JPH0387867A - Developer concentration control method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer concentration control device for keeping the developing effect of an electrophotographic developer containing toner and carrier constant.

[Conventional technology]

Generally, a developing device in a dry type electrophotographic or electrostatic copying machine uses a two-component developer consisting of a carrier and a toner.

The weight mixing ratio of toner and carrier in this developer is an extremely important factor for determining copy density. Particularly in so-called Victorian full-color copying apparatuses that produce full-color images by overlapping a plurality of toners using a plurality of developing devices, this is important in ensuring the reproducibility of the color tone.

When the ratio of toner to carrier (hereinafter abbreviated as toner concentration) is small, that is, when the toner concentration of the developer decreases, the image density becomes low. or,
On the other hand, if the toner ratio becomes too large, the image density becomes too high and fog increases.

Therefore, in order to continuously obtain images with desirable color tones, it is necessary to set the toner concentration of the developer at an appropriate level and to maintain this level constant during development.

For this purpose, a detection means for detecting the toner concentration of the developer and a toner replenishing device for replenishing only toner according to the signal are required.

Conventionally, the following methods have been used to detect the toner concentration of a developer.

(1) A method of detecting toner concentration by utilizing the fact that the optical reflectance of a mixture of toner and carrier depends on toner concentration. ...Optical developer reflection detection (2) A method of detecting toner concentration by utilizing the fact that the magnetic permeability of a mixture of toner and carrier depends on toner concentration.
...Magnetic detection (3) A method of detecting toner concentration by providing an area to be developed on a trial basis and utilizing the fact that the optical reflectance of the developed area depends on the toner concentration.

...Optical Toner Reflection Detection Regarding (1) to (3) above, regarding (1), it is necessary to use light of a wavelength in which the reflectance of the toner and the carrier are significantly different. Fe.

The light reflectance of a carrier such as ferrite is such that it absorbs at all wavelengths, and it is necessary to select light at a wavelength that has high reflection characteristics from the colorant or resin component of the toner. However, in toners using carbon black, which is widely used as a colorant for two-component black toners, carbon black absorbs at all wavelengths, making detection using this method impossible. Furthermore, since the developer comes into contact with the detection optical system, contamination of the optical system has been a major problem.

Regarding (2), the packing density of the carrier and toner can be mentioned as a factor that changes the magnetic permeability. This packing density also depends on the toner concentration, but the rest time of the developer in the developer container, the stirring time, and the toner It is extremely difficult to distinguish between true dependence on toner concentration and the fact that it depends greatly on the charge amount of the carrier and other factors, and there are many fluctuation factors.

Therefore, possibility (3) remains as a toner concentration detection method for a two-component black toner using carbon black as a colorant.

However, even with method (3), the toner density is not necessarily kept constant because the developing ability of the developer is detected in order to keep the reflection density of the developed image constant. Therefore,
Even if the developing ability drops due to so-called carrier deterioration, where the carrier is coated with toner resin, toner needs to be replenished, resulting in high toner concentration, causing scattering, fogging, and eventually the developer overflowing from the container. Occur.

There were also problems with stability, such as an inability to obtain accurate signals when the sensor surface and light source were contaminated with toner or the like.

[Means for solving problems]

According to the present invention, light reflection signals from the surface of the image carrier include a light reflection signal from a toner-attached area where a standard latent image has been developed, and a light reflection signal from a fogged area where a latent image at the same level as the white background area has been developed. By controlling the toner replenishing means based on these three signals: the signal and the light reflection signal of the image carrier not subjected to the development action, it has become possible to control the toner density without overflowing the developer.

〔Example〕

Next, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

FIG. 1 schematically shows a full-color electrophotographic image forming apparatus according to an embodiment of the present invention.

In this embodiment, a latent image bearing member that is rotatably supported on a shaft and rotates in the direction of the arrow, that is, a photosensitive drum l having a photosensitive layer such as OPC, Se, A-8i, etc., is provided.
is uniformly charged using a negative charger 2. Then,
The photosensitive drum 1 is irradiated with a color-separated optical image or a corresponding optical image 3 to form an electrostatic latent image on the photosensitive drum 1.

As the irradiation means, for example, an exposure system such as a laser beam exposure means 4 is used. The potential of the electrostatic latent image formed on the photosensitive drum is measured by an electrometer 20 to determine the primary charge amount, laser exposure amount, and development bias.

Next, the electrostatic latent image on the photosensitive drum l is developed at a developing section, that is, a developing position 5, by a developing unit 6 mounted on a movable table 10 and conveyed in a tangential direction with respect to the photosensitive drum 1. Ru. In this embodiment, the developing unit 6 includes a magenta developing unit 6M, a cyan developing unit 6C, a yellow developing unit 6Y, and a black developing unit 6B.

As a developer, a high resistance carrier and colored powder (toner) are used.
using a mixture of Examples of colored powder include magenta,
Cyan, yellow and black colored resin powders are used.

At the development position, the image on the photosensitive drum visualized by being supplied with developer by each development unit is transferred to a transfer material supplied onto the transfer drum 12 from a transfer material cassette 18 by a transfer charger 13. transcribed.

The developer remaining on the photosensitive drum 1 without being transferred is removed from the photosensitive drum 1 by the cleaning device 15.

Following the completion of the development operation of the first color latent image by the first magenta development unit 6M, the movable stage 1 of the development device
0 moves, and the second cyan developing unit 6C moves to the developing position. Then, the second latent image is developed. The visible image is transferred to the transfer material on the transfer drum in alignment with the first toner image.

The above-described development and transfer are performed in each development unit, and multiple transfers are performed onto the transfer material on the transfer drum, thereby obtaining a color image.

The multiple-transferred transfer material is separated from the transfer drum 12 by a separation charger 14 and conveyed onto a conveyor belt 16.
The image is guided to the fixing device 17 and fixed.

In order to apply the present invention to the image recording apparatus described above, a detection element 21 consisting of a light source and a light receiving element that receives the reflected light is arranged downstream of the developing section 5 around the photoreceptor 1. A position like the detection element 22 between the transfer and the cleaner is preferable because there is less dirt on the detection surface.

The configuration of the sensing element is shown in a sectional view in FIG.

A light-emitting element 51 disposed inside the detection element housing 5, for example, a double-sided emitting LED with a wavelength of 960 nm (preferably a light-condensing LED to reduce the detection surface), an optically transparent window 52, and the light-emitting element 51 A light-receiving element 53 receives light A reflected from the photoreceptor with and without toner and outputs an electric signal corresponding to the amount of received light, and a light-emitting element 53 that directly emits light emitted from the light-emitting element. It consists of a light receiving element 54 that receives the light and monitors the amount of light received. Here, the wavelength of the light from the light emitting element and the spectral sensitivity of the sensor are selected differently depending on whether the reflected light of the toner material is detected or the light absorption of the toner material is detected. In the method of detecting the light absorption of the toner material, a wavelength of light is used that has a small absorption by the photoreceptor and a large absorption by the toner material.

The signals captured in the initial setting state of the device (i.e., reference signals) are v, , v2, v3, v4', and the signals (i.e., measurement signals) at the time when the device is in operation are vI.
When r V 2t V 3+ v4, the signal from the toner image plane to be tested is corrected in accordance with the deterioration state of the light emitting element and the dirt state of the detection window, and is compared with the reference density signal. Based on this, the operation time of the toner replenishment switch is determined. V+'/V+ is a correction for light source (light emitting element) deterioration,
V 4 ′/V 4 is a dirt correction on the detection surface (window 52) of the sensor. (The subscript 1 indicates the output signal of the light-receiving element 54, and the subscript 2.3.4 indicates the output signal of the light-receiving element 53.The subscript 2 indicates that a reference latent image is formed at substantially the same level as the white background part of the image. A signal resulting from the reflected light from the white surface to be tested which has been subjected to the development action, that is, a signal corresponding to the fog density, and the subscript 3 indicates the toner image surface to be tested which has undergone the development action by forming a reference latent image at the reference potential level. Signal due to reflected light from, subscript 4
indicates a signal due to reflected light from the surface to be tested that is not subjected to the development action. ) The value of Δ■ and the toner replenishment operation time are determined as shown in FIG. When ΔV is positive, the toner concentration is high, and when ΔV is negative, it is low. Only when the toner concentration is low, toner replenishment is performed according to the magnitude of 1ΔV.

That is, the control circuit 55 consisting of a microcomputer performs the calculations based on the respective signals and closes the switch 64 that supplies power to the motor 63 from the power source 65 (FIG. 4) for a time corresponding to the value of 1Δv1. The motor 63 is energized.

The motor 63 uses its bias to rotate a screw 62 that supplies toner from a hopper 61 containing toner to the developing unit 6, thereby supplying the required amount of toner to the developing unit 6.

In this method of toner concentration control, since the toner concentration of the developer is not directly determined, it is preferable to detect whether replenishment is normal.

The control circuit 55 uses the above-mentioned signals to determine whether the state is one of (1) to (4).

Lamp (light emitting element) error (lamp burnout, lamp deterioration) ■■3 objects ■4ξv2 Development error (not developed) ■ΔV＜Oor ΔV＞0 ATR error (extremely different) Developing material deterioration error (abnormal fogging) In particular, regarding (2), when we examined the state of deterioration of a developer that uses toner and carrier, we found that deterioration due to spent carrier is accompanied by an increase in background fog as Dmax decreases. We performed deterioration detection using this method. This detection made it possible to prevent agent overflow during deterioration.

Further, by placing the latent image control electrometer 20 and the detection element at substantially the same position in the longitudinal direction of the drum, it is possible to check the state of formation of the detection latent image. This check allows you to check the cause of the latent image needle.

In the case of toner reflection detection, V4<V2<V3, and Δ
When ■ is positive, the toner concentration is low, and when it is negative, it is high. The relationship between the toner replenishment amount and ΔV is opposite in sign to that of absorption detection. Also, you can issue the equipment deterioration error mentioned above.

In other words, when the control circuit 55 is in the states (1) to (2), the switch 64 shown in FIG. The operation is prohibited, and a display means 66 such as a lamp is activated to inform the operator that the conditions ① to ③ have occurred.

The timing of capturing these signals will be explained.

In order to apply the present invention to the recording apparatus of this embodiment, the timing of capturing the signal is important.

This is particularly important in a method in which the detection element is set in the longitudinal direction of the photoreceptor, and a detection area is set before or after the area in which an image is formed in the image-formable area of the photoreceptor in the direction of movement of the photoreceptor. Although it is possible to adopt a method in which a sensor is provided outside the conveyance area of the transfer material in the longitudinal direction, both the developing area and the drum area must be made longer in the longitudinal direction, which increases the size of the apparatus.

FIG. 5 shows a sequence in which the above-mentioned detection is performed in the image-formable circumferential area of the drum. A reference image that obtains the V3 signal is formed on the area of the drum circumference facing the transfer drum connecting part, and the timing is set to prevent toner from adhering to the transfer drum from the photosensitive drum in the transfer part, thereby preventing dirt on the transfer drum. is prevented. Further, the developing action is performed by biasing the developing device from its non-active position in the developing area to its working position close to the photoreceptor, or by recovering the porcelain brush from its cutting state. Switching the developing bias was insufficient to generate background fogging areas on the drum surface and reflective areas on the drum surface. In FIG. 5, so-called reversal development is performed in which toner is attached to the exposed portion of the photoreceptor.

Regarding the method of forming an electrostatic latent image at a reference level to which toner is attached, it is desirable to set a latent image potential having the greatest toner concentration dependence of the signal. On the other hand, since all the toner for this detection is cleaned by a cleaner,
In order to reduce the load on the cleaner, the amount of adhesion must be reduced. In addition, as the amount of adhesion increased, the amount of particles scattered inside the aircraft also increased. Figure 6 shows the toner adhesion amount, sensor sensitivity,
A graph showing the relationship between the amount of signal change when the unit toner concentration changes is shown. It is desirable to select a setting value with high sensor sensitivity and low scattering. As for scattering, it is possible to reduce the degree of scattering by forming halftone dots on the latent image pattern and performing edge development. In particular, in a system using a laser exposure system, when the ratio of laser lighting was changed and the amount of toner adhesion and the extent of its scattering were examined, the extent was greatly improved.

〔Effect of the invention〕

As explained above, by performing toner density detection control according to the present invention, detection without the following problems has become possible.

■ Correction of light source deterioration ■ Correction of dirt on the detection element ■ Detection of developer deterioration In this embodiment, the present invention is described for the case where it is applied to a full-color copying machine, in which it is particularly effective, but the present invention is also effective in ordinary black-and-white copying machines. It is.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a transfer type recording device embodying the present invention, Fig. 2 is a graph of signals and toner replenishment operation time, Fig. 3 is a sectional view of the detection element section, and Fig. 4 is an explanation of the toner replenishment device. Figure 5 is a sequence diagram, and Figure 6 is a graph of toner adhesion amount and sensor sensitivity. l is a photoreceptor, 6M, 6C, 6Y, 6B are developing units,
21 and 22 are detection elements, 55 is a control circuit, 61 is a hopper, and 62 is a toner feed screw. Toki 3: Seki-Kai-Uu-zu Moan-Henten--J-Ichigami Kazuichi

Claims (1)

[Scope of Claims] After forming a reference electrostatic latent image on an image carrier and developing the reference image to form a toner image, detecting the amount of toner adhering to the toner image on the image carrier; forming an electrostatic latent image equivalent to the white background portion of the image area on an image bearing member, developing it, and then detecting the amount of toner adhering to the image bearing member; optical density of the image bearing member not subjected to development action; A developer concentration control method, comprising: detecting the following: and controlling a toner replenishing means based on the three detection signals.