Optical device, optical member and image forming apparatus with the same

1. An optical device, comprising:

a laser light source for outputting a laser beam;

an optical member including an aspherical lens with an incident surface on which the laser beam is incident and an output surface from which the laser beam is output, and configured to scan the laser beam output from the output surface across a predetermined target; and

a housing for housing the optical member;

wherein:

the optical member further includes a first positioning portion at a side of the incident surface and a second positioning portion at a side of the output surface, the first positioning portion includes a first upper projection and a first lower projection or a first upper recess and a first lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to a main scanning direction in which the laser beam is scanned, the second positioning portion includes a second upper projection and a second lower projection or a second upper recess and a second lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to the main scanning direction;

the housing includes a first engaging portion to be engaged with the first positioning portion and a second engaging portion to be engaged with the second positioning portion, the first engaging portion is formed as a first recess to be engaged with the first lower projection, or a first projection to be engaged with the first lower recess, the second engaging portion is formed as a second recess to be engaged with the second lower projection, or a second projection to be engaged with the second lower recess; and

the first upper projection, the first lower projection, the second upper projection and the second lower projection, or the first upper recess, the first lower recess, the second upper recess and the second lower recess have mutually different shapes.

2. An optical device according to claim 1 , wherein:

the first upper projection and the first lower projection or the first upper recess and the first lower recess have incident surface side widths along the main scanning direction in which the laser beam is scanned and incident surface side lengths along an optical axis direction in which the laser beam passes through the lens;

the second upper projection and the second lower projection or the second upper recess and the second lower recess have output surface side widths along the main scanning direction and output surface side lengths along the optical axis direction;

the incident surface side widths and the output surface side widths differ; and

the incident surface side lengths and the output surface side lengths differ.

3. An optical device according to claim 1 , wherein:

the first upper projection or the first upper recess has a first width along the main scanning direction and a first length along the optical axis direction in which the laser beam passes through the lens;

the first lower projection or the first lower recess has a second width along the main scanning direction and a second length along the optical axis direction;

the second upper projection or the second upper recess has a third width along the main scanning direction and a third length along the optical axis direction;

the second lower projection or the second lower recess has a fourth width along the main scanning direction and a fourth length along the optical axis direction; and

the first to fourth widths and the first to fourth lengths are so specified that the first upper projection, the first lower projection, the second upper projection and the second lower projection or the first upper recess, the first lower recess, the second upper recess and the second lower recess have mutually different shapes.

4. An optical device according to claim 3 , wherein:

the first width and the second width are set to be equal;

the first length is set to be longer than the second and third lengths;

the second length is set to be shorter than the fourth length;

the third and fourth widths are set to be equal to each other and longer than the first and second widths; and

the third length is set to be shorter than the fourth length.

5. An optical device according to claim 3 , wherein:

the first and second lengths are set to be equal;

the first width is set to be longer than the second and third widths;

the second width is set to be shorter than the fourth width;

the third and fourth lengths are set to be equal to each other and longer than the first and second lengths; and

the third width is set to be shorter than the fourth width.

6. An optical device according to claim 1 , wherein:

the first and second positioning portions are integrally molded to the lens.

7. An image forming apparatus, comprising:

a photoconductive drum; and

an optical device for irradiating the circumferential surface of the photoconductive drum with a laser beam, the optical device including:

a laser light source for outputting a laser beam;

an optical member including an aspherical lens with an incident surface on which the laser beam is incident and an output surface from which the laser beam is output, and configured to scan the laser beam output from the output surface across a predetermined target; and

a housing for housing the optical member;

wherein:

the optical member further includes a first positioning portion at a side of the incident surface and a second positioning portion at a side of the output surface, the first positioning portion includes a first upper projection and a first lower projection or a first upper recess and a first lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to a main scanning direction in which the laser beam is scanned, the second positioning portion includes a second upper projection and a second lower projection or a second upper recess and a second lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to the main scanning direction;

the housing includes a first engaging portion to be engaged with the first positioning portion and a second engaging portion to be engaged with the second positioning portion, the first engaging portion is formed as a first recess to be engaged with the first lower projection, or a first projection to be engaged with the first lower recess, the second engaging portion is formed as a second recess to be engaged with the second lower projection, or a second projection to be engaged with the second lower recess; and

the first upper projection, the first lower projection, the second upper projection and the second lower projection, or the first upper recess, the first lower recess, the second upper recess and the second lower recess have mutually different shapes.

8. An image forming apparatus according to claim 7 , wherein:

the first upper projection and the first lower projection or the first upper recess and the first lower recess have incident surface side widths along the main scanning direction in which the laser beam is scanned and incident surface side lengths along an optical axis direction in which the laser beam passes through the lens;

the second upper projection and the second lower projection or the second upper recess and the second lower recess have output surface side widths along the main scanning direction and output surface side lengths along the optical axis direction;

the incident surface side widths and the output surface side widths differ; and

the incident surface side lengths and the output surface side lengths differ.

9. An image forming apparatus according to claim 7 , wherein:

the first upper projection or the first upper recess has a first width along the main scanning direction and a first length along the optical axis direction in which the laser beam passes through the lens;

the first lower projection or the first lower recess has a second width along the main scanning direction and a second length along the optical axis direction;

the second upper projection or the second upper recess has a third width along the main scanning direction and a third length along the optical axis direction;

the second lower projection or the second lower recess has a fourth width along the main scanning direction and a fourth length along the optical axis direction; and

the first to fourth widths and the first to fourth lengths are so specified that the first upper projection, the first lower projection, the second upper projection and the second lower projection or the first upper recess, the first lower recess, the second upper recess and the second lower recess have mutually different shapes.

10. An image forming apparatus according to claim 9 , wherein:

the first width and the second width are set to be equal;

the first length is set to be longer than the second and third lengths;

the second length is set to be shorter than the fourth length;

the third and fourth widths are set to be equal to each other and longer than the first and second widths; and

the third length is set to be shorter than the fourth length.

11. An image forming apparatus according to claim 9 , wherein:

the first and second lengths are set to be equal;

the first width is set to be longer than the second and third widths;

the second width is set to be shorter than the fourth width;

the third and fourth lengths are set to be equal to each other and longer than the first and second lengths; and

the third width is set to be shorter than the fourth width.

12. An image forming apparatus according to claim 7 , wherein:

the first and second positioning portions are integrally molded to the lens.

13. An optical member to be housed in a housing including a first engaging portion and a second engaging portion, comprising:

an optical member body including an aspherical lens with an incident surface on which a laser beam is incident and an output surface from which the laser beam is output, and configured to scan the laser beam output from the output surface across a predetermined target;

a first positioning portion arranged at a side of the incident surface of the optical member body and to be engaged with the first engaging portion of the housing, the first positioning portion including a first upper projection and a first lower projection or a first upper recess and a first lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to a main scanning direction in which the laser beam is scanned; and

a second positioning portion arranged at a side of the output surface of the optical member body, shaped differently from the first positioning portion and to be engaged with the second engaging portion of the housing, the second positioning portion including a second upper projection and a second lower projection or a second upper recess and a second lower recess facing each other with the lens located therebetween in a direction substantially perpendicular to the main scanning direction; wherein

the first engaging portion is formed as a first recess to be engaged with the first lower projection or a first projection to be engaged with the first lower recess;

the second engaging portion is formed as a second recess to be engaged with the second lower projection or a second projection to be engaged with the second lower recess; and

the first upper projection, the first lower projection, the second upper projection and the second lower projection, or the first upper recess, the first lower recess, the second upper recess and the second lower recess have mutually different shapes.

14. An optical member according to claim 13 , wherein:

the first upper projection and the first lower projection or the first upper recess and the first lower recess have incident surface side widths along the main scanning direction in which the laser beam is scanned and incident surface side lengths along an optical axis direction in which the laser beam passes through the lens;

the second upper projection and the first lower projection or the first upper recess and the first lower recess have output surface side widths along the main scanning direction and output surface side lengths along the optical axis direction;

the incident surface side widths and the output surface side widths differ; and

the incident surface side lengths and the output surface side lengths differ.