JPH04166859A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent carriers from adhering to an image holder by forming a density adjusting means with at least either one of a developing bias means or an exposure means and a charging means. CONSTITUTION:An image density adjusting means changes DC bias voltage to a developing bias and grid bias voltage to a primary charger 8, rather than lighting voltage to a halogen lamp 2, for a set value of density to change the density of an image. That is, the developing bias DC voltage is changed for a set value of standard density to make the contrast of a photosensitive drum 6 with a drum potential larger, the density higher, the DC voltage to the developing bias and the halogen lighting voltage constant, so that the controlled grid bias voltage to the primary charger 8 lowers the umbra potential of the photosensitive drum 6 and makes the density weak. It is thus possible to prevent carriers from adhering to an image holder.

Description

DETAILED DESCRIPTION OF THE INVENTION No. 1 A The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, and in particular to an image forming apparatus that improves the density adjustment device for an image obtained by development using a two-component developer. The present invention relates to a forming device.

In image forming apparatuses that use electrophotography, such as copying machines, a latent image formed on a photoreceptor as an image carrier is developed and visualized. 2. Description of the Related Art Image forming apparatuses that use a developer are known.

The density of an image obtained by development using such a two-component developer is adjusted by an image density □ adjustment device, and the density adjustment method is as follows: (1) Constant exposure amount applied to the photoconductor (2) A method of adjusting the image density by changing the amount of exposure given to the photoreceptor while keeping the developing bias voltage constant; (3) Image density Two adjustment means, a developing bias voltage control means and an exposure amount control means, are provided, and when increasing the image density, the developing bias voltage is lowered while keeping the exposure amount constant.
When lowering the image density, increase the exposure amount while keeping the developing bias voltage constant; (4) In (3) above, when increasing the image density, keep the developing bias voltage constant and increase the exposure amount. There are various density adjustment methods, such as a method of increasing the developing bias voltage while keeping the exposure amount constant when lowering the image density.

Normally, when adjusting the density by the user, as shown in Figure 2, for example, the F value (density adjustment value, aperture value) F5 is set to the standard value, and the density adjustment lever is adjusted from F6 to F9 (then the density becomes thinner). Even if the base density is high, such as newspaper, by adjusting the density adjustment lever to make the density lighter, it is possible to obtain a clear copy image without fogging on the base. The density adjustment lever is F4~
When F1 is set to a small value, the density becomes high, and it is possible to obtain a clear copy image even with thin characters such as pencil characters, for example.

However, the conventional image density adjustment device described above has the following problems: (A)
The amount of exposure applied to the photoconductor is changed independently, (B) the developing bias voltage is changed alone, or (C) the amount of exposure and the developing bias voltage are changed in combination, so as described below. There were some drawbacks.

That is, when changing the exposure amount in (A) alone, when the sensitivity of the photosensitive drum is insufficient for the process speed,
The lamp lighting voltage of F5 is high (and the life of the lamp is short).
This may cause problems such as not being able to obtain the necessary lighting voltage from F5 to F9, and as a result, the lens diameter must be increased (which increases the cost or increases the exposure slit). This may lead to a decrease in resolution.

When changing the developing bias of (B) alone, Fl
As you go from F8 to F9, the developing bias DC voltage is increased to decrease the contrast with the latent image potential to adjust the density. The contrast between the latent image potential after exposure and the development bias potential becomes large, and in a developing device using a two-component developer, problems such as carrier adsorption to the photoreceptor occur.

Specifically, an example in which a negatively chargeable OPC photoreceptor is used will be described. (Black potential) knee 650V, ■L
(White background potential) = -130V (7), development bias VI at F5 (standard aperture). = -200■, then
An appropriate image with good resolution and no fog was obtained. Normally, F9 (the aperture value for the thinnest aperture) is set so that newspapers and the like do not become foggy. When the white background potential is 1130V, the potential of the newspaper background is 1300V, so to make a good image without fogging on this newspaper, press F9. c=-37
It will be set to 0■. The potential after blank exposure is about -30V, and at F9 (Voc-vsL)
The contrast potential of = (370-30) = -340V
becomes. For two-component developers, the limit of contrast potential that does not allow carrier to be adsorbed to the photoconductor side is usually -270 to -3.
00■, and if this value is exceeded, the carrier will be adsorbed to the photoreceptor side, causing problems such as developer scattering and image quality deterioration.

Even with the method (C) in which changes in exposure amount and developing bias voltage are combined, the above-mentioned problems often occur.

Therefore, an object of the present invention is to enable image density adjustment that prevents carrier adhesion on an image bearing member during development using a two-component developer, which is a drawback of the conventional method, and to provide an inexpensive density adjustment device.
It is an object of the present invention to provide an image forming apparatus that is simple and capable of obtaining high quality, high resolution images without fogging.

To do 2 of 5 problems The above object is achieved by an image forming apparatus according to the present invention.

To summarize, the present invention provides an image by exposing and charging an image bearing member to form an electrostatic latent image, and developing the electrostatic latent image with a two-component developer to visualize it, and obtaining an image by increasing the density of the image. The image forming apparatus is equipped with an adjusting means, characterized in that the density adjusting means comprises at least one of a developing bias means and an exposing means, and a charging means.

According to the image forming apparatus of the present invention, when obtaining a high-density image as the image, one of the developing bias means and the exposure means is adjusted; when obtaining a low-density image, the charging means is adjusted. Then, image density adjustment is performed, and if an image having a density near the appropriate density is to be obtained as the image, image density adjustment is performed by adjusting at least one of the developing bias means and the exposure means.

'L' down Examples of the present invention will be described in detail below.

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus for implementing the present invention.

In this image forming apparatus, the image density adjustment device performs density adjustment using the method shown in Table 1, which will be described later.

First, the image forming process of the image forming apparatus will be explained.

In FIG. 1, 1 is a document glass stand of an image forming apparatus;
An original (not shown) is placed at a predetermined position on the original glass table 1 . The manuscript will be discussed later. An original placed on an original glass stand 1 is exposed to light by an original irradiation lamp, for example, a halogen lamp 2.

A scanning mirror 3 housed in an optical scanning unit (not shown) guides reflected light from a document due to exposure to an optical system unit 4 while reciprocating in the main scanning direction. Optical system unit 4
is composed of an imaging lens, etc., and the reflection mirror 5 forms an image of the reflected light from the original guided by the scanning mirror 3 onto the photosensitive drum 6 after primary charging, thereby forming an electrostatic latent image on the photosensitive drum 6. An image is formed.

In preparation for image formation, the photosensitive drum 6 has its charge removed in advance by a pre-exposure lamp 7, and is uniformly primary charged by a primary charger 8. The primary charger 8 is composed of a corona wire, a shield, and a grid wire.

The electrostatic latent image formed on the photosensitive drum 6 is developed by a fixed type developing device 10 containing, for example, black toner, and is visualized as a toner image.

The toner image thus formed on the photosensitive drum 6 is transferred by the transfer charger 12 onto a transfer sheet (not shown) fed to the photosensitive drum 6. The transfer sheet is fed into the main body of the image forming apparatus by a paper feed roller from a paper feed cassette (not shown), and after stopping at the position of the registration roller 15, the timing of the transfer position of the toner image formed on the photosensitive drum 6 is determined. The paper is then fed to the photosensitive drum 6.

The transfer sheet on which the toner image has been transferred is separated from the photosensitive drum 6 by the separation charger 13 and conveyed to the fixing device 14 by the conveyor belt 16, where the toner image is transferred by applying heat by the fixing device 14. The image is fixed on the sheet and then discharged outside the main body of the image forming apparatus.

According to the present invention, the image density adjusting means of the image forming apparatus performs density adjustment using the method shown in Table 1.

Table 1 In Table 1, the halogen lamp column indicates the lighting voltage of the halogen lamp 2, the DC bias column indicates the DC bias voltage of the developing bias to the developing sleeve of the developing device 10, and the grid column indicates the primary charger. 8 grid bias voltage is shown.

In this example, for nine density setting values from F1 to F9, the lighting voltage of the halogen lamp etc. does not change, but the DC bias voltage of the developing bias and the grid bias voltage of the primary charger are changed. The density of the image is changing.

According to this embodiment, for the standard density setting value F5, F5~
For F1 and F6, the developing bias voltage is changed by 20 V, and as you go from F5 to Fl, ■Dc is lowered to thicken the contrast with the drum potential of the photosensitive drum 6 and increase the density.F6 ~F9 changes the bias voltage applied to the grid wire of the primary charger, and as you go to F9, the grid bias value decreases,
Lowers the photosensitive drum dark potential (V,).

Tables 2 to 4 show the results of image density adjustment in the conventional case and this embodiment.

Table 2 shows the case of a conventional light aperture.

Table 2 In the case of the light aperture shown in Table 2, at F9 (V.

-VOC) contrast potential is about 20V,
Although it is possible to completely remove the background of newspapers and obtain fresh images even with dense backgrounds such as newspapers, on the other hand, the lighting voltage of the halogen lamp increases to 75.8V, and the white background potential decreases due to fatigue of the photosensitive drum, etc. When the voltage rises, or when variations in the brightness of the optical system are detected, it becomes necessary to turn on the light at 80V or higher. In this case, considering the lamp life, temperature rise, and ballast efficiency, it is practically impossible. As a result, in order to further lower the lighting voltage of the lamp, negative costs arise, such as increasing the aperture of the imaging lens of the optical system unit 4 shown in the figure.

Table 3 shows the case of a conventional developing bias aperture.

Table 3 (Unit: 2 ■) In the case of the developing bias aperture shown in Table 3, there is no increase in the lighting voltage of the halogen lamp, but when the developing bias is set to F9,
. C rises to 370v, and as a result, (■1IL-■
. V) increases to 340V.

Incidentally, Vn is the dark potential, and VH is the halftone (D=0.
3), VL is the white background potential, and VIIL is the potential after blank exposure by the blank exposure unit 9. From the above, for example, if you want to make a part of the image white by masking, you will need to perform blank exposure irradiation on that part, the photosensitive drum potential in that part will be VIIL, and a two-component developer will be used in the developing device 10 during development. This obviously causes the problem of carrier adhesion to the photoreceptor.

Table 4 shows the case of this example.

Table 4 In the case of this embodiment shown in Table 4, F6 to F9 keep the developing bias DC voltage and halogen lighting voltage constant, and control the grid bias voltage of the primary charger to lower the photosensitive drum dark area potential. By doing so, the concentration is reduced.

According to this embodiment, as with conventional light apertures and bias apertures, it is now possible to adjust to a clear image without fogging even when the background density is high, such as in newspapers. Further, when reducing the density, it is not necessary to increase the halogen lighting voltage, and there is no need to increase the DC voltage of the developing bias.

Therefore, the cost of the optical system can be reduced, carrier adhesion to the photosensitive drum can be eliminated, and it has become possible to provide an image forming apparatus that can form high-quality images at low cost.

In this embodiment, the developing bias voltage is set to F1 to F6.

. The aperture is changed by 2OV, and from F6 to F9 it is 1
Next, change the grid bias of the charger to 50 to 55 aperture.
The rate of change is increased by changing V increments. This is to reduce the change in the vicinity of the normally used aperture of F5.

Table 5 shows the results of image density adjustment in other embodiments of the image forming apparatus of the present invention.

Table 5 (unit: 2v) In this example, when thinning, the grid bias of the primary charger is lowered to lower the dark area potential, and the halftone potential is also necessarily lowered to make it thinner. The contrast between ■ and the developing bias ■Dc is 280■, which is the amount at which the solid black density does not decrease due to the development characteristics (potential V to density D), and the solid black density is completely saturated. is clear and dark (it is also possible to reproduce it. dark (
In this case, the halogen lighting voltage is lowered and the white background and halftone potentials are increased to make it darker. Effects similar to those of the previous examples were confirmed.

Table 6 shows the results of image density adjustment in still other embodiments of the present invention.

Table 6 (Unit 2■) In this example, up to Fl-F5, the halogen lighting voltage is
The density was adjusted by changing the developing bias voltage from F5 to F7 and by changing the primary charger grid bias voltage from F7 to F9, and the same effect as in the previous example was confirmed.

In the above embodiments, the exposure means varies the halogen lighting voltage, the developing bias means varies the DC voltage, and the charging means varies the grid bias of the primary charger. The invention is not necessarily limited to this, but as long as the exposure means changes the exposure slit width and the development bias means applies an AC voltage to the development bias, the AC voltage (peak-to-peak) can be changed. Alternatively, the charging means may be changing the voltage or current applied to the corona wire of the primary charger.

In addition, although the above description has been made using an image forming apparatus having a two-component developing means, the present invention can also be applied to an image forming apparatus having both a two-component developing means and a one-component developing means, and the same effects as in the embodiments can be obtained. I can do it.

As described above, the image forming apparatus of the present invention has the following effects.

(1) It is now possible to adjust image density while preventing carrier adhesion to an image bearing member such as a photosensitive drum in development using a two-component developer, which is a disadvantage of the conventional method.

(2) It has become possible to provide an inexpensive and easy image density adjustment device.

(3) It has become possible to provide an image forming apparatus that can form fog-free, high-quality, high-resolution images on any image original.

Furthermore, if the image forming apparatus is equipped with a CCD light-receiving element equipped with a filter or the like, it becomes necessary to turn on the halogen lamp by DC lighting when performing color recognition, and if you try to raise the lighting voltage to the same level as AC lighting, Negative conditions such as increased cost of the ballast occur, and in order to cope with this, it is necessary to suppress the lighting voltage to a low level, but the present invention is extremely effective as an image density adjustment device that can cope with this.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus for implementing the present invention. FIG. 2 is a schematic diagram showing an image density adjustment aperture value for a user provided in a conventional image forming apparatus. 1
: Document glass 2: Halogen lamp 4: Optical system unit 6: Photosensitive drum 8: Primary charger 1O: Developing device

Claims (1)

[Scope of Claims] 1) An image is obtained by exposing and charging an image carrier to form an electrostatic latent image, and visualizing the electrostatic latent image by developing it with a two-component developer. An image forming apparatus equipped with a density adjusting means, characterized in that the density adjusting means is comprised of at least one of a developing bias means and an exposing means, and a charging means. 2) When obtaining a high density image as the image, adjusting at least one of the developing bias means and the exposure means,
2. The image forming apparatus according to claim 1, wherein when obtaining a low density image, the image density is adjusted by adjusting the charging means. 3) When obtaining an image near the appropriate density as the image,
3. The image forming apparatus according to claim 1, wherein the image density is adjusted by adjusting at least one of the developing bias means and the exposure means.