Drum unit and image forming apparatus having drum unit

1. A drum unit comprising:

a photosensitive drum including a hollow cylindrical drum sleeve having a surface on which a latent image is formed and bearing a toner image corresponding to the latent image, a flange press-fitted into an end portion of the drum sleeve and rotatably supporting the drum sleeve, and a supporting portion made of resin, protruding from a lateral face of the flange in an axial direction of the drum sleeve, and serving as a rotating shaft for rotation of the drum sleeve;

a circular tube member made of metal, extending in the axial direction, and having a first inner peripheral surface forming a space, and a first outer peripheral surface that is opposite from the first inner peripheral surface;

a housing rotatably supporting the photosensitive drum; and

a bearing portion fixed to the housing, having a second inner peripheral surface facing the first outer peripheral surface and forming a space,

wherein the supporting portion is press-fitted into the first inner peripheral surface of the circular tube member, and the circular tube member is inserted into the second inner peripheral surface of the bearing portion, and

wherein the flange has a helical gear to which a rotational driving force or reaction force associated with a rotational driving force moving the photosensitive drum toward the outer side in the axial direction is imparted, and wherein the circular tube member has a flange portion protruding from the first outer peripheral surface toward the outer side in a radial direction of the drum sleeve and located between the bearing portion and the lateral face of the flange in the axial direction.

2. The drum unit according to claim 1 , wherein the first inner peripheral surface of the circular tube member decreases in diameter in a direction in which the supporting portion is press-fitted.

3. The drum unit according to claim 1 , wherein the first outer peripheral surface of the circular tube member decreases in diameter in a direction in which the circular tube member is inserted into the bearing portion.

4. The drum unit according to claim 1 , wherein the flange has therein a plurality of ribs extending in the axial direction and exposed on a lateral face, and the flange portion is located so as to face ends of the plurality of ribs exposed on the lateral face.

5. The drum unit according to claim 1 , comprising a charging device substantially uniformly charging the peripheral surface of the photosensitive drum.

6. The drum unit according to claim 1 , wherein the housing has an upstanding wall facing the flange in the axial direction, the bearing portion has a hollow cylindrical shape having a second outer peripheral surface attached to the upstanding wall and having therein the second inner peripheral surface, the supporting portion penetrates the circular tube member, and has a coupling through which a rotational driving force is transmitted to the photosensitive drum, at the distal end in the axial direction of the penetrating supporting portion, and by inserting the circular tube member into the bearing member, the coupling protrudes on the outer side in the axial direction of the second inner peripheral surface of the bearing portion.

7. The drum unit according to claim 6 , wherein the bearing portion has a third inner peripheral surface connected to the outer side in the axial direction of the second inner peripheral surface and facing the coupling in the radial direction, and the third inner peripheral surface has an internal diameter greater than that of the second inner peripheral surface.

8. An image forming apparatus comprising:

a drum unit including:

a photosensitive drum including a hollow cylindrical drum sleeve having a surface on which a latent image is formed and bearing a toner image corresponding to the latent image, a flange press-fitted into an end of the drum sleeve and rotatably supporting the drum sleeve, and a supporting portion made of resin, protruding from a lateral face of the flange in an axial direction of the drum sleeve, and serving as a rotating shaft for rotation of the drum sleeve,

a charging device substantially uniformly charging a peripheral surface of the photosensitive drum,

a circular tube member made of metal, extending in the axial direction, and having a first inner peripheral surface forming a space, and a first outer peripheral surface that is opposite from the first inner peripheral surface,

a housing rotatably supporting the photosensitive drum, and

a bearing portion fixed to the housing, having a second inner peripheral surface facing the first outer peripheral surface and forming a space;

an exposure device that irradiates the peripheral surface of the photosensitive drum charged by the charging device with light and forms the latent image;

a developing device that supplies toner to the peripheral surface of the photosensitive drum on which the electrostatic latent image is formed;

a transfer device that transfers the toner image formed on the peripheral surface of the photosensitive drum; and

a cleaning device that removes toner remaining on the peripheral surface of the photosensitive drum after the transfer,

wherein the supporting portion is press-fitted into the first inner peripheral surface of the circular tube member, and the circular tube member is inserted into the second inner peripheral surface of the bearing portion, and

wherein the flange has a helical gear to which a rotational driving force or reaction force associated with a rotational driving force moving the photosensitive drum toward the outer side in the axial direction is imparted, and wherein the circular tube member has a flange portion protruding from the first outer peripheral surface toward the outer side in a radial direction of the drum sleeve and located between the bearing portion and the lateral face of the flange in the axial direction.

9. The image forming apparatus according to claim 8 , wherein the first inner peripheral surface of the circular tube member decreases in diameter in a direction in which the supporting portion is press-fitted.

10. The image forming apparatus according to claim 8 , wherein the first outer peripheral surface of the circular tube member decreases in diameter in a direction in which the circular tube member is inserted into the bearing portion.

11. The image forming apparatus according to claim 8 , wherein the flange has therein a plurality of ribs extending in the axial direction and exposed on a lateral face, and the flange portion is located so as to face ends of the plurality of ribs exposed on the lateral face.

12. The image forming apparatus according to claim 8 , wherein the housing has an upstanding wall facing the flange in the axial direction, the bearing portion has a hollow cylindrical shape having a second outer peripheral surface attached to the upstanding wall and having therein the second inner peripheral surface, the supporting portion penetrates the circular tube member, and has a coupling through which a rotational driving force is transmitted to the photosensitive drum, at the distal end in the axial direction of the penetrating supporting portion, and by inserting the circular tube member into the bearing member, the coupling protrudes on the outer side in the axial direction of the second inner peripheral surface of the bearing portion.

13. The image forming apparatus according to claim 12 , wherein the bearing portion has a third inner peripheral surface connected to the outer side in the axial direction of the second inner peripheral surface and facing the coupling in the radial direction, and the third inner peripheral surface has an internal diameter greater than that of the second inner peripheral surface.