JP3486255B2 - Slit plate mounting structure of optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slit plate mounting structure for an optical scanning device used in an image forming apparatus utilizing electrophotography such as a laser beam printer.

[0002]

2. Description of the Related Art In an image forming apparatus utilizing electrophotography, such as a laser beam printer, an optical scanning device is used to expose a photosensitive member to form a latent image.
In general, an optical scanning device uses a semiconductor laser to emit a laser beam modulated according to image information so as to scan (main scan) the surface of the photoconductor in a predetermined angular range. At the same time, a two-dimensional latent image is formed on the surface of the photoconductor by moving the photoconductor relative to the scanning line in the direction orthogonal to the scanning direction of the laser beam (sub scanning).

In the scanning optical system using the semiconductor laser as described above, the scanning pitch of the image forming apparatus in which the scanning optical system is mounted is compensated for while compensating for individual differences in the divergence angle of the beam emitted by the semiconductor laser. It is necessary to set the spot diameter of the beam on the scanning plane so as to match. For example,
A laser beam emitted from a semiconductor laser is converted into parallel light by a collimator lens, is guided to a deflector such as a polygon mirror via a cylindrical lens as an anamorphic lens, and the deflected beam is applied to a scanning surface via an fθ lens. In the case of the scanning optical system having the configuration, the spot diameter in the sub-scanning direction is changed by changing the focal length of the cylindrical lens while keeping the image forming position in the sub-scanning direction by the cylindrical lens near the reflecting surface of the polygon mirror. Methods are known in the art.

However, in the method of changing the focal length of the cylindrical lens, it is necessary to prepare a plurality of cylindrical lenses corresponding to a plurality of focal lengths for one scanning optical system in advance, and the adjustment thereof is complicated. It was a thing. Therefore, for example, Japanese Examined Patent Publication No. 63-61824 discloses a scanning optical system having an anamorphic scanning lens system, in which light is converged by a cylindrical lens in the sub-scanning direction once before the polygon mirror. There is disclosed a configuration in which a slit is provided therein and the spot diameter is set so that only a part of the light flux passes therethrough. In such a configuration, since the position of the slit in the optical path has a great influence on beam formation, it is necessary to position and fix the slit at an accurate position, and therefore a configuration in which the slit can be mounted with a simple configuration is desired. Was there.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a slit for an optical scanning device, which is capable of accurately locating the slit at a predetermined position with a simple structure and further suppressing return light from the slit plate as much as possible. It is intended to provide a plate mounting structure.

[0006]

Therefore, the optical scanning device of the present invention comprises a light source for emitting a laser beam, a collimator lens for converting the laser beam emitted from the light source into parallel light, and a collimator lens for collimating the laser beam. An anamorphic lens for transmitting a laser beam converted into light, a slit means for transmitting only a predetermined portion of the laser beam transmitted through the anamorphic lens, a deflecting means for deflecting the beam transmitted through the slit means, and the deflection The slit means has a plane portion made of an elastic member provided with a window portion having a predetermined shape, and a fθ lens for transmitting the beam deflected by the means, and the slit means is formed on the plane portion at a side end of the plane portion. On the other hand, a slit plate having a spring portion bent at a predetermined angle, and the spring portion elastically deforms toward the plane portion side. And configured to have a slit plate holding means having a holding surface facing each other respectively in contact to so that the flat portion and the spring portion.

In the above structure, the beam exit surface of the anamorphic lens may be a flat surface, and one of the holding surfaces facing each other may be the beam exit surface of the anamorphic lens. In this case, the flat portion of the slit plate comes into contact with the beam exit surface. Further, the optical scanning device can fix the anamorphic lens by the elastic force of the slit plate by providing an abutting member that abuts the beam incident surface of the anamorphic lens without blocking the incident beam.

[0008]

1 is a diagram for explaining a scanning optical unit 100 to which the present invention is applied. The scanning optical unit 100 is used as a scanning optical system in an image forming apparatus utilizing electrophotography, such as a laser beam printer.

The scanning optical unit 100 includes a casing 2
00, a collimator unit 10 having a semiconductor laser and a collimator lens, a lens unit 20 having the characteristic configuration of the present invention, and a polygon mirror 3 as a deflecting means.
It has a configuration including 0 and fθ lenses 40.

Emitted from the scanning optical unit 100,
The scanning laser beam modulated according to the image information mainly scans the surface of the photosensitive drum 50 in a direction parallel to the rotation axis 51. The photosensitive drum 50 is rotated simultaneously with the main scanning, and as a result, a two-dimensional image is formed as a latent image on the surface of the photosensitive drum.

The laser beam emitted from the semiconductor laser of the collimator unit 10 is converted into parallel light by the collimator lens and emitted toward the lens unit 20. The lens unit 20 has a convex cylindrical lens as an anamorphic optical system, which will be described later, and a slit plate in which predetermined slits are formed. The cylindrical lens is arranged in the main scanning direction (the rotation shaft 51 of the photosensitive drum 50).
Direction), and has power only in the sub-scanning direction (direction perpendicular to the rotary shaft 51 of the photosensitive drum). The beam that has passed through the cylindrical lens and the slit is incident on the polygon mirror 30. Due to the power of the cylindrical lens in the sub-scanning direction, the component in the sub-scanning direction of the laser beam is reflected by the reflecting surface 30R of the polygon mirror 30.
It converges slightly on the near side.

The laser beam deflected by the polygon mirror 30 passes through the f.theta.
The surface 0 is exposed by scanning. The fθ lens 40 is composed of a spherical cylindrical lens 41 and a toric lens 42. The polygonal mirror-side refracting surface 41A of the spherical cylindrical lens 41 is a cylindrical surface having a negative curvature in the cross section in the sub-scanning direction, and the opposite surface 41B is a concave spherical surface. The spherical cylindrical lens side surface 42A of the toric lens 42 has a curvature in both the main scanning direction and the sub-scanning direction, but the latter has a stronger curvature than the former.

FIG. 2 shows the lens unit 20 of the first embodiment.
It is a perspective view explaining the structure of. Lens unit 20
Is composed of a substrate 23, a cylindrical lens 21 and a slit plate 22. The cylindrical lens 21 has power only in the sub-scanning direction and is arranged with the cylindrical surface 21a facing the semiconductor laser. The other surface 21b of the cylindrical lens 21 is a flat surface, and the lens holding surface 24a of the holding portion 24 formed by projecting the flat surface 21b onto the substrate 23 and the upper surface 23 of the substrate 23.
The cylindrical lens 21 is fixed on the substrate 23 by adhering it while being in contact with a. As shown in FIG. 2, the protrusion 24 is notched in the center so as not to obstruct the optical path, and a pair of grooves 25 for inserting the slit plate 22 are formed inside. X of a pair of grooves 25
The width of the direction (see the xyz coordinate axes shown in the figure) is set to d. On the other hand, the slit plate 22 is made of a metal having a predetermined elasticity, and has a flat surface portion 22b in which the slits 22s are formed and a pair of arm portions formed by bending a part of the flat surface portion 22b in the x direction by a predetermined angle. 22a. When the distance between the tip of the arm portion 22a and the flat surface portion 22b in the x direction is T, the relationship of d <T is established between the width d of the pair of grooves 25 in the x direction.

According to the above construction, the arm portion 22a is elastically deformed in a state where the slit plate 22 is inserted and pushed into the pair of grooves 25, and the slit plate 22 is fixed in the pair of grooves 25 by the elastic force. (See FIG. 3). The width of the arm portion 22a in the z direction is set to be smaller than the depth of the pair of grooves 25 in the z direction. Further, the slit plate 22 is completely pushed in until the lower side comes into contact with the substrate 23,
The center of the slit 22s coincides with the optical axis. Therefore, when the slit 22 is mounted, the notch of the protrusion 24 is completely closed by the slit plate 22.
That is, only the light that is incident on the cylindrical surface 21 a of the cylindrical lens 21 from the left side in the figure and that is transmitted through the slit 22 s formed in the slit plate 22 is directed to the polygon mirror 30. The inner surface and the bottom surface of the pair of grooves 25 prevent the slit plate 22 from slipping,
It has a rough finish.

FIG. 4 shows the lens unit 12 of the second embodiment.
It is a perspective view explaining 0. The lens unit 120 is
It is composed of a substrate 123, a cylindrical lens 21, and a slit plate 122. The cylindrical lens 21 has power only in the sub-scanning direction, and has a cylindrical surface 2
1a is arranged so as to face the semiconductor laser. The other surface of the cylindrical lens 21 is a flat surface 21b. A lens housing portion 125 is formed on the substrate 123, and the cylindrical lens 21 is housed in the lens housing portion 125.
Is inserted and the refracting surface 21a of the cylindrical lens 21 is brought into contact with the front wall 124a of the housing portion 124, and the slit plate 122 is inserted between the other refracting surface 21b and the rear wall 124b of the housing portion 124. As a result, the slit plate 122 is held at a predetermined position between the lens 21 and the rear wall 124b by its own elastic force while fixing the lens 21.

The slit plate 122 is provided on the surface 21 of the lens 21.
A surface 122c that abuts b and a pair of arm portions 122a that are bent at a predetermined angle with respect to the surface 122c are provided. When the distance between the arm portion 122a and the surface 122c is the longest, the surface 21b of the lens 21 and the rear wall 124 are located.
The distance is larger than the distance from the inner surface of b, and when inserted between the lens 21 and the rear wall 124b, it elastically deforms and presses the lens 21 against the front wall 124a by the elastic force. A lens pressing portion 122b is formed above the slit plate 122. Lens holding part 1
22b, the tip of the surface 122c is bent to the lens side,
Further, the bent portion is formed into a loose “<” shape to elastically urge the side surface of the cylindrical lens 21 toward the bottom surface of the housing portion 125. In addition, the inner surface of the storage portion 125 is a rough finish surface, which prevents the lens 21 and the slit plate 122 from slipping inside the storage portion, and the positional relationship between the lens 21 and the slit 122s is maintained.

The front wall 124a is formed with a window portion 124w so as not to obstruct the optical path, and the rear wall 124b is notched near the optical axis so as not to obstruct the optical path of the light transmitted through the slit 122s. With the above-described configuration, the cylindrical lens 21 is fixed in a state of being urged toward the bottom surface of the storage section 125 and the inner surface of the front wall 125a of the storage section 125, so that the cylindrical lens 21 is simply used without using an adhesive or the like. The assembly of the lens unit 120 is completed only by inserting the slit plate 122 into the gap between the lens and the housing portion 125.

[0018]

According to the slit plate mounting structure of the optical scanning device of the present invention, the slit plate can be mounted easily and accurately, so that a desired spot size can be obtained while reducing the number of assembly steps such as bonding. It will be possible. Furthermore, if the slit plate has the structure of the second embodiment that also functions as a fixing member for the cylindrical lens, the work for fixing the lens can be omitted.

[Brief description of drawings]

FIG. 1 is a top view showing a schematic configuration of a laser unit that is an embodiment of the present invention.

FIG. 2 is a perspective view showing the configuration of a lens unit of Example 1. FIG.

FIG. 3 is a side sectional view of the lens unit according to the first embodiment having a slit plate attached thereto.

FIG. 4 is a perspective view showing a configuration of a lens unit according to a second example.

FIG. 5 is a side sectional view of a lens unit according to a second embodiment in which a slit plate is mounted.

[Explanation of symbols]

10 Collimating unit 20 lens unit 21 Cylindrical lens 22 Slit plate 30 polygon mirror 40 fθ lens 50 photosensitive drum 122 slit plate

Claims (4)

(57) [Claims] 1. A light source for emitting a laser beam, a collimator lens for converting the laser beam emitted from the light source into parallel light, and an anamorphic lens for transmitting the laser beam converted into parallel light by the collimator lens, Slit means for transmitting only a predetermined portion of the laser beam transmitted through the anamorphic lens, deflection means for deflecting the beam transmitted through the slit means, and fθ lens for transmitting the beam deflected by the deflection means are provided. The slit means has a flat portion made of an elastic member provided with a window having a predetermined shape and a spring portion bent at a side edge of the flat portion at a predetermined angle with respect to the flat portion. A plate, and the flat portion and the spring portion respectively so that the spring portion elastically deforms toward the flat portion. A slit plate mounting structure for an optical scanning device, comprising: a slit plate holding means having holding surfaces facing each other. 2. A beam exit surface of the anamorphic lens is a flat surface, one of the holding surfaces facing each other is constituted by the flat surface of the anamorphic lens, and at least a part of the flat surface portion of the slit plate is the flat surface. The slit plate mounting structure of the optical scanning device according to claim 1, wherein the slit plate mounting structure is in contact with the flat surface of the anamorphic lens. 3. The optical scanning device has a contact member that abuts on a beam incident surface of the anamorphic lens without disturbing the incident beam, and the anamorphic lens is pressed against the abutting member by the slit plate. The slit plate mounting structure for an optical scanning device according to claim 2, wherein the slit plate mounting structure is abutted against the slit plate. 4. The optical scanning device has a mounting portion for mounting the anamorphic lens, and the slit plate has a second spring portion for elastically pressing the anamorphic lens against the mounting portion. Wherein the anamorphic lens is elastically fixed by the spring portion and the second spring portion of the slit plate while being in contact with the mounting portion and the contact member. Item 3. The slit plate mounting structure of the optical scanning device according to item 3.