JP7274770B2 - inkjet printer - Google Patents

Description

The present invention relates to a continuous ink jet printer, and more particularly to correction of print 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-mentioned continuous type inkjet printer, the air resistance of the ink droplets flying toward the printing surface causes an air current (air flow), and depending on the degree of the air current, the printed dots formed on the printing surface may be adversely affected. may affect

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, non-charged ink droplets are inserted between the landing ink droplets to suppress the occurrence of turbulence in the airflow (see Patent Document 1, paragraph 0006).

Japanese Patent Application Laid-Open No. 2008-137197

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 printed material at a relatively low speed (approximately 1 to 30 m/min), the ink droplets flying in each row are sufficiently spaced to take into consideration the effects of air resistance. No need.

On the other hand, when printing while the substrate is moving at high speed (approximately 200 m/min or more), the cycle of the rows becomes shorter, so the effect of the air current formed by the flying ink droplets in the preceding row remains. During this time, the next row of ink droplets is launched. As a result, the ink droplets are drawn into the remaining air current, and the flying speed increases, causing the position of the printed dots to shift, resulting in printing distortion.

At present, however, there is no effective solution to the above-mentioned problems that arise with the increase in printing speed, and improvements have been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances. To provide an inkjet printer capable of minimizing

In order to achieve the above object, a first inkjet printer according to the present invention comprises:
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;
An inkjet printer that prints characters and symbols in a matrix-like dot pattern on the printing surface of an object to be printed,
In the storage unit of the controller,
Print data indicating positions for forming dots in a matrix, and a plurality of waiting times obtained through experiments corresponding to different periods of columns of the matrix and corresponding to lengths of intervals during which printing is not performed. data is stored,
A control unit of the controller,
generating a charging voltage to be applied to the charging electrode for each column of the matrix based on the print data and the cycle data of the column ;
creating print data for one time including the individual print data, and specifying the interval period from the print data for one time;
Waiting time data corresponding to a specific cycle and a specified interval period of the columns is read out from the storage unit, and the waiting time is set between the columns of the matrix.

A second inkjet printer according to the present invention for achieving the above object is
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;
An inkjet printer that prints characters and symbols in a matrix-like dot pattern on the printing surface of an object to be printed,
In the storage unit of the controller,
print data indicating the positions to form dots in the matrix, and
Data of multiple calculation formulas corresponding to the length of the interval period when printing is not performed are stored,
A control unit of the controller,
generating a charging voltage to be applied to the charging electrode for each column of the matrix based on the print data and the cycle data of the column ;
creating print data for one time including the individual print data, and specifying the interval period from the print data for one time;
Data of a calculation formula corresponding to the specified interval period is read from the storage unit , a waiting time corresponding to the period of the columns is calculated using the calculation formula, and a waiting time is set between the columns of the matrix. characterized by

In the inkjet printer according to the present invention, the effect of airflow is suppressed by setting a waiting time corresponding to the period of each row of the dot matrix and adjusting the value of the waiting time. By keeping the intervals between the print dot rows formed on the print surface substantially uniform, print distortion caused by high-speed printing is minimized.

1 is a diagram showing a schematic configuration of a continuous inkjet printer according to Embodiment 1 of the present invention; 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 print data (a) of a test pattern and charging voltage (b) for one row; FIG. 10 is a diagram showing an example (a) of a conventional stepped charging voltage and an example (b) of a stepped charging voltage according to the present invention; It is the figure which showed the print example of the inkjet printer in low speed (a) and high speed (b*c). FIG. 10 is a diagram for explaining the relationship between the interval period and print distortion;

An inkjet printer 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 ink jet printer according to the first embodiment. 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 sent from the ink tank 9 by the pump 8 a and supplied to the gun body 21 through the pipe 7 is jetted from the hole of the nozzle 23 while being vibrated by the ultrasonic vibrator 22 .

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, correction of printing distortion in the present embodiment will be described with reference to FIGS. 3 to 7. FIG. 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, data indicating the positions of dots to be formed in the frames of the matrix, and the repetition cycle of the columns of the matrix (hereinafter simply referred to as “cycle”). data is stored. When printing, the control unit 11 reads print data and period data from the storage unit 12, creates a stepped charging voltage for each column based on the printing data, and applies the charging voltage to the charging electrode 3. do.

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

Next, the relationship between the moving speed of the object to be printed and the charging of ink droplets will be described. Not all ink droplets produced by gun 2 are used to produce printed dots. For example, 9 ink droplets are required for printing one row of the dot 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.

On the other hand, since the dot matrix column period shortens in inverse proportion to the moving speed of the printing medium, the number of thinned ink droplets decreases as the moving speed increases.

FIG. 5A shows 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. 5A is test data for forming print dots of 9 rows×5 columns on the print surface.

The storage unit 12 stores print data indicating positions for forming dots in the frame of the matrix shown in FIG. 5A and period data of the columns of the matrix. , the print data is read for each column to create a stepped charging voltage shown in FIG.

In the stepwise charging voltage shown in FIG. be recovered. Then, the nine charged ink droplets land on positions deflected by different charging voltages, forming one line of printing dots on the printing surface.

In the actual charging voltage, a charging elastic pressure (0 V) for thinning is inserted in each stage of FIG. The same applies to the following description.

FIG. 6(a) shows the stepwise charging voltage generated by the above procedure based on the print data of FIG. 5(a). FIG. 7(a) shows an example of printing on an object to be printed moving horizontally at a speed of 1 m/min using the same voltage.

When the object to be printed reaches the position of the first row of the dot matrix, the ink droplets ejected from the nozzles 23 are deflected upward according to the amount of charge, and the ● mark is printed at the specified position on the printing surface. A dot is formed. As shown in FIG. 7A, when printing for five columns is completed, all the frames of the matrix of 9 rows×5 columns are filled with print dots, and printing is completed.

Next, the printing distortion that occurs as the printing speed increases will be described. When an ink droplet flies, an air current directed from the print head toward the printing surface is generated by the air resistance associated with the flight of the ink droplets in the preceding row, which affects the flight of the ink droplets in the next row.

When the moving speed of the substrate is relatively low, the column period is long, so that the influence of the air flow generated in the preceding column disappears before the next column of ink droplets flies. In the printing example shown in FIG. 7(a), the moving speed of the material to be printed is relatively low at 1 m/min, and the printing dots are accurately formed at the positions specified by the printing data, and no printing distortion occurs. not

On the other hand, when the moving speed of the substrate is high (200 m/min or more), the cycle of the columns is short, and while the airflow generated in the preceding column remains, the ink droplets in the following column fly. As a result, the flying speed of the ink droplets is increased by being drawn into the remaining air current, and a phenomenon is observed in which the landing point of the ink droplets deviates from the intended position.

FIG. 7(b) shows an example in which the object to be printed is moved at a high speed of 600 m/min and printed using the stepwise charging voltage shown in FIG. 6(a). As is clear from the figure, the printed dots formed in the first row and the printed dots formed in the second row overlap, and the space between the printed dots in the second row and the printed dots in the third row becomes narrower. ing. When compared with the print example shown in FIG. 7A, it can be seen that the print dots are greatly distorted.

As described above, the printing distortion that occurs as the printing speed increases is attributed to the fact that the ink droplets in the succeeding row are drawn into the air current generated by the flying ink droplets in the preceding row, and the flying speed increases. Conceivable.

Therefore, in the present invention, in order to reduce the influence of the airflow generated in the preceding row, a waiting time is provided between each row until the airflow generated in the preceding row no longer affects the flight of the ink droplets in the succeeding row. , the printing timing is staggered.

FIG. 6(b) shows the charging voltage with the standby time set between the rows. When setting the waiting time, the time at which the intervals between the print dots formed in each row are substantially equal is confirmed through experiments. Also, since the value of the waiting time changes in accordance with the moving speed of the printed material, the experiment is repeated while changing the value of the period of the rows. Values confirmed through experiments are stored in the storage unit 12 of the controller 10 .

In the example shown in FIG. 6(b), the waiting time _t1 between the first and second columns is 100 μS, the waiting time _t2 between the second and third columns is 70 μS, and the third and third columns The waiting time t ₃ between the 4 rows was 50 μS, and the waiting time t ₄ =0 between the 4th and 5th rows.

FIG. 7(c) shows an example in which printing was performed using the charging voltage shown in FIG. 6(b) while moving the object to be printed with respect to the print head at a speed of 600 m/min. The intervals between the print dots formed in each row are substantially uniform, and the print quality is dramatically improved compared to the case where printing is performed without adopting the waiting time shown in FIG. 7(b).

There are two methods for storing the standby time setting data in the storage unit 12 . In the first method, the data of the waiting time confirmed through the experiment is stored in the storage unit 12 together with the period data of the columns. In the second method, a formula for approximately calculating the waiting time is created based on experimental results, and the data of the formula is stored in the storage unit 12 together with the period data of the columns. Considering the advantages/disadvantages of each method, either method may be adopted.

At the time of printing, along with the print data, the column period data and waiting time data or calculation formula data are read out from the storage unit 12, and the thinning ratio of the ink droplets is determined according to the column period, and the data is read out between the columns. , or set the calculated standby time.

In the printing examples shown in FIGS. 7B and 7C, the print dot rows formed in each row are curved to the right. However, it is caused by the extension of the flight time until the ink hits the target position, and its influence on printing distortion is small compared to the pitch between rows.

In addition, the positions of the printed dots in the bottom row of each row are shifted downward. It is not specifically mentioned here because it is of a different nature than the distortion caused by the airflow generated in the preceding row, and therefore the method of correcting the distortion is also different.

(Embodiment 2)
In the first embodiment, correction of printing distortion due to speeding up was described with reference to printing at the beginning of printing. However, as shown in FIG. Interval period") continues, the same distortion as described in the first embodiment occurs.

FIG. 8 shows an example in which 9 print dots are continuously printed as a test pattern, and interval periods T1 to T5 of different lengths are inserted in between.

Comparing the print example of the short interval period T1 shown in FIG. 8(a) with the print example of the long interval period T5 shown in FIG. 8(e), in FIG. and the second print dot row are separated from each other. On the other hand, in the print example of FIG. 8E, the print dot rows of the first row and the second row are overlapped, and the print distortion is large.

Therefore, as in the first embodiment, it is necessary to set the standby time and correct the interval between the print dot rows. Furthermore, unlike Embodiment 1, even if the moving speed of the printing material is the same, if the interval period is different, it is necessary to adjust the waiting time according to the period.

This is probably because when there is an interval period in the middle of printing, the influence of the airflow formed by the preceding printing remains, and the degree of this effect increases as the interval period becomes shorter. Therefore, it is necessary to adjust the standby time according to the length of the interval period.

Table 1 shows an example of the waiting time set based on the above idea. The horizontal axis of the table indicates the lengths T1 to T5 of the interval period, corresponding to the print examples of FIGS. 8(a) to 8(e). The vertical axis of the table indicates the length of waiting time. The interval period T∞ in Table 1 indicates an infinite interval period, that is, the waiting time at the beginning of printing as described in the first embodiment.

As is clear from Table 1, the shorter the interval period, the shorter the standby time. This is thought to be because the shorter the interval period, the stronger the effect of the airflow formed by the preceding printing remains, and the effect increases the flight speed of the ink droplets in the first row when printing is resumed.

In Table 1, the waiting time is set between the first and third columns, and the waiting time after the fourth column is set to zero. If so, set the wait time accordingly.

Next, a procedure for setting the standby time will be described. As described above, the storage unit 12 stores standby time data or standby time calculation formula data corresponding to each interval period. At the time of printing, along with the print data and the period data of the columns, data of the standby time corresponding to the period data or data of the calculation formula is read from the storage unit 12 .

The control unit 11 of the controller 10 creates print data for one time including character data based on the read individual print data, stores it in the work memory, specifies an interval period from the data, and specifies an interval period during that period. Data on the corresponding standby time is taken out, or the standby time is calculated using a calculation formula.

Further, the control unit 11 generates a stepped charging voltage for each column based on the extracted data, and applies the voltage to the charging electrode 3 after the standby time has elapsed. In this way, as shown in FIG. 7(c), it is possible to realize less distorted printing with substantially equal intervals between rows.

In addition, in FIG. 8, as a test pattern, a case in which nine print dots are consecutively printed in one line and the dot line is repeatedly printed has been described. Needless to say, the data is used to create print data for one time, and printing is performed based on that data.

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 (2)

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;
An inkjet printer that prints characters and symbols in a matrix-like dot pattern on the printing surface of an object to be printed,
In the storage unit of the controller,
Print data indicating positions for forming dots in a matrix, and a plurality of waiting times obtained through experiments corresponding to different periods of columns of the matrix and corresponding to lengths of intervals during which printing is not performed. data is stored,
A control unit of the controller,
generating a charging voltage to be applied to the charging electrode for each column of the matrix based on the print data and the cycle data of the column ;
creating print data for one time including the individual print data, and specifying the interval period from the print data for one time;
An ink jet printer, wherein waiting time data corresponding to a specific period and a specified interval period of the columns is read out from the storage unit, and the waiting time is set between the columns of the matrix. 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;
An inkjet printer that prints characters and symbols in a matrix-like dot pattern on the printing surface of an object to be printed,
In the storage unit of the controller,
print data indicating the positions to form dots in the matrix, and
Data of multiple calculation formulas corresponding to the length of the interval period when printing is not performed are stored,
A control unit of the controller,
generating a charging voltage to be applied to the charging electrode for each column of the matrix based on the print data and the cycle data of the column ;
creating print data for one time including the individual print data, and specifying the interval period from the print data for one time;
Data of a calculation formula corresponding to the specified interval period is read from the storage unit , a waiting time corresponding to the period of the columns is calculated using the calculation formula, and a waiting time is set between the columns of the matrix. An inkjet printer characterized by:

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