JP3333651B2 - Optical scanning device - Google Patents

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.

[0002]

2. Description of the Related Art An optical scanning device that deflects a laser beam from a light source device by an optical deflector and condenses it as a light spot on a surface to be scanned by an imaging optical system is an optical printer or a digital copying machine. It is widely known in connection with machines.

In recent years, there has been a strong demand for high quality images in an image output device using such an optical scanning device. In the optical scanning device, the stability of the spot diameter of the optical spot that scans the surface to be scanned and the light spot of the optical spot have to be improved. Smaller diameters are intended.

In reducing the diameter of the light spot, there is a problem of how to make the processing accuracy and the assembly accuracy of each optical element constituting the optical system close to the design value.

In order to reduce the diameter of the light spot, it is important to match the beam waist position of the laser beam converging toward the surface to be scanned with the surface to be scanned. Generally, the beam waist position and the surface to be scanned are "displaced" due to the processing error and the assembly error, which makes it difficult to achieve the target specification.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides a novel optical scanning device capable of easily realizing a coincidence between a beam waist position of a deflected light beam and a surface to be scanned. Aim.

[0007]

According to an optical scanning apparatus of the present invention, "a laser beam from a light source device is formed into a long line image in a main scanning direction by an image forming element, and a deflecting reflection surface is provided near the line image. Is deflected at an equal angular velocity by an optical deflector having
An optical scanning device that performs uniform optical scanning by converging a deflected light beam as a light spot on a surface to be scanned by an imaging optical system for uniform scanning, characterized by the following points.

That is, an "imaging optical system for scanning at a constant speed" for condensing a deflected light beam on a surface to be scanned has a lens system, a cylindrical reflecting mirror and a plane mirror. Further, it has a cylindrical reflecting mirror adjusting means.

The "lens system" is a lens system having an fθ function in the main scanning corresponding direction and condensing the deflected light beam on the surface to be scanned in the main scanning corresponding direction.

Here, the "main scanning direction" corresponds in parallel with the main scanning direction on a virtual optical path obtained by linearly developing the optical path from the light source device to the surface to be scanned along the optical axis. The direction that is parallel to the sub-scanning direction on the virtual optical path is referred to as “sub-scanning corresponding direction”.

The "cylindrical reflecting mirror" has a positive power only in the sub-scanning direction and cooperates with the lens system to focus the deflected light beam on the surface to be scanned in the sub-scanning direction. It is.

Therefore, the deflected light beam is focused on the surface to be scanned by the lens system only in the main scanning direction, and is focused on the surface by the lens system and the cylindrical reflecting mirror in the sub-scanning direction. I do.

As described above, the imaging optical system for constant velocity scanning has a conjugate relationship between the line image and the surface to be scanned in the direction corresponding to the sub-scanning. Since the lens system has the “fθ function” in the main scanning direction, optical scanning is performed at a constant speed according to the fθ characteristics of the lens system.

The "plane mirror" is provided on the optical path from the lens system to the surface to be scanned, and bends the optical path in the direction corresponding to the sub-scan.

"Cylindrical reflector adjustment means" is means for moving and adjusting the cylindrical reflector in a predetermined direction in order to finely adjust the optical path length from the lens system to the surface to be scanned. This circle
The fine adjustment of the optical path length by the cylindrical reflector adjustment means
For displacement of beam waist of deflected light beam due to movement of reflector
Adjust the position between the beam waist position and the surface to be scanned.
It is done to "do."

The cylindrical mirror is moved and adjusted in the "predetermined direction" as described above. The predetermined direction may be various directions, and may be, for example, "the direction of the optical axis of the reflecting surface" (claim 2), or "the incidence of a light beam passing through the optical axis of the lens system and entering the cylindrical reflecting mirror". Direction ”(claim 3),
The “reflection direction of light rays that are incident on and reflected by the cylindrical reflecting mirror through the optical axis of the lens system” may be used.

Further, various known methods can be used for adjusting the movement of the cylindrical reflecting mirror by the adjusting means for adjusting the cylindrical reflecting mirror. Then, the surface is moved by sliding the surface with respect to the reference surface "(claim 5).

The position of the plane mirror is as described above.
The distance between the lens system and the surface to be scanned can be appropriately set, but “between the lens system and the cylindrical reflecting mirror” is preferable as the position of the plane mirror.

Further, it is possible to have "plane mirror adjusting means for swinging and adjusting the plane mirror about an axis parallel to the main scanning direction" (claim 7). The part can be independently adjusted for movement "(claim 8). The plane mirror adjusting means is a flat mirror.
Rotate the surface mirror by a small angle around the axis in the desired direction to adjust
Adjust. This adjustment is based on the assumption that the deflection of the deflected
The displacement of the beam waist position of the directional light beam is
Combined with beam waist displacement accompanying position adjustment,
The main scanning direction and sub-scanning direction of the deflected light beam to the surface to be scanned
To adjust the beam waist position of the direction.
The beam waist position adjusting method according to the present invention is a light source device.
These laser beams are lengthened in the main scanning direction by the imaging device.
Image, and has a deflecting / reflective surface near the line image.
Deflects light at a uniform angular velocity with a deflector
A light spot is formed on the surface to be scanned by an imaging optical system for fast scanning.
Optical scanning device that performs uniform speed optical scanning by focusing
The beam waist position of the deflected light beam to the surface to be scanned.
A method of adjusting by any one of claims 1 to 8
The method is performed by using the optical scanning device according to 1.
(Claim 9).

[0020]

As described above, in the optical scanning device of the present invention, the imaging optical system for scanning at a constant speed has a "cylindrical reflecting mirror", and the lens system is moved by adjusting the cylindrical reflecting mirror. Since the optical path length from to the scanned surface can be finely adjusted, the beam waist position of the deflected light beam can be finely adjusted with respect to the scanned surface.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments will be described below.

FIG. 1 schematically shows only an essential part of an optical scanning device according to an embodiment of the present invention. The light source device denoted by reference numeral 1 includes, for example, a semiconductor laser and a coupling lens that converts a divergent light beam from the semiconductor laser into a parallel light beam, and emits a parallel laser light beam.

The parallel laser beam emitted from the light source device 1 is condensed only in the sub-scanning corresponding direction by the cylinder lens 2 as an "imaging element", and is deflected by a rotary polygon mirror 3 as an "optical deflector". An image is formed near the reflection surface 4 as a long line image in the main scanning corresponding direction.

The light beam reflected by the deflecting / reflecting surface 4 is deflected at a constant angular velocity with the rotation of the rotary polygon mirror 3 in the direction of the arrow.
As a periodic deflection light beam, it enters the imaging optical system for constant speed scanning.

The imaging optical system for scanning at a constant speed includes a lens 5,
A “lens system” constituted by 6 and 7, a plane mirror 8,
And a cylindrical reflecting mirror 9. The deflected light beam first passes through the “lens system”, is reflected by the plane mirror 8, bends the optical path in the sub-scanning corresponding direction, and enters the cylindrical surface reflecting mirror 9.
The light is reflected by the cylindrical reflecting mirror 9 and condensed on the surface to be scanned 10 as a light spot, and the surface to be scanned 10 is optically scanned.

The cylindrical mirror 9 has "positive power" only in the direction corresponding to the sub-scan, and the plane mirror 8 has no power.
The light is condensed on the surface to be scanned 10 only by the “lens system” by 6 and 7. Since the “lens system” has the “fθ function” in the main scanning corresponding direction, the light spot moves at a constant speed.

The deflected light beam is converged on the surface to be scanned 10 by the "lens system" and the cylindrical reflecting mirror 9 in the direction corresponding to the sub-scanning.

The cylindrical reflecting mirror 9 can be moved and adjusted in a "predetermined direction" by an adjusting mechanism 11 which is "cylindrical reflecting mirror adjusting means".

On the other hand, the plane mirror 8 is disposed on the optical path "between the lens system and the cylindrical reflecting mirror 9" in this embodiment (claim 6), and the adjusting mechanism 1 as "plane mirror adjusting means".
According to 2, the swing adjustment can be performed about an axis l (passing through the mirror surface of the plane mirror 8) parallel to the main scanning corresponding direction (claim 7).

FIG. 2 shows a state in which the optical path from the deflecting / reflecting surface 4 to the surface to be scanned 10 is viewed from the direction corresponding to the main scanning.

Here, a specific example of an imaging optical system for scanning at a constant speed will be described. Counting from the deflection reflecting surface side, the radius of curvature of the i-th surface is “R _iS ” in the main scanning corresponding direction, “R _iM ” in the sub-scanning corresponding direction, and the radius of curvature of the i-th and (i + 1) -th surfaces. the distance on the optical axis D _i, the refractive index of the material of the j-th lens counted from the deflecting reflective surface represented by N _j. Further, D ₀ is the distance on the optical axis from the deflecting / reflecting surface 4 to the incident side surface of the lens 5.

Each numerical value is a value relative to the focal length when the entire system focal length is normalized to 100.

[0033] _{i R iS R iM D i j} N j 0 14.558 1 -22.393 -22.393 2.715 1 1.58700 2 -322.184 -322.184 1.147 3 -95.79 -95.79 5.633 2 1.70831 4 -31.253 -31.253 0.722 5 221.807 221.807 6.644 3 1.49483 6 -45.935 -45.935 14.4427 ∞ ∞ -76.48 (plane mirror) 8 ∞ 48.752 (cylindrical reflecting mirror).

[0034] 2, the angle of incidence of the plane mirror 8 and the cylindrical reflecting mirror 9: theta _1, the design value of theta _2, respectively, theta ₁
= 17.25 degrees and θ ₂ = 13 degrees.

Returning to FIG. 2, the cylindrical reflecting mirror 9 is positioned in the “direction of the optical axis of the reflecting surface”, that is, in the sub-scanning direction (in the plane of FIG. 2).
It is possible to adjust the movement in the intermediate direction between the incident light and the reflected light in the design in the above.

Even if the above optical element is assembled in accordance with the above numerical values, a processing error or an assembly error of the optical element actually occurs inevitably. Therefore, the condensing position of the deflected light beam, that is, the position of the beam waist is generally set. Deviates from the scanned surface 10 by a very small distance.

According to the experiment conducted by the inventor of the above embodiment, when the cylindrical reflecting mirror 9 is moved by 0.1 mm in the direction of the optical axis, the beam waist in the main scanning corresponding direction is changed due to the change in the optical path length accompanying the movement. Position is 0.196 at full image height
mm, the beam waist position in the direction corresponding to the sub-scanning was 0.092 mm at the entire image height, and it was found that the beam moved in the same direction as the moving direction of the cylindrical reflecting mirror 9 (to approach or move away from the surface to be scanned).

That is, the influence of the movement of the cylindrical reflecting mirror on the change of the beam waist position differs between the main scanning corresponding direction and the sub-scanning corresponding direction, and the main / sub scanning corresponding direction accompanying the movement of the cylindrical reflecting mirror. The ratio of the displacement amounts of the beam waist positions is “approximately 2: 1”.

Therefore, for example, when the beam waist position of the deflected light beam is deviated from the surface to be scanned by 0.1 mm in both the main and sub scanning directions, the movement adjustment amount d of the cylindrical reflecting mirror 9 is set to 0.07 mm. In this case, the surface to be scanned is located exactly halfway between the beam waist position in the main scanning corresponding direction and the beam waist position in the sub-scanning corresponding direction, so that the light spot diameter on the surface to be scanned is as designed. However, by further adjusting the amount of movement adjustment near d, a light spot having a desired shape can be realized with a size close to the designed light spot diameter. That is, the deviation of the beam waist position from the design value can be effectively reduced only by adjusting the movement of the cylindrical reflecting mirror (claims 1 to 4).

When the plane mirror 8 is rotated by a small angle around the axis l without displacing the cylindrical reflecting mirror 9, only the beam waist position in the sub-scanning corresponding direction is displaced by a small amount. .

That is, in the case of the above embodiment, when the plane mirror 8 is rotated by 0.1 degrees around the axis l, only the beam waist position in the sub-scanning corresponding direction becomes 0.2 at the full image height.
It was displaced by 64 mm. This is because, as the plane mirror 8 rotates, the angle of incidence of the deflected light beam on the cylindrical reflecting mirror 9 increases (decreases) by a very small angle in the direction corresponding to the sub-scanning, and the action of the power of the cylindrical reflecting mirror 9 increases ( Smaller).

Therefore, as in the above-described example, the beam waist position of the deflected light beam is 0.1 m in both the main and sub-scanning directions.
When the position is shifted by m from the surface to be scanned, the cylindrical reflecting mirror 9 is displaced by 0.51 mm (this causes the beam waist position in the main / sub-scanning corresponding direction to be displaced by about 0.1 mm and about 0.046 mm, respectively). By rotating the plane mirror 8 by 0.02 degrees (this changes only the beam waist position in the sub-scanning corresponding direction by approximately 0.0528 mm),
The beam waist position of the deflected light beam can be made substantially coincident with the surface to be scanned in both the main and sub-scanning directions.

Incidentally, with the above adjustment of the beam waist position, the position of the main scanning line (line drawn by scanning the light spot) is shifted in the sub-scanning direction. Such a shift can be measured in advance. Therefore, the correction can be performed by shifting the timing of starting writing by optical scanning.

FIG. 3 shows cylindrical reflecting mirrors 9A, 9B and 9C.
, Three types of movement adjustment directions are shown. FIG. 3 (a)
In the same manner as in the embodiment described with reference to FIGS. 1 and 2, the cylindrical surface reflecting mirror 9A in the direction of the optical axis of the reflecting surface (the surface obtained by connecting the optical axis of the cylindrical reflecting surface in the generatrix direction). Is adjusted (claim 2).

The cylindrical reflecting mirror 9B in FIG.
The movement is adjusted in the incident direction of the light beam passing through the optical axis of the “lens system” and entering the cylindrical reflecting mirror. Also,
The cylindrical surface reflecting mirror 9C in (c) is moved and adjusted in the direction of reflection of light rays that enter the cylindrical surface reflecting mirror and pass through the optical axis of the “lens system”. There is no significant difference in the movement adjustment in either direction.

The cylindrical reflecting mirrors 9A and 9 shown in FIG.
The side surfaces α, β, γ other than the reflection surface in B, 9C are “planes parallel to the movement direction for movement adjustment”, and these surfaces α, β, γ are slid with respect to the “reference plane”. When the cylindrical reflecting mirror adjusting means is configured to be moved by
Adjustment is easy.

FIG. 4 shows an example of the adjusting mechanism (cylindrical reflector adjusting means) indicated by reference numeral 11 in FIG. The cylindrical surface reflecting mirror 9A (see FIG. 3A) slides the side surface α on the “reference surface” which is the surface of the support member 110, so that the left-right direction in the drawing (the direction of the optical axis of the reflecting surface). It can move freely.

On the surface of the support member 110, the holding member 11
1 is provided. The upper part of the holding member 111 is a leaf spring 1
By pressing the upper side surface of the cylindrical reflecting mirror 9A, the cylindrical reflecting mirror 9A is pressed against the reference plane.

A compressible leaf spring 112 is interposed between the rising portion of the holding member 111 and the rear surface of the cylindrical reflecting mirror 9 to apply an elastic force to the cylindrical reflecting mirror 9A in the left direction in the drawing. Act.

An abutment piece 9A1 is protruded from the longitudinal end of the cylindrical reflecting mirror 9A. The contact piece 9A1 is attached to the tip of an adjusting screw 114 screwed into a threaded portion 113 planted on the surface of the support member 110. Abut

The cylindrical reflecting mirror 9A is moved in the horizontal direction in the figure by the adjusting screw 114, and the elastic force of the leaf spring 112 and the contact force of the adjusting screw 114 are balanced at a desired position. 9A can be moved and adjusted.

FIG. 4 shows a state of one end in the longitudinal direction of the cylindrical reflecting mirror 9A, and a similar adjusting mechanism is provided at the other end in the longitudinal direction. The adjustment can be performed independently at both ends in the longitudinal direction (claim 8).

In this manner, even when the image plane of the light spot is tilted, the correction can be performed.

FIG. 5 shows an example of the adjusting mechanism (plane mirror adjusting means) indicated by reference numeral 12 in FIG.

The stationary member 130 of the optical scanning device has a support surface formed in accordance with the design arrangement of the plane mirror 8, and the support member 122 is fixed to the support surface. A part of the support 122 is formed as a bearing 123 and holds a shaft 124 (the shaft 1 in FIG. 1).

The plane mirror 8 is fixedly held by a holding body 121, and a bearing formed as a part of the holding body 121 has a shaft 1.
24. Therefore, the plane mirror 8 is swingable about the axis 124. The geometric pivot axis of the shaft 124 coincides with the mirror surface of the plane mirror 8.

Compressible leaf springs 125 and 126 are interposed between the holder 121 and the support 122, and the support 122
The tip of the adjusting screw 127 screwed into the bent portion of the holder abuts a part of the holding body 122.

By adjusting the adjusting screw 127, the swinging of the plane mirror 8 about the axis 124 parallel to the main scanning corresponding direction can be performed.

[0059]

As described above, according to the present invention, a novel optical scanning device can be provided. Since the optical scanning device of the present invention is configured as described above, the deviation between the beam waist position of the deflected light beam and the surface to be scanned due to a processing error or an assembly error of the optical element is effectively corrected. A good light spot can be realized on the surface to be scanned, and good light scanning can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an optical path from a deflecting reflection surface to a surface to be scanned in the above embodiment as viewed from a main scanning corresponding direction.

FIG. 3 is a diagram showing three types of directions for moving and adjusting a cylindrical reflecting mirror;

FIG. 4 is a diagram illustrating an example of a cylindrical reflecting mirror adjusting unit.

FIG. 5 is a diagram for explaining an example of a plane mirror adjusting unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source device 2 cylinder lens (imaging element) 3 rotating polygon mirror (optical deflector) 4 deflecting reflecting surface 8 plane mirror 9 cylindrical reflecting mirror 10 scanning surface

Claims (9)

(57) [Claims] 1. A laser beam from a light source device is formed into a long line image in a main scanning direction by an image forming element, and is deflected at an equal angular velocity by an optical deflector having a deflecting / reflecting surface in the vicinity of the line image. In an optical scanning apparatus that performs uniform-speed optical scanning by condensing a deflected light beam as a light spot on a surface to be scanned by an imaging optical system for uniform-speed scanning, the imaging optical system for uniform-speed scanning includes: , Fθ in the main scanning corresponding direction
A lens system for focusing the deflected light beam on the surface to be scanned in the main scanning direction, and having a positive power only in the sub-scanning direction, and cooperating with the lens system to deflected the deflected light beam. A cylindrical reflecting mirror for focusing light on the surface to be scanned in the scanning corresponding direction, and a plane mirror disposed on an optical path from the lens system to the surface to be scanned and bending the optical path in the sub-scanning corresponding direction; the optical path length reaching the surface to be scanned from the system in order to fine-tune, have a cylindrical reflecting mirror adjusting means for moving and adjusting the cylindrical reflecting mirror in a predetermined direction, the deflection caused by the movement of the cylindrical reflector Beam waist of luminous flux
The beam waist position and the scanned surface
An optical scanning device , wherein the position of the optical scanning device can be adjusted . 2. The optical scanning device according to claim 1, wherein the direction of movement adjustment of the cylindrical reflecting mirror is in the direction of the optical axis of the reflecting surface. 3. The optical scanning device according to claim 1, wherein the direction of movement adjustment of the cylindrical surface reflecting mirror is an incident direction of a light beam passing through the optical axis of the lens system and entering the cylindrical surface reflecting mirror. Optical scanning device. 4. The optical scanning device according to claim 1, wherein the direction of movement adjustment of the cylindrical surface reflecting mirror is a reflection direction of a light beam that passes through the optical axis of the lens system and is incident on and reflected by the cylindrical surface reflecting mirror. An optical scanning device characterized by the above-mentioned. 5. The optical scanning device according to claim 1, wherein the cylindrical reflecting mirror has a surface parallel to a movement direction for movement adjustment, and this surface is positioned with respect to a reference surface. An optical scanning device, wherein a cylindrical reflecting mirror adjusting means is configured to be moved by sliding. 6. The optical scanning device according to claim 1, wherein the plane mirror is provided between the lens system and the cylindrical reflecting mirror. 7. The optical scanning device according to any one of claims 1 to 6, have a plane mirror adjusting means for swinging adjustment about an axis parallel to the plane mirror in the main scanning corresponding direction, of the plane mirror Sub-scanning direction of deflected light beam due to minute rotation
The beam waist position is adjusted by adjusting the position of the cylindrical mirror.
Scanning in combination with beam waist displacement accompanying adjustment
Of the deflected light beam to the surface in the main scanning direction and sub-scanning direction.
An optical scanning device wherein the position of a beam waist is adjustable . 8. The optical scanning device according to claim 1, wherein both ends of the cylindrical reflecting mirror in the longitudinal direction can be independently adjusted. apparatus. 9. A laser beam from a light source device is applied to an image forming element.
Form a line image longer in the main scanning corresponding direction, and
At constant angular velocity by an optical deflector with a deflecting / reflecting surface in the vicinity
And deflects the deflected light beam by an imaging optical system for scanning at a constant speed.
Light scanning at uniform speed by condensing as a light spot on the scanning surface
Beam waist of the deflected light beam
A method for adjusting a position with respect to the surface to be scanned, wherein the position is adjusted using the optical scanning device according to any one of claims 1 to 8.
Beam waist in an optical scanning device
Position adjustment method.