JPH08278741A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device which compensates for an apparent sensitivity-decrease resulting from a decrease in the thickness of the photoreceptive layer of a photoreceptor and, thus, prevents image quality deterioration. CONSTITUTION: This imagee forming device comprises the image carrier (photoreceptor drum 1), an electrifying means (scorotron electrifier 2) for uniformly electrifying the surface of the image carrier 1, and an image forming means for forming an image on the image carrier 1 electrified by the electrifying means 2. It further comprises a characteristic change detection means (film- thickness meter 7) for detecting a change in the characteristics of the image carrier 1, and an image-carrier temperature control means (heating element W) for controlling the temperature of the image carrier 1 based on the result of the detection by the detection means 7.

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,
In particular, the present invention relates to an image forming apparatus including a photoconductor.

[0002]

2. Description of the Related Art There is a copying machine as an example of an image forming apparatus equipped with this type of photoconductor, and the "film scraping" in which the photoconductor layer on the surface of the photoconductor drum is scraped off is caused on the photoconductor drum after the transfer / separation process. It is generated by the cleaning operation of the cleaning blade that scrapes off the toner remaining on the surface of the photosensitive drum.

That is, every time the cleaning operation is performed, the surface of the photoconductor drum is rubbed by the cleaning blade, so that the organic photoconductor layer is gradually shaved and the film thickness is reduced to cause film scraping.

When such film scraping occurs, the apparent sensitivity of the photosensitive drum is lowered. Here, "apparent sensitivity reduction due to film abrasion" means that when the photosensitive layer thickness is reduced, if the charge position is kept constant, the charge density on the surface of the photosensitive layer increases and the photosensitivity of the photoreceptor is increased. It means that the same phenomenon as when the image quality deteriorates occurs and the obtained image quality deteriorates.

That is, if the surface potential when the film is not scraped (initial state) is applied as it is when the film is scraped, the same image forming conditions (original exposure amount,
With the development bias), the potential of the white background of the original does not drop sufficiently, and unnecessary toner adheres to this area during development, causing the background fog to be printed in black on the copy paper. Is significantly impaired. It is necessary to compensate for such a characteristic change of the photoconductor due to the accumulation of the number of copies.

As a proposal of such sensitivity compensating means, there is a means disclosed in Japanese Patent Publication No. 61-29505. In this proposal, the relationship between the number of copies and the characteristics of the photosensitive drum is programmed in advance. Then, the number of copies, the paper size, the exposure time, etc. are counted, and the image forming conditions such as the exposure amount of the original are changed according to the program based on the counted values.

[0007]

However, in the case of increasing the exposure amount of the original document as a means for preventing the apparent sensitivity reduction, it is limited to an apparatus having a margin of the exposure amount, and the original exposure amount is increased. When the amount is increased, the exposure exposure amount of the photosensitive drum is increased, and as a result, the life of the photosensitive drum is shortened.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus which compensates for the apparent decrease in sensitivity due to the decrease in the thickness of the photosensitive layer of the photosensitive member and prevents the deterioration of image quality.

[0009]

In order to solve the above-mentioned problems, the present invention provides an image carrier, charging means for uniformly charging the surface of the image carrier, and the image charged by the charging means. In an image forming apparatus including an image forming unit for forming an image on a carrier, the image carrier based on a characteristic change detecting unit detecting a characteristic change of the image carrier and a detection result by the characteristic change detecting unit. And an image carrier temperature control means for controlling the temperature of the body.

[0010]

According to the present invention, the characteristic change detecting means detects the characteristic change of the image carrier. The image carrier temperature control means controls the temperature of the image carrier based on the detection result detected by the characteristic change detecting means.

[0011]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a side sectional view of the image forming apparatus of this embodiment. As shown in FIG. 1, a scorotron charger 2 is disposed so as to face a photoconductor drum 1 in which a CGL (charge generation layer) and a CTL (charge transport layer) are laminated on a conductive substrate made of aluminum or the like. It is set up. The photoconductor drum 1 is charged by the corona discharge from the scorotron charger 2. The photosensitive drum 1 is rotated in the arrow direction.

On the other hand, a document D is placed on the document table 8,
The document D is illuminated by the exposure lamp 9. Original exposure A, which is reflected light from original D, is applied to photoconductor drum 1 to form an electrostatic latent image. Toner is supplied to the electrostatic latent image from the developing device 3, and a toner image is formed on the photosensitive drum 1. The transfer member 4 is conveyed to the transfer / separation unit in synchronization with the toner image on the photosensitive drum 1, and the transfer / separation charger 5
Thus, the toner on the photosensitive drum 1 is transferred and separated. After that, the toner on the photosensitive drum 1 is scraped off by the cleaning blade 6 that cleans the toner that remains on the photosensitive drum 1 without being transferred.
The upper residual potential is eliminated by the pre-exposure device B, and the copying cycle around the photoconductor is completed.

The cleaning blade 6 forms a part of the cleaner unit C, and the film thickness meter 7 for measuring the film thickness of the organic photoconductor layer of the photoconductor drum 1 is the cleaner unit C.
Is disposed below. The film thickness meter 7 is moved along a generatrix direction of the photosensitive drum 1 by a drive gear and a support shaft (not shown) so that the photosensitive material coating area can be scanned all over. The film thickness meter 7 is preferably a non-contact type because it does not damage the surface of the photoconductor, and for example, a film thickness meter using a photosensor is preferable.

Inside the photosensitive drum 1, a heating element W whose temperature can be switched and a thermistor (not shown) are arranged so as not to hinder the rotation of the photosensitive drum 1, and when the film is scraped, the thermistor is exposed to light. The temperature of the body drum 1 is detected, and the heating element W is turned on / off according to the film thickness and the environmental temperature.

Since the photosensitive drum 1 has the temperature characteristic as shown in FIG. 2, the temperature characteristic of the photosensitive drum is previously obtained. As is clear from FIG. 2, as the temperature becomes higher, the potential contrast becomes wider and the white background (light portion) potential VL decreases, so that the effect of increasing the temperature of the photosensitive drum is clear. is there. The symbol VD indicates a black background (dark portion) potential.

By examining the temperature characteristics of the photosensitive drum in this way and obtaining the temperature (for example, 28 ° C.) at which the potential contrast is wide and the white background potential decreases,
By adopting a configuration of heating or cooling the photosensitive drum, it is possible to reduce the background fog based on the cumulative number of copies.

Next, the film thickness and temperature control will be specifically described. Here, taking a copying machine as an example, it is assumed that the potential of the white background portion increases by 20 V when the photoconductor drum of the copying machine is shaved by 2 μm with respect to the initial photosensitive layer thickness.

Then, when the copying operation is repeatedly performed and the abrasion amount of the photosensitive layer film thickness becomes 2 μm, the potential of the white background portion increases by 20 V, and the background fog on the white background portion becomes prominent in the output image. When the film thickness meter 7 detects that the film thickness is reduced by 2 μm, the thermistor detects the temperature of the photosensitive drum 1, and when the temperature is lower than 30 ° C., the heating element W is caused to generate heat and the photosensitive drum 1 is heated. Maintain the temperature of 30 ° C.

The photosensitive drum 1 maintained at 30 ° C. tends to have a potential due to the photosensitive member temperature characteristics (FIG. 2) and has apparently improved sensitivity, so that the initial state (a state in which no film scraping occurs). ), The white background potential drops even with the same exposure amount. Therefore, the background fog on the white background does not occur. When the temperature of the photosensitive drum 1 is 30 ° C. or higher, the heating element W does not generate heat.

When the film thickness meter 7 detects that the thickness of the photosensitive layer is reduced by 4 μm with respect to the initial photosensitive layer thickness and the background fog starts to stand out again by repeating the copying operation, the thermistor is used. The temperature of the photoconductor drum 1 is detected, and when the detected temperature is less than 45 ° C., the set temperature of the heating element W is switched to the 45 ° C. setting, and the temperature of the photoconductor drum 1 is heated to 45 ° C. By always maintaining the temperature of the photoconductor drum 1 at 45 ° C., the potential tends to be applied due to the temperature characteristic of the photoconductor drum 1 and the potential of the white background portion decreases, so that a good image can be always obtained.

In this embodiment, the photosensitive member having the temperature characteristic that the potential contrast becomes wider and the white background portion potential decreases as the temperature becomes higher, but the photosensitive member having the opposite characteristic is used. In the above, the photosensitive member may be cooled by using a cooling means, for example, a fan, instead of the heating element.

Further, although the above embodiments describe the copying machine using the organic photoconductor, the present invention is not limited to this, and the present invention can be applied to other types of photoconductors having temperature characteristics. Of course.

Further, in the present embodiment, the film thickness meter is used as a means for detecting the characteristic change of the photosensitive member due to the film thickness reduction of the photosensitive member photosensitive layer. The film scraping may be estimated.

[0024]

As described above, according to the present invention,
In an image forming apparatus including an image carrier, a charging unit that uniformly charges the surface of the image carrier, and an image forming unit that forms an image on the image carrier charged by the charging unit, Characteristic change detection means for detecting the characteristic change of the image carrier, based on the detection result by the characteristic change detection means,
The image carrier temperature control means for controlling the temperature of the image carrier is provided, and the temperature of the image carrier is controlled by the image carrier temperature control means based on the detection result of the characteristic change detecting means. It is possible to compensate for characteristic changes due to changes in the photosensitive layer thickness of the body (photoreceptor drum), and obtain appropriate image quality.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the temperature of the photoconductor and the surface potential of the photoconductor.

[Explanation of symbols]

 A document exposure W heating element (image carrier temperature control means) 1 photoconductor drum (image carrier) 2 scorotron charger (charging means) 6 cleaning blade 7 film thickness meter (characteristic change detecting means)

Claims (1)

[Claims] 1. An image bearing member, a charging unit for uniformly charging the surface of the image bearing member, and an image forming unit for forming an image on the image bearing member charged by the charging unit. In the image forming apparatus, a characteristic change detection unit that detects a characteristic change of the image carrier, and an image carrier temperature control unit that controls the temperature of the image carrier based on a detection result by the characteristic change detection unit are provided. An image forming apparatus characterized by the above.