Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2002-08-21
2004-02-03
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06685308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image by discharging liquid from a liquid discharge head onto a recording medium.
2. Description of Related Art
In conventional general image forming apparatus, an image is formed on a recording medium by discharging liquid such as ink and treatment liquid for adjusting a fixing ability of the ink from discharge ports of a liquid discharge head disposed in a spaced apart relationship from a surface of the recording medium by a proper distance. An ink tank for containing the ink to be discharged is provided on a carriage together with the liquid discharge head or is disposed out of the carriage.
FIG. 5
is a view showing a schematic construction of an image forming apparatus in which the ink tank is provided on the carriage.
A carriage
101
on which a liquid discharge head (not shown) for forming an image by discharging liquid such as ink onto a recording medium
102
and an ink tank (not shown) for storing the ink to be supplied to the head are mounted is secured to a part of a belt
104
mounted between and wound around two pulleys
106
a
and
106
b
. The belt
104
is shifted by rotatingly driving one
106
a
of the pulleys reversibly by means of a motor
107
, with the result that the carriage
101
is reciprocally shifted in directions A along a shaft
103
. A signal and an electric power for causing the liquid discharge head to discharge the ink are inputted from control means (not shown) of the image forming apparatus via a cable
105
.
Further, the image forming apparatus is provided with convey means (not shown) for conveying the recording medium
102
in a direction B, and the image is formed on the entire recording medium
102
by repeating a conveying operation for the recording medium
102
effected by the convey means and an image forming operation effected by the liquid discharge head mounted on the carriage reciprocally shifting with respect to the recording medium
102
.
The ink tank can be exchanged with respect to the carriage
101
in accordance with consumption of the ink or new ink can be replenished into the ink tank. Depending upon kind of device of the image forming apparatus, a head cartridge in which an ink tank and a liquid discharge head are integrally formed is used so that the ink tank and the head can be exchanged integrally or collectively. In this type, since an ink storing amount is determined by a dimension of the carriage
101
, it is disadvantageous when a large amount of ink is consumed.
FIG. 6
is a view showing a schematic construction of an image forming apparatus in which the ink tank is disposed out of the carriage.
An operation of the carriage
101
in the image forming apparatus shown in
FIG. 6
is substantially the same as that of the carriage shown in FIG.
5
. However, the image forming apparatus shown in
FIG. 6
is designed so that the ink is supplied to a sub-tank
109
(refer to
FIG. 7
) on the carriage
101
through a tube
108
from a main tank
106
disposed out of the carriage
101
.
FIG. 7
is a sectional view showing an internal construction of the carriage shown in FIG.
6
.
The sub-tank
109
for storing a small amount of ink is mounted on the carriage
101
, and ink flow passages are communicated from the sub-tank
109
to nozzles
110
of a liquid discharge head. The sub-tank
109
also acts as a buffer for replenishing new ink from the main tank
106
(
FIG. 6
) and for collecting a bubble generated in the flow passage.
As such, by designing so that the main tank
106
is disposed out of the carriage
101
and the ink is supplied to the sub-tank
109
on the carriage
101
through the tube
108
, limitation regarding the dimension of the ink tank occupying the space on the carriage
101
is relaxed and, thus, the ink reserving amount of the entire apparatus can be increased. Therefore, recording regarding a recording medium
102
having a large size and recording regarding a large number of recording media
102
become possible.
However, when the ink is supplied from the main tank
106
disposed out of the carriage
101
to the liquid discharge head through the tube
108
during the recording operation, there arises a problem that pressure of the ink within the sub-tank
109
is greatly changed to affect an influence upon a discharging ability of the liquid discharge head, thereby worsening appearance quality of a recorded image. In general, it is preferable that the pressure within the sub-tank
109
is within a proper negative pressure range for balancing with discharge energy of the liquid discharge head. If the pressure is increased above such a proper range, i.e., if the pressure becomes near a positive pressure condition or it attains a positive pressure, the ink is apt to be dropped from the nozzles
110
. On the other hand, if the pressure is decreased below such a proper range, i.e., if the negative pressure is further increased, the ink is hard to be discharged from the nozzles
110
and the ink discharging amount tends to be decreased.
Main factors for causing the change in pressure inherent to the case where the ink is supplied from the main tank
106
disposed out of the carriage
101
to the liquid discharge head through the tube
108
during the recording operation are (1) dynamic pressure of the tube, (2) pressure loss in the tube and (3) difference in posture.
Here, the “dynamic pressure of the tube” is a phenomenon that the tube
108
connected to the sub-tank
109
on the carriage
101
is vibrated as the carriage
101
is reciprocally shifted, with the result that inertia of the ink within the tube
108
acts to increase or decrease the pressure with respect to the sub-tank
109
, which phenomenon is generated in accordance with acceleration/deceleration of the carriage and vibration due to such acceleration/deceleration.
Further, the “pressure loss in the tube” is flow resistance in the tube
108
. If a consumed amount of ink due to ink discharging from the liquid discharge head becomes greater than the amount of ink supplied from the tube
108
, the pressure in the sub-tank
109
will gradually be decreased, i.e., the negative pressure will be further increased. When an inner diameter of the tube
108
is sufficiently great, such a phenomenon is not noticeable, but, since the ink amount existing within the tube
108
is increased, the influence of the dynamic pressure of the tube tends to increase, contrary to the influence of the pressure loss in the tube.
Further, the “difference in posture” is inclination of the installed recording apparatus. If the recording apparatus is inclined with respect to the scanning direction of the carriage
101
, since at both stroke ends of the reciprocating carriage
101
, height of the carriage
101
with respect to the main tank, that is, height of the nozzles
110
is differentiated, change in pressure is generated due to difference in water head.
As countermeasure for such change in pressure, in the conventional image forming apparatuses, for example, as proposed in Japanese Patent Application Laid-open No. 1-281948 (1989), a fluidity suppressing member for suppressing fluidity of ink is added to each flow passage, or, as proposed in Japanese Patent Application Laid-open No. 5-201015 (1993), a sub-tank has a pressure dampening function as a pressure damper. In the image forming apparatus, in addition to consideration of such countermeasure, effort is generally made to provide a head in which use conditions mainly including a recording speed condition are stipulated to suppress the change in pressure within the sub-tank and to permit possible pressure change.
Further, as countermeasure for dampening the influence of the pressure change of the ink, it is considered that an open/close valve is provided in a flow passage between the main tank and the sub-tank so that the valve is opened to suppress the change of pressure within the tube during the recording operation and the valve is opened to supply the ink intermittently durin
Hirai Yasuyuki
Inamura Shusuke
Inoue Hiroyuki
Iwasaki Takeshi
Nojima Takashi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Vo Anh T. N.
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