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

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.

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.