JP3379122B2 - Ink jet recording device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for recording by ejecting ink droplets, and more particularly to a method for driving an ink jet head used therein.

[0002]

2. Description of the Related Art An ink jet head in which a side wall of a pressure chamber is formed of a shear mode actuator made of a piezoelectric material is disclosed in JP-A-63-252750 (EP02785).
90).

There, the structure of the head and the principle of ejection are explained, and various features are mentioned. In particular, there is an excellent possibility of increasing the density of the nozzle arrangement.

However, in this type of head, the side wall of the pressure chamber is a piezoelectric substance that deforms in a shear mode, and since the side wall is shared with the adjacent pressure chambers, when a certain pressure chamber is driven, it will be naturally placed in the adjacent pressure chamber. Also causes pressure fluctuations. The higher the ejection pressure of the ink droplet, the larger the pressure fluctuation in the adjacent pressure chambers. This is a basic technical problem that this type of head has in principle.

[0005]

As described above, when a certain pressure chamber is driven to eject an ink droplet, a pressure fluctuation also occurs in the adjacent pressure chamber, and the pressure chamber communicates with the adjacent pressure chamber although it is not driven. If the ink flows out from the nozzles or if the ejection pressure is high, the ink droplets may fly out, and the surface of the paper and the area around the head may become dirty. In addition, the ejected ink drops adhere to the vicinity of the other nozzle openings, causing ejection down.

[0006] Such a problem is particularly remarkable in the central non-driving pressure chamber when the pressure chambers on both sides are driven.

The present invention solves these problems and provides an ink jet recording apparatus which realizes high frequency driving, high speed ink droplet ejection and stable ejection.

[0008]

The ink jet recording apparatus of the present invention is an ink jet recording apparatus provided with an ink jet head and a driving means for the head, the ink jet head having a bottom wall, a ceiling wall and two opposing side walls. A plurality of enclosed pressure chambers are provided, and adjacent pressure chambers are arranged with one common side wall as a sakai, and at least a part of each side wall is subjected to shear deformation in the direction of the electric field by applying an electric field perpendicularly to the wall. The driving means is made of a piezoelectric material, and the driving means has a driving circuit for applying an electric field to the piezoelectric materials on the two side walls facing each other, charging the material to deform the piezoelectric material, then maintaining the state, and then discharging the electric field. The discharge start timing is set by setting the discharge start timing in the vicinity of the time when the meniscus vibration induced by the application reaches the discharge direction most or the subsequent meniscus is retracted in the counter discharge direction. The meniscus vibration cycle as Tm, characterized in that the 0 <Tf <Tm. In the inkjet recording apparatus of the present invention, an electric field is applied to the driving unit to expand and contract the pressure chamber to change the ink pressure in the pressure chamber to eject ink, and the driving unit is charged. After the piezoelectric substance is deformed, it has a drive circuit that keeps the state and then discharges it.The discharge start timing is near the time when the meniscus vibration reaches the discharge direction most or the subsequent meniscus is in the reverse discharge direction. The discharge time Tf is set to 0 <Tf <Tm with the meniscus vibration period being Tm. Further, in the ink jet recording head, the pressure chamber is contracted by the electric discharge.

Further, in order to improve the responsiveness, as the driving means, the discharge start timing is set in the vicinity of the time when the meniscus first advances most among the meniscus vibrations of the adjacent nozzles or during the subsequent meniscus retreat period, The discharge time Tf is 0 <when the meniscus vibration period is Tm.
Set so that Tf <Tm.

[0010]

Embodiments will be described in detail below along with embodiments of the present invention.

FIG. 1 is a perspective view of an ink jet head used in the recording apparatus of the present invention, in which a part thereof is cut away to show the inside thereof. FIG. 2 is an enlarged view of a cross-sectional view taken along a line perpendicular to the pressure chamber.

In FIG. 1, a large number of pressure chambers 1 are arranged in parallel, one end of which communicates with a nozzle 2 of a nozzle plate 4 attached to the end. The pressure chamber 1 is a bottom wall 45 common to all pressure chambers.
And a long channel having a rectangular cross section surrounded by the ceiling wall 35 and the opposing side wall 6.

Ink is supplied from an ink cartridge (not shown) to the other end of the pressure chamber 1 through a supply portion 64 provided on the ceiling wall 35 and a hole provided in the ceiling wall 35. Reference numeral 60 denotes a lead electrode, and a drive voltage signal from a drive circuit (not shown) is applied through the lead electrode 60.

In FIG. 2, the side walls 20, 21, 22, 2 are shown.
Reference numeral 3 denotes an upper side wall and a lower side wall made of a piezoelectric material, and the upper side wall and the lower side wall are polarized in directions opposite to each other as indicated by an arrow 16. Electrodes 29, 30, 31, 32, 33 communicating with the extraction electrode 60 are vapor-deposited on the side wall.

Here, the electrodes 30, 32 are grounded and the electrodes 29, 3 are grounded with respect to the electrodes sandwiching the side walls 20, 21, 22, 23.
When an electric field is applied with 1 and 33 as positive voltages, the upper side wall and the lower side wall are sheared and deformed in a dogleg shape toward the pressure chamber as shown by a broken line. As a result, pressure is applied to the ink in the pressure chambers 24 and 26, and ink droplets are ejected from the nozzles 6 and 8.

Adjacent pressure chambers cannot be driven simultaneously due to the driving principle, so pressure chambers that are not adjacent to each other are divided into two groups and driven alternately. In FIG. 2, a group of pressure chambers 24, 26, 28 and the pressure chamber 2 are shown.
The groups of 5 and 27 are divided and driven alternately.

Since the principle of ejecting ink droplets and the head structure are the same as those of the conventional example, further detailed description will be omitted here.

The drive waveforms are shown in FIG. Waveform a drives the pressure chambers of one group and b drives the pressure chambers of the other group, and represents an alternating drive, and waveform b is located in the middle of waveform a.

An electric field is applied between the electrodes to rapidly charge the piezoelectric element (for a short time Tr) to deform the side wall toward the inside of the pressure chamber, hold it for a while, and then discharge at Tf time to return to the original state. Tk is the time from the start of charging to the start of discharging. T
Is the repetition period. Since this head has to be driven alternately as described above, in order to secure the same drive frequency as compared to other types of heads, the pulse width must be half that for high drive frequency. Pulse width T
It is important to reduce p.

FIG. 4 shows each parameter (Tr, T) of the drive waveform.
k, Tf, Vh) and ink droplet ejection speed (Droplet
2 shows the relationship of Velocity). Ink droplet ejection speed (Wanted Velocity) by simultaneously driving two pressure chambers (for example, by driving the pressure chambers 25 and 27 in FIG. 2) while changing each parameter of the drive waveform.
y), and the ejection speed (UnwantedVel) of the ink droplet from the nozzle communicating with the non-driven central pressure chamber (pressure chamber 26 in FIG. 2) generated by the driving
This is the result of investigating the ocity). In addition, a desired ejected ink droplet will be referred to as Wanted, and an ink droplet that ejects regardless of non-driving will be referred to as Unwanted.

Here, a supplementary explanation will be given on the cause of occurrence of Unwanted. When the two pressure chambers 25 and 27 in FIG. 2 are driven, the side wall undergoes shear deformation as indicated by the broken line. However, when the side wall is restored to the original state by the next discharge, the pressure in the pressure chamber 26 increases, and an ink droplet from the pressure chamber 26 passes through the nozzle.
That is, Unwanted occurs.

FIG. 4 shows that when Tr is changed from a small value to a large value as indicated by an arrow, the Wanted ink drop velocity decreases, and the Unwanted velocity also decreases. The same applies to Tk and others. From FIG. 4, it can be seen that it is preferable to increase Tr and Tf and reduce Vh to prevent Unwanted. However, if Tr is lengthened, Wante
The result is that the speed of d is extremely decreased, and it cannot be a countermeasure. Tr is set to 0 to several μs. Reducing Vh lowers the Wanted speed and at the same time reduces the amount of ejected ink droplets.
This is also difficult as a countermeasure. Un becomes when Tf is lengthened
Although the speed of the wanted is decreasing, it is known that the effect cannot be obtained unless it is considerably lengthened as described later. However, if Tf is too long, the pulse width Tp will increase,
The driving frequency decreases, so only Tf is Unwante
d It is difficult to obtain the effect of measures.

If Tk is set to t1 or more shown in FIG. 4, the ejected ink drop velocity and the proper ink amount become constant.
Tk is set to t1 or more. On the other hand, there is an optimum Tk for the Unwanted countermeasure. Next, the discharge start timing Tk will be described. The curve d in FIG. 5 shows the two pressure chambers 25, 27 in FIG.
Is Tr = 2 μs, Tf = 20 μs, and the ejected ink amount is 0.1.
The value of Unwanted discharged from the non-driving pressure chamber 26 sandwiched between the pressure chambers 25 and 27 when driven with μg and the discharge speed set to 7 m / s is plotted against the time Tk, that is, the discharge start timing. Is.

When Tk is changed, Unwant is periodically generated.
The speed of ed changes. In addition, the speed peak gradually decreases. It can be understood that the occurrence of Unwanted can be prevented by selecting Tk in the area indicated by the arrows 51, 52, 53, 54.

In order to analyze this phenomenon, the pressure chamber 25 with a driving waveform having a long Tk (for example, Tk = 300 μs),
A curve g is a result of observing the position of the meniscus formed in the nozzle 7 of the pressure chamber 26 when the pressure sensor 27 is driven.
The zero point is the state in which the meniscus is as shown in FIG. 6, and represents the standby state.

When a signal is input, the pressure chamber 26 expands rapidly,
The meniscus largely recedes to the pressure chamber side. The retracted meniscus repeats forward and backward vibrations and gradually attenuates, and finally returns to the initial state. This vibration period Tm is determined by the compliance of the ink in the pressure chamber, the compliance of the side wall, the flow channel size of the pressure chamber, and the ink density, and was about 40 μs in the example.

When the curves d and g are compared, the areas 51, 52, 53 and 54 indicated by the arrows are the sections from the vicinity of the apex of the curve g to the valleys. That is, the discharge is started in the vicinity of the time when the meniscus is most advanced in the ejection direction or during the subsequent retreat period of the meniscus.
It turns out that can be prevented.

If discharge is started during these periods, Unwa
It is considered that the reason why nted can be prevented is that the flow of ink in the direction toward the nozzle opening, which occurs when the side wall returns from the deformed state due to discharge, is suppressed by the flow in the opposite direction that appears in the vibration of the meniscus.

In the conventional example, the time from the start of charging to the start of discharging is specified by L / a (L is the pressure chamber length, a is the speed of sound in the ink), but this time is exactly the timing in FIG. It represents the vicinity of t1 and is rather unfavorable timing for Unwanted.

A more detailed description will be given below in order to increase the driving frequency.

The regions indicated by arrows 51, 52, 53 and 54 tend to widen as Tk is lengthened. But Tk
When is longer, the pulse width Tp is longer and the driving frequency is lowered. Therefore, it is preferable to set the regions 51 and 52, and preferably Tk in the region 51.

The curve of FIG. 5 can be obtained for several other types of Tf, and Unwa when Tf is changed.
It is possible to know the prevention range of nted.

In FIG. 7, Tf is plotted on the abscissa and Tk is plotted on the ordinate, and the Unwanted speed zero region is shown by hatching. The area 61 includes the area indicated by the arrow 51 in FIG. 5, and the area 62 includes the area indicated by the arrow 52.

When Tk is made infinitely long and the meniscus is allowed to stand by, the minimum value of Tf which does not cause unwanted is about 40 μs, which is represented by the region 63.

The chain double-dashed line 56 has a pulse width Tp = 100 μs.
Represents the limit line for a drive frequency of 5 KHz determined by
In the upper right area of 6, 5 kHz or higher is impossible. Similarly, the alternate long and short dash line 57 represents the limit line of 7.5 KHz.

It can be seen from FIG. 7 that when Tk is set in the region 61 where high frequency driving can be expected, if Tf is made longer, Unwanted occurs, so that Tf has an upper limit. The reason is that, referring to FIG. 5, the meniscus vibration has a large amplitude in the vicinity of the arrow 51, which is the initial stage of vibration, and the moving speed of the meniscus is high. Nevertheless, if Tf is too long, the damping effect against meniscus vibration is small, and since Tf is long, it is considered that the forward section of the meniscus and the period of Tf overlap.

The receding period of the meniscus is 1 of the vibration period Tm.
Considering that it is / 2, Tf is 1 / 2T
It can be inferred that a value around m is a preferable value. In fact, Figure 7
, Tf is about 0 around 1/2 Tm
<Tf <Tm was in the effective range.

Summarizing the above results and consideration: Tk and T are set so that the vibration of the meniscus settles in the standby state.
Unwanted can be prevented by lengthening f, but for that purpose, either or both of Tk and Tf must be lengthened considerably, and the driving frequency is significantly lowered.

However, among the meniscus vibrations induced by the nozzles of the adjacent pressure chambers, the discharge of liquid is started by starting the discharge at the time when the meniscus advances to the discharge port side most or after the meniscus retracts. Unwanted can be prevented despite the short Tk and Tf.

Further, in the meniscus vibration, the discharge start is started at the time when the meniscus is most advanced or after the meniscus is retracted, and Tf is 0 <Tf <Tm.
By setting in the range of (1), high frequency driving, for example, high response of 5 KHz or more is possible, and under this condition, 7.5 KHz is also possible.

In the above description of the embodiments, the characteristics of a typical head have been mainly described, but the principle according to the present invention is applicable as long as the head structure is the same even if the dimensions of the pressure chambers and nozzles are different. It is possible.

[0042]

As described above, according to the ink jet recording apparatus of the present invention, even in the case of high frequency driving and high speed ink droplet ejection, it is possible to perform non-driving which causes ejection down and paper surface contamination. Unwanted ink droplets that are ejected regardless of occurrence, that is, Unwanted can be prevented.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of an inkjet head used in the present invention.

FIG. 2 is a sectional view of a pressure chamber portion of an inkjet head used in the present invention.

FIG. 3 is a diagram showing an example of drive waveforms of an inkjet head used in the present invention.

FIG. 4 is a diagram showing a relationship between a driving condition and an ink droplet ejection speed according to the present invention.

FIG. 5 is a diagram showing an example of ejection velocity of unnecessary ink droplets from adjacent non-driving pressure chambers and vibration of meniscus.

FIG. 6 is a diagram showing a meniscus standby state.

FIG. 7 is a diagram of an example showing a range of drive conditions in which unnecessary ink droplets of the present invention are not ejected.

[Explanation of symbols]

1 pressure chamber 2 nozzles 4 nozzle plate 5-9 nozzles 16 Polarization direction 20-23 Side wall 24-28 pressure chamber 29 to 33 electrodes 35 roof wall plate 45 bottom wall plate 60 Extraction electrode

Claims (3)

(57) [Claims] 1. An ink jet recording apparatus comprising an ink jet head and a driving means for the head, wherein the ink jet head has a plurality of pressure chambers surrounded by a bottom wall, a ceiling wall and two opposite side walls, and adjacent to each other. The pressure chambers are arranged with one common side wall as a sakai, and at least a part of each side wall is made of a piezoelectric material that is sheared and deformed in the direction of the electric field by applying an electric field perpendicular to the wall, and the driving means is opposed to each other. An electric field is applied to the piezoelectric material on the two side walls to charge, the piezoelectric material is deformed by charging, the piezoelectric material is held in that state, and then the piezoelectric material is discharged, and the meniscus vibration induced by the application of the electric field is included. There set the most the discharge start timing during retraction period ejection direction point near or meniscus subsequent reaching the counter-discharge direction, the meniscus vibration frequency of the said discharge time Tf As Tm, 0 <Tf <ink jet recording apparatus is characterized in that the Tm. 2. An ink jet recording apparatus for ejecting ink by applying an electric field to a driving means to expand and contract the pressure chamber to change the ink pressure in the pressure chamber, wherein the driving means charges the piezoelectric element. After deforming the substance, it has a driving circuit that holds the state and then discharges it.The discharge start timing is near the time when the meniscus vibration reaches the discharge direction most or the subsequent meniscus recedes in the counter discharge direction. An ink jet recording apparatus, wherein the discharge time Tf is set to 0 <Tf <Tm, and the discharge time Tf is set to 0 <Tf <Tm. 3. The ink jet recording apparatus according to claim 2, wherein the discharge causes the pressure chamber to contract.