JP6033159B2 - Liquid ejecting head, liquid ejecting head driving method, and liquid ejecting apparatus - Google Patents

Description

  The present invention relates to a liquid ejecting head that ejects and records droplets on a recording medium, a method for driving the liquid ejecting head, and a liquid ejecting apparatus.

  In recent years, an ink jet type liquid ejecting head has been used in which ink droplets are ejected onto recording paper or the like to record characters and figures, or a liquid material is ejected onto the surface of an element substrate to form a functional thin film. In this method, a liquid such as ink or a liquid material is guided from a liquid tank to a pressure chamber via a supply pipe, pressure is applied to the liquid filled in the pressure chamber, and the liquid is discharged from a nozzle communicating with the pressure chamber. When discharging the liquid, the liquid ejecting head or the recording medium is moved to record characters and figures, or a functional thin film having a predetermined shape is formed.

  Patent Document 1 describes a liquid ejecting apparatus that records gradation expression on a recording medium. The gradation expression is performed by recording one dot (pixel) by ejecting a plurality of liquid droplets and changing the liquid amount. For example, large dots formed by combining three to four drops of liquid with one dot, medium dots formed by combining two drops of liquid, and standard dots formed with one drop of liquid are formed. One drop of liquid is ejected by applying one main pulse Pm to the pressure chamber in one drive cycle, and two drops of liquid are the same as the main pulse Pm in one drive cycle, and two pulses with a pulse interval of Tw. Is applied to the pressure chamber and discharged. A plurality of drops of liquid when forming a large ball has the same pulse width Tp as the main pulse Pm in one driving cycle, and a plurality of pulses having the same pulse interval Tw are applied to the pressure chamber and ejected. The pulse width Tp of the main pulse Pm and the pulse interval Tw of the plurality of pulses are determined by the time AL during which the pressure wave propagates one way through the pressure chamber. For example, 1.1AL ≦ Tp ≦ 1.5AL, 3.5AL ≦ Tw ≦ 4.5 AL. This one-way propagation time AL is influenced not only by the length of the liquid channel, but also by the viscosity of the liquid and the rigidity of each plate constituting the channel.

  Patent Document 2 describes another liquid ejecting apparatus that records gradation expression on a recording medium. FIG. 11 (FIG. 6 of Patent Document 2) shows a driving waveform, FIG. 11A shows a driving waveform for discharging one drop of liquid, and FIG. 11B shows a driving waveform for discharging two drops of liquid. FIG. 11C shows a driving waveform for discharging three drops of liquid, and FIG. 11D shows another driving waveform for discharging three drops of liquid. In the figure, the horizontal axis represents time, and the vertical axis represents drive voltage. A pressure chamber consists of a groove | channel, and the side wall of a groove | channel consists of a piezoelectric material. By applying a driving waveform to the piezoelectric body, the side wall is deformed and the volume of the pressure chamber is increased or decreased. The pulse width T1 represents a time width that maximizes the droplet ejection speed, and is determined by the resonance period of the liquid filled in the pressure chamber. When a voltage is applied to the side wall of the pressure chamber to rapidly increase the volume of the pressure chamber, the liquid in the pressure chamber becomes negative and the liquid is taken into the pressure chamber from the outside. The pressure of the liquid is reversed and reaches a maximum after a predetermined period of time due to the resonance period. At the same time as this pressure becomes maximum, the applied voltage is changed to 0 volts to contract the pressure chamber. With this driving method, it is possible to eject droplets at the maximum speed. Therefore, the pulse width T1 is made to coincide with 1/2 of the resonance period of the liquid filled in the pressure chamber.

  In all the drive waveforms shown in FIG. 11, the final drive pulse is made common to the pulse width T1, the time interval between the start of the final drive pulse and the previous initial drive pulse is set to 2T1, and the initial drive pulse of the previous drive pulse is similarly set. The start time interval is equally 2T1. In Patent Document 2, if the pulse width T2 of the initial drive pulse before the final drive pulse or the pulse width T3 of the initial drive pulse before that is the same time width T1 as the final drive pulse, it is more than the case of ejecting one drop. The ejection speed is higher when ejecting two drops, and the ejection speed is greater when ejecting three drops than ejecting two drops. Since the recording medium relatively moves while ejecting droplets from the liquid ejecting head, the difference in droplet ejection speed means that the position where the droplets land on the recording medium varies. Therefore, it is necessary to keep the droplet velocity constant even if the number of droplets, that is, the gradation changes.

  Therefore, the initial drive pulse before the final drive pulse or the pulse widths T2 and T3 of the initial drive pulse before the final drive pulse are made narrower than the pulse width T1 of the final drive pulse, and the ejection speed of one drop and two or three drops are set. Make the discharge speed equal. In FIG. 11 (d), the initial drive pulse before the final drive pulse and the pulse widths T2a and T3a of the previous initial drive pulse are made longer than T1, and the effect of equalizing the ejection speed is obtained. Is described.

JP 2007-7955 A JP 2008-272952 A

  The liquid ejecting head has a different driving frequency depending on the model of the liquid ejecting apparatus to be mounted. For this reason, the performance required for a liquid jet head that records gradation expression is that the droplet ejection speed is constant even when the drive frequency is different. That is, the frequency dependency of the ejection speed is reduced in recording of all gradation representations.

FIG. 12 is a diagram illustrating a relationship between a driving frequency of a conventionally known liquid jet head and a droplet discharge speed. 12A shows the shapes of the drive waveforms (A) to (E), and FIG. 12B shows the ejection of droplets when the drive frequency is changed for the drive waveforms (A) to (E). It represents the change in speed. For example, in the waveform (A), the pulse width Wz of the final drive pulse is 7.6 μs, the pulse width Wy of the initial drive pulse before the final drive pulse is 3.8 μs (Wy = Wz / 2), and the final The interval W ₀ between the drive pulse and the initial drive pulse (hereinafter referred to as the off period W ₀ ) is 11.4 μs. The resonance period of the liquid ejecting head is 2 Wz = 15.2 μs, and the pulse width of the driving pulse that maximizes the ejection speed when ejecting one drop of liquid is 7.6 μs. This pulse width is finally driven. The pulse width Wz of the pulse is used.

In the drive waveforms (a) to (e), the pulse width Wy of the initial drive pulse and the off period W ₀ between the final drive pulse and the initial drive pulse are added (Wy + W ₀ ) = 15.2 μs, and the resonance period The final drive pulse is fixed at a pulse width Wz = 7.6 μs. The drive voltage V is a voltage for obtaining the discharge speed when the reference speed is 5.0 m / s. In the waveforms (A) to (E), the pulse width of the initial drive pulse is gradually increased. Note that the reference speed of 5.0 m / s shown here is the discharge speed obtained when time has passed so that the influence of the final pulse discharge of the previous period pulse does not affect the discharge of the next period pulse when discharging continuously. It is.

  As can be easily understood from FIG. 12 (b), when the driving frequency is around 5 kHz, the driving waveform has a substantially constant ejection speed of 5.0 m / s, which is the target value, but at a driving frequency of 10 kHz to 15 kHz. The discharge speed becomes lower than 4.0 m / s, the discharge speed decreases to about 4.0 m / s at any drive waveform at a drive frequency of 15 kHz, and the target value is 5.0 m / s at a drive frequency of 15 kHz to 20 kHz. Is far from the discharge speed.

  That is, when the pulse width Wz of the final drive pulse is set to a pulse width that maximizes the ejection speed, it can be understood that even if the pulse width Wy of the initial drive pulse is changed, the dispersion of the ejection speed with respect to the drive frequency is not improved.

The liquid ejecting head of the present invention includes a pressure chamber surrounded by a wall including a driving wall and filled with a liquid, a nozzle communicating with the pressure chamber, and a driving unit that supplies a driving signal to the driving wall, When the ejection amount of droplets ejected from the nozzle is controlled according to the number of drive pulses included in one cycle of the drive signal, and the pulse width of a single drive pulse given as the drive signal is gradually increased , W ₁ is the pulse width at which the droplet discharge speed is first maximized, and W ₂ (> W ₁ ) is the pulse width at which the droplet discharge speed is first minimized when the pulse width is further increased. ), The pulse width Wz of the drive pulse Pz given at the end of the one cycle satisfies the following expression (1), is included in the one cycle, and is an off period between the drive pulse Py given before the drive pulse Pz The interval W ₀ satisfies the following formula (2) And
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2)

Further, the following equation (3) is satisfied by setting the pulse width of the drive pulse Py to Wy.
Wz = Wy (3)

Further, the following equation (3 ′) is satisfied, where Wx is the pulse width of the drive pulse Px given before the drive pulse Py.
Wz = Wy = Wx (3 ')

Further, a pulse given before the drive pulse Py is a drive pulse Px, and the pulse width Wz ₁ of the drive pulse Pz when only the drive pulse Pz is included in the one cycle, and the drive pulse Pz in the one cycle. And the pulse width Wz ₂ of the drive pulse Pz when only the drive pulse Py is included, and the drive pulse when at least the drive pulse Pz, the drive pulse Py, and the drive pulse Px are included in the one cycle. as the pulse width Wz ₃ of pz, both Wz _1, Wz ₂ and Wz ₃ satisfies expression (1), and it was decided to satisfy the following equation (4).
Wz ₁ <Wz ₂ <Wz ₃ (4)

The pulse width of the drive pulse Px given before the drive pulse Py is Wx, the pulse width when only the drive pulse Pz is included in the one cycle is Wz _1, and the drive pulse Pz and the drive pulse Pz wherein the Wz ₂ pulse width of the drive pulses Pz when only the drive pulse Py is included, in the one cycle, the drive pulse when that contains at least the drive pulses Pz, the drive pulse Py and the driving pulses Px Assuming that the pulse width of Pz is Wz ₃ , Wz ₁ , Wz _2, and Wz ₃ all satisfy the formula (1) and satisfy the following formulas (5), (6), and (7).
Wx = Wy (5)
Wz ₁ <Wz ₂ (6)
Wz ₁ <Wz ₃ (7)

The liquid ejecting head driving method of the present invention includes a pressure chamber surrounded by a wall including a driving wall and filled with a liquid, a nozzle communicating with the pressure chamber, and a driving unit that supplies a driving signal to the driving wall. The amount of droplets ejected from the nozzle is controlled in accordance with the number of drive pulses included in one cycle of the drive signal, and the pulse width of a single drive pulse given as the drive signal is gradually increased. The pulse width at which the droplet discharge speed is first maximized is W _1, and when the pulse width is further increased, the pulse width at which the droplet discharge speed is first minimized is W ₂ ( > W ₁ ), the drive unit has a pulse width Wz of the drive pulse Pz applied to the drive wall at the end of the one cycle that satisfies the following formula (1), and is preceded by the drive pulse Pz in the one cycle. Off period between drive pulse Py Interval W ₀ is decided to supply a driving signal which satisfies the following equation (2).
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2)

  The liquid ejecting apparatus according to the aspect of the invention includes the liquid ejecting head, a moving mechanism that relatively moves the liquid ejecting head and the recording medium, a liquid supply pipe that supplies liquid to the liquid ejecting head, and the liquid And a liquid tank for supplying the liquid to the supply pipe.

A liquid ejecting head of the present invention includes a pressure chamber surrounded by a wall including a drive wall and filled with liquid, a nozzle communicating with the pressure chamber, and a drive unit that supplies a drive signal to the drive wall. When the discharge amount of droplets discharged from the nozzle is controlled according to the number of drive pulses included in one cycle and the pulse width of a single drive pulse given as a drive signal is gradually increased, droplet discharge The pulse width at which the speed is first maximized is W ₁ , and the pulse width at which the droplet discharge speed is first minimized when the pulse width is further increased is W ₂ (> W ₁ ). The pulse width Wz of the drive pulse Pz given to the above satisfies the following expression (1), and the off periods W ₀ of the plurality of drive pulses included in one cycle satisfy the following expression (2).
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2)
As a result, it is possible to reduce variations in droplet discharge speed when the drive frequency is changed.

FIG. 2 is a schematic diagram illustrating a configuration of a liquid jet head according to a first embodiment of the invention. FIG. 5 is a schematic diagram for explaining driving of the head portion of the liquid jet head according to the first embodiment of the invention. FIG. 6 is an explanatory diagram of a driving waveform of the liquid jet head according to the first embodiment of the present invention. FIG. 6 is a diagram for explaining the characteristics of the liquid jet head according to the present invention. FIG. 6 is a diagram for explaining the characteristics of the liquid jet head according to the present invention. FIG. 10 is an explanatory diagram of a drive waveform of one cycle of a liquid jet head according to a second embodiment of the present invention. FIG. 10 is a diagram illustrating a drive waveform of one cycle of a liquid jet head according to a third embodiment of the present invention. FIG. 10 is a diagram illustrating a drive waveform of one cycle of a liquid jet head according to a fourth embodiment of the present invention. FIG. 10 is an exploded schematic view of a head portion of a liquid jet head according to a fifth embodiment of the present invention. FIG. 10 is a schematic perspective view of a liquid ejecting apparatus according to a sixth embodiment of the present invention. It is a figure showing the drive waveform used for a conventionally well-known liquid ejecting apparatus. It is a figure showing the relationship between the drive frequency of a conventionally well-known liquid jet head, and the discharge speed of a droplet.

(First embodiment)
1 to 5 are views for explaining the liquid jet head 1 according to the first embodiment of the present invention. FIG. 1 is a schematic diagram illustrating the configuration of the liquid jet head 1. FIG. 2 is a schematic diagram for explaining the driving of the head unit 2. As shown in FIG. 1, the liquid ejecting head 1 includes a head unit 2 that ejects liquid and a driving unit 7 that supplies a driving signal to a driving wall 5 of the head unit 2. The head unit 2 includes a pressure chamber 3 surrounded by a wall 4 including a drive wall 5 and filled with a liquid, and a nozzle 6 communicating with the pressure chamber 3.

  The operation of the head unit 2 will be described with reference to FIG. For example, the drive wall 5 is formed of a piezoelectric material made of PZT ceramics or the like, and is subjected to polarization processing in a direction orthogonal to the electric field direction. A drive electrode 8 is formed on the drive wall 5 so as to sandwich the drive wall 5 in the upper half thereof. A voltage is applied to the two drive electrodes 8 sandwiching the drive wall 5 by tilting the switch S to the on side. The drive wall 5 undergoes thickness-slip deformation in a direction that increases the volume of the pressure chamber 3, and the liquid is drawn into the pressure chamber 3. Next, the switch S is tilted off to short-circuit the two drive electrodes 8 sandwiching the drive wall 5. Then, the drive wall 5 returns to its original shape, the liquid in the pressure chamber 3 is compressed, and droplets are ejected from the nozzle 6.

FIG. 3 is an explanatory diagram of drive waveforms of the liquid jet head according to the first embodiment of the present invention. FIG. 3A shows the relationship between the pulse width and the droplet ejection speed when a single drive pulse is given as the drive signal. The horizontal axis represents the pulse width, and the vertical axis represents the ejection speed of the droplets ejected from the nozzle 6. As shown in FIG. 3A, when the pulse width of a single drive pulse is gradually increased, the droplet discharge speed gradually increases, and the pulse width at which the discharge speed is first maximized is W ₁ . Further a pulse width ejection speed of the droplet is initially minimized and W ₂ when increasing the pulse width. The pulse width W ₁ is considered to be a half period of the resonance period based on the natural vibration of the liquid filled in the pressure chamber 3, and the pulse width W ₂ is considered to be the resonance period. Therefore, in general, the relationship is W ₂ = 2W ₁ . The natural period varies depending on the shape of the pressure chamber 3, the viscosity of the liquid, the temperature, and the like.

FIG. 3B is an explanatory diagram of a drive waveform of one cycle of the liquid jet head 1 according to the first embodiment of the present invention. The upper part of FIG. 3B represents the last drive pulse given from the drive unit 7 to the drive wall 5 in one cycle period, and the lower part shows the last drive pulse given from the drive unit 7 to the drive wall 5 in one cycle period. And the shape of the drive pulse given before that. By selecting the number of driving pulses, it is possible to change the liquid discharge amount and record the gradation expression. Therefore, the gradation expression can be recorded by the number of pulses of 3 or more in one period. FIG. 3B shows a drive pulse given last among the plurality of pulses and a drive pulse given before that.

Here, the drive pulse given at the end of one cycle is Pz (hereinafter referred to as final drive pulse Pz), and the drive pulse given before the final drive pulse Pz is assumed as Py (hereinafter simply referred to as drive pulse Py). The pulse width Wz of the final drive pulse Pz satisfies Expression (1), and the OFF period W ₀ of the final drive pulse Pz and the drive pulse Py satisfies Expression (2).
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2)
Expressions (1) and (2) define the relationship between the final drive pulse Pz and the drive pulse Py, and are also applied to a drive waveform in which two or more pulses exist in one cycle.

The area | region of Formula (1) is represented by the oblique line of Fig.3 (a). Accordingly, the pulse width Wz of the final drive pulse Pz is set between 1/2 of the resonance period of the pressure chamber 3 and the resonance period, and is slower than the maximum discharge speed. If W ₂ = 2W ₁ , the pulse width Wz is a period 1.25 to 1.75 times W ₁ . By setting the drive waveform in this way, it is possible to reduce variations in the droplet ejection speed when the frequency of the drive signal is changed, and it is possible to provide a versatile liquid jet head 1.

The characteristics of the liquid jet head 1 according to the present invention will be described with reference to FIGS. 4 and 5. FIG. 4A shows the shapes of the drive waveforms [1] to [6]. FIG. 4B shows the relationship between the drive frequency and the droplet discharge speed when using the drive waveforms [1] to [6], and is an actual measurement value. The drive waveforms [1] to [5] satisfy the above expressions (1) and (2) and are included in the scope of the present invention, and the drive waveform [6] has a pulse width Wz exceeding the upper limit of the expression (1). It is not included in the scope of the invention. In the present embodiment, the head portion 2 has a pulse width W ₁ at which the droplet discharge speed is first maximized when the pulse width is gradually increased, which is 7.6 μs, and the droplet discharge speed is initially minimized. The pulse width W ₂ is 15.2 μs.

In the drive waveforms [1] to [5], the pulse width of the final drive pulse Pz is fixed to Wz = 11.4 μs, the pulse width Wy of the drive pulse Py, and the off period between the final drive pulse Pz and the drive pulse Py. the sum of the W ₀ and (Wy + W ₀₎ is fixed to the W ₂ = 15.2μs. Then, the pulse width Wy of the drive pulse Py is gradually increased according to the drive waveforms [1] to [5]. Further, the pulse voltage V of each of the drive waveforms [1] to [6] is a voltage at which the droplet discharge speed is 5.0 m / s. Note that the pulse width Wz = 11.4 μs of the final drive pulse Pz is an intermediate value between W ₂ and W ₁ in FIG.

In order to record gradation expression by ejecting a plurality of droplets, it is necessary to combine a droplet ejected by the drive pulse Py and a droplet ejected by the final drive pulse Pz. In the drive waveforms [1] to [3], the droplets ejected by the final drive pulse Pz do not catch up with the droplets ejected by the drive pulse Py, and the two droplets fly without being combined to express gradation. Not suitable for. On the other hand, the droplets ejected by the drive waveforms [4] to [6] are combined, and as shown in FIG. 4B, the variation in the ejection speed is small as a whole, and the speed depends on the frequency. The drop is significantly improved. Drive waveform [6], the pulse width Wz of the final drive pulse Pz is close to the pulse width W ₂ that the discharge rate is initially minimized, the discharge speed becomes slow. For this reason, since the drive voltage is increased to increase the ejection speed, the drive voltage is increased and the drive efficiency is lowered.

  In the conventional example, as shown in FIG. 12B, the drive frequency is 10 kHz to 15 kHz and the discharge speed is as low as 4.0 m / s or less, and the drive frequency of 15 kHz to 20 kHz has a target value even in the drive waveform of the discharge speed. It does not reach 5.0m / s. On the other hand, in the drive waveforms [4] and [5] included in the scope of the present invention, as shown in FIG. 4 (b), the discharge speed becomes 4.0 m / s or more at the drive frequency of 10 kHz to 15 kHz. It can be understood that the average discharge speed is 5.0 m / s at a driving frequency of 15 kHz to 20 kHz, which is significantly improved over the conventional example.

FIG. 5A shows the shapes of the drive waveforms [7] to [15]. FIG. 5B shows the relationship between the drive frequency and the droplet discharge speed when using the drive waveforms [7] to [15], and is an actual measurement value. In each of the drive waveforms [7] to [15], the pulse width Wz of the final drive pulse Pz is equal to the pulse width Wy of the drive pulse Py. Further, the drive waveforms [7] to [11] have a pulse width of the final drive pulse Pz of W ₁ or less and are not included in the scope of the present invention. The drive waveforms [12] to [14] satisfy the above expressions (1) and (2) and are included in the scope of the present invention. The drive waveform [15] exceeds the upper limit of the above formula (1) and is not included in the scope of the present invention. In addition, the total (Wy + W ₀ ) of the characteristics of the head unit 2, the pulse width Wy of the drive pulse Py, and the interval W ₀ of the off period between the drive pulse Py and the final drive pulse Pz is W ₂ = 15.2 μs. This is the same as in FIG.

The drive waveforms [7] to [11] are obtained when the width of the pulse width Wz of the final drive pulse Pz is changed from 2 μs to 7.6 μs. As shown in FIG. 5B, the drive waveform [7] cannot be employed because the variation in the ejection speed is remarkably large and the drive voltage is high. The drive waveforms [8] to [11] have a discharge frequency of about 4.0 m / s or less at a drive frequency of 10 kHz to 15 kHz, and the discharge speed does not reach 5.0 m / s even between the drive frequencies of 15 kHz to 20 kHz. . That is, when the pulse width Wz of the final drive pulse Pz is the same as the pulse width W _{1 at} which the discharge speed is maximum or narrower than the pulse width W ₁ , the dispersion of the discharge speed when the drive frequency is changed increases. The speed reduction due to the driving frequency appears remarkably.

On the other hand, the drive waveforms [12] to [15] included in the scope of the present invention have an ejection speed of about 5.0 m / s in the drive frequency range of 5 kHz to 20 kHz, and the drive waveform [7]. Less variation than ~ [11]. Further, the drive waveform [15] has the least variation in the ejection speed with respect to the drive frequency, but the pulse width Wz of the final drive pulse Pz is the pulse at which the ejection speed becomes the smallest first, as in the above drive waveform [6]. Near the width W ₂ , the discharge speed becomes slow. Therefore, the drive voltage is increased by increasing the drive voltage to increase the ejection speed. The drive voltage V shown in FIGS. 4A and 5A is a voltage for obtaining a reference speed of 5.0 m / s without being affected by the drive pulse of the previous period.

  As described above, the drive waveform satisfying the above formulas (1) and (2) has little variation in ejection speed even when the frequency of the drive signal applied from the drive unit 7 to the head unit 2 is changed, and is a versatile liquid jet. The head 1 can be configured.

(Second embodiment)
FIG. 6 is an explanatory diagram of a drive waveform of one cycle of the liquid jet head 1 according to the second embodiment of the present invention. The horizontal axis is time, and the vertical axis is voltage. As already described in the first embodiment, by selecting the number of drive pulses, it is possible to change the liquid ejection amount and record the gradation expression. Therefore, the gradation expression can be recorded by the number of pulses of 2 or more in one period, and FIG. 6 shows three pulses given at the end of these plural pulses. That is, the drive pulse Py having the pulse width Wy is given before the final drive pulse Pz having the pulse width Wz. Further, a drive pulse Px having a pulse width Wx is given before the drive pulse Py. The pulse width Wz of the final drive pulse Pz satisfies the expression (1), and each drive pulse satisfies the following expression (3) or (3 ′).
Wz = Wy (3)
Wz = Wy = Wx (3 ′)
Equation (3) represents the relationship between the final drive pulse Pz and the drive pulse Py among the two or more pulses, and includes the case of a drive waveform in which there are three or more pulses in one cycle. Similarly, Expression (3 ′) represents the relationship among the final drive pulse Pz, the drive pulse Py, and the drive pulse Px among the three or more pulses, and includes the case of a drive waveform in which four or more pulses exist in one cycle. It is.

In the driving waveform shown in FIG. 6, the off period W ₀ between the final drive pulse Pz and the drive pulse Py, and the off period W ₀ between the drive pulse Py and the driving pulse _{Px, W 0 = (W 2} -Wy ) = (W ₂ −Wx), and the expression (2) is satisfied. That is, the start timing of each drive pulse Pz, Py, Px is made to coincide with the natural period of the head unit 2.

  As shown in FIGS. 4 and 5, the drive waveforms [4], [12] to [14] all satisfy the above equation (3), and there is little variation in the droplet discharge speed even when the drive frequency is changed. It is clear. As described above, the drive waveforms satisfying the formulas (1) to (3) have very little variation in the droplet discharge speed even when the drive frequency is changed, and the versatile liquid jet head 1 can be configured. .

(Third embodiment)
FIG. 7 is a diagram illustrating a drive waveform of one cycle of the liquid jet head 1 according to the third embodiment of the present invention. FIG. 7A shows a drive waveform in which only the final drive pulse Pz is included in one cycle. FIG. 7B shows a drive waveform including only the final drive pulse Pz and the drive pulse Py before the final drive pulse Pz in one cycle. FIG. 7C shows a drive waveform including at least three pulses of a final drive pulse Pz, a drive pulse Py before the final drive pulse Pz, and a drive pulse Px before the drive pulse Py in one cycle. Represent. In each figure, the horizontal axis represents time and the vertical axis represents voltage. FIG. 7A corresponds to discharge of one drop, (b) corresponds to discharge of two drops, and (c) corresponds to discharge of three drops or more.

The pulse width Wz ₁ is the pulse width of the final drive pulse Pz when only the final drive pulse Pz is included in one cycle, and the final drive pulse Pz when only the final drive pulse Pz and the drive pulse Py are included in one cycle. a pulse width pulse width Wz _2, in one period, at least the final drive pulse Pz, the pulse width of the final drive pulse Pz as the pulse width Wz ₃ when including the driving pulse Py and the drive pulse Px, satisfies the formula (4) .
Wz ₁ <Wz ₂ <Wz ₃ (4)

In general, when a pressure wave is generated in the liquid filled in the pressure chamber 3, a natural vibration is induced in the liquid in the pressure chamber 3 by the pressure wave, and the vibration remains in the resonance cycle. In the first and second embodiments, the pulse width W ₂ is considered to correspond to the resonance period. Therefore, particularly when the sum (Wy + W ₀ ) of the pulse width Wy and the off-period interval W ₀ is set to the resonance period, the final drive pulse Pz is applied when the final drive pulse Pz is applied after the drive pulse Py is applied. The ejection speed of the liquid droplet is larger than that when only the liquid is applied to eject the liquid droplet. Furthermore, when the drive pulse Py is applied before the final drive pulse Pz and the drive pulse Px is applied before the drive pulse Py, the droplet ejection speed is higher than when only the final drive pulse Pz and the drive pulse Py are applied. growing.

Thus, the pulse width Wz ₂ when only the final drive pulse Pz and the drive pulse Py are applied is set wider than the pulse width Wz ₁ when only the final drive pulse Pz is applied, thereby reducing the droplet ejection speed. . Similarly, at least the final drive pulse Pz, the drive pulse Py, and the drive pulse Px are set to have a pulse width Wz ₃ wider than the pulse width Wz ₂ to reduce the droplet discharge speed. Thereby, even if the number of pulses in one cycle is changed, the droplet ejection speed can be set to be constant. Note that the pulse widths Wz ₁ , Wz ₂ , and Wz ₃ are all in a range that satisfies the equation (1), and the off-period interval W ₀ is a range that satisfies the equation (2). The droplet ejection speed by the final drive pulse Pz is most greatly influenced by the number of pulses in one period when (Wy + W ₀ ) or (Wx + W ₀ ) is set as the resonance period, and the interval of the off period W ₀ falls within the range of equation (1).

  In FIGS. 7A to 7C, for easy understanding, the start timing of the final drive pulse Pz is made coincident and the end timing is shifted. However, in the present invention, the expression (1) ), Equation (2), and Equation (4) may be satisfied. Therefore, the timing of the start end of the final drive pulse Pz may be shifted in each drive waveform, or may be any timing.

(Fourth embodiment)
FIG. 8 is a diagram illustrating a drive waveform of one cycle of the liquid jet head 1 according to the fourth embodiment of the present invention. FIG. 8A shows a drive waveform in which only the final drive pulse Pz is included in one cycle. FIG. 8B shows a drive waveform in which only the final drive pulse Pz and the drive pulse Py before the final drive pulse Pz are included in one cycle. FIG. 8C shows a drive waveform including at least three pulses of a final drive pulse Pz, a drive pulse Py before the final drive pulse Pz, and a drive pulse Px before the drive pulse Py in one cycle. Represent. In each figure, the horizontal axis represents time and the vertical axis represents voltage. FIG. 8A corresponds to discharge of one drop, (b) corresponds to discharge of two drops, and (c) corresponds to discharge of three drops or more.

The pulse width Wz ₁ is the pulse width of the final drive pulse Pz when only the final drive pulse Pz is included in one cycle, and the pulse width of the final drive pulse Pz when only the final drive pulse Pz and the drive pulse Py are included in one cycle. the pulse width Wz _2, one period, at least the final drive pulse Pz, the pulse width of the final drive pulse Pz as the pulse width Wz ₃ when including the driving pulse Py and the drive pulse Px, the formula (5), (6) And (7) is satisfied.
Wx = Wy (5)
Wz ₁ <Wz ₂ (6)
Wz ₁ <Wz ₃ (7)

As already described in the third embodiment, when a pressure wave is generated in the liquid filled in the pressure chamber 3, the vibration of the resonance period is induced and remains in the liquid, and when a plurality of pulses are applied in the resonance period, the number of pulses As the value increases, the droplet ejection speed increases. In the present embodiment, the droplet ejection speed is set by setting the pulse width Wz ₂ when applying only the final drive pulse Pz and the drive pulse Py to be wider than the pulse width Wz ₁ when applying only the final drive pulse Pz. Reduce. Similarly, at least the final drive pulse Pz, the drive pulse Py, and the drive pulse Px are set to have a pulse width Wz ₃ wider than the pulse width Wz ₁ to reduce the droplet discharge speed.

Since the time interval between the drive pulse Px and the final drive pulse Pz is wider than that of the drive pulse Py, the influence of the final drive pulse Pz on the ejection speed is less than that of the drive pulse Py. Therefore, the condition of Wz ₂ with respect to Wz ₁ when only the final drive pulse Pz and the drive pulse Py exist, and the condition of Wz ₃ with respect to Wz ₁ when at least the final drive pulse Pz, the drive pulse Py, and the drive pulse Px exist. And equalized. Further, the pulse width Wy of the drive pulse Py and the pulse width Wx of the drive pulse Px are made equal. Thereby, even if the number of pulses in one cycle is changed, the droplet ejection speed can be set to be constant. Note that the pulse widths Wz ₁ , Wz ₂ , and Wz ₃ are all in a range that satisfies the equation (1), and the off-period interval W ₀ is a range that satisfies the equation (2).

As described above, by setting the pulse widths of the drive pulse Py and the drive pulse Px equal to each other without providing a large or small restriction between the pulse width Wz ₂ and the pulse width Wz ₃ , the drive waveform of the third embodiment is improved. The conditions are simplified and the load on the drive unit 7 is reduced.

(Fifth embodiment)
FIG. 9 is an exploded schematic view of the head portion 2 of the liquid jet head 1 according to the fifth embodiment of the present invention. The same portions or portions having the same function are denoted by the same reference numerals. As shown in FIG. 9, the head unit 2 includes a piezoelectric plate 9, a cover plate 10 joined to the upper surface US of the piezoelectric plate 9, a nozzle plate 11 joined to the side surface SS of the piezoelectric plate 9, and the piezoelectric plate 9. And a flexible substrate 12 bonded to a rear upper surface US opposite to the nozzle plate 11. The piezoelectric plate 9 includes ejection grooves 9a and dummy grooves 9b that are alternately arranged on the upper surface US thereof. The discharge groove 9a and the dummy groove 9b have one side opened to the side surface SS and the other side terminated at the upper surface US. The discharge groove 9a and the dummy groove 9b are separated by a side wall 9e. On both side surfaces of the side wall 9e, the drive electrodes 8 are installed from the upper surface US to about ½ of the groove depth. The drive electrode 8 formed on the side surface on the ejection groove 9a side is electrically connected to the common terminal 9c formed on the upper surface US on the rear side of the piezoelectric plate 9. The drive electrode 8 formed on the side surface on the dummy groove 9 b side is electrically connected to the active terminal 9 d formed on the upper surface US on the rear side of the piezoelectric plate 9. The cover plate 10 includes a liquid supply chamber 10a that supplies a liquid to the discharge groove 9a through the slit 10b. The cover plate 10 is joined to the upper surface US of the piezoelectric plate 9 to cover the upper openings of the ejection grooves 9a and the dummy grooves 9b. The nozzle plate 11 includes a plurality of nozzles 6, and each nozzle 6 communicates with each ejection groove 9 a and is joined to the side surface SS of the piezoelectric plate 9. The discharge groove 9a is covered with the cover plate 10 at the upper opening, and the opening at the side surface SS is closed by the nozzle plate 11 to form the pressure chamber 3.

  The piezoelectric plate 9 is made of piezoelectric ceramic, for example, PZT ceramic. The piezoelectric plate 9 is previously polarized in the direction perpendicular to the upper surface US. The liquid is supplied to the liquid supply chamber 10a, and is supplied to each discharge groove 9a via the slit 10b. A driving waveform described in the first to fourth embodiments is applied to the common terminal 9c and the active terminal 9d through the flexible substrate 12 from the driving unit 7 (not shown). Then, both side walls 9e of the ejection groove 9a are deformed in thickness to induce a pressure wave in the liquid filled therein, and droplets are ejected from the nozzle 6. In the present invention, the head portion 2 is not limited to the structure shown in FIG.

(Sixth embodiment)
FIG. 10 is a schematic perspective view of a liquid ejecting apparatus 30 according to the sixth embodiment of the present invention. The liquid ejecting apparatus 30 includes a moving mechanism 40 that reciprocates the liquid ejecting heads 1 and 1 ′, and a flow path unit that supplies the liquid to the liquid ejecting heads 1 and 1 ′ and discharges the liquid from the liquid ejecting heads 1 and 1 ′. 35, 35 ′, liquid pumps 33, 33 ′ and liquid tanks 34, 34 ′ communicating with the flow path portions 35, 35 ′. Each liquid ejecting head 1, 1 ′ includes the liquid ejecting head 1, a piezoelectric plate, a nozzle plate, and a flow path member. As the liquid pumps 33 and 33 ′, either or both of a supply pump that supplies the liquid to the flow path portions 35 and 35 ′ and a discharge pump that discharges the liquid are installed, and the liquid is circulated. In addition, a pressure sensor and a flow rate sensor (not shown) may be installed to control the liquid flow rate. The liquid ejecting heads 1 and 1 ′ are driven by the driving waveforms described in the first to fourth embodiments, and for example, the head unit 2 described in the fifth embodiment can be used.

  The liquid ejecting apparatus 30 includes a pair of conveying units 41 and 42 that convey a recording medium 44 such as paper in the main scanning direction, liquid ejecting heads 1 and 1 ′ that eject liquid onto the recording medium 44, and a liquid ejecting head. 1, 1 ′ carriage unit 43, liquid tanks 34, 34 ′ and liquid pumps 33, 33 ′ that supply the liquid stored in the liquid tanks 34, 34 ′ to the flow path parts 35, 35 ′, And a moving mechanism 40 that scans 1 ′ in the sub-scanning direction orthogonal to the main scanning direction. A control unit (not shown) controls and drives the liquid ejecting heads 1, 1 ′, the moving mechanism 40, and the conveying units 41 and 42.

  The pair of conveying means 41 and 42 includes a grid roller and a pinch roller that extend in the sub-scanning direction and rotate while contacting the roller surface. A grid roller and a pinch roller are moved around the axis by a motor (not shown), and the recording medium 44 sandwiched between the rollers is conveyed in the main scanning direction. The moving mechanism 40 couples a pair of guide rails 36 and 37 extending in the sub-scanning direction, a carriage unit 43 slidable along the pair of guide rails 36 and 37, and the carriage unit 43 to move in the sub-scanning direction. An endless belt 38 is provided, and a motor 39 that rotates the endless belt 38 via a pulley (not shown) is provided.

  The carriage unit 43 mounts a plurality of liquid jet heads 1, 1 ′, and ejects, for example, four types of liquid droplets of yellow, magenta, cyan, and black. The liquid tanks 34 and 34 'store liquids of corresponding colors and supply them to the liquid jet heads 1 and 1' via the liquid pumps 33 and 33 'and the flow path portions 35 and 35'. Each liquid ejecting head 1, 1 ′ ejects droplets of each color according to the drive signal. An arbitrary pattern is recorded on the recording medium 44 by controlling the timing at which liquid is ejected from the liquid ejecting heads 1, 1 ′, the rotation of the motor 39 that drives the carriage unit 43, and the conveyance speed of the recording medium 44. I can.

  In this embodiment, the moving mechanism 40 moves the carriage unit 43 and the recording medium 44 to perform recording, but instead, the carriage unit is fixed and the moving mechanism is the recording medium. It may be a liquid ejecting apparatus that records the image by moving it two-dimensionally. That is, the moving mechanism may be any mechanism that relatively moves the liquid ejecting head and the recording medium.

DESCRIPTION OF SYMBOLS 1 Liquid ejecting head 2 Head part 3 Pressure chamber 4 Wall 5 Drive wall 6 Nozzle 7 Drive part 8 Drive electrode Pz Final drive pulse, Py, Px Drive pulse W _{1 The} pulse width W ₂ discharge speed at which the discharge speed is first maximized First minimum pulse width W ₀ off period

Claims (7)

A pressure chamber surrounded by a wall including a drive wall and filled with liquid, a nozzle communicating with the pressure chamber, and a drive unit that supplies a drive signal to the drive wall are included in one cycle of the drive signal. The ejection amount of droplets ejected from the nozzle is controlled according to the number of drive pulses,
When the pulse width of a single drive pulse given as the drive signal is gradually increased, the pulse width at which the droplet discharge speed is first maximized is W _1, and when the pulse width is further increased, Let W ₂ (> W ₁ ) be the pulse width at which the droplet discharge speed is first minimized.
The pulse width Wz of the drive pulse Pz given at the end of the one cycle satisfies the following expression (1), is included in the one cycle, and is an off-period interval W between the drive pulse Py given before the drive pulse Pz. _A liquid jet head in which ₀ satisfies the following expression (2).
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2) The liquid jet head according to claim 1, wherein a pulse width of the drive pulse Py is Wy and the following expression (3) is satisfied.
Wz = Wy (3) 3. The liquid jet head according to claim 2, wherein a pulse width of the drive pulse Px given before the drive pulse Py is Wx and the following expression (3 ′) is satisfied.
Wz = Wy = Wx (3 ') A pulse given before the drive pulse Py is defined as a drive pulse Px.
A pulse width Wz ₁ of the drive pulse Pz when only the drive pulse Pz is included in the one cycle;
A pulse width Wz ₂ of the drive pulse Pz when only the drive pulse Pz and the drive pulse Py are included in the one cycle;
As the pulse width Wz ₃ of the drive pulse Pz when at least the drive pulse Pz, the drive pulse Py, and the drive pulse Px are included in the one period, Wz ₁ , Wz _2, and Wz ₃ are all represented by the formula (1 ) And the following expression (4) is satisfied.
Wz ₁ <Wz ₂ <Wz ₃ (4) Assuming that the pulse width of the drive pulse Px given before the drive pulse Py is Wx,
The pulse width when only the drive pulse Pz is included in the one cycle is Wz ₁ ,
Wz ₂ is a pulse width of the drive pulse Pz when only the drive pulse Pz and the drive pulse Py are included in the one cycle,
Said one period, at least the drive pulses Pz, as Wz ₃ a pulse width of the drive pulses Pz when included the drive pulse Py and the driving pulses Px is, Wz _1, Wz ₂ and Wz ₃ Any formula ( The liquid jet head according to claim 1, wherein 1) is satisfied and the following expressions (5), (6), and (7) are satisfied.
Wx = Wy (5)
Wz ₁ <Wz ₂ (6)
Wz ₁ <Wz ₃ (7) A pressure chamber surrounded by a wall including a drive wall and filled with liquid, a nozzle communicating with the pressure chamber, and a drive unit that supplies a drive signal to the drive wall are included in one cycle of the drive signal. The ejection amount of droplets ejected from the nozzle is controlled according to the number of drive pulses,
When the pulse width of a single drive pulse given as the drive signal is gradually increased, the pulse width at which the droplet discharge speed is first maximized is W _1, and when the pulse width is further increased, Let W ₂ (> W ₁ ) be the pulse width at which the droplet discharge speed is first minimized.
In the drive unit, the pulse width Wz of the drive pulse Pz applied to the drive wall at the end of the one cycle satisfies the following formula (1), and the drive pulse Py applied to the drive wall before the drive pulse Pz in the one cycle: A method of driving a liquid jet head that supplies a drive signal in which the interval W ₀ between the off periods satisfies the following expression (2):
(W ₂ + 3W ₁ ) / 4 ≦ Wz ≦ (3W ₂ + W ₁ ) / 4 (1)
0 <W ₀ <W ₂ (2) A liquid ejecting head according to claim 1;
A moving mechanism for relatively moving the liquid ejecting head and the recording medium;
A liquid supply pipe for supplying a liquid to the liquid ejecting head;
And a liquid tank that supplies the liquid to the liquid supply pipe.

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