JP2866847B2 - Droplet discharge device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge device, and more particularly, to an on-demand type multi-nozzle ink jet recording device having a plurality of nozzles and ejecting ink droplets from each nozzle as required.

[0002]

2. Description of the Related Art Currently, an on-demand multi-nozzle ink jet apparatus uses a piezoelectric element to convert an electric signal into a mechanical displacement to apply pressure to ink in a flow path and eject ink droplets. There is a so-called bubble jet method in which ink droplets are ejected by the pressure of bubbles generated by applying heat to ink. A conventional ink jet recording apparatus using a piezoelectric element has an advantage that it has good energy efficiency and can use any kind of ink, but is not suitable for high density printing for high quality printing and a large number of nozzles. Further, the bubble jet method has problems such as low energy efficiency, large restrictions on ink, and poor durability.

The inventor of the present invention first provided a large-scale and inexpensive ink jet printing apparatus having a novel principle and configuration having a large number of nozzles arranged at high density and having high energy efficiency and high durability. A flow path substrate having a plurality of partitions provided in a direction substantially perpendicular to the direction and a plurality of flow paths defined by the partitions, and a piezoelectric element plate polarized in a thickness direction, and fixed to an end face of the partition. Of Japanese Patent Application No. 4-1 of Japanese Patent Application No.
No. 30419.

FIG. 13 is a perspective view of a droplet discharge device proposed by the present inventor, and FIG. 14 is a sectional view thereof. A plurality of flow path partition walls 1 are formed in the flow path substrate 3 in a direction substantially perpendicular to the plane direction, and the partition walls define the ink flow paths 2. The cross section of each flow path 2 and flow path partition 1 is substantially rectangular. Each channel 2 is independent on the nozzle plate 5 side and communicates with a common ink chamber 11 for supplying ink on the opposite side. Each flow path 3 and the flow path partition 1 extend in parallel from the nozzle portion to the common ink chamber portion, and have the same pitch as the nozzles 5a. Therefore, there is no need to adopt a fan-shaped channel arrangement as in the conventional inkjet head using a piezoelectric element, and it is possible to create a multi-nozzle inkjet head having an arbitrary number of nozzles. It has the advantage of being applicable to both serial printers and line printers.

On the flow path substrate 3, a common electrode 9 is
A cover plate (piezoelectric element plate) 4 on which a drive electrode 10 corresponding to each flow path is formed on the upper surface is mounted. The piezoelectric element plate serves as an actuator for deforming the flow path partition wall 1 and also has a function as a flow path cover. Each drive electrode 10 has an electrode terminal 12 for supplying a signal from a flexible cable or the like. On the front surface of the head, a nozzle plate 5 in which nozzles 5a corresponding to respective flow paths are formed.
Is attached.

Next, a driving method of the droplet discharge device proposed by the present applicant in the earlier application will be described with reference to FIG. Here, an operation of ejecting ink droplets from the flow path 2b will be described. In the following description, a flow path for ejecting ink droplets is indicated by “〇”, and a flow path that does not eject ink drops is indicated by “×”.

The three drive electrodes 10a to 1 shown
The voltage V is applied to only the drive electrode 2b corresponding to the flow path 2b in the direction 0c in the direction in which the piezoelectric element 4 contracts in a plane (the direction in which the electric field E is generated in the same direction as the polarization direction P). Piezoelectric element plate 4
Of the flow path 2b, only the upper part of the flow path 2b shrinks, the flow path partition walls 1b and 1c on both sides of the flow path 2b are drawn, and the volume of the flow path 2b decreases. Therefore, pressure is applied to the ink in the flow path 2b, and an ink droplet is ejected from the nozzle. In the non-selection flow path 2a, the piezoelectric element plate above the adjacent flow path 2b shrinks, so that the piezoelectric element plate above the flow path 2a and also the flow path partition walls 1a and 1b are drawn in the direction of the flow path 2b. Deform. However, in this case, since the flow path partition walls on both sides are deformed in the same direction, the volume of the flow path 2a does not change.
No pressure is applied to the ink inside. In this way, it is possible to select only a specific flow path and eject ink droplets by using the structurally integrated piezoelectric element plate 4.

[0008]

FIG. 16 is a diagram showing an example in which all the channels are simultaneously driven by the above-mentioned conventional driving method. FIG.
This does not pose a problem when driving a very small number of flow paths as described above, but when all or a large number of flow paths are driven simultaneously, the piezoelectric element cover plate 4 shrinks entirely in the in-plane direction. . Therefore, the piezoelectric element cover plate 4 and the flow path substrate 3 have a bimorph structure, and are curved and deformed as shown in FIG.

This phenomenon will be described with reference to a specific example. X
When a print density of [dpi (dots per inch)] is realized with n rows of flow paths, the adjacent flow path pitch DN is as follows: DN = 0.0254 × n / X (1) Assuming that the thickness of the piezoelectric element plate is T0, the width of the drive electrode is 0.8 times the flow path pitch (0.8 × DN), the applied voltage is V, and the lateral piezoelectric constant is d, the piezoelectric element plate per flow path Is as follows. .omega. = d.times.V.times.0.8.times.DN / T0 (2) Here, when a print density of 300 [dpi] is realized by a single line of flow paths, the flow path pitch DN is obtained from the equation (1). = 8.5 × 10 ^-5 [m]. The transverse piezoelectric strain constant d is 198 × 10 ⁻¹² [m /
V], the driving voltage V is 200 [V], the thickness T of the piezoelectric element plate.
When 0 is set to 1 × 10 ⁻⁴ [m], the contraction amount ω1 of the piezoelectric element plate per one channel is calculated from the equation (2) as ω1 = 2.7 × 10 ⁻⁸ [m], which is a sufficiently small value. The effect on other flow paths and the entire recording apparatus can be ignored. However, when a large number of channels are simultaneously driven by the multi-nozzle head, for example, when each channel of a printing apparatus having 100 nozzles is simultaneously driven, the contraction amount ω
2 has a large value of ω2 = 2.7 × 10 ⁻⁶ [m]. For this reason, there have been problems such as that the entire recording head is largely curved and noise is generated, and stress is generated in the base portion of the flow path substrate 3 and the recording head supporting portion, thereby deteriorating the durability of the recording apparatus.

In the conventional method, when ink is ejected by applying pressure to the ink by reducing the volume of the flow path, a reverse flow of the ink to the common ink chamber 11 opposite to the nozzle and pressure propagation occur. However, the state in the common ink chamber 11 has changed depending on the number of simultaneously driven flow paths. Therefore, when most of the flow paths are driven at the same time, a large pressure is generated also in the ink in the common ink chamber, and ink droplets are ejected from the non-selected flow paths, and are also ejected by the number of simultaneously driven flow paths. The characteristics such as the velocity volume of ink droplets change,
A phenomenon called so-called crosstalk was observed.

As described above, the droplet discharge device proposed earlier by the present inventor has a simple structure using the piezoelectric element cover plate as an actuator, and has a large number of nozzles and channels arranged at high density. When a large number of channels are driven simultaneously, there are disadvantages such as deterioration of durability due to internal stress, generation of noise, crosstalk, and the like.

It is therefore an object of the present invention to provide a quiet droplet discharge apparatus which has a simple structure, enables high-density printing, has excellent durability, can perform high-quality printing without crosstalk, and can perform printing.

[0013]

In order to achieve the above object, a droplet discharge device according to the present invention is defined by a plurality of partitions provided in a direction substantially perpendicular to a plane direction and the partitions. A flow path substrate having a plurality of flow paths, and a piezoelectric element plate which is polarized in the thickness direction and has a common electrode formed on one surface and a plurality of drive electrodes corresponding to the flow path formed on the other surface. And a cover plate fixed to the end face of the partition wall. Of the plurality of drive electrodes, the drive electrode corresponding to the flow path to perform droplet discharge has a polarization direction of a portion corresponding to the flow path of the cover plate. And an electric field in a direction opposite to the polarization direction of a portion corresponding to the flow path is applied to at least one of the drive electrodes corresponding to the flow path adjacent thereto.

The direction of polarization of the cover plate may be alternately reversed for each channel.

Alternatively, the cover plate is uniformly polarized in the same direction, and the drive electrode corresponding to the flow path is electrically connected to at least one of the drive electrodes corresponding to the flow path adjacent to the flow path. May be configured such that voltages in opposite directions are applied to each other.

In the method of driving these droplet discharge devices, the timing of droplet discharge is controlled by making the rising time constant and the falling time constant of the voltage applied to the drive electrode different.

Further, voltages of opposite polarities are alternately applied to the drive electrode group corresponding to the 2n-th (n is a natural number) flow path and the drive electrode group corresponding to the (2n-1) -th flow path. Thus, the even-numbered channel group and the odd-numbered channel group may be time-divisionally driven.

Alternatively, a driving electrode corresponding to the (m × n) -th (m is a natural number of 2 or more) flow path, and (m × n−1)
A voltage of the opposite polarity is always applied to the drive electrode corresponding to the second flow path, and the application of the voltage to the drive electrode is selectively stopped during droplet discharge. Time-division driving.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a view showing an ink jet recording apparatus adopting a first embodiment of a droplet discharging apparatus according to the present invention. This droplet discharge device comprises a plurality of partitions 1a, 1b, 1c, 1d, 1e, 1f, 1g substantially perpendicular to the surface direction.
Are formed, and the ink flow paths 2a, 2b, 2
Channel substrate 3 in which c, 2d, 2e, 2f are defined
And a cover plate 4 fixed to the flow path surface, and FIG.
And a nozzle plate 5 fixed to the end of the flow path. The cover plate 4 includes a common electrode 6 on one surface of the piezoelectric element plate, and drive electrodes 7a, 7b, which are separated on the other surface corresponding to the flow paths 2a to 2f.
7c, 7d, 7e, and 7f are formed, respectively, and are polarized so that the polarization directions are alternately opposite to each other corresponding to each of the ink flow paths 2a to 2f. That is, as shown in FIG. 1, the cover plate 4 includes the ink flow paths 2a, 2c, 2
The portion corresponding to e is polarized upward (in the direction of arrow P ') in the drawing, and the portion corresponding to the ink flow paths 2b, 2d, and 2f is polarized downward (in the direction of arrow P). In this embodiment, the common electrode 6 is grounded, and a positive or negative voltage can be selectively supplied to each of two adjacent drive electrodes. That is, the drive electrode 7a
And 7b, the driving electrodes 7c and 7d, and the driving electrodes 7e and 7f are connected to each other. In order to supply a positive or negative voltage as a set, a pair of power sources 8a and 8b It is connected.

The operation of ejecting ink droplets from only one flow path using the ejection device having the above configuration will be described. Channel 2d
In order to eject more ink droplets, the volume of the flow path 2d must be reduced by a predetermined amount to apply pressure to the ink in the flow path. In the present embodiment, the portion of the cover plate 4 corresponding to the ink flow path 2d is polarized in the direction (arrow P direction) from the drive electrode 7d toward the common electrode 6 perpendicular to the plate surface, so that the power source 8a is used. When a positive voltage is applied to the drive electrode 2d, an electric field E in the same direction as the polarization direction P is applied.
The portion corresponding to d shrinks in the in-plane direction of the plate.

On the other hand, a positive electric field E is similarly applied to the drive electrode 7c connected to the drive electrode 7d. However, since the cover plate 4 is polarized in this portion in the direction from the common electrode 6 to the drive electrode 7c (the direction of the arrow P '), the portion of the cover plate 4 corresponding to the drive electrode 7c is in the in-plane direction of the plate. Elongate.

As described above, the portion of the cover plate 4 corresponding to the ink flow path 2c extends, and the portion corresponding to the ink flow path 2d contracts. Deforms in the direction of the flow path 2d. Therefore, the volume of the ink flow path 2d is reduced, and the ink inside is discharged. Since the amount of elongation of the portion corresponding to the ink flow path 2c of the cover plate 4 is substantially the same as the amount of shrinkage of the portion corresponding to the ink flow path 2d, these distortions cancel each other out, and other ink flow No deformation or stress is applied to the path portion or the entire recording head.

When ink is to be ejected from the ink flow path 2c, the driving voltages 7c and 7d are connected to the power supply 8b, and a negative electric field E 'is applied. Then, contrary to the above example, the cover plate 4 contracts at the portion corresponding to the ink flow path 2c and expands at the portion corresponding to the ink flow path 2d.
Is deformed in the direction of the ink flow path 2c. Therefore, the volume of the ink flow path 2c decreases, and the ink inside is discharged.

FIG. 2 shows the operation when simultaneously driving a plurality of flow paths. By alternately applying a positive electric field and a negative electric field to each drive electrode, an even-numbered channel group (2n-th channel group) and an odd-numbered channel group (2n-1st-channel group) are alternately driven.
That is, when driving the even-numbered flow path group, a positive voltage is applied to each drive electrode group to reduce the volume of the even-numbered flow path and increase the capacity of the odd-numbered flow path, so that ink droplets from the even-numbered flow path are increased. Is discharged. This state is shown in FIG. Subsequently, the odd-numbered flow path group is driven, a negative voltage is applied to each drive electrode group, and the volume of the odd-numbered flow path is reduced to increase the capacity of the even-numbered flow path, thereby ejecting ink droplets from the odd-numbered flow path. I do.
In addition, in FIG. 2, ink is shown to be ejected from all the even channels. Subsequently, desired printing is performed by applying a negative voltage to the drive electrode of the flow path to be printed among the odd-numbered flow paths and the drive electrode adjacent thereto.

FIG. 3 shows a drive voltage waveform in the above example. That is, when discharging from an even-numbered flow path (2n flow path), one set of drive electrodes connected to each other
A positive voltage is applied. Then, when discharging from the odd-numbered flow path (2n-1 flow path), a negative voltage is applied to the drive electrode set. At the time of the ink discharge, when the voltage shifts from 0 [V] to the positive drive voltage + v [V] or the negative drive voltage -v [V], the rise time is extremely short, and the ink discharge ends and the voltage becomes 0 [V]. When returning, the fall time is set to be long. Therefore, the deformation of the cover plate 4 and the partition wall is performed quickly, and thereafter, the partition wall returns slowly while damping the vibration. The ink is actually ejected only at the moment when the voltage is applied, and the ink is not ejected during recovery or the like.

FIG. 4 shows a second example of the driving method of the droplet discharge device having this configuration. That is, when ink is ejected from the even-numbered flow path (2n flow path), a negative voltage -v [V] is supplied to the drive electrode with a slow time constant, contrary to the above-described example. At this point, the partition walls gradually move, the volume of the flow path (even number flow path) where ink should be ejected increases, and the volume of the adjacent flow path (odd number flow path) decreases,
Since the deformation of the cover plate and the partition is performed at a slow speed, no ink is ejected. Then, the voltage is rapidly returned to 0 [V]. As a result, the partition wall rapidly returns from the deformed state, and the volume of the even-numbered flow path quickly returns to the initial state.
Therefore, the ink inside is pressurized, and the ink is ejected from the even-numbered channels. When ink is ejected from an odd numbered flow path (2n-1 flow path), the positive voltage + v
After [V] is supplied to the drive electrode, the voltage is rapidly returned to 0 [V]. As described above, when the voltage is suddenly returned to the initial state from the voltage applied state, the internal ink is pressurized, and the ink is ejected from the odd-numbered flow paths. This is a so-called pulling method in which the ink is ejected by a pressure at which the ink flow path is quickly returned to the initial state after the volume of the ink flow path is once increased. In this driving method, extremely efficient driving can be performed by deforming the partition in accordance with the pressure vibration of the ink generated in the flow path when the partition is slowly deformed first.

According to the third example of the driving waveform shown in FIG.
As in the second example, when the ink is ejected from the even-numbered flow path, the volume of the even-numbered flow path is first increased slowly, and then the volume is reduced at once without returning to the initial state. . In other words, after slowly applying a negative voltage,
I changed it to positive voltage at once. When the ink is ejected from the odd-numbered flow path, a positive voltage is slowly applied to the drive electrode, and then the voltage is rapidly changed to a negative voltage. Therefore, the power supply voltage to be used is +0.5 v [V], which is half of the above-described example, and -0.5.
v [V], and the cost of the driving circuit can be reduced.

FIG. 6 shows a fourth example of the driving waveform. This is to selectively eject from each channel by adjusting the rise time and fall time of the voltage waveform. For example, after the ink is ejected from the even-numbered flow paths, the flow path shape is not returned to the initial state, but the vibration is attenuated as it is, and the state is set to the steady state. In this state, the voltage is rapidly set to 0 [V] to return the flow path to the initial state, thereby discharging ink from the odd-numbered flow path. According to this, the state in which a positive voltage is applied (the state in which the volume of the even-numbered flow path is increased and the volume of the odd-numbered flow path is reduced) and the voltage 0
The state of [V] (the initial state of all the flow paths) and the state where a negative voltage is applied (the state of the capacity of the even-numbered flow path decreasing and the capacity of the odd-numbering flow path expanding) can be held in three states. Things,
When ink is ejected from a certain flow path, the state is maintained as it is. When ink is ejected from the adjacent flow path, the drive is performed so that the flow path volume is reduced from that point.

That is, when the even flow path group and the odd flow path group are alternately driven, for example, as shown in FIG. 6, first, a positive voltage is applied to eject ink droplets from one of the even flow paths. Then, the volume of the adjacent odd-numbered flow path increases. afterwards,
The ink is replenished by holding it as it is. Then, the voltage is returned to 0 at the early fall, and both the even-numbered flow path and the odd-numbered flow path are returned to the initial state. At this time, the capacity of the even-numbered flow path increases, and at the same time, the capacity of the odd-numbered flow path sharply decreases. If the volume of the flow path is reduced), the voltage is returned to 0 [V] from there, so that the next flow path (even flow path)
Is performed. Subsequently, a negative voltage is applied when ink is ejected from the odd-numbered flow paths.

The cover plate 4 used in the above embodiment
FIG. 7 shows an example of a method for creating the above. When a piezoelectric ceramic such as PZT or PLZT is used as a material of the piezoelectric element plate forming the cover plate 4, when a large electric field of a certain value or more called a coercive electric field is applied to these materials, the polarization direction changes to the direction of the electric field. It is known. Therefore, after forming the common electrode 6 and the drive electrodes 7a to 7f separated from each other corresponding to the flow path shape on both surfaces of the piezoelectric element plate,
The common electrode 6 is grounded, and the drive electrodes 7b, 7d, 7f corresponding to the even-numbered flow path (2n-th flow path) and the odd-numbered flow path (2n-1
Drive electrodes 7a, 7c, 7e corresponding to the
By applying a voltage (+ HV, -HV) sufficient to polarize the piezoelectric element plate with polarities opposite to each other from the power supplies 13a and 13b, the polarized cover plate 4 can be obtained.

When the volume of the flow path is increased as described above, an electric field opposite to the direction of polarization may be applied to the cover plate 4, so that the direction of polarization changes during the recording operation. The electric field generated by the driving voltage is set to be equal to or smaller than the coercive electric field so as to eliminate the above.

In this embodiment, the polarization direction of the portion of the cover plate 4 corresponding to the even-numbered flow path (2n flow path) is defined as the direction P from the drive electrode 7 side to the common electrode 6 side, and the odd-numbered flow path (2n flow path) is used. Although the case where the polarization direction of the portion corresponding to (−1 flow path) is set to the opposite direction P ′ is shown, even when the polarization directions of the even flow path and the odd flow path are reversed, the applied electric fields are opposite to each other. It goes without saying that the drive can be performed in exactly the same manner by setting the drive waveform so that

Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. The basic configuration of the ink jet recording apparatus of this embodiment is similar to that of the first embodiment described above, except that the cover plate 15 is fixed on the partition wall end surface of the flow path substrate 3 having a plurality of partitions 1a to 1g perpendicular to the surface direction. , Ink channel 2
a to 2f are sectioned. On one surface of the cover plate 15, a grounded common electrode 16 is provided, and on the other surface, independent drive electrodes 17a, 17b, 17c,.
17d, 17e and 17f are formed. In this embodiment, the drive electrodes 17a to 17f are connected to the common electrode 1
6 (polarization direction P). Two power supplies 1 with the same voltage and opposite polarities for driving the head
4a and 14b.

In the recording apparatus having the above-mentioned configuration, in the initial state, all the driving electrodes 17a to 17f are in the ground state. First, an operation of ejecting ink droplets from only one flow path 2d will be described with reference to FIG.

In order to eject ink droplets from the flow path 2d, it is necessary to reduce the volume of the flow path 2d by a predetermined amount and apply pressure to the ink in the flow path. In this embodiment, an electric field E in the same direction as the polarization direction P is applied by applying a positive voltage from the power supply 14a to the drive electrode 17d, and the portion of the cover plate 15 corresponding to the drive electrode 17d contracts in the plate plane direction.

On the other hand, to the drive electrode 17c adjacent to the drive electrode 17d, a voltage having the same magnitude and opposite polarity as the voltage applied to the drive electrode 17d is applied from the power supply 14b. At this time, since the electric field E ′ in the direction opposite to the polarization direction P is applied, the portion of the cover plate 15 corresponding to the drive electrode 17c extends in the in-plane direction of the plate.

As described above, in the cover plate 15, the portion corresponding to the ink flow path 2c extends, and the portion corresponding to the ink flow path 2d contracts. Deforms to the 2d side. Thereby,
The volume of the ink flow path 2d is reduced, pressure is applied to the ink inside, and ink droplets are ejected. Since the amount of elongation of the portion corresponding to the ink flow path 2c of the cover plate 15 is substantially the same as the amount of shrinkage of the portion corresponding to the ink flow path 2d, these distortions only deform the partition wall 1d. No deformation or stress is applied to the ink flow path or the entire recording head.

When ink is ejected from the ink flow path 2c, the power supply 14a is connected to the drive electrode 17c (not shown).
By applying a positive voltage to the driving electrode 17d and a negative voltage from the power supply 14b, the partition 1d is deformed toward the ink flow path 2c, contrary to the above example.

FIG. 9 shows the operation when simultaneously driving a plurality of flow paths. In this case, the even drive electrode groups 17b, 17d, 1
7f and odd-numbered drive electrode groups 17a, 17c, and 17e, and drive waveforms having opposite polarities are alternately applied to these, as in the case of the above-described one-flow-path injection. Group (2n-th channel group) 2b, 2
d, 2f and an odd-numbered channel group (2n-1st channel group) 2a,
2c and 2e are alternately driven. That is, when driving the even-numbered flow channel group, a positive voltage is applied to the even-numbered driving electrode group, and a negative voltage is applied to the odd-numbered driving electrode group, and the volume of the odd-numbered channel is increased to increase the volume of the even-numbered channel. , The ink droplets are ejected from the even-numbered flow paths. This state is shown in FIG.
Is shown in

Subsequently, in order to drive the odd-numbered flow path group,
A negative voltage is applied to the even-numbered drive electrode groups 17b, 17d, and 17f.
By applying a positive voltage to each of the odd-numbered drive electrode groups 17a, 17c, and 17e to increase the volume of the even-numbered channels 2b, 2d, and 2f, and to reduce the volume of the odd-numbered channels 2a, 2c, and 2e, Discharge ink droplets from the road.

Although FIG. 9 shows that ink is ejected from all the even channels, the positive voltage is actually applied only to the drive electrode of the channel to be printed and the adjacent drive electrode of the even channels. Then, desired printing is performed by applying a negative voltage to the drive electrode of the flow path to be printed in the odd-numbered flow path and the drive electrode adjacent thereto.

FIG. 10 shows the drive voltage waveform in the above example. This is similar to the drive waveform shown in FIG. 3. First, when driving the even-numbered flow path, the even-numbered drive electrode is set to 0.
[V] is changed to a predetermined positive drive voltage + v [V], and the odd drive electrodes are changed from 0 [V] to a negative drive voltage -v [V] in a short rise time. The partition wall between the flow paths is suddenly deformed toward the even flow path side, and a large pressure is applied to the ink in the even flow path to eject ink droplets. After maintaining the voltage value for a predetermined time,
The voltage value of the even and odd electrodes is 0 with a long fall time.
It is returned to [V]. At this time, since the partition wall slowly returns to the center between the two flow paths, no large pressure is generated in the odd flow paths, and no ink droplets leak from the odd flow paths in this process. In the case of ejecting ink droplets from the odd-numbered flow paths, the driving may be performed with the polarity completely opposite to that of the even-numbered flow paths.

Another driving example to which the present invention is applied is shown in FIG. This is similar to the drive waveform shown in FIG. 4. When the ink droplets are ejected from the even-numbered channels, the partition between the even-numbered channels and the odd-numbered channels is slowly deformed to the odd-numbered channel side. And then increase the voltage to 0
This is a pulling method in which a strong pressure is generated in the even-numbered flow path and ink droplets are ejected from the even-numbered flow path by rapidly returning the partition wall to [V] with a short fall time.

FIG. 12 shows a driving waveform of another driving example. As in the example of FIG. 5, the volume of the even-numbered flow path is first slowly increased, and then the voltage is immediately changed to the reverse voltage. For this reason, the flow path volume once increased passes through the initial state and rapidly decreases. The power supply voltage used for this is shown in FIG.
The driving method can be reduced to half of the driving methods shown in FIGS.

In this embodiment, the case where the cover plate 15 is polarized from the front electrode side to the back electrode direction (in the case of the polarization direction P) is shown, but the cover plate 15 is polarized from the back electrode side to the front electrode direction. In this case, it is needless to say that the driving can be performed in exactly the same manner by changing the driving waveform so that the applied electric fields are in opposite directions.

Similarly to the above-described embodiment, when piezoelectric ceramic such as PZT is used as the cover plate material, the electric field applied during driving is set to be equal to or less than the coercive electric field so that the polarization direction does not change.

As described above, in the printing apparatus according to the present invention, in any of the embodiments, an electric field in the same direction as the polarization direction is applied to the drive electrode corresponding to the flow path from which the liquid droplets are to be ejected, and the adjacent flow is applied. By applying an electric field in the direction opposite to the polarization direction to the drive electrode corresponding to the path, droplet ejection can be performed efficiently.

In these embodiments, there is a concern that the maximum emission frequency of the entire printing apparatus is reduced when the even and odd channels are time-divisionally driven. However, for example, when injecting an even-numbered flow path after an odd-numbered flow path, there is no need to wait for the ink pressure oscillation in the odd-numbered flow path to attenuate or for ink refilling to be completely completed. The frequency is only slightly lower than the maximum injection frequency of one flow path.

FIGS. 2 and 9 show an example in which the even-numbered flow path and the odd-numbered flow path are time-divisionally driven. However, the driving method of the present invention is not limited to two-division time-division driving. With the above natural numbers, every m channels are selected, and the driving voltage corresponding to the (m × n) -th channel and the driving voltage corresponding to the (m × n−1) -th channel are opposite in polarity. It is also possible to apply a voltage.

In the recording apparatus of the present invention, the volume of the adjacent flow channel increases by substantially the same amount as the volume reduction amount of the flow channel selected for injection. Accordingly, the ink flows from the common ink chamber into the adjacent flow path by the same amount as the amount of the ink flowing backward to the common ink chamber side from the flow path selected for ejection. In addition, pressure waves having substantially reverse waveforms are transmitted from the adjacent flow passages to the common ink chamber and cancel each other, so that the state of the common ink chamber hardly changes. Therefore, crosstalk does not occur even if the number of simultaneously driven flow paths increases.

In the printing apparatus of the present invention, since the flow path partition is deformed to apply pressure to the liquid in the flow path and eject droplets from the nozzles, there is no restriction on the physical properties of the liquid, , Ink can also be used. Therefore, the present invention is not limited to a printing device as a computer terminal, but can be applied to a wide range of uses such as discharging various liquids, for example, an industrial printing device, a small amount discharge of a reagent, and facsimile.

[0052]

As described above, according to the present invention, it is possible to provide a quiet droplet discharge apparatus which has high energy efficiency, excellent durability, no crosstalk and high printing quality.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of a droplet discharge device according to the present invention.

FIG. 2 is an explanatory diagram showing the operation of the first embodiment.

FIG. 3 is a voltage waveform chart showing a first example of a method of driving the droplet discharge device shown in FIG.

FIG. 4 is a voltage waveform diagram showing a second example of the method of driving the droplet discharge device shown in FIG.

FIG. 5 is a voltage waveform diagram showing a third example of the method of driving the droplet discharge device shown in FIG.

FIG. 6 is a voltage waveform diagram showing a fourth example of the method of driving the droplet discharge device shown in FIG.

FIG. 7 is an explanatory view showing a method of manufacturing the cover plate of the first embodiment.

FIG. 8 is a sectional view of a second embodiment of the droplet discharge device according to the present invention.

FIG. 9 is an explanatory view showing the operation of the second embodiment.

FIG. 10 is a voltage waveform diagram showing a first example of a method of driving the droplet discharge device shown in FIG.

FIG. 11 is a voltage waveform diagram showing a second example of the method of driving the droplet discharge device shown in FIG.

FIG. 12 is a voltage waveform diagram showing a third example of the method of driving the droplet discharge device shown in FIG.

FIG. 13 is a perspective view of a conventional example.

FIG. 14 is a sectional view of a conventional example.

FIG. 15 is a sectional view showing the operation of the conventional example.

FIG. 16 is a sectional view showing another operation state of the conventional example.

[Explanation of symbols]

1a, 1b, 1c, 1d, 1e, 1f, 1g Partition walls 2a, 2b, 2c, 2d, 2e, 2f Ink flow path 3 Flow path substrate 4, 15 Cover plate 6, 16 Common electrode 7a, 7b, 7c, 7d, 7e, 7f Drive electrodes 17a, 17b, 17c, 17d, 17e, 17f
Drive electrode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/045 B41J 2/055

Claims (6)

(57) [Claims] 1. A flow path substrate having a plurality of partition walls provided substantially perpendicular to a surface direction and a plurality of flow paths defined by the partition walls, wherein the flow path substrate is polarized in a thickness direction and A cover plate fixed to an end surface of the partition wall, comprising a piezoelectric element plate having a common electrode formed on one surface and a plurality of drive electrodes corresponding to the flow paths formed on the other surface; Of the drive electrodes, a drive electrode corresponding to a flow path for performing droplet discharge is applied with an electric field in the same direction as the polarization direction of a portion of the cover plate corresponding to the flow path,
A droplet discharge device, wherein an electric field in a direction opposite to a polarization direction of a portion corresponding to a flow path is applied to at least one of drive electrodes corresponding to a flow path adjacent thereto. 2. The polarization direction of the cover plate,
2. The droplet discharge device according to claim 1, wherein the flow passages are alternately reversed for each of the flow paths. 3. The cover plate is uniformly polarized in the same direction, and the drive electrode corresponding to the flow path is at least one of the drive electrodes corresponding to a flow path adjacent to the flow path. 2. The droplet discharge device according to claim 1, wherein voltages that are opposite to each other are applied to the two drive electrodes. 3. 4. The droplet discharge timing is controlled by making a rising time constant and a falling time constant of a voltage applied to the driving electrode different from each other. 3. The method for driving a droplet discharge device according to claim 1. 5. The drive electrode group corresponding to the 2n-th (n is a natural number) flow path and the drive electrode group corresponding to the (2n−1) -th flow path are alternately opposite in polarity. The method according to any one of claims 1 to 3, wherein the even number channel group and the odd number channel group are time-divisionally driven by applying a voltage. 6. An (m × n) -th (m is a natural number of 2 or more)
The drive electrode corresponding to the flow path of (m × n-1)
A voltage of the opposite polarity is always applied to the drive electrode corresponding to the second flow path, and the application of a voltage to the drive electrode is selectively stopped at the time of discharging a droplet. The method according to any one of claims 1 to 3, wherein time-division driving is performed every m units.