JPS5830148B2 - 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

As mentioned above, this pressurized on-demand inkjet recording device does not pressurize the ink through the supply system, so if there is poor circulation in the ink supply system, air may be drawn in from the nozzles of the head. be.

Additionally, if 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 matter contained in the ink.

Therefore, although various devices for detecting and removing air bubbles have been proposed, none of them actively prevent or remove air bubbles and do not take any measures to prevent the 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, it has the disadvantage of being expensive because it is disposable and disposable.

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

Further, in the apparatus shown in FIG.
Once supplied to the dispensing device 21 in the jetting head 20,
The ink liquid is stored in the storage area, and the ink liquid is supplied to each recording nozzle 22 from there.

When bubbles and air 23 are collected above the dispensing device 21, the pressure of the ink 18 is increased by pressing the ink tank 17 with the instrument 25, and the bubbles and air 23 are collected.
3 is pushed out through the capillary tube 24.

After evacuation is performed in this manner, the capillary tube 24 is automatically closed (see Japanese Patent Laid-Open No. 52-49032).

However, since the device shown in FIG. 1 includes a bubble removal part that is integrated with the head 20, the structure of the head becomes complicated if the head is integrated, and if the structure of the head becomes complicated, It becomes impossible to accommodate a bubble eliminating portion sufficient to perform the i function.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and to provide a bubble removing device that is inexpensive, has a simple structure, and is highly effective.

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

FIG. 2 is a block diagram of a bubble removal device according to the present invention.

In FIG. 2, a bubble removing device according to the present invention is provided in the path from the ink tank 9 to the jet head 2 through the ink supply tube 8.

The bubble removing device according to the present invention includes a bubble collecting device 6 provided in an ink supply system, a stirring device 7 attached thereto,
It is comprised of a control circuit 5 that controls the operation of the stirring device 7, and a head drive and bubble detection circuit 4.

By applying a vibrator drive pulse PP from the outside, the head drive unit of the head drive rotation and bubble detection circuit 4 connects the electrostrictive vibrator 53 of the head 2 via the electrode lead wire 55 shown in FIG.
to drive.

In the ejection head 2, as shown in FIG.
3 is distorted by pulse driving, the diaphragm 54 bends, reducing the volume of the ink chamber 57, applying pressure to the ink, and ejecting ink droplets from the nozzle 1.

When the strain of the electrostrictive vibrator 53 becomes i, the volume of the ink liquid chamber 57 returns to its original value, so ink is thus replenished from the ink supply tube 8 to the ink liquid chamber 57.

When air bubbles enter the ink liquid chamber 57, the electrostrictive vibrator 53
Since the motional impedance of the diaphragm 54 and the ink chamber 57 changes, this change is detected by the detection section of the paddle drive rotation and bubble detection circuit 4, and the control circuit 5 is activated to operate the stirring device 7. .

The bubble collecting device 6 is constantly operating to remove unsteady bubbles, but when air bubbles are detected in the head 2, the agitation device I is activated to collect and remove bubbles even more efficiently. carry out an action.

FIG. 4 is a cross-sectional structural diagram of the bubble collector shown in FIG. 2.

In FIG. 4, a plurality of small ink chambers 10 communicating with each other, a collection hole 11 for collecting air bubbles attached to the upper part of each small liquid chamber 10, and a communication pipe 13 connecting the collection holes 11 are shown. A bubble collector 6 with a throttle valve 14 at the tip of the tube 13 and a stirring device 7 are provided.

Even when the agitation device 7 is not operating, the ink that enters the collection device 6 from the ink supply tube 8 on the right side passes through the small ink chambers 10 that communicate with each other in order and flows out into the tube 8 on the left side. The air bubbles contained in the ink rise while passing through the plurality of small liquid chambers 10 and reach the collection holes 11.
It is collected upward from the air, passes through the communication pipe 13, and is discharged from the throttle valve 14.

In addition to the structure shown in FIG. 4, various structures of the bubble trapping device 6 can be considered.

The stirring device 7 is composed of a motor and a screw 16.

Now, when the stirring device 7 is operated by the control circuit 5, the motor rotates and the screw 16 rotates, which speeds up the flow of the ink liquid in progress and removes the air bubbles contained in the ink in the small liquid chamber 10. becomes stimulated and easily floats upward.

Further, air bubbles and the like adhering to the wall 12 are also separated and floated, collected upward through the collection hole 11, and discharged to the outside from the throttle valve 14 through the communication pipe 13.

In this way, since the air bubbles in the ink liquid are expelled, the amount of air bubbles in the ink liquid can be reduced below a certain value, and the operation of the head 2 can be maintained stably.

FIG. 5 is a detailed circuit diagram of the bubble removing device shown in FIG. 2, and FIG. 6 is an operation time chart of FIG.

In FIG. 5, the electrostrictive vibrator 3, the head drive rotation and bubble detection circuit 4, and the stirring device 7 are each shown within the chain lines, and all parts outside the chain lines are included in the control circuit 5.

In FIG. 5, a bubble detection circuit previously proposed by the present inventors (see Japanese Patent Laid-Open No. 117530/1983) is used as the configuration of the head drive and bubble detection circuit 4.

Among them, the vibration drive pulse PP is a pulse for ejecting ink droplets (when printing a normal image), and may be generated particularly for checking the amount of air bubbles when the power is turned on.

Further, the reset signal Re5et is used as a signal to interrupt normal image printing or to generate an alarm.

When a vibration drive pulse PP as shown in FIG. 6g is applied to the head drive rotation and bubble detection circuit 8, the output signal of the NAND gate 1T turns off the transistor 28 and turns on the transistor 29, which turns off the electrostrictive oscillator. A pulse voltage is applied to 53 to drive it.

When a predetermined amount or more of air bubbles enters the ink chamber 57 of the ejection head 2, the impedance changes based on the change in the amount of air bubbles in the head, and the air bubble detection signal 1 with a superimposed oscillating voltage as shown in FIG. 6 is generated. A rectifier circuit consisting of a diode 35, a capacitor 36, and a resistor 49 produces the voltage shown in Fig. 6C.
An output voltage VC as shown in is generated.

The reference voltage Vref is input to the (→ inputs of the voltage comparator 37), and this reference voltage Vref and the output voltage .

are compared. Now, if the amount of bubbles is more than the predetermined amount,
The output 8 of the voltage comparator 37 is at the low level L as shown in FIG. .

This causes the flip-flop 40 to be set,
As shown in FIG. 6g, the output 4 (control signal C0NT) of the flip-flop 40 becomes a 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 low level L of the control signal C0NT turns off the transistor 44 and turns on the transistor 45, so that current flows through the motor windings of the stirring device 7, causing the motor to rotate and stirring to be performed by the screw 16. will be started.

Next, when the number of bubbles in the ink liquid chamber 57 of the ejection head 2 becomes less than a predetermined amount, the bubble detection signal 1 of the bubble detection circuit 4 is
As shown in the waveform at the right end of Figure 6, the vibration amplitude becomes smaller and the output of the rectifier circuit becomes ■.

As shown in FIG. 6C, the output voltage Vref becomes smaller than the reference voltage Vr e f, 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, and
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 no current flows to the motor of the stirring device 7.

In addition, this is the output of the rectifier circuit.The delay time is compensated using two mono multi-vibrators 47°48.

This is to avoid the transient time caused by the time constants of the capacitor 36 and the resistor 49, and to synchronize with the time of a stable voltage level.

The present invention is a bubble removal device equipped with a bubble detection device and a stirring device. In the embodiment, the case where the stirring device is driven when a predetermined amount or more of bubbles is detected in the head is explained, but the stirring device is driven at all times. , a stirring device may be driven.

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

As explained above, according to the bubble removing device of the present invention,
By providing a bubble detection device and a stirring 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 in the ink liquid,
The amount of dissolved air is suppressed below a certain value, ensuring stable operation of the jet head.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a conventional bubble removing device, FIG. 2 is a block diagram of a bubble removing device showing an embodiment of the present invention, FIG. 3 is a sectional view of the jetting head in FIG. 2, and FIG. FIG. 2 is a sectional view of the bubble collecting device, FIG. 5 is a detailed circuit diagram of the bubble removing device showing an embodiment of the present invention, and FIG. 6 is an operation time chart of FIG. 1: Nozzle, 2: Ejection head, 3: Electrostrictive vibrator, 4: Head drive rotation and bubble detection circuit, 5: Control circuit, 6: Bubble collector, T: Stirring device, 8: Ink supply tube, 9
: Ink tank, 10: Small ink chamber, 11: Bubble collection hole, 12: Wall, 13: Communication pipe, 14: Throttle valve, 16:
Screw, 37: Voltage comparator, 39: NAND gate, 4°: Flip-flop, 47.48: Mono-multi pie break

Claims (1)

[Claims] 1. A pressurized on-demand printer that ejects ink particles using pressure waves generated by a piezoelectric element attached to an ejecting head.
A bubble collecting means is inserted into the inkjet recording device from the ink tank to the ejecting head, and collects the bubbles that rise when the ink liquid passes through the small ink chambers communicating with the ink liquid. A bubble removing device comprising means for stirring the ink liquid inside the bubble collecting means. 2. The bubble removing device according to claim 1, wherein the stirring means operates when the presence of bubbles on a predetermined location within the ink liquid chamber of the ejecting head is detected.