JPH0690391B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, an optical system for image exposure of an image forming apparatus such as an electronic copying machine, and in particular, an image forming magnification can be changed depending on the vertical and horizontal directions of an image surface (single magnification change). Related to namono.

2. Description of the Related Art Conventionally, copying machines having different vertical and horizontal copying magnifications have been known. Such a device is used to copy American letters (so-called letter size) into domestic standard paper (A3 ・ A4 ・ A5 ・ ・ ・ or B3 ・ B4 ・
It is used when you want to make the size of stored documents uniform by copying to B5 ...). In order to make the vertical and horizontal magnifications different, the image forming magnification of the copying optical system is made different depending on the direction of the image plane.

For example, in an electronic copying machine whose main part is shown in FIG. 1, a cylindrical lens 20 is provided in a part A in the optical path of the optical system as shown in FIG.
It is filled. In FIG. 1, 1 is a photosensitive drum, 2
Is a primary charger, 3 is a developing device, 4 is a transfer charger, 5 is a fixing device, 7 is a cleaner, 8 is a transfer paper, 10 is a platen glass plate,
Reference numeral 11 is a document illumination lamp, and 12 is a slit plate. The functions of the above respective units are well known and will not be described.
Further, 14 is a first mirror, 15 is a second mirror, 16 is an image forming lens, 17 is a third mirror, and 18 is a fourth mirror, which constitute a scanning image forming optical system. That is, the first mirror 14 is the original illumination lamp 11
-Move with the slit plate 12 in the arrow X direction at a speed twice that of the second mirror 15. Then, this scanning optical system
An image is formed on the surface of the drum 1 rotating in the arrow R direction while scanning the document O on the sheet 10. Position A on the optical path of the optical system
By disposing the convex cylindrical lens 20 in the axial direction of the drum 1 in the axial direction, the imaging magnification is different between the axial direction and the rotation direction of the drum 1 in the entire optical system, and the magnification is unilaterally varied. .

However, with such an optical system, not only theoretically impossible to focus correctly in the vertical and horizontal directions of the screen, but also it is approximately difficult. That is, in order to form an image on the surface of the drum 1 in the minor axis direction (meldional direction) where the power of the cylindrical lens 20 is present, the position of the third mirror 17 or the fourth mirror 18 is adjusted, and the image forming lens 16 When the position is adjusted, the ray bundle is in the rear focus state even when it reaches the surface of the drum 1 in the major axis direction (sagittal direction) in which the cylindrical lens 20 has no power. On the contrary, when the image is adjusted so as to form an image on the surface of the drum 1 in the saddle direction, the light flux in the meldional direction is in the front focus state on the surface of the drum 1. Even if the cylindrical lens 20 is moved to the position A without adjusting the position, the image is not accurately formed because the optical path length is changed in the medallional direction and also in the saddal direction. Further, there is also a case where a transparent parallel plate such as glass is placed at the position A for adjusting the optical path when the univariate magnification is not performed (when the cylindrical lens 20 is removed). However, even with such a configuration, when the cylindrical lens 20 is inserted, the inconvenience of not forming an image on the surface of the drum 1 in one or both of the medallional direction and the saddal direction still remains.

In order to eliminate such an inconvenience, there is one in which a lens unit 21 having a structure as shown in FIG. 3 is placed at the optical path position A in FIG. 3A is a view of the lens 21 in the minor axis direction, and FIG. 3B is a view of the same in the major axis direction. The lens unit 21 is a lens unit in which a convex cylindrical lens 23 and a lens 24 having a cylindrical concave surface 24a in the minor axis direction and a cylindrical convex surface 24b in the major axis direction are combined. An optical system including such a lens unit 21 theoretically forms an image on the surface of the drum 1 in both the major axis direction and the minor axis direction. However, since the shape of the lens 24 is a very special shape in which the curved surface directions are different on both sides, there is a drawback that the manufacturing process is difficult to perform. Therefore, the accuracy of the lens is deteriorated, and the obtained image of univariable magnification is not as clear as expected. At the same time, the magnification in the major axis direction also deviates from the same size. In addition, it is an obstacle to the cost reduction of the device.

The present invention has been made in view of such a situation, and an object thereof is to provide at low cost an optical system capable of obtaining an extremely clear image-formed image regardless of whether the magnification is changed to one side or not. is there.

The present invention that achieves this object is an image forming apparatus including a photoconductor and an image forming optical unit that forms an image of light reflected from a document surface on the photoconductor. A single-variable lens unit that includes a convex cylindrical lens having only a curved surface and a concave cylindrical lens having a curved surface on one side and a flat surface on the other side in a cross section in the minor axis direction, and a convex cylindrical lens and a concave cylindrical lens made of the same material. A transparent flat plate having a thickness approximately equal to the sum of the thicknesses of the light transmitting portions of the two cylindrical lenses, and holding the single variable lens unit and the transparent flat plate in parallel on the same substrate, and transparent to the single variable lens unit. The flat plate and the flat plate can be alternately switched in the same image forming optical path.

Examples of the present invention will be described in detail below.

FIG. 4 is a perspective view of an essential part of an optical system to which the present invention is applied, and FIG. 5 is a side view of the same. In these figures, the cylindrical lens unit 25 is a combination of a cylindrical convex lens 26 and a cylindrical concave lens 27, both of which are curved only in the minor axis direction. Cylindrical lens unit 25
The transparent parallel plate 28 is attached to the rotary substrate 30 in parallel. The rotary substrate 30 is pivotally supported by a rotary shaft 38 so that the cylindrical lens unit 25 or the parallel plate 28 comes to a position corresponding to the position A in FIG. The cylindrical lens unit 25 and the parallel plate 28 can be selectively moved into the optical path of the optical system by the rotating mechanism including the solenoid 31 and the spring 32.

The sum of the optical path length of the central portion of the convex lens 26 and the optical path length of the central portion of the concave lens 27 is equal to the optical path length of the parallel plate 28 in the plate thickness direction. Note convex lens 26, concave lens 27, the parallel plate 28 all glass of the same material, if formed like in plastics, among each thickness t ₁ - t ₂ - t, by the t ₁ + t ₂ = t Good. Although not shown in FIGS. 4 and 5, other optical systems 14, 15, 16, 17, 18 (see FIG. 1) are arranged at positions when the parallel plate 28 is in the optical path. Then, it is designed to form an image on the surface of the drum 1. The focal length and principal point position of the cylindrical lens unit 25 in the meldinal direction are designed so as to form an image on the surface of the drum 1 at a desired univariable magnification. Since the lens unit 21 is a two-lens lens including a convex lens 26 and a concave lens 27, if the respective curvatures and relative positions (distance between both lenses) are appropriately selected, such a combination of focal length and principal point position is obtained. It is possible.

In an electronic copying machine incorporating such an image exposure optical system, the moving speed of the light source 11, the slit 12, and the first mirror 14 in the X direction (scanning speed of the optical system) and the surface speed of the drum 1 by the rotation R are shown. When the magnification is changed, the speed ratio is changed so that the ratio of ## EQU1 ## matches the magnification of the optical system in the scanning direction.

In the electronic copying machine configured as described above, when forming a copy image of the same size in the vertical and horizontal directions, if the solenoid 31 is de-energized, the spring 30 pulls the substrate 30, and the substrate 30 is at the position shown by the solid line in FIG. The parallel plate 28 is in the optical path of the optical system. Therefore, the optical system scans and exposes the image of the document O on the surface of the drum 1 at the same magnification. Solenoid 31
When the power is turned on, the substrate 30 is attracted and rotated to the position shown in FIG. 5 (corresponding to FIG. 4), and the cylindrical lens unit 25 advances into the optical path of the optical system. Therefore, the optical system scans and exposes the image of the original document O at a single magnification. At this time, the image formation position is on the drum 1 surface in both the Meldional and Sadital directions.

As described above, according to the image forming apparatus using the optical system of the present invention, an extremely clear image can be formed regardless of whether the image formation is for single-magnification or equal-magnification. In addition, since the cylindrical lens, which is a unit component of the optical system, has no special shape, it is easy to process and can be procured at a low cost.

Further, since the univariable magnification lens unit and the transparent flat plate are held in parallel on the same substrate, the univariable magnification mode and the equal magnification mode can be easily switched.

[Brief description of drawings]

FIG. 1 is a schematic view of an image forming apparatus equipped with an optical system to which the present invention can be applied, and FIGS. 2 and 3 are views showing a conventional optical system.
FIG. 4 is a perspective view of an essential part of an optical system to which the present invention is applied, and FIG. 5 is a side view of the same. 1 is a photosensitive drum, 10 is a platen glass plate, 11 is a document illumination lamp, 12 is a slit plate, 14, 15, 17, and 18 are mirrors, 16 is an image forming lens, 26 is a cylindrical convex lens, 27 is a cylindrical concave lens, 28 Is a transparent parallel plate.

Claims (1)

[Claims] 1. An image forming apparatus having a photoconductor and an image forming optical unit for forming an image of light reflected from a document surface on the photoconductor, wherein the image forming optical unit has a curved surface only in a cross section in a minor axis direction. Of the convex cylindrical lens and a concave cylindrical lens having a curved surface on one side and a flat cylindrical surface on the other side of the cross section in the minor axis direction, and a convex cylindrical lens and a concave cylindrical lens of two cylindrical lenses made of the same material. A transparent flat plate having a thickness substantially equal to the sum of the thicknesses of the light transmitting portions, and holding the single variable lens unit and the transparent flat plate in parallel on the same substrate, and the single variable lens unit and the transparent flat plate are the same. An image forming apparatus characterized in that it can be switched alternately in an image forming optical path.