JP3318568B2 - 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 which performs printing by ejecting ink droplets from small ejection openings. In particular, the present invention relates to a structure of a pressure chamber for discharging ink droplets and an electric signal applied to the pressure chamber. The present invention relates to an improvement for excluding, from a pressure chamber, an element that inhibits normal printing, such as a bubble generated in the pressure chamber.

[0002]

2. Description of the Related Art In an ink jet recording apparatus, ink is introduced into a pressure chamber having a small discharge port on a wall surface and ink in the pressure chamber is pressurized at a controlled timing.
Printing is performed by ejecting ink droplets from the ejection ports. At this time, it is necessary that the pressure chamber is full of ink, and if the ink in the pressure chamber contains small bubbles or small foreign matters having different densities are mixed, printing is performed. Will not be performed properly. Conventionally, in order to eliminate such bubbles and foreign substances from the pressure chamber, a technique of performing an operation for recovering the ink head at the time of first use or when resuming use after a long pause has been used. Are known.

As a technique for recovering the ink head, there is a technique of heating the pressure chamber during non-printing and applying vibration to the pressure chamber (Japanese Patent Laid-Open No. 58-132563). This is a fundamentally superior technique, widely practiced, and this publication discloses varying the frequency of oscillating the pressure chamber over the period of this recovery operation.

As another technique, there is a technique for gradually attenuating the vibration energy applied to the pressure chamber at the timing when the recovery operation is completed (Japanese Patent Laid-Open No. 61-227061). Furthermore, this publication also discloses a technique for covering the ink discharge port when performing a recovery operation and excluding ink sent from the discharge port into an ink pool.

Further, as another technique, a technique of intermittently controlling the vibration applied to the pressure chamber in accordance with the moving state of the foreign matter in the pressure chamber from the ink introduction path is known (Japanese Patent Laid-Open No. Sho 59-218866). Gazette).

[0006]

In order to always discharge a proper amount of ink at a proper speed from an ink discharge port, ink should be properly applied to a pressure chamber in a printing state so that printing is not disturbed by bubbles or foreign matter. The technique of controlling the charging is not sufficient even by the above-described technique. In particular, it is not desirable to introduce new components, such as extra parts, to eliminate air bubbles in the pressure chamber. Also, the application of extra energy to the pressure chambers for this requires additional energy-generating devices, such as heating devices, which can lead to other unexpected disadvantages, which is also undesirable. .

The present invention has been made in view of such a background, and an object of the present invention is to provide an apparatus capable of appropriately removing air bubbles and foreign substances having different densities generated in a pressure chamber. SUMMARY OF THE INVENTION It is an object of the present invention to provide a device that can reduce bubbles and foreign substances by reducing energy applied to a pressure chamber. SUMMARY OF THE INVENTION It is an object of the present invention to provide a device capable of eliminating bubbles in a pressure chamber without providing an extra element by using an electromechanical converter used for printing as it is. SUMMARY OF THE INVENTION An object of the present invention is to improve the production yield of an inkjet recording head.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the pressure chamber is resonated by the vibration of an electromechanical transducer for ejecting ink by changing the pressure in the pressure chamber, and the air bubbles and other density adhered to the wall of the pressure chamber are reduced. It is characterized in that different foreign substances are peeled and eliminated. This is desirably performed as one of the cleaning operations during non-recording.

That is, the present invention provides a pressure chamber, which is surrounded by a wall partially formed with a small ink ejection port and is filled with ink, an ink tank communicating with the pressure chamber via an introduction path, and the pressure chamber. An electromechanical transducer that fluctuates the pressure, and a driving circuit that supplies an electric signal to the electromechanical transducer, in the ink jet recording apparatus, the electric signal has a frequency approximate to the natural vibration frequency of the pressure chamber. It is characterized by including a signal. Here, the frequency approximating the natural vibration frequency of the pressure chamber is a frequency at which the pressure chamber can be brought into a resonance state. This is a frequency that can bring the pressure chamber into a continuous resonance state even for a short time. The frequency does not necessarily have to be equal to the natural vibration frequency of the pressure chamber. When there are a plurality of natural vibration frequencies in the pressure chamber, it is desirable that the frequency cause the largest resonance state in the pressure chamber, but it may be a frequency capable of causing a small resonance state. Further, the frequency is not limited to the fundamental frequency of the natural vibration frequency of the pressure chamber, but may be any frequency that can cause a resonance state of the pressure chamber, such as a frequency that is an integral multiple or a fraction of the integer.

As described above, by setting the driving frequency to a frequency approximating the natural vibration frequency of the pressure chamber, the pressure chamber resonates, and even if the supplied electric signal has a small energy, the pressure chamber has a large amplitude vibration. Will be done. This means that even if a particularly large amount of energy is not supplied, a small amount of energy is accumulated in the standing wave, and a large-amplitude vibration is applied to the ink in the pressure chamber.

The drive circuit includes means for intermittently and repeatedly generating a signal having a frequency approximating the natural vibration frequency of the pressure chamber as the electric signal during non-recording, and the time for applying the natural vibration frequency is several cycles. It is preferable to provide a means for suctioning the ink ejection port over a period in which the signal of the frequency is intermittently and repeatedly generated, which is a pause time that is several times to several tens times the time. A diaphragm pump can be used as the suction means.

The ink stored in the ink tank is fed into the pressure chamber surrounded by the wall via the introduction path and is filled. The electromechanical transducer provided on the wall surface of the pressure chamber changes the pressure in the pressure chamber by an electric signal from a drive circuit driven under the control of the control means. Due to this pressure fluctuation, ink droplets are ejected from small ink ejection ports formed in a part of the pressure chamber, and printing is performed.

The ink stored in the ink tank is supplied to the pressure chambers from which the ink droplets have been ejected. The supplied ink contains foreign matters having different densities, such as small air bubbles. Air may remain in the room. Bubbles and foreign matter floating in the ink are ejected from the ejection port together with the ink droplets, but the air bubbles adhering to the pressure chamber wall are hardly separated from the wall by suction from the ink ejection port or pressure feeding from the ink tank. It is hard to be done.

According to the present invention, all foreign matters including air bubbles adhering to the wall surface are properly removed, and an electric signal for causing the pressure chamber to resonate is applied to the electromechanical transducer to intensify the ink in the pressure chamber. Vibrates, and the vibration separates air bubbles adhering to the pressure chamber wall from the pressure chamber wall,
The ink containing the air bubbles is discharged to the outside by suction. It is effective to apply the electric signal periodically, which generates a drive waveform with a frequency close to the natural vibration frequency of the pressure chamber by the drive circuit during non-recording, and intermittently outputs this to the electromechanical transducer. Is applied repeatedly.

More specifically, the application of a frequency approximating the natural vibration frequency is performed for a period of several cycles, and the ink discharge ports are preferably sucked by a diaphragm pump. It is most effective to supply the electric signal for several cycles, and to repeat this cycle intermittently as a rest time until the reverberation converges for several to several tens times the following time.

As a result of the test, it was found that the natural vibration frequency of the pressure chamber slightly changed in accordance with the movement of the ink and the change in the state of bubble generation. Therefore, rather than continuously applying the natural vibration frequency, as described above, the natural vibration frequency is applied every several cycles, for example, every 5 to 10 cycles, and the vibration is paused for several to several tens times the time. It turned out to be good. It is considered that the natural oscillation frequency recovers to the state where the first resonance occurs during this pause period.

In the present invention, the electromechanical transducer used for printing is used as it is, and bubbles and foreign matter in the pressure chamber for pressurizing ink can be reduced with a small energy without newly providing extra components or other elements. Can be eliminated with
Appropriate printing can be performed.

Further, when the pressure chamber after the manufacture is filled with ink for the first time, the air inside may adhere to the wall surface as air bubbles and remain in a state where it is difficult to peel off. When vibration is given by an electric signal having a frequency close to the above, the pressure chambers resonate and vibrate the ink violently, so that both large and small bubbles can be easily peeled off and simultaneously operated. The suction is almost completely eliminated. As a result, it is possible to avoid discarding the pressure chamber which can normally be filled with ink as a defective product, thereby improving the production yield of the inkjet head.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[0020]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a main part of the apparatus of the embodiment of the present invention, and FIG. 2 is a conceptual diagram showing a structure of a recording head unit of the apparatus of the embodiment of the present invention.

The apparatus according to the embodiment of the present invention includes a recording head 1, an ink tank 3 storing ink 2, a driving circuit 4 for supplying an electric signal to the recording head 1, and a diaphragm for sucking the ink 2 from the recording head 1. The pump 5, the waste liquid tank 6 for storing the ink 2 sucked by the diaphragm pump 5, the driving circuit 4, the diaphragm pump 5, the recording head driving means 21 for driving the recording head 1, and the recording paper 22 are brought into close contact with each other. Control circuit 1 for controlling platen driving means 24 for driving platen 23 to be conveyed
0 is provided.

The recording head 1 is provided with a pressure chamber 8 which is surrounded by a wall partially formed with a small ink discharge port 7 and fills the ink 2, and is provided inside the wall of the pressure chamber 8 to reduce the pressure inside the pressure chamber 8. And an electromechanical conversion element 9 that varies. The pressure chamber 8 is communicated with the ink tank 3 via the introduction path 11, and the electromechanical transducer 9 is connected to the drive circuit 4 by an electric signal line.

The diaphragm pump 5 includes a diaphragm 12 for sucking the ink 2 in the pressure chamber 8 and a driving means 13 for driving the diaphragm 12 under the control of the control circuit 10. The diaphragm 12 is connected to the cap 15 facing the ink discharge port 7 when sucking the ink 2 from the inside of the pressure chamber 8 via the suction path 14, and is connected to the waste liquid tank 6 via the discharge path 16.

The feature of the present invention is that the electric signal supplied from the drive circuit 4 to the electromechanical transducer 9 includes a signal having a frequency approximating the natural vibration frequency of the pressure chamber 8.
The drive circuit 4 includes means for intermittently and repeatedly generating an electric signal having a frequency approximate to the natural vibration frequency of the pressure chamber 8 during non-recording under the control of the control circuit 10.

The driving means of the diaphragm pump 5 includes means for sucking the ink discharge port 7 over a period in which a signal having a frequency approximating the natural vibration frequency of the pressure chamber 8 is intermittently and repeatedly generated under the control of the control circuit 10. included.

The time for applying an electric signal approximating the natural vibration frequency to the pressure chamber 8 is set to several cycles, and the time several times to several tens times this time is repeatedly applied as a pause time.

Next, the operation of the apparatus according to the embodiment of the present invention will be described.

When printing is performed, the recording head driving means 21 moves the recording head 1 under the control of the control circuit 10, and the platen driving means 24 controls the platen 23.
While the recording paper 22 is conveyed by rotating the
Supplies an electric signal to the electromechanical conversion element 9 and the pressure chamber 8
Is ejected from the ink discharge port 7. Thereby, printing is performed on the surface of the recording paper 22.

When the ink 2 in the pressure chamber 8 is ejected, the ink 2 stored in the ink tank 3 is fed into the pressure chamber 8 via the introduction path 11 under pressure and filled. As shown in FIG. 2, small bubbles 17 or foreign matter may be mixed in the filled ink 2. When these are ejected together with the ink 2 from the ink discharge port 7, a part of the print is missing or a foreign substance adheres, so that proper printing is not performed. Further, the air bubbles adhered to the wall surface of the pressure chamber 8 are hard to peel off, and the air bubbles 17 remain in the pressure chamber 8, so that the pressure generated by the electromechanical transducer 9 is not transmitted normally, and proper printing cannot be performed. .

In the present invention, in order to prevent this, the control circuit 10 controls the recording head driving means 2 during non-printing such as when ink is filled.
1, the recording head 1 is moved to the position of the cap 15 as shown in FIG. 1, and the ink discharge port 7 is opposed to the cap 15 as shown in FIG. Further, the control circuit 1
0 drives the drive circuit 4 in this state, supplies an electric signal having a frequency approximate to the natural vibration frequency of the pressure chamber 8 to the electromechanical conversion element 9, and gives vibration to the ink 2 in the pressure chamber 8.
As a result, the pressure chamber 8 causes resonance vibration, and the filled ink 2 vibrates violently.

FIG. 3 is a diagram showing an example of an electric signal applied to the electromechanical transducer in the apparatus according to the embodiment of the present invention. In the figure, t is a cycle approximating the natural cycle of the pressure chamber 8, n is the number of applied cycles (for example, several cycles), and T is the time until the reverberation converges (for example, several times to several tens times of t). .

By repeatedly and intermittently applying an electric signal having a frequency approximating the natural vibration frequency of the pressure chamber 8, resonance occurs in the pressure chamber 8 and the filled ink 2
Vibration is applied to the pressure chamber 8, whereby the air bubbles 17 attached to the wall surface of the pressure chamber 8 are efficiently separated.

At the same time as the application of the electric signal to the pressure chamber 8, the control circuit 10 controls the driving means 1 of the diaphragm pump 5.
3 to drive the diaphragm 12 to pulsate,
The ink 2 in the pressure chamber 8 is intermittently sucked into the inside 5. As a result, the separated bubbles 17 and the ink 2 containing the foreign matter are discharged from the pressure chamber 8. The ink 2 sucked into the cap 15 passes through the diaphragm 12 from the suction path 14 and is discharged from the discharge path 16 to the waste liquid tank 6. With this discharging operation, new ink 2 is discharged from the ink tank 3.
Is filled into the pressure chamber 8 via the introduction path 11 without bubbles.

The inventor conducted the following experiment using such an apparatus according to the present invention. First, as shown in FIGS. 1 and 2, a state in which the recording head 1 is opposed to the cap 15 and the ink 2 is filled is set, and the drive circuit 4 instructs the electromechanical transducer 9 to approximate the natural vibration frequency of the pressure chamber 8. An electric signal having a period t is applied for 7 cycles, and a similar electric signal is applied again at a time interval (T) at which reverberation converges.

At the same time, the driving means 13 of the diaphragm pump 5 is driven so that the diaphragm 1
The ink 2 in the pressure chamber 8 was sucked into the pressure chamber 8 by pulsation, and the ink 2 was filled in the pressure chamber 8 from the ink tank 3. FIG. 4 shows the ink filling rate in the pressure chamber with respect to the vibration period of the electromechanical transducer according to the embodiment of the present invention. As shown in FIG. 4, the air bubbles 17 remaining in the pressure chamber 8 are discharged. Was performed efficiently, and the filling rate of the ink 2 in the pressure chamber 8 was 97%.

On the other hand, when the ink is filled only by the pressure feeding from the ink tank 3, the filling rate is about 82%, and the filling is performed only by the suction from the ink discharge port 7 by the suction of the diaphragm pump 5. About 88% if you go
showed that.

An experiment was conducted on the number of pressure chambers that were not ejected when the ejection operation was performed after the pressure chambers were initially filled with ink, and the number of recovered chambers after the elimination operation was obtained. The results shown in Table 1 were obtained. .

[0038]

[Table 1] That is, in the case of the present invention, six out of sixteen pressure chambers (3
7.5%), and 16 out of 21 (76.
2%), and the number of recoveries after performing the ink elimination operation on the non-ejection pressure chamber is all six in the case of the apparatus of the present invention, and is recoverable in the case of the conventional apparatus in the case of thirteen. Three obtained unrecoverable results.

According to the present invention based on the results of these experiments,
When printing is performed after the initial filling of ink, there are pressure chambers where ink is not ejected, but the occurrence rate is lower than that of the conventional apparatus, and all of them are recovered by performing the ink elimination operation according to the present invention I understand.
That is, it has been proved that the present invention makes it possible to avoid making the pressure chamber that performs normal ejection abnormal.

[0040]

As described above, according to the present invention, by using the electromechanical transducer used for printing as it is without providing any extra elements, bubbles or bubbles generated in the pressure chamber can be obtained. Foreign matter can be properly removed with small energy. Further, almost all non-ejection states that occur during the initial filling of ink after manufacturing are recovered by performing an ink elimination operation, so that what is originally normal is considered defective and the manufacturing yield is reduced. Can be avoided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a main part of an apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a structure of a recording head unit of the apparatus according to the embodiment of the present invention.

FIG. 3 is a diagram showing an example of an electric signal applied to the electromechanical transducer in the apparatus according to the embodiment of the present invention.

FIG. 4 is a diagram showing an ink filling rate in a pressure chamber with respect to a vibration cycle of an electromechanical transducer according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 recording head 2 ink 3 ink tank 4 drive circuit 5 diaphragm pump 6 waste liquid tank 7 ink discharge port 8 pressure chamber 9 electromechanical conversion element 10 control circuit 11 introduction path 12 diaphragm 13 drive means 14 suction path 15 cap 16 discharge path 17 bubble 21 Recording Head Driving Unit 22 Recording Paper 23 Platen 24 Platen Driving Unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B41J 2/045 B41J 2/055 B41J 2/18 B41J 2/185

Claims (3)

(57) [Claims] 1. A pressure chamber which is surrounded by a wall having a small ink discharge port formed therein and is filled with ink, an ink tank which communicates with the pressure chamber via an introduction path, and a pressure in the pressure chamber which fluctuates. An electro-mechanical conversion element to be driven, and a drive circuit for supplying an electric signal to the electro-mechanical conversion element, wherein the drive circuit has a signal having a frequency approximate to the natural vibration frequency of the pressure chamber during non-printing. Reverberation converges on electrical signals containing
An ink jet recording apparatus including means for intermittently repeatedly generating and outputting a pause time . 2. The time for applying the natural vibration frequency is a number.
Cycle time, the pause time being the number of this time
2. The ink jet recording apparatus according to claim 1 , wherein the time is twice to several tens times . 3. The signal of the frequency is intermittently and repeatedly generated.
Means for sucking the ink ejection port over a period of time
The ink jet recording apparatus according to claim 1, further comprising: