JPH0760959A - Liquid drop discharge and its driving method - Google Patents

Abstract

PURPOSE:To realize a silent liquid drop discharger wherein high density printing can be carried out by a simple structure, its durability is excellent without any crosstalk, and high quality printing can be carried out. CONSTITUTION:A cover plate 4 consisting of a piezoelectric element board is fixed to an end surface of a passage substrate 3 having a plurality of passages 2a-2f divided with partition walls 1a-1g. In the cover plate 4 a common electrode 6 is formed to one surface, and a plurality of driving electrodes 7a-7f corresponding to the passages are formed on the other surface, which are alternately and reversedly polarized per passage. By adding an electric field of the same direction as a polarized direction P of a part corresponding to the passage to driving electrodes 7b, 7d, 7f corresponding to the passages 2b, 2d, 2f discharging a liquid drop, a passage volume is reduced. By adding an electric field in the same way, i.e., the electric field in a reverse direction to the polarized direction P of the part to driving electrodes 7a, 7c, 7e corresponding to passages 2a, 2c, 2e adjacent thereto, the passage volume is increased. By balancing increase or decrease of the volume, and influence on the other passages in discharging the liquid drop is removed.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Presently, as an on-demand multi-nozzle ink jet device, a method of converting an electric signal into a mechanical displacement by using a piezoelectric element to apply pressure to ink in a flow path to eject an ink droplet, 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 inkjet recording device using a piezoelectric element has the advantages of high energy efficiency and the ability to use any ink, but is not suitable for high density printing with a large number of nozzles for high quality printing. Further, the bubble jet method has problems such as low energy efficiency, large restrictions on ink, and poor durability.

Therefore, the present inventor firstly provided a large number and low cost of an ink jet printing apparatus having a novel principle and configuration having a large number of nozzles arranged at high density, which is energy efficient and has good durability. And a flow path substrate having a plurality of partition walls provided in a direction substantially perpendicular to the direction and a plurality of flow paths partitioned by the partition walls, and a piezoelectric element plate polarized in the thickness direction and fixed to the partition wall end surface. Patent application Japanese Patent Application No. 4-1
Proposed by 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 surface direction, and the partition walls partition the ink flow paths 2. The cross section of each flow path 2 and flow path partition 1 is substantially rectangular. Each flow path 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 flow path partition wall 1 extend in parallel from the nozzle portion to the common ink chamber portion and have the same pitch as the nozzles 5a. For this reason, it is not necessary to take a fan-shaped flow path arrangement as seen in a 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.

A common electrode 9 is formed on the lower surface of the flow path substrate 3,
A cover plate (piezoelectric element plate) 4 having a drive electrode 10 corresponding to each flow path formed on the upper surface is mounted. This piezoelectric element plate serves as an actuator that deforms 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. Nozzle plate 5 in which nozzles 5a corresponding to each flow path are formed on the front surface of the head
Is installed.

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

The three drive electrodes 10a-1 shown in FIG.
The voltage V is applied only to the drive electrode 2b corresponding to the flow path 2b of 0c in the direction in which the piezoelectric element 4 contracts in the plane (direction in which the electric field E is generated in the same direction as the polarization direction P). Piezoelectric element plate 4
Since only the upper portion of the flow channel 2b contracts, the flow channel partition walls 1b and 1c on both sides of the flow channel 2b are attracted to reduce the volume of the flow channel 2b. Therefore, pressure is applied to the ink in the flow path 2b, and ink droplets are ejected from the nozzle. To explain the non-selected channel 2a, since the piezoelectric element plate above the adjacent channel 2b contracts, the piezoelectric element plate above the channel 2a and the channel partition walls 1a and 1b are also attracted toward the channel 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, and 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 using the structurally integrated piezoelectric element plate 4 and eject ink droplets.

[0008]

FIG. 16 is a diagram showing an example in which all the flow paths are simultaneously driven by the above-mentioned conventional driving method. Figure 15
When driving a very small number of flow paths as described above, there is no problem, but when all the flow paths or a large number of flow paths are driven at the same time, the piezoelectric element cover plate 4 shrinks entirely in the in-plane direction. . For this reason, 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 using a specific example. X
When a print density of [dpi (dots per inch)] is realized in n rows of channels, the adjacent channel pitch DN is DN = 0.0254 × n / X (1) When the thickness of the piezoelectric element plate is T0, the width of the drive electrode is 0.8 times the channel pitch (0.8 × DN), the applied voltage is V, and the lateral piezoelectric constant is d, the piezoelectric element plate per channel The contraction amount ω of is as follows. ω = d × V × 0.8 × DN / T0 (2) Here, when a print density of 300 [dpi] is realized with a single row of flow passages, the flow passage pitch DN is expressed by the equation (1) as DN. = 8.5 × 10 ^-5 [m]. The lateral 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 flow path is given by the formula (2), and ω1 = 2.7 × 10 ⁻⁸ [m], which is a sufficiently small value. The influence on other channels and the entire recording apparatus can be ignored. However, when many flow paths are simultaneously driven by the multi-nozzle head, for example, when each flow path of a recording apparatus having 100 nozzles is simultaneously driven, the shrinkage amount ω
2 has a large value of ω2 = 2.7 × 10 ⁻⁶ [m]. Therefore, there are problems that the entire recording head is largely curved and noise is generated, stress is generated in the base portion of the flow path substrate 3 and the recording head supporting portion, and the durability of the recording apparatus is deteriorated.

Further, in the conventional system, when the flow path volume is reduced and pressure is applied to the ink to eject the ink droplet, backflow and pressure propagation of the ink to the common ink chamber 11 side opposite to the nozzle occur. However, the state of the inside of the common ink chamber 11 has changed depending on the number of channels that are simultaneously driven. Therefore, when most of the flow paths are driven at the same time, a large pressure is also generated in the ink in the common ink chamber, and ink droplets are ejected from the non-selected flow paths, and are ejected depending on the number of flow paths that are driven at the same time. The characteristics such as the velocity volume of the ink drop change,
A phenomenon called so-called crosstalk was observed.

As described above, the droplet discharge device previously proposed by the present inventor has a simple structure in which the piezoelectric element cover plate is used as an actuator, and has a large number of nozzles and channels arranged in high density. However, when multiple channels are driven simultaneously, there are drawbacks such as deterioration of durability due to internal stress, generation of noise, and crosstalk.

Therefore, an object of the present invention is to realize a quiet droplet discharge device which has a simple structure and is capable of high-density printing, has excellent durability, is free from crosstalk, and is capable of high-quality printing.

[0013]

In order to achieve the above object, the droplet discharge device of the present invention is partitioned by a plurality of partition walls provided in a direction substantially perpendicular to the plane direction and the partition walls. A flow path substrate having a plurality of flow paths, and a piezoelectric element plate polarized in the thickness direction and having a common electrode formed on one surface and a plurality of drive electrodes corresponding to the flow path formed on the other surface. Of the plurality of drive electrodes, the drive electrode corresponding to the flow path through which droplets are to be discharged includes the polarization direction of the portion of the cover plate corresponding to the flow path. The electric field in the same direction is applied, and the electric field in the direction opposite to the polarization direction of the portion corresponding to the flow path is applied to at least one of the drive electrodes corresponding to the flow path adjacent thereto.

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

Alternatively, the cover plate is uniformly polarized in the same direction, and the drive electrodes corresponding to the flow paths are electrically connected to at least one of the drive electrodes corresponding to the flow paths adjacent to the flow paths. May have a configuration in which voltages in opposite directions are applied.

The driving method of these droplet discharge devices controls the timing of droplet discharge 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. By doing so, the even channel group and the odd channel group may be driven in a time division manner.

Alternatively, a drive electrode corresponding to a (m × n) th (m is a natural number of 2 or more) flow path, and (m × n−1)
A voltage having a reverse polarity is always applied to the drive electrode corresponding to the second flow path, and the voltage application to the drive electrode is selectively stopped at the time of droplet discharge. You may drive by time division.

[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 diagram showing an ink jet recording apparatus adopting a first embodiment of a droplet discharge device of the present invention. This droplet discharge device includes a plurality of partition walls 1a, 1b, 1c, 1d, 1e, 1f, 1g substantially perpendicular to the surface direction.
Are formed, and the partition walls form the ink flow paths 2a, 2b, 2
A flow path substrate 3 in which c, 2d, 2e, and 2f are formed by partitioning
And the cover plate 4 fixed to this flow path surface, and FIG.
The nozzle plate 5 is the same as that shown in FIG. In the cover plate 4, the common electrode 6 is formed on one surface of the piezoelectric element plate, and the drive electrodes 7a, 7b, which are separated on the other surface in correspondence with the flow paths 2a to 2f.
7c, 7d, 7e and 7f are formed respectively, and are polarized such that the polarization directions are alternately opposite to each other corresponding to each ink flow path 2a to 2f. That is, as shown in FIG. 1, the cover plate 4 has the ink flow paths 2a, 2c, 2
The portion corresponding to e is polarized upward in the drawing (direction of arrow P '), and the portion corresponding to the ink flow paths 2b, 2d, 2f is polarized downward (direction of arrow P). In this embodiment, the common electrode 6 is grounded and a positive or negative voltage can be selectively supplied to every two adjacent drive electrodes. That is, the drive electrode 7a
And 7b, the drive electrodes 7c and 7d, and the drive electrodes 7e and 7f are connected to each other, and in order to supply a positive or negative voltage with these as a set, a pair of power supplies 8a and 8b are set in opposite directions. It is connected.

The operation of ejecting ink droplets from only one flow path using the ejection device having the above structure will be described. Channel 2d
In order to eject more ink droplets, it is necessary to reduce the volume of the channel 2d by a predetermined amount and apply pressure to the ink in the channel. In the present embodiment, since 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 to the common electrode 6 perpendicular to the plate surface, the power source 8a is used. By applying a positive voltage to the drive electrode 2d by applying the electric field E in the same direction as the polarization direction P, the drive electrode 7 of the cover plate 4 is
The part corresponding to d contracts in the in-plane direction of the plate.

On the other hand, the 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 (direction of arrow P '), the portion of the cover plate 4 corresponding to the drive electrode 7c is in the plate in-plane direction. Extend.

In this way, the cover plate 4 expands at the portion corresponding to the ink flow path 2c and contracts at the portion corresponding to the ink flow path 2d, so that the partition wall 1d located between the two flow paths is caused to contract. It 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 ejected. Since the amount of expansion of the portion of the cover plate 4 corresponding to the ink flow passage 2c is approximately the same as the amount of contraction of the portion corresponding to the ink flow passage 2d, these distortions cancel each other out, and the other ink flow No deformation or stress is applied to the road portion or the entire recording head.

When ink is ejected from the ink flow path 2c, the driving voltages 7c and 7d are connected to the power source 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, so that the partition wall 1d is formed.
Deforms in the direction of the ink flow path 2c. Therefore, the volume of the ink flow path 2c decreases, and the ink inside is ejected.

The operation when simultaneously driving a plurality of flow paths is shown in FIG. By alternately applying a positive electric field and a negative electric field to each drive electrode, the even channel groups (2nth channel group) and the odd channel groups (2n-1th channel group) are driven alternately.
That is, when driving the even-numbered channel group, a positive voltage is applied to each drive electrode group to decrease the volume of the even-numbered channel and increase the volume of the odd-numbered channel, so that the ink droplets from the even-numbered channel are increased. Is discharged. This state is shown in FIG. Subsequently, the odd-numbered channel group is driven, and a negative voltage is applied to each drive electrode group to reduce the volume of the odd-numbered channel and increase the volume of the even-numbered channel, thereby ejecting ink droplets from the odd-numbered channel. To do.
Note that in FIG. 2, ink is shown to be ejected from all even-numbered channels, but in reality, a positive voltage is applied only to the drive electrode of the even-numbered channel to be printed and the drive electrode next to it. Subsequently, a desired voltage is printed 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.

The drive voltage waveform in the above example is shown in FIG. That is, when discharging from an even numbered channel (2n channel), for one set of drive electrodes connected to each other,
Positive voltage is applied. Then, when discharging from the odd-numbered flow paths (2n-1 flow paths), a negative voltage is applied to the drive electrode set. In this ink ejection, when the voltage is changed 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 ejection is completed to reach the voltage 0 [V]. The fall time is set to be long when returning. Therefore, the cover plate 4 and the partition wall are rapidly deformed, and then the partition wall is slowly restored 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 the recovery.

FIG. 4 shows a second example of the driving method of the liquid droplet ejecting apparatus of this structure. That is, when ink is ejected from the even-numbered flow paths (2n flow paths), the negative voltage −v [V] is supplied to the drive electrodes with a slow time constant contrary to the above example. At this point, the partition gradually moves to increase the volume of the flow path (even flow path) through which the ink should be ejected, and the volume of the adjacent flow path (odd flow path) decreases.
Deformation of the cover plate and the partition wall is performed at a slow speed, so that ink is not ejected. Then, the voltage is suddenly returned to 0 [V]. As a result, the partition walls are quickly returned from the deformed state, and the volume of the even-numbered channels is rapidly returned 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 odd-numbered channels (2n-1 channels), positive voltage + v with a slow time constant
After supplying [V] to the drive electrode, the voltage is rapidly returned to 0 [V]. In this way, when the voltage application state is rapidly returned to the initial state, the internal ink is pressurized and the ink is ejected from the odd-numbered flow paths. This is a so-called hitting method in which the volume of the ink flow path is once increased and then the ink is ejected by the pressure when rapidly returning to the initial state. In this driving method, extremely efficient driving can be performed by deforming the partition wall in accordance with the pressure vibration of the ink generated in the flow channel when the partition wall is slowly deformed first.

According to the third example of the drive waveform shown in FIG. 5,
Similar to the second example, when ink is ejected from even-numbered channels, the volume of even-numbered channels is first slowly increased, and then the volume is reduced at once without returning to the initial state. . That is, after applying a negative voltage slowly,
The positive voltage is changed all at once. When ink is ejected from odd-numbered channels, on the contrary, a positive voltage is slowly applied to the drive electrodes, and then a negative voltage is rapidly changed. Therefore, the power supply voltage to be used is + 0.5v [V], -0.5 which is half of the above-mentioned example.
Since it can be set to v [V], the cost of the drive circuit can be reduced.

Further, FIG. 6 shows a fourth example of the drive waveform. This is to selectively eject from each flow path by adjusting the rising time and the falling time of the voltage waveform. For example, after the ink is ejected from the even-numbered channels, the flow channel shape is not returned to the initial state, but the vibration is attenuated to the steady state as it is. From that state, the voltage is suddenly set to 0 [V] to return the flow path to the initial state, and ink is ejected from the odd-numbered flow path. According to this, when the positive voltage is applied (the volume of the even-numbered channel is expanded and the volume of the odd-numbered channel is decreased), the voltage of 0 is applied.
It can be held in three states: a state of [V] (initial state of all flow paths) and a state in which negative voltage is applied (volume of even flow paths is reduced and volume of odd flow paths is expanded). Is something
When ink is ejected from a certain flow path, it is held as it is. When ink is ejected from the adjacent flow passage, the flow passage volume is reduced from that point onward.

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

The cover plate 4 used in the above embodiment
FIG. 7 shows an example of a method of creating the. When piezoelectric ceramics such as PZT and PLZT are used as the material of the piezoelectric element plate constituting the cover plate 4, when a large electric field above a certain value called a coercive electric field is applied to these materials, the polarization direction changes to the electric field direction. It is known. Therefore, after forming the common electrode 6 and the drive electrodes 7a to 7f separated from each other in accordance with the shape of the flow path 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 paths (2n-th flow path) and the odd-numbered flow paths (2n-1).
The drive electrodes 7a, 7c, 7e corresponding to the (th channel),
The polarized cover plate 4 can be obtained by applying voltages (+ HV, -HV) of opposite polarities from the power supplies 13a and 13b, which are sufficient to polarize the piezoelectric element plates.

Incidentally, when the flow path volume is expanded as described above, an electric field in the opposite direction to the polarization direction may be applied to the cover plate 4, so that the polarization direction changes during the recording operation. The electric field generated by the drive voltage is set to have a magnitude equal to or less than the coercive electric field so that there is no electric field.

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

Next, a second embodiment of the present invention will be described with reference to FIGS.
Will be described with reference to. The basic configuration of the ink jet recording apparatus of this embodiment is similar to that of the first embodiment described above, in which the cover plate 15 is fixed on the partition wall end face of the flow path substrate 3 having the plurality of partition walls 1a to 1g perpendicular to the surface direction. , Ink flow path 2
a to 2f are sectioned and formed. A grounded common electrode 16 is provided on one surface of the cover plate 15, and independent drive electrodes 17a, 17b, 17c, and
17d, 17e, and 17f are formed. Further, in this embodiment, the drive electrodes 17a to 17f are changed to the common electrode 1
It is polarized in the direction toward 6 (polarization direction P). Two power supplies with the same voltage but opposite polarities for driving the head 1
It has 4a and 14b.

In the recording apparatus having the above structure, all the driving electrodes 17a to 17f are grounded in the initial state. First, the 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 channel 2d, it is necessary to reduce the volume of the channel 2d by a predetermined amount and apply pressure to the ink in the channel. In this embodiment, by applying a positive voltage from the power source 14a to the drive electrode 17d, an electric field E in the same direction as the polarization direction P is applied, and the portion of the cover plate 15 corresponding to the drive electrode 17d contracts in the in-plane direction of the plate.

On the other hand, to the drive electrode 17c adjacent to the drive electrode 17d, a voltage having the same magnitude as the voltage applied to the drive electrode 17d but a reverse polarity is applied from the power source 14b. At this time, since an 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 plate in-plane direction.

As described above, in the cover plate 15, the portion corresponding to the ink flow passage 2c expands and the portion corresponding to the ink flow passage 2d contracts, so that the partition wall 1d located between both ink flow passages has an ink flow passage. It transforms to the 2d side. Thereby,
The volume of the ink flow path 2d decreases, pressure is applied to the ink inside, and ink droplets are ejected. Since the amount of expansion of the portion of the cover plate 15 corresponding to the ink flow passage 2c is approximately the same as the amount of contraction of the portion corresponding to the ink flow passage 2d, these distortions only deform the partition wall 1d. There is no deformation or stress on the ink flow path and the entire recording head.

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

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

Subsequently, in order to drive the odd-numbered channel group,
A negative voltage is applied to the even-numbered drive electrode groups 17b, 17d, 17f,
A positive voltage is applied to each of the odd-numbered drive electrode groups 17a, 17c, and 17e to increase the volume of the even-numbered flow paths 2b, 2d, and 2f to reduce the volume of the odd-numbered flow paths 2a, 2c, and 2e. Ink drops are ejected from the path.

Although FIG. 9 shows that ink is ejected from all even-numbered channels, in reality, only positive voltage is applied to the drive electrode of the even-numbered channel to be printed and the drive electrode adjacent thereto. Then, a desired voltage is printed 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.

The drive voltage waveforms in the above example are shown in FIG. This is similar to the drive waveform shown in FIG. 3, and 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 odd drive electrodes are changed from 0 [V] to a negative drive voltage -v [V] in a short rise time. The partition walls between the flow paths are rapidly deformed toward the even-numbered flow paths, and a large pressure is applied to the ink in the even-numbered flow paths to eject ink droplets. After maintaining the voltage value for a predetermined time,
The voltage values of the even and odd electrodes are 0 with a long fall time.
Returned to [V]. At this time, since the partition walls slowly return to the center between both flow paths, a large pressure is not generated in the odd flow paths, and ink drops do not leak from the odd flow paths in this process. When ejecting the ink droplets from the odd-numbered flow paths, the polarity may be reversed from that when the even-numbered flow paths are ejected.

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, and when the ink droplets are ejected from the even-numbered channels, the partition between the even-numbered channels and the odd-numbered channels is gradually deformed to the odd-numbered channel side and the even-numbered channels are changed. Increase the volume of the
This is a pulling-out method in which a strong pressure is generated in the even-numbered channels to eject ink drops from the even-numbered channels by rapidly returning the partition walls to [V] with a short fall time.

The drive waveforms of another drive example are shown in FIG. As in the example of FIG. 5, the volume of the even-numbered passage is first slowly increased, and then the reverse voltage is changed all at once. For this reason, the once increased flow path volume passes through the initial state and sharply decreases. The power supply voltage used for this is shown in Fig. 1.
The driving method shown in FIGS. 0 and 11 can be halved, and the cost of the driving circuit can be reduced.

In this embodiment, the case where the cover plate 15 is polarized from the front surface electrode side to the back surface electrode direction (in the case of the polarization direction P) is shown, but it is polarized from the back surface electrode side to the front surface electrode direction. In this case, it goes without saying that the driving can be performed in exactly the same way by changing the driving waveform so that the applied electric fields are in opposite directions.

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

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

In these embodiments, there is a concern that the maximum ejection frequency of the entire printing apparatus may decrease when the even-numbered flow path and the odd-numbered flow path are driven in a time-division manner. However, for example, when ejecting the even-numbered channels after ejecting the odd-numbered channels, it is not necessary to wait until the ink pressure oscillation in the odd-numbered channels is dampened or the ink refilling is completely completed. The frequency is only slightly lower than the maximum emission frequency of one flow path.

2 and 9 show an example of time-divisional driving of even-numbered channels and odd-numbered channels, the driving method of the present invention is not limited to time-divisional driving of two divisions, and m is 3 With the above natural numbers, every m channels are selected, and the drive voltage corresponding to the (m × n) -th channel and the drive voltage corresponding to the (m × n−1) -th channel have opposite polarities. It is also possible to apply a voltage.

In the recording apparatus of the present invention, the volume of the adjacent flow passage increases by about the same as the volume reduction amount of the flow passage selected for injection. Therefore, the ink flows from the common ink chamber into the adjacent flow channel by substantially the same amount as the amount of the ink that flows back to the common ink chamber side from the flow channel selected for ejection. Further, since pressure waves having substantially reverse waveforms propagate to the common ink chamber from the adjacent flow paths, they cancel each other out, and the state of the common ink chamber hardly changes. Therefore, crosstalk does not occur even if the number of channels driven at the same time increases.

In the printing apparatus of the present invention, the flow path partition is deformed and pressure is applied to the liquid in the flow path to eject droplets from the nozzle. Can also be used with ink. Therefore, the present invention is not limited to a printing device as a computer terminal, and can be applied to a wide range of applications such as ejecting any liquid, for example, an industrial printing device, a small amount of reagent ejection, and a facsimile.

[0052]

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

[Brief description of drawings]

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

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

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

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

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

6 is a voltage waveform diagram showing a fourth example of the driving method of 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 cross-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.

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

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

12 is a voltage waveform diagram showing a third example of the driving method of 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 cross-sectional view showing another operating state of the conventional example.

[Explanation of symbols]

1a, 1b, 1c, 1d, 1e, 1f, 1g Partition walls 2a, 2b, 2c, 2d, 2e, 2f Ink channel 3 Channel 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

Claims (6)

[Claims] 1. A flow channel substrate having a plurality of partition walls provided in a direction substantially perpendicular to a plane direction and a plurality of flow channels partitioned by the partition walls, and polarized in the thickness direction. A piezoelectric element plate having a common electrode formed on one surface and a plurality of drive electrodes corresponding to the flow path on the other surface, and a cover plate fixed to the partition wall end surface, Among the drive electrodes of, the drive electrode corresponding to the flow path for discharging droplets is applied with an electric field in the same direction as the polarization direction of the 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 the flow path is applied to at least one of the drive electrodes corresponding to the flow path adjacent thereto. 2. The polarization direction of the cover plate is
The droplet discharge device according to claim 1, wherein the flow paths are alternately arranged in opposite directions. 3. The cover plate is uniformly polarized in the same direction, and the drive electrode corresponding to the flow channel is at least one of the drive electrodes corresponding to a flow channel adjacent to the flow channel. The droplet discharge device according to claim 1, wherein the driving electrodes are applied with voltages opposite to each other. 4. The droplet ejection timing is controlled by making the rising time constant and the falling time constant of the voltage applied to the drive electrode different. 7. A method of driving the droplet discharge device according to. 5. A drive electrode group corresponding to the 2n-th (n is a natural number) flow path and a drive electrode group corresponding to the (2n-1) -th flow path are alternately opposite in polarity. The driving method of the droplet discharge device according to claim 1, wherein the even-numbered flow channel group and the odd-numbered flow channel group are time-divisionally driven by applying a voltage. 6. (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 opposite polarity is always applied to the drive electrode corresponding to the th channel, and the voltage application to the drive electrode is selectively stopped at the time of droplet ejection. The driving method of the droplet discharge device according to claim 1, wherein the driving is performed every m units in a time division manner.