JP2827531B2 - Driving method of inkjet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an ink jet recording head, and more particularly to a driving method for an on-demand type ink jet recording head capable of stabilizing and speeding up ink discharge and improving printing quality. About the method.

[0002]

2. Description of the Related Art Conventionally, there are many types of ink jet recording heads and their driving devices, which can be roughly classified into a continuous ejection type on demand type (impulse type).
There are three types of electrostatic suction type. Among them, on-demand type ink jet recording heads are widely used as recording heads for printers and the like because of their relatively simple construction and low cost.

FIG. 2 shows a main part of a recording head of this type. In this figure, 1 is an ink tank, 2 is an ink supply path, 3 is an ink pressurizing chamber, 4 is an ink nozzle, and 5 is an ink nozzle. An ink supply passage communicating with 4; a vibration plate 6 provided outside the ink pressurizing chamber 3; a piezoelectric element 7 as an electromechanical conversion element adhered to the vibration plate 6;
A bimorph is constituted by the vibration plate 6 and the piezoelectric element 7. When a pulse-like voltage is applied to the piezoelectric element 7 in such a configuration, the piezoelectric element 7 expands in the thickness direction and contracts in the length direction. Bend. As a result, the volume of the ink pressurizing chamber 3 slightly decreases, and the pressure wave generated by the deformation of the vibration plate 6 causes the ink to be ejected from the ink nozzle 4 in the direction a in FIG.

The waveforms of the voltage pulses applied to the piezoelectric element 7 are often those shown in FIGS. First, FIG. 3 shows that the voltage is V ₁ at time t ₁ , and (t ₂ −
t ₁ ) At time t ₂ after the lapse of time, the voltage is unloaded to zero, and the ink droplet is ejected at time t ₁ , and this is repeated n times (n is a natural number) according to the target frequency. Here, the voltage pulse width A is made equal to the natural vibration period of the bimorph composed of the vibration plate 6 and the piezoelectric element 7. A driving method using such a voltage pulse waveform is called a “push” driving method. Next, FIG. 4 is a voltage zero at the time t _1, the voltage at (t ₂ -t ₁₎ period has elapsed after the time t ₂ is intended to be V _1, the ink droplet is ejected at time t _2, This is repeated n times according to the target frequency. Here, (t ₂
−t ₁ ) is a time B which is 固有 of the natural oscillation period of the bimorph.
And A driving method using such a voltage pulse waveform is called a “pulling” driving method. FIG. 5 is a modified example of the driving method of "punching" shown in FIG.
The voltage at time t ₁ and _{V 1, (t 2 -t 1} ) after the voltage -V ₂ at time t ₂ after a time, the voltage at (t ₃ -t ₂₎ the time t ₃ after a time Is set to zero, and the ink droplet is ejected at time t ₁ , and this is repeated n times according to the target frequency.

In the driving method of "pulling" shown in FIG. 4, the volume of the ink pressurizing chamber 3 is temporarily increased, and the meniscus (ink coming and going) in the so-called ink nozzle 4 is retracted before the ink is discharged. According to this driving method, as described in Japanese Patent Application Laid-Open No. 55-17589, ink droplets can be ejected more stably as compared to the "punching" of FIG. It is also known that it has excellent frequency response.

[0006]

As described above, the on-demand type ink jet recording head is driven by applying a voltage pulse. The applied voltage pulse is
As is well known, each type of waveform produces an ink jet by a different mechanism. In the waveforms shown in FIGS. 3 to 5, only the peak value and the pulse width of the voltage pulse are focused on, and the ejection of the ink is controlled by these two parameters. However, when considering the behavior at the time of ink ejection, there are various undesired phenomena that cannot be controlled only by the above two parameters. For example, in addition to non-ejection of ink due to intrusion of bubbles from the outside of the ink nozzle, what is more important is the generation of a so-called satellite. That is, when a single voltage pulse waveform is applied, several satellites (sub-ink droplets) with a time delay are ejected from the ink nozzles following the main ink droplet, and the dots forming the character are formed by the satellite. A problem arises in that bleeding and the print quality are reduced. In addition, the ink droplets ejected from the ink nozzles may bend and lose straightness, and a desired character font may not be printed.

These phenomena can be easily observed using a strobe observation device. In an observation experiment in which the voltage pulse waveforms shown in FIGS. 3 to 5 were actually applied to the piezoelectric element 7, the area of the piezoelectric element 7 was reduced. It is confirmed that satellites are more likely to be generated. It is considered that this is because the behavior of the ink meniscus in the ink nozzle becomes non-uniform. Attempts have been made to stabilize the behavior of the ink meniscus by controlling the shape of the ink nozzle, but there are many restrictions in terms of manufacturing and shape, and practical use is difficult. For this reason, as a simple method, it is required to improve the printing quality by stabilizing the ejection of ink droplets by devising a drive waveform.

The inventor also applied the pulse waveform of the driving voltage shown in FIGS. 3 and 4 to the recording head shown in FIG. 2 and examined the ink ejection characteristics. As an experimental condition, the voltage V
₁ for 100 to 150 V, time A and B for 20 to 150 μs
ec, the rise time and fall time of the pulse were all 5 μsec or less, and the drive frequency was 1 to 5 kHz. As a result of the experiment, it was confirmed that under these conditions, a large amount of satellites were generated, and a large number of bubbles penetrated into the ink nozzles 4 were also observed, so that good print quality could not be obtained. Therefore, focusing on the pulse waveform of the “pulling” drive voltage, which is considered to be the most stable among the voltage application methods, the fall time Td and the rise time Te of the waveform shown in FIG. An experiment was performed with a wider range of values set for V than in the above experiment, but good results were not obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to drive an ink-jet recording head capable of performing high-speed and stable ink-jet recording by eliminating generation of satellites and bubbles. It is to provide a method.

[0010]

To achieve the above object of the Invention The present invention provides a voltage pulse waveform of "pull-push" in which a basic, pre voltages V ₁ to the electromechanical conversion element at the time of ink discharge failure The volume of the ink pressurizing chamber is reduced by applying the voltage, and in printing, the voltage V ₁ is passed through a fall time Ta so that the volume of the ink pressurizing chamber does not change abruptly.
Was unloaded, retain their time Tb, then, after applying a low voltage V ₂ than the voltages V ₁ at the rising time Tc, the volume of the ink pressure chamber by return instantaneously voltages V ₁ That is, the ink is discharged from the ink nozzle.

Here, the voltages V ₁ and V ₂ and the times Ta and T
It is desirable that b and Tc fall within the following ranges. V ₁ : 90 to 120 V V ₂ : 40 to 60 V Ta: 5 to 10 μsec Tb: Tb ≦ 20 μsec−Ta Tc: Tc ≒ 60 μsec−Tb−Tc

[0012]

According to the present invention, at the time of the ink non-ejection voltage V ₁ is applied to the electromechanical transducer the volume of the ink pressure chamber decreases. Since voltages V ₁ over the fall time Ta when printing is unloaded, the volume of the ink pressurizing chamber does not decrease abruptly. After the voltage V ₁ is unloaded, the time T
b after the elapse of, it is boosted over the rise time Tc to about half of the voltage V ₂ of the voltage V _1. After boosted to voltage V ₂ is returned immediately to the voltage V _1. By applying the voltage through these processes, the ink discharge speeds up and becomes stable.

Further, the voltage V ₁ is 90 to 120 V (volt), the voltage V ₂ is 40 to 60 V (volt), the time Ta is 5 to 10 μsec, and the sum of the time Ta and the time Tb is 20 μm.
It has been confirmed that when the sum of the time Ta, the time Tb, and the time Tc is about 60 μsec or less, the ink discharge speed is higher and the ink is most stable.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a waveform diagram of a voltage pulse used in the method of driving an ink jet recording head according to the present invention. The voltage pulse is applied to the recording head shown in FIG. 2 to eject ink droplets. Since the structure of the recording head of FIG. 2 has already been described, description thereof will be omitted. The inventor pays attention to the waveform effect when the meniscus advances and ink is ejected,
FIG. 1 shows a waveform that exhibits the best ink ejection characteristics.
Were found, and the conditions were specified.

Hereinafter, the relationship between the waveform and the operation of the recording head will be described in detail with reference to FIG. First, the voltage V ₁ is applied to the piezoelectric element 7 in advance. The voltage V ₁ is unloaded during the operation of the recording head and falls uniformly, and becomes zero when the fall time Ta has elapsed. The falling time Ta is a period during which the contracted ink pressurizing chamber 3 is restored, ink is sucked from the ink tank 1, and the meniscus in the ink nozzle 4 is retracted. If the fall time Ta is too short, it will cause air bubbles to enter from the ink nozzles 4. Therefore, specifically, the fall time Ta is preferably in the range of 5 to 10 μsec. Further, the holding time Tb from when the voltage becomes zero to when the voltage is boosted again is:
It is determined by the relationship with the rising time Tc at the time of the next ink ejection, and specifically, it is preferably 10 μsec or less, and the sum of the falling time Ta and the holding time Tb needs to be 20 μsec or less. is there.

Next, the voltage is increased to the voltage V ₂ at substantially uniform slope for ink ejection is increased instantaneously to voltages V ₁ and reaches the voltage V _2. If the rising time Tc at this time is 5 μsec or less, the ink is ejected, but the ink column is likely to bend and the ejection amount is likely to vary. Therefore the results of various experiments, and about half the value of the voltages V ₁ to the voltage V _2, by the rise time Tc and 40 .mu.sec, to return after reaching the voltage V ₂ to the voltages V ₁ to the following periods 3 .mu.sec, It has been found that stable ejection characteristics can be obtained. This is because the operation of the meniscus is gradual until a certain stage, so that the shape of the tip of the meniscus is matched during that period, and non-uniformity in the ink nozzle 4 is eliminated, so that good ejection characteristics can be obtained. It is estimated to be. Further, the pattern width of the voltage pulse is the sum of the fall time Ta, the hold time Tb, and the rise time Tc (Ta + Tb + Tc). As a result of the experiment, if this pattern width is set to 60 μsec or less, the speed of ink discharge is increased and the ink discharge is stabilized. Turned out to be the most suitable in terms of. When the pattern width becomes longer than 60 μsec, the ink column becomes gradually thinner and cut, and becomes a satellite. Also, the pattern width is less than 60 μsec and is 40 to 5
In the range of 0 μsec, the ink column is bent. In any case, when the pattern width is approximately 60 μsec, the ink column is most stable, and high quality printing is possible. That is, even if the pattern width exceeds 60 μsec,
Otherwise, the print quality will be degraded.

The pulse height is determined by the voltage V ₁
There 90～120V, voltage V ₂ is in the case of 40 to 60 volts V, was confirmed to improve the printing quality satisfies the conditions between the time of the above-described Ta, Tb, Tc each other.

[0018]

As described above, according to the present invention, the voltage pulse waveform applied to the electromechanical transducer of the recording head is controlled by focusing on the movement of the meniscus in the ink nozzle (ink volume velocity), and the meniscus retreats gradually. And a voltage pulse waveform capable of controlling the meniscus advancement (ink ejection) in two stages of slow and steep. Specifically, at the time of ink discharge failure by applying voltages V ₁ to the electromechanical conversion element to reduce the volume of the ink pressure chamber, by unloading the voltages V ₁ over the fall time Ta when printing while preventing a rapid decrease in the volume of the ink pressure chamber, boosts over the rise time Tc after the elapse of the time Tb after unloading the voltages V ₁ to about half the voltage V ₂ of the voltages V _1, then , A voltage pulse waveform that instantaneously returns to the voltage V ₁ . As a result, it is possible to achieve high-speed and stable ink ejection and to improve the print quality, and it is possible to apply the present invention to a recording head used for a multi-nozzle.

[Brief description of the drawings]

FIG. 1 is a waveform diagram of a voltage pulse according to an embodiment of the present invention.

FIG. 2 is a sectional view of an ink jet recording head to which the present invention is applied.

FIG. 3 is a waveform diagram showing a conventional voltage pulse.

FIG. 4 is a waveform diagram showing a conventional voltage pulse.

FIG. 5 is a waveform diagram showing a conventional voltage pulse.

FIG. 6 is a waveform diagram showing a conventional voltage pulse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink tank 2 Ink supply path 3 Ink pressurization chamber 4 Ink nozzle 5 Ink supply path 6 Vibration plate 7 Piezoelectric element

Continuation of the front page (72) Inventor Masaki Shinoda 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi Fuji Electric Co., Ltd. (56) References JP-A-2-192947 (JP, A) JP-A-55-65562 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B41J 2/045 B41J 2/055

Claims (2)

(57) [Claims] 1. An ink pressurizing chamber, an ink nozzle communicating with the ink pressurizing chamber, and a volume of the ink pressurizing chamber which is arranged outside the ink pressurizing chamber and deformed by applying a voltage pulse. And an electromechanical conversion element that changes
In an on-demand type ink jet recording head which pressurizes ink in the ink pressurization chamber by a pressure wave generated when the electromechanical transducer is deformed and discharges the ink from the ink nozzle, the ink jet recording head is pre-applied to the electromechanical transducer when no ink is ejected. advance by applying voltages V ₁ reduces the volume of the ink pressure chamber, unloading the voltages V ₁ through the time Ta falls so that the volume of the ink pressurizing chamber does not change abruptly when printing And hold the time Tb as it is,
Then, after applying a low voltage V ₂ than the voltages V ₁ at the rising time Tc, instantly to return to voltages V ₁ reduces the volume of the ink pressure chamber, the ink is ejected from said ink nozzles A method for driving an ink jet recording head. 2. The method according to claim ₁ , wherein the voltages V ₁ and V ₂ and the times Ta, Tb and Tc are in the following ranges. V ₁ : 90 to 120 V V ₂ : 40 to 60 V Ta: 5 to 10 μsec Tb: Tb ≦ 20 μsec−Ta Tc: Tc ≒ 60 μsec−Tb−Tc