Optical scanner

This application claims priority from Japanese Patent Application No. 2012-011398 filed on Jan. 23, 2012, the disclosure of which is incorporated herein by reference in its entirety.

The present invention relates to an optical scanner in which a scanning lens is fixed to a frame by adhesive.

In a generally known structure, an optical scanner used for a laser printer and the like has a frame to which a plastic scanning lens is fixed by adhesive.

However, since the scanning lens has a coefficient of linear expansion greater than that of the frame, if the scanning lens of the conventional structure undergoes thermal expansion, for example, under high temperature environment, distortion occurs due to difference between a linear expansion of the scanning lens and a linear expansion of the frame. Accordingly, a lens attachment portion where the scanning lens is fixed to the frame is subject to a load, with the result that the scanning lens may disadvantageously come off the frame.

In view of the above, it would be desirable to provide an optical scanner which can prevent the scanning lens from coming off the frame when the optical scanner is used under high temperature environment.

According to an aspect of the present invention, there is provided an optical scanner for scanning a target surface with a light beam in a main scanning direction, which comprises: a light deflector configured to deflect the light beam; a scanning lens made of resin and configured to condense the light beam deflected by the light deflector onto the target surface to form an image thereon; a frame to which the scanning lens is fixed and having a coefficient of linear expansion smaller than that of the scanning lens. In this optical scanner, the scanning lens is fixed to the frame at a first attachment portion and at least one second attachment portion of the scanning lens using adhesives. Further, the first attachment portion is located closer to a center portion of a scanning range in a main scanning direction of the scanning lens than the second attachment portion is, and a first adhesive used for the first attachment portion has an elastic coefficient greater than that of a second adhesive used for the second attachment portion.

To better understand the claimed invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

FIG. 1 is a top view of an optical scanner according to one exemplary embodiment of the present invention;

FIG. 2 is a top view similar to FIG. 1 , but the optical scanner is shown without a scanning lens;

FIG. 3 is a perspective view showing a positioning portion of the scanning lens and frame-side attachment portions of the frame; and

FIG. 4 is an enlarged view showing the scanning lens fixed to the frame by adhesive.

A detailed description will be given of an illustrative embodiment of the present invention with reference to the accompanying drawings. In the following description, a general arrangement of an optical scanner according to one exemplary embodiment of the present invention will be briefly described, and thereafter the structure for mounting a scanning lens to a frame will be described in detail.

As seen in FIG. 1 , an optical scanner 1 includes a light source device 2 , a cylindrical lens 3 , a polygon mirror 4 as an example of a light deflector, a scanning lens 5 , and a frame 6 .

The light source device 2 includes a light source configured to emit a laser beam, a coupling lens (not shown) configured to converge the laser beam from the light source and convert it into a parallel beam of light.

The cylindrical lens 3 is a lens for correcting optical face tangle errors of the polygon mirror 4 and configured to converge the light beam from the light source device 2 in a sub-scanning direction (i.e., direction orthogonal to a main scanning direction) and to direct it onto the polygon mirror 4 .

The polygon mirror 4 is configured to rotate at high speeds and four sides constituting mirror surfaces are formed around the rotating axis. The mirror surfaces of the rotating polygon mirror 4 reflect the light beam having passed through the cylindrical lens 3 , so that the light beam is deflected in the main scanning direction.

In the range of deflection where the polygon mirror 4 deflects the light beam, the range shown by angle R 1 corresponds to the scanning range used for the image formation.

The scanning lens 5 is made of resin (plastic). The scanning lens is configured to convert the laser beam having been swept out by the polygon mirror 4 at a constant angular velocity into a laser beam sweeping at a constant linear velocity, and to condense it onto a target surface to form an image thereon.

The scanning lens 5 has an elongate shape extending in the main scanning direction. Further, the scanning lens 5 has a positioning portion 5 C having a rectangular section and protruding from a light beam exit surface 5 D of the scanning lens 5 .

As seen in FIG. 3 , the positioning portion 5 C is formed on the light beam exit surface 5 D of the scanning lens 5 at an edge closer to the frame 6 , such that the positioning portion 5 C does not interfere with the light beam from the polygon mirror 4 .

The frame 6 is configured to support various optical elements constituting the optical scanner 1 . As seen in FIGS. 2 and 3 , the frame 6 has a first frame-side attachment portion 6 A and a pair of second frame-side attachment portions 6 B for supporting the scanning lens 5 . The first frame-side attachment portion 6 A is provided substantially at a center portion of the scanning range of the light beam deflected by the polygon mirror 4 . The second frame-side attachment portions 6 B are provided at both sides of the first frame-side attachment portion 6 A in the main scanning direction. The first frame-side attachment portion 6 A is located in the middle of the pair of second frame-side attachment portions 6 B.

The frame 6 is made of a material having a coefficient of liner expansion smaller than that of the scanning lens 5 . According to this embodiment, the frame 6 is made of a metal plate.

As seen in FIG. 3 , the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B are formed as planar portions protruding toward the scanning lens 5 . This makes it possible to reduce the size of the planar surfaces of the first and second frame-side attachment portions 6 A, 6 B, with the result that the dimension accuracy of the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B can be readily ensured. It is noted that the frame 6 has rectangular through-holes 6 D extending in the main scanning direction, at both sides of the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B corresponding to the light beam incident side and the light beam exit side of the scanning lens 5 . The stiffness of the frame 6 around the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B is weak because of these through-holes 6 D, and thus formation of the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B can be readily made by drawing process.

The first frame-side attachment portion 6 A has a pair of cut-raised portions 6 C protruding toward the scanning lens 5 . The cut-raised portions 6 C are spaced apart from each other and arranged at positions corresponding to the size of the positioning portion 5 C of the scanning lens 5 in the main scanning direction.

As seen in FIG. 1 , the scanning lens 5 is fixed to the frame 6 at the first frame-side attachment portion 6 A and at the second frame-side attachment portions 6 B by adhesives 7 A, 7 B. To be more specific, a first adhesive 7 A is adhered to the first frame-side attachment portion 6 A, and a portion of the scanning lens 5 which corresponds to the first frame-side attachment portion 6 A and to which the first adhesive 7 A is adhered is referred to as a first attachment portion 5 A. Similarly, a second adhesive 7 B is adhered to the second frame-side attachment portions 6 B, and portions of the scanning lens 5 which correspond to the second frame-side attachment portions 6 B and to which the second adhesive 7 B is adhered are referred to as second attachment portions 5 B. The first attachment portion 5 A is disposed in a center portion of the scanning lens 5 such that it overlaps the positioning portion 5 C in the main scanning direction. The two second attachment portions 5 B are arranged in line in the main scanning direction and symmetrical with respect to the first attachment portion 5 A.

Further, the first adhesive 7 A for fixing the scanning lens 5 at the first attachment portion 5 A has an elastic coefficient greater than that of the second adhesive 7 B for fixing the scanning lens 5 at the second attachment portions 5 B.

Further, as seen in FIG. 4 , the scanning lens 5 and the frame 6 are fixed together such that the second attachment portions 5 B and the second frame-side attachment portions 6 B are spaced apart by a distance D and bonded together by the second adhesive 7 B. Although not shown in the drawings, the scanning lens 5 and the frame 6 are fixed together such that the first attachment portion 5 A and the first frame-side attachment portion 6 A are spaced apart by the distance D and bonded together by the first adhesive 7 A.

When mounting the scanning lens 5 to the frame 6 , the first adhesive 7 A having a higher elastic coefficient is applied on the first frame-side attachment portion 6 A, and the second adhesive 7 B having a smaller elastic coefficient is applied on the second frame-side attachment portions 6 B. For the purpose of rapidly curing the adhesives, it is preferable that the first and second adhesives 7 A, 7 B are ultraviolet curable resins.

Next, positioning of the scanning lens 5 in the main scanning direction is carried out by engaging the positioning portion 5 C of the scanning lens 5 with the pair of cut-raised portions 6 C of the frame 6 . This allows the first attachment portion 5 A to be positioned in the center portion of the scanning range in the main scanning direction of the scanning lens 5 .

Thereafter, adjustment of the scanning lens 5 is carried out. To be more specific, while the light source device 2 emits the light beam, the scanning lens 5 is moved to adjust its position until the light beam passing through the scanning lens 5 and condensed onto a target surface of an inspection device creates an appropriate image point. In this process, the angle of the scanning lens 5 may be adjusted where necessary. Once the angle of the scanning lens 5 is determined, the first and second adhesives 7 A, 7 B are cured by illumination with ultraviolet light.

In this process, since the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B are formed to ensure a sufficient thickness of the first and second adhesives 7 A, 7 B, the scanning lens 5 does not come in contact with the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B during the adjustment of the angle of the scanning lens 5 . This makes it possible to readily adjust the position of the scanning lens 5 .

According to the optical scanner 1 as described above, if the temperature changes in the usage environment (e.g., the temperature increases), the scanning lens 5 undergoes a dimensional change larger than the frame 6 does, because the coefficient of linear expansion of the scanning lens 5 is greater than that of the frame 6 . In this instance, since the first adhesive 7 A used for the first attachment portion 5 A has an elastic coefficient greater than that of the second adhesive 7 B used for the second attachment portions 5 B, the first adhesive 7 A is less deformable than the second adhesive 7 B.

For this reason, the position of the scanning lens 5 in the main scanning direction is determined mainly based on the first attachment portion 5 A to which the first adhesive 7 A is adhered. The second adhesive 7 B deforms to absorb a shift in position, after expansion, between each second attachment portion 5 B of the scanning lens 5 and the corresponding second frame-side attachment portion 6 B of the frame 6 .

It is noted that since the first attachment portion 5 A is located at the center portion of the scanning lens 5 in the main scanning direction, even if the temperature increases, the scanning lens 5 remains accurately positioned in the main scanning direction relative to the frame 6 . Further, since the elastic coefficient of the second adhesive 7 B is small, the second adhesive 7 B deforms under high temperature environment to absorb the difference in the dimensional change between the frame 6 and the scanning lens 5 . This can prevent the scanning lens 5 from coming off the frame 6 . Especially, in this embodiment, since the scanning lens 5 is fixed to the frame 6 such that the second attachment portions 5 B are spaced apart from the second frame-side attachment portion 6 B by the distance D, the thickness of the second adhesive 7 B can be ensured to ease the deformation of the second adhesive 7 B.

Further, since the second attachment portions 5 B are symmetrically arranged with respect to the first attachment portion 5 A, forces applied from the first and second adhesives 7 A, 7 B to the scanning lens 5 through the first attachment portion 5 A and the second attachment portions 5 B are symmetrical with respect to the first attachment portion 5 A. Therefore, even if the temperature increases, the deformation in the shape of the scanning lens 5 is relatively small. Especially, in this embodiment, since the first attachment portion 5 A is located at the center portion of the scanning range in the main scanning direction of the scanning lens 5 , distortion caused by the temperature change can be smaller.

It is to be understood that if the temperature decreases, similar advantageous effects as those described in the case of temperature increase can be obtained.

In the optical scanner 1 as described above, since the frame 6 is made of a metal plate, it is possible to considerably reduce the cost as compared to a frame made of plastic.

Although an illustrative embodiment of the present invention has been described in detail, the present invention is not limited to this specific embodiment. It is to be understood that various changes and modifications may be made without departing from the scope of the appended claims.

In the above exemplary embodiment, two sets of second attachment portions 5 B and second frame-side attachment portions 6 B are provided. However, the number of these sets may be one, or alternatively, three or more.

In the above exemplary embodiment, only one scanning lens 5 is provided. However, a plurality of scanning lenses 5 may be provided. In this instance, at least one of the plurality of scanning lenses 5 may be fixed to the frame 6 using the first and second adhesives having different elastic coefficients as described in the claims.

In the above exemplary embodiment, the same second adhesive 7 B is used for the two second attachment portions 5 B. However, a plurality of different adhesives with different elastic coefficients may be used as the second adhesives, as long as their elastic coefficients are smaller than that of the first adhesive used for the first attachment portion 5 A.

In the above exemplary embodiment, the scanning lens 5 includes the protruding positioning portion 5 C having a rectangular section. However, the present invention is not limited to this specific configuration. For example, the positioning portion may be formed as a circular cylindrical projection.

Further, in the above embodiment, the distance D between the first attachment portion 5 A and the first frame-side attachment portion 6 A is the same as the distance D between each second attachment portion 5 B and the corresponding second frame-side attachment portion 6 B. However, the present invention is not limited to this specific configuration. For example, the first frame-side attachment portion 6 A and the second frame-side attachment portions 6 B can be formed such that the distance between the first attachment portion 5 A and the first frame-side attachment portion 6 A is smaller than the distance between each second attachment portion 5 B and the corresponding second frame-side attachment portion 6 B. With this configuration, the thickness of the first adhesive 7 A is smaller than that of the second adhesive 7 B, so that the first adhesive 7 A is less likely to deform and thus the scanning lens 5 can be accurately fixed to the frame 6 .