JP2002144604A - Liquid ejector equipped with bubble detecting means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid ejector in which ejection of a liquid drop can be stabilized by preventing a piezoelectric element from deteriorating due to a bubble intruding into the pressure chamber or the nozzle in a piezoelectric element type liquid ejection head. SOLUTION: The liquid ejector is provided with a bubble detecting means 100 comprising a section 100a for applying a voltage between a common electrode 16 formed on the surface of a piezoelectric element in a shear mode type liquid ejection head and an electrode 28 formed at a part in a manifold 4 for distributing liquid to each pressure chamber 5, a section 100b for detecting a value varying depending on the presence/absence of a bubble in the liquid when a voltage is applied from the voltage applying section 100a, and a section 100c for judging presence/absence of a bubble based on a value detected at the detecting section 100b. Presence/absence of a bubble in the liquid is checked in the manifold 4 for distributing liquid to each pressure chamber 5, and recovery processing of a liquid ejection head is performed before the bubble enters each pressure chamber 5, thus preventing deterioration of the piezoelectric element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid ejecting apparatus for ejecting liquid from a nozzle hole, and more particularly, to a liquid ejecting apparatus for detecting the presence or absence of bubbles in liquid in a manifold which is a part of a liquid supply passage communicating with the nozzle hole. The present invention relates to a liquid ejecting apparatus including a detecting unit.

[0002]

2. Description of the Related Art There are various types of recording apparatuses used in printers, facsimile machines, etc., such as an electrophotographic system, a thermal system, and a liquid jet (ink jet) system. Among them, the liquid ejecting method is an effective recording method because the recording speed is high, the noise associated with the recording is relatively small, and colorization is easy. In recent years, various types of liquid ejecting systems have been proposed depending on the ejection system, and these have been put to practical use with improvements.

[0003] The liquid ejecting method is a method in which a recording liquid such as ink is ejected as small droplets by various ejection methods, and the droplet is attached to a recording medium such as paper. There are various methods, one of which is a method in which thermal energy is applied to a liquid to obtain a driving force for droplet discharge. That is, the liquid that has been subjected to the action of the thermal energy undergoes a state change accompanied by a sharp increase in volume, and the liquid is discharged from the discharge hole at the tip of the ejection head by an action force based on this state change.

On the other hand, as a method using a piezoelectric element (piezo element), there is a method in which a piezoelectric element is formed using piezoelectric coefficients d31 and d33 of a piezoelectric material. For example, it is configured by a liquid supply chamber communicating with the discharge hole, a pressure chamber communicating with the liquid supply chamber, a diaphragm provided in the pressure chamber, and a piezoelectric element joined thereto. The liquid discharge direction and the vibration direction of the piezoelectric element are the same. In such a configuration, when a predetermined voltage is applied to the piezoelectric element, the piezoelectric element expands and contracts, so that the piezoelectric element and the vibration plate generate a drum-shaped vibration, and the liquid in the pressure chamber is compressed, thereby causing the liquid to flow out of the discharge hole. Droplets are ejected.

There is another method using a piezoelectric coefficient d15 of a piezoelectric material. As a liquid jet head (usually called a shear mode) using this method, the surface of a piezoelectric material made of a piezoelectric material is used. A plurality of groove-shaped pressure chambers in parallel with each other, a plurality of connection terminals on the back surface, and selectively applying a voltage from each connection terminal to an electrode on the side of each pressure chamber to deform a partition wall between the pressure chambers. There is.

In manufacturing this type of liquid ejecting head, first, a plurality of grooves are formed in parallel on one surface of a piezoelectric body made of a piezoelectric material, and then the entire surface of the piezoelectric body including the inside of the grooves is electroless. A conductive layer is formed by plating or the like. Then, the conductive layer is divided into individual grooves by grinding or laser processing to form electrodes made of the conductive layer on the partition walls of each groove, and is also divided from the front end surface of the piezoelectric body to the conductive layer on the back surface. Thus, a plurality of connection terminals individually connected to the electrodes of each groove are formed. Then, by connecting a wiring material such as a flexible printed wiring board to the connection terminal, it is connected to the drive control unit of the liquid ejecting apparatus, and the drive voltage output from the drive control unit based on the ejection data is applied to the flexible printed wiring board. The liquid is applied to each partition via each connection terminal to deform the partition, and the liquid in each groove is ejected from the nozzle hole.

[0007]

The liquid jet head using the d15 mode piezoelectric material discharges the liquid in each groove (pressure chamber) from the nozzle hole.
When air bubbles enter the pressure chamber, particularly when the air bubbles enter the entire pressure chamber, the wall surface for discharging the liquid is driven without the resistance of the liquid, thereby deteriorating the piezoelectric material itself. For example, mechanical deterioration of the vibrating wall and the fixed portion, deterioration of polarization of the piezoelectric material, and the like occur.

As a result, stable ejection of droplets cannot be achieved,
Since a droplet cannot be attached to an appropriate position, an image drawn by a liquid jet recording head in particular deteriorates. Further, when the above phenomenon occurs continuously, there has been a problem that the droplet cannot be discharged.

In view of the above, the present invention has been made in view of the above-mentioned unresolved problems of the prior art, and has been made in consideration of the above problem. In a piezoelectric element type liquid ejecting head, a liquid in a manifold for distributing liquid to each pressure chamber is provided. Provided is a liquid ejecting apparatus which is provided with a bubble detecting means for detecting the presence or absence of air bubbles, and which can prevent the deterioration of a piezoelectric element caused by air bubbles entering a pressure chamber or a nozzle portion and stabilize the ejection of droplets. The purpose is to do so.

[0010]

In order to achieve the above object, a liquid ejecting apparatus according to the present invention comprises a plurality of pressure chambers each composed of at least a portion of a partition made of a polarized piezoelectric material; A plurality of electrodes for applying discharge energy to the liquid, and a plurality of connection terminals connected to the respective electrodes at positions outside the side surfaces of the partition wall of the piezoelectric material; and supplying the plurality of pressure chambers with the liquid. In the liquid ejecting apparatus having a manifold for performing the operation, a current is supplied between a part of the electrode formed on the surface of the piezoelectric element and at least one electrode formed in the manifold, so that bubbles in the liquid in the manifold are formed. And a bubble detector that detects a value that changes in accordance with the presence or absence of air bubbles and determines the presence or absence of air bubbles in the liquid in the manifold from the detected value.

In the liquid ejecting apparatus according to the present invention, the bubble detecting means may include a voltage applying unit for supplying a current between a part of the electrodes formed on the surface of the piezoelectric element and at least one electrode formed in the manifold. It is preferable to have a detecting unit that detects a value that changes according to the presence or absence of bubbles in the liquid due to energization by the voltage application unit, and a determining unit that determines the presence or absence of bubbles based on the value detected by the detecting unit. .

In the liquid ejecting apparatus according to the present invention, the value that changes according to the presence or absence of the bubble is a voltage value between a part of an electrode formed on the surface of the piezoelectric element and at least one electrode formed in a manifold. It is preferred that

In the liquid ejecting apparatus according to the present invention, it is preferable that the liquid ejecting apparatus further includes a bubble removing unit for removing bubbles in the liquid when the presence of bubbles in the liquid is detected by the bubble detecting unit. .

[0014]

According to the present invention, in a shear mode liquid jet head, a voltage is applied between a common electrode of a piezoelectric element and at least one electrode formed in a manifold to detect a potential difference between the electrodes. By detecting the presence or absence of bubbles in the liquid in the manifold that distributes the liquid to each pressure chamber, before the bubbles enter each pressure chamber or nozzle section,
Refreshing can be performed by the recovery processing of the liquid ejecting head, deterioration of the piezoelectric element can be prevented, and the liquid can be discharged stably, so that a high-quality and stable image can be obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an exploded perspective view showing the structure of a liquid ejecting head in a liquid ejecting apparatus according to the present invention.
FIG. 3 is a partial perspective view showing a state where the liquid ejecting head in the liquid ejecting apparatus of the present invention is viewed from below.

As shown in FIG. 1, the liquid ejecting head of the liquid ejecting apparatus according to the present invention includes a piezoelectric body 1, a plate member 2, an orifice plate 3, and a manifold 4. The piezoelectric body 1 is made of zirconium titanate. A plurality of piezoelectric materials made of ceramics such as lead oxide (PZT) or lead titanate (PT) are laminated. As shown in FIG. 2, a plurality of grooves (5, 6) cut through the respective layers are formed on the lower surface of the piezoelectric body 1, and the plurality of grooves alternately fill the liquid. A pressure chamber 5 for discharging and an air chamber 6 are formed. Each of the pressure chambers 5 has a liquid supply port 7 for receiving liquid supply and a liquid discharge port 8 for discharging liquid at both ends. Each air chamber 6 is formed to have a predetermined depth from the liquid discharge port 8 to the liquid supply port 7 at the rear end, and each air chamber 6 is formed to have a predetermined depth from the front end to the vicinity of the rear end. Arrow A at the rear end
As shown by, the piezoelectric body 1 is raised and closed so as to be flush with the lower surface of the piezoelectric body 1, and the rear end side is sealed so that liquid does not substantially flow. Also, at the tip of the piezoelectric body 1,
A vertical groove 10 is formed at a position corresponding to the air chamber 6.
As described above, the pressure chambers 5 and the air chambers 6 are alternately arranged in parallel with the piezoelectric partition 11 interposed therebetween.
Numeral 1 is composed of a plurality of layers of piezoelectric material polarized in directions opposite to each other with respect to the depth direction of the grooves (5, 6).

The electrodes of the piezoelectric body 1 are formed as follows. Ni (nickel) is deposited on the entire surface of the piezoelectric body 1 including the pressure chambers 5 and the air chambers 6 by vapor deposition or electroless plating.
After that, the front end surface 13 and the lower surface 14 of the piezoelectric body 1 are planarly cut or ground to remove the conductive layer. In the upper surface 12 of the piezoelectric body 1, as shown in FIG. 1, divided grooves 17 extending rearward from the front end side are formed at the center in the width direction of the upper surface corresponding to each air chamber 6. And the dividing groove 17
Divided groove 1 that intersects a plurality of divided grooves 17 at the rear end side
8 are formed, the conductive layer on the upper surface 12 of the piezoelectric body 1 is divided by the plurality of division grooves 17 and the division grooves 18, and the plurality of signal electrodes 15 and the common electrode 16 at other locations are formed. As a result, one electrode is formed on the inner surface of each pressure chamber 5, and two independent electrodes are formed on the inner surface of each air chamber 6. Then, the plurality of divided grooves 17 and the divided grooves 1
A connection terminal 21 is formed on each of the plurality of signal electrodes 15 divided by 8, and a connection terminal 22 is formed on the common electrode 16 therearound.

One pressure chamber 5 and two adjacent piezoelectric partition walls 11, which sandwich the pressure chamber 5, constitute a set of piezoelectric bodies, and the electrodes of the piezoelectric body in the pressure chamber 5 are formed on the rear end face of the piezoelectric body 1. Are electrically connected to the connection terminals 22 on the common electrode 16 side through the conductive layers of the piezoelectric chambers 11, and the electrodes of the piezoelectric partition walls 11, 11 on both sides of the pressure chamber 5 are connected to the conductive layers in the respective vertical grooves 10 of the air chamber 6. Is electrically connected to the connection terminal 21 of the electrode 15 via the first and second electrodes, and is separated and independent from the other sets of piezoelectric members by the dividing grooves 17 and 18.

A wiring material, that is, a flexible printed wiring board 23 is connected to the upper surface 12 of the piezoelectric body 1 on which the connection terminals 21 and 22 are formed by soldering or the like. A plurality of wirings 24 are formed on the flexible printed wiring board 23, and terminals 25 for connecting to the connection terminals 21 and 22 of the piezoelectric element by soldering or the like are formed at the ends of the wirings 24. . Flexible printed wiring board 2
The third wiring 24 is a drive control unit (not shown) of the liquid ejecting apparatus.
Connected to.

As shown in FIGS. 1 and 2, a flat plate member 2 made of a ceramic material or a resin material is formed on the lower surface of the piezoelectric body 1 constructed as described above using an epoxy adhesive or the like. And joined in a liquid-tight state. Thus, each pressure chamber 5 is covered with the plate member 2 so that only the front end and the rear end are opened. In addition, each air chamber 6 is covered with the plate member 2 so that only the front end is opened.

An orifice plate 3 in which a plurality of nozzle holes (discharge holes) 9 are formed is joined to the ends of the piezoelectric body 1 and the plate member 2 in a liquid-tight state using an epoxy-based adhesive or the like. The plurality of nozzle holes (discharge holes) 9 of the orifice plate 3 can discharge droplets corresponding to the pressure chambers 5, respectively.

A manifold 4 (FIG. 1) is joined to the rear ends of the piezoelectric body 1 and the plate member 2. A liquid supply hole 27 is formed in the center of the manifold 4, and the liquid supply hole 27 is a liquid tube 26. The manifold 4 receives the supply of the liquid from the liquid tube 26 and distributes the liquid to each of the pressure chambers 5. The manifold 4 is formed of an insulating member such as an organic resin (polypropylene).
This electrode 28 is for detecting a state such as the presence or absence of bubbles in the liquid in the manifold 4. Regarding the material of the electrode 28, the liquid used for the liquid ejecting apparatus may have an acidic or alkaline hydrogen ion concentration (pH). Therefore, the selection of the material depends on the composition of the liquid, but platinum Pt or gold Au or the like is used. It is preferable to use a metal stable to an acid or an alkali. FIG.
In (2), the electrodes are provided in a planar manner in the manifold 4, but the shape of the electrodes is not limited to this, and may be a pin shape or a large number of divided electrodes. A predetermined voltage is applied to the electrode 28 from a later-described bubble detection unit via a signal line 29.

According to the liquid ejecting apparatus having the liquid ejecting head configured as described above, the drive signal output from the drive control unit (not shown) through the flexible printed circuit board 23 is applied to the pair of electrodes of each piezoelectric body. 15 and 16, and grounding the electrode 16, an electric field is generated in the pair of piezoelectric bulkheads 11 in a direction perpendicular to the polarization direction, and the piezoelectric bulkheads 11 are deformed and the liquid in the pressure chamber 5 is formed. From the nozzle hole 9 as small droplets.

Next, a description will be given of a bubble detecting means for detecting the presence or absence of bubbles in the liquid in the manifold and a mode for detecting bubbles in the liquid in the liquid ejecting apparatus, with reference to FIGS.

FIG. 3 is a schematic view of bubble detecting means for detecting the presence or absence of bubbles in the liquid in the manifold for distributing the liquid to each pressure chamber in the liquid ejecting apparatus according to the present invention. (B) shows a state in which bubbles are mixed in the liquid in the manifold. FIG. 4 is a schematic diagram showing an example of a specific configuration of the bubble detecting means in the liquid ejecting apparatus of the present invention. FIG. 5 is an example of a signal waveform at each point in the bubble detecting means shown in FIG. Is shown.

The bubble detecting means 100 is connected to an electrode 28 formed in the manifold 4 to detect the presence or absence of bubbles in the liquid in the manifold 4 of the liquid jet head. The electrode 16 is grounded. Bubble detection means 10
0 is a voltage application unit 100a that conducts electricity between the electrodes 16 and 28.
And a detection unit 100b for detecting a value that changes according to the presence or absence of bubbles in the liquid due to energization by the voltage application unit 100a
And a determining unit 100c for determining the presence or absence of air bubbles from the value detected by the detecting unit 100b. The voltage is applied between the electrodes by the voltage applying unit 100a and a voltage is applied, so that the liquid in the manifold 4 is discharged. The detection unit 100b detects a value that changes according to the presence or absence of bubbles, and
At 00c, the presence or absence of bubbles in the liquid is determined. The values that change according to the presence or absence of bubbles include current, voltage, and resistance values between the electrodes, and the presence or absence of bubbles in the liquid in the manifold is determined by measuring any of these values. It is possible to do. When the bubble detecting means 100 detects and determines the state in which the bubbles 30 are mixed in the liquid in the manifold 4 as shown in FIG. 3B, it outputs a signal to that effect to the liquid ejecting apparatus. To the control means (not shown). The control means performs a recovery process of the liquid ejecting head according to the signal to remove bubbles in the liquid. In this recovery process, the liquid ejecting head performs a cleaning operation such as suctioning the liquid in the pressure chamber 5 from the nozzle hole 9 and refreshes the liquid ejecting head to ensure stable ejection of the liquid.

Next, an example of a specific structure of the bubble detecting means 100 will be described with reference to FIG. In FIG. 4, the bubble detecting means 100 includes a pulse generator 101, a capacitor C
102, a resistor R103, and a differentiating circuit composed of electrodes in the manifold 4; a gate 104; a peak hold unit 105; and a comparator unit 106. 5 is input to a differentiating circuit composed of a resistor R103 and an electrode (the waveform at point a in FIG.
Is shown as a waveform A). The differentiating circuit includes a pulse generator 10
The pulse signal generated in step 1 is differentiated and supplied to the electrodes. When there is a sufficient amount of liquid in the manifold 4 and the number of bubbles is extremely small, the waveform at the point b has a positive / negative voltage like a waveform B in FIG. Signal is generated. In addition, the gate 104
Open only when the voltage is in a positive state based on the pulse signal from the pulse generation unit 101 to allow only the positive voltage of the voltage signal applied to the electrode to pass. The waveform at point c is as shown in signal waveform C in FIG. That is, no matter what the voltage at the point b is, no negative voltage is generated at the point c. Then, since the output waveform of the gate 104 is a discontinuous waveform at zero when a negative voltage is applied to the liquid, as shown in a signal waveform C of FIG. The circuit supplies only a continuous positive signal to the comparator unit 106 as a continuous positive signal like the signal waveform D in FIG. Therefore, the peak hold unit 105 can be driven only by a positive power supply because only a positive signal is input.

As shown in FIG. 3B, when many bubbles 30 are mixed in the liquid in the manifold 4, the capacity and conductivity of the liquid between the electrodes 16 and 28 change. The value of the current, voltage or resistance between the electrodes changes. Therefore, in the comparator unit 106, for example, by setting a threshold voltage in advance, by comparing the detected value with the set threshold value,
The presence or absence of air bubbles can be detected. That is,
The pulse signal generated from the pulse generation unit 101 is supplied to the electrode of the differentiating circuit, and the voltage signal applied to the electrode is input to the comparator unit 106 as a continuous positive voltage signal via the gate 104 and the peak hold unit 105. You. The comparator unit 106 compares the detected voltage with a preset threshold voltage,
The presence or absence of air bubbles in the manifold 4 is detected. At this time, the comparator unit 106 includes the peak hold unit 1
5, a continuous positive signal like the signal waveform D of FIG. 5 is supplied, so that it is possible to perform comparison with an accurate threshold value without malfunction and to accurately detect and determine the presence or absence of a bubble. be able to. Further, for example, a built-in A / D converter can be configured to detect a multi-stage bubble level.

With the above configuration, it is possible to accurately detect the state in which the bubbles 30 are mixed in the liquid in the manifold 4 for distributing the liquid to each pressure chamber 5 in the liquid ejecting head with a simple configuration. Thus, the presence or absence of air bubbles can be detected before the air bubbles enter each of the pressure chambers and nozzles of the liquid ejecting head, and if air bubbles are mixed in the manifold 4, the recovery processing of the liquid ejecting head can be immediately performed. It can be carried out. Therefore, it is possible to avoid driving the piezoelectric element in a state in which bubbles enter the pressure chamber and there is no resistance of the liquid, prevent deterioration of the piezoelectric element, and refresh the liquid ejecting head by an operation such as cleaning. And the liquid can always be stably discharged.

[0031]

As described above, according to the present invention,
By detecting the presence or absence of bubbles in the liquid in the manifold, which is a part of the liquid supply path, in the liquid ejection head in the share mode, the recovery processing of the liquid ejection head is performed before the bubbles enter each pressure chamber or nozzle. Thus, the piezoelectric element can be prevented from deteriorating, and the liquid can be discharged stably, so that a high-quality and stable image can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a configuration of a liquid ejecting head in a liquid ejecting apparatus according to the present invention.

FIG. 2 is a partial perspective view showing a state where the liquid ejecting head in the liquid ejecting apparatus of the present invention is viewed from below.

FIG. 3 is a schematic view of bubble detecting means for detecting the presence or absence of bubbles in the liquid in the manifold for distributing the liquid to each pressure chamber in the liquid ejecting apparatus of the present invention. Indicating a normal state of filling, (b)
Indicates a state in which bubbles are mixed in the liquid in the manifold.

FIG. 4 is a schematic diagram illustrating an example of a specific configuration of a bubble detection unit in the liquid ejecting apparatus of the present invention.

5 shows an example of a signal waveform at each point in the bubble detecting means shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric body 2 plate member 3 orifice plate 4 manifold 5 pressure chamber 6 air chamber 7 liquid supply port 8 liquid discharge port 9 nozzle hole (discharge hole) 10 vertical groove 11 piezoelectric partition wall 12 (piezoelectric body) upper surface 13 (piezoelectric body) Tip surface 14 (piezoelectric) lower surface 15 Signal electrode 16 Common electrode 17, 18 Dividing groove 21, 22 Connection terminal 23 Flexible printed wiring board 24 Wiring 25 Connection terminal 26 Liquid tube 27 Liquid supply hole 28 Electrode 29 Signal line 30 Bubbles 100 Bubbles Detecting unit 100a Voltage applying unit 100b Detecting unit 100c Judging unit 101 Pulse generating unit 102 Capacitor 103 Resistance 104 Gate 105 Peak hold unit 106 Comparator unit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Atsuto Yamaguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2C056 EA15 EB09 EB33 EB39 EC24 EC49 EC54 FA04 2C057 AF78 AF80 AG45 AL18 AM33 BA05 BA14

Claims (4)

[Claims] 1. A plurality of pressure chambers, each of which is composed of a partition wall of a piezoelectric material at least partly polarized, and a plurality of electrodes that provide discharge energy to a liquid on a side wall of the partition wall of the piezoelectric material.
A liquid ejecting apparatus comprising: a piezoelectric element having a plurality of connection terminals connected to the respective electrodes at positions outside the partition wall side of the piezoelectric material; and a manifold for supplying a liquid to a plurality of pressure chambers. A current is applied between a part of the electrodes formed on the surface of at least one of the electrodes and at least one electrode formed in the manifold to detect a value that changes depending on the presence or absence of bubbles in the liquid in the manifold, and the detection is performed. A liquid detection device for determining whether there is a bubble in the liquid in the manifold from the measured value. 2. A voltage applying unit that applies current between a part of an electrode formed on a surface of the piezoelectric element and at least one electrode formed in a manifold,
A detection unit that detects a value that changes in accordance with the presence or absence of bubbles in the liquid due to energization by the voltage application unit, and a determination unit that determines the presence or absence of bubbles from the value detected by the detection unit. The liquid ejecting apparatus according to claim 1, wherein 3. A value that changes according to the presence or absence of the bubble is:
3. The liquid ejecting apparatus according to claim 1, wherein the voltage value is a voltage value between a part of the electrodes formed on the surface of the piezoelectric element and at least one electrode formed in the manifold. 4. The apparatus according to claim 1, further comprising a bubble removing unit for removing bubbles in the liquid when the bubble detecting unit detects the presence of bubbles in the liquid. 4. The liquid ejecting apparatus according to claim 3.