JP2000089551A - Electrophotographic image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of an abnormal image due to discharge between a developing sleeve and an image carrier caused when a developing bias is applied to the developing sleeve at a high humidity, in an electrophotographic image forming device. SOLUTION: A temperature detection means 40 is disposed near the developing sleeve 30 provided for a developing device 14, and is connected to a microcomputer (MPU) 45. In the case a humidity equal to or higher than a fixed humidity is detected by the humidity detection means 40 when images are recorded, the developing device 14 is replenished with toner by a toner replenishment device to increase the concentration of the toner in it. Thus an amount of the toner electrostatically stuck to the surface of carrier in the developer is increased, to cause the toner to hinder the electrical connection in a developer surface on the developing sleeve. It prevents easy flow of a current in the developer surface even the humidity is high, and hence the occurrence of discharge between the developing sleeve 30 and the photoreceptor 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent image formed on an image carrier such as a photoreceptor such as a copying machine, a printer, a facsimile, and a multifunction machine thereof, by using a two-component developer (mixing toner and carrier). Into a visible image using
The present invention relates to an electrophotographic image forming apparatus that performs recording by transferring the visible image to a recording medium such as paper.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
In the developing device, for example, as shown in FIG. 4, a bias applying device 3 is connected to a developing sleeve 2 provided to face the photoconductor 1. At the time of image recording, a bias voltage is applied to the developing sleeve 2 by the bias applying device 3, the developing sleeve is rotated, and the developer is conveyed while being stirred while being stirred by a stirring member (not shown). On the other hand, the developer is thinned to a predetermined thickness by a doctor blade 4, toner is electrostatically attached to the surface of the photoconductor 1 by a bias voltage, and an electrostatic latent image formed on the photoconductor 1 by the toner. Is being developed.

[0003]

By the way, in such a developing device, usually, a magnet is built in the developing sleeve 2 and when the developer is carried on the outer periphery, the developer is attracted by the magnet. A so-called magnetic brush is formed in a state of being connected in a chain.

However, conventionally, when the humidity becomes high, water molecules adhere to the carrier of the developer connected in such a manner, and a current easily flows on the surface of the developer.
When a bias voltage is applied to the developing sleeve 2 in such a state, a discharge is easily generated between the developing sleeve 2 and the photoconductor 1, and there is a problem that an abnormal image such as a blank image occurs due to the discharge.

[0005]

Therefore, according to the first aspect of the present invention, a two-component developer is used as a developer and a developing sleeve 30 is developed, as in the embodiment described with reference to the following drawings. In an electrophotographic image forming apparatus which applies a bias to electrostatically attach toner to the surface of an image carrier such as the photoconductor 12 to develop a latent image formed on the image carrier, a developing device 14 is provided. A humidity detecting means 40 for detecting the humidity in the inside, and when the humidity detecting means 40 detects humidity equal to or higher than a certain level, the toner is replenished in the developing device 14 to increase the toner concentration in the developing device 14. It is characterized by that.

According to a second aspect of the present invention, in the electrophotographic image forming apparatus according to the first aspect, for example, as described in the embodiment described below with reference to the accompanying drawings, the humidity detecting means 40 determines whether or not the humidity is higher than a predetermined value. When the humidity is detected, the recycled toner collected from the image carrier by the cleaning device 16 is supplied into the developing device 14 and the developing device 1
4 is characterized in that the toner density in the area 4 is increased.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic configuration diagram of a laser printer which is an example of the image forming apparatus according to the present invention.

Reference numeral 10 in the figure denotes a body case 11
This is the device body covered by The apparatus main body 10 is provided with a drum-shaped photoreceptor 12 which is an image carrier at a slightly right center in the main body case 11.

Around the photoreceptor 12, a developing device 14, a transfer device 15, a cleaning device 16 and the like are provided in order from a charging device 13 at the upper left thereof in a rotational direction indicated by an arrow in the drawing. Further, a toner replenishing device 17 is provided on the left side of the cleaning device 16, and an optical writing device 18 is provided from the left to the bottom of the toner replenishing device 17. A fixing device 19 is provided above the photoconductor 12.

Further, under the optical writing device 18, a sheet cassette 20 is detachably mounted with a part thereof protruding outside the main body case 11. On the paper feed cassette 20 and behind the optical writing device, an electrical control device 2 containing an electrical board or the like is stored.
1 is provided.

When recording an image using the printer shown in the figure, the photosensitive member 12 is rotated, the surface is uniformly charged by the charging device 13 with the rotation, and then the optical writing device 18 is used in accordance with the image signal. The writing is performed by irradiating the laser beam L to form an electrostatic latent image on the photoconductor 12.

Subsequently, when the photosensitive member 12 is rotated and passes through the position of the developing device 14, toner is adhered by the developing device to sequentially visualize the electrostatic latent image.

On the other hand, together with the photoconductor 12, the paper feed roller 2
2 is rotated to feed out the paper P, which is a recording medium, in the paper feed cassette 20, and abuts against the registration roller pair 23 to be stopped. Then, the registration roller pair 23 is rotated in synchronization with the image on the photoconductor 12, and the sheet P is transferred to the photoconductor 1.
2. Send it to the right side in the figure.

Then, the image on the photoconductor 12 is transferred to the sheet P by the transfer device 15. After the image transfer, the paper P
The sheet is conveyed to the fixing device 19, where the transferred image is fixed, sent out by the sheet discharge roller pair 24, and stacked on the sheet discharge stack 25 on the apparatus main body 10.

On the other hand, the toner remaining on the surface of the photoreceptor 12 after the image transfer is removed by a cleaning device 16. Thereafter, for example, the charge is removed by a charge removing device (not shown) to prepare for the next image formation.

By the way, the developing device 14 described above is
As shown in the figure, the main body case 27 containing the two-component developer
A developing window 28 is opened on the side of the main body case facing the photoconductor 12, and a developing sleeve 30 is rotatably provided at the position of the developing window. The developing sleeve 30 has a built-in magnet (not shown), and the distal end of a doctor blade 29 whose base end is supported by the main body case 27 is arranged close to the outer periphery.
Then, a bias applying device 35 is attached to the developing sleeve 30.
Connected.

A partition wall 27a extending from the bottom is provided in the main body case 27, and the developer storage chamber 31 is partitioned by the partition wall 27a to form two stirring chambers 31a and 31b. Then, stirring members 32 and 33 are provided in each stirring chamber.
The center support shaft is provided rotatably in parallel with the developing sleeve 30.

In the developing device 14, at the time of image recording, a developing drive motor (not shown) is driven, and the drive is transmitted to rotate the developing sleeve 30 and the stirring member 3
The developer is agitated by rotating 2.33, and the toner and the carrier are conveyed to the developing sleeve 30 while being frictionally charged. Thus, a so-called magnetic brush is formed by adsorbing the developer on the outer periphery of the developing sleeve 30 with the magnet, and the developer is thinned to a predetermined thickness by the doctor blade 29.

On the other hand, a predetermined developing bias is applied to the developing sleeve 30 from a bias applying device 35, and the toner is electrostatically attached to the surface of the photoconductor 12 from the developer with the bias, and the static electricity on the surface is Visualizes the latent image.

Although not shown, the developing device 14 includes a toner concentration sensor for detecting the toner concentration in the developer storage chamber 31. After repeatedly performing the development as described above, when the toner density sensor detects that the toner concentration, that is, the toner ratio in the developer has decreased to a certain value, for example, 3 wt% or less, the toner concentration is determined based on the detection result. The replenishing device 17 is operated, and the toner is supplied from the toner replenishing device to the developer storage chamber 31 through a falling path (not shown).
Replenish inside.

In the printer shown in the drawing, a humidity detecting means 40 is disposed near the developing sleeve 30 in the developing device 14 as shown in FIG. Humidity detecting means 40
Is a humidity sensor, for example, a microcomputer (M
PU) 45. The MPU 45 is further connected to the toner replenishing device 17 so that the operation of the toner replenishing device can be controlled according to the detection result of the humidity detecting means 40.

In the illustrated printer, when the humidity detecting means 40 detects that the humidity has become constant humidity, for example, a high humidity of 80% or more, at the time of image recording, the MPU 45 uses the toner replenishing device 17 based on the detection result. Is operated to supply toner from the toner replenishing device into the developer storage chamber 31 through the falling path, thereby increasing the toner concentration in the developer storage chamber 31. When the toner concentration sensor detects that the toner concentration has increased to, for example, 5 wt% or more, the operation of the toner replenishing device 17 is stopped.

Thus, by increasing the toner concentration in this manner, the amount of toner electrostatically adhering to the carrier surface in the developer is increased, and a large amount of toner is interposed between the carriers connected in a chain on the developing sleeve 30. Then, the surface of the developer is not electrically connected with the toner. As a result, the electric resistance value of the developer surface increases, and even if the humidity is high, it is possible to prevent the current from easily flowing on the developer surface, and to prevent the occurrence of discharge between the developing sleeve 30 and the photoconductor 12. To prevent.

FIG. 3 shows the relationship between the toner density and the number of occurrences of abnormal images in the case of such a high humidity. As shown in FIG. 3, an abnormal image is generally hardly generated when the toner density is high. , We know from experiments.

In the above example, when the humidity detecting means 40 detects a constant high humidity, the toner replenishing device 17
Then, new toner was supplied to increase the toner density in the developing device 14. However, although not shown, the image forming apparatus includes:
The cleaning device is equipped with a toner transport device that returns the residual toner after transfer collected from the photoreceptor to the developing device for recycling. Replenishment can be used to increase the toner concentration in the developing device.

[0026]

Therefore, according to the first aspect of the present invention, when the humidity detecting means detects humidity equal to or higher than a certain level, toner is supplied to the developing device to increase the toner concentration in the developing device. By doing so, the amount of toner electrostatically attached to the carrier surface in the developer is increased, and the developer surface on the developing sleeve is not electrically connected with the toner,
As a result, even when the humidity is high, the current is prevented from easily flowing on the developer surface, and the occurrence of electric discharge between the developing sleeve and the image carrier is prevented. Can be prevented from occurring.

According to the second aspect of the present invention,
When raising the toner concentration in the developing device, the recycled toner collected from the image carrier by the cleaning device
Since the toner is supplied into the developing device, the toner can be effectively used.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a developing device provided in an electrophotographic image forming apparatus according to the present invention.

FIG. 2 is an overall schematic configuration diagram of the image forming apparatus.

FIG. 3 is a graph showing the relationship between the toner density and the number of occurrences of abnormal images when the inside of the developing device is at high humidity.

FIG. 4 is a schematic diagram of a conventional developing device.

[Explanation of symbols]

 Reference Signs List 12 photoreceptor (image carrier) 14 developing device 16 cleaning device 17 toner replenishing device 30 developing sleeve 35 bias applying device 40 humidity detecting means 45 microcomputer

Continued on the front page (72) Inventor Takahiko Tokumasu 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H034 AA06 CA01 2H077 AD06 AD13 AD35 DA10 DA42 DA51 DA51 EA03

Claims (2)

[Claims] A two-component developer is used as a developer, and a developing bias is applied to a developing sleeve to electrostatically adhere toner to the surface of the image carrier to form a latent image formed on the image carrier. In an electrophotographic image forming apparatus for developing, a humidity detecting unit for detecting humidity in the developing device is provided, and when the humidity detecting unit detects a certain level of humidity or more, toner is supplied into the developing device and the developing is performed. An electrophotographic image forming apparatus in which the toner density in the apparatus is increased. 2. When the humidity detecting means detects humidity equal to or higher than a predetermined value, recycled toner collected from the image carrier by a cleaning device is supplied into the developing device to reduce the toner concentration in the developing device. The electrophotographic image forming apparatus according to claim 1, wherein the electrophotographic image forming apparatus is raised.