Liquid ejection head

Abstract

To provide a liquid discharge head capable of suppressing deterioration in print quality while making a drive frequency high.SOLUTION: A liquid discharge head comprises a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate comprises a nozzle. The pressure chamber discharging liquid communicates with the nozzle. The actuator varies capacity of the pressure chamber according to an electric signal. The drive circuit generates the electric signal driving the actuator. A drive waveform that the drive circuit outputs has a discharge pulse part having a plurality of pulses in cycles 1.8 to 2.2 times as long as a pressure propagation time. The discharge pulse part has a first pulse having a contraction element and a second pulse having a contraction element which is different from the contraction element of the first pulse and 0.5 to 1.5 times as long as the pressure propagation time.SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] Conventionally, liquid ejection methods using liquid ejection heads that eject liquid include continuous methods and on-demand piezo methods. The continuous method ejects liquid continuously even when not printing, and when not printing, the ink is bent by a deflection electrode so that it does not print on the medium. The continuous method has a high print drive frequency, but has a complex structure and wastes a lot of ink. The piezo method prints by applying a drive waveform to a piezoelectric element to operate it, changing the capacity of the pressure chamber in the liquid ejection head. The piezo method does not waste ink, but it is difficult to increase the drive frequency.

[0003] One method of providing ejection control signals to a piezo-type liquid ejection head is to transfer setting data such as drive waveforms to the head drive circuit in advance, and then transfer print image data line by line to the head drive circuit in accordance with the print synchronization signal for each line. Gradation is achieved by controlling the number of drops and ejection volume of each nozzle on each line.

[0004] The drive waveform is composed of ejection pulses on a line-by-line basis, pre-drive boost pulses, and cancel pulses that cancel out pressure vibrations. However, as speeds increase, the time for each line (line time) becomes shorter, leaving less time to insert boost pulses, cancel pulses, etc. If the time from the end of the pulse for each line to the start of the pulse for the next line (inter-cycle delay) becomes shorter, there is a risk that the pressure vibrations that were not completely canceled out will not be sufficiently attenuated, resulting in crosstalk that will degrade print quality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4764038 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-35271 [Patent Document 3] Japanese Patent Application Publication No. 10-296976 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid ejection head that can increase the drive frequency while suppressing degradation in print quality. [Means for solving the problem]

[0007] The liquid ejection head of the embodiment includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate includes a nozzle. A pressure chamber that ejects liquid communicates with the nozzle. The actuator changes the volume of the pressure chamber in response to an electric signal. The drive circuit generates an electric signal that drives the actuator. The drive waveform output by the drive circuit has an ejection pulse portion that includes multiple pulses at a period that is 1.8 to 2.2 times the pressure propagation time. The ejection pulse portion includes a first pulse that includes a contraction element, and a second pulse that has a contraction element that is different from the contraction element of the first pulse and has a length that is 0.5 to 1.5 times the pressure propagation time. The first pulse has multiple pulses PA, and the second pulse has one or more pulses PB and one or more pulses PC, and the contraction element of the pulse PB is shorter than the contraction element of the pulse PA, and the contraction element of the pulse PC is shorter than the contraction element of the pulse PB. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing the configuration of a liquid ejection head according to an embodiment, with some parts omitted. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a liquid ejection head according to the embodiment, with some parts omitted. [Figure 3] FIG. 2 is a cross-sectional view showing the configuration of a liquid ejection head according to the embodiment, with some parts omitted. [Figure 4] FIG. 1 is an explanatory diagram showing the configuration of a liquid ejection apparatus using a liquid ejection head according to an embodiment. [Figure 5] FIG. 1 is a block diagram showing an example of the configuration of a liquid ejection apparatus according to an embodiment. [Figure 6] FIG. 10 is an explanatory diagram showing an example of a driving waveform of a comparative example. [Figure 7] FIG. 10 is an explanatory diagram showing an example of a driving waveform in Comparative Example 1. [Figure 8] FIG. 10 is an explanatory diagram showing the relationship between the inter-cycle delay and the ejection speed in a comparative example. [Figure 9] FIG. 10 is an explanatory diagram showing an example of a driving waveform in Comparative Example 2. [Figure 10] FIG. 3 is an explanatory diagram showing an example of a driving waveform according to the first embodiment. [Figure 11] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to the second embodiment. [Figure 12] FIG. 10 is an explanatory diagram showing an example of a driving waveform according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] 1 to 3, 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, a frame member 60, and a drive circuit 70.

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

[0012] The actuator 20 is a piezoelectric member including, for example, a plurality of piezoelectric pillars 21 and non-driven piezoelectric pillars 22 arranged alternately with the plurality of piezoelectric pillars 21. The actuator 20 is formed in a comb shape by arranging the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 in one direction at a predetermined interval. For example, such an actuator 20 is formed by dicing a stacked piezoelectric member bonded to the base 10 from the end face opposite the base 10 side to form a plurality of rectangular pillar-shaped piezoelectric elements at predetermined intervals for each piezoelectric member. The formed plurality of piezoelectric elements are then provided with electrodes or the like to form the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 arranged alternately as piezoelectric elements. That is, the actuator 20 is divided at one end side by the formed plurality of grooves 23, and the other end side (the base 10 side) is connected. That is, the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 are arranged in parallel alternately with the grooves 23 between them along one direction (first direction).

[0013] The laminated piezoelectric member that constitutes the actuator 20 is formed by stacking and sintering sheet-shaped piezoelectric materials. The actuator 20 is not limited to a laminated piezoelectric member. For example, the actuator 20 may be a chip type, a multi-stage chip type, or other configuration. In other words, the actuator 20 may be of a piezoelectric type that can vary the volume of a pressure chamber.

[0014] 1 to 3, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 are, for example, laminated piezoelectric elements serving as driving elements. The piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 each include a plurality of laminated piezoelectric layers 211, a dummy layer 212 on the base 10 side, and internal electrodes 221 and 222 and external electrodes 223 and 224 formed on the main surfaces of the piezoelectric layers 211. As an example, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 have the same configuration.

[0015] The piezoelectric layers 211 are formed in the form of thin plates from piezoelectric materials such as PZT (lead zirconate titanate) or lead-free KNN (potassium sodium niobate). The multiple piezoelectric layers 211 are stacked in the thickness direction (second direction) and bonded by sintering. Note that the stacking direction (second direction) of the multiple piezoelectric layers 211 is perpendicular to the arrangement direction (first direction) of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22.

[0016] The internal electrodes 221, 222 are conductive films formed into a predetermined shape using a sinterable conductive material such as silver-palladium. The internal electrodes 221, 222 are formed in predetermined regions on the main surface of each piezoelectric layer 211. The internal electrodes 221, 222 have opposite polarities. For example, as shown in FIG. 3, one internal electrode 221 is formed in a region that reaches one end of the piezoelectric layer 211 but does not reach the other end of the piezoelectric layer 211 in a direction (third direction) that is perpendicular to both the arrangement direction (first direction) of the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 and the stacking direction (second direction) of the piezoelectric layer 211. The other internal electrode 222 is formed in a region that does not reach one end of the piezoelectric layer 211 but reaches the other end of the piezoelectric layer 211 in the third direction, as shown in FIG. 3. The internal electrodes 221 and 222 are connected to external electrodes 223 and 224 formed on the side surfaces of the piezoelectric pillars 21 and 22, respectively.

[0017] The external electrodes 223, 224 are formed on the surfaces of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22, and are configured by collecting the ends of the internal electrodes 221, 222. For example, the external electrodes 223, 224 are formed on one end face and the other end face in a third direction perpendicular to the stacking direction of the piezoelectric layer 211. The external electrodes 223, 224 are formed by depositing Ni, Cr, Au, or the like using a known method such as plating or sputtering. The external electrodes 223 and 224 have different polarities. The external electrodes 223 and 224 are disposed on different side surfaces of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22, respectively. Note that the external electrodes 223 and 224 may be routed to different regions of the same side surfaces of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22.

[0018] In this embodiment, as an example, the external electrode 223 is an individual electrode, and the external electrode 224 is a common electrode. The external electrodes 223, which serve as individual electrodes for the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22, have electrode layers divided by grooves 23 and are arranged independently of each other. The external electrode 224, which serves as a common electrode, has electrode layers connected to each other in a region closer to the base 10 than the grooves 23, and is, for example, grounded.

[0019] The external electrodes 223, 224 are connected to, for example, a drive circuit 70. For example, each of the external electrodes 223, 224 is connected by wiring to a control unit 150 as a drive unit via a driver 723 (described later) of the drive circuit 70, and is configured to be drive-controllable by control by a processor 151.

[0020] The dummy layer 212 is made of the same material as the piezoelectric layer 211. The dummy layer 212 has an electrode on only one side, and is not subjected to an electric field, so it does not deform. In other words, the dummy layer 212 does not function as a piezoelectric body, but serves as a base for fixing the actuator 20 to the base 10, or as a polishing allowance for polishing to achieve precision during and after assembly.

[0021] As an example, each piezoelectric pillar 21 and each non-driven piezoelectric pillar 22 has 50 or less laminated piezoelectric layers 211, each layer has a thickness of 10 μm to 40 μm, and the product of the thickness and the total number of laminated layers is less than 1000 μm.

[0022] When a voltage is applied to the internal electrodes 221 and 222 via the external electrodes 223 and 224, the piezoelectric pillars 21 and the non-driven piezoelectric pillars 22 vibrate longitudinally along the stacking direction of the piezoelectric layer 211. The longitudinal vibration here refers to, for example, "vibration in the thickness direction defined by the piezoelectric constant d33." For example, as shown in FIG. 2, every other piezoelectric pillar 21 is arranged corresponding to the pressure chamber 31 with the vibration plate 30 interposed therebetween, and the remaining non-driven piezoelectric pillars 22 are arranged in positions facing the partition wall 42 with the vibration plate 30 interposed therebetween.

[0023] 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 31. The non-driven piezoelectric pillars 22 are disposed in positions facing the partition walls 42. No voltage is applied to the non-driven piezoelectric pillars 22.

[0024] The vibration plate 30 is bonded to one side in the stacking direction of the piezoelectric layers 211 of the multiple piezoelectric pillars 21, 22, i.e., the surface on the nozzle plate 50 side. The vibration plate 30 is configured to be deformable, for example. The vibration plate 30 is bonded to the piezoelectric pillars 21 and non-driven piezoelectric pillars 22 of the actuator 20 and to the frame member 60.

[0025] The vibration plate 30 is, for example, a flat plate arranged so that the thickness direction is the stacking direction of the piezoelectric layers 211. The surface direction of the vibration plate 30 extends in the direction in which the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22 are arranged. The vibration plate 30 is, for example, a metal plate. The vibration plate 30 has multiple vibration parts that face each pressure chamber 31 and can be displaced individually. The vibration plate 30 is formed by integrally connecting the multiple vibration parts.

[0026] 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 as a SUS plate, for example. The thickness of the vibration plate 30 is configured to be approximately 5 μm to 15 μm. Note that the vibration plate 30 may have folds or steps formed in areas adjacent to the vibration parts or between adjacent vibration parts so that the multiple vibration parts can be easily displaced.

[0027] The vibration plate 30 deforms the pressure chamber 31 and changes the volume of the pressure chamber 31 by displacing the part of the vibration plate 30 opposite the piezoelectric pillar 21 due to the expansion and compression of the piezoelectric pillar 21 caused by the longitudinal vibration of the piezoelectric pillar 21.

[0028] The vibration plate 30 is bonded to the end faces of the piezoelectric pillars 21, 22 on one side in the second direction and to the end face of the frame member 60. As an example, in this embodiment, the main surface of the vibration plate 30 on one side in the second direction is bonded to the flow path plate 40. A pressure chamber 31 capable of accommodating ink and a guide flow path 34 are formed between the vibration plate 30 and the flow path plate 40. The main surface of the vibration plate 30 on the other side in the second direction is bonded to the piezoelectric pillars 21, 22. In addition, the main surface of the vibration plate 30 on the other side in the second direction is bonded to the end face of the frame member 60.

[0029] The vibration plate 30 forms a common chamber 32 capable of containing ink between itself and the frame member 60. One main surface of the vibration plate 30 faces the piezoelectric pillars 21, 22, the frame member 60, and the common chamber 32, respectively, and the other main surface faces the pressure chamber 31, the partition wall portion 42, and the guide flow path 34, respectively.

[0030] The vibration plate 30 has a plurality of openings 33 that penetrate through the thickness direction and communicate between the pressure chambers 31 and the common chamber 32. The plurality of openings 33 communicate between the plurality of pressure chambers 31 formed on one side in the thickness direction of the vibration plate 30 and the common chamber 32 formed on the other side in the thickness direction of the vibration plate 30. The vibration plate 30 deforms in accordance with the deformation of the piezoelectric pillars 21, thereby changing the volume of the pressure chambers 31.

[0031] The flow path plate 40 is bonded to one side of 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 forms predetermined flow paths 35. The flow path plate 40 includes a frame-shaped portion 41 bonded to the outer edge of the vibration plate 30, a plurality of partition wall portions 42 that separate the plurality of flow paths 35, and a guide wall 43 that forms the guide flow paths 34.

[0032] The specified flow path 35 includes a plurality of pressure chambers 31 separated by partition portions 42, a common chamber 32, a plurality of openings 33 in the vibration plate 30, and a plurality of guide flow paths 34 separated by partition portions 42 that connect the pressure chambers 31 and the openings 33.

[0033] The multiple pressure chambers 31 are aligned in a first direction, which is the alignment direction of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22. The multiple pressure chambers 31 aligned in one direction are separated by partition walls 42. One side of the multiple pressure chambers 31 in the second direction is closed by the vibration plate 30. The multiple pressure chambers 31 are formed on the side of the vibration plate 30 opposite to the side on which the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22 are provided. Each pressure chamber 31 communicates with a nozzle 51 formed in a nozzle plate 50 arranged on the opposite side from the vibration plate 30 in the second direction.

[0034] The multiple pressure chambers 31 communicate with the common chamber 32 via guide channels 34 and openings 33. The pressure chambers 31 hold liquid supplied from the common chamber 32 via the guide channels 34, and are deformed by vibration of the vibration plate 30 that forms part of the pressure chambers 31, thereby ejecting the liquid from the nozzles 51.

[0035] The common chamber 32 is formed inside the frame member 60. The common chamber 32 communicates with the pressure chamber 31 through a plurality of openings 33 and a plurality of guide channels 34 provided in the diaphragm 30.

[0036] The openings 33 are formed in the vibration plate 30. The multiple openings 33 communicate the common chamber 32 with the multiple guide channels 34. The guide channels 34 communicate the openings 33 with the pressure chambers 31, and guide ink in the common chamber 32 to the pressure chambers 31.

[0037] The partition wall portion 42 is a wall member that separates the multiple pressure chambers 31 aligned in the first direction and separates the multiple guide flow paths 34 aligned in the first direction, and constitutes both side portions of the pressure chambers 31 and the guide flow paths 34. The partition wall portion 42 is disposed opposite the non-driven piezoelectric pillar 22 with the vibration plate 30 interposed therebetween, and is supported by the non-driven piezoelectric pillar 22.

[0038] The nozzle plate 50 is configured as a rectangular plate with a thickness of approximately 10 μm to 100 μm, made of a metal such as SUS or Ni, or a resin material such as polyimide. The nozzle plate 50 is disposed on one side of the flow path plate 40 so as to cover the openings on one side of the pressure chambers 31. The nozzle plate 50 is formed with a plurality of nozzles 51 that penetrate through the thickness direction. The nozzles 51 are aligned in the third direction to form a nozzle row. Each nozzle 51 is provided at a position corresponding to one of the pressure chambers 31.

[0039] The frame member 60 is disposed on the other side of the vibration plate 30 in the first direction. The frame member 60 is a structure that is joined to the vibration plate 30 together with the piezoelectric pillars 21, 22. The frame member 60 is provided in a direction perpendicular to the vibration direction of the vibration plate 30, that is, the piezoelectric pillars 21, 22, and is disposed around the actuator 20 in this embodiment, for example. The frame member 60 forms the outer shell of the liquid ejection head 1. The frame member 60 may also have a liquid flow path formed therein. In this embodiment, the frame member 60 is joined to the other side of the vibration plate 30, and forms a common chamber 32 between itself and the vibration plate 30.

[0040] The drive circuit 70 includes a wiring film 71 having one end connected to the external electrodes 223 and 224, 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.

[0041] The drive circuit 70 is a drive signal generating means that generates a drive signal for the actuator 20. The drive circuit 70 applies a drive voltage to the external electrodes 223 and 224 using a driver IC 72, thereby driving the piezoelectric pillars 21 and 22, increasing or decreasing the volume of the pressure chamber 31, and causing droplets to be ejected from the nozzle 51.

[0042] The wiring film 71 is connected to a plurality of individual electrodes, that is, individual electrodes 223 and a common electrode 224. For example, the wiring film 71 is an ACF (anisotropic conductive film) that is fixed by thermocompression bonding or the like to the connection portions of the external electrodes 223 and 224. The wiring film 71 is, for example, a COF (chip on film) on which a driver IC 72 is mounted.

[0043] The driver IC 72 is connected to the external electrodes 223, 224 via the wiring film 71. The driver IC 72 may be connected to the external electrodes 223, 224 by other means, such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste), instead of the wiring film 71.

[0044] The driver IC 72 generates control signals and drive signals for operating each of the piezoelectric pillars 21 and 22. The driver IC 72 generates control signals for controlling the timing of ink ejection and the selection of the piezoelectric pillars 21 from which ink is to be ejected, in accordance with an image signal input from the control unit 150 of the liquid ejection device 100. The driver IC 72 also generates a voltage, i.e., a drive signal (electrical signal), to be applied to the piezoelectric pillars 21 in accordance with the control signal. When the driver IC 72 applies the drive signal to the piezoelectric pillars 21, the piezoelectric pillars 21 are driven to displace the diaphragm 30 and change the volume of the pressure chambers 31. This causes pressure vibrations in the ink filled in the pressure chambers 31. The pressure vibrations cause ink to be ejected from the nozzles 51 provided in the pressure chambers 31. The liquid ejection head 1 may be configured to achieve 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 ink ejections. In this way, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pillar 21.

[0045] For example, the driver IC 72 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data in chronological order for each of the piezoelectric pillars 21 and 22. The decoder 722 controls the driver 723 for each of the piezoelectric pillars 21 and 22 based on the print data stored in the data buffer 721. The driver 723 outputs drive signals that operate each of the piezoelectric pillars 21 and 22 under the control of the decoder 722. The drive signals are voltages that are applied to each of the piezoelectric pillars 21 and 22.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0064] The ROM 152 stores various programs, etc. The RAM 153 temporarily stores various variable data, image data, etc. The I / O port 154 is an interface unit that inputs and outputs data from the outside, such as the externally connected device 200. Print data from the externally connected device 200 is sent to the control unit 150 via the I / O port 154 and saved in the image memory 155.

[0065] The drive waveform of the drive signal generated by the drive circuit 70 of the liquid ejection head 1 used in the liquid ejection device 100 according to the embodiment will be described below in comparison with a drive waveform of a comparative example, which is an example of a conventional drive waveform.

[0066] [Driving waveform of comparative example] First, the drive waveforms of the comparative example will be described with reference to FIGS.

[0067] 6, the drive waveform of the comparative example is configured on a line-by-line basis. The drive waveform of the comparative example includes an ejection pulse portion, a boost pulse portion for pre-driving, and a cancel pulse portion for canceling pressure vibrations, etc.

[0068] Here, the drive waveform of the comparative example is provided with an ejection pulse portion that maintains pressure oscillation with a period of 1.8AL to 2.2AL (i.e., 2.0AL±0.2AL (variation)) relative to the pressure propagation time AL (Acoustic Length), which is half the pressure oscillation period of the pressure chamber 31 filled with ink. Also, the boost pulse portion of the drive waveform of the comparative example is provided with a pulse that is in phase with the ejection pulse portion for a time of 2AL, or a pulse that is out of phase with the ejection pulse portion for a time of 1AL. Also, the cancel pulse portion of the drive waveform of the comparative example is provided with a pulse that is out of phase with the ejection pulse portion for a time of 2AL, or a pulse that is in phase with the ejection pulse portion for a time of 1AL. Also, except for the boost pulse portion and cancel pulse portion, an inter-cycle delay is provided in which no pulse is provided when ejection is not being performed.

[0069] As examples of comparative drive waveforms, Figure 7 shows the relationship between a conventional drive waveform and pressure vibration as Comparative Example 1, and Figure 9 shows the relationship between a drive waveform of a comparative example in which multiple pulses are consecutively driven without a boost pulse portion between adjacent lines, an inter-cycle delay, or a cancel pulse portion, and pressure vibration due to continuous drive as Comparative Example 2. Figure 8 also shows the relationship between inter-cycle delay and ejection speed when pressure vibration remains.

[0070] [Comparative Example 1] In the drive waveform of Comparative Example 1, if any pressure vibration remains that cannot be canceled by the cancel pulse portion, as in the case of the pressure vibration shown in Figure 7, it will attenuate during the delay between cycles. However, as shown in Figure 8, if the delay between cycles is short, the ejection speed and ejection volume will be affected. Furthermore, the short delay between cycles makes it difficult to increase the drive frequency.

[0071] Comparative Example 2 Comparative Example 2 in Figure 9 shows the drive waveform and pressure oscillations in the case of continuous drive. While this waveform theoretically allows for the maximum drive frequency, it reduces stability and robustness, resulting in poor print quality. Furthermore, the pressure propagation time varies depending on the ink viscosity and processing errors of each pressure chamber, resulting in differences in the degree to which pressure oscillations caused by ejection pulses remain. Even slight differences accumulate and have a significant impact when ejecting ink continuously.

[0072] [Driving waveform of the embodiment] Next, the drive waveform of the liquid ejection head 1 of this embodiment will be described. The drive waveform of the liquid ejection head 1 of this embodiment has an ejection pulse portion that includes multiple ejection pulses. The drive waveform of the liquid ejection head 1 also includes a non-ejection pulse portion that includes a non-ejection pulse that maintains the pressure vibration to a level that does not cause ejection. The ejection pulse portion maintains pressure vibration with a period of 1.8AL to 2.2AL (i.e., 2.0AL±0.2AL (variation)) with respect to the pressure propagation time AL, which is half the pressure vibration period of the pressure chamber 31 filled with ink.

[0073] That is, the ejection pulse section has multiple ejection pulses that operate consecutively at a timing of a period that is 1.8 times (1.8AL) to 2.2 times (2.2AL) the pressure propagation time AL, and these multiple ejection pulses have two or more different periods that contract the pressure chamber 31. As a specific example, the ejection pulse section is configured by combining one or more first pulses and one or more second pulses.

[0074] The first pulse includes a contraction element that contracts the pressure chamber 31. The contraction element of the first pulse contracts the pressure chamber 31 for a time period that is 0.9 times (0.9AL) to 1.1 times (1.1AL) the pressure propagation time AL. For example, a plurality of first pulses are consecutive in the ejection pulse portion.

[0075] The second pulse is a pulse different from the first pulse. Like the first pulse, the second pulse is a pulse that maintains pressure vibration with a period of 1.8 times (1.8AL) to 2.2 times (2.2AL) the pressure propagation time AL. The second pulse is at least one type of pulse that contracts the pressure chamber 31 for a time of 0.5 times (0.5AL) to 1.5 times (1.5AL) the pressure propagation time AL at the timing of ink ejection. Here, the contraction element of the second pulse can be set to a plurality of periods between 0.5 and 1.5 times the pressure propagation time AL. For example, when the first pulse is pulse PA, the second pulse can be set to a plurality of different pulses (multiple types of pulses), such as different pulses PB to Pn.

[0076] That is, the ejection pulse portion has a pulse PA which is a first pulse, and at least one of different pulses PB to Pn which are second pulses.

[0077] The non-ejection pulse section maintains pressure oscillation to the extent that ink is not ejected. The non-ejection pulse section is provided between the ejection pulse sections. The non-ejection pulse section does not have a contraction element or an expansion element, or has an expansion element that is 0.5 times (0.5AL) or less of the pressure propagation time AL.

[0078] As specific examples of the drive waveform of such a liquid ejection head 1 and examples of pressure vibrations caused by the drive waveform, Examples 1 to 3 will be described below with reference to FIGS. [Example 1] FIG. 10 shows a drive waveform according to Example 1. The drive waveform of Example 1 has no cycle delay between adjacent lines, and has an ejection pulse portion including a plurality of pulses PA as a first pulse, and a plurality of pulses PB and a plurality of pulses PC as a second pulse. For example, the duration of the contraction element of the pulse PB is shorter than the duration of the contraction element of the pulse PA, and the duration of the contraction element of the pulse PC is shorter than the duration of the contraction element of the pulse PB. Furthermore, the drive waveform of Example 1 has, for example, two pulses PA, four pulses PB, and two pulses PC in the ejection pulse portion after the boost pulse portion. The drive waveform of Example 1 also has a cancel pulse portion as a non-ejection pulse portion after the ejection pulse portion, which has an expansion element that is 0.5 times (0.5AL) or less than the pressure propagation time AL.

[0079] [Example 2] FIG. 11 shows a drive waveform according to Example 2. The drive waveform of Example 2 has a non-ejection pulse portion between adjacent ejection pulse portions. The ejection pulse portion has multiple pulses PA as first pulses, and one or more pulses PB and one or more pulses PC as second pulses. Specifically, the ejection pulse portion before the non-ejection pulse portion has two pulses PA as first pulses and one pulse PB as second pulses. The ejection pulse portion after the non-ejection pulse portion has three pulses PA as first pulses and one pulse PB and one pulse PC as second pulses. For example, the duration of the contraction element of the pulse PB is shorter than the duration of the contraction element of the pulse PA, and the duration of the contraction element of the pulse PC is shorter than the duration of the contraction element of the pulse PB. The non-ejection pulse portion between adjacent ejection pulse portions does not have a contraction element or an expansion element. The drive waveform of Example 2 also has, for example, a boost pulse portion, an ejection pulse portion, a non-ejection pulse portion, an ejection pulse portion, and a cancel pulse portion, in that order. The drive waveform of Example 2 has, after the ejection pulse portion, a cancel pulse portion as a non-ejection pulse portion having an expansion element of 0.5 times (0.5AL) or less the pressure propagation time AL.

[0080] [Example 3] FIG. 12 shows a drive waveform according to Example 3. The drive waveform of Example 3 has a non-ejection pulse portion between adjacent ejection pulse portions. The ejection pulse portion has multiple pulses PA as first pulses, and one or more pulses PB and one or more pulses PC as second pulses. Specifically, the ejection pulse portion before the non-ejection pulse portion has two pulses PA as first pulses and one pulse PB as second pulses. The ejection pulse portion after the non-ejection pulse portion has three pulses PA as first pulses and one pulse PB and one pulse PC as second pulses. For example, the duration of the contraction element of pulse PB is shorter than the duration of the contraction element of pulse PA, and the duration of the contraction element of pulse PC is shorter than the duration of the contraction element of pulse PB. The non-ejection pulse portion has an expansion element that is 0.5 times (0.5AL) or less than the pressure propagation time AL. The drive waveform of Example 3 also has, for example, a boost pulse portion, an ejection pulse portion, a non-ejection pulse portion, an ejection pulse portion, and a cancel pulse portion, in that order. The drive waveform of Example 3 has, after the ejection pulse portion, a cancel pulse portion as a non-ejection pulse portion having an expansion element of 0.5 times (0.5AL) or less the pressure propagation time AL.

[0081] Unlike the single ejection pulse of the comparative example, the drive waveform of such an embodiment is composed of an ejection pulse section having multiple types of ejection pulses that attenuate and amplify pressure vibrations, or is composed of an ejection pulse section plus a non-ejection pulse that maintains the pressure vibrations to a level that does not eject them.

[0082] That is, the pressure vibration is highest when the pulse width of the contraction element is 1AL, and the pressure vibration decreases as the pulse width deviates. For this reason, the drive waveform of the embodiment combines pulses PA to Pn, which are multiple types of ejection pulses, and can adjust the pressure vibration by using the pulse width, voltage, etc. to individually control the pressure vibration during continuous ejection, as shown in the pressure vibrations of Figures 10 to 12.

[0083] Furthermore, the drive waveform of the embodiment includes a non-ejection pulse section that maintains the pressure vibration to a level that does not eject ink between ejection pulse sections. For example, as shown in Figure 11, if no expansion element pulse is provided during non-ejection between ejection pulse sections, the pressure vibration will attenuate based on factors such as the viscosity of the ink. In this case, the pressure vibration in the ejection pulse section following the non-ejection pulse section will weaken, leading to a decrease in the ejection volume. For this reason, it is also preferable to control the pressure vibration even during non-ejection, as shown in Figure 12, in order to stably eject ink in the next ejection pulse section.

[0084] As described above, the liquid ejection head 1 is configured to use two or more pulses PA to Pn having a plurality of different contraction elements in the ejection pulse portion that ejects ink as a drive waveform that is generated by the drive circuit 70 for driving the actuator 20. This allows the liquid ejection head 1 to attenuate pressure vibrations without providing an inter-cycle delay, and suppress deterioration in print quality while increasing the drive frequency.

[0085] It should be noted that the embodiments are presented as examples and are not limited to the above-described examples. For example, the specific configuration of the piezoelectric pillars 21 and 22 described above, the shape of the flow paths, and the configuration and positional relationship of various components including the flow path plate 40, nozzle plate 50, and frame member 60 are not limited to the above-described examples and can be modified as appropriate. Furthermore, the arrangement of the nozzles 51 and pressure chambers 31 is not limited to the above. For example, the nozzles 51 may be arranged in two or more rows. Furthermore, dummy chambers may be formed between multiple pressure chambers 31. Furthermore, various actuators can be used in the piezoelectric liquid ejection head 1.

[0086] Furthermore, in the above example, a roofshooter type liquid ejection head 1 was described in which an actuator drives a diaphragm, thereby deforming a pressure chamber and ejecting liquid, but the present invention is not limited to this example. In other words, the above drive waveforms can be applied to various types of liquid ejection heads that deform a pressure chamber using an actuator. For example, the liquid ejection head may be a sideshooter type liquid ejection head.

[0087] In the above example, the liquid ejected by the liquid ejection head 1 and the liquid ejection device 100 is described as being ink for printing. However, the liquid is not limited to the above-described ink. Transparent glossy ink, ink that changes color when irradiated with infrared or ultraviolet light, or other special inks can also be ejected. Furthermore, the liquid ejection head 1 may be capable of ejecting liquids other than ink. The liquid ejected by the liquid ejection head 1 may be a dispersion liquid such as a suspension. Examples of liquids other than ink that can be ejected by the liquid ejection head 1 include liquids containing conductive particles for forming wiring patterns on printed wiring boards, liquids containing cells for artificially forming tissues or organs, binders such as adhesives, wax, and liquid resins. Therefore, the liquid ejection device can also be used in, for example, 3D printers, industrial manufacturing machines, medical applications, and the like.

[0088] According to at least one of the embodiments of the liquid ejection head described above, by using a drive waveform having two or more pulses with a plurality of different contraction elements, it is possible to increase the drive frequency while suppressing degradation of print quality.

[0089] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. The following is a description equivalent to the invention described in the original claims of the present application. [1] A nozzle plate having a nozzle for discharging a liquid; a pressure chamber communicating with the nozzle; an actuator that changes the volume of the pressure chamber in response to an electrical signal; a drive circuit that generates an electrical signal to drive the actuator; The drive waveform output by the drive circuit has an ejection pulse portion having a plurality of pulses at a period 1.8 to 2.2 times the pressure propagation time, The ejection pulse section includes a first pulse having a contraction element, and a second pulse having a contraction element different from the contraction element of the first pulse and having a length 0.5 to 1.5 times the pressure propagation time. [2] The liquid ejection head according to [1], wherein the contraction element of the first pulse has a length 0.9 to 1.1 times the pressure propagation time. [3] The liquid ejection head according to [2], wherein the contraction element of the second pulse is shorter than the contraction element of the first pulse. [4] The liquid ejection head according to any one of [1] to [3], wherein the drive waveform has a non-ejection pulse portion between adjacent ejection pulse portions. [5] The liquid ejection head according to [4], wherein the non-ejection pulse portion has an expansion element that is 0.5 times or less the pressure propagation time. [Explanation of symbols]

[0090] 1...liquid ejection head, 10...base, 20...actuator, 21...piezoelectric pillar, 22...non-driven piezoelectric pillar, 23...groove, 30...vibration plate, 31...pressure chamber, 32...common chamber, 33...opening, 34...guide flow path, 35...flow path, 40...flow path plate, 41...frame-shaped portion, 42...partition wall portion, 43...guide wall, 50...nozzle plate, 51...nozzle, 60...frame member, 70...drive circuit, 71...wiring film, 72...driver IC, 100...liquid ejection device, 111...casing, 112...medium supply unit, 113...image forming unit, 114...medium discharge unit, 115...conveyor device, 117...support portion, 118...conveyor belt, 119 ...Support plate, 120...belt roller, 121...pair of guide plates, 122...conveyor roller, 130...head unit, 132...ink tank, 133...connecting flow path, 134...supply pump, 150...control unit, 151...processor, 154...I / O port, 155...image memory, 161...drive motor, 162...operation unit, 163...type sensor, 200...externally connected device, 211...piezoelectric layer, 212...dummy layer, 221...internal electrode, 222...internal electrode, 223...external electrode (individual electrode), 224...external electrode (common electrode), 721...data buffer, 722...decoder, 723...driver

Claims

1. a nozzle plate having nozzles for discharging liquid; a pressure chamber communicating with the nozzle; an actuator that changes the volume of the pressure chamber in response to an electrical signal; a drive circuit that generates an electrical signal to drive the actuator; The drive waveform output by the drive circuit has an ejection pulse portion having a plurality of pulses at a period 1.8 to 2.2 times the pressure propagation time, the ejection pulse portion includes a first pulse having a contraction element, and a second pulse having a contraction element different from the contraction element of the first pulse and having a length that is 0.5 to 1.5 times the pressure propagation time, A liquid ejection head, wherein the first pulse has a plurality of pulses PA, and the second pulse has one or more pulses PB and one or more pulses PC, the contraction element of the pulse PB being shorter than the contraction element of the pulse PA, and the contraction element of the pulse PC being shorter than the contraction element of the pulse PB.

2. 2. The liquid ejection head according to claim 1, wherein the contraction element of the first pulse has a length that is 0.9 to 1.1 times the pressure propagation time.

3. The liquid ejection head according to claim 2 , wherein the contraction element of the second pulse is shorter than the contraction element of the first pulse.

4. 4. The liquid ejection head according to claim 1, wherein the drive waveform has a non-ejection pulse portion between adjacent ejection pulse portions.

5. The liquid ejection head according to claim 4 , wherein the non-ejection pulse portion has an expansion element that is 0.5 times or less the pressure propagation time.

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