JP2003122125A - Developing roller, developing device, image forming device and production of the developing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize a shaving that occurs at the positioning fixed chuck of a magnet block in a conventional production method. SOLUTION: In a developing roller 41 in which a magnetic roller is disposed within a non-magnetic sleeve and the magnetic roller holds at least one magnet block 48 forming a developing pole, the magnet block forming the developing pole extends parallel to the axial direction of the developing roller, and the cross-sectional shape of the magnet block perpendicular to the axial direction has a tapering portion, which gradually becomes thinner toward the outside of the developing roller.

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 such as a copying machine, a printer and a facsimile, a developing device mounted on the image forming apparatus, a developing roller and a manufacturing method thereof.

[0002]

2. Description of the Related Art Magnetic brush development is well known in electrophotography and other image formation using powder toner.
It is widely used in image forming apparatuses.

In this type of magnetic brush development, a magnetic brush is formed by magnetically adsorbing the developer on the outer peripheral surface of the developer carrying member, and a developing electric field is secured between the developing region (the developer carrying member and the image carrying member). Area), the toner is transferred from the magnetic brush to the latent image surface of the opposing image carrier by the electric field between the image carrier on which the electrostatic latent image is formed and the sleeve to which the electric bias is applied. Development is performed by selectively supplying and adhering.

The developer carrying member is usually constructed as a cylindrical sleeve (developing sleeve), and a sleeve is provided with a magnet body (magnet roller) for forming a magnetic field on the surface of the sleeve so as to cause a spike of the developer. Prepared inside. At the time of the spikes, the carriers are spiked on the sleeve along the lines of magnetic force generated by the magnet roller, and the charged toner is attached to the carriers related to the spikes. The magnet roller has a plurality of magnetic poles, the magnets forming the respective magnetic poles are formed in a rod shape, and particularly, a developing pole for raising the developer is provided in the developing area portion of the sleeve surface. By moving at least one of the sleeve and the magnet roller, the developer that has risen on the surface of the sleeve is moved, and the developer conveyed to the developing area is moved along the magnetic line of force emitted from the developing pole. The ears of the developer chain come into contact with the surface of the image carrier so as to bend, and the ears of the chain of the developer that have come into contact rub against the electrostatic latent image based on the relative linear velocity difference with the image carrier. , Toner supply is performed.

In such a magnetic brush development, the development conditions for increasing the image density, which were conventionally considered to be opposite to each other, and the development conditions for obtaining a good low-contrast image are made compatible at a high time, and The applicant of the present application has previously proposed a developing device and the like for obtaining a high-quality image over the density range (Japanese Patent Application No. 2000-29637).

[0006]

A conventional roller structure of a developing roller and a method of manufacturing the same will now be described. The developing roller manufacturing method shown in FIG. 8 is a magnet in which a sintered magnet (ferrite block) 54 constituting a pumping pole, a transporting pole, a developing pole and the like is attached to a core 53 integrated holder 53 made of metal or resin. The roller is provided inside the sleeve 52 to form the developing roller 51. When this is applied to the developing roller of the developing device previously proposed by the applicant of the present application, as shown in FIG. 9, three rare earth magnet blocks 48 constituting the developing pole in the holder 23 integrated with the core metal are provided.
A magnet roller to which a plurality of ferrite blocks 24 constituting magnetic poles other than the main pole are attached is provided in the sleeve 22 to form the developing roller 21. In this case, the advantage is that the magnetic pole position accuracy is high, and the disadvantage is that the cost of the component for attaching the magnet block is high, and the man-hours are large and the manufacturing cost is high.

In the method of manufacturing the developing roller shown in FIG. 10, a magnet roller having a plurality of magnets (ferrite blocks) 63 forming a pumping pole, a transporting pole, a developing pole and the like attached to a core metal is arranged inside the sleeve 62. Install the developing roller 61
It is what When this is applied to the proposed developing roller, as shown in FIG. 11, a ferrite block 33a in which three rare earth magnet blocks 48 forming a developing pole are attached to a core metal 35 and a plurality of magnetic poles other than the main pole are formed. A magnet roller to which a ferrite block 33 is attached is arranged in the sleeve 32 to form the developing roller 31. In this case, the merit is almost the same as in the case of FIG.
The cost of the core metal is lower than that of the manufacturing method described above. However, it is difficult to secure the accuracy of the magnetic pole position as a whole, and the main pole has a complicated shape.

In the method of manufacturing the developing roller shown in FIG. 12, a developing roller 71 is provided by disposing a magnet roller composed of a core metal 75 and a magnet roll 73 inside a sleeve 72. It has an integrated shape with
There are methods by injection molding and extrusion molding. When applied to the proposed developing roller, as shown in FIG. 13, a magnet roller having three rare earth magnet blocks 48 attached to a portion corresponding to the developing pole of a magnet roll 83, which is a ferrite magnet molded product, is disposed in the sleeve 82. The developing roller 81 is installed. Reference numeral 85 is a cored bar. As a merit of injection molding, high magnetic force is easily obtained and relatively stable characteristics such as magnetic pole position are obtained, but the equipment is complicated and processing tact takes. Further, while the processing tact is short as an advantage of extrusion molding, it is difficult to control the characteristics of the molded product as a disadvantage.

Such a conventional developing roller manufacturing method is
When applied to the developing roller of the developing device previously proposed by the applicant of the present application, in the developing roller of the developing device according to the proposal as described above, the gap between the main pole portions is narrow and the magnet material needs to have high magnetic characteristics. The accuracy of the main pole is required to be higher than that of the conventional developing roller.
It is difficult to manufacture the developing roller, and the manufacturing cost is high.

Further, when the conventional developing roller manufacturing method is applied to the developing roller of the developing device previously proposed by the applicant of the present invention in the continuous production process, the magnet block is positioned and fixed by the chuck shown in FIG. , The magnet block was adhered to a predetermined position (groove portion), but when the magnet block is attached to the groove portion,
Since the magnet block moves while rubbing the surface of the chuck claw, dust on the magnet block is generated at the claw portion. When positioning and fixing the next magnet block, there is a problem that scraps generated on the claw part are present in the positioning reference (on one side of the claw), causing positioning failure, and if they are bonded in that state, poor quality occurs. It was

An object of the present invention is to suppress as much as possible the generation of dust that would be generated in the positioning and fixing chuck portion of the magnet block in the conventional manufacturing method.

[0012]

In order to solve the above-mentioned problems, according to the present invention, there is provided a developing roller having a magnet roller arranged inside a non-magnetic sleeve, said magnet roller forming a developing pole. In the developing roller holding two magnet blocks, the magnet block forming the developing pole extends in parallel to the developing roller axial direction, and the magnet block cross-sectional shape of a plane perpendicular to the axial direction faces the outside of the magnetic roller. It is configured to have a tapered portion.

In manufacturing such a developing roller, in order to hold the magnet block, an embedding groove is formed in the magnet roller in the axial direction of the developing roller, and a magnet block to be embedded in the groove is formed.
The magnet block is formed in a predetermined shape with respect to the groove for embedding by using a gripping means having a cross-section having a taper portion tapering outwardly of the magnet roller and having chuck claws having a portion corresponding to the magnet block taper portion. It is preferable that the magnet block is brought to the position and pressed until the magnet block is sufficiently fixed to the embedding groove.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. First, an image forming unit of an image forming apparatus equipped with a developing device according to the present invention will be described with reference to FIG. Although this image forming apparatus is of a monochrome type, it can of course be applied to a color type.

In FIG. 1, around a photosensitive drum 1 which is an electrostatic latent image carrier, a charging device 2 for charging the surface of the drum, and a laser beam for forming a latent image on a uniformly charged surface. Exposure 3, and a developing device 4 that forms a toner image by attaching charged toner to the latent image on the drum surface,
A transfer device 5 for transferring the formed toner image on the drum to the recording paper, a cleaning device 7 for removing the residual toner on the drum, and a discharge lamp 8 for removing the residual potential on the drum are arranged in order. It is set up.

In such a structure, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2 is
An electrostatic latent image is formed by the exposure 3 and a toner image is formed by the developing device 4. The toner image is transferred from the surface of the photoconductor drum 1 to the recording paper conveyed from a paper feed tray (not shown) by the transfer device 5 including a transfer belt. The recording paper electrostatically attached to the photosensitive drum during this transfer is separated from the photosensitive drum 1 by the separating claw. Then, the toner image on the unfixed recording paper is fixed on the recording paper by the fixing device 9. On the other hand, the toner remaining on the photosensitive drum without being transferred is removed and collected by the cleaning device 7. The photoconductor drum 1 from which the residual toner has been removed is initialized by the static elimination lamp 8 and is used in the next image forming process. Reference numeral 6 is a registration roller for sending the recording paper from a paper feed tray (not shown) in time with the toner image on the photoconductor 1.

A developing roller 41, which is a developer carrier, is arranged in the developing device 4 so as to be close to the photosensitive drum 1, and the photosensitive drum and the magnetic brush are in contact with each other at their opposing portions. A development area is formed.

As shown in FIG. 2, the developing roller 41 includes a developing sleeve 45 formed by cylindrically forming a non-magnetic material such as aluminum, brass, stainless steel, and conductive resin by a rotation driving mechanism (not shown). It is designed to rotate clockwise. Around the developing roller 41, at the upstream side of the developing region in the developer conveying direction (clockwise direction in FIG. 1), the height of the chain of the developer chain, that is, the developer on the developing sleeve. A doctor blade 42 that regulates the amount is installed. The doctor gap, which is the distance between the doctor blade 42 and the developing sleeve 45, is 0.4.
It is set to mm. Further, a screw 44 for pumping up the developer in the developing device casing to the developing roller 41 while agitating the developer is installed in a region of the developing roller opposite to the photosensitive drum. Reference numeral 43 is an inlet seal member.

In the developing sleeve 45 of the developing roller 4,
As clearly shown in FIG. 2, a magnet roller that forms a magnetic field so as to cause the developer to rise is provided on the peripheral surface of the developing sleeve 45 in a fixed state. The magnet roller of the present embodiment is configured such that a non-magnetic block holder 49 is provided in a portion corresponding to the developing pole portion of a substantially cylindrical magnet 47, and the magnet block 48 is joined to the block holder 49. The carrier of the developer causes chain-like spikes on the developing sleeve 45 so as to follow the magnetic force lines in the normal direction emitted from the magnet body, and the charged toner is attached to the chain-like spike-like carriers. , A magnetic brush is constructed. The magnetic brush is transferred in the same direction as the developing sleeve 45 (clockwise in the figure) by the rotation of the developing sleeve 45.

A magnet body composed of a substantially cylindrical magnet 47 and a magnet block 48 has a plurality of magnetic poles.
As shown in FIG. 2, a developing pole that causes the developer to rise in the developing region by the three magnet blocks 48 (the middle magnet block is the original main magnetic pole, and both ends assist magnetic force formation of the main magnetic pole). Auxiliary magnetic pole)
A pumping pole for pumping up the developer onto the developing sleeve 45 (N pole spreading diagonally downward to the left of the sleeve 45 in FIG. 2), and a transporting pole (magnet for transporting the pumped up developer to the developing area). The upstream side of the main developing magnetic pole by the block 48: an S pole which spreads to the left side of the figure) and the magnetic pole which conveys the developer in the area after development (the upstream side of the main developing magnetic pole by the magnet block 48: the S pole on the right side of the figure). Is. In the present embodiment, the developing pole is formed by three (3 poles) magnet blocks 48, but the developing pole may be formed by a single magnet block 48 or two (2 poles) magnet blocks. In FIG. 2, the magnetic force distribution in the roller radial direction (normal direction) and its magnitude in the developing roller 1 are shown by broken lines.

The developing device 4 of the present embodiment is constructed such that the attenuation rate of the magnetic flux density in the normal direction of the developing main pole is 40% or more, or the half width of the developing main pole is 22 degrees or less. There is. By setting the attenuation rate of the magnetic flux density in the normal direction of the main magnetic pole that causes the spikes in the developing region to 40% or more, preferably 50% or more, the attenuation rate of the magnetic pole becomes large, and the magnetic brush is increased between rising and falling of the magnetic brush. The spike width becomes smaller. As a result, the magnetic brush stands up short and densely.
Such a short and dense rising magnetic brush brings about uniform rising and falling when considered in the sleeve longitudinal direction (roller axis direction). Further, it has been found that the attenuation rate increases by narrowing the half width of the magnetic pole. The full width at half maximum is 22 degrees or less, preferably 18 degrees or less. The half-value width is half the maximum normal magnetic force (vertex) of the magnetic force distribution curve in the normal direction (for example, when the maximum normal magnetic force of the magnet made of the N pole is 120 mT (millitesla), half value) 50% is 60 mT and half value is 80%.
There is also the expression, and in this case it is 96 mT).

The substantially cylindrical magnet 47 is a portion for forming magnetic characteristics other than the developing pole, and is manufactured by injection molding or extrusion molding. As a material, a plastic magnet or a rubber magnet in which a polymer compound is mixed with magnetic powder is often used. Sr ferrite or Ba ferrite is used as the magnetic powder, PA (polyamide) -based material such as 6PA or 12PA, EEA (ethylene-ethyl copolymer) as the polymer compound
Alternatively, an ethylene compound such as EVA (ethylene-vinyl copolymer), a chlorine material such as CPE (chlorinated polyethylene), or a rubber material such as NBR can be used. Of course, a ferrite magnet block may be attached to the polymer compound roller so as to be arranged at each magnetic pole portion.

On the other hand, the magnet block 48 forming the developing pole is a rod-shaped block extending in the axial direction of the developing roller, and its cross-section has a flat bottom and an upper half which coincide with the block holder groove as shown in FIG. Has a tapered side and has a modified hexagonal cross section in the illustrated example. As described above, when the attenuation rate of the magnetic flux density in the normal direction of the developing main magnetic pole is 40% or more or the half width of the developing main magnetic pole is 22 degrees or less, for example, a developing roller having a diameter of 16 to 20 mm has a sleeve surface. The magnetic flux density of 80 to 90 mT is required, and the shape of the rare earth magnet block 48 of the main pole portion needs to be set to a width of about 2 mm and a height of about 3 mm. In this case, in order to obtain high magnetic characteristics, the material characteristic of the magnet block 48 is Br>
0.5T (terrace), holding power iHc <1200kA / m
Is desirable. Most are Ne-based (Ne / Fe / B)
Etc.) or Sm-based (Sm.Co, Sm.Fe.N, etc.) rare earth magnets or a plastic magnet or rubber magnet in which these magnet powders are mixed with a polymer compound similar to the above.

Further, by using the highly accurate non-magnetic holder 49 only in the portions where the magnet blocks of two or more poles having mutually different polarities are embedded, the developing roller with the highly precise position of the developing pole can be manufactured at a low cost with a small number of steps. Therefore, it is possible to realize a developing roller having the characteristics required for uniform rising and uniform falling of the magnetic brush in the longitudinal direction (roller axis direction) of the developing sleeve with a simple configuration.

In the present invention, a highly accurate magnetic pole arrangement is required for the developing pole, and the rare earth magnet block 48 of the main pole portion having high magnetic characteristics is joined to the highly accurately processed holder 49 made of a non-magnetic material. As a result, it is possible to improve the accuracy of the magnetic pole position, and it is possible to provide a developing roller having the characteristics necessary for obtaining a high-quality image over the entire density range at a low cost and with a simple structure. The material of the rare earth magnet holder 49 needs to be a non-magnetic material, and may be metal or resin.

The developing roller according to the present invention can be roughly classified into the following two methods. : Cylindrical magnet is molded, (core bar is inserted), magnetized, and integrated magnet roll 47 is manufactured.
A method of attaching a holder 49, to which a magnetized rare earth magnet block 48 is joined, to a magnet roll 47. : A method of integrally molding the holder 49 when molding (injection molding or extrusion molding) a cylindrical magnet, then magnetizing the substantially cylindrical magnet roll 47, and attaching the rare earth magnet block 48 to the holder 49. .

As a method of manufacturing the substantially cylindrical magnet roll 47, as described above, it is general to mold the material using ferrite magnetic powder by extrusion molding or injection molding. In the case of the developing roller used in the developing device of the present embodiment, since the main pole portion having the highest magnetic flux density is embedded with the magnet block 48, magnetic characteristics other than the main pole can be obtained only by magnetizing without magnetic field orientation. You can From these facts, the substantially cylindrical magnet roll 47 is isotropically formed and the magnet block 48 is formed in the groove portion.
With the holder structure in which the groove is embedded, the groove portion is not deformed, and the developing roller having the characteristics necessary for obtaining a high-quality image over the entire density range can be easily obtained with high accuracy.

In the case of the developing device of this embodiment, the accuracy of the main pole angle is higher than before. Since the main pole angle is determined by the positional accuracy of the reference surface of the cored bar 46 and the embedding groove of the holder 49, the following method is preferable as the manufacturing process of the developing roller.

In the case of magnetic field molding, i): the reference surface 4 of the groove for embedding the holder when the core metal is inserted.
The core metal reference surface 46a is inserted at a predetermined angle with respect to 7a, and the holder 49 to which the rare earth magnet block 48 is attached is attached (FIG. 4). ii): The bottom surface of the holder attaching groove 47c has an R shape (arc shape) and is manufactured with a dimension having a margin with respect to the width of the holder 49a, and a roller is used when the holder 49a having an R shape bottom surface is attached. The core metal reference surface 46a is detected, the magnetic characteristic of the rare earth magnet block 48 is detected with respect to the core metal reference surface, and the holder 49a is joined (FIG. 5). iii): Cylindrical magnet roll 47 when inserting the core metal
The core metal reference surface is inserted into the holder-embedding groove on the side so as to form a predetermined angle, and the holder 49b to which the rare earth magnet block 48 is attached is joined to the holder-embedding groove. At this time, the holder 49b has a fan-shaped cross-sectional shape, and the reference surface of the groove for embedding the holder is made to correspond to a plane other than the circular arc surface of the fan-shaped holder, and the positioning is realized with a simple shape to perform the joining (FIG. 6). If the central angle of the fan-shaped holder is larger than the angle formed by the groove for embedding the holder, the shape of each member does not require extremely high precision,
The position accuracy of the main pole can be reliably achieved.

In these manufacturing steps, by increasing the surface roughness of the mounting surface of the holder, it is possible to increase the adhesion between the surface and the adhesive or the like at the time of bonding. Furthermore,
In the case of not forming a magnetic field, by magnetizing the other pole in accordance with the main pole position (or groove portion) by the following method, it is possible to obtain a developing roller with a very high total magnetic pole position. That is,
iv): In the above i) to iii), the magnets other than the main pole are magnetized based on the core metal, and the holders 49 (49a, 49b) to which the rare earth magnet block 48 is adhered are attached.

In the case of i) above, the manufacturing apparatus can be simplified because it is a method of detecting the mechanical position of the rare earth magnet block 48 with respect to the reference surface of the core metal and joining it. In addition, since the magnetic position is detected in ii), the accuracy is higher than in i). In iii), there is an effect that positioning can be performed at the same time as joining, the number of steps can be reduced, and high positional accuracy can be manufactured at low cost without using a device for positioning (eg, magnetic detector). In iv), not only the main pole but also the other poles can be manufactured with extremely high positional accuracy.

There are various conceivable methods for joining the magnet block 48 and the holder 49, and for joining the holder 49 and the substantially cylindrical magnet 47, and ultrasonic vibration may be applied depending on the method of adhering with an adhesive or the material used. There is a welding method used. Since the joining of the holder 49 and the substantially cylindrical magnet 47 has already been described, the joining of the magnet block 48 and the holder 49 will be described below.

In a preferred example of using an adhesive, the holder 49 is made of a transparent material and an ultraviolet curable adhesive is used as the adhesive. The magnet block mounting groove of the holder is processed with high accuracy in the axial straightness so that no waviness occurs in the axial direction of the block. The device for joining was built in the holding unit for holding the magnet block 48 and setting it in the holder, the straightening unit for straightening the undulations of the magnet block, the coating unit for coating the ultraviolet curable adhesive, and the coating unit. It is composed of an ultraviolet irradiation unit. The chuck portion for gripping the magnet block in the gripping unit and the undulation correction unit are preferably made of a non-magnetic material so that the magnet block can be easily attached and detached. Since the configuration of each of these units is known, a description of each of these units will be omitted.

In this known joining apparatus, the magnet block is pressed against the undulation correcting unit to correct the undulation in the axial direction of the magnet block, and as shown in FIG.
8 is gripped by the chuck 11 of the gripping unit, while an ultraviolet ray curable adhesive is applied to the groove portion of the holder 49 for adhering the magnet block 48 using an application unit, and then the magnet block 48 is held by the pressing plate 12 in the holder. Set it to the bonding position of 49. At that time, the gripping unit keeps the magnet block chucked. The chuck 11 includes a claw portion that comes into contact with the tapered surface of the magnet block 48, and a magnetic plate that holds the magnet block. In FIG. 7, the holder 49 is shown in a cylindrical shape for the sake of convenience, but as shown in FIG. 2 etc., it has a substantially fan shape. The magnet block 48 is pressed against the groove block adhesion surface of the holder 48 by the pressing plate 12. At that time, the taper surface of the magnet block does not rub against the chuck claw portion. While pressing the magnet block 48 against the holder groove, the holder is irradiated with ultraviolet rays to cure the adhesive,
Join the magnet block to the holder. After joining, the pressing plate 12 is returned, and the work of adhering the magnet block is completed. Holder 49 for all magnet blocks 48
The above steps are repeated so as to bond to.

[0035]

According to the developing roller of the present invention, the magnet block forming the developing pole extends parallel to the axial direction of the developing roller, and the magnet block has a cross-sectional shape perpendicular to the axial direction. The roller has a taper portion that tapers outward, and when manufacturing such a developing roller, an embedding groove is formed in the magnet roller in the axial direction of the developing roller in order to hold the magnet block. A holding means having a chuck claw having a portion corresponding to the magnet block taper portion is formed by forming a magnet block to be embedded in the groove so that a cross section thereof has a taper portion that tapers outwardly of the magnet roller. The magnet block to a predetermined position with respect to the embedding groove, and the magnet block is firmly fixed to the embedding groove. In so adapted to the pressing,
It is possible to manufacture the developing roller with higher accuracy than before and avoiding block residue generated during processing, and it is possible to improve quality and productivity.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus in which a developing device according to the present invention is mounted.

FIG. 2 is a diagram showing the magnetic force distribution and the magnitude of magnetic force of the developing roller of the developing device according to the present invention.

FIG. 3 is a partial cross-sectional view showing another example of a magnet block of the developing roller.

FIG. 4 is an explanatory view showing an example of a developing roller manufacturing method according to the present invention.

FIG. 5 is an explanatory view showing another example of the developing roller manufacturing method according to the present invention.

FIG. 6 is an explanatory view showing still another example of the developing roller manufacturing method according to the present invention.

[Figure 7]

FIG. 8 is an explanatory view showing an example of a conventional developing roller manufacturing method.

FIG. 9 is a sectional view illustrating a developing roller to which a conventional developing roller manufacturing method is applied and a manufacturing method thereof.

FIG. 10 is an explanatory diagram showing another example of a conventional developing roller manufacturing method.

FIG. 11 is a sectional view illustrating another example of the developing roller to which the conventional developing roller manufacturing method is applied and the manufacturing method thereof.

FIG. 12 is an explanatory diagram showing still another example of a conventional developing roller manufacturing method.

FIG. 13 is a cross-sectional view illustrating still another example of the developing roller to which the conventional developing roller manufacturing method is applied and the manufacturing method thereof.

FIG. 14 is a conceptual diagram illustrating the operation of a conventional chuck for bonding a magnet block.

[Explanation of symbols]

41 developing roller 45 Development sleeve (developer carrier) 46 core 47 Cylindrical magnet 48 magnet block 49 holder

Claims (4)

[Claims] 1. A developing roller in which a magnet roller is arranged inside a non-magnetic sleeve, wherein the magnet roller holds at least one magnet block forming a developing pole, wherein the magnet forming the developing pole is a magnet. A developing roller, wherein the block extends parallel to the axial direction of the developing roller, and the magnet block cross-sectional shape of a surface perpendicular to the axial direction has a taper portion that tapers outward of the magnet roller. 2. A developing device comprising the developing roller according to claim 1. 3. An image forming apparatus comprising the developing roller according to claim 1. 4. A developing roller in which a magnet roller is disposed inside a non-magnetic sleeve, wherein the magnet roller holds at least one magnet block forming a developing pole. In order to hold the magnet block, an embedding groove is formed in the magnet roller in the axial direction of the developing roller, and the magnet block to be embedded in the groove has a taper portion whose cross section tapers outwardly of the magnet roller. As described above, the magnet block is brought to a predetermined position with respect to the embedding groove by using the gripping means having the chuck claw having the portion corresponding to the magnet block taper portion, and the magnet block is sufficiently fixed to the embedding groove. A method for manufacturing a developing roller, wherein the developing roller is pressed down.