Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1998-06-12
2001-05-29
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C362S581000, C355S001000
Reexamination Certificate
active
06239421
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rod lens array, and image read apparatus and image read system using the rod lens array.
With the recent rapid spread of personal computers, there exists demand for a system for reading an image, such as a photograph and an illustration, using an information processing apparatus for image input purpose, called scanner, processing the read image on a computer, and printing the processed image on a postcard or other document. When using the scanner in a residence, a setting space, utilization convenience, and the appearance of the scanner are important. Accordingly, a small and light-weight scanner is demanded.
As an example achieving down-sizing and down-weighing, there is a scanner using a contact type image sensor, as an image read unit, for reading an original image upon contacting the original image.
FIG. 15
is an external perspective view of a conventional contact type image sensor. In
FIG. 15
, reference numeral
1
denotes a frame for supporting the entire image sensor; and
5
, a cover glass for determining a reading surface upon contacting an original image. The frame
1
includes many photodetectors arranged along the length (in the direction of an arrow DM) of the frame
1
as a sensor array. Here, the direction of the arrow DM is denoted as the main scanning direction and the widthwise direction (direction of an arrow DS which is perpendicular to the direction DM) of the frame
1
is denoted as the sub-scanning direction.
FIG. 16
is a cross-sectional view taken along a line B-B′ in
FIG. 15. A
rod lens array
7
, as an image forming device, is arranged in a first space
1
A, and an illumination device
6
is set in a second space
1
B. The first and second spaces
1
A and
1
B are connected. The illumination device
6
comprises a light guide
61
having the function of guiding the light, emitted from one or more LED light sources
63
, in the main scanning direction DM and illuminating an original image
500
by reflecting the guided light on a reflection surface
64
toward the original image
500
, and a housing
62
, or a frame, having the function for preventing light from leaking from the light guide
61
and fixing the position of the light guide plate
61
so that the original image
500
is effectively illuminated. The light emitted from the above light source
6
illuminates the original image
500
on a cover glass
5
, and the rod lens array
7
and a sensor substrate
4
, which is arranged in a third space
1
C, are arranged so that the reflected light from the original image forms an image on a sensor IC
3
on the sensor substrate
4
.
The foregoing image sensor is assembled in such manner that the illumination device
6
is fixed on a clamp face
1
D of the frame
1
by adhesive or screws, and the rod lens array
7
is inserted into the first space
1
A and fixed on a clamp face
1
E of the frame
1
by adhesive or screws. Then, the sensor substrate
4
on which the sensor IC
3
is mounted is fixed on the frame
1
via a frame
2
. Thereby, the image sensor is assembled.
The rod lens array
7
is formed in such manner, as shown in
FIG. 17
, that a plurality of rod lenses
71
are arranged in one or more lines, sandwiched by thin supporting plates, or side plates,
72
and
73
, and the spaces between the rod lenses
71
and the supporting plates
72
or
73
are filled with resin to fix the positions of the rod lenses
71
.
Each rod lens
71
is made by gradually decreasing index of refraction from the peripheral portion toward the central portion. The diameter of the rod lens
71
is about 0.6 mm, and the thickness of the side plates
72
and
73
is about 0.5 mm. The rod lens array
7
has characteristics of forming an image of the original image
500
on the object plane of the same size on the image plane. Therefore, the rod lens array
7
is suitable for forming an image of an original image on the sensor surface to read the image when the original image is placed on the object plane and photodetection surface is arranged on the image plane.
FIG. 18
shows relationship between the rod lens array
7
, an object plane
74
, and an image plane
75
. The distance between the object plane
74
and the image plane
75
depends upon the characteristics of each rod lens, and is called “conjugate distance” (TC). Further, the distance between the end of the lens and the object plane
74
or the image plane
75
is called “working distance” (L
0
). Further, the distance denoted by Z
0
is the length of each rod lens forming the rod lens array
7
, or the height of the rod lens array
7
.
As for the rod lens array
7
mainly used in this type of the image sensor, there are two types of lens arrays; those having the conjugate distance TC of 9 mm and those having the conjugate distance TC of 18 mm. When down-sizing is given priority, an image sensor of the former type is used; whereas, when resolution and depth of focus are given priority, an image sensor of the latter type is used. Below, an image sensor using a rod lens array whose conjugate distance TC is 9.1 mm is explained.
FIG. 19
is an image sensor using a rod lens array
7
whose conjugate distance TC is 9.1 mm, and
FIG. 20
shows position relationship between the rod lens array
7
, the illumination device
6
, the cover glass
5
, and the sensor substrate
4
. Note, the illumination device
6
has a plurality of LED chips arranged in a line on a substrate. The height Z
0
of the rod lens array
7
is 4.3 mm, and the distance from the end of the rod lens array
7
to the surface of the sensor IC
3
corresponds to the working distance L
0
, and it is 2.4 mm. Further, the distance L
0
′ from the end of the rod lens array
7
to the original image
500
is slightly larger than the working distance L
0
, since there is the cover glass
5
of the thickness d of 1 mm having the index of refraction of about 1.5 between the end of the rod lens array
7
and the original image
500
, and the distance L
0
′ is 2.7 mm. Therefore, the distance from the original
500
to the sensor IC
3
is 9.4 mm, which is slightly longer then the conjugate distance TC of the rod lens array
7
, and the thickness of the image sensor is about 11 mm including the thickness of the sensor substrate
4
.
In order to make the best use of the advantage of the above contact type image sensor to realize a compact image sensor and further minimize the image sensor, utilization of an image forming device having a shorter conjugate distance TC than the above is proposed.
The conjugate distance TC of a rod lens array is known to be determined by the following equations;
TC=Z
0
+2
×L
0
L
0
=−1/(
n
0
×
{square root over (A)}
)×tan(
Z
0
×&pgr;/
P
)
P=
2×&pgr;/
{square root over (A)}
(1)
In the above equations (1), A denotes a distributed constant of the index of refraction of each rod lens, n
0
denotes the index of refraction of each rod lens on the optical axis, Z
0
denotes the length of each rod lens, P denotes wavelength, and L
0
denotes the working distance.
As a method for shortening the conjugate distance TC expressed by the above equations (1), there is a method for slightly increasing the length of the each rod lens forming the rod lens array
7
, or the height Z
0
of the rod lens array
7
. For example, in the rod lens array having the conjugate distance TC of 9.1 mm as shown in
FIG. 20
, the value of the variables are:
n
0
=1.639
{square root over (A)}=0.8637
Z
0
=4.3 mm
Among the above values, with n
0
and {square root over (A)} fixed, Z
0
is slightly increased to 4.5 mm, and the conjugate distance TC becomes 8.1 mm according to the above equations (1).
FIG. 21
shows a lens array
7
having the height Z
0
of 4.5 mm and the conjugate distance TC of 8.1 mm. With this configuration, it is possible to shorten the conjugate distance TC without changing distribution of index of refraction of the rod lenses. In this method, however, the length of
Kawai Tatsundo
Nagata Kenji
Tabata Masami
Canon Kabushiki Kaisha
Lee John R.
Morgan&Finnegan LLP
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