Ink jet recording apparatus and ink jet recording method

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink jet recording apparatus and a recording method, in which liquid such as ink is ejected from a fine nozzle, thereby forming a liquid pattern on recording paper or sheet so as to draw characters or graphics.

2. Description of the Related Art

In recent years, a printer using an ink jet recording apparatus has become widely pervasive as a printing apparatus for a personal computer or the like because of easy handling, excellent printing performance, a low cost or the like. Such ink jet recording apparatuses include various types, for example, a thermal type in which bubbles are generated in ink by thermal energy so as to eject ink droplets by pressure waves caused by the bubbles, an electrostatic type in which ink droplets are sucked to be ejected by electrostatic force, a piezoelectric type in which vibrator such as a piezoelectric element is used, or the like.

Furthermore, there has been proposed an amalgam of a piezoelectric system and an electrostatic system. For example, an amalgam of a piezoelectric system and an electrostatic system is disclosed in Japanese Patent Application Laid-Open No. 5-278212, which will be explained below in reference to FIG.

15

. In

FIG. 15

, reference numeral

110

denotes a nozzle from which ink is ejected;

112

, a pressure chamber communicating with the nozzle

110

and containing the ink therein;

115

, a piezoelectric element for applying a pressure to the pressure chamber

112

;

120

, a convex ink meniscus formed at the tip of the nozzle

110

;

108

, a charging electrode for electrically charging the ink portion forming the ink meniscus

120

; and

104

, an opposite electrode disposed opposite to the charging electrode

108

via a recording sheet

107

. A high voltage is applied between the charging electrode

108

and the opposite electrode

104

by a high voltage power source

105

.

With this configuration, first, a voltage is applied to the piezoelectric element

115

, so that a volume of the pressure chamber

112

is reduced by force generated by the piezoelectric element

115

, thereby forming the ink meniscus

120

at the nozzle

110

. Subsequently, when the ink meniscus

120

is electrically charged by the charging electrode

108

, the ink is ejected from the ink meniscus

120

toward the opposite electrode

104

by an electric field formed between the charging electrode

108

and the opposite electrode

104

. At this time, since the recording sheet

107

is interposed between the ink meniscus

120

and the opposite electrode

104

, an ink image is formed on the recording sheet

107

.

In

FIG. 15

, although the ink meniscus

120

is formed by the piezoelectric element

115

, an ink droplet may be ejected. Normally, as the voltage to be applied to the piezoelectric element

115

is made higher, the diameter of the ink droplet to be ejected becomes greater and the ejection rate of the ink droplet becomes higher. In contrast, as the voltage to be applied to the piezoelectric element

115

is made lower, the diameter of the ink droplet to be ejected becomes smaller and the ejection rate of the ink droplet becomes lower. In the configuration shown in

FIG. 15

, it is possible to accelerate the ink droplet by electrostatic force and enhance the flying stability of the ink droplet even in the case where the voltage applied to the piezoelectric element

115

is made lower so that the diameter and ejection rate of the ink droplet to be ejected is made smaller and lower, respectively. Moreover, as the diameter of the nozzle

110

becomes smaller, clogging or the like is more liable to be generated and a manufacturing yield becomes worse. Consequently, in the ink jet recording apparatus, it is very useful to eject an ink droplet having a small diameter from a large-diameter nozzle. Therefore, in the configuration shown in

FIG. 15

, it is possible to provide an ink jet head in which the flying stability of a small-diameter droplet ejected from a large-diameter nozzle can be enhanced, clogging of the nozzle can be reduced, and a good manufacturing yield can be achieved.

However, although in the method illustrated in

FIG. 15

a small droplet ejected from a nozzle having a large diameter is accelerated in an electrostatic field so as to enhance the flying stability of the ink droplet, the flying rate of the ink droplet is low since the ejection rate of the ink droplet is low. At the low flying rate of the ink droplet, a deviation of an impact position on the recording sheet

107

becomes great due to variations in flying rate, thereby deteriorating a quality of an image There arises no problem in the case where the relative moving speed between the recording sheet

107

and the nozzle

110

is low; whereas in the case where it is high, the deviation of the impact position becomes too great to be practical.

Additionally, in the case where the voltage to be applied to the piezoelectric element

115

can be varied so that the volume of the droplet to be ejected is changed for dot modulation in the method illustrated in

FIG. 15

, there arises the deviation of impact positions of a large dot (a large droplet) and a small dot (a small droplet) on the recording sheet

107

. Although the deviation of the impact positions can be reduced more in the case where the electrostatic field is applied than in the case it is not applied, the deviation of the impact positions becomes too great to be practical in the case where the relative moving speed between the recording sheet

107

and the nozzle

110

is high.

SUMMARY OF THE INVENTION

The present invention has been accomplished in an attempt to solve the above problems observed in the prior art. An object of the present invention is to provide an ink jet head recording apparatus in which clogging in a nozzle can be reduced and a manufacturing yield is favorable by reducing the deviation of an impact position of an ink droplet in the case where a small droplet is ejected from a large-diameter nozzle.

Furthermore, another object of the present invention is to provide an ink jet recording apparatus in which dot modulation can be achieved by reducing the deviation of impact positions of a large droplet and a small droplet on a recording sheet.

One aspect of the present invention is an ink jet recording apparatus comprising:

an ink jet head for ejecting ink from a nozzle;

relative movement means for relatively moving said ink jet head and a recording sheet;

an opposite electrode disposed at a position opposite to said ink jet head; and

voltage applying means for applying a voltage between said ink and said opposite electrode;

wherein an ejection direction of the ink to be ejected from said nozzle is inclined with respect to a direction of an electric field generated by said voltage applying means and has a component in a relative movement direction of said ink jet head relative to said recording sheet.

Another aspect of the present invention is an ink jet recording apparatus, wherein the direction of said electric field signifies a direction of an electric field in the vicinity of said opposite electrode;

the ejection direction of said ink being inclined with respect to the direction of said electric field signifies the ejection direction of said ink being inclined with respect to a plane perpendicular to the relative movement direction by said relative movement means; and

the ejection direction of the ink to be ejected from said nozzle is parallel to or within a plane including a perpendicular line drawn from said nozzle down to said opposite electrode and a straight line drawn from said nozzle toward the relative movement direction by said relative movement means.

Still another aspect of the present invention is an ink jet recording apparatus, wherein said ink jet head includes: a pressure chamber containing said ink therein; the nozzle communicating with said pressure chamber and ejecting the ink; and pressure applying means for applying a pressure to said pressure chamber.

Yet another aspect of the present invention is an ink jet recording apparatus, further comprising pressure varying means for varying the pressure of said pressure applying means, so as to vary a quantity of the ink to be ejected from said nozzle.

Still yet another aspect of the present invention is an ink jet recording apparatus, wherein said pressure applying means includes a vibrating plate attached to said pressure chamber and a piezoelectric element for vibrating said vibrating plate, and said pressure varying means switches an energizing waveform to said piezoelectric element.

A further aspect of the present invention is an ink jet recording apparatus, wherein a nozzle surface having an ejection port of said nozzle is arranged slantwise with respect to a plane perpendicular to a perpendicular line drawn from said nozzle down to said opposite electrode, and said ink is ejected perpendicularly to said nozzle surface.

A still further aspect of the present invention is an ink jet recording apparatus, wherein a nozzle surface having an ejection surface of said nozzle is arranged in parallel with respect to a plane perpendicular to a perpendicular line drawn from said nozzle down to said opposite electrode, and said ink is ejected slantwise to said nozzle surface.

A yet further aspect of the present invention is an ink jet recording apparatus, wherein the axis of said nozzle is inclined with respect to said nozzle surface.

A still yet further aspect of the present invention is an ink jet recording apparatus, further comprising:

relative moving speed switching means for switching a relative moving speed between said ink jet head and said recording sheet which are relatively moved by said relative movement means; and

ejection angle switching means for switching an ejection angle of the ink according to the relative moving speed between said ink jet head and said recording sheet.

One aspect of the present invention is an ink jet recording apparatus, wherein said relative movement means allows a shuttling operation of said ink jet head with respect to said recording sheet, the ink being ejected from said nozzle during both an advancing operation and a returning operation, wherein the ejection directions of ink droplets during the advancing and returning operations are symmetrical with respect to a plane perpendicular to the relative movement direction by said relative movement means.

Another aspect of the present invention is an ink jet recording method comprising the steps of:

inputting a desired recording quality;

switching a relative moving speed of an ink jet head for ejecting ink from a nozzle onto a recording sheet according to said recording quality; and

switching an ejection direction of the ink to be ejected from said nozzle according to said relative moving speed.

Still another aspect of the present invention is an ink jet recording method, wherein the ejection direction of said ink is inclined with respect to a plane perpendicular to said relative movement direction, and has a component in the relative movement direction of said ink jet head with respect to said recording sheet.

Yet another aspect of the present invention is an ink jet recording method comprising the steps of:

determining a relative movement direction of an ink jet head for ejecting ink from a nozzle onto a recording sheet; and

switching an ejection direction of the ink to be ejected from said nozzle according to said relative movement direction;

wherein the ejection direction of said ink is inclined with respect to a plane perpendicular to said relative movement direction, and has a component in the relative movement direction of said ink jet head with respect to said recording sheet.

Still yet another aspect of the present invention is an ink jet recording method, wherein said ink jet head or said recording sheet performs a shuttling operation, the ejection directions of said ink during advancing and returning operations are symmetrical with respect to the plane perpendicular to said relative movement direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic view showing the configuration of an ink jet recording apparatus in a first embodiment according to the present invention;

FIG. 2

is a cross-sectional view showing an ink jet head in the first embodiment according to the present invention;

FIG. 3

is a graph illustrating voltage waveforms to be applied to a piezoelectric element in the first embodiment according to the present invention;

FIG. 4

is a graph illustrating the relationship between peak voltages in the voltage waveforms and a quantity of ink droplets in the first embodiment according to the present invention;

FIG. 5

is a graph illustrating the relationship between the quantity of ink droplets and impact positions of the ink droplets in the first embodiment according to the present invention;

FIG. 6

is a view illustrating another slantwise ejecting method in the first embodiment according to the present invention;

FIG. 7

is a cross-sectional view showing the ink jet head in the first embodiment according to the present invention;

FIG. 8

is a schematic cross-sectional view illustrating the ink jet recording apparatus for the explanation of the concept and effects of “slantwise ejection” in the embodiment;

FIG.

9

(

a

) is a graph illustrating the relationship between ejection rates V

0

and impact positions Ld, wherein ejection angle θ range from 0° to 90°;

FIG.

9

(

b

) is a graph illustrating the relationship between the ejection angles θ and the impact positions Ld, wherein the abscissa is changed to the ejection angles θ in the relationship between the ejection rates V

1

and the impact positions Ld shown in FIG.

9

(

a

);

FIGS.

10

(

a

) and

10

(

b

) are a table and a graph illustrating the relationship between speeds Vc of a carriage and limit values of the ejection angles θ of droplets, wherein deviations fall within an allowable range (±17.7 μm);

FIGS.

11

(

a

) and

11

(

b

) are a table and a graph illustrating the relationship between speeds Vc of the carriage and limit values of the ejection angles θ of droplets, wherein deviations fall within an allowable range (±8.8 μm);

FIG. 12

is a cross-sectional view showing an ink jet head in a second embodiment according to the present invention;

FIG. 13

is a schematic view showing the configuration of an ink jet recording apparatus in a third embodiment according to the present invention;

FIG. 14

is a schematic view showing the configuration of an ink jet recording apparatus in a fourth embodiment according to the present invention; and

FIG. 15

is a schematic cross-sectional view showing an ink jet recording apparatus in the prior art.

(Description of the Reference Numerals)

1

Ink jet head

2

Carriage

3

Carriage shaft

4

Opposite electrode

5

Power source

6

Recording sheet feeder

7

Recording sheet

8

Nozzle plate

9

Ink

10

Nozzle

11

Nozzle surface

12

Pressure chamber

13

Pressure chamber structure

14

Ink supply port

15

Piezoelectric element

16

Vibrating plate

17

Ink droplet

18

Eccentric cam

19

Ink-jet head rotating shaft

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described with reference to

FIGS. 1

to

14

.

(First Embodiment)

FIG. 1

is a schematic view showing the configuration of an ink jet recording apparatus in a first embodiment according to the present invention.

In

FIG. 1

, reference numeral

1

denotes an ink jet head, which is mounted on a carriage

2

and is configured in such a manner as to be driven by drive means, not shown, for a reciprocating operation under the guidance of a carriage shaft

3

. The carriage

2

, the carriage shaft

3

and the drive means constitute one example of relative movement means claimed in the section of “What Is Claimed Is.” Reference numeral

4

denotes an opposite electrode made of metal with a distance of 1 mm from the ink jet head

1

. To the opposite electrode

4

and the ink jet head

1

, a high voltage of −1.8 KV is applied by a power source

5

in the state in which the side of the ink jet head

1

is grounded. The power source

5

is one example of voltage applying means claimed in the section of “WHAT IS CLAIMED IS.” Reference numeral

6

denotes a recording sheet feeder, for feeding a recording sheet

7

in a direction perpendicular to the carriage shaft

3

.

Next,

FIG. 2

is a cross-sectional view showing the ink jet head

1

. In

FIG. 2

, reference numeral

8

denotes a nozzle plate made of stainless steel, having a nozzle

10

for ejecting ink

9

. Between the nozzle plate

8

and the opposite electrode

4

is applied a high voltage of about −1.8 KV by the power source

5

. Water ink is used as the ink

9

. Reference numeral

11

denotes a nozzle surface, which is arranged in such a manner as to be inclined with respect to the opposite electrode

4

. An axis

10

a

of the nozzle

10

is set perpendicularly to the nozzle surface

11

. Reference numeral

12

denotes a pressure chamber communicating with the nozzle

10

and containing the ink

9

therein. Reference numeral

13

denotes a pressure chamber structure, which defines the pressure chamber

12

together with the nozzle plate

8

. In the pressure chamber structure

13

is formed an ink supply port

14

for supplying the ink

9

to the pressure chamber

12

. The ink supply port

14

communicates with a common liquid chamber and an ink tank, neither shown. Reference numeral

15

denotes a piezoelectric element made of PZT (here, Pb(Zr

0.53

Ti

0.47

)O

3

is used) in a thickness of 0.02 mm, which is adapted to vibrate a vibrating plate

16

made of stainless steel in a thickness of 0.01 mm. Reference numeral

17

denotes an ink droplet to be ejected from the nozzle

10

. Although only one pressure chamber

12

and only one nozzle

10

are shown in

FIG. 2

which is the cross-sectional view, actually, there are provided a plurality of pressure chambers

12

, each having one nozzle

10

.

Explanation will be made below on the operation of the ink jet recording apparatus such configured as described above in reference to

FIGS. 1

to

7

, and simultaneously, a description will be given of an ink jet recording method in one embodiment according to the present invention.

First, the operation of the ink jet recording apparatus will be explained in reference to FIG.

1

. In

FIG. 1

, the recording sheet feeders

6

feed the recording sheet

7

to a desired position. While the carriage

2

is moved from a position A to a position B by the device, not shown, the ink droplet

17

is ejected from the nozzle

10

. Consequently, a recording image can be recorded on the recording sheet

7

by a quantity equivalent to one scanning of the ink jet head

1

. Thereafter, while the carriage

2

is returned from the position B to the position A, the recording sheet feeders

6

feed the recording sheet

7

by a desired distance. Furthermore, while the carriage

2

is moved once again from the position A to the position B, the ink droplet

17

is ejected from the nozzle

10

. In this way, a recording image is recorded on the recording sheet

7

by a quantity equivalent to one scanning of the ink jet head

1

. This operation is repeated, so that the entire image can be formed on the recording sheet

7

.

Subsequently, the ejection operation of the ink droplet

17

from the nozzle

10

will be explained below in reference to

FIG. 2. A

voltage is applied to the piezoelectric element

15

. And then, the vibrating plate

16

is flexed together with the piezoelectric element

15

in a direction in which the volume of the pressure chamber

12

is reduced. Therefore, a pressure inside the pressure chamber

12

is increased, so that the ink

9

is ejected in the form of the ink droplet

17

from the nozzle

10

toward the recording sheet

7

. At this moment, since the electrostatic field is applied between the nozzle plate

8

and the opposite electrode

4

, a positive electric charge is induced before the ink

9

is turned into the ink droplet

17

. Consequently, the ink

9

is turned into the positively charged ink droplet

17

, to be ejected from the nozzle

10

. Furthermore, the ink droplet

17

is flown toward the recording sheet

7

while being accelerated by the force of the electrostatic field.

At this time, even if the ejection rate of the ink droplet

17

is low, the ink droplet

17

is accelerated by the electrostatic force, to be easily landed at a desired position of the recording sheet

7

.

Moreover, since the nozzle surface

11

is inclined with respect to the opposite electrode

4

, the ink droplet

17

is ejected slantwise with respect to a perpendicular line drawn from the nozzle down to the opposite electrode

4

. That is, the ink is ejected from the nozzle slantwise with respect to the direction of a positively electric field generated between the nozzle plate

8

and the opposite electrode

4

. Hereinafter, such ejection is simply referred to as “slantwise ejection.” Furthermore, the ejection direction

201

of the slantwise ejection is parallel to (or within) a plane including a perpendicular line

202

from the nozzle

10

down to the opposite electrode

4

(corresponding to the direction of the electric field in the vicinity of the opposite electrode

4

) and a straight line from the nozzle

10

toward the relative movement direction

203

of the ink jet head

1

with respect to the recording sheet

7

, and further, is oriented toward the relative movement direction of the ink jet head

1

with respect to the recording sheet

7

.

Subsequently, the effects of the slantwise ejection will be explained based upon experimental data and simulation results. A theoretical explanation of the effects of the slantwise ejection will be explained later.

First, explanation will be made on required dimensions of the ink jet head

1

for use in experiments and simulations.

The width, depth and length of the pressure chamber are 0.34 mm, 0.16 mm and 2.2 mm, respectively. The width and length of the vibrating portion of the vibrating plate

16

are 0.34 mm and 2 mm, respectively. The width and length of the piezoelectric element

15

are 0.24 mm and 2 mm, respectively. The diameter of a small-diameter portion of each of the nozzle

10

and the ink supply port

14

is 0.035 mm.

Next, explanation will be made on the conditions of the experiments.

The relative moving speed of the ink jet head

1

was 500 mm/s. A gap between the ink jet head

1

and the recording sheet

7

was 1 mm. Consequently, the strength of the electric field in the gap was 1.8 kv/mm.

FIG. 3

graphically shows voltage waveforms to be applied to the piezoelectric element

15

. Peak voltages within the range of 12 V to 36 V were applied in the voltage waveforms graphically shown in FIG.

3

. The experiments were conducted at a repeating cycle of 2 kHz and at the angles of the slantwise ejection of 0° to 16°.

FIG. 4

graphically shows the peak voltages in the voltage waveforms and the masses of the ink droplets

17

when the voltage waveforms graphically shown in

FIG. 3

were applied to the piezoelectric element

15

. The experimental results show that there was no difference between the case where the electrostatic field was applied and the case where it was not applied, and further, that the mass of the ink droplets

17

became greater as the peak voltage became higher.

Subsequently, Table 1 and

FIG. 5

illustrate the relationship between the mass of the ink droplets

17

and the impact positions on the recording sheet

7

in the case where the voltage waveforms illustrated in

FIG. 3

were applied. Here, an intersection between the perpendicular line drawn from the nozzle

10

down to the opposite electrode

4

and the recording sheet

7

when the voltage was started to be applied to the piezoelectric element

15

was used as an origin, and a distance from the origin to the actual impact position of the ink droplet

17

on the recording sheet

7

was defined as an impact position. Table 1 and

FIG. 5

illustrate the relationship at each of the angles of the slantwise ejection of 0°, 4°, 8°, 12° and 16°, respectively, and at the same time, illustrate the case where the electrostatic field was not applied and the ink droplet was ejected straight and the cases where the electrostatic field was not applied and the ink droplet was ejected at the angles of 12° and −4°, respectively. In Table 1 and

FIG. 5

, the state at the angle of the slantwise ejection of 0° resulted from the experiment, but the states of the other angles of the slantwise ejection resulted from the simulations by using theoretical equations described later.

As apparent from these results, variations of ±0.06 mm in impact position are generated within the range of 18 ng to 72 ng of the ink droplets (corresponding to the dot modulation system in which small droplets and large droplets are ejected) in the case where the electrostatic field is applied and the ink droplet is ejected straight (at the ejection angle of 0°). In this case, it is not practical although the deviation of the impact position can be considerably reduced more than the case where the electrostatic field is not applied. The greater the quantity of the ink droplets is, the higher the ejection rate becomes. The ejection rate is 1.3 m/s at 18 ng of the quantity of the ink droplets; and 11.6 m/s, at 72 ng.

The deviation of the impact position becomes considerably great at the slantwise ejection angle of −4°. Although the deviation of the impact position can be reduced if the electrostatic field is made stronger, the limit of the electrostatic field is almost −4 KV/mm, wherein the deviation of the impact position becomes ±0.04 mm. This is not practical. Moreover, in the case where the electrostatic field is strengthened, it is difficult to set the gap between the ink jet head

1

and the opposite electrode

4

to 1 mm or less, Consequently, it is necessary to increase the applied voltage, thereby unfavorably raising problems in a cost of the apparatus, insulating measures or the like.

In contrast, the deviation of the impact position can be suppressed within ±0.011 mm within the range of 18 ng to 72 ng of the ink droplets when the angle of the slantwise ejection is 12°.

TABLE 1

Impact

Impact

Impact

Impact

Impact

Impact

Impact

Impact

Position

Position

Position

Position

Position

Position

Position

Position

(μm) with

(μm) with

(μm) with

(μm) with

(μm) with

(μm) without

(μm) without

(μm) with

Quantity

Application

Application

Application

Application

Application

Application

Application

Application

of Ink

of

of

of

of

of

of

of

of

Droplets

Electrostatic

Electrostatic

Electrostatic

Electrostatic

Electrostatic

Electrostatic

Electrostatic

Electrostatic

(ng)

Field, at 0°

Field, at 4°

Field, at 8°

Field, at 12°

Field, at 16°

Field, at 0°

Field, at 12°

Field, at −4°

17.6

165.0

194.9

224.6

254.1

283.1

385.0

592.9

132.2

20.3

142.5

182.3

221.8

261.0

299.6

250.0

457.9

100.8

23.2

130.0

176.5

222.8

268.6

313.8

195.0

402.9

82.0

26.2

115.0

165.9

216.6

266.8

316.3

157.5

365.4

63.0

28.6

105.0

158.9

212.4

265.5

317.8

136.0

343.9

50.3

34.0

84.0

138.5

192.7

246.5

299.4

107.5

315.4

28.9

39.1

73.0

131.9

190.4

248.5

305.6

86.5

294.4

13.7

43.8

64.5

125.3

185.8

245.7

304.7

74.0

281.9

3.4

48.5

59.5

122.4

185.0

246.9

308.0

66.0

273.9

−3.6

52.7

54.5

118.9

183.1

246.5

309.1

59.0

266.9

−10.2

56.7

52.5

119.1

185.3

251.0

315.6

55.0

262.9

−14.3

60.4

48.0

115.0

181.6

247.6

312.6

50.0

257.9

−19.2

64.3

46.5

114.1

181.3

247.9

313.5

48.0

255.9

−21.3

67.6

43.8

112.7

181.3

249.3

316.3

44.3

252.2

−25.4

70.9

43.3

113.0

182.4

251.2

318.9

43.3

251.2

−26.7

Consequently, it is not practical because the deviations of the impact positions become great if the large droplets and the small droplets are ejected at the relative moving speed of 500 mm/s in the case where the ink droplet

17

is ejected straight even if the electrostatic field is applied. In contrast, the deviations of the impact positions can be reduced both in the case of the ejection of large droplets and in the case of the ejection of small droplets in the case where the ink droplet

17

is ejected slantwise with the application of the electrostatic field; namely, it is possible to achieve so-called dot modulation.

Next, explanation will be made on the operation of the slantwise ejection in the case of not dot modulation but binary recording. Normally, although the quantity of ink droplets can be reduced if the peak voltage is decreased, the ejection rate of the ink droplet

17

becomes lower. In such a state, the deviation of the impact position is markedly influenced by the variation in ejection rate.

In

FIG. 5

, the deviation of the impact position was ±0.073 mm without any application of the electrostatic field (at the ejection angle of 0°) when the quantity of the ink droplets was 20 ng ±2 ng. As a result, from the point of view of the deviation of the impact position, it is impossible to put into practice the method in which the quantity of the ink droplets is decreased by reducing the peak voltage, thereby ejecting the small ink droplets from the large-diameter nozzle. In contrast, the deviation of the impact position was ±0.016 mm in the case where the ink droplets were ejected straight with the application of the electrostatic field. Furthermore, the deviation of the impact position was ±0.002 mm in the case of the slantwise ejection (at the ejection angle of 12°). The application of the electrostatic field can reduce the deviation of the impact position, and the slantwise ejection can further reduce the deviation of the impact position.

As described above, in the first embodiment, the slantwise ejection in the electrostatic field can reduce the deviations of the impact positions of the large and small ink droplets, thus providing the ink jet recording apparatus capable of the dot modulation.

The slantwise ejection in the electrostatic field produces the effects in conducting the dot modulation, and further, can reduce the deviation of the impact position even in the case of the ejection of the small droplet from the large-diameter nozzle at the time of the binary recording. The ejection of the small droplet from the large-diameter nozzle can prevent clogging and provide the ink jet recording apparatus which is manufactured at a good yield.

Although the angle of the slantwise ejection of 12° is preferable in the present embodiment, it is to be understood that an optimum ejection angle depends upon the conditions such as the gap between the nozzle

10

and the opposite electrode

4

and the relative moving speed.

Although the nozzle surface

11

is configured to be perpendicular to the longitudinal direction of the pressure chamber

12

in the present embodiment, the nozzle surface

11

may be inclined with respect to the longitudinal direction of the pressure chamber

12

, as shown in FIG.

6

.

Although the ink jet head

1

is moved with respect to the recording sheet

7

in the present embodiment, the ink jet head

1

may be stationary while the recording sheet

7

may be moved. The direction of the slantwise ejection in this case is shown in FIG.

7

.

Although the direction of the slantwise ejection is parallel to the plane including the perpendicular line drawn from the nozzle

10

down to the opposite electrode

4

and the straight line drawn from the nozzle

10

toward the relative movement direction of the ink jet head

1

with respect to the recording sheet

7

in the present embodiment and is oriented toward the relative movement direction of the ink jet head

1

with respect to the recording sheet

7

, the direction of the slantwise ejection may be oriented toward a direction intersecting the above-described plane within the range where no problem is arisen in view of the image as long as the direction of the slantwise ejection is oriented toward the above-described relative movement direction.

Although the piezoelectric element

15

and the vibrating plate

16

are used as the pressure applying means for the ink ejection in the present embodiment, such pressure applying means may include means for generating bubbles in the ink by thermal energy, high frequency energy means by the use of a piezoelectric element, means for fusing solid ink so as to eject the fused ink by the use of a piezoelectric element, or the like.

Subsequently, as described above, the effects of “the slantwise ejection” in the present embodiment will be theoretically described in reference to

FIGS. 8 and 9

.

FIG. 8

is a schematic cross-sectional view illustrating the ink jet recording apparatus for the explanation of the principle and effects of the slantwise ejection in the present embodiment.

First, the equation expressing the impact position Ld of the droplet can be introduced as follows:

The density of electric charges in the droplet is represented by q (=9 μ

0

/g); the speed of the ink jet head (also referred to as the speed of the carriage), Vc (=500 mm/sec); the lapse of time after the ejection of the droplet from the nozzle, t; the gap between the ink jet head and the recording sheet, d (=1 mm); the voltage for generating the electric field, Ve (=−1800 V/mm); the ejection rate of the droplet from the nozzle, V

0

; and the ejection angle of the droplet from the nozzle, θ.

Under the above-described conditions force F of the electrostatic field acting on the droplet is expressed by Equation 1. The acceleration acting on the droplet can be expressed by Equation 2 with transformation of Equation 1.

F=ma=mqVe/d (Equation 1)

a=Ve·q/d (Equation 2)

Meanwhile, the ejection rate V

0

of the droplet is expressed by V

0

sin θ as a horizontal component and V

0

cos θ as a vertical component, as illustrated in FIG.

8

. As a result, in consideration of the acceleration expressed by Equation 2, a horizontal rate component Vh and a vertical rate component Vv of the droplet are expressed by Equations 3 as follows:

Vh=Vc+V

0

sin θ (Equation 3)

Vv=V

0

cos θ+(Ve·q/d)t

Thus, the flying distance of the droplet will be expressed by Equations 4 and 5 as follows:

L=(Vc+V

0

sin θ)t (Equation 4)

Lv=V

0

cos θ·t+(Ve·q/2d)t

2

(Equation 5)

wherein L represents the distance in the horizontal direction; and Lv, the distance in the vertical direction.

Here, the time when the distance Lv in the vertical direction becomes equal to d, that is, a time t

d

until the droplet reaches the recording sheet

7

will be expressed by Equation 6 as follows:

t

d

={−2V

0

cos θ+(4V

0

2

cos

2

θ+8Ve·q)

½

}d/2Ve·q (Equation 6)

Therefore, the impact position Ld of the droplet can be obtained by substituting t

d

for Equation 4.

Ld=(Vc+V

0

sin θ)t

d

(Equation 7)

Next, for the comparison with the present invention, explanation will be made on the impact position in the case where the electric field is zero and the droplet is ejected slantwise, based upon Equations 4 to 7.

That is to say, Lv=d and Ve=0 are substituted for Equation 5, thereby obtaining the following equation:

d=V

0

cos θ·t (Equation 8)

From this equation, the impact time t is expressed by the following Equation 9:

t=d/(V

0

cos θ) (Equation 9)

When Equation 9 is substituted for Equation 4, the impact position L is expressed by the following Equation 10:

\begin{matrix} \begin{matrix} L = (Vc + V_{0} \sin θ) d / (V_{0} \cos θ) \\ = (dVc / \cos θ) / V_{0} + (\sin θ / \cos θ) d \end{matrix} & (Equation 10) \end{matrix}

As apparent from Equation 10, the higher the ejection rate V

0

of the droplet is, namely, the larger the quantity of the droplet is, the smaller the reciprocal 1/V

0

becomes, and accordingly, the shorter the impact distance L becomes. With respect to the different ejection rates V

0

, there exists no ejection angle θ at which their impact distances L become equal to each other.

Consequently, it is found that it is theoretically impossible to equalize the impact distances of the large and small droplets to each other.

Subsequently, a description will be given of that there can exist the ejection angles θ at which the impact positions of the large and small droplets accord with each other by the slantwise ejection in the present embodiment, wherein the impact positions at the angles of 0° and 90° are exemplified for simple explanation.

In case of 0°, θ=0 is substituted for Equation 6, thereby obtaining the following Equation 11:

t

d

={−2V

0

+(4V

0

2

+8Ve·q)

½

}d/2Ve·q (Equation 11)

Furthermore, when this Equation 11 is substituted for Equation 7, the impact position Ld will be expressed by the following Equation 12:

\begin{matrix} \begin{matrix} Ld = Vc \cdot t_{d} \\ = Vc {- 2 V_{0} + {(4 V_{0}^{2} + 8 Ve \cdot q)}^{\frac{1}{2}}} d / 2 Ve \cdot q \end{matrix} & (Equation 12) \end{matrix}

Here, V

0

=0 and V

0

=∞ are substituted for Equation 12, thus obtaining the following Equations 13:

Ld=Vc(8Ve·q)

½

d/2Ve·q(wherein V

0

=0) (Equation 13)

Ld=0(wherein V

0

=0)

Therefore, the relationship between Ld and V

0

in Equation 12 is expressed by a curve

901

graphically shown in FIG.

9

(

a

).

Next, in case of 0=90°, θ=90 is substituted for Equation 6, thus obtaining the following Equation 14:

t

d

={8Ve·q)

½

d/2Ve·q (Equation 14)

Furthermore, this Equation 14 is substituted for Equation 7, the impact position Ld is expressed by the following Equation 15:

\begin{matrix} \begin{matrix} Ld = (Vc + V_{0}) t_{d} \\ = (Vc + V_{0}) {(8 Ve \cdot q)}^{\frac{1}{2}} d / 2 Ve \cdot q \end{matrix} & (Equation 15) \end{matrix}

Here, when Equation 15 is arranged by representing the term (8Ve·q)

½

d/2Ve·q by k, it is expressed by the following Equation 16, which is a linear function of V

0

intersecting the Ld axis at kV

0

.

Ld=kV

0

+kV

0

(Equation 16)

As a result, the relationship between Ld and V

0

in Equation 16 is expressed by a straight line

902

in FIG.

9

(

a

).

The curve

901

and the straight line

902

representing the relationship between the impact position Ld and the ejection rate V

0

which are obtained in the above-described mariner are converted into straight lines

903

and

904

representing the relationship between the impact position Ld and the ejection angle θ in FIG.

9

(

b

). In FIGS.

9

(

a

) and

9

(

b

), points P

1

and P

2

correspond to P′

1

and P′

2

, respectively; and Q

1

and Q

2

correspond to Q′

1

and Q′

2

, respectively.

In other words, as apparent from FIG.

9

(

a

), the curve

901

indicates that the impact position Ld becomes smaller in the case of the large droplet (for example, at the ejection rate V

2

) than the case of the small droplet (for example, at the ejection rate V

1

); the straight line

902

indicates that the impact position Ld becomes greater in the large droplet than in the small droplet. Moreover, from FIG.

9

(

a

), it is found that in the case where the droplet is ejected slantwise, that is, the ejection angle θ ranges from 0° to 90°, the coordinates representing the relationship between the impact position and the ejection rate exist between the curve

901

and the straight line

902

.

Meanwhile, it is apparent that changes in impact position Ld with respect to the ejection angle θ at a certain ejection rate V

1

may be drawn continuously, although it is not always a straight line, since it is clear that the line

903

(i.e., the line connecting the points P′

1

and P′

2

) becomes continuous in consideration of the continuity of a physical phenomenon. This is true for the line

904

connecting the points Q′

1

and Q′

2

.

Therefore, both the continuous lines

903

and

904

always intersect at a point R at an angle between 0° and 90°. The impact position of the large droplet (at the ejection rate of V

2

) accords with that of the small droplet (at the ejection rate of V

1

) at the ejection angle θ

R

of the intersection R.

As a result, it is found that there always exists an ejection angle θ (0°<θ<90°) at which the respective impact positions of the large and small droplets accord with each other according to the slantwise ejection in the present embodiment.

Subsequently, explanation will be made below on the simulation results for determining an optimum angle (limit angle) of the slantwise ejection based upon Equation 7 or the like for determining the impact position of the droplet.

First, there will be described only conditions different from the conditions established for the simulation as described in the above Table 1.

Here, a moving speed of the carriage ranges from 100 to 1100 mm/sec; the gap d is 1.5 mm; the applied voltage Ve for generating the electric field is −3 kv; and accordingly, the strength of the electric field is 2 kv/mm. The other conditions are the same as described above.

Although the ejection rates V

0

of the ink droplet in this simulation are basically 1.3 m/s, 2.5 m/s and 11.6 m/s, these values correspond to 18 ng, 20 ng and 72 ng of the quantity of the ink droplets, respectively.

Next, there will be explained an allowable range, which is required for dot modulation, of a deviation between the impact positions of the large droplet (72 ng) and the small droplet (18 ng). The impact position is defined as described above.

Namely, if the density of a pixel in recording is 360 dpi, a pitch of the pixel is 70.6 μm based upon the following Equation 17:

25.4×10

3

/360=70.6(μm) (Equation 17)

If a deviation between the impact positions of the large and small droplets ranges within ±¼ pixel, recording can be performed with excellent dot modulation. In this case, the allowable range of the deviation between both the droplets falls within ±17.7 μm.

Moreover, explanation will be made below on an allowable range of a deviation between the impact positions in the case where the small droplet (20 ng) is ejected from the large-diameter nozzle (corresponding to binary recording).

In this case, if the deviation between the impact positions of the small droplets ranges within ±⅛ pixel, excellent recording can be performed. Consequently, the allowable range of the deviation between the impact positions of the droplets falls within ±8.8 μm.

Here, the reason why the allowable range is set rigorously in comparison with the allowable range in the case of the dot modulation is as follows: namely, such nature is considered that the deviation between the impact positions of the large and small droplets generally appears inconspicuous to human eyes if the variations in deviation are slight; whereas the deviation of the impact positions of only the small droplets appears conspicuous to human eyes.

In the present embodiment, the deviation between the impact positions of the small droplets (20 ng) which are ejected from the large-diameter nozzle was calculated as caused by the variations in ejection rate (2.5 m/s ±30%). Such variations in ejection rate are caused by variations in quantity (20 ng) of the small droplets to be ejected per se.

First the respective simulations in the case where the large droplets (72 ng) and the small droplets (18 ng) are ejected are explained in reference to FIGS.

10

(

a

) and

10

(

b

). FIGS.

10

(

a

) and

10

(

b

) are a table and a graph illustrating the relationship between the speeds Vc of the carriage and the limit values of the ejection angles θ of the droplets in which the deviation falls within the above-described allowable range (±17.7 μm). A specific method for calculating the limit values of the ejection angles θ will be described later.

In FIG.

10

(

a

), a column denoted by reference numeral

1001

represents the moving speeds (mm/s) of the carriage; a column denoted by reference numeral

1002

, the limit values of the ejection angles θ at which the deviation between the impact positions of the large and small droplets becomes ±17.7 μm or less in such a manner as to correspond to the speed of the carriage in the column

1001

; and a column denoted by reference numeral

1003

, the limit values of the ejection angles θ at which the deviation between the impact positions of the large and small droplets becomes −17.7 μm or less.

For example, in order to make the deviation of the impact positions fall within the range of ±17.7 μm when the moving speed of the carriage is 500 mm/s, it is found from FIG.

10

(

a

) that the ejection angle θ is needed to be set within the range of 5.4°≦θ≦7.4°.

FIG.

10

(

b

) graphically shows the results illustrated in FIG.

10

(

a

). In FIG.

10

(

b

), the ejection angles θ existing in the coordinates between a straight line

1004

and a straight line

1005

fall within the allowable range with respect to a certain speed of the carriage.

Subsequently, explanation will be made on a method for determining the limit values of the ejection angles at the moving speed of the carriage of 500 mm/s in reference to Tables 2 to 4.

Tables 2 to 4 illustrate the simulation results of the impact positions of the large droplets (at the ejection rate of 11.6 m/s) and the small droplets (at the ejection rate of 1.3 m/s) and the differences (deviations) between the respective impact positions when the ejection angles θ are varied from 5° to 7.9° in increments of 0.1°.

As apparent from Table 2, the impact positions of the small droplets and the large droplets at the ejection angle θ of, for example, 5.4° are 0.0002041 m (204.1 μm) and 0.0001876 m (187.6 μm), respectively. The deviation between both the impact positions is 16.5 (μm) obtained by subtracting 187.6 from 204.1. At the ejection angle θ of 5.3°, the deviation between both the impact positions is almost 18.2 (μm), which exceeds ±17.7 (μm) of the limit value of the allowable range.

From the above results, the ejection angle θ of 5.4° becomes one limit angle determining the allowable range.

TABLE 2

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

1.3

5

1.2950534

3000

0.0015

0.01

0.0003279

4.5742672

0.5

0.0002011

23.126125

11.6

5

11.555861

3000

0.0015

0.01

0.0001178

12.733826

0.5

0.000178

1.3

5.1

1.2948537

3000

0.0015

0.01

0.0003279

4.5741509

0.5

0.0002019

21.473713

11.6

5.1

11.554079

3000

0.0015

0.01

0.0001178

12.732195

0.5

0.0001804

1.3

5.2

1.29465

3000

0.0015

0.01

0.0003279

4.5740322

0.5

0.0002026

19.820618

11.6

5.2

11.552262

3000

0.0015

0.01

0.0001178

12.730532

0.5

0.0001828

1.3

5.3

1.2944424

3000

0.0015

0.01

0.0003279

4.5739113

0.5

0.0002034

18.166829

11.6

5.3

11.550409

3000

0.0015

0.01

0.0001178

12.728836

0.5

0.0001852

1.3

5.4

1.2942309

3000

0.0015

0.01

0.000328

4.5737881

0.5

0.0002041

16.512333

11.6

5.4

11.548522

3000

0.0015

0.01

0.0001179

12.727108

0.5

0.0001876

1.3

5.5

1.2940154

3000

0.0015

0.01

0.000328

4.5736626

0.5

0.0002048

14.857117

11.6

5.5

11.546599

3000

0.0015

0.01

0.0001179

12.725349

0.5

0.00019

1.3

5.6

1.293796

3000

0.0015

0.01

0.000328

4.5735349

0.5

0.0002056

13.20117

11.6

5.6

11.544641

3000

0.0015

0.01

0.0001179

12.723557

0.5

0.0001924

1.3

5.7

1.2935726

3000

0.0015

0.01

0.000328

4.5734048

0.5

0.0002063

11.544478

11.6

5.7

11.542648

3000

0.0015

0.01

0.0001179

12.721733

0.5

0.0001948

1.3

5.8

1.2933453

3000

0.0015

0.01

0.000328

4.5732724

0.5

0.0002071

9.8870309

11.6

5.8

11.54062

3000

0.0015

0.01

0.0001179

12.719876

0.5

0.0001972

1.3

5.9

1.2931141

3000

0.0015

0.01

0.000328

4.5731377

0.5

0.0002078

8.2288147

11.6

5.9

11.538556

3000

0.0015

0.01

0.0001179

12.717988

0.5

0.0001996

Table 3 illustrates the simulation results of the deviations between the impact positions at the ejection angles θ ranging from 6.0° to 6.9°. It is clearly found from Table 3 that the ejection angle θ at which the impact positions of the large and small droplets substantially accord with each other is 6.4°.

TABLE 3

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

1.3

6

1.2928789

3000

0.0015

0.001

0.000328

4.5730008

0.5

0.0002086

6.5698175

11.6

6

11.536458

3000

0.0015

0.01

0.000118

12.716068

0.5

0.000202

1.3

6.1

1.2926398

3000

0.0015

0.01

0.000328

4.5728615

0.5

0.0002093

4.9100268

11.6

6.1

11.534324

3000

0.0015

0.01

0.000118

12.714115

0.5

0.0002044

1.3

6.2

1.2923967

3000

0.0015

0.01

0.000328

4.57272

0.5

0.0002101

3.2494304

11.6

6.2

11.532155

3000

0.0015

0.01

0.000118

12.71213

0.5

0.0002068

1.3

6.3

1.2921497

3000

0.0015

0.01

0.000328

4.5725762

0.5

0.0002108

1.5880159

11.6

6.3

11.529951

3000

0.0015

0.01

0.000118

12.710114

0.5

0.0002092

1.3

6.4

1.2918988

3000

0.0015

0.01

0.0003281

4.5724301

0.5

0.0002116

−0.074229

11.6

6.4

11.527712

3000

0.0015

0.01

0.000118

12.708065

0.5

0.0002116

1.3

6.5

1.2916439

3000

0.0015

0.01

0.0003281

4.5722817

0.5

0.0002123

−1.737318

11.6

6.5

11.525438

3000

0.0015

0.01

0.0001181

12.705984

0.5

0.000214

1.3

6.6

1.2913851

3000

0.0015

0.01

0.0003281

4.572131

0.5

0.0002131

−3.401261

11.6

6.6

11.523129

3000

0.0015

0.01

0.0001181

12.703871

0.5

0.0002165

1.3

6.7

1.2911224

3000

0.0015

0.01

0.0003281

4.571978

0.5

0.0002138

−5.066073

11.6

6.7

11.520784

3000

0.0015

0.01

0.0001181

12.701726

0.5

0.0002189

1.3

6.8

1.2908557

3000

0.0015

0.01

0.0003281

4.5718228

0.5

0.0002145

−6.731765

11.6

6.8

11.518405

3000

0.0015

0.01

0.0001181

12.699549

0.5

0.0002213

1.3

6.9

1.2905851

3000

0.0015

0.01

0.0003281

4.5716652

0.5

0.0002153

−8.39835

11.6

6.9

11.51599

3000

0.0015

0.01

0.0001181

12.69734

0.5

0.0002237

As apparent from Table 4, the impact positions of the small droplets and the large droplets at the ejection angle θ of, for example, 7.4° are 0.000219 m (219 μm) and 0.0002358 m (235.8 μm), respectively. The deviation between both the impact positions is −16.8 (μm) obtained by subtracting 235.8 from 219. At the ejection angle θ of 7.5°, the deviation between both the impact positions is almost −18.4 (μm), which exceeds −17.7 (μm) of the limit value of the allowable range.

From the above results, the ejection angle θ of 7.4° becomes the other limit angle determining the allowable range.

TABLE 4

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

1.3

7

1.2903106

3000

0.0015

0.01

0.0003281

4.5715054

0.5

0.000216

−10.06584

11.6

7

11.51354

3000

0.0015

0.01

0.0001182

12.695099

0.5

0.0002261

1.3

7.1

1.2900321

3000

0.0015

0.01

0.0003281

4.5713433

0.5

0.0002168

−11.73425

11.6

7.1

11.511056

3000

0.0015

0.01

0.0001182

12.692826

0.5

0.0002285

1.3

7.2

1.2897497

3000

0.0015

0.01

0.0003281

4.5711789

0.5

0.0002175

−13.40359

11.6

7.2

11.508536

3000

0.0015

0.01

0.0001182

12.690521

0.5

0.0002309

1.3

7.3

1.2894634

3000

0.0015

0.01

0.0003282

4.5710122

0.5

0.0002183

−15.07387

11.6

7.3

11.505981

3000

0.0015

0.01

0.0001182

12.688183

0.5

0.0002334

1.3

7.4

1.2891731

3000

0.0015

0.01

0.0003282

4.5708433

0.5

0.000219

−16.7451

11.6

7.4

11.503391

3000

0.0015

0.01

0.0001182

12.685814

0.5

0.0002358

1.3

7.5

1.288879

3000

0.0015

0.01

0.0003282

4.5706721

0.5

0.0002198

−18.41731

11.6

7.5

11.500766

3000

0.0015

0.01

0.0001183

12.683413

0.5

0.0002382

1.3

7.6

1.2885809

3000

0.0015

0.01

0.0003282

4.5704986

0.5

0.0002205

−20.0905

11.6

7.6

11.498106

3000

0.0015

0.01

0.0001183

12.68098

0.5

0.0002406

1.3

7.7

1.2882788

3000

0.0015

0.01

0.0003282

4.5703228

0.5

0.0002213

−21.76467

11.6

7.7

11.495411

3000

0.0015

0.01

0.0001183

12.678515

0.5

0.000243

1.3

7.8

1.2879729

3000

0.0015

0.01

0.0003282

4.5701447

0.5

0.000222

−23.43986

11.6

7.8

11.492681

3000

0.0015

0.01

0.0001183

12.676018

0.5

0.0002455

1.3

7.9

1.287663

3000

0.0015

0.01

0.0003282

4.5699643

0.5

0.0002228

−25.11606

11.6

7.9

11.489916

3000

0.0015

0.01

0.0001184

12.673489

0.5

0.0002479

TABLE 5

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

2.5

6

2.4863055

3000

0.0015

0.01

0.0002824

5.31076

0.5

0.000215

1.75

6

1.7404139

3000

0.0015

0.01

0.0003099

4.8397485

0.5

0.0002117

3.25

6

3.2321972

3000

0.0015

0.01

0.0002581

5.8127371

0.5

0.0002167

−5.030292

2.5

6.1

2.4858457

3000

0.0015

0.01

0.0002825

5.3104598

0.5

0.0002163

1.75

6.1

1.740092

3000

0.0015

0.01

0.0003099

4.8395523

0.5

0.0002126

3.25

6.1

3.2315994

3000

0.0015

0.01

0.0002581

6.8123231

0.5

0.0002182

−5.551442

2.5

6.2

2.4853783

3000

0.0015

0.01

0.0002825

5.3101547

0.5

0.0002175

1.75

6.2

1.7397648

3000

0.0015

0.01

0.00031

4.8393528

0.5

0.0002136

3.25

6.2

3.2309918

3000

0.0015

0.01

0.0002581

5.8119023

0.5

0.0002196

−6.072742

2.5

6.3

2.4849033

3000

0.0015

0.01

0.0002825

5.3098447

0.5

0.0002187

1.75

6.3

1.7394323

3000

0.0015

0.01

0.00031

4.8391501

0.5

0.0002145

3.25

6.3

3.2303743

3000

0.0015

0.01

0.0002581

5.8114747

0.5

0.0002211

−6.594196

2.5

6.4

2.4844207

3000

0.0015

0.01

0.0002825

5.3095297

0.5

0.00022

1.75

6.4

1.7390945

3000

0.0015

0.01

0.00031

4.8389442

0.5

0.0002155

3.25

6.4

3.2297469

3000

0.0015

0.01

0.0002581

5.8110403

0.5

0.0002226

−7.115804

2.5

6.5

2.4839306

3000

0.0015

0.01

0.0002825

5.3092098

0.5

0.0002212

1.75

6.5

1.7387514

3000

0.0015

0.01

0.00031

4.8387351

0.5

0.0002164

3.25

6.5

3.2291098

3000

0.0015

0.01

0.0002581

5.8105991

0.5

0.000224

−7.637568

2.5

6.6

2.4834329

3000

0.0015

0.01

0.0002825

5.308885

0.5

0.0002225

1.75

6.6

1.738403

3000

0.0015

0.01

0.00031

4.8385228

0.5

0.0002174

3.25

6.6

3.2284628

3000

0.0015

0.01

0.0002582

5.8101512

0.5

0.0002255

−8.159491

2.5

6.7

2.4829276

3000

0.0015

0.01

0.0002826

5.3085552

0.5

0.0002237

1.75

6.7

1.7380493

3000

0.0015

0.01

0.00031

4.8383072

0.5

0.0002183

3.25

6.7

3.2278059

3000

0.0015

0.01

0.0002582

5.8096964

0.5

0.000227

−8.681573

2.5

6.8

2.4824148

3000

0.0015

0.01

0.0002826

5.3082205

0.5

0.0002249

1.75

6.8

1.7376904

3000

0.0015

0.01

0.00031

4.8380884

0.5

0.0002193

3.25

6.8

3.2271392

3000

0.0015

0.01

0.0002582

5.8092349

0.5

0.0002285

−9.203816

2.5

6.9

2.4818944

3000

0.0015

0.01

0.0002826

5.3078809

0.5

0.0002262

1.75

6.9

1.7373261

3000

0.0015

0.01

0.0003101

4.8378664

0.5

0.0002202

3.25

6.9

3.2264627

3000

0.0015

0.01

0.0002582

5.8087666

0.5

0.0002299

−9.726223

In the same manner, the ejection angle θ of 3.4° is obtained as the other limit value from Table 8.

It is clearly found from Table 6 that the ejection angle θ at which the impact positions of the large and small droplets substantially accord with each other exists between 5.0°and 5.1°.

TABLE 6

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

2.5

5

2.4904873

3000

0.0015

0.01

0.0002823

5.3134904

0.5

0.0002027

1.75

5

1.7433411

3000

0.0015

0.01

0.0003098

4.8415332

0.5

0.0002022

3.25

5

3.2376335

3000

0.0015

0.01

0.0002579

5.8165027

0.5

0.000202

0.173257

2.5

5.1

2.4901032

3000

0.0015

0.01

0.0002823

5.3132396

0.5

0.0002039

1.75

5.1

1.7430723

3000

0.0015

0.01

0.0003098

4.8413693

0.5

0.0002031

3.25

5.1

3.2371342

3000

0.0015

0.01

0.0002579

5.8161568

0.5

0.0002035

−0.346473

2.5

5.2

2.4897116

3000

0.0015

0.01

0.0002823

5.3129839

0.5

0.0002051

1.75

5.2

1.7427981

3000

0.0015

0.01

0.0003098

4.8412021

0.5

0.0002041

3.25

5.2

3.2366251

3000

0.0015

0.01

0.0002579

5.8158041

0.5

0.0002049

−0.866338

2.5

5.3

2.4893124

3000

0.0015

0.01

0.0002823

5.3127232

0.5

0.0002064

1.75

5.3

1.7425187

3000

0.0015

0.01

0.0003099

4.8410317

0.5

0.000205

3.25

5.3

3.2361061

3000

0.0015

0.01

0.0002579

5.8154446

0.5

0.0002064

−1.386338

2.5

5.4

2.4889056

3000

0.0015

0.01

0.0002824

5.3124575

0.5

0.0002076

1.75

5.4

1.7422339

3000

0.0015

0.01

0.0003099

4.8408581

0.5

0.000206

3.25

5.4

3.2355772

3000

0.0015

0.01

0.000258

5.8150782

0.5

0.0002079

−1.906477

2.5

5.5

2.4884912

3000

0.0015

0.01

0.0002824

5.312187

0.5

0.0002088

1.75

5.5

1.7419438

3000

0.0015

0.01

0.0003099

4.8406812

0.5

0.0002069

3.25

5.5

3.2350385

3000

0.0015

0.01

0.000258

5.8147051

0.5

0.0002093

−2.426754

2.5

5.6

2.4880692

3000

0.0015

0.01

0.0002824

5.3119115

0.5

0.0002101

1.75

5.6

1.7416484

3000

0.0015

0.01

0.0003099

4.8405011

0.5

0.0002079

3.25

5.6

3.23449

3000

0.0015

0.01

0.000258

5.8143251

0.5

0.0002108

−2.947173

2.5

5.7

2.4876397

3000

0.0015

0.01

0.0002824

5.311631

0.5

0.0002113

1.75

5.7

1.7413478

3000

0.0015

0.01

0.0003099

4.8403178

0.5

0.0002088

3.25

5.7

3.2339315

3000

0.0015

0.01

0.000258

5.8139383

0.5

0.0002123

−3.467734

2.5

5.8

2.4872025

3000

0.0015

0.01

0.0002824

5.3113456

0.5

0.0002126

1.75

5.8

1.7410418

3000

0.0015

0.01

0.0003099

4.8401313

0.5

0.0002098

3.25

5.8

3.2333633

3000

0.0015

0.01

0.000258

5.8135447

0.5

0.0002137

−3.988440

2.5

5.9

2.4867578

3000

0.0015

0.01

0.0002824

5.3110553

0.5

0.0002138

1.75

5.9

1.7407305

3000

0.0015

0.01

0.0003099

4.8399415

0.5

0.0002107

3.25

5.9

3.2327852

3000

0.0015

0.01

0.000258

5.8131443

0.5

0.0002152

−4.509292

TABLE 7

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

2.5

4

2.4939105

3000

0.0015

0.01

0.0002822

5.3157262

0.5

0.0001903

1.75

4

1.7457373

3000

0.0015

0.01

0.0003097

4.8429946

0.5

0.0001927

3.25

4

3.2420836

3000

0.0015

0.01

0.0002578

5.8195864

0.5

0.0001873

5.363547

2.5

4.1

2.4936023

3000

0.0015

0.01

0.0002822

5.3155249

0.5

0.0001915

1.75

4.1

1.7455216

3000

0.0015

0.01

0.0003097

4.842863

0.5

0.0001936

3.25

4.1

3.241683

3000

0.0015

0.01

0.0002578

5.8193088

0.5

0.0001888

4.845067

2.5

4.2

2.4932866

3000

0.0015

0.01

0.0002822

5.3153187

0.5

0.0001928

1.75

4.2

1.7453006

3000

0.0015

0.01

0.0003097

4.8427282

0.5

0.0001946

3.25

4.2

3.2412726

3000

0.0015

0.01

0.0002578

5.8190243

0.5

0.0001902

4.326469

2.5

4.3

2.4929632

3000

0.0015

0.01

0.0002822

5.3151075

0.5

0.000194

1.75

4.3

1.7450743

3000

0.0015

0.01

0.0003098

4.8425902

0.5

0.0001955

3.25

4.3

3.2408522

3000

0.0015

0.01

0.0002578

5.818733

0.5

0.0001917

3.807752

2.5

4.4

2.4926323

3000

0.0015

0.01

0.0002822

5.3148913

0.5

0.0001952

1.75

4.4

1.7448426

3000

0.0015

0.01

0.0003098

4.8424489

0.5

0.0001965

3.25

4.4

3.240422

3000

0.0015

0.01

0.0002578

5.8184349

0.5

0.0001932

3.288914

2.5

4.5

2.4922938

3000

0.0015

0.01

0.0002822

5.3146702

0.5

0.0001965

1.75

4.5

1.7446057

3000

0.0015

0.01

0.0003098

4.8423044

0.5

0.0001974

3.25

4.5

3.2399819

3000

0.0015

0.01

0.0002578

5.8181299

0.5

0.0001946

2.769954

2.5

4.6

2.4919477

3000

0.0015

0.01

0.0002822

5.3144442

0.5

0.0001977

1.75

4.6

1.7443634

3000

0.0015

0.01

0.0003098

4.8421566

0.5

0.0001984

3.25

4.6

3.293532

3000

0.0015

0.01

0.0002578

5.8178181

0.5

0.0001961

2.250869

2.5

4.7

2.491594

3000

0.0015

0.01

0.0002823

5.3142131

0.5

0.0001989

1.75

4.7

1.7441158

3000

0.0015

0.01

0.0003098

4.8420056

0.5

0.0001993

3.25

4.7

3.2390722

3000

0.0015

0.01

0.0002578

5.8174995

0.5

0.0001976

1.731659

2.5

4.8

2.4912327

3000

0.0015

0.01

0.0002823

5.3139772

0.5

0.0002002

1.75

4.8

1.7438629

3000

0.0015

0.01

0.0003098

4.8418514

0.5

0.0002003

3.25

4.8

3.2386025

3000

0.0015

0.01

0.0002579

5.8171741

0.5

0.0001991

1.212322

2.5

4.9

2.4908638

3000

0.0015

0.01

0.0002823

5.3137363

0.5

0.0002014

1.75

4.9

1.7436046

3000

0.0015

0.01

0.0003098

4.8416939

0.5

0.0002012

3.25

4.9

3.2381229

3000

0.0015

0.01

0.0002579

5.8168418

0.5

0.0002005

0.692855

TABLE 8

Quantity

Deviation

Ejec-

Ejec-

Electro-

of

between

tion

tion

Vertical

static

Electric

Flying

Average

Speed of

Impact

Impact

Rate

Angle

Rate

Field

Gap

Charges

Time

Rate

Carriage

Position

Positions

(m/s)

(°)

(m/s)

(V)

(m)

(C/kg)

(S)

(m/s)

(m/s)

(m)

(μm)

2.5

3

2.496574

3000

0.0015

0.01

0.0002821

5.3174664

0.5

0.000178

1.75

3

1.7476018

3000

0.0015

0.01

0.0003097

4.8441319

0.5

0.0001832

3.25

3

3.2455463

3000

0.0015

0.01

0.0002576

5.8219865

0.5

0.0001726

10.542274

2.5

3.1

2.4963419

3000

0.0015

0.01

0.0002821

5.3173147

0.5

0.0001792

1.75

3.1

1.7474393

3000

0.0015

0.01

0.0003097

4.8440328

0.5

0.0001841

3.25

3.1

3.2452445

3000

0.0015

0.01

0.0002577

5.8217773

0.5

0.0001741

10.024873

2.5

3.2

2.4961021

3000

0.0015

0.01

0.0002821

5.317158

0.5

0.0001804

1.75

3.2

1.7472715

3000

0.0015

0.01

0.0003097

4.8439304

0.5

0.0001851

3.25

3.2

3.2449328

3000

0.0015

0.01

0.0002577

5.8215612

0.5

0.0001756

9.507372

2.5

3.3

2.4958548

3000

0.0015

0.01

0.0002821

5.3169964

0.5

0.0001817

1.75

3.3

1.7470984

3000

0.0015

0.01

0.0003097

4.8438248

0.5

0.000186

3.25

3.3

3.2446112

3000

0.0015

0.01

0.0002577

5.8213383

0.5

0.000177

8.989769

2.5

3.4

2.4955998

3000

0.0015

0.01

0.0002821

5.3168299

0.5

0.0001829

1.75

3.4

1.7469199

3000

0.0015

0.01

0.0003097

4.8437159

0.5

0.000187

3.25

3.4

3.2442798

3000

0.0015

0.01

0.0002577

5.8211086

0.5

0.0001785

8.472062

2.5

3.5

2.4953373

3000

0.0015

0.01

0.0002821

5.3166583

0.5

0.0001841

1.75

3.5

1.7467361

3000

0.0015

0.01

0.0003097

4.8436038

0.5

0.0001879

3.25

3.5

3.2439385

3000

0.0015

0.01

0.0002577

5.820872

0.5

0.00018

7.954250

2.5

3.6

2.4950671

3000

0.0015

0.01

0.0002821

5.3164818

0.5

0.0001854

1.75

3.6

1.746547

3000

0.0015

0.01

0.0003097

4.8434884

0.5

0.0001889

3.25

3.6

3.2435872

3000

0.0015

0.01

0.0002577

5.8206285

0.5

0.0001814

7.436331

2.5

3.7

2.4947894

3000

0.0015

0.01

0.0002822

5.3163004

0.5

0.0001866

1.75

3.7

1.7463525

3000

0.0015

0.01

0.0003097

4.8433698

0.5

0.0001898

3.25

3.7

3.2432262

3000

0.0015

0.01

0.0002577

5.8203783

0.5

0.0001829

6.918302

2.5

3.8

2.494504

3000

0.0015

0.01

0.0002822

5.3161139

0.5

0.0001878

1.75

3.8

1.7461528

3000

0.0015

0.01

0.0003097

4.843248

0.5

0.0001908

3.25

3.8

3.2428552

3000

0.0015

0.01

0.0002577

5.8201211

0.5

0.0001844

6.400163

2.5

3.9

2.494211

3000

0.0015

0.01

0.0002822

5.3159226

0.5

0.0001891

1.75

3.9

1.7459477

3000

0.0015

0.01

0.0003097

4.8431229

0.5

0.0001917

3.25

3.9

3.2424743

3000

0.0015

0.01

0.0002577

5.8195872

0.5

0.0001858

5.881912

As apparent from the above description, the same simulation as described above is conducted while the moving speed of the carriage is changed, thus obtaining the limit values of the ejection angles illustrated in FIG.

11

(

a

).

As a consequence, it is found from FIG.

11

(

b

) that in order to eject the small droplets (20 ng) from the large-diameter nozzle and make the deviation between the impact positions caused by the variations in ejection rate fall within the above-described allowable range at the moving speed of the carriage of 400 mm/s or higher, the ejection angle of the ink droplet is needed to be at least 2.4° or more.

(Second Embodiment)

FIG. 12

shows a cross-sectional view showing an ink jet head

1

in a second embodiment according to the present invention. Differences from the ink jet head

1

shown in

FIG. 2

reside in that a nozzle surface

11

is disposed in parallel to an opposite electrode

4

, and further, that an axis

10

a

of a nozzle

10

is inclined with respect to -the nozzle surface

11

. The other configuration is the same as that in the first embodiment. With this configuration, an ink droplet

17

can be ejected slantwise in an electrostatic field, thus producing the same advantageous results as those in the first embodiment. Moreover, with the configuration in the first embodiment, the width

801

of the nozzle plate

8

in the moving direction

203

of the ink jet head

1

need be increased in the case where the plurality of nozzles

10

are disposed in the moving direction of the ink jet head

1

, thereby inducing nonuniform electrostatic field unfavorably. However, in the present embodiment, since the nozzle surface

11

is parallel to the opposite electrode

4

, a uniform electrostatic field can be achieved even if the plurality of nozzles

10

are disposed in the moving direction of the ink jet head

1

and the width of the nozzle plate

8

in the moving direction of the ink jet head

1

is increased.

As described above, in this second embodiment, the nozzle surface

11

is disposed in parallel to the opposite electrode

4

and the axis of the nozzle

10

is inclined with respect to the nozzle surface

11

, thus readily achieving the configuration in which the plurality of nozzles

10

are provided in the moving direction of the ink jet head

1

.

(Third Embodiment)

FIG. 13

schematically shows the configuration of an ink jet recording apparatus in a third embodiment according to the present invention. Differences from the ink jet recording apparatus in the first embodiment reside in that the speed of a carriage can be varied as relative moving speed switching means claimed under the section of “What Is Claimed Is,” and that an eccentric cam

18

and an ink jet head rotating shaft

19

are provided as ejection angle switching means claimed under the section of “What Is Claimed Is.”

Explanation will be made on the operation of the ink jet recording apparatus configured as described above. In some cases, recording resolution may be changed as required for a high quality of an image or a high speed in the ink jet recording apparatus. In this case, the recording resolution is increased while the moving speed of the carriage

2

is decreased if a high quality of an image is required. The recording resolution is decreased while the moving speed of the carriage

2

is increased if a high speed is required. In the case where the speed of the carriage

2

is varied, it is preferable that the ejection angle of the slantwise ejection should be changed according to the speed of the carriage

2

in view of the deviation of the impact positions. In the present embodiment, the eccentric cam

18

is rotated by a device, not shown, according to the speed of the carriage

2

, and then, the ink jet head

1

is rotated accordingly on the ink jet head rotating shaft

19

, so that the election angle of the slantwise ejection can be switched to a desired angle. For example, if the speed of the carriage

2

is high, the ink is ejected more slantwise.

As described above, the ink jet recording apparatus in the present embodiment is configured such that the slantwise ejection angle is switched to a desired angle according to the speed of the carriage

2

. Thus, it is possible to provide the ink jet recording apparatus in which the deviation of the impact positions is small even at the mode of a high quality of an image and the mode of a high speed and the dot modulation can be achieved.

(Fourth Embodiment)

FIG. 14

schematically shows the configuration of an ink jet recording apparatus In a fourth embodiment according to the present invention. Differences from the ink jet recording apparatus shown in

FIG. 13

reside in that ink droplets

17

are ejected during both an advancing operation and a returning operation of a carriage

2

with respect to a recording sheet

7

, and that an ink jet head

1

is rotated in such a manner that the ejection directions of the slantwise ejection during both the advancing operation and the returning operation become symmetric with respect to a plane perpendicular to the moving direction of the carriage

2

.

Explanation will be made on the operation of the ink jet recording apparatus configured as described above. An eccentric cam

18

is rotated in such a manner that the ink jet head

1

is positioned at a position indicated by a solid line during the operation from a point A to a point B or at a position indicated by a broken line during the operation from the point B to the point A. At this moment, it is preferable that there should be provided a sensor or the like for detecting the moving direction relative to the recording sheet, and that the eccentric cam

18

should switch the ejection direction of the ink to be ejected from a nozzle according to the relative movement direction determined by the sensor.

As described above, in this fourth embodiment, the ink ejection direction is inclined with respect to the plane perpendicular to the moving direction of the carriage

2

, and is set in the moving direction of the ink jet head relative to the recording sheet, in particular, the slantwise ejection directions during the advancing and returning operations of the carriage

2

are symmetrical with respect to the plane perpendicular to the moving direction of the carriage

2

. Consequently, it is possible to provide the ink jet recording apparatus in which the deviation of the impact positions is small and the dot modulation can be achieved even if so-called shuttle recording is performed.

As described above, according to the present invention, it is possible to provide the ink jet recording apparatus comprising: the ink jet head including the pressure chamber containing the ink therein, the nozzle communicating with the pressure chamber and being adapted to eject the ink, and the pressure applying means for applying the pressure to the pressure chamber; the relative movement means for relatively moving the ink jet head and the recording sheet; the opposite electrode disposed at the position opposite to the ink jet head; and the voltage applying means for applying the voltage between the ink and the opposite electrode, wherein the ink is ejected from the nozzle in the direction slantwise with respect to the plane perpendicular to the relative movement direction by the relative movement means and in the relative movement direction of the ink jet head with respect to the recording sheet by the relative movement means, thereby reducing the deviation of the impact positions and generation of clogging and enhancing the manufacturing yield if the small droplets are ejected from the large-diameter nozzle.

Furthermore, the pressure varying means for varying the pressure of the pressure applying means is provided so as to vary the quantity of the ink to be ejected from the nozzle, thus providing the ink jet recording apparatus in which the dot modulation can be achieved.

Moreover, the axis of the nozzle is inclined with respect to the nozzle surface, so that it is possible to readily achieve the configuration where the plurality of nozzles are provided in the moving direction of the ink jet head.

Additionally, there are provided the relative moving speed switching means for switching the relative moving speed of the ink jet head relative to the recording sheet by the relative movement means and the ejection angle switching means for switching the ejection angle of the ink according to the relative moving speed of the ink jet head relative to the recording sheet by the relative movement means, thus providing the ink jet recording apparatus and recording method in which the deviation of the impact positions is small and the dot modulation can be achieved even at the mode of the high quality of an image and the mode of the high speed.

Furthermore, the ink jet head is operated in a shuttling manner with respect to, e.g., the recording sheet by the relative movement means, and the ink is ejected from the nozzle during both the advancing operation and the returning operation, wherein the ejection directions of the ink droplets during the advancing operation and the returning operation are symmetrical with respect to the plane perpendicular to the relative movement direction by the relative movement means, thus providing the ink jet recording apparatus and recording method in which the deviation of the impact positions is small and the dot modulation can be achieved even in the shuttle recording operation.

As apparent from the above description, the present invention has the advantage in that it is possible to further reduce the deviation between the impact positions of the ink droplets in the case where the small droplets are ejected from the large-diameter nozzle.

Moreover, the present invention has the advantage in that the deviation between the impact positions of the large and small ink droplets on the recording sheet can be further reduced to thus achieve the dot modulation.

Number	Name	Date	Kind
5619234	Nagato et al.	Apr 1997	A
5975683	Smith et al.	Nov 1999	A
6086186	Bergman et al.	Jul 2000	A
6164773	Oikawa	Dec 2000	A

Ink jet recording apparatus and ink jet recording method

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Abstract

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Priority Claims (1)

US Referenced Citations (4)