JPH04336549A - Image forming device - 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]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process.

0002

2. Description of the Related Art FIG. 5 shows an example of a schematic configuration of a conventional image forming section of an image forming apparatus such as a laser beam printer or a facsimile machine in which development is performed by a reversal development process using high-resistance toner.

Around the photosensitive drum 1, in the order of rotation direction indicated by the arrow, there is a charger 2, an exposure optical system 3,
A developing device 4 and a transfer charger 5 are provided, the charger 2 is formed as a scorotron, a grid potential is applied to the grid electrode 6 by a grid electrode power source 7, and the scorotron casing electrode 8 is grounded. Further, a high voltage is applied to the scorotron charger wire 9 by a high voltage power source 10 for charging.

The base conductor 11 of the photosensitive drum 1 is grounded. Further, the center conductor 1 of the developing roller of the developing device 4
2 can apply a developing bias using a developing bias power source 13. The transfer charger 5 is configured as a corotron, its casing electrode 18 is grounded, and a high voltage is applied to the charger wire 14 by a high voltage power source 15 for transfer.

In the image forming apparatus having the above configuration, when changing the image density, the output voltage of the developing bias power supply 13 is usually changed. Explain in detail. FIG. 6 is a diagram showing the relationship between electrostatic latent image potential and developing bias. In the same figure (a) showing the "standard" state, the exposed part Von of the electrostatic latent image is 50V, and the unexposed part Voff is 600V.
It is. In the case of a reversal development process, the development bias VB is usually set to about 550V with respect to these latent image potentials. In FIG. 6(b), which shows the "dark" state, the developing bias is increased by 200 V, for example, as described above.
50V, and on the other hand, in FIG. 6(c) representing the "thin" state, the developing bias is lowered by, for example, 200V to 350V. At this time,

[0006]

[Math 1]

If it is expressed as 0007, then

[0008]

[Math 2]

When ΔV takes a positive value.

FIG. 7 shows the relationship between the development potential difference ΔV and the optical reflection density of the image. The exposed area, which becomes the image area, is set so that ΔV is a positive value in order to obtain sufficient image density. On the other hand, the non-exposed area, which becomes the background area, is set at around oV so that so-called "background stain" does not occur. In order to change the image density, specifically, the relationship between the image density of the image area and the background area when the developing bias shown in FIGS. 6(a), (b), and (c) is changed by ±200V is shown in FIG. The results are read and listed in Table 2. Optical reflection density 0.60 to 1.4 in the image area
0 and it is possible to give a sufficient change to the image density. On the other hand, in the background part, the optical reflection density is 0.05 to 0.27. Generally, it is said that when the optical reflection density is greater than 0.10, humans recognize toner adhesion in the background area, so-called "background stain." In other words, in this case, undesirable development such as background staining occurs.

As described above, conventional image forming apparatuses have had the problem that when attempting to change the image density with a sufficient variation range, background stains occur in the background area. In order to avoid this, it is possible to reduce the range of change in the developing bias and limit it to a range where the optical reflection density of the background area is always around 0.10, but in this case, the image density The range of change becomes small, and the original purpose of changing the image density with a sufficient range of change is not achieved.

0012

[Table 1]

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to improve the image density while maintaining the function of changing the image density within a sufficient range. An object of the present invention is to provide an image forming apparatus that does not cause background stains on the image forming apparatus.

[0014]

[Means for Solving the Problems] In order to solve such problems, the image forming apparatus of the present invention includes a potential generation section for potential shift that can shift both the developing bias and the grid electrode potential at the same time. are provided so as to be connected in series to each of the developing bias power source and the grid electrode power source.

[0015]

[Operation] Since the image density is adjusted by changing the output voltage of the potential shift voltage generating section, the density of the image area changes within a sufficient range, and background staining in the background area never occurs.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram in which the present invention is applied to the image forming apparatus previously explained with reference to FIG. Therefore, the same members as those in the apparatus of FIG. 5 will be described with the same reference numerals.

The difference between this embodiment and the conventional example described above is that a voltage generating section 20 for potential shifting is provided, which enables simultaneous shifting of both the developing bias and the grid electrode potential. There is no place.

The potential shifting voltage generating section 20 is connected in series to the grid electrode power source 7 and the developing bias power source 13, and the developing bias and grid electrode potential are shifted by the potential generated by the voltage generating section 20. It is something to do. In the apparatus of this embodiment, in order to make the development conditions the same as those in FIG.
Similarly, it is only necessary to shift the grid electrode power source 7 to a lower level.

The relationship between the grid electrode potential and the charged potential of the photoreceptor will be explained with reference to FIG. According to the inventor's experiments,
When a scorotron type charger is used, the charging potential is in a proportional relationship with the grid electrode potential with extremely good linearity in a charging potential range of 100 V, which is a practical use range. Specifically, the grid electrode potential is 65
When changing from 0V to 850V, the charging potential changes from 600V to 800V.

Based on the above explanation, FIG. 3 shows the relationship between the electrostatic latent image potential and the developing bias according to the present invention. In FIG. 3A showing the standard state, the conditions are exactly the same as in the conventional example shown in FIG. 6A, and the image area density and background area density are the same as in the conventional example. Next, in FIG. 6(b) showing the "dark" state, as mentioned earlier, the potential shift voltage generating section is
00V is increased. As described above, the developing bias and the grid electrode potential are simultaneously shifted by 200 V, and the charging potential is also shifted by 200 V as the grid electrode potential changes. As a result of the above, the development potential difference in the image area increases by 200V, and a high image density corresponding to the 200V is obtained. On the other hand, in the background area, the development potential difference is 50 V, as in the "standard" state, so no background stain occurs. Next, FIG. 6(c) shows a "thin" state. In this case, the potential shift voltage generating section is lowered by 200V. The concept is similar to the explanation in FIG. 6(b), and a thin image density corresponding to the 200V can be obtained in the image area. On the other hand, in the background area, the development potential difference is 50 V as described above, so no background stain occurs. Figure 4 shows the relationship between these development potential differences and the optical reflection density of the image.
Shown below. Further, Table 1 lists the relationship between the image density of the image area and the background area in the present invention. In the image area, the optical reflection density is 0.60 to 1.40, making it possible to provide a sufficient change in image density. On the other hand, in the background area, the optical reflection density is always stable at 0.05, and background stains never occur.

[0022]

[Table 2]

[0023]

As described above, in the present invention, a sufficient change in density can be imparted to an image area without causing background stains in the background area. It also prevents toner from adhering to the background, reducing toner consumption.
The lifespan of the cleaning unit and waste toner container can be extended, and as a result, running costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the grid electrode potential and the charged potential of the photoreceptor.

FIG. 3 is a diagram showing the relationship between electrostatic latent image potential and developing bias according to the present invention.

FIG. 4 is a diagram showing the relationship between the development potential difference and the optical reflection density of an image according to the present invention.

FIG. 5 is a schematic diagram showing an example of a conventional image forming apparatus.

FIG. 6 is a diagram showing the relationship between a conventional electrostatic latent image potential and a developing bias.

FIG. 7 is a diagram showing the relationship between the conventional development potential difference and the optical reflection density of an image.

[Explanation of symbols]

20 Voltage generation section for potential shift

Claims (1)

[Claims] Claim 1: In an image forming apparatus that obtains a toner image by developing an electrostatic latent image formed on a photoconductor by a reversal development process, it is possible to simultaneously shift both the development bias and the grid electrode potential. An image forming apparatus characterized in that a voltage generating section for potential shift is provided so as to be connected in series to each of a developing bias power source and a grid electrode power source.