Illumination – Revolving
Reexamination Certificate
2001-10-22
2004-10-26
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S035000, C362S026000, C362S027000, C385S146000
Reexamination Certificate
active
06808280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a line-illuminating device which is used in a contact-type image sensor (CIS).
2. Description of the Prior Art
A contact-type image sensor is used as a device for reading a document (i.e. a document reading device) using a facsimile machine, a copying machine, a scanner and the like. This contact-type image sensor is provided with a line-illuminating device for linearly illuminating a document surface along a main scanning range.
The line-illuminating device using a light guide is known. The line-illuminating device using a bar-shaped or plate-shaped light guide and a document reading device provided with such a line-illuminating device are disclosed in Japanese Unexamined Patent Publication Nos. Hei 8-163320 and Hei 10-126581.
FIG. 7
is a cross-sectional view of a document reading device incorporating a conventional line-illuminating device therein and
FIG. 8
is an exploded perspective view of the conventional line-illuminating device.
FIG. 9
is a perspective view showing one example of a light-scattering pattern formed on the reverse surface of a light guide.
As shown in
FIG. 7
, the document reading device is provided with a frame
101
in which recesses
101
a
and
101
b
are formed. A line-illuminating device
110
is arranged in the recess
101
a
of which the opening section is closed by a glass plate
102
. A sensor substrate
104
provided with a photoelectric conversion element (sensor)
103
is attached to the recess
101
b.
A rod lens array
105
is also held within the frame
101
. The document reading device allows the light emitted from an emission plane
111
of the line-illuminating device
110
to be incident on a reading surface of a document through a cover glass
106
serving as a document stand. The document is read by detecting the reflected light using the photoelectric conversion element (sensor)
103
through the rod lens array
105
.
In the line-illuminating device
110
shown in
FIG. 8
, a light guide
111
is housed in a white light guide casing
112
in such a manner that the emission plane
111
a
is exposed. A light emitting source substrate
113
provided with a light-emitting source such as a light-emitting diode (LED) is attached to one end of the light guide casing
112
. The light guide
111
is made of glass or transparent resin and its basic cross-sectional shape in the direction at right angles to a main-scanning direction (i.e. a longitudinal direction) is rectangular, wherein the corner section is chamfered in a C-shape to form the emission plane
111
a.
As shown in
FIG. 9
, the light guide
111
is provided, on its reverse surface, with a light-scattering pattern
111
b
for scattering the light from the light-emitting source incident from an incident plane. The light-scattering pattern is formed by screen printing a white coating material.
This line-illuminating device
110
is arranged to allow light from the light-emitting source such as an LED to enter from one end of the light guide
111
(i.e. the incident plane) into the inside of the light guide
111
, to allow the light spreading through the light guide
111
to be scattered by the light-scattering pattern
111
b
which is formed on the reverse surface of the light guide
111
, and to allow the scattered light to be emitted from the emission plane
111
a
(see FIG.
7
).
Intensity of light incident from the light-emitting source is high near the incident plane, while the intensity of light becomes lower as the light advances further from the incident plane. Now, as shown in
FIG. 9
, by broadening a forming area of the light-scattering pattern as the light advances further from the incident plane, it is intended that the intensity of light emitted from the emission plane
111
a
be uniform over the full length of the main-scanning direction.
As shown in
FIGS. 7 and 8
, covering the light guide
111
by the light guide casing
112
not only protects the light guide
111
, but also prevents the scattered light from being uselessly emitted outside the light guide
111
and increases the intensity of light emitted.
FIG. 10
is a view showing dimensions of an emission plane of a conventional line-illuminating device. In the conventional line-illuminating device
110
, a chamfer dimension of the emission plane
111
a
is about 20~25% of the board thickness of the light guide
111
. For example, when the height (i.e. the board thickness) of the light guide
111
is 2 mm, the chamfer dimension is about 0.4~0.5 mm. In this manner, by making the chamfer dimension smaller, directivity of emitted light is narrowed to improve intensity of the emitted light.
FIG. 11
is a graph showing light output distribution characteristics of the conventional line-illuminating device and
FIG. 12
is a view showing a measuring position of the light output distribution.
FIG. 13
is a graph enlargedly showing the light output distribution characteristics of the conventional line-illuminating device shown in
FIG. 11
in which the position in a sub-scanning direction is a range between 0.4 and 1.2 mm.
In
FIG. 11
, the vertical axis shows the light output and the horizontal axis shows the position in the sub-scanning direction. The position in the sub-scanning direction is, as shown in
FIG. 12
, arranged so that an end surface of the light guide
111
where the emission plane
111
a
is formed is the origin 0. Measurement of the light output distribution was made in a condition where the line-illuminating device
110
contacts the lower surface of the cover glass. Thickness of the cover glass is 1.1 mm. The upper surface of the cover glass is the origin
0
in the position in the Z-direction.
In
FIG. 11
, a round black dot indicates the light output distribution characteristics in which a document surface contacts the cover glass (Z=0.0 mm). A square mark indicates the light output distribution characteristics in which the document surface is elevated from the cover glass by 0.5 mm (Z=0.5 mm). A triangular mark indicates the light output distribution characteristics in which the document surface is elevated from the cover glass by 1.0 mm (Z=1.0 mm). An x mark indicates the light output distribution characteristics in which the document surface is elevated from the cover glass by 1.5 mm (Z=1.5 mm). A round mark indicates the light output distribution characteristics in which the document surface is elevated from the cover glass by 2.0 mm (Z=2.0 mm). Measurement of the light output distribution characteristics was made at a central position in the main scanning direction (i.e. the central position of the light guide in the longitudinal direction).
In the conventional document reading device, an optical axis of the rod lens array
105
is arranged at a place where the position in the sub-scanning direction is about 0.7 mm (0.6-0.8 mm). A light-receiving surface of the photoelectric conversion element (sensor)
103
is arranged on the optical axis.
In the conventional document reading device in which an optical axis of the rod lens array
105
is arranged at a position where the position in the sub-scanning direction is 0.7 mm and that position is a document reading position, decrease of the quantity of light becomes 45% when the document is elevated by 2 mm. Even when a position where the position in the sub-scanning direction is 1.2 mm is a document reading position, decrease of the quantity of light becomes 30% relative to the elevation of the document (Z=0-2.0 mm).
Accordingly, in the document reading device incorporating the conventional line-illuminating device therein, the quantity of illuminating light decreases remarkably when the document surface is elevated by a fold or two facing pages of the document, and unnatural shades are produced on the image read through the photoelectric conversion element (sensor).
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve such problems as stated above and to provide a line-illuminating
Saito Tomihisa
Uemura Yoshiyuki
Merchant & Gould P.C.
Nippon Sheet Glass Co. Ltd.
O'Shea Sandra
Zeade Bertrand
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