JPH0114874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink jet printing device that prints and images images on recording paper using liquid ink.

In conventional ink jet printing devices, one method of expressing the shading of recorded characters and images is to control the particle size of the jetted ink droplets, so that large grains are darker on the recording paper, and smaller grains are darker. is expressed in a light manner. Ink ejection devices that use electrostatic phenomena control the voltage applied to the nozzle, and ink ejection devices that use piezoelectric phenomena control the ink particle size by changing the amplitude or waveform of the electric pulse applied to the piezoelectric element. However, both methods have the disadvantage that the range of change in shading is small.

The present invention uses a plurality of nozzles and a multipolar electric field in the head of the ink jet printing device to obtain an ink jet printing device that can widen the range of changes in shading of recorded characters and images. The purpose is

The present invention will be explained based on the drawings. Example 1 is shown in FIGS. 1 and 2. FIG. 1 shows a case where three nozzles and a quadrupole electrode are used to obtain an electrical multipole field. High voltages 9, 10, and 11 are applied to the nozzles 1, 2, and 3, respectively, and the ink droplets ejected from each nozzle pass through the small hole 7 of one accelerating electrode 4, as shown in Figure 2. to 2
It reaches the recording paper 6 through the quadrupole electrode 5 which has a cross section of the following curved line. In the head constructed as described above, the gradation expression is basically determined by the number of ink droplets ejected from a plurality of nozzles simultaneously or at staggered timing. The ink droplets ejected from the nozzle are charged to the same polarity as the voltage applied to the nozzle. The ink droplets ejected from the nozzles 1, 2, and 3 coalesce near the small hole 7 of the accelerating electrode 4. The particle size when ink droplets are ejected only from nozzle 1 is minimized, and as the number of ink ejection nozzles increases and the number of ink droplets ejected increases, the ink droplet size formed by coalescence increases. Example 1
In the case of , ink droplets are ejected from three nozzles, and the ink droplet size formed by combining the three ink droplets becomes maximum.

After the ink droplets coalesce, they try to move in the direction that is the result of the vectors of the motion directions of the individual ink droplets before they coalesced, but when they enter the quadrupole electric field, the ink droplets are charged and move as shown in Figure 2. Then, the ink droplets are affected by an electric field that is constantly changing at a certain frequency from the AC power supply 2, and the ink droplets receive a force that pushes them toward the center axis of the quadrupole electrode 15. The trajectory of the ink droplets is corrected, and the ink droplets are pushed toward the center axis of the quadrupole electrode 15. 15, and reaches the recording paper to form dot 8.

In order to eliminate the difference in the flight speed of the ink droplets after passing through the quadrupole electrode, which is caused by the difference in the number of combined particles,
The voltages 9, 10, 11 applied to individual nozzles are changed by electrical signals. When multiple ink droplets are combined, the speed of the combined ink droplets increases, so the voltage applied to each nozzle is lowered.
When ejecting ink droplets from a single nozzle, the flight speed of the ink droplets is adjusted by increasing the applied voltage and increasing the speed of the ink droplets. The grains fly at the same speed.

The positions of the nozzles 1, 2, and 3 are geometrically adjusted in order to coalesce the ink particles near the small hole 7 of the accelerating electrode 4, and the timing of the voltage applied to the nozzles is shifted, so that the ink particles fly at a high speed. is fired late.

Example 2 is shown in FIG. Nozzles 15, 16,
In order to maintain a constant velocity after coalescence of ink droplets ejected from 17, the positions of the nozzles are adjusted geometrically, and the accelerating electrode 1 of each nozzle is
8, 19, 20 and power supplies 28, 29, 30 are provided.

Embodiments 1 and 2 relate to the head of an ink jetting device that utilizes electrostatic phenomenon, but in the head of an ink jetting device that utilizes piezoelectric phenomenon, an ink chamber is installed as shown in FIG. 4 in order to charge ink droplets. 32
An ink charging electrode 35 is provided inside to charge the ejected ink droplets.

As described above, according to the present invention, the positive electrodes and the negative electrodes are arranged side by side and alternately in point symmetry with respect to the central axis which is the flight path of the charged and ejected ink, and the positive electrodes and the negative electrodes face each other. The electrodes each have a semi-cylindrical shape with a curved surface having a quadratic cross section facing the central axis and the flight direction of the ink being the longitudinal direction, and the electrode has an AC It is connected to a power source so that the positive electrode and the negative electrode are alternately replaced, and an electric field is generated in the direction from the positive electrode to the negative electrode to move the ink to the adjacent electrode and draw it onto the central axis. Therefore, the electric lines of force generated between adjacent electrodes come out perpendicularly from a curved surface with a quadratic cross section and enter perpendicularly to an adjacent similar curved surface, so they force the ink droplet toward the central axis. Creates an effective electric field effect. Therefore, when multiple nozzles are driven, the ink droplets ejected from the nozzles are attracted to the central axis no matter where they are ejected between the electrodes, ensuring that they coalesce at the same point and become a large ink droplet. When a single nozzle is driven, small ink droplets fly on the central axis between the electrodes due to the action of the electric field and are deposited on the recording medium without positional deviation. Therefore, it is possible to reliably express halftones and to realize accurate gradation expression of characters and images without dot shift.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention. Figure 2 shows the state of the electric lines of force inside the quadrupole electrode. This is the case. FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 4 shows an embodiment in which a piezoelectric element 34 is used in the head and an ink charging electrode 35 is provided in the ink chamber 32. 1, 2, 3, 15, 16, 16, 17... nozzle, 4, 18, 19, 20... acceleration electrode, 5...
Quadrupole electrode, 6... Recording paper, 7, 21, 22, 2
3...Small hole, 8...6...dot, 9,10,1
1, 28, 29, 30...variable high voltage power supply, 31...
... Fixed high voltage power supply, 34 ... Piezoelectric element, 12 ... AC power supply, 36, 37 ... Electrode, 32 ... Ink chamber, 33, 38 ... Lead wire, 35 ... Ink charging electrode.

Claims (1)

[Scope of Claims] 1. In an ink jet printing device having a plurality of nozzles arranged to jet ink from different directions toward the same point in the direction of a recording medium, selectively applying a voltage to the plurality of nozzles. a means for applying electricity; a means for charging the ejected ink; and a means for charging the ink to be ejected from the nozzle in a point symmetrical manner with respect to a central axis that is to be a flight path of the ink while the charged ink is ejected from the nozzle and reaches the recording medium. Moreover, the positive electrodes and negative electrodes are placed next to each other alternately, and the positive electrodes are connected to each other.
A plurality of electrodes are arranged such that negative electrodes face each other, and each electrode has a semi-cylindrical shape with a curved surface having a quadratic cross section facing the central axis and the flight direction of the ink being the longitudinal direction. Further, the electrodes are connected to an AC power source so that the positive electrode and the negative electrode are alternately replaced, and an electric field is generated in the direction from the positive electrode to the negative electrode to move the ink to the adjacent electrode and draw it onto the central axis. An ink jet printing device characterized by: