Liquid dispensing head

Abstract

The ejection force of each droplet should be approximately the same, while increasing the ejection speed of subsequent droplets. [Solution] The liquid discharge head is equipped with a drive circuit that generates a drive signal to drive an actuator and includes multiple discharge waveforms that discharge multiple droplets from the nozzle, all of which have the same waveform width. The discharge waveform of the drive signal includes an expanding potential difference that expands the volume of the pressure chamber, a contracting potential difference that reduces the volume of the pressure chamber, and at least one intermediate potential difference between the expanding and contracting potential differences. The drive circuit cancels out vibrations at an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency of the liquid in the pressure chamber caused by the change in potential difference by at least one more change in potential difference performed after the change in potential difference. The interval between the multiple discharge waveforms is matched to the period that strengthens the residual vibration of the liquid in the pressure chamber caused by the previously generated discharge waveform and the vibration of the liquid in the pressure chamber caused by the subsequently generated discharge waveform, thereby increasing the discharge speed of subsequent droplets.

Description

Technical Field

[0001] Embodiments of the present invention relate to a liquid ejection head.

Background Art

[0002] Conventionally, in a liquid ejection head that ejects liquid, by continuously ejecting a plurality of droplets, the dot diameter when the droplets land on the medium is increased, and a gradation expression of the ink concentration on the medium is realized. However, when there is variation in the main acoustic vibration frequencies of a plurality of pressure chambers, if the same drive waveform (a drive waveform with different ejection waveform widths for the first drop and the last drop) is input to the plurality of pressure chambers to continuously eject a plurality of droplets, the continuously ejected droplets may not coalesce, which may cause deterioration of the printing quality.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a liquid ejection head that makes the ejection force of each droplet substantially the same and can increase the ejection speed of subsequent droplets.

Means for Solving the Problems

[0005] The liquid discharge head comprises a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate is equipped with a nozzle for discharging liquid. The pressure chamber communicates with the nozzle. The actuator varies the volume of the pressure chamber in response to a drive signal. The drive circuit generates the drive signal for driving the actuator. The drive signal includes a plurality of discharge waveforms that cause a plurality of liquid droplets to be discharged from the nozzle. The waveform widths of the plurality of discharge waveforms are the same. The discharge waveform of the drive signal includes an expansion potential difference that expands the volume of the pressure chamber, a contraction potential difference that reduces the volume of the pressure chamber, and at least one intermediate potential difference between the expansion potential difference and the contraction potential difference. The drive circuit cancels out vibrations of the acoustic resonance frequency in a frequency range higher than the principal acoustic resonance frequency of the liquid in the pressure chamber caused by the change in potential difference by at least one more change in potential difference performed after the change in potential difference. The intervals between the multiple discharge waveforms coincide with the period that amplifies the residual vibration of the liquid in the pressure chamber caused by the discharge waveform generated first and the vibration of the liquid in the pressure chamber caused by the discharge waveform generated afterward. [Brief explanation of the drawing]

[0006] [Figure 1] A cross-sectional view showing the configuration of the liquid discharge head according to the embodiment, with some parts omitted. [Figure 2] A cross-sectional view showing the configuration of the liquid discharge head according to the embodiment, with some parts omitted. [Figure 3] A schematic block diagram showing the configuration of the drive circuit for the liquid discharge head according to the embodiment. [Figure 4] An explanatory diagram showing the configuration of a liquid dispensing device using a liquid dispensing head according to the embodiment. [Figure 5] A block diagram showing an example of the configuration of a liquid dispensing device according to the embodiment. [Figure 6] An explanatory diagram showing an example of a drive waveform, including the discharge waveform and cancellation waveform, of a liquid discharge head relating to a comparative example. [Figure 7] An explanatory diagram showing an example of the drive waveform and acoustic vibration of a liquid discharge head according to an embodiment. [Figure 8]An explanatory diagram showing the relationship between the drive waveform and the discharged liquid droplet in an example of a liquid discharge head according to the embodiment. [Figure 9] An explanatory diagram showing an example of a liquid droplet discharged from a liquid discharge head according to the embodiment. [Figure 10] An explanatory diagram showing an example of frequency analysis of a liquid dispensing head related to a comparative example. [Figure 11] An explanatory diagram showing an example of the synthesis of the main acoustic vibration and parasitic vibration of a liquid discharge head in a comparative example. [Figure 12] An explanatory diagram showing an example of frequency analysis of a liquid dispensing head related to a comparative example. [Figure 13] An explanatory diagram showing an example of the drive waveform and acoustic vibration of a liquid discharge head in a comparative example. [Figure 14] An explanatory diagram showing an example of the drive waveform and acoustic vibration of a liquid discharge head in a comparative example. [Figure 15] An explanatory diagram showing an example of the drive waveform of the liquid discharge head according to the embodiment. [Figure 16] An explanatory diagram showing an example of the drive waveform of a liquid discharge head according to another embodiment. [Figure 17] An explanatory diagram showing an example of the drive waveform of a liquid discharge head according to an embodiment and a comparative example. [Figure 18] An explanatory diagram showing an example of the drive waveform of a liquid discharge head according to another embodiment. [Figure 19] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 20] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 21] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 22] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 23]An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 24] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 25] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 26] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 27] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 28] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 29] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 30] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 31] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 32] An explanatory diagram showing the relationship between the waveform width and the ejection force based on the conditions of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 33] An explanatory diagram showing an example of the drive waveform of a liquid ejection head according to another embodiment. [Figure 34] An explanatory diagram showing an example of the drive waveform of another embodiment. [Figure 35] An explanatory diagram showing an example of the drive waveform of another embodiment. [Modes for carrying out the invention]

[0007] The configuration of the liquid discharge head 1 and the liquid discharge device 100 using the liquid discharge head 1 according to the embodiment will be described below with reference to Figures 1 to 5. Figure 1 is a cross-sectional view showing the configuration of the liquid discharge head 1 according to the embodiment with some parts omitted, and Figure 2 is a cross-sectional view showing the configuration of the liquid discharge head 1 with some parts omitted. Figure 3 is a block diagram schematically showing the configuration of the drive circuit 70 of the liquid discharge head 1. Figure 4 is an explanatory diagram showing the configuration of the liquid discharge device 100 using the liquid discharge head 1 according to the embodiment, and Figure 5 is a block diagram showing an example of the configuration of the liquid discharge device 100. Note that in each figure, the configuration is shown enlarged, reduced, or omitted as appropriate for explanatory purposes.

[0008] The liquid ejection head 1 according to this embodiment is, for example, an inkjet head that ejects ink as a liquid. As shown in Figures 1 and 2, the liquid ejection head 1 comprises a base 10, an actuator 20, a diaphragm 30, a flow path plate 40, a nozzle plate 50 having a plurality of nozzles 51, and a drive circuit 70.

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

[0010] The actuator 20 is a piezoelectric member comprising, for example, a plurality of piezoelectric columns 21 and non-driven piezoelectric columns 22 arranged alternately with the plurality of piezoelectric columns 21. The actuator 20 is formed in a comb-like shape by arranging the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 in one direction at predetermined intervals. For example, in such an actuator 20, a laminated piezoelectric member joined to a base 10 is processed by dicing grooves from the end face opposite to the base 10 side to form a plurality of piezoelectric elements formed in a rectangular column shape at predetermined intervals on a single piezoelectric member. The formed plurality of piezoelectric elements are then provided with electrodes, etc., to constitute a plurality of alternately arranged piezoelectric columns 21 and a plurality of non-driven piezoelectric columns 22 as piezoelectric elements. That is, the actuator 20 is divided into multiple parts at one end (diaphragm 30 side) by the formed plurality of grooves, and the other end (base 10 side) is connected.

[0011] For example, the laminated piezoelectric member constituting the actuator 20 is formed by laminating and sintering sheet-shaped piezoelectric material. As a specific example, as shown in Figures 1 and 2, the piezoelectric column 21 and the non-driven piezoelectric column 22 are, for example, laminated piezoelectric bodies used as driving elements. The piezoelectric column 21 and the non-driven piezoelectric column 22 comprise a plurality of laminated piezoelectric layers, a plurality of internal electrodes formed on the main surface of each piezoelectric layer, and a plurality of external electrodes. For example, the piezoelectric column 21 and the non-driven piezoelectric column 22 have the same configuration.

[0012] The piezoelectric layer is constructed in the form of a thin plate from a piezoelectric material such as PZT (lead zirconate titanate) or lead-free KNN (potassium sodium niobate). Multiple piezoelectric layers are stacked in the thickness direction and bonded together by sintering. Here, the stacking direction of the multiple piezoelectric layers is perpendicular to the alignment direction of the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22.

[0013] The internal electrodes are conductive films formed in a predetermined shape from a sinterable conductive material such as silver-palladium. The internal electrodes are formed in predetermined regions on the main surface of each piezoelectric layer. Multiple internal electrodes are configured as alternating poles in the direction of arrangement.

[0014] The external electrodes are formed on the surfaces of multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and are constructed by gathering the ends of the internal electrodes. The external electrodes are deposited using known methods such as plating or sputtering, using materials such as Ni, Cr, and Au. The multiple external electrodes are arranged on different side surfaces of the multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and are configured as different poles. Note that the external electrodes of different poles may be routed to different regions within the same side surface of the multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22.

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

[0016] These external electrodes are connected, for example, to a drive circuit 70. For example, each external electrode is connected by wiring to a control unit 150, which acts as a drive unit, via a driver 723 of the drive circuit 70 (described later), and is configured to be controllable by control of a processor 151.

[0017] The piezoelectric columns 21 and non-driven piezoelectric columns 22 vibrate longitudinally along the stacking direction of the piezoelectric material layers when a voltage is applied to their internal electrodes via external electrodes. This longitudinal vibration refers to, for example, "vibration in the thickness direction defined by the piezoelectric constant d33". For example, as shown in Figure 2, multiple piezoelectric columns 21, arranged every other, are positioned corresponding to the pressure chamber 46 with the diaphragm 30 in between, while the remaining non-driven piezoelectric columns 22 are positioned opposite the partition wall 42 with the diaphragm 30 in between.

[0018] The piezoelectric column 21 vibrates vertically when a voltage is applied, displacing the diaphragm 30. That is, the piezoelectric column 21 deforms the pressure chamber 46. The non-driven piezoelectric column 22 is positioned opposite the partition wall 42. No voltage is applied to the non-driven piezoelectric column 22. That is, each piezoelectric column 21 constitutes an actuator that deforms the pressure chamber 46 when driven, and each non-driven piezoelectric column 22 constitutes a support column. That is, the piezoelectric column 21 expands and contracts the pressure chamber 46 to vary the volume of the pressure chamber 46.

[0019] The diaphragm 30 is joined to one side of the piezoelectric layers of the plurality of piezoelectric pillars 21 and 22 in the stacking direction, i.e., the side facing the nozzle plate 50. The diaphragm 30 deforms, for example, by driving the piezoelectric pillar 21. The diaphragm 30 is joined to the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 of the actuator 20.

[0020] The diaphragm 30 is, for example, a flat plate arranged such that its thickness direction is the same as the stacking direction of the piezoelectric layers. The diaphragm 30 has a surface direction that extends in the direction of the arrangement of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22. The diaphragm 30 is, for example, a metal plate. The diaphragm 30 has a plurality of vibrating parts 301 that face each pressure chamber 46 and are individually displaceable. The diaphragm 30 is formed by the plurality of vibrating parts 301 being integrally connected.

[0021] For example, the diaphragm 30 is constructed as a single flat plate, and each region joined to the piezoelectric column 21 is displaced individually. The diaphragm 30 is made of, for example, a stainless steel plate. The diaphragm 30 may have folds or steps formed between the vibrating parts 301 and adjacent parts, or between adjacent vibrating parts 301, so that the multiple vibrating parts 301 can be easily displaced.

[0022] The diaphragm 30 expands and contracts the pressure chamber 46 by displacing a portion of the piezoelectric column 21 that is positioned opposite the piezoelectric column 21 due to the extension and compression of the piezoelectric column 21 caused by the longitudinal vibration of the piezoelectric column 21, thereby varying the volume of the pressure chamber 46.

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

[0024] The diaphragm 30 has one main surface facing the piezoelectric columns 21 and 22, respectively, and the other main surface facing the pressure chamber 46 and the partition wall 42, respectively.

[0025] The flow path plate 40 is joined to the diaphragm 30. The flow path plate 40 is positioned between the nozzle plate 50 and the diaphragm 30. The flow path plate 40 has a plurality of partition walls 42. The flow path plate 40 also forms a predetermined flow path 45. The flow path plate 40 is formed, for example, by stacking a plurality of plates 401, each with a portion open, to form the plurality of partition walls 42 and the predetermined flow path 45.

[0026] Multiple partition walls 42 are arranged in the direction of the alignment of the multiple piezoelectric columns 21 and 22, and face the non-driven piezoelectric columns 22 via the diaphragm 30. The partition walls 42 separate the multiple pressure chambers 46 of a predetermined flow path 45 (described later), as well as the multiple individual flow paths 47.

[0027] The predetermined flow path 45 includes a plurality of pressure chambers 46 separated by partition walls 42 of the flow path plate 40, a plurality of individual flow paths 47 separated by partition walls 42, and a common flow path 48 communicating with the plurality of individual flow paths 47.

[0028] Multiple pressure chambers 46 are arranged in the direction of the arrangement of multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and face the multiple piezoelectric columns 21 via a diaphragm 30. Multiple pressure chambers 46 arranged in one direction are separated by partition walls 42. Multiple partition walls 42 positioned between the multiple pressure chambers 46 face the multiple non-driven piezoelectric columns 22 via a diaphragm 30. Multiple pressure chambers 46 are formed when a flow path plate 40 is closed on one side by a diaphragm 30 and closed on the other side by a nozzle plate 50 in the stacking direction of the piezoelectric material layers. Nozzles 51 formed on the nozzle plate 50 are also arranged in the pressure chambers 46.

[0029] Multiple pressure chambers 46 communicate with a common channel 48 via individual channels 47. Each pressure chamber 46 holds liquid supplied from the common channel 48 through the individual channels 47, and discharges the liquid from the nozzle 51 by deforming due to the vibration of a vibrating plate 30 that forms part of the pressure chamber 46. The individual channels 47 connect the common channel 48 and the pressure chambers 46. The same number of individual channels 47 as pressure chambers 46 are provided. The cross-sectional shape of the individual channels 47 differs from the cross-sectional shape of the pressure chambers 46. The cross-sectional area of ​​the individual channels 47 is smaller than the cross-sectional area of ​​the pressure chambers 46. The common channel 48 is fluidically connected to the multiple individual channels 47 and communicates with the pressure chambers 46 through each individual channel 47.

[0030] The nozzle plate 50 is formed from a metal such as SUS or Ni, or a resin material such as polyimide. The nozzle plate 50 is joined to the flow path plate 40 and covers a plurality of pressure chambers 46. The nozzle plate 50 has a plurality of nozzles 51 formed opposite the plurality of pressure chambers 46 and penetrating in the thickness direction. A nozzle row is formed by the plurality of nozzles 51.

[0031] As shown in Figure 5, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data chronologically for each piezoelectric pole 21, 22. The decoder 722 controls the driver 723 for each piezoelectric pole 21, 22 based on the print data stored in the data buffer 721. Based on the control of the decoder 722, the driver 723 outputs a drive signal to operate each piezoelectric pole 21, 22. The drive signal is the voltage applied to each piezoelectric pole 21, 22.

[0032] As a specific example, as shown in Figure 1, the drive circuit 70 comprises a wiring film 71 with one end connected to an external electrode, a driver IC 72 mounted on the wiring film 71, and a printed circuit board mounted on the other end of the wiring film 71. For example, the driver IC 72 has a data buffer 721, a decoder 722, and a driver 723. Alternatively, the driver IC 72 may have some of the components of the data buffer 721, decoder 722, and driver 723, while the printed circuit board or the like may have the remaining components.

[0033] The drive circuit 70 drives the piezoelectric column 21 by applying a drive voltage to the external electrodes using the driver IC 72, thereby varying the volume of the pressure chamber 46 and causing droplets to be ejected from the nozzle 51.

[0034] The wiring film 71 is connected to multiple individual electrodes and a common electrode. For example, the wiring film 71 is an ACF (anisotropic conductive film) fixed to the connection part of the external electrode by thermocompression or the like. The wiring film 71 is, for example, a COF (Chip on Film) on which the driver IC 72 is mounted.

[0035] The driver IC 72 is connected to the external electrodes via the wiring film 71. Alternatively, the driver IC 72 may be connected to the external electrodes by other means, such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste), instead of the wiring film 71.

[0036] The driver IC 72 applies signals to each piezoelectric column 21 and 22 to generate control signals and drive signals for operating the piezoelectric column 21. The driver IC 72 generates control signals for control purposes, such as selecting the timing for ink ejection and which piezoelectric column 21 to eject the ink, according to the image signal input from the control unit 150 of the liquid ejection device 100. The driver IC 72 also generates a voltage to be applied to the piezoelectric column 21, i.e., a drive signal (electrical signal), according to the control signals. When the driver IC 72 applies a drive signal to the piezoelectric column 21, the piezoelectric column 21 is driven by displacing the diaphragm 30, thereby varying the volume of the pressure chamber 46 to expand and contract. This causes pressure vibrations in the ink filled in the pressure chamber 46. Due to these pressure vibrations, ink is ejected from the nozzle 51 provided in the pressure chamber 46. The liquid ejection head 1 may be configured to achieve gradation expression by changing the amount of ink droplets that land on one pixel. Alternatively, the liquid ejection head 1 may be configured to change the amount of ink droplets that land on one pixel by changing the number of times the ink is ejected. Thus, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pole 21.

[0037] Next, an example of the drive circuit 70 will be described as shown in Figure 3. The drive circuit 70 includes, for example, a voltage control unit 724 and the same number of voltage switching units 725 as there are pressure chambers 46, all located within the driver IC 72. However, in Figure 3, only two voltage switching units 725 are shown, and the other voltage switching units 725 are not shown.

[0038] The drive circuit 70 is connected to the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85. The drive circuit 70 applies the voltage supplied from the first voltage source 81 to each wiring electrode 726. The drive circuit 70 also selectively applies the voltage supplied from the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85 to each wiring electrode 727. Here, since the actuator 20 is a stacked PZT, applying bipolar voltage tends to degrade it, the voltages supplied by the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85 are set to either the ground voltage or one of either positive or negative polarity relative to the ground voltage.

[0039] The output voltage of the first voltage source 81 is, for example, the ground voltage, and its voltage value is V0 (V0 = 0 [V]). The voltage value indicated by the output voltage of the second voltage source 82 is V1. Note that the voltage value V1 is higher than V0. The voltage value indicated by the output voltage of the third voltage source 83 is, for example, V2. Note that the voltage value V2 is higher than V0 and lower than V1. The voltage value indicated by the output voltage of the fourth voltage source 84 is V3. Note that the voltage value V3 is lower than V0. The voltage value indicated by the output voltage of the fifth voltage source 85 is, for example, V4. Note that the voltage value V4 is lower than V0 and higher than V3.

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

[0041] The voltage control unit 724 is connected to each of the multiple voltage switching units 725. The voltage control unit 724 outputs a command to each voltage switching unit 725 indicating which voltage source to select from the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85. For example, the voltage control unit 724 receives an image signal from the control unit 150 and determines the switching timing of the voltage source in each voltage switching unit 725. Then, at the determined switching timing, the voltage control unit 724 outputs a command to the voltage switching unit 725 to select one of the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85. The voltage switching unit 725 switches the voltage source connected to the wiring electrode 727 according to the command from the voltage control unit 724.

[0042] The voltage switching unit 725 is composed of, for example, a semiconductor switch. The voltage switching unit 725 connects the wiring electrode 727 to one of the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85 under the control of the voltage control unit 724. Therefore, the internal electrodes of different poles of the piezoelectric column 21 are connected to the wiring electrode 726 and the wiring electrode 727 via external electrodes (common electrode and individual electrode).

[0043] In this drive circuit 70, the drive circuit switches the connection wiring between the voltage sources 81, 82, 83, 84, and 85 and the actuator 20 using a switching circuit composed of a voltage control unit 724 and multiple voltage switching units 725, thereby inputting drive waveforms having at least three types of potential differences between the electrodes of the actuator 20 as drive signals. Here, the drive waveform is the drive waveform that causes the actuator 20 to discharge droplets when driven. In this embodiment, potential differences other than the largest and smallest potential differences are called intermediate potential differences.

[0044] The printed circuit board is a Printing Wiring Assembly (PWA) on which various electronic components and connectors are mounted. The printed circuit board is connected to the control unit 150 of the liquid dispensing device 100.

[0045] Next, an example of a liquid ejection device 100 equipped with a liquid ejection head 1 will be described with reference to Figures 4 and 5. The liquid ejection device 100 is, for example, an inkjet recording device. The liquid ejection device 100 comprises a housing 111, a media supply unit 112, an image forming unit 113, a media discharge unit 114, and a transport device 115. The liquid ejection device 100 also includes a control unit 150.

[0046] The liquid dispensing device 100 is a liquid dispensing device that performs image forming processing on paper P by dispensing a liquid such as ink while transporting paper P, which is the printing medium to be dispensed, along a predetermined transport path A from the media supply unit 112 through the image forming unit 113 to the media discharge unit 114.

[0047] The housing 111 constitutes the outer casing of the liquid dispensing device 100. The housing 111 is provided with an outlet at a predetermined location for discharging the paper P to the outside.

[0048] The media supply unit 112 is equipped with multiple paper feed cassettes and is configured to hold multiple sheets of paper P of various sizes stacked on top of each other.

[0049] The media discharge unit 114 includes a paper output tray configured to hold the paper P discharged from the discharge port.

[0050] The image forming unit 113 includes a support unit 117 that supports the paper P, and a plurality of head units 130 that are positioned opposite each other above the support unit 117.

[0051] 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, and a plurality of belt rollers 120 provided on the back of the conveyor belt 118.

[0052] During image formation, the support unit 117 supports the paper P on the 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.

[0053] The head unit 130 comprises a liquid ejection head 1, a plurality of ink tanks 132 which serve as liquid tanks and are mounted on the liquid ejection head 1, a connecting channel 133 that connects the liquid ejection head 1 and the ink tanks 132, and a supply pump 134.

[0054] In this embodiment, multiple head units 130 are provided. Each head unit 130 uses a different color of ink. For example, the multiple head units 130 include four liquid ejection heads 1 for cyan, magenta, yellow, and black, and ink tanks 132 that each contain ink of these colors. The ink tanks 132 are connected to a common flow path 48 of the liquid ejection heads 1 by a connecting flow path 133.

[0055] Furthermore, 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 forming the ink supplied to each nozzle 51 of the liquid ejection head 1 into a meniscus of a predetermined shape.

[0056] The supply pump 134 is a liquid transfer pump, for example, a piezoelectric pump. The supply pump 134 is installed in the supply flow path. The supply pump 134 is connected to the control unit 150 by wiring and controlled by the control unit 150. The supply pump 134 supplies liquid to the liquid discharge head 1.

[0057] The transport device 115 transports the paper P along a transport path A, which runs from the media supply unit 112 through the image forming unit 113 to the media discharge unit 114. The transport device 115 comprises a plurality of guide plate pairs 121 and a plurality of transport rollers 122 arranged along the transport path A.

[0058] Each of the multiple guide plate pairs 121 comprises a pair of plate members positioned opposite each other with the paper being transported P in between, and guides the paper P along the transport path A.

[0059] The transport roller 122 is driven and rotated by the control unit 150 to feed the paper P downstream along the transport path A. Sensors for detecting the paper transport status are placed at various points along the transport path A.

[0060] The control unit 150 is, for example, a control board. The control unit 150 is equipped with a processor 151, ROM (Read Only Memory) 152, RAM (Random Access Memory) 153, I / O ports 154 which are input / output ports, and image memory 155.

[0061] The processor 151 is a processing circuit such as a CPU (Central Processing Unit) which is a controller. The processor 151 controls the head unit 130, drive motor 161, operating unit 162, and various sensors 163, etc., provided in the liquid dispensing device 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.

[0062] ROM 152 stores various programs and other data. RAM 153 temporarily stores various variable data and image data. Note that ROM 152 and RAM 153 are examples of storage media; other storage media may be used as long as they can store various programs and data. I / O port 154 is an interface unit for inputting data from external devices such as external devices 200 and outputting data to external devices. Print data from external devices 200 is transmitted to the control unit 150 via I / O port 154 and stored in image memory 155.

[0063] The following describes the characteristics of the liquid discharge head 1 used in the liquid discharge device 100 and the drive waveform (drive signal for discharging droplets) of the liquid discharge head 1 in relation to a comparative example of prior art.

[0064] First, the drive waveform of the liquid discharge head 1 according to the comparative example will be explained using Figures 6 to 14. Figure 6 is an explanatory diagram showing an example of a drive waveform including a multi-drop discharge waveform and a cancellation waveform for discharging multiple droplets in succession from the liquid discharge head 1 according to the comparative example. Figure 7 is an explanatory diagram showing an example of one discharge waveform and acoustic vibration of the liquid discharge head 1 according to the embodiment. Figure 8 is an explanatory diagram showing the relationship between the discharge waveform and discharged droplets in an example of the liquid discharge head 1. Figure 9 is an explanatory diagram showing an example of a discharged droplet from the liquid discharge head 1. Figures 10 to 14 are diagrams explaining a conventional liquid discharge head as a comparative example. Figure 10 is an explanatory diagram showing an example of frequency analysis of pressure vibration of the liquid discharge head according to the comparative example. Figure 11 is an explanatory diagram showing an example of the main acoustic vibration and parasitic vibration of Figure 10 combined. Figure 12 is an explanatory diagram showing an example of frequency analysis of a liquid discharge head according to a comparative example, Figure 13 is an explanatory diagram showing an example of drive waveform and acoustic vibration of a liquid discharge head according to a comparative example, and Figure 14 is an explanatory diagram showing an example of drive waveform and acoustic vibration of a liquid discharge head according to a comparative example.

[0065] First, conventional liquid dispensing heads employ a driving method called "pull-and-shoot," which increases the dispensing force by driving the piezoelectric column 21 in accordance with the half-period AL of the main acoustic vibration of the pressure chamber. However, as shown in the example of frequency analysis of nozzle pressure vibration in Figure 10, when the liquid dispensing head (actuator) is driven and liquid droplets are dispensed from the nozzle, parasitic vibrations may occur in the pressure chamber at higher frequencies than the main acoustic vibration, in addition to the main acoustic vibration caused by the fluid vibration of the ink.

[0066] When the actuator is driven to eject droplets from the nozzle, if parasitic vibrations with a higher frequency than the main acoustic vibration occur, the pressure in the pressure chamber will produce a pressure peak with a shorter period than half a period of the main acoustic vibration, as shown in Figure 11. That is, the composite wave, which is a combination of the main acoustic vibration and the parasitic vibration, will have a sharper initial vibration. The short-period pressure peak increases the ejection velocity at the tip of the ejected droplet, but does not persist until the end of ejection, decreasing the ejection velocity at the trailing end of the droplet. As a result, as shown in Figure 9 (a), when the droplet is ejected, the volume of the satellite relative to the tip droplet increases, leading to a deterioration in print quality. Here, a satellite is a droplet that follows the first ejected droplet (tip droplet) and is ejected at a distance from the tip droplet when the piezoelectric column 21 is driven and the pressure chamber deforms, causing liquid to be ejected from the nozzle.

[0067] Furthermore, in a conventional liquid discharge head similar to the liquid discharge head 1 of this embodiment, as shown in the frequency analysis in Figure 12, parasitic vibrations of approximately three times (for example, 2.8 times) the principal acoustic vibrations occur. The following are possible causes for the occurrence of parasitic vibrations with a higher frequency than the principal acoustic vibrations in the pressure chamber of the liquid discharge head.

[0068] One example of the cause is an odd-numbered vibration of 3 or more in the liquid column vibration of a closed pipe. An example of such a liquid discharge head is an end chute, which has an open end at the connection point with the common flow path, as shown in Figure 12, similar to the liquid discharge head 1 of the embodiment.

[0069] Another example of a cause is an integer multiple of two or more vibrations in the liquid column vibration of an open pipe. An example of such a liquid discharge head is a side chute, which has an open end at the connection point with the common flow path, as shown in Figure 13. In the main acoustic vibration of an open pipe, the amplitude of the pressure vibration is largest at the center of the pipe, so the nozzle is placed near the center of the pipe. As shown in Figure 13, when an even multiple of two or more vibrations occurs in the liquid column vibration of an open pipe, the center of the pipe becomes a node of vibration with a small amplitude of pressure vibration. Therefore, if the nozzle is placed near the center of the pipe, the shape of the discharged droplet is less affected by even multiples of two or more vibrations. For this reason, when the nozzle is placed near the center of the pipe, odd multiples of three or more vibrations are more likely to increase the volume of the satellite and worsen print quality than even multiples of two or more vibrations.

[0070] Another example of a cause is vibration caused by the reflection of pressure vibrations when the cross-sectional area of ​​the pressure chamber and the individual flow channels differ, resulting in a change in the speed of sound in each flow channel.

[0071] Another example of a cause is vibration caused by the fact that when the rigidity of the wall surface or a part of the wall surface of an individual flow channel is lower than that of the pressure chamber, the pressure generated in the pressure chamber is reduced in the less rigid flow channel, and a node of pressure oscillation is created between the pressure chamber and the less rigid flow channel. This occurs, for example, when the installation range of an actuator (piezoelectric column 21) such as a PZT, shown by the dashed line in Figure 1, is uneven due to manufacturing errors, etc., relative to the range of the diaphragm on the wall surface of the pressure chamber, as shown by the solid line in Figure 1, and the area of ​​the pressure chamber wall surface that is supported only by the diaphragm and not by the actuator is relatively large. Furthermore, for a head where the area without actuator support, consisting only of the upper right diaphragm of the pressure chamber in Figure 1, is approximately 30% of the longitudinal length of the pressure chamber (the width of pressure chamber 46 in Figure 1), the deformation of the PZT and pressure chamber was structurally analyzed, the liquid behavior in the flow path was analyzed using compressible fluid analysis, and the droplet discharge from the nozzle was analyzed using fluid surface analysis. The graphs in Figures 10 and 12 show the results of the frequency analysis of the nozzle pressure vibration when these simulations were performed.

[0072] As shown in Figure 14, when the rectangular wavewidth Dp of the discharge waveform is AL, the third harmonic vibration AI generated by the pre-discharge pressure chamber expansion (falling waveform) and the third harmonic vibration AII of the liquid column vibration due to the pressure chamber contraction (rising waveform) during discharge reinforce each other. As a result, the third harmonic vibration generates a pressure peak with a short period, leading to a deterioration of print quality.

[0073] Next, as a conventional example, the drive and drive waveform of the liquid discharge head 1 according to the comparative example will be described. In this comparative example, the pressure vibration of the pressure chamber 46 of the liquid discharge head 1 is likened to the vibration of a liquid column in a closed pipe, and the drive waveform is set to suppress third harmonic vibrations where the acoustic resonance frequency (parasitic vibration) in the frequency range higher than the principal acoustic resonance frequency (principal acoustic vibration) of the liquid in the pressure chamber 46 is approximately an odd multiple of approximately three times or more of the principal acoustic resonance frequency. Here, approximately three times includes 2.8 times, as shown in Figure 10. In this example, the drive waveform of the liquid discharge head 1 is shown as an example of a multi-drop discharge where multiple droplets are discharged in succession, as shown in Figure 6, where droplets are discharged in succession twice.

[0074] First, when the potential difference is smallest, the pressure chamber 46 of the liquid ejection head 1 is expanded to its largest size by the piezoelectric column 21 of the actuator 20, and when the potential difference is largest, the pressure chamber 46 of the ink is contracted to its smallest size by the piezoelectric column 21 of the actuator 20. When the liquid ejection head 1 ejects ink, the pressure chamber 46 is contracted in advance before ejection, expanded just before ejection, and contracted at the time of ejection to eject the ink. In this example, the ejection waveform of the drive waveform of the liquid ejection head 1 is such that the potential difference (expanded potential difference), including the intermediate potential difference, is reduced twice in a row when the pressure chamber 46 is expanded just before ejection, or the potential difference (contracted potential difference), including the intermediate potential difference, is increased twice in a row when the pressure chamber 46 is contracted during ejection. More preferably, the ejection waveform changes the potential difference twice in a row both when the pressure chamber 46 is expanded and when it is contracted. The liquid discharge head 1 then receives this discharge waveform twice in succession, thereby discharging two droplets.

[0075] Furthermore, in order to eject ink multiple times (twice in this example) from liquid ejection head 1, after inputting the second ejection waveform consecutively, a cancellation waveform is input to cancel out the residual vibrations that occur after ink ejection. In the following explanation, the first ejection waveform may be described as the ejection waveform of the first drop, and the second ejection waveform as the ejection waveform of the second drop.

[0076] In this example, the cancellation waveform of the drive waveform of the liquid discharge head 1 has a waveform width (cancellation width) Cp smaller than AL. In addition, in this example, in addition to the reduction of the pressure chamber 46 performed during discharge, the potential difference including the intermediate potential difference is increased multiple times in a row twice when the pressure chamber 46 is reduced, and the potential difference including the intermediate potential difference is decreased multiple times in a row twice when the pressure chamber 46 is expanded. More preferably, the cancellation waveform changes the potential difference twice in a row both when the pressure chamber 46 is expanded and when it is reduced, similar to the discharge waveform.

[0077] Figure 6 shows an example of a drive waveform in which two consecutive ejection waveforms are input at a predetermined interval when ejecting ink from the liquid ejection head 1. Figure 7 also shows an example of an ejection waveform. In Figures 6 and 7, the vertical axis is voltage (potential difference) and the horizontal axis is time. The drive waveform is generated by the driver IC 72 of the drive circuit 70. As shown in Figure 6, in both the two ejection waveforms and the cancellation waveform, the drive waveform reduces the expansion potential difference in two stages when the pressure chamber 46 expands, and increases the contraction potential difference in two stages when the pressure chamber 46 contracts during ejection. In addition, when changing the potential difference during both the expansion and contraction of the pressure chamber 46, after applying the first potential difference, the first potential difference is maintained for a predetermined time, and then the second potential difference is applied. If the pressure chamber 46 expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to contract the pressure chamber 46 before the ejection waveform is input.

[0078] First, we will specifically explain an example of the ejection waveform for the first drop among the drive waveforms, using Figures 6 and 7. As shown in Figure 7, when the pressure chamber 46 is expanded in advance before ink ejection, Dp is defined as the time interval from the start of the first expansion due to the expanding potential difference when the potential difference is reduced twice in a row, to the start of the first contraction due to the shrinking potential difference after the potential difference has been reduced twice in a row by the expanding potential difference. Also, as shown in Figure 7, when the pressure chamber 46 is contracted during ejection, Dp is defined as the time interval from the start of the second expansion due to the expanding potential difference when the potential difference is reduced twice in a row before the potential difference is increased, to the start of the second contraction due to the shrinking potential difference when the potential difference has been reduced twice in a row by the expanding potential difference and then increased twice in a row by the shrinking potential difference.

[0079] Furthermore, the time interval Dp is greater than 0.5 AL and less than 1.5 AL. More preferably, Dp = AL. This is because if Dp is greater than 0.5 AL and less than 1.5 AL, reinforcement occurs between the main acoustic vibration generated by expanding the pressure chamber 46 before discharge and the main acoustic vibration generated by contracting the pressure chamber 46 during discharge.

[0080] Here, the drive waveform is defined as follows: the period of parasitic vibrations such as the third harmonic is λn, and Tm is the time interval between the start time of the first potential difference change and the start time of the second potential difference change when the potential difference is increased or decreased twice consecutively, with Tm = λn / 2. When the piezoelectric column 21 (actuator) is driven with such a drive waveform, as shown in Figure 7, the phase difference between the parasitic vibrations generated during the first potential difference change and the parasitic vibrations generated during the second potential difference change becomes 180 degrees and they cancel each other out. This suppresses the deterioration of print quality due to parasitic vibrations such as the third harmonic. Note that in Figure 7, the pressure is at its maximum at the moment the pressure chamber 46 shrinks due to the rise waveform. Also, in the case of a meniscus flow velocity of a downward nozzle as shown in Figure 1, the velocity is at its maximum downward 1 / 4 period after the moment the pressure chamber 46 shrinks due to the rise waveform, with the amplitude centered at that moment. Thereafter, the main acoustic vibrations are shown with a period of 2AL, and the third harmonic is shown with a period of λn.

[0081] More preferably, as shown in Figure 7, by making the amount of potential difference change for the first potential difference change the same as the amount of potential difference change for the second potential difference change, parasitic vibrations with nearly the same amplitude but a 180-degree phase difference in the pressure chamber 46 cancel each other out, and subsequent residual vibrations originating from parasitic vibrations can be significantly suppressed.

[0082] Thus, when the potential difference is increased twice in a row or decreased twice in a row, if the time width Dp of the discharge waveform (drive waveform) is AL and the time interval Tm is λn / 2, as shown in Figure 7, the phase difference between the parasitic oscillation (3rd harmonic oscillation AI) generated by the pressure chamber contraction (rising waveform) during the first potential difference change and the parasitic oscillation (3rd harmonic oscillation AII) generated by the pressure chamber contraction (rising waveform) during the second potential difference change becomes 180 degrees and they cancel each other out. Furthermore, if the time interval Tm is less than 0.5AL, the main acoustic vibration generated by the pressure chamber contraction (rising waveform) during the first potential difference change and the main acoustic vibration generated by the pressure chamber contraction (rising waveform) during the second potential difference change reinforce each other. Also, by setting Dp to AL, the main acoustic vibration generated by the pre-discharge pressure chamber expansion (falling waveform) and the main acoustic vibration generated by the pressure chamber contraction (rising waveform) during discharge reinforce each other, increasing the discharge force due to the main acoustic vibration. Furthermore, if the pressure chamber 46 expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to reduce the pressure chamber 46 before the discharge waveform is input.

[0083] Here, we will explain the condition for Tm at which parasitic oscillations with period λn destructively cancel each other out in the drive waveform. First, let A be the oscillation with period λn that occurs when the potential difference is changed for the first time, and let A' be the oscillation vector at time Tm after A. Let B be the oscillation vector with period λn that occurs when the potential difference is changed for the second time after Tm. The absolute value of the combined vector of A' and B is minimized when Tm is an odd multiple of λn / 2 (the phase difference between A' and B is 180 degrees). From the equation for the combination of simple harmonic motions with period λn, we can find the condition under which the absolute value of the combined vector of A' and B is less than or equal to the larger of the absolute values ​​of A' and B (if the absolute values ​​of A' and B are the same, then less than or equal to that), which means that the phase difference between oscillation vectors A' and B is within 180 degrees ± 60 degrees.

[0084] The absolute value of the resultant vector of A' and B can be transformed into the following equation. Here, if θA is the phase of A' and θB is the phase of B, then A' = |A'|(cosθA, sinθA) and B = |B|(cosθB, sinθB). In this case, the absolute value of the resultant vector of A' and B is: √(|A'|^2+|B|^2+2*|A'|*|B|*cos(θA-θB))...(Formula 1) This is the result. Here, if we let |A'|≦|B|, then the phase difference (θA-θB) between A' and B such that |B|≧Equation 1 holds is the condition under which the oscillations with period λn destructively interfere with each other. Squaring both sides of |B|≧Equation 1 and rearranging it, 0≧|A'|+2*|B|*cos(θA-θB)...(Formula 2) Therefore, Equation 2 holds true if the phase difference (θA-θB) between A' and B is within the range of 180 degrees ± 60 degrees.

[0085] Also, if |B|≦|A'|, then |A'|≧, squaring both sides of equation 1 and rearranging it, 0≧|B|+2*|A'|*cos(θA-θB)...(Formula 3) Therefore, if the phase difference between A' and B (θA-θB) is within the range of 180 degrees ± 60 degrees, then equation 3 holds true.

[0086] From these, the conditions for parasitic oscillations of period λn to destructively interfere with each other are: (k / 2-1 / 6)λn ≤ Tm ≤ (k / 2+1 / 6)λn···(Equation 4) This is the result. Here, k is an odd number greater than or equal to 1.

[0087] Furthermore, when the potential difference is changed twice consecutively both during expansion and contraction of the pressure chamber 46, it is preferable that the Tm of the drive waveform be (k / 2-1 / 6)λn ≤ Tm ≤ (k / 2+1 / 6)λn (where k is an odd number greater than or equal to 1) for both the intermediate potential difference holding time during pressure chamber expansion and the intermediate potential difference holding time during pressure chamber contraction.

[0088] Furthermore, from the perspective of reducing power consumption by reinforcing the main acoustic vibrations that occur when changing from the potential difference immediately preceding the relevant intermediate potential difference and when changing to the next potential difference, a shorter Tm is desirable.

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

[0090] Next, as an evaluation of the first drop ejection waveform among the drive waveforms of the liquid ejection head 1, Figure 8 shows the results when the liquid ejection head 1 with 2AL = 5.24 μs is driven with various waveforms and one drop of ink is ejected. Note that the voltage was adjusted so that the first drop velocity was approximately 8 m / s for all the results of the various waveforms in Figure 8.

[0091] In Figure 8, the topmost drive waveform is a trapezoidal drive waveform as shown in Figure 14, with a rise time tr of 0.2 μs, as a comparative example. The others are drive waveforms that perform two potential difference changes, as shown in Figure 7, with different Tm values, and all with a rise time of 0.2 μs. The output voltage represents the difference between the expanded potential difference and the reduced potential difference. The intermediate potential difference is the midpoint between the expanded and reduced potential differences.

[0092] As shown in the frequency analysis in Figure 12, for example, the liquid discharge head 1 generates parasitic vibrations approximately three times the frequency of the principal acoustic vibrations. The period λn of the parasitic vibrations is 1.85 μs, and λn / 2 is 0.925 μs.

[0093] Figure 9 also shows the results of a simulation of the state of the ejected droplet when one drop of ink is dispensed. In Figure 9, the top figure (a) is an example of an ejected droplet using a trapezoidal drive waveform with tr = 0.2 μs, the middle figure (b) is an example of an ejected droplet using a drive waveform that performs two potential difference changes with Tm = 0.62 μs, and the bottom figure (c) is an example of an ejected droplet using a drive waveform that performs two potential difference changes with Tm = 0.93 μs.

[0094] As shown in the lower part of Figures 8 and 9 (c), the waveform with Tm = 0.93 μs, which is closest to the half-period of the parasitic oscillation, has the largest ratio of the first drop volume to the total discharge volume. As shown in the middle part of Figures 8 and 9 (b), it can be seen that the ratio of the first drop volume tends to decrease as Tm deviates from 0.925 μs. It can also be seen that the discharge voltage per unit volume (discharge voltage / total discharge volume) tends to decrease as Tm decreases. These results also show that, depending on the drive waveform of the liquid discharge head 1 for the first drop, it is possible to suppress vibrations with a frequency higher than the main acoustic vibration while keeping power consumption down.

[0095] Next, an example of the discharge waveform for the second drop of the drive waveform will be specifically explained using Figure 6. In this comparative example, the discharge waveform for the second drop has a smaller time width Dp compared to the discharge waveform for the first drop, from the point of reduction due to the contraction potential difference after being reduced twice consecutively by the expansion potential difference. For example, Dp21 of the discharge waveform for the first drop is the same as AL, while Dp22 of the discharge waveform for the second drop is set to be smaller than AL.

[0096] For simplicity, we ignore vibration damping due to viscous resistance in the flow path, and let tin be the time at which the potential difference change occurs due to tr, and let t0 be the time at the phase reference point (0). Schematically, the pressure oscillation in the pressure chamber 46 due to pressurization is given by cos((t0-tin)*(π / AL)). The velocity of the liquid in the nozzle is given by -sin((t0-tin)*(π / AL)). Note that if the nozzle is oriented downwards, the liquid velocity in the nozzle changes downwards due to the pressurization of the pressure chamber 46, so a negative sign is added to the formula for the liquid velocity in the nozzle. Furthermore, let tin be the time at which the potential difference change occurs due to tf, and schematicly, the pressure oscillation in the pressure chamber 46 due to depressurization is given by cos(-π+(t0-tin)*(π / AL)). The velocity of the liquid in the nozzle is given by -sin(-π+(t0-tin)*(π / AL)). Note that, if the nozzle is facing downwards, the liquid velocity at the nozzle changes upwards due to the reduced pressure in the pressure chamber 46; therefore, a negative sign is added to the formula for the liquid velocity at the nozzle.

[0097] From this point forward, the phase reference point (0) or (0'') will be used as the baseline, and the time elapsed (phase advance) from the point of occurrence of each voltage step input to the baseline will be substituted into (t0-tin). This will allow us to describe the phase of each potential difference change and its composite wave with respect to the baseline point (0) or (0'').

[0098] For the sake of explanation, in Figure 6, the first to fourth potential difference changes in the discharge waveform of the first drop will be denoted as (1) to (4), and the first to fourth potential difference changes in the discharge waveform of the second drop will be denoted as (21) to (24) for the following explanation. Furthermore, the reference point for the phase of the discharge waveform of the first drop will be (0), and the reference point for the phase of the discharge waveform of the second drop will be denoted as (0'') for the following explanation. Here, the reference point for the phase of the discharge waveform of the first drop (0) is set midway between potential difference changes (2) and (3), and the reference point for the phase of the discharge waveform of the second drop (0'') is set midway between potential difference changes (22) and (23). Also, the voltage drop time tf in the figure is assumed to be approximately the same as the voltage rise time tr. Furthermore, the amount of potential difference change in (1) and (2), and the amount of potential difference change in (21) and (22) (the amount of height change in Figure 6) are assumed to be approximately the same, and the amount of potential difference change in (3) and (4), and the amount of potential difference change in (23) and (24) are assumed to be approximately the same.

[0099] First, let's look at the main acoustic vibration of the discharge waveform in Figure 6. In the discharge waveform that discharges the first drop in Figure 6, when a potential difference change is made and an intermediate voltage for expanding the pressure chamber 46 is input as shown in (1), the pressure chamber 46 expands due to the potential difference in (1), and the pressure inside the pressure chamber 46 decreases. The vibration resulting from this is an vibration with a phase lead of -π + (Dp21 + Tm21) / 2*(π / AL). Furthermore, when the potential difference change shown in (2) is made, the vibration in (2) is an oscillation with a phase lead of -π + (Dp21 - Tm21) / 2*(π / AL). The composite wave of (1) and (2) is an oscillation with a phase lead of -π + Dp21 / 2*(π / AL).

[0100] The potential difference changes in (3) and (4), which are for shrinking the pressure chamber 46, are inversely related to the potential difference changes in (1) and (2), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (3) is an oscillation with a phase lead of -(Dp21-Tm21) / 2*(π / AL). Similarly, (4) can be considered an oscillation with a phase lead of -(Dp21+Tm21) / 2*(π / AL). Therefore, the combined wave of (3) and (4) is an oscillation with a phase lead of -Dp21 / 2*(π / AL).

[0101] If we assume a composite wave of (1), (2), (3), and (4) at time (0), then the composite wave of (1), (2), (3), and (4) will be an oscillation with a phase lead of -π / 2.

[0102] Next, we will discuss the main acoustic oscillation of the discharge waveform at the second drop in Figure 6. When the potential difference is changed and an intermediate voltage is input to expand the pressure chamber 46 as shown in (21), the pressure chamber 46 expands due to the potential difference in (21), and the pressure inside the pressure chamber 46 decreases. If the discharge waveform width at the second drop is Dp22, then the oscillation will be advanced in phase by -π + (Dp22 + Tm22) / 2*(π / AL). Furthermore, when the potential difference is changed as shown in (22), in (22), it can be considered that the oscillation is advanced in phase by -π + (Dp22 - Tm22) / 2*(π / AL). Therefore, the composite wave of (21) and (22) will be an oscillation advanced in phase by -π + Dp22 / 2*(π / AL).

[0103] The potential difference changes (23) and (24), which are for shrinking the pressure chamber 46, change in the opposite direction to the potential difference changes (21) and (22), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (23) becomes an oscillation with a phase lead of -(Dp22-Tm22) / 2*(π / AL). Similarly, (24) becomes an oscillation with a phase lead of -(Dp22+Tm22) / 2*(π / AL). Therefore, the combined wave of (23) and (24) becomes an oscillation with a phase lead of -Dp22 / 2*(π / AL).

[0104] If we assume a composite wave of (21), (22), (23), and (24) at time (0''), then the composite wave of (21), (22), (23), and (24) will be an oscillation with a phase lead of -π / 2.

[0105] Therefore, if the phase difference between (0) and (0'') is an even multiple of π (or AL if time interval), the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will have the same phase and reinforce each other. In the example in Figure 6, the time difference (time interval) between (0) and (0'') is 2AL. Furthermore, by reducing the time width Dp22 between (21) and (23), the amplitude of the composite wave of (21), (22), (23), and (24) (the discharge waveform of the second drop) can be adjusted. Thus, the discharge velocity of the second drop can be adjusted by the reinforcement between the residual vibration from the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24). Thus, in a multi-drop drive waveform in which the liquid ejection head 1 ejects multiple inks in succession, by adjusting Dp in the ejection waveform following any of the ejection waveforms, the ejection speed of the ink ejected later can be adjusted to be higher than or equal to the ejection speed of the droplets ejected earlier.

[0106] However, in the comparative example shown in Figure 6, the waveform widths of Dp21 and Dp22 may differ significantly due to the viscosity of the ink and the flow resistance of the ink supply path to each nozzle 51. When driving a liquid ejection head 1 in which the main acoustic vibration frequencies of multiple pressure chambers 46 differ significantly due to manufacturing variations, etc., with a drive waveform in which the waveform widths of Dp21 and Dp22 differ significantly, the print quality may deteriorate.

[0107] The liquid ejection head 1 of this embodiment performs gradation expression by the number of droplets ejected continuously. Here, if there are multiple nozzles 51 that eject the same number of droplets, the same drive waveform is input to multiple piezoelectric pillars 21 that vary the volume of multiple pressure chambers 46 communicating with these multiple nozzles 51. On the other hand, the main acoustic vibration frequencies of the multiple pressure chambers 46 are not necessarily the same due to manufacturing variations, etc. For example, the drive waveform for driving an inkjet head in which the maximum value of the half-period AL of the main acoustic vibration frequencies of the multiple pressure chambers 46 is 3.5 μs, the minimum value is 2.5 μs, and the average value is 3.0 μs will be described below.

[0108] Furthermore, the AL of multiple pressure chambers 46 can be determined by individually inputting a rectangular wave to the piezoelectric column 21 that varies the volume of each pressure chamber 46, and measuring the velocity of the droplet discharged from the nozzle 51 at that time. For example, by measuring the velocity of the discharged droplet while changing the time width Dp of the rectangular wave, if the droplet discharge velocity is maximum when the time width Dp of the rectangular wave is 3.0 μs, then 3.0 μs can be considered to be the AL of the corresponding pressure chamber 46.

[0109] Next, we will explain the challenges of conventional drive waveforms. For example, when printing is performed by ejecting droplets from a liquid ejection head 1 while transporting the media to be printed (e.g., paper P), it is necessary to adjust the velocity of droplets of each volume so that the landing position of the droplets on the media does not change even if the volume of the droplets ejected from the nozzle 51 changes.

[0110] First, an example of a driving waveform (1-drop waveform) for discharging 1 drop is shown in FIG. 17. As shown in FIG. 17, the time width Dp11 of the discharge waveform is set to Dp11 = AL. Also, the center-to-center distance (time interval between centers) 2UL of the discharge waveform and the cancellation waveform is set to 2UL = 2AL. And the wavelength λn of the parasitic vibration is set to be the wavelength of the third harmonic of the main acoustic vibration, and Tm11 = λn / 2 (= UL / 3). And for the waveform width Dp of the discharge waveform for discharging each droplet of the driving waveform (n-drop waveform) for continuously discharging a plurality of droplets, the waveform width of the discharge waveform of the first or last droplet is set to 1AL, and the waveform width Dp of the discharge waveforms of the other droplets is made smaller (Dp < AL) or larger (Dp > AL) than 1AL. Thereby, when continuously discharging droplets, the speed of the droplets is adjusted to be close to the discharge speed of 1 drop. For example, in the example of FIG. 6, the waveform width Dp21 of the discharge waveform of the first droplet is set to 1AL, and the waveform width Dp22 of the discharge waveforms of the other droplets is made smaller than 1AL. When continuously discharging droplets, residual vibration occurs in the pressure chamber 46 due to the previously discharged droplets, so by discharging the next droplet in accordance with the phase of the residual vibration, the discharge speed of the subsequent droplets increases. In the case of 1 drop, no speed increase due to residual vibration can be expected, so the waveform width Dp11 of the 1-drop discharge waveform is set to 1AL, and the discharge waveform width is adjusted when continuously discharging droplets.

[0111] Also, it is considered that the wavelength λn of the parasitic vibration also varies in the same way as the half period AL of the main acoustic vibration frequency. In this example, in order to weaken the parasitic vibration in more pressure chambers 46, here, assuming that the average λn / 2 was 1 μs, Tm11 is adjusted to match the average λn / 2.

[0112] For example, among a plurality of pressure chambers 46, in the pressure chamber 46 where AL is approximately 3.0 μs, as shown in FIG. 6, the driving waveform for continuously discharging 2 drops is adjusted, and the 2-drop waveform is set to Dp21 = 3.0 μs, UL = 3.0 μs, Dp22 = 2.1 μs, Cp = 1.5 μs, Tm21 = Tm22 = 1.0 μs (= UL / 3). In this case, consider the case where the speed of the second discharged droplet of the 2-drop waveform becomes larger than the speed of the first discharged droplet of the 2-drop waveform.

[0113] In this 2-drop waveform, the distance between the centers of the Dp21 and Dp22 discharge waveforms (time interval between centers) 2UL is set to twice the AL of the pressure chamber 46 in order to align the phase of the residual vibration generated by the Dp21 discharge waveform with the Dp22 discharge waveform. Furthermore, even if the waveform width of Dp22 is smaller than the AL of the pressure chamber 46, the velocity of the second discharge droplet in the 2-drop waveform is greater than the velocity of the first discharge droplet in the 2-drop waveform.

[0114] Here, the 2-drop waveform is input to a piezoelectric column 21 that varies the volume of one of the multiple pressure chambers 46, specifically the pressure chamber 46 where AL reaches its maximum value of 3.5 μs. In this case, the difference between the waveform width of Dp22 and AL of the pressure chamber 46 becomes large, and the difference between the center-to-center distance 2UL of the ejection waveform of Dp21 and the ejection waveform of Dp22 and 2AL of the pressure chamber 46 also becomes large. Therefore, there is a concern that the velocity of the ejected droplet of the second drop will be smaller than the velocity of the ejected droplet of the first drop in the 2-drop waveform. If the timing of the ejected droplet of the second drop hitting the media is delayed compared to the ejected droplet of the first drop, it will lead to a decrease in print quality.

[0115] For example, Figures 19 to 32 show the relationship between waveform width and discharge force based on the time width Dp of the leading and succeeding droplets. Figures 19 to 32 are diagrams that schematically show the discharge force characteristics of the pressure chamber 46 with dashed lines, where the horizontal axis is the waveform width of the discharge waveform and the vertical axis is the discharge force as a function of the waveform width when there is no residual vibration. Figures 19 to 26 show examples where the time width Dp21 of the discharge waveform of the leading droplet and the time width Dp22 of the discharge waveform of the succeeding droplet are different (Dp21 ≠ Dp22), and Figures 27 to 32 show examples where the Dp21 of the leading droplet and the Dp22 of the succeeding droplet are the same or approximately the same (Dp21 ≈ Dp22). Here, avrAL is the average value of AL of multiple pressure chambers 46 that receive the same drive waveform. minAL is the minimum value of AL of multiple pressure chambers 46 that receive the same drive waveform. maxAL is the maximum value of AL of multiple pressure chambers 46 that receive the same drive waveform. Furthermore, the upward-convex, arc-shaped dashed lines in Figures 19 to 22 and Figures 27 and 28 indicate that AL has approximately the same discharge force characteristics in the pressure chamber 46 as avrAL.

[0116] Figure 21 shows the relationship between waveform width and discharge force when Dp21 has the same time width as avrAL and Dp22 has a shorter time width than avrAL in the waveform of Figure 6. In Figure 21, the discharge force of Dp22 is slightly smaller than that of Dp21, but in the waveform of Figure 6, the residual vibration generated by Dp21 reinforces Dp22, so the droplet velocity discharged by Dp22 is equal to or greater than that discharged by Dp21.

[0117] Figure 25 shows the relationship between waveform width and discharge force when driving a pressure chamber 46 where AL is maxAL, using the drive waveforms shown in Figure 6, which have the waveform widths of Dp21 and Dp22 as shown in Figure 21. In Figure 25, Dp21 has a waveform width of avrAL, so it represents the discharge force near the peak of the discharge force characteristic of the pressure chamber 46, and the change in discharge force is relatively small. On the other hand, in Figure 25, Dp22 has a waveform width that is considerably smaller than avrAL, so the change in discharge force due to the expansion of AL in the pressure chamber 46 is large. Also, the difference between the center-to-center distance 2UL of the discharge waveform of Dp21 and the discharge waveform of Dp22 is large compared to 2AL (=2*maxAL) of the pressure chamber 46. Therefore, compared to Figure 21, in Figure 25, the discharge force is reduced for both Dp21 and Dp22, but the reduction in Dp22 is greater. Therefore, even if Dp22 and residual vibration reinforce each other, the droplet velocity ejected by Dp22 may still be lower than the droplet velocity ejected by Dp21.

[0118] Next, the drive waveform is adjusted to continuously discharge 2 drops in one of the pressure chambers 46 where AL is approximately 3.0 μs, so that the 2-drop waveform is Dp21=2.1 μs, UL=3.0 μs, Dp22=3.0 μs, Cp=1.5 μs, and Tm21=Tm22=1.0 μs (=UL / 3). In this case, consider the case where the velocity of the second discharged droplet in the 2-drop waveform becomes greater than the velocity of the first discharged droplet in the 2-drop waveform.

[0119] In the aforementioned 2drop waveform, the distance 2UL between the centers of the discharge waveforms Dp21 and Dp22 is set to twice the AL of the pressure chamber 46 in order to align the phase of the residual vibration generated by the discharge waveform Dp21 with that of the discharge waveform Dp22. As a result, the velocity of the second drop of the discharged droplet in this 2drop waveform is greater than the velocity of the first drop of the discharged droplet in this 2drop waveform.

[0120] Here, the 2-drop waveform is input to a piezoelectric column 21 that varies the volume of the pressure chamber 46 where AL is the minimum value of 2.5 μs.In this case, the difference between the waveform width of Dp21 and AL of the pressure chamber 46 becomes smaller, increasing the ejection speed of the first drop, while the difference between the waveform width of Dp22 and AL of the pressure chamber 46 becomes larger, and furthermore, the difference between the center-to-center distance 2UL of the ejection waveform of Dp21 and the ejection waveform of Dp22 and 2AL of the pressure chamber 46 becomes larger.Therefore, there is a concern that the ejection speed of the second drop will be smaller than that of the first drop ejected droplet in the 2-drop waveform.As a result, the timing of the second drop ejected droplet's impact on the media will be delayed compared to that of the first drop ejected droplet, leading to a decrease in print quality.

[0121] Figure 19 shows the relationship between waveform width and discharge force when Dp22 has the same time width as avrAL and Dp21 has a shorter time width than avrAL. As shown in Figure 19, Dp22 has a greater discharge force than Dp21. Also, the residual vibrations generated by Dp21 reinforce Dp22, so the droplet velocity discharged by Dp22 is greater than the droplet velocity discharged by Dp21.

[0122] Figure 23 shows the relationship between waveform width and discharge force when a drive waveform is input to a pressure chamber 46 where AL in the pressure chamber 46 is minAL, with Dp22 having the same time width as avrAL and Dp21 having a time width smaller than avrAL.

[0123] As shown in Figure 23, the waveform width of Dp21 is closer to the value of minAL than that of Dp22, resulting in a higher discharge force for Dp21. Furthermore, the difference between the center-to-center distance 2UL of the discharge waveform of Dp21 and the discharge waveform of Dp22 and the pressure chamber 46's 2AL (2*minAL) becomes larger. Therefore, even if Dp22 and residual vibration reinforce each other, the droplet velocity discharged by Dp22 may still be lower than the droplet velocity discharged by Dp21.

[0124] Next, the drive waveform of this embodiment will be explained using Figure 15. In this embodiment, the time width Dp21 of the first drop (early discharge) discharge waveform and the time width Dp22 of the second drop (later discharge) discharge waveform are the same (here, "same" includes "approximately the same"), and the interval between discharge waveforms matches the period that strengthens the residual vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated first and the vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated afterward. Alternatively, for example, Dp21 and Dp22 may be made different from 1AL. For example, in one of the multiple pressure chambers 46, in a pressure chamber 46 where AL is approximately 3.0 μs, the drive waveform for continuously discharging 2 drops as shown in Figure 15 is adjusted, and the 2-drop waveform is set to Dp21=Dp22=2.4 μs, UL=3.0 μs, Cp=1.5 μs, and Tm21=Tm22=1.0 μs (=UL / 3). In this case, the velocity of the second droplet discharged in the 2-drop waveform becomes greater than the velocity of the first droplet discharged in the 2-drop waveform, and the velocity of the droplet discharged in the 1-drop waveform becomes close to the velocity of one of the droplets discharged in the 2-drop waveform. More preferably, Dp21=Dp22 is adjusted so that the velocity of the combined droplet is approximately the same as the discharge velocity of the droplet in the 1-drop waveform.

[0125] When the waveform widths of Dp21 and Dp22 are the same or nearly the same, as shown in Figure 15, the pressure exerted on the liquid in the pressure chamber 46 by the respective discharge waveforms of Dp21 and Dp22 will be the same or nearly the same. In addition, by making the distance between the centers of the discharge waveforms of Dp21 and Dp22 nearly the same as 2AL, the residual vibration of the pressure chamber 46 generated by Dp21 and the pressure exerted on the liquid in the pressure chamber 46 by Dp22 reinforce each other. For this reason, the velocity of the droplets discharged by Dp22 is usually greater than that of the droplets discharged by Dp21.

[0126] Figures 27, 29, and 31 show the relationship between waveform width and discharge force when Dp21 and Dp22 have time widths smaller than minAL in the waveform of Figure 15. In Figures 27, 29, and 31, the discharge forces of Dp22 and Dp21 are equivalent. In the waveform of Figure 15, the residual vibration generated by Dp21 reinforces Dp22, so the droplet velocity discharged by Dp22 is equal to or greater than the droplet velocity discharged by Dp21.

[0127] Next, the conditions under which the residual vibration of the pressure chamber 46 generated by Dp21 and the pressure exerted by Dp22 on the liquid inside the pressure chamber 46 reinforce each other will be specifically explained using Figure 15. In this embodiment, the waveform width of the discharge waveform of the second drop and the discharge waveform of the first drop are assumed to be approximately the same. Furthermore, in order to make the velocity of the discharged droplet in the first drop waveform and the velocity of the discharged droplet in the second drop waveform approximately the same, Dp21 and Dp22 are set to be smaller than the average value of the half-period AL of the main acoustic vibration frequencies of the multiple pressure chambers 46, which is 3.0 μs.

[0128] Here, if the 1-drop waveform is as shown in Figure 17, constructive interference of residual vibrations does not occur. Therefore, when the voltage height of the discharge waveform is the same for the 1-drop waveform and the multiple-drop waveform, in order to obtain the same discharge speed as the multiple-drop waveform, it is necessary to set the discharge waveform width of the 1-drop waveform to be large enough to produce a large discharge force. For example, it is desirable to set the discharge waveform width of the 1-drop waveform between minAL and maxAL so as to produce a large discharge force. In this case, for example, consider the case where the waveform width of each discharge waveform of the multiple-drop waveform is set to minAL. In pressure chamber 46 where AL is minAL, the discharge force of the multiple-drop waveform with a discharge width of minAL is greater than that of the 1-drop waveform with an average discharge width of AL.

[0129] Furthermore, reinforcement of residual vibrations occurs, which can result in the discharge velocity of multiple droplets being significantly higher than that of a single droplet. If the waveform width of each discharge waveform of multiple droplets is set between minAL and maxAL, a similar concern arises in any pressure chamber 46 where AL is between minAL and maxAL. For this reason, it is desirable to set the waveform width of each discharge waveform of multiple droplets to be either smaller than minAL or larger than maxAL.

[0130] For the sake of explanation, in Figure 15, the first to fourth potential difference changes in the discharge waveform of the first drop will be denoted as (1) to (4), and the first to fourth potential difference changes in the discharge waveform of the second drop will be denoted as (21) to (24) for the following explanation. Also, the reference point for the phase of the discharge waveform of the first drop will be (0), and the reference point for the phase of the discharge waveform of the second drop will be denoted as (0'') for the following explanation. Here, the reference point for the phase of the discharge waveform of the first drop (0) is set midway between potential difference changes (2) and (3), and the reference point for the phase of the discharge waveform of the second drop (0'') is set midway between potential difference changes (22) and (23). Furthermore, the voltage drop time tf in Figure 15 is assumed to be approximately the same as the voltage rise time tr in Figure 15. Furthermore, the amount of potential difference change in (1), (2), (21), and (22), and the amount of potential difference change in (3), (4), (23), and (24) (the amount of height change in Figure 15) are assumed to be approximately the same.

[0131] The main acoustic vibration of the discharge waveform for the first drop shown in Figure 15 will be explained. As shown in Figure 15, in the discharge waveform for the first drop, a potential difference change is performed, and when a voltage for expanding the pressure chamber 46 is input as shown in (1), the pressure chamber 46 expands due to the potential difference in (1), and the pressure inside the pressure chamber 46 decreases. The vibration resulting from this is an vibration with a phase lead of -π + (Dp21 + Tm21) / 2*(π / AL). Furthermore, when the potential difference change shown in (2) is performed, the vibration in (2) is an oscillation with a phase lead of -π + (Dp21 - Tm21) / 2*(π / AL). The composite wave of (1) and (2) is an oscillation with a phase lead of -π + Dp21 / 2*(π / AL).

[0132] The potential difference changes in (3) and (4), which are for shrinking the pressure chamber 46, are the opposite of the potential difference changes in (1) and (2), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (3) is an oscillation with a phase lead of -(Dp21-Tm21) / 2*(π / AL). Similarly, (4) can be considered an oscillation with a phase lead of -(Dp21+Tm21) / 2*(π / AL). Therefore, the combined wave of (3) and (4) is an oscillation with a phase lead of -Dp21 / 2*(π / AL).

[0133] If we assume a composite wave of (1), (2), (3), and (4) at time (0), then the composite wave of (1), (2), (3), and (4) will be an oscillation with a phase lead of -π / 2.

[0134] Next, we will discuss the main acoustic oscillation of the discharge waveform at the second drop in Figure 15. When the potential difference is changed and a voltage is input to expand the pressure chamber 46 as shown in (21), the pressure chamber 46 expands due to the potential difference in (21), and the pressure inside the pressure chamber 46 decreases. If the discharge waveform width at the second drop is Dp22, then the oscillation will be advanced in phase by -π + (Dp22 + Tm22) / 2*(π / AL). Furthermore, when the potential difference is changed as shown in (22), in (22), it can be considered that the oscillation is advanced in phase by -π + (Dp22 - Tm22) / 2*(π / AL). Therefore, the composite wave of (21) and (22) will be an oscillation advanced in phase by -π + Dp22 / 2*(π / AL).

[0135] The potential difference changes (23) and (24), which are for shrinking the pressure chamber 46, change in the opposite direction to the potential difference changes (21) and (22), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (23) becomes an oscillation with a phase lead of -(Dp22-Tm22) / 2*(π / AL). Similarly, (24) becomes an oscillation with a phase lead of -(Dp22+Tm22) / 2*(π / AL). Therefore, the combined wave of (23) and (24) becomes an oscillation with a phase lead of -Dp22 / 2*(π / AL).

[0136] If we assume a composite wave of (21), (22), (23), and (24) at time (0''), then the composite wave of (21), (22), (23), and (24) will be an oscillation with a phase lead of -π / 2.

[0137] Therefore, if the phase difference between (0) and (0'') is an even multiple of π (or AL if time interval), the composite waves of (1), (2), (3), and (4) and the composite waves of (21), (22), (23), and (24) will have the same phase and reinforce each other. In the example shown in the figure, the time difference (time interval) between (0) and (0'') is 2AL.

[0138] Here, we consider the time difference (time interval) between (0) and (0'') that causes constructive interference between the combined waves of (1), (2), (3), and (4) and the combined waves of (21), (22), (23), and (24). If the time difference between (0) and (0'') 2UL is greater than 1.5AL and less than 2.5AL, then the combined waves of (1), (2), (3), and (4) and the combined waves of (21), (22), (23), and (24) cause constructive interference.

[0139] Furthermore, due to manufacturing variations, the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 of the liquid discharge head 1 will not be the same. Here, the maximum value of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 is defined as maxAL, and the minimum value as minAL. In this case, the value when 1.5AL is largest in the multiple pressure chambers 46 is 1.5maxAL, and the value when 2.5AL is smallest is 2.5minAL. Therefore, the time difference between (0) and (0'') should be set to 2UL such that 1.5AL ≤ 1.5maxAL < 2UL < 2.5minAL ≤ 2.5AL holds true. From this, if the time difference 2UL between (0) and (0'') of the 2drop waveform shown in Figure 15 is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the above-mentioned pressure chambers 46, the phase difference between the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will be less than ±90 degrees, and the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will reinforce each other.

[0140] Furthermore, since the time widths Dp21 of (1) and (3) and Dp22 of (21) and (23) are approximately the same, even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveforms with time widths Dp21 and Dp22 will be the same. In addition, the discharge speed of the second drop, which is discharged due to the reinforcement of the residual vibrations from the combined waves of (1), (2), (3), and (4) and the combined waves of (21), (22), (23), and (24), will be greater than the discharge speed of the first drop. In this way, with the multi-drop drive waveform that discharges multiple inks in succession as shown in Figure 15, the discharge speed of the ink discharged later can be adjusted to be greater than or equal to the discharge speed of the previously discharged droplets in all of the multiple pressure chambers 46 due to the residual vibrations generated by the previous discharge waveform.

[0141] Furthermore, the time interval between (1) and (2) of depressurizing the pressure chamber 46 is Tm21, and the time interval between (3) and (4) of pressurizing the pressure chamber 46 is also Tm21. Therefore, if Tm21 is set according to the conditions of equation 4 described above, the parasitic oscillations of (1) and (2) will cancel each other out, and the parasitic oscillations of (3) and (4) will also cancel each other out. In addition, the time interval between (21) and (22) of depressurizing the pressure chamber 46 is Tm22, and the time interval between (23) and (24) of pressurizing the pressure chamber 46 is also Tm22. Therefore, if Tm22 is set according to the conditions of equation 4 described above, the parasitic oscillations of (21) and (22) will cancel each other out, and the parasitic oscillations of (23) and (24) will also cancel each other out.

[0142] While it has been described how residual vibrations generated by the previous ejection waveform can be used to adjust the ejection speed of ink ejected later to be greater than that of previously ejected droplets, it is also possible to adjust the ejection speed to be greater than that of previously ejected droplets by shortening the Tm of the ejection waveform input after the Tm of the previous ejection waveform. This is because the shorter Tm, the greater the reinforcement of the main acoustic vibrations caused by the rising and falling waveforms, as shown in Figure 7, for example. Specifically, in the case of a drive waveform like that shown in Figure 15, by making the time width of Tm22 shorter than that of Tm21, the droplet velocity of the second drop can be made greater than that of the first drop. Furthermore, by setting the time widths of Tm21 and Tm22 within the range of the conditions in Equation 4 mentioned above, parasitic vibrations can also be weakened.

[0143] For example, consider the case where the period λn of the parasitic oscillation is the third harmonic of the principal acoustic oscillation. Here, λn is 2AL / 3 and AL = 3.0 μs. Substituting the above λn into equation 4 when k=1, we get 2 / 3 μs ≤ Tm ≤ 4 / 3 μs. For example, in the example of another embodiment in Figure 16, if Tm21 = 1.3 μs and Tm22 = 0.7 μs, the drive waveform is set to a Tm that satisfies equation 4.

[0144] Furthermore, due to manufacturing variations, the parasitic oscillation periods λn of the multiple pressure chambers 46 of the liquid discharge head 1 may not be identical. Here, let maxλn be the maximum value of the parasitic oscillation period λn of the multiple pressure chambers 46, and minλn be the minimum value. In this case, the lower limit of Equation 4 is largest at (k / 2-1 / 6)maxλn, and the upper limit of Equation 4 is smallest at (k / 2+1 / 6)minλn. Therefore, (k / 2-1 / 6)maxλn≦Tm≦(k / 2+1 / 6)minλn···(Equation 6) This is the result. Here, k is an odd number greater than or equal to 1.

[0145] By setting Tm within the range where equation 6 holds true, parasitic vibrations can be reduced in all of the aforementioned pressure chambers 46.

[0146] Here, we consider the case where the period λn of the parasitic oscillation is the third harmonic of the principal acoustic oscillation. Let minλn be 2*minAL / 3 = 5 / 3μs and maxλn be 2*maxAL / 3 = 7 / 3μs. Substituting the above minλn and maxλn into equation 6 when k=1, we get 7 / 9μs≦Tm≦10 / 9μs. If Tm is set within the above range, the parasitic oscillation can be weakened in all of the multiple pressure chambers 46. For example, in Figure 16, if Tm21=1.1μs and Tm22=0.8μs, the drive waveform will be set so that equation 6 holds true.

[0147] In this embodiment, the 1-drop waveform shown in Figure 17 has the same tf, tr time and voltage height as the 2-drop waveform shown in Figure 15. However, the 1-drop waveform may be completely different from the 2-drop waveform. In that case, to maintain print quality, it is necessary to reduce the difference in droplet velocity between the 1-drop waveform and the 2-drop waveform ejected from the same nozzle. In that case, the time width Dp21 (=Dp22) of the 2-drop waveform shown in Figure 15 should be adjusted so that the velocity of each droplet in the 2-drop waveform, or the velocity of the droplet formed by the combination of droplets ejected by Dp21 and Dp22, approaches the droplet velocity of a waveform different from the 1-drop waveform in Figure 17.

[0148] Furthermore, even if you want to set Dp21 and Dp22 to different values ​​in order to fine-tune the droplet velocity of each droplet in the 2drop waveform, it is desirable to set Dp21 and Dp22 to values ​​as close as possible so that the pressure on the liquid in the pressure chamber 46 due to Dp21 and Dp22 is similar. For example, it is desirable that the time difference between Dp21 and Dp22 be the smallest time difference other than zero that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0149] For example, if the 2-drop waveform has Dp21=Dp22=2.4μs, Tm21=Tm22=1.0μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets due to the 2-drop waveform will be greater than the velocity of the ejected droplets due to the 1-drop waveform. Conversely, if the 2-drop waveform has Dp21=Dp22=2.3μs, Tm21=Tm22=1.0μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets due to the 2-drop waveform will be less than the velocity of the ejected droplets due to the 1-drop waveform.

[0150] Furthermore, in the drive circuit 70 of the liquid discharge head 1, if the values ​​of Dp21 and Dp22 cannot be set to values ​​between 2.3 μs and 2.4 μs, then, for example, Dp21 = 2.3 μs, Dp22 = 2.4 μs, Tm21 = Tm22 = 1.0 μs, UL = 3.0 μs, and Cp = 1.5 μs may be used.

[0151] In this embodiment, the multi-drop drive waveform for discharging multiple droplets from the liquid discharge head 1 is not limited to a 2-drop waveform, but may also be an n-drop waveform that discharges a predetermined number of droplets n, such as a 3-drop waveform that discharges 3 or more droplets. Figure 18 shows an example of a 3-drop waveform that discharges 3 droplets as a drive waveform according to another embodiment. In the example of the drive waveform in Figure 18, the cancellation waveform is omitted. As shown in Figure 18, if the time difference between (0) and (0'') is set to be greater than 1.5 maxAL and less than 2.5 minAL, the phase difference between the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will be less than ±90 degrees in all of the multiple pressure chambers 46. As a result, the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) reinforce each other.

[0152] Furthermore, as shown in Figure 18, if the time difference between (0'') and (0''') is set to be greater than 1.5 maxAL and less than 2.5 minAL, then in all of the multiple pressure chambers 46, the phase difference between the composite wave of (21), (22), (23), and (24) and the composite wave of (31), (32), (33), and (34) will be less than ±90 degrees. As a result, the composite wave of (21), (22), (23), and (24) and the composite wave of (31), (32), (33), and (34) will reinforce each other. Furthermore, by setting Dp31 (=Dp32=Dp33) and adjusting the time width of Dp31 (=Dp32=Dp33), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveforms with time widths of Dp31, Dp32, and Dp33 will be the same. In addition, the discharge velocity of the second drop, discharged due to the reinforcement of the combined waves of (21), (2), (3), and (24) and the residual vibrations from the combined waves of (21), (22), (23), and (24), will be greater than the discharge velocity of the first drop. Also, the discharge velocity of the third drop, discharged due to the reinforcement of the combined waves of (31), (32), (33), and (34), will be greater than the discharge velocity of the second drop.

[0153] As described above, the multi-drop drive waveform (ndrop waveform) that ejects multiple inks in succession allows the ejection speed of subsequently ejected ink to be adjusted to be higher than the ejection speed of previously ejected droplets in all of the multiple pressure chambers 46, due to residual vibrations generated by the previous ejection waveform.

[0154] Furthermore, the time interval between (1) and (2) of depressurizing the pressure chamber 46 is Tm31, and the time interval between (3) and (4) of pressurizing the pressure chamber 46 is also Tm31. Therefore, if Tm31 is set according to the conditions of equation 4 described above, the parasitic oscillations of (1) and (2) will cancel each other out, and the parasitic oscillations of (3) and (4) will also cancel each other out. In addition, the time interval between (21) and (22) of depressurizing the pressure chamber 46 is Tm32, and the time interval between (23) and (24) of pressurizing the pressure chamber 46 is also Tm32. Therefore, if Tm32 is set according to the conditions of equation 4 described above, the parasitic oscillations of (21) and (22) will cancel each other out, and the parasitic oscillations of (23) and (24) will also cancel each other out. Furthermore, the time interval between (31) and (32), which depressurize the pressure chamber 46, is Tm33, and the time interval between (33) and (34), which pressurize the pressure chamber 46, is also Tm33. Therefore, if Tm33 is set according to the conditions of equation 4 described above, the parasitic oscillations of (31) and (32) cancel each other out, and the parasitic oscillations of (33) and (34) also cancel each other out.

[0155] Up to this point, we have described how to adjust the ejection speed of ink ejected later to be greater than that of previously ejected droplets by using residual vibrations generated by the previous ejection waveform. However, it is also possible to adjust the ejection speed to be greater than that of previously ejected droplets by shortening the Tm of the ejection waveform input after the Tm of the previous ejection waveform. This is because the shorter Tm, the greater the reinforcement of the main acoustic vibrations caused by the rising and falling waveforms, for example, as shown in Figure 7. Specifically, in the case of a 3-drop waveform as shown in Figure 18, by making the time width of Tm32 shorter than Tm31, the droplet velocity of the 2nd drop can be made greater than that of the 1st drop. And by making the time width of Tm33 shorter than Tm32, the droplet velocity of the 3rd drop can be made greater than that of the 2nd drop. Furthermore, if the time widths of Tm31, Tm32, and Tm33 are set within the range of the conditions in Equation 4, parasitic vibrations can also be weakened.

[0156] Note that, as shown in Figures 15 and 17, the 1-drop and 2-drop waveforms have the same tf and tr time and voltage height as the 3-drop waveform shown in Figure 18. However, the 1-drop and 2-drop waveforms may be completely different from the 3-drop waveform. Even in that case, in order to maintain print quality, it is necessary to minimize the difference in droplet velocity between the 1-drop, 2-drop, and 3-drop waveforms ejected from the same nozzle. Here, it is assumed that the 1-drop and 2-drop waveforms are adjusted so that the difference in droplet velocity between the droplets ejected from the same nozzle is small. The time width Dp31 (=Dp32=Dp33) of the 3-drop waveform in Figure 18 should be adjusted so that the velocity of each droplet in the 3-drop waveform, or the velocity of the combined droplet formed by the droplets ejected by Dp31, Dp32, and Dp33, is close to the droplet velocity of a waveform different from the 1-drop waveform in Figure 17 or the 2-drop waveform in Figure 15.

[0157] Furthermore, even if you want to set Dp31, Dp32, and Dp33 to different values ​​in order to fine-tune the droplet velocity of each droplet in the 3drop waveform, it is desirable to set Dp31, Dp32, and Dp33 to values ​​as close as possible so that the pressure on the liquid in the pressure chamber 46 caused by Dp31, Dp32, and Dp33 is similar. For example, it is desirable that the time difference between Dp31, Dp32, and Dp33 be the smallest time difference other than zero that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0158] For example, if the 3-drop waveform is defined as Dp31=Dp32=Dp33=2.4μs, Tm31=Tm32=Tm33=1.0μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets in the 3-drop waveform will be greater than the velocity of the ejected droplets in the 1-drop waveform. Conversely, if the 3-drop waveform is defined as Dp31=Dp32=Dp33=2.3μs, Tm31=Tm32=Tm33=1.0μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets in the 3-drop waveform will be less than the velocity of the ejected droplets in the 1-drop waveform.

[0159] In the drive circuit 70 of the liquid discharge head 1, if the values ​​of Dp31, Dp32, and Dp33 cannot be set to values ​​between 2.4 μs and 2.3 μs, for example, Dp31=Dp32=2.3 μs, Dp33=2.4 μs, Tm31=Tm32=Tm33=1.0 μs, UL=3.0 μs, and Cp=1.5 μs may be used. Alternatively, Dp31 =2.3 μs, Dp32=Dp33=2.4 μs, Tm31=Tm32=Tm33=1.0 μs, UL=3.0 μs, and Cp=1.5 μs may be used.

[0160] Furthermore, even with multi-drop drive waveforms (ndrop waveforms) different from 2drop and 3drop waveforms, if the phase reference point of the first discharge waveform input among two consecutive discharge waveforms is set to (0), and the phase reference point of the next discharge waveform is set to (0''), and the time difference between (0) and (0'') is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the aforementioned pressure chambers 46, all discharge waveforms discharging from the second drop onward will reinforce each other with the residual vibrations of the previous discharge waveform. Also, by setting all discharge waveform widths to Dpn1 (=Dpn2=~=Dpnn) and adjusting the time width of Dpn1 (=Dpn2=~=Dpnn), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by discharge waveforms with a time width of Dpn1~Dpnn will be the same. In this way, the multi-drop drive waveform (ndrop waveform) that ejects multiple inks in succession allows the ejection speed of ink ejected later in all of the multiple pressure chambers 46 to be adjusted to be higher than the ejection speed of previously ejected droplets due to residual vibrations generated by the previous ejection waveform.

[0161] Furthermore, if Tmn1 (=Tmn2=~=Tmnn) is set according to the conditions of equation 4 described above, the parasitic oscillations caused by the pressure changes at the beginning and end of each Tm cancel each other out. In addition, by making the Tm of the discharge waveform input after the Tm of the previous discharge waveform shorter, it is possible to adjust the velocity of the droplet discharged by any discharge waveform to be greater than the discharge velocity of the droplet discharged before that. This is because the shorter the Tm, the greater the reinforcement of the main acoustic vibrations caused by the rising and falling waveforms, for example, as shown in Figure 7. If the time of any Tm from Tmn1 to Tmnn is made shorter than the previous Tm in order to adjust the droplet discharge velocity, it is desirable that the subsequent Tm be less than or equal to the time of the aforementioned arbitrary Tm in order to maintain or increase the droplet velocity with the subsequent discharge waveform. In this case, the last Tm (=Tmnn) will be shorter than the first Tm (=Tmn1). By setting Tmn1 to Tmnn within the range where equation 6 holds true, parasitic oscillations caused by all discharge waveforms can be reduced in all of the multiple pressure chambers 46.

[0162] Furthermore, the ndrop waveform and the drive waveform for ejecting a number of drops other than n may be completely different waveforms. Even in this case, in order to maintain print quality, it is necessary to minimize the difference in droplet velocity between the ndrop waveform and the drive waveform for ejecting a number of drops other than n, both ejected from the same nozzle. Here, it is assumed that the drive waveform for ejecting a number of drops other than n, ejected from the same nozzle, is adjusted to minimize the difference in droplet velocity. Then, the time width Dpn1 (=Dpn2=~=Dpnn) of the ndrop waveform should be adjusted so that the velocity of each droplet in the ndrop waveform, or the velocity of the droplet formed by the merging of droplets ejected by Dpn1~Dpnn, approaches the droplet velocity of the drive waveform for ejecting a number of drops other than n. Furthermore, in drive waveforms that eject multiple numbers of drops, if the time elapsed after ejection is short, multiple droplets exist before merging. Also, satellites may occur after multiple droplets. When comparing droplet velocities under different drive waveforms with varying drop counts before multiple droplets merge, the time width Dpn1 (=Dpn2=~=Dpnn) of the ndrop waveform should be adjusted so that the velocity of the droplet with the largest volume (largest droplet diameter) among those ejected by the ndrop waveform is similar to (more preferably nearly identical to) the velocity of the droplet with the largest volume (largest droplet diameter) among those ejected by drive waveforms with a drop count other than n.

[0163] Furthermore, even if you want to set Dpn1 to Dpnn to different values ​​in order to fine-tune the droplet velocity of each droplet in the ndrop waveform, it is desirable to set Dpn1 to Dpnn to values ​​as close as possible so that the pressure on the liquid in the pressure chamber 46 due to Dpn1 to Dpnn is similar. For example, it is desirable that the time difference between Dpn1, Dpn2, ..., and Dpnn be the smallest time difference other than zero that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0164] In the example described above, an example was explained in which the time difference (center-to-center distance) 2UL between adjacent discharge waveforms is set to be greater than 1.5 maxAL and less than 2.5 minAL in order to strengthen the residual vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated first and the vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated afterward. However, the liquid discharge head 1 according to the embodiment is not limited to this configuration.

[0165] Specifically, the drive waveform includes multiple discharge waveforms, and any one of the discharge waveforms from the 1st drop onward is designated as drop a, and any one of the discharge waveforms after drop a is designated as drop b. In this case, the time difference 2*(ba)*UL between the centers of the discharge waveforms of drop a and drop b is set to be greater than (2*(ba)-0.5) times the maximum value (maxAL) of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 whose volume is varied by the actuator 20 that inputs the drive signal, and less than (2*(ba)+0.5) times the minimum value (minAL) of the half-period AL. As a result, when there are two discharge waveforms, or three or more discharge waveforms, the time difference 2UL between adjacent discharge waveforms is 1.5maxAL < 2UL < 2.5minAL, as described above. Furthermore, in the case of a drive waveform containing three or more discharge waveforms, the time difference 2*(ba)*UL between two discharge waveforms that are not adjacent but have one or more discharge waveforms in between is (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. In this way, by setting the time difference of at least two of the multiple discharge waveforms contained in the drive waveform to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL, the discharge velocity of subsequent droplets increases due to the reinforcement of residual vibrations and discharge waveforms.

[0166] A liquid discharge head 1 according to another embodiment will be described with reference to Figures 18 and 33. Figure 33 is an explanatory diagram showing an example of a drive waveform for discharging ndrop droplets, as an example of a drive waveform for a liquid discharge head 1 according to another embodiment.

[0167] First, in the drive waveforms that dispense three or more droplets as shown in Figures 18 and 33, each droplet from the third drop to the ndorp is affected by the discharge waveforms of the preceding droplets. A specific example will be explained below.

[0168] For example, using the example of a drive waveform for dispensing three droplets shown in Figure 18, the third droplet is affected not only by the dispensing waveform of the second droplet but also by the dispensing waveform of the first droplet. Therefore, even if the dispensing waveforms for the second and third droplets reinforce each other, if the dispensing waveforms for the first and third droplets destructively interfere with each other, the dispensing force of the third droplet will be weakened by the influence of the dispensing waveform of the first droplet, raising concerns that the velocity of the third droplet will not increase sufficiently and it will not catch up with the preceding droplets.

[0169] Therefore, in the 3-drop waveform, the waveform for ejecting the first drop and the waveform for ejecting the third drop may reinforce each other. For example, as shown in Figure 18, if the time difference 4UL between (0) and (0''') is set to be greater than 3.5 maxAL and less than 4.5 minAL, then in all of the multiple pressure chambers 46, the phase difference between the composite wave of (1), (2), (3) and (4) and the composite wave of (31), (32), (33) and (34) will be less than ±90 degrees. As a result, the composite wave of (1), (2), (3) and (4) and the composite wave of (31), (32), (33) and (34) will reinforce each other. Furthermore, by setting Dp31 (=Dp32=Dp33) and adjusting the time width of Dp31 (=Dp32=Dp33), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveforms with time widths of Dp31, Dp32, and Dp33 will be the same. In addition, the discharge velocity of the 3rd drop, which is discharged due to the reinforcement of the residual vibrations from the composite waves of (1), (2), (3), and (4) and the composite waves of (31), (32), (33), and (34), will be greater than the discharge velocity of the 1st drop.

[0170] Furthermore, as shown in Figure 33, in a drive waveform (ndrop waveform) that continuously dispenses multiple n droplets, we consider the dispensing waveform of the adrop (after the 1st drop) and the dispensing waveform of the bdrop (two drops after the adrop, but before the ndrop), which is designated as the bdrop. In Figure 33, the reference point for the phase of the ndrop dispensing waveform is shown as (0n). In such a drive waveform that dispenses ndrops, it is conceivable that the bdrop is affected by the dispensing waveform of the adrop. If the dispensing waveform of the adrop and the dispensing waveform of the bdrop cancel each other out, the dispensing force of the bdrop will be weakened by the influence of the adrop's dispensing waveform, raising concerns that the bdrop's velocity will not increase sufficiently and it will not catch up with the preceding droplets. Therefore, if we set the reference point for the phase of the discharge waveform of the adrop to (0a) and the reference point for the phase of the discharge waveform of the bdrop, which is 2 drops later than the adrop, to (0b), and set the time difference 4UL between (0a) and (0b) to be greater than 3.5*maxAL and less than 4.5*minAL, then in all of the aforementioned pressure chambers 46, the residual vibrations of the adrop and bdrop discharge waveforms will reinforce each other.

[0171] Furthermore, in a drive waveform (ndrop waveform) that continuously dispenses multiple n droplets, we consider the dispensing waveform of the adrop (after the 1st drop) and the dispensing waveform of the bdrop (after the adrop but before the ndrop). In a drive waveform that dispenses bdrop or more droplets, it is conceivable that the bdrop droplet will be affected by the dispensing waveform of the adrop. If the dispensing waveform of the adrop droplet and the dispensing waveform of the bdrop droplet are in a destructive relationship, the dispensing force of the bdrop will be weakened by the influence of the adrop dispensing waveform, raising concerns that the velocity of the bdrop will not increase sufficiently and will not catch up with the preceding droplets. Therefore, if we set the reference point for the phase of the discharge waveform of the adrop to (0a) and the reference point for the phase of the discharge waveform of the bdrop to (0b), and set the time difference between (0a) and (0b) 2*(ba)*UL to be greater than (2*(ba)-0.5)*maxAL and less than (2*(ba)+0.5)*minAL, then in all of the aforementioned pressure chambers 46, the residual vibrations of the discharge waveform of the adrop and the discharge waveform of the bdrop will reinforce each other.

[0172] In the ndrop waveform, which dispenses multiple droplets as described above, any one of the dispensing waveforms after the first drop is designated as the adrop, and any one of the dispensing waveforms after the adrop is designated as the bdrop. The liquid dispensing head 1 sets the time interval (time difference) 2*(ba)*UL between the centers of the adrop and bdrop dispensing waveforms to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. This causes the residual vibration from the earlier (adrop) dispensing waveform and the vibration from the subsequent (bdrop) dispensing waveform to reinforce each other, thereby increasing the dispensing speed.

[0173] Furthermore, the two discharge waveforms whose time difference 2*(ba)*UL is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL may be any combination of the two discharge waveforms from the multiple discharge waveforms of the ndrop waveform, or any one or more combinations of the two discharge waveforms.

[0174] Next, when there is variation in the principal acoustic vibration frequencies of multiple pressure chambers 46, we consider dividing the multiple pressure chambers 46 into multiple groups and adjusting the drive waveform to match the maximum and minimum values ​​of the half-period AL of the principal acoustic vibration frequency of each group, and then inputting it. For example, if the maximum value of the half-period AL of the principal acoustic vibration frequencies of multiple pressure chambers 46 is 3.5 μs and the minimum value is 2.5 μs, then pressure chambers 46 with AL between 3.5 μs and 3.0 μs or more are designated as the first group, and pressure chambers 46 with AL between 3.0 μs and 2.5 μs or more are designated as the second group. Here, a pressure chamber 46 that satisfies the conditions of both the first and second groups (for example, a pressure chamber 46 with AL of 3.0 μs) is assigned to one of the groups. For example, if a group of pressure chambers 46 that satisfies the conditions of both the first and second groups is the same as a group of adjacent pressure chambers 46, then the management and distinction of each group becomes simpler.

[0175] As a result, the maxAL of the pressure chamber 46 of the first group becomes 3.5 μs and the minAL becomes 3.0 μs. The time interval (time difference) 2*(ba)*UL between the centers of the a-drop discharge waveform and the b-drop discharge waveform of the n-drop waveform input to the pressure chamber 46 of the first group is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL.

[0176] Furthermore, the maxAL of the pressure chamber 46 in the second group is 3.0 μs, and the minAL is 2.5 μs. The time interval (time difference) 2*(ba)*UL between the centers of the a-drop discharge waveform and the b-drop discharge waveform of the n-drop waveform input to the pressure chamber 46 in the second group is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL.

[0177] Next, using Figures 34 and 35, we will explain the drive waveform of the liquid discharge head 1, which increases the potential difference (expanded potential difference) between the discharge waveform or the cancellation waveform (2 or more consecutive times) in the drive waveform of the drive circuit 70.

[0178] First, the discharge waveform among the drive waveforms according to other embodiments will be described. In the discharge waveform of the liquid discharge head 1 of this embodiment, one of the potential difference changes from 1 to h-1 is defined as the i-th potential difference change, and one of the potential difference changes from i+1 to h is defined as the j-th potential difference change. If the time interval between the start times of the i-th and j-th potential difference changes is Tij, then either time interval Tij is: (k / 2-1 / 6)λn ≤ Tij ≤ (k / 2+1 / 6)λn···(Equation 7) This is the result. Here, k is an odd number greater than or equal to 1.

[0179] According to the discharge waveform that satisfies this equation 7, the parasitic oscillations with period λn caused by the corresponding two or more potential difference changes cancel each other out, and the parasitic oscillations with period λn generated in the pressure chamber 46 can be suppressed. This is also true when the number of times the pressure chamber 46 is reduced in size is three or more times (h times).

[0180] Furthermore, when i+1=j, that is, when Tij is the time interval of a continuous change in potential difference, considering the reduction of power consumption, the time interval Tij is: (k / 2-1 / 6)λn ≤ Tij ≤ kλn / 2···(Equation 8) It is desirable that this be the case. Here, k is an odd number greater than or equal to 1.

[0181] Furthermore, if the discharge waveform satisfies (k / 2-1 / 6)λn ≤ Tij ≤ (k / 2+1 / 6)λn (where k is an odd number greater than or equal to 1) for all potential difference changes from the 1st to the hth time, or if there are other potential difference changes that satisfy (k / 2-1 / 6)λn ≤ Tij ≤ kλn / 2 (where k is an odd number greater than or equal to 1), then parasitic oscillations of period λn occurring in the pressure chamber 46 can be further suppressed.

[0182] Furthermore, by making the potential difference change amounts for the i-th and j-th potential difference changes the same, given the time interval Tij satisfying (k / 2-1 / 6)λn ≤ Tij ≤ (k / 2+1 / 6)λn (where k is an odd number greater than or equal to 1), subsequent residual vibrations originating from parasitic vibrations can be further suppressed. More preferably, assuming that the potential difference of each stage is the same and pressure vibrations do not attenuate, the optimal holding time for each stage is λn / stage(h), so the time interval Tij for all consecutive potential difference changes should be λn / stage(h).

[0183] Furthermore, from the perspective of reducing power consumption by reinforcing the main acoustic vibrations, if the discharge waveform involves two or more h times of potential difference changes that continuously expand the pressure chamber 46, it is desirable that the time interval Tij between the first potential difference change and the h-th potential difference change is within 0.5 times the half-period AL of the main acoustic vibration. This is because by keeping the time interval Tij between the first and h-th potential difference changes within 0.5 times the half-period AL of the main acoustic vibration, the main acoustic vibrations generated by all potential difference changes from the first to the h-th will reinforce each other, contributing to a reduction in power consumption.

[0184] As an example of the discharge waveform described above, Figure 34 shows an example with 4 stages (4 times) in the rising waveform, and Figure 35 shows an example with 3 stages in the rising waveform. In Figure 34, the number of stages, h, is shown in parentheses. It goes without saying that the same method should be used for the falling waveform. As shown in Figures 34 and 35, assuming that the potential difference at each stage is the same and that the pressure oscillation does not attenuate, the optimal holding time for each stage is λn / stage(h). Therefore, if the phase difference (time interval) of any two of the potential difference displacements from the 1st stage to the hth stage is in the range of (k / 2-1 / 6)λn to (k / 2+1 / 6)λn, the parasitic oscillations generated by the corresponding two potential difference displacements will cancel each other out. For example, the time interval between the 1st and 3rd potential difference displacements in Figure 34 is λn / 2, and Tij in the case of i=1&j=3 satisfies equation 7. Furthermore, the time interval between the second and fourth potential difference displacements in Figure 34 is λn / 2, and Tij in the case of i=2 and j=4 also satisfies equation 7. Therefore, the parasitic oscillations will destructively cancel each other out.

[0185] Furthermore, pressure vibrations within the pressure chamber 46 are attenuated over time due to the viscous resistance of the ink. Also, parasitic vibrations usually attenuate more over time than principal acoustic vibrations. For this reason, the potential difference change from 0.5 AL before ejection to immediately after ejection has a greater impact on satellites and print quality than the potential difference change in the time range from 1.5 AL before ejection to 0.5 AL before ejection, and the impact on satellites and print quality is greater from 1.5 AL before ejection to 0.5 AL before ejection (the range in which the principal acoustic vibrations reinforce each other as described above) than the potential difference change in the time range before 1.5 AL. Therefore, it is desirable to adjust the value of Tm or Tij in the ejection waveform so that the parasitic vibrations cancel each other out for the Tm or Tij closer to immediately before or after ejection among the time intervals of any two potential difference changes.

[0186] Furthermore, due to manufacturing variations, the parasitic oscillation periods λn of the multiple pressure chambers 46 of the liquid discharge head 1 may not be identical. Here, let maxλn be the maximum value of the parasitic oscillation period λn of the multiple pressure chambers 46, and minλn be the minimum value. In this case, the lower limit of equation 7 is largest for the multiple pressure chambers 46 at (k / 2-1 / 6)maxλn, and the upper limit of equation 7 is smallest at (k / 2+1 / 6)minλn. Therefore, (k / 2-1 / 6)maxλn≦Tij≦(k / 2+1 / 6)minλn···(Equation 9) This is the result. Here, k is an odd number greater than or equal to 1.

[0187] By setting Tij within the range where equation 9 holds true, parasitic vibrations can be reduced in all of the aforementioned pressure chambers 46.

[0188] According to the liquid discharge head 1 of the multiple embodiments described above, the time width of the first discharge waveform and the time width of the subsequent discharge waveform are made the same (including approximately the same), and the interval between the discharge waveforms is matched to the period that strengthens the residual vibration of the liquid in the pressure chamber generated by the first discharge waveform and the vibration of the liquid in the pressure chamber generated by the subsequent discharge waveform. That is, the drive waveform has approximately the same discharge waveform width when discharging multiple droplets in succession, and the distance between the centers of two of the multiple discharge waveforms 2*(ba)*UL when discharging multiple droplets in succession is (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. The liquid discharge head can make the discharge force of each droplet approximately the same and increase the discharge speed of subsequent droplets. Since the ejection waveform widths are approximately the same, the ejection force of each ejection waveform is approximately the same for the droplets. The distance between the centers of two of the multiple ejection waveforms, 2*(ba)*UL, is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. As a result, the ejection velocity of subsequent droplets increases due to the reinforcement of residual vibrations and ejection waveforms. The liquid ejection head improves print quality by canceling out parasitic vibrations.

[0189] Furthermore, the liquid discharge head 1 can adjust the discharge waveform width when many droplets are discharged continuously, so that the velocity remains approximately the same regardless of the number of droplets. The liquid discharge head 1 also cancels out parasitic oscillations by setting the intermediate voltage time to approximately half a period of the parasitic oscillation. Additionally, the intermediate voltage time of the discharge waveform for the last droplet can be made shorter than the intermediate voltage times of the previous discharge waveforms.

[0190] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0191] 1…Liquid discharge head, 10…Base, 20…Actuator, 21…Piezoelectric column, 22…Non-driven piezoelectric column, 30…Vibrator, 40…Flow path plate, 42…Partition wall, 45…Flow path, 46…Pressure chamber, 47…Individual flow path, 48…Common flow path, 50…Nozzle plate, 51…Nozzle, 70…Drive circuit, 71…Wiring film, 72…Driver IC, 81…First voltage source, 82…Second voltage source, 83…Third voltage source, 84…Fourth voltage source, 85…Fifth voltage source, 100…Liquid discharge device, 111…Housing, 112…Media supply unit, 113…Image forming unit, 114…Media discharge unit, 115…Transport device, 117…Support unit 118...Conveyor belt, 119...Support plate, 120...Belt roller, 121...Guide plate pair, 122...Conveyor 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...Type sensor, 200...External connection device, 301...Vibration part, 721...Data buffer, 722...Decoder, 723...Driver, 724...Voltage control unit, 725...Voltage switching unit, 726...Wiring electrode, 727...Wiring electrode.

Claims

1. A nozzle plate equipped with a nozzle for dispensing liquid, A pressure chamber communicating with the nozzle, An actuator that varies the volume of the pressure chamber in response to a drive signal, The system comprises a drive circuit that generates the drive signal for driving the actuator, The drive signal includes a plurality of discharge waveforms that cause a plurality of droplets to be discharged from the nozzle. The waveform widths of the aforementioned multiple discharge waveforms are the same. The output waveform of the drive signal includes an expanding potential difference that expands the volume of the pressure chamber, a reducing potential difference that reduces the volume of the pressure chamber, and at least one intermediate potential difference between the expanding potential difference and the reducing potential difference. The drive circuit cancels out vibrations at an acoustic resonance frequency in a frequency range higher than the main acoustic resonance frequency of the liquid in the pressure chamber, which are caused by a change in the potential difference, by at least one more change in the potential difference performed after the change in the potential difference. A liquid discharge head in which the intervals between the multiple discharge waveforms match the period that amplifies the residual vibration of the liquid in the pressure chamber caused by the discharge waveform generated first and the vibration of the liquid in the pressure chamber caused by the discharge waveform generated afterward.

2. Let λn be the period of the acoustic resonance frequency in a frequency range higher than the principal acoustic resonance frequency of the liquid in the pressure chamber, and let h be the number of potential difference changes included in the drive signal. When one of the potential difference changes from the 1st to the (h-1)th time is defined as the i-th potential difference change, and one of the potential difference changes from the (i+1)th time to the h-th time is defined as the j-th potential difference change, the time interval Tiij between the i-th and j-th potential difference changes, which are any two of the h changes, is: (k / 2-1 / 6)λn ≦ Tij ≦ (k / 2+1 / 6)λn The liquid dispensing head according to claim 1, wherein k in this formula is an odd number of 1 or more.

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

4. The liquid discharge head according to claim 1, wherein the drive circuit has a switching circuit connecting electrodes and a voltage source, and the drive signal is generated by switching the switching circuit.

5. The liquid discharge head according to claim 1, wherein, when any one of the discharge waveforms from the first drop onward among the plurality of discharge waveforms is designated as drop a, and any one of the discharge waveforms after drop a is designated as drop b, the time interval between the centers of the discharge waveform of drop a and the discharge waveform of drop b is greater than (2*(ba)-0.5) times the maximum value of the half-period of the main acoustic vibration frequency of the plurality of pressure chambers whose volume is varied by the actuator that inputs the drive signal, and less than (2*(ba)+0.5) times the minimum value of the half-period.

6. The liquid discharge head according to claim 1, wherein the acoustic resonance frequency in a frequency range higher than the principal acoustic resonance frequency of the liquid in the pressure chamber is approximately three times or more and approximately an odd multiple of the principal acoustic resonance frequency.

7. The liquid dispensing head according to claim 1, wherein the time interval of the intermediate potential difference of any of the plurality of dispensing waveforms is greater than or equal to the time interval of the intermediate potential difference of the next dispensing waveform after the arbitrary dispensing waveform.

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