JPH06121119A - Image reader - Google Patents

Abstract

PURPOSE:To eliminate the density nonuniformity of a read image caused by the angle error of a mirror. CONSTITUTION:At a position C advanced from an original reading position A of an original surface 2a just for a distance (a) in the scanning direction, an elevation angle theta2 of a light source 3 is decided so that the center of an opening part 3b of the light source 3 can be just faced. Thus, a position E1 of a peak value Emax for illuminance distribution e' of the original surface 2a can be coincident with the reading position A. As a result, illuminance error between a read start point and a read end point can be eliminated even when there is a little error at the angle 90 deg. between second and third mirrors 6 and 7.

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 which scans a document surface by moving a long light source in a direction orthogonal to its central axis and reads the image by a photoelectric conversion element.

[0002]

2. Description of the Related Art As an optical system of an image reading apparatus of this type used in an image forming apparatus such as a copying machine, a reduction optical system as shown in FIG. 6 is conventionally known.

This is to set the original 2 on the original glass 1 to the first
Irradiate with the long light source 3 mounted on the carriage 5,
The image is sequentially reflected by the first mirror 4 mounted on the first carriage 5 together with the light source 3 and the second mirror 6 and the third mirror 7 mounted on the second carriage 8, and then the imaging lens 9 is formed.
The image is read by forming an image on the photoelectric conversion element 10 such as a charge transfer element (CCD). Here, the positions of the original 3 and the photoelectric conversion element 10 are fixed, and the first carriage 5 and the second carriage 8 have a speed ratio of 2: 1 and the central axis X of the light source 3.
It moves in the scanning direction indicated by the arrow Y orthogonal to.

As the light source 3, a long tube such as a fluorescent lamp corresponding to the reading width of the original 2 is used, and as shown in FIG. 7, a part of the phosphor layer 3a on the inner wall of the glass tube is shaved to have an opening angle θ. Opening 3b
To improve irradiation efficiency.

In the conventional image reading apparatus,
As shown in FIG. 7, the elevation angle θ1 is set so that the center of the opening 3b of the light source 3 faces the reading position A of the original 2. In such a positional relationship between the light source 3 and the reading position A, the document surface 2
The illuminance distribution of a is as shown by the original surface illuminance distribution curve e in the same figure, and the position E indicating the peak value Emax on the original surface is shown.
1 is closer to the light source 3 than the reading position A.

[0006]

However, in such a conventional image reading apparatus, the elevation angle is set so that the center of the opening of the light source faces the original reading position. At the reading position, the illuminance distribution curve e is largely inclined with respect to the document surface 2a as shown in FIG. Therefore, if the reading position A on the document surface deviates in the scanning direction (including the reverse direction) for some reason, the illuminance on the document surface also largely changes.

There are various causes of deviation of the reading position on the document surface. For example, it is conceivable that the angle between the second mirror and the third mirror is deviated. FIG. 8 shows the state.
Now, assuming that the angle 90 degrees between the second mirror 6 and the third mirror 7 is increased by the angle φ, the reading start position B1 is displaced from the predetermined reading start position A1 in the scanning direction Y by the distance x, and as a result, the original document is scanned. The surface illuminance E decreases by the illuminance ΔE.

Further, at the reading end position B2, the deviation amount is further increased, and is displaced from the predetermined reading end position A2 in the scanning direction Y by a distance x ', and the original surface illuminance E'is the illuminance Δ.
It decreases by E '.

Here, the scanning distance of the first carriage 5 is set to L
Then, x′−x = L / 2 · tan2φ, and the illuminance difference E′− on the document surface at the reading start point B1 and the reading end B2.
There is a problem that a density difference of the image based on E occurs and uneven density occurs when one original is read.

The present invention has been made in view of the above points, and even if there is a slight error in the angle between the second mirror and the third mirror, the difference in illuminance on the document surface at the reading start point and the reading end point. Is intended to eliminate unevenness in the density of the read image.

[0011]

In order to achieve the above object, the present invention scans the surface of an original by moving a long light source in a direction perpendicular to the central axis of the light source, and scans the image with a photoelectric conversion element. In an image reading device for reading, the image reading device is provided in which the light source is arranged so that the reading position on the document surface coincides with the position showing the peak value of the illuminance distribution on the document surface.

Also provided is an image reading device in which the position adjusting means for arranging the light source in parallel with the scanning direction is provided in the image reading device.

Further, in the above-mentioned image reading device, there is also provided an image reading device provided with an angle adjusting means for rotatably arranging the light source around the central axis.

[0014]

The present invention is constructed as described above,
The peak value of the illuminance distribution comes to the reading position on the document surface. Since the inclination of the illuminance distribution curve with respect to the document surface is gentle in the vicinity thereof, even if the reading position of the document surface is slightly displaced in the scanning direction, the influence on the illuminance difference is almost negligible.

Further, in the above-mentioned apparatus, the position adjusting means for arranging the light source so as to be movable in parallel in the scanning direction is provided. The deviation of the peak value can be easily corrected.

Further, in the above-mentioned device, the device provided with the angle adjusting means for rotatably arranging the light source around the central axis of the device has a compact light source mounting portion rather than the device for moving the light source in parallel in the scanning direction. Will be possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an explanatory view showing a configuration similar to that of FIG. 7 showing the principle of the present invention and an illuminance distribution state of a document surface. The parts corresponding to those in FIG. .

In this document reading device, a position C which is advanced from the document reading position A on the document surface 2a in the scanning direction Y by a distance a.
The elevation angle θ2 so that the center of the opening 3b of the light source 3 faces directly
By setting, the position of the light source 3 is set so that the peak value of the illuminance distribution e ′ on the document surface 2a comes to the document reading position A.

At this time, since the processing accuracy of the opening angle θ and the elevation angle θ2 of the light source 3 involves a deviation of about 5 to 10 degrees, the position of the peak value of the illuminance distribution e ′ on the document surface 2a is caused by the deviation amount. May deviate from the predetermined reading position A. Therefore, it is necessary to correct the mounting position and mounting angle of the light source 3 so that the peak value of the illuminance distribution e ′ comes to the reading position A.

FIG. 2 is a perspective view showing an embodiment of the present invention in which the correction is made, and FIG. 3 is an explanatory view showing a sectional view of the same with an illuminance distribution curve of the original surface. Installed between a pair of sockets 3c, 3c, this socket 3
c and 3c, a plurality of long holes 3d for attaching to the first carriage 5
Are formed respectively so that the pair of sockets 3c, 3c can be moved within a predetermined range in the scanning direction Y, and can be fixed by the setscrew 11 at that position to configure the position adjusting means of the light source 3.

According to this embodiment, a pair of sockets 3
When the position of the peak value of the illuminance distribution on the document surface 2a of the light source 3 mounted between the positions c and 3c deviates from the reading position A due to variation in either or both of the opening angle θ and the elevation angle θ2. , The set screw 11 is loosened and the pair of sockets 3c, 3
c is shifted in the scanning direction Y or in the opposite direction to set screw 11
The adjustment is extremely easy and can be performed in a short time.

Next, FIG. 4 is a perspective view showing another embodiment of the present invention, and FIG. 5 is an explanatory view showing a sectional view thereof together with an original surface illuminance distribution curve. Both ends of the light source 3 are mounted between a pair of cylindrical sockets 3e, 3e, and the sockets 3e, 3e are rotatably fixed to the first carriage 5 by arch-shaped holders 12, 12 and four set screws 11. Thus, the angle adjusting means of the light source 3 is configured.

In this embodiment, when the position of the peak value of the illuminance distribution on the document surface 2a deviates from the reading position A due to the variations in the opening angle θ and the elevation angle θ2, the set screw 11 is loosened and the light source 3 is turned on. It suffices that the socket 3e is rotated around the central axis X together with the sockets 3e and 3e, the set screw 11 is screwed in at a required angular position, and the socket 3e is fixed by the holder 12. It becomes possible to make space,
The central axis of the long light source can always be held accurately in the direction orthogonal to the scanning direction.

[0024]

As described above, in the image reading apparatus according to the present invention, the reading position on the document surface is made to coincide with the position showing the peak value of the illuminance distribution on the document surface. Even if the reading position at the end point is slightly deviated in the scanning direction, the influence on the illuminance difference on the document surface can be minimized, and uneven density of the read image can be virtually eliminated.

Further, in the above-mentioned device in which the light source is arranged so as to be movable in parallel in the scanning direction, it is possible to easily correct the deviation of the peak value of the illuminance distribution due to the variation of the light source.

Further, in the above-mentioned device, the light source arranged so as to be rotatable about its central axis has the same effect as the above, and the space for the light source mounting portion is small, and the angle is adjusted. It becomes possible to always keep the light source of (4) always in an orthogonal state with respect to the scanning direction.

[Brief description of drawings]

FIG. 1 is an explanatory view of a configuration showing a principle of the present invention and a document surface illuminance distribution state.

FIG. 2 is a perspective view showing a main part of an embodiment of the present invention.

FIG. 3 is an explanatory view showing a sectional view of the same with an illuminance distribution curve of a document surface.

FIG. 4 is a perspective view showing a main part of another embodiment of the present invention.

FIG. 5 is an explanatory view showing a sectional view of the same with an illuminance distribution curve of a document surface.

FIG. 6 is a configuration and an optical path diagram of an image reading apparatus that has been conventionally used.

FIG. 7 is an explanatory view of the configuration and the distribution of illuminance on the document surface.

8A and 8B are a configuration and an optical path diagram showing the cause of the deviation of the document surface reading position.

[Explanation of symbols]

1 Document Glass 2 Document 3 Light Source 4 First Mirror 5 First Carriage 6 Second Mirror 7 Third Mirror 8 Second Carriage 9 Imaging Lens 10 Photoelectric Conversion Element 11 Set Screw 12 Holder A Reader on Document Surface X Light Source Central axis Y scanning direction

Claims (3)

[Claims] 1. An image reading apparatus for scanning a document surface by moving a long light source in a direction orthogonal to a central axis of the document and reading the image by a photoelectric conversion element, wherein the reading position of the document surface is An image reading apparatus wherein the light source is arranged so as to coincide with a position showing a peak value of an illuminance distribution on a document surface. 2. The image reading apparatus according to claim 1,
An image reading apparatus comprising position adjusting means for arranging the light source so as to be movable in parallel in a scanning direction. 3. The image reading device according to claim 1,
An image reading apparatus comprising an angle adjusting means for rotatably arranging the light source around the central axis.