JPS6157967A - Developer density controller - Google Patents

Abstract

PURPOSE:To stabilize the detection output of a sensor to control the density of a developer more surely by providing the sensor which detects the toner concentration so that the sensor faces a sleeve constituting a developing roll and providing a magnet, which has a magnetic pole different from one magnetic pole of a magnet in the sleeve, near the sensor. CONSTITUTION:A sensor 20 which detects the toner concentration of a developer 2 is arranged to face a pole N2 of a magnet 11. The sensor 20 is attached to an upper cover 18 of a developing tank 19 and is attached a considerable length aprat from a sleeve 10 so that the center of the sensor 20 coincides with the center of the pole N2 of the magnet 11. A magnet 17 is provided nar the sensor 20, and the magnet 17 is so arranged that the S pole differant from the pole N2 faces the magnet 11 in the sleeve 10 especially. The sensor 20 is provided in this manner to restrict a part of the developer 2 by the magnetic force of the magnet 17, and the flow of the developer 2 is controlled. Thus, a certain qualntity of the developer is accumulated in this part to uniform the flow of the developer to the sensor 20.

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 C4 degree by 1b.

Prior Art Electrophotographic copying machines, electrostatic recording devices, laser beam printers, etc. form electrostatic latent images on recording media according to image information, and are equipped with developing devices 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 two-component developer described above, if the mixing ratio of the two-component recarrier and toner is not appropriate, the image density will be low and it will be difficult to see. This may cause problems such as increased fog or other problems. Therefore, for a certain period of time, a manual toner supply adjustment device was attached to the supply device that supplied toner into the developing device, and the user could easily use this device to make copies.
．． ) I was trying to make adjustments as soon as I noticed a change in the temperature.

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 make appropriate adjustments. Furthermore, it was extremely troublesome for the user to perform various adjustments.

In order to overcome the above drawbacks, various automatic development density control methods have been proposed and implemented. Among these, there are those that detect and control the magnetic permeability that changes depending on the mixing ratio of carrier and toner, or those that detect and control the color that changes depending on the mixing ratio of carrier and toner that are colored in different colors. There are some that control the amount of toner by using a fixed amount of carrier, and others that control by capturing the 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. 5. The developer 2 is sufficiently stirred and put into the developing device 1 by the stirring roller 4, 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 contact between the developer and the ceramic vibrator 6 (sensing element) installed at the reference position is lost, causing the vibrator to vibrate. is started and 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 reaches the reference position, the vibration of the vibrator 6 stops and the supply of the toner 7 also stops. By repeating these steps thereafter, it is clear that this method assumes that the carrier and toner are sufficiently stirred 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 volume decreases in the opposite direction. This is due to the fact that the amount of toner increases and decreases and the standard density 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. The above method has the problem that capri occurs as the number of copies increases, since the amount of carrier decreases within the paper.

On the other hand, if the magnetic permeability, which changes depending on the mixing ratio of carrier and toner, is detected and controlled, there is an advantage that the mixing ratio of toner can be kept constant even if the carrier decreases. An example thereof is shown in FIG. In FIG. 6, the same parts as in FIG. 5 are indicated by the same reference numerals. In the figure, the developing roller 3 is a cylindrical sleeve 1 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 in the magnet 11, 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 rotates in the direction of the arrow. be done. As a result, the developer 2 adhering to the sleeve 10 is conveyed to the development area, and by facing the N1 pole, stands up like a brush and rubs the surface of the photoreceptor 5, thereby adhering the toner to the electrostatic latent image. I'm letting you do it. 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 arranged particularly at a position facing the N2 pole after the development is completed. That is, as the sleeve 10 rotates, the developer 2 after development faces the N2 pole, 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 maintain a constant toner concentration. If this is the case,
Even if the amount of carrier in the developer 2 decreases, the toner concentration can always be controlled to be constant because the magnetic permeability, which changes depending on the mixed state of the toner, is detected regardless of changes in the volume of the developer.

However, since the developer 2 whose adhesion amount is regulated by the doctor 12 flows on the surface of the sensor 13, the doctor 1
According to the change in the amount regulated by the developer 2, 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 detection output of the sensor 13 changes greatly depending on the size of the space (air) 14 formed between the sensor 13 and the developer 2, as shown in FIG. For example, as shown in the characteristic diagram of FIG.
The output of No. 3 changes sharply depending on the amount of control (width X) of the doctor 12. In this way, changing the doctor width X means changing the space 14 by controlling the amount of developer 2 conveyed by the sleeve 10. Therefore, as shown in FIG. Depending on the size, sensor 13
This means that the output is greatly affected and the output is not stable.

Also, the mounting position of the sensor 13 is the same as that of the magnet 11.
2 Even if you shift left or right, the output changes greatly.

In other words, the same applies even if the fixed position of the magnet 11 is shifted. Its characteristics are shown in FIG. In this figure, for example, the distance between the N1 pole facing the photoconductor 5 and the fixed position at the position where the center of the N2 pole and the center of the sensor 13 coincide is set as 20-, and the main pole of N1 in FIG. By shifting clockwise, 19.18... is bound, and by shifting counterclockwise, 21.22... is illustrated. As shown in the figure, the output from the sensor 13 changes greatly even when the sensor 13 or the magnet 11 is misaligned.

Furthermore, since the developer 2 is conveyed at high speed by the rotation of the sleeve 10, 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, and the primary purpose of the present invention is to keep the toner concentration constant. The purpose is to stabilize the

Another object of the present invention is to keep the flow rate of developer to a sensor for detecting toner concentration constant and stabilize the output from the sensor.

<Embodiment> 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. 6 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 includes a developing roller 3 consisting of a cylindrical non-magnetic sleeve 10 and a magnet 11 with an odd number of poles provided inside the sleeve in a developing tank 21. The sleeve 10 rotates clockwise in the figure. The magnet 11 is fixed so that the Nl pole (main pole) in particular faces the developing position of the photoreceptor 5. Therefore, sleeve 1
The developer 2 is attracted onto the developer 2 by the magnetic force of the magnet 11, and this developer 2 is conveyed to the developing position facing the photoreceptor 5 as the sleeve 10 rotates, and after this conveyance, it is attracted onto the developing leap 10. While the developer 2 is being conveyed to a position facing the photoreceptor 5, the amount of the developer 2 adhered to the developer 2 is regulated to a constant amount by a doctor 12. The doctor 12 is fixed to the side plate of the developer tank 19 with screws so as to be spaced apart by the sleeve 10 area X.

In the developing device configured as described above, the sensor 20 for detecting the toner concentration of the developer 2 is connected to the N2 magnet.
It is placed facing the pole.

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. Further, the sensor 20 is provided with a magnet 17 near the sensor as shown in FIG. Magnet 7) 17 is particularly used for magnet 1 in sleeve 10.
The opposite N2 pole of one and the opposite S pole are arranged to face each other. In other words, the magnets 17 having opposing magnetic poles and different polarities are provided.

By providing the sensor 20 as described above, the magnet 1
A part of the developer 2 is restrained by the magnetic force of 7, 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 7 17 always binds a certain amount of developer 2, and this developer 2 causes
A pool is always formed around the sensor 20 surface, and the sensor 20
The space 14 of the unstable element is filled by filling the surrounding area with developer, thereby acting to always feed a constant amount of developer. For example, when the amount of developer 2 transported increases, the flow rate is suppressed to a constant level in the sensor 20 area by the action of the magnet 17, 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 2
The amount of developer flowing into part 0 is always constant.

Therefore, even if the amount of developer regulated by the doctor 12 changes, the amount of developer flowing to the sensor 20 is kept constant by the action of the magnet 17.

Therefore, the output of the sensor 20 is stable, it is possible to accurately detect the toner concentration, and the developer concentration can be controlled at a constant level.Also, although the developer 2 flows at high speed according to the 100 revolutions of the sleeve, the sensor 20 A part of it is restrained by the magnet 17, resulting in a low speed, which also has the effect of reducing variations in concentration changes due to pressure.

FIG. 2 is a block diagram showing an example of toner concentration control based on the output of the sensor 20 according to the present invention. As shown in the figure, the sensor 20 has a coil L1 for applying a reference signal to a ferrite core 21, a coil L2 for detecting the magnetic permeability of the developer 2, and a coil L3 for adjusting the reference. facing the developer 2 that detects the
The developer 2 and the ferrite core 21 constitute a closed magnetic path. Further, on the coil L3 side, a screw-shaped reference adjustment core 22 is provided that forms another closed magnetic path with the ferrite core 21, and the core 22 adjusts the magnetic flux passing through the coil L3. The coil L2 and the coil L3 are wound in opposite directions and have one end commonly connected. The other end of the coil L3 is grounded, and the other end of the coil L2 is connected to one terminal of the phase detector 23.

An oscillator 24 that outputs a reference signal is connected to the coil Ll, and an oscillator 24 that is supplied with the reference signal.
An inverted signal of the reference signal 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, as 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. A composite signal of the voltage of the coil L2 and the voltage of the coil L2 is supplied to the position detector 23, so that the phase relationship with the reference signal is compared, and the resultant signal is supplied to the comparator 26 of the output signal. Therefore, the voltage comparator 26 outputs a signal (H''). This causes the output section 27 to drive the motor etc. that rotate the toner supply roller 8.

However, if the toner concentration is at a constant level, the output of the voltage comparator 26 becomes (L''), and the supply roller 8 is not rotated.
The reference adjustment core 22 of the sensor 20 is adjusted so that the output from the smoothing circuit 25 when accommodated in the sensor 9 is lower than (or equal to) the reference voltage of the voltage comparator 26.

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 diagram showing the details of FIG. 2.

In the figure, the power supply voltage V is supplied via a resistor R1 to a constant voltage circuit 28 consisting of a Zener diode ZDI and a capacitor C1, and is supplied as a constant voltage to one input terminal of an exclusive OR circuit EXI that constitutes an oscillator 24. Supplied. The oscillation output of circuit EXI is supplied to coil L1 of sensor 20 and to capacitor C3. The other terminal of the coil L1 is connected to the connection part with the resistor R2 and the capacitor C2, and an oscillation output signal having the opposite phase to the output of the circuit EXI is supplied to the other input terminal of the circuit EXI via the resistor R2. It is also supplied to one input terminal of an exclusive OR circuit EX3 of a 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 L2 and the reference toner concentration adjustment coil L3 of the sensor 20 is supplied to the pace terminal of the amplification 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 Ql 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 having 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 sent to a smoothing circuit 25 consisting of a resistor R5 and a capacitor C6, which generates a signal (voltage) according to the pulse width.
and is applied to one input terminal of the exclusive OR circuit EX4 of the comparison circuit 26 as a signal to be detected.

The exclusive OR circuit EX4 has its reference input terminal grounded, and outputs a signal (H'') when a voltage higher than the threshold is input to one input terminal.Therefore, one input terminal of the circuit EX4 The detected signal value added to is
The reference adjustment core 22 is adjusted so that the developer has a value less than (or equal to) a threshold at 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 than the exclusive OR circuit EX3 is output.

Then, the smoothing circuit 25 converts it to a voltage value higher than the reference value and applies it to the circuit EX4. As a result, circuit EX4
An H" signal is output from this. This signal ('"H") is
The signal 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. Transistor Q2 becomes conductive, thereby activating, for example, a motor for rotating toner supply row 28.

The above is an example of a control circuit for detecting magnetic permeability based on a change in toner concentration, replenishing toner, and keeping 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. In addition, it is also possible to detect the toner concentration by detecting not only the magnetic permeability but also the conductivity of the developer.Also, as shown in Figure 4, the magnet is connected to the sensor 20 of the developer 2. Even if the magnet 17A is provided on the exclusion side without providing it on the entrance side, the same effects as in FIG. 1 can be obtained. That is, the magnet 17A restrains a portion of the developer 2, and this serves as a stopper. Therefore, it acts to form a developer pool on the developer entrance side of the sensor 20 section, and the developer flowing into the sensor 20 is arranged so that the magnetic pole N2 of the magnet 11 and the magnet 1-17A face each other as shown in the figure. , the arrangement position of the sensor 20 may be shifted. By arranging the magnet 17A to face the magnetic pole N2 of the magnet 11 in this way, the binding force on a portion of the developer is strengthened, and the sensor 20 enters the sensor 20 on the entrance side (the opposite side to the magnet 17A).
This increases the effect of keeping the amount of developer at a constant level.

Normally, in order to adjust the image density, the angle of the main pole Nl of the magnet 11 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 2o does not change with respect to a predetermined (reference) toner concentration of the developer. In this regard, according to the present invention, since the magnet 17 (17A) is provided to keep the amount of developer flowing to the sensor 2o constant, even if the width・As shown in the figure, stable output can be obtained without 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. In other words, if the toner concentration is high,
The conductivity decreases, and conversely, if the conductivity decreases, the amount of toner mixed into the carrier decreases, 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, a sensor for detecting toner concentration is provided so as to face the sleeve constituting the developing roller, and the sensor is disposed opposite to the magnetic pole of one of the magnets in the sleeve. Since the pole magnet 7 is provided near the sensor, the area around the sensor is filled with developer due to the magnetic force between the magnets and the developer. Since the amount of developer flowing through the sensor is regulated at a constant level, the detection output of the sensor becomes stable and more reliable developer concentration control is possible.

[Brief explanation of the drawing]

FIG. 1 is a cross-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. 3 is a detail of FIG. 2. FIG. 4 is a sectional view of a developing section showing another embodiment of the present invention, FIG. 5 is a sectional view of a developing section related to conventional developer concentration control based on volume change, and FIG. 6 is a sectional view of a developing section showing another embodiment of the present invention. Cross-sectional view of a developing section related to conventional developer concentration control by changing magnetic permeability, No. 7
8 and 8 are characteristic diagrams showing the sensor output according to FIG. 6. 2: Developer 3: Developing roller 5: Photoreceptor 8: Toner supply row 210 sleeve 11: @stone 12: Doctor 17.17A: Magnet 20: Sensor 23:
Phase detector 24: Reference signal oscillator 26: Comparator 27
: Output section

Claims (1)

[Claims] 1. A magnet consisting of multiple poles, a non-magnetic sleeve rotated to cover the magnet, and detecting the toner concentration of the developer that faces one pole of the magnet and is conveyed by the rotation of the sleeve. A developer characterized in that it is equipped with a sensor, a magnet disposed near the sensor and having a polarity opposite to one of the magnets, and a control means for controlling toner supply in accordance with the output of the sensor. concentration control device.