JPS5830149B2 - 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 inkjet recording apparatus, and more particularly to a vibration type bubble removing device.

As an inkjet recording device, the single-pressure on-demand method is widely used due to its simplicity, which is a method in which an electric signal is applied to a piezoelectric element attached to the ejection head, and the resulting pressure waves are used to eject ink droplets. It is used.

In this pressurized on-demand inkjet recording apparatus, ink is supplied from an ink supply tube 6 to an ink liquid chamber in an ejection head 2, as shown in FIG.

In the ejection head 2, by applying a vibrator driving pulse to the electrostrictive vibrator 3 through the lead 5, the electrostrictive vibrator 3 is distorted and the diaphragm 4 is bent, reducing the volume of the ink liquid chamber and causing the ink to Pressure is applied to eject ink droplets from nozzle 1.

When the strain in the electrostrictive vibrator 3 disappears, the volume of the ink liquid chamber returns to its original level, so ink is replenished from the ink supply tube 6 to the ink liquid chamber.

In such an ejecting head 2, the ink is not pressurized through the supply system, so if the flow rate of the ink supply system is poor, air may be drawn in from the nozzles 1 of the head 2.

In addition, in the ink supply system, the ink in the tank usually bleeds when it comes into contact with air, so when refilling the ink, air bubbles may form from outside or dissolve into the ink itself due to external temperature changes. The air in the ink may be liberated, causing bubbles to form, or the organic matter contained in the ink may also cause bubbles to form.

Then, when air bubbles get mixed into the ink liquid chamber of the head 2,
Since the ink liquid is compressible and absorbs pressure waves, the vibration of the piezoelectric element is not transmitted to the ink, resulting in a reduction in the amount of ejection or a stoppage of the ejection function.

Therefore, various methods have been proposed to detect and remove air bubbles from entering the jet head 2.
In either case, no measures are taken to actively prevent or remove air bubbles, and no measures are taken to prevent an increase in the amount of dissolved air.

Conventionally, for example, "exhaust device for ink supply device in inkjet recording device" (Japanese Patent Laid-Open No. 52-4903
(Refer to Publication No. 2), when ink is supplied to the ejection head, it is stored in a distribution device, from which the ink liquid is supplied to each nozzle, and air bubbles and air are collected above the distribution device. Then, by pressing the ink tank side, bubbles and air are pushed out through the capillary tube connected to the dispensing device.

However, in this method, since the head and the bubble eliminating section are integrated, the structure becomes complicated when the head is integrated, and the function of the bubble eliminating section is degraded.

Therefore, the inventors of the present invention first developed A: a bubble trap that provided a plurality of small liquid chambers through which the ink liquid passed sequentially, and discharged the air bubbles floating in the small liquid chambers through an upper communication pipe and a throttle valve. Collecting device” (see specification of Japanese Patent Application No. 141430/1983), B “
"Bubble removal device provided with a bubble collecting means, a means for accelerating bubble collection and removal, and a means for detecting air bubbles mixed in the head on the way from the ink tank to the jetting head" (Patent application No. 5)
3-141429), and C “Ink・
A bubble removal device that is equipped with a bubble collecting means and a means for stirring the ink liquid inside the bubble collecting means on the way from the tank to the jetting head.
(See the specification of Japanese Patent Application No. 53-165016).

However, since the device A is not provided with a bubble collection promoting means, it is not possible to enhance the bubble collection effect, and it is not possible to detect the inclusion of air bubbles in the head.

Next, in the device B described above, only a method of heating the ink liquid to grow and float the bubbles is used as a means for promoting bubble collection and removal.

Furthermore, the device C described above is only provided with a means for stirring the ink liquid as a means for promoting bubble collection and removal.

An object of the present invention is to propose a bubble removing device that is inexpensive, simple in structure, and highly effective, and also to provide a device that uses a method other than heating and stirring the ink liquid as a means for promoting bubble removal. .

The bubble removing device according to the present invention is a pressurized on-demand inkjet recording device, in which a bubble collecting means is provided on the way from the ink tank to the ejection head, and a bubble removing device is provided to promote the bubble collecting and removing action. It is characterized by the addition of a vibration means and a means for detecting air bubbles in the ejection head.

Hereinafter, embodiments of the present invention will be explained with reference to the drawings. Fig. 2 is a block diagram of a bubble removing device according to the present invention.

The present invention provides an ink supply tube 6 from an ink tank 9.
A bubble collecting device 8 provided on the way to the ejection head 2 through the
The head drive and bubble detection circuit 10 includes a control circuit 11 that controls the operation of the head drive and bubble detection circuit 10.

In FIG. 2, when a bubble enters the ink chamber of the ejection head 2, the motional impedance of the electrostrictive vibrator 3, diaphragm 4, and ink chamber changes, so the head drive rotation and bubble detection circuit change. This change is detected by the detection unit 10, and the control circuit 11 is activated to operate the vibration device 7.

The air bubble collecting device 8 is always in operation and removes air bubbles mixed in the ink liquid being supplied. However, when air bubbles are mixed into the head 2, this is detected by the detection circuit 10. By operating the vibration device 7, the bubble collection and removal action is promoted.

FIG. 3 is a cross-sectional structural diagram of the bubble collector shown in FIG. 2.

In FIG. 3, a plurality of small ink chambers 12 that communicate with each other, a collection hole 14 installed above each small liquid chamber 12, a communication pipe 15 connecting each collection hole 14, and a communication pipe 15 are shown. A bubble collecting device 8 having a throttle valve 16 at the tip thereof is provided, and a vibrating device 7 is added below the bubble collecting device 8.

When the vibration device 7 is in full operation, ink entering the collection device 8 from the ink supply tube 6 on the right side passes through the small ink chambers 12 that communicate with each other in order and flows out into the tube 6 on the left side.

On the other hand, air bubbles contained in the ink are stored in a plurality of small liquid chambers 12.
While passing through the ink, it floats in the ink, is collected upward through the collection hole 14, passes through the communication pipe 15, and is discharged from the throttle valve 16.

The vibration device 7 is, for example, an electrostrictive vibrator.

Now, when the vibration device 7 is activated by the control circuit 11,
Due to the vibration of the electrostrictive vibrator, the air dissolved in the ink liquid is excited and precipitated in the liquid, and further floats to the top of the bubble collection device 8 due to buoyancy and passes through the collection hole 14 and the communication pipe 15.
Since the air is discharged from the throttle valve 16, the amount of air is reduced, and the air bubbles adhering to the tube wall 13 and the like are peeled off, thereby promoting the buoyancy of the air bubbles.

As a result, the action of collecting and removing air bubbles is promoted, and a large amount of air and air bubbles are collected upward from the collection hole 14.
Since the ink is discharged to the outside from the throttle valve 16, the amount of bubbles in the ink liquid becomes less than a certain value, and the operation of the head 2 is maintained stably.

FIG. 4 is a detailed circuit diagram of the bubble removing device shown in FIG. 2, and FIG. 5 is an operation time chart of FIG. 4.

In FIG. 4, the part within the broken line is the drive circuit 3 of the electrostrictive vibrator 3 attached to the head 2 and the bubble detection circuit, which is the bubble detection circuit (specifically (See Japanese Patent Publication No. 117530/1983) is used.

The vibration drive pulse PP in FIG. 4 may be a pulse for ejecting ink droplets applied during normal image printing, or a pulse applied for checking the amount of bubbles when the power is turned on.

Further, the reset signal Re5et is a signal for interrupting normal image printing or a signal for generating an alarm.

When the vibration drive pulse Pp is applied, the NAND gate 1
Since the output signal of 7 turns off the transistor 18 and turns on the transistor 19, a pulse voltage is applied to the electrostrictive vibrator 3 of the ejection head 2, and this is driven.

Now, when bubbles exist in the ink liquid chamber of the ejection head 2, both the number of bubbles and the size of each bubble are detected, and due to the change in impedance, an oscillating voltage as shown in Figure 5 is superimposed. A bubble detection signal (1) is generated, and a rectifier circuit consisting of a diode 35, a capacitor 36, and a resistor 49 produces an output voltage (2) as shown in FIG. 5C.

occurs. The reference voltage V is input to the (→) input of the voltage comparator 37.
ref is input, and the reference voltage V is input as shown in Figure 5C.
r e f and output voltage■.

are compared. Now, if the amount of bubbles is more than the predetermined amount,
The output vR of the voltage comparator 37 becomes a low level L9 as shown in FIG. 5d, and the output of the NAND gate 39 becomes a low level L at the timing of the output MM2 of the monostable multivibrator 48.

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

As a result, the transistor 44 is turned off and the transistor 45 is turned on, so a voltage is applied to the electrostrictive vibrator 46 and vibration starts.

When the vibrating device 7 is driven and the number of bubbles in the ink liquid chamber of the ejecting head 2 becomes smaller than a predetermined amount, the bubble detection signal 1 of the bubble detection circuit has an amplitude as shown in the waveform at the right end of Figure 5. ■The output of the rectifier circuit becomes smaller.

As shown in FIG. 5C, the output VR of the voltage comparator 37 becomes a high level H.
becomes.

At the generation timing of the output MM2 of the multivibrator 48, the output of the AND gate 41 becomes high level H.
Since the flip-flop 40 is reset and the Q output becomes high level H, the transistor 44 is turned on and the transistor 45 is turned off, so that no voltage is applied to the electrostrictive vibrator 46 of the vibration device I.

Note that the Q output of flip-flop 40 is the control signal C
As 0NT, it is used to interrupt printing of a normal image or to generate an alarm.

In the embodiment, the vibration device 7 is driven when a predetermined amount or more of bubbles are detected in the head 2, but the vibration device 7 can also be driven constantly.

As explained above, according to the bubble removing device of the present invention,
By providing a bubble detection device and a vibrating 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 maintained below a certain value, ensuring stable operation of the injection head.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the jetting head, 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 bubble collecting device in FIG. 2, and FIG. This figure is a detailed circuit diagram of the bubble removing device shown in FIG. 2, and FIG. 5 is an operation time chart of FIG. 4. 1: Nozzle, 2: Ejection head, 3: Electrostrictive vibrator, 4: Vibration plate, 5: Lead wire, 6: Ink supply tube, 7: Vibrator, 8: Bubble collector, 9: Ink tank , 10
: Head drive rotation and bubble detection circuit, 11: Control circuit, 1
2: Small ink chamber, 13: Pipe wall, 14: Bubble collection hole, 1
5: Communication pipe, 16: Throttle valve, 37: Voltage comparator, 39:
Nando Gate, 40: Flip Flop, 47.4
8: Monostable multivibrator, child. 46 dielectrostrictive vibration

Claims (1)

[Scope of Claims] 1. In a bubble removing device in which a bubble collecting means is provided on the way from an ink tank to an ejection head of a pressurized on-demand inkjet recording device, the ink liquid inside the bubble collecting means is What is claimed is: 1. A bubble removing device comprising: a vibrating means including an electrostrictive vibrator controlled by a control circuit to vibrate the air bubbles. 2. The vibrating means is driven by a bubble detecting means detecting a change in mechanical impedance that changes depending on the amount of bubbles in the liquid as seen from an electrostrictive vibrator of an ejection head. Air bubble removal device as described in section.