JP2638962B2 - Image exposure equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an image exposure apparatus, and more particularly to one of the properties of an optical system for slit-illuminating an image on an original table surface, which is a surface to be irradiated, with illumination means. It is an object of the present invention to provide an image exposure apparatus capable of correcting unevenness in illuminance distribution in a longitudinal direction of a slit on a document table surface according to a certain COS4 law, and capable of always performing uniform illumination regardless of an imaging magnification.

2. Description of the Related Art Various types of variable-magnification electrophotographic copying apparatuses which illuminate a document table surface with a slit method have been proposed.

In general, when a slit area on a document table is projected and imaged on a photosensitive drum surface by an imaging lens, illuminance non-uniformity occurs in a longitudinal direction of the slit on the photosensitive drum surface according to a so-called COS4 law according to an angle of view. As a method of removing the illuminance unevenness at this time, for example, when a light source having a uniform luminance distribution is used, a method of providing an aperture plate (light shield plate) in the optical path having a shape that corrects the COS fourth law is used. is there.

At this time, if the imaging lens is a variable magnification system, (a) an appropriate slit is selected from a number of slits according to the magnification of the imaging lens and inserted into and removed from the optical path.

(B) At the time of zooming, the slit plate near the photosensitive drum is moved in a direction (scanning direction) perpendicular to the slit longitudinal direction with respect to the movement of the imaging lens.

And so on.

However, in the direction (a), the number of components is mechanically increased, and the entire apparatus tends to be complicated, such as a switching operation at each magnification and a shape adjustment of a slit plate for each magnification.
In addition, the method (b) has a problem that the moving mechanism is difficult to be mounted spatially, and the whole apparatus becomes large.

On the other hand, as shown in FIG. 6, for example, a part of the area corresponding to the pupil area 108 of the imaging lens in the optical path is shielded by an arc-shaped light shielding plate 110 to form an image from each object point in the slit area. There is a method of correcting the illuminance unevenness by making the cross-sectional area of the light flux substantially equal regardless of the magnification.

That is, an aperture plate 110 that corrects the COS4 power law and acts as a brightness aperture is disposed at a position near the imaging lens, and is integrated with the imaging lens while maintaining the relative relationship during zooming of the imaging lens. By moving the aperture plate 110, uneven illuminance on the photosensitive drum surface at each magnification change is corrected.

The method shown in FIG. 6 requires only one diaphragm plate 110 irrespective of the magnification, and the mechanism is simple because it is not necessary to change the relative positional relationship of the diaphragm plate 110 with respect to the pupil 108 of the imaging lens for each magnification. There is a feature that is made. However, it is necessary to block the luminous flux on the axis of the imaging lens by the amount of light reduction by the COS4 law at the maximum angle of view, and the FNO of the imaging lens must be used in a darkened state. It was very inefficient.

(Problems to be Solved by the Invention) According to the present invention, the aperture shape of the stop of the imaging lens and the light shielding member are appropriately set, and the pupil area when observed from the image plane side is determined by the pupil and the light shielding member on the optical axis. Image exposure of a simple configuration suitable for an electrophotographic copying apparatus or the like in which the illuminance distribution in the longitudinal direction of the slit on the surface of the photosensitive drum is always uniform regardless of the magnification by making it invariable by relative movement with respect to The purpose is to provide the device.

(Means for Solving the Problems) In an image exposure apparatus for projecting an image on a document table surface illuminated by an illuminating means onto a predetermined surface at various magnifications by an imaging lens, when the magnification is a predetermined magnification, The luminous flux from the illuminating means is controlled so that the illuminance distribution on the predetermined surface is uniform, and the position of the pupil of the imaging lens in the direction orthogonal to the optical axis is adjusted at a magnification other than the predetermined speed. The luminous flux passing through the pupil is regulated by a light blocking member arranged near the imaging lens so that the effective pupil area on the optical axis when observed from the image plane is the same.

In particular, the present invention is characterized in that the pupil of the imaging lens is displaced in a direction perpendicular to the optical axis and the light shielding member is displaced in a direction perpendicular to the optical axis to restrict the light flux passing through the pupil. .

(Embodiment) FIG. 1 is a schematic view of an embodiment in which the image exposure apparatus of the present invention is applied to an electrophotographic copying machine having a variable power system.

In FIG. 1, reference numeral 1 denotes a document table, which is made of, for example, a transparent platen glass. Reference numeral 2 denotes image information of a document or the like, which is placed on the document table 1. Reference numeral 3 denotes an illumination unit which slit-illuminates the image information 2. Reference numeral 4 denotes a slit restricting member, and its opening width is always constant irrespective of the magnification of an image forming lens 8 described later. Reference numerals 5, 6, 7, and 11 denote mirrors, and reference numeral 8 denotes an imaging lens. Inside the diaphragm plate 9, an aperture 9a and an aperture 9b of a flat circular hole for regulating the amount of light passing therethrough are arranged. Reference numeral 10 denotes a light blocking member, which is arranged near the imaging lens 8. Reference numeral 12 denotes a photosensitive drum.

In this embodiment, the image information 2 on the document table 1 illuminated by the slit 3 by the illumination means 3 is condensed by the imaging lens 8 via the mirrors 5, 6, 7, and slit on the surface of the photosensitive drum 12 via the mirror 11. An image is formed at a predetermined magnification.

When the image information 2 is formed on the surface of the photosensitive drum 12 by changing the magnification, the focal length of the imaging lens 8 is changed while moving in the optical axis direction to a position indicated by a broken line, for example, to change the magnification. As a result, the distance between object images during zooming is kept constant.

Generally, in an image exposure apparatus that forms image information illuminated by illumination means on a photosensitive drum surface at various magnifications by an imaging lens, the illuminance distribution on the photosensitive drum surface is uniform at a predetermined magnification (reference magnification). The illuminance distribution on the image information surface by the illumination means is appropriately set so as to be as follows.

At a magnification other than the predetermined magnification, for example, as shown in FIG. 7, the pupil in the imaging lens is displaced in a direction perpendicular to the optical axis, and the light beam is regulated by a light shielding member 210 arranged near the imaging lens. Each element is set so that the illuminance distribution on the photosensitive drum surface is uniform.

However, in this method, as shown in FIG. 8, the light beam on the axis of the imaging lens must be blocked at the magnification compared to the predetermined magnification, and the absolute illuminance on the photosensitive drum surface at the magnification is the predetermined magnification. There was a tendency to decrease from time to time.

On the other hand, in the present embodiment, by appropriately setting the shapes of the aperture plate 9 and the light shielding member 10, the illuminance distribution on the photosensitive member surface is made uniform over the entire zoom range, and the absolute contrast is maintained constant. The feature is that.

That is, as shown in FIG. 2, the illuminating means 3 corrects the COS4 law of the imaging lens 8 at a predetermined magnification (for example, equal to the reference magnification) so that the illuminance distribution on the surface of the photosensitive drum 12 becomes uniform. For example, the luminance distribution of the light source is changed such that the peripheral portion has a light distribution characteristic that is brighter than the central portion.

In this case, when the magnification is changed, the illuminance distribution on the surface of the photosensitive drum 12 becomes non-uniform. That is, when the light distribution characteristic of the illumination means 3 is corrected at the same magnification, the illuminance increases in the peripheral portion at the time of reduction and decreases in the peripheral portion at the time of enlargement as shown in FIG.

Therefore, in the present embodiment, the iris plate 9 disposed in the imaging lens 8 is moved in the direction orthogonal to the optical axis with the magnification, to change the pupil position of the imaging lens 8, The positional relationship is changed, and the pupil area on the optical axis when observed from the image plane side is made constant. This makes the ninth
As shown in the figure, the illuminance distribution at the magnification is made constant to make the illuminance distribution uniform over the entire zoom range, and the absolute illuminance is made substantially constant.

FIG. 3 shows an embodiment of the aperture shape of the diaphragm plate 9 arranged in the imaging lens 8 at this time.

In the figure, 9a is observed from the image plane side at the reference magnification (for example, at the time of the maximum reduction magnification) for correcting the illuminance unevenness due to the COS power law caused by the imaging lens 8 by the illuminance distribution on the original table shown in FIG. The aperture corresponds to the pupil area at the time. Reference numeral 9b denotes an opening for correcting an area where a pupil area corresponding to the opening 9a on the optical axis is blocked when the magnification is larger than the reference magnification.

FIG. 4 shows an imaging lens 8 at a reference magnification (maximum reduction magnification).
FIG. 4 is a cross-sectional view of the projection light flux on the image plane side, and a pupil corresponding to the aperture opening 9 a forms an image on the photosensitive drum surface 12 without being blocked by the light blocking member 10. This reference magnification (maximum reduction magnification)
At this time, the illuminating means 3 is set so that the light distribution is set so as to correct the angle-of-view illuminance under the nail of the imaging lens 8, so that the photosensitive drum surface 12
Above, a uniform illuminance distribution can be obtained in the longitudinal direction of the slit. FIG. 5 is a cross-sectional view of the projection light beam at the time of enlargement magnification, and the aperture plate 9 in the imaging lens 8 is displaced downward orthogonal to the optical axis in FIG. The pupil corresponding to 9a is blocked, the light beam from the pupil corresponding to the opening 9b passes through, and the amount of blocking of the opening at the periphery decreases. At this time, of the pupil corresponding to the opening 9a, the area blocked by the light shielding member 10 and the pupil corresponding to the opening 9b appear from the light shielding member 10 so that the effective area of the pupil is the same as that at the time of the reference magnification (maximum reduction). Thus, the illuminance distribution in the longitudinal direction of the slit on the photosensitive drum 12 is made uniform, and the absolute illuminance by zooming is made the same.

In the above embodiment, the aperture plate 9 in the imaging lens 8 is used.
Instead of displacing in the direction perpendicular to the optical axis to change the relative positional relationship with the light shielding member 10, only the light shielding member 10 may be displaced to control the light beam passing from the pupil.

(Effects of the Invention) According to the present invention, as described above, the shape of the aperture plate and the light shielding member in the imaging lens are appropriately set, and the pupil observed from the image area by the relative movement between the aperture plate and the light shielding member. An image exposure device that makes the area invariant on the optical axis, thereby achieving uniform illuminance distribution in the longitudinal direction of the slit on the surface of the photosensitive drum and maintaining the absolute illuminance constant over the entire zoom range can do.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment in which the image exposure apparatus of the present invention is applied to an electrophotographic copying apparatus having a variable magnification system, FIG. 2 is an explanatory view of the illuminance distribution on the document table of FIG. 1, FIG. 3 is an explanatory view of the aperture plate of FIG. 1, FIG. 4, FIG. 5 is an explanatory view showing the relationship between the projection light beam and the light shielding member in the present invention, FIG.
7 and 8 are explanatory diagrams of illuminance unevenness in a conventional image exposure apparatus, and FIG. 9 is an explanatory diagram of illuminance distribution on a photosensitive drum surface in the present invention. In the figure, 1 is a document table, 2 is image information, 3 is an illuminating means, 4 is a slit regulating member, 5, 6, 7, and 11 are mirrors, 8 is an imaging lens, 9 is an aperture plate, 10 is a light shielding member, 12 Is the photosensitive drum,
It is.

Claims (3)

(57) [Claims] An image exposure apparatus for projecting an image on a document table surface illuminated by an illuminating means onto a predetermined surface by an image forming lens at various magnifications. The luminous flux from the illuminating means is controlled so that the illuminance distribution becomes uniform, and at a magnification other than a predetermined magnification, the position of the pupil of the imaging lens in the direction orthogonal to the optical axis is adjusted and the vicinity of the imaging lens is adjusted. A light beam passing through the pupil is regulated by a light-blocking member disposed in the image exposure apparatus, so that the effective pupil area on the optical axis when observed from an image plane is the same. 2. A luminous flux passing through the pupil of the imaging lens is regulated by displacing a pupil of the imaging lens in a direction perpendicular to an optical axis and displacing the light blocking member in a direction perpendicular to the optical axis. The image exposure apparatus according to claim 1. 3. An image exposure apparatus according to claim 1, wherein said light shielding member is displaced in a direction orthogonal to an optical axis.