JPH0915520A - Optical device for optical scanning - Google Patents

Abstract

PURPOSE: To execute optical scanning with optically high performance by an inexpensively constituted device. CONSTITUTION: A light source unit is constituted by forming a light source 1 and an anamorphic single lens 2 into one body, a luminous flux from the light source 1 is collimated by the single lens 2, a beam diameter is adjusted by an aperture diaphragm 3, then, the collimated light is emitted to the deflection point P of a rotary polygon mirror 4. The luminous flux is reflected and deflectively scanned by the mirror 4, then, an image is formed through a plastic f lens 5 on a surface to be scanned 6 which has common interests with the deflection point P, optical scanning is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning optical device for optically scanning laser light using a plastic f.theta. Lens.

[0002]

2. Description of the Related Art Heretofore, an optical scanning optical device of this kind has been disclosed in Japanese Patent Publication No. 62-36210, Japanese Patent Publication No. 21565/1990, Japanese Patent Application Laid-Open No. 4-50908 and the like. It converts a light beam deflected and scanned at a constant angular velocity by a mirror into a light spot that moves at a constant velocity on a surface to be scanned. Generally, an fθ lens having a tilt correction function for a reflecting surface of a rotary polygon mirror is used. It is used.

[0003]

However, in the above-mentioned conventional example, for example, in Japanese Patent Publication No. 62-36210, 2
Since a toric lens composed of a single rotationally asymmetric glass lens is used, the device is very expensive. Further, in JP-A-4-50908, since the fθ lens is made of plastic, there is a problem in that when the ambient temperature changes, the refractive index of the plastic changes and the focus shifts.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an optical scanning optical device that is optically high-performance and inexpensive.

[0005]

An optical scanning optical device according to the present invention for achieving the above object comprises a light source unit in which a light source and an optical member are integrated, and a deflecting means for reflecting and deflecting a light beam from the light source unit. And an image forming unit formed of a plastic lens for forming an image of the light beam reflected by the deflecting unit on the surface to be scanned, the deflection of the deflecting unit in the sub-scanning direction perpendicular to the scanning section of the deflecting unit. It is characterized in that the point and the surface to be scanned are in a substantially optically conjugate relationship.

[0006]

In the optical scanning optical device having the above-mentioned structure, the light source and the optical member are integrated to form the light source unit, the light flux from the light source unit is guided to the deflection point of the deflection means, and the light is reflected and deflected by the deflection means. In the sub-scanning direction perpendicular to the scanning section of the deflecting unit, the light beam is imaged by the image forming unit formed of a plastic lens on the surface to be scanned having a substantially optical conjugate relationship with the deflection point, and optical scanning is performed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a plan view of the first embodiment, showing the arrangement of optical elements in the deflection scanning plane which is the main scanning plane. An anamorphic single lens 2 for collimating laser light and an aperture stop 3 for adjusting the beam diameter of the laser light are arranged on the front surface of the semiconductor laser light source 1, and in front of the aperture stop 3, high speed in the direction of the arrow. A rotating polygon mirror 4 is arranged,
A plastic fθ lens 5 is arranged in the reflection direction of the rotary polygon mirror 4, and a scan surface 6 is arranged at the image forming position of the fθ lens 5. Here, the deflection point P where the optical axis from the light source 1 and the reflecting surface of the rotary polygonal mirror 4 intersect is the surface 6 to be scanned.
The anamorphic single lens 2 and the fθ lens 5 have optical powers different from each other in the scanning section in the main scanning direction and the scanning section in the sub-scanning direction perpendicular to the main scanning surface. doing.

FIG. 2 shows a light source 1 and an anamorphic single lens 2.
2 is a cross-sectional view of a light source unit in which is integrated, the light source 1 is pressed into a plastic holder 7, and the anamorphic single lens 2 is fixed to a lens barrel 8. Then, the positional relationship between the light source 1 and the anamorphic single lens 2 is three-dimensionally adjusted, and then the adhesive is poured into the site 9 to fix the holder 7 and the lens barrel 8.

The light beam emitted from the light source 1 passes through the anamorphic single lens 2 so that the divergence of the main scanning surface is converted into substantially parallel light. This parallel light passes through the aperture stop 3 and its beam diameter is adjusted,
It is reflected at the deflection point P of the rotary polygon mirror 4. The rotary polygon mirror 4 is rotating at a high speed, the reflected light beam is deflected and scanned as shown by a broken line, and passes through the fθ lens 5,
The surface 6 to be scanned is optically scanned while undergoing a correction for making the scanning speed of the light beam on the surface 6 to be scanned constant and a condensing action for forming a beam spot.

FIG. 3 is a state of convergence of a light beam in the main scanning direction, FIG.
Indicates the convergent state of the light beam in the sub-scanning direction. In FIG. 3, the light beam emitted from the light source 1 is converted into parallel light by the anamorphic single lens 2, reflected as it is at the deflection point P of the rotary polygon mirror 4, passes through the fθ lens 5, and the surface to be scanned 6 is scanned. Image as a beam spot on top.

On the other hand, in the sub-scanning direction, as shown in FIG. 4, the light beam emitted from the light source 1 passes through the anamorphic single lens 2, its divergence is converted into focusing, and passes through the aperture stop 3. Then, the light flux width is adjusted and an image is formed at the deflection point P of the rotary polygon mirror 4. The light beam reflected at the deflection point P passes through the f.theta. Lens 5 while diverging, so that the divergence is converted again into a converging property and an image is formed on the surface 6 to be scanned.

Here, the deflection point P in FIG. 4 and the image forming position of the surface to be scanned 6 are in an optically conjugate relationship as described above, and the adverse effect of the surface tilt of the reflecting surface of the rotary polygon mirror 4 is corrected. A so-called face-tilt correction optical system for performing the above is formed. In addition,
The initial adjustment of the focus position of the fθ lens 5 in the sub-scanning direction is performed by moving the entire light source unit back and forth on the optical axis.

The plastic material forming the fθ lens 5 has a larger change in the refractive index due to the ambient temperature than the glass material, and there is a problem that the power of the lens changes due to the temperature change and the focus position shifts. Further, since the plastic material has a larger coefficient of linear expansion than the glass material, the power of the lens is affected by the change in the curvature or thickness of the lens. The change in the refractive index is somewhat different depending on the plastic material, but there is a decrease in the refractive index of about 0.0001 to 0.00012 / ° C. due to the temperature rise, and the power of the lens shifts in the direction of weakening as the temperature decreases.

In this embodiment, the optical conjugate lateral magnification of the deflection point P in the sub-scanning direction and the surface 6 to be scanned is set to -3.
Since it is a magnifying optical system, when the effect of the fθ lens 5 alone is taken into consideration, the focus shift amount in the sub-scanning direction becomes larger than the focus shift amount due to the temperature increase in the main scanning direction. That is, when the temperature rises by 25 ° C., it is about 1 in the main scanning direction.
mm, about 3 mm in the sub-scanning direction, the focus position moves farther than the fθ lens 5.

Considering only the light source unit portion of FIG. 2, the holder 7 and the lens barrel 8 change in the extending direction when the ambient temperature rises, and the focus shift occurs. However, this amount of defocusing tends to cancel out the defocusing due to the change in the refractive index of the plastic if the elongation due to the temperature of the holder 7 and the lens barrel 8 is large to some extent.

In this embodiment, the focal length of the fθ lens 5 in the main scanning direction is set to 160 mm, and the focal length of the anamorphic single lens 2 in the main scanning direction is set to 20 mm.
Lateral magnification of the light source 1 and the surface 6 to be scanned in the main scanning direction,
The vertical magnifications are -8 times and 64 times, respectively. Further, by selecting the materials of the holder 7 and the lens barrel 8, the effect amount of focus shift of the light source unit when the temperature rises 25 ° C. is 15.6 μm.
It is set to be. Therefore, when the temperature of the fθ lens 5 increases by 25 ° C. in the main scanning direction, the amount of focus deviation is 1 mm.
Is approximately equal to the amount of focus shift of the light source unit converted to the image plane side of 15.6 μm × 64 times ≈1 mm, and the shift of focus is offset.

Further, the lateral magnification and the vertical magnification of the light source 1 and the surface to be scanned 6 are set to be 13.9 times and 192.3 times, respectively, so as to cancel out the focus shift in the sub-scanning direction. There is. Here, since the conjugate lateral magnification of the deflection point P and the surface to be scanned 6 in the sub-scanning direction is set to −3,
The conjugate lateral magnification of the light source 1 and the deflection point P is -4.6. Here, since the distance between the light source 1 and the anamorphic single lens 2 is the focal length of the main scanning cross section of 20 mm, the distance between the anamorphic single lens 2 and the deflection point P is about 90 mm, and the distance from the light source 1 to the deflection point P is approximately 90 mm. As for the distance, since the anamorphic single lens 2 has almost no influence in the length direction,
It can be set as short as 110 mm, and the device can be made compact.

In order to reduce the size of the plastic fθ lens 5, it is necessary to bring the fθ lens 5 closer to the deflection point P side. In this case, the magnification of the deflection point P and the surface to be scanned 6 in the sub-scanning direction becomes large, and the influence of the change in the refractive power due to the temperature change of the plastic becomes significant. Therefore,
Especially when the absolute value of the conjugate lateral magnification is 1.5 times or more, a great effect can be obtained by applying this embodiment. Also,
As the lateral magnification between the light source 1 and the deflection point P becomes larger, the distance between the light source 1 and the deflection point P becomes longer. Therefore, if the present embodiment is applied to the case where the absolute value of the lateral magnification is 2 times or more, the effect is further enhanced. growing.

FIG. 5 is a sectional view of the light source unit of the second embodiment, showing a spherical lens 10 and a cylindrical lens 11.
The same effect as that of the first embodiment can be obtained by integrally forming the light source units and compactly storing them in the lens barrel 8.

[0020]

As described above, the optical scanning optical device according to the present invention can be made into a compact and low-priced structure by using the plastic lens as the imaging lens, and the light source and the optical member can be provided. By integrally forming a unit, even if thermal expansion occurs in the lens due to ambient temperature change, its optical performance can be stabilized and high-performance optical scanning can be performed.

[Brief description of the drawings]

FIG. 1 is a plan view of a first embodiment.

FIG. 2 is a sectional view of a light source unit.

FIG. 3 is an explanatory diagram of a light flux in a main scanning section.

FIG. 4 is an explanatory diagram of a light flux on a sub-scanning section.

FIG. 5 is a sectional view of a light source unit according to a second embodiment.

[Explanation of symbols]

 1 Semiconductor Laser Light Source 2 Anamorphic Single Lens 3 Aperture Stop 4 Rotating Polygonal Mirror 5 Plastic fθ Lens 6 Scanned Surface 10 Spherical Lens 11 Cylindrical Lens

Claims (4)

[Claims] 1. A light source unit in which a light source and an optical member are integrated, a deflecting unit for reflecting and deflecting a light beam from the light source unit, and a plastic lens for forming an image of the light beam reflected by the deflecting unit on a surface to be scanned. And an image forming unit including the image forming unit, and the deflection point of the deflecting unit and the surface to be scanned have a substantially optical conjugate relationship in the sub-scanning direction perpendicular to the scanning section of the deflecting unit. apparatus. 2. The optical scanning optical device according to claim 1, wherein the absolute value of the conjugate lateral magnification of the image forming unit in the sub-scanning direction is 1.5 or more. 3. The optical scanning optical device according to claim 1, wherein the absolute value of the conjugate lateral magnification of the light source and the deflection point in the sub-scanning direction is 2 or more. 4. The optical scanning optical device according to claim 1, wherein an anamorphic single lens is used for the light source unit.