075] Next, an example of the drive and drive waveform of the liquid ejection head 1 of this embodiment will be described. In this example, the pressure vibration of the pressure chamber 46 of the liquid ejection head 1 is likened to the vibration of a liquid column in a closed tube, and the drive waveform is such that the acoustic resonance frequency (parasitic vibration) in a frequency range higher than the main acoustic resonance frequency (main acoustic vibration) of the liquid in the pressure chamber 46 suppresses third harmonic vibration, which is an odd multiple of the main acoustic resonance frequency that is approximately three times or more. Here, approximately three times includes 2.8 times, as shown in FIG. 11. Furthermore, in this example, the drive waveform of the liquid ejection head 1 is an example of a multi-drop that continuously ejects multiple droplets, as shown in FIG. 6, in which droplets are continuously ejected twice, but may also be an example in which droplets are continuously ejected three or more times.

[0076] First, when the potential difference is greatest, the liquid ejection head 1 causes the pressure chamber 46 to expand to the greatest extent by the piezoelectric pillar 21 of the actuator 20, and when the potential difference is smallest, the piezoelectric pillar 21 of the actuator 20 causes the ink pressure chamber to contract to the smallest extent by the piezoelectric pillar 21 of the actuator 20. When ejecting ink from the liquid ejection head 1, the pressure chamber 46 is expanded in advance before ejection and then contracted at the time of ejection, thereby ejecting ink. In this embodiment, the ejection waveform (ejection pulse) of the drive waveform of the liquid ejection head 1 is a drive waveform in which at least one ejection waveform for ejecting one drop of liquid droplets from among the ejection waveforms for each droplet when multiple droplets are continuously ejected is a trapezoidal wave (a single-stage rectangular wave) input twice at a period of Tm2, ​​which is half the period of the parasitic vibration, to eject ink. Furthermore, in this embodiment, at least one of the ejection waveforms before and after the ejection waveform that forms a square wave is increased twice consecutively by a potential difference (expansion potential difference) including an intermediate potential difference multiple times when the pressure chamber 46 is expanded in advance before ejection, or decreased twice consecutively by a potential difference (contraction potential difference) including an intermediate potential difference multiple times when the pressure chamber 46 is contracted during ejection. More preferably, the ejection waveform is such that the potential difference is changed twice consecutively for at least one of the ejection waveforms before and after the ejection waveform that forms a square wave, both when the pressure chamber 46 is expanded and when it is contracted.

[0077] In the example of this embodiment, the ejection waveform is an ejection waveform that changes the potential difference twice consecutively, at least one of which is before and after the rectangular ejection waveform, both when the pressure chamber 46 is expanded and contracted, and then an ejection waveform that is a rectangular wave is used, to eject droplets twice in succession. In the following explanation, the first ejection waveform may be referred to as the ejection waveform for the first drop, and the second ejection waveform may be referred to as the ejection waveform for the second drop.

[0078] Furthermore, after inputting the second ejection waveform in succession to eject ink multiple times from the liquid ejection head 1, twice in this example, a cancellation waveform is input to cancel out the residual vibration that occurs after the ink is ejected.

[0079] In this embodiment, the cancel waveform of the drive waveform of the liquid ejection head 1 has a waveform width (cancel width) Cp of the cancel waveform that is smaller than AL, and increases the potential difference (expansion potential difference) including the intermediate potential difference multiple times in succession when the pressure chamber 46 is expanded, and decreases the potential difference (contraction potential difference) including the intermediate potential difference multiple times in succession when the pressure chamber 46 is contracted. More preferably, the cancel waveform changes the potential difference twice in succession when the pressure chamber 46 is both expanded and contracted, similar to the ejection waveform.

[0080] FIG. 6 shows an example of a drive waveform in which an ejection waveform is input twice consecutively at a predetermined interval when ejecting ink from the liquid ejection head 1. The first drop of the ejection waveform increases the expansion potential difference twice when the pressure chamber 46 expands, and then decreases the contraction potential difference twice when the pressure chamber 46 contracts during ejection. The second drop of the ejection waveform is a trapezoidal wave (one-stage rectangular wave) with a width of Dpc2 input twice with a period of Tm2, ​​which is half the period of the parasitic oscillation. In this case, the width of Dpc2 is equal to or less than Tm2-tf. FIG. 8 also shows an example of an ejection waveform in which the potential difference changes twice consecutively, as in the example of the first drop of the ejection waveform. In FIGS. 6 and 8, the vertical axis represents voltage (potential difference), and the horizontal axis represents time. As shown in FIG. 6 , the cancel waveform of the drive waveform, like the ejection waveform of the first dorp, increases the expansion potential difference in two steps when the pressure chamber 46 expands, and then decreases the contraction potential difference in two steps when the pressure chamber 46 contracts during ejection. Here, the ejection waveform and cancel waveform of the first dorp change the potential difference both when the pressure chamber 46 expands and contracts. After applying the first potential difference, the first potential difference is maintained for a predetermined time, and then the second potential difference is applied. If the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to contract the pressure chamber before inputting the ejection waveform. Next, the voltage (potential difference) is reduced in two steps by inputting the ejection waveform, thereby expanding the pressure chamber in two steps. Then, when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased in two steps, thereby contracting the pressure chamber. The drive waveform is generated by the driver IC 72 of the drive circuit 70.

[0081] First, an example of the drive waveform, the ejection waveform for the first drop, will be specifically described with reference to FIGS. 6 and 8. As shown in FIG. 8, when expanding the pressure chamber 46 in advance before ejecting ink, UL is the time interval (duration) from the start of expansion due to the first expansion potential difference when the potential difference is increased twice consecutively to the start of contraction due to the first reduction potential difference after the expansion potential difference is increased twice consecutively. Also, as shown in FIG. 8, when contracting the pressure chamber 46 during ejection, UL is the time interval from the start of expansion due to the second expansion potential difference when the potential difference is increased twice consecutively before being reduced to the start of contraction due to the second reduction potential difference when the expansion potential difference is increased twice consecutively and then the reduction potential difference is reduced twice consecutively. Note that in the following description, the time interval UL from the start of expansion due to the first expansion potential difference when the potential difference is increased twice consecutively to the start of contraction due to the first reduction potential difference after the expansion potential difference is increased twice consecutively may be referred to as Dp1.

[0082] That is, as shown in FIG. 8 , the drive waveform that deforms the pressure chamber 46 and ejects ink from the nozzle 51 changes the potential difference twice consecutively when the pressure chamber 46 is expanded and contracted. The drive waveform defines UL as the time interval between the first time the potential difference is increased when the pressure chamber 46 is expanded and the first time the potential difference is decreased when the pressure chamber 46 is contracted, and the time interval between the start of the second expansion, in which the potential difference is increased twice consecutively when the pressure chamber 46 is expanded, and the start of the second contraction, in which the potential difference is decreased twice consecutively when the pressure chamber 46 is contracted. The time interval UL is greater than 0.5 AL and less than 1.5 AL. More preferably, UL = AL. This is because if UL is greater than 0.5 AL and less than 1.5 AL, constructive interaction occurs between the main acoustic vibration generated by expanding the pressure chamber 46 before ejection and the main acoustic vibration generated by contracting the pressure chamber 46 during ejection.

[0083] Here, the drive waveform is set to Tm=λn / 2, where λn is the period of parasitic vibrations such as third harmonic waves, and Tm is the time interval between the start time of the first potential difference change and the start time of the second potential difference change when the potential difference is increased twice consecutively or decreased twice consecutively. When the piezoelectric pillar 21 (actuator) is driven with such a drive waveform, as shown in Figure 8, the phase difference between the parasitic vibrations generated during the first potential difference change and the second potential difference change is 180 degrees, and they cancel each other out. This makes it possible to suppress deterioration of print quality due to parasitic vibrations such as third harmonic waves.

[0084] More preferably, as shown in Figure 8, by making the amount of potential difference change in the first potential difference change the same as the amount of potential difference change in the second potential difference change, parasitic vibrations in the pressure chamber 46 that have approximately the same amplitude but a phase difference of 180 degrees cancel each other out, and subsequent residual vibrations resulting from the parasitic vibrations can be significantly suppressed.

[0085] In this way, when the time interval UL of the ejection waveform (drive waveform) when the potential difference is increased twice consecutively or decreased twice consecutively is set to AL and the time interval Tm is set to λn / 2, the phase difference between the parasitic vibrations (triple harmonic vibration AI) generated by the pressure chamber contraction (falling waveform) during the first change in potential difference and the parasitic vibrations (triple harmonic vibration AII) generated by the pressure chamber contraction (falling waveform) during the second change in potential difference is 180 degrees, and they cancel each other out, as shown in Figure 8. Note that when the time interval Tm when the potential difference is increased twice consecutively and the pressure chamber is expanded twice consecutively is also set to λn / 2, similarly the phase difference between the parasitic vibrations (triple harmonic vibration AI) generated by the pressure chamber expansion (rising waveform) during the first change in potential difference and the parasitic vibrations (triple harmonic vibration AII) generated by the pressure chamber expansion (rising waveform) during the second change in potential difference is 180 degrees, and they cancel each other out. Furthermore, by setting UL to AL, the main acoustic vibration generated by the expansion of the pressure chamber before ejection (rising waveform) and the main acoustic vibration generated by the contraction of the pressure chamber during ejection (falling waveform) reinforce each other, increasing the ejection force due to the main acoustic vibration. Furthermore, if the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in order to contract the pressure chamber in advance before inputting the ejection waveform. Next, the voltage (potential difference) is reduced in two steps by inputting the ejection waveform, expanding the pressure chamber in two steps, and then, when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased in two steps, contracting the pressure chamber.

[0086] Here, we will explain the condition Tm under which parasitic oscillations with a period λn in the drive waveform cancel each other out. First, let A be the oscillation with a period λn that occurs during the first change in potential difference, and let A' be the oscillation vector a time Tm after A. Let B be the oscillation vector with a period λn that occurs during the second change in potential difference after Tm. The absolute value of the resultant vector of A' and B is minimum when Tm is an odd multiple of λn / 2 (the phase difference between A' and B is 180 degrees). Using the equation for the synthesis of a simple harmonic motion with a period λn, we can find the condition under which the absolute value of the resultant vector of A' and B is less than or equal to the larger of the absolute values ​​of A' and B (or less than or equal to the larger absolute value if the absolute values ​​of A' and B are the same), which results in the phase difference between the oscillation vectors A' and B being within 180 degrees ±60 degrees.

[0087] The absolute value of the resultant vector of A' and B can be transformed into the following equation. Here, θA is the phase of A' and θB is the phase of B, then the absolute value of the resultant vector of A' and B is √(|A'|^2+|B|^2+2*|A'|*|B|*cos(θA-θB))...(Formula 1) Here, if |A'|≦|B|, then the phase difference (θA-θB) between A' and B, which satisfies |B|≧Equation 1, is the condition under which the vibrations of period λn weaken each other. By squaring both sides of |B|≧Equation 1 and rearranging it, we get 0≧|A'|+2*|B|*cos(θA-θB)...(Formula 2) From the above, if the phase difference (θA-θB) between A' and B is within the range of 180 degrees ±60 degrees, then Equation 2 is established.

[0088] Also, if |B|≦|A'|, then |A'|≧ Equation 1 can be transformed by squaring both sides to get 0≧|B|+2*|A'|*cos(θA-θB)...(Formula 3) From the above, if the phase difference (θA-θB) between A' and B is within the range of 180 degrees ±60 degrees, then Equation 3 is established.

[0089] From these, the condition for the parasitic oscillations with period λn to cancel each other out is (k / 2-1 / 6)λn ≦ Tm ≦ (k / 2+1 / 6)λn Here, k is an odd number greater than or equal to 1.

[0090] Furthermore, when the potential difference is changed twice consecutively when the pressure chamber 46 is expanded and contracted, it is preferable that the Tm of the drive waveform is set to (k / 2-1 / 6)λn ≦ Tm ≦ (k / 2+1 / 6)λn (k is an odd number greater than or equal to 1) for both the time during which the intermediate potential difference is held when the pressure chamber is expanded and the time during which the intermediate potential difference is held when the pressure chamber is contracted.

[0091] Furthermore, from the viewpoint of reducing power consumption by making the main acoustic vibrations generated when the intermediate potential difference changes from the previous potential difference and when the intermediate potential difference changes to the next potential difference reinforce each other, it is desirable that Tm be short.

[0092] Considering the above points and also considering the reduction of power consumption, Tm of the drive waveform is as follows: (k / 2-1 / 6)λn≦Tm≦kλn / 2 Here, k is an odd number greater than or equal to 1.

[0093] Next, to evaluate the ejection waveform of the first drop among the drive waveforms of the liquid ejection head 1 according to this embodiment, Fig. 9 shows the results when the liquid ejection head 1 with 2AL = 5.24 μs was driven with various waveforms and one drop of ink was ejected. Note that the voltage was adjusted so that the speed of the first drop was approximately 8 m / s for all of the results of the various waveforms in Fig. 9.

[0094] The top drive waveform in Figure 9 is a comparative example, a trapezoidal drive waveform with a rise time tr and fall time tf of 0.2 μs as shown in Figure 15. The rest are drive waveforms with two potential difference changes as shown in Figure 8, with different Tm values ​​and all rise and fall times of 0.2 μs. The ejection voltage indicates the difference between the expansion potential difference and the contraction potential difference. The intermediate potential difference is the intermediate value between the expansion potential difference and the contraction potential difference.

[0095] In the liquid ejection head 1 of the embodiment and the liquid ejection head of the comparative example, parasitic vibrations that are approximately three times larger than the main acoustic vibrations occur, as shown in the frequency analysis of Fig. 13. The period λn of the parasitic vibrations is 1.85 μs, and λn / 2 is 0.925 μs.

[0096] Fig. 10 shows the results of a simulation of the state of ejected droplets when one drop of ink is ejected. In Fig. 10, the upper diagram (a) is an example of ejected droplets using a trapezoidal drive waveform with tr = 0.2 μs in the comparative example, the middle diagram (b) is an example of ejected droplets using a drive waveform with Tm = 0.62 μs in the embodiment and changing the potential difference twice, and the lower diagram (c) is an example of ejected droplets using a drive waveform with Tm = 0.93 μs in the embodiment and changing the potential difference twice.

[0097] As shown in the bottom diagram (c) of Figures 9 and 10, the waveform with Tm = 0.93 μs, which is closest to the half cycle of the parasitic vibration, has the largest ratio of the leading droplet volume to the total ejection volume. As shown in the center diagram (b) of Figures 9 and 10, the ratio of the leading droplet volume tends to decrease as Tm deviates from 0.925 μs. It can also be seen that the ejection voltage per unit volume (ejection voltage / total ejection volume) tends to decrease as Tm decreases. These results also show that the drive waveform of the liquid ejection head 1 of this embodiment can suppress vibrations at frequencies higher than the main acoustic vibration while keeping power consumption low.

[0098] Next, for comparison with the drive waveform of this embodiment shown in FIG. 6, a comparative example having a drive waveform including a step waveform at the second drop, rather than a trapezoidal waveform, as shown in FIG. 7 will be described below.

[0099] FIG. 7 shows an example of a drive waveform in which an ejection waveform is input twice consecutively at a predetermined interval when ejecting ink from the liquid ejection head 1. FIG. 7 also shows an example of an ejection waveform. In FIGS. 7 and 8, the vertical axis represents voltage (potential difference) and the horizontal axis represents time. The drive waveform is generated by the driver IC 72 of the drive circuit 70. As shown in FIG. 7, in both the two ejection waveforms and the cancel waveform, the drive waveform increases the expansion potential difference twice when the pressure chamber 46 expands, and decreases the contraction potential difference twice when the pressure chamber 46 contracts during ejection. When changing the potential difference both when the pressure chamber 46 expands and when it contracts, the first potential difference is applied, and then maintained for a predetermined time, after which the second potential difference is applied. If the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in order to contract the pressure chamber beforehand before inputting the ejection waveform. Next, by inputting an ejection waveform, the voltage (potential difference) is reduced in two steps, expanding the pressure chamber in two steps, and then, when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased in two steps, contracting the pressure chamber.

[0100] An example of the ejection waveform for the second drop among the drive waveforms of the comparative example will be specifically described with reference to Fig. 7. Note that in the example of this embodiment, the ejection waveform for the second drop has a smaller Dp, which is the time interval UL from when the expansion potential difference is increased twice consecutively to when contraction due to the first contraction potential difference begins, compared to the ejection waveform for the first drop. For example, Dp1 of the ejection waveform for the first drop is the same as AL, whereas Dp2 of the ejection waveform for the second drop is set to be smaller than AL.

[0101] For ease of explanation, in FIG. 7, the first to fourth potential difference changes in the ejection waveform for the first drop will be referred to as (1) to (4), and the first to fourth potential difference changes in the ejection waveform for the second drop will be referred to as (21) to (24). The following explanation will also be given with the reference point for the phase of the ejection waveform for the first drop as (0) and the reference point for the phase of the ejection waveform for the second drop as (0''). Note that the reference point (0) for the phase of the ejection waveform for the first drop is midway between the potential difference changes (2) and (3), and the reference point (0'') for the phase of the ejection waveform for the second drop is midway between the potential difference changes (22) and (23). The voltage drop time tf of (23) in FIG. 7 is assumed to be approximately the same as the voltage rise time tr of (22). In addition, the amount of change in potential difference between (1) and (2) and the amount of change in potential difference between (21) and (22) (the amount of change in height in Figure 7) are approximately the same, and the amount of change in potential difference between (3) and (4) and the amount of change in potential difference between (23) and (24) are also approximately the same.

[0102] For simplicity, let us ignore vibration damping due to factors such as viscous resistance in the flow path. Let us assume that the time when the potential difference change due to tf occurs is tin, and the time of the phase reference point (0) is t0. The pressure vibration in the pressure chamber due to pressurization can be schematically represented as cos((t0 - tin) * (π / AL)). The velocity of the liquid in the nozzle section is -sin((t0 - tin) * (π / AL)). Note that a minus sign has been added because the nozzle is facing downward in the head flow path diagram, and the liquid velocity in the nozzle section changes downward due to pressurization of the pressure chamber. Let us also assume that the time when the potential difference change due to tr occurs is tin, and the pressure vibration in the pressure chamber due to depressurization can be schematically represented as cos(-π + (t0 - tin) * (π / AL)). The liquid velocity in the nozzle section is -sin(-π + (t0 - tin) * (π / AL)). Note that a minus sign has been added because the nozzle is facing downward in the head flow path diagram, and the liquid velocity in the nozzle section changes upward due to depressurization of the pressure chamber.

[0103] From here on, the phase reference point (0), (0'') or (0') will basically be used as the reference point, and the time elapsed from the occurrence of each voltage step input to the reference point (phase lead) will be substituted for (t0-tin). This will describe the phase of each potential difference change and its composite wave when the reference point (0), (0'') or (0') is used as the reference point.

[0104] First, the main acoustic vibration of the ejection waveform in Figure 7 will be described. In the ejection waveform for ejecting the first drop in Figure 7, when the potential difference is changed and an intermediate voltage for expanding the pressure chamber 46 is input as shown in (1), the pressure chamber 46 expands with the potential difference of (1) and the pressure inside the pressure chamber 46 is reduced. The vibration generated by this is a vibration with a phase lead of -π + (Dp1 + Tm) / 2 * (π / AL). Furthermore, when the potential difference is changed as shown in (2), the vibration in (2) is a vibration with a phase lead of -π + (Dp1 - Tm) / 2 * (π / AL). The composite wave of (1) and (2) is a vibration with a phase lead of -π + Dp1 / 2 * (π / AL).

[0105] The potential difference changes (3) and (4) that cause the pressure chamber 46 to contract are opposite to the potential difference changes (1) and (2) that cause the pressure chamber 46 to expand, causing the pressure chamber 46 to contract and pressurize the pressure chamber 46. Therefore, (3) is a vibration with a phase lead of -(Dp1-Tm) / 2*(π / AL). Also, (4) can be considered to be a vibration with a phase lead of -(Dp1+Tm) / 2*(π / AL). Therefore, the composite wave of (3) and (4) is a vibration with a phase lead of -Dp1 / 2*(π / AL).

[0106] Here, if we assume a composite wave of (1), (2), (3), and (4) at time (0), the composite wave of (1), (2), (3), and (4) will oscillate with a phase lead of -π / 2.

[0107] Next, the main acoustic vibration of the ejection waveform of the second drop in Figure 7 will be shown. When the potential difference is changed and an intermediate voltage for expanding the pressure chamber 46 is input as shown in (21), the pressure chamber 46 expands with the potential difference of (21) and the pressure inside the pressure chamber 46 is reduced. As a result, if the ejection waveform width of the second drop is Dp2, the vibration will have a phase lead of -π + (Dp2 + Tm) / 2 * (π / AL). Furthermore, when the potential difference is changed as shown in (22), the vibration in (22) can be considered to have a phase lead of -π + (Dp2 - Tm) / 2 * (π / AL). Therefore, the composite wave of (21) and (22) will have a phase lead of -π + Dp2 / 2 * (π / AL).

[0108] The potential difference changes (23) and (24) for contracting the pressure chamber 46 are opposite to the potential difference changes (21) and (22) for expanding the pressure chamber 46, causing the pressure chamber 46 to contract and pressurize the pressure chamber 46. Therefore, (23) is a vibration with a phase lead of -(Dp2-Tm) / 2*(π / AL). Also, (24) is a vibration with a phase lead of -(Dp2+Tm) / 2*(π / AL). Therefore, the composite wave of (23) and (24) is a vibration with a phase lead of -Dp2 / 2*(π / AL).

[0109] Here, assuming a composite wave of (21), (22), (23), and (24) at time (0''), the composite wave of (21), (22), (23), and (24) becomes an oscillation with a phase lead of -π / 2.

[0110] Therefore, when the phase difference between (0) and (0'') is an even multiple of π (the time interval is an even multiple of AL), the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) become in phase and constructively interact with each other. In the example of Figure 7, the time difference (time interval) between (0) and (0'') is 2AL. Furthermore, by reducing the time width Dp2 of (21) and (23), the amplitude of the composite wave of (21), (22), (23), and (24) (the ejection waveform of the second drop) can be adjusted. Therefore, the ejection speed of the second drop can be adjusted by constructively interacting with the residual vibration of the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24). In this way, in a multi-drop driving waveform in which the liquid ejection head 1 ejects multiple ink droplets in succession, by adjusting Dp in the ejection waveform following any one of the ejection waveforms, the ejection speed of the ink to be subsequently ejected can be adjusted to be equal to or faster than the ejection speed of the droplet ejected previously.

[0111] Furthermore, the time interval between (21) and (22) when the pressure chamber is depressurized is Tm, and the time interval between (23) and (24) when the pressure chamber 46 is pressurized is also Tm. Therefore, if Tm is set to half the period λn of the parasitic vibration, the parasitic vibrations of (21) and (22) cancel each other out, and the parasitic vibrations of (23) and (24) also cancel each other out.

[0112] However, in the drive waveform of Figure 7, the width of Dp2 cannot be made smaller than Tm+tr. The magnitude of the residual vibration of the main acoustic vibration generated by (1), (2), (3), and (4) of the ejection waveform of the first drop in Figure 7 at the timing of ejection of the second drop varies depending on the viscosity of the ink filled in the liquid ejection head 1 and the flow path resistance of the head. When the ink viscosity is low or the flow path resistance is low, if the width of Dp2 is Tm+tr or greater, the ejection speed of the second drop will be too large, which may deteriorate print quality. In this case, as in the drive waveform of the second drop shown in Figure 6 of this embodiment, a trapezoidal wave (one-step rectangular wave) with a width of Dpc2 equal to or less than Tm2-tf can be input twice with a period of Tm2, ​​which is half the period of the parasitic vibration. Furthermore, although it depends on the surface tension and viscosity, if the period Tm2 of the two trapezoidal waves is shorter than the period of the main acoustic vibration, the droplet extruded from the nozzle at time (28) and the droplet extruded from the nozzle at time (30) will remain connected and become a single droplet due to surface tension.

[0113] Next, as an example of the drive waveform for the second drop, the main acoustic vibration caused by inputting a trapezoidal wave (one-stage rectangular wave) with a Dpc2 width twice in FIG. 6 is shown. Hereinafter, of the two trapezoidal waves in the drive waveform for the second drop, the first trapezoidal wave may be referred to as the first trapezoidal wave with a Dpc2 width, and the second trapezoidal wave may be referred to as the second trapezoidal wave with a Dpc2 width. In the first trapezoidal wave with a Dpc2 width, a first change in potential difference for expanding the pressure chamber 46 is made, and when the potential difference shown in (27) is input, the pressure chamber 46 expands and the pressure inside the pressure chamber 46 is reduced. For this reason, the vibration caused by inputting the potential difference shown in (27) is a vibration whose phase is advanced by -π + (Tm2 + Dpc2) / 2 * (π / AL) when the phase reference point is (0'').

[0114] In the first trapezoidal wave with a width of Dpc2 in Figure 6, the second potential difference change (28) for contracting the pressure chamber 46 is the opposite change in potential difference to the potential difference change (27) for expanding the pressure chamber 46. Therefore, when the potential difference shown in (28) is input, the pressure chamber 46 contracts, pressurizing the pressure chamber 46. For this reason, the vibration generated by inputting the potential difference shown in (28) is a vibration with a phase lead of (Tm2-Dpc2) / 2*(π / AL). The composite wave of (27) and (28) is a vibration with a phase lead of -π / 2+Tm2 / 2*(π / AL).

[0115] 6, when the first potential difference change for expanding the pressure chamber 46, i.e., the potential difference shown in (29), is input, the pressure chamber 46 expands and the pressure inside the pressure chamber 46 is reduced. Therefore, the vibration generated by inputting the potential difference shown in (29) is a vibration with a phase lead of -π-(Tm2-Dpc2) / 2*(π / AL). Note that the potential difference change of the first and second trapezoidal waves of the second drop is not limited to an intermediate potential difference.

[0116] In the second trapezoidal wave with a width of Dpc2 in Figure 6, the second potential difference change (30) for contracting the pressure chamber 46 is the opposite change in potential difference to the potential difference change (29) for expanding it. Therefore, when the potential difference shown in (30) is input, the pressure chamber 46 contracts, pressurizing the pressure chamber 46. For this reason, the vibration generated by inputting the potential difference shown in (30) is a vibration with a phase lead of -(Tm2 + Dpc2) / 2 * (π / AL). The composite wave of (29) and (30) is a vibration with a phase lead of -π / 2 - Tm2 / 2 * (π / AL).

[0117] Here, assuming a composite wave of (27), (28), (29), and (30) at time (0''), the composite wave of (27), (28), (29), and (30) becomes an oscillation with a phase lead of -π / 2.

[0118] Therefore, when the phase difference between (0) and (0'') is an even multiple of π (the time interval is an even multiple of AL), the composite waves of (1), (2), (3), and (4) and the composite waves of (27), (28), (29), and (30) are in phase and constructive with each other. In addition, by matching the time widths of (27) and (28) (the Dpc2 width of the first trapezoidal wave in FIG. 6) with the time widths of (29) and (30) (the Dpc2 width of the second trapezoidal wave in FIG. 6) and keeping them small and equal to or less than Tm2-tf, the amplitude of the composite waves of (27), (28), (29), and (30) can be adjusted. Therefore, by setting the time duration Dpc2 of (27), (28), (29), and (30), the residual vibration due to the composite wave of (1), (2), (3), and (4) can be strengthened by the composite wave of (27), (28), (29), and (30).

[0119] From the above, it is desirable to set the time difference between (0) and (0'') to an even multiple of AL.

[0120] Furthermore, since the time interval between (27) and (29) for depressurizing the pressure chamber 46 is Tm2, ​​and the time interval between (28) and (30) for pressurizing the pressure chamber 46 is also Tm2, ​​if Tm2 is set to half the period λn of the parasitic vibration, the parasitic vibrations of (27) and (29) cancel each other out, and the parasitic vibrations of (28) and (30) also cancel each other out.

[0121] As described above, when ejecting multiple droplets continuously, at least one of the ejection pulses for each droplet is set to two consecutive trapezoidal waves (one-stage rectangular waves) at a time interval of Tm2, ​​thereby adjusting the ejection speed of the droplets by the corresponding ejection pulse.

[0122] In addition, if the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in order to contract the pressure chamber beforehand before inputting the ejection waveform. Next, the voltage (potential difference) is reduced by inputting the ejection waveform to expand the pressure chamber, and then when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased to contract the pressure chamber.

[0123] Next, we will explain the condition Tm2 when parasitic vibrations with a period λn cancel each other out. First, among the Dpc2 width ejection waveforms in Figure 6, the first trapezoidal wave, i.e., the waveforms (27) and (28), has a period λn oscillation vector that occurs when the potential difference is changed at (28). Let A2728 be the oscillation vector of A2728 after time Tm2. Among the Dpc2 width ejection waveforms in Figure 6, the second trapezoidal wave, i.e., the waveforms (29) and (30), has a period λn oscillation vector that occurs when the potential difference is changed at (30). Let A2930 be the oscillation vector of A2930. Because waveforms (27) and (28) and waveforms (29) and (30) are both trapezoidal waves with a waveform width of Dpc2, the absolute value of the resultant vector of A2728' and A2930 is smallest when Tm2 is an odd multiple of half λn (the phase difference between A2728' and A2930 is 180 degrees). The condition under which the absolute value of the resultant vector of A2728' and A2930 is less than or equal to the larger of the absolute values ​​of A2728' and A2930 (or less if the absolute values ​​of A2728' and A2930 are the same) can be found from the formula for the synthesis of simple harmonic motion with a period of λn: the phase difference between the vibration vectors A2728' and A2930 is within 180° ± 60°.

[0124] Therefore, the condition for the oscillations of period λn to weaken each other is (kkk / 2-1 / 6)λn ≦ Tm2 ≦ (kkk / 2+1 / 6)λn Here, kkk is an odd number greater than or equal to 1.

[0125] Therefore, by setting Tm2 under the above conditions, the parasitic vibrations generated by the corresponding ejection waveform can be suppressed, and the parasitic vibrations can be prevented from affecting the ejected droplets.

[0126] For simplicity, the ejection waveform described above is a trapezoidal wave with a waveform width of Dpc2, but even if the waveform is of an arbitrary shape, if an arbitrary waveform of the same shape is input twice at the time interval Tm2 specified above, the parasitic vibrations caused by the arbitrary waveform can be canceled out, suppressing the occurrence of parasitic vibrations. Note that, depending on the surface tension and viscosity, if the time interval Tm2 between the two arbitrary waveforms is short compared to the period of the main acoustic vibration, the droplets pushed out of the nozzle by the first arbitrary waveform and the droplets pushed out of the nozzle by the second arbitrary waveform of the same shape will remain connected and form a single droplet due to surface tension. Therefore, in this embodiment, two waveforms of an arbitrary shape input at the time interval Tm2 are treated as a set and as one ejection waveform.

[0127] Next, an example of the cancel waveform will be specifically described with reference to FIG. 6. For ease of explanation, the first to fourth potential difference changes in the cancel waveform will be referred to as (11) to (14) in FIG. 6. The following description will also be given with the reference point of the phase of the ejection waveform for the second drop as (0'') and the reference point of the phase of the cancel waveform as (0'). Here, the reference point (0'') of the phase of the ejection waveform for the second drop is midway between the potential difference changes (27) and (30), and the reference point (0') of the phase of the cancel waveform is midway between the potential difference changes (12) and (13). In the example of FIG. 6, the voltage fall time tf of (28), (30), (13), and (14) is approximately the same as the voltage rise time tr of (27), (29), (11), and (12).

[0128] First, let us consider the main acoustic vibration of the ejection waveform. As mentioned above, the vibration generated by inputting the potential difference shown in (27) is a vibration whose phase is advanced by -π+(Tm2+Dpc2) / 2*(π / AL) when the reference point of the phase is (0'').

[0129] Furthermore, the oscillation caused by inputting the potential difference shown in (28) is an oscillation with a phase lead of (Tm2-Dpc2) / 2*(π / AL). The composite wave of (27) and (28) is an oscillation with a phase lead of -π / 2+Tm2 / 2*(π / AL). As mentioned above, the composite wave of (29) and (30) is also an oscillation with a phase lead of -π / 2-Tm2 / 2*(π / AL).

[0130] Here, assuming a composite wave of (27), (28), (29), and (30) at time (0''), the composite wave of (27), (28), (29), and (30) becomes an oscillation with a phase lead of -π / 2.

[0131] Next, the main acoustic vibration of the cancellation waveform will be described. When the potential difference is changed in the cancellation waveform and an intermediate voltage for expanding the pressure chamber 46 is input as shown in (11), the pressure chamber 46 expands with the potential difference of (11) and the pressure inside the pressure chamber 46 is reduced. Therefore, if the cancellation width is Cp1, the vibration will have a phase lead of -π+(Cp1+Tm) / 2*(π / AL). Furthermore, when the potential difference is changed as shown in (12), the vibration in (12) can be considered to have a phase lead of -π+(Cp1-Tm) / 2*(π / AL).

[0132] The potential difference changes (13) and (14) for contracting the pressure chamber 46 are opposite to the potential difference changes (11) and (12) for expanding the pressure chamber 46, causing the pressure chamber 46 to contract and pressurize the pressure chamber 46. Therefore, (13) is a vibration with a phase lead of -(Cp1-Tm) / 2*(π / AL). Also, (14) is a vibration with a phase lead of -(Cp+Tm) / 2*(π / AL). Therefore, the composite wave of (13) and (14) is a vibration with a phase lead of -Cp / 2*(π / AL).

[0133] Here, assuming a composite wave of (11), (12), (13), and (14) at time (0'), the composite wave of (11), (12), (13), and (14) becomes an oscillation with a phase lead of -π / 2.

[0134] Therefore, when the phase difference between (0'') and (0') is an odd multiple of π (the time interval is an odd multiple of AL), the composite wave of (27), (28), (29), and (30) and the composite wave of (11), (12), (13), and (14) are in opposite phase and weaken each other. Furthermore, by adjusting the time width Cp1 of (11) and (13), the amplitude of the composite wave (cancellation waveform) of (11), (12), (13), and (14) can be adjusted, and the residual vibration caused by the composite wave of (27), (28), (29), and (30) can be canceled out by the composite wave of (11), (12), (13), and (14).

[0135] From the above, it is possible to cancel out the residual vibration caused by the composite wave of (27), (28), (29), and (30) by setting the time difference between (0'') and (0') to 1AL. However, if the time difference between (0'') and (0') is set to 1AL, the residual vibration will be canceled out during droplet ejection by inputting the ejection waveform, weakening the droplet ejection force. Therefore, it is desirable to set the time difference between the reference point (0'') of the phase of the ejection waveform and the reference point (0') of the phase of the cancellation waveform to an odd multiple of AL of 3AL or more.

[0136] Furthermore, the time interval between (11) and (12) when the pressure chamber is depressurized is Tm, and the time interval between (13) and (14) when the pressure chamber 46 is pressurized is also Tm. Therefore, if Tm is set to half the period λn of the parasitic vibration, the parasitic vibrations of (11) and (12) cancel each other out, and the parasitic vibrations of (13) and (14) also cancel each other out.

[0137] As described above, by setting the cancel waveform to a cancel waveform with a Cp width such that the median voltage holding time Tm of the final drop's ejection waveform is half the period λn of the parasitic vibration, the cancel waveform can suppress both the residual vibration of the main acoustic vibration caused by the final drop's ejection waveform and the parasitic vibration caused by the cancel waveform. This makes it possible to reduce the influence of the residual vibration of the main acoustic vibration and the parasitic vibration on the droplets ejected by the first ejection waveform of the next drive waveform input after the input of the cancel waveform.

[0138] The cancel waveform may have a different polarity from the ejection waveform, for example, a negative potential difference. For example, in this example, the negative potential difference changes at (11) and (12) cause the pressure chamber to contract, and the negative potential difference changes at (13) and (14) cause the pressure chamber to return to its original state. In this cancel waveform, the potentials at (12) to (13) are the lowest potentials in the drive waveform, so these are considered ground voltages, and the other potentials are higher than ground voltage. Each ejection waveform and cancel waveform has four potential differences higher than ground voltage. Therefore, when using such a cancel waveform, the drive circuit 70 may be connected to a fourth voltage source and a fifth voltage source in addition to the first voltage source 81 to the third voltage source 83, and the wiring electrode 727 may be connected to any of the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source, and the fifth voltage source under the control of the voltage control unit 724. In this case, the potential difference of the cancellation waveform can be set to a different value from the potential difference of the ejection waveform. Therefore, by adjusting not only the Cp1 width of the cancellation waveform but also the potential difference of the cancellation waveform, it is possible to suppress residual vibrations caused by the main acoustic vibrations generated by the ejection waveform.

[0139] In the case where the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to contract the pressure chamber before inputting the ejection waveform. Next, the voltage (potential difference) is reduced in two steps by inputting the ejection waveform, thereby expanding the pressure chamber in two steps. Then, when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased in two steps, thereby contracting the pressure chamber. The cancel waveform increases the voltage (potential difference) in two steps, thereby contracting the pressure chamber in two steps, and then, when the pressure chamber 46 expands, the voltage (potential difference) is reduced in two steps, thereby expanding the pressure chamber. In this case, the potential from when the voltage (potential difference) is reduced in two steps to expand the pressure chamber in the ejection waveform until just before the pressure chamber contraction begins is the lowest potential in the drive waveform, so these are referred to as the ground voltage, and the other potentials are referred to as potentials higher than the ground voltage.

[0140] Even in the case of a cancel waveform that changes the potential difference in a polarity different from that of the ejection waveform, for example, in a negative polarity, the reference point of the phase between (12) and (13) of the cancel waveform is (0'), and the main acoustic vibration will be explained below. If we assume a composite wave of (11), (12), (13), and (14) at time (0'), the sign will be opposite to that of the cancel waveform in the example of Figure 6, and the composite wave of (11), (12), (13), and (14) will be a vibration with a phase lead of π / 2.

[0141] Therefore, if the phase difference between (0'') and (0') is an even multiple of π (the time interval is an even multiple of AL), for example, 2AL, the composite wave of (27), (28), (29), and (30) and the composite wave of (11), (12), (13), and (14) will be in opposite phase and will weaken each other. Furthermore, by adjusting the time width Cp1 between (11) and (13), the amplitude of the composite wave (canceling waveform) of (11), (12), (13), and (14) can be adjusted, and the residual vibration caused by the composite wave of (27), (28), (29), and (30) can be canceled out by the composite wave of (11), (12), (13), and (14). Furthermore, the time interval between (13) and (14) when the pressure chamber is depressurized is Tm, and the time interval between (11) and (12) when the pressure chamber is pressurized is also Tm. Therefore, if Tm is set to half the period λn of the parasitic vibration, the parasitic vibrations of (13) and (14) cancel each other out, and the parasitic vibrations of (11) and (12) also cancel each other out.

[0142] Next, we will explain the condition for Tm, under which parasitic oscillations with a period λn cancel each other out in the cancellation waveform shown in Figure 6. First, let A11 be the oscillation with a period λn generated by waveform (11) during the first change in potential difference, and let A11' be the oscillation vector after time Tm of A11. Let A12 be the oscillation vector with a period λn generated by waveform (12) during the second change in potential difference after Tm. Because waveforms (11) and (12) are both rising waveforms in Figure 6, the absolute value of the composite vector of A11' and A12 is smallest when Tm is an odd multiple of λn / 2 (the phase difference between A11' and A12 is 180 degrees). Using the formula for the composition of a simple harmonic motion with a period λn, we can determine the condition under which the absolute value of the composite vector of A11' and A12 is smaller than the larger of the absolute values ​​of A11' and A12: the phase difference between the oscillation vectors A11' and A12 is within 180 degrees ±60 degrees.

[0143] Therefore, the condition for the oscillations with period λn to cancel each other out is (k / 2-1 / 6)λn≦Tm≦(k / 2+1 / 6)λn Here, k is an odd number greater than or equal to 1.

[0144] By setting Tm under the above conditions, it is possible to reduce the influence of residual vibration due to parasitic vibration on the next droplet to be ejected after the cancellation waveform.

[0145] Regarding the main acoustic vibration, when the residual vibration of the ejection waveform is cancelled out by the cancellation waveform, the time interval between (0'') and (0') is set to 3AL in the example of Figure 6. However, if the cancellation waveforms ((11), (12), (13), and (14)) first depressurize and then pressurize like the ejection waveforms ((1), (2), (3), and (4)), the conditions under which the vibrations with a period of 2AL weaken each other for the composite waves of (27), (28), (29), and (30) and the composite waves of (11), (12), (13), and (14) can be found from the formula for the composition of simple harmonic motion in the same way as for the period λn: (kkkk / 2-1 / 6)2AL≦Time interval between (0'') and (0')≦(kkkk / 2+1 / 6)2AL where kkkk is an odd number greater than or equal to 1.

[0146] Furthermore, in the case of a cancel waveform which changes the potential difference with a polarity different from that of the ejection waveform, for example, a negative polarity, the time interval between (0'') and (0') is 2AL. However, the cancel waveforms ((11), (12), (13), and (14)) are opposite to the ejection waveforms ((1), (2), (3), and (4)), and first pressurize and then depressurize. Therefore, the condition for the composite wave of (27), (28), (29), and (30) and the composite wave of (11), (12), (13), and (14) to weaken each other with a period of 2AL can be found from the formula for the composition of simple harmonic motion in the same way as for the period λn: (kkkk-1 / 6)2AL≦Time interval between (0) and (0')≦(kkkk+1 / 6)2AL where kkkk is an integer greater than or equal to 1.

[0147] As described above, by adjusting the time interval between (0'') and (0') as well as adjusting the Cp1 width according to the above conditions, it is possible to reduce the influence of residual vibration of the main acoustic vibration generated by the cancel waveform on droplets ejected by the next ejection waveform after the cancel waveform. In this way, the residual vibration generated after droplets are ejected by the ejection waveform is canceled out by the pressure vibration caused by the cancel waveform, thereby reducing the residual vibration caused by the ejection waveform. Note that when the ink viscosity is high, the residual vibration after droplets are ejected by the ejection waveform is greatly attenuated, so the cancel width Cp1 is adjusted to be smaller accordingly. However, the cancel width Cp cannot be made less than Tm+Tr. Note that the cancel waveform may be a trapezoidal wave, as shown in Figures 18 and 19.

[0148] A drive waveform including such a cancel waveform can suppress both the residual vibration of the main acoustic vibration caused by the ejection waveform and the parasitic vibration caused by the cancel waveform by setting the intermediate voltage holding time Tm for the ejection waveform to half the period λn of the parasitic vibration and adjusting the Cp1 width to cancel out the residual vibration after ejection. Therefore, the liquid ejection head 1 can reduce the influence of the residual vibration caused by the main acoustic vibration on the next droplet ejected after the cancel waveform. Furthermore, because the cancel waveform can suppress the parasitic vibration caused by the cancel waveform, it can also prevent the residual vibration caused by the parasitic vibration from affecting the droplet ejected by the next ejection waveform.

[0149] Furthermore, the liquid ejection head 1 changes the potential difference of the drive waveform that drives the actuator 20 in two steps, including an intermediate potential difference, thereby reducing power consumption and preventing deterioration of print quality due to vibrations at frequencies higher than the main acoustic vibration.

[0150] According to the liquid ejection head 1 of the embodiment described above, the ejection waveform for the second drop is a single-step rectangular wave, and a trapezoidal wave (single-step rectangular wave) with a Dpc2 width of Tm2-tf or less is input twice with a period of Tm2, ​​which is half the period of the parasitic vibration. This suppresses the parasitic vibration generated by the ejection waveform for the second drop, and therefore prevents the parasitic vibration from affecting the ejected droplets. Therefore, the liquid ejection head 1 achieves the same effect as when the width of Dp2 in the stepped waveform is made smaller than Tm+tr.

[0151] Note that the embodiment is not limited to the above example. For example, in the above example, the drive waveform for ejecting the second droplet is a trapezoidal wave (one-step rectangular wave) with a Dpc2 width of Tm2-tf or less, input twice at a period of Tm2, ​​which is half the period of the parasitic oscillation. However, the present invention is not limited to this. For example, the number of droplets ejected when two consecutive trapezoidal waves (one-step rectangular wave) are input at a time interval of Tm2 varies depending on the viscosity and surface tension of the liquid, the nozzle diameter, the period of the main acoustic oscillation, and the time Tm2. Generally, the smaller the nozzle diameter and the longer the period of the main acoustic oscillation, the longer the liquid column ejected from the nozzle 1141. As the ratio of the time Tm2 to the period of the main acoustic oscillation increases, the liquid column is more likely to become constricted, leading to droplet separation. Furthermore, the lower the liquid viscosity and the higher the surface tension, the more likely droplet separation occurs. Therefore, when two consecutive trapezoidal waves (one-stage rectangular wave) are input at a time interval of Tm2 under the above conditions, the droplets ejected will either be ejected as a single droplet or will separate into two or more droplets. If the droplets separate into two or more large droplets, this may have a negative impact on print quality when they land on the media.

[0152] As a countermeasure for this, for example, as shown in Fig. 16, the ejection waveform for ejecting the first drop may be a trapezoidal wave (one-step rectangular wave) with a Dpc2 width of Tm2-tf or less, input twice at a period of Tm2, ​​which is half the period of the parasitic vibration, similar to the ejection waveform for the second drop in Fig. 6, and the drive waveform for ejecting the second drop may be a stepped waveform adjusted to cancel out the parasitic vibration, similar to the ejection waveform for the first drop in Fig. 6. Note that when inputting a drive waveform for three or more drops, a trapezoidal wave that ejects consecutive Nth and N+1th drops (for example, the first and second drops) at a time interval of Tm2 may be input. In this case, the 1st drop (or the Nth drop and the N+1th drop) will be a droplet with a low ejection speed, and the drop ejected with the next step-like waveform will combine with the drop ejected with two consecutive trapezoidal waves (one-step square wave) at a time interval of Tm2, ​​and the speed of the combined droplet will be greater than the speed of the drop ejected with two consecutive trapezoidal waves (one-step square wave) at a time interval of Tm2. In this way, when a droplet ejected with a subsequent step-like waveform combines with a preceding droplet, even if a droplet ejected with two consecutive trapezoidal waves (one-step square wave) at a time interval of Tm2 separates into two or more droplets, adverse effects on print quality can be prevented.

[0153] Furthermore, when different numbers of droplets are ejected from different nozzles 51 in the same nozzle row, for example, a drive waveform for ejecting only one droplet is set as shown in Fig. 17, and the ejection waveform widths of Dp1 in Fig. 17 and Dpc1 and Dp2 in Fig. 16 are adjusted so that the ejection speed of the drive waveform for ejecting only one droplet approaches the speed of the combined droplet of the first and second drops when ejecting two drops as shown in Fig. 16. Note that, when suppressing parasitic vibrations when two consecutive trapezoidal waves (one-stage rectangular waves) are input at a time interval of Tm2 in Fig. 16, Tm2 is (kkk / 2-1 / 6)λn ≦ Tm2 ≦ (kkk / 2+1 / 6)λn Here, kkk is an odd number greater than or equal to 1.

[0154] This allows the speed of droplets ejected from each nozzle 51 in the nozzle row to be approximated, making it possible to synchronize the timing of their impact on a moving recording medium. Note that the voltage of Dpc1 may be changed as necessary when adjusting the ejection speed of a drive waveform that ejects only one drop of droplet and the speed of the first and second drops of droplets in Figure 16. Figure 16 illustrates a case where the potential difference of Dpc1 is made higher than the intermediate potential difference, thereby increasing the expansion of the pressure chamber volume before the ejection of the first drop.

[0155] In the above example, the number of droplets ejected continuously is limited to two, but when three or more droplets are ejected continuously, one or more of the ejection waveforms for ejecting each droplet may be two arbitrarily shaped waveforms input at a time interval Tm2, ​​and the others may be stepped waveforms, and the time interval Tm2 width of the two arbitrarily shaped waveforms or the Tm width of the stepped waveform may be adjusted so as to suppress parasitic vibration in one or more of the ejection waveforms.More preferably, the time interval Tm2 width of the two arbitrarily shaped waveforms and the Tm width of the stepped waveform may be adjusted so as to suppress parasitic vibration in all of the ejection waveforms.

[0156] Alternatively, all of the ejection waveforms for ejecting each droplet may be input twice with an arbitrary waveform at a time interval Tm2, ​​and the Tm2 width may be adjusted so as to suppress parasitic vibration in one or more of the ejection waveforms for ejecting each droplet.More preferably, the Tm2 width may be adjusted so as to suppress parasitic vibration in all of the ejection waveforms.

[0157] As described above, an example was described in which one of the drive waveforms for ejecting multiple droplets is a stepped ejection waveform. However, as shown in FIGS. 18 and 19, all of the ejection waveforms for ejecting each droplet may be two trapezoidal waves (one-step rectangular waves) input at a time interval Tm2, ​​and the time interval Tm2 may be adjusted to suppress parasitic vibrations in one or more of the ejection waveforms for ejecting each droplet. More preferably, the time interval Tm2 may be adjusted to suppress parasitic vibrations in all of the ejection waveforms. In the case of FIG. 19, the potential difference of the cancellation waveform can be set to a value different from the potential difference of the ejection waveform. Therefore, residual vibrations due to the main acoustic vibrations generated by the ejection waveform can be suppressed by adjusting not only the Cp2 width of the cancellation waveform but also the potential difference of the cancellation waveform.

[0158] In the above example, the driving waveform used in the liquid ejection head 1 includes one intermediate potential difference, but the driving waveform is not limited to this. The driving waveform may include one or more intermediate potential differences.

[0159] Below, as another embodiment, a drive waveform of a liquid ejection head 1 in which the potential difference (expansion potential difference) of the ejection waveform or cancellation waveform is increased consecutively two or more times h times in the drive waveform of the drive circuit 70 will be described using Figures 20 and 21.

[0160] First, the discharge waveform of the drive waveform according to another embodiment will be described. In the discharge waveform of the liquid discharge head 1 of this embodiment, if one of the 1st to h-1th potential difference changes is the i-th potential difference change, and one of the (i+1)th to h-th potential difference changes is the j-th potential difference change, and the time interval between the start of the i-th and j-th potential difference changes is Tij, then either of the time intervals Tij can be expressed as follows: (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn Here, k is an odd number greater than or equal to 1.

[0161] With an ejection waveform that satisfies this formula, the parasitic vibrations with a period λn that occur due to the corresponding two or more potential difference changes weaken each other, and the parasitic vibrations with a period λn that occur in the pressure chamber can be suppressed. This also applies when the number of times the pressure chamber 46 is reduced or changed is three or more times (h times).

[0162] Furthermore, when i+1=j, that is, when Tij is the time interval between successive changes in the potential difference, taking into consideration the reduction in power consumption, the time interval Tij is (k / 2-1 / 6)λn ≦ Tij ≦ kλn / 2 Here, k is an odd number equal to or greater than 1.

[0163] Furthermore, if the ejection waveform is such that the time interval Tij satisfies (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (k is an odd number greater than or equal to 1) in all potential difference changes from the first to hth, or if there is another potential difference change that satisfies (k / 2-1 / 6)λn ≦ Tij ≦ kλn / 2 (k is an odd number greater than or equal to 1), the parasitic vibration with period λn occurring in the pressure chamber 46 can be further suppressed.

[0164] Furthermore, by setting the same amount of change in potential difference for the ith and jth potential difference changes that result in a time interval Tij that satisfies (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (k is an odd number greater than or equal to 1), it is possible to further suppress residual vibrations resulting from subsequent parasitic vibrations. More preferably, since the optimal holding time for each stage is λn / number of stages (h) when it is assumed that the potential difference at each stage is the same and that pressure vibrations do not attenuate, the time interval Tij for all successive potential difference changes should be set to λn / number of stages (h).

[0165] Furthermore, from the perspective of reducing power consumption by making the main acoustic vibrations constructive with each other, when the number of potential difference changes that continuously expand and change the pressure chamber is two or more times, h times, it is desirable that the time interval Tij between the first potential difference change and the hth potential difference change be within 0.5 times the main acoustic vibration period. This is because by making the time interval Tij between the first potential difference change and the hth potential difference change within 0.5 times the main acoustic vibration period, the main acoustic vibrations generated by all of the potential difference changes from the first to the hth constructive with each other, which contributes to reducing power consumption.

[0166] As examples of the above-mentioned ejection waveforms, Figure 20 shows an example in which the rising waveform has four stages (four times), and Figure 21 shows an example in which the rising waveform has three stages. In Figure 20, the number of stages, h, is shown in parentheses. Naturally, the same applies to the falling waveform. As shown in Figures 20 and 21, assuming that the potential difference at each stage is the same and that the pressure vibration does not attenuate, the optimal retention time for each stage is λn / number of stages (h). Therefore, if the phase difference (time interval) between any two of the potential difference displacements from the first to the hth stages is in the range of (k / 2-1 / 6)λn to (k / 2+1 / 6)λn, the parasitic vibrations generated by the corresponding two potential difference displacements will cancel each other out. For example, the time interval between the first and third potential difference displacements in Figure 20 is λn / 2, and Tij for i=1&j=3 satisfies Equation 7. Furthermore, the time interval between the second and fourth potential difference displacements in Figure 20 is also λn / 2, and Tij when i=2&j=4 also satisfies Equation 7. Therefore, the parasitic oscillations weaken each other.

[0167] The pressure vibrations inside the pressure chamber 46 decay over time due to the viscous resistance of the ink. Also, parasitic vibrations typically decay more over time than main acoustic vibrations. Therefore, the change in potential difference from 0.5AL before ejection to immediately after ejection has a greater effect on satellites and print quality than the change in potential difference from 1.5AL before ejection to 0.5AL before ejection, and the change in potential difference from 1.5AL before ejection to 0.5AL before ejection has a greater effect on satellites and print quality than the change in potential difference from 1.5AL before ejection to 0.5AL before ejection. Therefore, it is desirable to adjust the value of Tm or Tij of the ejection waveform, whichever is closer to immediately before or after ejection, so that the condition for parasitic vibrations to cancel each other out is satisfied.

[0168] According to at least one embodiment of the liquid ejection head described above, when ejecting multiple droplets continuously, the ejection speed of the droplets can be further adjusted by making the width of the ejection waveform (Dp width) shorter than half the period of the parasitic vibration.

[0169] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0170] 1...liquid ejection head, 10...base, 20...actuator, 21...piezoelectric pillar, 22...non-driven piezoelectric pillar, 30...vibration plate, 40...flow path plate, 42...partition wall portion, 45...flow path, 46...pressure chamber, 47...individual flow path, 48...common flow path, 50...nozzle plate, 51...nozzle, 70...drive circuit, 71...wiring film, 72...driver IC, 81...first voltage source, 82...second voltage source, 83...third voltage source, 100...liquid ejection device, 111...casing, 112...medium supply unit, 113...image forming unit, 114...medium discharge unit, 115...conveyor device, 117...support unit, 118...conveyor belt , 119...support plate, 120...belt roller, 121...pair of guide plates, 122...conveyor roller, 130...head unit, 132...ink tank, 133...connecting flow path, 134...supply pump, 150...control unit, 151...processor, 154...I / O port, 155...image memory, 161...drive motor, 162...operation unit, 163...various sensors, 200...externally connected equipment, 301...vibration part, 721...data buffer, 722...decoder, 723...driver, 724...voltage control unit, 725...voltage switching unit, 726...wiring electrode, 727...wiring electrode.

Claims

1. a nozzle plate having nozzles for discharging liquid; a pressure chamber communicating with the nozzle; an actuator that varies the volume of the pressure chamber in response to a drive signal; a drive circuit that generates the drive signal that drives the actuator; the drive signal includes a plurality of ejection waveforms that cause the nozzle to eject a plurality of droplets, At least one of the ejection waveforms of the drive signal is a waveform of an arbitrary shape that occurs twice consecutively, the drive circuit cancels vibrations of an acoustic resonance frequency in a frequency range higher than a main acoustic resonance frequency of the liquid in the pressure chamber, which are caused by a change in the potential difference, by changing the potential difference at least once after the change in the potential difference; A liquid ejection head, wherein the intervals between the plurality of ejection waveforms are substantially the same as the period of the main acoustic vibration frequency.

2. The period of an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency of the liquid in the pressure chamber is defined as λn, and the time interval Tm2 of at least one set of two consecutive waveforms of an arbitrary shape included in the drive signal is defined as: (kkk / 2-1 / 6)λn ≦ Tm2≦ (kkk / 2+1 / 6)λn 2. The liquid ejection head according to claim 1, wherein kkk in this formula is an odd number equal to or greater than 1.

3. at least one of the ejection waveforms of the drive signal includes an expansion potential difference that expands the volume of the pressure chamber, a contraction potential difference that contracts the volume of the pressure chamber, and at least one intermediate potential difference between the expansion potential difference and the contraction potential difference; When the period of an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency of the liquid in the pressure chamber is λn, and the number of potential difference changes included in the drive signal is h, among the potential difference changes that are expansions or contractions of the volume of the pressure chamber, one of the 1st to (h-1th) potential difference changes is the i-th potential difference change, and one of the (i+1)th to (h)th potential difference changes is the j-th potential difference change, the time interval Tij between any two of the h potential difference changes, i.e., the i-th and j-th potential difference changes, is (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn 2. The liquid ejection head according to claim 1, wherein k in this formula is an odd number equal to or greater than 1.

4. 4. The liquid ejection head according to claim 3, wherein the time interval between the two ejections is within a range from the time point of ejecting the liquid to 1.5 times a half period of the main acoustic vibration.

5. the expansion potential difference, the intermediate potential difference, and the contraction potential difference are potential differences input between electrodes of the actuator, 2. The liquid ejection head according to claim 1, wherein the drive circuit has a switching circuit that connects the electrodes and a voltage source, and the expanding potential difference, the intermediate potential difference, and the contracting potential difference are generated by switching the switching circuit.

6. 2. The liquid ejection head according to claim 1, wherein an acoustic resonance frequency in a frequency range higher than a main acoustic resonance frequency of the liquid in the pressure chamber is approximately an odd multiple of at least three times the main acoustic resonance frequency.

7. 2. A liquid ejection head according to claim 1, wherein the time width from when the pressure chamber starts to expand due to the expansion potential difference of the multiple ejection waveforms to when the pressure chamber starts to contract due to the contraction potential difference is a time width in which the velocity of the liquid ejected by the ejection waveforms after the first one is approximately the same as or faster than the velocity of the liquid ejected by the first ejection waveform.

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