JPH1096856A - Original reading optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image formation lens whose cost is low while keeping performance. SOLUTION: This original reading optical system is provided with an illuminating system 3 illuminating an original, the image formation lens 9 by which reflection light from the original is reduced and image-formed, and a line sensor 8 photoelectrically converting an original image. The lens 9 has a reflection surface inside the lens. The reflection surface may be either a spherical surface or an aspherical surface. Plastic can be used on the mirror of an in-mirror lens. Specified wavelength can be absorbed by the reflection surface. The sensor 8 can have plural lines in a sub-scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an original reading optical system applicable to, for example, a copying machine, a scanner, and the like.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a document reading optical system used for a copying machine or a scanner. FIG.
The original reading optical system includes a contact glass 32 on which an original 31 is placed, an original illumination system 33 for illuminating the original 31, a line sensor 38 for guiding reflected light from the original 31, and an illumination light to the line sensor 38. Guide mirror 34, 3
5, 36, an imaging lens 37 for forming an image on the line sensor 38, and the like.

The mirrors 34, 35, 36 are provided below the contact glass 32. The mirror 34 is inclined at an angle of 45 ° and has a function of changing the vertical reflected light from the document 31 placed on the contact glass 32 to the horizontal direction. An original illumination system 33 for illuminating the original 31 placed on the contact glass 32 is provided at a position adjacent to the mirror 34 (upper right in the figure). The reflected light in the vertical direction from the original 31 is turned in the horizontal direction by the mirror 34. A mirror 35 is provided in the direction in which the reflected light whose direction has been changed in the horizontal direction by the mirror 34 travels. The mirror 35 is a mirror 34
And the reflecting surface faces the reflecting surface of the mirror 34 at the same height as that of the mirror 34, and is inclined at 45 ° to be parallel to the mirror 34. The reflected light in the horizontal direction is changed again by the mirror 35 in the vertical direction. Further, a mirror 36 is provided below the mirror 35. The mirror 36 is mounted such that the mirror surface faces the mirror surface of the mirror 35, and the angle between the two mirror surfaces is 90 °. With such a mirror surface of the mirror 36, the direction of the reflected light from the mirror 35 can be changed from the vertical direction to the horizontal direction. The reflected light whose direction has been changed to the horizontal direction is applied to an image forming lens 37, and the image of the original is converted by the image forming lens 37 into, for example, a CCD.
The image is formed on a line sensor 38 composed of

[0004] The mirrors 35 and 36 constitute folding mirrors, and can be moved in the horizontal direction as a unit. In addition, the mirror 34 and the illumination optical system 33 are integrally movable in the horizontal direction. Mirrors 35 and 36 constituting a return mirror, mirror 34 and illumination optical system 3
3 are different from each other, and the mirrors 35 and 36 are 1 / the moving speed of the mirror 34 and the illumination optical system 33.
It moves at a speed of 2. For this reason, the mirror 34 and the illumination optical system 33 move to move the contact glass 3.
When the end portion 2 (position A) is reached, the positions of the mirrors 35 and 36 are at the center of the contact glass 32 (position B).

As the imaging lens 37 used in the above-mentioned original reading optical system, a Gaussian type having a four-group and six-element configuration as shown in FIG. 5 is generally used. More specifically, the imaging lens 37 includes lenses 37a, 37b, 37c, 37d,
It is composed of six lenses 37e and 37f. The lenses 37a, 37b, 37e and 37f are all convex lenses, and the lenses 37c and 37d are concave lenses. Among them, the lens 37a and the lens 37f, the lens 37b and the lens 37e, the lens 37c and the lens 37d
Have the same shape.

The lenses 37a and 37f of the same shape are
The curved portions are spaced apart on both sides so as to be opposite to each other. The lens 37b is provided on a plane portion of the lens 37a, and the lens 37b is provided on a plane portion of the lens 37f.
e are arranged in such a manner that each curved surface portion faces a flat surface portion. Lens 37b and lens 37
c is joined, and the lens 37e and the lens 37d are joined. The lenses 37c and 37d are configured such that concave curved surface portions face each other. Six lenses 37a, 37b, 37c, 3 arranged in such a positional relationship
Among the lenses 7d, 37e, and 37f, the lens 37a is the lens of the first group, the joined lenses 37b and 37c are the lenses of the second group, the joined lenses 37d and 37e are the lenses of the third group, and the lens 37 is the fourth lens. It constitutes a group of lenses. The lenses 37a, 37b, and 37c are in the first group,
The lenses 37d, 37e, and 37f form a second group, and the first group and the second group are in a line-symmetric positional relationship with each other.

The Gaussian type imaging lens 37 is
The document can be read up to a half angle of view of about 20 ° and the brightness can be increased to a large aperture of about F / 4, so that the document can be read with high accuracy.

[0008]

However, a through-type imaging lens represented by the Gaussian type uses a glass material having a high refractive index and a high unit price for a convex lens in order to satisfactorily correct various aberrations. Have to do
Further, since the number of lenses increases and the outer diameter increases, the cost becomes extremely high, and the height of the reading optical system is disadvantageously increased.

The present invention has been made in order to solve the above-mentioned problems of the prior art.
An object of the present invention is to provide an original reading optical system which can be reduced in size at low cost.

[0010]

According to the first aspect of the present invention,
Document reading optics including an illumination system for illuminating a document, an imaging lens for reducing and forming reflected light of the document illuminated by the illumination system, and a line sensor for photoelectrically converting the document image formed by the imaging lens A system, wherein the imaging lens is an in-mirror lens having a reflecting surface inside the lens.

According to a second aspect of the present invention, in the first aspect, the reflection surface of the in-mirror lens is spherical.

According to a third aspect of the present invention, in the first aspect, the reflection surface of the in-mirror lens is an aspherical surface.

According to a fourth aspect of the present invention, in the first, second or third aspect, the mirror of the in-mirror lens is made of plastic.

The invention according to claim 5 is the invention according to claims 1, 2, and 3
In the fourth aspect, the reflection surface of the in-mirror lens has a characteristic of absorbing a specific wavelength.

[0015] The invention according to claim 6 is the invention according to claims 1, 2,
In 3, 4, or 5, the line sensor is a sensor having a plurality of lines in the sub-scanning direction.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a document reading optical system according to the present invention will be described below with reference to the drawings. In FIG. 1, a document reading optical system includes a contact glass 2 on which a document 1 is placed, a document illumination system 3 for illuminating the document 1, a line sensor 8 for guiding reflected light from the document 1, and a line sensor for reflecting the reflected light. Mirrors 4, 5, 6, leading to 8
It is composed of an imaging lens 9 for forming an image on the line sensor 38 and the like.

The mirrors 4, 5 and 6 are provided below the contact glass 2. The mirror 4 is inclined at an angle of 45 ° and has a function of changing the vertical reflected light from the document 1 placed on the contact glass 2 to the horizontal direction. A document illumination system 3 for illuminating the document 1 placed on the contact glass 2 is positioned adjacent to the mirror 4.
Is provided. The reflected light in the vertical direction from the original 1 is turned in the horizontal direction by the mirror 4. Mirror 4
A mirror 5 is provided in the direction in which the reflected light, whose direction has been changed in the horizontal direction, travels. Mirror 5 is mirror 4
At the same height, the reflecting surface faces the reflecting surface of the mirror 4 and is inclined at 45 ° to be parallel to the mirror 4. The reflected light in the horizontal direction is again changed to the vertical direction by the mirror 5. Further, a mirror 6 is provided below the mirror 5. The mirror 6 has a mirror surface of mirror 5.
Are mounted so that the angle between the two mirror surfaces is 90 °. With such a mirror surface of the mirror 6, the direction of the reflected light from the mirror 5 can be changed from the vertical direction to the horizontal direction. The reflected light whose direction has been changed to the horizontal direction is an imaging lens 9 which is an in-mirror lens.
And is reflected by a mirror provided on the imaging lens 9, passes through the imaging lens 9 in the opposite direction, and forms an image of the original 1 on a line sensor 8 composed of, for example, a CCD or the like.

The mirrors 5 and 6 constitute folding mirrors, and can be moved in the horizontal direction integrally.
Further, the mirror 4 and the illumination optical system 3 can be moved in the horizontal direction as one body. The moving speeds of the mirrors 5 and 6 constituting the folding mirror, the mirror 4 and the illumination optical system 3 are different from each other, and the moving speed of the mirrors 5 and 6 is 1/2 of the moving speed of the mirror 4 and the illumination optical system 3. It is designed to move with. For this reason, when the mirror 4 and the illumination optical system 3 move and reach the end portion (position A) of the contact glass 2, the positions of the mirrors 5 and 6 are shifted to the center of the contact glass 2 (reference number B). Position).

Next, an imaging lens 9 serving as an in-mirror lens
Will be described. In FIG. 2, the imaging lens 9 includes 3
It is composed of lenses 9a, 9b, 9c and a mirror 9d. Lenses 9a and 9b are convex lenses, lens 9c
Is a concave lens, and is the leftmost in the figure, that is,
The lens 9a is arranged on the side where the reflected light is applied.
The lens 9a has a protruding curved surface on the side where the reflected light is applied, and a flat portion on the side opposite to the curved surface. The lens 9a has a gap on the flat surface side of the lens 9a.
b is arranged. The lens 9b has a curved surface shape at a portion on the flat surface side of the lens 9a, and a portion at a side opposite to the projected curved surface has a flat shape. Lens 9
c has a depressed curved surface portion and a flat surface portion on the opposite side to the curved surface portion, and the flat portion of the lens 9c and the flat portion of the lens 9b are joined. Further, a mirror 9d is arranged on the concave surface side of the lens 9c with a certain gap. The reflecting surface of the mirror 9d faces the concave curved surface of the lens 9c with a certain gap.

The imaging lens 9 which is an in-mirror lens having the above-mentioned structure is composed of three lenses, and the lens 9a
And a second group of lenses 9b and 9c. Therefore, although the number of lenses and the group configuration are halved as compared with the conventional Gaussian type, the reflected light input to the lenses 9a, 9b, 9c is reflected by the mirror 9d, and the lenses 9c, 9b, 9
Since the reflected light is guided to the line sensor 8 by following the path a, the same effect as when the reflected light is guided by the Gaussian type imaging lens having four groups and six elements as in the conventional example described above is obtained. Can be In addition, the number of expensive lenses to be configured can be reduced by half,
This can contribute to cost reduction. In addition, because the number of lenses is reduced, the configuration is simpler,
This can also contribute to cost reduction and downsizing of the device.

Next, another embodiment of the imaging lens will be described. In FIG. 3, the imaging lens 11, which is an in-mirror lens, has a two-group, two-lens configuration. The imaging lens 11 includes one lens 11a, which forms the first group, and one lens 11b, which forms the second group. Become. The lens 11a is a biconvex lens. In addition, a second lens 11b is provided on one of the lenses 11a with a certain gap. The lens 11b has a curved surface portion in which the lens 11a side is depressed, and a portion opposite to the curved surface portion is a flat mirror surface 11b.
c. The reflected light input from the lens 11a side is reflected by the mirror surface 11c through the lenses 11a and 11b, guided again to the line sensor 8 (not shown) through the lenses 11a and 11b, and forms an image of the original. .

According to the imaging lens 11 configured as described above, since the lens configuration includes two groups and two lenses, the cost can be further reduced and the configuration is simplified.
This can further contribute to downsizing of the device.

Although two types of lens are shown in the above two embodiments, there is no particular limitation on the number of lenses used. Needless to say, similar effects can be obtained by setting the number of components according to the specifications of the lens.

Further, in the original reading optical system, it is necessary to suppress distortion in order to accurately read the original information. As shown in FIG. 2, the mirror 9d used for the imaging lens 9 is a flat mirror. In some cases, the mirror 9d becomes symmetrical with respect to the optical axis position. Normally, the original reading optical system forms an image of the original 1 at a magnification of about 1/5 to 1/10, so that it is difficult for the symmetrical imaging lens 9 to correct distortion. Therefore, in FIG.
The reflecting surface of the mirror 9d disposed on the concave curved surface side of the lens 9c is made to be a spherical surface having a radius of curvature. By doing so, the direction of the reflected light reflected by the mirror 9d can be changed, and distortion can be satisfactorily corrected. The direction of the radius of curvature can be freely set by the configuration of the lens. For example, the shape may be a protruding shape or a depressed shape.

Further, also in the imaging lens 11 shown in FIG. 3, the mirror surface 11c has a radius of curvature and has a convex or concave spherical surface according to the lens configuration, so that distortion can be favorably reduced. It becomes possible to correct.

Further, the reflecting surface for reflecting the reflected light is not limited to a spherical surface having a radius of curvature, but may be an aspherical surface, that is, a curved shape depending on the lens configuration. By doing so, the degree of freedom in design is increased, and an imaging lens having good imaging properties can be obtained.

Further, in the imaging lens 9 shown in FIG. 2, the mirror 9 is disposed at a distance from the lenses 9a, 9b, 9c.
By making d a plastic instead of a glass, it is possible to further reduce the cost. In addition, plastic has a non-uniform interior and a birefringence as compared with glass. For this reason, when plastic is used for a member such as a lens through which light passes, the imaging performance is adversely affected. However, when plastic is used as the mirror, light does not pass through the inside of the mirror and is only reflected on the surface, so that good image forming properties can be obtained.

Further, when a halogen lamp or the like is used in the document illumination system 3 in the document reading optical system, for example,
In order to prevent the line sensor 8 from deteriorating due to the heat generated by the infrared rays, a filter for cutting off the infrared rays is arranged on the optical path of the reflected light, but the reflection surface of the mirror 9d shown in FIG. 2 and the mirror surface shown in FIG. By making the 11c have a characteristic of absorbing infrared rays, it is not necessary to provide a filter for cutting off infrared rays as a separate member, which can contribute to cost reduction.

In recent years, copiers and scanners have
With the advance of full color, the line sensor 8 of the original reading optical system
Also, a three-line CCD capable of color separation has been used. An imaging lens used in an original reading optical system using a three-line CCD has to suppress chromatic aberration extremely small as compared with a monochrome lens. For this reason,
The number of lens components increases, anomalous dispersion glass,
It is necessary to use a large amount of low-dispersion glass, resulting in a high-cost optical system. However, even in such a full-color original reading optical system, the number of expensive anomalous dispersion glass and low dispersion glass can be reduced by using an imaging lens that is an in-mirror lens as in the above-described embodiment. Therefore, it is possible to contribute to cost reduction without deteriorating performance.

[0030]

According to the first aspect of the present invention, the imaging lens is
Since this is an in-mirror lens having a reflecting surface inside the lens, the number of components of the imaging lens can be greatly reduced, and a compact and low-cost original reading optical system can be obtained.

According to a second aspect of the present invention, in the first aspect of the present invention, since the reflecting surface of the in-mirror lens has a spherical surface with a radius of curvature, a compact and low-cost original reading device in which distortion is satisfactorily corrected. An optical system can be obtained.

According to the third aspect of the present invention, since the reflecting surface of the in-mirror lens is aspherical in the first aspect of the present invention, it is possible to obtain a document reading optical system in which various aberrations are well corrected. .

According to the fourth aspect of the present invention, since the mirror of the in-mirror lens is made of plastic in the first, second or third aspect of the invention, a low-cost original reading optical system can be obtained.

The fifth aspect of the present invention provides the first, second, and third aspects.
In the invention described in the fourth aspect, since the reflection surface of the in-mirror lens has a characteristic of absorbing a specific wavelength, optical components other than the imaging lens can be reduced, and a very low-cost reading optical system can be obtained. It becomes possible.

[0035] The invention according to claim 6 is the first or second aspect of the present invention.
In the invention described in 3, 4, or 5, since the line sensor is a sensor having a plurality of lines in the sub-scanning direction, a low-cost original reading optical system can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of a document reading optical system according to the present invention.

FIG. 2 is a side view showing an embodiment of an in-mirror lens used in the original reading optical system.

FIG. 3 is a side view showing another embodiment of the in-mirror lens used in the original reading optical system.

FIG. 4 is a schematic diagram showing an example of a conventional document reading optical system.

FIG. 5 is a schematic diagram showing an example of a through-type lens used in the original reading optical system according to the first embodiment;

[Explanation of symbols]

 3 Illumination system 8 Line sensor 9 Imaging lens

Claims (6)

[Claims] An illumination system for illuminating an original, an imaging lens for reducing and forming an image of reflected light of the original illuminated by the illumination system, and a line sensor for photoelectrically converting the original image formed by the imaging lens A document reading optical system comprising: an image forming lens, wherein the imaging lens is an in-mirror lens having a reflection surface inside the lens. 2. The original reading optical system according to claim 1, wherein a reflection surface of said in-mirror lens is spherical. 3. The original reading optical system according to claim 1, wherein the reflection surface of the in-mirror lens is an aspherical surface. 4. The original reading optical system according to claim 1, wherein the mirror of the in-mirror lens is made of plastic. 5. The original reading optical system according to claim 1, wherein the reflection surface of the in-mirror lens has a characteristic of absorbing a specific wavelength. 6. The original reading optical system according to claim 1, wherein said line sensor is a sensor having a plurality of lines in a sub-scanning direction.