Ink jet type printing device

Abstract

An ink jet type printing device is adapted to jet ink droplets from a nozzle to print a character, pattern etc. on a recording medium. The device includes a high tension generator connected to the nozzle to supply electric charges to an ink to be jetted and a heat sensitive element arranged in the neighborhood of the nozzle to detect the temperature change of ink which causes the resistance of the heat sensitive element to be varied to permit an output voltage of the high tension generator to be variably controlled, thereby making the size of the ink droplets uniform for accurate printing.

Description

BACKGROUND OF THE INVENTION

This invention relates to an improved ink jet type printing device adapted to effect an accurate printing by making uniform the size of ink droplets jetted from a nozzle.

An ink jet type printing device is adapted to print characters etc. on a recording paper by jetting ink droplets from a nozzle having an inner diameter of about 100 .mu. and deflection controlling them. In this case, the ink jetting is controlled by an ink feeding pressure relative to the nozzle and a potential difference applied in the ink jetting direction. An accelerating plate is disposed between the nozzle and a platen on which a recording paper is carried. For example, a high voltage is applied between the accelerating plate and the nozzle to impart electric charge to an ink present in the nozzle and ink droplets are jetted, under the attraction of the accelerating plate, in the direction of a recording paper carried on a platen connected at the same potential as that of the accelerating plate. Then, the ink droplets are deflection controlled through deflection electrodes and a desired character is printed on a recording paper. To print an accurate character, pattern etc. on the recording paper it is required that the size of ink droplets jetted from the nozzle be made uniform. If the ink feeding pressure is kept constant, the size of ink droplets corresponds to the number of ink particles (ink jetting frequency) jetted per unit time and the ink jetting frequency is influenced by the viscosity of ink and the voltage applied to the nozzle. The viscosity of ink is varied by the temperature of ink prevalent in the nozzle, and a relation between the temperature and the ink jetting frequency is such that, as shown in FIG. 2, the number of ink droplets to be jetted per unit time i.e. the ink jetting frequency is increased with a rise in temperature of ink. As a result, the size of ink droplets is made smaller in proportion to the raise of the ink jetting frequency and the ink particle is strongly subjected to an action by the deflection electrode to increase its deflection angle, failing to print an accurate character etc. on a recording paper.

It is accordingly the object of this invention to provide an ink jetting type printing device which is capable of controlling any temperature variation of ink present in a nozzle due to ambient temperature to permit ink droplets of uniform size to be jetted from the nozzle which and is free from the variation of concentration of ink due to a temperature change, so that an accurate character etc. is printed on a recording paper.

SUMMARY OF THE INVENTION

The object of this invention can be achieved by providing an ink jet type printing device comprising an ink jetting nozzle, a high voltage generator for applying electric charges to an ink to be jetted from the nozzle, a heat sensitive element for detecting the temperature of ink present in the nozzle and a control section for controlling an output voltage of the high tension generator in response to the output of the heat sensitive element. According to this arrangement, the variation of the viscosity of ink due to the variation of temperature of ink present in the nozzle i.e. the number of ink droplets jetted per unit time can be made constant. This prevents ink droplets from being deflected to an unnecessary extent, thus enabling an accurate character, pattern etc. to be printed on a recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial block diagram showing one embodiment of this invention;

FIG. 2 is a graphical representation showing a relation between the ink jetting frequency and the temperature of ink present in the nozzle;

FIG. 3 is a detailed circuit arrangement of a high tension generator of FIG. 1;

FIG. 4 is a graphical representation showing a relation between the ink jetting frequency and a voltage applied to the nozzle; and

FIG. 5 is a graphical representation showing a relation between the temperature of ink present in the nozzle and an output voltage impressed to the nozzle from the high tension generator when the ink jetting frequency is made constant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will be explained one embodiment of this invention by reference to the drawings.

As shown in FIG. 1, ink is supplied from an ink tank 12 to an ink jetting nozzle 11 by driving a pump 14 and jetted as ink droplets 17 through the orifice of the nozzle 11. A platen 16 on which a recording paper 15 is carried is located at a predetermined distance from the forward end of the nozzle. Deflection electrodes 18 are provided in the X-axis and Y-axis directions. An accelerating plate 30 is arranged between the deflection electrode 18 and the forward end of the nozzle 11. An ink target 19 is disposed in the neighborhood of the platen and adapted to introduce ink droplets thereinto when printing is not effected. Ink present in the ink jetting nozzle 11 is charged by application of an output of a high voltage from a high tension (i.e., high voltage) generator 20 connected to the nozzle. As the high tension generator 20 use may be made of a known DC-DC converter comprising a collector tuned type oscillator 31 and a voltage doubler circuit 32 as shown, for example, in FIG. 3. The accelerating plate 30, platen 16 and ink target 19 are grounded relative to the nozzle to which is applied a high voltage, so that a high potential difference is created therebetween. In an input circuit of the high tension generator 20 is provided a constant voltage circuit 40 having an input potential control transistor 21 whose emitter terminal is connected to the input of the high tension generator 20 and whose collector terminal is grounded, a constant voltage diode 22, and a comparison control transistor 23 for comparing a constant voltage detected from the constant voltage diode 22 with an input voltage of the high tension generator 20 to control the transistor 21. The output of the constant voltage circuit 40 is set by the control of a variable resistor 24.

A heat sensitive element 25 is provided in the neighborhood of the ink jetting nozzle 11. One of the terminals of the heat sensitive element is connected one to the input terminal of the high tension (i.e., high voltage) generator 20 and the other to the base terminal of the transistor 23 through a resistor.

The X-electrodes and Y-electrodes of the deflection electrodes 18 are respectively connected to a deflection circuit 41. The deflection circuit 41 is connected through a character generator 42 to an input device 43. The character generator 42 issues, as neccessary, a driving instruction to the pump driving circuit 13 for driving a pump 14. The detailed interrelation between the deflection circuit 41, character generator 42 and pump driving circuit 13 is disclosed in FIG. 2 of U.S. patent application Ser. No. 314,999.

An ink jetting frequency corresponding to the number of ink droplets jetted per unit time is increased with a rise in temperature of ink present in the nozzle 11 as shown in FIG. 2, and, as shown in FIG. 4, an increase in voltage applied to the nozzle 11 results in an increase in the ink jetting frequency. Therefore, the variation of the ink jetting frequency due to the variation in temperature0105 of ink present in the nozzle can be rectified by the control of a high tension output applied to the nozzle from the high tension generator 20. The temperature of ink present in the nozzle is detected by the heat sensitive element 25 arranged in proximity to, and in parallel with, the nozzle 11 as shown in FIG. 1. The heat sensitive element 25 has one end connected to one output terminal of the constant voltage circuit 40 and the other end connected between the resistors which are serially connected to the variable resistor 24 of the constant voltage circuit 40. Suppose, for example, that the temperature of ink present in the nozzle is raised. Then, the heat sensitive element 25 senses the rise in temperature to cause its resistive value to be decreased to permit a base current of the transistor 23 to be increased, thereby decreasing the impedance between the emitter and the collector of the transistor 23. Thus, the emitter potential of the input potential controlling transistor 21 is decreased and the input voltage of the high tension (i.e., high voltage) generator is decreased. As a result, the output voltage from the high tension generator 20 is decreased. When a voltage applied to the nozzle 11 is decreased, then the ink jetting frequency is decreased as is evident from FIG. 4. The relation between a decrease in temperature of ink present in the nozzle 11 and decrease in output voltage is as shown in FIG. 5. Therefore, the size of ink droplets jetted from the orifice of the nozzle 11 is controlled to be held uniform irrespective of the temperature and the ink droplets are subject to a stable deflection through the deflection electrode 18. This permits an accurate character to be printed on a recording medium. Though in the above embodiment the heat sensitive element 25 is arranged in the neighborhood of the nozzle 11, it may be located in contact with the ink after a sufficient insulation is effected. In a working embodiment:

a. Nozzle 11 is, for example, a glass nozzle;

b. Element 25 is a posister (Murata Seisakusho in Japan - TYPE PTH60.T322M), positioned near the nozzle 11 within the housing of the printer, the internal temperature within the housing being substantially uniform throughout;

c. Pump 14 pumps ink at a constant pressure of 20 to 30 cm. Aq.;

d. Field between plate 30 and nozzle 11 was about 2.4 kv;

e. Ink Viscosity was 3 c.p. at 20.degree.C;

f. Ink temperature was 0.degree.C to 50.degree.C;

g. Jetting frequency was 2.9 kHz at 25.degree.C (FIG. 2);

h. When temperature sensed by the posister rose to about 30.degree.C (FIG. 2), the jetting frequency would have risen to about 3.0 kHz. However, the field voltage was decreased to about 2.6 kv which reduced the jetting frequency back to about 2.45 kHz (FIG. 4).

This invention should not be taken in a restrictive way and it is to be noted that this invention is capable of any modification without departure from the spirit and scope of the invention.

Claims

What is claimed is:

1. An ink jet type printing device for ejecting ink droplets of substantially uniform size, comprising:

a high voltage generator (20);

a nozzle (11);

means for supplying ink to said nozzle at substantially constant pressure;

means coupled to said high voltage generator and responsive to the high voltage supplied from said high voltage generator for creating an electrostatic force in the vicinity of said nozzle for causing ink particles to be ejected from said nozzle under the influence of said electrostatic force at substantially constant ink pressure so as to record characters, patterns, etc. on a recording medium;

a heat sensitive element (25) disposed adjacent to said nozzle (11) to detect the temperature of the ink supplied to said nozzle and for generating a detection output; and

control means (40) variably controlling the output voltage from the high voltage generator (20) as a function of the detection output of said heat sensitive element (25), which detection output represents the ambient temperature of the ink supplied to said nozzle (11).

2. An ink jet type printing device according to claim 1 wherein said heat sensitive element comprises a variable resistance element, the resistance of which varies with the temperature thereof, said control means variably controlling the output voltage from the high voltage generator as a function of the resistance of said heat sensitive element.

3. An ink jet type printing device according to claim 2 wherein the resistance of said heat sensitive element decreases with a rise in temperature and increases with a drop in temperature.

4. An ink jet type printing device according to claim 1 wherein said control means comprises a constant voltage circuit, the constant voltage output of which is a function of the detection output of said heat sensitive element.

5. An ink jet type printing device according to claim 4 wherein said high voltage generator comprises a DC-DC converter, the input of which is connected to the output of said control means whereby when the constant voltage output of said control means decreases, the high voltage output of said high voltage generator decreases, and when the constant voltage output of said control means increases, the high voltage output of said high voltage generator increases.