JP3205264B2 - Optical scanning optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical scanning optical system.

[0002]

2. Description of the Related Art In an optical scanning optical system well-known in connection with a digital copying apparatus or an optical printer, a deflected light beam heading to an optical scanning start position is detected by a photodetector, and a light beam for starting the optical scanning is detected. Generating a synchronization signal has been performed.
In order to perform detection by the photodetector, the deflected light beam is referred to as fθ
A method is known in which the light is guided to an optical deflector through a portion outside the effective angle of view of the lens (Japanese Patent Laid-Open No. 3-221913).
In this method, a portion for guiding the deflected light beam to the photodetector is required outside the effective angle of view required for optical scanning, so that the angle of view of the fθ lens needs to be larger than the angle of view required for optical writing. And the diameter of the fθ lens is increased.

[0003] Also, JP-A-5-19186 discloses that
An optical system in which a scanning lens unit corresponding to an fθ lens and a BD imaging lens unit that guides a deflected light beam to a photodetector is disclosed, is disclosed in Japanese Patent Application Laid-Open No. 7-281113. The light beam from the side is directed to the deflection / reflection surface position of the optical deflector in the main scanning direction (the direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned, and in the sub-scanning direction on the optical path). The direction that corresponds in parallel with
An optical system is disclosed in which a cylinder lens for forming a long linear image and an anamorphic lens for guiding a deflected light beam to an optical deflector are integrally formed.

[0004] When the two lenses are integrally formed as described above, the shape of the integrated lens is generally complicated. Therefore, when the integrated lens is formed of plastic, the processing of the gold piece is complicated, and each lens is separately formed. This can be more costly than forming into a body. In addition, since the two integrated lenses have different imaging performances, the mounting accuracy tends to be stricter than when the two lenses are separately mounted. Even if there is a slight mounting error, one or both of the two lenses may be mounted. There is a possibility that the imaging performance is deteriorated.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has been made in view of the fact that the second optical system for converging a deflected light beam on a surface to be scanned can be easily assembled to a housing and has a large diameter. It is an object to realize a light scanning optical system without any.

[0006]

An optical scanning optical system according to the present invention includes a light source unit, first to third optical systems, an optical deflector, and a photodetector. The “light source section” emits a light beam for optical scanning, and a light source using a semiconductor laser, a light emitting diode, or the like as a light source can be suitably used. The “first optical system” is an optical system that forms a light beam from the light source unit into a long linear image in the main scanning corresponding direction. The first optical system can be configured as, for example, a combination of a coupling lens and a cylinder lens. The light beam from the first optical system is converged in the sub-scanning corresponding direction and formed as a long line image in the main scanning corresponding direction, but is "parallel light beam" in the main scanning corresponding direction.
Alternatively, it may be a "weakly converging light beam" or a "weakly diverging light beam".

The "optical deflector" has a deflecting / reflecting surface near the image forming position of the line image, and reflects a light beam from the first optical system by the deflecting / reflecting surface to deflect the reflected light beam. The direction in which the light beam deflected by the light deflector is displaced is referred to as a “scanning direction”, and the direction orthogonal to a plane ideally swept by the deflected light beam is referred to as a “scanning orthogonal direction”. The scanning direction corresponds to the aforementioned “main scanning corresponding direction” when considered on the optical path from the light source unit to the surface to be scanned, and the orthogonal scanning direction is the sub-scanning direction when considered on the optical path. A well-known "polygon mirror" can be used as the optical deflector.

The "second optical system" is an optical system for condensing the light beam deflected by the optical deflector as a light spot on the surface to be scanned. The light beam from the first optical system is a parallel light beam in the scanning direction. If so, a so-called fθ lens can be used. As the second optical system, a lens system having the above function (a single lens or a sub lens may be used) or a concave mirror having the above function can be used.

The "photodetector" detects a deflected light beam heading toward the optical scanning start position and emits an output. Based on the output, a synchronization signal for starting the optical scanning is generated. The "third optical system" guides the deflected light beam toward the optical scanning start position to the photodetector.

The first, second and third optical systems are separate from each other. The third optical system is a “single anamorphic lens”, and one surface thereof is a cylinder surface. This cylinder surface has a light condensing function in the scanning orthogonal direction. The lens surface on the side opposite to the cylinder surface is a convex spherical surface.

As described above, the light beam from the first optical system is a parallel light beam or a light beam having a weak convergence or a weak divergence in the main scanning corresponding direction, and the main scanning corresponding light near the deflecting reflection surface in the sub-scanning corresponding direction. The light beam deflected by the optical deflector is a parallel light beam or a weakly convergent or weakly divergent light beam in the scanning direction, and is divergent in the scanning orthogonal direction because it forms a long line image in the scanning direction. The divergence in the scanning orthogonal direction is stronger than that of. Therefore, in order to converge and guide the deflected light beam to the photodetector, the third optical system needs to be an anamorphic lens having different powers in the scanning direction and the scanning orthogonal direction. When a cylinder surface having a light condensing action in the scanning orthogonal direction and a convex spherical surface are combined in this manner, it is preferable that the cylinder surface having a light condensing action in the scanning orthogonal direction is directed to the photodetector side.

As described above, in the optical scanning optical system according to the first aspect, the third optical system is a "single anamorphic lens", and one surface thereof has a cylinder surface having a light condensing function in the scanning orthogonal direction. The other lens surface on the side opposite to the cylinder surface is a convex spherical surface. Instead of this, the other surface of the third optical system is replaced by a convex spherical surface, A cylinder surface having a light condensing function in the scanning direction may be used (claim 3). In this case, it is preferable to "turn the cylinder surface having the light condensing action in the scanning orthogonal direction to the photodetector side". Further, instead of the third optical system in the optical system configuration of the optical scanning optical system according to claim 1, one surface of the “single anamorphic lens” is a cylinder surface having a “diverging action in the scanning direction”, and the other surface. A surface having a convex spherical surface may be referred to as a “third optical system”. Further, the light condensing action of each surface of the third optical system can be adjusted so as to “guide the deflected light beam to a photodetector provided at a position close to the optical deflector from the surface to be scanned”. 6).

[0013]

FIG. 1 shows a "semiconductor laser".
The divergent light beam emitted from the light source unit 10 using the light source as a light source is coupled by a coupling lens 11a and converted into a parallel light beam or a weakly convergent or weakly divergent light beam. `` Polygon mirror ''
Is formed in the vicinity of the deflecting reflection surface 12a of the optical deflector 12 as a "long line image in the main scanning corresponding direction". The coupling lens 11a and the cylinder lens 11b constitute a "first optical system", but the first optical system is not limited to this mode, and may have another lens configuration. Deflective reflection surface 1
The light beam reflected by 2a becomes a deflected light beam that is deflected clockwise at a constant angular velocity as the light deflector 12 rotates at a constant speed in the direction of the arrow. The deflected light beam is condensed as a light spot on the scanned surface 14 by the second optical system 13,
Is optically scanned. The second optical system 13 has a function of equalizing the scanning speed of the light spot. The line image is a deflection reflection surface 1
2a, and the second optical system 13 forms a light spot on the surface to be scanned with the line image as an object point in the sub-scanning corresponding direction. Therefore, the optical scanning optical system of FIG. It has a function of correcting “surface tilt” of the surface 12a.

Although the second optical system 13 has a single lens configuration in the embodiment of FIG. 1, it may be composed of two or more lenses, and is composed of a concave mirror having an image forming function similar to these lenses. You can also. Needless to say, there is a cost advantage to forming the second optical system in a single lens configuration. The deflected light beam is supplied to the third optical system 1 prior to optical scanning by a light spot focused on the surface to be scanned by the second optical system.
5 and enters the optical deflector 17. When the light deflector 17 receives the deflected light beam in this way, it generates an output, and based on the output, generates a synchronization signal for starting optical scanning.
On the basis of this synchronization signal, optical scanning with the deflected light beam is started from the optical scanning start position A on the surface 14 to be scanned. In order to keep the optical scanning start position A constant, the synchronization signal must be stable. For this reason, the third optical system must form the deflected light beam toward the optical scanning start position A as a light spot having a spot diameter that is somewhat small on the light receiving surface of the photodetector. In order to generate a stable synchronization signal, it is better that the output of the photodetector is steep in time, but if the diameter of the light spot formed on the light receiving surface of the photodetector becomes large, the output of the photodetector will increase. This is because the temporal steepness is deteriorated and the synchronization signal becomes unstable.

Therefore, the light receiving surface of the photodetector 17 is positioned “near the image forming position of the deflected light beam” by the third optical system 15. If necessary, a knife edge or a slit may be provided between the light receiving surface and the third optical system 15 to restrict the deflecting light flux incident on the light receiving surface, thereby reducing the time sharpness of the output of the photodetector. These slits and knife edges may be provided integrally with the housing of the optical scanning optical system. The deflected light beam is a parallel light beam or a weakly convergent or divergent light beam in the scanning direction, and is divergent in the scanning orthogonal direction. Therefore, the deflected light beam is a light spot having an appropriate spot diameter on the light receiving surface of the photodetector. In order to form an image, it is necessary that the third optical system is an “anamorphic lens having a stronger positive power in the scanning orthogonal direction”. Although there are various methods for constructing such an anamorphic lens, in the present invention, a simple cylinder surface and a convex spherical surface are selected as surface shapes, with emphasis on the fact that the lens surface can be formed easily and accurately with low cost. At least one surface is a cylinder surface, and the other surface is a convex spherical surface or a cylinder surface. In the following description, it is assumed that the coupling lens in the first optical system is a collimating lens. Therefore, the light beam from the first optical system is a “parallel light beam in the main scanning corresponding direction”.

FIG. 2 shows a deflecting and reflecting surface 1 as a third optical system.
The third optical system 1 in which the 2a side is a “convex spherical surface” and the photodetector 17 side is a “cylinder surface having a light condensing action in the scanning orthogonal direction”.
The state of image formation (claims 1 and 2) when 5A is used is described in the scanning direction (FIG. 2A) and the scanning orthogonal direction (FIG. 2B).
It was shown about. In this way, by allocating the strong positive power required in the scanning orthogonal direction to the convex spherical surface and the cylinder surface, the light condensing power (positive power) on each surface can be reduced. In the case where the third optical system is manufactured by molding, the surface with lower power is less affected by molding errors. Accordingly, by dispersing the positive power in the scanning orthogonal direction to both surfaces and weakening the power of each surface, the influence of the molding error on the third optical system is reduced as compared with the case where one surface has a large power. It is hard to receive. Further, by setting the convex spherical surface on the deflecting / reflecting surface side, the focal length in the scanning direction becomes longer with respect to the photodetector at the same position, and the light spot formed on the light receiving surface of the photodetector 17 by the deflected light beam Increases the speed of crossing the light receiving surface, so that the temporal steepness of the output of the photodetector 17 is improved. Further, by directing the cylinder surface toward the photodetector, the lateral magnification in the scanning orthogonal direction can be reduced, and the effect of the tilting of the deflecting reflection surface can be reduced.

FIG. 3 shows a deflecting and reflecting surface 1 as a third optical system.
2a side is the “cylinder surface that has a light condensing function in the scanning direction”
The image formation state (claims 3 and 4) when the third optical system 15B in which the photodetector 17 side is a “cylinder surface having a light condensing action in the scanning orthogonal direction” is used in the scanning direction (FIG. )) And the scanning orthogonal direction ((b)). In this way, by allocating the positive power in the scanning orthogonal direction and the positive power in the scanning orthogonal direction to different cylinder surfaces, the light condensing action in the scanning direction and in the scanning orthogonal direction can be separated. Further, since each surface is a cylinder surface, the precision of optical axis alignment of both surfaces is relaxed, and manufacturing is facilitated. In addition, since the cylinder surface that has a light condensing effect in the scanning direction faces the deflecting reflection surface side,
The focal length in the scanning direction is longer than that of the photodetector at the same position, and the lateral magnification in the scanning orthogonal direction can be reduced by directing the cylinder surface having the light condensing function in the scanning orthogonal direction toward the photodetector. . Therefore, as in the case of the embodiment of FIG. 2, the output of the photodetector 17 has good temporal steepness, and is hardly affected by the tilting of the deflecting reflection surface.

FIG. 4 shows a deflecting and reflecting surface 1 as a third optical system.
The third optical system 15C in which the 2a side is a “convex spherical surface” and the photodetector 17 side is a “cylinder surface having a diverging action in the scanning direction”.
The state of image formation (claim 5) when using is shown in the scanning direction (FIG. 4A) and the scanning orthogonal direction (FIG. 4B).

As described above, the focal length in the scanning direction is extended by weakening the convergence in the scanning direction due to the convex spherical surface by the "cylinder surface having a diverging effect in the scanning direction", thereby improving the light flux condensing property in the scanning orthogonal direction. Is balanced, and the deflected light beam is collected near the light receiving surface of the photodetector 17. FIG. 5 shows a modification of the embodiment of FIG. In this embodiment, the surface of the third optical system 15D on the optical deflector side is a “cylinder surface having a diverging action in the scanning direction”, and the optical deflector side is a “convex spherical surface”. As in the embodiment shown in FIGS.
By making the lens surface of the optical system a combination of a cylinder surface and a convex spherical surface and giving the cylinder surface a "diverging effect in the scanning direction", the lens shape in the scanning direction becomes a positive meniscus shape. The image performance can be improved, the temporal steepness of the output of the photodetector can be increased, and the synchronization accuracy at the start of optical scanning can be improved.

By adjusting the action (light-collecting action or light-collecting action and diverging action) of each surface of the third optical system in the optical scanning optical system of the present invention, as shown in FIG. The position can be arranged at “a position close to the optical deflector from the surface to be scanned”. By doing so, the degree of freedom of the arrangement position of the photodetector is increased, and it is not necessary to provide the photodetector on the extension of the surface to be scanned. There is no need to adjust the relationship, and the optical scanning optical system can be made compact.

[0021]

As described above, according to the present invention, a novel optical scanning optical system can be realized. In the optical scanning optical system according to the present invention, the third optical system for guiding the deflected light beam to the photodetector for generating the synchronization signal is separate from the second optical system for condensing the deflected light beam on the surface to be scanned. The diameter of the second optical system can be made smaller than when the deflected light beam is guided to the photodetector via the second optical system, and each of the first to third optical systems is separately mounted on the housing. The mounting position of the optical system can be easily and accurately adjusted independently. Further, since a simple spherical surface such as a convex spherical surface and a cylinder surface or a cylinder surface and a cylinder surface is employed as the lens surface of the third optical system, the third optical system can be formed with high precision by molding, easily and at low cost. realizable.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an optical scanning optical system according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 2;

FIG. 3 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 4;

FIG. 4 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 5;

FIG. 5 is a diagram for explaining a characteristic portion of another embodiment of the invention described in claim 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source part 11a, 11b 1st optical system 12 Optical deflector 12a Deflection / reflection surface 13 2nd optical system 14 Scanning surface A Optical scanning start position 15 3rd optical system 17 Photodetector

Continuation of the front page (56) References JP-A-6-3610 (JP, A) JP-A-61-193116 (JP, A) JP-A-8-43754 (JP, A) JP-A-5-323221 (JP, A) , A) JP-A-7-281113 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (6)

(57) [Claims] A light source unit, a first optical system for forming a light beam from the light source unit into a long line image in the main scanning direction, and a deflecting / reflecting surface near an image forming position of the line image; An optical deflector for deflecting a light beam from the first optical system, a second optical system for condensing the deflected light beam as a light spot on a surface to be scanned, and detecting a deflected light beam toward an optical scanning start position; A photodetector for generating a synchronization signal for starting optical scanning, and a third optical system for guiding a deflected light beam toward the optical scanning start position to the photodetector; And the third optical system is separate from the other, the third optical system is a single anamorphic lens,
An optical scanning optical system characterized in that one of the surfaces is a cylinder surface, the cylinder surface has a light condensing function in a direction perpendicular to the scanning direction, and the lens surface opposite to the cylinder surface is a convex spherical surface. 2. The optical scanning optical system according to claim 1, wherein a cylinder surface of said third optical system having a light condensing function in a direction orthogonal to scanning is directed to a photodetector. system. 3. A light source unit, a first optical system for forming a light beam from the light source unit into a line image long in the main scanning direction, and a deflecting / reflecting surface near an image forming position of the line image; An optical deflector for deflecting a light beam from the first optical system, a second optical system for condensing the deflected light beam as a light spot on a surface to be scanned, and detecting a deflected light beam toward an optical scanning start position; A photodetector for generating a synchronization signal for starting optical scanning, and a third optical system for guiding a deflected light beam toward the optical scanning start position to the photodetector; And the third optical system is separate from the other, the third optical system is a single anamorphic lens,
An optical scanning optical system characterized in that one surface of the third optical system is a cylinder surface having a light condensing action in a scanning orthogonal direction, and the other surface is a cylinder surface having a light condensing action in a scanning direction. 4. An optical scanning optical system according to claim 3, wherein a cylinder surface of said third optical system having a light condensing function in a scanning orthogonal direction is directed to the photodetector. system. 5. A light source unit, a first optical system for forming a light beam from the light source unit into a long line image in the main scanning direction, and a deflecting / reflecting surface near an image forming position of the line image; An optical deflector for deflecting a light beam from the first optical system, a second optical system for condensing the deflected light beam as a light spot on a surface to be scanned, and detecting a deflected light beam toward an optical scanning start position; A photodetector for generating a synchronization signal for starting optical scanning, and a third optical system for guiding a deflected light beam toward the optical scanning start position to the photodetector; And the third optical system is separate from the other, the third optical system is a single anamorphic lens,
An optical scanning optical system characterized in that one surface is a cylinder surface, the cylinder surface has a diverging action in the scanning direction, and the other surface in the third optical system is a convex spherical surface. 6. The optical scanning optical system according to claim 1, wherein the third optical system includes a light beam deflected by a photodetector provided at a position close to the light deflector from the surface to be scanned. An optical scanning optical system characterized in that the operation of each surface is adjusted so as to guide the optical scanning.