JPH08227217A - Developing device - Google Patents

Abstract

PURPOSE: To control the concentration of toner without causing undershooting and overshooting with high accuracy, even in a copying mode having a great change in the consumption of the toner by making the carrying speed of a two-component developer in the developing chamber of a developing container fast and the time lag of the detection of the toner concentration with a detecting means on this side, out of two concentration detecting means installed in the container less. CONSTITUTION: As a magnet in a developing sleeve, a magnet having the following magnetic pole constitution is used. When a magnetic pole (x) having weak magnetic force which exists between the repulsive magnetic poles N3 and N2 of the magnet is on the N-pole side having the same polarity as that of the repulsive magnetic poles, the magnetic flux density of the magnetic pole (x) is made <=100G and when the magnetic pole (x) is on the S-pole side having the different polarity, the magnetic flux density is made <=50G. Since the magnetic flux density of the magnetic pole (x) having weak magnetic force set between the repulsive magnetic poles N2 and N3 is prescribed, the developer is completely scraped down from the developing sleeve into the developing chamber in the vicinity of the repulsive pole to be circulated and the carrying speed of the developer in the developing chamber is made fast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image formed on an image carrier by an electrophotographic method or an electrostatic recording method, and more particularly to a two-component apparatus having a magnetic carrier and a toner. The present invention relates to a two-component developing device using a developer.

[0002]

2. Description of the Related Art Conventionally, a developing device as shown in FIG. 5 has been proposed as one mode of a two-component developing device using a two-component developer. The developing device 9 supplies the two-component developer housed in the developing container 9 a to the surface of the developing sleeve 3 by stirring screws 11 and 12, and the developer is magnetically brushed by a magnetic force of a magnet 13 in the developing sleeve 3. In this state, the developing sleeve 3 is conveyed toward a developing area facing the photosensitive drum 4 as the developing sleeve 3 rotates, and a developer returning member (a regulating member that regulates the amount of developer accumulated on the developing sleeve) 1 Further, the magnetic brush is cut by the brush cutting member (blade) 2 so that the amount of the developer conveyed to the developing area is maintained at an appropriate amount.

More specifically, the inside of the developing container 9a is divided into a developing chamber (first chamber) 16 and a stirring chamber (second chamber) 17 by a partition wall 6 extending in the direction perpendicular to the plane of the drawing.
The above-mentioned two-component developer is contained in the developing chamber 16 and the stirring chamber 17.

In the developing chamber 16 and the agitating chamber 17, first and second conveying screws 11 and 12 are provided as developer agitating / conveying means, respectively. The first conveying screw 11 conveys the developer inside the developing chamber 16 while stirring, and the second conveying screw 12 is controlled by the developer concentration controller from a toner replenishing tank (not shown) into the stirring chamber 17. Further, the toner supplied to the upstream side of the second conveying screw 12 and the developer already in the stirring chamber 17 are conveyed while being stirred, and the toner concentration of the developer is made uniform.

The partition wall 6 has openings (developer passages) (not shown) for communicating the developing chamber 7 and the stirring chamber 8 with each other at both front and rear sides in FIG. The toner in the developing chamber 16 in which the toner is consumed and the toner concentration is lowered by the moving force of the conveying screws 11 and 12 is moved into the stirring chamber 17 through one of the developer passages. There is.

The first conveying screw 11 is the developing chamber 1
As shown in FIG. 6, a screw structure in which a blade member is provided in a spiral shape around the rotation axis is disposed in the bottom portion of the roller 6 substantially parallel to the axial direction (developing width direction) of the developing sleeve 3. Then, the developer in the developing chamber 17 is rotated and conveyed in one direction along the axial direction of the developing sleeve 3 at the bottom of the developing chamber 16. The second conveying screw 12 also has a screw structure similar to that of the first conveying screw 11 (however, a blade member is provided in a spiral shape around the rotating shaft in the direction opposite to that of the first screw 11). ,
It is arranged substantially parallel to the first screw 11 at the bottom of the stirring chamber 17 and rotates in the same direction as the first screw 11 to convey the developer in the stirring chamber 17 in the opposite direction to the first screw 11. . Thus, the first and second screws 11
6 and 11, the developer passes through the openings at both ends of the partition wall 6 and the developing chamber 16 and the stirring chamber 1 as shown in FIG.
It is circulated between 7 and.

The toner concentration detecting means (concentration sensor) 7 for the developer circulating in this way is conventionally located near the developing sleeve 3 in the developing chamber 16 in the thrust direction (axial direction of the developing sleeve 3). It is provided on the front side in the longitudinal direction). The density sensor 7 is provided on the front side instead of the back side. When the density sensor 7 is provided on the back side, that is, on the upstream side of the developer circulation in the developing chamber 16, when the toner of the developer is consumed on the downstream side, This is because the toner density cannot be detected. When it is provided on the front side, the detection position is on the downstream side in the thrust direction in the developing chamber 16, so that it is possible to detect the decrease in the toner concentration of the developer regardless of the position in the thrust direction at which the toner is consumed.

However, in a copy mode in which the change in the amount of toner consumption is large, for example, in the case of making a continuous copy of a substantially solid black image → a continuous copy of a substantially solid white image, the toner density control overshoots. There was a drawback. That is, during solid black continuous copying, the toner is replenished with the maximum replenishment amount so that the developer on the developing sleeve 3 has a normal toner density. But,
When the copying of the solid white image is started, this balance is lost, and excessive toner is replenished from the stirring chamber 17 to the developing chamber 16. Therefore, the toner concentration starts to be excessive from the back side of the developing chamber 16, and the developer having the excessive concentration is conveyed to the front side in the developing chamber 17 until the concentration sensor 7 detects and relaxes the concentration. , The maximum amount of supply is continued.

In contrast to such a drawback, conventionally, the first and second density sensors are installed at both ends in the thrust direction of the developing container 9a, that is, at the back side and the front side. The toner replenishment control is performed based on the detection output information from the first and second density sensors to deal with the problem. FIG. 7 shows a state in which concentration sensors are installed at two positions in the thrust direction, and FIG. 8 shows a typical control flow thereof.

As shown in FIG. 7, the first and second density sensors 7a and 7b are provided with magnetic poles in a region on the thrust direction from the developer scooping position until the developer is conveyed to the blade 2. It is incorporated in the developer return member 1 so as to face the developing sleeve 3 between S2 and the magnetic pole N1. In this example, the density sensors 7a and 7b are configured as a developer reflection type density sensor, and the bidirectional LEDs 71a and 71b and the reference light receiving element 7 are provided.
2a and 72b, reflected light receiving elements 73a and 73b, and detection windows 8a and 8b. Detection windows 8a, 8b
Is made of transparent acrylic resin, and a PFA sheet 81 is attached to the developing sleeve 3 side of the return member 1 so as to cover the detection surface in order to prevent the toner from adhering to the detection surface facing the developer. ing.

Toner replenishment using a conventional density sensor will be described. First, a case where only the density sensor 7a is provided as the density sensor on the front side in the thrust direction in the developing container 9a will be described. This concentration sensor 7
The characteristic a is that the toner in the two-component developer reflects infrared light and the carrier absorbs infrared light. The developer in the developing container 9a is irradiated with infrared light from the LED 71a, and the reflected light amount of the reflected infrared light is detected by the light receiving element 73.
The light is received by a, the toner concentration in the developer is calculated from the reflected light amount, and the toner is replenished based on this. As a result, the toner density can be stably maintained.

To control the replenishment of toner, the two-component developer is put into the developing container 9a, and the output sig-in from the light receiving element 73a by the reflection of infrared light of the developer in the unused state.
It is measured and this value is stored in the memory in the image forming apparatus main body. When copying is started and the use of the developer is started, the output sig-cur from the light receiving element due to the reflection of the developer at that time is measured for each copy. And the difference Δsi with the sig-init stored in the memory
Calculate g.

Δsig = (sig-init)-(sig-cur) (1) By the equation (1) and the output sensitivity value rate per 1 wt% fluctuation of the toner concentration measured in advance, the toner at that time is calculated. A deviation amount ΔD from the initial value of the density is calculated.

ΔD = Δsig / rate (2) The amount of toner replenished in the developing container is determined by the calculated value of ΔD. That is, when the deviation amount of the toner density from the initial value is negative, the amount of toner corresponding to the deviation amount is replenished, and when it is positive, the toner replenishment is stopped. For example, when ΔD = −1 wt%, 1 wt% of toner is replenished, and when ΔD = + 1 wt%, toner is not replenished. In this way, control is performed to maintain the initial toner density.

Next, as a density sensor, the developing container 9a
A case will be described in which the concentration sensors 7a and 7b are provided at two positions on the front side and the back side in the thrust direction inside. Regarding the circulation of the developer in the developing container 9a, the density sensor 7b on the back side is the upstream side, and the density sensor 7a on the front side is the downstream side. Therefore, there is a slight difference between the two density sensors in detecting the toner density. That is, the density sensor 7b on the back side reflects the toner concentration of the developer in the stirring chamber 17, whereas the density sensor 7a on the front side reflects the toner concentration of the developer whose toner is consumed in the developing chamber 18. Is reflected, the density sensor 7b on the far side shows a higher toner density value. By utilizing this property, it is possible to detect the excessive replenishment of toner by the density sensor 7b on the back side. FIG. 8 shows a flowchart of toner concentration control utilizing detection of excessive replenishment by the back side sensor. Initial toner density is 5w
The case of t% will be described. 5 wt% of this initial concentration serves as a reference value for the toner concentration.

First, the toner concentration of the developer is detected by the sensor 7b on the inner side, and 5w which is the reference value of the toner concentration is detected.
Judge whether t% or more. If it is 5 wt% or less, toner replenishment control is performed based on the difference in detection output between the front side sensor 7a and the back side sensor 7b, which will be described later. When the back side sensor 7b determines that the concentration is 5 wt% or more, the toner concentration of the developer is detected by the front side sensor 7a to determine whether the concentration is 5 wt% or more. When it is determined that the front side sensor 7a is 5 wt% or more, the toner supply is stopped because it is excessive supply. When the determination by the front side sensor 7a is 5 wt% or less, the front side sensor 7a
The toner is replenished based on the output difference of the toner density detection of the a and the back side sensor 7b.

That is, in this method, the front sensor 7
The back side sensor 7b has an output value having a higher toner density than the sensor a, and the larger the toner consumption amount, the larger the difference between the outputs of the two sensors. The maximum value of 0. D. = 1.5 when copying a full-scale image (full-scale solid uniform image), the output difference between both sensors becomes the maximum, and in the developing device of this example, about 0.
It will be about 5 wt%.

That is, when the difference between the detection outputs of both sensors is 0.5 wt%, it is determined that the full-density image with the maximum density is copied, and the maximum toner amount Vmax consumed by the original document is determined. Replenish. Further, when a solid white image with no toner consumption is being output as an image, the output difference between both sensors disappears, and the supply difference is 0 wt%, so supply is stopped. Furthermore, when the output difference of both sensors is 0 wt% or more and 0.5 wt% or less,
Due to the output difference, replenishment is performed by proportional distribution of the toner amount Vmax and 0.

As described above, the density sensors 7a and 7b are provided in the developing container 9a at two positions on the front side and the back side in the thrust direction, and the density sensor 7b on the back side performs over-supply of toner. As a result, even in the conventional case, it is possible to eliminate the overshoot of the toner replenishment control during the copying of the original document in which the fluctuation of the toner consumption amount is large.

[0020]

However, as described above, even if the density sensors are provided at two positions in the developing container in the thrust direction, that is, the back side and the front side, as shown in FIG.
It takes time for the developer to be conveyed from the toner supply port to the detection surface of the density sensor. The developer transport speed in the stirring chamber 17 (the developer transport amount per unit time) is high depending on the transport speed of the screw 12 as it is, but the developer transport speed in the developing chamber 16 is higher than that on the developing sleeve 3. The developer is pumped up and scraped off by the screw 11 and conveyed, so that it is slow. For this reason, when the toner of the developer is consumed, the toner concentration of the consumed toner on the developing sleeve is measured by the sensor 7a on the front side.
Takes a long time to detect, and an undershoot is caused in the toner density control due to the time delay until the detection. Further, when the toner is replenished, it takes time for the front side sensor 7a to detect the toner concentration of the developer replenished with the toner, so that the ripple (fluctuation) of the toner replenishment control can be completely eliminated. There wasn't.

An object of the present invention is to increase the conveying speed of the two-component developer in the developing chamber of the developing container, reduce the time lag of toner concentration detection by the concentration detecting means on the front side, and greatly change the toner consumption amount. It is an object of the present invention to provide a two-component developing device that enables highly accurate toner density control without causing undershoot or overshoot even in the copy mode.

[0022]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention provides a rotatable developer carrier that carries a two-component developer in a developer container and conveys the developer to a developing area facing the image carrier, and a non-rotatably arranged developer carrier. Having a plurality of magnetic poles, an agitating / conveying means for agitating and supplying the developer in the developer container to the developer carrier, and a magnetic brush of the developer carried on the developer carrier. Is provided with a spike-cutting member for cutting the spikes to a predetermined spike height and supplying the developer to the developing area, wherein the magnet is a developing magnetic pole located in the developing area, and a transport area from the developer supply position to the spike-cutting position. In a two-component developing device having a carrying magnetic pole located inside and a repelling magnetic pole located inside the developing container, the two-component developing device is provided at positions in the developing container corresponding to both longitudinal ends of the developer carrier. First and second detection means for detecting the toner concentration of the developer are provided. In addition, the magnetic flux density of the weak magnetic poles existing between the magnetic poles of the repulsive magnetic pole is 100 gauss or less on the same pole side as the repulsive magnetic pole and 50 gauss or less on the different pole side. Is.

According to another aspect of the present invention, a rotatable developer carrying member carrying a two-component developer in a developing container and carrying it to a developing area opposed to an image carrying member, and a non-rotatable developer carrying member are provided. A magnet having a plurality of magnetic poles arranged in rotation, an agitating / conveying means for agitating and supplying the developer in the developer container to the developer carrier, and an amount of the developer supplied to the developer carrier. A regulating return member, and a spike-cutting member that cuts the spikes of the magnetic brush of the developer carried on the developer carrying member to a predetermined spike height, and supplies the developer to the developing area, wherein the magnet is A developing magnetic pole located in the developing region, a carrying magnetic pole located in the carrying region from the developer supply position to the cutting edge position, and a repelling magnetic pole located between the carrying magnetic poles existing in the developing container. In a two-component developing device having: First and second detecting means for detecting the toner concentration of the two-component developer are provided at positions in the developing container corresponding to both ends of the magnetic recording medium, and the regulating member is obliquely downward from the brush cutting member of the magnetic brush. The invention is characterized in that the amount of the developer supplied to the developer carrier is regulated by regulating the developer constrained on the developer carrier by a member having a linearly inclined shape. It is a component developing device. Preferably, one of the transport magnetic poles is located immediately before the ear cutting position in the rotational direction of the developer carrier, and has a magnetic flux density of 500 Gauss or less.

[0024]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a sectional view showing an embodiment of the two-component developing apparatus of the present invention. As shown in FIG. 1, the main developing device 9 arranged so as to face the photosensitive drum 4 has a two-component developer in a developer container 9a containing a two-component developer, as in the case shown in FIG. First and second density sensors 7a and 7b for detecting the toner density of the developer are installed. The other mechanical structure of the main developing device 9 is basically the same as that of the conventional developing device shown in FIG. 5, and the developing sleeve 9 as the developer carrying member and the developer supplying position are provided in the developing container 9a. A return member 1 that controls the amount of developer drawn up onto the developing sleeve 3 up to the brush cutting position, a blade 2 that functions as a brush height controlling member that controls the brush of the magnetic brush on the developing sleeve 3, and the above-mentioned first,
The second concentration sensors 7a and 7b are provided.

Similarly, the inside of the developing container 9a is formed by a partition wall 6 extending in the direction perpendicular to the paper surface of the developing container (first chamber) 1.
6 and an agitating chamber (second chamber) 17, and the two-component developer is contained in the developing chamber 16 and the agitating chamber 17.
The developer contains a non-magnetic toner and a magnetic carrier. Further, the upper portion of the partition wall 6 is opened so that the excess developer in the developing chamber 16 is collected on the stirring chamber 17 side.

The developing chamber 16 and the agitating chamber 17 are provided with first and second conveying screws 11 and 12, respectively, as developer agitating / conveying means. The first conveying screw 11 conveys the developer in the developing chamber 16 while stirring, and the second conveying screw 12 is controlled from the toner replenishing tank (not shown) from the toner replenishing tank under the control of the developer concentration controller.
The toner supplied to the upstream side of the second conveying screw 12 into the inside of 7 and the developer already in the stirring chamber 17 are conveyed while being stirred, and the toner concentration of the developer is made uniform.

The partition wall 6 has openings (developer passages) (not shown) for communicating the developing chamber 7 and the agitating chamber 8 with each other at both front and rear ends in FIG. The toner in the developing chamber 16 in which the toner is consumed and the toner concentration is lowered by the moving force of the conveying screws 11 and 12 is moved into the stirring chamber 17 through one of the developer passages. There is.

The first conveying screw 11 is arranged substantially parallel to the bottom of the developing chamber 16 along the axial direction of the developing sleeve 3 (developing width direction). It has a screw structure in which the blade member is provided in a spiral shape, and rotates to convey the developer in the developing chamber 17 in one direction along the axial direction of the developing sleeve 3 at the bottom of the developing chamber 16. The second conveying screw 12 also has a screw structure similar to that of the first conveying screw 11 (however, a blade member is provided in a spiral shape around the rotating shaft in the direction opposite to that of the first screw 11). ,
It is arranged substantially parallel to the first screw 11 at the bottom of the stirring chamber 17 and rotates in the same direction as the first screw 11 to convey the developer in the stirring chamber 17 in the opposite direction to the first screw 11. . Thus, the first and second screws 11
The developer is circulated between the developing chamber 16 and the agitating chamber 17 through the openings at the both ends of the partition wall 6 by the conveyance by the rollers 12 and 12.

The developing chamber 16 of the developing container 9a has an opening at a position corresponding to the developing area facing the photosensitive drum 4,
The developing sleeve 3 is disposed in this opening so as to be partially exposed in the direction of the photosensitive drum 4, and rotates in the arrow direction during the developing operation. The developing sleeve 3 is made of a non-magnetic material, a magnet 13 as a magnetic field generating means is installed inside the developing sleeve 3 in a non-rotating manner, and a blade 2 is arranged above the developing sleeve 3 with a small gap therebetween. There is. In this embodiment, the magnet 13 includes a developing magnetic pole S1 and a magnetic pole N1 that conveys the developer.
S2, N2, N3. The blade 2 is made of a non-magnetic material such as aluminum.

The developer in the developing chamber 17 is agitated and conveyed as the first screw 11 rotates, and is drawn and carried by the drawing pole N2 of the magnet 13 toward the developing sleeve 3. At this time, the developer drawn up by the return member 1 is regulated to limit the amount of the developer conveyed to the developing sleeve 3 to some extent. The developer drawn up by the magnetic pole N2 is formed by the magnetic field from the next magnetic pole S2, acts toward the center of the developing sleeve 3, and has a magnetic binding force determined according to the amount of the developer regulated by the return member 1. Then, the developing sleeve 3 is conveyed to the portion of the blade 2 by the conveying force acting in the rotation direction.

The developer conveyed to the blade 2 is regulated to have a predetermined layer thickness there, and is then supplied to the developing area to be used for developing the electrostatic latent image on the photosensitive drum 4. Development efficiency,
That is, in order to improve the toner application rate to the latent image, the developing sleeve 3 is applied with a developing bias voltage in which a DC voltage and an AC voltage are superposed from the power supply 15. The developer left undeveloped in the developing area is conveyed again to the developing chamber 16 by the developing sleeve 3, and the repulsive pole structure by the intake pole N3 and the scooping pole N2 causes the developer to flow from the developing sleeve 3 to the inside of the developing chamber 16. It is scraped off and collected.

The first and second concentration sensors 7a and 7b are
As in the conventional case, the developing sleeve 3 is provided between the magnetic pole S2 and the magnetic pole N2 in a region on the thrust direction from the developer scooping position until the developer is conveyed to the blade 2.
Is incorporated into the developer return member 1 so as to face the above.

The density sensors 7a and 7b are provided with bidirectional LEDs 71a and 71b, reference light receiving elements 72a and 72b, and reflected light receiving elements 73a and 73b, respectively.
b and the detection windows 8a and 8b are provided, and the developer reflection type density sensor is configured. Its detection window 8
Reference characters a and 8b are made of a transparent acrylic resin, and in order to prevent the toner from adhering to the detection surface facing the developer, the developing sleeve 3 side of the return member 1 is covered with the detection surface.
The A sheet 81 is attached.

In the present embodiment, the non-magnetic toner of the two-component developer comprises 5 to 15 wt% of a pigment for coloring dispersed in 80 to 90 wt% of a polyester resin, and a metal complex of alkyl-substituted salicylic acid as a negative charge control agent. Dispersed,
The toner is composed of toner having an average particle diameter of 5 to 11 μm, and 0.2 to ₂ wt% of titanium oxide TiO ₂ is externally added and used. Other silica may be used as the external additive.

As the magnetic carrier of the two-component developer, any ferrite carrier, especially sintered ferrite particles, is used. That is, as the core material, Zn-based ferrite, Ni-based ferrite, Cu-based ferrite, Mn-Zn-based ferrite, Mn-Mg-based ferrite, Cu-Zn-based ferrite, Ni-Zn-based ferrite, etc. are used, and triboelectrification property, Acrylic resin coated with 0.5 to 2 wt% has an average particle size of 30 to 6 for the purpose of improving environmental stability and durability.
A carrier of 0 μm was used. In addition to this, as the coating material, polyester resin, fluorine resin, silicone resin or the like can be appropriately selected and used.

The first and second concentration sensors 7a and 7b are
As in the case of FIG. 7, the developing sleeve 3 is opposed to the developing sleeve 3 between the magnetic pole S2 and the magnetic pole N2 in the thrust direction area from the developer scooping position until the developer is conveyed to the blade 2. As described above, the developer return member 1 is incorporated.

Similarly, the density sensors 7a and 7b have bidirectional LEDs 71a and 71b, reference light receiving elements 72a and 72b, and reflected light receiving element 73, respectively.
a, 73b and detection windows 8a, 8b,
It is configured as a developer reflection type density sensor. The detection windows 8a and 8b are made of a transparent acrylic resin, and in order to prevent toner from adhering to the detection surface facing the developer, the PFA is provided so as to cover the detection surface on the developing sleeve 3 side of the return member 1. The sheet 81 is attached.

Next, the toner density control using the density sensors 7a and 7b will be described. The toner density control in the present invention is basically performed using the same flow as the conventional flow chart shown in FIG. that time,
In the present invention, even in the copy mode in which the change in the consumption amount is large, the following magnetic pole configuration of the magnet 13 is adopted in order to eliminate the undershoot and the overshoot of the toner density control. The developer conveyance speed is increased so that the sensor 7a on the front side detects the toner consumption on the developing sleeve 3 and the toner concentration of the developer replenished with the toner from the toner replenishing port is detected earlier.

That is, in this embodiment, as the magnet 13 fixedly arranged in the developing sleeve 3, the magnetic pole x of weak magnetic force existing between the intake pole N3 and the scooping pole N2, which have a repulsive magnetic pole relationship (see FIG. 4) is on the same pole side as these repulsive magnetic poles, that is, the N pole side, the magnetic flux density is 10
0 Gauss or less, 5 on the other side, that is, on the south side
A magnet having a magnetic pole configuration of 0 Gauss or less was used.

By thus defining the magnetic flux density of the weak magnetic pole x between the repulsive magnetic poles N2 and N3, the developer near the repulsive pole has a small magnetic flux density of the repulsive pole, so that the developing sleeve 3 has The developer is completely scraped from the developing chamber 16 into the developing chamber 16 and circulates without being accumulated as shown by a thick arrow in FIG.

On the other hand, as in the conventional case, the magnetic flux density of the weak magnetic poles between the repelling magnetic poles is 10 on the same side as the repelling magnetic poles.
When it exceeds 0 Gauss and exceeds 50 Gauss on the opposite pole side, as indicated by a dotted arrow in FIG.
Part of the developer is not scraped off and is carried while being carried on the developing sleeve 3. Therefore, the developing room 1
The developer transport speed on the No. 6 side becomes slow.

To reduce the transport speed, toner is replenished from the toner replenishing port (the toner replenishment amount may be small), and the toner concentration of the developer replenished with the toner is detected by the concentration sensor 7a on the front side. It can be confirmed by measuring the time T up to. In the conventional configuration, this time T is about 25 seconds, whereas in the present invention it is about 15 seconds.
It was accelerated to about a second.

As described above, in this embodiment, since the developer conveying speed on the side of the developing chamber 16 is increased, the toner concentration of the developer on the developing sleeve 3 is lowered by the sensor 7a on the front side. Further, the replenishment toner supplied from the toner replenishment port can be detected quickly. Therefore, even in the copy mode in which the change in toner consumption is large, undershoot and overshoot can be eliminated as compared with toner density control based on toner density detection by the two density sensors 7a and 7b, and highly accurate toner density control is possible. I was able to.

Second Embodiment In the first embodiment, in order to increase the transport speed of the developer on the developing chamber 16 side, a weak magnetic pole between the repulsion magnetic poles N3 and N2 of the magnet fixed in the developing sleeve 3. Although the magnetic pole density of x has been defined, another method may be used as long as it can increase the transport speed of the developer on the developing chamber 16 side.

In this embodiment, focusing on the developer returning member,
As shown in FIG. 3, the return member 101 does not have a shape having a large curvature along the developing sleeve 3 as in the first embodiment, but the return member 101 is inclined obliquely downward from the blade 2 as shown in FIG. And By using the inclined return member 101, the developer conveyed by the developing sleeve 3 but regulated by the blade 2 and returned to the inside of the developing container 9a without passing through the blade 2 is A flow of the developer indicated by an arrow in the drawing occurs such that the developer flows to the screw 11 in the developing chamber 16 again. Due to the flow of the developer, the transport speed in the developing chamber 16 was increased, and the same effect as that of the example 1 was obtained.

Third Embodiment In the second embodiment, the developer return member 101 has a shape inclined obliquely downward from the blade 2.
Conveyance magnetic pole (cut pole) immediately before the developer cutting position of 3
You may combine the structure which makes the magnetic flux density of S2 low, as shown in FIG. Cutting pole S2 immediately before the developer cutting position
Conventionally, the magnetic flux density was about 800 Gauss, but in this embodiment, it was lowered to 500 Gauss or less.

In this case, since the magnetic restraining force on the developer near the cut pole becomes small, the circulation of the developer in this vicinity becomes good, and the amount of the developer flowing as shown by the arrow in FIG. 3 increases. Therefore, the developer transport speed in the developing chamber 16 is increased. As a result, the time T shown in the first embodiment until the toner is supplied from the toner supply port and detected by the density sensor 7a on the front side is shortened to about 12 seconds in this embodiment.

According to the present embodiment, since the developer conveying speed on the developing chamber 16 side is further increased, undershoot and overshoot of toner density control can be prevented even in the copy mode in which the consumption change is large. In addition to the above effect, the magnetic restraining force of the developer in the vicinity of the cut pole S2 is reduced, so that the compressive force between the developers and the rubbing force of the developer with the surface of the developing sleeve 3 are reduced. As a result, the effect of reducing the deterioration of the developer and extending the life is also obtained.

[0050]

As described above, according to the developing device of the present invention, the speed of transporting the developer on the side of the developing chamber of the developing container is increased. Among the two toner concentration detecting means provided along the side, the detecting means on the front side can reduce the time lag between the toner consumption and the replenishment detection. Therefore, even in the copy mode in which the change in toner consumption is large, the toner density control using the two detection means can be performed with high accuracy without causing undershoot or overshoot.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of a two-component developing device of the present invention.

2 is a diagram of a magnetic flux density pattern along a circumferential direction of a magnet in a developing sleeve of the developing device of FIG.

FIG. 3 is a schematic sectional view of another embodiment of the two-component developing device of the present invention.

FIG. 4 is a diagram of a magnetic flux density pattern along a circumferential direction of a magnet in a developing sleeve in still another embodiment of the two-component developing device of the present invention.

FIG. 5 is a schematic sectional view of a conventional two-component developing device.

FIG. 6 is a plan view showing how the developer circulates in the developing device of FIG.

FIG. 7 is a plan view showing that two density sensors are installed in a developing container of a conventional two-component developing device.

8 is a flowchart of toner density control when the two density sensors of FIG. 7 are used.

[Explanation of symbols]

 1 developer return member 2 blade 3 developing sleeve 7a front side density sensor 7b back side density sensor 13 magnet 101 developer return member

Claims (3)

[Claims] 1. A two-component developer in a developing container is carried,
A rotatable developer carrying member that conveys to a developing area facing the image carrying member, a magnet having a plurality of magnetic poles that are non-rotatably arranged in the developer carrying member, and a developer carrying member that is provided inside the developing container. An agitating / conveying means for agitating and supplying the developer, and an ear cutting member for cutting the ear of the magnetic brush of the developer carried on the developer carrying body to a predetermined ear height and supplying the developer to the developing area. The magnet has a developing magnetic pole located in the developing area, a carrying magnetic pole located in the carrying area from the developer supply position to the cutting edge position, and a repelling magnetic pole located in the developing container. In the two-component developing device, the first and second toner concentration detecting means for detecting the toner concentration of the two-component developer are provided at positions in the developing container corresponding to both longitudinal ends of the developer carrying member.
And a magnetic flux density of the weak magnetic pole existing between the magnetic poles of the repulsion magnetic pole is 100 gauss or less on the same pole side as the repulsion magnetic pole and 50 gauss or less on the different pole side. Two-component developing device. 2. A two-component developer in a developing container is carried,
A rotatable developer carrying member that conveys to a developing area facing the image carrying member, a magnet having a plurality of magnetic poles that are non-rotatably arranged in the developer carrying member, and a developer carrying member that is provided inside the developing container. An agitating / conveying means for agitating and supplying the developer, a developer return for controlling the amount of the developer supplied to the developer carrier, and a magnetic brush brush of the developer carried on the developer carrier. The magnet is provided with a brush cutting member that cuts the brush to a predetermined brush height and supplies the developer to the developing area, wherein the magnet is a developing magnetic pole located in the developing area and a conveying area from the developer supplying position to the brush cutting position. In a two-component developing device having a carrying magnetic pole located at a position and a repelling magnetic pole located between the carrying magnetic poles present in the developing container, the two-component developing device corresponds to both ends in the longitudinal direction of the developer carrier. The toner concentration of the two-component developer is In addition to providing known first and second detecting means, the regulating member is a member having a shape inclined in a straight line obliquely downward from the brush cutting member of the magnetic brush, and is restrained on the developer carrying member. A two-component developing device, wherein the amount of the developer supplied to the developer carrier is regulated by regulating the developer. 3. The developing device according to claim 2, wherein one of the carrying magnetic poles is located immediately before the ear cutting position in the rotational direction of the developer carrier, and has a magnetic flux density of 500 Gauss or less.