JPH05313496A - Developing device for electrophotographic device - Google Patents

Abstract

PURPOSE:To directly detect a toner amount used during developing so as to effectively control toner concentration in developer, to disuse a toner concentration sensor and to reduce cost. CONSTITUTION:In the developing unit of a copying machine which develops an electrostatic latent image formed on the surface of a photosensitive body 4 by the magnetic brush 30 of the developer formed on the surface of a developing sleeve 29b; a current flowing to a conductive plate 31 from the sleeve 29b in the case that the magnetic brush 30 abuts on the conductive plate 31 provided at a position on which the leading edge of the brush 30, which finishes rubbing the photosensitive body 4, abuts on is detected by a current detector 32; and the consumption of the toner at the time of developing is calculated based on the change of the detected current value by a CPU 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an electrophotographic apparatus such as a copying machine for forming an image using toner.

[0002]

2. Description of the Related Art For example, in an image forming process in a copying machine, reflected light corresponding to the density of an original image when the original is irradiated with light is guided to a photoconductor to form an electrostatic latent image. The latent image was developed by rubbing a magnetic brush of a developer (mixture of toner and carrier) formed on the surface of the developing sleeve in the developing device, and the toner image obtained by this development was transferred to copy paper. After fixing, a copied image is formed.

As described above, the developer for developing the electrostatic latent image on the photosensitive member does not change the amount of carriers in the developer by being subjected to development, but the amount of toner is consumed and reduced. When a copy image is formed with a developer having a reduced amount of toner, problems such as a decrease in image density will occur. Therefore, conventionally, a toner concentration sensor is provided in the developing device to detect the ratio of toner in the developer, that is, the toner concentration, so that a predetermined toner concentration can be set based on this. In addition, measures such as toner replenishment are performed.

[0004]

However, in the above-mentioned conventional structure, there is a problem that the detection value of the toner concentration sensor varies due to the flowing state of the developer, and the accurate toner concentration cannot be detected. ing.

The toner concentration sensor has a coil of a resonance circuit, and the change of the magnetic permeability of the developer, that is, the amount of carriers as magnetic particles flowing in the magnetic field causes the inductance to change. Considered as frequency change,
Thus, the toner density in the developer is detected. Therefore, for example, when the toner concentration in the developer is the same, but the toner is in a dense state or a rough state due to the flow of the developer, a rough state with a small amount of carriers is detected as overtoner. Therefore, if a measure such as keeping the toner concentration in the developer constant is performed based on the toner concentration detected in this way, the toner concentration control becomes inaccurate and It causes an influence and causes a situation such as deterioration of image quality.

Further, since the toner concentration sensor has a resonance circuit and the like, the cost is high and the cost of the apparatus is increased.

Therefore, an object of the present invention is to provide a developing device for an electrophotographic apparatus which directly detects the amount of toner consumed for development without being influenced by the state of the developer and the like, and which is low in cost. I am trying.

[0008]

In order to solve the above-mentioned problems, a developing device for an electrophotographic apparatus of the present invention covers the outer circumference of a magnet having a plurality of magnetic poles in the circumferential direction, and the surface of the developer is covered by this magnet. In the developing device for developing the electrostatic latent image formed on the surface of the photoconductor by the magnetic brush, the tip of the magnetic brush after rubbing the photoconductor contacts A conductive portion provided at a contact position, a current detecting means for detecting a current flowing from the developing sleeve to the conductive portion when the magnetic brush comes into contact with the conductive portion, and a current detecting means for detecting the current. It is characterized in that a toner consumption amount detecting means for calculating the toner consumption amount at the time of development based on the change of the current value is provided.

Further, in the developing device provided with each of the above means of the present invention, the conductive portion is arranged at a position facing one magnetic pole of the magnet.

[0010]

According to the above construction, the current detecting means reads the current flowing from the developing sleeve to the conductive portion via the magnetic brush, and outputs the read current value to the toner consumption amount detecting means. The current value detected by the current detection means is
The amount of toner in the magnetic brush varies during development, and the toner consumption amount detecting means calculates the amount of toner consumption during development based on the variation in the current value. Therefore, when the toner replenishing roller or the like is controlled on the basis of the value detected by the toner consumption amount detecting means to keep the toner concentration in the developer constant, for example, the toner consumption amount at the time of development is reduced. Since the control directly corresponding to the above can be performed, the control can be performed more accurately than the conventional control based on the detection value of the toner concentration sensor for the carrier in the developer.

Further, since the conductive portion is opposed to one magnetic pole of the magnet, the spikes of the magnetic brush formed on the developing sleeve are substantially vertical, and the conductive portion and the developer which is the magnetic brush are separated from each other. The contact state is stable. Therefore, it is possible to eliminate uneven detection and enable more accurate current detection.

Further, according to the above construction, the conductive portion and the current detecting means are relatively inexpensive members, and the toner consumption detecting means also serves as the control system provided in the main body of the electrophotographic apparatus. As a result, the conventional expensive toner concentration sensor can be eliminated, and the cost of the developing device can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. In this example,
The case where the developing device is applied to a color copying machine which is an electrophotographic device is illustrated.

As shown in FIG. 2, the color copying machine according to the present embodiment (hereinafter abbreviated as copying machine) is provided with a transparent manuscript table 1 on the upper surface thereof, and below the manuscript table 1. An exposure optical system 2 is provided. The exposure optical system 2 includes two exposure lamps 2a, 2a for irradiating the original 3 placed on the original table 1 with light, and reflected light from the original 3 as indicated by a dashed line in the drawing. , A plurality of reflecting mirrors 2b that are guided onto the drum-shaped photoconductor 4 and an optical filter 2c having color filters of three primary colors (red, green, and blue). The exposure lamps 2a and 2a are attached to a mirror base 2d, and the mirror base 2d is horizontally reciprocated along the lower surface of the document table 1.

In the figure on the right side of the photoconductor 4 above,
A black and white developing unit 5a is provided. On the other hand, on the left side, color developing units 5b, 5c and 5d are sequentially arranged from the upper side to the lower side. The color developing units 5b, 5c, and 5d individually store yellow, magenta, and cyan color developers for color copying. The developing units 5a, 5b, 5c and 5d will be described later.

Two sheet feeding cassettes 6 for each size are provided below the photoconductor 4 on the right side, and further, a belt-shaped intermediate transfer member 7 is conveyed from below the photoconductor 4 to the left side. The belt 8 and the fixing unit 9 are arranged in this order.

The intermediate transfer member 7 comprises three rollers 10
It is adapted to be rotationally driven by 11.12. The lower surface side of the photosensitive member 4 is pressed against one side surface of the intermediate transfer member 7, and the first transfer charger 13 is provided on the back surface of the intermediate transfer member 7 at the position where the photosensitive member 4 is pressed against the intermediate transfer member 7. The second transfer chargers 14 are arranged on the lower side of the respective units 7.

Here, the developing units 5a and 5b described above are used.
5c and 5d based on FIG. 1 and FIGS. 3 to 6,
explain.

As shown in FIG. 4, each developing unit 5a
Each of 5b, 5c and 5d has a developing tank 21 and a toner hopper 22 provided above the developing tank 21. In the toner hopper 22, it is located in the vicinity of the toner stirring rollers 23, 23 for stirring the toner and the communication opening between the toner hopper 22 and the developing tank 21, and supplies the toner to the developing tank 21 as necessary. And a toner replenishing roller 24. The toner supply roller 24 is rotationally driven by the toner supply motor 16 (see FIG. 3).

In the developing tank 21, a stirring screw 25 for stirring and mixing the toner supplied from the toner hopper 22 at a position below the communication opening and the developer contained in the developing tank 21 in advance. Is provided. Below the stirring screw 25, a paddle roller 28 that conveys the developer with the separator 26 interposed is provided. A developing roller 29 for supplying the developer to the photoconductor 4 is provided on the left side of the paddle roller 28 and in the vicinity of the opening 21a formed on the left side of the developing tank 21.
The amount of the developer carried by 9 is adjusted by a doctor 27 provided above the separator 26.

The developer contained in the developing tank 21 is composed of, for example, a conductive carrier made of iron powder and resin fine powder colored in each of yellow, magenta, cyan and black as described above. The toner and the carrier are rubbed with each other by stirring with the stirring screw 25, and in the present embodiment, the toner is positively charged and the carrier is negatively charged. Toner is adsorbed on the surface of the carrier.

As shown in FIG. 1, the developing roller 29 extends along the longitudinal direction of the photoconductor 4 and has an arrow B.
It is formed so as to be rotatable in the direction indicated by and is connected to the negative electrode of the DC power source E. The developing roller 29 is composed of a magnet roller 29a in which permanent magnets of N polarity and S polarity are alternately arranged in the circumferential direction, and a non-magnetic conductive member such as aluminum or martensite stainless steel. The developing sleeve 29b is provided so as to cover the outer peripheral surface of the.

A magnetic brush 30 made of a developer is formed on the surface of the developing sleeve 29b by an alternating magnetic field generated by the rotation of the magnet roller 29a provided inside (the black circles in the drawing represent toner and the white circles represent carriers). Is formed. As the developing roller 29 rotates, the magnetic brush 30 rubs the surface of the photoconductor 4 rotating in the direction indicated by the arrow A to develop the electrostatic latent image formed on the photoconductor 4. Is becoming When the tip of the magnetic brush 30 comes into contact with the surface of the photoconductor 4, the positively charged toner in the magnetic brush 30 is electrically attracted to the negatively charged electrostatic latent image formed on the photoconductor 4, The electrostatic latent image is developed by being separated from the carrier and adsorbed on the surface of the photoconductor.

On the lower left side of the developing roller 29, and
A conductive plate 31, which is a conductive portion, is arranged at a position where the tip of the magnetic brush 30 can come into contact. This conductive plate 3
No. 1 is grounded, and when the above magnetic brush 30 comes into contact, a current flows from the developing sleeve 29b through the carrier in the magnetic brush 30.

A current detector 32, which is a current detecting means, is connected to the conductive plate 31, and the current detector 32 is connected to the current detector 32.
Is connected to the CPU 15 which constitutes the control system of this copying machine. The CPU 15 is also a toner consumption amount detecting means. Therefore, the current flowing through the conductive plate 31 is detected by the current detector 32, and this current value is input to the CPU 15 and processed by the CPU 15. The CPU 15
The processing by will be described later with reference to FIG.

The current flowing through the conductive plate 31 and the developing roller 2
The relationship with the toner density in the magnetic brush 30 formed on the surface 9 has the characteristics shown in FIG. That is, the lower the toner concentration in the magnetic brush 30, the larger the current flowing through the conductive plate 31, and conversely, the higher the toner concentration, the smaller the current. This is used for development and the magnetic brush 3
This is because the non-conductive toner in 0 moved from the magnetic brush 30 to the photoconductor 4 and decreased, and the resistance value of the magnetic brush 30 decreased, so that the current easily flowed.

The current detector 3 detects such a change in current.
As shown in FIG. 3, the CPU 15 input via the storage unit 1 stores a toner consumption conversion table in advance.
7 and the toner replenishment motor 16 are connected,
The U15 calculates the toner consumption amount based on the current value input from the current detector 32, controls the toner replenishment motor 16 based on this, and performs the toner density control described later. Next, the copying operation of the copying machine will be described with reference to the color copying mode. For example, as shown in FIG. 6A, a striped original 3 having image portions A and non-image portions B formed alternately is placed on the original placing table 1 and a copy start switch (not shown) is placed. When is pressed, the original 3 is irradiated with light from the exposure lamps 2a, 2a,
The scan is performed 3 times. As a result, the reflected light from the original 3 through the reflecting mirrors 2b ... Is sequentially decomposed by the optical filter 2c into red, green, and blue color components. And
The photoconductor 4 is exposed to light of different color components for each scan, and the photoconductor 4 is exposed. As a result, an electrostatic latent image for each color component corresponding to the image of the original 3 is sequentially formed on the photoconductor 4. It should be noted that these electrostatic latent images are formed such that exposed portions and non-exposed portions are alternately and continuously formed corresponding to the striped pattern of the original image.

Each electrostatic latent image formed on the photosensitive member 4 at the time of each of the above three scans is a color having a developer of each color of yellow, magenta, and cyan which are complementary colors of each color filter in the optical filter 2c. Developing unit 5b ・ 5
It is developed with the toners respectively supplied from c and 5d, visualized, and formed as a toner image. The toner images for the respective color components are sequentially transferred to the intermediate transfer body 7 by the first transfer charger 13, and the toner images for the respective color components are sequentially superimposed to form a color toner image.

Then, the toner image on the intermediate transfer body 7 is transferred to the second transfer sheet when the copy sheet fed from one of the sheet feeding cassettes 6 is brought into close contact with the lower surface of the intermediate transfer body 7. It is transferred to the copy sheet by the charger 14. After that, the copy paper is separated from the intermediate transfer body 7, and is sent to the fixing unit 9 via the conveyor belt 8 to fix the image transferred to the copy paper and form a color copy image. By the way, when the toner in the developer in the developing tank 21 is consumed during the copying operation as described above, the toner replenishment motor 16 is driven based on the current value detected by the current detector 32. Then, the toner is supplied from the toner hopper 22 to the developing tank 21. Such toner density control will be described based on the flowcharts of FIGS. 6 and 7.

During development of the electrostatic latent image, the current detector 32
6 alternately detects two types of current values as shown in FIG. 6 (b) (S1). Larger value V _{h of the} two types of current values
Is the magnetic brush 3 that rubs the exposed portion corresponding to the image portion A.
The non-conductive toner in the magnetic brush 30 moved to the photoconductor 4 at the time of development by the current flowing through 0,
The resistance value of the magnetic brush 30 decreases and becomes a large value. On the other hand, the small value V _l is the current flowing through the magnetic brush 30 that rubs the non-exposed portion corresponding to the non-image portion B, and the amount of toner in the magnetic brush 30 does not change.
The resistance value of 0 is large and small.

The CPU 15 determines the difference between these two current values,
That is, to detect the current difference _{a = V h -V l (S2} ), whereas, reading the toner consumption conversion table from the storage unit 17 (S3). Then, the current difference a is associated with the toner consumption conversion table to calculate the toner consumption (S4). Based on this calculated value, the toner replenishment motor 16 is controlled to rotate the toner replenishment roller 24, and the toner hopper 22 supplies the same amount of toner as the amount consumed during development to the developing tank 21 (S5). .. As a result, the toner density in the developing units 5b, 5c, 5d is always kept constant.

The electrical contact between the developer after development and the conductive plate 31 is improved because the contact state becomes better.
Current detection is more stable. In the example shown in FIG. 1, the conductive plate 3
Reference numeral 1 denotes a developing pole (N) for rubbing a magnetic brush against the surface of the photoconductor 4 to perform development, and a collecting pole (S) for collecting the developer after development into the developing tank 21 of the paddle roller 28. And (in the vicinity of the central portion between the magnetic poles). In this case, the developer lies on the peripheral surface of the developing sleeve 29b between the magnetic poles, so that the contact between the developer and the conductive plate 31 tends to be partial.
It is possible that current detection becomes unstable.

Therefore, the conductive plate 31 is disposed so as to face the recovery pole (S) located next to the developing pole (N) in the development,
At this position, the magnetic pole brush of the developer is brought into contact. In this case, in the developer, the spikes are almost vertical at the position corresponding to the recovery electrode, and the electric contact with the conductive plate 31 is surely and stable. In particular, with respect to the arrangement of the conductive plate 31, since the developer stands in a vertical state, the distance between the surface of the developing sleeve 29b and the tip of the developer becomes long, and the electrical contact between the conductive plate 31 and the developer is improved. Therefore, the positional adjustment of the positional relationship between the conductive plate 31 and the developing sleeve 29b becomes easy.

As described above, the toner density control in the copying machine of this embodiment is performed through the magnetic brush 30 through the conductive plate 3.
It is carried out based on the change in the value of the current flowing in No. 1. Therefore, as compared to the case where the toner concentration sensor is used for control as in the conventional copying machine, the control that directly corresponds to the toner consumption amount can be performed, so that the toner concentration can be maintained more accurately. It is possible to improve the copied image.

Further, the simple conductive plate 31 and the current detector 3
2 and the CPU 15 which is the control system of the copying machine, the conventional expensive toner concentration sensor can be eliminated, and the cost can be reduced.

In the above embodiments, the color copying machine was described as an example, but the developing device of the present invention is applied to other electrophotographic devices such as black and white copying machines and printers. It is possible.

[0037]

As described above, the developing device of the electrophotographic apparatus of the present invention, the conductive portion provided at the position where the tip of the magnetic brush after rubbing the photosensitive member comes into contact, and the magnetic portion The current consumption means for detecting the current flowing from the developing sleeve to the conductive portion when the brush comes into contact, and the toner consumption amount at the time of development are calculated based on the change in the current value detected by the current detection means. The toner consumption amount detecting means is provided.

As a result, when the toner replenishing roller or the like is controlled on the basis of the value detected by the toner consumption amount detecting means to keep the toner concentration in the developer constant, or the like, the Since the control directly corresponding to the toner consumption amount can be performed, there is an effect that the control can be performed more accurately than the conventional control based on the detection value of the toner concentration sensor for the carrier in the developer. ..

In particular, by arranging the magnet as a conductive portion so as to face one magnetic pole forming a magnetic brush, the contact with the developer is surely and stable, so that the current detection becomes accurate.

Further, since the conventional expensive toner concentration sensor is abolished, it is composed of a conductive portion, a relatively inexpensive member such as a current detecting means, and a control system provided in the main body of the electrophotographic apparatus. The effect that the cost of the developing device can be reduced is also obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of a developing device in a copying machine according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the copying machine.

FIG. 3 is a block diagram showing a main part of a control system of the copying machine.

FIG. 4 is a schematic configuration diagram of a developing device in the copying machine.

FIG. 5 is a graph showing the relationship between the toner concentration in the magnetic brush and the current flowing through the magnetic brush.

6A is an image of a document, and FIG. 6B is a graph showing a current flowing through a conductive plate when the image of FIG.

FIG. 7 is a flowchart of toner density control of the copying machine.

[Explanation of symbols]

 4 Photoconductor 5a Developing unit (developing device) 5b Developing unit (developing device) 5c Developing unit (developing device) 5d Developing unit (developing device) 15 CPU (toner consumption detecting means) 29 Developing roller 29a Magnet roller 29b Developing sleeve 30 Magnetic brush 31 Conductive plate (conductive portion) 32 Current detector (current detecting means)

Claims (2)

[Claims] 1. A developing sleeve which covers the outer circumference of a magnet having a plurality of magnetic poles in the circumferential direction, and a magnetic brush of a developer is formed on the surface by the magnet. The developing sleeve is formed on the surface of a photoconductor by the magnetic brush. In a developing device for an electrophotographic apparatus that develops a formed electrostatic latent image, a conductive portion is provided at a position where the tip of the magnetic brush that has finished rubbing the photoconductor abuts, and the magnetic brush contacts the conductive portion. A current detecting means for detecting a current flowing from the developing sleeve to the conductive portion when contacted, and a toner consumption calculating a toner consumption amount at the time of development based on a change in the current value detected by the current detecting means. A developing device for an electrophotographic apparatus, characterized in that an amount detecting means is provided. 2. The developing device for an electrophotographic apparatus according to claim 1, wherein the conductive portion is arranged corresponding to a position of one magnetic pole of a magnet forming a magnetic brush of the developer.