Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-07-17
2004-01-06
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S235000, C313S491000
Reexamination Certificate
active
06674061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to contact image sensor units and more particularly to electrode lead-out structures of light sources included in contact image sensor units.
2. Description of the Background Art
Contact image sensors (CIS's) for reading contents such as diagrams shown on manuscripts conventionally have been known.
In
FIGS. 15 and 16
, one example of a conventional CIS unit
100
is shown.
FIG. 15
is a plan view of CIS
100
disclosed in Japanese Patent Laying-Open No. 4-360458 (Japanese Patent No. 2953595) and,
FIG. 16
is a sectional view of CIS unit
100
shown in FIG.
15
.
As shown in
FIGS. 15 and 16
, CIS unit
100
includes a light emitting diode (LED) array
101
as a light source, a casing
102
, a sensor IC (Integrated Circuit)
103
, a rod lens array
104
and a glass plate
105
.
LED array
101
directs light on a manuscript
106
placed between a platen
107
and glass plate
105
and, the reflected light passes through rod lens array
104
and reaches sensor IC
103
. Then, the reflected light is converted into an electrical signal by sensor IC
103
and thus the content of manuscript
106
is read.
When LED array
101
is employed as the light source of the contact image sensor unit as described above, however, the following problems arise.
When the LED chip is employed, as a light output of an LED chip has a strong directivity and an amount of light directed forward largely differs from an amount of light directed diagonally forward, the following problems arise. When the LED chips are arranged to form a linear light source, due to a constraint in a mounting pitch, a gap is formed between LED chips and the amount of light on the LED chip becomes different from the amount of light on the gap. Hence, a corrugation of the light amount is produced (the light amount fluctuates) according to the LED mounting pitch in a direction the LED chips are arranged.
In addition, due to a fluctuation in a mounting accuracy of the LED (the accuracy of centers of light emission of the LED's to be aligned on a line) and the directivity of the light as described above, the corrugation (fluctuation) mentioned above further increases.
In addition, as brightness of the LED chips themselves largely differ from each other, when the LED chips are arranged, the variation in brightness appears in a distribution of brightness on the line. Thus, it is hard to obtain a uniform light amount across the entire length of the lighting.
Further, a light amount required as the light source of the image sensor varies according to a time required for the image sensor to read one line. This means that the following relation holds with regards to a signal output I of the sensor, a reading speed (read time T of one line) and brightness B of the light source: I∝T×B. Therefore, even if the LED array is employed as the light source, as far as the read time T is long enough (in the case of devices such as a facsimile, the speed of the reading of the manuscript is about ~10 ms/line), a resulting sensor output has practically no problem.
The sensor output is, however, not satisfactory in a fast reading with the reading speed of not more than 0.5 ms/line, for example.
When a strong brightness is needed, the LED chips must be mounted with high density to increase a current which contributes to light emission. Both high densification and current increase cause the heating of the light source, therefore adversely affect the life of the LED chip.
Through the vigorous researches, the inventor have reached an idea of using a light source which emits light by electric discharge as the light source of the contact image sensor and, have succeeded in developing a light source of such type. In
FIG. 1
, an example of a structure of a discharging and light emitting element
1
usable as the light source is shown.
As shown in
FIG. 1
, discharging and light emitting element
1
includes a substrate
2
, a transparent substrate
3
, an internal electrode
4
, an external electrode
5
, a metal bus
6
, an insulating layer (dielectric layer)
7
, a first fluorescent substance
8
, a second fluorescent substance
9
, an sealing layer
10
and a discharging space
11
.
Substrate
2
and transparent substrate
3
are formed of glass, for example. Transparent substrate
3
is placed on substrate
2
and has a wall
3
a
extending toward substrate
2
. Wall
3
a
is connected to substrate
2
via sealing layer
10
and insulating layer
7
. Thus, discharging space
11
is formed between substrate
2
and transparent substrate
3
. In discharging space
11
, a discharge gas such as xenon is charged. Here, sealing layer
10
is formed of a glass layer made by melting a frit, for example.
Internal electrode
4
is formed on substrate
2
and covered by insulating layer
7
. Insulating layer
7
is formed of a glass layer, for example. On insulating layer
7
, first fluorescent substance
8
is formed and, on a surface of transparent substrate
3
, second fluorescent substance
9
is formed.
External electrode
5
is formed of ITO (Indium Tin Oxide) or SnO
2
, for example, and has transmittancy. External electrode
5
is formed on an outer surface of transparent substrate
3
and metal bus
6
is formed on a peripheral portion of external electrode
5
.
To make discharging and light emitting element
1
with the above-described structure emit light, a voltage of a predetermined level (about 1000 V, for example) is applied between internal electrode
4
and external electrode
5
. Then, the discharge gas is electrolytically dissociated and emits ultra-violet light, and the ultra-violet light is directed upon first and second fluorescent substances
8
and
9
. Thus, first and second fluorescent substances
8
and
9
emit light as shown in FIG.
2
.
The inventor has found that the brightness of the resulting light is stronger than that obtained in the conventional example where the LED has been employed. In addition, the brightness distribution is uniform and the life of discharging and light emitting element
1
becomes far longer than the case of LED. Still further, ratio of a effective lighting length can be improved and the size reduction in longitudinal direction can be easily realized. Still further, as no toxic substance such as mercury is employed, damage on the environment can be obviated.
Though discharging and light emitting element
1
shown in
FIG. 1
has various superior characteristics to the conventional example as described above, the inventor has found the following problem in actually mounting discharging and light emitting element
1
as described above in the CIS unit.
The voltage can be applied between internal electrode
4
and external electrode
5
by leading out lead lines from respective electrodes
4
and
5
and applying the voltage through the lead lines.
When the lead lines are led out from end portions of substrate
2
and transparent substrate
3
at opposite sides, however, a big current loop running from a power supply, discharging and light emitting element
1
and to the power supply is formed. When the current flows through this loop, a large noise is externally radiated. The inventor has found that the noise affects the characteristic of the CIS unit by causing a variation of an electric signal output with time and severely degrades the performance.
SUMMARY OF THE INVENTION
The present invention is made to solve the above described problems. An object of the present invention is to provide a compact and high-performance CIS unit allowing prevention of failure caused by discharge generated by an insulation breakdown between electrodes and led-out lines, reduction in external noise, and having a line with a read width close to a CIS contour width.
A contact image sensor (CIS) unit according to the present invention includes, a discharging and light emitting element serving as a light source and a photoelectric conversion element converting light directed to a manuscript from the discharging and light emitt
Kao Glen
Kim Robert H.
Mitsubishi Denki & Kabushiki Kaisha
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