Liquid ejection head

Abstract

To provide a liquid discharge head which enables fine gradation control.SOLUTION: A liquid discharge head includes a drive circuit for driving a liquid discharge part for discharging liquid in a plurality of gradations, wherein in at least any one gradation, a drive waveform driving the liquid discharge part is a multi-drop waveform having a plurality of drop waveforms discharging droplets, and has the plurality of drop waveforms having different discharge volumes in one printing period.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Multi-drop driving is known as one method of gradation control for liquid ejection devices such as inkjet heads. In multi-drop driving, a drive signal having multiple unit drive waveforms for ejecting ink droplets is supplied within one printing cycle, thereby achieving a total ejection volume that is an integer multiple of the unit ejection volume obtained by one unit drive waveform.

[0003] In order to improve the printing performance of such inkjet heads, more precise gradation control is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-87801 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 liquid ejection head that is capable of finely controlling gradation. [Means for solving the problem]

[0006] The liquid ejection head according to the embodiment includes a drive circuit that drives a liquid ejection unit that ejects liquid at a plurality of gradations, and the drive waveform that drives the liquid ejection unit at at least one of the gradations is a multi-drop waveform that has a plurality of drop waveforms that eject droplets, and the plurality of drop waveforms have different ejection volumes in one printing cycle. At the same time, the cycles of the plurality of drop waveforms are constant, and the plurality of drop waveforms each include an expansion element that expands a pressure chamber provided in the liquid ejection unit by an expansion voltage, and a contraction element that contracts the pressure chamber by a contraction voltage higher than the expansion voltage, and the durations of the contraction elements of the plurality of drop waveforms are different. . [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] 6 is a graph showing a driving waveform according to the embodiment; [Figure 4] FIG. 3 is an explanatory diagram showing gray scales and driving waveforms according to the first embodiment. [Figure 5] FIG. 10 is an explanatory diagram showing gray scales and driving waveforms according to the second embodiment. [Figure 6] 10 is a graph showing the ejection volume for each tone of the driving waveform according to Example 2. [Figure 7] FIG. 10 is an explanatory diagram showing gray scales and driving waveforms according to the third embodiment. [Figure 8] FIG. 10 is an explanatory diagram showing gray scales and driving waveforms according to the fourth embodiment. [Figure 9] FIG. 10 is an explanatory diagram showing gray scales and driving waveforms according to the fifth embodiment. [Figure 10] 10 is a graph showing gray levels and driving waveforms according to Example 5. [Figure 11] FIG. 13 is an explanatory diagram showing gray scales and driving waveforms according to the sixth embodiment. [Figure 12] FIG. 10 is an explanatory diagram showing grayscales and driving waveforms according to Comparative Example 1. [Figure 13] FIG. 10 is an explanatory diagram showing grayscales and driving waveforms according to Comparative Example 2. 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 3. 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 graph showing a plurality of unit drive waveforms in the first embodiment. 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, a maintenance device 2117, 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 211, an actuator substrate 22, a manifold 23 bonded to the actuator substrate 22, and a drive circuit 24.

[0017] The actuator substrate 22 is disposed opposite the nozzles 211 and includes an actuator 25 as a liquid ejection unit having a plurality of pressure chambers 26 communicating with the nozzles 211 and a drive element unit 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] An electrode connected to the drive circuit 24 is formed on the drive element portion adjacent to the pressure chamber 26 of the actuator 25. The electrode is connected to the control unit 2118 via a driver of the drive circuit 24 (described later) by, for example, a wire connected to the drive circuit 24, and is configured to be drive-controllable by control by a processor.

[0019] 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 211 arranged opposite to the actuator 25.

[0020] 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.

[0021] 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.

[0022] 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 the maintenance device 2117, and if the liquid ejection head 1 is a circulation type, the recovery flow path is connected to the supply tank 2132.

[0023] 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.

[0024] The maintenance device 2117, for example, during maintenance, sucks and recovers ink remaining on the outer surface of the nozzle plate 21. Furthermore, if the liquid ejection head 1 is a non-circulation type, the maintenance device 2117 recovers ink inside the liquid ejection head 1 during maintenance. Such a maintenance device 2117 has a tray, tank, or the like for storing the recovered ink.

[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 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.

[0028] The following describes the characteristics of the liquid ejection head 1 used in the liquid ejection device 2 according to this embodiment, and the drive waveforms generated by the drive signals of the drive circuit 24 of the liquid ejection head 1. For example, the liquid ejection head 1 is multi-drop driven, and can be driven in multiple gradations by combining multiple drop waveforms with different ejection volumes. In other words, the drive circuit 24 drives the head with multi-gradation drive waveforms using multi-gradation (multiple types) multi-drop signals.

[0029] The drive waveform for each gradation is a multi-drop waveform having multiple drop waveforms, and is composed of a combination of multiple drop waveforms. Figure 3 is a graph showing two types of drop waveforms, WvA and WvB, as an example, with the vertical axis representing voltage [V] and the horizontal axis representing time [μs]. Each drop waveform WvA and WvB has an expansion element and a contraction element, and the pulse width of the contraction element varies, resulting in different ejection volumes due to the multiple drop waveforms. Note that the cycle of the multiple drop waveforms is constant. In Figures 4, 5, 7, 8, 9, 11, 12, and 13, WaveA represents the drop waveform WvA, and WaveB represents the drop waveform WvB.

[0030] As shown in Figure 3, each of the drop waveforms WvA and WvB includes an expansion element that reduces the voltage from the intermediate voltage Vb to an expansion voltage Va to expand the pressure chamber 26, then returns to the intermediate voltage Vb after a certain period of time has passed, and a contraction element that increases the voltage from the intermediate voltage Vb to a contraction voltage Vc higher than the intermediate voltage Vb to contract the pressure chamber 26 to eject ink, then returns to the intermediate voltage Vb. For example, the intermediate voltage Vb = 0 V. Note that the contraction voltage Vc is higher than the expansion voltage Va. In the drop waveforms WvA and WvB, the state at the intermediate voltage Vb is called the steady state.

[0031] In this embodiment, the drive waveform for driving the liquid ejector has multiple drop waveforms with different ejection volumes at any one of the gradations. That is, the drive circuit 24 drives the actuator at multiple gradations with different total ejection volumes of liquid within one printing cycle by combining multiple drop waveforms with different ejection volumes.

[0032] At least one of the gradations may be a gradation that does not eject liquid. Also, in this embodiment, the drive waveform of at least one of the gradations may be different from the drive waveforms of the other gradations in the number of drops that accompany the ejection of liquid.

[0033] According to this embodiment, by combining a plurality of different drop waveforms to perform gradation control, the ejection volume can be controlled in small increments. By varying the ejection volume of the drop waveforms, it is possible to provide gradation depending on the difference in the ejection volume of the drop waveforms. Therefore, the ejection volume can be set as desired.

[0034] For example, Comparative Example 1 shown in FIG. 12 is an example in which gradation is achieved by increasing or decreasing the number of waveforms of one type. In this case, the ejection volume for each gradation is an integer multiple of the ejection volume for each drop waveform. Comparative Example 2 shown in FIG. 13 is an example in which the same waveform is inserted at timings when ejection is not performed in Comparative Example 1, resulting in the same ejection volume for all gradations. On the other hand, according to the above embodiment, by combining multiple drop waveforms WvA and WvB with different ejection volumes, it is possible to adjust the ejection volume by an increase or decrease amount that is smaller than an integer multiple of the ejection volume for each of the first drop waveform WvA and the second drop waveform WvB.

[0035] Furthermore, for example, when printing a solid image using all the nozzles of the liquid ejection head 1, differences occur in the ejection volume of each dot depending on the dimensions of the nozzle 211, the actuator 25, etc., but according to the above embodiment, by setting the ejection volume to adjust for unevenness caused by this difference in ejection volume, it is possible to make the adjustment unevenness less noticeable.

[0036] Below, several examples 1 to 6 of the embodiment will be described. In the examples described below, one printing cycle has four drops, and the periodic length of each drop waveform is the same. In other words, even if the ejection volume differs depending on the gradation, one printing cycle has the same length. For example, one printing cycle for each of gradations 0 to 4 has four drops, and the periodic length of each drop waveform is the same, so as a result, one printing cycle including four drops is the same for each.

[0037] [Example 1] 4 is a table showing the driving waveforms of multiple gradations in Example 1. In Example 1, the driving waveform has a maximum of four drop waveforms (elements) in one printing cycle, and is driven in five gradations from gradation 0 to gradation 4. In Example 1, one printing cycle has four drops, and the periodic length of each drop waveform is equal.

[0038] The drive waveform for each gradation is a multi-drop waveform having multiple drop waveforms, and is composed of a combination of multiple drop waveforms WvA and WvB as shown in Figure 3. Each drop waveform WvA and WvB has an expansion element and a contraction element, and the ejection volume by the drop waveforms WvA and WvB differs because the pulse width of the contraction element differs. The cycle of the multiple drop waveforms WvA and WvB is constant.

[0039] 3, each of the drop waveforms WvA and WvB includes an expansion component that reduces the voltage from the intermediate voltage Vb to an expansion voltage Va to expand the pressure chamber 26, and then returns to the intermediate voltage Vb after a certain time has passed, and a contraction component that increases the voltage from the intermediate voltage Vb to a contraction voltage Vc that is higher than the intermediate voltage Vb to contract the pressure chamber 26 to eject ink, and then returns to the intermediate voltage Vb again. For example, the intermediate voltage Vb=0V.

[0040] Each drop waveform WvA, WvB is a waveform that expands and contracts, and four waveforms are arranged at a regular interval within one printing cycle. Each drop waveform WvA, WvB has an expansion element that expands the pressure chamber 26 to draw liquid into the pressure chamber 26, and a contraction element that contracts the pressure chamber 26 to eject liquid.

[0041] The two drop waveforms WvA and WvB have different contraction element pulse widths and are waveforms that eject ink at different ejection volumes. In Example 1, the second drop waveform WvB has a narrower contraction element pulse width than the first drop waveform WvA, resulting in a smaller ejection volume. On the other hand, the first drop waveform WvA has a wider contraction element pulse width than the second drop waveform WvB, resulting in a larger ejection volume. As an example, the second drop waveform WvB is a waveform that results in an ejection volume of 5.5 pL, and the first drop waveform WvA is a waveform that results in an ejection volume of 6 pL.

[0042] In the drive waveform for each grayscale, a plurality of drop waveforms WvA and WvB are arranged at a constant cycle.

[0043] The pulse width of the expansion element in each waveform is the same for the two drop waveforms WvA and WvB. AL (Acoustic Length) is defined as half the natural vibration period of the pressure chamber 26 of the liquid ejection head 1. The pulse width of the expansion element is a value determined by AL. The width between the center of the expansion element and the center of the contraction element of WvA is 2AL, while the width between the center of the expansion element and the center of the contraction element of WvB is longer than 2AL. For example, the width of the contraction element of the first drop waveform WvA of the actuator 25 is set to a width that minimizes the residual vibration generated inside the actuator 25, and the width of the second drop waveform WvB is set to a shorter width than that of the first drop waveform WvA. 3, when the two drop waveforms WvA and WvB are superimposed, the timing at which the voltage in the contraction element of the two drop waveforms WvA and WvB increases from the intermediate voltage Vb to the contraction voltage Vc is different, but the timing at which the voltage returns from the contraction voltage Vc to the intermediate voltage Vb is the same. In other words, the steady-state pulse width between the expansion element and contraction element of the drop waveform WvB is longer than the steady-state pulse width between the expansion element and contraction element of the drop waveform WvA.

[0044] In Example 1, the first to fourth drops of the drive waveform for gradation 0 are all the second drop waveform WvB. Therefore, for gradation 0, the total of the four drops is 22.0 pL.

[0045] In the drive waveform for gradation 1, the first drop is a first drop waveform WvA, and the second to fourth drops are a second drop waveform WvB. Therefore, in gradation 1, the total of the four drops is 22.5 pL.

[0046] In the drive waveform for gradation 2, the first and second drops are the first drop waveform WvA, and the third and fourth drops are the second drop waveform WvB. Therefore, in gradation 2, the total of the four drops is 23.0 pL.

[0047] In the drive waveform for gradation 3, the first to third drops are the first drop waveform WvA, and the fourth drop is the second drop waveform WvB. In gradation 3, the total of the four drops is 23.5 pL.

[0048] The first drop waveform WvA is used for all gradation levels 4. The total of the four drops for gradation level 4 is 24.0 pL.

[0049] According to Example 1, the ejection volume can be arbitrarily controlled by controlling the ejection volume by combining two drop waveforms WvA and WvB in the drive waveform for each gradation. That is, according to Example 1, the ejection volume can be controlled in increments of 0.5 pL from 22.0 to 24.0 pL.

[0050] [Example 2] FIG. 5 is a table showing multiple gradations and drive waveforms in Example 2. FIG. 6 is a graph showing experimental results. Example 2 uses a drive waveform having a maximum of four drop ejection elements in one printing cycle, and is a drive waveform for driving at four gradations from gradation 1 to gradation 4. One printing cycle has four drops, and each drop has an equal period. That is, each drop waveform WvA, WvB is a waveform that expands and contracts, and four waveforms are arranged at a constant period within one printing cycle. Each drop waveform WvA, WvB has an expansion element that expands the pressure chamber 26 to draw liquid into the pressure chamber 26, and a contraction element that contracts the pressure chamber 26 to eject liquid.

[0051] The width of the expansion element of the waveform is the same for the two drop waveforms WvA and WvB. The pulse width of the expansion element is determined by AL. The width between the center of the expansion element and the center of the contraction element is 2AL.

[0052] The waveforms WvA and WvB have different widths of the contraction element or expansion element, and eject different ejection volumes. In Example 2, the second drop waveform WvB has a narrow contraction element pulse width, i.e., a short contraction time and a small ejection volume. On the other hand, the first drop waveform WvA has a wide contraction element pulse width and a large ejection volume.

[0053] For example, the width of the contraction element of the first drop waveform WvA is set to a width that minimizes the residual vibration generated inside the actuator, and the width of the second drop waveform WvB is set to a shorter width than that of the first drop waveform WvA.

[0054] The first to fourth drops all had the second drop waveform WvB in gradation 1. As shown in Figures 5 and 6, the ejection volume in gradation 1 was 23.4 pL.

[0055] In gradation 2, the first drop is the first drop waveform WvA, and the second to fourth drops are the second drop waveform WvB. As shown in Figures 5 and 6, in gradation 2, the total of the four drops was 23.8 pL.

[0056] In gradation 3, the first and second drops are the first drop waveform WvA, and the third and fourth drops are the second drop waveform WvB. As shown in Figures 5 and 6, in gradation 3, the total length of the four drops was 24.2 pL.

[0057] In gradation 4, the first to third drops are the first drop waveform WvA, and the fourth drop is the second drop waveform WvB. As shown in Figures 5 and 6, in gradation 4, the total of the four drops was 24.3 pL.

[0058] As shown in Figure 6, with the contraction element of WvA set to P (reference), the experimental result when the contraction element of WvB is 0.1 μs shorter than that of WvA is P-0.1 μs, the experimental result when it is 0.2 μs shorter is P-0.2 μs, and the experimental result when it is 0.3 μs shorter is P-0.3 μs. Therefore, Figure 6 shows that the ejection volume decreases as the contraction element width of WvB is made shorter than that of WvA.

[0059] [Example 3] Fig. 7 is a table showing driving waveforms for multiple gradations in Example 3. Example 3 is an example in which a drop waveform WvC with a smaller ejection volume than the second drop waveform WvB is used in Example 2 in order to reduce the ejection volume of gradation 3. WaveC in Fig. 7 indicates the drop waveform WvC.

[0060] Example 3 is a drive waveform having a maximum of four drop ejection elements per printing cycle, and is a drive waveform for driving in five gradations from gradation 0 to gradation 4. That is, one printing cycle has four drops, and the periodic length of each drop is equal. Each drop waveform WvA, WvB is a waveform that expands and contracts, and four waveforms are arranged at a regular interval within one printing cycle. Each drop waveform WvA, WvB has an expansion element that expands the pressure chamber 26 to draw liquid into the pressure chamber 26, and a contraction element that contracts the pressure chamber 26 to eject liquid.

[0061] The width of the expansion element of the waveform is the same for the two drop waveforms WvA and WvB. The pulse width of the expansion element is determined by AL. The width between the center of the expansion element and the center of the contraction element is 2AL. The drop waveforms WvA and WvB have different widths of the contraction element or expansion element, resulting in different ejection volumes. In Example 3, the second drop waveform WvB has a narrow contraction element pulse width, resulting in a small ejection volume. On the other hand, the first drop waveform WvA has a wide contraction element pulse width, resulting in a large ejection volume. Furthermore, the drop waveform WvC has an even narrower contraction element width than the second drop waveform WvB, resulting in a small ejection volume.

[0062] For example, the width of the contraction element of the actuator is set so that the first drop waveform WvA is set to a width that minimizes residual vibration generated inside the actuator, the second drop waveform WvB is set to a width that is shorter than the first drop waveform WvA, and the drop waveform WvC is set to a width that is even shorter than the second drop waveform WvB, and conditions are set so that the target ejection volume and adjustment amount are obtained.

[0063] At gradation 0, the first to fourth drops all had the second drop waveform WvB, and the ejection volume was 23.4 pL.

[0064] In gradation 1, the first drop is the first drop waveform WvA, and the second to fourth drops are the second drop waveform WvB.

[0065] In gradation 2, the first and second drops are of the first drop waveform WvA, and the third and fourth drops are of the second drop waveform WvB.

[0066] In gradation 3, the first to third drops are the first drop waveform WvA, and the fourth drop is the drop waveform WvC.

[0067] In gradation 4, the first to fourth drops are all the first drop waveform WvA.

[0068] In this embodiment, too, by combining multiple waveforms that result in different ejection volumes, it is possible to finely control the ejection volume. Furthermore, according to this embodiment, by combining a drop waveform WvC that has a smaller ejection volume than the second drop waveform WvB, it is possible to adjust the amount of change in the ejection volume in Example 2, and ensure linearity in the change in the ejection volume.

[0069] [Example 4] 8 is a table showing driving waveforms of multiple gradations in Example 4. Example 4 is an example in which the timing of the first drop waveform WvA and the second drop waveform WvB, which have different ejection speeds in Example 1, is reversed to ensure the desired landing shape.

[0070] In Example 4, the first to fourth drops are all the second drop waveform WvB at gradation 0. Therefore, at gradation 0, the total of the four drops is 22.0 pL.

[0071] In gradation 1, the first to third drops are the second drop waveform WvB, and the final fourth drop is the first drop waveform WvA. Therefore, in gradation 2, the total of the four drops is 22.5 pL.

[0072] In gradation 2, the first and second drops are of the second drop waveform WvB, and the third and fourth drops are of the first drop waveform WvA. Therefore, in gradation 2, the total of the four drops is 23.0 pL.

[0073] In gradation 3, the first drop is the second drop waveform WvB, and drops 2 to 4 are the first drop waveform WvA. In gradation 3, the total of the four drops is 23.5 pL.

[0074] The first drop waveform WvA is used for all gradation levels 4. The total of the four drops for gradation level 4 is 24.0 pL.

[0075] By controlling the ejection as described above, the ejection volume can be controlled in small increments. That is, according to Example 4, the ejection volume can be controlled in 0.5 pL increments from 22.0 to 24.0 pL. For example, if the ejection speeds of WvA and WvB are VA and VB, respectively, using the drive waveform of Example 1, dot separation may occur if VA > VB. In this case, adjusting the timing as in this example reduces the ejection time difference, preventing dot separation and ensuring the correct shape of the impacted dots.

[0076] [Example 5] Fig. 9 is a table showing drive waveforms for multiple gradations in Example 5. Fig. 10 is a graph showing drive waveforms for each gradation in Example 5. In addition to the five gradations in Example 1, Example 5 has a gradation with an ejection volume of 0, for a total of six gradations from gradation 0 to gradation 5. In other words, in Example 5, at least one of the gradations is a gradation in which no liquid is ejected.

[0077] Gradation 0 is a gradation in which none of the first to fourth drops are driven. Therefore, in gradation 0, the total ejection volume of the four drops is 0 pL.

[0078] In gradation 1, the first to fourth drops are all the second drop waveform WvB. Therefore, in gradation 1, the total of the four drops is 22.0 pL.

[0079] In gradation 2, the first drop is the first drop waveform WvA, and the second to fourth drops are the second drop waveform WvB. Therefore, in gradation 2, the total of the four drops is 22.5 pL.

[0080] In gradation 3, the first and second drops are the first drop waveform WvA, and the third and fourth drops are the second drop waveform WvB. Therefore, in gradation 3, the total of the four drops is 23.0 pL.

[0081] In gradation 4, the first to third drops are the first drop waveform WvA, and the fourth drop is the second drop waveform WvB. In gradation 4, the total of the four drops is 23.5 pL.

[0082] The first drop waveform WvA is used for all gradation levels 5. The total of the four drops in gradation level 5 is 24.0 pL. By controlling the discharge as described above, the discharge volume can be controlled in small increments. That is, according to Example 1, the discharge volume can be controlled in increments of 0.5 pL from 22.0 to 24.0 pL. Furthermore, by providing a gradation where no discharge occurs when the gradation value is 0, it is possible to reproduce blank spaces in a printed image using a gradation where the discharge volume is 0.

[0083] [Example 6] 11 is a table showing drive waveforms for multiple gradations in Example 6. In Example 6, in addition to the six gradations in Example 5, there are three more gradations in which the number of drops in the first drop waveform WvA is reduced, resulting in a total of nine gradations. That is, in Example 6, the drive waveform for at least one gradation has a different number of drops from the drive waveforms for the other gradations.

[0084] Gradation 0 is a gradation in which none of the first to fourth drops are ejected. Therefore, in gradation 0, the total ejection volume of the four drops is 0 pL.

[0085] In gradation 1, the first drop is driven by the first drop waveform WvA, and the second to fourth drops are not ejected. Therefore, the total ejection volume in gradation 1 is 6.0 pL.

[0086] In gradation 2, the first and second drops are driven with the first drop waveform WvA, and the third and fourth drops are not ejected. The total ejection volume in gradation 2 is 12.0 pL.

[0087] Gradation 3 is a gradation in which the first to third drops are driven with the first drop waveform WvA, and the fourth drop is not ejected. Therefore, the total ejection volume of gradation 3 is 18.0 pL.

[0088] In gradation 4, the first to fourth drops are all the second drop waveform WvB. Therefore, in gradation 4, the total of the four drops is 22.0 pL.

[0089] In gradation 5, the first drop is the first drop waveform WvA, and the second to fourth drops are the second drop waveform WvB. Therefore, in gradation 5, the total of the four drops is 22.5 pL.

[0090] In gradation 6, the first and second drops are the first drop waveform WvA, and the third and fourth drops are the second drop waveform WvB. Therefore, in gradation 6, the total of the four drops is 23.0 pL.

[0091] In gradation 7, the first to third drops are the first drop waveform WvA, and the fourth drop is the second drop waveform WvB. In gradation 4, the total of the seven drops is 23.5 pL.

[0092] The first drop waveform WvA is used for all gradations 8. The total of the four drops for gradation 8 is 24.0 pL.

[0093] By controlling the discharge as described above, the discharge volume can be controlled in small increments. That is, according to Example 6, the discharge volume can be controlled in increments of 0.5 pL from 22.0 to 24.0 pL. Furthermore, by providing a gradation in which no discharge occurs when the gradation value is 0, it is possible to reproduce blank spaces in a printed image using a gradation with a discharge volume of 0. Furthermore, according to this example, the range of gradation expression can be further expanded by combining it with general gradation expression using different numbers of drops.

[0094] The embodiment of the present invention is not limited to the above-described configuration.

[0095] For example, in the above embodiment, an example of four-drop driving is shown, but the present invention is not limited to this, and the number of drops may be three or less, or five or more. Furthermore, the number of drop waveforms is not limited to two types, and a combination of three or four or more types may be used.

[0096] In the above embodiment, the ejection volume is varied depending on the pulse width of the contraction element, but this is not limitative and it is also possible to vary the ejection volume depending on, for example, the voltage value or the pulse width of the expansion element.

[0097] For example, the configuration of the liquid ejection head 1 is not limited to the above example, and may be used in other types of heads. For example, the liquid ejection head may be configured to drive the liquid ejection unit by vibrating a diaphragm provided between the pressure chamber and the drive element unit through deformation of the drive element unit.

[0098] According to at least one of the embodiments described above, it becomes possible to perform fine gradation control.

[0099] 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. The following is a description equivalent to the invention described in the claims of the original application. (1) a drive circuit for driving a liquid ejection unit that ejects liquid at a plurality of gradations; At least in one of the gradations, the drive waveform for driving the liquid ejection unit is a multi-drop waveform having a plurality of drop waveforms for ejecting droplets; A liquid ejection head having a plurality of drop waveforms with different ejection volumes in one printing cycle. (2) The liquid ejection head according to (1), wherein the drive circuit drives the liquid ejection section at a plurality of gradations with different total ejection volumes of liquid within one printing cycle by combining a plurality of the drop waveforms with different ejection volumes. (3) The plurality of drop waveforms have a constant period; each of the plurality of drop waveforms includes an expansion element that expands a pressure chamber provided in the liquid ejection unit by an expansion voltage, and a contraction element that contracts the pressure chamber by a contraction voltage higher than the expansion voltage; The liquid ejection head according to (1) or (2), wherein the contraction element durations of the plurality of drop waveforms are different. (4) The liquid ejection head according to any one of (1) to (3), wherein the number of drops of a drive waveform of at least one gradation is different from the number of drops of a drive waveform of other gradations. (5) The liquid ejection head according to any one of (1) to (4), wherein at least one of the gradations is a gradation at which liquid is not ejected. [Explanation of symbols]

[0100] 1...liquid ejection head, 2...liquid ejection device, 21...nozzle plate, 22...actuator substrate, 23...manifold, 24...drive circuit, 25...actuator, 26...pressure chamber, 211...nozzle, 241...driver IC, 242...wiring board, 2001...transport path, 2111...casing, 2112...medium supply unit, 2113...image forming unit, 2114...medium discharge unit, 2115...transport device, 2117... Maintenance 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...conveyor belt, 21202...support plate, 21203...belt roller, 21211 to 21218...guide plate pair, 21221 to 21228...conveyor roller.

Claims

1. a drive circuit for driving a liquid ejection unit that ejects liquid at a plurality of gradations; At least in one of the gradations, the drive waveform for driving the liquid ejection unit is a multi-drop waveform having a plurality of drop waveforms for ejecting droplets; In one printing cycle, a plurality of drop waveforms having different ejection volumes are provided, and The period of the plurality of drop waveforms is constant, each of the plurality of drop waveforms includes an expansion element that expands a pressure chamber provided in the liquid ejection unit by an expansion voltage, and a contraction element that contracts the pressure chamber by a contraction voltage higher than the expansion voltage; The contraction elements of the plurality of drop waveforms have different times. Liquid ejection head.

2. The liquid ejection head according to claim 1 , wherein the drive circuit drives the liquid ejection section at a plurality of gradations that vary in total ejection volume of liquid within one printing cycle by combining a plurality of the drop waveforms that vary in ejection volume.

3. 3. The liquid ejection head according to claim 1, wherein the number of drops of the drive waveform of at least one of the gradations is different from the number of drops of the drive waveforms of the other gradations.

4. 4. The liquid ejection head according to claim 1, wherein at least one of the gradations is a gradation at which liquid is not ejected.

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