JPH06289498A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of preventing an electrostatic latent image from deterioration caused when the difference between a rotational speed of an image carrier and a scanning speed of an optical scanning system is changed in order to prevent a void, and obtaining an excellent image copy. CONSTITUTION:In the image forming device, the image information on an original is slit projected, by the image formation optical system 6 through the scanning system, on the image carrier 8 on the surface of rotating drum rotated is synchronism with the speed different from the scanning speed of the scanning system, and the image information formed on the image carrier 8 is transferred and recorded on the recording material 9 moved in synchronism with the same speed with the scanning speed, where the image formation optical system 6 is provided with the first lens system 6A equipped with at least a part of movable lens moved in accordance with projection power and the second lens system 6B composed of a fixed anamorphic lens whose image formation power in a longitudinal direction of the slit 4 is different from the power in a lateral direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a speed of a photosensitive member (photosensitive drum) as an image carrier and a scanning optical system for scanning an original by appropriately forming an image forming optical system. The present invention relates to an image forming apparatus suitable for an apparatus such as a copying machine, which prevents deterioration of an electrostatic latent image due to a difference and obtains a high quality copied image (image formed product).

[0002]

2. Description of the Related Art Conventionally, in a slit exposure type image forming apparatus such as a copying machine, a reflected light beam from a document illuminated by an illumination means is passed through a slit to an image-forming optical system and is formed on a surface of a photoconductor as an image carrier. It is projected in a slit shape.

FIG. 6 is a schematic view of a main part of an optical system of this type of image forming apparatus. In the figure, the document (image) 62 placed on the document glass 63 is illuminated by the illumination means 61. Then, the reflected light beam from the original 62 is slit 6
The reflection mirrors 65a, 65b, 65 for scanning are limited by 4
The optical path is bent via c, and an optical path bending mirror 67a, 67b,
Images are formed on the surface of the photoconductor 68 at various magnifications via 67c.

In the same figure, at the same magnification, the photoconductor 68 rotates in the direction of arrow A at a rotational speed (peripheral speed) V, and the light source 61 and the first reflecting mirror 65a are integrated into a speed V.
Further, the second and third reflection mirrors 65b and 65c are united to scan the document 62 in the direction of arrow B at the speed V / 2. As a result, the original 62 is imaged (exposed) in a slit shape at the same size while keeping the optical path length from the surface of the original 62 to the surface of the photoconductor 68 constant.

On the other hand, when the magnification is changed, the imaging optical system 66 has a magnification β
Accordingly, the light source 61 and the first reflecting mirror 65a are integrally moved at a speed V / β, and the second and third reflecting mirrors 65b and 65c are integrally moved at a speed V / β. The original 62 is scanned at 2β. As a result, an image (projection image) is formed on the surface of the photoconductor 68 at a predetermined magnification.

An electrostatic latent image is formed on the surface of the photoconductor 68 in accordance with the shading of the original 62, is visualized after development by a known electrophotographic process, and at the same speed V as the rotation speed V of the photoconductor 62. A copy image (image information) of the original 62 is obtained by being transferred and fixed on a transfer paper 69 as a recording material that has been fed and conveyed.

[0007]

In the conventional image forming apparatus shown in FIG. 6, the rotational speed V of the photosensitive member 68 and the transfer speed (moving speed) of the transfer paper 69 are moved at the same speed, and the photosensitive member is moved. When the 68-sided toner image (transferable image) is transferred onto the transfer paper 69, the toner of only the edge portions of the characters and line portions of the original 62 is transferred and the toner in the central portion is sufficient by a known electrophotographic process. There is a case where a phenomenon of so-called hollow image, that is, not transferred, occurs. For this reason, there are cases where the image is output as a poor quality copy image (image-formed product) such as a framed image.

Therefore, in the conventional image forming apparatus, in order to prevent the hollow image phenomenon, for example, a slight speed difference is provided between the rotation speed of the photoconductor 68 and the conveyance speed of the transfer paper 69, whereby the original document is formed. The toner of the character 62 and the line portion is evenly transferred.

However, in this case, in order to set the magnification in the scanning direction on the transfer paper 69 to the desired magnification, the conveying speed of the transfer paper 69, the light source 61, the first, second and third reflection mirrors 65.
The scanning speed (moving speed) of the scanning optical system including a, 65b, 65c and the like is set according to the magnification, and a slight speed difference is provided in the rotational speed of the photoconductor 68 with respect to the set speed. There was a need.

Therefore, a slight speed difference occurs between the moving speed of the original image (projected image) of the original 62 formed on the surface of the photoconductor 68 and the rotational speed of the photoconductor 68, and this speed difference causes the difference. Therefore, there is a problem that the electrostatic latent image on the surface of the photoconductor 68 deteriorates.

The state at this time will be described with reference to FIGS.

FIG. 7 is an explanatory diagram showing the contrast of the original in the sub-scanning direction, and FIGS. 8 and 9 are explanatory diagrams showing the contrast of the electrostatic latent image on the surface of the photoconductor 68 in the sub-scanning direction.

For example, as shown in FIG. 7, when a document 62 having a constant contrast in the lateral direction of the slit 64 is slit-exposed, the rotation speed of the photoconductor 68 and the scanning speed of the scanning optical system are synchronized with each other. Therefore, as shown in FIG. 8, the contrast of the electrostatic latent image on the surface of the photoconductor 68 can be maintained sufficiently high although it is slightly deteriorated by the imaging performance of the imaging optical system 66.

However, as described above, when the rotation speed of the photoconductor 68 and the scanning speed of the scanning optical system are not synchronized with each other, the contrast of the electrostatic latent image on the surface of the photoconductor 68 is as shown in FIG. However, there is a problem in that the copy image is adversely affected as a result.

According to the present invention, the imaging optical system has the same imaging magnification in the longitudinal direction and the lateral direction of the slit, and the first lens system in which some of the lenses can be moved according to the imaging magnification, and the longitudinal direction of the slit. By using a second lens system composed of an anamorphic lens having different imaging magnifications in the horizontal direction and the lateral direction,
The moving speed of the original image of the original formed on the surface of the photoconductor and the rotation speed of the photoconductor can be made to be the same irrespective of the scaling ratio, whereby a good quality copy image (image-formed product) can be obtained. It is an object of the present invention to provide an image forming apparatus that can be used.

[0016]

In the image forming apparatus of the present invention, the image information on the surface of the original is rotated by a focusing optical system via a scanning system at a speed different from the scanning speed of the scanning system. Slit projection onto the image carrier on the surface of the rotating drum, and transfer and record the image information formed on the image carrier onto the surface of the recording material that moves at the same speed as the scanning speed in synchronization with the scanning system. At this time, the image forming optical system is composed of a first lens system having at least a part of a movable lens movable according to a projection magnification, and a fixed anamorphic lens having different image forming magnifications in the longitudinal direction and the lateral direction of the slit. It is characterized by having a second lens system.

[0017]

1 is a schematic view of a main part of an optical system according to a first embodiment of the present invention, and FIG. 2 is a lens cross-sectional view in the sub-scanning direction of the imaging optical system shown in FIG.

In the figure, reference numeral 1 is a lighting means, which is composed of, for example, a halogen lamp or a fluorescent lamp. 2 is the manuscript (image)
And is placed on the platen glass 3. Denoted at 4 is a slit (slit member), which is arranged in the vicinity of the original platen glass 3 and limits the reflected light beam from the original 2 to project the surface of the photoconductor 8 in a slit shape.

Reference numeral 5 denotes a reflecting means for scanning, which is composed of three reflecting mirrors, namely first, second and third reflecting mirrors 5a, 5b and 5c, which reflects the light flux passing through the slit 4 and bends the optical path. The light is incident on the image forming optical system 6 described later.

The illumination means 1, the slit 4, and the reflection means 5
These elements constitute a scanning optical system, and the document 2 is scanned in the direction of arrow B at a predetermined speed.

Reference numeral 6 denotes an image forming optical system having a variable power portion, which forms a light beam based on image information from the original 2 on the surface of the photoconductor 8 at various magnifications.

The image forming optical system 6 according to this embodiment has a slit 4
A first lens system 6A in which the imaging magnification is equal in the longitudinal direction (main scanning direction) and the lateral direction (sub scanning direction), and at least some of the lenses are movable on the optical axis according to the imaging magnification. It has a second lens system 6B which is fixedly provided in the vicinity of the photoconductor 8 regardless of the copy magnification and is composed of an anamorphic lens having different image forming magnifications in the longitudinal direction and the lateral direction of the slit 4.

That is, the image forming optical system 6 in this embodiment is constructed so that the ratio of the image forming magnification in the main scanning direction to the image forming magnification in the sub scanning direction is constant regardless of the copy magnification.

Here, the first lens system 6A comprises a so-called symmetrical lens in which lenses having a similar shape to each other with a diaphragm interposed therebetween are arranged substantially symmetrically. That is, as shown in FIG. 2, the first lens system 6A is concave (negative) in order from the document 2 surface side.
Lens 6a, convex (positive) lens 6b, concave (negative) lens 6
c, and a convex (positive) lens 6d is composed of 8 elements in 8 groups symmetrically arranged with the diaphragm 6e in between. When changing the magnification, by moving some lenses on the optical axis according to the magnification, the air distances L1 and L2 are changed, and the entire lens system is moved to the position indicated by the dotted line as indicated by arrow C in FIG. There is.

The second lens system 6B comprises a cylindrical lens having a positive refractive power only in the sub-scanning direction,
As shown in FIG. 2, both lens surfaces have a meniscus shape with a convex surface facing the photoconductor 8 side in the sub-scan section.

Further, the second lens system 6B is fixedly arranged in the vicinity of the photoconductor 8 regardless of the copy magnification, and the surface of the original 2 and the surface of the photoconductor 8 are optically substantially conjugate with each other in the sub-scan section. It is set to be. The image forming magnification α of the second lens system 6B in this embodiment is α = 0.986, which is used in the reduction system.

Reference numeral 7 is an optical path bending means, which is composed of three reflecting mirrors, namely, first, second and third bending mirrors 7a, 7b and 7c. Reference numeral 8 denotes a photoconductor (photoconductor drum) as an image carrier, which rotates in the direction of arrow A at a predetermined speed. A transfer paper 9 is a recording material, and an arrow D
The photoconductor 8 is moved in the direction at a speed different from the rotation speed of the photoconductor 8 to prevent the hollow defect.

In the present embodiment, the image (copy image) on the surface of the original 2 illuminated by the luminous flux emitted from the illuminating means 1 having such a configuration is used for the slit 4, the first, the second and the second for scanning. The first lens system 6 via the three reflection mirrors 5a, 5b, 5c
A, the folding mirrors 7a, 7b and 7c, and the second lens system 6B form an image on the surface of the photoconductor 8 at a predetermined magnification.

Next, the toner image (transferable image) formed on the surface of the photosensitive member 8 by a known electrophotographic process is transferred onto the transfer paper 9
After the transfer, the image is fixed to obtain a copy image of the original 2.

In the present embodiment, at the same magnification, the first lens system 6A is located at the same magnification position of the solid line shown in FIG. 1, the light source 1 and the first reflecting mirror 5a are integrated at the speed V, and The second and the third reflecting mirrors 5b and 5c are united to scan the document 2 in the direction of arrow B at a speed V / 2, and the transfer paper 9 is fed and conveyed at a speed V in the direction of arrow D in synchronization with this scanning. is doing.

On the other hand, the rotational speed (peripheral speed) of the photosensitive member 8 is a predetermined rotational speed α · V (α is the photosensitive member 8 relative to the transfer speed of the transfer paper 9) with respect to the transfer speed (moving speed) V of the transfer paper 9. It rotates in the direction of arrow A in the figure at the ratio of rotational speeds).

Since the second lens system 6B has a positive refracting power only in the sub-scanning direction and the image forming magnification is set to α times as described above, the photoconductor 8 is scanned by the scanning optical system to scan the original. The magnification in the main scanning direction on the surface is the same magnification determined by the first lens system 6A, and the magnification in the sub scanning direction is the first lens system 6A.
Due to the mutual optical action of A and the second lens system 6B, slit exposure is performed at a magnification of α times.

At this time, the original 2 formed on the surface of the photoconductor 8
The moving speed of the original image is α which is the same as the rotating speed of the photoconductor 8.
・ V. This prevents the deterioration of the electrostatic latent image due to the speed difference between the moving speed of the original image and the rotating speed of the photoconductor 8 which has been a problem in the past.

Further, since the transfer paper 9 is fed and conveyed at the speed V in synchronization with the scanning speed (moving speed) V of the scanning optical system, it is possible to obtain a 1: 1 copy also in the scanning direction.

On the other hand, at the time of zooming, by moving some lenses on the optical axis so that the first lens system 6A has a predetermined magnification while the second lens system 6B remains fixed, the air gap L
1 and L2 are changed, and the entire lens system 6A is further moved to the position indicated by the dotted line in the figure.

Further, the rotational speed of the photosensitive member 8 and the transfer speed of the transfer paper 9 at the time of changing the magnification are the same as those at the above-mentioned equal magnification. On the other hand, the speed of the light source 1 and the first reflection mirror 5a that form the scanning optical system is V / β (β is the first lens system 6A).
Magnification), and the second and third reflection mirrors 5b and 5c scan the document 2 at a speed V / 2β.

Since the image forming magnification of the image forming optical system 6 in the sub-scanning direction is β · α times from the above, the moving speed of the original image of the original 2 formed on the surface of the photoconductor 8 is α. -V, which can be made equal to the rotation speed α · V of the photoconductor 8.

That is, in the present embodiment, the image forming optical system 6 is configured so that the ratio of the image forming magnification in the main scanning direction to the image forming magnification in the sub scanning direction of the image forming optical system 6 is constant regardless of the copy magnification. By configuring 6 as described above, the moving speed of the original image of the original 2 formed on the surface of the photoconductor 8 and the rotation speed of the photoconductor 8 can be made equal to each other regardless of the magnification change ratio. It is possible to prevent the deterioration of the electrostatic latent image due to the speed difference between these speeds, which is a problem, and obtain a good quality copy image.

Here, when a document having an arbitrary contrast in the sub-scanning direction shown in FIG. 7 is slit-exposed by this apparatus, the contrast of the document (image) on the surface of the photoconductor 8 is as shown in FIG. It can be seen that there is almost no deterioration in optical performance as compared with the contrast of the document in the conventional image forming apparatus shown in FIG.

FIG. 4 is a lens cross-sectional view in the sub-scanning direction of the second lens system which constitutes a part of the image forming optical system according to the second embodiment of the present invention.

This embodiment is different from the first embodiment described above in that the second lens system 46B is a cylindrical lens having negative refractive power only in the sub-scanning direction in which both lens surfaces are concave toward the photoconductor. That is, the image forming magnification of the second lens system 46B is used as a magnifying system.
Other configurations and optical functions are substantially the same as those in the first embodiment.

That is, although the image forming magnification α of the second lens system 6B is set to α = 0.986 in the reduction system in the first embodiment, the second lens system 46B is used in the present embodiment. The imaging magnification α of is set to α = 1.014 and used in the magnifying system.

As described above, in the present embodiment, even if the image forming magnification of the second lens system 46B is used in the magnifying system, the above-mentioned Embodiment 1 is used.
The same effect as can be obtained.

FIG. 5 is a schematic view of the essential parts of an optical system according to Example 3 of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, the difference from the first embodiment is that the second lens system 56B is arranged in the optical path between the second bending mirror 7b and the third bending mirror 7c forming the optical path bending means 7. That is what I did. Other configurations and optical functions are substantially the same as those in the first embodiment.

In this way, the position of the second lens system 56B is changed from the vicinity of the photoconductor 8 to the second and third folding mirrors 7b and 7c.
The present embodiment can obtain the same effect as that of the above-described first embodiment by changing to the optical path between

The second lens system 56 is used in this embodiment.
B is the second folding mirror 7b and the third folding mirror 7c
It is arranged in the optical path between the
It can be applied in the same way as in the third embodiment even if it is arranged in the optical path between the first bending mirror 7a and the first bending mirror 7a or in the optical path between the first bending mirror 7a and the second bending mirror 7b.

Next, Numerical Examples 1 to 3 of the imaging optical system according to Examples 1 to 3 of the present invention will be described. R in Numerical Examples 1 to 3
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness from the object side and the air gap, Ni
And νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

In Numerical Example 1, the focal length f ₁ of the first lens system 6A is f ₁ = 195.2 mm, and the focal length f ₂ of the second lens system 6B in the sub-scanning direction is f ₂ = 123.
4.63 mm, the imaging magnification α is α = 0.986.

In the numerical example 2, the numerical example of the first lens system 6A is omitted because it is the same as the numerical example 1. In Numerical Embodiment 2, the focal length f ₂ of the second lens system 46B in the sub scanning direction is f ₂ = −1046.14 m.
m, imaging magnification α is α = 1.014, air space L3 is L3
= 350 mm.

In Numerical Example 3, the numerical example of the first lens system 6A is omitted because it is the same as Numerical Example 1. In Numerical Embodiment 3, the focal length f ₂ of the second lens system 56B in the sub-scanning direction is f ₂ = 3536.59 m.
m, the imaging magnification α is α = 0.986, and the air gap L3 is L3.
= 277.99 mm.

[0052]

[Outer 1]

[0053]

[Table 1]

[0054]

[Outside 2]

[0055]

[Outside 3]

[0056]

According to the present invention, as described above, the imaging optical system has the same imaging magnification in the longitudinal direction (main scanning direction) and the lateral direction (sub-scanning direction) of the slit, and the imaging magnification is adjusted according to the imaging magnification. At least a part of the lenses is movable, and the second lens system is composed of an anamorphic lens having different imaging magnifications in the longitudinal direction and the lateral direction of the slit. It is possible to equalize the moving speed of the original image of the original formed on the surface of the photoconductor serving as the image carrier and the rotation speed of the photoconductor, whereby the speed of the photoconductor and the scanning optical system for preventing the hollow portion. It is possible to achieve an image forming apparatus capable of preventing the electrostatic latent image from deteriorating due to the difference and capable of obtaining a good quality copy image (image-formed product).

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an optical system according to a first embodiment of the present invention.

FIG. 2 is a lens cross-sectional view of the image forming optical system shown in FIG.

FIG. 3 is an explanatory diagram showing the contrast of an electrostatic latent image on the surface of the photoconductor of Example 1 of the present invention.

FIG. 4 is a lens sectional view of a second lens system according to Example 2 of the present invention.

FIG. 5 is a schematic view of a main part of an optical system according to a third embodiment of the present invention.

FIG. 6 is a schematic view of a main part of an optical system of a conventional image forming apparatus.

FIG. 7 is an explanatory diagram showing the contrast of a document in the sub-scanning direction.

FIG. 8 is an explanatory diagram showing the contrast of the electrostatic latent image on the surface of the photoconductor.

FIG. 9 is an explanatory diagram showing the contrast of the electrostatic latent image on the surface of the photoconductor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illuminating means 2 Original 3 Original platen glass 4 Slit 5 Reflecting means 6,56 Imaging optical system 6A First lens system 6B, 46B, 56B Second lens system 7 Optical path bending means 8 Image carrier 9 Recording material

Claims (2)

[Claims] 1. Slit projection of image information on the surface of an original by an imaging optical system via a scanning system onto an image carrier on a rotating drum surface that rotates synchronously at a speed different from the scanning speed of the scanning system. When the image information formed on the image carrier is transferred to and recorded on a recording material surface that moves at the same speed as the scanning speed in synchronization with the scanning system, the imaging optical system is adapted to the projection magnification. A first lens system having at least a part of the movable lens that is movable, and a second lens system including a fixed anamorphic lens having different imaging magnifications in the longitudinal direction and the lateral direction of the slit. A characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the second lens system is a cylindrical lens whose cross section in the lateral direction of the slit has a meniscus shape.