Liquid ejecting head

Abstract

The invention provides a liquid ejection head which can make ejection forces of liquid droplets approximate or the same, and can improve the ejection speed of subsequent liquid droplets. The liquid ejection head includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate includes a nozzle that ejects a liquid. A pressure chamber communicates to the nozzle. An actuator varies the volume of the pressure chamber in accordance with a drive signal. A drive circuit generates the drive signal that drives the actuator. The drive signal includes a plurality of ejection waveforms that cause a plurality of droplets to be ejected from the nozzle. The plurality of discharge waveforms have substantially the same waveform width and differ from the half cycle of the main sound vibration frequency. The intervals of the plurality of ejection waveforms coincide with the period of enhancing the residual vibration of the liquid in the pressure chamber due to the previously generated ejection waveform and the vibration of the liquid in the pressure chamber due to the later generated ejection waveform.

Description

TECHNICAL FIELD

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

[0002] In the past, as a liquid ejection head, a technology of ejecting a liquid droplet such as ink has been known. The liquid ejection head increases a dot diameter when a liquid droplet lands on a medium by continuously ejecting a plurality of liquid droplets to achieve a gray scale expression of an ink density on the medium.

[0003] However, in this case, when the main acoustic vibration frequency of a plurality of pressure chambers is deviated, if the same drive waveform (a drive waveform in which the ejection waveform width of the first droplet and the last droplet is different) is input to the plurality of pressure chambers to continuously eject a plurality of liquid droplets, a situation in which the continuously ejected liquid droplets do not match occurs, and becomes a cause of deterioration of print quality.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent No. 6820704 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] An object of the present application is to provide a liquid ejection head capable of making the ejection force of each liquid droplet substantially the same and capable of increasing the ejection speed of a subsequent liquid droplet.

[0009] SOLUTION TO PROBLEM

[0010] A liquid ejection head includes a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate includes a nozzle that ejects a liquid. The pressure chamber is connected to the nozzle. The actuator makes the volume of the pressure chamber variable in accordance with a drive signal. The drive circuit generates the drive signal that drives the actuator. The drive signal includes a plurality of ejection waveforms that cause a plurality of liquid droplets to be ejected from the nozzle. The plurality of ejection waveforms have substantially the same waveform width and are different from a half period of a main acoustic vibration frequency. The interval of the plurality of ejection waveforms coincides with a period in which a residual vibration of the liquid in the pressure chamber due to a previously generated ejection waveform and a vibration of the liquid in the pressure chamber due to a subsequently generated ejection waveform are enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a cross-sectional view that shows the configuration of the liquid ejection head according to the embodiment with a part omitted.

[0012] Figure 2 is a cross-sectional view that shows the configuration of the liquid ejection head according to the embodiment with a part omitted.

[0013] Figure 3 This is a block diagram schematically illustrating the configuration of the drive circuit of the liquid ejector head according to the embodiment.

[0014] Figure 4 This is an explanatory diagram showing the configuration of a liquid ejection device using the liquid ejection head according to the embodiment.

[0015] Figure 5 This is a block diagram illustrating an example of the configuration of the liquid ejection device according to an embodiment.

[0016] Figure 6 This is an explanatory diagram showing an example of a liquid ejection head according to an embodiment, including an ejection waveform of two droplets being ejected continuously and a cancellation waveform of the drive waveform.

[0017] Figure 7 This is an explanatory diagram showing an example of the drive waveform and acoustic vibration of the liquid ejector head according to an embodiment.

[0018] Figure 8 This is an explanatory diagram showing an example of a liquid ejection head according to an embodiment, including an ejection waveform of three droplets being ejected continuously and a cancellation waveform of the drive waveform.

[0019] Figure 9 This is an explanatory diagram showing an example of the ejection waveform and the cancellation waveform of the liquid ejection head involved in the comparative example.

[0020] Figure 10 This is an explanatory diagram showing an example of a liquid ejection head according to an embodiment, including an ejection waveform of two droplets being ejected continuously and a cancellation waveform of the drive waveform.

[0021] Figure 11 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0022] Figure 12 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0023] Figure 13 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0024] Figure 14 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0025] Figure 15 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0026] Figure 16 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0027] Figure 17 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0028] Figure 18 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0029] Figure 19 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0030] Figure 20 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0031] Figure 21 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0032] Figure 22 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0033] Figure 23 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0034] Figure 24 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets.

[0035] Figure 25 This is a block diagram schematically illustrating the configuration of the drive circuit of a liquid ejector head according to other embodiments.

[0036] Figure 26 This is an illustrative diagram showing an example of a liquid ejection head according to other embodiments, including an ejection waveform of two droplets being ejected in succession and a drive waveform of canceling the ejection.

[0037] Figure 27 This is an illustrative diagram showing an example of the drive waveform and acoustic vibration of a liquid ejector head according to other embodiments.

[0038] Figure 28 This is an illustrative diagram showing an example of a liquid ejection head according to other embodiments, including an ejection waveform of two droplets being ejected in succession and a drive waveform of canceling the ejection.

[0039] Figure 29 This is an explanatory diagram illustrating an example of the drive waveform of a liquid ejector head according to other embodiments.

[0040] Explanation of reference numerals in the attached figures

[0041] 1: Liquid ejector head; 10: Base; 20: Actuator; 21: Piezoelectric column; 22: Non-driven piezoelectric column; 30: Vibrating plate; 40: Flow path plate; 42: Partition wall; 45: Flow path; 46: Pressure chamber; 47: Individual flow path; 48: Common flow path; 50: Nozzle plate; 51: Nozzle; 70: Drive circuit; 71: Wiring film; 72: Driver IC; 81: First voltage source; 82: Second voltage source; 83: Third voltage source; 100: Liquid ejection device; 111: Housing; 112: Medium supply unit; 113: Image forming unit; 114: Medium discharge unit; 115: Conveying device; 117: Support unit; 119: Conveyor belt; 119: Support plate; 120: Belt roller; 121: Guide plate; 122: Conveying roller; 130: Head unit; 132: Ink tank; 133: Connecting flow path; 134: Supply pump; 150: Control unit; 151: Processor; 154: I / O port; 155: Image memory; 161: Drive motor; 162: Operation unit; 163: Various sensors; 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. Detailed Implementation

[0042] The following reference Figures 1 to 5 The configuration of the liquid nozzle 1 and the liquid dispensing device 100 using the liquid nozzle 1 according to the embodiment will be described. Figure 1 This is a cross-sectional view showing the configuration of the liquid ejector head 1 according to the embodiment, with a portion omitted. Figure 2 This is a cross-sectional view showing the configuration of the liquid ejector head 1 according to the embodiment, with a portion omitted. Figure 3This is a block diagram schematically showing the configuration of the drive circuit 70 of the liquid ejector head 1. Figure 4 This is an explanatory diagram showing the configuration of the liquid ejection device 100 using the liquid ejection head 1 according to the embodiment. Figure 5 This is a block diagram showing an example of the configuration of the liquid ejection device 100. It should be noted that, for ease of explanation, the configuration may be shown enlarged, reduced, or omitted as appropriate in each figure.

[0043] The liquid ejector head 1 involved in this embodiment is, for example, an inkjet head that ejects ink as a liquid. Figure 1 and Figure 2 As shown, the liquid ejector head 1 includes a base 10, an actuator 20, a vibrating plate 30, a flow path plate 40, a nozzle plate 50 having multiple nozzles 51, and a drive circuit 70.

[0044] The base 10 is formed, for example, in the shape of a rectangular plate. The actuator 20 is engaged with the base 10.

[0045] The actuator 20 is, for example, a piezoelectric component having a plurality of piezoelectric pillars 21 and a plurality of non-driven piezoelectric pillars 22 arranged alternately with the plurality of piezoelectric pillars 21. The actuator 20 is formed in a comb-like shape by arranging the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 at predetermined intervals in one direction. For example, with such an actuator 20, a plurality of rectangular columnar piezoelectric elements are formed on a piezoelectric component by cutting grooves from the end face opposite to the base 10 side to the base 10. Then, the plurality of formed piezoelectric elements are configured as a plurality of piezoelectric pillars 21 and a plurality of non-driven piezoelectric pillars 22 arranged alternately as piezoelectric elements by setting electrodes, etc. That is, the actuator 20 is divided into a plurality of sections on one end side (vibrating plate 30 side) and connected on the other end side (base 10 side) by the formed grooves.

[0046] For example, the stacked piezoelectric component constituting actuator 20 is formed by stacking and sintering sheet-like piezoelectric materials. As a specific example, such as... Figure 1 and Figure 2 As shown, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 are, for example, stacked piezoelectric elements serving as driving elements. The piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 have multiple stacked piezoelectric layers, multiple internal electrodes formed on the main surface of each piezoelectric layer, and multiple external electrodes. It should be noted that, as an example, the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 have the same configuration.

[0047] The piezoelectric layer is formed into a thin plate shape, for example, by a piezoelectric material such as PZT (lead zirconate titanate) or lead-free KNN (sodium potassium niobate). Multiple piezoelectric layers are stacked along the thickness direction and bonded together by sintering. It should be noted that, here, the stacking direction of the multiple piezoelectric layers is orthogonal to the arrangement direction of the multiple piezoelectric pillars 21 and the multiple non-driven piezoelectric pillars 22.

[0048] The internal electrodes are conductive films formed in a predetermined shape using a sinterable conductive material such as silver or palladium. The internal electrodes are formed in predetermined regions on the main surface of each piezoelectric layer. Multiple internal electrodes are alternately configured as different poles in the arrangement direction.

[0049] External electrodes are formed on the surfaces of multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22, and are assembled at the ends of the internal electrodes. The external electrodes are deposited using known methods such as electroplating or sputtering with materials such as Ni, Cr, and Au. The multiple external electrodes are respectively disposed on different side portions of the multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22, and are configured as different electrodes. It should be noted that external electrodes of different electrodes may also surround different regions of the same side portion of the multiple piezoelectric pillars 21 and multiple non-driven piezoelectric pillars 22.

[0050] In this embodiment, as an example, the plurality of external electrodes have individual electrodes formed on the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22, respectively, and a common electrode continuously formed on the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22. The plurality of individual electrodes formed on the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22 are configured to be independent of each other. The common electrode is grounded, for example.

[0051] These external electrodes are connected, for example, to the drive circuit 70. For example, each external electrode is connected to the control unit 150, which is the drive unit, via wiring through the driver 723 described later in the drive circuit 70, and is configured to be driven and controlled by the processor 151.

[0052] The piezoelectric column 21 and the non-driven piezoelectric column 22 vibrate longitudinally along the stacking direction of the piezoelectric layers by applying a voltage to the internal electrodes via the external electrodes. The longitudinal vibration referred to herein is, for example, "vibration in the thickness direction as defined by the piezoelectric constant d33". For example, as... Figure 2 As shown, a plurality of piezoelectric columns 21 are arranged at intervals and correspond to the pressure chamber 46 across the vibrating plate 30, while the remaining non-driven piezoelectric columns 22 are arranged at positions opposite to the partition wall portion 42 across the vibrating plate 30.

[0053] The piezoelectric column 21 vibrates longitudinally when a voltage is applied, displacing the vibrating plate 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 by driving it, and each non-driven piezoelectric column 22 constitutes a support. In other words, the piezoelectric column 21 expands and contracts the pressure chamber 46, making the volume of the pressure chamber 46 variable.

[0054] The vibrating plate 30 is attached to one side of the piezoelectric layer of the plurality of piezoelectric pillars 21, 22, i.e., the side of the nozzle plate 50. The vibrating plate 30 is deformed, for example, by driving the piezoelectric pillars 21. The vibrating plate 30 is attached to the piezoelectric pillars 21 and non-driven piezoelectric pillars 22 of the actuator 20.

[0055] The vibrating plate 30 is, for example, a flat plate with its thickness direction aligned with the stacking direction of the piezoelectric layers. The surface direction of the vibrating plate 30 extends in the arrangement direction of the plurality of piezoelectric pillars 21 and the plurality of non-driven piezoelectric pillars 22. The vibrating plate 30 is, for example, a metal plate. The vibrating plate 30 has a plurality of vibrating portions 301 opposite to each pressure chamber 46 and capable of individual displacement. The vibrating plate 30 is formed by connecting the plurality of vibrating portions 301 together.

[0056] For example, the vibrating plate 30 is configured as a flat plate, and the regions where it is joined to the piezoelectric post 21 are individually displaced. The vibrating plate 30 is, for example, made of SUS plate. The vibrating plate 30 may have creases or steps formed in the regions adjacent to the vibrating parts 301 or between adjacent vibrating parts 301 to facilitate the displacement of the multiple vibrating parts 301.

[0057] The vibrating plate 30 utilizes the elongation and compression of the piezoelectric column 21 generated by the longitudinal vibration of the piezoelectric column 21 to displace the part of the plate that is positioned opposite to the piezoelectric column 21, thereby expanding and shrinking the pressure chamber 46 so that the volume of the pressure chamber 46 is variable.

[0058] The main surface of the vibrating plate 30 is bonded to the actuator 20 on one side, and to the flow path plate 40 on the other side. A pressure chamber 46 capable of containing ink is formed between the vibrating plate 30 and the flow path plate 40.

[0059] The main surface of the vibrating plate 30 faces the piezoelectric columns 21 and 22 on one side, while the main surface of the other side faces the pressure chamber 46 and the partition wall 42.

[0060] The flow path plate 40 is joined to the vibrating plate 30. The flow path plate 40 is disposed between the nozzle plate 50 and the vibrating plate 30. The flow path plate 40 has a plurality of partition walls 42. In addition, the flow path plate 40 forms a predetermined flow path 45. The flow path plate 40 forms the plurality of partition walls 42 and the predetermined flow path 45, for example, by stacking a plurality of plates 401 with partial openings.

[0061] The partition wall 42 is arranged in multiple directions along the arrangement of the multiple piezoelectric columns 21, 22, and is opposite to the non-driven piezoelectric column 22 across the vibrating plate 30. The partition wall 42 separates the multiple pressure chambers 46 of the predetermined flow path 45 (described later) and the multiple individual flow paths 47.

[0062] 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.

[0063] Multiple pressure chambers 46 are arranged along the direction of the arrangement of multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and are opposite to the multiple piezoelectric columns 21 separated by a vibrating plate 30. The multiple pressure chambers 46 arranged in one direction are separated by partition walls 42. Multiple partition walls 42 disposed between the multiple pressure chambers 46 are opposite to the multiple non-driven piezoelectric columns 22 separated by a vibrating plate 30. The multiple pressure chambers 46 are formed by a flow path plate 40, which is closed on one side by the vibrating plate 30 and on the other side by a nozzle plate 50 in the piezoelectric layer stacking direction. Furthermore, nozzles 51 formed on the nozzle plate 50 are disposed in the pressure chambers 46.

[0064] Multiple pressure chambers 46 are connected to a common flow path 48 via individual flow paths 47. Each pressure chamber 46 holds liquid supplied from the common flow path 48 through the individual flow paths 47 and is ejected from a nozzle 51 by deformation caused by the vibration of a vibrating plate 30 forming part of the pressure chamber 46. Individual flow paths 47 connect the common flow path 48 and the pressure chambers 46. The number of individual flow paths 47 is the same as the number of pressure chambers 46. The cross-sectional shape of the individual flow paths 47 differs from that of the pressure chambers 46. The cross-sectional area of ​​the individual flow paths 47 is smaller than that of the pressure chambers 46. The common flow path 48 is fluidly connected to the multiple individual flow paths 47 and is connected to the pressure chambers 46 via each individual flow path 47.

[0065] The nozzle plate 50 is formed of 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 at positions opposite to the plurality of pressure chambers 46 and extending through in the thickness direction. A nozzle array is formed by a plurality of nozzles 51.

[0066] like Figure 5As shown, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data in a time sequence for each piezoelectric post 21, 22. The decoder 722 controls the driver 723 for each piezoelectric post 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 that actuates each piezoelectric post 21, 22. The drive signal is the voltage applied to each piezoelectric post 21, 22.

[0067] As a specific example, such as Figure 1 As shown, the driving circuit 70 includes 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 wiring substrate mounted on the other end of the wiring film 71. For example, the driver IC 72 includes a data buffer 721, a decoder 722, and a driver 723. It should be noted that the driver IC 72 may also have a configuration where the data buffer 721, decoder 722, driver 723 are partially present, and the printed wiring substrate and other components are partially present.

[0068] The drive circuit 70 drives the piezoelectric column 21 by applying a drive voltage to the external electrode using the driver IC 72, thereby making the volume of the pressure chamber 46 variable so as to eject droplets from the nozzle 51.

[0069] 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 portion of an external electrode by means of thermoforming or the like. The wiring film 71 is, for example, a COF (Chip on Film) on which a driver IC 72 is mounted.

[0070] The driver IC 72 is connected to the external electrode via the wiring film 71. It should be noted that the driver IC 72 may also be connected to the external electrode via other methods such as ACP (Anisotropic Conductive Paste), NCF (Non-Conductive Film), and NCP (Non-Conductive Paste) instead of the wiring film 71.

[0071] The driver IC 72 generates control signals and drive signals applied to each piezoelectric column 21, 22 to actuate the piezoelectric columns 21. Based on the image signal input from the control unit 150 of the liquid ejection device 100, the driver IC 72 generates control signals for selecting the timing of ink ejection and controlling the piezoelectric columns 21 that eject ink. Additionally, the driver IC 72 generates a voltage, i.e., a drive signal (electrical signal), applied to the piezoelectric columns 21 according to the control signals. When the driver IC 72 applies a drive signal to the piezoelectric columns 21, the piezoelectric columns 21 cause the vibrating plate 30 to shift, and the volume of the pressure chamber 46 is variably driven by expanding and contracting the pressure chamber 46. This causes pressure vibration in the ink filling the pressure chamber 46. Through this pressure vibration, the ink is ejected from the nozzle 51 provided in the pressure chamber 46. It should be noted that the liquid ejection head 1 can also be configured to achieve grayscale representation by changing the amount of ink droplets falling on a single pixel. Alternatively, the liquid ejector head 1 can be configured to change the amount of ink droplets falling on a pixel by altering the number of ink ejections. Thus, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric column 21.

[0072] Next, as Figure 3 As shown, an example of the drive circuit 70 will be described. The drive circuit 70, for example, includes a voltage control unit 724 and a voltage switching unit 725, the same number as the pressure chambers 46, within the driver IC 72. However, in... Figure 3 The diagram shows two voltage switching units 725, while the diagrams of other voltage switching units 725 are omitted.

[0073] The drive circuit 70 is connected to the first voltage source 81, the second voltage source 82, and the third voltage source 83. The drive circuit 70 supplies the voltage from the first voltage source 81 to each wiring electrode 726. Furthermore, the drive circuit 70 selectively supplies the voltages from the first voltage source 81, the second voltage source 82, and the third voltage source 83 to each wiring electrode 727. Here, in the case where the actuator 20 is a stacked PZT, because there is a tendency for degradation if a binary voltage is applied, the voltages supplied by the first voltage source 81, the second voltage source 82, and the third voltage source 83 are set to ground voltage and polarity that is either positive or negative relative to ground voltage.

[0074] The output voltage of the first voltage source 81 is, for example, the ground voltage, and its value is set to V0 (V0 = 0 [V]). The output voltage of the second voltage source 82 is set to V1. It should be noted that voltage V1 is set to a voltage higher than V0. The output voltage of the third voltage source 83 is set to, for example, V2. For example, voltage V2 is set to a voltage higher than V0 and lower than V1.

[0075] Wiring electrode 726 is connected to a common electrode of actuator 20 that serves as a ground electrode. Multiple wiring electrodes 727 are respectively connected to individual electrodes of actuator 20 that serve as non-ground electrodes.

[0076] The voltage control unit 724 is connected to multiple voltage switching units 725. The voltage control unit 724 outputs a command to each voltage switching unit 725 indicating which voltage source among the first voltage source 81, second voltage source 82, and third voltage source 83 to select. 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, and third voltage source 83. 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.

[0077] The voltage switching unit 725 is, for example, a semiconductor switch. Under the control of the voltage control unit 724, the voltage switching unit 725 connects to one of the first voltage source 81, the second voltage source 82, and the third voltage source 83, and to the wiring electrode 727. Therefore, the internal electrodes of different poles of the piezoelectric post 21 are connected to the wiring electrode 726 and the wiring electrode 727 via external electrodes (a common electrode and individual electrodes).

[0078] In this drive circuit 70, the drive circuit switches the connection wiring between voltage sources 81, 82, and 83 and actuator 20 using a switching circuit composed of a voltage control unit 724 and multiple voltage switching units 725, thereby inputting drive waveforms with at least three potential differences as drive signals to the electrode space of actuator 20. Here, the drive waveform is the drive waveform that ejects droplets by driving actuator 20. It should be noted that, in this embodiment, potential differences other than the largest and smallest potential differences are referred to as intermediate potential differences.

[0079] The printed wiring board is a PWA (Printed Wiring Assembly) that houses various electronic components and connectors. The printed wiring board is connected to the control unit 150 of the liquid ejection device 100.

[0080] Next, refer to Figure 4 and Figure 5 An example of a liquid ejection device 100 equipped with a liquid ejection head 1 will be described. The liquid ejection device 100 is, for example, an inkjet recording device. The liquid ejection device 100 includes a housing 111, a media supply unit 112, an image forming unit 113, a media discharge unit 114, and a transport device 115. In addition, the liquid ejection device 100 includes a control unit 150.

[0081] The liquid ejection device 100 is a liquid ejection device that performs image forming processing on paper P by ejecting liquid such as ink while conveying, for example, paper P as the ejection object, i.e., printing medium, along a predetermined transport path A from the medium supply unit 112 through the image forming unit 113 to the medium discharge unit 114.

[0082] The housing 111 forms the outline of the liquid ejection device 100. A discharge port for discharging paper P to the outside is provided at a predetermined location on the housing 111.

[0083] The media supply unit 112 has multiple paper feed boxes and is configured to hold various sizes of paper P in a stacked manner.

[0084] The media discharge section 114 has a paper discharge tray configured to hold the paper P discharged from the discharge port.

[0085] The image forming unit 113 includes a support portion 117 for supporting the paper P and a plurality of head units 130 disposed opposite to each other above the support portion 117.

[0086] The support portion 117 includes a conveyor belt 118 arranged in a ring in a predetermined area for image formation, a support plate 119 supporting the conveyor belt 118 from the back side, and a plurality of belt rollers 120 arranged on the back side of the conveyor belt 118.

[0087] During image formation, the support portion 117 supports the paper P on the holding surface that serves as the upper surface of the conveyor belt 118, and conveys the paper P downstream by using the rotation of the belt roller 120 to transport the conveyor belt 118 at a predetermined time.

[0088] The head unit 130 includes a liquid ejector head 1, multiple ink tanks 132 which are respectively mounted on the liquid ejector head 1, a connecting flow path 133 connecting the liquid ejector head 1 and the ink tanks 132, and a supply pump 134.

[0089] In this embodiment, multiple head units 130 are provided. Each head unit 130 uses ink of a different color. For example, the multiple head units 130 include liquid ejector heads 1 of four colors: cyan, magenta, yellow, and black, and ink tanks 132 that respectively contain these various colors of ink. The ink tanks 132 are connected to a common flow path 48 of the liquid ejector heads 1 via a connecting flow path 133.

[0090] Additionally, a negative pressure control device, such as a pump (not shown), is connected to the ink tank 132. Furthermore, the negative pressure control device controls the negative pressure inside the ink tank 132 in accordance with the head value of the liquid nozzle 1 and the ink tank 132, thereby forming the ink supplied to each nozzle 51 of the liquid nozzle 1 into a curved surface of a predetermined shape.

[0091] The supply pump 134 is a liquid delivery pump, such as a piezoelectric pump. The supply pump 134 is located in the supply flow path. The supply pump 134 is connected to and controlled by the control unit 150 via wiring. The supply pump 134 supplies liquid to the liquid nozzle 1.

[0092] The conveying device 115 conveys paper P along a conveying path A from the media supply unit 112 through the image forming unit 113 to the media discharge unit 114. The conveying device 115 includes a plurality of guide plate pairs 121 and a plurality of conveying rollers 122 arranged along the conveying path A.

[0093] Multiple guide plates 121 each have a pair of plate components that clamp the paper P being conveyed and are arranged opposite each other, and guide the paper P along the conveying path A.

[0094] The conveying roller 122 is driven to rotate under the control of the control unit 150, thereby conveying the paper P downstream along the conveying path A. It should be noted that sensors for detecting the conveying status of the paper are arranged at various points along the conveying path A.

[0095] The control unit 150 is, for example, a control board. The control unit 150 is equipped with a processor 151, a ROM (Read Only Memory) 152, a RAM (Random Access Memory) 153, an I / O port 154 as an input / output port, and an image memory 155.

[0096] The processor 151 is a processing circuit, including a CPU (Central Processing Unit), which acts as a controller. The processor 151 controls the head unit 130, drive motor 161, operating unit 162, and various sensors 163, etc., installed in the liquid ejection device 100, via I / O port 154. The processor 151 sends the print data stored in the image memory 155 to the drive circuit 70 in the order of drawing.

[0097] ROM 152 stores various programs, etc. RAM 153 temporarily stores various variable data, image data, etc. It should be noted that ROM 152 and RAM 153 are just examples of storage media; any other storage medium can be used as long as it can store various programs and data. I / O port 154 is an interface for inputting data from external external connection devices 200 and outputting data to external devices. Print data from external connection devices 200 is sent to the control unit 150 through I / O port 154 and stored in image memory 155.

[0098] The characteristics of the liquid ejection head 1 used in the liquid ejection device 100 according to the embodiment and the driving waveform (driving signal for ejecting liquid droplets) of the liquid ejection head 1 will be described below. The ejection waveform of the driving signal of the liquid ejection head 1 according to the embodiment includes an expansion potential difference that expands the volume of the pressure chamber 46, a contraction potential difference that reduces the volume of the pressure chamber 46, and at least one intermediate potential difference between the expansion potential difference and the contraction potential difference.

[0099] First, use Figures 6 to 24 The driving waveform of the liquid ejection head 1 in this embodiment will be explained. It should be noted that... Figure 6 This is an explanatory diagram showing an example of the ejection waveform of a liquid ejector head 1, which includes the ejection waveform of multiple drops including two droplets ejected in succession and the drive waveform of the cancellation waveform. Figure 7 The accompanying drawing is used as a comparative example to illustrate an existing liquid ejector head. It is an explanatory diagram showing an example of the ejection waveform of the liquid ejector head involved in the comparative example, which includes the ejection waveform of multiple droplets continuously ejected and the drive waveform of the cancellation waveform.

[0100] Figure 8 An example of a drive waveform for a liquid ejection head 1 according to other embodiments is shown, which includes a multi-drop ejection waveform of three droplets being ejected in succession; the cancellation waveform is omitted from the diagram. Figure 9 This is an explanatory diagram illustrating an example of a liquid ejection head, including the ejection waveform of ejecting a single droplet and the drive waveform of canceling the ejection waveform. Figure 10 This is an explanatory diagram illustrating an example of a liquid ejection head 1, which includes a multi-drop ejection waveform comprising two consecutively ejected droplets and a cancellation waveform, and wherein the time width Dp of the ejection waveform is greater than the half-cycle AL of the dominant acoustic vibration frequency of the pressure chamber 46, as an example of another embodiment.

[0101] in addition, Figures 11 to 24 This is an illustrative diagram showing the relationship between the waveform width and the ejection force based on the time width Dp of the initial and subsequent droplets in the ejection waveform of two ejected droplets. Figures 11 to 18 Examples are shown where the time width Dp21 of the initial droplet ejection waveform differs from the time width Dp22 of the subsequent droplet ejection waveform (Dp21 ≠ Dp22). Figures 19 to 24 Examples are shown where the initial droplet's Dp21 is the same as or approximately the same as the subsequent droplet's Dp22 (Dp21≈Dp22).

[0102] First, the liquid ejector head 1 of this embodiment implements grayscale representation, for example, by the number of ink droplets continuously ejected. When there are multiple nozzles 51 ejecting the same number of droplets, the same drive waveform is input to multiple piezoelectric columns 21 whose volumes are variable and connected to multiple pressure chambers 46 of the multiple nozzles 51. On the other hand, the dominant acoustic vibration frequencies of the multiple pressure chambers 46 are not necessarily the same due to manufacturing deviations, etc. For example, the drive waveform for driving the liquid ejector head 1 with a maximum value of 3.5 μs, a minimum value of 2.5 μs, and an average value of 3.0 μs for the half-cycle AL of the dominant acoustic vibration frequencies of the multiple pressure chambers 46 will be described next.

[0103] It should be noted that by individually inputting a rectangular wave into the piezoelectric column 21, which makes the volume of each pressure chamber 46 variable, and measuring the velocity of the droplets ejected from the nozzle at that time, the AL of the plurality of pressure chambers 46 can be determined. For example, by changing the time width of the rectangular wave and measuring the velocity of the ejected droplets, when the ejection velocity of the droplets is maximum at a time width of 3.0 μs, 3.0 μs can be considered as the AL of the corresponding pressure chamber 46.

[0104] Next, the technical problems of the existing drive waveform will be explained. For example, when printing on a medium that is being transported for printing, droplets are ejected from the liquid ejector head 1, and the speed of each droplet volume needs to be adjusted so that the landing position of the droplets on the medium does not change even if the volume of the droplets ejected from the nozzle 51 changes.

[0105] First, such as Figure 9 As shown, the driving waveform for ejecting a single droplet is set to a rectangular wave with a time width of 1AL and a time width of Dp11. Then, regarding the waveform width of the ejection waveform for each droplet in the driving waveform for continuously ejecting multiple droplets, the waveform width of the ejection waveform for the first or last droplet is set to 1AL, and the waveform width of the ejection waveform for other droplets is set to be less than or greater than 1AL. This adjusts the velocity of the droplets during continuous ejection, making it close to the ejection velocity of a single droplet. Thus, in the case of continuous droplet ejection, the residual vibration of the pressure chamber 46 generated by the first ejected droplet causes the next droplet to be ejected in phase with the residual vibration, increasing the ejection velocity of subsequent droplets. In the case of a single droplet, since the velocity increase caused by the residual vibration is not anticipated, the waveform width of the ejection waveform for a single droplet is set to 1AL, and the ejection waveform width during continuous droplet ejection is adjusted.

[0106] For example, in one of the plurality of pressure chambers 46, where the AL is approximately 3.0 μs, the pressure chamber 46 is used for... Figure 7The driving waveform for continuously ejecting two drops is adjusted, and the two drop waveforms are set to Dp21 = 3.0 μs, UL = 3.0 μs, Dp22 = 2.1 μs, and Cp = 1.5 μs. In this case, the velocity of the second drop ejected from the two drop waveforms is considered to be greater than the velocity of the first drop ejected from the two drop waveforms.

[0107] Because the residual vibration generated by the ejection waveform of Dp21 and the phase of the ejection waveform of Dp22 are combined in the two droplet waveforms, the center-to-center distance (time interval) 2UL between the ejection waveforms of Dp21 and Dp22 is twice the AL of the pressure chamber 46. Even if the waveform width of Dp22 is less than the value of AL of the pressure chamber 46, the velocity of the second ejection droplet of the two droplet waveforms is greater than the velocity of the first ejection droplet of the two droplet waveforms.

[0108] Here, the piezoelectric column 21, whose volume is variable, is input to the pressure chamber 46, which has an AL value of 3.5 μs in the plurality of pressure chambers 46, to achieve the maximum value. Figure 7 In the case of two-droplet waveforms, besides the increased difference between the waveform width of Dp22 and the AL of pressure chamber 46, the difference between the center distance 2UL of the ejection waveforms of Dp21 and Dp22 and the 2AL of pressure chamber 46 also increases. This raises concerns that the velocity of the second ejected droplet may be lower than that of the first ejected droplet in the two-droplet waveform. Consequently, if the timing of the second ejected droplet landing on the medium is later than that of the first ejected droplet, print quality will degrade.

[0109] Figures 11 to 24 This is a graph that schematically shows the ejection force characteristics of pressure chamber 46 with the horizontal axis representing the waveform width of the ejection waveform and the vertical axis representing the ejection force relative to the waveform width under conditions of no residual vibration, using dashed lines. Here, avrAL is the average AL of multiple pressure chambers 46 inputting the same drive waveform. minAL is the minimum AL of multiple pressure chambers 46 inputting the same drive waveform. maxAL is the maximum AL of multiple pressure chambers 46 inputting the same drive waveform. Additionally, Figures 11 to 14 as well as Figure 19 and Figure 20 The upward-convex, bow-shaped dashed line shows the ejection force characteristics in pressure chamber 46, which are roughly the same as those in AL and avrAL.

[0110] Showing when in Figure 7 The waveform shows the relationship between waveform width and ejection force when Dp21 is set to the same time width as avrAL and Dp22 is set to a time width less than avrAL. Figure 13 .exist Figure 13 In comparison, the DP22's thrust is slightly less than that of the DP21, but...Figure 7 In the waveform, the residual vibration generated by Dp21 and Dp22 reinforce each other, so that the velocity of the droplets ejected through Dp22 becomes equal to or greater than the velocity of the droplets ejected through Dp21.

[0111] Figure 17 It is shown by having Figure 13 The lower left shows the waveform widths of Dp21 and Dp22. Figure 7 The graph shows the relationship between the waveform width and the ejection force when the pressure chamber is 46 with the driving waveform of that type and the driving AL is maxAL. Figure 17 Since the waveform width of Dp21 is avrAL, it represents the ejection force near the peak of the ejection force characteristic of pressure chamber 46, and the change in ejection force is relatively small. On the other hand, Figure 17 Because the waveform width of Dp22 is much smaller than that of avrAL, the change in ejection force caused by the elongation of AL in pressure chamber 46 is large.

[0112] Furthermore, because the difference between the center distance 2UL between the ejection waveforms of Dp21 and Dp22 and the 2AL (=2*maxAL) of the pressure chamber 46 increases, therefore, with Figure 13 In comparison, Figure 17 In the process, although the ejection force of both Dp21 and Dp22 decreased, the decrease of Dp22 was greater. Even if Dp22 and the residual vibration reinforce each other, there is still a possibility that the droplet velocity ejected through Dp22 is lower than that ejected through Dp21.

[0113] Next, the drive waveform for continuously ejecting two drops in the pressure chamber 46 where AL is approximately 3.0 μs is adjusted, and the two drop waveforms are set to Dp21 = 2.1 μs, UL = 3.0 μs, Dp22 = 3.0 μs, and Cp = 1.5 μs. In this case, the velocity of the second drop ejected from the two drop waveforms is considered to be greater than the velocity of the first drop ejected from the two drop waveforms.

[0114] Since the residual vibration generated by the ejection waveform of Dp21 and the phase of the ejection waveform of Dp22 are also present in the two droplet waveforms, the center distance 2UL between the ejection waveforms of Dp21 and Dp22 is twice that of the pressure chamber 46, and the velocity of the second ejection droplet of the two droplet waveforms is greater than the velocity of the first ejection droplet of the two droplet waveforms.

[0115] Here, we will explain the case where the two droplet waveforms are input into a piezoelectric column 21 with a variable volume, where the AL value of the pressure chamber 46 is 2.5 μs, which minimizes the AL value among the plurality of pressure chambers 46. Since the difference between the waveform width of Dp21 and the AL value of the pressure chamber 46 decreases, the ejection velocity of the first droplet increases. On the other hand, the difference between the center distance 2UL between the ejection waveforms of Dp21 and Dp22 and the 2AL value of the pressure chamber 46 increases. Therefore, there is a concern that the velocity of the second ejected droplet is lower than that of the first ejected droplet in the two-droplet waveform. Consequently, if the timing of the second ejected droplet landing on the medium is later than that of the first ejected droplet, print quality will also degrade.

[0116] Figure 11 This diagram illustrates the relationship between waveform width and ejection force when Dp22 is set to the same time width as avrAL and Dp21 is set to a time width less than avrAL. In this case, Dp22 has a greater ejection force than Dp21. Furthermore, because the residual vibration generated by Dp21 reinforces Dp22, the droplet velocity ejected through Dp22 is greater than the droplet velocity ejected through Dp21.

[0117] On the other hand, the graph showing the relationship between waveform width and ejection force when Dp22 is set to the same time width as avrAL and Dp21 is set to a time width less than avrAL is input to pressure chamber 46 where AL is minAL is shown. Figure 15 In this case, since Dp21 has a waveform width closer to the value of minAL than Dp22, the ejection force of Dp21 becomes higher. Furthermore, since the difference between the center distance 2UL between the ejection waveforms of Dp21 and Dp22 and 2AL (2*minAL) of the pressure chamber 46 becomes larger, even if Dp22 and the residual vibration mutually reinforce each other, there is still a possibility that the droplet velocity ejected through Dp22 will still be lower than the droplet velocity ejected through Dp21.

[0118] Next, an example of the driving waveform in this embodiment will be described. For example, in one of the plurality of pressure chambers 46, where the AL is approximately 3.0 μs, a driving waveform is generated. Figure 6 The driving waveform for the continuous ejection of two drops is adjusted, and the two drop waveforms are set to Dp21 = Dp22 = 2.4 μs, UL = 3.0 μs, and Cp = 1.5 μs. In this case, the velocity of the second drop ejected from the two-drop waveform is greater than the velocity of the first drop ejected from the two-drop waveform, and the velocity of the single-drop waveform ejected from the single-drop waveform becomes close to either ejection velocity of the two-drop waveform ejected from the single-drop waveform. More preferably, Dp21 = Dp22 is adjusted so that the velocities of the combined droplets are approximately the same. It should be noted that in Figure 6In the example of the driving waveform shown, when the two droplet waveforms are set to Dp21 = Dp22, Dp21 and Dp22 are set to waveforms smaller than AL. However, as shown... Figure 10 As shown in the example of the driving waveform, when the two droplet waveforms are set to Dp21 = Dp22, Dp21 and Dp22 can also be set to waveforms greater than AL.

[0119] like Figure 6 As shown, when the waveform widths of Dp21 and Dp22 are approximately the same, the pressure exerted on the liquid in pressure chamber 46 by each ejected waveform is the same. Furthermore, by making the center-to-center spacing between Dp21 and Dp22 the same or approximately the same as 2AL, the residual vibration of pressure chamber 46 generated by Dp21 and the pressure exerted on the liquid in pressure chamber 46 by Dp22 mutually reinforce each other. Therefore, the velocity of the droplets ejected through Dp22 is generally greater than that of the droplets ejected through Dp21.

[0120] Showing when in Figure 6 The waveform shows the relationship between waveform width and ejection force when Dp21 and Dp22 are set to be less than the time width of minAL. Figure 19 In addition, for Figure 21 and Figure 23 .

[0121] exist Figure 19 , Figure 21 and Figure 23 In all diagrams, the ejection forces of Dp22 and Dp21 are equivalent. Figure 6 In the waveform, the residual vibration generated by Dp21 and Dp22 reinforce each other, and the velocity of the droplets ejected through Dp22 becomes equal to or greater than the velocity of the droplets ejected through Dp21.

[0122] Next, the conditions under which the residual vibration of pressure chamber 46 generated by Dp21 and the pressure of the liquid in pressure chamber 46 supplied by Dp22 mutually reinforce each other will be explained in detail using figures. It should be noted that, in this embodiment, the waveform widths of the ejected waveforms of the second drop and the first drop are set to be approximately the same. Furthermore, since the velocity of the ejected droplet of the one-drop waveform and the velocity of the ejected droplets of the two-drop waveform are set to be approximately the same, Dp21 and Dp22 are set to be smaller than the average half-cycle AL of the dominant acoustic vibration frequency of the plurality of pressure chambers 46, which is 3.0 μs.

[0123] However, the waveform of a single droplet ejected is Figure 9In such a waveform, there will be no mutual reinforcement of residual vibrations. Therefore, when the voltage levels of the ejected waveforms are the same in both single-drop and multi-drop ejected waveforms, in order to obtain the same ejection velocity as the multi-drop ejected waveform, it is necessary to set a larger ejection waveform width in the single-drop ejected waveform to maximize the ejection force. For example, the ejection waveform width of a single drop is preferably set between minAL and maxAL to increase the ejection force.

[0124] In this case, consider, for example, the waveform width of each ejected droplet being set to minAL. In pressure chamber 46 where AL is minAL, the ejection force of the multi-droplet waveform with an ejection width of minAL is greater than that of a single droplet when the ejection width is set to the average AL. Furthermore, since the residual vibrations also reinforce each other, there is a situation where the ejection velocity of the multi-droplet becomes extremely high compared to that of a single droplet.

[0125] When the waveform width of each jet of multiple drops is set between minAL and maxAL, for example, the same concern arises in any pressure chamber 46 where AL is between minAL and maxAL. Therefore, it is preferable to set the waveform width of each jet of multiple drops to be less than minAL or greater than maxAL.

[0126] For ease of explanation, here, Figure 6 In this context, the first and second potential difference changes in the ejection waveform of the first drop are set as (1) and (2), and the first and second potential difference changes in the ejection waveform of the second drop are set as (21) and (22), as explained below. Additionally, the reference point for the phase of the ejection waveform of the first drop is set as (0), and the reference point for the phase of the ejection waveform of the second drop is set as (0"), as explained below. It should be noted that here, the reference point (0) for the phase of the ejection waveform of the first drop is set between the potential difference changes (1) and (2), and the reference point (0") for the phase of the ejection waveform of the second drop is set between the potential difference changes (21) and (22). Furthermore, the reference point for the phase of the ejection waveform of the second drop is set between the potential difference changes (21) and (22). Figure 6 In (21), the voltage fall time tf is set to be approximately the same as the voltage rise time tr in (22). Additionally, the amount of potential difference change in (1) and (21) is compared with the amount of potential difference change in (2) and (22). Figure 7 The change in height (in the chamber) is set to be approximately the same. In this embodiment, the pressure chamber 46 is pressurized according to tr and depressurized according to tf.

[0127] For simplicity, vibration attenuation caused by viscous resistance in the flow path is ignored. The time of potential difference change based on tr is set as tin, and the time of the phase reference point (0) is set as t0. If the pressure vibration based on the pressurized pressure chamber 46 is schematically shown, it is cos((t0-tin)*(π / AL)). The velocity of the liquid at the nozzle is -sin((t0-tin)*(π / AL)). It should be noted that in the head flow path diagram, since the nozzle faces downwards and the liquid velocity at the nozzle changes downwards due to pressurization in the pressure chamber 46, it has a negative sign. The time of potential difference change based on tf is set as tin. If the pressure vibration based on the depressurized pressure chamber 46 is schematically shown, it is cos(-π+(t0-tin)*(π / AL)). The velocity of the liquid at the nozzle is -sin(-π+(t0-tin)*(π / AL)). It should be noted that in the head flow diagram, since the nozzle faces downward and the liquid velocity at the nozzle changes upward due to the pressure reduction in the pressure chamber 46, it has a negative sign.

[0128] Then, basically using the reference point (0) or (0") of the phase as the reference, the time elapsed from the occurrence time of each voltage step input to the reference point (the phase advance case) is substituted into (t0-tin). Thus, the phase is described with reference point (0) or (0") as the reference for each potential difference change and its composite wave.

[0129] Show Figure 6 The dominant acoustic vibration of the ejection waveform. During the ejection... Figure 6 In the first drop ejection waveform, a potential difference change is performed, as shown in (1). If a voltage for the expansion of pressure chamber 46 is input, pressure chamber 46 expands with the potential difference in (1), and pressure is reduced inside pressure chamber 46. The resulting vibration is a phase advance of -π + Dp21 / 2 * (π / AL).

[0130] In (2), which is a change in potential difference for the reduction of pressure chamber 46, the potential difference changes in the opposite way to (1), which is a change in potential difference for the expansion. Pressure chamber 46 is reduced, and pressure is applied to the inside of pressure chamber 46. Therefore, (2) is a vibration with a phase advance of -Dp21 / 2*(π / AL).

[0131] Here, assuming the composite wave of (1) and (2) at time (0), then the composite wave of (1) and (2) is a vibration with a phase advance of -π / 2.

[0132] Next, show Figure 6The dominant vibration of the second drop ejection waveform. When the voltage for the expansion of pressure chamber 46 is input as shown in (21), pressure chamber 46 expands with the potential difference of (21), and pressure is reduced in pressure chamber 46. Therefore, if the width of the second drop ejection waveform is set to Dp22, it is a phase advance of -π + Dp22*(π / AL) vibration.

[0133] In (22), which is a change in potential difference for the reduction of pressure chamber 46, the potential difference undergoes a change opposite to (21), which is a change in potential difference for expansion, and pressure chamber 46 is reduced, thus pressurizing the pressure chamber 46. Therefore, (22) becomes a oscillation with a phase advance of -Dp22 / 2*(π / AL).

[0134] Here, assuming the composite wave of (21) and (22) at time (0), the composite wave of (21) and (22) becomes a vibration with a phase advance of -π / 2.

[0135] Therefore, when the phase difference between (0) and (0") is an even multiple of π (or AL if it is a time interval), the composite wave of (1) and (2) is in phase with the composite wave of (21) and (22) and they reinforce each other. Figure 6 In the example, the time difference (time interval) 2UL between (0) and (0") is 2AL.

[0136] Here, the condition of the time difference (time interval) between (0) and (0") for the amplitude of the composite waves of (1) and (2) and the composite waves of (21) and (22) mutually reinforcing each other is considered. If the time difference 2UL between (0) and (0") is greater than 1.5AL and less than 2.5AL, then the composite waves of (1) and (2) and the composite waves of (21) and (22) mutually reinforce each other.

[0137] As mentioned earlier, due to manufacturing deviations, the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 is not the same. Here, the maximum value of the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 is set as maxAL, and the minimum value is set as minAL. In this case, the value is 1.5maxAL when 1.5AL is the maximum value among the multiple pressure chambers 46, and the value is 2.5minAL when 2.5AL is the minimum value. Therefore, the 2UL that holds true for 1.5AL≤1.5maxAL<2UL<2.5minAL≤2.5AL can be set as the time difference between (0) and (0”). Thus, if the time difference 2UL between (0) and (0”) of the two drop waveforms is set to be greater than 1.5maxAL and less than 2.5minAL, then in all the pressure chambers 46, the phase difference between the composite wave of (1) and (2) and the composite wave of (21) and (22) is less than ±90 degrees, and the composite wave of (1) and (2) and the composite wave of (21) and (22) mutually reinforce each other.

[0138] Furthermore, since the time widths Dp21 of (1) and (2) are approximately the same as those of (21) and (22), even if the half-cycle AL of the dominant acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the ejection waveforms with time widths of Dp21 and Dp22 exert the same pressure on the liquid in the corresponding pressure chamber 46. In addition, due to the mutual reinforcement of the residual vibration caused by the composite wave of (1) and (2) and the composite wave of (21) and (22), the ejection velocity of the second drop is greater than that of the first drop. In this way, by continuously ejecting the driving waveforms of the aforementioned multiple drops of ink, it is possible to adjust the ejection velocity of the ink ejected afterward due to the residual vibration caused by the previous ejection waveform to be greater than that of the droplets ejected before in all of the multiple pressure chambers 46.

[0139] It should be noted that, Figure 9 The waveform shown has the same tf, tr time, voltage height as the two-drop waveform, but the waveform can also be completely different. Even in this case, to maintain print quality, it is necessary to reduce the difference in droplet velocity between the one-drop waveform and the two-drop waveform from the same nozzle. In this case, the time width Dp21 (=Dp22) of the two-drop waveform in this embodiment is adjusted and set so that the velocity of each droplet in the two-drop waveform (or the velocity of the droplet obtained after the droplets ejected through Dp21 and Dp22 combine) is close to that of the two-drop waveform. Figure 9 The velocity of a droplet with different waveforms can be determined.

[0140] It should be noted that even if it is desirable to have different values ​​for Dp21 and Dp22 in order to fine-tune the droplet velocities of the two droplets, it is preferable to have Dp21 and Dp22 as close as possible to ensure that the pressure of Dp21 and Dp22 on the liquid in the pressure chamber 46 is similar. For example, it is preferable that the time difference between Dp21 and Dp22 is the smallest time difference (other than zero) that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0141] For example, let's assume that when the waveforms of the two drops are set to Dp21 = Dp22 = 2.4 μs, UL = 3.0 μs, and Cp = 1.5 μs, the velocity of the combined droplet based on the two drop waveforms is greater than the velocity of the ejected droplet based on the single drop waveform; and when the waveforms of the two drops are set to Dp21 = Dp22 = 2.3 μs, UL = 3.0 μs, and Cp = 1.5 μs, the velocity of the combined droplet based on the two drop waveforms is less than the velocity of the ejected droplet based on the single drop waveform.

[0142] In the drive circuit 70 of the corresponding liquid nozzle 1, if the values ​​of Dp21 and Dp22 cannot be set to values ​​between 2.3μs and 2.4μs, for example, Dp21 = 2.3μs, Dp22 = 2.4μs, UL = 3.0μs, and Cp = 1.5μs.

[0143] Next, as an example of a multi-drop waveform, the time interval 2UL between the ejection waveforms of two adjacent drops in a three-drop waveform will be explained.

[0144] like Figure 8 As shown, even for the driving waveform that ejects three droplets, as long as the time difference between (0) and (0”) is set to be greater than 1.5maxAL and less than 2.5minAL, then in all the pressure chambers 46, the phase difference between the composite wave of (1) and (2) and the composite wave of (21) and (22) is less than ±90 degrees, and the composite wave of (1) and (2) and the composite wave of (21) and (22) (vibration of the liquid in the pressure chamber 46) mutually reinforce each other. In addition, if the time difference between (0”) and (0”’) is set to be greater than 1.5maxAL and less than 2.5minAL, then in all the pressure chambers 46, the phase difference between the composite wave of (21) and (22) and the composite wave of (31) and (32) is less than ±90 degrees, and the composite wave of (21) and (22) and the composite wave of (31) and (32) mutually reinforce each other.

[0145] Furthermore, even if Dp31 (=Dp32=Dp33) is set and the time width of Dp31 (=Dp32=Dp33) is adjusted, the half-cycle AL of the dominant acoustic vibration frequency of pressure chamber 46 is different from the waveform UL, and the ejection waveforms with time widths of Dp31, Dp32, and Dp33 give the same pressure to the liquid in the corresponding pressure chamber 46. In addition, due to the mutual reinforcement of the residual vibration caused by the composite waves of (1) and (2) and the composite waves of (21) and (22), the ejection velocity of the second drop is greater than that of the first drop. In addition, due to the mutual reinforcement of the residual vibration caused by the composite waves of (21) and (22) and the composite waves of (31) and (32), the ejection velocity of the third drop is greater than that of the second drop. In this way, by continuously ejecting the aforementioned multiple droplets in a driving waveform, the ejection speed of the ink ejected afterward due to the residual vibration caused by the previous ejection waveform can be adjusted to be higher than the ejection speed of the droplets ejected before in all of the multiple pressure chambers 46.

[0146] It should be noted that, in this embodiment, the waveforms of one drop and two drops are as follows: Figure 9 and Figure 6 As shown, the time, voltage height, and tf and tr of the ejection waveform are related to... Figure 8 The three droplet waveforms are identical, but the one-drop and two-drop waveforms can be completely different. Even in this case, to maintain print quality, it is necessary to reduce the difference in droplet velocities from the same nozzle for the one-drop, two-drop, and three-drop waveforms. Here, it is assumed that an adjustment has been made to reduce the difference in droplet velocities between the one-drop and two-drop waveforms from the same nozzle. This is achieved by adjusting the time width Dp31 (=Dp32=Dp33) of the three-drop waveform in this embodiment, and setting the velocity of each droplet of the three-drop waveform, or the velocity of the droplet obtained by combining the droplets ejected through Dp31, Dp32, and Dp33, to be close to... Figure 9 A drop of waveform Figure 6 The velocity of the two droplets with different waveforms can be determined.

[0147] It should be noted that even when it is desirable to have different values ​​for Dp31, Dp32, and Dp33 in order to fine-tune the droplet velocities of the three droplets, it is preferable to have Dp31, Dp32, and Dp33 as close as possible to ensure that the pressure of Dp31, Dp32, and Dp33 on the liquid in the pressure chamber 46 is similar. For example, it is preferable that the time difference between Dp31, Dp32, and Dp33 is the smallest time difference other than zero that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0148] For example, let's assume that when the three-drop waveform is set to Dp31 = Dp32 = Dp33 = 2.4 μs, UL = 3.0 μs, and Cp = 1.5 μs, the velocity of the combined droplet generated by the three-drop waveform is greater than the velocity of the ejected droplet of the single-drop waveform; and when the three-drop waveform is set to Dp31 = Dp32 = Dp33 = 2.3 μs, UL = 3.0 μs, and Cp = 1.5 μs, the velocity of the combined droplet generated by the three-drop waveform is less than the velocity of the ejected droplet of the single-drop waveform.

[0149] In the drive circuit 70 of the corresponding liquid nozzle 1, if it is not possible to set the values ​​of Dp31, Dp32, and Dp33 to values ​​between 2.4μs and 2.3μs, for example, Dp31 = Dp32 = 2.3μs, Dp33 = 2.4μs, UL = 3.0μs, and Cp = 1.5μs. Alternatively, Dp31 = 2.3μs, Dp32 = Dp33 = 2.4μs, UL = 3.0μs, and Cp = 1.5μs.

[0150] Furthermore, even for a drive waveform that ejects n drops, if the reference point of the phase of the ejection waveform of any one of the first to the (n-1)th drops is set to (0), and the reference point of the phase of the ejection waveform of the next drop is set to (0"), and if the time difference between (0) and (0") is set to be greater than 1.5maxAL and less than 2.5minAL, then in all the pressure chambers 46, the residual vibrations of all ejection waveforms after the second drop are ejected will mutually reinforce each other. Furthermore, even if the width of all ejection waveforms is set to Dpn1 (=Dpn2=~=Dpnn), and the time width of Dpn1 (=Dpn2=~=Dpnn) is adjusted, the half-cycle AL of the dominant acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, and the pressure exerted on the liquid in the corresponding pressure chamber 46 by the ejection waveforms with time widths of Dpn1, Dpn2~Dpnn is the same. In this way, by continuously ejecting multiple drops of the multiple inks in a driving waveform, the ejection speed of the ink ejected afterward due to residual vibration caused by the previous ejection waveform can be adjusted to be higher than the ejection speed of the droplets ejected before in all of the multiple pressure chambers 46.

[0151] It should be noted that the ejection waveforms of the n-drop waveform and the drive waveform for ejecting more than n drops can be completely different waveforms. Even in this case, to maintain print quality, it is necessary to reduce the difference in droplet velocity between the n-drop waveform and the drive waveform for ejecting more than n drops ejected from the same nozzle. Here, it is assumed that the drive waveform for ejecting more than n drops has been adjusted to reduce the difference in droplet velocity from the same nozzle. This can be achieved by adjusting the time width Dpn1 (=Dpn2=~=Dpnn) of the n-drop waveform in this embodiment, and setting the velocity of each droplet of the n-drop waveform or the velocity of the droplet obtained after the droplets ejected by Dpn1~Dpnn combine to be close to the droplet velocity of the drive waveform for ejecting more than n drops. It should be noted that in the drive waveform for ejecting multiple drops, if the time elapsed after ejection is short, there may be multiple droplets before they combine. In addition, there may be cases where satellite droplets are generated after multiple droplets. When comparing the droplet velocities in drive waveforms with different droplet numbers before multiple droplets merge, it is sufficient to adjust the time width Dpn1 (=Dpn2=~=Dpnn) of the n-droplet waveform so that the velocity of the droplet with the largest volume (largest droplet diameter) ejected by the n-droplet waveform is close to (more preferably approximately the same as) the velocity of the droplet with the largest volume (largest droplet diameter) ejected by the drive waveform ejecting a number of droplets other than n.

[0152] It should be noted that even when it is desirable to have different values ​​for Dpn1, Dpn2, ..., Dpnn in order to fine-tune the droplet velocity of the n-droplet waveform, it is preferable to set Dpn1 to Dpnn to be as close as possible so that the pressure of the liquid in the pressure chamber 46 through Dpn1 to Dpnn is similar. For example, it is preferable that the time difference between Dpn1, Dpn2, ..., Dpnn is the smallest time difference (other than zero) that can be set in the drive circuit that generates the corresponding drive waveform.

[0153] Furthermore, in the above example, a liquid ejector head 1 that outputs a drive waveform that makes the ejection waveform a rectangular wave was described, but it is not limited to this. For example, the ejection waveform may also be a waveform with an intermediate voltage. The following description will illustrate another embodiment of a liquid ejector head 1 that outputs a drive waveform with an intermediate voltage. It should be noted that in this embodiment, the same reference numerals are used for components that are the same as in the above embodiment, and detailed descriptions thereof are omitted.

[0154] First, use Figure 25 The drive circuit 70 for the liquid ejector head 1 will be described. For example... Figure 25As shown, in other embodiments, the driving circuit of the liquid ejector head 1, i.e., the driving circuit 70, includes, for example, a voltage control unit 724 and a voltage switching unit 725, the same number as the pressure chamber 46, within the driver IC 72. However, in Figure 25 The diagram shows two voltage switching units 725, but the diagrams of other voltage switching units 725 are omitted.

[0155] 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 supplies the voltage from the first voltage source 81 to each wiring electrode 726. Furthermore, the drive circuit 70 selectively supplies the voltages 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, in the case where the actuator 20 is a stacked PZT, because there is a tendency for degradation if a binary voltage is applied, 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 ground voltage and polarity that is either positive or negative relative to ground voltage.

[0156] The output voltage of the first voltage source 81 is, for example, ground voltage, with a value of V0 (V0 = 0 [V]). The output voltage of the second voltage source 82 is shown as V1. It should be noted that voltage V1 is set to a voltage higher than V0. The output voltage of the third voltage source 83 is shown as V2, for example. For example, voltage V2 is set to a voltage higher than V0 and lower than V1. The output voltage of the fourth voltage source 84 is shown as V3. It should be noted that voltage V3 is set to a voltage lower than V0. The output voltage of the fifth voltage source 85 is shown as V4, for example. For example, voltage V4 is set to a voltage lower than V0 and higher than V3.

[0157] Wiring electrode 726 is connected to a common electrode of actuator 20 that serves as a ground electrode. Multiple wiring electrodes 727 are respectively connected to individual electrodes of actuator 20 that serve as non-ground electrodes.

[0158] The voltage control unit 724 is connected to multiple voltage switching units 725. The voltage control unit 724 outputs a command indicating the selection of one of the following voltage sources: a first voltage source 81, a second voltage source 82, a third voltage source 83, a fourth voltage source 84, and a fifth voltage source 85, to each voltage switching unit 725. 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 following voltage sources: 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 voltage switching unit 725 switches the voltage source connected to the wiring electrode 727 according to the command from the voltage control unit 724.

[0159] The voltage switching unit 725 is, for example, composed of a semiconductor switch. Under the control of the voltage control unit 724, the voltage switching unit 725 connects to one of 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, and to the wiring electrode 727. Therefore, the internal electrodes of different poles of the piezoelectric post 21 are connected to the wiring electrode 726 and the wiring electrode 727 via external electrodes (a common electrode and individual electrodes).

[0160] Such a drive circuit 70 switches the connection wiring between voltage sources 81, 82, 83, 84, and 85 and actuator 20 via a switching circuit composed of a voltage control unit 724 and multiple voltage switching units 725, thereby inputting drive waveforms with at least three potential differences as drive signals to the electrode space of actuator 20. Here, the drive waveform is the ejection waveform that is driven by actuator 20 to eject droplets. It should be noted that, in this embodiment, potential differences other than the maximum and minimum potential differences are referred to as intermediate potential differences.

[0161] exist Figure 26 The image shows an example of a drive waveform for a liquid ejector head 1, in which two ejection waveforms are input consecutively at predetermined intervals during ink ejection. Additionally, in... Figure 27 An example of the ejection waveform is shown below. Figure 26 and Figure 27 In the diagram, the vertical axis represents voltage (potential difference), and the horizontal axis represents time. It should be noted that the driving waveform is generated by the driver IC 72 of the driving circuit 70. For example... Figure 26As shown, in both the ejection and cancellation waveforms, the driving waveform divides the expansion potential difference into two decreases during the expansion of the pressure chamber 46, and then divides the contraction potential difference into two increases during the contraction of the pressure chamber 46 during ejection. Furthermore, during both the expansion and contraction of the pressure chamber 46, when changing the potential difference, after applying the first potential difference, the first potential difference is maintained for a predetermined time before the second potential difference is applied. It should be noted that when the pressure chamber 46 expands with a reduced voltage (potential difference), the voltage (potential difference) is increased beforehand to allow the pressure chamber 46 to contract before the ejection waveform input.

[0162] First, use Figure 26 and Figure 27 A specific example of the ejection waveform of the first droplet in the driving waveform is provided. For example... Figure 27 As shown, when the pressure chamber 46 is expanded before ink ejection, the time interval from the start point of the first amplification caused by the expansion potential difference decreasing twice consecutively to the start point of the first contraction caused by the contraction potential difference after the expansion potential difference decreases twice consecutively is set as Dp. Additionally, as... Figure 27 As shown, the time interval from the start of the second amplification caused by the expansion potential difference after two consecutive decreases in the expansion potential difference before the increase in the potential difference, to the start of the second shrinkage caused by the shrinkage potential difference after two consecutive decreases in the expansion potential difference and two consecutive increases in the shrinkage potential difference, when the pressure chamber 46 shrinks during the ejection, is set as Dp.

[0163] Then, the time width Dp is greater than 0.5AL and less than 1.5AL. More preferably, Dp = AL. This is because if Dp is set to be greater than 0.5AL and less than 1.5AL, there will be mutual reinforcement of the main acoustic vibration generated by pre-expanding the pressure chamber 46 before ejection and the main acoustic vibration generated by shrinking the pressure chamber 46 during ejection.

[0164] Additionally, when the time width Tm is less than 0.5AL, by Figure 27 The two rising waveforms cause the primary acoustic vibrations to reinforce each other. By adjusting the time width Tm, the mutual reinforcement of the primary acoustic vibrations caused by the two rising waveforms can be adjusted, and the... Figure 27 The ejection force of the droplets is caused by the ejection waveform. Furthermore, by making Tm less than 0.5minAL, in all pressure chambers 46 of the multiple pressure chambers 46 with the same input drive waveform, the ejection force of the droplets is generated by... Figure 27 The two rising waveforms cause the main acoustic vibrations to reinforce each other.

[0165] Moreover, in Figure 26In the driving waveform, the Tm22 of the ejection waveform of the second drop is smaller than the Tm21 of the ejection waveform of the first drop. Therefore, the mutual reinforcement of the main acoustic vibrations caused by the rising waveforms of (23) and (24) is greater than that caused by (3) and (4). The mutual reinforcement of the main acoustic vibrations caused by the falling waveforms of (21) and (22) is also greater than that caused by (1) and (2). In addition, since Dp21 is the same as Dp22, the mutual reinforcement of the main acoustic vibrations of (1) and (3) is the same as that of (21) and (23). The mutual reinforcement of the main acoustic vibrations of (2) and (4) is also the same as that of (22) and (24). Therefore, even through Figure 26 The waveform drives AL to different pressure chambers 46. The ejection force of the second drop's ejection waveform is greater than that of the first drop's ejection waveform, and the relationship between the magnitudes of their ejection forces remains unchanged. Therefore, the ejection velocity of the second drop is greater than that of the first drop.

[0166] exist Figure 26 In the driving waveform, by adjusting Tm21 and Tm22 within a range less than 0.5 minAL, the adjustment is achieved by... Figure 26 The waveform generates the velocity difference between the first and second drops. Furthermore, by adjusting the values ​​of Dp21 = Dp22, it is possible to make the velocities of droplets ejected by other drive waveforms with different ejection volumes approximately the same.

[0167] For ease of explanation, here, Figure 26 In this context, the first to fourth potential difference changes in the ejection waveform of the first drop are set as (1) to (4), and the first to fourth potential difference changes in the ejection waveform of the second drop are set as (21) to (24), as explained below. Additionally, the reference point for the phase of the ejection waveform of the first drop is set as (0), and the reference point for the phase of the ejection waveform of the second drop is set as (0"), as explained below. It should be noted that here, the reference point (0) for the phase of the ejection waveform of the first drop is set between the potential difference changes (2) and (3), and the reference point (0") for the phase of the ejection waveform of the second drop is set between the potential difference changes (22) and (23). Furthermore, the reference point for the phase of the ejection waveform of the second drop is set between the potential difference changes (22) and (23). Figure 26 The voltage drop time tf in the middle is set to the same as the voltage drop time tf in the middle. Figure 26 The voltage rise time tr in each case is approximately the same. Furthermore, the amount of change in potential difference for (1), (2), (21), and (22) is similar to the amount of change in potential difference for (3), (4), (23), and (24). Figure 26 The change in height (within) is roughly the same.

[0168] right Figure 26 The dominant acoustic vibration of the ejected waveform of the first droplet is illustrated. Figure 26As shown, a potential difference change is performed in the ejection waveform of the first drop. When the voltage for the expansion of pressure chamber 46 is input as shown in (1), pressure chamber 46 expands with the potential difference in (1), and the pressure inside pressure chamber 46 is reduced. The resulting vibration is a phase advance of -π + (Dp21 + Tm21) / 2 * (π / AL). Moreover, when the potential difference change shown in (2) is performed, the vibration in (2) is a phase advance of -π + (Dp21 - Tm21) / 2 * (π / AL). The composite wave of (1) and (2) is a phase advance of -π + Dp21 / 2 * (π / AL).

[0169] In (3) and (4), which are changes in potential difference for the reduction of pressure chamber 46, the potential difference changes in the opposite direction to those in (1) and (2), which are changes in potential difference for expansion. Pressure chamber 46 is reduced, and pressure is applied to the inside of pressure chamber 46. Therefore, (3) is a vibration with a phase advance of -(Dp21-Tm21) / 2*(π / AL). In addition, (4) can be considered as a vibration with a phase advance of -(Dp21+Tm21) / 2*(π / AL). Therefore, the composite wave of (3) and (4) is a vibration with a phase advance of -Dp21 / 2*(π / AL).

[0170] Here, assuming the composite wave of (1), (2), (3) and (4) at time (0), the composite wave of (1), (2), (3) and (4) is a vibration with a phase advance of -π / 2.

[0171] Next, show Figure 26 The dominant vibration of the second droplet ejection waveform. When a potential difference change is performed and a voltage for the expansion of pressure chamber 46 is input as shown in (21), the pressure chamber 46 expands with the potential difference in (21), and the pressure chamber 46 is depressurized. Therefore, if the width of the second droplet ejection waveform is set to Dp22, it is a vibration with a phase advance of -π + (Dp22 + Tm22) / 2*(π / AL). Furthermore, when the potential difference change shown in (22) is performed, in (22), it can be considered that the phase advance is -π + (Dp22 - Tm22) / 2*(π / AL). Therefore, the composite wave of (21) and (22) is a vibration with a phase advance of -π + Dp22 / 2*(π / AL).

[0172] In (23) and (24), which are changes in potential difference for the reduction of pressure chamber 46, the potential difference changes in the opposite direction to those in (21) and (22), which are changes in potential difference for expansion. Pressure chamber 46 is reduced, and pressure is increased within pressure chamber 46. Therefore, (23) is a vibration with a phase advance of -(Dp22-Tm22) / 2*(π / AL). In addition, (24) is a vibration with a phase advance of -(Dp22+Tm22) / 2*(π / AL). Therefore, the composite wave of (23) and (24) is a vibration with a phase advance of -Dp22 / 2*(π / AL).

[0173] Here, assuming the composite wave of (21), (22), (23) and (24) at time (0), the composite wave of (21), (22), (23) and (24) is a vibration with a phase advance of -π / 2.

[0174] Therefore, when the phase difference between (0) and (0") is an even multiple of π (or AL if it is a time interval), the composite waves of (1), (2), (3), and (4) are in phase with the composite waves of (21), (22), (23), and (24) and reinforce each other. In the example in the figure, the time difference (time interval) between (0) and (0") is 2AL.

[0175] Here, the condition of the time difference (time interval) between (0) and (0") for the amplitudes of the composite waves of (1), (2), (3) and (4) and the composite waves of (21), (22), (23) and (24) mutually reinforcing each other is considered. If the time difference 2UL between (0) and (0") is greater than 1.5AL and less than 2.5AL, then the composite waves of (1), (2), (3) and (4) mutually reinforce each other with the composite waves of (21), (22), (23) and (24).

[0176] Furthermore, due to manufacturing deviations, the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 in the liquid ejector head 1 is not the same. Here, the maximum value of the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 is set as maxAL, and the minimum value is set as minAL. In this case, the value is 1.5maxAL when 1.5AL is the maximum among the multiple pressure chambers 46, and the value is 2.5minAL when 2.5AL is the minimum. Therefore, 2UL, which holds for 1.5AL≤1.5maxAL<2UL<2.5minAL≤2.5AL, can be set as the time difference between (0) and (0)". If based on this... Figure 26If the time difference 2UL between (0) and (0") of the two drop waveforms shown is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the plurality of pressure chambers 46, the phase difference between the composite waves of (1), (2), (3) and (4) and the composite waves of (21), (22), (23) and (24) is less than ±90 degrees, and the composite waves of (1), (2), (3) and (4) and the composite waves of (21), (22), (23) and (24) mutually reinforce each other.

[0177] Even as described, the half-cycle AL of the dominant acoustic vibration frequency of pressure chamber 46 differs from the waveform UL. Figure 26 The ejection force of the second droplet's ejection waveform is also greater than that of the first droplet's ejection waveform. Furthermore, through the mutual reinforcement of the residual vibrations caused by the composite waves of (1), (2), (3), and (4) and the composite waves of (21), (22), (23), and (24), the ejection velocity of the second droplet is greater than that of the first droplet. Thus, through... Figure 26 The driving waveform shown, which continuously ejects multiple drops of ink, can adjust the ejection speed of the ink ejected later due to residual vibration caused by the previous ejection waveform to be higher than the ejection speed of the droplets ejected earlier in all of the multiple pressure chambers 46.

[0178] exist Figure 27 The example shows a two-droplet scenario. However, even in drive waveforms that eject three or more droplets, by making the Dp width of all ejected waveforms the same and ensuring that the intermediate voltage time of the ejected waveform of subsequent droplets is less than 0.5 minAL compared to the previous ejected waveform, it is possible to adjust the ejection speed of the ink ejected later due to residual vibrations from the previous ejected waveform to be higher than the ejection speed of the previously ejected droplets in all pressure chambers 46. This is because the shorter the intermediate voltage time Tm, for example... Figure 28The mutual reinforcement of the dominant acoustic vibrations caused by the rising and falling waveforms becomes greater. Here, consider the case where the intermediate voltage time of the initial ejection waveform of the n-droplet waveform is set to Tmn1, and the intermediate voltage time of the final ejection waveform is set to Tmnn, with positions numbered sequentially from Tmn1 to Tmnn. If, for the purpose of adjusting the droplet ejection velocity, the time of any Tm among Tmn1 to Tmnn is set shorter than the previous Tm, then to maintain and increase the droplet velocity based on subsequent ejection waveforms, it is desirable to set the subsequent Tm to a time shorter than the aforementioned arbitrary Tm. In this case, the final Tm (=Tmnn) becomes shorter than the initial Tm (=Tmn1). Furthermore, for the Dp width of all ejection waveforms, by adjusting the Dp width while making them the same, it is possible to make the droplets ejected by drive waveforms with different ejection volumes and velocities approximately the same.

[0179] Next, use Figure 28 Examples of driving waveforms for other implementation methods are provided. Figure 26 The driving waveform is Figure 28 The driving waveform Tm22 is set to zero. Figure 28 In the waveform, it can be considered that the Tm22 of the ejection waveform of the second drop is zero and less than the Tm21 of the ejection waveform of the first drop. Compared with the synthesized wave of the main acoustic vibration caused by the rising waveforms of (3) and (4), the amplitude of the main acoustic vibration generated by the rising waveform of (22) is larger. Compared with the synthesized wave of the main acoustic vibration caused by the falling waveforms of (1) and (2), the amplitude of the main acoustic vibration caused by the falling waveform of (21) is larger. In addition, since Dp21 and Dp22 are the same, the amplitude of the main acoustic vibration of the synthesized wave of (21) and (22) is larger than that of the synthesized waves of (1), (2), (3) and (4). Therefore, even using Figure 28 The waveform drives different pressure chambers 46 of AL. The ejection force of the second drop's ejection waveform is greater than that of the first drop's ejection waveform, and the relationship between the magnitudes of their ejection forces remains unchanged. Therefore, the ejection velocity of the second drop is greater than that of the first drop.

[0180] exist Figure 26 In the waveform, Tm21 is adjusted within a range less than 0.5 minAL to adjust the waveform. Figure 26 The waveform causes the velocity difference between the first and second drops. Furthermore, by adjusting the values ​​of Dp21 = Dp22, it is possible to make the droplets ejected by other drive waveforms with different ejection volumes have approximately the same velocity.

[0181] exist Figure 26As described in the waveform description, when assuming the composite wave of (1), (2), (3) and (4) at time (0), the composite wave of (1), (2), (3) and (4) is a vibration with a phase advance of -π / 2.

[0182] exist Figure 28 As described in the waveform description, when assuming the composite wave of (21) and (22) at time (0), the composite wave of (21) and (22) is a vibration with a phase advance of -π / 2.

[0183] Therefore, when the phase difference between (0) and (0") is an even multiple of π (or AL if it is a time interval), the composite waves of (1), (2), (3), and (4) have the same phase as the composite waves of (21) and (22) and reinforce each other. Figure 28 In the example, the time difference (time interval) 2UL between (0) and (0") is 2AL.

[0184] Here, the condition of the time difference (time interval) between (0) and (0") for the amplitude of the composite waves of (1), (2), (3) and (4) and the composite waves of (21) and (22) mutually reinforcing each other is considered. If the time difference 2UL between (0) and (0") is greater than 1.5AL and less than 2.5AL, then the composite waves of (1), (2), (3) and (4) mutually reinforce the composite waves of (21), (22), (23) and (24).

[0185] Furthermore, due to manufacturing deviations, the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 in the liquid ejector head 1 is not the same. Here, the maximum value of the half-cycle AL of the dominant acoustic vibration frequency of the multiple pressure chambers 46 is set as maxAL, and the minimum value is set as minAL. In this case, the value is 1.5maxAL when 1.5AL is the maximum among the multiple pressure chambers 46, and the value is 2.5minAL when 2.5AL is the minimum. Therefore, 2UL, which holds for 1.5AL≤1.5maxAL<2UL<2.5minAL≤2.5AL, can be set as the time difference between (0) and (0)". If based on this... Figure 28 If the time difference 2UL between (0) and (0") of the two drop waveforms shown is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the plurality of pressure chambers 46, the phase difference between the composite waves of (1), (2), (3) and (4) and the composite waves of (21) and (22) is less than ±90 degrees, and the composite waves of (1), (2), (3) and (4) and the composite waves of (21) and (22) reinforce each other.

[0186] Furthermore, even if through Figure 28The waveform drives different pressure chambers 46 of AL, and the ejection force of the second drop's ejection waveform is also greater than that of the first drop's ejection waveform. In addition, through the mutual reinforcement of the residual vibration caused by the composite waves of (1), (2), (3) and (4) and the composite wave of (22) of (21), the ejection velocity of the second drop is greater than that of the first drop. Thus, through Figure 28 The driving waveform shown, which continuously ejects multiple drops of ink, can adjust the ejection speed of the ink ejected later due to residual vibration caused by the previous ejection waveform to be higher than the ejection speed of the droplets ejected earlier in all of the multiple pressure chambers 46.

[0187] exist Figure 28 The example shows two drops, but even in the drive waveform that ejects more than three drops, the initial few ejection waveforms are set as... Figure 28 The ejection waveform with an intermediate voltage, like the first drop, will be set as the ejection waveform from the middle to the last. Figure 28 The second droplet, without an intermediate voltage ejection waveform, has its Dp width set to be the same for all ejection waveforms. In the ejection waveform with the intermediate voltage, the intermediate voltage time of the subsequent ejection waveform is made shorter than that of the previous ejection waveform within a range of less than 0.5 minAL. Therefore, in all pressure chambers 46, the ejection speed of the ink ejected later due to residual vibrations from the previous ejection waveform can be adjusted to be higher than the ejection speed of the previously ejected droplets. More preferably, only the final ejection waveform is set to... Figure 8 The second droplet, without an intermediate voltage, is used as the ejection waveform. All other ejection waveforms are set to... Figure 29 The ejection waveform should have an intermediate voltage, similar to the first droplet. Specifically, it is preferable to set the drive waveform such that the number of potential difference changes for all ejection waveforms except the first and last one is greater than the number of potential difference changes for the last ejection waveform. Furthermore, by adjusting the Dp width while setting all ejection waveforms to the same value, it is possible to make the droplets ejected through drive waveforms with different ejection volumes have approximately the same velocity.

[0188] Furthermore, in the above example, an example was described in which the time difference (center-to-center distance) 2UL between adjacent ejection waveforms was set to be greater than 1.5maxAL and less than 2.5minAL in order to enhance the period of residual vibration of the liquid in the pressure chamber 46 caused by the previously generated ejection waveform and the vibration of the liquid in the pressure chamber 46 caused by the subsequently generated ejection waveform. However, the liquid ejection head 1 according to the embodiment is not limited to this structure.

[0189] That is, as a driving waveform comprising multiple ejection waveforms, any one of the ejection waveforms after the first drop is designated as droplet a, and any one of the ejection waveforms after droplet a is designated as droplet b. In this case, the time difference 2*(ba)*UL between the centers of the ejection waveforms of droplet a and droplet b is set to be greater than (2*(ba)-0.5) times the maximum value (maxAL) of the half-cycle AL of the main acoustic vibration frequency of the multiple pressure chambers 46 whose volume is variable due to the actuator 20 of the input driving signal, and less than (2*(ba)+0.5) times the minimum value (minAL) of the half-cycle AL. Thus, in the case of two ejection waveforms or three or more ejection waveforms, the time difference 2UL between adjacent ejection waveforms becomes 1.5maxAL < 2UL < 2.5minAL as described above. Furthermore, in the case of a drive waveform comprising three or more ejection waveforms, the time difference 2*(ba)*UL between two ejection waveforms that are not adjacent but have one or more ejection waveforms positioned between them becomes (2*(ba)-0.5)*maxAL<2*(ba)*UL<(2*(ba)+0.5)*minAL. In this way, by setting the time difference between at least any two ejection waveforms among the multiple ejection waveforms included in the drive waveform to (2*(ba)-0.5)*maxAL<2*(ba)*UL<(2*(ba)+0.5)*minAL, the residual vibration of the subsequent droplets and the ejection waveform mutually reinforce each other, thereby increasing the ejection velocity.

[0190] For liquid ejector head 1 involved in such other embodiments, using Figure 29 as well as Figure 8 An explanation is needed. It should be noted that... Figure 29 This is an explanatory diagram showing an example of the driving waveform of the liquid ejection head 1 that ejects n drops, as an example of the driving waveform of the liquid ejection head 1 in other embodiments.

[0191] First of all, Figure 8 as well as Figure 8 In the driving waveform shown, which ejects more than 3 droplets, each droplet from the third droplet to the nth droplet is influenced by the ejection waveforms preceding them. A specific example is given below.

[0192] For example, if we take Figure 29Taking the example of the driving waveforms of three ejected droplets as an illustration, the third droplet is affected by both the ejection waveforms of the second and first droplets. Therefore, for example, if the waveforms of the second and third droplets are mutually reinforcing, but the waveforms of the first and third droplets are mutually destructive, the ejection force of the third droplet is weakened due to the influence of the first droplet's waveform. This raises concerns that the third droplet's velocity may not be sufficiently increased to catch up with the advancing droplets.

[0193] Therefore, in a three-drop waveform, the waveform of the first droplet ejected can be made to reinforce the waveform of the third droplet ejected. For example, as... Figure 29 As shown, if the time difference 4UL between (0) and (0''') is set to be greater than 3.5maxAL and less than 4.5minAL, then in all of the plurality of pressure chambers 46, the phase difference between the composite waves of (1) and (2) and the composite waves of (31) and (32) is less than ±90 degrees. Thus, the composite waves of (1) and (2) and the composite waves of (31) and (32) reinforce each other. In addition, even if Dp31 (=Dp32=Dp33) is set and the time width of Dp31 (=Dp32=Dp33) is adjusted, the half-cycle AL of the dominant acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, and the ejection waveforms with time widths of Dp31, Dp32, and Dp33 give the same pressure to the liquid in the corresponding pressure chamber 46. In addition, the ejection velocity of the third droplet is greater than that of the first droplet due to the mutual reinforcement of the residual vibration caused by the composite waves of (1) and (2) and the composite waves of (31) and (32).

[0194] In addition, such as ​ As shown, in the multiple driving waveforms (n-drop waveforms) of continuously ejected n drops, the ejection waveform after the amount of two drops from the first drop (a-th drop) and before the nth drop is designated as the b-th drop. The ejection waveforms of the a-th drop after the first drop and this b-th drop are considered. It should be noted that in... ​In this context, the reference point for the phase of the ejection waveform of the nth droplet is shown as (0n). In such a driving waveform of ejecting n drops, consider the influence of the ejection waveform of the ath droplet on the bth droplet. When the waveforms of the ath droplet and the bth droplet are mutually weakening, the ejection force of the bth droplet is weakened due to the influence of the ath droplet's ejection waveform, leading to concerns that the bth droplet's velocity may not be sufficiently increased to catch up with the advancing droplets. Therefore, the reference point for the phase of the ath droplet's ejection waveform is set as (0a), and the reference point for the phase of the bth droplet's ejection waveform, which is two drops later than the ath droplet's ejection waveform, is set as (0b). If the time difference 4UL between (0a) and (0b) is set to be greater than 3.5*maxAL and less than 4.5*minAL, then in all of the plurality of pressure chambers 46, the residual vibrations of the ath droplet's ejection waveform and the bth droplet's ejection waveform mutually reinforce each other.

[0195] Furthermore, in the driving waveform (n-drop waveform) of continuously ejecting multiple n drops, the ejection waveform of the a-th drop after the first drop and the ejection waveform of the b-th drop, which is further back than the a-th drop and before the n-th drop, are considered. In the driving waveform of droplets ejected beyond b drops, the influence of the ejection waveform of the a-th drop on the b-th drop is considered. When the waveforms of the a-th droplet and the b-th droplet are mutually weakening, the ejection force of the b-th droplet is weakened due to the influence of the a-th droplet's ejection waveform, raising concerns that the b-th droplet's velocity may not be sufficiently increased to catch up with the advancing droplets. Therefore, if the reference point of the phase of the ejection waveform of the a-th droplet is set as (0a) and the reference point of the phase of the ejection waveform of the b-th droplet is set as (0b), and if the time difference 2*(ba)*UL between (0a) and (0b) is set to be greater than (2*(ba)-0.5)*maxAL and less than (2*(ba)+0.5)*minAL, then in all of the plurality of pressure chambers 46, the residual vibrations of the ejection waveforms of the a-th droplet and the b-th droplet mutually reinforce each other.

[0196] As described above, in the n-drop waveform that ejects multiple droplets, any one of the ejection waveforms after the first drop is designated as droplet a, and any one of the ejection waveforms after droplet a is designated as droplet b. Furthermore, the liquid ejector head 1 sets the time interval (time difference) 2*(ba)*UL between the centers of the ejection waveforms of droplet a and droplet b to (2*(ba)-0.5)*maxAL<2*(ba)*UL<(2*(ba)+0.5)*minAL, thereby mutually reinforcing the residual vibration caused by the previous (droplet a) ejection waveform and the vibration caused by the ejection waveform of the subsequent droplet (droplet b), which can increase the ejection speed.

[0197] It should be noted that the two ejection waveforms that set the time difference 2*(ba)*UL between the two ejection waveforms to (2*(ba)-0.5)*maxAL<2*(ba)*UL<(2*(ba)+0.5)*minAL can be any combination of two ejection waveforms from the multiple ejection waveforms of the n-drop waveform, or any one or more combinations of any combination of two ejection waveforms.

[0198] Next, considering the case where the dominant vibration frequencies of the multiple pressure chambers 46 deviate, the multiple pressure chambers 46 are divided into multiple groups. The drive waveform is adjusted according to the maximum and minimum values ​​of the half-cycle AL of the dominant vibration frequency of each group, and then input. For example, if the maximum value of the half-cycle AL of the dominant vibration frequency of the multiple pressure chambers 46 is 3.5 μs and the minimum value is 2.5 μs, the pressure chambers 46 with AL ranging from below 3.5 μs to above 3.0 μs are designated as the first group, and the pressure chambers 46 with AL ranging from below 3.0 μs to above 2.5 μs are designated as the second group. Here, the pressure chambers 46 that satisfy both the conditions of the first and second groups (e.g., the pressure chamber 46 with AL of 3.0 μs) are designated as any group. For example, if the group of the pressure chambers 46 that satisfy both the conditions of the first and second groups is designated as the same as the group of the adjacent pressure chambers 46, the management and differentiation of each group becomes simple.

[0199] Therefore, the maximum AL of the pressure chamber 46 in the first group becomes 3.5 μs, and the minimum AL becomes 3.0 μs. The time interval (time difference) 2*(ba)*UL between the centers of the ejection waveforms of the a-th drop and the b-th drop of the n-drop waveform input to the pressure chamber 46 in the first group is set to (2*(ba)-0.5)*maxAL<2*(ba)*UL<(2*(ba)+0.5)*minAL.

[0200] In addition, the maximum AL of the pressure chamber 46 in the second group is 3.0 μs, and the minimum AL is 2.5 μs. The time interval (time difference) 2*(ba)*UL between the centers of the ejection waveforms of the a-th drop and the b-th drop 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.

[0201] According to at least one embodiment of the liquid ejector head described above, the waveform widths of the multiple ejection waveforms that eject multiple droplets are approximately the same, and are different from the half-cycle of the dominant acoustic vibration frequency. Furthermore, the interval between the multiple ejection waveforms is set to coincide with the period of the period that enhances the residual vibration of the liquid in the pressure chamber caused by the previously generated ejection waveform and the vibration of the liquid in the pressure chamber caused by the subsequently generated ejection waveform. Thus, the liquid ejector head makes the ejection force of each droplet approximately the same, i.e., nearly the same, and can increase the ejection velocity of subsequent droplets.

[0202] Several embodiments of the present invention have been described, but these embodiments are merely illustrative and not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, 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, and are also included in the scope of the invention as set forth in the claims and its equivalents.

Claims

1. A liquid ejector head, comprising: Nozzle plate, equipped with nozzles for spraying liquid; The pressure chamber is connected to the nozzle; An actuator that makes the volume of the pressure chamber variable according to a drive signal; as well as The drive circuit generates the drive signal that drives the actuator. The driving signal includes multiple ejection waveforms that cause multiple droplets to be ejected from the nozzle. The multiple ejected waveforms have the same width and are different from the half-cycle of the dominant acoustic vibration frequency. The intervals of the plurality of ejection waveforms are consistent with the period of the residual vibration of the liquid in the pressure chamber caused by the previously generated ejection waveform and the vibration of the liquid in the pressure chamber caused by the subsequently generated ejection waveform.

2. The liquid ejector head according to claim 1, wherein, The driving circuit has a switching circuit that connects the electrode and the voltage source, and the driving signal is generated by switching the switching circuit.

3. The liquid ejector head according to claim 1, wherein, When any one of the ejection waveforms after the first drop in the plurality of ejection waveforms is designated as drop a, and any one of the ejection waveforms after drop a is designated as drop b, the time interval between the centers of the ejection waveforms of drop a and drop b is greater than (2*(ba)-0.5) times the maximum value of the half-cycle of the main acoustic vibration frequency of the plurality of pressure chambers with variable volume caused by the actuator inputting the driving signal, and less than (2*(ba)+0.5) times the minimum value of the half-cycle.

4. The liquid ejector head according to claim 1, wherein, The ejection waveform of the driving 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 time interval of the intermediate potential difference of any ejection waveform in the plurality of ejection waveforms is greater than the time interval of the intermediate potential difference of the next ejection waveform of the arbitrary ejection waveform.

5. The liquid ejector head according to claim 1, wherein, At least one of the ejection waveforms 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 first ejection waveform has more potential difference changes than the last ejection waveform.

6. The liquid ejector head according to any one of claims 1 to 5, wherein, The driving circuit selectively generates one or more other driving signals with an ejection volume different from the driving signal, along with the driving signal. The waveform width of the plurality of ejection waveforms included in the driving signal is such that the velocity of the droplets ejected due to the driving signal is the same as the velocity of the droplets ejected due to at least one of the other driving signals.

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