JPS63141750A - Detecting device of air bubble for ink jet recording head - Google Patents

Abstract

PURPOSE:To detect the presence of air bubbles and the state of filling-up of ink in an ink chamber, by detecting the repetition cycle of a vibration waveform in a driving circuit of a piezoelectric element and in a vibration waveform shaping circuit at the time of driving, and by detecting therefrom the presence of the air bubbles in the ink chamber. CONSTITUTION:When a piezoelectric element driving waveform deformation Vo deformation of a piezoelectric element 9 is observed, it is seen that the piezoelectric element driving waveform Vo vibrates with a certain cycle after the piezoelectric element 9 is distorted. In the case when there are air bubbles in an ink chamber 23 or when ink is not filled up therein at all, a vibration waveform observed in this case is different from the one in a normal case since the impedance of the piezoelectric element changes, and therefore it can be distinguished from the latter. Based in that there is a large distinction between the frequency of this vibration waveform in the normal case and that in an abnormal case, it can be detected that air bubbles are present in the ink chamber 23 and that the ink is not filled up therein, by detecting the cycle of the vibration waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bubble detection device for an inkjet recording head such as an on-demand type inkjet printer head using a piezoelectric element used in a printer or the like.

[Conventional technology]

In the inkjet recording head used in conventional inkjet printers, a piezoelectric element is driven with pulses and the volume of the ink chamber inside the inkjet head is changed by the electrostrictive phenomenon, thereby applying pressure to the ink inside the ink chamber to create a nozzle. (These heads are tube-shaped or have a substrate with a groove fully formed on at least one of the substrates, and the groove is used as a flow path, and a piezoelectric element is placed around the tube or on the outside of the substrate corresponding to the groove.) (The groove corresponding to the piezoelectric element becomes the ink chamber, and the nozzle communicates with the ink chamber.)

[Problem that the invention seeks to solve]

However, if there are air bubbles in the ink chamber or if there are nozzles that are not filled with ink, the ink droplet ejection efficiency may drop significantly, or no ink droplets will be ejected at all due to nozzle clogging. Sometimes. For this reason, when used in an inkjet printer, it becomes impossible to print all of the input information, resulting in printing errors.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, it is an object of the present invention to provide a bubble detection device configured to detect bubbles and ink filling in an ink chamber.

[Means for solving problems]

The present invention is characterized in that the presence or absence of air bubbles in the ink chamber is detected by detecting the repetition period of a vibration waveform in a piezoelectric element drive circuit and a vibration waveform shaping circuit when driving the piezoelectric element.

〔Example〕 Embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 3, an ink chamber 23 is formed inside the ink jet recording head 28, and this ink chamber 25 is connected to an ink reservoir 24 at the rear. Further, the nozzle 25 is configured in the front part of the ink chamber 23. There is a diaphragm 26 above the ink chamber 26, a common electrode of a piezoelectric element is formed on the diaphragm 26, and a piezoelectric element 9 is formed above the diaphragm 26.

Also, as shown in FIG. 1, the output terminal of buffer 1 is NP.
It is connected to the pace of NPN transistor 4, and the emitter of this NPN transistor 4 is grounded. The collector of the NPN transistor 4 is connected to a high voltage power supply VH via a bias resistor 13 and to one electrode of a piezoelectric element 9 via a discharge resistor 14. The electrode on the opposite side of the piezoelectric element 9 is grounded. The one electrode of the piezoelectric element 9 is connected to the collector of a PNP transistor 6 via a charging resistor 15.

Next, the output terminal of the buffer 2 is connected to the base of an NPN transistor 5, and the emitter of this NPN transistor 5 is grounded. The collector of the NPN transistor 5 is connected to the high voltage power supply VH via a resistor 12, and is connected to the P
It is connected to the base of NP transistor 60. These buffers 1, 2, transistors 4, 5, 6, resistor 12
15 constitute a drive circuit.

Further, a series circuit of a capacitor 10 and a resistor 16 is a piezoelectric element 9.
are connected in parallel. This capacitor 10 and resistor 1
Reference numeral 6 constitutes a filter, and its connection point is connected to the anode of the diode 11. The cand of diode 11 is connected to the pace of NPN transistor 7 and via resistor 17 to the emitter of NPN transistor 7. The emitter of this NPN transistor 7 is grounded via a resistor 18. The collector of the NPN transistor is connected to the logic power supply VCC. The emitter of NPN transistor 7 is connected to the pace of NPN transistor 8 via resistor 19,
The pace of the NPN transistor 8 is connected to the emitter of the NPN transistor 8 via a resistor 20. The emitter of NPN transistor 8 is grounded. The collector of the NPN transistor 8 is connected to the input terminal of the output sofa 6 and connected to the logic power supply VCC via a resistor 21.
It is connected to the. A detection signal is output from the output end of the output buffer 3. These buffers 6, transistors 7
．． 8, diode 11, capacitor 10, resistor 16-2
1 constitutes a vibration waveform detection circuit.

In the inkjet device configured as described above,
Initially, one terminal of the piezoelectric element 9 is connected to the high-voltage power supply vH via the resistor 13, 14.
The voltage V at the one terminal of .

is almost the same as VH. Also, at the initial stage, the piezoelectric element 9
is in a distorted state υ, and naturally the volume of the ink chamber 23 is also reduced. When ejecting ink droplets, first, a predetermined pulse width t1 shown in FIG. 2 is applied to the input terminal of the buffer 1.
When a pulse voltage DPW having a value of DPW is applied, the transistor 4 turns on and discharges the charge stored in the piezoelectric element 9 through the discharge resistor 14. At this time, the distortion of the piezoelectric element 9 returns to its normal state, the volume of the ink chamber 23 increases, and ink flows into the ink chamber 25 from the ink reservoir 24 at the rear. Next, when the predetermined pulse width ends, wait for tw until the transistor 4 is sufficiently turned off, and apply another predetermined pulse ll1iiiI shown in FIG. 2 to the input terminal of the buffer 2.
A pulse voltage CPW with t2 is applied. Naturally, the transistor 5 is turned on at this time as well, and the base potential of the transistor B is lowered from the emitter potential of the transistor 6.

In synchronization with this, transistor 6 turns on, and charging resistor 15
A charge is applied to the piezoelectric element 9 from the high voltage power supply VH through the piezoelectric element 9. At this time, the piezoelectric element 9 begins to distort, the volume of the ink chamber 23 also decreases, and ink droplets are ejected from the nozzle 25.

Ink is continuously ejected by repeating this operation. The repetition period T depends on the characteristic response frequency of the head.

During this series of operations, the piezoelectric element drive waveform v of the piezoelectric element 9
When observing O, as shown in FIG. 2, after the piezoelectric element 9 is distorted, the piezoelectric element drive waveform vO oscillates at a certain period.

If there are bubbles in the ink chamber 23 or if the ink chamber 23 is not filled with ink at all, the impedance of the piezoelectric element changes, so it is possible to distinguish between vibration waveforms different from normal ones. Since the frequency of this vibration waveform varies greatly between normal and abnormal conditions, by detecting the period of this vibration waveform, it is possible to detect the presence of air bubbles in the ink chamber 2 and the fact that the ink is not filled.

4 to 6 show detected waveforms from the piezoelectric element drive waveform Vo up to detection by the detection circuit shown in FIG. 1 of the present invention. Figure 4 shows the case where there are no air bubbles in the ink chamber.
) is the piezoelectric element drive waveform VO. The DC component of this piezoelectric element driving waveform vO is cut off by a filter composed of a capacitor 10 and a resistor 16, and it becomes an oscillating waveform on the anode side of the diode 11 as shown in FIG. 4('b). Only the positive component is taken out by the diode 11, resulting in a waveform as shown in FIG. 4(c). The transistor 7 and resistors 17 and 18 form an emitter follower to lower the input impedance. Next, the transistor 8, the resistors 19, 20.degree. 21, and the buffer 3 constitute a waveform shaping circuit, and the detected waveform shown in FIG. 4(d) appears. It is compared and judged whether the time T2 from the first shot to the second shot of the detection waveform is within the normal time (bubble heat).

Figure 5 shows the case where air bubbles have entered the ink chamber.
) is the piezoelectric element drive waveform Vo. The DC component of this piezoelectric element driving waveform Vo is cut off by a filter composed of a capacitor 10 and a resistor 16, and the waveform becomes an oscillating waveform on the anode side of the diode 11 as shown in FIG. 5(b). Only the positive component is extracted by the diode 11, resulting in a waveform as shown in FIG. 5(c). The transistor 7 and resistors 17 and 18 form an emitter follower to lower the input impedance. Next, a waveform shaping circuit is configured with the transistor 8, resistors 19 to 21, and buffer 5, and the detected waveform shown in FIG. Compare and judge whether it is inside.

FIG. 6 shows a case where the ink is not filled, and FIG. The vibration waveform becomes as shown in b).

Only the positive component is extracted by the diode 11, as shown in Fig. 6 (c
) will have a waveform like this. Transistor 7, resistor 17.1
8 constitutes an emitter follower to lower the input impedance. Next, the transistor 8, the resistors 19 to 21, and the buffer 5 constitute a waveform shaping circuit, and the detected waveform shown in FIG. 6(d) appears. A comparison is made to determine whether the time T2 from the first to the second detection waveform is within the normal time.

From the explanations in Figures 4 to 6, the normal T2 is initially measured, and the normal T2 is applied to the processing device such as a microprocessor.
By storing 2fc and comparing the repetition time of the detection waveform with normal T2 at the time of detection, the presence of air bubbles and unfilled ink can be easily detected. After detecting an abnormality, the printer device automatically enters inkjet head cleaning operation, discharges air bubbles from the ink chamber, and fills the ink chamber, then drives the inkjet head, performs a detection operation, confirms that it is normal, and resumes normal operation. Automatic bubble detection recovery is now possible.

〔Effect of the invention〕

As explained above, according to the present invention, since the repetition frequency of the driving vibration waveform of the piezoelectric element is detected, it is possible to detect air bubbles in the ink chamber, unfilled ink, and clogged nozzles, and it is also possible to detect missing dots. When used in printers, etc., it is extremely effective in preventing and early detection of malfunctions such as printing mistakes. In addition, since the method detects the repetition frequency of the vibration waveform, even if the drive voltage of the print head has to change significantly due to temperature characteristics, the amplitude of the vibration waveform is proportional to the drive voltage, but the vibration period does not change, so detection is possible. The equipment is highly reliable.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a bubble detection device according to an embodiment of the present invention, Fig. 2 is a timing signal diagram showing a driving method of the same embodiment, and Fig. 3 is a cross section showing the mechanism of an inkjet head. Figure 4 (a), (b). (c) and (d) are timing signal diagrams explaining the detection circuit of Fig. 1 when no air bubbles are mixed in, and Fig. 5 (a) and (b).
), (c), (d) are timing signal diagrams explaining the detection circuit of FIG. 1 when air bubbles are mixed in, and FIG. 6(a),
(b), (c), and (d) are timing signal diagrams illustrating the detection circuit of FIG. 1 when ink is not filled. Applicant: Seiko Epson Co., Ltd. Representative Patent Attorney Tsutomu Mogami and 1 other person - No. 11)
20 Figure 3 Figure 5

Claims (1)

[Claims] In a bubble detection device for an on-demand inkjet recording head that performs inkjet recording by driving a piezoelectric element, the bubble detection device is connected to one end of the piezoelectric element via a resistor to the output terminal of a PNP transistor. The output terminal is connected to the one end of the piezoelectric element through another resistor, the emitter of the NPN transistor and another terminal of the piezoelectric element are connected to a common electrode, and the output terminal of the NPN transistor is connected to a high voltage power supply through a resistor. a piezoelectric element drive circuit to which an output end is connected and an emitter of the PNP transistor is connected to a high voltage power supply; a capacitor and a resistor are connected in parallel to the one end of the piezoelectric element; a connection end between the capacitor and the resistor; The apparatus further comprises a vibration waveform shaping circuit to which a diode anode is connected, and a means for detecting the repetition period of the piezoelectric element vibration waveform when the piezoelectric element is driven to detect the presence or absence of air bubbles in the head. Features: Air bubble detection device for inkjet recording heads.