JPH08248350A - Image reader - Google Patents

Abstract

PURPOSE: To provide an image reader which is hardly influenced by flare light by changing not only a read area by an image-formation optical system but also an illumination area by an illumination optical system in accordance with the change of reading resolution. CONSTITUTION: This cylindrical scanning type image reader is provided with the illumination optical system E and the image-formation optical system F. The illumination optical system E is an optical system irradiating the illumination area on an original 2 with the light, and a variable field stop FS is arranged at a position conjugate with the original 2. In the image-formation optical system F, the image of the read area on the original 2 is formed on an image-formation surface by a pickup lens 27, and the light passing through one hole of a main aperture plate 25 arranged on the image-formation surface is read by a photomultiplier tube 21. In the device, the read area and the illumination area are changed by changing the aperture size of the main aperture plate 25 and the size of the field stop FS in the case of changing the reading resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having an illumination optical system for irradiating an illumination area of a document with light and an imaging optical system for focusing light from the reading area of the document on an imaging surface. Regarding

[0002]

2. Description of the Related Art FIG. 10 is a diagram showing an example of an image reading apparatus as a background art of the present invention, showing an input scanning optical system of a scanning head. As shown in the figure, this image reading apparatus includes an original 102 attached to an original cylinder 101.
The light from is received by a pickup lens (imaging lens) 103 provided in the scanning head, and a real image of the original 102 is imaged at a position of a main aperture plate 104 in which a plurality of holes (apertures) having different sizes are formed. Then, the light passing through one hole (aperture) of the main aperture plate 104 is made to enter the photomultiplier tube 105 and is converted into an electric signal. When changing the reading resolution, the hole diameter (aperture size) of the main aperture plate 104 through which light passes is changed according to the reading resolution.

In order to read the original 102 with the image reading apparatus configured as described above, it is necessary to illuminate the original 102 under appropriate conditions. Therefore, conventionally, various illumination optical systems have been proposed and incorporated in the image reading apparatus. In this illumination optical system, a light source lamp 106 and a collector lens 107 that takes in light from the light source lamp 106.
And the field stop 108 are arranged in this order, and the light from the light source lamp 106 is emitted through the collector lens 107 and the field stop 108 into the ray pipe 111 extending parallel to the rotation axis of the original cylinder 101. .

Inside the ray pipe 111, an aperture stop 109 and a mirror 112 are arranged. After the light incident on the ray pipe 111 passes through the aperture stop 109,
It is reflected by the mirror 112. Then, the reflected light is applied to the original 102 on the original cylinder 101 via the condenser lens 110 fixed to the surface of the ray pipe 111. Thus, the original 102 is illuminated.

Here, the field stop 108 and the aperture stop 1
09 is fixed.

As described above, while the document cylinder 101 is rotated in the main scanning direction X and the scanning head and the illumination optical system are integrally moved in the sub-scanning direction Y in synchronization with the rotational movement, the document 102 is scanned. The light from is guided to the photomultiplier tube 105 and the photoelectrically converted electrical signals are sequentially output.

[0007]

By the way, as shown in FIG. 11, for example, when the reading resolution for reading an original is changed, the hole diameter of the main aperture plate 104 changes, so that the reading area AR on the original changes. However, since the hole diameter (aperture size) of the field stop 108 is fixed, the illumination area AE is constant regardless of the reading resolution. There is no problem when the illumination area AE is slightly wider than the reading area AR, but when the illumination area AE is considerably wider than the reading area AR (when the reading resolution is high).
In some cases, light from the illumination area AE other than the reading area AR may enter the photomultiplier tube 105 as flare light. For this reason, the image cannot be accurately read especially on the high resolution side.

The present invention has been made in view of the above-mentioned problems, and even if the reading area is changed, the influence of flare light is reduced so that the image is accurately read even if the reading resolution is changed. It is an object of the present invention to provide an image reading device for reading.

[0009]

According to a first aspect of the present invention, there is provided an illumination optical system for irradiating an illumination area of a document with light, and an imaging optical system for forming an image of a reading area of the document on an imaging surface. An image reading apparatus for reading an image on the image plane with a photoelectric conversion element, an instruction unit for instructing a change in the reading resolution, and a reading region for changing the reading region according to the reading resolution instructed by the instructing unit. The image forming apparatus further includes a changing unit and an illumination area changing unit that changes the illumination area according to the reading resolution instructed by the instructing unit.

According to a second aspect of the present invention, the illumination optical system includes a light source, a collector lens for condensing light from the light source, and a condenser lens for condensing light passing through the collector lens in the illumination area. A field stop arranged at a position conjugate with the original with respect to the condenser lens is provided, and the illumination area changing means changes the illumination area by changing a size of the field stop.

According to a third aspect of the present invention, the illumination optical system focuses a light source, a collector lens for focusing light from the light source, a field lens, and light passing through the field lens on the illumination area. A condenser lens and a field stop arranged at a position conjugate with the original with respect to the condenser lens are provided, and the illumination area changing means changes the illumination area by changing a size of the field diaphragm.

According to a fourth aspect of the present invention, the illumination optical system includes a light source, a collector lens for condensing light from the light source, a zoom lens for condensing light passing through the collector lens in the illumination area, A field diaphragm arranged at a position conjugate with the original with respect to the zoom lens is provided, and the illumination area changing means changes the illumination area by changing a magnification of the zoom lens.

According to a fifth aspect of the present invention, the illumination optical system has a light source, a collector lens for condensing light from the light source, a field lens, and a zoom for condensing light passing through the field lens in the illumination area. A lens and a field stop arranged at a position conjugate with the original with respect to the zoom lens are provided, and the illumination area changing means changes the illumination area by changing a magnification of the zoom lens.

According to a sixth aspect of the present invention, the illumination optical system further includes a relay lens between the field lens and the condenser lens.

According to a seventh aspect of the present invention, the illumination optical system further includes an aperture stop arranged at a position where a light source image of the light source is formed or at a position conjugate with the light source image.

According to an eighth aspect of the present invention, the image forming optical system includes an image forming lens and an aperture plate at a position conjugate with the original with respect to the image forming lens, and the size of the aperture of the aperture plate is changed. The reading area is changed by, and the amount of light passing through the aperture is read by the photoelectric conversion element.

According to a ninth aspect of the present invention, the image forming optical system includes an image forming lens and an aperture plate at a position conjugate with the original with respect to the image forming lens, and the magnification of the image forming lens is changed. The reading area is changed.

In a tenth aspect of the present invention, the image forming optical system is
The reading area is changed by changing the magnification of the image forming lens, which includes an image forming lens arranged at a position where the document and the photoelectric conversion element have a conjugate positional relationship.

In the eleventh aspect of the present invention, the illumination area is set larger than the reading area by a size corresponding to a mechanical assembly error of the illumination optical system and the imaging optical system.

According to the twelfth aspect of the present invention, the ratio of the illumination area to the reading area is set so that the high resolution is larger than the low resolution.

[0021]

According to the first aspect of the present invention, the illumination optical system irradiates the illumination area of the document with light, and the imaging optical system forms an image of the reading area of the document on the imaging surface. Further, the image on the image plane is read by the photoelectric conversion element. Here, when the reading resolution is instructed by the instructing means, the reading area changing means changes the reading area according to the reading resolution, and the illumination area changing means changes the illumination area. As a result, the illumination area by the illumination optical system can be changed along with the change of the reading area by the imaging optical system.
It is possible to narrow the illumination area other than the reading area,
Therefore, the influence of flare light can be reduced.

According to the second and third aspects of the invention, the light from the light source is condensed by the collector lens, and further the light is applied to the illumination area of the original by the field lens and the condenser lens. By changing the size of the field stop arranged at a position conjugate with the original with respect to the condenser lens, the illumination area can be changed with a simple configuration.

According to the present invention, the light from the light source is collected by the collector lens, and the illuminated area of the original is irradiated with the light by the field lens and the sume lens. A field diaphragm is arranged at a position conjugate with the original with respect to this zoom lens. Here, even when the size of the field stop is fixed, the illumination area can be changed with a simple configuration by changing the percentage of the zoom lens.

According to the sixth aspect of the invention, since the relay lens is provided between the field lens and the condenser lens, the distance between the light source and the document can be increased without attenuating the light quantity.

According to the seventh aspect of the invention, since the aperture stop is provided at the position where the light source image of the light source is formed or at the position conjugate with the light source image, the illumination condition (numerical aperture) is set according to the characteristics of the original. Can be changed.

According to the eighth aspect of the present invention, the reading area can be changed with a simple structure by changing the size of the aperture arranged at a position conjugate with the original with respect to the imaging lens.

According to the ninth to tenth aspects of the present invention, the reading area can be changed with a simple structure by changing the magnification of the imaging lens.

According to the eleventh to twelfth aspects of the present invention, even if there is a mechanical assembly error of the illumination optical system and the imaging optical system, the reading area is included in the illumination area, so that an accurate image signal can be read. it can.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

<Cylindrical Scanning Image Reading Device> FIGS. 1 and 2 are a perspective view and a plan view showing an embodiment of an illumination optical system E and an imaging optical system F of a cylindrical scanning image reading device according to the present invention, respectively. Is.

As shown in FIG. 1, the illuminating optical system E illuminates the original 2 mounted on the original cylinder 1 and the transmissive optical system ET for illuminating the original 2 from the direction opposite to the transmissive optical system ET. And a reflection optical system ER. The illumination optical system E (transmission optical system ET + reflection optical system ER) described below can also be applied to an apparatus that reads an image by placing the original 2 on a transparent flat plate such as a glass plate. it can.

The transmission optical system ET has a light source 30 and a collector lens 40 arranged in the lamp house 28 (see FIG. 2). A ray pipe 29 extending in the sub-scanning direction Y is connected to the lamp house 28. Inside the ray pipe 29, a field lens 43, a relay lens 44, a mirror 48, and a condenser lens 4 are connected.
9 and are provided.

In the light source 30, as shown in FIG. 1, a perforated elliptical mirror 32 is arranged so as to surround a light source lamp 31 such as a xenon lamp or a halogen lamp. A part of the light emitted from the light source lamp 31 is reflected by the elliptical mirror 32, guided to the reflection optical system ER, and irradiated on the original 2.
Further, a hole 32S is formed on the side surface of the elliptical mirror 32, and a part of the light emitted from the light source lamp 31 has a hole 32S.
After passing through S, it is condensed at a predetermined position P30 by a secondary light source forming lens system 35 composed of two lenses 33 and 34, and 2
A secondary light source is formed. Reference numeral 36 reflects the light emitted from the secondary light source forming lens system 35 to reflect the light source lamp 31.
It is a mirror for guiding the light from the collector lens 40.

Thus, in this embodiment, the element 31
The light source 30 is constituted by the components 35 to 35, and the light emitted from the light source lamp 31 is divided into two optical paths and made incident on the reflection optical system ER and the transmission optical system ET, respectively. Further, in this embodiment, since the light from the light source lamp 31 is distributed to the two directions orthogonal to each other by using the perforated elliptical mirror 32 configured as described above, the light from the light source lamp 31 is divided. Can be used spatially and efficiently.

When the transparent original is used as the original 2, the transparent optical system ET is used, and when the reflective original is used, the reflective optical system ER is used, so that the optical path selectively enters each optical path. A shutter (not shown) is provided.

Further, in this embodiment, FIG. 1 and FIG.
As can be seen from the above, since the secondary light source forming lens system 35 is composed of the focal type optical system, the optical path length can be shortened as compared with the case of using the afocal system, and the light source 3
It is possible to reduce the size to 0.

As shown in FIG. 2, the collector lens 40 collects the light emitted from the light source 30 and guides it to the field lens 43.

FIG. 3A is a diagram showing the optical configuration of the transmission optical system ET. In this optical system, 2
A variable aperture stop AS is arranged at a position P30 where the next light source is formed. The variable aperture stop AS is formed with a plurality of apertures having different aperture sizes, and the aperture size of the aperture stop can be appropriately changed by rotating the aperture stop motor 7 (see FIG. 2) at a predetermined angle. You can do it.

The collector lens 40 is arranged at a position separated from the secondary light source by the focal length f41S of the lens 40, and takes in the light from the secondary light source through the mirror 42,
The parallel light is emitted to the field lens 43 side. Behind the collector lens 40, a variable field stop FS is arranged at a position having a conjugate relationship with the original 2. The hole diameter (size) of the variable field diaphragm Fs can be adjusted by the field diaphragm motor 6 (see FIG. 2).

In this embodiment, the light source image of the light source lamp 31 is formed at the pupil position 99 of the condenser lens 49, and the illumination optical system is a Koehler illumination system.

Next, returning to FIG. 1, the collector lens 4
The process until the light emitted toward 0 is applied to the original 2 will be described. This emitted light is emitted from the field lens 43.
It is incident on the relay lens 44 via the. The two lenses 45 and 46, which form the relay lens 44, are spaced apart from each other by a distance obtained by adding their focal lengths to each other to form a so-called afocal optical system. Here, by using the relay system 44 lens as an afocal optical system, it is possible to perform good relaying without being affected by dust or the like adhering to the lens surface as compared with the case of forming with a focal system. That is, in the case of a focal optical system, a light source image (or a field stop image) is formed inside or on the surface of a lens. Therefore, when dust or the like adheres to the lens surface of the lens, the light source image (or the field stop image). ) Is disturbed and has an adverse effect. On the other hand, when the relay system is formed by the afocal optical system as in this embodiment, the light source image and the field stop image are formed in the space area between the lenses, so that they are affected by dust on the lens surface. Instead, the light source image can be satisfactorily transmitted to the condenser lens 49 side, and the field stop image can be satisfactorily transmitted to the original 2.

The light emitted from the relay lens 44 is reflected by the mirror 48 and then condensed by the condenser lens 49, and the original 2 on the original cylinder 1 (see FIG. 2).
Is irradiated.

In such an illumination optical system E, the original 2
By adjusting the hole diameter (size) of the field stop FS arranged at a position conjugate with, it is possible to change the illumination area where the light is irradiated on the original 2.

Next, the reflection optical system ER will be described with reference to FIG. As shown in FIG. 1, the reflection optical system ER is composed of a bundle fiber (light guiding means) 130 for guiding the light from the light source 30 to the vicinity of the original cylinder 1. The one end 131 of the bundle fiber 130 is arranged above the perforated elliptical mirror 32 so as to face the opening 32R of the perforated elliptical mirror 32, and the light emitted through the opening 32R is the one end. The light enters the bundle fiber 130 from 131, is guided to the other end (not shown), and is then emitted from the other end toward the document 2. Thus, the illumination for reflecting the original 2 is performed.

As shown in FIGS. 1 and 2, the image forming optical system F includes a main aperture plate 25 and a pickup lens (image forming lens) 27 for forming an image of the original 2 on the main aperture plate 25. ing. The main aperture plate 25 is arranged on the image forming surface on which the image of the document 2 is formed by the pickup lens 27. The main aperture plate 25 has a variable aperture stop A of the illumination optical system described above.
Similar to S, a plurality of holes (apertures) having different diameters are formed, and one of the plurality of holes (apertures) is selected by the main aperture motor 5 (see FIG. 2) to pick up the pickup lens 27. The main aperture plate 25 is rotated so that it is located on the optical axis. The light passing through the hole (aperture) of the main aperture plate 25 is converted into a parallel light flux by the collimator lens 24, and further separated into three primary colors by the two dichroic mirrors 23R and 23B and the mirror 23G, and further the color filter 22R, 22
It is led to the photomultiplier tubes 21R, 21B and 21G which are photoelectric conversion elements via B and 22G, respectively.

In such an imaging optical system F, the reading area can be changed by changing the hole diameter (size) of the main aperture plate 25.

In the image reading apparatus having the illumination optical system E and the image forming optical system F, when the reading resolution is changed, the variable aperture stop Fs is adjusted.
The reading area is adjusted by adjusting the illumination area on the original 2 and the hole diameter (aperture size) of the main aperture plate 25. The relationship between the illumination area and the reading area is shown in FIGS. 5 (a), 5 (b) and 5 (c).

As shown in FIGS. 9A and 9B, the reading area AR is determined by the reading resolution, and its size corresponds to the reciprocal of the reading resolution. Since the entire reading area must be illuminated with light, the illuminated area AE
Needs to include the reading area AR. Further, in order to minimize the influence of flare light, it is necessary to make the illumination area AE0 except the reading area AR as small as possible. Therefore,
Although it is the most preferable mode that the illumination area AE and the reading area AR are the same, the reading area AR and the illumination area A are the same.
It is necessary to make the position of E completely coincident with that of the aperture plate 25.
It is difficult in terms of mechanical positioning accuracy of the illumination optical system E and the image forming optical system F such as the field stop FS.

Therefore, as shown in FIG. 5 (c), regardless of the reading resolution, the error TB of 2 obtained by adding the positioning allowable error of the reading area AR and the positioning allowable error of the illumination area AE.
By setting the illumination area AE larger than the reading area AR by a factor of two, the illumination area AE includes the reading area AR and excludes the reading area, regardless of mechanical positioning error due to assembly of the optical system. Can be made narrower, so that the density of the original 2 can be read faithfully and the influence of flare can be suppressed to a minimum.

Due to this mechanical positioning error, the positional deviation between the illumination area AE and the reading area AR is substantially constant regardless of the reading resolution, so the ratio of the illumination area AE to the reading area AR is lower than that on the low resolution side. It can be said that the high resolution side is set larger.

The reading resolution and the main aperture plate 2
As for the relationship with the hole diameter of 5, the reading resolution is RES, the hole diameter is d,
When the magnification of the pickup lens (imaging lens) 27 is M, the relational expression d = M / RES (1) is satisfied. Therefore, assuming that the magnification M is constant, the hole diameter d may be changed in inverse proportion to the reading resolution.

However, when the reading resolution is relatively high,
Due to a problem in processing the hole of the aperture plate 25, it may not be possible to form a hole having a size that satisfies the relational expression (1). In this case, as shown in FIG. 5B, the reading area AR may be slightly increased only on the high resolution side, and the illumination area AE may be increased accordingly. in this case,
Since a wider range is read than the ideal reading area,
The output density is an image signal that is slightly smoothed as compared with an accurate image signal, but an error of this degree has little effect.

Therefore, by adjusting the illumination area AE to be slightly wider than the reading area AR, the illumination area AE0 excluding the reading area AR is changed even if the reading resolution is changed.
Is not so wide, the adverse effect due to flare light can be reduced.

FIG. 4 is a control block diagram of an image reading apparatus including the illumination optical system E and the image forming optical system F.

The image reading device is controlled by a main control section 55 which is mainly composed of a microcomputer and the like. Main controller 55
Is composed of a CPU, a ROM, a RAM, and the like, and the CPU controls each load based on a control program stored in the ROM, control data stored in the RAM, and information from the operation panel 54.

Further, the photomultiplier tubes 21R, 21B, 21
Image signals IR, IB, and IG respectively output from G
Is converted into a voltage value by the current / voltage converter 50, logarithmically converted by the LOG conversion circuit 51, and further converted into digital data by the A / D conversion circuit 53. The A / D conversion circuit 53 has a sampling clock C
L is input, and A / D conversion is performed at the timing of this sampling clock CL. Therefore, the reading resolution in the main scanning direction X can be changed by adjusting the frequency of the sampling clock CL. For example,
If the frequency of the sampling clock CL is multiplied by N, the reading resolution will be increased by N.

When the operator inputs the reading resolution RES through the operation panel (instructing means) 54 including a keyboard or the like, the main controller 55 sends the reading resolution data RES to the magnification control circuit 56. The magnification control circuit 56 sets the sub-scanning speed Vy, the hole diameter of the main aperture plate 25, and the hole diameter of the variable field stop FS according to the reading resolution RES in order to set the rotation speed of the sub-scanning motor 4 and the motor for the main aperture. 5 and the amount of rotation of the field stop motor 6 are controlled. Further, the magnification control circuit 56 includes the A / D conversion circuit 52.
Sampling clock C with a frequency corresponding to the reading resolution
Output L.

For example, the reading resolution is RES (line / m
m), the radius of the original cylinder 1 is r (mm), and the rotation cycle of the original cylinder 1 is T (sec), the sub-scanning speed V
y (mm / sec) is represented by Vy (mm / sec) = 1 / (RES · T) (2). The frequency f _CL of the sampling clock CL is represented by f _CL = 2πr / (RES · T) (3).

The magnification control circuit 56 controls the sub-scanning speed data V
y is output to the sub-scanning control circuit 58, and the sub-scanning motor 4 is driven at that speed. Further, it outputs a selector signal SEL that changes according to the reading resolution RES to the reading area control circuit 59. The reading area control circuit 59 includes a memory that stores the relationship between the reading area AR and the illumination area AE shown in FIG. 5, and according to the relationship, the main aperture motor 5 is provided.
And driving the field stop motor 6. It should be noted that the document cylinder 1 is rotated at a constant peripheral speed Vx regardless of the reading resolution, via the main scanning control circuit 57.
Control the speed of. Further, the aperture stop control circuit 60 controls the aperture stop motor 7 so that the variable aperture stop AS can be adjusted according to the information from the operation panel 54. The aperture size of the variable aperture stop AS is increased when the original has scratches or irregularities, and is decreased when more accurate density reading is desired.

As described above, the document cylinder 1 is rotated in the main scanning direction X, and in synchronism with the rotational movement thereof, the scanning head 20 including the imaging optical system F and the illumination optical system E is integrated with the sub scanning direction Y. The light from the original 2 is guided to the photomultiplier tubes 21R, 21B and 21G while being moved to the original 2
The image of the original 2 is read by photoelectrically converting the image of.

As described above, according to this embodiment, the reading area AR on the original is changed by the imaging optical system F as the reading resolution is changed, and the illumination area AE by the illumination optical system E is also changed. Since the illumination area AE does not become excessively large compared to the reading area AR, the light incident on the photoelectric conversion element such as the photomultiplier tube 5 is less likely to be affected by the flare light. Therefore, an accurate image signal can be read.

In this embodiment, as can be seen from FIG. 3A, the field lens 43 and the condenser lens 49 are arranged so as to form an afocal optical system. An afocal relay lens 44 is arranged between the field lens 43 and the condenser lens 49. Moreover, as described above, since the collector lens 40 is arranged at the position separated from the secondary light source by the focal length, this transmission optical system E
Since T is telecentric on the image side, the original 2 can be illuminated well.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments,
Various modifications are possible.

In this embodiment, the reading area AR by the imaging optical system F is realized by changing the hole diameter of the main aperture plate 25. However, the hole diameter of the main aperture plate 25 is fixed and the pickup lens (imaging lens ) 27, a zoom lens may be adopted, and the reading area AR may be changed by changing the magnification of the zoom lens.

Further, in this embodiment, the condenser lens 49 is used as a part of the illumination optical system E in FIG. 3A, but a zoom lens may be used instead. In this case, by changing the magnification of the zoom lens while the size of the field stop FS is fixed, the illumination area can be changed as in the above embodiment. Similar modifications are possible in the configurations of FIGS. 3B and 3C described later.

In this embodiment, the variable aperture stop A is used.
Although S is arranged at the position where the secondary light source is formed, the position where the variable aperture stop AS is arranged is not limited to this. Good. However, when it is arranged at the position P30 where the secondary light source is formed as described above, the variable aperture stop AS is located inside the lamp house 28, so that the aperture size of the aperture stop AS is automatically changed. There is an advantage that an adjustment mechanism (such as a drive source and a driving force transmission unit) can be easily incorporated. On the other hand, when the aperture stop is arranged at a position conjugate with the light source image and closest to the original 2 (in this embodiment, the pupil position (AS ′) of the condenser lens 49), the influence of the vibration of the ray pipe 29 or the like may occur. It can be minimized, and the document 2 can be illuminated stably.

Further, in this embodiment, the transmission optical system E is used.
T is a so-called Koehler illumination system, but it is also possible to make a critical illumination system by adjusting the intervals between the optical elements without changing the basic constituent elements. Even in this case, the Koehler illumination system is also available. The same effect as in the case of the illumination system can be obtained.

Further, the transmission optical system T according to this embodiment includes a relay lens 44, but the relay lens 44 is not an essential component of the present invention. As shown, the transmission optical system T can be configured without providing the relay lens 44,
The same effects as those of the cylindrical scanning type embodiment can be obtained. In this case, the position of the variable aperture stop AS is as shown in FIG.
Similar to the above case, it may be provided at the position AS where the light source image is formed or at the pupil position (AS ′) of the condenser lens 49. Further, as shown in FIG. 3C, the light source lamp 31 may be arranged at the position of the secondary light source of the above embodiment. At this time, the aperture stop AS may be provided at the pupil position (AS ′) of the condenser lens 49.

Further, in the above embodiment, the reading resolution in the main scanning direction X is realized by adjusting the frequency of the sampling clock CL.
With the frequency of L constant, the rotation speed Vx of the document cylinder 1
It can also be achieved by adjusting. It can also be realized by adjusting both the sampling clock and the rotation speed Vx of the original cylinder. However, also in this case, it is necessary to satisfy the relational expressions (2) and (3) as in the above embodiment.

<Plane Scanning Type Image Reading Device> FIGS. 6 and 7 show one embodiment of an illumination optical system E and an imaging optical system F of a plane scanning type image reading device according to another embodiment of the present invention. FIG. 3 is a perspective view and a plan view showing FIG. Note that FIG.
(A) And (b) is sectional drawing of the main scanning direction X, and sectional drawing of the subscanning direction Y, respectively. The planar scanning type image reading device has the same basic principle and configuration as the cylindrical scanning type image reading device, except that the reading area is changed from a spot shape to a slit shape.

This image reading apparatus, as shown in FIG.
An illumination optical system E for illuminating the original 12 placed on the original table 11 and an image forming optical system F for reading an image of the original are provided.

The illumination optical system E includes a linear light source 80 made of a fluorescent lamp, a collector lens 81 made of a cylindrical lens, a variable field stop Fs, a mirror 88, and a variable aperture stop A.
s, a condenser lens 89 including a cylindrical lens is arranged in order. The field stop FS is arranged at a position optically conjugate with the original 12 with respect to the condenser lens 89. Further, the variable aperture stop AS is arranged at the position of the front focus of the condenser lens 89.
In the illumination optical system E, the illumination area on the original 12 can be adjusted by adjusting the slit width (size) of the variable field stop FS.

In the image forming optical system F, a mirror 76, a zoom lens (image forming lens) 77, and a line sensor 71 which is a photoelectric conversion element are arranged in order. Line sensor 71
Is a sensor such as a CCD, for example, and is arranged on the image plane which is an optically conjugate position with respect to the zoom lens 77. Therefore, the original 1
The image on line 2 can be read.

In the image forming optical system F, when the reading resolution is changed, the image forming magnification of the zoom lens 77 is adjusted by the magnification converting motor 15 in the main scanning direction X, so that the line sensor 71 is connected. The image magnification to be imaged can be changed. Regarding the sub-scanning direction, by adjusting the relative speed (sub-scanning speed) between the document 2, the optical system 70 including the imaging optical system F, and the illumination optical system E, as in the above-mentioned cylindrical scanning type image reading apparatus. realizable.

FIG. 8 shows a plan view of the variable field diaphragm FS. The variable field stop FS adjusts the slit size Δd formed by the pair of slit plates 91a and 91b by driving the field stop motor 16. Blocks 92a and 92b are fixed to both ends of the slit plate 91, and a screw 93 is attached to one of the blocks 92.
However, rails 94 pass through to the other side. The screw 93 is divided into upper and lower parts and the forming direction of the screw is changed. Therefore, when the screw 93 is rotated, the slit 9
1a and 91b move in opposite directions. Therefore, by rotating the field stop motor 16, the slit size Δd
Can be adjusted. The variable aperture stop AS has the same structure as this variable field stop, and the aperture stop motor 1
By rotating 7 the slit size of the variable aperture stop AS can be changed.

In the image reading apparatus having the illumination optical system E and the imaging optical system F, when the reading resolution is changed, the illumination area of the original 12 is adjusted by adjusting the slit size of the variable field stop FS. Can be changed. The relationship between the illumination area and the reading area is shown in FIG. As shown in this figure, the illumination area AE is adjusted so as to be slightly wider than the reading area AR, and the extent to which the illumination area AE is widened is similar to that of the cylindrical scanning type embodiment described above. This corresponds to the mechanical assembly error of system F, and
Regarding the sub-scanning direction Y, the ratio of the size of the reading area AR to the size of the illuminating area AE in the sub-scanning direction Y is set to be larger on the high resolution side than on the low resolution side. As a result, even if the reading resolution is changed, the illumination area AE necessarily includes the reading area AR, and the illumination area AE0 excluding the reading area AR is not so wide, so that an accurate image signal can be read.

The control block diagram of this plane scanning type image reading apparatus is basically the same as the control block diagram of the cylindrical scanning type image reading apparatus, and therefore its illustration is omitted. However, since the zoom processing in the main scanning direction X is optically performed by the zoom lens 77, it is not necessary to change the frequency of the sampling clock CL shown in FIG.

As described above, according to this embodiment, also in the plane scanning type image reading apparatus using the line sensor 71, the reading area AR and the illumination optical system E by the imaging optical system F are changed with the change of the reading resolution. Since the illumination area AE can be changed, the illumination area A suitable for the reading area AR
Since E can be set, the adverse effect of flare light can be reduced.

[0078]

According to the first aspect of the present invention, since the reading area by the imaging optical system and the illumination area by the illumination optical system can be changed according to the change of the reading resolution, the illumination suitable for the reading area can be obtained. You can set the area. Therefore, the influence of flare light can be reduced, and an accurate image signal can be read.

According to the second and third aspects of the invention, the illumination area can be changed with a simple structure by changing the size of the field stop arranged at a position conjugate with the original.

According to the invention of claims 4 to 5, the illumination area can be changed with a simple structure by adjusting the magnification of the zoom lens of the illumination optical system.

According to the sixth aspect of the present invention, since the relay lens is further provided, the distance between the light source and the document can be increased, so that the degree of freedom of the arrangement position of the light source and the like increases.

According to the invention of claim 7, since the aperture stop is further provided, the illumination condition (numerical aperture) can be adjusted according to the characteristics of the original.

According to the eighth aspect of the present invention, the reading area can be changed with a simple structure by changing the size of the aperture of the imaging optical system.

According to the ninth to tenth aspects of the present invention, the reading area can be changed with a simple structure by changing the magnification of the image forming lens of the image forming optical system.

According to the eleventh to twelfth aspects of the present invention, an accurate image signal can be read even if there is a mechanical assembly error of the illumination optical system or the imaging optical system.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an illumination optical system and an imaging optical system of a cylindrical scanning type image reading device according to the present invention.

FIG. 2 is a plan view showing the outline of an illumination optical system and an imaging optical system of a cylindrical scanning type image reading device according to the present invention.

3A is a diagram showing an optical configuration of the illumination optical system of FIG. 1, FIG. 3B is a diagram showing an optical configuration of an illumination optical system of another embodiment, and FIG. It is a figure which shows the optical structure of the illumination optical system of embodiment.

FIG. 4 is a control block diagram of the image reading apparatus according to the present invention.

5A is a diagram showing that the illumination area and the reading area change according to a change in the reading resolution, FIG. 5B is a graph showing the relationship between the illumination area and the reading area, and FIG. It is a figure which shows the relationship between an illumination area | region and a reading area.

FIG. 6 is a perspective view showing an embodiment of an illumination optical system and an imaging optical system of a plane scanning type image reading device.

FIG. 7A is a horizontal sectional view of a plane scanning type image reading apparatus, and FIG. 7B is a vertical sectional view.

FIG. 8 is a front view showing the configurations of a field stop and an aperture stop.

FIG. 9 is a diagram showing a relationship between a reading area and an illumination area.

FIG. 10 is a diagram showing an illumination optical system and an imaging optical system of a conventional image reading apparatus.

FIG. 11 is a diagram showing a relationship between a reading area and an illumination area in a conventional image reading apparatus.

[Explanation of symbols]

 1 Document Cylinder 2, 12 Document 5 Main Aperture Motor 6,16 Field Aperture Motor 7,17 Aperture Stopper Motor 11 Document Plate 15 Magnification Conversion Motor 20 Scanning Heads 21R, 21G, 21B Photomultiplier Tube 25 Main Aperture Plate 27 pickup lens (imaging lens) 30 light source 31 light source lamp 35 secondary light source forming lens system 40 collector lens 43 field lens 44 relay lens 49 condenser lens 50 current / voltage converter 51 LOG conversion circuit 53 A / D conversion circuit 54 Operation panel (instruction means) 55 Main control unit 59 Reading area control circuit 60 Aperture diaphragm control circuit 70 Optical system 71 Line sensor 77 Imaging lens 80 Light source 81 Collector lens 89 Condenser lens 99 Pupil position FS Field diaphragm AS Aperture diaphragm E Meiko Science-based ER reflective optical system ET transmitting optical system F imaging optical system AE illumination region AR reading area RES reading resolution

Front page continuation (72) Inventor Kizo Takao 5 East Higashikujo Minami Ishida-cho, Minami-ku, Kyoto Daijo Screen Mfg. Co., Ltd., Jujo Plant Tenjin Kitamachi No. 1 1 Dainippon Screen Manufacturing Co., Ltd.

Claims (12)

[Claims] 1. An illumination optical system for irradiating an illumination area of a document with light and an image forming optical system for forming an image of a reading area of the document on an image forming surface, and the image of the image forming surface is photoelectrically converted. In an image reading apparatus for reading with an element, an instruction means for instructing a change of a reading resolution, a reading area changing means for changing the reading area according to a reading resolution instructed by the instructing means, and an instruction by the instructing means An image reading apparatus, comprising: an illumination area changing unit that changes the illumination area according to a reading resolution. 2. The illumination optical system includes a light source, a collector lens that collects light from the light source, a condenser lens that collects light that has passed through the collector lens into the illumination area, and an original document with respect to the condenser lens. The image reading apparatus according to claim 1, further comprising a field stop disposed at a position conjugate with the field stop, wherein the illumination area changing unit changes the illumination area by changing a size of the field stop. 3. The illumination optical system includes a light source, a collector lens that collects light from the light source, a field lens, and a condenser lens that collects light that has passed through the field lens in the illumination area. The image reading apparatus according to claim 1, further comprising a field stop disposed at a position conjugate with the original with respect to the condenser lens, wherein the illumination area changing unit changes the illumination area by changing a size of the field stop. 4. The illumination optical system includes a light source, a collector lens that collects light from the light source, and a zoom lens that collects light passing through the collector lens in the illumination area.
The image reading apparatus according to claim 1, further comprising: a field stop disposed at a position conjugate with the original with respect to the zoom lens, wherein the illumination area changing unit changes the illumination area by changing a magnification of the zoom lens. . 5. The illumination optical system includes a light source, a collector lens that collects light from the light source, and a field lens.
A zoom lens that condenses light that has passed through the field lens into the illumination area, and a field stop that is arranged at a position conjugate with the original with respect to the zoom lens, and the illumination area changing unit includes a magnification of the zoom lens. The image reading apparatus according to claim 1, wherein the illumination area is changed by changing the. 6. The image reading apparatus according to claim 3, wherein the illumination optical system further includes a relay system lens between the field lens and the condenser lens. 7. The illumination optical system according to claim 2, further comprising an aperture stop arranged at a position where a light source image of the light source is formed or at a position conjugate with the light source image. Image reading device. 8. The image forming optical system includes an image forming lens and an aperture plate at a position conjugate with the original with respect to the image forming lens, and the reading area is changed by changing the size of the aperture of the aperture plate. The image reading apparatus according to claim 1, wherein the amount of light that has been changed and has passed through the aperture is read by the photoelectric conversion element. 9. The image forming optical system includes an image forming lens and an aperture plate at a position conjugate with the original with respect to the image forming lens, and the reading area is changed by changing a magnification of the image forming lens. The image reading device according to claim 1. 10. The image forming optical system includes an image forming lens arranged at a position where the original and the photoelectric conversion element have a conjugate positional relationship, and the magnification of the image forming lens is changed. The image reading apparatus according to claim 1, wherein the reading area is changed. 11. The illumination area is more than the reading area,
The image reading apparatus according to claim 1, wherein the size is set large by a size corresponding to a mechanical assembly error of the illumination optical system and the imaging optical system. 12. The image reading apparatus according to claim 1, wherein the ratio of the illumination area to the reading area is set to be higher on the high resolution side than on the low resolution side.