JPH048794B2 - - 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 sometimes 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 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. 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. 9, the same parts as in FIG. 8 are indicated by the same reference numerals. In the figure, the developing roller 3 is a cylindrical sleeve 10 made of a non-magnetic material.
Magnet 11 consisting of many poles with N ₁ pole as the main pole
The sleeve 10 is rotated in the direction of the arrow, with the main pole of the magnet 11 being fixed in a developing area facing the photoreceptor 5. This results in
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 against the surface of the photoreceptor 5, causing the toner to adhere to the electrostatic latent image. There is. 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 in Figure 10,
The output of the sensor 13 changes greatly depending on the amount regulated by the doctor 12. In this figure, the horizontal axis shows the doctor width, that is, the distance x between the doctor blade 12 and the sleeve 10, and the vertical axis shows the detection output by the sensor 13. As shown in the figure, as the distance x between the doctor blades 12 increases, the amount of developer 2 deposited also increases, and the output from the sensor increases. This is due to the regulated amount of doctor 12.
This means that the output of the sensor 13 is greatly influenced 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 by shifting it counterclockwise, it becomes 21,
Illustrated as 22... 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, 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 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.

In addition, the present invention takes into account the mounting position of the sensor,
The purpose is to stabilize the output from 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. 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 includes a developing roller 3 disposed in a developing tank 19, which includes a cylindrical non-magnetic sleeve 10 and a magnet 11 provided inside the sleeve and having an odd number of poles.
has been established. The sleeve 10 is rotated clockwise in the figure, and the magnet 11 is fixed so that the _N1 pole (main pole) in particular faces 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. Sleeve 11
While the developer 2 adsorbed on the photoreceptor 5 is conveyed to a position facing the photoreceptor 5, the amount of adhesion is regulated by a doctor 12 to a constant amount. The 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 14 configured as described above,
A sensor 20 for detecting the toner concentration of the developer 2 is arranged to face the _N2 pole of the magnet 11 after development. This sensor 20 is the developer tank 1
9 is attached to the upper lid 18 of the magnet 11.
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. That is, the sensor 20 is arranged so that the distance y between the sleeve 10 and the sensor 20 is x>y with respect to the doctor width x.

By arranging the sensor 20 as shown in FIG. 1, the amount of developer that comes into contact with the surface of the sensor 20 does not change much even if the distance x between the doctor blades 12 changes, ensuring stable magnetic permeability detection ability. Obtainable. In other words, as shown in FIG. 9, the space (air) 15 that is an unstable element around the sensor 13 is eliminated, and the amount of developer that comes into contact with the sensor 20 surface becomes constant, allowing for stable detection. .

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 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 1 is wrapped around the coil and detects the coil _L2 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 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 is connected to the connection with the resistor R2 and the capacitor C2, and is connected to the circuit EX via 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 14 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 detected signal value applied to one input terminal of circuit EX4 is below (or equal to) the threshold when the developer has a reference toner concentration.
The reference adjustment core 22 is adjusted so that the value becomes . 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. Then, the smoothing circuit 25 converts the voltage value to a higher voltage value than the value at the reference time, and
Add to 4. As a result, an "H" signal is output from the circuit EX4. This signal (“H”) is output from the output section 2.
It is supplied to the base terminal of the transistor Q2 through the resistor R7 of 7, making 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. Furthermore, the toner concentration can be detected by detecting the conductivity of the developer instead of the magnetic permeability.

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. Here, if it is shown in FIG. 1, a part of the developer 2 is regulated at the sensor 20,
It is conceivable that a developer pool is gradually formed near the sensor section on the entrance side of the developer 2. Therefore, it is thought that the magnetic permeability detection output of the sensor 20 changes in accordance with changes in the amount of developer accumulated. Therefore, as shown in FIG. 4, a rectifying plate 16 is attached to the sensor 20 facing the developer 2 entrance side. This current plate 16 is preferably made of a non-magnetic material. FIG. 5 shows a state in which the rectifying plate 16 is attached to the sensor 20 and installed in a developing device. The sensor 20 is fixed to a mounting plate 17, and is fixed to the upper lid 18 via the mounting plate 17 as shown in FIG. The sensor 20
The developer 2 flowing in contact with is always new and transported by the sleeve 10, and the amount of developer 2 is x>
Since the sensors 20 are arranged in a relationship of y, the guide to the sensors 20 is always kept constant.
Therefore, the output of the sensor 20 can be detected more stably.

Although the sensor 20 is provided with the rectifying plate 16, the sensor 20 itself may be formed into a shape having the same effect as the rectifying plate 16. Therefore, if the sensor 20 has a circular shape as shown in the figure, the regulated developer does not accumulate at that position, but flows left and right according to the rotation of the sleeve 10 and is conveyed to the stirring roller 4.

FIG. 6 shows the output characteristics of the sensor 20 shown in FIG. FIG. 6 shows the distance x between the doctor 12 and the sleeve 10, which regulates the amount of developer attached.
2 shows the detection output of the sensor 20 when changing . Also, the distance y between the sensor 20 and the sleeve 10 when the above distance x is defined as 2.0 mm.
is set to 1.5mm. It can be seen that the output change due to the sensor 20 in the present invention is much smaller than the one shown in FIG. 6 and the conventional one shown in FIG.

Further, FIG. 7 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 in the same way as in Figure 11, the magnet 11 is set at a fixed position with the height H of the main pole _N1 being 20 mm from the reference position, and the magnet 11 is rotated clockwise 19...16 or counterclockwise 21...23. It shows the output change when As shown in the figure, when compared with FIG. 11, it was found that almost no output change occurred due to the present invention. Further, by providing the circular sensor 20 without providing the rectifying plate 16, almost the same results as the characteristics shown in FIGS. 6 and 7 were obtained.

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. 6 and 7, the output changes are much smaller than those in FIGS. 10 and 11, 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, even if the distance between the sleeve and the sensor is smaller than the distance between the doctor and the sleeve, which regulates the developer, the developer entrance side remains wedge-shaped. Because the developer is formed on the sensor entrance side, no stagnation occurs on the sensor entrance side, and new developed developer can always be guided to the sensor, and a constant amount of developer can always be supplied. The toner concentration can be detected more stably.

Furthermore, since the center of the sensor is aligned with the center of one magnetic pole of the magnet, stable toner concentration can be detected by changing the magnetic permeability without being affected by the magnetic force of the magnet.

Therefore, since the sensor can accurately detect the toner concentration, the toner concentration of the developer can be easily maintained within a predetermined range.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a developer related to developer concentration control 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 Fig. 2, Fig. 4 is a plan view showing an example in which a rectifying plate is attached to the sensor, and Fig. 5 is a sectional view of a developing device in which the sensor shown in Fig. 4 is installed in the developing device. 6 and 7 are characteristic diagrams related to concentration control of the present invention, FIG. 8 is a sectional view of a developing section related to conventional developer concentration control based on volume change, and FIG. 9 is a characteristic diagram related to conventional developer concentration control based on change in magnetic permeability. 10 and 11 are characteristic diagrams showing the sensor output according to FIG. 9, which are cross-sectional views of the developer related to developer concentration control. 2: developer, 3: developing roller, 5: photoreceptor,
8: Toner supply roller, 10: Sleeve, 11:
Magnet, 12: Doctor, 16: Rectifier plate, 20: Sensor, 23: Phase detector, 24: Reference signal oscillator, 26: Comparator, 27: Output section, x: Doctor interval, y: Interval between sensor and sleeve.

Claims (1)

[Claims] 1. A developing device that develops a latent image formed on a recording medium using a developing roller consisting of a magnet with multiple poles and a non-magnetic sleeve that is rotated so as to cover the magnet. , A sensor for detecting the concentration of the developer as a change in magnetic permeability and controlling toner supply according to this detection output is placed at a position opposite to the upper part of the sleeve after development, and the center of the sensor is aligned with the magnet. The distance y between the sleeve and the sensor maintains a relationship of y<x with respect to the distance x between the doctor and the sleeve, which is arranged to coincide with the center of one magnetic pole and regulates the amount of developer adhering to the sleeve. A developer concentration control device, characterized in that the sensor is arranged so that the developer approaches the sensor, and a wedge-shaped developer accumulation prevention member is provided on the front surface of the sensor on the developer entrance side.