JPH045386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a developing device for visualizing an electrostatic latent image formed on a recording medium, and particularly to a device for controlling developer concentration.

<Prior art> Electrophotographic copying machines, electrostatic recording devices, laser beam printers, etc. form an electrostatic latent image on a recording medium according to image information, and are equipped with a developing device to visualize this latent image. ing. That is, the developing device creates a visible image by selectively attaching toner to the electrostatic latent image. In this case, the developing device uses, for example, a two-component developer consisting of the above-mentioned toner and carrier.

When visualizing an electrostatic latent image using the above two-component developer, if the concentration of the two components, that is, the mixing ratio of carrier and toner is not appropriate,
The image density may be low and difficult to see, or it may be too dark, causing problems such as increased fogging. Therefore, until a certain point in time, a manual toner supply amount adjustment device was attached to the supply device that supplied toner into the developing device, and the user was able to adjust this when he noticed a change in the copy density. . However, even if the amount of toner supplied is adjusted, the mixing ratio within the developing device does not change rapidly, resulting in a problem with responsiveness. Moreover, it was therefore difficult to adjust the concentration to an appropriate level. Furthermore, it was extremely troublesome for the user to perform operations for each adjustment.

In order to overcome the above drawbacks, various automatic development density control methods have been proposed and implemented. Among these, there is one that detects and controls magnetic permeability that changes depending on the mixing ratio of carrier and toner, or one that detects and controls the color that changes depending on the mixing ratio of carrier and toner that are colored at different points. There are some that perform control by using a fixed amount of carrier, and others that control by capturing a change in the amount of toner with respect to a fixed amount of carrier as a change in volume.

Among these methods, the method of controlling the change in the amount of toner as a change in volume is often used because the reference value can be easily detected. This method will be explained with reference to FIG.
The mixture is sufficiently stirred and its height is approximately constant as long as the concentration is constant. Now, when the toner in the developer 2 is consumed by copying, the volume decreases by that amount and the surface position of the developer lowers. When the developer surface position falls below the reference position in this way, the ceramic vibrator 6 (sensing element) installed at the reference position loses contact with the developer, and the vibrator starts to vibrate. , a detection signal is sent to the control circuit. Based on this signal, a drive motor (not shown) that drives the toner supply roller 8 of the toner supply device 9 is energized by the control circuit, and toner supply is started. Thereafter, when the volume of the developer 2 increases again and rises to the reference position, the vibration of the vibrator 6 stops and the toner 7
supply will also be suspended. Thereafter, by repeating these steps, the concentration of the developer 2 is automatically controlled. In the figure, 3 is a developing roller, and 5 is a photoreceptor.

It is clear that this method assumes that the carrier and toner are sufficiently agitated and that the amount of carrier is always constant. That is, for the former, the volume of the mixture of carrier and toner decreases to a certain extent as it is stirred, and for the latter, as the amount of carrier increases or decreases, the amount of toner increases in the opposite direction. This is due to the fact that the amount increases or decreases and the standard concentration cannot be maintained.

However, it cannot be said that the replacement developer during maintenance is sufficiently agitated and the volume change converges, and the carrier also adheres to the photoreceptor during development, albeit in a small amount, and this repeats over and over again. Since a considerable amount of the carrier is reduced during printing, the above method has the problem of fogging as the number of copies increases.

On the other hand, if the magnetic permeability which changes depending on the carrier and toner mixing ratio is detected and controlled, there is an advantage that the toner mixing ratio can be kept constant even if the carrier decreases. An example is shown in FIG. In FIG. 5, the same parts as in FIG. 4 are indicated by the same symbols. In the figure, the developing roller 3 is housed in a cylindrical sleeve 10 made of a non-magnetic material.
A magnet 11 consisting of a large number of poles with the _N1 pole as the main pole is provided, and the main pole of the magnet 11 is fixed so as to be located in the developing area facing the photoreceptor 5, and the sleeve 10 is rotated in the direction of the arrow. . As a result, the developer 2 adhering to the sleeve 10 is transported to the development area, and by facing the _N1 pole, it stands like a brush and rubs against the surface of the photoreceptor 5, converting the toner into an electrostatic latent image. It is attached. While the developer 2 is being conveyed to the development area, the amount of the developer 2 adhering to the sleeve 10 is regulated by a doctor 12 to a constant amount.

In the structure as described above, the sensor 13 for detecting the toner concentration is used especially after the completion of development.
It is placed opposite the _N2 pole. In other words,
The developer 2 after development due to the rotation of the sleeve 10 is
By facing the _N2 pole, it stands up like a brush and flows so as to come into sliding contact with the detection surface of the sensor 13. Thereby, the magnetic permeability of the developer 2 is detected and the drive of the toner supply roller 8 of the toner supply device 9 is controlled to keep the toner concentration constant. With this, even if the carrier of developer 2 decreases, the toner concentration can always be controlled at a constant level because the magnetic permeability that changes depending on the mixed state of toner is detected regardless of changes in the volume of the developer. Become.

However, since the developer 2 whose adhesion amount is regulated by the doctor 12 flows on the surface of the sensor 13,
According to a change in the amount regulated by the doctor 12, the area where the developer 2 contacts the sensor 13 changes greatly. As a result, the sensor 13 erroneously detects a change in magnetic permeability, making toner concentration control unstable. In particular, the sensor 13 shown in FIG.
The detection output of the sensor 13 changes greatly depending on the size of the space (air) 14 created between the developer 2 and the developer 2 . For example, as shown in the characteristic diagram of FIG. 6, the output of the sensor 13 changes greatly depending on the amount of restriction (width x) of the doctor 12. In this way, changing the doctor width x
By controlling the amount of developer 2 transported by
Space 14 will change. Therefore, as shown in FIG. 6, depending on the size of the space 14, the sensor 1
This means that the output of 3 is greatly affected and the output is not stable.

Further, even if the mounting position of the sensor 13 is shifted to the left or right from the magnetic pole _N2 of the magnet 11, its output changes greatly. In other words, the same applies even if the fixed position of the magnet 11 shifts. Its characteristics are shown in FIG. This figure shows, for example, N ₁ facing the photoreceptor 5 at a position where the center of the N ₂ pole and the center of the sensor 13 coincide.
By setting the distance between the pole and the fixed position as 20 mm, and shifting the main pole of N ₁ clockwise in Figure 5, 1
9, 18... and shift it counterclockwise to 2.
Illustrated as 1, 22... As shown in the figure, even if the sensor 13 or magnet 11 is misaligned,
The output from the sensor 13 changes significantly.

Furthermore, due to the rotation of the sleeve 10, the developer 2 is
Since the developer is transported at high speed, the magnetic permeability varies depending on the fluidity of the developer itself, the internal pressure of the developer, etc., which causes the detection output to become unstable.

<Object of the Invention> The present invention controls the toner concentration by detecting the magnetic permeability of the developer, for example, by keeping the flow rate of the developer constant to the sensor for detecting the toner concentration. The purpose is to stabilize the detection output.

<Example> FIG. 1 is a sectional view of a developing device portion showing a specific example of a developer concentration control device according to the present invention. In the figure, the same parts as in FIG. 5 are given the same reference numerals. This detects a change in toner concentration as a change in magnetic permeability, and performs toner replenishment by comparing the magnetic permeability at a reference toner concentration with the magnetic permeability when the toner concentration decreases. In the figure, 5 is a drum-shaped photoreceptor, and 15 is a developing device that develops an electrostatic latent image formed on the photoreceptor. The developing device 15 is the developing tank 2
1 is provided with a developing roller 3 consisting of a cylindrical non-magnetic sleeve 10 and magnets 11 each having an odd number of poles and provided within the sleeve. The sleeve 10 is rotated clockwise in the figure, and the magnet ₁₁ is particularly
A pole (main pole) is fixed to face the developing position of the photoreceptor 5. Therefore, the developer 2 is attracted onto the sleeve 10 by the magnetic force of the magnet 11, and as the sleeve 10 rotates, the developer 2 is conveyed to a developing position facing the photoreceptor 5. After this conveyance, a developer tank 19 and is stirred by the stirring roller 4.
The developer 2 adsorbed onto the sleeve 10 is transferred to the photoreceptor 5
While being transported to a position opposite to Doctor 1,
2, the amount of adhesion is regulated to a certain amount. Doctor 1
2 is screwed to the side plate of the developer tank 19 at a distance x from the sleeve 10.

In the developing device configured as described above, a sensor 20 for detecting the toner concentration of the developer 2 is provided.
is placed so as to face the _N2 pole of the magnet.
This sensor 20 is attached to the upper lid 18 of the developer tank 19, and is attached at a considerable distance from the sleeve 10 so that the center of the sensor 20 coincides with the center of the _N2 pole of the magnet 11. Also,
As shown in FIG. 1, the sensor 20 is provided with magnets 17 on the inlet and outlet sides of the developer near the sensor. The magnet 17 is particularly suitable for sleeve 1.
The opposing N ₂ pole and the opposite S pole of the magnet 11 in 0 are arranged so as to face the N ₂ pole. In other words,
A magnet 17 with opposing magnetic poles and different polarities is provided.

By providing the sensor 20 as described above, a part of the developer 2 is restrained by the magnetic force of the magnet 17, and the flow of the developer 2 is regulated. Therefore, a certain amount of developer accumulates in that portion, and the flow of the developer flowing to the sensor 20 can be made constant. The magnet 17 always binds a certain amount of developer 2, and this developer 2 always forms a pool around the sensor 20 surface.
The space 14 of the unstable element is removed by filling the surrounding area with developer. This acts to always feed a constant amount of developer. For example, if the amount of developer 2 conveyed increases, the sensor 20 will
7, the flow rate is suppressed to a constant level, and the flow rate increases in areas other than the sensor 20 area.
Moreover, if the conveyance amount of the developer 2 decreases, the developer 2 is attracted by the magnet 17 and the sensor 20
The amount of developer flowing into the area is always constant.

Therefore, even if the amount of developer regulated by doctor 12 changes, the amount of developer flowing to sensor 20 is kept constant by the action of magnet 17.
Therefore, the output of the sensor 20 is stabilized, it is possible to accurately detect the toner concentration, and the developer concentration can be controlled to be constant.

Further, although the developer 2 flows at high speed as the sleeve 10 rotates, a part of the developer 2 is restrained by the magnet 17 in the sensor 20 and flows at a low speed. There is also.

FIG. 2 is a block diagram showing an example of toner concentration control based on the output of sensor 20 according to the present invention. As shown in the figure, the sensor 20 includes a coil L ₁ that applies a reference signal to a ferrite core 21, a developer 2
A coil L ₂ for detecting magnetic permeability and a coil L ₃ for reference adjustment are wound around the coil L 2 , and in particular, the coil L ₂ side is made to face the developer 2 to be detected, and the developer 2 and the ferrite core 21 are It forms a closed magnetic circuit. Further, on the coil L ₃ side, a screw-shaped reference adjustment core 22 is provided which forms another closed magnetic path with the ferrite core 21.
Adjust the magnetic flux passing through L ₃ . Coil L ₂ & Coil
L ₃ is wound in the opposite direction, and one end is connected in common. The other end of the coil L ₃ is connected, and the other end of the coil L ₂ is connected to one terminal of the phase detector 23 .

An oscillator 24 that outputs a reference signal is connected to the coil _L1 , and is supplied with the reference signal. An inverted signal of the reference signal of the oscillator 24 is supplied to the other terminal of the phase detector 23. The phase detector 23 outputs a square wave (pulse) signal according to the phase difference between the two signals, and this output signal is supplied to the smoothing circuit 25. In other words, when the toner concentration of the developer 2 decreases, the magnetic permeability increases, and the voltage induced in the coil _L2 increases in proportion to this, and the phase shifts as well. Then, a composite signal of the induced voltage of the coil L ₃ that hardly changes and the voltage of the coil L ₂ is supplied to the position detector 23, so that
The phase relationship with the reference signal is compared, and the pulse width of the output signal is increased. Therefore, since the pulse width is wide in the smoothing circuit 25, the voltage is supplied to the next voltage comparator 26 as a high voltage. Therefore, the voltage comparator 26 outputs a signal (“H”). As a result, the output unit 27 drives the motor that rotates the toner supply roller 8 .

However, if the toner concentration is at a certain level,
The output of the voltage comparator 26 becomes (“L”), and the supply roller 8 is not rotated. In other words, the sensor 2
0 reference adjustment core 22 is being adjusted. Therefore, if the toner concentration decreases, the phase detector 23 outputs a signal (pulse width) that is larger than the reference voltage of the comparator 26, and the toner supply is controlled until the reference toner concentration is reached.

FIG. 3 is a circuit configuration diagram showing details of FIG. 2. In the figure, the power supply voltage V _D is connected to a Zener diode ZD1 and a capacitor C through a resistor R1.
an exclusive OR circuit that is supplied to the constant voltage circuit 28 consisting of 1 and constitutes the oscillator 24 as a constant voltage.
It is supplied to one input terminal of EX1. circuit
The oscillation output of EX1 is supplied to coil _L1 of sensor 20 and to capacitor C3. Coil L ₁
The other terminal of is connected to the connection part with resistor R2 and capacitor C2, and the circuit is connected via resistor R2.
The oscillation output signal with the opposite phase to the output of EX1 is the circuit EX1.
It is also supplied to the other input terminal of the phase detector 23 and one input terminal of an exclusive OR circuit EX3 of the phase detector 23, which will be described later. The oscillation frequency of the oscillator 24 is determined by capacitors C2, C3, etc.

The combined induced voltage of the detection coil L ₂ and the reference toner concentration adjustment coil L ₃ of the sensor 20 is supplied to the base terminal of the amplifying transistor Q1 with the direct current component cut off via the capacitor C5.
A constant voltage is supplied to the collector of the transistor Q1 via the resistor R3, and the emitter is grounded. The amplified collector output of the transistor Q1 is supplied to the other terminal of the above-mentioned exclusive OR circuit EX3 for phase detection via an exclusive OR circuit EX2 for waveform shaping. In other words,
The circuit EX3 outputs a pulse signal with a width corresponding to the phase difference between the reference signal and the detection signal due to the change in magnetic permeability. This pulse signal is then converted into a signal (voltage) according to the pulse width by a smoothing circuit 25 consisting of a resistor R5 and a capacitor C6, and is sent to one input terminal of an exclusive OR circuit EX4 of a comparator circuit 26 to be detected. It is added as a signal.

The exclusive OR circuit EX4 has a reference input terminal grounded, and outputs a signal ("H") when a voltage equal to or higher than the threshold is input to one input terminal. Therefore, the reference adjustment core 22 is adjusted so that the detected signal value applied to one input terminal of the circuit EX4 has a value less than (or equal to) the threshold when the developer has a reference toner concentration. Therefore, when the toner concentration decreases, the phase of the detection signal deviates significantly from the reference phase due to a change in magnetic permeability, and a signal with a wider pulse width is output from the exclusive OR circuit EX3. And smoothing circuit 25
is converted to a higher voltage value than the reference value, and the circuit
Add to EX4. This causes “H” from circuit EX4.
A signal is output. This signal (“H”) is supplied to the base terminal of the transistor Q2 via the resistor R7 of the output section 27, and makes the transistor Q2 conductive. When the transistor Q2 becomes conductive, it drives a motor for rotating the toner supply roller 8, for example.

The above is an example of a control circuit for detecting magnetic permeability based on changes in toner concentration and replenishing toner to keep the toner concentration constant. It is not limited to circuits such as That is, although magnetic permeability is detected by phase detection in FIG. 3, changes in magnetic permeability may be detected directly as voltage changes. Further, it is also possible to detect the toner concentration by detecting not only the magnetic permeability but also the electrical conductivity of the developer.

Here, in order to perform the above-mentioned action more effectively, the arrangement position of the sensor 20 may be shifted so that the magnetic pole _N2 of the magnet 11 and the magnet 17A face each other as shown in the figure. Magnet 17 like this
By arranging A to face the magnetic pole _N2 of the magnet 11, the restraining force on a portion of the developer is strengthened, and the effect of making the developer pool constant on the entrance side of the sensor 20 (the side opposite to the magnet 17A) is enhanced.

Usually, the main pole N ₁ of the magnet 11 is used to adjust the image density.
The angle with respect to the photoreceptor 5 and the doctor width are adjusted in the initial state. Therefore, it is desirable that the output of the sensor 20 does not change with respect to a predetermined (reference) toner concentration of the developer. In this regard, according to the present invention, since the magnets 17 and 17A are provided to keep the amount of developer flowing to the sensor 20 constant, even if the width It is possible to obtain stable output without causing large output changes.

According to the present invention, the toner concentration is detected by detecting the magnetic permeability of the developer, but the same effect may be achieved by detecting the electrical conductivity of the developer. That is, if the toner concentration is high, the electrical conductivity will be low, and conversely, if the electrical conductivity is low, the amount of toner mixed into the carrier will be reduced, and by detecting this, the toner concentration can be easily detected.

<Effects of the Invention> According to the developer concentration control device of the present invention, the sensor for detecting the toner concentration is provided to face the sleeve constituting the developing roller, and the sensor is provided opposite to one magnetic pole of the magnet in the sleeve. Magnetic magnets are installed on the inlet and outlet sides of the developer near the sensor, so the magnetic force between the magnets causes the developer to bind to the developer around the sensor. Since the amount of developer flowing to the sensor can be regulated to be constant, the detection output of the sensor is stabilized, and more reliable developer concentration control is possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a developing section for controlling developer concentration according to the present invention, FIG. 2 is a block diagram showing an example of a developer concentration control circuit according to the present invention, and FIG.
The figure is a circuit diagram showing the details of Figure 2, Figure 4 is a cross-sectional view of the developing section related to the conventional developer concentration control by volume change, and Figure 5 is the conventional developer concentration control by magnetic permeability change. The cross-sectional views of the developing section, FIGS. 6 and 7, are characteristic diagrams showing the sensor output shown in FIG. 2: developer, 3: developing roller, 5: photoreceptor,
8: Toner supply roller, 10: Sleeve, 11:
Magnet, 12: Doctor, 17, 17A: Magnet, 20: Sensor, 23: Phase detector, 24:
Reference signal oscillator, 26: comparator, 27: output section.

Claims (1)

[Scope of Claims] 1. A developer concentration control device for a developing device comprising a multi-pole magnet and a non-magnetic sleeve rotated to cover the magnet, comprising: a sensor for detecting the toner concentration of the developer after development, which is conveyed as the sleeve rotates and is disposed so as to face one pole and the top of the sleeve on the downstream side in the developer conveyance direction; a magnet with a magnetic pole opposite to the magnetic pole of the magnet in the opposing sleeve, which is provided on the developer inflow side and outflow side to the sensor so as to face the magnetic pole of the magnet in the sleeve facing the sensor; A developer concentration control device comprising: a toner supply means for controlling toner supply according to the output of a sensor; and a developer concentration control device.