JPH06194960A - Developing device - Google Patents

Abstract

PURPOSE:To improve the accuracy of detecting toner concentration, to prevent erroneous detection and to perform the appropriate control of the supply of toner. CONSTITUTION:Before the toner concentration detecting action by a toner concentration sensor 8, the revolving speed of a stirring paddle 4 is set to be high. When the toner concentration detecting action is finished, the revolving speed thereof is restored to the ordinary one. An aperture part 41c for discharging developer may be provided in the center part of the carrying tube 41 of the paddle 4 above the sensor 8. Further, a film having a smooth surface may be stuck to the detection surface 8a of the sensor 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., and more specifically, a toner concentration for detecting the toner concentration in a developer accommodating portion while flowing a developer. Based on the output value of the detection means, the toner is replenished from the toner storage portion and controlled so that the toner concentration in the developer storage portion becomes constant, and the developer transport means agitates the developer in the developer storage portion. However, the present invention relates to a developing device that conveys the developer carrier so as to circulate in the rotation axis direction.

[0002]

2. Description of the Related Art Conventionally, as a toner concentration detecting means used in this type of developing apparatus, for example, a magnetic permeability sensor which utilizes the non-magnetic property of toner and the magnetic property of carrier to measure the magnetic permeability of a developer has been used. Things are known. From the measured value of the magnetic permeability of this developer, the ratio of toner to carrier can be known.

The magnetic permeability sensor must be arranged at a position where the developer constantly passes and the developer constantly circulates while flowing. Further, the magnetic permeability sensor forms a magnetic circuit by a coil, passes the developer through the magnetic circuit, measures the magnetic permeability of the developer, and converts the change in the magnetic permeability into a change in an electric signal. Since the toner concentration of the developer is detected, it has a characteristic that it cannot be detected if there is another magnetic material or conductor in the magnetic circuit. Therefore, the vicinity of the magnetic permeability sensor as the toner concentration detecting means must be made of a non-magnetic insulator such as resin, and if the main body casing of the developing device is made of a metal material, a non-magnetic insulator such as plastic will not be used. The permeability sensor is fixed using a magnetic insulator adapter.

[0004]

By the way, when the fluidity of the developer is lowered due to the moisture absorption of the developer and the decrease in the charge amount of the developer during the rainy season or in a high humidity environment, the developer and the developing device are not affected. The coefficient of friction with the inside surface of the main body casing or with the detection surface of the toner concentration detection means increases, and the developer enters a pulsating flow state or stays, and the toner concentration detection means can accurately detect the toner concentration. Disappear. The decrease in the fluidity of the developer occurs even when the toner concentration of the developer increases.

Further, due to the influence of the blade as the stirring member of the developer carrying means, the output of the toner concentration detecting means shows a periodic change (ripple) with a certain amplitude, and the accurate toner concentration is obtained. Becomes difficult to detect.

As described above, when the toner density detection accuracy, detection sensitivity, and responsiveness deteriorate, accurate toner replenishment control cannot be performed, and the toner density becomes higher or lower than a predetermined range and image quality deteriorates. There is a problem of doing. Further, there is also a problem that the toner is scattered due to an excessive increase in the toner density, and conversely, the image density is insufficient and the carrier is adhered due to an excessive decrease in the toner density. Further, it is known that a film is attached so as to cover the detection surface of the toner concentration detection means to make the frictional force on the detection surface uniform and improve the fluidity of the developer (Japanese Patent Laid-Open No. 3-239275). ). However, there is a problem in that when the toner adheres to the surface of the film and the frictional resistance becomes large, the effect is not exhibited at all simply by sticking this film.

The present invention has been made in view of the above problems. An object of the present invention is to improve accuracy of toner concentration detection of a developer, prevent erroneous detection, and perform proper toner supply control. It is an object of the present invention to provide a developing device capable of obtaining stable image quality and free of toner scattering.

[0008]

In order to achieve the above object, a developing device according to a first aspect of the present invention is a toner concentration detecting device for detecting a toner concentration in a developer accommodating portion while flowing a developer comprising a toner and a carrier. Means, control means for replenishing toner from the toner containing portion based on the output value of the toner concentration detecting means, and controlling the toner concentration in the developer containing portion to be constant, and a developer in the developer containing portion. A developer carrying means for carrying while circulating the developer carrying body so as to circulate in the rotation axis direction of the developer carrying body, the developer carrying means at the time of detecting the toner concentration by the toner concentration detecting means, It is characterized in that a control means for controlling the stirring and circulating ability of the developer to be higher than that at the time of non-detection is provided.

According to a second aspect of the present invention, in the developing apparatus according to the first aspect, there are provided a toner replenishment position of the developer accommodating portion from the toner accommodating portion and a toner concentration detecting position by the toner concentration detecting means. It is characterized in that the developer transport path between them is configured to be short.

According to a third aspect of the invention, in the developing apparatus according to the first or second aspect, the surface is smooth so as to cover the detection surface of the toner concentration detecting means with which the developer in the developer accommodating portion is in contact. It is characterized in that a film member is attached.

[0011]

In the developing device of the present invention, the stirring and circulating ability of the developer by the developer transporting means at the time of detecting the toner concentration by the toner concentration detecting means is controlled to be higher than that during non-detection. ing. For example, control is performed so as to increase the number of rotations of the developer transport means. As a result, the flowability of the developer passing through the detection surface of the toner concentration detecting means in the developer accommodating portion is improved, the pulsating flow and the retention of the developer are eliminated, and the stirring member of the developer conveying means is used. The effect of ripple is reduced.

According to another aspect of the present invention, there is provided a toner replenishment position of the developer accommodating portion from the toner accommodating portion,
The developer carrying path between the toner density detecting means and the toner density detecting position is shortened. For example, an opening is provided in the developer transporting means in the vicinity of the toner concentration detecting means, and the developer circulating inside the developer transporting means is quickly supplied onto the detection surface of the toner concentration detecting means. I am trying to do it. As a result, the toner replenished from the toner accommodating portion to the developer accommodating portion immediately reaches the detection surface of the toner concentration detecting means, and the toner concentration of the developer replenished with the toner can be quickly measured. Like

In the developing device of the third aspect, a film-like member having a smooth surface is attached so as to cover the detection surface of the toner concentration detecting means with which the developer in the developer accommodating portion is in contact. As a result, the coefficient of friction between the developer and the detection surface of the toner concentration detecting means to which the film-shaped member is attached is reduced, and the flow of the developer on the detection surface is further improved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developing device used in a color electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 2 is a front view showing a schematic configuration of the developing device according to this embodiment. The copying machine according to this embodiment includes four developing devices 2 for developing electrostatic latent images corresponding to four colors of black Bk, cyan C, magenta M, and yellow Y formed on the photosensitive drum 1. I have it.

Each developing device 2 (2bk, 2c, 2m, 2
y) is a developing sleeve 3 in which a magnet is arranged and which can be rotated normally and reversely, a developer accommodating portion 5 in which an agitating paddle 4 as a developer conveying means is arranged, and a toner as a toner accommodating portion. A hopper 6, a toner concentration sensor 8 as a toner concentration detecting means, which is attached to the casing 7 of the developer accommodating portion 5, and the like, respectively. Since the developing devices 2 (2bk, 2c, 2m, 2y) have the same configuration, only the members of the developing device 2y for yellow are denoted by reference numerals in FIG.

FIG. 3 is a partial cross-sectional side view showing a schematic structure of the toner supply portion of the developing device 2, and FIG.
FIG. 3 is a partial cross-sectional side view showing a schematic configuration of a developer accommodating portion 5 of The developer accommodating portion 5 has a toner supply port 5a on the front side.
The agitating paddle 4 disposed inside the conveying pipe 41 extends to the lower side of the conveying pipe 41. Side (left side in the drawing) to the inner side (right side in the drawing), an inner screw 42 for conveying the developer, an outer screw 43 fixed outside the conveying pipe 41 for conveying the developer from the rear side to the front side, and It is composed of a blade member 44 as a stirring member for carrying the developer onto the developing sleeve 3 while stirring the developer, a driving unit 45 for independently rotating and driving the carrying pipe 41 and the inner screw 42. Toner supply port 5a
An opening 41a for taking in the developer inside is formed at the end of the transfer pipe 41 below the transfer pipe 41.
An opening 41b for discharging the developer from the inner side to the outer side is formed at the end portion on the back side of the. As the toner concentration sensor 8, for example, a magnetic permeability sensor can be used, and it is attached to the casing 7 below the center of the stirring paddle 4 with the detection surface 8a inside.

The developer in the developer accommodating portion 5 enters the inside of the rotating conveying pipe 41 through the opening 41a on the front side (left side in the drawing) and is fed to the inner side (right side in the drawing) by the inner screw 42. ), Is discharged from the opening 41b to the outside of the transport pipe 41, and is agitated by the blade-shaped member 44,
It is sent to the front side by the outer screw 43 and circulates while flowing.

The toner in the toner hopper 6 is replenished into the developer accommodating portion 5 from the toner replenishing port 5a by toner replenishing means (not shown) at a predetermined timing. As described above, the replenished toner is also circulated while flowing along with the existing toner and carrier inside the developer accommodating portion 5 while being agitated with the front side, the back side, and the front side.

By the way, when the charge amount (Q / M) of the developer decreases in a high humidity environment or with the passage of time, as shown in FIG. 5, the fluidity of the developer deteriorates, and the toner concentration sensor in the developer accommodating portion 5 is deteriorated. In the vicinity of 8, the developer tends to stay. If the developer stays in this way, the output value of the toner concentration sensor 8 changes with respect to the control reference voltage, which is not preferable. Generally, when the charge amount of the developer decreases, the fluidity of the developer deteriorates, the magnetic permeability is detected to be high, and the output voltage of the toner concentration sensor 8 increases.

Further, for example, in a low-temperature and low-humidity environment, the charge amount of the toner rises and the density of the copy image becomes insufficient, so it is necessary to control the toner density to a high value in order to obtain an appropriate image density. . Generally, a color developer has a large environmental change over time, and therefore the toner concentration is controlled in a wide range, for example, in the range of 2 to 10 wt%. When such control is performed, when the toner concentration is 10 wt% rather than 2 wt%, the bulk of the developer increases, and the fluidity of the developer deteriorates as shown in FIG. In the vicinity of the toner concentration sensor 8 of 5, the developer is likely to stay. When the toner concentration of the developer becomes high, the amount of the magnetic substance, that is, the carrier to be detected becomes small, the magnetic permeability is detected low, and the output voltage of the toner concentration sensor 8 becomes low as shown in FIG.

Therefore, in this embodiment, as shown in FIG. 1, the stirring paddle 4 is rotationally driven at a predetermined rotation speed (hereinafter, referred to as a normal rotation speed) by each driving means 45 at the same time when the copying is started to develop each color. The stirring paddle 4 is rotatably driven at a high rotation speed (hereinafter, referred to as a high rotation speed), and after a predetermined time has elapsed, the toner density is detected by the toner density sensor 8, and the stirring is performed at the same time when the detection of the toner density is completed. CP to return the speed of paddle 4 to the normal speed
The drive unit 45 is controlled by a control unit (not shown) including a U, a storage unit, an I / O unit, and the like.

The normal rotation speed is not required to be set so high as long as the target mixing ratio of the developer can be obtained. On the contrary, if it is set higher than necessary, stress may be applied to the gear and the developer, and the deterioration of the developer may be accelerated.

Further, as described above, the toner hopper 6
The toner replenished from the inside enters the inside of the conveying pipe 41 from the opening 41a, is sent to the inner side by the inner screw 42, is sent to the front side again by the outer screw 43 on the outer side, and is circulated. It takes a long time for the toner supplied from the port 5a to reach the position of the detection surface 8a of the toner concentration sensor 8. Therefore,
It takes a longer time for the replenishment toner to be reflected in the detection of the toner concentration, the toner replenishment is started, and the toner is continuously replenished until the toner replenishment is confirmed. The fluctuation range of the density becomes large. In view of this, in the present embodiment, as shown in FIG. 8, an opening 41c for discharging the developer is provided in the center of the conveying pipe 41 above the toner concentration sensor 8.

Further, in this embodiment, as shown in FIG. 9A, a film 9 having a smooth surface is attached to the detection surface 8a of the toner concentration sensor 8. FIG. 9B shows a modification in which the toner concentration sensor 8 is fixed to the casing 7 using the adapter 10.

As described above, according to this embodiment, since the rotation speed of the stirring paddle 4 is set high when the toner density is detected,
As shown in FIG. 10, the detection surface 8 a of the toner concentration sensor 8
The flowability of the developer in the state of the toner is improved, and the retention and pulsation of the developer are suppressed.

Further, as shown in FIG. 11, when the rotation speed of the stirring paddle 4 at the time of detecting the toner concentration becomes high, the ripple of the output voltage of the toner concentration sensor 8 due to the influence of the blade member 44 is suppressed. This is because, as shown in the explanatory diagram of the time variation of the amplitude of the ripple in FIG. 12, as the number of revolutions of the stirring paddle 4 is increased from A ′ → B ′ → C ′, the amplitude of the ripple becomes smaller, This is because averaging proceeds.

The time-dependent fluctuation curves A, B, and C of the output voltage of the toner concentration sensor 8 shown in FIG. 11 have the rotation numbers of the developing and conveying means 4 of 100, 150, and 20, respectively.
It shows the case of 0 rpm, and if the sensitivity of the toner concentration sensor 8 is 0.5 V / wt%, the curve A at the rotation speed of 100 rpm is shown.
The fluctuation range of the output voltage of the toner concentration sensor 8 is about 0.8V
Therefore, the toner concentration fluctuation range is about 1.6 wt%.
Similarly, the toner concentration fluctuation range of the curve B at the rotation speeds of 150 and 200 rpm is about 1 wt%, and the toner fluctuation range of the curve C at the rotation speed of 200 rpm is about 0.6 wt%. Here, the allowable range of toner concentration fluctuation on the image is from the target value to the change of 1 wt%, and if it exceeds this range, the density difference is easily recognized. Therefore, the fluctuation range of the ripple is 1 wt% as the toner concentration. The following is desirable.

Further, as shown in FIG. 11, the stirring paddle 4
Since the output voltage of the toner concentration sensor 8 decreases when the rotation speed is set to a high value, it is necessary to adjust the control reference voltage when setting the output voltage level with good sensitivity.

As described above, when the retention and pulsation of the developer on the toner concentration sensor 8 are suppressed and the influence of ripples is reduced, the toner concentration detection accuracy is improved and erroneous detection can be prevented. Toner can be replenished and the image quality can be stabilized. Further, it is possible to prevent toner scattering due to excessive increase in toner concentration.

Further, according to the present embodiment, as shown in FIG. 8, the toner replenished from the toner hopper 6 into the developer accommodating portion 5 is located below the toner replenishing port 5a together with the existing toner and carrier. The toner enters the inside of the conveying pipe 41 through the opening 41a, is conveyed to the inner side by the inner screw 42, and part of the developer is discharged onto the toner concentration sensor 8 through the opening 41c at the center. As a result, assuming that the developer conveyance speed by the stirring paddle 4 is constant, the toner concentration of the developer replenished with toner from the toner hopper 6 is about the same as that in the case where the opening 41c is not provided. 1 /
It is reflected in the output of the toner density sensor 8 at the time of 3. Therefore, the toner density of the developer to which the toner has been replenished can be detected quickly, the toner density control can be finely performed, and the fluctuation range of the toner density during the toner density control can be reduced.

Further, according to this embodiment, the film 9 having a smooth surface attached to the detection surface 8a of the toner density sensor 8 is used.
As a result, the frictional force with respect to the developer on the detection surface 8a becomes smaller and uniform, the developer flows smoothly, and the speed fluctuation is eliminated. As a result, the toner concentration detection accuracy of the toner concentration sensor 8 is further improved, and erroneous detection can be prevented.

It should be noted that if the film 9 is simply attached,
If the toner adheres to the surface of the film 9, the film 9
The frictional force between the surface of the developer and the developer increases, and the fluidity of the developer decreases, but if the moving speed of the developer is high to some extent as in the present embodiment, the flow of the developer does not deteriorate.

[0033]

According to the developing device of the first aspect, the flowability of the developer passing through the detection surface of the toner concentration detecting means in the developer accommodating portion is improved, and the pulsating flow and the retention of the developer are suppressed. As a result, the influence of the ripple due to the stirring member of the developer transporting means is reduced, and thereby the accuracy of detecting the toner concentration by the toner concentration detecting means is improved and erroneous detection can be prevented, so that proper toner replenishment becomes possible. The effect is that the image quality can be stabilized. Further, there is an effect that it is possible to prevent toner scattering due to an excessive increase in toner concentration.

Further, since the developer agitating and circulating ability by the developer conveying means at the time of non-detection is not set high, the developing member can be developed without giving excessive stress to the driving member such as gears and the developer. It also has the effect of not promoting the deterioration of the agent.

According to the developing device of the second aspect, the toner replenished from the toner accommodating portion to the developer accommodating portion immediately reaches the detection surface of the toner concentration detecting means and is replenished with the toner. Since the toner concentration of the developer can be measured quickly, the toner concentration can be controlled finely, and the fluctuation range of the toner concentration during the toner concentration control can be reduced.

According to the developing apparatus of claim 3, the coefficient of friction between the developer and the detection surface of the toner concentration detecting means to which the film-shaped member is attached is reduced, and the flow of the developer on the detection surface is reduced. As a result, the accuracy of toner concentration detection by the toner concentration detecting means is further improved, and erroneous detection can be prevented.

[Brief description of drawings]

FIG. 1 is a toner concentration detection and stirring paddle 4 according to an embodiment.
6 is a timing chart of rotational drive of the.

FIG. 2 is a front view showing a schematic configuration of a developing device according to an embodiment.

FIG. 3 is a partial cross-sectional side view showing a schematic configuration of a toner supply unit of the developing device 2.

FIG. 4 is a partial cross-sectional side view showing a schematic configuration of a developer accommodating portion 5 of a conventional developing device.

FIG. 5 is a characteristic diagram showing the relationship between the absolute value of the toner charge amount and the fluidity of the developer.

FIG. 6 is a characteristic diagram showing the relationship between toner concentration and developer fluidity.

FIG. 7 is a characteristic diagram showing the relationship between the toner concentration and the output voltage of the toner concentration sensor 8.

FIG. 8 is a partial cross-sectional side view showing a schematic configuration of a developer accommodating portion 5 of the developing device 2 according to the embodiment.

9A is a sectional view showing a structure of a mounting portion of the toner concentration sensor 8 according to the embodiment, and FIG. 9B is a sectional view showing a modified structure of a mounting portion of the toner concentration sensor 8.

FIG. 10 is a characteristic diagram showing the relationship between the number of revolutions of the developer transporting means and the retention of the developer.

FIG. 11 is a characteristic diagram showing a measured value of time variation of the output voltage of the toner concentration sensor 8 by the blade-shaped member 44.

FIG. 12 is an explanatory diagram of the time variation of the output voltage of the toner concentration sensor 8 by the blade-shaped member 44.

[Explanation of symbols]

 2 developing device 3 developing sleeve 4 stirring paddle 5 developer accommodating portion 5a toner replenishing port 6 toner hopper 7 casing 8 toner concentration sensor 8a detection surface 9 film 41 conveying pipe 41a, 41b, 41c opening 42 inner screw 43 outer screw 44 blades Member

Claims (3)

[Claims] 1. A toner concentration detecting means for detecting a toner concentration of a developer accommodating portion while flowing a developer comprising a toner and a carrier, and toner is replenished from the toner accommodating portion based on an output value of the toner concentration detecting means. Control means for controlling the toner concentration in the developer accommodating portion to be constant, and a developer for conveying the developer in the developer accommodating portion so as to circulate in the rotation axis direction of the developer carrier while stirring. In a developing device including a conveying unit, a control unit that controls the stirring and circulating ability of the developer conveying unit when the toner concentration is detected by the toner concentration detecting unit to be higher than that during non-detection. And a developing device. 2. A developer conveying path between a toner replenishment position of the developer accommodating portion from the toner accommodating portion and a toner concentration detecting position of the toner concentration detecting means is shortened. The developing device according to claim 1. 3. The development according to claim 1, wherein a film member having a smooth surface is attached so as to cover the detection surface of the toner concentration detecting means with which the developer in the developer accommodating portion comes into contact. apparatus.