Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-05-22
2002-10-01
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S062000, C347S040000
Reexamination Certificate
active
06457796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording head, and more particularly to an ink jet recording head of a thermal ink jet type.
2. Description of the Prior Arts
There has been known an ink jet recording head of a thermal ink jet type as an ink jet recording apparatus wherein an ink droplet is ejected onto a recording sheet according to an image signal for recording an image, a character and the like.
The ink jet recording apparatus of such a thermal ink jet type has, for example, an ink jet recording head;
70
having a construction shown in FIG.
7
. This ink jet recording head
70
is provided with a heating substrate
52
and a flowing path substrate
50
formed on the heating substrate
52
. The heating substrate
52
has electricity/heat converting elements
60
, each of which is arranged at a position corresponding to each ink flowing path
58
described later and has the same size. An electric pulse is applied to the electricity/heat converting element
60
via a device not shown or wiring according to an image signal.
Provided at the flowing path substrate
50
are an ink supplying opening
56
that introduces ink from an ink tank not shown, an ink chamber
54
for temporarily keeping ink introduced from the ink supplying opening
56
and plural ink flowing paths
58
, which is ends on one side are open to the ink chamber
54
and ends on the other side form an ejecting opening
59
.
The ink chamber
54
and the ink flowing path
58
are filled with ink upon recording an image. When the electric pulse is applied to the electricity/heat converting element, i.e. thermal element,
60
from the heating substrate
52
according to the image signal, the electricity/heat converting element
60
generates heat to form a bubble at the heating portion. This bubble brings a pressure to ink in the ink flowing path to eject ink from the ejecting opening
59
, whereby the ejected ink is adhered onto a recording sheet arranged so as to oppose to the ejecting opening
59
, thereby recording an image.
Generally, a high resolution of 600 dpi or more or an ejection of an extremely minute ink droplet of 10 pl or less are required for recording an image of a high quality. In the case of recording an image of a high quality by using the ink jet recording head of a thermal ink jet type having the above-mentioned construction, a period for one scan increases since an area where an ink droplet is adhered by one ejection is small. Further, a relative moving speed of the head in the slow-scanning direction becomes slow, resulting in considerable slowdown of the printing speed.
Moreover, the smaller the size of the ejected ink droplet is made for obtaining an image of higher quality, the less the ink amount adhered onto the recording sheet for one scan becomes, whereby the density of the image becomes low. Therefore, it is required that a slow-scan is repeated in plural times for ejecting ink droplets in plural times at the same position on a recording sheet to adjust the density to a desired one (multi-scan). This brings a slower printing speed.
Accordingly, printing is conventionally performed by changing a dot number between normal printing and high-speed printing. As one of such methods, a method has been known wherein an image is formed by all dots as shown in
FIG. 8A
in normal printing while an image is formed in high-speed printing by dots fewer than the dots in number in normal printing as shown in
FIG. 8B
, i.e., an image is formed by thinning-out printing, thereby enhancing a relative printing speed in the fast-scanning direction and slow-scanning direction to perform high-speed printing.
Japanese Published Unexamined Patent Application No. Hei 8-332727 discloses an ink jet recording head having large and small heaters
62
and
64
arranged laterally in an ink flowing path
58
as shown in
FIG. 9A
, or arranged longitudinally in the ink flowing path
58
as shown in
FIG. 9B
, wherein the small heater
62
is turned on in the normal printing to eject small ink droplets, while only the large heater
64
or both of the small and large heaters
62
and
64
are turned on in high-speed printing to eject large ink droplets.
Generally, ejectable ink droplets having a smaller size is preferable for recording an image with high resolution, while ejectable ink droplets having a larger size is preferable for performing thinning-out printing to print at a high speed. Therefore, it is required to have a construction such that the size of ink droplets which can be ejected from a single ink jet recording head can be greatly switched over.
For example, a volume of an ink droplet required for forming dots on a sheet with a resolution of 800 dpi without a space is approximately 7 pl to 15 pl per one droplet. In order to obtain an image with higher resolution than 800 dpi for rendering graininess unnoticeable, ink droplet having smaller volume is required. On the other hand, in the case where dots are thinned out every other one dot for high-speed printing, a volume of an ink droplet required for filling the space between each dot with a resolution of 400 dpi is approximately 20 to 50 pl per droplet.
Specifically, it is desired that a ratio of a dot diameter of the minimum ink droplet that can be ejected from a single ink jet recording head and a dot diameter of the maximum ink droplet has a wide range of at least approximately 1:3 to 1:7.
However, it is difficult to greatly change the size of an ink droplet in the ink jet recording head having the conventional construction.
For example, in the case where two heaters
62
and
64
are arranged laterally in the ink flowing path
58
as shown in
FIG. 9A
, the volume of an ejectable ink droplet is limited by the size of the heater (i.e., amount of generated heat) and the width of the flowing path.
Specifically, if the width of the flowing path is enlarged, the size of the heater that can be arranged can be made large, so that an ink droplet having greater volume can be ejected to increase the dot diameter that can be formed. However, since the resolution at the ejecting opening becomes low, that brings a wide space between each dot formed by ejecting ink droplets of a small volume, thereby unpreferable. Accordingly, the limit is the volume ratio of approximately 1:2 of a volume of the minimum ink droplet that can be ejected from the ink jet recording head and a volume of the maximum ink droplet in the case of laterally arranging the heating element.
Further, in the case where two heaters
62
and
64
are longitudinally arranged in the ink flowing path
58
shown in
FIG. 9B
, the size of the heating element can be enlarged without widening the width of the flowing path compared to the case where the heating element is laterally arranged. However, a signal electrode for selecting two heating elements and an electrode for applying a voltage need to be wired for every flowing path. Since the width of the flowing path for such electrodes are required, a heating element having a sufficient size cannot be arranged. Therefore, the limit is the volume ratio of approximately 1:2.5 of a volume of the minimum ink droplet that can be ejected from the ink jet recording head and a volume of the maximum ink droplet.
If the width of the flowing path is enlarged for ejecting ink droplets having a larger volume, a low resolution at the ejecting opening is inevitable. Although a slight improvement is made compared to the case where the heating element is laterally arranged, it is impossible to greatly increase the ratio of the dot diameter of the minimum ink droplet to the dot diameter of the maximum ink droplet.
Moreover, the length of the flowing path becomes long in the longitudinal arrangement compared to the lateral arrangement, thereby enlarging a fluid resistance from the ink chamber to the orifice. Therefore, this longitudinal arrangement has a problem that the resupply of the ink jet becomes slow after ejecting ink droplets, whereby high-speed printing cannot be performed.
Specifically, the conve
Fuji 'Xerox Co., Ltd.
Nguyen Lamson
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