JPH0429851A - Ink-jet recording device - Google Patents

Abstract

PURPOSE:To detect the place of bubble formation and to efficiently remove the bubbles by a method wherein a detection control means inputting output signals from a piezolelctric element is provided, and monitoring is made therewith either on the duration of periodic damping or on the amplitude of peak values of the output signals from the piezoelectric element to find out whether the bubbles are existent in a pressuer chamber or in an ink chamber. CONSTITUTION:A detection control means 11 is able to detect whether bubbles are formed or not and whether the formation is in a pressure chamber 2 or in an ink chamber 3 by monitoring at least one of the following two: the amplitude of peak values and the time of periodic damping of output voltage of a piezoelectric element 7. When the detection control means 11 detects the formation of the bubbles, printing is stopped and the formation is judged whether it is made in the ink chamber 3. In the case where the formation is made in the ink amber 3, a purge pump 10 is operated under 0.1kg/cm<2> pressure for 5 seconds. In the case where the bubbles are formed in the pressure chamber 2, not in the ink chamber 3, the purge pump 10 is operated under 0.2kg/cm<2> pressure for 10 seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet recording apparatus capable of detecting and removing air bubbles generated within an inkjet head.

[Background of the invention]

FIG. 9 shows an example of a conventional bubble removing device. The ink in the ink tank 26 is supplied to the pressure chamber 27 via an ink supply port 30, an ink supply path 31, and an orifice path 28 in the head.
sent to. Ink in the pressure chamber 27 is ejected as ink particles through the orifice path 28 and the orifice 29 when the piezoelectric element 32 is driven.

As is well known, on-demand inkjet heads have the problem of air bubbles occurring within the head. When bubbles are generated, the vibration energy of the pressure chamber 27 is absorbed by the bubbles, making it impossible to sufficiently pressurize the ink within the pressure chamber 27, making it impossible to properly eject ink particles.

Figure 10 shows the state of ink droplet ejection, and (A)
(B) shows an example where the ejection direction is downward due to the generation of air bubbles, and (C) shows an example where large air bubbles were generated and could not be ejected as ink droplets.

When air bubbles occur, the speed of ink droplets decreases or the direction of ejection is disturbed, making it impossible to print normally.

Therefore, if bubbles are generated, the purge pump 33 pressurizes the ink in the reink crank 26 to remove the bubbles in the head. Further, a method for detecting the generation of air bubbles in the head by monitoring the electrical output of the piezoelectric element 32 is disclosed in Japanese Patent Publication No. 59-2620, for example.
This is proposed in Utility Model Publication No. 59-5570. By driving the purge pump 33 for a predetermined period of time when generation of bubbles is detected by the bubble detecting means, it is possible to remove bubbles in the head configured as shown in FIG.

However, in the case of an inkjet head as shown in FIG. 1 in which an ink chamber is provided between the pressure chamber 27 and the orifice 29 to absorb pressure fluctuations, bubbles may be generated in the pressure chamber.
Since it is not possible to distinguish and detect whether air bubbles have occurred in the ink chamber, the following problems arise with respect to subsequent removal of air bubbles.

In other words, it is better to change the pressure and operation time of the purge pump 33 depending on whether bubbles are generated in the pressure chamber or the ink chamber, but if the pressure and operation time are increased, if bubbles are generated in the ink chamber, the pressure and operation time of the purge pump 33 will be changed. Excess ink will be ejected, and if the pressure and operating time of the purge pump are reduced, there is a risk that air bubbles generated within the pressure chamber may not be completely removed.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to detect the location where bubbles are generated and to efficiently remove bubbles.

[Summary of the invention]

The present invention focuses on the fact that the output of the piezoelectric element for bubble generation detection changes depending on whether bubbles are generated in the ink chamber or the pressure chamber, and that the pressure and operating time of the purge pump can be reduced to remove bubbles in the ink chamber. However, the bubble detection method and bubble removal method have been devised. The present invention will be described below with reference to the drawings.

[Embodiments of the invention]

FIG. 1 is an explanatory diagram showing an embodiment of the apparatus of the present invention. Ink in the ink tank 1 is sent into the pressure chamber 2 via an ink supply port 5 and an ink supply path 6. As described above, the ink chamber 3 is provided between the pressure chamber 2 and the orifice 4 and has a volume smaller than that of the pressure chamber 2 to absorb pressure fluctuations. A piezoelectric element 7 is mounted behind the partition wall 9 of the pressure chamber 2 . The detection control circuit 11 generates a signal to drive the piezoelectric element 7 via the lead wire 8, receives the output of the piezoelectric element 7, detects bubble generation and the generation location, and operates the purge pump 10 in response to the detection result. Generates a signal to drive.

When the piezoelectric element 7 is driven by the pulse signal shown in FIG. 2, the volume of the pressure chamber 2 is rapidly reduced, and ink particles are ejected from the orifice 4. When the pulse signal disappears, the pressure chamber 2 returns to its original state.

The vibration of the ink during this return is transmitted from the pressure chamber 2 to the partition wall 9, and the piezoelectric element 7 generates an electric signal.

FIG. 3 shows the voltage output by the piezoelectric element 7. In a normal state where no bubbles are generated, the output voltage causes minute vibrations for a short period of time and then converges. This is pressure chamber 2
This means that the energy that deforms the ink is consumed by ejecting it as ink particles from the orifice, which means that the attenuation is fast.

FIG. 4 shows the output voltage of the piezoelectric element 7 when bubbles are generated within the head. Figure 4 (A) shows the ink chamber 3.
This shows the case where bubbles are generated, and the vibration damping time is longer than in normal conditions. FIG. 4(B) shows a case where bubbles are generated in the pressure chamber 2, and the peak value becomes larger compared to the normal state, and the vibration damping time becomes longer. Fourth
Figure (C) shows the case where the head is filled with air bubbles,
Nearly 100% of the energy applied by the piezoelectric element 7 is absorbed by the bubbles, resulting in an infinitely long vibration damping time.

When air bubbles are generated in the head, the energy applied by the piezoelectric element 7 is absorbed by the air bubbles, which means that the energy is not consumed as ink droplets and returns to the pressure chamber 2 as vibration waves because the energy attenuation is small. There is.

Therefore, the detection control means 11 monitors at least one of the width of the peak value of the output voltage of the piezoelectric element 7 and the vibration damping time, so that the bubble generation and the bubble generation location are detected in the pressure chamber 2.
It is possible to detect whether it is inside the ink chamber 3 or inside the ink chamber 3. Also, depending on the detection result, especially the location where bubbles are generated, the purge pump 1
By changing the driving conditions of 0, it becomes possible to efficiently remove air bubbles.

FIG. 5 is a flowchart showing the bubble removal routine.

When the detection control means II detects the generation of bubbles in step 50, the process proceeds to step 51, where printing is stopped, and the process proceeds to step 52.

In step 52, it is determined whether bubbles are generated in the ink chamber 3. If bubbles are generated in the ink chamber 3, the process proceeds to step 54, where the purge pump 10 is set to a pressure of (1.1 Kg/cm'') and operated for 5 seconds. If bubbles are generated in the pressure chamber 2 instead of the ink chamber 3, the process proceeds to step 53, where the purge pump 10 is set to a pressure of 0.2 Kg/cm'' and operated for 10 seconds.

When the purge operation by the purge pump 10 is completed, the process proceeds to step 55, in which the piezoelectric element 7 is driven to detect whether or not air bubbles still remain in the head, and in step 56, the output of the piezoelectric element 7 is monitored to detect air bubbles. If there are still bubbles remaining, step 52
Return to step 1 and operate the purge pump 10 again to perform purging. If the air bubbles have been completely removed and no air bubbles remain, the process advances to step 57 and printing is restarted.

As described above, according to this embodiment, the location where bubbles are generated can be detected and the driving conditions of the purge pump 10 can be changed depending on the location where bubbles are generated, so that bubbles can be removed efficiently.

FIG. 6 shows another embodiment of the head 16, and FIG. 7 shows a bubble removing device for the head 16 of FIG.

The pressure chamber 2 is supplied with ink from the first ink tank 12 via an ink supply path 21 and an ink supply port 20, and is communicated with the atmosphere via a bubble removal port 24. As in the above embodiment, the ink chamber 3 communicating with the pressure chamber 2 and the orifice 4 is supplied with ink from the second ink tank 13 via the ink supply path 23, ink supply port 22, and communication path 14, and at the same time, air bubbles are removed. It communicates with the atmosphere via a port 25.

The first ink tank 12 and the second ink tank 13 communicate with each other via a solenoid valve 15 that is open during printing.

Therefore, during printing, the ink in the first ink tank 12 and the second ink tank 13 are at the same height. The ink tanks 12 and 13 are connected to the first purge pump 17 and the second purge pump, respectively.
It is connected to the purge pump 18. Note that the pressure and operating time of the second purge pump 18 are set to be smaller than the pressure and operating time of the first purge pump 17. Further, since air bubbles generated in the pressure chamber 2 and the ink chamber 3 are removed from the air bubble removal ports 24 and 25, respectively, air bubbles can be easily removed.

FIG. 8 is a flowchart showing the bubble removal routine in the configuration of FIG.

Close the solenoid valve 15 when air bubbles are detected (step 62)
, it is determined whether or not the bubble generation location is within the pressure chamber 2 (step 63), and if the bubble generation location is within the pressure chamber 2, the first purge pump 17 and the second purge pump 18 are operated (step 64 and 65) to remove the bubbles. If the occurrence location is inside the ink chamber 3, only the second purge pump 18 is operated (step 65), and after the bubbles are removed, the solenoid valve 15 is opened (step 6).
8) This embodiment differs from the above embodiment in that printing is restarted after

〔Effect of the invention〕

As described above, according to the present invention, the locations where air bubbles are generated can be detected separately, and the driving conditions of the purge pump can be changed depending on the location where air bubbles are generated, so that air bubbles can be removed efficiently. .

[Brief explanation of drawings]

Fig. 1 is an explanatory side view showing one embodiment of the bubble removing device which is the main part of the device of the present invention, Fig. 2 is a waveform diagram showing an example of the piezoelectric element recording voltage, and Fig. 3 is the piezoelectric voltage during normal operation. FIG. 4 is a waveform diagram showing the output voltage of the piezoelectric element during an abnormality. FIG. 5 is a flowchart showing an example of the bubble removal routine. FIG. 7 is an explanatory side view showing another embodiment of the bubble removal device, FIG. 8 is a flowchart showing another embodiment of the bubble removal routine, and FIG. 9 is a diagram of the conventional device. FIG. 10 is an explanatory side view showing an example, and FIG. 10 is an explanatory side view showing an ink ejection state. In the figure, 1 is an ink tank, 2 is a pressure chamber, 3 is an ink chamber, 4 is an orifice, 7 is a piezoelectric element, 9 is a partition wall, 10
1 is a purge pump, and 11 is a detection control means. Name of patent applicant Hitachi Koki Co., Ltd. Figure 9 to figure

Claims (1)

[Claims] 1. A pressure chamber filled with ink and whose volume is changed by a piezoelectric element to eject ink particles from an orifice; An inkjet recording apparatus that prints using an inkjet head having an ink chamber provided between a chamber and an orifice, the apparatus comprising: a detection control means receiving an output signal of the piezoelectric element as an input; An inkjet recording apparatus characterized in that it determines and detects whether a bubble is located in a pressure chamber or an ink chamber by monitoring at least one of the length of a vibration damping time and the peak value width of an output signal. 2. The inkjet according to claim 1, further comprising a purge means for supplying pressurized ink to the pressure chamber, and when the control detection means detects air bubbles, the purge means is operated to remove the air bubbles. Recording device. 3. The inkjet recording apparatus according to claim 2, wherein when there are bubbles in the ink chamber, the pressure of the purge means is reduced and the operating time is shortened. 4. The inkjet recording apparatus according to claim 2, wherein when there are bubbles in the pressure chamber, the pressure of the purge means is increased and the operating time is lengthened. 5. Supplying pressurized ink to the pressure chamber and the ink chamber 2
2. The inkjet recording apparatus according to claim 1, further comprising two purge means, and said two purge means are selectively operated to remove air bubbles based on the detection output of said control detection means.