JPH07156408A - Bubble jet recording head and apparatus - Google Patents

Abstract

PURPOSE:To freely perform high-grade gradation recording by simple constitution without decreasing a recording speed. CONSTITUTION:In a BJ recording head 1 wherein an ink droplet 26A is emitted from an ink emitting orifice 4 by driving the electrothermal converter 9 arranged at the position opposed to the ink emitting orifice 4 of a pressure chamber 5, a means 10 changing the shape of the pressure chamber in order to change the size of the emitted ink droplet is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses foaming energy generated by a heating element in a recording head of an ink jet recording apparatus for recording characters and images by ejecting minute ink droplets toward a recording material such as paper. A bubble jet (BJ) recording head and a recording device for ejecting ink,
In particular, the present invention relates to a BJ recording head and a recording device capable of changing the volume of ejected ink droplets.

[0002]

2. Description of the Related Art Conventionally, an ink jet recording apparatus has been known which ejects fine ink droplets for recording. Compared to other recording devices, this device has many advantages such as high-speed recording, easy colorization, recording on plain paper, low noise, and good recording quality.

In such an ink jet recording apparatus,
The BJ recording head is provided with at least an ink ejection port for ejecting ink and a pressure chamber communicating with the ink ejection port and emitting energy for ejecting ink, and selectively according to recording information input to the recording head. An ink droplet is ejected from the ink ejection port to form characters and images on the recording material.

FIG. 7 shows an example of the structure of a conventional ink jet recording head.

Here, 21 is the BJ recording head, 22
Is a base material formed by pressing, molding, electroforming, or the like, 23 is an orifice plate whose peripheral portion is joined to the base material 22, and 24 is an ink discharge port formed in the orifice plate 23. It should be noted that the base material 22 is provided with an ink supply path 27 for guiding the ink 26 from the ink containing portion (not shown) to the pressure chamber 25. 28 is the base material 2
2 is a substrate provided with an electrothermal converter (heating element) 29 on the pressure chamber 25 side.

The BJ recording head 21 constructed as described above
Then, a drive signal for ejecting ink is supplied to the heating element 29 to heat the heating element 29,
By generating bubbles in the ink 26 near the heating element 29, the pressure in the pressure chamber 25 is rapidly increased, and the pressure causes the ink 26 to be ejected from the ink ejection port 24 as an ink droplet 26A. Dot recording can be performed by flying the recording material and landing it.

[0007]

However, it has been difficult for the conventional BJ recording head 21 to change the size of the ink droplets to be ejected and perform gray gradation recording. The reason is that even if the amount of energy supplied to the heating element 29 is changed, the change in the ejected ink droplet 26A itself is small. A known means for changing the size of such an ink droplet has been disclosed in, for example, Japanese Patent Laid-Open No. 62-151348. In this example, an electrostatic force is applied between the ejection nozzle formed of the ink ejection port and the liquid passage of the recording head and the back surface side of the recording material to control the retreat amount of the meniscus formed in the ejection nozzle. Thus, the size of the ejected ink droplet is changed.

However, in the above example, an electrode is required on the back surface side of the recording material, the structure is complicated, and a high electrostatic field control is required, so that the cost of the electric circuit construction is too high. Therefore, in the gradation recording by the BJ recording head so far, the recording pixel data is divided into further subdivided units, and the minimum recording unit is formed by dots of one ink droplet. Has been implemented by the method.

However, with the above-described conventional digital area gradation method, the recording speed must be slowed down, or the recording resolution must be reduced otherwise, and as a result, the characteristics of the recording head are deteriorated. It will be.

An object of the present invention is to pay attention to the above-mentioned conventional problems, and in order to solve the problems, a BJ recording head and recording which can freely realize high-quality gray gradation recording with a simple structure without lowering the recording speed. To provide a device.

[0011]

In order to achieve the above object, a BJ recording head according to the present invention is configured so that an electrothermal converter disposed at a position facing an ink ejection port of a pressure chamber drives the inside of the pressure chamber. In a bubble jet recording head that increases pressure and ejects ink droplets from the ink ejection port, it has means for changing the shape of the pressure chamber to change the size of the ejected ink droplets. Is.

[0012]

According to the BJ recording head and the recording apparatus of the present invention, the electrothermal converter of the pressure chamber is selected by selecting the driving timing of both the means for changing the shape of the pressure chamber and the electrothermal converter. The size of the ink droplets ejected from the ink ejection ports arranged at the opposite positions can be freely changed, which enables gradation recording, and the use of ink and recording heads. It is also possible to perform control so that the size of the ink droplet that changes depending on the environmental temperature is corrected to an appropriate size.

[0013]

Embodiments of the BJ recording head of the present invention will be described in detail and specifically below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. Here, 1 is the BJ recording head, 2 is the base material, 3 is an orifice plate whose peripheral portion is joined to the base material 2, and 4 is an ink ejection port. Further, the configurations of the pressure chamber 5, the ink supply path 7, the substrate 8 and the heating element 9 are the same as those of the conventional example shown in FIG. 7, but in this example, the ink is formed around the ink discharge port 4 of the orifice plate 3. A donut-shaped annular piezoelectric element 10 whose center substantially coincides with the center of the discharge port 4 is arranged. The orifice plate 3 is the base material 2
Similar to the above, it is formed with high precision together with the ink discharge port 4 by pressing, molding, electroforming, or the like, but it is preferable that it is formed of a flexible material that easily vibrates.

One electrode of the ring-shaped piezoelectric element 10 is electrically connected to the orifice plate 3 with a conductive adhesive, and a lead wire (not shown) is connected to the other electrode. A drive voltage is supplied to the element 10. Although only one ink ejection port 4 is shown in FIG. 1 for the purpose of explaining the operation based on the principle configuration, a plurality of ink ejection ports 4 and corresponding piezoelectric elements 9 and pressure chambers 5 are provided. Of course, it is acceptable.

The basic ink ejection operation by the BJ recording head 1 having such a structure is the same as the conventional one, and the pressure in the pressure chamber 5 is controlled by supplying a pulsed voltage to the heating element 9 as a recording signal. Higher ink ejection port 4
At the same time as recording is performed by ejecting an ink droplet 26A from the ink, ink 26 is supplied to the pressure chamber 5 via the ink supply path 7 by the amount of the ejected ink. By the way, in the BJ recording head 1 configured as described above, the piezoelectric element 10 is driven in accordance with the timing of the ejection to change the orifice from the state shown in FIG. 1A to the orifice shown in FIG. 1B. It is possible to deform the plate 3 and change the volume of the pressure chamber 5.

The principle will be described with reference to FIG.

In this example, the piezoelectric element 10 is driven by using an AC voltage, and V _p (v) is the driving voltage thereof.
Further, V _h (v) represents the voltage of the pulse waveform that urges the heating element 9, respectively. Further, T _i (μsec) indicates the timing of driving the heating element 9 with respect to the drive waveform of the piezoelectric element 10 shown in (A), and the frequency F is applied to the AC voltage supplied to the piezoelectric element 10 here. A 20 kHz sine waveform is used. Assuming that an AC voltage as shown in (A) is applied to the piezoelectric element 10, the orifice plate 3 is deformed according to the applied voltage V _p , and heat is generated along with the ink ejection port 4 in the pressure chamber 5 according to the deformation. The ink amount C between the body 9 can be changed. Therefore, the piezoelectric element 10
When the drive voltage V _p is highest, the orifice plate 3 is deformed in a convex shape toward the outside, so that the ink amount C is maximized. On the contrary, when V _p is the lowest, the orifice plate 3 is deformed into the largest concave shape as shown in FIG. 1B, and the ink amount C is minimized.

Therefore, the size C _D of the ink droplet 26 ejected from the pressure chamber 5 is controlled by controlling the timing (timing difference from the driving of the piezoelectric element) T _i for driving the heating element 9 as shown in (B). , Can be changed as shown in FIG. Conventionally, JP-A-60-27548 and the like have proposed BJ recording heads in which the pressure of ink in a pressure chamber is changed. However, the inventions by these proposals use ink supply paths or the like. The pressure of the ink in the pressure chamber is changed, and the amount of the ink introduced between the heating element and the ink ejection port is not changed as in the case of the present application.

FIG. 4 shows a second embodiment of the present invention. In this example, the orifice plate 3 and the piezoelectric element 20 are integrally formed, and when the orifice plate 3 and the piezoelectric element 20 are made of the same material, they need not be further laminated. Further, as shown in this figure, when two layers are both formed as a piezoelectric element, one electrode or one of the layers is embedded, whereas both sides thereof are separated in the same direction. Therefore, when a sinusoidal voltage as shown in FIG. 2A is applied to the electrodes at both ends, the laminated piezoelectric element 20 configured as an orifice plate operates as a bimorph element and is parallel to the paper surface in FIG. The ink amount C described above can be changed by vibrating in the direction indicated by the arrow. Note that the shape of the piezoelectric element 20 and the electrode arrangement thereof are not limited to the above-described configuration, and any point is essential as long as the piezoelectric element 20 is integrally formed with the orifice plate 3 and is vibratingly deformed. It may have such a form.

FIG. 5 shows a third embodiment of the present invention. In this example, the orifice plate 3 itself is configured as a film-shaped piezoelectric element 30, and a suitable film-shaped piezoelectric element 30 is, for example, a piezoelectric film such as PVDF (polyvinylidene fluoride). By the way,
In the example disclosed in Japanese Examined Patent Publication No. 60-34469, the contraction force of the film is indirectly applied to the pressure chamber. However, as in this embodiment of the present invention, the orifice plate itself is a piezoelectric film. The amount C of the ink formed by the method described above and introduced between the ink ejection port and the heating element is not directly controlled.

In FIG. 5, the film-shaped piezoelectric element 30 is provided with a coating on the pressure chamber 5 side to prevent ink erosion and to limit contraction when a voltage is applied. Second piezoelectric element 30
It can be operated similarly to the embodiment. Further, as the processing for forming the ink discharge port 4 in the piezoelectric element 30, for example, in the case of the piezoelectric element 30 having a thickness of about 50 μm, a highly accurate circular hole having a diameter of 50 μm ± 1 μm by irradiation of a laser beam or the like. Can be drilled.

FIG. 6 shows a fourth embodiment of the present invention. In this embodiment, the piezoelectric element 40 is arranged on the back surface side of the substrate 8 supporting the heat generating element 9, that is, on the back surface side of the pressure chamber 5, and the piezoelectric element 40 arranged in this manner has the same structure as described above. By applying the voltage, the ink amount C between the ink ejection port 4 and the ink ejection port 4 can be similarly changed. However, in this example, the substrate 8 is preferably as thin and flexible as possible, such as a thin plate made of polyimide.

In each of the embodiments described above, the driving voltage V _p of the piezoelectric element is the AC voltage having the sinusoidal waveform as shown in FIG. _{The p} is not limited to such a sine waveform, but may be, for example, a sawtooth waveform voltage. By applying the sawtooth waveform voltage, the drive timing difference T _i between the piezoelectric element and the heating element shown in FIG. 26 drops
It is possible to maintain a linear relationship with the size C _D of C, and there is an advantage that it is easy to control.

FIG. 8 shows an example of the construction of an ink jet recording apparatus to which the BJ recording head of the present invention can be applied. Where I
JC is an inkjet cartridge in which the ink tank and the inkjet recording head 1 are integrated, and is mounted on the carriage HC. Reference numeral 5002 is a platen for holding the recording sheet P at the recording position, 5003 and 5004 are guide shafts and lead screws for moving the carriage HC along the recording sheet P, and a screw screw 5005 is formed on the lead screw 5004. Then, the engagement pin (not shown) on the carriage HC side engages with the screw screw 5005 to move the carriage HC in accordance with the rotation of the lead screw 5004.

Further, 5006 is a shielding projection protruding from the carriage HC, 5007 is a stopper, 5008 is a sensor for detecting the home position position of the carriage HC by shielding the shielding projection 5006, 5009 and 5
Reference numeral 011 denotes a gear driven by a drive motor 5013. At the time of recording, the lead screw 5004 is driven at a predetermined timing via these gears 5009 and 5011, and the recording head 1 is scanned together with the carriage HC so that the ink is ejected from the recording head 1. Can be discharged to perform recording on the recording sheet P. Reference numerals 5016 and 5017 are a cap member and a wiping member involved in the recovery operation for the recording head 1 when the carriage HC is near the home position.

Thus, according to the present embodiment, the size of the ink droplet ejected is controlled by controlling the driving of the piezoelectric element and the heating element provided in the BJ recording head 1 by the control unit (not shown) at the timing described above. It is possible to freely change and implement desired gray gradation recording.

Although FIG. 8 shows the case of the inkjet recording apparatus IJRA in which a single inkjet cartridge IJC is mounted on the carriage HC for recording, the application of the BJ recording head 1 of the present invention is not limited to this. The ink tank and the recording head may be separately provided, and the present invention can be applied not only to a color ink jet recording apparatus but also to a full line recording capable of recording over the width of a recording material instead of serial. There is no end.

[0029]

As described above, according to the present invention, since the means for changing the shape of the pressure chamber to change the size of the ejected ink droplet is provided, the size of the ink droplet can be freely changed. It has become possible to carry out recording of gray gradation by changing the. Therefore, high-quality and high-speed recording can be performed, and furthermore, deterioration of image quality due to ambient temperature can be prevented by controlling the size of ink droplets.

[Brief description of drawings]

FIG. 1 shows a configuration of a BJ recording head according to a first embodiment of the present invention in a non-driving state (A) and a driving state (B) of a piezoelectric element.
It is sectional drawing shown by.

FIG. 2 is a waveform diagram showing a drive waveform of a piezoelectric element and a drive wave of a heating element according to the present invention by (A) and (B).

FIG. 3 is a characteristic curve diagram showing changes in ink droplet size according to the present invention.

FIG. 4 is a sectional view showing a structure according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a structure according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing a configuration according to a fourth exemplary embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a configuration of a conventional example.

FIG. 8 is a perspective view showing the configuration of an inkjet recording apparatus to which the present invention can be applied.

[Explanation of symbols]

1 (BJ) Recording Head 2 Base Material 3 Orifice Plate 4 Ink Ejection Port 5 Pressure Chamber 7 Ink Supply Channel 8 Substrate 9 Heating Element 10, 20, 30, 40 Piezoelectric Element 26 Ink 26A Ink Droplet IJRA Inkjet Recording Device IJC Inkjet Cartridge HC Carriage P Recording sheet _Vp Piezoelectric element drive voltage _Vh Heating element drive pulse voltage C Ink amount between ink ejection port and heating element C _D Ink drop size

Claims (9)

[Claims] 1. A bubble jet recording head in which an electrothermal converter disposed at a position facing an ink ejection port of a pressure chamber increases the pressure in the pressure chamber to eject an ink droplet from the ink ejection port. A bubble jet recording head comprising means for changing the shape of the pressure chamber so as to change the size of the ejected ink droplet. 2. The bubble jet recording head according to claim 1, wherein the means for changing the shape of the pressure chamber is a piezoelectric element. 3. The bubble jet recording head according to claim 2, wherein the piezoelectric element is provided on a surface on which the ink ejection port is formed. 4. The bubble jet recording head according to claim 2, wherein the piezoelectric element is provided on a substrate on which the electrothermal converter is provided. 5. The piezoelectric element is cyclically driven, and is controlled so that the size of the ejected ink droplet is changed by selecting the drive timing of driving the piezoelectric element and driving the electrothermal converter. The bubble jet recording head according to any one of claims 1 to 4, wherein 6. The bubble jet recording head according to claim 5, wherein the size of the ink droplet changes smaller as the shape of the pressure chamber is changed smaller. 7. The bubble jet recording head according to claim 1, wherein gradation recording is possible by means for changing the shape of the pressure chamber. 8. The size of the ink droplet that changes depending on the ambient temperature can be corrected by means for changing the shape of the pressure chamber.
The bubble jet recording head according to any one of items. 9. A bubble jet recording head for ejecting ink droplets from the ink ejection port by increasing the pressure in the pressure chamber by driving an electrothermal converter arranged at a position facing the ink ejection port of the pressure chamber. A recording apparatus comprising means for changing the shape of the pressure chamber so as to change the size of an ink droplet, and recording is performed by the bubble jet recording head.