Liquid ejection head

Abstract

To provide a liquid ejection head capable of performing stable ejection of liquid by suppressing the influence of crosstalk received from surrounding drive channels.SOLUTION: There is provided a liquid ejection head which has a plurality of drive channels, a delay amount setting part and a delay amount allocation part. The plurality of drive channels are each equipped with a nozzle and an actuator corresponding to the nozzle. The delay amount setting part sets a plurality of delay amounts of drive waveforms to be given to the actuator. The delay amount allocation part allocates the plurality of delay amounts set to the plurality of nozzles arranged in a row to the drive channel in a periodically repetitive manner in the arranging direction of the nozzles.SELECTED DRAWING: Figure 9

Description

Technical Field

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

Background Art

[0002] A liquid ejection head that supplies a predetermined amount of liquid to a predetermined position is known. The liquid ejection head is mounted on, for example, an inkjet printer, a 3D printer, a dispensing device, or the like. An inkjet printer ejects ink droplets from an inkjet head to form an image or the like on the surface of a recording medium. A 3D printer ejects droplets of a modeling material from a modeling material ejection head and cures them to form a three-dimensional object. A dispensing device ejects droplets of a sample and supplies a predetermined amount to a plurality of containers or the like.

[0003] The liquid ejection head has a plurality of channels for ejecting liquid. Each channel includes a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and an actuator for changing the volume of the pressure chamber. The liquid ejection head selects a channel for ejecting liquid from among the plurality of channels, and gives a drive signal to the actuator to drive it. When the actuator is driven, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle.

[0004] A multi-nozzle liquid ejection head that ejects liquid from a plurality of nozzles is affected by the liquid ejection operations of surrounding channels due to mechanical factors, fluid factors, electrical factors, etc., and the ejection speed and ejection amount of the liquid change, and the ejection of the liquid may not be stable. This is called crosstalk. In particular, crosstalk due to mechanical factors is strongly affected by channels arranged nearby. For example, when the nozzles are arranged in a row, it is strongly affected by the two adjacent channels on both sides.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a liquid ejection head that can suppress the influence of crosstalk received from surrounding drive channels and perform stable liquid ejection.

Means for Solving the Problems

[0007] The liquid ejection head according to an embodiment of the present invention includes a plurality of drive channels, a delay amount setting unit, and a delay amount allocation unit. The plurality of drive channels each include a nozzle and an actuator corresponding to the nozzle. The delay amount setting unit sets a plurality of delay amounts of a drive waveform applied to the actuator. The delay amount allocation unit periodically repeats the plurality of set delay amounts in the arrangement direction of the nozzles and allocates them to the drive channels for a plurality of nozzles arranged in a row.

Brief Description of the Drawings

[0008]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a liquid ejection head according to an embodiment will be described in detail with reference to the accompanying drawings. In each figure, the same components are denoted by the same reference numerals.

[0010] As an example of an image forming apparatus equipped with the liquid ejection head of the embodiment, an inkjet printer 10 that prints an image on a recording medium will be described. FIG. 1 shows a schematic configuration of the inkjet printer 10. The inkjet printer 10 includes, inside a housing 11, a cassette 12 that stores a sheet S which is an example of a recording medium, an upstream conveyance path 13 of the sheet S, a conveyance belt 14 that conveys the sheet S taken out from the cassette 12, a plurality of inkjet heads 100 to 103 that eject ink droplets toward the sheet S on the conveyance belt 14, a downstream conveyance path 15 of the sheet S, a discharge tray 16, and a control board 17. An operation unit 18 which is a user interface is arranged on the upper side of the housing 11.

[0011] Image data to be printed on the sheet S is generated, for example, by a computer 200 which is an external connection device. The image data generated by the computer 200 is sent to the control board 17 of the inkjet printer 10 through a cable 201 and connectors 202, 203.

[0012] A pickup roller 204 supplies the sheets S from the cassette 12 to the upstream conveyance path 13 one by one. The upstream conveyance path 13 is composed of a pair of feed rollers 131, 132 and sheet guide plates 133, 134. The sheet S is sent to the upper surface of the conveyance belt 14 via the upstream conveyance path 13. Arrow 104 in the figure indicates the conveyance path of the sheet S from the cassette 12 to the conveyance belt 14.

[0013] The conveyance belt 14 is a net-like endless belt having a large number of through holes formed on its surface. Three rollers, a driving roller 141, and driven rollers 142, 143 rotatably support the conveyance belt 14. A motor 205 rotates the driving roller 141 to rotate the conveyance belt 14. The motor 205 is an example of a driving device. Arrow 105 in the figure indicates the rotation direction of the conveyance belt 14. A negative pressure container 206 is arranged on the back side of the conveyance belt 14. The negative pressure container 206 is connected to a decompression fan 207. The fan 207 creates a negative pressure inside the negative pressure container 206 by the formed air flow, and adsorbs and holds the sheet S on the upper surface of the conveyance belt 14. Arrow 106 in the figure indicates the flow of the air current.

[0014] Examples of liquid ejection heads, inkjet heads 100 to 103, are arranged to face a sheet S adsorbed and held on a conveyance belt 14 with a slight gap of, for example, 1 mm therebetween. The inkjet heads 100 to 103 eject ink droplets toward the sheet S, respectively. The inkjet heads 100 to 103 print an image when the sheet S passes below. Each of the inkjet heads 100 to 103 has the same structure except that the color of the ejected ink is different. The colors of the ink are, for example, cyan, magenta, yellow, and black.

[0015] The inkjet heads 100 to 103 are respectively connected to ink tanks 315 to 318 and ink supply pressure adjusting devices 321 to 324. Each of the ink tanks 315 to 318 is arranged above each of the inkjet heads 100 to 103. During standby, each of the ink supply pressure adjusting devices 321 to 324 adjusts the inside of each of the inkjet heads 100 to 103 to a negative pressure with respect to atmospheric pressure, for example, -1.2 kPa, so that ink does not leak from nozzles 20 (see FIG. 2) of the inkjet heads 100 to 103. During image formation, the ink in each of the ink tanks 315 to 318 is supplied to each of the inkjet heads 100 to 103 by the ink supply pressure adjusting devices 321 to 324.

[0016] After image formation, the sheet S is sent from the conveyance belt 14 to a downstream conveyance path 15. The downstream conveyance path 15 includes a pair of feed rollers 151, 152, 153, 154 and sheet guide plates 155, 156 that define the conveyance path of the sheet S. The sheet S is sent from the downstream conveyance path 15 to a discharge tray 16 through a discharge port 157. Arrow 107 in the figure indicates the conveyance path of the sheet S.

[0017] Subsequently, the configuration of the inkjet heads 100 to 103 will be described. The following describes the inkjet head 100 with reference to FIGS. 2 to 4, but the inkjet heads 101 to 103 also have the same structure as the inkjet head 100.

[0018] As shown in FIGS. 2 to 4, the inkjet head 100 includes a head portion 2 which is an example of a liquid ejection portion. The head portion 2 is connected to a flexible printed wiring board 3 which is an example of a film wiring board. The flexible printed wiring board 3 is connected to a printed circuit board 4 which is an example of an intermediate substrate.

[0019] The multi-nozzle head portion 2 includes a nozzle plate 21 in which a plurality of nozzles 20 are arranged, an actuator substrate 22 forming an actuator corresponding to each nozzle 20, a frame member 23 forming a common ink chamber 26, and an ink supply portion 24 for supplying ink to the common ink chamber 26.

[0020] The nozzle plate 21 is a rectangular plate formed of a resin such as polyimide or a metal such as stainless steel. The nozzles 20 for ejecting ink are arranged in a row in the X direction of the first direction on the surface of the nozzle plate 21. Note that the arrangement in a row does not necessarily require the centers of the nozzles 20 to be in a straight line, and for example, there may be a shift in the Y direction which is the second direction. The nozzle density is set, for example, within a range of 150 to 1200 dpi. The actuator substrate 22 is a rectangular substrate formed of, for example, insulating ceramics.

[0021] The frame member 23 surrounds the periphery of the lower portion of the actuator substrate 22. The opening on the lower surface of the frame member 23 is sealed by the nozzle plate 21. The space partitioned by the frame member 23, the actuator substrate 22, and the nozzle plate 21 forms a common ink chamber 26 (261, 262). The common ink chamber 26 has two common ink chambers 261 and 262 with the actuator substrate 22 interposed therebetween. One common ink chamber 261 communicates with the ink supply port 27 and serves as an ink supply path for supplying ink to the plurality of pressure chambers 5. The ink supply port 27 is connected to the ink supply pressure adjusting device 321 in FIG. 1 via the ink supply pipe 28. The other common ink chamber 262 communicates with an ink discharge port, which is an opening similar to the ink supply port 27 although not shown in the figure, and serves as an ink discharge path for discharging ink from the plurality of pressure chambers 5. When the ink is circulated and supplied, the ink discharge port is connected to the ink supply pressure adjusting device 321 via the ink discharge pipe 29.

[0022] As shown in FIGS. 3 and 4, the plurality of pressure chambers 5 and the air chambers 51 are formed so as to be alternately arranged on the surface of the actuator substrate 22 located in the common ink chamber 26 (261, 262). The pressure chambers 5 and the air chambers 51 are partitioned by piezoelectric members 6 (61, 62) serving as side walls. The piezoelectric members 6 (61, 62) are piezoelectric bodies such as piezo elements. The pressure chambers 5 and the air chambers 51 are formed on the surface of the actuator substrate 22 by grooves formed by notching two piezoelectric members 61 and 62 laminated in the Z direction, which is the third direction, in a rectangular shape in the Y direction. The two piezoelectric members 61 and 62 are laminated in directions where the polarization directions are opposite (for example, the opposing direction). Each pressure chamber 5 communicates with each nozzle 20 on a one-to-one basis. The air chambers 51 are located on both sides of the pressure chambers 5.

[0023] Furthermore, a pair of cover members 67 that form side walls on both sides in the Y direction of the air chamber 51 are respectively provided on both side surfaces of the actuator substrate 22. The air chamber 51 is separated from the common ink chambers 26 (261, 262) by the cover members 67. Groove-shaped openings 68 corresponding to the shape of the pressure chamber 5 are formed in the cover members 67 so that the pressure chamber 5 communicates with the left and right common ink chambers 261 and 262. The openings 68 of the cover members 67 are adjusted to be narrower than the cross-section of the pressure chamber 5 to brake the vibration of the ink entering and leaving between the common ink chambers 26 (261, 262) and the pressure chamber 5. The opening 68 of the cover member 67 on the common ink chamber 261 side is an ink supply port, and the opening 68 of the cover member 67 on the common ink chamber 262 side is an ink discharge port. Ink is supplied to and discharged from the pressure chamber 5 through the ink supply port and the ink discharge port. FIG. 3 shows an example of a cover member 67 formed of a plate material, but the cover member 67 may be formed of, for example, resin or a plate material. Furthermore, the cover member 67 may be configured to fill only the portions of the side walls on both sides in the Y direction of the air chamber 51.

[0024] As shown in FIG. 4, the individual electrodes 63 are integrally formed on the bottom surface in the Z direction and both side surfaces in the X direction of the pressure chamber 5. The common electrode 64 is integrally formed on the bottom surface in the Z direction and both side surfaces in the Y direction of the air chamber 51. The individual electrodes 63 of each pressure chamber 5 are respectively connected to individual wirings 65. The common electrodes 64 of each air chamber 51 are commonly connected to a common wiring 66 respectively. The individual electrodes 63, the common electrodes 64, the individual wirings 65, and the common wiring 66 are formed of, for example, a nickel thin film and are insulated by being covered with, for example, an insulating layer (not shown).

[0025] The connection point between the individual electrode 63 and the individual wiring 65 is the individual terminal of the actuator 8. The individual terminals of the actuator 8 are respectively connected to the drive driver D (i.e., the drive circuit) of the drive IC 31 via the individual wiring 65. To the drive driver D, V1, V2, and ground (GND) are connected as the power sources of the drive voltage. On the other hand, the connection point between the common electrode 64 and the common wiring 66 is the common terminal of the actuator 8. The common terminals of each actuator 8 are commonly connected to, for example, ground (GND) or a common potential of a predetermined constant voltage. The drive driver D of each drive channel (#1ch, #2ch, ··· #nch) respectively applies a drive voltage to the individual terminals of each actuator 8 to drive them independently. With this configuration, in the actuator 8 to which the drive voltage is applied, an electric field is applied in a direction intersecting (preferably, orthogonal) to the polarization axis of the piezoelectric members 6 (61, 62), and the piezoelectric members 6 (61, 62) that form the side walls in the X direction of the pressure chamber 5 are deformed symmetrically in the X direction in the shear mode.

[0026] That is, the pressure chamber 5 is formed by being sandwiched between a pair of columnar actuators 8 using the piezoelectric members 6 (61, 62). By applying a potential difference to both walls of the columnar actuator 8, that is, the inner wall and the outer wall of the pressure chamber 5, and charging the actuator 8, the actuator 8 is deformed. As a result, the volume of the pressure chamber 5 changes, and consequently, the ink pressure inside the pressure chamber 5 changes. By adjusting the magnitude and timing of this change, ink is ejected from the nozzle 20.

[0027] Fig. 5 shows an example of a driving waveform. The driving waveform (DPR waveform) in Fig. 5 is a driving waveform for multi-drop ejection of ink three drops in one driving cycle. Before the ink ejection operation, a voltage Vb is applied to the individual terminals of the actuator 8. Then, from time t1 to time t2, voltage Va, from time t2 to time t3, voltage Vc, from time t3 to time t4, voltage Va, from time t4 to time t5, voltage Vb, from time t5 to time t6, voltage Va, from time t6 to time t7, voltage Vb, from time t7 to time t8, voltage Vc, and at time t8, voltage Vb are applied as drive signals to the individual terminals of the actuator 8. The voltage Va is, for example, 0 V and is supplied from the GND in Fig. 4. The voltages Vb and Vc are positive voltages and are supplied from the power supplies V2 and V1 in Fig. 4, respectively. Va < Vb < Vc. The common terminals of each actuator 8 are commonly connected to, for example, a ground (GND) of 0 V. Instead of connecting the common terminal of the actuator 8 to the GND, it may be connected to the power supply V2 of the voltage Vb, for example, to give a predetermined potential to the common terminal.

[0028] The periods from time t1 to time t2, from time t2 to time t3, from time t3 to time t4, from time t4 to time t5, from time t5 to time t6, from time t6 to time t7, and from time t7 to time t8 are each set to, for example, half of the pressure oscillation period of the head unit 2. That is, the basic pulse width of the driving waveform for ejecting ink is made the same as half of the pressure oscillation period of the head unit 2. When the pressure oscillation period of the head unit 2 is, for example, 4 μs, the time from time t1 to time t2, which is the basic pulse width, is 2 μs.

[0029] Prior to the ink ejection operation, the actuator 8 with a voltage Vb applied to the individual terminals causes the piezoelectric members 6 (61, 62) on both sides of the pressure chamber 5 to deform in a shear mode inward, respectively, as shown in FIG. 6(b), and the volume inside the pressure chamber 5 contracts. Then, the actuator 8 with a voltage Va applied to the individual terminals at time t1 causes the piezoelectric members 6 (61, 62) that were deformed in the shear mode to return to their original state, as shown in FIG. 6(a), and the volume inside the pressure chamber 5 expands relatively from the state in FIG. 6(b), thereby supplying ink into the pressure chamber 5. Subsequently, the actuator 8 with a voltage Vc applied to the individual terminals at time t2 causes the piezoelectric members 6 (61, 62) to deform in a shear mode inward, respectively, as shown in FIG. 6(c), and the volume inside the pressure chamber 5 contracts. Due to this series of volume changes in the pressure chamber 5, the pressure of the ink increases, and the first drop of ink is ejected from the nozzle 20.

[0030] Subsequently, the actuator 8 with a voltage Va applied to the individual terminals at time t3 causes the volume inside the pressure chamber 5 to expand from the state in FIG. 6(c) to the state in FIG. 6(a), and by applying the voltage Vb at time t4, the volume inside the pressure chamber 5 contracts to the state in FIG. 6(b), ejecting the second drop of ink. Subsequently, the actuator 8 with a voltage Va applied to the individual terminals at time t5 causes the volume inside the pressure chamber 5 to expand from the state in FIG. 6(b) to the state in FIG. 6(a), and by applying the voltage Vb at time t6, the volume inside the pressure chamber 5 contracts to the state in FIG. 6(b), ejecting the third drop of ink.

[0031] Then, the actuator 8 with the voltage Vc applied to the individual terminals at time t7 causes the volume in the pressure chamber 5 to contract to the state shown in Fig. 6(c). By applying the voltage Vb at time t8, the volume in the contracted pressure chamber 5 returns to the state shown in Fig. 6(b). This contraction and return attenuate the residual amount vibration. When the common terminal of the actuator 8 is connected to another predetermined potential instead of being connected to GND, the shape of the actuator 8 is offset by the amount of deformation with respect to that predetermined potential. However, since the pressure applied to the ink in the pressure chamber 5 is determined by the relative change with respect to immediately before the volume of the pressure chamber 5, even if the common terminal of the actuator 8 is connected to another predetermined potential instead of being connected to GND, the above-described behavior of the ink does not change. The potential of the common terminal of the actuator 8 may be selected at a location advantageous for the characteristics of the actuator 8.

[0032] In this embodiment, a plurality of delay amounts that shift the timing of applying the drive waveform to the actuator 8 are set, and the delay amounts are periodically assigned in the arrangement direction of the nozzles 20 arranged in a row. Fig. 7 shows an example in which nine different delay amounts are set for nine delay resources (Delay 1 to Delay 9). Fig. 8 shows the timing shift due to the delay amounts in Fig. 7 represented by the waveform diagram in Fig. 5.

[0033] As shown in Figs. 7 and 8, the nine different delay amounts include a first group with a small delay amount and a second group with a large delay amount. The grouping is performed by setting the main delay amount. The main delay amount is preferably equal to the basic pulse width of the drive waveform. As described above, the basic pulse width of the drive waveform is usually set to 1 / 2 of the pressure vibration period of the head unit 2. 1 / 2 of the pressure vibration period of the head unit 2 is, for example, 2 μs.

[0034] In the examples of FIGS. 7 and 8, among the nine delay resources (delays 1 to 9), for the main delay amounts of the odd delay resources (delays 1, 3, 5, 7, 9), a delay amount of, for example, 0 μs, which is the first group, is set. For the main delay amounts of the even delay resources (delays 2, 4, 6, 8), a delay amount of, for example, 2 μs, which is the second group, is set. Therefore, when arranging the nine delay resources in numerical order as shown in FIG. 7, the first group with a smaller delay amount and the second group with a larger delay amount are arranged alternately. Note that the delay amount is, for example, a value when the print trigger at which the inkjet head 100 starts printing is used as the reference timing. However, the reference timing is not limited to the print trigger. Even if the reference timing is changed, the relationship of the delay amounts between the drive channels that can suppress crosstalk is maintained.

[0035] Both the first group and the second group have different delay amounts within the group. The shift of the delay amounts within the group is performed by setting different sub delay amounts. That is, the delay amount set for each delay resource (delays 1 to 9) is the sum of the main delay amount and the sub delay amount. The sub delay amount is provided to disperse the timing of the charge or discharge operation in order to avoid electrical problems such as voltage drops due to the temporary concentration of current in the common wiring 66 etc. when many channels are charged and discharged simultaneously, that is, to avoid electrical crosstalk. From the viewpoint of avoiding electrical crosstalk, it is desirable to arrange the sub delay amounts at intervals of 0.05 μs to 0.1 μs or more. However, from the viewpoint of avoiding mechanical crosstalk, it is desirable that the delay difference from the adjacent channel does not deviate significantly from 2 μs set by the main delay amount. As an example, when the main delay amount is set to 1 / 2 of the pressure vibration period of the head unit 2 (for example, 2 μs), it is set to 1 / 4 or less thereof. In the examples of FIGS. 7 and 8, the sub delay amounts are set within the range of 0.02 μs to 0.38 μs. In addition, for each group, the sub delay amounts are set so that the delay amount monotonically increases in the numerical order of the delay resources.

[0036] The delay amounts thus set are: Delay 1 is 0.02 μs, Delay 2 is 2.04 μs, Delay 3 is 0.10 μs, Delay 4 is 2.16 μs, Delay 5 is 0.20 μs, Delay 6 is 2.26 μs, Delay 7 is 0.30 μs, Delay 8 is 2.36 μs, and Delay 9 is 0.38 μs.

[0037] Figure 9 shows an example of a drive circuit 9 having a delay amount setting unit capable of setting a plurality of delay amounts. The drive circuit 9 is configured to set a plurality of delay amounts, assign the set delay amounts to each drive channel (1ch, 2ch, ··· nch), and start generating a drive waveform with the assigned delay amount. The drive circuit 9 is included in, for example, the drive IC 31. The following description explains an example of assigning the plurality of delay amounts in FIG. 7 to each drive channel and generating the drive waveform in FIG. 5, but this circuit configuration can also be applied to other drive waveforms and other delay amounts.

[0038] As shown in FIG. 9, the drive circuit 9 includes a waveform generation circuit 91 and a waveform assignment circuit 92. The waveform generation circuit 91 and the waveform assignment circuit 92 are an example of a delay amount setting unit. The waveform generation circuit 91 includes a plurality of delay circuits 93, a delay amount setting memory 94, a plurality of drive waveform generation circuits 95, and a drive waveform setting memory 96. The plurality of delay circuits 93 and the plurality of drive waveform generation circuits 95 are connected in series respectively. The number of pairs of the delay circuit 93 and the drive waveform generation circuit 95 is, for example, nine. That is, it corresponds to nine delay resources (Delay 1 to 9).

[0039] The delay amount setting memory 94 stores the set values of a plurality of delay amounts. That is, the delay amount information in FIG. 7 is stored in the delay amount setting memory 94. The set values of the delay amounts stored in the delay amount setting memory 94 can be changed. For example, depending on the type of ink, the basic vibration period of the ink in the pressure chamber 5 may change and the pressure vibration period of the head unit 2 may also change. Therefore, for example, the delay amount is set from the firmware of the inkjet printer 10. Or, it may be done, for example, during the process of manufacturing the inkjet head 100.

[0040] The drive waveform setting memory 96 stores the information on the drive waveforms shown in FIG. 5. However, the types of drive waveforms stored in the drive waveform setting memory 96 are not limited to one, and a plurality of types of drive waveforms may be stored so that any one of them can be selected.

[0041] The waveform assignment circuit 92 includes a selector 97 and a drive waveform selection memory 98. As an example, the drive waveform selection memory 98 may store an "assignment pattern" that periodically repeats and assigns a plurality of delay amounts in the arrangement direction of the nozzles 20 arranged in a row. As shown in an example in FIG. 10, for the assignment pattern P, after assigning delays 1, 2, 3, 4, 5, 6, 7, 8, 9 in ascending order in the order of the numbers of the drive channels (ch) corresponding to the arrangement direction of the nozzles 20, delays 8, 7, 6, 5, 4, 3, 2 are assigned in descending order. The assignment pattern P applies this 16-step repetition to the drive channels after the 17th ch as well. That is, in the example of FIG. 10, the assignment pattern P is taken as one period of the assignment period, and this is periodically repeated in the arrangement direction of the nozzles 20. The number of assignments in one period of the assignment pattern P is an even number (for example, 16), and the number of delay resources (delays 1 to 9) is one more than half of the number of assignments in one period. This prevents the same value from continuing in the sub-delay amounts described later even when the assignment pattern P is repeated.

[0042] The selector 97 of the drive circuit 9 is, for example, a 16-channel "9 to 1" selector. The selector 97 is respectively connected to the output terminals of each drive waveform generation circuit 95. Further, the 16-channel output terminals of the selector 97 are respectively connected to each drive channel via the switch 99. The drive channels are grouped in sets of 8 drive channels, and two sets of drive channel groups (a total of 16 drive channels) constitute one area. For the convenience of drawing, two areas, area 1 and area 2, are shown, but it may be composed of three or more areas. And, for example, the same channel of the selector 97 is shared by a plurality of drive channels among a plurality of areas so that the drive channel (1ch) of area 1 and the drive channel (17ch) of area 2 are the same channel of the selector 97. The number of drive channels in one area is equal to the number of one cycle of the above-described assignment pattern P. Further, the number of 16 channels of the selector 97 is also equal to the number of one cycle of the assignment pattern P.

[0043] The switch 99 performs switching control to supply or not supply the drive waveform from the selector 97 to the drive channel. The switch 99 performs an ON-OFF operation according to the signal from the print data buffer 90. The drive waveform may be partially turned ON according to the signal from the print data buffer 90 to change the number of drops to be ejected. The print data buffer 90 is provided, for example, in the drive IC 31.

[0044] In the above-described drive circuit 9, when a print trigger is given to the delay circuit 93, each delay circuit 93 waits for its respective delay amount to elapse and then activates each drive waveform generation circuit 95. Each drive waveform generation circuit 95 outputs the drive waveform stored in the drive waveform setting memory 96. Therefore, the start timing of the generation of the drive waveform is shifted from each other by the delay amounts set for delays 1 to 9.

[0045] Nine types of drive waveforms with different delay amounts output from each drive waveform generation circuit 95 are supplied to the selector 97. The selector 97 assigns the nine types of drive waveforms to each set of 16 drive channels in each region (region 1, region 2 ··· region n) according to the assignment pattern P stored in, for example, the drive waveform selection memory 98. As a result, as shown in FIG. 10, it is possible to set the delay amount for all drive channels. Note that the pre-delay difference, post-delay difference, and average in FIG. 10 will be described later.

[0046] Each drive waveform assigned to each drive channel by the selector 97 is supplied to each switch 99 respectively. When the switch 99 is ON, the drive waveform is supplied to the actuator 8 of that drive channel. The actuator 8 to which the drive waveform is supplied is driven to eject ink. On the other hand, when the switch 99 is OFF, the drive waveform is not supplied to the drive channel. It is the print data that determines the ON / OFF of the switch 99. The switch 99 turns ON / OFF the switch 99 of each drive channel based on the print data transferred to the print data buffer 90. That is, it controls whether or not to eject ink from the nozzles 20 of each drive channel.

[0047] In the example of FIG. 10, the delay amounts assigned to each drive channel by the waveform assignment circuit 92 are such that the first group with a smaller delay amount (delays 1, 3, 5, 7, 9) and the second group with a larger delay amount (delays 2, 4, 6, 8) are arranged alternately in the order of the drive channel numbers corresponding to the arrangement direction of the nozzles 20. As shown in FIG. 7, for each group, the sub-delay amounts are set so that the delay amount monotonically increases in the order of the delay resource (delays 1 to 9). And after assigning delays 1, 2, 3, 4, 5, 6, 7, 8, 9 in ascending order based on the assignment pattern P, and then assigning delays 8, 7, 6, 5, 4, 3, 2 in descending order, the delay amounts of each group monotonically increase in the arrangement direction of the nozzles 20 in the region that is half of the assignment period (1ch to 16ch), and monotonically decrease in the remaining half region.

[0048] Furthermore, in the example of FIG. 10, the delay amounts of 10ch and 8ch, 11ch and 7ch, 12ch and 6ch, 13ch and 5ch, 14ch and 4ch, 15ch and 3ch, and 16ch and 2ch are the same, respectively. As a result, the number of delay resources required to obtain a 16-step delay profile is reduced to nine types. To effectively prevent crosstalk, it is desirable to increase the number of delay amounts. However, since delay resources require relatively large logic circuit resources, it is desirable to reduce the number of delay resources as much as possible. In this embodiment, a waveform assignment circuit 92 that maps a limited number (nine types) of delay resources is provided to effectively prevent crosstalk. In the example of FIG. 10, although the delay amounts of seven pairs are the same, if at least one pair of delay amounts is equal, the number of delay resources can be saved accordingly.

[0049] The relationship between the delay amounts of each drive channel for an assignment period of about two periods is as shown in the graph of FIG. 11. Each drive channel can be separated from the adjacent drive channels by approximately 2 μs. Since this 2 μs is equal to the basic pulse width of the drive waveform, for example, when ejecting ink, the expansion and contraction of the pressure chamber 5 of adjacent drive channels drive in opposite directions, and as a result, the deterioration of print quality due to mechanical crosstalk can be suppressed. A deviation from 2 μs can cause the mechanical crosstalk to deteriorate, so the delay amount is finely adjusted so that the mechanical crosstalk does not deteriorate.

[0050] Here, the forward delay difference in FIG. 10 refers to the delay difference from the drive channel with the previous number when focusing on a certain drive channel. The backward delay difference is the delay difference from the drive channel with the next number. The average is the average value of the forward delay difference and the backward delay difference. Since the array of nozzles 20 is in a single row, the forward delay difference and the backward delay difference respectively indicate the delay amounts with respect to the drive channels adjacent to both sides in the array direction of the nozzles 20. FIG. 10 also shows the absolute value of the forward delay difference, the absolute value of the backward delay difference, and the average of the absolute value of the forward delay difference and the absolute value of the backward delay difference. The absolute value of the forward delay difference is, that is, the absolute value of the relative delay from the forward adjacent drive channel. Since the first group and the second group are assigned alternately, the adjacent drive channel is in a different group from the said drive channel.

[0051] When plotting the absolute value of the relative delay (the absolute value of the forward delay difference in FIG. 10) from the forward adjacent drive channel for each drive channel with the drive channel number on the horizontal axis, the graph in FIG. 12 is obtained. The graph in FIG. 12 also plots the average before and after of the absolute value of the relative delay (the average of the absolute values in FIG. 10). Since the mechanical crosstalk is affected by both the forward adjacent drive channel and the backward adjacent drive channel, its average dominates the mechanical crosstalk. That is, in order to minimize the mechanical crosstalk as much as possible, it is desirable that the average before and after of the absolute value of the relative delay (the average of the absolute values in FIG. 10) is close to the target delay amount of 2 μs. However, if the average before and after of the absolute value of the relative delay for all drive channels is aligned with the target delay amount of 2 μs, the number of simultaneous operations becomes too large, and although the mechanical crosstalk can be avoided, the electrical crosstalk cannot be avoided. Therefore, this embodiment provides an allowable range in which the average before and after of the absolute value of the relative delay is within 2 μs ± 0.02 μs to achieve both the avoidance of mechanical crosstalk and the avoidance of electrical crosstalk. As is clear from FIG. 12, with the allocation of the delay amounts shown in FIG. 10, the average before and after of the absolute value of the relative delay for all drive channels can be kept within the range of 2 μs ± 0.02 μs.

[0052] However, if the absolute value of the relative delay from the adjacent front drive channel continues to exceed or fall below the target delay amount of 2 μs, the delay amount will continue to increase. Therefore, the phase of the change in the delay amount is inverted midway to prevent the delay amount from becoming too large. Specifically, the delay amount is set large in the 9th drive channel to bring the absolute value of the relative delay from the adjacent front drive channel close to the target delay amount (point a in Fig. 12). Then, in the adjacent 10th drive channel, the absolute value of the relative delay from the adjacent front drive channel is set to a value below the same target delay amount as that of the 9th drive channel (point b in Fig. 12), thereby folding back the change in the delay amount.

[0053] Furthermore, the delay amount is set small in the 17th drive channel to bring the absolute value of the relative delay from the adjacent front drive channel close to the target delay amount (point c in Fig. 12). Then, in the adjacent 18th drive channel, the absolute value of the relative delay from the adjacent front channel is set to a value above the same target delay amount as that of the 17th drive channel (point d in Fig. 12), thereby folding back the change in the delay amount again.

[0054] Similarly, the delay amount is set large in the 25th drive channel to bring the absolute value of the relative delay from the adjacent front drive channel close to the target delay amount (point e in Fig. 12). Then, in the adjacent 26th drive channel, the absolute value of the relative delay from the adjacent front drive channel is set to a value below the same target delay amount as that of the 25th drive channel (point f in Fig. 12), thereby folding back the change in the delay amount. By repeating this, it is possible to prevent the delay amount from continuously increasing in the order of the drive channel numbers. The number of delay resources is also sufficient with 9, and the waveform allocation circuit 92 can also allocate the delay amount in a 16-step repetition. In the example of Fig. 12, the phase of the change is inverted at the center and both ends of the 16 steps corresponding to one cycle of the delay amount allocation period. However, the phase may be inverted at least once within one cycle of the delay amount allocation period.

[0055] Figure 13(a) is a graph plotting the pre-delay difference, post-delay difference, and average of the first group. The first group is the odd-numbered drive channels with the main delay amount set to 0 μs. As shown in Figure 13(a), since the 1ch drive channel is an end channel, there is no pre-delay difference. For the 3ch, 5ch, and 7ch drive channels, the absolute value of the pre-delay difference is smaller than the target delay amount, and the absolute value of the post-delay difference is larger than the target delay amount. For the 9ch drive channel, the absolute value of the pre-delay difference and the absolute value of the post-delay difference are again equal. For the 11ch, 13ch, and 15ch drive channels, they are reversed, with the absolute value of the pre-delay difference being larger than the target delay amount and the absolute value of the post-delay difference being smaller than the target delay amount. For the 17ch drive channel, the absolute value of the pre-delay difference and the absolute value of the post-delay difference are again equal. For the 19ch, 21ch, and 23ch drive channels, they are reversed, with the absolute value of the pre-delay difference being smaller than the target delay amount and the absolute value of the post-delay difference being larger than the target delay amount. For the 25ch drive channel, the absolute value of the pre-delay difference and the absolute value of the post-delay difference are again equal. For the 27ch, 29ch, and 31ch drive channels, they are reversed, with the absolute value of the pre-delay difference being larger than the target delay amount and the absolute value of the post-delay difference being smaller than the target delay amount. For the 33ch drive channel, the absolute value of the pre-delay difference and the absolute value of the post-delay difference are again equal. The odd-numbered drive channels after 35ch also repeat this sequence.

[0056] That is, within the first group, the absolute value of the delay difference from the forward adjacent drive channel (the absolute value of the forward delay difference, the same hereinafter) is greater than the target delay amount, and the absolute value of the delay difference from the rear adjacent drive channel (the absolute value of the rear delay difference, the same hereinafter) is smaller than the target delay amount, and the setting where the absolute value of the delay difference from the forward adjacent drive channel is smaller than the target delay amount and the absolute value of the delay difference from the rear adjacent drive channel is greater than the target delay amount are periodically switched. By repeating this, it is possible to prevent the delay amount from continuously increasing in the order of the drive channel numbers within the group. The number of delay resources is also sufficient at 9, and the waveform allocation circuit 92 can also allocate the delay amount with a 16-step repetition. Furthermore, within the group, the average value of the absolute value of the forward delay difference and the absolute value of the rear delay difference also falls within the allowable range of 2 μs ± 0.02 μs, and it is possible to minimize mechanical crosstalk.

[0057] Figure 13(b) is a graph plotting the forward delay difference, rear delay difference, and average of the second group. The second group is the even-numbered drive channels with the main delay amount set to 2 μs. As shown in Figure 13(b), for the drive channels of 2ch, 4ch, 6ch, and 8ch, the forward delay difference is greater than the target delay amount, and the rear delay difference is smaller than the target delay amount. For the drive channels of 10ch, 12ch, 14ch, and 16ch, it is reversed, with the forward delay difference smaller than the target delay amount and the rear delay difference greater than the target delay amount. For the drive channels of 18ch, 20ch, 22ch, and 24ch, it is reversed again, with the forward delay difference greater than the target delay amount and the rear delay difference smaller than the target delay amount. For the drive channels of 26ch, 28ch, 30ch, and 32ch, it is reversed again, with the forward delay difference smaller than the target delay amount and the rear delay difference greater than the target delay amount. The even-numbered drive channels after 34ch also repeat this sequence.

[0058] That is, similar to the first group, the second group also has a setting where the delay difference from the forward adjacent drive channel is greater than the target delay amount and the delay difference from the rear adjacent drive channel is smaller than the target delay amount, and a setting where the delay difference from the forward adjacent drive channel is smaller than the target delay amount and the delay difference from the rear drive channel is greater than the target delay amount, which periodically alternate. By repeating this, similar to the first group, it is possible to prevent the delay amount from continuously increasing in the order of the drive channel numbers within the group. Furthermore, for each group, the average value of the absolute value of the forward delay difference and the absolute value of the rear delay difference is within the allowable range of 2 μs ± 0.02 μs, enabling minimization of mechanical crosstalk.

[0059] That is, in order to minimize mechanical crosstalk, it is advisable to ensure that the average of the absolute values of the delay amounts from the two adjacent drive channels on both sides is within a predetermined range. In the example of FIG. 10, the delay amount of each drive channel is allocated so that the average of the absolute values of the delay amounts from the two adjacent drive channels on both sides is within 2.0 μs ± 0.02 μs. In this way, since the average of both sides of the absolute value of the delay amount between adjacent drive channels (the average of the absolute values of the forward delay difference and the rear delay difference) is maintained at approximately 2 μs (the basic pulse width of the drive waveform), as a result, the influence of mechanical crosstalk can be avoided.

[0060] Also, the sub-delay amount between drive channels for one cycle of the allocation period is as shown in FIG. 14. The odd channels 1, 3, 5, 7, 9, … 17, … in FIG. 14 are the first group, and a main delay amount of 0 μs is allocated. The even channels 2, 4, 6, 8, … 16, … in FIG. 14 are the second group, and a main delay amount of 2 μs is allocated. The delay amount of each channel is the sum of the main delay amount and the sub-delay amount. The sub-delay amount is allocated in a 16-channel cycle, monotonically increasing in channels 1 to 9, which is half of it, and monotonically decreasing in channels 9 to 17. Even if we only focus on the odd channels of the first group, it monotonically increases in channels 1, 3, 5, 7, 9 in the first half of the cycle and monotonically decreases in channels 9, 11, 13, 15, 17 in the second half of the cycle. Even if we only focus on the even channels of the second group, it monotonically increases in channels 2, 4, 6, 8, 10 in the first half of the cycle and monotonically decreases in channels 10, 12, 14, 16 in the second half of the cycle. Within the first group of odd channels or within the second group of even channels, the sub-delay amount is dispersed so that the same value does not appear more than three times within the allocation period at intervals of 0.08 μs to 0.1 μs between drive channels. Therefore, even if a plurality of drive channels are driven within the same drive cycle, the simultaneous drive number is 1 / 8 or less, and the influence of electrical crosstalk caused by current concentration on the common wiring 66 can be suppressed. Also, as described above, the number of allocations in one cycle of the allocation pattern P is set to an even number, and the number of delay resources is set to an odd number that is one more than half of the number of allocations in one cycle. Therefore, even if the sub-delay amount is repeatedly allocated, the same sub-delay amount does not continue, which works advantageously to prevent electrical crosstalk.

[0061] According to the above-described embodiment, it is possible to suppress the influence of crosstalk received from surrounding drive channels and perform stable ink ejection.

[0062] Figures 15 and 16 show other examples of drive waveforms applied to the actuator 8. The drive waveform in Fig. 15 is a drive waveform that discharges ink once in one drive cycle. For the drive waveform in Fig. 15, a negative voltage (-V) is applied to the individual terminals of the actuator 8 from time t1 to time t2, ground (GND) from time t2 to time t3, a positive voltage (+V) from time t3 to time t4, and ground (GND) at time t4. Time t1 to time t2 is set to, for example, half the time of the pressure oscillation period of the head unit 2. That is, the basic pulse width of the drive waveform for discharging ink is made the same as half the time of the pressure oscillation period of the head unit 2. When the pressure oscillation period of the head unit 2 is, for example, 4 μs, time t1 to time t2, which is the basic pulse width, is 2 μs. The common terminals of each actuator 8 are commonly connected to ground (GND).

[0063] For the actuator 8 to which a negative voltage (-V) is applied to the individual terminals at time t1, the piezoelectric members 6 (61, 62) on both sides of the pressure chamber 5 deform outward in the shear mode, respectively, so that the volume of the pressure chamber 5 expands and ink is supplied into the pressure chamber 5. At the subsequent time t2, when the potential of the individual terminals of the actuator 8 is set to ground (GND), the volume of the expanded pressure chamber 5 returns to its original state. That is, it relatively contracts. By contracting the volume of the pressure chamber 5 at the end of half the time of the pressure oscillation period in this way, the pressure of the ink in the pressure chamber 5 increases and the ink is discharged from the nozzle 20. At the subsequent time t3, for the actuator 8 to which a positive voltage (V) is applied to the individual terminals, the piezoelectric members 6 (61, 62) deform inward, respectively, so that the volume of the pressure chamber 5 contracts. Then, by setting the potential of the individual terminals to ground (GND) at time t4, the volume of the contracted pressure chamber 5 returns. This contraction and return attenuate the residual amount oscillation.

[0064] The drive waveform in Fig. 16 is a drive waveform of a single-pulse draw. The period from time t1 to t2 is set to 1 / 2 (for example, 2 μs) of the pressure oscillation period of the head portion 2 as the basic pulse width. First, a bias voltage is applied to the individual terminals of the actuator 8, and the pressure chamber 5 is expanded by setting the drive voltage V0 (for example, 0 V) at time t1. Then, by applying the drive voltage V2 of the intermediate potential at time t2 to contract the pressure chamber 5, the ink is ejected. Thereafter, the residual vibration is attenuated by applying the drive voltage V1 at time t3 to contract the pressure chamber 5. The drive waveform in Fig. 16 is a draw drive waveform, but it may also be a push drive, a push-draw drive, etc. Of course, the drive waveforms applicable to this embodiment are not limited to the drive waveforms in Figs. 5, 15, and 16.

[0065] Note that the inkjet head 100 is not limited to the shear mode actuator 8 in which the pressure chambers 5 and the air chambers 51 are alternately arranged. For example, a configuration in which a plurality of both the nozzles 20 and the actuators 8 are arranged on the surface of the nozzle plate 21 may be adopted. Other drop-on-demand piezo type actuators 8 may also be used. Further, the actuator 8 may be a laminated piezoelectric actuator formed by alternately laminating piezoelectric members and internal electrodes in layers.

[0066] In the above-described embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection head, but the liquid ejection head may be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0067] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0068] 10 Inkjet Printer 100 - 103 Inkjet Heads 2 Head Parts 20 Nozzles 5 Pressure Chambers 51 Air Chambers 8 Actuators 9 Drive Circuits 91 Waveform Generation Circuits 92 Waveform Allocation Circuits 93 Delay Circuits 94 Delay Amount Setting Memories 95 Drive Waveform Generation Circuits 96 Drive Waveform Setting Memories 97 Selectors 98 Drive Waveform Selection Memories 99 Switches

Claims

1. A nozzle, a plurality of drive channels each including an actuator corresponding to the nozzle, a delay amount setting unit that sets a plurality of delay amounts of a drive waveform applied to the actuator, a delay amount allocation unit that allocates the plurality of set delay amounts to the plurality of nozzles arranged in a row in a periodic manner in the arrangement direction of the nozzles to the drive channels, wherein the liquid discharge head is characterized by comprising the delay amount allocation unit.

2. The plurality of set delay amounts include a first group with a small delay amount and a second group with a large delay amount, the delay amount of the first group and the delay amount of the second group are alternately allocated in the arrangement direction of the nozzles, wherein the delay amount of each group monotonically increases in the arrangement direction of the nozzles in a region that is half of the allocation period and monotonically decreases in the remaining half region, and the liquid discharge head according to claim 1 is characterized by this.

3. The delay amount in the region where the amount monotonically increases and the delay amount in the region where the amount monotonically decreases are such that at least one set of the delay amounts is equal, and the liquid discharge head according to claim 1 is characterized by this.

4. The number of allocations in one period of the allocation period is an even number, and the number of types of the delay amounts set in the delay amount setting unit is one more than half of the allocation period, and the liquid discharge head according to claim 1 is characterized by this.

5. The difference between the delay amounts of the first group and the second group is equal to the basic pulse width of the drive waveform applied to the actuator or is 1 / 2 of the pressure vibration period of the head portion, and the liquid discharge head according to claim 1 is characterized by this.

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