JPH01165451A - Application of ink discharge signal - Google Patents

Abstract

PURPOSE:To enable a delay of time for the start of ink discharge to be reduced without increasing a voltage of an ink discharge signal by overlapping the ink discharge signal over a DC bias voltage and oscillating a DC bias voltage while the ink discharge signal is not generated. CONSTITUTION:An ink jet recording head 60 is of a multinozzle type and has an ink electrode 22 installed independently to each ink discharge port on the rear of an orifice plate 12. Further, the head has one piece of common electrode 23 installed to each air discharge port 17 on the front of a nozzle plate 14, and also a signal source connected between each ink electrode 22 and a common electrode 25. The signal source 61 outputs an ink discharge signal 62 in such a manner that it overlaps a DC bias voltage VB, and further, oscillates the DC bias voltage VB during a period when the ink discharge signal 62 is absent. As an example, if a total voltage VT during application of the ink discharge signal 62 is set to be 700-800V, the DC voltage VB should preferably be 300-400V, and the voltage V1 be 300-500V.

Description

[Detailed Description of the Invention] <Industrial Application> The present invention relates to an inkjet recording head that uses electrostatic force and airflow, and in particular, to an inkjet recording head that uses electrostatic force and air flow, and in particular, an inkjet recording head that uses electrostatic force and air flow to shorten the time delay of ink ejection to improve gradation. The present invention relates to a method of applying an ink ejection signal.

<Prior Art> Conventionally, inkjet recording heads have been proposed that use air flow in addition to electrostatic force to improve high-speed response. FIG. 4 is a schematic configuration diagram showing an example of a conventional multi-nozzle type inkjet recording head of this type.

As shown in FIG. 4, the body 11 has an orifice plate 1.
2, and an air chamber 15 covered with a nozzle plate 14 is provided on the outside of the ink chamber 13.The orifice plate 12 and the nozzle plate 14 each have a plurality of ink chambers 13 at positions facing each other. An ink discharge port 16 and an air discharge port 17 are provided. High-pressure air is supplied into the air chamber 15 from an external supply source 19 via an air supply path 18, and air is constantly jetted out from the air outlet 17 at high speed. On the other hand, an ink supply path 20 is provided in the ink chamber 13.
Oil-based ink is supplied from an external ink tank 21 via an air chamber 15 near the ink discharge port 16.
A constant pressure is applied to the ink tank 21 from the air supply source 19 so that the air pressure in the ink chamber 13 is made almost equal to the ink pressure in the ink chamber 13 so that the meniscus of ink generated at the ink discharge port 16 can be kept stationary. There is. Also,
An independent ink electrode 22 is attached to the rear of each ink discharge port 16, and one common electrode 23 is attached to the front of each air discharge port 17.
and the common electrode 23 as an ink ejection signal.
A signal source 24 generating a pulse voltage of 800v is provided respectively.

In such an ink jet recording head, when an ink ejection signal is applied between the corresponding ink electrode 22 and the common electrode 23 by a desired signal source 24 and a pulse-like potential difference is generated, a pulse-like potential difference is generated at the ink ejection port 16. The meniscus of the ink is stretched in the direction of the air discharge port 17 by the electrostatic force caused by the potential difference. At this time, since a rapid air flow is generated in the space from the ink discharge port 16 to the air discharge port 17, the ink meniscus generated at the ink discharge port 16 is stretched while the ink discharge signal is applied. ,
The ink is torn off by the air flow, and the ink flies out from the air outlet 17 in a string-like shape.

To perform gradation modulation, the dot diameter is controlled by changing the pulse width of the ink ejection signal to change the length of ejected ink. For example, the main scanning speed for drawing one line is 40 cm/s, and the S pixel density is 8 pixels/-
Then, since there is a time of 300p1 per pixel, 3
．． The pulse width of the voltage pulse generated at 31& is changed. To reproduce the maximum density, the pulse width is 300. Therefore, a DC voltage is applied. For example, if the flying speed of the ejected ink is 10 m/s, the ink is continuously ejected with a length of 3IIll per pixel. . Decreasing the pulse width shortens the ejected ink, ejecting ink in the shape of droplets and reproducing low density.

<Problems to be Solved by the Invention> However, if the pulse width is reduced below a certain level, ink will no longer be ejected. The reason for this is that even if an ink ejection signal is applied, the ink is not ejected immediately due to the viscosity, inertia, etc. of the ink, but there is a time delay in the start of ejection. Therefore, it is necessary to apply an ink ejection signal with a pulse width longer than the time delay, which limits the gradation. This tendency is remarkable when the meniscus of the ink is concave.

In order to shorten the time delay, the voltage of the ink ejection signal may be increased to, for example, 100 OV or more, but it is not possible to apply a very high voltage because the insulation of the electric wire may be insufficient or discharge may occur. Further, it is not necessarily easy to increase the voltage of the signal source 24.

The present invention is intended to solve the problems of the prior art described above, and provides an ink ejection signal application method that can shorten the time delay in starting ink ejection without increasing the voltage of the ink ejection signal. It is an object.

Means for Solving the Problems> A method for applying an ink ejection signal according to the present invention to solve the above problems includes directing an air flow outward to face an ink ejection port provided in an ink chamber. While an air ejection port is provided, an electrode is provided on each of the ink ejection port and the air ejection port, and an ink ejection signal is applied between the two electrodes to draw out the ink meniscus from the ink ejection port using electrostatic force. In a method of applying an ink ejection signal in an inkjet recording head in which a meniscus drawn out at the same time is ejected from an air ejection port by an air flow, the ink ejection signal is superimposed on a DC bias voltage, and while there is no ink ejection signal, the DC bias voltage is A special action characterized by vibrating the air> The electrostatic force caused by the DC bias voltage applied between the electrode of the ink ejection port and the electrode of the air ejection port pulls out the ink meniscus from the ink ejection port, albeit slightly. Therefore, when an ink ejection signal is applied, the meniscus is quickly pulled out.

Moreover, since the DC bias voltage oscillates, the electrostatic force caused by this oscillates, and the meniscus is already oscillating along the drawing direction, so when an ink ejection signal is applied,
The meniscus begins to move without resistance.

Therefore, ink ejection starts with a short time delay without increasing the voltage of the ink ejection signal.

Note that while the ink ejection signal is being applied, the DC bias voltage does not oscillate and does not affect the amount of ink ejected.

Embodiment Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.

First, the overall configuration of an example of an inkjet recording apparatus to which the method of applying an ink ejection signal according to the present invention can be applied will be described with reference to FIG. 3, which is a schematic diagram thereof. As shown in FIG. 3, this inkjet recording apparatus includes a digital color scanner 31, an image information processing device 32, and an inkjet printer 33.

The digital color scanner 31 scans each part of the color original image 34 to measure the density values of blue, green, and red. , illumination light source 37, lenses 3B, 39, and three-color separation photometry section 40
The photoelectric conversion head 41 has a photoelectric conversion head 41 attached thereto, and a drive device that reciprocates the photoelectric conversion head 41 in a direction parallel to the axial direction of the rotating cylinder 36 by a sub-scanning pulse motor 43 via a feed screw shaft 42. There is. Therefore, the rotating cylinder 3
Each time the photoelectric conversion head 41 rotates once, the rotating cylinder 36
The color original image 34 is moved by one scanning line in the axial direction to two-dimensionally scan each part of the color original image 34, and the blue, green, and red reflection densities of each part of the color original image 34 are measured.

The image information processing device 32 is composed of a central processing unit 44, an internal storage device 45, a UCR circuit 46, and a table memory circuit g847. Write the color density signal into the internal memory bag g145, and
The R circuit 46 performs gradation correction, undercolor removal, smudge removal, etc. on the signal read from the internal storage device 45 to form cyan, magenta, yellow, and black density signals, and the table memory circuit 47 The inkjet printer 3 determines the pulse width of the ink ejection signal by referring to the table memory for each level of the density signal from the UCR circuit 46.
3. Supply ink ejection signal.

The inkjet printer 33 reproduces a color image by attaching ink droplets ejected from a head unit 50 to a white paper 49 wrapped around a rotating cylinder 48. ,
A yellow inkjet recording head 5 is arranged along the axial direction of the rotating cylinder 48 so as to be close to its outer peripheral surface.
2. A head section 50 including an inkjet recording head 53 for magenta, an inkjet recording head 54 for cyan, and an inkjet recording head 55 for black, and this head section 5α are rotated by a sub-scanning pulse motor 57 via a feed screw shaft 56. It has a drive device that reciprocates in a direction parallel to the axial direction of the cylinder 48. Then, the rotating cylinder 48 is rotated by the signal from the central processing unit 44.
Each time the head unit 50 rotates, the head unit 50 moves by one scanning line, and in the process, each of the recording heads 52 to 5
5 are driven to eject ink droplets at the same time and deposit the ink onto the white paper 49 to perform recording. Note that the four inkjet recording heads 52 to 55 are shifted in position in the scanning direction of the head unit 50, so each inkjet recording head 52 to 55 stores data in the internal storage device i45 according to the pixels to be recorded at each scanning position. Addressing is done sequentially.

Next, a method of applying an ink ejection signal according to the present invention will be described. FIG. 1 is a sectional view of a main part of an inkjet recording head according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of applied voltage. However, in FIG. 1, the same parts as those of the conventional head shown in FIG. 4 are given the same reference numerals.

As shown in FIG. 1, the inkjet recording head 60 is of a multi-nozzle type, and ink electrodes 22 are attached to the rear surface of the orifice plate 12 independently for each ink ejection port 16, and each air outlet is attached to the front surface of the nozzle plate 14. Discharge port 17
One common electrode 23 is attached to each ink electrode 22 and a signal source 61 is connected between each ink electrode 22 and the common electrode 23.

As shown in FIG.
is superimposed on the DC bias voltage v8 and output, and during a period 63 in which there is no ink ejection signal 62, the DC bias voltage v8
A vibration 64 is added to the . DC bias voltage v8
is set to a voltage as high as possible within a range in which ink is not ejected from the nozzles during a period 63 in which there is no ink ejection signal 62. Moreover, the magnitude of the vibration 64 of the DC bias voltage v8 is
A range of ±5% to ±50% of the DC bias voltage input is appropriate, and a frequency range of several times to several ten times the driving frequency of the ink ejection signal 62 is appropriate. Note that the waveform of the vibration 64 may be arbitrary, such as a sine wave, a rectangular wave, or a triangular wave.

Incidentally, - as an example, the diameter of the ink discharge port 16 is 50μ.
m1 The diameter of the air discharge port 17 is 150 μm1 The distance between the orifice plate 12 and the nozzle plate 14 is 80 μm, and the ink electrode 2
2 and the common electrode 23 is 480 μm, the total voltage when applying the ink ejection signal 62 is 700 to 800 μm.
v, the DC bias voltage v6 is 300 to 400v
It was suitable to do so.

Therefore, the voltage vI of the ink ejection signal 62 itself is 300~
500■ was good.

In addition, under the above-mentioned dimensional conditions, (1) the peripheral speed of the rotating cylinder 48, which is the main scanning speed, is 40 cm.
/s, the pixel density is 8 pixels/second, the drive frequency of the ink ejection signal is 3.3, and (2) the voltage vl of the ink ejection signal 62 itself is 400 vS, the DC bias voltage v8.
400V1, and the swing $64 was set to ±100V at 50-. (3) When the air pressure and ink pressure were set so that the flying speed of the ejected ink was 1 Om/s, the ink ejection stopped with a time delay of 3011s. It started.

On the other hand, when an 800V ink ejection signal was simply applied without DC bias (conventional), there was a long time delay of 5011 seconds.

Therefore, the gradation is significantly improved compared to the conventional method.

If the gradation is still insufficient, matrix recording such as 2X2, 3X3, or 4X4 (dots) is performed, although the resolution is reduced.

<Effects of the Invention> As described above in detail with reference to embodiments, according to the present invention, an ink ejection signal is superimposed on a DC bias voltage, and the DC bias voltage is oscillated while there is no ink ejection signal. Therefore, the time delay for starting ink ejection can be shortened without increasing the voltage of the ink ejection signal.
Therefore, it is possible to improve gradation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of an inkjet recording head according to an embodiment of the present invention, FIG. 2 is a waveform diagram of applied voltage, and FIG.
The figure is a general schematic diagram of an example of an inkjet recording apparatus to which the present inkjet recording head can be applied, and FIG. 4 is a schematic diagram of an inkjet recording head according to a conventional example. In the drawings, 12 is an orifice plate, 13 is an ink chamber, 14 is a nozzle plate, 15 is an air chamber, 16 is an ink discharge port, 17 is an air discharge port, 22 is an ink electrode, 23 is a common electrode, 61 is a signal source, 62 is an ink ejection signal, 63 is a period in which there is no ink ejection signal, and 64 is vibration.

Claims (1)

[Scope of Claims] An air discharge port is disposed opposite to an ink discharge port provided in an ink chamber to eject an air flow outward, and an electrode is provided at each of the ink discharge port and the air discharge port. , a method for applying an ink ejection signal in an inkjet recording head, in which an ink ejection signal is applied between both electrodes to draw out an ink meniscus from an ink ejection port by electrostatic force, and the drawn meniscus is ejected from the air ejection port by an air flow. , superimposing the ink ejection signal on a DC bias voltage, and
A method for applying an ink ejection signal, characterized by oscillating a DC bias voltage while there is no ink ejection signal.