Linear illumination device

Details Linear illumination device Linear illumination device

1999-06-25

2001-07-31

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S234000, C362S551000, C362S555000, C362S806000

Reexamination Certificate

active

06268600

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear illumination device for illuminating a surface of a document in an optical image reading apparatus such as a direct contact type image sensor unit.
2. Description of the Related Art
Optical image reading apparatuses have been widely used in apparatuses such as a compact facsimile machine or a bar cord reader which optically read a document. Such an optical image reading apparatus illuminates the document, receives the light reflected by the document, and then obtains electric signals corresponding to an image on the document in accordance with the amount of the reflected light. As an illumination device of the apparatus of this kind, an LED array constituted by LED chips arranged in a line is used.
With reference to the drawings, an example of the conventional linear illumination device used as the optical image reading apparatus will be described.
FIG. 28
shows the configuration of a conventional optical image reading apparatus. In
FIG. 28
, a document
141
is placed below the optical image reading apparatus. The optical image reading apparatus includes: an LED array as a linear illumination device
142
for illuminating the document
141
; a rod lens array
143
for focusing light beams reflected by the document
141
; and a photoelectric conversion element array
144
for receiving the focused light beams so as to convert the light beams into electric signals. As shown in
FIG. 29
, the LED array is constituted by arranging a plurality of LED chips
152
in a linear manner on a substrate
151
on which a circuit conductor layer is formed.
The operations of the optical image reading apparatus and the linear illumination device having the above configurations will be described below.
First, light beams emitted from the LED array
142
are radiated onto the document
141
to be read. The light beams reflected from the document
141
are focused by the rod lens array
143
, and then are directed to the photoelectric conversion element array
144
so as to convert the light beams into electric signals corresponding to an image on the document
141
.
In general, the document
141
is optically read while the optical image reading apparatus is scanning the document
141
. In the case of using the LED array
142
as the illumination device, a direction along which the document
141
is scanned (hereinafter, simply referred to as a sub-scanning direction) is perpendicular to a direction in which the LED chips are arranged. In order to accurately read the document
141
, the optical image reading apparatus requires that the illumination device illuminates a portion of the document
141
with a narrow width in the sub-scanning direction. In addition, illumination is required to be uniform in a direction perpendicular to the sub-scanning direction (hereinafter, referred to as a main scanning direction).
In the case of using the LED array
142
, however, it is difficult to illuminate the document
141
uniformly in the main scanning direction due to variation in the amount of light emitted from each of the LED chips
152
and effects of the directionality thereof. In order to reduce the adverse effect of the directionality of the LED chips
152
, the number of the LED chips
152
needs to be increased. Alternatively, when the distance between the surface of the document
141
and the LED array
142
is made larger, the effects of the directionality of the LED chips
152
can be reduced. For example, in the case where an array of 24 LED chips is used as the illumination device, the distance between the document and the LED array should be set to be 9-10 mm in order to illuminate an A4 sized document with a satisfactory uniform light.
If illumination is not uniform in the main scanning direction, the electric signals obtained in accordance with the amount of light received by the photoelectric conversion element array
144
are also poor in uniformity (PRNU). The poor uniformity of the electric signals increases the production cost of the optical image reading apparatus in the case where the obtained electric signals are subjected to a signal correction processing (for example, shading correction). In addition, the electric signals with poor uniformity burden the signal correction processing ability. On the other hand, in the case where the signal correction processing is not performed, for example, when a uniformly gray document is read by the optical image reading apparatus, a brightly illuminated part may be displayed as white. Likewise, an insufficiently illuminated dark part may be displayed as black.
FIGS. 31A and 31B
show cross-sectional views of a direct contact type image sensor unit using the above-mentioned conventional illumination device. A document
64
is placed so as to be in close contact with one end of an optical fiber array
63
and is irradiated with light from an LED array
65
placed above. The reflected light which carries information of the document is directed toward a light receiving array
62
which is provided on the other end of the optical fiber array
63
so as to be converted into image signals.
In the image sensor unit as described above, however, illuminance on the surface of the document greatly varies since the LED array
65
is used as the illumination device. Therefore, since sensitivity of the sensor varies greatly, image reading performance is deteriorated. Moreover, since it is necessary to space the document
64
from the LED array
65
as described above, the unit itself becomes large. Therefore, a larger number of LED chips are required, thereby raising the cost of the unit.
Moreover, when the LED array
65
is brought closer to the surface of the document
64
in order to increase an S/N ratio, PRNU of the electric signals are further deteriorated due to the adverse effect of the directionality of each of the LED chips.
Next, another example of a conventional optical image reading apparatus will be described with reference to FIG.
30
.
FIG. 30
shows the configuration of another conventional optical color image reading apparatus. In
FIG. 30
, three fluorescent lamps
142
R,
142
G and
142
B are used as an illumination device. The three fluorescent lamps
142
R,
142
G and
142
B are respectively for red light, green light and blue light (hereinafter, respectively referred to simply as R, G and B). The fluorescent lamps
142
R,
142
G and
142
B are each lit separately in a time divided manner. A colored light beam emitted from one of the respective fluorescent lamps is reflected by a document
141
so as to be focused onto a photoelectric conversion element array
144
by a rod lens array
143
. The photoelectric conversion element array
144
receives the focused light beam to convert it into an electric signal. The operation is successively repeated for R, G and B, thereby allowing the color of the document
141
to be analyzed.
In this configuration, the document
141
can be illuminated uniformly in the main scanning direction. However, the three fluorescent lamps
142
R,
142
G and
142
B respectively corresponding to R, G and B are required, making it difficult to realize low cost and reduction in size of the optical color image reading apparatus.
SUMMARY OF THE INVENTION
The linear illumination device of this invention, includes: a guide made of a light transmitting material extending in a first direction, having a side face and at least one end face; light emitting means for allowing light to enter interior of the guide from the at least one end face of the guide; and a light diffusing section formed on part of the side face of the guide, for diffusing the light incident thereon, wherein at least part of the light entering the interior of the guide goes out from part of the side face of the guide facing the light diffusing section, thereby providing substantially linear illumination light along the first direction.
In one embodiment of the present invention, the light transmitting material has a light transmittance of 80% or more (ac

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