JPS60192933A - image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical system for image exposure of an image forming apparatus such as an electronic copying machine, in particular, it is possible to make the imaging magnification different depending on the length and width of the image plane (unilateral variable magnification). relating to things.

2. Description of the Related Art Copying machines with different vertical and horizontal copying magnifications have been known. This type of device converts American letters (so-called letter size) into domestic standard paper (A3, A4, A5, paper, or B).
This is used when you want to make copies on 3, B4-B5, etc. files to make the size of the stored documents the same. In order to make the vertical and horizontal magnifications different, the imaging magnification of the copying optical system is made to differ 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 as shown in FIG. 2 is inserted in a part A of the optical path of the optical system. In FIG. 1, l is a photosensitive drum, 2 is a primary charger, 3 is a developing device, 4 is a transfer charger, and 5 is a photosensitive drum.
1 is a fixing device, 7 is a cleaner, 8 is a transfer paper, 10 is an original glass plate, 11 is an original illumination lamp, and 12 is a slit plate.

Since the functions of the above-mentioned parts are well known, the explanation thereof will be omitted. Further, 14 is a first mirror, 15 is a second mirror,
16 is an imaging lens, 17 is a third mirror, and 18 is a fourth mirror, which constitute a scanning imaging optical system. That is, the first mirror 1
4, along with the original illumination lamp 11 and the slit plate 12, the second
It moves in the direction of arrow X at twice the speed of the mirror 15. Then, this scanning optical system scans the original 0 on the original platen lO while forming an image on the surface of the drum l rotating in the direction of arrow R. If a convex cylindrical lens 20 is disposed at position A on the optical path of the optical system with the major diameter direction facing the axial direction of the drum 1, the imaging magnification of the entire optical system will be increased in the axial direction and rotational direction of the drum 1. are different, resulting in unilateral magnification.

However, with such an optical system, it is not only theoretically impossible to accurately focus the screen in both the vertical and horizontal directions, but also approximately difficult. That is, in an attempt to form an image on the surface of the drum l in the short axis direction (meridional direction) where the cylindrical lens 20 has power, the third
Adjust the position of the mirror 17 or the fourth mirror 18,
When the position of the imaging lens 16 is adjusted, in the long axis direction (sagittal direction) where the cylindrical lens 20 has no power, the light beam remains in focus even when it reaches the surface of the drum l. On the other hand, when adjusting to form an image on the surface of the drum 1 in the sagittal direction, the rays in the meridional direction are brought into focus on the surface of the drum 1. Without adjusting the 0 position, the cylindrical lens 20 is moved to position A. Even if you put it in, the optical path length changes not only in the meridional direction but also in the sagittal direction, so the image will not be formed accurately. Also,
When one side magnification is not changed (when the cylindrical lens 20 is removed), a transparent parallel flat plate made of glass or the like is placed at position A in order to adjust the optical path. However, even with this configuration, there is still a problem that when the cylindrical lens 20 is inserted, an image is not formed on the drum surface in either the meridional direction or the sagittal direction, or both.

In order to eliminate such inconvenience, the lens unit) 21 having the configuration as shown in FIG.
What you put in is worth it. FIG. 3(a) is a view of the lens 21 in the minor axis direction, and FIG. 3(b) is a view of the lens 21 in the major axis direction. The lens unit 21 is a combination of 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. koyona lens unit 2
1, theoretically an image is formed on one surface of the drum in both the major axis direction and the minor axis direction. However, since the shape of the lens 24 is extremely unique in that the curved surfaces are different in direction on both sides, there is a drawback that it is difficult to process the lens 24 in manufacturing. As a result, the precision of the lens deteriorates, and the resulting one-sided variable magnification image is not as clear as expected. At the same time, the magnification in the major axis direction deviates from the same magnification, which also becomes an obstacle to reducing the cost of the device.

The present invention was made in view of this situation, and the object thereof is to provide an optical system at a low cost that can obtain an extremely clear image regardless of whether or not variable magnification is used. be.

To achieve this object, the present invention provides an image forming apparatus equipped with an optical system that forms and exposes an original image onto a photoreceptor, which includes a lens unit consisting of at least two cylindrical lenses, and a center portion of the lens unit. By inserting either a transparent parallel plate having an optical path length approximately equal to the optical path length into the optical path of the optical system, it is possible to determine whether the imaging magnification of the optical system differs depending on the direction of the imaging plane. This optical system is characterized in that it is possible to select whether the image plane is uniform regardless of the direction of the image plane.

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

FIG. 4 is a perspective view of essential parts 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 includes a cylindrical convex lens 26 and a cylindrical concave lens 27, both of which have a curved surface only in the short axis direction.
It is a combination of The cylindrical lens unit 25 and the transparent parallel plate 28 are attached to the rotating board 30 in parallel. The rotating base plate 30 is pivotally supported by a rotating wheel 38 so that the cylindrical lens unit 25 or the parallel plate 28 is located at a position corresponding to position A in FIG. The cylindrical lens unit 25 and the parallel plate 28 can be selectively advanced into the optical path of the optical system by a rotation mechanism including a solenoid 31 and a 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 thickness direction. Note that when the convex lens 26, concave lens 27, and parallel plate 28 are all made of the same material such as glass or plastic, the thickness dimension of each is 1. Between @12 and t, it is sufficient to set t, +t2=t.Although not shown in FIGS. 4 and 5, other optical systems 14, 15-16, and 1
The arrangement position of 7.1B (see FIG. 1) is designed so that an image is formed on the surface of the drum when the parallel plate 28 is advanced into the optical path. The focal length in the meridional direction and the position of the principal point of the cylindrical lens unit 25 are designed so that an image is formed on the surface of the drum at a desired one-sided variable magnification. The lens unit 25 includes two lenses, a convex lens 26 and a concave lens 27.
Since the lens is composed of two lenses, it is possible to create such a combination of focal lengths and principal point positions by appropriately selecting the respective curvatures and relative positions (distance between both lenses).

In addition, in an electronic copying machine incorporating such an image exposure optical system, the surface speed of the drum l due to the X direction movement speed (scanning speed of the optical system) of the light source 11, slit 12, and first mirror 14 and the rotation H If the magnification changes, the speed ratio is also changed so that the ratio between the two is the same as the magnification in the scanning direction of the optical system.

When using an electronic copying machine configured in this manner to form a copy image with vertical and horizontal spacing, if the solenoid 31 is de-energized, the circuit board 30 is pulled by the spring 32 and moved to the position shown by the solid line in FIG. There is a parallel plate 28 in the optical path of the optical system. Therefore, the optical system scans and exposes the image of document 0 onto one surface of the drum at the same magnification.

When forming an image that is twice as large in length and width, when the solenoid 31 is energized, the substrate 30 is attracted and rotated to the position shown by the chain line in FIG. 5 (corresponding to the position shown in FIG. 4), and the cylindrical lens unit 25 Proceed into the optical path of the system. Therefore, the optical system scans and exposes the image of the original O at a one-sided variable magnification. At this time, the imaging position is on the drum surface in both meridional and sagittal directions.

As explained above, according to the image forming apparatus using the optical system of the present invention, an extremely clear image can be formed, whether it is a one-sided variable magnification image formation or an intermittent image formation. Furthermore, since the cylindrical lenses, which are each unit part of the optical system, do not have a special shape, they are easy to process and can be procured at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus equipped with an optical system to which the present invention can be applied, FIG. 2 is a diagram showing a conventional optical system, and FIG. 3 is a diagram showing a conventional optical system.
FIG. 4 is a perspective view of essential parts 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, 1O is an original glass plate, 1 is an original illumination lamp, 12 is a slit plate, 14, 15, 17, 1
8 is a mirror, 16 is an imaging lens, 26 is a cylindrical convex lens, 27 is a cylindrical concave lens, and 28 is a transparent parallel plate.

Claims (1)

[Claims] (1) In an image forming apparatus equipped with an optical system that forms and exposes an original image onto a photoreceptor, a lens unit consisting of at least two cylindrical lenses and an optical path approximately equal to the central optical path length of the lens unit are provided. 1. An optical system capable of variable magnification on one side, characterized in that a transparent parallel plate having a length can be exchanged into an optical path of the optical system.