JPS6052838A - Exposing device of copying machine - Google Patents

Abstract

PURPOSE:To correct uneven exposing by the cosine law and to enable control of exposure with good accuracy by providing a correction plate on an optical path connecting an original and a photosensitive body, providing a detector for quantity of light on the correcting plate and detecting the change in the exposure owing to staining of an optical system. CONSTITUTION:A correcting plate 12 which corrects uneven exposing by the cosine law is installed in the position apart by a distance (l) behind a lens 9 which maintains an imaging relation in the stage of variable power. Said plate moves integrally with the lens 9 during variable power. The plate 12 of which the center is provided on an optical axis 13' shields most the projected luminous flux near the axis 13' and decreases gradually the quantity of the shielded light toward the direction further from the axis 13' and therefore said plate can correct the uneven exposing by the cosine law. If the shape and distance (l) of the plate 12 are preliminarily set in conformity with the magnification at which the max. angle of view is attained at each magnification, the correction for the projected luminous flux incident at all angles within the max. angle of view is possible. A detector 15 for quantity of light is provided in the central part of the plate 12 to detect exactly the change in the exposure owing to the staining and deterioration of the optical system, by which the control of the exposure with high accuracy is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an exposure device for a copying machine with an improved exposure system 2.

2. Description of the Related Art In a copying machine that uses a conventional optical system to project an original onto a photoreceptor, exposure unevenness due to Co54 to the power m occurs depending on the angle of view. In addition, the exposure amount changes over time due to dirt in the optical system and deterioration of the light source, mirror, etc., resulting in problems such as fogging in the resulting copied images.

Among these problems, regarding exposure unevenness, a method has been proposed in which the brightness distribution is changed in the longitudinal direction of the light source and the exposure unevenness is corrected according to the fourth power of the width. It is necessary to manufacture a light source with a high magnification, which increases costs, and in the case of a variable magnification copying machine, there is a drawback that there is a limit to the correction ability, such as the fact that it cannot be corrected if the variable magnification range becomes large. In addition, in copying machines that use fluorescent lights as light sources,
The slit plate installed in the optical path can be switched depending on the magnification ratio, or the slit plate can be tilted to move it in and out of the optical path.
Alternatively, there are known methods in which the slit plate is moved in the longitudinal direction of the slit near the photoreceptor, or the slit plate is moved in the scanning direction perpendicular to the longitudinal direction of the slit in response to the movement of the lens. In the case of tilting, a complicated drive device is required to move the slit plate, which is expensive, and there are also drawbacks such as a limited correction ability, such as the inability to correct it when the variable magnification range becomes large.

- To prevent image fogging due to dirt or deterioration of the knife edge system, install a light amount detector in a position in the optical path that does not affect the image, or detect the amount of exposure by installing a light amount detector in a position that does not affect the image, or By inserting a light intensity detector near the axis to detect the exposure amount, comparing the obtained detection signal with a reference value, and controlling the light source etc. according to the difference, it is possible to detect dirt and deterioration of the optical system. A control device has been proposed that can obtain the optimum exposure amount without any noise, but since the amount of light detected by a device with a light amount detector installed in the peripheral area of the optical path is small, it is more susceptible to the effects of noise, etc., resulting in poor accuracy. It is difficult to control the amount of light to a high degree, and in the case where a light amount detector is inserted near the optical axis, a mechanism for inserting and removing the detector is required, resulting in high cost.

Purpose of the Invention The present invention has been made to eliminate such drawbacks, and it is an object of the present invention to provide an exposure device for a copying machine with a simple configuration that can correct exposure unevenness due to the cos fourth power law and can control the exposure amount with high precision. That is.

Components of the Invention A correction plate is provided on the optical path connecting the original and the photoreceptor, and has a high light-shielding property near the optical axis, and gradually lowers the light-shielding property toward the periphery, thereby correcting exposure unevenness due to the 0084 power law. An exposure device for a copying machine, which includes a light amount detector provided on the correction plate to detect changes in the amount of exposure due to dirt in the optical system.

EXAMPLE Below, an example implemented in a variable magnification copying machine according to the present invention will be described in detail with reference to the drawings.
The document 2 is placed below this platen 1.
A light source 3 and a rectifier 4 are installed to illuminate the copy surface.

The reflected light from the original 2 passes through the slits 5, first, second, third . . . provided on the optical path 13. The light that is guided to the lens 9 via the lens 6t7e8 and further transmitted through the lens 9 is the fourth
It is reflected toward the photoreceptor 11 side by the mirror lO, and the photoreceptor 1
10 surfaces are exposed. Further, in the optical system, the second and third mirrors 7.8 and the lens 9 move in the directions of the arrows b-c and bl-C1 according to the variable magnification.

A correction plate 12 that corrects exposure unevenness due to the K134 power law is installed at a distance mt behind the lens 9 that maintains the image formation relationship when changing the magnification, and moves together with the lens 9 when changing the magnification. This correction plate 12 is, for example, a circular plate provided so that its center coincides with the optical axis 13'.
Exposure unevenness due to the power law is corrected as follows.

That is, the cross section of the projected light beam of each object point in the slit area of the original 2 in one plane perpendicular to the optical axis 13' becomes a circle □ with the same cross-sectional area as shown in FIG. The center of the correction plate 12 is located on the optical axis 13', and the maximum amount of light blocking of the projection light beam near the optical axis 13' occurs, and the amount of light blocking gradually decreases as the distance from the optical axis 13' increases. It becomes possible to correct unevenness.

By the way, when variable-magnification copying is performed, the maximum angle of view differs for each magnification, but if the shape and distance qt of the correction plate 12 are set according to the magnification that provides the maximum angle of view, the maximum angle of view can be adjusted. Correction is possible for projection light beams incident at any angle within this angle.

Specifically, as shown in FIG. 4, the correction plate 12 may be provided at a position outside the point where the projection light beams incident at the maximum angle of view intersect.

On the other hand, a light amount detector 15 is provided in the center of the correction plate 12, and the light amount detector 15 detects a white reference reflective surface provided on the lower surface of the platen holder 16, etc., as shown in FIG. The reflected light from 17 is detected. The detection value detected by the light amount detector 15 is compared with a reference value set in advance by a control system, and the amount of change in exposure amount due to dirt or deterioration of the optical system is calculated. The light source 30 input voltage etc. are controlled according to the obtained change amount,
This makes it possible to obtain a constant amount of exposure regardless of dirt or deterioration of the optical system.

The required exposure amount when changing magnification changes depending on the magnification, so
By setting reference values in advance according to the magnification and comparing these values with the values detected by the light amount detector 15 for each magnification, it is possible to deal with all magnifications.

In addition, in a corner resist type copying machine, the position of the optical axis 13' changes depending on the magnification, but the reference reflective surface 17 is
No problem arises by forming it long in advance in the moving direction of '. Furthermore, in the above embodiment, the correction plate 12 is replaced by the lens 9.
Although it is provided behind the lens 9, it may be provided in front of the lens 9.

Effects of the Invention As described in detail above, the present invention provides a correction plate 1 which has a high light-shielding property near the optical axis and has a lower light-shielding property toward the periphery.
2 is installed on the optical path 13 to correct exposure unevenness due to the fourth power law. Even when used in a variable magnification copying machine, it moves together with the lens according to the variable magnification, so the structure is simple and inexpensive. In addition, there is no possibility that correction will not be possible even if the zooming range becomes large. In addition, since the light amount detector 15 is provided in the center of the correction plate 12 to detect the amount of exposure, changes in the amount of exposure due to dirt or deterioration of the optical system can be detected.
Accurate detection is now possible without the use of complicated mechanisms,
This makes it possible to control the exposure amount with high precision.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is an overall configuration diagram, FIG. 2 is a perspective view of a lens and a correction plate, and FIGS. 3 and 4.
The figure and FIG. 5 are action explanatory diagrams. 2 is a document, 9 is a lens, 11 is a photoreceptor, 12 is a correction plate,
13' is an optical axis, and 15 is a light amount detector. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Masaaki Yonehara Patent Attorney Tadashi Hamamoto Figure 1 Figure 2 5 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a device that guides the reflected light from the copying surface of the original 2 to be copied to the photoreceptor 11 using an optical system, there is a light shielding feature near the optical axis 13' in front or behind the lens 9 constituting the optical system. A correction plate 12 which is high and whose light shielding properties gradually decrease toward the periphery is provided so as to be movable without changing the relative relationship with the lens 9, and a light amount detector 1 is mounted on the correction plate 12.
5. An exposure device for a copying machine.