Driving device

Abstract

To provide a driving device which can improve a drive frequency.SOLUTION: A driving device comprises a drive part that applies a driving signal for driving a pressure chamber communicating with a liquid discharging nozzle to an actuator. The driving signal includes: a large liquid droplet ejection signal which has an expansion pulse, a dead time and a contraction pulse, and ejects a large liquid droplet; and a small liquid droplet ejection signal which has an expansion pulse, a contraction pulse, a second expansion pulse and a second contraction pulse, and ejects a small liquid droplet smaller than the large liquid droplet. A time of the contraction pulse and a time of the second contraction pulse of the small liquid droplet ejection signal are included in the dead time of the large liquid droplet ejection signal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a drive device. [Background technology]

[0002] Among liquid ejection devices such as inkjet heads, shared-wall piezoelectric inkjet heads are well known. In shared-wall piezoelectric inkjet heads, a unipolar voltage signal is applied to the drive channel that ejects ink and the adjacent channel, expanding and contracting the volume of the pressure chamber in the drive channel to eject ink droplets. For example, by applying a binary voltage (low and high) to control the volume of the pressure chamber in three stages (expansion, pause, and contraction), complex drive control can be performed using an inexpensive drive circuit.

[0003] On the other hand, piezoelectric inkjet heads can achieve gradation recording by varying the drive waveform to change the ejection volume. For example, in gradation drive, if 1AL is half the acoustic resonance period of the ink in the pressure chamber, to eject large droplets, the pressure chamber expands by 1AL, pauses for more than 1AL, and then contracts for less than 1AL. To eject small droplets, the pressure chamber expands by approximately 0.6AL, contracts by 0.4AL, expands again, and then contracts. In this type of gradation drive for inkjet heads, the voltage signal applied to adjacent channels must be common to multiple channels, so the waveforms for small and large droplets must not overlap in time. This increases the length of the drive waveform, making it difficult to improve the drive frequency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4237382 [Patent Document 2] Patent No. 4247043 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a drive device capable of improving the drive frequency. [Means for solving the problem]

[0006] The driving device according to the embodiment includes a driving unit that applies a driving signal to an actuator to drive a pressure chamber that communicates with a nozzle that ejects liquid, and the driving signal includes a large droplet ejection signal that has an expansion pulse, a pause time, and a contraction pulse and ejects large droplets, and a small droplet ejection signal that has an expansion pulse, a contraction pulse, a second expansion pulse, and a second contraction pulse and ejects small droplets that are smaller than the large droplets, and the time of the contraction pulse of the small droplet ejection signal and the time of the second expansion pulse are included in the pause time of the large droplet ejection signal. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a liquid ejection device according to a first embodiment. [Figure 2] FIG. 1 is a perspective view showing the configuration of a liquid ejection head according to a first embodiment. [Figure 3] FIG. 2 is an explanatory diagram showing the configuration of the liquid ejection head. [Figure 4] FIG. 3 is an explanatory diagram showing a driving waveform according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A liquid ejection head 1 according to a first embodiment and a liquid ejection device 2 using the liquid ejection head 1 will be described below with reference to FIGS. 1 to 4. FIG. 1 is an explanatory diagram showing the configuration of the liquid ejection device 2 according to the first embodiment, and FIG. 2 is a perspective view showing the configuration of the liquid ejection head 1. FIG. 3 is a cross-sectional view showing the configuration of a portion of the liquid ejection head 1. FIG. 4 is an explanatory diagram showing the drive waveforms of this embodiment. FIG. 4(a) shows the waveform of the bipolar drive voltage of Example 1, and FIG. 4(b) shows the waveform of the unipolar drive voltage of Example 2. Note that in each figure, the configuration is enlarged, reduced, or omitted as appropriate for ease of explanation.

[0009] A liquid ejection device 2 having a liquid ejection head 1 will be described with reference to Fig. 1. The liquid ejection device 2 includes a housing 2111, a medium supply unit 2112, an image forming unit 2113, a medium ejection unit 2114, a conveying device 2115 which is a support device, and a control unit 2118.

[0010] The liquid ejection device 2 is an inkjet printer that performs an image formation process on paper P by ejecting liquid such as ink while transporting the paper P as a recording medium, which is the object of ejection, along a predetermined transport path 2001 that runs from a medium supply section 2112 through an image forming section 2113 to a medium ejection section 2114.

[0011] The medium supply unit 2112 includes a plurality of paper feed cassettes 21121. The image forming unit 2113 includes a support unit 2120 that supports paper, and a plurality of head units 2130 that are arranged above and facing the support unit 2120. The medium discharge unit 2114 includes a paper discharge tray 21141.

[0012] The support section 2120 includes a conveyor belt 21201 that is looped in a predetermined area where image formation is performed, a support plate 21202 that supports the conveyor belt 21201 from the back side, and a plurality of belt rollers 21203 that are provided on the back side of the conveyor belt 21201.

[0013] The head unit 2130 includes liquid ejection heads 1 which are multiple inkjet heads, multiple supply tanks 2132 as liquid tanks mounted on each liquid ejection head 1, a pump 2134 which supplies ink, and a connection flow path 2135 which connects the liquid ejection heads 1 and the supply tanks 2132.

[0014] The liquid ejection head 1 is supplied with ink as a liquid stored in a supply tank 2132. The liquid ejection head 1 may be a non-circulation type head that does not circulate ink, or may be a circulation type head that circulates ink.

[0015] In this embodiment, the liquid ejection heads 1 are provided with four colors of liquid ejection heads 1 (cyan, magenta, yellow, and black), and four color supply tanks 2132 that respectively store ink of each color. The supply tanks 2132 are connected to the liquid ejection heads 1 by connection flow paths 2135.

[0016] As shown in FIG. 2, the liquid ejection head 1 is an inkjet head and includes a nozzle plate 21 having a plurality of nozzles 201 (2011 to 2016), an actuator substrate 22, a manifold 23 bonded to the actuator substrate 22, and a drive circuit 24 (drive unit).

[0017] The actuator substrate 22 is disposed opposite the nozzle 201 and includes an actuator 25 as a liquid ejection unit having a plurality of pressure chambers 26 communicating with the nozzle 201 and a drive element unit 27 adjacent to the plurality of pressure chambers 26. The actuator substrate 22 is configured in a predetermined shape that forms a predetermined flow path including the plurality of pressure chambers 26 between it and the nozzle plate 21.

[0018] Electrodes 28 (281-286) connected to the drive circuit 24 are formed on the drive element portion 27 adjacent to the pressure chamber 26 of the actuator 25. The electrodes 28 are connected to the control unit 2118 via a driver of the drive circuit 24 (described later) by wiring 29 connected to the drive circuit 24, for example, and are configured to be drive-controllable by control by a processor.

[0019] FIG. 3 is an example of a cross-sectional view of an inkjet head according to this embodiment. Pressure chambers 261-266 are formed in an actuator substrate 22, which is composed of a pair of piezoelectric members polarized in opposite directions, and each of these pressure chambers 201 (2011-2016) is fluidly connected to a corresponding one of the nozzles 201 formed in the nozzle plate 21. Electrodes 281-286 are formed on the inner surfaces of the pressure chambers 261-266, and each of the electrodes 281-286 is connected to the drive circuit 24 by wiring 291-296. FIG. 3 shows a so-called side shooter type inkjet head, in which the ink ejection direction of the nozzle 201 is perpendicular to the longitudinal direction of the pressure chamber 26. However, the ink ejection direction of the nozzle 201 is not limited to the side shooter type, and may be a so-called edge shooter type inkjet head, in which the ink ejection direction of the nozzle 201 is parallel to the longitudinal direction of the pressure chamber 26.

[0020] The drive circuit 24 includes a driver IC 241 and various wiring boards 242. The drive circuit 24 drives the actuator 25 by applying a drive voltage to the wiring pattern of the actuator 25 via the driver IC 241, thereby increasing or decreasing the volume of the pressure chamber 26 and causing droplets to be ejected from the nozzles 201 arranged opposite to the actuator 25.

[0021] The liquid ejection head 1 comprises a nozzle plate 21, an actuator substrate 22, and a manifold 23, and defines a predetermined flow path having a pressure chamber 26 therein. The flow path of the liquid ejection head 1 is connected to a connection flow path 2135 of the liquid ejection device. For example, the liquid ejection head 1 is a shared-wall type inkjet head.

[0022] The pump 2134 is a liquid-transfer pump that is configured, for example, as a piezoelectric pump. The pump 2134 is connected to the control unit 2118, and is controlled by the control unit 2118.

[0023] The connection flow path 2135 includes a supply flow path that is connected to the ink supply pipe of the liquid ejection head 1. The connection flow path 2135 also includes a recovery flow path that is connected to the ink discharge pipe of the liquid ejection head 1. For example, if the liquid ejection head 1 is a non-circulation type, the recovery flow path is connected to a maintenance device, and if the liquid ejection head 1 is a circulation type, the recovery flow path is connected to the supply tank 2132.

[0024] The transport device 2115 transports the paper P along a transport path 2001 that runs from a paper feed cassette 21121 in the medium supply unit 2112, through the image forming unit 2113, to a paper discharge tray 21141 in the medium discharge unit 2114. The transport device 2115 includes a plurality of guide plate pairs 21211-21218 and a plurality of transport rollers 21221-21228 that are arranged along the transport path 2001. The transport device 2115 supports the paper P so that it can move relative to the liquid ejection head 1.

[0025] The control unit 2118 is, for example, a control board, and includes a processor, a ROM (Read Only Memory), a RAM (Random Access Memory), an I / O port that is an input / output port, and an image memory.

[0026] The processor is a processing circuit such as a CPU (Central Processing Unit) that is a controller. The processor controls, via an I / O port, the head unit 2130, drive motor, operation unit, various sensors, and the like that are provided in the liquid ejection device 2. The processor transmits the print data stored in the image memory to the drive circuit 24 in the order of drawing.

[0027] The control unit 2118 also determines an adjusted drop waveform based on the adjustment data, for example, selecting an adjusted drop waveform to be applied from among adjusted drop waveforms that can be set in multiple stages.

[0028] The ROM stores various programs, etc. The RAM temporarily stores various variable data, image data, etc. The I / O port is an interface unit that inputs and outputs data from the outside. Print data from an externally connected device is sent to the control unit 2118 through the I / O port and saved in the image memory.

[0029] The print data is data converted from image data including information on the color and density of each area and input to the head to eject liquid. The liquid ejection head 1 selects a drive waveform based on the print data and applies the drive waveform to the actuator 25.

[0030] The characteristics of the liquid ejection head 1 used in the liquid ejection device 2 according to this embodiment and the drive waveform of the drive signal generated by the drive circuit 24 of the liquid ejection head 1 will be described below.

[0031] The control unit 2118 sets the drive waveform to be applied to each drive element based on the print data. For example, the control unit 2118 may select a drive pattern for each element from a plurality of patterns that are set and stored in advance. For example, the control unit 2118 drives each of the plurality of drive elements corresponding to each nozzle of the liquid ejection unit using a waveform pattern based on the print data.

[0032] FIG. 4(a) is an explanatory diagram showing a bipolar drive waveform of Example 1 of this embodiment, and FIG. 4(b) is an explanatory diagram showing a unipolar drive waveform of Example 2. FIG. 4 shows the waveform of the voltage applied to the electrodes 281-286 of the seven adjacent pressure chambers 261-266 formed by the drive element section 27 (271-277) shown in FIG. 3. The drive waveform based on the bipolar voltage in FIG. 4(a) and the drive waveform based on the unipolar voltage in FIG. 4(b) perform exactly the same operation on the inkjet head of FIG. 3. In each waveform diagram in FIGS. 4(a) and 4(b), the vertical axis represents voltage [V] and the horizontal axis represents time [μs].

[0033] For example, the inkjet head according to this embodiment is a shared-wall type inkjet head in which the drive element portion 27 is shared by adjacent pressure chambers 26, and as an example, is a three-division drive type inkjet head in which every third nozzle is driven in turn in three divisions. In other words, pressure chambers 26 are formed on both sides of the drive element portion 27 (271-277) which forms one partition wall.

[0034] The drive waveforms in Example 2 are waveforms that apply unipolar voltage signals to the pressure chamber to be driven that ejects ink and to the adjacent channel adjacent to the pressure chamber to be driven, and expand and contract the volume of the pressure chamber of the drive channel to eject ink droplets. This waveform controls the volume of the pressure chamber in three stages: expansion, rest, and contraction, by combining a first voltage and a voltage higher than the first voltage. In this embodiment, large droplets and small droplets are achieved by combining two voltage levels.

[0035] First, the driving operation using the bipolar waveform in Example 1 will be described using Figure 4. For example, in the example in Figure 4, two large droplets are ejected from nozzle 2012, and one small droplet smaller than the large droplet is ejected from nozzle 2015, while no ink is ejected from the other nozzles 2011, 2013, 2014, and 2016. In Examples 1 and 2 shown in Figure 4, the first droplet is ejected from time ta to tb, and the second droplet is ejected from time tb to tc. For example, one small droplet of 6 pl, one large droplet of 9 pl, and two large droplets of 18 pl are ejected, and gradation control is performed by changing the size of these ink droplets according to the gradation information of the printed image.

[0036] The waveform WA is a large droplet ejection waveform that ejects a large droplet, and is composed of an expansion pulse (expansion pulse waveform) WAA, a pause time WAB, and a contraction pulse (contraction pulse waveform) WAC. In other words, the large droplet ejection signal is a signal that causes the pressure chamber to eject one droplet through the expansion state, steady state, and contraction state.

[0037] The expansion pulse WAA is a pulse that ejects ink, and the contraction pulse WAC is a pulse that cancels the pressure vibrations generated by the expansion pulse WAA. The expansion pulse WAA and the contraction pulse WAC have the same voltage amplitude, V. The pulse width of WAA is preferably 1AL, where AL represents half the acoustic natural vibration period of the ink in the pressure chamber 26. The pulse width of the contraction pulse WAC is preferably 1AL or less, and the optimal length varies depending on factors such as the damping rate of the ink pressure vibrations. If the damping rate is large, it is desirable to shorten the width of the contraction pulse WAC. The length of the pause time WAB is preferably determined so that the time difference between the temporal center of the expansion pulse WAA and the temporal center of the contraction pulse WAC is 2AL.

[0038] The waveform WB is a small droplet ejection waveform that ejects small droplets, and is composed of an expansion pulse (expansion pulse waveform) WBA, a contraction pulse (contraction pulse waveform) WBB, a second expansion pulse (second expansion pulse waveform) WBC, and a second contraction pulse (second contraction pulse waveform) WBD. That is, the small droplet ejection signal is a signal that causes the pressure chamber to eject one droplet through an expanded state, a contracted state, a second expanded state, and a second contracted state.

[0039] The expansion pulse WBA and contraction pulse WBB are pulses that eject ink. The second expansion pulse WBC and second contraction pulse WBD are pulses that cancel the pressure vibrations generated by the expansion pulse WBA and contraction pulse WBB. The expansion pulse WBA, contraction pulse WBB, second expansion pulse WBC, and second contraction pulse WBD all have the same voltage amplitude, V.

[0040] The pulse width of WBA is preferably 0.6 AL. The pulse width of WBB is preferably 0.4 AL. Since ink is ejected only during the pulse width of the contraction pulse WBB, the ink ejection volume of the small droplet waveform WB is smaller than the ink ejection volume of the large droplet waveform WA. The pulse widths of the second expansion pulse WBC and the second contraction pulse WBD are preferably each 1 AL or less, with the optimal length varying depending on factors such as the damping rate of the ink pressure vibration.

[0041] In this embodiment, the control unit 2118 sets the time difference between the large droplet waveform WA and the small droplet waveform WB so that the contraction pulse WBB and the second expansion pulse WBC of the small droplet ejection waveform WB are included in the pause time WAB of the large droplet ejection waveform WA. That is, in the ejection waveforms of the drive device according to this embodiment, the time difference between the large droplet waveform WA and the small droplet waveform WB is such that the contraction pulse WBB and the second expansion pulse WBC of the small droplet ejection waveform WB are included in the pause time WAB of the large droplet ejection waveform WA.

[0042] 4(a), the start of the contraction pulse WBB in the drive waveform of electrode 285 is the same timing as the start of the rest time of electrode 282, and the end of the second expansion pulse WBC of electrode 285 is earlier than the end of the rest time of electrode 282, so that the contraction pulse WBB and the second expansion pulse WBC are included in the rest time WAB of the large droplet ejection waveform WA. Therefore, the timing when electrode 285 becomes a negative voltage (-V) and the timing when electrode 282 becomes a positive voltage (+V) are arranged so as not to overlap. This makes it possible to avoid a situation where the voltage of one of the waveforms WA and WB becomes +V when the voltage of the other waveform is -V.

[0043] Using Figures 4(a) and (b), we will explain how to convert the bipolar voltage waveforms WA and WB into the unipolar voltage waveforms WC, WD, and WE. The waveform WC is a non-ejection waveform that is applied when no ink is ejected. The waveform WD is a large droplet ejection waveform. The waveform WE is a small droplet ejection waveform.

[0044] Waveforms WC to WE are obtained by raising the voltages of the negative polarity pulses WAA, WBA, and WBC of waveforms WA to WB to 0 across all channels, including non-ejection channels. Pulse WCa is the inverted voltage of pulse WAA. Pulse WCB is the inverted voltage of pulse WBC. Pulse WDA is the inverted voltage of pulse WBC. Pulse WDB is the same as pulse WAC. Pulse WEA is the inverted voltage of pulse WAA excluding pulse WBA. Pulse WEB is the same as pulse WBB. Pulse WEC is the same as pulse WBD.

[0045] In a shear mode inkjet head, the drive element 27 of the actuator 25 is driven by the voltage difference between the drive channel and the adjacent channel, so even if the voltage is changed by the same amplitude across all channels simultaneously, the ejection operation does not change. Therefore, the unipolar voltage waveforms WC to WE in Figure 4(b) perform exactly the same operation as the bipolar voltage waveforms WA to WB in Figure 4(a).

[0046] According to this embodiment, the contraction pulse WBB and the second expansion pulse WBC are set to be included in the pause time WAB of the large droplet waveform WA. Therefore, even if the small droplet waveform WB and the large droplet waveform WA overlap in time, they can be driven with unipolar drive waveforms WC to WE. That is, for example, the timing when electrode 285 becomes a negative voltage (-V) and the timing when electrode 282 becomes a positive voltage (+V) do not overlap, so the voltage applied to two adjacent electrodes can be divided into binary waveforms to realize waveforms for large droplet ejection and small droplet ejection, respectively. For example, large droplet ejection and small droplet ejection are possible by setting the binary values ​​of 0 and positive voltage.

[0047] This embodiment improves the drive frequency. Specifically, because the contraction pulse WBB and the second expansion pulse WBC are set to be included in the pause time WAB of the large droplet waveform WA, the small droplet waveform WB and the large droplet waveform WA can be driven with unipolar drive waveforms WC to WE even when they overlap in time. Therefore, an inkjet recording device can be provided that is inexpensive, has high print quality, and is fast to print, even with an inkjet head with an inexpensive drive circuit that outputs only unipolar drive waveforms, and can print multi-tone images containing small and large droplets in a short drive cycle.

[0048] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and modifications and improvements can be made as appropriate.

[0049] For example, the specific conditions of the waveforms in the above embodiments are not limited to those in the above embodiments and can be changed as appropriate. For example, the voltage value applied to each piezoelectric element can be adjusted as appropriate depending on various conditions. For example, a potential difference can be generated by grounding one of adjacent piezoelectric elements and applying a voltage to the other, or by applying a voltage to both of them. The drive waveform is not limited to a pull-stroke waveform, and can also be a push-stroke or push-pull-stroke waveform.

[0050] For example, the configuration of the liquid ejection head 1 is not limited to the above example, and may be used for other types of heads. Furthermore, although the liquid ejection device 2 has been exemplified as an inkjet printer that forms a two-dimensional image using ink on an image forming medium, it is not limited to this and may be, for example, a 3D printer, industrial manufacturing machinery, or medical machinery, and may be, for example, a device that forms a three-dimensional object by ejecting a material or a binder for solidifying the material from an inkjet head.

[0051] In addition, in the above embodiment, an example was shown in which the control operation was performed by the control unit 2118, but the present invention is not limited to this. For example, the liquid ejection head 1 may be provided with a drive circuit that drives the actuator, and the liquid ejection head 1 itself may be a drive device, or may be equipped with a drive device.

[0052] According to at least one of the embodiments described above, the contraction pulse WBB and the second expansion pulse WBC are set to be included in the pause time WAB of the large droplet waveform WA, so that even if the small droplet waveform WB and the large droplet waveform WA overlap in time, they can be driven with unipolar drive waveforms WC to WE, thereby improving the drive frequency.

[0053] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0054] 1...liquid ejection head, 2...liquid ejection device, 21...nozzle plate, 22...actuator substrate, 23...manifold, 24...drive circuit, 25...actuator, 26...pressure chamber, 27 (271-276)...drive element section, 201 (2011-2016)...nozzle, 242...wiring board, 2001...transport path, 2111...casing, 2112...medium supply section, 2113...image forming section, 2114...medium discharge section, 2115... Conveying device, 2118...control unit, 2120...support unit, 2130...head unit, 2132...supply tank, 2134...pump, 2135...connecting flow path, 21121...paper feed cassette, 21141...paper output tray, 21201...conveying belt, 21202...support plate, 21203...belt roller, 21211 to 21218...guide plate pair, 21221 to 21228...conveying roller, IC241...driver.

Claims

1. a drive unit that applies a drive signal to the actuator to drive a pressure chamber that communicates with a nozzle that ejects liquid; The drive signal is a large droplet ejection signal having an expansion pulse, a pause period, and a contraction pulse for ejecting a large droplet; a small droplet ejection signal having an expansion pulse, a contraction pulse, a second expansion pulse, and a second contraction pulse, for ejecting a small droplet smaller than the large droplet; A driving device, wherein the time of the contraction pulse of the small droplet ejection signal and the time of the second expansion pulse are included in the pause time of the large droplet ejection signal.

2. The driving device according to claim 1 , wherein the driving signal is composed of unipolar pulses.

3. 3. The drive device according to claim 2, wherein the actuator is a shared-wall type actuator having a plurality of the pressure chambers and a drive element portion disposed between adjacent ones of the pressure chambers.

4. The driving device according to claim 1 , wherein the driving signal is formed of a binary pulse waveform.

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