JP7517868B2 - Charge control method for inkjet recording device - Google Patents

Description

The present invention relates to a charge control method for an inkjet recording device, and in particular to a charge control method for a continuous-jet charge-controlled inkjet recording device.

A typical continuous-jet charge-controlled inkjet recording device has an ink container that stores ink in the main body, and the ink from the ink container is supplied to the print head by an ink supply pump. The ink supplied to the print head is continuously ejected from the ink nozzle and turned into ink droplets. Among the ink droplets, the ink droplets used for printing are charged and deflected, and are then sent to the desired printing position on the printing object to form characters (hereinafter, the printed characters are defined as "printed characters"). Ink droplets not used for printing are not charged or deflected, but are collected in a gutter and returned to the ink container by an ink recovery pump.

In this type of inkjet recording device, for example, Japanese Patent Application Laid-Open No. 2012-162036 (Patent Document 1) proposes adding uncharged ink droplets to the vertical array of dots aligned vertically along the direction in which the charged ink droplets are deflected, and placing uncharged ink droplets between the first charged ink droplet printed and the next charged ink droplet printed, in order to reduce the merging of flying charged ink droplets and the repulsion caused by Coulomb force.

For example, JP2005-506227A (Patent Document 2) proposes determining the charge amount so that the height at which the ink droplet of interest lands on the printing target is at a desired position, taking into consideration the presence or absence of charge on several ink droplets before and after the ink droplet of interest and their charge amounts.

JP 2012-162036 A Special Publication No. 2005-506227

Continuous-jet charge-controlled inkjet recording devices print by ejecting tens of thousands of ink droplets per second, which allows for high-speed printing. However, flying charged ink droplets are subject to Coulomb force, which is caused by the charge on the ink droplet, and air resistance, which depends on the diameter of the ink droplet and the surrounding flow field. Therefore, when multiple charged ink droplets flying close to each other are considered, two types of printing defects, "merging" and "scattering," may occur.

Merge is a phenomenon in which charged ink droplets approaching each other while flying collide and merge, increasing in diameter and landing on the printing target. Scatter is a phenomenon in which when charged ink droplets approach each other while flying, the flight direction of the two charged ink droplets changes due to the influence of Coulomb force, causing the spacing between print dots formed on the printing target to become unnatural.

Patent Document 1 discloses a control method for reducing the occurrence of merging or scattering of flying charged ink droplets. In the control method described in Patent Document 1, uncharged ink droplets are inserted into the vertical array of vertically aligned print dots. This causes a problem in that the printing speed decreases by the amount of newly inserted uncharged ink droplets. In addition, the control method described in Patent Document 1 focuses on merging and scattering that occurs between the first charged ink droplet to be printed and the next charged ink droplet to be printed following it. Therefore, there is an issue that merging or scattering that occurs with other charged ink droplets cannot be reduced.

Patent Document 2 also shows a control method for determining the charge amount so that the landing height of a focused ink droplet is at a desired position, taking into consideration the presence or absence of charge and the charge amount of several ink droplets before and after the focused ink droplet. In the control method described in Patent Document 2, the order in which the ink droplets are charged is not changed, and only the charge amount is changed to adjust the landing height of the charged ink droplets. Therefore, the change in the flight trajectory of the charged ink droplets is minute, and the charged ink droplets cannot be avoided from approaching each other, making it difficult to reduce merging or scattering.

In particular, when performing a multi-level printing method in which multiple characters are printed by stacking them in the vertical direction, the method of Patent Document 1 slows down the printing speed, and the method of Patent Document 2 is highly likely to cause merging or scattering.

In the following, "column" refers to the printed characters in the height direction, and if there are two stacked printed characters, it is called two-column printing, if there are three stacked characters, it is called three-column printing, if there are Y stacked characters, it is called Y-column printing. In addition, these are collectively defined as multi-column printing.

The object of the present invention is to provide a charge control method for an inkjet recording device that can suppress the occurrence of merging and scattering without reducing the printing speed when performing multi-stage printing.

The feature of the present invention is that when performing multi-stage printing, at least between two charged ink droplets that are deemed to be at high risk of merging or scattering in the same predetermined stage, a charged ink droplet used for printing in another stage is inserted, and charging control is performed to change the direction of the Coulomb force acting on the two charged ink droplets in the same stage.

The present invention provides a charge control method for an inkjet recording device that can print without reducing the printing speed during multi-stage printing and without causing merging or scattering.

1 is a schematic diagram illustrating a configuration of an inkjet recording apparatus and a method of using the same. FIG. 1 is a schematic diagram illustrating the printing principle of an inkjet recording device. FIG. 11 is an explanatory diagram illustrating a print matrix during two-line printing. FIG. 11 is an explanatory diagram for explaining charge control in a conventional two-stage print control method. 5 is an explanatory diagram illustrating a flying state of ink droplets inside a deflection electrode when the two-stage print control method shown in FIG. 4 is applied. 5 is an explanatory diagram illustrating a flying state of ink droplets outside the deflection electrodes when the two-stage print control method shown in FIG. 4 is applied. FIG. 4 is an explanatory diagram illustrating charge control in a two-stage print control method according to the first embodiment of the present invention. 5A to 5C are explanatory diagrams illustrating the flying state of ink droplets inside a deflection electrode by ink droplet charging control according to the first embodiment. 5 is an explanatory diagram for explaining charge control by a conventional two-stage print control method different from the conventional two-stage print control method shown in FIG. 4 . 10 is an explanatory diagram illustrating the flying state of ink droplets inside a deflection electrode when the two-stage print control method shown in FIG. 9 is applied. FIG. 11 is an explanatory diagram illustrating charge control in a two-stage print control method according to a second embodiment of the present invention. FIG. 13 is an explanatory diagram illustrating a print matrix when three-line printing is performed. FIG. 11 is an explanatory diagram for explaining charge control in a conventional three-stage print control method. FIG. 13 is an explanatory diagram illustrating charge control in a three-stage print control system according to a third embodiment of the present invention. 13A and 13B are explanatory diagrams illustrating the flying state of ink droplets inside a deflection electrode by ink droplet charging control according to a third embodiment. 14 is an explanatory diagram for explaining charge control by a conventional three-stage print control method different from the conventional three-stage print control method shown in FIG. 13 . FIG. 13 is an explanatory diagram illustrating charge control in a three-stage print control system according to a fourth embodiment of the present invention. 13A and 13B are explanatory diagrams illustrating the flying state of ink droplets inside a deflection electrode by ink droplet charging control according to a fourth embodiment.

The following describes in detail an embodiment of the present invention with reference to the drawings. However, the present invention is not limited to the following embodiment, and the scope of the present invention includes various modifications and applications within the technical concept of the present invention.

Before describing the embodiments of the present invention, the configuration and usage of a continuous-jet charge-controlled inkjet recording device to which the present invention is applied will be briefly described with reference to FIG. 1.

In FIG. 1, the print contents are determined using the input section of the display 2 provided on the inkjet recording device main body 1. The determined print contents are printed on the print target 100, which is being transported by a transport means 5 such as a belt conveyor, by continuously ejecting ink droplets from the print head 4. The inkjet recording device main body 1 supplies ink to the print head 4 and controls its operation via a cable 3.

Next, the principle of the continuous-jet charge-controlled inkjet recording device to which the present invention is applied will be explained with reference to FIG.

Figure 2 shows a schematic diagram of the printing principle of an inkjet recording device. In Figure 2, ink liquid 109 stored in an ink container 101 is pressurized by an ink supply pump 102 and supplied to an ink nozzle 103. By periodically applying a voltage to a piezoelectric element 104 installed in the ink nozzle 103, the ink in the ink nozzle 103 is excited. The excited ink is ejected from the ink nozzle 103 as an ink column 110, and then becomes an ink droplet.

The ink used for printing is charged by the charging electrode 105 at the same time as the ink is turned into droplets. The charged ink droplets 111 are deflected by the electric field generated between the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107, and then land on the print target 100. On the other hand, the ink droplets 112 that are not used for printing are not charged, and since these uncharged ink droplets 112 are not deflected, they are collected in the gutter 108 and reused.

The inkjet recording device main body 1 shown in FIG. 1 houses the ink container 101 and the ink supply pump 102 shown in FIG. 2. The print head 4 houses the ink nozzle 103, the charging electrode 105, the deflection electrode positive electrode 106, the deflection electrode negative electrode 107, the gutter 108, and the like shown in FIG. 2.

Next, the charging control performed on ink droplets by the charging electrode 105 when performing two-stage printing in an inkjet recording device will be explained using Figures 3 and 4.

The charging control of the charging electrode 105 is performed by a control means (not shown) provided in the inkjet recording device main body 1. The control means has a microcomputer as its main control element, and has a charging control function that selects the ink droplets to be charged and controls the amount of charge according to the print content inputted at the input section. Therefore, the charging control of the ink droplets described below is performed by the charging control function provided in the microcomputer.

Figure 3 shows a printing matrix for printing the number "9" and the alphabet letter "t" in two lines. Here, "line" refers to the stacking of printed characters in the height direction, and Figure 3 shows an example of two lines, with two printed characters arranged in a lower line and an upper line.

Normally, the position of the print dots 113 formed by ink droplets by an inkjet recording device is determined based on a print matrix. In FIG. 3, a character formed with 5 columns and 7 rows of print dots is stacked in two layers to form a two-level print. However, the print matrix used when two-level printing is not limited to print characters composed of 5 columns and 7 rows of print dots. Below, a print character composed of 5 columns and 7 rows of print dots is referred to as a "5x7 font" print character.

If the number of rows in the top row where print dots can be placed is N, and the number of rows in the bottom row where print dots can be placed is M, then in the case of two-line printing of a 5x7 font, N = 7 and M = 7. Furthermore, the positions (rows) in the top row where print dots can be placed are n_1 to n_7 from the bottom, and the positions (rows) in the bottom row where print dots can be placed are m_1 to m_7 from the bottom.

In the following, the ink droplets that form the upper printed characters will be referred to as "upper ink droplets" and the ink droplets that form the lower printed characters will be referred to as "lower ink droplets."

Figure 4 shows a conventional two-level printing control method when printing according to the printing matrix shown in Figure 3. In an inkjet recording device, the print content is formed by repeatedly scanning one row. When performing two-level printing of a 5 x 7 font, by using only 14 ink droplets when scanning one row, it is possible to print without generating unnecessary ink droplets.

When two-level printing is performed, control is executed to print the print dots present in the upper and lower levels alternately, starting from the "bottom row" of the lower level. When printing is performed using this control according to the printing matrix shown in FIG. 3, for example, of the 14 ink droplets, as shown in FIG. 4, lower level ink droplets 116, upper level ink droplets 115, and upper level ink droplets 114 are printed in order as charged ink droplets by the charging electrode 105. On the other hand, if there are no print dots on the printing matrix, the ink droplets are collected by the gutter 108 without being charged.

Next, the problems that arise when implementing the above-mentioned two-level print control method will be explained with reference to Figs. 4 to 6. When printing the first row according to the print matrix shown in Fig. 4, the upper level ink droplets 115 and 114 that form the upper level print character come close to each other during flight, causing scattering. The reason for this is as follows.

As shown in FIG. 4, when printing is performed using the two-stage printing control method, for example, the lower stage ink droplets 116 and the upper stage ink droplets 115 in the first row are adjacent to each other. In addition, one non-charged ink droplet is inserted between the upper stage ink droplets 115 and 114. This non-charged ink droplet is to ensure a distance between the upper stage ink droplets 115 and 114.

Coulomb force acts on flying ink droplets depending on the charge of the ink droplets and the distance between the ink droplets. If we assume that two ink droplets of interest are point charges, the Coulomb force F is expressed as F = {1/(4πε ₀ )}·(Q ₁ ·Q ₂ )/r ² , where "ε ₀ " is the dielectric constant in a vacuum (F/m), "Q ₁ " and "Q ₂ " are the charge amounts (C) of the two ink droplets of interest, and "r" is the distance (m) between the two ink droplets.

Now, let us focus on one flying charged ink droplet. The focused charged ink droplet is subjected to Coulomb force from all other charged ink droplets depending on the distance between the ink droplets and the amount of charge. The Coulomb force is inversely proportional to the square of the distance between the ink droplets. Therefore, the focused ink droplet is more susceptible to the influence of Coulomb force from charged ink droplets flying near the focused ink droplet, such as a charged ink droplet adjacent to the focused ink droplet.

Figure 5 shows a schematic of the lower ink droplet 116, the upper ink droplet 115, and the upper ink droplet 114 flying through a region 117 in the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107.

Note that area 117 indicates the position on the nozzle side of the deflection electrode, near where the deflection of ink droplets 116-114 begins. If an area like that in Figure 5 is cut out, uncharged ink is also present, but the uncharged ink is not shown in Figure 5, and this is also the case in the examples described below (Figures 8, 10, 15, and 18).

In addition, Figure 5, as well as Figures 6, 8, 10, 15, and 18 described below, are diagrams that show the positional relationships of multiple ink droplets in flight for the purpose of explanation, and do not precisely depict the diameter of the ink droplets or the distance between the ink droplets, etc.

In the deflection electrode region 117, a strong Coulomb force acts between the adjacent lower ink droplets 116 and upper ink droplets 115 because the distance is short. Therefore, in the upper ink droplets 115, the Coulomb force acts in the negative direction, which is opposite to the flight direction of the ink droplets (defined as the positive direction). This causes the upper ink droplets 115 to decelerate, and the upper ink droplets 114 enter the wake region formed by the upper ink droplets 115. As a result, the air drag acting on the upper ink droplets 114 becomes smaller, and the deceleration of the upper ink droplets 114 weakens. In other words, the speed reduction of the upper ink droplets 114 becomes smaller.

Figure 6 shows the upper ink droplets 115 and 114 flying through region 118 after passing through the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107. As described above, the speed of the upper ink droplets 114 decreases little, so when the upper ink droplets 114 and 115 approach each other in region 118, they are repelled in the vertical direction by Coulomb force and do not land in the correct position, resulting in scattering. Note that the upper and lower print matrices that are considered to be at high risk of causing scattering are not limited to the number "9" and the letter "t".

The arrangement positions (arrangement pattern) of three print dots in one row, which are caused by two charged ink droplets forming adjacent print dots in the "same row" that cause scattering due to Coulomb force, and a charged ink droplet forming a print dot in the "other row" adjacent in front of these two charged ink droplets, are as follows, assuming that "x" is any row:
(1-1) m_x, n_x, n_x+1
(1-2) m_x, n_x-2, n_x-1
(1-3) n_x, m_x+1, m_x+2
(1-4) n_x, m_x-1, m_x
Either:

Note that print dot positions (1-1) and (1-2) are for when two print dots are placed adjacent to each other on the upper row, and print dot positions (1-3) and (1-4) are for when two print dots are placed adjacent to each other on the lower row.

The pattern of the arrangement positions of the four print dots described above is an example of the first column in Figure 3. Even if there are four or more print dots, there is a high possibility that scattering or merging will occur if the print character has print dots that match the pattern described above.

In the print matrix shown in FIG. 4, print dots exist at m_5, n_5, and n_6, which corresponds to the print dot arrangement position (1-1) described above. Also, when print dots exist at the print dot arrangement positions described above, if the flight trajectories of ink droplets landing on the same stage are similar and the repulsion due to Coulomb force between ink droplets landing on the same stage is small, merging will occur.

In this way, when printing two adjacent print dots in the same row, if an ink droplet from another row is adjacent to the two ink droplets, the two ink droplets in the same row are likely to approach each other while flying, resulting in scattering or merging.

The charging control of ink droplets in the first embodiment of the present invention, which solves the above problems, will be described with reference to Figures 7 and 8. This charging control is performed by the charging control function of the microcomputer as described above. This charging control function is the same as the conventional charging control function, but essentially it controls to change the charging order of the charged ink droplets printed in the upper and lower rows.

In other words, the printing pattern of the printing dots for each row is read, and if the printing pattern to be printed that is read includes any of the four printing patterns described above, there is a risk of scattering, etc. occurring, so the charging control shown below is executed. Note that printing patterns other than these may be configured to be printed in the normal order.

Figure 7 shows the charging sequence of ink droplets in the first embodiment of the present invention. In the first embodiment, the lower ink droplet 119 for forming the first row of print dots of the letter "t" is charged and controlled so that it exists adjacent to and consecutively between the upper ink droplet 114 and upper ink droplet 115 for forming the first row of print dots of the number "9". As shown in Figure 7, with charging control that produces charged ink droplets continuously, the amount of charged ink droplets produced per unit time is the same as with conventional charging control. This makes it possible to maintain the printing speed.

In the example of FIG. 7, the ink droplets are charged in the order of upper ink droplets 115 ⇒ lower ink droplets 119 ⇒ upper ink droplets 114. However, uncharged ink can be inserted between the upper ink droplets 115 and the lower ink droplets 119, or between the lower ink droplets 119 and the upper ink droplets 114, to the extent that no problem occurs. By inserting this uncharged ink, the distance between the charged ink droplets landing on the same level can be further increased, making it possible to avoid the interaction of Coulomb forces between the charged ink droplets.

In this way, inserting one ink droplet adjacent to two ink droplets in the same stage to form a print dot in another stage includes the case where charged ink droplets are generated consecutively and placed adjacent to each other, as shown in Figure 7, and the case where uncharged ink droplets are inserted to generate charged ink droplets and placed adjacent to each other, and this also applies to the other embodiments described below.

Figure 8 shows the state in the first embodiment where ink droplets 114, 115, and 119 fly through the region 120 in the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107. As shown in Figure 8, inside the deflection electrode, the upper ink droplet 114 and the lower ink droplet 119, as well as the upper ink droplet 115 and the lower ink droplet 119, are repelled by Coulomb force, as shown by the arrows.

The upper ink droplet 115 experiences a Coulomb force acting in the positive direction of the ink droplet's flight direction, and the upper ink droplet 114 experiences a Coulomb force acting in the negative direction of the ink droplet's flight direction, so even if both of them head toward the upper side, the upper ink droplet 114 and the upper ink droplet 115 are prevented from approaching each other during flight. As a result, merging or scattering does not occur between the upper ink droplet 114 and the ink droplets that land on the upper stage 115.

In addition, since the lower ink droplets 119 move toward the lower side, no merging or scattering occurs between the upper ink droplets 114 and 115.

In this way, when printing two adjacent print dots in the same row, by inserting one charged ink droplet that forms a print dot in another row between two charged ink droplets, the distance between the two charged ink droplets in the same row can be increased for the reasons shown in Figure 8. This makes it possible to prevent scattering or merging between the flying ink droplets that form adjacent print dots.

The first embodiment described above can be summarized as follows. First, when performing two-line printing in which characters are printed in the upper and lower rows, "N" is the number of rows in the upper row where print dots can be placed, "M" is the number of rows in the lower row where print dots can be placed, "x" is an arbitrary row, and "p" is the number of print dots printed in one scan, and the relationships are set as N ≥ x, M ≥ x, and N + M ≥ p.

From the above relationship, when performing a scan to form a vertical row of print dots using charged ink droplets, there are N positions where print dots can be placed in the top row, and the positions where the N print dots in the top row can be placed are n_1 to n_N, starting from the bottom. Also, when performing a scan, there are M positions where print dots can be placed in the bottom row, and the positions where the M print dots in the bottom row can be placed are m_1 to m_M, starting from the bottom.

Then, within the positions where print dots in the upper and lower rows can be placed, print dots are formed at p positions in one scan, and this scan is repeated any number of times to form a printed character. Based on the above, charging control of the ink droplets that form the print dots is performed as follows.

(1-1) When forming print dots in the lower row m_x, the upper row n_x, and the upper row n_x+1, a charged ink droplet forming a print dot in the lower row m_x is inserted adjacent to two charged ink droplets for forming the print dots in the upper row n_x and the upper row n_x+1.

(1-2) When forming print dots in the lower row m_x, the upper row n_x-2, and the upper row n_x-1, a charged ink droplet that forms a print dot in the lower row m_x is inserted adjacent to two charged ink droplets that form print dots in the upper row n_x-2 and the upper row n_x-1.

In this way, the upper ink droplets are charged in the order of the lower ink droplets and then the upper ink droplets, which prevents the two upper ink droplets from coming close to each other while flying, and prevents merging or scattering from occurring in the print dots formed by these.

The above example shows the case where two print dots are printed in the upper row, but the same applies when two print dots are printed in the lower row as shown below.

(1-3) When forming print dots in the upper row n_x, the lower row m_x+1, and the lower row m_x+2, the charged ink droplet that forms the print dot in the upper row n_x is inserted adjacent to the two charged ink droplets that form the print dots in the lower row m_x+1 and the lower row m_x+2.

(1-4) When forming print dots in the upper row n_x, the lower row m_x-1, and the lower row m_x, the charged ink droplets that form the print dots in the upper row n_x are inserted adjacent to each other between the two charged ink droplets that form the print dots in the lower row m_x-1 and the lower row m_x.

In this way, the ink droplets are charged in the order of lower ink droplets ⇒ upper ink droplets ⇒ lower ink droplets, which prevents the two lower ink droplets from coming close to each other during flight and prevents merging or scattering from occurring.

Next, a second embodiment of the present invention will be described with reference to Figs. 9 to 11. Fig. 9 shows a two-line print control method according to the second embodiment, which differs from the two-line print control method (printing from the bottom line of the lower line) shown in the first embodiment.

In this embodiment, as shown in Figure 9, when printing dots that exist in upper and lower rows alternately between the upper and lower rows, the printing dots are printed in order starting from the printing dots in the "top row" of the upper row. However, if there are no printing dots on the printing matrix, uncharged ink droplets are inserted, which is the same as the two-row printing control method shown in the first embodiment.

Next, the problems encountered when implementing the above-mentioned two-stage printing control method will be described with reference to Figures 9 and 10. When printing the first row as shown in Figure 9, printing is performed in the order of upper ink droplets 203, upper ink droplets 202, and lower ink droplets 201. However, the upper ink droplets 203 and 202 approach each other while flying, causing scattering. The reason for this is as follows. An uncharged ink droplet is inserted between the upper ink droplets 203 and 202. This uncharged ink droplet would normally land on m_6, but since no print dot is placed on m_6 in the printing matrix in Figure 9, it becomes an uncharged ink droplet.

Figure 10 shows a schematic of upper ink droplets 203, 202, and lower ink droplets 201 flying through the area 204 within the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107.

First, inside the deflection electrode, a Coulomb force, indicated by the arrows, acts between the adjacent lower ink droplet 201 and upper ink droplet 202. In the upper ink droplet 202, a force acts in the positive direction, the same as the flight direction of the ink droplet. On the other hand, the upper ink droplet 203 is subjected to air drag in the negative direction, opposite to the flight direction of the ink droplet, and decelerates.

Furthermore, the upper ink droplet 203 forms a wake, and when the upper ink droplet 202 enters the wake region, the air drag acting on the upper ink droplet 202 becomes smaller, and the deceleration of the ink droplet 202 weakens. Therefore, as the flight of the ink droplet progresses, the upper ink droplet 202 and the upper ink droplet 203 gradually approach each other, the Coulomb force becomes larger, and scattering occurs.

The upper and lower printing matrices where scattering occurs are not limited to the number "9" and the letter "t". As with the first embodiment, any printing matrix that has printing dots at the printing dot arrangement positions (2-1) to (2-4) shown below is likely to cause scattering.

The arrangement positions of three print dots in one column, which are caused by two charged ink droplets forming adjacent print dots in the "same row" that cause scattering due to Coulomb force, and a charged ink droplet forming a print dot in the "other row" adjacent behind these two charged ink droplets, are as follows, assuming that "x" is any row:
(2-1) n_x, n_x+1, m_x
(2-2) n_x-2, n_x-1, m_x
(2-3) m_x+1, m_x+2, n_x
(2-4) m_x-1, m_x, n_x
This arrangement pattern is basically the same as that in the first embodiment.

As in the first embodiment, the print dot positions (2-1) and (2-2) are for the case where two print dots are arranged adjacent to each other in the upper row, and the print dot positions (2-3) and (2-4) are for the case where two print dots are arranged adjacent to each other in the lower row.

The pattern of the arrangement positions of the four print dots described above is an example in the first column of Figure 9. Even if there are four or more print dots, there is a high possibility that scattering or merging will occur if the print character has print dots that match the pattern described above.

In the print matrix shown in FIG. 9, print dots exist at n_5, n_6, and m_5, which corresponds to the print dot arrangement position (2-1) described above. Also, when print dots exist at the print dot arrangement positions described above, if the flight trajectories of ink droplets landing on the same stage are similar and the repulsion due to Coulomb force between ink droplets landing on the same stage is small, merging will occur.

In this way, when two adjacent print dots are printed in one row, if two ink droplets are followed by an ink droplet in another row, the Coulomb force between the two ink droplets in the same row affects each other, causing scattering or merging.

The ink droplet charge control according to the second embodiment of the present invention, which solves the above problems, will be described with reference to Figures 8 and 11. This charge control is performed by the charge control function of the microcomputer, as in the first embodiment. In other words, the print pattern of the print dots for each row is read out, and if the print pattern to be printed that is read out includes any of the four print patterns described above, there is a risk of scatter or the like occurring, so the charge control described below is performed. Note that other print patterns are configured to be printed in the normal order.

Figure 11 shows the charging sequence of ink droplets in the second embodiment of the present invention. In the second embodiment, the lower ink droplet 205 for forming the first row of print dots of the letter "t" is adjacent to and charged between the upper ink droplets 203 and 202 so as to be continuous.

In the second embodiment, the flying positional relationship of the charged ink droplets inside the deflection electrode is similar to that shown in FIG. 8. The upper ink droplet 202 corresponds to the upper ink droplet 114, the upper ink droplet 203 corresponds to the upper ink droplet 115, and the lower ink droplet 205 corresponds to the lower ink droplet 119.

The upper ink droplet 203 and the lower ink droplet 205, as well as the upper ink droplet 202 and the lower ink droplet 205, are repelled by Coulomb force, as shown by the arrows.

The upper ink droplet 203 is subjected to a Coulomb force in the positive direction of the ink droplet flight direction, and the upper ink droplet 202 is subjected to a Coulomb force in the negative direction of the ink droplet flight direction, so even if both move toward the upper side, the upper ink droplet 203 and the upper ink droplet 202 are prevented from approaching each other during flight. As a result, merging and scattering do not occur between the upper ink droplet 202 and the upper stage 203.

In addition, since the lower ink droplets 205 move toward the lower side, no merging or scattering occurs between the upper ink droplets 202 and the upper ink droplets 205.

In this second embodiment, the ink droplets are charged in the order of upper ink droplets ⇒ lower ink droplets ⇒ upper ink droplets, and the upper ink droplets 203 and 202 are prevented from approaching each other during flight, preventing merging and scattering.

In addition, by applying a two-stage printing control method like the second embodiment, it is possible to reduce the deviation in the landing position of a line of printing dots in the transport direction of the printing object. The reason for this is as follows.

When comparing the flight of ink droplets used when scanning a certain row, the deflection amount is greater for ink droplets that land at the top of the print target. Therefore, the flight time of ink droplets that land at the top of the print target is longer after being ejected from the nozzle until they land on the print target.

In a two-stage printing control method such as the second embodiment, ink droplets with the longest flight time are generated and printed in order. As a result, the landing time difference between ink droplets during scanning of one row is reduced by the generation time difference between each ink droplet. Therefore, the transport distance of the print object within the landing time difference is reduced. For these reasons, the deviation in the landing position of the print dots in one row in the transport direction of the print object is reduced.

In this way, when printing two adjacent print dots in the same row, by inserting one charged ink droplet that forms a print dot in another row between two charged ink droplets, the distance that the two ink droplets in the same row take while flying can be increased for reasons shown in Figure 8. This makes it possible to prevent scattering and merging.

The second embodiment described above can be defined as follows. First, when performing two-line printing in which characters are printed in the upper and lower rows, "N" is the number of rows in the upper row where print dots can be placed, "M" is the number of rows in the lower row where print dots can be placed, "x" is an arbitrary row, and "p" is the number of print dots printed in one scan, and the relationships are set as N ≥ x, M ≥ x, and N + M ≥ p.

From the above relationship, when performing a scan to form a vertical row of print dots using charged ink droplets, there are N positions where print dots can be placed in the top row, and the positions where the N print dots in the top row can be placed are n_1 to n_N, starting from the bottom. Also, when performing a scan, there are M positions where print dots can be placed in the bottom row, and the positions where the M print dots in the bottom row can be placed are m_1 to m_M, starting from the bottom.

Then, within the positions where print dots in the upper and lower rows can be placed, print dots are formed at p positions in one scan, and this scan is repeated any number of times to form a printed character. Based on the above, charging control of the ink droplets that form the print dots is performed as follows.

(2-1) When forming print dots in the upper row n_x, the upper row n_x+1, and the lower row m_x, a charged ink droplet forming a print dot in the lower row m_x is inserted adjacent to two charged ink droplets for forming the print dots in the upper row n_x and the upper row n_x+1.

(2-2) When forming print dots in the upper row n_x-2, the upper row n_x-1, and the lower row m_x, a charged ink droplet that forms a print dot in the lower row m_x is inserted adjacent to two charged ink droplets that form print dots in the upper row n_x-2 and the upper row n_x-1.

In this way, the ink droplets are charged in the order of upper ink droplets ⇒ lower ink droplets ⇒ upper ink droplets, which prevents the two upper ink droplets from coming close to each other during flight and prevents merging or scattering from occurring.

The above example shows the case where two print dots are printed in the upper row, but the same applies when two print dots are printed in the lower row as shown below.

(2-3) When forming print dots in the lower row m_x+1, the lower row m_x+2, and the upper row n_x, a charged ink droplet that forms a print dot in the upper row n_x is inserted adjacent to the two charged ink droplets that form print dots in the lower row m_x+1 and the lower row m_x+2.

(2-4) When forming print dots in the lower row m_x-1, the lower row m_x, and the upper row n_x, a charged ink droplet that forms a print dot in the upper row n_x is inserted adjacent to the two charged ink droplets that form print dots in the lower row m_x-1 and the lower row m_x.

In this way, the ink droplets are charged in the order of lower ink droplets ⇒ upper ink droplets ⇒ lower ink droplets, which prevents the two lower ink droplets from coming close to each other during flight and prevents merging or scattering from occurring.

In this way, in the first embodiment in which printing is performed from the bottom to the top, and in the second embodiment in which printing is performed from the top to the bottom, at least between two charged ink droplets in the same predetermined stage (the top or bottom stage) that are deemed to be at high risk of merging or scattering, charged ink droplets used for printing in another stage (the bottom or top stage) are inserted, and the charging of the ink droplets is controlled to change the direction of the Coulomb force acting on the two charged ink droplets in the same predetermined stage.

This prevents two ink droplets from approaching each other during flight, which can cause merging or scattering, making it possible to provide an inkjet recording device that can print without reducing the printing speed during multi-stage printing and without causing merging or scattering.

Next, a third embodiment of the present invention will be described with reference to Figs. 12 to 14. First, the charging control performed on ink droplets when performing three-level printing in an inkjet recording device will be described with reference to Figs. 12 and 13. When performing three-level printing, print dots present in the top, middle and bottom levels are printed starting from the "bottom line" of the bottom level, then the middle level, then the top level, and this is repeated for each scan.

Figure 12 shows a print matrix for printing the number "9," the letter "t," and the number "4" in three lines. In Figure 12, three lines of 5x7 font printing are stacked on top of each other to form a three-line print. However, the print matrix used when printing in three lines is not limited to 5x7 font printing.

In three-line printing, if the number of rows in the top row where print dots can be placed is N, the number of rows in the middle row where print dots can be placed is M, and the number of rows in the bottom row where print dots can be placed is Q, then in the case of three-line printing with a 5x7 font, N = 7, M = 7, and Q = 7. Furthermore, the positions in the top row where print dots can be placed are n_1 to n_7 from the bottom, the positions in the middle row where print dots can be placed are m_1 to m_7 from the bottom, and the positions in the bottom row where print dots can be placed are q_1 to q_7 from the bottom.

Figure 13 shows a conventional three-level printing control method when printing according to the printing matrix shown in Figure 12. When printing three levels of a 5x7 font, it is possible to print without generating unnecessary ink droplets by using only 21 ink droplets when scanning one row. Also, when performing three-level printing, starting from the bottom row of printing dots in the lower level, printing dots are printed in the order of the lower level, middle level, and upper level, and then printing dots are printed again starting from the bottom level.

When using this control to print, for example, according to the print matrix shown in FIG. 12, as shown in FIG. 13, of the 21 ink droplets, the following are printed as charged ink droplets in the order of lower ink droplet 305, lower ink droplet 304, middle ink droplet 303, upper ink droplet 302, and upper ink droplet 301. On the other hand, if there are no print dots on the print matrix, the ink droplets are not charged, as in the case of the two-stage print control method.

Here, the lower ink droplets 305 and 304 are adjacent print dots, but because ink droplets from other stages are not generated adjacent to each other before or after them, and because two uncharged ink droplets are inserted, scattering or merging is unlikely to occur between the lower ink droplets 305 and 304.

Next, the problems that arise when implementing the above-mentioned three-stage print control method will be explained using Figures 4, 5, 6, 12, and 13. When printing the first row as shown in Figure 13, the upper ink droplets 302 and 301 approach each other during flight, causing scattering. The reason for this is as follows.

As shown in FIG. 13, when printing is performed using the above-mentioned three-stage printing control method, the middle ink droplet 303 and the upper ink droplet 302 are adjacent to each other. Also, the flight positional relationship of the charged ink droplets in the third embodiment is similar to that shown in FIG. 4, FIG. 5, and FIG. 6. The upper ink droplet 301 corresponds to the upper ink droplet 114, the upper ink droplet 302 corresponds to the upper ink droplet 115, and the middle ink droplet 303 corresponds to the lower ink droplet 116.

Therefore, inside the deflection electrode, a large Coulomb force acts between the middle ink droplet 303 and the upper ink droplet 302 because the distance is short. In the upper ink droplet 302, a Coulomb force acts in the negative direction opposite to the flight direction of the ink droplet. This causes the upper ink droplet 302 to decelerate, and the upper ink droplet 301 enters the wake region formed by the upper ink droplet 302.

As a result, the air resistance acting on the upper ink droplet 301 becomes smaller, and the deceleration of the upper ink droplet 301 weakens. Therefore, as the flight of the ink droplets progresses, the upper ink droplets 302 and 301 gradually approach each other, the Coulomb force increases, and scattering occurs. Note that the three-stage printing matrix in which scattering occurs is not limited to the number "9", the letter "t", and the number "4".

The arrangement position (arrangement pattern) of three print dots in one row, which are caused by two charged ink droplets forming adjacent print dots in the "same row" that cause scattering due to Coulomb force, and a charged ink droplet forming a print dot in the "other row" adjacent in front of these two charged ink droplets, is as follows, assuming that "x" is any row:
(3-1) m_x, n_x, n_x+1
(3-2)q_x, n_x-2, n_x-1
(3-3)q_x, m_x, m_x+1
(3-4)n_x, m_x, m_x-1
(3-5) m_x, q_x, q_x-1
(3-6)n_x, q_x+1, q_x+2
Either:

Note that print dot positions (3-1) and (3-2) are when two print dots are placed adjacent to each other in the upper row, print dot positions (3-3) and (3-4) are when two print dots are placed adjacent to each other in the middle row, and print dot positions (3-5) and (3-6) are when two print dots are placed adjacent to each other in the lower row.

Here, the arrangement pattern of the arrangement positions of the six print dots described above is the example in the first column of Figure 13. Even if there are four or more print dots, if the printed character has print dots that match the arrangement pattern described above, there is a high possibility that scatter will occur.

In the print matrix shown in FIG. 12, print dots exist at m_5, n_5, and n_6, which corresponds to the print dot arrangement position described above in (3-1). Also, when print dots exist at the print dot arrangement positions described above, if the flight trajectories of ink droplets landing on the same row are similar and the repulsion due to Coulomb force between ink droplets landing on the same row is small, merging will occur.

In this way, when printing two adjacent print dots in one stage, if an ink droplet from another stage is adjacent to the two ink droplets in front of them, the Coulomb force between the two ink droplets in the same stage will affect each other, causing scattering or merging.

The charge control of ink droplets in the third embodiment of the present invention, which solves the above problems, will be described with reference to Figures 14 and 15. This charge control is performed by the charge control function of the microcomputer, as in the first embodiment. In other words, the print pattern of the print dots for each row is read out, and if the print pattern to be printed that is read out includes any of the six print patterns described above, there is a risk of scatter or the like occurring, so the charge control shown below is performed. Note that other print patterns may be configured to be printed in the normal order.

Figure 14 shows the charging order of ink droplets in the third embodiment of the present invention. In the third embodiment, the middle ink droplet 306 for forming the first row of print dots of the alphabet letter "t" is controlled to be charged so that it exists between the upper ink droplet 302 and the upper ink droplet 301. However, in this case, one uncharged ink droplet is inserted between the upper ink droplet 302 and the middle ink droplet 306.

This uncharged ink is inserted because three-level printing is being performed. In three-level printing, charged ink droplets are generated in the following order to land: bottom level ⇒ middle level ⇒ top level. Therefore, after the top level ink droplet 302 is generated, there is no ink droplet to land on the bottom level, so an uncharged ink droplet is inserted between the top level ink droplet 302 and the middle level ink droplet 306. The next ink droplet to land is the middle level ink droplet 306. This middle level ink droplet 306 must form the first row of print dots for the letter "t," so it is considered to be a charged middle level ink droplet 306.

In the third embodiment, FIG. 15 shows ink droplets 302, 306, and 301 flying through a region 307 in the deflection electrode positive electrode 106 and the deflection electrode negative electrode 107. As shown in FIG. 15, a large Coulomb force acts between the adjacent upper ink droplet 301 and middle ink droplet 306 inside the deflection electrode because the distance is short.

At this time, a force acts on the upper ink droplet 301 in the negative direction opposite to the ink droplet flight direction, and the ink droplet 301 decelerates. As a result, the upper ink droplet 301 and the upper ink droplet 302 are prevented from approaching each other during flight, the effect of the Coulomb force is reduced, and merging or scattering does not occur in the upper ink droplet 301 and the upper ink droplet 302.

In this third embodiment, the ink droplets are charged in the order of upper ink droplets ⇒ middle ink droplets ⇒ upper ink droplets, and the upper ink droplets 302 and 301 are prevented from approaching each other during flight, preventing merging or scattering.

The third embodiment described above can be defined as follows. First, when performing three-line printing in which characters are printed in the upper, middle, and lower rows, "N" is the number of rows in the upper row where print dots can be arranged, "M" is the number of rows in the middle row where print dots can be arranged, "Q" is the number of rows in the lower row where print dots can be arranged, "x" is an arbitrary row, and "p" is the number of print dots printed in one scan, and the relationships are set as N ≥ x, M ≥ x, Q ≥ x, and N + M + Q ≥ p.

From the above relationship, when performing a scan to form a vertical row of print dots using ink droplets, there are N positions where print dots can be placed in the top row, and the positions where the N print dots in the top row can be placed are n_1 to n_N, starting from the bottom. When performing a scan, there are M positions where print dots can be placed in the middle row, and the positions where the M print dots in the middle row can be placed are m_1 to m_M, starting from the bottom. When performing a scan, there are Q positions where print dots can be placed in the bottom row, and the positions where the Q print dots in the bottom row can be placed are q_1 to q_Q, starting from the bottom.

Then, within the positions where print dots can be placed in the upper, middle, and lower rows, print dots are formed at p positions in one scan, and this scan is repeated any number of times to form the print content. Based on the above, charging control of the ink droplets that form the print dots is performed as follows.

(3-1) When forming print dots in the middle row m_x, the top row n_x, and the top row n_x+1, a charged ink droplet that forms a print dot in the middle row m_x is inserted adjacent to two charged ink droplets that form print dots in the top row n_x and the top row n_x+1.

(3-2) When forming print dots in the lower row q_x, the upper row n_x-2, and the upper row n_x-1, a charged ink droplet for forming a print dot in the lower row q_x is inserted adjacent to two charged ink droplets for forming print dots in the upper row n_x-2 and the upper row n_x-1.

In this way, the ink droplets are charged in the order of upper ink droplets ⇒ middle ink droplets ⇒ upper ink droplets, or upper ink droplets ⇒ lower ink droplets ⇒ upper ink droplets, which prevents the two upper ink droplets from approaching each other while flying, and the print dots formed by these dots do not merge or scatter. The same is true when printing two print dots in the middle row as shown below.

(3-3) When forming print dots in the lower row q_x, the middle row m_x, and the middle row m_x+1, the charged ink droplets forming the print dots in the lower row q_x are inserted adjacent to each other between the two charged ink droplets for forming print dots in the middle row m_x and the middle row m_x+1.

(3-4) When forming print dots in the top row n_x, the middle row m_x-1, and the middle row m_x, the charged ink droplets forming the print dots in the top row n_x are inserted adjacent to each other between the two charged ink droplets for forming print dots in the middle row m_x-1 and the middle row m_x.

In this way, the ink droplets are charged in the order of middle ink droplets ⇒ lower ink droplets ⇒ middle ink droplets, or middle ink droplets ⇒ upper ink droplets ⇒ middle ink droplets, which prevents the two middle ink droplets from approaching each other while flying, and the print dots formed by these dots do not merge or scatter. The same is true when printing two print dots in the lower row as shown below.

(3-5) When forming print dots in the middle row m_x, the lower row q_x-1, and the lower row q_x, the charged ink droplets forming the print dots in the middle row m_x are inserted adjacent to each other between the two charged ink droplets for forming print dots in the lower row q_x-1 and the lower row q_x.

(3-6) When forming print dots in the upper row n_x, the lower row q_x+1, and the lower row q_x+2, a charged ink droplet for forming a print dot in the upper row n_x is inserted adjacent to two charged ink droplets that form print dots in the lower row q_x+1 and the lower row q_x+2.

In this way, the ink droplets are charged in the order of lower ink droplets ⇒ middle ink droplets ⇒ lower ink droplets, or lower ink droplets ⇒ upper ink droplets ⇒ lower ink droplets, which prevents the two lower ink droplets from coming close to each other during flight and prevents merging or scattering from occurring.

Next, a fourth embodiment of the present invention will be described with reference to Figs. 16 and 17. Fig. 16 shows a three-line print control method that differs from the three-line print control method (printing from the bottom line of the lower line) shown in the third embodiment.

As shown in Figure 16, when performing three-level printing according to the fourth embodiment, the difference is that the print dots present in the top, middle and bottom rows are printed starting from the "top row" of the top row, then the middle row, then the bottom row, and this is repeated for each scan. However, if there are no print dots on the print matrix, uncharged ink droplets are injected, which is the same as the three-level print control method shown in the third embodiment.

Next, the issues that arise when implementing the above-mentioned three-stage printing control method (printing from the top row of the upper stage) will be explained using FIG. 10 and FIG. 16. When printing the first row as shown in FIG. 16, the upper stage ink droplets 405 and 40 come close to each other while flying, causing scattering. The reasons for this are as follows.

In FIG. 16, the flying positional relationship of the charged ink droplets is similar to that shown in FIG. 10. The upper ink droplet 405 corresponds to the upper ink droplet 203, the upper ink droplet 404 corresponds to the upper ink droplet 202, and the middle ink droplet 403 corresponds to the lower ink droplet 201. Therefore, the following explanation will follow this.

Inside the deflection electrode, Coulomb force acts between the upper ink droplet 404 and the middle ink droplet 403. In the upper ink droplet 404, a force acts in the positive direction of the ink droplet flight direction. On the other hand, the upper ink droplet 405 is subjected to air drag in the negative ink droplet flight direction, and decelerates.

Furthermore, the upper ink droplet 405 forms a wake, and when the upper ink droplet 404 enters the wake region, the air drag acting on the upper ink droplet 404 becomes smaller, and the deceleration of the upper ink droplet 404 weakens. Therefore, the upper ink droplets 404 and 405 gradually approach each other, causing scattering.

Note that the three-level printing matrices in which scattering occurs are not limited to the number "9," the letter "t," and the number "4." Scattering may occur in any printing matrix in which printing dots exist at the printing dot arrangement positions (1) to (6) shown in the third embodiment described above.

The arrangement positions of three print dots in one column, which are caused by two charged ink droplets forming adjacent print dots in the “same row” and a charged ink droplet forming a print dot in the “other row” adjacent to these two charged ink droplets, are as follows, assuming that “x” is any row:
(4-1)n_x, n_x+1, m_x
(4-2)n_x-2, n_x-1, q_x
(4-3) m_x, m_x+1, q_x
(4-4) m_x, m_x-1, n_x
(4-5)q_x, q_x-1, m_x
(4-6)q_x+1, q_x+2, n_x
Either:

Note that print dot positions (4-1) and (4-2) are when two print dots are placed adjacent to each other in the upper row, print dot positions (4-3) and (4-4) are when two print dots are placed adjacent to each other in the middle row, and print dot positions (4-5) and (4-6) are when two print dots are placed adjacent to each other in the lower row.

The pattern of the arrangement positions of the six printing dots described above is the example in the first row of Figure 16, but even when there are four or more printing dots, there is a high risk of scatter occurring in printed characters that have printing dots that match the pattern described above.

In the print matrix shown in FIG. 16, print dots exist at m_5, n_5, and n_6, which corresponds to the print dot arrangement position of (4-1) described above. Also, when print dots exist at the print dot arrangement positions described above, if the flight trajectories of ink droplets landing on the same row are similar and the repulsion due to Coulomb force between ink droplets landing on the same row is small, merging will occur.

In this way, when two adjacent print dots are printed in one row, if two ink droplets are followed by an ink droplet in another row, the Coulomb force between the two ink droplets in the same row affects each other, causing scattering or merging.

The charge control of ink droplets in the fourth embodiment of the present invention, which solves the above problems, will be described with reference to Figures 17 and 18. This charge control is performed by the charge control function of the microcomputer, as in the first embodiment. In other words, the print pattern of the print dots for each row is read out, and if the print pattern to be printed that is read out includes any of the six print patterns described above, there is a risk of scatter or the like occurring, so the charge control shown below is performed. Note that other print patterns are configured to be printed in the normal order.

Figure 17 shows the charging sequence of ink droplets in the fourth embodiment of the present invention. In the fourth embodiment, the middle ink droplet 406 for forming the first row of print dots of the letter "t" is present between the upper ink droplet 405 and the upper ink droplet 406.

Figure 18 shows the upper ink droplet 405, the middle ink droplet 406, and the upper ink droplet 4064 flying through the deflection electrode positive electrode 106 and the region 407 within the deflection electrode negative electrode 107 in the fourth embodiment.

As shown in FIG. 18, inside the deflection electrode, a large Coulomb force acts between the upper ink droplet 405 and the middle ink droplet 406. At this time, a Coulomb force acts on the upper ink droplet 405 in the positive direction of the ink droplet flight direction, suppressing the deceleration of the upper ink droplet 405. As a result, the upper ink droplet 405 and the upper ink droplet 404 are prevented from approaching each other during flight, weakening the Coulomb force, and merging and scattering do not occur in the print dot formed by the upper ink droplet 405 and the upper ink droplet 404.

In this fourth embodiment, the ink droplets are charged in the order of upper ink droplets ⇒ middle ink droplets ⇒ upper ink droplets, and the upper ink droplets 405 and 404 are prevented from approaching each other during flight, and the print dots formed by these do not suffer from merging or scattering.

In addition, by applying a three-stage print control method like the fourth embodiment, it is possible to reduce the deviation in the landing position of a line of print dots in the transport direction of the print target. The reason for this is as follows.

When comparing the flight of ink droplets used when scanning a single row, the amount of deflection is greater for ink droplets that land on the upper side of the print target. For this reason, the flight time of ink droplets that land on the upper side of the print target is longer after being ejected from the nozzle until they land on the print target.

In a three-stage printing control method like the fourth embodiment, ink droplets with the longest flight time are charged, generated, and printed in sequence. As a result, the landing time difference between ink droplets when scanning one row is reduced by the generation time difference between each ink droplet. Therefore, the transport distance of the print object within the landing time difference is reduced. For these reasons, the deviation in the landing position of the print dots in one row in the transport direction of the print object is reduced.

The fourth embodiment described above can be defined as follows. First, when performing three-line printing in which characters are printed in the upper, middle, and lower rows, "N" is the number of rows in the upper row where print dots can be arranged, "M" is the number of rows in the middle row where print dots can be arranged, "Q" is the number of rows in the lower row where print dots can be arranged, "x" is an arbitrary row, and "p" is the number of print dots printed in one scan, and the relationships are set as N ≥ x, M ≥ x, Q ≥ x, and N + M + Q ≥ p.

From the above relationship, when performing a scan to form a vertical row of print dots using ink droplets, there are N positions where print dots can be placed in the top row, and the positions where the N print dots in the top row can be placed are n_1 to n_N, starting from the bottom. When performing a scan, there are M positions where print dots can be placed in the middle row, and the positions where the M print dots in the middle row can be placed are m_1 to m_M, starting from the bottom. When performing a scan, there are Q positions where print dots can be placed in the bottom row, and the positions where the Q print dots in the bottom row can be placed are q_1 to q_Q, starting from the bottom.

Then, within the positions where print dots can be placed in the upper, middle, and lower rows, print dots are formed at p positions in one scan, and this scan is repeated any number of times to form the print content. Based on the above, charging control of the ink droplets that form the print dots is performed as follows.

(4-1) When forming print dots in the top row n_x, top row n_x+1, and middle row m_x, a charged ink droplet that forms a print dot in the middle row m_x is inserted adjacent to two charged ink droplets that form print dots in the top row n_x and top row n_x+1.

(4-2) When forming print dots in the upper row n_x-2, upper row n_x-1, and lower row q_x, a charged ink droplet for forming a print dot in the lower row q_x is inserted adjacent to two charged ink droplets for forming print dots in the upper row n_x-2 and upper row n_x-1.

In this way, the ink droplets are charged in the order of upper ink droplets ⇒ middle ink droplets ⇒ upper ink droplets, or upper ink droplets ⇒ lower ink droplets ⇒ upper ink droplets, which prevents the two upper ink droplets from approaching each other while flying, and the print dots formed by these dots do not merge or scatter. The same is true when printing two print dots in the middle row as shown below.

(4-3) When forming print dots in the middle row m_x, the middle row m_x+1, and the lower row q_x, a charged ink droplet that forms a print dot in the lower row q_x is inserted adjacent to two charged ink droplets that form print dots in the middle row m_x and the middle row m_x+1.

(4-4) When forming print dots in the middle row m_x-1, the middle row m_x, and the upper row n_x, the charged ink droplets forming the print dots in the upper row n_x are inserted adjacent to each other between the two charged ink droplets for forming the print dots in the middle row m_x-1 and the middle row m_x.

In this way, the ink droplets are charged in the order of middle ink droplets ⇒ lower ink droplets ⇒ middle ink droplets, or middle ink droplets ⇒ upper ink droplets ⇒ middle ink droplets, which prevents the two middle ink droplets from approaching each other while flying, and the print dots formed by these dots do not merge or scatter. The same is true when printing two print dots in the lower row as shown below.

(4-5) When forming print dots in the lower row q_x-1, the lower row q_x, and the middle row m_x, a charged ink droplet that forms a print dot in the middle row m_x is inserted adjacent to two charged ink droplets that form print dots in the lower row q_x-1 and the lower row q_x.

(4-6) When forming print dots in the lower row q_x+1, the lower row q_x+2, and the upper row n_x, a charged ink droplet for forming a print dot in the upper row n_x is inserted adjacent to the two charged ink droplets that form print dots in the lower row q_x+1 and the lower row q_x+2.

In this way, the ink droplets are charged in the order of lower ink droplets ⇒ middle ink droplets ⇒ lower ink droplets, or lower ink droplets ⇒ upper ink droplets ⇒ lower ink droplets. This prevents the two lower ink droplets from coming close to each other while flying, and the print dots formed by this do not merge or scatter.

In this way, in the third and fourth embodiments, charged ink droplets used for printing in another tier (lower tier, middle tier, or upper tier) are inserted between two charged ink droplets that are deemed to be at high risk of merging or scattering in at least one of the same predetermined tiers (upper tier, middle tier, or lower tier), and ink droplet charging control is performed to change the direction of the Coulomb force acting on the two charged ink droplets in the same predetermined tier.

This prevents two ink droplets from approaching each other during flight, which can cause merging or scattering, making it possible to provide an inkjet recording device that can print without reducing the printing speed during multi-stage printing and without causing merging or scattering.

Finally, we will explain a generalized version of the first to fourth embodiments, which is a case where Y-level printing is performed, in which a string of characters in Y levels, each of which is stacked, is printed simultaneously.

The topmost printed character is designated as the Yth row, the bottommost row as the 1st row, and any row as "t", with a relationship of 1≦t≦Y. When performing a scan to form one vertical row of print dots in the tth row, there are _Yt positions (number of rows) at which print dots can be placed, and the positions at which the _Yt print dots in the tth row can be placed are designated _{yt_1} to _{yt_Yt} , starting from the bottom. For example, in the first row, the positions are _{y1_1} to _{y1_Y1 ,} starting from the bottom, and in the Yth row, _the positions are _{yY_1} to _{yY_YY ,} starting from the bottom.

Then, within the positions where print dots to be printed in the Y row can be placed, print dots are formed at p positions in one scan, and this scan is repeated any number of times to form a printed character. Based on the above, the charged ink droplets that form the print dots are controlled as follows. Here, "x" is defined as any row.

(Y-1) When _Yt ≧x and Yt ₊₁ ≧x, in the case where print dots are formed at _yt _x in the tth stage, yt ₊₁ _x in the t+1th stage, and yt _{+1 _x+1 in the t} +1th stage (e.g., the upper stage), charging is controlled so that a charged ink droplet forming a print dot of _yt _x in the tth stage is inserted between two charged ink droplets for forming print dots at yt ₊₁ _x in the _{t+1th stage, and yt+1} _x+1.

(Y-2) When _Yt ≧x and Yt _-1 ≧x, in the case where print dots are formed in _yt _x in the t-th stage, as well as _yt-1 _x-1 in the t-1th stage and yt- ₁ _x in the t-1th stage, charging is controlled so that a charged ink droplet forming a print dot of yt _x in the t-th stage is inserted between two charged ink droplets forming print dots in yt- ₁ _x-1 in the t-1th stage and yt _{- 1} _x in the t-1th stage.

(Y-3) When _Y1 ≧x and _YY ≧x, in the case where print dots are formed at _{yY_x} in the Yth stage, and at _{y1_x} +1 in the first stage, and at _{y1_x} +2 in the first stage, charging is controlled so that a charged droplet forming a print dot of _{yY_x} in the Yth stage is inserted between two charged ink droplets for forming print dots at _{y1_x} +1 in the first stage, and at _{y1_x} +2 in the first stage.

(Y-4) When _Y1 ≧x and _YY ≧x, in the case where print dots are formed in _{y1_x} in the first stage, and _{yY_x} -2 in the Y stage and _{yY_x} -1 in the Y stage, charging is controlled so that a charged ink droplet forming a print dot in y1_x in the first stage is inserted between two charged ink droplets for forming print dots in _{yY_x} -2 in the Y stage and _{yY_x} - ₁ in the Y stage.

This prevents two ink droplets from approaching each other during flight, which can cause merging or scattering, making it possible to provide an inkjet recording device that can print without reducing the printing speed during multi-stage printing and without causing merging or scattering.

As described above, according to the present invention, when performing multi-stage printing, charged ink droplets used for printing in other stages are inserted between two charged ink droplets that are deemed to be at high risk of merging or scattering in at least one specified same stage, and ink droplet charging control is performed to change the direction of the Coulomb force acting on the two charged ink droplets in the specified same stage.

This makes it possible to provide an inkjet recording device that can print without reducing the printing speed during multi-stage printing and without causing merging or scattering.

The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1... Continuous jet charge-controlled inkjet recording body, 2... Display, 3... Cable, 4... Print head, 100... Printing object, 103... Ink nozzle, 105... Charged electrode, 106... Deflection electrode positive electrode, 107... Deflection electrode negative electrode, 111... Charged ink droplet, 112... Uncharged ink droplet, 113... Printing dot.

Claims (5)

1. A charge control method for an ink jet recording apparatus including an ink nozzle which ejects ink liquid as ink droplets, a charging electrode which charges the ink droplets, a positive deflection electrode and a negative deflection electrode which deflect the charged ink droplets, a gutter which collects the ink droplets not used for printing, and a control means which controls the charge of the ink droplets by the charging electrode,
When multi-stage printing is performed, the control means
Charging control is performed so that the same column in each of different stages is printed in order from the bottom row to the top row or from the top row to the bottom row,
A charge control method for an inkjet recording device, characterized in that, during the process of printing in the order, if there are at least two ink droplets that are used for printing at least a specified same stage and are considered to have a high risk of merging or scattering, and an ink droplet used for printing another stage is present consecutively before or after these two ink droplets, an ink droplet used for printing the other stage is inserted between the two ink droplets, and charge control is performed to change the direction of the Coulomb force acting on the two ink droplets in the same stage. 2. A method for controlling charging of an ink jet recording apparatus according to claim 1, comprising the steps of:
The method for controlling charging of an ink jet recording apparatus, wherein the two ink droplets considered to be highly likely to cause the merge or scatter are adjacent print dots in the same stage. 3. A method for controlling charging of the ink jet recording apparatus according to claim 2, comprising the steps of:
The multi-level printing is two-level printing consisting of upper level printed characters and lower level printed characters, and when the two-level printing is performed, N is the number of rows in the upper level vertical column at which print dots can be arranged, M is the number of rows in the lower level vertical column at which the print dots can be arranged, x is an arbitrary row, p is the number of the print dots printed in one scan, and the relationships N≧x, M≧x, and N+M≧p are set,
When performing a scan to form the printing dots in the vertical row, the number of positions at which the printing dots can be arranged in the upper row is N, and the positions at which the N printing dots in the upper row can be arranged are n_1 to n_N, in order from the bottom up; the number of positions at which the printing dots can be arranged in the lower row is M, and the positions at which the M printing dots can be arranged in the lower row are m_1 to m_M, in order from the bottom up;
forming the printing dots at p positions in one scan within positions where the printing dots present in the upper row and the lower row can be arranged, and forming a print character by repeating the scan an arbitrary number of times;
(1) When forming the print dots in the lower row m_x, the upper row n_x, and the upper row n_x+1, the ink droplets forming the print dots in the lower row m_x are inserted adjacent to each other between the two ink droplets for forming the print dots in the upper row n_x and the upper row n_x+1.
(2) when forming the print dots in the lower row m_x, the upper row n_x-2, and the upper row n_x-1, inserting the ink droplets forming the print dots in the lower row m_x adjacently between the two ink droplets for forming the print dots in the upper row n_x-2 and the upper row n_x-1;
(3) When forming the print dots in the upper row n_x, the lower row m_x+1, and the lower row m_x+2, the ink droplets forming the print dots in the upper row n_x are inserted adjacent to each other between the two ink droplets forming the print dots in the lower row m_x+1 and the lower row m_x+2.
(4) A charge control method for an inkjet recording device, characterized in that when forming the print dots in the upper row n_x, the lower row m_x-1, and the lower row m_x, charge control is performed by performing any one or a combination of the following: inserting the ink droplets forming the print dots in the upper row n_x adjacent to each other between the two ink droplets forming the print dots in the lower row m_x-1 and the lower row m_x. 3. A method for controlling charging of the ink jet recording apparatus according to claim 2, comprising the steps of:
The multi-level printing is three-level printing consisting of upper level print characters, middle level print characters, and lower level print characters, and when the three-level printing is performed, N is the number of rows in the upper level vertical column at which the print dots can be arranged, M is the number of rows in the middle level vertical column at which the print dots can be arranged, Q is the number of rows in the lower level vertical column at which the print dots can be arranged, x is an arbitrary row, p is the number of the print dots printed in one scan, and the relationships N≧x, M≧x, Q≧x, and N+M+Q≧p are set,
When performing a scan to form the printing dots in the single vertical row, there are N positions at which the printing dots can be arranged in the top row, and the positions at which the N printing dots in the top row can be arranged are designated n_1 to n_N, in order from bottom up; there are M positions at which the printing dots can be arranged in the middle row, and the positions at which the M printing dots in the middle row can be arranged are designated m_1 to m_M, in order from bottom up; there are Q positions at which the printing dots can be arranged in the bottom row, and the positions at which the Q printing dots can be arranged in the bottom row are designated q_1 to q_Q, in order from bottom up;
Within the positions where the print dots present in the upper, middle, and lower rows can be arranged,
The printing dots are formed at p positions in one scan, and the printing content is formed by repeating the scan an arbitrary number of times.
(1) When forming the print dots in the middle row m_x, the upper row n_x, and the upper row n_x+1, the ink droplets forming the print dots in the middle row m_x are inserted adjacent to each other between the two ink droplets for forming the print dots in the upper row n_x and the upper row n_x+1.
(2) when forming the print dots in the lower row q_x, the upper row n_x-2, and the upper row n_x-1, inserting the ink droplets for forming the print dots in the lower row q_x adjacently between the two ink droplets for forming the print dots in the upper row n_x-2 and the upper row n_x-1;
(3) when forming the print dots in the lower row q_x, the middle row m_x, and the middle row m_x+1, inserting the ink droplets forming the print dots in the lower row q_x adjacently between the two ink droplets for forming the print dots in the middle row m_x and the middle row m_x+1;
(4) When forming the print dots in the upper row n_x, the middle row m_x-1, and the middle row m_x, the ink droplets forming the print dots in the upper row n_x are inserted adjacent to each other between the two ink droplets for forming the print dots in the middle row m_x-1 and the middle row m_x.
(5) when forming the print dots in the middle row m_x, the lower row q_x-1, and the lower row q_x, inserting the ink droplets forming the print dots in the middle row m_x adjacently between the two ink droplets for forming the print dots in the lower row q_x-1 and the lower row q_x;
(6) A charge control method for an inkjet recording apparatus, characterized in that when forming the print dots in the upper row n_x, the lower row q_x+1, and the lower row q_x+2, charge control is performed by inserting the ink droplets for forming the print dots in the upper row n_x adjacent to each other between the two ink droplets that form the print dots in the lower row q_x+1 and the lower row q_x+2, or a combination of two or more of the above. 3. A method for controlling charging of the ink jet recording apparatus according to claim 2, comprising the steps of:
The multi-column printing is Y-column printing consisting of Y-column printed characters, and when the Y-column printing is performed, the topmost printed character is defined as the Yth column, the bottommost column is defined as the 1st column, and an arbitrary column is defined as t, such that 1≦t≦Y;
In the case of performing a scan to form one vertical column of the print dots in the t-th row, the number of rows in which the print dots can be arranged is Yt, and the positions in the t-th row in which the Yt print dots can be arranged are yt_1 to yt_Yt, in order from the bottom;
Within positions where the printing dots to be printed in Y rows can be arranged, the printing dots are formed at p positions in one scan, and the scan is repeated an arbitrary number of times to form a print character, and when x is defined as an arbitrary row,
(1) When Yt≧x and Yt+1≧x, in the case where the print dots are formed in the t-th row yt_x, the t+1th row yt+1_x, and the t+1th row yt+1_x+1, the ink droplets forming the print dots in the t-th row yt_x are inserted between the two ink droplets for forming the print dots in the t+1th row yt+1_x and the t+1th row yt+1_x+1.
(2) When Yt≧x and Yt-1≧x, in the case where the print dots are formed in the t-th row yt_x, the t-1-th row yt-1_x-1, and the t-1-th row yt-1_x, the ink droplets forming the print dots in the t-th row yt_x are inserted between the two ink droplets for forming the print dots in the t-1-th row yt-1_x-1 and the t-1-th row yt-1_x.
(3) When Y1≧x and YY≧x, in the case where the print dots are formed in the Yth row yY_x, the first row y1_x+1, and the first row y1_x+2, the ink droplets forming the print dots in the Yth row yY_x are inserted between the two ink droplets for forming the print dots in the first row y1_x+1 and the first row y1_x+2.
(4) A charge control method for an inkjet recording device, characterized in that, when Y1≧x and YY≧x, when forming the print dots in the first row y1_x, the Y-th row yY_x-2, and the Y-th row yY_x-1, the charge control is performed by performing one or a combination of the following: inserting the ink droplets that form the print dots in the first row y1_x between the two ink droplets for forming the print dots in the Y-th row yY_x-2 and the Y-th row yY_x-1.

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