JP2023145089A - liquid discharge head - Google Patents

Abstract

[Problem] To provide a liquid ejection head that can suppress specific natural vibrations even when used as a simple drive circuit. [Solution] A liquid ejection head of an embodiment includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. , is provided. The nozzle plate includes nozzles that discharge liquid. A pressure chamber communicates with the nozzle. The actuator varies the volume of the pressure chamber in response to an electrical signal. A drive circuit generates the electrical signal that drives the actuator. A frequency response characteristic of the liquid in the nozzle with respect to the electric signal is a first peak frequency FA and a second peak frequency FB larger than the first peak frequency FA, and an upper limit voltage VH and a lower limit voltage VL of the electric signal, When n is a natural number greater than or equal to 1 and less than N, the drive circuit sets the intermediate voltage VM=n·(VH-VL)/N at time t=at at least one of the rise and fall of the drive waveform of the actuator. 1/FB/N is held, and a drive waveform including N step waveform elements is output to the actuator. [Selection diagram] Figure 6

Description

Embodiments of the present invention relate to a liquid ejection head.

2. Description of the Related Art Liquid ejection heads that use piezoelectric actuators to vibrate a diaphragm are conventionally known. This piezoelectric actuator is produced by, for example, cutting a laminated piezoelectric member bonded onto a base member into grooves by dicing, and forming a comb-like shape in which a required number of piezoelectric columns are arranged at predetermined intervals for one piezoelectric member. Ru. For example, the piezoelectric pillars of the piezoelectric member are alternately arranged such as driving piezoelectric pillars that apply a driving waveform to drive the diaphragm, and non-driving piezoelectric pillars that do not apply a driving waveform and are used as mere supports. In such a liquid ejection head, the upper end surface of a driving piezoelectric pole is connected to a diaphragm to apply vibration to a liquid such as ink in a pressure chamber, and ink droplets are ejected from a nozzle communicating with the pressure chamber. As the drive waveform for this liquid ejection head, a combination of diagonal waveform elements in which the voltage rises or falls diagonally with respect to time is used.

Generation of such a waveform element whose voltage changes obliquely requires controlling the speed of voltage change to be constant, which complicates the drive circuit. However, unless a combination of diagonal waveform elements is used as the drive waveform, certain natural vibrations will occur significantly, and this vibration may cause cavitation of the liquid or generation of ink mist.

Japanese Patent Application Publication No. 2021-11108

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.

The liquid ejection head of the embodiment includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate includes nozzles that discharge liquid. A pressure chamber communicates with the nozzle. The actuator varies the volume of the pressure chamber in response to an electrical signal. A drive circuit generates the electrical signal that drives the actuator. A frequency response characteristic of the liquid in the nozzle with respect to the electric signal is a first peak frequency FA and a second peak frequency FB larger than the first peak frequency FA, and an upper limit voltage VH and a lower limit voltage VL of the electric signal, When n is a natural number greater than or equal to 1 and less than N, the drive circuit sets the intermediate voltage VM=n·(VH-VL)/N at time t=at at least one of the rise and fall of the drive waveform of the actuator. 1/FB/N is held, and a drive waveform including N step waveform elements is output to the actuator.

FIG. 1 is a perspective view showing a partially omitted configuration of a liquid ejection head according to an embodiment. FIG. 1 is a cross-sectional view showing a partially omitted configuration of a liquid ejection head according to an embodiment. FIG. 1 is a cross-sectional view showing a partially omitted configuration of a liquid ejection head according to an embodiment. FIG. 1 is an explanatory diagram showing the configuration of a liquid ejection device using a liquid ejection head according to an embodiment. FIG. 1 is a block diagram showing an example of the configuration of a liquid ejection device according to an embodiment. FIG. 2 is an explanatory diagram showing an example of waveform elements of a drive waveform in the prior art. FIG. 3 is an explanatory diagram showing an example of pressure vibration caused by a waveform element of a drive waveform in the prior art. FIG. 2 is an explanatory diagram showing an example of flow velocity vibration due to waveform elements of a drive waveform in the prior art. FIG. 4 is an explanatory diagram showing an example of a specific natural vibration frequency due to a waveform element of a drive waveform in the prior art. FIG. 4 is an explanatory diagram showing an example of a two-step waveform element of the drive waveform of the present embodiment and a diagonal waveform element of the drive waveform of the prior art. FIG. 3 is an explanatory diagram showing an example of pressure vibration due to a two-step waveform element of the drive waveform of the present embodiment and a pressure vibration due to an oblique waveform element of the drive waveform of the conventional technology. FIG. 4 is an explanatory diagram showing an example of velocity vibration caused by the two-step waveform element of the drive waveform of the present embodiment and flow velocity vibration caused by the diagonal waveform element of the drive waveform of the prior art. FIG. 3 is an explanatory diagram showing an example of a drive waveform including a two-step waveform element according to the present embodiment and a drive waveform of a conventional technique. FIG. 3 is an explanatory diagram showing an example of pressure vibration caused by a drive waveform including a two-step waveform element of the present embodiment and a pressure vibration of a drive waveform of a conventional technique. FIG. 2 is an explanatory diagram showing an example of flow velocity vibration caused by a drive waveform including a two-step waveform element of the present embodiment and a flow velocity vibration of a drive waveform of a conventional technique. FIG. 3 is an explanatory diagram showing an example of a three-step step waveform element of the drive waveform of the present embodiment and a diagonal waveform element of the drive waveform of the prior art. FIG. 3 is an explanatory diagram showing an example of pressure vibration due to the three-step waveform element of the drive waveform of the present embodiment and pressure vibration due to the diagonal waveform element of the drive waveform of the prior art. FIG. 4 is an explanatory diagram showing an example of flow velocity vibration due to the three-step step waveform element of the drive waveform of the present embodiment and flow velocity vibration due to the diagonal waveform element of the drive waveform of the prior art. FIG. 2 is an explanatory diagram showing an example of a drive waveform including a three-step waveform element according to the present embodiment and a drive waveform of a conventional technique. FIG. 2 is an explanatory diagram showing an example of pressure vibrations caused by a drive waveform including a three-step waveform element of the present embodiment and a pressure vibration of a drive waveform of a conventional technique. FIG. 3 is an explanatory diagram showing an example of flow velocity vibration caused by a drive waveform including a three-step waveform element of the present embodiment and a flow velocity vibration of a drive waveform of a conventional technique.

Below, the configuration of a liquid ejection head 1 according to an embodiment and a liquid ejection apparatus 100 using the liquid ejection head 1 will be described with reference to FIGS. 1 to 5. FIG. 1 is a perspective view showing the structure of the liquid ejection head 1 with some parts omitted, FIG. 2 is a sectional view showing the structure of the liquid ejection head 1 with some parts omitted, and FIG. FIG. 2 is a cross-sectional view showing the configuration of the head with some parts omitted. FIG. 4 is an explanatory diagram showing the configuration of a liquid ejection apparatus 100 using the liquid ejection head 1, and FIG. 5 is a block diagram showing an example of the configuration of the liquid ejection apparatus 100. In addition, in each figure, the structure is enlarged, reduced, or omitted as appropriate for explanation.

The liquid ejection head 1 according to this embodiment is, for example, an inkjet head that ejects ink as a liquid. As shown in FIGS. 1 to 3, the liquid ejection head 1 includes a base 10, an actuator 20, a diaphragm 30, a channel plate 40, a nozzle plate 50 having a plurality of nozzles 51, and a frame member 60. , and a drive circuit 70.

The base 10 is formed into a rectangular plate shape, for example. An actuator 20 is joined to the base 10.

The actuator 20 is, for example, a piezoelectric member including a plurality of piezoelectric columns 21 and non-driven piezoelectric columns 22 arranged alternately with the plurality of piezoelectric columns 21. The actuator 20 is formed into a comb-teeth shape by arranging a plurality of piezoelectric columns 21 and a plurality of non-driving piezoelectric columns 22 in one direction at predetermined intervals. For example, such an actuator 20 can be manufactured by cutting grooves 23 into a laminated piezoelectric member joined to the base 10 by dicing from the end face on the opposite side to the base 10 to form a rectangular columnar shape in one piezoelectric member. A plurality of piezoelectric elements are formed at predetermined intervals. The formed piezoelectric elements are provided with electrodes and the like, thereby forming a plurality of piezoelectric columns 21 and a plurality of non-driven piezoelectric columns 22 arranged alternately as piezoelectric elements. That is, the actuator 20 is divided into a plurality of parts at one end by the plurality of grooves 23 formed, and connected at the other end (base 10 side). That is, the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are alternately arranged in parallel along one direction (first direction) with the grooves 23 in between.

Note that the laminated piezoelectric member constituting the actuator 20 is formed by laminating and sintering sheet-shaped piezoelectric materials.

As a specific example, as shown in FIGS. 1 to 3, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 are, for example, laminated piezoelectric bodies serving as driving elements. The piezoelectric pole 21 and the non-driven piezoelectric pole 22 include a plurality of laminated piezoelectric layers 211, a dummy layer 212 on the base 10 side, and internal electrodes 221 and 222 formed on the main surface of each piezoelectric layer 211. External electrodes 223 and 224 are provided. Note that, as an example, the piezoelectric pole 21 and the non-driven piezoelectric pole 22 have the same configuration.

The piezoelectric layer 211 is formed in a thin plate shape from a piezoelectric material such as PZT (lead zirconate titanate) or lead-free KNN (sodium potassium niobate). The plurality of piezoelectric layers 211 are stacked in the thickness direction (second direction) and bonded together by sintering. Note that here, the stacking direction (second direction) of the plurality of piezoelectric layers 211 is perpendicular to the direction (first direction) in which the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are arranged.

The internal electrodes 221 and 222 are conductive films made of a sinterable conductive material such as silver palladium and formed into a predetermined shape. Internal electrodes 221 and 222 are formed in predetermined regions of the main surface of each piezoelectric layer 211. Internal electrodes 221 and 222 have different poles. For example, as shown in FIG. 3, one internal electrode 221 is arranged in the direction in which the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are arranged (first direction), and in the stacking direction of the piezoelectric layers 211 (second direction). It is formed in a region that reaches one end of the piezoelectric layer 211 and does not reach the other end of the piezoelectric layer 211 in a direction (third direction) perpendicular to both of the piezoelectric layer 211 (the third direction). As shown in FIG. 3, 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. The internal electrodes 221 and 222 are connected to external electrodes 223 and 224 formed on the side surfaces of the piezoelectric columns 21 and 22, respectively.

The external electrodes 223 and 224 are formed on the surfaces of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22, and are configured by collecting the ends of the internal electrodes 221 and 222. For example, the external electrodes 223 and 224 are formed on one end surface and the other end surface in a third direction perpendicular to the stacking direction of the piezoelectric layer 211, respectively. The external electrodes 223 and 224 are formed of Ni, Cr, Au, or the like by a known method such as plating or sputtering. External electrode 223 and external electrode 224 are different poles. The external electrodes 223 and 224 are arranged on different side surfaces of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22, respectively. Note that the external electrodes 223 and 224 may be arranged in different areas of the same side surface of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22.

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 serving as individual electrodes for the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 have electrode layers divided by grooves 23 and are arranged independently of each other. The external electrodes 224, which serve as common electrodes, have electrode layers connected to each other in a region closer to the base 10 than the groove 23, and are grounded, for example.

The external electrodes 223 and 224 are connected to the drive circuit 70, for example. For example, the individual external electrodes 223 and 224 are connected to a control section 150 as a drive section via a driver 723 (described later) of the drive circuit 70 by wiring, and are configured to be drive controllable under the control of the processor 151.

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 deformed because no electric field is applied thereto. That is, 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 serves as a polishing allowance for polishing to improve accuracy during and after assembly.

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

The piezoelectric column 21 and the non-driven piezoelectric column 22 vibrate longitudinally along the stacking direction of the piezoelectric layer 211 by applying a voltage to the internal electrodes 221 and 222 via the external electrodes 223 and 224. The longitudinal vibration referred to here is, for example, "vibration in the thickness direction defined by the piezoelectric constant d33." For example, as shown in FIG. 2, a plurality of piezoelectric poles 21 arranged every other place are arranged corresponding to pressure chambers 31 with a diaphragm 30 in between, and the remaining non-driven piezoelectric poles 22 are arranged with a diaphragm 30 in between. It is arranged at a position opposite to the partition wall part 42 on both sides.

The piezoelectric pole 21 longitudinally vibrates when a voltage is applied, displacing the diaphragm 30. That is, the piezoelectric pole 21 deforms the pressure chamber 31. The non-driven piezoelectric pole 22 is arranged at a position facing the partition wall portion 42 . No voltage is applied to the non-driven piezoelectric pole 22.

The diaphragm 30 is bonded to one side of the plurality of piezoelectric columns 21 and 22 in the stacking direction of the piezoelectric layers 211, that is, to the surface on the nozzle plate 50 side. The diaphragm 30 is configured to be deformable, for example. The diaphragm 30 is joined to the piezoelectric pole 21 and the non-driven piezoelectric pole 22 of the actuator 20 and the frame member 60.

The diaphragm 30 has, for example, a flat plate shape arranged so that the thickness direction is the lamination direction of the piezoelectric layers 211. The plane direction of the diaphragm 30 extends in the direction in which the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are arranged. The diaphragm 30 is, for example, a metal plate. The diaphragm 30 has a plurality of vibrating parts that face each pressure chamber 31 and are individually movable. The diaphragm 30 is formed by integrally connecting a plurality of vibrating parts.

For example, the diaphragm 30 is formed into a single flat plate, and the regions joined to the piezoelectric columns 21 are individually displaced. The diaphragm 30 is made of, for example, a SUS plate. The thickness of the diaphragm 30 is approximately 5 μm to 15 μm. Note that the diaphragm 30 may have creases or steps formed between adjacent vibrating portions or between vibrating portions adjacent to each other so that the plurality of vibrating portions can be easily displaced.

The diaphragm 30 deforms the pressure chamber 31 by displacing the portion facing the piezoelectric column 21 due to the expansion and compression of the piezoelectric column 21 caused by the longitudinal vibration of the piezoelectric column 21. Change volume.

The diaphragm 30 is joined to one end surface of the piezoelectric columns 21 and 22 in the second direction and to the end surface of the frame member 60. As an example, in the present embodiment, the main surface of the diaphragm 30 on one side in the second direction is joined to the channel plate 40 . A pressure chamber 31 that can accommodate ink and a guide channel 34 are formed between the diaphragm 30 and the channel plate 40. The other main surface of the diaphragm 30 in the second direction is joined to the piezoelectric columns 21 and 22. Further, the other main surface of the diaphragm 30 in the second direction is joined to the end surface of the frame member 60.

The diaphragm 30 and the frame member 60 form a common chamber 32 that can accommodate ink. The diaphragm 30 has one main surface facing the piezoelectric columns 21 and 22, the frame member 60, and the common chamber 32, and the other main surface facing the pressure chamber 31, the partition wall 42, and the guide channel. 34, each facing 34.

The diaphragm 30 has a plurality of openings 33 that penetrate in the thickness direction and allow the pressure chamber 31 and the common chamber 32 to communicate with each other. The plurality of openings 33 communicate between the plurality of pressure chambers 31 formed on one side of the diaphragm 30 in the thickness direction and the common chamber 32 formed on the other side of the diaphragm 30 in the thickness direction. The diaphragm 30 changes the volume of the pressure chamber 31 by deforming as the piezoelectric column 21 deforms.

The channel plate 40 is joined to one side of the diaphragm 30. The flow path plate 40 is arranged between the nozzle plate 50 and the diaphragm 30. The channel plate 40 forms a predetermined channel 35 . The channel plate 40 includes a frame portion 41 joined to the outer edge of the diaphragm 30, a plurality of partition walls 42 that separate the plurality of channels 35, and a guide wall 43 forming the guide channel 34. .

The predetermined flow path 35 is separated by a partition wall 42 that communicates the plurality of pressure chambers 31 separated by the partition wall 42, the common chamber 32, the plurality of openings 33 of the diaphragm 30, and the pressure chambers 31 and the openings 33. A plurality of guide channels 34 are included.

The plurality of pressure chambers 31 are arranged in a first direction, which is the direction in which the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are arranged. The plurality of pressure chambers 31 arranged in one direction are separated by a partition wall 42 . One side of the plurality of pressure chambers 31 is closed off by the diaphragm 30 in the second direction. The plurality of pressure chambers 31 are formed on the opposite side of the diaphragm 30 from the side where the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are provided. Each pressure chamber 31 communicates with a nozzle 51 formed in a nozzle plate 50 arranged on the opposite side of the diaphragm 30 in the second direction.

The plurality of pressure chambers 31 communicate with a common chamber 32 via a guide channel 34 and an opening 33. The pressure chamber 31 holds liquid supplied from the common chamber 32 through the guide channel 34, and is deformed by the vibration of the diaphragm 30 forming a part of the pressure chamber 31, thereby discharging the liquid from the nozzle 51.

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 provided in the diaphragm 30 and a plurality of guide channels 34 .

The opening 33 is formed in the diaphragm 30. The plurality of openings 33 communicate the common chamber 32 and the plurality of guide channels 34 . The guide channel 34 communicates the opening 33 and the pressure chamber 31 and guides the ink in the common chamber 32 to the pressure chamber 31 .

The partition wall portion 42 is a wall that separates the plurality of pressure chambers 31 arranged in the first direction, separates the plurality of guide channels 34 arranged in the first direction, and constitutes both sides of the pressure chambers 31 and the guide channels 34. It is a member. The partition wall portion 42 is arranged to face the non-driven piezoelectric pole 22 with the diaphragm 30 in between, and is supported by the non-driven piezoelectric pole 22 .

The nozzle plate 50 is made of a metal such as SUS/Ni or a resin material such as polyimide and has a rectangular plate shape with a thickness of about 10 μm to 100 μm. The nozzle plate 50 is arranged on one side of the channel plate 40 so as to cover the opening on one side of the pressure chamber 31 . A plurality of nozzles 51 are formed in the nozzle plate 50 to penetrate in the thickness direction. The nozzles 51 are arranged along the third direction to form a nozzle row. Each nozzle 51 is provided at a position corresponding to the plurality of pressure chambers 31, respectively.

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

As shown in FIG. 5, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data for each piezoelectric pole 21 and 22 in chronological order. The decoder 722 controls the driver 723 for each piezoelectric pole 21, 22 based on the print data stored in the data buffer 721. The driver 723 outputs a drive signal to operate each piezoelectric pole 21, 22 under the control of the decoder 722. The drive signal is a voltage applied to each piezoelectric pole 21, 22.

As a specific example, as shown in FIG. 3, the drive circuit 70 includes a wiring film 71 whose one end is connected to the external electrodes 223 and 224, a driver IC 72 mounted on the wiring film 71, and a driver IC 72 mounted on the wiring film 71 at the other end. A mounted printed wiring board. 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 a portion of the data buffer 721, the decoder 722, and the driver 723, and the remaining portion may be included in a printed wiring board or the like.

The drive circuit 70 drives the piezoelectric columns 21 and 22 by applying a drive voltage to the external electrodes 223 and 224 using the driver IC 72, increases and decreases the volume of the pressure chamber 31, and causes droplets to be ejected from the nozzle 51.

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

The driver IC 72 is connected to the external electrodes 223 and 224 via the wiring film 71. Note that the driver IC 72 is connected to the external electrodes 223 and 224 not by the wiring film 71 but by other means such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste). May be connected.

The driver IC 72 generates control signals and drive signals for operating each piezoelectric pole 21, 22. The driver IC 72 generates a control signal for control such as selecting the timing for ejecting ink and the piezoelectric pole 21 for ejecting ink, in accordance with the image signal input from the control unit 150 of the liquid ejecting apparatus 100. Further, the driver IC 72 generates a voltage to be applied to the piezoelectric pole 21, that is, a drive signal (electric signal) according to the control signal. When the driver IC 72 applies a drive signal to the piezoelectric column 21, the piezoelectric column 21 is driven to displace the diaphragm 30 and change the volume of the pressure chamber 31. As a result, the ink filled in the pressure chamber 31 causes pressure vibrations. Ink is ejected from the nozzle 51 provided in the pressure chamber 31 due to the pressure vibration. Note that the liquid ejection head 1 may be configured to realize gradation expression by changing the amount of ink droplets that land on one pixel. Furthermore, the liquid ejection head 1 may be configured to be able to change the amount of ink droplets that land on one pixel by changing the number of times the ink is ejected. In this way, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pole 21.

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 the control section 150 of the liquid ejection device 100.

Hereinafter, an example of the liquid ejection apparatus 100 including the liquid ejection head 1 will be described with reference to FIGS. 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 section 112 , an image forming section 113 , a medium discharge section 114 , and a transport device 115 . The liquid ejection device 100 also includes a control section 150.

The liquid ejection apparatus 100 conveys ink, etc., as a printing medium, which is an object to be ejected, along a predetermined transport path A from a medium supply section 112 to a medium discharge section 114 through an image forming section 113. This is a liquid ejecting device that performs an image forming process on paper P by ejecting liquid.

The housing 111 constitutes the outer shell of the liquid ejection device 100. A discharge port for discharging the paper P to the outside is provided at a predetermined location of the casing 111.

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

The medium ejection unit 114 includes a paper ejection tray configured to hold the paper P ejected from the ejection port.

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 opposite to each other above the support section 117.

The support unit 117 includes a conveyor belt 118 provided in a loop shape in a predetermined area where image formation is performed, a support plate 119 that supports the conveyor belt 118 from the back side, and a plurality of belt rollers 120 provided on the back side of the conveyor belt 118. , is provided.

During image formation, the support section 117 supports the paper P on a holding surface that is the upper surface of the conveyor belt 118, and also transports the paper P downstream by feeding the conveyor belt 118 at a predetermined timing by rotation of the belt roller 120. Transfer to the side.

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 , and a connection channel 133 that connects the liquid ejection head 1 and the ink tanks 132 . A supply pump 134 is provided.

In this embodiment, a plurality of head units 130 are provided. Each head unit 130 uses ink of a different color. For example, the plurality of head units 130 include liquid ejection heads 1 of four colors, cyan, magenta, yellow, and black, and ink tanks 132 that respectively accommodate inks of these colors. The ink tank 132 is connected to the liquid ejection head 1 through a connection channel 133.

Further, a negative pressure control device such as a pump (not shown) is connected to the ink tank 132. Then, the ink supplied to each nozzle 51 of the liquid ejection head 1 is controlled by controlling the internal pressure of the ink tank 132 by the negative pressure control device in accordance with the water head values of the liquid ejection head 1 and the ink tank 132. It is formed into a meniscus of a predetermined shape.

The supply pump 134 is, for example, a liquid pump configured with a piezoelectric pump. The supply pump 134 is provided in the 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 .

The conveyance device 115 conveys the paper P along a conveyance path A that extends from the medium supply section 112 through the image forming section 113 to the medium discharge section 114. The conveyance device 115 includes a plurality of guide plate pairs 121 arranged along the conveyance path A and a plurality of conveyance rollers 122.

Each of the plurality of guide plate pairs 121 includes a pair of plate members disposed opposite to each other with the paper P to be transported interposed therebetween, and guides the paper P along the transport path A.

The conveyance roller 122 is driven and rotated under the control of the control unit 150 to convey the paper P along the conveyance path A to the downstream side. Note that sensors for detecting the conveyance status of the paper are arranged at various locations on the conveyance path A.

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

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 section 162, various sensors 163, etc. provided in the liquid ejection apparatus 100 through the I/O port 154. The processor 151 transmits the print data stored in the image memory 155 to the drive circuit 70 in the order of drawing.

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

Hereinafter, the characteristics of the liquid ejection head 1 used in the liquid ejection apparatus 100 according to the embodiment and the drive waveform of the liquid ejection head 1 will be described.

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

First, in the liquid ejection head 1, in addition to the natural vibration caused by the fluid vibration of the ink, there is a tendency for the natural vibration caused by the structural vibration of the actuator to occur noticeably.

For example, when a waveform element WA of a drive waveform that falls sharply, such as the waveform element WA of a drive waveform of the prior art shown by a solid line in FIG. As shown by the solid line in FIG. 7, PA occurs when pressure vibrations with a short period are superimposed on pressure vibrations with a long period. This also occurs when a waveform element of a drive waveform that rises steeply is applied to the liquid ejection head 1, as pressure vibrations with a short period are superimposed on pressure vibrations with a long period. Further, the flow velocity vibration UA generated in the nozzle 51 during the pressure vibration PA due to the waveform element WA is generated by superimposing flow velocity vibrations with short periods, as shown by the solid line in FIG.

The results of frequency spectrum analysis from the pressure vibration PA in FIG. 7 are shown in FIG. 9 by a solid line. 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. Recognize. For example, the first natural vibration frequency FA is a fluid natural vibration frequency, and the second natural vibration frequency FB, which is larger than the first natural vibration frequency FA, is a structural natural vibration frequency that is desirable for the operation of ejecting ink. There is no parasitic vibration. Here, for example, the second natural vibration frequency FB, which is a structural natural vibration with a large frequency, is not only unnecessary for ink ejection, but also may cause ink cavitation and ink mist.

For example, in order to suppress such second natural vibration frequency FB, as shown by the broken line in FIG. When the liquid ejection head 1 is driven, the second natural vibration frequency FB can be suppressed as shown in the pressure vibration PB shown by the broken line in FIG. 7 and the flow velocity vibration UB shown by the broken line in FIG. 8, so that ink cavitation and ink mist are generated. can be reduced. For example, when frequency spectrum is analyzed from the pressure vibration PB in FIG. 7, it can be seen that the second natural vibration frequency FB is reduced, as shown by the broken line in FIG.

However, although the diagonal waveform element such as the waveform element WB can suppress the second natural vibration frequency FB, it requires a drive waveform generation section that changes the voltage diagonally, making the drive circuit 70 complicated.

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

Specifically, in the liquid ejection head 1, the frequency response characteristic of the ink within the nozzle 51 with respect to the waveform element WA of the driving waveform that falls sharply is a first peak frequency FA and a second peak frequency that is larger than the first peak frequency FA. Becomes FB.

The drive circuit 70 of the liquid ejection head 1 according to the embodiment generates a drive waveform including multi-stage step waveform elements at the rise and fall of the voltage as an electric signal for driving the actuator 20. In the following description, "multiple stages" will be explained as "N stages". Here, N is a natural number of 2 or more.

The drive waveform of the drive signal generated by the drive circuit 70 is, for example, an intermediate voltage in at least one of the rising and falling waveform elements of the drive waveform of the actuator, when the upper limit voltage VH and the lower limit voltage VL of the electric signal are set. VM=n·(VH−VL)/N is held for a time t=1/FB/N=1/(FB·N), and an N step waveform is output to the actuator.

Here, N is the same as the number of steps in the step waveform, and in the case of a two-step step waveform, N is 2, and in the case of a three-step step waveform, N is 3. Further, here, n is a natural number from 1 to N-1. For example, n is the number of stages of the intermediate voltage VN to be determined when the lower limit voltage is the 0th stage. As a specific example, n is 1 for a two step waveform, and n is 1 and 2 for a three step waveform.

Next, as an example of the drive waveform, a drive waveform including a two-stage step waveform element generated by the drive circuit 70 will be explained using FIGS. 10 to 15. The waveform element WC of the drive waveform shown in FIG. 10 is a two-step waveform element in which N=2 at the falling edge. Further, in the example of the drive waveform shown in FIG. 10, the upper limit voltage VH of the electric signal is set to V, and the lower limit voltage VL is set to 0.

When changing the driving voltage 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
becomes.

Also, 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
becomes.

Therefore, 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 holding the intermediate voltage is 0.5/FB.

Pressure vibration PC caused by such a waveform element WC is shown by a solid line in FIG. As is clear from FIG. 11, the pressure vibration PC exhibits substantially the same behavior as the pressure vibration PB caused by the diagonal waveform element WB. This also shows that the waveform element WC of the drive waveform can sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

Further, the flow velocity vibration UC due to the waveform element WC is shown by a solid line in FIG. As is clear from FIG. 12, the flow velocity vibration UC exhibits substantially the same behavior as the flow velocity vibration UB caused by the diagonal waveform element WB. This also shows that the waveform element WC of the drive waveform can sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

Next, as an example of a drive waveform using an N-stage step waveform element generated by the drive circuit 70, a two-stage step waveform element is used 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. An example of the drive waveform WE used in this case is shown in FIG. 13 by a solid line. Note that the example of the drive waveform WE shown in FIG. 13 consists of three ejection pulses WEa to WEc and WEd for canceling residual pressure vibrations. Further, for comparison with the drive waveform WE of the embodiment, a drive waveform WD including a diagonal waveform element of the prior art is shown by a broken line in FIG.

Further, the holding time TA of the intermediate voltage VM is TA=1/FB/2=0.5 with respect to the second natural vibration frequency FB, which is a parasitic vibration that is undesirable for the ink ejection operation, such as a structural natural vibration. /FB. Further, with respect to the first natural vibration frequency FA, which is a fluid-like natural vibration, the widths of the pulses WEa to WEd are TB=TE=0.5/FA and TC=TD=1/FA. Furthermore, the lower limit voltages are different between the three ejection pulses WEa to WEc and WEd for canceling the residual pressure vibration.

The pressure vibration PE caused by the drive waveform WE including the two-step waveform element is shown by a solid line in FIG. 14, and the pressure vibration PD caused by the drive waveform WD of the prior art is shown by a broken line in FIG. As shown in FIG. 14, the pressure vibration PE caused by the drive waveform WE exhibits substantially the same behavior as the pressure vibration 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 vibrations similar to the drive waveform WD using the diagonal waveform element of the prior art.

Further, the flow velocity vibration UE of the nozzle caused by the drive waveform WE including the two-step waveform element is shown by a solid line in FIG. 15, and the flow velocity vibration UD of the nozzle caused by the drive waveform WD of the prior art is shown by a broken line in FIG. As shown in FIG. 15, the flow velocity vibration UE caused by the drive waveform WE exhibits substantially the same behavior as the flow velocity vibration UD 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 flow velocity oscillations similar to the drive waveform WD using the diagonal waveform element of the prior art.

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 explained using FIGS. 16 to 21. The waveform element WF as a 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. Further, in the example of the drive waveform shown in FIG. 16, the upper limit voltage VH of the electric signal is set to V, and the lower limit voltage VL is set to 0.

When changing the drive voltage from voltage V to voltage 0, VH=V, VL=0, N=3, and n=1, 2. Therefore, among 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
Therefore, the intermediate voltage VM on the higher voltage value side is n=2,
VM=n・(VH-VL)/N=2・(V-0)/3=2V/3
becomes.

Moreover, the time t for applying the intermediate voltage VM of the waveform element WF is:
t=1/FB/N=1/FB/3=1/(3FB)
becomes.

Therefore, when the voltage falls from V to 0, the waveform element WF of the drive waveform changes the voltage in three stages from V to 2V/3, V/3, and 0 as an intermediate voltage. Further, voltages of 2V/3 and V/3 as intermediate voltages are each held for a time of 1/(3FB).

Pressure vibration PF caused by such a waveform element WF is shown by a solid line in FIG. As is clear from FIG. 17, the pressure vibration PF exhibits substantially the same behavior as the pressure vibration PB caused by the oblique waveform element WB. This also shows that the waveform element WF of the drive waveform can sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

Furthermore, as is clear from FIGS. 11 and 17, the pressure vibration PF of the waveform element WF, which is a three-step waveform element, is more diagonal than the pressure vibration PC of the waveform element WC, which is a two-step waveform element. The behavior is closer to the pressure vibration PB due to the waveform element WB. From this, it can be seen that by increasing the number of stages of the waveform elements, the pressure vibration can be more closely approximated to the diagonal waveform element WB.

Further, the flow velocity vibration UF due to the waveform element WF is shown by a solid line in FIG. As is clear from FIG. 18, the flow velocity vibration UF exhibits substantially the same behavior as the flow velocity vibration UB caused by the oblique waveform element WB. This also shows that the waveform element WF of the drive waveform can sufficiently suppress the second natural vibration frequency FB, which is a parasitic vibration such as a structural natural vibration.

Furthermore, as is clear from FIGS. 12 and 18, the flow velocity vibration UF of the waveform element WF, which is a three-step waveform element, is more diagonal than the flow velocity vibration UC of the waveform element WC, which is a two-step waveform element. The behavior is closer to the flow velocity vibration UB due to the waveform element WB. From this, it can be seen that by increasing the number of stages of the waveform elements, the flow velocity vibration can be more approximated to the oblique waveform element WB.

Next, as an example of a drive waveform using an N-stage step waveform element generated by the drive circuit 70, a three-stage step waveform element is used 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. An example of the drive waveform WG used in this case is shown in FIG. 19 by a solid line. Note that the example of the drive waveform WG shown in FIG. 19 consists of three ejection pulses WGa to WGc and WGd for canceling residual pressure vibrations. Further, 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 a broken line in FIG.

In addition, the holding time TA of the intermediate voltage VM is determined per stage as TA=1/FB/ N=1/(3FB). Furthermore, with respect to the first natural vibration frequency FA, which is a fluid-like natural vibration, the widths of the pulses WGa to WGd are TB=TE=0.5/FA and TC=TD=1/FA. Furthermore, the lower limit voltages are different between the three ejection pulses WGa to WGc and WGd for canceling residual pressure vibration.

The pressure vibration PG caused by the drive waveform WG including the three-step waveform element is shown by a solid line in FIG. 20, and the pressure vibration PD caused by the drive waveform WD of the prior art is shown by a broken line in FIG. As shown in FIG. 20, the pressure vibration PG caused by the drive waveform WG exhibits substantially the same behavior as the pressure vibration PD caused by the drive waveform WD of the prior art. This also shows that the drive waveform WG using the three-step waveform element of the embodiment can generate pressure vibrations similar to the drive waveform WD using the diagonal waveform element of the prior art.

Further, the flow velocity vibration UG of the nozzle caused by the drive waveform WG including the three-step waveform element is shown by a solid line in FIG. 21, and the flow velocity vibration UD of the nozzle caused by the drive waveform WD of the prior art is shown by a broken line in FIG. As shown in FIG. 21, the flow velocity vibration UG caused by the drive waveform WG exhibits substantially the same behavior as the flow velocity vibration UD caused by the drive waveform WD of the prior art. This also shows that the drive waveform WG using the three-step waveform element of the embodiment can generate flow velocity oscillations similar to the drive waveform WD using the diagonal waveform element of the prior art.

As described above, the liquid ejection head 1 divides and changes the voltage of the drive waveform as a drive signal generated by the drive circuit 70 for driving the actuator 20 into N stages, and holds each intermediate voltage for 1 time. /f2/N. Thereby, the liquid ejection head 1 can suppress the second natural vibration frequency FB, which is a parasitic vibration that is undesirable for the ink ejection operation. Although this effect has been shown in the embodiment for N=2 and N=3 as a plurality of stages N, the same effect can be obtained when N is 4 or more.

Further, the drive circuit 70 may generate a drive waveform including a multi-stage step waveform element without generating a drive waveform including a diagonal waveform element. Therefore, the configuration of the drive circuit 70 may be simpler than that of a drive circuit that generates waveform elements including diagonal waveform elements. The drive circuit 70 and the liquid ejection head 1 can suppress parasitic vibrations without increasing cost.

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

As described above, according to the liquid ejection head 1 according to one embodiment, by using a waveform element including a multi-step waveform element that applies an intermediate voltage for a predetermined period of time, the drive circuit 70 can also be used as a Vibration can be suppressed.

Note that the embodiments are presented as examples, and are not limited to the examples described above. For example, the specific configuration of the piezoelectric columns 21 and 22 described above, the shape of the flow path, the configuration and positional relationship of various parts including the flow path plate 40, nozzle plate 50, and frame member 60 are limited to the example described above. Rather, it can be changed as appropriate. Further, 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. Further, a dummy chamber may be formed between the plurality of pressure chambers 31.

Further, in the above-mentioned example, in the liquid ejection head 1 and the liquid ejection device 100, the liquid ejected is ink for printing, but the liquid is not limited to the above-mentioned ink, but transparent glossy ink, infrared rays, infrared rays, etc. Ink that develops color when irradiated with ultraviolet light or other special inks can also be ejected. Furthermore, the liquid ejection head 1 may be capable of ejecting liquid other than ink. Note that the liquid ejected by the liquid ejection head 1 may be a dispersion liquid such as a suspension. Examples of liquids other than ink ejected by the liquid ejection head 1 include liquids containing conductive particles for forming wiring patterns on printed wiring boards, and liquids containing cells for forming artificial tissues or organs. , binders such as adhesives, waxes, liquid resins, and the like. Therefore, the liquid ejection device can also be used in, for example, 3D printers, industrial manufacturing machines, medical applications, and the like.

According to the liquid ejection head of at least one embodiment described above, by using a waveform element including a multi-stage step waveform element that applies an intermediate voltage for a predetermined period of time, a specific natural vibration can be generated even as a simple drive circuit. It can be suppressed.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1...Liquid ejection head, 10...Base, 20...Actuator, 21...Piezoelectric pole, 22...Non-driven piezoelectric pole, 23...Groove, 30...Vibration plate, 31...Pressure chamber, 32...Common chamber, 33...Opening, 34 ...Guide channel, 35... Channel, 40... Channel plate, 41... Frame-shaped part, 42... Partition part, 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... Housing, 112... Medium supply section, 113... Image forming section, 114... Medium discharge section, 115... Transport device, 117... Support section, DESCRIPTION OF SYMBOLS 118... Conveyance belt, 119... Support plate, 120... Belt roller, 121... Guide plate pair, 122... Conveyance roller, 130... Head unit, 132... Ink tank, 133... Connection channel, 134... Supply pump, 150... Control unit, 151... Processor, 154... I/O port, 155... Image memory, 161... Drive motor, 162... Operation unit, 163... Seed sensor, 200... External connection 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 (5)

a nozzle plate including a nozzle that discharges liquid;
a pressure chamber communicating with the nozzle;
an actuator that changes the volume of the pressure chamber according to an electrical signal;
generating the electric signal that drives the actuator, and having a frequency response characteristic of the liquid in the nozzle with respect to the electric signal as a first peak frequency FA and a second peak frequency FB higher than the first peak frequency FA; When the upper limit voltage VH and lower limit voltage VL of the electric signal are set, and n is a natural number greater than or equal to 1 and smaller than N, the intermediate voltage VM=n・(VH -VL)/N for a time t=1/FB/N and outputs a drive waveform including N step waveform elements to the actuator. The actuator is formed of a laminated piezoelectric member, and includes a plurality of piezoelectric columns that change the volume of the pressure chamber and a plurality of non-driven piezoelectric columns that are arranged alternately with the plurality of piezoelectric columns that do not change the volume of the pressure chamber. have,
The liquid ejection head according to claim 1. The liquid ejection head according to claim 1 or 2, wherein the step waveform element has two stages. 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. The first peak frequency FA is the natural vibration frequency of the liquid,
The liquid ejection head according to any one of claims 1 to 4, wherein the second peak frequency FB is a natural vibration frequency of the actuator.