JPS58121069A - Electrophotocopy machine with selectable image expression - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic copying machine that is capable of switching and selecting image expression characteristics for originals versus copies.

As a copying machine of this type, one is known that allows a user to select between a functional copy of the original painting and a pictorial copy of the original painting, depending on whether or not a screen is inserted into the exposure optical path. . However, when a screen is used, moiré fringes occur in the halftone image.

When achieving color balance in a color electrophotographic copying machine, it is necessary to compensate for toner that does not have ideal chromaticity, transparency, etc.

An object of the present invention is to improve the operability or ease of use of an electrophotographic copying machine by making it possible to select the following two copying methods with excellent image expressivity without using a screen. be.

(1) A copying method that can produce copies that emphasize information, that is, line images, that can be expressed with strong contrast without leaking the slight contrast difference t1 in the original image.Especially line images are surface images! ll is also strongly expressed.

(21) A copying method that emphasizes painterly images that can produce copies of images that are as faithful as possible to the originals.The gradation of solid images and the solid areas of photographic images are expressed with clear uniform density, and lines are not emphasized.

Another object of the present invention is to enable the following third copying method to be selected in addition to the above (1) copying method that emphasizes line images and (2) copying method that emphasizes pictorial images. . That is, C3) A copying method that is suitable for copying without background fog (background smudge), particularly for color balance in the case of a color electrophotographic copying machine, and that produces copies with the required chromaticity and less color mixture.

In the present invention, by changing the developing electric field by the development compatible electrode during development, the copying method (a) that emphasizes line images and the copying method that emphasizes painterly images (mackerel) are switched. In the copying method (3) above, the transfer electric field is strengthened.

Hereinafter, a specific example of the present invention will be explained in the case of a color electrophotographic copying machine, which is fully illustrated.

In FIG. 1, a charger 2 is placed around the photoreceptor drum 1.
, an exposure system 3, a developing device 4, a transfer device 5, a static eliminator 6, and a cleaner 7 are arranged. The developing device 4 includes a developing unit 4a having yellow developing toner, a developing unit 4b having magenta developing toner, and a developing unit 4c having cyan developing toner. Transfer device 5
The apparatus has a transport transfer drum 12 constructed by winding a dielectric film between two annular frames, and the transfer drum 12 is in contact with the photosensitive drum 1 so that it can rotate in the same direction.

A transfer charger 13 is provided on the transfer drum 12 near where the photosensitive drum 1 and the transfer drum 12 come into contact with each other. For the transfer drum 12, a preliminary charger 14 is provided upstream of the transfer charger 13 when viewed in the rotational direction of the drum.
Further, a static elimination charger 15 is provided downstream from the transfer charger 13.
is provided. The preliminary charger 14 and the charger 15 are provided on both sides of the film of the transfer drum 12, respectively.
It is configured as a so-called double charger with 15 bi arranged. This is one charger body 14b, 15
b is the other charger body 14. This is to allow it to function as a partner electrode for as15a.

When forming a color electrophotographic image, a color original image is scanned with light, and the light beam is projected onto a photoconductive photoreceptor 1 through separate filters in a full exposure system 3 to create an electrostatic latent image.
A complete color copy is produced by registering each developed toner image of a different color onto a transfer sheet and repeating the transfer.

First, a light image is projected onto the photoreceptor 1, which has been uniformly charged to +800 to 100 OV by the charger 2, through a blue filter (not shown) to form a latent image.This latent image is transferred to the developing unit. The yellow toner 4a is visualized and sent to the transfer device 5.On the other hand, on the transfer device 5 side, in order to increase the transfer efficiency, the transfer drum 12 is charged as a preliminary charger by an AC corona discharge p containing a DC bias component by a preliminary charger 14. The transfer paper, which has been sent out in advance by the paper feed roller 9 from the value feed unit 8 and is waiting on the registration rollers 10, is charged so that the visualized image is transferred to a position corresponding to the original image. , are fed synchronously.The transfer charger 13 applies direct current corona discharge to the transfer drum 12 to perform the transfer.

In order to maintain the same transfer rate regardless of the gradation, a pre-transfer static elimination lamp 24 is provided between the transfer device 4 and the transfer device 5, and the lamp is connected to the lamp power source 25 via a switch 26. is connected to.

After the transfer, the photosensitive drum 1 is neutralized by an AC corona by a static eliminator 6, cleaned by a cleaner 7, and uniformly charged again by a charger 2.

On the other hand, the transfer paper on which the yellow toner image has been transferred moves as the transfer drum 12 rotates. The pre-charger 14 is deenergized before this yellow toner image arrives.

This time, the same original image is exposed through a green filter (not shown) and its latent image is visualized with magenta toner by a developer unit 4b.

This magenta toner image is also transferred to the transfer paper on the transfer drum 12 in the same manner as described above, forming a two-color aligned image. After the photosensitive drum 1 is neutralized and cleaned, it is uniformly charged again by the charger 2. The transfer paper on which the yellow toner image and the magenta toner image are aligned is also sent to the transfer charger 13 as the transfer drum 12 rotates again.

Next, the same original image is exposed to light through a red filter (not shown), and the latent image is visualized with sheer/toner by the production unit 4c. This cyan toner image is also transferred to the transfer paper on the transfer drum in the same manner as described above, forming a three-color registered image to provide a copy of the desired original image.

The copy is separated from the transfer drum 12 by a separating claw 16 after its attraction force with the transfer drum 12 is relaxed by alternating current corona discharge from the static elimination charger 15, and is transported along the conveyor belt 11 to a fixing device (not shown). Sent. The transfer drum 12 is cleaned by a cleaning device 7.

The other photosensitive drum 1 is also cleaned and neutralized by the static eliminator 6 and the cleaner 7, and is reused.

The curve γ in FIG. 2 is the so-called γ characteristic, and the original density is 0. DC original 1. density) on the horizontal axis, and copy density 1. D (image, tensity)
When taken on the vertical axis, it becomes S-shaped as shown in the figure. This means that in general, areas with low density in the original are copied in a much darker manner.
A darker area means that it will be copied even darker. !
Developing rollers 18a, 18b of each developing unit,
If 18c is electrically floated so that it does not function as a developing electrode, the so-called edge effect will cause line images to be copied as darkly as curves, and solid images to be copied as thinly as curve B, resulting in the outline of the solid image being copied. The toner will only stick to the area. On the contrary, the developing roller 18a.

If 18b and 18c are connected to a low bias voltage or grounded to function as development compatible electrodes, an electric field will be generated within the area of the solid image, thereby eliminating the edge effect and improving the expressiveness of the solid image. Therefore, depending on whether or not the developing roller is used as a developing electrode and how much electric field is created between the developing roller and the corresponding electrode, it is possible to change the copy image expression for the same original image.

Therefore, each developing roller 18a*18b*18c of each developing unit l' 4as 4bt4c is connected to a multi-voltage terminal developing bias power supply circuit 20 via a selection switch 19, respectively. This bias power supply circuit 2
0, a constant voltage circuit including a Zener diode is attached to the DC bias power supply 21, respectively, to create two high and low bias voltages Eb and Ed at terminals A and A, which can be selected by a selection switch 19. ing. When the photosensitive drum 1 is charged to +800 to 100 OV by the charger 2, the relatively high voltage Eb is 400 to 500 V, and the relatively low voltage Ea is 1100 to 200 V. The selection switch 19 is designed so that it can also switch over the unconnected float terminal cK.

FIG. 3 shows the relationship between the transfer voltage VT and the transfer rate in the transfer charger 13, and shows the curve 41.

C is each original density 0. D is 0.4, 0.7.1.6
Transferability in case of. It is gender. It can be seen that in the order of A, B, and C, that is, where the original density is high, the peak of the curve indicating the best transfer rate shifts to the higher transfer voltage side. In addition, in the case of any original density, it is possible to obtain a transfer rate of about 85% at the normal voltage indicated by vb, that is, by using this transfer voltage vb, it is possible to transfer uniformly across all gradations. I understand. However, when the transfer voltage Van is relatively high, the transfer rate rises to nearly 90% in the high density area (0,D=1.6) shown by the curve /1, and the low contrast area (0,D=1.6) shown by the curve A =0.4), there is almost no transfer, resulting in a clear copy with no background stains.

Therefore, the transfer charger 13 is connected to the transfer voltage changeover switch 23.
connected to the multi-voltage terminal transfer corona power supply 22 via
A relatively high transfer voltage Va and a relatively low transfer voltage Vb can be selected.

The inventors of the present invention have determined that the relationship in which the transfer rate changes depending on the level of the transfer voltage shown in FIG. I suspect that this is because they are transcribed together. That is, it seems that this is because the negatively charged toner is made positive through the film and paper as the transfer voltage is increased. Therefore, it is believed that even without the film, theoretically the same transfer rate decline curve would be obtained. Further, it is considered that the reason why the best transfer voltage shifts to the higher side as the original density is higher is because the toner becomes thicker in one layer, two layers, and three layers.

When selecting this copying method that emphasizes line images, switch 19 of the developing section
Switch to float terminal C. The switch 23 in the transfer section can be left as a normal voltage terminal. Developing roller 18 a +
By electrically floating 18b and 18c, a so-called Etzzu effect appears, and line and halftone images are well emphasized as shown by dotted lines in Figure 4(a), and solid images are enhanced as shown in Figure 4(a). The curve of this line image and the curve B of the solid image are expressed weakly as shown by the solid line B. In other words, the curve of this line image and the curve B of the solid image are the side where the density is made larger and the side where the density is made smaller (
The upper left and lower right sides of FIG. 4(a) are mutually swollen.

When selecting this copying method, switch 19 of the developing section
is switched to a terminal a having a relatively low potential Ea, and a switch 23 in the transfer section is set to a normal voltage vb that uniformly transfers all gradations. In this way, the developing roller 18ae18b=18
By setting c to a low potential Ea, the edge effect disappears, line images and solid images have similar expressivity, and photographic images and the like are reproduced with high fidelity. The image characteristics at this time are as shown in FIG.

Emphasis on vivid colors This copying method improves flatness expression and erases low-contrast gradation areas.In the case of color electrophotographic copying machines, the required chromaticity mixture is reduced, resulting in vivid colors. It has the feature that you can get a copy of. When this copying method is selected, the switch 19 of the developing section is switched to a terminal with a relatively high voltage Eb, and the switch 23 of the transfer section may be set to the normal voltage Vb of the terminal, but preferably a higher voltage Va. Set the terminal to the a side. The reason for this is that although there is no need to change the transfer conditions if the low-contrast areas are eliminated in the developing section, the image density of the high-density areas may also decrease if the low-contrast areas are eliminated in the developing section. If the transfer voltage is set to Va, as is clear from FIG. 3, low-contrast areas are hardly transferred, so that copies with the same density and no background stains can be obtained for both solid and line images. The image characteristics at this time are as shown in FIG. 4(c), where the original density is 0. Where D is small, the copy density is 1. D does not change at all, and the original density becomes 0. The curve suddenly rises from D, and the curve of the line image and the curve B of the solid image follow the same process.

In order to maintain the same transfer rate regardless of the gradation, a pre-transfer static elimination lamp 24 is provided between the developing device 4 and the transfer device 5, but as a means of intentionally erasing low contrast areas, another method It is also effective to turn off the lamp 24.

As described above, according to the present invention, it is possible to select between a copying method that emphasizes line images and a copying method that emphasizes pictorial images without using a screen. ? ! It is also possible to obtain clear color copies by making it possible to select a copying method that emphasizes solid images and erases low-contrast areas.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the electrophotographic copying machine of the present invention, FIG. 2 is a diagram for explaining the edge effect, FIG. 3 is a diagram showing the relationship between gradation and transfer rate depending on the level of transfer voltage, and FIG. Diagram (a)
(b) and (e) are diagrams showing image characteristics of each copying method emphasizing line images, pictorial images, and vivid colors, respectively. l...Photosensitive drum 4...Developer 4a
, 4b, 4c...Developing unit 5...Transfer device 12...Conveyance transfer drum 13...Transfer charger 14...Preliminary charger 15...Static neutralization charger 18a, 18b, 18cm developing roller 19. ... Selection switch 20 ... Bias power supply circuit 21 ... DC bias power supply 22 ... Corona power supply for transfer 23 ... Transfer voltage changeover switch 24 ... Pre-transfer static elimination lamp 25 ... Lamp power supply'@ Figure 2 Figure 3 Figure 4 1-○, D -O, D O, D

Claims (2)

[Claims] (1) In an electrophotographic copying machine that develops a latent image on a photoreceptor with toner in a developing unit and transfers it to transfer paper using a transfer charger, select a developing roller located opposite to the photoreceptor drum. It is connected to a bias power supply via a switch, and when a copying method that emphasizes line images is selected, the selection switch is switched to an electrically floating terminal, and when a copying method that emphasizes pictorial images is selected, the selection switch is switched to an electrically floating terminal. An electrophotographic copying machine capable of selecting image expression, characterized in that all selection switches are switched to the bias power supply side. (2) Developing the latent image on the photoreceptor with toner in a developing unit,
In an electrophotographic copying machine that transfers this onto transfer paper using a transfer charger, the developing roller located opposite the photosensitive drum is connected to a bias power supply via a first selection switch, and the transfer charger is connected to a bias power supply via a first selection switch. When selecting a copying method emphasizing line images, the first switch is switched to an electrically floating terminal, and the second selection switch is connected to the corona power supply for transfer via the second selection switch. When switching to a normal voltage with a uniform transfer rate over all gradations and selecting a copying method that emphasizes painterly images, use the first method described above.
switch to the bias power supply side and switch the second switch to the bias power supply side.
When selecting a copying method in which both the peta image and the line image have the same density and erase low gradation contrast areas by switching the first switch to the normal voltage, set the first switch to the relatively high voltage side. An electrophotographic copying machine capable of selecting image expression, characterized in that the second switch is switched to a relatively high voltage at which low contrast areas are not transferred.