JPH05197282A - Developing device - Google Patents

Abstract

PURPOSE:To replenish toner following the change of toner concentration. CONSTITUTION:Voltage is supplied to two stirring rollers 4 and 5 and a current flowing through developer is detected to measure the resistance of the developer. When the measured value is lower than a threshold level, the toner concentration becomes low, so that a toner motor 12 is driven to replenish the toner. When the measured value is higher than the threshold level, the toner is not replenished.

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 visualizing a latent image formed on a photoreceptor or the like with a developer, and to toner concentration control based on the resistance of the developer.

[0002]

2. Description of the Related Art In a developing device using a two-component developer composed of toner and carrier, the toner concentration of the developer has a great influence on the image quality. That is, if the toner density is low,
The image density decreases, and if the toner density is high, fogging to the non-image area is likely to occur.

Therefore, in order to control the toner concentration of the developer, conventionally, the toner concentration is detected by measuring the magnetic permeability of the developer or measuring the volume change,
Based on this, control such as toner replenishment is performed. However, the physical properties of the developer are not measured and the toner density is not controlled based on the measured physical properties.

[0004]

Although the developer deteriorates with repeated use and the resistance value changes due to changes in environmental conditions, the toner concentration is controlled to be constant. In some cases, poor image quality may occur.

Therefore, the change in the resistance value of the developer is measured by detecting the bias current when the bias voltage is applied to the magnet roller of the developing device.

However, when trying to obtain a stable measurement current when measuring the resistance of the developer, there is a linear relationship between the bias voltage and the bias current, and it is difficult to perform reproducible measurement. It was Because the carrier of the developer and the counter electrode come into direct contact with each other, sometimes an excessive current flows, which destroys the measurement circuit, or the measurement result is abnormal, resulting in stable and reproducible measurement. I couldn't do it.

Further, in the conventional toner density detecting method, when the response speed to the toner density is low, the toner replenishment control tends to be delayed, and when the change in the image density occurs due to the failure to follow the change in the black background ratio of the original document. I have a problem.

That is, as the number of copies increases, the carrier coating material in the developer is peeled off due to mechanical stress, or the toner is stuck to the surface of the carrier due to temperature stress, resulting in development. This is because the resistance value of the agent is changed and normal frictional electrification is hindered. For this reason, deterioration of image quality such as a decrease in image density and background fog is caused.

In view of the above, it is an object of the present invention to provide a developing device which controls the toner replenishment based on the change in the resistance of the developer so as to detect the change in toner density without delay and stabilize the image quality. ..

[0010]

The means for solving the problems according to the present invention is, as shown in FIG.
And at least two stirring rollers 4 and 5 are internally provided,
In a developing device provided with a toner replenishing means for replenishing toner to the developing tank 1, a voltage supply circuit 14 for applying a voltage to the two stirring rollers 4, 5 and the voltage supply circuit 14
Measuring unit 15 for measuring the resistance of the developer by the electric current flowing in
And a control unit 17 for controlling the toner replenishing means according to the detection signal from the measuring unit 15.

[0011]

In the above means for solving the problems, the stirring rollers 4, 5
When a voltage is applied to the developer, a current flows through the developer, and the resistance of the developer is measured by measuring the current. When a decrease in the toner density is detected from the measurement result, the toner replenishing means is operated to replenish the toner to immediately prevent a change in the image.

[0012]

1 is a block diagram of a developing device showing an embodiment of the present invention, in which a developing tank 1 is internally provided with a magnet roller 2, a conveying roller 3 and two stirring rollers 4 and 5. Has been done. In the figure, 6 is a doctor, and 7 is a toner concentration sensor.

The magnet roller 2 is arranged so as to face the photoconductor 8 and is composed of a cylindrical sleeve made of a conductive non-magnetic metal and a plurality of magnets fixedly arranged inside the sleeve. Is rotatable by a motor.

The doctor 3 is made of a conductive non-magnetic material, for example, an aluminum extrusion molded product, SUS304 stainless steel, and is developed above the magnet roller 2 with a space of 0.5 mm from the magnet roller 2. It is fixed to tank 1.

A toner hopper 9 is mounted on the developing tank 1, and a toner replenishing roller 11 is rotatably arranged at a toner replenishing port 10. The toner supply roller 11 is rotationally driven by the toner motor 12. Toner supply port 10
Agitating rollers 4 and 5 that agitate the toner to perform stable triboelectric charging are disposed below the.

Further, a power supply circuit 13 for applying a bias voltage to the magnet roller 2, a voltage supply circuit 14 for applying a voltage to the two stirring rollers 4, 5, and a resistance of the developer by a current flowing through the circuit 14. A measuring unit 15 for measuring
In accordance with the detection signal from the measuring unit 15, the toner motor 12
Control unit 17 for driving and controlling the toner motor drive circuit 16 of
And are provided.

The power supply circuit 13 is provided with the magnet roller 2 in order to prevent toner from adhering to the non-image portion of the photoconductor 8.
The sleeve is provided with a power source for applying a bias voltage of about 200 V, and constant voltage control is performed.

A resistor 18 for detecting a developer passing current is interposed in the voltage supply circuit 14, and the detected value is amplified by an amplifier 19 and output to an analog port of the CPU 17, and the resistor 18 is connected to the resistor 18. Measuring unit 15 from amplifier 19
Is configured.

The control unit having the CPU 17 includes a measuring unit 15
Has a function of driving the toner motor 12 to replenish the toner when the output is lower than the threshold level, and a function of stopping the toner replenishment when the output is lower than the threshold level. ing. In addition,
The threshold level is set to the output value of the measuring unit 15 when the toner density is 4%.

FIG. 2 shows the result of measuring the resistance of the developer by applying a voltage to the stirring rollers 4 and 5 using such a developing device. As you can see, the stirring rollers 4, 5
It can be seen that stable resistance measurement can be performed even when the applied voltage to V is about 5 to 24V. At this time, as the developer, a carrier obtained by coating a ferrite with a silicone resin and having an average particle size of 80 μm and a toner made of styrene-acrylic resin and having an average particle size of 10.5 μm were mixed with stirring so as to be 4% by weight. It is a component developer.

Next, the toner density of this developer is set to 2% and 6%.
Even when the resistance of each developer is measured by adjusting the value to%, it is clearly shown that the resistance value is different due to the difference in toner concentration as shown in FIG. Stable measurement results can be obtained in the range of 24V.

Here, when the resistance of the developer is measured at various toner concentrations with the applied voltage of 20 V, when the toner concentration decreases as shown in FIG. 3, the output voltage from the amplifier 19 decreases and the developer concentration decreases. Resistance increases.

Using this relationship, the output voltage of 2.8 V when the toner density is 4% is set as the threshold level,
When the resistance of the developer is measured and the output is higher than this, the toner density is low, so the toner motor 12
Is driven to replenish the toner. If the toner replenishment is low, the toner concentration is sufficiently high, so it is not necessary to replenish the toner, and the toner concentration control is performed so that the toner replenishment is prohibited.

As described above, while controlling the toner density, a document having a black background ratio of 6% and a document having a black background ratio of 35% are alternately used as a document, and a test of responsiveness to a change in toner density is performed to determine image density and background stain. Was measured.

The results are shown in FIG. For reference, FIG. 5 shows the result of the same test when the magnetic permeability sensor of the conventional method is arranged in the vicinity of the magnet roller and the toner replenishment is controlled by the detected value.

In the case of the conventional method, when the black background ratio of the original changes from 6% to 35%, the response of the sensor to the decrease of the toner density is slow, so that the toner replenishment is delayed and the image density is spread over several tens of sheets. Is seen to decrease. On the other hand, when the black background ratio of the original document changes from 35% to 6%, the toner consumption amount decreases, so that the toner density temporarily becomes high and the background stain increases. In this case also, the toner density returns to the original level with a delay of several tens of sheets.

On the other hand, when the toner density is controlled based on the result of measuring the resistance of the developer, even if the original is changed, the reaction to the change in the toner density is fast and the fluctuation range of the toner density is reduced. Moreover, the original level is restored with a response time of about several sheets, and in terms of copy image quality, changes in image density and background stains are almost inconspicuous.

Therefore, according to this method, a stable developer current signal can be taken out even with an extremely low applied voltage to the stirring roller, so that the secondary side voltage used in the copying machine can be used.

Further, it is possible to use the existing stirring roller without the need to provide a new electrode. The stirring roller is for efficiently stirring and mixing the developer and the toner to be newly supplied to give a stable triboelectric charge, and since the contact area with the developer is large and is rotated at high speed,
It is suitable as an electrode for measuring the resistance of the developer. Moreover, since the agitating roller exists just below the toner to be replenished, it is possible to measure the change in the toner concentration of the developer due to the toner replenishment without sending the response time, and it is possible to perform a quick process control. ..

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

[0031]

As is apparent from the above description, according to the present invention, the resistance of the developer is measured by the voltage supply circuit for applying a voltage to the two stirring rollers and the current flowing in the voltage supply circuit. By controlling the toner replenishment according to the measurement result, the stirring roller is located directly below the toner to be replenished, so that it is possible to immediately respond to changes in the characteristics of the developer due to toner replenishment, and to perform quick process control. it can.

Moreover, it is not necessary to provide a new electrode for measuring the resistance of the developer, and by using the existing stirring roller, the contact area with the developer is large and it is rotated at high speed. It is possible to measure the resistance of a developer having a high resistance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a developing device showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a measured resistance value of a developer and a voltage applied to a stirring roller.

FIG. 3 is a diagram showing a relationship between toner concentration and developer resistance.

FIG. 4 is a diagram showing a change in image quality when toner replenishment control is performed based on a measured resistance value of a developer.

FIG. 5 is a diagram showing a change in image quality when toner replenishment control is performed using a conventional magnetic permeability sensor.

[Explanation of symbols]

 1 developing tank 2 magnet roller 4,5 stirring roller 12 toner motor 14 power supply circuit 15 measuring unit 17 control unit

Claims (1)

[Claims] 1. A developing device in which a developing roller is internally provided with a magnet roller and at least two stirring rollers, and a toner replenishing means for replenishing the developing tank with toner is provided. A voltage supply circuit that applies a voltage, a measurement unit that measures the resistance of the developer by the current that flows in the voltage supply circuit, and a control unit that controls the toner replenishing unit according to a detection signal from the measurement unit are provided. A developing device characterized in that