46. Note that the liquid ejection head 1 may realize gradation expression (e.g., gray scale) by changing the volume of ink droplets that land per one pixel. In addition, the liquid ejection head 1 may change the number of the ink droplets that lands per one pixel by changing the number of times of the ejection of the ink. In this manner, the driver IC 72 is an example of an application unit that applies a driving signal to the piezoelectric column 21.

Next, as illustrated in FIG. 3, an example of the drive circuit 70 is described. The drive circuit 70 includes in the driver IC 72, for example, a voltage control unit 724 and voltage switching units 725 in the same number as the number of the pressure chambers 46. However, in FIG. 3, just two voltage switching units 725 are illustrated as representative, and the other voltage switching units 725 are not separately illustrated.

The drive circuit 70 is connected to a first voltage source 81, a second voltage source 82, and a third voltage source 83. The drive circuit 70 applies the voltage supplied from the first voltage source 81 to each wiring electrode 726. Note that the drive circuit 70 applies the voltage supplied from the first voltage source 81, the second voltage source 82, and the third voltage source 83 selectively to each wiring electrode 727. Here, if the actuator 20 is a stacked PZT, the actuator 20 may be deteriorated in the case of application of a bipolar voltage. Therefore, the voltage supplied by the first voltage source 81, the second voltage source 82, and the third voltage source 83 is the ground voltage and one of positive and negative polarities with respect to the ground voltage.

For example, the output voltage of the first voltage source 81 is the ground voltage, and the voltage value thereof is indicated as V0 (V0=0 V). Also, the voltage value indicated by the output voltage of the second voltage source 82 is indicated as V1. Here, the voltage value V1 is the voltage higher than V0. The voltage value indicated by the output voltage of the third voltage source 83 is indicated as V2. In this example, the voltage value V2 is a voltage higher than V0 but lower than V1.

A wiring electrode 726 is connected to a common electrode as the ground electrode of the actuator 20. The plurality of wiring electrodes 727 are connected to individual electrodes as non-ground electrodes of the actuator 20, respectively.

The voltage control unit 724 is connected to each of the plurality of voltage switching units 725. The voltage control unit 724 outputs a command indicating which voltage source of the first voltage source 81, the second voltage source 82, and the third voltage source 83 is to be selected, to each of the voltage switching units 725. For example, the voltage control unit 724 receives an image signal from the control unit 150 and accordingly determines a switch timing of the voltage source in each voltage switching unit 725. Also, the voltage control unit 724 outputs a command for selecting any one of the first voltage source 81, the second voltage source 82, and the third voltage source 83 to the voltage switching unit 725 at a determined switch timing. The voltage switching unit 725 switches the voltage source connected to the wiring electrode 727 according to the command from the voltage control unit 724.

The voltage switching unit 725 is configured, for example, as a semiconductor switch. The voltage switching unit 725 connects any one of the first voltage source 81, the second voltage source 82, and the third voltage source 83 to the wiring electrode 727 by the control of the voltage control unit 724. However, the internal electrode having a polarity different from the piezoelectric column 21 is connected to the wiring electrode 726 and the wiring electrode 727 via an external electrode (common electrode and individual electrode).

The drive circuit 70 inputs a drive waveform having at least three types of potential differences as the driving signal between the electrodes of the actuator 20 by switching the connection wiring between the voltage sources 81, 82, and 83 and the actuator 20 by the switching circuit including the voltage control unit 724 and the plurality of voltage switching units 725. Here, the drive waveforms are the ejection waveform for ejecting the liquid droplet by the driving of the actuator 20 and a cancellation waveform for cancelling a residual waveform generated in the pressure chamber 46 driven by the input of the ejection waveform. Note that in the present discussion, any potential difference other than the largest potential difference and the smallest potential difference is referred to as an intermediate potential difference.

The print wiring substrate is a printing wiring assembly (PWA) on which various electronic components and connectors are mounted. The print wiring substrate is connected to the control unit 150 of the liquid ejection device 100.

Next, an example of the liquid ejection device 100 including the liquid ejection head 1 is described with reference to FIGS. 4 and 5. The liquid ejection device 100 is, for example, an inkjet recording device. The liquid ejection device 100 includes a housing 111, a medium supply unit 112, an image forming unit 113, a medium discharge unit 114, and a conveyance device 115. Also, the liquid ejection device 100 includes the control unit 150.

The liquid ejection device 100 is a liquid ejection device that performs image forming process on paper P by ejecting liquid such as ink while conveying, for example, the paper P as a printing medium that is an ejection target along a conveyance path A from the medium supply unit 112 to the medium discharge unit 114 via the image forming unit 113.

The housing 111 forms the outer shell of the liquid ejection device 100. A discharge port through which the paper P can be discharged to the outside is provided in the housing 111.

The medium supply unit 112 includes a plurality of paper feed cassettes and is configured to be able to stack and hold a plurality of sheets of paper P of various sizes.

The medium discharge unit 114 includes a paper discharge tray configured to be able to hold the paper P discharged from the discharge port.

The image forming unit 113 includes a support unit 117 that supports the paper P and a plurality of head units 130 arranged to face the upper side of the support unit 117.

The support unit 117 includes a conveyance belt 118 that is provided in a loop shape for image formation, a support plate 119 that supports the conveyance belt 118 from the back side, and a plurality of belt rollers 120 that are provided on the back side of the conveyance belt 118.

The support unit 117 conveys the paper P downstream by movement of the conveyance belt 118 by the rotation of the belt rollers 120 while the paper P is on the outer surface of the conveyance belt 118 during the image formation.

The head units 130 includes liquid ejection heads 1, a plurality of ink tanks 132 for the liquid ejection heads 1, connection channels 133 that connect the liquid ejection heads 1 and the ink tanks 132, and supply pumps 134.

According to the present embodiment, a plurality of head units 130 are provided. The head units 130 use ink of different colors, respectively. For example, as the plurality of head units 130, liquid ejection heads 1 for four colors (cyan, magenta, yellow, and black) and ink tanks 132 that contain ink of these different colors are provided. The ink tanks 132 are connected to the common channel 48 of the liquid ejection head 1 by the connection channel 133.

In addition, negative pressure control devices such as pumps can be connected to the ink tanks 132. The ink supplied to each nozzle 51 forms a meniscus having a predetermined shape by the negative pressure control of the inside of the ink tanks 132 and the water head value of the ink being supplied to the liquid ejection heads 1 from the ink tanks 132.

The supply pump 134 is, for example, a liquid feed pump configured as a piezoelectric pump. The supply pump 134 is provided in a supply channel. The supply pump 134 is connected to the control unit 150 by wiring and controlled by the control unit 150. The supply pump 134 supplies liquid to the liquid ejection head 1.

The conveyance device 115 conveys the paper P along the conveyance path A from the medium supply unit 112 to the medium discharge unit 114 via the image forming unit 113. The conveyance device 115 includes a plurality of guide plate pairs 121 arranged along the conveyance path A and a plurality of conveyance rollers 122.

The plurality of guide plate pairs 121 each include a pair of plate members arranged to face each other with the conveyed paper P interposed therebetween and guide the paper P along the conveyance path A.

The conveyance rollers 122 send the paper P downstream along the conveyance path A by being rotated and driven by the control of the control unit 150. Note that sensors for detecting the conveyance state of the paper are arranged at each location along the conveyance path A.

The control unit 150 is, for example, a control substrate. The processor 151, a read only memory (ROM) 152, a random access memory (RAM) 153, an I/O port 154 that is an input and output port, and an image memory 155 are mounted on the control unit 150.

The processor 151 can be a processing circuit such as a central processing unit (CPU) that functions as a controller. The processor 151 controls the head units 130, a drive motor 161, an operation unit 162, various sensors 163, and the like provided in the liquid ejection device 100 via the I/O port 154. The processor 151 transmits the print data stored in the image memory 155 to the drive circuit 70 in the drawing order.

The ROM 152 stores various programs. The RAM 153 temporarily stores various kinds of variable data, image data, and the like. Note that the ROM 152 and the RAM 153 are examples of storage media, but other storage media may be used or incorporated as long as the storage media can store various programs or data. The I/O port 154 is an interface unit that receives data from the outside such as an externally connected device 200 and outputs data to the outside. The print data from the externally connected device 200 is transmitted to the control unit 150 via the I/O port 154 and is stored in the image memory 155.

Hereinafter, the ejection waveform and the cancellation waveform of a driving signal are described for the characteristics of a liquid ejection head 1 used in the liquid ejection device 100 according to an embodiment. The ejection waveform and the cancellation waveform may together be described as a drive waveform of the liquid ejection head 1 and/or as non-exclusive components of a drive waveform.

A drive waveform for the liquid ejection head 1 according to the present embodiment is described with reference to FIGS. 6 to 14. Note that FIG. 6 is an explanatory diagram illustrating an example of the drive waveform including the ejection waveform and the cancellation waveform. FIG. 7 is an explanatory diagram illustrating an example of the drive waveform and the acoustic oscillation of the liquid ejection head 1 according to the embodiment, FIG. 8 is an explanatory diagram illustrating the relationship between the drive waveform and the ejected liquid droplet(s) in an example of the liquid ejection head 1, and FIG. 9 is an explanatory diagram illustrating examples of the ejected liquid droplet(s) from the liquid ejection head 1 according to the embodiment. FIGS. 10 to 14 are drawings for describing the liquid ejection head in a comparative example. FIG. 10 is an explanatory diagram illustrating an example of frequency analysis of pressure oscillation of a liquid ejection head according to the comparative example. FIG. 11 is an explanatory diagram illustrating an example of synthesizing main acoustic oscillation and parasitic oscillation of FIG. 10. FIG. 12 is an explanatory diagram illustrating an example of the frequency analysis of the liquid ejection head according to the comparative example. FIG. 13 is an explanatory diagram illustrating an example of a drive waveform and the acoustic oscillation of a liquid ejection head according to the comparative example. FIG. 14 is an explanatory diagram illustrating an example of a drive waveform and the acoustic oscillation of a liquid ejection head according to the comparative example.

First, the liquid ejection head in the comparative example has a driving method that may be referred to as “pulling,” or a “pull-type” for which the ejection force can be increased by driving the piezoelectric columns 21 in accordance with a half cycle AL of the main acoustic oscillation of the pressure chamber. However, as illustrated in the example of the frequency analysis of the nozzle unit pressure oscillation of FIG. 10, if the liquid ejection head (actuator) is driven to eject the liquid droplet from the nozzle, parasitic oscillation may occur in a frequency region higher than the main acoustic oscillation in the pressure chamber in addition to the main acoustic oscillation by ink fluidic oscillation.

When a droplet is ejected from a nozzle by driving an actuator, if parasitic oscillation with a frequency higher than that of the main acoustic oscillation occurs, the pressure in the pressure chamber has a shorter cycle pressure peak than the half cycle of the main acoustic oscillation, as illustrated in FIG. 11. That is, the synthesized wave obtained by combining the main acoustic oscillation and the parasitic oscillation has a sharp initial oscillation. A pressure peak having a short cycle increases the ejection speed of the leading end portion of the ejected liquid droplet but does not last until the end of the ejection and this lowers the ejection speed of the trailing end portion of the ejected liquid droplet. As illustrated in portion (a) of the upper part of FIG. 9, when the droplet is ejected, the volume of the satellite with respect to the leading end liquid droplet increases and this deteriorates print quality. In this context, a satellite is a liquid droplet that is ejected after the first ejected droplet (leading end liquid droplet) with a gap from the leading end liquid droplet if liquid is ejected from a nozzle by driving the piezoelectric column 21 and deforming the pressure chamber.

In the liquid ejection head in the comparative example, as illustrated in the frequency analysis of FIG. 12, in addition to the main acoustic oscillation, parasitic oscillation occurs at about 3 times (for example, 2.8 times) the frequency. Here, the following is considered as the causes of the parasitic oscillation having a frequency higher than that of the main acoustic oscillation in the pressure chamber of the liquid ejection head.

An example of the cause is oscillation of an odd multiple of three or more in the liquid column oscillation of a closed tube, and an example of such a liquid ejection head is an end shooter having a connection point to a common channel as an open end, similarly to the liquid ejection head 1 of the embodiment, as illustrated in FIG. 12.

Another example of the cause is oscillation of an integer multiple of two or more in the liquid column oscillation of the open tube, and an example of such a liquid ejection head is a side shooter having a connection point to a common channel as an open end, as illustrated in FIG. 13. Note that in the main acoustic oscillation of the open tube, the amplitude of the pressure oscillation becomes the greatest in the central portion of the open tube, and thus a nozzle is usually provided near the central portion (middle point) of the open tube. As illustrated in FIG. 13, if oscillation of an even multiple (2 or more) occurs in the liquid column oscillation of the open tube, the central portion of the open tube becomes a node of the oscillation having the small pressure oscillation amplitude. Therefore, if the nozzle is provided near the central portion of the open tube, the shape of the ejected liquid droplet is not likely to receive the full influence of the oscillation of an even multiple. Therefore, if the nozzle is provided near the central portion of the open tube, the oscillation of an odd multiple (3 or more) increases the volume of the satellite more than the oscillation of an even multiple, and thus the print quality is deteriorated more easily.

Another example of the cause is oscillation caused by reflection of the pressure oscillation when the pressure chamber and the individual channel have different channel cross-sectional surfaces.

Also, another example of the cause is oscillation caused because the pressure generated in the pressure chamber is reduced in the channel having a low rigidity when the rigidity of the wall surface or a part of the wall surface of the individual channel is less than the pressure chamber, and a node of the pressure oscillation is generated between the pressure chamber and the channel having low rigidity. This occurs when, for example, the installation range (position) of an actuator (the piezoelectric columns 21) is as illustrated with a two-dot chain line in FIG. 1 as compared to the actuator (piezoelectric column 21) indicated by the solid line in FIG. 1. That is, the position of the piezoelectric column 21 may be mispositioned or misaligned with respect to the position of the diaphragm due to manufacturing errors, tolerances, and the like. Note that, results of the frequency analysis of the pressure oscillation of the nozzle unit if simulation of structural analysis of deformation of PZT or a pressure chamber, compressible fluid analysis of a liquid behavior in the channel, and fluid surface analysis of liquid droplet ejection from the nozzles is performed with respect to the head in a case where the range, which is supported only by the diaphragm and is not supported by the actuator, on the upper right of the pressure chamber of FIG. 1 is a range of about less than 30% of the length of the pressure chamber in the longitudinal direction (the horizontal width of the pressure chamber 46 in FIG. 1) are the graphs illustrated in FIGS. 10 and 12.

Also, as illustrated in FIG. 14, if a rectangular wave width UL of the ejection waveform is AL, third harmonic oscillation AI generated by the pressure chamber expansion (rising waveform) in advance before ejection and third harmonic oscillation AII of the liquid column oscillation by the pressure chamber contraction (falling waveform) during ejection strengthen each other, and thus pressure peaks with a short cycle are generated due to the third harmonic oscillation, thereby causing the deterioration of print quality.

Next, an example of the driving and the drive waveform of the liquid ejection head 1 according to the present embodiment is described. In the present embodiment, the pressure oscillation of the pressure chamber 46 of the liquid ejection head 1 is considered as a liquid column oscillation of a closed tube, an acoustic resonance frequency (parasitic oscillation) in a frequency region higher than the main acoustic resonance frequency (main acoustic oscillation) of the liquid in the pressure chamber 46 is a drive waveform that suppresses third harmonic oscillation of an odd multiple of about three or more of the main acoustic resonance frequency. Here, about three times include 2.8 times as illustrated in FIG. 10.

When the potential difference is the greatest, the pressure chamber 46 is expanded the greatest amount by the piezoelectric column 21 of the actuator 20. When the potential difference is the smallest, the pressure chamber 46 of the ink is contracted the smallest size by the piezoelectric columns 21 of the actuator 20. Also, when the ink is to be ejected by the liquid ejection head 1, the pressure chamber 46 is expanded in advance of the ejection, and the ink is then ejected by contracting the pressure chamber 46.

In the example of the present embodiment, the drive waveform voltage is increased at least two times consecutively by an expansion potential difference so the pressure chamber 46 is expanded in advance of ejection, or is reduced at least two times consecutively by a contraction potential difference so the pressure chamber 46 is contracted for ejection. More preferably, the ejection waveform of the drive waveform changes the potential twice consecutively for both the expansion and the contraction of the pressure chamber 46.

After the ejection waveform for ejecting the ink is supplied, the cancellation waveform is supplied to cancel the residual oscillation that is generated after the ejection of the ink. In the present embodiment, the cancellation waveform uses a waveform width (cancellation width) Cp that is less than AL (the acoustic length of the liquid ejection head 1). The cancellation waveform includes at least two increases in potential supplied consecutively (at least two stages) to expand the pressure chamber 46 followed by at least two decreases in potential supplied consecutively (at least two stages) to contract the pressure chamber 46. In the depicted example, the cancellation waveform changes the potential two times consecutively in equal stages during both the expansion and the contraction of the pressure chamber 46, similarly to the ejection waveform.

FIGS. 6 and 7 illustrate drive waveforms when ink of the liquid ejection head 1 is ejected. In FIGS. 6 and 7, the vertical axis is the voltage (potential difference), and the horizontal axis is time. Note that the drive waveform is generated by the driver IC 72 of the drive circuit 70. As illustrated in FIG. 6, for both the ejection waveform and the cancellation waveform, the drive waveform increases the potential difference in two steps, and reduces the potential difference in two steps. The stages in the ejection waveform may be equally spaced in time as may the stages in the cancellation waveform.

Ab example of the ejection waveform is specifically described with reference to FIG. 7. As illustrated in FIG. 7, the potential difference is increased two times consecutively from the expansion start by the expansion potential difference, and the time interval until the time of the contraction start is set as UL. In addition, as illustrated in FIG. 7, the time interval from the time of the second expansion potential change until the start of the second contraction is also set as UL. Note that in FIG. 6 and the following description, the time interval UL from the time of the expansion start until the time of the contraction start may be described as the time Dp (see FIG. 6).

As illustrated in FIG. 7, the drive waveform that ejects the ink from the nozzle 51 deforms the pressure chamber 46 and changes the potential difference two times consecutively in the same direction during both expansion and contraction of the pressure chamber 46. Also, in the drive waveform, the time interval from the start of the expansion of the pressure chamber 46 until the contraction of the pressure chamber 46 begins and the time interval from the start of the second consecutive expansion until the start of the second consecutive contraction are both set to UL. The time interval UL is greater than 0.5 AL but less than 1.5 AL. More preferably, UL=AL. When UL is set to be greater than 0.5 AL but less than 1.5 AL, the main acoustic oscillation generated by the expansion of the pressure chamber 46 in advance before ejection and the main acoustic oscillation generated by the contraction of the pressure chamber 46 during ejection strengthen (reinforce) each other.

Here, if the cycle of the parasitic oscillation such as the third harmonic wave is set as λn, and the time interval between the first potential difference change start time and the second potential difference change start time is set as Tm, the drive waveform satisfies Tm=λn/2. If the piezoelectric column 21 (actuator) is driven by such a drive waveform, as illustrated in FIG. 7, the phase difference between the parasitic oscillation generated when the potential difference is changed at the first time and the parasitic oscillation generated when the potential difference is changed at the second time will be 180 degrees, and the parasitic oscillation cancels each other out. Therefore, the deterioration of the print quality can be suppressed.

As illustrated in FIG. 7, the drive waveform may preferably have the potential difference changes for the first and second changes (steps) be the same. Therefore, the residual oscillation derived from the parasitic oscillation thereafter can be better suppressed.

If the time interval UL of the ejection waveform is set as AL, and a time interval Tm is set as λn/2, as illustrated in FIG. 7, the phase difference between the parasitic oscillation generated by the pressure chamber contraction (falling waveform) when the potential difference at the first time is changed (the third harmonic oscillation AI) and the parasitic oscillation generated by the pressure chamber contraction (falling waveform) when the potential difference at the second time is changed (the third harmonic oscillation AII) will be 180 degrees, and the parasitic oscillations cancel each other out. Further, by causing the time interval Tm to be λn/2, the phase difference between the parasitic oscillation generated by the pressure chamber expansion (rising waveform) when the potential difference at the first time is changed (the third harmonic oscillation AI) and the parasitic oscillation generated by the pressure chamber expansion (rising waveform) when the potential difference at the second time is changed (the third harmonic oscillation AII) becomes 180 degrees, and the parasitic oscillations cancel each other out. In addition, by setting UL to be AL, the main acoustic oscillation generated by the pressure chamber expansion (rising waveform) before ejection and the main acoustic oscillation generated by the pressure chamber contraction during ejection (falling waveform) reinforce each other to increase the ejection force generated by the main acoustic oscillation. The pressure chamber can be expanded in two steps (stages) so that the total voltage change is not applied immediately. Similarly, the pressure chamber can be contracted for ejection in two steps (stages) so that the total voltage change is not applied immediately.

Here, in the example drive waveform, the value of Tm for which the parasitic oscillation of the cycle λn weakens each other is described. The oscillation of the cycle λn generated when the potential difference at the first time is changed is set as A, and an oscillation vector of A after the period of time Tm is set as A′. An oscillation vector of the cycle λn generated when the potential difference at the second time is changed is set as B. The absolute value of the composite vector of A′ and B when Tm is an odd multiple of λn/2 (the phase difference between A′ and B is 180 degrees) is minimized. If the absolute value of the composite vector of A′ and B from an expression for synthesizing the simple harmonic motion of the cycle λn is equal to or less than the larger of the absolute values of A′ and B (if the absolute value of A′ and the absolute value of B are the same value, equal to or less than the value) is obtained, the phase difference between the oscillation vectors A′ and B may be within ±60 degrees of 180 degrees.

The absolute value of the composite vector of A′ and B can be represented by the following expression, in which θA is a phase of A′ and θB is a phase of B:

√

(

❘
"[LeftBracketingBar]"

A
′

❘
"[RightBracketingBar]"

^
2

+

❘
"[LeftBracketingBar]"

B

❘
"[RightBracketingBar]"

^
2

+

2
*

❘
"[LeftBracketingBar]"

A
′

❘
"[RightBracketingBar]"

*

❘
"[LeftBracketingBar]"

B

❘
"[RightBracketingBar]"

*

cos
⁡
(

θ
⁢
A

-

θ
⁢
B

)

)

.

(

Numerical
⁢

Expression
⁢

1

)

Here, if |A′|≤|B|, the phase difference between A′ and B (θA−θB) in which |B|≥Numerical Expression 1 is satisfied becomes the condition in which the oscillation of the cycle λn weakens each other. If |B|≥Numerical Expression 1 is manipulated by squaring both sides, the following results:

- 0≥|A′|+2*|B|*cos(θA−θB) (Numerical Expression 2). From the above, if the phase difference between A′ and B (θA−θB) is within ±60 degrees of 180 degrees, Numerical Expression 2 is satisfied.

Also, when |B|≤|A′|, if |A′|≥Numerical Expression 1 is manipulated by squaring both sides, the following results:

- θ≥|B|+2*|A′|*cos(θA−θB) (Numerical Expression 3). With the above, if the phase difference between A′ and B (θA−θB) is within ±60 degrees of 180 degrees, Numerical Expression 3 is satisfied.

From these, the condition in which the parasitic oscillations of the cycle λn weakens each other is represented in the following:

(

k
/
2

-

1
/
6

)

⁢

λ
⁢
n

≤
Tm
≤

(

k
/
2

+

1
/
6

)

⁢

λ
⁢
n

(

Numerical
⁢

Expression
⁢

4

)

Here, k is an odd number of 1 or more.

If the potential difference is changed in two consecutive stages during both the expansion and contraction of the pressure chamber 46, Tm of the drive waveform is preferably (k/2−1/6)λn≤Tm≤(k/2+1/6) λn (where k is an odd number of 1 or more) for both the intermediate potential difference holding time during the pressure chamber expansion and the intermediate potential difference holding time during the pressure chamber contraction.

In addition, in view of reduction of power consumption by causing the main acoustic oscillations to strengthen each other, Tm is preferably short.

For this, if the reduction of power consumption is considered, Tm of the drive waveform may be represented by the following:

(

k
/
2

-

1
/
6

)

⁢

λ
⁢
n

≤
Tm
≤

k
⁢
λ
⁢

n
/
2.

(

Numerical
⁢

Expression
⁢

5

)

Here, k is an odd number of 1 or more.

Next, as an evaluation of the drive waveform of the liquid ejection head 1 according to the present embodiment, FIG. 8 illustrates results in a case where the liquid ejection head 1 having a 2 AL value equal to 5.24 μs is driven by various waveforms for the nominal ejection of one ink drop. Note that the voltage is adjusted so that the leading drop speed becomes approximately 8 m/s for all the various waveforms in FIG. 8.

The first drive waveform in FIG. 8 is, as a comparative example, set to a drive waveform having the trapezoidal shape illustrated in FIG. 14 for which the rise time tr is 0.2 μs, the other table entries are set to drive waveforms that change the potential difference in two stages as illustrated in FIG. 7, Tm is varied as indicated, but all rise times are set to 0.2 μs. Also, the “ejection voltage” column value indicates the difference between the expansion potential difference and the contraction potential difference. Note that the intermediate potential difference is an intermediate (e.g., midpoint) value of the total expansion potential difference and the total contraction potential difference.

In a liquid ejection head 1 of the embodiment and a liquid ejection head of the comparative example, as indicated by the frequency analysis of FIG. 12, parasitic oscillation of about three times occurs in addition to the main acoustic oscillation. The cycle λn of the parasitic oscillation is 1.85 μs, and λn/2 becomes 0.925 μs.

In each part (a), (b), (c) of FIG. 9, one drop of ink is to be ejected, and the result obtained by simulating the state of the ejected liquid droplet is indicated. FIG. 9, part (a) illustrates an example showing the ejected liquid droplet for the drive waveform having a trapezoidal shape according to the comparative example in which tr=0.2 μs. FIG. 9, part (b) illustrates an example showing the ejected liquid droplet for the drive waveform in which the potential difference is changed in two stages and Tm=0.62 μs. FIG. 9, part (c) illustrates an example showing the ejected liquid droplet for the drive waveform in which the potential difference is changed in two stages and Tm=0.93 μs.

As illustrated in FIG. 8 and FIG. 9, part (c), in the waveform in which Tm=0.93 μs that is the closest to the half cycle of the parasitic oscillation has the largest ratio of the leading drop volume to the total ejection volume, and it can be understood that the ratio of the leading drop volume gets smaller, as Tm gets farther from 0.925 μs as illustrated in the center figures (b) of FIGS. 8 and 9. Also, it can be understood that, as Tm gets smaller, the ejection voltage per unit volume (ejection voltage/total ejection volume) tends to be lower. From these results, the drive waveform of the liquid ejection head 1 according to the embodiment can suppress the oscillation having the frequency higher than the main acoustic oscillation, while suppressing the power consumption.

Next, an example of the cancellation waveform is specifically described with reference to FIG. 6. Note that for convenience of explanation, in FIG. 6, the following description of the potential difference changes in the ejection waveform are labeled as (1) to (4), and the potential difference changes in the cancellation waveform are labeled as (11) to (14). Also, the reference point of the phase of the ejection waveform is set as (0) and the reference point of the phase of the cancellation waveform is set as (0′). Note that, here, the reference point (0) is between changes (2) and (3), and the reference point (0′) is between changes (12) and (13). Also, in the example of FIG. 6, the voltage falling time tf is set to be substantially the same as the voltage rising time tr.

First, the main acoustic oscillation of the ejection waveform is illustrated. In the ejection waveform, when the potential difference is changed, and the intermediate voltage for expanding the pressure chamber 46 as illustrated in at point (1) is input, the pressure chamber 46 is expanded, and the pressure in the pressure chamber 46 is reduced. The oscillation caused by this becomes an oscillation for which the phase is advanced by −π+(Dp+Tm)/2. When the potential difference is changed as illustrated at point (2), the oscillation an becomes oscillation for which the phase is advanced by −π+(Dp−Tm)/2. The synthesized wave of (1) and (2) becomes an oscillation for which the phase is advanced by −π+Dp/2.

Potential differences at points (3) and (4) for contracting the pressure chamber 46 are changed in an opposite way as at points (1) and (2), the pressure chamber 46 is contracted, and the pressure chamber 46 is pressurized (pressure in the pressure chamber 46 is increased). Therefore, the change at point (3) causes an oscillation for which the phase is advanced by −(Dp−Tm)/2. Also, the change at point (4) causes an oscillation for which the phase is advanced by −(Dp+Tm)/2. Therefore, the synthesized wave of changes at points (3) and (4) becomes an oscillation for which the phase is advanced by −Dp/2.

Here, for the synthesized wave for changes at points (1), (2), (3), and (4) at the time point of (0), the oscillation has a phase which is advanced by −π/2.

Next, the main acoustic oscillation of a cancellation waveform is illustrated. In the cancellation waveform, the potential difference is changed as illustrated at point (11). Here, the pressure chamber 46 is expanded by the potential difference change at point (11), and the pressure in the pressure chamber 46 is reduced). When the cancellation width is Cp, an oscillation for which the phase is advanced by −π+(Cp+Tm)/2 is obtained. Next, potential difference change illustrated at point (12) is performed, and an oscillation for which the phase is advanced by −π+(Cp−Tm)/2 is obtained.

The potential difference changes at points (13) and (14) are in the opposite direction from the changes at points (11) and (12). In this example, the changes at points (13) and (14) are in the direction of contraction of the pressure chamber 46. The change at point (13) causes an oscillation for which the phase is advanced by −(Cp−Tm)/2. The change at point (14) also causes an oscillation for which the phase is advanced by −(Cp+Tm)/2. Therefore, the synthesized wave of changes at points (13) and (14) becomes an oscillation for which the phase is advanced by −Cp/2.

Here, for the synthesized wave of the changes at points (11), (12), (13), and (14) at the time point of (0′) the oscillation has a phase advanced by −π/2.

Therefore, if the time difference (time interval) between (0) and (0′) is set to be an odd multiple of π/2 (AL), the synthesized wave of (1), (2), (3), and (4) and the synthesized wave of (11), (12), (13), and (14) have opposite phases and weaken each other. Furthermore, by reducing the time width Cp for changes at points (11) and (13), the amplitude of the synthesized wave (the cancellation waveform) for the points (11), (12), (13), and (14) can be adjusted, and the residual oscillation from the synthesized wave for the points (1), (2), (3), and (4) can be cancelled).

The residual oscillation from the synthesized wave of points (1), (2), (3), and (4) can be cancelled by causing the time difference of (0) and (0′) as above to be 1 AL. However, if the time difference of (0) and (0′) is caused to be 1 AL, the residual oscillation during the liquid droplet ejection caused by the input of the ejection waveform will be cancelled, and the ejection force of the liquid droplet weakened. Therefore, it is preferable that the time difference between the reference point (0) and the reference point (0′) be an odd multiple of AL (three or more).

Also, the time interval between points (11) and (12) is Tm, and the time interval between points (13) and (14) is also Tm. Therefore, if Tm is a half of the cycle λn of the parasitic oscillation, the parasitic oscillation for changes at points (11) and (12) cancel each other out, and the parasitic oscillation for changes at points (13) and (14) also cancel each other out.

As described above, by setting the cancellation waveform to be a cancellation waveform with the Cp width in which the intermediate value voltage holding time Tm for the ejection waveform becomes a half of the cycle λn of the parasitic oscillation, the cancellation waveform can suppress both the residual oscillation of the main acoustic oscillation from the ejection waveform and the parasitic oscillation caused by the cancellation waveform. As a result, it is possible to prevent the liquid droplet ejected by the next ejection waveform input after the cancellation waveform from being influenced by the residual oscillation and the parasitic oscillation of the previous ejection process.

Note that the potential difference of the cancellation waveform may be changed to have the polarity different from the ejection waveform with respect to the ground voltage of the ejection waveform. For example, the cancellation waveform may have negative polarity with respect to ground potential. For example, FIG. 15 illustrates an example of a cancellation waveform with a negative polarity according to another embodiment. The example illustrated in FIG. 15 is a cancellation waveform in which the pressure chamber is contracted by potential difference change at points (11) and (12), and the pressure chamber returns (expands) with the potential difference change at points (13) and (14). In the example of FIG. 15, in the ejection waveform and the cancellation waveform, there are four potential differences having a potential higher than the ground voltage. Therefore, if such a cancellation waveform is used, the drive circuit 70 may be connected to a fourth voltage source and a fifth voltage source, in addition to the first voltage source 81, second voltage source 82, the third voltage source 83, and may be configured to connect any one of the first voltage source 81, the second voltage source 82, the third voltage source 83, the fourth voltage source, and the fifth voltage source to the wiring electrode 727 under the control of the voltage control unit 724.

Further, if the pressure chamber is expanded in a case where the voltage (potential difference) is reduced, the voltage (potential difference) is increased in order to contract the pressure chamber in advance before the ejection waveform input. The pressure chamber is expanded in two steps (stages) by reducing the voltage (potential difference) in two steps by the ejection waveform input, and the pressure chamber is contracted by increasing the voltage (potential difference) in two steps at the time of contracting the pressure chamber 46 during ejection. The cancellation waveform contracts the pressure chamber by increasing the voltage (potential difference) in two steps and thereafter expands the pressure chamber by reducing the voltage (potential difference) in two steps during the expansion of the pressure chamber 46. In this case, since the potential after the voltage (potential difference) is reduced in two steps for pressure chamber expansion in the ejection waveform and immediately before the pressure chamber contraction starts becomes the lowest potential in the drive waveform, the potential is set as the ground voltage, and the other potentials have potentials higher than the ground voltage.

Also in the cancellation waveform of the example of FIG. 15, main acoustic oscillation is described below by using the reference point of the phase between points (12) and (13) of the cancellation waveform as (0′). Assuming a synthesized wave for points (11), (12), (13), and (14) at the time point of (0′), the polarity becomes opposite to that of the cancellation waveform of the example of FIG. 6, and thus the synthesized wave of points (11), (12), (13), and (14) becomes oscillation of which the phase is advanced by π/2.

Therefore, if the time difference between (0) and (0′) is set as the even multiple of π/2 (AL), for example, 2 AL, the synthesized wave of (1), (2), (3), and (4) and the synthesized wave of (11), (12), (13), and (14) have opposite phases and weaken each other. Further, by causing the time width Cp between points (11) and (13) to be smaller, the amplitude of the synthesized wave (cancellation waveform) of points (11), (12), (13), and (14) can be adjusted, and the residual oscillation can be cancelled by the synthesized wave of points (11), (12), (13), and (14). In addition, the time interval between points (13) and (14) and the time interval between points (11) and (12) are equal values (Tm). Therefore, if Tm is caused to be a half of the cycle λn of the parasitic oscillation, the parasitic oscillation for points (13) and (14) cancel each other out, and the parasitic oscillation for points (11) and (12) cancel each other out.

Next, a condition of Tm in which parasitic oscillation of the cycle λn weakens each other in the cancellation waveform is described. Here, the oscillation of the cycle λn that is generated by the waveform of (11) during the first potential difference change is denoted by A11, and the oscillation vector of A11 after the time Tm is denoted by A11′. The oscillation vector of the cycle λn that is generated in the waveform of (12) during the second potential difference change after Tm is set as A12. The waveform of (11) and the waveform of (12) are rising waveforms as in FIG. 6, and thus the absolute value of the composite vector of A11 and A12 if Tm is an odd multiple of λn/2 (the phase difference of A11 and A12 is 180 degrees) becomes minimum. If a condition in which the absolute value of the composite vector of A11 and A12 from an expression for synthesizing the simple harmonic motion of the cycle an is less than the larger of the absolute values of A11 and A12 is obtained, the phase difference between the oscillation vectors A11 and A12 becomes within 180 degrees±60 degrees.

Therefore, the condition in which oscillation of the cycle λn weakens each other is:

(

k
/
2

-

1
/
6

)

⁢

λ
⁢
n

≤
Tm
≤

(

k
/
2

+

1
/
6

)

⁢

λ
⁢

n
.

(

Numerical
⁢

Expression
⁢

6

)

Here, k is an odd number of 1 or more.

By setting Tm to be under the above condition, it is possible to prevent the next ejection liquid droplet after the cancellation waveform from receiving the influence of the residual oscillation by the parasitic oscillation. Even in the falling waveform of (13) and (14) of FIG. 6, the falling waveform of (11) and (12) of FIG. 15, and the rising waveform of (13) and (14) of FIG. 15, the condition in which oscillation of the cycle λn weakens each other become the same as above.

Note that, with respect to the main acoustic oscillation, the time interval of (0) and (0′) if the residual oscillation of the ejection waveform is cancelled by the cancellation waveform is set as 3 AL in the example of FIG. 6. However, if the pressure is reduced first, and then pressurization is performed in the cancellation waveform ((11), (12), (13), and (14)) as in the ejection waveform ((1), (2), (3), and (4)), if the condition in which oscillation having the cycle of 2 AL weakens each other in the synthesized wave of (1), (2), (3), and (4) and synthesized wave of (11), (12), (13), and (14) is obtained similarly as in the case of the cycle λn from the expression of the synthesis of the simple harmonic motion, the potential difference between the synthesized wave of (1),

(

kkkk
/
2

-

1
/
6

)

⁢

2
⁢

AL

≤

time
⁢

interval
⁢

of
⁢

(
0
)

⁢

to
⁢

(

0
′

)

≤

(

kkkk
/
2

+

1
/
6

)

⁢

2
⁢

AL

- is satisfied, and kkkk here is an odd number of 1 or more.

Also, in the example of FIG. 15, the time interval of (0) to (0′) is set as 2 AL. However, since the pressurization is performed first, and then the pressure is reduced in the cancellation waveform ((11), (12), (13), and (14)), if the condition in which the oscillation having the cycle of 2 AL weakens each other for the synthesized wave of (1), (2), (3), and (4) and the synthesized wave of (11), (12), (13), and (14) is obtained as in the case of the cycle λn from the expression of the synthesis of the simple harmonic motion, the relationship:

(

kkkk
-

1
/
6

)

⁢

2
⁢

AL

≤

time
⁢

interval
⁢

of
⁢

(
0
)

⁢

to
⁢

(

0
′

)

≤

(

kkkk
+

1
/
6

)

⁢

2
⁢

AL

- is satisfied, and kkkk here is an integer of 1 or more.

In the example of FIG. 6, in each case of the cancellation waveform in which the pressure is reduced first, and then the pressurization is performed similarly to the ejection waveform, it is possible to prevent the liquid droplet ejected by the next ejection waveform after the cancellation waveform from receiving the influence of the residual oscillation of the main acoustic oscillation generated by the cancellation waveform by adjusting the time interval between (0) and (0′) and adjusting Cp width as the above condition. In this manner, the residual oscillation caused by the ejection waveform can be canceled by the pressure oscillation caused by the cancellation waveform, and the residual vibration caused by the ejection waveform is reduced. Note that if the viscosity of the ink is high, the attenuation of the residual oscillation after the ejection of the liquid droplet by the ejection waveform may be large, and the cancellation width Cp may be adjusted to be smaller as necessary. However, the cancellation width Cp cannot be less than Tm+Tr.

The liquid ejection head 1 configured in this manner can suppress both the residual oscillation of the main acoustic oscillation by the ejection waveform and the parasitic oscillation by the cancellation waveform by setting the cancellation waveform of the Cp width so that the intermediate value voltage holding time Tm for the ejection waveform becomes a half of the cycle λn of the parasitic oscillation. Therefore, the liquid ejection head 1 can prevent the next ejection liquid droplet after the cancellation waveform from receiving the influence of the residual oscillation by the main acoustic oscillation. Also, the cancellation waveform can prevent the residual oscillation by the parasitic oscillation from giving the influence to the liquid droplet ejected by the next ejection waveform while suppressing the parasitic oscillation generated by the cancellation waveform.

Also, the liquid ejection head 1 can suppress the deterioration of the print quality by oscillation having a frequency higher than that of the main acoustic oscillation while suppressing power consumption, by changing the potential difference of the drive waveform for driving the actuator 20 in two steps, together with the intermediate potential stages.

By the liquid ejection head 1 according to the embodiment described above, the parasitic oscillation generated by the cancellation waveform can be suppressed.

Note that, the embodiment is not limited to the examples described above. In the examples described above, the drive waveforms include two consecutive stages in the same direction (one intermediate potential difference level), but the embodiments are not limited thereto. The drive waveform may have more than one intermediate potential difference level (e.g., more than two consecutive stages in the same direction).

Hereinafter, as another embodiment, the drive waveform of the liquid ejection head 1 of which the potential difference (expansion potential difference) of the drive waveform of the drive circuit 70 is increased h times of two or more times consecutively is described with reference to FIGS. 16 and 17.

First, the ejection waveform in the drive waveform according to another embodiment is described. In the ejection waveform of the liquid ejection head 1 according to the present embodiment, if one of the first to h−1-th potential difference changes is set as the i-th potential difference change, one of the i+1-th to h-th potential difference changes is set as the j-th potential difference change, and the time interval of the i-th and the j-th potential difference change start time is set as Tij, the time intervals Tij satisfy: