JP2001250713A - Magnet roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnet roller that is simple in structure and capable of enhancing a specific pole in magnetic force. SOLUTION: A magnet roller 20 comprises magnet pieces 22A to 22D formed of ferrite bonded magnets, a flat 21K is formed on the side of a shaft 21, and a magnet piece 22B forming a specific pole N1 is arranged on the flat 21K, by which the above magnet piece 22B can be increased in volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet roller used in a copying machine using a magnetic toner such as a laser printer.

[0002]

2. Description of the Related Art Conventionally, in a copying machine such as an electrophotographic copying machine or a laser printer, an electrostatic latent image is formed on a photosensitive drum, and a magnetic toner is attached to the electrostatic latent image by a developing device. This is transferred to a storage medium such as paper and developed. FIG. 4 is a view showing a configuration of a conventional developing device. In the developing device 1, a cylindrical magnet roller 3 having a predetermined magnetic force pattern magnetized is disposed inside a rotating cylindrical sleeve 2. After the developing roller 4 is provided, the magnetic toner 6 stored in the developing container 5 is sucked up onto the surface of the sleeve 2 and transported according to the magnetic force pattern, and the magnetic toner 6 is formed into a uniform thin layer by the layering blade 7. To be attached on the electrostatic latent image on the photosensitive drum 8,
The magnetic toner 6 remaining on the surface of the sleeve 2 is then separated from the sleeve 2 and collected.

Since various patterns are required for the magnetic force pattern depending on the specifications of the copying machine, the magnet roller 3 may be made of metal or resin as shown in FIGS. 5 (a) and 5 (b). A plurality of shafts 31 and a plurality of side surfaces of a bar-shaped magnet piece 32P having a fan-shaped cross section in which the magnetic poles on the outer peripheral side are previously magnetized to the N pole or the S pole are bonded to the outer peripheral side of the shaft 31. And a cylindrical roll main body 32 manufactured in this manner. These magnet pieces 32P are generally formed of inexpensive ferrite-based bonded magnets using magnetic powder such as St ferrite or Ba ferrite.

Meanwhile, in the magnet roller 3, a specific pole such as a developing pole (for example, N1 in FIG.
Pole) may be required to have a high magnetic force, and various proposals have been made to realize this requirement. For example, as a magnet piece constituting the specific pole N1, Sm-C
A high magnetic force magnet piece made of a rare earth based bonded magnet such as o or Sm-Fe-N is used, or a concave portion is provided on the outer peripheral surface of the magnet piece constituting the specific pole N1, and the high magnetic force magnet piece is embedded in this concave portion. Thus, the magnetic force of the specific pole N1 is improved. However, the use of a rare earth-based high magnetic force material for the magnet pieces not only requires the production of magnet pieces of two different materials, but also has the problem of increasing the material cost. Also, a method of embedding a high magnetic material in a magnet piece constituting a specific pole has the advantage of using less high magnetic material, but requires processing and embedding of the magnet piece. However, there is a disadvantage that the number increases. Therefore,
As shown in FIG. 6, the magnet pieces are all inexpensive ferrite bond magnets, and the shaft 31 of the magnet roller 3 is eccentric with respect to the center axis of the sleeve 2 so that the specific pole (here, N1 pole) , The volume of the magnet piece 32B disposed at a position corresponding to
7 (a) and 7 (b), as shown in FIGS. 7 (a) and 7 (b), a modified shaft 3 having a polygonal cross-section at a position where magnet pieces 32A to 32D on the side of the shaft are bonded.
Using 1Z, a magnet piece of a specific pole (here, 32B, 3
A method of increasing the volume of 2D) has been proposed (JP-A-6-308835).

[0005]

However, when the shaft 31 of the magnet roller 3 is eccentric, the volume of the magnet piece 32D constituting the magnetic pole N2 on the opposite side of the specific pole N1 decreases. The magnetic pole N2 has a problem that a required magnetic force cannot be obtained. Further, when a modified shaft 31Z having a polygonal cross section is used, the influence on other magnetic poles is small,
Not only is it necessary to machine Z into a prismatic shape, but also in order to make the rotation of the sleeve 2 smooth, it is necessary to perform secondary machining to make the end 31a of the shaft 31Z, which is the bearing sliding portion, into a substantially cylindrical shape. Become. Therefore, there has been a problem that the number of manufacturing steps increases and the cost increases.

The present invention has been made in view of the conventional problems, and has as its object to provide a magnet roller capable of increasing the magnetic force of a specific pole with a simple configuration.

[0007]

According to a first aspect of the present invention, there is provided a magnet roller provided with a flat portion extending in a length direction on a part of an outer periphery of a shaft, and a specific pole contacting the flat portion. Are arranged.

According to a second aspect of the present invention, each magnet piece is made of a magnetic material having the same composition.

According to a third aspect of the present invention, each magnet piece is formed of a ferrite bond magnet.

According to a fourth aspect of the present invention, the cutout thickness of the shaft for forming the flat portion is 10% to 40% of the diameter of the shaft.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B are diagrams showing a configuration of a developing roller 10 provided with a magnet roller according to the first embodiment. FIG. 1A is a front view, and FIG.
The figure is a sectional view taken along the line AA in FIG. Developing roller 10
Is a cylindrical sleeve 11 made of a non-magnetic material, a holding portion 12 fitted to both ends of the sleeve 11 and fixing the sleeve 11, and a coaxially disposed inside the sleeve 11 And a cylindrical magnet roller 20 magnetized in the designed magnetic force pattern. The holding portion 12 is a stepped cylinder having a stepped portion 12 a whose outer diameter on the side of the sleeve 11 is smaller by the thickness of the sleeve 11,
A cylindrical shaft 12b projecting outward is provided at the center of the outer end surface, and a circular concave portion 12c is provided at the center of the inner short surface. A fixing portion 12d provided on the holding portion 12a is fixed to the holding portion 12 with an adhesive or the like. Further, as shown in FIGS. 2A and 2B, the magnet roller 20 cuts a part of a cylindrical side surface along a plane parallel to an axis over its entire length, and extends the flat portion 2 extending in the length direction.
1K, and a roller body 22 provided on an outer peripheral portion of the shaft 21 and magnetized in a predetermined magnetic force pattern.
1a and 21a are pivotally connected to the holding part 12 via, for example, a bearing 13 (see FIG. 1B).

Roller body 22 of magnet roller 20
Are four bar-shaped magnet pieces having a fan-shaped cross-section in which magnetic poles on the outer peripheral side are respectively magnetized to N1, S1, N2, and S2 poles along the circumferential direction of the outer peripheral portion of the shaft 21. 22
A to 22D are formed by bonding side surfaces of adjacent magnet pieces together. In the present embodiment, each of the magnet pieces 22A
-22D, a magnetic powder obtained by turning a ferrite-based sintered magnet such as St ferrite or Ba ferrite into a fine powder; a binder such as a thermoplastic resin such as nylon, polyethylene, or EVA (ethylene-vinyl acetate copolymer); After molding the resin magnet composition dispersed in the binder) by injection molding or the like, a ferrite bond magnet magnetized so that the outer magnetic poles become predetermined magnetic poles was used. In the present embodiment, the magnet piece 22B constituting the N1 pole which is the specific pole
Is different from the other magnet pieces 22A, 22C, 22D in that the outer peripheral side is arc-shaped but the inner peripheral side is linear. Corresponding to this, the flat portion 21K described above is provided at the place where the magnet piece 22B is disposed on the side surface of the shaft 21, and the straight portion that is the inner peripheral portion of the magnet piece 22B contacts the flat portion 21K. Thus, the magnet piece 22B is attached. Thereby, the volume of the magnet piece 22B increases, so that the magnetic force of the specific pole N1 can be increased. Although the shaft 21 has a flat portion 21K, the outer shape is substantially cylindrical, so that the sleeve 11 rotates smoothly.
That is, the shaft 21 of the present embodiment can be used without particularly processing the both end portions 21a, 21a of the shaft 21, which is the bearing sliding portion.

FIG. 3 shows that the outer diameter of the roller body 22 is D = 15.
The figure which shows the change of the magnetic force of the specific pole N1 when the cut thickness (cut thickness) t for forming the flat part 21K is changed in the magnet roller 20A where φ and the diameter of the shaft 21 are d = 6φ. And the horizontal axis is the cut thickness t (m
m), the vertical axis indicates the magnitude of the magnetic force of the specific pole N1, and the magnitude of the magnetic force without the conventional flat portion 21K (t = 0) by 10
It is represented by a relative value when 0 is set. However, as the magnet roller 20A, a 5-pole magnet roller more practical than that shown in FIG. 2 was used. As is clear from FIG. 3, the magnitude of the magnetic force of the specific pole N1 is determined by the increase in the cut thickness t, that is, the magnet piece 2 forming the specific pole N1.
As the volume of 2B increases, the magnetic force of the specific pole N1 increases by about 5% at t = 1 and about 9% at t = 2. When the cut thickness t of the flat portion 21K is small, the increase in the magnetic force of the specific pole N1 is small. Therefore, the cut thickness t of the flat portion 21K is preferably 0.6 mm or more, that is, 10% or more of the diameter of the shaft 21. When the cut thickness t increases, the outer shape of the shaft 21 deviates from the cylinder, and the sleeve 11
Therefore, it is desirable that the cut thickness t is 2.4 mm or less, that is, 40% or less of the diameter of the shaft 21.

As described above, according to the present embodiment, each of the magnet pieces 22A to 22D of the magnet roller 20 is formed of a ferrite-based bonded magnet, and
A flat portion 21K is formed on the side surface of each of them, and a magnet piece 22B constituting the specific pole N1 is disposed on the flat portion 21K to increase the volume of the magnet piece 22B. Magnetic force can be increased. In addition, since the outer shape of the shaft 21 is substantially cylindrical, both ends 21a of the shaft 21 can be used without any particular post-processing.

In the above embodiment, the magnet roller 20 in which each magnet piece is magnetized to the N1, S1, N2, and S2 poles has been described. However, the magnetization pattern of the magnet roller is not limited to this. Not something.
In the above example, the magnet roller 20 having four poles has been described. However, it is needless to say that another pole number may be used, and the specific pole is not limited to the N1 pole. Further, in the above example, each of the magnet pieces 22A to 22D is formed of a ferrite bond magnet. However, a magnet roller using a rare earth high magnetic material for all the magnet pieces, such as a small high magnetic force magnet roller, is used. Also in the above, the magnetic force of the specific pole can be increased by increasing the volume of the magnet piece forming the specific pole by the same configuration as the above embodiment.

[0016]

As described above, according to the first aspect of the present invention, a flat portion extending in the length direction is provided on a part of the outer periphery of the shaft, and the specific electrode is in contact with the flat portion. Are arranged to increase the volume of the magnet piece forming the specific pole of the magnet roller, so that the magnetic force of the specific pole can be increased with a simple configuration.

According to the second aspect of the present invention, since each magnet piece is made of a magnetic material having the same composition, only one kind of material is required for manufacturing the magnet piece. Can be simplified.

According to the third aspect of the present invention, since each magnet piece is made of an inexpensive ferrite-based bonded magnet,
The cost of the magnet roller can be reduced.

According to the fourth aspect of the present invention, since the cutout thickness of the shaft for forming the flat portion is set to 10% to 40% of the diameter of the shaft, the shaft which is the bearing sliding portion is formed. The magnetic force of a specific pole can be increased without specially processing both end portions.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a developing roller.

FIG. 2 is a diagram showing a configuration of a magnet roller according to the embodiment.

FIG. 3 is a diagram showing a relationship between a thickness of a flat portion, a developing pole, and a magnetic force.

FIG. 4 is a diagram illustrating a configuration of a conventional developing device.

FIG. 5 is a diagram showing a configuration of a conventional magnet roller.

FIG. 6 is a diagram showing another configuration of a conventional magnet roller.

FIG. 7 is a diagram showing another configuration of a conventional magnet roller.

[Explanation of symbols]

10 developing roller, 11 sleeve, 12 holder, 1
2a Step, 12b Developing roller shaft, 12c
Recess, 12d fixed part, 13 bearing, 20 magnet roller, 21 shaft of magnet roller,
21K Flat part on shaft side, 21a Shaft end, 22A-22D magnet piece.

Claims (4)

[Claims] 1. A magnet roller comprising a plurality of magnet pieces arranged along a circumferential direction on an outer peripheral portion of a cylindrical shaft, wherein a flat portion extending in a longitudinal direction is provided on a part of the outer periphery of the shaft. Wherein a magnet piece of a specific pole is disposed in contact with the flat portion. 2. The magnet roller according to claim 1, wherein each magnet piece is made of a magnetic material having the same composition. 3. The magnet roller according to claim 2, wherein each magnet piece is formed of a ferrite bond magnet. 4. The magnet roller according to claim 1, wherein a cut-out thickness of the shaft for forming the flat portion is 10% to 40% of a diameter of the shaft.