JPH08327926A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a scanning optical device with a lens excellent in shock resistance as being capable of mass-production and lighter weight. SOLUTION: A scanning optical device comprises a light source 10 to generate laser beam, a collimator lens 20, a cylindrical lens 40, a rotatable polygon mirror 50 and a scanning lens system 60. The collimator lens, the cylindrical lens and the scanning lens system are molded of acrylic plastic or polycarbonate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device in an optical instrument utilizing optical means such as a laser beam printer, and more particularly, to a lens used in the scanning optical device injection-molded from an acrylic resin or polycarbonate to form a shaft. A symmetric aspheric lens having f-theta
The present invention relates to a scanning optical device which is provided with a (F-θ) function to facilitate the manufacture, assembly and adjustment of a lens.

[0002]

2. Description of the Related Art Recently, an optical device using a laser diode has been developed and is used in a laser printer, a laser scanning micrometer (LC).
M) and the like are examples thereof.

Generally, an optical system applying a laser is composed of a laser generator, a laser deflector, a laser scanning lens system, and a light receiving section.

In recent years, copying machines, printers and the like have frequently used a monochromatic laser beam by utilizing an electrophotographic process system.

In such a device, a laser beam emitted from a laser light emitting device such as a semiconductor laser diode is converted into parallel light through a collimator lens or a prism complex and is guided to a polygon mirror which rotates at a high speed, and then a deflecting mirror. The rotation of the laser beam changes the reflection direction of the laser beam and scans in the direction of the photoconductor to form an electrostatic latent image on the photoconductor.

An example of such a scanning optical device is disclosed in Japanese Patent Laid-Open No. 2-161410, and the device disclosed in this publication will be described as a conventional example of the scanning optical device with reference to FIG.

As shown in FIG. 3, the laser light from the light source 1 is reflected by a collimator lens 2, a slit 3, a cylindrical lens 4 and a polygon mirror 5 as it rotates. Then, a rotationally asymmetric aspherical surface F-θ6 which is a scanning lens
The image is scanned on the image forming surface (photosensitive drum surface 9) via the line ′.

Here, a scanning lens system (F-θ) 6'for scanning laser light includes a first lens 6 having a rotational symmetry axis whose first and second surfaces are spherical or flat surfaces, and a cylindrical lens. Lens 7 having a fourth surface composed of a third surface composed of and a rotational axis asymmetric aspherical surface for correction of the number difference
It consists of and. Further, when the rotary polygon mirror 5 which is the first and second spherical surfaces of the scanning lens system 6'rotates equiangularly, the locus of the spot on the image plane 9 makes a linear movement.

On the other hand, after passing through the rotary polygon mirror 5 and the first lens 6, the deflection of the rotary polygon mirror 5 is caused by the third cylindrical surface and the fourth aspheric surface of the second lens 7 located between the image forming surfaces 9. Correct the effect of.

However, according to the conventional device as shown in FIG. 3, after the emitted laser light is collimated by the collimator lens, it is incident on the cylindrical lens through the aperture, where the beam is a tomographic pattern. Then, the light is deflected by the rotary polygon mirror, and is focused by the scanning lens on the image formation surface in the form of equiangular lines.

Here, a glass-based lens, which has little thermal deformation and is advantageous for bonding and coating, has been used for some of the main lenses or all of the optical lenses. That is, some lenses may have polymethylmethacryla
te: PMMA), but when using two lenses, a cylindrical lens and a scanning lens, 2
It was common to use one or one glass-based lens. However, the glass-based lens has problems that it is difficult to reduce the weight of the product due to its large specific gravity, its impact resistance is weak, mass production is difficult, and the material cost is high. Further, since the degree of freedom of the shape is low, it is technically difficult to make some of the lenses aspherical.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to make a lens used in a scanning optical device an acrylic plastic (PMMA). Or polycarbonate (P
It is intended to provide a scanning optical device that can be mass-produced by using C) as a material, can be manufactured at a low cost, has a high degree of freedom in shape, and can be easily assembled by integrating lens coupling parts. .

[0013]

To achieve the above object, a scanning optical device according to the present invention comprises a light source for generating a laser beam, a collimator lens, a cylindrical lens, a rotary polygon mirror and a scanning lens system. A scanning optical device, characterized in that a collimator lens, a cylindrical lens, and a scanning lens system are molded from acrylic plastic or polycarbonate.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a scanning optical device according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a scanning optical device according to the present invention, showing the scanning direction. As shown in FIG. 1, the laser light emitted from the laser diode 10 of the light source is reflected by the rotation of the rotary polygon mirror 50 through the collimator lens 20, the long hole-shaped opening 30 and the cylindrical lens 40, and then the scanning lens system. F-θ lens 60 as
An image is formed and scanned on the image forming surface (photosensitive drum surface) 110 via the.

The collimator lens 20 is an aspherical surface, and at least one of the aspherical surface coefficients has a negative (-) sign.

Scan lens system 60 for scanning laser light
Is equipped with two lenses having a magnification in the scanning direction / sub-scanning direction, two of the four surfaces have the form of a cylindrical lens, and the cylindrical lens that forms light in the scanning direction and the light in the sub-scanning direction And a cylindrical lens for forming an image. The scanning lens system 60 has a function of F-θ in the scanning direction, and has a spherical lens shape in the sub-scanning direction.

Further, in the scanning optical apparatus of the present invention, in order to detect the starting point of the scanned optical signal, the reflecting mirror 70 for detecting a part of the scanned light, the signal detecting cylindrical lens 80, and the slit. 90 and a photodetector 100.

Here, the above lenses, that is, the collimator lens 20, the cylindrical lens 40, and the scanning lens 6 are used.
0, the signal detecting cylindrical lens 80 is made of acrylic plastic (PMMA) or polycarbonate (PC) and has a refractive index of 1.48 to 1.6.
And the Abe constant is between 30 and 60.

Scanning lens 60 of plastic acrylic type
The curvature in the scanning direction / sub-scanning direction is parallel to the direction of the rotary polygon mirror 50 or has a concave shape.

One of the two plastic scanning lenses is provided by moving the central axis of the lens parallel to the optical axis, and the axial ray passing through this lens is designed to be a ray parallel to the optical axis. .

In the scanning optical device of the present invention thus constructed, the monochromatic laser light emitted from the laser diode 10 of the light source is collimated by the collimator lens 20, and then the elongated aperture 30 and the cylindrical shape are formed. The light passes through the lens 40, is parallel to the scanning direction, and is converged in the sub-scanning direction that is perpendicular to this direction.

Thereafter, this light beam is deflected by the rotary polygon mirror 50 rotating on the rotation axis of a spindle motor (not shown), and then has a function of F-θ in the scanning direction.
An image is formed on the image forming surface 110 of the photosensitive drum by the scanning lens system 60 having a spherical lens shape in the sub scanning direction.

A part of the scanned light is detected by the photodetector 100 through the reflecting mirror 70, the signal detecting cylindrical lens 80, and the slit 90 to detect the starting point of the scanned optical signal.

As described above, the light, which is parallel to the scanning direction and is converged in the sub-scanning direction, simultaneously forms the image plane 1 of the photosensitive drum.
The shapes of the lenses of the scanning optical device for forming an image on 10 are as shown in Table 1, and these are formed of acrylic plastic (PMMA) or PC.

[0026]

[Table 1]

[0027]

As described above, according to the scanning optical device of the present invention, since the scanning optical system lens is injection-molded using acrylic plastic or polycarbonate as a material, mass production and weight reduction of the product are possible. The cost can be saved and the impact resistance can be improved.

Furthermore, since the degree of freedom in designing is increased and a frame having an appropriate shape can be made for the lens, the coupling parts of the lens can be integrated to facilitate the assembly.
It is also easy to make the shape of some lenses aspheric.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a scanning direction of a scanning optical device according to the present invention.

FIG. 2 is a schematic view showing a sub scanning direction of the scanning optical device according to the present invention.

FIG. 3 is a schematic view of a conventional scanning optical device.

[Explanation of symbols]

 10 Light Source 20 Collimator Lens 30 Aperture 40 Cylindrical Lens 50 Rotating Polygonal Mirror 60 Scanning Lens System 70 Reflector 80 Signal Detection Cylindrical Lens 90 Slit 100 Photodetector 110 Imaging Surface

Claims (11)

[Claims] 1. A scanning optical device comprising a light source for generating a laser beam, a collimator lens, a cylindrical lens, a rotary polygon mirror and a scanning lens system, wherein the collimator lens, the cylindrical lens and the scanning lens system are made of acrylic plastic or A scanning optical device characterized by being molded from polycarbonate. 2. The scanning optical device according to claim 1, wherein the collimator lens is formed into an aspherical surface. 3. The scanning optical device according to claim 1, wherein at least one of aspherical surface coefficients of the collimator lens has a negative sign. 4. The scanning optical apparatus according to claim 1, wherein the scanning lens system includes two lenses having a magnification in a scanning direction / a sub-scanning direction. 5. The scanning lens system is configured so that two of the four surfaces are composed of a cylindrical lens for focusing light in the scanning direction and a cylindrical lens for focusing light in the sub-scanning direction. The scanning optical device according to claim 1. 6. The scanning lens system has an F-type in a scanning direction.
The scanning optical device according to claim 1, wherein the scanning optical device has a function of θ and is configured to have a spherical lens shape in the sub-scanning direction. 7. The scanning optical device according to claim 1, wherein the curvature of the scanning lens system in the scanning direction / the sub-scanning direction is parallel to the direction of the rotary polygon mirror. 8. The scanning optical device according to claim 1, wherein the curvature of the scanning lens system in the scanning direction / the sub-scanning direction is concave in the direction of the rotary polygon mirror. 9. One of the two lenses of the scanning lens system is provided parallel to the optical axis by utilizing the central axis of the lens, and a ray on the axis passing through the lens is a ray parallel to the optical axis. The scanning optical device according to claim 1, wherein 10. The refractive index of each lens is from 1.48 to
2. The scanning optical device according to claim 1, wherein the scanning optical device is 1.6. 11. The Abe constant of each lens system is 30 to 6
The scanning optical device according to claim 1, wherein the scanning optical device is 0.