JPH0562329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a developing method for an electronic copying machine.

PRIOR ART Conventional developing methods, particularly magnetic brush developing methods, in electronic copying machines generally have developing characteristics as shown in FIG. That is, the horizontal axis represents the development potential V _D (=Vimage−
Vbias: Vimage: electric potential on the sensitive material, Vbias (developing bias) and plotting the development density Dout on the vertical axis, a linear relationship is established (when V _D is greater than V _S , Vout is saturated). Furthermore, if the toner concentration in the developer is constant, the slope γD of this straight line is constant, and it is not possible to arbitrarily change γD or the development characteristic curve. Therefore, the output image for the processless curve PRC (input image density _DIN (also called input density, which is the density of the original image to be input, and the image includes the background of the original) of the copying machine. The curve representing the density _Dput (also referred to as output density, see FIG. 3) is mostly controlled by the characteristics of the photosensitive material shown in FIG. In other words, since the sensitive materials generally used in electrophotography have a narrow dynamic range as shown in FIG. 2, the PRC has a narrow dynamic range as shown in FIG. 3, resulting in sharp tone reproducibility.

For example, as shown in FIG. 15, the input concentration D _IN is D ₁ <D _IN < in FIGS. 2 and 3.
For an image with D ₂ , the output density of (a)
D _put is output, and when D _IN =D ₂ , the output concentration D _put of (b) is output, so that the relationship between the input concentration and the output concentration is approximately linear. However, when the input concentration is D _IN > D ₂ , the output concentration D _put becomes smaller than the input concentration as shown in (d) because the PRC is saturated.
It doesn't change much from _D2 .

As a result, the width of the surface potential of the photosensitive material that can be used to express gradations faithful to the input image density is limited by the characteristics of the photosensitive material, so PRC can express gradations within a narrow dynamic range with linearity. Therefore, tone reproducibility becomes difficult.

Purpose of the Invention The object of the present invention is to obtain a desired PRC by changing the development characteristics without being influenced by the characteristics of the photosensitive material.

Structure of the Invention The present invention provides a developing method for an electronic copying machine in which an electrostatic latent image on an electrostatic latent image carrier is developed using a developer held on a magnetic roll in a developing machine. Areas where the process response curve (PRC), which represents image density, does not have linearity in the first development are treated with a magnetic roll that independently controls the development efficiency and the applied development bias. Development of an electronic copying machine characterized by performing development a total of multiple times including the first development, and controlling the total amount of developer deposited by a magnetic roll to the input image density to an amount corresponding to the output image density of the ideal PRC. It's in the method.

Examples Examples of the present invention will be described in detail below with reference to the drawings.

For example, when trying to obtain a PRC as shown in FIG. 4 using a photosensitive material (selenium drum for Xerox 7200) having the characteristics as shown in FIG. 2, the developing characteristics may be set as shown in FIG. 5. However, the actual development characteristics are as shown in FIG. Therefore, when the characteristics of the photosensitive material are as shown in Fig. 2, the bias potential is set to V _B1 , and γD is set to an appropriate value using a developing machine with the developing characteristics shown in Fig. 1.
For example, when developed using Xerox 7200 developer, the 6th
PRC(a) shown by the solid line in the figure is obtained. The difference from the ideal PRC (characteristics shown in Figure 4) to be obtained here is the shaded area. The linearity of the ideal PRC shown in Figure 4 is necessary for faithful gradation reproduction, and the reason why the straight line does not pass through the origin is to avoid fogging in copies. This is because the image with the input image density is truncated.

Next, set the bias potential to Vimage and _VB2 when D _IN = D ₂ and develop with a developing machine with the development characteristics shown in Fig. 1 with γD set to an appropriate value. PRC (b) in Fig. 7 is obtained.
is obtained. By overlapping these PRC(a) and PRC(b) on the same transfer paper, PRC(c) in FIG. 8 is obtained. In this way, development is performed multiple times by appropriately combining the developing bias and the value of γD.

FIG. 10 shows the configuration of a developing machine according to the present invention, in which the photosensitive drum 3 is rotating in the direction of the arrow.

This developing machine is constructed so that the developing bias and rotational speed of the two magnetic rolls 1 and 2 can be controlled separately. That is, the development efficiency of each magnetic roll is obtained by the independent magnetic roll rotation speed. Let us now consider the case where the PRC shown in Figure 4 is obtained using a photosensitive material having the characteristics shown in Figure 2. Magnetic rolls 1 and 2 are each considered to be independent magnetic brush developing machines having the characteristics shown in FIG.

First, by setting the potential of the developing bias 4 of the magnetic roll 1 to V _B2 in Figure 2 and setting the rotational speed to an appropriate value, the image is developed on the drum to the density shown by the curve (b) in Figure 7. Ru. After that, the drum is moved to the position of the magnetic roll 2 and developed again, but the potential on the drum just before the magnetic roll 2 is the same as the part developed by the magnetic roll 1, as shown by the solid line in Figure 9. Although the potential drops slightly, there is not much change. Therefore, if the developing bias potential of the magnetic roll 2 is set to V _B1 in FIG. 2, and the rotational speed of the magnetic roll 2 is set so that the density on the drum developed by the magnetic roll 2 becomes the curve shown in FIG. As shown in the figure, it is shown by curve (c) which is superimposed on curve (a) and curve (b).
Coming to get PRC.

In the above embodiment, the diameters and rotation directions of the two magnetic rolls may be the same or different, and it goes without saying that the number of magnetic rolls may be three.

FIG. 11 shows a method for obtaining the developing efficiency of each developing roll in the developing method of the present invention.
In the embodiment shown in the figure, the rotational speed of each of the magnetic rolls 1 and 2 was made variable, but in this example, the magnetic rolls 1,
2, trimmer gap adjustment plate 7,
7' is provided, and the development characteristics are controlled by making these trimmer gaps variable. Fig. 12 is a partially enlarged view of Fig. 11, and shows an embodiment of a method for making the trimmer gap variable.The trimmer gap adjustment plates 7, 7', which are supported by the shaft, are rotated in the direction of the arrow to rotate the magnetic roll. 2, the plate 7, and the magnetic roll 3
and plate 7'.
Note that the desired objective can also be achieved by combining the gap control and rotational speed mechanisms.

FIG. 13 shows an example in which the present invention is applied to a color electronic copying machine, in which developing machines A, B, and C for yellow, magenta, and cyan are located around the photosensitive drum 3. .

When making PCR variable, it is sufficient to select a combination of development bias potential and development characteristics to obtain the desired PCR.

FIG. 14 shows an example of application realized by selecting the diameters of the magnetic rolls 1 and 2. In this case, the desired objective can be achieved even if the rotational speeds of the magnetic rolls 1 and 2 are the same.

In this way, the desired PRC can be obtained by developing with the method described above, so even if the dynamic range of the photosensitive material is narrow, the D range of the PRC can be widened.

For example, even when the input concentration D _IN in FIGS. 2 and 3 is D _IN >D ₂ , as shown in FIG. 15(c), the PRC is not saturated and the output concentration increases. In other words, even in the surface potential region where PRC does not have linearity due to the characteristics of the sensitive material, a gradation surface can be created, expanding the dynamic range of PRC.

Effects of the Invention As detailed above, in the present invention, the PRC, which is a characteristic curve of output density relative to input density, is not controlled by the characteristics of the photosensitive material, so even if the dynamic range of the photosensitive material is narrow, the dynamics of the PRC can be maintained. At the same time you can expand the range
Since the PRC can be brought closer to the ideal development curve, the range of image tones is widened and image reproducibility is also improved.

[Brief explanation of the drawing]

Figure 1 is a development characteristic diagram of a general developing machine, Figure 2 is a characteristic diagram of a general photosensitive material, and Figure 3 is a diagram of the development characteristics of a general developing machine.
The PRC characteristic diagram obtained by combining the diagrams, Figure 4 is the PRC characteristic diagram to be obtained, Figure 5 is the PRC characteristic diagram obtained by combining Figure 4, Figure 2
The development characteristic diagram obtained from the combination of the figures, Figure 6 is the PRC characteristic diagram obtained by one development, Figure 7 is the PRC characteristic diagram obtained by the second development, Figure 8 is the PRC characteristic diagram obtained by the second development,
A PRC characteristic diagram obtained by transferring FIG. 7 onto a sheet of paper, FIG. 9 is a diagram showing the surface potential of the photosensitive drum after development with the magnetic roll of FIG. 1, and FIG. 10 is an example of the present invention. 11 is a diagram showing a specific example of changing the developing efficiency in the present invention, and FIG. 12 is a developing machine of 1.
FIG. 1 is an enlarged view of the trimmer cap section, FIG. 13 is an example of application to a color electronic copying machine, and FIG. 14 is an example of application in which the desired development characteristics are fixed. 15th
The figure shows an example of output density relative to input density. Codes in the figure: 1, 2...Developing magnetic roll, 3...
Photosensitive drum, 4... Development bias power supply, 5...
Mixer, 6... Toner, 7, 7'... Trimmer gap adjustment plate, A, B, C... Developing machine.

Claims (1)

[Scope of Claims] 1. A developing method for an electronic copying machine in which an electrostatic latent image on an electrostatic latent image carrier is developed using a developer held on a magnetic roll in a developing machine, comprising: Areas where the process response curve (PRC), which represents image density, does not have linearity in the first development are treated with a magnetic roll that independently controls the development efficiency and the applied development bias. Development of an electronic copying machine characterized by performing development a total of multiple times including the first development, and controlling the total amount of developer deposited by a magnetic roll to the input image density to an amount corresponding to the output image density of the ideal PRC. Method. 2. The method according to claim 1, wherein the magnetic roll is composed of a magnetic roll corresponding to the first development and a magnetic roll corresponding to the second and subsequent development. 3. The method according to claim 1 or 2, wherein the developing efficiency of the magnetic roll is determined by the rotational speed of the magnetic roll. 4. The method according to claim 1 or 2, characterized in that the developing efficiency is obtained by varying the trimmer gap of the magnetic roll. 5. The method according to claim 1 or 2, wherein the developing efficiency of the magnetic roll is obtained by keeping the rotation speed of the magnetic roll constant and varying the roll diameter.