Development device and image formation apparatus

1. A development device comprising:

a developer carrier configured to develop an electrostatic latent image with a developer while rotating, the electrostatic latent image being carried on a surface of a rotating electrostatic latent image carrier; and

first and second developer supply members configured to, while rotating in the same rotation direction, supply the developer carrier with the developer contained in a developer container, wherein

the first developer supply member and the second developer supply member are disposed at positions opposed to the developer carrier, and in contact with the developer carrier,

the first developer supply member is disposed downstream of the second developer supply member in a rotational direction of the developer carrier, and

a first contact amount at which the first developer supply member is in contact with the developer carrier is set smaller than a second contact amount at which the second developer supply member is in contact with the developer carrier, wherein the first contact amount is not less than 30 percent but not greater than 40 percent of a sum total of the first contact amount and the second contact amount.

2. The development device according to claim 1 , wherein

the second contact amount is not less than 60 percent but not greater than 70 percent of the sum total of the first contact amount and the second contact amount.

3. The development device according to claim 2 , wherein both the first contact amount and the second contact amount are in a range of 0.1 mm to 2.00 mm.

4. The development device according to claim 2 , wherein the first contact amount and the second contact amount are in a range of 0.2 mm to 1.00 mm.

5. An image formation apparatus comprising:

an electrostatic latent image carrier configured to carry an electrostatic latent image on its surface while rotating; and

the development device according to claim 1 , configured to develop the electrostatic latent image on the electrostatic latent image carrier.

6. The development device according to claim 1 , wherein

each of the first and second developer supply members has axial end portions and an axial middle portions between the axial end portions, wherein the diameters of axial end portions are less than that of the axial middle portion.

7. The development device according to claim 1 , wherein

each of the first and second developer supply members has axial end portions and an axial middle portion between the axial and portions, wherein the diameters of axial end portions are greater than that of the axial middle portion.

8. The development device according to claim 1 , wherein

a ratio of a circumferential speed of the first developer supply member to that of the developer carrier is less than a ratio of a circumferential speed of the second developer supply member to that of the developer carrier.

9. The development device according to claim 1 , wherein

a ratio of a circumferential speed of the first developer supply member to that of the electrostatic latent image carrier is less than a ratio of a circumferential speed of the second developer supply member to that to that of the electrostatic latent carrier.

10. A development device comprising:

a developer carrier configured to develop an electrostatic latent image with a developer while rotating, the electrostatic latent image being carried on a surface of a rotating electrostatic latent image carrier; and

first and second developer supply members configured to, while rotating, supply the developer carrier with the developer contained in s developer container, wherein

the first developer supply member and the second developer supply member are disposed at positions opposed to the developer carrier, and in contact with the developer carrier,

the first developer supply member is disposed downstream of the second developer supply member in a rotational direction of the developer carrier, and

a first contact amount at which the first developer supply member is in contact with the developer carrier is set smaller that a second contact amount at which the second developer supply member is in contact with the developer carrier, wherein, letting N 2 denote the second contact amount and defining a target life of the development device as continuing until the electrostatic latent image carrier completes M rotations, the second contact amount N 2 satisfies the following expression (A):

N 2 ≧M× 5×(10 −6 )+0.1 [mm]  (A).

11. The development device according to claim 10 , wherein

the first contact amount is not less than 30 percent but not greater than 40 percent of a sum total of the first contact amount and the second contact amount, and

the second contact amount is not less than 60 percent but not greater than 70 percent of the sum total of the first contact amount and the second contact amount.

12. The development device according to claim 11 , wherein both the first contact amount and the second contact amount are in a range of 0.1 mm to 2.00 mm.

13. The development device according to claim 11 , wherein the first contact amount and the second contact amount are in a range of 0.2 mm to 1.00 mm.

14. An image formation apparatus comprising:

an electrostatic latent image carrier configured to carry an electrostatic latent image on its surface while rotating; and

the development according to claim 10 , configured to develop the electrostatic latent image on the electrostatic latent image carrier.