JPS5938905B2 - Inkjet type recording machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impulse pump type inkjet recording machine.

A conventional impulse pump type inkjet recording machine is explained with reference to FIG. 1. Reference numeral 1 is an impulse pump type recording head, which includes an ink chamber 3 with an orifice 2 at its tip, and an ink chamber 3 that injects ink into the ink chamber 3. An ink inlet 4 for introducing ink and a pressure chamber 5 located at the rear end of the ink chamber 3 are formed.

A bimorph-shaped diaphragm 8 comprising a disk-shaped piezoelectric element 6 and a metal disk T is attached to the back surface of the ink chamber 3. A rotating cylindrical drum 9 has a recording medium 10 wound around its outer periphery.

Ink is supplied to the recording head 1 from an ink tank (not shown). The supplied ink is led into the ink chamber 3 through the ink inlet 4 and is filled from the pressure chamber 5 to the tip of the orifice 2. The ink level of the ink tank is set to be slightly lower than the orifice 2, and since the orifice 2 is filled with ink by capillary force, in a steady state, the ink does not reach the orifice. There is no leakage from 2. To eject ink droplets, the disc-shaped piezoelectric element 6 is driven in pulses by a known driving means (not shown). Then, the diaphragm 8 bends, a pressure wave proportional to the pulse voltage is generated in the pressure chamber 5, the pressure wave propagates inside the ink chamber 3, and an ink droplet with a size approximately proportional to the pulse voltage is produced from the tip of the orifice 2. 11
is injected. The recording head 1 is mounted on a lead screw (not shown) provided parallel to the axis of a rotating cylindrical drum 9 so that the orifice 2 faces the recording medium 10 with a predetermined distance therebetween.

The scanning method is to rotate the rotating cylindrical drum 9 around its axis at the same angular velocity, and drive the diaphragm 8 of the recording head 1 in appropriate pulses using a synchronization signal and a recording information signal obtained from a rotary encoder or the like. Scanning is performed, and sub-scanning is performed, for example, by driving the read screw in steps for each rotation of the rotating cylindrical drum 9 to move the recording head 1 one pitch parallel to the axis of the rotating cylindrical drum 9.

When the recording head 1 is fed from one end to the other, scanning of the entire surface of the recording medium 10 is completed. In the recording method described above, ink droplets 11 can be obtained by applying a driving pulse to the diaphragm 8 of the recording head 1 only when necessary, so there is no need to collect unnecessary ink pools and unnecessary ink droplets, and there is no need for recording or non-recording. Since there is no need for deflection to distinguish between recordings, the ink system and control circuit are very simple, and by increasing the amplitude of the drive pulse applied to the diaphragm 8 Furthermore, since it is possible to increase the size of the ejected ink droplets, it also has the advantage of facilitating gradation recording and color recording.

By the way, as already mentioned, when the diaphragm 8 is pulse-driven, ink droplets 11 having a size substantially proportional to the pulse voltage are ejected.

However, as a result of observing the situation, it was found that at a certain pulse voltage, one ink droplet 11 is formed per pulse, and as the pulse voltage is increased, the size of each droplet increases, but at a certain level. When the voltage is reached, the droplet size stops increasing and instead the tail portion of the ink droplet 11 independently
When the droplet 11a and the second droplet 11b are separated and the pulse voltage is further increased, the size of the first droplet 11a remains constant and only the size of the second droplet 11b increases. It became clear that it was going to happen. The second and subsequent drops are generally called satellites,
When the satellites are formed, there is no problem if an axially symmetrical force acts on the ink droplet with the flight trajectory of the ink droplet as an axis, but the force acting on the ink droplet may be affected by disturbances such as uneven ink viscosity or air flow. When the axial symmetry is disrupted, the satellite deviates from its predetermined flight trajectory, resulting in a reduction in recording quality. It is an object of the present invention to solve these drawbacks, and for this purpose, a charging electrode and a focusing electrode are provided between the orifice of the recording head and the rotating cylindrical drum, and the electrode focuses most of the flight path of the ink droplets. An electric field is applied to push the ink droplets back to a predetermined flight trajectory over the entire area, and to create electric lines of force that cause the ink droplets to fly in the direction of the recording medium, so that all ink droplets fly on the predetermined trajectory. It is characterized by reducing recording distortion and the like.

An embodiment of the present invention will be described with reference to FIG. 2. Reference numeral 1 indicates a boundary bend, 2 an orifice, 3 an ink chamber, 4 an ink inlet, 5 a pressure chamber, 6 a disc-shaped piezoelectric element, and 7 8 is a metal disk, 8 is a bimorph-shaped diaphragm consisting of a disk-shaped piezoelectric element 6 and a metal disk 7, 9 is a rotating cylindrical drum, and 10 is a recording medium, which are the same as those in FIG. Has a function.

A ground electrode 12 is attached to the orifice 2 and grounded when the orifice 2 is made of a non-conductor material.

If the orifice 2 is a conductor, the orifice 2 may be grounded as is. Reference numeral 13 denotes a charging electrode, and 14 a hollow cylindrical focusing electrode.The charging electrode 13 is placed on the orifice 2 side, and the focusing electrode 14 is placed on the rotating cylindrical drum 9 side, between the recording head 1 and the rotating cylindrical drum 9. It has been placed.

This charging electrode 13 is located very close to the orifice 2, and is connected to the anode of a DC power source 15 to maintain a positive potential. On the other hand, the focusing electrode 14 is connected to the cathode of a DC power source 16 to maintain a negative potential. The rotating cylindrical drum 9 is assumed to have at least its outer peripheral surface made of a conductor, and is connected to the anode of the DC power source 15 or maintained at a higher positive potential.

In this embodiment, ink is supplied to the recording head 1 in the same manner as before, and filling of the orifice 2 with ink is also carried out by capillary force as in the conventional case, so ink leaks from the orifice in a steady state. There's nothing to do.

Note that the potential of the charging electrode 13 is desirably set to a value that causes the ink in the orifice 2 to swell in a half-moon shape. To eject ink droplets, the disc-shaped piezoelectric element 6 is driven in pulses by a known driving means, as in the conventional case. Then, the diaphragm 8 bends, a pressure wave proportional to the pulse voltage is generated in the pressure chamber 5, and the pressure wave is transmitted to the ink chamber 3.
The pulse voltage propagates, and ink droplets 11 are ejected from the orifice 2 in an amount approximately proportional to the pulse voltage. At this time, the orifice 2 is grounded as described above, and the charging electrode 13
is at a positive potential, all of the ejected ink droplets 11 are negatively charged due to electrostatic induction during droplet formation, and the focusing electrode 1
Enter into 4.

As described above, the focusing electrode 14 has a hollow cylindrical shape and is axially symmetrical with respect to the flight trajectory of the ink droplet 11, and is also kept at a negative potential, so that it collects the ink droplet 11 that deviates from the predetermined flight trajectory. The Kulonka acts to push it back to its original flight trajectory. Therefore, as the pulse voltage increases, the ink droplet 1
1 is separated into droplets 11a and 11b, and when the separated second droplet 11b, that is, the satellite, deviates from the predetermined flight trajectory due to disturbances such as uneven ink viscosity or air flow, it flies within the focusing electrode 14. Since the focusing electrode 14 is present over almost the entire length of the flight path of the ink droplets 11, all the ink droplets 11 are constantly corrected and attached to a predetermined position on the recording medium 10. I will do it. As described above, since all the ink droplets 11 follow the same flight trajectory, recording distortion can be significantly reduced, but since the charging electrode 13 has a positive potential,
A suction force acts on the negatively charged ink droplet 11, reducing the flight speed of the ink droplet 11. This means that when the flight speed i of the ink droplet 11 is lower than the circumferential speed Vd of the rotating cylindrical drum 9, when the ink droplet 11 separates into the first droplet 11a and the second droplet 11b, the recording medium A difference occurs between the adhesion positions of the two on the recording material 10, resulting in a decrease in recording quality. Therefore, in order to eliminate the influence of the charging electrode 13, it is necessary to make the potential of the rotating cylindrical drum 9 equal to the potential of the charging electrode 13, or more preferably to a high potential. By doing so, the negatively charged ink droplets 11 are attracted toward the rotating cylindrical drum 9 and their flying speed is increased, so that even if they are separated into the first droplet 11a and the second droplet 11b, There is almost no difference in the adhesion position between the two, and the recording quality is improved. In the embodiment described above, an electric charge is applied to an ink droplet ejected from an orifice, and the ink droplet is directed to a focusing electrode that is axially symmetrical with respect to the flight trajectory of the ink droplet and that exists over almost the entire length of the flight path of the ink droplet. By applying a potential of the same polarity as
Ink droplets that have deviated from their predetermined flight trajectory are pushed back to their original trajectory, and the electric field formed by the focusing electrode and rotating cylindrical drum increases the flight speed of the ink droplets, improving recording quality. effective. Next, other embodiments will be described.

Although the focusing electrode 14 in the embodiment described above has a hollow cylindrical shape, it is also possible to use a focusing electrode 17 that has a substantially hollow conical shape and whose cross-sectional area gradually increases as it moves away from the orifice 2, as shown in FIG. A similar effect can be obtained.

Note that FIG. 3 shows only the focusing electrode 17, in which a smaller diameter end faces the charging electrode 13 and a larger diameter end faces the recording medium 10. shall be.

For convenience of explanation, a model of electric lines of force when the focusing electrode 17 kept at a negative potential is placed in an electrically free space is shown as a solid line, and a model of an equipotential surface is shown as a broken line. .
In reality, there are charged electrodes 13 and rotating cylindrical drums 9 on both sides of the focusing electrode 17, so the equipotential surfaces and electric lines of force are more complicated than shown in this figure, and their influence is felt at the ends of the focusing electrode 17. Although it is large, it is small in the center, and when considering the general trend, it can be said that there is not much difference when considering this figure. As is clear from the equipotential surface in this figure,
Inside the focusing electrode 17, the potential is low on the charging electrode side (the absolute value is the highest because it is a negative potential), and the potential is high on the recording medium side (the absolute value is the lowest because it is a negative potential). It has a slope. Therefore, the negatively charged ink droplets that have deviated from the predetermined flight trajectory, that is, the axis of the focusing electrode 17, are pushed back to the original predetermined flight trajectory by the force along the electric lines of force, and at the same time are pushed back onto the recording medium. Therefore, in this practical example, there is an advantage that the focusing electrode 17 itself also plays the role of accelerating the ink droplet. In the two embodiments described above, the convergence electrode is of a single structure made of a conductor, but as shown in FIG.
0 and cylindrical insulators 191, 192...19.

-1 are arranged alternately to form a convergence electrode 20 with a composite structure, and the cylindrical conductors 18, to 180 have a maximum potential at 18, a lowest potential at 18n, and 181 to 18n.
Even if a direct current is applied so that the potential gradually decreases toward , the same effect as in the embodiment shown in FIG. 3 can be obtained. As described above, in the present invention, many modifications can be made to the focusing electrode, and the focusing electrode in the present invention is not limited to what is shown in the drawings.

Note that each of the above-mentioned embodiments is an ic-jet recording machine that performs rotational recording by winding a recording medium around a rotating drum.
We have explained the case of a recording machine in which the head is stopped during line recording and the recording medium moves, but an impulse pump type multihead equipped with multiple orifices is scanned serially, and one line is recorded in one scan. After recording, a serial printer that feeds the recording medium line-feeds the recording medium, that is, the recording medium is stopped during one line recording.
It is clear that the present invention can also be applied to a recording machine with a moving head.

Further, in each of the above-mentioned embodiments, an impulse pump recording head equipped with a disc-shaped diaphragm is used.
The present invention can also be applied to impulse pump recording heads with other structures, such as impulse pump recording heads that have a cylindrical vibrator fitted into a glass pipe with an orifice at the tip. It is.

As explained above, the present invention disposes a charging electrode and a focusing electrode between a recording head and a rotating cylindrical drum, and pushes back charged ink droplets that have deviated from a predetermined flight trajectory by a Coulomb force, so that all ink droplets are Since the droplets fly on the same trajectory, it is possible to realize an impulse pump type quick-jet head with high recording quality.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main part of a conventional example, Fig. 2 is a cross-sectional view of the main part showing an embodiment of the present invention, and Fig. 3 is a schematic cross-section showing another embodiment of the focusing electrode used in the present invention. 4 are schematic cross-sectional views showing other embodiments of the focusing electrode. 1... Recording head, 2... Orifice, 3... Ink chamber, 5... Pressure chamber, 8
... diaphragm, 9 ... rotating cylindrical drum,
10... Recording medium, 11... Ink drop, 13... Charged electrode, 14... Focusing electrode, 17... Focusing Electrode, 181~18n・
...Cylindrical conductor, 191-19.

Claims (1)

[Claims] 1 A pressure wave corresponding to the amplitude of the electrical drive pulse is generated in a pressure chamber provided in the recording head, and an ink droplet corresponding to the amplitude of the electrical drive pulse is ejected from an orifice, and the ink droplet is connected to the orifice. In an inkjet recording machine that performs recording by attaching the recording medium to a recording medium on an opposing rotating cylindrical drum, a charging electrode is disposed at a position very close to the orifice between the orifice and the rotating cylindrical drum, and the charging electrode and A focusing electrode is disposed between the rotating cylindrical drum and is axially symmetrical with respect to the flight trajectory of the ink droplets, and is present over almost the entire length of the flight path of the ink droplets, and at least the surface of the rotating cylindrical drum is made of a conductor. All the ink droplets ejected from the orifice are charged by the charging electrode, and a potential of the same polarity as that of the ink droplets is applied to the focusing electrode, and the absolute value of the potential of the rotating cylindrical drum is set to the charging electrode. An inkjet recording machine characterized in that the absolute value is equal to or greater than the absolute value.