Liquid dispensing head

Abstract

To provide a liquid dispensing head that can approximate or equalize the dispensing force of each droplet while increasing the dispensing speed of subsequent droplets. [Solution] The liquid discharge head comprises a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate is equipped with a nozzle for discharging liquid. The pressure chamber communicates with the nozzle. The actuator varies the volume of the pressure chamber in response to a drive signal. The drive circuit generates the drive signal for driving the actuator. The drive signal includes a plurality of discharge waveforms that cause a plurality of liquid droplets to be discharged from the nozzle. The waveform widths of the plurality of discharge waveforms are substantially the same and differ from half a period of the principal acoustic vibration frequency. The interval between the plurality of discharge waveforms coincides with the period that amplifies the residual vibration of the liquid in the pressure chamber generated by the discharge waveform generated first and the vibration of the liquid in the pressure chamber generated by the discharge waveform generated later.

Description

Technical Field

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

Background Art

[0002] Conventionally, as a liquid ejection head, a technology for ejecting droplets such as ink is known. By continuously ejecting a plurality of droplets, the liquid ejection head increases the dot diameter when the droplets land on the medium, and realizes a harmonious expression of the ink density on the medium.

[0003] However, in this case, when there is variation in the main acoustic vibration frequencies of a plurality of pressure chambers, if the same drive waveform (a drive waveform with different ejection waveform widths for the first drop and the last drop) is input to the plurality of pressure chambers and a plurality of droplets are continuously ejected, the continuously ejected droplets may not coalesce, which may cause deterioration of the printing quality.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a liquid ejection head that can make the ejection force of each droplet substantially the same and increase the ejection speed of subsequent droplets.

Means for Solving the Problems

[0006] The liquid discharge head comprises a nozzle plate, a pressure chamber, an actuator, and a drive circuit. The nozzle plate is equipped with a nozzle for discharging liquid. The pressure chamber communicates with the nozzle. The actuator varies the volume of the pressure chamber in response to a drive signal. The drive circuit generates the drive signal for driving the actuator. The drive signal includes a plurality of discharge waveforms that cause a plurality of liquid droplets to be discharged from the nozzle. The waveform widths of the plurality of discharge waveforms are substantially the same and differ from half a period of the principal acoustic vibration frequency. The intervals between the plurality of discharge waveforms coincide with the period that amplifies the residual vibration of the liquid in the pressure chamber caused by the discharge waveform generated first and the vibration of the liquid in the pressure chamber caused by the discharge waveform generated later. [Brief explanation of the drawing]

[0007] [Figure 1] A cross-sectional view showing the configuration of the liquid discharge head according to the embodiment, with some parts omitted. [Figure 2] A cross-sectional view showing the configuration of the liquid discharge head according to the embodiment, with some parts omitted. [Figure 3] A schematic block diagram showing the configuration of the drive circuit for the liquid discharge head according to the embodiment. [Figure 4] An explanatory diagram showing the configuration of a liquid dispensing device using a liquid dispensing head according to the embodiment. [Figure 5] A block diagram showing an example of the configuration of a liquid dispensing device according to the embodiment. [Figure 6] An explanatory diagram showing an example of a drive waveform including a discharge waveform and a cancellation waveform for discharging two droplets in succession from a liquid discharge head according to the embodiment. [Figure 7] An explanatory diagram showing an example of the drive waveform and acoustic vibration of a liquid discharge head according to an embodiment. [Figure 8] An explanatory diagram showing an example of a drive waveform including a discharge waveform and a cancellation waveform for discharging three droplets in succession from a liquid discharge head according to the embodiment. [Figure 9] An explanatory diagram showing an example of a drive waveform including a discharge waveform and a cancellation waveform for continuously discharging a single droplet of liquid from a comparative example liquid discharge head. [Figure 10]An explanatory diagram showing an example of a drive waveform including a discharge waveform and a cancellation waveform for discharging two droplets in succession from a liquid discharge head according to the embodiment. [Figure 11] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 12] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 13] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 14] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 15] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 16] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 17] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 18] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 19] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 20] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 21] This diagram illustrates the relationship between waveform width and discharge force in a discharge waveform that dispenses two droplets, based on the time width Dp of the leading and trailing droplets. [Figure 22] Explanatory drawing showing the relationship between the waveform width and ejection force based on the condition of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 23] Explanatory drawing showing the relationship between the waveform width and ejection force based on the condition of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 24] Explanatory drawing showing the relationship between the waveform width and ejection force based on the condition of the time width Dp of the leading droplet and the subsequent droplet in an ejection waveform for ejecting two droplets. [Figure 25] Block diagram schematically showing the configuration of a drive circuit of a liquid ejection head according to another embodiment. [Figure 26] Explanatory drawing showing an example of a drive waveform including an ejection waveform and a cancellation waveform for continuously ejecting two droplets of a liquid ejection head according to another embodiment. [Figure 27] Explanatory drawing showing an example of a drive waveform and acoustic vibration of a liquid ejection head according to another embodiment. [Figure 28] Explanatory drawing showing an example of a drive waveform including an ejection waveform and a cancellation waveform for continuously ejecting two droplets of a liquid ejection head according to another embodiment. [Figure 29] Explanatory drawing showing an example of a drive waveform of a liquid ejection head according to another embodiment.

Mode for Carrying Out the Invention

[0008] Hereinafter, the configuration of the liquid ejection head 1 according to the embodiment and the liquid ejection device 100 using the liquid ejection head 1 will be described with reference to FIGS. 1 to 5. FIG. 1 is a cross-sectional view showing a part of the configuration of the liquid ejection head 1 according to the embodiment with some omissions, and FIG. 2 is a cross-sectional view showing a part of the configuration of the liquid ejection head 1 with some omissions. FIG. 3 is a block diagram schematically showing the configuration of the drive circuit 70 of the liquid ejection head 1. FIG. 4 is an explanatory drawing showing the configuration of the liquid ejection device 100 using the liquid ejection head 1 according to the embodiment, and FIG. 5 is a block diagram showing an example of the configuration of the liquid ejection device 100. In each figure, for the sake of explanation, the configuration is appropriately enlarged, reduced, or omitted.

[0009] The liquid ejection head 1 according to this embodiment is, for example, an inkjet head that ejects ink as a liquid. As shown in Figures 1 and 2, the liquid ejection head 1 comprises a base 10, an actuator 20, a diaphragm 30, a flow path plate 40, a nozzle plate 50 having a plurality of nozzles 51, and a drive circuit 70.

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

[0011] The actuator 20 is a piezoelectric member comprising, for example, a plurality of piezoelectric columns 21 and non-driven piezoelectric columns 22 arranged alternately with the plurality of piezoelectric columns 21. The actuator 20 is formed in a comb-like shape by arranging the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 in one direction at predetermined intervals. For example, in such an actuator 20, a laminated piezoelectric member joined to a base 10 is processed by dicing grooves from the end face opposite to the base 10 side to form a plurality of piezoelectric elements formed in a rectangular column shape at predetermined intervals on a single piezoelectric member. The formed plurality of piezoelectric elements are then provided with electrodes, etc., to constitute a plurality of alternately arranged piezoelectric columns 21 and a plurality of non-driven piezoelectric columns 22 as piezoelectric elements. That is, the actuator 20 is divided into multiple parts at one end (diaphragm 30 side) by the formed plurality of grooves, and the other end (base 10 side) is connected.

[0012] For example, the laminated piezoelectric member constituting the actuator 20 is formed by laminating and sintering sheet-shaped piezoelectric material. As a specific example, as shown in Figures 1 and 2, the piezoelectric column 21 and the non-driven piezoelectric column 22 are, for example, laminated piezoelectric bodies used as driving elements. The piezoelectric column 21 and the non-driven piezoelectric column 22 comprise a plurality of laminated piezoelectric layers, a plurality of internal electrodes formed on the main surface of each piezoelectric layer, and a plurality of external electrodes. For example, the piezoelectric column 21 and the non-driven piezoelectric column 22 have the same configuration.

[0013] The piezoelectric layer is constructed in the form of a thin plate from a piezoelectric material such as PZT (lead zirconate titanate) or lead-free KNN (potassium sodium niobate). Multiple piezoelectric layers are stacked in the thickness direction and bonded together by sintering. Here, the stacking direction of the multiple piezoelectric layers is perpendicular to the alignment direction of the multiple piezoelectric columns 21 and the multiple non-driven piezoelectric columns 22.

[0014] The internal electrodes are conductive films formed in a predetermined shape from a sinterable conductive material such as silver-palladium. The internal electrodes are formed in predetermined areas on the main surface of each piezoelectric layer. Multiple internal electrodes are configured as alternating poles in the direction of arrangement.

[0015] The external electrodes are formed on the surfaces of multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and are constructed by gathering the ends of the internal electrodes. The external electrodes are deposited using known methods such as plating or sputtering, using materials such as Ni, Cr, and Au. The multiple external electrodes are arranged on different side surfaces of the multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and are configured as different poles. Note that the external electrodes of different poles may be routed to different regions within the same side surface of the multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22.

[0016] In this embodiment, as an example, the plurality of external electrodes include individual electrodes formed on each of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22, and a common electrode formed continuously on the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22. The plurality of individual electrodes formed on each of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22 are arranged independently of each other. The common electrode is, for example, grounded.

[0017] These external electrodes are connected, for example, to a drive circuit 70. For example, each external electrode is connected by wiring to a control unit 150, which acts as a drive unit, via a driver 723 of the drive circuit 70 (described later), and is configured to be controllable by control of a processor 151.

[0018] The piezoelectric columns 21 and non-driven piezoelectric columns 22 vibrate longitudinally along the stacking direction of the piezoelectric material layers when a voltage is applied to their internal electrodes via external electrodes. This longitudinal vibration refers to, for example, "vibration in the thickness direction defined by the piezoelectric constant d33". For example, as shown in Figure 2, multiple piezoelectric columns 21, arranged every other, are positioned corresponding to the pressure chamber 46 with the diaphragm 30 in between, while the remaining non-driven piezoelectric columns 22 are positioned opposite the partition wall 42 with the diaphragm 30 in between.

[0019] The piezoelectric column 21 vibrates vertically when a voltage is applied, displacing the diaphragm 30. That is, the piezoelectric column 21 deforms the pressure chamber 46. The non-driven piezoelectric column 22 is positioned opposite the partition wall 42. No voltage is applied to the non-driven piezoelectric column 22. That is, each piezoelectric column 21 constitutes an actuator that deforms the pressure chamber 46 when driven, and each non-driven piezoelectric column 22 constitutes a support column. That is, the piezoelectric column 21 expands and contracts the pressure chamber 46 to vary the volume of the pressure chamber 46.

[0020] The diaphragm 30 is joined to one side of the piezoelectric layers of the plurality of piezoelectric pillars 21 and 22 in the stacking direction, i.e., the side facing the nozzle plate 50. The diaphragm 30 deforms, for example, by driving the piezoelectric pillar 21. The diaphragm 30 is joined to the piezoelectric pillar 21 and the non-driven piezoelectric pillar 22 of the actuator 20.

[0021] The diaphragm 30 is, for example, a flat plate arranged such that its thickness direction is the same as the stacking direction of the piezoelectric layers. The diaphragm 30 has a surface direction that extends in the direction of the arrangement of the plurality of piezoelectric columns 21 and the plurality of non-driven piezoelectric columns 22. The diaphragm 30 is, for example, a metal plate. The diaphragm 30 has a plurality of vibrating parts 301 that face each pressure chamber 46 and are individually displaceable. The diaphragm 30 is formed by the plurality of vibrating parts 301 being integrally connected.

[0022] For example, the diaphragm 30 is constructed as a single flat plate, and each region joined to the piezoelectric column 21 is displaced individually. The diaphragm 30 is made of, for example, a stainless steel plate. The diaphragm 30 may have folds or steps formed between the vibrating parts 301 and adjacent parts, or between adjacent vibrating parts 301, so that the multiple vibrating parts 301 can be easily displaced.

[0023] The diaphragm 30 expands and contracts the pressure chamber 46 by displacing a portion of the piezoelectric column 21 that is positioned opposite the piezoelectric column 21 due to the extension and compression of the piezoelectric column 21 caused by the longitudinal vibration of the piezoelectric column 21, thereby varying the volume of the pressure chamber 46.

[0024] One main surface of the diaphragm 30 is joined to the actuator 20, and the other main surface is joined to the flow path plate 40. A pressure chamber 46 capable of containing ink is formed between the diaphragm 30 and the flow path plate 40.

[0025] The diaphragm 30 has one main surface facing the piezoelectric columns 21 and 22, respectively, and the other main surface facing the pressure chamber 46 and the partition wall 42, respectively.

[0026] The flow path plate 40 is joined to the diaphragm 30. The flow path plate 40 is positioned between the nozzle plate 50 and the diaphragm 30. The flow path plate 40 has a plurality of partition walls 42. The flow path plate 40 also forms a predetermined flow path 45. The flow path plate 40 is formed, for example, by stacking a plurality of plates 401, each with a portion open, to form the plurality of partition walls 42 and the predetermined flow path 45.

[0027] Multiple partition walls 42 are arranged in the direction of the alignment of the multiple piezoelectric columns 21 and 22, and face the non-driven piezoelectric columns 22 via the diaphragm 30. The partition walls 42 separate the multiple pressure chambers 46 of a predetermined flow path 45 (described later), as well as the multiple individual flow paths 47.

[0028] 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.

[0029] Multiple pressure chambers 46 are arranged in the direction of the arrangement of multiple piezoelectric columns 21 and multiple non-driven piezoelectric columns 22, and face the multiple piezoelectric columns 21 via a diaphragm 30. Multiple pressure chambers 46 arranged in one direction are separated by partition walls 42. Multiple partition walls 42 positioned between the multiple pressure chambers 46 face the multiple non-driven piezoelectric columns 22 via a diaphragm 30. Multiple pressure chambers 46 are formed when a flow path plate 40 is closed on one side by a diaphragm 30 and closed on the other side by a nozzle plate 50 in the stacking direction of the piezoelectric material layers. Nozzles 51 formed on the nozzle plate 50 are also arranged in the pressure chambers 46.

[0030] Multiple pressure chambers 46 communicate with a common channel 48 via individual channels 47. Each pressure chamber 46 holds liquid supplied from the common channel 48 through the individual channels 47, and discharges the liquid from the nozzle 51 by deforming due to the vibration of a vibrating plate 30 that forms part of the pressure chamber 46. The individual channels 47 connect the common channel 48 and the pressure chambers 46. The same number of individual channels 47 as pressure chambers 46 are provided. The cross-sectional shape of the individual channels 47 differs from the cross-sectional shape of the pressure chambers 46. The cross-sectional area of ​​the individual channels 47 is smaller than the cross-sectional area of ​​the pressure chambers 46. The common channel 48 is fluidically connected to the multiple individual channels 47 and communicates with the pressure chambers 46 through each individual channel 47.

[0031] The nozzle plate 50 is formed from a metal such as SUS or Ni, or a resin material such as polyimide. The nozzle plate 50 is joined to the flow path plate 40 and covers a plurality of pressure chambers 46. The nozzle plate 50 has a plurality of nozzles 51 formed opposite the plurality of pressure chambers 46 and penetrating in the thickness direction. A nozzle row is formed by the plurality of nozzles 51.

[0032] As shown in Figure 5, the drive circuit 70 includes a data buffer 721, a decoder 722, and a driver 723. The data buffer 721 stores print data chronologically for each piezoelectric pole 21, 22. The decoder 722 controls the driver 723 for each piezoelectric pole 21, 22 based on the print data stored in the data buffer 721. Based on the control of the decoder 722, the driver 723 outputs a drive signal to operate each piezoelectric pole 21, 22. The drive signal is the voltage applied to each piezoelectric pole 21, 22.

[0033] As a specific example, as shown in Figure 1, the drive circuit 70 comprises a wiring film 71 with one end connected to an external electrode, a driver IC 72 mounted on the wiring film 71, and a printed circuit board mounted on the other end of the wiring film 71. For example, the driver IC 72 has a data buffer 721, a decoder 722, and a driver 723. Alternatively, the driver IC 72 may have some of the components of the data buffer 721, decoder 722, and driver 723, while the printed circuit board or the like may have the remaining components.

[0034] The drive circuit 70 drives the piezoelectric column 21 by applying a drive voltage to the external electrodes using the driver IC 72, thereby varying the volume of the pressure chamber 46 and causing droplets to be ejected from the nozzle 51.

[0035] The wiring film 71 is connected to multiple individual electrodes and a common electrode. For example, the wiring film 71 is an ACF (anisotropic conductive film) fixed to the connection part of the external electrode by thermocompression or the like. The wiring film 71 is, for example, a COF (Chip on Film) on which the driver IC 72 is mounted.

[0036] The driver IC 72 is connected to the external electrodes via the wiring film 71. Alternatively, the driver IC 72 may be connected to the external electrodes by other means, such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste), instead of the wiring film 71.

[0037] The driver IC 72 applies signals to each piezoelectric column 21 and 22 to generate control signals and drive signals for operating the piezoelectric column 21. The driver IC 72 generates control signals for control purposes, such as selecting the timing for ink ejection and which piezoelectric column 21 to eject the ink, according to the image signal input from the control unit 150 of the liquid ejection device 100. The driver IC 72 also generates a voltage to be applied to the piezoelectric column 21, i.e., a drive signal (electrical signal), according to the control signals. When the driver IC 72 applies a drive signal to the piezoelectric column 21, the piezoelectric column 21 is driven by displacing the diaphragm 30, thereby varying the volume of the pressure chamber 46 to expand and contract. This causes pressure vibrations in the ink filled in the pressure chamber 46. Due to these pressure vibrations, ink is ejected from the nozzle 51 provided in the pressure chamber 46. The liquid ejection head 1 may be configured to achieve gradation expression by changing the amount of ink droplets that land on one pixel. Alternatively, the liquid ejection head 1 may be configured to change the amount of ink droplets that land on one pixel by changing the number of times the ink is ejected. Thus, the driver IC 72 is an example of an application unit that applies a drive signal to the piezoelectric pole 21.

[0038] Next, an example of the drive circuit 70 will be described as shown in Figure 3. The drive circuit 70 includes, for example, a voltage control unit 724 and the same number of voltage switching units 725 as there are pressure chambers 46, all located within the driver IC 72. However, in Figure 3, only two voltage switching units 725 are shown, and the other voltage switching units 725 are not shown.

[0039] 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 applies the voltage supplied from the first voltage source 81 to each wiring electrode 726. The drive circuit 70 also selectively applies the voltages supplied from the first voltage source 81, the second voltage source 82, and the third voltage source 83 to each wiring electrode 727. Here, since the actuator 20 is a stacked PZT, applying bipolar voltage tends to degrade it, the voltages supplied by the first voltage source 81, the second voltage source 82, and the third voltage source 83 are set to either the ground voltage or one of two polarities relative to the ground voltage (positive or negative).

[0040] The output voltage of the first voltage source 81 is, for example, the ground voltage, and its voltage value is V0 (V0 = 0 [V]). The voltage value indicated by the output voltage of the second voltage source 82 is V1. Note that the voltage value V1 is higher than V0. The voltage value indicated by the output voltage of the third voltage source 83 is, for example, V2. For example, the voltage value V2 is higher than V0 and lower than V1.

[0041] The wiring electrode 726 is connected to a common electrode that serves as the ground electrode of the actuator 20. The multiple wiring electrodes 727 are each connected to individual electrodes that serve as non-ground electrodes of the actuator 20.

[0042] The voltage control unit 724 is connected to each of the multiple voltage switching units 725. The voltage control unit 724 outputs a command to each voltage switching unit 725 indicating which voltage source to select from the first voltage source 81, the second voltage source 82, and the third voltage source 83. 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, the second voltage source 82, or the 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.

[0043] The voltage switching unit 725 is composed of, for example, a semiconductor switch. The voltage switching unit 725 connects the wiring electrode 727 to one of the first voltage source 81, the second voltage source 82, and the third voltage source 83 under the control of the voltage control unit 724. Therefore, the internal electrodes of different poles of the piezoelectric pole 21 are connected to the wiring electrode 726 and the wiring electrode 727 via external electrodes (common electrode and individual electrode).

[0044] In this drive circuit 70, the drive circuit switches the connection wiring between the voltage sources 81, 82, and 83 and the actuator 20 using a switching circuit composed of a voltage control unit 724 and a plurality of voltage switching units 725, thereby inputting drive waveforms with at least three types of potential differences between the electrodes of the actuator 20 as drive signals. Here, the drive waveform is a drive waveform that causes the actuator 20 to discharge droplets when driven. In this embodiment, potential differences other than the largest and smallest potential differences are called intermediate potential differences.

[0045] The printed circuit board is a Printing Wiring Assembly (PWA) on which various electronic components and connectors are mounted. The printed circuit board is connected to the control unit 150 of the liquid dispensing device 100.

[0046] Next, an example of a liquid ejection device 100 equipped with a liquid ejection head 1 will be described with reference to Figures 4 and 5. The liquid ejection device 100 is, for example, an inkjet recording device. The liquid ejection device 100 comprises a housing 111, a media supply unit 112, an image forming unit 113, a media discharge unit 114, and a transport device 115. The liquid ejection device 100 also includes a control unit 150.

[0047] The liquid dispensing device 100 is a liquid dispensing device that performs image forming processing on paper P by dispensing a liquid such as ink while transporting paper P, which is the printing medium to be dispensed, along a predetermined transport path A from the media supply unit 112 through the image forming unit 113 to the media discharge unit 114.

[0048] The housing 111 constitutes the outer casing of the liquid dispensing device 100. The housing 111 is provided with an outlet at a predetermined location for discharging the paper P to the outside.

[0049] The media supply unit 112 is equipped with multiple paper feed cassettes and is configured to hold multiple sheets of paper P of various sizes stacked on top of each other.

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

[0051] The image forming unit 113 includes a support unit 117 that supports the paper P, and a plurality of head units 130 that are positioned opposite each other above the support unit 117.

[0052] The support unit 117 includes a conveyor belt 118 provided in a loop shape in a predetermined area where image formation is performed, a support plate 119 that supports the conveyor belt 118 from the back, and a plurality of belt rollers 120 provided on the back of the conveyor belt 118.

[0053] During image formation, the support unit 117 supports the paper P on the holding surface, which is the upper surface of the conveyor belt 118, and conveys the paper P downstream by moving the conveyor belt 118 at a predetermined timing by the rotation of the belt roller 120.

[0054] The head unit 130 comprises a liquid ejection head 1, a plurality of ink tanks 132 which serve as liquid tanks and are mounted on the liquid ejection head 1, a connecting channel 133 that connects the liquid ejection head 1 and the ink tanks 132, and a supply pump 134.

[0055] In this embodiment, multiple head units 130 are provided. Each head unit 130 uses a different color of ink. For example, the multiple head units 130 include four liquid ejection heads 1 for cyan, magenta, yellow, and black, and ink tanks 132 that each contain ink of these colors. The ink tanks 132 are connected to a common flow path 48 of the liquid ejection heads 1 by a connecting flow path 133.

[0056] Furthermore, a negative pressure control device, such as a pump (not shown), is connected to the ink tank 132. The negative pressure control device controls the negative pressure inside the ink tank 132 in accordance with the head value between the liquid ejection head 1 and the ink tank 132, thereby forming the ink supplied to each nozzle 51 of the liquid ejection head 1 into a meniscus of a predetermined shape.

[0057] The supply pump 134 is a liquid transfer pump, for example, a piezoelectric pump. The supply pump 134 is installed in the supply flow path. The supply pump 134 is connected to the control unit 150 by wiring and controlled by the control unit 150. The supply pump 134 supplies liquid to the liquid discharge head 1.

[0058] The transport device 115 transports the paper P along a transport path A, which runs from the media supply unit 112 through the image forming unit 113 to the media discharge unit 114. The transport device 115 comprises a plurality of guide plate pairs 121 and a plurality of transport rollers 122 arranged along the transport path A.

[0059] Each of the multiple guide plate pairs 121 comprises a pair of plate members positioned opposite each other with the paper being transported P in between, and guides the paper P along the transport path A.

[0060] The transport roller 122 is driven and rotated by the control unit 150 to feed the paper P downstream along the transport path A. Sensors for detecting the paper transport status are placed at various points along the transport path A.

[0061] The control unit 150 is, for example, a control board. The control unit 150 is equipped with a processor 151, ROM (Read Only Memory) 152, RAM (Random Access Memory) 153, I / O ports 154 which are input / output ports, and image memory 155.

[0062] The processor 151 is a processing circuit such as a CPU (Central Processing Unit) which is a controller. The processor 151 controls the head unit 130, drive motor 161, operating unit 162, and various sensors 163, etc., provided in the liquid dispensing device 100, through the I / O port 154. The processor 151 transmits the print data stored in the image memory 155 to the drive circuit 70 in the order of drawing.

[0063] ROM 152 stores various programs and other data. RAM 153 temporarily stores various variable data and image data. Note that ROM 152 and RAM 153 are examples of storage media; other storage media may be used as long as they can store various programs and data. I / O port 154 is an interface unit for inputting data from external devices such as external devices 200 and outputting data to external devices. Print data from external devices 200 is transmitted to the control unit 150 via I / O port 154 and stored in image memory 155.

[0064] The characteristics of the liquid discharge head 1 used in the liquid discharge device 100 according to this embodiment and the drive waveform of the liquid discharge head 1 (drive signal for discharging droplets) will be described below. The discharge waveform of the drive signal of the liquid discharge head 1 in this 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.

[0065] First, the drive waveform of the liquid discharge head 1 of this embodiment will be explained using Figures 6 to 24. Figure 6 is an explanatory diagram showing an example of a drive waveform including a multi-drop discharge waveform and a cancellation waveform for discharging two droplets in succession from the liquid discharge head 1. Figure 7 is a diagram illustrating a conventional liquid discharge head as a comparative example, and is an explanatory diagram showing an example of a drive waveform including a multi-drop discharge waveform and a cancellation waveform for discharging multiple droplets in succession from a liquid discharge head according to the comparative example.

[0066] Figure 8 shows an example of a drive waveform including a multi-drop discharge waveform for discharging three droplets in succession from the liquid discharge head 1, according to another embodiment, with the cancellation waveform omitted. Figure 9 is an explanatory diagram showing an example of a drive waveform including a discharge waveform and a cancellation waveform for discharging one droplet from the liquid discharge head, as a conventional example, and Figure 10 is an explanatory diagram showing an example of a drive waveform including a multi-drop discharge waveform and a cancellation waveform for discharging two droplets in succession from the liquid discharge head 1, as another embodiment, in which the time width Dp of the discharge waveform is greater than half a period AL of the main acoustic vibration frequency of the pressure chamber 46.

[0067] Figures 11 to 24 are explanatory diagrams showing the relationship between waveform width and discharge force based on the time width Dp of the leading droplet and the following droplet in a discharge waveform that discharges two droplets. Figures 11 to 18 show examples where the time width Dp21 of the discharge waveform of the leading droplet and the time width Dp22 of the discharge waveform of the following droplet are different (Dp21≠Dp22), while Figures 19 to 24 show examples where the Dp21 of the leading droplet and the Dp22 of the following droplet are the same or approximately the same (Dp21≒Dp22).

[0068] First, the liquid ejection head 1 of this embodiment performs gradation expression, for example, by the number of ink droplets ejected continuously. When there are multiple nozzles 51 that eject the same number of droplets, the same drive waveform is input to multiple piezoelectric columns 21 that vary the volume of multiple pressure chambers 46 communicating with the multiple nozzles 51. On the other hand, the main acoustic vibration frequencies of the multiple pressure chambers 46 are not necessarily the same due to manufacturing variations, etc. For example, the drive waveform for driving the liquid ejection head 1, where the maximum value of the half-period AL of the main acoustic vibration frequencies of the multiple pressure chambers 46 is 3.5 μs, the minimum value is 2.5 μs, and the average value is 3.0 μs, will be described next.

[0069] Furthermore, the AL of the multiple pressure chambers 46 can be determined by individually inputting a rectangular wave to the piezoelectric column 21 that varies the volume of each pressure chamber 46, and measuring the velocity of the droplet discharged from the nozzle at that time. For example, by measuring the velocity of the discharged droplet while changing the time width of the rectangular wave, if the droplet discharge velocity is maximum when the time width of the rectangular wave is 3.0 μs, then 3.0 μs can be considered to be the AL of the corresponding pressure chamber 46.

[0070] Next, we will explain the challenges of conventional drive waveforms. For example, when printing on media by discharging droplets from a liquid discharge head 1 while transporting the media to be printed on, it is necessary to adjust the velocity of each volume of droplet so that the landing position of the droplet on the media does not change even if the volume of the droplet discharged from the nozzle 51 changes.

[0071] First, the drive waveform for dispensing a single drop is a rectangular wave with a time width Dp11 of 1AL, as shown in Figure 9. Then, for the drive waveforms that dispense multiple droplets in succession, the waveform width of the discharge waveform for each droplet is set to 1AL for the discharge waveform of the first or last droplet, and the waveform width of the discharge waveforms of the other droplets is made smaller or larger than 1AL to adjust the droplet velocity when droplets are dispensed in succession, bringing it close to the discharge velocity of a single drop. In this way, when droplets are dispensed in succession, residual vibration occurs in the pressure chamber 46 due to the discharge of the first droplet, so by dispensing the next droplet in accordance with the phase of the residual vibration, the discharge velocity of subsequent droplets increases. In the case of a single drop, a velocity increase due to residual vibration cannot be expected, so the waveform width of the discharge waveform for a single drop is set to 1AL, and the discharge waveform width is adjusted when droplets are dispensed in succession.

[0072] For example, consider the case where, in one of the multiple pressure chambers 46, the AL is approximately 3.0 μs, and the drive waveform is adjusted to continuously discharge 2 drops as shown in Figure 7, and the 2-drop waveform is set to Dp21=3.0 μs, UL=3.0 μs, Dp22=2.1 μs, and Cp=1.5 μs, and the velocity of the second drop discharged droplet in the 2-drop waveform becomes greater than the velocity of the first drop discharged droplet in the 2-drop waveform.

[0073] In order to align the phase of the residual vibration generated by the discharge waveform of Dp21 with the phase of the discharge waveform of Dp22, the aforementioned 2drop waveform has a center-to-center distance (time interval between centers) 2UL between the discharge waveforms of Dp21 and Dp22 set to twice the AL of the pressure chamber 46. As a result, even if the waveform width of Dp22 is smaller than the AL of the pressure chamber 46, the velocity of the second drop of the discharged droplet in the 2drop waveform is greater than the velocity of the first drop of the discharged droplet in the 2drop waveform.

[0074] When the 2-drop waveform shown in Figure 7 is input to the piezoelectric column 21, which varies the volume of the pressure chamber 46 where AL is at its maximum value of 3.5 μs, the difference between the waveform width of Dp22 and AL of the pressure chamber 46 becomes large. In addition, the difference between the center-to-center distance 2UL of the ejection waveform of Dp21 and the ejection waveform of Dp22 and 2AL of the pressure chamber 46 also becomes large. This raises concerns that the velocity of the ejected droplet in the second drop of the 2-drop waveform will be smaller than the velocity of the ejected droplet in the first drop. As a result, if the timing of the ejected droplet in the second drop hitting the media is delayed compared to the ejected droplet in the first drop, it will lead to a decrease in print quality.

[0075] Figures 11 to 24 schematically show the discharge force characteristics of the pressure chamber 46, with the horizontal axis representing the waveform width of the discharge waveform and the vertical axis representing the discharge force as a function of the waveform width when there is no residual vibration, using dashed lines. Here, avrAL is the average value of AL for multiple pressure chambers 46 that receive the same drive waveform. minAL is the minimum value of AL for multiple pressure chambers 46 that receive the same drive waveform. maxAL is the maximum value of AL for multiple pressure chambers 46 that receive the same drive waveform. Furthermore, the upward-convex, bow-shaped dashed lines in Figures 11 to 14 and Figures 19 and 20 indicate the discharge force characteristics in the pressure chamber 46 where AL is approximately the same as avrAL.

[0076] Figure 13 shows the relationship between waveform width and discharge force when Dp21 has the same time width as avrAL and Dp22 has a shorter time width than avrAL, as shown in the waveform of Figure 7. In Figure 13, the discharge force of Dp22 is slightly smaller than that of Dp21, but in the waveform of Figure 7, the residual vibration generated by Dp21 reinforces Dp22, so the droplet velocity discharged by Dp22 is equal to or greater than that discharged by Dp21.

[0077] Figure 17 shows the relationship between waveform width and discharge force when driving a pressure chamber 46 where AL is maxAL, using a drive waveform like that in Figure 7, with the waveform widths Dp21 and Dp22 shown in the lower left of Figure 13. In Figure 17, Dp21 has a waveform width of avrAL, so it represents the discharge force near the peak of the discharge force characteristic of the pressure chamber 46, and the change in discharge force is relatively small. On the other hand, in Figure 17, Dp22 has a waveform width that is considerably smaller than avrAL, so the change in discharge force due to the expansion of AL in the pressure chamber 46 is large.

[0078] Furthermore, the difference between the center-to-center distance 2UL of the discharge waveform of Dp21 and the discharge waveform of Dp22 and the pressure chamber 46's 2AL (=2*maxAL) becomes large. Therefore, compared to Figure 13, Figure 17 shows a decrease in discharge force for both Dp21 and Dp22, but the decrease is greater for Dp22. Even with reinforcement between Dp22 and residual vibration, the droplet velocity discharged by Dp22 may still be lower than the droplet velocity discharged by Dp21.

[0079] Next, we adjust the drive waveform to continuously discharge 2 drops in one of the pressure chambers 46 where AL is approximately 3.0 μs, and consider the case where the velocity of the second discharged droplet in the 2-drop waveform becomes greater than the velocity of the first discharged droplet in the 2-drop waveform, when the 2-drop waveform is set to Dp21=2.1 μs, UL=3.0 μs, Dp22=3.0 μs, and Cp=1.5.

[0080] In the aforementioned 2drop waveform, in order to align the phase of the residual vibration generated by the discharge waveform of Dp21 with the phase of the discharge waveform of Dp22, the distance 2UL between the centers of the discharge waveforms of Dp21 and Dp22 is set to twice the AL of the pressure chamber 46, so that the velocity of the second drop of the discharged droplet in the 2drop waveform is greater than the velocity of the first drop of the discharged droplet in the 2drop waveform.

[0081] Here, we will explain the case where the 2-drop waveform is input to a piezoelectric column 21 that varies the volume of the pressure chamber 46 where AL is the minimum value of 2.5 μs among the multiple pressure chambers 46. As the difference between the waveform width of Dp21 and AL of the pressure chamber 46 decreases, the ejection speed of the first drop increases, while the difference between the center-to-center distance 2UL of the ejection waveform of Dp21 and the ejection waveform of Dp22 and 2AL of the pressure chamber 46 increases. Therefore, there is a concern that the ejection speed of the second drop will be lower compared to the ejection speed of the first drop of the 2-drop waveform. As a result, even if the timing of the second drop's impact on the media is delayed compared to the first drop's ejection, it will lead to a decrease in print quality.

[0082] Figure 11 shows the relationship between waveform width and discharge force when Dp22 has the same time width as avrAL and Dp21 has a shorter time width than avrAL. In this case, Dp22 has a greater discharge force than Dp21. Also, the residual vibration generated by Dp21 reinforces with Dp22, so the droplet velocity discharged by Dp22 is greater than the droplet velocity discharged by Dp21.

[0083] On the other hand, Figure 15 shows the relationship between waveform width and discharge force when a waveform is input to pressure chamber 46 where AL in pressure chamber 46 is minAL, with Dp22 having the same time width as avrAL and Dp21 having a time width smaller than avrAL. In this case, since the waveform width of Dp21 is closer to the value of minAL than that of Dp22, the discharge force of Dp21 is higher. Also, because the difference between the center-to-center distance 2UL of the discharge waveform of Dp21 and the discharge waveform of Dp22 and 2AL (2*minAL) of pressure chamber 46 becomes large, even if Dp22 and residual vibration reinforce each other, the droplet velocity discharged by Dp22 may still be lower than the droplet velocity discharged by Dp21.

[0084] Next, an example of the drive waveform of this embodiment will be described. For example, in a pressure chamber 46 among the plurality of pressure chambers 46 where AL is approximately 3.0 μs, the drive waveform for continuously discharging 2 drops as shown in Figure 6 is adjusted, and the 2-drop waveform is 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 of the 2-drop waveform is greater than the velocity of the first drop of the 2-drop waveform, and the velocity of the 1-drop waveform is close to the velocity of one of the droplets discharged by the 2-drop waveform. More preferably, Dp21 = Dp22 is adjusted so that the velocities of the combined droplets are approximately the same. In the example of the drive waveform shown in Figure 6, when the 2-drop waveform is set to Dp21 = Dp22, Dp21 and Dp22 are waveforms smaller than AL. However, as in the example of the drive waveform shown in Figure 10, when the 2-drop waveform is set to Dp21 = Dp22, Dp21 and Dp22 may be waveforms larger than AL.

[0085] As shown in Figure 6, when the waveform widths of Dp21 and Dp22 are approximately the same, the pressure exerted on the liquid in the pressure chamber 46 by each discharge waveform is the same. In addition, by making the distance between the centers of Dp21 and Dp22 the same as or approximately the same as 2AL, the residual vibration of the pressure chamber 46 generated by Dp21 and the pressure exerted on the liquid in the pressure chamber 46 by Dp22 reinforce each other, so the velocity of the droplets discharged by Dp22 is usually greater than that of the droplets discharged by Dp21.

[0086] Figure 19 shows the relationship between waveform width and discharge force when Dp21 and Dp22 have time widths smaller than minAL, as shown in the waveform of Figure 6. Figures 21 and 23 also illustrate this relationship.

[0087] In Figures 19, 21, and 23, the discharge forces of Dp22 and Dp21 are equivalent. In the waveform of Figure 6, the residual vibration generated by Dp21 reinforces Dp22, resulting in the droplet velocity discharged by Dp22 being equal to or greater than that discharged by Dp21.

[0088] Next, the conditions under which the residual vibration of the pressure chamber 46 generated by Dp21 and the pressure exerted by Dp22 on the liquid inside the pressure chamber 46 reinforce each other will be specifically explained with reference to a figure. In this embodiment, the waveform width of the discharge waveform of the second drop and the discharge waveform of the first drop are assumed to be approximately the same. Furthermore, in order to make the velocity of the discharged droplet in the first drop waveform and the velocity of the discharged droplet in the second drop waveform approximately the same, Dp21 and Dp22 are set to be smaller than the average value of the half-period AL of the main acoustic vibration frequencies of the multiple pressure chambers 46, which is 3.0 μs.

[0089] Incidentally, if the 1-drop discharge waveform is as shown in Figure 9, reinforcement of residual vibrations does not occur. Therefore, when the voltage height of the discharge waveform is the same for both the 1-drop discharge waveform and the multi-drop discharge waveform, in order to obtain the same discharge speed as the multi-drop discharge waveform, it is necessary to set the discharge waveform width of the 1-drop discharge waveform to a value that maximizes the discharge force. For example, it is desirable to set the discharge waveform width of the 1-drop discharge waveform between minAL and maxAL so that the discharge force is maximized.

[0090] In this case, consider the case where the waveform width of each discharge waveform of multiple drops is set to minAL. In pressure chamber 46 where AL is minAL, the discharge force of multiple drop waveforms with a discharge width of minAL will be greater than that of a single drop waveform with an average discharge width of AL. Furthermore, reinforcement of residual vibrations occurs, which can lead to situations where the discharge velocity of multiple drop droplets is extremely high compared to that of a single drop droplet.

[0091] If the waveform width of each discharge waveform in multiple drops is set between minAL and maxAL, the same concerns as described above arise in any pressure chamber 46 where AL is between minAL and maxAL. For this reason, it is desirable to set the waveform width of each discharge waveform in multiple drops to be either smaller than minAL or larger than maxAL.

[0092] For the sake of explanation, in Figure 6, the first and second potential difference changes in the discharge waveform of the first drop will be denoted as (1) and (2), and the first and second potential difference changes in the discharge waveform of the second drop will be denoted as (21) and (22), and the explanation will proceed accordingly. Furthermore, the reference point for the phase of the discharge waveform of the first drop will be set to (0), and the reference point for the phase of the discharge waveform of the second drop will be set to (0''), and the explanation will proceed accordingly. Here, the reference point for the phase of the discharge waveform of the first drop (0) is set to be midway between the potential difference changes of (1) and (2), and the reference point for the phase of the discharge waveform of the second drop (0'') is set to be midway between the potential difference changes of (21) and (22). Also, the voltage drop time tf (21) in Figure 6 is assumed to be approximately the same as the voltage rise time tr (22). Furthermore, the amount of potential difference change in (1) and (21), and the amount of potential difference change in (2) and (22) (the change in height in Figure 7) are assumed to be approximately the same. In this embodiment, the pressure chamber 46 is pressurized by tr and depressurized by tf.

[0093] For simplicity, we ignore vibration damping due to viscous resistance in the flow path, and let tin be the time at which the potential difference change occurs due to tr, and let t0 be the time at the phase reference point (0). Schematically, the pressure oscillation in the pressure chamber 46 due to pressurization is given by cos((t0-tin)*(π / AL)). The velocity of the liquid in the nozzle is given by -sin((t0-tin)*(π / AL)). Note that in the head flow path diagram, the nozzle is oriented downwards, and the pressurization of the pressure chamber 46 causes the liquid velocity in the nozzle to change downwards, hence the negative sign. Furthermore, let tin be the time at which the potential difference change occurs due to tf, and schematically, the pressure oscillation in the pressure chamber 46 due to depressurization is given by cos(-π+(t0-tin)*(π / AL)). The velocity of the liquid in the nozzle is given by -sin(-π+(t0-tin)*(π / AL)). Furthermore, in the head flow path diagram, the nozzle is oriented downwards, and the liquid velocity at the nozzle changes upwards due to the depressurization of the pressure chamber 46, hence the negative sign.

[0094] From this point forward, the phase reference point (0) or (0'') will be used as the baseline, and the time elapsed (phase advance) from the point of occurrence of each voltage step input to the baseline will be substituted into (t0-tin). This will allow us to describe the phase of each potential difference change and its composite wave with respect to the baseline point (0) or (0'').

[0095] The main acoustic vibration of the discharge waveform in Figure 6 is shown. In the discharge waveform for the first drop in Figure 6, when the potential difference is changed and a voltage for expanding the pressure chamber 46 is input as shown in (1), the pressure chamber 46 expands due to the potential difference in (1), and the pressure inside the pressure chamber 46 decreases. The vibration resulting from this is an vibration with a phase lead of -π + Dp21 / 2*(π / AL).

[0096] The potential difference change in (2), which is for shrinking the pressure chamber 46, is the opposite of the potential difference change in (1), which is for expanding it. As a result, the pressure chamber 46 shrinks and pressurizes the inside of the pressure chamber 46. Therefore, (2) is an oscillation that is phase-advancing by -Dp21 / 2*(π / AL).

[0097] If we assume a composite wave of (1) and (2) at time (0), then the composite wave of (1) and (2) will be an oscillation with a phase lead of -π / 2.

[0098] Next, we will show the main acoustic vibration of the discharge waveform at the second drop in Figure 6. When the potential difference is changed and a voltage for expanding the pressure chamber 46 is input as shown in (21), the pressure chamber 46 expands due to the potential difference in (21), and the pressure inside the pressure chamber 46 decreases. If the discharge waveform width at the second drop is Dp22, then the vibration will be phase-advancing by -π + Dp22 / 2*(π / AL).

[0099] The potential difference change (22) for shrinking the pressure chamber 46 is the opposite of the potential difference change (21) for expanding it, so the pressure chamber 46 shrinks and pressurizes the inside of the pressure chamber 46. For this reason, (22) is an oscillation that is phase-advancing by -Dp22 / 2*(π / AL).

[0100] If we assume a composite wave of (21) and (22) at time (0''), then the composite wave of (21) and (22) will be an oscillation with a phase lead of -π / 2.

[0101] Therefore, if the phase difference between (0) and (0'') is an even multiple of π (or AL if it is a time interval), the combined wave of (1) and (2) and the combined wave of (21) and (22) will have the same phase and reinforce each other. In the example in Figure 6, the time difference (time interval) 2UL between (0) and (0'') is 2AL.

[0102] Here, we consider the time difference (time interval) between (0) and (0'') for constructive interference between the amplitudes of the combined wave of (1) and (2) and the combined wave of (21) and (22). If the time difference 2UL between (0) and (0'') is greater than 1.5AL and less than 2.5AL, then the combined wave of (1) and (2) and the combined wave of (21) and (22) will reinforce each other.

[0103] As mentioned above, due to manufacturing variations, the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 will not be the same. Here, the maximum value of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 is defined as maxAL, and the minimum value as minAL. In this case, the value when 1.5AL is largest in the multiple pressure chambers 46 is 1.5maxAL, and the value when 2.5AL is smallest is 2.5minAL. Therefore, the time difference between (0) and (0'') should be set to 2UL such that 1.5AL ≤ 1.5maxAL < 2UL < 2.5minAL ≤ 2.5AL holds true. From these observations, if the time difference 2UL between (0) and (0'') of the 2drop waveform is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the aforementioned pressure chambers 46, the phase difference between the composite wave of (1) and (2) and the composite wave of (21) and (22) will be less than ±90 degrees, and the composite wave of (1) and (2) and the composite wave of (21) and (22) will reinforce each other.

[0104] Furthermore, since the time widths Dp21 of (1) and (2) and Dp22 of (21) and (22) are approximately the same, even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveform with time widths Dp21 and Dp22 will be the same. In addition, the discharge speed of the second drop, which is discharged due to the reinforcement interaction between the residual vibration from the combined wave of (1) and (2) and the combined wave of (21) and (22), will be greater than the discharge speed of the first drop. In this way, the multi-drop drive waveform that discharges multiple inks in succession as described above makes it possible to adjust the discharge speed of ink discharged later in all of the multiple pressure chambers 46 to be greater than or equal to the discharge speed of the previously discharged droplets due to the residual vibration generated by the previous discharge waveform.

[0105] Note that in the 1-drop waveform shown in Figure 9, the time and voltage height of the ejection waveform tf and tr are the same as those of the 2-drop waveform, but the 1-drop waveform may be a completely different waveform. Even in that case, in order to maintain print quality, it is necessary to reduce the difference in droplet velocity between the 1-drop waveform and the 2-drop waveform ejected from the same nozzle. In that case, the time width Dp21 (=Dp22) of the 2-drop waveform in this embodiment should be adjusted so that the velocity of each droplet in the 2-drop waveform (or the velocity of the droplet formed by the combination of droplets ejected by Dp21 and Dp22) is close to the droplet velocity of a waveform different from the 1-drop waveform in Figure 9.

[0106] Furthermore, even if you want to set Dp21 and Dp22 to different values ​​in order to fine-tune the droplet velocity of each droplet in the 2drop waveform, it is desirable to set Dp21 and Dp22 to values ​​that are as close as possible so that the pressure on the liquid in the pressure chamber 46 due to Dp21 and Dp22 is similar. For example, it is desirable that the time difference between Dp21 and Dp22 be the smallest time difference (other than zero) that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0107] For example, if the 2-drop waveform is set to Dp21 = Dp22 = 2.4 μs, UL = 3.0 μs, and Cp = 1.5 μs, then the velocity of the combined droplets produced by the 2-drop waveform will be greater than the velocity of the ejected droplets produced by the 1-drop waveform. Conversely, if the 2-drop waveform is set to Dp21 = Dp22 = 2.3 μs, UL = 3.0 μs, and Cp = 1.5 μs, then the velocity of the combined droplets produced by the 2-drop waveform will be less than the velocity of the ejected droplets produced by the 1-drop waveform.

[0108] In the drive circuit 70 of the liquid discharge head 1, if the values ​​of Dp21 and Dp22 cannot be set to values ​​between 2.3 μs and 2.4 μs, for example, Dp21 = 2.3 μs, Dp22 = 2.4 μs, UL = 3.0 μs, and Cp = 1.5 μs may be set.

[0109] Next, as an example of a multidrop waveform, we will explain the time interval of 2UL between two adjacent drop output waveforms in a 3drop waveform.

[0110] As shown in Figure 8, even with a drive waveform that dispenses 3 drops of liquid, if the time difference between (0) and (0'') is set to be greater than 1.5 maxAL and less than 2.5 minAL, the phase difference between the combined wave of (1) and (2) and the combined wave of (21) and (22) will be less than ±90 degrees in all of the multiple pressure chambers 46, and the combined wave of (1) and (2) and the combined wave of (21) and (22) (vibrations of the liquid in the pressure chamber 46) will reinforce each other. Also, if the time difference between (0'') and (0''') is set to be greater than 1.5 maxAL and less than 2.5 minAL, the phase difference between the combined wave of (21) and (22) and the combined wave of (31) and (32) will be less than ±90 degrees in all of the multiple pressure chambers 46, and the combined wave of (21) and (22) and the combined wave of (31) and (32) will reinforce each other.

[0111] Furthermore, by setting Dp31 (=Dp32=Dp33) and adjusting the time width of Dp31 (=Dp32=Dp33), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveforms with time widths of Dp31, Dp32, and Dp33 will be the same. In addition, the discharge velocity of the second drop, discharged due to the reinforcement of the residual vibrations from the combined waves of (1) and (2) and the combined waves of (21) and (22), will be greater than the discharge velocity of the first drop. Also, the discharge velocity of the third drop, discharged due to the reinforcement of the residual vibrations from the combined waves of (21) and (22) and the combined waves of (31) and (32), will be greater than the discharge velocity of the second drop. In this way, the multi-drop drive waveform that ejects multiple droplets in succession as described above allows the ejection speed of ink ejected later in all of the multiple pressure chambers 46 to be adjusted to be higher than the ejection speed of the droplets ejected beforehand, due to the residual vibrations generated by the previous ejection waveform.

[0112] In this embodiment, the 1-drop waveform and 2-drop waveform have the same tf and tr times and voltage heights as the 3-drop waveform in Figure 8, as shown in Figures 9 and 6. However, the 1-drop waveform and 2-drop waveform may be completely different. Even in that case, in order to maintain print quality, it is necessary to minimize the difference in droplet velocity between the 1-drop waveform, 2-drop waveform, and 3-drop waveform ejected from the same nozzle. Here, it is assumed that the 1-drop waveform and 2-drop waveform are adjusted so that the difference in droplet velocity between them ejected from the same nozzle is small. The time width Dp31 (=Dp32=Dp33) of the 3-drop waveform in this embodiment should be adjusted so that the velocity of each droplet in the 3-drop waveform, or the velocity of the combined droplet formed by the droplets ejected by Dp31, Dp32, and Dp33, approaches the droplet velocity of a different waveform from the 1-drop waveform in Figure 9 and the 2-drop waveform in Figure 6.

[0113] Furthermore, even if you want to set Dp31, Dp32, and Dp33 to different values ​​in order to fine-tune the droplet velocity of each droplet in the 3drop waveform, it is desirable to set Dp31, Dp32, and Dp33 to values ​​as close as possible so that the pressure on the liquid in the pressure chamber 46 caused by Dp31, Dp32, and Dp33 is similar. For example, it is desirable that the time difference between Dp31, Dp32, and Dp33 be the smallest time difference other than zero that can be set in the drive circuit 70 that generates the corresponding drive waveform.

[0114] For example, if the 3-drop waveform is set to Dp31=Dp32=Dp33=2.4μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets produced by the 3-drop waveform will be greater than the velocity of the ejected droplets produced by the 1-drop waveform. Conversely, if the 3-drop waveform is set to Dp31=Dp32=Dp33=2.3μs, UL=3.0μs, and Cp=1.5μs, then the velocity of the combined droplets produced by the 3-drop waveform will be less than the velocity of the ejected droplets produced by the 1-drop waveform.

[0115] In the drive circuit 70 of the liquid discharge head 1, if the values ​​of Dp31, Dp32, and Dp33 cannot be set to values ​​between 2.4 μs and 2.3 μs, for example, set Dp31=Dp32=2.3 μs, Dp33=2.4 μs, UL=3.0 μs, and Cp=1.5 μs. Alternatively, set Dp31=2.3 μs, Dp32=Dp33=2.4 μs, UL=3.0 μs, and Cp=1.5 μs.

[0116] Furthermore, even with a drive waveform that discharges in n-drop increments, if the phase reference point of any discharge waveform from the 1st to the (n-1)th drop is set to (0), and the phase reference point of the discharge waveform of the next drop is set to (0''), and the time difference between (0) and (0'') is set to be greater than 1.5 maxAL and less than 2.5 minAL, then in all of the aforementioned pressure chambers 46, all discharge waveforms discharged from the 2nd drop onward will reinforce each other with the residual vibrations of the previous discharge waveform. Also, by setting all discharge waveform widths to Dpn1 (=Dpn2=~=Dpnn) and adjusting the time width of Dpn1 (=Dpn2=~=Dpnn), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the discharge waveforms with time widths of Dpn1, Dpn2, and ~Dpnn will be the same. In this way, the multi-drop drive waveform that ejects multiple inks in succession allows the ejection speed of the ink ejected later in all of the multiple pressure chambers 46 to be adjusted to be higher than the ejection speed of the droplets ejected beforehand, due to the residual vibrations generated by the previous ejection waveform.

[0117] Furthermore, the ejection waveforms for the ndrop waveform and the drive waveform for ejecting a number of drops other than n may be completely different. Even in this case, in order to maintain print quality, it is necessary to minimize the difference in droplet velocity ejected from the same nozzle between the ndrop waveform and the drive waveform for ejecting a number of drops other than n. Here, it is assumed that the drive waveform for ejecting a number of drops other than n is adjusted so that the difference in droplet velocity ejected from the same nozzle is minimized. The time width Dpn1 (=Dpn2=~=Dpnn) of the ndrop waveform in this embodiment should be adjusted so that the velocity of each droplet in the ndrop waveform, or the velocity of the droplet formed by the merging of droplets ejected by Dpn1~Dpnn, approaches the droplet velocity of the drive waveform for ejecting a number of drops other than n. Furthermore, in drive waveforms that eject multiple numbers of drops, if the time elapsed after ejection is short, multiple droplets exist before merging. Also, satellites may occur after multiple droplets. When comparing droplet velocities under different drive waveforms with varying drop counts before multiple droplets merge, the time width Dpn1 (=Dpn2=~=Dpnn) of the ndrop waveform should be adjusted so that the velocity of the droplet with the largest volume (largest droplet diameter) among those ejected by the ndrop waveform is similar to (more preferably nearly identical to) the velocity of the droplet with the largest volume (largest droplet diameter) among those ejected by drive waveforms with a drop count other than n.

[0118] Furthermore, even if you want to set Dpn1, Dpn2, ..., Dpnn to different values ​​in order to fine-tune the droplet velocity of each droplet in the ndrop waveform, it is desirable to set Dpn1 to Dpnn to values ​​as close as possible so that the pressure on the liquid in the pressure chamber 46 due to Dpn1 to Dpnn is similar. For example, it is desirable that the time difference between Dpn1, Dpn2, ..., Dpnn be the smallest time difference (other than zero) that can be set in the drive circuit that generates the corresponding drive waveform.

[0119] Furthermore, although the above example describes a liquid discharge head 1 that outputs a drive waveform with a square wave discharge waveform, the invention is not limited to this. For example, the discharge waveform may be a waveform having an intermediate voltage. Below, an example of a liquid discharge head 1 that outputs a drive waveform having an intermediate voltage will be described as another embodiment. In this embodiment, components similar to those in the above embodiment are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0120] First, the drive circuit 70 of the liquid discharge head 1 will be explained using Figure 25. As shown in Figure 25, in the drive circuit of the liquid discharge head 1 according to another embodiment, the drive circuit 70 includes, for example, a voltage control unit 724 and the same number of voltage switching units 725 as the pressure chambers 46, within the driver IC 72. However, in Figure 25, two voltage switching units 725 are shown, and the other voltage switching unit 725 is not shown.

[0121] The drive circuit 70 is connected to the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85. The drive circuit 70 applies the voltage supplied from the first voltage source 81 to each wiring electrode 726. The drive circuit 70 also selectively applies the voltage supplied from the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85 to each wiring electrode 727. Here, since the actuator 20 is a stacked PZT, applying bipolar voltage tends to degrade it, the voltages supplied by the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source 84, and the fifth voltage source 85 are set to either the ground voltage or one of either positive or negative polarity relative to the ground voltage.

[0122] The output voltage of the first voltage source 81 is, for example, the ground voltage, and its voltage value is V0 (V0 = 0 [V]). The voltage value indicated by the output voltage of the second voltage source 82 is V1. Note that the voltage value V1 is higher than V0. The voltage value indicated by the output voltage of the third voltage source 83 is, for example, V2. Note that the voltage value V2 is higher than V0 and lower than V1. The voltage value indicated by the output voltage of the fourth voltage source 84 is V3. Note that the voltage value V3 is lower than V0. The voltage value indicated by the output voltage of the fifth voltage source 85 is, for example, V4. Note that the voltage value V4 is lower than V0 and higher than V3.

[0123] The wiring electrode 726 is connected to a common electrode that serves as the ground electrode of the actuator 20. The multiple wiring electrodes 727 are each connected to individual electrodes that serve as non-ground electrodes of the actuator 20.

[0124] The voltage control unit 724 is connected to each of the multiple voltage switching units 725. The voltage control unit 724 outputs a command to each voltage switching unit 725 indicating which voltage source to select from the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85. For example, the voltage control unit 724 receives an image signal from the control unit 150 and determines the switching timing of the voltage source in each voltage switching unit 725. Then, at the determined switching timing, the voltage control unit 724 outputs a command to the voltage switching unit 725 to select one of the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85. The voltage switching unit 725 switches the voltage source connected to the wiring electrode 727 according to the command from the voltage control unit 724.

[0125] The voltage switching unit 725 is composed of, for example, a semiconductor switch. The voltage switching unit 725 connects the wiring electrode 727 to one of the first voltage source 81, second voltage source 82, third voltage source 83, fourth voltage source 84, and fifth voltage source 85 under the control of the voltage control unit 724. Therefore, the internal electrodes of different poles of the piezoelectric column 21 are connected to the wiring electrode 726 and the wiring electrode 727 via external electrodes (common electrode and individual electrode).

[0126] In this drive circuit 70, the drive circuit switches the connection wiring between the voltage sources 81, 82, 83, 84, and 85 and the actuator 20 using a switching circuit composed of a voltage control unit 724 and multiple voltage switching units 725, thereby inputting drive waveforms with at least three types of potential differences between the electrodes of the actuator 20 as drive signals. Here, the drive waveform is the discharge waveform that ejects droplets when the actuator 20 is driven. In this embodiment, potential differences other than the largest and smallest potential differences are called intermediate potential differences.

[0127] Figure 26 shows an example of a drive waveform in which two consecutive ejection waveforms are input at a predetermined interval when ejecting ink from the liquid ejection head 1. Figure 27 also shows an example of an ejection waveform. In Figures 26 and 27, the vertical axis is voltage (potential difference) and the horizontal axis is time. The drive waveform is generated by the driver IC 72 of the drive circuit 70. As shown in Figure 26, in both the two ejection waveforms and the cancellation waveform, the drive waveform reduces the expansion potential difference in two stages when the pressure chamber 46 expands, and increases the contraction potential difference in two stages when the pressure chamber 46 contracts during ejection. In addition, when changing the potential difference during both the expansion and contraction of the pressure chamber 46, after applying the first potential difference, the first potential difference is maintained for a predetermined time, and then the second potential difference is applied. If the pressure chamber 46 expands when the voltage (potential difference) is reduced, the voltage (potential difference) is increased in advance to contract the pressure chamber 46 before the ejection waveform is input.

[0128] First, we will specifically explain an example of the ejection waveform for the first drop of the drive waveform using Figures 26 and 27. As shown in Figure 27, when the pressure chamber 46 is expanded in advance before ink ejection, Dp is defined as the time interval from the start of the first expansion due to the expanding potential difference when the potential difference is reduced twice in a row, to the start of the first contraction due to the shrinking potential difference after the potential difference has been reduced twice in a row by the expanding potential difference. Also, as shown in Figure 27, when the pressure chamber 46 is contracted during ejection, Dp is defined as the time interval from the start of the second expansion due to the expanding potential difference when the potential difference is reduced twice in a row before the potential difference is increased, to the start of the second contraction due to the shrinking potential difference when the potential difference has been reduced twice in a row by the expanding potential difference and then increased twice in a row by the shrinking potential difference.

[0129] Furthermore, the time interval Dp is greater than 0.5 AL and less than 1.5 AL. More preferably, Dp = AL. This is because if Dp is greater than 0.5 AL and less than 1.5 AL, reinforcement occurs between the main acoustic vibration generated by expanding the pressure chamber 46 before discharge and the main acoustic vibration generated by contracting the pressure chamber 46 during discharge.

[0130] Furthermore, when the time width Tm is less than 0.5 AL, the main acoustic vibrations caused by the two rising waveforms in Figure 27 reinforce each other. By adjusting the time width Tm, the reinforcement of the main acoustic vibrations caused by the two rising waveforms can be adjusted, and the discharge force of the droplets caused by the discharge waveform in Figure 27 can be adjusted. Also, by making Tm less than 0.5 min AL, the main acoustic vibrations caused by the two rising waveforms in Figure 27 reinforce each other in all of the pressure chambers 46 into which the same drive waveform is input.

[0131] Furthermore, in the drive waveform of Figure 26, since the Tm22 of the discharge waveform of the 2nd drop is smaller than the Tm21 of the discharge waveform of the 1st drop, the constructive interference of the main acoustic vibrations due to the rising waveforms of (23) and (24) is greater than that of (3) and (4). The constructive interference of the main acoustic vibrations due to the falling waveforms of (21) and (22) is also greater than that of (1) and (2). Also, since Dp21 is the same as Dp22, the constructive interference of the main acoustic vibrations of (1) and (3) is the same as that of (21) and (23). The constructive interference of the main acoustic vibrations of (2) and (4) is also the same as that of (22) and (24). Therefore, even if pressure chambers 46 with different ALs are driven with the waveforms of Figure 26, the relative magnitude of the discharge forces between the two, that the discharge force of the discharge waveform of the 2nd drop is greater than that of the discharge waveform of the 1st drop, remains unchanged. For this reason, the discharge velocity of the 2nd drop is greater than that of the 1st drop.

[0132] In the drive waveform shown in Figure 26, the velocity difference between the first and second drops is adjusted by adjusting Tm21 and Tm22 within a range smaller than 0.5 minAL. Furthermore, by adjusting the magnitude of Dp21=Dp22, the velocity of the droplets discharged can be made approximately the same as those discharged by other drive waveforms with different discharge volumes.

[0133] For the sake of explanation, in Figure 26, the first to fourth potential difference changes in the discharge waveform of the first drop will be denoted as (1) to (4), and the first to fourth potential difference changes in the discharge waveform of the second drop will be denoted as (21) to (24) for the following explanation. Also, the reference point for the phase of the discharge waveform of the first drop will be (0), and the reference point for the phase of the discharge waveform of the second drop will be denoted as (0'') for the following explanation. Here, the reference point for the phase of the discharge waveform of the first drop (0) is set midway between potential difference changes (2) and (3), and the reference point for the phase of the discharge waveform of the second drop (0'') is set midway between potential difference changes (22) and (23). Furthermore, the voltage drop time tf in Figure 26 is assumed to be approximately the same as the voltage rise time tr in Figure 26. Furthermore, the amount of potential difference change in (1), (2), (21), and (22), and the amount of potential difference change in (3), (4), (23), and (24) (the amount of height change in Figure 26) are assumed to be approximately the same.

[0134] The main acoustic vibration of the discharge waveform for the first drop shown in Figure 26 will now be explained. As shown in Figure 26, in the discharge waveform for the first drop, a potential difference change is performed, and when a voltage for expanding the pressure chamber 46 is input as shown in (1), the pressure chamber 46 expands due to the potential difference in (1), and the pressure inside the pressure chamber 46 decreases. The vibration resulting from this is an vibration with a phase lead of -π + (Dp21 + Tm21) / 2*(π / AL). Furthermore, when the potential difference change shown in (2) is performed, the vibration in (2) is an oscillation with a phase lead of -π + (Dp21 - Tm21) / 2*(π / AL). The composite wave of (1) and (2) is an oscillation with a phase lead of -π + Dp21 / 2*(π / AL).

[0135] The potential difference changes in (3) and (4), which are for shrinking the pressure chamber 46, are the opposite of the potential difference changes in (1) and (2), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (3) is an oscillation with a phase lead of -(Dp21-Tm21) / 2*(π / AL). Similarly, (4) can be considered an oscillation with a phase lead of -(Dp21+Tm21) / 2*(π / AL). Therefore, the combined wave of (3) and (4) is an oscillation with a phase lead of -Dp21 / 2*(π / AL).

[0136] If we assume a composite wave of (1), (2), (3), and (4) at time (0), then the composite wave of (1), (2), (3), and (4) will be an oscillation with a phase lead of -π / 2.

[0137] Next, we will discuss the main acoustic oscillation of the discharge waveform at the second drop in Figure 26. When the potential difference is changed and a voltage for expanding the pressure chamber 46 is input as shown in (21), the pressure chamber 46 expands due to the potential difference in (21), and the pressure inside the pressure chamber 46 decreases. If the discharge waveform width at the second drop is Dp22, then the oscillation will be advanced in phase by -π + (Dp22 + Tm22) / 2*(π / AL). Furthermore, when the potential difference is changed as shown in (22), in (22), it can be considered that the oscillation is advanced in phase by -π + (Dp22 - Tm22) / 2*(π / AL). Therefore, the composite wave of (21) and (22) will be an oscillation advanced in phase by -π + Dp22 / 2*(π / AL).

[0138] The potential difference changes (23) and (24), which are for shrinking the pressure chamber 46, change in the opposite direction to the potential difference changes (21) and (22), which are for expanding the pressure chamber 46. As a result, the pressure chamber 46 shrinks and pressurizes inside the pressure chamber 46. Therefore, (23) becomes an oscillation with a phase lead of -(Dp22-Tm22) / 2*(π / AL). Similarly, (24) becomes an oscillation with a phase lead of -(Dp22+Tm22) / 2*(π / AL). Therefore, the combined wave of (23) and (24) becomes an oscillation with a phase lead of -Dp22 / 2*(π / AL).

[0139] If we assume a composite wave of (21), (22), (23), and (24) at time (0''), then the composite wave of (21), (22), (23), and (24) will be an oscillation with a phase lead of -π / 2.

[0140] Therefore, if the phase difference between (0) and (0'') is an even multiple of π (or AL if time interval), the composite waves of (1), (2), (3), and (4) and the composite waves of (21), (22), (23), and (24) will have the same phase and reinforce each other. In the example shown in the figure, the time difference (time interval) between (0) and (0'') is 2AL.

[0141] Here, we consider the time difference (time interval) between (0) and (0'') that causes constructive interference between the combined waves of (1), (2), (3), and (4) and the combined waves of (21), (22), (23), and (24). If the time difference between (0) and (0'') 2UL is greater than 1.5AL and less than 2.5AL, then the combined waves of (1), (2), (3), and (4) and the combined waves of (21), (22), (23), and (24) cause constructive interference.

[0142] Furthermore, due to manufacturing variations, the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 of the liquid discharge head 1 will not be the same. Here, the maximum value of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 is defined as maxAL, and the minimum value as minAL. In this case, the value when 1.5AL is largest in the multiple pressure chambers 46 is 1.5maxAL, and the value when 2.5AL is smallest is 2.5minAL. Therefore, the time difference between (0) and (0'') should be set to 2UL such that 1.5AL ≤ 1.5maxAL < 2UL < 2.5minAL ≤ 2.5AL holds true. From this, if the time difference 2UL between (0) and (0'') of the 2drop waveform shown in Figure 26 is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the above-mentioned pressure chambers 46, the phase difference between the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will be less than ±90 degrees, and the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will reinforce each other.

[0143] As described above, even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the ejection force of the second drop ejection waveform of the drive waveform in Figure 26 is greater than the ejection force of the first drop ejection waveform. In addition, the ejection speed of the second drop, which is ejected due to the reinforcement of the residual vibrations from the composite waves of (1), (2), (3), and (4) and the composite waves of (21), (22), (23), and (24), is greater than the ejection speed of the first drop. In this way, with the multi-drop drive waveform that ejects multiple inks in succession as shown in Figure 26, the ejection speed of the ink ejected later can be adjusted to be greater than or equal to the ejection speed of the previously ejected droplets due to the residual vibrations generated by the previous ejection waveform in all of the multiple pressure chambers 46.

[0144] Although Figure 26 shows the case of 2 drops, even in drive waveforms that eject 3 or more droplets, by making the Dp width of all ejection waveforms the same and making the intermediate voltage time of the ejection waveform of the subsequent ejected droplet smaller than 0.5 minAL than the previous ejection waveform, it is possible to adjust the ejection speed of the ink ejected later in all of the multiple pressure chambers 46 to be greater than the ejection speed of the previously ejected droplet due to residual vibrations generated by the previous ejection waveform. This is because the shorter the intermediate voltage time Tm, the greater the reinforcement of the main acoustic vibrations by the rising and falling waveforms, for example, shown in Figure 27. Here, let's consider the case where the intermediate voltage time of the first ejection waveform of the ndrop waveform is Tmn1, the intermediate voltage time of the last ejection waveform is Tmnn, and we number them sequentially from Tmn1 to Tmnn. To adjust the droplet ejection speed, if any Tm time from Tmn1 to Tmnn is made shorter than the previous Tm time, it is desirable that subsequent Tm times be less than or equal to the time of the aforementioned arbitrary Tm time in order to maintain or increase the droplet speed with the subsequent ejection waveform. In this case, the last Tm (=Tmnn) will be shorter than the first Tm (=Tmn1). Furthermore, by adjusting the Dp width while keeping the Dp width the same for all ejection waveforms, it is possible to make the droplet speed approximately the same as that of droplets ejected by other drive waveforms with different ejection volumes.

[0145] Next, we will explain examples of drive waveforms for other embodiments using Figure 28. The drive waveform in Figure 28 is the same as the drive waveform in Figure 26, but with Tm22 set to zero. In the waveform of Figure 28, we can consider that Tm22 of the discharge waveform at the second drop is zero and smaller than Tm21 of the discharge waveform at the first drop, so the amplitude of the main acoustic vibration from the rising waveform of (22) is larger than the combined wave of the main acoustic vibration from the rising waveforms of (3) and (4). The amplitude of the main acoustic vibration from the falling waveform of (21) is larger than the combined wave of the main acoustic vibration from the falling waveforms of (1) and (2). Also, since Dp21 is the same as Dp22, the amplitude of the main acoustic vibration from the combined wave of (21) and (22) is larger than the combined wave of (1), (2), (3) and (4). Therefore, even if the pressure chambers 46 with different AL values ​​are driven by the waveforms in Figure 28, the relative magnitude of the discharge forces remains unchanged: the discharge force of the second drop's discharge waveform is greater than that of the first drop's discharge waveform. For this reason, the discharge velocity of the second drop is greater than that of the first drop.

[0146] In the waveform shown in Figure 28, the velocity difference between the first and second drops in the waveform shown in Figure 26 is adjusted by adjusting Tm21 to a range smaller than 0.5minAL. Furthermore, by adjusting the magnitude of Dp21=Dp22, the velocity of the droplets discharged can be made approximately the same as those discharged by other drive waveforms with different discharge volumes.

[0147] As explained above in the description of the waveform in Figure 26, assuming a composite wave of (1), (2), (3), and (4) at time (0), the composite wave of (1), (2), (3), and (4) will have an oscillation with a phase lead of -π / 2.

[0148] As explained above in the description of the waveform in Figure 6, assuming a composite wave of (21) and (22) at time (0''), the composite wave of (21) and (22) will have an oscillation with a phase lead of -π / 2.

[0149] Therefore, if 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) and the composite waves of (21) and (22) will have the same phase and reinforce each other. In the example in Figure 28, the time difference (time interval) 2UL between (0) and (0'') is 2AL.

[0150] Here, we consider the time difference (time interval) between (0) and (0'') that causes constructive interference between the amplitudes of the composite wave of (1), (2), (3), and (4) and the composite wave of (21) and (22). If the time difference 2UL between (0) and (0'') is greater than 1.5AL and less than 2.5AL, then the composite wave of (1), (2), (3), and (4) and the composite wave of (21), (22), (23), and (24) will cause constructive interference.

[0151] Furthermore, due to manufacturing variations, the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 of the liquid discharge head 1 will not be the same. Here, the maximum value of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 is defined as maxAL, and the minimum value as minAL. In this case, the value when 1.5AL is largest in the multiple pressure chambers 46 is 1.5maxAL, and the value when 2.5AL is smallest is 2.5minAL. Therefore, the time difference between (0) and (0'') should be set to 2UL such that 1.5AL ≤ 1.5maxAL < 2UL < 2.5minAL ≤ 2.5AL holds true. From this, if the time difference 2UL between (0) and (0'') of the 2drop waveform shown in Figure 28 is set to be greater than 1.5maxAL and less than 2.5minAL, then in all of the above-mentioned pressure chambers 46, the phase difference between the composite wave of (1), (2), (3), and (4) and the composite wave of (21) and (22) will be less than ±90 degrees, and the composite wave of (1), (2), (3), and (4) and the composite wave of (21) and (22) will reinforce each other.

[0152] Furthermore, even when AL drives different pressure chambers 46 with the waveforms shown in Figure 28, the ejection force of the second drop's ejection waveform is greater than that of the first drop's ejection waveform. In addition, the ejection speed of the second drop, which is ejected due to the reinforcement between the residual vibrations from the combined waves of (1), (2), (3), and (4) and the combined waves of (21) and (22), is greater than that of the first drop. Thus, with the multi-drop drive waveforms that eject multiple inks in succession as shown in Figure 28, the ejection speed of the ink ejected later can be adjusted to be greater than or equal to the ejection speed of the previously ejected droplets in all of the multiple pressure chambers 46 due to the residual vibrations generated by the previous ejection waveform.

[0153] Although Figure 28 shows the case of 2 drops, even in drive waveforms that eject 3 or more droplets, by setting the initial ejection waveforms to have an intermediate voltage like the first drop in Figure 28, and the ejection waveforms from the middle to the end to have no intermediate voltage like the second drop in Figure 28, setting the Dp width of all ejection waveforms to be the same, and making the intermediate voltage time of the ejection waveform of subsequent ejected droplets smaller than 0.5 minAL in the ejection waveforms with an intermediate voltage, the ejection speed of ink ejected later can be adjusted in all of the multiple pressure chambers 46 to be greater than or equal to the ejection speed of previously ejected droplets due to residual vibrations caused by the previous ejection waveform. More preferably, only the last ejection waveform is an ejection waveform without an intermediate voltage like the second drop in Figure 28, and all ejection waveforms other than the last one are ejection waveforms with an intermediate voltage like the first drop in Figure 28. That is, it is preferable that the drive waveform is one in which the number of potential difference changes of the first ejection waveform, or all ejection waveforms other than the last one, is greater than the number of potential difference changes of the last ejection waveform. Furthermore, by adjusting the Dp width while keeping it the same for all discharge waveforms, it is possible to make the droplet velocity approximately the same as that of droplets discharged by other drive waveforms with different discharge volumes.

[0154] Furthermore, in the example described above, an example was explained in which the time difference (center-to-center distance) 2UL between adjacent discharge waveforms is set to be greater than 1.5 maxAL and less than 2.5 minAL in order to strengthen the residual vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated first and the vibration of the liquid in the pressure chamber 46 generated by the discharge waveform generated afterward. However, the liquid discharge head 1 according to the embodiment is not limited to this configuration.

[0155] Specifically, the drive waveform includes multiple discharge waveforms, and any one of the discharge waveforms from the 1st drop onward is designated as drop a, and any one of the discharge waveforms after drop a is designated as drop b. In this case, the time difference 2*(ba)*UL between the centers of the discharge waveforms of drop a and drop b is set to be greater than (2*(ba)-0.5) times the maximum value (maxAL) of the half-period AL of the main acoustic vibration frequency of the multiple pressure chambers 46 whose volume is varied by the actuator 20 that inputs the drive signal, and less than (2*(ba)+0.5) times the minimum value (minAL) of the half-period AL. As a result, when there are two discharge waveforms, or three or more discharge waveforms, the time difference 2UL between adjacent discharge waveforms is 1.5maxAL < 2UL < 2.5minAL, as described above. Furthermore, in the case of a drive waveform containing three or more discharge waveforms, the time difference 2*(ba)*UL between two discharge waveforms that are not adjacent but have one or more discharge waveforms in between is (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. In this way, by setting the time difference of at least two of the multiple discharge waveforms contained in the drive waveform to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL, the discharge velocity of subsequent droplets increases due to the reinforcement of residual vibrations and discharge waveforms.

[0156] A liquid discharge head 1 according to another embodiment will be described with reference to Figures 8 and 29. Figure 29 is an explanatory diagram showing an example of a drive waveform for discharging ndrop droplets, as an example of a drive waveform for a liquid discharge head 1 according to another embodiment.

[0157] First, in the drive waveforms that dispense three or more droplets as shown in Figures 8 and 29, each droplet from the third drop to the ndorp is affected by the discharge waveforms of the preceding droplets. A specific example will be explained below.

[0158] For example, using the example of a drive waveform for dispensing three droplets shown in Figure 8, the third droplet is affected not only by the dispensing waveform of the second droplet but also by the dispensing waveform of the first droplet. Therefore, even if the dispensing waveforms for the second and third droplets reinforce each other, if the dispensing waveforms for the first and third droplets destructively cancel each other out, the dispensing force of the third droplet will be weakened by the influence of the dispensing waveform of the first droplet, raising concerns that the velocity of the third droplet will not increase sufficiently and it will not catch up with the preceding droplets.

[0159] Therefore, in the 3-drop waveform, the waveform for ejecting the first drop and the waveform for ejecting the third drop may reinforce each other. For example, as shown in Figure 8, if the time difference 4UL between (0) and (0''') is set to be greater than 3.5 maxAL and less than 4.5 minAL, then in all of the above-mentioned pressure chambers 46, the phase difference between the composite wave of (1) and (2) and the composite wave of (31) and (32) will be less than ±90 degrees. As a result, the composite wave of (1) and (2) and the composite wave of (31) and (32) will reinforce each other. Also, by setting Dp31 (=Dp32=Dp33) and adjusting the time width of Dp31 (=Dp32=Dp33), even if the half-period AL of the main acoustic vibration frequency of the pressure chamber 46 is different from the waveform UL, the pressure exerted on the liquid in the corresponding pressure chamber 46 by the ejection waveforms with time widths of Dp31, Dp32, and Dp33 will be the same. In addition, the discharge velocity of the third drop, which is discharged due to the reinforcement of the residual vibrations from the combined waves of (1) and (2) and the combined waves of (31) and (32), is greater than the discharge velocity of the first drop.

[0160] Furthermore, as shown in Figure 29, in a drive waveform (ndrop waveform) that continuously dispenses multiple n droplets, we consider the dispensing waveform of the adrop (after the 1st drop) and the dispensing waveform of the bdrop (two drops after the adrop, but before the ndrop), which is designated as the bdrop. In Figure 29, the reference point for the phase of the ndrop dispensing waveform is shown as (0n). In such a drive waveform that dispenses ndrops, it is conceivable that the bdrop is affected by the dispensing waveform of the adrop. If the dispensing waveform of the adrop and the dispensing waveform of the bdrop cancel each other out, the dispensing force of the bdrop will be weakened by the influence of the adrop's dispensing waveform, raising concerns that the bdrop's velocity will not increase sufficiently and will not catch up with the preceding droplets. Therefore, if we set the reference point for the phase of the discharge waveform of the adrop to (0a) and the reference point for the phase of the discharge waveform of the bdrop, which is 2 drops later than the adrop, to (0b), and set the time difference 4UL between (0a) and (0b) to be greater than 3.5*maxAL and less than 4.5*minAL, then in all of the aforementioned pressure chambers 46, the residual vibrations of the adrop and bdrop discharge waveforms will reinforce each other.

[0161] Furthermore, in a drive waveform (ndrop waveform) that continuously dispenses multiple n droplets, we consider the dispensing waveform of the adrop (after the 1st drop) and the dispensing waveform of the bdrop (after the adrop but before the ndrop). In a drive waveform that dispenses bdrop or more droplets, it is conceivable that the bdrop droplet will be affected by the dispensing waveform of the adrop. If the dispensing waveform of the adrop droplet and the dispensing waveform of the bdrop droplet are in a destructive relationship, the dispensing force of the bdrop will be weakened by the influence of the adrop dispensing waveform, raising concerns that the velocity of the bdrop will not increase sufficiently and will not catch up with the preceding droplets. Therefore, if we set the reference point for the phase of the discharge waveform of the adrop to (0a) and the reference point for the phase of the discharge waveform of the bdrop to (0b), and set the time difference between (0a) and (0b) 2*(ba)*UL to be greater than (2*(ba)-0.5)*maxAL and less than (2*(ba)+0.5)*minAL, then in all of the aforementioned pressure chambers 46, the residual vibrations of the discharge waveform of the adrop and the discharge waveform of the bdrop will reinforce each other.

[0162] In the ndrop waveform, which dispenses multiple droplets as described above, any one of the dispensing waveforms after the first drop is designated as the adrop, and any one of the dispensing waveforms after the adrop is designated as the bdrop. The liquid dispensing head 1 sets the time interval (time difference) 2*(ba)*UL between the centers of the adrop and bdrop dispensing waveforms to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL. This causes the residual vibration from the earlier (adrop) dispensing waveform and the vibration from the subsequent (bdrop) dispensing waveform to reinforce each other, thereby increasing the dispensing speed.

[0163] Furthermore, the two discharge waveforms whose time difference 2*(ba)*UL is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL may be any combination of the two discharge waveforms from the multiple discharge waveforms of the ndrop waveform, or any one or more combinations of the two discharge waveforms.

[0164] Next, when there is variation in the principal acoustic vibration frequencies of multiple pressure chambers 46, we consider dividing the multiple pressure chambers 46 into multiple groups and adjusting the drive waveform to match the maximum and minimum values ​​of the half-period AL of the principal acoustic vibration frequency of each group, and then inputting it. For example, if the maximum value of the half-period AL of the principal acoustic vibration frequencies of multiple pressure chambers 46 is 3.5 μs and the minimum value is 2.5 μs, then pressure chambers 46 with AL between 3.5 μs and 3.0 μs or more are designated as the first group, and pressure chambers 46 with AL between 3.0 μs and 2.5 μs or more are designated as the second group. Here, a pressure chamber 46 that satisfies the conditions of both the first and second groups (for example, a pressure chamber 46 with AL of 3.0 μs) is assigned to one of the groups. For example, if a group of pressure chambers 46 that satisfies the conditions of both the first and second groups is the same as a group of adjacent pressure chambers 46, then the management and distinction of each group becomes simpler.

[0165] As a result, the maxAL of the pressure chamber 46 of the first group becomes 3.5 μs and the minAL becomes 3.0 μs. The time interval (time difference) 2*(ba)*UL between the centers of the a-drop discharge waveform and the b-drop discharge waveform of the n-drop waveform input to the pressure chamber 46 of the first group is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL.

[0166] Furthermore, the maxAL of the pressure chamber 46 in the second group is 3.0 μs, and the minAL is 2.5 μs. The time interval (time difference) 2*(ba)*UL between the centers of the a-drop discharge waveform and the b-drop discharge waveform of the n-drop waveform input to the pressure chamber 46 in the second group is set to (2*(ba)-0.5)*maxAL < 2*(ba)*UL < (2*(ba)+0.5)*minAL.

[0167] According to the liquid discharge head of at least one embodiment described above, the waveform widths of the multiple discharge waveforms that discharge multiple droplets are made substantially the same and different from half a period of the main acoustic vibration frequency. The interval between the multiple discharge waveforms is set to match the period that strengthens the residual vibration of the liquid in the pressure chamber generated by the first discharge waveform and the period that strengthens the vibration of the liquid in the pressure chamber generated by the subsequent discharge waveform. As a result, the liquid discharge head can make the discharge force of each droplet substantially the same, i.e., approximate or identical, and increase the discharge speed of subsequent droplets.

[0168] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0169] 1…Liquid discharge 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 discharge device, 111…Housing, 112…Media supply unit, 113…Image forming unit, 114…Media discharge unit, 115…Conveying device, 117…Support unit, 118…Conveying bell T, 119...Support plate, 120...Belt roller, 121...Guide plate pair, 122...Transport roller, 130...Head unit, 132...Ink tank, 133...Connection channel, 134...Supply pump, 150...Control unit, 151...Processor, 154...I / O port, 155...Image memory, 161...Drive motor, 162...Operation unit, 163...Type sensor, 200...External connection device, 301...Vibration part, 721...Data buffer, 722...Decoder, 723...Driver, 724...Voltage control unit, 725...Voltage switching unit, 726...Wiring electrode, 727...Wiring electrode.

Claims

1. A nozzle plate equipped with a nozzle for dispensing liquid, A pressure chamber communicating with the nozzle, An actuator that varies the volume of the pressure chamber in response to a drive signal, The system comprises a drive circuit that generates the drive signal for driving the actuator, The drive signal includes a plurality of discharge waveforms that cause a plurality of droplets to be discharged from the nozzle. The waveform widths of the aforementioned multiple discharge waveforms are approximately the same, and differ from half a period of the main acoustic vibration frequency. A liquid discharge head in which the intervals between the multiple discharge waveforms match the period that amplifies the residual vibration of the liquid in the pressure chamber caused by the discharge waveform generated first and the vibration of the liquid in the pressure chamber caused by the discharge waveform generated afterward.

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

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

4. The output waveform of the drive signal includes an expanding potential difference that expands the volume of the pressure chamber, a reducing potential difference that reduces the volume of the pressure chamber, and at least one intermediate potential difference between the expanding potential difference and the reducing potential difference. The liquid dispensing head according to claim 1, wherein the time interval of the intermediate potential difference of any of the plurality of dispensing waveforms is greater than or equal to the time interval of the intermediate potential difference of the next dispensing waveform after the arbitrary dispensing waveform.

5. At least one of the output waveforms of the drive signal includes an expansion potential difference that expands the volume of the pressure chamber, a reduction potential difference that reduces the volume of the pressure chamber, and at least one intermediate potential difference between the expansion potential difference and the reduction potential difference. The liquid dispensing head according to claim 1, wherein the number of potential difference changes of the first dispensing waveform among the plurality of dispensing waveforms is greater than the number of potential difference changes of the last dispensing waveform.

6. The drive circuit selectively generates the drive signal and one or more other drive signals with different discharge volumes from the drive signal. The waveform widths of the plurality of discharge waveforms included in the drive signal are: The waveform width is such that the velocity of the droplet ejected by the aforementioned drive signal and the velocity of the droplet ejected by at least one of the other drive signals are approximately the same. A liquid dispensing head according to any one of claims 1 to 5.

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