Developing device, image supporter unit, and image formation apparatus

1. A developing device comprising:

a developer supporter that includes:

a magnet member that has a plurality of magnetic poles; and

a cylinder member that is placed on the outer periphery of the magnet member, and that rotates pre se, the developer supporter supporting a developer on a surface of the cylinder member; and

a thickness regulation member that has a cylindrical shape, that is made of a magnetic material, that is placed facing the surface of the cylinder member with a predetermined spacing, and that regulates the thickness of the developer deposited on the surface of the cylinder member,

wherein,

of the plurality of the magnetic poles, a magnetic pole, which is placed at a position nearest to the thickness regulation member downstream in a rotation direction of the cylinder member from the thickness regulation member, has a maximum position of a normal magnetic flux density distribution, and

the maximum position of the normal magnetic flux density distribution is placed outside the area of angle α downstream in the rotation direction of the cylinder member from the thickness regulation member, and

wherein

the diameter of the cylinder member is D, the projection width is W in a case where the thickness regulation member is projected onto the surface of the cylinder member, and the angle α is 180×W/(D×π).

2. The developing device as claimed in claim 1 ,

wherein

the maximum position of a normal magnetic flux density distribution of the upstream magnetic pole is placed upstream in the rotation direction of the cylinder member from the thickness regulation member, and

the maximum position of the normal magnetic flux density distribution of the magnetic pole, which is placed downstream in the rotation direction of the cylinder member from the thickness regulation member, is placed outside the area of the angle α×2 downstream in the rotation direction of the cylinder member from the thickness regulation member.

3. The developing device as claimed in claim 1 , further comprising:

a wall member that is placed in the surrounding of the thickness regulation member,

wherein

a part of the wall member is brought close to the surface of the cylinder member within the projection width downstream in the rotation direction of the cylinder member from the thickness regulation member.

4. The developing device as claimed in claim 1 ,

wherein

the thickness regulation member is supported in an unrotatable state.

5. The developing device as claimed in claim 4 , further comprising:

a notch part that is provided by cutting a part of an axial end part of the thickness regulation member; and

an unrotatable contact part that is provided in the wall member of the developing device, that comes in contact with the notch part, and that prevents the thickness regulation member from rotating.

6. An image supporter unit comprising:

an image supporter; and

a developing device as claimed in claim 1 that develops a latent image on a surface of the image supporter into a visible image.

7. An image formation apparatus comprising:

an image supporter;

a developing device as claimed in claim 1 that develops a latent image on a surface of the image supporter into a visible image;

a transfer device that transfers the visible image provided by the developing device to a medium; and

a fixing device that fixes the visible image transferred to the medium.