Liquid ejection head

Abstract

To provide a liquid discharge head capable of suppressing specific natural vibration even with a simple drive circuit.SOLUTION: A liquid discharge head includes a nozzle plate, a pressure chamber, an actuator and a drive circuit. The nozzle plate has a nozzle discharging liquid. The pressure chamber is communicated with the nozzle, The actuator changes a capacity of the pressure chamber according to an electric signal. The drive circuit generates the electric signal for driving the actuator. When frequency response characteristics of the liquid in the nozzle to the electric signal are a first peak frequency FA and a second peak frequency FB larger than the first peak frequency FA, an upper limit voltage of the electric signal is VH and a lower limit voltage is VL, and n is a natural number of 1 or more and smaller than N, the drive circuit holds an intermediate voltage VM=n (VH-VL) / N for a time of t=1 / FB / N, and outputs a drive waveform including a step waveform element of N stage to the actuator in at least one of rising and falling of a drive waveform of the actuator.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Conventionally, liquid ejection heads have been known that use a piezoelectric actuator to vibrate a diaphragm. This piezoelectric actuator is formed, for example, by dicing a laminated piezoelectric element bonded to a base member, forming grooves. A required number of piezoelectric pillars are arranged at predetermined intervals per piezoelectric element, forming a comb-like structure. For example, the piezoelectric pillars of the piezoelectric element are arranged alternately, consisting of driving piezoelectric pillars that apply a driving waveform to drive the diaphragm, and non-driving piezoelectric pillars that are simply used as support pillars without applying a driving waveform. In such liquid ejection heads, the upper end faces of the driving piezoelectric pillars are bonded to the diaphragm, causing vibrations in a liquid such as ink in a pressure chamber, thereby ejecting ink droplets from a nozzle connected to the pressure chamber. The drive waveform for this liquid ejection head combines oblique waveform elements, in which the voltage rises or falls obliquely with respect to time.

[0003] To generate such a waveform element with a diagonal voltage change, the drive circuit must be complicated because the rate of change of the voltage must be controlled to a constant value. However, unless a combination of diagonal waveform elements is used as the drive waveform, a specific natural vibration occurs significantly, which may cause cavitation in the liquid or the generation of ink mist. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-11108 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a liquid ejection head that can suppress specific natural vibrations even with a simple drive circuit. [Means for solving the problem]

[0006] 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 for ejecting liquid. The pressure chamber is connected to the nozzle. The actuator varies the volume of the pressure chamber in response to an electric signal. The drive circuit generates the electric signal for driving the actuator. When the frequency response characteristics of the liquid in the nozzle relative to the electric signal are a first peak frequency FA and a second peak frequency FB greater than the first peak frequency FA, ​​an upper limit voltage VH and a lower limit voltage VL of the electric signal, and n is a natural number greater than or equal to 1 and less than N, the drive circuit holds an intermediate voltage VM=n·(VH-VL) / N for a time t=1 / FB / N during at least one of the rising and falling edges of the drive waveform for the actuator, and outputs a drive waveform including N step waveform elements to the actuator. [Brief explanation of the drawings]

[0007] [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 waveform elements of a drive waveform according to the prior art. [Figure 7] FIG. 10 is an explanatory diagram showing an example of pressure oscillations caused by waveform elements of a drive waveform according to the prior art. [Figure 8]FIG. 10 is an explanatory diagram showing an example of flow velocity oscillation caused by waveform elements of a drive waveform according to the prior art. [Figure 9] FIG. 10 is an explanatory diagram showing an example of a specific natural vibration frequency due to a waveform element of a drive waveform of the prior art. [Figure 10] 10A and 10B are explanatory diagrams showing an example of a two-step waveform element of a drive waveform of the present embodiment and a diagonal waveform element of a drive waveform of the prior art. [Figure 11] 10A and 10B are explanatory diagrams showing examples of pressure vibrations caused by a two-step waveform element of the drive waveform of the present embodiment and pressure vibrations caused by a diagonal waveform element of the drive waveform of the prior art. [Figure 12] FIG. 10 is an explanatory diagram showing an example of flow velocity vibration caused by a two-step waveform element of the drive waveform of the present embodiment and a flow velocity vibration caused by a diagonal waveform element of the drive waveform of the prior art. [Figure 13] 10A and 10B are explanatory diagrams showing an example of a drive waveform including a two-step waveform element according to the present embodiment and a drive waveform according to the prior art. [Figure 14] 10A and 10B are explanatory diagrams showing examples of pressure oscillations caused by a drive waveform including a two-step waveform element according to the present embodiment and a drive waveform according to the prior art; [Figure 15] 10A and 10B are explanatory diagrams showing examples of flow velocity oscillations caused by a drive waveform including a two-step waveform element according to the present embodiment and a drive waveform according to the prior art; [Figure 16] 10A and 10B are explanatory diagrams showing an example of a three-step waveform element of a drive waveform of the present embodiment and a diagonal waveform element of a drive waveform of the prior art. [Figure 17] 10A and 10B are explanatory diagrams showing examples of pressure vibrations caused by a three-step waveform element of the drive waveform of the present embodiment and pressure vibrations caused by a diagonal waveform element of the drive waveform of the prior art. [Figure 18] FIG. 10 is an explanatory diagram showing an example of flow velocity vibration caused by a three-step waveform element of the drive waveform of the present embodiment and a flow velocity vibration caused by a diagonal waveform element of the drive waveform of the prior art. [Figure 19] 10A and 10B are explanatory diagrams showing an example of a drive waveform including a triple-step waveform element according to the present embodiment and a drive waveform according to the prior art. [Figure 20] 10A and 10B are explanatory diagrams showing examples of pressure oscillations caused by a drive waveform including a three-step waveform element according to the present embodiment and a drive waveform according to the prior art; [Figure 21] 10A and 10B are explanatory diagrams showing examples of flow velocity oscillations caused by a drive waveform including a triple-step waveform element according to the present embodiment and a drive waveform according to the prior art; DETAILED DESCRIPTION OF THE INVENTION

[0008] 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.

[0009] 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.

[0010] The base 10 is formed in the shape of, for example, a rectangular plate. The actuator 20 is joined to the base 10.

[0011] 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).

[0012] The laminated piezoelectric member that constitutes the actuator 20 is formed by laminating and sintering sheet-shaped piezoelectric materials.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 under control of a processor 151.

[0019] 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.

[0020] 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.

[0021] When a voltage is applied to the internal electrodes 221, 222 via the external electrodes 223, 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 portion 42 with the vibration plate 30 interposed therebetween.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] As shown in Fig. 5, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data in chronological order for each of the piezoelectric pillars 21 and 22. The decoder 722 controls the driver 723 for each of the piezoelectric pillars 21 and 22 based on the print data stored in the data buffer 721. The driver 723 outputs drive signals that operate each of the piezoelectric pillars 21 and 22 under the control of the decoder 722. The drive signals are voltages that are applied to each of the piezoelectric pillars 21 and 22.

[0040] 3, 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. For example, the driver IC 72 includes a data buffer 721, a decoder 722, and a driver 723. Note that the driver IC 72 may include some of the data buffer 721, the decoder 722, and the driver 723, and the remaining parts may be included in the printed wiring board or the like.

[0041] The drive circuit 70 applies a drive voltage to the external electrodes 223 and 224 via the driver IC 72 to drive the piezoelectric pillars 21 and 22, thereby 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] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The medium discharge unit 114 includes a paper discharge tray configured to be able to hold the paper P discharged from the discharge port.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The characteristics of the liquid ejection head 1 used in the liquid ejection device 100 according to this embodiment and the drive waveform of the liquid ejection head 1 will be described below.

[0065] First, the characteristics of the liquid ejection head 1 in which the laminated piezoelectric member of the liquid ejection head 1 of this embodiment is used as the actuator 20 will be described with reference to Figures 6 to 9. Note that the examples of waveform elements of the drive waveforms in Figures 6 to 9 are examples of the prior art.

[0066] First, the liquid ejection head 1 tends to have a pronounced natural vibration due to structural vibration of the actuator in addition to the natural vibration due to fluid vibration of the ink.

[0067] For example, when a waveform element WA of a drive waveform that falls sharply, such as the waveform element of the drive waveform of the prior art shown by the solid line in Fig. 6, is applied as an electrical signal to the liquid ejection head 1, the pressure vibrations PA generated in the pressure chamber 31 are generated by superimposing short-period pressure vibrations on long-period pressure vibrations, as shown by the solid line in Fig. 7. This also occurs when a waveform element of a drive waveform that rises sharply is applied to the liquid ejection head 1, whereby short-period pressure vibrations are superimposed on long-period pressure vibrations. Furthermore, when pressure vibrations PA due to the waveform element WA are generated, flow velocity vibrations UA generated in the nozzle 51 are generated by superimposing short-period flow velocity vibrations, as shown by the solid line in Fig. 8.

[0068] The results of frequency spectrum analysis of the pressure vibration PA in FIG. 7 are shown by the solid line in FIG. 9. From FIG. 9, it can be seen that the pressure vibration PA has two different natural vibration frequencies: a first natural vibration frequency (first peak frequency) FA and a second natural vibration frequency (second peak frequency) FB. For example, the first natural vibration frequency FA is a fluid natural vibration frequency, and the second natural vibration frequency FB, which is higher than the first natural vibration frequency FA, ​​is a structural natural vibration frequency or other parasitic vibration that is undesirable for the ink ejection operation. Here, for example, the second natural vibration frequency FB, which is a structural natural vibration with a higher frequency, is not only unnecessary for ink ejection, but may also cause ink cavitation and ink mist.

[0069] For example, in order to suppress this second natural vibration frequency FB, if the liquid ejection head 1 is driven using a diagonal waveform element that rises and falls diagonally, such as the waveform element WB of the drive waveform of the prior art, as shown by the dashed line in Fig. 6, the second natural vibration frequency FB can be suppressed, as shown by the pressure vibration PB shown by the dashed line in Fig. 7 and the flow velocity vibration UB shown by the dashed line in Fig. 8, thereby reducing the occurrence of ink cavitation and ink mist. For example, when a frequency spectrum analysis is performed on the pressure vibration PB in Fig. 7, it can be seen that the second natural vibration frequency FB is reduced, as shown by the dashed line in Fig. 9.

[0070] However, although a diagonal waveform element such as the waveform element WB can suppress the second natural vibration frequency FB, it requires a drive waveform generating section that changes the voltage diagonally, which makes the drive circuit 70 complicated.

[0071] Next, an example of the drive waveform and operation of the liquid ejection head 1 according to this embodiment will be described. The drive circuit 70 of the liquid ejection head 1 uses, as a waveform element, a multi-step waveform that maintains a voltage between a lower limit voltage VL and an upper limit voltage VH of the drive voltage that drives the actuator 20 for a predetermined period of time.

[0072] Specifically, in the liquid ejection head 1, the frequency response characteristics of the ink in the nozzle 51 in response to the waveform element WA of the drive waveform that falls sharply become a first peak frequency FA and a second peak frequency FB that is greater than the first peak frequency FA.

[0073] The drive circuit 70 of the liquid ejection head 1 of this embodiment generates a drive waveform that includes multiple step waveform elements in the rising and falling edges of the voltage as an electrical signal that drives the actuator 20. In the following explanation, "multiple steps" will be referred to as "N steps," where N is a natural number equal to or greater than 2.

[0074] For example, when the electrical signal has an upper limit voltage VH and a lower limit voltage VL, the drive waveform of the drive signal generated by the drive circuit 70 holds an intermediate voltage VM=n·(VH-VL) / N for a time t=1 / FB / N=1 / (FB·N) in at least one of the rising and falling waveform elements of the drive waveform for the actuator, and outputs an N-step waveform to the actuator.

[0075] Here, N is the same as the number of steps in the step waveform, and N is 2 for a two-step waveform and 3 for a three-step waveform. Here, n is a natural number between 1 and N-1. For example, n is the number of steps of the intermediate voltage VN to be obtained when the lower limit voltage is the 0th step. As a specific example, n is 1 for a two-step waveform and n is 1 or 2 for a three-step waveform.

[0076] Next, as an example of a drive waveform, a drive waveform including a two-step waveform element generated by the drive circuit 70 will be described using Fig. 10 to Fig. 15. The waveform element WC of the drive waveform shown in Fig. 10 is a two-step waveform element with N=2 at the falling edge. In addition, in the example of the drive waveform shown in Fig. 10, the upper limit voltage VH of the electrical signal is V, and the lower limit voltage VL is 0.

[0077] When the driving voltage is changed from voltage V to voltage 0, VH=V, VL=0, N=2, and n=1. Therefore, the intermediate voltage VM of the waveform element WC is VM=n(VH-VL) / N=1(V-0) / 2=V / 2 This becomes:

[0078] The time t for applying the intermediate voltage VM of the waveform element WC is t=1 / FB / N=1 / FB / 2=0.5 / FB This becomes:

[0079] For this reason, the waveform element WC of the drive waveform holds V / 2 as an intermediate voltage for a time of 0.5 / FB when the voltage falls from V to 0. Note that the intermediate voltage in the waveform element of the drive waveform where the voltage rises from V to 0 is V / 2, and the time for which the intermediate voltage is held is 0.5 / FB.

[0080] The pressure oscillation PC due to such a waveform element WC is shown by a solid line in Figure 11. As is clear from Figure 11, the pressure oscillation PC behaves in substantially the same way as the pressure oscillation PB due to the diagonal waveform element WB. This also shows that the waveform element WC of the drive waveform is able to sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

[0081] Furthermore, the flow velocity oscillation UC due to the waveform element WC is shown by a solid line in Fig. 12. As is clear from Fig. 12, the flow velocity oscillation UC behaves in substantially the same way as the flow velocity oscillation UB due to the diagonal waveform element WB. This also shows that the waveform element WC of the drive waveform is able to sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

[0082] Next, as an example of a drive waveform using an N-step waveform element generated by the drive circuit 70, an example of a drive waveform WE using a two-step waveform element when the voltage rises from the lower limit voltage to the upper limit voltage and when the voltage falls from the upper limit voltage to the lower limit voltage is shown by the solid line in Figure 13. Note that the example of the drive waveform WE shown in Figure 13 is composed of three ejection pulses WEa to WEc and WEd, which cancels out residual pressure vibration. Also, for comparison with the drive waveform WE of the embodiment, a drive waveform WD of the prior art including a diagonal waveform element is shown by the dashed line in Figure 13.

[0083] The holding time TA of the intermediate voltage VM is TA=1 / FB / 2=0.5 / FB, where FB is the second natural vibration frequency, which is a parasitic vibration undesirable for the ink ejection operation, such as a structural natural vibration. The widths TB=TE=0.5 / FA and TC=TD=1 / FA of the pulses WEa-WEd are TB=TE=0.5 / FA and TC=TD=1 / FA, where FA is the first natural vibration frequency, which is a fluid natural vibration. The lower limit voltages of the three ejection pulses WEa-WEc and WEd, which cancels out residual pressure vibrations, are different voltages.

[0084] The pressure oscillations PE caused by a drive waveform WE including a two-step waveform element are shown by a solid line in Fig. 14, and the pressure oscillations PD caused by a drive waveform WD of the prior art are shown by a dashed line in Fig. 14. As shown in Fig. 14, the pressure oscillations PE caused by the drive waveform WE behave in substantially the same way as the pressure oscillations PD caused by the drive waveform WD of the prior art. This also shows that the drive waveform WE using the two-step waveform element of the embodiment can generate pressure oscillations similar to those of the drive waveform WD using the diagonal waveform element of the prior art.

[0085] Furthermore, the flow velocity oscillation UE of the nozzle caused by the drive waveform WE including the double-step waveform element is shown by a solid line in Figure 15, and the flow velocity oscillation UD of the nozzle caused by the drive waveform WD of the prior art is shown by a dashed line in Figure 15. As shown in Figure 15, the flow velocity oscillation UE caused by the drive waveform WE exhibits substantially the same behavior as the flow velocity oscillation UD caused by the drive waveform WD of the prior art. This also shows that the drive waveform WE using the double-step waveform element of the embodiment can generate flow velocity oscillations similar to those of the drive waveform WD using the diagonal waveform element of the prior art.

[0086] Next, as a drive waveform of another embodiment, a drive waveform including a three-step waveform element generated by the drive circuit 70 will be described with reference to Figs. 16 to 21. The waveform element WF as the three-step waveform element of the drive waveform shown in Fig. 16 is a three-step waveform element with N=3 at the falling edge. In addition, in the example of the drive waveform shown in Fig. 16, the upper limit voltage VH of the electrical signal is V, and the lower limit voltage VL is 0.

[0087] When the drive voltage is changed from voltage V to voltage 0, VH=V, VL=0, N=3, n=1, 2. Therefore, of the two (N-1) intermediate voltages VM of the waveform element WF, the intermediate voltage VM on the lower voltage value side is n=1, VM=n(VH-VL) / N=1(V-0) / 3=V / 3 The intermediate voltage VM on the high voltage side is n=2, VM=n(VH-VL) / N=2(V-0) / 3=2V / 3 This becomes:

[0088] The time t for applying the intermediate voltage VM of the waveform element WF is t=1 / FB / N=1 / FB / 3=1 / (3FB) This becomes:

[0089] For this reason, when the voltage of the waveform element WF of the drive waveform falls from V to 0, it changes voltage in three steps as an intermediate voltage: from V to 2V / 3, V / 3, and 0. In addition, the intermediate voltages of 2V / 3 and V / 3 are each held for a time of 1 / (3FB).

[0090] The pressure vibration PF caused by such a waveform element WF is shown by a solid line in Figure 17. As is clear from Figure 17, the pressure vibration PF behaves in substantially the same way as the pressure vibration PB caused by the diagonal waveform element WB. This also shows that the waveform element WF of the drive waveform is able to sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

[0091] 11 and 17, the pressure oscillation PF of the waveform element WF, which is a three-step waveform element, behaves more similarly to the pressure oscillation PB of the diagonal waveform element WB than the pressure oscillation PC of the waveform element WC, which is a two-step waveform element. This shows that by increasing the number of stages of the waveform element, the pressure oscillation can be made to more closely resemble the diagonal waveform element WB.

[0092] Furthermore, the flow velocity oscillation UF caused by the waveform element WF is shown by a solid line in Fig. 18. As is clear from Fig. 18, the flow velocity oscillation UF exhibits substantially the same behavior as the flow velocity oscillation UB caused by the diagonal waveform element WB. This also shows that the waveform element WF of the drive waveform is able to sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

[0093] 12 and 18, the flow velocity oscillation UF of the wave element WF, which is a triple-step wave element, behaves more similarly to the flow velocity oscillation UB of the diagonal wave element WB than the flow velocity oscillation UC of the wave element WC, which is a two-step wave element. This shows that by increasing the number of wave element steps, the flow velocity oscillation can be made to more closely resemble the diagonal wave element WB.

[0094] Next, as an example of a drive waveform using an N-step waveform element generated by the drive circuit 70, an example of a drive waveform WG using a three-step waveform element when the voltage rises from the lower limit voltage to the upper limit voltage and when the voltage falls from the upper limit voltage to the lower limit voltage is shown by the solid line in Figure 19. Note that the example of the drive waveform WG shown in Figure 19 is composed of three ejection pulses WGa to WGc and WGd, which cancels residual pressure vibration. Also, for comparison with the drive waveform WG of the embodiment, a drive waveform WD including a diagonal waveform element of the prior art is shown by the dashed line in Figure 19.

[0095] The holding time TA of the intermediate voltage VM is TA=1 / FB / N=1 / (3FB) per step, where FB is a parasitic vibration undesirable for ink ejection, such as a structural natural vibration. The widths TB=TE=0.5 / FA and TC=TD=1 / FA of the pulses WGa-WGd are TB=TE=0.5 / FA and TC=TD=1 / FA, where FA is a first natural vibration, such as a fluid natural vibration. The lower limit voltages of the three ejection pulses WGa-WGc and WGd, which cancels out residual pressure vibrations, are different voltages.

[0096] The pressure oscillations PG generated by the drive waveform WG including the triple-step waveform element are shown by a solid line in Fig. 20, and the pressure oscillations PD generated by the drive waveform WD of the prior art are shown by a dashed line in Fig. 20. As shown in Fig. 20, the pressure oscillations PG generated by the drive waveform WG behave in substantially the same way as the pressure oscillations PD generated by the drive waveform WD of the prior art. This also shows that the drive waveform WG using the triple-step waveform element of the embodiment can generate pressure oscillations similar to those generated by the drive waveform WD using the diagonal waveform element of the prior art.

[0097] Furthermore, the nozzle flow velocity oscillation UG caused by the drive waveform WG including the triple-step waveform element is shown by a solid line in Figure 21, and the nozzle flow velocity oscillation UD caused by the conventional drive waveform WD is shown by a dashed line in Figure 21. As shown in Figure 21, the flow velocity oscillation UG caused by the drive waveform WG behaves in approximately the same way as the flow velocity oscillation UD caused by the conventional drive waveform WD. This also shows that the drive waveform WG using the triple-step waveform element of the embodiment can generate flow velocity oscillations similar to those of the drive waveform WD using the conventional oblique waveform element.

[0098] As described above, the liquid ejection head 1 divides and changes the voltage of the drive waveform serving as a drive signal generated by the drive circuit 70 for driving the actuator 20 into N stages, and sets the holding time of each intermediate voltage to 1 / f2 / N. This allows the liquid ejection head 1 to suppress the second natural vibration frequency FB, which is a parasitic vibration undesirable for ink ejection operation. While this effect has been shown in the examples for multiple stages N of N=2 and N=3, the same effect can be obtained when N is 4 or more.

[0099] Furthermore, the drive circuit 70 does not need to generate a drive waveform that includes a diagonal waveform element, but only generates a drive waveform that includes a multi-step waveform element. Therefore, the configuration of the drive circuit 70 can be simpler than a drive circuit that generates a waveform element that includes a diagonal waveform element. The drive circuit 70 and the liquid ejection head 1 can suppress parasitic vibrations without increasing costs.

[0100] That is, according to the liquid ejection head 1 of the embodiment, the occurrence of ink cavitation and ink mist can be reduced with a low-cost drive circuit 70 that does not require a drive waveform generation section that changes the voltage obliquely.

[0101] As described above, according to the liquid ejection head 1 of one embodiment, by using waveform elements including a multi-step waveform element that applies an intermediate voltage for a predetermined time, specific natural vibrations can be suppressed even with a simple drive circuit 70.

[0102] It should be noted that the embodiments are presented as examples and are not limited to the above-described examples. For example, the specific configurations of the piezoelectric pillars 21 and 22 described above, the shape of the flow paths, and the configurations and positional relationships of various components including the flow path plate 40, the nozzle plate 50, and the 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 the 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.

[0103] 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.

[0104] According to at least one of the embodiments of the liquid ejection head described above, by using waveform elements including a multi-step waveform element that applies an intermediate voltage for a predetermined period of time, it is possible to suppress specific natural vibrations even with a simple drive circuit.

[0105] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0106] 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 varies the volume of the pressure chamber in response to an electrical signal; a drive circuit that generates the electric signal that drives the actuator, and outputs a drive waveform that includes N-stage step waveform elements to the actuator, where the frequency response characteristics of the liquid in the nozzle to the electric signal are a first peak frequency FA and a second peak frequency FB that is greater than the first peak frequency FA, ​​an upper limit voltage VH and a lower limit voltage VL of the electric signal, and n is a natural number that is 1 or greater and smaller than N, and holds an intermediate voltage VM=n·(VH−VL) / N for a time t=1 / FB / N during at least one of the rising and falling edges of the drive waveform of the actuator.

2. the actuator is formed of a laminated piezoelectric member and includes a plurality of piezoelectric pillars that change the volume of the pressure chamber, and a plurality of non-driven piezoelectric pillars that are arranged alternately with the plurality of piezoelectric pillars and do not change the volume of the pressure chamber. The liquid ejection head according to claim 1 .

3. 3. The liquid ejection head according to claim 1, wherein the step waveform element has two stages.

4. 4. The liquid ejection head according to claim 3, wherein the step waveform element has an intermediate voltage VM=(VH-VL) / 2, and a time t for holding the intermediate voltage VM=0.5 / FB.

5. The first peak frequency FA is a natural vibration frequency of the liquid, 5. The liquid ejection head according to claim 1, wherein the second peak frequency FB is a natural vibration frequency of the actuator.

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