JP2002189338A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device having a developing sleeve, where an eddy current generated in the developing sleeve is restrained, heat generation, the insufficiency of driving torque and a phenomenon of magnetic field are not caused. SOLUTION: Stripe-shaped electrodes 1 extended long in the shaft direction of the sleeve are arranged cyclically in the peripheral direction of the sleeve and connected so that a closed circuit may not be formed between the electrodes or the total sum of induced electromotive force generated on the individual electrodes in the closed circuit may be about 0 (volt) even when a closed circuit is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic technique, such as a plain paper copying machine and a page printer.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, an electrostatic latent image corresponding to image information is placed on a latent image carrier such as a photosensitive drum or a photosensitive belt. An image is formed, a developing operation is performed by the developing device, and a visible image is obtained. In performing the developing operation as described above, a magnetic brush developing method using a two-component developer composed of a toner and a carrier from the viewpoints of transferability, halftone reproducibility, stability of developing characteristics with respect to temperature and humidity, and the like. Is the mainstream. That is, in the developing device, while the two-component developer is held on the developer carrier in a brush chain shape,
The toner is conveyed to a development area facing the latent image carrier, and replenishes the toner in the developer to the electrostatic latent image portion on the latent image carrier.

The above-mentioned developing carrier is usually a non-magnetic and conductive sleeve (developing sleeve) formed in a cylindrical shape, and a magnetic body which forms a magnetic field so as to make the developer stand on the surface of the sleeve. Is provided inside the sleeve. At the time of the earing, the carrier is eared on the sleeve so as to follow the lines of magnetic force generated by the magnet body, and the charged toner adheres to the eared carrier. The magnet body has a plurality of magnetic poles and is formed in a rod shape or the like. In particular, a developing main magnetic pole for causing a developer to stand on a developing region portion of the surface of the developing carrier is provided. When at least one of the sleeve and the magnet body moves, the developer raised on the surface of the sleeve moves. The developer conveyed to the developing area rises along the lines of magnetic force generated from the developing main magnetic pole, and the chain of the developer contacts the latent image carrier so as to bend. The toner is supplied while rubbing against the electrostatic latent image based on the relative linear velocity difference with the image carrier. When the developing sleeve or the magnet rotates, an eddy current is generated in the developing sleeve because the developing sleeve crosses a magnetic field generated from the magnet. This eddy current causes heat generation of the developing sleeve and insufficient driving torque, and also causes a problem that the magnetic field forming the magnetic brush decreases because the current flows in a direction to cancel the magnetic field.

[0004]

Conventionally, such a problem has been dealt with mainly by increasing the electric resistance of the material of the sleeve. This method certainly reduces the eddy current in inverse proportion to the electrical resistance, but materials with high electrical resistance, for example, stainless steel, are more expensive and more expensive to process than aluminum, which has been used for conventional sleeve materials. There is the problem of difficulty. In view of the above problems, in the present invention,
An object of the present invention is to provide a developing device having a developing sleeve, which suppresses eddy current generated in the developing sleeve and does not cause heat generation, insufficient driving torque, or a magnetic field phenomenon.

[0005]

According to the first aspect of the present invention, there is provided a developing device having a developing sleeve for a magnetic developer comprising a rotatable hollow cylinder. A plurality of stripe-shaped electrodes elongated in the axial direction of the sleeve are periodically arranged in the circumferential direction of the sleeve, and a closed circuit is not formed between the electrodes or a closed circuit is formed. The developing device is characterized in that the connection is made so that the sum of the induced electromotive forces generated in the individual electrodes in the closed circuit becomes substantially 0 (volt). According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the plurality of electrodes are not electrically connected to each other except at one axial end of the sleeve. According to the third aspect of the present invention, the plurality of electrodes are electrically connected to each other only at one end in the axial direction of the sleeve, and are connected to each other only at the opposite end in the axial direction of the sleeve. 2. The developing device according to claim 1, comprising an electrode group. In the invention described in claim 4, the plurality of electrodes are alternately connected at both ends in the axial direction of the sleeve, and one closed circuit is formed around one circumference of the sleeve. Developing device. According to a fifth aspect of the present invention, there is provided the developing device according to any one of the first to fourth aspects, wherein a cycle in which the plurality of electrodes are arranged is narrower than a width of the developing nip. According to a sixth aspect of the present invention, the developing sleeve has a configuration in which a plurality of stripe-shaped electrodes made of a conductive material are formed on the surface of a cylinder made of an insulating material. A developing device according to any one of the above.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. A developing sleeve for a magnetic developer according to the present invention will be described. FIGS. 1A to 1C show examples of electrode patterns arranged on the developing sleeve. On the sleeve, stripe-shaped electrodes 1 elongated in the axial direction of the sleeve are periodically arranged in the circumferential direction of the sleeve, and a closed circuit is not formed between the electrodes or a closed circuit is formed. Even if
The sum of induced electromotive forces generated at individual electrodes in a closed circuit is approximately 0
(Bolts).

[0007] This structure is basically the same as a magnetic core in which iron plates used for a power transformer and the like are stacked. The eddy current flows in a circle along the surface of the sleeve, and the larger the diameter of the circle, the larger the current flowing. Therefore, in the same way as the replacement of the iron block with the piled iron plate, the sleeve composed of one plate is replaced with an aggregate of elongated electrodes. Here, in the case of the transformer magnetic core, it is not necessary to take into account the electrical connection, but in the case of the developing sleeve, all electrodes need to be conductive somewhere to apply the developing bias. Yes. Therefore, for example, when a general aluminum sleeve is formed with a slit along the axial direction as shown in FIG. 2, an elongated strip-shaped electrode is certainly formed. Since conduction occurs at both ends, a closed circuit is formed through the plurality of stripe electrodes and both ends thereof, and an eddy current flows, which is not appropriate.

Therefore, each stripe electrode does not form a closed circuit between the electrodes, or even if a closed circuit is formed, the total sum of induced electromotive forces generated in the individual electrodes in the closed circuit is substantially 0 (volt). It is necessary to connect as follows. By connecting the wires so that the sum of the induced electromotive forces is substantially 0 (volt), generation of an eddy current can be suppressed, and heat generation of the developing sleeve and hindrance of rotation of the magnet can be eliminated.

Hereinafter, a specific electrode configuration is shown in FIGS.
It will be described with reference to (c). FIG. 1 (a) shows claim 2.
Described above, the plurality of electrodes are not electrically connected to each other except at one end in the axial direction of the sleeve. FIG.
FIG. 3B shows an electrode group in which the plurality of electrodes are electrically connected to each other only at one end in the axial direction of the sleeve, and the electrode group is electrically connected to each other only at the opposite end in the axial direction of the sleeve. And an electrode group. FIG. 1C shows a configuration according to claim 4, in which a plurality of electrodes are alternately connected at both ends in the axial direction of the sleeve, and one closed circuit is formed around one circumference of the sleeve. Although the electrodes appear to be interrupted at the upper and lower ends in the figure, this is because only the half surface of the sleeve is visible, and the actual electrode goes around the sleeve including the back surface (not shown). Note that FIG.
The connection examples illustrated in (a) to (c) are merely examples, and in addition to these, variations of the connection that match the description of claims 2 to 4, such as the combination of FIG. 1B and FIG. There are many.

[0010] In the developing device according to the fifth aspect, there is provided the developing device according to the first aspect.
In the developing device according to any one of the first to fourth aspects, the cycle in which the plurality of electrodes are arranged is narrower than the width of the developing nip. This is a configuration for reducing unevenness in developing ability in the sub-scanning direction. According to a sixth aspect of the present invention, in the developing device according to the first to sixth aspects, the developing sleeve is formed by forming a plurality of stripe-shaped electrodes made of a conductive material on a surface of a cylinder made of an insulating material. And

Hereinafter, examples showing the effects of the developing device of the present invention will be described in comparison with comparative examples. <Example 1> Ceramic outer diameter 20mmφ, thickness 1m
A circuit pattern of stripe-shaped electrodes was formed by printing on the surface of a tube having a length of 100 mm and a length of 100 mm, and a nickel layer having a thickness of 100 μm was formed by electroforming to produce a sleeve as shown in FIG. Here, the width of one electrode is 1 m
m, the period is about 1.5 mm, and the connection pattern is shown in FIG.
The type illustrated in (a) was used. A magnet roll composed of a barium / ferrite magnet is arranged in the inside, and under the condition that a two-component magnetic brush developer (trade name: Ricoh developer type 8200) is adsorbed on the sleeve surface, it is continuously rotated at a rotation speed of 1100 rpm. The test was performed.

Comparative Example 1 A solid pattern was formed on the same ceramic tube as in Example 1 by printing and a nickel layer having a thickness of 100 μm was formed by electroforming to produce a sleeve as shown in FIG. Using this sleeve, a continuous rotation test was performed under the same conditions as in Example 1. <Comparative Example 2> Aluminum outer shape 20 mmφ, thickness 1 mm,
A sleeve having a length of 100 mm was prepared, and the same continuous rotation test as in Example 1 was performed.

FIG. 5 is a graph showing the results of measuring the time history of the temperature rise for the above three examples. In Example 1, although the temperature rise at the beginning of the operation is early, the temperature converges to a constant value at an early point thereafter, and it can be seen that the temperature is lower than in Comparative Examples 1 and 2. From these results, it is understood that the amount of heat generated in the developing sleeve can be suppressed low by the developing device of the present invention.

[0014]

As described above, according to the first to fourth aspects of the present invention, a plurality of stripe-shaped electrodes elongated in the axial direction of the developing sleeve are periodically arranged in the circumferential direction of the sleeve. In addition, the electrodes are connected such that no closed circuit is formed between the electrodes, or even if a closed circuit is formed, the sum of induced electromotive forces generated in the individual electrodes in the closed circuit is substantially 0 (volt). Thereby, eddy current generated in the developing sleeve can be suppressed, and heat generation of the sleeve and hindrance of rotation of the magnet can be eliminated. According to the fifth aspect of the invention, by forming the period in which the plurality of electrodes are arranged to be narrower than the width of the developing nip, it is possible to reduce unevenness in developing ability in the sub-scanning direction. According to the invention described in claim 6, the developing sleeve has a configuration in which a plurality of stripe-shaped electrodes made of a conductive material are formed on the surface of a cylinder made of an insulating material, thereby suppressing eddy current. In addition, it is possible to provide a developing device of an electrophotographic apparatus which can be operated at high speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an electrode pattern arranged on a developing sleeve.

FIG. 2 is a diagram showing stripe-shaped electrodes that are conductive at both ends of a shaft of a developing sleeve.

FIG. 3 is a perspective view of a developing sleeve used in the first embodiment.

FIG. 4 is a perspective view of a developing sleeve used in Comparative Example 1.

FIG. 5 is a graph showing a change in sleeve surface temperature in a continuous rotation test of a magnet roll.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stripe electrode 2 Developing bias applying means 3 Developing sleeve 4 Slit 5 Developing electrode

Claims (6)

[Claims] 1. A developing device comprising a developing sleeve for a magnetic developer comprising a rotatable hollow cylinder, the sleeve having a plurality of stripe-shaped electrodes extending in the axial direction of the sleeve in a circumferential direction of the sleeve. And a closed circuit is not formed between the electrodes, or even if a closed circuit is formed, the sum of the induced electromotive forces generated in the individual electrodes in the closed circuit becomes substantially 0 (volt). A developing device characterized by being connected as follows. 2. The developing device according to claim 1, wherein the plurality of electrodes are not electrically connected to each other except at one end in the axial direction of the sleeve. 3. An electrode group in which the plurality of electrodes are conductive only at one end in the axial direction of the sleeve, and an electrode group that is conductive only at the opposite end in the axial direction of the sleeve. 2. The developing device according to claim 1, wherein the developing device is configured. 4. The developing device according to claim 1, wherein the plurality of electrodes are alternately connected at both ends in the axial direction of the sleeve, and one closed circuit is formed around one circumference of the sleeve. 5. The developing device according to claim 1, wherein a cycle at which the plurality of electrodes are arranged is narrower than a width of the developing nip. 6. The developing sleeve according to claim 1, wherein a plurality of stripe-shaped electrodes made of a conductive material are formed on a surface of a cylinder made of an insulating material. Developing device.