Liquid discharge head

Abstract

To provide a liquid discharge head which can increase discharge speed of droplets to be discharged later to discharge speed of droplets discharged previously or faster when continuously discharging a plurality of droplets.SOLUTION: A liquid discharge head includes: a nozzle plate; a pressure chamber; an actuator; and a drive circuit. The drive circuit generates a driving signal. The driving signal includes a plurality of discharge waveforms to discharge a plurality of droplets from the nozzle. The discharge waveform of the driving signal includes: an expansion potential difference for expanding the volume of the pressure chamber; a reduction potential difference for reducing the volume of the pressure chamber; and at least one or more intermediate potential differences between the expansion potential difference and the reduction potential difference. 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 generated by a change in the potential difference by at least one or more of times of changes in the potential difference executed after the change in the potential difference. Each interval of the plurality of discharge waveforms is the substantially 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, in a liquid ejection head that ejects liquid, multiple droplets are ejected continuously to increase the dot diameter when the droplets land on the media, thereby realizing the expression of gradations in ink density on the media. However, this technology is prone to satellites when driving a liquid ejection head that generates parasitic vibrations, and there is a risk of deterioration in print quality. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-045797 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a liquid ejection head that, when ejecting a plurality of liquid droplets in succession, can make the ejection speed of the subsequently ejected liquid droplets equal to or faster than the ejection speed of the previously ejected liquid droplets. [Means for solving the problem]

[0005] A liquid ejection head according to an 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 connected to 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 a plurality of ejection waveforms that eject a plurality of droplets from the nozzle. The ejection waveform 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. 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 generated by changing the potential difference, by changing the potential difference at least once after the change of the potential difference. The interval between the plurality of ejection waveforms is substantially the same as the period of the main acoustic vibration frequency. [Brief description of the drawings]

[0006] [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. [Diagram 2] FIG. 2 is a cross-sectional view showing the configuration of a liquid ejection head according to the embodiment, with some parts omitted. [Diagram 3] FIG. 2 is a block diagram 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 a configuration of a liquid ejection apparatus using a liquid ejection head according to an embodiment. [Diagram 5] FIG. 1 is a block diagram showing an example of a configuration of a liquid ejection apparatus according to an embodiment. [Figure 6] 5A and 5B are explanatory diagrams showing an example of a driving waveform including an ejection waveform and a cancellation waveform of the liquid ejection head according to the embodiment. [Figure 7] 4A to 4C are explanatory diagrams showing an example of a driving waveform and acoustic vibration of the liquid ejection head according to the embodiment. [Figure 8] 5A and 5B are explanatory diagrams showing the relationship between the drive waveform and the ejected liquid droplets in an example of a liquid ejection head according to the embodiment. [Figure 9]3A and 3B are explanatory diagrams showing an example of ejected droplets of the liquid ejection head according to the embodiment. [Figure 10] FIG. 11 is an explanatory diagram showing an example of a frequency analysis of a liquid ejection head according to a comparative example. [Figure 11] 6 is an explanatory diagram 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 12] FIG. 11 is an explanatory diagram showing an example of a frequency analysis of a liquid ejection head according to a comparative example. [Figure 13] 5A and 5B are explanatory diagrams showing an example of a driving waveform and acoustic vibration of a liquid ejection head according to a comparative example. [Figure 14] 5A and 5B 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] FIG. 11 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 16] FIG. 11 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 17] FIG. 11 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 18] FIG. 11 is an explanatory diagram showing an example of a driving waveform according to another embodiment. [Figure 19] FIG. 11 is an explanatory diagram showing an example of a driving waveform according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] 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 showing a schematic configuration of a drive circuit 70 of 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 the purpose of explanation.

[0008] 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.

[0009] The base 10 is formed, for example, in the shape of a rectangular plate. The actuator 20 is joined to the base 10.

[0010] The actuator 20 is a piezoelectric member including, for example, a plurality of piezoelectric columns 21 and non-driven piezoelectric columns 22 arranged alternately with the plurality of piezoelectric columns 21. The actuator 20 is formed in a comb shape by arranging the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 in one direction at a predetermined interval. For example, such an actuator 20 is formed by processing a groove by dicing a laminated piezoelectric member bonded to the base 10 from an end face opposite to the base 10 side, and forming a plurality of piezoelectric elements formed in a rectangular column shape at a predetermined interval for one piezoelectric member. Then, the formed plurality of piezoelectric elements are provided with electrodes or the like to constitute the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 arranged alternately as piezoelectric elements. That is, the actuator 20 is divided into a plurality of parts at one end side (the vibration plate 30 side) by the formed plurality of grooves, and the other end side (the base 10 side) is connected.

[0011] For example, the laminated piezoelectric member constituting the actuator 20 is formed by laminating and sintering sheet-shaped piezoelectric materials. As a specific example, as shown in Fig. 1 and Fig. 2, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 are laminated piezoelectric bodies serving as driving elements, for example. The piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 each include a plurality of laminated piezoelectric layers, a plurality of internal electrodes formed on the main surface 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.

[0012] The piezoelectric layers are made of thin plates of piezoelectric materials such as PZT (lead zirconate titanate) or lead-free KNN (potassium sodium niobate). The piezoelectric layers are laminated in the thickness direction and bonded by sintering. The laminated direction of the piezoelectric layers is perpendicular to the arrangement direction of the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22.

[0013] The internal electrodes are conductive films made of a sinterable conductive material such as silver-palladium, etc., and are 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 to have different poles alternately in the arrangement direction.

[0014] The external electrodes are formed on the surfaces of the multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22, and are configured by collecting the ends of the internal electrodes. The external electrodes are formed by a known method such as plating or sputtering, using Ni, Cr, Au, or the like. The multiple external electrodes are arranged on different side portions of the multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22, respectively, and configured to have different poles. Note that the external electrodes of different poles may be routed around different regions of the same side portion of the multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22.

[0015] As an example in this embodiment, the multiple external electrodes include individual electrodes formed on each of the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22, and a common electrode formed continuously with the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22. The multiple individual electrodes formed on each of the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22 are arranged independently of each other. The common electrode is, for example, grounded.

[0016] 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 of a processor 151.

[0017] When a voltage is applied to the internal electrode via the external electrode, 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 means, 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 disposed in correspondence with the pressure chamber 46 across the vibration plate 30, and the remaining non-driven piezoelectric pillars 22 are disposed in positions facing the partition wall 42 across the vibration plate 30.

[0018] 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 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.

[0019] 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.

[0020] The vibration plate 30 is, for example, a flat plate arranged such that the thickness direction is the stacking direction of the piezoelectric layers. The surface direction of the vibration plate 30 extends in the arrangement direction of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22. 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.

[0021] 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 of, for example, a SUS plate. The vibration plate 30 may have folds or steps formed in the areas adjacent to the vibration parts 301 or between adjacent vibration parts 301 so that the multiple vibration parts 301 can be easily displaced.

[0022] The vibration plate 30 expands and contracts the piezoelectric pillar 21 due to longitudinal vibration of the piezoelectric pillar 21, causing the portion of the vibration plate 30 opposite the piezoelectric pillar 21 to displace, thereby expanding and contracting the pressure chamber 46 and varying the volume of the pressure chamber 46.

[0023] One main surface of the diaphragm 30 is bonded to the actuator 20, and the other main surface is bonded to the flow path plate 40. Between the diaphragm 30 and the flow path plate 40, a pressure chamber 46 capable of containing ink is formed.

[0024] One main surface of the diaphragm 30 faces the piezoelectric pillars 21 and 22, respectively, and the other main surface faces the pressure chamber 46 and the partition wall portion 42, respectively.

[0025] 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 a predetermined flow path 45. The flow path plate 40 forms the plurality of partition walls 42 and the predetermined flow path 45, for example, by stacking a plurality of plates 401, some of which are open.

[0026] 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, which will be described later, of a predetermined flow path 45, as well as a plurality of individual flow paths 47.

[0027] 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 .

[0028] The multiple pressure chambers 46 are aligned in the alignment direction of the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22, and face the multiple piezoelectric columns 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 columns 22 via the vibration plate 30. The multiple pressure chambers 46 are formed by blocking one side of the flow path plate 40 with the vibration plate 30 and blocking the other side with the nozzle plate 50 in the stacking direction of the piezoelectric layers. Further, nozzles 51 formed in the nozzle plate 50 are arranged in the pressure chambers 46.

[0029] 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 eject the liquid from the nozzles 51 by being deformed by vibration of a vibration plate 30 forming part of the pressure chambers 46. 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 flow path cross-sectional shape of the individual flow paths 47 is different from the flow path cross-sectional shape of the pressure chambers 46. The flow path cross-sectional area of ​​the individual flow paths 47 is smaller than the flow path 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.

[0030] The nozzle plate 50 is formed of, for example, 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 in the thickness direction. The multiple nozzles 51 form a nozzle row.

[0031] 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 for each of the piezoelectric pillars 21 and 22 in chronological order. 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 for operating each of the piezoelectric pillars 21 and 22 based on the control of the decoder 722. The drive signals are voltages applied to each of the piezoelectric pillars 21 and 22.

[0032] 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 has a data buffer 721, a decoder 722, and a driver 723. Note that the driver IC 72 may have a portion of the data buffer 721, the decoder 722, and the driver 723, and the remaining portions may be provided by the printed wiring board or the like.

[0033] The drive circuit 70 applies a drive voltage to the external electrode via the driver IC 72 to drive the piezoelectric pillar 21 , thereby varying the volume of the pressure chamber 46 and causing droplets to be ejected from the nozzle 51 .

[0034] The wiring film 71 is connected to the individual electrodes and the common electrode. For example, the wiring film 71 is an ACF (anisotropic conductive film) fixed to the connection portion of the external electrode 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.

[0035] 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.

[0036] The driver IC 72 generates a control signal and a drive signal to be applied to each piezoelectric pillar 21, 22 to operate the piezoelectric pillar 21. The driver IC 72 generates a control signal for controlling the timing of ink ejection and the selection of the piezoelectric pillar 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 to be applied to the piezoelectric pillar 21, i.e., a drive signal (electrical signal), according to the control signal. When the driver IC 72 applies a drive signal to the piezoelectric pillar 21, the piezoelectric pillar 21 is driven by displacing the vibration plate 30 to vary the volume of the pressure chamber 46 so as to expand and contract. This causes the ink filled in the pressure chamber 46 to generate pressure vibration. The pressure vibration causes ink to be ejected from the nozzle 51 provided in the pressure chamber 46. The liquid ejection head 1 may be configured to realize gradation expression by changing the amount of ink droplets that land on one pixel. The liquid ejection head 1 may also be configured to change the amount of ink droplets that land on one pixel by changing the number of times ink is ejected. In this manner, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pillar 21.

[0037] 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, in a driver IC 72. However, in Fig. 3, two voltage switching units 725 are illustrated, and the other voltage switching units 725 are not illustrated.

[0038] 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, when the actuator 20 is a laminated PZT, it tends to deteriorate when voltages of both polarities are applied, 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.

[0039] 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.

[0040] The wiring electrode 726 is connected to a common electrode serving as a ground electrode of the actuator 20. The multiple wiring electrodes 727 are each connected to individual electrodes serving as non-ground electrodes of the actuator 20.

[0041] 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 an instruction 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 switching timing of the voltage source in each voltage switching unit 725. Then, the voltage control unit 724 outputs an instruction 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 to be connected to the wiring electrode 727 according to the instruction from the voltage control unit 724.

[0042] The voltage switching unit 725 is composed of, 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 poles of the piezoelectric pillar 21 are connected to the wiring electrodes 726 and 727 via the external electrodes (the common electrode and the individual electrodes).

[0043] Such a drive circuit 70 switches the connection wiring between the voltage sources 81, 82, and 83 and the actuator 20 using a switching circuit configured with a voltage control unit 724 and a plurality of 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 by driving the actuator 20. In this embodiment, potential differences other than the largest potential difference and the smallest potential difference are called intermediate potential differences.

[0044] The printed wiring board is a printing wiring assembly (PWA) 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.

[0045] Next, an example of a liquid ejection device 100 including the liquid ejection head 1 will be described with reference to Fig. 4 and Fig. 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.

[0046] The liquid ejection device 100 is a liquid ejection device that performs an image formation process on a sheet of paper P by ejecting a liquid such as ink while transporting the sheet of paper P as a printing medium, which is the ejection target, along a predetermined transport path A from a medium supply section 112 through an image forming section 113 to a medium ejection section 114.

[0047] The housing 111 constitutes the outer shell of the liquid ejection device 100. The housing 111 has a discharge port at a predetermined location for discharging the paper P to the outside.

[0048] The medium supply unit 112 includes a plurality of paper feed cassettes, and is configured to be able to hold a plurality of stacked sheets of paper P of various sizes.

[0049] The medium discharge unit 114 includes a paper discharge tray configured to be able to hold the paper P discharged from the discharge opening.

[0050] 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 so as to face the support section 117.

[0051] The support section 117 includes a conveyor belt 118 that is provided in a loop shape 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.

[0052] During image formation, the support section 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 feeding the conveyor belt 118 at a predetermined timing by the rotation of the belt roller 120.

[0053] 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.

[0054] 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 include liquid ejection heads 1 of four colors, cyan, magenta, yellow, and black, and ink tanks 132 that respectively contain ink of each of these colors. The ink tanks 132 are connected to the common flow path 48 of the liquid ejection heads 1 by a connection flow path 133.

[0055] In addition, a negative pressure control device such as a pump (not shown) is connected to the ink tank 132. Then, by controlling the negative pressure inside the ink tank 132 by the negative pressure control device according to the head value between the liquid ejection head 1 and the ink tank 132, the ink supplied to each nozzle 51 of the liquid ejection head 1 is formed into a meniscus of a predetermined shape.

[0056] The supply pump 134 is a liquid delivery 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.

[0057] The conveying device 115 conveys the paper P along a conveying path A that extends 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.

[0058] Each of the guide plate pairs 121 includes a pair of plate members disposed opposite each other with the paper P being transported therebetween, and guides the paper P along the transport path A.

[0059] 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. Sensors for detecting the conveying status of the paper are disposed at various points along the conveying path A.

[0060] The control unit 150 is, for example, a control board, and includes a processor 151, a read only memory (ROM) 152, a random access memory (RAM) 153, an I / O port 154 which is an input / output port, and an image memory 155.

[0061] 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, the drive motor 161, the operation unit 162, various sensors 163, and the like provided in the liquid ejection device 100 through an I / O port 154. The processor 151 transmits the print data stored in the image memory 155 to the drive circuit 70 in the drawing order.

[0062] The ROM 152 stores various programs and the like. The RAM 153 temporarily stores various variable data, image data and the like. The ROM 152 and the 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. The I / O port 154 is an interface unit that inputs data from the outside, such as the external connection device 200, and outputs data to the outside. Print data from the external connection device 200 is transmitted to the control unit 150 via the I / O port 154 and is stored in the image memory 155.

[0063] The characteristics of the liquid ejection head 1 used in the liquid ejection device 100 according to the embodiment and the drive waveform of the liquid ejection head 1 (ejection waveform of the drive signal) will be described below.

[0064] First, the driving waveform of the liquid ejection head 1 of this embodiment will be described with reference to Figs. 6 to 14. Fig. 6 is an explanatory diagram showing an example of a driving waveform including a multi-drop ejection waveform and a cancel waveform for continuously ejecting a plurality of droplets of the liquid ejection head 1. Fig. 7 is an explanatory diagram showing an example of one ejection waveform and acoustic vibration of the liquid ejection head 1 according to the embodiment, Fig. 8 is an explanatory diagram showing the relationship between the ejection waveform and the ejected droplets in an example of the liquid ejection head 1, and Fig. 9 is an explanatory diagram showing an example of the ejected droplets of the liquid ejection head 1. Figs. 10 to 14 are drawings for explaining a conventional liquid ejection head as a comparative example, Fig. 10 is an explanatory diagram showing an example of a frequency analysis of pressure vibration of the liquid ejection head according to the comparative example, and Fig. 11 is an explanatory diagram showing an example in which the main acoustic vibration and the parasitic vibration of Fig. 10 are combined. FIG. 12 is an explanatory diagram showing an example of a frequency analysis of a liquid ejection head according to a comparative example, FIG. 13 is an explanatory diagram showing an example of a driving waveform and acoustic vibration of a liquid ejection head according to a comparative example, and FIG. 14 is an explanatory diagram showing an example of a driving waveform and acoustic vibration of a liquid ejection head according to a comparative example.

[0065] First, the liquid ejection head of the prior art has a driving method called pull-and-shoot, which increases the ejection force by driving the piezoelectric pillars 21 in synchronization with the half period AL of the main acoustic vibration of the pressure chamber. However, as shown in the example of frequency analysis of the nozzle pressure vibration in Fig. 10, 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.

[0066] When the actuator is driven to eject droplets from the nozzle, if a parasitic vibration with a higher frequency than the main acoustic vibration occurs, the pressure in the pressure chamber will have a pressure peak with a shorter period than the half period of the main acoustic vibration, as shown in FIG. 11. That is, the composite wave of the main acoustic vibration and the parasitic vibration is sharp at the beginning of the vibration. The short-period pressure peak increases the ejection speed of the leading edge of the ejected droplet, but does not continue until the end of the ejection, decreasing the ejection speed of the trailing edge of the ejected droplet. Then, as shown in the upper diagram (a) of FIG. 9, when the droplet is ejected, the volume of the satellite increases relative to the leading edge droplet, resulting in deterioration of the print quality. Here, the satellite is a droplet that is ejected with a gap from the leading edge droplet, following the droplet that is ejected first (leading edge droplet) when the piezoelectric column 21 is driven and the pressure chamber is deformed to eject liquid from the nozzle.

[0067] 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 about three times (for example, 2.8 times) larger is generated, as shown in the frequency analysis of Fig. 12. Here, the following are considered to be the causes of the parasitic vibration having a higher frequency than the main acoustic vibration being generated in the pressure chamber of the liquid ejection head.

[0068] One example of a 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 12, in which the connection point with a common flow path is the opening end, similar to the liquid ejection head 1 of the embodiment.

[0069] Another example of the cause is an integer multiple vibration of 2 or more in the liquid column vibration of an open tube. An example of such a liquid ejection head is a side shooter with an opening at the connection point with a common flow channel, as shown in FIG. 13. In the main acoustic vibration of an open tube, the amplitude of the pressure vibration is largest at the center of the open tube, so a nozzle is provided near the center of the open tube. As shown in FIG. 13, when an even multiple vibration of 2 or more occurs in the liquid column vibration of an open tube, the center of the open tube becomes a vibration node with a small amplitude of the pressure vibration, so when a nozzle is provided near the center of the open tube, the shape of the ejected droplet is less affected by the even multiple vibration of 2 or more. Therefore, when a nozzle is provided near the center of an open tube, an odd multiple vibration of 3 or more is more likely to increase the volume of satellites and deteriorate the print quality than an even multiple vibration of 2 or more.

[0070] Another example of the cause is vibration caused by reflection of pressure vibrations due to changes in the sound speed in each flow path when the flow path cross section of the pressure chamber and the individual flow paths are different.

[0071] Another example of the cause is vibration caused by a pressure vibration node occurring between the pressure chamber and the flow path with a low rigidity when the wall surface or part of the wall surface of the individual flow path has a low rigidity compared to the pressure chamber, as a result of the pressure generated in the pressure chamber being reduced in the flow path with a low rigidity. This is the case, for example, when the installation range of an actuator such as a PZT (piezoelectric pillar 21) shown by the two-dot chain line in Fig. 1 is biased due to manufacturing errors or the like with respect to the range of the vibration plate on the wall surface of the pressure chamber, as in the actuator (piezoelectric pillar 21) shown by the solid line in Fig. 1, and the area of ​​the pressure chamber wall surface that is not supported by the actuator only by the vibration plate is relatively large. Note that for a head in which the area where the actuator is not supported by only the vibration plate at the upper right of the pressure chamber in Figure 1 is approximately 30% of the longitudinal length of the pressure chamber (the horizontal width of pressure chamber 46 in Figure 1), a structural analysis of the deformation of the PZT and pressure chamber was performed, a compressive fluid analysis of the liquid behavior in the flow path was performed, and a fluid surface analysis of the droplet ejection from the nozzle was performed. The results of the frequency analysis of the pressure vibration in the nozzle are shown in the graphs in Figures 10 and 12.

[0072] Furthermore, as shown in Figure 14, when the rectangular wave width UL of the ejection waveform is set to AL, the third harmonic vibration AI generated by the advance expansion of the pressure chamber before ejection (rising waveform) and the third harmonic vibration AII of the liquid column vibration generated by the contraction of the pressure chamber during ejection (falling waveform) reinforce each other, causing a short-period pressure peak to occur due to the third harmonic vibration, resulting in deterioration of print quality.

[0073] 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 liquid column vibration of a closed tube, and 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 is a drive waveform that suppresses the 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. 10. Also, in this example, the drive waveform of the liquid ejection head 1 shows an example of ejecting droplets twice in succession as shown in FIG. 6 as an example of a multi-drop that ejects multiple droplets in succession, but it may be an example of ejecting droplets three times in succession as shown in FIG. 16, or an example of ejecting droplets four or more times.

[0074] First, in the liquid ejection head 1, when the potential difference is the largest, the pressure chamber 46 is expanded by the piezoelectric pillar 21 of the actuator 20 to the largest extent, and when the potential difference is the smallest, the pressure chamber of the ink is contracted by the piezoelectric pillar 21 of the actuator 20 to the smallest extent. Then, when the liquid ejection head 1 ejects ink, the pressure chamber 46 is expanded in advance before ejection, and the pressure chamber 46 is contracted at the time of ejection, thereby ejecting ink. In the example of this embodiment, the ejection waveform of the drive waveform of the liquid ejection head 1 increases the potential difference (expansion potential difference) including the intermediate potential difference multiple times in two consecutive times when the pressure chamber 46 is expanded in advance before ejection, or decreases the potential difference (contraction potential difference) including the intermediate potential difference multiple times in two consecutive times when the pressure chamber 46 is contracted during ejection. More preferably, the ejection waveform changes the potential difference twice in succession both when the pressure chamber 46 is expanded and when it is contracted. Then, the liquid ejection head 1 ejects droplets twice by inputting such an ejection waveform twice in succession.

[0075] Furthermore, after inputting the second ejection waveform in succession to eject ink multiple times (twice in this example) from the liquid ejection head 1, a cancellation waveform is input to cancel residual vibrations that occur after the ejection of ink. 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.

[0076] In the example of 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 smaller than AL, and increases the potential difference (expansion potential difference) including the intermediate potential difference multiple times in succession two times when the pressure chamber 46 is expanded, and decreases the potential difference (contraction potential difference) including the intermediate potential difference multiple times in succession two times when the pressure chamber 46 is contracted. More preferably, the cancel waveform changes the potential difference two times in succession both when the pressure chamber 46 is expanded and when it is contracted, similar to the ejection waveform.

[0077] FIG. 6 shows an example of a drive waveform in which an ejection waveform is input twice in succession at a predetermined interval when ejecting ink from the liquid ejection head 1. FIG. 7 shows an example of an ejection waveform. In FIG. 6 and FIG. 7, the vertical axis is voltage (potential difference) and the horizontal axis is time. The drive waveform is generated by the driver IC 72 of the drive circuit 70. As shown in FIG. 6, in both the two ejection waveforms and the cancel waveform, the expansion potential difference is increased twice when the pressure chamber 46 is expanded, and the contraction potential difference is decreased twice when the pressure chamber 46 is contracted during ejection. In addition, when changing the potential difference both when the pressure chamber 46 is expanded and contracted, after applying the first potential difference, the first potential difference is maintained for a predetermined time, and then the second potential difference is applied. In addition, when 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, by inputting an ejection waveform, the voltage (potential difference) is reduced in two steps, thereby 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, thereby contracting the pressure chamber.

[0078] First, an example of the ejection waveform of the first drop among the drive waveforms will be specifically described with reference to Fig. 6 and Fig. 7. As shown in Fig. 7, when the pressure chamber 46 is expanded in advance before the ejection of ink, the time interval from the start of the expansion by the first expansion potential difference in the case where the potential difference is increased twice consecutively to the start of the contraction by the first contraction potential difference after the expansion potential difference is increased twice consecutively is defined as UL. Also, as shown in Fig. 7, when the pressure chamber 46 is contracted during ejection, the time interval from the start of the expansion by the second expansion potential difference in the case where the potential difference is increased twice consecutively before the potential difference is reduced to the start of the contraction by the second contraction potential difference in the case where the expansion potential difference is increased twice consecutively and the contraction potential difference is reduced twice consecutively is defined as UL. Note that in the following description, the time interval UL from the start of the expansion by the first expansion potential difference in the case where the potential difference is increased twice consecutively to the start of the contraction by the first contraction potential difference after the expansion potential difference is increased twice consecutively is also sometimes described as Dp.

[0079] That is, as shown in FIG. 7, the driving waveform for deforming the pressure chamber 46 to eject ink from the nozzle 51 changes the potential difference twice consecutively when the pressure chamber 46 is expanded and contracted. The driving waveform has a time interval UL between the time when the potential difference is increased for the first time when the pressure chamber 46 is expanded and the time when the potential difference is decreased for the first time when the pressure chamber 46 is contracted, and a time interval UL between the time when the potential difference is increased twice consecutively when the pressure chamber 46 is expanded and the time when the potential difference is decreased twice consecutively when the pressure chamber 46 is contracted. The time interval UL is greater than 0.5AL and less than 1.5AL. More preferably, UL=AL. This is because, if UL is greater than 0.5AL and less than 1.5AL, reinforcement 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.

[0080] Here, the drive waveform is Tm=λn / 2, where λn is the period of the parasitic vibration such as the third harmonic, 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 Fig. 7, the phase difference between the parasitic vibration generated at the first potential difference change and the parasitic vibration generated at the second potential difference change is 180 degrees and cancels each other out. This makes it possible to suppress deterioration of print quality caused by parasitic vibration such as the third harmonic.

[0081] More preferably, as shown in FIG. 7, the drive waveform is configured so that the amount of change in potential difference during the first change in potential difference is the same as the amount of change in potential difference during the second change in potential difference, thereby causing parasitic vibrations in the pressure chamber 46 that have approximately the same amplitude but a phase difference of 180 degrees to cancel each other out, thereby significantly suppressing residual vibrations resulting from the parasitic vibrations thereafter.

[0082] In this way, when the time interval UL of the ejection waveform (driving 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 vibration (3rd harmonic vibration AI) generated by the pressure chamber contraction (falling waveform) at the first potential difference change and the parasitic vibration (3rd harmonic vibration AII) generated by the pressure chamber contraction (falling waveform) at the second potential difference change is 180 degrees and cancels out, as shown in Fig. 7. Note that by also setting the time interval Tm when the potential difference is increased twice consecutively to expand the pressure chamber twice consecutively, the phase difference between the parasitic vibration (3rd harmonic vibration AI) generated by the pressure chamber expansion (rising waveform) at the first potential difference change and the parasitic vibration (3rd harmonic vibration AII) generated by the pressure chamber expansion (rising waveform) at the second potential difference change is 180 degrees and cancels 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. 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 to contract the pressure chamber.

[0083] Here, the condition Tm for the parasitic vibrations of period λn to cancel each other out in the drive waveform will be explained. First, let A be the vibration of period λn that occurs when the potential difference is changed for the first time, and let A' be the vibration vector after time Tm from A. Let B be the vibration vector of period λn that occurs when the potential difference is changed for the second time after Tm. The absolute value of the composite vector of A' and B is minimum when Tm is an odd multiple of λn / 2 (phase difference between A' and B is 180 degrees). From the formula for the composition of simple harmonic motion with period λn, the condition for the absolute value of the composite vector of A' and B to be equal to or less than the greater of the absolute values ​​of A' and B (or less than the greater, if the absolute values ​​of A' and B are the same) is found, and the phase difference between vibration vectors A' and B is within 180 degrees ±60 degrees.

[0084] The absolute value of the composite vector of A' and B can be transformed into the following formula. Here, θA is the phase of A' and θB is the phase of B. The absolute value of the composite 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 for the vibrations with period λn to weaken each other. |B|≧Equation 1 can be transformed by squaring both sides to 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 valid.

[0085] Also, if |B|≦|A'|, |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 valid.

[0086] 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 (Equation 4) Here, k is an odd number equal to or greater than 1.

[0087] Furthermore, when the potential difference is changed twice consecutively when the pressure chamber 46 is expanded and contracted, it is preferable that Tm of the drive waveform is (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 intermediate potential difference holding time when the pressure chamber is expanded and the intermediate potential difference holding time when the pressure chamber is contracted.

[0088] Also, 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 for Tm to be short.

[0089] Considering the above points and the need to reduce power consumption, the Tm of the drive waveform is as follows: (k / 2-1 / 6)λn≦Tm≦kλn / 2 (Equation 5) Here, k is an odd number equal to or greater than 1.

[0090] Next, as an evaluation of the ejection waveform for the first drop among the drive waveforms of the liquid ejection head 1 according to this embodiment, Fig. 8 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 leading drop speed was approximately 8 m / s for all the results of the various waveforms in Fig. 8.

[0091] The top drive waveform in Fig. 8 is a comparative example, a trapezoid drive waveform with a rise time tr of 0.2 μs as shown in Fig. 14, and the rest are drive waveforms with two potential difference changes as shown in Fig. 7, with different Tm and all rise 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.

[0092] In the liquid ejection head 1 of the embodiment and the liquid ejection head of the comparative example, in addition to the main acoustic vibration, a parasitic vibration that is approximately three times larger is generated, as shown in the frequency analysis of Fig. 12. The period λn of the parasitic vibration is 1.85 μs and λn / 2 is 0.925 μs.

[0093] Fig. 9 shows the results of simulating the state of ejected droplets when one drop of ink is applied. In Fig. 9, the upper diagram (a) is an example showing ejected droplets by a trapezoidal drive waveform with tr = 0.2 μs in the comparative example, the center diagram (b) is an example showing ejected droplets by 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 showing ejected droplets by a drive waveform with Tm = 0.93 μs in the embodiment and changing the potential difference twice.

[0094] As shown in the lower diagram (c) of Figures 8 and 9, 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, and as shown in the center diagram (b) of Figures 8 and 9, 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 the embodiment can suppress vibrations at frequencies higher than the main acoustic vibration while suppressing power consumption.

[0095] Next, an example of the ejection waveform for the second drop among the drive waveforms will be specifically described with reference to Fig. 6. In 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 the first reduction potential difference starts to reduce the potential difference, 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 Dp of the ejection waveform for the second drop is set smaller than AL.

[0096] For ease of explanation, in FIG. 6, the first to fourth changes in the potential difference in the ejection waveform for the first drop are designated as (1) to (4), and the first to fourth changes in the potential difference in the ejection waveform for the second drop are designated as (21) to (24), and the following explanation will be given. Also, the following explanation will be given with the reference point of the phase of the ejection waveform for the first drop as (0) and the reference point of the phase of the ejection waveform for the second drop as (0''). Here, the reference point (0) of the phase of the ejection waveform for the first drop is set to the middle of the potential difference changes (2) and (3), and the reference point (0'') of the phase of the ejection waveform for the second drop is set to the middle of the potential difference changes (22) and (23). Also, the voltage drop time tf in the figure is set to be substantially the same as the voltage rise time tr. 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 change in height in FIG. 6) 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.

[0097] First, the main acoustic vibration of the ejection waveform in Fig. 6 will be described. In the ejection waveform for ejecting the first drop in Fig. 6, 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 becomes a vibration with a phase lead of -π+(Dp1+Tm) / 2. Furthermore, when the potential difference is changed as shown in (2), the vibration in (2) becomes a vibration with a phase lead of -π+(Dp1-Tm) / 2. The composite wave of (1) and (2) becomes a vibration with a phase lead of -π+Dp1 / 2.

[0098] The potential difference changes (3) and (4) which are for contracting the pressure chamber 46 are opposite to the potential difference changes (1) and (2) which are for expanding the pressure chamber 46, so the pressure chamber 46 contracts and pressurizes the inside of the pressure chamber 46. Therefore, (3) is a vibration with a phase lead of -(Dp1-Tm) / 2. Also, (4) can be considered to be a vibration with a phase lead of -(Dp1+Tm) / 2. Therefore, the composite wave of (3) and (4) is a vibration with a phase lead of -Dp1 / 2.

[0099] 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 be an oscillation with a phase lead of -π / 2.

[0100] Next, the main acoustic vibration of the ejection waveform of the second drop in Fig. 6 is 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, so that if the ejection waveform width of the second drop is Dp2, the vibration has a phase lead of -π+(Dp2+Tm) / 2. 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. Therefore, the composite wave of (21) and (22) has a phase lead of -π+Dp2 / 2.

[0101] The potential difference changes (23) and (24) which are for contracting the pressure chamber 46 are opposite to the potential difference changes (21) and (22) which are for expanding the pressure chamber 46, so the pressure chamber 46 contracts and pressurizes the inside of the pressure chamber 46. Therefore, (23) is a vibration with a phase lead of -(Dp2-Tm) / 2. Also, (24) is a vibration with a phase lead of -(Dp2+Tm) / 2. Therefore, the composite wave of (23) and (24) is a vibration with a phase lead of -Dp2 / 2.

[0102] If we assume a composite wave of (21), (22), (23), and (24) at time (0''), the composite wave of (21), (22), (23), and (24) will be an oscillation with a phase lead of -π / 2.

[0103] For this reason, when the time difference (time interval) between (0) and (0'') is set to an even multiple of π / 2 (AL), the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) have the same phase and are mutually constructive. In the example of FIG. 6, the time difference (time interval) between (0) and (0'') is 2AL. Furthermore, by reducing the time width Dp2 between (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 ejected by the residual vibration due to the composite wave of (1), (2), (3), and (4) and the constructive interaction of the composite wave of (21), (22), (23), and (24) can be adjusted. In this way, in a multi-drop drive 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 subsequently ejected ink can be adjusted to be equal to or faster than the ejection speed of the previously ejected droplet.

[0104] In addition, the time interval between (21), (22) when the pressure chamber is depressurized is Tm, and the time interval between (23), (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.

[0105] In the example of Fig. 6, an example of a driving waveform in which the time width Dp of adjacent ejection waveforms is different has been described, but the present invention is not limited to this. As shown in Fig. 15, the ejection waveform of the first drop and the ejection waveform of the second drop may be the same. However, since residual vibration of a parasitic vibration caused by ejecting droplets using a previous ejection waveform affects the ejection of droplets using a subsequent ejection waveform, it is preferable to adjust the Dp of adjacent ejection waveforms.

[0106] Next, using FIG. 15, we will explain the effect of the parasitic vibration generated by the ejection waveform of the first drop on the droplet ejected by the ejection waveform of the second drop. In the drive waveform, the parasitic vibration generated by (1) is canceled by (2), and the parasitic vibration generated by (3) is canceled by (4), but there is a time difference of Tm between (1) and (2), and between (3) and (4). For example, the vibration generated by (3) attenuates in time Tm due to the viscosity of the ink in the flow path, so the vibration amplitude of (3) after time Tm becomes smaller than the vibration amplitude generated by (4), and the vibration amplitude generated by (4) is not completely canceled by the vibration amplitude generated by (3). As a result, some of the vibration generated by (4) remains as residual vibration and affects the ejection of the second drop. The vibration generated by (2) also remains as residual vibration to some extent. However, the residual vibration generated by (2) takes a longer time to eject the second drop than that of (4). As a result, due to attenuation of the vibration caused by the viscosity of the ink in the flow path, the vibration amplitude of (2) becomes smaller than that caused by (4). Therefore, here we consider the effect of the residual parasitic vibration caused by (4), which has a relatively large vibration amplitude, on the ejection of the second droplet.

[0107] Here, the possibility of air bubble entrainment due to the ejection of the second drop will be described. As described above, when the composite wave of the main acoustic vibration generated by (21) and (22) is based on (0''), the vibration is advanced in phase by -π+Dp2 / 2 (the vibration peak is shifted). Therefore, in the composite wave of the pressure vibrations of (21) and (22), the time when the positive pressure peak is shown is the time when the phase advances from (0'') by -π+Dp2 / 2. And the time when the negative pressure peak is shown is the time when the phase advances from (0'') by +Dp2 / 2 (the midpoint between (21) and (22)). However, the composite wave of (21) and (22) is actually generated in the pressure chamber 31 after the change in the potential difference of (22) is implemented. Therefore, in the ejection waveform of 2 drops, the moment when the negative pressure due to the main acoustic vibration is highest before the start of ejection (23) is the moment (22). As a result, the pulling force on the meniscus of the nozzle 51 becomes strongest at the point (22), increasing the possibility of air bubble entrainment.

[0108] For example, as shown in FIG. 15, if Dp1=Dp2=AL and the time interval between (0) and (0'') is 2AL, then the time interval between (22) and (4) is AL. Here, if the parasitic vibration is an odd-numbered harmonic of the main acoustic vibration, the positive pressure due to the residual vibration of the parasitic vibration generated in (4) turns into negative pressure at the input of (22) in FIG. 15. Therefore, the negative pressure at the input of (22) is greater than the negative pressure at the input of (2), and the amount of meniscus retraction for the second drop is greater than the amount of meniscus retraction for the first drop. For this reason, the possibility of air bubble entrainment due to meniscus retraction for the second drop is higher than that for the first drop.

[0109] Therefore, if the time interval between (22) and (4) is adjusted so that it does not coincide with an odd multiple of the half period of the parasitic vibration, as in the drive waveform shown in Figure 6, it is possible to mitigate the phenomenon in which the negative pressure at the time point (22) becomes even larger due to the residual vibration of the parasitic vibration generated at (4). As a result, it is possible to mitigate the increase in the amount of meniscus pull-in at the second drop due to the residual vibration of the parasitic vibration generated at (4), and the possibility of air bubble entrainment can be reduced.

[0110] Next, as an example, an example will be described in which 2AL=5.24 μs, the period λn of the parasitic vibration is 1.85 μs, and λn / 2 is 0.925 μs. Here, if Dp1=AL=2.62 μs, and Dp2 of the ejection waveform of the second drop is 2.31 μs, the time interval between (22) and (4) is 2.775 μs, which is three times the half period of the parasitic vibration. Therefore, in order to mitigate the increase in the meniscus pull-in amount of the second drop due to the residual vibration of the parasitic vibration generated in (4) and to reduce the possibility of air bubble entrainment, Dp2 ≠ 2.31 μs should be set. In other words, Dp2 should be adjusted so that it is larger or smaller than 2.31 μs and the ejection speed of the second drop is equal to or greater than that of the first drop. It is also possible to adjust the time interval between (22) and (4) so ​​that it does not coincide with an odd multiple of the half period of the parasitic oscillation by making the time interval Dp1, rather than the time interval Dp2, larger or smaller than AL.

[0111] Here, when droplets are continuously discharged, the droplets discharged from the nozzle 51 do not separate immediately, but continue for a while in the form of a constricted liquid column. The constrictions between the droplets cause the droplets to affect each other and change their speed. In addition, after the droplets are separated, the satellite of the preceding droplet merges with the succeeding droplet, changing the speed of each droplet. As a result, the speed of the succeeding droplet may become slower than that of the preceding droplet. In this case, it is necessary to adjust the speed of each droplet by making Dp1 a value that deviates from AL compared to the time width DpN of the other discharge waveforms. If the time widths DpN of all the discharge waveforms are time widths that deviate from AL, the voltage required for droplet discharge increases, and the power consumption of the head also increases accordingly. Therefore, in order to reduce power consumption, it is desirable that the time width Dp of any one of the discharge waveforms of the time widths DpN of the multiple discharge waveforms that discharge droplets is close to AL, and more preferably, it is desirable that any one of the time widths DpN is equal to AL.

[0112] Next, an example of the cancel waveform will be specifically described with reference to FIG. 6. For ease of description, in FIG. 6, the first to fourth potential difference changes in the ejection waveform of the second drop, which is the final drop, are designated as (21) to (24), and the first to fourth potential difference changes in the cancel waveform are designated as (11) to (14), and the following description will be given. Also, the following description will be given with the reference point of the phase of the ejection waveform of 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 of the second drop is set to the middle of the potential difference changes (22) and (23), and the reference point (0') of the phase of the cancel waveform is set to the middle of the potential difference changes (12) and (13). Also, in the example of FIG. 6, the voltage drop time tf is set to be substantially the same as the voltage rise time tr.

[0113] First, the main acoustic vibration of the ejection waveform will be described. In the ejection waveform, 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. The vibration generated by this is a vibration with a phase lead of -π+(Dp+Tm) / 2. Furthermore, when the potential difference is changed as shown in (22), the vibration in (22) is a vibration with a phase lead of -π+(Dp-Tm) / 2. The composite wave of (21) and (22) is a vibration with a phase lead of -π+Dp / 2.

[0114] The potential difference changes (23) and (24) which are for contracting the pressure chamber 46 are opposite to the potential difference changes (21) and (22) which are for expanding the pressure chamber 46, so the pressure chamber 46 contracts and pressurizes the inside of the pressure chamber 46. Therefore, (23) is a vibration with a phase lead of -(Dp-Tm) / 2. Also, (24) can be considered to be a vibration with a phase lead of -(Dp+Tm) / 2. Therefore, the composite wave of (23) and (24) is a vibration with a phase lead of -Dp / 2.

[0115] If we assume a composite wave of (21), (22), (23), and (24) at time (0''), the composite wave of (21), (22), (23), and (24) will be an oscillation with a phase lead of -π / 2.

[0116] Next, the main acoustic vibration of the cancellation waveform will be described. In the cancellation waveform, when the potential difference is changed 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 has a phase lead of -π+(Cp1+Tm) / 2. 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.

[0117] The potential difference changes (13) and (14) which are for contracting the pressure chamber 46 are opposite to the potential difference changes (11) and (12) which are for expanding the pressure chamber 46, so the pressure chamber 46 contracts and pressurizes the inside of the pressure chamber 46. Therefore, (13) is a vibration with a phase lead of -(Cp1-Tm) / 2. Also, (14) is a vibration with a phase lead of -(Cp+Tm) / 2. Therefore, the composite wave of (13) and (14) is a vibration with a phase lead of -Cp / 2.

[0118] If we assume a composite wave of (11), (12), (13), and (14) at time (0'), the composite wave of (11), (12), (13), and (14) will be an oscillation with a phase lead of -π / 2.

[0119] For this reason, if the time difference (time interval) between (0'') and (0') is made an odd multiple of π / 2 (AL), the composite wave of (21), (22), (23), and (24) will be in phase with the composite wave of (11), (12), (13), and (14), and will weaken each other. Furthermore, by adjusting the time width Cp1 of (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 (21), (22), (23), and (24) can be canceled out by the composite wave of (11), (12), (13), and (14).

[0120] From the above, it is possible to cancel out the residual vibration caused by the composite wave of (21), (22), (23), and (24) by setting the time difference between (0'') and (0') to 1 AL; however, if the time difference between (0'') and (0') is set to 1 AL, the residual vibration will be canceled out during droplet ejection by inputting the ejection waveform, weakening the ejection force of the droplets. 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 3 AL or more.

[0121] In addition, the time interval between (11), (12) when the pressure chamber is depressurized is Tm, and the time interval between (13), (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.

[0122] As described above, by setting the cancel waveform to a cancel waveform with a Cp width in which the intermediate voltage holding time Tm is half the period λn of the parasitic vibration for the final drop's ejection waveform, the cancel waveform can suppress both the residual vibration of the main acoustic vibration caused by the ejection waveform for the final drop and the parasitic vibration caused by the cancel waveform. This makes it possible to reduce the influence of the residual vibration and parasitic vibration caused by the main acoustic vibration on the droplets ejected by the first ejection waveform in the next drive waveform input after inputting the cancel waveform.

[0123] The cancel waveform may be a potential difference change with a different polarity from the ejection waveform, for example, a negative polarity. For example, FIG. 17 shows an example of a cancel waveform with a negative potential difference change as another embodiment. In the example shown in FIG. 17, the pressure chamber contracts due to the negative potential difference change at (11) and (12), and the pressure chamber returns to its original state due to the potential difference change at (13) and (14). In such a cancel waveform, the potentials from (12) to (13) are the lowest potentials in the drive waveform, so these are set as the ground voltage, and the other potentials have a potential higher than the ground voltage. Also, in the example of FIG. 17, there are four potential differences with a potential higher than the ground voltage in each ejection waveform and cancel waveform. Therefore, when such a cancellation waveform is used, for example, 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.

[0124] In addition, when the pressure chamber expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to reduce 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, and then, when the pressure chamber 46 contracts during ejection, the voltage (potential difference) is increased in two steps to reduce the pressure chamber. The cancel waveform reduces the pressure chamber in two steps by increasing the voltage (potential difference), and then, when the pressure chamber 46 expands, the voltage (potential difference) is reduced in two steps to expand 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 to just before the pressure chamber contraction starts is the lowest potential in the drive waveform, so these are set as ground voltages, and the other potentials have potentials higher than the ground voltage.

[0125] In the cancellation waveform of the example in Fig. 17, the reference point of the phase between (12) and (13) of the cancellation waveform is set to (0'), and the main acoustic vibration will be described 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 cancellation waveform in the example in Fig. 6, and the composite wave of (11), (12), (13), and (14) will be a vibration with a phase lead of π / 2.

[0126] For this reason, if the time difference between (0'') and (0') is set to an even multiple of π / 2(AL), for example 2AL, then the composite wave of (21), (22), (23), and (24) and the composite wave of (11), (12), (13), and (14) will be in phase with each other and will weaken each other. Furthermore, by adjusting the time width Cp 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 (21), (22), (23), and (24) can be canceled out by the composite wave of (11), (12), (13), and (14). In addition, 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.

[0127] Next, the condition of Tm where parasitic vibrations of period λn cancel each other out in the cancellation waveform will be explained. First, the vibration of period λn generated in the waveform (11) at the first potential difference change is A11, and the vibration vector of A11 after time Tm is A11'. The vibration vector of period λn generated in the waveform (12) at the second potential difference change after Tm is A12. Since the waveforms (11) and (12) are both rising waveforms in FIG. 6, the absolute value of the composite vector of A11' and A12 is minimum when Tm is an odd multiple of λn / 2 (phase difference between A11' and A12 is 180 degrees). When the condition where the absolute value of the composite vector of A11' and A12 is smaller than the larger absolute value of A11' and A12 is found from the formula for the composition of simple harmonic motion of period λn, the phase difference between the vibration vectors A11' and A12 is within 180 degrees ±60 degrees.

[0128] 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 (Equation 6) Here, k is an odd number equal to or greater than 1.

[0129] By setting Tm under the above conditions, it is possible to reduce the effect of residual vibration due to parasitic vibration on the next droplet discharged after the cancellation waveform. The conditions under which the vibrations of period λn weaken each other are the same as those described above for the falling waveforms (13) and (14) in Fig. 6, the falling waveforms (11) and (12) in Fig. 17, and the rising waveforms (13) and (14) in Fig. 17.

[0130] In the example of FIG. 6, the time interval between (0'') and (0') when the residual vibration of the ejection waveform is cancelled out by the cancellation waveform is 3AL. If the cancellation waveforms ((11), (12), (13), and (14)) are first depressurized and then pressurized like the ejection waveforms ((21), (22), (23), and (24)), the condition for the composite wave of (21), (22), (23), and (24) 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 / 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.

[0131] In the example of FIG. 17, the time interval between (0'') and (0') is 2AL. However, the cancellation waveforms ((11), (12), (13), and (14)) are opposite to the ejection waveforms ((21), (22), (23), and (24) in that they first pressurize and then depressurize. Therefore, the condition for the composite wave of (21), (22), (23), and (24) 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, as follows: (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.

[0132] In the example of FIG. 6, a cancel waveform that first reduces pressure and then increases pressure, like the ejection waveform, and in the opposite case of the ejection waveform of FIG. 17, a cancel waveform that first increases pressure and then reduces pressure, adjusting the time interval between (0'') and (0') as in the above condition and adjusting the Cp width can reduce the effect 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 the ejection of droplets by the ejection waveform is canceled by the pressure vibration by the cancel waveform, and the residual vibration by the ejection waveform is reduced. Note that when the ink viscosity is high, the attenuation of the residual vibration after the ejection of droplets by the ejection waveform is large, so the cancel width Cp is adjusted to be smaller accordingly. However, the cancel width Cp cannot be made less than Tm+Tr.

[0133] By setting a cancel waveform with a Cp width such that the intermediate voltage holding time Tm is half the period λn of the parasitic vibration for the ejection waveform, the 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. Therefore, the liquid ejection head 1 can reduce the influence of the residual vibration caused by the main acoustic vibration on the next ejected droplet after the cancel waveform. In addition, because the cancel waveform can suppress the parasitic vibration generated by the cancel waveform, it can suppress the residual vibration caused by the parasitic vibration from affecting the droplet ejected by the next ejection waveform.

[0134] In addition, 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.

[0135] According to the liquid ejection head 1 of the embodiment described above, the Dp of adjacent ejection waveforms among a plurality of ejection waveforms that are applied in succession with a predetermined time interval between them is adjusted. By using such driving waveforms, the liquid ejection head 1 can make the ejection speed of the subsequently ejected ink faster or faster than the ejection speed of the previously ejected droplets when ejecting a plurality of ink droplets in succession.

[0136] Note that the embodiment is not limited to the above-mentioned example. For example, in the above-mentioned example, as an example of a multi-drop driving waveform, an example of a driving waveform for ejecting droplets twice as an example of ejecting droplets multiple times was described using FIG. 6, but the number of drops N of multi-drop may be 2 or more. That is, in the driving waveform, an ejection waveform for Ndrops is input to the actuator 20 in a period of an even multiple of AL, for example, 2AL, and the time width DpN of each ejection waveform is adjusted so that the ejection speed of each drop is equal to or greater than that of the first drop. More preferably, the time width DpN of each ejection waveform is adjusted so that the ejection speed of each Ndrop is equal to or greater than that of the N-1th drop. By using a driving waveform with DpN adjusted in this way, the liquid ejection head 1 can reduce the change in the ejection speed of droplets due to the number of drops N, suppress the deviation of the landing position when the droplets land on the medium, and suppress the deterioration of the print quality.

[0137] Next, an example of a drive waveform with three drops will be described with reference to FIG. 16. For example, FIG. 16 shows an example of a drive waveform when three drops are continuously ejected. Note that the cancel waveform is omitted in the drive waveform of FIG. 16. Note that for ease of explanation, the first to fourth potential difference changes in the ejection waveform for the third drop in FIG. 16 are (31) to (34) in the following description. Also, the reference point of the phase of the ejection waveform for the third drop is (0''') in the following description. Note that here, the reference point of the phase of the ejection waveform for the third drop (0''') is set to the midpoint between the potential difference changes (32) and (33). Also, the voltage drop time tf in the figure is set to be approximately the same as the voltage rise time tr. In addition, the amount of change in the potential difference between (1) and (2), the amount of change in the potential difference between (21) and (22), and the amount of change in the potential difference between (31) and (32) are made approximately the same, and the amount of change in the potential difference between (3) and (4), the amount of change in the potential difference between (23) and (24), and the amount of change in the potential difference between (33) and (34) are also made approximately the same.

[0138] In the 3-drop ejection waveform, for example, the moment when the negative pressure caused by the main acoustic vibration before ejection is strongest is the moment (32). As a result, the pulling force on the nozzle meniscus is strongest at the moment (32), increasing the possibility of air bubble entrainment.

[0139] As shown in the waveform of Figure 16, if the time interval between (32) and (24) is adjusted so that it does not coincide with an odd multiple of the half period of the parasitic vibration, it is possible to mitigate the phenomenon in which the negative pressure at the time point (32) becomes even larger due to the residual vibration of the parasitic vibration generated at (24). As a result, it is possible to mitigate the increase in the amount of meniscus pull-in at the third drop due to the residual vibration of the parasitic vibration generated at (24), and the possibility of air bubble entrainment can be reduced.

[0140] This is also true for Ndrop, which is any one of the multiple drops. That is, the time interval between the time of the final pressurization of the N-1drop ejection waveform and the time of the time when the negative pressure due to the main acoustic vibration becomes maximum at the final decompression of the Ndrop ejection waveform should be adjusted so as not to match an odd multiple of the half period of the parasitic vibration. This can mitigate the phenomenon in which the negative pressure becomes even larger at the time when the negative pressure due to the main acoustic vibration becomes maximum in the Ndrop ejection waveform due to the residual vibration of the parasitic vibration generated at the final pressurization of the N-1drop ejection waveform. As a result, the multi-drop driving waveform can mitigate the increase in the meniscus retraction amount of the Ndrop due to the residual vibration of the parasitic vibration generated at the final pressurization of the N-1drop ejection waveform, and can reduce the possibility of air bubble entrainment.

[0141] Next, as an example, a case where 2AL=5.24 μs, the period λn of the parasitic vibration is 1.85 μs, and λn / 2 is 0.925 μs will be described. Here, as a result of the speed adjustment of the second drop, Dp2 is set to 2.52 μs. In this case, if Dp3 is set to 2.41 μs, the time interval between (32) and (24) becomes 2.775 μs, which is three times the half period of the parasitic vibration. Therefore, in order to mitigate the increase in the meniscus pull-in amount of the second drop due to the residual vibration of the parasitic vibration generated in (24) and to reduce the possibility of air bubble entrainment, Dp3 ≠ 2.41 μs should be set. That is, Dp3 should be adjusted to a value larger or smaller than 2.41 μs, and Dp3 should be adjusted so that the ejection speed of the third drop is equal to or greater than that of the first drop. More preferably, Dp3 should be adjusted so that the ejection speed of the third drop is equal to or greater than that of the second drop.

[0142] As another example, a case will be described in which, when 2AL=5.24 μs, the period λn of the parasitic vibration is 1.85 μs, and λn / 2 is 0.925 μs, and Dp2 is set to 2.72 μs, which is larger than AL, as a result of adjusting the speed of the second drop. In this case, if Dp3 is set to 2.21 μs, the time interval between (32) and (24) becomes 2.775 μs, which is three times the half period of the parasitic vibration. Therefore, in order to mitigate the increase in the amount of meniscus drawn in at the second drop due to the residual vibration of the parasitic vibration generated at (24) and to reduce the possibility of air bubble entrainment, Dp3 ≠ 2.21 μs should be set. That is, Dp3 should be adjusted to a value larger or smaller than 2.21 μs, and Dp3 should be adjusted so that the ejection speed of the third drop is equal to or greater than that of the first drop. More preferably, Dp3 should be adjusted so that the ejection speed of the third drop is equal to or greater than that of the second drop.

[0143] 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.

[0144] 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 with reference to Figures 18 and 19.

[0145] 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 the h-1th potential difference changes is the i-th potential difference change, one of the i+1th to the hth potential difference changes is the j-th potential difference change, and the time interval between the start time of the i-th and j-th potential difference changes is Tij, then either of the time intervals Tij is: (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (Equation 7) Here, k is an odd number equal to or greater than 1.

[0146] According to the ejection waveform satisfying the formula 7, the parasitic vibrations of the period λn generated by the corresponding two or more potential difference changes weaken each other, and the parasitic vibrations of the period λn generated in the pressure chamber can be suppressed. This also applies when the number of times the pressure chamber 46 is reduced is h times, which is three or more times.

[0147] In addition, when i+1=j, that is, when Tij is the time interval between successive potential difference changes, taking into consideration the reduction in power consumption, the time interval Tij is (k / 2-1 / 6)λn ≦ Tij ≦ kλn / 2 (Equation 8) Here, k is an odd number equal to or greater than 1.

[0148] Furthermore, when the ejection waveform has 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) in all potential difference changes from the 1st to the hth, or when 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.

[0149] Furthermore, by making the amount of change in potential difference the same for the i-th and j-th potential difference changes that results in a time interval Tij that satisfies (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (k is an odd number equal to or greater than 1), it is possible to further suppress residual vibrations resulting from subsequent parasitic vibrations. More preferably, since the optimal holding time for each stage when it is assumed that the potential difference at each stage is the same and the pressure vibration does not attenuate is λn / number of stages (h), the time interval Tij for all successive potential difference changes should be set to λn / number of stages (h).

[0150] Furthermore, from the viewpoint of reducing power consumption by making the main acoustic vibrations reinforce each other, when the number of potential difference changes that continuously expand and change the pressure chamber is two or more times, that is, h times, it is desirable that the time interval Tij between the first potential difference change and the hth potential difference change is 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 will reinforce each other, which contributes to reducing power consumption.

[0151] As an example of the above-mentioned discharge waveform, FIG. 18 shows an example in which the number of steps (number of times) of the rising waveform is four (four times), and FIG. 19 shows an example in which the number of steps of the rising waveform is three. In FIG. 18, the number of steps, h, is shown in parentheses. It goes without saying that the same can be done for the falling waveform. As shown in these FIG. 18 and FIG. 19, the optimal holding time of each step when it is assumed that the potential difference of each step is the same and the pressure vibration is not attenuated is λn / step number (h). Therefore, if the phase difference (time interval) of any two of the potential difference displacements from the 1st step to the hth step 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 weaken each other. For example, the time interval between the first and third potential difference displacements in FIG. 18 is λn / 2, and Tij when i=1&j=3 satisfies Equation 7. In addition, the time interval between the second and fourth potential difference displacements in Fig. 18 is also λn / 2, and Tij in the case of i=2&j=4 also satisfies Equation 7. Therefore, the parasitic oscillations weaken each other.

[0152] The pressure vibration in the pressure chamber 46 attenuates over time due to the viscous resistance of the ink. Also, parasitic vibrations usually attenuate over time more than main acoustic vibrations. For this reason, 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 in the time range 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 (the range in which the above-mentioned main acoustic vibrations constructively interact) has a greater effect on satellites and print quality than the change in potential difference in the time range before 1.5AL. Therefore, it is desirable to adjust the value of Tm or Tij of the ejection waveform so that the condition in which parasitic vibrations destructively interact is satisfied for Tm or Tij closer to immediately before and after ejection, out of the time intervals between any two potential difference changes.

[0153] Next, a cancellation waveform will be described among the driving waveforms according to another embodiment. In the cancellation waveform of the liquid ejection 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+1th 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, as with the ejection waveform, either of the time intervals Tij is: (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (Equation 7) Here, k is an odd number equal to or greater than 1.

[0154] According to the cancellation waveform satisfying the formula 7, the parasitic vibrations of the period λn generated by the corresponding two or more potential difference changes are weakened, and the parasitic vibrations of the period λn generated in the pressure chamber can be suppressed. This is also true when the number of times the pressure chamber 46 is reduced is three or more times, that is, h times. Note that, in the cancellation waveform, the suppression of residual vibration is prioritized, and the time interval Tij is not limited to the range of the formula 8.

[0155] Furthermore, if the cancellation waveform includes other potential difference changes in which 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 1st to the hth, the parasitic vibration of period λn occurring in the pressure chamber 46 can be further suppressed.

[0156] Furthermore, by making the amount of change in potential difference the same for the i-th and j-th potential difference changes that results in a time interval Tij that satisfies (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn (k is an odd number equal to or greater than 1), it is possible to further suppress residual vibrations resulting from subsequent parasitic vibrations. More preferably, since the optimal holding time for each stage when it is assumed that the potential difference at each stage is the same and the pressure vibration does not attenuate is λn / number of stages (h), the time interval Tij for all successive potential difference changes should be set to λn / number of stages (h).

[0157] As an example of the above-mentioned cancellation waveform, FIG. 18 shows an example in which the number of steps (number of times) of the rising waveform is four (four times) like the ejection waveform, and FIG. 19 shows an example in which the number of steps of the rising waveform is three. In FIG. 18, the number of steps, h, is shown in parentheses. It goes without saying that the same can be done for the falling waveform. As shown in these FIG. 18 and FIG. 19, the optimal holding time of each step when it is assumed that the potential difference of each step is the same and the pressure vibration is not attenuated is λn / step number (h). Therefore, if the phase difference (time interval) of any two of the potential difference displacements from the 1st step to the hth step 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 weaken each other. For example, the time interval between the first and third potential difference displacements in FIG. 18 is λn / 2, and Tij when i=1&j=3 satisfies Equation 7. In addition, the time interval between the second and fourth potential difference displacements in Fig. 18 is also λn / 2, and Tij in the case of i=2&j=4 also satisfies Equation 7. Therefore, the parasitic oscillations weaken each other.

[0158] The pressure vibrations in the pressure chamber 46 attenuate over time due to the viscous resistance of the ink. Also, parasitic vibrations usually attenuate over time more than main acoustic vibrations. For this reason, the closer the potential difference displacement is to the next ejection waveform, i.e., the closer the potential difference displacement is to the end of the cancellation waveform, the greater the effect of the residual vibrations on the next ejection waveform. Therefore, it is desirable to adjust the value of Tm or Tij for the potential difference displacement closer to the end of the cancellation waveform so as to satisfy the condition for the parasitic vibrations to cancel each other out.

[0159] For example, since the period λn of the parasitic vibration is smaller than the period 2AL of the main acoustic vibration, the parasitic vibration due to the potential difference displacement input before 2AL from the end of the cancellation waveform is expected to be greatly attenuated at the end of the cancellation waveform. Therefore, it is desirable to adjust the value of Tm or Tij so that the condition in which the parasitic vibrations cancel each other is satisfied preferentially for the potential difference change within 2AL from the end of the cancellation waveform. Also, it is desirable to adjust the value of Tm or Tij so that the condition in which the parasitic vibrations cancel each other is satisfied preferentially for the potential difference change within λn of the parasitic vibration from the end of the cancellation waveform than within 2AL from the end of the cancellation waveform.

[0160] According to at least one of the embodiments of the liquid ejection head described above, the Dp of adjacent ejection waveforms among a plurality of successive ejection waveforms that are spaced apart by a predetermined time is adjusted, so that when the liquid ejection head ejects a plurality of ink droplets in succession, the ejection speed of the subsequently ejected ink droplets can be made equal to or faster than the ejection speed of the previously ejected droplets.

[0161] Although some 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 implemented 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 in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0162] 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, 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...housing, 112...medium supply section, 113...image forming section, 114...medium discharge section, 115...transport device, 117...support section, 118...transport bell , 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...type sensor, 200...externally connected device, 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 ejecting 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 for ejecting a plurality of droplets from the nozzle; the ejection waveform 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, the driving 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 is generated by changing the potential difference, by changing the potential difference at least once after the change of the potential difference; A liquid ejection head, wherein the intervals between the plurality of ejection waveforms are substantially the same as a period of a main acoustic vibration frequency.

2. 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 which are expansions or contractions of the volume of the pressure chamber, one of the 1st to (h-1)th 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, that is, 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.

3. The time interval Tij is (k / 2-1 / 6)λn ≦ Tij ≦ kλn / 2 3. The liquid ejection head according to claim 2, wherein k in this formula is an odd number equal to or greater than 1.

4. 3. The liquid ejection head according to claim 2, wherein the time interval between the two ejections is within a range from the ejection of the liquid to 1.5 times a half period of the main acoustic vibration.

5. the expanding potential difference, the intermediate potential difference, and the contracting 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 reducing 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 the main acoustic resonance frequency, which is equal to or greater than approximately three times the main acoustic resonance frequency.

7. A liquid ejection head as described in claim 1, wherein the time width of the multiple ejection waveforms 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.

8. 2. A liquid ejection head as described in claim 1, wherein the time interval between the input point of the last expansion potential difference of any one of the plurality of ejection waveforms and the input point of the last reduction potential difference of the previous ejection waveform does not coincide with an odd multiple of a half period of vibration of an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency.

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