JPH0643376A - Scanning optical device - Google Patents

Abstract

PURPOSE:To suppress the distortion of optical elements and base plate by a change in temp., etc., by constituting an imaging lens system of the plural optical elements varying in coefft. of linear expansion and specifying the coefft. of linear expansion of the base plate fixing the optical elements. CONSTITUTION:A first lens 7 made of glass having a refracting power and a second lens 8 made of a synthetic resin having a toric surface and positive refracting power are fixed by an adhesive 12 of a photosetting type to the base plate 10 made of polycarbonate contg. glass fibers of the scanning optical system which executes optical scanning via the imaging lens system 6 after deflecting a laser beam by a rotary polyhedral mirror 5. The coefft. of linear expansion of the base plate 10 is set between the coefft. of linear expansion of the first lens 7 and the coefft. of linear expansion of the second lens 8. As a result, the stress applied to the fixing parts of the base plate 10 and the lenses 7, 8 is minimized even if the lenses 7, 8 and the base plate 10 are elongated or contracted by a change in the ambient temp. The deterioration in the optical performance by the distortion of the lenses 7, 8 and the destruction and adhesive peeling of the lenses 7, 8 are thus prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system for use in a device such as a laser beam printer or a digital copying machine in which a surface to be scanned such as a photoconductor or an electrostatic recording medium is optically scanned with a laser beam. It relates to the device.

[0002]

2. Description of the Related Art Conventionally, in this type of scanning optical device,
For example, as described in Japanese Examined Patent Publication No. 62-36210, the light beam is deflected by a deflector such as a rotary polygon mirror and then guided onto a surface to be scanned for optical scanning to write image information. It is carried out.

[0003]

However, in the above-mentioned conventional example, a toric lens having a complicated shape is manufactured from a glass material, which is disadvantageous in terms of cost. Therefore, recently, there is a tendency to use an inexpensive synthetic resin lens instead of the glass lens, but there is a problem that the optical characteristics of the synthetic resin material are likely to change depending on environmental conditions such as temperature and humidity. In order to improve such a problem, there is a proposal to reduce the cost and prevent the deterioration of environmental characteristics by combining a glass lens and a synthetic resin lens, for example, Japanese Patent Application No. Hei.
-27381.

However, when fixing such an optical element to a base or the like, considering the thermal expansion of the optical element or the base,
By fixing with an elastic member such as a spring, the strain on the optical element can be reduced, but in this case, a component such as a screw is required in addition to the spring, which leads to an increase in cost in terms of the number of components and workability. There's a problem.

An object of the present invention is to provide a scanning optical device capable of minimizing the distortion of the optical element, the base or the like caused by the environmental change such as temperature even if the optical element is fixed to the base or the like by adhesion. To do.

[0006]

In a scanning optical device according to the present invention for achieving the above object, a laser beam emitted from a light source section is deflected by a deflector, and then a laser beam is projected through an imaging lens system. In a scanning optical device that guides light onto a scanning surface to perform optical scanning, the imaging lens system includes at least two types of optical elements having different linear expansion coefficients, and at least one optical element is bonded on the same base. Fixed with an agent,
The linear expansion coefficient of the base is an intermediate value between the maximum value and the minimum value of the linear expansion coefficient of the optical element forming the imaging lens system.

[0007]

In the scanning optical device having the above-described structure, even if the base or the optical element of the imaging lens system adhered to the base expands or contracts due to a change in the ambient temperature, the base and the optical element are adhered to each other. The stress applied can be minimized.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the illustrated embodiments. FIG. 1 shows an outline of a laser beam printer to which the present invention is applied. The laser light flux emitted from the light source unit 1 composed of a semiconductor laser light source is made into a substantially parallel light flux by the collimator lens 2, the diameter of the light flux in the scanning cross section is adjusted by the aperture stop 3, and the laser light flux enters the cylindrical lens 4. The cylindrical lens 4 has a refracting power only in the sub-scanning cross section, and the passing laser light beam is a parallel light beam in the main scanning cross section, and is condensed substantially linearly in the sub-scanning cross section to the rotary polygon mirror 5 which is a deflector. Incident.
The rotating polygon mirror 5 is rotating at a constant speed and at high speed in the direction of the arrow,
The incident laser beam is reflected and deflected by the reflection surface 5a, and f
The light enters the imaging lens system 6 having the −θ characteristic. The imaging lens system 6 is composed of two types of lenses, a first lens 7 having a positive refractive power and a second lens 8 having a positive refractive power and having a toric surface. The laser light flux that has passed through the imaging lens system 6 is imaged on the surface of the photoconductor drum 9 which is the surface to be scanned, and the surface is optically scanned with a substantially uniform linear motion.

The laser beam emitted from the light source unit 1 has a wavelength of 780 nm, and the reflecting surface 5a of the rotary polygon mirror 5 has a wavelength of 780 nm.
And the surfaces of the lenses 7 and 8 of the imaging lens system 6 are positioned so that the S-polarized light always enters.

The first lens 7 is composed of a flat surface 7a and a spherical surface 7b, and the material thereof is SF6 (trade name) glass. The second lens 8 is a toric lens, the lens in the main scanning section is an aspherical surface, and the lens surface in the sub-scanning section is a spherical surface. The material is a synthetic resin whose main component is a polymer of PC (polycarbonate) and PS (polystyrene).

FIG. 2 shows a state in which the image forming lens 6 system is fixed to a base 10. A motor 10, a first lens made of glass, and a second lens 7 made of synthetic resin are fixed to the base 10.
The material of the base 10 is polycarbonate containing 30% of glass fiber. Motor 1 for driving rotating polygon mirror 5
Reference numeral 1 is fixed to the base 10 by screws, but the first lens 7 and the second lens 8 are adhered and fixed by a photo-curing adhesive 12.

Here, the linear expansion coefficient of the material of the first lens 7 made of glass is 8 × 10 ⁻⁶ , and the linear expansion coefficient of the second lens 8 made of synthetic resin is 7.1 × 10 ^−5. Therefore, the linear expansion coefficient of the material of the base 10 is 2.5 × 10 ⁻⁵ , and the linear expansion coefficient of the base 10 is set to an intermediate value between the linear expansion coefficients of the first lens 7 and the second lens 8. By setting the linear expansion coefficient in this way, even when the ambient temperature changes and the lenses 7 and 8 and the base 10 expand and contract, the stress applied to the fixed portions of the base 10 and the lenses 7 and 8 is minimized. It is possible to prevent the deterioration of the optical performance due to the distortion of the lenses 7 and 8, the destruction of the lenses 7 and 8 and the peeling of the adhesive.

FIG. 3 shows a second embodiment, in which the imaging lens system 6 is composed of lenses 21, 22 and 23, and these lenses 21, 22 and 23 and the folding mirror 24 are a base 25. Are bonded to each other with an adhesive 12. Lens 2
1 is a glass lens, the material is BK7, the coefficient of thermal expansion is 7 × 10 ⁻⁶ , the lens 22 is a glass lens, the material is BK6
The coefficient of thermal expansion is 8 × 10 ⁻⁶ , the lens 23 is an acrylic resin lens, the coefficient of thermal expansion is 8 × 10 ⁻⁵ , the base 25 is metallic aluminum, and the coefficient of thermal expansion is 2.15 × 10 ⁻⁵ . is there.

Also in this embodiment, the coefficient of linear expansion of the base 25 is set between the maximum value and the minimum value of the coefficient of linear expansion of the optical elements of the lenses 21, 22, 23. There are similar effects.

[0015]

As described above, in the scanning optical device according to the present invention, the linear expansion coefficient of the material of the base to which the imaging lens system is fixed is set to the middle of the linear expansion coefficient of the material of the imaging lens system. By setting, even if the imaging lens is bonded and fixed to the base, it is possible to reduce the distortion of the lens and the decrease in the adhesive force due to thermal expansion. In particular, a long optical element such as an fθ lens has a great effect because the amount of thermal expansion increases in the longitudinal direction of the lens. As described above, since the optical element can be fixed without using a conventional spring or screw, it is possible to reduce the cost and maintain good optical performance.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a laser beam printer.

FIG. 2 is an explanatory diagram of a fixed state of an imaging lens system.

FIG. 3 is an explanatory diagram of a fixed state of the imaging lens system of the second example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source part 5 rotating polygon mirror 6 imaging lens system 7 1st lens 8 2nd lens 9 photoconductor drums 10 and 25 bases 21, 22 and 23 lenses

Claims (2)

[Claims] 1. A scanning optical device for deflecting a laser beam emitted from a light source section by a deflector and then guiding the light beam onto a surface to be scanned through an imaging lens system for optical scanning. Is composed of at least two kinds of optical elements having different linear expansion coefficients, at least one optical element is fixed on the same base with an adhesive, and the linear expansion coefficient of the base constitutes the imaging lens system. A scanning optical device, wherein the linear expansion coefficient of the optical element is set between the maximum value and the minimum value. 2. The scanning optical device according to claim 1, wherein the imaging lens system is composed of a glass lens and a synthetic resin lens, and the base is composed of a synthetic resin material containing metal or glass fiber.