JPH0324671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image density control method, and particularly to a method for controlling the density of a developed image in an electrophotographic device or an electrostatic recording device.

As is well known, in electrophotographic devices and electrostatic recording devices, an electrostatic latent image formed on an image carrier such as a photoreceptor or dielectric is developed with colored fine particles called toner. , the image is played. It is known that the density of the toner image reproduced at this time is influenced by many factors. The density of a toner image typically depends on the toner concentration in the developer. The developer normally used in this type of device is called a two-component developer, and is composed of two components: toner and carrier. The carrier triboelectrically charges the toner to a predetermined polarity.
It has the role of attracting this and transporting it to the development position. At the development position, only toner is attracted to the electrostatic latent image, and the electrostatic latent image is developed. Therefore, due to repeated development, the toner concentration in the developer decreases, and if development is also performed using the developer with such a decreased concentration, the developed toner image will be
Naturally, the concentration will be low. Therefore, a method has been developed to constantly appropriately control the toner concentration in the developer by measuring the density of the developed image, that is, the amount of toner adhering to the image area. An example of such a method is
Special Publication No. 43-16199, Publication No. 29448-1970, Publication No.
No. 49-36341, JP-A No. 50-22642, JP-A No. 50-
It is disclosed in Publication No. 125745, etc. In these conventional methods, a toner adhesion area for measurement is provided on the surface of the photoreceptor outside the normal copying area, and a predetermined charge is applied to this area to attract toner, which requires a large photoreceptor. There are drawbacks. In addition, an image on a standard density plate placed outside the normal copying area of the photoreceptor, for example on the back of the front edge of the document platen, is exposed to light in the same way as a normal original to form a latent image, and this is developed to form a latent image. Methods of measuring quantities are known. In this method, problems may occur when the toner concentration in the developer is controlled based on the measurement results. For example, if the amount of toner adhesion is small, replenishing new toner into the developer will not cause any problems if the cause is truly a decrease in the toner concentration in the developer, but it may cause charging or photoreceptor deterioration. If the cause is insufficient charging due to voltage fluctuation, overexposure due to voltage fluctuation, etc., the toner concentration may become too high.
This may cause problems such as scumming and toner scattering.

As described above, the density of the developed image, that is, the amount of toner adhesion, is typically brought about by a decrease in the toner concentration in the developer, but it is also affected by other factors such as the amount of charge, amount of exposure, characteristics of the photoreceptor, and the amount of toner adhered to the developing image. Various factors are involved, such as agent properties, developing bias amount, toner charge amount, development gap, and development time. Therefore,
If toner is replenished immediately because the amount of toner adhesion has decreased, the above-mentioned problems may occur. In addition, recently, when using a one-component developer consisting only of toner,
Since different types of toners may be mixed or additives may be used, it is necessary to control the density of the developed image, including controlling the component composition of the developer. ing.

Furthermore, a technique is known in which the image density is detected by developing an electrostatic latent image by keeping the photoreceptor at a constant potential or saturation potential (Japanese Patent Application Laid-Open No. 125745/1982). Furthermore, Japanese Patent Application Laid-open No. 56-29251 or No. 57-173865
The publication describes a technique for forming a latent image using a pattern.

However, these technologies do not apply a voltage with the same polarity as the charged polarity of the toner to the photoconductor to make the toner adhere to the latent image by setting the photoconductor to a saturated residual potential, and instead detect only the toner concentration without being affected by other conditions. It is not a technique to do so.

An object of the present invention is to provide a method for maintaining image density appropriately by detecting changes in image density mainly due to changes in development characteristics and controlling development characteristics based on the detection results. Development characteristics include all factors related to development, such as the toner concentration in the developer, the amount of charge on the toner, the amount of development bias, the development time, the development gap between the development sleeve and the photoreceptor, and the rotation speed of the development sleeve. This includes: The method according to the present invention includes the steps of: bringing the surface potential of the image carrier close to the saturated residual potential;
applying a voltage having the same polarity as the charged polarity of the toner to a developing electrode to cause the toner to adhere to the surface of the image carrier; detecting the amount of toner adhering on the surface of the image carrier; This includes controlling the toner concentration of the component-based developer. According to this invention, since toner is attached to the image carrier surface using the vicinity of the saturated residual potential where the image carrier surface potential is most stable, changes in image density due to changes in charging characteristics, exposure characteristics, etc. can be excluded. This makes it possible to quickly and accurately control image density by controlling only changes in development characteristics.

Hereinafter, the present invention will be explained with reference to the accompanying drawings. FIG. 1 shows an example of an electrophotographic apparatus to which the image density control method according to the present invention is applied. A charger 2, an exposure optical system 3, an erase lamp 4, a developing device 5, a light emitting element 6 for detecting the amount of toner adhering, and a light receiving element are arranged around the photoreceptor drum 1 along the counterclockwise rotation direction thereof. 7, transfer charger 8, fixing device 9, static elimination charger 10, static elimination lamp 11, cleaning device 1
2nd place is placed. When the surface of the photoreceptor drum 1 is first uniformly charged to a predetermined polarity by the charging charger 2, a light image of the original to be copied is irradiated thereon through the exposure optical system 3, and the charge on the photoreceptor is The charge is selectively erased, and an electrostatic latent image corresponding to the original image is formed there. This electrostatic latent image is developed by being supplied with toner from the developing device 5. The developing device 5 consists of toner and magnetic carrier. It includes a container 14 containing a two-component developer 13, and during the process of stirring by an impeller 15 and pumping up by a pumping roller 16, the toner is charged to a polarity opposite to that of the electrostatic latent image due to friction with the carrier. . After both are transferred from the pumping roller 16 to the developing roller 17, only the toner is attracted to the electrostatic latent image at a position close to the photoreceptor, and development is performed. The developer on the developing roller 17 after the development is scraped off from the developing roller 17 by the scraper 18 . In a normal copying cycle, the toner image obtained by development is transferred from the paper feed cassette 19 to the paper feed roller 20 and the transport roller 2.
1 and 22, and is charged by the transfer charger 8 with a polarity opposite to that of the toner, so that the transfer paper 2
Transferred to 3. After the transfer, the transfer paper 23 separated from the photoreceptor surface enters the fixing device 9 where the transferred toner image is fixed, and is discharged onto the tray 24. On the other hand, the photoreceptor after the transfer is subjected to removal of residual charges by a charger 10 and a lamp 11, and removal of residual toner by a cleaning device 12.

In order to perform image density control in this electrophotographic apparatus, first, the timing generation circuit 25
The concentration detection circuit 26 is turned on, and the switch 27 is switched to the contact 27b side. switch 27
A bias power supply 28 is connected to the contact 27a side of the photoreceptor 1, and a bias power supply 28 is connected to the developing roller 17, which also serves as a developing electrode, during a normal copying cycle, at a voltage a little higher than the background potential on the photoreceptor 1, and having the same polarity as this. A bias potential having a polarity different from that of the toner is applied. This suppresses background development on the photoreceptor and prevents background stains on copies.
On the other hand, a bias power supply 29 having a polarity opposite to that of the bias power supply 28, that is, the same polarity as the charging polarity of the toner, is connected to the contact 27b side of the switch 27.

As shown in Figure 2, the amount of toner adhering to the latent image is generally determined by the toner concentration (T, C), the development potential, that is, the latent image potential (V _S ) and the bias potential (V It is almost uniquely determined by the difference between _B ). Therefore, by controlling the toner density by detecting the toner adhesion amount at a constant development potential, constant development characteristics can be obtained. Therefore, in this invention, the photoreceptor 1
The surface potential of the film is brought close to the saturated residual potential, preferably close to zero V, and the development potential is obtained by the bias potential described above. In this embodiment, the potential of the photoreceptor is brought close to zero V by irradiating light from the erase lamp 4. As shown in FIG. 3, in a typical arsenic selenium photoreceptor, when an exposure amount of 2 μJ/cm ² or more is applied, the surface potential becomes almost zero. In a normal copying cycle, an image is created by applying light of approximately 1.5 μJ/cm ² or less to the area corresponding to the background of the photoreceptor, so some potential remains in the background, and this background The bias potential described above is utilized to suppress the development of the area. Therefore,
When the erase lamp 4 applies light of 2 μJ/cm ² or more, the surface potential of the photoreceptor becomes almost zero, which is the most stable potential that is not easily affected by variations in charging potential or exposure amount. Instead of such light irradiation by the erase lamp 4, white light exposure may be performed by the exposure optical system 3 for forming a latent image, and even if the charging by the charging charger 2 is turned off, the photoreceptor will be exposed in the same way. The surface potential can be brought close to zero V.

As described above, when the photoreceptor surface potential is approximately zero V and a bias potential of the same polarity as the toner is applied to the developing roller 17 from the power supply 29, the toner on the developing roller 17 in the developing container 14 is affected by the electric field. It adheres to the surface of the photoreceptor due to the force of . The bias potential at this time should be -100V or more if the toner is negatively charged, but it is -200 to -
A range between 400V is most effective in actual image density detection. The amount of toner adhered to the surface of the photoreceptor in this manner is detected by a detection device including a light emitting element 6 and a light receiving element 7. Light emitting element 6 such as a lamp or light emitting diode
The light from the photoreceptor is reflected by the surface of the photoreceptor, and the reflected light is received by a light receiving element 7 such as a photodiode. At this time, the change in the amount of light received due to toner adhesion is extracted as an electrical signal, and compared with the electrical signal indicating the reference amount of adhesion in the circuit 26.
The amount of toner adhesion is detected.

In order for the light-receiving element 7 to detect the amount of toner adhesion, the width of the toner adhesion area may be at most several millimeters to several tens of millimeters, and the length thereof may also be approximately the same. Adhesion of toner in areas more than necessary is
To avoid wasting the developer, in order to limit the area, its length is controlled, for example, by the time of applying a bias potential to the developing roller 17, and its width is controlled, for example, by using a perforated scraper on the developing roller 17. It is controlled so that the developer is brought into contact with the developer and the developer is removed from areas other than the required areas. In this limiting method using a scraper, the length of the toner adhering area can also be controlled by controlling the contact time with the developing roller. Further, as another method for controlling the width of the toner adhesion area, there is a method shown in FIGS. 4 and 5. The pumping roller 16 is made up of a rotating non-magnetic sleeve 30 and a plurality of magnets 31 that are statically housed therein, and the developing roller 17 is also made of
Similarly, it consists of a rotating non-magnetic sleeve 32 and a plurality of magnets 33 statically housed therein. The magnet 33a in the developing roller in the vicinity where both rollers are close to each other is divided into a plurality of parts in the axial direction, and the divided magnet 33a-1 corresponds to the part where the developer is desired to remain.
The other divided magnets 33a-2 and 33a-3 can be moved to another position Q apart from the regular position P. Therefore, when detecting toner adhesion, by moving the other divided magnets 33a-2 and 33a-3 to position Q, the divided magnet 33a-1
The developer only in the portion 2 is transferred from the pumping roller 16 to the developing roller 17.

In this way, when the amount of toner adhesion on the photoreceptor is detected, based on the detection result, for example, if the amount of toner adhesion is less than the standard adhesion amount, the toner replenishment control circuit 34 is driven and the developing device A certain amount of toner in a toner replenishing device 35 attached to the toner replenishing device 5 is replenished into the developer container 14 to increase the toner concentration in the developer 13. After doing this, detect the toner adhesion amount again, and if the toner adhesion amount has not increased even though toner has been replenished,
It can be determined that the cause is not a lack of toner in the developer, and other development characteristic factors such as toner charge amount, development bias amount, development time, development gap, development roller rotation speed, etc. can be checked and adjusted. do.

As described above, according to the present invention, since the toner is attached to the surface of the photoreceptor by utilizing the surface potential near zero V of the photoreceptor, which is less affected by charging characteristics and exposure characteristics, the change in toner adhesion amount is almost controlled by the development characteristics. This allows for faster and more accurate image density control.

Although this invention has been described above with reference to the specific embodiments shown in the drawings, this invention can be modified in various ways, and all modifications within the spirit of this invention as set forth in the claims are as follows: It is included in this invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an electrophotographic apparatus to which the image density control method according to the present invention is applied;
The figure shows the relationship between different toner concentrations TC, development potential, and amount of adhered toner, Figure 3 shows the light attenuation characteristics of a certain photoreceptor, and Figure 4 shows
FIG. 5 is a schematic view of the device for limiting the toner adhesion area in this invention, and is an explanatory view of the operation of FIG. 4. 1...Photosensitive drum, 2...Electrostatic charger,
3... Exposure optical system, 4... Erase lamp, 5...
...developing device, 6...light emitting element, 7...light receiving element,
17... Developing roller, 28... Bias power source for copying, 29... Bias power source for measuring toner adhesion amount, 35... Toner replenishing device.

Claims (1)

[Scope of Claims] 1. An image forming method comprising developing an electrostatic latent image formed on an image carrier with a two-component developer consisting of a carrier and toner on a developing electrode, comprising: applying a voltage having the same polarity as the charged polarity of the toner to the developing electrode to cause the toner to adhere to the surface of the image carrier; and adhering the toner to the surface of the image carrier. An image density control method comprising: detecting the amount of toner; and controlling the toner density of the two-component developer based on the detection result. 2. The image density control method according to claim 1, wherein the saturated residual potential is approximately zero V.