Image forming apparatus, image forming method, and non-transitory computer readable medium with control of potential difference between components

1. An image forming apparatus comprising:

an application unit that applies to a holding unit a voltage that generates a potential difference between the holding unit and a photoconductor member such that a toner image is developed on the photoconductor member, the potential difference causing toner included in a two-component developer, held by the holding unit, to transfer from the holding unit to the photoconductor member;

a controller that controls the application unit, subsequent to an expiration of an image quality assurance period throughout which a predetermined image quality is assured, such that a potential of the holding unit is decreased according to a decrease of a thickness of a photosensitive film, and

a cylindrical member that has an outer circumferential surface covered with the photoconductor member

wherein if a portion of the outer surface of the cylindrical member is expose as a result of the wear of the photoconductor member, causing a potential difference between the exposed portion and the holding unit to be smaller than a predetermined potential difference at which a carrier contained in the two-component developer is transferred to the photoconductor member, the controller controls the application unit such that the potential of the holding unit is decreased, at a ratio of the predetermined potential difference to the potential difference between the exposed portion and the holding unit, in step with the wear of the photoconductor member.

2. The image forming apparatus according to claim 1 , further comprising a charging unit that charges the photoconductor member to generate the potential difference,

wherein the controller further controls the charging unit subsequent to the expiration of the image quality assurance period such that a charged potential provided on the photoconductor member by the charging unit is decreased in step with the wear of the photoconductor member.

3. The image forming apparatus according to claim 2 , wherein the controller controls the application unit and the charging unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit and the charged potential of the photoconductor member are decreased in step with the wear of the photoconductor member while the potential difference is maintained to within a predetermined range.

4. The image forming apparatus according to claim 3 , wherein the controller maintains a rate of decrease of the potential of the holding unit and a rate of decrease of the charged potential of the photoconductor member in concert with each other.

5. The image forming apparatus according to claim 4 , wherein the cylindrical member rotates about the central axis thereof in response to a torque received from a rotational driver,

wherein the controller controls the application unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit is decreased in step with a physical quantity corresponding to a cumulative amount of rotation of the cylindrical member.

6. The image forming apparatus according to claim 3 , wherein the cylindrical member rotates about the central axis thereof in response to a torque received from a rotational driver,

wherein the controller controls the application unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit is decreased in step with a physical quantity corresponding to a cumulative amount of rotation of the cylindrical member.

7. The image forming apparatus according to claim 3 , further comprising a sliding member that slides on the photoconductor member to remove residual toner.

8. The image forming apparatus according to claim 2 , wherein the controller maintains a rate of decrease of the potential of the holding unit and a rate of decrease of the charged potential of the photoconductor member in concert with each other.

9. The image forming apparatus according to claim 8 , wherein the cylindrical member rotates about the central axis thereof in response to a torque received from a rotational driver,

wherein the controller controls the application unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit is decreased in step with a physical quantity corresponding to a cumulative amount of rotation of the cylindrical member.

10. The image forming apparatus according to claim 2 , wherein the cylindrical member rotates about the central axis thereof in response to a torque received from a rotational driver,

wherein the controller controls the application unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit is decreased in step with a physical quantity corresponding to a cumulative amount of rotation of the cylindrical member.

11. The image forming apparatus according to claim 2 , further comprising a sliding member that slides on the photoconductor member to remove residual toner.

12. The image forming apparatus according to claim 2 , wherein the image quality assurance period is a period within which the quality of the photoconductor member is assured.

13. The image forming apparatus according to claim 1 , wherein the cylindrical member rotates about the central axis thereof in response to a torque received from a rotational driver,

wherein the controller controls the application unit subsequent to the expiration of the image quality assurance period such that the potential of the holding unit is decreased in step with a physical quantity corresponding to a cumulative amount of rotation of the cylindrical member.

14. The image forming apparatus according to claim 1 , further comprising a sliding member that slides on the photoconductor member to remove residual toner.

15. The image forming apparatus according to claim 1 , wherein the image quality assurance period is a period within which the quality of the photoconductor member is assured.

16. An image forming method comprising:

applying to a holding unit a voltage that generates a potential difference between the holding unit and a photoconductor member such that a toner image is developed on the photoconductor member, the potential difference causing toner included in a two-component developer, held by the holding unit, to transfer from the holding unit to the photoconductor member; and

controlling the voltage applying, subsequent to an expiration of an image quality assurance period throughout which a predetermined image quality is assured, such that a potential of the holding unit is decreased according to a decrease of a thickness of a photosensitive film,

causing a potential difference between an exposed portion of an outer surface of a cylindrical member, as a result of the wear on the photoconductor member, and the holding unit to be smaller than a predetermined potential difference at which a carrier contained in the two-component developer is transferred to the photoconductor member,

controlling the voltage such that the potential of the holding unit is decreased, at a ratio of the predetermined potential difference to the potential difference between the exposed portion and the holding unit, in step with the wear of the photoconductor member.

17. A non-transitory computer readable medium storing a program causing a computer to execute a process for forming an image, the process comprising:

applying to a holding unit a voltage that generates a potential difference between the holding unit and a photoconductor member such that a toner image is developed on the photoconductor member, the potential difference causing toner included in a two-component developer, held by the holding unit, to transfer from the holding unit to the photoconductor member; and

controlling the voltage applying, subsequent to an expiration of an image quality assurance period throughout which a predetermined image quality is assured, such that a potential of the holding unit is decreased according to a decrease of a thickness of a photosensitive film;

causing a potential difference between an exposed portion of an outer surface of a cylindrical member, as a result of the wear on the photoconductor member, and the holding unit to be smaller than a predetermined potential difference at which a carrier contained in the two-component developer is transferred to the photoconductor member,

controlling the voltage such that the potential of the holding unit is decreased, at a ratio of the predetermined potential difference to the potential difference between the exposed portion and the holding unit, in step with the wear of the photoconductor member.