JPS63145038A - Ink jet printer - Google Patents

Abstract

PURPOSE:To prevent the viscosity of the ink in a nozzle from increasing, by keeping the air around the nozzle in an ink saturated-steam state by an evaporator in the state that a printer is not used; and to discharge the ink contained in a head to return into a normal state, by sucking out the ink in the nozzle by an pump in the case of abnormal state that bubbles are generated in the ink. CONSTITUTION:In abnormal state that bubbles are generated in a jet channel system of a head 20; a three-way valve 32 is changed over so as to connect conduits 34 to 36, a nozzle portion 21 is covered with a cap 27, and the air contained in a small space 28 in the cap 27 is sucked by a pump 33 for decreasing the pressure. Simultaneously, the pressure in a cartridge case 22 is increased and, thereby, ink in a bag 23 is pushed out, and ink in the head 20 is discharged from the nozzle to the small space 28 to allow it to flow into an evaporator 30 through a conduit 29. On the other hand, when the power of a printer is cut, the three-way valve 32 is changed over so that the conduit 34 is connected with the conduit 36 after the nozzle portion 21 is covered with the cap 27 and thereby the small space 28 is kept in a saturated-steam state due to the ink contained in the evaporator 30.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is an inkjet printer, particularly a drop-on-demand type inkjet, which recovers ink droplet ejection in the event of an abnormality in which ink droplets cannot be ejected, and also prevents the ink in the nozzle from drying. The present invention relates to an inkjet printer equipped with a protection device for preventing this.

[Conventional technology]

Figure 4 is a structural diagram showing an example of a conventional drop-on-demand type inkjet printer head, and Figure 4(a)
is a plan view of the nozzle plate that constitutes the head, and Fig. 4 (
b) is a sectional view of the head taken along the line AA' shown in FIG.
The nozzle plate 13 includes a nozzle 10 for ejecting ink droplets, an ink guide path 11-1, a pressure chamber 11, and an ink supply path 11.
-2 and an ink chamber 12 that stores ink supplied from an externally provided ink tank via an ink supply pipe 16. An elastic plate 15 is laminated on the nozzle plate 13. A piezoelectric element 14, which is an electromechanical transducer made of zirconium titanate, barium titanate, or the like, is bonded to the elastic plate 15 at a position corresponding to each pressure chamber 11.

Next, to explain this operation, when a voltage is applied to the piezoelectric element 14, the elastic plate 15 momentarily bends due to the electrostrictive effect, a pressure wave is generated in the ink in the pressure chamber 11, and this pressure wave is transmitted to the ink conduction path. 11-1 to the ink within the nozzle 10.

Ink droplets 19 are ejected from the nozzle 10 by the propagated pressure waves.

A conventional problem with this inkjet printer head is that when ink droplets are ejected and there is no ejection channel system, if the nozzle 10 is exposed to the atmosphere, moisture in the ink inside the nozzle 10 etc. evaporates into the atmosphere, increasing the viscosity of the ink.

At this time, the pressure waves generated due to the deformation of the piezoelectric element 14 no longer propagate normally, making it impossible to eject ink from the nozzle 10. Therefore, the piezoelectric elements 14 of the entire injection channel system are
A method is adopted in which the ink in the nozzle 10 is metabolized by driving the ink droplet 19 to eject the ink droplet 19, thereby maintaining a normal state.

Furthermore, when the printer is turned off, the piezoelectric element 14
Since the rubber member 1 cannot be driven as shown in FIG.
There is a means for making the nozzle part 21 airtight and preventing the evaporation of water in the ink inside the nozzle 10 by pressing the cap 18 having the cap 7 onto the nozzle part 21. In addition, as shown in FIG. 6, the ink cartridge that supplies ink to the head has a bag 23 filled with ink attached to the cartridge case 22 (shown in a transparent state).
The injection needle 25 provided at the tip of the ink supply tube 16 is inserted into the rubber member 24 provided in the bag 23, and the ink in the bag 23 is poured into the injection needle
By adopting a configuration in which the ink is supplied to the ink chamber 12 of the head 20 shown in FIG. 4 through the ink supply pipe 16, the ink is isolated from the atmosphere and water is prevented from evaporating from the ink.

[Problem that the invention seeks to solve]

However, despite the above-mentioned inkjet printer head protection measures, the air (oxygen, nitrogen, etc.) dissolved in the ink in the ejection channel system within the head 20 may be affected by environmental changes ( Changes in temperature, atmospheric pressure, etc.) and cavitation that occurs while driving the piezoelectric element 14 may cause minute bubbles to be generated in the ink. At this time, apparent ink ejection becomes impossible. In this case, the above-mentioned conventional protection means for inkjet printer heads cannot cope with the problem, and recovery work cannot be performed by anyone other than an expert.

This recovery work involves increasing the ink supply pressure in the ink supply system to 2 to 3 times the atmospheric pressure and applying back pressure to create a pressure difference in the ink inside the head to remove air bubbles in the ejection channel system from the nozzle 10. It depends on the method of evacuation. However, the air bubbles in the ejection channel system often remain attached to the surface due to the effect of surface tension, and it is difficult to remove the air bubbles unless back pressure is applied for a relatively long period of time and the ink is forced to flow. . This has the problem of being uneconomical since a large amount of ink is wasted, and there is also the problem that there is no guarantee that the bubbles can be removed reliably.

[Means for solving problems]

The inkjet printer of the present invention includes an inkjet printer head that ejects ink droplets from a nozzle connected to a pressure chamber correspondingly provided with a piezoelectric element, a cap for covering the nozzle, and a cap for covering the nozzle. At the same time, the pump lowers the pressure in a small space inside the cap and simultaneously pressurizes an externally provided closed ink storage container to increase the pressure of ink in the ink supply system and discharge ink from the nozzle. and an evaporator connected to the cap to keep the ink in the small space saturated. Furthermore, the pump of the inkjet printer of the present invention is driven simultaneously with sweeping the piezoelectric element on the head from a high frequency band to a low frequency band, and pressurizes an externally provided sealed ink storage container. Alternatively, the ink may be discharged from the nozzle by increasing the pressure of the ink within the ink supply system.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. cap 2
A small space 28 provided in the evaporator 3 is connected to the evaporator 3 by a conduit 29.
0, and the evaporator 30 is connected to the cartridge case 22 via a conduit 31, a pump 33, and conduits 34, 36, and a three-way valve 32 is provided in the middle of the conduit 34. Further, by switching the three-way valve 32, a conduit 36 connected to the cartridge case 22 is connected to a conduit 35 that is previously opened to the atmosphere. As shown in the perspective view of the cartridge shown in FIG. 2, this ink cartridge has an airtight structure for the conventional ink car 1 to the cartridge shown in FIG. A rubber member 38 is provided to apply pressure to the space between the bag 23 and the bag 23.

Like the rubber member 24, this rubber member 38 is also pierced with an injection needle provided at the tip of the conduit 36, so that the space inside the cartridge case 22 is connected to the three-way valve.

In FIG. 1, when performing a recovery operation of the head 20 in the event of an abnormality in which air bubbles are generated in the injection channel system of the head 20, first, the three-way valve 32 is switched to connect to the conduits 34 and 36, and the inside of the cartridge case 22 is opened. The nozzle part 21 of the head 20 is covered with a cap 27, and the air in the small space 28 inside the cap 27 is sucked by the pump 33 to lower the pressure. At the same time, at pump 33,
By increasing the pressure inside the cartridge case 22 and pushing out the ink contained in the bag 23 inside the cartridge case 22, the ink inside the head 20 is discharged from the nozzle 10 into the small space 28 and sent to the evaporator via the conduit 29. 30. If the evaporator 30 is full,
Excess ink is discharged as waste liquid 37 into the cartridge case 22 via conduit 31 , pump 33 , conduit 34 , three-way valve 32 and conduit 36 . While carrying out the above operations, as shown in the timing chart of FIG. 3, after sealing the nozzle part 21 with the cap 27 and starting driving the pump 33, the piezoelectric element 14 of the head 20 is first driven at a relatively high frequency. The ink is violently vibrated, causing air bubbles attached to the walls of the pressure chamber to float. and,
The drive frequency is gradually lowered (swept) to a lower drive frequency. Then, the bubbles float out of the nozzle 10 along with the flow of ink. According to experiments, it was found that a high frequency of about 20 kHz and a low frequency of about 100 Hz were appropriate. Then, the drive of the piezoelectric element 14 is stopped, the cap 27 is opened, the ink remaining in the small space 28 in the cap 27 is collected into the evaporator 30, and then the pump 33 is stopped. Next, the three-way valve 32 is switched so that the conduits 35 and 36 are connected, and the pressure inside the cartridge case 22 is released to the atmosphere. As described above, by performing the operations of the apparatus of the present invention, the head 20 can be automatically recovered. When the printer is turned off, the head 20 is moved to a predetermined position, and after covering the nozzle part 21 with the cap 27, the small part inside the cap 27 is opened by switching the three-way valve 32 so that the conduits 34 and 36 are connected. The space 28 is kept in a saturated vapor state by the ink stored in the evaporator 30.

Therefore, the ink within the nozzle 10 does not evaporate, the viscosity is kept constant, and the ink is not solidified. When the inkjet printer is used, the head 20 is moved to the position where the cap 27 is provided at predetermined intervals, and ink droplets are ejected from all nozzles to regenerate the ink in the nozzles.

〔Effect of the invention〕

As explained in detail above, the present invention covers the nozzle with a cap when the inkjet printer is not in use.
The evaporator can maintain the air around the nozzle in a state of ink-saturated vapor to prevent the viscosity of the ink within the nozzle from increasing. In addition, in the event of an abnormal situation where bubbles form in the ink, the nozzle of the head can be covered with a cap and the ink inside the nozzle can be sucked out using a pump. The ink can be discharged to restore the normal state. Furthermore, by sweeping and driving the piezoelectric element on the head from 20 kHz to 100 Hz while sucking out the ink in the nozzle with a pump, it is possible to easily return to the normal state in a short time. It is possible to reduce the amount of ink sucked out from the nozzle before returning to the normal state.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a perspective view of an ink tank cartridge seen through the cartridge case used to supply the ink shown in FIG. 1, and FIG. 3 is a perspective view of an ink tank cartridge. A timing chart showing the operation of FIG. 1, FIGS. 4(a) and (b) are respectively a plan view of a nozzle plate used in the head shown in FIG. 1, and a sectional view of the head. FIG. FIG. 6 is a perspective view of a conventional cap used to prevent ink from drying, and FIG. 6 is a perspective view of an ink tank cartridge for supplying ink used in a conventional printer. 20... Head, 21... Nozzle part, 27... Cap, 28... Small space, 30... Evaporator, 32...
...Three-way valve, 33...pump. 1st ward 3rd ward Rui 4th ward ('b) ZO Hezuhi 7Z th ward 6th ward

Claims (2)

[Claims] (1) An inkjet printer head that ejects ink droplets from a nozzle connected to a pressure chamber provided with a corresponding piezoelectric element, a cap for covering the nozzle, and an inside of the cap when the nozzle is covered with the cap. a pump that simultaneously lowers the pressure in a small space of the pump and pressurizes an externally provided closed ink storage container to increase the pressure of ink in the ink supply system to discharge ink from the nozzle; an evaporator connected to the cap to keep ink vapor in the small space saturated. (2) The inkjet printer according to claim 1, wherein the pump is driven at the same time as the piezoelectric element on the head is driven while sweeping from a high frequency band to a low frequency band.