JPH048793B2 - - 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 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 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 device 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 in different colors. 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. To explain this method with reference to FIG. 7, the developer 2 is sufficiently stirred and put into the developing device 1 by the stirring roller 4, and its height is as follows.
If the concentration is constant, it will be approximately 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 a 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. 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. 8, the same parts as in FIG. 7 are indicated by the same symbols. In the figure, the developing roller 3 is a cylindrical sleeve 10 made of a non-magnetic material.
A magnet 11 consisting of multiple poles with the _N1 pole as the main pole is installed inside the magnet 11, and the main pole of the magnet 11 is fixed to be located in the developing area facing the photoreceptor 5, and the sleeve 10 is moved in the direction of the arrow. be rotated. 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. For example, as shown in the characteristic diagram of FIG. 9, the output of the sensor 13 changes greatly depending on the amount regulated by the doctor 12. In this figure, the horizontal axis represents the doctor width, that is, the distance x between the doctor 12 and the sleeve 10.
, where the vertical axis shows the detection output by the sensor 13. Moreover, the distance between the sensor 13 and the sleeve 10 is set to 2.2 mm. As shown in the figure, if the distance x between the doctor blades 12 becomes larger,
The amount of adhered developer 2 also increases, and the output from the sensor increases. This means that the output of the sensor 13 is greatly influenced by the amount regulated by the doctor 12, 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. In this figure, for example, the position where the center of the N ₂ pole and the center of the sensor 13 coincide is shown as 20, and by shifting the main pole of N ₁ clockwise in FIG.
18... and move 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 due to the internal pressure of the fluid developer itself, which causes the detection output to become unstable.

<Object of the Invention> The present invention controls toner concentration by detecting developer concentration, for example, magnetic permeability.
The first purpose is to keep the toner concentration constant, and in particular, the purpose is to stabilize the sensor detection output.

Another object of the present invention is to stabilize the output from the sensor by considering the mounting position of the sensor.

<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. 7 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 permeability when the toner concentration decreases. In the figure, 5 is a drum-shaped photoreceptor, and 14 is a developing device that develops an electrostatic latent image formed on the photoreceptor. The developing device 14 is the developing tank 1
A developing roller 3 comprising a cylindrical non-magnetic sleeve 10 and a magnet 11 having an odd number of poles is provided inside 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, and after being conveyed, it is transferred to the developer tank 19. It is returned and stirred by the stirring roller 4. The developer 2 adsorbed onto the sleeve 10 is conveyed to a position facing the photoreceptor 5 when it is transferred to a doctor 12.
The amount of adhesion is regulated to a certain amount. doctor 12
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 arranged to face the _N2 pole of the magnet 11. This sensor 20 is connected to the upper lid 18 of the developer tank 19.
The sensor 20 is mounted 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.

The sensor 20 also has a regulating plate 1 for regulating the developer flowing into the sensor section, as shown in FIG.
5 is set. The distal end of the regulating plate 15 extends to the upper lid 18, and that portion is fixed to the inside of the upper lid 18, for example. As shown in FIG. 1, the regulating plate 15 is provided along the circumferential surface of the sleeve 10, and regulates the amount of developer flowing toward the sensor section. In particular, as shown in the figure, the regulation plate 15
The magnetic pole S ₁ of the magnet 11 regulates the amount of spikes of the developer 2 and guides the developer 2 to the sensor 20 . Moreover, in the present invention, the sensor 20 has a distance y between the sleeve 10 and the sensor 20.
are arranged in such a manner that x>y with respect to the width x in which the developer is regulated by the doctor 12.

By arranging the sensor 20 as shown in FIG. 1, the amount of developer flowing in contact with the surface of the sensor 20 is always kept constant. In other words, even if the amount of developer conveyed by the sleeve 10 increases or decreases, the regulating plate 15
The developer flowing on the sensor 20 surface is connected to the sleeve 1.
The amount is regulated to a certain amount between 0 and the regulating plate 15. Therefore, even if the amount of developer 2 deposited by the doctor 12 changes, the amount of developer flowing through the sensor section is kept constant, making it possible to obtain a stable magnetic permeability detection output and keeping the toner concentration constant. Can be controlled.
Moreover, the distance y between the sensor 20 and the sleeve 10 is
Since this is made smaller than the distance x between the doctor 12 and the sleeve 10, the effect of regulating the developer by the regulating plate 15 increases, and it becomes more reliable to keep the amount of developer flowing to the sensor section constant. .

Further, since the developer is regulated and suppressed by the regulation plate 15, the flow velocity of the developer becomes gentler, and more stable detection becomes possible.

FIG. 3 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 ferrite core 21, a coil L ₁ for applying a reference signal, a coil L ₂ for detecting the magnetic permeability of the developer 2, and a coil L ₃ for setting the reference toner concentration. The developer 2 that is wrapped around the coil and detects the coil L ₂ side in particular.
The developer 2 and the ferrite core 21 form a closed magnetic path. Further, on the coil L ₃ 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 L ₃ .
Coil L ₂ and coil L ₃ are wound in opposite directions and have one end commonly connected. The other end of the coil L ₃ is grounded, 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 , which hardly changes, and the voltage of the coil L ₂ is supplied to the phase detector 23, so that the phase relationship with the reference signal is compared, and the pulse width of the output signal is becomes larger. 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, a signal (pulse width) larger than the reference voltage of the comparator 26 is output from the phase detector 23, and the toner supply is controlled until the reference toner concentration is reached.

FIG. 4 is a circuit configuration diagram showing details of FIG. 3. 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 is connected to the connection with the resistor R2 and the capacitor C2, and is connected to the circuit EX through the resistor R2.
An oscillation output signal having an opposite phase to the output of 1 is supplied to the other input terminal of the circuit EX1, and 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 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 is 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 2
5 is converted to a voltage value higher than the reference value and applied to circuit EX4. As a result, an "H" signal is output from the circuit EX4. This signal (“H”) is
Transistor Q2 via resistor R7 of output section 27
is supplied to the base terminal of Q2, making 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. In addition, by detecting the conductivity of the developer instead of the magnetic permeability,
Can detect toner density.

By arranging the sensor 20 for detecting changes in magnetic permeability at the position shown in FIG. 1 as in the present invention,
As described above, stable detection output can be obtained. Figure 5 shows its characteristics. This figure shows developer 2
Doctor 12 and sleeve 10 that regulate the amount of adhesion
It is a characteristic diagram showing the output change based on the sensor 20 when the distance x between the sensor 20 and the sensor 20 is changed. Furthermore, the distance y between the sensor 20 and the sleeve 10 was set to 1.5 mm, and the regulating plate was also provided to correspond to this distance. The resulting detection output V _PC from the sensor 20 is as shown in FIG. As you can see from this diagram,
It can be seen that the output change is much smaller than the conventional one shown in FIG.

Furthermore, FIG. 6 is a characteristic diagram showing changes in the output from the sensor 20 by shifting the position of the main pole _N1 . In this figure, the sensor 20 is fixed as in Fig. 10,
The height H of the main pole _N1 from the reference position of the magnet 11 is 20 mm.
is the normal position, and the output changes are shown when clockwise rotations 19...16 or counterclockwise rotations 21...23 are performed. As shown in the figure, if you compare it with Figure 10,
It has been found that the present invention causes almost no output change.

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, as shown in FIGS. 5 and 6, the output changes are much smaller than those in FIGS. 9 and 10, which is very effective in keeping the toner concentration constant.

<Effects of the Invention> According to the developer concentration control device of the present invention, the developer after development is regulated by the regulating member in correspondence with one magnetic pole of the magnet, and the regulated developer is directly directed to the sensor position. As a result, the developer is regulated more effectively, a constant amount of developer can always be stably supplied to the sensor while being pushed by the regulation member, and the flow rate of the developer is slowed down. A more stable density detection output can be obtained and accurate toner density detection can be performed.

In addition, since the distance between the sensor and the sleeve is set smaller than the distance between the sleeve and the doctor, a more stable supply of developer is possible, and the center of the sensor is aligned with the center of one magnetic pole of the magnet. Therefore, even if a magnetic permeability sensor is used, toner concentration detection is stable without being affected by the magnetic force of the magnet.

Therefore, it becomes easy to maintain the toner concentration of the developer within a predetermined range.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a developing section for controlling developer concentration according to the present invention, FIG. 2 is a plan view showing a sensor section according to FIG. 1, and FIG. 3 is a developer concentration control circuit according to the present invention. A block diagram showing an example, FIG. 4 is a circuit diagram showing details of FIG. 3, FIGS. 5 and 6 are characteristic diagrams related to density control of the present invention, and FIG. 7 is a developer using conventional volume change. FIG. 8 is a cross-sectional view of a developing section related to concentration control of a conventional developer by changing magnetic permeability.
9 and 10 are characteristic diagrams showing the sensor output according to FIG. 8. 2: developer, 3: developing roller, 5: photoreceptor,
8: Toner supply roller, 10: Sleeve, 11:
Magnet, 12: Doctor, 15: Regulation plate, 20: Sensor, 23: Phase detector, 24: Reference signal oscillator, 26: Comparator, 27: Output section, x: Doctor interval, y: Distance between sensor and sleeve .

Claims (1)

[Claims] 1. Using a developing roller consisting of a magnet with multiple poles and a non-magnetic sleeve that is rotated to cover the periphery of the magnet, In a developing device that develops a latent image formed on a recording medium by rubbing a recording medium with spikes of developer, the concentration of the developer is detected as a change in magnetic permeability, and toner is supplied according to this detection output. A sensor for controlling the sleeve is placed at a position facing the sleeve after development, and the distance y between the sleeve and the sensor is <x,
And the center of the sensor is one magnetic pole (N2) of the above magnet.
The magnetic pole (S1), which is different from the main pole of the magnet, regulates the amount of spikes of the developer after development, and the regulated developer is directly opposed to the sleeve. What is claimed is: 1. A developer concentration control device, comprising: a regulating member guided to a sensor disposed in a manner that controls toner replenishment according to a detection output of the sensor;