JP2002001956A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make ink drip splash by using resonance of liquid and to reduce driving voltage. SOLUTION: A piezoelectric body 12 and a frame 13 surrounding the piezoelectric body 12 are bonded on the surface of a substrate 11. The upper surfaces of the piezoelectric body 12 and the frame 13 are positioned at about the same plane and an elastic plate 14 is bonded on the surfaces. Further, a channel plate 17 having a nozzle 15, a pressurized liquid chamber channel 16, and a common liquid flow chamber 18 is adhered on the top face of the elastic plate 14 to form a channel portion 19. Plural number of the channels 16 of the pressurized liquid chambers are arranged in parallel with each other, and the piezoelectric bodies which are substantially divided and independent are arranged so as to correspond to each channel. Therefore, ink drips are jetted out from the nozzles by causing excitation to the ink in the channels of the pressurized liquid chambers by applying alternation voltage whose main component for frequency is resonance frequency of ink to the piezoelectric bodies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink jet head, and more particularly to an ink jet head capable of reducing a driving voltage by causing ink droplets to fly by utilizing resonance of a fluid. For example, the present invention is applied to various printing apparatuses.

[0002]

2. Description of the Related Art Known documents describing a conventional ink jet head include, for example, (1) Japanese Patent Laid-Open No. 4-1414.
No. 28, (2) JP-A-4-341849,
(3) Japanese Patent Application Laid-Open No. 5-508 is known. In the above (1), the pressure generating member is excited at the natural period of the thickness vibration. That is, the natural period of the pressure generating member is extremely high, and the pressure material vibrates at the natural period. By controlling the driving time, sufficient gradation can be obtained without lowering the resolution. .

In the method (2), a voltage is applied at the resonance frequency of the piezoelectric substrate. That is, by disposing a pair of electrodes on the front surface and the back surface of the piezoelectric substrate, and selectively applying a voltage that changes at a period equal to the resonance frequency of the piezoelectric substrate between the electrodes, a minute liquid droplet can be accurately formed. The ejection is controlled in the direction. Further, the above (3) resonates a piezoelectric substrate capable of vibrating in an edge mode, that is, an alternating voltage which causes an electrode to vibrate in an edge mode is applied to the piezoelectric substrate to generate a vibration. The vibration propagates into the ink held in the gap, and becomes a surface wave to the boundary between the ink and the atmosphere, causing the ink to fly as a mist. Thus, the amount of ink to be mist is proportional to the application time of the alternating voltage, and the optical density of the dot itself changes continuously.

Conventional ink jet heads of the on-demand type include Kaiser, Stemme, Gould, etc. in which independent ink chambers are deformed by piezoelectric elements and ink is projected from nozzles corresponding to the respective ink chambers by the pressure. (The former) is its basic form. Furthermore, the vibration of the piezoelectric element is converted into lens sound,
Focusing with a lens or the like (for example, see JP-A-63-166)
No. 547) and a method utilizing the focusing effect of surface acoustic waves, for example, US Pat. No. 4,753,153.
No. 0 and U.S. Pat. No. 469,719 (the latter). The former method has the advantages that the structure is simple, the size can be reduced, and printing on plain paper is possible, and the latter method does not require a nozzle, bubbles,
There is an advantage that a decrease in reliability due to the entry of dust or the like can be avoided.

However, in the former method, since the upper limit of the driving frequency is about 10 KHz, it takes a very long time to print the gradation data and the like, so that the resolution has to be reduced, which is a practical situation. It is very difficult to realize a perfect full-color printing device. In the case of the latter method, the driving frequency is megahertz or higher, and it is considered that the disadvantage of the former method is improved in principle.However, when an acoustic lens is used, a pressure generating member and an acoustic lens are used. Alignment is difficult, and the energy loss in the acoustic lens is large. Those using surface acoustic waves are several tens of MHz.
If the driving frequency is not the above, the efficiency for obtaining a sufficient energy density becomes extremely poor, and for these reasons, a great increase in cost cannot be avoided.

Further, as means for improving these, Japanese Patent Laid-Open Publication No.
As described in Japanese Patent Application Laid-Open No. 508-508, by driving a substrate formed by a piezoelectric element at the cycle of its resonance frequency, and by enabling the vibration of the piezoelectric body to vibrate in an edge mode, the ink can be efficiently printed. It has been proposed that droplets can be generated and the structure can be simplified. However, since these means drive the substrate, which is the structure of the head, as a piezoelectric element using a resonance frequency, mutual interference caused by mechanical vibration propagating between the liquid chambers, and after the application of the drive signal is completed. However, mechanical vibration tends to remain, which may degrade the print quality.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an ink jet head in which ink droplets are made to fly by utilizing the resonance of a fluid to reduce the driving voltage. The purpose of this is to provide.

[0008]

The invention according to claim 1 has voltage applying means for applying a voltage to a piezoelectric body via an elastic plate to a plurality of pressurized liquid chambers arranged in parallel, An ink jet head that forms a pixel by ejecting ink droplets by applying a drive signal from the voltage applying unit to the piezoelectric body to excite the ink in the pressurized liquid chamber through the elastic plate, The drive signal is generated by a pre-excitation signal for generating a pre-pressure in the pressurized liquid chamber in a state where the ink does not reach the droplet formation, a main drive signal for subsequently causing the ink droplet to fly, and the main drive signal. It has three functions of a suppression signal for canceling the liquid chamber natural vibration and suppressing the ink pressure in the pressurized liquid chamber.

According to a second aspect of the present invention, in the first aspect of the present invention, at least a part of the drive signal is formed of a rectangular wave or a triangular wave. According to a third aspect of the present invention, in the first aspect of the present invention, the piezoelectric body is formed of a laminated piezoelectric element. According to a fourth aspect of the present invention, in the first aspect, the piezoelectric body is formed of a single-plate piezoelectric element.

According to a fifth aspect of the present invention, there is provided a voltage applying means for applying a voltage to the piezoelectric body via an elastic plate to a plurality of pressurized liquid chambers arranged in parallel. By applying a drive signal from the to the piezoelectric body to excite the pressurized liquid chamber ink through the elastic plate, an ink jet head that forms a pixel by flying ink droplets, the drive signal, A pre-excitation signal for generating a pre-pressure in the pressurized liquid chamber in a state where the ink does not reach the droplet flight, a main drive signal for continuously ejecting ink droplets, and a liquid chamber natural vibration generated by the main drive signal. And a suppression signal for suppressing the ink pressure in the pressurized liquid chamber by canceling the pressure.

[0011]

1 (a) and 1 (b) are structural views for explaining an embodiment of an ink jet head according to the present invention. FIG. 1 (a) is a sectional view, and FIG. It is a top view. In the figure, 11 is a substrate, 12 is a piezoelectric body, 13 is a frame, 14 is an elastic plate, 15 is a nozzle, 16 is a flow path of a pressurized liquid chamber, 17 is a flow path plate, 18 is a common liquid chamber, and 19 is a flow path. It is a road board. Hereinafter, the principle of the ink droplet flying provided by the ink jet print head will be described based on the configuration of FIGS. 1 (a) and 1 (b).

On a surface of a substrate 11 made of ceramic, silicon, metal or the like, a piezoelectric body 12 and a piezoelectric body 1 are provided.
A frame 13 made of resin, ceramic, metal, or the like, which is arranged so as to surround the frame 2, is joined. The upper surfaces of the piezoelectric body 12 and the frame 13 are positioned substantially on the same plane, and an elastic plate 14 formed of a resin film, a thin film metal member, or the like is joined thereto. Further, on the upper surface of the elastic plate 14, a nozzle 15 formed of Si, a metal material, or the like, a flow path plate 17 in which a pressurized liquid chamber flow path 16 and a common liquid chamber 18 are arranged are joined, and a flow path portion 19 is formed. Is composed. A plurality of the flow paths 16 of the pressurized liquid chamber are arranged in parallel, substantially divided so as to correspond to each of them, and independent piezoelectric members are arranged correspondingly.

Here, the flow path 16 of the pressurized liquid chamber is approximately equivalent to a pipe having both ends open. That is, the natural frequency f of the ink in the flow path of the pressurized liquid chamber in the first mode is f = C / 2L (where C: sound velocity in the ink, L:
Pressurized liquid chamber flow path). Here, the sound speed C in the ink changes depending on the Young's modulus of the flow path constituting member of the pressurized liquid chamber, but approximately C = 12.
If the pressure liquid chamber flow path length is L = 2 mm, the natural frequency is f
= 300 to 375 KHz.

Therefore, an alternating voltage having a frequency represented by the above-mentioned natural frequency f as a main component is applied to the ink in the flow path of the pressurized liquid chamber, and the piezoelectric body is excited. As a result, ink droplets are ejected from the nozzles. At this time, the resonance frequency of the piezoelectric body itself is set to be sufficiently large with respect to the natural frequency of the flow path of the pressurized liquid chamber, so that the piezoelectric body responds to the drive voltage waveform without time delay. be able to.

Since the resonance frequency varies among the pressurized liquid chambers, the ejection ink droplets vary. In order to make this uniform, it is preferable to adjust the drive voltage value. Further, the Q value at the resonance point can be controlled by appropriately selecting the materials of the constituent members of the liquid chamber. Therefore, the above-mentioned variation can be reduced by optimizing in consideration of efficiency. It is preferable to use a resin as a part of the material of the flow path plate 17 for controlling the Q value.

The resonance frequency is practically 100 KHz or more.
It is preferable to set the frequency to about 1 MHz. This will be described later, but the number of pulses and the number of gradations for forming one pixel, printing quality restrictions due to the relative moving speed of the printing paper and the head, the printing speed, and the like. This is a level suitable for ensuring compactness and cost reduction of the drive circuit, and the like. In addition, the level of the resonance frequency is related to the shape and size of the head as described above.
In addition, the size is appropriate in terms of design and processing.

FIGS. 2A and 2B and FIGS.
(B) is a diagram for explaining a drive voltage waveform applied to a piezoelectric body that is a pressure generating member of the inkjet head according to the present invention. As described above, the drive voltage waveform is composed of a continuous pulse group whose main component is the resonance frequency of the ink in the pressurized liquid chamber. Therefore, a plurality of droplets are caused to fly by a plurality of pulses, and one pixel is formed by the plurality of droplets. At this time, the number of pulses and the number of drops are not necessarily the same.

At this time, by controlling the number of pulses of the continuous pulse group to be driven, the number of ink droplets to fly, that is, the amount of ink droplets can be made variable. Therefore, the pixel diameter on the recording medium can be multi-valued, and recording with gradation can be easily performed. The continuous pulse group for forming one pixel is composed of a driving main pulse section (B in FIG. 2) and a residual vibration canceling pulse section (C in FIG. 2) of the preliminary pressure generation pulse section (A in FIG. 2). It is divided into three parts.

The preliminary pressure generating pulse section is at the head of the continuous pulse group, and excites the inside of the pressurized liquid chamber so as not to cause the ink to drop and fly, thereby increasing the ink pressure near the nozzle. That is, it is possible to suppress ink dripping and inhalation of bubbles. The drive main pulse section causes the ink droplet to fly in response to the applied pulse, following the preliminary generation pulse section. Therefore, the control of the ink droplet amount described above is executed in this portion.
The pulse group is mainly composed of the resonance frequency of the ink in the pressurized liquid chamber.

The residual vibration canceling pulse section immediately after the drive main pulse section applies a frequency component having an opposite phase to the main frequency component of the drive main pulse section, thereby rapidly increasing the ink pressure in the pressurized liquid chamber. Suppress. Accordingly, when the next continuous pulse group is applied, the ink pressure near the nozzle and the meniscus surface of the ink in the nozzle can be returned to the initial state level. That is, the response frequency of the driving pulse group can be increased.

A series of drive voltage waveforms may be a sine wave as shown in FIG. 2A or a rectangular wave as shown in FIG. 2B. Further, a triangular wave or the like may be used. The frequency component may be one whose main component is the resonance frequency of the ink in the pressurized liquid chamber described above. In reality, the waveform itself rises and falls with a time constant in accordance with the capacitance component of the piezoelectric element itself, which is a pressure generating member. In addition, the pre-generation pulse section is set to have the same frequency component as the driving main pulse section and lower only in the voltage level as shown in FIG. 2, or is set to have the same voltage level and different only in the frequency component as shown in FIG. It is possible to do. The same applies to the residual frequency canceling pulse section. Further, for the sake of simplicity, it is also possible to omit the preliminary pressure generating pulse section by making the leading part of the driving main pulse section also serve as the preliminary pressure generating pulse section.

In the above-described example, the period of the driving main pulse portion is about 3 μs, so that one pixel is composed of about 1 to 10 drops, and the substantial driving frequency is set to about 10 KHz, and multi-gradation is performed. Good to get. Further, when the stability of the ejection of the first droplet varies, the deterioration of the image can be prevented by setting the minimum pixel to two or three droplets.

As described above, the head according to the present invention does not directly convert the displacement of the pressure generating member into the volume displacement in the liquid chamber and ejects ink droplets, but utilizes the fluid resonance of ink. As a result, the driving energy can be significantly reduced. Therefore, as the pressure generating member, a piezoelectric body or the like on a thin film can be used in addition to the conventionally used single-plate and laminated piezoelectric elements.

FIG. 4 is a diagram showing another embodiment of the ink jet according to the present invention. In the drawing, reference numeral 20 denotes a thin film piezoelectric material (PZ).
T) and 21 are protective layers, and other portions having the same functions as those in FIG. 1 are denoted by the same reference numerals. A thin-film piezoelectric body 20 is provided on the surface of the substrate 11, and the thin-film piezoelectric body 20 is covered with a protective layer 21. As shown in FIG.
Are formed as shown in FIG. With this configuration, since the head can be easily mass-produced by batch processing, it can be significantly superior in terms of head processing.

FIG. 5 is a sectional view showing a head form of the ink jet head according to the present invention. The ink jet head shown in FIG. It has an opening. With such a configuration, it is possible to develop the head into a plurality of rows and the like, and to apply the head to a full line type head. As another configuration, by further combining with a heater device, application as a head using hot melt ink is also possible.

[0026]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to the first aspect: Since ink droplets fly using the resonance of a fluid, the drive voltage (drive energy) can be reduced (the vibration amount of displacement of the drive unit is small). Energy consumption is small). In addition, since the resonance point of the length of the pressurized liquid chamber flow path is used, the integration becomes easy without increasing the size of the recording head. Also,
Since the mechanical resonance point of the drive unit is not used, mutual interference due to mechanical vibration propagation between the liquid chambers can be significantly reduced. Further, even if the amount of mechanical displacement and vibration of the drive unit is small, sufficient pressure can be generated on the ink, so that the durability and reliability of the drive unit are significantly improved.

(2) Effect according to the second aspect: By making the number of pulses required to form one pixel variable,
The pixel diameter can be multi-valued, and recording with gradation can be performed. (3) Effect corresponding to the third and fourth aspects: the provision of the preliminary pressure generating pulse section and the residual vibration canceling pulse section before and after the driving main pulse section enables stable ink discharge by preventing ink dripping and suction of bubbles. It is. Further, the residual vibration can be quickly attenuated, and the driving frequency can be increased.

(4) Effect corresponding to claim 5: Since the frequency of the alternating pulse to be driven is on the order of 100 to 1 MHz, the circuit can be formed relatively easily without increasing the complexity and size of the drive circuit. (5) Effect corresponding to claim 6: Since the driving energy can be reduced, not only a bulk type piezoelectric body or the like but also a piezoelectric body formed on a thin film can be used. This allows
It significantly contributes to the improvement of mass productivity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an inkjet head according to the present invention.

FIG. 2 is a diagram (part 1) for describing a drive voltage waveform applied to a piezoelectric body of an ink jet head according to the present invention.

FIG. 3 is a diagram (part 2) for describing a drive voltage waveform applied to a piezoelectric body of the inkjet head according to the present invention.

FIG. 4 is a view showing another embodiment of the ink jet head according to the present invention.

FIG. 5 is a diagram showing a head configuration of an inkjet head according to the present invention.

[Explanation of symbols]

11: substrate, 12: piezoelectric body, 13: frame, 14: elastic plate, 15: nozzle, 16: flow path of pressurized liquid chamber, 17: flow path plate, 18: common liquid chamber, 19: flow path plate.

Claims (5)

[Claims] 1. A voltage applying means for applying a voltage to a piezoelectric body via an elastic plate to a plurality of pressurized liquid chambers arranged in parallel, and a driving signal from the voltage applying means is supplied to the piezoelectric body. In the ink jet head which applies ink to the body and excites the ink in the pressurized liquid chamber through the elastic plate, thereby causing ink droplets to fly to form pixels, the driving signal is such that the ink reaches the droplet flying. A pre-excitation signal for generating a pre-pressure in the pressurized liquid chamber in a state where no pressure is applied, a main drive signal for continuously ejecting ink droplets, and a liquid chamber natural vibration generated by the main drive signal to cancel the pressurized liquid chamber. An ink-jet head having three functions: a suppression signal for suppressing the ink pressure. 2. The ink jet head according to claim 1, wherein at least a part of the drive signal is formed of a rectangular wave or a triangular wave. 3. The ink jet head according to claim 1, wherein the piezoelectric body comprises a laminated piezoelectric element. 4. The ink jet head according to claim 1, wherein the piezoelectric body comprises a single-plate piezoelectric element. 5. A voltage applying means for applying a voltage to the piezoelectric body via an elastic plate with respect to a plurality of pressurized liquid chambers arranged in parallel, and a driving signal from the voltage applying means is provided. In the ink jet head which applies ink to the piezoelectric body to excite the pressurized liquid chamber ink through the elastic plate, thereby causing ink droplets to fly to form pixels, the driving signal is such that the ink becomes a droplet A pre-excitation signal for generating a pre-pressure in the pressurized liquid chamber, a main drive signal for continuously ejecting ink droplets, and pressurization by canceling the liquid chamber natural vibration generated by the main drive signal. A printing apparatus equipped with an inkjet head, which has three functions of a suppression signal for suppressing ink pressure in a liquid chamber.