Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-04-21
2002-05-28
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S237000
Reexamination Certificate
active
06396529
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical printer head including a light source constituted of a plurality of luminous dots, a light-amount correction method for correcting a light amount of luminous dots in the optical printer head so as to render the light amount uniform, and an optical printer for emitting light therefrom toward a record medium to form an image thereon.
The assignee proposed an optical printer wherein a fluorescent luminous tube acting as a luminous device is used as a light source for an optical printer head to form an image on a record medium such as, for example, a silver salt convenience film or the like.
The optical printer head constituted by the fluorescent luminous tube in the proposed optical printer includes an envelope of which an interior is evacuated at a high vacuum. The envelope is formed by assembling insulating substrates made of a glass plate or the like into a box-like structure. An anode substrate which constitutes a part of the envelope is formed on an inner surface thereof with anodes on each of which a phosphor layer emitting light due to impingement of electrons thereon is deposited. The anodes and phosphor layers, as shown in
FIG. 6
, cooperate with each other to constitute two luminous dot trains
108
and
109
, which are formed by arranging a plurality of luminous dots
107
in two rows and in an offset manner in a main scanning direction. Also, the anode substrate is provided on the inner surface thereof with a plane control electrode, which is arranged so as to surround the luminous dots
107
and anode wirings. The envelope has filamentary cathodes stretchedly arranged therein so as to be positioned above the luminous dot trains
108
and
109
and extend along the luminous dot trains or in the main scanning direction. The filamentary cathodes each include a core wire made of tungsten or the like and an electron emitting material deposited on the core wire.
Feeding of electricity to each of the cathodes permits the core wire to generate heat, resulting in electrons being emitted from the electron emitting material. The electrons thus emitted are permitted to impinge on the phosphors of the anodes to which a drive voltage is selectively applied, resulting in the luminous dots selectively emitting light. The plane control electrode has a positive voltage constantly applied thereto during driving of the optical printer head, to thereby render an electric field in its neighboring region uniform.
In the optical printer thus constructed, a record medium and the optical printer head are moved relative to each other in a sub-scanning direction perpendicular to the main scanning direction of the luminous dot trains
108
and
109
during recording operation. Also, data on an image to be formed are fed to the optical printer head, to thereby permit the luminous dots
107
to emit light at predetermined timings in synchronism with relative movement between the record medium and the optical printer head. Such driving permits light of the luminous dots
107
of the optical printer head to be successively irradiated in a line parallel to the main scanning direction on the record medium for exposure thereof, leading to formation of the image on the record medium.
The luminous dots
107
of the optical printer head are varied in light amount or luminous intensity as indicated in FIG.
7
(
a
) wherein a light amount of each of the luminous dots is found by measuring light amounts of all luminous dots
107
. Also, the record medium on which recording operation is carried out by the optical printer head is generally constructed so as to carry out color development depending on a level of energy of light applied thereto or intensity of the light. Such construction of the record medium, when a light amount is varied among the luminous dots, causes a degree of color development of the record medium such as, for example, a density of a color developed on the record medium or the like to be varied at every portion of the record medium on which light is irradiated from each of the luminous dots.
In order to eliminate a variation in color development occurring on the record medium due to a variation in light amount among the luminous dots
107
, it is carried out to measure a light amount of each of all luminous dots
107
obtained when the luminous dots are driven for luminescence under the same conditions. Then, a value required to keep a level of luminescence of each of the luminous dots uniform or constant is calculated from the light amount of each of the luminous dots
107
and then stored in the form of information for correction in a ROM or the like. The value may be, for example, information for controlling lighting time of each of the luminous dots. When the luminous dots are used for an optical printer, the thus-stored correction information of each of the luminous dots is used for control which permits the light amounts of all luminous dots
107
to be kept constant or uniform. The control may be, for example, control of lighting time of the luminous dots. More specifically, as shown in
FIG. 7B
, a level of the light amount of each of the luminous dots is adjusted so that the light amount of each of the luminous dots is aligned with that of the luminous dot
107
having a minimum light amount, resulting in ensuring that an image at a uniform density is obtained on the record medium.
However, the fluorescent luminous tube acting as a light source for the optical printer head is so constructed that the filamentary cathodes each are welded at both end thereof to a stretch fitment, to thereby be stretchedly arranged in the envelope. Such construction causes a part of heat generated by the core wire of each of the filamentary cathodes to be absorbed by the stretch fitment. This fails to increase a temperature of the cathode to a level sufficient to permit the cathode to emit electrons, leading to an end cool phenomenon which causes both ends of the cathode to fail to emit a sufficient amount of electrons as compared with a central portion thereof. More specifically, this causes a substantial difference in light amount between the luminous dots
107
positioned at both ends of the cathodes and those positioned at other regions thereof, so that the luminous dots
107
at both ends are decreased in light amount as compared with those at the other regions.
Light-amount correction of the luminous dots
107
which is carried out in the prior art in order to eliminate such a difference in light amount causes light amounts of all luminous dots
107
to be corrected so as to be at a level of light amounts of the luminous dots positioned at both ends of the fluorescent luminous tube defined in the main scanning direction.
Also, in the record medium exposed to light emitted from the optical printer head, the luminous dots
107
arranged at both ends of the fluorescent luminous tube in the main scanning direction, as shown in
FIG. 6
, are positioned out of an effective printing range H or allocated to an ineffective printing range h which permits a variation in light amount of the luminous dots
107
to be substantially disregarded.
Thus, light-amount correction of the luminous dots
107
causes all luminous dots
107
to be set at a light-amount level equal to that of the luminous dots
107
which are out of the effective printing range H or in the ineffective printing range h which permits a variation in light amount of the luminous dots
107
to be substantially disregarded. This leads to a reduction in light amount of the luminous dots
107
in the effective printing range H which contributes to recording on the record medium, so that the luminous dot trains
108
and
109
fail to feed exposure energy at a sufficient level to the record medium without adversely affecting quality of an image to be formed, resulting in loss of the exposure energy.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a
Inoue Yawara
Miyoshi Rie
Shimizu Yukihiko
Futaba Corporation
Pham Hai
LandOfFree
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