JPH08123112A - Image density controller - Google Patents

Abstract

PURPOSE: To provide an image density controller for controlling image density and capable of forming a high-quality image by preventing surface staining even when the density of the surface of a photoreceptor becomes abnormally high. CONSTITUTION: Based on a P sensor pattern on the back surface of an optical table, a developing pattern image for detecting recording density is formed on a photoreceptor drum, and the recording density of the developing pattern image and the surface density of the photoreceptor drum are detected by a P sensor 16. Based on the detected value, the supply amount of toner to a developing device 13 by a toner supply device 13a is controlled. When the surface density of the photoreceptor drum detected by the P sensor 16 exceeds a set reference value, the potential by the electrification of the photoreceptor drum by an electrifier 19 is changed, pattern density is made thick and the density potential Vsp of the developing pattern image is lowered, the toner supply amount by the toner supply device 13a is restrained, and the toner in the developing device 13 is sufficiently stirred, so that the toner insufficiently electrified is prevented from adhering to the photoreceptor drum and accurate toner concentration for forming an image is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control apparatus which is incorporated in an image forming apparatus and is used to control and set an image density at the time of image formation of the image forming apparatus to perform high quality image formation.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a photosensor is usually used to detect the density of a developing pattern for density detection formed on a photosensitive drum and the background density of the photosensitive drum. By controlling the toner supply based on the calculated ratio value, variations in the characteristics of the P sensor for each device are compensated for, and the toner density is controlled.

Various methods have been proposed for controlling the toner density in this case.
Japanese Patent Laid-Open No. 8084 proposes a toner density control device that supplies high-speed toner when the detected pattern density is low and supplies low-speed toner when the pattern density is high. Further, in Japanese Patent Application Laid-Open No. 2-108085, when the detected pattern density is lower than a set value, the deviation is cumulatively stored, and when the cumulative storage value is large, a large amount of toner is supplied, and when the cumulative storage value is small. A toner density control device that supplies a small amount of toner has been proposed.

[0004]

By the way, in image formation using a two-component developer, when there is a toner that is not sufficiently charged, the toner does not adhere to the carrier but directly adheres to the photosensitive drum. become. When such toner adhesion occurs, copy background contamination occurs, and when severe toner adhesion occurs, toner density control based on the ratio calculation value of the density of the development pattern for density detection and the background density of the photoconductor drum is performed. Becomes impossible. The toner concentration control device according to the above-mentioned proposal cannot cope with the occurrence of such severe toner adhesion, and in this case, the toner concentration cannot be controlled.

The present invention has been made in view of the present situation of the toner density control of this kind as described above, and an object thereof is to prevent the background stain even if the density of the background of the photoconductor is abnormally increased. Another object of the present invention is to provide an image density control device for controlling the image density capable of forming a high quality image.

[0006]

In order to achieve the above object, the invention according to claim 1 forms a latent image of a document image on a photoconductor, and develops the latent image by a developing device to develop the document image. An image density control device that is incorporated in an image forming apparatus that forms a toner image corresponding to, transfers the toner image onto a transfer paper, and forms a print image of the original image, and controls the density of the print image. A development pattern image forming means for forming a development pattern image for recording density detection; a toner supply means for supplying toner to the developing device; and a density sensor for detecting the recording density of the development pattern image and the background density of the photoconductor. A control unit that controls the amount of toner supplied by the toner supply unit based on the detection value of the density sensor, and the background density of the photoconductor detected by the density sensor is a preset reference value. By weight, it is characterized in that it has a changing means for changing the toner image forming process conditions to the photosensitive member.

Similarly, in order to achieve the above object, the invention according to claim 2 is characterized in that, in the invention according to claim 1, the change of the process condition is a change of a charging potential of the photoconductor. To do.

[0008]

According to the present invention, the development pattern image forming means forms a development pattern image for recording density detection, and the density sensor detects the recording density of the development pattern image and the background density of the photoconductor. Based on the obtained detection value of the density sensor, the amount of toner supplied by the toner supply unit that supplies toner to the developing device is controlled by the control unit. In this case, when the background density of the photoconductor detected by the density sensor exceeds a preset reference value, the changing means changes the process condition for forming a toner image on the photoconductor under the changed process condition. The stable image density control is performed, and the image forming apparatus forms a high quality image of the original image under the obtained image density condition.

According to a second aspect of the present invention, the development pattern image forming means forms a development pattern image for recording density detection, and the density sensor detects the recording density of the development pattern image and the background density of the photoconductor. Based on the obtained detection value of the density sensor, the amount of toner supplied by the toner supply unit that supplies toner to the developing device is controlled by the control unit. In this case, when the background density of the photoconductor detected by the density sensor exceeds a preset reference value, the changing unit changes the charging potential by the charger that charges the photoconductor, and the changed charging potential condition is satisfied. Under this condition, stable image density control is performed, and the image forming apparatus forms a high quality image of the original image under the obtained image density condition.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of a main part of the present embodiment, FIG. 2 is an explanatory diagram showing a configuration of an image forming apparatus to which the present embodiment is applied, and FIG. 3 is a main part configuration of a CPU part of the present embodiment. FIG. 4 is an explanatory diagram showing the configuration of the optical table portion of FIG. 2, and FIG. 5 is an explanatory diagram of the development pattern image formation of this embodiment.

An image forming apparatus incorporating this embodiment is
As shown in FIG. 2, an optical table 4 is provided on the upper surface of the housing C, and a contact glass 3 on which an original is placed is filled in the optical table 4, and inside the housing C, the contact glass 3 is placed. Immediately below 3 is a scanner 5 which irradiates a document placed on the contact glass 3 with light from a halogen lamp and captures reflected light from the document image through a plurality of mirrors and through lenses. The photosensitive drum 10 is disposed below the scanner 5.

As shown in FIGS. 1 and 2, the image of the original image captured by the scanner 5 is exposed on the photosensitive drum 10 on the peripheral surface of the photosensitive drum 10 to correspond to the original image. Exposure device 11 for forming a latent image, erase 12 for removing the charging potential of the non-image portion, developing device 13 for developing the latent image formed on photoconductor drum 10 into a toner image, photoconductor drum before transfer 10, a pre-transfer charge eliminating lamp 14 for lowering the surface potential of the photosensitive drum 10, a transfer device 15 for transferring the toner image on the photoconductor drum 10 onto a transfer sheet, a P sensor 16, a cleaning device 17 for removing residual toner, a charge eliminating lamp 18, and a photoconductor. A charger 19 for charging the drum 10 is arranged clockwise in this order.

Here, the P sensor 16 is the photosensitive drum 1
A light emitting element for irradiating light on the peripheral surface of 0 and a light receiving element for receiving reflected light from the peripheral surface, and the recording density of the development pattern image for recording density detection formed on the photosensitive drum 10,
It has a function of detecting the background density of the photoconductor drum 10. Further, the developing device 13 is provided with a toner supply device 13a for supplying toner.

By the way, as shown in FIG. 4, a P sensor pattern 25 is formed on the side portion of the back surface of the optical table 4, and as shown in FIG. 5, the scanner 5 optically detects the P sensor pattern 25. Then, the exposure device 11 exposes the image of the P pattern on the photosensitive drum 10, and the developing device 13 forms a development pattern image for detecting the recording density on the photosensitive drum 10. , The recording density of the developed pattern image and the background density of the photosensitive drum 10 are P
It is configured to be detected by the sensor 16.
In the lower part of the housing C, a paper feeding unit 2 that supplies the transfer paper to the position of the transfer charger 15 is provided.

On the other hand, a CPU 20 for controlling the entire operation is provided. The CPU 20 has a supply amount control means for controlling the supply amount of toner by the toner supply device 13a based on the detection value of the density sensor 16, and a density sensor. When the background density of the photoconductor drum 10 detected by 16 exceeds a preset reference value, the charging potential of the photoconductor drum 10 by the charger 19 is changed, thereby reducing the toner supply amount of the supply amount control means. Change means are provided.

Next, the operation of this embodiment having such a configuration will be described with reference to the drawings. FIG. 6 is an explanatory diagram of the toner density of this embodiment, FIG. 7 is an explanatory diagram of the potential of the surface of the photoconductor of this embodiment, and FIG. 8 is a flow chart showing an operation of changing the charging potential of the photoconductor of this embodiment.

The control of the image density according to the present embodiment is executed every time image formation is performed by the image forming apparatus 10 times. First, in step S1 of FIG. 8, the scanner 5 irradiates the P sensor pattern 25 of the optical table 4 with light, the reflected light from the P sensor pattern 25 is taken in, and the P sensor pattern 25 of the P sensor pattern 25 is exposed by the exposure unit 11. The light image is exposed on the photosensitive drum 10, and the P sensor pattern 2
A latent image 5 is formed on the photosensitive drum 10. in this case,
The charging potential Vp of the photosensitive drum 10 is charged by the charger 19.
Is set to, for example, −520V. The latent image of the P sensor pattern 25 thus formed is visualized as a toner image by the developing device 13 under a predetermined developing bias voltage, and the developing pattern image for recording density detection is formed on the photosensitive drum 10. Is formed.

Next, in step S2, the P sensor 16 detects the density potential Vsp of the developed pattern image and the density potential Vsg of the photoconductor background, and the obtained detection data is input to the CPU 20. In the CPU 20, first, the gain of the P sensor 16 is adjusted based on the obtained detection data.

When the gain of the P sensor 16 is adjusted by the CPU 20 so that the density potential Vsg of the photoconductor background detected by the P sensor 16 becomes 4V, as shown in FIG. , The density potential Vsp of the developed pattern image detected by the P sensor 16 becomes almost 0V. In this case, when the toner density decreases, the density potential Vsp of the development pattern image detected by the P sensor 16 increases as shown in FIG. 7B, and when the toner density increases, as shown in FIG. In addition, the density potential Vsp of the development pattern image detected by the P sensor 16 decreases.

In this embodiment, in this case, the supply amount control means of the CPU 20 is activated to activate the density potential Vsp of the development pattern image.
The ratio Vsp / Vsg between the density potential Vsg of the toner and the background of the photoconductor is calculated, and the toner feeder 1 is operated according to the calculated ratio Vsp / Vsg.
3a, the supply operation and the toner end determination are performed,
Accurate toner supply operation control to the developing device 13 is performed.

By the way, in the present embodiment, in step S3, the P sensor 16 which normally has a voltage of 3.5V to 4.0V.
The density potential Vsg of the photoconductor background detected by
When it is determined that the voltage is lower than V, it is determined by the CPU 20 that excessive toner is attached to the photoconductor drum 10, and the changing unit of the CPU 20 is activated, and step S
4, the charging potential of the photoconductor drum 10 by the charger 19 is changed from -520V to -560V, whereby the toner supply device 13a controlled by the supply amount control means.
The toner supply amount is controlled so as to decrease. If it is determined in step S3 that the density potential Vsg of the photoconductor background detected by the P sensor 16 has not dropped to 3.5 V or less, the process proceeds to step S5 and the charging potential of the photosensitive drum 10 by the charger 19 is reached. Is held at -520V.

In this case, since the pattern density is increased as shown in FIG. 7 by changing the charging potential of the photoconductor drum 10 by the changing means of the CPU 20, the density potential Vsp of the developed pattern image is lowered and the ratio calculation value Vsp. / Vsg is reduced, and the toner supply amount by the toner supply device 13a is suppressed. For this reason, the toner in the developing device 13 is sufficiently agitated, and the insufficiently charged toner is prevented from adhering to the photosensitive drum 10.

As described above, according to this embodiment, when the density potential Vsg of the background of the photoconductor detected by the P sensor 16 becomes lower than the preset reference value, it is determined that the toner is excessively attached to the photoconductor drum 10. Then, the charging potential of the photoconductor drum 10 is changed to increase the pattern density and reduce the density potential Vsp of the development pattern image. Therefore, the toner supply amount by the toner supply device 13a is suppressed, and the developing device 1
The toner in 3 is sufficiently agitated, and the insufficiently charged toner is prevented from adhering to the photosensitive drum 10. Therefore, copy background stains and cleaning device 1
The abrasion of the cleaning blade 7 is prevented, wasteful consumption of toner is eliminated, and an appropriate toner concentration for image formation is set. Under this toner concentration condition, a high quality image formation is stably performed by the image forming apparatus. It becomes possible to do.

[0024]

According to the first aspect of the invention, the recording density of the development pattern image for detecting the recording density and the background density of the photoconductor are detected, and the toner supply amount to the developing device is determined based on the detected values. When the background density of the photoconductor that is controlled and detected by the density sensor exceeds a preset reference value, the process conditions for forming a toner image on the photoconductor are changed, and the image density control is performed under the changed process conditions. Therefore, the adhesion of the low-charged toner to the photoconductor is prevented, the photoconductor is prevented from being damaged, and the proper image density condition for stable toner supply is set. It is possible to allow the forming apparatus to perform high quality image formation. According to the second aspect of the invention, the recording density of the development pattern image for recording density detection and the background density of the photoconductor are detected, and the toner supply amount to the developing device is controlled based on the detected values, and the density sensor When the background density of the photoconductor detected by exceeds the preset reference value, the charging potential of the photoconductor is changed, and the image density control is performed under the changed charging potential. Adhesion to toner is prevented, damage to the photoconductor is prevented, and stable toner supply is performed. An appropriate image density condition is set, and a high quality image is formed on the image forming apparatus under the image density condition. It is possible to make it.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an image forming apparatus to which the embodiment is applied.

FIG. 3 is a block diagram showing a main configuration of a CPU portion of the embodiment.

FIG. 4 is an explanatory diagram showing a configuration of an optical table portion of FIG.

FIG. 5 is an explanatory diagram of development pattern image formation in the example.

FIG. 6 is an explanatory diagram of toner density of the example.

FIG. 7 is an explanatory diagram of a potential on the surface of the photoconductor of the example.

FIG. 8 is a flowchart showing an operation of changing the charging potential of the photoconductor of the embodiment.

[Explanation of symbols]

 ■ 1 image forming unit 2 paper feeding unit 3 contact glass 4 optical table 5 scanner 10 photoconductor drum 11 exposure unit 13 developing unit 13a toner supply unit 15 transfer unit 16 P sensor 19 charging unit 20 CPU 25 P sensor pattern

Claims (2)

[Claims] 1. A latent image of a document image is formed on a photoconductor, the latent image is developed by a developing device to form a toner image corresponding to the document image, and the toner image is transferred to a transfer paper, A development pattern image forming means incorporated in an image forming apparatus for forming a print image of the original image, for forming a development pattern image for recording density detection in an image density control device for controlling the density of the print image; Toner supply means for supplying toner to the container, a density sensor for detecting the recording density of the development pattern image and the background density of the photoconductor, and the toner supply amount by the toner supply means based on the detection value of the density sensor. When the background density of the photoconductor detected by the control unit and the density sensor exceeds a preset reference value, the process condition for forming a toner image on the photoconductor is changed. Image density control apparatus characterized by having a change unit that. 2. The image density control device according to claim 1, wherein the change of the process condition is a change of a charging potential of the photoconductor.