Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-10-06
2002-12-24
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06497476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid injection device or the like used for an ink jet printer or the like.
2. Related Art of the Invention
In recent years, ink jet printers have been rapidly becoming popular as a printer capable of implementing color printing at low price. It is an ink injection device that determines the performance of this ink jet printer, and it is a liquid injection device which intermittently injects fine liquid particles.
As a conventional liquid injection device, the description will be made by exemplifying a typical ink injection device for ink jet printers. The ink injection device for ink jet printers can be generally classified under the following two types: heat type and piezo-electric type.
The injection principle of the typical heat type will be described with reference to FIG.
24
.
FIG. 24
is a cross-sectional view showing an ink injection element constituting an ink injection device. An ink pressurizing chamber
803
is provided in space interposed between a substrate
801
and a substrate
802
, and a heater
804
is provided between the ink pressurizing chamber
803
and the substrate
801
. Ink is supplied from an ink storage (not shown) provided outside of the ink injection element by a capillary phenomenon or a suction operation from outside, and is supplied to the ink pressurizing chamber
803
through an ink passage
806
. When the heater
804
is electrically energized in this state, the ink intensely boils to generate air bubbles. The growth of these air bubbles increases the pressure within the ink pressurizing chamber
803
to inject the ink through an ink injection port
806
. An actual ink injection device is configured by a plurality of ink injection elements described above lined.
Next, an example of a typical piezo-electric type ink injection device for ink jet printers will be described with reference to
FIG. 25
, which is a cross-sectional view for an ink injection element. In
FIG. 25
, a reference numeral
813
denotes a piezo-electric actuator, which is driven by a piezo-electric operation, and is, for example, a bimorph element configured by two piezo-electric elements, or an unimorph element configured by a piezo-electric element and a diaphragm, or the like. A reference numeral
818
denotes an ink passage;
819
, an ink pressurizing chamber; and
820
, an ink injection port. A portion indicated by broken lines in the piezo-electric actuator
813
schematically shows deformation of the piezo-electric actuator. Ink is supplied from an ink storage (not shown) provided outside of the ink injection element at the beginning by a capillary phenomenon or a suction operation from outside, and is supplied to the ink pressurizing chamber
819
through the ink passage
818
. When the piezo-electric actuator
813
is caused to become deformed as indicated by the broken lines in a state in which the ink passage
818
and the ink pressurizing chamber
819
are filled with the ink, the pressure within the ink pressurizing chamber
819
increases to inject the ink through the ink injection port
820
. The actual ink injection device is constructed such that a plurality of elements described above are arranged in a line because of high-speed printing.
In recent years, requests for an ink jet printer capable of expressing more colorful colors at low price have been increasing, and in order to perform more colorful color printing by an ink jet printer using such a liquid injection device, it is necessary to increase a number of gradation levels perunitpicture element (pixel), that is, to implement multi-tone printing.
A method for implementing such multi-tone printing will be described below.
First, a method using an area modulation system is named. This method is to form an unit picture element (pixel) for expressing light and dark density by hitting a plurality of dots without superimposing one on another, and to express the gradation by changing a rate of ink per unit picture element.
Secondly, a method using superposedly dotting is named. This method is to inject ink on the same place a plurality of times and to express the gradation by changing the size of unit pixel.
Thirdly, a method using a density modulation system is named. This method is to express the gradation by using a plurality of inks of different coloring matter density.
Fourthly, a method using a dot modulation system is named. This method is to discharge ink drops having different sizes through the same injection port, and is capable of change the size of dot for each injection.
However, the above-described methods for implementing multi-tone printing have the following problems respectively.
First, problems of the area modulation system will be described. In the area modulation system, since dots to be recorded are thinned out to express light and dark density, the size of the unit pixel required to express the light and dark density becomes large to lower actual recording density. Therefore, when an attempt is made to express multi-tone light and dark density, print with conspicuous surface roughness in a low-density portion is produced. In order to reduce the lowered recording density, the size of the unit pixel is made as small as possible. In other words, it becomes necessary to make the minimum dot diameter smaller. In order to reduce the minimum dot diameter, or to discharge small ink drops, it is necessary to reduce the injection port diameter or to device the discharging method. Since, however, the conventional injection port diameter of the ink jet head is as small as 20 to about 30 microns, in order to bore an injection port with a smaller diameter than the injection port diameter, a more difficult manufacturing process is required and yet more injection ports must be provided, leading to an increase in manufacturing cost. Also, in such smaller injection ports, ink clogging or defective discharging due to dust or the like mixed into the ink is prone to occur, possibly deteriorating the reliability of the products. Also, even if the above-described problem was solved and ink drops having small dot diameter could be injected, a problem that the printing speed becomes slower would occur. This is a problem which occurs when more ink drops must be discharged in order to fill in the same area, and in order to solve this problem, there become necessary devices such as (1) to shorten discharge repeating time (high-speed driving of the ink injection device) and (2) to increase the number of elements (number of injection ports) The former (1) is difficult because of rate-determining of heat transmission time in the case of the heat type ink injection device. In the case of the piezo-electric type ink injection device, it may be driven at high speed as compared with the heat type, but there is a limit because of the trackability of the liquid to the piezo-electric actuator, and the like. Also, the latter (2) causes problems such as complicated device and reduced yields in the manufacture, leading to an increase in cost.
Secondly, as regards the method using superposedly dotting, the generally same problem occurs as the problem in the area modulation system because a multiplicity of smaller dots than the unit pixel must be hit in the unit pixel. Further, since liquid is shot onto the same point intensively in addition, a granulation phenomenon is prone to occur, easily causing print with surface roughness feeling.
Thirdly, the problem of density modulation system will be described. In the density modulation system, it is necessary to have a plurality of inks of different coloring matter density, and there arises a problem that the device becomes complicated and larger, and the cost is increased. Also, with an increase in type of the ink, there arise problems that the number of elements which can be actually used also reduces (number of elements/type of ink) and the printing speed is slowed down.
Fourthly, problems of the dot modulation system will be described. The dot modulation system modulates the dot dia
Kawasaki Osamu
Komatsu Atsushi
Namba Akihiko
Okano Masayuki
Tomita Yosihiro
Nguyen Thinh
Smith , Gambrell & Russell, LLP
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