OPTICAL SCANNING DEVICE AND IMAGE FORMATION APPARATUS

1 . An optical scanning device in which a plurality of optical beams from a light-emitting element are passed through a collimator lens, are thereby collimated, and are then deflected by a deflector, and which scans over an image carrier of an image formation apparatus by using the plurality of deflected optical beams, the optical scanning device comprising:

a device housing; and

a holder supported on a base of the device housing so as to be rotatable about an optical axis of the collimator lens, and penetrating through a through-hole in a side wall of the device housing in a direction along the optical axis without contacting the side wall, wherein

the holder includes a first holder part and a second holder part, the first holder part being located inside the device housing with respect to the side wall, and the second holder part being located outside the device housing with respect to the side wall,

the collimator lens is held by the first holder part, and the light-emitting element is held by the second holder part, and

the optical beams from the light-emitting element pass through the through-hole in the side wall, and reach the collimator lens.

2 . The optical scanning device of claim 1 further comprising:

a cylindrical lens provided between the collimator lens and the deflector on light paths of the optical beams from the light-emitting element to the deflector, and transmitting and condensing the optical beams in a vertical scanning direction, wherein

the cylindrical lens is supported on the device housing via a supporting member other than the holder.

3 . The optical scanning device of claim 1 , wherein

the holder includes:

a first part that is elongated along the optical axis, penetrates through the through-hole in the side wall, and is supported on the base; and

a second part that extends from a portion of the first part, the portion being located outside the device housing with respect to the side wall, and the second part extending away from the base along the side wall, and

the first holder part is provided on another portion of the first part, the other portion being located inside the device housing with respect to the side wall, and the second holder part is provided on the second part.

4 . The optical scanning device of claim 3 further comprising:

a sealing member inserted between, and thereby filling a gap between, the second part and a portion around an opening of the through hole on an outer surface of the side wall.

5 . The optical scanning device of claim 3 further comprising:

a cylindrical wall part provided on an outer surface of the side wall so as to surround an opening of the through-hole; and

a sealing member, wherein

the second part is located inside the cylindrical wall part so as to be covered with the cylindrical wall part, and

the sealing member is inserted between, and thereby fills a gap between, an inner surface of the cylindrical wall part and a surface of the second part, the surface facing the inner surface of the cylindrical wall part.

6 . The optical scanning device of claim 3 , wherein

the second holder part is supported on the second part such that the light-emitting element is movable in a direction perpendicular to the optical axis.

7 . The optical scanning device of claim 1 , wherein

the holder is supported at two points on the base of the device housing.

8 . The optical scanning device of claim 7 , wherein

a side of the holder facing the base is provided with a bottom part having an arc-shaped cross-section in a plane perpendicular to the optical axis,

a side of the base facing the holder is provided with a groove having a V-shaped cross-section and extending in the direction along the optical axis, and

the bottom part of the holder fits into the groove in order to support the holder at two points on the base.

9 . The optical scanning device of claim 1 further comprising:

a restricting member restricting the holder from moving in the direction along the optical axis with reference to the base.

10 . The optical scanning device of claim 9 , wherein

the restricting member is composed of a pin and an opening that is a slot or a notch, the pin being provided on one of the holder and the base, and the opening being provided in the other one of the holder and the base,

the opening extends in a direction perpendicular to the optical axis, and

sizes of the pin and the opening are defined such that when the pin fits into the opening, the holder is restricted from moving in the direction along the optical axis and is rotatable about the optical axis.

11 . The optical scanning device of claim 1 further comprising:

a lens barrel configured to hold the collimator lens, wherein

the collimator lens is supported by the holder via the lens barrel so as to be movable along the optical axis direction.

12 . The optical scanning device of claim 11 , wherein

a portion of the holder that supports the lens barrel is provided with a groove having a V-shaped cross-section in a plane perpendicular to the optical axis and extending in the direction along the optical axis, and

the lens barrel fits into the groove and is supported at two points in the groove.

13 . The optical scanning device of claim 1 further comprising:

a driver board provided outside the device housing, and providing power to the light-emitting element and controlling light emission timing and a light amount of the light-emitting element; and

one or more supporting members attached to the base of the device housing, and supporting the driver board and thereby fixing the driver board to the device housing.

14 . An image formation apparatus having the optical scanning device defined in claim 1 .