JPS5830146B2 - Air bubble remover - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bubble removing device for a pressurized on-demand ink jet recording apparatus.

For inkjet recording devices, the so-called pressurized on-demand method, in which an electric signal is applied to a piezoelectric element attached to an ejection head and ink particles are ejected using only the pressure waves generated by the electric signal, is widely used due to its simplicity. It is being

In this pressurized on-demand inkjet recording apparatus, as described above, the ink is not pressurized in the supply system, so if the ink supply system has poor circulation, air may be drawn in from the nozzles of the head.

In addition, when air bubbles enter the ink chamber of the head, the ink liquid becomes compressible and absorbs pressure waves, causing the vibrations of the piezoelectric element to not be transmitted to the ink, resulting in a reduction in the amount of ejection or a loss of ejection function. This will result in a suspension.

By the way, in an ink supply system, the ink in the tank is usually in contact with air, so air bubbles may get mixed in from the outside when refilling the ink, or air may dissolve in the ink itself due to external temperature changes. is liberated and air bubbles are generated, or air bubbles are generated due to organic substances contained in the ink.

Therefore, although various devices for detecting and removing air bubbles have been proposed in the past, all of them actively prevent and remove air bubbles, and do not take any measures to prevent an increase in the amount of dissolved air. It has not been erected either.

For example, the ink cartridge system (see Utility Model Publication No. 52-38215), which prevents air bubbles from entering the ink by supplying ink while blocking external air and ink, removes air bubbles that occur in the middle of the ink supply pipe. However, since it is disposable, it also has the disadvantage of being expensive.

Also, a method of installing an air trap device and a filter for removing air bubbles (JP-A-53-42033, JP-A-53-
45239), as the amount of air bubbles captured by the filter increases, fluid resistance also increases, the amount of ink supplied decreases, and jetting performance deteriorates, so a pressure sensing housing or flow rate sensing means must be provided separately.

The purpose of the present invention is to eliminate such drawbacks, to maintain stable head operation by always suppressing the amount of bubbles and dissolved air in the ink liquid below a certain value, and to provide an inexpensive and simple structure. The purpose of the present invention is to provide a bubble removing device.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of a bubble removal device according to the present invention.

Referring to FIG. 1, the path from the ink tank 12 through the ink supply tube 6 to the ejection head 2 is an ink supply system.

The air bubble removal device according to the present invention controls the operation of the air bubble removal device 10 provided in the ink supply system, the air bubble removal promotion device (for example, a heating device) 11 attached to the air bubble removal device 10, and the air bubble removal promotion device 11. It is comprised of a control circuit 9 for controlling, and a head drive and bubble detection circuit 8.

By applying a vibrator drive pulse PP from the outside, the head drive section of the head drive and bubble detection circuit 8 drives the electrostrictive vibrator 3 of the head 2 via the electrode lead wire 5.

In the injection head 2, as shown in FIG.
To correct the distortion by pulse driving, the diaphragm 4 bends to reduce the volume of the ink chamber 7, apply pressure to the ink, and eject ink droplets from the nozzle 1.

When the strain in the electrostrictive vibrator 3 disappears, the volume of the ink liquid chamber 70 returns to its original value.
Ink is replenished.

When air bubbles enter the ink liquid chamber T, the motional impedance of the electrostrictive vibrator 3, diaphragm 4, and ink liquid chamber 7 changes, so the head drive and bubble detection circuit 8
The detection unit detects this change, and activates the control circuit 9 to operate the bubble removal promoting device 11.

The bubble collection device 10 is constantly operating to remove bubbles, but when air bubbles are detected in the head 2, the bubble removal promotion device 11 is activated to collect and collect bubbles even more efficiently. Performs a removal action.

FIG. 3 is a cross-sectional structural diagram of the bubble collector shown in FIG. 1.

FIG. 3 shows a plurality of small ink chambers 13 communicating with each other, a collection hole 14 for collecting air bubbles attached to the upper part of each small liquid chamber 13, a communication pipe 16 connecting the collection holes 14, and a communication pipe 16. A bubble trapping device 10 and a bubble removal promoting device 11 each having a throttle valve 16' at the tip of 16 are provided.

Even when the bubble removal promotion device 11 is not operating, ink that enters the collection device 10 from the ink supply tube 6 on the right side sequentially passes through the small ink chambers 13 that communicate with each other and flows out into the tube 6 on the left side. On the other hand, the air bubbles contained in the ink rise while passing through the plurality of small liquid chambers 13, are collected upward through the collection hole 14, and are discharged through the communication pipe 16 through the throttle valve 16'. Ru.

In addition to the structure shown in FIG. 3, various structures of the bubble trapping device can be considered.

However, as used herein, detection of "bubbles" refers to detecting both the number of bubbles and the size of individual bubbles.

Next, when a heating device operates as the air bubble removal promoting device 11, for example, the ink passing through the collection device 10 is heated, and the amount of air or air bubbles dissolved in the ink liquid decreases as the temperature rises. As a result, a large amount of bubbles and dissolved air are removed from the ink liquid.

FIG. 4 is a detailed circuit diagram of the bubble removing device shown in FIG. 1, and FIG. 5 is an operation time chart of FIG. 4.

In FIG. 4, the electrostrictive vibrator 3, the head drive and bubble detection circuit 8, and the promoting device (heating device) 11 are shown within the chain line, and all parts outside the chain line are included in the control circuit 9.

In addition, in FIG. 4, the head drive and bubble detection circuit 8
As such, a bubble detection circuit previously proposed by the present inventors (see Japanese Patent Laid-Open No. 117530/1983) is used.

When a vibrator drive pulse PP as shown in FIG. 5a is applied to the head drive and bubble detection circuit 8, the output signal of the NAND gate 17 turns off the transistor 18 and turns on the transistor 19, causing the electrostrictive vibrator to turn off. A pulse voltage is applied to 21 to drive it.

When a predetermined amount or more of air bubbles enters the ink chamber 7 of the ejection head 2, the impedance changes based on the change in the amount of air bubbles in the head, resulting in a bubble detection signal (2) with a superimposed oscillating voltage as shown in FIG. is emitted, and a rectifier circuit consisting of a diode 35, a capacitor 36, and a resistor 49 produces
An output voltage VC as shown in is generated.

The (+)fltl input of the voltage comparator 37 has a reference voltage Vr.
ef is input, this reference voltage V ref and the output voltage ■.

are compared. 1. If the amount of bubbles is more than the specified amount,
The output (1)8 of the voltage comparator 37 becomes a low level L as shown in FIG.

This causes the flip-flop 40 to be set,
As shown in FIG. 5g, the output Q (control signal C0NT) of the flip-flop 40 becomes low level L.

The control signal C0NT is used as a signal to interrupt printing of a normal image or to generate an alarm.

On the other hand, the transistor 44 is turned off by the low level L of the control signal C0NT, so that the transistor 44 is turned off.
5 is turned on, the heating resistance element 46 of the bubble removal promoting device 11 is energized and generates heat.

Next, when the number of bubbles in the ink liquid chamber 7 of the ejecting head 2 becomes less than a predetermined amount, the bubble detection signal 1 of the bubble detection circuit 8 is
As shown in the waveform on the right end of 5th Eb, the vibration amplitude becomes smaller and the output of the rectifier circuit becomes ■.

As shown in FIG. 5C, the output voltage Vref becomes smaller than the reference voltage Vref, so the output 8 of the voltage comparator 37 becomes high level.

At the generation timing of the output MM2 of the multivibrator 48, the output of the AND gate 41 becomes high level H,
The signal passed through NOR gate 42 resets flip-flop 40.

Therefore, the control signal C0NT (Q output) becomes high level, transistor 44 is turned on, and transistor 45 is turned on.
is turned off, so that the heating resistance element 46 is no longer energized.

However, the delay time is guaranteed by using two mono-multi pie breaks 47°48, which avoids the transient time due to the time constant of the capacitor 36 and resistor 49 in the output VC of the rectifier circuit, and provides a stable This is to synchronize the voltage level with time.

Furthermore, the vibrator drive pulse Pp is a pulse for ejecting ink droplets during normal image printing, but it may also be generated specifically for checking the amount of air bubbles when the power is turned on.

Furthermore, the reset signal R8T may also be used as the device reset signal that is first generated when the power is turned on.

As described above, the present invention is a bubble removal device that includes a bubble detection device and a bubble removal promotion device, and in the embodiment, when a predetermined amount or more of bubbles is detected in the head, the bubble removal promotion device is activated. Although a case has been described in which the bubble removal promoting device is always driven.

In this case, the bubble detection device is used to interrupt normal image printing or generate an alarm using the control signal C0NT.

As explained above, according to the present invention, a bubble detection device,
By providing a bubble removal promoting device, when a predetermined amount or more of bubbles are detected, or at any time, the bubble collection and removal action is promoted, so the amount of bubbles and dissolved air in the ink liquid is suppressed to below a certain value. This ensures stable operation of the jet head.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a bubble removing device showing an embodiment of the present invention, FIG. 2 is a sectional view of the jetting head in FIG. 1,
3 is a cross-sectional structural diagram of the bubble collecting device shown in FIG. 1, FIG. 4 is a detailed circuit diagram of a bubble removing device showing an embodiment of the present invention, and FIG. 5 is an operation time chart of FIG. 4. . 1 nozzle, 2: injection head body, 3: electrostrictive vibrator, 4
: Vibration plate, 5: Electrode lead wire, 6: Ink supply tube, 7: Ink liquid chamber, 8: Head drive and bubble detection circuit, 9: Control circuit, 10: Bubble collection device, 11: Bubble removal promotion Device, 12: Ink tank, 13: Small ink chamber, 14: Air bubble collection hole, 15: Wall, 16: Communication pipe, 16
: Throttle valve, 17.39: NAND gate, 37: Voltage comparator, 40: Flip-flop, 47.48: Mono-multi vibrator.

Claims (1)

[Claims] 1. For a pressurized on-demand inkjet recording device that ejects ink particles by pressure waves generated by a piezoelectric element attached to an ejection head, an air bubble trap is provided on the way from an ink tank to the ejection head. A bubble removal device characterized in that a heating element is provided in at least a part of a small liquid chamber comprising an ink inflow hole, an outflow hole, and a portion for collecting gas, which constitute the bubble collection device. Device. 2. The bubble collecting device has a plurality of small liquid chambers each having an ink inflow hole, an ink outflow hole, and a portion for collecting gas, and is configured such that liquid flows through the plurality of small liquid chambers in order. A bubble removing device according to claim 1, characterized in that: 3. The heating element generates a motional current that changes depending on the presence or absence of air bubbles in the ejection head, among the current flowing through an electrostrictive vibrator for ejecting ink droplets attached to the ejection head.
2. The bubble removing device according to claim 1, wherein the bubble removing device is driven by the output of a bubble detection circuit that detects a current flowing in accordance with impedance.