KR101428025B1 - Feedback control type printing system - Google Patents

Abstract

The present invention relates to a feedback control type printing system, wherein the feedback control type printing system of the present invention comprises a stage on which a printing object is placed; A nozzle for ejecting ink toward the printing object side; A voltage applying unit for applying a voltage to the nozzle to generate an electric field between the nozzle and the stage; A shape obtaining unit for obtaining shape information of a liquid surface formed on a spray surface of the nozzle by a voltage applied from the voltage applying unit; And a control unit which receives the shape information from the shape obtaining unit and controls an ejection condition of the ink ejected to the printing object, wherein the shape obtaining unit obtains a meniscus at a plurality of different points spaced apart from the center of the nozzle, And the control unit controls the intensity of the voltage applied to the nozzle according to a height ratio of a liquid level at a plurality of points obtained from the shape obtaining unit.
Therefore, according to the present invention, there is provided a feedback control type printing system capable of improving overall printing quality by controlling droplet ejection conditions or feeding conditions of a stage by using shape information of a liquid surface or current information generated between a nozzle and a stage do.

Description

[0001] FEEDBACK CONTROL TYPE PRINTING SYSTEM [

The present invention relates to a feedback control type printing system, and more particularly, to a feedback control type printing system capable of improving print quality through feedback control.

Generally, in inkjet printing, ink droplets are ejected onto recording media such as paper from nozzles arranged side by side in an inkjet printer. The discharged ink droplets form points called "dots" to record characters and images. Inkjet printing is advantageous in that it is less expensive than other printing methods, has high quality, and is easy to form color images. The ink used for inkjet printing is prepared by dissolving or dispersing a water-soluble dye or pigment in a solvent containing water and a water-soluble organic solvent. If necessary, an additive such as a surfactant may be added.

In the ink-jet printing, a piezoelectric method in which ink is ejected using a piezoelectric element or a thermal method in which ink is ejected using a heating element is used according to a method of ejecting ink droplets.

However, in recent years, an electrohydrodynamic (EHD) type printing apparatus in which an electric field is generated between a substrate and a nozzle to eject ink has attracted attention. In particular, such EHD inkjet printing has an advantage that an ink having a viscosity higher than that of other inkjet printing can be used.

Despite the advantages described above, in the case of the conventional EHD printing apparatus in which the electric field is controlled, it is easy to control the printing conditions such as the ejection timing of the ink droplets, the size of the droplets, There was a problem that it was not.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a feedback control type printing system which can improve the overall print quality by controlling droplet ejection conditions using the shape information of the liquid surface.

The above object is achieved according to the present invention by a printing apparatus comprising: a stage on which a printing object is placed; A nozzle for ejecting ink toward the printing object side; A voltage applying unit for applying a voltage to the nozzle to generate an electric field between the nozzle and the stage; A shape obtaining unit for obtaining shape information of a liquid surface formed on a spray surface of the nozzle by a voltage applied from the voltage applying unit; And a control unit for receiving the shape information from the shape obtaining unit and controlling the ejection condition of the ink ejected to the printing object or the feeding condition of the stage, wherein the shape obtaining unit includes a plurality of different The control unit controls the intensity of the voltage applied to the nozzle according to a height ratio of a liquid level at a plurality of points obtained from the shape obtaining unit, Controlled printing system.

Further, the above objects are achieved according to the present invention by a printing apparatus comprising: a stage on which a printing object is placed; A nozzle for ejecting ink toward the printing object side; A voltage applying unit for applying a voltage to the nozzle to generate an electric field between the nozzle and the stage; A current measuring unit for measuring a current generated between the nozzle and the stage in discharging a droplet from the nozzle; And a control unit for receiving the measured current information from the current measuring unit and controlling an ejection condition of the ink ejected to the printing target or a feeding condition of the stage, The control unit may obtain the initial discharge timing information of the droplet based on the current information measured from the current measuring unit so as to transfer the stage and improve the accuracy of landing of the droplet to be discharged first, So as to start the feeding operation.

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In addition, the controller may control an electric field formed between the stage and the nozzle.

In addition, the controller may control an amount of voltage applied to the nozzle from the voltage application unit.

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Also, the controller may control the distance between the nozzle and the stage by transferring the nozzle unit.

The shape obtaining unit may be a vision sensor for measuring a liquid level formed on the nozzle.

In addition, the control unit may control an injection speed of the ink droplet ejected from the nozzle.

In addition, the controller may control the feeding speed of the nozzle.

According to the present invention, there is provided a feedback control type printing system capable of improving print quality by controlling ejection conditions of a droplet through shape information of a liquid surface.

In addition, by controlling the conditions such as the interval between the nozzle and the stage, the intensity of the voltage applied to the nozzle, and the intensity of the electric field formed between the nozzle and the stage, it is possible to control the injection speed and size of the droplet.

Further, by adjusting the ejection timing of the droplets, it is possible to improve the landing accuracy of the ink droplets on the printing object.

Further, by controlling the feeding speed of the nozzle, it is possible to easily control the jetting interval of the droplet.

In addition, the actual discharge timing of the droplet can be precisely measured through the measurement of the current value, thereby improving the accuracy of landing of the droplet.

In addition, the stability of the liquid surface and the uniformity of the diameter of the discharged liquid droplet can be improved by measuring the height of each liquid surface shape and varying the voltage condition applied according to the height ratio of each liquid surface.

1 is a schematic perspective view of a feedback control type printing system according to a first embodiment of the present invention,
Figure 2 schematically shows a cross-section of the feedback control type printing system of Figure 1,
3 schematically shows the principle of controlling the droplet diameter using the control unit in the feedback control type printing system of Fig. 1,
4 schematically shows an electric field control principle using a control unit in the feedback control type printing system of Fig. 1,
5 schematically shows the principle of the ejection liquid gap control using the control unit in the feedback control type printing system of Fig. 1,
6 schematically shows the principle of the ejection timing control of droplets using the control unit in the feedback control type printing system of Fig. 1,
7 schematically shows a feedback control principle for stabilizing the liquid level using the height information of the liquid level in the feedback control type printing system of FIG. 1,
Fig. 8 is a view for explaining information of mutually transmitted liquid level during liquid level stabilization feedback control of the feedback control type printing system of Fig. 7,
9 shows the height of the liquid level according to the time when the feedback control is performed using the feedback control type printing system of FIG. 7 and the voltage data applied to the nozzle when the feedback control is not performed,
10 is a schematic perspective view of a feedback control type printing system according to a second embodiment of the present invention,
FIG. 11 is current value data measured at the instant when a liquid droplet is ejected using the current measurement unit in the feedback control type printing system of FIG. 10,
12 is experimental data showing a phenomenon in which the initial ejection timing of the droplet is delayed regardless of the shape of the nozzle in the feedback control type printing system of FIG.

Prior to the description, components having the same configuration are denoted by the same reference numerals as those in the first embodiment. In other embodiments, configurations different from those of the first embodiment will be described do.

Hereinafter, a feedback control type printing system according to a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a schematic perspective view of a feedback control type printing system according to a first embodiment of the present invention, and Fig. 2 is a schematic view of a section of the feedback control type printing system of Fig.

1 and 2, the feedback control type printing system 100 according to the first embodiment of the present invention secures the shape information of the ink meniscus formed on the spray surface of the nozzle, A nozzle 120, a transfer unit 130, a voltage application unit 140, a shape acquisition unit 150, and a control unit 160. The control unit 160 controls the operation of the stage 110, the nozzle 120,

The stage 110 is a member for placing the printing object S and is movable in three directions (x-axis, y-axis, z-axis). In this embodiment, the stage 110 is electrically grounded to generate an electric field with the nozzle 120 described later. However, the stage 110 is not limited to this as long as it can generate an electric field with the nozzle 120 .

The nozzle 120 is a member for performing a direct printing process by injecting ink onto the stage 110 side by receiving ink, and an ink flow path is formed therein. An electrode (not shown) may be provided on the inner wall surface of the nozzle 120 where the ink flow path is formed to generate a potential difference with the opposing stage 110 by receiving a voltage from the voltage application unit .

In this embodiment, an electric field is generated between the stage 110 and the nozzle 120 by applying a voltage to the electrodes inside the nozzle 120 and electrically grounding the stage 110. However, The present invention is not limited to the structure described above as far as it is capable of generating a potential difference between the stage 120 and the stage 110. [

The voltage applying unit 130 is a member for generating an electric field between the stage 120 and the nozzle 120 on which the printing object is disposed by applying a predetermined voltage to the nozzle 120. [ In this embodiment, the voltage applied from the voltage applying unit 130 to the nozzle 120 is a form of a pulse voltage, but not limited thereto, an AC voltage may be applied depending on the printing conditions. .

The transfer unit 130 is a member for electrically transferring the nozzle 120 or the stage 110 in three axial directions by being controlled by a control unit 160 by being electrically connected to a control unit 160 to be described later.

The shape obtaining unit 150 obtains shape information of a meniscus, that is, a liquid surface, formed on the spray surface of the nozzle 120.

The shape obtaining unit 150 photographs and stores the shape of the liquid surface M formed on the spray surface of the end of the nozzle 120 and stores the shape of the liquid surface M To the control unit 160, which will be described later. At this time, the shape information of the liquid level M obtained from the shape obtaining unit 150 includes height information h of the liquid level M, diameter d of the liquid level M, and the like.

Meanwhile, in the present embodiment, the shape obtaining unit 150 uses a vision sensor, but it is not limited to a vision sensor if it can secure the shape of the liquid surface M.

The control unit 160 controls the injection condition of the ink using the shape information of the liquid level M obtained from the shape obtaining unit 150. The control unit 160 controls the transfer control module 161 and the voltage control module 162 .

The transfer control module 161 receives the shape information of the liquid level M from the shape obtaining unit 150 and controls the transfer unit 130 to adjust the intensity of the electric field between the nozzle 120 and the stage 110, The feed speed of the feed roller 120, and the like.

The voltage control module 162 receives the shape information of the liquid level M from the shape obtaining unit 150 and controls the voltage applying unit 140 so that the intensity of the electric field between the nozzle 120 and the stage 110 Or the injection speed of the discharged droplet, the size of the droplet, and the like.

Now, the operation of the first embodiment of the above-described feedback control type printing system will be described.

An electric field is formed between the nozzle 120 and the stage 110 by a voltage applied to the nozzle 120 when a predetermined voltage is applied from the voltage application unit 140 to the nozzle 120. [ A meniscus, that is, a liquid level M is formed on the jet surface of the end of the nozzle 120 under the influence of the electric field to be formed.

At the same time, the shape acquiring unit 150 operates to acquire the shape of the liquid surface M formed on the nozzle 120. That is, in the present embodiment, the shape obtaining unit 150 configured by the vision sensor calculates shape information such as the height h, the diameter d, and the volume of the liquid surface M formed on the spray surface of the nozzle 120 And transmits the shape information of the liquid level M to the control unit 160. [ The control unit 160, which receives the shape information of the liquid level, controls the ejection conditions of the liquid droplet, and will be described.

Through voltage control Droplet  Resize

3 schematically shows the principle of controlling the diameter of droplets using the control unit in the feedback control type printing system of Fig.

3 (a), the controller 160 controls the size of the droplet L discharged from the nozzle 120 according to the shape information of the liquid surface M.

3 (b), the controller 160 controls the voltage application unit 140 to control the voltages V ₁ and V ₂ applied to the nozzles 120, The size of the liquid level M formed at the end of the nozzle 120 can be controlled and the size of the droplet L finally discharged from the nozzle 120 can be controlled.

4 schematically shows an electric field control principle using a control unit in the feedback control type printing system of FIG.

3, the transfer control module 161 of the controller 160 controls the transfer unit 130 to bring the nozzle 120 closer to the stage 110, thereby increasing the strength of the electric field So that the size of the droplet to be discharged can be increased.

Droplet Discharge interval (Injection interval) control

5 schematically shows the principle of the ejection droplet gap control using the control unit in the feedback control type printing system of Fig.

5, when the injection interval of the droplet L is required to be adjusted according to the shape information of the liquid level M formed on the nozzle 120, the transfer control module 161 of the controller 160 controls the transfer unit 160, (130) to adjust the feeding speed of the nozzle (120). That is, the distance between the droplets L landing on the printing target S can be controlled by controlling the feeding speed of the nozzle 120 transferred along the printing direction.

The voltage control module 162 of the controller 160 controls the voltage application unit 140 to adjust the waveform of the voltage applied to the nozzle 120 to control the frequency of the pulse voltage, The injection speed of the droplet L can be controlled.

Droplet Discharge  Timing control

6 schematically shows the principle of the ejection timing control of droplets using the control unit in the feedback control type printing system of Fig.

6A, the controller 160 controls an electric field formed between the substrate 120 and the stage 110 according to the shape information of the liquid level M to control the ejection timing of the ink droplet . 6 (b), the controller 160 controls the frequency of the pulse voltage applied to the nozzle 120 from the voltage applying unit 140, that is, the pitches P ₁ and P ₂ between the pulse voltages, The timing at which the ink droplet L is ejected can be adjusted.

That is, when the ejection timing of the droplet L is slow according to the shape information of the liquid level formed on the nozzle 120, the ejection timing can be advanced by increasing the frequency of the pulse voltage applied to the nozzle 120.

That is, as described above, precise control of the ejection timing of the liquid droplet can improve the accuracy and uniformity of the droplet L landing on the printing target S, thereby improving the overall printing quality.

Stabilization of liquid surface and Discharge Droplet  Uniformity control

In addition, it is possible to increase the uniformity of droplets discharged by stabilizing the liquid level through feedback control.

That is, the liquid level can be stabilized by increasing the applied voltage when an excessive amount of liquid is supplied while monitoring the liquid level formed at the end of the nozzle 120, and by reducing the applied voltage when the liquid amount is insufficient.

When a relatively high voltage is applied to the nozzle 120, the amount of the ink ejected becomes larger than the amount of ink supplied to the nozzle 120, so that the uniformity of the liquid surface is destroyed and the size of the ejected droplet also changes, .

7 schematically shows a feedback control principle for stabilizing the liquid level using the height information of the liquid level in the feedback control type printing system of FIG.

7, the shape of the liquid surface formed immediately before discharge from the end of the nozzle 120 is acquired from the shape obtaining unit 150, and two coordinates are designated from the center to the outline of the nozzle 120 The center of the nozzle 120 and the designated coordinates are defined as X ₀ , X ₁ , and X ₂ , respectively, and the height of the obtained liquid level at the X ₀ position and the height of the obtained liquid level at the X ₁ position to the car △ Y ₁ d and d the difference between the height of the image of the obtained liquid level in the height and X ₂ position of the shape of the liquid level obtained in the X ₁ position △ Y ₂ △ Y between _1, △ Y ₂ Control the liquid surface through the relationship.

That is, FIG. 7 (a) a, △ Y ratio of ₁ and △ Y _{2, i.e., (△ Y 1 / △ Y} 2)> If 1 is the amount of ink to be supplied than the amount of discharged ink, as shown in is low or it is possible to judge to be applied with a voltage higher than required, as shown in Fig. 7 (c), if _{(△ Y 1 / △ Y 2} ) <1 is the ink to be supplied than the amount of ejected ink It may be judged that there is not enough voltage or sufficient voltage is applied.

Therefore, it is possible to real-time measurement values _{(△ Y 1 / △ Y 2} ) to stabilize by controlling the voltage, the liquid level.

On the other hand, in this embodiment, but setting the position of the X ₁ to be the mid-point of X ₀ and X _1, X ₁ and the position of X ₂ is not limited to this, proper ratio of △ Y ₁ / △ Y _2, which is defined in advance Is determined in consideration of the above.

Fig. 8 is a view for explaining the information of mutually transmitted liquid level during liquid level stabilization feedback control of the feedback control type printing system of Fig.

The height H ₀ of the actual liquid level obtained from the shape obtaining unit 150 is set by setting the height H of the desired liquid level while adjusting (ΔY ₁ / ΔY ₂ ) as shown in FIG. 8, It is possible to improve the uniformity of the size of the droplets to be finally ejected, and as a result, the overall print quality can be improved.

FIG. 9 shows the height of the liquid level according to the time when the feedback control is performed using the feedback control type printing system of FIG. 7 and the voltage data applied to the nozzle when the feedback control is not performed.

As shown in Fig. 9 (a), in the case of the feedback control according to the present embodiment, a liquid surface having a uniform height is formed as compared with the case where there is no feedback control. Also, as shown in FIG. 9 (b), when the feedback control according to the present embodiment is performed, it can be seen that the voltage applied to the nozzle 120 is not constant.

As described above, according to the various control methods of the present embodiment using various controls through the shape of the liquid surface, the voltage, the current, and the stage as described above, the accuracy of landing accuracy of the initial discharged liquid droplet, uniformity and stability of the liquid surface shape, And the like can be improved.

Next, a feedback control type printing system according to a second embodiment of the present invention will be described.

10 is a schematic perspective view of a feedback control type printing system according to a second embodiment of the present invention.

10, the feedback control type printing system 200 according to the second embodiment of the present invention includes a stage 110, a nozzle 120, a transfer unit 130, a voltage application unit 140, a controller 160, And a current measuring unit 270.

However, since the stage 110, the nozzle 120, the transfer unit 130, the voltage application unit 140, and the control unit 160 of the present embodiment are the same as those described in the first embodiment, redundant description will be omitted.

The current measuring unit 270 measures the amount of current generated between the stage 110 and the nozzle 120 and is connected to the controller 160. That is, the current measuring unit 270 measures the amount of current generated in the discharge of the droplet so as to transfer it to the controller 160, and acquires the precise discharge timing of the droplet to improve the accuracy of the droplet landing accuracy or control the droplet size .

Hereinafter, the operation of the feedback control type printing system of this embodiment will be described.

Feedback control through current measurement

11 is current value data measured at the instant when a liquid droplet is ejected using the current measuring unit in the feedback control type printing system of Fig.

In the case where droplet ejection does not occur substantially, the system forms an open circuit in which no current flows. However, as shown in FIG. 11, when a droplet is ejected, a gap is formed between the stage 110 and the nozzle 120 A closed circuit is formed and current flows.

Therefore, by measuring the amount of current flowing between the stage 110 and the nozzle 120 during the discharging of the droplet by using the current measuring unit 270 and performing the feedback control of the voltage applying unit 140 according to the amount of current, The stability and the uniformity of the size of the droplet can be improved.

12 is experimental data showing a phenomenon in which the initial ejection timing of the droplet is delayed regardless of the shape of the nozzle in the feedback control type printing system of FIG.

12, since the liquid droplet is not discharged simultaneously with the voltage application, when the time point when the voltage is applied by the voltage application unit 140 is assumed to be the time when the liquid droplet is discharged, .

Therefore, in the present embodiment, the point of time when the droplet is actually discharged is determined by measuring the time when the current is first generated by using the current measuring unit 270, the delay time between the voltage application time point and the discharge time point is calculated, The impact point of the ejected liquid droplet can be precisely controlled by moving the stage in accordance with the delay time.

That is, when the printing process is performed by fixing the nozzle 120 and transferring the stage 110, the stage starts to be conveyed at the timing when the droplet actually is discharged through the measurement of the current value, Can be improved.

The scope of the present invention is not limited to the above-described embodiments, but may be embodied in various forms of embodiments within the scope of the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

100: a feedback control type printing system according to the first embodiment of the present invention
110: stage 120: nozzle
130: transfer unit 140:
150: shape obtaining unit 160:
161: transfer control module 162: voltage control module

Claims (10)

A stage on which a print object is placed;
A nozzle for ejecting ink toward the printing object side;
A voltage applying unit for applying a voltage to the nozzle to generate an electric field between the nozzle and the stage;
A shape obtaining unit for obtaining shape information of a meniscus formed on a spray surface of the nozzle by a voltage applied from the voltage applying unit;
And a control unit for receiving the shape information from the shape obtaining unit and controlling the ejection condition of ink ejected to the printing object or the feeding condition of the stage,
Wherein the shape obtaining unit is provided with height information of a meniscus at a plurality of different points spaced from the center of the nozzle and the control unit calculates a height ratio of a meniscus at a plurality of points acquired from the shape obtaining unit, Wherein the control unit controls the intensity of the voltage applied to the nozzle according to the control signal. A stage on which a print object is placed;
A nozzle for ejecting ink toward the printing object side;
A voltage applying unit for applying a voltage to the nozzle to generate an electric field between the nozzle and the stage;
A current measuring unit for measuring a current generated between the nozzle and the stage in discharging a droplet from the nozzle;
And a control unit for receiving the measured current information from the current measuring unit and controlling an ejection condition of ink ejected to the printing object or a conveying condition of the stage,
The control unit controls the first ejection timing of the droplet based on the current information measured from the current measuring unit so as to transfer the stage from the nozzle to the droplet so that the printing object is printed, And controls to start conveying the stage at the initial stage of discharging the droplet after acquiring the information. 3. The method according to claim 1 or 2,
Wherein the control unit controls an electric field formed between the stage and the nozzle. 3. The method according to claim 1 or 2,
Wherein the control unit controls the amount of voltage applied to the nozzle from the voltage applying unit. The method according to claim 1,
Wherein the control unit controls the distance between the nozzle and the stage by feeding the nozzle. The method according to claim 1,
Wherein the shape obtaining unit is a vision sensor for measuring a liquid level formed on the nozzle. 3. The method according to claim 1 or 2,
Wherein the control unit controls the injection speed of the ink droplet ejected from the nozzle. 3. The method according to claim 1 or 2,
Wherein the control unit controls the feeding speed of the nozzle. delete delete

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