Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-07-26
2004-06-01
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S208100, C250S227200
Reexamination Certificate
active
06744033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bar-shaped light guide, a line-illuminating device incorporated with the light guide, and a contact-type image sensor incorporated with the line-illuminating device.
2. Description of the Prior Art
A contact-type image sensor has a smaller number of parts than an image sensor using a reducing optical system. A sensor and a lens array which are optical components can also be arranged closely. Accordingly, there is an advantage that the contact-type image sensor can be made comparatively thin. Thus, the contact-type image sensor is used as equipment for reading a document in a facsimile machine, a copying machine, a hand scanner and the like.
The contact-type image sensor is provided with a line-illuminating device for linearly illuminating a document-reading surface along the main scanning direction. The line-illuminating device using the light guide is known.
FIG. 22
is a cross-sectional view of a contact-type image sensor developed by the present inventor et al. and
FIG. 23
is a perspective view of a light guide which is used in that contact-type image sensor.
The contact-type image sensor
101
is provided with a frame
102
in which a line-illuminating device
110
is installed. A lens array
105
is arranged within the frame
102
. Mounted on the lower part of the frame
102
is a base plate
107
which is provided with a line image sensor (i.e. a photoelectric conversion element)
106
. The line-illuminating device
110
consists of a light guide
103
, a light guide casing
104
, and a light-emitting source base plate provided with an LED or the like (not shown).
The contact-type image sensor
101
allows illuminating light emitted from an emission plane
103
a
of the light guide
103
to be incident on a reading surface of a document through a cover glass
108
. The document is read by detecting the reflected light using the line image sensor
106
through the lens array
105
.
The light guide
103
is made of glass or transparent resin and as shown in
FIG. 23
, it has a cross-sectional shape substantially ¼ oval in the direction perpendicular to the longitudinal direction. A side surface of the light guide
103
along the longitudinal direction is provided with the emission plane
103
a
parallel to a minor axis direction of the oval, a plane
103
b
parallel to the major axis direction of the oval, and a reflecting curved plane
103
c
. Light scattering patterns
103
P are formed on the plane
103
b
parallel to the major axis direction of the oval by printing white coating materials. The light guide
103
allows the illuminating light incident from end surfaces in the longitudinal direction to be reflected by the inner surface and guides the reflected light in the longitudinal direction. The light guide
103
also allows the light scattered by the light scattering patterns
103
P to be reflected by the reflecting curved plane
103
c
and to emit the reflected light from the emission plane
103
a
. Now, by changing an area of the light scattering patterns
103
P in response to a distance from the end surfaces of the light guide
103
, it is intended that the intensity of light emitted from the emission plane
103
a
be uniform along the longitudinal direction of the light guide
103
.
The light guide
103
is, as shown in
FIG. 22
, housed in the white light guide casing
104
in such a manner that the emission plane
103
a
is exposed. In this manner, by covering the light guide
103
using the light guide casing
104
, the light emitted outside is caused to reflect by the light guide casing
104
and returned to the inside of the light guide
103
. Thus, loss of the scattered light is reduced and as a result, intensity of the emission light is improved. The light scattering patterns
103
P are formed at a position near a focal point on the plane
103
b
parallel to the major axis direction of the oval. With this, the light scattered by the light scattering patterns
103
P is reflected by the reflecting curved plane
103
c
and is condensed on the document reading surface. As a result, it is possible to improve the intensity of light on the document-reading surface.
The light emitting source base plate (not shown) provided with a light emitting source consisting of an LED or the like is attached to one end or both ends of the light guide casing
104
. In this manner, the line-illuminating device comprises the light guide
103
, the light guide casing
104
, and the light emitting source base plate.
The conventional light guide and line-illuminating device incorporated with the light guide described above have a first problem described below.
According to the conventional device, it is intended that quantity of illuminating light be maximum in a condition in which the document surface is not elevated. Accordingly, when the document surface is elevated by a fold or spread of the document, the quantity of illuminating light decreases, and an unnatural shade is caused on an image read by the line image sensor
106
.
FIG. 24
is a graph showing light intensity characteristics of the contact-type image sensor described above. In
FIG. 24
, the horizontal axis shows displacement of a sub-scanning direction of which the origin is the focal distance (which is on an upper surface of the cover glass plate
108
) of the lens array
105
and the vertical axis shows light intensity measured at each point.
Parameter of each curve means a distance upward from the surface of the glass plate (e.g. the distance 0.0 mm is the surface of the glass plate). Namely, data shown in
FIG. 24
is not that measured using a line sensor of the device, but that measured by a separate sensor provided above the glass plate. Accordingly, “light output characteristics when the document surface is elevated by x mm” specifically means “the light output characteristics measured by an optical sensor which is put at a distance of x mm above the upper side surface of the glass plate, corresponding to a state where the document surface is elevated by x mm”. However, this is described below as “the light output characteristics when the document surface is elevated by x mm” for clarification.
In
FIG. 24
, a position in which light intensity is maximum in a condition where the document surface is not elevated (i.e. the position where the illuminating light emitted from the light guide
103
is converged on the document surface) is set as the origin 0 of the displacement in the sub-scanning direction. A side of the light guide
103
from this position is shown by a minus value, while the opposite side is shown by a plus value. A black round mark indicates the light output characteristics when the document surface contacts the cover glass
108
and a square mark indicates the light output characteristics when the document surface is elevated by 0.5 mm from the cover glass
108
. A triangular mark indicates the light output characteristics when the document surface is elevated by 1 mm and an x mark indicates the light output characteristics when the document surface is elevated by 1.5 mm. A round mark indicates the light output characteristics when the document surface is elevated by 2.0 mm.
In the contact-type image sensor described above, an optical axis of the lens array
105
is arranged in a position where the displacement in the sub-scanning direction is the origin 0, wherein a light-receiving surface of the line image sensor
106
is arranged on the optical axis. Thus, as shown in
FIG. 24
, when the document is elevated by 1 mm, the quantity of illuminating light (i.e. quantity of reading light) decreases by 20% or more. Accordingly, unevenness in illumination is produced at a position where bending, crinkles, fold, or spread occur on the document surface and as a result, an embossed-like image has been produced even on a simple white document in an extreme case.
If the reflecting curved plane (i.e. the oval plane) of the light guide is sufficiently increased, the scattering patterns are relatively decreas
Blackman William D.
Carrier Joseph P.
Carrier Blackman & Associates P.C.
Lee Patrick J.
Nippon Sheet Glass Co. Ltd.
LandOfFree
Bar-shaped light guide, line-illuminating device... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bar-shaped light guide, line-illuminating device..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bar-shaped light guide, line-illuminating device... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3332132