Lens array, image sensor, information processor and...

Details Lens array, image sensor, information processor and... Lens array, image sensor, information processor and...

2002-04-25

2003-11-25

Epps, Georgia (Department: 2873)

Optical: systems and elements

Single channel simultaneously to or from plural channels

By surface composed of lenticular elements

C359S623000, C359S626000

Reexamination Certificate

active

06654173

ABSTRACT:

TECHNICAL FIELD
This invention relates to a lens array, an image sensor, and an information processor comprising the image sensor and an information processing system comprising the image sensor.
This application is based on Japanese Patent Application, No. Hei 11-306060 filed in Japan, the content of which is incorporated herein by reference.
BACKGROUND ART
Heretofore, an image sensor unified with a lighting device to light a document, a lens to form an image of the reflected light which is reflected by the document, and which has the information of the document, and a sensor to convert the reflected light image formed by the lens into electrical signals is used as the reading device in a facsimile device, a scanner device, or other information processor. Lenses may be divided into two basic kinds: reduction type lens and equal size type lens. The reduction type lens forms an image which has a size reduced relative to the size of the object, and which is formed by the reflected light from a document. The equal size type lens forms an image which has a size which is equal to an object, and which is formed b y the reflected light from a document.
Generally, the latter equal size type lens is often used as the shape of a so called lens array that has many lens elements arranged in line of a length equivalent to the width of a document.
Recently, the reduction type lens which requires a long optical path length is not used very much because of the desire to miniaturize information processors such as facsimile devices and scanner devices. Furthermore, the lens array which comprises the equal size type lens in which the optical path length is short is common.
The cylindrical lens which has a continuous refractive index profile inside is used as the equal size type lens. A lens, made of glass which has a continuous refractive index profile inside, was already proposed in Japanese Examined Patent Application, Second Publication No. Sho 47-816. Furthermore, a lens made of plastic which has a continuous refractive index profile inside was proposed in Japanese Examined Patent Application, Second Publication No. Sho 47-28059. Subsequently, the lens made of glass by various techniques and a lens made of plastic by various techniques were proposed. Generally both end surfaces of these graded index lenses are polished to mirror-finished surfaces which are vertical to the center axes of these lenses, and which are parallel mutually. Furthermore, these graded index lenses are used singly and as a micro-lens. Furthermore, the lens array in which a plurality of these lenses are arranged and adhered and unified is widely used as a part of line sensors used in copying machines, facsimile machines, scanners, and so on. Furthermore, the lens array is widely used as the writing devices used in LED printers and so on.
In addition, the range in which one lens forms an image of a size equal to that of an object is a circle of radius X
0
(radius of the field of view). The amount of light is the greatest at the optical axis and decreases with distance from the optical axis. The lens array causes a variation in the amount of light in t he length direction of the array with a period of the array pitch (2R) of the lens. The variation in the amount of light depends on the overlapping degree m defined by m=X
0
/2R.
A lens array designed so that the overlapping degree m satisfies 1.61≦m≦1.80 or 2.06≦m≦2.50 to make the variation in the amount of light small is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-64605.
However, there is a problem in that the amount of light reaching a light receiving sensor is reduced in this lens array because the overlapping degree m thereof is large and the radius X
0
of the field of view is large when an image sensor is composed by using this lens array. Therefore, the lens for a color scanner of the type whose chromatic aberration is small may be used in this lens array. However, generally an aperture angle is 15 degrees or less with this lens, that is, it is small. Therefore, the amount of light which can be taken in is ½ or less with this lens in comparison with a lens with an aperture angle of about 20 degrees typically used for a monochrome image sensor. Therefore, when this image sensor is used, it is necessary to lower the reading speed in accordance with the ability of the light receiving sensor. Furthermore, according to this, it becomes easy to be influenced by noise factors such as outside light.
Furthermore, the difference of conjugate length TC between each wavelength of RGB increases when the overlapping degree m is enlarged that when there is some chromatic aberration in the lens. Then, color blurring appears in the color image sensor comprising this lens. Furthermore, the resolution of the color image sensor comprising this lens is low.
DISCLOSURE OF INVENTION
An object of this invention is to provide a lens array in which the amount of light reaching the image forming surface is large and the variation in the amount of light is small. Furthermore, an object of this invention is to provide an image sensor in which reading speed is high, and an information processor comprising it. Reading speed of the image sensor is high even when a lens whose aperture angle is small and whose chromatic aberration is small, that the amount of light which can be taken in is small is used, by using the lens array in which the amount of light reaching the light receiving sensor is large. Furthermore, another object of this invention is to provide an image sensor whose resolution is high even if a lens with some chromatic aberration is used, and an information processor comprising it.
A point of this invention is that the lens array comprises cylindrical graded index lenses of radius r
0
wherein the refractive index continuously decreases from the center of the lens toward the periphery, said cylindrical graded index lenses are arranged in one line or plural lines with array pitch 2R, if R is R≧r
0
≧0.8R and if the refractive index profile of each graded index lens is approximated by n(r)
2
=n
0
2
{1−(g·r)
2
}, the overlapping degree m defined by m=X
0
/2R satisfies 1.05≦m≦1.2, wherein, said r is the distance from the optical axis, n(r) is the refractive index at the distance r from the optical axis, n
0
is the refractive index at the center, g is the refractive index profile constant, X
0
is the radius of the field of view (X
0
=−r
1
cos(Z
0
/P), r
1
is the effective radius of the graded index lens, Z
0
is the length of the graded index lenses, and P is the period length of the graded index lenses namely P=2&pgr;/g.
Furthermore, a point of this invention is that in the lens array the aperture angle of said graded index lens is 15 degrees or less.
Furthermore, a point of this invention is that in the lens array R is R>r
0
≧0.8R.
Furthermore, a point of this invention is that in the lens array the overlapping degree m is 1.1≦m ≦1.2.
Furthermore, a point of this invention is that in the lens array said graded index lens is made of plastic.
Furthermore, a point of this invention is that in the lens array said graded index lens is made of glass.
Furthermore, a point of this invention is that the image sensor comprises a lighting device which lights a document, said lens array which makes reflected light from a document form an image, and an opto-electronic conversion device which receives the light of the image formed by said graded index lens.
Furthermore, a point of this invention is that the image sensor comprises the lens array wherein an interval Lm between the end surface of one side of said graded index lens and the document satisfies 0.95·L
0
≦Lm≦1.05·L
0
with the air layer conversion, and wherein an interval Ls between the end surface of the other side of said graded index lens and the sensor satisfies 0.95·L
0
≦Ls≦1.05·L
0
with the air layer conversion, wherein said L
0
is L
0
=−(1

0
g)·tan(Z
0
&pgr;/P).
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