JP7199109B1 - Correction Method of Print Distortion in Inkjet Printer - Google Patents

Abstract

A correction method capable of minimizing print distortion without correcting the charge amount of ink droplets by changing the arrangement of print data is provided. A control unit of a controller inserts an empty row without dots between each dot when two or more dots are adjacent to each other in one line of print data consisting of a matrix dot pattern. and if there is only a single dot in one line of the print data, the print data is changed so as to move the dot formation position to the front row, and the changed print data and the number of rows read out from the storage unit are stored. A charging voltage to be applied to the charging electrode is generated based on the period data. [Selection drawing] Fig. 7

Description

The present invention relates to a printing distortion correction method in a continuous ink jet printer, and more particularly to correction of printing distortion during high-speed printing.

Inkjet printers are broadly classified into a continuous type and an on-demand type. In the continuous type inkjet printer, ink is ejected from a nozzle by a pump, and at the position where the ejected ink separates into ink droplets by vibration of a certain frequency, the ink droplets are charged by a charging electrode, and the ink is further deflected by a deflection electrode. The trajectory of the droplets is bent, and the droplets collide with predetermined positions on the substrate to form an arbitrary matrix-like dot pattern.

In the above-described continuous type ink jet printer, air resistance decelerates ink droplets flying toward the printing surface, and depending on the degree of deceleration, print dots formed on the printing surface may be adversely affected.

For example, the density of the ink droplets flying toward the printing surface causes a difference in air resistance, which disturbs the airflow and disturbs the flight path of the following ink droplets, which is one of the causes of degraded printing quality. was

As a countermeasure, conventionally, the flying trajectories of two ink droplets forming adjacent print dots in the same row of the dot matrix are spaced apart to reduce mutual aerodynamic interference, thereby printing due to variations in air resistance. I kept the disturbance of the dots to a minimum. (Patent Document 1)

JP-A-6-305147 JP-A-6-15827

On the other hand, it is known that the influence of air resistance on the flight of ink droplets between rows of the dot matrix differs depending on the moving speed of the printed material. For example, when printing while moving the print head at a relatively low speed (approximately 1 to 30 m/min) relative to the print surface, the distance between the ink droplets flying in each line is sufficiently maintained, so the effect of air resistance need not be considered.

On the other hand, when printing while the substrate is moving at high speed (approximately 200m/min or more), the cycle of the rows becomes shorter, so the turbulence of the airflow caused by the flying ink droplets in the preceding row becomes This greatly affects the flight of ink droplets in the succeeding rows, causing print distortion.

Conventionally, the printing distortion due to the disturbance of the air resistance between the rows has been dealt with by correcting the charge amount of the ink droplets in the succeeding row according to the flight state of the ink droplets in the preceding row. (See Patent Document 2).

However, in the above method, it is necessary to determine the charge amount of ink droplets in consideration of not only the arrangement of printed dots but also the moving speed of the printed material. not present.

The present invention has been made in view of such conventional problems. By changing the arrangement of print data, it is possible to minimize print distortion without correcting the charge amount of ink droplets. The purpose is to provide a fix that can

A printing distortion correction method according to the present invention for achieving the above object includes:
a gun that vibrates jetted ink at a constant frequency to produce continuous ink droplets;
a charging electrode that applies a voltage to the ink droplets to charge the ink droplets;
a deflection electrode that deflects the ink droplets flying toward a horizontally moving object to be printed in a vertical direction in accordance with the degree of electrification and causes the ink droplets to land on the object to be printed;
a controller that controls the amount of charge on the ink droplets by changing the voltage applied to the charging electrode;
In inkjet printers that print characters and symbols in a matrix-like dot pattern on the printing surface of the material to be printed,
The storage unit of the controller stores print data indicating positions for forming dots in the frame of the matrix and cycle data of the columns of the matrix,
A control unit of the controller,
In one line of the print data read out from the storage unit, if two or more dots are adjacent to each other, an empty column without dots is inserted between each dot, and in one line of the print data , if there is only a single dot, changing the print data so as to move the dot formation position to the front row;
A charging voltage to be applied to the charging electrode is generated based on the changed print data and the row period data read from the storage unit.

Here, it is preferable that the inkjet printer tilts the direction of deflection of the ink droplets from the vertical direction to the direction of movement of the object to be printed according to the moving speed of the object to be printed.

Further, it is preferable that, when there is a preceding dot in one line of the print data, the control section of the controller advances the charging timing of the ink droplets for generating the succeeding dot.

Furthermore, it is preferable that the control section of the controller delays the timing of charging the ink droplets in inverse proportion to the number of dots in one line of print data.

In the method for correcting printing distortion according to the present invention, the flight speed of the ink droplets in the preceding line is decelerated by air resistance, causing printing distortion, by changing the arrangement of the printing data represented by the dot pattern. , is kept to a minimum.

That is, the method of correcting printing distortion according to the present invention can be handled by simply changing the dot formation position of the printing data without modifying the hardware surface, so it can be easily introduced as an algorithm and can be applied to existing printers. can also be easily incorporated.

1 is a diagram showing a schematic configuration of a continuous-type inkjet printer, which is a prerequisite for correction of printing distortion; FIG. FIG. 2 is a diagram for explaining the operation of printing on a print target using the inkjet printer of FIG. 1; FIG. 4 is a diagram showing the process of generating ink droplets; FIG. 4 is a diagram of extracted blocks related to generation of charging voltage from the configuration of the controller; FIG. 4 is a diagram showing an example of print data; 6 is a diagram showing substantially stepped charging voltages created based on the print data of FIG. 5; FIG. FIG. 4 is a diagram illustrating first and second methods of correcting print distortion; FIG. 10 is a diagram showing a print example to which the printing distortion correction method according to the present invention is applied; It is a figure explaining the 4th method of correcting printing distortion. 10 is a diagram showing charging voltages created based on the print data of FIG. 9; FIG. FIG. 10 is a diagram showing a print example to which the printing distortion correction method according to the present invention is applied;

A printing distortion correction method according to an embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1)
<Configuration of inkjet printer>
FIG. 1 shows a schematic configuration of a continuous type ink jet printer, which is a premise for correction of print distortion. Also, FIG. 2 shows the operation of printing on a print target using the ink jet printer of FIG.

The ink jet printer 1 comprises a gun 2, a charging electrode 3, a detection electrode 4, a deflection electrode 5, a gutter 6, a pipe 7, pumps 8a and 8b, an ink tank 9 and a controller 10.

The gun 2 ejects ink droplets ID toward the surface of an object to be printed (such as a packaging box) 11 , and is composed of a gun body 21 , an ultrasonic vibrator 22 and a nozzle 23 . Ink is sent from the ink tank 9 by the pump 8 a and supplied to the gun body 21 through the pipe 7 .

The ink column IP ejected from the hole of the nozzle 23 is separated into individual ink droplets ID by vibration applied by the ultrasonic vibrator 22 and further charged by the charging electrode 3 . After that, only the ink droplets ID required for printing are deflected by the deflection electrode 5 according to the charge amount and land on the printing surface of the object 11 to be printed.

FIG. 2 shows the packaging box 11 moving at a constant speed in the direction indicated by the arrow on a belt conveyor (not shown). When the packaging box 11, which is the object to be printed, is moving in a direction perpendicular to the flight direction of the ink droplets ID, by changing the amount of deflection of the ink droplets ID, the side surface (printing surface) of the packaging box 11 is changed. When the position of the landing ink droplet ID changes and the deflection of the ink droplet ID is repeated in synchronism with the movement of the packaging box 11, characters and symbols (“A” in the figure) are printed.

On the other hand, the uncharged ink droplets ID and the charged ink droplets ID not used for printing are not deflected, but fly directly into the ink collection gutter 6 and are collected in the ink tank 9 . The ink collected by the gutter 6 is transferred to the ink tank 9 through the pipe 7 by the pump 8b and reused.

The controller 10 controls the operation of the ultrasonic transducer 22 of the gun 2, the pulse power source 31 of the charging electrode 3, the detection electrode 4, the DC power source 51 of the deflection electrode 5, and the pumps 8a and 8b. ROM, RAM, etc.), a timer and a display (not shown). Although the controller 10 and each component to be controlled are connected by signal transmission cables, they are omitted in FIG. 1 except for the cables between the pumps 8a and 8b to avoid complexity. are doing.

The controller 10 applies pressure to the ink contained in the ink tank 9 by driving the pump 8 a to supply the ink to the gun body 21 . The controller 10 also controls the timing of the pulse voltage applied from the pulse power source 31 to the charging electrode 3 based on the signal detected by the detection electrode 4, thereby adjusting the number and timing of the charged ink droplets ID. . Further, the controller 10 adjusts the amount of deflection of the ink droplets ID deflected by the deflection electrode 5 by controlling the voltage of the DC power supply 51 .

<Correction of printing distortion>
Next, referring to FIGS. 3 to 8, a printing distortion correction method according to the present embodiment will be described. First, the charging of ink droplets will be described.

FIG. 3 shows the process of generating an ink droplet ID from the ink column IP ejected from the nozzle 23. As shown in FIG. As described above, the piezoelectric vibrator 22 is used to vibrate the ink column IP ejected from the gun 2 at a constant frequency, thereby generating ink droplets ID having a predetermined particle size. For example, when the operating frequency of the piezoelectric vibrator is 73.5 kHz, 73500 droplets/sec of ink droplets are generated.

As shown in FIG. 1, since the gun 2 is grounded, the ink column IP ejected from the nozzle 23 is also held at a potential of 0V. When a positive pulse voltage is applied to the charging electrode 3, a negative charge is induced in the ink column IP. When the ink column IP separates into ink droplets ID, a negative charge remains on the ink droplets, which then continue flying with the ink droplets ID charged.

The flying ink droplets ID are deflected upward according to the amount of charge by the DC voltage applied to the deflection voltage 5, and collide with the surface of the material to be printed 11 to form print dots.

FIG. 4 is a diagram in which only blocks related to generation of the charging voltage are extracted from the functional blocks of the controller 10 described above. The controller 10 includes a control section 11 , a storage section 12 , an input/display section 13 , a D/A conversion section 14 and an amplification section 15 .

Among these, the functions of the control unit 11 are realized by executing a program stored in the storage unit 12 by a CPU (not shown). The input/display unit 13 is implemented by a touch panel type liquid crystal display, and displays input print data and the like.

The storage unit 12 stores print data represented by a matrix pattern, that is, print dot formation position data and dot matrix column repetition cycle data (hereinafter simply referred to as “cycle”). When printing, the control unit 11 reads the print data and the period data from the storage unit 12 , creates a substantially stepped charge voltage for each column based on the print data, and applies the charge voltage to the charge electrode 3 . apply.

The charging voltage set by the control section 11 is converted into an analog signal by the D/A conversion section 14 , amplified by the amplification section 15 , and then applied to the charging electrode 3 .

FIG. 5 shows an example of print data stored in the storage unit 12 of the controller 10. As shown in FIG. The print data is represented by a matrix-like dot pattern, in which the horizontal axis (row) of the matrix indicates the horizontal position of the material to be printed, and the vertical axis (column) indicates the landing position of the deflected ink droplets.

The print data shown in FIG. 5 is a dot pattern for forming the numeral "1" in a matrix of 5 rows×5 columns on the print surface. In the drawing, the numbers 1 to 25 displayed in each frame of the matrix are clock numbers indicating the order of printing, and print dots are formed at positions where the clock numbers are surrounded by circles.

The storage unit 12 stores matrix dot pattern data shown in FIG. 5 and row cycle data. A stepped charging voltage is created and applied to the charging electrode 3 .

When the printed material reaches the position of each row of the dot matrix, the ink droplets ID ejected from the nozzles 23 are deflected upward according to the amount of charge, and print dots ● are formed at designated positions on the printing surface. It is formed. When printing for five columns is completed, the frames indicated by ◯ marks in the matrix of 5 rows×5 columns are filled with print dots, and the printing is completed.

In addition to the 5 rows×5 columns, the matrix used for printing includes 7 rows×5 columns, 9 rows×9 columns, 12 rows×10 columns, 16 rows×16 columns, 24 rows×18 columns, and 32 rows. There are many options such as x24 columns.

Next, the relationship between the moving speed of the object to be printed and the charging of ink droplets will be described. In order to print on the object to be printed with a constant character width regardless of the moving speed of the object to be printed, it is necessary to change the distance between the ejected ink droplets according to the moving speed of the object to be printed.

Not all ink droplets produced by gun 2 are used to produce printed dots. For example, five ink droplets are required for printing one row of the matrix, but as described above, a large number of ink droplets are generated per second, and the speed does not change. Therefore, when the moving speed of the object to be printed is slow, most of the ink droplets do not participate in printing and are collected in the gutter without being charged. That is, when printing for one line, only ink droplets selected at a fixed timing are charged, and other ink droplets are thinned out without being charged.

In the substantially stepped charging voltage shown in FIG. 6, for example, in the third row, one ink droplet selected at a fixed timing is charged every five clocks, and the other ink droplets are thinned out. is collected in the gutter 6. Then, the five charged ink droplets land on the positions deflected by the charging voltage, forming one line of printing dots on the printing surface.

For example, with a printhead that produces ink drops on a 130 kHz cycle (i.e., produces one ink drop every 7.6 μs), a lateral dot spacing of 1 mm on a substrate moving laterally at 15 m/min If you try to print with , you have to charge the ink droplets at intervals of 526 and eject them.

When printing in a speed range where thinning is included, a charging voltage (0 V) for thinning is inserted for each stage of the third row, but is omitted in the drawing to avoid complication. The same applies to the following description.

Next, the printing distortion that occurs as the printing speed increases will be described. If printing is performed on a substrate moving at 30 m/min with the above settings, the distance between printed dots will be doubled to 2 mm. For this reason, the controller 10 calculates the intervals at which the ink droplets should be charged based on the data of the moving speed of the material to be printed. is adjusted to charge the ink droplets.

By the way, the faster the moving speed of the object to be printed, the closer the distance between the ink droplets to be printed. As a result, the preceding ink droplets are decelerated by air resistance during flight and collide with the succeeding ink droplets. Here, the preceding ink droplet means a state in which no ink droplet exists in front of the ink droplet, that is, ink droplets ejected with a sufficient time interval. This ink droplet is hereinafter referred to as the "first ink droplet".

Further, the faster the moving speed of the object to be printed is, the more the landing position of the ink droplet decelerated by the air resistance is shifted to the rear of the target position. This is because the flight time of the flying ink droplets is extended, and the object to be printed moves before reaching the target position.

When the moving speed of the object to be printed reaches 300 m/min or more, the first ink droplet and the subsequent ink droplets begin to approach or collide, and the higher the speed, the more likely they are to collide. Also, regarding the first ink droplet, which does not collide because there is no subsequent ink droplet, the faster the speed, the greater the displacement of the landing position.

In this way, the printing distortion that occurs as the printing speed increases is considered to be caused by the collision of the ink droplets and the displacement of the landing position due to the deceleration of the ink droplets due to the air resistance. Therefore, in the present invention, by correcting the print data and changing the positions where the print dots are formed, a leeway is given to the anteroposterior relationship of the ink droplets flying at the same height. correcting the deviation.

In the present invention, as a first method for correcting print distortion, when two or more dots are adjacent to each other in one line of print data, an empty column without dots is inserted between each dot. .

For example, when printing the numeral "1" as shown in FIG. 7A, the dots in the second and fifth lines are adjacent to each other. When printing is performed in this state, as shown in the example of printing in FIG. 8A, the printing dots of the second row and the printing dots of the third row collide on the printing surface. Also, the interval between dots becomes narrower as shown in the printed dots on the fifth line.

In order to avoid this, in the present invention, as shown in FIG. 7(b), an empty row is inserted between dots to move the printing position of the second row to the first row, and to move the printing position of the fourth row to the first row. Move the dot to the fifth column.

FIG. 7B shows an example of printing based on print data in which empty columns are inserted between each column. The moving speed of the material to be printed was set to 600 m/min. As is clear from a comparison of FIGS. 8(a) and 8(b), print dot collision can be avoided, and a sufficient interval is maintained between print dots, thereby greatly reducing print distortion.

In the present invention, as a second method of correcting printing distortion, when there is only a single dot in one line, the dot formation position is moved to the front row. FIG. 7(c) shows a specific example of position correction, in which the position of a print dot that exists alone in the same row is moved to the previous row as indicated by an arrow.

FIG. 8C shows an example of printing by moving the dot formation position in this way. It can be seen that the five print dots in the third row among the number "1" are corrected in the vertical direction compared to before the movement, and the print distortion is improved.

In the printing distortion correction method according to the present invention, the first and second methods described above are essential. FIG. 8(a) is a print example before applying the first and second methods, and FIG. 8(c) is a print example after applying the first and second methods. Comparing the two, it can be seen that the printing distortion caused by the increased printing speed is greatly improved, and the printing quality is improved.

(Embodiment 2)
Although not essential as a method of avoiding printing distortion, printing distortion can be further reduced by applying the third and fourth methods after applying the first and second methods described above. According to the present invention, as a third method, the deflection direction of the ink droplets is slightly inclined to the movement direction of the printed material.

When the movement speed of the printed material is 600 m/min for the ink droplet generation cycle of 130 kHz, the printed material moves 0.076 mm in the moving direction while generating one ink droplet (7.6 μs). do.

If the actual height of the printed characters is 4 mm, the theoretical distance between printed dots in the vertical direction is 1 mm. That is, since tan θ=1/0.076, the print is tilted by θ=85.79°. Therefore, if the deflection direction of the ink droplets is tilted by 4.21° with respect to the movement direction of the printed material, the characters will be upright. In an actual printer, the deflection direction of ink droplets can be tilted by rotating a cylindrical printhead (not shown) containing the components of FIG. 1 by 4.21° in the vertical plane.

FIG. 8(d) shows an example in which the direction of deflection of the ink droplets is tilted by 4.21° with respect to the direction of movement of the object to be printed, in contrast to the example of printing in FIG. 8(c). Comparing the two, it can be seen that the five print dots in the third row of the numeral "1" are erect in the vertical direction.

As in the third method, although not essential as a method of correcting printing distortion, the present invention employs a method of advancing the timing of charging ink droplets as a fourth method. A fourth method will be described with reference to FIGS.

As described above, the print example in FIG. 8D is an example in which the first, second, and third methods of correcting print distortion are applied. In the print example shown in FIG. 8(d), the print distortion is greatly improved compared to the print example before correction shown in FIG. 8(a). There is a problem that the ink droplets are separated more than necessary, and in order to solve this problem, the ink droplet charging timing is advanced.

FIG. 9(a) shows the print data of the matrix pattern when performing the printing of FIG. 8(d). FIG. 10(a) shows the charging voltage applied to the charging electrode 3 when printing the same pattern.

Comparing the print data on the bottom line of the print data shown in FIG. 9A with the print dots on the bottom line shown in FIG. In the printed dots in FIG. 8D, the interval between the center printed dot and the rightmost printed dot is widened. From this, it can be considered that when there are two or more ink droplets that fly precedingly in the same line, the effect of air resistance is reduced and the interval between dots is widened.

In the fourth method, considering the above phenomenon, when there is a preceding dot in one line of print data, the timing of charging the ink droplets for generating the succeeding dot is determined by changing the magnitude of the charging voltage. It moves forward without changing. FIG. 9B shows an example in which the dots of clock number 21 in the print data of FIG. 9A are shifted to clock number 19 by two clocks. FIG. 10(b) shows the charging voltage applied to the charging electrode 3 when printing the same pattern.

FIG. 8(e) described above shows an example of printing using the charging voltages shown in FIG. 10(b). As can be seen by comparing the print example of FIG. 8(d) with the print example of FIG. 8(e), in the print example of FIG. It can be seen that the dot intervals are almost equal, and the printing distortion is almost eliminated.

As a result of experiments, it was found that the timing of charging the ink droplets should be delayed in inverse proportion to the number of dots in one line of print data. In the print data shown in FIG. 9A, the number of dots is 3, but if the number of dots is 4, the forward movement timing can be half (one clock).

FIG. 11 shows print examples in which print distortion is corrected by applying the first to fourth methods according to the present invention in comparison with print examples before correction. 11(a) is an example of printing the number "2", FIG. 11(b) is an example of printing the number "3", FIG. 11(c) is an example of printing the alphabet "A", and FIG. 11(d) is an example of printing the alphabet " A printing example of "B", and FIG. 11E is a printing example of the alphabet "C". The left side shows an example of printing before correction, and the right side shows an example of printing after correction.

As is clear from each printing example in FIG. 11, by adopting the method of correcting printing distortion according to the present invention, printing distortion can be corrected to the extent that there is no practical problem, and printing quality can be greatly improved.

Furthermore, the first, second and fourth correction methods only need to change the dot arrangement of the print data, and do not require complicated processing such as correcting the charge amount of the ink droplets. Also for the third correction method, it is sufficient to simply rotate the printhead case in the vertical plane. Therefore, it is easy to introduce the printing distortion correction method, and it can be easily incorporated into existing printers.

IP ink column ID ink drop 2 gun 3 charge electrode 4 detection electrode 5 deflection electrode 6 gutter 7 pipe 8a, 8b pump 9 ink tank 10 controller 11 control section 12 storage section 13 input/display section 14 D/A conversion section 15 amplification section 21 gun body 22 ultrasonic transducer 23 nozzle 31 pulse power supply 51 DC power supply

Claims (4)

a gun that vibrates jetted ink at a constant frequency to produce continuous ink droplets;
a charging electrode that applies a voltage to the ink droplets to charge the ink droplets;
a deflection electrode that deflects the ink droplets flying toward a horizontally moving object to be printed in a vertical direction in accordance with the degree of electrification and causes the ink droplets to land on the object to be printed;
a controller that controls the amount of charge on the ink droplets by changing the voltage applied to the charging electrode;
In inkjet printers that print characters and symbols in a matrix-like dot pattern on the printing surface of the material to be printed,
The storage unit of the controller stores print data indicating positions for forming dots in the frame of the matrix and cycle data of the columns of the matrix,
A control unit of the controller,
In one line of the print data read out from the storage unit, if two or more dots are adjacent to each other, an empty column without dots is inserted between each dot, and in one line of the print data , if there is only a single dot, changing the print data so as to move the dot formation position to the front row;
A method of correcting printing distortion, wherein a charging voltage to be applied to the charging electrode is generated based on the changed printing data and the row cycle data read from the storage unit. 2. The method of correcting printing distortion according to claim 1, wherein said ink jet printer tilts a direction of deflection of said ink droplets from a vertical direction to a direction of movement of said object to be printed according to a moving speed of said object to be printed. 3. The control unit of the controller according to claim 1, wherein when there is a preceding dot in one line of print data, the control unit of the controller advances the charging timing of the ink droplets for generating the succeeding dot. How to correct print distortion. 4. The print distortion correction method according to claim 3, wherein the controller of the controller delays the timing of charging the ink droplets in inverse proportion to the number of dots in one line of print data.

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