JP2008049714A - Liquid discharge device and liquid discharge method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of streaks between dot rows as variations between discharge parts in a line system while eliminating variations in dot arrays. <P>SOLUTION: A liquid discharge device allows maximum N liquid droplets to be landed in one pixel region so as to form a dot corresponding to the pixel region. The discharge direction of a liquid droplet discharged from a liquid discharge part is set so that a landing target position of a liquid droplet in an arrangement direction of nozzles in one pixel region becomes any one position of M different positions where a region of the landed liquid droplet at least partially enters in the pixel region. Any one landing target position of the M landing target positions is randomly determined for each liquid droplet discharged from the liquid discharge part. The discharge direction of the liquid droplet discharged from the liquid discharge part is controlled so as to allow the liquid droplet to be landed at the determined landing target position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus and a liquid ejecting method for forming dots by landing one or more liquid droplets on a pixel region, thereby making the image quality of an image inconspicuous by making dispersion of liquid droplet landing positions inconspicuous. This is related to the technology to improve

  2. Description of the Related Art Conventionally, an ink jet printer that is one of liquid ejecting apparatuses usually includes a head in which ink ejecting portions having nozzles are linearly arranged. Then, from the respective ink ejection sections of this head, minute ink droplets are sequentially ejected toward a recording medium such as photographic paper disposed to face the nozzle surface, thereby arranging substantially circular dots vertically and horizontally. , Images and characters are represented as stipples.

  On the other hand, the ink jet printer ejects droplets with a certain degree of variation due to its structure. Looking at the dot arrangement when the ejected ink droplets land on the recording medium, the temporal variation (accidental) is averaged and is not very noticeable, but it is unique to the ink ejection unit (head). The variation becomes conspicuous even if it is slight as a linear variation (pairing).

  FIG. 13 is a diagram for explaining variation in dot arrangement. In FIG. 13, the portion indicated by the arrow shifts 1/36, 1/12, and 1/4 of the dot pitch (the distance between the centers of adjacent dots) to the right in the drawing, and also corresponds to the dot pitch. The magnitude of the dot diameter is divided into large, medium, and small, and the effect when the dot pitch is shifted is shown.

  As can be understood from FIG. 13, when the dot row is deviated by about 10% of the dot pitch, the deviation can be recognized visually, and those over 20% are generally conspicuous as recording defects. Note that whether or not the dot pitch deviation is noticeable depends on the color of the ink. For example, yellow has a large tolerance for misalignment (the misalignment is less conspicuous than other colors).

Here, in the case of a serial system in which the head performs a linear reciprocating movement in the horizontal direction with respect to the recording medium and the recording medium is conveyed in a direction substantially perpendicular to the reciprocating movement direction, The following two methods are known as methods for solving the pitch deviation.
In the present specification, in the serial system, the reciprocating direction of the head is defined as the main scanning direction, and the direction substantially perpendicular to this direction (the conveyance direction of the recording medium) is defined as the sub-scanning direction.

The first method is to overlap the dots so that the background of the recording medium cannot be seen even if there is a slight shift in the dot pitch. That is, the dot size (dot diameter) is increased with respect to the dot pitch.
According to this method, assuming that the dot is circular, if the dot diameter is larger than √2 times the dot pitch (diagonal line of the dot pitch), the gap between the dots is filled as long as the normal arrangement is made. Even if there is a deviation in the landing positions of dots, it is not so noticeable and white streaks can be prevented from being generated on the image.
FIG. 14 is a diagram illustrating an example in which the entire dot size is set to be slightly more than √2 times the dot pitch with respect to the same dot row shift as in FIG. 13.

  The second method is a method called “overstrike”. In this overstrike, since the large dots as shown in the first method are not used, the liquid droplets ejected at one time do not fill the gaps between the dots, but fill the gaps between the previously arranged dot rows. The gaps are filled by arranging dots on top of each other. FIG. 15 is a diagram showing a state when overstrike is performed as the second method. In FIG. 15, dots having different patterns are formed during different main scans, or formed by different heads. Since this overstrike can be used not only in the main scanning direction but also in the sub-scanning direction, an image can be formed from small dots.

Also, in the case of the line method in which the head is formed so as to cover the entire width of the recording medium (substantially the entire range in the main scanning direction of the serial method), the head is fixed and only the recording medium is conveyed. It is normal.
In this specification, in the line system, the conveyance direction of the recording medium is defined as the main scanning direction.
In the line system, the alignment accuracy of the ink discharge portions can be increased by integrally forming the heads that cover the entire width of the recording medium with a silicon wafer, glass, or the like. However, there are various problems such as a manufacturing method, a yield problem, a heat generation problem, and a cost problem, and in reality, it is almost impossible to manufacture a head having such a structure.

For this reason, when a line head is mounted on an inkjet printer, a small head chip (there are also various restrictions, and even if it is large, the length in the direction in which the ink ejection sections are arranged is about 1 inch or less is a practical limit. Are arranged side by side so that the end portions are connected to each other, and by performing appropriate signal processing on each head chip, at the stage of printing on the recording medium, recording connected to the entire width of the recording medium is performed. It is known to carry out (see, for example, Patent Document 1).
JP 2002-36522 A

However, the above-described conventional technology has the following problems.
The first method in the serial method (method of increasing the dot size) is more resistant to dot misalignment, but as a result of the increase in dot size, it becomes easier to see the particulate dots and intermediate gray levels are required. In the case of a print such as a photograph, there is a problem that the feeling of roughness increases.

  In addition, unlike the first method, the second method (overlaying) in the serial method does not require an increase in dot size, and therefore reduces the rough feeling of the entire image and improves the picture quality and the like. Can do. However, since a large number of dots must be arranged both in the main scanning direction and in the sub-scanning direction, there is a problem that the recording speed is correspondingly reduced. In order to solve this problem, it is necessary to operate a large number of ink ejection units as fast as possible. However, if this is done, there is a problem in that reliability is likely to decrease and cost increases.

Furthermore, in the case of the line method, it is possible to increase the dot diameter to reduce the variation in ejection between the ink ejection units, but there is a problem similar to the first method in the serial method.
Further, in the case of the line method, there is a problem that an error is likely to occur in the arrangement interval of the ink ejection units because the head chips are joined together. Further, there is a problem that an error occurs in the thickness between the head chips even when the head chips are bonded. The effects of these errors can be several times the variation in the ejection angle of ink droplets that occurs within a single head chip.

In the case of the line method, since the head does not move, it is not possible to perform overstrike by recording the area once recorded again. That is, the second method in the serial method cannot be adopted.
Here, as a special example, it is impossible to overprint if a recording medium is taken in and out many times (such as a sublimation printer) on the condition that a stiff recording medium is used only for photographs and the like. Absent. However, unlike a sublimation printer, an inkjet printer requires a certain amount of time for the dots arranged on the recording medium (landed ink) to dry. It is dangerous to go in and out without protection.

  Furthermore, the entry / exit of the recording medium is limited to a special recording medium, and the above-described entry / exit cannot be performed on a recording medium such as plain paper. In addition, since the line method has a merit of high recording speed, if the recording medium is taken in / out in the line method, the recording speed is lowered and the purpose of adopting the line method is lost. . Therefore, in the case of the line method, overprinting can be performed only in the recording medium feeding direction, that is, the main scanning direction.

And, in the case of the line method, it is possible to increase the gradation by performing the overstrike in the main scanning direction, but the overstrike in the main scanning direction has the effect of only increasing the gradation, It does not contribute to averaging discharge variation.
On the other hand, overprinting in the sub-scanning direction has an important effect of averaging discharge variation in addition to the effect of increasing the gradation like the overstrike in the main scanning direction.

That is, since the distance between the centers of the dots in the main scanning direction is merely an arrangement of dots ejected from the same ink ejection unit, the accuracy is extremely good, but the distance between the centers of the dots in the sub scanning direction is Since all are due to different ink discharge portions, the variation is large.
For the reasons described above, in the line method without sub-scanning, there is a problem that variations unique to the ink discharge portions remain in the direction in which the ink discharge portions are arranged, and may become noticeable as uneven stripes.

  Therefore, the problem to be solved by the present invention is a technique (for example, Japanese Patent Application No. 2002-161928, Japanese Patent Application No. 2002-320861, and Japanese Patent Application No. 2002) that has been proposed by the present inventors and that can deflect and discharge ink droplets. 320862) to eliminate the variation in dot arrangement, and in the line method in particular, it is to prevent streaks from entering between the dot rows as variations between the ejection units.

The present invention solves the above-described problems by the following means.
The invention according to claim 1, which is one of the present invention, includes a head capable of deflecting a discharge direction of a droplet discharged from a liquid discharge unit having a nozzle in a plurality of directions in a specific direction. A liquid ejecting apparatus that forms a single pixel having a plurality of gradations by overlapping and landing a maximum of N liquid droplets (N is a positive integer), and the liquid droplets in the specific direction in one pixel region The liquid target position is any one of M different positions (M is an integer of 2 or more) where at least a part of the landed droplet region falls within the pixel region. The ejection direction of droplets ejected from the ejection unit is set, and for each droplet ejected from the liquid ejection unit, one of the M landing target positions is randomly determined, Droplets land on the determined landing target position Wherein to control the discharge direction of the droplets discharged from the liquid discharge portion, and forming a pixel corresponding to the pixel region.

(Function)
In the above invention, each liquid ejection part of the head is formed so as to eject liquid droplets in a plurality of different directions.
Further, in one pixel region, droplet landing target positions are set to M different positions in a specific direction. Here, it is set so that at least a part of the droplet falls within the pixel area regardless of which of the M different positions the droplet reaches.

When the liquid droplets land on the pixel area, any one of the M landing target positions is randomly determined, and the liquid droplets land on the determined position.
Accordingly, the liquid droplets land so as to be included in at least a part of the pixel region, but the landed liquid droplets are at random positions with respect to the pixel region. As a result, the deviation of the landing positions of the droplets due to variations unique to the liquid ejection unit is eliminated, and the entire dot arrangement is uniform with no directivity.

  According to the present invention, since the droplets are randomly arranged in the pixel region, (1) variation in dot arrangement can be eliminated. In particular, in the line method, it is possible to prevent streaks from entering between dot rows as a variation between the liquid ejection units. As a result, it is possible to obtain a high-quality image by eliminating the deviation of the landing positions of the droplets due to variations unique to the liquid ejection unit and making the entire dot arrangement uniform with no directivity.

  Furthermore, according to the present invention, (2) it is possible to obtain the effect of masking variations due to the droplet ejection characteristics of the liquid ejection section. That is, even if there is a non-ejection liquid ejection portion, it is masked, so that the influence of the non-ejection liquid ejection portion is difficult to see. Also, (3) moire is eliminated. In particular, the occurrence of moire can be prevented by applying the present invention to color printing. Furthermore, (4) as a result of the effects (1) to (3), it is possible to obtain effects such as improved gradation characteristics.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification, “ink droplet” refers to a very small amount (for example, several picoliters) of ink (liquid) ejected from a nozzle 18 of an ink ejection unit described later. “Dot” refers to a dot formed by landing one ink droplet on a recording medium such as photographic paper. Furthermore, the “pixel” is a minimum unit of an image, and the “pixel area” is a dot formation area.
Accordingly, one or a plurality of ink droplets land on one pixel area, and one dot (one gradation) composed of one ink droplet, or a plurality of dots (multiple gradations) composed of a plurality of ink droplets. ) Is formed. That is, one or more dots correspond to one pixel area. An image is formed by arranging a large number of pixels on the recording medium.
Of course, one ink droplet may not land on the pixel region. In addition, as will be described later, each ink droplet does not completely enter the corresponding pixel region, and sometimes protrudes from the pixel region.

  Hereinafter, an embodiment of a liquid ejection apparatus according to the present invention will be described. The liquid discharge apparatus includes a liquid chamber that stores a liquid to be discharged, an energy generation element that imparts energy to the liquid in the liquid chamber, and a discharge port that discharges the liquid in the liquid chamber by the energy generation element. Is. Then, the ejection direction of the liquid ejected from the ejection port is deflected by controlling the manner in which energy is applied to the liquid by the energy generating element. For example, the energy generating element can constitute one surface of the liquid chamber and can deflect the discharge direction of the liquid discharged from the discharge port by controlling the energy distribution of the one surface that applies energy to the liquid. It becomes possible. In the following embodiments, a plurality of heating elements are used as energy generating elements, and a surface on which a plurality of heating elements are arranged is used as one surface for applying energy to a liquid, and the difference in giving energy to the plurality of heating elements is different. By controlling this, the energy distribution is controlled. Needless to say, the liquid ejection device used in the present invention is not limited to the following embodiments.

(Head structure)
FIG. 1 is an exploded perspective view showing a head 11 of an ink jet printer (hereinafter simply referred to as “printer”) to which a liquid ejection apparatus according to the present invention is applied. In FIG. 1, the nozzle sheet 17 is bonded onto the barrier layer 16, and the nozzle sheet 17 is shown in an exploded manner.
In the head 11, the substrate member 14 includes a semiconductor substrate 15 made of silicon or the like, and a heating resistor 13 deposited on one surface of the semiconductor substrate 15. The heating resistor 13 is electrically connected to an external circuit via a conductor portion (not shown) formed on the semiconductor substrate 15.

The barrier layer 16 is made of, for example, a photosensitive cyclized rubber resist or an exposure-curing dry film resist, and is laminated on the entire surface of the semiconductor substrate 15 on which the heating resistor 13 is formed, and then is subjected to a photolithography process. It is formed by removing unnecessary portions.
Furthermore, the nozzle sheet 17 is formed with a plurality of nozzles 18, and is formed by, for example, nickel electroforming, so that the position of the nozzle 18 matches the position of the heating resistor 13, that is, the nozzle 18. Is laminated on the barrier layer 16 so as to face the heating resistor 13.

  The ink liquid chamber 12 includes a substrate member 14, a barrier layer 16, and a nozzle sheet 17 so as to surround the heating resistor 13. That is, the substrate member 14 constitutes the bottom wall of the ink liquid chamber 12 in the figure, the barrier layer 16 constitutes the side wall of the ink liquid chamber 12, and the nozzle sheet 17 constitutes the top wall of the ink liquid chamber 12. To do. Thereby, the ink liquid chamber 12 has an opening region on the right front surface in FIG. 1, and the opening region communicates with an ink flow path (not shown).

  The one head 11 is usually provided with an ink chamber 12 and a heating resistor 13 disposed in each ink chamber 12 on a scale of 100 units, and in response to a command from the control unit of the printer. Each of the heating resistors 13 can be uniquely selected, and the ink in the ink liquid chamber 12 corresponding to the heating resistor 13 can be ejected from the nozzle 18 facing the ink liquid chamber 12.

  That is, the ink chamber 12 is filled with ink from an ink tank (not shown) coupled to the head 11. The heating resistor 13 is rapidly heated by passing a pulse current through the heating resistor 13 for a short time, for example, 1 to 3 μsec. As a result, gas-phase ink bubbles are formed in a portion in contact with the heating resistor 13. And a certain volume of ink is pushed away by the expansion of the ink bubbles (the ink boils). As a result, ink having a volume equivalent to the pushed ink in the portion in contact with the nozzle 18 is ejected as an ink droplet from the nozzle 18 and landed on the photographic paper to form dots.

  In the present specification, a portion composed of one ink liquid chamber 12, a heating resistor 13 disposed in the ink liquid chamber 12, and a nozzle 18 disposed on the upper portion is referred to as “ink ejection”. Part (liquid ejection part) ". That is, it can be said that the head 11 has a plurality of ink discharge portions arranged in parallel.

  Furthermore, in this embodiment, a plurality of heads 11 are arranged in the width direction of the recording medium to form a line head. FIG. 2 is a plan view showing an embodiment of the line head 10. In FIG. 2, four heads 11 (“N−1”, “N”, “N + 1”, and “N + 2”) are illustrated. In the case of forming the line head 10, a plurality of portions (head chips) excluding the nozzle sheet 17 from the head 11 are arranged side by side in FIG. 1. Then, the line head 10 is formed by laminating a single nozzle sheet 17 in which the nozzles 18 are formed at positions corresponding to the respective ink ejection portions of all the head chips. Here, the pitch between nozzles at each end of the adjacent head 11, that is, the nozzle 18 at the right end of the Nth head 11 and the left end of the (N + 1) th head 11 in FIG. The heads 11 are arranged so that the distance between the nozzles 18 in the head 11 is equal to the distance between the nozzles 18 of the head 11.

Next, the ink ejection unit of this embodiment will be described in more detail.
FIG. 3 is a plan view and a side sectional view showing the ink discharge portion of the head 11 in more detail. In the plan view of FIG. 3, the nozzle 18 is indicated by a one-dot chain line.
As shown in FIG. 3, in the head 11 of this embodiment, a heating resistor 13 divided into two is arranged in parallel in one ink liquid chamber 12. Furthermore, the arrangement direction of the two divided heating resistors 13 is the arrangement direction of the nozzles 18 (the left-right direction in FIG. 3).

Thus, when the heating resistor 13 divided into two is provided in one ink liquid chamber 12, the time until each heating resistor 13 reaches the temperature at which the ink is boiled (bubble generation occurs). At the same time, the inks boil simultaneously on the two heating resistors 13 and the ink droplets are ejected in the direction of the central axis of the nozzle 18.
On the other hand, if a time difference is given to the bubble generation time of the two divided heating resistors 13, the ink does not boil on the two heating resistors 13 simultaneously. As a result, the ejection direction of the ink droplets is deviated from the central axis direction of the nozzle 18 and deflected and ejected. Accordingly, the ink droplet can be landed at a position shifted from the landing position when the ink droplet is ejected without deflection.

FIG. 4 is a diagram for explaining deflection in the ejection direction of ink droplets. In FIG. 4, when the ink droplet i is ejected perpendicularly to the ejection surface of the ink droplet i, the ink droplet i is ejected without deflection as indicated by the dotted line in FIG. On the other hand, when the ejection direction of the ink droplet i is deflected and the ejection angle deviates by θ from the vertical position (Z1 or Z2 direction in FIG. 4), the ejection surface and the photographic paper P surface (ink) as the recording medium. When the distance to the surface of the droplet i is H (H is substantially constant), the landing position of the ink droplet i is
ΔL = H × tanθ
Will be shifted.
Thus, when the ejection direction of the ink droplet i is shifted by θ from the vertical direction, the landing position of the ink droplet is shifted by ΔL.

  FIGS. 5A and 5B are graphs showing the relationship between the ink bubble generation time difference of the heating resistor 13 divided into two and the ink ejection angle, and show the simulation results by the computer. In this graph, the X direction (X direction indicated by the vertical axis θx of the graph; attention; not the meaning of the horizontal axis of the graph) is the arrangement direction of the nozzles 18 (the direction in which the heating resistors 13 are arranged), and the Y direction (Y direction indicated by the vertical axis θy of the graph. Caution; not the meaning of the horizontal axis of the graph.) Is a direction perpendicular to the X direction (the conveyance direction of the photographic paper). FIG. 5C shows the difference in the amount of current generated between the two divided heating resistors 13, that is, the deflection current as the horizontal axis, as the ink bubble generation time difference between the two divided heating resistors 13. This is actually measured value data in the case where the vertical axis represents the deflection amount (actually measured with the above H being about 2 mm) at the ink landing position as the angle (X direction). In FIG. 5C, the main current of the heating resistor 13 is set to 80 mA, the deflection current is superimposed on one heating resistor 13, and the ink is deflected and discharged.

When there is a time difference in the generation of bubbles in the heating resistor 13 divided into two in the direction in which the nozzles 18 are arranged, as shown in FIG. 5, the ink ejection angle is not vertical, and the ink ejection angle in the direction in which the nozzles 18 are arranged θx (the amount of deviation from the vertical and corresponding to θ in FIG. 4) increases with the bubble generation time difference.
In this manner, if the heating resistors 13 divided into two are provided and the amount of current flowing through each heating resistor 13 is changed, control can be performed so that a time difference occurs between the bubble generation times on the two heating resistors 13. The ink ejection direction can be deflected according to the time difference.

Next, a method for deflecting the ink droplet ejection direction will be described more specifically.
FIG. 6 shows an embodiment in which the difference in bubble generation time between two divided heating resistors 13 can be set. In this example, the ink liquid deflection direction can be set to 8 types using the 3-bit control signal and the difference in the current value flowing through the resistor Rh-A and the resistor Rh-B can be set. The droplet discharge direction can be set in eight stages.

  In FIG. 6, resistors Rh-A and Rh-B are resistances of the heating resistor 13 divided into two, and both are connected in series. The resistance power source Vh is a power source for applying a voltage to the resistors Rh-A and Rh-B.

  The ejection control circuit 50 is a circuit for controlling the direction of ink droplet ejection by controlling the difference between the current values flowing through the resistors Rh-A and Rh-B, and includes M1 to M21 as transistors. Yes. Transistors M4, M6, M9, M11, M14, M16, M19 and M21 are PMOS transistors, and the others are NMOS transistors. The transistors M4 and M6, the transistors M9 and M11, the transistors M14 and M16, and the transistors M19 and M21 constitute a current mirror circuit (hereinafter referred to as “CM circuit”), respectively. Therefore, the discharge control circuit 50 includes four sets of CM circuits.

For example, in the CM circuit including the transistors M4 and M6, the gate and drain of the transistor M6 and the gate of the transistor M4 are connected, so that the same voltage is always applied to the transistors M4 and M6, and almost the same current flows. Has been. The same applies to other CM circuits.
The transistors M3 and M5 function as a differential amplifier of a CM circuit composed of the transistors M4 and M6, that is, a switching element (hereinafter referred to as “second switching element”). Here, the second switching element is for flowing current between the resistors Rh-A and Rh-B via the CM circuit or for flowing current from between the resistors Rh-A and Rh-B.
The transistors M8 and M10, the transistors M13 and M15, and the transistors M18 and M20 are second switching elements of a CM circuit including the transistors M9 and M11, the transistors M14 and M16, and the transistors M19 and M21, respectively.

  In the CM circuit including the transistors M4 and M6 and the transistors M3 and M5 which are the second switching elements, the drains of the transistors M4 and M3 and the transistors M6 and M5 are connected to each other. The same applies to the other second switching elements.

  Furthermore, the drains of the transistors M4, M9, M14, and M19 and the drains of the transistors M3, M8, M13, and M18 that form part of the CM circuit are connected to the midpoints of the resistors Rh-A and Rh-B. ing.

The transistors M2, M7, M12, and M17 serve as constant current sources for the respective CM circuits, and their drains are connected to the sources and back gates of the transistors M3, M8, M13, and M18, respectively.
Furthermore, the transistor M1 has its drain connected in series with the resistor Rh-B, and is turned on when the discharge execution input switch A is 1 (ON), and supplies current to the resistors Rh-A and Rh-B. It is configured to flow. That is, the transistor M1 functions as a switching element (hereinafter referred to as “first switching element”) that turns on / off the supply of current to the resistors Rh-A and Rh-B.

  The output terminals of the AND gates X1 to X9 are connected to the gates of the transistors M1, M3, M5,. The AND gates X1 to X7 are of the 2-input type, while the AND gates X8 and X9 are of the 3-input type. At least one of the input terminals of the AND gates X1 to X9 is connected to the discharge execution input switch A.

Furthermore, one input terminal of the XNOR gates X10, X12, X14, and X16 is connected to the deflection direction changeover switch C, and the other one input terminal is the deflection control switches J1 to J3 or the discharge angle. A correction switch S is connected.
The deflection direction switching switch C (deflection direction switching means) is a switch for switching to which side the ink droplet ejection direction is deflected in the direction in which the nozzles 18 are arranged. When the deflection direction changeover switch C is set to 1 (ON), one input of the XNOR gate X10 is set to 1.
The deflection control switches J1 to J3 are switches for determining the deflection amount when deflecting the ink droplet ejection direction. For example, when the input terminal J3 is 1 (ON), the XNOR gate X10 One of the inputs becomes 1.

  Further, each output terminal of the XNOR gates X10 to X16 is connected to one input terminal of the AND gates X2, X4,... And the AND gates X3, X5,.・ It is connected to one input terminal. One of the input terminals of the AND gates X8 and X9 is connected to the ejection angle correction switch K.

  Furthermore, the deflection amplitude control terminal B is a terminal for determining the current value of the transistors M2, M7,... That are constant current sources of the respective CM circuits, and is connected to the gates of the transistors M2, M7,. . When an appropriate voltage (Vx) is applied to the deflection amplitude control terminal B, Vgs (gate-source voltage) is applied to the gates of the transistors M2, M7,. Flows. Here, the transistors M2, M7,... Are different in the number of transistors connected in parallel, and therefore, in the ratio of the numbers indicated in parentheses of the transistors M2, M7,. Current flows through the transistors M3 to M2, the transistors M8 to M7,.

  Further, the source of the transistor M1 connected to the resistor Rh-B and the sources of the transistors M2, M7,... Serving as constant current sources of the CM circuits are grounded to the ground (GND).

  In the above configuration, the numbers “× N (N = 1, 2, 4, or 50)” attached to the transistors M1 to M21 in parentheses indicate the parallel state of the elements. For example, “× 1” (M12 -M21) indicates that a standard element is included, and "x2" (M7-M11) indicates that an element equivalent to two standard elements connected in parallel is included. Hereinafter, “× N” indicates that an element equivalent to N standard elements connected in parallel is included.

  As a result, the transistors M2, M7, M12, and M17 are “× 4”, “× 2”, “× 1”, and “× 1”, respectively, so that appropriate voltages are applied between the gates of these transistors and the ground. , Each drain current has a ratio of 4: 2: 1: 1.

Next, the operation of the ejection control circuit 50 will be described. First, the description will be focused on only the CM circuit including the transistors M4 and M6 and the transistors M3 and M5 which are the switching elements.
The ejection execution input switch A is 1 (ON) only when ejecting ink droplets. In this embodiment, when ink droplets are ejected from one nozzle 18, the ejection execution input switch A is set to 1 (ON) only for a period of 1.5 μs (1/64), and the resistance power supply Vh (5 V). Power is supplied to the resistors Rh-A and Rh-B. Further, 94.5 μs (63/64) is set to the ink replenishment period of the ink liquid chamber 12 of the ink discharge unit that discharges the ink droplets by setting the discharge execution input switch A to 0 (OFF).

For example, when A = 1, B = Vx (analog voltage), C = 1, and J3 = 1, the output of the XNOR gate X10 becomes 1, so this output 1 and A = 1 are input to the AND gate X2. As a result, the output of the AND gate X2 becomes 1. Therefore, the transistor M3 is turned on.
When the output of the XNOR gate X10 is 1, the output of the NOT gate X11 is 0. Therefore, since the output 0 and A = 1 are the inputs of the AND gate X3, the output of the AND gate X3 is 0. Thus, the transistor M5 is turned off.

  Therefore, since the drains of the transistors M4 and M3 and the drains of the transistors M6 and M5 are connected to each other, when the transistor M3 is ON and M5 is OFF as described above, the resistor Rh-A is connected to the transistor M3. Although current flows, the transistor M6 does not flow because the transistor M5 is OFF. Further, due to the characteristics of the CM circuit, when no current flows through the transistor M6, no current flows through the transistor M4. Since the transistor M2 is ON, in the above-described case, a current flows only from the transistors M3 to M2 among the transistors M3, M4, M5, and M6.

  In this state, when the voltage of the resistance power supply Vh is applied, no current flows through the transistors M4 and M6, and a current flows through the resistor Rh-A. Further, since a current flows through the transistor M3, the current flows through the resistor Rh-A and then branches to the transistor M3 side and the resistor Rh-B side. The current that flows to the transistor M3 side flows through the transistor M2 that determines the value of the flowing current, and then is sent to the ground. The current flowing through the resistor Rh-B flows to the ground after flowing through the transistor M1 which is ON. Therefore, the current flowing through the resistor Rh-A and the resistor Rh-B is Rh-A> Rh-B.

The above is the case of C = 1. Next, when C = 0, that is, when only the input of the deflection direction changeover switch C is changed (the other switches A and J3 are set to 1 in the same manner as described above). ) Is as follows.
When C = 0 and J3 = 1, the output of the XNOR gate X10 is zero. As a result, the input of the AND gate X2 becomes (0, 1 (A = 1)), and the output becomes 0. Therefore, the transistor M3 is turned off.
If the output of the XNOR gate X10 becomes 0, the output of the NOT gate X11 becomes 1, so that the input of the AND gate X3 becomes (1, 1 (A = 1)), and the transistor M5 is turned on.

When the transistor M5 is ON, a current flows through the transistor M6. However, due to this and the characteristics of the CM circuit, a current also flows through the transistor M4.
Therefore, current flows through the resistor Rh-A, the transistor M4, and the transistor M6 by the resistance power source Vh. Then, all the current flowing through the resistor Rh-A flows through the resistor Rh-B (since the transistor M3 is OFF, the current flowing out of the resistor Rh-A does not branch to the transistor M3 side). In addition, since the transistor M3 is OFF, all of the current flowing through the transistor M4 flows into the resistor Rh-B side. Furthermore, the current flowing through the transistor M6 flows through the transistor M5.

  From the above, when C = 1, the current that flows through the resistor Rh-A branches out to the resistor Rh-B side and the transistor M3 side, but when C = 0, the current flows through the resistor Rh-B. In addition to the current flowing through the resistor Rh-A, the current flowing through the transistor M4 enters. As a result, the current flowing through the resistor Rh-A and the resistor Rh-B is Rh-A <Rh-B. The ratio is symmetrical between C = 1 and C = 0.

As described above, by making the amount of current flowing through the resistor Rh-A and the resistor Rh-B different, a bubble generation time difference on the heating resistor 13 divided into two can be provided. Thereby, the ejection direction of the ink droplet can be deflected.
Further, when C = 1 and C = 0, the deflection direction of the ink droplet can be switched to a symmetrical position in the arrangement direction of the nozzles 18.

The above explanation is for when only the deflection control switch J3 is ON / OFF. However, if the deflection control switches J2 and J1 are further turned ON / OFF, the resistance Rh-A and the resistance Rh-B are more finely divided. The amount of current to flow can be set.
That is, the current flowing through the transistors M4 and M6 can be controlled by the deflection control switch J3, but the current flowing through the transistors M9 and M11 can be controlled by the deflection control switch J2. Furthermore, the current flowing through the transistors M14 and M16 can be controlled by the deflection control switch J1.

As described above, a drain current having a ratio of transistors M4 and M6: transistors M9 and M11: transistors M14 and M16 = 4: 2: 1 can be passed through each transistor. As a result, the deflection direction of the ink droplet is set to (J1, J2, J3) = (0, 0, 0), (0, 0, 1), (0) using the three bits of the deflection control switches J1 to J3. 1, 0), (0, 1, 1), (1, 0, 0), (1, 0, 1), (1, 1, 0), and (1, 1, 1) in 8 steps Can be changed.
Furthermore, since the amount of current can be changed by changing the voltage applied between the gates of the transistors M2, M7, M12 and M17 and the ground, the ratio of the drain current flowing through each transistor remains 4: 2: 1. The amount of deflection per step can be changed.

  Thereby, in addition to the landing position of the ink droplet when the ink droplet is discharged from the nozzle 18 without deflection (perpendicular to the surface of the recording medium of the ink droplet such as photographic paper), the ink liquid is placed on one side. The droplets can be discharged while being deflected, and further, can be discharged while being deflected to the other side. In the example of FIG. 6, the landing positions of the ink droplets can be changed at eight locations on one side. Further, when C = 1 and C = 0, the deflection direction of the ink droplets is the same as the alignment direction of the nozzles 18. It can be switched to a symmetrical position. And according to the input value of J1, J2, and J3, an ink droplet can be made to land in arbitrary positions among these eight positions.

  In the example of FIG. 6, an example in which the ejection direction of the ink droplet is deflected in 8 stages using a 3-bit control signal is described. However, in the present embodiment, the circuit illustrated in FIG. Ink droplets are ejected so that the ink droplets land on one of M different landing target positions.

Using the configuration described above, in this embodiment, ink droplets in the arrangement direction of the nozzles 18 corresponding to one pixel region (a specific direction in the present invention; a direction substantially perpendicular to the main scanning direction in the line method). The target landing position is set to be any one of M different positions (M is an integer of 2 or more) where at least a part of the landed droplet region falls within the pixel region. Yes. In other words, M landing target positions are set in one pixel region, and the ink droplet ejection direction is deflected so that the ink droplets land at any one of the M landing target positions. .
In the present embodiment, the M landing target positions are assigned at intervals of 1 / M of the arrangement pitch of the ink ejection units.

  Further, it is determined randomly (irregularly or without regularity) at which position of the M landing target positions the ink droplet is to land. Various methods can be used as the method of determining at random. In this embodiment, any one of M different landing target positions is determined using a random number generation circuit 22 described later.

Further, when two or more ink droplets are landed on one pixel area, that is, when printing with a plurality of gradations, any one of M landing target positions is performed for each ink droplet. A landing target position is randomly determined, and ink droplets are landed on the determined position.
FIG. 7 is a plan view showing a state in which ink droplets have landed on any one of M different landing target positions with respect to one pixel region, and shows a conventional landing state (left side in the figure). FIG. 6 is a diagram showing a landing state (right side in the figure) of this embodiment in comparison. In FIG. 7, a square area surrounded by a broken line is a pixel area. Also, what is indicated by a circle is a landed ink droplet.

  First, when the ejection command is 1, that is, when the gradation is 1 gradation, in the conventional printing, the ink droplet is almost contained in the pixel region (in FIG. 7, the size of the landed ink droplet is Ink droplets land on the pixel area (shown in a size inscribed in the pixel area).

  On the other hand, in the present embodiment, ink droplets are ejected so as to land at any one of the M landing target positions in the arrangement direction of the nozzles 18. In the example of FIG. 7, M = 8 landing target positions in one pixel area (one of the eight landing positions corresponds to no landing position, so that seven different landing positions are substantially illustrated. ) Shows a state where the ink droplet has landed at one determined landing position (in the figure, the circle indicated by the solid line is the position where the ink droplet has actually landed, and the other broken line) Circles indicated by indicate other landing target positions). In this example, the second position counted from the left in the figure is determined, and the ink droplet has landed at the determined position.

When the ejection command is 2, ink droplets are further overlapped and landed on the pixel area. In the example of FIG. 7, a state where the scale is shifted downward by one scale in the pixel area is illustrated in consideration of feeding of the photographic paper.
When the ejection command is 2, according to the conventional method, the second ink droplet is landed substantially in the same row as the first ink droplet landed (no deviation in the left-right direction).

  In contrast, in the case of the present embodiment, as described above, the first ink droplet is landed at a randomly determined position, but the second ink droplet is also the first ink liquid. Irrespective of the landing position of the droplet (independent of the first ink droplet), the landing position is determined at random, and the ink droplet is landed at the determined position. In the example of FIG. 7, the second ink droplet has landed at the center of the pixel region in the left-right direction.

  Furthermore, when the discharge command is 3, it is the same as when the discharge command is 2. In the conventional method, three ink droplets land without shifting the landing positions of the ink droplets in the left-right direction in one pixel region. However, in this embodiment, when the ejection command is 3, the landing target position of the third ink droplet is also determined regardless of the landing positions of the first and second ink droplets, and the determination is made. An ink droplet is landed at the position.

When ink droplets are landed as described above, when dots are arranged to form an image, it is possible to eliminate the occurrence of streaks due to variations in the characteristics of the ink ejection section and make the variations less noticeable. .
That is, the regularity of the landing positions of the ink droplets is lost, and each ink droplet is randomly arranged. As a result, the arrangement is microscopically non-uniform, but macroscopically rather uniform, etc. The variation becomes less noticeable.

Therefore, there is an effect of masking variations due to the ink droplet ejection characteristics of the respective ink ejection portions. When not randomized, the dots are arranged in a regular pattern as a whole, so that the portion that disturbs the regularity is easily visually recognized. In particular, in stipples, the color shading is expressed by the area ratio of the dots and the background (the part not covered by the dots on the photographic paper), but the more the remaining part of the background is regular, the easier it is to be visually recognized. Become.
On the other hand, if there is no regularity and dots are arranged at random, it will be difficult to visually recognize to the extent that the arrangement has changed slightly.

In addition, when a plurality of the above-described line heads 10 are provided and a color line head in which different color inks are supplied to each line head 10 is provided, the following effects are further obtained.
When forming dots by overlapping a plurality of ink droplets in a color ink jet printer, a landing position accuracy that is stricter than that of a single color is required to prevent moiré. However, if ink droplets are arranged at random as in the present embodiment, the problem of moire does not occur, and simple color misregistration can be stopped. Therefore, it is possible to prevent image quality deterioration due to the occurrence of moire.

  In particular, the moire is not a problem in the serial method in which the head is driven many times in the main scanning direction and the ink droplets are overlaid, but the moire is a problem in the line method. Therefore, if a method of randomly landing ink droplets as in the present embodiment is adopted, moire is less likely to appear, so that a line-type inkjet printer can be easily realized.

  Furthermore, by randomly landing the ink droplets, the landing range of the ink droplets is expanded even if the total amount of ink landed on the photographic paper is the same, so the drying time of the landed ink droplets can be shortened Can do. In particular, in the case of the line system, the printing speed is faster than the serial system (the printing time is short), so the effect is remarkable.

  The above is a case where the landing positions of the ink droplets are made random in the arrangement direction of the nozzles 18. Direction), ink droplet landing positions may be randomly arranged.

FIG. 8 is a plan view illustrating an example in which a maximum of N ink droplets (N = 8 in the present embodiment) are arranged in a single pixel area in the photographic paper feed direction, and are randomly arranged. Yes, as in FIG. 7, the conventional method is shown on the left side in the figure, and the method in this embodiment is shown on the right side in the figure. In this example, as in FIG. 7, the ink droplets land at one determined position among N = 8 landing target positions (one of eight corresponds to no landing position). Shows the state.
In this embodiment, N dischargeable periods are assigned to one pixel region in the main scanning direction.

  First, in the conventional method, when the ejection command is 1, it is the same as described above. On the other hand, in the case of the present embodiment, the landing target position of the ink droplet in one pixel region is shown in the vertical direction (the photographic paper feeding direction, the main scanning direction, or the nozzle 18 alignment direction). In the vertical direction), a maximum of N is set, and one of them is determined at random, and ink droplets are landed on the determined position.

In FIG. 8, in the present embodiment, when the ejection command is 1, an example is shown in which ink droplets are landed on the second landing target position from the top.
When ink droplets are randomly landed in the photographic paper feed direction, the ejection command is not used to deflect the ejection direction using the circuit described above, but at the timing of the photographic paper feed. To the head 11. For example, in FIG. 8, the position where the center of the pixel area and the center of the ink droplet substantially coincide is set as the reference position, and in FIG. 8, the difference in ejection time when the landing position is shifted by one scale is ΔT.

  In this case, in the present embodiment when the discharge command is 1 in FIG. 8, it is only necessary to land the ink droplet on the second scale (faster) than the reference position. Ink droplets may be ejected as early as × ΔT. On the other hand, for example, when ink droplets are ejected to the lowermost side in the pixel area, the ink droplets should be landed (slower) by 3 scales below the reference position, so that the reference ejection is performed. Ink droplets may be ejected 3 × ΔT later than the timing.

  Similarly, when the ejection command is 2, the conventional method is the same as in FIG. 7, but in the present embodiment, the ejection of the first ink droplet is the same as the ejection of the second ink droplet. Irrespective of this, the landing position is determined at random, and ink droplets are ejected to that position. In the example of FIG. 8, the landing position of the ink droplet when the ejection command is 2 shows a state of being shifted downward with respect to the reference position.

Thus, for the number of discharge commands 0 to N, the combination of patterns when the number of discharges is K is the number of combinations when K is extracted from N,
_N C _K = _N P _K / K!
It becomes.
Therefore, the probability that the same random pattern occurs for the same discharge command is
1 / _N C _K
It becomes.

As described above, if the landing positions of the ink droplets are made random, it becomes difficult to visually recognize the variation, and at the same time, it is possible to average the discharge power and the ink supply.
In the case of a thermal method in which the heating resistor 13 is heated to eject ink droplets as in this embodiment, considerable energy is required when ejecting ink droplets. For example, it is about 0.7 to 0.8 W per one ink ejection unit. When the line head 10 is configured by arranging a large number of heads 11 having such characteristics, power concentration occurs and the load on the power source becomes extremely large. However, by randomizing the ejection timing as in the present embodiment, the number of ink ejection units ejected at the same timing on the time axis can be reduced, so that power concentration can be reduced.

  In addition to the thermal method, this is also common to the piezo method. However, as the printing speed increases as in the line head 10, the moving speed of the ink in the ink flow path increases. When ink is supplied all at once in the ink flow path, the pressure of the ink in the ink flow path decreases, which causes a problem that bubbles dissolved in the ink are likely to be generated. These fluctuations appear as meniscus fluctuations, and the amount of ejected ink droplets changes. Therefore, it is desirable to move the ink in the ink flow path as averagely as possible and at a low speed. If the ejection timing is randomized as in the present embodiment, the amount of ink supplied from the ink flow path can be made uniform.

  Also, as shown in FIG. 8, the ink droplet landing position on the pixel region is randomly changed with respect to the photographic paper feed direction (a direction substantially perpendicular to the direction in which the nozzles 18 are arranged). As described with reference to FIG. 7, if ink droplets are deflected and ejected with respect to the arrangement direction of the nozzles 18 and the landing positions of the ink droplets on the pixel area are changed at the same time, the ink liquid The landing positions of the droplets are made more random, and the effect of the randomization can be enhanced.

FIG. 9 is a plan view for explaining an example in this case. In the figure, the left side shows a conventional method, and the right side shows a method of this embodiment.
If the conventional method is employed, the ink droplet landing target position will not vary in the direction in which the nozzles 18 are arranged or in the direction perpendicular thereto. On the other hand, in the present embodiment, ink droplets are randomly landed in the direction in which the nozzles 18 are arranged (left and right in the figure) and the direction substantially perpendicular to this direction (up and down in the figure). However, the landing positions will vary. In the present embodiment, a region that is enlarged around the area of the pixel region and that is larger by the radius of the dot is a region where ink droplets may be landed. As a result, the gap between the adjacent dots can be filled at random.

FIG. 10 is a diagram for explaining the outline of control when ink droplets are randomly landed as described above. FIG. 10 also shows an outline of the control in the conventional method.
In FIG. 10, a recording signal generation map 21 is used to determine at which position an ink droplet is landed in the photographic paper feed direction. For example, when two ink droplets are landed on one pixel region, it is for determining which two of the N positions in FIG. According to this recording signal generation map 21, the ejection timing in the photographic paper feed direction is controlled.

  In the conventional method, only a discharge command is sent to the head based on the recording signal generation map. In contrast, in this embodiment, an ejection command is sent to the head 11 via the recording signal generation map 21 and the random number generation circuit 22. That is, in the arrangement direction of the nozzles 18, the deflection direction (landing target position of the ink droplet) is randomly determined via the random number generation circuit 22, and a deflection command is sent to the head 11.

  At the same time, the recording signal generation map 21 is referred to determine at which ejection timing the ink droplets are ejected, and an ejection command is sent to the head 11. As a result, the ink droplets are ejected while being randomly deflected in the arrangement direction of the nozzles 18 with respect to the pixel region, and at a random ejection timing in a direction substantially perpendicular to the direction (main scanning direction). Discharged. Therefore, as shown in FIG. 9, the pixel area is randomized and landed in the direction in which the nozzles 18 are arranged and in a direction substantially perpendicular to this direction.

Next, how to give an ink droplet deflection ejection command will be described.
In principle, it is only necessary to give a deflection ejection command to each ink ejection unit independently, but in order to land ink droplets from each ink ejection unit on M different positions, log ₂ M A bit is needed. For example, when M = 8 as in the above example, 3 bits are required.

  When different timings, voltages, and data are requested for all the ink ejection units, at least several hundreds of ink ejection units are arranged in one head 11, so that all these wirings can be performed. The head 11 becomes very large, which is practically impossible. Therefore, in the present embodiment, the bits that are the same for all the ink ejection units are connected in common to control the ejection direction of each ink ejection unit, or the ejection direction of all the ink ejection units is determined by a serialized signal. Is configured to control.

FIG. 11 is a diagram illustrating a connection state for each ink ejection unit in the present embodiment. In this example, M = 8, that is, 3 bits, and each bit is J1, J2, and J3. In addition, FIG. 11 illustrates four ink discharge units A to D.
At this time, each bit (J1 to J3) is connected in parallel and controlled by 3 bits as a whole, but in terms of circuit, the signal is serialized and the signal is distributed by one wiring. Also good. Even if such a connection method is adopted, the adjacent ink discharge portions can be randomized in different patterns for the following reason.

  First, all connected ink ejection units are not driven simultaneously to eject ink droplets. Further, although there are a plurality of ink ejection units that are driven simultaneously, adjacent ink ejection units are not selected as the ink ejection units that are driven simultaneously. Furthermore, there is a low probability that adjacent ink ejection portions will have the same randomized pattern.

  Normally, ink droplets are simultaneously ejected from a plurality of ink ejection units, but the ink ejection unit selected at this time is an ink ejection unit that is separated to some extent. Here, for example, when an ink droplet is ejected from one ink ejection unit, vibration during ejection is transmitted to the ink liquid chamber and the ink flow path, and the adjacent ink ejection unit is affected by the ejection.

  This effect appears as a fluctuation of the meniscus (position of the ink liquid level in the nozzle), and if the ink droplet is ejected in a state where the meniscus fluctuates, the size of the landed dot changes. Avoid such discharge. Therefore, when an ink droplet is ejected from one ink ejection unit, the ink ejection unit adjacent to the ink ejection unit is controlled so as not to eject the ink droplet until the meniscus fluctuation is suppressed. At the same time, an ink discharge unit at a remote position is selected as the ink discharge unit that discharges ink droplets. As a result, even if a 3-bit signal is sent simultaneously to all the ink ejection units, there is no particular problem because adjacent ink ejection units do not eject ink droplets simultaneously by the signal.

  When there is a possibility that the signals given to the adjacent ink ejection units are completely the same in graphic data or the like, a plurality of recording signal generation maps 21 are provided in advance and are used by switching them. Also good. Further, for example, when the same number of ink droplet landings is given to adjacent pixel regions, the discharge commands of the adjacent ink discharge units may be different. Furthermore, the ejection pattern of the adjacent pixel region may be different by changing the deflection command before the ink droplet is ejected from the adjacent ink ejection unit.

The embodiment described above is a case of the line system in which the heads 11 are arranged side by side by an amount corresponding to the entire width of the photographic paper as shown in FIG. 2, but it can also be applied to a serial system.
When applied to the serial method, one head 11 is used to relatively move the head 11 and photographic paper in the scanning direction, and ink droplets are landed on the pixel area during the relative movement. As the relative movement, the photographic paper is usually stopped and the head 11 is moved in the width direction of the photographic paper.

FIG. 12 is a diagram illustrating a comparison between a conventional serial printing method and a printing method to which the present invention is applied.
In this comparison, it is assumed that one pixel is formed by landing four ink droplets on one pixel region.

In this case, in the conventional printing method, the pixels are formed by printing in the main scanning direction four times. For example, after one ink droplet is landed on one pixel area by one printing in the main scanning direction, the printing paper is slightly fed, and further printing in the main scanning direction is performed again. The ink droplet is landed on the ink droplet landed on the ink. Pixels are formed by repeating such printing in the main scanning direction four times.
In the example of FIG. 12, the return time of the head and the printing time for one printing in the main scanning direction are set approximately at the same time.

On the other hand, when the present invention is applied to the serial system, the head 11 is arranged so that the longitudinal direction of the head 11 is the sub-scanning direction (the feeding direction of the photographic paper). That is, the arrangement is rotated by 90 degrees with respect to the arrangement of the head 11 when the line head 10 is configured.
When printing is performed by moving the head 11 in the main scanning direction, ink droplets are ejected with the ejection direction being randomly deflected. As a result, in the case of the serial system to which the present invention is applied, the head 11 is arranged in a state rotated by 90 degrees, so that the deflection direction when ink droplets are ejected is the sub-scanning direction (of the photographic paper). (Feed direction).

  In this example, four ink droplets are landed on one pixel region. In the present invention, this is performed during one movement of the head 11 in the main scanning direction. For this reason, in the method according to the present invention, the movement time of the head 11 in one main scanning direction is four times as long as the conventional method. In other words, in the present invention, one printing time in the main scanning direction is the same as the total of four printing times in the conventional main scanning direction.

  However, in the conventional printing method, four printings in the main scanning direction and four head return times are required to finish printing on the pixel regions arranged in the main scanning direction. That is, in the conventional method, ink droplets cannot be ejected while being deflected. Therefore, when a plurality of ink droplets are landed on one pixel region, the number of ink droplets to land is equal to the number of landed ink droplets. This is because it is necessary to repeat the printing on.

On the other hand, in the present invention, it is possible to finish printing on pixel areas arranged in the main scanning direction by one printing in the main scanning direction. That is, this means that overprinting can be performed with one print in the main scanning direction.
For this reason, the printing method according to the present invention requires only one head return as compared with the conventional printing method, so that the printing time can be shortened by the return time of the three heads.

  In the serial method, the variation of the landed ink droplets becomes a streak in the width direction of the photographic paper in the sub-scanning direction (the longitudinal direction of the photographic paper, that is, the traveling direction of the photographic paper). (Variation in the main scanning direction is not conspicuous). If ink droplets are deflected and ejected in the sub-scanning direction as in the present invention, variation in landing of ink droplets can be made inconspicuous.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following various deformation | transformation is possible.
(1) In this embodiment, ink droplets are ejected from the pixel region corresponding to the ink ejection unit, that is, the ink ejection unit located almost directly above the pixel region, and the ink droplets are landed on the pixel region. However, the present invention is not limited to this, and it is also possible to land an ink droplet on the pixel region from another adjacent ink ejection unit.
For example, when ink droplets are ejected from the adjacent ink ejection part “X” and the ink ejection part “X + 1”, the pixel areas corresponding to the ink ejection part “X” and the ink ejection part “X + 1” The region “Y” and the pixel region “Y + 1” are assumed.

In this case, ink droplets can be ejected from the ink ejection section “X” and landed on the pixel region “Y”, and ink droplets can be landed on the adjacent pixel region “Y + 1”. . Similarly, ink droplets can be ejected from the ink ejection section “X + 1” and landed on the pixel region “Y + 1”, and ink droplets can be landed on the adjacent pixel region “Y”.
Here, for example, when ink droplets ejected from the ink ejection unit “X” are landed on the pixel area “Y + 1”, they land on any one of the M target landing positions in the pixel area “Y + 1”. Let The same applies to other cases.

In this way, for example, when ink droplets are landed on the pixel area “Y”, ink droplets can be ejected from the ink ejection part “X” and landed, and the ink ejection part “X” It is also possible to eject ink droplets from “−1” and land the ink droplets on the pixel region “Y”. Furthermore, it is also possible to eject ink droplets from the ink ejection unit “X + 1” and land the ink droplets on the pixel region “Y”.
For example, when ink droplets are ejected from the ink ejection unit “X”, the ink droplets are not necessarily landed on the pixel regions “Y−1” and “Y + 1”, but the pixel region “Y-2”. Or “Y + 2”, that is, not only the pixel region “Y−1” and “Y + 1” adjacent to the pixel region “Y” corresponding to the ink ejection unit “X”, but also ink droplets in the neighboring pixel regions. You may make it land.

As described above, when a single dot is formed by landing a plurality of ink droplets on one pixel region, the dot can be formed using a plurality of ink discharge units. It is possible to make the variation of the image more inconspicuous.
In addition, although the same ink discharge unit is used for one pixel region, dots may be formed using another ink discharge unit for the pixel region located below the pixel region.

(2) When randomizing ink droplets at M different positions for one pixel area, any number of M may be used as long as it is a positive integer of 2 or more. It is not limited to the number shown in the form. Similarly, the number N of ink droplets to be landed on one pixel area in the conveyance direction of the photographic paper (direction substantially perpendicular to the direction in which the ink ejection units are arranged) may be any number. Therefore, the relationship of M = N may be sufficient, and the relationship of M ≠ N may be sufficient.
In addition, the present invention can be applied to any number of maximum ink droplets (maximum number of gradations) to be landed on one pixel region.

  (3) In the present embodiment, the landing position of the ink droplet is randomly changed within the range so that the center of the landed ink droplet falls within the pixel region with respect to one pixel region. However, the present invention is not limited to this, and it is possible to vary the landing positions within the range of the present embodiment or more as long as at least a part of the landed ink droplets falls within the pixel area.

(4) In the present embodiment, the random number generation circuit 22 is used to randomly determine the target landing position of the ink droplets. However, as a method for determining the ink droplet randomly, there is no regularity in the selected landing positions. Any method can be used. Further, as a random number generation method, for example, a square center method, a congruence method, a shift register method, or the like can be given.
(5) In this embodiment, the 3-bit control signals J1 to J3 are used in FIG. 11, but the present invention is not limited to this, and any number of control signals may be used.

  (6) In the present embodiment, two heating resistors 13 are arranged in parallel, the current value flowing through each is changed, and the time difference until the ink boils on each heating resistor 13 (bubble generation time) is changed. I made it. However, the present invention is not limited to this, and the resistance values of the two heating resistors 13 may be the same, and a difference may be provided in the timing of current flow. For example, if an independent switch is provided for each of the two heating resistors 13 and each switch is turned on with a time difference, a time difference can be provided in the time until bubbles are generated in the ink on each heating resistor 13. . Furthermore, it is possible to use a combination of changing the value of the current flowing through the heating resistor 13 and providing a time difference in the current flowing time.

  (7) In the present embodiment, an example in which two heating resistors 13 are arranged in parallel in one ink liquid chamber 12 has been shown. However, it has been sufficiently demonstrated that the two resistances are durable. In addition, the circuit configuration can be simplified. However, the present invention is not limited to this, and it is also possible to use a structure in which three or more heating resistors 13 are arranged in parallel in one ink liquid chamber 12.

(8) In the present embodiment, an example in which the heating resistor 13 is provided as a thermal type ink discharge unit has been described as an example. However, the present invention is not limited to this, and an electrostatic discharge type or a piezoelectric type can also be applied. .
The electrostatic discharge type energy generating element (corresponding to the heating resistor 13) is provided with a vibration plate and two electrodes on the lower side of the vibration plate via an air layer. And a voltage is applied between both electrodes, a diaphragm is bent below, and a voltage is set to 0V after that and an electrostatic force is released. At this time, ink droplets are ejected using the elastic force when the diaphragm returns to its original state.
In this case, in order to provide a difference in energy generation of each energy generating element, a time difference is provided between the two energy generating elements when, for example, the diaphragm is returned (when the voltage is set to 0 V and the electrostatic force is released). Alternatively, the voltage value to be applied may be different between the two energy generating elements.

In addition, a piezoelectric energy generating element is provided with a laminate of a piezoelectric element having electrodes on both sides and a diaphragm. When a voltage is applied to the electrodes on both sides of the piezo element, a bending moment is generated in the diaphragm due to the piezoelectric effect, and the diaphragm is bent and deformed. By utilizing this deformation, ink droplets are ejected.
Also in this case, as described above, in order to provide a difference in energy generation of each energy generating element, when applying a voltage to the electrodes on both sides of the piezoelectric element, a time difference is provided between the two piezoelectric elements or applied. What is necessary is just to make the voltage value to perform into a different value by two piezoelectric elements.

  (9) In the present embodiment, the ink droplet ejection direction can be deflected in the direction in which the ink ejection sections (nozzles 18) are arranged. This is because the two heating resistors 13 are arranged side by side in the direction in which the ink discharge portions are arranged. However, the direction in which the ink ejection sections are aligned and the direction in which the ink droplets are deflected do not necessarily coincide with each other. Even if there is a slight difference, the direction in which the ink ejection sections are aligned and the direction in which the ink droplets are deflected The effect can be expected to be almost the same as when they are completely matched. Therefore, there is no problem even if there is such a deviation.

It is a disassembled perspective view which shows the head of the inkjet printer to which the liquid discharge apparatus by this invention is applied. It is a top view which shows embodiment of a line head. FIG. 2 is a plan view and a side cross-sectional view showing an ink discharge portion of the head of FIG. It is a figure explaining the deflection | deviation of the discharge direction of an ink. (A), (b) is a simulation result showing the relationship between the difference between the bubble generation time of the ink by each heating resistor and the ink ejection angle when having divided heating resistors, (c), It is measured value data which shows the relationship between the difference (deflection current) of the electric current amount between the divided heating resistors, and the deflection amount. An embodiment in which a bubble generation time difference between two divided heating resistors can be set is shown. FIG. 6 is a plan view showing a state where ink droplets are landed on any one of M different landing target positions with respect to one pixel region. FIG. 6 is a plan view showing an example of randomly arranging N ink droplets in one pixel area in the photographic paper feed direction. FIG. 6 is a plan view showing an example in which ink droplets are randomly landed in both the nozzle arrangement direction and the photographic paper feeding direction. It is a figure explaining the outline of control when an ink droplet is made to land at random. It is a figure which shows the connection state for every ink discharge part in this embodiment. It is a figure which compares and demonstrates the printing method in the conventional serial system, and the printing method to which this invention is applied. It is a figure explaining the variation in dot arrangement. It is a figure which shows the example at the time of setting the whole dot size to just over 2 times of dot pitch with respect to the shift | offset | difference of the same dot row as FIG. It is a figure which shows a state when overstrike.

Explanation of symbols

10 Line Head 11 Head 12 Ink Liquid Chamber 13 Heating Resistor 18 Nozzle 21 Recording Signal Generation Map 22 Random Number Generation Circuit

Claims (9)

Provided with a head capable of deflecting the discharge direction of liquid droplets discharged from a liquid discharge unit having nozzles in a plurality of directions in a specific direction, a maximum of N (N is a positive integer) liquid droplets in one pixel region A liquid ejecting apparatus that forms a single pixel having a plurality of gradations by being repeatedly landed,
The target landing positions of the droplets in the specific direction in one pixel area are M (M is an integer of 2 or more) different positions where at least a part of the landed droplet area falls within the pixel area. Set the ejection direction of the droplets ejected from the liquid ejection part so as to be in any position,
For each of the droplets ejected from the liquid ejection unit, any one of the M landing target positions is randomly determined, and the droplets land on the determined landing target position. A liquid discharge apparatus characterized by controlling a discharge direction of liquid droplets discharged from a liquid discharge unit and forming pixels corresponding to the pixel region. The liquid ejection apparatus according to claim 1,
The target position of the droplet in one pixel region is set to any one of the N different positions where at least a part of the landed droplet region enters the pixel region in a direction different from the specific direction. Set to
When the number of droplets to be landed on one pixel area is 1 or more and less than N, any one of the N landing target positions is randomly determined, and the determined position A liquid discharge apparatus characterized by causing droplets to land on the surface. The liquid ejection apparatus according to claim 1,
The control of the M landing target positions is performed using a plurality of bits.
Bits that are the same for all of the liquid ejection units are connected in common to control the ejection direction of each of the liquid ejection units, or the ejection direction of all the liquid ejection units is controlled by a serialized signal It is comprised in these. The liquid discharge apparatus characterized by the above-mentioned. A head provided with a liquid ejection unit having a nozzle is provided, and a recording medium on which droplets are landed and the head are relatively moved in a specific direction, and a maximum of N (N is a single pixel area) during the relative movement. , A positive integer) liquid droplets that overlap and land to form one pixel having a plurality of gradations,
There are M landing target positions of droplets in a direction substantially perpendicular to the specific direction in one pixel region, where at least part of the landed droplet region falls within the pixel region (M is an integer of 2 or more). Set the ejection direction of the liquid droplets ejected from the liquid ejection section so that it is any one of the different positions,
For each of the droplets ejected from the liquid ejection unit, any one of the M landing target positions is randomly determined, and the droplets land on the determined landing target position. Control the ejection direction of the liquid droplets ejected from the liquid ejection part, form pixels corresponding to the pixel area,
When two or more droplets are landed on one pixel area, two or more of the M ejection directions are ejected onto the pixel area during relative movement of the recording medium and the head in the specific direction. A liquid ejecting apparatus comprising: ejecting a liquid droplet in a direction to form a pixel corresponding to the pixel region by relative movement between the recording medium and the head in the specific direction. A head including a plurality of liquid ejection units having nozzles arranged in parallel in a specific direction, and relatively moving a recording medium on which a droplet is landed and the head in a direction substantially perpendicular to the specific direction, and during the relative movement, A liquid ejecting apparatus that forms a single pixel having a plurality of gradations by overlapping and landing a maximum of N (N is a positive integer) liquid droplets in one pixel region,
The target landing positions of the droplets in the specific direction in one pixel area are M (M is an integer of 2 or more) different positions where at least a part of the landed droplet area falls within the pixel area. Set the ejection direction of the droplets ejected from the liquid ejection part so as to be in any position,
For each of the droplets ejected from the liquid ejection unit, any one of the M landing target positions is randomly determined, and the droplets land on the determined landing target position. A liquid discharge apparatus characterized by controlling a discharge direction of liquid droplets discharged from a liquid discharge unit and forming pixels corresponding to the pixel region. The liquid ejection device according to any one of claims 1, 4, or 5,
A plurality of the heads are provided,
Each of the heads is different in the supplied liquid,
A droplet discharged from the liquid discharge portion of any one of the heads and a droplet discharged from the liquid discharge portion of any one of the other heads are landed on one pixel region, and the pixel region A liquid ejection apparatus characterized by forming corresponding pixels. A liquid discharge method for forming one pixel having a plurality of gradations by overlapping and landing a maximum of N (N is a positive integer) liquid droplets in one pixel region,
The target landing position of a droplet in a specific direction in one pixel area is any of M (M is an integer of 2 or more) different positions where at least part of the landed droplet area falls within the pixel area. Set the discharge direction of the droplets so that
For each droplet to be ejected, one of the M landing target positions is randomly determined, and the droplet ejection direction is controlled so that the droplets land on the determined landing target position. And forming a pixel corresponding to the pixel region. A head provided with a liquid ejection unit having a nozzle and a recording medium on which droplets are landed are moved relative to each other in a specific direction, and a maximum of N (N is a positive integer) in one pixel area during the relative movement. ) In a liquid discharge method for forming a single pixel having a plurality of gradations.
There are M landing target positions of droplets in a direction substantially perpendicular to the specific direction in one pixel region, where at least part of the landed droplet region falls within the pixel region (M is an integer of 2 or more). Set the droplet discharge direction to be one of the different positions,
For each droplet to be ejected, one of the M landing target positions is randomly determined, and the droplet ejection direction is controlled so that the droplets land on the determined landing target position. And forming a pixel corresponding to the pixel region,
When two or more droplets are landed on one pixel area, two or more of the M ejection directions are ejected onto the pixel area during relative movement of the recording medium and the head in the specific direction. A liquid ejection method, wherein a pixel corresponding to the pixel region is formed by relative movement of the recording medium and the head in the specific direction by ejecting a droplet in a direction. A head in which a plurality of liquid ejection units having nozzles are arranged in parallel in a specific direction and a recording medium on which droplets are landed are relatively moved in a direction substantially perpendicular to the specific direction, and one pixel region is being moved during the relative movement. A liquid ejection method in which a maximum of N droplets (N is a positive integer) are landed and landed to form one pixel having a plurality of gradations,
The target landing positions of the droplets in the specific direction in one pixel area are M (M is an integer of 2 or more) different positions where at least a part of the landed droplet area falls within the pixel area. Set the droplet discharge direction to be at any position,
For each droplet to be ejected, one of the M landing target positions is randomly determined, and the droplet ejection direction is controlled so that the droplets land on the determined landing target position. And forming a pixel corresponding to the pixel region.

Images