JP3419410B2 - Inkjet head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a nozzle for ejecting ink, a pressure generating chamber communicating with the nozzle for applying pressure to the ink, and pressure generating means for changing the pressure of the pressure generating chamber. The present invention relates to an ink jet head which ejects ink from the nozzle by changing the volume of the pressure generating chamber according to a signal applied to the means.

[0002]

2. Description of the Related Art A nozzle opening is provided in a pressure generating chamber whose one end communicates with an ink tank through an ink supply channel,
A means for generating pressure in the pressure generating chamber, for example, a part of the pressure generating chamber is formed into a diaphragm shape to form a deformable region, and an electromechanical displacement means for pressing this region is provided, and an ink droplet is ejected from the nozzle opening. Is configured to generate. Such an inkjet recording apparatus is required to have a high quality output image and a high output speed.
There is an urgent need to develop a technique for stably ejecting finer ink droplets at a higher frequency.

In determining the ejection characteristics of the ink droplets of the ink jet head, the main ink droplets are ejected at high speed, the generation of unnecessary ink droplets thereafter is suppressed, and the frequency at which ink droplets are repeatedly ejected is increased. It is very important to properly control the pressure oscillation in the pressure generating chamber. A technique in which an elastic wall that is deformed by pressure is formed as a thin portion in a pressure generating chamber and is optimally configured is disclosed in JP-A-6-320725.
Are disclosed in the specification. A technique for controlling the pressure in the pressure generating chamber by devising a driving method is disclosed in Japanese Patent Laid-Open No. 2-1.
It is disclosed in Japanese Patent No. 92947.

These conventional techniques focus on the natural vibration of the vibration system determined by the structure of the ink jet head, and try to control the generation of the vibration unique to this system.

In order to obtain good ink ejection characteristics, it is necessary to make the vibration peculiar to this system large when the ink droplets are ejected and small after the ink droplets are ejected, but it is necessary to make these two conditions compatible. Was very difficult because the natural vibration changes due to environmental changes such as temperature and manufacturing errors of the inkjet head.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel print quality and print speed. An object is to provide an inkjet head.

[0007]

In order to solve such a problem, in an ink jet head of the present invention, a nozzle for ejecting ink, a pressure generating chamber communicating with the nozzle for applying pressure to the ink, and the pressure A vibration plate serving as a bottom wall of the generation chamber, a piezoelectric element that is laminated on the vibration plate and deforms the vibration plate when a voltage is applied to expand or reduce the volume of the pressure generation chamber; There is provided an elastic wall that is deformable by the pressure generated in the pressure generating chamber, and an opposing wall that is arranged outside the pressure generating chamber so as to face the elastic wall, and is elastic by the pressure of the pressure generating chamber. When the wall is deformed,
The elastic wall is brought into contact with the facing wall. The elastic wall bends in proportion to the pressure when not in contact with the opposing wall. That is, it has the characteristic that the compliance defined by the volume change due to the deformation of the wall with respect to the unit pressure is constant. However, when the elastic wall comes into contact with the opposing wall, the deformation of the elastic wall due to the increase in pressure becomes small. That is, the compliance changes and becomes smaller. Since this compliance determines the natural period of the vibration system of the ink, the natural period changes depending on whether the elastic wall is in contact or not, and the natural period becomes short when the elastic wall is in contact. The natural period also changes depending on the degree of contact. When ink is ejected, a large positive pressure is generated. At this time, if the elastic wall abuts and the responsiveness of the system becomes faster, it is possible to eject ink droplets at high speed. Further, since the elastic wall is separated from the opposing wall after the ejection, the response of the system is delayed, and the fluid motion after the ejection can be relaxed. Further, in such a system in which the system characteristics change non-linearly, a specific vibration does not strongly oscillate, and unnecessary ink ejection is suppressed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The ink jet head of the present invention will be described in detail below.

A sectional view of an ink jet head of a reference example of the present invention is shown in FIG. 1, a plan view is shown in FIG. 2, and a sectional view in a plane orthogonal to FIG. 1 is shown in FIG. The silicon substrate 1 is subjected to etching from one surface of the substrate, so that the pressure generating chamber 4,
The ink supply path 5 and the groove serving as the common ink chamber 6 are processed and closed with the nozzle plate 2 to form a flow path. A nozzle 11 is formed in the nozzle plate 2 and communicates with the pressure generating chamber 4. The bottom wall of the pressure generating chamber 4 is composed of thin elastic walls 7 and 8 of the silicon substrate 1.

As shown in FIG. 2, ink from an external ink tank (not shown) is supplied from the ink supply port 14 to the common ink chamber 6, and from there, through the ink supply passage 5 to the plurality of pressure generating chambers 4. To be distributed.

A borosilicate glass substrate 3 having a thermal expansion coefficient close to that of silicon is bonded to the surface of the silicon substrate 1 on which the elastic walls 7 and 8 are formed. On the bonding surface of the glass substrate 3 with the silicon substrate 1, there are formed recesses 9 that are shallowly etched corresponding to the pressure generating chambers 4 of the silicon substrate 1, and the elastic walls 7 and 8 have very small gaps. It is opposed to the bottom wall of the recess 9 of the glass substrate 3 with a space between them.

A segment electrode 10 is formed on the bottom wall of the recess 9 of the glass substrate 3 so as to face the elastic walls 7 and 8 which also function as electrodes common to the pressure generating chambers. Insulating layer 1 made of formed inorganic glass
5, the elastic walls 7 and 8 and the segment electrode 10 are sandwiched by a gap.
Form a counter electrode.

The voltage applying means 13 applies a drive voltage to the counter electrode corresponding to the pressure generating chamber in response to a print signal from the outside (not shown). One output of the voltage applying means 13 is connected to each segment electrode 10, and the other output is connected to the common electrode terminal 12 formed on the silicon substrate 1. Since the silicon substrate 1 itself has conductivity,
A voltage can be supplied from the common electrode terminal 12 to the common electrodes of the elastic walls 7 and 8. Further, when it is necessary to supply a voltage to the common electrode with lower electric resistance, for example, a thin film of a conductive material such as gold is formed on one surface of the silicon substrate 1 by vapor deposition or sputtering. In this example, since the anodic bonding is used for bonding the silicon substrate 1 and the glass substrate 3, the conductive film is formed on the flow path forming surface side of the silicon substrate 1.

As described above, in this embodiment, the counter electrode is formed between the elastic wall and the counter wall which sandwiches the gap to form the pressure generating means. That is, when the driving voltage from the voltage applying means 13 is applied between the opposing electrodes, a Coulomb force is generated by the electric charges charged between the opposing electrodes, the elastic walls 7 and 8 are deflected toward the segment electrodes, and the pressure generating chamber is generated. Expand the volume of 4. Next, when the driving voltage from the voltage applying means 13 is drastically dropped to discharge the electric charge between the opposite electrodes, the elastic wall 8 is restored by the elastic force, and the volume of the pressure generating chamber 4 is rapidly contracted. Due to the ink pressure generated at this time, a part of the ink filling the pressure generating chamber 4 is ejected as an ink droplet from the nozzle 11 communicating with the pressure generating chamber 4.

In this example, the elastic wall has a thin portion 7 and a thick portion 8 in the longitudinal direction of the pressure generating chamber 4. Since the thin elastic wall 7 has low rigidity, the voltage applying means 13
When a voltage is applied between the segment electrode 10 and
It flexes more easily than the thick elastic wall 8, and as shown in FIG.
Abut the opposing wall at a lower voltage. In an actuator that applies a voltage between opposing electrodes to drive by Coulomb force, the driving force is proportional to the square of the voltage between opposing voltages and inversely proportional to the distance between opposing electrodes. When the elastic wall 7 is bent by applying a voltage,
The elastic wall 7 side is brought into contact with the opposing wall so that the elastic wall 7 side is pulled by the elastic wall 7. This action is due to the elastic wall 7 of the elastic wall 8.
The elastic wall 8 propagates from the side, and as a result, the elastic wall can be brought into contact with the opposing wall at a very low voltage as compared with the case where there is no elastic wall 7 having low rigidity and only the elastic wall 8 having high rigidity. It has become possible.

When the voltage is released after the elastic wall is brought into contact with the opposing wall, the Coulomb force disappears and the elastic wall tries to recover due to the elastic force. At this time, since the elastic wall 8 having high rigidity has a large elastic force, the elastic wall 8 responds faster than the elastic wall 7 having low rigidity, abruptly contracts the volume of the pressure generating chamber 4 at the elastic wall 8 portion, and Generates high ink pressure. The elastic wall 7, which has low elasticity, tries to recover very gently, but is prevented from being deformed by the ink pressure generated by the elastic wall 8 and maintains the state of being in contact with the opposing wall. In this state as shown in FIG. 4, the elastic wall 7 cannot be further deformed toward the opposing wall side by the ink pressure, so the compliance is very small. That is, the rigidity of the pressure generating chamber 4 is high (the compliance is small) at the time of ejecting the ink droplet, the large flow of the ink is rapidly generated, and the ink droplet is ejected at a high speed. The ink pressure in the pressure generating chamber 4 rises sharply and then sharply decreases to a negative pressure. Due to this negative pressure, the elastic wall 7 having low rigidity separates from the opposing wall and bends toward the pressure generating chamber 4 side as shown in FIG. When the elastic wall is separated from the opposing wall in this way, the elastic wall deforms in proportion to the pressure, so that the pressure generating chamber 4 has low rigidity (large compliance), reduces the vibration of the ink flow, and discharges the ink droplets. Vibration of the subsequent nozzle meniscus can be suppressed to a small level. After that, the vibration of the ink flow is gradually attenuated by the viscosity of the ink, and the elastic wall 7 absorbs the pressure of the pressure generating chamber 4 without contacting the opposing wall,
It is possible to suppress the generation of unnecessary ink droplets and shorten the time interval until the next ink droplet is ejected. That is, the frequency of ink droplet ejection can be increased. As mentioned above,
In this example, the elastic wall 8 having high rigidity functions as a pressure generating means, and the elastic wall 7 having low rigidity functions as an elastic wall that is deformable by the pressure of the pressure generating chamber.

In order to bring the elastic wall into contact with the opposing wall by the pressure of the pressure generating chamber 4, it is necessary to properly set the thickness of the elastic wall and the distance between the opposing wall and the gap. For example, a case where the pressure generating chambers are arranged at a density of 90 per inch will be specifically described. The width of the pressure generating chamber is 200 μm, the length of the pressure generating chamber is 3 mm, the thickness of the thin elastic wall is 3 μm, the thickness of the thick elastic wall is 5 μm, and the length of the thin elastic wall is 0.8 mm.
The length of the thick elastic wall is 2.2 mm, and the distance between the elastic wall and the opposing wall is 1 μm. At this time, the thin elastic wall abuts the opposing wall at a pressure of about 1 atm. Since the compliance is inversely proportional to the cube of the thickness of the elastic wall and proportional to the length of the elastic wall, the compliance ratio of the elastic wall is 5 for the thin elastic wall portion and 3 for the thick elastic wall portion. Therefore, when the thin elastic wall comes into contact with the opposing wall, the compliance is reduced to about 1/3, and the natural vibration period of the ink is shortened by 40%. That is, when the ink droplets are ejected, the pressure generating chamber 4
Is hard and becomes three times softer after ejection, and vibration of the meniscus after ejecting ink droplets quickly can be suppressed sufficiently small.

In this example, the elastic wall is made of B-doped silicon. That is, a layer having high etching resistance is formed by diffusing B from the surface of the silicon substrate 1, and an elastic wall is formed by leaving this layer by etching. Therefore, in order to change the thickness of the elastic wall, the silicon substrate 1 was masked to change the B doping depth.

In this example, the actuator utilizing the Coulomb force is used as the elastic wall deforming means for bringing the thin elastic wall 7 into contact with the bottom wall of the concave portion 9 serving as the opposing wall. It also serves as a pressure generating means for the wall 8 and a drive circuit. It is also possible to provide separate drive circuits for the regions of these two elastic walls, in which case finer control is possible. However, in this example, the elastic wall 8 is formed by a very simple electrode formation and driving method.
The elastic wall 7 abuts on the opposing wall in the preparatory stage of discharge for deflecting the pressure generating chamber 4 toward the opposing wall side. Therefore, the rigidity of the pressure generating chamber 4 becomes high from the beginning when the pressure of the pressure generating chamber 4 increases. The energy of the elastic wall 8 can be efficiently converted into ink droplet ejection.

As the elastic wall deforming means for bringing the elastic wall into contact with the opposing wall, in addition to the actuator using the Coulomb force, a very thin piezoelectric material is formed on the elastic wall by sputtering or the like, and the elastic wall and the piezoelectric element are separated from each other. It is also possible to apply a method in which the unimorph actuator is formed and the elastic wall is bent by applying a voltage to the piezoelectric element.

Next, FIG. 6 shows a sectional view of an ink jet head of another reference example.

In this example, the elastic wall 7 having low rigidity is formed on the ink supply path 5 side of the pressure generating chamber 4. This inkjet head provided more excellent characteristics as compared with the embodiment of the present invention shown in FIG. That is, when a voltage is applied between the opposing electrodes and the elastic wall 7 comes into contact with the opposing wall, the elastic wall 7 side is brought into contact with the opposing wall so that the elastic wall 7 side is pulled by the elastic wall 7. At this time, the elastic wall 8 bends from the ink supply path 5 side of the pressure generating chamber 4 toward the nozzle 11 side and contacts the opposing wall, so that a flow from the ink supply path 5 toward the nozzle 11 is generated. As a result, more ink can be ejected at a higher speed. This effect is effective in designing a smaller inkjet head.

Next, an ink jet head of another reference example will be described with reference to the plan view of FIG.

In this example, the width of the pressure generating chamber 24 is partially widened, and the width of the concave portion 29 of the glass substrates 23 to be laminated is also wide corresponding to the width of the pressure generating chamber 24, and the elastic wall 2 is formed in this portion.
Widened the width of 7. Further, in order to arrange the pressure generating chambers 24 at a higher density, the positions where the widths of the adjacent pressure generating chambers 24 are widened are shifted in the longitudinal direction of the pressure generating chambers. Compliance is approximately inversely proportional to the fourth power of the width of the elastic wall. Therefore, this wide elastic wall 27 has lower rigidity than the other narrow elastic wall 28 portions.

In this example, the width of the elastic wall 27 is set to 1.3 times the width of the elastic wall 28, and 50% of the compliance of the pressure generating chamber 24 is provided in the elastic wall 27 portion. When the elastic wall 27 comes into contact with the opposing wall by the elastic wall deforming means using Coulomb force or the ink pressure of the pressure generating chamber,
The rigidity of the pressure generating chamber 24 is halved, and the response of the ink flow can be improved. In addition, the width of the segment electrode 30 serving as the counter electrode is formed correspondingly to the width of the elastic wall 27, and the elastic wall 27 is brought into contact with the counter wall at a low voltage.

Next, the ink jet head of the embodiment of the present invention will be described with reference to the sectional view of FIG.

FIG. 8 is a cross-sectional view of the pressure generating chamber 4 taken along the longitudinal direction. The common ink chamber 6, the ink supply passage 5, and the flow passage connecting to the pressure generating chamber 4 are formed in the flow passage forming substrate 44. One surface of the flow path forming substrate 44 is closed by the nozzle plate 2, and the other surface is sealed by the vibration plate 48 to form a flow path. A nozzle 11 is formed in the nozzle plate 2 and communicates with the pressure generating chamber 4. The elongated piezoelectric element 40 is connected to the vibration plate 48 that serves as the bottom wall of the pressure generating chamber 4, and the other end of the piezoelectric element 40 is fixed to the frame 42. When a voltage is applied to this piezoelectric element 40,
The piezoelectric element 40 expands and contracts in the lengthwise direction, that is, perpendicularly to the vibrating plate 48 with the fixed portion as a fulcrum, and expands or contracts the volume of the pressure generating chamber 4. The pressure generating means using the piezoelectric element 40 has a large generating force and can eject ink droplets at high speed. However, when ink droplets are ejected at high speed, residual vibration of the ink flow after ejection is large, and unnecessary ink droplets are ejected after the main ink droplet. It is necessary to arrange an elastic wall that is deformed by the pressure of ink in the chamber 4 so as to mitigate a rapid rise of pressure. However, when such an elastic wall is provided, the ejection speed of the ink droplets decreases, the driving force of the piezoelectric element 40 is not effectively used, and the inkjet head has low efficiency. In this embodiment, the elastic wall 47 that is not joined to the fixed substrate 41 is formed at the end of the pressure generating chamber 4. The portion of the fixed substrate 41 that overlaps the elastic wall 47 forms a groove deeply in the periphery,
The adhesive for joining the diaphragm 48 and the fixed substrate 41 is the elastic wall 4
It is designed so that it does not flow into section 7. An island-shaped convex portion 43 was formed slightly indented from the surface of the fixed substrate 41 at the center where the groove was formed, and was formed as an opposed wall facing the elastic wall 47. The elastic wall 47 does not largely bend because it abuts on the opposing wall against a high positive pressure, and functions to eject ink droplets at a high pressure. For negative pressure, the bending pressure increases sharply in proportion to the pressure. Function to mitigate such changes.

[0028]

As described above, according to the ink jet head of the present invention, the elastic wall functions to eject the ink drop at a high pressure when ejecting the ink drop, and the ink vibrates after ejecting the ink drop. Since the main ink droplets are ejected at high speed, the ejection of unnecessary ink droplets after the main ink droplets can be suppressed and the time interval until the next ejection can be shortened. . This has the effect of providing an inkjet head with high responsiveness and excellent print quality.

Further, the rigidity of the pressure generating chamber, in other words, the degree of change in the volume of the pressure generating chamber due to the pressure of the ink chamber as defined by the compliance, can be set passively or actively by providing elastic wall deforming means. Can be changed to. When the compliance value of the pressure generating chamber changes, the natural vibration period of the ink flow in the pressure generating chamber changes. In the conventional inkjet head, since the natural period is constant, resonance between adjacent pressure generating chambers or driving of multiple pressure generating chambers emphasizes the deformation of the entire inkjet head, and ink droplet ejection becomes unstable. However, the print quality is deteriorated by inducing unnecessary ink droplet ejection, but in the present invention, the vibration after ink droplet ejection is not constant, and such crosstalk between pressure generating chambers is prevented. It has become possible to reduce it ultimately.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of an inkjet head according to a reference example of the present invention.

FIG. 2 is a diagram showing a planar structure of the inkjet head of FIG.

3 is a diagram showing a cross section of a pressure generating chamber of the inkjet head of FIG.

FIG. 4 is a diagram showing the operation of the elastic wall of the inkjet head of FIG.

FIG. 5 is a diagram showing the operation of the elastic wall of the inkjet head of FIG.

FIG. 6 is a diagram showing a cross section of an inkjet head of another reference example of the present invention.

FIG. 7 is a diagram showing a planar structure of an inkjet head of another reference example of the present invention.

FIG. 8 is a diagram showing a cross section of an inkjet head of an embodiment which is a feature of the present invention.

[Explanation of symbols]

1 Silicon substrate 2 nozzle plate 3 glass substrates 4 Pressure generation chamber 5 ink supply path 6 common ink chamber 7, 8 elastic wall 10 segment electrode 11 nozzles 13 Voltage applying means 15 Insulation layer 40 Piezoelectric element 41 Fixed board 43 Opposite wall 44 flow path forming substrate 47 elastic wall 48 diaphragm

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Claims (3)

(57) [Claims] 1. A nozzle for ejecting ink, a pressure generating chamber communicating with the nozzle for applying a pressure to the ink, a vibration plate serving as a bottom wall of the pressure generation chamber, and a vibration plate laminated on the vibration plate to which a voltage is applied. A piezoelectric element that expands or contracts the volume of the pressure generating chamber by deforming the vibration plate, an elastic wall in the pressure generating chamber that is deformable by the pressure generated in the pressure generating chamber, and the elastic member. And a facing wall arranged outside the pressure generating chamber so as to face the wall, and the elastic wall contacts the facing wall when the elastic wall is deformed by the pressure of the pressure generating chamber. Inkjet head to do. 2. The fixed substrate according to claim 1, further comprising: a fixed substrate to which a substrate forming the diaphragm is joined, the opposed wall is formed by a recessed portion of the fixed substrate, and the elastic wall is An ink jet head characterized by being formed by a portion of a substrate forming a diaphragm that faces the facing wall and is not joined to the fixed substrate. 3. The ink jet head according to claim 2, wherein a groove is formed around the opposing wall of the fixed substrate.