Liquid ejection head drive circuit, liquid ejection head

Abstract

To provide a liquid discharge head drive circuit capable of achieving a delay of a drive timing between channels and a liquid discharge head.SOLUTION: This liquid discharge head drive circuit comprises: a common waveform generation unit; a timing generation unit; and a selection drive circuit. The common waveform generation unit generates a common waveform in which waveform elements of a plurality of drive waveforms of different start points are mixed where a waveform of a delay side starts before a preceding waveform ends and the preceding waveform ends before the waveform of the delay side ends. The timing generation unit generates a plurality of extraction timings different from each other. The selection drive circuit extracts the drive waveforms of the different start points by extracting the waveform elements in accordance with the extraction timings, and provides the drive waveforms to a capacitance actuator of a plurality of channels that discharges a liquid.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] An embodiment of the present invention relates to a liquid ejection head drive circuit and a liquid ejection head. [Background technology]

[0002] Liquid ejection heads that supply a predetermined amount of liquid to a predetermined position are known. Liquid ejection heads are mounted on, for example, inkjet printers, 3D printers, and dispensing devices. Inkjet printers eject droplets of ink from an inkjet head to form an image or the like on the surface of a recording medium. 3D printers eject droplets of modeling material from a modeling material ejection head, harden the droplets, and form a three-dimensional object. Dispensing devices eject droplets of a sample and supply a predetermined amount to a plurality of containers, etc.

[0003] A liquid ejection head has multiple channels that eject liquid. Each channel has a nozzle that ejects liquid, a pressure chamber that communicates with the nozzle, and an actuator. The liquid ejection head selects a channel from the multiple channels that ejects liquid, and drives the actuator by providing a drive signal. When the actuator is driven, the volume of the pressure chamber filled with liquid changes, and liquid is ejected from the nozzle.

[0004] Liquid ejection heads with multiple channels have problems such as crosstalk between channels caused by pressure vibrations and voltage drops caused by current concentration when driving multiple channels. One solution to these problems is to shift the drive timing between surrounding channels. However, to achieve a delay in the drive timing between channels, a drive waveform and its wiring pattern must be prepared for each delay amount. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3264422 [Patent Document 2] Patent No. 3618733 [Patent Document 3] JP 2001-246738 A [Patent Document 4] Japanese Patent Application Publication No. 10-315451 [Patent Document 5] JP 2002-154207 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a liquid ejection head drive circuit and a liquid ejection head that are capable of realizing a delay in drive timing between channels. [Means for solving the problem]

[0007] A liquid ejection head drive circuit according to an embodiment of the present invention includes a common waveform generator, a timing generator, and a selection drive circuit. The common waveform generator generates a plurality of drive waveforms with different start points, in which a delayed waveform starts before a preceding waveform ends and a preceding waveform ends before the delayed waveform ends. Multiple Waveform elements One waveform The timing generating unit generates a common waveform that includes a plurality of extraction timings that are different from each other. The selective drive circuit extracts drive waveforms with different starting points by extracting waveform elements according to the extraction timings, and applies the drive waveforms to the capacitive actuators of the plurality of channels that eject liquid. [Brief description of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram of an inkjet printer equipped with an inkjet head according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of the inkjet head. [Diagram 3] FIG. 2 is a cross-sectional view of an actuator of the inkjet head. [Figure 4]FIG. 2 is a block diagram of an inkjet head drive circuit according to an embodiment. [Diagram 5] FIG. 4 is a detailed diagram of a selection drive circuit in the inkjet head drive circuit. [Figure 6] 4 is a timing chart of the operation of the inkjet head driving circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] As an example of an image forming apparatus equipped with a liquid ejection head according to an 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. Inside a housing 11, the inkjet printer 10 has a cassette 12 that stores a sheet S, which is an example of a recording medium, an upstream transport path 13 for the sheet S, a transport belt 14 that transports the sheet S taken out of the cassette 12, a plurality of inkjet heads 100-103 that eject ink droplets toward the sheet S on the transport belt 14, a downstream transport path 15 for the sheet S, an ejection tray 16, and a control board 17. An operation unit 18 that is a user interface is disposed 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 externally connected device. The image data generated by the computer 200 is sent to a control board 17 of the inkjet printer 10 via a cable 201 and connectors 202 and 203.

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

[0013] The conveyor belt 14 is a mesh-like endless belt with many through holes formed on its surface. Three rollers, a drive roller 141 and driven rollers 142 and 143, support the conveyor belt 14 so that it can 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 device. In the figure, 105 indicates the rotation direction 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 fan 207 for reducing pressure. The fan 207 creates a negative pressure inside the negative pressure container 206 by forming an airflow, and adsorbs and holds the sheet S on the upper surface of the conveyor belt 14. In the figure, 106 indicates the flow of the airflow.

[0014] Inkjet heads 100-103, which are an example of liquid ejection heads, are arranged to face sheet S, which is attracted to and held on conveyor belt 14, with a small gap of, for example, 1 mm between them. Each of inkjet heads 100-103 ejects ink droplets toward sheet S. When sheet S passes below inkjet heads 100-103, the inkjet heads print images. Each of inkjet heads 100-103 has the same structure, except that they eject different colors of ink. The ink colors are, for example, cyan, magenta, yellow, and black.

[0015] The inkjet heads 100-103 are connected to ink tanks 315-318 and ink supply pressure adjusting devices 321-324 via ink flow paths 311-314, respectively. The ink tanks 315-318 are disposed above the inkjet heads 100-103. During standby, the ink supply pressure adjusting devices 321-324 adjust the pressure inside the inkjet heads 100-103 to a negative pressure, for example, -1.2 kPa, relative to atmospheric pressure so that ink does not leak from the nozzles 25 (see FIG. 2) of the inkjet heads 100-103. During image formation, the ink in the ink tanks 315-318 is supplied to the inkjet heads 100-103 by the ink supply pressure adjusting devices 321-324.

[0016] After the image is formed, the sheet S is sent from the conveyor belt 14 to a downstream conveying path 15. The downstream conveying path 15 is composed of pairs of feed rollers 151, 152, 153, and 154, and sheet guide plates 155 and 156 that define the conveying path of the sheet S. The sheet S passes through the downstream conveying path 15 and is sent from a discharge port 157 to a discharge tray 16. An arrow 107 in the figure indicates the conveying path of the sheet S.

[0017] Next, a description will be given of the configuration of the inkjet heads 100 to 103. The inkjet head 100 will be described below with reference to Figures 2 and 3, but the inkjet heads 101 to 103 have the same structure as the inkjet head 100.

[0018] 2, the inkjet head 100 includes a nozzle head section 2 which is an example of a liquid ejection section, and a flexible printed wiring board 3 which is an example of a printed wiring board. The nozzle head section 2 includes a nozzle plate 21, an actuator substrate 22, a sealing member 23 which seals the openings of a pressure chamber 51 and an air chamber 52 formed in the actuator substrate 22, and an ink supply port 24 formed in the sealing member 23. The ink supply port 24 is connected to an ink supply pressure adjustment device 321 shown in FIG. 1 via an ink flow path 311.

[0019] The flexible printed wiring board 3 is connected to the actuator board 22 of the nozzle head unit 2 and to a printed circuit board 4 that serves as a relay board. The flexible printed wiring board 3 is equipped with a driving IC (Integrated Circuit) 31 that is a driver chip (hereinafter referred to as a driving IC). The driving IC 31 temporarily stores print data sent from the control board 17 of the inkjet printer 10 via the printed circuit board 4, and provides driving signals to each channel so as to eject ink at a predetermined timing.

[0020] The nozzle plate 21 is a rectangular plate made of, for example, a resin such as polyimide or a metal such as stainless steel. A plurality of nozzles 25 for ejecting ink are formed on the surface of the nozzle plate 21. The nozzle density is set within the range of, for example, 150 to 1200 dpi.

[0021] The actuator substrate 22 is a rectangular substrate made of, for example, insulating ceramics. As shown in FIG. 3, a plurality of ink pressure chambers 51 and air chambers 52 are alternately formed in the actuator substrate 22 along a first direction, for example, the X direction. The pressure chambers 51 communicate with the nozzles 25. The pressure chambers 51 communicate with the ink supply ports 24 via a common ink chamber (not shown) formed in, for example, the actuator substrate 22 or the sealing member 23. That is, the nozzle head section 2 supplies ink to the pressure chambers 51 of each channel through the ink supply ports 24. That is, the nozzle head section 2 serves both as a liquid ejection section and a liquid supply section. On the other hand, the air chambers 52 arranged adjacent to the pressure chambers 51 are closed spaces that do not communicate with the nozzles 25 and the common ink chamber (not shown). The pressure chamber 51 and the air chamber 52 are formed by cutting out, for example, a rectangular groove shape in a second direction, for example, the Z direction, two piezoelectric members 26, 27 that are stacked in directions with opposite polarization directions (for example, facing directions) on the actuator substrate 22. That is, the pressure chamber 51 and the air chamber 52 are partitioned by the side walls of the piezoelectric members 26, 27 that are stacked in a third direction, for example, the Y direction.

[0022] The electrode 53 is integrally formed on the bottom and both side surfaces of the pressure chamber 51. The electrode 53 of the pressure chamber 51 is connected to an individual wiring 54, which is a wiring member. The electrode 55 is integrally formed on the bottom and both side surfaces of the air chamber 52. The electrode 55 of the air chamber 52 is connected to a common wiring 56, which is a wiring member. That is, the connection point of the electrode 53 of the pressure chamber 51 and the individual wiring 54 is one terminal of the actuator 5. The connection point of the electrode 55 of the air chamber 52 and the common wiring 56 is the other terminal of the actuator 5. The electrodes 53, 55, the individual wiring 54 and the common wiring 56 are formed of, for example, a nickel thin film. The individual wiring 54 is connected to the driving IC 31 (i.e., the driving circuit of each channel). The driving IC 31 provides a driving voltage as a driving signal to the actuator 5 of each channel. The voltages V1 and V2 are provided to the driving IC 31 as a power source for the driving voltage. The common wiring 56 is connected to, for example, ground (GND). As an example, the voltage V1 is a positive voltage, the voltage V2 is a negative voltage, and the voltage V3 is 0 V (=GND). With this configuration, when a drive voltage is applied to the actuator 5, an electric field is applied in a direction intersecting (preferably perpendicular to) the polarization axes of the piezoelectric members 26 and 27, and the piezoelectric members 26 and 27, which form the side walls of the actuator 5 in the X direction, deform symmetrically in the X direction in shear mode.

[0023] That is, the ink pressure chamber 51 is formed by being sandwiched between a pair of columnar actuators 5 using piezoelectric members 26, 27. A potential difference is applied to both walls of the columnar actuator 5, i.e., the inner wall and the outer wall of the pressure chamber 51, and the capacitive actuator 5 using the piezoelectric members 26, 27 is charged / discharged, thereby deforming the actuator 5. This changes the volume of the pressure chamber 51, and as a result, the ink pressure inside the pressure chamber 51 changes. Ink is ejected from the nozzle 25 by adjusting the magnitude and timing of this change.

[0024] 4 is a block diagram of the inkjet head drive circuit 6 in the drive IC 31. The inkjet head drive circuit 6 includes a common waveform generator 61, a timing generator 62, an image generator 63, and a selection drive circuit 64.

[0025] The common waveform generating unit 61 generates a common waveform, which will be described in detail later. The common waveform is sent to a selection drive circuit 64. The timing generating unit 62 sends the waveform passing pulses of groups A and B to the selection drive circuit 64, and synchronizes the operation timing of the common waveform generating unit 61 and the image generating unit 63. The image generating unit 63 generates image data for each channel and sends it to the selection drive circuit 64. The image data generated for each channel includes information on whether or not to eject ink from that channel.

[0026] The selection drive circuit 64, the detailed circuit configuration of which is shown in FIG. 5, is provided with a selection section 7 and an output section for each channel (ch1 to chN). An example of the selection section 7 is an AND circuit. The output section is, for example, a switch 71. An example of the switch 71 is a CMOS analog switch. Image data (ch1 image to chN image) from the image generation section 63 is input to each of the selection sections 7 of the corresponding channels. As an example, a 1-bit signal is given that is "1" when ink is to be ejected and "0" when ink is not to be ejected.

[0027] The multiple channels (ch1 to chN) are divided into groups. As an example, the odd-numbered channels (ch1, 3...n-1) are group A, and the even-numbered channels (ch2, 4...n) are group B. The waveform passing pulses of group A from the timing generation unit 62 are input to the selection units 7 of the odd-numbered channels (ch1, 3...n-1), respectively. The waveform passing pulses of group B from the timing generation unit 62 are input to the selection units 7 of the even-numbered channels (ch2, 4...n), respectively. The selection units 7 of the odd-numbered channels (ch1, 3...n-1) output passing signals based on the waveform passing pulses of group A when ejecting ink based on image data. The selection units 7 of the even-numbered channels (ch2, 4...n) output passing signals based on the waveform passing pulses of group B when ejecting ink based on image data. The passing signals control the ON / OFF of the switch 71. While the switch 71 is ON, the common waveform passes through the switch 71 and applies a drive voltage to the actuator 5. That is, some waveform elements of the common waveform pass through the switch 71 and become a drive waveform which is applied to the actuator 5.

[0028] As shown in the time chart of FIG. 6, the common waveform is a waveform in which the waveform elements of the drive waveform of group A and the waveform elements of the drive waveform of group B are mixed together so that the change points of each do not overlap in time series. FIG. 6 shows, as an example, a common waveform in which the waveform elements of the back-pulse pulse of the drive waveform of group A, the waveform elements of the back-pulse pulse of the drive waveform of group B, the waveform elements of the cancel pulse of the drive waveform of group A, and the waveform elements of the cancel pulse of the drive waveform of group B are mixed together in time series. That is, as an example of the drive waveform of the preceding group A and the drive waveform of the delayed group B, drive waveforms having different waveform start points but the same waveform shape are shown. As long as the condition that the waveform of the delayed group B starts before the waveform of the preceding group A ends and the waveform of the preceding group A ends before the waveform of the delayed group B ends is satisfied, the waveform shapes do not have to be the same, and may be different. In this case, the waveform of the preceding group A and the waveform of the delayed group B have parts that overlap and parts that do not overlap with each other. In Fig. 6, the ejection pulse portions overlap, but the cancel pulse portions do not. As long as the waveforms overlap as a whole, each portion may or may not overlap, and only a portion may overlap as in Fig. 6. Note that a back-to-back drive waveform is given as an example, but a drive waveform other than back-to-back drive may also be used. Furthermore, a multi-drop drive waveform may also be used. Multi-drop is a method of forming one dot by the sum of multiple drops.

[0029] The waveform passing pulse is an example of a plurality of different extraction timings generated by the timing generating section 62. In other words, the plurality of extraction timings are a plurality of waveform passing pulses having different intervals for extracting waveform elements from the above-mentioned common waveform. The waveform passing pulses are prepared as pulse trains for groups A and B. An example of a pulse train for group A is the group A waveform passing pulse shown in FIG. 6. An example of a pulse train for group B is the group B waveform passing pulse shown in FIG. 6. The group A waveform passing pulse and the group B waveform passing pulse have the same pulse width and interval, but the timings at which the pulses are turned ON are different from each other.

[0030] Next, the operation of the inkjet head drive circuit 6 will be described with particular reference to Figures 5 and 6. The common waveform generator 61 generates a common waveform and sends it to the selection drive circuit 64. The image generator 63 generates image data for each channel based on data sent from the control board 17 of the inkjet printer 10 and sends it to the selection drive circuit 64. The timing generator 62 synchronizes the operation timing of the common waveform generator 61 and the image generator 63, and sends waveform passing pulses for group A and group B to the selection drive circuit 64.

[0031] When ink is to be ejected based on image data, the selection unit 7 of each channel provides a passing signal according to the waveform passing pulse to the switch 71, which is the output unit. First, in the channels belonging to group A, the pulse turns ON at the falling edge of the common waveform that constitutes the back-firing pulse, turning the switch 71 ON. While the pulse is ON, the switch 71 maintains its ON state and negatively charges the actuator 5 toward voltage V2. This causes both side walls of the pressure chamber 51 to deform outward, expanding the volume of the pressure chamber 51. After that, the pulse turns OFF and the switch 71 turns OFF, but the capacitive actuator 5 retains the voltage of the drive waveform at the moment the switch 71 turned OFF, even though the switch 71 turns OFF.

[0032] Next, for the channels belonging to group B, the pulse turns ON at the falling edge of the common waveform that constitutes the push-pull pulse, turning ON the switch 71. While the pulse is ON, the switch 71 maintains its ON state and negatively charges the actuator 5 toward voltage V2. This causes both side walls of the pressure chamber 51 to deform outward, expanding the volume of the pressure chamber 51. After that, the pulse turns OFF and the switch 71 turns OFF, but the capacitive actuator 5 retains the voltage of the drive waveform at the moment the switch 71 turned OFF, even after the switch 71 turns OFF.

[0033] Next, in the channels belonging to group A, the pulse turns ON at the rising edge of the common waveform that constitutes the back-firing pulse, and switch 71 turns ON. While the pulse is ON, switch 71 maintains the ON state, discharging actuator 5. This discharge causes actuator 5, which had been deformed outward, to return to its original state, and the expanded pressure chamber 51 contracts to its original volume, causing ink to be ejected from nozzle 25.

[0034] Next, in the channels belonging to group B, the pulse turns ON at the rising edge of the common waveform that constitutes the back-firing pulse, and switch 71 turns ON. While the pulse is ON, switch 71 maintains the ON state, discharging actuator 5. This discharge causes actuator 5, which had been deformed outward, to return to its original state, and the expanded pressure chamber 51 contracts to its original volume, causing ink to be ejected from nozzle 25.

[0035] Next, for the channels belonging to group A, a pulse turns ON at the rising edge of the common waveform that constitutes the cancel pulse, turning switch 71 ON. While the pulse is ON, switch 71 remains ON, positively charging the actuator 5 toward voltage V1. This charging causes both side walls of the pressure chamber 51 to deform inward, contracting the volume of the pressure chamber 51. This contraction damps residual vibration. Next, a pulse turns ON at the falling edge of the common waveform that constitutes the cancel pulse, turning switch 71 ON. While the pulse is ON, switch 71 remains ON, discharging the actuator 5.

[0036] Next, for the channels belonging to group B, a pulse turns ON at the rising edge of the common waveform that constitutes the cancel pulse, turning switch 71 ON. While the pulse is ON, switch 71 remains ON, positively charging the actuator 5 toward voltage V1. This charging causes both side walls of the pressure chamber 51 to deform inward, contracting the volume of the pressure chamber 51. This contraction damps residual vibration. Next, a pulse turns ON at the falling edge of the common waveform that constitutes the cancel pulse, turning switch 71 ON. While the pulse is ON, switch 71 remains ON, discharging the actuator 5.

[0037] In this way, each channel extracts the waveform elements of the corresponding group from the common waveform that combines the waveform elements of the drive waveforms of group A and group B, and uses the waveform elements to drive the actuator 5. In this embodiment, multiple channels are divided into groups, and simultaneous driving is allowed in the same group, while simultaneous driving is avoided in different groups. By delaying between channels in this way, crosstalk due to pressure vibration can be suppressed. The reason for grouping by odd numbers and even numbers is that crosstalk between adjacent channels is the largest. Crosstalk between channels includes crosstalk through the ink flow path, crosstalk due to mechanical coupling, and electrical coupling (such as that due to common impedance), and all of these are effective. In addition, it is possible to suppress voltage drops due to current concentration when multiple channels are driven simultaneously. However, as a preferred example, the groups are divided by odd numbers and even numbers, but this is not limited to this. Of course, the number of groups is not limited to two, group A and group B, and may be three or more.

[0038] Furthermore, when the actuator 5 is repeatedly driven, for example, a flat portion may be formed at voltage V3 (=0V) after the waveform elements constituting the cancel pulse of group B, and the pulse may be turned ON here to reset (discharge) the actuator 5 to 0V. Furthermore, for example, a waveform passing pulse without a pulse may be applied to a channel that does not eject ink. When performing a precursor, that is, when it is necessary to apply a slight vibration to the actuator 5 of a channel that does not eject ink, a waveform passing pulse with a short pulse width that drives the actuator at a low voltage that does not eject ink may be applied.

[0039] According to the above-described embodiment, a common waveform is used in which the waveform elements of multiple drive waveforms are mixed so that the change points do not overlap, and each channel that ejects ink passes a portion of the common waveform to form a drive waveform. This makes it possible to realize a delay in drive timing between channels, for example, without having to prepare a drive waveform and its wiring pattern for each delay amount.

[0040] The inkjet head 100 is not limited to the actuator 5 of a shear mode type in which the pressure chambers 51 and the air chambers 52 are arranged alternately. For example, both the nozzles 25 and the actuators 5 may be arranged in multiples on the surface of the nozzle plate 21. Other drop-on-demand piezoelectric actuators 5 may also be used.

[0041] In the above embodiment, the inkjet head 100 of the inkjet printer 10 has been described as an example of a liquid ejection device, but the liquid ejection device may also be a modeling material ejection head of a 3D printer or a sample ejection head of a dispensing device.

[0042] 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, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0043] 10. Inkjet Printer 100~103 Inkjet head 2 Nozzle head 25 Nozzles 31 Driver IC 5 Actuators 51 Pressure Chamber 52 Air chamber 6 Inkjet head drive circuit 61 Common waveform generator 62 Timing Generation Unit 63 Image Generation Unit 64 Selective drive circuit 7 Selection section 71 Switch

Claims

1. a common waveform generating unit that generates a common waveform by mixing together multiple waveform elements of multiple driving waveforms having different starting points, in which a delayed waveform starts before a preceding waveform ends and a preceding waveform ends before the delayed waveform ends; a timing generating unit that generates a plurality of extraction timings different from each other; a selective drive circuit that extracts drive waveforms having different starting points by extracting the waveform elements according to the extraction timing, and applies the drive waveforms to capacitive actuators of multiple channels that eject liquid, respectively.

2. 2. The liquid ejection head drive circuit according to claim 1, wherein the plurality of drive waveforms have different starting points but the same waveform shape.

3. The channels are classified into one of a plurality of groups; 3. The liquid ejection head drive circuit according to claim 1, wherein the common waveform is a mixture of waveform elements of a plurality of drive waveforms having different start points corresponding to the number of the groups.

4. 3. The liquid ejection head drive circuit according to claim 2, wherein the common waveform includes a waveform element group in which waveform elements of the liquid ejection pulses of the groups are arranged, and a waveform element group in which waveform elements of the cancel pulses of the groups are arranged.

5. A plurality of channels each having a nozzle and an actuator for ejecting liquid; A liquid supply unit that supplies a liquid to the channel; A liquid ejection head comprising the liquid ejection head drive circuit according to any one of claims 1 to 4.

Images