Electric lamp and discharge devices – With gas or vapor – Having electrode exterior to envelope
Reexamination Certificate
2000-08-24
2003-09-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode exterior to envelope
C313S484000, C313S631000, C313S635000, C358S482000, C358S496000, C358S498000, C250S208100
Reexamination Certificate
active
06621218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to line light sources and image sensors using the same and, more particularly to a line light source of an image sensor which can be used for an image inputting portion of a large image input/output apparatus of a size exceeding A3 (JIS (see Japanese Industrial Standard) B0191) and an image sensor provided with the same.
2. Description of the Background Art
FIG. 16
is a cross sectional view showing a conventional image sensor
13
, and
FIG. 17
is a partial view showing a hot cathode fluorescent lamp, which is a line light source
51
of image sensor
13
.
Referring to
FIG. 16
, image sensor
13
includes: a casing (a sensor frame)
19
holding components therein; the hot cathode fluorescent lamp used as line light source
51
; a rod lens array
15
for erect and equimagnification imaging including a plurality of rod lens; a sensor substrate
16
; a sensor IC
17
linearly placed on sensor substrate
16
; and a glass plate
18
serving as a surface over which a manuscript
14
is transported. A heater
41
is arranged at the periphery of line light source
51
.
Referring to
FIG. 17
, line light source
51
is provided with a glass tube
42
, a lead wire
45
, and an electrode
44
. A fluorescent material is applied to the inner wall of glass tube
42
, and glass tube
42
internally includes mercury and an inactive gas (argon, neon and the like). A filament
43
forming a part of electrode
44
is provided, to which an emissive material called an emitter is applied.
Now, the operation will be described. The light from the hot cathode fluorescent lamp passes through glass plate
18
, so that manuscript
14
is uniformly illuminated with light. The illumination light is reflected by manuscript
14
in accordance with the shading information of an image to be directed into the rod lens of rod lens array
15
and to sensor IC
17
.
Sensor IC
17
accumulates electric charges in accordance with the intensity of the reflected light, and data is output through sensor substrate
16
. The vapor pressure of the mercury in the hot cathode fluorescent lamp varies according to the temperature, and the luminance of the hot cathode fluorescent lamp changes by the variation in the vapor pressure of the mercury. Thus, heater
41
is used to keep the temperature of the hot cathode fluorescent lamp constant. The luminance of the hot cathode fluorescent lamp is kept constant by heater
41
.
The hot cathode fluorescent lamp emits light by the following operation.
{circle around (1)} A current is applied to electrode
44
through lead wire
45
to preliminary heat filament
43
.
{circle around (2)} Thermoelectrons are discharged from the emitter (emissive material) applied to filament
43
.
{circle around (3)} The thermoelectrons move toward electrode
44
on the opposite side as attracted.
{circle around (4)} The thermoelectrons collide with mercury atoms as attracted to electrode
44
to produce ultraviolet rays.
{circle around (5)} The ultraviolet rays are directed to the fluorescent material applied to the inner wall of glass tube
42
to produce visible rays.
A light emitting diode, an external electrode rare gas fluorescent lamp or the like is used as a light source of the image inputting portion, instead of the hot cathode fluorescent lamp. However, for a large image inputting portion having a size exceeding A3, the hot cathode fluorescent lamp producing a sufficient amount of light and allowing an illumination length exceeding A3 is used.
The above described structure of the hot cathode fluorescent lamp of the conventional line light source requires heater
41
to keep the ambient temperature of the hot cathode fluorescent lamp and the vapor pressure of mercury therein constant so that the luminance of the hot cathode fluorescent lamp is kept constant, and further requires a control circuit for heater
41
. In addition, the use of mercury adversely affects the environment when the hot cathode fluorescent lamp is discarded, and therefore, the mercury should not be used.
An external electrode rare gas fluorescent lamp causing less variation in luminance according to a temperature may be used in place of the hot cathode fluorescent lamp suffering from the aforementioned problems. The external electrode rare gas fluorescent lamp will be described with reference to
FIGS. 18
to
21
.
FIG. 18
is a side view showing an external electrode rare gas fluorescent lamp. As shown in
FIG. 18
, a line light source (external electrode rare gas fluorescent lamp)
1
includes a glass tube
2
, outer electrodes
4
,
5
, a lamp holder
8
provided at both ends, and two lead wires
10
.
A fluorescent material is applied to the inner wall of glass tube
2
, and glass tube
2
internally includes an inactive gas (xenon or the like). Outer electrodes
4
,
5
are arranged opposite to each other with glass tube
2
therebetween, each connected to one lead wire
10
. Lamp holder
8
is used for holding the external electrode rare gas fluorescent lamp to a contact image sensor.
FIG. 19
is a cross sectional view taken along the line
300
—
300
of the external electrode rare gas fluorescent lamp shown in FIG.
18
.
FIG. 20
is a cross sectional view taken along the line
400
—
400
of the external electrode rare gas fluorescent lamp shown in FIG.
19
.
FIG. 21
is a graph showing a distribution of illumination light from line light source
1
shown in
FIG. 18
, where an abscissa represents the position of line light source
1
and an ordinate represents brightness.
The above described external electrode rare gas fluorescent lamp emits light by the following operation.
{circle around (1)} A high frequency high voltage is applied to outer electrodes
4
,
5
through lead wire
10
.
{circle around (2)} Xenon atoms are discharged to produce ultraviolet light.
{circle around (3)} The ultraviolet light is directed to a fluorescent material applied to the inner wall of glass tube
2
to produce visible rays.
However, the length of the external electrode rare gas fluorescent lamp is limited. This is because the external electrode rare gas fluorescent lamp is mainly used for a copier for which the size of A3 is sufficient and there is little demand for lamps having the size exceeding A3. In addition, a large amount of investment must be put to manufacture large external electrode rare gas fluorescent lamps having the large size exceeding A3. Consequently, external electrode rare gas fluorescent lamps which are large enough to be used for large image inputting portions having a size exceeding A3 are not presently supplied.
SUMMARY OF THE INVENTION
The present invention is made to solve the above mentioned problems. An object of the present invention is to provide a line light source which has a luminance stable with respect to an ambient temperature and which can used for a large image inputting portion having a size exceeding A3 by using a rare gas fluorescent while not using mercury, which may adversely affect the environment.
A line light source according to the present invention is provided with the first and second rare gas fluorescent lamps, and a fixing member. The first rare gas fluorescent lamp includes a first hollow body having an inner wall to which the fluorescent material is applied and including an inactive gas in an internal space thereof, and first and second electrodes positioned on the opposite sides of the internal space of the first hollow body. The second rare gas fluorescent lamp includes a second hollow body having an inner wall to which a fluorescent material is applied and including an inactive gas in an internal space thereof, and third and fourth electrodes positioned on the opposite sides of the internal space of the second hollow body. The fixing member fixes the first and second rare gas fluorescent lamps as arranged in the longitudinal direction thereof.
If the first and second rare gas fluorescent lamps are fixed by the fixing member as arranged in the longitudinal direction as described above, the li
Mitsubishi Denki & Kabushiki Kaisha
Patel Nimeshkumar D.
Roy Sikha
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