JP2000263766A - Image-forming apparatus of ink jet system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-forming apparatus of an ink jet system which forms ink drops to hit a recording medium nearly in a true circle. SOLUTION: A discharge direction D of ink discharged from four printing heads 20K, 20C, 20M and 20Y is inclined by an angle θ(approximately 4 deg.) to a perpendicular direction E perpendicular to a recording medium 12. An inclination of ink drops caused by a movement speed V=705.6 mm/sec of each printing head 20K, 20C, 20M, 20Y is negated. Ink drops hit a surface of the recording medium 12 from a nearly perpendicular direction nearly perpendicular to the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet type image forming apparatus for forming an image on a recording medium by discharging ink from a print head.

[0002]

2. Description of the Related Art As one of output devices of computers and workstations, there is known an image forming apparatus of an ink jet system which forms an image on a recording medium such as recording paper by discharging ink. The inkjet type image forming apparatus includes, for example, a print head in which a plurality of nozzles for ejecting ink are formed, a carriage on which the print head is mounted and which reciprocates in a predetermined scanning direction, and which is orthogonal to the predetermined direction. And a transport device for transporting the recording paper in the sub-scanning direction.

When an image is formed on a recording sheet, generally, the recording sheet being conveyed by the conveying device is temporarily stopped, and the image signal carrying the image information is moved while the carriage is reciprocated in the predetermined direction. Eject ink from the nozzle based on
An image for one band is formed on a portion of the recording paper located in an image forming area facing the nozzle. Thereafter, the recording paper is conveyed by the width of one band and stopped, and ink is ejected from the nozzles based on the image signal while the carriage is reciprocated again in the above-mentioned predetermined direction. An image is formed in a portion newly located in the area. By repeating such an operation, an image is formed on the recording paper.

In the image forming apparatus of the ink jet type as described above, it is necessary to increase the resolution in order to improve the image quality. In order to increase the resolution, the arrangement pitch of a plurality of nozzles formed in the print head is, for example, 72
It is as small as 0 DPI (the number of ink ejections per inch, dot per inch) or 1440 DPI. As described above, when the arrangement pitch of the nozzles becomes minute, the nozzles themselves become small, and the ink droplets ejected from the reduced nozzles also become small. Further, as the ink droplets (dots) ejected from the thus reduced nozzle and landed on the recording medium are more perfect circles, the resolution is increased and the image quality is improved.

[0005]

However, in a conventional print head, ink droplets that land on a recording medium often have an oval shape. For this reason, dots adjacent to each other overlap, or a gap is formed between adjacent dots, and the resolution of the formed image is reduced.

[0006] Some inkjet image forming apparatuses use a print head having a length substantially equal to the width of a recording medium. Also in this type of print head, the arrangement pitch of the nozzles is reduced to improve the image quality. Therefore, the size of the nozzle itself is reduced, and the size of the ink droplet ejected from the reduced nozzle is also reduced. As a result, the above-described dot oval or gap is generated, causing the same problem as described above, and the resolution of the formed image may be reduced.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide an ink jet type image forming apparatus in which ink droplets that have landed on a recording medium have a substantially perfect circle.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising:
In an ink-jet image forming apparatus for forming an image on a recording medium while relatively moving a print head for ejecting ink and a recording medium on which the ink ejected from the print head lands at a predetermined moving speed, 1) The print head adjusts the ejection direction of the ink with respect to the substantially vertical direction based on the predetermined moving speed so that the ink lands on the recording medium from a substantially perpendicular direction substantially perpendicular to the recording medium. And discharges ink while tilted.

A second ink jet type image forming apparatus according to the present invention includes a print head which ejects ink while reciprocating in a predetermined scanning direction, and is conveyed in a sub-scanning direction substantially orthogonal to the scanning direction. In an ink jet type image forming apparatus for forming an image on a recording medium by ejecting ink from the print head to the recording medium, (2) the print head is disposed on the recording medium from a substantially perpendicular direction substantially perpendicular to the recording medium. The ink is ejected by inclining the ejection direction of the ink with respect to the substantially vertical direction based on the predetermined moving speed so that the ink lands. (3) While the print head reciprocates, The ink ejection direction at the time of the forward movement and the ink ejection direction at the time of the backward movement of the reciprocation are different from each other.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an ink jet type image forming apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a schematic configuration of a printer which is an example of an ink jet type image forming apparatus of the present invention. FIG. 2 is a perspective view showing the carriage unit of FIG.

The printer 10 has a platen 14 on which the recording paper 12 conveyed in the direction of arrow A is placed. Above the platen 14, two guide rails 16 are extended in parallel with the platen 14. A slide base 40 is attached to the guide rail 16 so as to freely reciprocate in directions of arrows B and B '(a direction orthogonal to the direction of arrow A) by a motor (not shown) and a belt (not shown). . The print head 2 having the nozzles 21 (see FIG. 6) for discharging ink is provided on the slide base 40.
The head holder 60 on which the “0” is mounted is detachably fixed. The carriage unit 30 is constituted by the slide base 40 and the head holder 60.

In front of the nozzles of the print head 20 mounted on the head holder 60 is an image forming area 18 on which an image is to be formed.
The ink is ejected from the nozzles to the portion located at the position, and an image is formed. FIG. 1 shows a schematic configuration of the print head 20, the slide base 40, and the head holder 60. Further, in FIG. 1, the print head 20 is represented as one print head 20. However, as shown in FIG.
The print heads 20K (black), 20C (cyan), 20M (magenta), and 20Y (yellow).

In forming an image on the recording paper 12,
The recording paper 12 is placed on the platen 14, and the recording paper is transported to a conveying roller 22 having a part of the outer peripheral surface exposed from an opening (not shown) formed in the platen 14, and both ends in the width direction of the recording paper 12. The portion is nipped by a pinch roller 24 that presses from above, and is transported by rotating a transport roller 22 by a motor (not shown). The slide base 40 is reciprocated in the directions of arrows B and B ′ above the recording paper 12, and ink is ejected based on an image signal carrying image information transmitted from the control device 26 to the print head 20, and the recording paper is discharged. Out of 12,
An image is formed on a portion located in the image forming area 18.

Referring to FIGS. 3 and 4, the ink ejected from the print head 20 will be discussed.

FIG. 3 is an explanatory view showing the movement of the ink ejected from the print head. FIG. 4 is an explanatory view schematically showing an example in which the ejecting directions of the ink ejected from the four print heads are inclined. It is. In these drawings, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 3, suppose that the print head 20 ejects ink at a speed v vertically toward the recording medium 12 while moving at a moving speed V in the direction of arrow B '. In this case, the ink droplet lands on the recording medium 12 while being inclined by tan ^-1 (V / v) = Θ. Accordingly, the ink droplets become substantially elliptical and penetrate into the recording medium 12 to form dots. The angle Θ is, for example, the moving speed V of the print head 20 = 705.6 mm / sec, and the ink ejection speed v =
When it is 10 m / sec, it is about 4 °.

Therefore, as shown in FIG. 4, the direction of ejection D of the ink ejected from the four print heads 20K, 20C, 20M and 20Y is changed by an angle Θ (about 4 °) to the recording medium 1.
2 with respect to a vertical direction E perpendicular to 2. As a result, the inclination of the ink droplet caused by the moving speed V of each of the print heads 20K, 20C, 20M, and 20Y is canceled, and the surface of the recording medium 12 is substantially perpendicular to the surface. Ink droplets land from the direction. As a result, the dots formed by the ink droplets that have landed on the surface of the recording medium 12 have a circular shape that is almost close to the circular nozzle outlet (ink ejection port), so that overlapping of adjacent dots can be prevented, or adjacent dots can be prevented. For example, it is possible to prevent the occurrence of a gap between them, thereby increasing the resolution of the image and improving the image quality.

In the above example, the print head 20 has the arrow B '
The case where the print head 20 moves in the directions indicated by arrows B and B ′ has been described above.
This will be described with reference to FIG.

FIG. 5 is an explanatory view schematically showing a technique for making the dots circular even when the print head 20 reciprocates in the directions of arrows B and B '.

As described above, the four print heads 20
When K, 20C, 20M, and 20Y move in the direction of arrow B ', the ejection direction D of the ink ejected from the print heads 20K, 20C, 20M, and 20Y is applied to the recording medium 12 by an angle Θ (about 4 °). Tilt with respect to the vertical vertical direction E.
As a result, the dots formed by the ink droplets that have landed on the surface of the recording medium 12 have a substantially circular shape.

On the other hand, even when the print head moves in the direction of arrow B, in order to make the dots formed by the ink droplets landed on the surface of the recording medium 12 substantially circular, the ink ejection direction D ' The print heads 20'K, 20'C, 20'M, and 20'Y are mounted on the head holder 60 (see FIG. 1) such that the angles' (about 4 °). Angle Θ '
Is an angle opposite to the angle に 対 し て with respect to the vertical direction E perpendicular to the recording medium 12, and the print heads 20K, 20C,
20M, 20Y, 20'K, 20'C, 20'M, 2
The ink ejection directions are different between the forward movement and the backward movement when 0′Y reciprocates. In this manner, the four print heads 20K, 20C, 20M, and 20Y are used to move in the direction of arrow B ', and the four print heads 20'K,
By using 20'C, 20'M, and 20'Y when moving in the direction of arrow B, the order in which each color is formed becomes the same in both directions, and the color of the formed image becomes the same.

In the above-described embodiment, the two print heads 20K, 20C, 20M, 20M which are different from each other in the forward movement and the backward movement when reciprocating to make the dot substantially circular.
Y, and print heads 20'K, 20'C, 20'M, 2
Although 0'Y is used, dots can be made substantially circular by using only one print head for each color.

With reference to FIGS. 6 and 7, a description will be given of a print head that can make dots substantially circular with one print head for each color.

FIG. 6 is a plan view schematically showing a print head in which dots can be made substantially circular by one print head for each color. FIG. 7 is a plan view showing dots made substantially circular by one print head for each color. FIG. 7 is a plan view schematically showing another example of a print head that can be used.

The print head shown in FIG. 6 includes four color print heads 20K, 20C, 20M and 20Y. On the side surface of each of the print heads 20K, 20C, 20M, and 20Y, an electrical connection unit 20 to which a signal carrying image information is input and output is provided.
Ka, 20Ca, 20Ma, and 20Ya are formed. In addition, each print head 20K, 20C, 20M, 20
In Y, a plurality of nozzles 21 are formed. Each nozzle 2
1, the recording medium 1 has an ink ejection direction D corresponding to angles Θ and Θ ′ (for example, about 4 °), similarly to the print head shown in FIG.
2 is formed so as to be inclined with respect to a vertical direction E perpendicular to 2. In addition, each print head 20K, 20C, 20M, 20
Y has a symmetric shape in the front-rear direction (the direction of arrow A and the opposite direction) about the nozzle 21.

Each print head 20K, 20C, 20M, 2
When 0Y moves in the direction of arrow B ', it is used in a state surrounded by a dashed line G. Conversely, each print head 20
When K, 20C, 20M, and 20Y move in the direction of arrow B, the print head in the state of G is rotated by 180 ° and used in a state surrounded by a dashed line H. As a result, one print head 20K, 20C, 20M, 20
With Y, the dots can be made substantially circular.

The print head shown in FIG. 7 includes four color print heads 50K, 50C, 50M, and 50Y. On the side surface of each of the print heads 50K, 50C, 50M, and 50Y, there is provided an electrical connection portion 50 to which a signal carrying image information is input / output.
Ka, 50Ca, 50Ma, and 50Ya are formed. In addition, each print head 50K, 50C, 50M, 50
In Y, a plurality of nozzles 51 are formed. Each nozzle 5
1, the recording medium 1 has an ink ejection direction D corresponding to angles Θ and Θ ′ (for example, about 4 °), similarly to the print head shown in FIG.
2 is formed so as to be inclined with respect to the vertical direction E perpendicular to 2. In addition, each print head 50K, 50C, 50M, 50
Y has an asymmetric shape in the front-rear direction (the direction of the arrow A and the direction opposite thereto) around the nozzle 21.

Each print head 50K, 50C, 50M, 5
When 0Y moves in the direction of arrow B ', it is used in a state surrounded by a dashed line I. Conversely, each print head 50
When K, 50C, 50M, and 50Y move in the direction of arrow B, the print head in the state of I is rotated by 180 ° and used in a state surrounded by a dashed line J. As a result, one print head 50K, 50C, 50M, 50
With Y, the dots can be made substantially circular. Note that, regardless of whether the print heads 50K, 50C, 50M, and 50Y are in the I state or the J state, the plurality of nozzles 51 are surrounded by a two-dot chain line K and are arranged in a row.

Referring to FIG. 8, a print head for preventing color mixture will be described.

FIG. 8 is a plan view schematically showing a print head in which color mixing is prevented.

The print head 90 for preventing color mixing is indicated by an arrow B.
Print head 70 that ejects ink when moving in the direction
K, 70C, 70M, 70Y, and print heads 80K, 80C, which discharge ink when moving in the direction of arrow B '.
80M and 80Y. Print head 70K, 7
0C, 70M, 70Y and print heads 80K, 80C,
80M and 80Y have electrical connection portions 70Ka, 70Ca and 70M for inputting and outputting signals carrying image information and the like.
a, 70Ya, 80Ka, 80Ca, 80Ma, 80Y
a is formed. In addition, the print heads 70K, 70
C, 70M, 70Y and print heads 80K, 80C, 8
0M and 80Y are alternately arranged as shown in the figure. With such an arrangement, these print heads can be mounted in a relatively narrow space.

The print heads 70K, 70C, 70
M, 70Y and print heads 80K, 80C, 80M, 8
A plurality of nozzles 71 and 81 are formed in 0Y, respectively. Similar to the print head shown in FIG. 5, the nozzles 71 and 81 are arranged such that the ink ejection direction D is inclined by an angle Θ, Θ ′ (for example, about 4 °) with respect to a vertical direction E perpendicular to the recording medium 12. Is formed.

Referring to FIG. 9, a case of a print head (line head) having a length substantially equal to the length in the width direction of the recording medium will be described.

FIG. 9 is a perspective view showing a printer on which a line head is mounted. In this figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

The line head 100 is fixed to a fixing member (not shown) of the main body of the printer 110. In the line head 100, a head main body 102 having a plurality of nozzles (not shown) arranged in one or two rows in a direction substantially perpendicular to the conveying direction of the recording medium 12 (the direction of arrow A) is formed. . In addition, the line head 100 includes an electric wiring printed board 104 for inputting / outputting a signal carrying image information and the like, a connector and a bundle 106,
8 and an ink inlet 109.

In the line head 100 shown in FIG. 9, an example of one color is given. However, a line head capable of forming a color image can be formed by arranging the line heads in a plurality of rows in the traveling direction of the recording medium. Further, if power is supplied to all the nozzles simultaneously so as to drive all the nozzles of the line head at the same time, not only the power consumption becomes enormous but also the heat generation becomes large. For this reason, a method is adopted in which power is sequentially supplied to all the nozzles and the nozzles are sequentially driven. If the driving is performed sequentially as described above, a printing time difference occurs, so that a horizontal straight line cannot be hit on a continuously moving recording medium. For this reason, the line head itself is inclined with respect to the traveling direction of the recording medium so that a horizontal straight line can be printed.

The plurality of nozzles formed in the head main body 102 are arranged such that the ink ejection direction D is perpendicular to the recording medium 12 by an angle ° (for example, about 4 °), similarly to the print head shown in FIG. It is formed so as to be inclined with respect to. As a result, the dots formed by the ink droplets that have landed on the surface of the recording medium 12 have a circular shape that is almost close to the circular nozzle outlet (ink ejection port), so that overlapping of adjacent dots can be prevented or adjacent dots can be prevented. For example, it is possible to prevent the occurrence of a gap between them, thereby increasing the resolution of the image and improving the image quality.

[0039]

As described above, according to the first ink jet type image forming apparatus of the present invention, ink lands on the recording medium from a substantially vertical direction substantially perpendicular to the recording medium. The ink becomes almost a perfect circle. For this reason, among a plurality of dots formed by a plurality of inks that have landed on a recording medium, overlapping of adjacent dots is prevented, and a gap is prevented from being generated between adjacent dots. As a result, the image resolution is improved and the image quality is improved.

According to the second ink jet type image forming apparatus of the present invention, when the print head ejects ink while reciprocating, the ink is applied to the recording medium from a substantially perpendicular direction substantially perpendicular to the recording medium. Although it is difficult to land, in the print head of the ink jet type image forming apparatus of the present invention, the ink ejection directions at the time of reciprocating movement are made different from each other, and in any case of reciprocating movement, Since the ink lands on the recording medium, the ink arriving on the recording medium has a substantially perfect circle. For this reason, among a plurality of dots formed by a plurality of inks that have landed on a recording medium, overlapping of adjacent dots is prevented, and a gap is prevented from being generated between adjacent dots. As a result, the image resolution is improved and the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a printer which is an example of an inkjet type image forming apparatus of the present invention.

FIG. 2 is a perspective view showing the carriage unit of FIG. 1;

FIG. 3 is an explanatory diagram illustrating the movement of ink ejected from a print head.

FIG. 4 is an explanatory diagram schematically showing an example in which the ejection direction of ink ejected from four print heads is inclined.

FIG. 5 is an explanatory diagram schematically showing a technique for making dots circular even when the print head reciprocates.

FIG. 6 is a plan view schematically showing a print head capable of making dots substantially circular with one print head for each color.

FIG. 7 is a plan view schematically showing another example of a print head capable of making dots substantially circular with one print head for each color.

FIG. 8 is a plan view schematically showing a print head in which color mixing is prevented.

FIG. 9 is a perspective view showing a printer on which a line head is mounted.

[Explanation of symbols]

10, 110 printer 12 recording medium 20K, 20C, 20M, 20Y, 50K, 50C, 5
0M, 50Y, 70K, 70C, 70M, 70, 80
K, 80C, 80M, 80Y print head 100 line head

Claims (2)

[Claims] An inkjet image forming an image on a recording medium while relatively moving a print head for discharging ink and a recording medium on which the ink discharged from the print head lands at a predetermined moving speed. In the forming apparatus, the print head is configured to change an ejection direction of the ink based on the predetermined moving speed so that the ink lands on the recording medium from a substantially vertical direction substantially perpendicular to the recording medium. An ink jet type image forming apparatus which discharges ink while being inclined with respect to the image forming apparatus. A print head for ejecting ink while reciprocating in a predetermined scanning direction, wherein the print head ejects ink to a recording medium conveyed in a sub-scanning direction substantially orthogonal to the scanning direction. In the ink jet type image forming apparatus for forming an image on a recording medium, the print head is configured to set the ejection direction of the ink to the predetermined direction so that the ink lands on the recording medium from a substantially vertical direction substantially perpendicular to the recording medium. The ink is ejected while being inclined with respect to the substantially vertical direction based on the moving speed of the ink, and the ink ejection direction at the time of forward movement while the print head reciprocates, and the backward movement of the reciprocating movement. An ink jet type image forming apparatus characterized in that ink ejection directions at the time are different from each other.