Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-12
2002-09-03
Hallacher, Craig A. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000
Reexamination Certificate
active
06443546
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a printing apparatus and printing control method. More particularly, the invention relates to a printing apparatus and printing control method for discharging ink droplets in accordance with the ink-jet method and printing character, images and the like on a recording medium.
An ink-jet printing apparatus known in the art performs printing by discharging extremely small ink droplets from a printhead. In comparison with other types of printing apparatus, such an ink-jet printing apparatus not only produces little noise, makes possible high-speed printing and facilitates color printing but also can be used to print on printing media such as plain paper as a matter of course and fabric as well. The apparatus makes high-quality printing possible.
In general, the printhead of an ink-jet printing apparatus has one to two thousand orifices which discharge ink droplets. The printhead is caused to scan in relative to the printing medium to thereby perform printing over the entire area of the printing medium. In an actual printing operation, the printhead is mounted on a carriage, the carriage is moved back and forth along the traveling path thereof (the traveling direction is referred to as the “main-scan direction”), and the printing medium is conveyed in a direction (referred to as the “sub-scan direction”) orthogonal to the carriage traveling direction a prescribed amount whenever the carriage is moved back and forth one time.
Usually an arrangement is adopted in which the printhead mounted on the carriage is mounted on the carriage removably or in which an ink tank containing the ink supplied to the printhead is removably attached to the printhead.
Thus, the structure of the conventional ink-jet printing apparatus is such that the ink tank is removably attached to the carriage or to the printhead. This makes it necessary for the printing apparatus to check automatically whether the ink tank has been installed in the printing apparatus correctly at the time of printing.
FIG. 11
is a perspective view showing a conventional detection principle for detecting whether an ink tank has been installed.
As shown in
FIG. 11
, an ink tank
102
containing ink
101
has a bottom provided with a light reflecting surface
103
. A light-emitting element
104
such as an infrared LED emits light that is reflected by the light reflecting surface
103
. The reflected light is received by a light-receiving element
105
such as a phototransistor. In a case where the ink tank
102
has been mounted correctly on the carriage of a printing apparatus, the light emitted by the light-emitting element
104
is reflected by the light reflecting surface
103
and reaches upon the light-receiving element
105
. The latter converts the light to an electric signal in accordance with the amount of light received and issues an output signal (I) serving as a detection signal indicating that the ink tank has been installed.
If the ink tank
102
has not been mounted on the carriage, on the other hand, the light emitted by the light-emitting element
104
continues traveling straightforward and is not returned to the light-receiving element
105
owing to the absence of a reflecting body. Thus an electric signal generated by the light-receiving element
105
varies, depending in whether the ink tank
102
is mounted or not.
Thus, whether or not the ink tank is present can be discriminated based upon the erectric signal generated by the light-receiving element
105
.
More specifically, let I represent the electric signal output by the light-receiving element
105
. If the ink tank has been installed correctly, the electric signal output I will be I
1
. If the ink tank has not been installed, however, the electric signal output I of the light-receiving element
105
will be “0”. This conventional art assumes that no extraneous light enters into the apparatus. Thus, the output of the light-receiving element
105
differs depending upon whether the ink tank is present or not.
If &agr; is decided beforehand to satisfy the inequality 0<&agr;<I
1
and the output (I) of the light-receiving element
105
is greater than &agr;, then it is judged that the ink tank
102
has been installed.
In the prior art, the ink-jet printing apparatus is provided with means inclusive of a sensor, which is fixed to the main body of the apparatus, for automatically detecting existence/absence of ink in the ink tank by utilizing the movement of the carriage and alerting the user based upon the result of the sensing operation. For example, the residual ink detection means includes electrodes provided within the ink tank and measures the electrical conductivity between the electrodes or is adapted to sense discharged ink droplets optically. In general, the method using the electrodes results in a more complicated structure for the ink tank itself. For this reason, the most usual practice is to adopt the means for detecting existence/absence of ink in optical fashion.
An ink-jet printhead or an ink tank equipped with detecting means for optically detecting residual ink is disclosed in the specifications of Japanese Patent Application Laid-Open (KOKAI) Nos. 60-31021, 2-102062 and 7-218321.
FIG. 12
is a diagram showing an example of the conventional arrangement of an ink detection unit for optically detecting whether ink is present or not.
As shown in
FIG. 12
, the ink tank
102
, which comprises a member such as semi-transparent plastic having a light transmitting property, accommodates ink
101
. The bottom of the ink tank
102
is formed to have an optical prism
106
that performs the function of an optical ink sensing unit. Here the optical prism
106
is a triangular prism having an apex angle of 90°. The optical prism
106
consists of a nearly transparent material such as polypropylene and is formed as an integral part of the ink tank
102
.
Light emitted from the light-emitting element
104
under conditions in which there is no ink in the ink tank
102
reaches the light-receiving element
105
upon being reflected at boundary surfaces
106
A,
106
B between the optical prism
106
and ink
101
. Let the electric signal output,I from the light-receiving element
105
under these conditions be represented by I
2
.
Under conditions where the ink tank
102
is filled with the ink
101
, the reflectance of the emitted light at the boundary surfaces
106
A,
106
B differs from that in the absence of ink owing to the refractive indices of the ink tank
102
itself and ink
101
. As a result, there is a reduction in the amount of light from the light-emitting element
104
that arrives at the light-receiving element
105
via the boundary surfaces
106
A,
106
B. Accordingly, the output (I) of the light-receiving element
105
in this case satisfies the equation I=I
3
<I
2
. Thus, it is possible to detect whether or not the ink
101
is present within the ink tank
102
based upon the amount of light sensed by the light-receiving element
105
.
Thus, the output of the light-receiving element
105
differs depending upon whether the ink
101
is present or not.
If &bgr; is decided beforehand to satisfy the inequality 0<I
3
<&bgr;<I
2
and the output (I) of the light-receiving element
105
is greater than &bgr;, then it is judged that there is no ink in the ink tank
102
.
However, various factors in addition to the light from the light-emitting element
104
contribute to the output of the light-receiving element
105
and cause the output to fluctuate.
For example, the phototransistor used in the light-receiving element
105
produces current (referred to as “dark current”) even when it is not receiving light. The output of dark current depends upon the ambient temperature and rises exponentially as the temperature rises. In addition, there is the possibility that extraneous light, not the light for which the light-emitting element
104
is the source, will reach upon the light-receiving element
105
. The extraneous light is such that the amount of incident light
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hallacher Craig A.
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