JPH0926696A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the contact reliability of a contact point and a shaft holding the developing roller of a developing device and to improve printing quality by improving the constitution to impress a bias voltage on the developing roller. SOLUTION: The contact point 12 fixed to a conductive permanent magnet 13 is pressed by a spring 11 to the shaft 6 holding the developing roller 5. The spring 11 and the contact point 12 are composed of a soft magnetic material in order to form a magnetic circuit. A conductive and magnetic fluid 5 is disposed between the contact point and shaft. The generation of arcs and the oxidation and corrosion of the surfaces of the contact point 12 and the shaft 6 are prevented by magnetic fluid 15 even if chattering arises when the bias voltage is impressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for causing charged toner on a developing roller to fly to a photosensitive member on which a charged image is formed, and more particularly to a structure for applying a bias voltage to the developing roller. Is.

[0002]

2. Description of the Related Art FIG. 5 shows a general developing device. The toner 2 in the developing unit 1 is agitated by the mixer 3,
It is charged by the brush roller 4. The toner 2 supplied to the developing roller 5 is adjusted to a uniform thickness by the doctor blade 7. The toner 2 on the developing roller 5 is applied to the photoconductor 8 by the bias voltage applied to the developing roller 5.
And the charged image formed on the photosensitive belt 8 is developed.

The bias voltage that controls the flight of toner is
Generally, the voltage is high (about 300 to 500 V), and if the voltage is not applied even for a moment, the flying of the toner is hindered and the print quality is impaired. Therefore, conventionally, as shown in FIG. 6, in order to apply a bias voltage to the rotating developing roller, a contact point 9 is pressed against one end of the shaft 6 by a spring 10 connected to a high-voltage control circuit to maintain the connection between both. It was

[0004]

However, in the above-mentioned conventional structure, the shaft 6 is rotating, so that chattering occurs at the contact portion. Due to the chattering, an arc is generated between the contact 9 and the shaft 6, the surface of the contact 9 and the surface of the shaft 6 are oxidized and consumed, and the surfaces of these are corroded because they are exposed to the air. Will end up. Due to this oxidation and corrosion, the application of the bias voltage becomes unstable, the flying of the toner is affected, and the print quality is impaired.

Therefore, the present invention is intended to eliminate the problem caused by chattering by adding a conductive magnetic fluid to the contact portion.

[0006]

In order to solve the above-mentioned problems, the present invention applies a bias voltage to a shaft holding a developing roller through a contact pressed by a spring, thereby applying a bias voltage on the developing roller. Charged toner,
In a developing device that causes toner to fly to a photoconductor on which a charged image is formed, by supporting a permanent magnet on the spring,
A conductive magnetic fluid is held between the shaft and the contact.

[0007]

In the above structure, the magnetic flux between the contact and the shaft is maximized in the magnetic flux distribution generated by the permanent magnet, and the magnetic fluid can be retained. Therefore, even if chattering occurs and the contact state becomes unstable, the conductive magnetic fluid is interposed, so that the connection can be stably maintained. Moreover, since the magnetic fluid covers the contact and the shaft, it is possible to prevent oxidation and corrosion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The developing device of the present invention will be described below with reference to the accompanying drawings. The present invention is characterized by the structure between the contact and the shaft for applying a bias voltage to the developing roller, and this point will be specifically described.

In FIG. 1, the spring 11 has a permanent magnet 13
And the contact 12 is fixed to the permanent magnet 13,
A pressing force is applied to the shaft 6. Since the spring 11 and the contact 12 form part of the yoke of the magnetic circuit, it is necessary to use a soft magnetic material, and the permanent magnet 13 uses a conductive material to form an electric circuit of bias voltage. There is a need to. The distribution of the magnetic field between the contact points is shown in FIG. The distribution of the magnetic flux by the permanent magnet 13 has the maximum magnetic flux density in the contact portion, and the magnetic fluid 15 can be retained in the contact portion.

In the above structure, even if chattering occurs between the contact 12 and the shaft 6 when a bias voltage is applied, the magnetic fluid 15 maintains the electrical contact. Further, since the magnetic fluid 15 covers the contact portion, the contact 12 is corroded due to the generation of an arc or the air atmosphere.
It is possible to prevent consumption and oxidation.

FIG. 3 shows an embodiment in which a ring-shaped permanent magnet 14 is used. A contact 12 is installed inside the ring-shaped permanent magnet 14, and a conductive material is provided between the contact 12 and the shaft 6. A magnetic fluid 15 having a property is added. FIG. 4 shows the distribution of the magnetic field in this embodiment, and the magnetic flux density between the contact portions is the maximum. Therefore, the conductive magnetic fluid 15
Can be held. In this embodiment, the ring-shaped permanent magnet 14 is used to form a magnetic circuit. Therefore, in addition to the above-mentioned effects being obtained by this magnetic fluid 15,
Since the ring-shaped permanent magnet 14 does not form an electric circuit of the bias voltage via the contact 12, there is an advantage that a permanent magnet made of a non-conductive material can be used.

[0012]

As described above, by using the permanent magnet between the contact and the shaft and holding the conductive magnetic fluid, the electrical contact can be maintained even if chattering occurs. Also, because the contacts and shaft are covered with magnetic fluid, arcing and oxidation due to air atmosphere,
Corrosion and wear can be prevented. Therefore, the bias voltage is stably applied, and the printing quality is improved.

[Brief description of drawings]

FIG. 1 is an enlarged view of a main part of a developing device according to an embodiment of the present invention.

[Fig. 2] Distribution map of magnetic flux of the device

FIG. 3 is an enlarged view of a main part of a developing device according to another embodiment of the present invention.

FIG. 4 is a magnetic flux distribution map of the device.

FIG. 5 is a schematic configuration diagram showing a conventional developing device.

FIG. 6 is an enlarged view of the main part of the device.

[Explanation of symbols]

 1 Development Unit 2 Toner 3 Mixer 4 Brush Roller 5 Development Roller 6 Shaft 7 Doctor Blade 8 Photoreceptor 9,12 Contact 10,11 Spring 13,14 Permanent Magnet 15 Magnetic Fluid

Claims (3)

[Claims] 1. A bias voltage is applied to a shaft holding a developing roller through a contact pressed by a spring to fly the charged toner on the developing roller to the photosensitive member on which a charged image is formed. In the developing device, a permanent magnet is supported by the spring to hold a conductive magnetic fluid between the shaft and the contact. 2. The developing device according to claim 1, wherein a magnetic circuit is formed by a permanent magnet by using a soft magnetic material for the spring and the contact. 3. The permanent magnet is formed of a conductive material so that the contact is supported by a permanent magnet provided on a spring so that the contact can be pressed against a shaft to apply a bias voltage. Item 1. The developing device according to Item 1.