JPS6252576A - Copying machine - Google Patents

Abstract

PURPOSE:To realize picture quality switching with improved reproducibility at a high speed by switching electrostatic charging potentials of a photosensitive body with a high voltage output. CONSTITUTION:When a switch on a control panel is operated so as to select desired picture quality, the output of a lamp power source 11 connected to an exposure lamp 10 is switched automatically associatively with the switching of the output of a high voltage power source 8 connected to a primary electrostatic charger 7. Further, the quantity of exposure is switched in seven steps so as to vary the density of an image according to a document mode and a photograph mode. For example, in the document mode where the electrostatic charging potential is 700V, the lamp voltage has five steps between 60-70V and in the photograph mode where the electrostatic charging potential is 500V, the voltage is switched in seven steps between 55-65V. Consequently, the difference in image density between the document mode and photograph mode when the original density is low or 0.2-0.3 is reduced.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electrophotographic apparatus such as a copying machine.

2. Description of the Related Art Most conventional copying apparatuses are capable of varying the shade of an image depending on the original or the user's preference. However, depending on the document, there are various types of documents, such as text only or photographs with subtle shading, and it is difficult to obtain the desired image simply by changing the shading.

For manuscripts containing only text, the so-called gamma is set high to create a clear black-and-white contrast, which makes light text appear darker and makes the image easier to see.

On the other hand, for originals with many photographs, a lower gamma and more subtle reproduction of nof tones will produce a more faithful image.

Therefore, some conventional copying apparatuses are equipped with means for varying the gamma characteristics, so that the image quality can be varied depending on the original or the user's preference. For example, the patent application 1986-15
RAat No. 2079 is an example of this, and in this case, it is a copying apparatus that is equipped with a means for changing the surface potential of a photoreceptor and changing the amount of exposure in conjunction therewith, thereby making it possible to vary gamma characteristics.

Problems to be Solved by the Invention However, although it was possible to select the image quality depending on the original or preference using only the above configuration, there were drawbacks such as a decrease in image density at high speeds. .

There are also ways to increase the image density at high speeds, such as increasing the surface potential of the photoreceptor, or increasing the number of revolutions of the developer sleeve or magnet roll to improve the developing ability. Increasing the surface potential of the photosensitive layer deteriorates the voltage resistance of the photosensitive layer, and increasing the number of revolutions of the developer sleeve and magnet roll increases toner scattering and noise, and neither of these measures is effective.

In view of the above problems, the present invention provides a copying apparatus that realizes image quality switching at high speed and with improved reproducibility.

Means for Solving the Problems In order to solve the above problems, the copying apparatus of the present invention includes a developing device and a developer capable of changing gamma characteristics, a means capable of changing the charging potential of the photoreceptor, and a DC It has a configuration of a developing bias power source on which AC is superimposed.

Operation The present invention, with the above-described configuration, allows image quality to be changed by changing gamma characteristics with a single switch, without impairing image density even when the copying speed is high.

Embodiment Hereinafter, a copying apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the main structure of a copying apparatus according to a first embodiment of the present invention. In FIG. 1, the drum-shaped photoreceptor 1 is a selenium-based photoreceptor, and the developer 2 is 10 μm thick.
It consists of a high-resistance toner containing a magnetic material with a diameter of m and a high-resistance carrier containing a magnetic material with a diameter of 40 μm, and the toner concentration is 10% by weight. Magnet roll 4ba1 of developing device 3
The sleeve 6 is rotating in the direction of arrow A at a high speed of 500 rpm, and the sleeve 6 is rotating in the direction of arrow B at a low speed of 1 BO rpm.

The distance between the surface of photoreceptor 1 and the surface of sleeve 5 is 0.4
At m+n, the distance between the sleeve 5 and the doctor blade 6 is 0.6 mm. The photoreceptor 1 is rotating in the direction of arrow C at a circumferential speed of 2oown/sec. - The secondary charger 7 is supplied with high voltage output from a high voltage power supply 8, and by operating a switch 9 on the control panel of the copying machine,
It is possible to change the surface potential of the photoreceptor 1. At this time, the exposure amount is automatically adjusted by switching the voltage of the lamp power supply 11 connected to the exposure lamp 10 in conjunction with the switching of the high voltage output. The developing bias power supply 12 is D
The output in which C and AC are superimposed is supplied to the developing sleeve 5. Note that the distance between the photoreceptor 1 and the sleeve 5 is 0.
3 to 0.6 is very preferable, and the distance ij:o between the sleeve 5 and the doctor blade 6 is very preferably 4 to 0.8.

FIG. 2 is a characteristic diagram showing the relationship between original density and image density when the charged potential of the photoreceptor and the amount of exposure are varied using the copying apparatus having the above-described configuration. As is clear from Figure 2, the saturated image density is 1 when the charging potential is 700V and 500V.
．． There is a slight difference between 4 and 1.2, but the original density is 0.3~
The gamma value differs greatly in the range of 1.0, and 700V
It is high (in SOOV, it is low at 1).

Therefore, character images have a large contrast of 700
■ is appropriate, and for photographic images, the gamma value is 6, which is close to 1.
00v is appropriate. The former and latter images are named document mode and photo mode image quality, respectively.

In the copying apparatus of this embodiment, when a switch on the control panel is operated to select the desired image quality,
- In conjunction with the switching of the output of the high-voltage power supply 8 connected to the secondary charger 7, the output of the lamp power supply 11 connected to the exposure lamp 1o is automatically switched. Although not shown, the exposure amount can be switched in 7 steps for each of the document mode and photo mode so that the shading of the image can be varied. For example, if the charging potential is 7o
In document mode of Qv, lamp voltage is 60~7
There are 6 steps in the 0V range, and in the photo mode where the charging potential is 5ooV, there are 7 steps in the 55-65V range. Accordingly, the image density difference in document mode and auto mode is reduced at a low document density of 0.1 to 0.3. In addition, the output of the developing bias power supply is DCl
ooV, ACl 500H2, zero-peak 300V.

By using this bias power source in which DC and AC are superimposed, it is possible to perform development without decreasing density even at high speeds, and it also effectively prevents carrier adhesion that occurs during development.

When I copied an image using the above-mentioned copying device, it produced high contrast with 8 levels of gradation in document mode.
Even thin text was clearly reproduced.

When in photo mode, the halftones of photos were reproduced with high fidelity in 10 levels of gradation.

Furthermore, by increasing the toner concentration of the developer to 15% by weight and replacing the exposure lamp, the circumferential speed of the photoreceptor was increased to 300%.
Even at rrrm/sea, the above effects were obtained without impairing the image density.

In this example, the exposure amount is switched in conjunction with switching the charging potential of the photoreceptor, but instead of switching the exposure amount, it is also possible to switch only the DC output of the developing bias power supply in conjunction with the switching. It is possible.

Effects of the Invention As described above, the present invention includes a developing bias power source in which DC and AC are superimposed, a developing device and developer having characteristics that can vary gamma, and changing the charging potential of the photoreceptor and interlocking with the developing bias power source. Since the structure includes a means for changing the exposure amount, the copying speed is fast, and the user can easily change the image quality depending on the difference in the original or preference, and it is possible to easily change the image quality depending on the difference in the original or the user's preference. Appropriate images can be easily obtained for both originals with high contrast and multi-tone originals such as photographs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of a copying apparatus according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing an example of gradation changes when the charging potential of a photoreceptor is changed. 1...Photoreceptor, 2...Developer, 3...
...Developer, 4...Magnet roll, 5
······vinegar! J7", 6...Doctor blade, 7...Next charger, 8...High voltage power supply, 9...Switch, 10...・Exposure lamp, 11... Lamp power supply, 12...
・Development bias power supply.

Claims (1)

[Claims] The developing bias power supply includes a power source in which direct current and alternating current are superimposed, and image quality switching means between photo mode and document mode, and the image quality switching means is characterized in that the charging potential of the photoreceptor is switched by high voltage output. copying equipment.