Information
-
Patent Grant
-
6582054
-
Patent Number
6,582,054
-
Date Filed
Friday, July 27, 200122 years ago
-
Date Issued
Tuesday, June 24, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Birch, Stewart, Kolasch & Birch, LLP
-
CPC
-
US Classifications
Field of Search
US
- 347 21
- 347 43
- 347 103
- 347 110
-
International Classifications
-
Abstract
An image forming method and apparatus for ejecting a recording fluid constituted by a plurality of inks from a common ink ejection port while a mixing ratio of the plurality of inks is changed with respect to one pixel based on an image signal, and transporting the plurality of inks to an image receiving medium which is moved with respect to the ink ejection port to form an image. An opening area Ai of a channel of an image forming ink is smaller than the opening area of the channel of an image non-forming ink in a confluence (mixing section) of the plurality of inks, and the opening area Ai has the following relationship with a minimum ejection volume Vi of the image forming ink:Ai≦1.2×Vi(⅔),so that with an excessively small amount of the image forming ink to be mixed with the image non-forming ink, a leading end of the ink is cut well, an image density having fidelity to the image signal can be obtained, and an image quality can be enhanced.
Description
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for generating a recording fluid having a predetermined density and/or a predetermined color by changing a mixing ratio of a plurality of inks based on an image signal and leading the thus obtained fluid to an image receiving medium to form an image.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,109,282 (hereinafter referred to as a prior art reference 1) discloses a printer having a structure such that a valve called a flap valve is disposed in a flow channel for leading two types of liquid, i.e., clear ink and black ink onto a substrate for forming an image. The flow channel for each ink is opened/closed by displacing this valve so that the two types of liquid are mixed in a desired density to be transferred onto the substrate. This enables printout of an image having gray scale information which is the same as that of the image information displayed on a TV screen. In this reference is disclosed that a voltage is applied between the flap valve and an electrode disposed on a surface opposite to the flap valve and the valve itself is mechanically deformed by an electrostatic attracting force to cause displacement of the valve. Furthermore, the ink is absorbed in paper by a capillary phenomenon between fibers of the print paper.
U.S. Pat. No. 4,614,953 (hereinafter referred to as a prior art reference 2) discloses a printer head apparatus by which only a desired amount of multiple types of ink having different colors and solvent is led to a third chamber to be mixed therein. In this reference is disclosed that a chamber and a diaphragm-type piezoelectric effect device attached to this chamber are used as means for check-weighing the desired amount of ink and a pressure pulse obtained by driving this piezoelectric device is utilized.
Unexamined Japanese Patent Publication (KOKAI) No. 201024/1993 (hereinafter referred to as a prior art reference 3) discloses an ink jet print head including: a liquid chamber filled with a carrier liquid; ink jet driving means disposed in the liquid chamber; a nozzle communicating with the liquid chamber; and a mixing portion for mixing ink to the carrier liquid in this nozzle. In this reference is also disclosed that adjusting means having a check valve structure for adjusting an amount of mixture of ink to a desired value is provided.
Similarly, Unexamined Japanese Patent Publication (KOKAI) No. 125259/1995 (hereinafter referred to as a prior art reference 4) discloses an ink jet recording head including: first and second supplying means for supplying inks having first and second densities, respectively; and controlling means for controlling an amount of supply of the second ink by the second supplying means so that a desired ink density can be obtained.
In this reference 4, employment of a micro-pump which has an exclusive heating device and is driven by its heat energy is disclosed. As this micro-pump, there is disclosed an example such that the heat energy is generated by the heating device and a pressure obtained by nucleate boiling caused by the heat energy is used to drive, for example, a piston-type valve or a cantilever-like valve. Furthermore, this reference 4 describes that an inflow of ink can effectively be controlled in an area where the inflow is particularly small by adopting an actuator consisting of a shape memory alloy to this valve.
Unexamined Japanese Patent Publication (KOKAI) No. 207664/1991 (hereinafter referred to as a prior art reference 5) discloses a structure which is similar to that in the prior art reference 2 but does not use a third chamber for mixing a plurality of types of ink.
Unexamined Japanese Patent Publication (KOKAI) No. 156131/1997 (hereinafter referred to as a prior art reference 6) discloses an ink jet printer comprising a plurality of printer heads for forming an image having multiple colors based on image data. Ink and diluent are mixed at a predetermined ratio to obtain diluted ink which is jetted from a nozzle so that a recording image is formed on a recording medium. The ink jet printer ejects the diluent from at least one printer head out of the multiple printer heads when all-white image data, that is, data representing that amount of mixture of ink is too small to realize a clear printing density, is input. As a result, a rapid change in tone (a tone jump) is prevented and the additional consumption of the diluent is suppressed to improve drying characteristics.
In the prior art disclosed in the prior art reference 1, the ejection ports for two types of liquid are separately open directly to the print paper, and the respective types of liquid are separately attracted on the print paper by the capillary phenomenon immediately after ejection. Therefore, a quantity of attraction of each liquid on the paper readily fluctuates under influence of a paper quality of the print paper, which results in the unstable image quality or difficulty of formation of an image having high fidelity to the image signal.
In any of the prior art references 2 to 6, a plurality of inks are mixed beforehand or caused to be confluent, and thereafter the mixed liquid (including the confluent liquid) is led onto the print paper. However, when a mixing ratio of one ink is remarkably small (ejection amount is remarkably small), the ink cannot smoothly be confluent with other ink. That is, when the ejection amount of the ink is small, an amount (ingress amount) of the ink advancing to the mixing portion (or a confluence portion) for mixing with the other ink becomes small. Therefore, a leading end of the ink cannot cut in a flow of the other ink by a surface tension of the ink. Therefore, the density of a mixed liquid (confluent liquid) cannot follow the image signal with fidelity, and a problem that an image quality is deteriorated occurs.
Furthermore, in any of the prior arts disclosed in the prior art references 2 to 6, a plurality of inks are brought into contact with one another in the mixing section (the confluence portion), and each ink is ejected by a predetermined amount to be mixed. That is, the ejection port for each ink is formed and assembled in the mixing section. Each ink cannot therefore be prevented from being naturally diffused from one another.
For example, even if a given ink is not ejected into a mixing chamber in accordance with the image signal, this ink is naturally diffused in the mixing chamber. Thus, the density and/or color of the finally mixed ink liquid differs from the image signal, and an image which has fidelity to the image signal cannot be formed. Even if the natural diffusion of the ink is small, distortion of a contact interface occurs due to a vibration in the mixing portion or any other disturbance, and therefore the undesired mixing of ink is facilitated and the above-described problem becomes more prominent.
Additionally, the prior art reference 3 discloses that adjusting means functioning as a check valve is disposed in the vicinity of the opening of the ink channel formed in the mixing portion in order to mainly prevent the inks from being naturally diffused from one another. However, the adjusting means having the check valve structure complicates a print head configuration and leads to problems such as difficulty in manufacturing, reduction of productivity or increase of a manufacturing cost.
Furthermore, the prior art reference 6 discloses that a colorless diluent continues to flow in case of all-white image data in order to avoid a rapid change in tone (tone jump), but the ink which is not colorless and transparent is continuously diffused in this diluent in this case, and hence the above-mentioned problems can not be prevented.
To solve the problem, the present applicant has considered that the small amount of image forming ink is constantly and continuously supplied to the other ink such as a transparent liquid (image non-forming ink) (e.g., Unexamined Japanese Patent Publication (KOKAI) No. 246920/2000 corresponding to EP 101653A2 and U.S. patent application Ser. No. 09/472,970). For example, when the density is controlled in 256 tones, and the image signal indicates “white”, the image forming ink corresponding to a smallest density is continuously supplied. In this case, the ejection amount of the image forming ink is remarkably small, and the problem occurs that the leading end of the image forming ink does not cut and cannot be mixed (confluent) with the image non-forming ink.
Particularly in this case, when the “white” image signal continues, the leading end of the image forming ink enters the image non-forming ink by a small amount in accordance with the image signal. When the ingress amount of the image forming ink exceeds a certain limit, the ink is cut and ejected. Therefore, the cut ink soils the image and deteriorates the image quality.
SUMMARY OF THE INVENTION
The present invention has been accomplished under the aforementioned circumstances, and an object thereof is to provide an image forming apparatus in which with a small amount of image forming ink, a leading end of the ink is cut well, and an image density having fidelity to an image signal can be obtained, and an image quality can be enhanced.
According to the present invention, the object is attained by an image forming apparatus for ejecting a recording fluid constituted by a plurality of inks from a common ink ejection port while a mixing ratio of the plurality of inks is changed with respect to one pixel based on an image signal, and transporting the recording fluid to an image receiving medium which is moved with respect to the ink ejection port to form an image; said image forming apparatus comprising:
an ink ejection port for ejecting the recording fluid to the image receiving medium;
a first ink channel for supplying an image non-forming ink to said ink ejection port, the image non-forming ink being an ink for forming no image after dried out;
a second ink channel for supplying an image forming ink to said ink ejection port, the image forming ink being an ink for forming the image after dried out; and
a mixing section disposed upstream of said ink ejection port, for mixing the image non-forming ink supplied from said first ink channel and the image forming ink supplied from said second ink channel;
wherein an opening area Ai of said second ink channel is smaller than the opening area of said first ink channel in said mixing section; and the opening area Ai of said second ink channel has the following relationship with a minimum ejection volume Vi of the image forming ink:
Ai
≦1.2×
Vi
(⅔)
.
The image non-forming ink is constantly supplied, and confluent with the image forming ink, until a predetermined density is obtained. Particularly, when a total flow rate of both inks is constant, the ink is steadily transported to the image receiving medium, and this is further suitable for enhancement of the image quality.
Print paper may be used as the image receiving medium, and the image can directly be formed on this print paper. However, it is also possible to provide a drum-like or belt-like intermediate image receiving medium between the ejection port and the image receiving medium. In this case, an ink liquid supplied from the ejection port is loaded onto an intermediate image receiving medium, and then the ink liquid is transferred to the image receiving medium. Preferably, the ink ejection ports may be separately provided for respective pixels aligned in a width direction of the image receiving medium (a direction perpendicular to a moving direction). The ink ejection ports may be formed into a slot-shaped opening which is elongated in the width direction of the image receiving medium when changing the density and/or the color only in the moving direction of the image receiving medium.
The image non-forming ink is or becomes colorless and transparent after dried out and forms no image (hereinafter referred to as image non-forming ink or clear ink), and the density can be controlled by changing a mixing ratio of the image non-forming ink. It is preferable to constantly add the image non-forming ink to the ink liquid so that a supply amount of the image non-forming ink should not become zero. In this case, when decoloration preventing agents such as antioxidant, ultraviolet ray absorber or other components are included in the image non-forming ink beforehand, a color degradation preventing property and other properties can be imparted to the image. A plurality of image forming inks are determined as inks having colors of yellow, magenta and cyan, and the mixing ratio of these inks can be changed during formation of a color image.
When flow rates of a plurality of inks are controlled, an image can be formed having density and/or color varying in both the moving direction and the width direction of the image receiving medium.
A plurality of inks ejected from the ink ejection port may be transported, that is, jetted onto the image receiving medium as droplets by an ink jet mode, but it is also possible to transport/apply the inks to the image receiving medium as a continuous flow instead of the droplets (continuous coating mode). In this continuous coating mode, a flow of liquid can be ejected or extruded as a continuous flow and transported to the image receiving medium through a slot-opening connecting the ink ejection ports provided for the respective pixels in the width direction.
The image forming ink is controlled in such a manner that a volumetric flow rate per unit time does not constantly turn to zero, and it is then possible to smoothly control the small amount of ink. In this case, a minimum addition amount of the image forming ink may be the same as or larger than a flow rate necessary for refreshing a volume of the image forming ink mixed into another ink by natural diffusion. However, the addition amount should be suppressed to such an extent that a change in density and/or color due to addition of this ink does not result in degradation of the image quality. Therefore, it is preferable to set the additional amount in such a manner that a change in optical density of the ink liquid due to addition of this ink is less than 0.1. Here, the optical density means a degree by which a substance absorbs light. When it is assumed that the optical density is represented as D, an intensity of an incident light is I
0
, and an intensity of a transmitted light is I, the optical density can be defined by D=log
10
(I
0
/I). Vibration is preferably absorbed in a portion where a plurality of inks becomes confluent, so that turbulence of a contact interface is prevented from occurring due to vibration and disturbance of the ink, and diffusion may be prevented.
The flow rates of a plurality of inks can be controlled by the various methods. For example, an ink supply pressure with respect to each ink channel can be maintained to be constant while a sectional area of each ink channel can be changed by a piezoelectric device. In this case, a diaphragm valve facing the ink channel is opened/closed by the piezoelectric device. The piezoelectric device can be driven by a mechanical natural frequency (a resonance frequency) of the device itself, and a time period for driving the device is changed by varying a pulse number of this frequency in order to control the flow rate. It is also possible to continuously control a quantity of distortion (opening of the diaphragm valve) of the piezoelectric device by an analog signal and, in this case, the flow rate is controlled by a voltage of the analog signal.
A flow rate supplied to each ink channel may be controlled by changing a discharged quantity of an ink feed pump. For example, the ink feed pump is driven by a pulse motor (stepping motor), and the ink flow rate can be controlled by the driving pulse number of this pulse motor. The ink feed pump includes: at least one check valve disposed in the ink channel; a cavity provided in the vicinity of this check valve; and a movable member for changing a volumetric capacity of the cavity, so that the pump discharges the ink by changing the volumetric capacity of the cavity. Such pump can be used as an ink feed pump.
The check valve used in the ink feed pump may be constituted by a geometrical form by which a resistance relative to an ink flow direction becomes small and that relative a reverse direction becomes large. Such a check valve has no movable portion and can be produced by utilizing a method for manufacturing an integrated circuit or a printed wiring board or that for manufacturing a micro-machine. The ink feed pump may be driven by the pulse motor.
When the ink feed pump driven by the pulse motor is provided, the ink feed pump may preferably be of a volumetric capacity type by which an ejection amount is proportional to a quantity of rotation of the motor. Suitable examples include a pump for squeezing a flexible tube appressed against the inner surface of a circular case on an inner peripheral side by an eccentric ring in a defined direction, a vane pump, a gear pump, and the like.
The ink feed pump disposed in each ink channel can be formed by the piezoelectric device and the check valve. In this case, the piezoelectric device is a diaphragm valve driven by a mechanical resonance frequency inherent to the device. When the pulse number (pulse number in a defined time or a unit time) of the driving frequency of each piezoelectric device is controlled, an ejection volume flow rate from each ink channel can be controlled.
The opening area of the ink channel of the image forming ink in the ink confluence portion is set to be smaller than that of the ink channel of the image non-forming ink. Therefore, an ink ejection length of the image forming ink increases, and the amount of the image forming ink advancing into the another ink increases. Therefore, the leading end of the image forming ink is easily cut, the density having fidelity to the image signal can be obtained, and the image quality is enhanced.
The flow rate (volume flow rate per unit time) of the image forming ink whose ejection amount is minimum is managed so as not to be constantly zero, and a mixture amount of this image forming ink can always be grasped and managed. In this case, since the natural diffusion of the image forming ink with respect to one pixel is considerably short, it is preferable to determine the flow rate required for refreshing the volumetric capacity by the diffusion as a minimum flow rate. As a result, a fluctuation in color and/or density due to natural diffusion of the ink can be suppressed, and a high-quality image can be formed.
In the present invention, the image formed on the image receiving medium includes graphical intelligence patterns such as alphanumeric characters, graphical display, line art, and other image information.
In another aspect of the present invention, there is provided an image forming method for ejecting a recording fluid constituted by a plurality of inks from a common ink ejection port while a mixing ratio of the plurality of inks is changed with respect to one pixel based on an image signal, and transporting the fluid to an image receiving medium which is moved with respect to the ink ejection port to form an image;
wherein said plurality of inks include an image non-forming ink which forms no image after dried out and at least one image forming ink which forms the image after dried out,
an opening area Ai of a channel of said image forming ink is smaller than the opening area of the channel of said image non-forming ink in a confluence of said plurality of inks; and
the opening area Ai of the channel of the image forming ink has the following relationship with a minimum ejection volume Vi of the image forming ink:
Ai
≦1.2×
Vi
(⅔)
.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a view showing a concept of an image forming apparatus according to a first embodiment of the present invention to which a continuous coating mode is applied;
FIG. 2
is an enlarged sectional view of an image forming section (recording head) for use in the image forming apparatus of
FIG. 1
;
FIG. 3
is a perspective view showing an image forming section (recording head) for zonally transporting an ink to print paper according to a second embodiment of the present invention;
FIG. 4
is an enlarged sectional view showing a state of coating applied by a recording head of
FIG. 3
;
FIG. 5
is a sectional view showing an image forming section (recording head) according to a third embodiment;
FIG. 6
is a sectional view showing an image forming section (recording head) according to a fourth embodiment;
FIG. 7
is a sectional view showing an image forming section (recording head) according to a fifth embodiment;
FIG. 8
is a sectional view showing an image forming section (recording head) according to a sixth embodiment having ink transporting means to which a piezo ink jet mode is applied;
FIG. 9
is a sectional view showing an image forming section (recording head) according to a seventh embodiment having the ink transporting means to which a thermal ink jet mode is applied;
FIG. 10
is a sectional view showing an image forming section (recording head) according to an eighth embodiment having ink transporting means to which a continuous ink jet mode is applied;
FIG. 11
is a sectional view showing an image forming section (recording head) according to a ninth embodiment having the ink transporting means to which an electrostatic attraction ink jet mode is applied;
FIG. 12
is a sectional view showing an image forming section (recording head) according to a tenth embodiment having the ink transporting means to which an ultrasonic ink jet mode is applied;
FIG. 13
is a sectional view showing an image forming section (recording head) according to an eleventh embodiment to which a continuous coating mode is applied;
FIG. 14
is a sectional view showing an image forming section (recording head) according to a twelfth embodiment to which the continuous coating mode is applied;
FIG. 15
is a sectional view showing an image forming section (recording head) according to a thirteenth embodiment to which the continuous coating mode is applied;
FIGS. 16
to
18
are perspective views showing various structures of a check valve for use in ink feed pumps
334
,
434
and
634
shown in
FIGS. 7
,
13
and
14
;
FIG. 19A
is an explanatory view showing a detailed structure of the check valve shown in
FIGS. 16
to
18
;
FIG. 19B
is an explanatory view showing another detailed structure of the check valve;
FIG. 20
is a view showing an example of arrangement of the image forming section (recording head) with respect to an image receiving medium;
FIG. 21
is a view showing another example of arrangement of the image forming section;
FIG. 22
is an enlarged view of the image forming section; and
FIG. 23
is an enlarged view showing another embodiment of the image forming section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
An image forming apparatus according to one embodiment of the present invention to which a continuous coating mode is applied will be described hereinafter with reference to
FIGS. 1 and 2
. In
FIG. 1
, reference numeral
10
designates a platen and
12
denotes a print paper as an image receiving medium wound around the platen
10
. The print paper
12
is fed in a direction of an arrowhead at a fixed speed by clockwise rotation of the platen
10
as shown in FIG.
1
.
Reference numeral
14
represents an undercoating section for applying a transparent undercoating liquid onto the print paper
12
in order to enhance the adherability of ink and improve an image quality. Reference numeral
16
denotes a recording head which serves as an image forming section for forming an image on the print paper
12
. First ink and second ink are mixed or combined in the recording head and led to the print paper
12
. Reference numeral
18
denotes a heater for heating the print paper
12
on which the image is formed by the image forming section
16
so that the ink is dried out.
As shown in
FIG. 2
, the recording head
16
includes: a first ink channel
20
; a second ink channel
22
; and flow control valves
24
and
26
as ink flow rate controlling means for changing channel sectional areas of the respective channels
20
and
22
. The first ink is an image non-forming ink (clear ink), that is, an ink which substantially forms no image when dried out. The first ink includes decoloration preventing agents such as antioxidant and ultraviolet ray absorber. The second ink is an image forming ink for substantially forming the image after dried out, for example, a black ink.
The first ink and second ink are respectively contained in ink tanks
28
and
30
, and fed to the first and second ink channels
20
and
22
with a fixed pressure from the ink tanks
28
and
30
by ink feed pumps
32
and
34
. As the pumps
32
and
34
used in this example, those having a structure in which a pressure adjusting valve is disposed on an ink discharge side (outlet port side of the pump) to maintain an ejection pressure constant are suitable.
The first ink channel
20
for supplying a clear ink and the second ink channel
22
for supplying a colored ink are set in such a manner that an opening area A
1
of the first ink channel
20
is larger than an opening area A
2
of the second ink channel
22
in a mixing section or confluence
21
of these channels. Therefore, a density having high fidelity to an image signal can be obtained by properly mixing the second ink (colored ink) with the first ink (clear ink), even if an ejection amount of the second ink is small.
More specifically, when the ejection amount of the second ink is reduced, and the ink channel area is not reduced, an ejection length of the ink becomes excessively small. Therefore, a flow of the second ink (colored ink) cannot smoothly be disconnected from the second ink channel at the mixing section (confluence with the first ink). The ejection amount of the second ink cannot be controlled in a small amount range. As a countermeasure, the opening area A
2
of the second ink channel is reduced so as to increase the ejection length of the second ink from the second ink channel to the confluence. Even if the ejection amount is small, a leading end of the second ink joins to and flows together with the first ink and is smoothly disconnected from the second ink channel.
For example, in a widely-used ink jet printer, an amount of ink used for forming one pixel is of the order of about 10 pL (pico-liter, =10
−12
L=10
−9
cm
3
). In order to represent a density change, for example, of 100 tones with this amount, the amount of colored ink must be controlled by the order of 10 pL×({fraction (1/100)})=0.1 pL. Assuming that the amount of 0.1 pL is perfectly ensphered, an ink droplet having a diameter of 5.8 μm (micrometer, =10
−3
mm) can be obtained.
It is assumed that a volume of the mixed first and second inks with respect to one pixel is 30 pL and a ratio of flow rate of the first ink (clear ink) is {fraction (99/100)} and that of the second ink (colored ink) is {fraction (1/100)}.
A flow rate V
1
of the first ink (clear ink) and a flow rate V
2
of the second ink (colored ink) can be respectively expressed as follows:
V
1
=29.7 pL=29.7×10
−12
L=29.7×10
−6
mm
3
V
2
=0.3 pL=0.3×10
−6
mm
3
Assuming that a section of the first ink channel
20
is a square having one side of 40 μm, the sectional area A
1
can be represented as A
1
=40×40×10
−6
mm
2
=16×10
−4
mm
2
. Therefore, a distance x
1
by which the first ink (clear ink) flows in the first ink channel
20
can be represented as follows:
x
1
=V
1
/A
1
=({fraction (29.7/16)})×10
−2
mm
=18.6×10
−3
mm
=18.6 μm
Here, it is presumed that the opening sectional area A
2
of the second ink channel
22
in the vicinity of the confluence
21
is equal to the sectional area A
1
of the first ink channel
20
. That is, A
2
=A
1
is assumed. A distance x
2
by which the second ink flows into the first ink channel
20
can be represented as follows.
x
2
=V
2
/A
2
=({fraction (0.3/16)})×10
−2
mm
=0.186 μm
That is, a ratio of the moving amount x
2
of the second ink (colored ink) to the distance x
1
of the first ink (clear ink) becomes {fraction (1/100)}.
In this case, the second ink flows into the first ink channel
20
only by the moving amount x
2
. However, since this moving amount, that is, an ingress amount x
2
is extremely small, the second ink cannot overcome the surface tension thereof and is not discharged into the first ink. At this time, the leading end of the second ink just slightly moves into or from the first ink channel
20
, and the first ink is not mixed with the second ink. That is, the leading end of the second ink cannot smoothly be disconnected.
As a countermeasure, a front edge of the second ink channel
22
, that is, a portion (opening area A
2
) in which the second ink channel
22
becomes confluent with the first ink channel
20
is formed to have a nozzle-like shape having a small diameter. This increases the ingress amount of the second ink into the first ink channel
20
to improve disconnection of the second ink. Thereby, an extremely small amount of the second ink can be controlled.
For example, the opening of area A
2
of the second ink channel
22
open to the confluence
21
can be determined as follows. To simplify the description, the opening has a circular shape with a radius R. Assuming that a minimum ejection volume of the second ink is Vi, half of ink particles need to be ejected toward the confluence from a nozzle in order to disconnect the ink particles having the minimum ejection volume Vi toward the confluence
21
from the ink channel
22
. That is, the radius of the ink particle needs to agree with an opening radius of the second ink channel.
Assuming that the opening area A
2
=πR
2
, and the ink particle is a sphere having the radius R, the minimum ejection volume Vi is Vi=({fraction (4/3)})πR
3
, and the opening area A
2
can therefore be represented as follows.
Ai
(=
A
2
)=(¾)
(⅔)
×π
⅓
×Vi
(⅔)
=1.21
×Vi
(⅔)
Therefore, when
A
2
≦1.2×
Vi
(⅔)
the ink particle of the second ink having the minimum ejection volume Vi projects from the opening in a sharper shape rather than a spherical shape, and can smoothly be disconnected toward the confluence. As a result, the excessive small amount of the second ink can be controlled.
Flow control valves
24
,
26
include, for example, piezoelectric devices
24
A,
26
A and diaphragms
24
B,
26
B which move into/from the ink channels
20
,
22
by distortions of the devices
24
A,
26
A, respectively. For these piezoelectric devices
24
A,
26
A, supply amounts S
1
and S
2
of the first and second inks supplied from the respective ink channels
20
and
22
are controlled by a controller
36
(FIG.
1
).
The controller
36
includes a processor
38
and drivers
40
,
42
as shown in FIG.
2
. The processor
38
calculates a mixing ratio (S
1
/S
2
) of the first and second inks based on a density signal (image signal). Here, the supply amount S
2
of the second black ink is constantly controlled so as not to be zero. Additionally, the supply amounts S
1
and S
2
of the first and second inks are determined so that a sum (S
1
+S
2
) becomes a fixed amount S
0
. Therefore, the flow of an ink fluid is stabilized, a turbulence or a whirlpool is not generated as described later, and stable formation of the image is enabled. The drivers
40
and
42
drive the piezoelectric devices
24
A and
26
A in order that the supply amounts from the respective channels
20
and
22
become S
1
and S
2
.
For example, the piezoelectric devices
24
A and
26
A are driven by a pulse having a mechanical resonance frequency inherent to the device, and the pulse number controls a number of times of opening/closing the diaphragms
24
B and
26
B, thereby controlling flow rate S
1
and S
2
. In this case, if the channel resistance of the ink channels
20
,
22
, ink feed pressure, condition for opening/closing the diaphragms
24
B,
26
B, and the like are satisfied, a total flow rate S
0
=S
1
+S
2
can be managed to be constant by controlling a sum of the pulse number for driving the piezoelectric devices
24
A,
26
A to indicate a fixed value.
A minimum supply amount S
20
of the second ink supply amount S
2
is set in such a manner that a change in optical density of the ink liquid due to addition of this ink becomes not more than 0.1, for example. In this case, the density change of all-white portion (background portion, and the like) in the image can be suppressed to such an extent that the change can hardly be identified visually. Incidentally, even in case of all white, a density tone is corrected in the processor
38
of the controller
36
in accordance with addition of a small amount (minimum supply amount) S
20
of the second ink supply amount S
2
if necessary.
The first and second inks whose flow rates are controlled are ejected as a continuous flow from an ink ejection port
44
in which the first and second channels
20
and
22
become confluent, and continuously applied onto the print paper
12
opposite to the ink ejection port
44
. In this case, the first and second inks are applied as a layer or laminar flow having no turbulence without being mixed with each other as shown in FIG.
2
. Here, the layer flow includes a flow which is mixed only in the vicinity of a border between the first and second inks. Although the first and second inks may uniformly be mixed, the surface of the image formed on the print paper
12
can be covered with any ink (the first ink in this example) by providing the layer flow in this manner. When any ink (the second ink in this example) is an ink having conformability to an undercoating layer of the print paper
12
, the image quality can be improved.
When a large number of sets of the first and second ink channels
20
,
22
and flow control valves
24
,
26
are provided to be aligned in a width direction of the print paper (direction perpendicular to the moving direction of the print paper), and are disposed for the respective pixels, the image can be formed by controlling the flow control valves
24
,
26
for the respective pixels based on the density signal (image signal). In this case, the ink ejection port
44
can independently be disposed to face the print paper
12
for each pixel. Further, these ink ejection ports
44
can be formed in the slot-shaped openings elongated in the width direction of the print paper
12
, and the ink liquid constituted by the first and second inks can be transported and applied onto the print paper
12
from this slot opening in a band shape.
Second Embodiment
FIG. 3
is a perspective view showing an image forming section (recording head)
16
A for use in a second embodiment for performing continuous zonal application as described above, and
FIG. 4
is an enlarged sectional view showing the state of application. The recording head
16
A includes ink ejection ports
44
which are independent for the respective pixels and a slot opening
44
A which is disposed in parallel with the ink ejection ports
44
for the respective pixels. The ink liquid continuously ejected from each ink ejection port
44
congregates in the band shape as the layer flow in the slot opening
44
A, and is ejected or extruded onto the print paper
12
.
An undercoating section
14
A is integrally incorporated in the recording head
16
A. The undercoating section
14
A includes an undercoating liquid channel
14
B which is disposed in parallel to the first and second ink channels
20
,
22
and a slot opening
14
C which is disposed in parallel to the slot
44
A. Here, the opening areas A
1
, A
2
in the confluence (mixing section)
21
of the first and second ink channels
20
,
22
have a relation A
1
>A
2
. Since an undercoating liquid L is transparent and colorless and used in a preliminary treatment for stably attaching the ink liquid to the surface of the print paper
12
, the undercoating liquid is positioned on the upstream side of the slot
44
A of the recording head
16
A with respect to the moving direction of the print paper
12
.
The undercoating liquid L also has a function of preventing turbulence or whirlpool from being generated in the flow of an ink liquid I
NK
during continuous application of the ink liquid I
NK
and improving the image quality. Specifically, as shown in
FIG. 4
, a part of the undercoating liquid L which has been just ejected from the slot
14
C flows to the upstream side of the slot
14
C to form a liquid pool L
1
in a gap G formed between the recording head
16
A and the print paper
12
. The whirlpool of the undercoating liquid L may be generated in the liquid pool L
1
, but this does not adversely affect a coating surface because the undercoating liquid L is transparent.
The undercoating liquid L comes in front of the slot
44
A as a stable layer flow having a fixed thickness with movement of the print paper
12
. Accordingly, the ink liquid I
NK
ejected from the slit
44
A is loaded onto the stable layer flow of the undercoating liquid L to be applied. Therefore, the image quality can be improved without generating distortion or whirlpool in the flow of the ink liquid I
NK
.
A third ink channel
23
may be provided in the recording head
16
A. A third ink supplied from the third ink channel
23
is led to the ink ejection port
44
through the flow control valve (not shown) and transported to the print paper
12
together with the first and second inks. When the third ink channel
23
is disposed, inks having colors of yellow, magenta and cyan is supplied to the first, second and third ink channels
20
,
22
and
23
, respectively, and a mixing ratio of the color inks is varied, thus enabling formation of a color image.
Third Embodiment
FIG. 5
is a sectional view showing an image forming section (recording head)
116
according to a third embodiment. In the recording head
116
, the flow rate of ink supplied to the first and second ink channels
20
,
22
is controlled by changing discharge quantity of ink feed pumps
132
,
134
, instead of using the flow control valves
24
,
26
described with reference to
FIGS. 1
to
4
.
The pumps
132
,
134
are of a volumetric capacity type having the discharged quantity which is proportional to a rotation amount. For example, a pump for squeezing a flexible tube appressed against the inner surface of a circular case from the inner peripheral side by an eccentric ring in a defined direction is suitable. The pumps
132
,
134
are driven by a pulse motor (stepping motor). The rotation amount of this motor can be controlled by a driving pulse number and, as a result, the discharged amount of the ink from the pumps
132
,
134
can be controlled.
A controller
136
is formed of a processor
138
and drivers
140
,
142
. The processor
138
determines a mixing ratio of the first and second inks based on the density signal (image signal) and calculates pulse numbers n
1
and n
2
to be fed to the motors of the respective pumps
132
,
134
in accordance with the mixing ratio. The drivers
140
,
142
send driving pulses having pulse numbers n
1
, n
2
to the respective motors to actuate the pumps
132
,
134
. Consequently, predetermined amounts of the first and second inks are supplied to the first and second ink channels
20
,
22
, and are transferred as a fixed flow rate of the ink liquid from the ink ejection port
44
to the print paper
12
. In this case, the sum of amounts of ejected ink is adjusted to be always constant in such manner that n
1
+n
2
becomes a fixed value n
0
.
Fourth Embodiment
FIG. 6
is a sectional view showing an image forming section (recording head)
216
according to a fourth embodiment. In this embodiment, ink feed pumps
232
,
234
for feeding the first and second inks are used instead of the flow rate control valves
24
,
26
of
FIGS. 1
to
4
. The pump
232
,
234
are formed by cylinder pump. Since the pumps
232
,
234
have the same structure, only one pump
232
will be described.
The cylinder pump
232
includes a cylinder
232
a
, a piston
232
b,
a feed screw
232
c
for pushing/pulling the piston
232
b,
and a pulse motor
232
d
for driving to rotate the feed screw
232
c.
The piston
232
b
is pushed and pulled in the cylinder
232
a
by the normal/reverse rotation of the motor
232
d.
The first ink is sucked in the cylinder
232
a
from the ink tank
28
through a one-way valve
232
e
with the movement of the piston
232
b,
and the ink is fed into the first ink channel
20
through one-way valve
232
f
with the movement of the piston
232
b.
A quantity of movement of the piston
232
b
is proportional to a quantity of rotation of the motor
232
d
. Therefore, the piston
232
b
is fully moved in a retreating direction of recession before forming one page of image, and the first ink is sufficiently sucked in the cylinder
232
a
. Thereafter, the motor
232
d
is rotated by a quantity of rotation corresponding to the density signal to move the piston
232
b
in a direction of ingress only by a predetermined quantity of movement, thereby feeding out a predetermined amount of the first ink to the ink channel
20
. The motor
232
d
can be driven by a controller
136
similar to that in the embodiment shown in FIG.
5
.
Fifth Embodiment
FIG. 7
is a sectional view showing an image forming section
316
(recording head) according to a fifth embodiment. In this embodiment, ink feed pumps
332
,
334
using the piezoelectric devices are used instead of the ink feed pumps
132
,
134
in
FIG. 5 and 232
,
234
in FIG.
6
. The pumps
332
,
334
include: piezoelectric devices
332
a,
334
a;
cavities
332
b
,
334
b
using each of the piezoelectric devices
332
a,
334
a
as one wall surface; inlets
332
c,
334
c
having such a shape as that conductance (inverse number of the resistance) varies with respect to the cavities
332
b,
334
b
in accordance with a flow direction of the ink; and outlets
332
d,
334
d
, respectively. Here, any surface treatment is preferably applied or a protection layer is provided on the surfaces of the piezoelectric devices
332
a,
334
a
with which the cavities
332
b,
334
b
come into contact.
Accordingly, when the piezoelectric devices
332
a
,
334
a
are driven and deformed, volumetric capacities of the cavities
332
b,
334
b
vary, and the ink flows from the inlets
332
c,
334
c
toward the outlets
332
d,
334
d.
The piezoelectric devices
332
a,
334
a
are driven by a pulse voltage having a mechanical resonance frequency for each device. Therefore, when the pulse number for driving the piezoelectric devices
332
a
and
334
a
is controlled, the supply amounts of the first and second inks can be controlled. In this case, a controller similar to the controller
36
shown in
FIG. 2
can be used.
Sixth to Tenth Embodiments
FIGS. 8
to
12
show each image forming section having ink transporting means according to sixth to tenth embodiments, respectively.
FIG. 8
shows a piezo ink jet mode;
FIG. 9
, a thermal ink jet mode;
FIG. 10
, a continuous ink jet mode;
FIG. 11
, an electrostatic attraction ink jet mode; and
FIG. 12
, an ultrasonic ink jet mode.
In these embodiments, the first and second inks controlled by the flow control valves
24
,
26
using the piezoelectric devices
24
A,
26
A, respectively, similar to those shown in
FIG. 2
are led to the ink ejection port
44
. Moreover, the opening areas A
1
, A
2
of the first and second ink channels
20
,
22
in the confluence (mixing section)
21
have a relation of A
1
>A
2
. The ink transporting means A in
FIG. 8
ejects the ink as a droplet
402
by using an ejecting piezoelectric device
400
disposed in the vicinity of the ink ejection port
44
, and leads the droplet onto the print paper
12
.
The ink transporting means B in
FIG. 9
generates a bubble
406
by heating the ink liquid by a heater
404
disposed in the vicinity of the ink ejection port
44
in order to eject or jet an ink droplet
402
. In ink transporting means C of
FIG. 10
, a high voltage in accordance with the image signal is applied between electrodes
408
(
408
a,
408
b
) disposed before the ink ejection port
44
by an oscillator
410
. As a result, an electric charge in accordance with the image signal is imparted to the ink droplet
402
drawn from the ink ejection port
44
. The ink droplet is deflected by deflecting electrodes
409
(
409
a,
409
b
) so that only a necessary droplet
402
a
is led to the print paper
12
while removing an unnecessary droplet
402
b
by a baffle plate
412
.
Ink transporting means D of
FIG. 11
narrows down the ink ejection port
44
to a small diameter and applies a direct-current high voltage associated with the image signal between the ink ejection port
44
and the print paper
12
by an oscillator
414
. The high voltage is used to draw the ink droplet
402
from the ink ejection port
44
so that the ink droplet
402
is attracted onto the print paper
12
. In ink transporting means E of
FIG. 12
, an ultrasonic transducer
416
is disposed on an outer wall of the ink ejection port
44
, and an ultrasonic wave emitted from the ultrasonic transducer
416
is converged on the ink liquid by a Fresnel lens
418
disposed on the inner wall of the ink ejection port
44
to excite the ink liquid so that the droplet
402
is generated.
When the inks are mixed with one another by natural diffusion between the inks in the confluence of a plurality of inks, and a vibration occurs in the confluence, or vibration or turbulence is generated in the ink flow, the turbulence is produced on a contact interface of the inks due to these disturbances, thereby facilitating mixture of the inks. Therefore, a minimum addition amount of the ink which is not transparent or colorless must be increased, and this may result in restriction of the density tone or degradation of the image quality.
Thus, it is preferable to provide a vibration absorption mechanism in the confluence of the inks. For example, the image forming section (recording head)
16
can be supported by an antivibration spring
450
or an attenuator
452
as shown in FIG.
1
. Moreover, in order to suppress the pulse of the ink or the vibration of the flow control valves
24
,
26
, it is preferable to additionally dispose a damper for absorbing the ink pulses or to adopt the flow control valves
24
and
26
which are of a vibration absorbing type.
In the first to tenth embodiments described with reference to
FIGS. 1
to
12
, since two types of ink are mixed or combined and one of them is used as the image non-forming ink, the image can be formed by changing the density. However, in the present invention, the color and density can simultaneously be changed by mixing two or more types of ink having colors of, for example, yellow, magenta, cyan and black or mixing these types of ink with the image non-forming ink. Instead of using the image forming section
16
for forming the image directly on the image receiving medium such as the print paper
12
, the image may be formed temporarily on an intermediate image receiving medium such as an intermediate transfer drum, so that the image can be transferred from the intermediate image receiving medium to a final image receiving medium such as the print paper.
Eleventh Embodiment
FIG. 13
is a sectional view showing an image forming section (recording head)
516
according to an eleventh embodiment adopting a continuous coating mode. This embodiment employs an ink feed pump
534
driven by the piezoelectric device, instead of the ink feed pump
234
formed by the cylinder pump in the recording head
216
shown in FIG.
6
.
This ink feed pump
534
is constituted similarly as the ink feed pump
334
shown in FIG.
7
. That is, a cavity
534
b,
and check valves
534
c
and
534
d
which are positioned before and after the cavity
534
b
are disposed in the second ink channel
22
, and a diaphragm which is driven by a piezoelectric device
534
a
or a diaphragm which is integral with the piezoelectric device
534
a
is used to change a volumetric capacity of the cavity
534
b.
Twelfth Embodiment
FIG. 14
is a sectional view showing an image forming section (recording head)
616
according to a twelfth embodiment similarly adopting the continuous coating mode. This embodiment uses an ink feed pump
634
instead of the flow control valve
26
in the recording head
16
shown in FIG.
2
.
The first ink is supplied to the first ink channel
20
with a fixed pressure by a pump (not shown), and the flow rate of the first ink is controlled by a flow control valve
624
disposed in the first ink channel
20
. An effective sectional area of the ink channel in the flow control valve
624
is controlled by displacement of a diaphragm
624
b
driven by a piezoelectric device
624
a.
An ink feed pump
634
disposed in the second ink channel
22
has a piezoelectric device
634
a,
a cavity
634
b,
and check valves
634
c,
634
d.
Thirteenth Embodiment
FIG. 15
is a sectional view showing an image forming section (recording head)
716
according to a thirteenth embodiment similarly adopting the continuous coating mode. In this embodiment, an ink feed pump
734
is used instead of the ink feed pump
234
formed by the cylinder pump in the image forming section
216
shown in FIG.
6
.
The ink feed pump
734
includes a piezoelectric device
734
a
facing the second ink channel
22
, and a pair of wedge-shaped protrusions
734
b,
734
c
disposed opposite to each other. The protrusion
734
b
is disposed on the piezoelectric device
734
a,
and the other protrusion
734
c
is disposed on an inner wall of the ink channel
22
opposite to the piezoelectric device
734
a.
The protrusions
734
b,
734
c
have inclined surfaces extending toward an ink flow direction from each other. The vibration of the piezoelectric device
734
a
allows the protrusion
734
b
to move forward/backward in the ink channel
22
. Consequently, the ink sandwiched between the inclined surfaces of the protrusions
734
b,
734
c
is pushed out in a direction of the ink ejection port
44
. Therefore, the ejection amount of the second ink is controlled by a number of vibrations and an amplitude of the piezoelectric device
734
a.
Structure of Check Valve
FIGS. 16
,
17
and
18
are perspective views showing different structures of a check valve, and
FIG. 19
is detailed explanatory drawings of these structures. Check valves
800
,
802
and
804
shown in the drawings are used in the ink feed pumps
334
(FIG.
7
),
534
(
FIG. 13
) and
634
(
FIG. 14
) shown in
FIGS. 7
,
13
and
14
. Each of these check valves
800
,
802
and
804
is a restriction or restrictor having a geometrical shape such that the resistance with respect to the ink flow direction becomes larger than the resistance with respect to the reverse direction. Therefore, each check valve has no movable portion and can readily be produced by a method for manufacturing a micro-machine.
The check valve
800
shown in
FIG. 16
has a substrate
800
a,
an inclined surface
800
b
whose ink channel sectional area substantially-continuously increases from the right side toward the left side of the substrate
800
a,
and a flat surface
800
c
whose ink channel sectional area rapidly increases in the reverse direction.
When a cavity having a fluctuating volumetric capacity is disposed in the vicinity of the check valve
800
, the ink reciprocates through the check valve
800
by a fluctuation in the volumetric capacity of the cavity. In such a case, the resistance decreases when the ink flows toward the left-hand-side direction in
FIG. 16
, and the resistance increases when the ink flows toward the reverse direction (the right-hand-side direction). Therefore, the fluctuation in the volumetric capacity of the cavity causes the ink to flow in a direction in which the resistance decreases (the left-hand-side direction in the drawing), and the cavity functions as the check valve.
The check valve
802
shown in
FIG. 17
uses a quadrangular-pyramid-shaped restriction formed on a substrate
802
a.
The check valve
804
shown in
FIG. 18
uses a conical aperture restriction formed on a substrate
804
a.
These check valves
802
and
804
also function similarly as the check valve
800
shown in FIG.
16
.
These check valves
800
,
802
and
804
have a detailed structure shown in FIG.
19
. In
FIG. 19A
, an inclination θ of an inclined surface
800
b
of the check valve
800
should be appropriately determined in accordance with a relationship to a length t of a component (hereinafter referred to simply as a thickness) with respect to the ink flow direction on the inclined surface
800
b
of the substrate
800
a.
Also, the inclinations θ of pyramidal and conical surfaces
802
b
and
804
b
of the check valves
802
and
804
are determined in accordance with the relationship to thicknesses t of
802
a
and
804
a,
respectively.
According to the experiment, a flow resistance of fluid to the upward direction in
FIG. 19A
is smaller than the flow resistance to the downward direction when the inclination θ is set in a range of 2°<θ<15°, and the fluid flows upwards. Further, it was found that conversely the upward flow resistance is larger than the downward flow resistance when the inclination θ in a range of 20°<θ<70°, and the fluid flows downwards. When the flowing direction changes in accordance with the angle θ of the restriction, the angle θ must appropriately be determined.
Further,
FIG. 19B
shows another detailed structure of the check valve. This check valve
800
A connects two conical surfaces
800
B,
800
C with each other. Assuming that angles defined by both the conical surfaces
800
B,
800
C and a central line are θ
1
, θ
2
, respectively, the angle θ
2
is set so as to be larger than at least the angle θ
1
(θ
2
>θ
1
), preferably not less than 80°, most preferably substantially 90°.
If the angle θ
2
is greatly larger than 90°, air bubbles undesirably adhere to the conical surface
800
C and accumulate when the liquid flows downwards from the upper side in FIG.
19
B. Additionally, it has been revealed that the function as the check valve prominently lowers when the angle θ
2
is not more than 60°. When a connection portion between both the conical surfaces
800
B and
800
C is formed into an appropriate arc-like curved surface as shown by R in the drawing, a flow of fluid can further be smoothed, which is more desirable.
Arrangement of Recording Head
FIGS. 20 and 21
are views showing examples of arrangement of the image forming section (recording head) for use in each of the foregoing embodiments. A recording head
810
shown in
FIG. 20
has a plurality of ink ejection ports
44
aligned on a straight line A which is wider than the width of the image receiving medium, i.e., print paper. This recording head
810
is provided in such a manner that an angle Θ defined by an intersection of the straight line A on which the ink ejection ports
44
are aligned and a feeding direction B of the print paper
12
becomes 90° or substantially 90°. The image forming section
810
shown in
FIG. 21
is inclined in such a manner that the angle Θ defined by an intersection of the straight line A and the feeding direction B does not become 90°.
According to the example shown in
FIG. 20
, the ink ejection ports
44
of the recording head
810
must be disposed at intervals which are equal to those of the pixels. According to the example shown in
FIG. 21
, an interval between the ink ejection ports
44
can be larger than that between the ink ejection ports shown in FIG.
20
. As a result, production of the recording head
810
can be facilitated.
FIG. 22
is an enlarged view of the image forming section
810
, and
FIG. 23
is an enlarged view showing another embodiment of the image forming section. As described above, the image forming section
810
has a large number of ink ejection ports
44
aligned on the straight line A. On the other hand, the adjacent ink ejection ports
44
are distributed on two parallel straight lines A
1
and A
2
in an image forming section
810
A shown in FIG.
23
.
According to the image forming section (recording head)
810
A shown in
FIG. 23
, the interval between the adjacent ink ejection ports
44
on the respective straight line A
1
and A
2
can be enlarged to double the interval shown in FIG.
22
. This can facilitate production of the image forming section
810
A. Additionally, the ink ejection ports
44
can be distributed on three or more straight lines instead of the two straight lines A
1
and A
2
, which further facilitates the production of the image forming section. When the ink ejection ports
44
are aligned on the different straight lines A
1
and A
2
, a plurality of image forming sections having the ink ejection ports
44
aligned on one straight line can be displaced by an amount of pitch of the pixel in the width direction of the print paper
12
so as to closely overlap one on another.
In the aforementioned embodiments, the flow control valve (
24
,
26
or
624
) changes the sectional area of the ink channel by driving the diaphragm valve by the piezoelectric device. In the ink flow controlling means including the check valve, cavity and movable member, the movable member is driven by the piezoelectric device. However, the flow control valve or the movable member may utilize the driving force based on a principle other than the piezoelectric device. For example, a heat-pressure effect, electrostatic attraction force, or electrostatic repulsive force can be used. On the heat-pressure effect described herein, the fluid (this may be the ink itself) whose flow resistance largely changes with a temperature is used and the diaphragm is driven by utilizing a fluid pressure change caused by changing a fluid temperature by a heater at one point in the fluid channel.
Furthermore, the diaphragm valve or the movable member may be driven by utilizing a magnetic distortion effect or an effect of interfacial tension of fluid different from fluids used for forming an image. Also, heat of fluids different from the fluid for use in forming the image and/or a pressure of a bubble generated by electrolytes may be used. Moreover, instead of changing the channel resistance by the heat with the heat-pressure effect, the channel resistance of the fluid different from a plurality of fluids for use in forming the image can be changed to generate a change in pressure of this fluid by changing other physical or chemical characteristics such as an electric field and magnetic field. This pressure change may be utilized to drive the diaphragm or the movable member.
It is possible to use the diaphragm for opening/closing the ink channel, which has a structure for holding a valve plate for closing the ink channel by a center impeller beam or a cantilever beam. That is, when the diaphragm has a structure such that the opening of the ink channel is substantially-vertically disposed opposite to the valve plate and this valve plate is pushed by an actuator such as a piezoelectric device from the opposite side of the opening of the ink channel, the center impeller beam or the cantilever beam is used as this valve plate.
In the embodiment shown in
FIG. 2
, the pumps
32
,
34
eject or extrude the ink with a fixed pressure, and the ejection amount of each type of ink is separately controlled by the flow adjusting valves
24
,
26
. Further, in the embodiments shown in
FIGS. 5 and 6
, the ejection amounts of the ink from the pumps
132
,
134
,
232
and
234
are independently variable. Furthermore, in the embodiment shown in
FIG. 7
, each ink ejection amount is variable by the ink feed pumps
332
and
334
.
In the present invention, each type of ink is supplied with the fixed pressure and the ejection amount is controlled by the flow adjusting valve (embodiment in FIG.
2
), the ink ejection amount can be varied by each pump (the embodiments of
FIGS. 5
,
6
and
7
), but a part of ink may be supplied with the fixed pressure and the ejection amount of any other type of ink may be varied. For example, the clear ink which becomes transparent and colorless at least after dried out may continuously be supplied with the fixed or constant pressure without using the flow adjusting valve. On the other hand, the ejection amount of any other colored ink may be varied by the flow control valve (shown in FIG.
2
), the pump with a variable ejection amount (shown in
FIGS. 5 and 6
) or the ink feed pump with the variable ejection amount (shown in FIG.
7
).
In this case, the sectional area of the ink channel through which all types of ink collectively pass is always constant, and the flow rate of one type of ink supplied with the fixed pressure naturally changes by varying the controllable ejection amount of the other type of ink. When the clear ink is supplied with the fixed pressure without using the flow control valve, the ink channel for the clear ink may be branched into a plurality of array-like channels in the recording head so that the clear ink can uniformly be led to each ink ejection port from one ink pump. Therefore, the constitution of the recording head can be simplified.
The above has been described as the embodiments for forming the image. That is, two-dimensionally drawing of the image on a sheet of paper or a film has been described. However, the present invention can be used for manufacturing a mosaic filter for use in an image display device such as a liquid crystal color display, that is, a color filter in which color mosaics of yellow, magenta and cyan are repeatedly arranged. Furthermore, the present invention can also be applied to manufacturing of an industrial product for forming a spatially repeated pattern.
In the present invention, the opening area of the channel of the ink whose ejection amount is minimum in the confluence is set to be smaller than the opening area of the other ink channel. Therefore, when the excessively small amount of ink is ejected into the confluence, an advancing amount of the leading end of the ink increases, and the leading end of the ink is easily disconnected. Therefore, the plurality of inks can be ejected with fidelity to the image signal, and the image quality can be enhanced.
The plurality of inks include at least one image non-forming ink and at least one image forming ink, and the opening area of the ink channel of the image forming ink in the ink confluence is set to be smaller than the opening area of the ink channel of the image non-forming ink, so that the ejection amount of the image forming ink can finely be controlled. This can realize a high-precision density control. In this case, when the opening of the image forming ink channel is circular, the opening area is Ai, the minimum ejection volume of the ink is Vi, and a relation Ai≦½×V
(⅔)
is established, a preferable effect can usually be obtained.
When the plurality of inks constantly include the image non-forming ink, the ink is smoothly confluent. Particularly, when the ink total flow rate is constantly fixed, the ink fluid can steadily be transferred to the image receiving medium, and this is further suitable for enhancement of the image quality.
The ink ejection ports can be independently disposed for each pixel and opposite to the image receiving medium, and the ink liquid can be led into the image receiving medium by the ink transporting means of the ink jet mode. Examples of the ink jet mode for use herein include a piezo ink jet mode, thermal ink jet mode, continuous ink jet mode, electrostatic attraction ink jet mode, ultrasonic ink jet mode, and the like.
The ink liquid can be transferred as a continuous fluid flow to the image receiving medium via the ink ejection ports (continuous coating mode). In this case, when the respective ink ejection ports are formed in a common slot-opening and the ink liquid is ejected through this slot, a plurality of inks can be applied as the layer flow without being homogeneously mixed. A special property can be imparted to the ink coming into contact with the image receiving medium or the ink exposed on the surface. Therefore, the image quality can be improved. Additionally, the image receiving medium includes an intermediate image receiving medium such as a drum as well as the final image receiving medium such as the print paper.
The flow rate of at least one image forming ink for substantially forming the image when dried out among the plurality of inks is controlled in order to constantly prevent the volumetric flow rate per unit time from becoming zero. Then, the image quality can be prevented from being deteriorated by the diffused/mixed inks.
Claims
- 1. An image forming apparatus for ejecting a recording fluid constituted by a plurality of inks from a common ink ejection port while a mixing ratio of the plurality of inks is changed with respect to one pixel based on an image signal, and transporting the recording fluid to an image receiving medium which is moved with respect to the ink ejection port to form an image; said image forming apparatus comprising:an ink ejection port for ejecting the recording fluid to the image receiving medium; a first ink channel for supplying an image non-forming ink to said ink ejection port, the image non-forming ink being an ink for forming no image after dried out; a second ink channel for supplying an image forming ink to said ink ejection port, the image forming ink being an ink for forming the image after dried out; and a mixing section disposed upstream of said ink ejection port, for mixing the image non-forming ink supplied from said first ink channel and the image forming ink supplied from said second ink channel; wherein an opening area Ai of said second ink channel is smaller than the opening area of said first ink channel in said mixing section; and the opening area Ai of said second ink channel has the following relationship with a minimum ejection volume Vi of the image forming ink:ps Ai≦1.2×Vi(⅔).
- 2. The image forming apparatus according to claim 1, wherein the mixing ratio of the plurality of inks is controlled in such a manner that the image non-forming ink is always included.
- 3. The image forming apparatus according to claim 1, wherein a plurality of said ink ejection ports are provided to be aligned in accordance with respective pixels in a direction substantially perpendicular to a moving direction of the image receiving medium, and each of the ink ejection ports is independently disposed opposite to the image receiving medium.
- 4. The image forming apparatus according to claim 1, wherein said recording fluid is ejected from said ink ejection port and transported as a continuous recording fluid flow to the image receiving medium.
- 5. The image forming apparatus according to claim 4, wherein said image receiving medium is an intermediate image receiving medium for receiving the continuous recording fluid ejected from said ink ejection port and transferring the recording fluid to a final image receiving medium.
- 6. The image forming apparatus according to claim 1, wherein a plurality of ink ejection ports disposed for respective pixels are open into a slot, and the recording fluid ejected from each ink ejection port is transported as a band-shaped continuous fluid flow to the image receiving medium from the slot.
- 7. The image forming apparatus according to claim 6, wherein said image receiving medium is an intermediate image receiving medium for receiving the continuous recording fluid ejected from the ink ejection port and transferring the recording fluid to a final image receiving medium.
- 8. The image forming apparatus according to claim 1, further comprising ink transporting means for leading the recording fluid ejected from the ink ejection port to the image receiving medium by an ink jet mode.
- 9. The image forming apparatus according to claim 8, wherein the ink jet mode is any one selected from the group consisting of a piezo ink jet mode, a thermal ink jet mode, a continuous ink jet mode, an electrostatic attraction ink jet mode, and an ultrasonic ink jet mode.
- 10. The image forming apparatus according to claim 1, wherein an ink flow rate of the image forming ink is controlled in order to constantly prevent a volumetric flow rate per unit time from becoming zero.
- 11. An image forming method for ejecting a recording fluid constituted by a plurality of inks from a common ink ejection port while a mixing ratio of the plurality of inks is changed with respect to one pixel based on an image signal, and transporting the fluid to an image receiving medium which is moved with respect to the ink ejection port to form an image;wherein said plurality of inks include an image non-forming ink which forms no image after dried out and at least one image forming ink which forms the image after dried out, an opening area Ai of a channel of said image forming ink is smaller than the opening area of the channel of said image non-forming ink in a confluence of said plurality of inks; and the opening area Ai of the channel of the image forming ink has the following relationship with a minimum ejection volume Vi of the image forming ink: Ai≦1.2×Vi(⅔).
- 12. The image forming method according to claim 11, wherein the mixing ratio of the plurality of inks is controlled in such a manner that the image non-forming ink is always included.
- 13. The image forming method according to claim 11, wherein a plurality of said ink ejection ports are provided to be aligned in accordance with respective pixels in a direction substantially perpendicular to a moving direction of the image receiving medium, and each of the ink ejection ports is independently disposed opposite to the image receiving medium.
- 14. The image forming method according to claim 11, wherein said fluid is ejected from said ink ejection port and transported as a continuous fluid flow to the image receiving medium.
- 15. The image forming method according to claim 14, wherein said image receiving medium is an intermediate image receiving medium for receiving the continuous recording fluid ejected from said ink ejection port and transferring the recording fluid to a final image receiving medium.
- 16. The image forming method according to claim 11, wherein a plurality of ink ejection ports disposed for respective pixels are open into a slot, and the recording fluid ejected from each ink ejection port is transported as a band-shaped continuous fluid flow to the image receiving medium from the slot.
- 17. The image forming method according to claim 16, wherein said image receiving medium is an intermediate image receiving medium for receiving the continuous recording fluid ejected from the ink ejection port and transferring the recording fluid to a final image receiving medium.
- 18. The image forming method according to claim 11, wherein the recording fluid ejected from the ink ejection port is transported to the image receiving medium by an ink jet mode.
- 19. The image forming method according to claim 18, wherein the ink jet mode is any one selected from the group consisting of a piezo ink jet mode, a thermal ink jet mode, a continuous ink jet mode, an electrostatic attraction ink jet mode, and an ultrasonic ink jet mode.
- 20. The image forming method according to claim 11, wherein an ink flow rate of the image forming ink is controlled so that a volumetric flow rate per unit time is constantly prevented from becoming zero.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-227622 |
Jul 2000 |
JP |
|
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