JPH02211465A - Variable power device for copying machine - Google Patents

Abstract

PURPOSE:To provided wider variable powers and to miniaturize an optical system by combining mirror movement and a zoom lens, setting the conjugation length at the time of variable powers smaller than the conjugation length at the time of unmagnification and executing the adjustment of the space distance between an object and an image by the movement of half the lens by means of a mirror group. CONSTITUTION:The zoom lens 11 can be changed to a prescribed focal length by a lens motor 15. First and second scanners 12, 13 are driven at 2:1 linear speed ratio by a scanner motor 17 connected in the form of a loop by a wire 16. The original on contact glass 1 can, therefore, be projected onto a photosensitive body 10 by maintaining the rule of imaging even if the scanners 12, 13 move. The scanner 13 can also be changed in the distance from the scanner 12 by a scanner motor 19. The conjugation length at the time of the variable powers is made small by the combination of the mirror movement and the zoom lens in such a manner and the adjustment of the space distance between the object and the image is enabled by the moving quantity of half the lens movement. The variable power device is thus miniaturized in spite of the wider variable powers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable-magnification device for a copying machine, and particularly to a variable-magnification device for an analog copying machine of a document fixing type.

[Conventional technology]

FIG. 6 is a schematic diagram of the optical system of a conventional copying machine, in which 1 is a contact glass fixed to the main body of the copying machine and on which an original is placed with the original surface facing downward; 2.3. 4 receives the reflected light from the original illuminated by a light source (not shown). Second. This is the third mirror. The reflected light 5 guided by these mirror groups is imaged by a (fixed focus) lens 6, passes through a fourth mirror 7, a fifth mirror 8, and a sixth mirror 9, and forms an electrostatic latent image on the photoreceptor 10. do.

In the optical system of such a copying machine, as a device for changing magnification, (1) a variable magnification device that moves the object-side mirror group such as the first mirror 2, the second mirror 3, and the third mirror 4 and the lens 6; (2) A variable magnification device that changes the conjugate length by a group of image-side mirrors such as the fourth mirror 7, the fifth mirror 8, and the sixth mirror 9 is well known.

However, in the variable magnification device shown in (1), when enlarging, the conjugate length is changed by the second mirror 3 and the third mirror 4.
, the optical path length to the third mirror 4 becomes long, which has the disadvantage that wide variable power cannot be achieved.

In the variable magnification device shown in (2), on the other hand, during reduction, the optical path length from the fourth mirror 7, fifth mirror 8, sixth mirror 9, to the photoreceptor lO becomes longer, and the variable magnification is also reduced. The drawback was that it could not be achieved.

Therefore, in order to achieve wide variable power, a variable power device that uses movement of an object-side mirror group and a movement of an image-side mirror group has already been proposed.

[Problem to be solved by the invention]

However, in the above-mentioned prior art, it is necessary to secure a movement space for the mirror group toward the object side mirror group during reduction. Further, when enlarging, a similar space is required for the image-side mirror group.

Therefore, there is a problem in that the entire device becomes large in size.

Further, a variable magnification device by moving a zoom lens is widely known, but even in this device, it is necessary to shorten the optical path length from the contact glass 1 to the third mirror 4 or from the photoreceptor 10 to the fourth mirror 7. This has disadvantages in that it becomes impossible to achieve a magnification of magnification and the device becomes larger, and conversely, if the device is made more compact, the range of variable power becomes narrower.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable magnification device for a copying machine that eliminates the drawbacks of the above-mentioned prior art, enables wide variable magnification, and allows the optical system to be miniaturized.

[Means to solve the problem]

The above purpose is to configure an optical system with a zoom lens, an object-side mirror group between the zoom lens and the contact glass, and an image-side mirror group between the zoom lens and the photoreceptor, and to move these mirror groups and the zoom lens. In a magnification changing device for a copying machine that changes magnification by moving the image side mirror group and the zoom lens during reduction, the moving means moves the object side mirror group and the zoom lens when enlarging. This is achieved by providing a moving means for changing the magnification.

[Effect]

By combining mirror movement and a zoom lens, the present invention can make the conjugate length during magnification smaller than when changing magnification, and also reduces the spatial distance from the contact glass to the zoom lens and from the zoom lens to the photoreceptor. Since the image spatial distance is adjusted by a group of mirrors, it can be done with half the amount of movement required by moving the lens, resulting in a compact optical system that can be used for wide zooming.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are a plan view and a side view of an embodiment of the optical system of a copying machine according to the present invention, and parts that are the same as those in FIG. 6 or that can be considered to be the same are given the same symbols. It is.

In the figure, 1 is a zoom lens, 12 is a first mirror 2
13 is a second mirror 3. A second scanner 14 is composed of a third mirror 4, a fourth mirror 7, and a fifth mirror 14.
This is a third scanner consisting of mirror 8.

The zoom lens 11 can be changed to a predetermined focal length by a lens motor 15.

As shown in FIG. 3, the first scanner 12 and the second scanner 13 are connected in a loop shape by a wire 16, and are driven by the rotation of a scanner motor 17. 12 and the second scanner 13, which is indirectly driven by the pulley 18, are driven at a linear speed ratio of 2:1.

As a result, as can be seen from Fig. 2, the scanner 12.1
The original fixed on the contact glass 1 can be projected onto the photoreceptor 10 while maintaining the law of image formation even with the movement of the contact glass 1.

By the way, the second scanner 13 also has a second scanner motor 19.
As shown in FIGS. 1 and 3, the rotation of the second scanner motor 19 causes the first scanner 1 to
You can change the distance from 2. Further, the third scanner 14 is also driven by the third scanner motor 20, so that the above-mentioned image space distance can be changed.

Here, the magnification changing operation according to the present invention will be explained.

In Figure 4, 1/a + 1/b = 1/f,
From b/a=m, a=(1+1/m)f b=(1+m) f L=(m+(1/m)+2) f a; object spatial distance b; image spatial distance f; focal length.

The variable magnification is determined by the object space distance a, the image space distance Mb, and the conjugate length.

This can be achieved by changing either the focal length f.

In this embodiment, at the time of reduction, the third scanner 14 is moved closer to the zoom lens 11 by the variable magnification time and image space length b4 from the same magnification time and image space length shown in FIG.

In other words, the zoom lens 11
get closer to Next, the focal length of the zoom lens 11 is changed to a predetermined value. When changing the focal length, if the angle of view becomes too large, the aberrations of the zoom lens 11 will cause the peripheral areas to be out of focus. Therefore, in this embodiment, an example in which the angle of view at the same magnification is maintained will be explained.

Focal length of the zoom lens 11 when changing the magnification without changing the angle of view atomi2f0 b = 2mf.

L = 2 (m + 1)'f.

f = (m/(m+1)) f.

fo; The zoom lens 11 is controlled by the lens motor 15 so that the focal length at the same magnification is achieved.

Furthermore, if the magnification is changed while keeping the angle of view unchanged during enlargement, the image space distance S is fixed and the object space distance is a.

Change from to a. The change is made by moving the second scanner 13. In other words, the amount of movement is (a, -a4)/2. Next, the focal length of the zoom lens 11 is changed to a predetermined focal length for the reduction mode.

In the conventional magnification changing device by moving a fixed focus mirror, the conjugate length when changing magnification, that is, L2. L! are both larger than when the image is at the same magnification, and the amount increases rapidly as the magnification ratio increases.

In addition, in order to achieve wide magnification in a magnification device using a zoom lens with a fixed conjugate length, it is necessary to minimize the distance between the mirrors on the object side and the image side and maximize the movement width of the lens. I can't hope for a system.

However, in the present invention, by combining mirror movement and a zoom lens, the conjugate length when changing magnification can be made smaller than when changing magnification, and since the object spatial distance and image spatial distance are determined by the mirror group, the lens This is possible with half the amount of movement required by the movement of , making it a compact optical system even for wide variable magnification.

In addition, the lens motor 15, wire 16, scanner motor 1
7. Second scanner motor 19, third scanner motor 20
All of these constitute means for moving the mirror group (and therefore the scanner group or a single scanner).

〔Effect of the invention〕

As described above, according to the present invention, it is possible to maintain a compact optical system while enabling wide variable power.

[Brief explanation of the drawing]

1 and 2 are a plan view and a side view of an embodiment of the optical system of a copying machine according to the present invention, FIG. 3 is a schematic diagram of the drive system of the first and second scanners, and FIG. 4 is an object space. distance, image space distance,
FIG. 5 is an explanatory diagram of the variable magnification system according to the present invention, and FIG. 6 is a side view of the optical system of a conventional copying machine. 1... Contact glass, 2, 3.4... Object side mirror group, ? , 8.9... Image side mirror group, 11... Zoom lens, 15... Lens motor, 16... Wire, 17... Scanner motor, 19... Second scanner, 20...・Third scanner motor. Figure 2 Figure 3

Claims (1)

[Claims] An optical system is composed of a zoom lens, an object-side mirror group between the zoom lens and the contact glass, and an image-side mirror group between the zoom lens and the photoconductor, and the magnification can be changed by moving these mirror groups and the zoom lens. In a magnification changing device for a copying machine, a moving means moves an image-side mirror group and a zoom lens to change magnification during reduction, and a moving means changes magnification by moving an object-side mirror group and zoom lens during enlargement. A variable magnification device for a copying machine, characterized in that it is equipped with a moving means for performing the following steps.