JP2672582B2 - Light beam scanning device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning device for scanning with a light beam, and more particularly to a light beam scanning device used in, for example, a laser beam printer.

[Conventional technology]

In a scanning device using a light beam, a rotary polygon mirror (polygon mirror) is often used as a light beam deflecting device. Such a rotating polygon mirror has its polarization plane (anti-slope) tilted (tilted) with respect to the plane parallel to the rotation axis due to dimensional errors that are unavoidable in manufacturing. That is, the light beam shifts in the direction perpendicular to the scanning direction, causing unevenness in the pitch of the scanning line. To correct this, a method of using an imaging optical system in which a deflecting surface and a surface to be scanned (for example, a photosensitive drum surface) have a conjugate relationship in a plane perpendicular to the scanning direction is disclosed in, for example, Japanese Patent Laid-Open No. 52-2866
It is known from publication No. 6.

Further, the optical system of the scanning device has a characteristic (generally referred to as f.theta. Characteristic) for the light beam to scan the surface to be scanned at a constant speed in the plane in the scanning direction, and The ability to correct the field curvature so that the spot diameter of the light beam is always uniform with respect to the position in the scanning direction is also required.

As described above, in order to simultaneously realize the characteristics in the plane in the scanning direction and the characteristics in the plane perpendicular to this, an optical system having different powers in both planes is required, and a cylinder lens or the like is used.

On the other hand, in order to make the optical system compact, it is desirable to reduce the number of lenses and make the configuration as simple as possible. As an optical system in which the number of lenses is reduced and the configuration is simplified while correcting the above-mentioned troubles, for example, JP-A-58-93021 is available.
A single lens having a spherical single lens and a long cylinder lens as disclosed in Japanese Patent Publication No. 57-144515, and a single lens having a spherical single lens and a toric surface (toroidal surface) as disclosed in Japanese Patent Laid-Open No. 144515/1982. It is known that it is composed of.

[Problems to be solved by the invention]

Although the conventional optical system disclosed in the above-mentioned Japanese Patent Laid-Open No. 58-93021 has a simple lens structure, when such an optical system is used for high resolution, it is particularly useful for a surface perpendicular to the scanning plane (hereinafter referred to as a sub-surface). The field curvature in the scanning direction) becomes large. For this reason, when the spot diameter is reduced for high resolution, the smaller the focusing spot diameter is, the larger the spread of the light beam diameter near the focusing point along the optical axis is. There was a problem of becoming prominent.

FIG. 23 is a diagram showing how the long cylinder lens 70 causes field curvature in the sub-scanning direction. As shown,
The beam 71 incident on the scanning center is focused on the surface 74 to be scanned, whereas the beam 72 incident on the scanning end forms an angle θ, so that the beam obliquely passes through the surface of the cylinder lens 70, so that it is apparent. The curvature of the image becomes stronger and the image curvature 73 is generated. Therefore, in order to reduce the field curvature, it is necessary to make the deflection angle θ as small as possible, and depending on the applicable paper size, the optical path length from the deflecting device to the scanned surface becomes enormous and the optical system can be downsized. Absent.

On the other hand, the other example of the prior art described above (Japanese Patent Laid-Open No. 57-
In Japanese Patent No. 144515), a toric surface (toroidal surface) is used in place of the cylindrical lens to perform the tilt correction. Since the toric surface also has a curvature in the scanning direction, the occurrence of field curvature in the sub-scanning direction is alleviated, the lens can be arranged close to the deflector, and the optical system can be made compact. The remaining field curvature in the sub-scanning direction is corrected by the concave cylindrical surface formed on the back surface of the toric surface.

However, when correcting the field curvature in the sub-scanning direction with one cylindrical surface as described above, there is no problem if the deflection angle is as small as ± 20 °, but if the deflection angle is further increased, higher-order aberrations occur. However, the field curvature in the sub-scanning direction largely occurs as shown in FIG. Note that in FIG. 24, the vertical axis represents the relative scanning position, and the maximum scanning position 1.
0 corresponds to a deflection angle of ± 30 ° and a scanning width of ± 148.5 mm.

Further, this conventional technique uses a lens whose toric surface (toroidal surface) and its back surface are cylindrical surfaces. Since the toric surface (toroidal surface) has different curvatures in the scanning direction and in the direction perpendicular to it, it is difficult to process. In addition, the other surface of the lens is a cylindrical surface, so it is different from the toric surface. There is a problem that it is very difficult to exactly match the optical axes of the cylindrical surfaces in terms of lens processing technology.

Therefore, a toric lens having a toric surface and a cylindrical surface becomes very expensive, and there is a disadvantage that the manufacturing cost of the optical system increases.

The present invention has been made in view of the above points, and its object is to reduce the curvature of field as much as possible while having a compact structure, and to be compatible with a large polarization angle and high resolution, Another object of the present invention is to provide a light beam scanning device that can be manufactured at low cost.

[Means for solving the problem]

The above-described object of the present invention is to provide a light beam generator and a first image forming linear image of the light beam generated from the light beam generator.
Optical system, a deflecting device that deflects and reflects the linear light beam, a second optical system that focuses the light beam deflected by the deflecting device onto the object to be scanned, and the object to be scanned. In the light beam scanning device based on the premise that one of the surfaces is a spherical surface having a negative power and the other surface is perpendicular to the scanning direction in order from the deflection device. The first lens, which is a cylindrical surface having negative power only, and one of the surfaces is a cylindrical surface having negative power only in the direction perpendicular to the scanning direction, and the other surface is a flat surface, Alternatively, a second lens, both surfaces of which are cylindrical surfaces having negative power only in a direction perpendicular to the scanning direction, and a surface on the side of the deflecting device are flat surfaces of the object to be scanned are relatively large in the scanning direction. Positive power at radius of curvature And a radius of curvature of a cylindrical surface of the first lens, which is composed of a third lens that is a surface (toroidal surface) having a positive power with a relatively small radius of curvature in a direction perpendicular to the scanning direction. To R ₃ ,
When the radius of curvature of the cylindrical surface of the second lens is represented by R ₄ , it is achieved by setting (1 / R ₃ )> (1 / R ₄ ).

Here, the above-mentioned toroidal surface is a donut-shaped surface having an arc having a relatively large radius of curvature in the cross section in the main scanning direction and having a relatively small radius of curvature in the cross section in the sub-scanning direction. I mean.

(Operation)

In the above-described configuration, the radius of curvature of the spherical surface of the first lens, the radius of curvature of the toroidal surface of the third lens in the cross section in the main scanning direction, the distance from the first lens to the deflection device, and The distance from the third lens to the first lens mainly corrects the field curvature and linearity in the main scanning direction.

In addition, the deflecting device is mainly based on the radius of curvature of the cylindrical surface of the first lens, the radius of curvature of the cylindrical surface of the second lens, and the radius of curvature of the toroidal surface of the third lens in the sub-scanning cross-sectional direction. The reflective surface and the surface to be scanned are made to have a substantially conjugate relationship in the cross section in the sub-scanning direction to prevent fluctuation of the scanning position of the light beam due to tilting (surface tilting) of the reflecting surface of the deflecting device.

Furthermore, the curvature of field in the sub-scanning direction is corrected by adjusting the radius of curvature of the cylindrical surface having negative power of the first lens and the radius of curvature of the cylindrical surface having negative power of the second lens. There is.

Furthermore, when the radius of curvature of the cylindrical surface of the first lens is represented by R ₃ and the radius of curvature of the cylindrical surface of the second lens is represented by R ₄ , (1 / R ₃ )> (1 / R ₄ ) As a result, the field curvature in the sub-scanning direction is corrected to be sufficiently small so as to be compatible with a wide deflection angle and high resolution.

By making the surface of the third lens on the deflecting device side a flat surface, the manufacture of the third lens having a toroidal surface is facilitated and the cost of the lens is reduced.

〔Example〕

 Hereinafter, the present invention will be described with reference to illustrated embodiments.

FIG. 1 is a perspective view of a light beam scanning device according to an embodiment of the present invention. The first optical system includes a light source 4, a coupling lens 5, and a cylindrical lens 6, and a rotary polygon mirror 8 driven by a motor 7. A first lens 1 having one cylindrical surface 1a and the other spherical surface 1b, and a second lens 2 having one cylindrical surface 2a and the other flat surface 2b,
The second optical system is composed of a third lens 3 one of which is a flat surface 3a and the other of which is a toroidal surface 3b, and an object to be scanned (for example, a photosensitive drum) 9.

Next, the details of each will be described. The light source 4 is a semiconductor laser in this embodiment, and divergent light is emitted from the beam from the light source 4. The coupling lens 5 collimates the divergent light into a substantially parallel light beam, and adjusts its position to focus the light beams (10a to 10c) on the surface of the object 9 to be scanned within the cross section in the main scanning direction. To focus on. Cylindrical lens 6 is shown in Fig. 2 (where
FIG. 2 is a development configuration diagram of a cross section in the sub-scanning direction of FIG. ), The light beam 10d has a power only in the cross section in the sub-scanning direction, and the light beam 10d is reflected by the reflecting surface 11
Focus once above. At this time, the cylindrical lens 6
Has no power in the cross section in the main scanning direction, and therefore forms a line image on the reflecting surface 11 as shown in FIG. (Note that
The cross section of the lens system in the sub-scanning direction refers to a surface that is perpendicular to the main scanning surface and that includes the optical axis or the deflection optical axis. The polygon mirror 8 of the deflecting device rotates in the direction of the arrow in FIG. 1, and the light beam is deflected as 10a → 10b → 10c by changing the reflection angle of the reflecting surface 11. Scanning is performed once while irradiating one reflecting surface with the light beam, and scanning is performed by the number of reflecting surfaces while the polygon mirror 8 makes one rotation. In this embodiment, the deflection angle of the light beam is ± 30 °.
The deflection scanning of the light beam is performed in a plane (main scanning plane) substantially perpendicular to the rotation axis of the deflecting device (that is, the rotation center axis of the polygon mirror 8), and the optical axis from the light source 4 to the cylindrical lens 6 is the same. Are arranged so as to be in the main scanning plane.

In the second optical system (hereinafter referred to as a deflection system) arranged between the deflecting device and the object to be scanned 9, the first optical system
Lens 1 has one surface, a cylindrical surface 1a
Are arranged so that the direction having the power of 1 corresponds to the sub-scanning direction of the optical system. In the first lens 1, the cylindrical surface 1a functions to correct the field curvature in the sub-scanning direction, and the spherical surface 1b on the other surface mainly corrects the field curvature and the linearity in the main scanning direction, as described later. Work.

The second lens 2 is arranged so that the direction having the power of the cylindrical surface 2a, which is one surface thereof, coincides with the sub-scanning direction of the optical system.
Cooperates with the cylindrical surface 1a to correct the field curvature in the sub-scanning direction.

The third lens 3 is arranged so that the direction with a relatively large radius of curvature of the toroidal surface 3b, which is the surface on the side of the object 9 to be scanned, coincides with the main scanning direction of the optical system, and the toroidal surface 3b is The curvature radius in the main scanning direction serves to correct field curvature and linearity in the main scanning direction, and the curvature radius in the sub scanning direction causes the reflecting surface 11 of the deflecting device and the surface of the object 9 to be scanned. Even if the reflecting surface 11 is tilted and changes to the state 11 '(that is, the surface is tilted) as shown in FIG. 2, the beam is caused to pass as shown by the broken line and the object to be scanned 9 is maintained. It works to prevent the upper beam displacement.

The scanned object 9 is, for example, a photosensitive drum and records a light beam signal as a latent image.

Next, the aberration correcting action by the lens of the deflection system in the present embodiment will be described with reference to FIGS.

FIG. 3 is a schematic diagram showing the structure and arrangement of lenses for explaining the aberration correcting action, and FIG. 3 (a) is a cross section in the main scanning direction, showing a cross section from the reflecting surface 11 of the deflecting device to the scanned object. 9
The configuration up to is shown. Where R ₁ is the first lens 1
Is the radius of curvature of the spherical surface 1b, and R ₂ is the radius of curvature of the toroidal surface 3b of the third lens 3 in the cross section in the main scanning direction. Further, l ₁ is the distance on the optical axis from the reflecting surface 11 to the first lens 1, l ₂ is the distance on the optical axis from the first lens 1 to the second lens 2, and l ₃ is the second distance. The distance from the lens 2 to the third lens 3 on the optical axis, l ₄ is the distance from the third lens 3 to the scanned object 9 on the optical axis, and l ₅ is the first lens 1 to the third lens The distances up to 3 on the optical axis are shown.

FIG. 3B shows a cross section in the sub-scanning direction, and shows the structure from the reflecting surface 11 of the deflecting device to the object 9 to be scanned, as in FIG. 3A. Here, R ₃ represents the radius of curvature of the cylindrical surface 1a of the first lens 1, R ₄ represents the radius of curvature of the cylindrical surface 2a of the second lens 2, and R ₅ represents the third radius.
Shows the radius of curvature of the toroidal surface 3b of the lens 3 in the sub-scan section.

4 to 6 show the radius of curvature R ₁ of the spherical surface 1b of the first lens ₁ and the radius of curvature R ₂ of the toroidal surface 3b of the third lens 3 in the cross section in the main scanning direction of FIG. 3 (a). When, the distance l ₁ between the reflecting surface 11 and the first lens 1, the distance of the first lens 1 and the distance l ₅ of the third lens 3, and the third lens 3 and the scanning object 9 l ₄ shows changes in the field curvature in the main scanning direction and linearity when ₄ and ₄ are changed. In each drawing, the vertical axis represents the field curvature in the main scanning direction at the maximum deflection (deflection angle θ = 30 °, scanning position h on the scanned object 9 = 148.5 mm), and the horizontal axis represents linearity. .

In FIG. 4, the solid line 21 shows the locus of change in both aberrations when R ₁ and R ₂ are appropriately changed, and as can be seen from this solid line 21, the radius of curvature R ₁ and R ₂ By optimally determining the combination, the field curvature in the main scanning direction can be corrected to near zero.

Further, the solid lines 22 and 23 show the loci of changes in both aberrations when the radii of curvature R ₁ and R ₂ are changed in the same manner as the solid line 21 after changing only l ₁ with respect to the condition of the solid line 21. It is shown. It can be seen that the solid line 23 has changed to a direction in which the linearity becomes smaller as a whole than the solid line 21.

FIG. 5 shows that after changing only l _{5 based on} the condition of the solid line 21 in FIG. 4, the radii of curvature R ₁ , R are the same as in the solid line 21 of FIG.
The locus of changes in both aberrations when ₂ is changed is shown. By changing l ₅ , solid line 21 becomes solid line 24,2
It can be seen that the value changes to 4, that is, the linearity changes, and that the field curvature in the main scanning direction changes by changing the curvature radii R ₁ and R ₂ .

FIG. 6 shows the locus of changes in both aberrations when l ₄ is changed based on the condition of the solid line 21 in FIG. 4 and then the radii of curvature R ₁ and R ₂ are changed in the same manner as in FIG. Is shown. By changing the distance l ₄ between the two, the solid line 21 becomes the solid lines 26, 27.
Change, that is, the linearity changes, and the radii of curvature R ₁ , R
It can be seen that the field curvature in the main scanning direction changes by changing ₂ .

As described above, according to the results of FIGS. 4 to 6, in the present embodiment, among the parameters shown in FIG. 3, l ₁ , l ₄ , and l ₅ are set to appropriate values, respectively, to correct the linearity. Can be done. In this case, it is possible to reduce the lens outer diameter as a whole by making l ₁ as small as possible and setting l ₄ and l ₅ based on this.

Of the parameters shown in FIG. 3, the radii of curvature R ₁ , R
The field curvature in the main scanning direction can be corrected by setting ₂ to an appropriate value.

As described above, the field curvature and the linearity of the first lens 1 and the third lens 3 can be corrected by the positions of both lenses and the radius of curvature of one surface of each of the two lenses.

Therefore, the second lens 2 does not need to have power on both surfaces in the cross section in the main scanning direction, and its position can be freely changed between the first lens 1 and the third lens 3. However, it can be seen that the performance in the main scanning direction does not change.

Therefore, the correction function of the field curvature in the sub-scanning direction, which is another aberration to be corrected, will be described next. FIG. 7 shows the curvature radius R ₃ of the cylindrical surface 1a of the first lens 1 and the curvature radius R ₃ of the second surface as shown in FIG. After setting the radius of curvature R ₄ of the cylindrical surface 2a of the lens 2, the value of the radius of curvature R ₅ of the toroidal surface 3b of the third lens 3 in the sub-scanning direction becomes conjugate with the reflecting surface 11 and the scanned object 9. To adjust
The change in the field curvature in the sub-scanning direction when the balance of the set values of R ₃ and R ₄ is changed is shown.

In FIG. 7, the horizontal axis represents the amount of field curvature in the sub-scanning direction, and the vertical axis represents the scanning position as a relative value. As can be seen from the figure, the smaller the value of R ₃ and the larger the value of R ₄ , the better the field curvature in the sub-scanning direction can be corrected.

Particularly, when the relationship between R ₃ and R ₄ is (1 / R ₃ )> (1 / R ₄ ), the correction effect is remarkable in the light beam scanning optical system of the present embodiment, and (1 / R _{If 3} )> (1 / R ₄ ), it was confirmed that the field curvature in the sub-scanning direction can be contained within a range that does not pose a problem in actual use.

FIG. 8 is a graph showing the correlation between the ratio of R ₃ and R ₄ shown in FIG. 7 and the field curvature in the sub-scanning direction. As is clear from the figure, (R ₃ / R ₄ ) Within the range of ≦ 0.9, that is, (0.9 / R ₃ ) ≧ (1 / R ₄ ), the field curvature in the sub-scanning direction can be kept within 3 mm, and a so-called high resolution correction effect can be guaranteed. . Therefore, it is more effective if the relationship between R ₃ and R ₄ is set within this range.

This correction condition is the same regardless of which surface of the second lens 2 the cylindrical surface is set to. Furthermore, under such conditions, it relates the position of the second lens 2, although there is a position that can best sub-scanning curvature, seventh and eighth figure of course, such a l _2, l ₃ The one after adjusting the conditions of is shown.

Further, in order to correct the curvature of field in the sub-scanning direction, as shown in FIG. 3, a cylindrical surface having negative power is used.
In this embodiment, it is desired to provide the first lens 1 and the second lens 2 respectively.

In order to prove this point, FIG. 9 shows that the radius of curvature of the cylindrical surface of the first lens 1 is infinite, the negative cylindrical surfaces are set on both surfaces of the second lens 2, and the radius of curvature of one is R ₄ shows the curvature of field in the sub-scanning direction when R ₅ is adjusted in the same manner as in FIG. 7 by changing the setting ratio of the values of R ₄ and R ₄ ′ with the other radius of curvature being R ₄ ′. .

As can be seen from FIG. 9, even if cylindrical lenses are set on both surfaces of the second lens 2, the field curvature in the sub-scanning direction cannot be corrected well, and the first lens 1 needs to have a cylindrical surface. I understand.

As described above, according to the present embodiment, the surface tilt correction, the field curvature correction in the main scanning direction, the linearity correction, and the field curvature correction in the sub scanning direction can be effectively performed, and within ± 30 °. Large polarization angle and high resolution can be guaranteed. Further, since the above-mentioned respective corrections are achieved by making the other surface of the third lens 3 having the toroidal surface 3b a flat plate, the manufacture of the third lens 3 is facilitated and the cost is reduced. Can be measured.

The lens shape data of the deflection system in the present embodiment described above is shown below.

(First Experimental Example) The lens configuration of the deflection system (second optical system) of the present experimental example is the same as in FIGS. 1 to 3, and the first to third lenses 1 to 3 are used.
The details are as follows.

(1) First lens Spherical curvature radius R ₁ : 532.67mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface curvature radius R ₃ : 20mm Distance to reflective surface 11 l ₁ : 44mm (2) Second Lens (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 34.915mm Lens thickness t ₂ : 10mm Lens material: F2 Distance from first lens l ₂ : 11mm Distance from third lens l ₃ : 25mm (3) Third lens (the surface on the deflector side is a flat surface) Radius of curvature of toroidal surface in the main scanning direction R ₂ : 164.5mm Curvature of curvature of toroidal surface in the sub scanning direction R ₅ : 40.948mm Lens thickness t ₃ : 20mm Lens Material: SF11 Distance to scanned object 9 l ₄ : 291mm Fig. 10 is a graph showing the aberration state of this experimental example. Fig. 10 (a) shows the field curvature, the solid line is the main scanning direction, and the broken line is In the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 10, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Second Experimental Example) The lens configuration of the deflection system (second optical system) of this experimental example is as follows.
Similar to FIGS. 1 to 3, details of each lens of the deflection system are as follows.

(1) First lens Spherical radius of curvature R ₁ : 859.77mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface radius of curvature R ₃ : 20.16mm Distance to reflective surface 11 l ₁ : 25mm (2) Second Lens No. ₂ (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 29.902mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 40mm Distance with third lens l ₃ : 25mm (3) Third lens (surface on deflector side is flat) Curvature radius of toroidal surface in main scanning direction R ₂ : 203.82mm Curvature radius of toroidal surface in sub scanning direction R ₅ : 42.362mm Lens thickness t ₃ : 20mm Lens material: SF11 Distance from scanning object 9 l ₄ : 261 mm FIG. 11 is a graph showing the aberration state of this experimental example. FIG. 11 (a) shows the field curvature, and the solid line represents the main scanning direction. The broken lines respectively show those in the sub-scanning direction, and the linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 11, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Third Experimental Example) In this experimental example, as shown in FIG. 12, the side of the second lens 2 facing the first lens 1 is a flat surface 2b, and the other surface of the second lens 2 is The cylindrical surface 2a was used, and the other structures were the same as those in FIGS. Details of each lens of the deflection system are as follows.

(1) First lens Spherical curvature radius R ₁ : 532.67mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface curvature radius R ₃ : 50mm Distance to reflective surface 11 l ₁ : 44mm (2) Second Lens (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 52.375mm Lens thickness t ₁ : 10mm Lens material: F2 Distance from first lens l ₂ : 11mm Distance from third lens l ₃ : 25mm (3) Third lens (surface on deflector side is flat) Curvature radius of toroidal surface in main scanning direction R ₂ : 164.5mm Curvature radius of toroidal surface in sub-scanning direction R ₅ : 42.899mm Lens thickness t ₃ : 20mm Lens Material: SF11 Distance from scanning object 9 l ₄ : 291mm Fig. 13 is a graph showing the aberration state of this experimental example. Fig. 13 (a) shows the field curvature, the solid line is the main scanning direction and the broken line. In the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 13, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Fourth Experimental Example) The lens configuration of the deflection system of this experimental example is the same as that of FIG. 12, and the details of each lens of the deflection system are as follows.

(1) 1st lens Spherical curvature radius R ₁ : 857.03mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface curvature radius R ₃ : 20.16mm Distance to reflective surface 11 l ₁ : 25mm (2) Second Lens No. ₂ (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 23.888mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 35mm Distance with third lens l ₃ : 30mm (3) Third lens (the surface on the deflector side is a plane) Curvature radius R ₂ : 203.78mm in the main scanning direction of the toroidal surface R ₅ : 40.207mm Curvature radius in the sub-scanning direction of the toroidal surface Lens thickness t ₃ : 20mm Lens material: SF11 Distance from scanning object 9 l ₄ : 261 mm FIG. 14 is a graph showing the aberration state of this experimental example. FIG. 14 (a) shows the field curvature, and the solid line is the main scanning direction. The broken lines respectively show those in the sub-scanning direction, and the linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 14, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Fifth Experimental Example) The lens configuration of the deflection system of this experimental example is the same as that of FIG. 12, and the details of each lens of the deflection system are as follows.

(1) First lens Spherical radius of curvature R ₁ : 726.65mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface radius of curvature R ₃ : 16.26mm Distance to reflective surface 11 l ₁ : 28mm (2) Number Lens No. ₂ (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 31.088mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 27mm Distance with third lens l ₃ : 25mm (3) Third lens (the surface on the deflector side is a flat surface) Radius of curvature of the toroidal surface in the main scanning direction R ₂ : 190.35mm Radius of curvature of the toroidal surface in the sub scanning direction R ₅ : 39.145mm Lens thickness t ₃ : 20mm Lens material: SF11 Distance from scanning object 9 l ₄ : 271 mm FIG. 15 is a graph showing the aberration behavior of this experimental example. FIG. 15 (a) shows the field curvature, and the solid line is the main scanning direction. The broken lines respectively show those in the sub-scanning direction, and the linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 15, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Sixth Experimental Example) The lens configuration of the deflection system of this experimental example is the same as that of FIG. 12, and the details of each lens of the deflection system are as follows.

(1) First lens Spherical curvature radius R ₁ : 526.57mm Lens thickness t ₁ : 10mm Lens material: F2 Cylindrical surface curvature radius R ₃ : 32.29mm Distance to reflective surface 11 l ₁ : 49mm (2) Second 2 lenses (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 72.896mm Lens thickness t ₂ : 10mm Lens material: F ₂ Distance from first lens l ₂ : 21mm Distance from 3rd lens l ₃ : 25 mm (3) third lens (deflector-side surface is flat) toroidal surface in the main scanning direction of curvature radius R _2: 173.72mm toroidal surface in the sub-scanning direction curvature radius R _5: 45.488mm lens thickness t _3: 20 mm lens Material: SF11 Distance from scanning object 9 l ₄ : 281 mm FIG. 16 is a graph showing the aberration performance of this experimental example. The figure (a) shows the field curvature, the solid line is the main scanning direction, and the broken line is Each of them is shown in the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 16, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Seventh Experimental Example) In this experimental example, as shown in FIG. 17, the side facing the reflecting surface 11 of the first lens 1 is a spherical surface 1b, and the other surface of the first lens 1 is a cylindrical surface 1a. And the others are 1st
The configuration is equivalent to that of FIG. Details of each lens of the deflection system are as follows.

(1) First lens Spherical radius of curvature R ₁ : 500mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface radius of curvature R ₃ : 15.317mm Distance to reflective surface 11 l ₁ : 32.5mm (2) Second 2 lenses (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 16.013mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 22.5mm Distance with third lens l ₃ : 25mm (3) Third lens (the surface on the deflector side is a flat surface) Curvature radius R _{2 of the} toroidal surface in the main scanning direction R ₂ : 186.83mm Curvature radius R _{5 of the} toroidal surface in the sub scanning direction R ₅ : 36.641mm Lens thickness t ₃ : 20mm Lens material: SF11 Distance from scanning object 9 l ₄ : 271 mm FIG. 18 is a graph showing the aberration performance of this experimental example. FIG. 18 (a) shows the field curvature, the solid line is the main scanning direction, and the broken line is In the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 18, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Eighth Experimental Example) The lens configuration of the deflection system of this experimental example is the same as that of FIG. 17, and the details of each lens of the deflection system are as follows.

(1) First lens Spherical curvature radius R ₁ : 655.44mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface curvature radius R ₃ : 20.41mm Distance to reflective surface 11 l ₁ : 30mm (2) Second 2 lenses (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 29.432mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 35mm Distance with third lens l ₃ : 25mm (3) Third lens (surface on deflector side is flat) Curvature radius of toroidal surface in main scanning direction R ₂ : 202.09mm Curvature radius of toroidal surface in sub-scanning direction R ₅ : 41.227mm Lens thickness t ₃ : 20mm Lens Material: SF11 Distance from scanned object 9 l ₄ : 261 mm Fig. 19 is a graph showing the aberration performance of this experimental example. Fig. 19 (a) shows the field curvature, where the solid line is the main scanning direction and the broken line is Each of them is shown in the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 19, it was confirmed that the field curvature in the main and sub-scanning directions and the linearity were in good ranges.

(Ninth Experimental Example) In this experimental example, as shown in FIG.
The side facing the reflecting surface of is a spherical surface 1b, the other surface of the first lens 1 is a cylindrical surface 1a, and the side facing the plane 3a of the third lens 3 of the second lens 2 is a cylindrical surface. 2a and the other surface of the second lens 2 is a flat surface 2b. Details of each lens of the deflection system are as follows.

(1) First lens spherical radius of curvature R ₁ : 292.15mm Lens thickness t ₁ : 20mm Lens material: F2 Cylindrical surface radius of curvature R ₃ : 20.41mm Distance to reflective surface 11 l ₁ : 35mm (2) No. 2 lenses (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 41.253mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 15mm Distance with third lens l ₃ : 25mm (3) Third lens (surface on deflector side is flat) Curvature radius of toroidal surface in main scanning direction R ₂ : 166.96mm Curvature radius of toroidal surface in sub-scanning direction R ₅ : 38.726mm Lens thickness t ₃ : 20mm Lens Material: SF11 Distance to scanned object 9 l ₄ : 281 mm Fig. 21 is a graph showing the aberration performance of this experimental example. Fig. 21 (a) shows the field curvature, the solid line is the main scanning direction, and the broken line is Each of them is shown in the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 21, it was confirmed that the field curvatures in the main and sub-scanning directions and the linearity were in good ranges.

(Tenth Experimental Example) The lens configuration of the deflection system of this experimental example is the same as that of FIG. 20, and the details of each lens of the deflection system are as follows.

(1) First lens Spherical radius of curvature R ₁ : 655.78mm Lens thickness t ₁ : 15mm Lens material: F2 Cylindrical surface radius of curvature R ₃ : 19.852mm Distance to reflective surface 11 l ₁ : 30mm (2) Number 2 lenses (one surface is flat) Radius of curvature of cylindrical surface R ₄ : 23.145mm Lens thickness t ₂ : 10mm Lens material: F2 Distance with first lens l ₂ : 30mm Distance with third lens l ₃ : 30mm (3) Third lens (the surface on the deflector side is flat) Curvature radius R ₂ : 202.1mm in the main scanning direction of the toroidal surface R ₅ : 39.178mm Curvature radius in the sub-scanning direction of the toroidal surface Lens thickness t ₃ : 20mm Lens Material: SF11 Distance from scanned object 9 l ₄ : 261 mm Figure 22 is a graph showing the aberration performance of this experimental example. Figure (a) shows the field curvature, the solid line in the main scanning direction and the broken line in the figure. Each of them is shown in the sub-scanning direction, and linearity is shown in FIG. In both figures, the vertical axis is the relative scanning position, and the maximum value 1.0 is the deflection angle of 30 ° and the scanning width of 148.5 mm.
Corresponding to

As is clear from FIG. 22, it was confirmed that the field curvature in the main / sub-scanning direction and the linearity were in good ranges.

In each of the above experimental examples, one surface of the second lens 2 is a flat surface, but the same effect can be obtained by using this as a cylindrical surface.

Further, it goes without saying that the present invention described above can be applied not only to the laser printer as in the present embodiment but also to an apparatus for performing scanning by a rotary polygon mirror, for example, an optical system such as an image reading apparatus. .

〔The invention's effect〕

As described above, according to the present invention, important field curvature is satisfactorily corrected and production is improved particularly in the case of high resolution (that is, the beam spot diameter is relatively small) while having a compact structure with a large deflection angle. It is possible to realize a light beam scanning device that is easy and inexpensive, and its industrial value is high.

[Brief description of the drawings]

1 to 22 relate to the present invention, FIG. 1 is a perspective view of a light beam scanning device according to an embodiment of the present invention, and FIG. 2 is a sub-scan of FIG. 1 for explaining surface tilt correction. FIG. 3 (a) is a schematic diagram in the main scanning direction cross section of the second optical system (deflection system) in the configuration of FIG. 1, and FIG. 3 (b) is the same sub scanning direction cross section. 4 to 6 are characteristic diagrams showing changes in the field curvature and linearity in the main scanning direction, FIG. 7 is a characteristic diagram showing changes in the field curvature in the sub scanning direction, and FIG. FIG. 7 is a graph showing the correlation between the ratio of R ₃ and R ₄ in FIG. 7 and field curvature in the sub-scanning direction.
FIG. 10 is a characteristic diagram showing changes in the field curvature in the sub-scanning direction when the cylindrical surface of the first lens is set to infinity, which is shown for comparison with the figure. FIG. 10 is an aberration characteristic in the first experimental example of the present invention. FIG. 11 is an aberration characteristic diagram in the second experimental example of the present invention, FIG. 12 is a schematic diagram of the second optical system used in the third to sixth experimental examples, and FIG. 13 is the third example of the present invention. FIG. 14 is an aberration characteristic diagram in the experimental example, FIG. 14 is an aberration characteristic diagram in the fourth experimental example of the present invention, and FIG. 15 is an aberration characteristic diagram in the fifth experimental example of the present invention.
FIG. 16 is an aberration characteristic diagram in the sixth experimental example of the present invention,
The figure is a schematic diagram of the second optical system used in the seventh and eighth experimental examples, FIG. 18 is the aberration characteristic diagram in the seventh experimental example of the present invention, and FIG. 19 is the aberration in the eighth experimental example of the present invention. Characteristic diagram,
FIG. 20 is a schematic diagram of the second optical system used in the ninth and tenth experimental examples, FIG. 21 is an aberration characteristic diagram in the ninth experimental example of the present invention, and FIG. 22 is a tenth experimental example of the present invention. FIG. 23 and FIG. 24 are aberration characteristic diagrams in FIG.
The figure is a conceptual diagram showing the occurrence of field curvature in the sub-scanning direction by a long cylindrical lens, and Fig. 24 is the field curvature in the sub-scanning direction when only one surface of a single lens having a toric surface is a cylindrical surface. FIG. 1 ... 1st lens, 1a ... Cylindrical surface, 1b ...
Spherical surface, 2 ... second lens, 2a ... Cylindrical surface,
2b ... plane, 3 ... third lens, 3a ... plane, 3b ...
Toroidal surface, 4 ... Light source, 5 ... Coupling lens, 6 ...
Cylindrical lens, 7 ... Motor, 8 ... Rotating polygon mirror, 9 ... Scanned object, 10a-10c ... Light beam, 11 ... Reflecting surface.

Claims (1)

(57) [Claims] 1. A light beam generator, a first optical system for linearly focusing the light beam generated from the light beam generator, a deflector for deflecting and reflecting the linear light beam, and In a light beam scanning device including a second optical system that focuses a light beam deflected by a deflecting device onto an object to be scanned, and the object to be scanned, the second optical system is arranged in order from the deflecting device.
A first lens in which one surface is a spherical surface having negative power and the other surface is a cylindrical surface having negative power only in a direction perpendicular to the scanning direction, and one surface is in the scanning direction. Lens having a negative power only in the direction perpendicular to the vertical direction and one of the other surfaces being a flat surface, or both surfaces being cylindrical surfaces having a negative power only in the direction perpendicular to the scanning direction And the surface on the side of the deflecting device is a flat surface, and the surface of the object to be scanned has a positive power with a relatively large radius of curvature in the scanning direction and is positive with a relatively small radius of curvature in the direction perpendicular to the scanning direction. The third lens is a surface having a power (toroidal surface), and the radius of curvature of the cylindrical surface of the first lens is R ₃ , and the curvature of the cylindrical surface of the second lens is A light beam scanning device characterized in that when the radius is represented by R ₄ , (1 / R ₃ )> (1 / R ₄ ).