JPH0330141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image reproduction method, and more specifically,
The present invention relates to an image reproducing method that changes the potential-density curve during development according to the amount of adjustment of the exposure amount and obtains a suitably easy-to-see reproduced image.

Conventionally, when copying a business document using an electrophotographic apparatus, an operator considers the content written on the document, the background, etc., and adjusts the exposure amount adjustment dial accordingly to obtain a reproduced image that is easy to read. For example, when copying a document consisting mainly of text written on blank paper, copy at position 5 in the center of the adjustment dial. When copying lightly written characters, dial 3 or 1.
Reduce the exposure, couple the background slightly, and copy. Further, when copying a document written on a colored background such as a diazo paper document or a newspaper document, the dial is opened to 7 or 9 and the exposure amount is increased so that the background is copied white.

Images reproduced as described above generally have the following drawbacks. In other words, when the adjustment dial is turned down to make a copy of a light text portion of a document easier to read, the dark portions of the document, and in extreme cases even the halftone portions, are reproduced as black, resulting in an image that is extremely difficult to read. If you open the dial and copy the colored background of a document to white, the half-tone areas of the document will be reproduced faintly, making it very difficult to read.

These contents are explained as follows with reference to FIG. FIG. 1 shows a curve representing the relationship between the density D _O of the original and the density D _C of the reproduced image, and this curve is called the D _O -D _C curve. D _W of D _O axis,
D _H1 , D _H2 , and D _B indicate the densities of the white area, halftone areas 1 and 2, and black paper area of the original, respectively. The D _O -D _C curve of the adjustment dial 5 is indicated by A1.

On the other hand, if you turn down the adjustment dial to reproduce the thin half-tone parts of the original in an easy-to-read manner, D _O -
The D _C curve is a curve A2 obtained by moving the D _O −D _C curve A1 parallel to the left of the D _O axis when the dial is set to 5 in Figure 1.
It is shown as follows. However, while the halftone portion D _H1 is reproduced in an easy-to-read manner, the half-tone portion D _H2 is reproduced as almost black, resulting in a copy image that is difficult to read.

Conversely, when the background is a colored document with a background area of about D _H1 , as the adjustment dial is opened, the D _O - _D
In the figure, the D _O - D _C curve A1 when the dial is set to 5 is shifted in parallel to the right of the D _O axis, as shown by a curve A3. In this case, the background D _H1 is reproduced as white, but the background D _H2 becomes too light, resulting in a copy image that is difficult to read.

An object of the present invention is to provide a method that eliminates the above-mentioned conventional drawbacks and reproduces images that are always easy to view.

SUMMARY OF THE INVENTION In order to achieve the above objects, the present invention provides an image reproduction method for an electrophotographic apparatus that adjusts the density of a reproduced image formed through a developing means by adjusting the amount of light that exposes a photoreceptor. When adjusting the density, when the exposure amount is decreased by changing the developing conditions of the developing means, the slope of the photoreceptor surface potential - toner concentration curve is decreased, and when the exposure amount is increased, the above curve This method is characterized by increasing the slope of . This is achieved by:

Embodiments of the present invention will be described in detail below based on the drawings.

In order to avoid the drawbacks shown in Figure 1,
It would be good if the D _O -D _C curve characteristic as shown in Fig. 2 could be obtained. In other words, D _O when the adjustment dial is turned down
-D _C curve B2 is D _O -D _C when the dial is set to 5
The slope is gentler than that of curve B1.
Using the image reproduction method modified in this way,
It is possible to copy an image in which both halftones D _H1 and D _H2 are easy to read. Also, when the dial is opened, the D _O −D _C curve B3 is the D _O at the dial 5 position.
-D The slope is steeper than _C curve B1.
Using the image reproduction method modified in this way,
It is possible to copy images without fogging and with the D _H2 part easy to read.

FIG. 3 shows an embodiment of the present invention. In the figure, 1 is a photosensitive drum, and 2 is a sleeve-type magnetic brush developing device that uses a developer containing a carrier and toner. A feature of the magnetic brush is that the carrier in the developer acts as a group of minute contact electrodes, so that it has halftone image reproducibility with an effective electrode effect. Of course, a one-component magnetic toner may be used as the developer.

By the way, image reproducibility can be changed by connecting a resistor 3 in series to the sleeve of the developing device 2 and changing the resistance value. For example, resistance
When the sleeve is grounded as OΩ, it exhibits extremely high contrast reproducibility with a strong electrode effect.

This situation is shown by curve C3 in FIG. FIG. 4 is a graph showing the relationship between the surface potential V of the photoreceptor and the toner density D after development, and is called a V-D curve. As the variable resistor 3 is increased to 10 ⁶ to ^{10 8} Ω, the electrode effect is alleviated, and image reproducibility with a slightly softer tone is exhibited. The V-D curve at this time is C1
It is indicated by. Furthermore, when the variable resistor 3 is set to 10 ⁹ Ω or more, the sleeve becomes electrically close to a floating state, the electrode effect is weakened, and the image reproducibility shown in V-D curve C2 is accompanied by a slight edge phenomenon. It's coming. Change the value of the resistor connected in series to the sleeve from 0 to 10 ⁹ Ω by linking it to the exposure adjustment dial 4. When the dial is set to 9 and the exposure is increased, it is set to C3, and when the dial is set to 5, it is set to C3. If you adjust the C1 dial to 1 and reduce the exposure so that you get the C2 V-D curve, you will get the D _O -D _C curve shown in Figure 2.
It becomes possible to correct image reproducibility.

The above is an example of self-bias during development, but
A bias power supply may be connected to the sleeve to change the bias voltage value.

FIG. 5 shows an embodiment of the present invention in which a developing device of another type is used. In the figure, 5 is a developing roller that forms a thin layer of toner on its surface to develop the latent image on the photosensitive drum 1, and 6 is an applicator roller that coats the surface of the developing roller with toner. When the toner polarity is negative, the developing roller 5 side is biased with a positive voltage and the applicator roller 6 side is biased with a negative voltage by a variable power source 7, and the negative toner on the applicator roller 6 is coated on the surface of the developing roller 5. It is structured as follows. When the toner polarity is positive, the bias is applied in the opposite way. By changing the bias voltage value between both rollers, the thickness of the toner coated on the surface of the developing roller can be changed, and the developing characteristics can be changed. For example, if the bias voltage value is 300V,
By changing the voltage to 450V and 600V, the thickness of the toner coated on the developing roller 5 can be continuously increased, and the V-D curve can be changed from C2 to C1 to C3 in FIG. By interlocking with the amount adjustment dial 4, the second
It becomes possible to obtain the corrected image reproducibility shown in the figure.

FIG. 6 shows another embodiment of the present invention. This embodiment has a developing roller 5 and an applicator roller 6 as in Fig. 5, and a voltage of 450 V is applied between both rollers.
A bias voltage of 1 is applied from the power supply 7. By changing the relative speed between both rollers, it is possible to change the development characteristics. For example, a motor M that rotates the applicator roller 6
The rotation speed of the two rollers is adjusted by the adjusting means 8, and the relative speed between both rollers is set to 60 mm/sec, 90 mm/sec, and 120 mm/sec.
By increasing the speed to mm/sec, the thickness of the toner coating on the developing roller 5 can be increased. As a result, the V-D curve in Figure 4 is changed to C2→
It can be changed from C1 to C3, and by interlocking with the exposure adjustment dial 4, it is possible to obtain the corrected image reproducibility shown in FIG. In FIG. 6, only the rotational speed of the applicator roller 6 is controlled to change the relative speed, but the rotational speed of only the developing roller 5 or both may be changed.

In explaining the embodiments shown in FIGS. 3, 5, and 6, an example was shown in which the voltage applied to the document illumination lamp 9 was changed using the exposure adjustment dial 4.
In order to change the amount of exposure to the photosensitive drum 1, a diaphragm may be provided before and after the lens 10, and the aperture of the diaphragm may be adjusted by the dial 4, and a light source may be provided separately from the illumination lamp 9. Various other modifications are conceivable, such as a configuration in which the illuminance of the separate light source is changed in conjunction with the adjustment dial 4 in a device in which the photosensitive drum is irradiated with light at the same time as the exposure light of the original or before and after the exposure light of the original. It will be done.

As described in detail above, in the present invention, since the development characteristics are changed according to the exposure adjustment amount of the exposure adjustment means, it is possible to obtain a copy image with high image reproducibility regardless of the condition of the original. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between original density D _O and reproduced image density D _C , and Figure 2 is an ideal graph of D _O - D _C.
Graph showing the curve, FIG. 3 is a schematic diagram showing an example of the present invention, FIG. 4 is a graph showing the relationship between the surface potential V of the photoreceptor and the toner density D after development, and FIGS. 5 and 6 FIG. 2 is a schematic diagram showing another embodiment of the present invention. In the figure, 1... photosensitive drum, 2 and 5... developing roller, 3... variable resistor, 4... exposure amount adjustment dial, 6... applicator roller.

Claims (1)

[Scope of Claims] 1. An image reproduction method for an electrophotographic apparatus that adjusts the density of a reproduced image formed through a developing means by adjusting the amount of light that exposes a photoreceptor, comprising: By changing the developing conditions of the means, when the exposure amount is reduced, the slope of the photoreceptor surface potential-toner density curve is reduced,
An image reproduction method characterized by increasing the slope of the curve when the exposure amount is increased.