JPH0377500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable magnification image forming apparatus, and more particularly to an improvement of an apparatus that prevents harmful leakage light (flare light) from entering a photoreceptor from an object side.

For example, in a variable magnification copying device, in which the side edge of the original image is always focused on the side edge of the photoreceptor at each magnification, the lens is In addition to moving in the optical axis direction, in order to image the edge of the document image at a predetermined position, it must also move in a direction perpendicular to the optical axis, that is, it must move obliquely to the optical axis. For this reason, a light-shielding material is provided around the lens, but since the lens must be moved diagonally, there is not enough clearance between it and the side plate, which is the structural body of the optical device. For this reason, flare light from around the light shielding material could not be sufficiently prevented.

A conventional example is shown in FIG. 1. In order to image the edge X of the document P at a predetermined position Z on the side edge of the electrophotographic photosensitive drum D in each magnification mode, the lens moves to the enlargement mode position E by changing the magnification. , the same magnification mode position X1, and the reduced mode position R, the positions change in a direction oblique to the optical axis. Dotted line position P _E , P _R of original P
shows the optical position of the document P in the enlargement and reduction modes when the optical path length is changed by a mirror (not shown). A mask 3 is fixed to the side plates 1 and 2, which are the structural bodies of the optical device, and an image forming light beam passage aperture 3' is formed approximately in the center to a region that does not cause any actual damage on the optical path. A light shielding plate 4 for shielding flare light is fixed to the lens. The width of the light shielding plate 4 is such that it has a gap a' which is somewhat larger than the displacement a of the lens moving in the direction perpendicular to the side plates 1 and 2. Side plate 1 is shown at E when enlarged in the figure.
Since there is a very small gap between the light shielding plate 4 and the light shielding plate 4, flare light does not enter from there. However, the gap between the side plate 2 and the light shielding plate 4 is large, and flare light enters from there.
Similarly, when reducing R, there is a gap between the side plate 1 and the light shielding plate 4.
Since there is a gap a′, flare light enters through the gap. In the case of X1 at the same magnification, the light enters from two directions.

The present invention prevents the flare light from entering, and includes a lens that forms an original image on a photoreceptor, and a first light shielding member that is fixedly provided to the lens and blocks flare light around the lens. and a variable magnification image forming device in which the lens moves obliquely with respect to the optical axis in response to a change in magnification, the variable magnification image forming device having a variable magnification image forming apparatus, wherein the lens is disposed close to a first light shielding member that blocks flare light around the first light shielding member. It has a second light shielding member, and the second light shielding member moves in the optical axis direction together with the movement of the lens.

An embodiment of the present invention is shown in FIG. 2. Side plates 1 and 2
A light-shielding mask 5 having a width that makes the gap as small as possible is provided, and it is not fixed to the side plate but is placed at a certain distance from the lens (to which the light-shielding plate 4 is fixed) in the optical axis direction during magnification change operation. and move them together. This mask 5 is provided with an image forming light beam passage opening 5', which has a width that does not cause any actual damage to the optical path in each mode. Since this aperture 5' moves together with the lens, a light shielding plate is provided around the lens, which does not require a wide aperture as in the conventional example.

Therefore, since the mask 5 moves in the optical axis direction, that is, parallel to the side plates 1 and 2, the gap between it and the side plates can be minimized. On the other hand, the mask 5 and the light shielding plate 4 fixed to the lens
If the two overlap during the entire stroke, there will be no flare light incident. Therefore, flare light does not enter the photosensitive drum.

Referring to FIG. 3, a concrete example is shown. Reference numeral 5 denotes a mask disposed close to the light shielding plate 4. The back side of the mask is movably supported via a sliding bearing 7 on a shaft 6 arranged parallel to the optical axis direction. On the other hand, the front side is slidably supported via a slider 9 on a rail 8 arranged parallel to the optical axis. One end of the slider 9 is fixed to the mask base 5,
Press screw 10 on one end (upper part in the figure)
It is shaped like this. The mask 5 has an aperture 5' having at least the displacement amount a of the lens plus the maximum field angle width.

The lens stand 13 on which the lens L is mounted is movably supported at one end on a shaft 12 fixed to the mask base 11, and the other end is supported so as to be parallel to the shaft 6 by a sliding member (not shown). . The compression spring 14 presses the lens stand 13 in the direction of the axis 6. The lens L is fixed to the lens stand by means not shown, and is inserted into a hole formed in the light-shielding part 4 into which the lens loosely fits.

An adjusting plate 18 with a cam follower 16 that loosely fits into the grooved cam 15 is crimped on the lens stand, and is attached with a screw 1.
It is fixed by 7.

The grooved cam 15 is fixed obliquely to the optical axis so that when the lens L moves in the optical axis direction, it can also move in a direction perpendicular to the optical axis, and the cam projects the edge of the document onto a predetermined position on the drum. It is shaped to be The optical axis center is adjusted by loosening the screw 17 and displacing the adjustment plate 18. After adjustment, fix the screw 17.

The wire 19 is wound around a drive device (not shown) and fixed to the mask base, thereby moving the lens unit in the optical axis direction. The light shielding plate 4, mask 5, and lens L are then moved as shown in FIG. (In addition, from Fig. 2, the lens when forming a 1-magnification image,
The illustration of the mask and light shielding plate is omitted to avoid complexity. ) According to the present invention, flare light can be extremely effectively prevented in a variable magnification copying apparatus or the like.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional example, FIG. 2 is an explanatory diagram of an embodiment of the present invention, and FIG. 3 is a perspective view of an embodiment of the present invention. L is a lens, 4 is a light shielding plate, 5 is a movable mask, 6
is a guide rail, and 15 is a cam.

Claims (1)

[Claims] 1. A lens that forms an original image on a photoreceptor, and a first light shielding member that is fixedly provided to the lens and blocks flare light around the lens, and that can be used to change magnification. A variable magnification image forming apparatus in which the lens moves obliquely with respect to the optical axis according to the variable magnification image forming apparatus includes a second light shielding member disposed close to the first light shielding member that blocks flare light around the first light shielding member; A variable magnification image forming apparatus characterized in that the second light shielding member moves in the optical axis direction together with the movement of the lens.