JPS6157966A - Developer density controller - Google Patents

Abstract

PURPOSE:To stabilize the detection output of a sensor by arranging the sensor, which detects the density of a developer, a certain gap apart from a sleeve so that this sensor faces the part between magnetic poles especially and keeping alwyas the quantity of the developer passing the sensor constant. CONSTITUTION:A sensor 20 which detects the toner concentration of a developer 2 is arranged to face the part betwen pones S1 and N2 of a magnet 11. This sensor 20 is attached to 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 approximate middle between poles S1 and N2 of the magnet 11. If the sensor 20 detects that the toner concentration is lower than a reference value, a tone supply roll 8 is rotated to supply a toner 7 into the developing tank 19, and the supplied toner is agitated sufficiently with the developer 2 by an agitating roll 4 and is sent to a developing roll 3. Thus, the toner concentration of the developer is raised gradually; and when the sensor 20 detects that the toner concentration is a certain value, the rotation of the toner supply roll 8 is stoped to stop the supply of the toner.

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. Or, it may become too dark, causing problems such as increased fogging. Therefore, for a certain period of time, a manual toner supply amount adjustment device was installed in the supply device that supplied toner into the developing device, and the user
I tried to adjust it 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 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 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. 4. The developer 2 is sufficiently stirred and put into the developing device 1 by a 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. In this way, when the developer surface position falls below the reference position, the developer no longer comes into contact with the ceramic vibrator 6 (sensing element) installed at the reference position, and the vibrator starts to vibrate. 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. 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 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 caused by not being able to maintain the standard concentration.

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 carrier is lost during printing, the above method has the problem of fogging as the number of copies increases.

On the other hand, if the device detects and controls the magnetic permeability that changes depending on the mixing ratio of carrier and toner, it has the advantage that the mixing ratio of toner can be kept constant even if the amount of carrier decreases. An example of this is shown in FIG. In FIG. 5, the same parts as in FIG. 4 are indicated by the same reference numerals. In the figure, the developing roller 3 is provided with a magnet 11 consisting of multiple poles with the N1 pole as the main pole on a cylindrical sleeve 10 made of a non-magnetic material. The sleeve 10 is rotated in the direction of the arrow. As a result, the developer 2 adhering to the sleeve 10 is conveyed to the development area, and by facing the Nl 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 to a constant level by a treater 12.

In the structure as described above, the sensor 13 for detecting the toner concentration is disposed at a position facing the N2 pole especially 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 W 9 (7) is controlled to keep the toner concentration constant. With this, even if the carrier in developer 2 decreases, the toner concentration can always be controlled at a constant level because the magnetic permeability, which 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 amount is regulated by the doctor 12 flows on the surface of the sensor 13, the amount of the developer 2 which is regulated by the doctor 12 flows on the sensor 13. The contact area changes significantly.

This causes the sensor 13 to erroneously detect a change in magnetic permeability, making toner concentration control unstable. For example, as shown in the characteristic diagram of FIG. 8, 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 xt' between the doctor blade 12 and the sleeve lO, 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 means that the output of sensor +3 is greatly influenced by the amount regulated by doctor 12, and the output is not stable.

Furthermore, even if the mounting position of the sensor 13 is shifted to the left or right from the magnetic pole N2 of magnet 1, the output will change greatly. In other words,
The same thing happens even if the fixed position of magnet 1 is shifted. Its characteristics are shown in FIG. In this figure, for example, the position where the center of the N2 pole and the center of the sensor 13 coincide is indicated as 20,
In Fig. 7, by shifting the main pole of N1 clockwise, 19.18... is closed, and by shifting it counterclockwise, 2
1.22...Illustrated together. As shown in the figure, the output from the sensor 13 changes significantly even when the sensor 13 or the magnet 11 is misaligned.

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.

<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 output from the sensor by considering the position.

<Embodiment> FIG. 1 is a sectional view of a developing device portion showing an 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 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 @+5 is provided with a developing roller consisting of a cylindrical non-magnetic sleeve 1O and a magnet 11 with an odd number of poles provided inside the sleeve. The sleeve 10 is rotated clockwise in the figure,
The magnet 11 is fixed so that the N1 pole (in particular, the N1 pole) 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 transported to a developing position facing the photoreceptor 5, and after this transport, it is returned to the developer tank 19. It is stirred by a stirring roller 4. While the developer 2 adsorbed on the sleeve 10 is conveyed to a position facing the photoreceptor 5, the adhesion amount is regulated by a doctor 12 to a constant amount.

The doctor 12 is fixed to the side plate of the developer tank 19 with screws 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 disposed between the S1 pole and the N2 pole of the magnet 11 so as to face each other. 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 3 is approximately midway between the 81st pole and the N2 pole of the magnet II. There is.

In the device configured as described above, when the sleeve IO is rotated, the developer 2 attracted onto the sleeve by the magnetic force of the magnet 11 is conveyed in accordance with the rotation of the sleeve 10. The amount of the developer 2 that is transported during this transport, especially while facing the photoreceptor 5, is limited by a doctor 12.
The photoreceptor 5 is transported to the developing area. The developer that has passed through this development area will then pass through the sensor 20. At this time, the sensor 20 detects a change in magnetic permeability in order to detect the toner concentration of the developer 2 passing through. Therefore,
If the sensor 20 detects that the toner concentration is below the standard, it rotates the toner supply roller 8 and supplies the toner 7 into the developer tank 19 . The supplied toner is sufficiently stirred with the developer 2 by the stirring roller 4 and sent to the developing roller 3. Then, the toner concentration of the developer gradually increases, and when the sensor 20 detects that the toner concentration is constant, the rotation of the toner supply roller 8 is stopped, and the toner supply is stopped.

An example of the above toner density control is shown in FIG. 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 ferrite core 21 wound with a coil L1 for applying a reference signal, a coil L2 for detecting permeable slag of the developer 2, and a coil L3 for reference adjustment. In particular, the coil L2 side is opposed to the developer 2 to be detected, and the developer 2 and the ferrite core 21 constitute a closed magnetic path. Further, on the upper side of the coil 3, a screw-shaped reference adjustment core 22 is provided which forms another closed magnetic path (11η) 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 L1, and is supplied with a 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. Then, 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 position detector 23, so that the phase relationship with the reference signal is compared, and the pulse of the output signal is Width increases. Therefore,
Since the pulse width is wide in the smoothing circuit 25, it is supplied as a high voltage to the next voltage comparator 26. 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 density is at a constant reference level, the output of the voltage comparator 26 becomes ("L") and the supply roller 8 is not rotated. In other words, the output from the smoothing circuit 25 when the developer 2 with the reference toner permeability is contained in the developer ig l 9 is lower than (or equal to) the reference voltage of the voltage comparator 26.
The reference adjustment core 22 of the sensor 20 is adjusted so that. Therefore, if the toner concentration decreases, the comparator 2
A signal (pulse width) larger than the reference voltage of 6 is output from the phase detector 23, 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 vD 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. has been done. The oscillation output of circuit EXI is supplied to coil L1 of sensor 20 and to capacitor C3. The other terminal of the coil L 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 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 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 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 reference adjustment core 22 is adjusted so that the detected signal value applied to one input terminal of the circuit EX4 has a value below (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 changes 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, the circuit EX4 outputs an H" signal. 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. 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 the convex magnetic ratio based on a change in toner concentration and replenishing toner to keep the toner concentration constant. It is not limited to circuits. In other words, the third
In the figure, magnetic permeability is detected by phase detection, but changes in magnetic permeability may also be detected directly as voltage changes.

Further, the toner concentration can be controlled to a constant reference level by detecting the conductivity, which changes according to the toner mixing ratio of the developer 2, without detecting the magnetic permeability. For example, toner supply control may be performed by comparing the conductivity in the reference state and the detected conductivity.

Here, as shown in the first part, the sensor 20 is connected to the sleeve I.
Magnetic pole S1 of magnet I+ fixed at a constant distance from O
and N2.

By arranging it in this way, the developer passing through the sensor 20 is not restrained by the magnetic pole, but tends to move toward the magnetic pole N2 on the downstream side so as to be attracted. Moreover, since the developer 2 is conveyed along the rotational direction of the sleeve IO, the force with which the developer flows becomes stronger. As a result, the fluidity of the developer 2 is substantially improved, and factors such as variations in fluidity of toner and carrier and changes in fluidity affected by humidity etc. are greatly reduced, and the developer flowing through the sensor 20 section is It becomes possible to keep the amount of agent constant.

This allows the flow of developer to be kept constant regardless of changes in the master control of the doctor 12, and changes in the output of the sensor 20 are made very small, allowing for stable detection.

Furthermore, the flow force of the developer 2 passing through the sensor 20 is increased by the action of the downstream boron 2 as the sleeve 10 rotates, so that even if the distance between the sensor 20 and the sleeve 10 is narrowed, , the developer can be sufficiently passed between the sensors 20. Therefore, even if the amount of developer flowing changes by adjusting the interval can always be kept constant. Therefore, the output of the sensor 20 becomes extremely stable as described above, and more accurate toner density control can be achieved. Incidentally, the developer that does not pass between the sensors 20 flows on the side of the sensor 20 and passes through the gate stirring roller 4.
highly respected.

Furthermore, by arranging the sensor 20 so as to face the magnetic poles of the magnet II, no change in the output of the sensor 20 was observed even when the angle x of the pole N1 of the magnet 11 was adjusted during image quality adjustment.

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 X 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, large output changes as shown in FIGS. 6 and 7 do not occur, and the output changes due to the sensor 20 are very small, which is highly effective in keeping the toner concentration constant. .

<Effects of the Invention> According to the developer concentration control device of the present invention, since the sensor for detecting the developer concentration is arranged at a certain distance from the sleeve and in particular facing between the magnetic poles, it is possible to can increase the force of the agent flowing through the sensor,
Even if the distance between the sensor and the sleeve is narrowed, the developer can sufficiently pass through a portion of the sensor. Therefore, even if the flow plate for developer passing through the sensor is restricted and the amount of developer regulated by the doctor changes, the amount of developer passing through the sensor is always kept constant, and the detection output from the sensor is extremely stable. This enables more accurate concentration control.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a developing section according to the present invention that varies the developer concentration RIJtE, FIG. 2 is a block diagram showing an example of a developer concentration control circuit according to the present invention, and FIG. Figure 2 is a circuit diagram showing the details of Figure 4. Figure 4 is a cross-sectional view of a developing unit that uses conventional volume change to control developer concentration. Figure 5 is a conventional developer unit that uses magnetic permeability change to control developer concentration. 6 and 7 are characteristic diagrams showing the sensor output according to FIG. 5. 2: Developer 3: Developing roller 5° photoreceptor 8: Toner supply roller lOnisleeve 11: Magnet 12:
Doctor 20: Sensor 23: Phase detector
24: Reference signal oscillator 26: Comparator 27: Output section agent Patent attorney Yoshihiko Fukushi (and 2 others) Figure 4, λδ diagram

Claims (1)

[Claims] 1. A magnet consisting of a large number of poles, a sleeve whose rotation is controlled so as to surround the magnet, and a magnet that is spaced apart from the sleeve by a certain distance to detect the concentration of the developer conveyed by the sleeve. What is claimed is: 1. A developer concentration control device comprising: a sensor disposed facing each other between magnetic poles; and a control means for controlling supply of toner in accordance with concentration detection by the sensor.