JPH0836297A - Developing device - Google Patents

Abstract

PURPOSE:To detect toner concentration with higher accuracy without being affected by the quantitative change of developer in a developing tank and to maintain a copied image in a good state. CONSTITUTION:The developer is successively replenished from a developer replenishing part to the developing tank 16 in accordance with the detection output of a toner concentration sensor 34 installed in the developing tank 16, while the developer in the developing tank 16 is discharged from a developer discharging part 23 formed in the developing tank 16. The toner concentration sensor 34 is installed on the base of developing tank 16 under an agitator 19. The agitator 19 is constituted of a 1st agitating part 19a for carrying the developer near to the installation position of the toner concentration sensor 34 and a 2nd agitating part 19b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention contains a two-component developer composed of a toner and a carrier and visualizes the electrostatic latent image on the surface of the photoconductor in an electrophotographic apparatus such as a copying machine. The present invention relates to a developing device that supplies the surface.

[0002]

2. Description of the Related Art For example, in a dry copying machine or the like, a developing device for visualizing (developing) an electrostatic latent image on the surface of a photoconductor with a two-component developer composed of a carrier and a toner is often used. In such a developing device, the toner is consumed by the developing operation, while the carrier remains in the developing device without being consumed. Therefore, the carrier agitated with the toner in the developing device increases as the agitation frequency increases.
Peeling of the resin coat layer on the surface and adhesion of the toner to the surface may cause deterioration, which causes the charging performance of the developer to gradually decrease.

Therefore, in addition to the replenishment of the toner consumed by the developing operation, a device is also provided in which the carrier is replenished little by little in the developing device so that the deterioration of the charging performance can be suppressed. It is disclosed in the official gazette. In this publication, in a developing device that develops with a developer composed of a carrier and toner, a developer discharge opening for discharging the developer is provided at a predetermined position of the developing device, and a new developer supply means is provided by copying the developer. By supplying the developer to the developing device and discharging the developer that has become excessive due to the supply of the developer from the developer discharge opening, deterioration of the developer is prevented, and a stable developer is always provided. A so-called successive developer exchange type developing device for forming an image is disclosed. By repeating such replenishment and discharge successively, the deteriorated developer in the developing tank is replaced by the newly supplied toner and carrier, thereby maintaining the charging performance and deteriorating the copy image quality. It is designed to hold back.

Further, a toner concentration sensor for detecting the toner concentration is provided in the developing tank, and toner is supplied to the developing tank by the output of the toner concentration sensor.
The toner density in the developing tank is kept constant.
Further, as the toner concentration sensor, a magnetic permeability sensor that comes into contact with a carrier in the developer and detects the magnetic permeability thereof is used. In this case, the ratio of the toner to the carrier is detected from the detected magnetic permeability. Whether the toner is replenished or not is controlled by increasing or decreasing the toner ratio, and the toner density in the developing tank is kept constant. It is designed to keep

[0005]

However, since the magnetic permeability detected by the magnetic permeability sensor is determined by the amount of carriers contained in a certain volume, even if the mixing ratio of the toner and the carrier is constant, the development is performed. If the density of the agent changes, the magnetic permeability changes. Therefore, if the developer amount in the developer tank changes due to the inclination of the developing device and the developer density changes, the carrier amount in contact with the magnetic permeability sensor changes, and the toner concentration of the developer is erroneously determined. There is a risk that

For example, when the developing device is tilted due to the movement of a copying machine and the amount of developer in the developing tank is decreased, the accurate toner ratio cannot be detected due to the decrease in the amount of carrier contacting the magnetic permeability sensor. However, there arises a problem that the toner ratio is lowered and the image density is lowered.

On the other hand, when the developing device is inclined due to the movement of the copying machine and the amount of the developer in the developing tank is increased, the accurate toner ratio cannot be detected due to the increase of the amount of carrier in contact with the magnetic permeability sensor. However, there is a problem that the amount of toner becomes excessive with respect to an appropriate amount, which adversely affects the image quality, and the copy image quality deteriorates.

The present invention has been made in view of the above problems, and an object thereof is to detect a detection level of a toner concentration sensor without being affected by a change in the amount of developer in a developing tank due to a tilt of a developing device. It is an object of the present invention to provide a developing device capable of keeping a constant toner concentration in a developing tank and keeping a copied image excellent.

[0009]

A developing device according to claim 1 is
A developing tank for accommodating the developer composed of toner and carrier is provided rotatably with stirring means for stirring and conveying the developer in the developing tank and a developing roller for supplying the developer to the photosensitive member. In accordance with the detection output of the toner concentration detecting means provided in the developing tank, the developer is sequentially replenished from the developer replenishing section to the developing tank, while the developer in the developing tank is developed in the developing tank. In the developing device discharged from the developer discharge opening, the toner concentration detecting means is provided on the bottom surface of the developing tank, and the means for stirring and transporting the developer is located near the disposition position of the toner concentration detecting means. It is characterized in that it is formed so as to be collectively transported.

According to the second aspect of the present invention, the developing means for agitating the developer in the developing tank and conveying the developer in the developing tank for accommodating the developer composed of toner and carrier is used as a photosensitive member. Each developing roller to be supplied is rotatably provided, and the developer is sequentially replenished from the developer replenishing section to the developing tank in accordance with the detection output of the toner concentration detecting means provided in the developing tank. In a developing device in which the developer inside is discharged from a developer discharge opening formed in the developing tank, the toner concentration detecting means is provided on the bottom surface of the developing tank, and the toner concentration detecting means is provided in the vicinity of the disposition position. However, it is characterized in that it is formed lower than the other bottom surface of the developing tank.

Further, the developing device of claim 3 is the same as that of claim 2.
The developing device described above is characterized in that an overflow member is provided near the position where the toner concentration detecting means is provided in the developing tank so as to prevent the developer conveyed by the stirring means from overflowing.

[0012]

According to the first aspect of the invention, the stirring means is formed so as to convey the developer to the vicinity of the position where the toner concentration detecting means is arranged, so that the developing is forcibly performed near the toner concentration detecting means. The agent can be delivered. As a result, the amount of developer in the vicinity of the toner concentration detecting means can be made larger than the amount of developer in other developing tanks. Therefore, always
Since the stable detection signal can be obtained by the toner concentration detecting means, the toner concentration can be detected more accurately without being affected by the change in the developer amount in the developing tank. Can be maintained at.

Further, according to the second aspect of the invention, since the vicinity of the position where the toner concentration detecting means is provided in the developing tank is formed lower than the other bottom surface of the developing tank, the developer in the developing tank is formed. Are naturally conveyed in the vicinity of the toner concentration detecting means. As a result, the amount of developer in the vicinity of the toner concentration detecting means can be made larger than the amount of developer in other developing tanks. Therefore, it is possible to always obtain a stable detection signal by the toner concentration detecting means, and it is possible to detect a more accurate toner concentration without being affected by the change in the developer amount in the developing tank. The copied image can be maintained well.

Further, the stirring means need not be formed so that the developer is collectively conveyed in the vicinity of the position where the toner concentration detecting means is disposed, and the existing stirring means can be used as it is. Therefore, the manufacturing of the developing device can be simplified, and the manufacturing cost can be reduced.

Further, according to the third aspect of the present invention, an overflow member is provided near the position where the toner concentration detecting means is provided in the developing tank so as to stop and overflow the developer conveyed by the stirring means. Thus, the developer can be retained near the position where the toner concentration detecting means is provided. As a result, even if the amount of developer in the developing tank changes, it is possible to suppress the change in the amount of developer in the vicinity of the position where the toner concentration detecting means is provided. Therefore, it is possible to always obtain a stable detection signal by the toner concentration detecting means, and it is possible to detect a more accurate toner concentration without being affected by the change in the developer amount in the developing tank. The copied image can be maintained well.

[0016]

【Example】

[Embodiment 1] An embodiment of the present invention will be described with reference to FIGS.
The explanation is based on the following.

As shown in FIG. 4, the copying machine constructed by applying the present invention is provided with an original placing table 1 on the upper surface thereof, and an exposure optical system 2 is provided under the original placing table 1. ing.
The exposure optical system 2 includes a light source lamp 3 for scanning an original (not shown) placed on the original placing table 1 while irradiating the original, and a plurality of reflecting mirrors for guiding the reflected light from the original to the photoconductor 4. 5
..., and the lens unit 6 arranged in the optical path of the reflected light
Made of.

On the outer periphery of the photoconductor 4, a charger 7 for charging the surface to a predetermined potential, an interimage eraser (not shown), and a developing device 8 for developing the electrostatic latent image formed on the surface of the photoconductor 4. There are provided a transfer charger 9 for transferring the toner image on the surface of the photoconductor 4 to a sheet, a cleaning device 10 for collecting the residual toner on the surface of the photoconductor 4, and a destaticizing device (not shown). Further, a timing roller 11, a feeding roller 12, a paper feed cassette 13, and a paper feed roller 14 for supplying a sheet at a predetermined timing are provided on the paper input side of the photoconductor 4, while the paper output side of the photoconductor 4 is provided. Is provided with a fixing device 15 for fixing the toner image transferred on the paper to the paper.

The developing device 8 is shown in FIGS.
As shown in FIG. 3, a developing tank 16 having a container shape is provided. Inside the developing tank 16, a developing roller 17 composed of a magnet roller, a stirring screw 18 as a second stirring means,
An agitator 19 as a first stirring means, and a first conveying screw 20a and a second conveying screw 20b as a conveying means are rotatably arranged.

The developing roller 17 and the stirring screw 1 described above.
8, the agitator 19, the first conveying screw 20a and the second conveying screw 20b are adapted to rotate in the directions of the arrows, respectively, as shown in FIG. As a result, the developer supplied from the developer supply unit (developer replenishing section) 25 disposed above the developing tank 16 is conveyed in the arrow C direction by the first conveying screw 20a and the second conveying screw 20b. The developer carried by the agitator 19 and the stirring screw 18 is agitated together with the developer. Therefore, the agitator 19
The stirring screw 18 serves as a means for stirring and conveying the developer in the developing tank 16.

The developer contained in the developing tank 16 is composed of a carrier and a toner, and the carrier made of a magnetic material has a resin coat layer for suppressing the adhesion of the toner on the surface. This carrier and toner are mixed with a stirring screw 1.
When agitated by 8, the toner becomes triboelectrically charged. The developing roller 17 attracts the carrier by magnetic force, forms a magnetic brush and conveys it, so that the toner adhered to the carrier by the Coulomb force is supplied to the photoconductor 4.
It is attracted to the electrostatic latent image on the photoconductor 4 and developed.

As shown in FIG. 1, a developer replenishing opening 16a is formed in the upper wall portion of the developing tank 16, and the developer supplying unit 25 is fitted into the replenishing opening 16a from above. ing. The interior of the developer supply unit 25 is partitioned into a toner storage chamber and a carrier developer storage chamber. One of the toner storage chambers stores toner, and the other carrier developer storage chamber stores developer in the carrier only or a developer in which toner is mixed in a predetermined ratio in the carrier (hereinafter, carrier developer). Say)
Is stored.

On the other hand, on the side wall of the developing tank 16, there is provided a developer discharge section 23 having a developer overflow 23a. The developer discharge section 23 is provided at the developer overflow outlet 23.
The developer overflowing from a is discharged to a developer collecting container (not shown).

At the bottom of each of the storage chambers described above, a toner replenishing roller 21 driven and controlled by a controller 32 shown in FIG.
And a carrier developer replenishing roller 22 are respectively provided. When the toner replenishing roller 21 is rotationally driven, the toner in the toner storage chamber is rotated, and the carrier developer replenishing roller 22 is rotationally driven. The carrier developer in the carrier developer storage chamber is transferred to each roller 2
An amount corresponding to the drive time of 1.22 is supplied to the inside of the developing tank 16 through the replenishment opening 16a.
Conveying screw 20a and second conveying screw 20b
Are conveyed to the agitator 19 and the stirring screw 18 side.

Further, inside the developing tank 16, there is provided a toner density sensor 34 as a toner density detecting means for detecting the toner density in the developing tank 16. The toner concentration sensor 34 uses, for example, a magnetic bridge type toner sensor manufactured by Hitachi Metals, Ltd. as a magnetic permeability sensor. This magnetic bridge type toner sensor is used for a two-component developer which is a mixture of a magnetic substance (carrier) and a non-magnetic substance (toner) used in this embodiment.
This is to detect a change in apparent magnetic permeability due to the mixing ratio of the magnetic carrier and the non-magnetic toner, and convert it into an electric signal.

That is, the apparent magnetic permeability of the above developer is
It is determined by the amount of the carrier occupying in the constant volume, and under normal use conditions, the amount of the carrier in the constant volume is determined by the mixing ratio of the toner and the carrier.
For example, when the amount of carriers contacting the toner concentration sensor 34 is small, the apparent magnetic permeability is small, and it is detected that the toner ratio is high. When the amount of carriers contacting the toner concentration sensor 34 is large, the apparent magnetic permeability is large. Therefore, it is detected that the toner ratio is low.

The detection signal of the toner density sensor 34 is
The toner replenishment roller 21 of the developer supply unit 25 is output to the control device 32 shown in FIG. 5 and based on this detection signal.
The carrier developer replenishing roller 22 is driven to replenish the developing tank 16 with toner or carrier developer.

Further, the toner concentration sensor 34 is shown in FIG.
As shown in FIG. 3, it is arranged below the agitator 19 in the developing tank 16. As a result, the uniformly stirred developer always comes into contact with the toner concentration sensor 34 regardless of the increase or decrease in the amount of the developer in the developing tank 16.

Further, when the agitator 19 is rotated in the direction of the arrow shown in FIG. 3, as shown in FIG. 1, the agitator 19 is formed so as to convey the developer in the direction of the arrow B around the toner concentration sensor 34. The first agitating section 19a having a screw formed therein and the second agitating section 19b having a screw formed so as to convey the developer in the arrow A direction. As a result, the developer stirred by the agitator 19 is conveyed in the direction of arrow B by the first stirring unit 19a, and is conveyed in the direction of arrow A by the second stirring unit 19b. Therefore, when the agitator 19 is rotated to agitate the developer, the developer is removed by the toner concentration sensor 34.
Concentrated to the installation position of. Therefore, the toner concentration sensor 34 can always come into contact with a fixed amount of the developer without being affected by the increase and decrease of the developer in the developing tank 16.

Now, the transport of the developer in the developing tank 16 will be described with reference to FIGS. 1 and 3.

First, based on the detection signal of the toner concentration sensor 34, the toner replenishing roller 21 or the carrier developer replenishing roller 22 of the developer supplying unit 25 is rotated to replenish the developing tank 16 with toner or carrier developer. It is supplied from the opening 16a.

Next, the developer supplied from the replenishment opening 16a of the developing tank 16 is conveyed in the direction of arrow A by the first conveying screw 20a and in the direction of arrow B by the second conveying screw 20b. . Further, the developer is transported in the direction of arrow C by the first transport screw 20a and the second transport screw 20b and is transported to the position where the agitator 19 is disposed.

Next, the developer conveyed to the position where the agitator 19 is disposed is agitated by the rotation of the agitator 19 so that the toner and the carrier are uniformly mixed.
At this time, the developer stirred on the stirring screw 18 side, the first conveying screw 20a and the second conveying screw 2
The new developer conveyed by 0b is mixed. The developer mixed by the agitator 19 is conveyed to the position where the toner concentration sensor 34 is provided by the first stirring section 19a and the second stirring section 19b of the agitator 19.

After that, the developer overflowing from the agitator 19 in the direction of the arrow C is sufficiently stirred by the stirring screw 18 to frictionally charge the toner. After that, the developing roller 17 attracts the carrier by magnetic force, forms a magnetic brush and conveys the toner, so that the toner adhered to the carrier by the Coulomb force is supplied to the photoconductor 4 and the electrostatic latent image on the photoconductor 4 is formed. Is adsorbed on and development is performed.

On the other hand, the excess developer in the developing tank 16 is conveyed to the developer discharge section 23 by the agitator 19 and discharged to the outside from the developer overflow 23a of the developer discharge section 23.

The controller 32 controls the driving of the developing roller 17, the stirring screw 18, the agitator 19, the first conveying screw 20a and the second conveying screw 20b.

Further, when the tilt state of the developing device 8 which exceeds the tilt allowable limit is detected by a tilt sensor (not shown) in the control device 32, an alarm comprising a light emitting diode as a warning means for notifying the tilt state. Lamp 3
5 is connected.

Next, the copy operation in the copying machine having the above configuration will be described. Power switch (not shown) is ON
Then, the warm-up process is first performed. After this is completed, the copy start switch 31 described later will be described.
When is turned on, the light source lamp 3 of the exposure optical system 2 scans the original placed on the original placing table 1. The light reflected from the original at this time is applied to the photoconductor 4 via the reflecting mirror 5 and the lens unit 6, and an electrostatic latent image is formed on the surface of the photoconductor 4 which is charged to a predetermined potential by the charger 7. It is formed. Next, this electrostatic latent image is developed with toner supplied from the developing device 8. The toner image on the surface of the photoconductor 4 is transferred by the transfer charger 9 to the paper feed cassette 13
The image is transferred to a sheet supplied from and is fixed by heat on the sheet by the fixing device 15. As a result, a copy image corresponding to the original image is formed on the sheet.

In order to control such a series of copying operations, the control device 3 including the above-mentioned microcomputer.
2 is provided in this copying machine, and this control device 32 has
An ON operation signal of the copy start switch 31 is input. Further, a copy counter 33 for counting the cumulative number of copying operations is further provided, and this count value (hereinafter referred to as copy count value) n is also input to the control device 32.

When the copying operation as described above is repeated, the toner in the developer accommodated in the developing tank 16 of the developing device 8 is gradually consumed, and the ratio of the toner to the carrier, that is, the toner concentration decreases. To go. The drive control of the toner supply roller 21 based on the output of the toner density sensor 34 is further performed by the control device 32.
That is, when it is detected that the detection signal of the toner concentration sensor 34 has dropped to the lower limit value of the proper range required for development, driving of the toner replenishing roller 21 is started. As a result, the toner in the toner storage chamber of the developer replenishing unit 25 is replenished in the developing tank 16 and the toner concentration in the developing tank 16 increases. Then, when it is detected that the toner density reaches the upper limit value of the appropriate range, the driving of the toner supply roller 21 is stopped. By such control,
The toner concentration in the developing tank 16 is maintained within the proper range.

The toner replenished as described above is agitated with the developer in the developing tank 16, controlled to have a constant charge amount, supplied to the photoconductor 4, and used for development. on the other hand,
Since the carrier in the developer does not decrease and is repeatedly used, it is gradually deteriorated by stirring with the developing roller 17 and the stirring screw 18 and contact with the photoconductor 4. As the carrier deteriorates in this way, it becomes impossible to impart a predetermined charge amount to the toner, resulting in deterioration of image quality. Therefore, by additionally replenishing the carrier in the developing tank 16 and replacing the deteriorated carrier in the developing tank 16, the above-mentioned deterioration of the charging performance can be suppressed.
For this reason, the control device 32 is also configured to perform replenishment / discharge control for replenishing the carrier developer from the carrier developer storage chamber and discharging the developer in the developing tank 16.

By the way, in the magnetic bridge type toner sensor used as the toner concentration sensor 34, even if the mixing ratio of toner and carrier is constant, if the density of the developer itself changes, the amount of carrier in a certain volume changes. However, this changes the apparent magnetic permeability of the developer. In this case, the magnetic bridge type toner sensor cannot distinguish whether the density of the developer has changed or the mixing ratio of the toner and the carrier has changed, and the toner concentration in the developing tank 16 may be erroneously detected. There is. Therefore, it is necessary to always keep the density of the developer near the toner concentration sensor 34 constant.

Further, in general, in a developing device of a sequential developer replacing type in which a developer overflows from a developer overflow port formed in a developing tank and discharges the developer, due to the inclination of the developing device,
When the developer overflow becomes lower than the reference position, the developer discharge amount from the developer overflow increases, the developer amount in the developer tank decreases, and the developer overflow becomes When it becomes higher than the above, the discharge amount of the developer from the developer overflow outlet decreases and the developer amount in the developing tank increases. As a result, the amount of developer near the toner concentration sensor changes, and the density of the developer also changes.

That is, when the amount of the developer in the developing tank decreases, the density of the developer in the vicinity of the toner concentration sensor decreases and the magnetic permeability also decreases, so the sensor output value of the toner concentration sensor also decreases. Even if the toner concentration is normal, over toner is detected. The developer is not replenished until it is determined from the sensor output value of the toner concentration sensor that the toner concentration in the developing tank is normal. Therefore, when it is determined that the toner density in the developing tank is normal, the actual toner density is low and the inside of the developing tank is in the under toner state.

Further, when the amount of the developer in the developing tank increases, the density of the developer near the toner concentration sensor increases and the magnetic permeability also increases, so the sensor output value of the toner concentration sensor also increases. Under toner is detected even if the toner concentration is normal. Then, the developer is replenished until it is determined that the toner concentration in the developing tank is normal based on the sensor output value of the toner concentration sensor. Therefore, when it is determined that the toner density in the developing tank is normal, the actual toner density is high and the inside of the developing tank is in the over toner state.

Further, in this embodiment, the developing device 8 is
If the initial developer amount in the developing tank 16 is 480 g,
If the copier tilts 1 °, it will be 40 when the developer amount decreases.
It becomes 0 g, and becomes 560 g when the developer amount increases. As described above, when the copier tilts by 1 °, the initial developer amount changes by about 17%. As a result, the influence on the toner concentration sensor, that is, the change in developer density increases, and the toner in the developing tank 16 is increased. It will greatly affect the concentration.

However, in the developing device having the above-described structure, the developer in the developing tank 16 is collectively conveyed by the agitator 19 to the vicinity of the position where the toner concentration sensor 34 is arranged. The developer amount can be made larger than that in the other developing tanks 16. As a result, even if the developing device 8 tilts and the amount of developer in the developing tank 16 changes, the amount of change in the amount of developer in the vicinity of the toner concentration sensor 34 becomes small. Even if it changes, the change in the density of the developer in the vicinity of the toner concentration sensor 34 can be suppressed to be small. Therefore, the toner concentration sensor 34 can always detect the toner concentration in the developing tank 16 more accurately.

Therefore, the density of the developer in the vicinity of the toner concentration sensor 34 can be kept constant at all times, so that the toner concentration can be accurately controlled by the output value of the toner concentration sensor 34.

Here, in the developing device 8 having the configuration of the present embodiment, the relationship between the developer weight change value (g) in the developing tank 16 and the toner concentration sensor output value (V) by the toner concentration sensor 34 is shown in FIG. Shown in.

However, in the developing device 8 described above, the rotation speed of the developing roller 17 is 292 rpm, the rotation speed of the stirring screw 18 is 120.9 rpm, and the rotation speed of the agitator 19 is 1.
67.9 rpm, first conveying screw 20a and second
The rotation number of the conveying screw 20b is 167.9 rpm, and the rotation direction of each member is the arrow direction shown in FIG. The pitch of the stirring plate of the stirring screw 18 is 23.5 mm, the pitch of the screw of the agitator 19 is 18 mm, and the pitch of the screws of the first conveying screw 20a and the second conveying screw 20b is 16 mm. Further, the initial amount of developer stored in the developing tank 16 is 480 g. It should be noted that the higher the developer conveying speed (if it is extremely high, the uneven distribution of the developer is unsuitable),
The larger the developer amount and the larger the developing device, the less the influence on the change in the developer amount.

As a comparative example with respect to FIG. 6, when the developing device 8'shown in FIG. 7 is used, the developer weight change value (g) in the developing tank 16 and the toner concentration sensor output value by the toner concentration sensor 34 ( The relationship with V) is shown in FIG.

The developing device 8'shown in FIG. 7 uses an agitator 19 'instead of the agitator 19 provided in the developing device 8 of this embodiment. This agitator 19 ′ has a configuration in which a plurality of fins extending in the longitudinal direction are provided, and the rotation speed is the same as that of the agitator 19. Also,
The other members of the developing device 8 ′ are similar to those of the developing device 8.

From the above, when the developer stored in the developing tank 16 is in the initial state and the copying machine is tilted by about 3 °, the toner amount when the amount of the developer in the developing tank 16 changes by ± 60 g. In the developing device 8 ′ of the comparative example, the output value of the density sensor changes ± 0.2V to 0.25V as shown in FIG. This change value is a change of about 1% when converted into toner density. This is because the toner concentration in the developer is 4% to 6%.
Therefore, if the toner density changes by 1%, problems such as toner fogging, toner scattering, and carrier rising due to the increase in toner density occur, while problems such as image blurring due to a decrease in toner density occur.

In general, when the toner concentration in the developer changes, the greatest effect appears in the case of a black solid image, and if the toner concentration becomes too thin, the black solid becomes thin. Therefore, to obtain the required image density,
The entire copied image becomes dark. There is, for example, a Macbeth densitometer as a device for measuring the black solid density of such an image, and the black solid density for obtaining a normal image requires a density value of 1.3 or more by the Macbeth densitometer. The density value 1.3 at this time corresponds to a change value of the toner density of 0.5%.

In the initial stage of use of the developer, even if the change in toner concentration in the developer is about 1%, the influence on the copied image is small, but the carrier and toner in the developer deteriorate with use of the developer. Then, when the toner density change is about 1%, the influence on the copied image increases. Therefore, in consideration of the life of the developer, it is desirable to suppress the toner concentration change in the developer to about 0.5% in order to maintain a good copy image.

Therefore, in order to prevent the above-mentioned problems due to the change in toner concentration from occurring, the change in toner concentration must be 0.5% or less.

On the other hand, from the time when the developer stored in the developing tank 16 is in the initial state, if the copying machine is tilted about 3 °, the toner concentration sensor output when the amount of developer in the developing tank 16 changes by ± 60 g In the developing device 8 of this embodiment, the value changes ± 0.08V to 0.12V as shown in FIG. This change value is half the output value of the toner concentration sensor in the developing device 8'of the above comparative example, and is approximately 0.5% when converted to toner concentration.

Therefore, in the developing device 8 of this embodiment,
Since the change in toner concentration in the developer in the developing tank 16 can be reduced, it is possible to eliminate problems such as toner fog and toner scattering due to the increase or decrease in toner concentration, and as a result, the copied image can be favorably maintained. be able to.

From the above, the developing device 8 having the above structure
Since the developer in the developing tank 16 is collectively conveyed by the agitator 19 to the vicinity of the position where the toner concentration sensor 34 is provided, the developing device 8 is inclined and the developing tank 16 is inclined.
Even if the amount of the developer inside is changed, the amount of change in the amount of the developer near the toner concentration sensor 34 becomes small.

As a result, the density of the developer in the vicinity of the toner density sensor 34 can be kept constant at all times, so that the toner density can be accurately controlled by the output value of the toner density sensor 34. As a result, the copy image can be obtained. Can be maintained well.

[Second Embodiment] The following will describe another embodiment of the present invention with reference to FIGS. 9 to 11. The members having the same functions as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 9, the developing device 28 according to this embodiment uses an agitator 29 instead of the agitator 19 of the developing device 8 shown in FIG. 1 of the first embodiment. The agitator 29 is a stirring means that is composed of a plurality of fins 29a that are orthogonal to the axis and extend in the longitudinal direction.

The developing tank 16 below the agitator 29
As shown in FIG. 10, a recess 30 is formed on the bottom surface of the. As shown in FIG. 11 (a), the recess 30 has a substantially rectangular parallelepiped shape of 100 mm in the directions of arrows A and B, and 20 mm in the directions of arrows C and D and a depth of 3 mm as shown in FIG. 11 (b). ing. A toner concentration sensor 34 is arranged almost at the center of the recess 30. The toner concentration sensor 34 has a contact surface with the upper developer, that is, a detection surface, which is substantially flush with the bottom surface of the recess 30. At this time, the developer level is set to the concave portion 3 of the developing tank 16.
The height from the bottom surface other than 0 is 12 mm.

The conveyance of the developer in the developing device 28 having the above structure will be described with reference to FIGS. 9 and 10.
The developing roller 17, the stirring screw 18, the agitator 29, the first conveying screw 20a, and the second conveying screw 20b are assumed to rotate in respective arrow directions, as shown in FIG.

First, based on the detection signal of the toner concentration sensor 34, the toner replenishing roller 21 or the carrier developer replenishing roller 22 of the developer supplying unit 25 is rotated to supply the toner or the carrier developer to the developing tank 16. It is supplied from the opening 16a.

Next, the developer supplied from the replenishment opening 16a of the developing tank 16 is conveyed in the direction of arrow A by the first conveying screw 20a and in the direction of arrow B by the second conveying screw 20b. . Further, the developer is transported in the direction of arrow C by the first transport screw 20a and the second transport screw 20b, and is transported to the position where the agitator 29 is disposed.

Next, the developer conveyed to the position where the agitator 29 is disposed is agitated by the rotation of the agitator 29 so that the toner and the carrier are uniformly mixed.
At this time, the developer stirred on the stirring screw 18 side, the first conveying screw 20a and the second conveying screw 2
The new developer conveyed by 0b is mixed. The developer mixed by the agitator 29 collects in the recess 30 formed on the bottom surface of the developing tank 16 below the agitator 29, and is conveyed to the position where the toner concentration sensor 34 is provided.

After that, the developer overflowing from the agitator 29 in the direction of arrow C is sufficiently stirred by the stirring screw 18 to frictionally charge the toner. After that, the developing roller 17 attracts the carrier by magnetic force, forms a magnetic brush and conveys the toner, so that the toner adhered to the carrier by the Coulomb force is supplied to the photoconductor 4 and the electrostatic latent image on the photoconductor 4 is formed. Is adsorbed on and development is performed.

On the other hand, the excess developer in the developing tank 16 is conveyed to the developer discharge section 23 by the agitator 29 and discharged to the outside from the developer overflow 23a of the developer discharge section 23.

As described above, by providing the toner concentration sensor 34 substantially in the center of the concave portion 30 of the developing tank 16, the vicinity of the position where the toner concentration sensor 34 is provided is recessed from the other bottom surface of the developing tank 16 and the developing process is performed. The agent will be concentrated and transported. As a result, even if the amount of developer in the developing tank 16 changes, the change in developer density near the toner concentration sensor 34 can be reduced. Therefore, the output value of the toner concentration sensor 34 can be set to a more accurate value, so that the toner concentration in the developing tank 16 can be kept constant and the copied image can be favorably maintained.

In the developing device 28, the inventors of the present application conducted an experiment and found that if the depth of the recess 30 is less than 2 mm, the developer is hard to collect in the recess 30,
A change in the amount of the developer in the developing tank 16 causes a change in the developer density near the toner concentration sensor 34. Therefore, it is not possible to obtain an appropriate toner density sensor output value, and it is not possible to maintain a good copy image. If the depth of the recess 30 is larger than 3 mm, the flow of the developer on the recess 30 is deteriorated, and the developer is retained in the recess 30. In such a case, the developer that comes into contact with the toner concentration sensor 34 is always the same developer, so the change in toner concentration cannot be accurately detected, and the copied image cannot be maintained well.

Further, the depth of the concave portion 30 is set to 2 mm or more and 3 mm.
By setting the range below, the concave portion 30 will be
It is about 25% deeper than the other portions, and makes it easy for the developer to collect to the extent that the developer does not stay. by this,
Since the developer having a constant density can be always brought into contact with the toner concentration sensor 34 without being affected by the change in the developer amount in the developing tank 16, the toner concentration sensor output value of the toner concentration sensor 34 is always appropriate. It can be a value.

From the above, in order to maintain a good copy image, it is necessary to always obtain an appropriate toner density sensor output value without changing the amount of developer contacting the toner density sensor 34. . Therefore, it is understood that it is desirable to set the depth of the concave portion 30 in the range of 2 mm or more and 3 mm or less.

Further, since the vicinity of the position where the toner concentration sensor 34 is provided in the developing tank 16 is formed lower than the other bottom surface of the developing tank 16 by the recess 30 provided in the developing tank 16, The developer in 16 is naturally conveyed to the vicinity of the toner concentration sensor 34.

As a result, the agitator 29 does not have to be formed so that the developer is conveyed in the vicinity of the position where the toner concentration sensor 34 is provided, and the existing agitator 29 can be used as it is. Therefore, the manufacturing of the developing device 8 can be simplified, and the manufacturing cost can be reduced.

[Third Embodiment] The following description will explain still another embodiment of the present invention with reference to FIGS. 12 to 15. It should be noted that members having the same functions as those of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 12, the developing device 38 of this embodiment uses an agitator 39 instead of the agitator 29 of the second embodiment. The agitator 39 is a stirring means composed of a plurality of fins 39a extending in the longitudinal direction.

The developing tank 16 below the agitator 39
A toner concentration sensor 34 is disposed substantially in the center on the bottom surface of the rib, and as shown in FIG. 13, ribs 40 serving as overflow means that are orthogonal to the axis of the agitator 39 in the vicinity of the toner concentration sensor 34 (in the figure). Shaded) is provided.

The rib 40 is, as shown in FIG.
The developing tank 16 is provided below the agitator 39 in the directions of arrows A and B at intervals of 100 mm via the toner density sensor 34. At this time, the height of the rib 40 is 9 mm from the bottom surface of the developing tank 16, and the developer level is 12 mm from the bottom surface of the developing tank 16.

Further, the rib 40, as shown in FIG.
It is formed in a notched state so as not to contact the shaft of the agitator 39, that is, to prevent the rotation of the agitator 39 from being blocked. Also, the fins 39a of the agitator 39 ...
Is in a notched state at the position where the rib 40 is arranged, and this also prevents the rotation of the agitator 39.

Therefore, by providing the ribs 40 ... In the vicinity of the arrangement position of the toner concentration sensor 34 as described above, the conveyed developer is transferred between the ribs 40, 40 in the vicinity of the arrangement position of the toner concentration sensor 34. The ribs 40 can be dammed and overflowed. As a result, the developer collected in the vicinity of the toner concentration sensor 34 can be dammed by the ribs 40, so that the change in the amount of developer in the vicinity of the toner concentration sensor 34 can be suppressed even if the developing device 38 tilts.

Here, the conveyance of the developer by the developing device 38 will be described with reference to FIGS. 12 and 13. The developing roller 17, the stirring screw 18, the agitator 39, the first conveying screw 20a, and the second conveying screw 20b are assumed to rotate in the respective arrow directions, as shown in FIG.

First, based on the detection signal of the toner concentration sensor 34, the toner replenishing roller 21 or the carrier developer replenishing roller 22 of the developer supplying unit 25 is rotated to replenish the developing tank 16 with toner or carrier developer. It is supplied from the opening 16a.

Next, the developer supplied from the supply opening 16a of the developing tank 16 is conveyed in the direction of arrow A by the first conveying screw 20a and in the direction of arrow B by the second conveying screw 20b. . Further, the developer is carried in the direction of arrow C by the first carrying screw 20a and the second carrying screw 20b, and carried to the position where the agitator 39 is disposed.

Next, the developer transported to the position where the agitator 39 is disposed is agitated by the rotation of the agitator 39 so that the toner and the carrier are uniformly mixed.
At this time, the developer stirred on the stirring screw 18 side, the first conveying screw 20a and the second conveying screw 2
The new developer conveyed by 0b is mixed. The developer mixed by the agitator 39 collects between the ribs 40 provided on the bottom surface of the developing tank 16 below the agitator 39, and the toner concentration sensor 34
Are transported to the position where they are arranged.

After that, the developer overflowing from the agitator 39 in the direction of arrow C is sufficiently stirred by the stirring screw 18 to frictionally charge the toner. After that, the developing roller 17 attracts the carrier by magnetic force, forms a magnetic brush and conveys the toner, so that the toner adhered to the carrier by the Coulomb force is supplied to the photoconductor 4 and the electrostatic latent image on the photoconductor 4 is formed. Is adsorbed on and development is performed.

On the other hand, the excess developer in the developing tank 16 is conveyed to the developer discharge section 23 by the agitator 39 and discharged to the outside from the developer overflow port 23a of the developer discharge section 23.

As described above, the toner density sensor 34 is provided substantially in the center between the ribs 40 formed on the bottom surface of the developing tank 16, so that the amount of the developer near the position where the toner density sensor 34 is provided can be reduced. Can be increased over other parts of. As a result, even if the amount of developer in the developing tank 16 changes, the change in developer density near the toner concentration sensor 34 can be reduced. Therefore, the output value of the toner concentration sensor 34 can be set to a more accurate value, so that the toner concentration in the developing tank 16 can be kept constant and the copied image can be favorably maintained.

[Fourth Embodiment] The following description will explain still another embodiment of the present invention with reference to FIGS. The members having the same functions as those of the above-described respective embodiments are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 16, the developing device 48 according to the present embodiment uses the agitator 29 shown in FIG. 9 of the second embodiment as a stirring means. The second conveying screw 20b provided in the developing device 48 is provided with ribs 50 (shown by hatching in the figure) on the screw portion facing the toner concentration sensor 34. As shown in FIGS. 17 and 18, the rib 50 is formed in the longitudinal direction of the second conveying screw 20b and in the direction orthogonal to the axis of the second conveying screw 20b.

Therefore, the second conveying screw 20
b is rotated in the direction of the arrow shown in FIG.
As shown in FIG. 16, the developer carried by the first carrying screw 20a is carried in the direction of arrow B, and the rib 50 carries it to the toner concentration sensor 34 side.

Further, in the first carrying screw 20a, a screw-free region E is formed on the front side from the position where the rib 50 of the second carrying screw 20b is provided. As a result, the developer conveyed by the first conveying screw 20a stays in the area E, and the developer overflowing from the area E is again indicated by the arrow A by the first conveying screw 20a.
In addition to being conveyed in the direction, the second conveying screw 20b is conveyed in the direction of the arrow B from the rib 50 arranging position.

Therefore, when the developer carried from the first carrying screw 20a is carried by the rib 50 from the position where the rib 50 of the second carrying screw 20b is provided to the direction of arrow C, that is, to the side where the toner concentration sensor 34 is provided. The problem that the ribs 50 of the second conveying screw 20b are not conveyed in the direction of arrow B is eliminated.

Here, the conveyance of the developer by the developing device 48 will be described with reference to FIGS. 16 and 17. Incidentally, the developing roller 17, the stirring screw 18, the agitator 29, the first conveying screw 20a, and the second conveying screw 20b are assumed to rotate in respective arrow directions, as shown in FIG.

First, based on the detection signal of the toner density sensor 34, the toner replenishing roller 21 or the carrier developer replenishing roller 22 of the developer supplying unit 25 is rotated to replenish the developing tank 16 with toner or carrier developer. It is supplied from the opening 16a.

Next, the developer supplied from the supply opening 16a of the developing tank 16 is conveyed in the direction of arrow A by the first conveying screw 20a and in the direction of arrow B by the second conveying screw 20b. . Further, the developer is transported in the direction of arrow C by the first transport screw 20a and the second transport screw 20b, and is transported to the position where the agitator 29 is disposed.

At this time, the developer replenished from the replenishment opening 16a is fed by the first conveying screw 20a in the arrow A direction.
Is conveyed in the direction E, stays in the area E, overflows from the area E to the arrow A direction side of the first conveyor screw 20a, and overflows to the arrow B direction side from the rib 50 arrangement position of the second conveyor screw 20b. . As a result, the developer is conveyed again in the direction of arrow A by the first conveying screw 20a and is conveyed in the direction of arrow B by the second conveying screw 20b.

The developer carried by the first carrying screw 20a is carried to the rib 50 side by the second carrying screw 20b, and is carried to the toner concentration sensor 34 side by the rib 50.

Next, the developer is agitated by the rotation of the agitator 29 so that the toner and the carrier are uniformly mixed. At this time, the developer stirred on the stirring screw 18 side and the new developer transported by the first transport screw 20a and the second transport screw 20b are mixed.

After that, the developer overflowing from the agitator 29 in the direction of arrow C is sufficiently stirred by the stirring screw 18 to frictionally charge the toner. After that, the developing roller 17 attracts the carrier by magnetic force, forms a magnetic brush and conveys the toner, so that the toner adhered to the carrier by the Coulomb force is supplied to the photoconductor 4 and the electrostatic latent image on the photoconductor 4 is formed. Is adsorbed on and developed.

On the other hand, the excess developer in the developing tank 16 is conveyed to the developer discharge section 23 by the agitator 29 and discharged to the outside from the developer overflow 23a of the developer discharge section 23.

As described above, the developer conveyed by the second conveying screw 20b is transferred to the second conveying screw 20b.
Since the ribs 50 formed forcibly convey the toner to the toner concentration sensor 34 side, the amount of developer in the vicinity of the toner concentration sensor 34 can always be made larger than that in other portions of the developing tank 16. As a result, even if the amount of the developer in the developing tank 16 changes, the change in the amount of the developer near the toner concentration sensor 34 can be reduced.

Therefore, the output value of the toner density sensor 34 can be made a more accurate value.
The toner density in the inside can be kept constant, and the copied image can be favorably maintained.

[Fifth Embodiment] The following description will explain still another embodiment of the present invention with reference to FIGS. 19 to 21. The members having the same functions as those of the above-described respective embodiments are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 19, the developing device 58 according to this embodiment has a stirring screw 59 instead of the stirring screw 18 provided in the developing device 28 shown in FIG. 9 of the second embodiment. .

The stirring screw 59 has a rib 60 formed on the shaft 59a of the stirring screw 59 at a position facing the toner concentration sensor 34. This rib 60 is shown in FIG.
0 and the longitudinal direction on the shaft 59a of the stirring screw 59 and the shaft 59 of the stirring screw 59 as shown in FIG.
It is formed in a direction orthogonal to a.

Therefore, the stirring screw 59 is
By rotating in the direction of the arrow shown in FIG.
As shown in, the developer stirred in the developing tank 16 is conveyed to the developing roller 17 side, and is also conveyed to the toner concentration sensor 34 side by the rib 60.

In this way, the rib 6 is attached to the stirring screw 59.
By setting 0, the developer can be forcibly transported to the vicinity of the toner concentration sensor 34 by rotating the stirring screw 59. As a result, the amount of developer in the vicinity of the toner concentration sensor 34 can be made larger than that in other portions in the developing tank 16, so that the toner concentration sensor 3
The output of 4 can be stabilized.

Moreover, since the developer detected by the toner concentration sensor 34 is the developer after being developed by the developing roller 17, that is, the developer in the under toner state, the toner in the developer is more accurate. The concentration can be detected. As a result, the developer concentration can always be stabilized, and the copied image can be maintained well.

[0110]

As described above, the developing device according to the first aspect of the present invention is a stirring means for stirring and transporting the developer in the developing tank to the developing tank containing the developer consisting of toner and carrier. And developing rollers for supplying the developer to the photoconductor are rotatably provided, and the developer is sequentially supplied from the developer replenishing section to the developing tank in accordance with the detection output of the toner concentration detecting means provided in the developing tank. In the developing device in which the developer in the developing tank is discharged while being replenished, the toner concentration detecting means is provided on the bottom surface of the developing tank to remove the developer. The means for agitating and carrying is configured so as to collectively carry the developer to the vicinity of the position where the toner concentration detecting means is provided.

As a result, the amount of developer in the vicinity of the toner concentration detecting means can be made larger than the amount of developer in the other developing tanks. Therefore, it is possible to always obtain a stable detection signal by the toner concentration detecting means, and it is possible to detect a more accurate toner concentration without being affected by the change in the developer amount in the developing tank. The effect that the copied image can be favorably maintained is exhibited.

In the developing device according to the second aspect of the invention, as described above, the agitating means for agitating and transporting the developer in the developing tank into the developing tank containing the developer consisting of toner and carrier. And developing rollers for supplying the developer to the photoconductor are rotatably provided, and the developer is sequentially supplied from the developer replenishing section to the developing tank in accordance with the detection output of the toner concentration detecting means provided in the developing tank. In the developing device in which the developer in the developing tank is discharged while being discharged, the toner density detecting means is provided on the bottom surface of the developing tank. The configuration is such that the vicinity of the arrangement position of the detection means is formed lower than the other bottom surface of the developing tank.

With this, in addition to the effect of the first aspect, it is not necessary to form the stirring means so that the developer is conveyed to the vicinity of the position where the toner concentration detecting means is disposed, and the existing stirring means is used as it is. Can be used. Therefore, it is possible to simplify the manufacturing of the developing device and to reduce the manufacturing cost.

Further, in the developing device of the third aspect of the present invention, as described above, the overflow member for stopping the developer conveyed by the stirring means and causing it to overflow in the vicinity of the position of the toner concentration detecting means in the developing tank. Is provided.

As a result, even if the amount of the developer in the developing tank changes, it is possible to suppress the change in the amount of the developer near the position where the toner concentration detecting means is provided. Therefore, it is possible to always obtain a stable detection signal by the toner concentration detecting means, and it is possible to detect a more accurate toner concentration without being affected by a change in the developer amount in the developing tank.
As a result, there is an effect that the copied image can be favorably maintained.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a developing device according to an embodiment of the present invention.

FIG. 2 is a side view of the developing device shown in FIG.

FIG. 3 is a sectional view of the developing device shown in FIG. 1, taken along the line XX.

FIG. 4 is a schematic configuration diagram of a copying machine including the developing device shown in FIG.

5 is a control block diagram of the copying machine shown in FIG.

6 is a graph showing a relationship between a developer weight change value and a toner concentration sensor output value in the developing device shown in FIG.

7 is a schematic plan view of a developing device of a comparative example with respect to the relationship between the developer weight change value and the toner concentration sensor output value of the developing device shown in FIG.

8 is a graph showing a relationship between a developer weight change value and a toner concentration sensor output value in the developing device shown in FIG.

FIG. 9 is a schematic plan view of a developing device according to another embodiment of the present invention.

10 is a sectional view of the developing device shown in FIG. 9, taken along the line YY.

11 is a schematic cross-sectional view showing the structure in the vicinity of the toner concentration sensor provided on the bottom surface of the developing tank provided in the developing device shown in FIG. 9, in which (a) is a cross-sectional view in the directions of arrows A and B. And (b) is a sectional view taken along line ZZ of (a).

FIG. 12 is a schematic plan view of a developing device according to still another embodiment of the present invention.

13 is a sectional view of the developing device shown in FIG. 12, taken along the line WW.

14 is a schematic cross-sectional view showing a structure near a toner concentration sensor provided on the bottom surface of a developing tank provided in the developing device shown in FIG.

15 is a perspective view of the vicinity of ribs formed on the bottom surface of the developing tank of the developing device shown in FIG.

FIG. 16 is a schematic plan view of a developing device according to still another embodiment of the present invention.

17 is a cross-sectional view of the developing device shown in FIG. 16 taken along the line VV.

FIG. 18 is a sectional view of the developing device shown in FIG. 16, taken along the line RR.

FIG. 19 is a schematic plan view of a developing device according to still another embodiment of the present invention.

20 is a sectional view of the developing device shown in FIG. 19, taken along the line U-U.

21 is a sectional view of the developing device shown in FIG. 19, taken along the line SS.

[Explanation of symbols]

 4 Photoreceptor 8 Developing Device 16 Developing Tank 17 Developing Roller 18 Stirring Screw (Second Stirring Means) 19 Agitator (First Stirring Means) 20a First Conveying Screw (Conveying Means) 20b Second Conveying Screw (Conveying Means) 23 Developer discharging part (developer discharging opening) 28 Developing device 29 Agitator (first stirring means) 30 Recessed portion 34 Toner concentration sensor (toner concentration detecting means) 38 Developing device 39 Agitator (first stirring means) 40 Rib ( Overflow member) 48 Developing device 49 Agitator (first stirring means) 50 Rib (conveying member) 58 Developing device 59 Stirring screw (first stirring means) 60 Rib (conveying member)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G03G 15/09 Z (72) Inventor Masatoshi Kanekoshi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Osaka Prefecture Incorporated (72) Inventor Takashi Miyaji 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (3)

[Claims] 1. An agitating means for agitating and transporting a developer in a developer tank and a developing roller for supplying the developer to a photoconductor are rotatable in a developer tank containing a developer composed of toner and carrier. In accordance with the detection output of the toner concentration detecting means provided in the developing tank, the developer is sequentially replenished from the developer replenishing section to the developing tank, while the developer in the developing tank is replenished in the developing tank. In the developing device discharged from the developer discharge opening formed in the above, the toner concentration detecting means is provided on the bottom surface of the developing tank, and the means for stirring and conveying the developer is the toner concentration detecting means. The developing device is formed so as to be collectively conveyed in the vicinity of the arrangement position of. 2. An agitating means for agitating and transporting the developer in the developer tank and a developing roller for supplying the developer to the photoconductor are rotatable in a developer tank containing a developer composed of toner and carrier. In accordance with the detection output of the toner concentration detecting means provided in the developing tank, the developer is sequentially replenished from the developer replenishing section to the developing tank, while the developer in the developing tank is replenished in the developing tank. In the developing device discharged from the developer discharge opening formed in the above, the toner concentration detecting means is provided on the bottom surface of the developing tank, and the vicinity of the position where the toner concentration detecting means is disposed is the other bottom surface of the developing tank. A developing device, which is formed to be lower than the above. 3. An overflow member is provided near the position where the toner concentration detecting means of the developing tank is provided, for preventing the developer conveyed by the stirring means from overflowing. Developing device.