Charging device and image forming apparatus

1. A charging device comprising:

a first charging unit that charges a target unit, which is to be charged, by coming into contact with the target unit; and

a second charging unit that charges the target unit by coming into contact with the target unit and in which distribution of a contact region in contact with the target unit is different from distribution of a contact region between the target unit and the first charging unit,

wherein the first charging unit and the second charging unit are respectively a first charging roller and a second charging roller each of which rotates while being in contact with the target unit as a result of end portions of each of the first and second charging rollers in a direction in which rotation axes of the first and second charging rollers extend being pressed against the target unit, and

wherein a pressing force applied to the first charging roller and a pressing force applied to the second charging roller are different from each other.

2. The charging device according to claim 1 ,

wherein a diameter of the first charging roller when the first charging roller is not in contact with the target unit and a diameter of the second charging roller when the second charging roller is not in contact with the target unit both have a symmetrical distribution in a direction in which rotation axes of the first and second charging rollers extend, and the distribution of the diameter of the first charging roller and the distribution of the diameter of the second charging roller are different from each other.

3. The charging device according to claim 2 ,

wherein at least one of the first charging roller and the second charging roller is a crowned charging roller that has a relatively large diameter at the center and a relatively small diameter at two ends in a direction in which a rotation axis of the crowned charging roller extends.

4. The charging device according to claim 3 ,

wherein one of the first charging roller and the second charging roller that receives a relatively small pressing force is a crowned charging roller that has a relatively large diameter at the center and a relatively small diameter at two ends in a direction in which a rotation axis of the crowned charging roller extends.

5. The charging device according to claim 4 , further comprising:

a power supply that increases a voltage applied to the crowned charging roller over time.

6. The charging device according to claim 2 ,

wherein one of the first charging roller and the second charging roller that receives a relatively small pressing force is a crowned charging roller that has a relatively large diameter at the center and a relatively small diameter at two ends in a direction in which a rotation axis of the crowned charging roller extends.

7. The charging device according to claim 6 , further comprising:

a power supply that increases a voltage applied to the crowned charging roller over time.

8. The charging device according to claim 1 ,

wherein one of the first charging roller and the second charging roller that receives a relatively small pressing force is a crowned charging roller that has a relatively large diameter at the center and a relatively small diameter at two ends in a direction in which a rotation axis of the crowned charging roller extends.

9. The charging device according to claim 8 , further comprising:

a power supply that increases a voltage applied to the crowned charging roller over time.

10. An image forming apparatus comprising:

the charging device according to claim 1 ; and

an image holding unit that serves as a unit to be charged by the charging device and that is charged by the charging device, the image holding unit being configured to hold an electrostatic latent image formed through light exposure and to hold a toner image formed through development with a toner,

wherein the image forming apparatus forms, onto a sheet, an image derived from the toner image formed on the image holding unit.

11. A charging device comprising:

first charging means for charging a target unit, which is to be charged, by coming into contact with the target unit; and

second charging means for charging the target unit by coming into contact with the target unit and in which distribution of a contact region in contact with the target unit is different from distribution of a contact region between the target unit and the first charging means,

wherein the first charging means and the second charging means are respectively pressed against the target unit, and

wherein a pressing force applied to the first charging means and a pressing force applied to the second charging means are different from each other.

12. The charging device according to claim 11 further comprising:

a power supply that increases a voltage applied to at least one of the first charging means and the second charging means over time.