JPH11344776A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image reader which can be made compact as a whole without causing fogging in a copied image. SOLUTION: This image reader is constituted so that the image 1 illuminated by an illumination means is formed on the surface of a recording medium 12 with the various kinds of image forming magnification by using an image forming means 8 having a variable power function and read. When the distributing irregularity of light quantity is caused on the medium 12 at a variable power time by the forming means 8, the light quantity of the variable power time is controlled with the light quantity of the part of the distributing irregularity of the light quantity being easiest to cause the fogging at the image as a reference.

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, and more particularly to an image reading apparatus having a variable magnification function, which is suitable for an analog copying machine, for example.

[0002]

2. Description of the Related Art Conventionally, various copying apparatuses (copiers) having a variable magnification function (zoom function) of, for example, about 50 to 200% have been proposed in which a glass surface of a document table is illuminated by a slit method. ing.

In general, when a slit area on a platen glass is projected and imaged on a photosensitive drum surface by an imaging lens, a longitudinal direction (main scanning direction) of the slit on the photosensitive drum surface is a so-called image forming direction according to an angle of view. Light amount distribution unevenness (illuminance unevenness) occurs due to the cos4 power law of the image lens. As a method of removing the uneven light amount distribution at this time, for example, when a light source having a uniform luminance distribution (illumination distribution) is used, c
There is a method of providing a light amount distribution correcting means for correcting the os4 power law in the optical path. At this time, when the imaging lens is a variable magnification system, at the time of zooming, the light amount distribution correcting means is moved according to the movement of the imaging lens.

As this light amount distribution correcting means, a light amount distribution correcting plate (light shielding plate) integrated with an image forming lens is conventionally known, and the light amount on the photosensitive drum surface generated by the cos 4 power law of the image forming lens. In order to correct the distribution unevenness, for example, the image forming lens is divided into a light beam passing through the center of the image forming lens (center light beam) and a light beam passing through the end portion (end light beam), that is, in the optical axis direction. The light amount distribution unevenness is corrected based on the difference in the amount of vignetting between the central light beam and the end light beam.

[0005]

However, the above-described conventional copier having a zooming function requires a large space for moving the light amount distribution correction plate during zooming. And it is difficult to reduce the size of the entire apparatus.

The present invention relates to an image reading apparatus having a zooming function. In particular, in the image reading apparatus, the unevenness of the light amount distribution on the surface of the recording medium which occurs when the image forming means changes the magnification, is the most fogging on the image. An object of the present invention is to provide an image reading apparatus capable of controlling the light amount at the time of zooming based on the light amount of a portion where the image is likely to occur without causing fog on a copied image and reducing the size of the entire apparatus. And

[0007]

According to the present invention, there is provided an image reading apparatus comprising: (1) an image illuminated by an illuminating means on a recording medium surface at various image forming magnifications by using an image forming means having a zooming function; In an image reading apparatus that forms an image and reads the image, the fog on the image is the most out of the light amount distribution unevenness with respect to the light amount distribution unevenness on the recording medium surface generated at the time of zooming by the image forming unit. It is characterized in that the light quantity at the time of zooming is controlled on the basis of the light quantity of a portion which is likely to occur.

In particular, (1-1) when the imaging magnification of the imaging means is the same, the illumination distribution of the illumination means is corrected so that the light quantity distribution on the recording medium surface becomes substantially uniform. It is characterized by doing.

(2) In an image reading apparatus which forms an image illuminated by the illuminating means on a recording medium surface at various image forming magnifications by using an image forming means having a zooming function, and reads the image, When the image forming means is located at a position where the image forming magnification is reduced or enlarged, a light amount distribution correcting means is arranged so that the light amount distribution on the recording medium surface becomes substantially uniform. With respect to the uneven light amount distribution on the recording medium surface which occurs at the time of zooming, the light amount at the time of zooming is controlled based on the light amount of the portion where fogging is most likely to occur on the image among the uneven light amount distribution. It is characterized by having.

In particular, (2-1) by correcting the illumination distribution of the illumination means when the imaging magnification of the imaging means is the same, so that the light quantity distribution on the recording medium surface becomes substantially uniform. It is characterized by doing.

[0011]

(Embodiment 1) FIG. 1 is a schematic view of a main part of Embodiment 1 of the present invention. FIG. 2 is a schematic view of a main part of the optical system when FIG. 1 is viewed from above.

In FIG. 1, reference numeral 2 denotes a platen glass, which is made of, for example, a transparent platen glass. 1 is an image (document)
And is placed on the platen glass 2. Reference numeral 3 denotes a light source which constitutes one element of the illuminating means, and is formed of, for example, a fluorescent lamp having a linear light emitting surface extending in a direction perpendicular to the paper surface (main scanning direction). Reference numeral 4 denotes a slit, which has an opening that is long in the direction perpendicular to the paper surface, and regulates a light beam from one surface of the document. Reference numerals 5, 6, and 7 denote scanning mirrors, respectively, and an image forming lens 8 as an image forming means to be described later, which reflects a light beam from one surface of the original to bend the optical path.
The light is guided. The imaging lens 8 has a mechanism for changing the imaging magnification by changing the position on the optical axis, or a magnification unit such as a zoom system. In the figure, when changing the magnification (when changing the imaging magnification),
It is configured to be movable on the optical axis. 9,10,
Numerals 11 denote reflecting mirrors for bending the optical path, which reflect the light flux passing through the imaging lens 8 to bend the optical path and guide the light onto the surface of a photosensitive drum 12 as a recording medium.

In this embodiment, the image (original) 1 illuminated by the light source 3 is moved in the direction of arrow 1a (sub-scanning direction) by a transport mirror (not shown). At this time slit 4
The light flux based on the image information from one surface of the document, which is regulated by the above, is reflected via the scanning mirrors 5, 6, and 7 and is incident on the imaging lens 8. The light beam that has passed through the imaging lens 8 is guided onto the surface of the photosensitive drum 12 via reflection mirrors 9, 10, and 11 for bending the optical path. As a result, an image is formed on the surface of the photosensitive drum 12 at a predetermined magnification, and image information is sequentially written.

In the present embodiment, when writing the image 1 on the platen glass 2 in an enlarged or reduced manner, the image 1 is enlarged and reduced by the imaging lens 8. For example, when writing the image 1 in an enlarged manner, the imaging lens 8 is moved from the same magnification position A as the reference magnification indicated by the solid line in FIG.
When writing the image 1 in a reduced size, the imaging lens 8 is moved to a reduced position C indicated by a dotted line in FIG.
Further, the reflection mirrors 9 and 10 are moved to a reduced position D indicated by a dotted line in the figure as shown by an arrow 8b.

In this embodiment, unlike the above-described conventional example, there is no light amount distribution correcting means (light amount distribution correcting mechanism) for correcting the light amount distribution on the surface of the photosensitive drum 12 substantially uniformly. As can be seen, for example, when the imaging magnification is reduced (50%), the position on the optical axis of the imaging lens 8 is located at the reduced position C indicated by the dotted line, and accordingly, the position on the optical axis of the reflection mirrors 9 and 10 is adjusted accordingly. Are arranged at a reduced position D indicated by a dotted line. Thereby, in the present embodiment, the distance (space) between the imaging lens 8 and the reflection mirrors 9 and 10 can be made very short (narrow) as compared with the conventional image reading apparatus having the light amount distribution correcting means. As a result, the size of the entire device is reduced.

However, in this embodiment, since the light amount distribution correcting means is not provided, for example, the imaging magnification is reduced (50%).
%) And enlargement (200%), the light amount distribution on the surface of the photosensitive drum 12 is uneven due to the cos4 law of the imaging lens 8 as shown in FIGS. 3A and 3B. . At this time, the halftone (intermediate)
Density, uneven density occurs at the center and edge of the copied image.However, ordinary originals generally have many character originals, and the white and black densities of such originals are clear. 5 (the ratio between the density of the document and the density of the copy image) is as shown in FIG. 5, and there is almost no effect on the density change (light quantity change) in the white background portion and the black character portion. Therefore, even if the light amount distribution unevenness occurs, there is almost no problem in copying a character document.

However, for example, when the background of the original is slightly darker, such as original paper or color background, there is a problem that fogging is likely to occur in a portion where the light amount (light amount distribution) is reduced.

Therefore, in the present embodiment, with respect to the light amount distribution unevenness on the surface of the photosensitive drum 12 at the time of zooming, the light amount at the portion where fogging is most likely to occur on an image among the light amount unevenness is used as a reference. By controlling the light amount, that is, increasing the light amount so that the light amount in the portion where fogging is most likely to occur becomes an appropriate image, for example, even when the background of the document is slightly dark, a copied image (copied image) can be obtained. Fog is prevented.

The portion where fogging is likely to occur is, for example, a place where the light amount distribution is the lowest, a place where the drum sensitivity distribution is the lowest, or a place where the charging unevenness is the highest (a place where the charge amount is large).

On the other hand, the light amount distribution on the surface of the photosensitive drum 12 at the same magnification, which is most often used as a copying machine, is the same as that at the time of zooming, because of the cos4 power law of the imaging lens 8 and the like.
As shown in (1), the light amount decreases at the end. Therefore, in the present embodiment, the illumination distribution (luminance distribution) of the illumination means is corrected so as to be higher in the peripheral part than in the central part.
The document 1 is illuminated after being corrected so as to have an illumination distribution as shown in FIG. Thus, the light amount distribution on the surface of the photosensitive drum 12 can be made substantially flat as shown in FIG.

As described above, in this embodiment, the photosensitive drum 1 generated when the light amount distribution correcting means is not disposed as described above.
By controlling the light amount at the time of zooming on the basis of the light amount of the portion of the light amount distribution unevenness where the light amount is reduced, the fogging does not occur in the copied image. A high quality copy image has been obtained. At the same magnification, the illumination distribution of the illumination means is corrected as described above, whereby the cos4 power law of the imaging lens 8 is corrected so that the light amount distribution on the surface of the photosensitive drum 12 becomes substantially uniform. Further, in the present embodiment, since no space is required for providing the light amount distribution correcting means, the size of the entire apparatus can be reduced.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described.

The present embodiment is different from the first embodiment in that the imaging means (imaging lens) is arranged such that the light amount distribution correcting means is used when the imaging magnification is located at one of the zoom positions where the magnification is reduced or enlarged. That is, the present invention is applied to a configuration in which the light amount distribution correcting means does not operate in other zooming regions. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in this embodiment, the light amount distribution correcting means is provided so that the light amount distribution on the photosensitive drum surface becomes substantially uniform when the image forming magnification of the image forming lens is reduced or enlarged. Then, with respect to the uneven light amount distribution on the photosensitive drum surface generated in the variable magnification area where the light amount distribution correcting means does not operate, the light amount unevenness at the time of zooming is determined based on the light amount of the portion where fogging is most likely to occur on the image among the uneven light amount distribution. The amount of light is controlled. Even in such a case, in the present embodiment, the size of the apparatus can be reduced as compared with the conventional image reading apparatus.

The light amount distribution correcting means in the present embodiment is, for example, a shape which sequentially increases the passing light flux from the optical axis of the imaging lens to the periphery to correct a decrease in the peripheral light amount distribution due to the cos4 power law of the imaging lens. For example, a light shielding plate or the like is used.

[0026]

According to the present invention, in the image reading apparatus having the zooming function as described above, in particular, the unevenness of the light intensity distribution on the recording medium surface caused by the zooming by the image forming means. By controlling the light amount at the time of zooming based on the light amount of the portion where fogging is most likely to occur on the image,
It is possible to achieve an image reading apparatus that does not cause fog on a copied image and that can reduce the size of the entire apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of the optical system when FIG. 1 is viewed from above.

FIG. 3 is a light amount distribution diagram at each magnification on a photosensitive drum surface.

FIG. 4 is a distribution diagram relating to correction of the cos4 power law of the imaging lens.

FIG. 5 is an explanatory diagram showing a DD curve of an electrophotographic process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original (image) 2 Original platen glass 3 Light source 4 Slit 5,6,7 Reflection mirror 8 Imaging means 9,10,11 Reflection mirror 12 Recording member (photosensitive drum)

Claims (4)

[Claims] 1. An image reading apparatus which forms an image illuminated by an illuminating means on a recording medium surface at various image forming magnifications using an image forming means having a zooming function, and reads the image. With respect to the uneven light amount distribution on the recording medium surface which occurs at the time of zooming by the image forming means, the light amount at the time of zooming is based on the light amount of the portion where fogging is most likely to occur on the image among the uneven light amount distribution. An image reading apparatus characterized by controlling the following. 2. An image forming apparatus according to claim 1, wherein when the imaging magnification of said imaging means is the same, an illumination distribution of said illuminating means is corrected so that a light amount distribution on said recording medium surface becomes substantially uniform. 2. The image reading apparatus according to claim 1, wherein: 3. An image reading apparatus which forms an image illuminated by an illuminating means on a recording medium surface at various image forming magnifications using an image forming means having a zooming function, and reads the image. When the image forming means is at a position where the image forming magnification is reduced or enlarged, a light amount distribution correcting means is provided so that the light amount distribution on the recording medium surface becomes substantially uniform. In response to the uneven light amount distribution on the recording medium surface which occurs at the time of magnification, the light amount at the time of zooming is controlled based on the light amount of the portion where fog is most likely to occur on the image among the uneven light amount distribution. An image reading apparatus, comprising: 4. A light quantity distribution on the recording medium surface is made substantially uniform by correcting an illumination distribution of the illumination means when an imaging magnification of the imaging means is the same magnification. 4. The image reading device according to claim 3, wherein: