JPH05127002A - Plastic lens and lens optical system - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent lens deformation and center shift due to stress generated when the temperature rises. [Structure] Protrusions 13 _L are formed on the left and right ends of the elongated lens body 11 at positions corresponding to the center O ₂ in the vertical direction.
13 _R is formed, and the projection 14 is formed on the lower surface of the lens body 11 at a position corresponding to the center O ₁ in the left-right and front-rear direction, and even if a thermal expansion force is generated due to temperature rise, Stress F is applied to each protrusion 13 _L , 13 _R ,
It is configured so as to be dispersed in multiple directions centering on 14 to prevent the center shift and deformation of the lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic lens and a lens optical device used as an imaging element in a laser writing image forming apparatus such as a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art Generally, in a digital copying machine, an optical writing device is constructed as shown in FIG. That is, the laser light modulated and emitted from the laser light source 1 is emitted from the cylinder lens 2
Then, it is made into a parallel light beam having a predetermined beam diameter, and then is deflected by reflection on one surface of the polygon mirror 3 which rotates at a high speed. The deflected laser light is imaged on the charged photoconductor 5 through an imaging lens, for example, an fθ lens 4, and is scanned as the polygon mirror 3 rotates. A mirror 6 for synchronization and a synchronization detection element 7 are provided outside the effective image range.

In such an optical writing device, in recent years, a plastic lens (molded lens) is used as the fθ lens 4 in order to reduce the weight.

The plastic fθ lens 4 is attached and fixed to the main body housing 8 as shown in FIG. 6, for example. That is, the fθ lens 4 with respect to the main body housing 8
Both ends are fixed by the leaf springs 9 or the like in a state where the reference surface 4a of 4 is brought into contact. In addition, at this time,
As shown in the conventional example in Japanese Patent Laid-Open No. 196601, fθ
There is also a lens in which a positioning protrusion is provided at the center of the lower surface of the lens to be fitted into a positioning hole formed on the housing side for positioning.

[0005]

However, although the ambient temperature of the fθ lens 4 can rise in this type of optical writing device, when the temperature rises, the plastic fθ lens 4 undergoes thermal expansion. A force is generated, and an external stress F is generated based on the force. At this time, since both ends of the fθ lens 4 are fixed by the leaf springs 9, stress F may cause the lens to deform, and the lens may be displaced from the left, right, up, and down front and rear centers. This is the same even in the case where the positioning projection is formed at the center of the lower surface of the lens as in the conventional example in the above publication.

[0006]

According to a first aspect of the present invention, projections are formed at the left and right ends of the elongated lens body at the vertical center thereof, and the left and right sides are formed on the lower surface of the lens body. -Protrusions were formed at the center of the front-back direction.

In this case, according to the second aspect of the present invention, the projections at the left and right ends of the lens body are formed in the shape of a round shaft at the tip through the lens shake / rotation preventing structure.

According to a third aspect of the present invention, in such a plastic lens, a lens is formed in which mounting holes are formed in the projections and the lens shake / rotation preventing structure, each of which has a size having a minute gap. The lens optical device is provided with a support.

[0009]

Since the projections located at the centers of the left and right ends and the lower surface of the long lens body are located at the respective centers, the lens body is supported through these projections.
Even if a thermal expansion force is generated due to a temperature rise, the stress can be dispersed in multiple directions centering on each protrusion, the center shift and deformation of the lens can be prevented, and the initial lens characteristics can be maintained. Becomes

At this time, since the lens shake / rotation preventing structure is also provided, a supporting state capable of preventing the rotation and shake of the lens due to the temperature rise is established.

Particularly, on the support side as well, if three-point fitting support is used in which the mounting holes corresponding to the respective projections, including these lens runout / rotation preventing structures, are formed slightly larger, reliable support is provided. The state is obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows the entire lens optical device.
1A is a plan view, FIG. 1B is a front view, and FIGS. 2 to 4 are enlarged views of a part of them. First, the plastic lens 10 of this embodiment is used as an fθ lens or the like in an optical writing device as shown in FIG. 5, for example. The plastic lens 10 is formed, for example, on the basis of an elongated lens body 11 whose front surface is formed into a predetermined curved surface shape and whose upper and lower surfaces are flat and which is long in the left and right directions.

At the left and right ends of the lens body 11 as described above, rectangular lens shake / rotation preventing structures 12 _L and 12 _{R are provided.}
The round shaft-shaped projections 13 _L and 13 _R are integrally formed via the. Here, these protrusions 13 _L and 13 _R are shown in FIG.
It is formed at a position corresponding to the vertical center O ₂ shown in (b). The center of the lower surface of the lens body 11, that is,
A round shaft-shaped projection 14 that projects downward is integrally formed at a position corresponding to the center O ₁ in the left-right and front-rear directions shown in FIG.

On the other hand, as described above, the plastic lens 10
A mounting hole 16 in the shape of a round hole into which the protrusion 14 is fitted is formed in a housing 15 that serves as a support body on the side of the apparatus main body that supports the protrusion 13.
Round hole-shaped mounting hole 17 (only the right side is shown)
Is integrally formed with the rectangular mounting hole 18 corresponding to the lens shake / rotation preventing structure 12. These mounting holes 16, 17 and 18 are formed to be slightly deeper than the projections 14 and 13 and the lens shake / rotation preventing structure 12, that is, have a size capable of having a minute gap in a fitted state.

According to this structure, the centers O ₁ ,
It becomes possible to support three points by the three protrusions 14, 13 _L and 13 _R positioned at O ₂ , and the stress F is F _F , F _B , while maintaining the center point of the lens even during thermal expansion. _FU ,
As shown by F _D , F _L , and F _R , it is possible to escape in multiple directions such as front and back, up and down, and left and right. Therefore, even if the temperature rises, the plastic lens 10 does not deform, and
Since the center point position can be maintained, the lens characteristics such as the refractive index can be maintained in the initial state.

At this time, since the lens body 11 has the lens shake / rotation preventing structure 12 on both left and right sides and is fitted and supported through the slightly larger mounting holes 18, the lens shake and the lens shake are prevented in the supported state. , The rotation of the lens is prevented, and the lens function can be surely exhibited.

Further, the projections 14 and 13 and the mounting holes 16 and 1
Regarding the relationship with 7, since the hole side is slightly larger,
The stress generated as described above can be surely released.

[0018]

As described above, according to the present invention, the protrusions are formed at three positions, that is, the left and right ends and the lower face of the elongated lens body, respectively, at the vertical center and the front, rear, left and right centers. By supporting the lens main body at three points through these protrusions, even if a thermal expansion force is generated due to a temperature rise, the stress can be dispersed in multiple directions centering on each protrusion. The lens center deviation and deformation can be prevented, and the initial lens characteristics can be maintained.

At this time, since the projections at the left and right ends are also provided with a lens shake / rotation preventing structure, it is possible to secure a supporting state capable of preventing the rotation and shake of the lens due to a temperature rise.

In particular, on the support side as well, the mounting holes corresponding to the respective projections, including these lens runout / rotation preventing structures, are formed to be slightly larger so that they can be fitted and supported at three points. In addition, a reliable support state can be obtained.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a plan view and (b) is a front view.

FIG. 2 is a plan view showing a part of the device in an enlarged manner.

FIG. 3 is a front view thereof.

FIG. 4 is a front view showing another part in an enlarged manner.

FIG. 5 is a perspective view showing a general optical writing device.

FIG. 6 shows a conventional example, in which (a) is a plan view and (b) is a front view.

[Explanation of symbols]

10 plastic lens 11 lens body 12 _L , 12 _R lens runout / rotation prevention structure 13 _L , 13 _R projections on both left and right ends 14 projections on the lower surface 15 support 16-18 mounting holes

Claims (3)

[Claims] 1. A projection is formed at the left and right ends of a long lens body at the center in the vertical direction, and a projection is formed on the bottom surface of the lens body at the center in the left, right, front-back direction. A plastic lens that is characterized. 2. The plastic lens according to claim 1, wherein the projections at the left and right ends of the lens body are formed in a round shaft shape at the tip thereof through a lens shake / rotation preventing structure. 3. A projection is formed at the center of the vertical direction of the elongated lens body through lens shake / rotation preventing structures at the left and right ends of the elongated lens body, and the projection is formed on the lower surface of the lens body in the left-right and front-back directions. A plastic lens having protrusions formed at the center of the lens was provided, and a lens support having mounting holes formed with a small gap for each protrusion and lens shake / rotation preventing structure was provided. A lens optical device characterized by the above.