JP2698138B2 - Scanning optical device with surface tilt correction function - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device used for scanning a light beam in, for example, a laser beam printer or the like. Even if the deflecting / reflecting surface of the light beam is slightly inclined from a predetermined posture and is in an inclined state, the path of the light beam is optically automatically adjusted so that the scanning beam reflected from the reflecting surface scans a correct predetermined scanning position. Correction function).

[Conventional technology]

In a scanning optical device that scans a light beam, a rotary polygon mirror is widely used as a deflector for the light beam. At this time, if there is a tilt error (this tilt is called tilting or tilting) of each reflecting surface (deflecting surface) of the rotary polygon mirror with respect to the rotation center axis, the scanning position fluctuates for each surface and the scanning pitch unevenness. Is generated. In order to correct this and enable scanning at the same position on the surface to be scanned irrespective of the inclination of the reflection surface, the positional relationship between the polygon mirror surface (deflection surface) and the surface to be scanned (for example, the photosensitive drum surface). Is optically useful (relation between object point and image point)
A method of using such an imaging optical system by disposing it between the polygon mirror and the surface to be scanned is known, for example, from Japanese Patent Publication No. 52-2866.

In addition, the deflection scanning optical system of such a scanning optical device has a constant speed scanning characteristic (generally referred to as f · θ characteristic) that enables a light beam to scan a scanning surface at a constant speed. It is also required to have a function of correcting the field curvature so that the spot diameter of the light beam on the surface to be scanned is always uniform at each position in the scanning direction.

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 the scanning direction, it is necessary to use optical systems having different powers in both planes.
A cylindrical lens or the like is disposed in the optical path before and after the above, and its cylinder surface 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 surface tilt as described above, for example, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-open No. 93021/1993 discloses a lens composed of a single spherical lens and a long cylinder lens.
As disclosed in Japanese Patent Application Publication No. 15-315, there is known a device composed of a spherical single lens and a single lens having a toric surface.

[Problems to be solved by the invention]

The above-described conventional optical system has a simple lens configuration, but can cope with a case where the spot diameter on the surface to be scanned is 80 to 100 μm and the resolution is relatively low.

In such an optical system, if the spot diameter on the surface to be scanned is reduced to, for example, 40 to 50 μm in order to correspond to a high resolution, the conventional optical system has a field curvature (in particular, a direction perpendicular to the scanning direction). 3), the spot 4 has a small diameter and a large diameter depending on the position in the scanning direction, and the spot diameter is not uniform.

FIG. 21 is a schematic diagram showing a relationship between a spot diameter on the scanned surface 51 and a change in the spot diameter when the field curvature 50 remains in the scanning direction. In the figure, 52 and 53 indicate beam envelopes, 52 indicates a case where the spot diameter is relatively large, and 53 indicates a case where the spot diameter is relatively small. When the spot diameter is large, the variation between the spot d1 at the scanning center (center position in the scanning range) 54 and the spot d2 at the scanning end 55 is small, but when the spot diameter is small, the spot d1 'at the scanning center 54 is small. Scan end 55 spot d
This indicates that the fluctuation from 2 ′ is larger than when the spot diameter is large. Therefore, in order to reduce the spot diameter, it is necessary to bring the curvature of field 50 shown by the broken line as close as possible to the surface to be scanned 51, in other words, to keep the curvature of field small.

When the spot diameter is as large as 80 to 100 μm, the allowable value of the curvature of field is said to be about ± 3 to ± 5 mm. for that reason,
In order to further reduce the spot diameter for high resolution, it is necessary to reduce the allowable value of the field curvature accordingly.

Here, in the conventional optical system described above, a direction perpendicular to the scanning direction when the long cylinder lens is used (hereinafter, the scanning direction is referred to as the main scanning direction, and the direction perpendicular thereto may be referred to as the sub-scanning direction). The appearance of curvature of field
See Figure 22. In the figure, a beam 71 incident on the scanning center of a long cylinder lens 70 is focused on a surface 74 to be scanned, while a beam 72 incident on the scanning end is a cylinder lens.
In order to form the angle θ with respect to 70, the apparent curvature of the cylinder lens 70 with respect to the beam 72 is increased, and the field curvature 73 is generated (the focal position of the beam 72 is shifted from the surface to be scanned 74 by the distance 73).

In the method using a long cylinder lens, it is necessary to reduce the beam deflection angle to 7 ° or less in order to keep the above-mentioned field curvature to ± 1 mm or less, and the optical path length from the deflecting device to the surface to be scanned becomes enormous. However, there is a problem that the optical system becomes large.

In the other conventional optical system described above,
The curvature of field in the sub-scanning direction generated on the toric surface is corrected by providing one cylindrical surface having a negative power on the other surface of the single lens having the toric surface. . However, when the curvature of field in the sub-scanning direction is corrected with only one cylindrical surface as described above, if the deflection angle is increased (for example, ± 30 ° or more), higher-order aberrations occur, and as a result, high resolution is obtained. The effect of correcting the field curvature, which only corresponds to the image formation, is lost.

FIG. 23 shows an example of characteristics in the case where the curvature of field in the sub-scanning direction that occurs on the toric surface is corrected with only one cylindrical surface. In the figure, the vertical axis represents the relative scanning position, the maximum scanning position (scanning end) 1.0 is a deflection angle ± 30 °,
In this case, the scanning width is ± 148.5 mm.

As described above, the conventional technology has a simple configuration with two lenses, but does not have sufficient performance for high resolution.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam scanning optical device which has a simple and small configuration, has surface tilt correction, and can scan with a small scanning spot diameter so as to correspond to high resolution.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a first beam forming and outputting a light beam of a light beam generated from a light beam source in a linear manner is provided.
An imaging optical system, and a deflector that, when a linear light beam from the first imaging optical system is incident, reflects the light beam on its deflecting / reflecting surface, deflects it, and scans it on the surface to be scanned, The scanning surface and the deflection / reflection surface are disposed between the scanning surface and the deflection / reflection surface.
A second imaging optical system for realizing a function of correcting the tilt of the deflecting / reflecting surface while maintaining the positional relationship between the reflecting surface and the optically conjugate relationship, and a scanning optical system having a function of correcting the surface tilt. In the apparatus, the second imaging optical system may be configured such that one surface forms a cylindrical surface having negative power only in a cross section in the main scanning direction, and the other surface is a direction perpendicular to the main scanning direction, that is, a sub-scanning direction. An anamorphic first single lens that forms a cylindrical surface having negative power only in the cross section in the direction, and one surface forms a cylindrical surface that has negative power only in the cross section in the sub-scanning direction; The other surface has a relatively large curvature in the cross section in the main scanning direction and a relatively small curvature in the cross section in the sub scanning direction. Troy with power A second single lens forming the Le plane, constituted by.

[Action]

In the above configuration, the curvature of the cylindrical surface having negative power only in the main scanning direction of the first single lens and the curvature of the toroidal surface of the second single lens in the main scanning direction are adjusted. Roughly correct the field curvature and linearity in the main scanning direction, which are aberrations, and furthermore, the distance between the surfaces from the deflector to the first single lens and the distance between the surfaces from the first single lens to the second single lens. , And each of the inter-surface distances from the second single lens to the surface to be scanned is adjusted to correct the curvature of field and the linearity aberration in the main scanning direction.

Regarding aberrations in the sub-scanning direction, there are two cylindrical surfaces, a cylindrical surface having a negative power only in the sub-scanning direction of the first single lens and a cylindrical surface having a negative power only in the sub-scanning direction of the second single lens. By adjusting the curvature of the surfaces, the curvature of field in the sub-scanning direction generated on the toroidal surface is corrected, and at the same time, the curvature of the two cylindrical surfaces and the curvature of the cross-section in the sub-scanning direction of the toroidal surface are reflected by the deflector. The tilt of the anti-slant surface of the deflector is corrected so that the surface and the surface of the object to be scanned have a conjugate relationship.

The first single lens has a cylindrical surface having a negative power only in the main scanning direction on the deflector side, and a cylindrical surface having a negative power only in the sub-scanning direction on the second single lens side. If you do, Where f _{0 is} the combined focal length of the second imaging optical system in the cross section in the main scanning direction.

l ₄ : Inter-plane distance (on the axis) from the reflecting surface of the deflector to the toroidal surface of the second single lens.

R ₂ : radius of curvature of the cross section in the scanning direction of the toroidal surface of the second single lens.

Is satisfied, the effectiveness of the aberration correction effect is increased.

In addition, the first single lens has a cylindrical surface having negative power only in the sub-scanning direction on the deflector side, and a cylindrical surface having negative power only in the main scanning direction on the second single lens side. If you do, (Where f ₀ , l ₄ , and R ₂ are the same as the above symbols), the effectiveness of the aberration correction effect increases.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First
FIG. 1 shows an external view of a scanning optical device having surface tilt correction according to the present invention. This scanning optical device consists of a light source 3, a coupling lens
4, a first imaging optical system 5, a deflector (motor 6, rotating polygon mirror 7), one from the deflector side has a cylindrical surface 1a having a curvature in the main scanning direction, and the other has a curvature in the sub-scanning direction. A second imaging optical system and a first imaging lens comprising a first single lens 1 comprising a cylindrical surface 1b, a cylindrical surface 2a having one curvature in the sub-scanning direction, and a second single lens 2 comprising a toroidal surface 2b; Scanned object (for example, photosensitive drum) 8
It is composed of

Next, each operation will be described. The light source 3 is a semiconductor laser in this embodiment, and the beam from the light source 3 emits divergent light. The coupling lens 4 collimates the divergent light into a substantially parallel light flux, and adjusts the position of the divergent light in the optical axis direction in the cross section in the main scanning direction.
The focus adjustment for focusing the light beams (9a to 9c) on the surface is performed. The first imaging optical system 5 is a cylindrical lens in this embodiment, and as shown in FIG. 2 (here, FIG. 2 is a configuration diagram of a cross section in the sub-scanning direction of FIG. 1). Has a power only in the cross section in the sub-scanning direction, and once converges the light beam 9d near the reflecting surface 10 of the rotary polygon mirror 7 of the deflector. At this time, since the first imaging optical system 5 has no power in the cross section in the main scanning direction, the first
It becomes a line image as shown in the figure.

The rotating polygon mirror 7 of the deflector rotates in the direction of the arrow in FIG. 1 and deflects the light beam from 9a to 9b to 9c by changing the reflection angle of the reflection surface 10. One scan is performed while one light reflecting surface is irradiated with the light beam, and scanning is performed by the number of the reflecting surfaces during one rotation of the rotary polygon mirror 7. In this embodiment, the deflection angle is ± 30 °. The deflection scanning of the light beam is performed by the rotation axis of the deflector (that is, the rotating polygon mirror 7).
Is made in a plane (main scanning plane) perpendicular to the rotation center axis of
The light source 3 to the first imaging optical system 5 are arranged such that the optical axis is in the main scanning plane.

The first single lens 1 of the two lenses constituting the second imaging optical system is arranged so that its optical axis substantially coincides with the light beam at the center of scanning in the main scanning plane. The first
In the single lens 1, the cylindrical surface 1a has an action of mainly correcting the field curvature in the main scanning direction and the aberration of the linearity described later, and the other cylindrical surface 1b has the field curvature in the sub-scanning direction described later. It has the function of mainly correcting aberration.

The second single lens 2 of the two lenses constituting the second imaging optical system is arranged so that its optical axis coincides with that of the first single lens 1 like the first single lens 1. Finally, the light beam is converged to one point on the surface of the object 8 to be scanned, and the cylindrical surface 2a is balanced with the cylindrical surface 1b of the first single lens 1 by the toroidal surface 2b. It has a function of correcting a field curvature in the sub-scanning direction that mainly occurs.

The other toroidal surface 2b of the second single lens 2 has a curvature in a cross section in the main scanning direction, and has a field curvature and a linearity in a main scanning direction, which will be described later, due to the balance with the cylindrical surface 1a of the first single lens 1. FIG. 2 shows that by adjusting the reflection surface 10 of the deflector and the surface of the object 8 to be conjugated by the curvature of the section in the sub-scanning direction, As shown in the figure, the second imaging optics is formed even when the position is changed to the position 10 'by tilting in the direction perpendicular to the deflecting surface between the plurality of reflecting surfaces 10 of the rotary polygon mirror 7 (that is, the surface tilts). The light beam passing through the first single lens 1 and the second single lens 2 of the system changes as shown by the broken line in FIG. 2, but the focusing position of the light beam on the surface of the scanning object 8 changes. To prevent the light beam from oscillating in the cross section in the sub-scanning direction due to surface tilt. it can.

The scanned object 8 is, for example, a photosensitive drum in a laser beam printer or the like, and exposes a signal with a light beam.

Next, the second image forming optical system according to the present embodiment will be described.
The operation of correcting aberrations of the first and second single lenses 1 and 2 will be described with reference to FIGS.

3 (A) and 3 (B) are schematic diagrams of the lens configuration and arrangement for explaining the effect of correcting aberration. 3 (A) shows a cross section in the main scanning direction, and FIG. 3 (B) shows a cross section in the sub scanning direction from the anti-slope surface 10 of the deflector.
Is shown in the range. In FIG. 3A, R ₁ is the radius of curvature of the cylindrical surface _{1 a} of the first single lens 1 and has a negative refractive power, and R ₂ is the main scanning direction of the toroidal surface of the second single lens 2. It is a radius of curvature of a cross section and has a refractive power. Also, l ₁ is the distance between the surfaces on the optical axis 60 from the reflecting surface 10 to the first single lens 1, and l ₂ is the surface on the optical axis 60 from the first single lens 1 to the second single lens 2 The distance, l _3, is the distance between the toroidal surface of the second single lens 2 and the surface of the object 8 on the optical axis 60, and l ₄ is the distance between the reflecting surface 10 of the deflector and the second single lens 2. The distance between the surfaces to the toroidal surface is shown. Third
In FIG. 3B, R ₃ is the radius of curvature of the cylindrical surface 1 b of the first single lens 1 and has a negative refractive power, and R ₄ is the radius of curvature of the cylindrical surface 2 a of the second single lens 2. There has negative refractive power, R ₅ has the positive refractive power is the radius of curvature of the second single lens 2 toroidal surfaces 2b, respectively.

Figure 4 - Figure 6 is a third view of the main scanning cross section first radius of curvature R ₁ of the cylindrical surface of the single lens 1 and the second toroidal surface curvature radius R ₂ and the single lens 2 in each Field curvature and linearity in the main scanning direction when the inter-plane distances l ₁ , l ₂ , and l ₃ are respectively changed (this is the value of (h−f ₀ · θ), where f ₀ is the The composite focal length of the second imaging optical system, h indicates the change in the scanning width, and θ indicates the change in the deflection angle. In each figure, the vertical axis indicates the curvature of field in the main scanning direction, and the horizontal axis indicates the magnitude of the linearity.

In FIG. 4, the solid line 20 is the distance between the surfaces shown in FIG.
When l ₁ , l ₂ , and l ₃ are set to arbitrary values and the maximum deflection angle θ is 30 °, the scanning width h on the surface to be scanned 8 is 148.5 mm, and
FIG. 3 shows trajectories of changes in both the curvature of field and the linearity in the main scanning direction when the radii of curvature R ₁ and R ₂ of each lens shown in FIG. 3 are appropriately changed. By optimizing the combination of the radii of curvature R ₁ and R _{2 as described above} , the field curvature in the main scanning direction can be corrected to be small. Also, solid lines 21 and 22 are the two aberrations when the radius of curvature R ₁ and R ₂ are appropriately changed similarly after changing only l _{1 of the} distances between the surfaces determined by the solid line 20. It shows a locus of change. It can be seen that the solid line 21 can further correct the field curvature in the main scanning direction to near zero as compared with the solid line 20.

FIG. 5 shows the change in both aberrations when the radii of curvature R ₁ and R ₂ are appropriately changed in the same manner as in FIG. 4 while changing only the inter-plane distance l ₂ with reference to the solid line 21 in FIG. It shows a trajectory. By appropriately changing the distance l2 between the _two , the solid line 21
The (reference) changes to solid lines 23 and 24, that is, changes in the direction in which the linearity becomes smaller, and the curvature radii R ₁ and R ₂ are optimally determined so that the two aberrations become almost zero as shown by a point 25. You can see that it can be corrected.

FIG. 6 shows the change in both aberrations when the radii of curvature R ₁ and R ₂ are appropriately changed in the same manner as in FIG. 4 while changing only the distance l ₃ between the two based on the solid line 21 in FIG. It shows a trajectory. By both between distance l ₃ appropriately changed, a solid line 21
(Reference) changes to solid lines 26 and 27, and it can be seen that correction can be made in a direction in which the linearity decreases.

As described above, in this embodiment the result of FIG. 4-FIG. 6, among the parameters shown in Figure 3, the radius of curvature R _1, R ₂ and lattice distance l ₁ of each single lens 1, By optimizing l ₂ and l ₃ , both field curvature and linearity aberration in the main scanning direction are corrected simultaneously. When the thickness of each of the single lenses 1 and 2 is also taken into consideration, the correction effect is remarkable in the optical beam scanning optical device of this embodiment when the range of the following condition is satisfied.

Next, the operation of correcting the curvature of field in the sub-scanning direction will be described. The correction of the curvature of field in the sub-scanning direction is performed by using a cylindrical surface (for example,
It is known that this can be achieved by using R ₃ or R ₄ in the figure (for example, JP-A-57-144514). In order to be able to correct, it is necessary to optimize the value of the radius of curvature (R _{2 in} FIG. 3) in the cross section of the toroidal surface in the main scanning direction.

FIG. 7, the third by changing the radius of curvature R ₂ in the main scanning cross section of the toroidal surface shown in FIG., Each time the sub-scanning direction of the field curvature by a radius of curvature R ₄ of the cylindrical surface as shown in Figure 3 13 shows the field curvature characteristics in the sub-scanning direction after the correction has been made.

The horizontal axis in FIG. 7 is the magnitude of the field curvature in the sub-scanning direction,
The vertical axis indicates the scanning position as a relative value.

In the graph of FIG. 7, the leftmost curve 30 is R ₂ = 20
0 mm, and the rightmost curve 31 is the case where R ₂ = 90 mm. The curve is a characteristic when changing at appropriate intervals between the values of R ₂ from 90mm to 200 mm.

FIG. 7 shows an allowable range of curvature of field in a case where high resolution is supported by a region sandwiched between two straight lines M1 and M2 parallel to the vertical axis.

Depending Thus the R ₂ value may not be sufficiently corrected in the sub-scanning direction field curvature.

Conversely, for the value of the sub-scanning direction field curvature within the allowable value, the value of R ₂ is, it can be seen that it should be in the range of values when the case of the curve 32 and the curve 33 .

Further tolerance of such a R ₂ value was found that the reflecting surface 10 of the deflector shown in Figure 3 differs by the second face-to-face distance l ₄ value up toroidal surface of the single lens 2.

Figure 8 is for interplanar distance l ₄ from the reflecting surface 10 of the deflector to the second toroidal surface of the single lens 2, the change in the permissible range of the radius of curvature R ₂ in the main scanning cross section of the toroidal surface It is shown. In Figure 8, the ordinate indicates the value of the main scanning direction of curvature radius R ₂ of the toroidal surface and the horizontal axis represents the distance l ₄ from the reflecting surface 10 of the deflector to the second toroidal surface of the single lens 2 . Allowable range of the R ₂ in the present embodiment, a region 35 hatched between dashed lines 37 and broken lines 38.

On the other hand, as described above, the condition of field curvature in the main scanning direction and the linearity of the correction, there is a range to be taken by the main scanning direction of curvature radius R ₂ of the toroidal surface, which, when shown simultaneously in FIG. 8 , The region above the solid line 40.

Therefore, in order to keep all the aberration performance of the field curvature in the main scanning direction and the linearity and the sub-scanning direction field curvature in tolerance, in FIG. 8, and the values of R ₂ solid 40 or more, a broken line
Must be 38 or less.

Solid 40 and the broken line 38, since the intersect at point 41, the range of satisfying the above condition R ₂ is present, as can be seen from FIG. 8 and interplanar distance from the reflecting surface 10 of the deflector to the toroidal surface
l ₄ is where more than the value indicated by the straight line 42. This is to arrange the toroidal surface separately from the deflector,
The size of the lens becomes extremely large, the device becomes large, and the manufacture of the toroidal lens becomes difficult.

Here, what is important in the present invention is that the present optical system has another cylindrical surface (on the side of the first single lens) as shown in FIG. That is, it has two cylindrical surfaces (radius of curvature R ₃ , R ₄ ) having power in the cross section in the sub-scanning direction.

FIG. 9 is an example showing the effectiveness of using two cylindrical surfaces. In the figure, the horizontal axis represents the magnitude of the curvature of field in the sub-scanning direction, and the vertical axis represents the scanning position as a relative value, and the curvature of field in the sub-scanning direction cannot be within an allowable value for one cylindrical surface. when the value of R _2, such as (outside the region 35 shown in FIG. 8), when changing the balance of the curvature of the two cylindrical surfaces radius R _3, R ₄ (shown in FIG. 3) sub 9 shows a change in the curvature of field in the scanning direction.

9 in the scanning optical apparatus as shown in FIG first cylindrical surface curvature radius R ₃ of the single lens 1 and the second relationship is 1 / R ₃ and the radius of curvature R ₄ of the cylindrical surface of the single lens 2 > 1 / R ₄ (2) Under the condition of (2), the curvature of field in the sub-scanning direction is favorably corrected.

As described above, by correcting using two cylindrical surfaces, it is possible to set the R ₂ in which the curvature of field in the sub-scanning direction can be within an allowable value.
Has been found to have a wider range of values. This is shown in FIG. 8 in a region 36 surrounded by a broken line 37 and a dashed line 39. In this case, the field curvature in the main scanning direction and the linearity and the range of values of R ₂ to obtain all aberrations as within the allowable value in the sub-scanning direction field curvature, and a solid line 40 or more, the one-dot chain line 39 or less , so that the l ₄ may be present in sufficiently short value.

As a result, it has been found that even if the second single lens 2 having a toroidal surface is arranged near the deflector, the aberration performance can be favorably corrected, and the miniaturization of the optical device is realized.

Eighth dashed line in Figure 39 can be approximated by a straight line, with this, the range of the radius of curvature R ₂ in the main scanning cross section of the toroidal surface capable of simultaneously characterized by using a three aberrations as follows become.

The lens data of the second imaging optical system (between the reflecting surface 10 of the deflecting device and the eight surfaces of the object to be scanned) in this embodiment described above is shown below.

First Example (Aberration Diagram: FIG. 10) (1) First Single Lens 1 Radius of Curvature R _{1 of} Cylindrical Surface: 191.52 mm Radius of Curvature R ₃ of Cylindrical Surface: 10 mm Lens Thickness t ₁ : 10 mm Glass Material: SF11 Reflection Distance between the upper surface of the axis from the surface 10 to the first single lens 1
l ₁ : 18.5 mm (2) Second single lens 2 Radius of curvature of cylindrical surface R ₄ : 114.15 mm Radius of curvature of toroidal surface in main scanning direction R ₂ : 109.80 mm Radius of curvature of toroidal surface in sub-scanning direction R ₅ : 26.26 mm Lens thickness t ₂ : 30 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 to the second single lens 2 l ₂ : 16.5 mm Axis from the second single lens 2 to the eight surfaces of the object to be scanned Upper surface distance l ₃ : 321mm (3) Conditions FIG. 10 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Second Example (Aberration Diagram: FIG. 11) (1) First Single Lens 1 Radius of Curvature R _{1 of} Cylindrical Surface: 293.41 mm Radius of Curvature R ₃ of Cylindrical Surface: 30 mm Lens Thickness t ₁ : 10 mm Glass Material: SF11 Reflection Distance between the upper surface of the axis from the surface 10 to the first single lens 1
l ₁ : 28 mm (2) Second single lens 2 Radius of curvature of cylindrical surface R ₄ : 149.7 mm Radius of curvature of toroidal surface in main scanning direction R ₂ : 139.15 mm Radius of curvature of toroidal surface in sub-scanning direction R ₅ : 34.88 mm Lens thickness t ₂ : 30 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 to the second single lens 2 l ₂ : 27 mm Distance between the axial upper surfaces from the second single lens 2 to the eight surfaces to be scanned Distance l ₃ : 301mm (3) Condition FIG. 11 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Third Embodiment (Aberration Diagram: FIG. 12) (1) First Single Lens 1 Radius of Curvature R _{1 of} Cylindrical Surface: 769.33 mm Radius of Curvature R of Cylindrical Surface R ₃ : 100 mm Lens Thickness t ₁ : 10 mm Glass Material: SF11 Reflection Distance between the upper surface of the axis from the surface 10 to the first single lens 1
l ₁ : 32.5mm (2) Second single lens 2 Radius of curvature of cylindrical surface R ₄ : 153.44mm Curvature radius of toroidal surface in main scanning direction R ₂ : 200.06mm Radius of curvature of toroidal surface in sub scanning direction R ₅ : 46.93 mm Lens thickness t ₂ : 30 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 to the second single lens 2 l ₂ : 62.5 mm Axle from the second single lens 2 to the eight surfaces to be scanned Distance between upper surfaces l ₃ : 261mm (3) Conditions FIG. 12 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Fourth Example (Aberration Diagram: FIG. 13) (1) First Single Lens 1 Radius of Curvature of Cylindrical Surface R ₁ : 469.26 mm Radius of Curvature of Cylindrical Surface R ₃ : 50 mm Lens Thickness t ₁ : 10 mm Glass Material: SF11 Reflection Distance between the upper surface of the axis from the surface 10 to the first single lens 1
l ₁ : 34 mm (2) Second single lens 2 Radius of curvature of cylindrical surface R ₄ : 160.05 mm Curvature radius of toroidal surface in main scanning direction R ₂ : 169.9 mm Curvature radius of toroidal surface in sub-scanning direction R ₅ : 41.43 mm Lens thickness t ₂ : 30 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 to the second single lens 2 l ₂ : 41 mm Distance between the axial upper surfaces from the second single lens 2 to the eight surfaces to be scanned Distance l ₃ : 281mm (3) Condition FIG. 13 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Next, a description will be given of a second embodiment of the scanning optical apparatus having the surface tilt correction according to the present invention.

FIG. 14 is an external view of a scanning optical device having surface tilt correction according to the present invention. In the drawing, the difference from the embodiment shown in FIG. 1 is that the first single lens 1 ′ of the second imaging optical system is different.
Are different from each other. That is, the surface configuration of the first single lens 1 ′ is such that the cylindrical surface 1 a having negative power only in the sub-scanning direction and the second
Has a cylindrical surface 1b having a negative power only in the main scanning direction on the single lens 2 side. In FIG. 14, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The principle of aberration correction is basically the same as that of the first embodiment. That is, in the schematic diagrams of the lens configurations and arrangements shown in FIGS. 15A and 15B, regarding the curvature of field in the main scanning direction, which is the aberration in the main scanning direction, and the linearity, the first single lens 1 main scanning direction only with the radius of curvature R ₁ of the cylindrical surface having a power second main scanning direction of the radius of curvature of the toroidal surface of the single lens 2 of '
By defining R ₂ and the surfaces between the distance l _1, l _2, l ₃ optimally, it is corrected both aberration simultaneously. Also, in consideration of the thickness of each of the single lenses 1 'and 2, in the second embodiment, it was found that the aberration correction effect was remarkable when the conditional expression below was satisfied.

The above equation (4) is shown in FIG. 8 in the region above the solid line 43, which is slightly different from the first embodiment (solid line 40).

The correction of the field curvature in the sub-scanning direction, which is the aberration in the sub-scanning direction, is also performed in the same manner as in the first embodiment described above with reference to FIG.
And the radius of curvature R ₃ of the cylindrical surface of the first single lens 1 ′ and the radius of curvature of the cylindrical surface of the second single lens 2 shown in FIG.
Under the condition that the relationship with R ₄ is 1 / R ₃ > 1 / R ₄ (5), the correction effect is effective, and the main scanning of the toroidal surface is such that the curvature of field in the sub-scanning direction can be within an allowable value. It found that the range of the direction of the value of the curvature radius R ₂ is widened. That is, as shown in the first embodiment, returning to FIG. 8, the region 36 surrounded by a broken line 37 and a dashed line 39 is shown.
It is.

As a result, the range of the radius of curvature R ₂ in the main scanning cross section of the toroidal surface capable of simultaneously characterized by using a three aberrations is as follows.

The lens data of the second imaging optical system (between the anti-slope surface 10 of the deflecting device and the eight surfaces of the object to be scanned) in the second embodiment of the present invention described above is shown below.

First Embodiment (Aberration Diagram: FIG. 10) (1) First Single Lens 1 'Radius of Curvature R _{1 of} Cylindrical Surface: 522.47 mm Radius of Curvature R ₃ of Cylindrical Surface: 10 mm Lens Thickness t ₁ : 15 mm Glass Material: F2 Distance between the upper surface of the axis from the reflecting surface 10 to the first single lens 1 '
l ₁ : 50mm (2) Second single lens 2 Radius of curvature of cylindrical surface R ₄ : 458.63mm Curvature radius of toroidal surface in main scanning direction R ₂ : 168mm Curvature radius of toroidal surface in sub-scanning direction R ₅ : 42.57mm Lens thickness t ₂ : 20 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 ′ to the second single lens 2 l ₂ : 40 mm Between the axial upper surfaces from the second single lens 2 to the eight surfaces to be scanned Distance l ₃ : 320mm (3) Condition FIG. 16 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Second Embodiment (aberration diagram FIG. 17) (1) of curvature of the first single lens 1 'cylindrical surface radius R _1: 542.53mm cylindrical surface of radius of curvature R _3: 10 mm lens thickness t _1: 15 mm glass material: F2 Distance l ₁ : 50 mm between the upper surface of the axis from the reflecting surface 10 to the first single lens 1 ′ (2) Second single lens 2 Radius of curvature R of the cylindrical surface R ₄ : 353.58 mm Radius of curvature R of the toroidal surface in the main scanning direction ₂ : 179.1 mm Curvature radius R in the sub-scanning direction of the toroidal surface R ₅ : 45.45 mm Lens thickness t ₂ : 20 mm Glass material: SF11 Distance between the upper surfaces of the shafts from the first single lens 1 ′ to the second single lens 2 l ₂ : 50 mm Distance between the upper surfaces of the shafts from the second single lens 2 to the eight surfaces to be scanned l ₃ : 310 mm (3) Conditions FIG. 17 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Third Embodiment (the aberration diagrams FIG. 18) (1) of curvature of the first single lens 1 'cylindrical surface radius R _1: 417.97mm cylindrical surface of radius of curvature R _3: 50 mm lens thickness t _1: 15 mm glass material: F2 Distance l ₁ : 60 mm between the upper surface of the axis from the reflecting surface 10 to the first single lens 1 ′ (2) Second single lens 2 Radius of curvature R of the cylindrical surface R ₄ : 437.79 mm Radius of curvature R of the toroidal surface in the main scanning direction ₂ : 156 mm Curvature radius R in the sub-scanning direction of the toroidal surface R ₅ : 51.876 mm Lens thickness t ₂ : 20 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 ′ to the second single lens 2 l ₂ : 40 mm Distance l ₃ : 340 mm between the upper surface of the axis from the second single lens 2 to the eight surfaces to be scanned (3) FIG. 18 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Fourth Embodiment (aberration diagrams Fig. 19) (1) of curvature of the first single lens 1 'cylindrical surface radius R _1: 569.32mm cylindrical surface of radius of curvature R _3: 30 mm lens thickness t _1: 15 mm glass material: F2 The distance l ₁ between the upper surfaces of the axes from the reflecting surface 10 to the first single lens 1 ′ ₁ : 57 mm (2) The second single lens 2 The radius of curvature R of the cylindrical surface R ₄ : 369.23 mm The radius of curvature R of the toroidal surface in the main scanning direction ₂ : 184 mm Curvature radius R of the toroidal surface in the sub-scanning direction R ₅ : 50.109 mm Lens thickness t ₂ : 23 mm Glass material: SF11 Distance between the axial upper surfaces from the first single lens 1 ′ to the second single lens 2 l ₂ : 47 mm Distance l ₃ between the upper surfaces of the axes from the second single lens 2 to the eight surfaces to be scanned l ₃ : 300 mm (3) Condition FIG. 19 shows the aberration performance of this example. (A) shows the curvature of field, the broken line (main) is the main scanning direction, and the solid line (sub) is the sub scanning direction. (B) shows linearity. Also,
In both (A) and (B), the vertical axis represents the relative scanning position, and the maximum scanning position 1.0 is when the deflection angle is ± 30 ° and the scanning width is ± 148.5 mm.

Here, in the present embodiment described so far,
As shown in FIG. 20 (A), the two single lenses each have a cylindrical surface 1a, 1b, 2a and a toroidal surface 2b to simplify the configuration. For example, in the case of manufacturing the above single lens By dividing each single lens at a broken line 62 in FIG. 7A and manufacturing one surface of each single lens as a flat surface as shown in FIG. Can be easily manufactured.

Further, it goes without saying that the present scanning optical apparatus can be applied to not only a laser printer as shown in the embodiment but also to any apparatus that performs scanning with a rotary polygon mirror, for example, an image reading apparatus. No.

〔The invention's effect〕

As described above, according to the present invention, the second imaging optical system has a simple configuration having two single lenses, and particularly, the main scanning direction and the main scanning direction, which are important in increasing the resolution (that is, sharpening the beam spot). The aberration correction of the curvature of field in the sub-scanning direction can be satisfactorily performed, and the deflection angle can be set to ± 30 ° or more, so that it is possible to realize a scanning optical system device having surface tilt correction effective for downsizing.

[Brief description of the drawings]

FIG. 1 is an external view showing an embodiment of the present invention, and FIG.
3 is a schematic diagram for explaining the aberration correction function and the lens configuration according to the present invention, and FIGS. 4 to 6 are diagrams each showing the field curvature and linearity in the main scanning direction. FIG. 7 is a characteristic diagram showing a change in curvature of field in the sub-scanning direction. FIG. 8 is a characteristic diagram showing a change in an allowable aberration range of a radius of curvature of the toroidal surface in the main scanning direction with respect to a distance between the surfaces. FIG. 9 is a characteristic diagram showing a change in curvature of field in the sub-scanning direction. FIGS. 10 to 13 are aberration characteristic diagrams of the embodiment of the present invention, respectively. FIG. 14 is a second embodiment of the present invention. FIG. 15 is a schematic view for explaining aberration correction and a lens configuration of the second embodiment of the present invention, and FIGS. 16 to 19 are diagrams of the second embodiment of the present invention. Aberration characteristic diagram,
FIG. 20 is an explanatory view showing an embodiment relating to a lens manufacturing method,
FIG. 21 is a conceptual diagram showing a change in spot diameter due to field curvature, FIG. 22 is a conceptual diagram showing occurrence of field curvature in the sub-scanning direction by a long cylindrical lens, and FIG. 23 is a conceptual diagram showing only one cylindrical surface. FIG. 9 is a characteristic diagram when the field curvature in the scanning direction is corrected. Description of reference numerals 1,1 ': first single lens, 1a: cylindrical surface having power only in main scanning direction, 1b, 2a: cylindrical surface having power only in sub-scanning direction, 2 ... second Single lens, 2b ... toroidal surface, 3 ... light source, 4 ... coupling lens, 5 ... first imaging optical system, 6 ... motor, 7
... Rotating polygon mirror, 8 ... Scanned object, 9a-9d ... Light beam, 10,10 '... Reflective surface, 20-27,30-33,37-40,43 ...
Aberration characteristic diagram, 35, 36… Aberration correction area, 41, 42, 62… Explanation point (lead line), 50, 73… Field curvature, 51, 74…
... Surface to be scanned, 52,53 ... Beam envelope, 54 ... Principal ray at the center of scanning, 55 ... Principal ray at scanning end, 70 ... Long cylindrical lens, 71,72 ... Incoming beam

Claims (4)

(57) [Claims] A light beam generating source; a first imaging optical system for linearly imaging and outputting a light beam of a light beam generated from the light source; When a linear light beam from the imaging optical system is incident, the light beam is reflected by the deflecting / reflecting surface (10) and deflected to scan on the surface to be scanned of the object (8). ), And between the scanned surface of the object (8) and the deflecting / reflecting surface (10) of the deflector to optically determine the positional relationship between the scanned surface and the deflecting / anti-sloping surface. A second imaging optical system (1, 2) that realizes a function of correcting the surface tilt of the deflecting / reflective surface while maintaining a symmetrical relationship, and a scanning optical device having a surface tilt correcting function. The imaging optical system of No. 2 has one surface forming a cylindrical surface (1a) having a negative power only in the cross section in the scanning direction, and the other surface in a direction perpendicular to the scanning direction. Anamorphic first forming a cylindrical surface (1b) having a negative power only to the plane
A single lens (1), wherein one of the one cylindrical surface (1a) and the other cylindrical surface (1b) is directed toward the deflector (7, 6), and the other is the object. The first single lens (1) arranged toward the object (8), and a cylindrical surface (2a) having one surface having a negative power only in a section perpendicular to the scanning direction. ), The other surface has a relatively large curvature in a cross section in the scanning direction, and a relatively small curvature in a cross section in a direction perpendicular to the scanning direction. Toroidal surface with positive power in both directions (2b)
Wherein the one cylindrical surface (2a) faces the first single lens (1) and the other toroidal surface (2b) faces the object ( 8)
The second single lens (2) arranged toward the side
And a scanning optical device having a surface tilt correction function. 2. A light beam generating source (3), a first image forming optical system (5) for linearly forming and outputting a light beam of a light beam generated from the light source, and a first image forming optical system (5). When a linear light beam from the imaging optical system is incident, the light beam is reflected by the deflecting / reflecting surface (10) and deflected to scan on the surface to be scanned of the object (8). ), And between the scanned surface of the object (8) and the deflecting / reflecting surface (10) of the deflector to optically determine the positional relationship between the scanned surface and the deflecting / anti-sloping surface. A second imaging optical system (1, 2) that realizes a function of correcting the surface tilt of the deflecting / reflective surface while maintaining a symmetrical relationship, and a scanning optical device having a surface tilt correcting function. The imaging optical system of No. 2 has one surface forming a cylindrical surface (1a) having a negative power only in the cross section in the scanning direction, and the other surface in a direction perpendicular to the scanning direction. Anamorphic first forming a cylindrical surface (1b) having a negative power only to the plane
A single lens (1) having one cylindrical surface (1a) directed toward the deflector (7, 6) and the other cylindrical surface (1b) directed toward the object (8). The first single lens (1) arranged, and one surface forms a cylindrical surface (2a) having negative power only in a cross section perpendicular to the scanning direction, and the other surface performs scanning. Has a relatively large curvature in the cross section in the direction and a relatively small curvature in the cross section in the direction perpendicular to the scanning direction, and has a positive power in both the cross section in the scanning direction and the cross section in the direction perpendicular to the scanning direction. Toroidal surface with a pattern (2b)
Wherein the one cylindrical surface (2a) faces the first single lens (1) and the other toroidal surface (2b) faces the object ( 8)
The second single lens (2) arranged toward the side
And, A scanning optical device having a surface tilt correction function characterized by satisfying the following relationship (where f _{0 is} the combined focal length of the second imaging optical system in the cross section in the scanning direction. L ₄ : from the reflecting surface of the deflector) The distance between the surfaces of the second single lens to the toroidal surface (on the axis) R ₂ : radius of curvature of the scanning direction cross section of the toroidal surface of the second single lens. 3. A light beam generation source (3), a first imaging optical system (5) for linearly imaging and outputting a light beam of a light beam generated from the light source, and a first imaging optical system (5). When a linear light beam from the imaging optical system is incident, the light beam is reflected by the deflecting / reflecting surface (10) and deflected to scan on the surface to be scanned of the object (8). ), And between the scanned surface of the object (8) and the deflecting / reflecting surface (10) of the deflector to optically determine the positional relationship between the scanned surface and the deflecting / anti-sloping surface. A second imaging optical system (1, 2) that realizes a function of correcting the surface tilt of the deflecting / reflective surface while maintaining a symmetrical relationship, and a scanning optical device having a surface tilt correcting function. The imaging optical system of No. 2 has one surface forming a cylindrical surface (1a) having a negative power only in the cross section in the scanning direction, and the other surface in a direction perpendicular to the scanning direction. Anamorphic first forming a cylindrical surface (1b) having a negative power only to the plane
A single lens (1) having one cylindrical surface (1a) facing the object (8) and the other cylindrical surface (1b) facing the deflector (7, 6). The first single lens (1) arranged, and one surface forms a cylindrical surface (2a) having negative power only in a cross section perpendicular to the scanning direction, and the other surface performs scanning. Has a relatively large curvature in the cross section in the direction and a relatively small curvature in the cross section in the direction perpendicular to the scanning direction, and has a positive power in both the cross section in the scanning direction and the cross section in the direction perpendicular to the scanning direction. Toroidal surface with a pattern (2b)
Wherein the one cylindrical surface (2a) faces the first single lens (1) and the other toroidal surface (2b) faces the object ( 8)
The second single lens (2) arranged toward the side
And, A scanning optical device having a surface tilt correction function characterized by satisfying the following relationship (where f _{0 is} the combined focal length of the second imaging optical system in the cross section in the scanning direction. L ₄ : from the reflecting surface of the deflector) The distance between the surfaces of the second single lens to the toroidal surface (on the axis) R ₂ : radius of curvature of the scanning direction cross section of the toroidal surface of the second single lens. 4. A scanning optical apparatus having a surface tilt correction function according to claim 1, wherein the second imaging optical system has a direction perpendicular to a scanning direction in the first single lens. Let R _{3 be} the radius of curvature of the cylindrical surface having power only in the cross section of R, and R ₄ be the radius of curvature of the cylindrical surface having power only in the cross section perpendicular to the scanning direction of the second single lens. A scanning optical device having a surface tilt correction function, wherein the relationship 1 / R ₃ > 1 / R ₄ is satisfied.