JPH09141857A - Ink-jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet head in which the influence of an ink cavity on the replenishment of ink by the effect of a reflected wave is eliminated by a method in which a damper membrane is a single mode and oscillated at an intrinsic frequency to prevent the generation of the resonance of the reflected wave. SOLUTION: Part of the partition wall of an ink manifold 8 is formed with a flexible damper membrane 9, which is oscillated by the pressure wave of ink to absorb the pressure wave, and an oscillation mode in which the entire damper membrane 9 oscillates in the same phase and an intrinsic frequency which prevents the resonance of the reflected wave are given to the damper membrane 9 to eliminate the influence by the backward component of the pressure wave so that uniform discharge characteristics can be obtained every time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head for ejecting ink from an ink ejecting nozzle for printing and recording. More specifically, the vibration of a damper film absorbing a backward pressure wave propagating from an ink cavity to an ink manifold. The present invention relates to an inkjet head in which the mode and the natural frequency are adjusted to suppress the influence of reflected pressure waves on the ink ejection performance.

[0002]

2. Description of the Related Art In general, an ink jet head has a cavity plate 71 and a piezoelectric element plate 72 as shown in FIG.
And are combined via the diaphragm 73. And
A nozzle plate 78 having a nozzle hole 75 is provided at one end of the cavity plate 71, and a cavity chamber 76 for supplying ink to the nozzle hole 75 from the inside is provided inside the cavity plate 71.

The cavity chamber 76 and the nozzle hole 75
Are provided in parallel with each other in the thickness direction of the paper. Each cavity chamber 76 faces the piezoelectric element plate 72 via the vibrating plate 73, and the vibrating portion 72 of the piezoelectric element plate 72.
When a vibrates, it is selectively pressurized by the vibration. An ink manifold 77, which is a common ink supply path to each cavity chamber 76, is formed in the cavity plate 71.

With this ink jet head, the piezoelectric element plate 7
When 2 is driven to vibrate the vibrating portion 72a, each cavity chamber 76 is selectively pressurized and the pressure is propagated to the corresponding nozzle hole 75 to perform print recording by ejecting ink droplets. However, the pressure wave due to being pressurized in the cavity chamber 76 has not only the forward component toward the nozzle hole 75 but also the backward component toward the ink manifold 77.

The backward component is reflected by the ink manifold 77 and travels toward the nozzle hole 75 later than the forward component. Since the reflected wave is dispersed because the ink manifold 77 is common to the cavity chambers 76, the ejection of ink in the nozzle holes 75 cannot be caused by only a single reflected wave. This affects the recovery speed of the reduced ink amount, which in turn affects the ejection amount and ejection speed at the next ejection. Moreover, the degree of the influence varies depending on the number of channels that are driven at the same time, so that the amount and speed of the ejected ink vary each time, which causes the deterioration of print recording quality.

As measures against this, for example, Japanese Patent Publication No. 3-3050
A part of the wall surface of the ink manifold (for example, a portion indicated by an arrow A in FIG. 4) as described in Japanese Patent Laid-Open No. 2
There was a flexible film material. This is intended to eliminate the above-mentioned adverse effect by causing the volume variation in the ink manifold due to the vibration of the flexible film material, absorbing the backward component of the pressure wave, and preventing the generation of the reflected wave.

[0007]

However, even if a part of the wall surface of the ink manifold is made of a flexible film material as in the ink jet head described in the above publication, the generation of reflected waves is completely prevented. Can not do it. Especially,
Depending on the shape and material of the flexible film material, it may vibrate in a compound mode with nodes in the surface, in which case the volume fluctuation effect is greatly diminished, and the reflected wave of a size that cannot be ignored. Will occur. Further, although the generated reflected wave travels from the ink manifold to the nozzle hole via the cavity chamber, it is reflected again at the nozzle hole and returns to the ink manifold, so it may resonate depending on the natural frequency of the flexible film material. May occur and the attenuation may be significantly delayed.

In these cases, since the reflected wave of a magnitude that cannot be ignored affects ink replenishment from the ink manifold to the ink cavity, the amount and speed of ejected ink vary depending on the number of channels driven at the same time. The quality of print records will be reduced.

The present invention has been made to solve the above-mentioned problems of conventional ink jet heads.
By preventing the damper film from causing multi-mode vibration and having a natural frequency that does not cause resonance of the reflected wave, the influence of the reflected wave on ink replenishment of the ink cavity is eliminated, and print recording An object of the present invention is to provide an inkjet head that prevents deterioration in quality.

[0010]

In order to achieve the above object, the invention of claim 1 is such that an ink cavity filled with ink, an ink discharge nozzle provided in the ink cavity, and the ink cavity are in communication with each other. An ink jet head that has an ink manifold that supplies ink together, and an energy generation unit that faces the ink cavity, and presses the ink cavity by the energy generation unit to eject ink from the ink ejection nozzle, The damper film is provided on at least a part of the partition wall forming the ink manifold, and has a damper film having a vibration mode in which the entire surface in contact with the ink manifold vibrates in the same phase, and the damper film is reflected by the ink manifold. To the ink ejection nozzle,
It is characterized by having a natural frequency that does not resonate with the pressure wave that is reflected by the ink ejection nozzle again and reaches the ink manifold.

In this ink jet head, when the energy generating section is driven, the ink cavity filled with ink is pressurized by the energy generating section, and a pressure wave is generated in the ink. The advancing component of the pressure wave propagates from the ink cavity to the ink ejection nozzle, ejects ink, and prints and records. The receding component of the pressure wave propagates from the ink cavity to the ink manifold, causing the damper film to deform and vibrate. Since the vibration mode of the damper film is a mode in which the entire surface in contact with the ink manifold vibrates in the same phase, the volume variation effect of the ink manifold is large, and the backward component of the pressure wave is efficiently absorbed. In addition, since the damper film has a natural frequency at which the reflected wave reflected by the ink ejection nozzle again does not resonate, the reflected wave is quickly attenuated, which affects ink replenishment from the ink manifold to the ink cavity. Absent. Here, the energy generating unit is realized by, for example, a piezoelectric element.

The invention according to claim 2 is the ink jet head according to claim 1, wherein the natural frequency of the damper film is within the range described by the following equation.

[0013]

(Equation 1)

In this ink jet head, since the natural frequency of the damper film is within the range defined by the above mathematical formula, even if the damper film is reflected by the ink manifold, reflected again by the ink discharge nozzle and returned to the ink manifold, It does not resonate with the natural vibration of and decays early.

According to a third aspect of the present invention, there is provided the ink jet head according to the first or second aspect, which has a damper chamber provided on the opposite side of the damper film from the ink manifold. , The ink manifold and the damper chamber are separated from each other, and the ink manifold and the damper chamber are partitioned from each other, and also serve as a vibration plate that is sandwiched between the energy generating unit and the ink cavity to transmit a pressure applied by the energy generating unit to the ink cavity. And

In this ink jet head, the vibration of the damper film due to the backward component of the pressure wave is generated between the ink manifold and the damper chamber, and the pressure wave is absorbed. Since the damper film also serves as a vibration plate that transmits the pressure applied by the energy generating unit to the ink cavity, the number of parts is small, and the damper film does not form the outer shape of the inkjet head.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described in detail below with reference to the drawings. As shown in the cross-sectional view of FIG. 1, the inkjet head according to the present embodiment generally includes a combination of a cavity plate 1 and a piezoelectric element plate 2 with a flexible diaphragm 3 interposed therebetween. A nozzle plate 6 having a nozzle hole 5 is provided at one end of the cavity plate 1, and a cavity chamber 7 for supplying ink to the nozzle hole 5 from the inside is provided inside the cavity plate 1.

The cavity chamber 7 and the nozzle hole 5 are provided in parallel with each other in multiple channels in the thickness direction of the paper surface.
Each cavity chamber 7 faces the piezoelectric element plate 2 through the vibrating plate 3, and when the piezoelectric element plate 2 vibrates, it is selectively pressurized by the vibration so that a pressure wave is generated in the ink. There is. The cavity plate 1 is formed with an ink manifold 8 that is a common ink supply path to each cavity chamber 7. Ink manifold 8
Are provided so as to pass through the cavity plate 1 in the vertical direction in the figure, and the piezoelectric element plate 2 side (upper side in FIG. 1) is the vibration plate 3
And the opposite side is closed by a damper film 9 having flexibility similar to the diaphragm 3.

The piezoelectric element plate 2 is made of a material having a piezo effect such as PZT, and a portion facing the respective cavity chambers 7 through the vibrating plate 3 is a vibrating portion 2a.
The vibrating portions 2a are provided in parallel with each other in a multi-channel manner in the thickness direction of the paper, like the respective cavity chambers 7, and correspond one-to-one.
It is adapted to be selectively driven according to an input signal. Thereby, each cavity chamber 7 can be selectively pressurized.

The damper film 9 in the ink jet head is deformed when the ink in the ink manifold 8 is fluctuated in pressure, and vibrates due to its elasticity. Vibration characteristics are given so that the entire part to be vibrated becomes a single mode that vibrates in the same phase. The vibration characteristics of the damper film 9 are determined by the material, film thickness, aspect ratio, and the like. FIG. 2 shows an example of the situation of vibration of the damper film 9 in the single mode. Further, the natural frequency of the vibration is set within the range given by the following equation in order to effectively attenuate and eliminate the pressure wave of the ink.

[0021]

(Equation 1)

This equation is obtained by using the natural frequency fr and the required time AL.
It is required to have the product of 2 times the value of 0.2 to 1.5, and more preferably the range is 0.6 to 1.
2, and more preferably 0.8 to 1.1. Ideally it is 1. Here, the required time AL is twice as long as the reciprocating movement of the pressure wave of the ink is reflected after being reflected by the ink manifold 8 and then again by the nozzle hole 5 and returning to the ink manifold 8. is there. Here, the required time AL is determined by the distance from the ink manifold 8 in the cavity plate 1 to the nozzle holes 5 and the speed of sound in the ink (about 900 m / s).

When the product of fr and 2AL is equal to 1, the pressure wave reflected by the nozzle hole 5 and returned to the ink manifold 8 and the natural vibration of the damper film 9 are completely synchronized.
Since the nozzle hole 5 acts as a free end, the phases are reversed, and the phases cancel each other out and disappear. Then, if the value is in each of the ranges close to 1, the pressure wave is attenuated early and practically disappears. On the contrary, when the value is out of the range of 0.2 to 1.5, the pressure wave is not sufficiently canceled and remains without being attenuated, and a standing wave may be generated in some cases. It should be noted that the value is ideally 1 but is often about 0.9 due to the specific configuration of the inkjet head.

In such an ink jet head, ink is supplied from the ink manifold 8 to each cavity chamber 7 to fill it, and an input signal is applied to the piezoelectric element plate 2 to vibrate the vibrating portion 2a. The cavity chamber 7 corresponding to the vibrating vibrating portion 2a is pressurized,
A pressure wave is generated. This pressure wave has a forward component that propagates from the cavity chamber 7 to the corresponding nozzle hole 5 and a backward component that propagates to the ink manifold 8 in reverse.

When the pressure wave of the forward component reaches the nozzle hole 5 from the cavity chamber 7, ink droplets are ejected from the nozzle hole 5. The ink droplets adhere to the printing paper to form dots, so that print recording is performed. In addition,
Although the amount of ink in the cavity chamber 7 is reduced by ejecting ink droplets, ink is replenished from the ink manifold 8 in preparation for the next ejection.

On the other hand, when the pressure wave of the receding component reaches the ink manifold 8 from the cavity chamber 7, the pressure wave causes the damper film 9 to deform and vibrate. Along with this vibration, the volume of the ink manifold 8 fluctuates periodically, and the pressure wave is absorbed. This vibration is caused by the ink manifold 8
Is a single-mode vibration in which the entire part facing to the same phase vibrates in the same phase, and since no node is generated in the damper film 9 in the single-mode vibration, the volume is larger than that in the case of the vibration of other modes (composite mode). Large fluctuation and high vibration absorption efficiency.

The pressure wave cannot be completely absorbed even by the single mode vibration of the damper film 9, so that the pressure wave of the receding component is reflected in the ink manifold 8 and passes through the cavity chamber 7 of each channel. It goes to the nozzle hole 5 and is reflected again there to reach the ink manifold 8. Since the natural frequency of the damper film 9 is within the above range, the pressure wave returning to the ink manifold 8 cancels the vibration of the damper film 9 and disappears. Therefore, the pressure wave of the ink disappears early and the cavity chamber 7
It does not affect the ink replenishment from the ink manifold 8. Therefore, the state of the cavity chamber 7 is the same regardless of how many channels of the nozzle holes 5 are ejected at the same time during the previous ejection, and the print recording is performed with the same ejection amount and ink speed each time. Is good.

Next, a second embodiment will be described. As shown in the cross-sectional view of FIG. 3, the inkjet head according to the second embodiment is roughly composed of the cavity plate 1
1 and the piezoelectric element plate 12 are combined via a flexible diaphragm 3. A nozzle plate 6 having a nozzle hole 5 is provided at one end of the cavity plate 11, and a cavity chamber 7 and an ink manifold 18 are provided inside the cavity plate 11. That is, it has almost the same structure as that of the first embodiment. The base plate 4 is a base on which the inkjet head is mounted.

As a difference, the one shown in FIG. 3 does not have the damper film 9, and the cavity plate 11 itself forms the partition wall of the ink manifold 18 in that portion. Instead, a damper chamber 19 is provided in the piezoelectric element plate 12 and faces the ink manifold 18 with the vibration plate 3 interposed therebetween, where the vibration plate 3 partitions the damper chamber 19 and the ink manifold 18. The vibrating plate 3 in this portion can be deformed on both the damper chamber 19 side and the ink manifold 18 side, and can be vibrated by a pressure wave of ink. That is, in this ink jet head, by providing the damper chamber 19 in the piezoelectric element plate 12, a part of the vibration plate 3 plays a role of the damper film 9, and the number of parts is reduced. The vibration mode and the natural frequency of the relevant portion of the diaphragm 3 are given the same characteristics as those of the first embodiment. A vent hole 10 is provided to connect the damper chamber 19 to the outside.

In this ink jet head, the piezoelectric element plate 12 is driven to vibrate the vibrating portion 12a, so that ink droplets are ejected from the nozzle holes 5 by the advancing component of the pressure wave as in the first embodiment. Discharge is performed. Then, the receding component of the pressure wave is absorbed and disappeared by the vibration of the portion of the vibration plate 3 that divides the ink manifold 18 and the damper chamber 19. Here, the vibration is a single mode as in the case of the first embodiment, and the natural frequency thereof is within the range of the above mathematical formula, so that the pressure wave absorption efficiency is high.

Further, since the damper chamber 19 is communicated with the outside through the vent hole 10, even if the volume of the damper chamber 19 changes due to the vibration of the diaphragm 3, the pressure of the damper chamber 19 hardly changes. Contributes to efficiency. Furthermore, since the damper chamber 19 is covered with the piezoelectric element plate 12, the flexible diaphragm 3 is located inside the inkjet head and does not form an outer shape.

As described above in detail, in the ink jet head according to each of the above-described embodiments, a flexible member such as the damper film 9 or the diaphragm 3 is provided on a part of the partition wall forming the ink manifold 8 (18). By providing a specific vibration mode and a natural frequency within a specific range, the pressure wave of the ink is efficiently absorbed and disappears early. For this reason, the ink is replenished in the cavity chamber 7 without being affected by the reflected wave of the pressure wave. Also, print recording is performed at the ink speed, and high quality print results are obtained.

Further, in the second embodiment, since the part of the vibration plate 3 for transmitting the pressure from the piezoelectric element plate 12 to the cavity chamber 7 is made to play the role of the damper film 9, the flexibility is improved. The member does not form an inkjet head, and has high reliability in strength. Further, since the ventilation hole 10 is provided, the efficiency of pressure wave absorption is further increased. Further, it can be configured with a small number of parts.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various improvements and modifications can be made without departing from the gist of the present invention. For example, in the above-described respective embodiments, the entire piezoelectric element plate 2 (12) is formed of a material having a piezoelectric effect such as PZT.
It is sufficient that at least the vibrating portion 2a (12a) is formed of the material, and the damper chamber 19 in the second embodiment is used.
The surrounding portion and the like may be formed of ordinary ceramics, metal, resin or the like.

[0035]

As described above, according to the first aspect of the present invention, the damper film is prevented from causing the composite mode vibration, and has the natural frequency so that the resonance of the reflected wave does not occur. There is provided an inkjet head that eliminates the influence of the reflected wave on the ink replenishment of an ink cavity and prevents deterioration of print recording quality.

In particular, according to the second aspect of the invention, the natural frequency of the damper film is set with respect to the time required for the pressure wave to propagate from the ink manifold to the ink discharge nozzle in the ink cavity filled with ink. Since it is within the predetermined range determined by the above, there is provided an inkjet head in which resonance of reflected waves does not occur.

Further, according to the third aspect of the invention, the damper film divides the ink manifold from the damper chamber provided on the opposite side thereof, and transmits the pressure from the energy generating portion to the ink cavity. Therefore, the inkjet head that efficiently absorbs the reflected wave and eliminates the influence of the reflected wave on the ink replenishment of the ink cavity is provided with a small number of parts.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating single mode vibration of a damper film.

FIG. 3 is a sectional view showing a configuration of an inkjet head according to another embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a conventional inkjet head.

[Explanation of symbols]

 2, 12 Piezoelectric element plates 2a, 12a Vibration part 3 Vibration plate 5 Nozzle hole 7 Cavity chamber 8, 18 Ink manifold 9 Damper film 19 Damper chamber

Claims (3)

[Claims] 1. An ink cavity filled with ink, an ink discharge nozzle provided in the ink cavity, an ink manifold communicating with the ink cavity and supplying ink, and energy generation facing the ink cavity. And an ink manifold that is provided on at least a part of a partition wall that forms the ink manifold, and that uses the energy generation unit to pressurize the ink cavity to eject ink from the ink ejection nozzle. Has a damper film having a vibration mode in which the entire surface in contact with is vibrated in the same phase. The damper film is reflected by the ink manifold toward the ink discharge nozzle, and is reflected again by the ink discharge nozzle to reach the ink manifold. Resonance with pressure wave Jet head is characterized by having a free natural frequency. 2. The ink jet head according to claim 1, wherein a natural frequency of the damper film is The inkjet head is characterized by being within the range. 3. The ink jet head according to claim 1, further comprising a damper chamber provided on a side of the damper film opposite to the ink manifold, the damper film including the ink manifold and the damper chamber. And an ink jet head which is sandwiched between the energy generating section and the ink cavity and which also functions as a vibration plate for transmitting pressure applied by the energy generating section to the ink cavity.