inkjet head

Abstract

The present application provides an inkjet head capable of suppressing atomization at the time of ink ejection. The inkjet head of the embodiment includes an ink ejection portion and an actuator drive circuit. The ink ejection portion includes a nozzle that ejects ink, an ink pressure chamber that communicates with the nozzle, and an actuator that changes the volume of the ink pressure chamber; the actuator drive circuit applies a drive signal including a drive waveform of an ejection pulse portion to the actuator, the ejection pulse portion changes from a first voltage to a second voltage that expands the ink pressure chamber compared to the first voltage, and then changes to a third voltage that contracts the ink pressure chamber with a potential between the second voltage and the first voltage to eject ink from the nozzle, and in the drive waveform, the potential difference between the second voltage and the third voltage is greater than the potential difference between the third voltage and the first voltage.

Description

Technical Field

[0001] Embodiments of the present invention relate to inkjet heads. Background Technology

[0002] An inkjet head is known as an ink-ejecting head. The inkjet head drives an actuator to change the volume of the ink pressure chamber, and ejects ink droplets from a nozzle connected to the ink pressure chamber. Inkjet heads are primarily mounted in inkjet printers. The inkjet printer ejects ink droplets from the inkjet head to form images, etc., on the surface of a recording medium.

[0003] Various studies have been conducted on the drive waveforms that enable the actuator to eject ink. One type of drive waveform involves expanding the ink pressure chamber and then partially contracting it to eject the ink droplet. This drive waveform is sometimes referred to as the DD (Draw-Draw) drive waveform. However, in actual attempts to eject ink using this drive waveform, especially the very first droplet, it can sometimes atomize. Ink atomization can contribute to reduced print quality. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an inkjet head that can suppress atomization during ink ejection.

[0005] An inkjet head according to an embodiment of the present invention includes an ink ejection section and an actuator drive circuit. The ink ejection section includes a nozzle for ejecting ink, an ink pressure chamber communicating with the nozzle, and an actuator for changing the volume of the ink pressure chamber; the actuator drive circuit applies a drive signal including a drive waveform of an ejection pulse to the actuator, wherein the ejection pulse changes from a first voltage to a second voltage that expands the ink pressure chamber relative to the first voltage, and then changes to a third voltage that contracts the ink pressure chamber at a potential between the second voltage and the first voltage to eject ink from the nozzle, wherein in the drive waveform, the potential difference between the second voltage and the third voltage is greater than the potential difference between the third voltage and the first voltage. Attached Figure Description

[0006] Figure 1 This is an overall configuration diagram of an inkjet printer equipped with an inkjet head according to the first embodiment.

[0007] Figure 2 This is a 3D view of the inkjet head mentioned above.

[0008] Figure 3 This is a top view of the nozzle plate of the inkjet head mentioned above.

[0009] Figure 4 This is a longitudinal sectional view of the inkjet head mentioned above.

[0010] Figure 5This is a longitudinal sectional view of the nozzle plate of the inkjet head mentioned above.

[0011] Figure 6 This is a block diagram of the control system of the aforementioned inkjet printer.

[0012] Figure 7 It is the drive waveform applied to the actuator of the above inkjet head.

[0013] Figure 8 This is an explanatory diagram illustrating the operation of the aforementioned actuator.

[0014] Figure 9 The above-mentioned driving waveform is used to make the actuator move. This is the test result.

[0015] Figure 10 It is a schematic diagram illustrating the atomization of ink.

[0016] Figure 11 This is a characteristic graph showing the relationship between the deviation from the optimal λ / 2 and the residual vibration when the actuator is operated with the above-mentioned driving waveform.

[0017] Figure 12 It is a multi-drop drive waveform applied to the actuator of the inkjet head according to the second embodiment.

[0018] Figure 13 This is a variation of the drive waveform applied to the aforementioned actuator.

[0019] Explanation of reference numerals in the attached figures

[0020] 10: Inkjet printer; 100-103: Inkjet head; 2: Nozzle plate; 23: Drive circuit; 24: Nozzle; 25: Ink pressure chamber; 3: Actuator; 300: Drive waveform. Detailed Implementation

[0021] The inkjet head according to the embodiment will now be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals are used for the same components in each figure.

[0022] (First Implementation)

[0023] The inkjet printer 10 equipped with the inkjet heads 100 to 103 of the first embodiment will be described. Figure 1 A simplified view of the inkjet printer 10 is shown. Inside the housing 11, the inkjet printer 10 includes a cartridge 12 for storing a sheet S (an example of a recording medium), an upstream transport path 13 for the sheet S, a conveyor belt 14 for transporting the sheet S removed from the cartridge 12, multiple inkjet heads 100-103 for ejecting ink droplets toward the sheet S on the conveyor belt 14, a downstream transport path 15 for the sheet S, an ejection tray 16, and a control board 17. An operation unit 18, serving as a user interface, is located on the upper side of the housing 11.

[0024] Image data printed on sheet S is generated by computer 200, for example, an externally connected device. The image data generated by computer 200 is sent to control board 17 of inkjet printer 10 via cable 201 and connectors 202 and 203.

[0025] Pick-up roller 204 feeds sheets S one by one from cassette 12 to upstream conveyor path 13. Upstream conveyor path 13 consists of feed roller pairs 131 and 132 and sheet guide plates 133 and 134. Sheets S are conveyed to the upper surface of conveyor belt 14 via upstream conveyor path 13. Arrow 104 in the figure shows the conveying path of sheet S from cassette 12 to conveyor belt 14.

[0026] The conveyor belt 14 is a ring-shaped belt with a mesh-like structure formed on its surface. Three rollers—drive roller 141, driven rollers 142, and 143—support the conveyor belt 14, allowing it to rotate freely. A motor 205 rotates the conveyor belt 14 by rotating the drive roller 141. The motor 205 is an example of a drive unit. Figure 105 shows the direction of rotation of the conveyor belt 14. A negative pressure container 206 is disposed on the back side of the conveyor belt 14. The negative pressure container 206 is connected to a pressure-reducing fan 207. The fan 207 creates a negative pressure inside the negative pressure container 206 through the airflow, causing the sheet S to adhere and remain on the upper surface of the conveyor belt 14. Figure 106 shows the airflow.

[0027] The inkjet heads 100-103 are configured to face the sheet S, which is adsorbed and held on the conveyor belt 14, with a small gap of, for example, 1 mm. The inkjet heads 100-103 each eject ink droplets toward the sheet S. The inkjet heads 100-103 print images as the sheet S passes underneath. Each inkjet head 100-103 has the same structure except for the color of the ejected ink. The ink colors are, for example, cyan, magenta, yellow, and black.

[0028] Inkjet heads 100-103 are connected to ink containers 315-318 and ink supply pressure adjustment devices 321-324 via ink flow paths 311-314, respectively. Each ink container 315-318 is positioned above each inkjet head 100-103. In standby mode, each ink supply pressure adjustment device 321-324 adjusts the pressure within each inkjet head 100-103 to a negative pressure relative to atmospheric pressure, for example, -1.2 kPa, to prevent ink from flowing out of the nozzles 24 (see reference 24) of the inkjet heads 100-103. Figure 2 (Leakage). During image formation, ink from each ink container 315 to 318 is supplied to each inkjet head 100 to 103 by ink supply pressure adjustment devices 321 to 324.

[0029] After image formation, sheet S is fed from conveyor belt 14 to downstream conveyor path 15. Downstream conveyor path 15 consists of feed roller pairs 151, 152, 153, 154 and sheet guide plates 155, 156 that define the conveying path of sheet S. Sheet S is fed from discharge port 157 to discharge tray 16 via downstream conveyor path 15. Arrow 107 in the figure shows the conveying path of sheet S.

[0030] Next, the structure of inkjet heads 100-103 will be explained. (Refer to the following...) Figures 2-5 The inkjet head 100 has been described, but inkjet heads 101 to 103 have the same structure as inkjet head 100.

[0031] Figure 2 This is a perspective view of the inkjet head 100. The inkjet head 100 includes a nozzle plate 2, a substrate 20, an ink supply section 21, a flexible substrate 22, and a drive circuit 23. Multiple nozzles 24 for ejecting ink are formed on the nozzle plate 2. Ink ejected from each nozzle 24 is supplied from the ink supply section 21. An ink flow path 311, starting from the previously described ink supply pressure adjustment device 321, is connected to the upper side of the ink supply section 21. Arrow 105 indicates the rotation direction (i.e., printing direction) of the conveyor belt 14 carrying the sheet S (see reference). Figure 1 ).

[0032] Figure 3 yes Figure 2 The enlarged top view of the portion enclosed by frame P. The nozzles 24 are arranged in two dimensions in the row direction (X-axis direction) and column direction (Y-axis direction). However, the nozzles 24 arranged in the row direction (X-axis direction) are arranged obliquely such that the nozzles 24 do not overlap on the X-axis axis. Each nozzle 24 is arranged at intervals of distance X1 in the X-axis direction and at intervals of distance Y1 in the Y-axis direction. As an example, distance X1 is set to 338 μm and distance Y1 is set to 84.5 μm. That is, distance Y1 is determined in a way that achieves a recording density of 300 DPI in the Y-axis direction. Furthermore, in order to print at 300 DPI in the X-axis direction as well, distance X1 is determined based on the relationship between the rotation speed of the conveyor belt 14 and the time required for ink to fall. Multiple nozzles 24 are arranged in the Y-axis direction, with groups of four nozzles 24 arranged in the X-axis direction. Although the illustration is omitted, for example, 75 groups of nozzles 24 are arranged in the Y-axis direction, and further, two groups of 75 nozzles 24 are arranged in the X-axis direction, thus arranging a total of 600 nozzles 24 (see figure). Figure 2 ).

[0033] Actuators 3, which drive the ink ejection action, are arranged for each nozzle 24. A group of nozzles 24 and actuators 3 form a channel. Each actuator 3 is formed in a ring shape and is configured such that the nozzle 24 is located in the center of it. The dimensions of the actuator 3 are, for example, an inner diameter of 30 μm and an outer diameter of 140 μm. Each actuator 3 is electrically connected to an independent electrode 31. Furthermore, each actuator 3 is electrically connected to four actuators 3 arranged in the X-axis direction via a common electrode 32. Each independent electrode 31 and the common electrode 32 are also electrically connected to mounting pads 33. The mounting pads 33 serve as input ports for applying the drive waveform described later to each actuator 3. It should be noted that, although the figures are omitted, the four independent electrodes 31 enclosed by the box 350 in the figures are respectively connected to... Figure 2 Another group of actuators 3 is connected as shown. The other independent electrodes 31 arranged in the X-axis direction are also connected in the same way. As a variation, pads 33 and a flexible substrate 22 can be added for another group of actuators 3. In this case, it is not limited to the configuration that ejects ink of the same color; it can also be configured to divide the ink flow path into groups to eject ink of different colors. Furthermore, for ease of explanation, Figure 3 The actuator 3, the independent electrode 31, and the common electrode 32 are shown in solid lines; however, these are located inside the nozzle plate 2 (see reference). Figure 4 (Longitudinal sectional view). Of course, the position of actuator 3 is not limited to inside nozzle plate 5.

[0034] The mounting pads 33 are electrically connected to the wiring pattern formed on the flexible substrate 22 via, for example, anisotropic contact film (ACF). Furthermore, the wiring pattern on the flexible substrate 22 is electrically connected to the driving circuit 23. The driving circuit 23 is, for example, an integrated circuit (IC). The driving circuit 23 selects the ink ejection channel based on the printed image data and applies a driving waveform to the actuator 3 of the selected channel.

[0035] Figure 4 This is a longitudinal sectional view of the inkjet head 100. (See image.) Figure 4As shown, the nozzle 24 penetrates the nozzle plate 2 in the Z-axis direction. The size of the nozzle 24 is, for example, a diameter of 20 μm. Inside the substrate 20, ink pressure chambers (independent pressure chambers) 25 are provided, each communicating with one of the nozzles 24. The ink pressure chamber 25 is, for example, an open cylindrical space at the top. Each ink pressure chamber 25 has an open top and communicates with a common ink chamber 26. The ink flow path 311 communicates with the common ink chamber 26 via an ink supply port 27. Each ink pressure chamber 25 and the common ink chamber 26 are filled with ink. The common ink chamber 26 may sometimes be formed, for example, into a flow path for ink circulation. The ink pressure chamber 25 is constructed by forming, for example, a cylindrical hole with a diameter of 200 μm in the substrate 20 of a single-crystal silicon wafer with a thickness of, for example, 400 μm. The ink supply section 21 is, for example, formed of alumina (Al2O3) to correspond to the space of the common ink chamber 26.

[0036] Figure 5 This is a partially enlarged longitudinal section view of the nozzle plate 2. The nozzle plate 2 is constructed by stacking a protective layer 28, an actuator 3, and a vibrating plate 29 sequentially, starting from the bottom side. The actuator 3 is constructed by stacking an upper electrode 34, a thin-plate piezoelectric element 35, and a lower electrode 36. The lower electrode 36 is electrically connected to the independent electrode 31, and the upper electrode 34 is electrically connected to the common electrode 32. An insulating layer 37, which prevents short circuits between the independent electrode 31 and the common electrode 32, is located at the boundary between the protective layer 28 and the vibrating plate 29. The insulating layer 37 is formed of, for example, a silicon dioxide film (SiO2) with a thickness of 0.5 μm. The upper electrode 34 and the common electrode 32 are electrically connected through contact holes 38 formed in the insulating layer 37. The piezoelectric element 35 is formed of, for example, PZT (lead zirconate titanate) with a thickness of 5 μm or less. The lower electrode 36 and the upper electrode 34 are formed of, for example, platinum with a thickness of 0.1 μm. The independent electrode 31 and the common electrode 32 are formed of, for example, gold (Au) with a thickness of 0.3 μm.

[0037] The vibrating plate 29 is formed of an insulating inorganic material. For example, the insulating inorganic material is silicon dioxide (SiO2). The thickness of the vibrating plate 29 is, for example, 2–10 μm, preferably 4–6 μm. As will be described in detail later, the vibrating plate 29 and the protective layer 28 are subjected to d-type bonding with a piezoelectric element 35 to which a voltage is applied. 31 The shape deforms and bends inward. It returns to its original state once the voltage applied to the piezoelectric element 35 is stopped. The volume of the ink pressure chamber (independent pressure chamber) 25 expands and contracts through this reversible deformation. Once the volume of the ink pressure chamber 25 changes, the ink pressure within the ink pressure chamber 25 changes. Ink is ejected from the nozzle 24 using the expansion and contraction of the volume of the ink pressure chamber 25 and the change in ink pressure.

[0038] That is, the nozzle 24, the actuator 3, and the ink pressure chamber 25 constitute the ink ejection section of the inkjet head 100.

[0039] The protective layer 28 is formed of, for example, polyimide with a thickness of 4 μm. The protective layer 28 covers a surface of the nozzle plate 2 on the bottom side opposite to the sheet S, and covers the inner peripheral surface of the orifice of the nozzle 24.

[0040] Figure 6 This is a block diagram of the control system of the inkjet printer 10. The control board 17, serving as the control unit, houses a CPU 170, ROM 171, RAM 172, I / O ports 173 (input / output ports), and an image memory 174. The CPU 170 controls the motor 205, ink supply pressure adjustment devices 321-324, the operation unit 18, and various sensors via the I / O ports 173. Image data from the computer 200, an externally connected device, is transmitted to the control board 17 via the I / O ports 173 and stored in the image memory 174. The CPU 170 transmits the image data stored in the image memory 174 to the drive circuits 23 of the inkjet heads 100-103 in the order of image rendering. The transmitted data may include grayscale data based on the grayscale of specified points in the image data.

[0041] The drive circuit 23 includes a data buffer 231, a decoder 232, and a drive driver 233. The data buffer 231 stores image data for each actuator 3. The decoder 232 controls the drive driver 233 for each actuator 3 based on the image data stored in the data buffer 231. The drive driver 233 activates each actuator 3 by outputting a drive signal based on the control output of the decoder 232. The drive signal is a voltage applied to the actuator 3 according to a drive waveform.

[0042] That is, each drive circuit 23 of the inkjet head 100 to 103 has the function of an actuator drive circuit that applies a drive waveform to each actuator 3.

[0043] Next, refer to Figure 7 The drive waveform 300 of the drive actuator 3 will be explained. Figure 7 The drive waveform 300 for ejecting ink once is shown. Drive waveform 300 is an example of a so-called pull-compression drive waveform. In the case of forming a dot with a single ink ejection, actuator 3 is driven by drive waveform 300. In the case of grayscale printing with two or more ink ejections to form dots, actuator 3 is driven by a multi-drop drive waveform. A detailed description of the multi-drop drive waveform will be given later.

[0044] When voltages V1 and V3 are set to positive voltages (V1 > V3), and voltage V2 is set to 0V, as follows: Figure 7As shown, the drive waveform 300 applies a voltage V1, an example of a first voltage, as a bias voltage to the actuator 3. That is, voltage V1 is applied to the lower electrode 36 of the actuator 3 through the independent electrode 31. The common electrode 32, connected to the upper electrode 34 of the actuator 3, is set to 0V. Then, voltage V2, an example of a second voltage, is applied to the actuator 3 through the independent electrode 31 for a time Ta as a first expansion pulse that expands the ink pressure chamber 25 compared to voltage V1. Then, voltage V3, an example of a third voltage, is applied to the actuator 3 through the independent electrode 31 for a time Ta as a first contraction pulse that contracts the ink pressure chamber 25. This first contraction pulse is a contraction pulse that ejects ink. Further, voltage V1, an example of a fourth voltage, is applied to the actuator 3 through the independent electrode 31 as a second contraction pulse that contracts the ink pressure chamber 25. This second contraction pulse is a contraction pulse that attenuates residual vibrations.

[0045] In the drive waveform 300, the first expansion pulse and the first contraction pulse constitute the "ejection pulse section" of ink ejection. That is, the ejection pulse section includes a DD drive waveform (DD; Draw-Draw) in which the ink pressure chamber 25 is expanded and then incompletely contracted to the middle to eject ink droplets.

[0046] After applying a voltage V1 for the second contraction pulse of time Ta, the drive waveform 300 applies a voltage V3, an example of a fifth voltage, to the actuator 3 via the independent electrode 31 as a second expansion pulse to expand the ink pressure chamber 25. Then, the same voltage V1 as the first voltage that contracts the ink pressure chamber 25 is applied to the actuator 3 via the independent electrode 31. This voltage V1 can be applied as a bias voltage for the next first expansion pulse. Then, in the next ink ejection drive cycle, the actuator 3 is driven with the same drive waveform 300.

[0047] In the drive waveform 300, the second contraction pulse and the second expansion pulse constitute a "cancellation pulse" that attenuates the residual vibration following the first contraction pulse of the ejection pulse section. In this way, the drive waveform 300 forms a DDRD drive waveform (DDRD; Draw-Draw-Release-Draw) by combining the ejection pulse section and the cancellation pulse section.

[0048] The magnitudes of voltages V1 to V3 are in the order V1 > V3 > V2. In the driving waveform 300, the potential difference Δ between voltages V2 and V3 in the ejection pulse section is... V2-V3 The potential difference Δ between voltage V3 and voltage V1 in the same ejection pulse section V3-V1 Large (Δ) V2-V3 >Δ V3-V1 ). Preferably, Δ V2-V3 With Δ V3-V1The ratio is set within the range of 6:4 to 8:2. More preferably, Δ V2-V3 With Δ V3-V1 The ratio is set to 7:3 (when the potential difference Δ V1-V2 When set to 1, Δ V2-V3 :Δ V3-V1 =0.7:0.3). As an example, the values ​​of voltages V1 to V3 are set as follows: V1 = 24V, V3 = 16.8V, and V2 = 0V. During the series of operations, the voltage of the common electrode 32 is kept constant at 0V. Δ V2-V3 With Δ V3-V1 The ratio is 7:3 (Δ V2-V3 =16.8V, Δ V3-V1 =7.2V).

[0049] Preferably, the pulse width (i.e., time Ta) is set to half the period (λ / 2) of the actuator 3's natural vibration period λ when the ink pressure chamber 25 and nozzle 24 are filled with ink. The natural vibration period λ can be measured, for example, by detecting the change in impedance of the actuator 3 when it is filled with ink. Impedance detection is performed, for example, using an impedance analyzer. As another method for measuring the natural vibration period λ, the actuator 3 can be vibrated by inputting an electrical signal such as a stepped waveform from the drive circuit 23 to the actuator 3 and measuring the vibration of the actuator 3 using a laser Doppler vibrometer. Alternatively, it can be calculated using a computer simulation. As a variation, the time Ta of each pulse width can be set to a multiple of λ / 2, or it can be a time shorter than λ / 2. Furthermore, the time Ta of each pulse width can be different from each other. λ / 2 is also sometimes referred to as AL (Acoustic Length).

[0050] It should be noted that, in Figure 7 In the example, voltages V1 and V3 are set to positive voltages (V1 > V3), and voltage V2 is set to 0V, but this is not a limitation. As a variation, voltages V1 and V3 can be set to positive voltages, and voltage V2 can be set to a negative voltage. In this case, voltage V2 is set to a negative voltage greater than or equal to the polarization reversal voltage of the piezoelectric element 35. For example, voltage V1 / V3 / V2 = 17V / 9.8V / -7V.

[0051] Figure 8 It schematically shows that in Figure 7 The driving waveform 300 causes the actuator 3 to eject ink. It should be noted that reference numeral M in the attached diagram indicates the meniscus of the ink. If in Figure 8 When a bias voltage V1 is applied in the standby state of (a), an electric field field will be generated in the thickness direction of the piezoelectric body 35, and a d-field will be generated in the piezoelectric body 35. 31The pattern is modified. Specifically, the annular piezoelectric element 35 elongates in the thickness direction and shortens in the radial direction. This deformation of the piezoelectric element 35 generates flexural stress in the vibrating plate 29, such as… Figure 8 As shown in (b), the actuator 3 bends inward. That is, the actuator 3 deforms into a concave shape centered on the nozzle 24, and the volume of the ink pressure chamber 25 shrinks.

[0052] Next, if the voltage V2 of the first expansion pulse is applied, the actuator 3 will... Figure 8 As shown in (c), the system returns to its state before deformation. At this time, within the ink pressure chamber 25, the ink pressure decreases due to the expansion of the volume to the original state; however, ink from the common ink chamber 26 flows into it, causing the ink pressure to continue to rise. Then, the supply of ink to the ink pressure chamber 25 is stopped, and the rise in ink pressure also stops. That is, it becomes a so-called pulled state.

[0053] Next, if the voltage V3 of the first contraction pulse is applied, then as follows: Figure 8 As shown in (d), the piezoelectric element 35 of actuator 3 deforms, causing the volume of ink pressure chamber 25 to shrink. As previously mentioned, the ink pressure inside ink pressure chamber 25 is increasing. Therefore, by shrinking the volume of ink pressure chamber 25, the ink pressure is increased, and ink is ejected from nozzle 24. If a voltage V1 of a second contraction pulse is applied to the subsequent cancel pulse section, then as... Figure 8 As shown in (e), the volume of the ink pressure chamber 25 is further reduced. That is, if ink is ejected, the ink pressure in the ink pressure chamber 25 decreases, and the vibration of the residual ink in the ink pressure chamber 25 is reduced. Therefore, by further reducing the volume of the ink pressure chamber 25, the residual vibration is attenuated.

[0054] If a voltage V3 of a second extended pulse is further applied to the cancel pulse section, then as follows: Figure 8 As shown in (f), the deformation of the piezoelectric element 35 of actuator 3 becomes smaller than that under voltage V1, and correspondingly the volume of ink pressure chamber 25 expands. This cancel pulse section attenuates the residual vibration. Then, if a third contraction pulse voltage V1 is applied, then as... Figure 8 As shown in (g), the volume of the ink pressure chamber 25 shrinks. That is, it becomes... Figure 8 (b) is the same state.

[0055] Here, as previously mentioned, there is an ink atomization problem in the DD drive waveform. Figure 9 The results of an actual inkjet printing test are shown. Figure 9 The changes in the position of the ink meniscus M are shown together with the driving waveform used in the experiment and the changes in ink flow rate during the ink ejection action. It should be noted that, regarding the ink flow rate, the direction of inflow into the ink pressure chamber 25 is shown as a negative value, and the direction of outflow from the ink pressure chamber 25 is shown as a positive value. Regarding the position of the meniscus, for example... Figure 8Using the position of the meniscus M in the initial state of (a) as a reference, the change toward the ejection direction is shown as a positive value, and the change toward the inward direction is shown as a negative value.

[0056] Regarding the DD drive waveform in Comparative Example 1, the potential difference Δ between voltage V2 and voltage V3 is... V2-V3 Let it be less than the potential difference Δ between voltage V3 and voltage V1. V3-V1 (the potential difference Δ) V1-V2 When set to 1, Δ V2-V3 :Δ V3-V1 =0.25:0.75). In this case, the first drop of ink is prone to atomization when it is ejected. Figure 10 This diagram schematically illustrates the state of the first ink droplet after it has been atomized. The reason why the driving waveform in Comparative Example 1 is prone to atomization is explained by... Figure 9 The change in the position of the meniscus M shown suggests that, in order to prevent the formation of a naturally protruding meniscus M (circled in a circle) from the nozzle surface, pressure vibration is used when the ink droplets are ejected.

[0057] On the other hand, as in Comparative Example 2, when the DD drive waveform is not used, it is difficult for the first droplet to atomize. However, when the DD drive waveform is not used, if the half-cycle (λ / 2) of the natural vibration period λ of the inkjet head 100-103 deviates from the optimal λ / 2, there are other problems such as increased residual vibration after ink ejection. Figure 11 The magnitude of the residual vibration accompanying the deviation from the optimal λ / 2 is shown. Figure 11 The results show that, as in Comparative Example 2, when the waveform is not driven by DD, the residual vibration deviating from the optimal λ / 2 increases. If the residual vibration is large, it may affect the subsequent ink ejection state or cause crosstalk between other channels.

[0058] Typically, regarding the driving waveform, the optimal λ / 2 based on the construction and dimensions of the inkjet head 100–103 is set as time Ta. An example of the optimal λ / 2 is 2.5 μs. However, due to reasons such as the limits of head manufacturing precision, the half-cycle (λ / 2) of the actual natural vibration period λ sometimes deviates from the optimal λ / 2. Figure 1 The inkjet printer 10 also has multiple inkjet heads 100-103 of the same shape and size, but their inherent vibration cycles λ are not necessarily exactly the same.

[0059] In contrast, the embodiment using the driving waveform 300 confirms that by making the potential difference Δ between voltage V2 and voltage V3 in the ejection pulse section... V2-V3 The potential difference Δ between voltage V3 and voltage V1 V3-V1 Large (in the potential difference Δ) V1-V2 When set to 1, Δ V2-V3 :Δ V3-V1=0.75:0.25) can prevent atomization. The reason for this ability to prevent atomization is explained by... Figure 9 The change in the position of the meniscus shown suggests that the pressure vibration during ink droplet ejection can create a meniscus M that naturally protrudes from the nozzle surface.

[0060] Therefore, it can be seen that the driving waveform 300 increases the potential difference Δ in the ejection pulse section. V2-V3 It can prevent atomization, and because it corresponds to the potential difference Δ V3-V1 As the amplitude decreases, the residual vibration attenuation effect of the second contraction pulse weakens accordingly. Therefore, the residual vibration is attenuated by setting the drive waveform to DDRD. And regarding the drive waveform 300, as... Figure 11 As shown, even if the half-cycle (λ / 2) of the natural vibration period λ of the inkjet head 100-103 deviates from the optimal λ / 2, the residual vibration does not increase as much as in Comparative Example 2. That is, as... Figure 11 As summarized in the comparison table, the drive waveform 300 possesses the two advantages of balanced anti-fogging and residual vibration stability. Furthermore, it can be said that by using Δ... V2-V3 With Δ V3-V1 The ratio is set to 7:3 (when the potential difference Δ V1-V2 When set to 1, Δ V2-V3 :Δ V3-V1 =0.7:0.3), which can generate waveforms with the minimum number of voltages V1 to V3 required to drive the waveform with DDRD, and selects the optimal point to obtain the effect of balanced anti-fogging and residual vibration stability.

[0061] It should be noted that, in Figure 7 In the example, the waveform is formed using the minimum number of voltages V1 to V3 required for the DDRD drive waveform, preventing the circuit configuration from becoming complex. However, there is no limit to the number of voltages, and more than four voltages can be used to form the drive waveform 300. As one example, the fourth voltage can be lower than voltage V1, or conversely, the fourth voltage can be higher than voltage V1. As another example, the fifth voltage can be lower than voltage V3, or conversely, the fifth voltage can be higher than voltage V3.

[0062] (Second Implementation)

[0063] Next, the inkjet heads 100 to 103 according to the second embodiment will be described. In this embodiment, the multi-drop drive waveform for grayscale printing will be described in detail. Since the configuration of the inkjet heads 100 to 103 other than the drive waveform is the same as that of the first embodiment, detailed descriptions will be omitted.

[0064] Figure 12Multi-drop drive waveforms of 2 to 4 drops are shown respectively. The multi-drop drive waveform (2 drops) for two-grayscale printing by ejecting ink twice includes an ejection pulse for the first drop and an ejection pulse for the second drop. The multi-drop drive waveform (2 drops) applies voltage V1 as a bias voltage to actuator 3. Then, voltage V2 is applied to actuator 3 as an expansion pulse for a time of 0.6Ta. Then, voltage V3 is applied to actuator 3 as a contraction pulse for a time of Ta to eject the first drop of ink. That is, except that the application time of voltage V3 is adjusted, it is the same as the ejection pulse section of the first embodiment. Furthermore, voltage V1 is applied to actuator 3 as a contraction pulse to attenuate residual vibration.

[0065] The second drop's ejection pulse and Figure 7 The ejection pulse portion of the driving waveform 300 shown is the same. Furthermore, the cancellation pulse following the ejection pulse is also the same. Figure 7 The cancellation pulse portion of the drive waveform 300 shown is the same. Therefore, detailed explanation is omitted. For the first and second drops in the multi-drop drive waveform (2 drops), the potential difference Δ between voltage V2 and voltage V3 under the contraction pulse of the ejected ink is used. V2-V3 The potential difference Δ between voltage V3 and voltage V1 V3-V1 Large (Δ) V2-V3 >Δ V3-V1 ).

[0066] It should be noted that an intermediate time Tm is set between the first and second drops. For example, the intermediate time Tm is 2Ta. Furthermore, the ejection velocity of the second droplet is increased by setting the pulse width of the expansion pulse for the first droplet to 0.6Ta and the pulse width of the expansion pulse for the second droplet to Ta. When the time Ta is set to λ / 2, the pulse width of the expansion pulse for the first droplet is 0.6λ / 2, the pulse width of the expansion pulse for the second droplet is λ / 2, and the intermediate time Tm is λ. Setting the intermediate time Tm while simultaneously increasing the ejection velocity of the final droplet can suppress ink satellite formation.

[0067] The multi-drop drive waveform (3 drops) for printing at 3 gray levels or higher by dropping ink three times includes an ejection pulse for the first drop, an ejection pulse for the second drop, and an ejection pulse for the third drop. The multi-drop drive waveform (3 drops) applies voltage V1 as a bias voltage to actuator 3. Then, voltage V2 is applied to actuator 3 for a duration of 0.6Ta as an expansion pulse. Then, voltage V3 is applied to actuator 3 as a contraction pulse to eject the first drop of ink. That is, except for adjusting the application time of voltage V3, it is the same as the ejection pulse section of the first embodiment. Next, voltage V2 is applied to actuator 3 for a duration of 0.3Ta as an expansion pulse. Then, voltage V3 is applied to actuator 3 as a contraction pulse to eject the second drop of ink. Voltage V1 is further applied to actuator 3 as a contraction pulse to attenuate residual vibration.

[0068] The third droplet's ejection pulse and Figure 7 The ejection pulse portion of the driving waveform 300 shown is the same. Furthermore, the cancellation pulse following the ejection pulse is also the same. Figure 7 The cancellation pulse portion of the drive waveform 300 shown is the same. Therefore, detailed description is omitted. In the multi-drop drive waveform (3 drops), the potential difference Δ between voltage V2 and voltage V3 under the contraction pulse of the ejected ink is used in all drops from the first to the third drop. V2-V3 The potential difference Δ between voltage V3 and voltage V1 V3-V1 Large (Δ) V2-V3 >Δ V3-V1 ).

[0069] It should be noted that an intermediate time Tm is set between the second and third drops. The intermediate time Tm is, for example, 2Ta. Furthermore, the ejection speed of the final droplet (the third drop) is increased by setting the pulse width of the expansion pulse for the first droplet to 0.6Ta, the pulse width of the expansion pulse for the second droplet to 0.3Ta, and the pulse width of the expansion pulse for the third droplet to Ta. When the time Ta is set to λ / 2, the pulse width of the expansion pulse for the first droplet is 0.6λ / 2, the pulse width of the expansion pulse for the second droplet is 0.3λ / 2, the pulse width of the expansion pulse for the third droplet is λ / 2, and the intermediate time Tm is λ. If the intermediate time Tm is set while simultaneously increasing the ejection speed of the final droplet, ink satellite formation can be suppressed. The interval between the expansion pulses of the first and second drops is set to the midpoint between them, which is called time Ta.

[0070] The multi-drop drive waveform (4 drops) has the same structure as the multi-drop drive waveform (3 drops). Although the illustration is omitted, the multi-drop drive waveform that ejects ink 5 or more times can also be constructed in the same way. It should be noted that when using... Figure 12In the case of a series of multi-drop drive waveforms shown, for the drive waveform that ejects ink once, the width of the expansion pulse can also be set to 0.6Ta to make the ink ejection state uniform.

[0071] The first and second embodiments described above describe a configuration in which a drive signal is applied to the lower electrode 36 of the actuator 3 via an independent electrode 31 (see reference). Figure 5 That is, the voltage application direction is consistent with the piezoelectric film polarization direction of the piezoelectric body 35 (i.e., the direction from the lower electrode 36 towards the upper electrode 34). As a variation, the driving signal can also be applied to the upper electrode 34 of the actuator 3. That is, the voltage application direction is not consistent with the piezoelectric film polarization direction of the piezoelectric body 35 (i.e., the direction from the lower electrode 36 towards the upper electrode 34). In this case, such as Figure 13 As shown, the driving waveform 301 is set to be the waveform obtained by flipping the driving waveform 300 up and down. The multi-drop waveform is the same.

[0072] According to any of the above embodiments, an inkjet head capable of suppressing atomization during ink ejection can be provided.

[0073] It should be noted that, regarding the inkjet heads 100 to 103, it is not necessary to arrange both the actuator 3 and the nozzle 24 on the surface of the nozzle plate 2. For example, it can be an inkjet head with an actuator having any of the following driving methods: on-demand piezoelectric, shared wall type, or shared mode type.

[0074] The embodiments of the present invention are presented by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and likewise included within the scope of the invention as described in the claims and their equivalents.

Claims

1. An ink jet head characterized by comprising: Possessing: An ink ejection portion, which has a nozzle that ejects ink, an ink pressure chamber that communicates with the nozzle, and an actuator that changes the volume of the ink pressure chamber; And An actuator drive circuit that applies a drive signal including a drive waveform of an ejection pulse portion to the actuator, the ejection pulse portion changing from a first voltage to a second voltage that expands the ink pressure chamber compared to the first voltage, and then changing to a third voltage that contracts the ink pressure chamber at a potential between the second voltage and the first voltage to eject ink from the nozzle, in the drive waveform, the potential difference between the second voltage and the third voltage being greater than the potential difference between the third voltage and the first voltage, The drive waveform includes a cancellation pulse portion that changes to a fourth voltage that contracts the ink pressure chamber after the ejection pulse portion, and changes from the fourth voltage to a fifth voltage that expands the ink pressure chamber compared to the fourth voltage.

2. The ink jet head according to claim 1, wherein The third voltage of the ejection pulse portion and the fifth voltage of the cancellation pulse portion are the same voltage value.

3. The ink jet head according to claim 1, wherein The drive waveform is a multiple drop drive waveform that allocates the ejection pulse portion to any one of a first drop to an n-th drop of a final drop, where n ≥ 2.

4. The ink jet head according to claim 2, wherein The drive waveform is a multiple drop drive waveform that allocates the ejection pulse portion to any one of a first drop to an n-th drop of a final drop, where n ≥ 2.

5. The ink jet head according to any one of claims 1 to 4, wherein The ratio of the potential difference between the second voltage and the third voltage to the potential difference between the third voltage and the first voltage is 7:

3.

6. The ink jet head according to any one of claims 1 to 4, wherein The actuator drive circuit selects a channel that ejects ink according to image data of printing, and applies the drive waveform to the actuator of the selected channel.

7. The ink jet head according to claim 5, wherein The actuator drive circuit selects a channel that ejects ink according to image data of printing, and applies the drive waveform to the actuator of the selected channel.

8. The ink jet head according to any one of claims 1 to 4, wherein The actuator is made of a laminated upper electrode, a thin plate-shaped piezoelectric body, and a lower electrode.

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