JPH09197317A - Optical scanning device and lens unit for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of components of the optical system of an optical scanning device and to reduce the cost of the optical scanning device by integrating three kinds of lens into a unit. SOLUTION: A cylinder lens 16 converges luminous flux, which is coupled by a coupling lens 12, in a sub-scan corresponding direction to form a linear image which is long in a mainscan corresponding direction. Further, a scan imaging lens 20 converges deflected luminous flux, which is deflected at an equal angular speed by an optical deflector having a deflection reflecting surface 18 nearby the image formation position of the linear image on a scanned surface to equalize the speed of an optical scan on the scanned surface. Further, a synchronizing lens 22 converges the deflected luminous flux on a synchronous optical detecting element 28 which detects the deflected luminous flux which is deflected by the optical deflector to travel to an effective image area. Those cylinder lens 16, scan imaging lens 20, and synchronizing lens 22 are integrated successively in the main scan corresponding direction to constitute the lens unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device and a lens unit for the optical scanning device.

[0002]

2. Description of the Related Art Optical scanning devices generally include four types of lenses. That is, generally a semiconductor laser (abbreviated as LD)
Is a "coupling lens" for coupling the light flux from the light source, the coupled light flux is expanded in the sub-scanning corresponding direction (the optical path from the light source to the scanned surface is linearly expanded along the optical axis of the optical system. It converges in a direction parallel to the sub-scanning direction on the virtual optical path) and forms a long line image in the main scanning corresponding direction (direction parallel to the main scanning direction on the virtual optical path). "Cylinder lens" for forming an image, a deflected light beam deflected at a constant angular velocity by an optical deflector having a deflecting / reflecting surface in the vicinity of the image forming position of the above line image is condensed toward the surface to be scanned, and optical scanning of the surface to be scanned "Scanning imaging lens" for uniform speed
There are four types of "synchronous lens" for converging the deflected light flux toward the effective image area toward the synchronous light detecting element.

Recently, in order to reduce the cost of an optical scanning device, it has been proposed to integrate one or more of these four types of lenses as a lens unit. For example, Japanese Patent Laid-Open No. 3-274016 discloses a lens unit in which a collimating lens that is a coupling, a synchronizing lens, and a scanning imaging lens are integrated.

When this lens unit is molded with a plastic material, if the focal length of the collimator lens changes due to the influence of temperature and humidity, the image forming position of the optical scanning beam with respect to the surface to be scanned changes greatly. An expensive control means for controlling the temperature / humidity inside the optical scanning device to a predetermined state is required to suppress the fluctuation of the light spot diameter due to the fluctuation of humidity. Therefore, although such a lens unit can reduce the cost of the lens system, the cost of the optical scanning device as a whole may be rather high.

[0005]

In view of the above-mentioned circumstances, the present invention aims to reduce the cost of the lens unit and the optical scanning device itself by integrating a plurality of lenses as a lens unit in the optical scanning device. To do.

[0006]

A lens unit for an optical scanning device according to the present invention comprises a cylinder lens, a scanning imaging lens, and a synchronous lens, which are integrated with each other (claim 1).

The "cylinder lens" is a lens which converges the light beam emitted from the light source and coupled by the coupling lens in the sub-scanning corresponding direction to form a long line image in the main-scanning corresponding direction. The coupled light beam may be a “parallel light beam” or a “weakly divergent light beam or a weakly convergent light beam”.

The "scanning / imaging lens" condenses a deflected light beam deflected at a constant angular velocity by an optical deflector having a deflecting / reflecting surface in the vicinity of an image forming position of a line image toward a surface to be scanned and scans the surface to be scanned. It is a lens that makes the optical scanning of the surface uniform.

The "synchronous lens" collects the deflected light beam toward a synchronous light detecting element which detects the deflected light beam deflected by the optical deflector and directed to the effective image region (the region where the optical scanning should be effectively performed). It is a lens.

As described above, in the lens unit of the present invention, the "coupling lens for coupling the light flux from the light source" is not unitized.

The cylinder lens, the scanning imaging lens and the synchronizing lens which are unitized are integrated in a state where they are connected to each other in the main scanning corresponding direction. In that case, the order may be, for example, the order of the cylinder lens, the scanning imaging lens, and the synchronous lens, or may be the order that "the synchronous lens is sandwiched between the cylinder lens and the scanning imaging lens" (claim 2). .

In the ordinary optical arrangement, when the cylinder lens and the scanning lens are separately provided, a space is formed between the two lenses. However, when the three lenses are integrated in the same order as the lens unit according to claim 2. By disposing the synchronous lens in the space, the space can be effectively used without waste.

In the lens unit according to the second aspect, the angle formed by the light beam incident on the optical deflector with the optical axis of the scanning imaging lens is θ _i , the maximum angle of view of the effective image area is θ _S , and the light is deflected and reflected from the cylinder lens. the distance reaching the surface l _0, the maximum angle of view: theta first side of the deflected deflected light beam scanning and imaging lens _S distance between the position and the deflection reflecting surface is incident on (the surface of the optical deflector side) When the component of the scanning imaging lens in the optical axis direction is l ₁ , these conditions are: (1) 5 mm <l ₀ (θ _i −θ _S ) <40 mm (2) | l ₀ · cos θ _S −l ₁ | < It is desirable to satisfy 20 mm 2 (Claim 3).

The lens unit for the optical scanning device according to the first aspect, the second aspect, or the third aspect can be manufactured by molding glass, and can be manufactured by "integral molding with plastic". Yes (claim 4).

The optical scanning device according to the present invention includes: "A light beam from a light source is coupled by a coupling lens, and the coupled light beam is condensed by a cylinder lens in the sub-scanning corresponding direction to form a long line image in the main-scanning corresponding direction. To form an image on the scanning line, and deflect the beam at a constant angular velocity by an optical deflector having a deflecting / reflecting surface near the image forming position of the line image. An optical scanning device for performing constant-speed optical scanning of a surface, which has a synchronous lens for converging the deflected light beam toward a synchronous light detection element for detecting the deflected light beam toward the effective image area, and a cylinder lens The lens unit for an optical scanning device according to claim 1 or 2 or 3 or 4 is used as the scanning and imaging lens and the synchronizing lens (claim 5).

In the optical scanning device according to the fifth aspect, "a circuit for arranging a synchronous light detecting element in the vicinity of the LD which is a light source, and a circuit for controlling light emission of the LD and a detecting circuit for the synchronous light detecting element are provided on the same circuit board. Can be provided ”(Claim 6). Of course, in the optical scanning device of the sixth aspect, the arrangement of the three lenses in the lens unit is the lens arrangement of the lens unit of the second aspect.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an embodiment of the invention described in claims 1-6. The divergent light beam emitted from the LD 10 which is the light source is coupled by the coupling lens 12 to be a parallel light beam, a weak convergent light beam, or a weak divergent light beam. Since the coupling lens 12 is made of optical glass, it is hardly affected by temperature and humidity.

The coupled light beam passes through the beam shaping aperture 14 and has a positive power only in the sub-scanning corresponding direction (direction orthogonal to the drawing).
The light is condensed by 6 to form a long line image in the main scanning corresponding direction in the vicinity of the deflection reflection surface 18 of the optical deflector. As the optical deflector, a known one such as a polygon mirror, a rotating single-sided mirror, a rotating double-sided mirror or the like can be appropriately used. In this embodiment, a rotating single-sided mirror is assumed, and the line image is the rotation axis of the deflective reflection surface 18. The image is formed so that the position of 18A is the center of the line image in the longitudinal direction.

The light beam reflected by the deflecting / reflecting surface 18 is deflected in a clockwise direction at a constant angular velocity as the deflecting / reflecting surface 18 rotates (clockwise). The polarized light beam first enters the synchronous lens 22. The synchronous lens 22 condenses the incident deflected light flux toward the synchronous light detecting element 28 (light receiving element). The condensed light flux passes through the synchronizing slit 30 and enters the synchronizing light detecting element 28, and a light receiving signal is emitted from the synchronizing light detecting element 28. The angle θd in FIG. 1 is the angle formed by the principal ray of the deflected light beam and the optical axis of the scanning imaging lens 20 at this time.

The deflected light beam is further deflected and enters the scanning and imaging lens 20. The scanning imaging lens 20 focuses the deflected light beam toward the surface to be scanned 26. Scanning imaging lens 20
The deflected light flux condensed by the above forms a light spot on the surface to be scanned 26, and the light spot scans the surface to be scanned 26.

When the light spot reaches a position P (light scanning start position) on the surface to be scanned 26, which is separated by W / 2 from the optical axis 24 of the scanning imaging lens 20, optical scanning is started. That is,
The optical scanning is synchronized so that the optical scanning is started at the optical scanning start position P based on the light reception signal generated by the synchronous light detection element 28. The “W” is an effective image area. The scanning / imaging lens 20 has a function of making the optical scanning by the light spot uniform in the effective image area.

Now, in the embodiment shown in FIG. 1, a cylinder lens 16 for converging the light beam coupled by the coupling lens 12 in the sub-scanning corresponding direction to form a long line image in the main scanning corresponding direction, A scan for converging a deflected light beam deflected at a constant angular velocity by an optical deflector having a deflecting / reflecting surface 18 in the vicinity of the image forming position of a line image toward a surface to be scanned to make the optical scanning of the surface to be scanned at a constant speed. The image forming lens 20 and the synchronous lens 22 that collects the deflected light beam toward the synchronous light detection element 28 that detects the deflected light beam that is deflected by the optical deflector and travels toward the effective image area are described as "continuous in the main scanning corresponding direction. Unity "
And constitutes a "lens unit" (claim 1).
This lens unit is "integrally molded from plastic"
(Claim 4).

Assuming that the focal length of the coupling lens 12 is f _C and the focal length of the scanning imaging lens 20 in the main scanning corresponding direction is f _m , when the coupled light flux is a parallel light flux, "lateral magnification" in the main scanning corresponding direction by the scanning and imaging lens 20 (f _m /
f _C ) (since the cylinder lens 16 has no power in the main scanning corresponding direction, it does not affect the above magnification), and the “vertical magnification” in the main scanning corresponding direction is (f _m / f _C ) ² . Usually f _m
Since >> f _C , the vertical magnification becomes large. If the coupling lens 12 is made of plastic,
When the focal length: f _C fluctuates due to the influence of humidity, the vertical magnification largely fluctuates, and the light spot diameter fluctuates greatly in the main scanning direction.

In the embodiment shown in FIG. 1, since the coupling lens 12 is formed separately from the lens unit, the coupling lens is made of a glass material which is not affected by temperature and humidity while the lens unit is made of plastic. Therefore, it is possible to effectively reduce the problem of the fluctuation of the light spot diameter in the main scanning direction due to the above-mentioned “variation of the focal length of the coupling lens”.

The "longitudinal magnification in the sub-scanning corresponding direction" of the lens system including the coupling lens 12, the cylinder lens 16 and the scanning imaging lens 20 is generally smaller than the vertical magnification in the main scanning corresponding direction. Therefore, the influence of temperature and humidity on the cylinder lens is small with respect to the vertical magnification in the sub-scanning corresponding direction. Therefore, the cylinder lens can be made plastic.

As shown in FIG. 1, the lens unit has a form in which a synchronous lens 22 is integrated so as to be sandwiched between the cylinder lens 16 and the scanning imaging lens 20 (claim 2). That is, the synchronization lens 22 is provided in the space formed between the cylinder lens 16 and the scanning imaging lens 20.
Is provided and the cylinder lens 16 and the scanning imaging lens 20 are connected and integrated by the synchronous lens 22, so that the above-mentioned space portion is effectively used.

The "length in the lens connecting direction" of the lens unit can be shortened as compared with the case where the synchronous lens 22 is arranged on the side opposite to the cylinder lens 16 with respect to the scanning imaging lens 29 while leaving the above space as it is. The unit can be made compact.

FIG. 2 shows the positional relationship between the lens unit and the deflecting / reflecting surface 18 in the embodiment of FIG.
As illustrated, the cylinder lens 16 is deflected to the deflecting / reflecting surface 18
Maximum distance leading to the starting point 18A of the deflection of the "l _0", the angle which the light beam makes with the scanning and imaging lens optical axis 24 via the cylindrical lens 16 is incident on the light deflector "theta _i", the effective image area of the In the direction of the optical axis 24, the distance between the deflection reflection surface 18 and the incident position b of the deflected light beam deflected at the angle of view “θ _S ” and the maximum angle of view: θ _S on the first surface of the scanning imaging lens 20. Let the component be "l ₁ ". In addition, when the intersection point (the principal ray) of the deflected light beam deflected at the maximum angle of view: θ _S is a, the arc CR having the origin of the deflection by the deflecting / reflecting surface 18 as the center and having the radius of l ₀ is “ The component of the “distance between points a and b” in the direction of the optical axis 24 is “m”.

Then, the distance S between the center "c" of the cylinder lens 16 in the main scanning corresponding direction and the point "a" is represented by "S≈l ₀ (θ _i -θ _S )". If the distance: S exceeds the upper limit value of 40 mm of the condition (1): 40 mm, the length in the main scanning corresponding direction as the lens unit becomes long, the cost of materials and molding technology becomes high, and the merit of unitization disappears. When the lower limit value of the condition (1) is less than 4 mm, the synchronous lens 2 is provided between the cylinder lens 16 and the scanning imaging lens 20.
2 becomes difficult to deploy.

“M” is given by “(l ₀ · cos θ _S −l ₁ )”, and when | m | exceeds the upper limit value of the condition (2): 20 mm, the cylinder lens 16 and the scanning imaging lens 20 are separated. Due to the positional relationship, it becomes difficult to integrate them via the synchronous lens 22, and if they are attempted to be integrated by force, the lens unit becomes long, the cost of materials and molding technology increases, and the merit of unitization disappears.

FIG. 3 shows the LD1 in the embodiment of FIG.
FIG. 3 is a diagram for explaining a state in the vicinity of 0 and the synchronous light detecting element 28. The LD 10 and the coupling lens 12 are unitized as a light source unit 40, and a housing 50
It is provided in. The synchronous light detecting element 28 is arranged in the vicinity of the LD 10, and a circuit (not shown) for controlling the light emission of the LD 10 and a detecting circuit (not shown) for the synchronous light detecting element 28.
Are provided on the same circuit board 60 (claim 6).
With such a configuration, it becomes possible to further reduce the size and cost of the optical scanning device.

[0032]

As described above, according to the present invention, the optical scanning device and the lens unit for the optical scanning device can be realized. In the lens unit according to the first to fourth aspects, the three types of lenses are integrated into a unit, and the number of parts of the optical system in the optical scanning device is reduced, thereby enabling a large cost reduction of the optical scanning device.

The lens unit according to claim 4 is easy to manufacture, and the positional accuracy between the three types of lenses is improved by sufficiently increasing the positional accuracy between the lenses in the manufacturing die. Enables easy assembly of the lens.

The optical scanning device according to claims 5 and 6 enables cost reduction and downsizing of the device.

[Brief description of drawings]

FIG. 1 is a diagram for describing one embodiment of the present invention.

FIG. 2 is a diagram for explaining conditions (1) and (2) of the invention according to claim 3 in the form of FIG.

FIG. 3 is a diagram illustrating a characteristic part of the invention according to claim 6 in the form of FIG. 1;

[Explanation of symbols]

 10 LD (Light Source) 12 Coupling Lens 16 Cylinder Lens 18 Deflection / Reflection Surface 20 Scanning Imaging Lens 22 Synchronization Lens 26 Scanned Surface

Claims (6)

[Claims] 1. A cylinder lens for converging a light beam emitted from a light source and coupled by a coupling lens in a sub-scanning corresponding direction to form a long line image in the main scanning corresponding direction, and an image formation of the line image. A scanning imaging lens for converging a deflected light beam deflected at a constant angular velocity by a light deflector having a deflecting / reflecting surface in the vicinity of the position toward a surface to be scanned to make optical scanning of the surface to be scanned at a constant speed. A synchronous lens that condenses the deflected light beam toward a synchronous light detection element that detects the deflected light beam that is deflected by the optical deflector and heads for the effective image area is integrated in a line in the main scanning corresponding direction. A lens unit for a characteristic optical scanning device. 2. A lens unit for an optical scanning device according to claim 1, wherein the synchronizing lens is integrated so that the cylinder lens and the scanning imaging lens are sandwiched therebetween. Lens unit for. 3. The lens unit for an optical scanning device according to claim 2, wherein an angle formed by a light beam incident on the optical deflector with the optical axis of the scanning imaging lens is θ _i , and a maximum angle of view of the effective image area is θ _S. , The distance from the cylinder lens to the deflecting / reflecting surface is l ₀ , and the distance between the deflecting / reflecting surface and the position where the deflected light beam deflected at the maximum angle of view: θ _S is incident on the first surface of the scanning imaging lens. When the component in the optical axis direction of the scanning / imaging lens is l ₁ , these conditions are: (1) 5 mm <l ₀ (θ _i −θ _S ) <40 mm (2) | l ₀ · cos θ _S −l ₁ | A lens unit for an optical scanning device, which satisfies <20 mm. 4. A lens unit for an optical scanning device according to claim 1, 2, or 3, wherein the lens unit is integrally molded of plastic. 5. A light beam from a light source is coupled by a coupling lens, and the coupled light beam is condensed by a cylinder lens in a sub-scanning corresponding direction to form a long line image in the main-scanning corresponding direction. An optical deflector having a deflecting / reflecting surface in the vicinity of the image forming position of the line image deflects it at a constant angular velocity, and the deflected light beam is condensed toward the surface to be scanned by the scanning image forming lens. In an optical scanning device for performing optical scanning, a synchronous lens for condensing the deflected light beam toward a synchronous light detecting element for detecting the deflected light beam toward the effective image area is provided, and the cylinder lens, the scanning imaging lens, and the synchronous lens. An optical scanning device comprising: a lens unit for an optical scanning device according to claim 1 or 2 or 3 or 4. 6. The optical scanning device according to claim 5, wherein a synchronous light detecting element is provided in the vicinity of the LD which is a light source, and the circuit for controlling the emission of the LD and the detecting circuit for the synchronous light detecting element are the same. An optical scanning device provided on a circuit board.