Method of driving fluorescent print head and image forming...

Details Method of driving fluorescent print head and image forming... Method of driving fluorescent print head and image forming...

2002-04-05

2003-12-16

Tran, Huan H. (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S247000, C313S496000, C313S497000, C315S169100, C315S169300

Reexamination Certificate

active

06664997

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of driving a fluorescent print head used as a light source for an optical printer (an image forming apparatus) such as a color printer, which forms an image on a recording medium such as a photosensitive film (e.g. an instant film) or a photographic paper (e. g. a silver salt paper), and to an image forming apparatus.
A fluorescent print head mounted on an optical printer such as a color printer, which uses light emitted due to electrons hitting a fluorescent substance and creates a desired image on a recording medium (e.g. a photosensitive film and a photographic paper), is well known.
FIG. 3
is a cross-sectional view partially illustrating a fluorescent print head of the above-mentioned type.
FIG. 4
is a plan view illustrating luminous dots of a fluorescent print head. FIG.
5
(
a
) is a perspective view partially illustrating the anode substrate of a fluorescent print head. FIG.
5
(
b
) is a plan view partially illustrating the anode portion.
FIG. 6
is a side view illustrating an optical printer having three fluorescent print heads for R (red), G (green) and B (blue) luminous colors.
As shown in
FIG. 6
, the optical printer
1
has as a dot array three fluorescent print heads
2
(
2
R,
2
G,
2
B). Each fluorescent print head
2
has luminous dots emitting R (red), G (green) or B (blue) color (or a R, G, or B filter is combined with a luminous dot of a fluorescent substance with a broad wavelength (e.g. a ZnO:Zn fluorescent substance) containing R, G and B components). A recording medium such as a film is exposed to the light beams from respective print heads
2
to form a desired image.
The three fluorescent print heads
2
R,
2
G, and
2
B have the same structure (However, the combination of either fluorescent substances or fluorescent substances and R, G, and B filters is different). Here, the structure of a fluorescent print head
2
R emitting red color light will be described below as an example.
As shown in
FIG. 3
, the fluorescent print head
2
R has a container
6
, being a box assembled with an anode substrate
3
, side plates
4
, and a rear substrate
5
by bonding together with a sealing glass. The inside of the container
6
is evacuated in a vacuum state.
As shown in
FIG. 4
, a first luminous dot column
8
of plural luminous dots
7
and a second luminous dot column
9
of plural luminous dots
7
are arranged in parallel along the longitudinal direction of the anode substrate
3
over the inner surface of the anode substrate
8
. Each luminous dot
7
has an anode electrode
10
(made of a frame-like conductive thin film of aluminum), patterned on the anode substrate
10
using the sputtering and the photolithography, and a fluorescent substance layer
11
coated on the anode
10
.
The fluorescent substance layer
11
, for example, made of zinc oxide fluorescent substance (ZnO:Zn), or cadmium sulfide series fluorescent substance ((Zn,Cd)S:Ag,Cl), is formed in such a way that the layer
11
has an opening wider than the square opening
10
a
of the anode
10
and does not run off the frame. The light emitted from the surface of the fluorescent substance layer
11
radiated outside through the fluorescent substance and the anode substrate
3
from the opening of the anode
10
. Hence, the area of each luminous dot
7
corresponds to the effective luminous area of the fluorescent substance layer
11
defined by the opening
10
a
of the anode
10
.
In the first and second luminous dot columns
8
and
9
, respective luminous dots
7
are led out with the anode conductor
12
and are electrically connected to the control circuit
14
on the circuit substrate
13
, using, for example, TAB (tap-automated bonding, as shown in
FIGS. 3 and 6
.
Here, the shape of each luminous dot
7
and the arrangement of the first and second luminous dot columns
8
and
9
will be described. As shown in
FIG. 4
, each luminous dot
7
is in a square form of which one side has a length (a). In the first and second luminous dot columns
8
and
9
, a large number of luminous dots
7
are arranged at intervals of (a) in the primary scanning direction. The luminous dots in the luminous dot column
8
and the luminous dots in the luminous dot column
9
are shifted to each other by the pitch P (=a) in the scanning direction. Moreover, the luminous dots in the luminous dot column
8
and the luminous dots in the luminous dot column
9
are spaced away from each other by the pitch (b) (an integer multiple of the pitch P in the primary scanning direction) in the secondary scanning direction. The luminous dot columns
8
and
9
also are arranged in parallel and in zigzag form.
As shown in
FIG. 3
, a flat control electrode
15
is arranged as a control electrode on the upper surface of the anode substrate
3
. The flat control electrode
15
, which is made of a conductive film (e.g. aluminum), surrounds the luminous dots
7
and anode conductors
12
and is disposed so as to be flush with the luminous dots
7
. A positive voltage is always applied to the flat control electrode
15
upon drive operation to maintain the adjacent electric field at a fixed level.
In the container
6
, as shown in
FIG. 3
, the first filament cathode
16
and the second filament cathode
17
, each being a thermionic cathode, are suspended above the first and second luminous dot columns
8
and
9
. The first filament cathode
16
and the second filament cathode
17
are arranged in the primary scanning direction and are spaced substantially at equal distances from the centers of the luminous dot columns
8
and
9
. In the filament cathodes
16
and
17
, an electron emission material is coated on an ultra-fine tungsten alloy wire (e.g. tungsten or rhenium tungsten) of a diameter of 7 &mgr;m to 50 &mgr;m. The electron emission material is made of a ternary oxide containing barium oxide, calcium oxide, and strontium oxide. That oxide is uniformly coated at a thickness of 5 &mgr;m to 10 &mgr;m over a tungsten of a diameter of several &mgr;m to several tens &mgr;m. The filament voltage is adjusted to set the filament cathodes
16
and
17
to 600° C. to 700° C. Thus each of the filament cathodes
16
and
17
functions as a thermal electron source.
A NESA film
18
a
, being an anti-static translucent conductive film, is formed on the inner surface of the rear substrate
5
. A anti-reflection layer
18
b
formed of graphite is formed on the NESA film
18
a
. The anti-static layer
18
b
absorbs light from the luminous dot
7
(anode
10
) to prevent it from being reflected back to the luminous dot
7
. With omission of the anti-static layer
18
b
, the light reflected back to the light emission side leaks from the gap between the anode
10
and the flat control electrode
15
. This decreases the display contrast.
Inside the enclosure
6
shown in
FIG. 3
, a first shield electrode
19
of a stainless steel thin plate is disposed outside the luminous dot column
8
and the first filament cathode
16
. Similarly, the second shield electrode
20
of a stainless steel thin plate is disposed outside the luminous dot column
9
and the second filament cathode
17
. The shield electrodes
19
and
20
are connected together to the same potential. Each of the shield electrodes
19
and
20
is a plate having a nearly L-shaped cross section, viewed from the plane perpendicular to the primary scanning direction. The flange plates are disposed in parallel on the surface of the anode substrate
3
. The shield electrode
19
or
20
may be a flat plate. The flange plate of each of the shield electrode
19
,
20
is disposed above the anode substrate
3
via the insulating layer
21
containing main components (e.g. a low-melting point glass) (or with the gap of about 0.5 mm or less). The shield electrodes
19
and
20
surround the filament cathodes
16
and
17
and the upper ends thereof are positioned above the filament cathodes
16
and
17
. The shield electrode
19
,
20
prevents the surface of the insulating layer
21
from being c

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