JPS6157972A - Developer concentration controller - Google Patents

Abstract

PURPOSE:To keep always the quantity of a developer flowed to a sensor part constant to stabilize the toner concentration detection output by arranging a sensor which detects the density of the developer and providing a control plate which controls the quantity of the developer flowed to 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 o an upper cover 18 of a developing tank 19 and is attached a considerable length apart from a sleeve 10 so that the center of the sensor 20 coincides with the center of the pole N2 of the magnet 11, and a control plate 15 which controls the quantity of the developer flowed to the sensor part is provided. The control plate 15 has the front end extended up to the upper cover 18, ad this extended part is fixed to the inside of the upper cover 18. The control plate 15 is provided along the peripheral surface of the sleeve 10 and controls the quantity of the developer flowed to the sensor part and controls especially the height of crest of the developer 2 due to a magnetic pole S1 of the magnet 11 and guides the developer 2 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 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 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 will be low and difficult to see. Otherwise, problems such as increased fogging may occur due to excessive heating. 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 adjusted it when he noticed a change in the copy density. Ta. 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 is extremely troublesome for the user to perform various adjustment operations.

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 constant carrier as a change in volume.

Among these, changes in toner amount are controlled as changes in volume,
6 methods are often used to easily detect reference value 0. This method will be explained 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 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.
The developer surface position is lowered. When the developer surface position falls below the reference position in this way, the developer loses contact with, for example, the ceramic vibrator 6 (sensing element) installed at the reference position, 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. After this, the volume of the developer 2 increases again and rises to the reference position, and the vibrator 6 stops vibrating.
The supply of toner 7 is also stopped. Thereafter, by repeating these steps, the concentration of the developer 2 is automatically controlled. 3 in the diagram
5 is a developing roller, and 5 is a photoreceptor.

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, regarding the former,
This is due to the fact that the volume of the mixture of carrier and toner decreases to a certain extent as it is stirred, and for the latter, if the amount of carrier increases or decreases, the amount of toner increases or decreases in the opposite direction. This is due to the inability to maintain the standard concentration.

However, it cannot be said that the developer used for replacement during maintenance is sufficiently stirred and converged in terms of volume change, and the carrier also adheres to the photoreceptor during development, and this occurs many times. Since a considerable amount of carrier is reduced as the process is repeated, the above method has the problem of fogging as the number of copies increases.

With respect to kneading, if the magnetic permeability that changes depending on the mixing ratio of carrier and toner is detected and controlled, it has the 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. 8, the same parts as in FIG. 7 are indicated by the same symbols. In the figure, the developing roller 3 is a magnet made up of multiple poles with the N1 pole as the main pole inside a cylindrical sleeve 10 made of a non-magnetic material! 1 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 inside of the sleeve 10 is transported to the development area, and by facing the N1 pole, it rises like a brush and rubs the surface of the photoreceptor 5, turning 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 to a constant level by a doctor 12.

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 1O 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 keep the toner concentration constant. 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. 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 shows the doctor width, that is, the distance X between the doctor doctor 12 and the sleeve 10, and 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.
．． I set it to 2ro. As shown in the figure, the distance between the doctor 12
As the amount of the developer 2 increases, the amount of adhesion of the developer 2 also increases, and the output from the sensor increases. This means that Doctor 1
This means that the output of the sensor 13 is greatly influenced by the regulation amount 2, 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 is shifted. Its characteristics are shown in the +og. In this figure, for example, the position where the center of the N2 pole and the center of the sensor 13 coincide is shown as 20, and in FIG. 8, by shifting the main pole of N1 clockwise, it becomes 19°18... By shifting it counterclockwise, the numbers 21, 22, etc. are closed. As shown in the figure, even if the sensor 13 or magnet 11 is misaligned,
The output from the sensor 13 changes significantly.

Furthermore, since the developer 2 is transported at high speed by the rotation of the sleeve 10, the magnetic permeability varies due to the internal pressure of the fluid developer itself, which causes the detection output to become unstable.

It controls the toner concentration, and its primary purpose is to keep the toner concentration constant, and in particular, to stabilize the sensor detection output.

Further, the present invention aims to stabilize the output from the sensor by considering the mounting position of the sensor.

<Example> No. 11m is a sectional view of a developing device portion showing a specific example of a developer concentration control device according to the present invention. 7th in the figure
The same parts as those in the figure 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 14 is a developing device that develops an electrostatic latent image formed on the photoreceptor. The developing device 14 includes a developing roller 3 in a developing tank 19, which is composed of a cylindrical non-magnetic sleeve 10 and a magnet 11 provided inside the sleeve and having an odd number of poles. The sleeve 1O 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 sleeve 1
0, the developer 2 is attracted by the magnetic force of the magnet 11, and this developer 2 is conveyed to the development position facing the photoreceptor 5 as the sleeve 10 rotates. J
+9 and stirred by stirring roller 4. The developer 2 adsorbed onto the sleeve 10 is regulated to a fixed amount by a doctor 12 while being conveyed to a position facing the photoreceptor 1 . The doctor 12 is screwed to the measuring plate of the developer 1gl9 so as to be spaced apart from the sleeve 10 by a distance of X.

In the developing device configured as described above, the sensor 20 for detecting the toner concentration of the developer 2 is arranged to face the N2 pole of the magnet 11. This sensor 2
0 is attached to the upper lid 18 of the developer tank 19, and the magnet 1
The sensor 20 is attached at a distance of 100 degrees from the sleeve 1O so that the center of the sensor 20 coincides with the center of the N2 pole of the sensor 20.

Further, the sensor 20 is provided with a regulating plate 15 for regulating the developer flowing to a part of the sensor, as shown in FIG. 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. A regulating plate 5 is provided along the circumferential surface of the sleeve 10 as shown in FIG. 1, and regulates the amount of developer flowing toward a portion of the sensor. In particular, as shown in the figure, the regulating plate 15 regulates the amount of spikes of the developer 2 caused by the magnetic pole S1 of the magnet 11, and guides the developer 2 to the sensor 20.

Moreover, in the present invention, the sensor 20 is connected to the sleeve 1.
The distance y between the sensor 20 and the sensor 20 is set in such a manner that x>y with respect to the width X that regulates the developer with the doctor 2.

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. That is, even if the amount of developer conveyed by the sleeve IO increases or decreases, the amount of developer flowing on the surface of the sensor 20 is regulated by the regulating plate 15 to a constant amount between the sleeve 10 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 a part of the sensor is kept constant, making it possible to obtain a stable magnetic permeability detection output and keeping the toner concentration constant. can be controlled. Moreover, since the distance HY between the sensor 20 and the sleeve 10 is made smaller than the distance X by the doctor 12, the effect of regulating the developer by the regulation plate I5 is increased, and the amount of developer flowing toward a part of the sensor is kept constant. It will be more reliable to do so.

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 the sensor 20 according to the present invention.

As shown in the figure, the sensor 20 has a ferrite core 21,
A coil L1 for applying a reference signal, a coil L2 for detecting the magnetic permeability of the developer 2, and a coil L3 for setting the reference toner concentration are wound around the coil L1, and in particular, the film 2 side is opposed to the developer 2 for detecting the toner concentration. The developer 2 and the ferrite core 2 constitute a closed magnetic path. Further, on the coil L3 side, a screw-shaped reference adjustment core 22 is provided which forms another closed magnetic circuit with the ferrite core 21.
The magnetic flux passing through the coil L3 is adjusted. The coil L2 and the coil L3 are wound in opposite directions and have one end commonly connected. The other end of the fill L3 is grounded,
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 L1, and is supplied with the reference signal. Oscillator 24
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, 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 also shifts. A composite signal of the induced voltage of the coil L3, which hardly changes, and the voltage of the coil L2 is supplied to the phase detector 23, so that the phase relationship with the reference signal is compared, and the output signal is compared. 26. Therefore,
Voltage comparator 26 outputs a signal (“H”). As a result, the output section 27 drives the motor that rotates the toner supply roller 8. However, if the toner concentration is at a constant level, the output of the voltage comparator 26 becomes ("L"), The supply roller 8 is not rotated. That is, the reference voltage of the sensor 20 is set such that the output from the smoothing circuit 25 when the developer 2 with the reference toner concentration is stored in the developer tank 19 is lower than (or equal to) the reference voltage of the voltage comparator 26. The 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 determined by the reference toner diagram. A constant voltage circuit 2 consisting of a Zener diode ZDI and a capacitor C1 via
8, and is supplied as a constant voltage to one input terminal of an exclusive OR circuit EXI constituting the oscillator 24. The oscillation output of the circuit EXI is the coil Ll of the sensor 20.
and is supplied to capacitor C3. Coil L1 and other terminals are connected to resistor R2 and capacitor C2 with mH
An oscillation output signal having an opposite phase to the output of the circuit EXI is supplied to the other input terminal of the circuit EXI via the resistor R2, and is also supplied to one of the exclusive OR circuits EX3 of the phase detector 23, which will be described later. Supplied to the input terminal. 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 filter L3 of the sensor 20 is supplied to the base 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 outputs a pulse signal having a width corresponding to the phase difference with the exclusive OR circuit for phase detection described above via the exclusive OR circuit EX2 for waveform shaping.

This H/L/S signal is then applied to resistor R5 and capacitor C6.
It is converted into a signal (voltage) according to the pulse width by the smoothing circuit 25 consisting of
4 as a detected 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 a threshold is input to one input terminal. Therefore,
The detected signal value applied to one input terminal of the circuit EX4 is adjusted to the reference adjustment core 22 so that the value of the detected signal is less than (or equal to) the threshold when the developer has a reference toner concentration.
are being adjusted. 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 wide pulse width is output from the exclusive OR circuit EX3. 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, an "H" signal is output from the circuit EX4. This signal (“H”) is supplied to the base terminal of the transistor Q2 via the resistor R7 of the output section 27, and is supplied to the base terminal of the transistor Q2.
Make it into a conductive state. The transistor Q2 is an example of a control circuit that conducts, for example, replenishes toner to rotate the toner supply roller 8 and keeps the toner concentration constant, but this is just an example and is performed by detection. However, by arranging -20, which directly detects changes in magnetic flux, at the position shown in FIG. 1, stable detection output can be obtained as described above. Figure 5 shows its characteristics. This figure shows the sensor 20 when changing the distance
FIG. 2 is a characteristic diagram showing output changes based on Moreover, the Ry between the sensor 20 and the sleeve 0 was set to 1.5M, and the regulating plate was also provided to correspond to this. The resulting detection output VPC by the sensor 20 is as shown in FIG. As can be understood from this figure, it can be seen that the output change is very small compared to the conventional one shown in FIG.

In addition, FIG. 1 shows the sensor 20 with the position of the main pole N1 shifted.
FIG. 2 is a characteristic diagram showing output changes due to In this figure, the sensor 20 is fixed in the same way as in Figure 10, and the magnet II is set at a fixed position with the height H of the main pole N1 being 20 mm from the reference position. (21...
・23) It shows the output change when As shown in the figure, if compared with FIG. 10, the output change according to the present invention is as follows.
It was found that this rarely occurs.

Normally, in order to adjust the image density, the angle of the main pole N1 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 respect, according to the present invention, as shown in FIGS. 5'' and 6, the output changes are much smaller than those in FIGS. 9 and 20, and this invention has a great effect in keeping the toner density constant.

<Effects of the Invention> 2. Since the sensor is equipped with a regulation plate that regulates the amount of developer flowing through the sensor, the amount of developer flowing through a part of the sensor can always be kept constant, and the amount of toner flowing through the sensor can be kept constant. The density detection output is stabilized, and thereby the density of the developer can be kept constant. Furthermore, since the developer is pushed by the regulating plate when it passes through the sensor, the flow rate of the developer is slowed down, making it possible to obtain a more stable detection output.

In addition, since the distance y between the sensor and the sleeve is set smaller than the doctor-regulated distance [X, it is more effective in keeping the amount of developer flowing to the sensor constant regardless of changes in the developer flow rate. be.

[Brief explanation of the drawing]

1 [J is a cross-sectional view of a developing section related to the developer concentration control according to the present invention, FIG. 2 is a plan view showing a part of the sensor according to FIG. 1, and FIG. 47 is a block diagram showing an example of a control circuit, FIG. 47 is a circuit diagram showing details of FIG. 3, FIGS. 9 and 6 are characteristic diagrams related to density control of the present invention, and FIG. 7 is a conventional development using volume change. FIG. 8 is a cross-sectional view of a developing section related to developer concentration control, and FIG.
8 and 10 are characteristic diagrams showing the sensor output according to FIG. 8. 2: Developer 3: Developing roller 5: Photoreceptor 8: Toner supply roller 1O; 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. In a developing device that develops a latent image formed on a recording medium using a developing roller consisting of a magnet and a sleeve, the concentration of developer is detected and toner supply is performed according to the detected output. A control sensor is provided facing the sleeve after development, and a regulating member is provided on the sensor to regulate the amount of developer attached to the sleeve after development. Device. 2. The sensor is arranged so that the distance y between the sensor and the sleeve has a relationship of x>y with respect to the distance x that regulates the amount of developer that adheres to the sleeve before development. The developer concentration control device according to item 1.