JPS6226464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic copying method, and more particularly to an electrophotographic copying method in which a focusing optical fiber is used for transmitting a light beam in an exposure optical system.

In the general configuration of an exposure optical system, the image light reflected from the image surface of the original is formed on a photoreceptor through a predetermined optical path in which an imaging lens is arranged. An exposure optical system is known that uses a known focusing optical fiber instead of using a focusing optical fiber. In this configuration, since only the focusing optical fiber is disposed between the image surface of the original and the photoreceptor, the optical path length can be significantly shortened, which has the advantage that the copying apparatus can be designed compactly.

However, according to research conducted by the inventor of the present application, it has been found that when a focusing optical fiber is used, there is a characteristic that the reproduced image is accompanied by a defect in image quality. The technical problems that cause image quality problems will be specifically explained below.

First, between glass lenses and focusing optical fibers,
There are some differences in light transmission characteristics. In other words, as shown in the characteristic curve in Figure 1, the air frequency of the transmitted light and its transparency, i.e.
Looking at the relationship of Modulation Transfer Function (hereinafter referred to as MTF), convergent optical fibers exhibit significantly higher MTF characteristics than lenses in high spatial frequency (hereinafter referred to as frequency) bands. This means that there is a significant difference in the transmission of image light containing many high frequency components between the lens and the converging optical fiber, so if the converging optical fiber is used, the image will be transmitted more than necessary. This shows that there are characteristics that are emphasized. Therefore, it can be easily estimated that in areas containing a large amount of high frequency components, such as the edge of the image, that is, the boundary between light and shade, the contrast of the copied image is stronger than that of the original image.

By the way, according to the theory of operation in the exposure process and development process of electronic copying, as shown in FIG. However, when this latent image 2 is developed, since a constant operation start voltage V is set in the developing mechanism, the developer does not adhere to the electrostatic charge at the end of the pattern 3, which causes the coloring to occur. The resulting visible image forms a flat density image corresponding to the image area.

However, in actual operation when a lens is used in the optical path, there is no characteristic that the edges of the image are emphasized (as described above), so as shown in Figure 3, the developed visible image is A high-quality reproduction image that exactly corresponds to the original image can be obtained.

On the other hand, in actual operation when a focusing optical fiber is placed between the image surface of the original and the photoreceptor, the edge of the image is emphasized as described above, so as shown in FIG. A freezing field 5 with an opposite potential exceeding the voltage -V is generated at both ends of the electric field pattern 4, and as a result, when developing using a developer made of toner charged with an opposite polarity,
Unnecessary toner adheres to the sides of the visible image, resulting in a problem of deteriorating image quality.

In order to prevent such problems from occurring, it is possible to mix the carrier and toner using a two-component developer, thereby making all the toners of the same polarity. When using a one-component developer, it is difficult to avoid the above-mentioned problems.

Based on the results of the above research, the present invention solves the above problems by interposing a filter in the optical path of the image light to cut out the high frequency band A of the MTF characteristic of the focusing optical fiber. . SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic copying method that can reproduce visible images with good image quality.

The present invention will be described below based on an illustrated embodiment.

In the copying apparatus using the method of the embodiment, as shown in FIG. The fiber 8 and appropriate locations before and after it (in the illustration, the upper end of the focusing optical fiber 8,
In other words, a filter 9 is provided on the image light incident surface.

The filter 9 may be a solid or liquid glass thin plate with many small spots randomly formed, a resin thin plate mixed with a coloring agent, or a resin filter with small spots formed on its surface. etc., but it is sufficient if its optical transmission characteristics are such that it cuts off light in a high frequency band. That is, a filter having a characteristic that cuts the high frequency band A of the MTF characteristic shown in FIG. 1 is used.

The cutoff frequency S in the optical transmission characteristic of the filter is expressed as follows: S=Φ/fλ Φ: diameter of unit speck (mm) f: focal length (mm) λ: wavelength (mμ).

Further, the light transmittance of the filter 9 is preferably 50% or more, and a light transmittance of 20% or less is unsuitable for use. Further, it is desirable that the distribution is such that the total area of small spots is approximately 1/2 of the area of the pupil. In addition, the filter may be one spread on the contact glass 10.

The operation of a copying apparatus in which a filter is interposed in the optical path of the image light according to the present invention to cut out the high frequency band A of the MTF characteristic of the focusing optical fiber 8 is similar to the operation of a conventional general copying apparatus. A portion of the light reflected from the original 6 by the illumination light from the light source 11 passes through the filter 9 and enters the focusing optical fiber 8 as image light.

At this time, the high frequency components in the image light are filtered through the filter 9.
The image light guided through the focusing optical fiber 8 does not have a high frequency component because the light is blocked by the cut-off effect of the optical fiber 8.

Next, the image light emitted from the lower end surface of the focusing optical fiber 8, that is, the light exit surface, is projected onto the photoreceptor 7 to expose the photoreceptor 7, and the electrostatic image on the photoreceptor 7 is further developed by the developing mechanism 12. After the image is visualized, it is transferred to copy paper in the transfer mechanism 13.

Therefore, during the above-mentioned exposure operation, the high frequency components contained in the image light that hit the edge of the image are absorbed by the filter 9 and are not projected onto the photoreceptor 7. Toner stains caused by the freezing field 5 do not occur in the visible image.

As described above, in the copying method of the embodiment, there are no particular restrictions on the developer used.

As described above, according to the electrophotographic copying method according to the present invention, a filter that cuts off light in a high frequency band is interposed in the optical path of the image light that exposes the photoreceptor, so that the reproduced visible image is There is no toner stain inside, which has the effect of improving the operability of a copying device using a focusing optical fiber.

[Brief explanation of the drawing]

Fig. 1 is a graph of the light transmission characteristics of a lens and a focusing optical fiber, Fig. 2 is a schematic diagram of the operating state of the exposure and development process of electronic copying, and Fig. 3 is a graph of the light transmission characteristics of the lens and the focusing optical fiber. FIG. 4 is a diagram showing the developing process, and FIG. 5 is a schematic diagram of a copying apparatus in an electrophotographic copying method showing an embodiment of the present invention. be. 6... Original, 7... Photoreceptor, 8... Focusing optical fiber, 9... Filter.

Claims (1)

[Claims] 1. A copying method in which image light of a document to be copied is imaged onto an electrophotographic photoreceptor via a focusing optical fiber, and an electrostatic image obtained is visualized,
An electrophotographic copying method characterized in that the image light is imaged through a filter having a transmission characteristic that acts as a cutoff for light in a high spatial frequency band.