JPH0247744B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color copying machine, and more particularly to a color copying machine that forms a black and white image using black toner in addition to a toner image separated into three primary colors, thereby producing a color copy. Regarding.

In a color copying machine, a document is separated into colors using a filter, each separated image is developed with toner of a corresponding color, and a fixed color copy is obtained by sequentially overlapping and transferring these toner images onto a single sheet of paper. but,
It is technically difficult to obtain black color only by mixing the three primary colors during fixing. For this reason, a four-color color copying machine has been proposed in which a color copy is obtained by separately forming a black toner image in addition to toner images of the three primary colors.

This four-color copying machine is preferable because it can easily produce black when needed, but it has the disadvantage that alignment during transfer is more difficult than with a three-color copying machine, especially when black images are Since it has the effect of clarifying patterns such as outlines, it has the disadvantage that the three primary colors separately protrude from the black part and the color shift is easily noticeable.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a color copying machine that can eliminate color misregistration that is easily noticeable in color copying machines that also form black toner images in addition to color toner images.

In order to achieve this objective, according to the present invention,
A color separation member that separates a light image from an original into colors and projects the color-separated image onto a photoreceptor has a lower resolving power than a member that projects a black and white image from the original onto the photoreceptor. Copy machine provided;
As a result, the parts of the three primary colors that protrude from the black part of the image become blurred, and even if a color shift actually occurs, it is not visually felt, and the resolving power of the image itself (i.e., the degree to which the image outline is blurred) is blurred. ) has the effect that the black image is determined and therefore does not deteriorate in any way. Therefore, color copies with high resolution and no color shift can be obtained.

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

FIG. 1 schematically shows a color copying machine suitable for applying the principles of the present invention. However, the present invention is not only applicable to this copying machine; such a copying machine is merely an example; for example, the photoreceptor may be belt-shaped instead of drum-shaped, and the color separation may be performed using three primary colors. It is not limited to separating into two colors, for example, it may be separated into two colors, and furthermore, not only total color separation but also partial color separation may be used. In any case, any type of color copying machine may be used as long as it is a color copying machine that transfers a color image of two or more colors and a black toner image showing brightness and darkness onto a single sheet of copy paper.

In FIG. 1, a color original (not shown) placed on a platen 1 is illuminated by a lamp 2, and a reflected light image from the original is transmitted via mirrors 3, 4 and a lens 5, which will be described in detail later. The light image is projected onto a color separation filter plate 6, which passes through the filter on the plate 6, and is projected onto a drum-shaped photoreceptor 9 via mirrors 7 and 8.

The photoreceptor 9 is designed to rotate in the direction of the arrow, and a corona charger 10 is provided upstream of the exposure position where the optical image is projected, and uniformly charges the surface of the photoreceptor 9 to make it photosensitive. do. When an optical image is projected onto the photoreceptor 9 imparted with photosensitivity at an exposure position, a latent image is formed on the surface. Developing device 1 that develops this latent image
1, 12, 13, and 14 contain color toner and black toner. For convenience of explanation, the developing device 11 is a yellow toner developing device, and the developing device 1 is a yellow toner developing device.
2 is a magenta toner developer, developer 13 is a cyan toner developer, and developer 14 is a black toner developer. A transfer drum 15 is disposed downstream of the developing device so as to support a copy sheet on its surface and transfer the sheet into contact with the surface of the photoreceptor 9. The transfer drum 15 has a paper feed device 1.
6, the paper is sent to the transfer drum 15.
The sheet is then sent to the fixing device 18 through the sheet feeding path 17, and after being fixed, is discharged to the collection tray 19. Note that a cleaning device 20 is provided on the photoreceptor 9 downstream from the transfer drum 15, and is designed to remove static electricity and clean the latent image and residual toner on the photoreceptor in preparation for the next image formation.

The operation of obtaining a color copy in the copying machine having the above configuration will be schematically explained. First, regarding the filter plate 6, referring to FIG. 2, four filters 21, 22, 23, and 24 are provided on a disk, and can be rotated by a shaft 25 provided at the center. There is. For example, the filter 21 is colorless or gray and serves as a black-and-white image projection member that projects a bright and dark image of the document onto the photoreceptor 9, and the other filters 22, 2
3 and 24 are color separation members that color separate the optical image from the original document. For convenience of explanation, it is assumed that the filter 22 is a red filter, the filter 23 is a green filter, and the filter 24 is a blue filter.

As shown in FIG. 1, the shaft 25 of the filter plate 6 is driven by a rotary drive device 26 such as a motor, and a predetermined one of the filters 21 to 24 is arranged in the optical path. For example, when the filter 21 is selected, a black and white image showing brightness and darkness is projected onto the photoreceptor 9, and a black and white latent image is formed on the photoreceptor 9. This image is developed by a black toner developer 14 to form a black toner image. On the other hand, a copy sheet is sent to the transfer drum 15 from a paper feeder 16 and held by a gripper (not shown) of the drum 15. The black toner image is transferred to the paper on the transfer drum, and then the surface of the photoreceptor 9 is cleaned by a cleaner 2.
The charger 10 removes static electricity and cleans it, and the charger 10 uniformly charges it again. On the other hand, the black toner image is transferred to the paper on the transfer drum 15, and the drum 15 rotates to receive the next toner image while holding the paper in the gripper.

Next, the filter 22 (red filter) of the filter plate 6 is selected, and the red-resolved light image is projected onto the photoreceptor 9 to form a red-resolved latent image. This latent image is developed by the cyan toner developing device 13, and the cyan toner image is transferred again onto the sheet of paper on which the black toner image has already been transferred on the transfer drum 15. After the transfer, the photoreceptor 9 is cleaned. The transfer drum 15 continues to rotate while holding the paper, and the magenta toner image by the magenta toner developer 12 is transferred onto the paper. be prepared to do so. After the magenta toner image is transferred to the same sheet of paper, the cyan toner image is superimposed and transferred onto the sheet of paper on the transfer drum 15 in the same manner, and after the transfer, the sheet of paper is moved away from the transfer drum 15 for the first time. The image passes through a path 17, is fixed by a fixing device 18, and is discharged onto a collection tray 19 to obtain a color copy.

As mentioned above, since the four-color toner images are transferred and fixed one after another onto the same paper, it is difficult to align them, resulting in misalignment, resulting in an image with color misregistration and a loss of image quality. Ta. As a result of measurement, this positional deviation was usually about 0.5 mm. In order to prevent this positional shift, attempts have been made to lower the resolving power of the lens 5 to visually obtain images without color shift, but this has resulted in a decrease in the resolution of the entire image and a loss of image quality. There were flaws.

In the present invention, the resolution of the filters 22, 23, and 24, which are color separation members, is lower than the resolution of the filter 21, which is a monochrome image projection member. As an example, in order to lower the resolving power of the filters 22 to 24, a resolving power deteriorating filter 27 is added as shown in FIG. As shown in FIG. 4, this resolution deterioration filter 27 can be easily made by printing a mesh pattern on a transparent plate. The pattern does not need to be mesh-like, but can be, for example, dot-like, and any other pattern can be used as long as the resolution can be lowered. Further, if the resolution of the filters 22 to 24 itself can be lowered, the use of the resolution deteriorating filter 27 becomes unnecessary. Furthermore,
When the color separation member is a lens, the resolving power of the lens may be lowered without using a filter. In any case, the structure or members may be of any type as long as the resolution can be lowered. Normally, the resolution of the optical system in a copying machine is 5~
In one example of the present invention, the resolving power of the optical system was set to 2 to 4 lines/mm when passing through a color separation member. In the thus obtained color copy, a high-quality color image was formed in which no color shift was visually perceived, and the resolution was maintained at a high level.

This is because the positional deviation of the toner images of each color due to color separation does not appear visually because the resolution of the image is low, and the resolution of the black image is high, so the contours of the image appear sharply and the resolution of the entire image is This is because it is maintained high. In other words, according to the present invention, the parts of the three primary colors that protrude from the black part of the image are blurred, so that even if a color shift actually occurs, it is not visually felt, and moreover, the part of the three primary colors that protrudes from the black part of the image becomes blurred. Since the resolving power is determined by the black image, it exhibits the effect that there is no deterioration in the resolution, so it is possible to obtain color copies with no color shift and with high resolution. In particular, in a copying machine using a magnetic brush developer, the lines are brighter than in solid areas, so color shift is noticeable, but the present invention eliminates this problem.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a color copying machine, FIG. 2 is a front view of a filter plate, FIG. 3 is a side view of a color separation filter, and FIG. 4 is a front view of a resolution deterioration filter. 1...Platen, 2...Lamp, 3, 4, 7, 8...
Mirror, 5...Lens, 6...Filter plate, 9...Photoreceptor, 10...Corona charger, 11-14...Developer, 15...Transfer drum, 16...Paper feeding device, 18...
Fixing device, 19... Collection tray, 20... Cleaning device, 21
...monochrome image projection member, 22-24...color separation filter, 26...filter plate rotation driver, 27...resolution deterioration filter.

Claims (1)

[Claims] 1 Three types of color separation members that color separate the light image from the original and project the color-separated images onto the photoreceptor, a monochrome image projection member that projects the light image from the original onto the photoreceptor, and a color separation member on the photoreceptor. The apparatus includes means for developing each of the separated latent image and the black latent image with toner of a corresponding color, and means for transferring these toner images onto paper, and sequentially transfers the toner images of each color onto the same paper in an overlapping manner, A color copying machine which obtains color copies by fixing this paper is characterized in that each of the color separation members is provided with means for lowering the resolving power thereof than the resolving power of the monochrome image projection member. color copying machine.