Electrostatic charging apparatus, and image forming assembly and image forming apparatus which employ the same

1. An electrostatic charging apparatus, comprising:

an endless-shaped electrostatic charging belt having electrical conductivity, the electrostatic charging belt being arranged in a state of having a predetermined contact zone being in contact with a moving to-be-charged body and moving in the same direction as a moving direction of the to-be-charged body;

a plurality of electrode members including at least a first electrode member and a second electrode member, the plurality of electrode members being provided inside the electrostatic charging belt, and the first and second electrode members being provided on both sides of the contact zone of the electrostatic charging belt in the moving direction thereof so as to press the electrostatic charging belt against the to-be-charged body and forming gaps that permit electric discharge between the to-be-charged body and an outer surface of the electrostatic charging belt, the gaps being adjacent to the respective sides of the contact zone of the electrostatic charging belt; and

a bias application unit that applies mutually different electrostatic charging biases to the respective plurality of electrode members such that an AC component of a first electrostatic charging bias applied on the first electrode member is smaller than an AC component of a second electrostatic charging bias applied on the second electrode member, the second electrode member being located downstream of the first electrode member in the moving direction of the to-be-charged body, and

wherein the bias application unit supplies the AC components to both of the first electrode member and the second electrode respectively.

2. The electrostatic charging apparatus according to claim 1 ,

wherein the bias application unit applies the first electrostatic charging bias to the first electrode member, an AC component of the first electrostatic charging bias being equal to or below an inclination change point of a surface potential of the to-be-charged body for the AC component.

3. The electrostatic charging apparatus according to claim 1 ,

wherein the bias application unit applies the second electrostatic charging bias to the second electrode member, an AC component of the second electrostatic charging bias exceeding an inclination change point of a surface potential of the to-be-charged body for the AC component and falling within a range where uniform electric discharge can be performed between the second electrode member and the to-be-charged body.

4. The electrostatic charging apparatus according to claim 1 ,

wherein the first and second electrode members are rotatable roll-shaped members about which the electrostatic charging belt is entrained.

5. The electrostatic charging apparatus according to claim 1 ,

wherein the bias application unit has an operating environment determination section that determines an operating environment and changes the electrostatic charging biases applied to the individual electrode members on the basis of a determination result from the operating environment determination section.

6. The electrostatic charging apparatus according to claim 1 , further comprising:

a press member that presses the plurality of electrode members toward the to-be-charged body so as to form the contact zone and the gaps comprising a pre-nip gap and a post-nip gap adjacent to the respective sides of the contact zone in the moving direction of the to-be-charged body,

wherein the press member presses the plurality of electrode members so that the post-nip gap does not substantially fluctuate.

7. An image forming assembly, comprising:

a photosensitive body serving as a to-be-charged body; and

an electrostatic charging apparatus according to claim 1 located to face the photosensitive body,

wherein the image forming assembly is detachably attached to an image forming apparatus body.

8. An image forming apparatus, comprising:

a photosensitive body serving as a to-be-charged body; and

an electrostatic charging apparatus according to claim 1 located to face the photosensitive body.

9. An electrostatic charging apparatus, comprising:

an endless-shaped electrostatic charging belt being arranged in a state of having a predetermined contact zone being in contact with a moving to-be-charged body and moving in the same direction as a moving direction of the to-be-charged body; and

a plurality of electrode members including at least a first electrode member and a second electrode member, the plurality of electrode members being provided inside the electrostatic charging belt,

the first and second electrode members being provided on both end sides of the contact zone of the electrostatic charging belt in the moving direction thereof so as to press the electrostatic charging belt against the to-be-charged body and forming gaps that permit electric discharge between the to-be-charged body and an outer surface of the electrostatic charging belt, the gaps being adjacent to the both end sides; and

a bias application unit that applies mutually different electrostatic charging biases to the respective plurality of electrode members such that an AC component of a first electrostatic charging bias applied on the first electrode member is smaller than an AC component of a second electrostatic charging bias applied on the second electrode member, the second electrode member being located downstream of the first electrode member in the moving direction of the to-be-charged body,

wherein the bias application unit supplies the AC components to both of the first electrode member and the second electrode respectively.