JPS59206851A - Developing device - Google Patents

Abstract

PURPOSE:To prevent increase of size of developer particles by controlling replenishment of the developer into a developer vessel with an electric detection signal produced from a detecting electrode formed near the outer circumference of a developer carrying roller and this roller. CONSTITUTION:When an amt. of developer on the circumference of a developer carrying roller 4 decreases, a detection electrode 7 is insulated from the roller 4, or high resistance occurs between them. Voltage at the point A rises and when it is higher than a reference voltage Vs, output of a voltage comparator 10 is made the level H to actuate a monostable multivibrator 11. As a result, a replenishing roller 9 is driven and the replenishment of the developer is finished by keeping the output of the multivibrator at the level H for a sufficient time necessary to replenish it.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to a developing device, for example, a developing device used in an electrostatic recording device such as an electrophotographic copying machine.

2. Prior Art First, to outline the copying process in an electrophotographic copying device as shown in column 1, for example, in a fixed type document table, a document to be copied is placed on the document table, and when the copy button is pressed, an exposure lamp illuminates the document. At the same time, exposure scanning is performed in a predetermined relationship with an optical system having a reflecting mirror and the like. Reflected light corresponding to the density of the original is irradiated onto a uniformly charged image bearing drum (i.e., a photoreceptor drum) via the optical system, and an electrostatic latent image is formed on the photoreceptor drum. Ru. A toner image corresponding to the density of the original is formed on the photoreceptor drum by the developing device.

On the other hand, copy paper (transfer material) is fed from the paper feeder in synchronization with the rotation of the photoreceptor drum, and is overlapped with the toner image formed on the surface of the photoreceptor drum, after which the copy paper is transferred by the transfer electrode. transcribed into. During this time, the photosensitive drum continues to rotate in a predetermined direction, and the toner image is gradually transferred onto the copy paper. Thereafter, the copy paper onto which the toner image has been transferred is separated from the photoreceptor drum and sent to a commonly used roller fixing device. The roll fixing device includes two rolls, at least one of which is heated, and heats and transfers an image formed by a developer onto copy paper.

Thereafter, the copy paper is ejected out of the main body of the copying apparatus.

By the way, the above-mentioned developing device is installed near the photoreceptor drum, and in order to convert the electrostatic latent image formed on the photoreceptor drum into a visible image, for example, in the magnetic brush development method, a developer is brought into contact with the photoreceptor drum. There must be. When the developer comes into contact with the photoreceptor drum, the electrostatic force attracts the developer to the charged portion of the photoreceptor, forming a visible image as a toner image on the photoreceptor drum. be done. During copying, the developer is constantly brought into contact with the photoreceptor and the developer is consumed, so the developing device must always have enough developer necessary for development in the developing section.

Now, in a developing device using a negative-component magnetic toner and a magnetic developer regardless of whether it is conductive or insulating, a magnetic brush developing device as shown in FIG. 1 is common.

The outline of this magnetic brush developing device will be explained.

The developing device is provided in a location close to the photoreceptor drum 1,
The main parts of the developing device are composed of a developer container 2 and a developer carrier 4 containing a magnet roll 3 therein.

Even if the magnetic developer T and the developer carrier 4 are fixed,
When the magnet roll 3 rotates clockwise, the magnetic developer T is conveyed counterclockwise on the circumferential surface of the developer carrier 4. The thickness of the developer T being conveyed is regulated by the bristling regulating member 5, so that the thickness becomes approximately constant, and the developer T is conveyed to the developing section 8. The developer T that has reached the developing section 8 is charged to a polarity different from that of the photoreceptor drum in the charged portion of the photoreceptor drum 1 by the time the developer T reaches the development area. The static electricity is attracted to the photosensitive drum 1 and consumed. Conventionally, when the developer T is consumed and there is a shortage of developer T in the developer container 2, a signal is output from the remaining amount detection section 6 provided on the inner wall surface of the container 2, and the developer is stored in the developer container 2. Agent T was to be replenished. During copying, the developer T is always transported to the developing section 8, and if there is a shortage of developer in the developer container 2, it is replenished.
It has been avoided that the lack of developer T causes non-uniformity in the thickness of the developer layer on the developer carrier, resulting in poor development.

However, if you use a copying machine with this developing device for a long time,
It is clear that the toner image on the photosensitive drum 1 that is to be transferred to the copy paper becomes progressively rougher and sometimes the developer T is not attracted to the area where the toner image should be formed, resulting in white streaks and cracks. It became.

Therefore, if such a toner image on the photosensitive drum 1 is transferred to copy paper, the image on the copy paper will also be rough and white streaks will appear.

As a result of extensive efforts, the inventors of the present invention have found that the image on the photoreceptor drum 1 becomes gradually rougher9 and the appearance of white streaks is caused by the factors described below.

Developer particles have various particle sizes. As a result of detailed investigation, it was found that in the developing section 8, developer particles with a small diameter are easily attracted to the charged portion of the photoreceptor drum 1, while developer particles with a large diameter are relatively difficult to attract. Ta. When copying is repeated many times, a dense toner image is formed on the photoreceptor drum 1 because the developer particles are initially developed with small diameters (this is called selective development). However, developer particles with larger diameters gradually come to remain in the developer container 2. When using a magnetic brush developing device and magnetic toner as shown in Figure 1, assuming that the content of magnetic powder (such as magnetite) in the toner particles is uniform for all toner particles, the toner particles with a larger diameter will have a larger diameter than those with a smaller diameter. It was also found that because the force of magnetic attraction to the sleeve surface is large, it is difficult to adhere to the latent image on the photoreceptor drum. As a result, development is performed using developer particles having a large diameter, and thus a toner image on the photosensitive drum 1 is formed coarsely.

Also, when a large amount of developer is put into the developer container 2 as in a conventional developing device, the developer at the bottom of the developer container 2 aggregates due to pressure, temperature, humidity, etc. from above. Show trends. This caused a repeating vicious cycle in which the diameter of the developer particles increased.

It is difficult to develop toner particle agglomerates that have increased in particle size in this way, and they tend to clog the blistering control member and cause white streaks.

3. Purpose of the Invention After considering the above, the present inventor believes that the above-mentioned problem can be eliminated by replenishing the developer container 2 in small amounts without putting too much developer. , which led me to invent this invention. The present invention provides a developing device that is capable of replenishing such a small amount and that eliminates the above-described deficiencies of the prior art.

4. Structure of the Invention In other words, the present invention provides a magnetic brush developing device using a magnetic developer, which includes a sensing portion near the circumferential surface of the developer carrier in order to measure the amount of developer on the circumferential surface of the developer carrier. is provided, an electrical value between the detection unit and the developer carrier is detected, and replenishment of the developer into the developer container is controlled based on this detection signal. This relates to a developing device.

5 Example Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a schematic diagram of a developing device according to an embodiment of the present invention.

A developing device is provided adjacent to the photosensitive drum 1, and the main part of the developing device is composed of a developer container 2 and a developer carrier 4 containing a rotatable magnet roll 3 therein. The process of conveying the developer T from inside the developer container 2 to the developing section 8 is not different from the conventional example.

A notable configuration of the embodiment of the present invention is that a detection electrode 7 is provided near the circumferential surface of the developer carrier (sleeve) 4 in order to measure the amount of developer T on the circumferential surface of the developer carrier (sleeve) 4. That is what we are doing. The gap between the two is set to be wider than the gap between the spike regulating member 5 and the sleeve 4 so that the developer thickness can be well controlled by the spike regulating member 5.

The developer T is conveyed on the circumferential surface of the developer carrier 4 during development. If the developer T is insufficient at the bottom of the developer container 2, the developer T is absorbed by the photoreceptor drum 1 in the developing section 8 and is consumed, so the thickness of the developer on the circumferential surface of the developer carrier 4 is It's getting thinner. Here, as will be explained in detail later, by applying a voltage between the developer carrier 4 and the detection electrode 70 and measuring the change in electrical value during this time, the shortage of developer can be electrically expressed. . When there is sufficient developer on the circumferential surface of the developer carrier 4, the developer on the supporting member and the detection electrode 7 are in contact with each other, and when the amount of developer is insufficient, the detection electrode 7 is located at a position where they do not come into contact. If provided, electrical quantities such as electrical resistance and dielectric constant between the detection electrode 7 and the developer carrier 4 change depending on the amount of developer on the circumferential surface of the developer carrier 4. This change is detected, and if the amount of developer is insufficient, the replenishment roller 9 is driven to replenish the developer little by little.

FIG. 3 is an enlarged sectional view of the replenishment roller 9.

As the replenishment roller 9 rotates, the developer taken into the four parts 9a provided on the replenishment roller 9 is caused to fall downward and is replenished into the container 2. The position of this roller 9 is preferably slightly offset so that the developer does not fall directly onto the electrode 7.

In the conventional developing device, the remaining amount of the developer T in the developer container 2 was detected, and if this amount was insufficient, the developer was replenished, but in the embodiment of the present invention, the developer carrying member 4 The amount of developer on the circumferential surface is detected, and if this amount is insufficient, the amount of developer is gradually increased (i.e., a slightly larger amount of developer than the required minimum amount corresponding to the -turn of the sleeve 4 is always held). We are planning to replenish the supply. Note that it is desirable that the inner surface of the electrode 7 be curved or arcuate along the outer peripheral surface of the sleeve 4 in order to accurately detect the amount of developer.

That is, in the conventional developing device, since there is always sufficient developer on the circumferential surface of the developer carrier 4, the developer with small particle size is applied to the charged portion of the photoreceptor drum 1 in the developing section 8. There was enough room to suck up only those parts and perform selective development.
This margin has resulted in the disadvantageous result that only the large particles of the developer remain in the developer container 4. As a result, when copying is performed thereafter, a toner image is formed on the photoreceptor drum 1 mainly by developer T with a large particle size, so the image transferred from there to the copy paper will not be dense. It has become rough.

However, as in the embodiment of the present invention, if the developer is replenished little by little by detecting the amount of developer T on the circumferential surface of the developer carrier 4, as in the conventional example, In order to reduce the possibility that a toner image is formed on the charging portion of the photoreceptor drum 1 in the developing section 8 using only small developer particles (that is, to cause selective development), the average particle diameter of the entire developer is reduced. increase can be suppressed. As shown in FIG. 2, a relatively small amount of developer is present on the circumferential surface of the developer carrier 4 and at the bottom of the developer container 2. Therefore, if the charging section of the photoreceptor drum 1 selects and adsorbs only the developer having a small particle size, the small particle size will not be consumed immediately. Therefore, even developer particles with a relatively large particle size are transported to the developing section and consumed for development.
This makes it possible to avoid a situation where only large particles are left in the developer container 2, as in the conventional example.

The above effects will be explained with reference to FIG. If the vertical axis is the average particle diameter of the developer rotating on the peripheral surface of the developer carrier 4, and the horizontal axis is the number of copies, then in the conventional example (indicated by the dotted line), the average particle diameter increases in proportion to the number of copies. It is clear that developers with large particles and large particle sizes are left behind. On the other hand, in the embodiment of the present invention (indicated by the solid line), the average particle size that once increased becomes smaller again as the developer is replenished, and in the conventional example (indicated by the dotted line in FIG. 4). This does not lead to a situation where the average particle size continues to increase in proportion to the number of copies made.

If only a small amount of developer is stored in the developer container 2, no pressure is applied from above, and the developer is consumed roughly in the order in which it is replenished, so the developer does not aggregate. It never solidifies. Therefore, when the developer that hardens and becomes large in particle size gathers at the spike control member 5 and its conveyance is stopped as in the conventional example, it obstructs the conveyance of other developers and leaves white streaks. Although such a phenomenon occurs, this embodiment makes it possible to prevent such a situation.

FIG. 5 shows an electrical circuit of an embodiment of the present invention using a conductive magnetic developer.

The voltage V is applied to the developer carrier 4 using a power supply VCC that always has a constant voltage. 0 divided by variable resistor VR and resistor R8 (VB) is input as a reference voltage to the inverting input terminal of voltage comparator 100, and voltage ■ is input to the non-inverting input terminal of the voltage comparator. A voltage obtained by dividing C by resistors R2 and R3 (point A in the figure) is input, and a detection electrode 7 provided facing the developer carrier 4 is connected to the point A.

Here, if there is enough developer on the circumferential surface of the developer carrier 4,
Since the developer comes into contact with the detection electrode 7, the detection electrode 7 and the developer carrier 4 are electrically short-circuited or connected through a resistance depending on the degree of conductivity of the magnetic developer. , if the resistance is very small, no voltage is applied to the non-inverting input terminal of the voltage comparator 10. Therefore, the output of the voltage comparator 10 is at L level, and the voltage comparator 10 connected to this output terminal is triggered by a rising wave.
1 does not work. R4 is a resistor that provides hysteresis to prevent malfunction.

On the other hand, when there is only a small amount of developer on the circumferential surface of the developer carrier 4, there will be a high resistance or insulation between the detection electrode 7 and the developer carrier 4, and the voltage at point A will increase. If the voltage is higher than the reference voltage (2), the output of the voltage comparator 10 becomes H level, and the one-shot multi 11 is activated. As a result, the replenishment roller 9 is driven, and the output of the multi-purpose roller 11 is maintained at the H level for a sufficient period of time required to replenish the developer, thereby completing the replenishment of the developer.

In principle, the electric circuit described above operates, but in this electric circuit, if a voltage of 78 or more is applied to the non-inverting input terminal of the voltage comparator 10 even for a moment, the developer will be replenished, and the developer will be replenished. Accurate control may not be possible. In other words, since there is some variation in the thickness of the developer on the carrier 4, if the electric current is instantly turned off and developer is replenished at the thinner part, more developer than necessary will be used. It may be replenished. Therefore, in order to reliably determine the lack of developer on the circumferential surface of the developer carrier 4, the following electric circuit is better.

The electric circuit on the input side of the voltage comparator 10 has the same configuration as the electric circuit described above, but the configuration of the electric circuit on the output side of the voltage comparator 10 has been devised.

The output terminal of the voltage comparator 10 is branched into two, one of which is connected to a one-shot multi 11, and the output of the one-shot multi 11 is connected to one input of a NAND circuit 12. The other branched output terminal of the voltage comparator 10 is connected to a NAND terminal via a resistor R5 and a diode D.
It is connected to the other input of circuit 12. A resistor R and a capacitor C are connected to both ends of the diode D, and the other terminal of the resistor and the capacitor are directly connected.

Here, when the output of the voltage comparator 10 instantaneously becomes H level, the one-switch date multi 11 is activated and its output becomes H level, and this level signal is input to the NAND circuit 12. However, when the NAND circuit 1 is off, the capacitor C connected between the voltage comparator 10 and the NAND circuit 12 is on the other side, so even if the output of the voltage comparator 10 becomes H level, the capacitor C is connected to the other side. It takes time to reach H level due to charging. Here, the voltage across capacitor C is ■. shall be. Therefore, even if the output of the voltage comparator 10 momentarily becomes H level, one input of the NAND circuit 12 does not become H level, its output also remains at H level, and replenishment roller 9 is not driven. When the developer on the developer carrier 4 is insufficient and the output of the voltage comparator 10 maintains the H level for a certain period of time, the capacitor C is charged and the input of the NAND circuit 12 connected to the diode also becomes H level.
As a result, the output of the NAND circuit 12 becomes L level.

Therefore, the replenishment roller 9 is driven and the developer is replenished.

The above explanation can be expressed as a time chart as shown in FIG. 7. 100 voltage comparators! When a voltage higher than 8 is momentarily applied to the inverting input terminal, the one-shot multi 11 operates, but the input terminal connected to the capacitor C of the NAND circuit 12 does not go to H level, and the NAND circuit 1 The gravity does not reach the L level.However, when the output of the voltage comparator 10 remains at the H level for a long time, the NAND is applied.The present invention can be further modified based on this technical idea.

For example, this can be achieved by measuring the change in dielectric constant or impedance between the developer carrier and the sensing electrode, even when using not only the conductive magnetic developer described in the example but also an insulating magnetic developer. I can do it.

6. Effects of the Invention As described above, according to the present invention, even after copying is repeated many times, it is possible to avoid a situation where only developer particles with a large average particle size remain. do not have. Therefore, unlike the conventional example, there is no large difference in the density of toner images between copy paper copied immediately after developer is replenished and copy paper copied later, and it is possible to copy an average toner image. It becomes.

Further, since there is always only a small amount of developer in the developer container, the developer does not solidify due to pressure. Therefore, the developer hardens and becomes large in particle size, and this is regulated by the bristling regulating member, so that it does not interfere with the conveyance of other developers.

This allows the entire surface of the photoreceptor to come into contact with the developer during copying, which prevents the developer from adhering to the charged part of the photoreceptor, resulting in white streaks on the copy paper being transferred. Such things will no longer occur.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional developing device in rows, FIG. 2 is a schematic diagram of a developing device according to an embodiment of the present invention, FIG. 3 is a sectional view of a replenishment roller, and FIG. 4 is a conventional developing device and the present invention. 5 is an electric circuit diagram of the embodiment of the present invention, FIG. 6 is an electric circuit diagram improved from the electric circuit of FIG. 5, and FIG. is an output waveform diagram of an electric circuit element. In addition, in the symbols used in the drawings, 1...
・・・・・・・・・Photoreceptor drum 2・・・・・・・・・
......Developer container 3...
・・・McNet Roll 4・・・・・・・・・・・・・・・
・・Developer carrier 5 ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・......Development section 9...
......Replenishment roller 10...
......Voltage comparator 11...
・・・Wanshi Sotto Multi 12・・・・・・・・・・・・
・・・・・・NAND circuit T-・・・・・・・・・・・・
...Developer. Agent: Patent attorney Hiroshi Aisaka (1 other person) @1 Figure 21 @Figure 3 @Figure 4 Figure 50

Claims (1)

[Claims] 1. In a magnetic brush developing device using a magnetic developer,
In order to measure the amount of developer on the circumferential surface of the developer carrier, a detection part is provided near the circumferential surface of the developer carrier, and the electrical value between the detection part and the developer carrier is measured. is detected,
A developing device characterized in that replenishment of developer into a developer container is controlled by this detection signal. 2. The detection unit is configured to be able to measure the amount of developer based on the current M between the developer carrier and an electrode provided in the vicinity thereof. Visualization device as described. 3. The electrode is located upstream of the spike adjustment member in terms of developer transport, and at a position separated from the developer carrier by a distance between the spike trimming adjustment member and the developer carrier. A developing device according to claim 1 or 2, which is provided. 4. Using a conductive magnetic toner as the magnetic developer,
A developing device according to any one of claims 1 to 3.